| |
| Illustration 1 | g06320779 |
|
Proportional reducing valve (power shift solenoid) (1) Solenoid (3) Body (drive pump regulator) (9) Line (pilot oil flow) | |
The proportional reducing valve for the power shift pressure is located on the drive 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 machine ECM. The PWM signal that is sent from the machine ECM 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 drive pump and the idler pump. The output flow of the drive pump and the idler pump is controlled in accordance with the power shift pressure. The power shift pressure is used to control the maximum allowable hydraulic pump output.
| |
| Illustration 2 | g01237695 |
|
Proportional reducing valve (increase in PWM signal) (1) Solenoid (2) Spring (3) Body (drive 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 machine ECM senses a decrease in engine speed. A decrease in engine speed causes the machine ECM 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 (4) moves in a downward direction against the force of the spring. The downward movement of spool (4) 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 drive pump regulator and the idler pump regulator. The drive pump and the idler pump destroke as a result of an increase in power shift pressure.
| |
| Illustration 3 | g01237696 |
|
Proportional reducing valve (decrease in PWM signal) (1) Solenoid (2) Spring (3) Body (drive 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 machine ECM senses an increase in engine speed. An increase in engine speed causes the machine ECM 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 (4) moves in an upward direction. The upward movement of spool (4) 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 drive pump regulator and the idler pump regulator causes the drive pump and the idler pump to move to an upstroke position. The drive pump and the idler 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".