JP5064174B2 - Piston for internal combustion engine - Google Patents

Description

  The present invention relates to an improvement in a piston for an internal combustion engine that contributes to improvement in engine output and fuel efficiency by reducing frictional resistance of a skirt portion against an inner wall of a cylinder.

In internal combustion engine pistons, in order to reduce the frictional resistance of the skirt portion against the cylinder inner wall, it has been widely known to form innumerable fine streaks on the thrust surface of the skirt portion and hold oil in them. (For example, refer to Patent Documents 1 and 2).
JP 2003-13799 A JP 2005-2889 A

  The present invention not only holds oil on the thrust surface of the skirt portion, but also constitutes a hydrodynamic bearing on the thrust surface with the oil using piston motion, and the friction resistance against the cylinder inner wall of the skirt portion is An object of the present invention is to provide a piston for an internal combustion engine that can be more effectively reduced.

In order to achieve the above-mentioned object, the present invention provides a first portal-shaped first portion defining an oil pocket having an inlet opening downward on a first thrust surface of a skirt portion pressed against an inner wall of a cylinder during an expansion stroke of a piston. A large number of oil guide walls are protruded, and during the expansion stroke, oil interposed between the skirt portion pressed against the cylinder inner wall and the cylinder inner wall is introduced into the oil pocket of the first oil guide wall as the piston moves. Thus, a hydrodynamic bearing is formed between the first thrust surface and the cylinder inner wall, and an inlet opening upward is provided on the second thrust surface of the skirt portion pressed against the cylinder inner wall during the compression stroke of the piston. many second oil guide wall of gate-shaped defining an oil pocket projecting, during the compression stroke, the skirt portion and the cylindrical which is pressed against the cylinder inner wall Engine oil interposed between the inner wall and so the second thrust surface and a hydrodynamic bearing between the cylinder inner wall is constituted by being introduced into the oil pocket companion no second oil guide wall motion of the piston Pistons, wherein the number of the first oil guide walls is set to be larger than the number of the second oil guide walls, and the circumferential direction of the skirt portion of each oil pocket of the first and second oil guide walls Is set so as to narrow toward the back from the inlet, and each oil pocket of the first oil guide wall has a bottom surface higher than the first thrust surface and each oil of the second oil guide wall. In the pocket, a bottom surface higher than the second thrust surface is formed, and a first step portion is provided between each thrust surface and the corresponding bottom surface of each oil pocket, and each oil guide is formed. That the second step portion between the wall and the bottom surface of each oil pocket corresponding thereto are formed respectively shall be the first feature.

Further, in addition to the first feature, the present invention is configured such that the first and second oil guide walls and the bottom surface of the oil pocket are constituted by wear-resistant coating layers printed on the first and second thrust surfaces, respectively. Is the second feature.

  In the piston of the present invention, upward refers to the top surface side of the head portion, and downward refers to the opposite side of the top surface of the head portion, and does not refer to the top-to-bottom direction.

According to the first feature of the present invention, during the reciprocating movement of the piston, when the thrust surface of the skirt portion projecting a large number of oil guide walls slides against the cylinder inner wall, the oil guide walls define the thrust surfaces. Each oil guide wall scrapes the lubricating oil that intervenes in the skirt and the cylinder inner wall while moving, and pushes it inward from the inlet of each oil pocket. As a result, a sufficient amount of oil can be secured in the oil pocket. Therefore, when a thrust load is applied to the thrust surface, an oil film pressure is generated by the squeezing action (skew action) against the oil, and between the thrust surface and the cylinder inner wall. The hydrodynamic bearing is constructed.

  That is, during the expansion stroke of the piston, the first thrust surface of the skirt portion pressed against the cylinder inner wall is supported on the cylinder inner wall via the hydrodynamic bearing, and during the compression stroke, the first skirt portion pressed against the cylinder inner wall is supported. Since the two thrust surfaces are supported on the cylinder inner wall via the hydrodynamic bearing, the frictional resistance between the piston and the cylinder inner wall can be effectively reduced, and the engine output and fuel efficiency can be greatly improved.

