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| Illustration 1 | g02178204 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for Fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (Right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (Left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
Service Brake Operation
Brake Charge Operation Below Cut-In Pressure
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| Illustration 2 | g02178235 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (Right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (Left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
The transmission Electronic Control Module (ECM) reads pressure sensors (9) and (10) to determine brake accumulator pressure. When the brake accumulator pressure drops to cut-in, the transmission ECM de-energizes brake charge solenoid (5). The brake charge solenoid (5) allows a small amount of oil to flow through damping orifice (4). This oil flows to the brake charge pressure signal side of priority valve (1) and shuttle valve (14). The brake charge pressure signal tells the priority valve to shift and provide pump flow to the brake accumulators. The brake accumulator charge flow rate is controlled by orifice (19). The priority valve allows any excess oil not needed for accumulator charging to flow out port (8) to the fan motor. Shuttle valve (14) shifts to the right and allows the brake charge pressure signal to exit the load sensing port (15) to upstroke the pump.
Pump flow enters the control manifold through the pump supply port (16). Pump flow goes through the following components to reach the brake accumulators: priority valve (1), screen (2), orifice (19), check valve (12), and inverse shuttle valve (18). The orifice (19) controls the oil flow rate to the brake accumulators. Check valve (12) prevents brake accumulator oil from flowing back into the manifold. Inverse shuttle valve (18) senses the brake accumulator pressure at ports (13) and (11). The higher of the two brake accumulator pressures shifts the inverse shuttle to provide oil to the port with the lower brake accumulator pressure.
The pressure sensors (9) and (10) read the brake accumulator oil pressure. The transmission ECM chooses the lowest of the two pressure readings. The transmission ECM uses the pressure reading to determine when to start charging (cut-in) or stop charging (cut-out). If brake accumulator pressure is low, the pressure sensor readings are also used to activate the low-pressure warning.
Brake Charge Operation at Cut-Out Pressure
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| Illustration 3 | g02178282 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
The transmission ECM reads pressure sensors (9) and (10). When the lowest of the two readings reaches the cut-out pressure, the transmission ECM energizes brake charge solenoid valve (5). The brake charge pressure signal side of the priority valve (1) is drained through the tank return port. The brake charge pressure signal side of the shuttle valve (14) is also drained through the tank return port (7). The shuttle valve (14) shifts to the left to allow the fan control pressure signal to exit the pump load sense port (15). This movement of the shuttle valve allows the pump to sense the pressure requirements of the fan system. The priority valve (1) shifts to allow pump flow to the fan through the fan supply port (8). Pressure that is maintained in the passage between the priority valve (1) and the check valve (12). This pressure is sufficient enough to balance the priority valve spring setting and allow oil flow to the fan. No pump oil will flow to the brake accumulators while the brake charge solenoid (5) is energized.
Operation of the Hydraulic Fan System
Operation at the Brake Cut In Pressure
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| Illustration 4 | g02178317 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
If the brake accumulator pressure is at the cut-in pressure or below the cut-in pressure. The brake accumulator charge system to receive a higher pump flow priority than the fan system. Priority valve (1) is shifted to provide flow to the brake accumulators. The brake charge flow rate is controled by orifice (4) Any excess flow is allowed to flow to the fan system.
Operation with the Fan Speed Solenoid De-Energized
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| Illustration 5 | g02178502 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for the fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
The fan system has priority when the brake accumulator charge system is at the cut out pressure. Fan speed control solenoid (6) controls the load sensing pressure for the pump when the brake accumulator system is fully charged. Fan speed control solenoid (6) is a proportional pressure control solenoid. As the current to the fan speed control solenoid increases, the output pressure decreases. When fan speed control solenoid (6) is de-energized, the output control pressure to the load sensing port is maximum. The pump will be fully stroked and the pump will send maximum flow to the fan motor.
