WO2017073235A1 - Piston for engine - Google Patents

Piston for engine Download PDF

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Publication number
WO2017073235A1
WO2017073235A1 PCT/JP2016/078878 JP2016078878W WO2017073235A1 WO 2017073235 A1 WO2017073235 A1 WO 2017073235A1 JP 2016078878 W JP2016078878 W JP 2016078878W WO 2017073235 A1 WO2017073235 A1 WO 2017073235A1
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Prior art keywords
piston
cavity
lip
curve
curved
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PCT/JP2016/078878
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French (fr)
Japanese (ja)
Inventor
朋彦 俊野
功 橘川
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いすゞ自動車株式会社
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Publication of WO2017073235A1 publication Critical patent/WO2017073235A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/02—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/26—Pistons  having combustion chamber in piston head
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • This disclosure relates to an engine piston, and more particularly to a direct injection engine piston.
  • fuel is injected from a injector into a cavity recessed in the center of the top of a piston and burned.
  • a lip portion is formed at the periphery of the opening of the cavity, and fuel sprayed in the vicinity of the compression top dead center is caused to collide with the lip portion.
  • a structure is disclosed that is dispersed in the squish area.
  • Patent Document 2 discloses a structure for optimizing the ratio of fuel spray dispersed in the cavity and the squish area by providing a step portion in the lip portion. Yes.
  • the structure having a stepped portion 330 on the piston 300 is lip 320, that the amount of fuel spray F U to squish area S is secured, the air utilization rate of the squish area S Can be improved.
  • the energy of the fuel spray F L in the cavity 310 is made weaker than the structure having no stepped portion (see FIG. 5), the energy and the angle is steeper portion and straight portion and a curved portion in the cavity 320 It tends to be easily attenuated at the connecting portion. For this reason, there is a problem that combustion control by combustion pressure or multistage injection becomes difficult.
  • the technology of the present disclosure aims to effectively prevent the energy of the fuel spray from being attenuated in the cavity by smoothing the shape of the bottom of the combustion chamber.
  • the technology of the present disclosure is a piston of an engine, and includes a cavity recessed at the top of the piston, a lip provided radially inwardly at the periphery of the opening of the cavity, and a bottom of the cavity.
  • a curved portion that protrudes in a curved shape in the longitudinal section toward the side, and the longitudinal sectional shape of the curved portion includes a curve that has a curvature that increases toward the center of the piston.
  • the vertical cross-sectional shape between them may be formed as a curve whose curvature increases as it goes to the piston center side.
  • the curve may be a clothoid curve.
  • the raised portion may be provided so as to protrude upward in a longitudinal section from the bottom of the cavity, and at least a part of a curve defining the longitudinal sectional shape of the raised portion may be formed by a clothoid curve.
  • the lip portion may be provided with an annular step portion that is recessed at a predetermined depth from the inner peripheral upper surface of the lip portion.
  • the stepped portion may include an annular flat portion extending radially outward from the inner peripheral edge of the lip portion and an annular inclined portion inclined obliquely upward from the outer peripheral edge of the flat portion.
  • FIG. 1 is a schematic longitudinal sectional view showing a part of an engine according to an embodiment of the present disclosure.
  • FIG. 2 is a schematic diagram for explaining fuel spray distribution when fuel is injected in the vicinity of the compression top dead center of the piston in the present embodiment.
  • FIG. 3 is a schematic diagram illustrating the first half of combustion according to the present embodiment.
  • FIG. 4 is a schematic diagram for explaining the latter half of the combustion according to the present embodiment.
  • FIG. 5 is a view for explaining the flow of fuel spray having a conventional structure having no stepped portion in the lip portion.
  • FIG. 6 is a diagram for explaining the flow of fuel spray having a conventional structure having a step portion at the lip portion.
  • FIG. 1 is a schematic longitudinal sectional view showing a part of the engine according to the present embodiment.
  • the engine 10 of the present embodiment is preferably a direct injection diesel engine, and includes a cylinder block 11 and a cylinder head 12 disposed on the cylinder block 11.
  • the cylinder head 12 is formed with an intake port 14 that introduces fresh air into the combustion chamber A by opening and closing the intake valve 13 and an exhaust port 16 that leads exhaust gas from the combustion chamber A by opening and closing the exhaust valve 15. .
  • An injector 17 that directly injects fuel into the combustion chamber A is provided between the ports 14 and 16 of the cylinder head 12.
  • a plurality of fine nozzle holes are formed in the nozzle portion 17A of the injector 17, and fuel is injected radially into the combustion chamber A from these nozzle holes.
  • the cylinder block 11 is formed with a cylindrical cylinder bore 11A.
  • a piston 20 is accommodated in the cylinder bore 11A so as to be reciprocally movable in the vertical direction.
  • a cavity 21 that is recessed at a predetermined depth from the top surface 20 ⁇ / b> A of the piston 20 is recessed at the top of the piston 20.
  • An annular lip portion 22 that protrudes radially inward is provided on the periphery of the opening of the cavity 21.
  • a step portion 23 formed by cutting the upper corner portion of the lip portion 22 into a substantially L-shaped cross section with a predetermined depth. More specifically, the step portion 23 includes an annular flat surface portion 23A that extends flatly from the inner peripheral edge portion (protruding end) of the lip portion 22 radially outward, and the top surface of the piston 20 from the outer peripheral edge of the flat surface portion 23A. And an annular inclined surface portion 23B extending obliquely toward 20A.
