JP6642256B2 - piston - Google Patents

Description

  The present invention relates to a piston, and more particularly to a piston having a striation on a piston skirt.

  Conventional pistons having improved lubricity by providing a plurality of striations on the outer peripheral surface of the piston skirt are disclosed in, for example, JP-A-2008-232172 (Patent Document 1) and JP-A-2011-220267 (Patent Document 2). ), And Japanese Patent Application Laid-Open No. 10-103511 (Patent Document 3).

  Patent Document 1 discloses a configuration in which, in a piston skirt having a plurality of striations formed on an outer peripheral surface, a flat surface is provided between adjacent striations, and when a thrust force acts on the piston, the flat surface receives the thrust force. Have been.

  Patent Literature 2 discloses a piston in which a plurality of projections having an arc-shaped cross section are formed on the outer peripheral surface of a piston skirt in order to secure a wide sliding area when reciprocating in a cylinder bore.

  Patent Literature 3 discloses a piston in which a tapered circumferential groove having a divergent cross section is formed in multiple stages on an outer peripheral surface of a piston skirt, and a flat portion is formed between adjacent circumferential grooves.

JP 2008-232172 A JP 2011-220267 A JP-A-10-103511

  In an internal combustion engine having a piston that reciprocates in a cylinder bore, the timing at which the sliding friction loss between the piston and the cylinder bore wall (hereinafter also referred to as the bore wall) becomes largest is in the first half of the expansion stroke. This is because the piston explodes in the combustion chamber and receives a large thrust load and is pressed against the bore wall. Therefore, if the frictional force on the sliding surface between the piston and the cylinder bore can be reduced in the first half of the expansion stroke, that is, in the early stage of the piston descending stroke, the friction work in one cycle can be reduced.

  Then, this invention is made in order to solve the said subject, and an object of this invention is to provide the piston which can reduce the sliding friction loss at the time of a piston lowering.

  The piston according to the present invention is a piston that slides on the inner surface of a cylinder bore of an internal combustion engine via lubricating oil, and the piston has a piston skirt, and at least a thrust-side piston skirt of the piston skirt. A plurality of striations extending in the circumferential direction of the piston skirt are provided on the outer peripheral surface, and the plurality of striations are two corners arranged at a distance from each other along the reciprocating motion direction of the piston. And a lubricating oil holding groove provided between the two corners to hold the lubricating oil, and an inclined portion disposed adjacent to an end of the lubricating oil holding groove on the piston ascending direction. The inclination angle is more than 0 ° and not more than 6 ° with respect to a straight line connecting the two corners so as to become farther from the inner surface of the cylinder bore as approaching the lower end of the piston skirt.

  In the piston configured as described above, the sliding friction loss between the piston skirt and the cylinder bore wall can be reduced by the wedge effect (dynamic pressure effect). Specifically, lubricating oil is held in the lubricating oil holding groove. When the piston descends, the lubricating oil in the lubricating oil holding groove flows into a narrow space formed between the inclined portion and the cylinder bore wall. Pressure is generated in the space, and the piston is brought into a fluid lubrication state in which the piston is lifted from the cylinder bore wall. This phenomenon is called a wedge effect (dynamic pressure effect) because the location where the lubricating oil enters is shaped like a wedge. That is, kinetic energy is imparted to the lubricating oil by utilizing the movement of the inclined portion of the piston skirt with respect to the cylinder bore wall, and the kinetic energy enables the fluid lubrication state to be maintained between the cylinder bore wall and the piston skirt. .

  Preferably, the inclination angle is 1 ° or more and 3 ° or less. In this case, the dynamic pressure effect can be maximized.

  Preferably, the lubricating oil holding groove has a groove having an arc-shaped cross section. In this case, since the cross-sectional shape of the lubricating oil holding groove is an arc shape, the lubricating oil flows smoothly from the lubricating oil holding groove to the inclined portion. The “arc shape” means that the roundness / radius of the arc is 10% or less. The roundness is measured by a roundness measuring instrument of JIS B7451: 1997.

  Preferably, the plurality of streaks are provided continuously, and the lubricating oil holding groove of another streak is provided adjacent to an end of the inclined portion of the one stride in the piston ascending direction. Further, since the streaks are provided continuously, many inclined portions can be formed. As a result, a greater dynamic pressure effect can be obtained in the piston lowering step.

  According to the present invention, a dynamic pressure effect can be generated by the piston skirt in the piston lowering process. As a result, frictional work between the piston skirt and the bore wall can be reduced.

