Engine starting system

Starting device

In order to start the engine which is in the stopstate, initial combustion needs to be caused by rotating the crank shaft in some way. This is called cranking. There are the manual type and the electric type for the starting device for performing cranking.

(1) Manual type

The manual type starting device has the “recoil type” in which the rope wrapped around the reel on the side of the flywheel of the engine is pulled, and the “handle type” in which a detachable handle is attached to the engine and rotated.

1) Recoil type

In general, the recoil type is used for small-sized air-cooled gasoline engines. Because the compression ratio of the gasoline engine is not very high (about 8 to 11), some are equipped with an automatic decompression device for starting to reduce the force of pulling the rope
in recoil at the time of starting.

■ Example of an automatic decompression device

As the release lever attached to the cam shaft is opened by centrifugal force when the engine is in operation, the part corresponding to the chord of the crescentic cam attached to the release lever coincides with the surface of the cam. As the release lever is on the cam shaft side when the engine is being started, the part corresponding to the arc of the crescentic cam appears on the surface of the cam. Therefore, the rocker arm is pushed up temporarily, which removes the compression pressure and reduces the force of pulling the rope of the recoil starter.

2） Handle type

In general, the handle type is used for smallsized diesel engines. Because the compression ratio of the diesel engine is high, it is equipped with a decompression device to make it easy to rotate the handle.

In the decompression device, the exhaust valve or the intake valve is pushed open by
operating the decompression lever to remove the compression pressure of the cylinder. Therefore, the engine starts when the starter handle is rotated while operating the decompression lever and the decompression lever is released to exceed the compression position once momentum is gathered.

(2) Electric type

The electric type starting device performs starting by the direct current motor which uses a battery as a power source, and the motor is called a starter motor.

In the starting method by the starter motor, power is transmitted by engaging the pinion gear of the starter with the ring gear fitted on the outer circumference of the flywheel.