  • the cavity 21 is connected to a raised portion 25 that is formed so as to protrude upward from the center of the bottom of the cavity 21 so as to protrude upward, a lower end 22A of the lip portion 22, and a lower end 25A of the raised portion 25. And a curved portion 24 that is curved in a longitudinally curved shape so as to protrude radially outward and downward.
  • the first curved portion CL1 that defines the vertical cross-sectional shape of the curved portion 24 and the second curved portion CL2 that defines the vertical cross-sectional shape from the lower end of the raised portion 25 to the vicinity of the top portion are each formed by a clothoid curve.
  • the first curved portion CL1 of the curved portion 24 is defined by a first clothoid curve that is convex radially outward and downward and has a curvature that increases toward the piston center side.
  • the two curve portions CL2 are defined by a second clothoid curve that is convex upward.
  • the first curved line portion CL1 includes at least a first line portion 24A directly below the lip where a vertical line VL descending in the piston axial direction from the most protruding end that protrudes most radially inward of the lip portion 22 intersects the first curved portion CL1.
  • a range up to the lowermost end 24B where the first curved portion CL1 is most depressed downward is formed by a first clothoid curve.
  • the longitudinal cross-sectional shape of the cavity 21 is formed in a substantially S shape by the first and second clothoid curves that do not include a straight portion, and the curvature of the first curved portion CL1 is set to increase toward the piston center side. becomes as smooth flow towards the ridge 25 where the fuel spray F L flowing into the cavity 21 is located at the center of the combustion chamber a.
  • step portion 23 to the lip portion 22 since the step portion 23 to the lip portion 22 is provided, optimization of the spray distribution of the fuel spray F U dispersed in the squish area S, the fuel spray F L which is dispersed in the cavity 21 Is designed.
  • the fuel spray F L is moved along the two first and second clothoid curve CL1,2 defining a longitudinal sectional shape of the cavity 21, in particular the first clothoid curve CL1, the piston Since the curvature is set to be larger toward the center side, the fuel spray FL is smoothly flowed toward the raised portion 25 located in the center of the combustion chamber A without greatly reducing its energy. Become.
  • the second half of the combustion that the fuel spray F L which flows along the clothoid curve reaches smoothly to near the center of the combustion chamber A, used to maximize the energy of the fuel spray F L
  • combustion using the air (oxygen) near the center of the combustion chamber A is realized.
  • the fuel spray F U dispersed in the squish area S
  • the fuel spray F is dispersed into the cavity 21 optimization of the spray distribution of the L is to be achieved.
  • the first half of the combustion the fuel spray F U is effectively diffused into the squish area S, can be achieved effectively utilizing combustion air (oxygen) in the squish area S.
  • first clothoid curve CL1 is set to have a larger curvature as it goes toward the piston center, so that the fuel spray FL is located at the center of the combustion chamber A without greatly reducing its energy. It flows toward the raised portion 25.
  • the first half of the combustion is performed using the outer peripheral side (squish area S side) in the combustion chamber A, and the second half of the combustion is performed near the center in the combustion chamber A.
  • the first curve portion CL1 may be formed with a clothoid curve from the outermost end portion 24C protruding most outward in the radial direction to the lowermost end portion 24B recessed most downward.
  • first curved portion CL1 may be formed with a clothoid curve from the outermost end portion 24C that protrudes most outward in the radial direction to the lower end 25A of the raised portion.
  • first curved portion CL1 may be formed with a clothoid curve from the lower end of the lip portion to the lower end 25A of the raised portion.
  • first curve portion CL1 may be formed with a clothoid curve from the lower end of the lip portion to the lowest end portion 24B that is most depressed downward.
  • regulates the longitudinal cross-sectional shape of the cavity 21 is not limited to a clothoid curve, If it does not prevent the flow of fuel spray, a cubic parabola (cubic curve) or a sine curve (sine half-wave decreasing curve) etc. Other curves may be used.
  • the engine 10 is not limited to a direct injection diesel engine, and may be another direct injection engine such as a direct injection gasoline engine.
  • the piston of the engine according to the present disclosure has an effect of effectively preventing the attenuation of the energy of the fuel spray in the cavity, and enables a highly accurate combustion control to achieve a low fuel consumption and high efficiency engine. Is useful in that it can be realized.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Combustion Methods Of Internal-Combustion Engines (AREA)

Abstract

A cavity 21 is recessed in a head part of a piston 20, an annular ring part 22 protruding diametrically inward is provided to the edge of the opening of the cavity 21, a bulging part 25 that protrudes upward is provided to the bottom part of the cavity 21, between a lip part 22 of the cavity 21 and the bulging part 25 is provided a curved part 24 that connects the lower end of the lip part 22 and the lower end of the bulging part 25 and that protrudes diametrically outward and downward in a curved shaped in longitudinal cross-section, and the longitudinal cross-sectional shape of the curved part 24 is formed into a curve of which the radius of curvature increases toward the center of the piston.

