JP2015007395A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston of an internal combustion engine, in which an increase in thickness of the side wall of the piston is suppressed and besides, contact surface pressure between the inner wall of each pin hole and each bush is reduced.SOLUTION: Pin holes 12a are formed in a side wall 12 of a piston 11 of the internal combustion engine, and both ends of a piston pin 15 are inserted through the pin holes 12a, respectively. At both ends of the piston pin 15, bushes 13 are mounted which contact the inner walls of the pin holes 12a. The bushes 13 each have an enlarged part 13a whose cross section perpendicular to the axis of the piston pin 15 is gradually larger toward the end side of the piston pin 15. In the axial direction of the piston pin 15, the length of the enlarged part 13a is greater than the half of the length of the side wall 12.

Description

  The present invention relates to a piston for an internal combustion engine.

  As shown in FIG. 3, Patent Document 1 describes a piston 31 in which a pin hole 32 a through which a piston pin 35 is inserted is formed in a side wall 32. In the piston 31, spherical bushes 33 that come into contact with the inner wall of the pin hole 32 a are provided at both ends of the piston pin 35.

Japanese Patent Laid-Open No. 7-243348

  By the way, as shown by a broken line in FIG. 3, the outer peripheral end of the top surface of the piston 31 may be deformed downward due to the in-cylinder pressure during abnormal combustion of the internal combustion engine. When such a deformation occurs, the bush 33 tilts and both ends of the piston pin 35 bend downward, so that a load is applied to the bush 33 from the obliquely upper side toward the end of the piston pin 35. This load is concentrated on the outer peripheral surface of the enlarged portion 33a of the upper portion of the bush 33 where the cross section perpendicular to the axis of the piston pin 35 increases toward the end of the piston pin 35. As a result, the contact surface pressure between the inner wall of the pin hole 32a and the bush 33 may be excessively increased. Here, if the diameter of the bush 33 is increased, the pressure receiving surface for the load described above is increased, so that it is possible to suppress the generation of an excessive contact surface pressure. However, since the bush 33 of the piston 31 described in Patent Document 1 is formed in a spherical shape, when the pressure receiving surface of the load is increased as described above, the entire side wall 32 of the piston 31 extends in the axial direction of the piston pin 35. It will become thick and will cause an increase in piston weight.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the contact surface pressure between the inner wall of the pin hole and the bush while suppressing the increase in the thickness of the side wall of the piston of the internal combustion engine. To do.

  In a piston of an internal combustion engine for solving the above problems, a pin hole into which a piston pin is inserted is formed in a side wall. Bushings are provided at both ends of the piston pin, including enlarged portions that come into contact with the inner wall of the pin hole and have a cross section orthogonal to the axis of the piston pin that increases toward the end of the piston pin. The bush has a shape in which the length of the enlarged portion in the axial direction is longer than half of the length of the side wall in the axial direction.

  Here, in the spherical bush, the enlarged portion where the cross section orthogonal to the axis of the piston pin becomes larger toward the end of the piston pin functions as the pressure receiving portion for the load from above, but the acting load is small. Sites other than the enlarged portion have a low function as a pressure receiving portion. That is, in the case where a spherical bush having the same length as the side wall in the axial direction of the piston pin is provided on the side wall, a portion having a low function as the pressure receiving portion occupies half of the entire side wall.

  In this regard, according to the above-described configuration, the ratio of the portion having a low function as the pressure receiving portion as described above on the side wall can be reduced as compared with the spherical bush. For this reason, even if it does not make the side wall of a piston thick, the pressure receiving surface of the said load in a bush can be enlarged. Therefore, it is possible to reduce the contact surface pressure between the inner wall of the pin hole and the bush while preventing the side wall of the piston from becoming thick. In order to obtain such an effect, it is desirable to employ a bush formed only by the enlarged portion and further enlarge the pressure receiving surface of the load.

The fragmentary sectional view which shows the piston of an internal combustion engine. The fragmentary sectional view which shows the modification of the piston of an internal combustion engine. The fragmentary sectional view which shows the piston of the conventional internal combustion engine.

Hereinafter, an embodiment of a piston of an internal combustion engine will be described.
As shown in FIG. 1, the piston 11 of the internal combustion engine includes two side walls 12 extending downward, and both end portions of the piston pins 15 are inserted into pin holes 12 a formed in the side walls 12. The piston 11 is connected to the connecting rod 20 by the piston pin 15. Further, the bush 13 formed only by the enlarged portion 13 a having a cross section orthogonal to the axis of the piston pin 15 that is larger toward the end of the piston pin 15 is attached to both ends of the piston pin 15. That is, in this embodiment, when the length of the enlarged portion 13a is L1 and the length of the side wall 12 is L2 in the axial direction of the piston pin 15, the relationship in which the values of L1 and L2 are approximately the same is satisfied. ing. Further, the entire inner wall of the pin hole 12 a is in contact with the outer peripheral surface of the bush 13. The bush 13 is made of carbon fiber reinforced plastic.

