Decompressor for 4-stroke cycle internal combustion engines

Abstract

In a 4 stroke cycle internal combustion engine 1 having intake and exhaust valves 9, 10 opened and closed by respective intake and exhaust cams 27, 28 made integral with a camshaft 13, the engine comprises a decompression cam 38 fitted on the camshaft 13 so as to rotate freely, a one-way clutch 29 fitted on the camshaft 13 capable of transmitting reverse rotation torque to the decompression cam 38 only when the camshaft 13 rotates in reverse, a torque limiter 40 inserted between the decompression cam 38 and the one-way clutch 29, and decompression cam stoppers 42, 43 provided on a fixed portion engaging with an engaging section 41 formed on the decompression cam 38 for stopping rotation of the decompression cam 38 at respective positions in normal rotational direction and reverse rotational direction. A lift of a cam section 38a of the decompression cam 38 is higher than a base circle of the exhaust cam 28 and lower than a maximum lift of a cam section 28a of the exhaust cam 28. The exhaust valve 10 is not opened by the decompression cam when the camshaft 13 rotates normally and the decompression cam stopper 43 engages with the engaging section. A decompression device that is simple in construction, small-sized and of low-cost is provided.

Description

technical field [0001] The present invention relates to a pressure reducing device for assisting the starting of a 4-stroke cycle internal combustion engine by means of a starter motor. Background technique [0002] When starting by the rotation of the starter motor, in the state below the specified rotation speed, the decompression device that opens either side of the intake and exhaust valve operates. Heavy centrifugal force, the mechanical decompression device that this decompression device is set in non-operating state is known (referring to Japanese Patent Application Laid-Open No. 11-107727, No. 2000-199412 and Patent No. 2890218 Bulletin). [0003] In addition, when starting by the rotation of the starter motor, the decompression device is operated by the excitation of the electromagnetic solenoid to assist the rotation of the crankshaft, and the internal combustion engine can start to rotate by its own power without using the power of the starter motor. An electric...

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Problems solved by technology

[0004] In the above-mentioned mechanical decompression device, since the operation and non-operation of the decompression are automatically switched by using the centrifugal force, the counterweight for generating the centrifugal force is indispensable, and the inertia of the valve cam system becomes large, requiring a large output starter motor, it is difficult to miniaturize the starter motor

[0005] In addition, in the above-mentioned electric decompression device, only when the decompression device is necessary to operate, it is only necessary to energize the electromagnetic solenoid, so that it is possible to reduce the size of the decompression device, but it is necessary to distinguish the decompression device. The action / non-action electronic judging device is difficult to apply to a small 4-stroke cycle internal combustion engine that does not have an electronic control device. Furthermore, even in an internal combustion engine with an electronic control device, there is a disadvantage that the electronic control device is complicated.

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