D330, D333, 3304, 3306 – Pierce Output Shaft Governor

1. Flexible drive cable. 2. Output shaft governor. 3. Terminal lever. 4. Rocker shaft. 5. Rate adjusting screw. 6. Speed change lever. 7. Governor spring. 8. Bumper screw. 9. Link. 10. Lever. 11. Lever. 12. Low speed adjusting screw. 13. High speed adjusting screw. 14. Bracket.

The output shaft governor (2) is driven by a flexible cable assembly (1) which connects to the governor drive mechanism on the torque converter. The output shaft governor (2) and hydraulic servo mechanism are connected by means of an adjustable link (9).

The output shaft governor acts as an “assistant operator,” automatically reducing engine speed, which in turn reduces converter output shaft speed whenever the load on the converter output shaft decreases. Thus, it acts as a speed limiting device by preventing the output shaft and drive equipment from suddenly and perhaps dangerously, overspeeding. This also relieves the operator of making speed adjustments through the engine governor.

The torque converter output shaft maximum speed is either a high speed setting or a low speed setting, which is determined by changing the position of speed change lever (6), normally by remote control. High speed screw (13) determines the maximum speed for the high speed setting, and low speed screw (12) determines the maximum low speed setting. In other words, for either setting there is a predetermined maximum speed which the output shaft cannot exceed.

The operation of the governor is the same as most rotating weight-type governors. The governor operates only when the torque converter output shaft attempts to exceed a predetermined maximum speed. This speed is determined by the amount of tension placed on governor spring (7). On a variable speed governor, the spring tension is controlled by rate adjusting screw (5) and the position of the speed change lever. Increasing the spring tension increases the maximum speeds.

When the output shaft speed approaches the predetermined governed speed setting, weights (15) are forced out moving thrust sleeve (17) and bearing assembly (18) against the rocker yoke (19). As the output shaft speed reaches the predetermined governor speed setting, the force of the weights overcomes the force of the governor spring and the rocker yoke is moved, rotating the rocker shaft (4). Linkage attached to the rocker shaft overrides the diesel engine governor and reduces engine speed which in turn reduces converter output shaft speed. As the rocker yoke moves outward, it contacts small bumper spring (16) in the end of the governor body, which dampens oscillation of the yoke preventing erratic governor control. A bumper screw positions the bumper spring.

As torque converter output shaft speed drops below the maximum governed speed limit, the force exerted by the output shaft governor weights is reduced. Since the governor is then no longer effective, the diesel engine governor takes over full engine control and increases engine speed toward its full governed setting.

The terminal lever (3) mounted on the rocker shaft is connected to the hydraulic servo mechanism by the adjustable link (9) and actuating lever (10). Any movement of the rocker shaft is thus transmitted to the hydraulic servo mechanism.

15. Weight. 16. Bumper spring. 17. Thrust sleeve. 18. Bearing assembly. 19. Rocker yoke.

The hydraulic servo mechanism consists essentially of a servo piston (24), control valve and the necessary connecting linkage. The piston (24) fits into the cylinder bore and is connected to the actuating lever by shaft (20), link (21) and lever (22).

20. Shaft. 21. Link. 22. Lever. 23. Shaft. 24. Piston. 25. Cam.

Oil, delivered from the engine oil pump, flows into the servo mechanism and normally flows through the piston, valve and back to the crankcase. When the output shaft governor takes effect, due to an increase in the torque converter output shaft speed, the governor linkage moves the control valve in the piston. The flow of oil through the piston is blocked and results in an oil pressure build-up. This pressure moves the piston to follow the movement of the valve. This movement continues until the piston ports are uncovered and oil flows through the piston once again.

The piston movement is transmitted to cam (25), shaft (23) and the governor linkage, and in turn decreases the amount of fuel being delivered to the engine.

When the load on the output shaft is increased, the output shaft speed is reduced and the force exerted by the output shaft governor weights decreases. The force exerted by the output shaft governor spring then overcomes the force exerted by the weights and the actuating linkage moves the servo mechanism valve into the piston. The movement of the valve into the piston uncovers dump ports and allows oil to flow unrestricted through the servo mechanism. The valve and piston are inactive and then the diesel engine governor takes over full control of the engine and the fuel rack moves in the direction of increased fuel, increasing engine speed to its full governed speed.

The whole operational sequence of the torque converter governor overriding the diesel engine governor and then relinquishing control again to the engine governor occurs each time the load variations are severe enough to permit the output shaft speed to increase or decrease and activate the output shaft governor.

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