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| Illustration 1 | g02689217 |
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Location of the brake pump (1) Torque converter housing (2) Brake pump (3) Pressure compensator valve | |
The braking system uses an automatically controlled variable displacement piston pump. The pump can detect pressure requirements and flow requirements. The pump is mounted on the engine side of the torque converter housing. The pump supplies oil flow to charge the two accumulators.
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| Illustration 2 | g00103377 |
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Component locations for the brake pump (3) Pressure compensator valve (4) Actuator piston (5) Swashplate control spring (6) Swashplate (7) Pump drive shaft (8) Pump outlet passage (9) Pump inlet passage (10) Piston (11) Cylinder barrel (12) Shoe plate (13) Piston shoe | |
When pump drive shaft (7) is rotated, cylinder barrel (11) also turns. Nine pistons (10) and cylinder barrel (11) turn together. Each piston has an attached piston shoe. Piston shoes (13) are held against nonrotating swashplate (6) by shoe plate (12).
When the pistons are almost out of cylinder barrel (11), the swashplate is at the maximum angle. This action draws oil from pump inlet passage (9) and into the piston bore in cylinder barrel (11). As this barrel rotates, the angled swashplate pushes the pistons back into the cylinder barrel. This action pushes oil out of the piston bore and through pump outlet passage (8) to the hydraulic system.
Pressure compensator valve (3) keeps the pump pressure and the pump flow at the necessary level to fulfill the load requirements and the flow requirements.
Maximum pump output is available when the engine is on and the oil pressure is less than the pressure of pressure compensator valve (3).
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| Illustration 3 | g00103379 |
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Pressure compensator valve (3) Pressure compensator valve (14) Pressure compensator spool (15) Spring (16) Screw (17) Pump outlet passage (18) Passage (19) Drain passage to pump case | |
Oil from the outlet passage (8) is sent to passage (17). The oil is then held in passage (17) by the pressure compensator spool (14).
When the service brakes are not applied, the pressure of the oil through pump outlet passage (8) increases until the oil in pump outlet passages (8) and (17) has more force on spool (14) than spring (15).
The oil in pump outlet passage (17) then moves pressure compensator spool (14). To move pressure compensator spool (14), the pressure must be at least
With the movement of pressure compensator spool (14), the oil in pump outlet passage (17) can flow through passage (18). The oil that flows through passage (18) controls actuator piston (4) in the pump. The force of the oil from passage (18) moves actuator piston (4) and the piston moves swashplate (6) toward the minimum angle (approximate zero degree angle).
When the pump drive shaft (7) and cylinder barrel (11) turn with swashplate (6) at the minimum angle position, pistons (10) have little movement in cylinder barrel (11). This movement occurs when the reaction plate and piston shoes (13) follow the approximate zero degree angle of swashplate (6).
The minimal movement of pistons (10) keeps the pressure of the oil in pump outlet passage (8) at the pressure setting of pressure compensator valve (3). The extra oil from pump outlet passage (8) flows into the pump body for pump lubrication. The oil in the pump body flows through a drain line to the hydraulic tank.
When the pressure of the oil in the braking system decreases, there is a decrease in the pressure of the oil in pump outlet passage (8) and passage (17). Spring (15) moves pressure compensator spool (14). Passage (18) is then open to passage (19). This action causes a lack of oil pressure in passage (18) to control actuator piston (4) in the pump. The lack of oil pressure for actuator piston (4) allows spring (5) to move swashplate (6). Swashplate (6) is able to move to the maximum angle position. This action will cause the pump to upstroke again.