JPH0693927A - Piston of internal combustion engine - Google Patents

Abstract

PURPOSE:To set clearance between cylinder walls or a skirt part and a cylinder part in a small level so as to greatly reduce generation of slap noise in the skirt part, and maintain working accuracy of the abut surface of the skirt part abuts on a crown part in a high level so as to stabilize the position of the crown part, and greatly reduce generation of slap noise in the skirt part. CONSTITUTION:In a piston which consists of a crown part 2 and an different skirt part 3 which is arranged downward thereof, and being formed in such constitution that a piston pin is inserted in piston pin holes 2b, 5a formed respectively on the crown part 2 and the skirt part 3, the skirt part 3 is formed on concentric and multiple layers 4, 5, and also at least the skirt part 4 of an most outer layer is formed by a member having a thermal expansion coefficient which is approximate to the cylinder wall of a cylinder in which a piston 1 is slid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-body type piston in which a piston pin hole is formed in each of a crown portion and a skirt portion of a piston which are formed separately, and the piston pin is fitted into these holes to integrate them. Regarding the improvement of.

[0002]

2. Description of the Related Art In recent high-power engines, especially large diesel engines, in order to improve durability against heat load, the crown portion and the skirt portion of the piston are formed separately, and the crown portion and the skirt are formed separately. A two-body type piston is used in which a piston pin is fitted in a piston pin hole formed in the portion and these are integrated.

As described above, the piston is separated into the crown portion and the skirt portion, and a slight clearance is provided between the lower surface of the crown portion and the upper surface of the skirt portion, so that the combustion heat from the combustion chamber is received and the temperature becomes high. The heat of the crown portion is made difficult to conduct to the skirt portion, the temperature of the skirt portion of the piston is kept low to some extent, and heat damage such as seizure of the piston is prevented.

By the way, in such a two-body type piston, the crown portion swinging around the piston pin as the center of rotation collides with the cylinder liner at the portion farthest from the piston pin hole, that is, the top land portion.
The slap sound caused by this collision was a problem.

[0005]

Therefore, for the purpose of reducing the slap noise generated in the crown portion and reducing the noise of the engine, the pin boss portion of the crown portion into which the piston pin is fitted is placed inside the skirt portion. The invention of JP-A-61-1855, in which the pin boss portion is extended and brought into contact with the inner peripheral surface of the skirt portion to suppress the swinging of the crown portion, and pressure oil is applied to the crown portion and the skirt portion. A device of Japanese Utility Model Laid-Open No. 61-120061 has been proposed in which the rocking of the crown portion is suppressed by introducing the gap between them.

However, while the piston skirts described in these publications are generally made of a material such as aluminum alloy, the cylinder liner on which the piston slides is made of an iron-based material. Therefore, it is necessary to secure a clearance between the skirt portion and the cylinder liner in advance with a certain margin in consideration of the difference in the coefficient of thermal expansion depending on the material.

In this way, the conventional two-body type piston is
Since a relatively large clearance has to be provided between the skirt portion and the cylinder liner, the reaction force of the posture control of the crown portion, that is, the crown portion collides with the cylinder liner, so that the rocking is stopped. The posture of the skirt that receives the force applied when it is applied becomes unstable, and the skirt hits the cylinder liner, which causes a problem that a slap sound is likely to be generated in the skirt.

The inner peripheral surface of the skirt is in contact with the pin boss portion of the crown portion in order to stabilize the posture of the crown portion. However, the swing of the crown portion is suppressed to stabilize the posture. In order to reduce the slap sound in the crown portion, it is necessary to keep the machining accuracy of the inner peripheral surface of the skirt portion with which the pin boss portion abuts extremely high. However, in actually manufacturing the piston, there is a problem that it is considerably difficult to keep the machining accuracy of the inner peripheral surface of the skirt portion high because the surface shape of the inner peripheral surface of the skirt portion is complicated.

In view of the above problems, the present invention can set the clearance between the skirt portion and the cylinder wall of the cylinder as small as possible to significantly reduce the generation of slap sound in the skirt portion. Of the internal combustion engine capable of maintaining the processing accuracy of the contact surface of the skirt portion that contacts the crown portion with high accuracy, stabilizing the posture of the crown portion, and significantly reducing the generation of slap sound in the crown portion. The purpose is to provide a piston.

