Direccion

Service Training MALAGA

777D Off Highway Truck STEERING SYSTEM

CROSSOVER RELIEF VALVES

HAND METERING UNIT (HMU)

HOLD ELECTRONIC CONTROL MODULE STEERING HYDRAULIC TANK

OIL FILTER MAGNETIC SWITCH

SECONDARY STEERING PUMP

MAIN RELIEF CHECK VALVE

CHECK VALVE

FLOW SWITCH ACCUMULATOR STEERING PUMP FLOW CONTROL VALVE

STEERING CYLINDERS

VII STEERING. 1. 2. 3. 4.

Components Layout Operation Maintenance Testing & Adjusting Adolfo August 1997

777D Off Highway Truck CHAPTER : STEERING

TYPICAL OFF-HIGHWAY TRUCK STEERING COMPONENT LOCATIONS SECONDARY STEERING PUMP ELECTRIC MOTOR

FLOW CONTROL VALVE STEERING CYLINDERS STEERING PUMP

HYDRAULIC TANK

HMU

STEERING ECM OIL FILTER

HOIST PUMP ACUMULATOR

HMU

CROSSOVER RELIEF VALVES

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STEERING PUMP

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STEERING SYSTEM

CROSSOVER RELIEF VALVES

HAND METERING UNIT (HMU)

HOLD ELECTRONIC CONTROL MODULE STEERING HYDRAULIC TANK

SECONDARY STEERING PUMP

MAIN RELIEF CHECK VALVE

CHECK VALVE

FLOW SWITCH ACCUMULATOR STEERING PUMP FLOW CONTROL VALVE

STEERING CYLINDERS

777D Off Highway Truck

MAGNETIC SWITCH

CHAPTER : STEERING

OIL FILTER

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STEERING SYSTEM RIGHT TURN

HAND METERING UNIT (HMU)

CROSSOVER RELIEF VALVES

ELECTRONIC CONTROL MODULE STEERING HYDRAULIC TANK

OIL FILTER

SECONDARY STEERING PUMP

STEERING PUMP

ACCUMULATOR FLOW CONTROL VALVE STEERING CYLINDERS

777D Off Highway Truck

CHAPTER : STEERING

MAGNETIC SWITCH

777D Off Highway Truck CHAPTER : STEERING

STEERING FLOW CONTROL VALVE TO HMU

MAIN RELIEF VALVE

CHECK VALVE

FROM HMU

FLOW CONTROL ORIFICE

CHECK VALVE

TO TANK CHECK VALVE FROM SECONDARY STEERING PUMP

SIGNAL TO SECONDARY STEERING

FLOW SWITCH CLOSED

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VI-4

FROM PUMP

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HAND METERING UNIT

VI-5

HOLD

INPUT SHAFT

BALL IN HELICAL GROOVE

STATIONARY GEAR

COMMUTATOR

VALVE SPOOL

TO TO TO TANK CYLINDER CYLINDER

ROTATING GEAR

FROM PUMP

DRIVE LINK

777D Off Highway Truck

CHAPTER : STEERING

TORSION BAR

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HAND METERING UNIT LEFT TURN

COMMUTATOR STATIONARY GEAR BALL INPUT SHAFT

VALVE SPOOL

TO TANK

FROM TO PUMP CYLINDER

FROM CYLINDER

ROTATING GEAR

DRIVE LINK

777D Off Highway Truck

CHAPTER : STEERING

TORSION BAR

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HAND METERING UNIT RIGHT TURN STATIONARY GEAR COMMUTATOR INPUT SHAFT

BALL

TO TANK

TO CYLINDER

FROM PUMP

ROTATING GEAR

DRIVE LINK

777D Off Highway Truck

FROM CYLINDER

VALVE SPOOL

CHAPTER : STEERING

TORSION BAR

777D Off Highway Truck CHAPTER : STEERING

CROSSOVER RELIEF SYSTEM EXTERNAL IMPACT

CROSSOVER RELIEF VALVES

HAND METERING UNIT

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777D Off Highway Truck CHAPTER : STEERING

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)

Steering Hydraulic Tank

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777D Off Highway Truck CHAPTER : STEERING

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 ?_______

Oil Filter Examination ______

Suction Screen Debris ? _______

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.

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777D Off Highway Truck CHAPTER : STEERING

LAB EXERCISES 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 • Steering system when the steering wheel is turned to the right or left HAND METERING UNIT (HMU)

CROSSOVER RELIEF VALVES

STEERING HYDRAULIC TANK OIL FILTER

STEERING CYLINDERS SECONDARY STEERING PUMP

ACCUMULATOR FLOW CONTROL VALVE

STEERING PUMP

HAND METERING UNIT (HMU)

CROSSOVER RELIEF VALVES

STEERING HYDRAULIC TANK OIL FILTER

STEERING CYLINDERS SECONDARY STEERING PUMP

ACCUMULATOR FLOW CONTROL VALVE

STEERING PUMP

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777D Off Highway Truck CHAPTER : STEERING

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 • Flow control valve when system pressure exceeds the setting of the main relief valve.

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777D Off Highway Truck CHAPTER : STEERING

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 ?_______

Oil Filter Examination ______

Suction Screen Debris ? _______

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

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777D Off Highway Truck CHAPTER : STEERING

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) Page:

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777D Off Highway Truck CHAPTER : STEERING

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

J

A I

B

F

E D

H K

C

G

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

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777D Off Highway Truck CHAPTER : STEERING

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

B

A

D

H

E G F Page:

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