Also, since the width of the oil pocket along the circumferential direction of the skirt portion is narrowed from the inlet to the back, the oil between the skirt and the cylinder inner wall moves from the inlet of the oil pocket to the back as the piston moves. The pressure in the oil pocket can be effectively increased and the strength of the hydrodynamic bearing can be effectively increased.

Moreover, than the bottom surface of each oil pocket of the first and second oil guide wall to form high first and second, respectively from the thrust surface, no wake the movement of the piston, the skirt portion and the lubricating oil interposed cylinder inner wall Sequentially passes through the oil pocket by a first step between the thrust surface and the bottom of the higher oil pocket and a second step between the bottom of the oil pocket and the higher oil guide wall. The wedge effect (wedge action) generates a higher oil film pressure. The synergistic effect of the wedge effect and the oil scraping effect by the oil pocket further increases the strength of the hydrodynamic bearing. Can be enhanced.

According to the second feature of the present invention, the oil guide wall and the bottom surface of the oil pocket are formed by printing the wear-resistant coating layer on the thrust surface. By controlling the size and thickness of the wearable coating layer, the dimensions of each part of the oil pocket, such as the height of the oil guide wall and the bottom of the oil pocket, can be obtained accurately and easily. The performance of the fluid dynamic bearing can be easily stabilized.

  Embodiments of the present invention will be described below on the basis of preferred embodiments of the present invention shown in the accompanying drawings.

  1 is a longitudinal front view of a piston for an internal combustion engine according to a first embodiment of the present invention, FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1, FIG. 3 is a view taken in the direction of arrow 3 in FIG. FIG. 5 is a reference example diagram corresponding to the enlarged portion of FIG. 2.

  First, the first embodiment of the present invention will be described. In FIG. 1, a piston P that reciprocates in a cylinder C of an internal combustion engine includes a head portion 1 that faces the top surface of a combustion chamber above the cylinder C, and a pair of front and rear that are integrally connected to the lower surface of the head portion 1. The pin boss part 2 and a cylindrical skirt part 3 integrally provided at the peripheral edge of the lower end of the head part 1, and on the outer peripheral surface of the head part 1, a plurality of strips on which the piston ring 4 is mounted. A ring groove 5 is provided, and a piston pin 7 that supports the small-diameter end of the connecting rod R is mounted in the pin hole 2 a of the pair of pin boss portions 2. The piston P is made of an aluminum alloy.

In this piston P, the skirt portion 3 is slidably fitted to the cylinder inner wall Ca to properly maintain the reciprocating posture of the entire piston P. In particular, in the expansion stroke and compression stroke of the piston P, It is strongly pressed to the cylinder inner wall Ca by the reaction force of the connecting rod R or we inclined. Here, one side surface of the skirt portion 3 pressed against the cylinder inner wall Ca in the expansion stroke of the piston P is referred to as a first thrust surface 3a, and the other side of the skirt portion 3 pressed against the cylinder inner wall Ca in the compression stroke of the piston P. The side surface is referred to as a second thrust surface 3b.

As shown in FIG. 2, above the first thrust surface 3a, the first oil guide wall 11 of the portal defining an oil pocket 13 having an open inlet 13a downwardly are projected number. Also as shown in FIG. 3, the second thrust surface 3b, the second oil guide wall 12 of the portal defining an oil pocket 13 having an inlet 13a opening downward is protruded number. At that time, each of the oil pockets 13 is defined by the first and second oil guide walls 11 and 12 so that the lateral width w along the circumferential direction of the skirt portion 3 is narrowed from the inlet 13a toward the back thereof. The bottom surface 13b of the oil pocket 13 is formed one step higher than the corresponding thrust surfaces 3a and 3b. Thus, the first step portion 14a is formed between the thrust surfaces 3a and 3b and the oil pocket bottom surface 13b, and the second step portion 14b is formed between the oil pocket bottom surface 13b and the oil guide walls 11 and 12.

  Next, a method of forming the first and second oil guide walls 11 and 12 will be described with reference to FIGS.

