1prelim994D STMG

Service Training SESV1XXXMeeting Guide XXX Month 199X

TECHNICAL PRESENTATION

994D WHEEL LOADER

INSTRUCTOR NOTES

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1

994D WHEEL LOADERIMPLEMENT HYDRAULIC SYSTEM

IMPLEMENT PUMPS

MAIN SYSTEM COOLING SYSTEMPILOT SYSTEM

PILOT PUMP

MAIN RELIEF VALVESMAIN CONTROL VALVES

PILOT RELIEF VALVEPILOT FILTER

PILOT CONTROL VALVEIMPLEMENT OIL COOLING PUMP

IMPLEMENTOIL TANK

COOLINGOIL FILTER

IMPLEMENTOIL COOLERS

LIFTCYLINDERS

TILTCYLINDERS

IMPLEMENT PUMP CASE DRAIN FILTERS

HIGH PRESSUREOIL SCREENS

IMPLEMENT HYDRAULIC SYSTEM

The 994 Wheel Loader implement hydraulic system consists of two basicsystems plus a common cooling system.

The color codes for the components in each system are:

Red -System or high pressureBlue -Main hydraulic systemGreen -Cooling system (common)

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2

TO LIFTCONTROLVALVES

TO TILTCONTROLVALVES

PILOT RELIEFVALVE

PILOTFILTER

PILOTPUMP

PILOT CONTROLVALVES

CHECKVALVE

CHECKVALVE

SELECTOR AND PRESSURECONTROL VALVE

994D IMPLEMENT PILOT SYSTEM

FROMLIFT CYLINDERS

IMPLEMENTHYDRAULIC TANK

TILT LIFT

SELECTORVALVES

TO COOLINGCIRCUIT

Pilot System

Shown is a block diagram of the pilot system. The pilot system is aclosed center design. Oil (green) is drawn from the tank by the pump.Pump oil (orange) flows through the filter, past the relief valve andthrough the inlet (left) check valve to the pilot control valve. The oil isblocked at the pilot control valve until either the tilt or lift control lever ismoved. Moving the tilt or lift control lever sends pilot oil to the respectivespool in the main control valve. When system pressure reaches the reliefvalve setting, the relief valve opens and allows pump oil to return to thetank. The pilot system will constantly operate at the relief valve pressuresetting.

Tank pressure oil(green)

Pilot oil (orange)

When the engine is running, the pilot pump oil is at a higher pressure thanthe oil from the pressure and selector control valve. Pilot oil opens theinlet check valve in the pilot oil line and seats the check valve (right) tothe pressure and selector valve.

Pressurized oil from the lift cylinders flows to the selector and pressurecontrol valve. The pressure and selector control valve reduces thepressure and makes the low pressure oil available for emergency use inthe pilot system. When the engine is not running, no pump flow isavailable. Oil from the pressure and selector valve flows through thecheck valve (right) to the pilot control valves. The inlet check valveblocks flow to the pilot relief valve, pilot filter and pump.

INSTRUCTOR NOTE: The color codes used for hydraulic oilthroughout this section of the presentation are:

Red - -System or high pressureRed and White Stripes -Reduced pressureOrange- -Pilot pressureBlue - -Blocked oilGreen - -Tank or return oil

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1. Pilot relief valve2. Selector and

pressure controlvalve

3. S.O.S tap

3

The pilot relief valve (1) is located on the front frame above the maincontrol valve and to the left of the selector and pressure control valve (2).The pilot relief valve maintains the pilot pressure at 2400 kPa (350 psi).Pilot system oil samples are taken at the oil sampling tap (3).

Two selector valves (4) are mounted near the main control valve. Theselector valves provide a path for the pilot oil to circulate when the pilotcontrol valve is in the hold position. Constantly circulating the pilot oilthrough the selector valves helps keep the oil warm during cold weatherconditions.

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4.-Selector valves

P0002499.JPG

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4

PILOT CONTROLVALVE

TILT BACKHOLDDUMP

RAISELOWER

FLOATHOLD

TO TANK

FROMPUMP

FROM MAKEUPAND VENT VALVE

TILTLIFT

TO LIFTCONTROL VALVE

TO TILTCONTROL VALVE

LOWER

This sectional view shows the lift pilot control spool in the LOWERposition. The oil pressure in the implement control valve is the same asthe pilot supply pressure.

Movement of the lift pilot control spool is the same as the tilt pilot controlspool.

In the LOWER position, the lift pilot control spool is not pushed into thevalve body far enough to open the passage from the makeup valve to thetank.

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5

PILOT CONTROLVALVE

TILT BACKHOLDDUMP

RAISELOWER

FLOATHOLD

TO TANK

FROMPUMP

FROM MAKEUPAND VENT VALVE

TILTLIFT

TO LIFTCONTROL VALVE

TO TILTCONTROL VALVE

FLOAT

This sectional view shows that the lift pilot control spool has been movedfarther into the valve body to the FLOAT position. The flow of pilot oil tothe lift control valve is the same as when the control spool was in theLOWER position. However, in the FLOAT position, the passage from themakeup valve is open to the tank.

When the passage from the makeup valve is open to the tank, oil behindthe makeup valve flows to the tank. The decrease in pressure behind themakeup valve allows the makeup valve to open.

When the makeup valve opens, oil normally used to lower the implementgoes through the makeup valve to the tank. The implement is allowed tomove with the contour of the ground. (The main control valve FLOATposition is discussed in slide No. 10.)

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6

IMPLEMENTHYDRAULIC TANK

LEFT MAINCONTROL VALVE

GROUP

RIGHT MAINCONTROL VALVE

GROUP

RIGHTIMPLEMENT

PUMP

LEFTIMPLEMENT

PUMP

CENTERIMPLEMENT

PUMP

RELIEFVALVE

RELIEFVALVE

RELIEFVALVE

994D IMPLEMENT HYDRAULIC SYSTEM

Main Hydraulic System

The implement hydraulic circuit has three fixed displacement, piston-typepumps, three main relief valves, two main control valves, two liftcylinders, and two tilt cylinders.

Oil flow from the three implement pumps operates the lift and tiltcylinders. Oil flow is metered to the cylinders by the main control valvespools. The main control valve spools are controlled by the pilot circuit(not shown).

Oil flow from the right pump enters the top of the right control valve. Oilflow from the left pump enters the top of the left control valve. Oil flowfrom the center pump enters both control valves between the auxiliary andtilt spools.

The operator controls the pilot oil flow and pressure which moves themain control valve spools. The movement of the main valve spools openspassages for pump oil flow to one end of the tilt and lift cylinders.Movement of the valve spools also opens a passage for oil in the oppositeend of the cylinders to return to the tank.

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1. Main implementhydraulic pumps

2. Case drain filters

7

The three main implement hydraulic pumps (1) are located on the frontpump drive between the lift arms. The pumps are fixed displacement,piston-type pumps, each with the same output.

Three case drain filters (2), one for each pump, are mounted nearby.

A manifold (1) with a pressure tap (2) is bolted to the underside of eachmain implement pump. Each manifold contains a pressure relief valve (3)and a check valve (4). The check valves isolate each pump and itspressure relief valve from reverse flow from the other pumps. The checkvalves allow the pressure relief valves for each pump to be set on themachine.

INSTRUCTOR NOTE: See the 994 Wheel Loader HydraulicSystems Operation, Testing and Adjusting module (Form SENR4753)for the relief valve testing and adjusting procedure.

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P0000886.JPG

Implement highpressure screens(arrows)

8

Three high pressure screens (arrows) are mounted near the implementcontrol valve. Oil flow from each pump passes through a screen beforeentering the implement control valve.

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IMG0003.PCD

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9

Identify components

Explain makeup andvent valve functions

- Engine OFF

- FLOAT position

LOAD CHECKVALVE

LIFT CYLINDERROD END

MAKEUP AND VENTVALVE LOCATION

LINE RELIEF AND MAKEUPVALVE LOCATION

LIFT CYLINDERHEAD END

OIL FROM PILOTCONTROL VALVE

OIL TO TANK THROUGHPILOT CONTROL VALVE

FROM PUMP

TO TANK

ROD END

ROD END HEAD END

HEAD END

FROM PUMP

994D WHEEL LOADERMAIN CONTROL VALVE

FLOAT

RACK DUMP

LIFTLOWERFROM TANKTO TANK

TO PILOT CONTROLVALVE

FLOAT MAKEUP

ROD ENDCYLINDER

OIL

ROD ENDCYLINDER

OIL

TO PILOT CONTROLVALVE

MAKEUP AND VENT VALVE

LIFT CONTROL VALVECUTAWAY

The makeup and vent valve functions as a makeup valve when thepressure in the cylinder decreases below the pressure in the hydraulictank.

