JP4254634B2 - Piston for internal combustion engine - Google Patents

Description

  The present invention relates to a piston for an internal combustion engine that can improve lubrication performance and reduce friction loss.

  A piston used in an internal combustion engine is connected to a connecting rod and a crankshaft, and moves up and down in a cylinder bore to generate an axial output in the crankshaft. Generally, at least one compression ring groove and an oil ring groove are formed in the piston, and an oil for mainly optimizing an oil film on the compression ring and the cylinder bore wall surface, which mainly maintains the airtightness of the combustion chamber. A ring is attached. The piston is also provided with a piston skirt that mainly suppresses rolling and releases heat to the cylinder.

  Here, the piston moves up and down while its compression ring, oil ring, and piston skirt are in contact with the cylinder bore wall surface. For this reason, conventionally, various measures have been taken to prevent abnormal wear and seizure.

  For example, the following Patent Document 1 discloses a piston in which a deep streak is formed on the shoulder of the piston skirt and a shallow streak is formed on the lower side of the piston skirt. Further, in Patent Document 2 below, there is provided a difference in the shape of the streak so that the outer peripheral surface roughness of the upper side of the piston skirt is larger than the outer peripheral surface roughness of the lower side on the thrust side of the piston. It is disclosed. Furthermore, Patent Document 3 below discloses a piston in which the surface of the piston skirt is processed so that the average roughness is 10 μm or less, and grooves having a groove width of 30 to 100 μm are formed on the surface.

  In addition, although the following Patent Document 4 does not mention the detailed positional relationship on the outer peripheral surface of the piston skirt, a fine concave portion whose depth regularly changes on the sliding surface of the piston is formed. A technique for providing a plateau-like convex portion between concave portions is disclosed.

Japanese Utility Model Publication No. 2-80748 JP-A-4-76254 JP 2000-88101 A JP 2002-235852 A

  Here, the surface pressure between the outer peripheral surface of the piston skirt and the cylinder bore wall surface is the uppermost and lowermost, middle, lower (between the middle and lowermost), upper (upper and middle) of the piston skirt. It increases in the order of

  For this reason, the pistons of the above-mentioned Patent Documents 1 and 2 are lubricated in such a way that oil is not collected in the lower part of the piston skirt even if the oil is accumulated in the striations in the upper part of the piston skirt to obtain a desired lubricating performance. There was a possibility that the performance deteriorated and abnormal wear or seizure could occur. Further, in the pistons of these Patent Documents 1 and 2, since the surface roughness of the intermediate portion of the piston skirt is rough, there is a disadvantage that friction and wear increase in the intermediate portion.

  Moreover, in the piston of the above-mentioned patent document 3, even if oil can be accumulated in the upper part and the lower part of the piston skirt, friction and wear increase in the middle part of the piston skirt.

  Further, in the piston of the above-mentioned Patent Document 4, even if the friction in the middle part of the piston skirt is reduced and the wear is suppressed, the oil cannot be accumulated in the upper and lower parts of the piston skirt, and the lubrication performance is deteriorated. As a result, abnormal wear and seizure could occur.

  Therefore, an object of the present invention is to provide a piston for an internal combustion engine that improves the disadvantages of the conventional example and can achieve both improvement in piston lubrication performance and reduction in friction loss.

To achieve the above Symbol purpose, in the first aspect of the present invention, to form a plurality of pistons circumferential direction of the coarse streak grooves at the top and bottom of the outer peripheral surface of the piston skirt, the the outer circumferential surface of the piston skirt An oil sump smaller than the coarse streak groove is formed in the uppermost part above the upper part, the lowermost part below the lower part, and the intermediate part between the upper part and the lower part .

According to the first aspect of the present invention, oil is held between the upper and lower portions of the piston skirt having a high surface pressure between the outer peripheral surface of the piston skirt and the wall surface of the cylinder bore. Friction is reduced at the top, bottom and middle.

