JP2008223663A - Engine piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently suppress both a problem in which a piston skirt part is scuffed in a high-surface pressure area and a problem in which sliding resistance is continued for a long period of time in a low-surface pressure area, in an engine piston having a plurality of streak grooves which is circumferentially formed in the outer surface of the skirt part being in sliding contact with the cylinder inner wall surface of an engine. <P>SOLUTION: On the outer surface of the skirt part 4 of the piston 1, the streak grooves 7 are formed deeper in the high-surface pressure area a where surface pressure between the outer surface and the cylinder inner wall surface is relatively high, than in the low-surface pressure area b where surface pressure therebetween is relatively is low, and the ratio of the width of a top part between the adjacent streak grooves 7, 7 with respect to the sum of the width of the top part between the adjacent streak grooves 7, 7 and the width of the streak groove 7 (pitch of the streak groove 7) is made small. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piston of an engine, and belongs to the technical field of lubrication of a piston skirt portion that is in sliding contact with the cylinder inner wall surface of the engine.

  In general, a piston is reciprocally disposed in a cylinder of an engine cylinder block, and a skirt portion is formed on the piston so as to be in sliding contact with the inner wall surface of the cylinder. In this specification, the cylinder inner wall surface is slid on the crankshaft side with respect to the groove lower surface where the oil ring, which is the piston ring closest to the crankshaft side, is mounted, or on the crankshaft side with respect to the oil ring. The part that contacts is called the skirt. A space between the outer surface of the skirt portion and the inner wall surface of the cylinder is kept in a lubrication state by oil, so that the piston can reciprocate smoothly in the cylinder.

  Conventionally, it is known that a plurality of streak grooves are formed in a piston skirt (see, for example, Patent Documents 1 and 2). Here, the streak groove is a U-shaped or V-shaped cross-sectional groove formed so as to extend in the circumferential direction on the outer surface of the skirt portion, and the depth of the streak groove is several μm to several tens μm. The interval between adjacent streak grooves (that is, the pitch of the streak grooves) is several tens μm to several hundreds μm.

  Thus, by forming a streak groove on the outer surface of the piston skirt portion that is in sliding contact with the inner wall surface of the cylinder, oil accumulates in the streak groove, and this oil causes a gap between the outer surface of the skirt portion and the inner wall surface of the cylinder. As a result, even if the piston reciprocates at high speed, the oil does not run out and scuffing (burn-in) between the outer surface of the skirt and the inner wall surface of the cylinder is prevented. Is done.

  In Patent Document 1, for example, a sliding smooth surface of a sliding member such as a piston of an automobile engine is provided with fine recesses (striking grooves) whose depth regularly changes, and a plateau is provided between the recesses. It is disclosed to form a convex (trapezoidal) convex portion. On the other hand, in Patent Document 2, a plurality of streak grooves are formed in the upper and lower portions of the outer surface of the piston skirt, and the uppermost part above the upper streak groove and the bottom part below the lower streak groove. It is disclosed that a plurality of microdimples are respectively formed in the lower portion and an intermediate portion between the upper and lower streak grooves.

JP 2002-235852 (paragraph 0010, FIG. 1) JP 2006-16982 (paragraphs 0030 and 0037, FIG. 1)

  By the way, the surface pressure between the outer surface of the piston skirt and the inner wall surface of the cylinder varies depending on the design factors such as the shape of the piston, the clearance between the two, and the engine operating conditions. In order to avoid a significant increase in surface pressure, structural measures such as forming the piston skirt portion into a barrel shape in which the intermediate portion in the piston axial direction bulges outward are applied to the piston. However, it is difficult to completely equalize the surface pressure distribution of the piston skirt, and the surface pressure between the outer surface of the piston skirt and the inner wall of the cylinder is relatively higher than the high surface pressure region. A low low surface pressure region is formed. As a result, in the high surface pressure region, the tops between the streak grooves formed on the outer surface of the piston skirt portion (more specifically, between adjacent streak grooves) are likely to wear, and the streak grooves tend to become shallow. The oil reservoir function of the streak groove is reduced early, and scuffing is likely to occur. In order to cope with this, when the depth of the streak groove is increased, in the low surface pressure region, since the wear of the top part between the streak grooves is small, the state of the depth of the streak groove is large (in other words, , A state in which the width of the top portion between the streak grooves is small) continues for a long period of time, and as a result, a problem arises that a state in which the friction coefficient of the skirt portion and thus the sliding resistance of the piston is large continues for a long period of time.

  The present invention addresses the above-described problems in the piston of an engine in which a plurality of streak grooves are formed in the circumferential direction on the outer surface of the skirt portion that is in sliding contact with the cylinder inner wall surface of the engine. It is an object to satisfactorily suppress both the problem of scuffing in the surface pressure region and the problem of long-lasting sliding resistance in the low surface pressure region.

  In order to solve the above-described problem, the invention according to claim 1 is an engine piston in which a plurality of streak grooves are formed in a circumferential direction on an outer surface of a skirt portion that is in sliding contact with an inner wall surface of a cylinder of the engine. On the outer surface of the skirt portion, the depth of the streak groove is larger in the first region where the surface pressure relative to the inner wall surface of the cylinder is relatively higher than in the second region where the surface pressure is relatively low, and The ratio of the width of the top part between adjacent streak grooves to the sum of the width of the top part between adjacent streak grooves and the width of the streak groove is reduced.

  Next, an invention according to claim 2 is an engine piston in which a plurality of streak grooves are formed in a circumferential direction on an outer surface of a skirt portion that is in sliding contact with a cylinder inner wall surface of the engine, and the skirt portion includes: A piston head that is formed in a barrel shape in which an intermediate portion in the piston axial direction bulges outward, and includes a bulging top portion that has the largest amount of bulging outward of the skirt portion on the outer surface of the skirt portion. The first region belonging to the portion on the side is larger in depth of the streak groove than the second region belonging to the portion on the anti-piston head side than the portion on the piston head side, and the adjacent streak The ratio of the width of the top part between the adjacent streak grooves to the sum of the width of the top part between the grooves and the width of the streak groove is reduced.