When lowering the bucket with the engine OFF or when the lowering thebucket faster than the pump can fill the rod end of the cylinder, pistondisplacement causes a vacuum (cavitation) in the rod end of the liftcylinders. When the oil pressure in the hydraulic tank exceeds thepressure in the cylinders, the higher tank pressure opens the makeup valveand tank oil flows into the cylinders.

The makeup and vent valve functions as a vent valve when the hydrauliccontrol valve is moved to the FLOAT position. When the lift pilot controlvalve is moved to the float position, the oil behind the makeup valve isopened to the tank. The small orifices in the base of the makeup valverestrict oil flow to the chamber behind the valve.

With oil flowing from behind the makeup valve faster than oil flowing in,the pressure difference between the oil around the makeup valve and theoil behind the makeup valve becomes high enough to lift the makeupvalve off its seat. When the makeup valve moves off its seat, the oil fromthe implement pump flows past the makeup valve to the tank. Both endsof the lift cylinders are opened to the tank allowing the bucket to floatalong the ground.

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10

PILOT CONTROLVALVE

TILT LIFT

AUX

TILT

LIFT

AUX

TILT

MAIN CONTROL VALVE GROUP

FILTER COOLING/PILOTPUMP MAIN

PUMPS

MAINRELIEFVALVES

PILOTRELIEFVALVE

FLUIDSAMPLING


TILT LIFT

994D WHEEL LOADERBUCKET LOWER


COOLER BYPASSRELIEF VALVE

COOLER BYPASSVALVE

OIL COOLER

SELECTOR ANDPRESSURE REDUCING

VALVE

LIFT

T

BREAKER ANDRELIEF VALVE

T

SELECTOR VALVES

MAKEUP AND VENTVALVE


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11

Explain schematic

PILOT CONTROLVALVE

TILT LIFT

AUX

TILT

LIFT

AUX

TILT


FILTER COOLING/PILOTPUMP MAIN

PUMPS

MAINRELIEFVALVES

PILOTRELIEFVALVE

FLUIDSAMPLING


TILT LIFT

994D WHEEL LOADERBUCKET FLOAT


COOLER BYPASSRELIEF VALVE

COOLER BYPASSVALVE

OIL COOLER

SELECTOR ANDPRESSURE REDUCING

VALVE

LIFT

T

BREAKER ANDRELIEF VALVE

T

SELECTOR VALVES



This schematic shows the hydraulic flow when the control lever is movedto the FLOAT position.

When the pilot control valve is in the FLOAT position, pilot oil is sent tothe left ends of the lift control spools which causes the spools to moveagainst the centering springs to the LOWER position. The control spoolsopen passages for oil flow from the implement pumps, through the loadcheck valves, the lift control spools and the rod end of the lift cylinders tolower the bucket. Also, when the pilot control valve is in the FLOATposition, oil behind the lift control spool rod end makeup valves is ventedthrough the pilot control valve to the tank. The small orifices in themakeup valves cause a restriction to the implement pump oil when fillingthe cavities behind the makeup valves. With oil flowing from behind themakeup valves faster than oil flows in, the pressure difference between theoil around the makeup valves and the oil behind the makeup valvesbecomes high enough to lift the makeup valves off their seats.

When the makeup valves move off their seats, oil from the implementpumps flows past the makeup valves to the tank. Both ends of the liftcylinders are open to the tank allowing the bucket to float along theground.

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12

Identify components

- Cooling pump- Bypass relief valve- Filter- Oil-to-air cooling core- Oil-air-cooler

FILTER

COOLER BYPASSVALVE

OIL COOLER

FROM PILOTRELIEF VALVE

COOLINGPUMP

IMPLEMENTOIL COOLING SYSTEM

Implement Oil Cooling System

The hydraulic oil cooling system consists of a pump, a bypass relief valve,two filters, and an oil-to-air cooler with a bypass valve.

Hydraulic oil from the cooling system pump joins with oil from the pilotrelief valve and flows to the bypass relief valve, filter and coolers. Whenthe oil is cold, the high resistance to flow through the filters and coolerscauses the pressure to increase. The high pressure opens the bypass reliefvalve allowing cold oil to bypass the coolers and flow to the tank. [Thebypass relief valve is set to open at 1680 kPa (245 psi).] As thetemperature of the oil increases, the resistance to flow through the filterand coolers decreases. When the higher temperature causes pressure todecrease below the bypass relief valve setting, the bypass relief valvecloses. The hot oil flows through the filter to the coolers. When the hotoil flows through the coolers, air from the cooling fan removes the heatfrom the oil. The cooler hydraulic oil returns to the tank.

Explain hydraulic oilcooler

1. Hydraulic oil cooler

2. Multiple row modular radiator group

13

Shown is the hydraulic oil cooler (1) located between the multiple rowmodular radiator group (2) and the cooling fan (not shown) at the rear ofthe engine.

The oil cooler and five modules in the multiple row modular radiatorgroup act as heat exchangers. The pump sends hot hydraulic oil flowthrough the filter and the inner passages of the oil cooler and modules.The cooling fan sends cooler air flow through the outer fins of the oilcooler and modules. Heat from the hot oil transfers to the cooler air. Thewarmer air is discharged to the atmosphere. The cooler oil is returned tothe hydraulic tank.

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dentify components:

1. Auto lube control valve

2. Regulator

3. Vent valve

4. Vent hose

5. Pump

6. Check valve

7. Lube hose

8. Tank

9. Unloader

14

Shown are components of the automatic lubrication system.

When the auto lube control valve (1) solenoid energizes, air from thereservoir flows through the auto lube control valve and the regulator (2) tothe vent valve (3). In the vent valve, air pressure closes the lubricantpassage to the vent hose (4). Air flow continues from the vent valve tothe pump (5). The pump draws lubricant from the tank and sendspressurized lubricant through the check valve (6), the vent valve and thelube hose (7) to the injector banks (not shown).

When the auto lube control valve solenoid de-energizes, the control valveblocks air flow to the vent valve and pump. The vent valve opens thepassage to the vent hose. The pressurized lubricant seats the check valveand flows through the vent hose to the tank (8).

The unloader (9) protects the system from excessive pressure.

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IRON SHOT OF LUBE RESERVOIR

15

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16

Explain power flow

- Engine

- Spring coupling

- Rear pump drive

- Torque converter

- Universal joints andinput drive shaft

- Input transfer gear

994D WHEEL LOADER

3516B ENGINE

TRANSMISSION

FINAL DRIVE

FINALDRIVE

TRANSMISSIONPUMP

OUTPUT TRANSFER GEAR

INPUT TRANSFER GEAR

DRIVESHAFT

PARKINGBRAKE

SPRINGCOUPLING

REAR PUMP DRIVE

TORQUE CONVERTER INPUTDRIVE SHAFT

SECONDARYSTEER PUMP

POWER TRAIN

Power Flow

Power from the diesel engine is sent from the flywheel through the springcoupling to the rear pump drive. The rear pump drive is splined to thetorque converter. Other components (not shown on this slide) that aredriven by the rear pump drive are: the two steering pumps, the brakeactuation pump, the brake cooling pump and the steering cooling pump.

Two universal joints and the input drive shaft connect the torque converterto the transmission input transfer gear.

The input transfer gear is splined to the transmission input shaft. Thetransmission output shaft is splined to the output transfer gear. Powerfrom the output transfer gear is sent through the front drive shaft and itsrespective pinion, bevel gear, differential carrier and axles to the frontfinal drives and similarly to the rear final drives.

dentify Impeller ClutchTorque Converter

Components:1. Impeller clutch pressure sensor

2. Lockup clutch pressure tap

3. Lockup clutch solenoid valve

4. Converter and transmission pump pressure tap

5. Priority valve6. Impeller clutch solenoid valve

7. Impeller clutch pressure tap

8. Torque converter output speed sensor

9. Output shaft10. Torque converter

outlet relief valve

17

The impeller clutch torque converter is bolted on the rear pump drive.

