OUTLOOKDevelopment and Future Outlook of Steering Systems
H. MATSUOKA

This report first describes the history of steering systems, as well as the predicted future trends of ADAS
(Advanced Driving Assist System) and the role of the steering system within ADAS as a steering function, including
mechanical and electronic controls. It also describes the steer-by-wire system recognized as the means for achieving
ADAS. Furthermore, this report illustrates the development of electric power steering and the achievement ofequipment safety for safety requirements such as in ISO26262, which have accompanied its development. It also
explains the application of the technologies achieving the required safety (achieving product safety conforming to
the requirements of standards such as ISO26262) on ADAS.
Key Words: EPS, ADAS, SBW, ISO26262

1. Introduction
Modern day vehicles became able to detect thesurrounding area and driving conditions with highaccuracy, advancements have been made in the realizationof active safety technologies such as automatic emergency
braking systems. At the same time, the Electric Power
Steering (EPS) system, which was first mass-producedby JTEKT in 1988, has spread widely, to the point
where, currently, over half of all passenger vehicles areequipped with EPS systems. Furthermore, advanced
driver assistance systems which use the degree of control
freedom offered by EPS such as automatic parking
systems and Lane Departure Warning (LDW) systems/
Lane Keeping Assist (LKA) systems are also gaining
popularity. The further advancement of these technologies
foreshadows the rise of the Advanced Driver Assistance
Systems (ADAS) and the automated driving systems,
therefore the function and performance of steeringsystems must be improved in order to facilitate ADAS
systems. This paper reviews the history of steering systemdevelopment, as well as describes the predicted futureadvancement of ADAS, the steering functions required forsuch advancement, and the concepts behind the systemand safety design which enable the ADAS to be created.

2. History of steering systems
The realization of Hydraulic Power Steering (HPS) in
the 1960’s decreased the necessary steering force to turnthe steering wheel (SW), thus reducing the burden on thedriver. Moreover, the reduction of steering force required
to turn the steering wheel while parking, stability in

8high-speed driving and good steering feeling have beenachieved by controlling the assist power corresponding tovehicle speed. Furthermore, the first practical applicationof EPS, developed by JTEKT, contributed greatly to the
reduction of fuel consumption.
Figure 1 shows production volume and forecast forvehicles on a global scale, according to the steering type.
In 2001, HPS accounted for the majority of vehicles
which adopted power steering, however the recent
expansion of EPS to use in large size vehicles has led toa rapid increase of EPS production volume since 2010.
At the same time, the installation ratios of each EPS
type have changed. In addition to C-EPS, which has an
assist mechanism incorporated in columns suitable forsmall vehicles, which were mainstream up until now,gear type EPS (DP-EPS, RP-EPS) which has an assist
mechanism incorporated in rack shafts suitable for large
vehicles have been increasing (Fig. 2). The transition to
EPS in vehicles is predicted to continue increasing in linewith stricter fuel economy regulations, popularizationof advanced driving assist technology, and realizationof various ADAS functions. The transition of JTEKT
steering products is shown in Fig. 3. In order to respondto the various steering requirements of OEMs, JTEKT
offers product series containing each product lineup andis constantly developing new technologies. We consider
the development of steering systems which respond to theevolution of vehicles as well as the related technologies
for such systems to be our mission.

JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)

120 000
100 000

Production volume, millions

Production volume, thousand/year−Development and Future Outlook of Steering Systems−

Unknown

80 00060 000HPS

40 000H-EPS

20 000

EPS

0
2001

2006

2011

2016

H-EPS
DP-EPS

120

RP-EPS
C-EPS

Total number of vehicles

100
80
60

56%

61%

65%

66%

68%

69%

64%

2015

2016

2017

2018

2019

40
20
0

2013

2021

Year

RD-EPS
P-EPS

2014

Fig. 2 Production volume percentage (global) by EPS typeFig. 1 Results and forecast (global) of automobile production
volume by steering type
1960

Markettrend

Steering
system

1980

1990

1995

2000

2005

2010

Spread of vehicles
Expansion of
manufactured in population owningJapan
vehiclesDemand for low fuel consumption

Manual steering

2015

2020

Year

Number of passenger vehicles in Japan reaches 58 million

Increase of large size passenger
Tighten up theOpening of the Tomei
vehicles in Japan
expressway
CO2 restrictions
Number of passenger vehicles in Japan reaches 10 million