  Next, the invention according to claim 3 is the piston of the engine according to claim 1 or 2, wherein a top portion between the streak grooves has a plateau shape, and a fine recess is formed at the top portion of the plateau shape. It is characterized by being.

  Next, the invention according to claim 4 is the piston of the engine according to any one of claims 1 to 3, wherein the first region is deeper than the second region. The depth of the streak groove in the first region is 5 μm or more and 50 μm or less, and the depth of the streak groove in the second region is 2 μm or more and 10 μm or less. It is characterized by being.

  Next, the invention according to claim 5 is the piston of the engine according to any one of claims 1 to 4, wherein the sum in the first region and the second region is 50 μm or more and 500 μm. The ratio in the first region is 20% or less, and the ratio in the second region is greater than 20% and 80% or less.

  According to the first aspect of the present invention, in the engine piston in which a plurality of streak grooves are formed in the circumferential direction on the outer surface of the skirt portion that is in sliding contact with the cylinder inner wall surface of the engine, In the first region of the piston skirt portion having a relatively high surface pressure, that is, in the high surface pressure region, since the depth of the streak groove is relatively large, the capacity of the streak groove is relatively large, As a result, even if the top wear between the streak grooves progresses quickly in the high surface pressure region, the reduction of the oil reservoir function of the streak grooves is suppressed, and the problem of scuffing is reduced. On the other hand, in the second region of the piston skirt where the surface pressure between the cylinder inner wall surface is relatively low, that is, in the low surface pressure region, the depth of the streak groove is relatively small. Even if there is little wear at the top between the streak grooves in the region, the state where the depth of the streak groove is large or the state where the top width between the streak grooves is small does not continue for a long time, and the friction of the skirt part As a result, the problem that the state in which the sliding resistance of the piston is high lasts for a long time is reduced.

  In the present invention, the first region and the second region are not defined by the sliding direction of the piston. For example, the surface pressure on the thrust side of the piston skirt is higher than that on the anti-thrust side. As will be described later with reference to FIG. 5, the head is swung so that the piston head tilts toward the thrust side during the downward expansion stroke, and the head is swung so that the piston head tilts toward the anti-thrust side during the ascending exhaust process. This is because an explosive force acts on the thrust side during the swinging motion of the piston. Therefore, in the present invention, the first region may be a thrust side skirt portion, and the second region may be an anti-thrust side skirt portion.

  In addition, according to the first aspect of the present invention, in the high surface pressure region, adjacent to the sum of the width of the top and the width of the streak groove between adjacent streak grooves (that is, the pitch of the streak grooves). Since the ratio of the width of the tops between the streak grooves (hereinafter sometimes simply referred to as “top width ratio”) is relatively small, in other words, the ratio of the width of the streak grooves to the pitch of the streak grooves (Hereinafter, simply referred to as “groove width ratio”) is relatively large, and this also increases the capacity of the streak groove, and as a result, the streak groove even in the high surface pressure region. Even if the wear of the top portion in the meantime progresses quickly, the decrease in the oil reservoir function of the streak groove is suppressed, and the problem of scuffing is reduced. On the other hand, in the low surface pressure region, since the top width ratio is relatively large, the width of the top portion between the streak grooves can be reduced even if there is little wear on the top portion between the streak grooves in the low surface pressure region. A large state is obtained from the beginning, and a state in which the friction coefficient of the skirt portion and thus the sliding resistance of the piston is small is obtained from the beginning.

  Thus, according to the first aspect of the present invention, the striation groove depth and the top width ratio are simultaneously varied between the high surface pressure region and the low surface pressure region of the piston skirt portion. Since the groove is created separately, the effect of varying the depth of the streak groove and the effect of varying the top width ratio combine to cause the problem of scuffing in the high surface pressure region of the piston skirt, The problem of long-lasting sliding resistance in the low surface pressure region is better suppressed together. In other words, in the high surface pressure region, the effect of suppressing the decrease in the oil reservoir function of the streak groove and thus the effect of reducing the scuff generation can be obtained satisfactorily, and in the low surface pressure region, the effect of reducing the friction coefficient of the skirt portion and hence the sliding resistance of the piston Is obtained satisfactorily.

  Next, according to the invention described in claim 2, as in the invention described in claim 1, a plurality of streak grooves are formed in the circumferential direction on the outer surface of the skirt portion that is in sliding contact with the cylinder inner wall surface of the engine. In the piston of an engine, when the skirt portion is formed in a barrel shape in which an intermediate portion in the piston axial direction bulges outward, the piston includes a bulging top portion having the largest bulging amount outward of the skirt portion. In the first region belonging to the head side portion (that is, the high surface pressure portion), that is, the high surface pressure region, since the depth of the streak groove is relatively large, the capacity of the streak groove is relatively large. As a result, even if the top wear between the streak grooves progresses quickly in the high surface pressure region, the decrease in the oil reservoir function of the streak grooves is suppressed, and the problem of scuffing is reduced. On the other hand, in the second region belonging to the portion on the side opposite to the piston head than the portion on the piston head side (that is, the low surface pressure portion), that is, the bottom surface pressure region, the depth of the streak groove is relatively small. Even if there is little wear at the top between the streak grooves in the low surface pressure region, the state where the depth of the streak grooves is large or the state where the top width between the streak grooves is small will not last for a long time, The problem that the friction coefficient of the skirt portion, and thus the sliding resistance of the piston is large, lasts for a long time is reduced.