Description

エンジンのピストンEngine pistons
　本開示は、エンジンのピストンに関し、特に、直噴式エンジンのピストンに関する。 This disclosure relates to an engine piston, and more particularly to a direct injection engine piston.
　一般的に、ディーゼルエンジン等の直噴式エンジンにおいては、ピストンの頂部中央に凹設されたキャビティ内にインジェクタから燃料を噴射して燃焼させている。 Generally, in a direct injection type engine such as a diesel engine, fuel is injected from a injector into a cavity recessed in the center of the top of a piston and burned.
　この種のピストンとして、例えば、特許文献１には、キャビティの開口部周縁にリップ部を形成し、圧縮上死点近傍で噴射した燃料をリップ部に衝突させることで、燃料噴霧をキャビティ内とスキッシュエリアとに分散させる構造が開示されている。 As this type of piston, for example, in Patent Document 1, a lip portion is formed at the periphery of the opening of the cavity, and fuel sprayed in the vicinity of the compression top dead center is caused to collide with the lip portion. A structure is disclosed that is dispersed in the squish area.
　また、この種のピストンとして、例えば、特許文献２には、リップ部に段差部を設けることで、キャビティ内とスキッシュエリアとに分散される燃料噴霧の割合の最適化を図る構造も開示されている。 As this type of piston, for example, Patent Document 2 discloses a structure for optimizing the ratio of fuel spray dispersed in the cavity and the squish area by providing a step portion in the lip portion. Yes.
日本国特開２００８－１５１０８９号公報Japanese Unexamined Patent Publication No. 2008-151089 日本国特開２０１４－２２２０４１号公報Japanese Unexamined Patent Publication No. 2014-222041
　ところで、図５に示すように、ピストン２００がリップ部２２０に段差部を有しない構造では、燃料噴霧（図中矢印参照）がスキッシュエリアＳよりもキャビティ２１０内に多く分配される傾向がある。このため、燃焼室Ａの中央付近における燃料噴霧の分配を考慮すると、キャビティ２１０の底部に行くほど燃料噴霧の量が多くなり、噴霧のエネルギを利用し易くなるが、スキッシュエリアＳの空気（酸素）の利用効率は低下する課題がある。 Incidentally, as shown in FIG. 5, in the structure in which the piston 200 does not have a stepped portion in the lip portion 220, fuel spray (see arrow in the figure) tends to be distributed more in the cavity 210 than in the squish area S. For this reason, considering the distribution of the fuel spray in the vicinity of the center of the combustion chamber A, the amount of fuel spray increases toward the bottom of the cavity 210, making it easier to use the energy of the spray, but the air in the squish area S (oxygen) There is a problem that the use efficiency of) decreases.
　一方、図６に示すように、ピストン３００がリップ部３２０に段差部３３０を有する構造では、スキッシュエリアＳへの燃料噴霧ＦＵの量が確保されることで、スキッシュエリアＳの空気利用率を向上させることができる。しかしながら、キャビティ３１０内の燃料噴霧ＦＬのエネルギは、段差部を有しない構造（図５参照）に比べて弱くなり、そのエネルギはキャビティ３２０内の角度が急な部分や直線部と曲線部との接続部分で減衰し易くなる傾向がある。このため、燃焼圧や多段噴射による燃焼制御が難しくなる課題がある。 On the other hand, as shown in FIG. 6, the structure having a stepped portion 330 on the piston 300 is lip 320, that the amount of fuel spray F U to squish area S is secured, the air utilization rate of the squish area S Can be improved. However, the energy of the fuel spray F L in the cavity 310 is made weaker than the structure having no stepped portion (see FIG. 5), the energy and the angle is steeper portion and straight portion and a curved portion in the cavity 320 It tends to be easily attenuated at the connecting portion. For this reason, there is a problem that combustion control by combustion pressure or multistage injection becomes difficult.
　本開示の技術は、燃焼室底部の形状を滑らかにすることで、キャビティ内における燃料噴霧のエネルギの減衰を効果的に防止することを目的とする。 The technology of the present disclosure aims to effectively prevent the energy of the fuel spray from being attenuated in the cavity by smoothing the shape of the bottom of the combustion chamber.
　本開示の技術は、エンジンのピストンであって、ピストン頂部に凹設されたキャビティと、前記キャビティの開口部周縁に径方向内側に突出して環状に設けられたリップ部と、前記キャビティの底部に上方に向けて突出して設けられた***部と、前記キャビティの前記リップ部と前記***部との間に設けられ、前記リップ部下端と前記***部下端とを接続すると共に、径方向外側且つ下側に向けて縦断面曲線状に突出する湾曲部とを備え、前記湾曲部の縦断面形状は、ピストン中心側に向かうに従い曲率が大きくなる曲線を含む。 The technology of the present disclosure is a piston of an engine, and includes a cavity recessed at the top of the piston, a lip provided radially inwardly at the periphery of the opening of the cavity, and a bottom of the cavity. A bulge projecting upward, and provided between the lip and the bulge of the cavity, connecting the lower end of the lip and the lower end of the bulge, A curved portion that protrudes in a curved shape in the longitudinal section toward the side, and the longitudinal sectional shape of the curved portion includes a curve that has a curvature that increases toward the center of the piston.