In order to achieve the above object, in the invention described in claim 2 , a plurality of coarse groove grooves in the circumferential direction of the piston are formed in the upper and lower portions of the outer peripheral surface of the piston skirt on the thrust side, A plurality of streak grooves as an oil reservoir having a groove width equivalent to the coarse streak groove and shallower than the rough streak groove on the outer circumferential surface of the piston skirt in the circumferential direction of the piston, or A plurality of micro dimples are formed as oil reservoirs that are finer than the coarse streak grooves .

According to the invention described in claim 2 , on the outer peripheral surface of the piston skirt on the thrust side having a relatively high surface pressure, the oil is held at the upper and lower portions of the piston skirt having a higher surface pressure. Friction is reduced on the outer peripheral surface of the piston skirt on the anti-thrust side whose surface pressure is lower than that on the thrust side. Specifically, on the anti-thrust side, if the oil reservoir has a groove width equal to that of the coarse streak groove and a plurality of streak grooves having a shallower depth than the coarse streak groove, lubrication is possible. Friction can be reduced by reducing the shearing force by securing an appropriate amount of required oil and reducing the amount of oil retained. Further, in the case of micro dimples, the friction coefficient can be reduced, so that friction can be more effectively reduced.

In order to achieve the above object, according to a third aspect of the present invention, in the piston for an internal combustion engine according to the first or second aspect, the groove side surface on the piston lower side of the coarse streak groove is defined as a piston top surface. Or tilted toward the inside of the piston and downward of the piston.

According to the third aspect of the present invention, a large amount of oil can be held in the coarse streak groove, and further, the oil can be held even when the piston moves up and down.

  The piston for an internal combustion engine according to the present invention retains oil at a location where the surface pressure is high, thereby improving the lubrication performance, and reducing friction at locations where the surface pressure is low, thus reducing friction loss. As described above, according to the piston for an internal combustion engine according to the present invention, it is possible to reduce the friction loss while improving the lubrication performance. The amount can be reduced.

  Embodiments of a piston for an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  Embodiment 1 A piston 1 for an internal combustion engine according to the present invention will be described with reference to FIGS.

  1 denotes a piston for an internal combustion engine according to the first embodiment. The piston 1A is formed with a first compression ring groove 2a, a second compression ring groove 2b, and an oil ring groove 2c in this order from the top surface of the piston, whereby the top land 3a and the second land 3b are formed in the piston head portion. And the third land 3c is formed. Here, in each of the first compression ring groove 2a, the second compression ring groove 2b, and the oil ring groove 2c, a top ring and a second ring (not shown) that mainly maintain the airtightness of the combustion chamber, and a cylinder bore wall surface 20 are formed. An oil ring (not shown) is attached to optimize the oil film. The piston 1A is provided with a piston skirt 4 that suppresses the rolling and releases the heat to the cylinder.

  Here, as shown in FIG. 3A, when the piston 1 descends, the maximum thrust force F1 particularly in the explosion stroke is shown, and when the piston 1 rises as shown in FIG. 3-2, the thrust force F2 opposite to the thrust force F1 is obtained. (<F1) is applied from the piston 1 to the cylinder bore wall surface 20. Hereinafter, the side on which the thrust force F1 is applied in the downward stroke of the piston 1 is referred to as “thrust side”, and the side on which the thrust force F2 is applied in the upward stroke of the piston 1 is referred to as “anti-thrust side”.

  Such thrust forces F1 and F2 are similarly generated when the piston 1A of the first embodiment moves up and down. As a result, different surface pressures are generated on the thrust side and the anti-thrust side as shown in FIG. It hangs between the outer peripheral surface of the skirt 4 and the cylinder bore wall surface 20.

