JP2004308568A - Piston for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston for an internal combustion engine effectively reducing and eliminating both of deterioration of assemblability and interference of a piston ring and a ring groove bottom surface due to back clearance. <P>SOLUTION: A ring groove 16 in which the piston ring is fitted is provided on an outer circumference of the piston 10. The grove bottom surface 18 of the ring groove 16 is made in an ellipse shape having an major axis in a thrust-anti thrust direction F2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piston for an internal combustion engine used in an automobile or the like, and more particularly to an improvement in a ring groove in which a piston ring is fitted.
[0002]
[Prior art]
As described in Patent Literature 1 and the like, a ring groove into which a piston ring is fitted is recessed on the outer periphery of a piston of an internal combustion engine. Generally, the inner peripheral surface of the piston ring and the groove bottom surface of the ring groove are both set to be substantially circular, and the back clearance between the two is set to be a constant value over the entire circumference.
[0003]
[Patent Document 1]
JP 2000-205508 A
[Problems to be solved by the invention]
If the back clearance is too large, the piston ring may jump out of the ring groove when assembling the piston with the piston ring attached to the cylinder. There is.
[0005]
If the back clearance is too small, the piston temperature increases during operation of the internal combustion engine, and when the diameter of the groove bottom of the ring groove increases due to thermal expansion, the inner peripheral surface of the piston ring and the groove bottom of the ring groove are separated. Interference may cause problems such as early wear.
[0006]
The present invention has been made in view of such a problem, and is a novel technique that can effectively reduce and eliminate both the decrease in assemblability due to the back clearance and the interference between the piston ring and the ring groove bottom. It is an object to provide a piston for an internal combustion engine.
[0007]
[Means for Solving the Problems]
A ring groove in which the piston ring fits is formed in the outer periphery of the piston. The groove bottom surface of the ring groove has an elliptical shape that is long in the thrust-antithrust direction when viewed in the piston axial direction.
[0008]
【The invention's effect】
According to the present invention, it is possible to effectively avoid interference between the piston ring and the groove bottom of the ring groove at the time of actual operation of the internal combustion engine without impairing the workability of assembling the piston to the cylinder.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a top view showing a piston 10 according to one embodiment of the present invention, and corresponds to arrow A in FIG. FIG. 2 is a front view of the piston 10 and corresponds to arrow B in FIG. FIG. 3 is a sectional view taken along the line CC of FIG. 1, and FIG. 4 is a sectional view taken along the line DD of FIG. FIGS. 5A and 5B exaggerately show the deformation of the top of the piston due to thermal expansion. FIG. 5A is a cross-sectional view taken along line CC in FIG. 1 and FIG.
[0010]
The piston 10 is integrally formed of, for example, a lightweight and high-strength aluminum alloy, has a substantially bottomed cylindrical shape with an opening at the bottom, and is fitted into the cylinder 2 (see FIG. 5) of the internal combustion engine in a vertically movable manner. -Assembled. The piston 10 is connected to an upper end of a connecting rod (not shown) by a piston pin 6 and moves up and down in the cylinder 2 in conjunction with rotation of a crankshaft.
[0011]
On the top of the piston 10, a piston crown surface 14 facing the combustion chamber is formed on the upper surface, and three ring grooves 16 (16A, 16B) into which the piston ring 12 fits are fitted on the outer peripheral land 20. , 16C) are recessed. Each ring groove 16 has a groove bottom surface 18 facing the inner peripheral surface of the piston ring 12. However, the first ring groove 16A and the second ring groove 16B on the upper side (upper side in FIG. 2) of the piston on which the compression ring is mounted are generally smaller than the third ring groove 16C on the lower side of the piston on which the oil control ring is mounted. The diameter of the groove bottom surface 18 is set small over the entire circumference.
[0012]
A pin hole in which the piston pin 6 is fitted is formed in the lower part of the piston 10, and a piston skirt 22 is provided at two places on an outer peripheral portion in a thrust-anti-thrust direction F 2 orthogonal to the piston pin axial direction F 1. It is formed to extend downward. FIG. 1 illustrates a circumferential range 22A where a piston skirt is formed.
[0013]
In this embodiment, the groove bottom surface 18 of each ring groove 16 has an elliptical shape that is long in the thrust-anti-thrust direction F2 when viewed in the piston axial direction shown in FIG. The above-mentioned “elliptical shape” means a flat shape excluding a perfect circle, and includes an elliptical shape and the like. In the drawings, the degree of flatness of the ring groove 16 is exaggerated for clarity.
[0014]
Referring to FIGS. 3 and 4, the radial distance between the inner peripheral surface of piston ring 12 and bottom surface 18 of ring groove 16 with piston ring 12 assembled to piston 10 is referred to as back clearance 24. The radial distance between the outer peripheral surface of the land portion 20 of the piston 10 and the outer peripheral surface of the piston ring 12 is referred to as a protrusion amount 26. As described above, the groove bottom surface 18 of the ring groove 16 has an elliptical shape that is long in the thrust-anti-thrust direction F2, and the inner and outer peripheral surfaces of the piston ring 12 assembled to the piston 10 are substantially circular. , The back clearance 24 is not constant in the circumferential direction, and the back clearance 24a in the axial direction F1 of the piston pin is longer than the back clearance 24b in the thrust-anti-thrust direction F2. The amount of protrusion 26 is substantially constant in the circumferential direction.
