JP2005188303A - Piston structure of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely lower rigidity of a skirt part of a piston. <P>SOLUTION: In piston structure of an engine, the skirt part 1b continuous to a land part 1a in which an oil ring groove 4 is formed at a lowermost position of an outer periphery of a cylinder, and extending on a lower side in a piston sliding direction. A slit 5 is extended in a radial direction and a lower side of the oil ring groove 4, the wall thickness of the skirt part 1b under the slit 5 is thinner in a radial direction than the wall thickness forming the oil ring groove 4 above the slit 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine piston structure.

Conventionally, a piston is composed of a cylindrical land portion in which an oil ring groove or the like is formed, and a skirt portion extending continuously downward from the land in the piston sliding direction. The skirt portion is in contact with the inner peripheral surface of the cylinder liner and reciprocates in the vertical direction in the cylinder liner.
The skirt portion has a thick wall thickness in the vicinity of the land portion at the upper side and high rigidity, whereas the lower side is an open end, so that the rigidity is lower than the upper side.
Therefore, during the reciprocating motion of the piston, the upper side of the skirt portion is less distorted when the piston is pressed against the cylinder liner, and the contact area of the skirt portion with the cylinder liner is reduced. On the lower side, the distortion when the piston is pressed against the cylinder liner is large, and the contact area of the skirt portion with the cylinder liner is large, so that the sliding resistance is small. Therefore, there is a possibility that the lubricating oil film between the piston and the cylinder liner may be cut off on the upper side of the skirt portion, and it is necessary to reduce the rigidity on the upper side of the skirt portion to be equal to that on the lower side.

Moreover, since the top surface side of the piston is affected by heat from combustion, the temperature on the upper side becomes higher and the thermal expansion increases, and the sliding resistance increases. Therefore, in consideration of the thermal expansion, the clearance between the skirt portion and the cylinder liner is previously increased on the upper side of the skirt portion with respect to the lower side.
By the way, the piston is reciprocating while changing its posture during the reciprocating motion. In particular, immediately after the compression top dead center, the piston is urged against the thrust side in a thrust direction by the influence of the combustion pressure.
Therefore, when the clearance is provided as described above, the clearance above the skirt portion when the piston is inclined to the anti-thrust side becomes large and the momentum at the time of the posture change becomes large when the piston has a small thermal expansion. Therefore, there is a problem that a large slap sound is generated when pressed against the thrust side. Therefore, in order to suppress this slap sound, it is necessary to reduce the momentum at the time of posture change, and therefore, it is necessary to reduce the rigidity of the entire skirt portion.

Therefore, Patent Document 1 below discloses a piston structure in which a slit is formed in the oil ring groove.
According to such Patent Document 1, the rigidity of the skirt portion, in particular, the rigidity on the upper side of the skirt portion can be reduced, and sliding resistance and slap noise can be reduced.

Japanese Utility Model Publication No. 6-14454

However, according to the above-mentioned Patent Document 1, since the slit is formed in the oil ring groove, the following problem may occur.
That is, the oil ring groove has a problem that the rigidity reduction effect is low even if a slit is formed because the wall thickness of the piston is originally high and the rigidity is high.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an engine piston structure capable of reliably reducing the rigidity of the skirt portion.

  In order to achieve the above object, the present invention provides the following solution as a solution. That is, in the first configuration of the present invention, the piston structure of an engine having a skirt portion extending continuously downward in the piston sliding direction in a land portion where an oil ring groove is formed at the lowest position on the outer periphery of the cylinder. A slit extending in the radial direction below the oil ring groove is formed, and a wall thickness of the skirt portion below the slit is set to a wall thickness forming the oil ring groove above the slit. Thus, it is configured to be thin in the radial direction.