  According to the surface pressure distribution diagram of FIG. 4, as apparent from the fact that the thrust force F1 on the thrust side is larger than the thrust force F2 on the antithrust side, a higher surface pressure is applied on the thrust side than on the antithrust side. You can see that Further, between the outer peripheral surface of the piston skirt 4 and the cylinder bore wall surface 20 on the thrust side having a relatively high surface pressure, the uppermost portion 4a and the lowermost portion 4e, the intermediate portion 4c, and the lower portion (intermediate portion) of the piston skirt 4 It can be seen that the surface pressure increases in the order of 4d between the upper part and the lowermost part (4d) and upper part (between the uppermost part and the intermediate part) 4b.

  That is, on the outer peripheral surface of the piston skirt 4 on the thrust side, the reaction force of the thrust force F1 as described above acts, and the upper portion 4b thermally expands to press the cylinder bore wall surface 20, and further, the lower portion 4d by the tilt of the piston 1A. Presses the cylinder bore wall surface 20, so that the surface pressure becomes extremely high at the upper part 4b and the lower part 4d. For this reason, abnormal wear and seizure are likely to occur in the upper part 4b and the lower part 4d, and a large amount of oil is required. On the other hand, in the uppermost part 4a, the intermediate part 4c and the lowermost part 4e, the surface pressure is significantly lower than that of the upper part 4b and the lower part 4d.

  Therefore, on the outer circumferential surface of the thrust side piston skirt 4 in the first embodiment, as shown in FIGS. 1 and 2, a plurality of coarse grains (in other words, formed on the upper portion 4b and the lower portion 4d in the circumferential direction of the piston, respectively). The first streak groove 5a and the second streak groove 5b having a larger groove width are provided.

  As a result, the oil on the cylinder bore wall surface 20 is taken into the first and second streak grooves 5a and 5b by the vertical movement of the piston 1A as shown in FIG. 5A. And the film thickness of the oil between the lower part 4d and the cylinder bore wall surface 20 becomes thick, and it is possible to suppress abnormal wear and seizure at the part. Further, since the oil in the first and second streak grooves 5a and 5b is supplied to the entire outer peripheral surface of the piston skirt 4 by the vertical movement of the piston 1A, the abnormal wear and seizure of the entire piston skirt 4 can be suppressed. become.

  Furthermore, a collision effect (so-called piston slap) between the piston skirt 4 and the cylinder bore wall surface 20 can be reduced by a damping effect due to the thick film thickness.

  Here, generally, when time elapses after the engine is stopped, the oil between the outer peripheral surface of the piston skirt and the cylinder bore wall surface 20 is returned to the oil pan (not shown), so that abnormal wear is likely to occur during restart. . However, in the first embodiment, since the oil is retained in the first and second streak grooves 5a and 5b after the engine is stopped, the first and second streak grooves 5a, Oil is supplied to the entire outer peripheral surface of the piston skirt 4 from 5b, and abnormal wear at that time can also be suppressed.

  Thus, the first and second streak grooves 5a and 5b function as an oil reservoir that can hold the oil supplied to the piston skirt 4 regardless of whether it is operating or stopped.

  Here, the groove widths and depths of the first and second streak grooves 5a and 5b are optimal values obtained by performing experiments and simulations as appropriate according to the shape of the piston 1A itself and the applied internal combustion engine. If the micro dimple 6 described later and the third streak groove 7 of Example 2 are about 20 to 30 μm, it is preferably about 200 to 300 μm. Set to. In addition, the numerical value is an illustration to the last, and it does not necessarily limit to it.

  In the first embodiment, the cross-sectional shapes of the first and second streak grooves 5a and 5b are formed in an arc shape as shown in FIG. 2, but the cross-sectional shape is not necessarily limited to this mode. It is not a thing.

  Subsequently, in the first embodiment, the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the outer peripheral surface of the piston skirt 4 on the thrust side are subjected to microdimple processing to form a plurality of microdimples 6. Yes.

