JPWO2004081252A1 - Nitriding valve lifter and manufacturing method thereof - Google Patents
Nitriding valve lifter and manufacturing method thereof Download PDFInfo
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- JPWO2004081252A1 JPWO2004081252A1 JP2005503522A JP2005503522A JPWO2004081252A1 JP WO2004081252 A1 JPWO2004081252 A1 JP WO2004081252A1 JP 2005503522 A JP2005503522 A JP 2005503522A JP 2005503522 A JP2005503522 A JP 2005503522A JP WO2004081252 A1 JPWO2004081252 A1 JP WO2004081252A1
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- 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
- C23C8/28—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 one step
- C23C8/30—Carbo-nitriding
- C23C8/32—Carbo-nitriding of ferrous surfaces
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- 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
- C23C8/08—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 only one element being applied
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
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- 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
- C23C8/02—Pretreatment of the material to be coated
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- 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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
- F01L1/12—Transmitting gear between valve drive and valve
- F01L1/14—Tappets; Push rods
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
- F01L1/12—Transmitting gear between valve drive and valve
- F01L1/14—Tappets; Push rods
- F01L1/16—Silencing impact; Reducing wear
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L2303/00—Manufacturing of components used in valve arrangements
Abstract
バルブリフタ（１）又はシム（３）の摺動画（２）は、浸炭焼入焼戻処理をした後、その表面硬度がＨｖ６６０以上、化合物層（６）の厚さが１〜５μｍとなるようガス軟窒化処理を行う。表面の窒化層は空孔率１％以下の緻密な化合物層（６）である。The sliding image (2) of the valve lifter (1) or shim (3) is gas so that the surface hardness is Hv660 or more and the thickness of the compound layer (6) is 1 to 5 μm after carburizing, quenching and tempering treatment. Soft nitriding is performed. The nitride layer on the surface is a dense compound layer (6) having a porosity of 1% or less.
Description
本発明は、内燃機関の動弁系部品であって窒化を施したバルブリフタ及びその製造方法に関する。更に、バルブリフタとカムの組み合わせに関する。 The present invention relates to a valve lifter that is a valve operating system component of an internal combustion engine and is subjected to nitriding, and a method of manufacturing the valve lifter. Further, the present invention relates to a combination of a valve lifter and a cam.
図１０に示すように、内燃機関の直打式動弁機構１０においてカム１１の回転動作をバルブ１２の往復運動に変換するバルブリフタ１は、シリンダブロック１４との往復運動による摺動に加え、カム１１と当接するシム３又は冠面部２（図１参照）が高面圧での摺動および衝撃力を受けるため、優れた耐摩耗性及び耐衝撃性が要求されている。一方、カム１１は、耐摩耗性及び耐衝撃性を有する材質とし、バルブリフタ１への攻撃性低減のため、及び潤滑形態が不安定な境界潤滑とならないようにするため、摺動部表面の表面粗さを向上させる必要がある。 バルブリフタ１の耐摩耗性向上の簡単な手段として、窒化処理が一般に用いられているが、窒化によって最外表面部に形成される化合物層（当業者の間では白層とも呼ばれる。）は、高硬度である一方で非常に脆い性質があることから、従来は研削，研磨等により除去され、窒化拡散層のみを残す状態で用いられてきた。
ところが、近年における内燃機関の高出力化や低燃費化の要求への対応として、窒化による化合物層の高硬度且つ低摩擦係数である特性が着目され、カム１１と摺動するバルブリフタ１の冠面部２におけるフリクション低減の手段として、研磨後も化合物層を残した仕様の摺動部品及びその製造方法が提案され、例えば特開２００２−９７５６３号公報に示されている。
しかし、上記の特開２００２−９７５６３号公報における摺動部品及びその製造方法においては、従来の窒化処理方法が用いられており、窒化処理時に化合物層が比較的厚く（５〜１５μｍ）形成され、表面が脆い層となる上に、処理品の変形も大きく、表面粗さも低下する。このためにその後の工程では、化合物層を残しながら、なおかつ表面粗さの調整もおこなう必要を生じ、薄い化合物層を更に薄く加工する非常に難しく安定しない研磨処理を必要としている。
化合物層を形成させるための一般に行われているガス軟窒化等の処理では、１０μｍ程度の化合物層の形成を目標として、５７０℃前後の温度で数時間の処理を行っている。しかし、このような処理方法では、ポーラス層が発生し、脆くなったε相（Ｆｅ２〜３Ｎ）を生じるばかりでなく、処理品の変形も大きくなると共に表面粗さも大幅に悪化するという問題がある。また、前記の従来の窒化処理における化合物層は、最外層のポーラスなε相（Ｆｅ２〜３Ｎ）、並びにその下の緻密なγ’相（Ｆｅ４Ｎ）および／又はε相とγ’相の混合相からなり、これらは表面にほぼ垂直に配向した比較的粗大な柱状結晶を形成している。
このような窒化処理では、表面粗さが相手材の摩耗に大きく影響することから、相手材への攻撃性を低減する意味においても窒化後における研磨処理が不可欠となっているが、ポーラス層の厚さが不均一であるため研磨代を比較的多く設定する必要がある。更に、硬度バラツキ等により均一な研磨が困難であるために、研磨後にポーラス層が残る可能性もある。高面圧での摺動と衝撃を受けるバルブリフタ冠面においては、研磨後にポーラス層が残った状態では、ポーラス層が剥離脱落し、トラブル発生の原因となる。
特開２００２−９７５６３号公報において、ポーラス層除去、化合物層厚さおよび表面粗さの調整の手段として、バフ等の研磨手段を用いることが示されているが、前述のように化合物層はε相（Ｆｅ２〜３Ｎ）並びに緻密なγ’相（Ｆｅ４Ｎ）および／又はε相とγ’相の混合相からなり、各相の分布状態や硬度バラツキなどによって研磨量が均一とならないことから、同一の研磨面において化合物層が全て除去された部分やポーラス層が残存する部分などが生じやすく、均一な化合物層が得られない。このため、耐摩耗性にバラツキや摩擦トルク低減効果が得られない問題がある。
また、特開２００２−９７５６３号公報に示されるように、表面のうねりに沿うように研磨して均一な化合物層としても、表面粗さの改善に問題を生ずる。更に、上記の研磨処理は非常に高コストとなる問題がある。
一方、バルブリフタと摺動するカムは、摺動面に研磨加工を施して用いられるが表面粗さは比較的粗く、潤滑形態が境界潤滑となり、脆い化合物層を有する前記バルブリフタ冠面の表面粗さを増大させる。このため、運転初期から摩擦トルクを抑制し、潤滑形態が不安定な境界潤滑とならないようにするためには、一般的な研磨加工に加えてペーパーラップ仕上げ加工などの高価な設備と長い加工時間を要する高コストな手段を必要とする問題がある。As shown in FIG. 10, the valve lifter 1 that converts the rotational motion of the cam 11 into the reciprocating motion of the valve 12 in the direct-acting
However, in response to the recent demand for higher output and lower fuel consumption of internal combustion engines, attention has been paid to the characteristics of the compound layer due to nitriding, which is a high hardness and low friction coefficient, and the crown portion of the valve lifter 1 that slides with the cam 11 As a means for reducing friction in No. 2, a sliding part having a specification in which a compound layer remains after polishing and a method for manufacturing the same are proposed, and for example, disclosed in JP-A-2002-97563.