Increase of HEVs and EVs
Increase in the demand for low fuel consumption
High-output EPS

Electric power steering

Diversification of demands (steering feeling, quietness, weight reduction)

Hydraulic power steering

Functional safety

High-output EPS

Further demands for low fuel consumption
and expansion of the EPS’s covered area

RP-EPSElectric power assist

RP-EPS

RD-EPS

MC nylon
reduction gear
World-first

EPS
system

DP-EPS

DP-EPS
C-EPS (1988)

Product
development

Transition from hydraulic power assist toelectric power assist corresponding tolower fuel consumption

2-bobbin type
torque sensor
C-EPS
Brushed motor

P-EPS
Twin resolver type
torque sensor
Brushless motor

J-ISM
Hall IC type
torque sensor

ECU attached type motor
Motor ECU supporting
ECU integrated type motor functional safety

H-EPS
VFC pump

HPS
systemHydraulic assist

Manualsteering

Manual Rack and pinion Increase of power steering systems in line with the spread of vehicles
made in Japan and expansion of the population who possess vehicles
Ball screw

Rack and pinion
HPS

Ball screw

JWill (next-generation controls)
Redundant torque sensor

H-EPS

Offer products for all vehicle categories from light vehicles to small trucks

Vehicle trend(general)1970

Fig. 3 History of JTEKT steering products

3. Advancement of ADAS and evolutionof steering systems
3. 1 Market trends of ADAS
The type and number of driving assistance systems
able to enhance the safety performance of vehicles suchas automatic emergency braking system and LDW/LKA
system have increased dramatically in line with therecent rapid evolution of computer processing ability,
the dramatic improvement of sensing ability and the cost
reduction of environmental recognition sensors such as
cameras and radars. The penetration rate of these systems

JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)is expected to increase significantly in line with theirgradual legal enforcement and as they become an item
for NCAP rating, because the systems largely contributeto a decrease in the number of traffic accidents andthe number of victims. The possibility of the practicalapplication of automatic driving systems which fully
replace the operation of the system by the driver has
been growing due to the advancement of ADAS. The
advancement of functions and the expansion of applicableroads for the automated driving system will be expected
to increase in stages at almost the same time in Japan,
the United States and Europe (Fig. 4). These have the9−Development and Future Outlook of Steering Systems−

1)*The levels in Fig. 4 reference the NHTSA levels in
Table 1potential to drastically change the vehicle society as
well as people’s lifestyles, through a change of vehicle
themselves, the acceptance level of the system by society
and the revision of laws and regulations.
2013
U.S.A.

2015

Level 1
ACC, LDW
Simple function

2020

Level 2Highway only
Driver supervision required
Partial automation
Driver supervision
requiredEU

ACC, LDW/LKA

Japan

Individual driving assist(ACC, LDW/LKA, etc.)
Highway (same traffic lane)

2025

Level 3Highway only, Reading books is acceptable. Avoidance
maneuver is done by the driver in emergencies

2030

Level 4
Highway + urban areas
Sleeping is acceptable

Advanced automation, highway
Reading books is acceptable

Complex assist
High speed / multiple traffic lanes
Driver supervision required

Unmanned operation
Autonomous operation
Complete automation
Sleeping is acceptable

Sophistication of driving assist Highway(branching and merging support), system normally supervised by the driver

Driver intervention is required in emergencies

Automated driving
test runFig. 4 Roadmap of automated driving system introduction by country

Table 1 Levels of automation (Draft)1)

NHTSA SAE
level level

SAE
name

SAE deﬁnition

Driver themself monitors driving environment
0

1

2

0

Manual1

The driving assist system performs either steering
wheel operation or acceleration/deceleration
Assistance depending on the driving environment while thedriver operates parts that are not assisted by thesystem.

2

The driving assist system performs steering wheel
Partialoperation and acceleration/deceleration depending
automation on the driving environment while the driver operates
parts that are not assisted by the system.

The driver always performs all driving operations.

Responsible for
Responsible
steering wheel
Monitoring
for theoperation andof travelingbackupacceleration /environment of driving
deceleration ofoperation
the vehicle

Systemcapability(driving
mode)

Driver(human)Driver(human)Driver(human)−Driver(human)+ system

Driver(human)Driver(human)Somedriving
modes

SystemDriver(human)Driver(human)Somedriving
modes

SystemSystemDriver(human)Somedriving
modes

SystemSome
driving
modes

SystemAll
drivingmodes

Automated driving system monitors driving environment

3

3

The automated driving system performs all driving
Automation operations of the vehicle in the speciﬁed driving
mode, under the condition that the driver responds
withconditions appropriately to system requests for transfer ofdriving responsibility.