  Since the micro dimple 6 has a smaller diameter than the groove width of the first and second streak grooves 5a and 5b, the grooves of the first and second streak grooves 5a and 5b as shown in FIG. Although the amount of oil retained is small compared to the width, the coefficient of friction can be reduced. For this reason, the friction with the cylinder bore wall surface 20 can be reduced at the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the outer peripheral surface of the piston skirt 4. Further, since the oil holding amount is small, the shearing force of the oil when the piston 1A moves up and down can be reduced, and this can also reduce the friction.

  In this way, the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the piston skirt 4 are formed with oil reservoirs having a small friction coefficient, such as micro dimples 6, that can hold a small amount of oil. It is possible to reduce the friction loss when moving, and it is possible to improve the output and reduce the fuel consumption by increasing the rotation speed.

  As in the piston 1A of the first embodiment described above, the first and second oil holding amounts can be increased in the places where the surface pressure is high (the upper portion 4b and the lower portion 4d of the piston skirt 4) that require a large amount of oil. Micro dimple processing that forms streak grooves 5a and 5b and can reduce friction at locations with low surface pressure that do not require that much oil (uppermost part 4a, intermediate part 4c and lowermost part 4e of piston skirt 4) As a result, lubrication performance between the outer peripheral surface of the piston skirt 4 and the cylinder bore wall surface 20 is ensured, and abnormal wear and seizure can be suppressed, and friction loss is reduced to improve output and reduce fuel consumption. Can be achieved.

  In the first embodiment, the first and second streak grooves 5a and 5b and the microdimple 6 are formed only on the piston skirt 4 on the thrust side. It may also be formed on the piston skirt 4, whereby abnormal wear and seizure of the entire piston 1 </ b> A can be more effectively suppressed, and output can be further improved and fuel consumption can be reduced more suitably.

  Next, a second embodiment of the piston for an internal combustion engine according to the present invention will be described with reference to FIGS.

  6 indicates a piston for an internal combustion engine according to the second embodiment. This piston 1B is an oil reservoir with a small friction coefficient that can hold a small amount of oil at the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the outer peripheral surface of the piston skirt 4 on the thrust side in the piston 1A of the first embodiment. 6 and FIG. 7 is formed with a plurality of fine lines (in other words, a narrow groove width) as the third streak groove 7 in the circumferential direction of the piston. The other configuration is the same as that of the piston 1A of the first embodiment.

  Here, as shown in FIGS. 5A to 5C, the third streak groove 7 according to the second embodiment includes first and second portions formed on the upper portion 4b and the lower portion 4d of the outer peripheral surface of the piston skirt 4. The groove width is smaller than the groove grooves 5a and 5b, and the groove width is smaller than the diameter of the micro dimple 6 of the first embodiment, which is called a plateau.

  As described above, in the second embodiment, a plurality of fine details smaller than this are provided in place of the plurality of micro dimples 6 at the uppermost portion 4a, the intermediate portion 4c and the lowermost portion 4e of the piston skirt 4 having a low surface pressure. The third streak groove 7 is provided. For this reason, the friction coefficient is smaller, the oil retention amount is reduced and the shear force of the oil is reduced in such a part, so that the friction can be further reduced and the output can be improved more effectively and the fuel consumption can be reduced more effectively. Can do.

  Therefore, the piston 1B of the second embodiment has an outer periphery of the piston skirt 4 similar to the piston 1A of the first embodiment by the first and second streak grooves 5a and 5b of the upper portion 4b and the lower portion 4d of the piston skirt 4. The lubricating performance between the surface and the cylinder bore wall surface 20 can be secured to suppress abnormal wear and seizure, and the third streak groove 7 in the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the piston skirt 4 can be suppressed. Therefore, the output can be further improved and the fuel consumption can be reduced as compared with the piston 1A of the first embodiment.

  In the second embodiment, the first and second streak grooves 5a and 5b and the third streak groove 7 are formed only in the piston skirt 4 on the thrust side. It may also be formed on the piston skirt 4 on the side, whereby it is possible to more effectively suppress the abnormal wear and seizure of the entire piston 1A, and it is possible to further improve the output and reduce the fuel consumption.

