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| Illustration 1 | g00786718 |
Proportional reducing valve (power shift solenoid) (1) Solenoid (3) Body (right pump regulator) (9) Line (pilot oil flow) | |
The proportional reducing valve for the power shift pressure is located on the right pump regulator. The proportional reducing valve is a solenoid operated control valve. The proportional reducing valve receives supply oil from the pilot pump. The solenoid receives a pulse width modulated signal (PWM signal) from the engine and pump controller. The PWM signal that is sent from the engine and pump controller causes the proportional reducing valve to regulate the pilot pressure to a reduced pressure. This reduced pressure is called power shift pressure (PS). The proportional reducing valve sends the reduced pilot oil pressure to the regulators at the right pump and the left pump. The output flow of the right pump and the left pump is controlled in accordance with the power shift pressure. The power shift pressure is used to control the maximum allowable hydraulic pump output.
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| Illustration 2 | g00678718 |
Proportional reducing valve (increase in PWM signal) (1) Solenoid (2) Spring (3) Body (right pump regulator) (4) Spool (5) Passage (return oil flow) (6) Passage (power shift pressure to pump regulators) (7) Spool chamber (8) Passage (pilot oil flow) | |
A decrease in engine speed causes an increase in power shift pressure and a decrease in pump flow.
While the engine is operating, the engine and pump controller senses a decrease in engine speed. A decrease in engine speed causes the engine and pump controller to increase the PWM signal that is sent to solenoid (1). The magnetic force of the solenoid increases. As the magnetic force of the solenoid becomes greater than the force of spring (2), spool (3) moves in a downward direction against the force of the spring. The downward movement of spool (3) blocks the flow of oil from passage (6) to passage (5). Pilot oil in line (9) now flows through passage (8), into spool chamber (7) and into passage (6) at a reduced pressure (power shift pressure). The increased power shift pressure in passage (6) acts on the right pump regulator and the left pump regulator. The right pump and the left pump destroke as a result of an increase in power shift pressure.
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| Illustration 3 | g00678719 |
Proportional reducing valve (decrease in PWM signal) (1) Solenoid (2) Spring (3) Body (right pump regulator) (4) Spool (5) Passage (return oil flow) (6) Passage (power shift pressure to pump regulators) (7) Spool chamber (8) Passage (pilot oil flow) | |
An increase in engine speed causes a decrease in power shift pressure and an increase in pump flow.
While the engine is operating, the engine and pump controller senses an increase in engine speed. An increase in engine speed causes the engine and pump controller to decrease the PWM signal that is sent to solenoid (1). The magnetic force of the solenoid decreases. As the force of spring (2) becomes greater than the magnetic force of the solenoid, spool (3) moves in an upward direction. The upward movement of spool (3) blocks the flow of pilot oil from passage (8). Power shift pressure oil in passage (6) now drains into spool chamber (7) and into passage (5). The decreased power shift pressure in passage (6) that is acting on the right pump regulator and the left pump regulator causes the right pump and the left pump to move to an upstroke position. The right pump and the left pump upstroke as a result of a decrease in power shift pressure.
Reference: For more information concerning power shift pressure (PS), refer to Systems Operation, "Pilot Hydraulic System".