　前記湾曲部の、前記リップ部の径方向内側に最も突出する最突出端からピストン軸方向に下した鉛直線が交差するリップ直下方部と、前記湾曲部の下方に最も窪む最下端部との間の縦断面形状がピストン中心側に向かうに従い曲率が大きくなる曲線で形成されてもよい。 A portion directly below the lip where a vertical line extending in the piston axial direction from the most protruding end that protrudes most radially inward of the lip portion intersects with the bending portion; and a lowermost end portion that is most recessed below the bending portion. The vertical cross-sectional shape between them may be formed as a curve whose curvature increases as it goes to the piston center side.
　前記曲線がクロソイド曲線で形成されてもよい。 The curve may be a clothoid curve.
　前記***部が、前記キャビティの底部から上方に向けて縦断面曲線状に突出して設けられると共に、当該***部の縦断面形状を規定する曲線の少なくとも一部がクロソイド曲線で形成されてもよい。 The raised portion may be provided so as to protrude upward in a longitudinal section from the bottom of the cavity, and at least a part of a curve defining the longitudinal sectional shape of the raised portion may be formed by a clothoid curve.
　前記リップ部に、当該リップ部の内周側上面から所定の深さで窪む環状の段差部が設けられてもよい。 The lip portion may be provided with an annular step portion that is recessed at a predetermined depth from the inner peripheral upper surface of the lip portion.
　前記段差部が、前記リップ部の内周縁から径方向外方に延びる環状の平坦部と、当該平坦部の外周縁から上方に向かって斜めに傾斜する環状の傾斜部とを含むものでもよい。 The stepped portion may include an annular flat portion extending radially outward from the inner peripheral edge of the lip portion and an annular inclined portion inclined obliquely upward from the outer peripheral edge of the flat portion.
　本開示の技術によれば、燃焼室底部の形状を滑らかにすることで、キャビティ内における燃料噴霧のエネルギの減衰を効果的に防止することができる。 According to the technique of the present disclosure, it is possible to effectively prevent the energy of the fuel spray from being attenuated in the cavity by smoothing the shape of the bottom of the combustion chamber.
図１は、本開示の一実施形態に係るエンジンの一部を示す模式的な縦断面図である。FIG. 1 is a schematic longitudinal sectional view showing a part of an engine according to an embodiment of the present disclosure. 図２は、本実施形態において、ピストンの圧縮上死点近傍で燃料を噴射した際の燃料噴霧の分配を説明する模式的な図である。FIG. 2 is a schematic diagram for explaining fuel spray distribution when fuel is injected in the vicinity of the compression top dead center of the piston in the present embodiment. 図３は、本実施形態の燃焼の前半を説明する模式的な図である。FIG. 3 is a schematic diagram illustrating the first half of combustion according to the present embodiment. 図４は、本実施形態の燃焼の後半を説明する模式的な図である。FIG. 4 is a schematic diagram for explaining the latter half of the combustion according to the present embodiment. 図５は、リップ部に段差部を有しない従来構造の燃料噴霧の流れを説明する図である。FIG. 5 is a view for explaining the flow of fuel spray having a conventional structure having no stepped portion in the lip portion. 図６は、リップ部に段差部を有する従来構造の燃料噴霧の流れを説明する図である。FIG. 6 is a diagram for explaining the flow of fuel spray having a conventional structure having a step portion at the lip portion.
　以下、添付図面に基づいて、本開示の一実施形態に係るエンジンのピストンを説明する。同一の部品には同一の符号を付してあり、それらの名称および機能も同じである。したがって、それらについての詳細な説明は繰返さない。 Hereinafter, an engine piston according to an embodiment of the present disclosure will be described based on the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.
　図１は、本実施形態に係るエンジンの一部を示す模式的な縦断面図である。本実施形態のエンジン１０は、好ましくは直噴式ディーゼルエンジンであって、シリンダブロック１１と、シリンダブロック１１の上部に配置されたシリンダヘッド１２とを備えている。 FIG. 1 is a schematic longitudinal sectional view showing a part of the engine according to the present embodiment. The engine 10 of the present embodiment is preferably a direct injection diesel engine, and includes a cylinder block 11 and a cylinder head 12 disposed on the cylinder block 11.
　シリンダヘッド１２には、吸気バルブ１３の開閉動作により燃焼室Ａに新気を導入する吸気ポート１４及び、排気バルブ１５の開閉動作により燃焼室Ａから排気を導出する排気ポート１６が形成されている。また、シリンダヘッド１２の各ポート１４，１６間には、燃焼室Ａ内に燃料を直接噴射するインジェクタ１７が設けられている。 The cylinder head 12 is formed with an intake port 14 that introduces fresh air into the combustion chamber A by opening and closing the intake valve 13 and an exhaust port 16 that leads exhaust gas from the combustion chamber A by opening and closing the exhaust valve 15. . An injector 17 that directly injects fuel into the combustion chamber A is provided between the ports 14 and 16 of the cylinder head 12.
　インジェクタ１７のノズル部１７Ａには、複数の微細な図示しない噴孔が形成されており、これら噴孔から燃焼室Ａ内に燃料が放射状に噴射されるようになっている。 A plurality of fine nozzle holes (not shown) are formed in the nozzle portion 17A of the injector 17, and fuel is injected radially into the combustion chamber A from these nozzle holes.
