caterpiaar 966G steering and brake system

Service TrainingSEBV2659August 1999

SLIDE/TEXT REFERENCE

PART OF TECHNICAL INSTRUCTION MODULE SEGV2659

966G/972G WHEEL LOADERS

STEERING AND BRAKE SYSTEMS

SEBV2659 Slide/Text Reference8/99

TABLE OF CONTENTS

INTRODUCTION ..................................................................................................................3

STEERING SYSTEM COMPONENTS ................................................................................4Main Steering System.......................................................................................................7Pilot Steering System......................................................................................................11Secondary Steering System.............................................................................................15Caterpillar Monitoring System .......................................................................................16

STEERING SYSTEM OPERATION ...................................................................................18Pump and Compensator ..................................................................................................18Steering System Schematics ...........................................................................................20

STEERING SYSTEM TESTING AND ADJUSTMENT....................................................26

BRAKE SYSTEM COMPONENTS ....................................................................................31Service Brake System .....................................................................................................31Parking Brake System.....................................................................................................41

BRAKE SYSTEM OPERATION.........................................................................................45

BRAKE SYSTEM TESTING AND ADJUSTMENT..........................................................51Brake System .................................................................................................................51Brake Wear Indicator .....................................................................................................55

CONCLUSION.....................................................................................................................56

SLIDE LIST..........................................................................................................................57

SEBV2659 - 3 - Slide/Text Reference8/99

1

INTRODUCTION

This presentation discusses the component locations, systems operationand testing and adjusting procedures for the Steering and Brake Systemson the 966G and 972G Wheel Loaders.

When discussing systems operation, block diagrams, sectional views andgraphic symbol schematics will be used. The systems will be explainedby tracing oil flow from the tank, through the system and back to the tank.

INSTRUCTOR NOTE: Throughout this presentation, the steeringsystem component formerly know as the "Hand Metering Unit" iscall the "Metering Pump".

Introduce course

Distribute Lab A and BWorksheets

966G/972G WHEEL LOADERSSTEERING AND BRAKE SYSTEMS

© 1999 Caterpillar Inc.


2

Objectives 1 and 6Slides 1 - 13

• Steering systemcomponents

HYDRAULIC TANK METERINGPUMP

STEERINGCONTROL VALVE

NEUTRALIZERVALVES

STEERINGCYLINDER

SECONDARY STEERINGPUMP AND MOTOR

SECONDARYSTEERING VALVE

STEERINGPUMP PILOT SYSTEM

MAIN SYSTEM

SECONDARY SYSTEM

COMMON TOALL SYSTEMS

CONVENTIONAL STEERING SYSTEM COMPONENTS

STEERING SYSTEM COMPONENTS

Shown are the components of the steering system on the 966G and 972GWheel Loaders. The hydraulic tank is common to all hydraulic systemson the machine.

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

Red - System or high pressure

Red and White Stripes - Reduced pressure

Orange - Pilot pressure

Blue - Blocked oil

Green - Tank or return oil


3


STEERINGCYLINDERS

STEERING SYSTEMHOLD

STEERINGCONTROL

VALVE

SECONDARY STEERINGPUMP AND MOTOR

(Optional)

SECONDARYSTEERING

VALVE

NEUTRALIZERVALVE

NEUTRALIZERVALVE

METERINGPUMP

CHECK VALVE

PUMP

TANK

This diagram shows the components and oil flow for the 966G/972G thesteering system.

The primary steering system is made up of two basic circuits: maincircuit and pilot circuit. The steering system includes a third circuit if the966G/972G is equipped with the optional secondary steering system

The main steering circuit consists of the steering pump, the steeringcontrol valve, the steering cylinders, the hydraulic oil tank.

The variable displacement piston steering pump draws oil (green) fromthe tank and sends flow (red) to the steering control valve.

The steering control valve supplies oil (orange) to the steering pilotcircuit.

➥

• Three circuits

• Main steering circuit


• Steering pilot circuit The steering pilot circuit consists of the metering pump, a check valveand two neutralizer valves. The pilot system supply oil comes from thesteering control valve. When the steering wheel is moved to the left orright, the metering pump sends pilot oil through the respective neutralizervalve to the selector spool and directional control spool in the steeringcontrol valve. The pilot oil moves the directional spool and directs pumpsupply oil to the steering cylinders.

This diagram shows the system in the HOLD position. The oil (blue) tothe steering cylinders is blocked.

The optional secondary steering system consists of the secondarysteering pump and motor and the secondary steering valve. Thesecondary steering valve contains two check valves, the primary steeringpressure switch, and the secondary steering pressure switch.

• Optional secondarysteering system


• Main steering systemcomponents:

1. Hydraulic tank

2. Fill cap and tube

3. Sight glass

4. Breaker relief valve

4

1

2

3

4

Main Steering System Components

Hydraulic oil for the steering system is stored in the hydraulic tank (1)located on the left side of the machine below the operator's platform.Access to fill the tank is through the locking fill cap and tube (2). A sightglass (3) indicates the level of the oil in the tank.

The hydraulic tank has a breaker relief valve (4) that protects the tankfrom excessive pressure and/or vacuum and an ecology-type drain valve(not visible) for changing the oil. The vent valve is also used to releasepressure prior to servicing or repairing the hydraulic system.

INSTRUCTOR NOTE: Oil change intervals and procedures areprovided in the 966G/972G Wheel Loaders Operation andMaintenance Manual (Form SEBU7035).


• Main steering systemcomponents

1. Steering pump

2. Signal line

3. Compensator valve

4. Hydraulic tank

5. Supply line

6. Optional secondarysteering valve

7. Steering controlvalve

5

1

3

5

2

6

74

The 966G/972G steering pump (1) is mounted in the pump group betweenthe pilot/brake pump and the implement hydraulic pump. The pumpgroup is located below the operator's compartment on the right side of themachine.

The load sensing, pressure compensating, variable displacement pistonpump (1) senses the pressure requirements for the system through thesignal line (2) connected to the pump compensator valve (3). Thecompensator valve controls pump flow and limits the maximum systempressure. The steering pump draws oil from the hydraulic tank (4).

The oil flows from the steering pump to the steering control valve (7).

