TECHNICAL PRESENTATION
924G/924Gz WHEEL LOADERS
INTRODUCTION
INTRODUCTION
MEETING GUIDE 717
SLIDES AND SCRIPT
AUDIENCE
Level II--Service personnel who understand the principles of machine systems operation, diagnostic equipment, and procedures for testing and adjusting.
CONTENT
This presentation describes the significant changes from the 924F/IT24F in machine features and systems. This presentation covers component locations, nomenclature and a brief description of systems operation.
OBJECTIVES
After learning the information in this presentation, the serviceman will be able to: 1. identify the major changes in the machine features and systems;
2. explain the basic operation of each system; 3. locate and identify components; and
4. explain the function of the components and systems.
REFERENCES
924G/924Gz Wheel Loader Service Manual RENR3500
924G/924Gz Wheel Loader Parts Manual SEBP2974
PREREQUISITES
Interactive Video Course "Fundamentals of Mobile Hydraulics" (CD ROM) TEMV9001
STMG 546 "Graphic Fluid Power Symbols" SESV1546
SUPPLEMENTARY TRAINING MATERIAL
STMG 684 "928G Wheel Loader/IT28G Integrated Toolcarrier--Introduction" SESV1694 STMG 670 "914G Wheel Loader/IT14G Integrated Toolcarrier--Introduction" SESV1670 STMG 581 "910E/916F/IT12B/IT14B Power Shift Transmission" SESV1581 STMG 667 "Challenger 35/45/55 Agricultural
Tractors--Implement, Hitch and Steering Systems" SESV1667
Estimated Time: 1.5 Hours Visuals: 61 (2 X 2) Slides
Serviceman Handouts: 3 Work Sheets Form: SESV1717
Date: 10/99
TABLE OF CONTENTS
INTRODUCTION ...5 MACHINE CONFIGURATIONS ...6 924G...7 924Gz...8 MACHINE APPEARANCE...9 OPERATORÕS STATION ...10ENGINE AND ELECTRICAL SYSTEM...21
POWER TRAIN ...28
Torque Converter and Transmission ...29
Power Train Hydraulic System ...31
Electronic Transmission Control System...36
Axles ...39
HYDRAULIC SYSTEMS ...42
Work Tool Hydraulic System...44
Steering System ...65
Brake/Fan Drive System ...70
CONCLUSION...75
SLIDE LIST...76
¥ Explain coverage
1
INTRODUCTION
This presentation covers the 924G and the 924Gz Wheel Loaders. A Caterpillar 3056T direct injection, turbocharged engine provides 87 kW (116 hp) to the flywheel at 2300 rpm for the 924G and the 924Gz. An electronically controlled, four-speed forward, three-speed reverse autoshift transmission of countershaft design with a single stage torque converter transfers the engine power to the axles. The power train is similar to that on the 924F and the IT24F.
The 924G/924Gz use a parallel flow work tool hydraulic system with closed center, pilot operated control valves and a load sensing, variable flow, axial piston pump. The 924F/IT24F machines use an interrupted series flow hydraulic system with open center, pilot operated control valves and a fixed displacement pump.
The 924G/924Gz load sensing steering system uses a variable displacement pump, as did the 924G/IT24F.
The brake and fan drive hydraulic system has been redesigned, however this system is similar to that on the 928G wheel loader and the IT28G integrated tool carrier.
This presentation will cover machine orientation and the operation of the power train and machine hydraulic systems for the 924G and the 924Gz.
924G/924Gz WHEEL LOADERS
© 1999 Caterpillar Inc.
¥ Power train
¥ Work tool hydraulics
¥ Steering system
¥ Brake/fan drive system
¥ Machine Configurations
2
MACHINE CONFIGURATIONS
The 924G replaces both the 924F and the IT24F. The 924G combines the versatility of an integrated toolcarrier with the production of a wheel loader. Therefore, an integrated toolcarrier configuration is not necessary for this G series update.
The 924Gz retains the Z-bar linkage to satisfy market needs for areas that still require this configuration
Both the 924G and the 924Gz machines are wheel loaders.
The only systems that are different between the 924G and the 924Gz are the work tool hydraulic systems and the machine structures.
3
¥ 924G 924G Wheel Loader
The 924G is equipped with Versa Link©linkage for controlling the tilt of the bucket or tool. This linkage includes a box boom lift arm (1). The box boom lift arm offers the operator better visibility to the bucket or tool. A High Lift linkage option enhances the loading capability of the 924G by allowing the machine to load taller trucks.
A hydraulically controlled work tool coupler (2) is an option on the 924G. This coupler is the same interface as previous integrated toolcarriers and will connect to existing Caterpillar work tools.
The main difference between the work tool hydraulic systems of the 924G and the 924Gz is in the tilt control valve (3). The 924G tilt control valve regenerates the return oil from the tilt cylinder during the dump cycle. The tilt control valve equalizes the pressure on both sides of the piston in the tilt control cylinder with the pressure in the lift circuit during the dump operation. Hydraulic system operation will be discussed in greater detail later in this presentation.
924G Configuration BOOM
COUPLER
Versa Link linkage with box boom lift arm
Hydraulically controlled coupler
WORK TOOL HYDRAULICS
Regeneration and equalization of pressure by tilt control valve
2
1
3 3
3. Tilt control valve 2. Hydraulically
controlled coupler 1. Box boom lift arm
4
¥ 924Gz 924Gz Wheel Loader
The 924Gz is equipped with Z-bar linkage for controlling the tilt of the bucket. This linkage includes a conventional slab-type lift arm (1). The 924Gz can be equipped with a Caterpillar work tool coupler as an aftermarket attachment. However, these machines will be delivered only with pin-on linkage (2).
The 924Gz tilt control valve (3) does not regenerate oil or equalize pressure during the dump cycle.
924Gz Configuration BOOM
COUPLER
Z-Bar linkage
Can be equipped with Caterpillar work tool coupler WORK TOOL
HYDRAULICS
Conventional tilt control valve operation
2
1
3
3. Tilt control valve 2. Pin-on linkage 1. Lift arms
¥ Redesigned cab
5
MACHINE APPEARANCE
The redesigned cab and sloped hood visually differentiate the
924G/924Gz from the 924F Wheel Loaders and the IT24F Integrated Toolcarriers.
The cab is equipped with two doors for easier access. Improved ladders, handrails and platforms make entry and exit easier and offer room to maneuver while servicing the machine.
The sloping rear hood enhances the operator's view toward the rear of the machine. The rear hood configuration allows the operator to see objects close to the rear of the machine that cannot be seen with the rectangular shaped hood found on the previous "F" Series Wheel Loaders.
The 924G/924Gz is also larger in size than the 924F Wheel Loaders and the IT24F Integrated Toolcarriers. The 924G/924Gz is 14 mm (0.5 in.) taller and it has a 100 mm (4 in.) longer wheel base than the 924F/IT24F. ¥ Larger
¥ Sloping hood - Access doors - Handrails
¥ Cab components: - Right side door - Bonded glass
6
OPERATOR'S STATION
The 924G/924Gz cab is shared with the 928G and the IT28G. The two door design provides access from the right or left side of the cab.
