TECHNICAL PAPER

PairdriverTM
Steering Collaborative Control for Automated Driving*1
N. SHOJI T. NAKADE T. TAMURA

R. FUCHS

Safety and comfort in automated vehicles are related to how the driver and the automation system cooperate
during the driving task. We propose a control framework for electric power steering (EPS) where both manualand automated driving can coexist, and which enables cooperative driving. Sharing manual and automatedlateral control provides a new driving experience, where the driver can steer the vehicle over the automation
system without deactivation. Manual intervention is intuitive, as the driver only needs to hold, steer, and release
the steering wheel. Furthermore, this control provides haptic information about where the automation system isheading when manually steering.
Key Words: shared control, human machine interaction, electric power steering, automated driving, ADAS

1. Introduction

2. Sharing the Driving Task

Safety in automated vehicles is related to how the driverand the automation system collaborate in the driving
task1). Intuitive and consistent operation of the vehicle up
to SAE (Society of Automotive Engineers) automationlevel 4 through elaborated human-machine interaction isa key enabler for safety, comfort, and market acceptanceof driving automation2). This paper presents the control
framework Pairdriver TM*2 for electric power steering(EPS), which enables manual and automated driving tocoexist in order to achieve collaborative driving.
An overview of the prior art and of the proposed
control is presented following the division of thedriving tasks in Chapter 2. Issues related to control aredefined in Chapter 3. Chapter 4 provides details on
the proposed control, and Chapter 5 presents the resultsof verifications performed on an actual test vehicle. In
Chapter 6, the extension of the proposed control is
discussed and application examples are introduced in
Chapter 7. Finally, the paper is concluded in Chapter 8.

Driving collaboration is often simplified to theauthority transfer between manual and automated driving
at a low level of automation (SAE level 1 and 2). Override
or takeover when using lane centering assistance (LCA)
is straightforward as long as the level of intrusion remains
low. Typically, if the driver opposes the LCA torqueabove a certain threshold, the function is automaticallydisengaged. Because of the low level of intrusion of such
ADAS, the torque threshold is set to a relatively low
value and a seamless transfer of authority is achieved.
When the level of intrusion increases, or at higher levelof automation (SAE level 3 and 4), higher performanceof the angle control of the EPS is achieved, improving
the capability of the vehicle in tracking the lane center3).
The angle control in automated driving mode and theassist control in manual driving mode oppose eachother. A manual input is seen as a disturbance and isrejected by the angle control. Previous experiences havedemonstrated that seamless and robust authority transfer
is obtained by a weighted shared control mode during
the transition4). The proposed approach aims to combine
automated and manual operations into a single, nonexclusive control mode using a weighting function during
the transition triggered by the manually induced angle
error. While authority transfers are well performed, thefull potential of driver–automation shared steering control
is not exploited.
The literature shows that the concept of shared control
and, more generally, of mixing EPS assistance with angle*1 This paper is a revised version of the paper published in theproceedings of technical paper presentations at the 2019 JSAE
Annual Autumn Congress.
*2 Pairdriver™ is a registered trademark of JTEKT Corporation.

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Steering Collaborative Control for Automated Driving

Strategic planning
Tactical maneuvering
Operational control

Navigation
A to BGPS andstatic map>0.01 Hz

Trajectory(curve, lanechange, …)
Onboardsensors,
dynamic map

TorqueAccelerator DrivertorqueVehicleMotionControl〜 0.1 Hz

Steering
control

Plant
(EPS)

Brake

〜 1 Hz〜 10 Hz

Vehicle&Sensors

Angle

Fig. 1 Schematic structure of the automated driving control. Accelerator and brake controls are not illustrated for the sake of clarity

