Governors

Principles of Gasoline And Diesel Fuel Systems
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Governors

a. General.

All diesel engines require governors to prevent

overspeeding of the engines under light loads.

also demand control of idling speed.

Any of the governors provide a

variable-speed control which, in addition to controlling minimum and maximum

speeds, will maintain any intermediate speed desired by the operator.

Engine speed in a diesel is controlled by the amount of fuel injected. The

injection, therefore, is designed to supply the maximum amount of fuel that

will enable it to operate at full load while reaching a predetermined

maximum speed (rpm). If, however, the maximum fuel charge were supplied to

the cylinders while the engine was operating under a partial or unloaded

condition, the result would be overspeeding and certain engine failure.

Thus, it can be seen that the governor must control the amount of fuel

injected in order to control the engine speed.

b. Actuation.

Governors may be actuated through the movement of

centrifugal flyweights or by the air-pressure differential produced by a

governor valve and venturi assembly.

The centrifugal flyweight type may incorporate a mechanical linkage system

to control the injection pump, or it may include a hydraulic system to

transmit the action of the weights to the pump. On engines where the rate

of acceleration must be high, the governor-controlling weights must be small

to obtain the required rapid response from the governor.

The problem is

that the smaller flyweights will not exert enough force to control the

injection pump properly. When this is the case, the flyweights will be used

to control a hydraulic relay valve, which, in turn, will control the

injection pump through a servo piston.