However, in the sliding component and the manufacturing method thereof in the above Japanese Patent Laid-Open No. 2002-97563, a conventional nitriding method is used, and the compound layer is formed relatively thick (5 to 15 μm) during nitriding, The surface becomes a brittle layer, the deformation of the processed product is large, and the surface roughness is reduced. For this reason, in the subsequent steps, it is necessary to adjust the surface roughness while leaving the compound layer, and a very difficult and unstable polishing process for processing the thin compound layer further thinly is required.
In a generally used process such as gas soft nitriding for forming a compound layer, a process is performed at a temperature of about 570 ° C. for several hours with the goal of forming a compound layer of about 10 μm. However, in such a treatment method, a porous layer is generated and not only the ε phase (Fe 2 to 3 N) becomes brittle, but also the deformation of the treated product becomes large and the surface roughness is also greatly deteriorated. There is. Further, the compound layer in the conventional nitriding treatment is composed of the outermost porous ε phase (Fe 2 to 3 N), the dense γ ′ phase (Fe 4 N) and / or the ε phase and γ ′ below the outer layer. It consists of a mixed phase of phases, which form relatively coarse columnar crystals oriented almost perpendicular to the surface.
In such nitriding treatment, since the surface roughness greatly affects the wear of the counterpart material, polishing treatment after nitriding is indispensable also in the sense of reducing the aggressiveness to the counterpart material. Since the thickness is not uniform, it is necessary to set a relatively large polishing allowance. Furthermore, since uniform polishing is difficult due to hardness variations and the like, a porous layer may remain after polishing. On the valve lifter crown that receives sliding and impact at high surface pressure, if the porous layer remains after polishing, the porous layer peels off and causes troubles.
In JP-A-2002-97563, it is shown that a polishing means such as a buff is used as a means for adjusting the porous layer removal, the thickness of the compound layer, and the surface roughness. It consists of a phase (Fe 2 to 3 N) and a dense γ ′ phase (Fe 4 N) and / or a mixed phase of ε phase and γ ′ phase, and the polishing amount is not uniform due to the distribution state and hardness variation of each phase For this reason, a portion where the compound layer is completely removed or a portion where the porous layer remains is likely to occur on the same polished surface, and a uniform compound layer cannot be obtained. For this reason, there is a problem that variations in wear resistance and a friction torque reduction effect cannot be obtained.
Further, as disclosed in Japanese Patent Application Laid-Open No. 2002-97563, there is a problem in improving the surface roughness even when the uniform compound layer is polished so as to follow the waviness of the surface. Further, the above polishing process has a problem of being very expensive.
On the other hand, the cam that slides with the valve lifter is used by polishing the sliding surface, but the surface roughness is relatively rough, the lubrication form is boundary lubrication, and the surface roughness of the valve lifter crown surface having a brittle compound layer. Increase. For this reason, in order to suppress friction torque from the beginning of operation and prevent boundary lubrication from becoming unstable, expensive equipment such as paper lapping and long processing time in addition to general polishing processing There is a problem that requires a high-cost means requiring cost.
本発明は、上記の問題点を解決するもので、窒化処理の段階において表面部に均一で緻密な耐摩耗性の高い化合物層を形成し、且つ、窒化処理における表面粗さの増大および処理物の変形が小さく、耐摩耗性向上や表面粗さと寸法精度改善のための研磨処理を要さないバルブリフタとその製造方法を提供することを目的とする。更に、カム表面にペーパーラップ仕上げなどを必要とせずにカムと組み合わせて用いることができるバルブリフタを提供することを目的とする。
一般に、窒化層においては、窒素濃度の相対的に低い拡散層と、窒素濃度の高い化合物層とが層状に形成される。窒化処理温度が高いと化合物層が厚く形成され、最外表面が脆いポーラス状となるので、これをできるだけ少なくするためには処理温度を低く設定すればよいが、その場合には拡散層も薄くなってしまう。バルブリフタにおいては、拡散層厚さを５０〜１００μｍ必要とされるため、５０〜１００μｍの前記拡散層と高硬度で低摩擦係数を示す緻密で所定の表面粗さの化合物層を得ることが望まれている。
そこで、本発明者等は鋭意研究の結果、窒化前のバルブリフタ冠面の表面粗さを小さくし、且つ、窒化による化合物層の厚さを薄く抑えることによって、窒化後の冠面の表面粗さも小さく、耐摩耗性に優れたバルブリフタを得ることができるということを見いだした。更に、前記のバルブリフタをカムと組み合わせることで、ペーパーラップなどの高コストな仕上げ加工を必要とせずに、ならし運転によりカムの表面粗さを小さくさせ、総合的に耐摩耗性に優れ且つ摩擦トルクを低減したバルブリフタとカムの組合せを実現することができ、併せて低コスト化も実現できることを見出した。