  First, the first wear-resistant coating layer 15 is formed by printing on the entire area of the first and second thrust surfaces 3a and 3b, and then the first and second oil guides on the first wear-resistant coating layer 15 are formed. A second wear-resistant coating layer 16 is formed by printing on the walls 11, 12 and the region including the oil pockets 13, and finally, the first and second oil guide walls 11 on the second wear-resistant coating layer 16. , 12, a third wear-resistant coating layer 17 is formed. As the printing agent constituting the first to third wear-resistant coating layers 15 to 17, for example, a kneaded mixture of a solid lubricant containing graphite and a binder resin containing a polyamideimide resin is used. The third wear-resistant coating layers 15 to 17 are dried and solidified after printing. Thus, the thickness of the second wear-resistant coating layer 16 corresponds to the height of the bottom surface 13 b of the oil pocket 13, and the thickness of the third wear-resistant coating layer 17 corresponds to the height of the oil pocket 13.

  In order to increase the bonding strength of the first wear-resistant coating layer 15 to the thrust surfaces 3a and 3b, it is effective to form countless fine streaks on the thrust surfaces 3a and 3b.

  An example of the size of the oil pocket 13 and the oil guide wall 11 is shown in FIG. 2, and an example of the thickness of the first to third wear-resistant coating layers 15 to 17 is shown in FIG.

  Next, the operation of this embodiment will be described.

  In FIG. 1 to FIG. 3, it is assumed that the piston P is in the expansion stroke and is lowered as indicated by an arrow A. In this case, the first thrust surface 3 a having a large number of first oil guide walls 11 of the skirt portion 3 is lowered while being pressed toward the cylinder inner wall Ca, but an oil pocket defined by the first oil guide wall 11. 13 has its inlet 13a facing downward, and the first oil guide walls 11 scrape the lubricating oil interposed in the skirt portion 3 and the cylinder inner wall Ca while descending, so that the inlets of the respective oil pockets 13 are gathered. It is possible to secure a sufficient amount of oil in the oil pocket 13 by pushing it in from the rear side 13a. Therefore, when a thrust load is applied to the second thrust surface 3b, the oil film pressure is exerted by the squeezing effect (skew action) against the oil. And a hydrodynamic bearing is formed between the thrust surface and the cylinder inner wall. Since the first thrust surface 3a is supported by the cylinder inner wall Ca via such a hydrodynamic bearing, the frictional resistance between the first thrust surface 3a and the cylinder inner wall Ca is effectively reduced. The power loss due to the frictional resistance can be reduced, and the engine output and fuel efficiency can be improved.

  In particular, since the oil pocket 13 has a width in the circumferential direction of the skirt portion 3 narrowed from the inlet 13a toward the back, the oil between the skirt portion 3 and the cylinder inner wall Ca flows from the inlet 13a of the descending oil pocket 13 to the back. As it moves to the center of the oil pocket 13, the pressure in the oil pocket 13 can be effectively increased, thereby effectively increasing the strength of the hydrodynamic bearing. Can be increased.

  Next, in FIGS. 1 and 3, it is assumed that the piston P is in the compression stroke and is rising as indicated by an arrow B. In this case, the second thrust surface 3b having a large number of second oil guide walls 12 of the skirt portion 3 rises while being pressed toward the cylinder inner wall Ca, but the oil pockets defined by the second oil guide walls 12 13 is opposite to the oil pocket 13 and has its inlet 13a facing upward, so that the multiple second oil guide walls 12 collect the lubricating oil intervening in the skirt portion 3 and the cylinder inner wall Ca while ascending, Since the oil pockets 13 are pushed in from the inlets 13a, a powerful hydrodynamic bearing can be formed between the second thrust surface 3b and the cylinder inner wall Ca by the same action as in the expansion stroke of the piston P. Therefore, also in this case, the frictional resistance between the second thrust surface 3b and the cylinder inner wall Ca can be effectively reduced, and the frictional resistance can be reduced. According reduces power loss, it can lead to increased engine output and fuel economy.

  In any of the expansion stroke and the compression stroke, when the lubricating oil interposed between the skirt portion 3 and the cylinder inner wall Ca passes through each oil pocket 13 as the piston P moves, the thrust surfaces 3a and 3b And the first step portion 14a between the oil pocket bottom surface 13b and the second step portion 14b between the oil pocket bottom surface 13b and the oil guide walls 11 and 12 are sequentially squeezed step by step, and by this wedge effect (wedge action) Since a higher oil film pressure is generated, the oil film pressure can be further increased and the strength of the hydrodynamic fluid bearing can be further effectively increased by synergy between the wedge effect and the oil scraping effect by the oil pocket 13.

