JPH0219347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston connecting rod assembly mainly used in an engine, and more specifically, a piston pin is fitted into at least a pair of pin bosses formed on the piston to bridge the piston, and the piston connecting rod assembly is provided between the two pin bosses. This relates to a piston connected to a connecting rod.

In engines equipped with such piston/conrod assemblies, when the piston receives a large load due to gas pressure or inertia, extremely unbalanced stress is generated at both ends of the pin boss due to the deflection of the piston pin. Such stress is unfavorable from the viewpoint of durability of the pin boss. Therefore, in order to ensure the durability of the pin boss, conventional methods have been to form the piston pin with a large diameter to increase its bending rigidity, or to form the pin boss with a thick wall to increase its strength. However, doing so increases the weight of the assembly, which is undesirable from the viewpoint of high-speed performance.

The present invention was proposed in view of the above, and aims to reduce the maximum stress generated in the pin boss and piston pin, average the stress at both ends thereof, and at the same time prevent an excessive increase in the surface pressure between the pin boss and the piston pin. It is an object of the present invention to provide an assembly that is simple in structure, lightweight, and easy to process, which can improve the durability of the piston without increasing the weight of the piston.

In order to achieve this object, the present invention includes at least one pair of pin bosses formed on a piston, which are fitted with a hollow cylindrical piston pin to form a bridge, and a connecting rod is connected to the piston pin between the two pin bosses. In the piston and connecting rod assembly, a first tapered surface is formed on the inner peripheral surface of each of the pin bosses, the first tapered surface having a maximum diameter at the end surface of the pin boss on the connecting rod side, and further, the outer peripheral surface is fitted to both outermost pin bosses, respectively. A second tapered surface is formed on the inner circumferential surface of both ends of the piston pin, the second tapered surface being surrounded by the first tapered surface of the outermost pin bosses and having a maximum diameter at both end surfaces of the piston pin.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. E denotes an engine body of an internal combustion engine, which is composed of a cylinder block 1 and a cylinder head 2 joined to the upper surface of the cylinder block 1. A combustion chamber 3 is formed in the cylinder head 2. The piston 4 that defines the cylinder block 1
It is slid into the cylinder hole 5 of. The cylinder hole 5 and the piston 4 are each formed to have an oval cross section.

The small ends of a pair of left and right connecting rods 7 are connected to the piston 4 via a single hollow cylindrical piston pin 6 arranged in the longitudinal direction of the cross-sectional shape. This connection structure will be explained in detail below.

In order to support the piston pin 6 at four locations at appropriate intervals in the axial direction, two pairs of pin bosses 8,
9; 8, 9 are integrally formed on the inner surface of the side wall and the inner surface of the ceiling wall of the piston 4, the piston pin 6 is rotatably fitted into these pin bosses 8, 9, and a pair of pin bosses 8, 9 are formed to press both end surfaces of the piston pin 6. Retaining ring 10
are locked to the inner surfaces of the pin bosses 8 at both outer positions.
Thus, the piston pin 6 is connected to each pair of pin bosses 8,
9, and the small end of connecting rod 7 is rotatably fitted into the bridge, and the large end thereof is connected to a crank pin of a crankshaft (not shown) as in the conventional art. .

The connecting rod 7 side half of the inner peripheral surface of each pin boss 8, 9 is formed into a first tapered surface 8a, 9a, respectively, and each first tapered surface expands toward the connecting rod 7 side, and the end surface of each pin boss on the connecting rod 7 side It has a shape with a maximum diameter. Thus, when the piston 4 is not bent, a gap 11 having a wedge-shaped cross section and opening toward the connecting rod 7 is formed on the fitting surface between the piston pin 6 and the pin bosses 8 and 9.

Since the taper amounts of the first tapered surfaces 8a and 9a are approximately equal, only one of the first tapered surfaces 8a is shown in an exaggerated manner in FIG.
When the axial length of a is set to half the effective length of the corresponding pin boss 8, the difference between the maximum diameter D and the minimum diameter d of the first tapered surface 8a is D-d≒5/1000D. It is desirable to do so.

Furthermore, the inner circumferential surfaces of both ends of the piston pin 6 whose outer circumferential surfaces fit into the outermost pin bosses 8, 8, respectively, are surrounded by the first tapered surfaces 8a, 8a of the outermost pin bosses 8, 8. Second tapered surfaces 6a, 6a having the maximum diameter are formed on both end surfaces of the piston pin 6, and the special provision of each second tapered surface 6a reduces the weight of the piston pin 6 itself, and also reduces the weight of the piston pin 6. 6. Both ends can be made relatively easy to bend.

In the figure, reference numerals 12 and 12 indicate a pair of spark plugs screwed onto the cylinder head 2 so that the electrodes thereof face the combustion chamber 3.