すなわち、本発明による少なくとも冠面にガス窒化又はガス軟窒化を施したバルブリフタは、最外表面に窒化による化合物層が１〜５μｍ形成され、形成された該化合物層の表面粗さがＲａ０．０５以下であることを特徴とする。また、本発明によるバルブリフタの製造方法は、窒化前の冠面の表面粗さをＲａ０．０１〜０．０３に研磨加工することを特徴とする。そのように研磨加工したバルブリフタを窒化処理し、表面化合物層厚さが１〜５μｍとなる窒化条件を選択することにより、高硬度で低摩擦係数の窒化化合物層を冠面の最外表面に有し且つ表面粗さＲａ０．０５以下になるバルブリフタを得る。
窒化後の化合物層厚さが１μｍ以下では耐摩耗性や摩擦トルク低減効果が得られず、５μｍ以上ではポーラス層の形成や表面粗さの増大、並びに化合物層が厚いことによる使用時の化合物層剥離の問題が生じるため上限を５μｍとしている。また、一般に、表面粗さは、Ｒａ０．０５以下であれば摺動部品として問題なく使用することができる。表面粗さがＲａ０．０５以上では、相手材攻撃性が大きくなり、摩擦トルク低減効果も得られないことから本発明では冠面の表面粗さはＲａ０．０５以下としている。表面粗さは、Ｒａ０．０４５以下において、相手材カムを磨く機能を有し、よって摩擦トルクを低減する効果が得られるためより好ましい。
また、本発明によるバルブリフタにおいては、窒化後の化合物層の空孔率が５％以下であり、例えば図３に示すように、ＳＥＭによる倍率８０００倍での観察において表面部にポーラス層は認められず、比較的緻密な化合物層を形成している。一般に、空孔率が５％以下であればバルブリフタのような摺動部品としては十分緻密であるので、本発明では空孔率を５％以下とする。空孔率が５％以上では表面粗さに影響するため、耐摩耗性や摩擦トルク低減効果が得られない。
更に、図７に示すように、表面に平均径０．５μｍ以下の微細な炭化物，窒化物，硫化物或いは酸化物、又は前記化合物の２種以上からなる多数の突起を有していることを特徴とする。これらの突起は、カムと組み合わせて摺動したときに、その磨き機能によりカムの表面粗さをＲａ０．０２以下まで向上させ、バルブリフタ自身の表面粗さを増大させることなく離脱して表面にディンプルを残す特徴がある。尚、特開平６−２５１１にはカムと摺動する摺動面の表面粗さを０．２Ｒｚ乃至０．７Ｒｚとした窒化珪素とすることが示されているが、０．２Ｒｚ以下では表面粗さの改善効果が無いことが示され、構成が異なるものである。
本発明に係るバルブリフタと組み合わせる相手材カムには、一般的にカムシャフトに用いられる鋳鉄、鋳鋼およびそれらのチル、浸炭、焼入などの処理を施したものや、鉄系焼結材およびそれに焼入処理などを施したものを使用することができる。
更に、本発明によるバルブリフタの製造方法では、窒化処理において、バルブリフタに有害なポーラス層を生じない。バルブリフタの表面には１〜５μｍのγ’相及び／又はγ’相とε相の混合相からなる均一で緻密な等軸結晶を含む窒素化合物層を形成し、且つ，冠面の表面粗さはＲａ０．０５以下であり変形も殆どない。このため窒化処理後の研磨を必要としないばかりでなく、研磨によってポーラス層を取り除く場合に起こる、ポーラス層の研磨残りや、必要な窒素化合物層の研磨による取りすぎも無い。また、窒化により形成された均一な厚さで緻密な化合物層により、前記バルブリフタは冠面の表面硬度が均一にＨｖ６６０以上であることを特徴とする。
前記に加え本発明のバルブリフタの製造方法においては、前記バルブリフタの窒化処理温度が５００〜５６０℃であることを特徴とする。窒化処理温度が５００℃未満では窒化速度が遅く十分な窒素化合物層が形成されず、また５６０℃を超えるとポーラス層が形成されて窒化処理後に除去のための研磨が必要となる。更に、窒化処理の雰囲気を適切に調節することによりバルブリフタ冠面にγ’相及び／又はγ’相とε相の混合相を形成することを特徴とする。そして、窒化化合物層は等軸結晶を含んでなることを特徴とする。
前記のバルブリフタにおいて、母材としては一般にバルブリフタに用いられている機械構造用炭素鋼，合金鋼，工具鋼などを用いることができる。
また、上記材料に用いられる窒化処理法には、ガス窒化，ガス軟窒化以外にも、イオン窒化，ラジカル窒化や塩浴窒化などが挙げられるが、イオン窒化，ラジカル窒化法は１回の処理量が非常に少なくコスト面でのメリットがないこと、塩浴窒化法は環境問題と面粗度の確保が困難であることから好ましくなく、本発明においてはガス窒化およびガス軟窒化が適している。
ガス窒化及びガス軟窒化処理はＮＨ３を使用する方法が一般的であるが、鋼材に対して窒化作用を示す雰囲気を形成する尿素などの物質を使用してもかまわない。また、本発明では雰囲気の調節用にＮ２ガスを使用しているが、ＮＨ３の分解ガス，変成ガス（ＲＸガス），Ｎ２ガス等を単体又は混合して必要量を供給しても良い。さらに本発明では軟窒化用のガスとしてＣＯ２ガスを使用しているが、変成ガス等のＣＯを含むガスを使用する方法でもかまわない。また窒化処理に属する酸窒化、浸硫窒化等の窒素化合物層中に第三の元素を含む場合であっても、表面に形成された窒素化合物層がγ’相及び／又はγ’相とε相の混合した相で有れば本発明の効果を示す。
本発明の窒化バルブリフタにおいては、ガス窒化およびガス軟窒化法を用いて、窒化処理温度，時間，雰囲気等を調整し、窒化処理後においてポーラス層が無く、空孔率が５％以下の緻密な窒化化合物層を形成する。窒化前後を比較し、表面粗さの増大が殆どなく、窒化処理による歪みや変形も極めて小さい。よって、窒化後の化合物層厚さの調整，表面粗さの調整およびポーラス層除去のための研磨を必要とせずに均一な厚さの化合物層が得られ、これにより安定した耐摩耗性を確保できる。また、高コストな研磨処理を必要としないため、低コストで高性能なバルブリフタを得ることができる。更に、カムと組み合わせて摺動したときに、バルブリフタ自身の表面粗さを増大させることなく、その磨き機能によりカムの表面粗さを向上させることができる。
尚、バルブリフタには、バルブリフタ本体上面とカムとの間にシムを組み付けカムと摺動させるシムを使用した仕様のバルブリフタと、シムを用いずにバルブリフタ冠面で直接カムと摺動させるシムレス仕様のバルブリフタがあるが、本発明のバルブリフタおよびその製造方法は両仕様のバルブリフタとも適用が可能である。また、バルブリフタの冠面等に油孔やその他の目的の穴或いは面取，溝等を設けたバルブリフタについても適用できる。更に、本発明のバルブリフタおよびその製造方法による化合物層をバルブのステムエンド等と摺動するバルブリフタのボス部４への適用も可能である。The present invention solves the above-mentioned problems, and forms a uniform and dense compound layer with high wear resistance on the surface portion in the nitriding treatment stage, and increases the surface roughness in the nitriding treatment and the treated product. An object of the present invention is to provide a valve lifter that does not require a polishing process for improving wear resistance and improving surface roughness and dimensional accuracy, and a method for manufacturing the same. It is another object of the present invention to provide a valve lifter that can be used in combination with a cam without requiring a paper wrap finish on the cam surface.
In general, in a nitride layer, a diffusion layer having a relatively low nitrogen concentration and a compound layer having a high nitrogen concentration are formed in layers. When the nitriding temperature is high, the compound layer is formed thick and the outermost surface becomes brittle porous. To reduce this as much as possible, the processing temperature can be set low, but in that case the diffusion layer is also thin. turn into. In a valve lifter, since a diffusion layer thickness of 50 to 100 μm is required, it is desired to obtain a compound layer having a predetermined surface roughness with a high hardness and a low coefficient of friction with the diffusion layer of 50 to 100 μm. ing.
