COMPONENT

OPERATION ／ HST Motor

４．System pressure control (Automatic speed change control)

The check valve selects the higher pressure from the two sides in the main circuit pressure, and is led to the end of the pin built in the spool. When high pressure acts on the pin, the spool is moved to the left. When the HST motor capacity position is smaller position and the main circuit pressure is higher, the spool moves to the left side by acting high pressure to the pin. Then the capacity of the HST motor becomes large.

５．When the motor capacity changes from small to large the main circuit pressure is affected by the pilot pressure ( ΔPc) which itself changes with the engine speed. The higher the engine speed (pilot pressure), the higher the main circuit pressure to change the capacity of the HST motor.

６．In order to adjust the engine speed when the engine capacity is changed from large to small, the tension of the spring is set by using the adjusting screw.

COMPONENT OPERATION ／ HST Motor

・HST motor first-speed control （YUKEN ／ Serial No. 1001 ～ 4499）

The electromagnetic selector valve controls the direction of pilot pressure which is into port "G" to choose automatic shift mode or middle speed fixing mode. The following shows the hydraulic circuit. When the electromagnetic valve is turned OFF, the HST motor is functioned as automatic shift mode. When it is turned ON, the pilot pressure goes to the middle speed control piston, and then the HST motor changes to middle speed fixing mode.