The bonded glass in the front window eliminates distracting metal frames. The increase in cab glass area enhances the view around the machine. Molded nonmetallic materials inside the cab allow for easy installation of features such as a coat hook, lockable storage boxes, and cup, vacuum bottle and cooler holders.
Improved ventilation provides better air flow to the operator and the windows. The optional air conditioning keeps the cab temperature comfortable for operation in warm environments.
¥ Improved ventilation ¥ Molded nonmetallic
¥ Door latch release (arrow)
7
Both doors have latches that hold the doors fully open.
¥ Cab components: 1. Adjustable seat
2. Seat cushion angle lever 3. Front/rear lever 4. Suspension adjustment knob 5. Retractable seat belt 8
The six-way adjustable suspension seat (1) adds to the overall comfort level by smoothing the ride over rough ground.
The seat cushion angle lever (2) raises the front of the seat cushion to the desired position.
The front/rear lever (3) allows forward and rearward adjustment. The suspension adjustment knob (4) adjusts the stiffness of the seat suspension.
The backrest adjustment (not shown) allows the backrest centerline to conform to the operator's spinal curve and provides the proper support to the back's lumbar region.
A retractable seat belt (5) is also included with the seat. 2
1 5
2
3 4
¥ Left front console 1. Five position
headlamp switch
2. Rotating beacon switch
3. Thermal start aid switch
4. Transmission neutralizer override
9
A left front console has been added to the 924G/924Gz operatorÕs station. Some controls have been moved here for easy access by the operator. The headlamp switch (1) has the following positions: OFF, PARK (panel/tail lamps), ROADING (front headlamps), WORK 1 (front cab floodlamps) and WORK 2 (rear cab floodlamps). Each position of the switch illuminates more lamps than the previous positions.
The three switches below the headlamp switch include: rotating beacon (2), thermal starting aid (3) and the transmission neutralizer override (4). During normal operation, the transmission is neutralized when the brakes are applied. Use the transmission neutralizer override switch to override this feature.
Warning lamps are located on the left front console, including the brake pressure indicator lamp, engine oil pressure indicator lamp, coolant temperature indicator lamp, transmission oil temperature indicator lamp and differential lockup indicator lamp.
NOTE: Throughout the cab, some of the switches are for optional attachments, so not every machine will have all the switches that are shown in this presentation.
1
3 2
¥ Front console 1. Horn button 2. Lamps 3. Engine coolant temperature gauge 4. Hydraulic oil temperature gauge
5. Fuel level gauge
6. Transmission oil temperature gauge
10
In the center console, individual gauges with dial faces show the conditions of the various machine systems. The group includes the following gauges: engine coolant temperature (3), hydraulic oil
temperature (4), fuel level (5), and transmission oil temperature (6). An optional speedometer (not shown) is available. This gauge group is similar to the gauge group in the cab of the 928G/IT28G.
The horn button (1) is located in the center of the steering wheel.
The four lamps (2) spaced around the steering column are the turn signal indicators (left and right), the high beam indicator (optional) and the trailer light indicator (optional). The F-N-R indicator is located directly above the steering column.
1 2 3 4 5 5 6
¥ Right front console components: 1. Turn signal
(optional)
2. Engine start switch
3. Dimmer switch location (optional) 4. Lighter (24V) 5. Secondary steering test switch (optional) 6. Indicator lamps
7. Steering wheel tilt latch 8. Front windshield wiper switch 9. Rear windshield wiper switch 11 7 1 2 4 5 9 6 3 9
Shown in this view is the right side of the front console.
The optional turn signal lever (1) is on the right side of the steering column. Pulling the turn signal switch away from the console operates the hazard lights.
The engine start switch (2) is located on the right side of the front console.
A switch for dimming the roading lights (3) is optional.
A cigarette lighter (4) on the right front console provides a 24V power source for electrical components. An optional 12V power source is located on the lower left side of the seat.
The switch to activate the secondary steering system test (5) is located next to the indicator lamps.
Indicator lamps (6) include: alternator, park brake, cab floodlamps, and (if equipped) secondary steering motor ON lamp and a primary steering pressure fault lamp.
The steering wheel tilt latch (7) allows the operator to adjust the steering wheel to the desired angle.
Two switches are used to control the windshield wipers. One switch (8) controls the front windshield wiper and another switch (9) controls the rear windshield wiper.
¥ Lever functions: 1. Joystick control 2. Transmission control switch 3. Third function control 4. Fourth function control 12
Reduced lever efforts and shorter lever throws are achieved by using pilot operated work tool controls resulting in decreased operator fatigue. The 924G/924Gz will have one of several different work tool hydraulic control arrangements depending on the machine configuration. The standard configuration has a joystick pilot valve control lever (1). The joystick pilot valve control lever controls the bucket LIFT and DUMP functions. Additional control levers are used to control the third (3) and fourth (4) functions if the machine is so equipped. Some machines may be equipped with as many as four single function levers. However, the High Lift option will only allow for three functions.
The pilot valves contain normally energized solenoids which hold the lever in detent for the loader FLOAT position, the bucket kickout circuit, the loader lift kickout circuit, or the third function lever "rearward position."
A hydraulic control lock (pilot shutoff) lever is located between the seat and the right console. The lever controls a valve which interrupts the flow of oil to the pilot valves and also deactivates the control lever solenoid detents if moved out of the unlocked position. Fully raise the lever in order to shut off the pilot system. The lever should be all the way on or off, do not leave the lever in the middle position.
1
2
3 4
¥ Solenoids perform detent
The hydraulic control lock lever can be used to prevent a work tool from moving accidentally when maintenance is being performed or to prevent accidental movement of the work tools during roading.
A transmission control (F-N-R) switch (2) can be incorporated into the joystick pilot valve control lever. This switch allows the operator to shift from forward to reverse without releasing the steering wheel.
An optional downshift switch (not shown) is located at the front of the joystick pilot valve control lever.
¥ Right console switches
1. Fan speed switch
2. Temperature control knob 3. Autoshift ON/OFF 4. Ride control ON/OFF/AUTO 5. Kickout ON/OFF 6. Defrost ON/OFF 7. Air conditioning ON/OFF 8. Coupler control switch 13
Shown in this view is the right side console. Switches mounted on the console are used to control certain machine functions. The icon on the switch indicates the function that the switch performs. This location provides better accessibility to these controls. Controls that are located on the right console are autoshift on/off (3), ride control on/off/auto (4), kickout on/off (5), defrost on/off (6), air conditioning (7), temperature control (2) and fan speed switch (1).
A switch (8) controls the engagement and disengagement of the coupler on the 924G. Two actions are required to activate the switch. First, the slide on the switch must be moved forward, then the switch can be activated. This prevents inadvertent decoupling of the work tool. The steering system supplies oil to the control valve for the coupler.
