Introduction
Flow control by the pump regulator can be performed in the following manner:
Flow control by the pump regulator can be performed by constant horsepower control.
Pressure regulation is attained since the pump output horsepower is kept constant by varying the flow in response to pump delivery pressure. This state of control is realized when the joystick is in the FULL STROKE position. The pump output flow is controlled by pump output pressure and power shift pressure.
Flow control by the pump regulator can be performed by the duplicate load signal pressure.
True load signal pressure from the cylinders and the motors flows to the signal duplication valves in the main control valve. Delivery pressure from the main pumps flows through the signal duplication valve. The signal duplication valve shifts. A portion of the oil delivery from the main pumps flows through the signal duplication valve. A slight reduction in pressure occurs. This reduced pressure is now called duplicate load signal pressure. The duplicate load signal pressure is directed to the regulators at the front pump and the rear pump. Duplicate load signal pressure reduces flow below the constant horsepower flow control.
When the joysticks and/or pedals are in the NEUTRAL position, the pump regulators receive zero duplicate load signal pressure and low-power shift pressure. Pump delivery flow is reduced.
During the movement of a joystick and/or pedal, the varied pump flow will depend on the lever stroke.
The relief pressure of the signal relief valves determines maximum duplicate load signal pressure.
Flow control by the pump regulator can be performed by the true load signal pressure.
True load signal pressure of the cylinders and the motors is directed to the main pump regulators as signal pressure. True load signal pressure reduces flow below the constant horsepower flow control.
When the joysticks and/or pedals are in the NEUTRAL position, the pump regulators receive zero true load signal pressure and low-power shift pressure. Pump delivery flow is reduced.
During the movement of a joystick and/or pedal, the varied pump flow will depend on the lever stroke.
The highest true load signal pressure is sent to the pump regulators. The relief pressure of the signal relief valves is sent to the flow compensator valves and the load sensing differential pressure relief valves.
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| Illustration 1 | g03123416 |
P-Q characteristic curve (1) Pressure/flow point (2) Pressure/flow point (3) Point | |
Flow During Control - Refer to Illustration 1 for the pressure/flow points.
- When the joystick is in the FULL STROKE position under the constant horsepower flow control, the flow varies in accordance with the above P-Q characteristic curve. At pressure/flow point (1) , the flow is indicated as Q1 when the delivery pressure is indicated as P1. At pressure/flow point (2) , the flow is indicated as Q2 when the delivery pressure is P2. P2 is greater than P1 while Q1 is greater than Q2. Constant horsepower output of the pump is maintained.
- When the joystick is slightly moved, control by true load signal pressure or control by duplicate load signal pressure is carried out by reducing the flow below the point under the constant horsepower flow control.
When the joystick is at a particular stroke position and the delivery pressure is P1, the flow is reduced to Q3 at point (3) . This reduction is due to the effect of true load signal pressure or duplicate load signal pressure at the pump regulator. Flow Q3 will further decrease as the stroke of the joystick decreases. On the other hand, flow Q3 increases as the stroke of the joystick increases. Accordingly, the flow can be set lower than Q1 under constant horsepower flow control.
By this control operation, the flow can be reduced lower than each point along the P-Q characteristic curve in accordance with variable delivery pressures.
Note: Throughout the description of the operation of the pump control, duplicate load signal pressure and true load signal pressure will be referred to as load signal pressure (LS) .
Note: For more information concerning the operation of the load signal control valve, refer to Systems Operation, "Load Signal Control Valve".
STANDBY Position
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| Illustration 2 | g02156198 |
Main pump regulator in the STANDBY position (1) Solenoid valve for neutral flow (2) Main control valve (3) Pump discharge line (4) Minimum angle servo (5) Horsepower control adjustment (6) Power shift pressure (7) Load sensing control spool (8) Port "G" pressure (9) Maximum angle servo (10) Actuator piston (11) Lever (12) Constant horsepower control spool (13) Power shift pressure (14) Line (load signal pressure) | |
The pump servo pistons are connected to the swashplate. Full pilot system pressure is directed to the maximum angle servo. The load sensing control directs a lower regulated pump pressure to the minimum angle servo piston. The larger minimum angle servo piston also has a spring in order to assist in moving the servo. The combination of spring force and low regulated pump pressure moves the swashplate to the minimum angle for decreased pump flow.
When all control valves are in the NEUTRAL position, no load signal pressure is directed to the right side of the load sensing control group. With no load signal pressure on the right end of the load sensing spool, standby implement pump pressure moves the load sensing spool to the right. Pilot system oil pressure of 4000 kPa (580 psi) moves the resolver for pilot pressure in order to block standby implement pump pressure from entering any other area of the pump control.
When the implement controls and the travel controls are in the NEUTRAL position, the machine ECM energizes the solenoid valve for the neutral flow control valve. When the neutral flow control valve is energized, the neutral flow control valve is open and most of the pump oil flows through the neutral flow control valve to the hydraulic tank. When the implement controls and the travel controls are in the NEUTRAL position, the machine ECM also sets the power shift pressure to a level that is dependent on engine speed. The power shift pressure moves the horsepower control spool to the left until the center land on the horsepower control spool moves past the passage to the minimum angle piston. Delivery pressure from the main pumps is regulated around the load sensing spool and around the horsepower control spool to the minimum angle servo piston. The servo piston moves the swashplate toward the minimum angle.
Note: Throughout the description of the operation of the pump control, assume that the power shift pressure remains at a constant value. The pumps can upstroke or the pumps can destroke when the power shift pressure changes.
