JPH0235047Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a connecting rod that transmits the reciprocating motion of a piston of an internal combustion engine to a crankshaft, and particularly relates to a coupling mechanism between a small end of the connecting rod and a piston pin.

The connection means between the piston pin and the connecting rod is published by Yokendo Co., Ltd., December 10, 1960, No. 2.
The following has been known for some time, as shown in page 580 of the revised 13th edition of "Lectures on Internal Combustion Engines, Vol. 2," and this is shown in Figure 1. In the figure, 1 is a piston pin, 2 is a connecting rod, 2a is a small end portion thereof, and 2b is a rod portion.

Conventional piston pin 1 uses steel products such as carbon steel, nickel chrome steel, chrome molybdenum steel, etc.
It is formed by polishing the outer peripheral surface and then performing a lap finish. On the other hand, the connecting rod 2 is made of carbon steel, sintered metal, or the like.

In order to fix the piston pin 1 to the small end portion 2a of the connecting rod, press fitting or shrink fitting, or a floating means in which snap rings are fixed to both ends of the piston pin and a clearance fit is employed, is used.

By the way, when the weight of the connecting rod is reduced, the inertia force is reduced, which improves fuel efficiency and reduces noise or vibration. Furthermore, the weight of the crankshaft can also be reduced, which further enhances the above-mentioned effects.

Therefore, the weight of the connecting rod 2 is generally reduced, but even if the design is carried out to the limit using conventional carbon steel or the like, the effect is small, so there is a tendency to use lightweight alloy materials such as aluminum alloy.

However, the thermal expansion coefficients of the steel-based members that form the piston pin and the aluminum alloy-based members that form the connecting rod are approximately twice that of the former. I see,
As the temperature of the small end 2a, which has a high thermal load, increases, the clearance between the outer periphery 1a of the piston pin, the small end 2a of the connecting rod, and the inner periphery of the pin insertion hole 2c is increased, as shown in FIG. This tends to occur and spread.

In this state, when the inertial force of the piston is received by the small end 2a through the piston pin, the pin insertion hole 2c of the small end becomes elliptical, and its inner periphery becomes a connecting rod due to the inertial force of the piston. The pin insertion hole 2c is caused by a simple tensile stress in the axial direction and a bending force caused by the inward crushing deformation of the portion orthogonal to the axial direction due to the tensile stress.
Compressive stress and tensile stress are unevenly distributed on the inner circumference of
In particular, since the tensile stress based on the bending stress is maximum at a portion substantially perpendicular to the axial direction of the connecting rod, it is added to the simple tensile stress and tends to cause fatigue failure. This tendency is further exacerbated by the fact that aluminum light alloys have low high temperature strength.

Therefore, it is necessary to use an aluminum alloy connecting rod so that no clearance occurs even at around 150℃, but in order to do so, it is necessary to press fit the steel piston pin 1 and steel connecting rod 2 together at room temperature. It is necessary to take a larger press-fit allowance than the press-fitting allowance. However, as a result, the stress on the inner periphery of the small end pin insertion hole at the time of initial press-fitting, especially the stress when the engine is at low temperature, becomes excessive, so there is a limit to increasing the pressure allowance.

In view of the disadvantages of the conventional device, the present invention has been developed by forming the connecting rod with a material having a higher coefficient of thermal expansion than the piston pin, and by changing the cross-sectional shape of the pin insertion hole at the small end of the connecting rod and the pin insertion hole of the piston pin. One of the cross-sectional shapes of the insertion portion into the insertion hole is formed into a substantially oval shape and the other is formed into a substantially perfect circle, and the piston pin press-fitting distance into the pin insertion hole is substantially perpendicular to the axis of the connecting rod. By setting the maximum value in the direction, the stress increase due to crushing deformation when the small end of the connecting rod receives piston inertia force, which occurs at high temperatures such as when the engine is under high load, is suppressed to below the fatigue limit. This prevents damage to the small end.

Embodiments of the present invention will be described below based on the drawings.

In one embodiment shown in FIG. 3, the piston pin 1 is made of a conventional steel material such as carbon copper, nickel chrome steel, or chrome molybdenum steel, and the connecting rod 2 is made of a lightweight alloy material such as an aluminum alloy. Therefore, the coefficient of thermal expansion of the connecting rod 2 is greater than that of the piston pin 1.

The cross-sectional shape of the pin insertion hole A of the small end 2a of the connecting rod 2 is such that the diameter in the axial direction of the connecting rod is D ₁ and the diameter in the direction substantially perpendicular to the axial direction is D ₂ . Long (D ₁ > D ₂ )
It is approximately oval in shape. In addition, in the figure, the oval state is exaggerated.

The degree of ellipse (D ₁ − D ₂ ) is small, and (D ₂ −
D ₁ )/D ₁ ≒0.0008. The cross-sectional shape of the insertion portion of the piston pin 1 press-fitted into the pin insertion hole A is approximately a perfect circle.

The press-fitting allowance for press-fitting the piston pin 1 into the piston insertion hole A is maximized at the short axis direction portion of the pin insertion hole A.

The method for manufacturing this elliptical pin insertion hole A is, for example, by applying pressure and deforming the opposing small end portions of the ellipse in the direction of finishing as the long axis of the ellipse. Process into a perfect circle. As a result, after the pressure is released, a substantially elliptical pin insertion hole A having a long axis in the pressing direction is obtained.

With this configuration, even when the coefficient of thermal expansion of the small end of the connecting rod increases during high-load operation, the direction of the connecting rod axis is approximately perpendicular, that is, the approximately oval pin insertion hole A is There is no clearance in the short axis direction part because the press fit allowance is large. Therefore, when the piston inertia force acts on the small end 2a in the axial direction of the connecting rod through the piston pin 1, so-called crushing deformation occurs in which the small end 2a deforms inward in the short axis direction of the pin insertion hole. This is suppressed by the piston pin 1, and the increase in stress on the inner periphery of the pin insertion hole A due to crushing deformation is alleviated.