The fan speed switch controls the heating and air conditioning fan speed. The temperature control knob allows the operator to vary the air
temperature from the heating and air conditioning systems. 1 2 3 4 5 6 7 8
¥ Pedals
1. Accelerator
2. Service brake pedals
14
The brake pedals have changed to a suspended pedal from a clip pedal on the 924F/IT24F.
The pedal (1) on the right is the accelerator. The center pedal and the pedal on the left (2) are both service brake pedals. Linkage connects the brake pedals. Depressing either pedal ENGAGES the service brakes and NEUTRALIZES the transmission unless the transmission neutralizer override switch is activated.
The transmission neutralizer is controlled by two pressure switches on the brake control valve.
1 2
¥ Side console
1. Fuses
2. ET Connector
3. Relays
15
All the fuses (1) are located in the operatorÕs station inside the right side door. This helps protect the fuses from outside elements and provides easier access to the fuses.
A diagnostic indicator lamp is located at the bottom of the fuse compartment. The diagnostic indicator lamp can be used to identify active and logged faults.
The diagnostic port connector (2) for electronic technician is located just inside the right door of the cab.
Several relays (3) are located on this panel: Alarm "A" relay, Alarm "B" relay, Park brake light/Seat alarm relay, Park brake alarm relay, Ride control/Load check relay, and the backup alarm relay.
1
3
16
¥ 3056 Engine 1. Engine oil filters
2. Tool box
3. Fuel tank
4. Fuel fill tube
5. Battery disconnect switch
6. Engine oil S¥O¥S port
ENGINE AND ELECTRICAL SYSTEM
The engine is mounted in the rear frame. Doors on each side of the machine allow access to the engine compartment.
The engine in the 924G/924Gz is a Caterpillar 3056T, producing 87 kW (116 hp) to the flywheel, which is a 10% increase in power over the 924F/IT24F. The 3056T will meet the vehicular emissions regulations through the year 2002.
The engine oil filters (1), which have internal check valves to prevent oil leakage during filter changes, are located on the left side of the engine. The fuel tank (3) is located at the rear of the machine below the cooling system. The non-metallic tank prevents fabrication debris and corrosion and is more resistant to leakage. A tool box (2) is located directly above the fuel tank.
1 4 2 3 5 6 7 8
7. Fuel injection pump
8. Fuel-water separator
The fuel fill tube (4) can be accessed with the radiator closed and the right side door open.
The battery disconnect switch (5) is also located on the right side of the machine. The engine oil S¥O¥S port (6) is located on the right side of the engine.
The fuel-water separator (8) is located on the right side of the machine. The 924F/IT24F did not have a fuel-water separator.
The 3056T engine has a different fuel injection pump (7) and different injectors than the 3114 engine. The fuel system configuration in the 924G/924Gz is similar to the current fuel system configuration on the 914G/IT14G.
INSTRUCTOR NOTE: For additional information about the fuel system, see STMG 670 "914G Wheel Loader/IT14G Integrated Toolcarrier" (Form SESV1670).
17
¥ Cooling system
1. Fan drive motor
2. Fan and fan shroud
3. Air conditioning condenser
4. Hydraulic oil cooler
5. Radiator
The 924G/924Gz cooling system is different from that on the 924F/IT24F. The standard cooling system can be used in a wider variety of applications like waste handling, agricultural applications and landfill operations. The non-metallic fan pulls the air through the radiator. The incoming air flows through the screens in the engine compartment access doors. These screens have a vertical weave in order to allow foreign material to drop off the screen when the machine is not operating.
The fan is driven by a hydraulic motor (1), allowing the fan and the fan shroud (2) to be swung away from the radiator. A gear pump, which is shared with the brake system, provides the oil flow which drives the fan drive motor.
The hydraulic oil cooler (4) and the air conditioning condenser (3) are at the front of the radiator and can be swung forward to clean the radiator. The standard hydraulic oil cooler is included in the package with an optional heavy duty hydraulic oil cooler.
2 5
1
3
18
¥ Starting system
This slide shows the wiring schematic for the starting and charging system in the RUN condition.
The red colored wires have battery voltage when the key start switch is in the OFF position. When the key is moved to the "ON" or "START" positions, power flows from the batteries through the auxiliary breaker to the "B"terminal of the key start switch.
Power flows from the "R" terminal on the key start switch through the fuel shutoff resistor to the fuel shutoff solenoid. When the solenoid is energized, the fuel is allowed to enter the fuel injection pump. If the key is moved to the "OFF" position or if there is a loss of electrical power, the solenoid becomes de-energized and the flow of fuel to the pump is
interrupted. COOLANT SWITCH T° 399-OR DISCONNECT SWITCH (OPTIONAL) RESISTOR 396-PK-18 377-OR 310-PU RESISTOR START AID SWITCH FROM LAMP SWITCH FUEL SHUTOFF SOLENOID 10 A 115-RD G S MOTOR MTR BAT CST SHIFTER FIRST GEAR SECOND GEAR THIRD GEAR FOURTH GEAR START RELAY NEUTRAL REVERSE FORWARD + BATTERY GROUND EXTERNAL FWD EXTERNAL REV BACKUP REALY KEY SWITCH IN START RELAY STARTER RD-00 105-RD 307-OR 304-WH 109-RD 306-GN B-B+ D+ 109-RD MAIN RELAY ALTERNATOR KEY START SWITCH 308-YL 117-RD R C S B ST OFF ON ALT. BREAKER 101-RD 30 60 60 109-RD MAIN BREAKER 109-RD AUX. BREAKER 115-RD LAMP BREAKER 15 R
924G STARTING AND CHARGING SYSTEM
POS NEG POS NEG 15 A COLD START ADVANCE MOTOR MOTOR
TO SERVICE METER AND SECONDARY STEERING CONTROL
188-WH 102-RD 112-PU 373-GN COLD START HEATER
Power also flows from the key start switch, to the transmission control lever (CST shifter). If the lever is in the neutral position, power will flow through the shifter to the start relay.
When the start relay is energized, power flows from the batteries, through the alternator breaker and the start relay, to the starter.
The optional start aid system includes the following components: the fifteen amp fuse, start aid switch, cold start resistor, cold start heater, coolant switch and the cold start advance motor. When the key is in the "ON" position, the main relay is energized which connects the cold start system to the batteries.
The charging system includes the following components: the batteries, alternator breaker, alternator and the key start switch.
The "R" terminal on the key start switch provides the "exciting" current to the alternator in order to energize the electro-magnets in the alternator. As the alternator turns, power flows through the alternator breaker to charge the batteries. Power from the alternator also flows through the main breaker and the main relay to the accessories.
¥ Optional start aid system
19
1. Start relay
2. Cold start resistor
3. Fuel shutoff resistor 4. Main breaker 5. Alternator breaker 6. Auxiliary breaker 7. Starter
8. Cold start heater
9. Alternator
Shown in this slide are the major electronic components on the left side of the machine.
