JPH09264156A - Crankshaft supporting structure for 2-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the performance and durability of crankshaft supporting bearing irrespective of an assembling dimension error or the deviation of a dimension changing amount during thermal expansion in the crankshaft supporting structure of a 2-cycle engine. SOLUTION: One side of a crankshaft 4 and the other end thereof are supported on a crank case 1 via a cylindrical roller bearing 7. For the cylindrical roller bearing 7, a cylindrical roller 73 is positioned in an axial direction by one bearing ring 72 and a relative displacement between one bearing ring 72 and the cylindrical roller 73 is permitted by the other bearing ring 71. Even if opposing axial loads are applied to the inner and outer rings of a deep groove ball bearing 6 or the cylindrical roller bearing 7 by an assembling dimension error or the deviation of a dimension changing amount caused by an assembling width between the balance weights of the crankshaft 4 or the forming position of the step part 1a of the crank case 1, no unnecessary preloads are applied especially to the deep groove ball bearing 6. No damage is given to its bearing function even if the inner and outer rings 71 and 72 of the cylindrical roller bearing 7 is shifted in relative position.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crankshaft support structure for a two-cycle engine.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional crankshaft support structure for a two-cycle engine. In the figure, 1 is a crankcase, 2 is a piston, 3 is a connecting rod, and 4 is a crankshaft.

Both ends of the crankshaft 4 are supported by the crankcase 1 via deep groove type ball bearings 5 and 6, and oil seals 8 and 5 are provided on the outer sides of the deep groove type ball bearings 5 and 6, respectively.
8 are provided.

The deep groove type ball bearings 5 and 6 are the crankcase 1
Is fixed by press-fitting between the crankshaft 4 and the crankshaft 4, and is axially positioned by the step portion 1a of the crankcase 1.

In this way, in the structure in which the crankshaft 4 is firmly positioned on the crankcase 1 by using the deep groove type ball bearings 5 and 6, in general, the above deep groove type ball bearings 5 and 6 are provided with proper internal clearances. Ideally, it should be installed so that it will be in a neutral contact state with the state. This is because the crankshaft 4 rotates eccentrically, so that if a preload is applied, the load on the bearing is large and seizure easily occurs.
This is because the durability tends to decrease.

Although not shown, in the case where the rotational power is taken out from the one shaft end side of the crankshaft 4 with a belt or a chain, bending stress is applied to the crankshaft 4, The usage conditions of the deep groove type ball bearings 5 and 6 tend to be severe.

[0007]

By the way, in the structure of the above-mentioned conventional example, an assembly dimension error due to the assembly width between the balance weights of the crankshaft 4 and the formation position of the step portion 1a of the crankcase 1, and the crankshaft 4 and The deep groove ball bearings 5 on both sides of the crankshaft 4 are caused by the deviation of the amount of dimensional change at the time of thermal expansion caused by the difference in the linear expansion coefficient with the crankcase 1.
Axial loads that are contradictory in the axial direction act on the inner and outer rings of 6 and the balls of the deep groove ball bearings 5 and 6 may be in a state of oblique contact with the inner and outer rings. In such a situation, contrary to the design concept at the time of assembly as described above,
Unnecessary preload is applied to the deep groove type ball bearings 5 and 6, and the bearing performance and durability are inevitably lowered as described above.

On the other hand, the internal clearances of the deep groove type ball bearings 5 and 6 may be set to be large so as to suppress the occurrence of the above-mentioned problems even under the influence of the assembly dimensional error and thermal expansion. It is conceivable that the support rigidity of the crankshaft 4 may be insufficient, and it is pointed out that it is difficult to manage the internal clearance.

Therefore, it is an object of the present invention to make it possible to stabilize the performance and durability of a crankshaft support bearing in a crankshaft support structure for a two-cycle engine regardless of assembly dimensional errors and thermal expansion. .

[0010]

SUMMARY OF THE INVENTION The present invention has a structure in which both sides of a crankshaft are supported by a case via rolling bearings, and a rolling bearing on one side of the crankshaft is a deep groove type ball bearing. The other side rolling bearing is a cylindrical roller bearing, and in the cylindrical roller bearing, one bearing ring axially positions the cylindrical roller, and the other bearing ring is axial relative to the one bearing ring and the cylindrical roller. This allows for a mechanical displacement.

In the structure of the present invention described above, it is essential that one side of the crankshaft is firmly fixed to the crankcase instead of being firmly fixed to both sides of the crankshaft as in the conventional example. The side is loosely supported. Therefore, due to the assembly dimension error between the crankshaft and the crankcase and the deviation of the dimension change amount due to thermal expansion, axial loads that are axially contradictory to the inner and outer rings of the bearings on both sides of the crankshaft are caused. When it is applied, the inner and outer rings of the cylindrical roller bearing are displaced to opposite sides in the axial direction, whereby unnecessary deep preload is not applied to the deep groove ball bearing. Generally, in the cylindrical roller bearing, even if the inner and outer races are displaced in opposite axial directions, the contact state between the inner and outer races and the cylindrical roller does not change, so that the bearing function is not hindered.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the embodiments shown in FIGS.