　シリンダブロック１１には、円筒状のシリンダボア１１Ａが形成されている。このシリンダボア１１Ａ内には、ピストン２０が上下方向に往復移動自在に収容されている。 The cylinder block 11 is formed with a cylindrical cylinder bore 11A. A piston 20 is accommodated in the cylinder bore 11A so as to be reciprocally movable in the vertical direction.
　ピストン２０の頂部には、ピストン２０の頂面２０Ａから所定の深さで窪むキャビティ２１が凹設されている。また、キャビティ２１の開口部周縁には、径方向内側に突出する環状のリップ部２２が設けられている。ピストン２０が圧縮上死点近傍に達した際にインジェクタ１７から燃料が噴射されると、燃料の噴霧Ｆは、リップ部２２に衝突して、リップ部２２よりも上方のスキッシュエリアＳに流れ込む燃料噴霧ＦＵと、リップ部２２よりも下方のキャビティ２１内に流れ込む燃料噴霧ＦＬとに分散されるようになっている。 A cavity 21 that is recessed at a predetermined depth from the top surface 20 </ b> A of the piston 20 is recessed at the top of the piston 20. An annular lip portion 22 that protrudes radially inward is provided on the periphery of the opening of the cavity 21. When the fuel is injected from the injector 17 when the piston 20 reaches the vicinity of the compression top dead center, the fuel spray F collides with the lip portion 22 and flows into the squish area S above the lip portion 22. and the spray F U, is adapted to be dispersed in the fuel spray F L flowing into the lower portion of the cavity 21 than the lip portion 22.
　リップ部２２の上面には、リップ部２２の上側角部を所定の深さで断面略Ｌ字状に切り欠いて形成した段差部２３が設けられている。より詳しくは、段差部２３は、リップ部２２の内周縁部（突出端）から径方向外方に向かって平坦に延びる環状の平坦面部２３Ａと、平坦面部２３Ａの外周縁からピストン２０の頂面２０Ａに向かって斜めに傾斜して延びる環状の傾斜面部２３Ｂとを備えて構成されている。このように、リップ部２２の上面に段差部２３を設けたことで、スキッシュエリアＳに分散される燃料噴霧ＦＵと、キャビティ２１内に分散される燃料噴霧ＦＬとの噴霧分配の最適化が図られるようになる。 On the upper surface of the lip portion 22, there is provided a step portion 23 formed by cutting the upper corner portion of the lip portion 22 into a substantially L-shaped cross section with a predetermined depth. More specifically, the step portion 23 includes an annular flat surface portion 23A that extends flatly from the inner peripheral edge portion (protruding end) of the lip portion 22 radially outward, and the top surface of the piston 20 from the outer peripheral edge of the flat surface portion 23A. And an annular inclined surface portion 23B extending obliquely toward 20A. Thus, by providing the step portion 23 on the upper surface of the lip portion 22, the optimization of the spray distribution of the fuel spray F U dispersed in the squish area S, the fuel spray F L which is dispersed in the cavity 21 Comes to be planned.
　キャビティ２１は、キャビティ２１の底部中央から上側に凸となるように縦断面曲線状に***して形成された***部２５と、リップ部２２の下端２２Ａと***部２５の下端２５Ａとに接続されて、径方向外側且つ下側に凸となるように縦断面曲線状に湾曲して形成された湾曲部２４とを備えて構成されている。 The cavity 21 is connected to a raised portion 25 that is formed so as to protrude upward from the center of the bottom of the cavity 21 so as to protrude upward, a lower end 22A of the lip portion 22, and a lower end 25A of the raised portion 25. And a curved portion 24 that is curved in a longitudinally curved shape so as to protrude radially outward and downward.
　本実施形態において、湾曲部２４の縦断面形状を規定する第１曲線部ＣＬ１及び、***部２５の下端から頂部近傍に至る縦断面形状を規定する第２曲線部ＣＬ２は、それぞれクロソイド曲線で形成されている。より詳しくは、湾曲部２４の第１曲線部ＣＬ１は、径方向外側且つ下側に凸となり、ピストン中心側に向かうに従い曲率が大きく設定された第１クロソイド曲線で規定され、***部２５の第２曲線部ＣＬ２は上側に凸となる第２クロソイド曲線で規定されている。 In the present embodiment, the first curved portion CL1 that defines the vertical cross-sectional shape of the curved portion 24 and the second curved portion CL2 that defines the vertical cross-sectional shape from the lower end of the raised portion 25 to the vicinity of the top portion are each formed by a clothoid curve. Has been. More specifically, the first curved portion CL1 of the curved portion 24 is defined by a first clothoid curve that is convex radially outward and downward and has a curvature that increases toward the piston center side. The two curve portions CL2 are defined by a second clothoid curve that is convex upward.
　第１曲線部ＣＬ１は、少なくとも、リップ部２２の径方向内側に最も突出する最突出端からピストン軸方向に下した鉛直線ＶＬが第１曲線部ＣＬ１と交差するリップ直下方部２４Ａから、第１曲線部ＣＬ１が下方に最も窪む最下端部２４Ｂまでの範囲を第１クロソイド曲線で形成されている。 The first curved line portion CL1 includes at least a first line portion 24A directly below the lip where a vertical line VL descending in the piston axial direction from the most protruding end that protrudes most radially inward of the lip portion 22 intersects the first curved portion CL1. A range up to the lowermost end 24B where the first curved portion CL1 is most depressed downward is formed by a first clothoid curve.
