SHIELD 0340731 - Caterpillar

Illustration 1 g03535022
Service Brake Control Valve
The service brake control valve is located on the front left side, and underneath the operator platform. The service brake control valve is a pressure reducing valve. When the brake pedal is depressed, a lever and cam assembly actuates the service brake control valve. The control valve is a fully split modulating valve with two independent circuits. If there is a partial or full failure of one circuit, the other circuit will still have normal brakingModulation of the pressurized oil in the accumulators to the service brakes is controlled by the service brake control valve. The position of the brake pedal causes a specific pressure at each of the valve outlets ports. As the position of the pedal changes, the pressure at the service brakes also changes.
Illustration 2 g03540757
Service Brake Control Valve
(A) Outlet port to rear service brakes
(B) Outlet Port to front service brakes
(C) Inlet ports from accumulators
(D) Outlets for the pump signal to the hydraulic tank When the brake pedal is not depressed, the brake valve is sprung to the position shown in the schematic. Pump supply oil (C) from the accumulators does not flow to service brakes (A) and (B) . In the pedal released position, the brake valve allows oil from service brake ports (A) and (B) to flow to hydraulic tank port (D) releasing the brake force. For additional information on the service brakes, refer toSystems Operation, "Service Brakes". When the brake pedal is modulated through the pedals 'inching stroke', the action closes the service brake path to tank. The brake pedal then enters the 'braking stroke' and allows a proportional oil flow from the accumulators (C) to the service brakes (A) and (B) in order to apply braking force. Once the oil pressure at the service brakes is equal the supply pressure plus the spring force, the spool is balanced and maximum brake force has been achieved.Inching Mode
The inching mode is standard on all machines. The inching mode is operational during the first 25 mm (1.0 inch) to 50 mm (2.0 inch) of travel of either service brake pedal. This "inching stroke" action closes the service brake path to tank. Attached to the brake mechanism is a proportional position sensor that reads the brake pedal position and feeds the electrical signal to the machine ECM during the "inching stroke" part of the brake valve stroke. This electrical signal is processed and the machine ECM decreases the speed of the machine accordingly. Commanded engine rpm is also maintained. When the brake pedals are released, the inching mode is deactivated. For additional information on the electronic brake pedal calibration, refer to Systems Operation, "Brake Pedal Calibration".