This slide shows the external components that are mounted on the torqueconverter housing.

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18

The planetary power shift transmission (1) has three FORWARD andthree REVERSE speeds. Electronic solenoids located in the hydrauliccontrol valve shift the transmission. The solenoids are actuated by thetransmission electronic control module located on the rear of the cab.

The transmission output speed sensor monitors the transmission outputshaft. The signal is sent to the transmission electronic control module.The transmission output speed signal is to indicate when the clutcheshave engaged

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IRON SHOT OFTRANSMISSION FROM BACK

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19

- Sump- Two section gear

pump- Magnetic screens

IMPELLERCLUTCH

LOCKUPCLUTCH

LUC SOLENOID IC SOLENOID

TRANSMISSIONCONTROL VALVE

T/C OUTLETRELIEF VALVE

PUMP

T/CFILTER

TRANSFILTER

TORQUECONVERTER

COOLER

LUB INPUTTRANSFER

LUB OUTPUTTRANSFERBEARINGS

LUB REARPUMP DRIVE

LUB OUTPUTTRANSFER

GEAR

994D POWER TRAINSCHEMATIC

TRANSMISSION

OUTPUTTRANSFER GEAR

PRIORITYVALVE

TRANSMISSION HYDRAULIC SYSTEM

This schematic shows the components and the oil flow in the power trainhydraulic system. Oil from the sump (located in the bottom of thetransmission transfer case) flows thru two magnetic screens located in theoil sump to a two section gear pump.

Oil from the right (small) section of the pump flows through thetransmission filter to the priority valve. When a shift is made the priorityvalve prevents oil pressure in the lockup clutch and impeller clutch fromdropping below 2205 kPa (320 psi). From the priority valve, oil flows tothe lockup clutch solenoid and the impeller clutch solenoid. When thelockup clutch solenoid is energized, oil flow pressurizes the lockup clutchand places the converter in direct drive. When the impeller clutchsolenoid is energized, oil flow to the impeller clutch is stopped. Theimpeller clutch releases allowing the impeller to slip.

Right (small) sectionof pump

- Filter

- Priority valve

- Lockup clutchsolenoid

- Impeller clutchsolenoid

- Transmission controlvalve

When the priority valve opens, oil flows to the transmission control valve.The transmission control valve controls transmission clutch engagement,provides modulation and sequencing of the directional and speed clutches,limits the maximum clutch pressure, and limits the maximum inlet oilpressure to the torque converter. From the transmission control valve,surplus oil is sent to the torque converter inlet.

Oil from the left (large) section of the pump flows through the filter andjoins with the surplus oil from the transmission control valve. Thecombined oil flows to the torque converter inlet and to the input transfergear for lubrication. Oil pressure in the torque converter is maintained bythe outlet relief valve. An orifice in the outlet relief valve permits somelubrication oil to flow to the power train components at all times. Fromthe outlet relief valve, oil is sent through the oil cooler to the rear pumpdrive, the transmission, the output transfer bearing and the output transfergear lubrication circuits.

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Left (large) section ofpump

- Filter

- Input transfer gear

- Torque converter

- Outlet relief valve

1. Torque ConverterOil filter

2. Transmission Oilfilter

3. S O S Tap

20

The torque converter oil filter (1) and the transmission oil filter (2) arebolted to the inside of the engine housing on the left side of the machine.

The two filters are identical.

The power train oil S O S tap (3) is located on the inlet manifold for thetransmission filter facing the engine.

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1. Priority valve

2. Lockup clutchsolenoid valve

3. Impeller clutchsolenoid valve

4. Lockup clutchpressure tap

5. Impeller clutchpressure tap

21

The priority valve (1) is located on the upper rear of the torque converter.When the engine is running, the priority valve maintains a minimum of2205 kPa (320 psi) oil pressure to the lockup clutch solenoid valve (2)and impeller clutch solenoid valve (3).

Also shown are the lockup clutch pressure tap (4) and the impeller clutchpressure tap (5).

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Transmissionhydraulic controlvalve

1. Control valve cover

2. Torque converterinlet pressure tap

3. P1 pressure tap

4. Connector fortransmission shiftsolenoids

22

The transmission hydraulic control valve is bolted to the top of theplanetary group inside the transmission case [below the cover (1)]. Thecontrol valve consists of a top manifold, a pressure control group, aseparator plate, a bottom manifold and five shift solnoids. Also shownare the torque converter inlet pressure tap (2), the P1 pressure tap (2) andthe electrical harness connector for the transmission shift solenoids (4).

TJV 994D - 31 -5/99

1. Transmissionhydraulic controlvalve group

2. Five clutchsolenoids

3. Solenoid electricalharness

4. P1 pressure tap

5. P2 pressure tap

6. Load piston plug

23

The transmission hydraulic control valve group (1) is bolted to the top ofthe transmission planetary clutch group. Shown are five clutch solenoids(2), solenoid electrical harness (3), P1 pressure tap (4), P2 pressure tap (5)and the plug (6) for the load piston.

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IRON SHOTOFTRANS

HYDRAULICCONTROL VALVE

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23

TRANSMISSIONHYDRAULIC CONTROL VALVE

MODULATIONRELIEF VALVE

FIRST AND THIRD SPEEDSELECTOR SPOOL

LOAD PISTON

SECOND SPEEDSELECTOR SPOOL

PRESSUREDIFFERENTIAL

VALVE

DIRECTIONALSELECTORSPOOL

CONVERTER INLETRATIO VALVE

Also included in the transmission hydraulic controls are:

Modulation relief valve: Limits the maximum clutch pressure.

First and third speed selection spool: Directs oil flow to the No. 5 andNo. 3 clutches.

Load piston: Works with the modulation relief valve to control the rateof pressure increase in the clutches.

Second speed selector spool: Directs oil flow to the No. 4 clutch.

Pressure differential valve: Controls speed and directional clutchsequencing.

Directional selection spool: Directs oil to the FORWARD andREVERSE directional clutches.

Converter inlet ratio valve: Limits the pressure to the torque converter.

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24

IMPELLER CLUTCHTORQUE CONVERTER

HOUSING

LOCKUP CLUTCH

TURBINE

IMPELLER

IMPELLER CLUTCH

STATOR

Shown is a sectional view of the torque converter. The major componentsinclude the rotating housing, the impeller, the turbine, the stator, theimpeller clutch and the lockup clutch.

The rotating housing is splined to the engine flywheel and turns with theflywheel. The impeller is connected to the rotating housing through theimpeller clutch. The clutch discs are splined to the impeller. The clutchplates are splined to the rotating housing. Pressure oil moves the clutchpiston to engage the discs and plates. When the clutch is engaged, theimpeller rotates with the housing.

Impeller clutch

Lockup clutch

Freewheel stator

The turbine is splined to the output shaft. In torque converter drive, theturbine is turned by oil from the impeller. In direct drive, the lockupclutch connects the turbine to the rotating housing. The lockup clutchdiscs are splined to the turbine. The lockup clutch plates are splined tothe rotating housing. Pressure oil moves the clutch piston to engage thediscs and plates. When the clutch is engaged, the turbine, housing,impeller and output shaft rotate as a unit at engine rpm. The stator, whichis mounted on a freewheel assembly (also referred to as a "sprag clutch"),is driven by the force of the oil in the housing and will freewheel atapproximately the same rpm.

TJV 994D - 35 -5/99

1. Impeller clutchsolenoid valve

2. Lockup clutchsolenoid valve

3. Impeller clutchsolenoid

4. Lockup clutchsolenoid

5. Impeller clutchpressure tap

6. Lockup clutchpressure tap

25

The torque converter impeller clutch solenoid valve (1) and the lockupclutch solenoid valve (2) are bolted to the upper right rear of the torqueconverter housing (when facing the engine flywheel).

When the Power Train Electronic Control Module (ECM) increases thecurrent to the impeller clutch solenoid (3), pressure to the impeller clutchdecreases.

When the ECM increases the current to the lockup clutch solenoid (4),pressure to the lockup clutch increases.

Also shown are the impeller clutch pressure tap (5) and the lockup clutchpressure tap (6).