　すなわち、キャビティ２１の縦断面形状を直線部分が含まれない第１及び第２クロソイド曲線によって略Ｓ字状に形成し、第１曲線部ＣＬ１の曲率をピストン中心側に向かうに従い大きく設定したことで、キャビティ２１内に流れ込む燃料噴霧ＦＬが燃焼室Ａの中央に位置する***部２５に向かって円滑に流されるようになる。 That is, the longitudinal cross-sectional shape of the cavity 21 is formed in a substantially S shape by the first and second clothoid curves that do not include a straight portion, and the curvature of the first curved portion CL1 is set to increase toward the piston center side. becomes as smooth flow towards the ridge 25 where the fuel spray F L flowing into the cavity 21 is located at the center of the combustion chamber a.
　次に、図２～４に基づいて、本実施形態のピストン２０による作用について説明する。 Next, the operation of the piston 20 according to this embodiment will be described with reference to FIGS.
　図２に示すように、ピストン２０の圧縮上死点近傍でインジェクタ１７から燃料が噴射されると、燃料の噴霧Ｆは、キャビティ２１のリップ部２２に衝突することで、リップ部２２よりも上方のスキッシュエリアＳに流れ込む燃料噴霧ＦＵと、リップ部２２よりも下方のキャビティ２１内に流れ込む燃料噴霧ＦＬとに分散される。 As shown in FIG. 2, when the fuel is injected from the injector 17 in the vicinity of the compression top dead center of the piston 20, the fuel spray F collides with the lip portion 22 of the cavity 21, so that it is higher than the lip portion 22. a fuel spray F U flowing into the squish area S of and dispersed in the fuel spray F L flowing into the lower portion of the cavity 21 than the lip portion 22.
　本実施形態では、リップ部２２に段差部２３が設けられているので、スキッシュエリアＳに分散される燃料噴霧ＦＵと、キャビティ２１内に分散される燃料噴霧ＦＬとの噴霧分配の最適化が図られるようになっている。 In the present embodiment, since the step portion 23 to the lip portion 22 is provided, optimization of the spray distribution of the fuel spray F U dispersed in the squish area S, the fuel spray F L which is dispersed in the cavity 21 Is designed.
　すなわち、図３に示すように、燃焼の前半は、燃料噴霧ＦＵがスキッシュエリアＳ内に効果的に拡散されることで、スキッシュエリアＳ内の空気（酸素）を有効に利用した燃焼が実現される。 That is, as shown in FIG. 3, the first half of the combustion, by fuel spray F U is effectively diffused into the squish area S, effectively utilizing combustion air (oxygen) in the squish area S is realized Is done.
　再び図２に戻って、リップ部２２からキャビティ２１内に流れ込んだ燃料噴霧ＦＬの流れを説明する。図２中に破線で示す従来構造のキャビティ断面形状では、***部の急な傾斜角や、直線部と曲線部とのつながりの悪さによって、燃料噴霧ＦＬはエネルギの減衰が大きくなり、早期に巻き上げられることで、燃焼室Ａの中心部の空気を利用した燃焼を効果的に行えない課題があった。 Again back to FIG. 2, the flow of the fuel spray F L which flows from the lip portion 22 into the cavity 21. In the cavity cross-sectional shape of the prior art structure shown by a broken line in FIG. 2, and steep angle of inclination of the ridge, the poor connection between the straight portion and the curved portion, the fuel spray F L the attenuation of the energy is increased, early By being wound up, there was a problem that combustion using the air at the center of the combustion chamber A could not be effectively performed.
　これに対し、本実施形態では、燃料噴霧ＦＬがキャビティ２１の縦断面形状を規定する二つの第１及び第２クロソイド曲線ＣＬ１，２に沿って移動し、特に第１クロソイド曲線ＣＬ１は、ピストン中心側に向かうに従い曲率が大きく設定されているため、燃料噴霧ＦＬは、そのエネルギを大きく減衰されることなく、燃焼室Ａの中央に位置する***部２５に向かって円滑に流されるようになる。 In contrast, in the present embodiment, the fuel spray F L is moved along the two first and second clothoid curve CL1,2 defining a longitudinal sectional shape of the cavity 21, in particular the first clothoid curve CL1, the piston Since the curvature is set to be larger toward the center side, the fuel spray FL is smoothly flowed toward the raised portion 25 located in the center of the combustion chamber A without greatly reducing its energy. Become.
　すなわち、図４に示すように、燃焼の後半は、クロソイド曲線に沿って流される燃料噴霧ＦＬが燃焼室Ａの中央付近まで円滑に達することで、燃料噴霧ＦＬのエネルギを最大限に使用し、且つ、燃焼室Ａの中央付近の空気（酸素）を有効に利用した燃焼が実現される。 That is, as shown in FIG. 4, the second half of the combustion, that the fuel spray F L which flows along the clothoid curve reaches smoothly to near the center of the combustion chamber A, used to maximize the energy of the fuel spray F L In addition, combustion using the air (oxygen) near the center of the combustion chamber A is realized.