If the 966G/972G is equipped with the optional secondary steeringsystem, the oil flows from the steering pump through a line (5) to thesecondary steering valve (6). The oil continues through the secondarysteering valve to the steering control valve. If the machine is notequipped with the optional secondary steering system, the steering pumpsends flow directly to the steering control valve.

The machine in this view is equipped with the secondary steering system.


• Main steering systemcomponents


2. Crossover reliefvalve

3. Inlet line

4. Outlet line

6

1

2

34

Shown is the steering control valve (1). This valve is mounted on the leftside of the machine between the operator's station and the engine.

The steering control valve directs the oil flow to the steering cylinders.Oil also flows through the flow control orifice located inside of thesteering control valve to supply the metering pump.

The steering control valve contains:

- directional control spool

- two pilot load check valves

- two crossover relief valves (one is shown at (2))

- two makeup check valves

- backup relief valve

- dampening orifices

- selector spool

- flow control orifice

Also shown are the inlet line from the steering pump (3) and the outletline (4) to tank.


• Main steering systemcomponents:

1. Steering cylinder

2. Rear frame

3. Front frame

7

2

3

1

The two steering cylinders (1) are mounted on each side of the machinebetween the rear frame (2) and the front frame (3). The steering controlvalve directs oil flow to the head end of one cylinder and the rod end ofthe opposite cylinder, causing the machine to articulate.

A crossover relief valve in the steering control valve protects the steeringsystem from shock loads from the steering cylinders if the wheels contacta stationary object. If the shock load pressure exceeds the setting of thecrossover relief valve, the valve will open and permit the higher pressureoil to flow to the lower pressure side of the circuit.


• Pilot systemcomponents:

- Steering wheel(arrow)

8

Pilot System Components

The round steering wheel (arrow) identifies the 966G/972G WheelLoader as being equipped with the metering pump controlled steeringsystem.

The steering wheel and the steering column are mechanically connectedto the metering pump (not visible) located below the operator's station.



1. Metering pump

2. Signal hose

3. Pressure tap

9

12

3

The metering pump (1) is attached to the bottom of the steering columnand is located below the front of the cab.

Oil supplied to the metering pump flows from the load sensing pressurecompensating variable displacement piston steering pump. The oil fromthe steering pump passes through a flow control orifice in the steeringcontrol valve. The flow control orifice reduces the amount of oil flowingthe the metering pump.

When the steering wheel is turned, the metering pump directs pilot oilthrough one of the two neutralizer valves to the main control valve.

The metering pump also sends signal pressure oil through the signal hose(2) to the compensator valve on the steering pump.

A pressure tap (3) for measuring signal pressure to the compensator valveon the steering pump (not shown) is also shown.



1. Neutralizer valves

2. Rear frame

3. Adjustable stops

4. Front frame

10

1 3

2

4

Oil from the metering pump (not shown) flows through one of twoneutralizer valves (1) mounted on the rear frame (2). The pilot oil flowsto the selector spool in the main steering control valve.

Oil from the metering pump will flow through the neutralizer valves untilthe machine articulation causes one of the adjustable stops (3) mountedon the front frame (4) to push against a neutralizer valve. Pushing in aneutralizer valve stops the flow of oil from the metering unit to thesteering control valve. Stopping the flow of oil from the metering pumpcauses the machine to stop turning.

The steering system uses high pressure neutralizer valves because thepressure and flow is from the main steering system.

INSTRUCTOR NOTE: The neutralizer valves used on the meteringpump controlled steering system are not interchangeable with the lowpressure neutralizer valves used on the Command Control Steeringsystem.

• High pressureneutralizer valves


11


STEERING CONTROL VALVE

BACK-UPRELIEF VALVE

RIGHTNEUTRALIZER

VALVE

SELECTORSPOOL

FLOWCONTROLORIFICE

FROMSTEERING

PUMP

LEFTNEUTRALIZER

VALVE

METERINGPUMP

DIRECTIONALSPOOL

MAKEUPCHECK VALVES

CROSSOVERRELIEF VALVE

TO PUMP

STEERING CONTROL VALVEGRADUAL LEFT TURN

SIGNAL LINE

The oil supply for the metering pump comes from the steering pumpthrough the flow control orifice located in the steering control valve.

This graphic shows the flow of oil from steering control valve to themetering pump.

Also shown is the flow of oil back from the metering unit through the leftneutralizer valve to the steering control valve selector spool.

The selector spool moves down allowing oil to flow through the spool toone side of the directional spool. The directional spool moves in the samedirection as the selector spool.

The new position of the directional spool allows oil to flow to the headend of one steering cylinder and the rod end of the other steering cylinder.This action causes the machine to turn.

• Flow control orifice

• Secondary steeringsystem components:

1. Secondary steeringpump (attachment)

2. Diverter valve

3. Primary pressureswitch

4. Secondarypressure switch

12


4 3

2

1

Secondary Steering System

The optional secondary steering pump (1) and motor are mounted on thelower left inner frame. The secondary steering valve (2) is also mountedto the frame near the secondary steering pump.

The primary steering pump oil flows through the secondary steering valveto the steering control valve. The primary pressure switch (3) is mountedon the secondary steering valve. If a primary steering pump or enginefailure occurs, the primary pressure switch closes, which causes aCategory 3 Warning to occur. The operator should safely shut down theengine as soon as possible.

After a one second delay, the relay for the secondary steering pump andelectric motor is energized. The oil flow from the secondary steeringpump causes the secondary pressure switch (4) to close. The secondarypressure switch then activates the secondary steering indicator to alert theoperator that the secondary system has started and steering action will bereduced.

Oil from the secondary steering pump flows through the secondarysteering valve to the steering control valve.

If an engine or primary pump failure occurs, the steering control valveuses the oil flow from the secondary steering pump as pilot system oil.

• Caterpillar monitoringsystem components:

1. Master action lamp

2. Monitoring panel

3. Primary steeringindicator

4. Secondary steeringindicator

13


4

2

1

3

Caterpillar Monitoring System

The 966G/972G Wheel Loaders are equipped with the CaterpillarMonitoring System. The Caterpillar Monitoring System consists of anaction alarm, a master action lamp (1), a monitoring panel (2) with ninealert indicators for the various machine systems, a tachometer (notshown), and a gauge display (not shown).

