COMPONENT OPERATION / HST Pump

The HST pump is a two-direction displacement angle swash plate type variable displacement plunger pump. The forward/reverse selection solenoid valve (3), the DE pump solenoid valve (2), the cutoff valve (4), the high pressure relief valves (5,10), the low pressure relief valve (8), and the HST charging pump (7) are provided in the HST pump. The HST pump (6) consists of the shaft, the plunger, the cylinder block, the displacement angle control cylinder, and the swash plate.

Engine power is transmitted to the shaft of the HST pump directly. The shaft rotation of the HST pump is also transmitted to the main pump unit through the coupling.

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COMPONENT OPERATION / HST Pump

COMPONENT OPERATION / HST Pump

Operation

COMPONENT OPERATION / HST Pump

The shaft is splined to the cylinder block. The plungers are installed in the cylinder block. Engine power is transmitted to the shaft of the HST pump directly. As the shaft is rotated, the plungers rotate with the cylinder block together. The plungers slide on the swash plate so that the plungers reciprocate in the cylinder block as the swash plate is positioned at an angle toward the plungers. By this reciprocation, hydraulic oil is drawn and delivered. Either port A or port B is selected as a delivery port by the displacement angle control of the swash plate.

Delivery Flow Rate Increasing and Decreasing Operation

HST pump delivery flow rate is varied by changing the displacement angle of the swash plate and changing the stroke of the plunger. As the swash plate is connected to the displacement angle piston of the displacement angle cylinder through the pin, the swash plate operates according to the movement of the displacement angle piston. The displacement angle piston has the built-in spring, which acts on the direction of the displacement angle piston to return to neutral. The displacement angle piston position is moved by the displacement angle control pressure applied to the displacement angle cylinder. Therefore, the displacement angle of the swash plate is changed.

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Rotary Group Part:

COMPONENT OPERATION / HST Pump

Displacement Angle Control Cylinder Part:

Piston