TECHNICAL REPORT

Development of Steer-by-Wire System (J-EPICS) withNo Mechanical Link*1
K. NISHIMURA I. NAMIKAWA

K. ABE Y. KAJISAWA

R. YAMAZAKI

Future steering systems need to not only be compatible with automated driving systems, but also allow for
improved driving space flexibility. To address these needs, we are currently developing a Steer-by-Wire systemwith no mechanical link. This document provides an explanation of the advantages of this new steering system, itsconcept of safety, and new technologies such as system redundancy and control based on the concept of safety.
Key Words: steer-by-wire, ADAS, SBW, EPS, EE, BPS, J-EPICS

1. Introduction
Recent years have seen a progression in the spreadof Advanced Driver Assistance Systems (hereinafter,“ADAS”) and their practical application for automateddriving1), 2). An example of this progression can be seenin Fig. 1, which shows a roadmap for the introductionof ADAS and automated driving systems in Japan3). In
Japan, vehicles compatible with Level 3 automation(Conditional Driving Automation)4) defined by the Societyof Automotive Engineers of America (SAE) are currently
being sold, and it is expected that automated driving
technology equivalent to Level 4 (conditional automationof driver response when it is difficult to continue driving)
will have become widespread by around 2030.
Currently
2020

Level 2 Level 3 Level 4 Level 5
2025

2030

Driver assistanceon ordinary roads

More advanced
Fully automated driving infrastructure-assisted
Driver assistanceon expressways
automated driving,on expressways
including on
Automated driving
ordinary roads
Passenger cars on expressways

Fig. 1 Roadmap of introduction of ADAS and automateddriving in Japan3)

Considering these developments, we assume that it
will be necessary for steering systems to not only becompatible with ADAS and AD but also provide comfort
and convenience during manual driving. Furthermore,in order to improve driving space flexibility, we can*1 This paper was created based on the proceedings of the 2021
JSAE Annual Spring Congress (20215095).

36

assume that the preferred layout for steering systems
will feature two separate structures: Human MachineInterface (hereinafter, “HMI”) unit for detecting handwheel operation by the driver and Steering unit forcontrolling the road wheel angle based on the level ofdriver operation.
To address these needs, we are currently developinga Steer-by-Wire system with no mechanical link
(hereinafter, “SBW”). This paper describes ourdevelopment results of the system that can be mounted on
a vehicle by implementing both system redundancy basedon our concept of safety and new control technology.
This system is the first implement example of J-EPICS(JTEKT Electronics Performed Intelligent Control
Steering), which we define as the steering system that
controls road wheel operation by electrical signals.

2. Development Objectives and Issues
2. 1 Development Objectives
SBW uses electrical signals in place of mechanicalparts to connect HMI unit and Steering unit, and has thefollowing main features:⑴Hand wheel operation and road wheel operation can becontrolled independently.
⑵There is no mechanically connected structure between
HMI unit and Steering unit.
⑴ above is advantageous because it prevents
interference between the road wheel angle and handwheel operation during automated driving performed via
ADAS-controlled driver assistance and vehicle systemcommands. This, in turn, improves compatibility between
ADAS, automated driving, and steering functions. During
manual driving, the amount of hand wheel operation
relative to the wheel turning angle can be minimized

JTEKT ENGINEERING JOURNAL English Edition No. 1019E (2023)

Development of Steer-by-Wire System (J-EPICS) with No Mechanical Linkthrough adjustments made by controlling the angle
ratio (gear ratio) of the road wheel angle (wheel turning
angle) to the hand wheel angle. This makes it possible
to improve comfort and convenience during hand wheel
operation. Also, ⑵ above enhances the system mounting
flexibility on vehicle. Furthermore, ⑴ and ⑵ above
block unnecessary road vibrations during manual driving
while enabling the transmission of necessary road surface
information, making it possible to reduce driver fatigue
while ensuring safety and security.
As described above, because SBW optimally combines
manual driving with ADAS/automated driving, we expectthat its application will increase in the future with the
spread of automated driving.

information between units, synchronizing the operationof both units, and responding to phase shifts between thehand wheel angle and the road wheel angle.
We have remained focused on solving these issues overthe course of our development.

