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| Illustration 1 | g00663688 |
Service Brake System Schematic (1) Service brake for the front axle (2) Spool for the center axle brakes (3) Accumulator for the front service brakes (4) Accumulator for the center service brakes (5) Manifold (6) Accumulator for the parking brake (7) Solenoid valve for the parking brake (8) Another service brake system (ASBS) valve (9) Service brake for the center axle (10) Parking brake (11) Shuttle valve (12) Slack adjuster for the center axle brakes (13) Solenoid valve for the secondary brakes (14) Test fitting (15) Check and pressure reducing valve (16) Relief valve (17) Pressure switch (18) Service brake for the center axle (19) Test fitting (20) Piston pump (21) Oil tank (22) Pressure switch (23) Service brake for the front axle (24) Check valve (25) Check valve (26) Pressure reducing valve (27) Pressure switch (28) Slack adjuster for the front axle (29) Service brake control valve (30) Spool for front axle brakes | |
Piston pump (20) delivers oil to check and pressure reducing valve (15) and to another service brake system (ASBS) valve (8) .
The oil that is delivered to check and pressure reducing valve (15) flows to pressure reducing valve (26), check valve (25), check valve (24), relief valve (16), pressure switch (17) and test fitting (19) .
Pressure reducing valve (26) supplies oil at approximately 5170 kPa (750 psi) to the pilot system for the hoist control valve. Test fitting (14) allows the pressure of this oil to be measured.
Check valve (24) opens. Oil flows to accumulator (3), to spool (30) within the service brake control valve and to solenoid valve (13) within (ASBS) valve (8) .
Check valve (25) opens. Oil flows to accumulator (4) and to spool (2) within the service brake control valve.
If there is a failure of the oil supply from the piston pump, check valve (25) and check valve (24) close. Oil is locked in the lines to service brake control valve (29), accumulator (3) and accumulator (4). The stored energy in accumulators (3) and (4) allows the service brakes to be engaged. This provides a number of brake applications even though the oil supply from the piston pump has failed.
If there is a failure of the oil supply from the piston pump, pressure switch (17) signals the Caterpillar Monitoring System that the oil pressure is low. The Caterpillar Monitoring System provides a warning (category 3).
Relief valve (16) is set to approximately 24100 kPa (3500 psi). The relief valve protects the system if the pressure from the piston pump exceeds the maximum setting. This could happen if the compensator valve for the piston pump fails or if the setting for the compensator valve is adjusted too high. Relief valve (16) will limit system pressure to a maximum of 24100 kPa (3500 psi).
While the machine is in operation, piston pump (20) supplies oil flow into the brake system. The brake system pressure is set to 20340 kPa (2950 psi). The brake system pressure is determined by the setting of the compensator valve for the piston pump. This brake system pressure is available at spools (30) and (2 ) within the service brake control valve. When the service brake control (pedal) is pressed, spools (30) and (2) are offset simultaneously.
The oil flow from spool (30) is sent to pressure switch (27) and to shuttle valve (11) within(ASBS) valve (8). Shuttle valve (11) offsets and oil flows to slack adjuster (28). The slack adjuster then sends oil to service brakes (1) and (23). The oil pressure engages the service brakes for the front axle.
The oil pressure at pressure switch (27) signals the Power Train Electronic Control Module (ECM) that the service brakes have been engaged. The Power Train ECM then allows rapid downshifting of the transmission to take place.
The oil flow from spool (2) is sent to pressure switch (22) and to slack adjuster (12). The slack adjuster then sends oil to service brakes (9) and (18). The oil pressure engages the service brakes for the center axle.
Pressure switch (22) operates the stop lights on the rear of the machine.
The pressure of the oil in the lines that lead to slack adjusters (28) and (12) is also felt on the underside of spools (30) and (2). As pressure increases, spools (30) and (2) move against the force that is being applied by the operator on the service brake control (pedal). Spools (30) and (2) are now in a balance position and oil flow to the slack adjusters is blocked.
When the service brake control (pedal) is released, the oil pressure on the underside of spools (30) and (2) and spring force move the spools to the original positions. The oil flow from piston pump (20) is then blocked at the spools. The oil in the lines to the slack adjusters (28) and (12) returns to the tank.