JP2008231972A - Piston of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure uniform lubricity between the outer surface of a piston skirt part and the inner wall surface of a cylinder by suppressing an increase in the oil retaining amount of a streak groove and the leakage of oil in the circumferential direction in a piston of an engine having a plurality of streak grooves circumferentially formed in the outer surface of the piston skirt part in slidable contact with the inner wall surface of the cylinder of the engine. <P>SOLUTION: In this piston of an engine, the plurality of streak grooves 7...7 are circumferentially formed in the outer surface of the skirt part in slidable contact with the inner wall surface of the cylinder of the engine. The streak grooves 7...7 are formed in a corrugated shape. The lengths of the streak grooves 7 are increased, and accordingly the oil retaining amounts of the streak grooves 7 are increased. Since the displaced portions A, B of the corrugated streak grooves 7 obstruct the leakage of oil, the oil in the streak grooves 7 must meander to escape in the circumferential direction. Consequently, the oil in the streak grooves 7 hardly escapes circumferentially along the streak grooves 7. <P>COPYRIGHT: (C)2009,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. The space between the outer surface of the skirt and the inner wall surface of the cylinder is kept in a lubrication state by the oil, whereby the sliding resistance is reduced and the piston can smoothly reciprocate in the cylinder.

  Conventionally, it is known to process and form a plurality of streak grooves in a piston skirt (see, for example, Patent Document 1). 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.

  Patent Document 1 discloses that an anodized film is placed on the surface of the streak groove formed on the outer surface of the piston skirt, and the anodized film is coated with a molybdenum disulfide film. Patent Document 2 discloses that a grinding mark is formed at an angle in the circumferential direction by a honing process on the inner peripheral sliding surface of the cylinder (cross hatch), and this is used as an oil reservoir.

JP2003-13802 (paragraph 0021, FIG. 4) JP 59-196954 (page 2, upper right column, lines 13-17, FIG. 3)

  By the way, since the groove groove formed in the circumferential direction on the outer surface of the piston skirt portion is conventionally linear, the amount of oil retained in the groove groove is not relatively large, and it is also caused by the passage of blow-by, etc. That is, the unburned gas leaks from the combustion chamber side to the crankcase side through a very small gap between the piston and the inner wall surface of the cylinder. Since it is easy to escape in the circumferential direction along the groove, it may be difficult to ensure uniform lubricity between the outer surface of the piston skirt and the inner wall surface of the cylinder.

  The present invention addresses the above-described problem 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. An object is to easily ensure uniform lubricity between the outer surface of the piston skirt and the inner wall surface of the cylinder by increasing the holding amount and suppressing oil escape in the circumferential direction.

  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. A piston for an engine, wherein the streak groove is formed in a wave shape.

  Here, FIG. 11 illustrates some preferred specific embodiments of the wavy groove groove in the present invention. In the present invention, for example, as shown in FIG. 11 (a), the wave-shaped streak groove has a square shape with wave-displaced portions A and B, and the line connecting these displaceable portions A and B is inclined. Including things. Further, the displacement portions A and B may be rounded as shown in FIG. 11B, or the displacement portions A and B may be trapezoidal as shown in FIG. 11C. Alternatively, as shown in FIG. 11D, the entire wave may be configured with a smooth curve.

  Next, the invention according to claim 2 is the piston of the engine according to claim 1, wherein the wavy streak grooves adjacent to each other where the displacement portion toward the anti-piston head side is adjacent to each other. The piston of the engine is characterized by being displaced in the circumferential direction.

  Next, the invention according to claim 3 is the piston of the engine according to claim 1, wherein the wavy streak groove of the wavy streak groove adjacent to the piston head side is located adjacent to the piston head side. Is located approximately in line with the displacement portion on the anti-piston head side, and the displacement portion on the anti-piston head side is adjacent to the displacement portion on the piston head side of the wavy groove groove adjacent on the anti-piston head side. An engine piston characterized by being positioned substantially coincident with the direction.

  Next, the invention according to claim 4 is the piston of the engine according to any one of claims 1 to 3, wherein the wavy streak grooves are not in contact with each other. .