FIG. 1 is a vertical sectional view of a crankshaft support structure for a two-cycle engine according to an embodiment of the present invention.
In the figure, 1 is a crankcase, 2 is a piston, 3 is a connecting rod, and 4 is a crankshaft.

The crankshaft 4 is supported by the crankcase 1 at one end thereof via a deep groove type ball bearing 6 and at the other end thereof via a cylindrical roller bearing 7, and these bearings 6, 7 are both supported. Oil seals 8, 8 are provided on the outer sides of the respective.

The deep groove type ball bearing 6 and the cylindrical roller bearing 7 are
It is fixed by press fitting between the crankcase 1 and the crankshaft 4, and is axially positioned by the step portion 1a of the crankcase 1.

This embodiment is different from the conventional example in that one side of the crankshaft 4 is supported by the cylindrical roller bearing 7. As the cylindrical roller bearing 7, a type in which at least one raceway surface of the inner and outer races is not formed with a roller positioning flange is used. Specifically, for example, there are NU type cylindrical roller bearings having JIS bearing series symbols as shown in FIG. 1 and N type cylindrical roller bearings as shown in FIG. It may be either the one with or without the cage. In addition to the above, as the cylindrical roller bearing 7, there may be mentioned one having no inner and outer rings, as shown in FIG.

The cylindrical roller bearing 7 in the illustrated example has an inner ring 71 having no roller positioning flanges at both axial ends, an outer ring 72 having roller positioning flanges 72a, 72a at both axial ends, and a plurality of cylindrical rollers 73. And a cage 74 of the machined type. The inner ring 71 is attached to the crankshaft 4 and the outer ring 7
2 are press-fitted into the crankcase 1, respectively.

Further, the deep groove type ball bearing 6 comprises an inner ring 61, an outer ring 62, a plurality of balls 63, and a cage 64. The inner ring 61 and the outer ring 62 are press-fitted into the crankshaft 4 and the crankcase 1, respectively.

In the structure of this embodiment, the assembly width between the balance weights of the crankshaft 4 and the crankcase 1
Of the bearings on both sides of the crankshaft 4 due to an error in assembly due to the formation position of the stepped portion 1a and a deviation in the amount of dimensional change during thermal expansion caused by a difference in linear expansion coefficient between the crankshaft 4 and the crankcase 1. When axially contradictory axial loads are applied to the inner and outer races 6 and 7, the inner and outer races 61 and 62 of the deep groove type ball bearing 6 on one side of the crankshaft 4 are not displaced so as to be opposite to each other in the axial direction. The inner ring 71 of the cylindrical roller bearing 7 on the other side of the crankshaft 4 and the mass of the outer ring 72, the cylindrical roller 73 and the cage 74 are relatively displaced in the axial direction, whereby the deep groove type ball bearing described above. 6 will be maintained in the preferred neutral contact state. Therefore, the bearings 6 and 7 on both sides of the crankshaft 4 are not unnecessarily burdened, and the desired rolling performance and durability can be achieved as designed and the crankshaft 4 can be stably supported. Like

[0020]

According to the present invention, in the cylindrical roller bearing arranged on one side of the crankshaft, an assembly dimensional error due to an assembly width between the balance weights of the crankshaft and a formation position of a step portion of the case, and a thermal expansion at the time of an expansion. By allowing the axial displacement due to the deviation of the dimensional change, the deep groove type ball bearing on the other side of the crankshaft can be maintained in a preferable neutral contact state. Therefore, the bearings on both sides of the crankshaft can exhibit desired stable rolling performance and durability, and the output loss of the engine can be prevented.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a crankshaft support structure for a two-cycle engine according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of the upper half showing another example of the cylindrical roller bearing for supporting the crankshaft.

FIG. 3 is a vertical sectional view of the upper half showing another example of the cylindrical roller bearing for supporting the crankshaft.

FIG. 4 is a vertical sectional view of a conventional crankshaft support structure for a two-cycle engine.

[Explanation of symbols]

 1 Crankcase 4 Crankshaft 6 Deep Groove Ball Bearing 7 Cylindrical Roller Bearing 71 Inner Ring 72 Outer Ring 73 Cylindrical Roller

Claims (1)

[Claims] 1. A structure in which both sides of a crankshaft are supported by a case via rolling bearings, wherein one side of the crankshaft is a deep groove type ball bearing and the other side of the crankshaft is a cylindrical roller. In the cylindrical roller bearing, one bearing ring axially positions the cylindrical roller, and the other bearing ring allows relative displacement of the one bearing ring and the cylindrical roller in the axial direction. A crankshaft support structure for a two-cycle engine, characterized in that