[0010]

A piston of an internal combustion engine according to the present invention for achieving the above object comprises a crown portion and a separate skirt portion arranged below the crown portion, and the crown portion and the skirt portion are provided. In a piston in which piston pins are fitted in piston pin holes formed respectively, the skirt portion is formed in a plurality of concentric layers, and at least the skirt portion of the outermost layer is slidable on the cylinder wall of the cylinder. This is a structure formed of a material having a coefficient of thermal expansion similar to.

The material of the skirt portion of the outermost layer is optimally formed of the same material as the cylinder cylinder wall, but the present invention is not limited to this, and thermal expansion close to that of the material forming the cylinder cylinder wall. The material having the ratio can be appropriately selected and used. Further, the cylinder cylinder wall and the skirt portion of the outermost layer are preferably made of a material having a coefficient of thermal expansion as low as possible, while the crown portion and the skirt portion of the inner layer are preferably made of a light material, and therefore, a material having a specific gravity as low as possible. It is good to form. The present invention can be applied whether the cylinder wall of the cylinder is a cylinder liner or a cylinder block without a liner.

[0012]

[Operation] The piston of the internal combustion engine of the present invention has the above-mentioned configuration, and since the skirt portion of the outermost layer has a thermal expansion coefficient similar to that of the cylinder cylinder wall,
The clearance between the thermally expanding skirt and the cylinder wall does not change much. Therefore, the clearance between the skirt portion and the cylinder wall when the engine is cold can be set as small as possible, and the slap noise in the skirt portion of the piston is reduced.

Further, since the skirt portion is formed in a plurality of concentric layers, and a cylindrical tubular body can be used for the skirt portion of the outer layer, the inner surface of the skirt portion of the outer layer is processed. This is extremely easy and the processing accuracy can be kept high. Therefore, by making the inner peripheral surface of the skirt portion of the outer layer the contact surface with the crown portion, the posture of the crown portion can be stabilized, and the slap sound in the crown portion of the piston is reduced.

[0014]

EXAMPLES Examples of the present invention will be described with reference to the drawings. First, as shown in FIGS. 1 to 4, the piston 1 of the present embodiment comprises a crown portion 2 having a piston ring groove 2a and a skirt portion 3 arranged below the crown portion 2. . The skirt portion 3 is composed of an outer layer skirt portion 4 that slides on a cylinder cylinder wall (cylinder liner) (not shown) and an inner layer skirt portion 5 provided inside the outer layer skirt portion 4.

In this embodiment, the crown portion 2 and the inner layer skirt portion 5 are made of aluminum alloy,
On the other hand, the outer layer skirt portion 4 is formed of a steel pipe having a coefficient of thermal expansion substantially the same as that of a cast iron cylinder liner. In addition, the crown portion 2 is provided with a pin boss portion 2c having a piston pin hole 2b and an abutting portion 2d that abuts on the outer layer skirt portion 4 and suppresses the swing of the crown portion 2.
On the other hand, the inner layer skirt portion 5 has a pin boss portion 5b having a piston pin hole 5a formed therein similarly to the crown portion 2, and a holding portion 5c for generating a tensile stress when the inner layer skirt portion 5 is press-fitted into the outer layer skirt portion 4. Is provided.

Further, the pin boss portion 2c of the crown portion 2
And a pin boss portion 5b of the inner layer skirt portion 5 are provided with clearances so that they can move independently of each other. Similarly, a holding portion 5c of the inner layer skirt portion 5 and a crown surrounding the holding portion 5c. A clearance is provided between the portion 2 and the portion 2 so as not to contact each other. Further, a certain amount of clearance C is provided between the contact portion 2d of the crown portion 2 and the inner peripheral surface 4a of the outer layer skirt portion 4, and when the crown portion 2 swings, By abutting the abutting portion 2d on the inner peripheral surface 4a, the posture change of the crown portion 2 is suppressed within the range of the clearance C.

On the other hand, the inner layer skirt portion 5 and the outer layer skirt portion 4 constituting the skirt portion 3 are fixed by press fit so as to move integrally with each other. When the crown portion 2, the inner layer skirt portion 5, and the outer layer skirt portion 4 are integrally assembled, as shown in FIG. 5, the inner layer skirt portion 5 divided into two by the holding portion 5c is attached to the piston. The pin hole 5a is the piston pin hole 2b of the crown portion 2.
And align the split surfaces from both sides,
The outer layer skirt portion 4 is press-fitted into the inner layer skirt portion 5,
The inner layer skirt portion 5 and the outer layer skirt portion 4 are fixed.