Next, the operation of the piston 11 of this internal combustion engine will be described.
At the time of abnormal combustion of the internal combustion engine, if the outer peripheral end of the top surface of the piston 11 is deformed downward by the in-cylinder pressure as shown by a broken line in FIG. 1, the bush 13 tilts and both end portions of the piston pin 15 bend downward. The bush 13 is subjected to a load from the oblique upper side toward the end of the piston pin 15. This load acts on the outer peripheral surface of the upper portion of the bush 13 and concentrates on the outer peripheral surface of the enlarged portion 13a where the cross section perpendicular to the axis of the piston pin 15 increases toward the end of the piston pin 15. become. Here, if a spherical bush is provided in the pin hole 12a of the side wall 12, the outer peripheral surface located on the center side of the piston pin 15 in the upper portion of the bush, that is, the half of the outer peripheral surface in the upper portion of the bush. Although the enlarged portion that functions as the pressure receiving portion that receives the load described above, the remaining half of the portion hardly functions as the pressure receiving portion. On the other hand, in this embodiment, the entire outer peripheral surface of the upper portion of the enlarged portion 13a of the bush 13 functions as a pressure receiving portion that receives the load. Therefore, compared with the spherical bush, the bush 13 of this embodiment can increase the pressure receiving surface of the load.

  Further, if a spherical bush is provided on the side wall 12 of the piston 11, a space is generated between the inner wall of the pin hole and the outer peripheral surface of the bush on the end side of the piston pin. For this reason, it is necessary to assemble a cap 34 as shown in FIG. 3 in such a space. On the other hand, in the present embodiment, since the entire inner wall of the pin hole 12a is in contact with the outer peripheral surface of the bush 13, there is no space between the inner wall of the pin hole 12a and the outer peripheral surface of the bush 13, and the cap 34 described above. No assembly is required.

According to the piston 11 of the internal combustion engine described above, the following effects can be obtained.
(1) Since the bush 13 is formed only by the enlarged portion 13a, the ratio of the portion having a low function as the pressure receiving portion for the load from the oblique upper side as described above in the upper portion of the bush 13 is reduced. For this reason, even if it does not make the side wall 12 of the piston 11 thick, the pressure receiving surface of the said load in the bush 13 can be enlarged. Therefore, the contact surface pressure between the inner wall of the pin hole 12a and the bush 13 can be reduced while suppressing the side wall 12 of the piston 11 from becoming thick.

  (2) Since there is no space between the inner wall of the pin hole 12a and the outer peripheral surface of the bush 13, it is not necessary to assemble the cap, which may occur due to sliding between the bush 13 and the cap. Seizure can be suppressed.

(3) Since the bush 13 is formed of carbon fiber reinforced plastic, the weight of the piston 11 can be reduced as compared with the configuration in which the bush 13 is formed of a metal material.
The above-described embodiment can be modified as follows.

  -You may change the shape of the bush 13 as shown in FIG. In short, the bush 13 has an enlarged portion 13a in which the cross section orthogonal to the axis of the piston pin 15 increases toward the end of the piston pin 15, and the length (L1) in the axial direction of the enlarged portion 13a is coaxial. If the shape is longer (L1> L2 / 2) than half the length (L2) of the side wall 12 in the direction, the shape can be freely changed. Further, for example, in this configuration, a cap may be provided at the end of the bush 13. Even in such a form, the same effects as the effects (1) and (3) that can be obtained in the above-described embodiment can be obtained.

  The bush 13 may be formed of a material other than carbon fiber reinforced plastic, such as a carbon fiber reinforced carbon composite material, a composite material including a foamed material such as calcium, or a composite material including a copper alloy.

  DESCRIPTION OF SYMBOLS 11 ... Piston, 12 ... Side wall of piston, 12a ... Pin hole, 13 ... Bush, 13a ... Enlarged part, 15 ... Piston pin, 20 ... Connecting rod.

Claims (2)

A piston of an internal combustion engine in which a pin hole through which a piston pin is inserted is formed on a side wall,
At both ends of the piston pin, a bush is provided that includes an enlarged portion that comes into contact with the inner wall of the pin hole and whose cross section perpendicular to the axis of the piston pin increases toward the end of the piston pin.
A piston of an internal combustion engine, wherein a length of the enlarged portion in the axial direction is longer than half of a length of the side wall in the axial direction. The piston of the internal combustion engine according to claim 1, wherein the bush is formed only by the enlarged portion.