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| Illustration 1 | g00663524 |
(1) Brake system pump (2) Steering pump (3) Pressure and flow compensator valve | |
The braking system uses an automatically controlled variable displacement piston pump (1). The brake pump has the capability to detect pressure requirements and flow requirements. The brake pump is mounted onto the rear of steering pump (2). The brake pump supplies oil flow in order to charge two accumulators. Pressure and flow compensator valve (3) keeps the pressure from the brake pump and the flow from the brake pump at the necessary levels in order to fulfill load and flow requirements.
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| Illustration 2 | g00663512 |
Component location for the Piston Pump (3) Pressure and flow compensator valve (4) Actuator piston (5) Pump outlet passage (6) Cylinder barrel (7) Pump inlet passage (8) Piston (9) Bias piston (10) Bias spring (11) Piston shoe (12) Swashplate (13) Shoe plate (14) Pump drive shaft | |
When pump drive shaft (14) is rotated, cylinder barrel (6) also turns. Nine pistons (8) and the cylinder barrel turn together. Each piston has an attached piston shoe (11). The piston shoes are held against nonrotating swashplate (12) by shoe plate (13) .
When pistons (8) have been moved fully out of cylinder barrels (6), swashplate (12) is at the maximum angle. This draws oil from pump inlet passage (7) and into the piston bores of the cylinder barrel. As the cylinder barrel rotates, the angled swashplate pushes the pistons back into the cylinder barrel. This pushes oil out of the piston bores and through pump outlet passage (5) to the hydraulic system.
The angle of swashplate (12) determines the stroke of pistons (8). The stroke of the pistons determines the quantity of oil that is delivered during each revolution of the pump drive shaft. The angle of the swashplate can be adjusted in order to provide a variable flow rate. The maximum angle of the swashplate equals the maximum flow rate. Zero angle of the swashplate equals no flow.
The brake pump is controlled by two pistons, bias piston (9) and actuator piston (4). Bias spring (10) in the assembly of the bias piston causes swashplate (12) to move. Swashplate (12) then causes the pump to upstroke.
Pressure and flow compensator valve (3) keeps the pressure from the piston pump at 20340 kPa (2950 psi). This is achieved by sending delivery pressure back to actuator piston (4). The delivery pressure operates against bias spring (10) and the angle of swashplate (12) is adjusted.
Maximum pump output is available when the engine is on and the oil pressure is less than the pressure of pressure and flow compensator valve (3).
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| Illustration 3 | g00663528 |
Pressure and Flow Compensator Valve (3) Pressure and flow compensator valve (15) Flow compensator spool (16) Pressure compensator spool (17) High pressure oil passage (18) Control oil passage (19) Drain passage (20) Pressure compensator spring | |
When the pressure of system oil is less than the pressure of pressure and flow compensator valve (3), oil from pump outlet passage (5) flows to high pressure oil passage (17). The oil is then stopped by pressure compensator spool (16) .
When the service brakes are not applied, the pressure of the oil through pump outlet passage (5) increases. The pressure increases until the oil in pump outlet passages (5) and the oil in high pressure oil passage (17) has more force on pressure compensator spool (16) than pressure compensator spring (20) .
The oil in high pressure oil passage (17) then moves pressure compensator spool (16). In order to move the pressure compensator spool, the pressure must be at least 20340 kPa (2950 psi). This is the pressure setting of pressure and flow compensator valve (3) .
With the movement of pressure compensator spool (16), the oil in high pressure oil passage (17) can flow through drain passage (19). The oil that flows through control oil passage (18) controls actuator piston (4) in the pump. The force of the oil from the control oil passage moves actuator piston (4) and pistons (8) move swashplate (12) toward the minimum angle (approximate zero degree angle).
When pump drive shaft (14) and cylinder barrel (6) turn with swashplate (12) at the minimum angle position, pistons (8) have very little movement in the cylinder barrel. This movement occurs when the reaction plate and piston shoes (11) follow the approximate zero degree angle of the swashplate.
The minimal movement of pistons (8) keeps the pressure of the oil in pump outlet passage (5) at the pressure setting of pressure and flow compensator valve (3). The extra oil from pump outlet passage (5) 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 of pressure in high pressure oil passage (17). Pressure compensator spring (20) moves pressure compensator spool (16). This causes a lack of oil pressure in control oil passage (18) which prevents control of actuator piston (4) in the pump. The lack of oil pressure for control of actuator piston (4) allows pressure compensator spring (20) to move swashplate (12). Swashplate (12) is then able to move to the maximum angle position. This will cause the pump to upstroke again.