  Here, “contact with each other” with respect to the streak groove means that two or more streak grooves intersect or merge so that the spaces in the streak groove communicate with each other. Therefore, when the groove grooves are “not in contact with each other”, the groove grooves are separated from each other, and the spaces in the groove grooves do not communicate with the spaces in the other groove grooves.

  First, according to the invention described in claim 1, in the piston of the 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 inner wall surface of the cylinder of the engine, the streak grooves are corrugated. Therefore, the length of the streak groove is increased as compared with the case where the streak groove is formed linearly, and as a result, the amount of oil retained in the streak groove is relatively increased. Further, the displacement portions A and B (see FIG. 11) of the wavy groove groove obstruct the oil escape, and the oil in the groove groove has to meander in order to escape in the circumferential direction. The oil in the groove becomes difficult to escape in the circumferential direction along the groove. As a result, the amount of oil retained in the streak groove can be increased and oil escape in the circumferential direction can be suppressed, and uniform lubricity can be easily ensured between the outer surface of the piston skirt and the inner wall surface of the cylinder. can do.

  Next, according to the second aspect of the present invention, the portion of the wavy streak groove that is displaced toward the anti-piston head side is positioned so that the adjacent wavy streak grooves are displaced from each other in the circumferential direction (piston head). The position of the displacement portion to the side is not a problem), and oil can be prevented from coming off to the side opposite to the piston head in the piston sliding direction. That is, by forming a groove groove extending in the circumferential direction in a wavy shape, the groove groove has a displacement part to the piston head side (hereinafter sometimes referred to as a “mountain part” for convenience) and a displacement to the anti-piston head side. Part (same as “valley part”). When the piston sliding direction is substantially vertical, the oil in the streak groove easily collects in the valley portion, that is, the downward displacement portion. At this time, if the valley portions are located in the circumferential direction between the adjacent wavy groove grooves, when the oil gathered in the valley portion moves to the groove groove directly below, The oil gathers in the valley portion in a short distance and in a short time, and this repetition makes it easy for oil in the streak groove to fall downward, that is, to the anti-piston head side. On the other hand, when the valley portions are positioned in the circumferential direction between the adjacent wavy groove grooves, when the oil gathered in the valley portion moves to the groove groove directly below, The movement distance and the movement time until it gathers in the valley portion becomes longer, and the repetition of this makes it difficult for the oil in the streak groove to come down, that is, to the anti-piston head side. As a result, oil can be prevented from slipping out to the anti-piston head side, and the amount of oil retained in the streak groove can be secured. From this point as well, it is uniform between the outer surface of the piston skirt and the cylinder inner wall surface. It is possible to easily ensure a good lubricity. Further, the oil consumption can be reduced by suppressing the oil from dropping downward.

  Next, according to the third aspect of the present invention, the displacement portion to the piston head side of the wavy groove groove and the displacement portion to the anti-piston head side of the adjacent wavy groove groove on the piston head side are arranged in the circumferential direction. Since the displacement part to the anti-piston head side is located substantially coincident with the displacement part to the piston head side of the adjacent wavy groove groove on the anti-piston head side, the piston slide Oil can be further prevented from coming off to the anti-piston head side in the moving direction. That is, first, in the context of the invention described in claim 2, since the valley portions are located at the maximum offset in the circumferential direction between the adjacent wavy streak grooves, the movement distance of the oil・ Movement time is maximized, and the oil in the streak groove is more difficult to escape on the lower side, that is, on the anti-piston head side. In addition, since the crest portion of one streak groove and the trough portion of the other streak groove are located in the circumferential direction with each other between adjacent wavy streak grooves, the streak groove directly above The distance in the piston sliding direction is the shortest between the valley portion of the groove and the peak portion of the groove groove immediately below, and the peak of the groove groove immediately below the valley portion of the groove groove immediately above is accompanied by the reciprocation of the piston. In addition to the movement of oil to the part, it also tends to occur from the crest part of the immediately below streak groove to the trough part of the directly above streak groove. This makes it difficult for the oil in the streak groove to come out downward, that is, on the side opposite to the piston head. As a result, it is possible to further suppress the oil loss to the anti-piston head side, to further secure the amount of oil retained in the streak groove, and to achieve a uniform gap between the outer surface of the piston skirt and the inner wall surface of the cylinder. Lubricity can be more easily ensured. Moreover, the oil consumption can be further reduced.

