Gear Pump with a Solenoid Valve
- (DJD1-2015)
- (WLG1-833)
- (RTA1-518)
- (WGX1-918)
- (DDA1-2277)
- (RBB1-1117)
- (WMB1-966)
- (EWF1-419)
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| Illustration 1 | g00904667 |
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| Illustration 2 | g00904668 |
The hydraulic oil flows into pump (6) from the line from tank (7) . The oil flows from the pump through check valve (5) to shuttle valve (3) . The shuttle valve directs the flow of oil to the accumulator with the lowest pressure through the lines to the brake accumulators (2) . The brake system pressure sensor (4) sends a signal to the machine ECM that is proportional to the pressure in the brake accumulators. When the accumulator pressure rises above 16000 ± 345 kPa (2300 ± 50 psi), the machine ECM sends a signal to the solenoid valve for brake charging (8) in order to shift the solenoid valve for brake charging more open.
When the solenoid valve for brake charging (8) shifts open, the pressure drop across orifice (10) increases. When the pressure drop across orifice (10) increases, flow control valve (9) for the brakes will shift open. When flow control valve (9) for the brakes shifts open, oil from pump (6) is also directed to the line to the fan motor (1) . Check valve (5) will close in order to prevent the flow of oil in the brake accumulators to the pump.
Note: The solenoid valve for brake charging (8) is a proportional valve. The amount of flow that flows through flow control valve (9) for the brakes is proportional to the amount of flow that flows through the solenoid valve for brake charging (8) . The amount of flow that flows through the solenoid valve for brake charging (8) is proportional to the amount of electric current that is sent from the ECM to the solenoid valve for brake charging (8) .
After several applications of the brakes, the pressure in the brake accumulators will decrease below 9800 ± 345 kPa (1400 ± 50 psi). Then, the machine ECM will send a signal to the solenoid valve for brake charging (8) in order to close the solenoid valve for brake charging (8) . When the solenoid valve for brake charging closes, the pressure drop across orifice (10) will decrease. When the pressure drop across orifice (10) decreases, flow control valve (9) for the brakes will close in order to direct more oil to the accumulators. This will charge the brake accumulators in order to provide the proper brake system pressure.
Gear Pump without a Solenoid Valve
- (DJD2016-UP)
- (WLG834-UP)
- (RTA519-UP)
- (WGX919-UP)
- (DDA2278-UP)
- (RBB1118-UP)
- (WMB967-UP)
- (EWF420-UP)
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| Illustration 3 | g01083279 |
Gear pump | |
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| Illustration 4 | g00424028 |
The idler gear (3) meshes with the drive gear (1) . The rotation of the two gears creates a partial vacuum. The partial vacuum is created at the pump inlet as the gear teeth separate. This draws the oil from the hydraulic tank. Oil enters the pump into cavity (4) . The turning of the two gears causes the low pressure oil from cavity (4) to move around the inner pump housing to cavity (2) . As the teeth mesh at the outlet port, the oil is forced out of the gear pump.
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| Illustration 5 | g01194725 |
(5) Shuttle Valves (6) Relief valve (7) Pressure sensor (8) Valve for Brake charging (9) Filter (10) Priority Valve (11) Brake and Fan Pump (12) Line to Tank (13) Line to fan (14) Orifice (15) Check valve (16) Lines to Accumulators | |
The brake and fan drive system contains a fixed displacement hydraulic pump. The brake system has priority over the fan drive system.
When the engine is started, hydraulic oil is drawn from tank (12) by the brake and fan drive pump (11) . The relief valve (6) is closed. Hydraulic oil flows from pump (11) to priority valve (10) . Then, the hydraulic oil flows through the priority valve (10) to the right side of the priority valve through the valve for brake charging (8) . Oil also flows to the left side of the priority valve. The hydraulic oil and the spring pressure counter the pressure of the pilot oil that flows to the left side of the priority valve. This holds the priority valve to the left as the accumulators charge.
The priority valve directs hydraulic oil to Through filter (9) . The oil flows through orifice (14) to check valve (15) . As the hydraulic oil pressure increases, the check valve opens. The hydraulic oil flows to the valve for brake charging (8) . Then, the oil flows to shuttle valves (5) . The spring keeps the valve for brake charging (8) open. The shuttle valves direct hydraulic oil to the accumulator with the lowest pressure first. As the hydraulic oil pressure to the first accumulator increases, the shuttle valve moves. This allows both accumulators to charge at equal pressures. Hydraulic oil also flows to the relief valve (6) through the valve for brake charging (8) .
As the accumulators charge, hydraulic oil pressure increases to the relief valve (6) . When the hydraulic oil pressure overcomes the spring pressure on the relief valve, the relief valve moves down. The hydraulic oil to the right side of the priority valve drains to the inlet side of the brake and fan drive pump (11) . Then, the oil pressure on the left side of the priority valve moves the priority valve to the right. This directs most of the flow of hydraulic oil to the fan drive system. A small amount of hydraulic oil flows to the right side of the priority valve and to the relief valve. Because the relief valve is open, the oil flows to the inlet side of the pump.
When the priority valve moves to the right, the hydraulic oil pressure below check valve (15) decreases. Then, the check valve seats in order to maintain hydraulic oil pressure in the brake accumulators (16) . The shuttle valves (5) will move to the left or to the right. This directs the lower accumulator pressure to the relief valve (6) .
The flow of hydraulic oil from the brake accumulators (16) is blocked at the brake control valve . When the brake pedal is pressed, the brake control valve routes hydraulic oil to the rear service brakes and to the front service brakes . This engages the service brakes. Pressure feedback is sensed by each spool in the brake control valve. This allows the operator to feel the application of the service brakes. The pressure to the brake lines varies. As the brake pedals are depressed, the hydraulic oil pressure in the brake lines increases. Due to the spring below the bottom brake valve, the maximum pressure to the front brakes is lower than the maximum pressure to the rear brakes.
When the accumulator charge pressure falls below the spring pressure on the relief valve, the relief valve moves up. This is the cut-in pressure. Then, the accumulator charging cycle begins again.