control has been addressed in various ways. The levels of
implementation in the automated system (Fig. 1) and thevariety of control objectives demonstrate the wide scopeof applications and implication of this concept. However,many publications focus on how to prioritize the driveror the automation system and how to manage conflict,providing limited answers to the technical challenge ofdeveloping a control framework enabling both agents tocoexist.
For example, Benloucif et al . propose a control thatenables driver input by modifying the trajectory of theautomated system accordingly 5). This implies regularrerouting of the trajectory whose response is not likely
to be optimal (slow bandwidth as indicated in Fig. 1).
Cerone et al . introduce a combined automatic lanekeeping and driver steering with a 2-dof control at thelower level of vehicle motion control 6). This has thebenefit of offering faster response, although the goal is toenable an exclusive manual or automated control mode.
Abbink et al . address the problem of shared control at theactuator level optimizing the response time7). The control
is based on knowledge of neuromuscular control, which
limits its market acceptance due to low robustness. Morerecently, Klesing et. al . presented a work on operatinga steering system in a dual-model vehicle8). A sharedcontrol scheme is proposed for a steer-by-wire system
where the two driving modes coexist only electronically.
At first, the driver’s performance in following the
trajectory of the automated system is evaluated prior toenabling driver input as a command of the wheel angle
control.
This paper presents a control framework for EPS where
both manual and automated driving can coexist to enable
collaborative steering. Shared control is implemented at
the operational level1) (Fig. 1). Technically, the classicalassist control of EPS active in manual driving and theangle control used for lane centering are mixed without
internal modification in a two degree-of-freedom control
architecture. It is a cost-effective solution because it
relies solely upon the sensors available in mass-produced
EPS. From an operational point of view, any manual

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

intervention is intuitive as the driver only needs to hold,steer and release the steering wheel. No switch or button
activation is required, reducing driver workload while
improving comfort and safety. The driver naturally steers
the vehicle over the automated actuation. Furthermore,this control provides haptic information regarding
where the automation system is heading when manuallysteering.

3. Control Problem Formulation
The definitions of shared and collaborative controls
used in this paper are first stated before formulating theconsidered problem. From a system (automated driving)
perspective, the operational or actuator control receives
a command from the higher tactical (guidance) andstrategical (navigation) levels (Fig. 1). Shared control
is implemented at the operational level or in the EPS.
Human-machine collaboration is considered at the tacticalor strategical level1).
The following specifications must be satisfied
concerning the shared control problem underconsideration:
・Prior to any driver steering action, the vehicle tracks
the trajectory planned by the automated system in acontinuous manner (no signal interruption).
・When the driver initiates a manoeuvre, the angle
control remains active, but the vehicle trajectory is
modified seamlessly (no external steering wheel jerk,i.e., a jerk that is caused by other sources than thedriver).
・While steering, the driver feels a torque indicating, forexample, where the AD is heading (haptic feedback forsafety).
・If the driver releases his hands from the steering wheel
when the vehicle is on the AD trajectory (i.e., the errorof the angle control is null), the vehicle lateral motion
is smooth (no external steering wheel jerk).
・If the driver releases his hands from the wheel whenthe vehicle deviates from the AD trajectory, the vehicle
automatically returns to that trajectory (safe vehicle

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return should be considered at tactical and strategicallevels).

4. Haptic Shared Control of EPS
This section first describes the proposed haptic sharedcontrol of EPS. Afterward, its performance and haptic
feedback are discussed along with test data.

4. 1 Control Structure
The structure of haptic shared control is illustrated
in Fig. 2. hm, ad, cmd is the automated driving (AD) angle
command, hm, md, cmd is the manual driving (MD) angle
command, hm, ma, cmd is the steering angle command, andhm is the actual steering angle. T d is the driver torque,
T tb is the torsion bar torque, T m is the motor torque, andT assist is the assistance torque.
The manual reference controller (MRC) is used toenable the two agents to work together on the plant.
Basically, it is composed of a model of the EPS (Fig. 3),
which computes the angular displacement generated
manually from the measured driver input. This angularcomponent or MD command is then added to the AD
command as input to be tracked by the angle controller.
In this way, both AD and MD commands are tracked
together by the EPS.
hm, md, cmdhm, ad, cmdhm, ma, cmd

With this, the reaction torque felt by the driver is related
to the manually induced deviation away from the AD
trajectory. The content of this feedback can be designed,
for example, to indicate the automation system heading
direction. Furthermore, because of the spring effect,
if the driver releases their hands, the steering wheel
automatically returns to the AD trajectory. This provides
significant benefits in terms of safety, firstly for the driver,as the haptic feedback informs them on where the AD is
heading, and secondly for the vehicle, in case of driver
misuse (e.g., the driver suddenly removing their handsfrom the steering wheel).

