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EPS
4610-00/4610-04/4620-01
ELECTRIC POWER STEERING
GENERAL INFORMATION
1. SPECIFICATION....................................
2. TIGHTENING TORQUE..........................
3
4
OVERVIEW AND OPERATING
PROCESS
1. OVERVIEW............................................
2. OPERATIONS........................................
5
6
CONFIGURATION AND FUNCTION
1. SYSTEM LAYOUT.................................
2. COMPONENTS......................................
3. CIRCUIT DIAGRAM................................
7
8
16
REMOVAL AND INSTALLATION
4610-00 CAUTIONS FOR OPERATION &
MISDIAGNOSIS CASES...............
4610-04 STEERING COLUMN AND
SHAFT.........................................
4620-01 STEERING GEAR BOX................
4610-00 INITIALIZATION & DIAGNOSTIC
TROUBLE CODE..........................
17
21
31
38
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1. SPECIFICATION
Unit
Description
Specification
System operation
Operating type
Motor driven power steering system
Operating temperature
- 40C to 80C
Rated voltage
12 V
Rated current
85 A
Network
8 to 16 V
C-EPS ECU
8 to 16 V
Full Performance
10 to 16 V
Type
3-Phase BLAC (Brushless AC)
Rated current/voltage
85 A / 12 V (at idle 0.5 A)
Position sensor type
Hall sensor type
Torque & angle sensor
Type
Non-contact type
Steering column
Operating type
Manual tilting & telescoping
Lower shaft
Type
Sliding (Ball slip) type
Steering gear
Gear ratio
46.94 mm/rev
Rack stroke
146 mm
Inner wheel
39
Outer wheel
31.24
Operating voltage
Motor
Maximum steering angle
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2. TIGHTENING TORQUE
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1. OVERVIEW
The electric power steering, EPS, does not have any belt-driven steering pump constantly
running, so it is lightweight and the motor consumes energy only when the steering wheel is
turned by the driver, and this leads to improvement in fuel efficiency. Also, the elimination of a
belt-driven pump and its accessories greatly simplifies manufacturing and maintenance. While
offering these benefits, as it does not contain any steering oil, the environment is not polluted
both when the steering system is produced and discarded.
In other words, the electric power steering (EPS) system uses the electric motor to assist the
steering force. It functions independently regardless of whether the engine is running or not,
unlike the existing hydraulic power steering.
The EPS system generates an assist steering force variably depending on the driving
conditions by controlling the motor's operation, based on the input signals from the sensors
such as torque sensor and angle sensor. In turn, the EPS receives the torque signal by the
driver's movements of the steering wheel, as well as the vehicle speed, and uses the motor to
determine the assist torque. The EPS controls the motor for this. Another features of EPS are
fail-safe function, diagnosis function, communication function between units and interface
function for external diagnostic device.
The EPS system components such as the torque sensor, steering angle sensor, fail-safe relay,
etc. are located in the steering column and EPS unit assembly.
Advantages:
(1)Assurance of improved steering
- Provides optimal steering force according
to the vehicle speed
- Enhanced steering stability while driving at
high speed
(2)Reduced fuel consumption
- Consumes energy only when steering
wheel is turned (improved by 3 to 5%)
- Energy saving (reduced by 85% compared
with hydraulic power steering)
- Reduced number of parts: Elimination of
steering pump, hydraulic hose, pump
pulley, oil reservoir, belt, bracket, etc.
Comparison between hydraulic power steering and electric power steering (EPS)
Hydraulic power steering
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Electric power steering
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2. OPERATION
Output torque = 1) Steering force (manual torque) + 2) Assist torque
When the driver turns the steering wheel, a torque is generated and the torque sensor and the
steering angle sensor in the EPS system detect the rotation of the steering column to run the
electric motor. At this time, the worm gear connected to the motor drives the helical gear
mounted to the steering column to generate the assist torque for the steering column. This
allows the driver to operate the steering wheel easier.
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1. SYSTEM LAYOUT
1. Steering wheel
2. Steering wheel tilting lever
3. Column shaft
4. Motor
5. ECU
6. Lower shaft
7. Steering gear box
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2. COMPONENT
1) BLAC Motor
The BLAC motor is brushless, and while the
coil had rotated for the existing DC motor,
the magnet rotates. In this way, high power
output, high responsiveness, high speed,
high torque performance and high heat
protection can be achieved.
Advantages:
-
High power output density
Low inertia (high responsiveness)
High speed/torque performance
Low maintenance cost
High torque ratio/inertia ratio
Good heat protection
2) Torque and Angle Sensor
The torque and angle sensor is one unit. The torque sensor outputs the analogue voltage and
the angle sensor outputs two PWM signals.