  Next, according to the invention described in claim 4, since the wavy streak grooves are not brought into contact with each other, this also further suppresses oil leakage to the anti-piston head side in the piston sliding direction. can do. That is, when the wavy groove grooves are in contact with each other, as described above, the spaces in the groove grooves are communicated with each other. It is easy for oil to come out downward, that is, on the side opposite to the piston head. On the other hand, if the wavy streak grooves are not in contact with each other, the space in the streak groove does not communicate with the space in the other streak grooves, and the streak groove formed in the upper part of the skirt portion. Therefore, it is difficult for oil to move to the groove groove formed in the lower part, so that the oil in the groove groove is difficult to escape downward, that is, to the anti-piston head side. As a result, it is possible to further suppress oil loss to the anti-piston head side, and also from this point, it is possible to further secure the amount of oil retained in the streak groove, and to ensure that the outer surface of the piston skirt and the inner wall surface of the cylinder During this, uniform lubricity can be more easily ensured. Moreover, the oil consumption can be further reduced. 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. 2, a plurality of streak grooves 7... 7 extending in the circumferential direction are formed on the outer surface of the skirt portion 4. In particular, the streak grooves 7 ... 7 are formed in a wave shape in order to increase the amount of oil retained in the streak grooves 7 ... 7 and to suppress oil escape in the circumferential direction. As a result, the streak groove 7 has a displacement portion toward the piston head 2 side, that is, a crest portion A, and a displacement portion toward the anti-piston head 2 side, that is, a trough portion B, as illustrated in FIG. . In particular, in this embodiment, since the sliding direction of the piston 1 (the same as the reciprocating direction of the piston 1 or the axial direction of the piston 1) is the vertical direction, the peak portion A is the upward displacement portion, and the valley portion. B is a downward displacement portion.

  Here, with reference to FIG. 6, a method for processing and forming the wavy streak grooves 7 to 7 on the outer surface of the skirt portion 4 will be described. That is, for example, using an NC (numerical control) lathe or an NC multifunction machine, the blade edge of the streak groove forming tool 50 is brought into contact with the outer surface of the skirt portion 4 from the outside, and the sliding direction of the piston 1 is changed. While rotating as a shaft, the streak groove forming tool 50 is reciprocated with a constant amplitude in the sliding direction (the vertical direction in the figure) as indicated by a black arrow, and at the same time, the sliding direction as indicated by a white arrow ( The wavy streak grooves 7... 7 are formed on the outer surface of the skirt portion 4 by moving them at a constant speed downward in the example of the figure.

  By such a processing method, the wavy streak grooves 7 ... 7 having the cross-sectional shape of the cutting edge of the streak groove forming tool 50 (U-shaped in the figure) are formed on the outer surface of the skirt portion 4 in the circumferential direction. It is formed in a spiral shape. At this time, the position of the tool 50 in the horizontal direction on the drawing is adjusted with respect to the outer surface of the skirt portion 4 so that the maximum depth of the streak groove 7 is constant. Further, the moving speed of the tool 50 in the sliding direction (the white arrow in FIG. 6) is adjusted so that the interval between the adjacent groove grooves 7 and 7 (that is, the pitch of the groove grooves 7) is constant.

  In that case, for example, the maximum depth of the streak groove 7 is preferably 5 to 50 μm in the high surface pressure region and 2 to 10 μm in the low surface pressure region. When the maximum depth of the streak groove 7 is less than 5 μm in the high surface pressure region, the oil reservoir function of the streak groove 7 and thus the scuff generation suppressing function is insufficient. Further, when the maximum depth of the streak groove 7 exceeds 50 μm in the high surface pressure region, the state in which the friction coefficient of the skirt portion 4 and thus the sliding resistance of the piston 1 is large extends for a long time. On the other hand, when the maximum depth of the streak groove 7 is less than 2 μm in the low surface pressure region, 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 Alongside) and the possibility of scuffing increases. Further, when the maximum depth of the streak groove 7 exceeds 10 μm in the low surface pressure region, the state in which the friction coefficient of the skirt portion 4 and thus the sliding resistance of the piston 1 is large extends for a long time.