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26

Solenoid ENERGIZED

TEST PORT

FROMPUMP

TO IMPELLERCLUTCH

SOLENOIDARMATUREASSEMBLY

BALLVALVESPOOL SPRINGORIFICESPRING

TEST PORT

IMPELLER CLUTCHSOLENOID DE-ENERGIZED

TEST PORT

FROMPUMP

TO IMPELLERCLUTCH

SOLENOIDARMATUREASSEMBLY

BALLVALVESPOOL SPRINGORIFICESPRING

IMPELLER CLUTCHSOLENOID ENERGIZED

IMPELLER CLUTCHSOLENOID VALVE

Shown is a sectional view of the impeller clutch solenoid valve.

When the impeller clutch solenoid is energized, the solenoid moves thepin assembly against the spring and away from the ball. Pump oil flowsthrough the center of the valve spool, through the orifice and past the ballto drain. The valve spring moves the valve spool to the left. The valvespool blocks the passage between the impeller clutch and the pump andopens the passage between the impeller clutch and drain. Pump flow tothe impeller clutch is blocked. The oil in the impeller clutch flows pastthe valve spool to drain.

When the impeller clutch solenoid is de-energized, the spring moves thepin assembly against the ball. The ball blocks the pump flow through theorifice to drain. The oil pressure increases at the left end of the valvespool and moves the valve spool to the right against the spring. The valvespool blocks the passage between the impeller clutch and drain and opensthe passage between the impeller clutch and the pump. Pump oil flowspast the valve spool to the impeller clutch.

Solenoid DE-ENERGIZED

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27

Solenoid ENERGIZED

TEST PORT

FROMPUMP

BALLVALVESPOOL SPRINGORIFICE

SOLENOID PIN

SOLENOID DE-ENERGIZED

TEST PORT

FROMPUMP

BALLVALVESPOOL SPRINGORIFICE

SOLENOID PIN

SOLENOID ENERGIZED

TOCLUTCH

LOCKUP CLUTCHSOLENOID VALVE

TOCLUTCH

When the lockup clutch solenoid is energized, the solenoid moves the pinassembly against the ball. The ball blocks pump oil flow through theorifice to drain. The oil pressure increases at the left end of the valvespool and moves the valve spool to the right against the spring. The valvespool blocks the passage between the lockup clutch and drain and opensthe passage between the lockup clutch and the pump. Pump oil flows pastthe valve spool to the lockup clutch.

When the lockup clutch solenoid is de-energized, the force that held thepin assembly against the ball is removed. The pump oil flows through theorifice and past the ball to drain. The spring moves the valve spool to theleft. The valve spool opens the passage between the lockup clutch anddrain and blocks the passage between the lockup clutch and the pump.Pump flow to the lockup clutch is blocked. The oil in the lockup clutchflows past the valve spool to drain.

Solenoid DE-ENERGIZED

TJV 994D - 39 -5/99

28

Conditions forDIRECT DRIVEoperation

3

1

25

2 3

1 5 4

TORQUECONVERTER

TOTRANSMISSION

TORQUECONVERTER

OUTLETRELIEFVALVE

TRANSMISSIONCONTROL VALVE

PUMP

SUMP

TRANSMISSIONFILTER

TORQUECONVERTER

FILTER

PRIORITYVALVE


LOCKUP CLUTCHSOLENOID VALVE

TRANSMISSION HYDRAULIC SYSTEMSECOND SPEED FORWARD

DIRECT DRIVE


4

TEST PORT

When the machine is operating in torque converter drive, five conditionsmust be present before the ECM will energize the lockup clutch solenoidand shift the torque converter to direct drive.

1. The transmission is in second or third gear.

2. The lockup clutch enable switch is in the ON position.

3. The torque converter output speed is above 1375 50 rpm.

4. The machine has been in the present speed and direction for morethan two seconds.

5. Neither brake pedal is depressed.

6. The lockup clutch has been released by the ECM for at least fourseconds.

Lockup clutchoperation

When the lockup clutch solenoid is energized, the lockup clutch solenoidvalve opens. The transmission pump oil flows past the lockup clutchsolenoid valve and fills the lockup clutch. The lockup clutch engages andconnects the turbine to the rotating housing.

In DIRECT DRIVE, both the impeller clutch and the lockup clutch areengaged. The torque converter rotating housing, the impeller and theturbine turn as a unit. The stator, which is mounted on a freewheelassembly, is driven by the force of the oil in the housing and willfreewheel at approximately the same rpm.

INSTRUCTOR NOTE: Operation of the modulating relief valve,torque converter inlet ratio valve and pressure differential valve isthe same as explained in STMG 421 "966D Wheel Loader Part 2--Power Train" (Form SESV1421).

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29

CLUTCH 33RD GEAR SOLENOID

LOCKUP CLUTCHSOLENOID

IMPELLER CLUTCHSOLENOID

CLUTCH 42ND GEAR SOLENOID

CLUTCH 51ST GEAR SOLENOID

CLUTCH 2FORWARD SOLENOID

CLUTCH 1REVERSE SOLENOID

CONTROL AND MONITORSYSTEMSPOWERTRAIN

ECM

REDUCED RIMPULLINDICATOR LAMP

REDUCED RIMPULLENABLE SWITCH

REDUCED RIMPULLSELECTION SWITCH

PARKING BRAKEPRESSURE SWITCH

LOCKUP CLUTCHENABLE SWITCH

STEERING/TRANSMISSIONLOCK SWITCH

TORQUE CONVERTER PEDAL POSITION SENSOR

AIR STARTSOLENOID

BACK-UP ALARMRELAY

STICUPSHIFT, DOWNSHIFT,FORWARD, NEUTRAL,

REVERSEIGNITION KEY SWITCH

TORQUE CONVERTEROUTPUT SPEED SENSORTRANSMISSION OUTPUT

SPEED SENSORIMPELLER CLUTCHPRESSURE SWITCH

CAT DATA LINK

INPUT COMPONENTS OUTPUT COMPONENTS

POWER TRAINELECTRICAL SYSTEM

TORQUE CONVERTER OILOUTLET TEMPERATURE

GEAR INDICATOR

LOCKUP CLUTCHENABLE LAMP

POWER TRAIN ELECTRICAL SYSTEM

This diagram of the Power Train Electrical System shows the componentswhich provide input signals to the Electronic Control Module (ECM).

Based on the input signals, the ECM energizes the appropriatetransmission control valve solenoids for speed and directional clutchengagement. The ECM also energizes the starter relay when starting themachine and the back-up alarm when the operator selects a reverse gear.

When required, the ECM energizes the impeller clutch control valvesolenoid, the lockup clutch control valve solenoid, and the reducedrimpull indicator lamp.

The CAT Data Link connects the power train ECM to the engine ECM.The data link also connects the ECMs to the Vital InformationManagement System (VIMS) and electronic service tools such asCaterpillar Electronic Technician (ET).

Input components The input components to the ECM are:

STIC: Combines control of the vehicle steering system and thetransmission shifting system in a single input device.

Ignition key switch: Provides a signal to the ECM when the operatorwants to start the engine. The STIC directional switch must be in theNEUTRAL position before the ECM will permit engine starting.

Reduced rimpull enable switch: When in the CLOSED position, causesthe power train ECM to use the position of the reduced rimpull selectorswitch to determine rimpull torque range (through the impeller clutch).

Reduced rimpull selection switch: When enabled by the reducedrimpull enable switch, this rotary switch determines the maximum rimpulltorque.

Torque converter oil outlet temperature sensor: Provides a pulsewidth modulated signal the ECM uses to determine the temperature of theoil flowing out of the torque converter through the outlet relief valve.

Park brake pressure switch: Monitors the park brake hydraulicpressure and the ECM can determine when pressure is applied to releasethe park brake.

Lockup clutch enable switch: When in the ON position, enables thelockup clutch to ENGAGE when the machine operating conditions arecorrect. The lockup clutch enable lamp is turned on by electrical contactsin the switch whenever the lockup clutch is enabled..

Steering and transmission lock switch: When in the LOCK position,causes the ECM to shift the transmission to NEUTRAL.

Torque converter pedal position sensor: Signals the position of thetorque converter pedal to the ECM. The ECM uses the positioninformation to vary torque to the drive train through the impeller clutch.The actual value of torque reduction is determined by a combination ofdifferent input signals.

Torque converter speed sensor: Provides a signal the ECM uses todetermine the output speed and direction of the torque converter.

