COMPONENT OPERATION ／ HST Motor

・ＨＳＴ Motor（UCHIDA ／ Serial No. 4501 ～）

Motor Start-up

The direction of the drive shaft's rotation is determined by whether the pressure-raised oil is connected to the port A or to port B. When the pressure-raised oil is led to the cylinder block, where the seven pistons are circularly located with a movable condition, the piston presses and rotates the drive shaft. A single piston a stroke takes a cycle, and it sucks and discharges the oil. The drive shaft is smoothly rotated by the continuous motion from the seven pistons. Because part of the hydraulic oil force works on the piston becomes the torque, when the tilt angle is larger, the torque is large. Also, when the tilt angle increases the volume of sucked oil is large, so the drive shaft speed is reduced.

The control plate is connected to the control piston through the connecting rod and the tilt angle is changed by the position of the control piston.

COMPONENT OPERATION ／ HST Motor

・Description of Pilot Pressure Proportion Control (HD Control) Operation

（UCHIDA ／ Serial No. 4501 ～）

The oil on each high-pressure side (A or B) is fed to the smaller diameter side (ring section) of the control piston through the check valve, which presses the rotary group to maximum tilting angle. The oil at each high-pressure side is also led to the primary side of the control bush. The secondary side of the control bush is connected to the larger diameter side of the control piston through the cut-off valve (describe later). So when the pilot pressure led from the X-port becomes higher than the initial load of the adjusting spring, then the pilot piston is moved to the spring side and the oil passage on the primary and secondary sides of the control bush is opened and highpressure oil enters the larger diameter side of the control piston. The control piston is then moved to the minimum tilt side (qmin) direction and the torque reduces and the shaft speed increases because the volume of motor has become smaller.

As above indicated, the movement of the control piston changes the tilt angle: and when the control piston is moved in the qmin direction, the feed-back spring is correspondingly compressed.

The thrust from the pilot pressure is now balanced by the feed-back spring force. That closes the oil passages on the primary and secondary sides of the control bush and keeps the tilt angle appropriate to the pilot pressure.

When the pilot pressure decreases the feed-back spring force exceeds it, so the pilot piston is pushed upward. Therefore, the secondary side of the control bush is led to the tank, and the oil in the larger diameter side of the control piston is returned to the tank. Thus the tilt angle becomes larger, because of the oil pressure on the smaller diameter side of the control piston and the feed-back spring force, and it is changed to an angle which will be appropriate for the pilot pressure.

・ Fixed Pressure Control（UCHIDA ／ Serial No. 4501 ～）

The pressure on the primary side of the control bush is also connected to the cut-off valve and is opposed against the cut-off pressure adjusting spring. When the high-pressure oil in the main circuit exceeds the set pressure of cutoff spring, the spool is moved and the oil on the larger diameter side of the control piston is returned to the tank. Then, as the motor tilts to maximum angle, the input torque is increased and the raised main circuit pressure is temporarily controlled. At that time the main circuit pressure is so controlled that the pressure is fixed until the motor is tilted to the maximum tilt side. When the load is further increased and the main circuit pressure is higher than the cut-off set pressure, the motor is fixed to the maximum tilt.

1-Pilot piston

2-Set screw

3-Adjusting Spring

4-Feed-back spring

5-Control piston

6-O-ring

7-Restriction valve

8-Check valve

9-O-ring

COMPONENT OPERATION ／ HST Motor

10-Back-up ring

11-O-ring

12-Cutoff valve

13-Adjust spring

14-Set screw

Ａ-Control bush (Primary port)

Ｂ-Control bush (Secondary port)

Ｃ-Control piston (Smaller diameter side: Ring section)

Ｄ-Control piston (Larger diameter side)