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| Illustration 1 | g00526848 |
Pilot manifold (1) Swing pump PRV (2) Main pump PRV | |
Swing pump PRV (1) and main pump PRV (2) are located on the bottom of the pilot manifold. These pressure reducing valves receive pulse width modulated signals from the Electronic Control Unit (ECU). The main pump PRV generates a reduced pilot pressure. This pressure is called power shift pressure. The power shift pressure is directed to the main hydraulic pump regulator. The power shift pressure regulates the amount of hydraulic horsepower output from the main pump in relation to engine speed.
The swing pump PRV is connected to the pilot signal lines and to the swing pump regulator. The swing pump PRV controls the amount of the swing circuit pilot activation pressure that is required to upstroke the swing pump. If the engine begins to lug during swing operation, the ECU changes the signal to the swing pump PRV in order to decrease the swing activation pressure. With less swing activation pressure, the swing pump does not upstroke completely and the hydraulic horsepower of the swing pump is reduced.
If the ECU fails, both of the proportional reducing valves have a manual override in order to permit the proportional reducing valves to operate without the signals from the ECU.
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| Illustration 2 | g00526847 |
The swing pump PRV and the main pump PRV are solenoid operated valves. When the solenoid has de-energized, pilot oil pressure enters port "P" of the valve block. The regulating spool is in the position that is shown. The connection between port "P" and port "A" is closed and the connection to tank return port "T" is open.
When the solenoid is energized, the shaft moves to the right in the solenoid coil in order to shift the valve spool. This allows pilot oil to flow from inlet port "P" through the passage. The pilot oil then flows to port "A" and to the pump control.
When the pilot pressure acts on the right end of the spool, the spool is pushed left against the force of spring. This closes the connection between port "P" and port "A". The oil pressure drops and the increased force of the spring moves the spool to the right again. Pilot pressure flows outward.
The movement of the spool keeps the pressure to the pump control constant.
When the solenoid is de-energized, the spool moves up in order to close the passage. The connection between the pilot oil supply and pump control is blocked.
The voltage to the solenoid is modulated by the controller which is determined by the power mode selection and the engine load.
Each PRV is equipped with the following backup systems: mechanical and electronic.
Mechanical backup - The mechanical backup system switch in the head of the solenoid provides a constant PRV pressure. This constant PRV pressure permits continued operation during a failure in the electrical system.
Electrical backup - The electronic backup switch is in the operator's compartment. When this switch is activated, the switch sends a fixed voltage to the PRV in order to maintain a constant pressure output. The electrical backup should be used if the controller fails in order to control the voltage to the solenoid in the PRV.