  Furthermore, the pitch of the streak grooves 7 is preferably 50 to 500 μm, for example. When the pitch of the groove 7 is less than 50 μm, the length of the entire groove 7 when the grooves 7... 7 are formed on the outer surface of the skirt portion 4 is extremely long. The processing time becomes longer and the productivity deteriorates. On the other hand, when the pitch of the streak grooves 7 exceeds 500 μm, the pitch of the streak grooves 7 becomes excessively large, so that the oil reservoir function is insufficient and scuffing occurs.

  Further, as shown in FIG. 6, the streak grooves 7 and 7 are formed so that the adjacent streak grooves 7 and 7 are spaced apart from each other, and the top portion 7a between the streak grooves 7 and 7 is formed as a flat plateau. The shape (trapezoid). Thereby, the streak grooves 7 ... 7 can be formed apart from each other without being in contact with each other. At this time, the space in the streak groove 7 does not communicate with the space in the other streak groove 7. In FIGS. 6 and 7, the width of the plateau-like top portion 7 a is denoted by reference sign Wp.

  Here, the wavy groove groove 7 is formed in various modes according to the condition for reciprocating the groove groove forming tool 50 in the vertical direction with a constant amplitude (black arrow in FIG. 6). For example, when the reciprocating speed in the vertical direction of the tool 50 is made constant while the rotational speed of the piston 1 is made constant, and the tool 50 is quickly turned at the upper and lower ends of the reciprocating movement, the above-described FIG. As described above, the peak portion A and the valley portion B of the wave are angular, and a straight line in which the line connecting the peak portion A and the valley portion B is inclined is obtained. Further, when the reciprocating speed of the tool 50 is loosened before and after the direction change of the tool 50 at the upper end and the lower end of the reciprocating motion, the wave crest A and trough B are rounded as shown in FIG. Can be obtained. Further, when the reciprocating motion of the tool 50 is temporarily stopped when the direction of the tool 50 is changed at the upper end and the lower end of the reciprocating motion, as shown in FIG. Is obtained. Alternatively, when the reciprocating speed of the tool 50 is gradually reduced to zero toward the upper end and the lower end of the reciprocating movement and gradually increased to the intermediate portion, the entire wave is smooth as shown in FIG. A sinusoidal shape composed of curves is obtained.

  In either case, the ratio of the amplitude and wavelength of the wavy groove groove 7 varies depending on the ratio between the vertical reciprocating speed of the groove groove forming tool 50 and the rotational speed of the piston 1. Generally, as the ratio of the reciprocating speed in the vertical direction of the tool 50 to the rotational speed of the piston 1 increases, the wavelength of the wavy streak groove 7 becomes shorter. As the wavelength becomes shorter, the inclination angle from the horizontal direction of the line connecting the crest portion A and the trough portion B of the wavy streak groove 7 becomes larger (the inclination becomes steeper). This is advantageous in that it suppresses oil escape in the circumferential direction because the oil in the stripe groove 7 works in a direction to increase the degree of difficulty in escaping along the groove groove 7 in the circumferential direction. However, since the oil in the streak groove 7 also works in the direction of increasing the degree to which the oil easily gathers in the valley portion B of the streak groove 7, in terms of suppressing oil loss in the piston sliding direction (downward). It will be disadvantageous. Therefore, from the viewpoint of balancing and suppressing oil escape in the circumferential direction and oil loss in the piston sliding direction, the reciprocating speed in the vertical direction of the streak groove forming tool 50 and the rotational speed of the piston 1 are It is necessary to select a ratio.