The breaker/relay panel is attached to the left side of the hydraulic tank. Included on this panel are the start relay (1), the cold start resistor (2), the fuel shutoff resistor (3), the main breaker (4), the alternator breaker (5), and the auxiliary breaker(6).
The starter (7) is located at the front of the engine compartment on the left side.
The alternator (9) is located at the rear of the engine compartment on the left side. There is a standard alternator and an optional high output alternator.
The cold start heater (8) is also located at the rear of the engine.
2 3 1 4 5 7 6 5 4 9 8
20 1. Transmission control lever 2. Main relay 3. Fuel shutoff solenoid 4. Battery
Shown in this slide are the major elecrical components in the cab and on the right side of the machine.
The transmission control lever (CST shifter) (1) is located on the steering column.
The main relay (2) is located below the fuse panel inside the cab right door.
The fuel shutoff solenoid (3) is on the top of the fuel injection pump. One battery (4) is located on each side of the machine in an enclosed battery box.
1
3
2
21
POWER TRAIN
The power train for the 924G/924Gz is very similar to that of the 924F/IT24F.
The transmission is the same transmission that is used in the 924F/IT24F. The axles use a larger casting. A new mounting of the front axle to the front frame provides a more rigid structure to the machine. An integrated lip was added to the casting to protect the Duo Cone seals in waste handling applications.
The differential and the inboard final drives are the same as those on the 924F/IT24F.
¥ Transmission ¥ Axles
¥ Final drives ¥ Differential
¥ Torque converter - Automotive style - Flex plate
22
Torque Converter and Transmission
One of the changes in the power train is the torque converter. The torque converter on this machine is a automotive type torque converter, similar to those used on other small Caterpillar machines. A flex plate is used on the 924G/924Gz to connect the engine and the torque converter.
23
¥ Same transmission as 924F/IT24F
- Torque converter - Power train pump - Input shaft - FORWARD
HIGH/LOW shaft - REVERSE and
SECOND shaft - THIRD and FIRST
shaft - Output shaft - Parking brake PUMP TORQUE CONVERTER INPUT SHAFT
LOW AND HIGH CLUTCH SHAFT
REVERSE AND SECOND CLUTCH SHAFT
THIRD AND FIRST CLUTCH SHAFT
OUTPUT SHAFT
PARKING BRAKE
924G/924Gz TRANSMISSION
The power shift transmission (countershaft design) provides four FORWARD speeds and three REVERSE speeds. This is the same transmission that is used in the 924F and the IT24F.
The gear-type transmission pump provides oil flow to the transmission control valve and transmission speed and directional clutches.
The transmission has five shafts. The input shaft is driven by the turbine of the torque converter. The FORWARD LOW and FORWARD HIGH clutch shaft and the REVERSE and SECOND clutch shaft are then driven by the input shaft. The third clutch shaft contains the THIRD and FIRST gear speed clutches. The output shaft directs power to the front and rear axles. The shoe-type parking brake is mounted on the transmission output shaft.
INSTRUCTOR NOTE: For additional information about the transmission, see STMG 581 "910E/916F/IT12B/IT14B Power Shift Transmission" (Form SESV1581).
24
¥ Identify components and trace oil flow
PUMP FILTER FLOW CONTROL VALVE CHECK VALVE RELIEF VALVE TORQUE CONVERTER COOLER TRANSMISSION LUBE 3 5 1 2 4 SUCTION SCREEN DIFFERENTIAL VALVE 1 3 4 5 2 CONTROL VALVE 6 DUMP VALVE 6
924G/924Gz POWER TRAIN HYDRAULIC SYSTEM
Power Train Hydraulic System
The power train hydraulic system on the 924G/924Gz is the same as the power train hydraulic system on the 924F/IT24F.
The gear pump is driven by the torque converter impeller through a transfer gear. The filter is externally mounted.
The flow control valve is mounted in the transmission case. The flow control valve sends oil to the transmission control valve and supplies the torque converter with the remainder of the oil.
The transmission control valve controls three directional clutches and three speed clutches. The differential valve, check valve and dump valve are part of the transmission control valve.
The torque converter inlet relief valve is located in the transmission case below the control valve.
¥ Transmission control valve controls: - Three speed clutches - Three directional clutches
The oil-to-water cooler is located in the bottom tank of the radiator. NOTE: The colors in the sectional views and hydraulic schematics throughout this presentation denote various pressures within the system. The legend of color codes is as follows:
Red - Pump supply and P1 pressure
Red and White Stripes - Reduced and P2 pressure
Red Dots - Second reduction of supply pressure
Pink - Third reduction of supply pressure
Orange - Signal, pilot or torque converter oil
Green - Open to tank
Blue - Blocked oil
Yellow - Activated valve envelopes or
moving parts
25 1. Transmission fill tube 2. Transmission oil filter 3. Transmission sight gauge 4. Side cover
The transmission fill tube (1) is on the left side of the machine near the articulation joint. The fill tube contains a dipstick.
The transmission oil filter (2) is on the inside of the frame on the left side of the machine. The filter housing contains a pressure tap to check transmission supply pressure and an S¥O¥S tap for taking transmission oil samples.
The transmission sight gauge (3) and the transmission filter are accessed through the opening behind the steps on the left side of the machine. The transmission sight gauge is on the left side of the machine behind the steps. Maintain the transmission oil level between the LOW mark and the HIGH mark on the sight gauge when the transmission is warm and to the top of the sight gauge when the transmission is cool.
Access to the transmission control valve and pressure taps can be obtained by removing the side cover (4) on the right side of machine.
1
3
2
¥ Identify components: 1. Dump valve
¥ Identify pressure tap locations: 2. Torque converter outlet 3. P1 4. P2 5. P3 26 2 4 5 3 1
Shown in this view is the transmission control valve mounted on the transmission. A dump valve (1) is mounted to the control valve. Three pressure taps are provided on the transmission control valve for checking P1 speed clutch pressure (2), P2 directional clutch pressure (4) and P3 torque converter inlet pressure (5).
27 ¥ Valve components 3 3 2 1 2 1 4 6 4 6 5 5 DIFFERENTIAL VALVE FWD HIGH FWD HI FWD LO REV 1ST SPD 2ND SPD 3RD SPD 2ND SPEED 3RD SPEED 1ST SPEED SELECTOR SPOOL DUMP SPOOL ORIFICE PISTON SLUG MODULATING RELIEF VALVE BACK FLOW CHECK VALVE PUMP SUPPLY LOAD PISTON ORIFICE CHECK VALVE
TRANSMISSION CONTROL VALVE
NEUTRAL
FWD LOW REV
The 4F/3R transmission control valve has six solenoids which control three directional clutches and three speed clutches. The transmission control valve also contains the following components: speed and
directional spools, dump valve, backflow check valve, differential valve, modulating relief valve and load piston, and orifice check valve.
Loss of electrical power to any speed or directional solenoid will prevent that particular clutch from engaging.
The transmission control valve for the 924G/924Gz is very similar to the transmission control valve that was used on the 924F/IT24F.
