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| Illustration 1 | g03662535 |
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(1) Hydraulic tank
(2) Service brake control valve (3) Parking brake actuator (4) Front service brake (5) Parking brake (6) Brake accumulators (7) Brake combination valve (8) Rear service brakes (9) Pump | |
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| Illustration 2 | g03663094 |
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824K brake hydraulic schematic with engine on, service brakes released, and parking brake engaged (1) Brake pump (2) Brake combination valve (3) Accumulator charging valve (4) Front brake accumulator (5) Rear brake accumulator (6) Parking brake control valve (7) Parking brake (8) Service brake control valve (9) Rear service brakes (10) Pilot pressure reducing valve (11) Sequence valve (12) Brake oil filter (13) Main relief valve (14) Front service brakes (15) Parking brake actuator (16) Transmission control (17) Stop lamp switch (18) Throttle lock disconnect switch (A) Implement pilot supply | |
This schematic shows the 824K brake hydraulic system with the service brakes "RELEASED" and the parking brake "ENGAGED". The brake/pilot pump (1) sends oil through the brake oil filter (12) to the brake combination valve (2). Inside the brake combination valve, oil flows to the main relief valve (13), the sequence valve (11), the pilot pressure reducing valve (10). The relief valve limits the maximum pressure for the brake system. The pressure reducing valve decreases the brake oil pressure, which is used as the pilot oil supply for the implement and steering systems. The sequence valve directs oil from the brake/pilot pump to the Clean Emissions Module (CEM) fan motor on the 826K machines equipped with a Tier 4 Final engine. In the 824K machines, the front brake accumulator (4) and rear brake accumulator (5) are continuously charged when the engine is running. The accumulators will continue to charge until the oil pressure increases to
If the machine loses power or if the hydraulic pump fails, the service brakes can still be "ENGAGED". The pressure in the accumulators permits several applications of the service brakes to stop the machine or slow the machine enough to engage the parking brake (7). When the right brake pedal is depressed, the stop lamp switch is closed, which illuminates the brake lights on the back of the machine. Also, when the right brake pedal is depressed, the right brake pedal switch signals the Engine ECM to disable the throttle lock function. The Engine ECM sends the switch position data over the Cat Data Link to the Power Train ECM. When the parking brake switch in the cab is in the ON position, the Power Train ECM de-energizes the parking brake solenoid in the parking brake control valve (6). Parking brake oil is directed to the tank, and spring force causes the parking brake actuator to engage parking brake.
When the right and left brake pedals are depressed. The service brake control valve (8) directs oil to the front and rear service brakes, which engages the service brakes. When the parking brake switch in the cab is in the" OFF" position, the power train ECM energizes the parking brake control valve solenoid in the parking brake control valve (6). The parking brake solenoid directs oil from the rear brake accumulator (5) to the parking brake spool inside the parking brake control valve. Rear brake accumulator oil is directed to the parking brake actuator (15), which releases the parking brake (7).
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| Illustration 3 | g03662985 |
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825K/ 826K hydraulic schematic with engine on, service brakes engaged, and parking brake released (1) Brake pump (2) Brake combination valve (3) Parking brake control valve (4) Service brake control valve (5) Parking Brake (6) Front service brake (7) Pilot pressure reducing valve (8) Sequence valve (9) Main relief valve (10) Pressure filter (11) Parking brake actuator (12) Throttle lock disconnect switch (13) Stop lamp switch (14) Transmission control (A) Implement pilot supply (B) CEM fan motor (826K) | |
The 825K and 826K brake hydraulic system operates the same as the 824K brake hydraulic system, but has only a front brake accumulator to provide oil to the front service brakes (6). The service brake control valve (4) has only one spool. This spoolch directs oil to the front service brakes when the right brake pedal or the left brake pedal is depressed.
When the right and left brake pedals are depressed. The service brake control valve (4) directs oil to the front service brakes, which engages the service brakes. When the parking brake switch in the cab is in the" OFF" position, the Power Train ECM energizes the parking brake control valve solenoid in the parking brake control valve (3). The parking brake solenoid directs oil from the brake accumulator (15) to the parking brake spool inside the parking brake control valve. Brake accumulator oil is directed to the parking brake actuator (11), which releases the parking brake (5).