JP2005344824A - Piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston capable of stably maintaining the seal function of a piston ring over a long period, by restraining an increase in flapping of the piston ring in a ring groove when reciprocating a piston. <P>SOLUTION: Projection parts 12 and 13 are formed on the respective outer peripheral edges of an upper surface 3a and an under surface 3b of a top ring groove 3 so as to project to the top ring 7 side being the moving direction of a piston body 2, and projection parts 14 and 15 are similarly projectingly formed in an inner peripheral side part of the upper surface 3a and the under surface 3b of the top ring groove 3. When a top ring 7 causes flapping in the top ring groove 3 in response to reciprocating motion of the piston body 2, the flapping of the top ring 7 is restrained by being supported at two points by the projection parts 12 and 13 and the projection parts 14 and 15. Thus, the outer peripheral edge corner of the top ring groove 3 can be restrained from becoming an abraded shape over a long period. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piston of an engine, and more particularly to a piston in which a piston ring is mounted in a ring groove formed on an outer peripheral surface of a piston main body.

Conventionally, for example, a piston as described in Patent Document 1 is known as an engine piston. As shown in FIG. 9, this piston has a ring groove 52 formed on the outer peripheral surface 51 a of a cylindrical piston main body 51, and a predetermined clearance C is provided in the ring groove 52 to fit the piston ring 53. Has been. During engine operation, when the piston main body 51 reciprocates in a cylinder liner (not shown), the outer peripheral edge of the piston ring 53 slides on the inner peripheral surface of the cylinder liner, so that the sliding portion is moved. Sealing is performed to maintain the airtightness of the combustion chamber (not shown).
Japanese Utility Model Publication No. 5-946 (Claim 1, FIG. 1)

  Here, a frictional resistance in the direction opposite to the moving direction is always applied to the piston ring 53 that reciprocates together with the piston main body 51 in the cylinder liner during engine operation when sliding with the inner peripheral surface of the cylinder liner. . Therefore, as shown by a broken line and an alternate long and short dash line in FIG. 9, the piston ring 53 may flutter in the ring groove 52 when the piston body 51 reciprocates. The outer peripheral edge of the ring groove 52 is pressed against the outer peripheral edge of the ring groove 52 and wears (including the plastic deformation associated therewith). When such wear progresses, as shown by a two-dot chain line in FIG. 9, the outer peripheral corner of the ring groove 52 becomes worn, and the piston main body 51 moves in the ring groove 52 during reciprocal movement. As a result of the increasing angle range T allowing the piston ring 53 to flutter, the sealing performance of the piston ring 53 may be degraded.

  The present invention has been made in view of such a situation, and its purpose is to suppress the piston ring sealing function in the ring groove during piston reciprocating movement, thereby suppressing the piston ring sealing function. An object of the present invention is to provide a piston that can be stably maintained over a long period of time.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, in the piston in which a ring groove for mounting a piston ring is provided on the outer peripheral surface of the piston body, at least one outer peripheral edge of the upper surface and the lower surface of the ring groove is provided on the piston. A protrusion protruding to the ring side is formed.

  According to the above configuration, even if the piston ring flutters in the ring groove during the reciprocating movement of the piston body and is pressed against the outer peripheral edge of the ring groove, at least one outer peripheral edge of the upper and lower surfaces of the ring groove Since the protrusion is formed on the, it is possible to prevent the corner of the outer peripheral edge where the protrusion is formed from being worn out at an early stage. Therefore, it is possible to suppress the piston ring fluttering in the ring groove during the reciprocating movement of the piston, and to maintain the sealing function of the piston ring stably for a long period of time.

  In the intake stroke and compression stroke, the piston ring is pressed against the upper and lower surfaces of the ring groove due to the inertial force associated with the reciprocating movement of the piston. It will be strongly pressed against the lower surface, and it is considered that the wear of the corner portion of the outer peripheral edge in the ring groove is promoted accordingly. Therefore, paying attention to this point, in the configuration according to claim 1, the protrusion is formed on the outer peripheral edge of at least one of the upper surface and the lower surface of the ring groove, and such a protrusion is at least the lower surface of the ring groove. It is desirable to form on the outer periphery of the. Further, from the same viewpoint, when the protrusions are formed on both the outer peripheral edges of the upper surface and the lower surface of the ring groove, the protrusions formed on the outer peripheral edge of the lower surface are the outer peripheral edges of the upper surface. It is desirable to make the protrusion height (protrusion amount) larger than the protrusion formed on the surface.

