WO2011077904A1 - Connecting rod, single-cylinder internal combustion engine comprising same, and saddle type vehicle - Google Patents

Connecting rod, single-cylinder internal combustion engine comprising same, and saddle type vehicle Download PDF

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Publication number
WO2011077904A1
WO2011077904A1 PCT/JP2010/071328 JP2010071328W WO2011077904A1 WO 2011077904 A1 WO2011077904 A1 WO 2011077904A1 JP 2010071328 W JP2010071328 W JP 2010071328W WO 2011077904 A1 WO2011077904 A1 WO 2011077904A1
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Prior art keywords
connecting rod
less
large end
inner peripheral
peripheral surface
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PCT/JP2010/071328
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French (fr)
Japanese (ja)
Inventor
剛 久保田
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ヤマハ発動機株式会社
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Priority to JP2011547427A priority Critical patent/JP5342655B2/en
Publication of WO2011077904A1 publication Critical patent/WO2011077904A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C7/00—Connecting-rods or like links pivoted at both ends; Construction of connecting-rod heads
    • F16C7/02—Constructions of connecting-rods with constant length
    • F16C7/023—Constructions of connecting-rods with constant length for piston engines, pumps or the like
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
    • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/34—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in more than one step

Definitions

  • the present invention relates to a connecting rod, and more particularly to a connecting rod formed from an iron alloy.
  • the present invention also relates to a single-cylinder internal combustion engine and a straddle-type vehicle provided with such a connecting rod.
  • a member called a connecting rod (sometimes abbreviated as “con'rod”) is used to connect a piston and a crankshaft.
  • the connecting rod includes a rod-shaped rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body. The small end is connected to the piston, while the large end is connected to the crankshaft. More specifically, the piston pin of the piston is inserted through the through hole formed in the small end portion. A crank pin of the crankshaft is inserted through a through hole formed at the large end. Thereby, the connecting rod is connected to the piston and the crankshaft.
  • ⁇ Connecting rods are roughly divided into a split type with the large end divided into two and an integrated type with the large end not split.
  • the integral connecting rod is mainly used for a single cylinder internal combustion engine.
  • ⁇ Rolling bearings such as needle bearings and ball bearings are arranged between the inner peripheral surface of the large end of the integral connecting rod and the crank pin in order to reduce friction loss.
  • the explosive force transmitted through the piston during operation of the internal combustion engine presses the connecting rod against the rolling bearing, so that a large stress is generated on the inner peripheral surface of the large end. When this stress is excessive, a fatigue fracture phenomenon called flaking occurs on the inner peripheral surface of the large end.
  • Patent Document 1 proposes high-concentration carburizing treatment as a technique for further increasing the surface hardness of the connecting rod.
  • carburization is performed a plurality of times in an atmosphere having a carbon potential (CP) of 0.8% or more.
  • CP carbon potential
  • Patent Document 1 also mentions high-concentration carbonitriding as a technique for increasing the surface hardness of the connecting rod, as in high-concentration carburizing.
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a connecting rod that suppresses the occurrence of flaking on the inner peripheral surface of the large end and has excellent fatigue strength.
  • a connecting rod according to the present invention includes a rod body, a small end provided at one end of the rod body, and a large end provided at the other end of the rod body, and is formed of an iron alloy.
  • the connecting rod according to the present invention has a nitrogen content of 0.04 wt% or more and 0.18 wt% or less at a depth of 0.1 mm from the inner peripheral surface of the large end.
  • the connecting rod according to the present invention has a nitrogen content of 0.05 wt% or more and 0.15 wt% or less at a depth of 0.1 mm from the inner peripheral surface of the large end.
  • the iron alloy includes 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon, and 0.3 wt% or more and 1.2 wt% or less of chromium. including.
  • the iron alloy has a nickel content of less than 0.7 wt%.
  • the connecting rod according to the present invention has a non-diffusible hydrogen content of 0.46 ppm or less.
  • the carbonitriding process, the carburizing process, and the nitriding process are performed in a furnace that is depressurized to 1/10 or less of standard atmospheric pressure.
  • the particle size of the carbide and carbonitride precipitated in the vicinity of the inner peripheral surface of the large end is 10 ⁇ m or less.
  • a single-cylinder internal combustion engine includes a connecting rod having the above configuration, and a crankshaft connected to the connecting rod.
  • the crankshaft includes a crankpin inserted into the large end portion of the connecting rod, and a crank web formed separately from the crankpin.
  • the single-cylinder internal combustion engine according to the present invention further includes a rolling bearing provided between the inner peripheral surface of the large end portion and the crank pin.
  • crank pin is subjected to a carburizing process or a carbonitriding process.
  • a straddle-type vehicle according to the present invention includes a single-cylinder internal combustion engine having the above-described configuration.
  • a method for manufacturing a connecting rod according to the present invention includes a rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body.
  • the carburizing treatment in the step (B) and the carbonitriding treatment in the step (C) are performed in a furnace reduced in pressure to 1/10 or less of standard atmospheric pressure.
  • a method of manufacturing a connecting rod according to the present invention includes a rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body.
  • the process is performed so that the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the region is 0.03 wt% or more and 0.19 wt% or less.
  • the carburizing treatment in the step (B) and the nitriding treatment in the step (C) are performed in a furnace reduced in pressure to 1/10 or less of standard atmospheric pressure.
  • the connecting rod according to the present invention is made of an iron alloy and is subjected to carbonitriding or carburizing and nitriding.
  • carbonitriding or carburizing and nitriding
  • the surface hardness of the connecting rod is increased and the fatigue strength is improved.
  • the carbon content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.8 wt% or more and 2.1 wt% or less.
  • CP carbon potential
  • the connecting rod according to the present invention the nitrogen content at a predetermined depth from the inner peripheral surface of the large end portion is set within a specific range.
  • the nitrogen content at a depth of 1 mm is 0.03 wt% or more and 0.19 wt% or less.
  • the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the large end is preferably 0.04 wt% or more and 0.18 wt% or less, More preferably, it is 0.05 wt% or more and 0.15 wt% or less.
  • the iron alloy which is the material of the connecting rod according to the present invention includes 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon, and 0.3 wt% or more and 1.2 wt% or less. Preferably it contains chromium.
  • the carbon content is 0.1 wt% or more and 0.4 wt% or less
  • the internal hardness of the connecting rod after the heat treatment can be 200 HV or more and 500 HV or less, so that the strength and toughness inside the connecting rod are sufficiently provided. Can be kept high. Further, when the silicon content is increased, the anti-flaking property is improved, but the toughness may be lowered.
  • the silicon content is 0.1 wt% or more and 0.5 wt% or less, the flaking resistance can be sufficiently improved and sufficient toughness can be ensured.
  • the chromium content is increased, the hardenability is improved.
  • temper embrittlement may occur.
  • the chromium content is 0.3 wt% or more and 1.2 wt% or less, the occurrence of temper embrittlement can be prevented while obtaining appropriate hardenability.
  • the nickel content of the iron alloy is preferably as low as possible, specifically, less than 0.7 wt%. When the nickel content increases, the amount of retained austenite after heat treatment increases, so the surface hardness may decrease.
  • the non-diffusible hydrogen content is preferably 0.46 ppm or less. Since the non-diffusible hydrogen content is 0.46 ppm or less, the occurrence of hydrogen brittle mold peeling can be suppressed, so that the flaking life can be further improved.
  • the carbonitriding process (or carburizing process and nitriding process) is preferably performed in a vacuum-evacuated furnace, and more specifically, in a furnace reduced in pressure to 1/10 or less of the standard atmospheric pressure. Preferably it is applied.
  • a gas containing nitrogen By introducing a gas containing nitrogen into such a furnace, the nitrogen content at a depth of 0.1 mm from the surface (the inner peripheral surface of the large end) can be adjusted with high accuracy.
  • the particle size of the carbide and carbonitride precipitated in the vicinity of the inner peripheral surface of the large end is preferably as small as possible, specifically 10 ⁇ m or less.
  • the particle size of the carbide and carbonitride exceeds 10 ⁇ m, the toughness may be lowered and sufficient strength may not be obtained.
  • the connecting rod according to the present invention is preferably used for a single cylinder internal combustion engine having one cylinder.
  • the crankshaft of a single cylinder internal combustion engine is typically an assembly type crankshaft. That is, the crankpin and the crank web are formed separately.
  • a rolling bearing for example, a needle bearing or a ball bearing
  • a rolling bearing is provided between the inner peripheral surface of the large end and the crank pin.
  • stress is generated on the inner peripheral surface of the large end portion by pressing the connecting rod against the rolling bearing. If this stress is excessive, the occurrence of flaking is a concern.
  • the connecting rod according to the present invention is excellent in anti-flaking property, the occurrence of flaking is prevented over a long period of time.
  • crankpin is subjected to carburizing or carbonitriding.
  • the single-cylinder internal combustion engine provided with the connecting rod according to the present invention is suitably used for various straddle-type vehicles (for example, motorcycles).
  • a carbonitriding process or a carburizing process and a nitriding process are performed on a workpiece formed of an iron alloy.
  • carbonitriding or carburizing and nitriding
  • the surface hardness of the connecting rod is increased and the fatigue strength is improved.
  • the carbonitriding process and the carburizing process are performed in an atmosphere having a carbon potential (CP) of 0.8% or more. That is, a high concentration carbonitriding process or a high concentration carburizing process is performed on the workpiece.
  • the carbonitriding treatment or nitriding treatment has a nitrogen content of 0.03 wt% or more and 0.19 wt% or less at a predetermined depth from the inner peripheral surface of the region that becomes the large end of the workpiece. To be executed.
  • the connecting rod manufactured by the manufacturing method according to the present invention has excellent fatigue strength as compared with a connecting rod that has been simply subjected to high-concentration carbonitriding or high-concentration carburizing.
  • the carbonitriding process (or carburizing process and nitriding process) is preferably performed in a vacuum-evacuated furnace, and more specifically, in a furnace reduced in pressure to 1/10 or less of the standard atmospheric pressure. Preferably it is applied.
  • a gas containing nitrogen By introducing a gas containing nitrogen into such a furnace, the nitrogen content at a depth of 0.1 mm from the surface (the inner peripheral surface of the large end) can be adjusted with high accuracy.
  • FIG. 4 is a cross-sectional view taken along line 1C-1C ′ in FIG. It is a figure which shows the stress distribution (stress distribution when a stress becomes the maximum at the time of the driving
  • FIG. 1 is a graph which shows distribution of the carbon concentration (carbon content) in the depth direction of the connecting rod. It is a graph which shows the hardness distribution in the depth direction of the connecting rod. It is a graph which shows the relationship between nitrogen content (wt%) in the depth of 0.1 mm from the internal peripheral surface of a large end part, and flaking lifetime (L50 lifetime). It is a flowchart which shows the manufacturing method of the connecting rod 1 in suitable embodiment of this invention.
  • FIG. 1 is a cross-sectional view schematically showing a single cylinder internal combustion engine 100 including a connecting rod 1 according to a preferred embodiment of the present invention.
  • Fig. 11 is a side view schematically showing a motorcycle including the internal combustion engine 100 shown in Fig. 10.
  • the inventor of the present application examined in detail the reason why flaking occurs even in a connecting rod subjected to high-concentration carburizing treatment or high-concentration carbonitriding treatment, and as a result, obtained the knowledge described below.
  • the cause of flaking is that a large stress is transmitted from the rolling bearing such as a needle bearing or a ball bearing to the inner peripheral surface of the large end. Therefore, it is considered that flaking can be prevented by increasing the surface hardness of the connecting rod by high-concentration carburizing treatment or high-concentration carbonitriding treatment. I can't. That is, even if the surface hardness of the connecting rod is simply increased, sufficient flaking resistance cannot be obtained.
  • the inventor of the present application analyzed the stress distribution in the depth direction of the connecting rod, it was found that the greatest stress acts at a certain depth from the surface, not the outermost surface. Furthermore, when the relationship between the element concentration at the depth at which the maximum stress acts and the anti-flaking property was verified, the nitrogen concentration (nitrogen content) at the depth at which the maximum stress acts greatly affected the anti-flaking property. I knew that I was giving.
  • FIG. 1A is a plan view schematically showing the connecting rod 1.
  • 1B is a cross-sectional view taken along line 1B-1B ′ in FIG. 1A, and FIG. 1C is taken along line 1C-1C ′ in FIG. FIG.
  • the connecting rod 1 is provided at the rod body 10, the small end 20 provided at one end of the rod body 10, and the other end of the rod body 10.
  • the large end 30 is provided.
  • the rod body part (shaft part) 10 has a rod shape.
  • the cross-sectional shape of the rod body 10 is typically H-shaped as shown in FIG.
  • the small end portion 20 has a through hole (piston pin hole) 22 through which the piston pin passes.
  • the small end 20 is connected to the piston via a piston pin.
  • the inner peripheral surface 20a (surface defining the outer edge of the piston pin hole 22) 20a typically contacts the piston pin without a bearing.
  • the large end portion 30 has a through hole (crank pin hole) 32 through which the crank pin passes.
  • the large end 30 is connected to the crankshaft via a crankpin. Since a rolling bearing is typically arranged in the crankpin hole 32, the inner peripheral surface 30a (the surface defining the outer edge of the crankpin 32) 30a of the large end 30 is in contact with the rolling bearing.
  • the connecting rod 1 is an integrated connecting rod in which the large end portion 30 is not divided into two.
  • the connecting rod 1 in this embodiment is formed from an iron alloy.
  • the connecting rod 1 is subjected to carbonitriding or carburizing and nitriding.
  • the carbon content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.8 wt% or more and 2.1 wt% or less.
  • the high-concentration carbonitriding process or the high-concentration carburizing process fine granular carbides and / or carbonitrides are precipitated in the vicinity of the surface of the connecting rod 1 and the crystal grain size of the martensite structure in the vicinity of the surface is reduced. . Therefore, the surface hardness is remarkably increased, and the effect of improving the fatigue strength is high.
  • the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.03 wt% or more and 0.19 wt% or less. This significantly improves the anti-flaking property.
  • FIG. 2 shows the result of calculating the stress distribution in the depth direction (stress distribution when the stress becomes maximum during operation of the internal combustion engine) on the inner peripheral surface of the large end portion of a general connecting rod.
  • the depth from the inner peripheral surface is shown as a negative value.
  • a position at a depth of 0.15 mm is written as “ ⁇ 0.15”.
  • a plurality of curves indicating stress are numbered 1 to 22, and the larger the number, the greater the stress.
  • the stress is not the largest on the outermost surface. Further, it can be seen from FIG. 2 that the stress becomes maximum at a depth of about 0.1 mm from the inner peripheral surface. Therefore, the inventor of the present application has examined in detail the relationship between the element concentration at a depth of 0.1 mm and the anti-flaking property. As a result, the nitrogen concentration at the depth of 0.1 mm (nitrogen content) It was found that the flaking property was greatly affected. Specifically, as will be described later together with the verification results, when the nitrogen content at this depth is not less than 0.03 wt% and not more than 0.19 wt%, the effect of improving the anti-flaking property is remarkably increased. I understood.
  • the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end portion 30 is 0.03 wt% or more and 0.19 wt% or less, so that the flaking resistance is remarkable. And the occurrence of flaking can be prevented over a long period of time. Therefore, the connecting rod 1 in this embodiment has an excellent fatigue strength compared to a connecting rod that has been simply subjected to high-concentration carbonitriding or high-concentration carburizing.
  • the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.04 wt% or more and 0.18 wt% or less. Preferably, it is 0.05 wt% or more and 0.15 wt% or less.
  • FIG. 3 is a flowchart showing manufacturing steps of the connecting rod 1.
  • a workpiece formed by forging from an iron alloy is prepared (step S1).
  • the composition of the iron alloy is not particularly limited, but the carbon (C) content of the iron alloy is preferably 0.1 wt% or more and 0.4 wt% or less.
  • the internal hardness (Vickers hardness) of the connecting rod 1 after the heat treatment can be 200 HV or more and 500 HV or less, so the inside of the connecting rod 1 Strength and toughness can be kept sufficiently high.
  • the silicon (Si) content of the iron alloy is preferably 0.1 wt% or more and 0.5 wt% or less. Increasing the silicon content improves anti-flaking properties but may reduce toughness. When the silicon content is 0.1 wt% or more and 0.5 wt% or less, the flaking resistance can be sufficiently improved and sufficient toughness can be ensured.
  • the chromium content is preferably 0.3 wt% or more and 1.2 wt% or less. Increasing chromium content improves hardenability (property of hardening by heat treatment), but excessive chromium content causes temper embrittlement (the iron alloy is kept in a predetermined temperature range for a long time). The embrittlement phenomenon that occurs when the When the chromium content is 0.3 wt% or more and 1.2 wt% or less, the occurrence of temper embrittlement can be prevented while obtaining appropriate hardenability.
