Internal-combustion engines – Poppet valve operating mechanism – Camshaft drive means
Reexamination Certificate
1999-11-23
2001-12-25
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Camshaft drive means
C123S090330, C123S1960CP
Reexamination Certificate
active
06332440
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a four-stroke cycle internal combustion engine, and in particular, to a four-stroke cycle internal combustion engine equipped with an OHC type valve drive mechanism which is suitable to be used for portable working machines or the like.
DESCRIPTION OF THE PRIOR ART
Recently, there has been an increasing demand for utilizing a four-stroke cycle internal combustion engine in portable working machine such as a portable grass trimmer, a chain saw or the like, in order to reduce noise and make the exhaust gas cleaner.
As means for transmitting rotation from the crankshaft to the camshaft, it has been known to use a toothed belt in an automotive four-stroke cycle internal combustion engine.
However, a four-stroke cycle internal combustion engine used in a portable working machine generally is rotatably driven at a high speed of over 7,000 to 10,000 r/min. It is generally structured so that inlet and exhaust valves are opened and closed by a rocker arm which is swung by a push rod, as disclosed in, for example, Japanese Patent Laid-open Publication No. Hei 8-260915. The power transmission mechanism with a toothed belt which is employed in an automotive engine or the like is suitable for use in a four-stroke cycle internal combustion engine for a portable working machine in the respect that it enables reduction of the weight of the machine and simplifying the structure thereof. However, such a four-stroke cycle internal combustion engine has hardly been put into practice because of poor durability due to the high speed of the four-stroke cycle internal combustion engine as described above. In addition, the toothed belt generally needs a tensioner. Therefore, the overall structure becomes complicated, more time and labor are required in assembly and further, the entire size of the working machine becomes larger. Therefore, it has been difficult to actually apply such a belt system to a four-stroke cycle internal combustion engine of a portable working machine of the type which is lifted up and held by an operator.
The object of the present invention is to provide a novel four-stroke cycle internal combustion engine with a toothed belt for a portable working machine or the like where it has previously been difficult to employ the toothed belt in a power transmission mechanism thereof.
SUMMARY OF THE INVENTION
The object of the present invention described above can be achieved by an OHC type four-stroke cycle internal combustion engine comprising: a cylinder portion; a crankshaft; a camshaft; and a power transmission mechanism disposed vertically along the cylinder portion and for transmitting rotation of the crankshaft to the camshaft, the power transmission mechanism having an intermediate transmission member which is drivably connected to the camshaft via a toothed belt, and a rotation speed transmission member for transmitting the rotation speed of the crankshaft to the intermediate transmission member.
The four-stroke cycle internal combustion engine of the present invention operates as follows. When the OHC type four-stroke cycle internal combustion engine is actuated, the crankshaft is rotatably driven by upward and downward movement of a piston. The rotation speed of the crankshaft is reduced by a rotation speed transmission member of the power transmission mechanism and is transmitted to the intermediate transmission member. Further, the rotation is transmitted from the intermediate member to the camshaft via the toothed belt.
In accordance with a four-stroke cycle internal combustion engine of the present invention, since the rotation speed transmission member is disposed between the crankshaft and the camshaft and the rotation of the crankshaft is transmitted by the rotation speed transmission member to the intermediate transmission member, the load exerted on the toothed belt, which runs between the intermediate transmission member and the camshaft, is reduced, whereby the durability of the toothed belt is improved. This allows the practical application of the toothed belt to a four-stroke cycle internal combustion engine running at high speed. Further, since the rotation speed transmitted from the crankshaft can be reduced to a predetermined value by the rotation speed transmission member, the diameter of a toothed driven pulley attached to the camshaft need not be made larger to reduce the rotation speed, whereby the size of a portion of the engine in the vicinity of a valve mechanism can be reduced, which allows the entire size of the four-stroke cycle internal combustion engine to be smaller.
In addition, since a toothed belt which does not slip is employed, the power transmission mechanism can be disposed inside a lubricating oil mist passage and no design restriction is placed thereon in this regard.
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Araki Tsuneo
Liu Yumin
Nagai Noboru
Jacobson & Holman PLLC
Kioritz & Corporation
Lo Weilun
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