  According to a second aspect of the present invention, in the piston according to the first aspect, the protrusion is formed in an annular shape over the entire circumference of the ring groove. According to such a configuration, when the piston body moves, the annular projecting portion that is continuous over the entire circumference of the ring groove abuts and supports the upper surface or the lower surface of the piston ring on the outer circumferential side over the entire circumference of the piston ring. By doing so, a good sealing state can be formed.

  According to a third aspect of the present invention, in the piston according to the first or second aspect, the protrusion is formed on each outer peripheral edge of the upper surface and the lower surface of the ring groove, while the upper surface of the ring groove and Each of the inner peripheral portions of the lower surface is formed with a protruding portion that protrudes toward the piston ring mounted in the ring groove.

  According to the above configuration, when the piston ring flutters in the ring groove during the reciprocating movement of the piston body, the piston ring has its inner circumferential surface pressed against the raised portion of the inner circumferential portion of the ring groove. The outer peripheral side comes into pressure contact with the protrusion on the outer peripheral edge of the ring groove. That is, the piston ring that has fluttered is supported at two points in the ring groove by the raised portion and the protruding portion. Therefore, unlike the case where the piston ring is supported by a single point with respect to the protrusion that is easily worn by the pressure contact of the piston ring, the pressure contact force received from the piston ring that has fluttered is also shared by the raised portion. Therefore, the degree of wear can be reduced accordingly. As a result, it can suppress that the angle of the outer periphery edge of a ring groove becomes a large-wearing shape, and can suppress that the angle range which accepts flapping of a piston ring becomes large.

  According to a fourth aspect of the present invention, in the piston according to the third aspect, the protrusions are formed on the outer peripheral edges of the upper surface and the lower surface of the ring groove, while the inner surfaces of the upper surface and the lower surface of the ring groove are formed. A protruding portion that protrudes toward the piston ring mounted in the ring groove is formed in the peripheral portion.

  According to said structure, when a protrusion is similarly formed in cyclic | annular form with a protruding part, the cyclic | annular recessed part over the perimeter will be formed between a protruding part and a protruding part. For this reason, the annular recess functions as an oil reservoir, so that lubricating oil can be supplied from the recess in the circumferential direction in the ring groove, and the piston ring is fixed and adhered to the ring groove as much as possible. It becomes possible to suppress.

  According to a fifth aspect of the present invention, in the piston according to the third or fourth aspect, the protruding height of the protruding portion is set to be higher than the protruding height of the protruding portion. And According to such a configuration, by reducing the clearance between the outer peripheral edge of the ring groove and the piston ring, the angle range for allowing the piston ring to flutter is reduced, and thus it is more desirable to suppress the fluttering on the outer peripheral edge side of the piston ring. It can be in the form.

Hereinafter, an embodiment in which the present invention is embodied in an engine piston will be described with reference to FIGS.
As shown in FIG. 1, the piston 1 of the present embodiment includes a cylindrical piston main body 2 whose top is closed, and a plurality of (three in the present embodiment) are provided on the outer peripheral surface 2 a of the piston main body 2. Ring grooves 3, 4, 5 are formed at positions above the piston pin hole 6. In FIG. 1, a top ring 7 is formed in the uppermost top ring groove 3, a second ring 8 is disposed in the second ring groove 4 from the top, and an oil ring 9 is disposed in the lowermost oil ring groove 5. Each is mounted in a fitting manner as a piston ring. When the piston body 2 reciprocates, the outer peripheral edge of each of the rings 7, 8, 9 comes into sliding contact with the inner peripheral surface 11 (see FIG. 5) of the cylinder liner 10 (see FIG. 5), so that the cylinder liner 10. A seal state is formed between the inner peripheral surface 11 and the inner peripheral surface 11.

  FIG. 2 is an enlarged view of a portion B (that is, a portion of the top ring groove 3) circled and indicated by a broken line in FIG. As shown in the figure, a pair of upper and lower protrusions 12 and 13 protrude toward the top ring 7 side, which is also the moving direction of the piston body 2, at the outer peripheral edges of the upper surface 3 a and the lower surface 3 b of the top ring groove 3. Is formed. These protrusions 12 and 13 are obliquely cut off from the upper surface 3a and the lower surface 3b of the top ring groove 3 so that the tips 12a and 13a facing each other are located on the outer peripheral surface 2a of the piston body 2. It is formed to have a triangular cross section. As shown in FIG. 3, the protrusions 12 and 13 are formed so as to form a continuous ring over the entire circumference in the circumferential direction at the outer peripheral edge of the top ring groove 3.