  In addition, as in the reference example shown in FIG. 5, the oil guide walls 11 and 12 are formed in a straight line that does not define the oil pocket, and the first and second step portions 14a and 14b that are sequentially increased in height are formed. Even if it is left alone, the effect of scraping the oil is weakened, but a sufficient wedge effect can be obtained for obtaining a hydrodynamic bearing. In FIG. 5, the same reference numerals are assigned to portions corresponding to the previous embodiment, and redundant description is omitted.

  The first and second oil guide walls 11 and 12 are formed by printing the first to third wear-resistant coating layers 15 to 17 on the first and second thrust surfaces 3a and 3b. Is not only easy, but by controlling the size and thickness of the wear-resistant coating layers 15 to 17, the height of the oil guide walls 11, 12 and the oil pocket bottom surface 13 b, etc. The dimensions can be obtained accurately and easily, and the performance of the hydrodynamic bearing including the oil pockets 13 can be easily stabilized.

  The present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the invention.

The longitudinal section front view of the piston for internal-combustion engines concerning the present invention. FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1. FIG. 3 is a view taken in the direction of arrow 3 in FIG. 1. FIG. 4 is an enlarged sectional view taken along line 4-4 of FIG. The reference example figure corresponding to the expansion part of FIG.

P ··· Piston w · · · Oil pocket width 3 · · · Skirt portion 3a · · · First thrust surface 3b · · · Second thrust surface 11 · · · ... First oil guide wall 12... Second oil guide wall 13... Oil pocket 13 a... Oil pocket inlet 13 b.・ Abrasion-resistant coating layer

Claims (2)

An oil pocket (13) having an inlet (13a) opening downward is defined on the first thrust surface (3a) of the skirt (3) pressed against the cylinder inner wall (Ca) during the expansion stroke of the piston (P). A plurality of gate-shaped first oil guide walls (11) projecting, and oil interposed between the skirt (3) and the cylinder inner wall (Ca) pressed against the cylinder inner wall (Ca) during the expansion stroke The hydrodynamic bearing is inserted between the first thrust surface (3a) and the cylinder inner wall (Ca) by being introduced into the oil pocket (13) of the first oil guide wall (11) as the piston (P) moves. To be configured,
An oil pocket (13) having an upwardly opening inlet (13a) is defined on the second thrust surface (3a) of the skirt portion (3) pressed against the cylinder inner wall (Ca) during the compression stroke of the piston (P). A large number of gate-shaped second oil guide walls (12) projecting, and oil interposed between the skirt portion (3) pressed against the cylinder inner wall (Ca) and the cylinder inner wall (Ca) during the compression stroke The hydrodynamic bearing is introduced between the second thrust surface (3b) and the cylinder inner wall (Ca) by being introduced into the oil pocket (13) of the second oil guide wall (12) as the piston (P) moves. A piston for an internal combustion engine configured ,
The number of the first oil guide walls (11) is set larger than the number of the second oil guide walls (12),
The lateral width (w) of each oil pocket (13) of the first and second oil guide walls (11, 12) along the circumferential direction of the skirt portion (3) is narrowed from the inlet (13a) toward the back. And set
Each oil pocket (13) of the first oil guide wall (11) has a bottom surface (13b) higher than the first thrust surface (3a), and each oil pocket (12) of the second oil guide wall (12). 13), a bottom surface (13b) higher than the second thrust surface (3b) is formed, and each thrust surface (3a, 3b) and a corresponding bottom surface (13b) of each oil pocket (13) Between the oil guide walls (11, 12) and the corresponding bottom surface (13b) of each oil pocket (13). A piston for an internal combustion engine characterized by being formed . The piston of claim 1 ,
The first and second oil guide walls (11, 12) and the oil pocket bottom surface (13a) are printed on the first and second thrust surfaces (3a, 3b), respectively. A piston for an internal combustion engine characterized by comprising:

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