  • the iron alloy that is the material of the workpiece is 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon and 0.3 wt%. % Or more and 1.2 wt% or less of chromium is preferable.
  • an iron alloy having a carbon content, a silicon content, and a chromium content within the above ranges for example, JIS SCM420 steel or JIS SCr420 steel can be used.
  • SCM420 steel is made of 0.18 wt% or more and 0.23 wt% or less of carbon, 0.15 wt% or more and 0.35 wt% or less of silicon, 0.90 wt% or more and 1.2 wt% or less of chromium, 0.60 wt% or more and 0.002 wt% or less. 85% by weight or less of manganese and 0.15% by weight or more and 0.30% or less of molybdenum are included.
  • the SCr420 steel is composed of 0.18 wt% or more and 0.23 wt% or less carbon, 0.15 wt% or more and 0.35 wt% or less silicon, 0.90 wt% or more and 1.2 wt% or less chromium, 0.60 wt% or more and 0. Contains 85 wt% or less manganese.
  • the nickel content of the iron alloy is preferably as small as possible. Specifically, it is preferably less than 0.7 wt%, and more preferably 0.25 wt% or less. When the nickel content increases, the amount of retained austenite after heat treatment increases, so the surface hardness may decrease.
  • molding method in the process of preparing a workpiece is not limited to this.
  • the workpiece may be formed by, for example, sintering, casting, sintering forging, or the like.
  • step S2 machining is performed on the workpiece (step S2).
  • the outer diameter of the workpiece after forging is adjusted. For example, deburring, formation of the piston pin hole 22 and the crank pin hole 32, and end face processing of the small end portion 20 and the large end portion 30 are performed. Thus, cutting is mainly performed in this step.
  • step S3 the workpiece is subjected to a first high-concentration carburizing process.
  • carburizing methods solid carburizing, liquid carburizing, gas carburizing, etc. are known.
  • gas carburizing is the mainstream, but here it is called vacuum carburizing (also called “vacuum gas carburizing” or “vacuum carburizing”).
  • vacuum carburizing also called “vacuum gas carburizing” or “vacuum carburizing”.
  • the high-concentration carburizing process in this step is performed in a vacuum-evacuated furnace (more specifically, in a furnace whose pressure is reduced to 1/10 or less of the standard atmospheric pressure).
  • Such a furnace is set to a temperature higher than the A1 transformation point (eutectoid transformation temperature of steel), and a hydrocarbon gas is introduced into the furnace so that the carbon potential is 0.8% or more, and carburized for a predetermined time.
  • a hydrocarbon gas is introduced into the furnace so that the carbon potential is 0.8% or more, and carburized for a predetermined time.
  • carburization is performed at 1000 ° C. for 170 minutes.
  • the surface of the iron alloy is excessively carburized by the first high-concentration carburizing treatment.
  • gas cooling is performed (step S4).
  • cooling is performed by introducing nitrogen (N 2) gas.
  • step S5 the workpiece is subjected to the second high concentration carburizing process.
  • vacuum carburization is performed.
  • the inside of the evacuated furnace is set to a temperature not lower than the A1 transformation point and not higher than the Acm transformation point (transformation temperature at which cementite precipitates from the austenite of the iron alloy), and carbonized so that the carbon potential is 0.8% or higher.
  • Hydrogen gas is introduced into the furnace and carburized for a predetermined time. For example, carburization is performed at 850 ° C. for 150 minutes. Due to the second high-concentration carburizing treatment, the carbon of the surface layer that has been excessively carburized diffuses inside. Thereafter, gas cooling is performed (step S6).
  • nitriding is performed on the workpiece (step S7).
  • This nitriding treatment is also performed in a vacuum-evacuated furnace.
  • the temperature that was evacuated (specifically, the inside of the furnace reduced to a pressure of 1/10 or less of the standard atmospheric pressure) was set to a temperature not lower than the A1 transformation point and not higher than the Acm transformation point, and ammonia gas was introduced into the furnace.
  • nitriding is performed for a predetermined time. For example, carburization is performed at 850 ° C. for 130 minutes. Thereafter, oil cooling (quenching) is performed (step S8).
  • step S9 tempering is performed. Tempering is performed at 190 ° C. for 120 minutes, for example. Thereafter, air cooling is performed (step S10).
  • step S11 machining is performed on the workpiece (step S11).
  • the inner peripheral surface 20a of the small end portion 20 and the inner peripheral surface 30a of the large end portion 30 are polished.
  • polishing is mainly performed in this step.
  • the connecting rod 1 is completed.
  • FIGS. 4A and 4B show the metal structure of the completed connecting rod 1.
  • 4A and 4B are metallographic micrographs of a cross section in the vicinity of the surface of the connecting rod 1, and FIG. 4B is an enlarged view of part of FIG. 4A.
  • fine granular carbides iron carbide
  • carbonitrides iron carbonitride
  • FIG. 5 shows the distribution of carbon concentration (carbon content) in the depth direction of the connecting rod 1.
  • the carbon concentration at a depth of 0.1 mm from the surface is about 0.92 wt%, and the carbon concentration (carbon content) at this depth is 0. It turns out that it becomes 8 wt% or more.
  • the carbon concentration distribution as shown in FIG. 5 can be measured by, for example, an electron beam microanalyzer (EPMA).
  • EPMA electron beam microanalyzer
  • FIG. 6 shows the hardness distribution in the depth direction of the connecting rod 1. As shown in FIG. 6, the hardness at a depth of 0.1 mm from the surface is about 770 HV.
  • the flaking life is a life with a cumulative failure probability of 50% (referred to as “L50 life”).
  • Table 1 shows Examples 1 to 4 in which the nitrogen content at a depth of 0.1 mm is in the range of 0.03 wt% to 0.19 wt%, and the nitrogen content at a depth of 0.1 mm. A verification result is shown about the comparative examples 1 and 2 which are outside the range of 0.03 wt% or more and 0.19 wt% or less. Examples 1 to 4 and Comparative Examples 1 and 2 are manufactured by the same manufacturing method except that nitriding conditions are different. Table 1 also shows Comparative Example 3 in which ordinary carburizing treatment (carburizing treatment other than high-concentration carburizing treatment) was performed as a conventional connecting rod, and high-concentration carburizing treatment as disclosed in Patent Document 1. 6 is shown together with Comparative Example 4 to which is applied. The distribution of the nitrogen content in the depth direction can be measured by, for example, an electron beam microanalyzer (EPMA).
  • EPMA electron beam microanalyzer
  • the nitrogen content at the surface layer and at a depth of 0.2 mm does not have a clear correlation with the flaking life.
  • Comparative Example 1 although the nitrogen content in the surface layer is significantly higher than those in Comparative Examples 3 and 4, only the same flaking life as that in the prior art can be obtained.
  • Examples 1 and 3 although the nitrogen content at the position of a depth of 0.2 mm is almost the same as that in Comparative Examples 3 and 4, a flaking life longer than that in the prior art is obtained.
  • FIG. 7 is a graph showing the relationship between the nitrogen content at a depth of 0.1 mm and the flaking life (L50 life).
  • the graph of FIG. 7 shows more examples than the example shown in Table 1.
  • a flaking life longer than the conventional one is realized when the nitrogen content at a depth of 0.1 mm from the surface is 0.03 wt% or more and 0.19 wt% or less (range A in FIG. 7). You can see that Further, from FIG. 7, a longer flaking life is realized when the nitrogen content at a depth of 0.1 mm from the surface is 0.04 wt% or more and 0.18 wt% or less (range B in FIG. 7). , 0.05 wt% or more and 0.15 wt% or less (range C in FIG. 7), it can be seen that a longer flaking life is realized.
  • the connecting rod 1 may be subjected to a high concentration carbonitriding process.
  • FIG. 8 the example of the manufacturing process of the connecting rod 1 in the case of performing a high concentration carbonitriding process is shown.
  • step S1 a workpiece formed by forging from an iron alloy is prepared (step S1), and then machining (mainly cutting) is performed on the workpiece (step S2). Subsequently, a high-concentration carburizing process is performed on the workpiece in a vacuum-evacuated furnace (step S3), and then gas cooling is performed (step S4).
  • step S5 a high concentration carbonitriding process is performed on the workpiece in a vacuum-evacuated furnace.
  • High concentration carbonitriding is performed by introducing ammonia gas together with hydrocarbon gas into the furnace.
  • oil cooling quenching
  • step S7 tempering is performed (step S7), and then air cooling is performed (step S8). Finally, machining (mainly polishing) is performed on the workpiece (step S9). As described above, the connecting rod 1 is completed.
  • the high-concentration carburizing treatment (steps S3 and S5 in FIG. 3 and the step S3 in FIG. 8) and the high-concentration carbonitriding treatment (step S5 in FIG. 8) are performed in the vacuum-evacuated furnace as described above. (That is, vacuum carburizing or vacuum carbonitriding).
  • gas cooling can be performed as a subsequent heat treatment instead of furnace cooling or quenching, so that the processing time can be shortened.
  • nitriding treatment (step S7 in FIG. 3) and high concentration carbonitriding treatment (Step S5 in FIG. 8) is preferably performed in a vacuum-evacuated furnace.
  • a nitrogen-containing gas for example, ammonia gas
  • the nitrogen content at a depth of 0.1 mm from the surface can be accurately adjusted.
  • FIG. 9 shows the nitrogen content at a depth of 0.1 mm from the surface when nitriding or high-concentration carbonitriding is performed in a gas carburizing furnace and in a vacuum carburizing furnace. Shows the relationship with time.
  • the appropriate nitriding time range C when processing in a gas carburizing furnace is significantly greater than the appropriate nitriding time range D when processing in a vacuum carburizing furnace. It is very difficult to actually keep the nitriding time within this range C. Since the technique disclosed in Patent Document 1 is premised on gas carburization, the nitrogen content at a depth of 0.1 mm from the surface can be reduced even when the high-concentration carbonitriding process taught in Patent Document 1 is used. It cannot be within the range of 0.03 wt% or more and 0.19 wt% or less.
  • the particle size (more specifically, circumscribed circle diameter) of carbides and carbonitrides precipitated in the vicinity of the inner peripheral surface 30a of the large end portion 30 is It is preferably as small as possible, specifically 10 ⁇ m or less.
  • the particle size of the carbide and carbonitride exceeds 10 ⁇ m, the toughness may be lowered and sufficient strength may not be obtained.
  • the rod main body part 10 has higher toughness than the large end part 30, the rod main body part before the first high-concentration carburizing process (step S3 in FIG. 3 and step S3 in FIG. 8). 10 may be masked with copper plating or a carbon-proofing agent.
  • the toughness of the rod body 10 can be increased.
  • the local tempering can be performed by, for example, high frequency induction heating.
  • the high-concentration carburization process is performed twice as shown in FIG. 3 and the high-concentration carburization process and the high-concentration carbonitriding process are performed once each as shown in FIG.
  • the high-concentration carburizing process and / or the high-concentration carbonitriding process may be performed three or more times in total.
  • non-diffusible hydrogen content of the connecting rod 1 has a great influence on the flaking life.
  • Hydrogen in the iron alloy is classified into two types depending on its solid solution state. Hydrogen that diffuses at room temperature is called diffusible hydrogen, and hydrogen that is trapped by inclusions and the like and hardly diffuses at temperatures from room temperature to about 200 ° is called non-diffusible hydrogen.
  • the non-diffusible hydrogen content is preferably 0.46 ppm or less. Since the non-diffusible hydrogen content is 0.46 ppm or less, the occurrence of hydrogen brittle mold peeling can be suppressed, so that the flaking life can be further improved.
  • Table 2 shows the non-diffusible hydrogen content for Examples 1 to 4 and Comparative Examples 1 to 4 shown in Table 1.
  • Table 2 also shows the non-diffusible hydrogen content for further Examples 5-7.
  • the nitrogen content at a depth of 0.1 mm is in the range of 0.03 wt% or more and 0.19 wt% or less.
  • Table 2 also shows whether the carburizing process (or carbonitriding process) in each example is gas carburizing (gas carbonitriding) or vacuum carburizing (vacuum carbonitriding). Note that the measurement of the non-diffusible hydrogen content was performed by a temperature rising desorption method. The test piece was gradually heated from 200 ° C. to 600 ° C., and the amount of hydrogen released from the test piece was quantitatively analyzed by a mass spectrometer.
  • Example 4 From the comparison between Example 4 and Example 6 in Table 2 or the comparison between Example 5 and Example 7, even if the nitrogen content at the depth of 0.1 mm is the same, non-diffusible hydrogen It can be seen that the smaller the content, the longer the flaking life, and the non-diffusible hydrogen content is preferably 0.46 ppm or less.
  • the non-diffusible hydrogen content is less when the carburizing process (carbonitriding process) is vacuum carburizing (vacuum carbonitriding) than when gas carburizing (gas carbonitriding). From this point, it can be seen that vacuum carburization (vacuum carbonitriding) is preferable.
  • the connecting rod 1 in the present embodiment is suitably used for a single cylinder internal combustion engine having one cylinder.
  • FIG. 10 shows an example of a single cylinder internal combustion engine 100 provided with the connecting rod 1 in the present embodiment.
  • the internal combustion engine 100 includes a crankcase 110, a cylinder block 120, and a cylinder head 130.
  • crankshaft 111 is accommodated in the crankcase 110.
  • the crankshaft 111 has a crankpin 112 and a crank web 113.
  • the crank pin 112 and the crank web 113 are formed separately. That is, the crankshaft 111 is an assembly-type crankshaft.
  • a cylinder block 120 is provided on the crankcase 110.
  • the cylinder block 120 is fitted with a cylindrical cylinder sleeve 121, and the piston 122 is provided so as to reciprocate within the cylinder sleeve 121.
  • a cylinder head 130 is provided on the cylinder block 120.
  • the cylinder head 130 forms a combustion chamber 131 together with the piston 122 and the cylinder sleeve 121 of the cylinder block 120.
  • the cylinder head 130 has an intake port 132 and an exhaust port 133.
  • An intake valve 134 for supplying air-fuel mixture into the combustion chamber 131 is provided in the intake port 132, and an exhaust valve 135 for exhausting the combustion chamber 131 is provided in the exhaust port 133. Yes.
  • the piston 122 and the crankshaft 111 are connected by the connecting rod 1. Specifically, the piston pin 123 of the piston 122 is inserted into the piston pin hole formed in the small end portion 20 of the connecting rod 1, and the crankshaft 111 is formed in the crankpin hole formed in the large end portion 30. The crank pin 112 is inserted, whereby the piston 122 and the crank shaft 111 are connected.
  • a needle bearing 114 is provided between the inner peripheral surface 30a of the large end 30 of the connecting rod 1 and the crank pin 112. Is provided.
  • the needle bearing 114 When the needle bearing 114 is provided, stress is generated on the inner peripheral surface 30 a of the large end portion 30 by pressing the connecting rod 1 against the needle bearing 114. If this stress is excessive, the occurrence of flaking is a concern.
  • the connecting rod 1 in this embodiment is excellent in anti-flaking property, the occurrence of flaking is prevented for a long period of time longer than that required for a product.
  • crankpin 112 is preferably subjected to carburizing or carbonitriding.
  • the needle bearing 114 is illustrated as the rolling bearing, but the rolling bearing is not limited to a roller bearing such as a needle bearing, and may be a ball bearing (ball bearing).
  • FIG. 11 shows a motorcycle including the internal combustion engine 100 shown in FIG.
  • a head pipe 302 is provided at the front end of the main body frame 301.
  • a front fork 303 is attached to the head pipe 302 so as to be able to swing in the left-right direction of the vehicle.
  • a front wheel 304 is rotatably supported at the lower end of the front fork 303.
  • a seat rail 306 is attached so as to extend rearward from the upper rear end of the main body frame 301.
  • a fuel tank 307 is provided on the main body frame 301, and a main seat 308 a and a tandem seat 308 b are provided on the seat rail 306.
  • a rear arm 309 extending backward is attached to the rear end of the main body frame 301.
  • a rear wheel 310 is rotatably supported at the rear end of the rear arm 309.
  • the internal combustion engine 100 shown in FIG. 10 is held at the center of the main body frame 301.
  • the internal combustion engine 100 includes the connecting rod 1 in the present embodiment.
  • a radiator 311 is provided in front of the internal combustion engine 100.
  • An exhaust pipe 312 is connected to the exhaust port of the internal combustion engine 100, and a muffler 313 is attached to the rear end of the exhaust pipe 312.