  On the other hand, a pair of upper and lower raised portions 14 and 15 are formed on the inner peripheral side portions of the upper surface 3a and the lower surface 3b of the top ring groove 3 so as to protrude toward the top ring 7 which is also the moving direction of the piston body 2. Yes. These raised portions 14 and 15 are formed so that the opposed surfaces 14a and 15a facing each other are parallel to each other in a direction perpendicular to the moving direction of the piston body 2 (that is, in the horizontal direction) and the top surface 3a of the top ring groove 3 It is formed so as to be continuous in a stepped shape from the lower surface 3 b to the bottom 16 of the top ring groove 3. As shown in FIG. 3, each of the raised portions 14 and 15 is formed on the inner peripheral side of the top ring groove 3 so as to form a continuous ring over the entire circumference in the circumferential direction. Accordingly, in the top ring groove 3, recesses 17 and 18 that function as oil sumps are formed in an annular shape between the protrusions 12 and 13 and the raised portions 14 and 15. The protruding heights of the protrusions 12 and 13 are configured to be higher than the protruding heights of the protruding parts 14 and 15.

  Further, as shown in FIG. 2, when the top ring 7 is fitted and mounted in the top ring groove 3, the tips 12 a and 13 a of the protrusions 12 and 13 formed on the outer peripheral edge of the top ring groove 3 and the top A clearance C <b> 1 that allows the top ring 7 to move along the axis M of the piston body 2 is formed between the ring 7 and the ring 7. Further, a clearance C <b> 2 that allows the top ring 7 to rotate about the axis M of the piston body 2 is formed between the bottom 16 of the top ring groove 3 and the inner peripheral portion 7 a of the top ring 7. It has become so. Accordingly, when the piston main body 2 reciprocates during the operation of the engine, the top ring 7 slightly moves in the top ring groove 3 as shown by a broken line and a chain line in FIG. 4 due to the clearances C1 and C2. It is possible to flutter in the vertical direction with the rotational movement. The piston main body 2 is made by grinding or cutting the upper surface 3a and the lower surface 3b of the top ring groove 3 with a file or the like after the outer shape including the top ring groove 3 is formed by casting an aluminum alloy. Thus, the protrusions 12 and 13, the raised portions 14 and 15, and the recesses 17 and 18 are formed.

Therefore, next, the operation of the piston 1 configured as described above will be described, particularly focusing on the movement of the top ring 7 in the top ring groove 3 during engine operation.
First, in the intake stroke during engine operation, as shown in FIG. 5A, the piston body 2 moves downward in the direction of the arrow a. Therefore, the top ring 7 is in pressure contact with the tip 12a of the protrusion 12 protruding from the upper surface 3a of the top ring groove 3 from below with an inertial force, and its outer peripheral edge is slidably contacted with the inner peripheral surface 11 of the cylinder liner 10. However, it moves downward together with the piston body 2.

  In the next compression stroke, as shown in FIG. 5B, the piston body 2 moves upward in the direction of arrow B. Therefore, the top ring 7 is in pressure contact with the tip 13a of the protrusion 13 protruding from the lower surface 3b of the top ring groove 3 from above with an inertial force, and its outer peripheral edge is slidably contacted with the inner peripheral surface 11 of the cylinder liner 10. However, it moves upward together with the piston body 2.

  Next, in the explosion stroke, as shown in FIG. 5 (c), the piston body 2 is pushed downward by the gas pressure (combustion pressure) P generated by the explosion of the air-fuel mixture in the combustion chamber (not shown). Move down in the direction of. At this time, the gas pressure P presses the top ring 7 downward through a gap between the outer peripheral surface 2 a of the piston body 2 and the inner peripheral surface 11 of the cylinder liner 10. Therefore, the top ring 7 receives the pressing force of the gas pressure P, and the outer peripheral edge of the top liner 7 is in contact with the tip 13a of the protrusion 13 protruding from the lower surface 3b of the top ring groove 3 from above. The piston body 2 moves downward while being brought into sliding contact with the inner peripheral surface 11.

  In the next exhaust stroke, as shown in FIG. 5D, the piston body 2 moves upward in the direction of arrow D. Therefore, the top ring 7 is in pressure contact with the tip 13a of the protrusion 13 protruding from the lower surface 3b of the top ring groove 3 from above with an inertial force, and its outer peripheral edge is slidably contacted with the inner peripheral surface 11 of the cylinder liner 10. However, it moves upward together with the piston body 2.