According to the first configuration of the present invention, the slit extending in the radial direction is formed at a location below the oil ring groove and having a wall thickness thinner than the wall thickness of the land portion where the oil ring groove is formed. Therefore, the continuity between the land portion and the skirt portion is interrupted by the slit, and the separated shape is obtained, so that the rigidity of the entire skirt portion can be reliably reduced.
In addition, the wall thickness of the piston is normally formed to be the thickest at the land portion, continuously decreased from the land portion to the skirt portion, and then formed to have a uniform wall thickness at the skirt portion. Even if the slit is formed below the ring groove, there is a possibility that a thick portion in the middle of continuously reducing the wall thickness remains below the slit and the rigidity cannot be sufficiently reduced.
According to the first configuration of the present invention, the wall thickness of the skirt portion below the slit is formed to be thin in the radial direction with respect to the wall thickness forming the oil ring groove above the slit, that is, the skirt portion. Since the wall thickness on the upper side of the skirt is reduced, the rigidity above the skirt can be reliably reduced, and the rigidity of the entire skirt can be reduced, so that the sliding resistance of the skirt can be reduced, Slap noise can be suppressed.

  In the second configuration of the present invention, the skirt portion is formed in a barrel profile shape, while the slit is more than the center position of the piston pin boss portion into which the piston pin is inserted when viewed in the height direction of the piston. The top of the barrel profile of the skirt portion is configured to be set at a height position substantially equal to the center position of the piston pin boss portion.

According to the second configuration of the present invention, since the continuity between the land portion and the skirt portion is interrupted by the slit and separated, the influence of heat transfer from the land portion to the skirt portion is suppressed. The difference in thermal expansion between the upper side and the lower side of the skirt portion is reduced. As a result, the difference in the profile of the skirt portion due to thermal expansion becomes small between the warm time and the cold time, so that the same skirt profile as that in the warm time can be set even in the cold time.
Therefore, the apex of the barrel profile of the skirt part can be set to a height position substantially equal to the center position of the piston pin boss part, and the piston pin boss that becomes the center to which a load is applied when the posture changes from the opposite thrust side to the thrust direction Since the clearance between the center position of the portion and the apex of the barrel profile can be reduced, the slap noise can be more reliably reduced.

  In the third configuration of the present invention, the outer dimension of the land part forming the oil ring groove directly above the slit is the outer dimension of the skirt part below the slit as seen in a state where the temperature in the vicinity of the piston is high and thermally expanded. It is configured to be set smaller than the dimension.

If the continuity between the land part and the skirt part is interrupted by the slit and separated, the thermal expansion amount of the land part becomes very large with respect to the skirt part, and the outer shape of the land part is larger than the outer shape of the skirt part. There is a possibility that the land portion may come into contact with the cylinder liner when it is warm.
According to the third configuration of the present invention, the outer dimension of the land part that forms the oil ring groove immediately above the slit is larger than the outer dimension of the skirt part below the slit when viewed in a state where the temperature in the vicinity of the piston is high and thermally expanded. Therefore, it is possible to prevent the land from becoming larger than the skirt portion even if it is thermally expanded, and to prevent the land portion from contacting the skirt portion.

  According to the 4th structure of this invention, the said slit is comprised so that it may straddle between the side walls which each connect the said skirt part and the both ends of the piston pin boss | hub part formed in the said skirt part inside.

Since the piston repeats deformation by repeatedly contacting the cylinder liner accompanying the reciprocating motion, the stress due to the repetition of the deformation concentrates on the slit end, and there is a possibility that a crack may occur at the slit end.
According to the fourth configuration of the present invention, both ends of the slit are extended to the side wall connecting the skirt portion and the piston pin boss portion inside thereof, so that both ends of the slit have a thick wall thickness. It will be located in a highly rigid side wall, the generation of cracks can be suppressed, and the durability can be improved.

  According to the present invention, the rigidity of the skirt portion can be reliably reduced, and sliding resistance and slap noise can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
1 is a front view of a piston relating to the first embodiment, FIG. 2 is a side view of the piston, FIG. 3 is a sectional view of the main part of the piston, and FIG.
1 and 2, 1 is a piston made of, for example, an aluminum alloy for a gasoline engine, and the piston 1 includes piston ring grooves 2, 3 into which piston rings (not shown) are respectively fitted. An oil ring groove 4 into which an oil ring (not shown) is inserted is composed of a land portion 1a formed on the outer periphery of the cylinder, and a skirt portion 1b extending from the land portion 1a to the lower side in the piston sliding direction. Has been.
A slit 5 extending in the radial direction is formed below the oil ring groove 4.
Reference numeral 6 denotes a piston pin boss portion into which a piston pin (not shown) for connecting the piston 1 and a connecting rod (not shown) is inserted.

