Hệ thống thủy lực máy đào CATERPILLAR SERIE D - P5

Caterpillar hydraulic excavators serie D

TECHNICAL PRESENTATION

320D336D HYDRAULIC EXCAVATORS

-TIER III ENGINES

MAIN HYDRAULIC PUMPS AND PUMP CONTROL

TIER III ENGINES

MAIN HYDRAULIC PUMPS AND PUMP CONTROL

This presentation provides an introduction and describes the components and systems operation

of the 320D-336D main hydraulic pumps and pump control valve groups Additional

presentations will cover the machine walkaround, engines, pilot system, main control valvegroup, implements swing system, travel system, and tool control systems in more detail Thispresentation may be used for self-paced and self-directed training

OBJECTIVES

After learning the information in this presentation, the technician will be able to:

1 identify the components and explain the operation of the 320D-336D hydraulic

excavators main hydraulic pumps and controls, and

2 diagnose problems in the main hydraulic pumps and controls

REFERENCES

Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,

iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems" SERV2693iTIM "325C Hydraulic Excavators-Hydraulic Systems" SERV2701

Estimated Time: 1 hour

Illustrations: 22

Form: SERV1852-02

Date: August 2008

© 2008 Caterpillar

TABLE OF CONTENTS

INTRODUCTION 5

320D - 329D MAIN HYDRAULIC PUMP GROUP 11

Pump Control Valve Group 16

330D / 336D MAIN HYDRAULIC PUMP GROUP 21

Pump Control Valve Group 27

CONCLUSION 36

"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002

"Fundamentals of Power Train Self Study Course" TEMV3003

"Fundamentals of Electrical Systems Self Study Course" TEMV3004

"Fundamentals of Engines Self Study Course" TEMV3001

NOTES

Nomenclature Change: During the fourth quarter of 2008, the 325D and 330D

nomenclature changed The 325D became the 329D and the 330D became the 336D for most arrangements.

The exceptions are as follows:

- The nomenclature for the 325D MH and 330D MH did not change.

- The nomenclature for the 325D FM and 330D FM did not change.

- The 325D HD HW did not change into 329D HD HW This model is being discontinued However, the 330D HD HW changed to the 336D HD HW.

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

Main Hydraulic Pumps M

Pilot Pump Fan

Motor

Pilot Manifold

Main Control Valve Group

Fan Pump Tank

The Fan Motor and Pump are only used on the 330D and 336D

MAIN HYDRAULIC PUMPS AND PUMP CONTROL VALVE GROUPS

When the engine speed dial is in position 10, the Machine ECM varies the power shift pressure

in 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

Engine Speed Sensor

Engine ECM

Machine

ECM

Pilot Pump

Drive Pump

Idler Pump

Pump Control Valve Power Shift PRV Solenoid

OK

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/or travel pressure switches at the end of an operation The Machine ECM then waits 2.5 seconds 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 to

maintain 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.

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 valve

to 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

Plunger

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

As the magnetic force of the proportional reducing solenoid valve becomes less than the force

of 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 upstroke

as a result of a decrease in power shift pressure

Plunger

320D - 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

5

1

3

6 4

2

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

The pump output pressure sensors (2) signals the Machine ECM of each pump's output

pressure 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 the

Machine ECM to cancel the AEC settings if the pump pressure increases above approximately

7370 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

This 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 controlled

hydraulic system Each pump control valve group receives a specific NFC signal that is basedupon the hydraulic demand for that specific pump

Drive Pump

Pilot Pump

Med Press Pump

Main Control Valve

Group (Right Side)

Pilot Filter and

Medium Pressure Circuit

Main Control Valve

Control Orifice

Right NFC Control Orifice

Output Pressure Sensor

Pump Control Valve

Case Drain

MAIN PUMP GROUP

STANDBY

Cross Sensing Orifice

M1

M2

PS2

Power Shift PRV Solenoid Valve

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 half

of 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 signal

pressure 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 of

the 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 As

pump flow or pressure increases, the horsepower demand increases As pump flow or pressure decreases, the horsepower demand decreases.

Pump 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 engine

is 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 work

together to control the angle of the pump swashplate to regulate the pump flow.

NFC

Pin A

Pivot Control Linkage

Control Piston Guide

Cross Sensing Signal Power Shift Signal

Pin B Horsepower

Control Spool Sleeve Shoulder Control Pilot

Actuator

D D

SECTION D-D

Swashplate

Actuator Pin A

Pin B

Control Signal Pivot MAIN PUMP CONTROL VALVE GROUP

STANDBY

The pumps must have a reduction in NFC pressure to upstroke from STANDBY The

illustration 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

D D

NFC

Pin A

Pivot Control Linkage

Control Piston Guide

Cross Sensing Signal Power Shift Signal

Pin B Horsepower

Control Spool Sleeve Shoulder Control Pilot

Actuator

SECTION D-D

Swashplate

Actuator Pin A

Pin B

Control Signal Pivot

MAIN PUMP CONTROL VALVE GROUP

UPSTROKED - NFC SIGNAL REDUCED

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

D D

NFC

Pin A

Pivot Control Linkage

Control Piston Guide

Cross Sensing Signal Power Shift Signal

Pin B Horsepower

Control Spool Sleeve Shoulder Control Pilot

Actuator

SECTION D-D

Swashplate

Actuator Pin A

Pin B

Control Signal Pivot

MAIN PUMP CONTROL VALVE GROUP

CONSTANT FLOW