  Here, the top ring 7 that reciprocates together with the piston main body 2 while sliding the outer peripheral edge portion in sliding contact with the inner peripheral surface 11 of the cylinder liner 10 in each stroke, the protrusion 12 has an annular upper surface or lower surface on the outer peripheral side. Or it is supported in the press-contact state over the perimeter by the protrusion 13. In particular, in the explosion stroke shown in FIG. 5C, the gas body P moves downward together with the piston body 2 in a state of being strongly pressed against the tip 13a of the protrusion 13 by the gas pressure P. Therefore, the combustion chamber formed on the upper side of the piston main body 2 in FIGS. 5A to 5D is press-contacted over the entire circumference by the protrusions 12 and 13 in which the upper surface or the lower surface of the top ring 7 forms an annular shape. By being supported, a good sealing state can be obtained in order to regulate gas leakage from the combustion chamber.

  In each stroke, the top ring 7 that reciprocates together with the piston body 2 is always subjected to frictional resistance in the direction opposite to the moving direction when sliding with the inner peripheral surface 11 of the cylinder liner 10. Therefore, when the piston body 2 reciprocates, the top ring 7 may be tilted within the top ring groove 3 and flutter as shown by the broken line and the alternate long and short dash line in FIG. When the top ring 7 is inclined and fluttered as described above, the upper and lower surfaces of the top ring 7 on the outer peripheral side protrude from the upper surface 3a and the lower surface 3b of the top ring groove 3, respectively. Will be pressed against each other. Normally, when the outer peripheral edge of the top ring groove 3 is only formed at a right angle, the outer peripheral edge gradually wears due to the pressure contact of the top ring 7, and finally, as shown by a two-dot chain line in FIG. As a result, the angle range T1 (see FIG. 4) allowing the top ring 7 to flutter is widened, resulting in a further increase in fluttering.

  In this respect, in the present embodiment, since the protrusions 12 and 13 having a protrusion height that allows for wear are provided in advance on the outer peripheral edge of the top ring groove 3 to which the top ring 7 is struck, first, the protrusion 12 is provided. , 13 are worn at the tips 12a, 13a. The protruding heights of the protrusions 12 and 13 are higher than the protruding heights of the protruding portions 14 and 15 on the inner peripheral side. Therefore, as shown in FIG. 6, even if the tips 12 a and 13 a of the protrusions 12 and 13 are worn, the protrusion height of the protrusions 12 and 13 is substantially the same as the height of the protrusions 14 and 15 due to the wear. Until this time, the angle range T1 (see FIG. 4) that allows the top ring 7 to flutter does not increase significantly. Therefore, since the angle range T1 that allows the flapping of the top ring 7 does not increase at an early stage, the top ring 7 can be prevented from greatly fluttering in the top ring groove 3.

  Further, in the present embodiment, as shown by a broken line and a one-dot chain line in FIG. 4, when the top ring 7 tilts in the top ring groove 3, the top ring 7 Two points are supported by both the protrusions 12 and 13 and the raised portions 14 and 15. For this reason, if the protrusions 12 and 13 are supported at one point when tilted with flapping, only the protrusions 12 and 13 receive the pressure contact force from the top ring 7, and the pressure contact force is raised. 14 and 15 are also distributed. Therefore, by reducing the impact received by the protrusions 12 and 13 (and the raised portions 14 and 15) by the pressure contact of the top ring 7 that has fluttered, the degree of wear can be reduced.

  Further, in the present embodiment, the protrusions 12 and 13 and the raised portions 14 and 15 are provided annularly over the entire circumference of the top ring groove 3, and therefore function as an oil sump in the top ring groove 3. The recesses 17 and 18 are formed so as to form an annular shape. Therefore, lubricating oil for lubricating the space between the top ring 7 and the top ring groove 3 is supplied in the circumferential direction in the top ring groove 3 through the recesses 17 and 18, and the top ring 7 is inside the top ring groove 3. It is possible to suppress sticking and sticking as much as possible.

  Incidentally, the clearance C1 is preferably as small as possible from the viewpoint of reducing the angle range in which the top ring 7 is allowed to flutter within the top ring groove 3. However, if the clearance C1 is made smaller than necessary, poor lubrication between the top ring 7 and the top ring groove 3 may be caused, and the top ring 7 may adhere to and adhere to the top ring groove 3. In addition, it is difficult to set the clearance C1 small.