  Here, in Examples 1 and 2 described above, the uppermost part 4a, the intermediate part 4c and the lowermost part 4e of the piston skirt 4 are exemplified as being provided with either the micro dimple 6 or the third streak groove 7, It is not necessarily limited to such an embodiment. For example, when the surface pressure between the uppermost part 4a, the intermediate part 4c and the lowermost part 4e is different from that of the cylinder bore wall surface 20, the microdimple 6 or the third streak groove 7 is appropriately set according to the size of the surface pressure. It may be formed. That is, the micro dimple 6 having a large amount of oil retention in both of them is formed in a portion where the surface pressure is high, and the third streak groove 7 is formed in a portion where the surface pressure is low giving priority to friction reduction. As a result, it is possible to take optimum measures to suppress abnormal wear and seizure according to the surface pressure, improve output, and reduce fuel consumption.

  Next, a third embodiment of the piston for an internal combustion engine according to the present invention will be described with reference to FIGS.

  Reference numeral 1C in FIG. 8 denotes the piston for the internal combustion engine of the third embodiment. The piston 1C is obtained by changing the machining shape of the outer peripheral surface of the piston skirt 4 on the thrust side with respect to the pistons 1A and 1B of the first and second embodiments. The configuration is the same as 1B.

  Specifically, on the outer peripheral surface of the piston skirt 4, a coarse streak groove 15 directed in the circumferential direction of the piston capable of holding a large amount of oil is formed on the lower end side, and friction is reduced on the remaining upper side. A plurality of micro dimples 6 similar to those in the first embodiment are formed.

  Accordingly, the oil on the cylinder bore wall surface 20 is taken into the streak groove 15 by the vertical movement of the piston 1C, and the film thickness of the oil between the lower end side of the piston skirt 4 and the cylinder bore wall surface 20 is increased. Abrasion and seizure can be suppressed. Further, the impact noise between the piston skirt 4 and the cylinder bore wall surface 20 can be reduced by the damping effect due to the thick film thickness.

  Further, since all the microdimple processing is performed on the upper side of the piston skirt 4, it is possible to reduce the friction loss over a wide range of the piston skirt 4, and to improve the output and fuel consumption by greatly increasing the rotation speed. Reduction can be achieved.

  Here, in the piston 1C of the third embodiment, since the micro dimple processing with a small oil holding amount is also performed on the upper portion 4b of the piston skirt 4 having a high surface pressure, the pistons 1A and 1B of the first and second embodiments are used. On the other hand, there is a concern about deterioration of the lubricating performance in the upper portion 4b.

  Therefore, in the third embodiment, as shown in FIGS. 8 and 9, a plurality of micro dimples 6 are formed on the uppermost portion 4a, upper portion 4b and intermediate portion 4c of the piston skirt 4, and coarse streak grooves are formed. 15 is formed in the lower part 4d and the lowermost part 4e of the piston skirt 4 to expand the range in which a large amount of oil can be held.

  As a result, more oil is retained on the lower end side of the piston skirt 4, so that the oil in the streak groove 15 is not removed from the piston skirt 4 when the piston 1 </ b> A moves up and down regardless of whether the engine is operating or restarted. It is supplied to the entire outer peripheral surface, and abnormal wear and seizure of the entire piston skirt 4 can be suppressed.

  Thus, according to the piston 1C of the third embodiment, the lubrication performance can be ensured by the streak groove 15 to suppress abnormal wear and seizure, and the microdimple 6 over the wide range of the piston skirt 4 can be obtained. As a result, the friction loss can be greatly reduced, and the output can be improved and the fuel consumption can be reduced more effectively than the pistons 1A and 1B of the first and second embodiments.