Further, as shown in FIG. 3, the wall thickness of the land portion 1a of the piston 1 is formed so that the wall thickness is gradually reduced from the top side toward the slit 5 above the skirt portion 1b.
Further, the wall thickness of the skirt portion below the slit 5 is formed at t1 which is sharply reduced with respect to the wall thickness forming the oil ring groove 4 above the slit, and the skirt portion 1a extends from the upper side to the lower side. The wall thickness is constant at t1.
That is, in the prior art, as indicated by a two-dot chain line in FIG. 3, the wall thickness is gradually reduced from the land portion 1b to the skirt portion 1a. The wall thickness is increased, and the rigidity on the upper side of the skirt cannot be sufficiently reduced.
On the other hand, in the present embodiment, the wall thickness below the slit 5 is formed at t1 that is sharply thinner than the wall thickness above the slit, so that the rigidity on the upper side of the skirt portion 1b can be sufficiently reduced. It is said that.

Further, the skirt portion 1b is formed in a so-called barrel profile shape in which the central portion in the height direction of the piston is curved and convex toward the cylinder liner (not shown) with respect to the upper and lower ends, and FIG. As shown in an enlarged view of the profile, the vertex 7 of the barrel profile is formed so as to be substantially perpendicular to the cylinder axis L1 and on the center line L2 passing through the center position of the piston pin boss portion 6.
In other words, in the conventional case, as indicated by a two-dot chain line in FIG. 4, the clearance T1 with the cylinder liner 8 above the skirt portion 1b is set in consideration of the thermal expansion above the skirt portion 1b in the warm state. Therefore, it is necessary to set a large value with respect to the clearance T2 on the lower side. For this reason, the slap noise is generated when the piston 1 is tilted by the clearance T1 when cold.
On the other hand, in the present embodiment, the continuity between the land portion 1a and the skirt portion 1b is interrupted by the slit 5, and heat transfer from the land portion to the skirt portion is suppressed. The profile of the skirt portion 1b can be set to an optimum shape without considering the difference in thermal expansion amount.
That is, the skirt portion 1b is formed in a barrel profile shape, and the apex 7 of the barrel profile is formed so as to be substantially perpendicular to the cylinder axis L1 and on the center line L2 passing through the center position of the piston pin boss portion 6. Therefore, since the clearance between the center position of the piston pin boss portion 6 which is a center to which a load is applied when the posture is changed from the anti-thrust side to the thrust direction and the apex 7 of the barrel profile can be reduced, the slap sound is further reduced in the cold state It is possible to suppress.

As described above, according to the first embodiment, the slit 5 that extends in the radial direction below the oil ring groove 4 at a location where the wall thickness is thinner than the wall thickness of the land portion where the oil ring groove is formed. Therefore, the continuity between the land portion 1a and the skirt portion 1b is interrupted by the slit 5, and the separated shape is obtained, so that the rigidity of the entire skirt portion 1b can be reliably reduced.
Further, the wall thickness of the skirt portion 1b below the slit 5 is formed to be t1 which is thin in the radial direction with respect to the wall thickness forming the oil ring groove 4 above the slit 5, that is, on the upper side of the skirt portion 1b. Since the wall thickness is reduced, the rigidity above the skirt portion 1b can be reliably reduced, and the rigidity of the entire skirt portion 1b can be reduced, so that the sliding resistance of the skirt portion 1b can be reduced and the slap can be reduced. Sound can be suppressed.
Further, since the continuity between the land portion 1a and the skirt portion 1b is interrupted by the slit 5, and the shape is separated, the influence of heat transfer from the land portion 1a to the skirt portion 1b is suppressed, and the skirt portion 1b The difference in thermal expansion between the upper side and the lower side is reduced. As a result, since the difference in the profile of the skirt portion 1b due to thermal expansion is small between the warm time and the cold time, the same profile of the skirt portion 1b can be set even during the cold time. it can. Therefore, the apex 7 of the barrel profile of the skirt portion 1b can be set to a height position substantially equal to the center position of the piston pin boss portion 6, and the center to which a load is applied when the posture is changed from the opposite thrust side to the thrust direction. Since the clearance between the center position of the piston pin boss portion 6 and the apex 7 of the barrel profile can be reduced, the slap noise can be more reliably reduced.