  In this regard, in this embodiment, as described above, as a secondary effect of providing the protrusions 12 and 13 and the raised portions 14 and 15 in an annular shape, the top ring is formed by the recesses 17 and 18 that function as oil sumps. 7 and the top ring groove 3 can be in a good lubrication state, so that the clearance C1 can be set small. The fact that the clearance C1 can be set small means that the angle range T1 in which the top ring 7 is allowed to flutter can be made small, so that the degree of wear due to the flapping of the top ring 7 can be suppressed accordingly.

  Therefore, as shown in FIG. 9, when the protrusions 12 and 13 and the raised portions 14 and 15 are not formed, the corners of the outer peripheral edge of the ring groove 52 are worn early, and the piston ring 53 flutters. Whereas the allowable angle range T is increased, in the present embodiment, the angle range T1 (<T) that allows the top ring 7 to flutter can be maintained small over a long period of time. In other words, in the present embodiment, by setting the clearance C1 to be small, the flutter of the top ring 7 can be reduced, and when the clearance C1 is reduced, the problem of insufficient lubrication and sticking is considered as an oil sump. It can be said that the problem is solved by forming the functioning concave portions 17 and 18 in an annular shape.

According to the piston 1 of the said embodiment, the following effects can be acquired.
(1) Projections 12 and 13 are formed on the outer peripheral edges of the upper surface 3 a and the lower surface 3 b of the top ring groove 3 so as to project toward the top ring 7 side, which is also the reciprocating direction of the piston body 2. For this reason, when the top ring 7 flutters with the movement of the piston body 2, the tips 12 a, 13 a of the protrusions 12, 13 are pressed by the top ring 7. Therefore, the protrusions 12 and 13 projected in advance in consideration of the amount of wear can suppress the wear of the corners of the outer peripheral edge of the top ring groove 3 although the tips 12a and 13a are worn. As a result, the fluctuation of the top ring 7 in the top ring groove 3 during the reciprocating movement of the piston 1 can be suppressed, and the sealing function of the piston ring 7 can be maintained for a long time.

  (2) On the inner peripheral side portion of the top ring groove 3, raised portions 14 and 15 are formed that protrude toward the top ring 7 side, which is also the moving direction of the piston body 2. For this reason, when the top ring 7 tilts and flutters in the top ring groove 3, the top ring 7 is supported at two points of the raised portions 14 and 15 and the protrusions 12 and 13. Fluttering can be restrained. Accordingly, the degree of wear of the protrusions 12 and 13 due to the pressure contact force from the top ring 7 is reduced, and the angle range T1 that allows the top ring 7 to flutter within the top ring groove 3 can be minimized. .

  (3) The protruding heights of the protrusions 12 and 13 are higher than the protruding heights of the protruding parts 14 and 15. That is, the clearance C1 on the outer peripheral side between the top ring groove 3 and the top ring 7 is reduced, and the angle range T1 that allows the top ring 7 to flutter is reduced, so that the fluttering on the outer peripheral side of the top ring 7 is suppressed. It can be in a desirable form.

  (4) The protrusions 12 and 13 and the raised portions 14 and 15 are both annular, and the recesses 17 and 18 that function as oil sumps are formed between them. Therefore, lubrication between the top ring 7 and the top ring groove 3 can be satisfactorily maintained by supplying the lubricating oil in the circumferential direction in the top ring groove 3 by the annular recesses 17 and 18.

  (5) Since the annular recesses 17 and 18 are formed as oil sumps, the top ring 7 and the top ring groove can be in a good lubricating state between the top ring 7 and the top ring groove 3. 3 can be set small. Therefore, the angle range T1 that allows the top ring 7 to flutter is narrowed, and a configuration suitable for suppressing the degree of wear of the outer periphery of the top ring groove 3 due to the flutter of the top ring 7 can be obtained. .

  (6) Further, the protrusions 12 and 13 are formed so as to form an annular shape, and the upper surface or the lower surface on the outer peripheral side of the top ring 7 can be contacted and supported over the entire circumference when the piston body 2 reciprocates. Therefore, a good sealing state can be obtained in order to regulate gas leakage from the combustion chamber.

The above embodiment may be changed to another embodiment (another example) as follows.
As shown in FIG. 7 (a), the protrusion may be a protrusion 31 having a substantially trapezoidal cross-sectional shape. Similarly, as shown in FIG. It is good also as the protrusion 32 of the shape cut off so that circular arc shape might be drawn from the upper surface 3a and the lower surface 3b. Even when the protrusion has such a shape, it is possible to achieve an effect as a protrusion that does not wear the corners of the outer peripheral edge of the top ring groove 3 as in the above embodiment.