Transmission speed sensor: Provides a signal the ECM uses todetermine the output speed of the transmission.

Impeller clutch pressure sensor: Provides a pulse width modulatedsignal the ECM uses to determine the impeller clutch hydraulicpressure.

TJV 994D - 42 -5/99

Output components The output components which receive signals from the ECM are:

Starter relay: The ECM energizes the air start solenoid valve when theappropriate conditions to start the machine have been met.

Reduced rimpull indicator lamp: The ECM illuminates the reducedrimpull indicator lamp when the appropriate machine operating conditionsare met and the ECM is providing reduced rimpull.

Clutch solenoids: The solenoids control pilot oil flow to the speed anddirectional control spools.

Impeller clutch solenoid: The ECM energizes the impeller clutchsolenoid with different levels of current to control hydraulic pressure tothe impeller clutch.

Lockup clutch solenoid: The ECM energizes the lockup clutch solenoidto ENGAGE the lockup clutch (attachment on 992G) when the correctmachine conditions have been met.

Back-up alarm relay: The ECM energizes the back-up alarm when theoperator selects the REVERSE direction with the STIC. The backupalarm relay energizes the two backup alarms.

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30

Component Locations and Functions

The Power Train Electronic Control Module (ECM) (arrow) is mountedon the exterior of the back wall of the operator cab.

The ECM makes decisions based on control program information inmemory and switch and sensor input signals.

The ECM responds to machine control decisions by sending outputvoltage to the appropriate circuit which creates an action. For example,the operator selects an upshift using the STIC. The ECM interprets theinput signals from the STIC, evaluates the current machine operatingstatus and energizes the appropriate clutch solenoids.

The ECM receives three different types of input signals:

1. Switch input: Provides the signal line to battery, ground, or open.

2. PWM input: Provides the signal line with a square wave of aspecific frequency and a varying positive duty cycle.

3. Speed signal: Provides the signal line with either a repeating, fixedvoltage level pattern signal or a sine wave of varying level andfrequency.

TJV 994D - 44 -5/99

Power train ECM(arrow)

Output signals The ECM has three types of output drivers:

1. ON/OFF driver: Provides the output device with a signal level of+Battery voltage (ON) or less than one Volt (OFF).

2. PWM solenoid driver: Provides the output device with a squarewave of fixed frequency and a varying positive duty cycle.

3. Controlled current output driver: The ECM will energize thesolenoid with 1.25 amps for approximately one half second andthen decrease the level to 0.8 amps for the duration of the on time.The initial higher amperage gives the actuator rapid response andthe decreased level is sufficient to hold the solenoid in the correctposition. An added benefit is an increase in the life of the solenoid.

The ECM controls the transmission speed and directional clutches and theoperation of the impeller clutch and lockup clutch. The ECM interpretssignals from the STIC, torque converter pedal position sensor, lockupclutch enable switch, and current machine operating status to determinethe appropriate output signals to the systems. Different conditions of theinputs affect the output conditions. These conditions will be discussedlater.

The ECM communicates through the CAT Data Link. The CAT DataLink allows high speed proprietary serial communications over a twistedpair of wires. The CAT Data Link allows different systems on themachine to communicate with each other and also with service tools suchas Caterpillar Electronic Technician (ET).

The ECM has built-in diagnostic capabilities. As the ECM detects faultconditions in the power train system, it logs the faults in memory anddisplays them on the VIDS/VIMS. The fault codes can also be accessedusing the ET service tool. On machines equipped with VIMS, softwarecan be used to view faults logged by the VIMS.

INSTRUCTOR NOTE: ECM faults displayed on the VIMS relatingto the Power Train ECM will have a Module Identifier (MID) of"81." For more information, refer to the Service Manual module"Power Train Electronic Control System, Systems Operation Testingand Adjusting" (Form RENR2522).

TJV 994D - 45 -5/99

ECM controls:

- Speed anddirection

- Impeller andlockup clutches

1. STIC

2. Transmissiondirectional controlswitch

3. Speed upshiftswitch

4. Speed downshiftswitch

31

The STIC (1) is bolted to the seat at the front of the left armrest. Thetransmission directional control switch (2) is a three position rockerswitch that the operator uses to select NEUTRAL, FORWARD, orREVERSE. The transmission speed upshift switch (3) and thetransmission speed downshift switch (4) are momentary contact switchesthat the operator uses to select the desired speed.

When the operator selects REVERSE by depressing the top of thedirectional control switch, the ECM energizes the reverse directionalsolenoid. The ECM also activates the back-up alarm. When the operatorselects FORWARD by depressing the bottom of the directional controlswitch, the ECM energizes the forward directional solenoid. When theoperator selects NEUTRAL by placing the directional control switch inthe center position, the ECM de-energizes both the forward and thereverse directional solenoids. After two seconds, the ECM energizesspeed solenoid No. 3 and the transmission is in NEUTRAL until theoperator selects a different gear.

When the operator presses the upshift switch, the ECM energizes theappropriate speed clutch solenoid to select the next higher gear, and thetransmission upshifts. When the operator presses the downshift switch,the ECM energizes the appropriate speed clutch solenoid to select the nextlower gear, and the transmission downshifts. The switch must be releasedand pressed again to continue shifting. If the operator presses and holds

TJV 994D - 46 -5/99

Gear indicator

32

Three indicator lamps(arrows) located in the front dash panel of the cabare used to identify the active speed of the transmission. The activedirection is determined by the position of the directional control switch onthe STIC controller.

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Steering andtransmission locklever (arrow)

Steering andtransmission lockswitch

33

When the steering and transmission lock lever (arrow) is moved to theLOCK position (shown), the STIC is held in the center position andsteering is disabled. In the LOCK position, the steering lock leverdepresses the steering and transmission lock switch (not visible). Thesteering and transmission lock switch signals the ECM to shift thetransmission to NEUTRAL.

When the steering and transmission lock lever is moved to the UNLOCKposition, the steering and transmission functions are enabled.

The power train portion of the STIC sends input signals to the ECM.Certain machine operating conditions will override the operator desiredfunction of the STIC. If the directional switch is in the FORWARD orREVERSE position when the steering and transmission lock lever ismoved to the UNLOCK position, the ECM will not shift fromNEUTRAL. The directional switch must first be moved to theNEUTRAL position, then to the direction desired before the ECM willengage a directional clutch.

If the steering and transmission lock lever is in the UNLOCK positionwhen the machine is started, the lever must be moved to the LOCKposition and then to the UNLOCK position before the ECM will shift thetransmission out of NEUTRAL.

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1. Key start switch

34

The operator turns the key start switch (1) clockwise to signal the ECM tostart the engine. The key start switch supplies a signal of +Battery to theECM. The ECM energizes the air start solenoid and the air start solenoidsupplies air to the starting motor and begin engine cranking. Threeconditions must be present before the ECM will energize the start relay:

1. The key switch is turned to the start position.

2. The transmission directional control switch is in neutral.

3. The system voltage is below +32 Volts.

If the machine is equipped with the engine prelube attachment the powertrain ECM will request prelube status from the engine ECM via thedatalink. If the engine ECM determines the need for prelube, the engineECM will perform the prelube function and signal the powertrain ECMwhen prelube has been completed. The power train ECM will make surethe three conditions stated above have been met and energize the air startsolenoid.

TJV 994D - 49 -5/99

Reduced rimpullenable switch

35

The reduced rimpull enable switch (arrow) is a two position rocker switchmounted on the implement lift lever.

In the OPEN position this switch signals the ECM the operator requestsmaximum rimpull. The ECM provides maximum rimpull when thetorque converter pedal is fully released by keeping the impeller clutchfully engaged. In this position, maximum rimpull will be providedregardless of the rimpull selection switch.

In the CLOSED position, this switch provides a +Battery signal to theECM. The ECM monitors the reduced rimpull selection switch todetermine the rimpull setting with the torque converter pedal fullyreleased. This condition occurs only when the machine is in FIRSTGEAR. If the machine is not in FIRST GEAR, the rimpull will stay atmaximum.

TJV 994D - 50 -5/99

Identify components:

1. Reduced rimpullselection switch

2. 85% rimpull

3. 70% rimpull

4. 55% rimpull

5. 45% rimpull

6. Torque converterpedal

7. Torque converterpedal positionsensor

8. Reduced rimpullindicator light

36

When the reduced rimpull enable switch is in the CLOSED position, thereduced rimpull selection switch (1) indicates the desired maximumrimpull setting to the ECM. The desired maximum rimpull setting will beactive when the torque converter pedal is fully released, and the machineis in FIRST GEAR.