  From the above viewpoint, as illustrated in FIG. 5 (a), one limit value of the ratio of the amplitude and wavelength of the wavy streak groove 7 is set to 1: 3.46, and as shown in FIG. 5 (b), The other limit value is preferably 1: 2. At this time, in the former, the inclination angle from the horizontal direction of the line connecting the peak portion A and the valley portion B of the wavy streak groove 7 is about 30 °, and in the latter is 45 °. If the tilt angle is less than 30 °, the effect of suppressing oil loss in the piston sliding direction is sufficient, but the effect of suppressing oil escape in the circumferential direction is insufficient. On the other hand, if the tilt angle is greater than 45 °, the effect of suppressing oil escape in the circumferential direction is sufficient, but the effect of suppressing oil loss in the piston sliding direction is insufficient.

  However, the preferable range of the ratio between the amplitude and the wavelength of the wavy groove groove 7 is not limited to the above, and an optimal range is appropriately selected according to the load of the engine 10, the shape of the piston 1, the amount of oil supplied, and the like. Should be decided.

  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. As illustrated in FIG. 7, since the streak grooves 7 ... 7 are formed in a wave shape, the length of the streak grooves 7 ... 7 is longer than when the streak grooves are formed linearly as in the prior art. As a result, the amount of oil retained in the streak grooves 7 ... 7 is relatively increased. Further, the peak portion A and the valley portion B of the wavy groove groove 7 become an obstacle to oil escape, and in order for the oil in the groove groove 7 to escape in the circumferential direction, it must meander as shown by the arrows. As a result, even if blow-by passes through the outer surface of the piston skirt portion 4, the oil in the streak groove 7 is difficult to escape along the streak groove 7 in the circumferential direction. As a result, the amount of oil retained in the streak groove 7 can be increased and the oil escape in the circumferential direction can be suppressed, and uniform lubricity can be provided between the outer surface of the piston skirt portion 4 and the cylinder inner wall surface 13. It can be secured easily.

  On the other hand, as illustrated in FIG. 10, when the streak grooves 7... 7 are formed in a straight line, when the blow-by passes through the outer surface of the piston skirt portion 4, the oil in the streak groove 7 is removed. It is easy to escape in the circumferential direction along the groove 7, and as a result, it is difficult to ensure uniform lubricity between the outer surface of the piston skirt portion 4 and the cylinder inner wall surface 13.

  Next, as illustrated in FIG. 8, when the valley portions B... B of the wavy streak grooves 7 are positioned so as to be shifted from each other in the circumferential direction between the adjacent wavy streak grooves 7, 7, Oil loss in the piston sliding direction (downward) can be suppressed.

  That is, by forming the groove groove 7 extending in the circumferential direction into a wave shape, the groove groove 7 has a peak portion A toward the piston head 2 side (upper side) and a valley portion toward the anti-piston head 2 side (lower side). B. At this time, when the valley portions B and B are positioned in the circumferential direction between the adjacent wavy streak grooves 7 and 7 (see FIG. 7), the oil gathered in the valley portion B is directly below. When moved to the groove 7, it gathers in the valley portion B of the groove 7 in a short distance and in a short time, and by repeating this, the oil in the grooves 7. On the other hand, as shown in FIG. 8, when the valley portions B and B are located in the circumferential direction in the adjacent wavy groove grooves 7 and 7, the oil gathered in the valley portion B is directly below. When moved to the streak groove 7, the moving distance and time required to gather at the valley portion B of the streak groove 7 become longer as indicated by the arrow, and by repeating this, the oil in the streak grooves 7. Is difficult to pull down. As a result, it is possible to prevent the oil in the streak grooves 7... 7 from being pulled downward, and to secure the oil retention amount of the streak grooves 7. From this point also, the outer surface of the piston skirt portion 4 can be secured. Uniform lubricity can be easily ensured between the cylinder inner wall surface 13 and the cylinder inner wall surface 13. Further, the oil consumption can be reduced by suppressing the oil from dropping downward.

  Next, as illustrated in FIG. 9, the crest portion A... A of the wavy streak groove 7 and the trough portion B... B of the wavy streak groove 7 adjacent on the piston head 2 side (upper side) and the circumferential direction. Of the wavy streak groove 7 and the crest part A ... A of the wavy streak groove 7 adjacent on the anti-piston head 2 side (lower side), and the circumferential direction If they are positioned so as to substantially coincide with each other, oil omission in the piston sliding direction (downward) can be further suppressed.

