SYSTEM / Hydraulic System

Charge Circuit

• Pressure oil from the HST charging pump flows to the orifice in the DE pump solenoid valve through the HST filter.

• A pressure difference occurs between the front and the rear of the orifice by the delivery flow rate of the HST charging pump. The DE pump solenoid valve reduces oil pressure from the HST charging pump according to this pressure difference and provides the control pressure for the HST pump displacement angle.

• The DE pump solenoid valve controls the HST pump displacement angle by supplying the reduced pressure oil to the displacement angle control cylinder.

• The high pressure relief valve provides the function of a check valve. When the flow rate on the low pressure side in the HST close circuit is insufficient, the check valve is opened and pressure oil from the HST charging pump is added.

NOTE: The delivery flow rate of the HST charged pump is changed in proportion to the engine speed. Therefore, the control pressure for the HST pump displacement angle is changed almost in proportion to the engine speed.

Neutral Circuit

• The forward/reverse selection solenoid valve is located between the DE pump solenoid valve and the displacement angle control cylinder. When the forward/reverse lever is in neutral, the forward/reverse selection solenoid valve is kept neutral as the forward/reverse selection solenoid valve is not excited.

• Therefore, the pressure oil reduced by the DE pump solenoid valve is not supplied to the displacement angle control cylinder. The HST pump displacement angle is kept neutral.

• Therefore, pressure oil is not delivered from HST pump. The HST motor does not rotate.

NOTE: When the forward/reverse lever is in neutral, the EP motor solenoid valve is excited.

T2-2-14