　以上詳述したように、本実施形態によれば、リップ部２２に段差部２３を設けたことで、スキッシュエリアＳに分散される燃料噴霧ＦＵと、キャビティ２１内に分散される燃料噴霧ＦＬとの噴霧分配の最適化が図られるようになる。これにより、燃焼の前半は、燃料噴霧ＦＵがスキッシュエリアＳ内に効果的に拡散され、スキッシュエリアＳ内の空気（酸素）を有効に利用した燃焼を実現することができる。 As described above in detail, according to this embodiment, it has a stepped portion 23 provided on the lip portion 22, and the fuel spray F U dispersed in the squish area S, the fuel spray F is dispersed into the cavity 21 optimization of the spray distribution of the L is to be achieved. Thus, the first half of the combustion, the fuel spray F U is effectively diffused into the squish area S, can be achieved effectively utilizing combustion air (oxygen) in the squish area S.
　また、湾曲部２４の縦断面形状を規定する第１曲線部ＣＬ１及び、***部２５の下端から頂部近傍に至る縦断面形状を規定する第２曲線部ＣＬ２を第１及び第２クロソイド曲線ＣＬ１，２で形成し、特に第１クロソイド曲線ＣＬ１は、ピストン中心側に向かうに従い曲率を大きく設定したことで、燃料噴霧ＦＬは、そのエネルギを大きく減衰させることなく、燃焼室Ａの中央に位置する***部２５に向かって流されるようになる。これにより、燃焼の後半は、燃料噴霧ＦＬが燃焼室Ａの中央付近まで円滑に達することで、燃料噴霧ＦＬのエネルギを最大限に使用し、且つ、燃焼室Ａの中央付近の空気（酸素）を有効に利用した燃焼を実現することが可能になる。 In addition, the first and second clothoid curves CL1, the first curved portion CL1 that defines the vertical cross-sectional shape of the curved portion 24, and the second curved portion CL2 that defines the vertical cross-sectional shape from the lower end of the raised portion 25 to the vicinity of the top portion. In particular, the first clothoid curve CL1 is set to have a larger curvature as it goes toward the piston center, so that the fuel spray FL is located at the center of the combustion chamber A without greatly reducing its energy. It flows toward the raised portion 25. Thus, the second half of the combustion, that the fuel spray F L reaches smoothly to near the center of the combustion chamber A, the energy of the fuel spray F L used maximally, and the air near the center of the combustion chamber A ( It is possible to realize combustion that effectively uses (oxygen).
　すなわち、本実施形態によれば、燃焼の前半は燃焼室Ａ内の外周側（スキッシュエリアＳ側）を利用した燃焼が行われ、さらに、燃焼の後半は燃焼室Ａ内の中央付近を利用した燃焼が行われることで、燃焼室Ａ内の空気を有効利用した燃焼が可能になり、燃焼効率を確実に向上することができる。 That is, according to the present embodiment, the first half of the combustion is performed using the outer peripheral side (squish area S side) in the combustion chamber A, and the second half of the combustion is performed near the center in the combustion chamber A. By performing the combustion, combustion using the air in the combustion chamber A can be performed effectively, and the combustion efficiency can be reliably improved.
　なお、本発明は、上述の実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で、適宜変形して実施することが可能である。 It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the spirit of the present invention.
　例えば、第１曲線部ＣＬ１は、その径方向外側に最も突出した最側端部２４Ｃから下方に最も窪んだ最下端部２４Ｂまでをクロソイド曲線で形成してもよい。 For example, the first curve portion CL1 may be formed with a clothoid curve from the outermost end portion 24C protruding most outward in the radial direction to the lowermost end portion 24B recessed most downward.
　また、第１曲線部ＣＬ１は、その径方向外側に最も突出した最側端部２４Ｃから***部の下端２５Ａまでをクロソイド曲線で形成してもよい。 Further, the first curved portion CL1 may be formed with a clothoid curve from the outermost end portion 24C that protrudes most outward in the radial direction to the lower end 25A of the raised portion.
　また、第１曲線部ＣＬ１は、リップ部の下端から***部の下端２５Ａまでをクロソイド曲線で形成してもよい。 Further, the first curved portion CL1 may be formed with a clothoid curve from the lower end of the lip portion to the lower end 25A of the raised portion.
　また、第１曲線部ＣＬ１は、リップ部の下端から下方に最も窪んだ最下端部２４Ｂまでをクロソイド曲線で形成してもよい。 Further, the first curve portion CL1 may be formed with a clothoid curve from the lower end of the lip portion to the lowest end portion 24B that is most depressed downward.
　また、キャビティ２１の縦断面形状を規定する曲線はクロソイド曲線に限定されず、燃料噴霧の流れを妨げないものであれば、三次放物線（三次曲線）又はサインカーブ（サイン半波長逓減曲線）等の他の曲線であってもよい。また、エンジン１０は直噴式ディーゼルエンジンに限定されず、直噴式ガソリンエンジン等の他の直噴式エンジンであってもよい。 Moreover, the curve which prescribes | regulates the longitudinal cross-sectional shape of the cavity 21 is not limited to a clothoid curve, If it does not prevent the flow of fuel spray, a cubic parabola (cubic curve) or a sine curve (sine half-wave decreasing curve) etc. Other curves may be used. The engine 10 is not limited to a direct injection diesel engine, and may be another direct injection engine such as a direct injection gasoline engine.