  • a transmission 315 is connected to the internal combustion engine 100.
  • a drive sprocket 317 is attached to the output shaft 316 of the transmission 315.
  • the drive sprocket 317 is connected to the rear wheel sprocket 319 of the rear wheel 310 via a chain 318.
  • the transmission 315 and the chain 318 function as a transmission mechanism that transmits the power generated by the internal combustion engine 100 to the drive wheels.
  • the connecting rod 1 in the present embodiment is also suitable for reducing the size and weight. This is because it is possible to apply a high load to the connecting rod 1 by extending the life.
  • the internal combustion engine 100 and the vehicle body are also lightened, and the running stability, ease of riding, and ease of handling of the motorcycle are improved, and the merchantability is improved.
  • the internal combustion engine 100 provided with the connecting rod 1 in the present embodiment is not limited to a motorcycle, and is preferably used for all saddle riding type vehicles on which riders ride. For example, it is also used for ATV such as buggy.
  • connecting rod 1 in the present embodiment can also be used for a small internal combustion engine used in a generator, an agricultural machine, or the like.
  • the connecting rod according to the present invention is widely used in internal combustion engines for various straddle-type vehicles (for example, internal combustion engines for motorcycles).

Abstract

Disclosed is a connecting rod (1) which comprises a rod main body (10), a small end part (20) that is provided on one end of the rod main body (10), and a large end part (30) that is provided on the other end of the rod main body (10). The connecting rod (1) is formed from an iron alloy, and has been subjected to a carbonitriding treatment or to a carburizing treatment and a nitriding treatment. The carbon content at a depth of 0.1 mm from the inner peripheral surface (30a) of the large end part (30) is 0.8-2.1 wt% (inclusive), and the nitrogen content at a depth of 0.1 mm from the inner peripheral surface (30a) of the large end part (30) is 0.03-0.19 wt% (inclusive). Consequently, the connecting rod is prevented from occurrence of flaking at the inner peripheral surface of the large end part, and has excellent fatigue strength.

Description

コネクティングロッドおよびそれを備えた単気筒内燃機関ならびに鞍乗型車両Connecting rod, single-cylinder internal combustion engine equipped with the same, and saddle riding type vehicle
　本発明は、コネクティングロッドに関し、特に、鉄合金から形成されたコネクティングロッドに関する。また、本発明は、そのようなコネクティングロッドを備えた単気筒内燃機関や鞍乗型車両に関する。 The present invention relates to a connecting rod, and more particularly to a connecting rod formed from an iron alloy. The present invention also relates to a single-cylinder internal combustion engine and a straddle-type vehicle provided with such a connecting rod.
　内燃機関には、ピストンとクランクシャフトとを連結するためにコネクティングロッドと呼ばれる（「コンロッド（con'rod）」と略称されることもある）部材が用いられている。コネクティングロッドは、棒状のロッド本体部と、ロッド本体部の一端に設けられた小端部と、ロッド本体部の他端に設けられた大端部とを備える。小端部がピストンに接続されるのに対し、大端部はクランクシャフトに接続される。より具体的には、小端部に形成された貫通孔にピストンのピストンピンが挿通される。また、大端部に形成された貫通孔にクランクシャフトのクランクピンが挿通される。これにより、コネクティングロッドがピストンおよびクランクシャフトに接続される。 In an internal combustion engine, a member called a connecting rod (sometimes abbreviated as “con'rod”) is used to connect a piston and a crankshaft. The connecting rod includes a rod-shaped rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body. The small end is connected to the piston, while the large end is connected to the crankshaft. More specifically, the piston pin of the piston is inserted through the through hole formed in the small end portion. A crank pin of the crankshaft is inserted through a through hole formed at the large end. Thereby, the connecting rod is connected to the piston and the crankshaft.
　コネクティングロッドは、大端部が２つに分割された分割型と、大端部が分割されていない一体型とに大別される。一体型のコネクティングロッドは、主に単気筒の内燃機関に用いられる。 ¡Connecting rods are roughly divided into a split type with the large end divided into two and an integrated type with the large end not split. The integral connecting rod is mainly used for a single cylinder internal combustion engine.
　一体型コネクティングロッドの大端部の内周面とクランクピンとの間には、フリクションロスを低減するためにニードルベアリングやボールベアリングなどの転がり軸受けが配置される。内燃機関の運転時にピストンを経由して伝わる爆発力は、コネクティングロッドを転がり軸受けに押し付けるので、大端部の内周面には、大きな応力が発生する。この応力が過大な場合、大端部の内周面には、フレーキング（flaking）と呼ばれる疲労破壊現象が発生する。 ¡Rolling bearings such as needle bearings and ball bearings are arranged between the inner peripheral surface of the large end of the integral connecting rod and the crank pin in order to reduce friction loss. The explosive force transmitted through the piston during operation of the internal combustion engine presses the connecting rod against the rolling bearing, so that a large stress is generated on the inner peripheral surface of the large end. When this stress is excessive, a fatigue fracture phenomenon called flaking occurs on the inner peripheral surface of the large end.
　コネクティングロッドにフレーキングが発生すると、内燃機関のスムーズな回転が妨げられるので、内燃機関や車両に不快な音と振動が発生して商品性や快適性を損なってしまう。そのため、コネクティングロッドにはフレーキングが発生しないことが求められる。 When flaking occurs in the connecting rod, smooth rotation of the internal combustion engine is impeded, and unpleasant sound and vibration are generated in the internal combustion engine and the vehicle, thereby impairing commerciality and comfort. Therefore, it is required that no flaking occurs in the connecting rod.
　従来、フレーキングの発生を抑制して長寿命化を実現するために、肌焼鋼（例えばＪＩＳ ＳＣＭ４２０）から形成されたコネクティングロッドに対し、浸炭処理を施すことが一般に行われている。浸炭処理によってコネクティングロッドの表面から炭素を浸透させることにより、表面近傍の炭素濃度が高くなる。そのため、焼入れ後に表面硬度が高くなり、そのことによりフレーキングの発生が抑制される。 Conventionally, in order to suppress the occurrence of flaking and achieve a long life, it is generally performed to carburize a connecting rod formed from case-hardened steel (for example, JIS SCM420). By infiltrating carbon from the surface of the connecting rod by carburizing, the carbon concentration in the vicinity of the surface is increased. Therefore, the surface hardness is increased after quenching, thereby suppressing the occurrence of flaking.
　また、特許文献１には、コネクティングロッドの表面硬度をさらに高くする技術として、高濃度浸炭処理が提案されている。この技術では、カーボンポテンシャル（ＣＰ）が０．８％以上である雰囲気下での浸炭を複数回行う。これにより、コネクティングロッドの表面近傍に微細な粒状の炭化物が析出するとともに、表面近傍におけるマルテンサイト組織の結晶粒径が小さくなる。そのため、表面硬度が著しく高くなるので、疲労強度のいっそうの向上が可能となる。また、特許文献１には、高濃度浸炭処理と同様にコネクティングロッドの表面硬度を高くする技術として、高濃度浸炭窒化処理にも言及がなされている。 Patent Document 1 proposes high-concentration carburizing treatment as a technique for further increasing the surface hardness of the connecting rod. In this technique, carburization is performed a plurality of times in an atmosphere having a carbon potential (CP) of 0.8% or more. Thereby, fine granular carbide precipitates in the vicinity of the surface of the connecting rod, and the crystal grain size of the martensite structure in the vicinity of the surface becomes small. Therefore, the surface hardness is remarkably increased, and the fatigue strength can be further improved. Patent Document 1 also mentions high-concentration carbonitriding as a technique for increasing the surface hardness of the connecting rod, as in high-concentration carburizing.
特開２０００－３１３９４９号公報JP 2000-313949 A
　しかしながら、近年、内燃機関を高性能化した場合、一般的な浸炭処理や、特許文献１に開示されているような高濃度浸炭処理、高濃度浸炭窒化処理が施されたコネクティングロッドでは、フレーキングが比較的短時間で発生するようになってきた。そのため、フレーキング寿命が内燃機関の高性能化の妨げとなり、内燃機関のさらなる高性能化のためには、フレーキング寿命の増大（つまりコネクティングロッドの長寿命化）が必須となってきた。 However, in recent years, when the performance of an internal combustion engine has been improved, flaking is not possible in a connecting rod that has been subjected to general carburizing treatment, high-concentration carburizing treatment, or high-concentration carbonitriding treatment as disclosed in Patent Document 1. Has occurred in a relatively short time. For this reason, the flaking life hinders the improvement in performance of the internal combustion engine, and in order to further improve the performance of the internal combustion engine, it has become essential to increase the flaking life (that is, to extend the life of the connecting rod).
　本発明は、上記問題に鑑みてなされたものであり、その目的は、大端部の内周面におけるフレーキングの発生が抑制され、疲労強度に優れたコネクティングロッドを提供することにある。 The present invention has been made in view of the above problems, and an object of the present invention is to provide a connecting rod that suppresses the occurrence of flaking on the inner peripheral surface of the large end and has excellent fatigue strength.
　本発明によるコネクティングロッドは、ロッド本体部と、前記ロッド本体部の一端に設けられた小端部と、前記ロッド本体部の他端に設けられた大端部と、を備え、鉄合金から形成され、浸炭窒化処理が施されたか、または、浸炭処理および窒化処理が施されたコネクティングロッドであって、前記大端部の内周面から０．１ｍｍの深さにおける炭素含有量が０．８ｗｔ％以上２．１ｗｔ％以下であり、前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下である。 A connecting rod according to the present invention includes a rod body, a small end provided at one end of the rod body, and a large end provided at the other end of the rod body, and is formed of an iron alloy. A connecting rod that has been subjected to carbonitriding or has been subjected to carburizing and nitriding, the carbon content at a depth of 0.1 mm from the inner peripheral surface of the large end portion being 0.8 wt. % And 2.1 wt% or less, and the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.03 wt% or more and 0.19 wt% or less.
　ある好適な実施形態において、本発明によるコネクティングロッドは、前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０４ｗｔ％以上０．１８ｗｔ％以下である。 In a preferred embodiment, the connecting rod according to the present invention has a nitrogen content of 0.04 wt% or more and 0.18 wt% or less at a depth of 0.1 mm from the inner peripheral surface of the large end.
　ある好適な実施形態において、本発明によるコネクティングロッドは、前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０５ｗｔ％以上０．１５ｗｔ％以下である。 In a preferred embodiment, the connecting rod according to the present invention has a nitrogen content of 0.05 wt% or more and 0.15 wt% or less at a depth of 0.1 mm from the inner peripheral surface of the large end.
　ある好適な実施形態において、前記鉄合金は、０．１ｗｔ％以上０．４ｗｔ％以下の炭素、０．１ｗｔ％以上０．５ｗｔ％以下のケイ素および０．３ｗｔ％以上１．２ｗｔ％以下のクロムを含む。 In a preferred embodiment, the iron alloy includes 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon, and 0.3 wt% or more and 1.2 wt% or less of chromium. including.
　ある好適な実施形態において、前記鉄合金のニッケル含有量は０．７ｗｔ％未満である。 In a preferred embodiment, the iron alloy has a nickel content of less than 0.7 wt%.
　ある好適な実施形態において、本発明によるコネクティングロッドは、非拡散性水素含有量が０．４６ｐｐｍ以下である。 In a preferred embodiment, the connecting rod according to the present invention has a non-diffusible hydrogen content of 0.46 ppm or less.
　ある好適な実施形態において、前記浸炭窒化処理、前記浸炭処理および前記窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施されている。 In a preferred embodiment, the carbonitriding process, the carburizing process, and the nitriding process are performed in a furnace that is depressurized to 1/10 or less of standard atmospheric pressure.
　ある好適な実施形態において、前記大端部の内周面近傍に析出している炭化物および炭窒化物の粒径は１０μｍ以下である。 In a preferred embodiment, the particle size of the carbide and carbonitride precipitated in the vicinity of the inner peripheral surface of the large end is 10 μm or less.
　本発明による単気筒内燃機関は、上記構成を有するコネクティングロッドと、前記コネクティングロッドに接続されたクランクシャフトと、を備える。 A single-cylinder internal combustion engine according to the present invention includes a connecting rod having the above configuration, and a crankshaft connected to the connecting rod.
　ある好適な実施形態において、前記クランクシャフトは、前記コネクティングロッドの前記大端部に挿通されたクランクピンと、前記クランクピンとは別体に形成されたクランクウェブと、を有する。 In a preferred embodiment, the crankshaft includes a crankpin inserted into the large end portion of the connecting rod, and a crank web formed separately from the crankpin.
　ある好適な実施形態において、本発明による単気筒内燃機関は、前記大端部の内周面と前記クランクピンとの間に設けられた転がり軸受けをさらに備える。 In a preferred embodiment, the single-cylinder internal combustion engine according to the present invention further includes a rolling bearing provided between the inner peripheral surface of the large end portion and the crank pin.
　ある好適な実施形態において、前記クランクピンは、浸炭処理または浸炭窒化処理を施されている。 In a preferred embodiment, the crank pin is subjected to a carburizing process or a carbonitriding process.
　本発明による鞍乗型車両は、上記構成を有する単気筒内燃機関を備える。 A straddle-type vehicle according to the present invention includes a single-cylinder internal combustion engine having the above-described configuration.
　本発明によるコネクティングロッドの製造方法は、ロッド本体部、前記ロッド本体部の一端部に設けられた小端部および前記ロッド本体部の他端部に設けられた大端部を備えるコネクティングロッドの製造方法であって、鉄合金から形成されたワークピースを用意する工程（Ａ）と、前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で浸炭処理を施す工程（Ｂ）と、前記工程（Ｂ）の後に、前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で浸炭窒化処理を施す工程（Ｃ）と、を包含し、前記工程（Ｃ）は、前記ワークピースの前記大端部となる領域の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下となるように実行される。 A method for manufacturing a connecting rod according to the present invention includes a rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body. A method of preparing a workpiece formed from an iron alloy (A), and a step of carburizing the workpiece in an atmosphere having a carbon potential of 0.8% or more (B); And after the step (B), subjecting the workpiece to carbonitriding in an atmosphere having a carbon potential of 0.8% or more, and the step (C), The process is performed so that the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the region to be the large end of the workpiece is 0.03 wt% or more and 0.19 wt% or less.
　ある好適な実施形態において、前記工程（Ｂ）における前記浸炭処理および前記工程（Ｃ）における前記浸炭窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施される。 In a preferred embodiment, the carburizing treatment in the step (B) and the carbonitriding treatment in the step (C) are performed in a furnace reduced in pressure to 1/10 or less of standard atmospheric pressure.
　あるいは、本発明によるコネクティングロッドの製造方法は、ロッド本体部、前記ロッド本体部の一端部に設けられた小端部および前記ロッド本体部の他端部に設けられた大端部を備えるコネクティングロッドの製造方法であって、鉄合金から形成されたワークピースを用意する工程（Ａ）と、前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で複数回浸炭処理を施す工程（Ｂ）と、前記工程（Ｂ）の後に、前記ワークピースに対して窒化処理を施す工程（Ｃ）と、を包含し、前記工程（Ｃ）は、前記ワークピースの前記大端部となる領域の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下となるように実行される。 Alternatively, a method of manufacturing a connecting rod according to the present invention includes a rod main body, a small end provided at one end of the rod main body, and a large end provided at the other end of the rod main body. A method of preparing a workpiece formed of an iron alloy (A), and a step of subjecting the workpiece to carburization multiple times in an atmosphere having a carbon potential of 0.8% or more. (B) and the step (C) of performing nitriding treatment on the workpiece after the step (B), and the step (C) becomes the large end portion of the workpiece. The process is performed so that the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the region is 0.03 wt% or more and 0.19 wt% or less.
　ある好適な実施形態において、前記工程（Ｂ）における前記浸炭処理および前記工程（Ｃ）における前記窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施される。 In a preferred embodiment, the carburizing treatment in the step (B) and the nitriding treatment in the step (C) are performed in a furnace reduced in pressure to 1/10 or less of standard atmospheric pressure.