  In addition, according to the invention described in claim 2, as in the invention described in claim 1, in the high surface pressure region, the top width ratio is relatively small. In other words, the groove width ratio is Because of the relatively large size, this also increases the capacity of the streak groove, and as a result, even if the top wear between the streak grooves progresses quickly in the high surface pressure region, the streak groove The oil reservoir function is prevented from decreasing, and the problem of scuffing is reduced. On the other hand, in the low surface pressure region, since the top width ratio is relatively large, the width of the top portion between the streak grooves can be reduced even if there is little wear on the top portion between the streak grooves in the low surface pressure region. A large state is obtained from the beginning, and a state in which the friction coefficient of the skirt portion and thus the sliding resistance of the piston is small is obtained from the beginning.

  As described above, according to the invention described in claim 2, as in the invention described in claim 1, the depth and the top width of the streak groove in the high surface pressure region and the low surface pressure region of the piston skirt portion. Since the groove is formed separately by changing the ratio at the same time, the action of changing the depth of the groove and the action of changing the top width ratio are combined to increase the height of the piston skirt. The problem of scuffing in the pressure region and the problem of long-lasting sliding resistance in the low surface pressure region are both better suppressed. In other words, in the high surface pressure region, the effect of suppressing the decrease in the oil reservoir function of the streak groove and thus the effect of reducing the scuff generation can be obtained satisfactorily, and in the low surface pressure region, the friction coefficient reduction effect of the skirt portion and hence the sliding resistance reduction effect of the piston. Is obtained satisfactorily.

  In that case, in the invention according to claim 2, when the first region is set at the bulging top, the depth of the streak groove is relatively increased also at the bulging top, and the groove Since the width ratio is relatively increased, the effect of suppressing the reduction of the oil reservoir function of the streak groove, and thus the effect of reducing the occurrence of scuffing can be obtained.

  Next, according to the third aspect of the present invention, since the top portion between the streak grooves has a flat plateau shape, the piston skirt portion is in sliding contact with the inner wall surface of the cylinder. On the other hand, when the apex portion between the streak grooves has an acute apex shape, for example, the piston skirt portion is in sliding contact with the cylinder inner wall surface with a line. Therefore, when the top part between the streak grooves has a flat plateau shape, the pressure per unit area acting on the top part between the streak grooves is reduced by the sliding contact between the piston skirt portion and the cylinder inner wall surface. Since the top part between the streak grooves is difficult to wear and the decrease in the depth of the streak grooves is suppressed, the decrease in the oil reservoir function of the streak grooves is suppressed in the first place.

  In addition, since the fine concave portion is formed on the plateau-shaped top, oil is collected in the fine concave portion, and not only the oil accumulated in the streak groove but also the oil accumulated in the fine concave portion, the piston skirt portion and the cylinder A good lubrication state is maintained between the inner wall surface.

  Next, according to the invention described in claim 4, first, the depth of the streak groove in the first region, that is, the high surface pressure region is set to the depth of the streak groove in the second region, that is, the low surface pressure region. Since the depth is increased to twice or more of the depth, the effect of suppressing the decrease in the oil reservoir function of the streak groove in the high surface pressure region, and thus the effect of reducing the occurrence of scuffing can be sufficiently obtained.

  In addition, since the depth of the streak groove in the high surface pressure region is set to 5 μm or more (5 μm ≦ the depth of the streak groove in the high surface pressure region), the reduction of the oil reservoir function of the streak groove in the high surface pressure region is suppressed. As a result, there is no shortage of scuffing reduction effect. Further, since the depth of the streak groove in the high surface pressure region is set to 50 μm or less (the depth of the streak groove in the high surface pressure region ≦ 50 μm), the friction coefficient of the skirt portion and the sliding of the piston in the high surface pressure region. A state of high resistance will not last for a long time.

  On the other hand, since the depth of the streak groove in the low surface pressure region is 2 μm or more (2 μm ≦ the depth of the streak groove in the bottom surface pressure region), the following problem, that is, the outer surface of the skirt portion is too smooth As a result, the problem that the familiarity of the skirt with the inner wall surface of the cylinder (alignment along the shape due to minute wear) is insufficient and the possibility of scuffing is increased is suppressed in the low surface pressure region. . In addition, since the depth of the streak groove in the low surface pressure region is set to 10 μm or less (the depth of the streak groove in the bottom surface pressure region ≦ 10 μm), the friction coefficient of the skirt and the sliding resistance of the piston in the low surface pressure region. There is no long-lasting situation.

  Next, according to the invention described in claim 5, first, the pitch of the streak grooves in the first region, that is, the high surface pressure region and the second region, that is, the low surface pressure region is set to 50 μm or more (50 μm ≦ high The pitch of the streak groove in the surface pressure region and the low surface pressure region) is the following problem, that is, the total length of the streak groove when the streak groove is formed on the outer surface of the skirt portion. Since it becomes very long, the processing time for forming the streak groove becomes long and the problem that productivity deteriorates is suppressed. In addition, since the pitch of the streak grooves in the high surface pressure region and the low surface pressure region is 500 μm or less (the pitch of the streak grooves in the high surface pressure region and the low surface pressure region ≦ 500 μm), the following problem, Since the pitch of the streak grooves becomes excessively large, the problem that the oil reservoir function is insufficient and scuffing occurs is suppressed.

  In addition, since the top width ratio in the high surface pressure region is 20% or less (top width ratio in the high surface pressure region ≦ 20%), in other words, the groove width ratio is 80% or more (80% ≦ high surface pressure). Therefore, the effect of suppressing the reduction of the oil reservoir function of the streak groove in the high surface pressure region and the effect of reducing the occurrence of scuffing will not be insufficient.

  On the other hand, since the top width ratio in the low surface pressure region is larger than 20% (20% <the top width ratio in the bottom surface pressure region), this reduces the wear of the top portion between the streak grooves in the low surface pressure region. However, a state where the width of the top portion between the streak grooves is large is obtained from the beginning, and a state where the friction coefficient of the skirt portion and thus the sliding resistance of the piston is small is obtained from the beginning. Further, since the top width ratio in the low surface pressure region is set to 80% or less (the top width ratio in the bottom surface pressure region ≦ 80%), the same problem as described above, that is, the outer surface of the skirt portion is too smooth, The problem that the familiarity of the skirt portion with respect to the wall surface (alignment along the shape due to minute wear) is insufficient, and the possibility of generating scuffing is increased in the low surface pressure region. Hereinafter, the present invention will be described in more detail through the best mode of the invention.