3. Development Concept
The issue to which we give the highest level of priority
during our development is ensuring the safety of thesteering system. During our development, in addition toutilizing two independent EE systems for the purposeof ensuring operability in the event of a failure, wedeveloped a configuration which uses the main battery
for both systems when the power supply configuration
is normal and which switches to a system-dedicatedbackup power supply (hereinafter, “BPS”) in the eventof a failure. This enables steering functionality to be
maintained during any primary failure of EE system
while allowing for subsequent evasive action. The power
supply capacity of BPS is designed to enable the vehicle
to be stopped safely on the road shoulder in most driving
scenarios.
Figure 2 shows our concept of safety.
①The minimum level of steering functionality when oneof EE systems fails is maintained by utilizing the one
system that remains operable.
②The minimum level of steering functionality when themain battery fails is maintained by switching the power
supply to BPS and utilizing one system within therange of BPS power supply capacity.
③The vehicle is stopped in the vehicle lane when both
systems fail.
Additionally, our development aims to achieve alevel of performance equal to or higher than EPS during
manual driving, while also providing high value-added
performance that utilizes compatibility with ADAS and
AD. In particular, as an approach to realizing performance

2. 2 Development Issues
When developing SBW, the main thing one notices
about its system configuration is that it differs fromconventional electric power steering (hereinafter,“EPS”) in that HMI unit and Steering unit are connected
electronically instead of mechanically. This difference
gives rise to two main issues:⑴Ensuring safety in the event of system failure⑵Basic function establishment when the system operates
normally
In regard to ⑴, conventional EPS enables the driver toperform road wheel operation using hand wheel operationin the event of an electrical/electronic (hereinafter,“EE”) system failure, by increasing manual steering
torque due to the loss of assist torque. On the other hand,because SBW does not have a mechanically connectedstructure, the driver will not be able to perform roadwheel operation using hand wheel operation in the eventof EE system failure. For this reason, SBW must havea mechanism for ensuring the continuation of system
operability in the event of a failure.
The specific issues presented by ⑵ are: providing
a method of transmitting torque and steering angle

Stopping on
the roadshoulderParking ina garage
Functionality is
maintained at 50%
of max. output

Stopping inthe same
vehicle lane

Functionality is
maintained for aset period of time

Functionality
stops

FailureFailureFailureWhen one of the two
redundant systems fails

When the mainbattery fails

When both of the two
redundant systems failFig. 2 Safety concept

JTEKT ENGINEERING JOURNAL English Edition No. 1019E (2023)

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Development of Steer-by-Wire System (J-EPICS) with No Mechanical Link

during manual driving, this system is equipped withfunctions for adjusting the angle ratio between the handwheel angle and the road wheel angle based on thesteering angle, for appropriately transmitting road surface
information to the driver, and for aligning the phases of
the hand wheel angle and the road wheel angle.

4. Outline of the System Configuration
F i g u re 3 s h ow s a n o u t l i n e o f t h i s s y s t e m ’s
configuration. The system is comprised mainly of HMI
unit, Steering unit, BPS, and the power and signal
harnesses that connect these components.
Mainbattery

HMI unit
Backup power
supply (BPS)MCU

Torque sensor
Centralgateway

Vehicle CAN

Mechanical stopper
Local CAN
Steering unit

Legend：Signal line
Power line
External
equipment

Pinion rotation angle sensor
MCU

type EPS and rack parallel type EPS, which have a proventrack record in mass production.

5. Safety
5. 1 Ensuring Safety in the Event of EE System
FailureFigure 4 shows an outline of EE system configuration.
Both HMI MCU and Steering MCU feature
configurations in which all EE components are redundant,
including the control calculation units (hereinafter,“micro controllers”), motor drive units, motor coils, andsensors (torque sensor/motor rotation angle sensor). Each
EE component is also arranged independently by being
separated into those for system 1 and those for system 2.
The motor drives one rotor based on the magnetomotive
force generated by each of the motor coils of both
systems. Furthermore, by establishing separate lines ofcommunication between HMI MCU and Steering MCU
for each system, the configuration is one in which thesystems can operate independently of each other. Such aconfiguration enables system operation to continue evenwhen any of EE components fail by using the normal
system that has not suffered a failure.
Main