A primary steering system indicator (3) is provided on the standard966G/972G for an alert when the primary steering pressure is low. If themachine is equipped with the optional secondary steering system, asecondary steering system alert indicator (4) is provided when thesecondary steering pump is activated.

The system continuously monitors the various machine systems. Thealert indicators show any abnormal conditions occurring on the machine.

The monitoring system provides three warning categories. A Category 1Warning requires only operator awareness. When a Category 1 Warningoccurs, the monitoring system causes an alert indicator to illuminate.

A Category 2 Warning requires operator response. When a Category 2Warning occurs, the monitoring system causes one or more indicators toilluminate. A Category 2 Warning also causes the master action lamp (4)to flash.

➥

• Category 1 Warning

• Category 2 Warning


• Category 3 Warning A Category 3 Warning requires a safe, immediate shutdown of themachine systems. When a Category 3 Warning occurs, the monitoringsystem causes one or more alert indicators to turn on. The monitoringsystem also causes the master action lamp to flash and sounds the actionalarm.

If a Category 3 Warning occurs during machine operation, stop themachine immediately and engage the parking brake. Stop the engine.Investigate the cause of the warning before returning the machine toservice.

A loss of primary steering oil pressure and the activation of the optionalsecondary steering system, if equipped, will initiate a Category 3 Warningfor the steering system. This condition causes the primary steering andsecondary steering indicators to turn on. The monitoring system alsocauses the master action lamp to flash and the action alarm sounds.

The condition of the secondary steering system is tested during enginestart-up. The secondary steering alert indicator, the master action lamp,and the action alarm come on for three seconds in order to verify thesystem is operational.

NOTICE

Do NOT operate the machine until the cause of the warning has beencorrected.

INSTRUCTOR NOTE: At this time, introduce and perform "Lab A:Steering System Component Identification." This lab will reinforcethe material discussed in the preceding slide presentation.

• Steering systemwarnings

• Secondary steeringoperational test

Introduce and performLab A

Summarize lab byasking questions


14


• System operation:

- CONSTANT FLOW

• Pump andcompensatorcomponents:

- Small actuatorpiston

- Large actuatorpiston

- Flow compensatorspool

- Pressurecompensator spool

PUMP OUTPUTSIGNAL

PUMP AND COMPENSATOR OPERATIONCONSTANT FLOW

PRESSURECOMPENSATOR

(CUTOFF) SPOOL

FLOW COMPENSATOR(MARGIN) SPOOL

SMALL ACTUATORAND BIAS SPRING

DRIVESHAFT

PISTON ANDBARREL ASSEMBLY

LARGE ACTUATOR

SWASHPLATE

YOKE PAD

STEERING SYSTEM OPERATION

Pump and Compensator

Shown is a sectional view of the steering pump and compensator valvegroup at CONSTANT FLOW with the engine ON.

The pump has two control pistons which work together to continuallyadjust the angle of the swashplate. The small actuator piston, assisted bythe small actuator spring, is used to upstroke the pump. The large actuatorpiston is used to destroke the pump.

The compensator valve group consists of a flow compensator (margin)spool and a pressure compensator (cutoff) spool. The valve groupmaintains the pump flow and pressure at a level needed to fulfill thedemands of the steering system.

➥

• Margin spring The margin spring maintains the pump supply pressure at 2400 ± 100 kPa(350 ± 15 psi) above the signal pressure. The cutoff spring limits thesystem pressure to 21000 ± 350 kPa (3000 ± 50 psi).

As pump flow increases, pump supply pressure also increases. When thepump supply pressure (red) increases and equals the sum of the loadpressure plus the margin spring pressure, the margin spool moves to ametering position and the system becomes stabilized. The swashplate isheld at a relatively constant angle to maintain the required flow.

INSTRUCTOR NOTE: A complete description of the operation ofthe pump and compensator operation can be found in "D6R/D7RTrack-Type Tractors - Introduction" (SESV1687) and "950G/962GWheel Loader Steering and Brake Systems" (SEGV2643).

SEBV2659 - 19 -8/99

Slide/Text Reference

15


• Steering system

- HOLD

• Pump

- LOW PRESSURESTANDBY

PUMPGROUP

SECONDARY STEERING VALVE

LEFTNEUTRALIZER

VALVE

METERING PUMP


BACK-UPRELIEF VALVE

SECONDARYSTEERINGPUMP AND

MOTOR

STEERING SYSTEMHOLD

FROM IMPLEMENT SYSTEM

BREAKERRELIEFVALVE

MECHANICALLINKAGE

FLOW CONTROLORIFICE

DIRECTIONALSPOOL

SELECTORSPOOL

Steering System Schematics

When the engine is running and the steering system is in HOLD, oil isdrawn from the hydraulic tank by the steering pump and flows past thesecondary steering valve to the back-up relief valve and the directionalspool in the steering control valve.

The pressure oil also flows through the flow control orifice in the steeringcontrol valve to the metering pump. A small amount of oil then flows tothe hydraulic tank through an orifice in the metering pump.

The metering pump and the steering pump are connected by a hydraulicoil line. This hydraulic oil line allows signal pressure oil to flow to thepressure and flow compensator valve attached to the steering pump. If thepressure of the signal oil is low, the steering pump will destroke. If thepressure of the signal oil is high, the steering pump will upstroke.

In the HOLD position, the flow of pressure oil from the steering pump tothe steering cylinders is blocked at the directional spool in the steeringcontrol valve.

➥

• Signal pressure topump

• Oil blocked bydirectional spool

In the HOLD condition, there is no signal pressure sensed at thecompensator valve on the steering pump. The steering pump goes to theLOW PRESSURE STANDBY position.

In LOW PRESSURE STANDBY, the pump produces enough flow tocompensate for system leakage and to maintain sufficient system pressureto provide instantaneous response when the steering wheel is turned.

SEBV2659 - 21 -8/99

Slide/Text Reference

• Pump supply forleakage and quickresponse

16


• Steering system

- LEFT TURN

PUMPGROUP


LEFTNEUTRALIZER

VALVE

METERING PUMP



MOTOR

STEERING SYSTEMGRADUAL LEFT TURN


BREAKERRELIEFVALVE

BACK-UPRELIEF VALVE

DIRECTIONALSPOOL

SELECTORSPOOL

FLOW CONTROLORIFICE

During a GRADUAL LEFT TURN with the engine running, the steeringpump sends supply oil past the secondary steering valve to the steeringcontrol valve and the metering pump.