  That is, first, in relation to FIG. 8, the valley portions B and B are located at the maximum in the circumferential direction between the adjacent wavy groove grooves 7 and 7, so that the movement of the oil The distance / travel time is maximized, and the oil in the streak grooves 7. In addition, between the adjacent wavy groove grooves 7, 7, the peak portions A... A of the one groove groove 7 and the valley portions B... B of the other groove groove 7 coincide with each other in the circumferential direction. Therefore, the distance in the piston sliding direction (that is, the plateau-like top portion 7a) between the valley portion B ... B of the immediately above-mentioned streak groove 7 and the crest portion A ... A of the immediately below streak groove 7 is determined. Width Wp (see FIGS. 6 and 7) is the shortest, and as indicated by the arrow in FIG. Not only the movement of oil to the crest portion A ... A of the streak groove 7 but also the movement of oil from the crest portion A ... A of the streak groove 7 directly below to the valley portion B ... B of the streak groove 7 immediately above. It becomes easy to occur, and by the oil exchange between the streak grooves 7 and 7, the oil in the streak grooves 7. As a result, the oil in the streak grooves 7... 7 can be further prevented from coming off, the amount of oil retained in the streak grooves 7 can be further secured, and the outer surface of the piston skirt 4 can be secured. Uniform lubricity between the cylinder inner wall surface 13 and the cylinder inner wall surface 13 can be more easily ensured. Moreover, the oil consumption can be further reduced.

  In each case (FIGS. 7 to 9), the wavy streak grooves 7 ... 7 are formed so as not to contact each other, so that the oil in the piston sliding direction (downward) is also formed. Omission can be further suppressed.

  That is, when the wavy streak grooves 7 ... 7 are in contact with each other, the spaces in the streak grooves 7 ... 7 communicate with each other. As a result, the oil movement path increases and the streak grooves 7 ... The oil in 7 is easily removed downward. On the other hand, if the wavy groove grooves 7... 7 are not in contact with each other, the space in the groove grooves 7... 7 does not communicate with the space in the other groove grooves 7. 4 becomes difficult to move from the groove grooves 7 ... 7 formed in the upper part of the groove 4 to the groove grooves 7 ... 7 formed in the lower part, so that the oil in the groove grooves 7 ... 7 falls out downward. It becomes difficult. As a result, the oil in the streak grooves 7... 7 can be further prevented from coming off, and from this point, the amount of oil retained in the streak grooves 7 can be further secured, and the piston skirt portion can be secured. Uniform lubricity between the outer surface 4 and the cylinder inner wall surface 13 can be more easily ensured. Moreover, the oil consumption can be further reduced.

  Further, when the plurality of groove grooves 7 ... 7 are crossed or merged so that the spaces in the groove grooves 7 ... 7 are communicated with each other, the grooves are formed at the intersection of the contacts. There are also disadvantages that the side walls of the grooves 7 ... 7 are broken and the cutting edge of the streak groove forming tool 50 is damaged.

  For example, 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 as in the present embodiment ( When the top portion 7a between the streak grooves 7 and 7 is formed into a flat plateau shape, the piston skirt portion 4 comes into sliding contact with the cylinder inner wall surface 13 on the surface. Therefore, the pressure per unit area acting on the top portion 7a between the streak grooves 7 and 7 is reduced by the sliding contact between the piston skirt portion 4 and the cylinder inner wall surface 13, thereby the top portion between the streak grooves 7 and 7 is reduced. 7a becomes hard to wear, the reduction of the maximum depth of the streak groove 7 is suppressed, and the decrease of the oil reservoir function of the streak groove 7 is suppressed.

  Although not shown, when the top 7a between the streak grooves 7 and 7 is formed into a flat plateau shape, a fine recess (micro dimple) may be formed in the plateau top portion 7a. Such fine recesses 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 can be controlled by adjusting the diameter and air pressure of the fine steel balls.