Therefore, as a result of diligent research, the inventors of the present invention have reduced the surface roughness of the valve lifter crown surface before nitriding and reduced the thickness of the compound layer by nitriding, thereby reducing the surface roughness of the crown surface after nitriding. It has been found that a valve lifter that is small and has excellent wear resistance can be obtained. Furthermore, by combining the above valve lifter with a cam, the surface roughness of the cam is reduced by running-in operation without the need for costly finishing such as paper wrap, and it has excellent overall wear resistance and friction. It has been found that a combination of a valve lifter and a cam with reduced torque can be realized, and cost can be reduced.
That is, in the valve lifter according to the present invention, at least the crown surface is subjected to gas nitriding or gas soft nitriding, a compound layer by nitriding is formed on the outermost surface by 1 to 5 μm, and the surface roughness of the formed compound layer is Ra 0.05. It is characterized by the following. In addition, the valve lifter manufacturing method according to the present invention is characterized in that the surface roughness of the crown surface before nitriding is polished to Ra 0.01 to 0.03. By nitriding the polished valve lifter and selecting a nitriding condition that the surface compound layer thickness is 1 to 5 μm, a nitrided compound layer having a high hardness and a low friction coefficient is provided on the outermost surface of the crown surface. In addition, a valve lifter having a surface roughness Ra of 0.05 or less is obtained.
When the compound layer thickness after nitriding is 1 μm or less, the wear resistance and the friction torque reduction effect cannot be obtained. When the compound layer thickness is 5 μm or more, the formation of a porous layer, the increase in surface roughness, and the compound layer in use due to the thick compound layer Since the problem of peeling occurs, the upper limit is set to 5 μm. In general, if the surface roughness is Ra 0.05 or less, it can be used as a sliding part without any problem. When the surface roughness is Ra 0.05 or more, the attacking property of the counterpart material is increased, and the effect of reducing the friction torque cannot be obtained. Therefore, in the present invention, the surface roughness of the crown surface is set to Ra 0.05 or less. The surface roughness is more preferably at Ra 0.045 or less because it has a function of polishing the mating material cam, and the effect of reducing the friction torque can be obtained.
Moreover, in the valve lifter according to the present invention, the porosity of the compound layer after nitriding is 5% or less. For example, as shown in FIG. However, a relatively dense compound layer is formed. Generally, if the porosity is 5% or less, it is sufficiently dense as a sliding part such as a valve lifter. Therefore, in the present invention, the porosity is 5% or less. When the porosity is 5% or more, the surface roughness is affected, so that the wear resistance and the friction torque reduction effect cannot be obtained.
Furthermore, as shown in FIG. 7, the surface has fine projections made of fine carbides, nitrides, sulfides or oxides having an average diameter of 0.5 μm or less, or two or more of the above compounds. Features. When these protrusions slide in combination with a cam, the polishing function improves the cam surface roughness to Ra 0.02 or less, and the valve lifter itself disengages without increasing the surface roughness and dimples on the surface. There is a feature to leave. Japanese Patent Laid-Open No. 6-2511 discloses that the surface roughness of the sliding surface sliding with the cam is 0.2 Rz to 0.7 Rz, but the surface roughness is 0.2 Rz or less. It is shown that there is no improvement effect, and the configuration is different.
The counterpart cam combined with the valve lifter according to the present invention includes cast iron, cast steel and their chill, carburizing and quenching treatments generally used for camshafts, iron-based sintered materials, It is possible to use a product that has been subjected to an incoming treatment.
Furthermore, in the method for manufacturing a valve lifter according to the present invention, a porous layer harmful to the valve lifter is not generated in the nitriding treatment. On the surface of the valve lifter, a nitrogen compound layer containing a uniform and dense equiaxed crystal composed of a γ ′ phase of 1 to 5 μm and / or a mixed phase of γ ′ phase and ε phase is formed, and the surface roughness of the crown surface Is less than Ra0.05 and there is almost no deformation. Therefore, not only the polishing after the nitriding treatment is not required, but also the polishing residue of the porous layer and the excessive removal by the polishing of the necessary nitrogen compound layer, which occur when the porous layer is removed by polishing, are eliminated. Further, the valve lifter has a uniform surface hardness of Hv660 or more due to the uniform thickness and the dense compound layer formed by nitriding.
In addition to the above, the valve lifter manufacturing method of the present invention is characterized in that a nitriding temperature of the valve lifter is 500 to 560 ° C. When the nitriding temperature is less than 500 ° C., the nitriding rate is slow and a sufficient nitrogen compound layer is not formed. When the nitriding temperature exceeds 560 ° C., a porous layer is formed and polishing for removal is required after the nitriding treatment. Furthermore, it is characterized in that a γ ′ phase and / or a mixed phase of γ ′ phase and ε phase is formed on the valve lifter crown by appropriately adjusting the nitriding atmosphere. The nitride compound layer includes equiaxed crystals.
In the above-described valve lifter, carbon steel for mechanical structure, alloy steel, tool steel, etc. generally used for valve lifters can be used as the base material.
In addition to gas nitridation and gas soft nitridation, nitriding methods used for the above materials include ion nitriding, radical nitriding, salt bath nitriding, etc., but ion nitriding and radical nitriding methods have a single throughput. However, the salt bath nitriding method is not preferable because it is difficult to ensure environmental problems and surface roughness, and gas nitriding and gas soft nitriding are suitable in the present invention.
Gas nitriding and gas soft nitriding are generally performed using NH 3 , but a substance such as urea that forms an atmosphere exhibiting nitriding action on a steel material may be used. In the present invention, N 2 gas is used for adjusting the atmosphere. However, even if NH 3 decomposition gas, metamorphic gas (RX gas), N 2 gas, or the like is used alone or mixed, the required amount is supplied. good. Furthermore, in the present invention, CO 2 gas is used as the soft nitriding gas, but a method using a gas containing CO such as a metamorphic gas may also be used. In addition, even when a third element is included in the nitrogen compound layer such as oxynitriding and nitrosulfiding belonging to nitriding treatment, the nitrogen compound layer formed on the surface is γ ′ phase and / or γ ′ phase and ε The effect of the present invention is exhibited if the phases are mixed.
In the nitriding valve lifter of the present invention, gas nitriding and gas soft nitriding methods are used to adjust the nitriding temperature, time, atmosphere, etc., and after the nitriding, there is no porous layer and the porosity is 5% or less. A nitride compound layer is formed. Compared with before and after nitriding, there is almost no increase in surface roughness, and distortion and deformation due to nitriding treatment are extremely small. Therefore, it is possible to obtain a compound layer with a uniform thickness without adjusting the thickness of the compound layer after nitriding, adjusting the surface roughness, and polishing for removing the porous layer, thereby ensuring stable wear resistance. it can. In addition, since a high-cost polishing process is not required, a high-performance valve lifter can be obtained at a low cost. Furthermore, when sliding in combination with the cam, the surface roughness of the cam can be improved by the polishing function without increasing the surface roughness of the valve lifter itself.