The ECM reduces rimpull by increasing the current to the impeller clutchsolenoid, which reduces the hydraulic pressure to the impeller clutch andallows slippage between the impeller and the torque converter housing.By additionally decreasing the impeller clutch pressure, the impeller willslip more resulting in lower torque to the power train. The resultingadditional engine horsepower can be used for the implements.

The reduced rimpull selection switch has four positions. Each positioncorresponds to a maximum allowable percentage of maximum rimpull.The default values for each position are indicated as follows:

- 85% Rimpull (2)

- 70% Rimpull (3)

- 55% Rimpull (4)

- 45% Rimpull (5)

TJV 994D - 51 -5/99

The ECM monitors the position of the torque converter pedal (6) with thetorque converter pedal position sensor (7) located behind the panel at thepivot for the pedal. As the operator depresses the pedal, the ECMincreases the current to the impeller clutch solenoid and reduces thehydraulic pressure to the impeller clutch. The rimpull will decrease withpedal travel from the reduced maximum setting to the minimum setting.When the operator releases the left pedal, the rimpull will return to themaximum percentage as set by the selector switch.

When the maximum allowable percentage is in the lower values, the totalchange of rimpull from maximum to minimum is decreased. Thiscondition results in a more gradual change of rimpull over the travel ofthe torque converter pedal.

If the machine is not in FIRST GEAR, the impeller clutch pressure willremain at the maximum level until the transmission is shifted into FIRSTGEAR.

The torque converter pedal functions similarly when the maximumrimpull enable switch is in the OPEN position, except the maximumallowable percentage is now 100%.

The reduced rimpull indicator light (8) will be illuminated when the ECMdetects the reduced rimpull enable switch is in the ENABLE (closed)position, and the system is providing reduced rimpull. The light will beoff when the switch is in the DISABLED (open) position.

NOTE: An increase in current to the impeller clutch solenoid fromthe ECM results in a decrease in pressure to the impeller clutch.

INSTRUCTOR NOTE: To change the setting for each position of thereduced rimpull selection switch, refer to the Service Manual module"Power Train Electronic Control System, Systems Operation Testingand Adjusting" (Form RENR2522).

TJV 994D - 52 -5/99

1. Impeller clutchsolenoid

2. Impeller clutchvalve

3. Impeller clutchpressure sensor

37

The impeller clutch solenoid (1) is mounted on the impeller clutch valve(2). The impeller clutch valve is located on the left side of the torqueconverter housing.

The ECM monitors the status of the impeller clutch solenoid and candetermine certain faults that may affect operation of the impeller clutch.These faults include: a short to +Battery, a short to ground, an opencircuit, or impeller clutch not responding properly.

The ECM receives a signal from the impeller clutch pressure sensor (3) tomonitor the impeller clutch pressure. The ECM can compare the controlof the impeller clutch solenoid with the response of the impeller clutchpressure to determine if the impeller clutch is responding properly.

When the ECM detects a fault in the impeller clutch solenoid circuit, afault will be displayed on the VIMS message center.

When a fault is detected, controlled throttle shifting is used. When adirectional shift is made above 1100 rpm, the ECM will request a desiredengine speed of 1100 rpm from the engine ECM for 1.9 seconds ifshifting into forward and for 2.5 seconds if shifting into reverse. Thisfeature helps decrease the energies absorbed in the transmission.

The torque converter pedal position sensor and the impeller clutchsolenoid must be calibrated through the VIMS to ensure

TJV 994D - 53 -5/99

Controlled throttleshifting used duringimpeller clutch faults

1

3

2

Also shown are the lockup clutch solenoid (4) and the lockup clutch valve(5). The lockup clutch solenoid and lockup clutch valve look similar tothe impeller clutch solenoid and impeller clutch valve but are differentand should not be interchanged.

The lockup clutch solenoid is mounted on the lockup clutch valve. Thelockup clutch valve is located on the left side of the torque converterhousing between the impeller clutch solenoid valve and the torqueconverter housing.

The ECM energizes the lockup clutch solenoid to allow oil to flowthrough the lockup clutch valve to the lockup clutch. The pressureincreases in the lockup clutch, causing it to engage and the machineoperates in DIRECT DRIVE.

The lockup clutch solenoid is a proportional solenoid and is energized bya modulated signal from the ECM. The ECM varies the amount ofcurrent to control the amount of oil flow through the lockup clutch valveto the lockup clutch.

INSTRUCTOR NOTE: An increase in current to the lockup clutchsolenoid from the ECM results in an increase in pressure to thelockup clutch.

TJV 994D - 54 -5/99

1. Lockup clutchenable switch(arrow)

38

The lockup clutch enable switch (1) is located on the front dash in thecab. When the switch is in the ON (closed) position and the properconditions have been met, the ECM will engage the lockup clutch toimprove the efficiency of the power train.

The power train ECM first energizes the lockup clutch to a hold level for.75 seconds to allow time for the clutch to fill. The current is then rampedup to full on in .65 seconds.

During normal operation, the ECM will energize the torque converterlockup clutch solenoid based on the following conditions:

1. Lockup clutch enable switch state: ON (closed).

2. Torque converter output speed: When the torque converteroutput speed is greater than1125 50 rpm.

3. Time in gear: The transmission must be in the present speed anddirection for at least two seconds.

4. Time since lockup clutch solenoid was de-energized: At leastfour seconds must have passed since the ECM de-energized thelockup clutch solenoid.

5. Left pedal and right brake pedal status: Both pedals must befully released.

TJV 994D - 55 -5/99

1

2

6. Current gear: The current gear is not first forward. All gearsother than first forward will allow the ECM to engage the lockupclutch when the appropriate conditions are met.

An indicator lamp (2) on the dash lights when the lockup clutch isenabled.

During normal operation, the following conditions will cause the ECM tode-energize the torque converter lockup clutch solenoid valve and releasethe lockup clutch:

1. Lockup clutch enable switch: OFF (open).

2. Torque converter output speed: When the torque converteroutput speed is less than 975 50 rpm.

3. A shift is made.

4. Left pedal and right brake pedal status: If either pedal isdepressed.

5. Rapid vehicle deceleration: If the machine slows down rapidly,such as when engaging the pile, the ECM will disengage the lockupclutch to prevent engine lugging.

6. Lockup clutch system fault: If the ECM detects a fault in any ofthe lockup clutch control inputs such as: enable switch, torqueconverter output speed sensor, left pedal position, or service brakepedal status.

The power train ECM will re-enable the lockup clutch four seconds after:the service brake is released, the left pedal is released, lockup clutchenable switch off-to-on transition, rapid vehicle deceleration, a fault in thelockup clutch control inputs has been cleared.

NOTE: To prevent engine overspeed, the ECM will not engage thelockup clutch when the torque converter output speed is higher than1750 rpm.

During lockup clutch engagement, the impeller clutch pressure ismaintained at the system pressure 2275 207 kPa (330 30 psi).

TJV 994D - 56 -5/99

TJV 994D - 57 -5/99

39

1. Torque converteroutput speedsensor

40

The power train ECM receives a signal from the torque converter outputspeed sensor (1). The speed sensor is mounted on the front of the torqueconverter housing above the drive shaft. The signal is a fixed voltagelevel patterned waveform which the ECM uses to determine the speed anddirection of the torque converter output.

If the machine is allowed to roll backwards on an incline when a forwardgear is selected the toque converter output can turn in reverse . Thiscondition is called reverse turbine and can result in high temperaturesinside the torque converter. If the ECM determines the output of thetorque converter is turning in the reverse direction greater than 500rpm,the ECM will ignore the left pedal position input and increase the impellerclutch pressure to prevent this condition. The ECM will also overide thereduced rimpull setting if necessary to try to eliminate the reverse turbine.

The power train ECM monitors the temperature of oil exiting the torqueconverter with the torque converter outlet oil temperature sensor (2)which is mounted on the front right of the torque converter housing, justabove the torque converter outlet relief valve.

Also shown is the power train oil temperature sender (3). The power trainoil temperature gauge in the dash of the cab uses the signal from thissender to display the power train oil temperature on the gauge.

