JP3339664B2 - Engine piston back side shape - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape of a corner portion between a side surface and a top surface forming a recess on the back surface of an engine piston.

[0002]

2. Description of the Related Art Conventionally, a recess 2 is formed on the back surface of a piston 1 as shown in FIG. 2 as a back surface shape of this type of piston, and a piston pin 8 is formed on a side wall 3 of the piston 1 so as to cross the recess 2. A single concave curved surface 9a is provided at the corner portion 9 between the side surface 2a and the top surface 2b which are inserted and further form the concave portion 2.
Is known. Side wall 3 of piston 1
Are formed with a pair of through holes 4 and 5.
A piston pin 8 is inserted through bushings 6 and 7. In this example, the diameter of the piston 1 is 114 mm, and the radius of curvature R of the concave curved surface 9a is 10 mm.

In the piston 1 configured as described above, when the piston 1 reaches a top dead center and fuel in a cylinder (not shown) explodes, an extremely large downward force acts on the upper surface of the piston 1. The force is applied to the crankshaft (not shown) via the piston pin 8 and the connecting rod (not shown).
Is transmitted to

[0004]

However, in the above-described conventional piston back surface shape of the engine, a large compression force is generated between the piston and the piston pin during the explosion stroke of the engine, and this compression force is applied to the corner of the recess. The formed single concave curved surface receives, and at point B ₁ (FIG. 2) of this concave curved surface, 1
Relatively large stress that 23kgf / mm ² had a defect that acts at 6.4kgf / mm _^2, B ² points. The above stress is a numerical value when a compressive force of 12 tons is applied between the piston and the piston pin.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a piston back surface shape of an engine capable of dispersing strain and reducing stress without increasing the weight of the piston and without significantly changing the piston shape.

[0006]

A configuration of the present invention for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The present invention includes a concave portion 12 formed on the back surface of the piston 11 and a side wall 1 of the piston 11 extending across the concave portion 12.
3 is an improvement of an engine piston provided with a piston pin 18 inserted into the piston 3. The characteristic configuration is that the recess 12
Corner portion 19 between side surface 12a and top surface 12b forming
Independent curvature radius R _1, R ₂ a plurality of concave curved surfaces 19a having, 19b are formed in a plurality of concave curved surfaces 19
a, 19b are connection points A ₃ in the longitudinal section of the piston 11
It is connected at.

[0007]

When an extremely large downward force acts on the upper surface of the piston 11 during the explosion stroke of the engine, the piston 1
A large compressive force is generated between the piston pin 1 and the piston pin 18. Since this compressive force acts on a plurality of concave curved surfaces 19a and 19b formed in the corner portion 19 of the concave portion 12, the distortion caused by the compressive force is also dispersed, and the stress at the corner portion 19 of the concave portion 12 is reduced. Is done.

[0008]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, a concave portion 12 is formed on the back surface of a piston 11 that reciprocates in the cylinder of the engine, and a pair of through holes whose hole centers coincide with a straight line crossing the concave portion 12 are formed on a side wall 13 of the piston 11. 14 and 15 are formed. A piston pin 18 is inserted into these through holes 14 and 15 via bushes 16 and 17 so as to cross the recess 12. An upper end of a connecting rod (not shown) is rotatably fitted into a center of the piston pin 18 exposed in the concave portion 12, and a lower end of the connecting rod is rotatably attached to a crankshaft (not shown).

This embodiment is characterized in that a plurality of concave curved surfaces 19 each having an independent radius of curvature are provided at a corner portion 19 between the side surface 12a and the top surface 12b forming the concave portion 12.
a, 19b are formed. Concave curved surface 19
In this example, the upper and lower corners 19a and 19b are formed at the upper and lower corners 19, the radius of curvature R ₁ of the upper concave curved surface 19a is 10 mm, and the radius of curvature R ₂ of the lower concave curved surface 19b is 10 mm.
It is. The outer diameter of the piston 11 is 114 m in this example.
m.

In the piston 11 configured as described above,
When the piston 11 reaches the top dead center and the fuel in the cylinder (not shown) explodes, an extremely large downward force acts on the upper surface of the piston 11, and this force is applied via a piston pin 18 to a connecting rod (not shown). ). At this time, a large compressive force is generated between the piston 11 and the piston pin 18, but this compressive force is dispersed and acts on the two concave curved surfaces 19 a and 19 b formed in the corner portion 19 of the concave portion 12, so that The strain due to the compressive force is also dispersed. That is, when allowed to act compression force of 12 tons between the piston 11 and the piston pin 18, the value maximum stress generated at _a point A in the upper concave curved surface 19a is 12.9k
gf / mm ² , and the maximum stress on the lower concave curved surface 19b is generated at the point A ₂ and the value is 20.4 kgf / m 2.
m ² , the stress in the corner portion 19 is reduced as compared with the conventional piston back surface shape in which a single concave curved surface is formed in the corner portion. As a result, the strength of the piston 11 is substantially improved. The piston 11 and the piston pin 1
When a compressive force of 12 tons is applied between
Stress at A _3-point is a connection point between the upper concave curved surface 19a and the lower concave curved surface 19b is as small as 6.2kgf / mm ^2. In the above embodiment, two concave curved surfaces are formed at the corners of the concave portions. However, this is an example, and three or more concave curved surfaces may be formed.

[0011]

As described above, according to the present invention, a plurality of concave curved surfaces each having an independent radius of curvature are formed at the corner between the side surface forming the concave portion and the top surface. Since the curved surface is connected at a point in the vertical section of the piston, even if a large compression force is generated between the piston and the piston pin during the explosion stroke of the engine, this compression force is generated by a plurality of concave shapes formed at the corners of the concave portion. It is dispersed on a curved surface, and the distortion due to the compressive force is also dispersed. As a result, the stress at the corner of the concave portion can be reduced, and the strength of the piston is substantially improved. Further, since the weight of the piston is not increased and the shape of the piston is not largely changed, the inertia force of the piston is not increased and the manufacturing cost is not increased.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a piston of an engine according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a conventional example and corresponding to FIG.

[Explanation of symbols]

11 the piston 12 recess 12a side 12b top surface 18 piston pin 19 corners 19a, 19b concave curved surface R _1, R ₂ radius of curvature

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02F 3/00 F16J 1/16

Claims (1)

(57) [Claims] A recess (1) formed on a back surface of a piston (11).
2) and a piston pin (18) inserted into a side wall (13) of the piston (11) so as to cross the recess (12), wherein the recess (12) is formed. side (12a) and top surface (12b) corner portion between (19) independently radius of curvature (R _1, R ₂₎ a plurality of concave curved surfaces (19a, 19b) having a are formed, the plurality of concave The curved surface (19a, 19b) is vertical to the piston (11).
A back surface shape of an engine piston, which is connected at a connection point (A ₃ ) in a cross section .