  As shown in FIG. 1, the piston 1 of the engine 10 according to the present embodiment can reciprocate up and down in a cylinder of a cylinder block 12 having a cylinder head 11 fixed to the cylinder (reference numeral 13 is attached to the inner wall surface of the cylinder). Is arranged. The piston 1 is connected to the upper end portion of the connecting rod 14 by a piston pin 15, and the lower end portion of the connecting rod 14 is connected to a crankshaft (not shown). Two piston rings 16a and 16b and one oil ring 16c are attached to the top of the piston 1 in this order from above.

  As shown in FIG. 2, the piston 1 is formed with ring grooves 3a, 3b, 3c for mounting the piston rings 16a, 16b and the oil ring 16c of FIG. 1 immediately below the piston head 2 that provides the top surface. In addition, a skirt portion 4 is formed on the lower side (crankshaft side) of the oil ring groove 3c (or oil ring 16c) so as to be in sliding contact with the cylinder inner wall surface 13.

  As shown in FIGS. 3 and 4, a support portion 5 for supporting the piston pin 15 of FIG. 1 is formed on the inner side of the skirt portion 4 so as to hang from the lower surface of the piston head 2. A pin hole 6 through which the piston pin 15 is inserted is provided.

  As shown in FIGS. 1, 3 and 4, the piston 1 is made of an aluminum alloy having a skirt portion 4, 4 provided only on the thrust side and the anti-thrust side as a base material in order to reduce the weight. Casting.

  As shown in FIG. 5, the skirt portions 4, 4 of the piston 1 have a barrel shape in which an intermediate portion in the piston axial direction (the same as the reciprocating direction of the piston 1, the vertical direction in this embodiment) bulges outward. In addition, the bulging top portion having the largest amount of bulging outward of the skirt portion 4 is provided at a position slightly lower than the center O of the pin hole 6 (or piston pin 15).

  As shown in FIG. 5 (a), the piston 1 swings its head so that the piston head 2 tilts toward the thrust side during the downward expansion stroke, and as shown in FIG. The head is swung so that the piston head 2 tilts to the anti-thrust side.

  In this case, as shown in FIG. 5 (a), on the thrust side, the portion closer to the piston head 2 (upper side) than the bulging top portion is between the cylinder inner wall surface 13 on the outer surface of the skirt portion 4. In this embodiment, all portions belonging to the high surface pressure portion are set to the first region (indicated by reference numeral), that is, the high surface pressure region. ing. Further, as shown in FIG. 5A, on the thrust side, the portion on the side opposite to the piston head 2 (lower side) from the bulging top portion is between the cylinder inner wall surface 13 on the outer surface of the skirt portion 4. In this embodiment, all the portions belonging to the low surface pressure portion are set to the second region (indicated by the symbol a), that is, the low surface pressure region. (See FIGS. 2 and 3). That is, the surface pressure of the high surface pressure region a> the surface pressure of the low surface pressure region a.

  Similarly, as shown in FIG. 5 (b), on the anti-thrust side, the portion on the piston head 2 side (upper side) than the bulging top portion is between the cylinder inner wall surface 13 on the outer surface of the skirt portion 4. In this embodiment, all the parts belonging to the high surface pressure portion are set to the first region (indicated by the reference symbol “U”), that is, the high surface pressure region. ing. Further, as shown in FIG. 5 (b), on the anti-thrust side, the portion on the anti-piston head 2 side (lower side) with respect to the bulging top portion is in contact with the cylinder inner wall surface 13 on the outer surface of the skirt 4. In the present embodiment, all the portions belonging to the low surface pressure portion are set to the second region (indicated by reference numeral d), that is, the low surface pressure region. (See FIG. 3). That is, the surface pressure in the high surface pressure region c> the surface pressure in the low surface pressure region d.

  However, when the thrust side and the anti-thrust side are compared, since an explosion force acts on the thrust side, generally, the thrust side is the first region, the anti-thrust side is the second region, and the thrust side (first Surface pressure> surface pressure on the anti-thrust side (second region). Further, the surface pressure of the thrust side high surface pressure region a> the surface pressure of the anti-thrust side high surface pressure region c, and the surface pressure of the thrust side low surface pressure region i> the anti-thrust side low surface pressure region e. Is the surface pressure. In this embodiment, the bulging top portion itself is included in the high surface pressure regions a and c.

  As shown in FIG. 2, a plurality of streak grooves 7... 7 extending in the circumferential direction are formed on the outer surface of the skirt portion 4. Here, with reference to FIG.6 and FIG.7, the method of processing and forming the stripe grooves 7 ... 7 in the outer surface of the skirt part 4 is demonstrated. That is, the groove groove forming tool 50 is moved at a constant speed while the cutting edge of the groove groove forming tool 50 is brought into contact with the outer surface of the skirt portion 4 from the outside and the piston 1 is rotated about the reciprocating direction. Then, the grooves 7... 7 are formed on the outer surface of the skirt portion 4 by being moved in the reciprocating direction (downward in the illustrated example) as indicated by arrows.

  By such a processing method, the streak grooves 7... 7 having the cross-sectional shape of the cutting edge of the streak groove forming tool 50 (U-shaped in the illustrated example) spiral on the outer surface of the skirt portion 4 in the circumferential direction. It is formed in a shape. At this time, the horizontal position of the tool 50 is adjusted with respect to the outer surface of the barrel-shaped skirt portion 4 so that the maximum depth D (see FIGS. 8 to 11) of the streak groove 7 is constant. Further, by adjusting the moving speed of the tool 50 in the reciprocating direction, the interval between the adjacent groove grooves 7 and 7 (the pitch P of the groove grooves 7 (see FIGS. 8 to 11)) is made constant. Can do.

  Moreover, as shown in FIG. 6, when the streak grooves 7 and 7 are formed so that the adjacent streak grooves 7 and 7 overlap each other, the apex portion 7a between the streak grooves 7 and 7 has an acute apex shape. (See FIG. 8). On the other hand, as shown in FIG. 7, when the streak grooves 7 and 7 are formed so that the adjacent streak grooves 7 and 7 are spaced apart from each other, the top portion 7a between the streak grooves 7 and 7 is formed into a flat plateau shape. (Trapezoidal shape) (see FIGS. 9 to 12). In addition, in FIGS. 9-11, the code | symbol Wp is attached | subjected to the width | variety of the plateau-shaped top part 7a.

  Returning to FIG. 2, as described above, the plurality of streak grooves 7... 7 are formed on the outer surface of the piston skirt portion 4 in the circumferential direction. If the streak grooves 7 ... 7 are formed under the same conditions as described above, in the high surface pressure regions a and u, the progress of wear of the top portion 7a between the streak grooves 7 and 7 is fast, Since the maximum depth D is quickly reduced and the oil sump function of the streak groove 7 is reduced early, there is a problem that scuffing is likely to occur. On the other hand, in the low surface pressure regions A and D, the streak groove A state in which the progress of wear of the top portion 7a between 7 and 7 is slow and the maximum depth D of the streak groove 7 is large (in other words, a state in which the width Wp of the top portion 7a between the streak grooves 7 and 7 is small). Since it lasts for a long time, the state that the friction coefficient of the skirt portion 4 and the sliding resistance of the piston 1 are large continues for a long time. Problems.

  Therefore, in order to satisfactorily reduce both the problem of scuffing in the high surface pressure region and the problem of long-lasting sliding resistance in the low surface pressure region, the high surface pressure region a and the low surface pressure region , And d, the grooves 7... 7 are made separately under different conditions. Specifically, the maximum depth D of the streak groove 7 is relatively large in the high surface pressure region A and c, where the surface pressure between the outer surface of the skirt portion 4 and the cylinder inner wall surface 13 is relatively high. In the low surface pressure region (a) and (d) where the surface pressure between the outer surface of the skirt portion 4 and the cylinder inner wall surface 13 is relatively low, the maximum depth D of the streak groove 7 is relatively small. . In the high surface pressure regions A and U, the ratio of the width Wp of the top portion 7a between the adjacent groove grooves 7 and 7 to the pitch P of the groove groove 7 (top width ratio: Wp / P) is relatively small. In the low surface pressure regions A and D, the top width ratio (Wp / P) is relatively large.

  For example, as shown in FIGS. 8A and 9A, in the high surface pressure regions a and c, the lower limit value of the maximum depth D of the streak groove 7 can be 5 μm. Moreover, as shown in FIG.8 (b) and FIG.9 (b), the upper limit of the maximum depth D of the streak groove 7 can be 50 micrometers in the high surface pressure area | region a and u. That is, the maximum depth D ≦ 50 μm of the streak groove 7 in the high surface pressure region a and 5 μm. On the other hand, as shown in FIGS. 10A and 11A, in the low surface pressure regions A and D, the lower limit value of the maximum depth D of the streak groove 7 is 2 μm, and FIG. ) And FIG. 11B, in the low surface pressure regions A and D, the upper limit value of the maximum depth D of the streak groove 7 is 10 μm. That is, the maximum depth D ≦ 10 μm of the streak groove 7 in 2 μm ≦ bottom pressure region (a) and (d).

  In this regard, when the maximum depth D of the streak groove 7 in the high surface pressure region A and c becomes less than 5 μm, the oil reservoir function reduction suppressing effect of the streak groove 7 in the high surface pressure region A and c and consequently the scuff generation reduction effect Is lacking. Further, when the maximum depth D of the streak groove 7 in the high surface pressure region A and c becomes larger than 50 μm, the friction coefficient of the skirt portion 4 and thus the sliding resistance of the piston 1 are large in the high surface pressure region A and c. The condition will last for a long time. In general, even if the maximum depth D of the streak groove 7 exceeds 50 μm, an increase in the scuff prevention effect cannot be expected, but the friction coefficient and thus the sliding resistance only becomes too large.

  In addition, when the maximum depth D of the streak groove 7 in the low surface pressure regions (a) and (d) is less than 2 μm, the outer surface of the skirt portion 4 is too smooth and the conformability of the skirt portion 4 to the cylinder inner wall surface 13 (micro wear) ), There is a high possibility that scuffing will occur. In addition, when the maximum depth D of the streak groove 7 in the low surface pressure region A and D exceeds 10 μm, the friction coefficient of the skirt portion 4 and the sliding resistance of the piston 1 in the low surface pressure region A and D are large. The condition will last for a long time.

  However, the maximum depth D of the high surface pressure region A and the groove groove 7 is always twice or more than the maximum depth D of the low surface pressure region A and the groove groove 7. That is, the maximum depth D of the high surface pressure region A and the chamfer groove 7 is ≧ 2 × (the low surface pressure region A, the maximum depth D of the groove groove 7). For example, when the maximum depth D of the high surface pressure region A and the groove groove 7 is 5 μm, the maximum depth D of the low surface pressure region B and the groove groove 7 is 2 to 2.5 μm. To do. For example, when the maximum depth D of the low surface pressure region A and the groove groove 7 is 10 μm, the maximum depth D of the high surface region A and the groove groove 7 is 20 to 50 μm. To do.

  As described above, the maximum depth D of the high surface pressure region A and the crevice groove groove 7 is increased to more than twice the maximum depth D of the low surface pressure region B and the groove groove 7 of the The effect of suppressing the decrease in the oil reservoir function of the streak groove 7 in the surface pressure regions a and c, and thus the effect of reducing the occurrence of scuffing can be sufficiently obtained. In other words, if the maximum depth D of the high surface pressure region A and the cave groove 7 is less than twice the maximum depth D of the low surface pressure region B and the d groove groove 7, the high surface pressure The above effects in areas a and c are insufficient.

  Further, for example, as shown in FIGS. 8A and 8B, in the high surface pressure region a and c, the top portion 7a between the adjacent groove grooves 7 and 7 with respect to the pitch P of the groove groove 7 is formed. The lower limit value of the width Wp ratio (top width ratio: Wp / P) can be set to 0 (zero). Further, as shown in FIGS. 9A and 9B, in the high surface pressure regions a and u, the upper limit value of the top width ratio (Wp / P) can be set to 0.2. That is, 0 ≦ the ratio (Wp / P) ≦ 20% in the high surface pressure region a. On the other hand, as shown in FIGS. 10A and 10B, in the low surface pressure regions A and D, the lower limit value of the top width ratio (Wp / P) is (> 0.2). (The figure is expressed by 0.2 for convenience), as shown in FIGS. 11 (a) and 11 (b), in the low surface pressure regions (a) and (d), the upper limit of the top width ratio (Wp / P). The value is 0.8. That is, 20% <the ratio (Wp / P) ≦ 80% in the bottom surface pressure area b and d.

  In this respect, when the top width ratio (Wp / P) in the high surface pressure region a and c becomes larger than 20%, in other words, when the top width ratio (Wp / P) becomes less than 80%, the high surface pressure The effect of suppressing the decrease in the oil reservoir function of the streak groove 7 in the areas A and C, and thus the effect of reducing the occurrence of scuffing is insufficient.

  Further, when the top width ratio (Wp / P) in the low surface pressure region A and D is 20% or less, in the low surface pressure region A and D, the wear of the top portion 7a between the streak grooves 7 and 7 is small. A state where the width of the top portion 7a between the trace grooves 7 and 7 is small continues for a long time, and a state where the friction coefficient of the skirt portion 4 and the sliding resistance of the piston 1 is large continues for a long time. Also, if the apex width ratio (Wp / P) in the low surface pressure region (a) and (b) exceeds 80%, the outer surface of the skirt portion 4 is too smooth, and the conformability of the skirt portion 4 to the cylinder inner wall surface 13 ( There is a shortage of shape alignment due to minute wear, which increases the possibility of scuffing.

  8 to 11 have been described in the case where the pitch P of the streak groove 7 is 50 μm, this is the case of the streak groove in any of the high surface pressure region A, c and the low surface pressure region A, D. 7 is a preferable value as the lower limit value of the pitch P, and a preferable value as the upper limit value of the pitch P of the streak groove 7 is, for example, 500 μm. That is, the pitch P of the streak grooves 7 in the high surface pressure regions a, c, and the low surface pressure regions a, d is P ≦ 500 μm.

  In this respect, when the pitch P of the high surface pressure regions a, c, and the low surface pressure region A, and the groove groove 7 is less than 50 μm, the groove grooves 7... 7 are formed on the outer surface of the skirt portion 4. Since the entire length of the streak groove 7 becomes extremely long, the processing time for forming the streak groove 7 becomes long, and the productivity deteriorates. Also, if the pitch P of the groove groove 7 of the high surface pressure area A, c, low surface pressure area B, and d is larger than 500 μm, the pitch P of the groove groove 7 becomes excessively large, so that the oil reservoir function There is a shortage of scuffs.

  Further, as described above, in this embodiment, the bulging top portion is included in the high surface pressure regions a and c, so that the bulging top portion also has the same conditions as the high surface pressure regions a and c as described above. The streak grooves 7 ... 7 are formed.

  Further, as described above, when the thrust side and the anti-thrust side are compared, explosive force acts on the thrust side, so that the surface pressure of the high surface pressure area a on the thrust side> the high surface pressure area U on the anti-thrust side. Since the surface pressure of the low surface pressure area i on the thrust side is greater than the surface pressure of the low surface pressure area D on the anti-thrust side, the high surface pressure area a, c and the low surface pressure area i, d While forming the streak grooves 7... 7 under different conditions, the thrust side high surface pressure region A and the anti-thrust side high surface pressure region c, and the thrust side low surface pressure region The streak grooves 7... 7 may be separately formed under different conditions between the a and the low thrust pressure region D on the anti-thrust side. In that case, specifically, the maximum depth D of the streak groove 7 is relatively increased in the high surface pressure region a on the thrust side, and the maximum depth of the streak groove 7 in the high surface pressure region c on the anti-thrust side. The length D is made relatively small. Similarly, the maximum depth D of the streak groove 7 is relatively increased in the low surface pressure region A on the thrust side, and the maximum depth D of the streak groove 7 is relatively increased in the low surface pressure region D on the anti-thrust side. Make it smaller. In addition, the ratio (Wp / P) of the width Wp of the top portion 7a between the streak grooves 7 and 7 with respect to the pitch P of the streak groove 7 in the high surface pressure region a on the thrust side is relatively small, The top width ratio (Wp / P) is relatively increased in the high surface pressure region c. Similarly, the ratio (Wp / P) of the width Wp of the top portion 7a between the streak grooves 7 and 7 with respect to the pitch P of the streak groove 7 in the low surface pressure region (a) on the thrust side is relatively small, and the anti-thrust side The apex width ratio (Wp / P) is relatively increased in the low surface pressure region d.

  Regardless of the thrust side or the anti-thrust side, the area between the high surface pressure area A, c and the low surface pressure area A, d (for example, slightly on the anti-piston head 2 side (lower side) than the bulging top part) (Refer to FIG. 5) is further distinguished as a medium surface pressure region. In this medium surface pressure region, the intermediate point between the conditions in the high surface pressure regions a and c and the conditions in the low surface pressure regions a and d as described above. The streak grooves 7 ... 7 may be formed under the following conditions.