UPSTROKE Position
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| Illustration 3 | g02156946 |
Main pump regulator in the UPSTROKE position (1) Solenoid valve for neutral flow (2) Main control valve (3) Pump discharge line (4) Minimum angle servo (5) Horsepower control adjustment (6) Power shift pressure (7) Load sensing control spool (8) Port "G" pressure (9) Maximum angle servo (10) Actuator piston (11) Lever (12) Constant horsepower control spool (13) Power shift pressure (14) Line (load signal pressure) | |
Three conditions that can cause an increase in flow from the main pumps are listed below.
- An increase of the load signal pressure
- An increase of power shift pressure
- A decrease of pump output pressure
Illustration 3 illustrates an increase in pump flow due to an increase of the load signal pressure.
When the load signal pressure increases and when the implement pumps upstroke, the increase in pump flow results in an increase in the system pressure of the main pumps. When the implement system pressure becomes higher than port "G" pressure, the resolver valve shifts. Pump output pressure enters the pump controls. The load signal pressure plus the force on the right end of the load sensing spool exceed the force of the pump output pressure on the left end of the load sensing spool. The combined forces on the right end of the load sensing spool moves the load sensing spool to the left. When the load sensing spool shifts to the left, the passage from the orifice and the slow return check valve is connected to the hydraulic tank.
When the pump is in balance, the horsepower control spool is positioned so that the passage is slightly open to the passage to the minimum angle servo. When the load sensing control spool shifts to the left, the oil in the minimum angle servo returns to the hydraulic tank through the slow return check valve and the load sensing control spool.
Since the minimum angle servo is open to the hydraulic tank, the swashplate rotates in a counterclockwise direction because of the pump output pressure on the maximum angle servo. The pump upstrokes.
When the maximum angle servo shifts to the left, the mechanical advantage of the actuator piston against the lever increases and the lever rotates in a clockwise direction. When the lever rotates in a clockwise direction, the horsepower control valve shifts to the right. This change restricts the oil in the minimum angle servo from returning to the hydraulic tank. The swashplate stops moving.
When the implement circuits or the travel circuits approach full flow and when the difference between the load signal pressure and the pump output pressure decreases below the margin pressure setting, the load sensing spool is shifted to the left and the load sensing spool becomes disabled. When the load sensing spool is disabled, the horsepower control spool regulates pump flow by alternating pressurizing the oil in the minimum angle servo or returning the oil to the hydraulic tank. When the load sensing regulator is disabled, either an increase in power shift pressure or a decrease in the pump output pressure will upstroke the pumps.
DESTROKE Position (increase of system pressure)
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| Illustration 4 | g02157521 |
Main pump regulator in the DESTROKE position (1) Solenoid valve for neutral flow (2) Main control valve (3) Pump discharge line (4) Minimum angle servo (5) Horsepower control adjustment (6) Power shift pressure (7) Load sensing control spool (8) Port "G" pressure (9) Maximum angle servo (10) Actuator piston (11) Lever (12) Constant horsepower control spool (13) Power shift pressure (14) Line (load signal pressure) | |
Three conditions that can cause a decrease in flow from the main pumps are listed below.
- A decrease of the load signal pressure
- A decrease of power shift pressure
- An increase of the system pressure
Illustration 4 illustrates a decrease in pump flow due to an increase of system pressure.
When the system pressure increases, the upward force on the shoulder area of the actuator piston increases and the piston rotates the lever in a clockwise direction. The lever forces the horsepower control spool to the right against the force of the power shift pressure. Shifting the horsepower control spool to the right connects the minimum angle servo to system pressure in the internal passage at the left of the horsepower control spool. Since the area of the minimum angle servo is larger than the area of the maximum angle servo, the swashplate rotates clockwise in order to destroke the pump. When the swashplate rotates clockwise, the maximum angle servo moves to the right. Moving the servo to the right decreases the mechanical advantage of the actuator piston on the lever. The reduction in the mechanical advantage allows the horsepower control spool to shift back to the left. When the horsepower control spool shifts to the left, the connection between the minimum angle servo and system pressure is blocked. The swashplate stops rotating and balances.
DESTROKE Position (decrease of load signal pressure)
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| Illustration 5 | g03871290 |
Main pump regulator in the DESTROKE position (1) Solenoid valve for neutral flow (2) Main control valve (3) Pump discharge line (4) Minimum angle servo (5) Horsepower control adjustment (6) Power shift pressure (7) Load sensing control spool (8) Port "G" pressure (9) Maximum angle servo (10) Actuator piston (11) Lever (12) Constant horsepower control spool (13) Power shift pressure (14) Line (load signal pressure) | |
Illustration 5 illustrates a decrease in flow due to a decrease of load signal pressure.
When the load signal pressure decreases, the pump output pressure moves the load sensing control spool to the right against spring force and load signal pressure. Shifting the load sensing control spool to the right connects the minimum angle servo to system pressure in the internal passage to the left of the horsepower control spool. Since the area of the minimum angle servo is larger than the area of the maximum angle servo, the swashplate rotates in a clockwise direction in order to destroke the pump. When the swashplate rotates in a clockwise direction, the maximum angle servo moves to the right. Moving the servo to the right decreases the mechanical advantage of the actuator piston on the lever. The reduction in the mechanical advantage allows the horsepower control spool to shift back to the left. The connection between the minimum angle servo and system pressure is blocked. The swashplate stops rotating and balances.