5. Actual Vehicle Verification
Figure 4 gives an example of shared control datameasured on a vehicle equipped with an EPS. The AD
trajectory follows the path of a winding road. Between
about eight and fourteen seconds of the simulation,
the driver steers the vehicle away from the roadwork.
The steering angular displacement shows that the AD
trajectory command is accurately tracked before andafter the driver maneuver. During the driver intervention,
the manual action is superimposed on the AD trajectory
according to the stated objective. Furthermore, the EPS
applies a small torque directed toward the AD trajectoryas haptic information.

TassistMRC
Angle
control

Steering Collaborative Control for Automated Driving

Td
Tm

Ttb
Plant
hm
(EPS)

Assistcontrol

6. Function Extension
This chapter describes function extensions for the basic
control structure described in Chapter 4.

Fig. 2 Structure of haptic shared control

6. 1 Extending Haptic Feedback
EPShm, md, cmd

TassistAD

Fig. 3 Example of structure of MRC

4. 2 Haptic Feedback
One objective of haptic shared control is to provide
haptic feedback to the driver while maneuvering. Thisfunction is realized with the load applied to the EPS
model of MRC (Fig. 3). This load can be designed andtuned according to the steering feel, safety, and any otherobjectives. In its simplest form, this load is represented
by a spring and a damper connecting the EPS inertia to
the ground. Instead of using an absolute ground, a relativereference corresponding to the AD command is preferred.

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Section 4. 2 provided an explanation regarding haptic
feedback as defined by springs and dampers. In this case,the characteristics of the reaction force felt by the driver
remain constant regardless of driving conditions. Here,using a variable load according to driver and vehicle
conditions is expected to improve the steering feel
during manual intervention. For example, changing thecharacteristics of the springs and dampers according to
the vehicle speed, or measuring the reaction torque fromthe actual road surface and setting the load accordingly
are available options. Furthermore, using sensors such as
cameras to recognize traffic environments would enable
the provision of haptic feedback based on the positionof the vehicle in the driving lane and its distance fromobstacles. This would enable the driver to intuitively feel
conditions around the vehicle via the steering wheel.
In other words, because driving can be performed ascollaboration between automated and manual steering,
driving safety would be improved.

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Steering Collaborative Control for Automated Driving

Driver torque2

Torque, N・m

Pairdriver

1
0

AD
40

AD command
SW angle

30
Angle, deg

20
10
0
10
20
30
0

5

10

15

20

25

AD

Fig. 4 Concept validation made on a vehicle equipped with an EPS. The AD trajectory follows the path of a winding
road. At the location of the roadwork, the driver adjusts the position of the vehicle. During this manualintervention, he feels a small torque in the direction of the AD trajectory.

6. 2 Shift to Manual or Automated Control
The previous section presented haptic shared control
that enables AD and MD to coexist. There is no switch
or weighting function for setting the steering mode.
However, a means to allocate the steering control
authority is still required for safety reasons. This willallow prioritization of manual, automated, or sharedmode according to higher-level instruction. The tacticaland strategical controls are responsible for evaluating
the traffic context as well as the driver awareness andreadiness necessary for the priority decision process.
One way to extend the proposed configurations is byadding a control authority selector after the AD and MD
commands (Fig. 5). Continuous and smooth fade-in/out
functions are preferred to ensure seamless prioritization.
For example, when driving in shared mode, if a transition
to manual is required, selector weighting over a certain
period of time will gradually shift the control authority.
However, this would require the characteristics ofthe control authority selector to be appropriately set
depending on the conditions. For example, it would
also be necessary to have a setting for giving priority toautomation during emergency avoidance by immediately
switching to automated mode.

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AuthoritycommandSelectorhm, md, cmdhm, ad, cmd

TassistMRC
Angle Td
control Tm

Ttb
Plant
h
(EPS) mAssistcontrol

Fig. 5 Haptic shared control framework. The selector
function enable an external input to allocate thesteering mode to manual, shared and automatedsteering.

