COMPONENT OPERATION / HST Pump

Recovery Moment Function

1. α (alpha) and β (beta) are the range of pressure oil applied to the plunger through the valve plate. The comparison between α and β is shown below.

α < β

2. When the HST motor is loaded, the pressure in the circuit from the HST pump to the HST motor increases. Increased pressure acts on the plunger of the HST pump.

3. As there is a rage difference between α (alpha) and β (beta) on the high-pressure port of the valve plate, the pressure oil force acting on the plunger through β (beta) is larger than that through α (alpha). The range difference of (β - α) × Circuit pressure force pushes the bottom of the swash plate as moment around the displacement angle center. Then, the swash plate is moved to neutral. (Recovery moment.)

4. The moving amount (angle) of the swash plate is in proportion to the HST circuit (between HST pump and HST motor) pressure. When pressure is low, the moving angle is small. When pressure is high, the moving angle is large.