　本発明によるコネクティングロッドは、鉄合金から形成され、浸炭窒化処理が施されているか、または、浸炭処理および窒化処理が施されている。浸炭窒化処理（または浸炭処理と窒化処理）により、コネクティングロッドの表面硬度が高くなり、疲労強度が向上する。また、本発明によるコネクティングロッドでは、大端部の内周面から０．１ｍｍの深さにおける炭素含有量が０．８ｗｔ％以上２．１ｗｔ％以下である。これは、上記の浸炭窒化処理または浸炭処理が、カーボンポテンシャル（ＣＰ）が０．８％以上である雰囲気下で行われたことを意味している。つまり、コネクティングロッドに対して、高濃度浸炭窒化処理または高濃度浸炭処理が施されたことを意味している。高濃度浸炭窒化処理または高濃度浸炭処理によれば、コネクティングロッドの表面近傍に微細な粒状の炭化物および／または炭窒化物が析出するとともに、表面近傍におけるマルテンサイト組織の結晶粒径が小さくなる。そのため、表面硬度が著しく高くなり、疲労強度の向上効果が高い。さらに、本発明によるコネクティングロッドでは、大端部の内周面から所定の深さにおける窒素含有量が特定の範囲に設定されており、具体的には、大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下である。このことにより、耐フレーキング性が顕著に向上し、フレーキングの発生を長期間にわたって防止することができる。そのため、本発明によるコネクティングロッドは、単に高濃度浸炭窒化処理や高濃度浸炭処理が施されたコネクティングロッドに比べ、優れた疲労強度を有する。 The connecting rod according to the present invention is made of an iron alloy and is subjected to carbonitriding or carburizing and nitriding. By carbonitriding (or carburizing and nitriding), the surface hardness of the connecting rod is increased and the fatigue strength is improved. In the connecting rod according to the present invention, the carbon content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.8 wt% or more and 2.1 wt% or less. This means that the above carbonitriding or carburizing treatment was performed in an atmosphere having a carbon potential (CP) of 0.8% or more. That is, it means that the high concentration carbonitriding process or the high concentration carburizing process was performed on the connecting rod. According to the high concentration carbonitriding treatment or the high concentration carburizing treatment, fine granular carbides and / or carbonitrides are precipitated in the vicinity of the surface of the connecting rod, and the crystal grain size of the martensite structure in the vicinity of the surface is reduced. Therefore, the surface hardness is remarkably increased, and the effect of improving the fatigue strength is high. Furthermore, in the connecting rod according to the present invention, the nitrogen content at a predetermined depth from the inner peripheral surface of the large end portion is set within a specific range. The nitrogen content at a depth of 1 mm is 0.03 wt% or more and 0.19 wt% or less. Thereby, the anti-flaking property is remarkably improved, and the occurrence of flaking can be prevented over a long period of time. Therefore, the connecting rod according to the present invention has excellent fatigue strength as compared with a connecting rod that has been simply subjected to high-concentration carbonitriding or high-concentration carburizing.
　耐フレーキング性のいっそうの向上を図る観点からは、大端部の内周面から０．１ｍｍの深さにおける窒素含有量は、０．０４ｗｔ％以上０．１８ｗｔ％以下であることが好ましく、０．０５ｗｔ％以上０．１５ｗｔ％以下であることがさらに好ましい。 From the viewpoint of further improving the flaking resistance, the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the large end is preferably 0.04 wt% or more and 0.18 wt% or less, More preferably, it is 0.05 wt% or more and 0.15 wt% or less.
　本発明によるコネクティングロッドの材料である鉄合金は、０．１ｗｔ％以上０．４ｗｔ％以下の炭素、０．１ｗｔ％以上０．５ｗｔ％以下のケイ素および０．３ｗｔ％以上１．２ｗｔ％以下のクロムを含むことが好ましい。炭素含有量が０．１ｗｔ％以上０．４ｗｔ％以下であることにより、熱処理後のコネクティングロッドの内部硬さを２００ＨＶ以上５００ＨＶ以下にすることができるので、コネクティングロッド内部の強度および靭性を十分に高く保つことができる。また、ケイ素含有量が増加すると、耐フレーキング性は向上するが、靭性は低下するおそれがある。ケイ素含有量が０．１ｗｔ％以上０．５ｗｔ％以下であることにより、耐フレーキング性を十分に向上させ、且つ、十分な靭性を確保することができる。また、クロム含有量が増加すると、焼入れ性が良くなる。ただし、クロム含有量が過度に多くなると、焼戻し脆化が発生することがある。クロム含有量が０．３ｗｔ％以上１．２ｗｔ％以下であることにより、適切な焼入れ性を得つつ、焼戻し脆化の発生を防止することができる。 The iron alloy which is the material of the connecting rod according to the present invention includes 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon, and 0.3 wt% or more and 1.2 wt% or less. Preferably it contains chromium. When the carbon content is 0.1 wt% or more and 0.4 wt% or less, the internal hardness of the connecting rod after the heat treatment can be 200 HV or more and 500 HV or less, so that the strength and toughness inside the connecting rod are sufficiently provided. Can be kept high. Further, when the silicon content is increased, the anti-flaking property is improved, but the toughness may be lowered. When the silicon content is 0.1 wt% or more and 0.5 wt% or less, the flaking resistance can be sufficiently improved and sufficient toughness can be ensured. Moreover, when the chromium content is increased, the hardenability is improved. However, if the chromium content is excessively large, temper embrittlement may occur. When the chromium content is 0.3 wt% or more and 1.2 wt% or less, the occurrence of temper embrittlement can be prevented while obtaining appropriate hardenability.
　鉄合金のニッケル含有量は、なるべく少ないことが好ましく、具体的には、０．７ｗｔ％未満であることが好ましい。ニッケル含有量が増加すると、熱処理後の残留オーステナイト量が増加するので、表面硬度が低下することがある。 The nickel content of the iron alloy is preferably as low as possible, specifically, less than 0.7 wt%. When the nickel content increases, the amount of retained austenite after heat treatment increases, so the surface hardness may decrease.
　フレーキング寿命のいっそうの向上を図る観点からは、非拡散性水素含有量が０．４６ｐｐｍ以下であることが好ましい。非拡散性水素含有量が０．４６ｐｐｍ以下であることにより、水素脆性型剥離の発生を抑制することができるので、フレーキング寿命をいっそう向上させることができる。 From the viewpoint of further improving the flaking life, the non-diffusible hydrogen content is preferably 0.46 ppm or less. Since the non-diffusible hydrogen content is 0.46 ppm or less, the occurrence of hydrogen brittle mold peeling can be suppressed, so that the flaking life can be further improved.
　浸炭窒化処理（または浸炭処理と窒化処理）は、真空引きされた炉内において施されることが好ましく、より具体的には、標準大気圧の１／１０以下の圧力に減圧された炉内において施されることが好ましい。このような炉内に窒素を含有するガスを導入することにより、表面（大端部の内周面）から深さ０．１ｍｍにおける窒素含有量を精度良く調節することができる。 The carbonitriding process (or carburizing process and nitriding process) is preferably performed in a vacuum-evacuated furnace, and more specifically, in a furnace reduced in pressure to 1/10 or less of the standard atmospheric pressure. Preferably it is applied. By introducing a gas containing nitrogen into such a furnace, the nitrogen content at a depth of 0.1 mm from the surface (the inner peripheral surface of the large end) can be adjusted with high accuracy.
　大端部の内周面近傍に析出している炭化物および炭窒化物の粒径は、なるべく小さいことが好ましく、具体的には１０μｍ以下であることが好ましい。炭化物および炭窒化物の粒径が１０μｍを超えると、靭性が低下して十分な強度が得られないことがある。 The particle size of the carbide and carbonitride precipitated in the vicinity of the inner peripheral surface of the large end is preferably as small as possible, specifically 10 μm or less. When the particle size of the carbide and carbonitride exceeds 10 μm, the toughness may be lowered and sufficient strength may not be obtained.
　本発明によるコネクティングロッドは、シリンダの数が１つである単気筒内燃機関に好適に用いられる。単気筒内燃機関のクランクシャフトは、典型的には、組立て式のクランクシャフトである。つまり、クランクピンと、クランクウェブとが別体に形成されている。単気筒内燃機関では、フリクションロスの低減が重要であるので、一般的には、大端部の内周面とクランクピンとの間に転がり軸受け（例えばニードルベアリングやボールベアリング）が設けられる。転がり軸受けが設けられている場合、コネクティングロッドが転がり軸受けに押し付けられることにより、大端部の内周面に応力が発生する。この応力が過大であると、フレーキングの発生が懸念されるが、本発明によるコネクティングロッドは、耐フレーキング性に優れているので、フレーキングの発生が長期間にわたって防止される。 The connecting rod according to the present invention is preferably used for a single cylinder internal combustion engine having one cylinder. The crankshaft of a single cylinder internal combustion engine is typically an assembly type crankshaft. That is, the crankpin and the crank web are formed separately. In a single cylinder internal combustion engine, since it is important to reduce friction loss, generally, a rolling bearing (for example, a needle bearing or a ball bearing) is provided between the inner peripheral surface of the large end and the crank pin. When a rolling bearing is provided, stress is generated on the inner peripheral surface of the large end portion by pressing the connecting rod against the rolling bearing. If this stress is excessive, the occurrence of flaking is a concern. However, since the connecting rod according to the present invention is excellent in anti-flaking property, the occurrence of flaking is prevented over a long period of time.
　内燃機関全体の耐久性を高める観点からは、クランクピンの表面硬度および疲労強度も高いことが好ましい。そのため、クランクピンは、浸炭処理または浸炭窒化処理を施されていることが好ましい。 From the viewpoint of enhancing the durability of the entire internal combustion engine, it is preferable that the surface hardness and fatigue strength of the crankpin are also high. Therefore, it is preferable that the crankpin is subjected to carburizing or carbonitriding.
　本発明によるコネクティングロッドを備えた単気筒内燃機関は、各種の鞍乗型車両（例えば自動二輪車）に好適に用いられる。 The single-cylinder internal combustion engine provided with the connecting rod according to the present invention is suitably used for various straddle-type vehicles (for example, motorcycles).
　本発明によるコネクティングロッドの製造方法では、鉄合金から形成されたワークピースに対し、浸炭窒化処理が施されるか、あるいは、浸炭処理および窒化処理が施される。浸炭窒化処理（または浸炭処理と窒化処理）により、コネクティングロッドの表面硬度が高くなり、疲労強度が向上する。また、本発明による製造方法では、上記の浸炭窒化処理や浸炭処理が、カーボンポテンシャル（ＣＰ）が０．８％以上である雰囲気下で行われる。つまり、ワークピースに対して、高濃度浸炭窒化処理または高濃度浸炭処理が施される。高濃度浸炭窒化処理または高濃度浸炭処理によれば、ワークピースの表面近傍に微細な粒状の炭化物および／または炭窒化物が析出するとともに、表面近傍におけるマルテンサイト組織の結晶粒径が小さくなる。そのため、表面硬度が著しく高くなり、疲労強度の向上効果が高い。さらに、本発明による製造方法では、浸炭窒化処理や窒化処理は、ワークピースの大端部となる領域の内周面から所定の深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下となるように実行される。このことにより、耐フレーキング性が顕著に向上し、フレーキングの発生を長期間にわたって防止することができる。そのため、本発明による製造方法により製造されたコネクティングロッドは、単に高濃度浸炭窒化処理や高濃度浸炭処理が施されたコネクティングロッドに比べ、優れた疲労強度を有する。 In the method for manufacturing a connecting rod according to the present invention, a carbonitriding process or a carburizing process and a nitriding process are performed on a workpiece formed of an iron alloy. By carbonitriding (or carburizing and nitriding), the surface hardness of the connecting rod is increased and the fatigue strength is improved. In the production method according to the present invention, the carbonitriding process and the carburizing process are performed in an atmosphere having a carbon potential (CP) of 0.8% or more. That is, a high concentration carbonitriding process or a high concentration carburizing process is performed on the workpiece. According to the high-concentration carbonitriding process or the high-concentration carburizing process, fine granular carbides and / or carbonitrides are precipitated in the vicinity of the surface of the workpiece, and the crystal grain size of the martensite structure in the vicinity of the surface is reduced. Therefore, the surface hardness is remarkably increased, and the effect of improving the fatigue strength is high. Furthermore, in the manufacturing method according to the present invention, the carbonitriding treatment or nitriding treatment has a nitrogen content of 0.03 wt% or more and 0.19 wt% or less at a predetermined depth from the inner peripheral surface of the region that becomes the large end of the workpiece. To be executed. Thereby, the anti-flaking property is remarkably improved, and the occurrence of flaking can be prevented over a long period of time. Therefore, the connecting rod manufactured by the manufacturing method according to the present invention has excellent fatigue strength as compared with a connecting rod that has been simply subjected to high-concentration carbonitriding or high-concentration carburizing.
　浸炭窒化処理（または浸炭処理と窒化処理）は、真空引きされた炉内において施されることが好ましく、より具体的には、標準大気圧の１／１０以下の圧力に減圧された炉内において施されることが好ましい。このような炉内に窒素を含有するガスを導入することにより、表面（大端部の内周面）から深さ０．１ｍｍにおける窒素含有量を精度良く調節することができる。 The carbonitriding process (or carburizing process and nitriding process) is preferably performed in a vacuum-evacuated furnace, and more specifically, in a furnace reduced in pressure to 1/10 or less of the standard atmospheric pressure. Preferably it is applied. By introducing a gas containing nitrogen into such a furnace, the nitrogen content at a depth of 0.1 mm from the surface (the inner peripheral surface of the large end) can be adjusted with high accuracy.
　本発明によると、大端部の内周面におけるフレーキングの発生が抑制され、疲労強度に優れたコネクティングロッドが提供される。 According to the present invention, it is possible to provide a connecting rod that suppresses the occurrence of flaking on the inner peripheral surface of the large end and is excellent in fatigue strength.
本発明の好適な実施形態におけるコネクティングロッド１を模式的に示す図であり、（ａ）は平面図、（ｂ）は（ａ）中の１Ｂ－１Ｂ’線に沿った断面図、（ｃ）は（ａ）中の１Ｃ－１Ｃ’線に沿った断面図である。BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the connecting rod 1 in preferable embodiment of this invention, (a) is a top view, (b) is sectional drawing along the 1B-1B 'line in (a), (c) FIG. 4 is a cross-sectional view taken along line 1C-1C ′ in FIG. 一般的なコネクティングロッドの大端部内周面における深さ方向の応力分布（内燃機関の運転時で応力が最大になるときの応力分布）を示す図である。It is a figure which shows the stress distribution (stress distribution when a stress becomes the maximum at the time of the driving | operation of an internal combustion engine) in the depth direction in the internal peripheral surface of the large end part of a general connecting rod. 本発明の好適な実施形態におけるコネクティングロッド１の製造方法を示すフローチャートである。It is a flowchart which shows the manufacturing method of the connecting rod 1 in suitable embodiment of this invention. （ａ）および（ｂ）は、コネクティングロッド１の表面近傍における断面の金属顕微鏡写真である。(A) And (b) is the metallographic micrograph of the cross section in the surface vicinity of the connecting rod 1. FIG. コネクティングロッド１の深さ方向における炭素濃度（炭素含有量）の分布を示すグラフである。It is a graph which shows distribution of the carbon concentration (carbon content) in the depth direction of the connecting rod. コネクティングロッド１の深さ方向における硬さ分布を示すグラフである。It is a graph which shows the hardness distribution in the depth direction of the connecting rod. 大端部の内周面から０．１ｍｍの深さにおける窒素含有量（ｗｔ％）と、フレーキング寿命（Ｌ５０寿命）との関係を示すグラフである。It is a graph which shows the relationship between nitrogen content (wt%) in the depth of 0.1 mm from the internal peripheral surface of a large end part, and flaking lifetime (L50 lifetime). 本発明の好適な実施形態におけるコネクティングロッド１の製造方法を示すフローチャートである。It is a flowchart which shows the manufacturing method of the connecting rod 1 in suitable embodiment of this invention. 窒化処理または高濃度浸炭窒化処理をガス浸炭用の炉内で行う場合と、真空浸炭用の炉内で行う場合とについて、コネクティングロッドの表面から深さ０．１ｍｍにおける窒素含有量と、窒化時間との関係を示すグラフである。When performing nitriding or high-concentration carbonitriding in a gas carburizing furnace and in a vacuum carburizing furnace, the nitrogen content at a depth of 0.1 mm from the surface of the connecting rod and the nitriding time It is a graph which shows the relationship. 本発明の好適な実施形態におけるコネクティングロッド１を備えた単気筒内燃機関１００を模式的に示す断面図である。1 is a cross-sectional view schematically showing a single cylinder internal combustion engine 100 including a connecting rod 1 according to a preferred embodiment of the present invention. 図１０に示す内燃機関１００を備えた自動二輪車を模式的に示す側面図である。Fig. 11 is a side view schematically showing a motorcycle including the internal combustion engine 100 shown in Fig. 10.
　本願発明者は、高濃度浸炭処理や高濃度浸炭窒化処理が施されたコネクティングロッドにおいてもフレーキングが発生する理由を詳細に検討し、その結果、以下に説明する知見を得た。 The inventor of the present application examined in detail the reason why flaking occurs even in a connecting rod subjected to high-concentration carburizing treatment or high-concentration carbonitriding treatment, and as a result, obtained the knowledge described below.
