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| Illustration 1 | g06255040 |
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(1) Brake release cylinder
(2) Pressure tap for the brake release system (3) Line to pilot circuit (4) Parking brake control valve (5) Parking brake oil pressure sensor (6) Pressure tap for the parking brake circuit (7) Front wheel brakes (8) Brake accumulator charging valve (9) Brake accumulator oil pressure switch - alert indicator (10) Pressure tap for the parking brake circuit (11) Check valve (12) Parking brake oil pressure switch (13) Brake accumulator oil pressure switch - brake application (14) Check valve (15) Portable hydraulic pump quick connect coupler (16) Brake accumulators (17) Service brake oil pressure sensor (Rear) (18) Service brake oil pressure sensor (Front) (19) Residual brake oil pressure switch (20) Service brake and transmission neutralizer pedal (21) Service brake pedal (22) Pressure tap for the brake accumulator circuit (23) Service brake oil pressure switch (24) Pilot oil pressure relief valve (25) Portable hydraulic pump quick connect coupler (26) Check valve (27) Breaker relief valve (28) Brake accumulators (29) Service brake control valve (30) Residual brake oil pressure switch (31) Rear wheel brakes (32) Pilot oil filter (33) Pressure tap for the pilot circuit (34) Pressure tap for the brake accumulator circuit (35) Engine overspeed control valve (36) Pilot and braking pump (37) Hydraulic filters (38) Hydraulic tank (39) Service brake return valve | |
Front wheel brakes (7) and rear wheel brakes (31) are divided into two sections. The service brake section is oil pressure engaged and spring disengaged brake. The parking brake section is an oil pressure disengaged and spring engaged brake. The service brake can be used when the parking brake is disengaged.
The service brakes are controlled by two brake pedals in the operator station. The left and right brake pedal assemblies are connected by a mechanical linkage. The left pedal is the service brake and transmission neutralizer pedal. The right pedal is the service brake pedal.
When the service brake pedal is depressed, only the service brakes are applied. When the service brake and transmission neutralizer pedal is depressed, the service brakes are applied and the transmission is neutralized. Full engine power can be used for the hydraulic system. When the service brake and transmission neutralizer pedal is released, the transmission engages and the service brakes are released.
With the engine running, oil flows from hydraulic tank (38) to pilot and braking pump (36) which is part of the steering, pilot, and braking pump. The oil then flows from pilot and braking pump (36) to brake accumulator charging valve (8).
The pistons in brake accumulators (16) and (28) are held against the oil intake end with dry nitrogen gas. Brake accumulators (16) and (28) store hydraulic oil pressure for the service brakes.
After the service brakes have been activated several times, the volume of oil in the accumulators are less. When the pressure in the brake accumulators decreases, brake accumulator charging valve (8) routes oil from pilot and braking pump (36) to brake accumulators (16) and (28). When the brake accumulator oil pressure rises, the charging spool in brake accumulator charging valve (8) blocks the flow of oil to brake accumulators (16) and (28), and routes the flow of oil to the pilot circuit.
From brake accumulators (16) and (28), the oil flows to engine overspeed control valve (35) then on to service brake control valve (29). Service brake control valve (29) is a tandem valve that routes brake oil back through engine overspeed control valve (35) to both the front axle service brakes and the rear axle service brakes.
When a brake pedal is depressed, oil flows through service brake control valve (29) where pressure to the service brakes is reduced. Oil flows out of the top port to rear wheel brakes (31), and out of the bottom port to front wheel brakes (7). Oil pressure is higher for the rear service brakes than the front service brakes.
Oil pressure flows into the service brake section of the wheel brakes and acts against the service brake piston, causing the machine to slow down or stop.
The parking brake is controlled by a switch on the dash panel in the operator station. The parking brake will not disengage until the engine is running and the service brake oil pressure reaches operating pressure. The parking brake will automatically engage if brake system oil pressure drops below the operating range. When the parking brake control switch is moved to the ON position, all parking brakes are engaged.
With the engine running, oil flows from pilot and braking pump (36) through pilot oil filter (32) to brake accumulator charging valve (8). Oil flows from brake accumulator charging valve (8) to pilot oil pressure relief valve (24). Pilot oil pressure relief valve (24) maintains a constant pressure in the pilot circuit. Pilot oil flows from pilot oil pressure relief valve (24) to parking brake control valve (4).
When the parking brake switch in the operator station is moved to the OFF position, the solenoids of parking brake control valve (4) are energized. Oil flows through parking brake control valve (4) to front wheel brakes (7) and rear wheel brakes (31). Oil pressure then disengages the parking brake in each wheel brake assembly.
The parking brake control valve solenoids are de-energized when the parking brake switch is moved to the ON position. The parking brake control valve solenoids are de-energized when the engine start switch key is turned to the OFF position. When the parking brake control valve solenoids are de-energized, parking brake control valve (4) causes parking brake oil to return to hydraulic tank (38). Spring pressure acting on the parking brake piston starts to engage the parking brake. Return oil from the service brake is restricted by service brake return valve (39), ensuring that the brake discs are held stationary between the service brake piston and the parking brake piston until the service brake piston is fully retracted. The parking brake is now engaged.
If the parking brake is engaged due to a machine fault, and the machine must be towed, the machine parking brake can be released manually.
Reference: For information on manually releasing the parking brake, refer to Systems Operation, Testing and Adjusting, "Parking Brake - Manual Release".
Certain Caterpillar machines equipped with the optional remote control system may be equipped with the optional brake release system. If the parking brake is engaged due to a machine fault and the machine must be towed, the brake release system can be used to release the machine parking brakes.
Reference: For information on the brake release system, refer to Systems Operation, Testing and Adjusting, "Brake Release System".