992G Wheel Loader and 854G Wheel Dozer Braking System Piston Pump (Brake) Caterpillar


Piston Pump (Brake)
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992G Wheel Loader and 854G Wheel Dozer Braking System [SENR1352]
BRAKING SYSTEM
PUMP GP
992G Wheel Loader and 854G Wheel Dozer Braking System Piston Pump (Brake)
992G Wheel Loader and 854G Wheel Dozer Braking System Piston Pump (Brake)



Illustration 1g00103376

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 has the capability to detect pressure requirements and flow requirements. The pump is mounted on the engine side of the torque converter housing. The pump supplies oil flow in order to charge the two accumulators.




Illustration 2g00103377

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 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 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 in order 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).




Illustration 3g00103379

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.

When the pressure of the oil is less than the pressure of pressure compensator valve (3), oil from pump outlet passage (8) flows to passage (17). The oil is then stopped by 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). In order to move pressure compensator spool (14), the pressure must be at least 16000 ± 345 kPa (2320 ± 50 psi). This is the pressure setting of pressure compensator valve (3) .

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 pump drive shaft (7) and cylinder barrel (11) turn with swashplate (6) at the minimum angle position, pistons (10) have very 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 (17). Spring (15) moves pressure compensator spool (14). This 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 will cause the pump to upstroke again.

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