The power steering gear assembly with tie rod is provided with a steering control valve. The steering control valve 
introduces the high-pressure oil from the power steering pump assembly to the two sides of the rack piston to push 
the rack piston. The integrated power cylinder piston is connected with the rack, so that the hydraulic power 
subject to the rack piston is converted into the linear force to move the rack left and right; the linear force is 
transmitted to the internal and external steering tie rods, and then transmitted to the steering knuckle; and the 
steering knuckle turns the wheel. If hydraulic auxiliary is invalid, need more steering force applied to the steering 
wheel for manual control of the steering. 

Description of power steering fluid 

Warning! 

When adding or completely replacing the oil, be sure to use the correct power steering fluid; if not, the hose and 
sealing element may be damaged and oil leaks. See power steering fluid recommended in this chapter. 

The power steering pipeline assembly with oil can is made of plastic; and the internal oil level height can be seen. 
An oil level scale mark at the side of the oil pot is used for indicating the correct level position in the power 
steering fluid. 

Be sure to correctly use oil. 

– 

Oil temperature after preheating will be 75℃-80℃ (167-176ºF). 

The liquid level shall be located between the marks HOT MAX and HOT MIN. 

– 

Oil fluid and oil fluid temperature after cooling is about20℃-25℃ (68-77ºF) The liquid level shall be located 
between the marks COLD MAX and COLD MIN. 

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7.2.3 System operating principle 

Hydraulic power gear rack and pinion steering operating principle 

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When there is no hydraulic pressure assisting to the hydraulic power rack and pinion steering gear, the operating 
principle of the steering gear is as shown in figure The torsional force applied on the steering wheel is transmitted 
to the steering gear pinion (steering control valve gear) through an intermediate shaft. Since the driving gear teeth 
(steering control valve gear teeth) are in engagement with the rack teeth, the torsional force transmitted from the 
steering wheel is converted into the linear force of the gear rack, so that the gear rack moves left and right. The 
linear force is further transmitted to the steering knuckle through the internal and external steering tie rods; and 
the steering knuckle reverses the direction of the wheel. 

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A hydraulic power rack and pinion steering system with is as shown in figure. the mechanical rack and pinion 
steering gear is designed with the steering power cylinder and the steering control valve integrally to form a whole 
power steering gear. The power cylinder piston and the rack are integrated to divide the power cylinder into left 
and right cavities. 

Oil can

Power 
steering 
pump 

Oil return 
hose 

Pressure hose 

Valve 
assembly 

Steering gear 
assembly 

Intermediate 
shaft 

Steering tie rod 

Drive gear 

Steering tie rod

Gear rack

Rotation axis 

rotation 

Lateral gear 

rack movement 

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When the steering wheel is not turned, the steering control valve is in the middle, and the oil from the power 
steering pump assembly is flowed into the valve cavity from the oil inlet of the steering control valve. The 
steering control valve is located in the middle, so that the left and right cavities of the power cylinder are 
communicated; thus, oil is flowed to the oil can from the oil outlet of the steering control valve, so that the 
hydraulic power does not work. 

When turning the steering wheel, the steering shaft rotates together with the steering control valve spool; due to 
road surface steering resistance transferred from the steering knuckle arm, the power cylinder piston and the rack 
can not move temporarily, so that the steering control valve gear also can not rotate together with the steering 
shaft temporarily. In this way, the torque transmitted by the steering shaft to the steering control valve gear can 
only make a torsion bar in the steering control valve to produce little torsional deformation, so that the steering 
shaft together with the steering control valve spool can rotate a little in respect to the steering control valve gear; 
therefore, the steering control valve leads the cavity at one side of the power cylinder to become a high-pressure 
oil inlet cavity and that at the other side to become a low-pressure oil return cavity. The high hydraulic acting 
force acted on the power cylinder piston helps the steering control valve gear to compel the steering rack to move 
to one side; and meanwhile, the steering control valve gear itself also begins to rotate with the steering shaft in the 
same direction. As long as the steering wheel continues to rotate, the torsional deformation of the torsion bar 
remains unchanged and the assistance action of the steering control valve is also unchanged. In case the steering 
wheel stops rotation, high hydraulic acting force in one side cavity of the power cylinder is still present 
temporarily, which causes that the steering control valve gear continues to rotating; thus, the deformation of the 
torsion bar is reduced until the torsion bar restores to its natural state. The steering control valve is restored to the 
middle position; the left and the right of the power cylinder are communicated, so that the hydraulic power does 
not work. At this time, the steering wheel keeps still in a certain position and the wheel rotation angle is kept 
constant. If re-rotating the steering wheel, hydraulic power also works. 

Hydraulic pressure subject to power cylinder piston is converted into linear force the help the rack to move left 
and right and promote the rotation of the knuckle and wheel through a steering tie rod. 

Torsion bar 

Valve plug 

Steering control valve 
gear 

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Control valve is in the middle position 

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Control valve turning left 

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Pressure 

Oil return 

Slidingvalve 
shaft 

Intermediate 
position 

Pressure 

Oil return 

Left turn 

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