7. Examples of Applications
This chapter introduces examples of applications forthe proposed shared control. It shows that well-known
steering functions required in automated vehicles do
not require separate development. The proposed sharedcontrols enable most of these issues to be addressed
within a single and generic framework.

7. 1 Lane Centering Assistance and Lane Keeping
AssistanceLevel 1 and 2 vehicles, in which the driver is the main
operator, are equipped with functions that assist the driverin keeping the vehicle at the center of the lane and in thelane. Shared control can be applied because it enables
guidance towards the lane center by superimposing
assistance torque on the manual steering. Typically,
the assistance function is deactivated when a large
amount of driver steering torque is applied. Applying
the configuration shown in Fig. 5 enables smooth shifts
between manual mode and shared mode, depending on
the steering torque. However, override free assistance

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Pairdriveris possible because of the absence of conflict in sharedcontrol even when high manual torque is applied.
Furthermore, shared control can be used for lane
keeping assistance. This function generally alerts thedriver by adding guidance torque for returning the vehicle
to the lane center when the distance between the vehicle
and lane markings falls below a certain threshold. Sharedcontrol is expected to improve safety because it enables
the virtual load of MRC to be adjusted based on the
distance to the lane edge, thereby enabling enhanced
control of the reaction torque to the driver operation.

Steering Collaborative Control for Automated Driving

harm to the driver when the steering wheel is subjected
to an abrupt and large angular displacement. The SBW
system and angle overlay device offer hardware solutions
to this second issue but at a cost that is not acceptable forall vehicles. Shared control provides a partial but costcompetitive solution because of the compliance withdriver input. Indeed, if one of the driver’s arms is placed
inside the steering wheel, the force felt by the driver willbe that generated by the spring in the sharing controller(Fig. 3) rather than that developed from the maximum
torque of the assist motor. Driver injury is prevented at
the cost of a deviation from the AD trajectory.

7. 2 Road Narrowing
Drivers often encounter road narrowing, for example,
at locations where roadwork is taking place. Intuitively,
they adjust the vehicle position between the lanes
and sometimes cross a lane in order to feel safe in thechanging road condition. For a driver in an automateddriving vehicle, such a situation might be uncomfortable
if enough space remains within the lane but the safetymargin of the vehicle position becomes narrower.
Moreover, if a lane has to be temporarily crossed, theautomation system might face limitations. In both cases,
shared control enables the driver to momentarily adjust
the vehicle position manually without deactivating theautomated driving system (Fig. 6).

Fig. 6 Example of adjustment of vehicle positioning using
shared control. During the driver intervention, theAD remains active.

7. 4 Take Over Request (TOR)
TOR is a demand sent by the vehicle to the driver
asking to regain manual control in the case of an
anticipated limitation of the automation system (Fig. 7).
Safe operation of the TOR has generated significant
attention due to the complexity of setting a reasonable
timeframe for the driver to recover their awareness of thetraffic situation. Shared control offers a partial solution to
the problem of authority transfer by avoiding an exclusive
interpretation. It can be activated instantly when the TOR
is released, enabling manual steering without immediate
disengagement of the AD mode. When the driver feels
confident in regaining control of the vehicle, they canturn off the shared mode. Even in a worst-case scenario
in which the driver fails to manually take control of thevehicle, a minimum-risk maneuver can be launchedwithout any particular setting of the EPS control. Thisillustrates the consistent operation of the proposed
framework.
Time budget
Take-over Time7. 3 Evasive Steering Assist and AutomatedEmergency Steering (AES)
Evasive steering assist and automated emergency
steering are technologies that are recently gaining
particular attention because of their potential in providing
additional contributions to vehicle and road safety9). The
former technology assists the driver after detecting theirintention in initiating an evasive maneuver. A small torqueis added to that of the driver for facilitating collision
avoidance. The responsibility remains that of the driveras the function is active only while manually steering.
Similarly to the application of guidance, shared control
can be applied to superimpose the evasive assist torque.
AES is more complicated as the driver is no longer
responsible. Technically, such a function has at least two
additional constraints. The first is to avoid causing anotheraccident during the emergency maneuver, especially if
it is necessary to cross lanes. The second is to ensure no26

MRM Time(1) Manually
AD switch off(2) No reaction
ÆMRMFig. 7 Application to a TOR. Shared control is set
immediately after the release of the TOR enabling thedriver to steer at any time. Only confirmed operationof the driver can turn-off the AD mode. Furthermore,shared control can remain active when launching theminimum risk manoeuvre in case of no reaction fromthe driver.