4

The automated driving system performs all
driving operations of the vehicle in the speciﬁed
Advanced
driving mode, even if the driver does not respondautomation
appropriately to the system requests for the transfer
of driving responsibility.

5

The automated driving system always performs
Complete driving operations of the vehicle, on the road andautomation with the driving conditions in which even the driveris able to operate as well.

4

10

SystemSystemSystemSystemJTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)

−Development and Future Outlook of Steering Systems−

3. 2 Requirements for steering systems

4. Ensuring safety

The functions which are required of steering system
are predicted to change in line with the advancement of
ADAS and automated driving systems.
Figure 5 shows the relationships between the functionsof each type of driving assist system, the level ofautomation of the automated driving and the requirementsof steering systems. LDW/LKA and TJA systems, which
are conventional systems, are either in mass production
or planned for mass production in the next few years
at many OEMs. Since they are driver responsibility
systems, an override function which prioritizes thedriver's intention in emergencies is mandatory for thesteering system. Maintaining of the steering function
until the driver takes over the responsibility of driving incases where emergency steering is required is mandatory
for the system responsibility automatic driving systems
which will be in mass produced around the year 2020.
Furthermore, if a system reaches the level where thejudgments made by the system are safer than the
judgments made by the driver, the steer-by-wire (SBW)system, in which coordination and interference with thedriver can be controlled freely, would be an extremely
effective system and highly likely to become mainstream.

4. 1 Support for functional safety
Recently, EE systems which are equipped on vehicles
have become more complex and significantly advancedin their performance and function, as seen in the exampleof the EPS system. Moreover, the number of EE systems
has increased rapidly. As such, these systems are required
to operate without failing or malfunctioning to enable
the safe operation of vehicles. Therefore, the concept offunctional safety, established as the international standard
IEC61508, has been introduced to the automotive industry
as the international standard ISO26262 for functionalsafety in vehicles. ISO26262 became effective from 2011.
According to ISO26262 specifications, failures and bugs
which occur within electronic control devices are ranked
corresponding to risk, the rate of occurrence of failure
and the ability to avoid collisions. (ASIL designation(Fig. 6), Failures and bugs are treated in a v-model for
product development which integrates safety measuresand traceability functions corresponding to their rank
(Fig. 7).

4. 2 Concept of ADAS support and ensuring safety
in EPS
The following failure modes are categorized as ASIL-D
in ISO26262 and are the most critical failure modes ofcurrent EPS systems.

Control details

Function
name

ACC

AEB

LDW

LKA

TJA

TJA (with lanechange function)

Automated steering

Automated steering/collision avoidance

Cruisecontrol

Deceleration
control
Tracking control

Mass production(predicted)
Automation
level
Steering
requirements

Mass production

2015−2018

Around 2020

Around 2025

Driver responsibility

Driver responsibility

Driver responsibility →System responsibility

Systemresponsibility

Avoid interference
Maintaining of basicwith driver input
functions in case of failure

Override by the driver

Steering
systemSBW

EPS

ACC: Adaptive Cruise Control
LKA: Lane Keeping Assist

AEB: Automatic Emergency Braking
TJA: Traffic Jam Assist

SBW
EPS

SBW

LDW: Lane Departure Warning
SBW: Steer by Wire

Fig. 5 Outline of advanced driving assist system controls and steering system requirements

JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)11

−Development and Future Outlook of Steering Systems−<Quantiﬁcation of risk>
Risk = Quantiﬁcation as Automotive Safety Integrity Levels (ASIL)<Deﬁnitions of risk>
Grade of severity
Driving conditions
Ease of troubleshooting

S1 (Low) through S3 (High)E1 (Rarely occurs) through E4 (Occurs whenever driving)C1 (Easy) through C3 (Diﬃcult)

S1

S2

S3

C1

C2

C3

E1

QM

QM

QM

E2

QM

QM

QM

E3

QM

QM

A

E4

QM

A

B

E1

QM

QM

QM

E2

QM

QM

A

E3

QM

A

B

E4

A

B

C

E1

QM

QM

A

E2

QM

A

B

E3

A

B

C

E4

B

C

D

Fig. 6 Definitions of ASIL2)