  As described above, in the present embodiment, in the piston 1 of the engine 10 in which the plurality of streak grooves 7... 7 are formed in the circumferential direction on the outer surface of the skirt portion 4 that is in sliding contact with the cylinder inner wall surface 13 of the engine 10. In the high surface pressure region (first region) a and c of the piston skirt portion 4 where the surface pressure between the cylinder inner wall surface 13 is relatively high, the maximum depth D of the streak groove 7 is relatively increased. Thus, the capacity of the streak groove 7 becomes relatively large. As a result, even if the wear of the top portion 7a between the streak grooves 7 and 7 progresses quickly in the high surface pressure region a, c, the streak groove 7 The oil reservoir function is prevented from decreasing, and the problem of scuffing is reduced. On the other hand, in the low surface pressure region (second region) (a) and (d) of the piston skirt portion 4 where the surface pressure between the cylinder inner wall surface 13 is relatively low, the maximum depth D of the streak groove 7 is relatively set. Even if there is little wear of the top part 7a between the streak grooves 7 and 7 due to the low surface pressure area a and d, the maximum depth D of the streak groove 7 is large or between the streak grooves 7 and 7. The state in which the width Wp of the top portion 7a is small does not continue for a long time, and the problem that the state in which the friction coefficient of the skirt portion 4 and the sliding resistance of the piston 1 are large continues for a long time is reduced.

  In addition, in the high surface pressure regions A and C of the piston skirt portion 4, the ratio (Wp / P) of the width Wp of the apex portion 7a between the adjacent groove grooves 7 and 7 to the pitch P of the groove groove 7 is relative. In other words, since the ratio of the width of the groove 7 to the pitch P of the groove 7 is relatively increased, the capacity of the groove 7 is also relatively increased. As a result, even if the wear of the top portion 7a between the streak grooves 7 and 7 progresses quickly in the high surface pressure region a and c, the decrease in the oil reservoir function of the streak groove 7 is suppressed, and the problem of scuffing occurs. Reduced. On the other hand, in the low surface pressure regions (a) and (d) of the piston skirt portion 4, the ratio (Wp / P) of the width Wp of the apex portion 7a between the adjacent groove grooves 7, 7 with respect to the pitch P of the groove groove 7 is relatively set. As a result, the state in which the width Wp of the top portion 7a between the streak grooves 7 and 7 is initially large even though the wear of the top portion 7a between the streak grooves 7 and 7 is small due to the low surface pressure regions a and d. From the beginning, a state in which the friction coefficient of the skirt portion 4 and thus the sliding resistance of the piston 1 is low is obtained.

  In addition, when the skirt portion 4 has a barrel shape in which an intermediate portion in the piston axial direction bulges outward, the piston head includes a bulging top portion where the bulging amount of the skirt portion 4 is largest. Since the regions belonging to the two side portions (high surface pressure portions) are the high surface pressure regions (first regions) a and c, the striation grooves are formed in the high surface pressure regions a and c belonging to the high surface pressure portions. Thus, the effect of suppressing the oil reservoir function decrease of 7 and the effect of reducing the occurrence of scuffing can be obtained. On the other hand, since the region belonging to the portion (low surface pressure portion) on the side opposite to the piston head 2 from the high surface pressure portion is defined as the low surface pressure region (second region) A and D, it belongs to the low surface pressure portion. In the low surface pressure regions (a) and (d), the effect of reducing the friction coefficient of the skirt portion 4 and the effect of reducing the sliding resistance of the piston 1 can be obtained.

  In this case, since the bulging top portion is included in the high surface pressure regions a and c, the effect of suppressing the oil reservoir function reduction of the streak groove 7 and the scuffing reduction effect can be obtained even at the bulging top portion.

  When the apex portion 7a between the streak grooves 7 and 7 has an acute apex shape, the piston skirt portion 4 is in sliding contact with the cylinder inner wall surface 13 by a line. When the flat plateau 7a is formed, the piston skirt portion 4 comes into sliding contact with the cylinder inner wall surface 13 on the surface. Therefore, when the top portion 7a between the streak grooves 7 and 7 is formed into a flat plateau shape, the unit area acting on the top portion 7a between the streak grooves 7 and 7 by the sliding contact between the piston skirt portion 4 and the cylinder inner wall surface 13. As a result, the top pressure 7a between the streak grooves 7 and 7 becomes difficult to wear, and the decrease in the maximum depth D of the streak groove 7 is suppressed. Reduction of the reservoir function is suppressed.

  When the top portion 7a between the streak grooves 7 and 7 has a flat plateau shape, fine concave portions (micro dimples) 7b... 7b may be formed on the plateau-shaped top portion 7a as shown in FIG. . Such fine recesses 7b... 7b can be formed using a shot peening technique in which fine steel balls are projected at high speed with high-pressure air or the like. In that case, the size and depth of the fine recesses 7b... 7b can be controlled by adjusting the diameter and air pressure of the fine steel balls.

  In this way, by forming the fine recesses 7b... 7b in the plateau-like top portion 7a, oil is accumulated in the fine recesses 7b... 7b, and not only the oil accumulated in the streak groove 7 but also the fine recesses 7b. Even between the oil accumulated in 7b, the space between the piston skirt portion 4 and the cylinder inner wall surface 13 is maintained in a good lubricating state.

  In this case, the surface roughness of the top portion 7a in which the fine recesses 7b... 7b are formed is 10-point average roughness Rz (JIS B0601-1994), and Rz <maximum depth D of the streak groove 7 is satisfied. When Rz ≧ maximum depth D of the streak groove 7, the friction coefficient reducing effect and the sliding resistance reducing effect due to the top plate 7 a between the streak grooves 7, 7 being flat is impaired, and the fine recess 7 b ... the meaning of forming 7b is lost.

  The outer surface of the skirt portion 4 may be coated with a solid lubricant (such as a polyamide-imide resin coating containing graphite powder, molybdenum disulfide powder, PTFE (Polytetrafluoroethylene), or the like). Such a covering material has an effect of reducing frictional resistance, and is softer than metal, and thus has an effect of filling the clearance with the cylinder inner wall surface 13 and an effect of absorbing slap noise.