  As shown in FIG. 8A, the protrusion is formed as a protrusion 33 protruding from the upper surface 3a and the lower surface 3b of the top ring groove 3 at a position slightly inward from the outer peripheral surface 2a of the piston body 2. May be. That is, even when the tip 33a of the protrusion 33 is not located on the outer peripheral surface 2a of the piston body 2 and is located slightly inward from the outer peripheral surface 2a, It is synonymous with being at the periphery, and an effect as a protrusion that does not wear the outer periphery of the top ring groove 3 can be achieved.

  As shown in FIG. 8 (b), the raised portion is not formed in a step shape that is continuous with the bottom portion 16 of the top ring groove 3, but is formed as a protruding raised portion 34 that is not continuous with the bottom portion 16 of the top ring groove 3. May be.

  The protrusion height of the protrusions 12 and 13 may be substantially the same as the protrusion height of the protrusions 14 and 15, as in another example shown in FIG. It need not be higher than the raised height.

  The protrusions 12 and 13 and the raised portions 14 and 15 have been described as being provided in the top ring groove 3, but are not limited to the top ring groove 3, and the second ring groove 4 and the oil ring groove 5 are also included. It is good also as a structure which forms the protrusions 12 and 13 and the protruding parts 14 and 15 similar.

  The protrusions 12 and 13 and the ridges 14 and 15 are both formed in an annular shape, but a plurality of independent protrusions and ridges are not provided in an annular shape and are provided at a plurality of locations along the circumferential direction of the top ring groove 3. May be formed at a predetermined pitch interval.

  In the above-described embodiment, the protrusions 12 and 13 may be formed on the outer peripheral edge of the top ring groove 3 without forming the raised portions 14 and 15. In this case, the top ring in the top ring groove 3 may be used. 7 can be effectively maintained. That is, if the top ring 7 comes into surface contact with the upper surface 3 a or the lower surface 3 b of the top ring groove 3 during the reciprocating movement of the piston body 2, the lubricating oil is pushed out from the top ring groove 3. If the protrusions 12 and 13 are formed, such a situation is avoided. Therefore, with respect to the protrusions 12 and 13, in addition to the case where the protrusions 12 and 13 form an annular shape, the protrusions 12 and 13 are also provided in the top ring groove 3 with respect to the inside of the top ring groove 3. It can be said that it functions as a sump. Further, the protrusion 12 may be formed only on the outer peripheral edge of the upper surface 3 a of the top ring groove 3, or the protrusion 13 may be formed only on the outer peripheral edge of the lower surface 3 b of the top ring groove 3. .

The longitudinal cross-sectional view which shows the piston of this embodiment. The partial enlarged view of the piston which shows a top ring groove periphery. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. The fragmentary sectional view of the piston explaining the flapping aspect of a top ring. It is a figure which shows the movement aspect of the top ring in an engine driving | operation, (a) is an intake stroke, (b) is a compression stroke, (c) is an explosion stroke, (d) is a piston which shows each movement aspect in an exhaust stroke. FIG. The fragmentary sectional view of the piston which shows the top ring groove after wear. (A), (b) is the fragmentary sectional view of the piston which shows the shape of the top ring groove of another embodiment. (A), (b) is the fragmentary sectional view of the piston which shows the shape of the top ring groove of other another embodiment. The fragmentary sectional view of the piston of a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piston, 2 ... Piston main body, 2a ... Outer peripheral surface, 3 ... Top ring groove (ring groove), 3a ... Upper surface, 3b ... Lower surface, 7 ... Top ring (piston ring), 12, 13 ... Projection, 14, 15 ... Bump.

Claims (5)

In the piston provided with a ring groove on the outer peripheral surface of the piston body for mounting the piston ring,
A piston characterized in that a protrusion projecting toward a piston ring mounted in the ring groove is formed on at least one outer peripheral edge of the upper surface and the lower surface of the ring groove. The piston according to claim 1, wherein the protrusion is formed in an annular shape over the entire circumference of the ring groove. The protrusions are formed on the outer peripheral edges of the upper surface and the lower surface of the ring groove, while the inner peripheral portions of the upper surface and the lower surface of the ring groove are directed toward the piston ring mounted in the ring groove. The piston according to claim 1, wherein a raised portion is formed. The piston according to claim 3, wherein the raised portion is formed in an annular shape over the entire circumference of the ring groove. The piston according to claim 3 or 4, wherein a protruding height of the protruding portion is set to be higher than a protruding height of the protruding portion.

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