Direccion

HOLD

CROSSOVER RELIEF VALVES

HAND METERING UNIT (HMU)

FLOW CONTROL VALVE SECONDARY STEERING PUMP STEERING HYDRAULIC TANK OIL FILTER STEERING PUMP MAGNETIC SWITCH ELECTRONIC CONTROL MODULE ACCUMULATOR STEERING CYLINDERS STEERING SYSTEM MAIN RELIEF FLOW SWITCH CHECK VALVE CHECK VALVE

Service Training

MALAGA

777D Off Highway Truck

Adolfo

August 1997

VII STEERING.

1. Components Layout

2. Operation

3. Maintenance

CHAPTER : STEERING

TYPICAL OFF-HIGHWAY TRUCK STEERING

COMPONENT LOCATIONS

CHAPTER : STEERING

777D Off Highway T

ruck

METERING UNIT (HMU)

FLOW CONTROL VALVE SECONDARY STEERING PUMP STEERING HYDRAULIC TANK OIL FILTER STEERING PUMP MAGNETIC SWITCH ELECTRONIC CONTROL MODULE ACCUMULATOR STEERING CYLINDERS

STEERING SYSTEM

CHAPTER : STEERING

777D Off Highway T

ruck

METERING UNIT (HMU)

FLOW CONTROL VALVE SECONDARY STEERING PUMP STEERING HYDRAULIC TANK OIL FILTER STEERING PUMP MAGNETIC SWITCH ELECTRONIC CONTROL MODULE ACCUMULATOR STEERING CYLINDERS

STEERING SYSTEM

CHAPTER : STEERING

777D Off Highway Truck

VI-4 Page:

TO

HMU

FROM PUMP

FROM

SECONDARY

STEERING PUMP

TO

TANK

MAIN

RELIEF

VALVE

FLOW

CONTROL

ORIFICE

FROM

HMU

CHECK VALVE

CHECK

VALVE

CHECK

VALVE

STEERING FLOW

CONTROL VALVE

FLOW SWITCH

CLOSED

CHAPTER : STEERING

777D Off Highway T

ruck

TORSION BAR

ROTATING

GEAR

COMMUTATOR

STATIONARY

GEAR

VALVE SPOOL

DRIVE

LINK

INPUT SHAFT

TO

TANK

CYLINDER

TO

TO

CYLINDER

FROM

PUMP

BALL IN

HELICAL

GROOVE

HAND METERING UNIT

HOLD

CHAPTER : STEERING

777D Off Highway T

ruck

COMMUTATOR

LEFT TURN

TORSION BAR

ROTATING

GEAR

STATIONARY

GEAR

VALVE SPOOL

DRIVE

LINK

INPUT SHAFT

TO

TANK

FROM

CYLINDER

TO

CYLINDER

FROM

PUMP

HAND METERING UNIT

CHAPTER : STEERING

777D Off Highway T

ruck

VI-7

RIGHT TURN

HAND METERING UNIT

TORSION BAR

ROTATING

GEAR

COMMUTATOR

STATIONARY

GEAR

VALVE SPOOL

DRIVE

LINK

INPUT SHAFT

TO

TANK

FROM

CYLINDER

TO

CYLINDER

FROM

PUMP

BALL

CHAPTER : STEERING

777D Off Highway Truck

VI-8 Page: CROSSOVER RELIEF VALVES HAND METERING UNIT

CROSSOVER RELIEF SYSTEM

CHAPTER : STEERING

VI-9 Page:

LAB EXERCISES

LAB A: STEERING SYSTEM COMPONENT IDENTIFICATION

Directions: Place the correct letter or number next to the component and briefly describe the function of each.

Steering System Components

Flow Control Valve and Flow Switch

Hand Metering Unit

Oil Filter

Steering Pump

Secondary Steering Electronic Control Module

Secondary Steering Magnetic Switch

Secondary Steering Pump

Crossover Relief Valves

Accumulator (777D truck only)

CHAPTER : STEERING

777D Off Highway Truck

VI-10 Page:

LAB EXERCISES

LAB B: STEERING SYSTEM TESTING

Machine Model __________________________ Date_______________________________ Serial Number ___________________________ Technician___________________________

VISUAL CHECKS:

Oil level _______________ Oil Viscosity _______________ Oil leaks ? ______________ Air/Water in Oil ?_______ Suction Screen Debris ? _______ Oil Filter Examination ______

PRESSURE TESTS

TEST SPECIFICATIONS ACTUAL

Full Cycle Time at High Idle

Main Relief Valve Pressure (Left Turn) at High Idle Main Relief Valve Pressure (Right Turn) at High Idle Crossover Relief Valve (Left Turn) at Low Idle Crossover Relief Valve (Right Turn) at Low Idle Accumulator Charge Pressure

SECONDARY STEERING SYSTEM TEST

The truck should be on flat level ground with the parking brake engaged. Turn the ignition switch ON (engine off) and actuate the secondary pump automatic/manual switch to the MANUAL position. Then, attempt to turn the steering wheel. You should be able to hear the secondary pump motor run and the front wheels of the truck should turn.