In the piston 1 of this embodiment assembled in this way, since the outer layer skirt portion 4 is formed of a steel pipe, the thermal expansion can be suppressed to a small level as compared with the case where it is formed of an aluminum alloy or the like. Moreover,
Since it is not necessary to consider the difference in the coefficient of thermal expansion from the cast iron cylinder liner, the clearance between the cylinder liner and the skirt portion 3 can be set as small as possible when the engine is cold. Further, as described above, since the outer layer skirt portion 4 is formed of the steel pipe, the inner peripheral surface 4a of the outer skirt portion 4 is very easily machined, and the machining accuracy can be kept high.

In this embodiment, the clearance C is provided between the contact portion 2d of the crown portion 2 and the inner peripheral surface 4a of the outer layer skirt portion 4. However, the clearance C is provided on the surface of the contact portion 2d. It is more preferable to provide a cushioning material such as resin or rubber having low elasticity and high damping characteristics to fill the clearance C so as to absorb the impact when the contact portion 2d hits the outer layer skirt portion 4.

Further, instead of using the inner layer skirt portion 5 divided into two by the holding portion 5c as shown in FIG. 5, an integral type inner layer skirt portion 5 as shown in FIG. 6 may be used.
In this case, the inner layer skirt portion 5 having an inner diameter larger than the outer diameter of the contact portion 2d of the crown portion 2 is used, but the contact portion 2d of the crown portion 2 and the inner peripheral surface of the outer layer skirt portion 4 are used. Since a large clearance C is formed with 4a, it is necessary to elastically insert the cushioning material 6 in that portion. On the other hand, on the other hand, it is not necessary to process the joint surface between the holding portions 5c of the inner layer skirt portion 5 divided into two parts, so that it is not necessary to consider a processing error in assembling, and the assembling work becomes easy.

The structure of the outer layer skirt portion 4 used in the piston 1 of the above-described embodiment can be modified in various ways. For example, as shown in FIG. 7, the outer layer skirt portion 4 is further formed into a plurality of layers. A thin film of resin such as polyester is sandwiched as a cushioning material 4d between a plurality of cylindrical steel pipes 4b and 4c that are fractionated and arranged concentrically with a minute gap therebetween to form a laminated body. Such a structure may be used.

With such a structure, the cushioning material 4d can attenuate a slight slap sound generated by the skirt portion 3 colliding with the cylinder wall.
Further noise reduction can be achieved. In this case, as the cushioning material 4d, in addition to the heat-resistant resin material, a metal material having vibration damping properties such as copper, magnesium and lead can be used.

Further, similarly to the above, for the purpose of further reducing the slap sound of the piston 1, as shown in FIG. 8, a gap 4e is formed in the outer layer skirt portion 4 so that the outer layer skirt portion 4 has a kind. Has a function as a spring of
The outer layer skirt portion 4 can be structured so as to be pressed against the cylinder wall with a minute pressure so as to be expanded in the circumferential direction.

However, in this case, sealing performance like that of the piston ring is not required, and if a too strong expansion force is applied, the sliding resistance of the piston 1 increases, which may cause seizure and other harmful effects. Therefore, piston 1
It is advisable to apply a minimum expansion force that can stabilize the posture of the. On the other hand, according to the present invention, in order to reduce the slap sound as described above, the clearance between the skirt portion 3 of the piston 1 and the cylinder wall can be made as small as possible. If it is feared that the oil film retainability will be deteriorated due to excessive scraping or scraping of the engine oil, a groove extending in the reciprocating direction of the piston 1 is formed on the outer peripheral surface 4f of the outer layer skirt portion 4 as shown in FIG. By forming 4 g, it is preferable that the oil is retained in the groove 4 g to improve the oil film retaining property.

By retaining the oil in the groove 4g, a damping effect can be obtained, so that the seizure of the piston 1 can be prevented and the slap noise can be reduced. Further, the number of the grooves 4g, the arrangement interval, and the like can be appropriately selected so that an appropriate oil film can be held while maintaining the strength of the outer layer skirt portion 4 to some extent, and the shape thereof is also illustrated. The groove 4g is not limited to the semi-circular shape described above, but may be a rectangular groove 4g.

