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 manufacturers 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.