Steering System
Steering System
Steering System
REFERENCE:
4WS (4 Wheel Steering)
Opposite direction at low speed Same direction at high speed
1’ 4WS is an abbreviation for 4 Wheel
Steering, which is a device with which
1
the direction is changed not only for the
front tires but for the rear tires as well.
When changing the direction of the vehi-
cle, a normal vehicle turns only the front
tires, but a 4WS vehicle also turns the
rear tires according to such factors as
2 2’
the angle the steering wheel is turned to
and the vehicle speed.
At medium and high speeds, when
changing lanes, negotiating an S curve,
or cornering, the rear tires move slightly
in the same direction as the front tires for
smooth, stable driving. On the other
hand, when the vehicle does not have
much speed, the rear tires are steered
the opposite direction from the front tires
for sharp turning.
(1/1)
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Diagnosis Technicain - Suspension and Steering Steering System
Impact-absorbing Mechanism
1. Description
Body
Pin When a vehicle involved in a collision, this mechanism
helps prevent the steering main shaft from injuring the
driver in two ways: by the breaking at the time of the
Lower bracket
Breakaway collision (primary shock); and by reducing the second-
Impact-absorbing bracket ary shock imposed upon the driver's body when it hits
plate
the steering wheel due to inertia.
Impact-absorbing steering columns are classified into
the following types.
• Bending bracket type
Breakaway • Ball type
bracket
• Sealed-in pulverized silicon-rubber type
• Mesh type
• Bellows type
Here, the bending bracket type is explained.
Intermediate shaft
NOTICE:
• Since the impact absorbing steering column is con-
structed so that it will absorb shock in the axial direc-
tion, never attempt to hammer the steering main shaft
when removing the steering wheel as the force may
break the pins in the impact-absorbing mechanism.
Always use the SST designed for removing the steer-
ing wheel safely.
• Since the steering column is no longer usable after
collapsing, it must be replaced with a new one.
(1/1)
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Diagnosis Technicain - Suspension and Steering Steering System
3. Operation
Steering main shaft
Here, the push type ignition key cylinder is explained.
Lock bar
Camshaft
Ignition switch
Stopper plate
Push plate
Key cylinder
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Diagnosis Technicain - Suspension and Steering Steering System
ACC position
ON position
"ON" to "ACC"
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Diagnosis Technicain - Suspension and Steering Steering System
Stopper plate
Stopper plate
(pushed down by spring)
Push plate
Cylinder rotor
Rotor case return spring
Camshaft
Rotor
Lock body
at "ACC" position
(Top view)
Lock bar
Lock release lever
Lock stopper
Lock spring
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Diagnosis Technicain - Suspension and Steering Steering System
Rotor
"ACC" to "LOCK"
(2/2)
Fulcrum
(1/2)
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Diagnosis Technicain - Suspension and Steering Steering System
2. Construction
Breakaway bracket The tilt steering mechanism consists
of a pair of tilt steering stoppers, tilt
Tilt lock bolt
lock bolt, breakaway bracket, tilt
Tilt attachment lever, etc.
Column tube
3. Operation
Steering main shaft
Tilt lever
The tilt steering stoppers turn
together with the operation of the tilt
lever.
When the tilt lever is in the lock posi-
tion, the peaks of the tilt steering
A’
Tilt steering stopper
stoppers are lifted up and the stop-
A pers push against the breakaway
bracket and tilt attachment, locking
"Lock"
the break away bracket and tilt
Breakaway bracket
attachment.
Tilt lock bolt
Cam mechanism
Tilt attachment
"Free" On the other hand, when the tilt lever
is moved to the free position, the
Cam
movement
"Lock" height difference on the tilt steering
Rotation
stoppers is eliminated, and the steer-
"Free" ing column can be adjusted in the
Tilt lever A-A’ cross section
vertical direction.
(2/2)
Telescopic Mechanism
1. Description
The telescopic steering mechanism
allows forward or backward adjust-
ment of the steering wheel position to
suit the driver's posture.
(1/2)
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Diagnosis Technicain - Suspension and Steering Steering System
2. Construction
"Lock"
Column Sliding The telescopic mechanism consists
upper bracket shaft tube
of the sliding shaft tube, two wedge
locks, stopper bolt, telescopic lever,
etc.
3. Operation
The wedge locks move together with
operation of the telescopic lever.
"Free"
Telescopic lever When the telescopic lever is in the
lock position, the telescopic lever
presses the wedge locks against the
sliding shaft tube, locking the sliding
Wedge locks shaft tube.