The valve lifter has a valve lifter that uses a shim that slides against the cam by assembling a shim between the upper surface of the valve lifter body and the cam. Although there is a valve lifter, the valve lifter and the manufacturing method thereof of the present invention can be applied to both types of valve lifters. Further, the present invention can also be applied to a valve lifter in which oil holes, holes for other purposes, chamfers, grooves or the like are provided on the crown surface of the valve lifter. Furthermore, the valve lifter of the present invention and the manufacturing method thereof can be applied to the
図１は本発明が適用可能なバルブリフタ（シムレス）の一例の断面図である。
図２は本発明が適用可能なバルブリフタ（シム有）の他の例の断面図である。
図３は本発明によるバルブリフタの窒化後の冠面断面の顕微鏡写真（８０００倍）である。
図４は図３の化合物層を明示する断面図である。
図５は従来技術によるバルブリフタの窒化後の冠面断面の顕微鏡写真（８０００倍）である。
図６は図５のポーラス層を明示する断面図である。
図７は本発明によるバルブリフタの窒化後の冠面表面の顕微鏡写真（８０００倍）である。
図８は従来技術によるバルブリフタの窒化後の冠面表面の顕微鏡写真（８０００倍）である。
図９はカム回転数と摩擦トルクとの関係を示すグラフ図である。
図１０はバルブリフタの使用例を示す断面図である。
図１１は本発明によるバルブリフタの窒化後における冠面断面のＴＥＭ観察写真（３００００倍）である。
図１２は従来技術によるバルブリフタの窒化後にポーラス層を除去した冠面断面のＴＥＭ観察写真（３００００倍）である。
図１３は本発明によるバルブリフタの摺動試験後における冠面表面の顕微鏡写真（８０００倍）である。
図１４は本発明及び従来技術によるバルブリフタと相手材カムのならし運転前後における表面粗さの変化を示す図である。
図１５は本発明によるバルブリフタと相手材カムとの摺動試験前後での表面粗さの変化を示す図である。FIG. 1 is a sectional view of an example of a valve lifter (shimless) to which the present invention can be applied.
FIG. 2 is a cross-sectional view of another example of a valve lifter (with shim) to which the present invention can be applied.
FIG. 3 is a photomicrograph (8000 magnifications) of the crown section after nitriding of the valve lifter according to the present invention.
4 is a cross-sectional view showing the compound layer of FIG.
FIG. 5 is a photomicrograph (8000 magnifications) of the cross-sectional surface of the crown surface after nitriding of a conventional valve lifter.
6 is a cross-sectional view clearly showing the porous layer of FIG.
FIG. 7 is a photomicrograph (8000 times) of the crown surface of the valve lifter according to the present invention after nitriding.
FIG. 8 is a photomicrograph (8000 magnifications) of the crown surface after nitriding of a conventional valve lifter.
FIG. 9 is a graph showing the relationship between cam rotation speed and friction torque.
FIG. 10 is a cross-sectional view showing an example of use of a valve lifter.
FIG. 11 is a TEM observation photograph (30000 times) of the crown cross-section after nitriding of the valve lifter according to the present invention.
FIG. 12 is a TEM observation photograph (magnified 30000 times) of the crown surface cross-section from which the porous layer was removed after nitriding of the valve lifter according to the prior art.
FIG. 13 is a photomicrograph (8000 times) of the crown surface after the sliding test of the valve lifter according to the present invention.
FIG. 14 is a diagram showing changes in surface roughness before and after the leveling operation of the valve lifter and the counterpart material cam according to the present invention and the prior art.
FIG. 15 is a diagram showing a change in surface roughness before and after a sliding test between the valve lifter and the counterpart material cam according to the present invention.
以下、本発明による実施の形態の一例を説明する。図１と図２に示す本発明のバルブリフタ１は、図１０に示すように、内燃機関の直打式動弁機構において、カム１１とバルブ１２との間に介装されてカム１１の回転動作をバルブ１２の往復運動に変換する摺動部品である。例えば、図１に示すように、バルブリフタ１のカム（図示せず）と摺接する摺動面２に対して、本発明のバルブリフタ１の製造方法が用いられる。尚、図２に示す如き、カムと直接摺接するシム３の摺動面２に対しても本発明は適用される。
本発明によるバルブリフタ１の具体的な実施例を以下に示す。まず、ＳＣＭ材を鍛造成形した素材を、表面硬さがＨＲＣ５８以上、有効硬化層深さが約１．０ｍｍとなるように浸炭焼入焼戻処理を施し、その後、冠面即ち摺動面２の表面粗さを砥石と研磨剤を用いる研削盤を使用し、Ｒａ０．０１〜０．０３に加工するが、好ましくは、摺動面２の表面粗さがＲａ０．０２となるように冠面仕上げ加工を行う。
次いで、摺動面２の表面硬度がＨｖ６６０以上、化合物層６（図４参照）の厚さが１〜５μｍになるように、処理温度５２０℃、処理時間７０分でガス軟窒化処理を行う。ガス軟窒化処理に使用するガスは、ＮＨ３とＮ２およびＣＯ２の混合ガスを使用している。
ガス軟窒化処理では、１〜５μｍの範囲で均一に化合物層を形成し、なおかつポーラス層の無い化合物層とするために、さらに変形が少なく表面粗さがＲａ０．０５以下とするために、温度の均一性と雰囲気ガスの攪拌に注意して処理をおこなう。また、雰囲気ガスの組成とＮＨ３の分解率を管理することも、１〜５μｍの範囲で均一に化合物層を形成し、なおかつポーラス層の無い化合物層を得るために重要である。バルブリフタは、所定のＮＨ３の分解率となった雰囲気中で窒化処理される。ＮＨ３の分解率は、ガス交換率（流量）あるいは混合ガスの構成比等で管理することができる。また、他炉にて所定のＮＨ３の分解率に雰囲気調整したガスを用いて窒化処理をおこなってもよい。本実施例におけるＮＨ３の分解率は２３％であった。
本実施例においては、前記処理条件でガス軟窒化をおこなっているが、処理温度５６０℃で処理時間３０分、及び処理温度５００℃で処理時間１５０分にても、それぞれ３．５μｍと２．５μｍのポーラス層の無い化合物層が得られた。なおこのときのＮＨ３の分解率は５２０℃処理と比較して、処理温度５６０℃では大きくする必要があったが、５００℃では同じであった。ＮＨ３の分解率は、窒化処理温度５００〜５６０℃に従って５〜５０％の範囲で管理する。また、バルブリフタは治具に整列して並べ、均一に雰囲気ガスに触れるようにガス軟窒化処理をおこなうことで、より変形の少ない均一な化合物層のバルブリフタが得られた。
なお、従来おこなわれているような５６０℃を超える温度のガス軟窒化処理では、必要とされる１〜５μｍの化合物層とするには処理時間が短く、適切な雰囲気に調節することができなかった。ＮＨ３の分解が表面で行われた場合のみ窒化に有効に作用することから、ＮＨ３の分解率の大きい雰囲気中においては処理品表面のＮＨ３の分解反応は減少し、ポーラス層の無い化合物層が形成されたが化合物層にバラツキを生じ、ＮＨ３の分解率の小さい雰囲気中においては処理品表面の窒化が活発に行われ、化合物層にポーラス層を生じた。