When the steering wheel is turned counterclockwise to make a LEFTTURN, pilot oil from the metering pump flows past the left neutralizervalve to the steering control valve to the selector spool. The selectorspool shifts down, and oil flows to the end of the directional spool. Thedirectional spool shifts down against the force of the centering spring.

When the directional spool moves down, main steering pump oil flowsthrough the directional spool to the rod end of the left steering cylinderand the head end of the right steering cylinder.

At the same time that oil flows into the two steering cylinders, return oilflows from the head end of the left steering cylinder and the rod end of theright steering cylinder through the directional spool and back to thehydraulic tank.

The machine articulates to the left for a left turn.

• Selector spool anddirectional spool shift

17


• Steering system

- FULL LEFT TURN

PUMPGROUP


LEFTNEUTRALIZER

VALVE

METERING PUMP



MOTOR

STEERING SYSTEMFULL LEFT TURN


BREAKERRELIEFVALVE

BACK-UPRELIEF VALVE

STRIKER

FLOW CONTROLORIFICE

DIRECTIONALSPOOL

SELECTORSPOOL

During a FULL LEFT TURN with the engine running, the left strikercontacts the left neutralizer valve. The neutralizer valve moves to theclosed position, and oil flow from the metering pump to the steering controlvalve is blocked at the left neutralizer valve.

The steering selector spool and the steering directional spool return to thecenter position. Flow to the steering cylinders is blocked at the directionalspool in the steering control valve, and the machine stops turning.

The neutralizer valves prevent the machine front frame from contacting themachine rear frame when articulating fully to the right or left.

• Neutralizer valves

18


• Secondary steeringsystem

- LEFT TURN

PUMPGROUP


LEFTNEUTRALIZER

VALVE

METERING PUMP



MOTOR

STEERING SYSTEMSECONDARY PUMP

GRADUAL LEFT TURNFROM IMPLEMENT

SYSTEM

BREAKERRELIEFVALVE

BACK-UPRELIEF VALVE

SELECTORSPOOL

FLOW CONTROLORIFICE

DIRECTIONALSPOOL

If the steering pump or the engine fails, the primary pressure switch willsense the low pressure in the steering system. The primary steeringpressure switch closes and sends a signal to the monitoring system whichcauses a Category 3 Warning to occur. After a one second delay, thetransmission electronic control module energizes the relay for thesecondary steering pump and electric motor actuates. At the same time,the secondary steering indicator on the monitoring system display turnsON.

The secondary steering pump draws oil from the hydraulic tank. The oilthen flows to the secondary steering valve, which causes the check valvein the hydraulic line from the steering pump to close and the check valvein the hydraulic line from the secondary steering pump to open. Theclosed check valve prevents pressure oil from flowing to the steeringpump.

Oil from the secondary steering pump flows past the secondary steeringvalve to the steering control valve and metering pump.

➥

• Primary steeringpressure switch alertstransmission ECM

• Secondary steeringpump and motor

• Secondary steeringvalve


Pilot oil from the metering pump flows past the left neutralizer valve andmoves the steering selector spool. The oil then flows through the steeringselector spool and moves the directional spool, allowing the pressure oilfrom the secondary steering pump to flow to the rod end of the leftsteering cylinder and to the head end of the right steering cylinder.

NOTE: The secondary steering pump does not produce the sameamount of flow as the main steering system pump. Secondarysteering operations are reduced compared to normal operation.Secondary steering provides a method to steer the machine to a safelocation if a failure occurs in the primary steering system or in theengine.


19

STEERING SYSTEM TESTING AND ADJUSTING

Before measuring pressures in the steering hydraulic system, the steeringframe lock (arrow) must be moved to the LOCKED position as shown inthis view.

Also, all pressure checks require the parking brake be ENGAGED and thetransmission direction selector be placed in the NEUTRAL position.

INSTRUCTOR NOTE: Testing and adjusting procedures areprovided in the 966G/972G Wheel Loaders "Steering System Testingand Adjusting Manual" (Form RENR2109).

• Steering frame lock(arrow)


• Steering system testlocations

1. Pressure tap


20

2 1

The pressure tap (1) for checking main steering system pressures islocated on the rear side of the steering control valve (2).

This is the pressure tap used for testing and adjusting of high pressurestall and low pressure standby.



1. Pressure tap

2. Signal pressure line

3. Metering pump

21

1

2

3

Signal pressure to the compensator valve on the steering pump can bemeasured at the pressure tap (1) located on the signal line (2) comingfrom the metering pump (3).



1. Pump pressurecompensator valve

2. Pressurecompensatoradjustment screw

3. Flow compensatoradjustment screw

22

1 3

2

Two steering system adjustment screws are located on the steering pumpcompensator valve (1). The pressure compensator adjustment (2) changesthe steering system maximum pressure. The flow compensator adjustment (3) changes the steering system margin pressure.

The cab has to be removed to access the two pump adjustment screws.



1. Neutralizer valves

2. Front frame

3. Rear frame

4. Adjustable stops

23

1

3

2

4

The neutralizer valves (1) are adjusted to provide interruption of the flowof oil from the metering pump group to the steering control valve.Correctly adjusted neutralizer valves will stop the articulation of themachine before the front frame (2) hits the rear frame (3).

The stops (4) mounted on the front frame can be retracted or extended toprovide the correct gap at the end of steering between the front frame andthe rear frame. The correct gap is 12.7 ± 3.0 mm (.50 ± .12 inch).

INSTRUCTOR NOTE: At this time, introduce and perform "Lab B:Steering System Testing and Adjusting." This lab will reinforce thematerial discussed in the preceding slide presentation.

Introduce and performLab B



24


SERVICE BRAKEVALVE

ACCUMULATORCHARGING VALVE

ACCUMULATORS PARKINGBRAKE

PILOT AND BRAKEPUMP

PARKING BRAKEVALVE

REAR WHEELBRAKES

FRONT WHEELBRAKES

BRAKE SYSTEM COMPONENTS

BRAKE SYSTEM COMPONENTS

Service Brake System

Shown are the brake system components on the 966G and 972G WheelLoaders. The hydraulic tank is common to all hydraulic systems on themachine.

