CARRIER-PLANETARY 3754476 - Caterpillar

Illustration 1 g02204295
(1) Service brake pedal
(2) Service brake pedal position sensor
Illustration 2 g02204296
(1) Service brake pedal
(2) Service brake pedal position sensor
(3) Foot brake valve
(A) Exhaust port (Tank port)
(B) Supply port (Pressure port)
(C) Outlet port (Brake port) Foot brake valve (3) for the service brakes is located in the cab below the service brake pedal.Oil flows from the brake accumulators through the control valve (brake) to supply port (B) of the foot brake valve.When service brake pedal (1) is depressed, internal passages in foot brake valve (3) route the oil from the service brake accumulator to outlet port (C). This signals oil flow back through the control valve (brake) to the control passage of the diverter valves for the front and rear service brakes. When signal oil is present at the control passage, oil will flow into passages in the wheels. This oil will apply the service brakes.When service brake pedal (1) is released, internal passages in foot brake valve (3) route the supply oil to exhaust port (A). The supply oil flows back through the control valve (brake) to the hydraulic tank. The service brakes will be released.The service brake pedal position sensor (2) sends a signal to the Brake ECM indicating service brake pedal position. The brake ECM uses the pedal position signal to disengage the Anti-Rollback feature.Anti-Rollback Feature
Anti-Rollback is a feature of the electric drive trucks that engages the service brakes when the truck is moving in the opposite direction from the requested gear command and the ground speed/direction signals.When a wrong direction is sensed and machine is moving 2.0 km/h (1.2 mph) in the wrong direction, the Drive Train and Chassis ECMs send information to the Brake ECM over the Cat Data Link and the Brake ECM sends current to the front and rear ARC solenoids. The service brakes engage and the truck comes to a stop. The alarm sounds and an "Anti-Rollback" message will be displayed through the Advisor panel. When the truck has the Anti-Rollback feature initiated, there will be no logged event.To disengage the Anti-Rollback feature, the operator must take operational control of the truck. The operator must fully depress service brake pedal (1) so that service brake pedal position sensor (2) will send a PWM signal of at least 90 percent threshold value to the Brake ECM.