INSTRUCTOR NOTE: For more detailed information about the operation of the transmission control valve, Technical Instruction Module "Electronically Controlled Power Shift Transmission Control Valve" (Form SEGV2572).
- Loss of electrical power prevents shifting
28 ¥ Electronic transmission control system components SOLENOID SOLENOID SOLENOID SOLENOID SOLENOID SOLENOID DIAGNOSTIC INDICATOR TRANSMISSION NEUTRALIZER OVERRIDE SWITCH SHIFT LEVER TRANSMISSION NEUTRALIZER SWITCH SERVICE CONNECTOR AUTO/MANUAL SWITCH HARNESS CODE CONNECTOR ENGINE SPEED SENSOR TRANSMISSION SPEED SENSOR TRANSMISSION
ELECTRONIC TRANSMISSION CONTROL SYSTEM
RIDE CONTROL/LOAD CHECK SWITCH PARK BRAKE SWITCH DOWNSHIFT SWITCH F-N-R SWITCH SPEEDOMETER ELECTRONIC CONTROL MODULE PARK BRAKE ALARM RELAY RIDE CONTROL LOAD CHECK RELAY
Electronic Transmission Control System
This graphic shows a block diagram for the electronic transmission control system. The electronic control module (ECM) receives inputs from the operational controls, harness code, and sensors. Based on the inputs that it receives, the ECM shifts the machine, activates relays or sends signals to the diagnostic indicator .
The electronic transmission control system inputs consist of the following components:
Shift lever - allows the operator to choose transmission speed and direction Downshift switch - allows the operator to manually
downshift the transmission
Neutralizer switch - neutralizes the transmission when the operator ENGAGES the service brakes
The electronic control system outputs consist of the following components:
INSTRUCTOR NOTE: This electronic control system is similar to that on the 928G/IT28G. For more information, refer to STMG 694 "928G Wheel Loader/IT28G Integrated Toolcarrier" (Form
SESV1694).
Neutralizer override switch - overrides the transmission neutralizer switch
Auto/Manual switch - ON/OFF switch for the electronic transmission control system Transmission speed sensor - indicates transmission speed Engine speed sensor - indicates engine speed
Transmission solenoids - control transmission speed and direction
Ride control/load check switch
- OFF/ON/AUTO switch for ride control
Park brake switch - neutralizes the transmission when the parking brake is ENGAGED
F-N-R switch - allows the operator to change the transmission direction
Diagnostic indicator - flashes fault codes
Park brake alarm relay - alerts the operator if the park brake is on during operation
Ride control/load check relay - activates/deactivates the ride control system
Speedometer - indicates machine speed to the
29 ¥ Operational inputs and ECM 1. Transmission control lever 2. Transmission control (F-N-R) switch 3. Downshift button 4. Pressure switches 5. Electronic control module (ECM)
Shown in these views are the main operational input mechanisms and the ECM.
The transmission control lever (1) is identical to the lever that is used in the 928G/IT28G.
A transmission control (F-N-R) switch (2) is an option. This switch is integrated into the joystick control lever if the machine is equipped with this option. The downshift button (3) is on the front of the joystick control lever.
The transmission neutralizer on the 924G/924Gz uses two pressure switches (4) located on the brake valve instead of one mechanical switch which was used on the 924F/IT24F. Using two pressure switches
provides smoother neutralization of the transmission when the brakes are applied and smoother engagement of the transmission when the brakes are released.
The ECM (5) is located under the cab on the right side. 1
4
3
2
¥ Axle contains inboard planetary final drives
30
Axles
The axles contain inboard planetary final drives. The front axle is fixed to the frame, but the pinned rear axle allows 15¡ oscillation in each direction with 15.5 or 17.5-25 tires.
The axles are an oversize casting to allow for future brake improvements. A new mounting of the front axle to the front frame gives a more rigid structure to the machine. An integrated lip was added to the casting to protect the Duo Cone seals in waste handling applications.
31
¥ Axle similar to other wheel loaders
FRONT / REAR AXLE
INBOARD PLANETARY BEVEL GEAR AND PINION DIFFERENTIAL SUN GEAR SHAFT AXLE
The axle is similar to the axles on other Caterpillar Wheel Loaders. The standard axle contains a conventional differential and fully enclosed wet disc brakes with a single disc for each wheel. The axle can be ordered with a limited slip differential. A NoSPIN differential is available for special orders.
The transmission output shaft transmits power to the bevel pinion shaft and bevel gear and pinion assembly in the front and rear axles. The bevel gear and pinion assembly transfers power to the differential. The
differential transmits power to the sun gear shafts. The sun gear shafts transmit power to the inboard planetaries. The motion of the planet carriers causes the axle shafts to rotate.
- Optional limited slip differential
- NoSPIN differential available
¥ Power flow: - Drive shaft
- Bevel pinion shaft - Differential
- Sun gear shaft - Planet gears - Planet carriers - Axle shaft
¥ Parking Brake
32
The transmission is neutralized when the parking brake is applied. This neutralizer is a mechanical switch and can be overridden. The parking brake transmission neutralizer switch is the same as that used on the 928G/IT28G.
¥ Three hydraulic systems
- Steering system - Brake/fan drive - Work tool hydraulic
system
33
HYDRAULIC SYSTEMS
There are three major hydraulic systems on the 924G/924Gz: the steering system, the brake system/fan drive system, and the work tool hydraulic system. All three systems share a common hydraulic tank.
The steering system and the brake/fan drive hydraulic system on the 924G/924Gz are very similar to those on the 928G/IT28G. The work tool hydraulic system, however, is different.
34
¥ Vented hydraulic tank 1. Clean-out hole
2. Sight glass
3. Hydraulic oil filter
4. Ecology drain
All three hydraulic systems share a common tank which is located behind the cab. The tank has changed from a pressurized tank to a vented tank. Also, a large clean-out hole (1) in the tank allows for easier flushing and cleaning for service.
The sight glass (2) on the hydraulic tank has been moved to the left side of the tank on the outside of the machine. This makes the sight glass easier to check during maintenance.
The hydraulic oil filter (3) on the 924G/924Gz is plumbed into the fan drive system and is located in front of the cooling package. The S¥O¥S port is part of the filter base. This filtration system is similar to the 928G/IT28G.
The ecology drain (4) function is now provided by a manual shut-off valve. This valve is located on the left side of the machine at the front of the engine access door.
1
3
2
¥ Work tool hydraulic system
- Closed center valves in parallel
- Variable flow axial piston pump
35
Work Tool Hydraulic System
The pilot operated work tool hydraulic system on the 924G/924Gz is very different from the previous hydraulic system. The 924F/IT24F machines use an interrupted series flow hydraulic system with open center, pilot operated control valves and a fixed displacement pump. The
924G/924Gz machines use a parallel flow hydraulic system with closed center, pilot operated control valves and a load sensing, variable flow axial piston pump. The improvements have been made to the hydraulic system in order to increase the versatility of the 924G.