FIG. 2 is a front view including a partial cross-sectional view of the piston according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of a piston enlarged and showing a portion surrounded by II in FIG. 1 and a bore wall facing the piston. It is sectional drawing which expands and shows one streak in FIG. 4 is a graph showing the relationship between the inclination angle θ of the inclined portion and the amount of lubricating oil scraped off by the corner when the piston descends. 6 is a graph showing the relationship between the inclination angle θ of the inclined portion and the dynamic pressure generated between the inclined portion and the bore wall when the piston descends. 4 is a graph showing a relationship between a crank angle and a piston speed of a reciprocating engine. FIG. 3 is a schematic diagram illustrating a force applied to a piston in an expansion process of a reciprocating engine. FIG. 10 is a cross-sectional view showing a striation provided on a piston according to a second embodiment and a bore wall. FIG. 14 is a cross-sectional view showing a striation provided on a piston according to a third embodiment and a bore wall. FIG. 14 is a cross-sectional view showing a striation provided on a piston according to a fourth embodiment and a bore wall.

  Hereinafter, a piston according to each embodiment of the present invention will be described with reference to the drawings. In the following description, the same or corresponding portions in the drawings have the same reference characters allotted, and description thereof will not be repeated. Further, it is also possible to combine the embodiments.

(Embodiment 1)
FIG. 1 is a front view including a partial cross-sectional view of a piston according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of a piston and a bore wall facing the piston, which are enlarged and show a portion surrounded by II in FIG.

  As shown in FIG. 1, the piston 10 has a land 12 and a piston skirt 14. The land 12 is provided with piston ring grooves 11a and 11b and an oil ring groove 11c. The piston 10 is provided with a through hole 13 for inserting a piston pin. The piston 10 may be for a diesel engine or a gasoline engine. Further, the piston 10 may be either an engine for directly injecting fuel into a cylinder or an engine for injecting fuel in an intake port. In FIG. 1, a hatched portion of the piston skirt 14 shows a cross section of the piston skirt 14. The arrow 10u indicates the upward direction of the piston 10. The arrow 10d indicates the downward direction of the piston 10. The piston 10 reciprocates within the cylinder bore in directions indicated by arrows 10u and 10d. The upward direction is a direction in which the piston 10 approaches the combustion chamber, and the downward direction is a direction in which the piston 10 approaches the crankshaft.

  FIG. 2 virtually illustrates the bore wall 101 facing the piston 10. As shown in FIG. 2, a plurality of striations 21 are provided on the piston skirt 14. Each striation 21 has an inclined portion 26 and a groove 27 connected to the inclined portion 26. The inclined portion 26 is inclined with respect to the straight line 25 in the cross section shown in FIG. A straight line 25 connects one corner 28 to another corner 28. In one streak 21, the inclined portion 26 is located on the upper side (side indicated by the arrow 10u), and the groove 27 is located on the lower side (side indicated by the arrow 10d). A corner 28 is located between each of the striations 21.

  In this embodiment, a plurality of striations 21 are provided continuously. That is, another streak 21 is provided adjacent to one streak 21. However, the plurality of striations 21 need not always be provided continuously. A shape (for example, a flat surface) other than the streak 21 may be provided so as to be adjacent to a certain streak 21, and another streak 21 may be provided so as to be adjacent to the flat surface.

  FIG. 3 is a cross-sectional view showing one streak in FIG. 2 in an enlarged manner. FIG. 4 is a graph showing a relationship between the inclination angle θ of the inclined portion and the amount of lubricating oil scraped off by the corner when the piston descends. When the piston 10 descends, the amount by which the corner 28 scrapes off the lubricating oil on the bore wall 101 changes depending on the inclination angle θ formed by the inclined portion 26 with respect to the central axis 10c. If the inclination angle θ is small, the amount by which the corner portion 28 scrapes off the lubricating oil decreases. If the inclination angle θ is 6 ° or less, the oil film can be held. When the inclination angle θ exceeds 6 °, the amount by which the lubricating oil of the bore wall 101 is scraped off by the corner 28 becomes too large.

  A boundary 26a between the inclined portion 26 and the groove 27 is provided below the inclined portion 26. At the boundary 26a, the slopes of the slope 26 and the groove 27 change discontinuously. The slope 26 is located above the boundary 26a (in the direction indicated by the arrow 10u).

  A groove 27 having an arc-shaped cross section is provided below the inclined portion 26, that is, below the boundary portion 26a. The arc-shaped groove 27 does not generate a dynamic pressure on the piston 10 in the process of raising the piston 10 like the inclined portion 26, but the thrust load due to the explosion process is generated in the process of raising the piston 10 in the first place. There is no need to generate dynamic pressure.

  The streak 21 has a substantially arc-shaped groove 27 and a substantially straight inclined portion 26. The upper end of the inclined portion 26 is closer to the bore wall 101 than the lower end, and the angle θ formed with the straight line 25 is more than 0 ° and 6 ° or less. The groove 27 and the inclined portion 26 are alternately repeated. One streak 21 is provided between two corners 28.

