BOLT 0003270 - Caterpillar

Solenoid Valve (Parking Brake)
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Parking Brake Valve Group (1) Outlet line to the parking brakes (2) Park brake solenoid (3) Override solenoid (4) Return line to the tank (5) Charge oil line from the front pump (6) Charge oil line from the rear pump
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Solenoid Valve (Parking Brake)The parking brake solenoid valve disengages the brakes. The brakes are spring applied and hydraulically released. When the operator activates the park brake switch, the ECM de-energizes the parking brake solenoid valve which relieves the hydraulic pressure and the brakes are engaged. When the machine is initially started, the Neutral Interlock Function will engage the park brake. When certain diagnostic codes are present, the ECM will deactivate the parking brake solenoid. Solenoid Valve (Override)
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The solenoid valve (override) is an on/off output of the ECM. The ECM de-energizes the solenoid valve in order to neutralize the transmission by releasing the pilot oil pressure in the pumps if certain fault conditions exist, or if the parking brake switch is engaged. This causes the pumps to destroke. Solenoid (Engine/Fuel Shutdown)
The machine ECM controls the engine fuel shutoff solenoid and fuel lift pump relay based on the status of the machine key start switch and the engine operating status. The engine will shut down when the key switch is turned to the off position.Solenoid Valves (Pump and Motor Displacement Control)
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Proportional Solenoid (Forward) of the Left Drive Pump Proportional Solenoid (Reverse) of the Left Drive PumpProportional Solenoid (Reverse) of the Right Drive Pump Proportional Solenoid (Forward) of the Right Drive Pump Proportional Solenoid of the Right Drive Motor Proportional 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 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 Accel Button Status
The Joystick Decel Button Status
The Joystick Steering Position Status
The Parking Brake Switch
The Engine Speed Sensor
The Left Track Speed Sensor
The Right Track Speed SensorThe 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.