Operation Under Load

Fig. 9 Variable Speed Governer:

In actual operation, the engine-speed control lever, Fig. 9, assumes a corresponding position for any given engine speed (or vehicle speed); the driver dictates this position by pressing on the accelerator pedal. At engine speeds above idle, the starting and idle springs are collapsed and have no more effect on governor action; the governor spring now assumes that function.
By pressing the accelerator pedal, the driver moves the engine-speed control lever into a position corresponding to a desired (higher) speed. This movement stretches the governor spring by a certain amount, with the result that spring force now exceeds that of the centrifugal weights.
Governor-spring tension pulls the starting and tensioning levers, which pivot around point M2, and move the control collar (according to the linkage geometry) into a position that increases fuel delivery. Increased engine speed is the result. The centrifugal weights then swing outward due to the increased speed, and move the sliding sleeve in opposition to the governor-spring tension. The control collar, however, remains in its "full" position until balance is attained. If engine speed continues to increase, the weights swing farther outward and sleeve force becomes dominant. Now the starting and tensioning levers pivot around M2, moving the control collar in its 'stop' direction so that the cutoff bore is opened earlier. Delivery can be reduced all the way to minimum in this process, which puts a cap on engine speed. For each position of the engine speed control lever, therefore, there is a precise engine-speed range between full load and no load, as long as the engine is not overloaded. The result is that the governor, working within the parameter of its speed droop, maintains the engine speed dictated by the accelerator pedal.
Should load increase to the point where the collar is in its full-load position but engine speed continues to fall, as when the vehicle is pulling a grade, the weights swing inward. But because the collar is already at its position of maximum delivery, fuel delivery cannot be increased further. The engine is thus overloaded and the driver must either downshift or ease off on the accelerator.