The amount of current that is supplied to the fan control solenoid is controlled by the engine Electronic Control Module (ECM). The engine ECM receives the following four inputs: hydraulic oil temperature sensor, ATAAC outlet temperature sensor, engine coolant temperature sensor, and transmission oil temperature sensor. If the engine ECM determines that the fan speed should be minimum, then the maximum current is sent the fan speed control solenoid (6). The load sense signal to the pump will decrease, the pump will de-stroke. This destroking will provide less flow, and fan speed will decrease. If one of the four temperature sensors shows a demand for more cooling. The engine ECM will reduce the amount of current to the fan speed control solenoid (6). Decreasing the current to the fan speed control solenoid (6) causes the load sense pressure to increase. The pump upstrokes to provide more flow, and fan speed increases.
Pump flow enters the control manifold through pump supply port (16). Oil flow from the pump flows through the priority valve (1). The oil flow exits the supply port for the fan motor (8). A small amount of pressurized oil flows through fan speed solenoid (6) .The fan speed solenoid (6) is a proportional pressure control solenoid. The solenoid assists the proportional pressure control function. The valve will meter flow to the tank return port until the required control pressure is reached. Oil that is at the required control pressure flows to the shuttle valve (14). Shuttle valve (14) shifts to the left. Pressurized oil exits through the pump load sense port (15) in order to upstroke the pump
Operation with the Fan Speed Solenoid Energized
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| Illustration 6 | g02178551 |
(1) Diverter valve (hydraulic fan) (2) Screen (3) Relief valve (brake accumulator) (4) Orifice (5) Solenoid valve (brake accumulator charging) (6) Solenoid valve (hydraulic fan (7) Tank return port (8) Supply port for fan motor (9) Pressure sensor (brake oil accumulator primary) (10) Pressure sensor (brake oil accumulator secondary) (11) Brake accumulator port (right side brakes) (12) Check valve (brake accumulator) (13) Brake accumulator port (left side brakes) (14) Shuttle valve (brake hydraulic fan) (15) Load sensing port (16) Pump supply port (17) Screen (18) Inverse shuttle valve (brake accumulator) (19) Orifice | |
The fan system has priority once the accumulators are at the cut out pressure. The fan speed control solenoid (6) controls the load sensing pressure for the pump when the brake accumulators are fully charged. The fan speed control solenoid (6) is a proportional solenoid. As current to the fan speed solenoid (6) increases, the output pressure to the load sensing port decreases and the fan speed decreases. The current to the fan speed control solenoid (6) decreases causing the solenoid out-put pressure to the pump load sensing port to increase. This increase causes the fan speed increases.
The amount of current that is applied to the fan speed control solenoid is controlled by the engine Electronic Control Module (ECM). The engine ECM receives the following four inputs: hydraulic oil temperature sensor, ATAAC outlet temperature sensor, transmission oil temperature sensor, and and engine coolant temperature sensor. If the engine ECM determines that the fan speed should be minimum, then the maximum current is sent to the fan speed control solenoid (6). The load sense signal to the pump will decrease, the pump will de-stroke to provide less flow, and the fan speed will decrease. If any one of the four sensors demands more cooling. This demand will cause the engine ECM to reduce the amount of current to the fan speed control solenoid (6). Decreasing the current to the fan speed solenoid, causes the load sense pressure to increase. Then the pump upstrokes to provide more flow and the fan speed increases.
Pump flow enters the control manifold through the pump supply port (1). Oil flows through priority valve (1) and out the fan motor supply port to the fan motor. A small amount of pressurized oil flows through fan speed control solenoid (6). The fan speed solenoid (6) is a proportional pressure control solenoid. The solenoid assists in the proportional pressure control function. The valve will meter flow to the tank return port (7) until the required control pressure is reached. Oil that is at the required control pressure flows to the shuttle valve (14). The shuttle valve (14) shifts to the left. Pressurized oil exits through pump load sense port (15) to destroke the pump. The pressurized oil changes the output flow to the pump in order to meet the system demands.