　フレーキングの原因は、既に説明したように、ニードルベアリングやボールベアリングなどの転がり軸受けから大端部の内周面に大きな応力が伝達されることにある。そのため、コネクティングロッドの表面硬度を、高濃度浸炭処理や高濃度浸炭窒化処理によって上昇させることにより、フレーキングの発生を防止することができると考えられるが、実際には、十分な効果を得ることができない。つまり、単純にコネクティングロッドの表面硬度を高くしても、十分な耐フレーキング性は得られない。 As described above, the cause of flaking is that a large stress is transmitted from the rolling bearing such as a needle bearing or a ball bearing to the inner peripheral surface of the large end. Therefore, it is considered that flaking can be prevented by increasing the surface hardness of the connecting rod by high-concentration carburizing treatment or high-concentration carbonitriding treatment. I can't. That is, even if the surface hardness of the connecting rod is simply increased, sufficient flaking resistance cannot be obtained.
　そこで、本願発明者が、コネクティングロッドの深さ方向における応力分布を分析したところ、最表面ではなく、表面からある程度の深さにおいてもっとも大きな応力が作用することがわかった。さらに、最大応力が作用する深さにおける元素濃度と、耐フレーキング性との関係を検証したところ、最大応力が作用する深さにおける窒素濃度（窒素含有量）が耐フレーキング性に大きな影響を与えていることがわかった。 Therefore, when the inventor of the present application analyzed the stress distribution in the depth direction of the connecting rod, it was found that the greatest stress acts at a certain depth from the surface, not the outermost surface. Furthermore, when the relationship between the element concentration at the depth at which the maximum stress acts and the anti-flaking property was verified, the nitrogen concentration (nitrogen content) at the depth at which the maximum stress acts greatly affected the anti-flaking property. I knew that I was giving.
　本発明は、本願発明者が見出した上記知見に基づいてなされたものである。以下、図面を参照しながら本発明の実施形態を説明する。なお、本発明は以下の実施形態に限定されるものではない。 The present invention has been made based on the above findings found by the present inventors. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.
　図１（ａ）～（ｃ）に、本実施形態におけるコネクティングロッド１を示す。図１（ａ）は、コネクティングロッド１を模式的に示す平面図である。また、図１（ｂ）は、図１（ａ）中の１Ｂ－１Ｂ’線に沿った断面図であり、図１（ｃ）は、図１（ａ）中の１Ｃ－１Ｃ’線に沿った断面図である。 1 (a) to 1 (c) show a connecting rod 1 according to this embodiment. FIG. 1A is a plan view schematically showing the connecting rod 1. 1B is a cross-sectional view taken along line 1B-1B ′ in FIG. 1A, and FIG. 1C is taken along line 1C-1C ′ in FIG. FIG.
　コネクティングロッド１は、図１（ａ）および（ｂ）に示すように、ロッド本体部１０と、ロッド本体部１０の一端に設けられた小端部２０と、ロッド本体部１０の他端に設けられた大端部３０とを備える。 As shown in FIGS. 1A and 1B, the connecting rod 1 is provided at the rod body 10, the small end 20 provided at one end of the rod body 10, and the other end of the rod body 10. The large end 30 is provided.
　ロッド本体部（軸部）１０は、棒状である。ロッド本体部１０の断面形状は、典型的には、図１（ｃ）に示すように、Ｈ字状である。 The rod body part (shaft part) 10 has a rod shape. The cross-sectional shape of the rod body 10 is typically H-shaped as shown in FIG.
　小端部２０は、ピストンピンを通すための貫通孔（ピストンピン孔）２２を有する。小端部２０は、ピストンピンを介してピストンに接続される。小端部２０の内周面（ピストンピン孔２２の外縁を規定する面）２０ａは、典型的には、ベアリングを介さずにピストンピンと接触する。 The small end portion 20 has a through hole (piston pin hole) 22 through which the piston pin passes. The small end 20 is connected to the piston via a piston pin. The inner peripheral surface 20a (surface defining the outer edge of the piston pin hole 22) 20a typically contacts the piston pin without a bearing.
　大端部３０は、クランクピンを通すための貫通孔（クランクピン孔）３２を有している。大端部３０は、クランクピンを介してクランクシャフトに接続される。クランクピン孔３２内には、典型的には、転がり軸受けが配置されるため、大端部３０の内周面（クランクピン３２の外縁を規定する面）３０ａは、転がり軸受けと接触する。コネクティングロッド１は、大端部３０が２つに分割されていない、一体型のコネクティングロッドである。 The large end portion 30 has a through hole (crank pin hole) 32 through which the crank pin passes. The large end 30 is connected to the crankshaft via a crankpin. Since a rolling bearing is typically arranged in the crankpin hole 32, the inner peripheral surface 30a (the surface defining the outer edge of the crankpin 32) 30a of the large end 30 is in contact with the rolling bearing. The connecting rod 1 is an integrated connecting rod in which the large end portion 30 is not divided into two.
　本実施形態におけるコネクティングロッド１は、鉄合金から形成されている。また、コネクティングロッド１は、浸炭窒化処理が施されているか、または、浸炭処理および窒化処理が施されている。 The connecting rod 1 in this embodiment is formed from an iron alloy. In addition, the connecting rod 1 is subjected to carbonitriding or carburizing and nitriding.
　ただし、大端部３０の内周面３０ａから０．１ｍｍの深さにおける炭素含有量は、０．８ｗｔ％以上２．１ｗｔ％以下である。これは、上記の浸炭窒化処理または浸炭処理が、カーボンポテンシャル（ＣＰ）が０．８％以上である雰囲気下で行われたことを意味している。つまり、コネクティングロッド１に対して施された浸炭窒化処理または浸炭処理は、普通の浸炭窒化処理や浸炭処理ではなく、高濃度浸炭窒化処理または高濃度浸炭処理である。高濃度浸炭窒化処理または高濃度浸炭処理によれば、コネクティングロッド１の表面近傍に微細な粒状の炭化物および／または炭窒化物が析出するとともに、表面近傍におけるマルテンサイト組織の結晶粒径が小さくなる。そのため、表面硬度が著しく高くなり、疲労強度の向上効果が高い。 However, the carbon content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.8 wt% or more and 2.1 wt% or less. This means that the above carbonitriding or carburizing treatment was performed in an atmosphere having a carbon potential (CP) of 0.8% or more. That is, the carbonitriding process or the carburizing process performed on the connecting rod 1 is not a normal carbonitriding process or a carburizing process but a high-concentration carbonitriding process or a high-concentration carburizing process. According to the high-concentration carbonitriding process or the high-concentration carburizing process, fine granular carbides and / or carbonitrides are precipitated in the vicinity of the surface of the connecting rod 1 and the crystal grain size of the martensite structure in the vicinity of the surface is reduced. . Therefore, the surface hardness is remarkably increased, and the effect of improving the fatigue strength is high.
　さらに、本実施形態におけるコネクティングロッド１では、大端部３０の内周面３０ａから０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下である。このことにより、耐フレーキング性が顕著に向上する。 Furthermore, in the connecting rod 1 in the present embodiment, the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.03 wt% or more and 0.19 wt% or less. This significantly improves the anti-flaking property.
　図２に、一般的なコネクティングロッドの大端部内周面における深さ方向の応力分布（内燃機関の運転時で応力が最大になるときの応力分布）を計算した結果を示す。図２中には、内周面からの深さが負の値で示されている。例えば、深さ０．１５ｍｍの位置は、「－０．１５」と表記されている。また、図２中で応力を示す複数の曲線には、１～２２の番号が付されており、番号が大きいほど大きな応力を示している。 FIG. 2 shows the result of calculating the stress distribution in the depth direction (stress distribution when the stress becomes maximum during operation of the internal combustion engine) on the inner peripheral surface of the large end portion of a general connecting rod. In FIG. 2, the depth from the inner peripheral surface is shown as a negative value. For example, a position at a depth of 0.15 mm is written as “−0.15”. Also, in FIG. 2, a plurality of curves indicating stress are numbered 1 to 22, and the larger the number, the greater the stress.
　図２からわかるように、応力は最表面においてもっとも大きいわけではない。また、図２から、内周面から約０．１ｍｍの深さにおいて応力が最大となることがわかる。そこで、本願発明者が、深さ０．１ｍｍの位置における元素濃度と耐フレーキング性との関係を詳細に検証したところ、深さ０．１ｍｍの位置における窒素濃度（窒素含有量）が、耐フレーキング性に大きな影響を与えることがわかった。具体的には、後に検証結果ともに説明するように、この深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下であることにより、耐フレーキング性の向上効果が格段に高くなることがわかった。 As can be seen from FIG. 2, the stress is not the largest on the outermost surface. Further, it can be seen from FIG. 2 that the stress becomes maximum at a depth of about 0.1 mm from the inner peripheral surface. Therefore, the inventor of the present application has examined in detail the relationship between the element concentration at a depth of 0.1 mm and the anti-flaking property. As a result, the nitrogen concentration at the depth of 0.1 mm (nitrogen content) It was found that the flaking property was greatly affected. Specifically, as will be described later together with the verification results, when the nitrogen content at this depth is not less than 0.03 wt% and not more than 0.19 wt%, the effect of improving the anti-flaking property is remarkably increased. I understood.
　本実施形態におけるコネクティングロッド１では、大端部３０の内周面３０ａから０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下であるので、耐フレーキング性が顕著に向上し、フレーキングの発生を長期間にわたって防止することができる。そのため、本実施形態におけるコネクティングロッド１は、単に高濃度浸炭窒化処理や高濃度浸炭処理が施されたコネクティングロッドに比べ、優れた疲労強度を有する。 In the connecting rod 1 in the present embodiment, the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end portion 30 is 0.03 wt% or more and 0.19 wt% or less, so that the flaking resistance is remarkable. And the occurrence of flaking can be prevented over a long period of time. Therefore, the connecting rod 1 in this embodiment has an excellent fatigue strength compared to a connecting rod that has been simply subjected to high-concentration carbonitriding or high-concentration carburizing.
　なお、耐フレーキング性のいっそうの向上を図る観点からは、大端部３０の内周面３０ａから０．１ｍｍの深さにおける窒素含有量は、０．０４ｗｔ％以上０．１８ｗｔ％以下であることが好ましく、０．０５ｗｔ％以上０．１５ｗｔ％以下であることがさらに好ましい。 From the viewpoint of further improving the flaking resistance, the nitrogen content at a depth of 0.1 mm from the inner peripheral surface 30a of the large end 30 is 0.04 wt% or more and 0.18 wt% or less. Preferably, it is 0.05 wt% or more and 0.15 wt% or less.
　続いて、図３を参照しながら、本実施形態におけるコネクティングロッド１の製造方法を説明する。図３は、コネクティングロッド１の製造工程を示すフローチャートである。 Subsequently, a method of manufacturing the connecting rod 1 in the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing manufacturing steps of the connecting rod 1.
　まず、鉄合金から鍛造により成形されたワークピースを用意する（工程Ｓ１）。鉄合金の組成に特に限定はないが、鉄合金の炭素（Ｃ）含有量は、０．１ｗｔ％以上０．４ｗｔ％以下であることが好ましい。炭素含有量が０．１ｗｔ％以上０．４ｗｔ％以下であることにより、熱処理後のコネクティングロッド１の内部硬さ（ビッカース硬さ）を２００ＨＶ以上５００ＨＶ以下にすることができるので、コネクティングロッド１内部の強度および靭性を十分に高く保つことができる。 First, a workpiece formed by forging from an iron alloy is prepared (step S1). The composition of the iron alloy is not particularly limited, but the carbon (C) content of the iron alloy is preferably 0.1 wt% or more and 0.4 wt% or less. When the carbon content is 0.1 wt% or more and 0.4 wt% or less, the internal hardness (Vickers hardness) of the connecting rod 1 after the heat treatment can be 200 HV or more and 500 HV or less, so the inside of the connecting rod 1 Strength and toughness can be kept sufficiently high.
　また、鉄合金のケイ素（Ｓｉ）含有量は、０．１ｗｔ％以上０．５ｗｔ％以下であることが好ましい。ケイ素含有量が増加すると、耐フレーキング性は向上するが、靭性は低下するおそれがある。ケイ素含有量が０．１ｗｔ％以上０．５ｗｔ％以下であることにより、耐フレーキング性を十分に向上させ、且つ、十分な靭性を確保することができる。 Further, the silicon (Si) content of the iron alloy is preferably 0.1 wt% or more and 0.5 wt% or less. Increasing the silicon content improves anti-flaking properties but may reduce toughness. When the silicon content is 0.1 wt% or more and 0.5 wt% or less, the flaking resistance can be sufficiently improved and sufficient toughness can be ensured.
　さらに、クロム含有量は、０．３ｗｔ％以上１．２ｗｔ％以下であることが好ましい。クロム含有量が増加すると、焼入れ性（熱処理による硬化のし易さを示す性質）が良くなるものの、クロム含有量が過度に多くなると、焼戻し脆化（鉄合金が所定の温度範囲に長時間保持された場合に生じる脆化現象）が発生することがある。クロム含有量が０．３ｗｔ％以上１．２ｗｔ％以下であることにより、適切な焼入れ性を得つつ、焼戻し脆化の発生を防止することができる。 Furthermore, the chromium content is preferably 0.3 wt% or more and 1.2 wt% or less. Increasing chromium content improves hardenability (property of hardening by heat treatment), but excessive chromium content causes temper embrittlement (the iron alloy is kept in a predetermined temperature range for a long time). The embrittlement phenomenon that occurs when the When the chromium content is 0.3 wt% or more and 1.2 wt% or less, the occurrence of temper embrittlement can be prevented while obtaining appropriate hardenability.
　このように、ワークピースの材料（コネクティングロッド１の材料）である鉄合金は、０．１ｗｔ％以上０．４ｗｔ％以下の炭素、０．１ｗｔ％以上０．５ｗｔ％以下のケイ素および０．３ｗｔ％以上１．２ｗｔ％以下のクロムを含むことが好ましい。炭素含有量、ケイ素含有量およびクロム含有量が上記の範囲内にある鉄合金としては、例えばＪＩＳ ＳＣＭ４２０鋼や、ＪＩＳ ＳＣｒ４２０鋼を用いることができる。ＳＣＭ４２０鋼は、０．１８ｗｔ％以上０．２３ｗｔ％以下の炭素、０．１５ｗｔ％以上０．３５ｗｔ％以下のケイ素、０．９０ｗｔ％以上１．２ｗｔ％以下のクロム、０．６０ｗｔ％以上０．８５ｗｔ％以下のマンガン、０．１５ｗｔ％以上０．３０％以下のモリブデンを含む。ＳＣｒ４２０鋼は、０．１８ｗｔ％以上０．２３ｗｔ％以下の炭素、０．１５ｗｔ％以上０．３５ｗｔ％以下のケイ素、０．９０ｗｔ％以上１．２ｗｔ％以下のクロム、０．６０ｗｔ％以上０．８５ｗｔ％以下のマンガンを含む。 Thus, the iron alloy that is the material of the workpiece (the material of the connecting rod 1) is 0.1 wt% or more and 0.4 wt% or less of carbon, 0.1 wt% or more and 0.5 wt% or less of silicon and 0.3 wt%. % Or more and 1.2 wt% or less of chromium is preferable. As an iron alloy having a carbon content, a silicon content, and a chromium content within the above ranges, for example, JIS SCM420 steel or JIS SCr420 steel can be used. SCM420 steel is made of 0.18 wt% or more and 0.23 wt% or less of carbon, 0.15 wt% or more and 0.35 wt% or less of silicon, 0.90 wt% or more and 1.2 wt% or less of chromium, 0.60 wt% or more and 0.002 wt% or less. 85% by weight or less of manganese and 0.15% by weight or more and 0.30% or less of molybdenum are included. The SCr420 steel is composed of 0.18 wt% or more and 0.23 wt% or less carbon, 0.15 wt% or more and 0.35 wt% or less silicon, 0.90 wt% or more and 1.2 wt% or less chromium, 0.60 wt% or more and 0. Contains 85 wt% or less manganese.
　また、鉄合金のニッケル含有量は、なるべく少ないことが好ましく、具体的には、０．７ｗｔ％未満であることが好ましく、０．２５ｗｔ％以下であることがさらに好ましい。ニッケル含有量が増加すると、熱処理後の残留オーステナイト量が増加するので、表面硬度が低下することがある。 Further, the nickel content of the iron alloy is preferably as small as possible. Specifically, it is preferably less than 0.7 wt%, and more preferably 0.25 wt% or less. When the nickel content increases, the amount of retained austenite after heat treatment increases, so the surface hardness may decrease.
