Geely Emgrand X7. Manual part — 407

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

NL07-1001b

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.

NL07-1002b

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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NL07-1003b

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

NL07-1004b

Control valve turning left

NL07-1005b

Pressure

Oil return

Slidingvalve
shaft

Intermediate
position

Pressure

Oil return

Left turn

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