The brake system components are:

- Pilot and brake pump

- Accumulator charging valve

- Brake accumulators

- Service brake valve

- Front and rear service brakes

- Parking brake valve

- Parking brake

• Brake systemcomponents


25


- Pilot and brakepump

- Accumulatorcharging valve

- Brake accumulators

- Service brakecontrol valve

- Service brakes

- Parking brake valve

- Parking brake

PILOT AND BRAKEPUMP

SERVICE BRAKECONTROL VALVE


BRAKEACCUMULATORS

TANK

BRAKESWITCHPRESSURE

PORT

TO PARKINGBRAKE

PARKING BRAKESWITCH

PARKINGBRAKEVALVE

TO IMPLEMENTPILOT SYSTEM

REAR SERVICEBRAKES

FRONT SERVICEBRAKES

BRAKE HYDRAULIC SYSTEMSERVICE BRAKE OFF

Shown is a simplified schematic of the brake hydraulic system found on966G and 972G Wheel Loaders with the Conventional Steering Systemand the Command Control Steering system. The brake hydraulic systemcomponent functions are:

Pilot and brake pump: Pulls oil from the tank and sends supply oil tothe implement pilot system and the accumulator charging valve.

Accumulator charging valve: When the machine is running, theaccumulator charging valve maintains the pressure in the accumulatorsbetween 11700 ± 345 kPa (1700 ± 50 psi) CUT-IN pressure and14500 ± 345 kPa (2100 ± 50 psi) CUT-OUT pressure.

Brake accumulators: When the engine is running, the accumulatorssupply oil within a controlled pressure range to the brake valves. If theengine stops running, the accumulators provide an emergency oil supplyto provide braking.

➥


Service brake control valve: The service brake control valve controlsbrake oil flow and pressure to the front and rear service brakes. When theoperator depresses either brake pedal, the two brake spools in the servicebrake control valve move to allow oil flow to the front and rear servicebrakes. The two brake valve spools function as pressure reducing valvesand maintain pressure in the service brakes in proportion to the force onthe brake pedal.

Service brakes: The service brakes are located inside each axle. Eachhydraulically engaged brake contains a piston, two discs and plate. Thebrake plate is attached to the brake housing and does not turn. The brakediscs are splined to the planetary sun gear and turns with the wheel.When either brake pedal is DEPRESSED, brake oil moves the piston andcompresses the discs between the piston and the plate. The frictionbetween the piston, discs and plate causes the wheels to turn slower or tostop.

Parking brake valve: Controls oil pressure to the parking brake. Whenthe parking brake valve is in the BRAKE OFF position, accumulator oilpressure is sent through the parking brake valve to the brake chamber. Oilpressure compresses the spring in the brake chamber and releases theparking brake. When the parking brake valve is moved to the BRAKEON position, accumulator oil pressure is blocked at the parking brakevalve. Oil in the parking brake chamber flows through the parking brakevalve to drain. The spring in the brake chamber applies the brake.

Parking brake: The spring engaged, hydraulically released, shoe-typeparking brake is in the drive line on the front end of the wheel loader.The parking brake consists of the brake drum, a camshaft, a plate, twoshoes, three springs and a star wheel adjuster. The brake drum isconnected to the front drive shaft and turns with the drive shaft. Theremaining components are stationary. When the parking brake is applied,the camshaft moves the stationary shoes against the turning drum. Thefriction between the shoes and the drum causes the drum to turn slower orto stop.


• Pilot and brake pump

1. Pilot and brakepump

2. Steering pump

26

1

2

The brake system oil supply is from the vane type pilot and brake pump (1). The pump pulls oil from the hydraulic tank and sends oil to theaccumulator charging valve (not shown).

The pilot and brake pump is mounted on the steering pump (2) under thecab on the right side of the machine.


• Accumulator chargingvalve

1. Accumulatorcharging valve

2. Rear brakeaccumulator

3. Front brakeaccumulator

4. Service brakepressure switch

27

2

1

3

4

When the engine is running, oil flows from the pilot and brake pump tothe accumulator charging valve (1) located on the left side of the machinebelow the operator's platform.

The accumulator charging valve maintains the pressure in the twoaccumulators between 11700 ± 345 kPa (1700 ± 50 psi) CUT-IN pressureand 14500 ± 345 kPa (2100 ± 50 psi) CUT-OUT pressure.

The rear brake accumulator (2) and the front brake accumulator (3) arelocated next to the accumulator charging valve. The two accumulatorssupply oil for the operation of the service brakes and the parking brakes.

If the engine stops running, the accumulators provide an emergency oilsupply to provide braking.

Also shown is the service brake pressure switch (4).


28

• Accumulator chargingvalve

BRAKEPRESSURE

SWITCH

CUT-IN/CUT-OUTSPOOL

CHARGECONTROL VALVE

PRESSURERELIEFVALVE

INVERSESHUTTLE

VALVE



TO REAR BRAKEACCUMULATOR

TO FRONT BRAKEACCUMULATOR

FROM PILOT ANDBRAKE PUMP

FLOWCONTROLORIFICE

ACCUMULATOR CHARGING VALVECUT-IN CYCLE

Shown is the accumulator charging valve during the CUT-IN cycle.

The accumulator charging valve is made up of a pressure relief valve, acharge control valve, a flow control orifice, a spool for cut-in and cut-outpressure, and an inverse shuttle valve.

The pressure relief valve limits the oil pressure that flows from the pilotand brake pump.

The charge control valve regulates the flow of oil to the other componentsin the accumulator charging valve and on to the brake circuit. The chargecontrol valve can be adjusted with shims. Excess oil that is not requiredby the brake circuit is diverted by the charge control valve back the thehydraulic oil tank.

The cut-in/cut-out spool controls the pressure in the two brakeaccumulators. When the pressure in the brake accumulators drops to11700 ± 345 kPa (1700 ± 50 psi), the cut-in/cut-out spool moves to theposition shown to allow oil to flow to the inverse shuttle valve and on tocharge the accumulators.

• Charge control valve

• Pressure relief valve

• Cut-in/cut-out spool


• Service brake valve

1. Service brake valve

2. Front service brakepressure tap

3. Rear service brakepressure tap

29

1

2

3

The service brake valve (1) is located below the right brake pedal. Theleft and right brake pedals are mechanically connected. This connectionallows the service brake valve to be actuated by either brake pedal in theoperator's station.