  Here, the streak groove 15 can be provided only in the lower part 4d of the piston skirt 4 in the same manner as the pistons 1A and 1B of the first and second embodiments. It is deeper than the first and second streak grooves 5a and 5b so that more oil can be retained. This also has the same effect as the above-described streak groove 15 whose range has been expanded. Moreover, the groove depth of the streak groove 15 whose range is enlarged may be made deeper than the first and second streak grooves 5a and 5b of the first and second embodiments, thereby retaining more oil. Since it becomes possible, the lubrication performance can be further improved by the abundant oil.

  In the third embodiment, the micro dimples 6 are formed from the uppermost part 4a to the intermediate part 4c of the piston skirt 4. The processing shape of such a part depends on the surface pressure between the cylinder bore wall surface 20 and the like. Thus, the fine third streak groove 7 of Example 2 may be formed.

  Further, the groove groove 15 and the micro dimple 6 (or the third groove groove 7) are formed only on the piston skirt 4 on the thrust side, but the same thing is formed on the piston skirt 4 on the anti-thrust side. As a result, the abnormal wear and seizure of the entire piston 1A can be suppressed more effectively, and the output can be improved and the fuel consumption can be reduced more suitably.

  Next, a fourth embodiment of the piston for an internal combustion engine according to the present invention will be described with reference to FIG.

  In the piston 1A of the first embodiment described above, the first and second streak grooves 5a and 5b capable of holding a large amount of oil are formed in the upper part 4b and the lower part 4d of the outer peripheral surface of the piston skirt 4 on the thrust side, Micro dimples 6 capable of reducing friction are formed on the uppermost part 4a, the intermediate part 4c and the lowermost part 4e. In the piston 1B of the second embodiment described above, the first and second streak grooves 5a and 5b are formed in the upper part 4b and the lower part 4d of the outer peripheral surface of the piston skirt 4 on the thrust side, and the uppermost part 4a, A third streak groove 7 capable of reducing friction is formed in the intermediate part 4c and the lowermost part 4e. Further, in the piston 1C of the third embodiment described above, the striation groove 15 capable of holding a large amount of oil is formed in the lower part 4d and the lowermost part 4e of the outer peripheral surface of the piston skirt 4 on the thrust side, and the uppermost part 4a, Micro dimples 6 are formed on the upper part 4b and the intermediate part 4c.

  Here, in each of the pistons 1A, 1B, and 1C of the first, second, and third embodiments, the processing shape of the piston skirt 4 on the thrust side is also formed on the outer peripheral surface of the piston skirt 4 on the anti-thrust side. It is possible to suppress abnormal wear and seizure of the entire 1A, 1B, and 1C, and to further improve output and reduce fuel consumption. However, on the other hand, on the anti-thrust side where the surface pressure is low, the amount of oil more than that required for lubrication is maintained, so that the shearing force of the oil when the pistons 1A, 1B, 1C move up and down increases, resulting in friction loss. May increase.

  Therefore, in the fourth embodiment, a processed shape substantially the same as that of the first embodiment is provided on the outer peripheral surface of the piston skirt 4 on the thrust side, and the outer peripheral surface of the piston skirt 4 on the opposite thrust side is substantially the same as that of the third embodiment. The machining shape is provided. FIG. 10 illustrates an internal combustion engine piston 1D according to the fourth embodiment.

  This piston 1D is formed with first and second streak grooves 5a and 5b in the first embodiment at the upper part 4b and the lower part 4d on the outer peripheral surface of the piston skirt 4 on the thrust side, and the uppermost part 4a and the intermediate part. The micro dimples 6 in the first embodiment are formed in 4c and the lowermost part 4e. Further, on the outer peripheral surface of the piston skirt 4 on the anti-thrust side, a groove groove 25 in the circumferential direction of the piston capable of holding a large amount of oil is formed in the lower part 4d and the lowermost part 4e, and the uppermost part 4a, upper part 4b and intermediate The micro dimple 6 in the third embodiment is formed in the portion 4c.