  The film thickness of the solid lubricant in that case is not particularly limited, but is preferably 20 μm or less, for example, on the surface of the plateau-like top portion 7a. If it exceeds 20 μm, the solid lubricant is easily worn as compared with the base material (aluminum alloy) of the piston 1, so that the change in clearance with the cylinder inner wall surface 13 becomes too large, and problems such as slap noise may occur. . In this regard, after the solid lubricant is coated, it may be polished and removed from the surface of the plateau-like top portion 7a and left only in the valleys of the streak groove 7.

  The above embodiment is the best embodiment of the present invention, but various changes and improvements can be added without departing from the scope of the claims. For example, in the above embodiment, the cross-sectional shape of the streak groove 7 is U-shaped, but the present invention is not limited to such a shape, and the cross-section is a V-shaped or polygonal shape. Applicable to the groove 7 as well. In this embodiment, the present invention is applied to a spark ignition engine using gasoline as a fuel. However, the present invention can also be applied to a piston of a diesel engine having a high compression ratio using light oil as a fuel. Further, in this embodiment, one streak groove 7 is formed on the outer surface of the skirt portion 4 so as to be spiral, but the single streak groove 7 is circular along the outer surface of the skirt portion 4. A plurality of such streak grooves 7 are arranged in the reciprocating direction with respect to the outer surface of the skirt portion 4, and the spacing between the plurality of streak grooves 7 ... 7 is predetermined. You may form so that it may become a pitch width.

  As described above in detail with reference to specific examples, the present invention provides a piston skirt in an engine piston in which a plurality of streak grooves are formed in the circumferential direction on the outer surface of a skirt portion that is in sliding contact with the cylinder inner wall surface of the engine. Because it is a technology that can satisfactorily suppress both the problem of scuffing in the high surface pressure region and the problem of long-lasting sliding resistance in the low surface pressure region, it is in sliding contact with the cylinder inner wall surface of the engine. Extensive industrial applicability is expected in the technical field of piston lubrication.

It is the front view which looked at the piston of the engine which concerns on the best embodiment of this invention from the side orthogonal to the thrust side and the anti-thrust side. It is the side view which looked at the piston from the thrust side. FIG. 3 is a cross-sectional view taken along arrow III-III in FIG. 2 (the left side is a thrust side). It is a bottom view of the piston. When the piston skirt has a barrel shape, (a) is the expansion stroke, the piston head swings the neck to the thrust side, and (b) is the exhaust process, the piston head swings the anti-thrust side to the neck. It is explanatory drawing of doing. It is explanatory drawing of the method of processing and forming a streak groove so that the top part between streak grooves may become an acute-angle top shape in the skirt part of the said piston. It is explanatory drawing of the method of processing and forming a streak groove so that the top part between streak grooves may become a flat plateau shape in the skirt part of the said piston. It is explanatory drawing which shows the preferable dimension range of the streak groove in a high surface pressure area | region. It is explanatory drawing which similarly shows another preferable dimension range in a high surface pressure area | region. It is explanatory drawing which shows the preferable dimension range of the streak groove | channel in a low surface pressure area | region. It is explanatory drawing which similarly shows another preferable dimension range in a bottom face pressure area | region. It is explanatory drawing at the time of forming a micro dimple in the plateau-shaped top part between the said streak grooves.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 2 Piston head 4 Skirt part 6 Pin hole 7 Streak groove 7a Top part 10 between adjacent streak grooves Engine 13 Cylinder inner wall surface 50 Streak groove formation tool O Pin hole center P Streak groove pitch (adjacent The sum of the width of the top between the streak grooves and the width of the streak grooves)
Wp Width between tops of adjacent streak grooves A thrust side high surface pressure region (first region)
I Thrust side low surface pressure area (second area)
Anti-thrust side high surface pressure region (first region)
D Anti-thrust side bottom surface pressure region (second region)

Claims (5)

An engine piston having a plurality of streak grooves formed in a circumferential direction on an outer surface of a skirt portion that is in sliding contact with an inner wall surface of an engine cylinder,
In the outer surface of the skirt portion, the depth of the streak groove is larger in the first region where the surface pressure between the cylinder inner wall surface is relatively higher than in the relatively lower second region, And the ratio of the width of the top part between adjacent streak grooves with respect to the sum of the width | variety of the top part between adjacent streak grooves and the width of a streak groove is made small, The piston of the engine characterized by the above-mentioned. An engine piston having a plurality of streak grooves formed in a circumferential direction on an outer surface of a skirt portion that is in sliding contact with an inner wall surface of an engine cylinder,
The skirt portion is formed in a barrel shape in which an intermediate portion in the piston axial direction bulges outward,
On the outer surface of the skirt portion, the first region belonging to the portion on the piston head side including the bulging top portion where the amount of bulging outward of the skirt portion is the largest is more anti-piston than the portion on the piston head side. Adjacent streak groove with respect to the sum of the width of the top part between adjacent streak grooves and the width of the streak groove is greater than the second region belonging to the head side portion. An engine piston characterized in that the ratio of the width of the top portion between them is reduced. The engine piston according to claim 1 or 2,
The top between the streak grooves is plateau-shaped,
An engine piston characterized in that a fine recess is formed in the plateau-shaped top. An engine piston according to any one of claims 1 to 3,
In the first region, the depth of the streak groove is twice or more larger than that of the second region, and the depth of the streak groove in the first region is 5 μm or more and 50 μm or less. The piston of the engine is characterized in that the depth of the streak groove in the second region is 2 μm or more and 10 μm or less. An engine piston according to any one of claims 1 to 4,
The sum in the first region and the second region is 50 μm or more and 500 μm or less, and the proportion in the first region is 20% or less, and the proportion in the second region is Is larger than 20% and not more than 80%.

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