Next, specific effects of this embodiment will be described with reference to FIGS.
FIG. 5 is a diagram showing a state of the stiffness test of the skirt portion 1b, and FIG. 6 is a graph showing a comparison of the stiffness test results of the skirt portion 1b. In FIG. 6, the graph indicated by ▲ indicates that the slit 5 is formed below the oil ring groove 4, the graph indicated by ● indicates that the slit 5 is formed in the oil ring groove 4, and the graph indicated by ■ indicates the slit 5. The characteristic when not forming is shown.

As shown in FIG. 5, in order to test the rigidity of the skirt portion 1b, the piston 1 is fixed to the base 10 of the test apparatus, and a constant load, for example, 245N is applied to the skirt portion 1b by the load applying portion 12, and at that time The displacement amounts at the four points of the skirt portion 1b are measured.
In this test, when the slit 5 is formed below the oil ring groove 4 (that is, equivalent to the first embodiment), when the slit 5 is formed in the oil ring groove 4 (that is, equivalent to Patent Document 1). , And three different pistons without the slit 5 being tested respectively.
As a result, as shown in FIG. 6, in any case, the distance from the oil ring groove 4 is short, that is, the upper side of the skirt portion 1b is long, and the distance from the oil ring groove 5 is long, that is, the lower side of the skirt portion 1b. On the other hand, it was confirmed that the displacement amount was large and the rigidity was high.
Further, as apparent from FIG. 6, when the slit 5 is formed below the oil ring groove 4 among the three pistons, the displacement amount on the upper side of the skirt portion 1b is the largest, and the upper side and the lower side of the skirt portion 1b. It was confirmed that the difference in stiffness from the side was reduced.

(Embodiment 2)
Next, Embodiment 2 will be described.
As in this embodiment, when the continuity between the land portion 1a and the skirt portion 1b is interrupted by the slit 5 and separated, the thermal expansion amount of the land portion 1a becomes very large with respect to the skirt portion 1b. The outer shape of the land portion 1a is larger than the outer shape of the skirt portion 1b, and the land portion 1a may come into contact with the cylinder liner when warm.
Therefore, in the second embodiment, in order to cope with this problem, the outer dimensions of the land portion 1a that forms the oil ring groove 5 immediately above the slit 5 are set below the slit 5 in a state where the temperature of the piston 1 is high and thermally expanded. This is set to be smaller than the outer dimension of the skirt portion 1b, and this point differs from the first embodiment.
Hereinafter, differences will be described with reference to FIG.

  FIG. 7 is an enlarged cross-sectional view of the main part of the piston 1 relating to the second embodiment, and the outer dimensions forming the wall thickness on the lower side 4 of the oil ring groove immediately above the slit 5 are high in the temperature of the piston 1. It is set to be smaller by t2 than the outer dimension of the skirt portion 1b on the lower side of the slit 5 in the thermally expanded state.

  Therefore, according to the second embodiment, the outer dimension of the land portion 1a that forms the oil ring groove 4 directly above the slit 5 is the skirt portion 1b below the slit 5 when viewed in a state where the temperature in the vicinity of the piston 1 is high and thermally expanded. Therefore, even if it thermally expands, it is suppressed from becoming larger than the skirt portion 1b, and the contact of the land portion 1a with the skirt portion 1b can be suppressed.

(Embodiment 3)
Next, Embodiment 3 will be described.
According to the present embodiment, the piston 1 is repeatedly deformed by repeating contact with the cylinder liner accompanying the reciprocating motion. Therefore, stress due to repeated deformation is concentrated on the end of the slit 5, and the end of the slit 5 is There is a risk of cracking.
Therefore, in the third embodiment, in order to cope with this problem, the slit 5 is configured to straddle between the sidewalls 9 that connect the skirt portion 1b and both ends of the piston pin boss portion 6 formed inside the skirt portion 1b. This point is different from the first and second embodiments.
Hereinafter, differences will be described with reference to FIGS. 8 and 9.

