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.
Flow control by the pump regulator can be performed by the load signal pressure.
Load signal pressure of the cylinders and the motors is directed to the main pump regulators as signal pressure.
The main pump hydraulic flow control is based on the load sensing signal pressure in order to keep the margin pressure constant. Margin pressure is the difference between the pump delivery pressure and the load sensing pressure.
When the joysticks and/or pedal are in the NEUTRAL position, the pump regulators receive zero load signal pressure and no electrical signal to the horsepower control solenoid. Pump delivery flow is reduced.
| |
| Illustration 1 | g03784885 |
|
Partial schematic (1) Electronic control module (2) Load sense spool (3) Horsepower control spool (4) Horsepower control solenoid (5) Regulator (6) Pressure sensor for main pump (on main control valve) (7) Control piston (8) Main pump (9) Counter piston (11) Case drain filter (12) Hydraulic oil tank | |
| |
| Illustration 2 | g03786719 |
|
Pump section view (typical example) (2) Load sense spool (3) Horsepower control spool (4) Horsepower control solenoid (5) Regulator (7) Control piston (9) Counter piston (13) Swashplate (14) Passage (15) Passage (16) Barrel (17) Piston | |
Pump regulator (5) is located on the side of the main pump housing. The following description is given for the main pump regulator.
Horsepower control solenoid (4) is controlled by the electronic control system. The machine ECM continually monitors various inputs. The machine ECM sends a pulse width modulated (PWM) driver to horsepower control solenoid (4) to control a constant power. Horsepower control solenoid (4) controls the output flow of the pump by changing the hydraulic signal pressure that flows to the actuator piston in the pump.
The machine ECM controls the PWM driver sent to the pressure reduction valve 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 pickup.
Main pump displacement - Determined by load sense signal.
Main pump delivery pressure - The main pump delivery pressure is measured by the main pump pressure sensor located on the main control valve.
The machine ECM supplies an electrical current in order to actuate horsepower control solenoid (4).
The machine ECM sends a PWM driver to horsepower control solenoid (4) to control the hydraulic signal to counter piston (9). When horsepower control solenoid (4) moves horsepower control spool (3) to the right, the pump destrokes. Horsepower control spool (3) directs oil from the pump to counter piston (9). This action causes the pump to destroke.
When horsepower control solenoid (4) moves horsepower control spool (3) to the left, the pump upstrokes. This action will allow oil within counter piston (9) to be sent to case drain in order to upstroke the pump.
| |
| Illustration 3 | g03339291 |
|
P-Q characteristic curve (A) Pressure/flow point (destroke point) (B) P-Q characteristic curve | |
The 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
- pump displacement
- pump delivery 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.
| |
| Illustration 4 | g03747286 |
|
Partial schematic (engine off) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
When the engine is not running, spring (20) positions swashplate (13) at the maximum angle. This FULLY UPSTROKED position allows the pump to provide flow as the engine is started.
Horsepower control spool (3) is held to the left by spring force. Load sense spool (2) to the right by spring force.
| |
| Illustration 5 | g03813148 |
|
Partial schematic (low-pressure standby) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
When the engine is started, the main pump sends oil out to the main control valve. With no implement activated, the pump flow is blocked by the closed-center spools in the control valve group. Pump supply pressure increase and moves the load sensing spool (2) to the left. Pump supply pressure is directed through the load sensing spool to the counter piston (9) and moves swashplate (13) against the minimum angle stop (22).
With the main control valve in the NEUTRAL position, no load sensing signal pressure is sent to the spool in the pump control group. The standby condition in NEUTRAL produces more pump output flow than is required for leakage makeup.
Also, at engine start-up, the machine ECM sends a signal to the horsepower control solenoid valve, which is on the left side of the horsepower control spool (3). The energized solenoid increases the force of the spring on the left side of the horsepower control spool, to match available engine horsepower.
Due to a larger surface area of counter piston (9), the reduced pump supply pressure directed to the counter piston is able to overcome the combination of the spring and the supply pressure acting on the right end of the smaller control piston (7). The swashplate moves toward minimum angle until reaching the minimum stop screw (22).
| |
| Illustration 6 | g03747299 |
|
Partial schematic (upstroke) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
At least three different conditions can cause the pump to be upstroked:
- An increase in the flow demand when the pump flow is being controlled only by load sensing spool (2) and the pump flow is not on the horsepower curve.
- A decrease in the horsepower control pressure when the pump flow is being controlled by the horsepower control spool (3).
- A decrease in the system pressure when the pump flow is being controlled by the horsepower control spool (3).
Illustration 6 shows the pump in the UPSTROKE position when flow increases due to a change in the position of load sensing spool (2).
The pump is upstroked because of an imbalance in the forces that are working on load sensing spool (2). This imbalance causes load sensing spool (2) to shift to the left. Counter piston (9) is open to the tank through load sensing spool (2) and horsepower control spool (3). Supply pressure and spring (20) move swashplate (13) toward maximum angle stop (21) in order to increase pump flow.
The force that is working on the left end of load sensing spool (2) and the force that is working on the right end of load sensing spool (2), are no longer balanced when the following conditions occur:
- A hydraulic circuit is activated from the low pressure standby condition.
- Additional circuits are operated.
- A single circuit is shifted and the circuit requires more flow.
Spring force and load sensing signal pressure through port (X) from the main control valve, work against the pump supply pressure on load sensing spool (2). When more flow is required, the forces on the right end of load sensing spool (2) are greater than the forces on the left end. When this condition occurs, load sensing spool (2) moves to the left.
This action opens the chamber in counter piston (9) to the tank and around load sensing spool (2) and horsepower control spool (3). Pump supply pressure and the force of spring (20), move control piston (7). This action moves swashplate (13) toward maximum angle stop (21) causing the pump flow to increase.
As the pump upstrokes, actuator piston (19) rides along the top of lever (18). Actuator piston (19) moves farther away from the pivot pin, which increases the mechanical advantage. If the increased force is not able to overcome the horsepower control solenoid, the change in flow demand will have no impact on horsepower control spool (3).
| |
| Illustration 7 | g03747315 |
|
Partial schematic (constant flow) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
As the pump flow increases to meet the flow demand, the pump supply pressure will increase. When the pump supply pressure equals the sum of load sensing signal pressure through port (X) and the spring force, load sensing spool (2) moves to a metering position. This action allows oil to be directed to counter piston (9), which will stabilize the system. Forces that are working on load sensing spool (2) are now balanced.
Swashplate (13) is held at a relatively constant angle in order to maintain the required flow. This position is called constant flow.
If the control spools in the main control valve are not shifted, the pump that is working with the compensator spools will provide a relatively constant flow.
Variations in load sensing pressure through port (X) have a minimal influence on the flow requirements, unless system pressure reaches the point that causes horsepower control spool (3) to start to destroke the pump.
As the pump upstrokes and destrokes, the actuator piston (19) moves along the lever (18).
When the pump upstrokes, the actuator piston moves farther away from the pivot pin and the mechanical advantage increases. The force working on the lever will also increase with an increase in system pressure if the pump is in a constant flow state.
When the force working on the lever overcomes the horsepower control pressure acting on horsepower control spool (3), the horsepower control spool shifts and takes control of the pump flow from load sensing spool (2).
| |
| Illustration 8 | g03813060 |
|
Partial schematic (destroke) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
At least three different conditions can cause the pump to destroke, which causes a decrease in pump flow:
- A decrease in the flow demand when the pump flow is being controlled by the load sensing spool (2).
- An increase in the horsepower control pressure when the pump flow is being controlled by horsepower control spool (3).
- An increase in the system pressure when the pump flow is being controlled by the horsepower control spool (3).
Illustration 8 shows the pump in the DESTROKE position when flow decreases due to a change in the position of load sensing spool (2).
As shown in Illustration 8, load sensing spool (2) is shifted to the right. Some of the pump supply oil is directed to counter piston (9). Counter piston (9) moves swashplate (13) toward minimum angle stop (22) in order to meet the new lower flow requirements.
The pump destrokes in order to provide less flow under any of the following conditions:
- A single hydraulic circuit is returned to the NEUTRAL position and the pump goes to a standby condition.
- An additional circuit or circuits are returned to the NEUTRAL position.
- A single circuit is shifted and less flow is required.
The force that is working on the right end of load sensing spool (2) and the force that is working on the left end are no longer balanced.
On the right end of load sensing spool (2), spring force and load sensing pressure from the main control valve through port (X) work against the pump supply pressure on the left end of load sensing spool (2). When less flow is required, the force on the left end of load sensing spool (2) is greater than the force on the right end of load sensing spool (2). Load sensing spool (2) moves to the right.
This action directs pump supply through load sensing spool (2) to counter piston (9). Counter piston (9) moves swashplate (13) toward minimum angle stop (22), which causes the pump flow to decrease. When the flow is lower, the system pressure will decrease.
As the pump supply pressure increases, load sensing spool (2) moves back to the left into a metering position. The pump again produces a constant flow and the pump remains in this condition until the flow requirements change.
As the pump destrokes, actuator piston (19) rides along the top of the lever (18). Actuator piston (19) moves closer to the pivot pin. The mechanical advantage is reduced. The reduced flow demand has no impact on horsepower control spool (3).
| |
| Illustration 9 | g03747873 |
|
Partial schematic for constant flow (horsepower control) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
If system pressure and pump flow do not affect horsepower control spool (3), load sensing spool (2) will control the pump.
As the pump upstrokes and destrokes, actuator piston (19) moves along lever (18).
When the pump upstrokes, actuator piston (19) moves farther away from the pivot pin and the mechanical advantage increases. The force that is working on lever (18) will also increase with an increase in system pressure, if the pump is in a state of constant flow.
When the force that is working on lever (18) overcomes the horsepower control solenoid, horsepower control spool (3) will shift and take over control of the pump flow.
| |
| Illustration 10 | g03747876 |
|
Partial schematic upstroke (horsepower control) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
When horsepower control spool (3) is controlling the main pump flow, an increase in horsepower solenoid pressure will cause the forces that are acting on the spool to become unbalanced. A decrease in the system pressure will cause the forces that are acting on horsepower control spool (3) to become unbalanced.
A decrease in horsepower solenoid pressure or a decrease in system pressure will cause lever (18) to pivot. This action will shift horsepower control spool (3) to the left in order to upstroke the pump.
The chamber in counter piston (9) is open to the tank around load sensing spool (2) and horsepower control spool (3). Pump supply pressure and force of spring (20) will move swashplate (13) toward maximum angle stop (21) and pump flow increases.
As pump flow increases, the forces on horsepower control spool (3) and horsepower solenoid pressure, will reach a balance point and maintain the swashplate at a relatively constant angle. The flow remains constant until either the pump supply pressure changes or horsepower solenoid pressure changes. Horsepower control spool (3) meters flow to counter piston (9).
Constant Flow (Horsepower Control)
| |
| Illustration 11 | g03747879 |
|
Partial schematic constant flow (horsepower control) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
As swashplate (13) moves toward minimum angle stop (22), actuator piston (19) moves along the bottom of lever (18). As actuator piston (19) moves closer to the pivot point of lever (18), the mechanical advantage is changed and horsepower solenoid pressure is able to push actuator piston (19) downward. Horsepower control spool (3) moves back to the right against the spring.
Horsepower control spool (3) reaches a balance point and the spool maintains the swashplate at a relatively constant angle. The flow remains constant until one of the following pressures is changed: system pressure, horsepower solenoid pressure and load sensing pressure.
Horsepower control spool (3) meters flow to and from counter piston (9).
For the selected spool displacement in the control valves, whenever horsepower control spool (3) is controlling the main pump, the pump is producing less flow than what is being required by the circuits. This action results in the cylinder speeds being reduced.
When less flow is being produced, load sensing spool (2) shifts to the right. This action occurs because of load sense pressure through port (X) and spring force work against pump supply pressure on load sensing spool (2).
When less flow is being produced, the pump supply pressure never increases. The forces that are working on the ends of load sensing spool (2) are not balanced. Load sensing spool (2) does not return to a metering position.
| |
| Illustration 12 | g03813064 |
|
Partial schematic for destroke (horsepower control) (2) Load sensing spool (3) Horsepower control spool (7) Control piston (9) Counter piston (13) Swashplate (18) Lever (19) Actuator piston (20) Spring (21) Maximum angle stop (22) Minimum angle stop | |
When the increased force that is working on lever (18) is able to overcome the horsepower solenoid, lever (18) pivots against the force of the horsepower solenoid. Spring force and load sense pressure move horsepower control spool (3) to the right.
Horsepower control spool (3) directs pump supply pressure oil through load sensing spool (2) to counter piston (9). The pump supply pressure in counter piston (9) and the spring force are able to overcome control piston (7) and the force of spring (20) in order to move swashplate (13) to a reduced angle, which reduces the flow.
Once horsepower control spool (3) takes control of the pump flow, horsepower control spool (3) will further destroke the pump due to either an increase in the system pressure or increase in electrical signal to the horsepower control solenoid.
An increase in electrical signal to the solenoid of horsepower control spool (3) can be caused by either lugging of the engine or a change in the power mode.
As the pump destrokes, actuator piston (19) moves closer to the pivot point of the lever (18). As actuator piston (19) moves closer to the pivot point, an increased system pressure is needed to overcome the mechanical advantage of lever (18).
Initially, the pump is destroked faster, but the system pressure is increased. The pump is destroked more slowly. This action causes the hydraulic horsepower output of the pump to follow the torque curve of the engine.
When horsepower solenoid pressure decreases, moving horsepower control spool (3) to the left becomes easier. The pump begins to destroke at a lower pump discharge pressure.
When horsepower solenoid pressure increases, moving horsepower control spool (3) to the left becomes more difficult. The pump begins to destroke at a higher pump supply pressure.
Horsepower control pressure will increase due to a change in the current signal from the machine ECM.