窒化処理の温度、時間と雰囲気が管理された前記ガス軟窒化処理によって、バルブリフタの冠面には、図４に示すように母材上に拡散層７及び表面にポーラス層を形成せず空孔率が５％以下の緻密な化合物層６からなる窒化層を形成している。
また、化合物層表面には、図７に示す平均径０．５μｍ以下の微細な炭化物，窒化物，硫化物或いは酸化物、又は前記化合物の２種以上からなる多数の突起（白い粒状部分）を有している。このときの表面粗さはＲａ０．０５以下である。更に、図１１に示すように窒素化合物層に０．５μｍ以下の等軸結晶を含んでいる。このようにして得られた本発明によるバルブリフタは、表面粗さと寸法精度改善のための研磨処理を要さない。
次に、比較例として、前記の本発明による実施例と同一の素材を使用し、窒化前の冠面の表面粗さを異にするが、本発明の窒化処理と同一条件の加工方法によりバルブリフタを作成した。
このときの摺動面２における、窒化処理前と後での表面粗さの変化の例を表１に示す。本発明の実施例では窒化前の摺動面の表面粗さをＲａ０．０１２〜０．０２８に研磨加工してあることから、窒化後の摺動面の表面粗さをＲａ０．０２４〜０．０４５とさせ得ることがわかる。これに対し比較例１、２、３では、窒化処理前の摺動面の表面粗さがＲａ０．０３を超えた場合、窒化処理後の表面粗さでＲａ０．０５を超えてしまう。
従来技術による比較例４のバルブリフタは、一般的な５７０℃でガス軟窒化されていて、柱状晶を含む化合物層６が厚く形成され、粗大なポーラス層８を有している（図６参照）。また、変形が大きく面粗度も悪化しているので、後工程のバフ研磨によりポーラス層の除去が必要となっている。図１２にポーラス層を加工により取り除いたバルブリフタ断面のＴＥＭ組織を示しているが、表面からほぼ垂直に配向した比較的粗大な柱状結晶を有している。
表２に、実施例２および比較例４のバルブリフタの窒化前後における寸法精度の変化および化合物層，ポーラス層の厚さを示す。変形は、窒化前のバルブリフタ冠面形状に対し、外周部を基準として窒化後の最大変位を示す。本発明によるバルブリフタは、窒化処理後において、表面粗さの増大がなく変形も非常に少なく、更に化合物層にポーラス層が形成されていない。これにより、後加工としての研磨を要しないため研磨による化合物層厚さにバラツキが生じることがない。
前記した本実施例の本発明によるバルブリフタと比較例４の従来技術によるバルブリフタおよびカム部をチル化したチルカムをエンジンに組付け、回転数１０００〜４０００ｒｐｍでモーターリング試験を行ない、摺動時の摩擦トルクを測定した。図１４は、本発明と従来技術によるバルブリフタのならし運転前後でのバルブリフタの冠面及び摺動相手材のカム（カムノーズ部）の表面粗さの変化を示している。本発明によるバルブリフタは、自身の表面粗さの増大を起こすことなく、その磨き機能によりカム側の表面粗さを向上（低減）させることができる。一方、従来技術によるバルブリフタは、ならし運転前後でバルブリフタ自身の表面粗さが大幅に増大する。
また、図１５は、本発明によるバルブリフタのならし運転前から耐久評価後のバルブリフタの冠面と相手材のカム（カムノーズ部）の表面粗さの変化を示している。本発明によるバルブリフタの冠面の表面粗さは殆ど変化がなく、一方相手材のカム側の表面粗さをその磨き機能によりＲａで０．０２μｍまで向上させている。また、バルブリフタとカムの総合摺動評価として用いられている表面粗さの二乗平均からも収束の傾向である。図１３は耐久評価後の本発明のバルブリフタの摺動表面を示している。摺動前の表面に見られた突起は、カムと組み合わせて摺動したときに、その磨き機能によりカムの表面粗さをＲａで０．０２μｍ以下まで向上させ、バルブリフタ自身の表面粗さを増大させることなく保油効果を向上させるディンプルを残して離脱している。
図９は回転数と摩擦トルクの関係を示したグラフである。この結果、本発明によるバルブリフタは、ならし運転前後及び耐久評価での自己の表面粗さの変化が殆どなく、且つ、磨き機能によりカム側の表面粗さを向上させ、摩擦トルクが従来技術によるものより低く、摺動抵抗においても優位であることがわかる。
先に述べたように、本発明によるバルブリフタは、窒化後の化合物層厚さが１〜５μｍであり、且つ、窒化後の冠面の面粗度がＲａ０．０５以下であり、更に化合物層表面部にポーラス層が形成されないことを特徴としているため、基本的にバフ研磨処理を必要としない。このようにして製造されるバルブリフタ１では、窒化処理後に高コストな研磨処理を基本的に必要とせず、摺動面２に高硬度且つ低摩擦係数な化合物層を均一に存在させることができるため耐摩耗性も安定しており、高性能を維持しつつ製造コストを大幅に低減することが可能である。更に、相手材のカムと組み合わせて摺動させることでバルブリフタ自身の表面粗さの増大を起こすことなく、その磨き機能によりカム側の表面粗さを向上させることができるため、相手材のカムについてもペーパーラップ仕上げ加工などの高価な設備と長い加工時間を要する高コストな手段を必要としない。
以上のように、本発明によるバルブリフタでは、ポーラス層の無い１〜５μｍの緻密で硬い窒化化合物層を形成し、窒化前後で表面粗さの増大が殆どなく、更に歪み変形が極めて小さいガス窒化処理をおこなうことで、表面粗さの調整およびポーラス層の除去など、窒化処理後の化合物層を調整する研磨を必要としない。これにより表面性状が均一で安定した耐摩耗性を確保できる。
また、均一な化合物層が得られることにより、従来技術によるバルブリフタに比べて摩擦トルクを低減することができる。更に高コストな研磨処理を必要としないため、低コストなバルブリフタを得ることができる。
更に、カムと組み合わせて摺動させることでバルブリフタ自身の表面粗さの増大を起こすことなく、その磨き機能によりカム側の表面粗さを向上させることができるため、耐摩耗性及び摩擦トルクの向上に加え、カム側の低コスト化も実現できる。Hereinafter, an example of an embodiment according to the present invention will be described. As shown in FIG. 10, the valve lifter 1 of the present invention shown in FIGS. 1 and 2 is interposed between a cam 11 and a valve 12 in a direct-acting valve operating mechanism of an internal combustion engine, and rotates the cam 11. Is a sliding part for converting the valve 12 into a reciprocating motion of the valve 12. For example, as shown in FIG. 1, the valve lifter 1 manufacturing method of the present invention is used for a sliding
Specific examples of the valve lifter 1 according to the present invention are shown below. First, a material obtained by forging the SCM material is subjected to carburizing, quenching and tempering treatment so that the surface hardness is HRC58 or more and the effective hardened layer depth is about 1.0 mm. The surface roughness is processed to Ra 0.01 to 0.03 using a grinder using a grindstone and an abrasive, but preferably the crown surface so that the surface roughness of the sliding
Next, gas soft nitriding is performed at a processing temperature of 520 ° C. and a processing time of 70 minutes so that the sliding
In the gas soft nitriding treatment, in order to form a compound layer uniformly in the range of 1 to 5 μm and to have a compound layer without a porous layer, the temperature is set to be less deformed and the surface roughness is Ra 0.05 or less. Be careful of the uniformity of the gas and stirring the atmosphere gas. Also, it is important to control the composition of the atmospheric gas and the decomposition rate of NH 3 in order to form a compound layer uniformly in the range of 1 to 5 μm and to obtain a compound layer without a porous layer. The valve lifter is nitrided in an atmosphere having a predetermined NH 3 decomposition rate. The decomposition rate of NH 3 can be managed by the gas exchange rate (flow rate) or the composition ratio of the mixed gas. Further, nitriding may be performed using a gas whose atmosphere is adjusted to a predetermined decomposition rate of NH 3 in another furnace. The decomposition rate of NH 3 in this example was 23%.
