If additional load is applied to the engine while it is running at full-load governed speed, there will be a reduction in engine rpm. A greater quantity of fuel is allowed to pass into the pumping chamber because of the increased time that the charging ports are open. Fuel delivery will continue to increase until the rpm drop to the engine manufacturer's predetermined point of maximum torque.
Do NOT attempt to adjust the torque curve on the engine at any time. This adjustment can be done only during a dynamometer test where fuel flow can be checked along with the measured engine torque curve or on a fuel pump test stand.
The DB2 fuel injection pump uses a mechanical type governor (fig. 5-20). The governor function is that of controlling the engine speed under various load settings. As with any mechanical governor, it operates on the principle of spring pressure opposed by weight force, with the spring attempting to force the linkage to an increased fuel position at all times. The centrifugal force of the rotating flyweights attempts to pull the linkage to a decreased fuel position.
Rotation of the governor linkage varies the valve opening, thereby limiting and controlling the quantity of fuel that can be directed to the fuel plungers. The position of the throttle lever controlled by the operator's foot will vary the tension of the governor spring. This force, acting on the linkage, rotates the metering valve to an increased or decreased fuel position as required.
At any given throttle position the centrifugal force of the rotating flyweights will exert force back through the governor linkage which is equal to that of the spring, resulting in a state of balance. Outward movement of the weights acting through the governor thrust sleeve can turn the fuel-metering valve by means of the governor linkage arm and hook. The throttle and governor spring position will turn the metering valve in the opposite direction.
The governor is lubricated by fuel received from the fuel housing. Fuel pressure in the governor housing is
Figure 5-20. - Governor assembly.Continue Reading