(1) Torque sensor
-
Type: Non-contact type
Operating voltage: 5 V 5%
Operating temperature: -40C to 85C
Torque output signal: Two output signals
Torque output voltage: 0.8 V to 4.2 V
Torque sensitivity: 0.44 V/deg
(2) Angle sensor
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Type: Non-contact type
Operating voltage: 8 to 16 V
Repeatability: 1 deg
Angle speed: Max. 1,016 deg/sec
Angle range: 720 deg
Locating absolute position after power up
: Power on True Signal Function
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(3) Characteristics
Torque sensor
- Detection
When a magnetic field is applied to a current flowing through a conductor, the electric current
carriers in the conductor experience a force in a direction perpendicular to the magnetic field and
current field. The newly developed electric field results in a potential difference and this effect is
called Hall-effect. A Hall-effect sensor is based on this effect. The sensor converts the intensity
of magnetic field into a voltage value. The torque sensor for EPS system uses a linear hall-IC to
convert the value of intensity change in magnetic field strength into a voltage value.
That is, the major function of the hall-effect type torque sensor is to detect the change in
magnetic flux around the hall IC in accordance with the twist amount (angle) between the input
shaft and the output shaft.
Structure of torque sensor
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- Operation
The operation range of the torque sensor built in this system, is 2.5 rotations ( 900
degrees) on both sides (left & right) which is the same as that of the steering wheel. And this
sensor should detect the twist amount (up to 4.5 degrees) between the input shaft and
the output shaft within the operation range of the steering wheel.
The torque sensor consists of a permanently magnetized multi-pole (16 poles) magnet rotor with
round shape connected to the input shaft of the steering wheel, upper and lower stators
connected to the output shaft with a number of teeth which contacts with the magnetized poles,
a collector which collects the magnetic flux induced to the stator which rotates as much as the
steering wheel rotates, into the hall IC, and a hall IC sensor which converts the value of flux
change into a voltage value.
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If the twist amount is zero, the magnet rotor poles and the stator teeth are equally spaced. Thus
the magnetic flux generated by the permanent magnet cannot be induced to the hall IC.
That is, the flux value around the hall IC is zero. But, if the twist amount is not zero, a contact
area difference is made between the permanent magnet poles and the upper & lower stator
teeth. This leads to the change in the magnetic flux around the hall IC (with a value
corresponding to the contact area difference). As a result, the output voltage value from the hall
IC is changed.
When the driver turns the steering wheel counterclockwise while the vehicle is stationary or
driven straight ahead, the permanent magnet rotor connected to the input shaft is turned
counterclockwise in conjunction with the input shaft; but the upper and lower stators do not rotate
as many as the rotor rotates.
If the amount of twist between the rotor and the stator reaches the maximum value (-4.5),
an upper stator tooth contacts completely with a South pole of the magnet and a lower stator
tooth contacts completely with a North pole. So the force of magnetic flows from the North pole
on the lower stator tooth to the upper stator tooth which rests against the South pole, through the
collector. At this time, the magnetic flux increases to its maximum level around the hall effect
sensor positioned in the collector.
The relation between the twist amount and the contact area of the stator teeth and the
permanent magnet is linear in the range between 0 and -4.5. And the contact area has
linear relation to the magnetic flux generated around the hall IC. The magnetic flux is converted
into voltage as a output value, therefore the output voltage and the twist amount also have a
linear relation.
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Angle sensor
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3) EPS ECU
The ECU controls the electric power
steering system depending on the driving
conditions, based on the signals from the
torque and angle sensor.
- Location: Steering column
- Operating voltage range: DC 8 V to 16 V
- Operating temperature range: -40C to
80C
(1) External connection terminal
Battery (2P)
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Vehicle (8P)
Torque angle sensor (8P)
Motor angle (8P)
Motor power (3P)
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(2) EPS ECU operation
(3) Warning lamp turning on conditions
Mode
EPS lamp
Initial check
ON
Faulty EPS
(Major fault)
ON
Serious faults, including a torque sensor signal
error, defective motor, internal defect, etc.
Faulty EPS
(Mild 1 fault)
ON
Faults that can be rectified such as problems
regarding battery, insufficient ignition power, etc.
Faulty EPS
(Mild 2 fault)
OFF
Faults that can be partially controlled such as
incorrect messages, O.H.P, issues regarding
vehicle speeds, etc.
EPS in operation
OFF
Diagnostic mode
Flashing (1 Hz)
Normal condition
OFF
CAN error (Signal nor
received by instrument
cluster, BUS OFF,
message time out)
ON
EPS warning lamp comes ON if a CAN error has
occurred within the same ignition cycle.
EPS not reinstalled
after removal
ON
See active lamp specifications
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(4) Fuse For EPS
- The vehicle with EPS has EPS fuse (80A)
mounted to the positive (+) terminal of the
battery, and this fuse supplies power to
the EPS unit directly.
