Speed changeover
1. When the pilot pressure at port Pi is disconnected, the spool moves upward by the spring force &
hydraulic force which is applied to the differential area between red section and yellow section. The oil in
chamber of swash piston flows to the drain line, and the swash plate moves to increase swash angle, so
the motor rotates at low speed.
2. When the pilot pressure at port Pi is connected, spool moves downward by the pressure at Pi. The
supply oil through check ball folws to the swash piston. Swash pisto pushs the swash plate and decrease
swash angle, so the motor rotates at high speed.
3. In this picture, the force by Pi port pressure acts against the force by supply pressure which is applied
on the differential area and spring. When the supply pressure reach to specified value, the force by supply
pressure and spring overcomes the force by Pi pressure. So the spool moves upward.
The oil in chamber of swash piston flows to the drain line, and the swash plate moves to increase swash
angle, so the motor rotates at low speed and high torque.
Picture text:
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