Next, to explain the operation of this embodiment, when a downward force is applied to the piston 4 due to the combustion pressure of the air-fuel mixture in the combustion chamber 3 during engine operation, the force is transferred from the pin bosses 8 and 9 to the piston pin 4. As a reaction force, the piston pin 6 is transmitted to the connecting rod 7 between the pair of pin bosses 8 and 9.
Since an upward bending load is applied to the piston pin 6, the piston pin 6 is bent upward between the pin bosses 8 and 9. As the amount of deflection increases, the upper surface of the piston pin 6 approaches and comes into contact with the upper part of the first tapered surfaces 8a, 9a of the pin bosses 8, 9, so that each pin boss 8, 9 supports the piston pin 6. The area increases as the amount of deflection of the piston pin 6 and, therefore, the downward force of the piston 4 increases. As a result, the stress generated in each pin boss 8, 9 is distributed to each part, so the maximum stress is reduced, and the stress at both ends of each pin boss 8, 9 is averaged, and between each pin boss 8, 9 and piston pin 6. It also reduces the surface pressure.

FIG. 3 shows the stress distribution state of each part of the two pairs of pin bosses 8, 9; 8, 9 measured at the maximum load of the piston 4 for the conventional one (dotted line A) and the one of the present invention (solid line B). For comparison, a to f on the horizontal axis indicate the measurement locations of each pin boss in FIG. This result also confirmed the effects of the present invention.

It goes without saying that the present invention can also be applied to a normal circular piston having pin bosses only on both side walls.

As described above, according to the present invention, a first tapered surface is formed on the inner circumferential surface of each pin boss, and the first tapered surface has a maximum diameter at the connecting rod side end surface of the pin boss. Since the amount of deflection increases as the amount of deflection of the pin increases, the maximum stress generated in the pin boss can be reduced and the stress at both ends can be averaged, and at the same time, the surface pressure between the pin boss and piston pin can be reduced. This can significantly improve the durability of the piston, and since the above configuration does not involve an increase in the weight of the piston or piston pin, it can also contribute to improving the high-speed performance of the engine. Furthermore, since the first tapered surface can be obtained by simply expanding the pin hole opening of the pin boss, the first tapered surface can be integrally molded at the same time when the piston is cast, and the first tapered surface can be integrally molded at the same time when the piston is cast. Even if the 1-tapered surface is formed by cutting, the processing is easy, and on the other hand, a hollow cylindrical pipe with a simple shape can be used as the piston pin, so overall it is excellent in mass production and can contribute to cost reduction. Furthermore, even with the special provision of the first tapered surface, no notch grooves or discontinuities that cause stress concentration are formed on the outer surfaces of both the pin boss and the piston pin, so the pin boss and the piston pin are locally vulnerable. There is no risk of parts forming,
Therefore, even if the piston pin is made hollow to reduce weight, it does not pose a problem in terms of strength.

Further, the inner circumferential surfaces of both ends of the piston pin whose outer circumferential surfaces fit into the outermost pin bosses are surrounded by the first tapered surfaces of the outermost pin bosses and have a maximum diameter at both end surfaces of the piston pin. Since the second tapered surface is formed, both ends of the piston pin, which are easily bent due to the formation of the second tapered surface, can be easily bent and deformed in correspondence with the first tapered surfaces of the outermost pin bosses, Therefore, stress can be averaged over substantially the entire area of both ends of the piston pin, and the strength of both ends can be increased. In addition, the special provision of the second tapered surface reduces the waste material at both ends of the piston pin, which, together with making the piston pin itself hollow, can greatly contribute to reducing the inertial mass of the piston pin. Moreover, since the second tapered surface widens toward both end surfaces of the piston pin, machining from the outside is easy. Notches or the like that cause stress concentration are not formed on the circumferential surface.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view of a main part of an internal combustion engine according to an embodiment of the present invention, FIG. 2 is an enlarged view of a portion of FIG. 1,
FIG. 3 is a stress distribution state diagram of a pin boss, where the dotted line A shows the conventional one and the solid line B shows the one according to the present invention. 4... Piston, 6... Piston pin, 6a...
...Second tapered surface, 7...Conrod, 8,9...
Pin boss, 8a, 9a...first tapered surface.

Claims (1)

[Claims] 1 A hollow cylindrical piston pin 6 is fitted into at least a pair of pin bosses 8 and 9 formed on the piston 4 to form a bridge, and a connecting rod 7 is connected to the piston pin 6 between the two pin bosses 8 and 9. In the piston connecting rod assembly, first tapered surfaces 8a and 9a are formed on the inner circumferential surface of each of the pin bosses 8 and 9, and the first tapered surfaces 8a and 9a have a maximum diameter at the end surface of the pin bosses 8 and 9 on the connecting rod 7 side, and The inner circumferential surfaces of both ends of the piston pin 6 whose outer circumferential surfaces fit into both pin bosses 8, 8, respectively, are surrounded by the first tapered surfaces 8a, 8a of the outermost pin bosses 8, 8. It is characterized by forming second tapered surfaces 6a, 6a having the maximum diameter at both end surfaces,
Piston conrod assembly.