TJV 994D - 58 -5/99

2. Torque converteroutlet oiltemperature sensor

3. Power train oiltemperature sender

12

3

Transmissionsolenoid valves

1. Reverse (No. 1clutch)

2. Forward (No. 2clutch)

3. First (No. 5 clutch)

4. Second (No. 4clutch)

5. Third (No. 3 clutch)

6. P1 pressure tap

7. P2 pressure tap

8. Load piston plug

41

The ECM shifts the transmission by energizing the solenoid valves(arrows) that are located in the transmission control valve group on top ofthe transmission.

Two solenoid valves are used to control REVERSE (1) or FORWARD (2)directional shifts and three solenoid valves are used to control speedshifts: FIRST (3), SECOND (4), THIRD (5).

The solenoid valves are two position, three way solenoid valves. Thesolenoid valves are normally open to drain. When energized, the solenoidvalve spool moves to direct pressure oil to one end of the transmissioncontrol valve spool. The transmission control valve spool then directs oilto the appropriate clutch.

The solenoids are operated by 12VDC max. The ECM first energizes thesolenoids with 12VDC for one second and then decreases the voltage toapproximately 8.25VDC for the remainder of the time that the solenoid isenergizes. The decreased voltage level is enough to keep pressure oil tothe control valve spool to maintain position while extending the servicelife of the solenoid.

Also shown are the pressure tap for the speed clutches P1 (6), thedirectional clutches P2 (7), and the plug for the load piston (8).

TJV 994D - 59 -5/99

IRON SHOT OFCLUTCH

SOLENOIDS

1. Park brake knob

41

The park brake lever has been changed to a park brake knob (1)located onthe dash in the cab. The park brake control knob is connected by a pushpull cable to the park brake control valve. The park brake control valvesupplies hydraulic oil to the park brake to release the park brake when thepark brake control knob is pushed in.

The park brake pressure pressure sensor (not shown) provides a signal tothe power train ECM so the ECM can determine if the park brake isapplied. When hydraulic pressure is present the ECM determines the parkbrake is released.

If the transmission is in FIRST FORWARD or REVERSE when the parkbrake is engaged the power train ECM will shift the transmission toneutral. If the transmission is in SECOND or THIRD, FORWARD ofREVERSE, when the park brake is engaged the transmission will remainin the current speed and direction.

The transmission can be shifted to SECOND or THIRD, FORWARD orREVERSE, when the parking brake is applied for normal serviceoperations.

TJV 994D - 60 -5/99

2. Park brakepressure sensor

1

To shift the transmission to FIRST FORWARD or REVERSE while thepark brake is applied, with the directional switch in neutral the downshiftswitch must be pressed until FIRST speed is indicated by the gearindicator on the dash. The directional switch must then be toggled to thedesired direction, to neutral and then back to the same desired direction asecond time. The transmission will shift into FIRST gear of the desireddirection when the directional switch is moved to the desired direction thesecond time.

This operation can be performed for service procedures requiring FIRSTSPEED or for emergencies requiring the machine to be moved when thepark brake can not be released due to hydraulic failure in the brake circuit.

Also shown is the service tool connecting port for connecting thediagnostic tool Electronic Technician. The connecting port gives accessto the Cat Data Link for the machine and engine as well as the ATA Linkfor the engine.

TJV 994D - 61 -5/99

3. Service toolconnecting port

42

- 62 -SEBV26021/95

Objective 1Slides 2 - 20

Objective 8Slides 2 - 29

Identify components:- Steering pilot system- Main steering system - Steering cooling system

STEERINGCYLINDER

STEERINGHYDRAULIC

TANK

STEERINGCOOLERS

STEERINGCOOLINGPUMP

STEERINGCONTROLVALVE

STEERINGPUMPS

COMPENSATORVALVE GROUP

PRESSUREREDUCINGVALVES

NEUTRALIZERVALVES

PILOTVALVE

STEERINGCOOLINGFILTER

SECONDARYSTEERINGPUMP

DIVERTERVALVE

994D WHEEL LOADERSTEERING SYSTEM

HIGHPRESSURESCREENS

CASEDRAINFILTERS

STEERING HYDRAULIC SYSTEM

Shown are the components of the steering hydraulic system on the 994Wheel Loader. The color codes for the components in the steeringhydraulic system are:

Orange - Steering pilot system

Red - Main steering system

Green - Steering cooling system

- 63 -

Hand metering unit (arrow)

43

SEBV26021/95

The pilot control valve for the steering system is mounted below the STICon the left side of the operator's seat. (arrow) is bolted to the bottom of thesteering column. The pilot control valve directs pilot oil through theneutralizer valves to the directional control valve in the steering valvebody.

- 64 -

Steering control valve (arrow)

44

SEBV26021/95

The steering control valve (arrow) is located behind the cab on the insideof the right frame below the deck access panel. The control valve housesthe system relief valve and the directional control spool. The controlvalve sends system oil to the steering cylinders and sends signal oil to themargin spool spring chamber in the compensator valve groups on thepumps.

- 65 -

Steering highpressure screens

45

SESV####12/01

This view shows the high pressure screens (arrows) for the steeringpumps. There is one screen for each pump mounted on the left side of therear frame below the access doors.

- 66 -

Steering case drainfilters

46

SESV####12/01

This view shows the case drain filter (1) for the right steering pumpmounted to the right side of the rear frame near the rear tire. The casedrain filter (2) for the left steering pump is mounted on the left side of therear frame near the rear tire.

21

47

- 67 -SESV####12/01

Identify components andexplain function

- Right steering pump- Left steering pump- Steering valve spool- Steering cylinders

- Margin spool- Pressure compensator spool- Actuator piston

PRESSUREAND

SELECTORVALVE 2

STEERING SYSTEMHOLD

STEERINGCYLINDERS

CROSSOVERRELIEFVALVES

BALLRESOLVERVALVE

RIGHTNEUTRALIZER

VALVE

LEFTNEUTRALIZER

VALVE

PRESSUREAND

SELECTORVALVE 1

RIGHT PUMPCOMPENSATOR VALVE

LEFT PUMPCOMPENSATOR

VALVE

CHECKVALVE

CHECKVALVE

RIGHT PUMP

LEFT PUMP

STEERING ANDBRAKE TANK

BACKUPRELIEFVALVE

CONTROLSPOOL

DIVERTER VALVE

RELIEFVALVE

DIRECTION CONTROL SPOOL

UNLOADERSPOOL


QUADCHECKVALVE

STEERINGPILOTVALVE

STEERINGWARNINGSWITCH

RIGHTTURN

Graphic Symbol Schematics

When the engine is running and the steering system is in HOLD, pilot oilfrom the right pump is blocked at the HMU. Oil from the left and rightsteering pumps flows through the respective check valves to the steeringcontrol valve. The control valve spool blocks oil flow to the steeringcylinders and no signal pressure is generated.

System pressure is sensed at the margin spool, pressure compensatorspool and small actuator piston (rod end symbol) of each pump . Assystem pressure increases, the margin spool moves against the springforce and opens a passage for pump oil to flow to the large actuator piston(head end symbol). The pressure in the large actuator piston overcomesthe combined force of the actuator spring and the pressure in the smallpiston and moves the swashplate to the LOW PRESSURE STANDBYposition.

- 68 -SEBV26021/95

In LOW PRESSURE STANDBY, the pump produces enough flow tocompensate for system leakage and sufficient pressure to provide forinstantaneous response when the steering control valve is moved.Machine pressures are found in the 994 Wheel Loader Steering SystemsOperation, Testing and Adjusting Module (Form SENR4749).

NOTE: In the above schematic, only one actuator piston is shown. Thesmall actuator piston is represented by the rod end of the actuator pistonand the large actuator piston is represented by the head end of the actuatorpiston.