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

  In this case, the surface roughness of the top portion 7a in which the fine recesses are formed is a ten-point average roughness Rz (JIS B0601-1994), where Rz <the maximum depth of the streak groove 7. When Rz ≧ maximum depth of the streak groove 7, the friction coefficient reduction effect and the sliding resistance reduction effect due to the top 7 a between the streak grooves 7, 7 being made flat is reduced, and fine recesses are formed. Meaning disappears.

  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 said embodiment, although the cross-sectional shape of the streak groove 7 was U-shaped, it is not limited to this, V-shape, polygonal shape, etc. may be sufficient. Moreover, in the said embodiment, although the engine was a spark ignition type engine which uses gasoline as a fuel, it is not limited to this, The diesel engine etc. which have the high compression ratio which uses light oil as a fuel may be sufficient. Moreover, in the said embodiment, although the single streak groove 7 was formed in the outer surface of the skirt part 4 so that it might become spiral shape, it is not limited to this, The single streak groove 7 of the skirt part 4 is formed. It is formed so as to draw a circle along the outer surface, and 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 plurality of streak grooves 7 ... You may form so that the space | interval of 7 may become a predetermined pitch width. 7 to 9 may be mixed with the outer surface of the same single skirt portion 4.

  As described above in detail with reference to specific examples, the present invention provides an 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. A technology that can easily ensure uniform lubricity between the outer surface of the piston skirt and the inner wall surface of the cylinder by increasing the amount of oil retained in the groove and suppressing oil escape in the circumferential direction. Therefore, a wide range of industrial applicability is expected in the technical field of piston lubrication in sliding contact with the cylinder inner wall surface of the engine.

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 a side view of the piston. It is sectional drawing which follows the arrow III-III of FIG. It is a bottom view of the piston. It is a figure which shows the preferable ratio of the amplitude of a wavy streak groove | channel, and a wavelength, Comprising: (a) is about 1: 3.46, (b) is a case of 1: 2. It is explanatory drawing of the method of processing and forming a wavy streak groove so that the top part between the streak grooves adjacent to the skirt part of the said piston may become flat plateau shape. It is an enlarged view of the outer surface of the skirt part which shows 1st Embodiment of this invention which formed the streak groove | channel in the waveform. Enlarged view of the outer surface of the skirt portion showing the second embodiment of the present invention, in which the displacement portion toward the anti-piston head side of the wavy streak groove is positioned with the adjacent wavy streak grooves shifted from each other in the circumferential direction. It is. Of the wavy streak groove, the displacement part to the piston head side is positioned so as to be substantially coincided with the displacement part to the anti-piston head side of the adjacent wavy streak groove on the piston head side. Enlarged view of the outer surface of the skirt portion showing the third embodiment of the present invention, in which the displacement portion is positioned so as to substantially coincide with the displacement portion of the adjacent wavy streak groove on the anti-piston head side toward the piston head side in the circumferential direction. It is. It is explanatory drawing which shows a problem in case a streak groove is linear in the circumferential direction. It is explanatory drawing which illustrates some of the preferable specific aspects of the wavy streak groove in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 4 Skirt part 7 Wavy groove groove 7a Top part 10 between adjacent groove grooves Engine 13 Cylinder inner wall surface 50 Inner groove forming tool A Mountain part (displacement part to the piston head side)
B trough part (displacement part to the anti-piston head side)
Wp Top width between adjacent streak grooves

Claims (4)

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,
An engine piston, wherein the groove is formed in a wave shape. The piston of the engine according to claim 1,
A piston for an engine characterized in that a portion of the wavy streak groove that is displaced toward the side opposite to the piston head is positioned so as to be offset in the circumferential direction between adjacent wavy streak grooves. The piston of the engine according to claim 1,
Of the wavy groove groove, the displacement portion to the piston head side is positioned substantially coincident with the displacement portion to the anti-piston head side of the adjacent wavy groove groove on the piston head side, toward the anti-piston head side. A piston of an engine characterized in that a displacement portion of is located substantially in the circumferential direction with a displacement portion toward the piston head side of a wavy groove groove adjacent on the anti-piston head side. An engine piston according to any one of claims 1 to 3,
The piston of an engine, wherein the wavy groove grooves are not in contact with each other.

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