The tilt circuit of the 924G is different from the tilt circuit of the 924Gz. With the Versa Link©linkage on the 924G, extending the cylinder will tilt the work tool forward and retracting the cylinder will rack the work tool back.
¥ 924Gz tilt circuit
36
On the 924Gz, the tilt cylinder must extend in order to tilt the bucket back and retract to dump the bucket.
The 924Gz and the 924G both benefit from the improved hydraulic system. The load sensing system only consumes horsepower from the engine when needed. The load check poppets in each bank valve allow almost zero drift and there is almost zero voiding in the cylinders.
37
¥ Work tool hydraulic system for 924G
The work tool hydraulic system on the 924G and the 924Gz consist of the following components: WORK TOOL PUMP STEERING PUMP FROM BRAKE/FAN DRIVE SYSTEM TO SECONDARY STEERING PRESSURE SWITCH MANIFOLD SIGNAL FROM STEERING SYSTEM COUPLER CONTROL VALVE PRESSURE REDUCING VALVE BACK PRESS. VALVE SINK VALVE
PILOT CONTROL VALVES
TO AUXILIARY FUNCTION TO AUXILIARY FUNCTION OPTIONAL RIDE CONTROL SYSTEM LIFT CYLINDERS COMBINATION VALVE TILT CYLINDER
924G WORK TOOL
HYDRAULIC SYSTEM
TO STEERING SYSTEM FROM BRAKE PISTONS AUXILIARY CONTROL VALVE AUXILIARY CONTROL VALVE LIFT CONTROL VALVE TILT CONTROL VALVEWork tool pump - Provides flow to the bank valves Steering pump
Pressure reducing valve
- Provides flow to the pressure reducing valve and the steering system
- Limits the maximum pressure of the pilot oil
Pilot control valves - Control the flow of pilot oil to the bank valves
- Control the flow of supply oil to the cylinders or the work tools
Bank valves
Ride control system - Functions as a shock absorber by cushioning the ride at high speeds Sink valve - Drains the oil from the signal network
when none of the bank valves are activated
The following components are on the 924G only: Coupler control valve
Coupler engagement cylinders Back pressure valve
- Controls the flow of oil to the coupler engagement cylinders
- Move the engagement pins on the work tool coupler
- Maintains a small amount of pressure in the return galley of the valve bank in order to assist in the opening of the makeup valves
Combination valve - Performs the relief function on the head end of the tilt cylinder
38
¥ Work tool hydraulic system for 924Gz
This view shows a block diagram of the 924Gz work tool hydraulic system. The machine is not equipped with a coupler control valve, coupler engagement cylinders or a combination valve.
Since the 924Gz tilt circuit is configured differently, the combination valve is not necessary.
WORK TOOL PUMP STEERING PUMP FROM BRAKE/ FAN DRIVE SYSTEM TO SECONDARY STEERING PRESSURE SWITCH MANIFOLD FROM STEERING SYSTEM PRESSURE REDUCING VALVE BACK PRESS. VALVE SINK VALVE
PILOT CONTROL VALVES
TO AUXILIARY FUNCTION TO AUXILIARY FUNCTION OPTIONAL RIDE CONTROL SYSTEM LIFT CYLINDERS TILT CYLINDER
924Gz WORK TOOL
HYDRAULIC SYSTEM
TO STEERING SYSTEM TILT CONTROL VALVE LIFT CONTROL VALVE AUXILIARY CONTROL VALVE AUXILIARY CONTROL VALVE FROM BRAKE PISTONS¥ Hydraulic pumps 1. Steering pump
2. Work tool pump
3. Signal pressure tap for steering pump
4. Signal pressure tap for work tool pump
39
The work tool hydraulic pump (2) has changed from a vane pump to a variable displacement axial piston pump. The steering (1) and work tool pumps are located under the left side of the cab, which is in the same area as the pumps on the 924F/IT24F. The steering pump is mounted onto the work tool pump.
The signal pressure taps (3) and (4) are located on the compensator valves for the steering and work tool pumps.
There are separate suction lines for the work tool and steering pumps. 1 3 2 4 - Separate suction lines
40
¥ Load sensing work tool hydraulic system and steering system use variable
displacement pumps
This view shows a cross sectional view of the work tool pump or the steering pump. These pumps are variable displacement axial piston pumps and are similar to the variable displacement pumps on other Caterpillar machines.
The pump has one swashplate actuator piston which adjusts the angle of the swashplate.
The compensator valve controls the flow of oil to the swashplate control piston and thereby controls the pump output. Inside the compensator valve are the margin spool and the cutoff spool.
The margin spring maintains the pump supply pressure higher than the signal pressure. The cutoff spring controls the maximum system pressure. The work tool pump provides flow for only the bank valves. The steering pump provides flow for the pilot system and the steering system.
MARGIN
SPRING MARGIN SPOOL
ACTUATOR PISTON BIAS SPRING SWASHPLATE SIGNAL PUMP OUTPUT CONSTANT FLOW
PUMP OPERATION
CUTOFF SPRING CUTOFF SPOOL - Steering pump provides pilot oil flowNOTE: Depending on the adjustments made to the margin spool and the amount of pump leakage, LOW PRESSURE STANDBY and margin pressure can be equal. However, margin pressure can never be higher than LOW PRESSURE STANDBY.
INSTRUCTOR NOTE: This pump is similar to the implement hydraulic pump on the Challenger 35/45/55 Agricultural Tractors. For information on the operation of this pump, see STMG 667-01 "Challenger 35/45/55 Agricultural Tractors--Implement, Hitch and Steering Systems" (Form SESV1667-01).
1. Pressure reducing valve
2. Combination valve
3. Pilot oil pressure tap
4. Steering system pressure tap
5. Tilt head end pressure tap
6. Tilt rod end pressure tap
41
The pressure reducing valve is located on the right side of the machine under the cab. Oil flows from the steering pump to the pressure reducing valve (1). The reduced pressure oil is the pilot oil.
The pressure reducing valve limits the maximum pressure in the pilot system. This is the same pressure reducing valve as that used in the 924F/IT24F.
The pilot oil pressure tap (3) and the steering system pressure tap (4) are located on the pressure reducing valve.
The combination valve (2) is located next to the pressure reducing valve. The combination valve is only on the 924G and consists of both a diverter valve and a relief valve. This valve performs the relief function for the head end of the tilt cylinder on the 924G.
The tilt head end pressure tap (5) and the tilt rod end pressure tap (6) are located on the combination valve.
1 2 3 4 5 6
¥ Pilot Control Valves
42
From the pressure reducing valve, pilot oil flows through a screen to the pilot control valves. This screen was not used on the 924F/IT24F. The pilot control valves are located in the right side console inside the cab.
The pilot control valves have been designed to allow for less lever effort. They operate in the same manner as the pilot control valves on the 924F/IT24F. The pilot control valves control the flow of pilot oil to the bank valves.
NOTE: There is no longer a mechanical lock on the pilot valve for the third function of the hydraulic system. The lock was used to prevent accidental uncoupling of the work tool. But, since this lever does not control the work tool coupler, the lock on this lever is not necessary. The work tool coupler is controlled by a switch on the right console.
