COMPONENT OPERATION ／

HST Motor

・ System pressure control valve（YUKEN ／ Serial No. 1001 ～ 4499）

１．Two kinds of pressurized oil are supplied from the HST pump to the system pressure control valve.

① Pilot Pressure to change the motor displacement - Connect to Port "G". It is connected from port "V" on the HST pump.

② Pilot Pressure (DPc) to control the system pressure - Connect to Port "H". It is connected from port "Q" on the HST pump.

２．When the engine speed is low;

A spring force is given to the right side of the spool, and the pilot pressure, which is used for the pump discharge rate control, is given to the left side of the spool. When the engine speed is low, the pilot pressure is also low. The spring force is stronger than the pilot pressure, so that the spool is moved to the left. When the spool is in this position the HST motor capacity becomes large. Therefore, when the engine speed is low the motor capacity is large.

３．When the Engine Speed is High;

As the engine speed increases, the pilot pressure rises gradually. When the pilot pressure rises, the force pressing the spool to the spring side also rises. As the force of the pilot pressure increases, the spool moves to right side. And then circuit of the chamber A is connected to drain port through the spool and port G is connected to chamber B to change HST motor capacity to small. After the spool position has been changed to the right side, the small HST motor capacity is maintained even though the engine speed is further increased.