COMPONENT OPERATION ／ HST Pump Hydro-Static Transmission HST is a hydraulic driving unit where the engine's power is transmitted to the wheels by the hydraulic pressure. The machine's HST is equipped with a combination of variable-displacement pump and variable-displacement motor. The engine's mechanical power is converted to hydraulic power using the pump. This hydraulic power is reconverted to mechanical power by the motor and transmitted to the wheels. HST functions both as clutch and transmission and the nonstage conversion is available using the hydraulic control. Basically, HST has a system where low-speed and high-pressure oil is used and the oil is circulated in the closed circuit consisting of pump and motor.
The HST is controlled by the following three factors: By controlling the above three factors properly, the machine can travel smoothly.
Oil Discharge → Machine speed Direction of oil flow → Machine moving forward and reverse. Oil Pressure → Driving Force
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The direction of the pump input shaft rotation is always the same. The direction of flow of oil discharged from the pump changes according to tilting of the swash plate and, thereby, the direction of motor output shaft rotation changes. In other words, the machine moves forward or backward according to the direction of swash plate tilting. Further, gear shifting (or speed changing) is done by changing the motor cylinder block tilting angle.
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