The service brake valve controls brake oil flow and pressure to the frontand rear service brakes.

When the operator depresses either brake pedal, the two brake spools inthe service brake valve move to allow oil flow from the front and rearbrake accumulators to the front and rear service brakes. The two brakevalve spools then function as pressure reducing valves and maintainpressure in the service brakes in proportion to the force on the brakepedal.

Also shown are the front service brake pressure tap (2) and the rearservice brake pressure tap (3).

INSTRUCTOR NOTE: The service brake valve found on the966G/972G Wheel Loaders was previously referred to as the tandembrake valve on the 966F II/970F Wheel Loaders.

• Acts as pressurereducing valve


• Service brakes

1. Piston

2. Friction plate

3. Reaction plate

4. Optional axle oilcooler

5. Bevel gear

30

4

1

2

3

5

This graphic shows a cut-away of the hydraulically engaged, double discservice brake located on both sides in both the front and rear axles.

Each service brake contains a piston (1), two friction discs (2) and tworeaction plates (3). The piston and reaction plate are held stationary bydowels fastened to the differential housing. The friction discs are splinedto the axle sun gear and rotate at the speed of the axle.

When either brake pedal in the operator's station is depressed, oil from thebrake accumulator moves the piston. The piston compresses the two discsbetween the piston and the reaction plates. The friction between thepiston, disc and plate causes the wheels to turn slower or to stop. Theheat from the brake friction is removed by the oil in the differentialhousing.

An optional axle oil cooler (4) has been added inside the axle assembliesbetween the bevel gear (5) and the service brake group. The axle oilcooler incorporates an internal heat exchanger in each axle. Hydraulic oilfrom the fan motor circuit is routed from the hydraulic oil cooler througheach axle cooler before being returned to the hydraulic oil tank. The axlecoolers uses the coolest available oil in the hydraulic system.

An optional axle oil cooler is recommended for the 966G/972G in highduty cycle applications such as a load and carry operation where axle oiltemperatures can approach 190°C (400°F). A brake temperature warningindicator is provided on the Caterpillar Monitoring System displaymodule.

• Optional axle oilcooler for harshapplications

• High duty cycles

31


• Brake systemcomponents:

1. Neutralizer switchcover

2. Left brake pedal

3. Neutralizer overrideswitch

4. Indicator light

5. Axle oil temperatureindicator

Other components in the brake system include the transmission neutralizerlimit switch (1), the neutralizer override switch (3), and the transmissionindicator light (6) on the center console in the operator's station.

When the operator depresses the left brake pedal (2), the neutralizerswitch open. The open neutralizer switch signals the transmission ECMto de-energize the transmission directional clutch solenoid. With only thespeed clutch solenoid energized, the transmission is neutralized.

The operator can override the operation of the transmission neutralizerswitch by activating the neutralizer override switch (3) located on theright overhead panel in the operator's station.

The neutralizer override switch is a two position switch with an indicatorlamp (4) that illuminates when the switch is in the ON position. Theindicator lamp is located on the center panel of the Caterpillar MonitoringSystem.

1

2

3

5

4

➥


• Neutralizer overrideON

When in the ON position, the neutralizer override switch closes a parallelcircuit that bypasses the neutralizer switch. If the left brake pedal isdepressed when the neutralizer override switch is in the ON position, thetransmission will not neutralize. No signal is sent to the transmissionECM.

In the OFF position, the neutralizer override switch closes a parallelcircuit that includes the neutralizer switch. If the left brake pedal isdepressed when the neutralizer override switch is in the OFF position, asignal is sent to the transmission ECM. The ECM will de-energize thedirectional proportional solenoid valve. The transmission will disengage.

This view shows the switch in the OFF position.

Also, the temperature sender (not shown) on the front and rear driveshafts will activate a Category 1 Warning on the Caterpillar MonitoringSystem panel in the operator's station when the axle oil temperatureexceeds 125°C (257°F). The warning will turn off when the axle oiltemperature cools to a minimum temperature of 117°C (243°F). Highaxle oil temperatures adversely affects brake performance.

• Neutralizer overrideOFF

• Brake performancewith hot axle oil


• Parking brakes

1. Parking brake

2. Drive line

32

21

Parking Brake System

The spring engaged, hydraulically released, shoe-type parking brake (1) islocated in the drive line (2) on the front end of the 966G/972G wheelloader.


• Parking brakes

1. Parking brake knob

2. Parking brake alertindicator

33

21

The parking brake is activated and de-activated with the parking brakeknob (1) located in the operator's station. When the knob is pulled out,mechanical linkage connecting the knob to the parking brake controlvalve below the operators station applies the parking brake (BRAKE ONposition). When the parking brake is applied, an alert indicator (2)illuminates on the Caterpillar Monitoring System panel.

The parking brake is disengaged when the knob is pushed in (BRAKE OFF position).


• Parking brakes

1. Parking brakecontrol valve

2. Actuator shaft

3. Oil supply line fromactuator

4. Oil supply line toactuator

5. Pressure switch

34

1

2

3

4

5

The parking brake control valve (1) is attached to the top of a platelocated on the left side of the machine below the operator's station. Theaccumulator charging valve (not shown) is attached to the bottom of thisplate. The parking brake control valve (1) controls the flow of oil to theparking brake actuator which operates the parking brake.

When the parking brake knob in the operator's station is in the BRAKEOFF position, the mechanical linkage connecting the knob to the parkingbrake control valve actuator shaft (2) moves the control valve spool. Thecontrol valve spool allows oil in the front service brake accumulator toflow through the parking brake valve to the parking brake actuatorchamber. This picture shows the supply line (3) from the accumulatorand the outlet line (4) to the parking brake actuator.

Oil pressure compresses the spring in the brake chamber and releases theparking brake.

When the parking brake knob in the operator's station is in the BRAKEON position, accumulator oil is blocked at the parking brake valve. Oil inthe parking brake chamber flows through the parking brake valve to drain.The spring in the brake chamber applies the brake. The drain line can beseen directly below the supply line (4) to the parking brake actuator.

Also shown is the brake pressure switch (5) for the Caterpillar MonitoringSystem.