  The piston skirt 14 of the piston 10 is provided with at least one streak 21 extending in a circumferential direction of the piston skirt 14 (a direction along a direction in which the piston ring grooves 11a and 11b extend). Has a slope 26 at a cross section parallel to the reciprocating direction of the piston 10, and the slope 26 is positioned at an angle with respect to the center axis 10c of the piston 10 so as to approach the center axis 10c of the piston 10 as approaching the lower part of the piston skirt 14. Has an inclination angle θ exceeding 6 ° and 6 ° or less.

  At least on the outer peripheral surface of the piston skirt 14 on the thrust side of the piston skirt 14, a plurality of striations 21 extending in the circumferential direction of the piston skirt 14 are provided. Two corners 28 arranged at a distance from each other along the groove, a groove 27 provided between the two corners 28 as a lubricating oil holding groove for holding lubricating oil, and a piston ascending direction side of the groove 27 And an inclined portion 26 disposed adjacent to the end. The inclined portion 26 is more than 0 ° and not more than 6 ° with respect to the straight line 25 connecting the two corners 28 so as to be further away from the bore wall 101 as the inner surface of the cylinder bore as approaching the lower end of the piston skirt 14. Of the inclination angle θ.

  FIG. 5 is a graph showing the relationship between the inclination angle θ of the inclined portion and the dynamic pressure generated between the inclined portion and the bore wall when the piston descends. As shown in FIG. 5, when the inclination angle θ of the inclined portion 26 is changed, the dynamic pressure generated in the inclined portion 26 changes. If the inclination angle θ is more than 0 ° and not more than 6 °, it is understood that sufficient dynamic pressure is generated. It can be seen that when the inclination angle θ is 1 ° or more and 3 ° or less, a larger dynamic pressure is generated.

  FIG. 6 is a graph showing the relationship between the crank angle and the piston speed of the reciprocating engine. FIG. 7 is a schematic diagram showing a force applied to a piston in an expansion process of the reciprocating engine. As shown in FIGS. 6 and 7, the speed of the piston 10 changes according to the crank angle. The piston 10 moves up and down (reciprocating motion) within the cylinder 101. A piston pin 15 is inserted into a through hole 13 of the piston 10. A connecting rod 16 is rotatably attached to the piston pin 15. The connecting rod 16 is connected to the crankshaft 17b by a bearing 17a.

  When the crank angle in FIG. 6 is 0 °, the piston 10 is located at the top dead center. In the expansion stroke (when the crank angle is 0 ° or later), the piston 10 is pushed downward by receiving a force from the direction indicated by the arrow 10a. At this time, this reaction force, which receives a reaction force in the direction indicated by arrow 13a from the connecting rod 16, is decomposed into a first component indicated by arrow 13b and a second component indicated by arrow 13c. The piston 10 is pressed toward the thrust by the action of the first component. Further, when it descends, it rotates in the direction shown by arrow 10r.

  By providing the inclined portion 26 in FIGS. 2 and 3, when the piston 10 moves downward, the dynamic pressure shown in FIG. 5 is generated between the inclined portion 26 and the bore wall 101. As a result, the fluid lubrication is maintained between the piston 10 and the bore wall 101, so that the frictional force is reduced as compared with the case where boundary lubrication is performed. Thereby, fuel efficiency can be improved.

  More specifically, the groove 27 holds the lubricating oil and prevents seizure. By providing the inclined portion 26, when the piston 10 approaches the lowering step, a dynamic pressure is generated between the inclined portion 26 and the bore wall 101 by a wedge effect. Therefore, the lubricating state of the piston skirt 14 can be shifted from boundary lubrication to fluid lubrication in a short time at the start of the descending step, as compared with a piston having no inclined portion 26. As a result, friction work can be reduced.

  In the expansion stroke, the piston 10 is pushed downward by receiving the explosion pressure (arrow 10a) of the combustion chamber as shown in FIG. At this time, the thrust component (arrow 13b) of the reaction force received from the connecting rod 16 pushes the piston toward the thrust while rotating clockwise (arrow 10r). Since it descends while being pressed, greater friction is more likely to occur in the expansion stroke than in other strokes. However, the generation of friction can be suppressed by the dynamic pressure effect in the inclined portion 26. Further, the speed of the piston is 0 at the top dead center of the crank angle of 0 ° in FIG. 6 and accelerates from there. Since a large thrust load is applied near the top dead center at a low speed, the oil film on the piston skirt 14 and the bore wall 101 becomes thin, and boundary lubrication tends to occur. The transition from boundary lubrication to fluid lubrication can be achieved early due to the dynamic pressure effect at the inclined portion 26.