Fig. 3 SBW system configuration
lC1

HMI unit operates by detecting the level of hand wheel
operation by the driver, after which it instructs Steering
unit to turn the road wheel angle, and generates a reaction
force appropriate for the hand wheel operation. Steering
unit operates by controlling the road wheel angle anddetecting information such as reaction force that is fed
back from the road surface, which it then transmits to
HMI unit. Both units are cooperatively controlled by theirrespective control software.
Angle and torque information required for control iscalculated based on the detected values from the torquesensor of HMI unit, the pinion rotation angle sensor ofSteering unit, and the motor rotation angle sensors ofboth units, which are then transmitted between both units.
Local CAN is used to communicate information between
the units and between HMI unit and BPS, while vehicle
CAN is used to communicate information between
vehicle systems.
This system is equipped with safety mechanisms in
the form of two EE systems centered on a Motor Control
Unit (hereinafter, “MCU”) with an integrated motor and
ECU, as well as BPS and prevention of hand wheel overrotation (described later in section 5. 3).
Furthermore, in order to ensure reliability, HMI unit
and Steering unit utilize technology from both column

38

INV1

HMI
MCU

lC1

INV1

Steering
MCU

TS1

MPS1 M1

MPS1 M1

TS2

MPS2 M2

MPS2 M2

lC2

Sub

INV2

lC2

INV2

lC ：Micro controller
INV ：Inverter
TS ：Torque sensor
MPS ：Motor position sensor
M：MotorFig. 4 EE system configuration

Figure 5 shows the system operation modes during
an assumed failure. During normal operation, both
systems cooperate in operating the system (SBW_
Mode1: Cooperative drive). At this time, with system
1 acting as the main system and system 2 acting as thesubsystem, information from other systems required formode switching when a malfunction occurs is sharedthrough information exchanges between both systems
via communication between the micro controllers.
Commands calculated by system 1 are then also shared
and the motor of system 2 is driven based on thosecommands. If communication between the microcontrollers fails, each system changes to a mode in

JTEKT ENGINEERING JOURNAL English Edition No. 1019E (2023)

Development of Steer-by-Wire System (J-EPICS) with No Mechanical Link

Steering unit

Main

Main

Sub

Sub

5. 3 Safety Functions for Hand Wheel Usage

SBW_Mode1
HMI unit

Steering unit

HMI unit

Steering unit

Main

Main

Main

Main

Main

Main

Sub

Sub

Sub

Sub

Sub

Sub

SBW_Mode4

HMI unit Steering unit

SBW_Mode2
HMI unit

Steering unit

Main

Main

Sub

Sub

SBW_Mode3：Failure

SBW_Mode5

Fig. 5 System operation mode

which the motor is driven based on commands calculated
by its own system (SBW_Mode2: Independent drive).
Once it has been confirmed that system 1 is normal, themode switches to one in which the motor is driven basedon command values obtained by doubling the values
calculated by system 1 (SBW_Mode3: One system drive).
If a failure occurs in either system, the operation of thefaulty system is stopped while communication between
the micro controllers and between the units is continued.
At this time, the mode switches to one in which operationis performed only on the side of the normal system(SBW_Mode3 / SBW_Mode4: One system drive). If a
failure (secondary failure) then occurs on the side of thenormal system as well, both systems are stopped (SBW_
Mode5: Both systems stopped).

5. 2 Ensuring Safety in the Event of a Main
Battery Failure
By using BPS in the power supply system, steeringfunctionality can be maintained even if the main battery
fails. Figure 6 shows a power supply diagram. Normally,
power is supplied from the main battery to system 1 via
BPS. When the main battery fails, steering functionality
can be maintained by having BPS supply power to system
1. At that time, because power stops being supplied tosystem 2, the mode switches to one system drive (SBW_
Mode3) using system 1.

Mainbattery

HMI unit

Steering unit

Main

Main

Sub

Sub

The fact that there is no mechanical connection
between HMI unit and Steering unit (road wheels) may
result in the failure of components such as spiral cables
due to over-rotation of the hand wheel, and may cause
drivers to feel inconvenienced because the hand wheel
moves when they place their hand on it as they attempt to
get in and out of the vehicle.
As a means of preventing over-rotation of the handwheel, during system is power-on status, SBW systemelectrically generates a response (steering reaction torque)to contact with the rack end (hereinafter, “the virtual rack
end reaction torque”) (Fig. 7) and communicates to thedriver the fact that the rack bar of Steering unit is about
to make contact with the rack end. Also, a mechanicalstopper is used to prevent over-rotation when SBW
system power is off and when the driver attempts to turnthe hand wheel with a steering effort that exceeds thevirtual rack end reaction force (Fig. 8).