　なお、ここでは鍛造を例示したが、ワークピースを用意する工程における成形手法はこれに限定されるものではない。ワークピースは、例えば、焼結や鋳造、焼結鍛造などによって成形されてもよい。 In addition, although forge was illustrated here, the shaping | molding method in the process of preparing a workpiece is not limited to this. The workpiece may be formed by, for example, sintering, casting, sintering forging, or the like.
　次に、ワークピースに対して機械加工を行う（工程Ｓ２）。この機械加工により、鍛造後のワークピースの外径寸法が整えられる。例えば、バリ取り、ピストンピン孔２２およびクランクピン孔３２の形成、小端部２０および大端部３０の端面加工などが行われる。このように、この工程では主に切削が行われる。 Next, machining is performed on the workpiece (step S2). By this machining, the outer diameter of the workpiece after forging is adjusted. For example, deburring, formation of the piston pin hole 22 and the crank pin hole 32, and end face processing of the small end portion 20 and the large end portion 30 are performed. Thus, cutting is mainly performed in this step.
　続いて、ワークピースに対して１回目の高濃度浸炭処理を施す（工程Ｓ３）。浸炭手法としては、固体浸炭、液体浸炭、ガス浸炭などが知られており、現在ではガス浸炭が主流であるが、ここでは、真空浸炭（「真空ガス浸炭」または「減圧浸炭」と呼ばれることもある）を行う。つまり、この工程における高濃度浸炭処理は、真空引きされた炉内（より具体的には、標準大気圧の１／１０以下の圧力に減圧された炉内）において施される。このような炉内をＡ１変態点（鋼の共析変態温度）以上の温度に設定するとともに、カーボンポテンシャルが０．８％以上になるように炭化水素ガスを炉内に導入し、所定時間浸炭を行う。例えば、１０００℃で１７０分間、浸炭を行う。１回目の高濃度浸炭処理により、鉄合金の表面は過剰浸炭される。その後、ガス冷却を行う（工程Ｓ４）。例えば、窒素（Ｎ２）ガスを導入することにより、冷却を行う。 Subsequently, the workpiece is subjected to a first high-concentration carburizing process (step S3). As carburizing methods, solid carburizing, liquid carburizing, gas carburizing, etc. are known. Currently, gas carburizing is the mainstream, but here it is called vacuum carburizing (also called “vacuum gas carburizing” or “vacuum carburizing”). Do). That is, the high-concentration carburizing process in this step is performed in a vacuum-evacuated furnace (more specifically, in a furnace whose pressure is reduced to 1/10 or less of the standard atmospheric pressure). Such a furnace is set to a temperature higher than the A1 transformation point (eutectoid transformation temperature of steel), and a hydrocarbon gas is introduced into the furnace so that the carbon potential is 0.8% or more, and carburized for a predetermined time. I do. For example, carburization is performed at 1000 ° C. for 170 minutes. The surface of the iron alloy is excessively carburized by the first high-concentration carburizing treatment. Thereafter, gas cooling is performed (step S4). For example, cooling is performed by introducing nitrogen (N 2) gas.
　次に、ワークピースに対して２回目の高濃度浸炭処理を施す（工程Ｓ５）。ここでも、真空浸炭を行う。真空引きされた炉内をＡ１変態点以上で、Ａｃｍ変態点（鉄合金のオーステナイトからセメンタイトが析出する変態温度）以下の温度に設定するとともに、カーボンポテンシャルが０．８％以上になるように炭化水素ガスを炉内に導入し、所定時間浸炭を行う。例えば、８５０℃で１５０分間、浸炭を行う。２回目の高濃度浸炭処理により、過剰浸炭された表面層の炭素が内部に拡散する。その後、ガス冷却を行う（工程Ｓ６）。 Next, the workpiece is subjected to the second high concentration carburizing process (step S5). Again, vacuum carburization is performed. The inside of the evacuated furnace is set to a temperature not lower than the A1 transformation point and not higher than the Acm transformation point (transformation temperature at which cementite precipitates from the austenite of the iron alloy), and carbonized so that the carbon potential is 0.8% or higher. Hydrogen gas is introduced into the furnace and carburized for a predetermined time. For example, carburization is performed at 850 ° C. for 150 minutes. Due to the second high-concentration carburizing treatment, the carbon of the surface layer that has been excessively carburized diffuses inside. Thereafter, gas cooling is performed (step S6).
　続いて、ワークピースに対して窒化処理を施す（工程Ｓ７）。この窒化処理も、真空引きされた炉内で施される。真空引きされた（具体的には標準大気圧の１／１０以下の圧力に減圧された炉内）をＡ１変態点以上で、Ａｃｍ変態点以下の温度に設定するとともに、アンモニアガスを炉内に導入し、所定時間窒化を行う。例えば、８５０℃で１３０分間、浸炭を行う。その後、油冷（焼入れ）を行う（工程Ｓ８）。 Subsequently, nitriding is performed on the workpiece (step S7). This nitriding treatment is also performed in a vacuum-evacuated furnace. The temperature that was evacuated (specifically, the inside of the furnace reduced to a pressure of 1/10 or less of the standard atmospheric pressure) was set to a temperature not lower than the A1 transformation point and not higher than the Acm transformation point, and ammonia gas was introduced into the furnace Then, nitriding is performed for a predetermined time. For example, carburization is performed at 850 ° C. for 130 minutes. Thereafter, oil cooling (quenching) is performed (step S8).
　次に、焼戻しを行う（工程Ｓ９）。焼戻しは、例えば、１９０℃で１２０分間行われる。その後、空冷を行う（工程Ｓ１０）。 Next, tempering is performed (step S9). Tempering is performed at 190 ° C. for 120 minutes, for example. Thereafter, air cooling is performed (step S10).
　最後に、ワークピースに対して機械加工を行う（工程Ｓ１１）。例えば、小端部２０の内周面２０ａや大端部３０の内周面３０ａの研磨が行われる。このように、この工程では主に研磨が行われる。上述したようにして、コネクティングロッド１が完成する。 Finally, machining is performed on the workpiece (step S11). For example, the inner peripheral surface 20a of the small end portion 20 and the inner peripheral surface 30a of the large end portion 30 are polished. Thus, polishing is mainly performed in this step. As described above, the connecting rod 1 is completed.
　図４（ａ）および（ｂ）に、完成したコネクティングロッド１の金属組織を示す。図４（ａ）および（ｂ）は、コネクティングロッド１の表面近傍における断面の金属顕微鏡写真であり、図４（ｂ）は図４（ａ）の一部を拡大したものである。図４（ａ）および（ｂ）に示されているように、マルテンサイトの結晶粒の間に、微細な粒状の炭化物（炭化鉄）および炭窒化物（炭窒化鉄）が析出している。 FIGS. 4A and 4B show the metal structure of the completed connecting rod 1. 4A and 4B are metallographic micrographs of a cross section in the vicinity of the surface of the connecting rod 1, and FIG. 4B is an enlarged view of part of FIG. 4A. As shown in FIGS. 4A and 4B, fine granular carbides (iron carbide) and carbonitrides (iron carbonitride) are precipitated between the martensite crystal grains.
　図５に、コネクティングロッド１の深さ方向における炭素濃度（炭素含有量）の分布を示す。図５に示されているように、表面から０．１ｍｍの深さにおける炭素濃度が約０．９２ｗｔ％であり、高濃度浸炭処理によって、この深さにおける炭素濃度（炭素含有量）が０．８ｗｔ％以上になることがわかる。なお、図５に示したような炭素濃度分布は、例えば電子線マイクロアナライザ（ＥＰＭＡ）により測定することができる。 FIG. 5 shows the distribution of carbon concentration (carbon content) in the depth direction of the connecting rod 1. As shown in FIG. 5, the carbon concentration at a depth of 0.1 mm from the surface is about 0.92 wt%, and the carbon concentration (carbon content) at this depth is 0. It turns out that it becomes 8 wt% or more. The carbon concentration distribution as shown in FIG. 5 can be measured by, for example, an electron beam microanalyzer (EPMA).
　図６に、コネクティングロッド１の深さ方向における硬さ分布を示す。図６に示されているように、表面から０．１ｍｍの深さにおける硬さは約７７０ＨＶである。 FIG. 6 shows the hardness distribution in the depth direction of the connecting rod 1. As shown in FIG. 6, the hardness at a depth of 0.1 mm from the surface is about 770 HV.
　次に、大端部３０の内周面３０ａの表層（つまり深さ０ｍｍ）、内周面３０ａから０．１ｍｍの深さ、内周面３０ａから０．２ｍｍの深さにおける窒素含有量（ｗｔ％）を変化させ、フレーキング寿命への影響を検証した結果を説明する。ここでいうフレーキング寿命は、累積破損確率５０％の寿命（「Ｌ５０寿命」と呼ばれる）である。 Next, the nitrogen content (wt) at the surface layer (that is, depth 0 mm) of the inner peripheral surface 30a of the large end portion 30, the depth of 0.1 mm from the inner peripheral surface 30a, and the depth of 0.2 mm from the inner peripheral surface 30a. %) And explain the results of examining the effect on flaking life. The flaking life here is a life with a cumulative failure probability of 50% (referred to as “L50 life”).
　表１に、深さ０．１ｍｍの位置における窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内にある実施例１～４と、深さ０．１ｍｍの位置における窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲外にある比較例１および２について、検証結果を示す。実施例１～４と、比較例１および２とは、窒化処理の条件が異なる点以外は同じ製法により製造されている。また、表１には、従来のコネクティングロッドとして、普通の浸炭処理（高濃度浸炭処理ではない浸炭処理）が施された比較例３と、特許文献１に開示されているような高濃度浸炭処理が施された比較例４とを併せて示している。なお、深さ方向における窒素含有量の分布は、例えば電子線マイクロアナライザ（ＥＰＭＡ）により測定することができる。 Table 1 shows Examples 1 to 4 in which the nitrogen content at a depth of 0.1 mm is in the range of 0.03 wt% to 0.19 wt%, and the nitrogen content at a depth of 0.1 mm. A verification result is shown about the comparative examples 1 and 2 which are outside the range of 0.03 wt% or more and 0.19 wt% or less. Examples 1 to 4 and Comparative Examples 1 and 2 are manufactured by the same manufacturing method except that nitriding conditions are different. Table 1 also shows Comparative Example 3 in which ordinary carburizing treatment (carburizing treatment other than high-concentration carburizing treatment) was performed as a conventional connecting rod, and high-concentration carburizing treatment as disclosed in Patent Document 1. 6 is shown together with Comparative Example 4 to which is applied. The distribution of the nitrogen content in the depth direction can be measured by, for example, an electron beam microanalyzer (EPMA).
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示されているように、深さ０．１ｍｍの位置における窒素含有量が０．０３ｗｔ％未満である比較例１および０．１９ｗｔ％を超える比較例２では、従来のコネクティングロッド（比較例３および４）と同程度のフレーキング寿命しか得られない。これに対し、深さ０．１ｍｍの位置における窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内にある実施例１～４では、従来のコネクティングロッド（比較例３および４）よりも長いフレーキング寿命が得られる。 As shown in Table 1, in Comparative Example 1 in which the nitrogen content at a depth of 0.1 mm is less than 0.03 wt% and in Comparative Example 2 exceeding 0.19 wt%, a conventional connecting rod (comparison) Only the same flaking life as in Examples 3 and 4) is obtained. In contrast, in Examples 1 to 4 in which the nitrogen content at a depth of 0.1 mm is in the range of 0.03 wt% or more and 0.19 wt% or less, compared to the conventional connecting rod (Comparative Examples 3 and 4). Long flaking life can be obtained.
　また、表１から、表層および深さ０．２ｍｍの位置における窒素含有量には、フレーキング寿命との明確な相関がないことがわかる。例えば比較例１では、表層における窒素含有量が比較例３および４よりも著しく多いにも関らず、従来と同程度のフレーキング寿命しか得られない。また、実施例１および３では、深さ０．２ｍｍの位置における窒素含有量は比較例３および４と同程度であるにも関らず、従来よりも長いフレーキング寿命が得られている。 Also, it can be seen from Table 1 that the nitrogen content at the surface layer and at a depth of 0.2 mm does not have a clear correlation with the flaking life. For example, in Comparative Example 1, although the nitrogen content in the surface layer is significantly higher than those in Comparative Examples 3 and 4, only the same flaking life as that in the prior art can be obtained. Moreover, in Examples 1 and 3, although the nitrogen content at the position of a depth of 0.2 mm is almost the same as that in Comparative Examples 3 and 4, a flaking life longer than that in the prior art is obtained.
　このように、表層や深さ０．２ｍｍの位置ではなく、深さ０．１ｍｍの位置における窒素含有量を所定の範囲内（０．０３ｗｔ％以上０．１９ｗｔ％以下）にすることにより、フレーキング寿命を従来よりも長くし得ることがわかった。なお、比較例２のように、深さ０．１ｍｍの位置における窒素含有量が多すぎるとフレーキング寿命が低下してしまうのは、窒素化合物が増えることによって、靱性が低くなり、金属組織がコネクティングロッドの使用中（内燃機関の運転中）の変形に追随できず、微小な欠陥が発生するためと考えられる。 Thus, by setting the nitrogen content at the position of 0.1 mm depth, not the surface layer and the position of 0.2 mm depth, within a predetermined range (0.03 wt% or more and 0.19 wt% or less), It was found that the king life can be longer than before. In addition, as in Comparative Example 2, if the nitrogen content at a depth of 0.1 mm is too much, the flaking life is lowered because the increase in nitrogen compounds decreases the toughness, and the metal structure This is probably because the connecting rod cannot follow the deformation while the internal combustion engine is in operation (i.e., the internal combustion engine is in operation) and a minute defect occurs.
　図７に、深さ０．１ｍｍの位置における窒素含有量と、フレーキング寿命（Ｌ５０寿命）との関係をグラフとして示す。図７のグラフには、表１に示した例よりもさらに多くの例が示されている。 FIG. 7 is a graph showing the relationship between the nitrogen content at a depth of 0.1 mm and the flaking life (L50 life). The graph of FIG. 7 shows more examples than the example shown in Table 1.
　図７からも、表面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下（図７中の範囲Ａ）であることにより、従来よりも長いフレーキング寿命が実現されることがわかる。また、図７から、表面から０．１ｍｍの深さにおける窒素含有量が０．０４ｗｔ％以上０．１８ｗｔ％以下（図７中の範囲Ｂ）であることにより、さらに長いフレーキング寿命が実現され、０．０５ｗｔ％以上０．１５ｗｔ％以下（図７中の範囲Ｃ）であることにより、いっそう長いフレーキング寿命が実現されることがわかる。 From FIG. 7 as well, a flaking life longer than the conventional one is realized when the nitrogen content at a depth of 0.1 mm from the surface is 0.03 wt% or more and 0.19 wt% or less (range A in FIG. 7). You can see that Further, from FIG. 7, a longer flaking life is realized when the nitrogen content at a depth of 0.1 mm from the surface is 0.04 wt% or more and 0.18 wt% or less (range B in FIG. 7). , 0.05 wt% or more and 0.15 wt% or less (range C in FIG. 7), it can be seen that a longer flaking life is realized.
　なお、本実施形態では、コネクティングロッド１に対し、高濃度浸炭処理と窒化処理とを別々に（順次）施す場合を説明したが、高濃度浸炭処理を施す際に窒化処理を同時に施してもよい。つまり、コネクティングロッド１に対し、高濃度浸炭窒化処理を施してもよい。図８に、高濃度浸炭窒化処理を施す場合のコネクティングロッド１の製造工程の例を示す。 In the present embodiment, the case where the high-concentration carburizing process and the nitriding process are separately (sequentially) performed on the connecting rod 1 has been described. However, the nitriding process may be performed simultaneously when the high-concentration carburizing process is performed. . That is, the connecting rod 1 may be subjected to a high concentration carbonitriding process. In FIG. 8, the example of the manufacturing process of the connecting rod 1 in the case of performing a high concentration carbonitriding process is shown.
　図８に示す例では、まず、鉄合金から鍛造により成形されたワークピースを用意し（工程Ｓ１）、次に、ワークピースに対して機械加工（主に切削）を行う（工程Ｓ２）。続いて、ワークピースに対して高濃度浸炭処理を真空引きされた炉内で施し（工程Ｓ３）、その後、ガス冷却を行う（工程Ｓ４）。 In the example shown in FIG. 8, first, a workpiece formed by forging from an iron alloy is prepared (step S1), and then machining (mainly cutting) is performed on the workpiece (step S2). Subsequently, a high-concentration carburizing process is performed on the workpiece in a vacuum-evacuated furnace (step S3), and then gas cooling is performed (step S4).
