This illustration shows a schematic of the electronic brake control valve with the brakes released. When the operator releases the travel control pedal, the PWM rotary position sensor (connected to the pedal) sends a signal to the Machine ECM. The Machine ECM increases the current to the proportional solenoid (1). The amount of current sent to the solenoid is directly proportional to the position of the travel control pedal.
The proportional solenoid moves to the right and blocks oil flow to the tank. Charge oil pressure moves the pressure reducing spool (2) to the right and oil is directed to the brake pistons. The brake pistons move the brake springs to release the brakes. The accumulator piston (3) acts as a cushion to prevent the reducing spool from moving too rapidly.
When the service brakes are fully engaged or the parking brake is engaged, the proportional brake solenoid is DE-ENERGIZED, the parking brake solenoid (4) is ENERGIZED, and the secondary brake solenoid (5) is ENERGIZED.