In the above embodiment, when the outer layer skirt portion 4 and the inner layer skirt portion 5 are integrated, in addition to the method of fixing by press fitting, as shown in FIG. 10, a stopper is provided at the outer peripheral upper end of the inner layer skirt portion 5. 5d may be provided in a protruding manner, the inner layer skirt portion 5 may be inserted into the outer layer skirt portion 4, and the ring plate 7 covering these lower end surfaces may be screwed into the screw holes 5e of the inner layer skirt portion 5 with screws 8. .

Further, as shown in FIG. 11, the inner layer skirt portion 5 having the same stopper 5d as described above is inserted into the outer layer skirt portion 4 and snap ringed to the ring groove 5f formed on the outer peripheral surface of the inner layer skirt portion 5. 9 may be fitted to fix the lower end surface of the outer layer skirt portion 4.

[0028]

The piston of the internal combustion engine of the present invention comprises a crown portion and a separate skirt portion disposed below the crown portion, and piston pins are provided in piston pin holes formed in the crown portion and the skirt portion, respectively. In the fitted piston, the skirt portion is formed in a plurality of concentric layers, and at least the outermost skirt portion is formed of a material having a thermal expansion coefficient similar to that of the cylinder wall of the cylinder on which the piston slides. Therefore, the following effects can be obtained.

Since the skirt portion of the outermost layer is formed of a material having a coefficient of thermal expansion similar to that of the cylinder wall,
When the engine is cold, the clearance between the skirt portion and the cylinder cylinder wall can be set as small as possible, and the slap sound in the skirt portion of the piston can be significantly reduced. Further, since the skirt portion is formed in a plurality of concentric layers, and a cylindrical tubular body can be used for the skirt portion of the outer layer, the inner peripheral surface of the skirt portion of the outer layer is referred to as a crown portion. By using the contact surface, the posture of the crown portion can be stabilized, and the slap sound at the crown portion of the piston can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a piston of an internal combustion engine according to a first embodiment of the present invention, (a) is an axial sectional view of a piston pin,
(B) is a circumferential sectional view of the piston pin.

2 is a cross-sectional view of the crown portion of the piston of FIG.
(A) is an axial direction sectional view of a piston pin, (b) is a circumferential direction sectional view of a piston pin.

3 is a cross-sectional view of the inner layer skirt portion of the piston of FIG. 1, (a) is an axial cross-sectional view of the piston pin, and (b) is a circumferential cross-sectional view of the piston pin.

4A and 4B are cross-sectional views of an outer layer skirt portion of the piston of FIG. 1, where FIG. 4A is an axial sectional view of the piston pin, and FIG. 4B is a circumferential sectional view of the piston pin.

5 is a perspective view showing a state in which the piston of FIG. 1 is assembled upside down.

FIG. 6 is a perspective view showing a state in which a piston of an internal combustion engine of Example 2 of the present invention is assembled upside down.

FIG. 7 is an outer layer skirt portion of a piston of an internal combustion engine according to a third embodiment of the present invention, (a) is an overall perspective view, and (b) is an enlarged view of part A of (a).

FIG. 8 is a perspective view of an outer layer skirt portion of a piston of an internal combustion engine of Embodiment 4 of the present invention.

FIG. 9 is an outer layer skirt portion of a piston of an internal combustion engine according to a fifth embodiment of the present invention, (a) is a perspective view of the whole, and (b) is an enlarged view of part B of (a).

FIG. 10 is a sectional view of a skirt portion of a piston of an internal combustion engine of Embodiment 6 of the present invention.

FIG. 11 is a sectional view of a skirt portion of a piston of an internal combustion engine according to a seventh embodiment of the present invention.

[Explanation of symbols]

1 Piston 2 Crown part 2b Piston pin hole 3 Skirt part 4 Outer layer skirt part 5 Inner layer skirt part 5a Piston pin hole

Claims (1)

[Claims] 1. A piston comprising a crown portion and a separate skirt portion arranged below the crown portion, wherein piston pins are fitted into piston pin holes formed in the crown portion and the skirt portion, respectively. A piston for an internal combustion engine in which the parts are formed in a plurality of concentric layers, and at least the skirt part of the outermost layer is formed of a material having a coefficient of thermal expansion similar to that of a cylinder wall of a cylinder on which the piston slides.