HARNESS AS 3255749 - Caterpillar

Operation
The regulators for pump 1 and pump 2 are identical in construction and operation. The pump regulators are located on the sides of the main pump housing.The pump regulators are controlled by the electronic control system. The machine ECM continually monitors various inputs. The machine ECM sends current flow to the pump control solenoids on the pump regulators. The pump control solenoids control the output flow of the pump by changing the hydraulic signal pressure that flows to the actuator.The machine ECM controls the current sent to the pump control solenoids and determines the required pump flow based off the following inputs.Desired engine speed - Determined by the engine speed dial.Actual engine speed - Determined by the engine speed sensor.Hydraulic torque output - The hydraulic torque output varies depending on the engine speed dial setting.Pump 1 displacement - Determined by pump 1 control solenoid current.Pump 2 displacement - Determined by pump 2 control solenoid current.Flow requested - Determined by the left-hand joystick position, right-hand joystick position, or the travel levers/pedals positions.Pump 1 oil pressure - Pump 1 oil pressure is measured by the pump 1 pressure sensor on the main control valve.Pump 2 oil pressure - Pump 2 oil pressure is measured by the pump 2 pressure sensor on the main control valve.
Illustration 1 g06336518
Partial schematic
(1) Main control valve
(2) Pump 1 solenoid
(3) Pilot supply
(4) Pump 2 solenoid
(5) Piston
(6) Actuator spool
(7) Actuator
(8) Pump 2
(9) Swashplate
(12) Pump 1
(13) Swashplate
(14) Actuator
(15) Actuator spool
(16) Piston
(17) Pump 1 pressure sensor
(18) Pump 2 pressure sensor
Illustration 2 g06212854
Pump displacement
Pump solenoids (2) and (4) are proportional solenoids. The machine Electronic Control Module (ECM) sends current flow to the solenoids to stroke the pumps. When more current is supplied, the displacement increases. If less current is supplied, the displacement decreases. The ECM changes current flow based on pressure in the pump circuits.
Illustration 3 g02149999
P-Q characteristic curve
(A) Pressure/flow point (destroke point)
(B) P-Q characteristic curveThe P-Q characteristic curve is determined by the machine ECM. The output characteristic of each pump depends on the following inputs.
Desired engine speed
Actual engine speed
Hydraulic torque output
Pump 1 displacement
Pump 2 displacement
Flow requested
Pump 1 pressure
Pump 2 pressureThe flow rate of each pump is represented on P-Q characteristic curve (B) from pressure/flow point (A). Each point on the P-Q characteristic curve represents the flow rate and pressure when pump output horsepower is maintained at a constant rate.Regulator Operation (Standby - Full Destroke)
Illustration 4 g06333660
Pump 1 regulator (standby - full destroke position)
(2) Pump 1 solenoid
(3) Pilot supply
(4) Pump 2 solenoid
(5) Piston
(6) Actuator spool
(7) Actuator
(8) Pump 2
(9) Swashplate
(12) Pump 1
(13) Swashplate
(14) Actuator
(15) Actuator spool
(16) PistonNote: The following description refers only to pump 1 components, however pump 2 works the same.Pilot oil enters the pump at passage (3), but is blocked by pump solenoid (2). Spring pressure pushes spool (15) to the left-most position. This action allows pump oil to flow through the spool and fill the cavities on both sides of actuator (14). The pressure is equal on both side of the actuator, but there is more surface area on the left side