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3. CIRCUIT DIAGRAM
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&
MISDIAGNOSIS CASES
1) Cautions For Operation
Possible
causes
Drop,
impact and
overload
Related
parts
Motor
ECU
Vehicle
symptom
Cause
Cautions
Noise increase
-Possible to cause
internal damage without
Malfunction due to
deformation and leads
broken circuit
to uneven load
-Out of welding
distribution when using
point
any dropped parts
-Damage to PCB
-Motor/precise parts in
-Damage to
ECU are sensitive to
precise parts
vibration and impact
and malfunction may
arise
-Excessive load weight
causes unexpected
faults
Torque
sensor
Impaired
steerability due to
torque sensor
malfunction
Shaft
-Impaired
steerability (not
same on left and
right sides)
-Difficult
installation
resulting from
shaft's
deformation
Torque sensor
malfunctions when
applying excessive
weight load to input
shaft
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-Do not use the EPS
exposed to an
impact
-Do not load weight
more than the weight
of the product itself
to each part
-Do not impact when
working on the
connections
-Always use the
specified tool when
removing steering
wheel (do not use a
hammer)
-Do not use the EPS
exposed to an
impact
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Possible
causes
Pull/
Dent
Related
parts
Harness
Motor/ECU
Incorrect
storage
temperature/h
umidity
Vehicle
symptom
Cause
Cautions
-Malfunction
(impossible to
switch on)
-Unstable EPS
performance
Harness connection
and harness itself will
be disconnected
-Do not load to the
harness
-Avoid an excessive
use of EPS
Poor steerability
due to
malfunctioning
motor/ECU
-Waterproof is available
in normal conditions but
water in the parts may
lead to breakdown
-A small amount of
water can lead to
malfunction of
motor/precise parts in
ECU
-Store at room
temperature and
proper humidity
-Avoid water
penetration due to
e.g. rain
1. Never impact the electronic parts. If those parts are exposed to a large impact such as
dropping, you should replace them with new ones.
2. Do not keep the electronic parts in a place with high temperature and humidity.
3. Do not touch the connector terminal by your hands since problems may arise due to
deformation and static electricity.
4. Never impact the motor and torque sensor. If those parts are exposed to a large impact such
as dropping, you should replace them with new ones.
5. You should connect and disconnect the connector with the ignition off.
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2) Misdiagnosis Cases
(1) Over heat protection control
1. When the driver turns the steering wheel and the twist between the input shaft and the
output shaft occurs, the motor generates an assist torque.
2. If the driver keeps the steering wheel at the maximum steering angle, the steering wheel is
stopped rotating by the stopper but the torque signal is generated continuously.
3. If the motor keeps running according to the torque signal, it becomes overheated and results
in system breakdown.
4. To prevent this, the C-EPS ECU gradually reduces the assist torque. (This can be confirmed
by checking the current output using a diagnostic device.)
5. As the motor control level decreases, the steering effort continues to increase.
6. This is not a malfunction but a simple C-EPS control to prevent the motor from overheating.
If the vehicle is equipped with EPS and is stationary, turning the steering wheel to the left or
right end over a long time triggers the overheating protection and you may feel the steering
becomes heavy. But it is not a malfunction and the system will be restored to its original
status.
(2) Operating sound of C-EPS
For the vehicles with C-EPS, the motor is installed inside the vehicle, so the driver may
misunderstand the operating sound of the motor as a noise. However, the system makes the
following sounds during normal operation:
1. C-EPS ECU operating sound (clicking sound): Occurs about 1 sec after turning ignition key
to on/off position
2. Motor operating sound (whining sound): Occurs primarily when the steering wheel is
operated suddenly
3. Contact sound of outer ring in the worm shaft bearing (knocking sound): Can occur at the
decelerator when driving on a poor road
4. In other cases, when creaking noise are heard, check the EPS assembly and check-tighten
the bolts on the body.
If one of the following occurs while no warning lamp on the instrument cluster is turned on,
the EPS is operating normally.
- The steering effort becoming heavy during the time for C-EPS system diagnosis (1 sec)
right after starting the engine, then it returns to normal.
- After turning the engine ON or OFF, a clicking relay sound is heard but this is not defective.
- When the steering wheel is turned while the vehicle is stationary or driving at low speed, a
motor operating sound may be heard. This occurs when the power steering motor rotates
and is not defective.
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(3) EPS operation delay and operating sound
If one of the following occurs while no warning lamp on the instrument cluster is turned on, the
EPS is operating normally.
- The steering effort becoming heavy during the time for EPS system diagnosis (1 sec) right
after starting the engine, then it returns to normal.
- After turning the engine ON or OFF, a clicking relay sound is heard but this is not defective.
- When the steering wheel is turned while the vehicle is stationary or driving at low speed, a
motor operating sound may be heard. This occurs when the power steering motor rotates
and is not defective.
Rattling sound due to contact between
gear teeth when driving on a poor road
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