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| Illustration 1 | g01394456 |
Hydraulic schematic for the steering and braking system (1) Left steering cylinder (2) Right steering cylinder (3) Brake release cylinder (4) Front wheel brakes (5) Steering control valve (6) Steering release diverter valve (7) Pressure tap for the brake release system (8) Line relief and make-up valve (9) Line relief and make-up valve (10) Shuttle valve (11) Spool (12) Check valve (13) Brake release sequence valve (14) Connection for recovery hook type brake release system (15) Shuttle valve (16) Steering relief valve (17) Parking brake oil pressure switch - electronic transmission control (18) Parking brake oil pressure switch - remote control light (19) Check valve (20) Steering system pressure tap (21) Steering pilot control valve (22) Implement and steering neutralizer valve (23) Pressure tap for the parking brake and the pilot system (24) Check valve (25) Service brake pedal (26) Service brake and transmission neutralizer pedal (27) Secondary steering diverter valve (if equipped) (28) Hydraulic oil cooler (29) Rear brake accumulator (30) Front brake accumulator (31) Primary steering flow switch (if equipped) (32) Left neutralizer valve (33) Right neutralizer valve (34) Residual brake oil pressure switch (35) Pressure tap for the steering pilot system (36) Parking brake control valve (37) Residual brake oil pressure switch (38) Rear wheel brakes (39) Service brake control valve (40) Secondary steering pump (if equipped) (41) Steering pilot pressure reducing valve (42) Line from the implement lift circuit (43) Selector and pressure control valve (44) Brake accumulator oil pressure switch - alert indicator (45) Brake accumulator oil pressure switch - brake application (46) Hydraulic tank (47) Pilot oil pressure reducing valve (48) Breaker relief valve (49) Portable hydraulic pump quick connect coupler (50) Pilot and braking pump (51) Steering pump (52) Implement pump (53) Hydraulic oil filters (54) Portable hydraulic pump quick connect coupler (55) Check valve (56) Brake accumulator charging valve (57) Pressure tap for brake accumulator charging system | |
Wheel brakes (4) and (38) are divided into two sections. The service brake is an oil pressure applied and spring released brake section. The parking brake is an oil pressure disengaged and spring engaged brake section. The service brake can be used when the parking brake is disengaged.
The service brakes are controlled by two brake pedals in the operator's station. The left and right brake pedal assemblies are connected by a mechanical linkage. The left pedal is service brake and transmission neutralizer pedal (26). The right pedal is service brake pedal (25) .
When service brake pedal (25) is depressed only the wheel brakes are applied. When service brake and transmission neutralizer pedal (26) is depressed, the wheel brakes are applied and the transmission is neutralized. This allows the full engine power to be used in the hydraulic system. When service brake and transmission neutralizer pedal (26) is released, the transmission engages and the wheel brakes are released.
With the engine running, oil flows from hydraulic tank (46) to pilot and braking pump (50) which is part of the implement, steering, pilot and braking pump. The oil then flows from pilot and braking pump (50) through check valve (55) and into brake accumulator charging valve (56) .
The pistons in the brake accumulators are held against the oil intake ends with dry nitrogen gas at a pressure of approximately 5515 kPa (800 psi). Rear brake accumulator (29) stores hydraulic oil pressure for the rear service brakes. Front brake accumulator (30) stores hydraulic oil pressure for the front service brakes.
After the service brakes have been activated several times, the volume of oil in the accumulators is less. When there is a decrease of oil pressure in the brake accumulators to 11725 ± 345 kPa (1700 ± 50 psi), brake accumulator charging valve (56) routes oil from pilot and braking pump (50) to brake accumulator (30) or (29). When brake accumulator oil pressure rises to 14485 ± 345 kPa (2100 ± 50 psi), shuttle valves block the flow of oil to the brake accumulators and cause the oil to return to hydraulic tank (46). The brake accumulator charging valve (56) process works the same whether one or both accumulators need to be recharged.
From brake accumulators (30) or (29), the oil flows to service brake control valve (39). Service brake control valve (39) is a tandem valve that routes brake oil to both front and rear axle service brakes.
When a brake pedal is depressed, oil flows through service brake control valve (39) where pressure to the wheel brakes is reduced to 5860 ± 345 kPa (850 ± 50 psi). Oil flows out of the top port to rear wheel brakes (38), and out of the bottom port to front wheel brakes (4). Oil pressure is approximately 207 kPa (30 psi) higher for the rear wheel brakes than that of the front wheel 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 in the operator station on the dash panel. The parking brake will not disengage until the engine is running and the service brake oil pressure reaches approximately 8270 kPa (1200 psi). The brake will automatically engage if brake system oil pressure is low. When the parking brake control switch is moved to the ON position, all wheel brakes are engaged.
With the engine running, oil flows from pilot and braking pump (50) through pilot oil pressure reducing valve (47) to parking brake control valve (36). Pilot oil pressure reducing valve (47) reduces pilot oil pressure for the pilot circuit. Pilot oil pressure reducing valve (47) is set at 3515 ± 70 kPa (510 ± 10 psi).
When the parking brake control switch in the operator station is moved to the OFF position, the solenoids of parking brake control valve (36) are energized. Oil flows through parking brake control valve (36) to both axles. 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 control switch is moved to the ON position, or the engine start switch key is turned to the OFF position. This will cause parking brake control valve (36) to return the parking brake oil to hydraulic tank (46). 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.
ReferenceFor information on manually releasing the parking brake, refer to Systems Operation, Testing and Adjusting, "Parking Brake - Manual Release".
Certain AVSpare machines fitted 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.
ReferenceFor information on the brake release system, refer to Systems Operation, Testing and Adjusting, "Brake Release System".