JP2016011598A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston for an internal combustion engine that can reduce friction to a cylinder bore.SOLUTION: In the piston 2 for an internal combustion engine sliding with respect to an inner surface 7 of the cylinder bore 6 of the internal combustion engine 1 via lubricant 8, a dimple 11 is formed at a surface of a piston skirt part 10 t positioned on a thrust side relative to the inner surface 7 of the cylinder bore 6 without providing streaks.

Description

  The present invention relates to a piston for an internal combustion engine connected to a crankshaft of the internal combustion engine via a connecting rod.

  As shown in FIG. 4, some piston 20 has a piston skirt portion 21 with a streak process. The streak 22 has a function of storing the lubricating oil 8 when the piston is stopped, and can prevent the lubricating oil from running out even when the internal combustion engine is stopped for a while.

JP 2010-127142 A JP 2006-016982 A JP-A-10-132076 JP 2001-304039 A

  However, since the streak 22 is a jagged unevenness, it causes friction to increase.

  On the other hand, it is conceivable to reduce local contact by eliminating the streaking of the piston skirt portion 21. However, in the thrust side piston skirt portion having a high surface pressure, there is still local contact, and mixed lubrication is mainly used. On the other hand, the anti-thrust piston skirt has a lower surface pressure than the thrust side, so fluid lubrication is the main component.

  FIG. 5 shows an image of oil film thickness and friction loss (friction coefficient). In the mixed lubrication region, the friction loss decreases as the oil film thickness of the sliding portion (thrust side piston skirt portion) increases. On the other hand, in the fluid lubrication region, the friction loss increases as the oil film thickness of the sliding portion increases. Therefore, it is necessary to select an appropriate friction loss reduction measure that matches the lubrication state. In particular, the thrust side piston skirt is severely lubricated and has a large friction loss.

  Further, as shown in FIG. 6, the thrust side piston skirt portion 23 without the streak is smooth, so that it is difficult to obtain a dynamic pressure effect, resulting in a low oil film pressure. Further, even in the state where the streak processing is abolished, in addition to the minute unevenness 24 on the piston skirt surface, the piston skirt surface is pressed against the cylinder bore inner surface 7 by the in-cylinder pressure, so local contact occurs. There is a problem that friction loss increases.

  An object of the present invention is to provide a piston for an internal combustion engine that can reduce friction loss.

  In a piston for an internal combustion engine that slides on the inner surface of a cylinder bore of the internal combustion engine via lubricating oil, dimples are not formed on the surface of the piston skirt portion that is on the thrust side with respect to the inner surface of the cylinder bore. Formed.

  According to the piston for an internal combustion engine of the present invention, friction loss can be reduced.

(A) is the side view which looked at the piston for internal combustion engines which concerns on one embodiment of this invention from the thrust side, (b) is plane explanatory drawing of the piston for internal combustion engines. (A) is an expanded sectional view of an anti-thrust side piston skirt part and a thrust side piston skirt part, (b) is an important section expansion explanatory view of (a). (A) is principal part sectional explanatory drawing of the internal combustion engine at the time of an expansion stroke, (b) is principal part sectional explanatory drawing of the internal combustion engine at the time of a compression stroke. It is sectional explanatory drawing of the thrust side piston skirt in which the streak process was given. It is a figure showing the image of the relationship between an oil film thickness and a friction coefficient. It is sectional explanatory drawing of the thrust side piston skirt which abolished the striation process.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, in the present embodiment, the direction of the piston toward the top dead center is defined as the upward direction, and the direction toward the bottom dead center is defined as the downward direction.

  As shown in FIGS. 3A and 3B, the piston 2 of the internal combustion engine 1 such as a gasoline engine or a diesel engine is connected to the crankshaft 3 via a connecting rod 4 and formed in the cylinder block 5. It is located in the cylinder bore 6 and slides on the inner surface 7 of the cylinder bore 6 via lubricating oil 8 (see FIGS. 2A and 2B). In the figure, the cylinder bore 6 above the piston 2 constitutes a part of the combustion chamber 15.

  As shown in FIG. 1A, a plurality of ring grooves 9 for attaching a piston ring (not shown) are formed close to the top surface side (upper side) of the piston 2 in the vertical direction. A piston skirt portion 10 is formed on the piston 2 below the lowermost ring groove 9. However, in the present embodiment, the entire lower piston 2 with the lowermost ring groove 9 as a boundary is the piston skirt portion 10. The ring groove 9 formed in the piston 2 may be single.

  Further, as shown in FIGS. 3 and 2A, the surface of the thrust side piston skirt portion 10t, which is on the thrust side with respect to the inner surface 7 of the cylinder bore 6, is made smooth by removing the streak, and the oil film The dimples 11 are formed so that the thickness Tt is thick. Here, the thrust side refers to the side (the right side in FIG. 3) in the direction in which the tip of the connecting rod 4 faces during the expansion stroke of the internal combustion engine 1 in the direction orthogonal to the axial direction of the piston pin 12. In the internal combustion engine 1, since the connecting rod 4 is inclined with respect to the axial direction of the cylinder bore 6, the piston 2 during the expansion stroke is always pressed against the inner surface 7 of the cylinder bore 6 on the thrust side. Further, the anti-thrust side means the side opposite to the thrust side (the left side in FIG. 3).

