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| Illustration 1 | g02176532 |
Pilot manifold (1) Proportional reducing valve (2) Pilot manifold (3) Line (Pilot pump output) (4) Line (Main pump regulator) | |
The proportional reducing valve for the power shift pressure (1) is located on the pilot manifold (2) . The proportional reducing valve is a solenoid operated control valve. The proportional reducing valve controls the flow of pilot system oil to the main pump regulators. The main pump regulators are used for horsepower control.
The solenoid receives a pulse width modulated signal (PWM signal) from the machine ECM. The PWM signal that is sent from the machine ECM causes the proportional reducing valve to regulate the pilot pressure at the main pump regulators. The engine speed is an input to the machine ECM. This input helps the machine ECM to determine the PWM signal that is required for the proportional reducing valve.
The PWM signal is a variable signal. The PWM signal allows the main pumps to be controlled more precisely. The reduced pressure that is created by the proportional reducing valve is called power shift pressure (PS). The output flow of the main pumps is controlled in accordance with the power shift pressure. The power shift pressure is used to control the maximum allowable hydraulic pump output when the engine is under load.
The pressure signal from the reducing valve is sent to the pump regulator. As the engine speed decreases, the power shift pressure decreases and pump flow decreases. As engine speed increases, the power shift pressure increases and pump flow increases.
ReferenceFor more information concerning the pump regulators, refer to Systems Operation, "Pump Control (Main Hydraulic) (Main Pump Regulator)".
Increased Power Shift Pressure
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| Illustration 2 | g02127235 |
Increased power shift pressure (1) Proportional reducing valve (2) Pilot manifold (5) Solenoid (6) Spring (7) Spool (8) Passage (Drain port) (9) Passage (Power shift pressure output) (10) Passage (Pilot oil supply from pilot pump) | |
As engine speed increases, power shift pressure increases. The power shift pressure that is controlled by proportional reducing valve (1) is variable. The power shift pressure depends on the PWM signal that is sent from the machine ECM. When the engine is under lighter loads, the PWM signal will increase. An increase in the PWM signal will produce a higher power shift pressure.
Solenoid (5) is energized by the PWM signal which causes spool (7) to shift downward against spring (6) . When spool (7) is shifted downward, passage (9) is blocked from passage (8) . Passage (9) is connected to passage (10) . Pilot oil flows from passage (10) to passage (9) . Pilot oil flows from passage (9) to line (4) , and then to the pump regulators. Increased power shift pressure that is in the main pump regulators increases the output of the main pumps.
Decreased Power Shift Pressure
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| Illustration 3 | g02127238 |
Decreased power shift pressure (1) Proportional reducing valve (2) Pilot manifold (5) Solenoid (6) Spring (7) Spool (8) Passage (Drain port) (9) Passage (Power shift pressure output) (10) Passage (Pilot oil supply from pilot pump) | |
As engine speed decreases, power shift pressure decreases. When the engine is under load during a hydraulic function, the output flow of main pumps is too high. The pump regulators control the output flow of the main pumps. Power shift pressure that is created by proportional reducing valve (1) is used by the pump regulators to reduce the main pump output. The engine speed is detected by the machine ECM. The machine ECM sends a PWM signal to the proportional reducing valve in order to decrease the power shift pressure. The decrease in power shift pressure at the pump regulators reduces the output of the main pumps. Reducing the main pump output allows the engine to run at an optimum speed.
As the PWM signal decreases, solenoid (5) creates less force to shift spool (7) downward. Spring (6) overcomes some of the force that is created by solenoid (5) . Spool (7) shifts upward. When spool (7) moves upward, the flow of pilot oil from passage (10) to passage (9) is restricted. The restriction of pilot oil flow from passage (10) to passage (9) reduces the pilot oil pressure that is in passage (9) . The pilot oil pressure that is delivered to the main pump regulators is reduced. The reduction of the pilot oil pressure to the main pump regulators allows the main pump flow to decrease.