HYD AR 1179602 - Caterpillar

Illustration 1 g03411862
Proportional reducing valve (power shift solenoid)
(1) Solenoid
(2) Valve body
(3) Line (pilot oil flow) The proportional reducing valve for the power shift pressure is located on the hydraulic pump housing. The proportional reducing valve is a solenoid operated control valve. The proportional reducing valve controls the flow of pilot system oil to the hydraulic pump regulators. The hydraulic 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 hydraulic pump regulators. The engine speed is an input to the machine ECM which 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 hydraulic 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 hydraulic 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.Reference: For more information concerning the pump regulators, refer to Systems Operation, "Pump Control (Main Hydraulic) (Main Pump Regulator)".Power Shift OFF
Illustration 2 g02131313
Power shift pressure OFF
(1) Solenoid
(2) Valve body
(4) Spring
(5) Spool
(6) Passage (drain port)
(7) Passage (power shift pressure output)
(8) Passage (pilot oil supply from pilot pump) The proportional reducing valve consists of solenoid (1), spring (4), and spool (5).When the machine is operating, oil from the pilot pump enters the proportional reducing valve through line (3). Pilot oil flows from line (3) to passage (8). When solenoid (1) is not energized by the PWM signal, spool (5) remains stationary. Spring (4) keeps spool (5) shifted upward. Pilot oil in passage (8) is blocked from entering passage (7) by spool (5). The oil that is present in passage (6) and passage (7) drains to the hydraulic tank. There is no power shift pressure on the hydraulic pump regulators.Power shift pressure is not needed when the engine is able to maintain the desired engine speed during a hydraulic operation. When the engine is not under load, there will be no PWM signal to the proportional reducing valve.Power Shift ON (Full Pressure)
Illustration 3 g02131333
Full Power shift Pressure
(1) Solenoid
(2) Valve body
(4) Spring
(5) Spool
(6) Passage (drain port)
(7) Passage (power shift pressure output)
(8) Passage (pilot oil supply from pilot pump) When the engine is under load during a hydraulic function, the output flow of the hydraulic pumps is too high. The pump regulators control the output flow of the hydraulic pumps. Power shift pressure that is created by the proportional reducing valve is used by the pump regulators to reduce the hydraulic 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 increase the power shift pressure. The increase