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| Illustration 1 | g03797697 |
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(1) Actuator piston
(2) Port for drive loop (3) Charge pump (4) Input shaft (5) Swashplate (6) Piston (7) Barrel (8) Spring (9) Port Plate (10) Port for the drive loop | |
The pump for the hydrostatic drive system is a variable displacement piston pump with two rotating groups. The pump is mounted to the rear of the engine. The input shaft of the pump engages a coupling that is mounted to the flywheel of the engine in order to drive the pump.
Note: The following description is for only one of the rotating groups in the pump.
When the engine is running, shaft (4) and barrel (7) are rotating. There are nine pistons (6) in barrel (7). Port plate (9) and swashplate (5) are stationary within the pump housing. Port plate (9) and swashplate (5) do not rotate. Spring (8) maintains a force against barrel (7) and port plate (9). When barrel (7) is rotating, each piston (6) follows the angle of swashplate (5).
If the angle of swashplate (5) is zero, pistons (6) do not move in and out of barrel (7) and there is no oil flow. Pilot oil from the charge pump maintains oil pressure in the system in order to perform the following tasks:
- Keep barrel (7) full of oil.
- Lubricate the pump components.
- Provide makeup oil for internal loss of oil that is due to leakage.
- Provide pilot oil to the servo valve in order to shift actuator piston (1) and change the angle of swashplate (5).
- The charge pump provides pilot oil in order to release the parking brakes.
The position of swashplate (5) is determined by charge pump. The transmission control lever that is located on the left console sends signals to the electronic control module (ECM). The ECM interprets the signals and the ECM sends pulse width modulated signals to the solenoids on either side of the servo valve. As the servo valve is shifted to either direction, signal oil gets filtered through the pilot oil screen. The signal oil then travels to the corresponding end of actuator piston (1).
As actuator piston (1) begins to move, the angle of swashplate (5) begins to increase. As piston (6) follows swashplate (5), pistons (6) begin to move in and out of barrel (7). As piston (6) moves out of barrel (7), oil is drawn from the passage of port (10) of the drive loop through port plate (9). As piston (6) follows swashplate (5) and the piston moves into barrel (7), the oil is pushed through port plate (9) into the passage to port (2) of the drive loop.
As the angle of swashplate (5) increases, the output flow of the pump also increases.
Reference: For more information on the charge pump, refer to Systems Operation, UENR4089, "Gear Pump (Implement)".