In this embodiment, gas soft nitriding is performed under the above processing conditions. However, even when the processing temperature is 560 ° C. and the processing time is 30 minutes and the processing temperature is 500 ° C. and the processing time is 150 minutes, 3.5 μm and 2. A compound layer without a 5 μm porous layer was obtained. It should be noted that the decomposition rate of NH 3 at this time had to be increased at a treatment temperature of 560 ° C. compared to the treatment at 520 ° C., but was the same at 500 ° C. The decomposition rate of NH 3 is controlled in the range of 5 to 50% according to the nitriding temperature of 500 to 560 ° C. In addition, the valve lifter was arranged in line with a jig and subjected to gas soft nitriding treatment so as to be uniformly exposed to the atmospheric gas, thereby obtaining a uniform compound layer valve lifter with less deformation.
In the conventional gas soft nitriding treatment at a temperature exceeding 560 ° C., the treatment time is short to obtain the required compound layer of 1 to 5 μm, and it cannot be adjusted to an appropriate atmosphere. It was. Since it effectively acts on nitridation only when NH 3 is decomposed on the surface, the decomposition reaction of NH 3 on the surface of the treated product is reduced in an atmosphere with a high NH 3 decomposition rate, and there is no compound having a porous layer. Although a layer was formed, the compound layer was varied, and the surface of the treated product was actively nitrided in an atmosphere with a small decomposition rate of NH 3 , and a porous layer was formed in the compound layer.
By the gas soft nitriding process in which the temperature, time and atmosphere of the nitriding process are controlled, the crown surface of the valve lifter has pores without forming a
Further, on the surface of the compound layer, fine carbides, nitrides, sulfides or oxides having an average diameter of 0.5 μm or less shown in FIG. Have. The surface roughness at this time is Ra 0.05 or less. Furthermore, as shown in FIG. 11, the nitrogen compound layer contains equiaxed crystals of 0.5 μm or less. The valve lifter according to the present invention thus obtained does not require polishing for improving the surface roughness and dimensional accuracy.
Next, as a comparative example, the same material as that of the above-described embodiment according to the present invention is used, and the surface roughness of the crown surface before nitriding is different, but the valve lifter is processed by the processing method under the same conditions as the nitriding treatment of the present invention. It was created.
Table 1 shows an example of the change in surface roughness before and after the nitriding treatment on the sliding
The valve lifter of Comparative Example 4 according to the prior art is gas soft-nitrided at a general 570 ° C., has a
Table 2 shows changes in dimensional accuracy and thicknesses of the compound layer and the porous layer of the valve lifters of Example 2 and Comparative Example 4 before and after nitriding. The deformation indicates the maximum displacement after nitriding with respect to the outer peripheral portion of the valve lifter crown shape before nitriding. The valve lifter according to the present invention has no increase in surface roughness and very little deformation after nitriding, and no porous layer is formed on the compound layer. Thereby, since polishing as post-processing is not required, the compound layer thickness due to polishing does not vary.
The above-described valve lifter according to the present embodiment and the conventional valve lifter according to Comparative Example 4 and the chill cam with the cam portion chilled are assembled to the engine, a motoring test is performed at a rotational speed of 1000 to 4000 rpm, and friction during sliding Torque was measured. FIG. 14 shows changes in the surface roughness of the crown of the valve lifter and the cam (cam nose portion) of the sliding partner material before and after the leveling operation of the valve lifter according to the present invention and the prior art. The valve lifter according to the present invention can improve (reduce) the cam-side surface roughness by its polishing function without increasing the surface roughness of the valve lifter. On the other hand, the valve lifter according to the prior art greatly increases the surface roughness of the valve lifter itself before and after the leveling operation.
FIG. 15 shows changes in the surface roughness of the crown surface of the valve lifter and the cam (cam nose portion) of the mating member after durability evaluation from before the leveling operation of the valve lifter according to the present invention. The surface roughness of the crown surface of the valve lifter according to the present invention hardly changes. On the other hand, the surface roughness on the cam side of the counterpart material is improved to 0.02 μm in Ra by the polishing function. Moreover, it is a tendency of convergence from the mean square of the surface roughness used for the overall sliding evaluation of the valve lifter and the cam. FIG. 13 shows the sliding surface of the valve lifter of the present invention after durability evaluation. The protrusion seen on the surface before sliding improves the surface roughness of the cam to 0.02 μm or less by Ra's polishing function and increases the surface roughness of the valve lifter itself when sliding in combination with the cam. It leaves without leaving dimples that improve the oil retention effect.
FIG. 9 is a graph showing the relationship between the rotational speed and the friction torque. As a result, the valve lifter according to the present invention has almost no change in its own surface roughness before and after running-in operation and durability evaluation, and improves the surface roughness on the cam side by the polishing function, and the friction torque is based on the conventional technology. It can be seen that it is lower than the above and superior in sliding resistance.