• Park brake OFF

• Park brake ON


• Parking brakecomponents:

1. Parking brakeactuator chamber

2. Parking brakeactuator shaft

3. Parking brake

35

1

3

2

This picture shows the parking brake actuator chamber (1) and actuatorshaft (2) which is located above the parking brake (3).

The parking brake valve controls oil pressure to the parking brakeactuator chamber. When the parking brake valve is in the BRAKE OFFposition, accumulator oil pressure is sent through the parking brake valveto the brake actuator chamber. Oil pressure compresses the spring in thebrake actuator chamber. As the spring compresses, the actuator shaftmoves the linkage that releases the parking brake.

When the parking brake valve is moved to the BRAKE ON position,accumulator oil pressure is blocked at the parking brake valve. Oil in theparking brake chamber flows through the parking brake valve to drain.The spring in the brake actuator chamber applies the brake.

INSTRUCTOR NOTE: At this time, introduce and perform "Lab C:Brake System Component Identification." This lab will reinforce thematerial discussed in the preceding slide presentation.

Introduce and performLab C



36

Objectives 5Slides 36 - 44

FRONT BRAKEACCUMULATOR

REAR BRAKEACCUMULATOR

RIGHT BRAKEPEDAL

LEFT BRAKEPEDAL

BRAKE LIGHTS

SERVICEBRAKE VALVE

REAR AXLEBRAKES

FRONT AXLEBRAKES

BRAKEPRESSURE

SWITCH

CUT-IN/CUT-OUTSPOOL

CHARGECONTROL

VALVE

PRESSURERELIEFVALVE

PILOT/BRAKEPUMP

STEERINGPUMP

INVERSESHUTTLE

VALVE


BRAKE SYSTEMCUT-IN CYCLE/SERVICE BRAKES ENGAGED


TO TRANSECM

TANK

IMPLEMENTPUMP

CHECKVALVE

BRAKE SYSTEM OPERATION

Service Brake Schematics

This schematic shows the brake system during the accumulator chargingvalve CUT-IN cycle with the service brakes ENGAGED and the parkingbrake RELEASED.

The left or right service brake pedal have been applied. By depressingeither the right or the left brake pedal, the service brakes are ENGAGED.The movement of the brake pedal is mechanically transmitted to theservice brake valve, which permits oil to flow through the service brakevalve to the rear and front axle brakes causing the rear brakes to justbefore the front brakes apply. The brake pistons are open to the brakeaccumulators through the service brake valve.

The service brake valve consists of two spools which are controlled by thebrake pedals and feedback oil pressure from the brakes when the servicebrakes are applied.

➥

• Service brakes CUT-IN/ brakesENGAGED

• Two spools in servicebrake valve- Controlled by brake

pressure andfeedback pressure


When the oil pressure in either of the two accumulators decreases below11700 ± 345 kPa (1700 ± 50 psi), the accumulator charging valve beginsthe recharging cycle (CUT-IN mode).

Pump supply oil enters the accumulator charging valve and flows to thecharge control valve. The charge control valve directs some oil back tothe tank through the orifice in the charge control valve spool, but most ofthe oil flows out the charge control valve, through the orifice and checkvalve, to the CUT-IN/CUT-OUT spool and the inverse shuttle valve. Thereduced pressure oil from the orifice opposes the CUT-OUT spring.

During the CUT-IN condition, the CUT-OUT spring force is higher thanthe force of the oil pressure acting against the opposite side of the CUT-OUT spool, and the CUT-OUT spool shifts to the left. With the CUT-OUT spool to the left, the reduced pressure oil at the spool flows throughthe orifice in the center of the spool and acts in conjunction with thecharge control valve spring. As long as the combined force from thepressure and the spring on the left side of the charge control valve ishigher than the force from the pressure on the right side of the valve, thevalve remains shifted to the right. Keeping the charge control valve to theright allows the pump to continue to supply oil to charge theaccumulators.

Oil at the inverse shuttle valve flows through the valve to theaccumulators. Oil will continue to flow to the accumulators until theaccumulators are fully charged.

If the machine looses power or if the hydraulic pump fails, the servicebrakes can still be ENGAGED. The pressure in the accumulators permitsseveral applications of the service brakes to stop the machine or slow themachine enough to engage the parking brake.

INSTRUCTOR NOTE: The charge control valve in the accumulatorcharging valve found on the 966G/972G Wheel Loaders waspreviously referred to as the unloading valve on the 966F II/970FWheel Loaders.

- Oil flows throughinverse shuttle toaccumulators

• CUT-IN is accumulatorrecharging

• CUT-OUT spool shiftsto left

• Unloading valveremains shifted toright


37

• Service brakesCUT-OUT



RIGHT BRAKEPEDAL

LEFT BRAKEPEDAL

BRAKE LIGHTS

SERVICEBRAKE VALVE

REAR AXLEBRAKES

FRONT AXLEBRAKES

BRAKEPRESSURE

SWITCH

CUT-IN/CUT-OUTSPOOL

CHARGECONTROL

VALVE

PRESSURERELIEFVALVE

PILOT/BRAKEPUMP

STEERINGPUMP

INVERSESHUTTLE

VALVE



TO TRANSECM

TANK

IMPLEMENTPUMP

CHECKVALVE

BRAKE SYSTEMCUT-OUT CYCLE

When the pressure in the accumulators increases to the CUT-OUT settingof 14500 ± 345 kPa (2100 ± 50 psi), oil pressure from the accumulatorsforces the inverse shuttle valve to close.

As the inverse shuttle valve closes, the oil pressure acting against the leftside of the CUT-IN/CUT-OUT spool moves the spool to the right.Moving the CUT-IN/CUT-OUT spool to the right causes the pressureacting against the left side of the charge control valve to graduallydecrease to tank pressure through the orifice in the CUT-IN/CUT-OUTspool.

As the pressure acting on the left side of the charge control valvedecreases, the pressure acting on the right side of the valve moves thevalve to the left against the spring force. Moving the charge control valveto the left directs the pump supply oil back to the tank. Returning thepump supply oil to the tank causes the check valve to close because thepressure on the left side of the check valve is higher than the pressure onthe right side.

➥

• CUT-IN/CUT-OUTspool shifts to right

• Charge control valveshifts to left

• Most supply oilreturns to tank

• Check valve closes


The accumulator charging valve will remain in the CUT-OUTcondition until the pressure in one of the accumulators decreases to 11700 ± 345 kPa (1700 ± 50 psi).