Reaction torque, arbitrary unit

HMI unit



0


100

50

0

50

100

Road wheel angle, %Fig. 7 Example of virtual rack end reaction torque

HMI unit
lower shaft

Hand wheel

Hand wheel rotation：
Left end

BPS

Legend：Power line
External
equipment

1st stopper
2nd stopper

Right end

Fig. 8 Example of mechanical stopper

Fig. 6 Power supply diagram

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Development of Steer-by-Wire System (J-EPICS) with No Mechanical Link

Because it is assumed that drivers may place theirhands on the hand wheel when attempting to get in andout of the vehicle, the hand wheel has also been provided
with a mechanical locking mechanism that activates when
SBW system power is off.
The timing at which each of the above functions
activate, as well as relationships between system modes,
are shown in Fig. 9.
Over-rotation range
Hand wheel angle(absolute value)

Mechanical stopper
Virtual rackend
Mechanicallock
SBW
statusPower off

Power onFig. 9 Countermeasure concept for wheel over-rotation

6. System Control
6. 1 System Startup/End Sequence
Figure 10 shows a timing chart indicating the systemstartup and end sequence. The system starts up whenthe vehicle ignition is turned on, after which it performs
an initial check. The steering lock then unlocks andthe phases of HMI unit and Steering unit are thenaligned. This alignment is performed because there is no
mechanical connection between these units, which may
result in the hand wheel angle and the road wheel angle
being misaligned before system startup. Once the phasealignment is complete, the engine (READY) is turned on
and BPS is activated, after which system control starts.
ON

OFF

Steeringlock

We will now explain the mode switching describedin section 5. 1 using a specific example in which modeswitching occurs in the event of failure. Figure 11 shows
an example in which a failure has occurred in the microcontroller on the system 1 side of HMI MCU. In thiscase, HMI MCU immediately stops operation of system
1 and switches to one system drive (SBW_Mode4) using
system 2. Although Steering MCU of system 1 is capableof operating normally, because its continued operation
would complicate control being performed, all operationof system 1 is stopped in order to ensure reliability.
Steering MCU

HMI MCU

Steering MCU

FailureMain

HMI MCU

Main

Main
stoppedMainstopped

Sub

Sub

Sub

Sub

SBW_Mode4

SBW_Mode1

SBW_Mode4

SBW_Mode4

Fig. 11 Transition of SBW_Mode

6. 3 Switching in the Event of Main Battery Failure
In the power supply system described in section 5. 2,
BPS detects the main battery failure and switches thepower supply source for system 1 from the main battery
to BPS internal power supply in order to continue
supplying power to MCU.

7. 1 Control Outline
OFF

Initial check

Locked

BPS

OFF

SBW

OFF

OFF

ON
Unlocked

Initial check
Initialcheck

LockedReady tobackupSynchronization Normal operation

OFF
OFF

：Transition trigger

Fig. 10 Timing chart of SBW system40

6. 2 Mode Switching in the Event of EE System
Failure7. Steering Control

Ignition
Engine(READY)At system end, system control ends once the vehicle
ignition has been turned off and the steering lock engages.
This sequence prevents the hand wheel from freely
turning when the system is stopped.

Figure 12 shows a control outline. HMI unit detects thehand wheel angle and sends that information to Steering
unit. Steering unit calculates the target road wheel angle
by taking into account factors such as the gear ratio basedon the hand wheel angle, and performs angle feedback
control based on the target road wheel angle and actualroad wheel angle. Conversely, Steering unit detects
things such as the motor current and the road wheel angle
and sends that information to HMI unit. HMI unit thengenerates reaction torque based on the road wheel motor
current, the road wheel angle, and the hand wheel angle.

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Development of Steer-by-Wire System (J-EPICS) with No Mechanical Link

with an obstacle on the road surface. For this reason,
the system includes a function for notifying the driverwhen the deviation between the hand wheel angle and theroad wheel angle exceeds a constant value. As shown in
Fig. 14, when the angle deviation between the hand wheel
angle and the road wheel angle exceeds a constant value,
reaction torque is increased to both notify the driver thatamount of road wheel operation is unable to keep up andto suppress road wheel operation by the driver in orderto prevent angle deviation from exceeding the current
amount.