On the other hand, when the tele-
Wedge locks scopic lever is moved to the free
Lock bolt position, a gap is created between
the wedge locks and the sliding shaft
tube and the steering column can be
adjusted in the forward or backward
direction.
(2/2)
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Diagnosis Technicain - Suspension and Steering Steering System
3. Operation
Power tilt mechanism
Telescopic screw
Contraction
Telescopic motor
(2/2)
• Recirculating-ball type
Amount of steering wheel rotation (in degrees)
Pitman arm movement (in degrees)
(1/1)
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Diagnosis Technicain - Suspension and Steering Steering System
Rack-and-pinion Type
1. Construction
Compression spring
The steering pinion at the lower end
Adjusting screw
of the steering main shaft meshes
Upper bearing
with the steering rack. As the steer-
Steering pinion ing wheel is turned, the steering pin-
Adjusting screw ion rotates to move the steering rack
Lower bearing to the right or left.
Rack guide
Steering rack
The movement of the steering rack is
transmitted to the knuckle arms via
Steering rack housing
the steering rack ends and tie rod
Rack guide Bushing Steering rack end ends.
Tie rod
2. Features
to • Construction is compact, simple, and
Knuckle arm
lightweight. Since the gear box is
Steering rack Steering pinion Band Rack boot
small, and the rack itself acts as the
steering linkage.
• Gear meshing is direct, so steering
response is very sharp.
• There is little sliding and rotational
resistance and torque transmission is
better, so steering is very light.
• The steering gear assembly is com-
pletely sealed so it is maintenance
free.
(1/1)
Recirculating-ball Type
Turning angle of
5 5 sector shaft
(1/1)
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Diagnosis Technicain - Suspension and Steering Steering System
Rack-and-pinion type
1. Description
A steering linkage is a combination of
(2) Tie rod end the rods and arms that transmit the
movement of the steering gear to the
left and right front wheels.
(1) Tie rod
Gear housing The steering linkage must accurately
transmit the movement of the steer-
ing wheel to the front wheels as they
move up and down while the vehicle
Power cylinder
(3) Knuckle arm is running.
There are various linkage arrange-
ments and joint constructions
Recirculating-ball type
designed to do this.
(3) Knuckle arm Steering gear Steering gear
(3) Knuckle arm 2. Construction
(4) Pitman arm
(1) Tie rod The steering linkage consists of the
(1) Tie rod
(7) Idler arm
following parts.
(2) Tie rod end
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Diagnosis Technicain - Suspension and Steering Steering System
(2/2)
Steering wheel
Engine
Reservoir tank
Control valve
Vane pump
Power Power
piston cylinder
Vane Pump
1. Description
Reservoir tank Power steering is a type of hydraulic device requiring
a very high pressure. It uses the power of the engine
to drive the vane pump uses that generates this
hydraulic pressure. Vanes are used in this pump, so
this name is used for this type of power steering.
Pump body
Idle-up device
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Diagnosis Technicain - Suspension and Steering Steering System
REFERENCE:
EHPS (Electric Hydraulic Power
Steering)
Generally, a power steering system uses
the power of the engine to drive the vane
Reservoir tank pump that generates hydraulic pressure.
Power steering
ECU
EHPS is a power steering system that
uses a motor to generate the hydraulic
pressure and reduces the power
required to operate the steering wheel.
Since this system reduces the load on
the engine, it improves fuel economy.
The motor rotation rate (pump discharge
volume) is controlled by the ECU
according to such data as the vehicle
Vane pump with motor
speed and steering wheel turning angle.
(1/1)
2. Construction
(1) Pump body
The pump is driven by the engine crank pulley and
drive belt, and sends fluid, under pressure, to the gear
housing. The discharge volume of the pump is in pro-
portion to the engine speed, but the amount of fluid
sent to the gear housing is regulated by a flow control
valve, with excess fluid being returned to the suction
side.
(2) Reservoir tank
The reservoir tank supplies the power steering fluid.
It is installed either directly to the pump body or sepa-
rately. If not installed to the pump body, it is connected
to it by two hoses.
Normally, the reservoir tank cap has a level gauge for
checking the fluid level. If the fluid in the reservoir falls
below the standard level, the pump will suck in air,
causing faulty operation.
(3) Flow control valve
The flow control valve controls the flow volume of the
fluid from the pump to the gear housing, maintaining a
constant flow regardless of the pump speed (rpm).