ReleaseRequirements
Concept design

Validation test

System design

Integration test

HW/SW design

Integration test

Implementation

Fig. 7 V-model of functional safety• Self Steering (SW rotates without steering input by
the driver or without any steering instructions, such as
automatic parking command, from the vehicle.)• Steering lock (SW in not able to rotated.)
These failures are managed by improvement of quality
corresponding to the function safety requirement ineach development, design and production phase and by
making the failure occurrence rate consistent with thefunction safety requirement by selecting electronic parts
with low failure rates. EPS systems are also designed
to prevent a situation from becoming more dangerous
in the case of system failure, including those describedabove, by shutting down the system using a dual-coremicrocontroller monitoring function and failsafe function.
Recently however, EPS assist power has been increased
in order to equip EPS to large vehicles (weight increase),12

hence the approach of shutting down systems in caseof failure became unacceptable because drivers can nolonger steer in a large vehicle without EPS assist power.
Moreover, in the case of ADAS and automated driving
systems, the system suspension of ADAS/automateddriving functions and/or EPS/SBW, which realize thesefunctions will be categorized as ASIL-D. There is ahigh possibility that maintaining of the steering system
function will become mandatory in the case of system
failure. JTEKT will supply fail-operational EPS systems
which either have minimal possibility of system shutdown(Table 2) or never stop system operation (refer to Fig. 8).
Step 1: Application of backup control (mass production)
Continuing of EPS operation by launching a
specific software in case of failure if it is possible.
Step 2: Hardware redundancy design. (Partially applied inmass production in 2015)
Continuation of partial EPS operations during
failures by duplicate circuits and EPS sensing
functions.
Step 3: Hardware and power supply redundancy design.
(Mass production scheduled in 2020: details
currently under discussion)
Continuation of full steering operation by
duplicate circuits and EPS sensing functions
combined with duplication of vehicle power
supply in case of system failure.

JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)

−Development and Future Outlook of Steering Systems−

Table 2 Fail-operational EPS system
ASIL relating toSystemsystem suspension
output during(including suspension
fail operation
by fail-safe)

Step

Concept

Method of achievement

3

Complete failoperational
function

Complete redundancy of
EPS system electronic
hardware including
vehicle power supply

ASIL-D

50％〜100％

2

Failoperational

Redundancy EPS systemelectronic hardware(ASIL-C)

50％

1

Partial failoperational

Backup using steering
wheel(ASIL-B)

20％

0

Systemsuspended incase of failure

Conventional EPS

QM

0% (Stopped)

Motor & ECU (1 package)

TargetADAS
systemASIL for selfrotation androtation lock

Automated
driving
TJA/
LKA
collision
avoidance

ASIL-D(Incident rate
less than
10FIT)LKA/
LDW*1 J-ISM is a registered trademark of JTEKT Corporation.

Power Supply
Power relay

TorqueSensor1

Battery1

References

inverter

VehicleCAN1

Current sensor

1)

Motor position sensor1
Redundant
Processing
Unit
TorqueSensor2

SensorMotor position sensor2

Sensor

Motor
Motor

Current sensor

VehicleCAN2

inverterBattery2
Power relay
Power Supply

Fig. 8 Fail-operational system block diagram (Example)

2)

5th Study meeting about the automatic pilot system
Document 2, p. 6 (Ministry of Land, Infrastructure,
Transport and Tourism)
http://www.mlit.go.jp/road/ir/ir-council/autopilot/doc05.
html
ISO26262-3 Road vehicles-Functional safety-Part 3:
Concept phase 7.4.4 Determination of ASIL and safety
goals Table.4

5. Conclusion
The realization of automated driving systems, which
would have been labeled science fiction only a decadeago, is rapidly becoming a conceivable reality. We standon the eve of a massive revolution in both vehicles andmotorized society. Despite many technical issues anddifficult legal issues such as where responsibility liesin the case of traffic accidents, industry, government
and academia in countries across the world are actively
engaging in the research and development of thistechnology and the prospect of realizing this dreamis rapidly progressing thanks to the achievement of
automated driving which dramatically increases theconvenience and safety of vehicles. As the company withthe top global share in steering systems, we at JTEKT
believe it is our duty to contribute by developing newtechnologies to support the realization of ADAS andautomated driving system that will continue to develop.

H. MATSUOKA**JTEKT ENGINEERING JOURNAL English Edition No. 1013E (2016)

Managing Officer

13