HMI unit
Reaction torquegenerator
Hand wheel angle
Variable gear
ratio function
Target road wheel angle
Angle feedback
control function
Steering MCU current, road wheel angle

Fig. 12 Control outline

7. 2 Transmission of Road Surface Information to
the Driver
Because there is no mechanical connection between
HMI unit and Steering unit, a function is necessary for
informing the driver of road surface conditions whiledriving. However, because there are certain types of
information that should not be provided to the driver, suchas brake vibration and kick-back on bad road surfaces, thedriver is only provided with the necessary information.
As shown in Fig. 13, HMI unit generates reaction torquebased on the motor current of Steering unit. Because thecurrent contains other information such as on the vehicle
behavior and road surface, the driver can perform handwheel operation based on that information, providingthem with the same sense of security as a conventional
steering system. Furthermore, if information transmissionis unnecessary, HMI unit generates reaction torque basedon the target road wheel angle obtained from the handwheel angle. This reduces the driver’s burden provided
with unnecessary information.
Target road wheel angle
based on handwheel angle
Reaction torque generation
based on angle
Steering MCU
current

Reaction torque generation
based on current

Reaction
torquearbitration

Fig. 13 Block diagram of reaction torque generators

7. 3 Transmission of System Status to the Driver
Because there is no mechanical connection between
HMI unit and Steering unit, there may be instances inwhich the driver feels a sense of discomfort, such as when
the hand wheel angle and the road wheel angle become
deviate from each other due to the tires coming in contact

JTEKT ENGINEERING JOURNAL English Edition No. 1019E (2023)

Reaction torque, N·m

Steering unit

50
45
40
35
30
25
20
15
10
5
0

Angle deviation, deg(between hand wheel and road wheel)

Fig. 14 Reaction torque against angle deviation

8. Conclusion
We have worked to develop SBW system that features
excellent compatibility with ADAS and AD and that
improves comfort and convenience during manual
driving. Because we made ensuring system safety
our number one priority during this development, we
equipped the system with redundant EE systems and
BPS to respond to EE system and power supply failures.
Additionally, we have succeeded in developing a systemthat ensures safety by incorporating a function that limits
the rotation angle to prevent hand wheel over-rotation.
Furthermore, we have worked to ensure system reliability
by employing technology established for EPS. On topof that, we have established basic SBW technology forachieving performance equal to or higher than EPS, suchas phase alignment of the hand wheel angle and the roadwheel angle.
In the future, we will continue to promote developmentwith the aims of providing comfort and convenienceduring manual driving by taking advantage of SBW andrealizing high added value by leveraging compatibility
with ADAS and AD.
We would like to express our deep gratitude to Toyota
Motor Corporation and Denso Corporation for thevaluable advice and cooperation they provided in thedevelopment of this system.
* J-EPICS is a registered trademark of JTEKT Corporation.

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Development of Steer-by-Wire System (J-EPICS) with No Mechanical Link

References
1)

2)
3)

4)

M. MATSUOKA: Development and Future Outlook ofSteering Systems, JTEKT ENGINEERING JOURNAL,
No. 1013E (2016) 8.
ERTRAC: Development paths, ERTRAC Connected
Automated Driving Roadmap 2019 (2020) 12.
CABINET SECRETARIAT Strategic Headquarters for
the Advanced Information and Telecommunications
Network Society: kongo no ITS kousou no kihontekina
kangaekata, sankoushiryou, Kanmin ITS kousou･roadmap
2021 (2021) 18-34, 35-37 (in Japanese).
SAE international: Taxonomy and Definitions for Terms
Related to Driving Automation Systems for On-Road
Motor Vehicles, J3016 (2016).

K. NISHIMURA* I. NAMIKAWA**K. ABE*

Y. KAJISAWA* R. YAMAZAKI****

Advanced System Development Dept., Automotive
Business Unit** Function and Software Engineering Dept., Automotive
Business Unit*** Engineering Planning Dept., Automotive Business Unit

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JTEKT ENGINEERING JOURNAL English Edition No. 1019E (2023)