Great Wall service chassis and body Manual - part 65

SR-11

Steering System

 Power Steering (General Introduction)

power steering oil pump

power steering gear

steering drive shaft

oil cup

Power steering

Introduction

Principal of Power Steering

The power steering is a kind of hydraulic device that use

the engine power to steer. The engine drive the power

steering oil pump to generate the hydraulic pressure, which

actuates the piston in steering gear, so that the worm shaft

can provide to the piston with a supplementary force, which

has relation with the pressure actuated on the piston.

Therefore, pressure increase is required if larger steering

force is needed, and the pressure variation is accomplished

through the control valve.

Intermediate position (forward straightly)

The liquid from the power steering oil pump is sent to

the control valve, which, if locates at the intermediate, will

allow the liquid to pass and enter into the drain outlet, finally

return the pump. At this time, it is difficult to increase the

pressure; meanwhile, due to the equal pressures at the both

sides of the power piston, it cannot move toward either side.

Steering time

When the steering drive shaft move toward either side,

the control valve will move together with it, in case one oil

passage is shut off, meanwhile open the other larger, the

liquid flow variation will increase the pressure, as result, the

unequal pressure at both sides of piston will make the piston

move toward the side of smaller pressure, therefore, the

liquid is pressed in the pump through the control valve.

pump

control valve

drain outlet

power cylinde

power piston

segmental gear shaft

worm shaft

steering gear

Pump

SR-12

Steering System

 Power Steering (Introduction)

Suggestion on maintenance

The failure of power steering system usually relates to the

steering difficulty due to lack of supplementary force. In such

case, it is the first to verify the problem is produced by the pump

or steering gear when repairing. In doing so, the problem can be

checked on vehicle with the pressure meter.

On-vehicle Inspection

As the power steering is a hydraulic pressure device, its

trouble usually caused by the lack of specified hydraulic

pressure or the abnormal work of control valve. As a result, it

cannot acquire the moderate hydraulic pressure.

In case the problem is caused by the pump, the steering

wheel will deflect toward right or left. On the other side, if the

problem is caused by control valve, when the steering wheel

rotates to left or right, the steering will become more difficult

due to the unequal supplementary force. However, when there

is wear on the piston sealing ring of power cylinder, it also cause

the hydraulic pressure loss that may lead into steering difficulty

toward right or left.

Before making inspection on vehicle, verify the power

steering system firstly to see whether there is air. If any, the air

volume will increase with the variation of hydraulic pressure,

which will cause the hydraulic pressure fluctuation that makes

the power steering work abnormally. In order to verify whether

there is any air in the system, check whether the liquid level

varies or not when the steering wheel rotates completely toward

the right or left. For instance, if there is air in the system, the air

will be compressed, which will reduce the liquid level

remarkably, when the steering wheel rotating. If there is no air

in system, the liquid level variation is very small even though

the hydraulic pressure increases. This is because the liquid

volume will not varies when being compressed. And the small

liquid level variation is caused by the expansion of hose

between the pump and steering gear when the hydraulic pres-

sure increasing.

Meanwhile, the air in system sometimes will cause the

pump or steering gear produce noise when the steering wheel

rotating completely toward a certain direction. After checking

or exchanging the pump or steering gear, the on-vehicle inspec-

tion should be often conducted to guarantee the normal work of

power steering system.

SR-13

Steering System

 Power Steering (On-Vehicle Inspection)

tensioning wheel

power steering oil
pump

crankshaft

On-vehicle inspection

Inspection on tension of driver conveyor

Measure the tension of drive conveyor.

Drive conveyor tension: under the condition of 98 N.

New conveyor: (5-7)mm

Old conveyor:

(7-9)mm

Remark:

ìnew conveyorî means the conveyor that is used on the

machine less than five minutes;

ìold conveyorî means the conveyor that is used on machine

more than five minutes

Check for height of liquid level

1.

Keep the body in horizontal status

2.

Increase the liquid temperature

When the engine runs idly by 1000 r/m or less, rotate the

steering wheel several times from the locking position to the

reverse locking position to increase the liquid temperature.

3.

Check to see whether there is foam or emulsification;

Remark: the foam or emulsification shows there is air in the

system or the liquid level is over-low.

4.

Check the liquid level height in oil cup;

Check the liquid level height and, if needed, add the oil.

SR-14

Steering System

 Power Steering (On-Vehicle Inspection)

Change of power steering liquid

1.

Tear down the oil-returning hose from the oil cup to

drain the liquid into the container;

2.

Run the engine in the idle status, and rotate the

steering wheel toward the max rotating angle for

several times in right or left direction while draining the

liquid, until the oil in steering liquid is drained up.

3.

Turn off the engine.

4.

Connect the oil-returning pipe and inject the new

power steering liquid in the liquid tank;

Hydraulic oil type: No.8 Liquid drive oil (Q/SH003.01.012-88)

5.

Start the engine, and make it running in the idle status.

Rotate the steering wheel to the max rotating angle repeatedly

several times, meanwhile, supplement new power steering

liquid in the liquid tank until there is no foam or turbidities in

the liquid tank, and the oil indicating lamp reaches the marked

range when the engine is turned off.

6.

Tighten the liquid tank cover

7.

Exhaust the air in the power steering system;

Ai-r bleeding in power steering system

1.

Check the liquid level height in the liquid tank

Check the liquid level and, if needed, supplement the liquid.

2.

Start the engine in the idle status and rotate the

steering wheel repeatedly to the max rotating angle

several times.

3.

Turn off the engine and connect the ethane pipe and

bleeding plug.

4.

Start the engine and rotate the steering wheel

repeatedly to the max rotating angle several times.

5.

Locate the steering wheel at the intermediate position.