　次に、ワークピースに対して高濃度浸炭窒化処理を真空引きされた炉内で施す（工程Ｓ５）。高濃度浸炭窒化処理は、炉内に炭化水素ガスとともにアンモニアガスを導入することにより行う。その後、油冷（焼入れ）を行う（工程Ｓ６）。 Next, a high concentration carbonitriding process is performed on the workpiece in a vacuum-evacuated furnace (step S5). High concentration carbonitriding is performed by introducing ammonia gas together with hydrocarbon gas into the furnace. Thereafter, oil cooling (quenching) is performed (step S6).
　次に、焼戻しを行い（工程Ｓ７）、その後、空冷を行う（工程Ｓ８）。最後に、ワークピースに対して機械加工（主に研磨）を行う（工程Ｓ９）。上述したようにして、コネクティングロッド１が完成する。 Next, tempering is performed (step S7), and then air cooling is performed (step S8). Finally, machining (mainly polishing) is performed on the workpiece (step S9). As described above, the connecting rod 1 is completed.
　なお、高濃度浸炭処理（図３中の工程Ｓ３、Ｓ５および図８中の工程Ｓ３）および高濃度浸炭窒化処理（図８中の工程Ｓ５）は、上述したように、真空引きされた炉内で施される（つまり真空浸炭または真空浸炭窒化である）ことが好ましい。真空浸炭および真空浸炭窒化では、その後の熱処理として炉冷や焼入れの代わりに、ガス冷を行うことができるので、処理時間の短縮を図ることができる。 As described above, the high-concentration carburizing treatment (steps S3 and S5 in FIG. 3 and the step S3 in FIG. 8) and the high-concentration carbonitriding treatment (step S5 in FIG. 8) are performed in the vacuum-evacuated furnace as described above. (That is, vacuum carburizing or vacuum carbonitriding). In vacuum carburizing and vacuum carbonitriding, gas cooling can be performed as a subsequent heat treatment instead of furnace cooling or quenching, so that the processing time can be shortened.
　また、表面から深さ０．１ｍｍにおける窒素含有量を０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内に制御するためには、窒化処理（図３中の工程Ｓ７）および高濃度浸炭窒化処理（図８中の工程Ｓ５）が、真空引きされた炉内で施されることが好ましい。真空雰囲気に窒素を含有するガス（例えばアンモニアガス）を導入することにより、表面（大端部３０の内周面３０ａ）から深さ０．１ｍｍにおける窒素含有量を精度良く調節することができる。 Further, in order to control the nitrogen content at a depth of 0.1 mm from the surface within the range of 0.03 wt% or more and 0.19 wt% or less, nitriding treatment (step S7 in FIG. 3) and high concentration carbonitriding treatment (Step S5 in FIG. 8) is preferably performed in a vacuum-evacuated furnace. By introducing a nitrogen-containing gas (for example, ammonia gas) into the vacuum atmosphere, the nitrogen content at a depth of 0.1 mm from the surface (the inner peripheral surface 30a of the large end portion 30) can be accurately adjusted.
　これに対し、ガス浸炭用の炉内（真空引きされていない炉内）で窒化処理や高濃度浸炭窒化処理を行うと、表面から深さ０．１ｍｍにおける窒素含有量を０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内にすることが困難である。図９に、窒化処理または高濃度浸炭窒化処理をガス浸炭用の炉内で行う場合と、真空浸炭用の炉内で行う場合とについて、表面から深さ０．１ｍｍにおける窒素含有量と、窒化時間との関係を示す。 On the other hand, when nitriding or high-concentration carbonitriding is performed in a gas carburizing furnace (in a furnace not evacuated), the nitrogen content at a depth of 0.1 mm from the surface is 0.03 wt% or more. It is difficult to make it within the range of 19 wt% or less. FIG. 9 shows the nitrogen content at a depth of 0.1 mm from the surface when nitriding or high-concentration carbonitriding is performed in a gas carburizing furnace and in a vacuum carburizing furnace. Shows the relationship with time.
　図９からわかるように、ガス浸炭用の炉内で処理を行う場合の適切な窒化時間の範囲Ｃは、真空浸炭用の炉内で処理を行う場合の適切な窒化時間の範囲Ｄよりも著しく短く、窒化時間を実際にこの範囲Ｃに収めることは非常に難しい。特許文献１に開示されている技術は、ガス浸炭を前提としているため、特許文献１に教示されている高濃度浸炭窒化処理を用いても、表面から０．１ｍｍの深さにおける窒素含有量を０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内にすることはできない。 As can be seen from FIG. 9, the appropriate nitriding time range C when processing in a gas carburizing furnace is significantly greater than the appropriate nitriding time range D when processing in a vacuum carburizing furnace. It is very difficult to actually keep the nitriding time within this range C. Since the technique disclosed in Patent Document 1 is premised on gas carburization, the nitrogen content at a depth of 0.1 mm from the surface can be reduced even when the high-concentration carbonitriding process taught in Patent Document 1 is used. It cannot be within the range of 0.03 wt% or more and 0.19 wt% or less.
　なお、図３に示したようにコネクティングロッド１に対して高濃度浸炭処理と窒化処理とを別々に（順次）施す場合、図８に示したように高濃度浸炭窒化処理を施す場合に比べ、窒素含有量の制御がより容易となる。真空引きされた炉内に導入されるガスが、窒素含有ガスのみであるからである。これに対し、図８に示したように高濃度浸炭窒化処理を施す場合、製造工程を簡略化し、処理時間を短縮できるという効果が得られる。 In addition, when performing high concentration carburizing process and nitriding process separately (sequentially) with respect to the connecting rod 1 as shown in FIG. 3, compared with the case where performing high concentration carbonitriding process as shown in FIG. Control of the nitrogen content becomes easier. This is because the gas introduced into the evacuated furnace is only nitrogen-containing gas. On the other hand, when the high concentration carbonitriding process is performed as shown in FIG. 8, the manufacturing process can be simplified and the processing time can be shortened.
　大端部３０の内周面３０ａ近傍（具体的には表面から深さ０．１ｍｍまでの領域）に析出している炭化物および炭窒化物の粒径（より具体的には外接円直径）は、なるべく小さいことが好ましく、具体的には１０μｍ以下であることが好ましい。炭化物および炭窒化物の粒径が１０μｍを超えると、靭性が低下して十分な強度が得られないことがある。 The particle size (more specifically, circumscribed circle diameter) of carbides and carbonitrides precipitated in the vicinity of the inner peripheral surface 30a of the large end portion 30 (specifically, the region from the surface to a depth of 0.1 mm) is It is preferably as small as possible, specifically 10 μm or less. When the particle size of the carbide and carbonitride exceeds 10 μm, the toughness may be lowered and sufficient strength may not be obtained.
　また、必ずしもコネクティングロッド１の全体に高濃度浸炭処理や窒化処理、高濃度浸炭窒化処理を施す必要はなく、少なくとも大端部３０の内周面３０ａ付近にこれらの処理を施せばよい。例えば、ロッド本体部１０は、大端部３０よりも靭性が高いことが好ましいので、１回目の高濃度浸炭処理（図３中の工程Ｓ３および図８中の工程Ｓ３）の前にロッド本体部１０を銅めっきや防炭剤等によりマスキングしてもよい。 Further, it is not always necessary to perform high concentration carburizing treatment, nitriding treatment, or high concentration carbonitriding treatment on the entire connecting rod 1, and these treatments may be performed at least in the vicinity of the inner peripheral surface 30 a of the large end portion 30. For example, since it is preferable that the rod main body part 10 has higher toughness than the large end part 30, the rod main body part before the first high-concentration carburizing process (step S3 in FIG. 3 and step S3 in FIG. 8). 10 may be masked with copper plating or a carbon-proofing agent.
　あるいは、２回目の高濃度浸炭処理、焼入れ、焼戻しの後（図３中の工程Ｓ９の後）や、高濃度浸炭窒化処理、焼入れ、焼戻しの後（図８中の工程Ｓ７の後）に、ロッド本体部１０に選択的なさらなる焼戻しを行うことによって、ロッド本体部１０の靭性を高くすることもできる。局所的な焼戻しは、例えば、高周波誘導加熱により行うことができる。 Alternatively, after the second high-concentration carburizing treatment, quenching, and tempering (after step S9 in FIG. 3) or after the high-concentration carbonitriding treatment, quenching, and tempering (after step S7 in FIG. 8), By further selectively tempering the rod body 10, the toughness of the rod body 10 can be increased. The local tempering can be performed by, for example, high frequency induction heating.
　なお、本実施形態では、図３に示したように高濃度浸炭処理を２回行う場合と、図８に示したように高濃度浸炭処理と高濃度浸炭窒化処理とを１回ずつ（計２回）行う場合とを例示したが、高濃度浸炭処理および／または高濃度浸炭窒化処理を計３回以上行ってもよい。 In the present embodiment, the high-concentration carburization process is performed twice as shown in FIG. 3 and the high-concentration carburization process and the high-concentration carbonitriding process are performed once each as shown in FIG. However, the high-concentration carburizing process and / or the high-concentration carbonitriding process may be performed three or more times in total.
　また、本願発明者の検討によれば、フレーキング寿命には、コネクティングロッド１の非拡散性水素含有量も大きな影響を与えることがわかった。鉄合金中の水素は、その固溶状態により２種類に分類される。室温で拡散する水素は拡散性水素と呼ばれ、介在物等にトラップされて室温から２００°程度までの温度では拡散しにくい水素は非拡散性水素と呼ばれる。 Further, according to the study of the present inventor, it was found that the non-diffusible hydrogen content of the connecting rod 1 has a great influence on the flaking life. Hydrogen in the iron alloy is classified into two types depending on its solid solution state. Hydrogen that diffuses at room temperature is called diffusible hydrogen, and hydrogen that is trapped by inclusions and the like and hardly diffuses at temperatures from room temperature to about 200 ° is called non-diffusible hydrogen.
　フレーキング寿命のいっそうの向上を図る観点からは、非拡散性水素含有量は、具体的には、０．４６ｐｐｍ以下であることが好ましい。非拡散性水素含有量が０．４６ｐｐｍ以下であることにより、水素脆性型剥離の発生を抑制することができるので、フレーキング寿命をいっそう向上させることができる。 From the viewpoint of further improving the flaking life, specifically, the non-diffusible hydrogen content is preferably 0.46 ppm or less. Since the non-diffusible hydrogen content is 0.46 ppm or less, the occurrence of hydrogen brittle mold peeling can be suppressed, so that the flaking life can be further improved.
　表２に、表１中に示した実施例１～４および比較例１～４について、非拡散性水素含有量を示す。また、表２には、さらなる実施例５～７についても、非拡散性水素含有量を示している。実施例５～７でも、深さ０．１ｍｍの位置における窒素含有量は０．０３ｗｔ％以上０．１９ｗｔ％以下の範囲内にある。さらに、表２には、各例における浸炭処理（あるいは浸炭窒化処理）が、ガス浸炭（ガス浸炭窒化）であるか真空浸炭（真空浸炭窒化）であるかも示している。なお、非拡散性水素含有量の測定は、昇温離脱法により行った。試験片を２００℃から６００℃まで徐々に昇温させ、試験片から放出された水素量を、質量分析計により定量分析した。 Table 2 shows the non-diffusible hydrogen content for Examples 1 to 4 and Comparative Examples 1 to 4 shown in Table 1. Table 2 also shows the non-diffusible hydrogen content for further Examples 5-7. Also in Examples 5 to 7, the nitrogen content at a depth of 0.1 mm is in the range of 0.03 wt% or more and 0.19 wt% or less. Further, Table 2 also shows whether the carburizing process (or carbonitriding process) in each example is gas carburizing (gas carbonitriding) or vacuum carburizing (vacuum carbonitriding). Note that the measurement of the non-diffusible hydrogen content was performed by a temperature rising desorption method. The test piece was gradually heated from 200 ° C. to 600 ° C., and the amount of hydrogen released from the test piece was quantitatively analyzed by a mass spectrometer.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２における実施例４と実施例６との比較、あるいは、実施例５と実施例７との比較から、深さ０．１ｍｍの位置における窒素含有量が同じであっても、非拡散性水素含有量が少ないほど、フレーキング寿命が長く、非拡散性水素含有量は０．４６ｐｐｍ以下が好ましいことがわかる。 From the comparison between Example 4 and Example 6 in Table 2 or the comparison between Example 5 and Example 7, even if the nitrogen content at the depth of 0.1 mm is the same, non-diffusible hydrogen It can be seen that the smaller the content, the longer the flaking life, and the non-diffusible hydrogen content is preferably 0.46 ppm or less.
　また、表２から、浸炭処理（浸炭窒化処理）が、ガス浸炭（ガス浸炭窒化）である場合よりも、真空浸炭（真空浸炭窒化）である場合の方が、非拡散性水素含有量が少なく、この点からも真空浸炭（真空浸炭窒化）が好ましいことがわかる。 Also, from Table 2, the non-diffusible hydrogen content is less when the carburizing process (carbonitriding process) is vacuum carburizing (vacuum carbonitriding) than when gas carburizing (gas carbonitriding). From this point, it can be seen that vacuum carburization (vacuum carbonitriding) is preferable.
　本実施形態におけるコネクティングロッド１は、シリンダの数が１つである単気筒内燃機関に好適に用いられる。図１０に、本実施形態におけるコネクティングロッド１を備えた単気筒内燃機関１００の一例を示す。内燃機関１００は、クランクケース１１０、シリンダブロック１２０およびシリンダヘッド１３０を有している。 The connecting rod 1 in the present embodiment is suitably used for a single cylinder internal combustion engine having one cylinder. FIG. 10 shows an example of a single cylinder internal combustion engine 100 provided with the connecting rod 1 in the present embodiment. The internal combustion engine 100 includes a crankcase 110, a cylinder block 120, and a cylinder head 130.
　クランクケース１１０内にはクランクシャフト１１１が収容されている。クランクシャフト１１１は、クランクピン１１２およびクランクウェブ１１３を有している。クランクピン１１２と、クランクウェブ１１３とは、別体に形成されている。つまり、クランクシャフト１１１は、組立て式のクランクシャフトである。 A crankshaft 111 is accommodated in the crankcase 110. The crankshaft 111 has a crankpin 112 and a crank web 113. The crank pin 112 and the crank web 113 are formed separately. That is, the crankshaft 111 is an assembly-type crankshaft.
　クランクケース１１０の上に、シリンダブロック１２０が設けられている。シリンダブロック１２０には、円筒状のシリンダスリーブ１２１がはめ込まれており、ピストン１２２は、シリンダスリーブ１２１内を往復し得るように設けられている。 A cylinder block 120 is provided on the crankcase 110. The cylinder block 120 is fitted with a cylindrical cylinder sleeve 121, and the piston 122 is provided so as to reciprocate within the cylinder sleeve 121.
　シリンダブロック１２０の上に、シリンダヘッド１３０が設けられている。シリンダヘッド１３０は、シリンダブロック１２０のピストン１２２やシリンダスリーブ１２１とともに燃焼室１３１を形成する。シリンダヘッド１３０は、吸気ポート１３２および排気ポート１３３を有している。吸気ポート１３２内には燃焼室１３１内に混合気を供給するための吸気弁１３４が設けられており、排気ポート１３３内には燃焼室１３１内の排気を行うための排気弁１３５が設けられている。 A cylinder head 130 is provided on the cylinder block 120. The cylinder head 130 forms a combustion chamber 131 together with the piston 122 and the cylinder sleeve 121 of the cylinder block 120. The cylinder head 130 has an intake port 132 and an exhaust port 133. An intake valve 134 for supplying air-fuel mixture into the combustion chamber 131 is provided in the intake port 132, and an exhaust valve 135 for exhausting the combustion chamber 131 is provided in the exhaust port 133. Yes.
　ピストン１２２とクランクシャフト１１１とは、コネクティングロッド１によって連結されている。具体的には、コネクティングロッド１の小端部２０に形成されたピストンピン孔にピストン１２２のピストンピン１２３が挿通されているとともに、大端部３０に形成されたクランクピン孔にクランクシャフト１１１のクランクピン１１２が挿通されており、そのことによってピストン１２２とクランクシャフト１１１とが連結されている。 The piston 122 and the crankshaft 111 are connected by the connecting rod 1. Specifically, the piston pin 123 of the piston 122 is inserted into the piston pin hole formed in the small end portion 20 of the connecting rod 1, and the crankshaft 111 is formed in the crankpin hole formed in the large end portion 30. The crank pin 112 is inserted, whereby the piston 122 and the crank shaft 111 are connected.
