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| Illustration 1 | g03880903 |
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| Illustration 2 | g03880146 |
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Location of the brake pump (1) Brake pump (2) Pressure compensator valve | |
The braking system uses automatically controlled variable displacement brake pump (1), which is mounted on the engine side of the torque converter housing. The pump detects pressure and flow requirements and supplies oil flow in order to charge two braking system accumulators. Attached to brake pump (1) is pressure compensator valve (2).
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| Illustration 3 | g03880403 |
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View of Piston Pump (2) Pressure compensator valve (3) Pump drive shaft (4) Cylinder barrel (5) Pistons (6) Swashplate (7) Pump inlet (8) Pump outlet (9) Actuator piston (10) Swashplate control spring | |
When pump drive shaft (3) is rotated, cylinder barrel (4) also turns. Nine pistons (5) and cylinder barrel (4) turn together.
When pistons (5) are almost out of cylinder barrel (4), swashplate (6) is at the maximum angle. This action draws oil from pump inlet (7) and into the piston bore in cylinder barrel (4). As cylinder barrel (4) rotates, the angled swashplate (6) pushes pistons (5) back into cylinder barrel (4). This action pushes oil out of the piston bore and through pump outlet (8) and to the brake hydraulic system.
Pressure compensator valve (2) controls the pressure and flow of brake pump (1). Controlled pressure and flow of brake pump (1) is necessary in order to fulfill load and flow requirements of the brake hydraulic system.
Maximum pump output is available when the engine is on and the oil pressure is less than the pressure of pressure compensator valve (2).
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| Illustration 4 | g03880362 |
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View of Pressure Compensator Valve (2) Pressure compensator valve (11) Passage from pump outlet (12) Spool (13) Spring (14) Passage (15) Drain passage to pump case | |
Oil from pump outlet (8) flows to passage from pump outlet (11). The oil is then held in passage from pump outlet (11) by spool (12).
When the service brakes are not applied, the braking system oil pressure increases until the force on spool (12) exceeds the pressure of spring (13).
The oil pressure in passage from pump outlet (11) then moves spool (12). In order to move spool (12), the oil pressure must exceed
With the movement of spool (12), the oil in passage from pump outlet (11) flows through passage (14). The oil that flows through passage (14) controls actuator piston (9) in the pump. The force of the oil from passage (14) moves actuator piston (9). Actuator piston (9) moves swashplate (6) toward the minimum angle (approximate zero degree angle).
When pump drive shaft (3) and barrel (4) turn with swashplate (6) at the minimum angle position, pistons (5) have little movement in barrel (4). This movement occurs when the reaction plate follows the approximate zero degree angle of swashplate (6).
The minimal movement of pistons (5) keeps the pressure of the oil in pump outlet (8) at the pressure setting of pressure compensator valve (2). The extra oil from pump outlet (8) flows into the pump body for pump lubrication. The oil in the pump body flows through a return line to the hydraulic tank.
When the braking system oil pressure decreases, there is a pressure decrease in pump outlet (8) and passage from pump outlet (11). The decreased pressure allows spring (13) to move spool (12). Passage (14) is then open to drain passage to pump case (15). This action causes a lack of oil pressure in passage (14) to control actuator piston (9) in the pump. The lack of oil pressure for actuator piston (9) allows actuator spring (10) to move swashplate (6). Swashplate (6) is able to move to the maximum angle position. This action will cause piston pump (1) to upstroke again.