CHAPTER : STEERING

LAB EXERCISES

METERING UNIT (HMU)

FLOW CONTROL VALVE SECONDARY STEERING PUMP STEERING HYDRAULIC TANK OIL FILTER STEERING PUMP ACCUMULATOR STEERING CYLINDERS CROSSOVER RELIEF VALVES HAND

METERING UNIT (HMU)

FLOW CONTROL VALVE SECONDARY STEERING PUMP STEERING HYDRAULIC TANK OIL FILTER STEERING PUMP ACCUMULATOR STEERING CYLINDERS

LAB C: TRACING STEERING SYSTEM OIL FLOW

I. Directions: Have each student trace the flow of oil during the conditions listed below

using different colored pencils to show each path: • Steering system when the steering wheel is stationary

CHAPTER : STEERING

777D Off Highway Truck

VI-12 Page:

LAB EXERCISES

LAB C: TRACING STEERING SYSTEM OIL FLOW (CONT.)

II. Directions: Have each student trace the flow of oil during the conditions listed below

using different colored pencils to show each path: • Flow control valve under normal conditions

• Flow control valve when the secondary steering system is in operation

CHAPTER : STEERING

VI-13 Page:

LAB EXERCISES

LAB D: STEERING SYSTEM TROUBLESHOOTING

Machine Model __________________________ Date_______________________________ Serial Number ___________________________ Technician___________________________

VISUAL CHECKS:

Oil level _______________ Oil Viscosity _______________ Oil leaks ? ______________ Air/Water in Oil ?_______ Suction Screen Debris ? _______ Oil Filter Examination ______

PRESSURE TESTS

TEST SPECIFICATIONS ACTUAL

Full Cycle Time at High Idle

Main Relief Valve Pressure (Left Turn) at High Idle Main Relief Valve Pressure (Right Turn) at High Idle Crossover Relief Valve (Left Turn) at Low Idle Crossover Relief Valve (Right Turn) at Low Idle Accumulator Charge Pressure

CHAPTER : STEERING

777D Off Highway Truck

VI-14 Page:

POST TEST

Off-Highway Trucks Steering System Posttest I. Directions: Match the component to the correct statement below.

1. Crossover Relief Valves 5. Steering Hydraulic Tank 2. Oil Filter 6. Secondary Steering Pump 3. Flow Control Valve 7. Flow Switch

4. Hand Metering Unit 8. Accumulator Dampens pressure surges in the steering system.

Contains an oil filter.

Contains a check valve to prevent pressure surges from the steering cylinders from returning to the HMU when a turn is in progress.

Meters and redirects oil to the steering cylinders as the steering wheel is turned.

Equalizes the pressure in both steering cylinders if the pressure in one cylinder exceeds the relief valve setting.

Utilizes a bypass valve to protect the steering system during cold oil start-up. Is energized by a magnetic switch.

Indicates to the electronic control module a loss of oil flow.

II. Directions: Indicate whether the statement is True or False by circling the corresponding

letter.

1. The secondary steering motor is tested every time the ignition switch is turned to the ON position. (T) or F

2. The crossover relief valve pressure setting is higher than the setting of the main steering relief valve (in the flow control valve). (T) or F

3. The crossover relief valves should be checked at low idle and are adjustable. T or (F) 4. When the steering wheel is stationary, steering oil circulates through the Hand Metering

Unit (HMU), back to the steering hydraulic tank, and oil flow is blocked to and from the steering cylinders. (T) or F

5. All truck models are equipped with an accumulator that uses a nitrogen gas charge to cushion the steering system from pressure surges. T or (F)

CHAPTER : STEERING

VI-15 Page:

POST TEST

III. Directions: Match the components with the associated letter. STEERING SYSTEM

Flow Control Valve Hand Metering Unit

Oil Filter Steering Pump

Crossover Relief Valves Steering Cylinders Secondary Steering Pump Accumulator Steering Hydraulic Tank Magnetic Switch

Automatic/Manual Panel Switch Electronic Control Module

A B D F E H I G C K J

CHAPTER : STEERING

777D Off Highway Truck

VI-16 Page:

POST TEST

IV. Directions: Match the components and ports with the associated letter. FLOW CONTROL VALVE

Flow Switch From Hand Metering Unit To Hand Metering Unit Steering Pump Inlet Relief Valve Flow Control Orifice Secondary Steering Pump Inlet To Steering Hydraulic Tank

C

F

E

H

B

D

A

G