　本出願は、2015年10月30日付で出願された日本国特許出願（特願2015-214478）に基づくものであり、その内容はここに参照として取り込まれる。 This application is based on a Japanese patent application (Japanese Patent Application No. 2015-214478) filed on October 30, 2015, the contents of which are incorporated herein by reference.
　本開示に係るエンジンのピストンは、キャビティ内における燃料噴霧のエネルギの減衰を効果的に防止することができるという効果を奏し、高精度な燃焼制御を可能とすることで低燃費・高効率なエンジンを実現することができるという点において有用である。 The piston of the engine according to the present disclosure has an effect of effectively preventing the attenuation of the energy of the fuel spray in the cavity, and enables a highly accurate combustion control to achieve a low fuel consumption and high efficiency engine. Is useful in that it can be realized.
　１０　エンジン
　１１　シリンダブロック
　１２　シリンダヘッド
　１３　吸気バルブ
　１４　吸気ポート
　１５　排気バルブ
　１６　排気ポート
　１７　インジェクタ
　２０　ピストン
　２１　キャビティ
　２２　リップ部
　２３　段差部
　２３Ａ　平坦面部
　２３Ｂ　傾斜面部
　２４　湾曲部
　２５　***部 DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder block 12 Cylinder head 13 Intake valve 14 Intake port 15 Exhaust valve 16 Exhaust port 17 Injector 20 Piston 21 Cavity 22 Lip part 23 Step part 23A Flat surface part 23B Inclined surface part 24 Curved part 25 Raised part

Claims (6)

  1. 　エンジンのピストンであって、
    　ピストン頂部に凹設されたキャビティと、
    　前記キャビティの開口部周縁に径方向内側に突出して環状に設けられたリップ部と、
    　前記キャビティの底部に上方に向けて突出して設けられた***部と、
    　前記キャビティの前記リップ部と前記***部との間に設けられ、前記リップ部下端と前記***部下端とを接続すると共に、径方向外側且つ下側に向けて縦断面曲線状に突出する湾曲部とを備え、
    　前記湾曲部の縦断面形状は、ピストン中心側に向かうに従い曲率が大きくなる曲線を含む
    　エンジンのピストン。     An engine piston,
    A cavity recessed in the top of the piston;
    A lip provided in an annular shape projecting radially inward at the periphery of the opening of the cavity;
    A raised portion provided to protrude upward at the bottom of the cavity;
    A curved portion that is provided between the lip portion and the raised portion of the cavity, connects the lower end of the lip portion and the lower end of the raised portion, and protrudes radially outward and downward in a curved shape in a longitudinal section. And
    The longitudinal cross-sectional shape of the curved portion includes a curve whose curvature increases toward the piston center.
  2. 　前記湾曲部において、前記リップ部の径方向内側に最も突出する最突出端からピストン軸方向に下した鉛直線が交差するリップ直下方部と、前記湾曲部の下方に最も窪む最下端部との間の縦断面形状は、ピストン中心側に向かうに従い曲率が大きくなる曲線とされている
    　請求項１に記載のエンジンのピストン。     In the curved portion, a portion directly below the lip where a vertical line extending in the piston axial direction from the most projecting end that projects most radially inward of the lip portion intersects, and a bottom end portion that is most depressed below the curved portion. The engine piston according to claim 1, wherein a longitudinal cross-sectional shape between the two is a curve whose curvature increases toward the piston center side.
  3. 　前記曲線は、クロソイド曲線を含む曲線である
    　請求項１又は２に記載のエンジンのピストン。     The engine piston according to claim 1, wherein the curve is a curve including a clothoid curve.
  4. 　前記***部は、前記キャビティの底部から上方に向けて縦断面曲線状に突出して設けられ、
    　前記***部は、縦断面形状を規定する曲線の少なくとも一部がクロソイド曲線とされている
    　請求項１から３の何れか一項に記載のエンジンのピストン。     The raised portion is provided so as to protrude upward in a curved shape in a longitudinal section from the bottom of the cavity.
    The piston of the engine according to any one of claims 1 to 3, wherein at least a part of a curve defining the vertical cross-sectional shape of the raised portion is a clothoid curve.
  5. 　前記リップ部は、当該リップ部の内周側上面から所定の深さで窪む環状の段差部を有する
    　請求項１から４の何れか一項に記載のエンジンのピストン。     5. The engine piston according to claim 1, wherein the lip portion has an annular stepped portion that is recessed at a predetermined depth from an upper surface on the inner peripheral side of the lip portion.
  6. 　前記段差部は、前記リップ部の内周縁から径方向外方に延びる環状の平坦部と、当該平坦部の外周縁から上方に向かって斜めに傾斜する環状の傾斜部とを含む
    　請求項５に記載のエンジンのピストン。     The step portion includes an annular flat portion extending radially outward from an inner peripheral edge of the lip portion, and an annular inclined portion inclined obliquely upward from the outer peripheral edge of the flat portion. The piston of the described engine.
PCT/JP2016/078878 2015-10-30 2016-09-29 Piston for engine WO2017073235A1 (en)

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