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Steering Collaborative Control for Automated Driving

7. 5 Override Function for SBW Systems
In terms of driver comfort, one of the benefits of
the SBW system in automated driving vehicles is thatit enables the steering wheel position to be locked.
Conversely, a drawback of a fixed steering wheel
arises during a driver takeover operation when thesteering wheel is not aligned with the wheels. If anangular synchronization is required, robot-like control(e.g., position control) is performed initially to cancel
the angular offset. The time allotted for the angularsynchronization should be short enough so as not toconstrain the driver in his maneuver but long enoughto prevent discomfort caused by too fast motion of thesteering wheel. Shared control provides a solution tothese issues.
As shown in Fig. 8, implementation is possible in a
two-stage form with the first stage applied to the rack
(gear) and the second to the steering wheel with thereaction force unit (column). In this implementation,
the angular synchronization is triggered by the detectionof the driver’s hands on the steering wheel (e.g., usinga hands-on detection function). The first advantage ofapplying the proposed control is that driver intervention
is enabled at any time throughout the synchronization.
The second advantage comes from the steering wheel
compliance that guarantees no harm to the driver during
sudden motions. In practice, the following two extreme
patterns are possible. Firstly, the driver holds the steering
wheel without applying much torque. In this case, thesteering wheel aligns with the wheels. Secondly, thedriver firmly holds the steering wheel. Here, the wheelsalign with the steering wheel.
hm, md, cmd
SW lock
positionhm, ad, cmd

HOD
trigger
SmoothswitchMRC

8. Conclusion
The proposed haptic shared control has been presented
as a generic control architecture for EPS where bothmanual and automated steering can coexist. During sharedsteering mode, the collaborative characteristics can betuned in a flexible manner by controlling haptic feedback
via the manual reference controller. Moreover, shifting
between manual, shared, and automated steering modes
is possible by applying a smooth control mode selector.
Haptic shared control provides solutions to various
functional requirements of EPS in highly automatedvehicles within a single, computationally efficient, andconsistent framework.
Technically, the concept is cost-efficient and has good
adaptability based on the existing hardware. The maturetechnologies of steering assistance and angle control canbe implemented in their original form and can still be
independently improved. Only an additional controller oflimited computational load is required to blend the twocontrols.
From a driver perspective, haptic shared control
enables AD and MD to be active at the same time without
the need for manual switching. Naturally, the driver cansteer over the AD operation. Conversely, they feel the AD
heading direction through haptic feedback.

References
1)

TassistAngle Td
control

Plant(Column)

Ttb Assist
control
hm, c

Angle
control

Plant(Gear)

hgear

Fig. 8 Example of haptic shared control applied to a SBW
system. The selector function for the driver input is
replaced by a smooth switch function triggered by thedetected hands state. For the sake of clarity, theselector functions for the steering authority allocation
are not shown.

2)

3)

4)

5)

6)

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F. Flemisch, D. Abbink, M. Itoh, M-P. PacauxLemoine, G. Webel: Shared Control is the Sharp End
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Scheme for Haptic Shared Lateral Control in Highway
Driving Using Trajectory Planning, 20 th IFAC World
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Automatic Lane-Keeping and Driver’s Steering Througha 2-DOF Control Strategy, IEEE Trans. On Control
Systems Technology, Vol. 17.1 (2008) 135-142.

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7)

8)

9)

Steering Collaborative Control for Automated Driving

D. A. Abbink, M. Mulder, E. R. Boer.: Haptic Shared
Control: Smoothly Shifting Control Authority, Cognition,
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NCAP, (2017).

N. SHOJI*

T. NAKADE**

T. TAMURA**

R. FUCHS**
*
**

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Advanced System Development Dept., Automotive
Business Unit
S y s t e m s I n n o v a t i o n R & D D e p t . , R e s e a rch &Development Division

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