Hydraulic system

5.12Travel drive Auto 2-speed (starting serial no. AC 02957)

The travel drive has an “automatic powershift” gearbox. The travel drive is basically in 2nd speed if the switch for 2nd speed range is turned on (high speed). 1st speed is automatically engaged if more power is required.

Ref. Description

1 Drive port (and record swivel joint 4a) forward hydraulic motor (left) Drive port (and record swivel joint 7a) forward hydraulic motor (right)

2

6a)

Function

Driving

If high pressure is applied to one of the drive ports, the brake release piston is actuated first and passes high pressure on to the brake cylinder, which releases the brake. The throttle slowly actuates the brake piston at the same time. Brake piston control causes high pressure to be applied to the motor, which starts turning.

Stopping

The oil flows from both ports to the tank upon releasing the joystick. The brake release piston and the brake piston (slowly actuated by the throttle) return to their base positions. The slow drop of the brake piston prevents the hydraulic motor from coming to an abrupt standstill. With the brake piston in neutral position, the ports are no longer connected to the motor, which can no longer turn. The brake release pressure is reduced via both throttles shortly afterward.

2nd Speed Range Function

1st speed range

• 2nd speed range switch: turned off

The directional valve for the 2nd speed range remains in home position (position as shown in diagram), and the hydraulic motor's swash plate is in maximum capacity position. The motor turns at low speed.

2nd speed range

• 2nd speed range switch: turned on

The directional valve for the 2nd speed range is enabled, and the hydraulic motor's swash plate is in minimum capacity position.

The motor turns at high speed.

If the pressure rises in the traveling drive, the directional valve for the 2nd speed range is forced back to home position and hydraulic motor's swash plate returns to maximum capacity.

The motor now turns at low speed.

The directional valve returns to 2nd speed range as soon as the pressure in the traveling drive drops again.

The motor turns at high speed again.

Switch operating point of the directional valve: 2611 psi (180 bar)