38

• Parking brakes



RIGHT BRAKEPEDAL

LEFT BRAKEPEDAL

BRAKE LIGHTS

SERVICEBRAKEVALVE

REAR AXLEBRAKES

FRONT AXLEBRAKES

PILOT/BRAKEPUMP

IMPLEMENTPUMP

STEERINGPUMP


TO TRANSECM

PARKINGBRAKE

PARKINGBRAKE

ACTUATOR

PARKINGBRAKEVALVE

BRAKEPRESSURE

SWITCH

TANK

BRAKE SYSTEMPARKING BRAKE RELEASED

BRAKEPRESSURE

SWITCHACCUMULATOR

CHARGINGVALVE

This schematic shows the brake system with the parking brakeRELEASED.

Pressure oil flows from the pilot and brake pump to the accumulatorcharging valve. The accumulator charging valve allows oil to flow to therear and front brake accumulators and to the tandem brake valve. Part ofthe oil that is sent to the front brake accumulator also flows to the parkingbrake valve.

In the RELEASED position, the pressure oil flows past the parking brakevalve to the parking brake actuator. The oil in the parking brake actuatoracts against the spring force that keeps the parking brake ENGAGED.When the pressure of the oil overcomes the force of the spring, theparking brake is RELEASED.

➥


During a normal application, the parking brake will remain RELEASEDuntil the flow of oil is blocked at the parking brake valve or the supplypressure from the brake accumulator charging valve decreases below 6050 ± 515 kPa (875 ± 75 psi).


39

BRAKE SYSTEM TESTING AND ADJUSTING

Brake System

Before performing testing and adjusting procedures on the brake, machineshould be moved to a smooth, horizontal location away form otheroperating machines and away from personnel.

The steering frame lock (arrow) must be moved to the LOCKED positionas shown in this view.

Also, put blocks in front of the front wheel and behind the rear wheels toinsure the machine does not move during testing and adjusting.

• Brake systemadjustmentprocedures

• Steering frame lock

• Block tires


• Brake system testpoints

1. Service brake valve

2. Front service brakepressure tap

3. Rear service brakepressure tap

40

1

2

3

The taps for the service brake pressure test are located on the servicebrake valve (1).

Shown are the front service brake pressure tap (2) and the rear servicebrake pressure tap (3).


• Brake systemadjustments

1. Accumulatorpressure tap

2. Accumulatorcharging valve

3. Service brakepressure switch

41

2

1

3

The pressure tap (1) for checking accumulator CUT-IN and CUT-OUTpressures is located on the accumulator charging valve (2).

Also shown is the service brake oil pressure switch (3). The switchactivation and deactivation pressures can be checked during theaccumulator CUT-IN and CUT-OUT tests. The pressure switchmaximum activation pressure is 10700 kPa (1550 psi). The deactivationpressure is 9000 ± 540 kPa (1300 ± 78 psi).

INSTRUCTOR NOTE: Refer to the 966G/972G Wheel Loader"Brake System Testing and Adjusting Manual" (RENR2112) for thecurrent pressure specifications.


• Brake systemadjustments

- Air purge screws(arrows)

42

2

1

Two service brake air purge screws are located on the top of both the front and the rear axles for bleeding the service brakes. The air purgescrews (arrows) for the rear axle are shown. Similar air purge screws arelocated on the front axle.


• Brake wear indicator:

1. Brake discs

2. Pin

3. Axle flange

4. Brake piston

43

2

4

3

1

Brake Wear Indicator

Brake disc thickness data for each of the four brake groups is stored in theTransmission ECM. This information can be retrieved using theCaterpillar Electronic Technician (ET) software.

The brake disc (1) thickness is measured during machine assembly at thefactory. Values for each brake group is stored in the Transmission ECMas the baseline information.

The brake disc thickness should be referenced over the service life of theservice brakes. The baseline values are used to help calculate the amountof brake discs wear in each brake group. This data should be changedonly when a new service brake group is installed. The brake discthickness for each replacement brake group is entered as the new baselinedata in the transmission ECM using the Caterpillar Electronic Technician(ET) software.

The brake disc thickness is determined by measuring the distance fromthe flange face (3) of the axle housing to the pin (2). As the brakes wear,the brake piston (4) will travel further to compress the brake pack. Thus,the distance between the flange face and the pin will increase.

INSTRUCTOR NOTE: The "Disc Thickness Wear Chart" used forcalculating brake disc wear is found in the 966G/972G Wheel Loader"Brake System Testing and Adjusting Manual" (RENR2112).

44

CONCLUSION

This concludes the slide/text portion of the 966G and 972G WheelLoaders Steering and Brake System.

Always check the Service Manual for the latest service information andspecifications when servicing, testing and adjusting, or making repairs.

INSTRUCTOR NOTE: At this time, introduce and perform "Lab D:Brake System Testing and Adjusting." This lab will reinforce thematerial discussed in the preceding slide presentation.


Introduce and performLab D


1. Model view2. Steering system components3. Steering system block diagram4. Hydraulic tank5. Steering pump6. main control valve7. Steering cylinder8. Steering wheel9. Metering pump

10. Neutralizer valves11. Steering control valve diagram12. Secondary steering components13. Caterpillar Monitoring System14. Pump and compensator - CONSTANT

FLOW15. Steering system - HOLD16. Steering system schematic - LEFT TURN17. Secondary steering system schematic18. Secondary steering - LEFT TURN19. Steering frame lock20. Main steering system pressure taps21. Pump signal pressure taps22. Pump compensator valve adjustments23. Neutralizer valve24. Brake system components25. Brake system block diagram26. Pilot and brake pump27. Brake accumulators28. Accumulator Charging Valve - CUT-IN29. Service brake valve30. Service brakes31. Service brake neutralizer valve/Neutralizer

override switch/Indicator light/Axle oiltemperature indicator

32. Parking brake33. Parking brake indicator34. Parking brake control valve35. Parking brake actuator36. Service brake schematic - CUT-IN37. Service brake schematic - CUT-OUT38. Parking brake schematic - RELEASED39. Steering frame lock40. Service brake pressure tap41. Brake accumulator pressure tap42. Service brake purge screws

43. Brake wear indicator44. Model view

SLIDE LIST


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caterpiaar 966G steering and brake system