　単気筒内燃機関１００では、フリクションロスの低減が重要であるので、図１０に示すように、コネクティングロッド１の大端部３０の内周面３０ａとクランクピン１１２との間には、ニードルベアリング１１４が設けられている。ニードルベアリング１１４が設けられている場合、コネクティングロッド１がニードルベアリング１１４に押し付けられることにより、大端部３０の内周面３０ａに応力が発生する。この応力が過大であると、フレーキングの発生が懸念される。しかしながら、本実施形態におけるコネクティングロッド１は、耐フレーキング性に優れているので、フレーキングの発生が商品として必要な期間以上の長期間にわたって防止される。 In the single-cylinder internal combustion engine 100, it is important to reduce friction loss. Therefore, as shown in FIG. 10, a needle bearing 114 is provided between the inner peripheral surface 30a of the large end 30 of the connecting rod 1 and the crank pin 112. Is provided. When the needle bearing 114 is provided, stress is generated on the inner peripheral surface 30 a of the large end portion 30 by pressing the connecting rod 1 against the needle bearing 114. If this stress is excessive, the occurrence of flaking is a concern. However, since the connecting rod 1 in this embodiment is excellent in anti-flaking property, the occurrence of flaking is prevented for a long period of time longer than that required for a product.
　内燃機関１００全体の耐久性を高める観点からは、クランクピン１１２の表面硬度および疲労強度も高いことが好ましい。そのため、クランクピン１１２は、浸炭処理または浸炭窒化処理を施されていることが好ましい。 From the viewpoint of enhancing the durability of the internal combustion engine 100 as a whole, it is preferable that the surface hardness and fatigue strength of the crankpin 112 are also high. Therefore, the crankpin 112 is preferably subjected to carburizing or carbonitriding.
　なお、図１０には、転がり軸受けとしてニードルベアリング１１４を例示したが、転がり軸受けは、ニードルベアリングのようなころ軸受けに限定されるものではなく、ボールベアリング（玉軸受け）であってもよい。 In FIG. 10, the needle bearing 114 is illustrated as the rolling bearing, but the rolling bearing is not limited to a roller bearing such as a needle bearing, and may be a ball bearing (ball bearing).
　図１１に、図１０に示した内燃機関１００を備えた自動二輪車を示す。図１１に示す自動二輪車では、本体フレーム３０１の前端にヘッドパイプ３０２が設けられている。ヘッドパイプ３０２には、フロントフォーク３０３が車両の左右方向に揺動し得るように取り付けられている。フロントフォーク３０３の下端には、前輪３０４が回転可能なように支持されている。 FIG. 11 shows a motorcycle including the internal combustion engine 100 shown in FIG. In the motorcycle shown in FIG. 11, a head pipe 302 is provided at the front end of the main body frame 301. A front fork 303 is attached to the head pipe 302 so as to be able to swing in the left-right direction of the vehicle. A front wheel 304 is rotatably supported at the lower end of the front fork 303.
　本体フレーム３０１の後端上部から後方に延びるようにシートレール３０６が取り付けられている。本体フレーム３０１上に燃料タンク３０７が設けられており、シートレール３０６上にメインシート３０８ａおよびタンデムシート３０８ｂが設けられている。 A seat rail 306 is attached so as to extend rearward from the upper rear end of the main body frame 301. A fuel tank 307 is provided on the main body frame 301, and a main seat 308 a and a tandem seat 308 b are provided on the seat rail 306.
　また、本体フレーム３０１の後端に、後方へ延びるリアアーム３０９が取り付けられている。リアアーム３０９の後端に後輪３１０が回転可能なように支持されている。 Also, a rear arm 309 extending backward is attached to the rear end of the main body frame 301. A rear wheel 310 is rotatably supported at the rear end of the rear arm 309.
　本体フレーム３０１の中央部には、図１０に示した内燃機関１００が保持されている。内燃機関１００は、本実施形態におけるコネクティングロッド１を備えている。内燃機関１００の前方には、ラジエータ３１１が設けられている。内燃機関１００の排気ポートには排気管３１２が接続されており、排気管３１２の後端にマフラー３１３が取り付けられている。 The internal combustion engine 100 shown in FIG. 10 is held at the center of the main body frame 301. The internal combustion engine 100 includes the connecting rod 1 in the present embodiment. A radiator 311 is provided in front of the internal combustion engine 100. An exhaust pipe 312 is connected to the exhaust port of the internal combustion engine 100, and a muffler 313 is attached to the rear end of the exhaust pipe 312.
　内燃機関１００には変速機３１５が連結されている。変速機３１５の出力軸３１６に駆動スプロケット３１７が取り付けられている。駆動スプロケット３１７は、チェーン３１８を介して後輪３１０の後輪スプロケット３１９に連結されている。変速機３１５およびチェーン３１８は、内燃機関１００により発生した動力を駆動輪に伝える伝達機構として機能する。 A transmission 315 is connected to the internal combustion engine 100. A drive sprocket 317 is attached to the output shaft 316 of the transmission 315. The drive sprocket 317 is connected to the rear wheel sprocket 319 of the rear wheel 310 via a chain 318. The transmission 315 and the chain 318 function as a transmission mechanism that transmits the power generated by the internal combustion engine 100 to the drive wheels.
　図１１に示した自動二輪車には、本実施形態におけるコネクティングロッド１を備えた内燃機関１００が用いられているので、商品として必要な期間以上の長期間にわたってフレーキングの発生が防止される。また、本実施形態におけるコネクティングロッド１は、小型軽量化にも適している。高寿命化により、高負荷をコネクティングロッド１にかけることが可能になるためである。コネクティングロッド１の小型軽量化により、内燃機関１００や車体も軽量化され、自動二輪車の走行安定性や、乗りやすさ、扱いやすさが向上し、商品性が向上する。 Since the motorcycle shown in FIG. 11 uses the internal combustion engine 100 provided with the connecting rod 1 in this embodiment, the occurrence of flaking is prevented over a long period of time longer than the period required for the product. Moreover, the connecting rod 1 in the present embodiment is also suitable for reducing the size and weight. This is because it is possible to apply a high load to the connecting rod 1 by extending the life. By reducing the size and weight of the connecting rod 1, the internal combustion engine 100 and the vehicle body are also lightened, and the running stability, ease of riding, and ease of handling of the motorcycle are improved, and the merchantability is improved.
　なお、本実施形態におけるコネクティングロッド１を備えた内燃機関１００は、自動二輪車に限定されず、ライダーが跨って乗る鞍乗り型車両全般に好適に用いられる。例えば、バギーなどのＡＴＶにも用いられる。 In addition, the internal combustion engine 100 provided with the connecting rod 1 in the present embodiment is not limited to a motorcycle, and is preferably used for all saddle riding type vehicles on which riders ride. For example, it is also used for ATV such as buggy.
　また、本実施形態におけるコネクティングロッド１は、発電機や農作業機器などで用いられる小型内燃機関にも用いることができる。 Further, the connecting rod 1 in the present embodiment can also be used for a small internal combustion engine used in a generator, an agricultural machine, or the like.
　本発明によると、大端部の内周面におけるフレーキングの発生が抑制され、疲労強度に優れたコネクティングロッドが提供される。 According to the present invention, it is possible to provide a connecting rod that suppresses the occurrence of flaking on the inner peripheral surface of the large end and is excellent in fatigue strength.
　本発明によるコネクティングロッドは、各種の鞍乗型車両用の内燃機関（例えば自動二輪車用の内燃機関）に広く用いられる。 The connecting rod according to the present invention is widely used in internal combustion engines for various straddle-type vehicles (for example, internal combustion engines for motorcycles).
　１　　　コネクティングロッド
　１０　　ロッド本体部
　２０　　小端部
　２０ａ　小端部の内周面
　２２　　ピストンピン孔
　３０　　大端部
　３０ａ　大端部の内周面
　３２　　クランクピン孔
　１００　単気筒内燃機関 DESCRIPTION OF SYMBOLS 1 Connecting rod 10 Rod main-body part 20 Small end part 20a Inner peripheral surface of 22 small end part 22 Piston pin hole 30 Large end part 30a Inner peripheral surface of large end part 32 Crank pin hole 100 Single cylinder internal combustion engine

Claims (17)

  1. 　ロッド本体部と、
    　前記ロッド本体部の一端に設けられた小端部と、
    　前記ロッド本体部の他端に設けられた大端部と、を備え、
    　鉄合金から形成され、
    　浸炭窒化処理が施されたか、または、浸炭処理および窒化処理が施されたコネクティングロッドであって、
    　前記大端部の内周面から０．１ｍｍの深さにおける炭素含有量が０．８ｗｔ％以上２．１ｗｔ％以下であり、
    　前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下であるコネクティングロッド。     The rod body,
    A small end provided at one end of the rod body,
    A large end provided at the other end of the rod body,
    Formed from iron alloy,
    A connecting rod that has been subjected to carbonitriding or that has been subjected to carburizing and nitriding,
    The carbon content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.8 wt% or more and 2.1 wt% or less,
    A connecting rod having a nitrogen content of 0.03 wt% or more and 0.19 wt% or less at a depth of 0.1 mm from the inner peripheral surface of the large end portion.
  2. 　前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０４ｗｔ％以上０．１８ｗｔ％以下である請求項１に記載のコネクティングロッド。 The connecting rod according to claim 1, wherein the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.04 wt% or more and 0.18 wt% or less.
  3. 　前記大端部の内周面から０．１ｍｍの深さにおける窒素含有量が０．０５ｗｔ％以上０．１５ｗｔ％以下である請求項１に記載のコネクティングロッド。 The connecting rod according to claim 1, wherein the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the large end is 0.05 wt% or more and 0.15 wt% or less.
  4. 　前記鉄合金は、０．１ｗｔ％以上０．４ｗｔ％以下の炭素、０．１ｗｔ％以上０．５ｗｔ％以下のケイ素および０．３ｗｔ％以上１．２ｗｔ％以下のクロムを含む請求項１から３のいずれかに記載のコネクティングロッド。 The said iron alloy contains 0.1 wt% or more and 0.4 wt% or less carbon, 0.1 wt% or more and 0.5 wt% or less silicon, and 0.3 wt% or more and 1.2 wt% or less chromium. The connecting rod according to any one of the above.
  5. 　前記鉄合金のニッケル含有量は０．７ｗｔ％未満である請求項１から４のいずれかに記載のコネクティングロッド。 The connecting rod according to any one of claims 1 to 4, wherein the iron alloy has a nickel content of less than 0.7 wt%.
  6. 　非拡散性水素含有量が０．４６ｐｐｍ以下である請求項１から５のいずれかに記載のコネクティングロッド。 The connecting rod according to any one of claims 1 to 5, wherein the non-diffusible hydrogen content is 0.46 ppm or less.
  7. 　前記浸炭窒化処理、前記浸炭処理および前記窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施されている請求項１から６のいずれかに記載のコネクティングロッド。 The connecting rod according to any one of claims 1 to 6, wherein the carbonitriding treatment, the carburizing treatment, and the nitriding treatment are performed in a furnace depressurized to a pressure of 1/10 or less of standard atmospheric pressure.
  8. 　前記大端部の内周面近傍に析出している炭化物および炭窒化物の粒径が１０μｍ以下である請求項１から７のいずれかに記載のコネクティングロッド。 The connecting rod according to any one of claims 1 to 7, wherein the carbide and carbonitride precipitated in the vicinity of the inner peripheral surface of the large end have a particle size of 10 µm or less.
  9. 　請求項１から８のいずれかに記載のコネクティングロッドと、
    　前記コネクティングロッドに接続されたクランクシャフトと、
    を備える単気筒内燃機関。     Connecting rod according to any one of claims 1 to 8,
    A crankshaft connected to the connecting rod;
    A single cylinder internal combustion engine.
  10. 　前記クランクシャフトは、前記コネクティングロッドの前記大端部に挿通されたクランクピンと、前記クランクピンとは別体に形成されたクランクウェブと、を有する請求項９に記載の単気筒内燃機関。 The single-cylinder internal combustion engine according to claim 9, wherein the crankshaft has a crankpin inserted into the large end portion of the connecting rod and a crank web formed separately from the crankpin.
  11. 　前記大端部の内周面と前記クランクピンとの間に設けられた転がり軸受けをさらに備える請求項１０に記載の単気筒内燃機関。 The single-cylinder internal combustion engine according to claim 10, further comprising a rolling bearing provided between an inner peripheral surface of the large end portion and the crank pin.
  12. 　前記クランクピンは、浸炭処理または浸炭窒化処理を施されている請求項１１に記載の単気筒内燃機関。 The single-cylinder internal combustion engine according to claim 11, wherein the crank pin is subjected to a carburizing process or a carbonitriding process.
  13. 　請求項９から１２のいずれかに記載の単気筒内燃機関を備えた鞍乗型車両。 A straddle-type vehicle comprising the single-cylinder internal combustion engine according to any one of claims 9 to 12.
  14. 　ロッド本体部、前記ロッド本体部の一端部に設けられた小端部および前記ロッド本体部の他端部に設けられた大端部を備えるコネクティングロッドの製造方法であって、
    　鉄合金から形成されたワークピースを用意する工程（Ａ）と、
    　前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で浸炭処理を施す工程（Ｂ）と、
    　前記工程（Ｂ）の後に、前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で浸炭窒化処理を施す工程（Ｃ）と、を包含し、
    　前記工程（Ｃ）は、前記ワークピースの前記大端部となる領域の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下となるように実行されるコネクティングロッドの製造方法。     A method for manufacturing a connecting rod comprising a rod body, a small end provided at one end of the rod body and a large end provided at the other end of the rod body,
    Preparing a workpiece formed from an iron alloy (A);
    A step (B) of performing a carburizing treatment in an atmosphere having a carbon potential of 0.8% or more with respect to the workpiece;
    After the step (B), a step (C) of performing a carbonitriding process on the workpiece in an atmosphere having a carbon potential of 0.8% or more, and
    The step (C) is performed such that the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the region that becomes the large end of the workpiece is 0.03 wt% or more and 0.19 wt% or less. Manufacturing method of connecting rod.
  15. 　前記工程（Ｂ）における前記浸炭処理および前記工程（Ｃ）における前記浸炭窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施される請求項１４に記載のコネクティングロッドの製造方法。 The connecting rod according to claim 14, wherein the carburizing treatment in the step (B) and the carbonitriding treatment in the step (C) are performed in a furnace reduced in pressure to 1/10 or less of standard atmospheric pressure. Manufacturing method.
  16. 　ロッド本体部、前記ロッド本体部の一端部に設けられた小端部および前記ロッド本体部の他端部に設けられた大端部を備えるコネクティングロッドの製造方法であって、
    　鉄合金から形成されたワークピースを用意する工程（Ａ）と、
    　前記ワークピースに対して０．８％以上のカーボンポテンシャルを有する雰囲気下で複数回浸炭処理を施す工程（Ｂ）と、
    　前記工程（Ｂ）の後に、前記ワークピースに対して窒化処理を施す工程（Ｃ）と、を包含し、
    　前記工程（Ｃ）は、前記ワークピースの前記大端部となる領域の内周面から０．１ｍｍの深さにおける窒素含有量が０．０３ｗｔ％以上０．１９ｗｔ％以下となるように実行されるコネクティングロッドの製造方法。     A method for manufacturing a connecting rod comprising a rod body, a small end provided at one end of the rod body and a large end provided at the other end of the rod body,
    Preparing a workpiece formed from an iron alloy (A);
    A step (B) of performing a carburizing process a plurality of times in an atmosphere having a carbon potential of 0.8% or more with respect to the workpiece;
    After the step (B), the step (C) of nitriding the workpiece,
    The step (C) is performed such that the nitrogen content at a depth of 0.1 mm from the inner peripheral surface of the region that becomes the large end of the workpiece is 0.03 wt% or more and 0.19 wt% or less. Manufacturing method of connecting rod.
  17. 　前記工程（Ｂ）における前記浸炭処理および前記工程（Ｃ）における前記窒化処理は、標準大気圧の１／１０以下の圧力に減圧された炉内において施される請求項１６に記載のコネクティングロッドの製造方法。 17. The connecting rod according to claim 16, wherein the carburizing treatment in the step (B) and the nitriding treatment in the step (C) are performed in a furnace depressurized to 1/10 or less of standard atmospheric pressure. Production method.
PCT/JP2010/071328 2009-12-24 2010-11-30 Connecting rod, single-cylinder internal combustion engine comprising same, and saddle type vehicle WO2011077904A1 (en)

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