Furthermore, even if a clearance is created between the short axis direction of the pin insertion hole A at the small end and the piston pin 1 due to large thermal expansion, the clearance value is small, so that crushing deformation occurs when the piston inertia acts as described above. The amount becomes smaller. Therefore, stress associated with crushing deformation can also be reduced.

Considering the stress when press-fitting a substantially perfect circular piston pin 1 into a substantially oval pin insertion hole A, the ellipse of the pin insertion hole A is deformed into a perfect circle by the piston pin 1 during press-fitting. As shown in FIG. 4a, a tensile force (+) is generated at the inner periphery of the pin insertion hole A in the long axis direction of the small end, and a compressive force (-) is generated at the inner periphery of the pin insertion hole A in the short axis direction. Furthermore, as shown in FIG. 4b, tensile stress generated by the press-fitting allowance is applied to the entire inner peripheral surface of the pin insertion hole. Therefore, the tensile stress in the long axis direction is greatest at the inner circumferential portion of the pin insertion hole, but the tensile stress due to the inertial force of the piston is mostly applied to the short axis direction, so it does not pose a problem in terms of strength.

The setting of the ellipticity (D ₁ - _{D 2} ) must be considered in conjunction with the press-fitting allowance (overlap width between the piston pin before press-fitting and the pin insertion hole at the small end of the connecting rod). In this case, it goes without saying that the maximum value of the press-fitting allowance is located in the short axis direction of the pin insertion hole.

Conventionally, the press-fitting distance between a steel piston pin and a steel connecting rod is 1.5/1000 of the inner circumferential diameter of a perfectly circular pin insertion hole. Furthermore, if the ellipticity and maximum press-fitting allowance of the pin insertion hole A according to this embodiment are made too large, the amount of crushing deformation caused by press-fitting a substantially perfect circular piston pin becomes excessive, and the small end pin insertion hole The inner circumference may undergo plastic deformation or cracks. Therefore, the diameter difference between the long axis and short axis of the ellipse, that is, the degree of ellipse (D ₁ - D ₂ ) is 3/1000D ₀ (however, D ₀ = 1/2D ₁ + D ₂ )
is desirable, and when the degree of ellipse is set large, the press-fitting allowance must be lowered accordingly to reduce stress. The total press-fitting allowance and degree of ellipse (D ₂ - _{D 1} ) should be within 3/1000D ₀ .

Another embodiment is shown in FIGS. 5a and 5b.

This one shows other shapes of the pin insertion hole A with a substantially oval cross section; Fig. 5a shows an elongated hole machined, and Fig. 5b shows a cutter with a small radius after the center is machined into a perfect circle. It is approximately oval in shape. The effects of these different shapes are the same as in the previous embodiment.

Also, from the purpose of the present invention, Figs. 6a and 6
b As shown in figure b, insert the pin insertion hole of piston pin 1'.
The cross-sectional shape of the press-fitted part 1b into A' is approximately oval, and the pin insertion hole of the connecting rod 2 small end 2a'
It is clear that the press-fit shape of A' may be approximately a perfect circle. In this case, the press-fitted part 1b of the piston pin
The long axis of the substantially elliptical cross section is aligned with the direction substantially perpendicular to the axis of the connecting rod 2. Also, when the piston pin 1' is press-fitted into the pin insertion hole A', the piston pin true circle part 1c that comes into contact with the bearing part 3a of the piston pin 3 does not yield the pin insertion hole A' of the connecting rod small end 2a'. Set the dimensions as follows.
(The figures are exaggerated.) It goes without saying that the entire piston pin may have an oval cross section.

As described above, according to the present invention, the cross-sectional shape of the pin insertion hole at the small end of the connecting rod, the cross-sectional shape of the insertion portion of the piston pin into the pin insertion hole,
one of them is formed into a substantially oval shape and the other is formed into a substantially perfect circle, and the piston pin is configured to be press-fitted into the pin insertion hole at its maximum in the direction substantially perpendicular to the axis of the connecting rod. , the crushing deformation of the small end due to the piston inertia force that occurs when the engine is under high load is suppressed, and the increase in stress accompanying this crushing deformation can be suppressed, so even connecting rods made of light alloy materials with a high coefficient of thermal expansion can be used. The stress state can be maintained sufficiently below the fatigue limit and durability can be improved.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a conventional connecting portion between a piston pin and a connecting rod, Fig. 2 is an explanatory view of the same working state, and Fig. 3 is a connecting device between a piston pin and a connecting rod according to the present invention. FIG. 4A and FIG. 4B are explanatory diagrams showing the state of stress when the same is applied. FIG. Figures 5a and 5b are side views of the small end of the connecting rod showing another embodiment of the present invention, and Figure 6a is a side view of the small end of the connecting rod showing another embodiment of the present invention, showing a section cut along the piston pin. A partial sectional view and FIG. 6b are a sectional view taken along the line X-X of the same as above. 1, 1'... Piston pin, 2... Connecting rod, 2a, 2a'... Small end, A, A'...
Pin insertion hole.

Claims (1)

[Scope of utility model registration request] In an internal combustion engine in which a piston pin is press-fitted into a pin insertion hole at the small end of a connecting rod made of a material with a larger coefficient of thermal expansion, The cross-sectional shape of the insertion part of the piston pin should be approximately oval and the other approximately perfect circle, and the amount of press-fitting of the piston pin into the pin insertion hole in the direction approximately perpendicular to the axis of the connecting rod should be maximized. A piston pin-connecting rod coupling device for an internal combustion engine, characterized in that: