06 nfc pump control system

1INTRODUCTION

This section of the presentation will cover the main hydraulic pumps and pump controls for the300D Hydraulic Excavators.

The main pump group consists of a variable displacement piston drive pump and a variabledisplacement piston idler pump. The drive pump and the idler pump are part of an integralhousing. The drive pump and the idler pump are identical in construction and operation.

The pumps are sometimes referred to as S.B.S. (side by side) pumps. The main differencebetween all of the pumps is the maximum pump flow for each model.

Both the drive pump and the idler pump have individual pump control valve groups to controlthe pump flow.

The 320D through the 329D use the same type of pump control valve group. The 330D/336Dpump control valve group is the same as the pump control valve group used on the 345C pump.

SERV1852-02 - 5 - Text Reference08/08 Main Pumps

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2Power shift pressure is controlled by the Machine ECM, and assists in pump regulation. Powershift pressure is one of three pressures to control the pump.

The pilot pump supplies the power shift PRV solenoid with pilot oil. The Machine ECMmonitors the selected engine speed (from the engine speed dial), the actual engine speed (fromthe engine speed sensor and Engine ECM), and the pump output pressures (from the outputpressure sensors). The power shift PRV solenoid valve regulates the pressure of the power shiftoil depending upon the signal from the Machine ECM to the pump control valve groups.

When the engine speed dial is in position 10, the Machine ECM varies the power shift pressurein relation to the actual speed of the engine.

The power shift pressure is set to specific fixed values dependent upon the position of theengine speed dial. The fixed power shift pressures assist cross sensing pressure (not shown)with constant horsepower control.


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When the engine speed dial is on position 10 and a hydraulic load is placed on the engine, thiscondition causes the engine speed to decrease below the engine's target rpm.

When this decrease occurs, the Machine ECM signals the power shift PRV solenoid valve tosend increased power shift pressure to the pump control valve groups. The increased powershift signal causes the pumps to destroke, and reduce the horsepower demand placed on theengine. With a decreased load from the hydraulic pumps the engine speed increases. Thisfunction is referred to as engine underspeed control.

Engine underspeed control prevents the engine from going into a "stall" condition where enginehorsepower cannot meet the demands of the hydraulic pumps. The power shift signal to thepump control valve groups enables the machine to maintain a desired or target engine speed formaximum productivity.

Power shift pressure has the following effect on the main hydraulic pumps:

- As power shift pressure decreases, pump output increases.

- As power shift pressure increases, pump output decreases.

Power shift pressure ensures that the pumps can use all of the available engine horsepower forthe hydraulic system at all times without exceeding the output of the engine.

NOTE: The target rpm is the full load speed for a specific engine "no load" rpm.Engine target rpm is determined by the opening of one of the implement, swing, and/ortravel pressure switches at the end of an operation. The Machine ECM then waits 2.5seconds and records the engine speed. This specific rpm is the "new" no load rpm.

The Machine ECM then controls the power shift pressure to regulate pump flow tomaintain the full load (target) rpm for the recorded no load rpm.

Target rpm can change each time the pressure switches open for more than 2.5 seconds.



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The proportional reducing solenoid valve (PRV) for the power shift pressure is located on thedrive pump control valve group. The proportional reducing solenoid valve receives supply oilfrom the pilot pump.

The solenoid receives a pulse width modulated signal (PWM signal) from the Machine ECM.The PWM signal sent from the Machine ECM causes the proportional reducing solenoid valveto regulate the pilot pressure to the pump control valve groups to a reduced pressure.

This reduced pressure is called power shift pressure (PS).

The output flow of the drive pump and the idler pump is controlled in accordance with thepower shift pressure. The power shift pressure is used to control the maximum hydraulic pumpoutput in relation to the engine rpm.

A decrease in engine speed causes an increase in power shift pressure and a decrease in pumpflow.

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When the speed dial is at dial position 10, if the Machine ECM senses a decrease in enginespeed below target rpm, the Machine ECM increases the PWM signal sent to the solenoid.

The magnetic force of the solenoid increases. As the magnetic force of the solenoid becomesgreater than the force of the spring, the spool moves down against the force of the spring.

The downward movement of the spool blocks the flow of oil to the tank.

More power shift pressure oil is now directed to the pump control valve group.

The increased power shift pressure acts on the drive pump control valve group and the idlerpump control valve group.

If both pumps are upstroked, then both pumps will destroke as a result of the increase in powershift pressure. If only one pump is upstroked, only the upstroked pump will destroke.


4If engine speed is above the target rpm, the Machine ECM decreases the power shift pressure toincrease the pump flow.

When the Machine ECM senses an increase in engine speed above the target speed the MachineECM decreases the PWM signal sent to the proportional reducing solenoid valve.

As the magnetic force of the proportional reducing solenoid valve becomes less than the forceof the spring, the spool moves up.

The upward movement of the spool restricts the pilot oil flow to the power shift passage andopens the power shift passage to the drain. The power shift pressure is reduced.

The reduced power shift pressure acts on the drive pump control valve group and the idlerpump control valve group.

Depending on which circuits are activated, the drive pump and/or the idler pump will upstrokeas a result of a decrease in power shift pressure.


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5320D - 329D MAIN HYDRAULIC PUMP GROUP

This illustration shows the main hydraulic pumps groups. The drive pump (1) is driven by theengine and the idler pump (2) is driven by the drive pump. The pilot pump (3) is mounted onthe drive pump. The medium pressure pump (4) is driven by the idler pump.

The drive pump supplies oil to the right half of the main control valve group and the followingvalves:

- stick 2 control valve

- boom 1 control valve

- bucket control valve

- attachment control valve

- right travel control valve


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The idler pump supplies oil to the left half of the main control valve group and the followingvalves:

- left travel control valve

- swing control valve

- stick 1 control valve

- boom 2 control valve

- auxiliary valve for tool control (if equipped)

The output of the variable-displacement piston pumps is controlled by the pump control valvegroups (5 and 6) mounted on the main hydraulic pumps.


6This illustration shows the pump control valve group for the drive pump. Except for the powershift solenoid, the components for the idler pump are identical.

The power shift PRV solenoid valve (1) provides a common power shift pressure for bothpumps. The power shift PRV solenoid valve is controlled by the Machine ECM.

The pump output pressure sensors (2) signals the Machine ECM of each pump's outputpressure. The Machine ECM uses the pump output pressure, actual engine speed, and desiredengine speed to determine the power shift pressure. The pressure sensors also signal theMachine ECM to cancel the AEC settings if the pump pressure increases above approximately7370 kPa (1100 psi) and the engine rpm is still at an AEC setting.

The horsepower adjusting screws (3) adjust the hydraulic horsepower output of each pump.The maximum angle screw (4) limits the maximum flow of each pump.

The pressure tap (5) above the power shift PRV solenoid valve can be used to check the PRVsignal pressure. The pressure tap (6) just above the pressure sensor can be used to check thedrive pump supply pressure. Another pressure tap (not shown) can be used to check the idlerpump supply pressure. Cat ET can also be used to check these two pressures.


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7This illustration shows the pumps in STANDBY condition.

The pump control valve groups will upstroke, destroke, or maintain the displacement of thepump depending on the conditions the pump control valve group senses. The pump controlvalve group controls oil pressure (stroking pressure) to the right side of the actuator, whichcontrols the angle of the pump swashplate.

Each pump has a pump control valve group which senses the three following control signals:

- a pump specific Negative Flow Control (NFC) signal from the main control valve group- a common power shift signal pressure generated by the power shift PRV- a common cross sensing signal pressure from the output of the two main pumps

NFC: NFC pressure is the most significant controlling signal in a negative flow controlledhydraulic system. Each pump control valve group receives a specific NFC signal that is basedupon the hydraulic demand for that specific pump.


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Flow from the drive pump supplies the right half of the main control valve group and has acorresponding NFC signal for the drive pump. Flow from the idler pump supplies the left halfof the main control valve group and has a corresponding NFC signal for the idler pump.

The open-center valves in the main control valve group allow pump output to flow throughunrestricted. An orifice in the NFC valve creates a restriction to the pump output whichincrease the NFC pressure. The NFC pressure then signals the corresponding pump controlvalve group. Each pump will remain at STANDBY as long as a full NFC signal pressure ispresent.

When a hydraulic control valve is shifted from the NEUTRAL position, the NFC signalpressure to the corresponding pump is reduced, which causes the pump to UPSTROKE. Anychange in the movement of a valve in the main control valve group will effect the NFC signalbecause the valves send a variable NFC signal to the pump depending on the needed pumpoutput.

Output of each pump is unaffected by a change in the NFC signal to the other pump. NFCpressure has the following effect on the main hydraulic pumps:

- As NFC pressure decreases, pump output increases,

- As NFC pressure increases, pump output decreases.

NFC signal pressure overrides all other control of the main hydraulic pumps.

Cross Sensing: Cross sensing pressure is essentially an average pressure from the output ofthe drive pump and the idler pump.

The output of each pump flows respectively to the left and right halves of the main controlvalve group. The output of each pump also flows to the cross sensing orifices.

The cross sensing pressure compensates for the horsepower demand of each pump individuallyand for the two pumps together. With cross sensing assistance, the pumps constantly regulatethe flow to effectively use all of the available engine horsepower at any given time. Thisregulation is referred to as constant horsepower control.

Cross sensing pressure has the following effect on the main hydraulic pumps:

- As cross sensing pressure decreases, pump output increases,

- As cross sensing pressure increases, pump output decreases.

Given a fixed NFC signal, cross sensing signal pressure regulates the output of the mainhydraulic pumps.

NOTE: Hydraulic horsepower is a function of pump output flow and pressure. Aspump flow or pressure increases, the horsepower demand increases. As pump flow orpressure decreases, the horsepower demand decreases.


8Pump Control Valve Group

The above illustration shows a cross sectional view of one of the main hydraulic pump controlvalve groups in STANDBY. The main pumps will be in STANDBY condition when the engineis running and all control valves are in NEUTRAL. Under these conditions the NFC pressuresignal to the pump control valve groups is high. The pump can not upstroke until NFC signalpressure is reduced.

The high NFC signal pressure causes the NFC control piston to move left against the force ofthe NFC spring on the right. When the NFC control piston moves left the piston contacts theshoulder on the pilot piston, which causes the pilot piston to move the horsepower control spoolagainst the spring force on the left end of the valve.

The passage between horsepower control spool and the sleeve is now open to tank, causing theright end of the actuator to be open to the tank. The actuator moves to the right, moving theswashplate to a minimum angle, which causes pump output flow to be minimum.

NOTE: With S.B.S. pumps, system pressure at STANDBY (maximum NFC signal)destrokes the pumps to minimum. When the pump is upstroked all three signals worktogether to control the angle of the pump swashplate to regulate the pump flow.


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9The pumps must have a reduction in NFC pressure to upstroke from STANDBY. Theillustration shows the pump control valve groups upstroking the pump due to a decrease in NFCsignal pressure. As shown, there is no NFC signal pressure, indicating that at least one controlvalve has been fully shifted.

When one of the joysticks or travel levers is moved from the NEUTRAL position, NFC signalpressure decreases proportionally to the amount the joystick or travel lever is moved. When theNFC signal pressure decreases, the spring on the control piston forces the control piston to theright. The horsepower control springs on the left overcome the cross sensing signal pressureand the power shift signal pressure to move the horsepower control spool to the right.

With the horsepower control spool shifted to the right, the passages between the sleeve and thehorsepower control spool are closed off to tank and pump output pressure is allowed to flow tothe right side of the actuator. Because the right side of the actuator is larger than the left side,the greater force generated by the pressure on the right side causes the actuator to move left toupstroke the pump.

The pump can also be upstroked by a decrease in either power shift or cross sensing pressure,but only after a reduction in NFC pressure has caused the pump to move from the minimumangle.


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As the pump upstrokes, the movement of the actuator causes the control linkage to move thesleeve around the horsepower control spool. The sleeve moves to the right as the actuatormoves to the left. Because of the geometry of the control linkage, a large movement of theactuator moves the sleeve a small amount (see Section D-D).

The small movement of the sleeve causes the passages between the sleeve and the horsepowercontrol spool to open partially to the tank and partially to the pump output. The pressure signalsent to the right side of the actuator is now metered, which causes the actuator to reach abalance point where the pump does not upstroke or destroke. With the actuator at a fixedposition the swashplate angle of the pump is fixed. Constant flow is now achieved.

Due to varying loading and operating conditions, this fixed output is rarely maintained for verylong. When operating conditions change, the pump will UPSTROKE or DESTROKE.


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The three things which can cause the pumps to DESTROKE are:

- an increase in NFC pressure

- an increase in cross sensing pressure

- in increase in power shift pressure

This illustration shows the system under a heavy hydraulic load. As the supply pressureincreases due to the heavy load, the cross sensing signal pressure rises as an average of the leftand right pump delivery pressures. The cross sensing signal acts on the difference of the twoareas on the pilot piston. As the cross sensing signal increases, the pilot piston moves to theleft, which pushes the horsepower control spool left against the force of the horsepower controlsprings on the left.

As the spool moves left, the large end of the actuator is opened to tank by a passage betweenthe horsepower control spool and the sleeve. The pressure decreases on the right end of theactuator and the actuator moves to the right, which causes the pump to DESTROKE.


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An increase in power shift signal pressure has a similar effect as an increase in cross sensingsignal pressure. If the hydraulic pump lugs the engine below full load speed, the MachineECM increases the current to the power shift PRV solenoid valve. The increased signal causesa higher power shift signal to be sent to the pump control valve groups.

The power shift pressure acts on the right side of the pilot piston. The force generated from thepower shift pressure assists cross sensing pressure to destroke the pump. As the pumpdestrokes the engine speed will increase due to the reduction in load.

An increase in NFC signal pressure will cause the pump to destroke. If all control valves werereturned to NEUTRAL, the NFC signal causes the pump to fully destroke and return toSTANDBY.


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330D /336D MAIN HYDRAULIC PUMP GROUP

The 330D and the 336D uses a new Kawasaki designed main hydraulic pump group (1) rated at 2 x 280 L/Min (2 x 74 gpm). The pump group is different from the pump group used on the330C, however it continues to use an NFC control system. This pump group is similar to thepump group used on the 345C.

The drive pump (2) is driven by the engine via a flexible coupling. The idler pump (3) isdriven directly off the drive pump. Each pump rotating group has its own pump control valvegroup. The pump control valve groups are used to adjust the output flow of the pumps. Eachpump rotating group also has its own pressure tap and pressure sensor.

A power shift PRV solenoid valve (4) is mounted on the top, center of the pump group case.The power shift PRV solenoid valve uses pilot system oil and sends some of the pilot oil to themain hydraulic pump control valve groups as a control signal pressure. The power shiftpressure is checked at pressure tap (5).

Additional pump components shown in this photo are: the drive pump control valve group (6),the idler pump swashplate minimum angle adjustment (7) and the idler pump control valvegroup (8). The pilot pump (9) is driven off the idler pump and the demand fan pump (10) isdriven off of the drive pump.


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This is a view of the drive pump pump control valve group. The pump control valve group islocated above and behind the power shift PRV solenoid valve. This illustration shows:

- the drive pump negative flow control adjustment (1)

- the drive pump horsepower control adjustment (2)

The idler pump control valve group has similar adjustment screws.

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Each pump receives four different signals to control the output flow of the pumps:

- power shift pressure

- system pressure from that pump

- cross sensing pressure (from the other pump)

- Negative Flow Control (NFC) pressure

Power Shift Pressure: The power shift PRV receives a control signal from the ECM. TheECM sends an electrical signal to the power shift PRV to regulate power shift pressure inrelation to the engine speed.

The power shift signal to the pump control valve groups enables the machine to maintain thetarget engine speed for maximum productivity.


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If the Machine ECM senses that the engine is below the target speed due to a high hydraulicload from the main pumps, the Machine ECM will increase the power shift pressure. Thetarget speed is the full load for the no load engine speed. (The new no load speed is taken 2.5seconds after the implement/swing and the travel pressure switches open when the joysticksand the travel control pilot controls are returned to NEUTRAL). As power shift pressureincreases, the pump control valve groups destroke the main pumps accordingly. This reducesthe load on the engine, and consequently enables the engine to maintain the target enginespeed.

If the engine speed is above the target speed, the Machine ECM will decrease power shiftpressure, causing the pumps to upstroke and produce more flow.

Cross sensing Control Pressure: Each pump control valve group gets a cross sensing controlpressure from the other pump system pressure. Cross sensing pressure is essentially an averagepressure from the output of the drive pump and the idler pump.

Negative Flow Control (NFC): NFC is the primary controlling signal for the main pumpoutput. The NFC signal to the main pump control valve group is generated in the main controlvalve group. The NFC signal is delivered to the left and right pump control valve groups fromthe left and right halves of the main control valve group, respectively.

When the joysticks or travel levers are in the NEUTRAL position, the oil flows from the mainpumps through the open center bypass passages of the control valves. The oil flows to thevalves and returns to the tank by way of the NFC control orifices. The restriction of the NFCorifices causes a pressure signal to be sent to the right and left pump control valve groups,respectively, as an NFC signal.

When the main pump control valve groups receive a high NFC signal from the main controlvalves, the pumps remain at a standby output flow at or near minimum pump displacement.

When a joystick or travel lever is moved from a NEUTRAL position, the open-center passageof the corresponding implement/travel function is closed in proportion to spool movement.This reduces the NFC signal to the main pump control valve and the pump output flow isincreased proportionally. When the control valve is fully shifted, the NFC pressure is reducedto slow return check valve pressure.

The use of an NFC hydraulic system maximizes efficiency of the machine by only producingflow from the pumps when the flow is needed.

NOTE: A high NFC signal will always overcomes the horsepower control and decreasepump flow to minimum.


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This illustration shows the pumps in STANDBY condition. Each pump control valve groupsenses the Negative Flow Control (NFC) signal, the power shift pressure, the cross sensingpressure, and the system pressure for that pump.

When one of more circuits are activated, the pump control valve groups will upstroke ordestroke the pumps to maintain the pump flow depending on the four signal pressures to thepump control valve groups.

The pump control valve group controls oil pressure to the left side of the actuator. Thiscontrols the angle of the pump swashplate.

The 330D/336D hydraulic pumps are always trying to upstroke to increase flow. The pumpcontrol valve groups vary the oil pressure used to destroke the hydraulic pumps.

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The idler pump supplies oil to the following valves:

- left travel control valve

- swing control valve

- stick I control valve

- boom II control valve

- idler (left) pump negative flow control valve

- auxiliary valve (if equipped)

The drive pump supplies oil to the following valves:

- right travel control valve

- standard attachment control valve

- bucket control valve

- boom I control valve

- stick II control valve

- drive pump negative flow control valve



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Pump Control Valve Group

This illustration shows the three separate control sections of the pump control group. The threecontrol sections are connected with a series of pins and linkages. The separate control sectionswork together to regulate pump flow by changing the angle of the pump swashplate, accordingto demand and hydraulic horsepower requirements.

Pump supply pressure is directed to the small end of the actuator piston to upstroke the pumptoward maximum angle. A regulated pressure signal is directed to the large end of the actuatorpiston to destroke the pump toward the minimum angle.

The horsepower control section directs some of the system pressure oil to and from the largeend of the large actuator piston. The lower end of the feedback lever is connected to theactuator piston. The feedback lever works as a follow-up linkage to move the horsepowercontrol spool when the large actuator piston moves.

The negative flow control (NFC) section works in conjunction with the horsepower controlsection to destroke the swashplate when all hydraulic controls are in NEUTRAL or duringimplement or travel MODULATION. The torque control section works in conjunction with thehorsepower control section to regulate pump flow when the hydraulic circuits are actuated.

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This illustration shows an end sectional view of the pump controls. The NFC spool isconnected to the lower end of the NFC lever with a pin. The upper end of the NFC lever pivotson a fixed pin in the housing.

The torque control spool is connected to the lower end of the torque control lever with a pin.The upper end of the torque control lever also pivots on a fixed pin in the housing.

The upper end of the feedback lever is connected to the horsepower control spool with a pin.The lower end of the feedback lever is connected to the actuator piston.

The feedback lever pin fits tightly into the feedback lever. The feedback lever pin extends intolarge holes in the torque control lever and the NFC lever.

The large holes permit individual control from the torque control lever and the NFC lever.Movement of the actuator piston causes the feedback lever to pivot on the feedback lever pinand move the horsepower control spool.


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This illustration shows the NFC portion of the pump control group. When all hydraulic controlvalves are in NEUTRAL, a high NFC pressure (system pressure) from the NFC orifice isdirected to the left end of the NFC spool. The NFC pressure pushes the NFC spool to the rightagainst the spring force.

In the STANDBY condition, the horsepower control spool directs a signal pressure, which ispart of system pressure, to the minimum angle end of the actuator piston. The increase inpressure moves the actuator piston to the right against the minimum angle stop screw. Thepump flow will remain constant until the NFC pressure from the control valve decreases.

The NFC adjusting screw changes the effect of the NFC pressure on the NFC spool. Turningthe screw in (clockwise) causes the NFC pressure to increase higher before the NFC spoolmoves. This condition causes the pump to upstroke sooner (less modulation) when thehydraulic control valve is ACTIVATED.

Turning the screw out (counterclockwise) causes the NFC spool to move at a lower NFCpressure. This condition causes the pump to upstroke later (more modulation) when thehydraulic control valve is ACTIVATED.


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This illustration shows the pump control group at the beginning of an upstroke caused by adecrease in NFC pressure.

The pivot pin is fixed to the pump control housing. The NFC lever pivots around this point.

When a hydraulic control valve in the main control valve is shifted, the NFC pressure isdecreased. Due to reduced NFC pressure, spring force moves the NFC piston to the left. TheNFC piston moves the lower end of the NFC lever to the left.

As the lower end of the NFC lever moves to the left, the large hole through the lever alsomoves to the left. As the large hole moves to the left, spring force pulls the horsepower controlspool and the upper end of the feedback lever to the left because the feedback lever pin isallowed to move to the left.

The minimum angle actuator piston is opened to case drain through the right orifice in thehorsepower control sleeve and the right end of the horsepower control spool. System supplypressure pushes the maximum angle actuator piston to the left to upstroke the pump.


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As the actuator piston moves, the lower end of the feedback lever moves to the left. Thefeedback lever rotates clockwise with the feedback lever pin as the pivot point.

The upper end of the feedback lever pulls the horsepower control spool to the right until theright land on the horsepower control spool reaches a balance point between the orifices throughthe horsepower control sleeve.

Flow to and from the minimum angle end of the actuator piston is metered by the horsepowercontrol spool and the horsepower control sleeve. The swashplate angle remains constant untilthe NFC pressure is again changed.


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The amount of reduction in NFC signal pressure determines the amount of pump upstroke. IfNFC pressure is reduced to minimum, the pump will upstroke until the actuator piston contactsthe maximum angle stop screw.

NOTE: A decrease in power shift pressure will cause an increase in flow from thepump in the same manner as described for a decrease in system pressure, since bothpower shift pressure and system pressures act on the torque control piston.

SERV1778 - 32 - Text Reference08/08 Main Pumps

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This illustration shows the torque control piston and horsepower control spool sections of thepump control valve group with the pump in the upstroked position at the beginning ofDESTROKE due to an increase in the load on the system.

For the purpose of this presentation, assume that power shift pressure from the power shiftPRV solenoid valve remains constant.

The pivot pin is fixed to the pump control housing. The torque control lever pivots around thispoint.

The large horsepower adjustment screw regulates the pressure or point that the pump starts todestroke (large spring adjustment). The small adjustment screw regulates the rate that the pumpdestrokes (small spring adjustment).

Power shift pressure from the power shift PRV solenoid valve enters the pump control groupand pushes on the plug at the left end of the torque control piston. System supply pressurefrom this pump enters the pump control valve group and goes to the right shoulder area on thetorque control piston.


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The cross sensing signal pressure from the other pump goes to the left shoulder area on thetorque control piston.

The combination of power shift pressure and the two system supply pressures push the torquecontrol piston to the right against the force of the horsepower control adjustment springs. Thehorsepower control spool directs the signal pressure to the minimum angle end of the actuatorpiston to destroke the hydraulic pump.

When the system supply pressures and power shift pressure push the torque control piston tothe right:

The torque control spool moves to the right to compress the horsepower control springs. Thetorque control spool moves the lower end of the torque control lever to the right with the fixedpin on the upper end of the torque control lever as the pivot point.

The torque control lever pulls the feedback lever pin and the upper end of the feed back leverto the right.

The feedback lever pulls the horsepower control spool to the right against the spring force.

System supply pressure is directed around the horsepower control spool through the centerorifice of the horsepower control sleeve and to the minimum angle end of the actuator piston.The increase in pressure in the minimum angle piston moves the actuator piston to destroke thepump.

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This illustration shows the pump control group at the end of a DESTROKE due to an increasein load on the system.

When the actuator piston moves toward minimum angle, the lower end of the feedback levermoves to the right, turning the lever counterclockwise with the feedback lever pin as the pivotpoint.

The feedback lever movement shifts the horsepower control spool to the left so system supplypressure is metered through the two orifices to and from the minimum angle end of the actuatorpiston. Pump flow is held constant until one of the signal pressures changes.

An increase in power shift pressure will cause a decrease in flow from the pump in the samemanner as described for an increase in system pressure since both the power shift pressure andsystem pressure act on the torque control piston.


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06 nfc pump control system

Documents

pilot pump

pump controls

pump regulation

main pump group

engine ecm

engine speed increases

pump output increases

pump output pressures