4-cycle engine

Details 4-cycle engine 4-cycle engine

1999-07-21

2001-06-26

Kamen, Noah P. (Department: 3747)

Internal-combustion engines

Frame construction

Horizontal cylinder

C123S090380, C123S1950HC

Reexamination Certificate

active

06250273

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a 4-cycle engine, particularly, an improvement in a 4-cycle engine including an engine body which is comprised of a crankcase having first and second bearing portions for supporting opposite ends of a crankshaft, and a head-integral type cylinder barrel having a cylinder bore with a piston received therein.
2. Description of the Related Art
It is known, as disclosed, for example, in Japanese Patent Application Laid-open No. 8-177441, that in a 4-cycle engine of the mentioned type, the crankcase is comprised of first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect the axis of the first and second bearing portions. The cylinder barrel and the first bearing portion are formed by being integrally molded on the first case half. The second bearing half is formed by being integrally molded on the second case half.
In this type of engine, it is effective to reduce the distance as much as possible between the first and second bearing portions for supporting the opposite ends of the crankshaft, in order to alleviate the bending moment generated on the crankshaft by a load applied from the piston to the crankshaft to enhance the durability of the crankshaft.
In the above conventional engine, however, a valve operating mechanism connected to the crankshaft is disposed adjacent the inside of the second case half. For this reason, when the distance between the first and second bearing portions is to be reduced, the valve operating mechanism is an obstacle. Namely, at least one of the bearing portions cannot be disposed adjacent a crank portion of the crankshaft, because it is hindered by the valve operating mechanism. When the engine is to be assembled, a portion of the valve operating mechanism is obliged to be temporarily assembled to the crankshaft before coupling the first and second case halves to each other. Hence, it cannot be said that assembling this type of engine is easy is good.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a 4-cycle engine of the above-described type, wherein the distance between the first and second bearing portions supporting the opposite ends of the crankshaft is reduced without being interfered with by the valve operating mechanism. The durability of the crankshaft is thereby enhanced. Moreover, the valve operating mechanism can be assembled to the crankshaft after coupling the first and second case halves to each other, which leads to easy assembling of the engine.
To achieve the above object, according to the present invention, there is provided a 4-cycle engine comprising an engine body which is comprised of a crankcase including first and second bearing portions for supporting opposite ends of a crankshaft. A head-integral type cylinder barrel has a cylinder bore in which a piston is received. The crankcase is comprised of first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect an axis of the first and second bearing portions. The cylinder barrel and the first bearing portion are formed by being integrally molded on the first case half to form an engine block. The second bearing portion is formed by being integrally molded on the second case half. A side cover is coupled to an outer side surface of the engine block which is opposite from the parting plane, so as to define a valve operating chamber for accommodation of a valve operating mechanism between the side cover and the outer side surface.
With the arrangement of the present invention, the valve operating chamber is defined between the first case half and the side cover coupled to the outer side surface of the first case half. Therefore, the first and second bearing portions formed on the first and second case halves are disposed adjacent opposite ends of a crank portion of the crankshaft, respectively, without encountering any interference by the valve operating mechanism accommodated in the valve operating chamber and the distance between the first and second bearing portions is minimized. Thus, the bending moment applied from the piston to the crankshaft is reduced to enhance the durability the crankshaft.
Moreover, even after coupling of the first and second case halves, the assembling of the valve operating mechanism can easily be carried out in a state in which the side cover has been removed.
Further, it is possible to provide a 4-cycle engine at a low cost in various forms which can be applied for various uses, only by changing the shapes of the second case half and the side cover which are relatively small parts.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 8-177441 (1996-07-01), None

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