COVER 6B7590 - Caterpillar

Solenoids
Solenoid Valve (Parking Brake)
The parking brake solenoid valve engages and disengages the parking brake. The brakes are applied by a spring and released by pressure. The ECM de-energizes the parking brake solenoid to apply the brake. The ECM energizes the parking brake solenoid to release the brake. The solenoid is always de-energized when the neutral interlock is active. The solenoid will not be energized under the following conditions:
The park brake lockout configuration is locked.
A stall test is attempted
The electronic pressure override calibration is attempted.
The neutral interlock is active.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 energizes the transmission pilot supply solenoid if the neutral interlock has been cleared. If the transmission pilot supply solenoid is de-energized, machine cannot be moved and the parking brake is applied. The ECM also de-energizes this solenoid during a fault that requires the transmission to shut down.Solenoid Valves (Pump and Motor Displacement Control)
Illustration 1 g00839868Forward Solenoid for the Left Drive Pump Reverse Solenoid for the Left Drive PumpReverse Solenoid for the Right Drive PumpForward Solenoid for the Right Drive PumpProportional Solenoid of the Right Drive MotorProportional Solenoid of the Left Drive MotorThe 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 displacements. 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 based on the information from the following devices:
The Joystick forward/neutral/reverse Position
The Joystick Thumbwheel 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 PedalThe solenoid valves are proportional pressure reducing valves. 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.Backup Alarm
Illustration 2 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.