330D, 336D and 340D Excavators Hydraulic System – Pump Control (Main Hydraulic) – Main Pump Regulator

Operation

The regulators for the drive pump and the idler pump are identical in construction and operation. The following description is given for the drive pump regulator.

The main pump regulators are controlled in the following manner.

Power Shift System – The pump regulators are controlled by the electronic control system. The machine ECM continually monitors the engine speed and the load on the engine. The machine ECM sends an electrical signal to the proportional reducing valve for power shift pressure. The proportional reducing valve assists in controlling the output flow of the pumps by changing the hydraulic signal pressure (power shift pressure) that flows to the pump regulators.

Cross sensing control – The pump regulators are controlled by cross sensing control. In order to maintain the engine horsepower to the pumps at a constant rate, the pump regulators receive average delivery pressure of the drive pump and the idler pump through the cross sensing control. This action is called constant horsepower control.

Negative Flow Control – When the joysticks and/or the travel levers/pedals are in the NEUTRAL position or when the joysticks and/or the travel levers/pedals are partially moved from the NEUTRAL position, the pump regulators receive negative flow control pressure from the main control valve. The main pumps are controlled by negative flow control pressure at this time.

ReferenceFor more information concerning the power shift system, refer to Systems Operation, “Pilot Hydraulic System”.

ReferenceFor more information concerning the negative flow control operation at the main control valve, refer to Systems Operation, “Negative Flow Control System”.

The output characteristics of each pump depends on the following pressures.

• Pump output circuit pressure

• Power shift pressure

• Negative flow control pressure

The 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.

Pump Regulator

Pump delivery pressure (PD) acts on pilot piston (3) and spool (1) of regulator (16) . Power shift pressure (PS) enters regulator (16) through a passage through the main pump housing. The oil then goes through passage (10) to piston (9) .

During constant horsepower flow control, pump delivery pressure (PD) is acting on the right shoulder of pilot piston (3) . Also during constant horsepower flow control, power shift pressure (PS) and cross sensing control pressure (CF) from the idler pump is acting on the left end of piston (3) . When the total force of the three pressures is less than the force of spring (7) and spring (8) , pilot piston (3) remains stationary. Swashplate (13) maintains the maximum angle for maximum pump flow. When the total force of the three pressures is greater than the force of spring (7) and spring (8) , pilot piston (3) is shifted in order to decrease the swashplate angle which will destroke the pump.

During negative flow control, negative flow control pressure (PN) from line (17) acts on the left end surface of pilot piston (18) . Pilot piston (18) shifts in order to move feedback lever (5) , spool (1) and related components. Negative flow control is maximum when all the control levers are in the NEUTRAL position which requires no pump flow.

Regulator Operation (full stroke position)

Main pump delivery pressure (PD) acts on shoulder (2) of pilot piston (3) . Power shift pressure (PS) from passage (10) acts on piston (9) and on the left end of pilot piston (3) . When the total force of main pump delivery pressure (PD) , power shift pressure (PS) , and cross sensing control pressure (CF) is less than the total force of spring (7) and spring (8) pilot piston (3) remains stationary. Plate (5) , feedback lever (6) , and spool (1) remain stationary. Passage (4) remains blocked. Main pump delivery pressure (PD) cannot enter piston chamber (11) while there is main pump delivery pressure (PD) in piston chamber (14) . Piston (12) is shifted all the way to the left. Swashplate (13) is held at a maximum angle which allows the pump to maintain maximum output flow. Main pump delivery pressure (PD) , power shift pressure (PS) , and cross sensing control pressure (CF) flow to the regulator from passages within the main pump housing.

Regulator Operation (minimum stroke position)

When all of the controls are in the NEUTRAL position, no load is present to the drive pump which causes an increase in power shift pressure (PS) and an increase in drive pump delivery pressure (PD) inside the pump. The larger pressures from power shift pressure (PS) , delivery pressure (PD) , and cross sensing control pressure (CF) combine in order to overcome the forces of spring (7) and spring (8) which shifts piston (3) .

Piston (3) shifts rod (15) to the right, rotating lever (6) , which rotates lever (5) . Lever (5) is connected to spool (1) . When lever (5) is rotated spool (1) shifts to the right. This action opens passage (4) . Delivery pressure (PD) now flows to chamber (11) . Lever (5) is also connected to piston (12) . When lever (5) is rotated, a force is placed against piston (12) . The combined force of delivery pressure (PD) and force from lever (5) causes piston (12) to shift to the right. Piston (12) then rotates swashplate (13) to zero angle. The pump displacement is now minimal.

Regulator Operation (standby position)

The regulator is in the standby mode when all the controls are in the NEUTRAL position and the machine ECM raises the power shift pressure to a level that is dependent on the engine speed. Power shift pressure (PS) acts on piston (9) . Cross sensing control pressure from the idler pump acts on piston (3) as well as delivery pressure (PD) . Negative flow control pressure is at maximum pressure, which acts against piston (18) . The engine speed keeps delivery pressure (PD) higher than the negative flow control pressure, power shift pressure (PS) , and cross sensing flow pressure (CF) . Spring (7) and spring (8) also act with delivery pressure to keep piston (12) from shifting to the right. The swashplate is at a maximum angle. Standby keeps the pump at a maximum angle, although little pressure is needed to destroke the pump.