[0015]
If the valve clearance 24 is excessively large, the piston ring 12 protrudes from the ring groove 16 when the piston 10 with the piston ring attached thereto is tilted and inserted into the cylinder 2 formed in the cylinder block 4. This may interfere with the periphery of the opening of the cylinder 2 of the cylinder block 4, thereby impairing the workability of assembling the piston. On the other hand, if the valve clearance 24 is excessively small, when the groove bottom surface 18 of the ring groove 16 expands due to thermal expansion of the piston 10 during operation of the engine, the groove bottom surface 18 interferes with the inner peripheral surface of the piston ring 12. , The reliability and durability may be reduced.
[0016]
Referring to FIG. 5, in a region (b) near the thrust-anti-thrust direction F <b> 2 in the outer peripheral portion of the piston 10, a piston skirt 22 is provided. Since heat is easily radiated to the cylinder 2 side, the change in thermal expansion is relatively small and the valve clearance may be relatively small as compared with the region (a) near the piston pin axial direction F1. However, when assembling the piston 10 with the piston ring 12 assembled into the cylinder 2, the piston 10 swings in the thrust-anti-thrust direction F <b> 2 with the piston pin 6 as an axis. The shorter the valve clearance in the anti-thrust direction F2, the better.
[0017]
In this embodiment, the back clearance 24b in the thrust-anti-thrust direction F2 is set relatively short. Therefore, the piston ring 12 does not come off from the ring groove at the time of assembling the piston, the workability is improved, and the thermal expansion in the thrust-anti-thrust direction F2 is relatively small as described above. Although 24b is relatively short, interference between the groove bottom surface 18 and the inner peripheral surface of the piston ring 12 during actual operation due to thermal expansion can be avoided.
[0018]
In the outer peripheral portion of the piston 10, in a region near the piston pin axial direction F <b> 1, there is no piston skirt 22 and the effect of thermal expansion is large. In order to avoid interference, it is necessary to set a large valve clearance in advance.
[0019]
In this embodiment, since the back clearance 24a in the piston pin axial direction F1 is set relatively large, the interference between the groove bottom surface 18 and the inner peripheral surface of the piston ring 12 during actual operation due to thermal expansion is effectively prevented. Can be avoided. When the piston 10 is inserted into the cylinder 2, the piston 10 oscillates in the thrust-anti-thrust direction F <b> 2. Therefore, although the valve clearance 24 in the piston pin axial direction F <b> 1 is relatively large, the piston ring 12 is moved from the ring groove 16. It does not come off and does not hinder the workability of assembling the piston.
[0020]
As described above, according to the present embodiment, the valve clearance 24 is intentionally made non-uniform in the circumferential direction, set relatively long in the piston pin axial direction F1, and set relatively short in the thrust-anti-thrust direction F2. Accordingly, it is possible to achieve a high level of both improvement in workability when assembling the piston 10 to the cylinder 2 and avoiding interference between the ring groove bottom surface 18 and the inner peripheral surface of the piston ring 12 during engine operation.
[0021]
In order to obtain the above-mentioned effects, preferably, the ring groove depth 28a in the piston pin axial direction F1 is set to be larger than the ring groove depth 28b in the thrust-anti-thrust direction F2 by 10% or more.
[0022]
Although the present invention has been described based on the specific embodiments as described above, the present invention is not limited to the above embodiments. For example, the outer peripheral surface of the piston is not limited to a perfect circle, but may be an appropriate elliptical shape in consideration of thermal expansion, back clearance, and the like.
[Brief description of the drawings]
FIG. 1 is a top view corresponding to an arrow A in FIG. 2 showing a piston of an internal combustion engine according to one embodiment of the present invention.
FIG. 2 is a front view showing the piston and corresponding to an arrow B in FIG. 1;
FIG. 3 is a sectional view taken along the line CC of FIG. 1;
FIG. 4 is a sectional view taken along the line DD of FIG. 1;
5A and 5B are exaggerated views of deformation of a piston top portion due to thermal expansion, wherein FIG. 5A is a cross-sectional view taken along line CC of FIG. 1 and FIG.
[Explanation of symbols]
Reference Signs List 10: piston 12: piston ring 16: ring groove 18: groove bottom surface 24: back clearance F1: piston pin axial direction F2: thrust-anti-thrust direction

Claims (3)

A piston for an internal combustion engine in which a ring groove in which a piston ring is fitted is formed in the outer periphery of the piston, and the groove bottom surface of the ring groove has an elliptical shape that is long in the thrust-antithrust direction when viewed in the piston axial direction. A ring groove in which the piston ring fits is recessed around the piston,
A back clearance is provided between the groove bottom surface of the ring groove and the inner peripheral surface of the piston ring,
A piston of an internal combustion engine in which a back clearance in a piston pin axial direction is set longer than a back clearance in a thrust-anti-thrust direction. The piston of an internal combustion engine according to claim 1 or 2, wherein the depth of the ring groove in the axial direction of the piston pin is greater than the depth of the ring groove in the thrust-anti-thrust direction by 10% or more.

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