(1/5)
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Diagnosis Technicain - Suspension and Steering Steering System
Gear housing
Vane pump
(2/5)
3. Operation
Suction
Rotor shaft (1) Vane pump
A rotor rotates within a cam ring secured to the pump
Vane plate
housing. There are grooves in the rotor and a vane
Discharge plate built into the grooves. The outer circumference
Discharge of the rotor is circular but the inner surface of the cam
ring is oval so there exists a clearance between the
rotor and cam ring. The vane plate partitions off this
Rotor Cam ring clearance to form a fluid chamber.
Suction The vane plate is held against the inner surface of the
from Reservoir cam ring by both centrifugal force and fluid pressure
Rear plate
Rotor against the back of the vane plate, forming a seal so
that when the pump produces fluid pressure, pressure
leakage from between the vane plate and cam ring is
prevented.
Flow control valve The capacity of this fluid chamber is increased or
Vane plate Cam ring decreased as the rotor rotates to operate the pump.
Vane plate
In other words, the capacity of the fluid chamber
Rotor increases at the suction port so that reservoir fluid is
drawn into the fluid chamber from the suction port.
The volume of the fluid chamber is decreased on the
discharge side, and when it reaches zero, the fluid
previously drawn into the chamber is forced out
Cam ring
through the discharge port. There are two suction and
Rear plate Orifice
to Gear housing two discharge ports. Therefore, fluid is drawn in and
discharged twice with each revolution of the rotor.
(3/5)
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Diagnosis Technicain - Suspension and Steering Steering System
P1
P2
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Diagnosis Technicain - Suspension and Steering Steering System
P1
P2
Spool movement
P2
Spool movement
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Diagnosis Technicain - Suspension and Steering Steering System
Relief valve
(5/5)
Gear Housing
1. Description
Control valve shaft The piston in the power cylinder is positioned on the
rack, and the rack moves due to fluid pressurized by
to Reservoir
the vane pump acting on the piston in either direction.
Fluid pressure leakage is prevented by a seal ring on
the piston. Also, there is an oil seal on both sides of
from Vane pump
the cylinder to prevent external leakage of the fluid.
The control valve shaft is connected to the steering
wheel. When the steering wheel is in the neutral
(straight-ahead) position, the control valve is also in
Seal ring the neutral position, so the fluid from the vane pump
Seal ring
Seal ring does not act on either chamber but flows back to the
reservoir tank. However, when the steering wheel is
turned in either direction, the control valve changes
the passage so the fluid flows into one of the cham-
Rack Piston bers. The fluid in the opposite chamber is forced out
and flows back to the reservoir tank by way of the con-
trol valve.
Currently, there are three different types of control
Cylinder left chamber Cylinder right chamber valves which perform this changeover action of the
passage; spool valves, rotary valves and flapper
valves. All types have a torsion bar between the con-
trol valve shaft and pinion, and the control valve func-
tions in accordance with the amount of twist applied to
the torsion bar.
(1/5)
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Diagnosis Technicain - Suspension and Steering Steering System
(2/5)
3. Construction
A-A’
Here, the rotary valve type is
Torsion bar Torsion bar explained.
The control valve in the gear housing
Control valve shaft Control valve housing Control
valve shaft
determines to which chamber the
Rotary valve fluid from the vane pump goes. The
Return port Sleeve "B"
control valve shaft (to which steering
Rotary valve
Sleeve "A"
wheel torque is applied) and the pin-
to Pump
reservoir ion gear are connected by means of
from Vane
to Cylinder right
chamber B-B’
Torsion bar
a torsion bar.
pump
A A The rotary valve and pinion gear are
Inlet port
to Cylinder left
chamber secured by a pin and rotate integrally.
B B Rotary valve If no vane pump pressure is applied,
Fixed pin
Sleeve "C"
the torsion bar is fully twisted and the
Pinion
Stopper (pinion) Control valve shaft control valve shaft and pinion gear
make contact at the stopper so the
Rotary valve type
control valve shaft torque is applied
directly to the pinion gear.
(3/5)
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Diagnosis Technicain - Suspension and Steering Steering System
4. Operation
Rotary valve
A restriction in the hydraulic circuit is formed by rotary
Control valve shaft
movement of the control valve shaft in relation to the
rotary valve. When the steering wheel is turned to the
right, pressure is restricted at orifices X and Y. When it
is turned to the left, a restriction is formed at X' and Y'.
When the steering wheel is turned, the control valve
Orifice X
shaft rotates, turning the pinion gear via the torsion
bar. In contrast to the pinion gear, as the torsion bar
Orifice X’
twists in proportion to road surface force at this time,
Orifice Y’ the control valve shaft rotates only to the extent of the
Orifice Y amount of twist, and moves to the right or left in rela-
from Pump to cylinder chamber tion to the rotary valve. Thus orifices X and Y (or X'
from cylinder chamber to reservoir
and Y') are formed and a difference in hydraulic pres-
sure between the right and left cylinder chambers is
Vane pump
created.