  Here, the anti-thrust side streak groove 25 is formed in the range of the lower portion 4d and the lowermost portion 4e of the piston skirt 4 as in the third embodiment. For this reason, in order to reduce the amount of oil retained in the part, the groove groove 25 has, for example, the groove width equal to that of the first and second groove grooves 5a and 5b on the thrust side. On the other hand, it is preferable to make the groove depth shallower than the first and second groove grooves 5a and 5b on the thrust side.

  According to the piston 1D of the fourth embodiment, on the thrust side having a high surface pressure, while maintaining the same lubricating performance and friction as the first embodiment, the abnormal wear and seizure are suppressed, the output is improved, and the fuel consumption is reduced. On the other hand, on the anti-thrust side where the surface pressure is low, it is possible to secure an appropriate amount of oil required for lubrication and reduce friction by reducing the shearing force by reducing the amount of oil retained. Therefore, by processing the piston skirt 4 on the thrust side and the anti-thrust side like the piston 1D of the fourth embodiment, the friction loss is more effectively reduced while suppressing abnormal wear and seizure in the entire piston 1D. be able to.

  Here, in the fourth embodiment, the micro dimples 6 are formed in the uppermost portion 4a, the intermediate portion 4c and the lowermost portion 4e on the thrust side, and the uppermost portion 4a, the upper portion 4b and the intermediate portion 4c on the anti-thrust side. The third streak groove 7 of the second embodiment may be formed in place of the micro dimple 6 in any or all of the parts.

  Next, a fifth embodiment of the piston for an internal combustion engine according to the present invention will be described with reference to FIG.

  The piston of the fifth embodiment is the same as the piston 1A, 1B, 1C, 1D of each of the first, second, third, or fourth embodiments described above, and the first and second streak grooves 5a, 5b, the streak grooves 15, 25. The side surface of the groove on the lower side of the piston is shaped so that oil is easily collected.

  Specifically, the groove side surface is formed substantially parallel to the piston top surface or tilted inward and downward of the piston to hold the oil on the groove side surface. As the shape having this type of groove side surface, for example, various shapes such as those having a sawtooth cross section are conceivable.

  FIG. 11 illustrates the piston of the fifth embodiment in which the sawtooth-shaped streak groove is formed. In the piston 1E of FIG. 11, the first and second streak grooves 5a and 5b of the piston 1A of the first embodiment described above are replaced with the sawtooth-shaped first and second streak grooves 35a and 35b shown in FIG. In this modification, each groove side surface on the lower side of the piston is formed substantially parallel to the piston top surface.

  In this manner, the groove side surface on the piston lower side in the groove groove (here, the first and second groove grooves 35a and 35b) intended to hold a large amount of oil is formed as in the fifth embodiment. Thus, oil leakage to the lower side of the piston can be suppressed, and even when the piston 1E moves up and down, the state in which the oil is accumulated can be maintained.

  For this reason, more reliable oil supply to the entire piston skirt 4 is possible, and abnormal wear and seizure can be suppressed. In particular, the oil in the first streak groove 35a located on the upper side of the piston can also be supplied to the piston ring (top ring, second ring, and oil ring (not shown)), so that lubrication at such a site is possible. Effects such as a reduction in friction loss due to improved performance can also be achieved.

  Next, a sixth embodiment of the piston for an internal combustion engine according to the present invention will be described with reference to FIG.

  In the piston 1F of the sixth embodiment, the pistons 1A, 1B, 1C, 1D, and 1E of the first to fifth embodiments are arranged on the outer peripheral surfaces of the second land 3b and the third land 3c in the piston head portion. In the piston skirt 4, the first and second streak grooves 35 a and 35 b having the same shape as the saw-tooth shape are formed in the piston circumferential groove 8.

  As a result, the piston 1F of the sixth embodiment can retain oil in the streak groove 8 even in the piston head portion, and supply oil to the top ring 9a, the second ring 9b, and the oil ring 9c when moving up and down. Is possible. Therefore, according to the piston 1F, the lubrication performance between the top ring 9a, the second ring 9b, the oil ring 9c, and the cylinder bore wall surface 20 is improved, and abnormal wear can be suppressed.