- Location
43
¥ Bank valves From the work tool pump, the oil flows to the closed center, pilot operated bank valves. Shown here is an individual bank valve.
The bank valves control the flow of hydraulic oil from the implement pump to the cylinders. The valves also send signal oil back to the work tool pump.
Each bank valve operates differently, but all of the valves share the same basic components.
A common galley carries pressure oil from the work tool pump to all the bank valves. Also, a common galley carries return oil away from the bank valves to the tank.
Resolvers determine which function in all of the valves has the highest demand. Then, the signal for the highest demand is sent to the pump. The resolvers are double check valves containing two balls.
RETURN GALLEY
SIGNAL NETWORK SUPPLY GALLEY DRAIN PASSAGE
COMBINATION VALVE TILT CONTROL
CALVE AREA CONTROL SPOOL AREA CONTROL SPOOL POPPET POPPET RESOLVER RELIEF VALVE MAKEUP VALVE CHECK VALVE MAIN CONTROL SPOOL SINK VALVE
924G TILT CONTROL VALVE
TILT BACK INLET MANIFOLD TO TANK SIGNAL TO COMPENSATOR VALVE FROM PUMP FROM PILOT
CONTROL VALVE CONTROL VALVETO PILOT TO TANK
- Control flow to the cylinders
¥ Common components
- Pressure galley
- Return galley
Each valve has two poppets which act as a lock valve. The poppets close off the ports so that there is almost zero drift of the work tools when the bank valve is in the HOLD position. Passages in the poppet allow a restricted amount of oil to flow from the port in the valve to the back side of the poppet.
Every poppet is controlled by an area control spool that is located directly behind the poppet. Pilot oil opens these spools by forcing the spool upward. Moving the spool upward opens the back side of the poppet to the tank. The poppet is opened by the area control spool in order to allow return oil to flow from the port to the main control spool.
The main control spool is controlled by pilot oil from the pilot control valves. The spool is machined differently for each bank valve.
- Main control spool - Area control spools - Poppets
44
¥ Bank valve components
This view shows the components of the tilt control valve for the 924G.
POPPET RESOLVER MAIN CONTROL SPOOL PRESSURE GALLEY RETURN GALLEY AREA CONTROL SPOOL
45
During the dump cycle, the tilt control valve on the 924G regenerates return oil from the rod end of the cylinder and sends it to the head end of the cylinder. This regenerated oil flows through the pressure galley and is equal to pump output pressure. The result is that the pressure on both sides of the piston is equal to the pressure in the pressure galley. Pressure equalization prevents the head end of the tilt cylinder from voiding, resulting in a powered dump rather than the bucket dumping due to the force of gravity. During simultaneous lift and dump operations, this action also provides additional supply oil so both the tilt and lift circuits operate smoothly. Without pressure equalization, the pump would not be able to mee the flow needs of both circuits, resulting in the lift function to be slower than desired.
The tilt control valve for the 924G is the only valve that regenerates oil and equalizes pressure.
MAIN CONTROL SPOOL RESOLVER AREA CONTROL SPOOL ORIFICE RETURN GALLEY ROD END PORT HEAD END PORT POPPET
924G TILT CONTROL VALVE
DUMP
SUPPLY GALLEY
¥ Tilt control valve for 924G - Regeneration of return oil - Pressure equalization in cylinder with pressure galley
¥ Dump Operation - Spool
To begin the dump cycle, pilot oil flows into the right end of the spool. The spool starts to shift to the left, connecting the pressure oil passage to the left poppet and the right poppet.
Pilot oil also flows through an orifice to the bottom side of the right area control spool and the area control spool shifts upward. The oil from the back side of the right poppet begins to flow to the return passage in the valve to be regenerated.
At the same time, supply oil flows past the spool and encounters the resolver which is next to the poppet. If the pressure oil in the valve is at a higher pressure than the pressure in the signal passage, the ball unseats and the oil signals the pump to upstroke to meet the flow demand. If the pressure oil in the valve is at a lower pressure than the signal passage, the pump will already be upstroked by another circuit, but the pump will upstroke more to meet the additional flow demand of the tilt circuit. The left poppet is opened by the supply oil and oil flows out to the head end of the cylinder.
As supply oil flows out to the cylinder, the pressure of the return oil increases. Return oil flowing through the right poppet causes a pressure drop across the poppet and it opens.
Now, system pressure is open to both the rod end and the head end of the tilt cylinder. The bucket dumps because of two factors: the effective area of the head side of the piston is greater than the effective area of the rod side of the piston and the weight of the load and the bucket. These two forces cause the cylinder to extend and the bucket dumps.
Pressure oil flows out to the head end of the cylinder. Return oil flows back from the rod end of the cylinder and is sent through the pressure oil passage to the head end of the cylinder. Oil from the back side of the right poppet also flows into the passage that is between the right poppet and the spool. In this manner, nearly all of the return oil is regenerated.
- Regeneration of oil - Pressure equalization - Right poppet - Left poppet - Resolver
46
¥ Tilt back operation During tilt back, the valve does not regenerate return oil, nor are the pressures equalized on each side of the piston in the cylinder.
Pilot oil flows into the left end of the spool. The spool starts to shift to the right. This connects the pressure oil passage to the right poppet and the return passage to the left poppet.
Pilot oil also flows through the orifice to the bottom side of the left area control spool and the area control spool shifts upward. The oil from the back side of the left poppet to begins to return to tank.
The pressure oil flows past the spool and encounters the resolver which is next to the poppet. The resolver senses the oil pressure and sends the appropriate signal to the pump. The pump upstrokes because of the increase in the flow demand.
MAIN CONTROL SPOOL RESOLVER AREA CONTROL SPOOL ORIFICE RETURN GALLEY ROD END PORT HEAD END PORT POPPET
924G TILT CONTROL VALVE
TILT BACK
SUPPLY GALLEY
- Resolver - Spool
- Right poppet The right poppet is opened by the supply oil and oil flows out to the rod
end of the cylinder.
As supply oil flows out to the cylinder, the pressure of the return oil increases. Return oil flowing through the left poppet causes a pressure drop across the poppet and it opens. Return oil flows from the head end of the cylinder to tank.
Supply oil continues to flow past the right poppet and out to the cylinder. Return oil flows past the left poppet. The cylinder retracts and the bucket tilts back.
47
¥ Pressure relief and makeup valves
The tilt control valve on the 924G also includes a pressure relief valve and a makeup valve.
The direct acting pressure relief valve is connected to the rod end of the tilt control cylinder. It is in parallel to the shoulder of the rod end poppet in the valve.
The makeup valve is connected to the head end of the tilt control cylinder. This valve is in parallel to the shoulder of the head end poppet in the valve. The makeup valveÕs purpose is to provide oil to the head end of the cylinder during dumping operations when extra supply oil is needed.