48

- 69 -SESV###512/01

Explain schematic

PRESSUREAND

SELECTORVALVE 2

STEERING SYSTEMGRADUAL RIGHT TURN

STEERINGCYLINDERS


BALLRESOLVERVALVE

RIGHTNEUTRALIZER

VALVE

LEFTNEUTRALIZER

VALVE

PRESSUREAND

SELECTORVALVE 1



VALVE

CHECKVALVE

CHECKVALVE

RIGHT PUMP

LEFT PUMP


BACKUPRELIEFVALVE

CONTROLSPOOL

DIVERTER VALVE

RELIEFVALVE


UNLOADERSPOOL


QUADCHECKVALVE

STEERINGPILOTVALVE


RIGHTTURN

When the operator turns the steering wheel to the right, pilot oil flowsthrough the pilot control valve and the right neutralizer valve to the rightside of the steering control spool. Pilot oil pressure moves the steeringcontrol spool to the left. System oil from the steering pumps flowsthrough the check valves and the control spool orifice to the steeringcylinders. As pressure increases in the steering cylinders, the pressure(signal pressure) is sensed in the margin valve spring chamber at eachpump. The signal pressure combines with the force of the margin spoolspring and moves the margin spool down. The margin spool restricts theflow of oil to the large actuator piston (head end). The spring andpressure in the small actuator piston overcome the pressure in the largepiston to move the swashplate toward maximum angle. The increase inswashplate angle increases pump oil flow. The increase in oil flowthrough the control spool orifice increases the system pressure. Thesystem pressure is sensed at the margin spool. The increased pressuremoves the margin spool against the combined forces of the spring andsignal pressure and sends oil to the large actuator piston. The actuatorpiston moves the swashplate to a reduced angle that produces flowrelative to the position of the control spool.

49

- 70 -SESV####12/01

Explain FULL RIGHTTURN function

PRESSUREAND

SELECTORVALVE 2

STEERING SYSTEMFULL RIGHT TURN

STEERINGCYLINDERS


BALLRESOLVERVALVE

RIGHTNEUTRALIZER

VALVE

LEFTNEUTRALIZER

VALVE

PRESSUREAND

SELECTORVALVE 1



VALVE

CHECKVALVE

CHECKVALVE

RIGHT PUMP

LEFT PUMP


BACKUPRELIEFVALVE

CONTROLSPOOL

DIVERTER VALVE

RELIEFVALVE


UNLOADERSPOOL


QUADCHECKVALVE

STEERINGPILOTVALVE


RIGHTTURN

When making a FULL RIGHT TURN, the right striker (not shown)contacts the right neutralizer valve. Oil flow from the pilot control valveto the steering control valve is blocked by the movement of the neutralizervalve. The steering control spool returns to the center position. Flow tothe steering cylinders is blocked and the machine stops turning. Thesteering pumps return to the LOW PRESSURE STANDBY position.

The neutralizer valves prevent the machine front frame from contactingthe machine rear frame when turning FULL RIGHT or FULL LEFT.Check the Service Manual for the correct adjustments.

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PRESSUREAND

SELECTORVALVE 2

STEERING SYSTEMSECONDARY STEERINGRIGHT

TURN


BALLRESOLVERVALVE

RIGHTNEUTRALIZER

VALVE

LEFTNEUTRALIZER

VALVE

PRESSUREAND

SELECTORVALVE 1



VALVE

CHECKVALVE

CHECKVALVE

RIGHT PUMP

LEFT PUMP


BACKUPRELIEFVALVE

CONTROLSPOOL

DIVERTER VALVE

RELIEFVALVE


UNLOADERSPOOL


QUADCHECKVALVE

STEERINGPILOTVALVE


STEERINGCYLINDERS

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Identify componentsand explain function

- Gear pump- Hydraulic tank- Fluid sampling valve- Filter- Oil cooler core- Cooler bypass relief

valve

STEERING & BRAKE OILCOOLING SYSTEM

STEERINGCOOLERPUMP

FLUIDSAMPLINGVALVE

FILTERS

FILTERBYPASSVALVE

OIL COOLER

COOLERBYPASSVALVE

BREATHER

SCREEN STEERING ANDBRAKE TANK

FILTERBYPASSSWITCH

STEERING AND BRAKE OIL COOLING SYSTEM

Shown is a block diagram of the steering and brake hydraulic oil coolingsystem.

The gear pump draws oil from the steering and brake hydraulic tank.Pump oil flows past the fluid sampling valve, through the filter, throughthe three oil cooler cores and back to the steering and brake hydraulictank. The cooler bypass relief valve allows pump oil to bypass the coolersat machine start-up or when the oil is cold. The cooler bypass relief valveis set to open at approximately 345 kPa (50 psi).

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Steering and brakehydraulic oil coolers(arrow)

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The steering and brake hydraulic oil cooler (arrow) is part of the radiatorassembly. Warm oil enters at the bottom of the cores, flows through theinternal passages and exits at the top. Air from the radiator cooling fanflows around the outer surfaces of the cores and removes the heat fromthe oil. The cooler oil flows back to the tank.

The unit core cooler is new to the 994D. It replaces a multiple coreconfiguration.

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Identify components

Service brake system- Steering and brake oil tank- Pump- Brake accumulators- Right and left brake pedals- Right and left brake valves- Neutralizer valve- Service brakes

LEFTBRAKEPEDAL

RIGHT BRAKEPEDAL

RIGHT BRAKEVALVE

PARKING BRAKEVALVE

BRAKEACCUMULATORS

LEFT FRONTSERVICE BRAKE

LEFT REARSERVICE BRAKE

RIGHT FRONTSERVICE BRAKE

RIGHT REARSERVICE BRAKE

PARKINGBRAKE

BRAKE OILCOOLER CORE GROUP

BRAKECOOLINGPUMP

BREATHER

BREATHER

VARIABLEDISPLACEMENTPISTON PUMP

PRESSURECOMPENSATOR

VALVE

PUMPACTUATOR


BRAKE COOLINGTANK

PRESSURERELEASE SPOOL

MANUALSPOOL

NEUTRALIZER VALVE

TRANSMISSIONNEUTRALIZER SIGNAL

BRAKE SYSTEMENGINE OFF

BRAKE SYSTEM

Shown is a schematic of the service brake system, the parking brakesystem and the brake cooling system.

Components of the service brake system are the steering and brake oiltank, the variable displacement pump, the brake accumulators, the rightand left brake pedals, the right and left brake valves, the neutralizer valveand the four service brakes.

The screens and check valves for the brake oil cooling circuit are new forthe 994D.

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Parking brake system- Tank- Pump- Brake accumulators- Parking brake valve- Parking brake

Brake cooling system- Tank- Pump- Cooler core group- Service brakes

SEBV26021/95

Components of the parking brake system are the steering and brake oiltank, the variable displacement pump, the brake accumulators, the parkingbrake valve and the parking brake.

Components of the brake cooling system are the brake cooling oil tank,the brake cooling pump, the brake oil cooler core group and the fourservice brakes.

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Identify componentsand explain function

1. Service brake valve2. Neutralizer valve3. Parking brake valve

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SEBV26021/95

The service brake valve (1) is bolted to the brake panel below theneutralizer valve. When either the left or right service brake pedal isdepressed, the service brake control valve sends oil to engage the wheelbrakes.

The neutralizer valve (2) is bolted to the top of the brake panel. When theoperator depresses the left service brake pedal, the neutralizer valve sendsoil to a pressure switch which signals the Transmission ECM.

The parking brake valve (3) is bolted to the lower right corner of thebrake panel. When the parking brake control lever is moved to theBRAKE OFF position, the parking brake control valve sends oil to releasethe parking brake.

Service Brake Valve

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1. Front service brakecooling screens

2. Check valves

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SEBV26021/95

The screens (1) for the front service brakes are mounted to the front axlehousing. Each screen has a check valve (2) to prevent oil from flowing inthe reverse direction.

1

2 2

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Screen for brakecooling circuit (arrow)

56

SEBV26021/95

This view shows the screen (arrow) for the brake cooling circuit. for therear left wheel. It is mounted to the axle housing between the axlehousing and the trunion.

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Screen for brakecooling circuit (arrow)

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This view shows the screen (arrow) for the brake cooling circuit. for therear right wheel. It is mounted to the axle housing between the axlehousing and the trunion.

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1. Front pump drivelubrication filter

2. Implementhydraulic tank sitegage

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This view shows the filter (1) for the front pump drive lubrication circuitwhich is mounted to the right side of the front frame near the articulationjoint.

Also shown is the site gage (2) for the fill level on the implementhydraulic tank.

12

59

CONCLUSION

This conclude the presentation on the 994D wheel loader.

SESV#### - 81 -12/01

SESV1690 Printed in U.S.A.10/97

Documents

1prelim994D STMG