In this manner, rotation of the control valve shaft
Orifice Y Orifice X’
(closed) (opened) directly performs changeover of the passages and
regulates the fluid pressure.
The fluid from the vane pump enters from the outer
circumference of the rotary valve, and the fluid return-
ing to the reservoir tank passes between the torsion
Orifice Y’ Orifice X bar and the control valve shaft.
(opened) (closed)
Reservoir
(4/5)
Chamber "D"
Port "A"
Port "D"
Chamber "D"
Port "B"
Sleeve "B"
Port "A"
to Cylinder right
Port "D" chamber
to Cylinder left
Port "C" chamber
Sleeve "A"
Sleeve "C"
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Diagnosis Technicain - Suspension and Steering Steering System
(5/5)
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Diagnosis Technicain - Suspension and Steering Steering System
Reservoir
Hydraulic reaction chamber Plunger
2. Operation
At low speeds At high speeds The hydraulic reaction type progres-
sive power steering uses a thinner
Cross section A-A’
torsion bar than in ordinary power
Reservoir
steering to reduce the steering effort
required during stationary steering or
A A’ when traveling at a low speed. How-
Orifice ever, this causes the steering
required effort to become too small
B B’
Vane pump (that is, the steering wheel feels too
Flow dividing "light'') when the vehicle speed
valve
ECU
Plungers increases.
Solenoid Rack
Speed valve
Hydraulic
To prevent this, the required steering
Cross section B-B’
sensor Pinion reaction effort is increased as when there is a
chamber
System diagram
thicker torsion bar, by the provision of
a hydraulic reaction chamber for sup-
pressing the rotation of the control
valve shaft (in the control valve hous-
ing) by means of four hydraulically
operated plungers. The hydraulic
pressure applied to the hydraulic
reaction chamber is low at low vehi-
cle speeds and high at high vehicle
speeds.
It also increases as the hydraulic
pressure in the power cylinder rises
as a result of steering operation. In
the hydraulic reaction type progres-
sive power steering, the required
steering effort varies according to the
vehicle speed and steering opera-
tion.
(1/1)
EPS EPS
1. Description
(7) Combination meter
(Warning light) EPS (Electric Power Steering) gener-
ates the assist torque by the motor
(1) EPS ECU for steering operation and reduces
the steering effort.
(3) DC Motor
Hydraulic power steering uses the
(2) Torque sensor
(4) Reduction power of the engine to generate the
mechanism
hydraulic pressure and obtain the
assist torque. Since EPS uses a
(8) Relay motor, it does not require the power
of the engine and improves fuel
economy.
2. Construction & Operation
(1) EPS ECU
(5) ABS Actuator
and ABS ECU
(6) Engine ECU
The EPS ECU receives signals from
various sensors, judges the current
vehicle condition, and determines the
assist current to be applied to the DC
motor accordingly.
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Diagnosis Technicain - Suspension and Steering Steering System
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Diagnosis Technicain - Suspension and Steering Steering System
Exercise
Use the Exercises to check your level of understanding for the material in this Chapter. After answering each
Exercise, you can use the reference button to check the pages related to the current question. When you get
a incorrect answer, please return to the text to review the material and find the correct answer. When all
questions have been answered correctly, you can go to the next Chapter.
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Diagnosis Technicain - Suspension and Steering Steering System
Question- 1
Mark each of the statements True or False.
The power steering system is always required that the handle can
3 True False
be steered with light operating force.
The vane pump of the hydraulic pressure type power steering which
4 True False
is driven in the engine generates the hydraulic pressure at all times.
Question- 2
The following illustration shows the steering linkage.
From the following word group, select the words that correspond to 1 to 5.
Rack-and-pinion type
1
4
5
(Independent type) (Rigid-axle type)
a) Pitman arm b) Tie rod end c) Drag link d) Knuckle arm e) Relay rod
Answer: 1. 2. 3. 4. 5.
Question- 3
The following statements pertain to the purpose of the steering lock mechanism. Select the statement that is True.
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Diagnosis Technicain - Suspension and Steering Steering System
Question- 4
The following illustration shows the hydraulic type power steering. From the following word group, select the words
that correspond to 1 to 5.
a) Gear housing (Power cylinder) b) Control valve c) Vane pump d) Steering column e) Reservoir tank
Answer: 1. 2. 3. 4. 5.
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