  The dimple 11 is formed by sand blasting, laser processing, or the like. As shown in FIG. 1B, the dimple 11 has a thrust direction orthogonal to the axial direction of the piston pin 12 as 0 °, and an angle θ with respect to the line 13 extending in the thrust direction is within a range of ± 45 °. Is formed. Further, the dimple 11 is formed in a range from directly below the ring groove 9 to the lower end of the piston 2. As shown in FIG. 2B, the dimple 11 is formed with an opening width W of 1 μm to 50 μm and a depth D of 1 μm to 50 μm.

  The area ratio of the dimple 11 (ratio of the total area of the dimple 11 to the area of the dimple region 14 where the dimple 11 is formed) is set to 2% or more and 50% or less. When the dimple 11 is formed by sandblasting, the area ratio is adjusted by adjusting the volume density of the particles with respect to the jet air.

  In addition, dimples are not formed on the surface of the anti-thrust side piston skirt portion 10a, but streaks (not shown) or smooth surfaces (see FIG. 2A) are formed. In the anti-thrust side piston skirt portion 10a mainly composed of fluid lubrication, since the friction loss increases when the oil film pressure increases, no dimple is formed.

  Next, the operation of this embodiment will be described.

  As shown in FIG. 3B, when the internal combustion engine 1 reaches the compression stroke, the piston 2 receives an upward force from the connecting rod 4 inclined with respect to the piston direction, and reacts from the gas in the combustion chamber 15. The anti-thrust side is pressed against the inner surface 7 of the cylinder bore 6. Thereby, the space | interval of the thrust side piston skirt part 10t and the cylinder bore 6 expands slightly, and the lubricating oil 8 collects on the inner surface 7 of the cylinder bore 6 by the side of a thrust.

  Thereafter, as shown in FIG. 3A, when the internal combustion engine 1 reaches the expansion stroke, the expansion force due to the combustion pushes the piston 2, and this force is transmitted to the crankshaft 3 via the connecting rod 4, and the crankshaft 3 Rotate. The connecting rod 4 is inclined with respect to the central axis c of the cylinder bore 6 in the process in which the piston 2 is pushed down from the top dead center, and the thrust side piston skirt portion 10t is pressed against the inner surface 7 of the cylinder bore 6. At this time, as shown in FIG. 2 (a), the thrust side piston skirt portion 10t is smoothed by eliminating the streak and the dimple 11 is formed, so that local contact is reduced by smoothing. And the synergistic effect of the oil film pressure increase by a dynamic pressure effect is acquired, the thick oil film 16 is formed in the thrust side piston skirt part 10t, and a friction loss is reduced. Further, the piston skirt portion 10a on the anti-thrust side has a low piston side pressure and a sufficiently thick oil film is already formed, so that fluid lubrication is mainly used. Therefore, an increase in the oil film thickness causes an increase in friction due to an increase in the shear resistance of the lubricating oil, but since no dimples are formed on the anti-thrust surface, the friction does not increase. Further, as shown in FIG. 2C, the amount of wear can be reduced by reducing local contact, the wear powder 18 can be drawn into the dimple 11, and the surface of the piston skirt 10 can be cleaned, Scuffing is suppressed.

  As described above, since the dimple 11 is formed on the surface of the thrust side piston skirt portion 10t without performing streaking, the dynamic pressure effect can be obtained and the friction loss can be reduced, and the wear amount of the piston skirt portion 10 and the cylinder bore inner surface 7 can be reduced. Can be reduced, and the occurrence of scuffing can be suppressed.

  A ring groove 9 for attaching a piston ring is formed on the top surface side of the piston 2, a piston skirt portion 10 is formed in the piston 2 below the ring groove 9, and the dimple 11 is a piston from directly below the ring groove 9. Since it is formed over the lower end of 2, it is possible to reduce the friction especially in the portion where the friction is large, and to efficiently reduce the friction loss.

  Since the dimple 11 is formed to have an opening width W of 1 μm to 50 μm and a depth D of 1 μm to 50 μm, the oil film pressure can be effectively increased.

  Since the area ratio of the dimple 11 is 2% or more and 50% or less, the oil film pressure can be effectively increased.

  Since the dimples 11 are formed within a range of ± 45 ° with respect to the line 13 extending in the thrust direction, it is possible to reduce the friction especially in the portion where the friction is large, and to efficiently reduce the friction loss.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Piston 6 Cylinder bore 7 Inner surface 8 Lubricating oil 10t Thrust side piston skirt part 10a Anti-thrust side piston skirt part 11 Dimple

Claims (6)

In the piston for an internal combustion engine that slides through the lubricating oil against the inner surface of the cylinder bore of the internal combustion engine,
2. A piston for an internal combustion engine, wherein dimples are formed on a surface of a piston skirt portion on a thrust side with respect to an inner surface of the cylinder bore without performing streaking.   A ring groove for attaching a piston ring is formed on the top surface side of the piston, the piston skirt portion is formed in a piston below the ring groove, and the dimple extends from directly below the ring groove to the lower end of the piston. The piston for an internal combustion engine according to claim 1, which is formed over the whole area.   The piston for an internal combustion engine according to claim 1 or 2, wherein a streak or a smooth surface is formed on a surface of the anti-thrust side piston skirt portion.   4. The piston for an internal combustion engine according to claim 1, wherein the dimple has an opening width of 1 μm to 50 μm and a depth of 1 μm to 50 μm.   The piston for an internal combustion engine according to any one of claims 1 to 4, wherein an area ratio of the dimple to a dimple region where the dimple is formed is 2% or more and 50% or less.   The internal combustion engine according to any one of claims 1 to 5, wherein the dimple is formed within a range of ± 45 ° with respect to a line extending in the thrust direction, with a thrust direction orthogonal to the axial direction of the piston pin being 0 °. Piston for engine.

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