As described above, the valve lifter according to the present invention has a compound layer thickness after nitriding of 1 to 5 μm, a surface roughness of the crown surface after nitriding is Ra 0.05 or less, and further the surface of the compound layer Since a porous layer is not formed on the portion, basically no buffing treatment is required. The valve lifter 1 manufactured in this way basically does not require high-cost polishing after nitriding, and a compound layer having a high hardness and a low coefficient of friction can be uniformly present on the sliding
As described above, the valve lifter according to the present invention forms a dense and hard nitride compound layer of 1 to 5 μm without a porous layer, has almost no increase in surface roughness before and after nitriding, and has a very small strain deformation. By performing this, polishing for adjusting the compound layer after the nitriding treatment such as adjustment of the surface roughness and removal of the porous layer is not required. This ensures uniform and stable wear resistance on the surface texture.
Further, by obtaining a uniform compound layer, it is possible to reduce the friction torque as compared with the conventional valve lifter. Furthermore, since a high-cost polishing process is not required, a low-cost valve lifter can be obtained.
In addition, by sliding in combination with the cam, the surface roughness on the cam side can be improved by its polishing function without causing an increase in the surface roughness of the valve lifter itself, improving wear resistance and friction torque. In addition, cost reduction on the cam side can be realized.
Claims (10)
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003063450 | 2003-03-10 | ||
| JP2003063450 | 2003-03-10 | ||
| PCT/JP2004/003022 WO2004081252A1 (en) | 2003-03-10 | 2004-03-09 | Nitrided valve lifter and method for manufacture thereof |
Publications (2)
| Publication Number | Publication Date |
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| JPWO2004081252A1 true JPWO2004081252A1 (en) | 2006-06-15 |
| JP4141473B2 JP4141473B2 (en) | 2008-08-27 |
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| JP2005503522A Expired - Fee Related JP4141473B2 (en) | 2003-03-10 | 2004-03-09 | Nitriding valve lifter and manufacturing method thereof |
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| Country | Link |
|---|---|
| US (2) | US20060144359A1 (en) |
| EP (1) | EP1602743B1 (en) |
| JP (1) | JP4141473B2 (en) |
| KR (1) | KR20050118175A (en) |
| CN (1) | CN1784505B (en) |
| DE (1) | DE602004010890T2 (en) |
| ES (1) | ES2295833T3 (en) |
| TW (1) | TW200506181A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4293370B2 (en) * | 2005-02-02 | 2009-07-08 | 株式会社リケン | Valve lifter |
| US20090314389A1 (en) * | 2005-08-05 | 2009-12-24 | Honda Motor Co., Ltd. | Ion Nitriding Method |
| JP5531407B2 (en) * | 2006-03-30 | 2014-06-25 | 株式会社ジェイテクト | Torque limiter |
| EP2003353B1 (en) * | 2006-03-30 | 2014-06-04 | JTEKT Corporation | Torque limiter |
| JP2008071738A (en) * | 2006-08-18 | 2008-03-27 | Nissan Motor Co Ltd | Manufacturing method of transition metal nitride, fuel cell separator, and transition metal nitride, manufacturing method of fuel cell separator, as well as fuel cell stack, and fuel-cell vehicle |
| KR100730615B1 (en) * | 2006-10-31 | 2007-06-20 | 다이모스(주) | Heat treating method of syncronizer hub for transmission |
| KR100906414B1 (en) * | 2008-01-03 | 2009-07-09 | 주식회사 킹텍코리아 | Swash plate for compressor and manufacturing method thereof |
| KR100887851B1 (en) | 2008-07-18 | 2009-03-09 | 현대자동차주식회사 | Valve lifter and method for surface treatment thereof |
| CN103189604A (en) * | 2010-12-13 | 2013-07-03 | 川崎重工业株式会社 | Drive cam and valve operating device for engine |
| JP6445293B2 (en) * | 2014-09-26 | 2018-12-26 | 株式会社リケン | Valve lifter and manufacturing method thereof |
| CN105033654B (en) * | 2015-07-17 | 2017-07-28 | 宜宾常达机械有限公司 | A kind of engine valve tappet and its manufacture method |
| CN107923027B (en) * | 2015-08-17 | 2020-02-07 | Ntn株式会社 | Sliding member and method for manufacturing same |
| CN105887000A (en) * | 2016-06-08 | 2016-08-24 | 连云港江南精工机械有限公司 | Nitriding heat treatment method of die-casting machine accessory |
| CN106011739B (en) * | 2016-07-02 | 2019-01-15 | 潍柴动力股份有限公司 | Tappet for internal combustion engine and its manufacturing method with high-wearing feature |
| CN109778120A (en) * | 2019-03-14 | 2019-05-21 | 江苏徐工工程机械研究院有限公司 | A kind of hydraulic valve stem and preparation method thereof |
| CN113263178A (en) * | 2021-04-23 | 2021-08-17 | 广东工业大学 | Coated cutting tool with cubic phase-rich gradient structure and preparation method thereof |
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| PL87552B1 (en) * | 1973-10-20 | 1976-07-31 | ||
| JPH0618841B2 (en) * | 1986-01-28 | 1994-03-16 | 三井東圧化学株式会社 | Process for producing block copolymer of propylene |
| JPS62253908A (en) * | 1986-04-26 | 1987-11-05 | Yamaha Motor Co Ltd | Valve lifter for overhead valve type internal combustion engine |
| JP3148362B2 (en) * | 1992-06-10 | 2001-03-19 | トヨタ自動車株式会社 | Cam contact structure of valve train |
| JP3023322B2 (en) * | 1997-03-04 | 2000-03-21 | 大同ほくさん株式会社 | Iron-based material nitriding method and iron-based material product obtained thereby |
| JP3303741B2 (en) * | 1997-09-25 | 2002-07-22 | トヨタ自動車株式会社 | Gas nitrocarburizing method |
| JPH11324858A (en) * | 1998-05-19 | 1999-11-26 | Toyota Motor Corp | Plunger pump |
| JP4269443B2 (en) * | 1998-12-24 | 2009-05-27 | マツダ株式会社 | Surface treatment method for sliding member and surface smoothing method for sliding member using the method |
| JP2001074053A (en) * | 1999-04-01 | 2001-03-23 | Nsk Ltd | Rolling bearing |
| JP3794255B2 (en) * | 2000-09-21 | 2006-07-05 | 日産自動車株式会社 | Sliding parts and manufacturing method thereof |
| JP2002212703A (en) * | 2001-01-11 | 2002-07-31 | Toyota Motor Corp | Method for processing iron-based alloy |
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| DE602004010890D1 (en) | 2008-02-07 |
| US20060144359A1 (en) | 2006-07-06 |
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| TW200506181A (en) | 2005-02-16 |
| EP1602743B1 (en) | 2007-12-26 |
| DE602004010890T2 (en) | 2008-12-11 |
| JP4141473B2 (en) | 2008-08-27 |
| US20080066703A1 (en) | 2008-03-20 |
| EP1602743A1 (en) | 2005-12-07 |
| WO2004081252A1 (en) | 2004-09-23 |
| KR20050118175A (en) | 2005-12-15 |
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| EP1602743A4 (en) | 2007-01-24 |
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