Solenoids
Solenoid Valve (Parking Brake)
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| Illustration 1 | g00794020 |
Parking Brake Valve Group (1) Outlet line to the parking brakes (2) Parking brake solenoid (3) Pilot solenoid (4) Return line to the tank (5) Charge oil line from the front pump (6) Charge oil line from the rear pump | |
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 joystick 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 transmission pilot supply solenoid provides hydraulic pilot oil to the hydrostatic pumps and the motors as well as the park brake solenoid. The ECM only engages the transmission pilot supply solenoid if the neutral interlock has been cleared. If the transmission pilot supply 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)
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| Illustration 2 | g00839868 |
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 Joystick Thumbrocker Position
- The Joystick Steering Position Status
- The Parking Brake Switch
- The Engine Speed Sensor
- The Left Track Speed Sensor
- The Right Track Speed Sensor
- The Brake/Decel 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.
Relays
Start Relay (Magnetic Switch)
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| Illustration 3 | g00785967 |
The start relay is an on/off solenoid that controls the starting motor. When the relay is not energized, the starting motor is not running. When the relay is energized, the starting motor is running.
Relay (Starting Aid)
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| Illustration 4 | g00875516 |
The starting aid relay is an attachment that enhances the starting capability of the engine by adding ether to the fuel mixture during start-up. The starting aid relay is an on/off switch that controls the valve for the starting aid. When the relay is not energized, ether aid is not provided. When the relay is energized, ether is supplied to the engine.
Relay (Lift Pump)
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| Illustration 5 | g00875516 |
The relay for the lift pump controls the fuel lift pump. When the relay coil for the lift pump is not energized, the fuel lift pump does not operate. When the relay coil is energized, the fuel lift pump operates. When the key start switch is in the run position, the output for the relay for the lift pump will energize. If the engine is not running and the run signal for the key switch has been on for longer than 60 seconds, the relay output will turn off. If the engine is being commanded to start (the start relay output is on) or if the engine is running, the relay output remains energized. The output will not energize the relay for the lift pump when the key start switch is in the OFF position.
Backup Alarm
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| Illustration 6 | g00391203 |
Backup Alarm | |
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.