Solenoid Valve (Parking Brake)
Parking Brake Valve Group
(1) Parking brake solenoid
(2) Outlet line to the parking brakes
(3) Return line to the tank
(4) Pilot solenoid
The parking brake solenoid valve disengages the brakes. The brakes are applied by a spring and released by pressure. When the operator activates the parking brake switch, the ECM disengages the parking brake solenoid valve which relieves the hydraulic pressure and the brakes are applied. The brakes are released when the solenoid is engaged. The solenoid is always disengaged when the neutral interlock is active. The neutral interlock must be released and the transmission lever is not in neutral in order for the parking brake solenoid to be engaged. The solenoid will not be engaged under the following conditions:
- The park brake lockout configuration is locked.
- A stall test is attempted.
- The electronic pressure override calibration is attempted.
Transmission Pilot Supply Solenoid
The solenoid for the pilot supply of the transmission provides hydraulic pilot oil to the hydrostatic pumps and the motors as well as the solenoid for the parking brake. The ECM only engages the solenoid for the pilot supply for the transmission if the neutral interlock has been cleared. If the pilot supply for the transmission is not energized, there is no oil to the transmission and the machine cannot be moved. The ECM also disengages this solenoid during a fault that requires the machine to shut down.
Solenoid Valves (Pump and Motor Displacement Control)
Forward Solenoid for the Left Drive Pump
Reverse Solenoid for the Left Drive Pump
Reverse Solenoid for the Right Drive Pump
Forward Solenoid for the Right Drive Pump
Proportional Solenoid of the Right Drive Motor
Proportional Solenoid of the Left Drive Motor
The four solenoid valves for the drive pumps are outputs of the ECM. The ECM uses these solenoid valves to control the speed and the direction of the machine by varying the pump displacement. The two solenoid valves for the drive motors are outputs of the ECM. The ECM uses these solenoid valves to control the machine speed by varying the motor displacements. The ECM applies electrical current to the appropriate solenoid valves. This electrical current is based on the information from the following devices:
- The Joystick forward/neutral/reverse position
- The Steering Pedal Position Status (Pedal Steering Configuration)
- The Parking Brake Switch
- The Engine Speed Sensor
- The Left Track Speed Sensor
- The Right Track Speed Sensor
- The Brake Pedal
The solenoid valves are pressure reducing valves. The solenoids are the proportional type. The ECM uses a pulse width modulated signal (PWM) to vary the current to the solenoid. The current varies the pressure output of the solenoid valve. The amount of pressure controls the swashplate angle of the pumps and motors.
The backup alarm is an output of the ECM. The backup alarm alerts nearby personnel that the machine is backing up. When the operator selects the REVERSE position the ECM energizes the backup alarm.