  8 is a side view of the piston 1 relating to the third embodiment, and FIG. 9 is a cross-sectional view taken along the line AA of FIG. 8, and as shown in FIGS. 8 and 9, the slit 5 includes a skirt portion 1b and its skirt portion 1b. It extends so that it may straddle between the side walls 9 which connect the both ends of the piston pin boss portion 6 formed inward.

  Therefore, according to the third embodiment, both ends of the slit 5 extend to the side wall 9 that connects the skirt portion 1b and the piston pin boss portion 6 inside thereof, so that both ends of the slit 5 It will be located in the sidewall 9 having a large thickness and high rigidity, so that the occurrence of cracks can be suppressed and the durability can be improved.

(Modification of Embodiment 3)
Moreover, as shown in FIGS. 10 and 11, both ends of the slit 5 may be further extended so as to extend until reaching the outer periphery of the skirt portion 1b. Similar to the embodiment shown in FIG. 6, both ends of the slit 5 are positioned on the sidewall 9 having a thick wall and a high rigidity, so that the occurrence of cracks can be suppressed and the durability can be improved.

By the way, it is known to apply an oil cooling system that injects and supplies oil to the back surface of the piston 1 for cooling the piston 1. In the case of forming the slit 5 in the piston provided with the oil cooling system, the above-described case is used. As disclosed in Patent Document 1, when the oil ring is formed in the oil ring groove 4, the supplied oil is supplied into the combustion chamber from the back surface of the oil ring through the slit 5, and the oil consumption may be deteriorated.
On the other hand, in the present embodiment, since the slit 5 extending in the radial direction is formed below the oil ring groove 4, the oil consumption is deteriorated in the piston 1 provided with the oil cooling system described above. Can be suppressed.

  In the present embodiment, an example of a piston 1 for a gasoline engine is shown, but the present invention can also be applied to a piston for a diesel engine.

The piston front view concerning Embodiment 1 of the present invention. The piston side view concerning Embodiment 1 of the present invention. FIG. 3 is a cross-sectional view of a main part of the piston according to the first embodiment of the present invention. Explanatory drawing explaining the shape of the piston skirt part which concerns on Embodiment 1 of this invention. The figure which shows the state of the rigidity test of a piston skirt part. The graph which shows the comparison state of the rigidity test result of a piston skirt part. Sectional drawing of the principal part of the piston which concerns on Embodiment 2 of this invention. The side view of the piston which concerns on Embodiment 3 of this invention. The AA sectional view concerning Embodiment 3 of the present invention. The side view of the piston which concerns on the modification of Embodiment 3 of this invention. BB sectional drawing concerning the modification of Embodiment 3 of this invention.

Explanation of symbols

1: Piston 1a: Land 1b: Skirt 4: Oil ring groove 5: Slit 6: Piston pin boss 7: Top of barrel profile 8: Cylinder liner 9: Side wall

Claims (4)

In the piston structure of the engine having a skirt portion extending continuously downward in the piston sliding direction in a land portion where an oil ring groove is formed at the lowest position on the outer periphery of the cylinder,
A slit extending in the radial direction is formed below the oil ring groove, and
A piston structure for an engine, wherein a wall thickness of a skirt portion below the slit is formed to be thinner in a radial direction than a wall thickness forming the oil ring groove above the slit. While the skirt is formed in a barrel profile,
The slit is formed above the center position of the piston pin boss portion into which the piston pin is inserted as viewed in the height direction of the piston, and the apex of the barrel profile of the skirt portion is the center of the piston pin boss portion. 2. The piston structure for an engine according to claim 1, wherein the piston structure is set to a height position substantially equal to the position.   The land dimension that forms the oil ring groove directly above the slit is set to be smaller than the dimension of the skirt part below the slit in a state where the temperature of the piston is high and thermally expanded. The piston structure of the engine according to claim 1 or 2.   The said slit is extended so that it may straddle between the side walls which each connect the said skirt part and the both ends of the piston pin boss | hub part formed in the said skirt part inside, The Claim 1 thru | or 3 characterized by the above-mentioned. The piston structure of the engine according to one.

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