MAKEUP VALVE RELIEF VALVE
- Makeup - Pressure relief
48
¥ Combination valve Plumbed into the tilt control cylinder on the 924G is a combination valve
with a diverter valve and a relief valve. The combination valve performs the relief function on the head end of the cylinder during backdragging. This slide shows the combination valve during a back drag operation. The bucket is forcing the cylinder piston in, thus causing a void on the rod end and pressure on the head end of the cylinder.
The spool in the diverter valve is connected to each end of the tilt
cylinder. The function of the diverter is to sense the pressure differential between the head end and the rod end of the cylinder. If the pressure differential exceeds 3000 KPa (435 psi), the diverter opens and oil from the head end of the cylinder flows to the relief valve. If the pressure on the relief valve exceeds 12,300 KPa (1780 psi), the relief valve opens and the oil is returned to tank.
The reason for the diverter valve is to keep the relief valve setting low and yet allow for the high pressures needed for the pressure equalization of the tilt circuit during the dump operation.
COMBINATION DIVERTER/RELIEF VALVE
BACK DRAG OPERATION
TILT CYLINDER
¥ Ride control system
49
Shown here is the ride control valve. This valve is located at the bottom of the frame on the left side of the machine.
The optional ride control system on the 924G/924Gz is very similar to the ride control system on the 924F/IT24F. However, the new auto ride control system is factory set to activate at 8 km/h (5 mph).
The auto ride activation speed is now programmable. The Electronic Technician (ET) service tool can be used to select an activation speed between 5 and 15 km/h (3 and 9 mph). This customizes the ride control activation to the job site and allows the operator to concentrate more on operating the machine rather than turning ON or OFF the ride control system.
¥ Ride control accumulator
50
The ride control system uses one accumulator (arrow). This accumulator is located on the left side of the machine.
A floating piston in the ride control accumulator separates the oil from the nitrogen gas. Since nitrogen gas is compressible, the gas serves as a spring. Any downforce on the lift arms is transferred through the oil at the head end of the lift cylinders to the accumulator. The force in the oil is transmitted to the accumulator piston, which compresses the nitrogen gas. Compressing the nitrogen gas absorbs the pressure spike and the oil displacement caused by the downward force on the lift arms. This operation results in less ground induced shocks on structures and components, reduced tire flexing and a greater payload retention.
51 ¥ Steering system components - Steering pump - Steering metering pump - Steering cylinders - Secondary steering system Steering System
The hydraulic steering system steers the machine by changing the machineÕs angle of the articulation.
The steering system consists of the following components: steering pump, steering metering pump and steering cylinders. A secondary steering system is an option on this machine.
The basic operation of the steering system has not changed from the 924F/IT24F. However, some modifications to the components of the system have improved the steering performance of the 924G/924Gz. INSTRUCTOR NOTE: The steering system is similar to that on the 928G/IT28G. For more information, refer to STMG 694 "928G Wheel Loader/IT28G Integrated Toolcarrier" (Form SESV1694).
METERING SECTION CONTROL VALVE SECTION CROSSOVER LINE RELIEF VALVES SUPP. STEERING PUMP IMPLEMENT PUMP STEERING METERING PUMP LEFT STEERING CYLINDER RIGHT STEERING CYLINDER
LOAD SENSING STEERING SYSTEM
M RELIEF VALVE STEERING PUMP TO IMPLEMENT VALVES TO PILOT SYSTEM FROM BRAKES RIGHT TURN
¥ Steering pump 1. Variable
displacement axial piston pump
2. Signal pressure tap
52
The steering pump (1) provides flow to the steering cylinders. The steering pump is a variable displacement axial piston pump. The steering metering pump sends a signal to the pump and the pump upstrokes or destrokes to meet the flow demand.
The steering pump is located on the left side of the machine under the cab and is driven by the implement pump.
Signal pressure tap (2) is located on the compensator valve. The steering pump output pressure tap is located on the pressure reducing valve. This is the same style of variable displacement piston-type pump as the work tool hydraulic pump.
1 2
¥ Steering metering pump components: - Control valve
section
- Metering section - Crossover line relief
and makeup valves - Check valves
53
The steering metering pump (arrow) controls the flow of oil from the steering pump to the steering cylinders. The steering metering pump is located under the front of the cab.
The steering metering pump consists of a control valve section, a metering section, crossover line relief and makeup valves, and a check valve. A mechanical linkage connects the steering wheel to the control valve and metering sections of the steering metering pump.
The new steering metering pump allows for a wider range of modulation. This provides smoother steering and better control of the machine.
¥ Steering cylinders
54
The steering cylinders change the machineÕs angle of articulation. A steering cylinder is located on each side of the articulation joint of the machine.
The pins and bores on the steering cylinders have been made longer on the 924G/924Gz than on the 924F/IT24F. Also, the bosses for the steering cylinders are thicker. These changes will decrease the contact stresses in the cylinders and increase the pin bore life.
- Located on each side of the machine - Pins and bores
¥ Supplemental steering system
1. Hydraulic pump
2. Electric motor
55
A secondary steering system is an option on the 924G/924Gz which allows the operator to continue to steer the machine if the engine fails or the steering pump stops. The system consists of a hydraulic pump (1) that is driven by an electric motor (2), which are located below the cooling package in front of the fuel tank. The ECM controls the motor through a relay.
If the steering pressure drops, a signal from the control module closes a contact and the secondary steering pump starts. The secondary steering motor, relay and pump are located at the rear of the machine in front of the fuel tank.
The secondary steering system is retrofittable onto a 924G/924Gz. The secondary steering system has a manual test and an auto test to ensure correct operation. The auto test consists of a three second test when the start key is in the ON position, prior to turning over the engine. During the test, the operator should steer the machine and confirm that the system works properly.
1 2
- Operation
- Retrofittable
- Manual test and auto test
56
¥ Brake hydraulic system
- Identify components
Brake/Fan Drive System
The brake hydraulic system maintains the hydraulic pressure necessary to apply the service brakes. The major components of this system are: the pump, the brake accumulator charging valve group, the accumulators, the brake control valve and the brake pistons (located in the axle).
This hydraulic system also powers the cooling fan. Therefore, it will be referred to as the brake/fan drive system.
The brake/fan drive system is a new design feature on the 924G/924Gz. However, this system is similar to the brake/fan drive system that is used on the 928G/IT28G.
INSTRUCTOR NOTE: The brake/fan drive system is similar to that on the 928G/IT28G. For more information, refer to STMG 694 "928G Wheel Loader/IT28G Integrated Toolcarrier" (Form SESV1694). FRONT BRAKE ACCUMULATOR REAR BRAKE ACCUMULATOR TANDEM BRAKE VALVE REAR AXLE BRAKES FRONT AXLE BRAKES PRIORITY VALVE MOTOR GROUP ENGINE FAN FILTER RELIEF VALVE SHUTTLE VALVE CHECK VALVE BRAKE AND FAN PUMP COOLER
BRAKE SYSTEM
CUT-IN/BRAKES RELEASEDCUT IN/CUT OUT VALVE ACCUMULATOR CHARGING
VALVE