  In other words, by employing the above configuration, the lubrication state of the piston skirt 14 can be shifted from boundary lubrication to fluid lubrication in a shorter time than in a conventional piston. As a result, frictional work (loss) is reduced, and it is possible to improve thermal efficiency, reduce fuel consumption, and improve output and torque.

  Further, in terms of reliability, the effect of reducing the wear of the piston skirt 14 and the wear of the bore wall 101 can be obtained.

(Embodiment 2)
FIG. 8 is a cross-sectional view showing striations provided on a piston according to the second embodiment and a bore wall. As shown in FIG. 8, in the piston skirt 14 of the piston 10 according to the second embodiment, the inclined portion 126 has a curved section in a cross section parallel to the reciprocating direction of the piston in FIG. A boundary 126a with the part 126 is an inflection point. Before and after the boundary part 126a, the inclination of the inclined part 126 and the groove 127 changes continuously.

  The upper side (the side of the arrow 10u) from the boundary 126a is the inclined portion 126, and the inclination angle θ of the inclined portion 126 with respect to the straight line 25 is more than 0 ° and 6 ° or less. The piston 10 configured as described above has the same effect as the piston 10 of the first embodiment.

(Embodiment 3)
FIG. 9 is a cross-sectional view showing striations provided on a piston according to Embodiment 3 and a bore wall. As shown in FIG. 9, the piston skirt 14 of the piston 10 according to the third embodiment has a straight portion with an inclined portion 26 in a cross section parallel to the reciprocating direction of the piston in FIG. The boundary 26a between the inclined portion 26 and the groove 27 is smoothly inclined. That is, at the transition from the inclined portion 26 to the groove 27, the inclination of the inclined portion 26 and the groove 27 continuously changes.

  The upper side (the side of the arrow 10u) from the boundary 126a is the inclined portion 126, and the inclination angle θ of the inclined portion 126 with respect to the straight line 25 is more than 0 ° and 6 ° or less. The piston 10 configured as described above has the same effect as the piston 10 of the first embodiment.

(Embodiment 4)
FIG. 10 is a cross-sectional view showing striations provided on a piston according to Embodiment 4 and a bore wall. As shown in FIG. 10, the piston skirt 14 of the piston 10 according to the fourth embodiment has a groove 27 having a straight portion in a cross section parallel to the reciprocating direction of the piston in FIG.

  The upper side (the side of the arrow 10u) from the boundary 126a is the inclined portion 126, and the inclination angle θ of the inclined portion 126 with respect to the straight line 25 is more than 0 ° and 6 ° or less. The straight portion of the groove 27 starts from the boundary 26a. The piston 10 configured as described above has the same effect as the piston 10 of the first embodiment.

  It is also possible to configure the piston skirt 14 by combining at least two striations of the first to fourth embodiments.

  Although the embodiments have been described above, the above disclosure is illustrative in all aspects and is not restrictive. The technical scope of the present invention is defined by the appended claims, and is intended to include any modifications within the scope and meaning equivalent to the appended claims.

  The present invention can be used, for example, in the field of an internal combustion engine mounted on a vehicle.

  Reference Signs List 10 piston, 10c central shaft, 11a, 11b piston ring groove, 11c oil ring groove, 12 land, 13 through hole, 14 piston skirt, 15 piston pin, 16 connecting rod, 17a bearing, 17b crankshaft, 21 streak, 25 Straight line, 26, 126 slope, 26a, 126a boundary, 27 groove, 28 corner, 101 bore wall.

Claims (3)

A piston that slides on the inner surface of a cylinder bore of an internal combustion engine via lubricating oil,
The piston has a piston skirt,
At least an outer peripheral surface of the piston skirt on the thrust side of the piston skirt is provided with a plurality of striations extending in a circumferential direction of the piston skirt,
The plurality of striations are respectively provided at two corners spaced apart from each other along a reciprocating direction of the piston, and a lubricating oil provided between the two corners to hold lubricating oil A retaining groove, an inclined portion disposed adjacent to the piston rising direction side end of the lubricating oil retaining groove, and a boundary portion in which the inclination of the lubricating oil retaining groove and the inclined portion changes discontinuously ,
The inclined portion, the so mow remoteness from the inner surface of the cylinder bore as the piston approaches the downward direction end portion of the skirt, have a tilt angle of 6 ° or less than 0 ° but with respect to a straight line connecting the two corners ,
The piston, wherein the lubricating oil holding groove has a groove having a circular cross section .   The piston according to claim 1, wherein the inclination angle is 1 ° or more and 3 ° or less.   The plurality of streaks are provided continuously, and the lubricating oil holding groove of another streak is provided adjacent to an end of the inclined portion of the one stride in the piston ascending direction. A piston according to claim 1 or claim 2.

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