  In addition, since the oil retained in the streak groove 8 is also supplied to the piston skirt 4 through the cylinder bore wall surface 20 when moving up and down, the piston 1F can more effectively suppress abnormal wear and seizure and reduce friction. Can be planned.

  Here, the streak groove 8 of the sixth embodiment can provide the above-described effect by providing it at least on the thrust side, but it is provided on the anti-thrust side or the entire piston circumferential direction in order to obtain a more effective effect. Is preferred.

  As described above, the piston for an internal combustion engine according to the present invention is useful as a technique capable of achieving both improvement in lubrication performance and reduction in friction loss.

It is the side view which looked at Example 1 of the piston for internal-combustion engines concerning the present invention from the piston skirt side. It is sectional drawing of the piston skirt in the piston for internal combustion engines of Example 1 seen from the XX line of FIG. It is a figure explaining the thrust force applied between a piston and a cylinder bore wall surface when a piston descends. It is a figure explaining the thrust force applied between a piston and a cylinder bore wall surface when a piston raises. It is a figure explaining the hydraulic pressure distribution between a piston skirt and a cylinder bore wall surface. It is a figure which shows the relationship between the coarse groove groove | channel formed in the piston skirt, and oil. It is a figure which shows the relationship between the micro dimple formed in the piston skirt, and oil. It is a figure which shows the relationship between the fine streak groove formed in the piston skirt, and oil. It is the side view which looked at Example 2 of the piston for internal-combustion engines concerning the present invention from the piston skirt side. It is sectional drawing of the piston skirt in the piston for internal combustion engines of Example 2 seen from the YY line of FIG. It is the side view which looked at Example 3 of the piston for internal combustion engines concerning the present invention from the piston skirt side. It is sectional drawing of the piston skirt in the piston for internal combustion engines of Example 3 seen from the ZZ line of FIG. It is the side view which looked at Example 4 of the piston for internal combustion engines concerning the present invention from the piston pin hole side. It is sectional drawing of the piston skirt shown about Example 5 of the piston for internal combustion engines which concerns on this invention. It is sectional drawing of the piston head part shown about Example 6 of the piston for internal combustion engines which concerns on this invention.

Explanation of symbols

1A, 1B, 1C, 1D, 1E, 1F Piston 3a Top land 3b Second land 3c Third land 4 Piston skirt 4a Top part of piston skirt 4b Top part of piston skirt 4c Middle part of piston skirt 4e Bottom part of piston skirt 4d Piston skirt 5a, 35a 1 streak groove 5b, 35b 2 streak groove 6 micro dimple 7 3 streak groove 8 streak groove 15, 25 streak groove 20 cylinder bore wall surface

Claims (3)

A plurality of piston circumferential coarse grooves are formed in the upper and lower portions of the outer peripheral surface of the piston skirt, and the uppermost portion above the upper portion and the lowermost portion below the lower portion in the outer peripheral surface of the piston skirt. A piston for an internal combustion engine, wherein an oil reservoir smaller than the coarse streak groove is formed in an intermediate portion between the upper portion and the lower portion. A plurality of coarse piston grooves in the circumferential direction of the piston are formed in the upper and lower portions of the outer peripheral surface of the piston skirt on the thrust side, and the coarse striations are formed on the outer peripheral surface of the piston skirt on the anti-thrust side in the circumferential direction of the piston. A plurality of micro-dimples as an oil reservoir having a groove width equivalent to that of the groove and a groove depth shallower than the coarse groove groove or a plurality of micro-dimples as an oil reservoir finer than the coarse groove groove. A piston for an internal combustion engine characterized by being formed. 3. The internal combustion engine according to claim 1, wherein a groove side surface of the coarse streak groove on the lower side of the piston is made substantially parallel to the top surface of the piston or inclined toward the inside of the piston and toward the lower side of the piston. Piston.

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