Stability control algorithm research improves handling and safety for Jaguar Land Rover drivers
Submitting InstitutionLoughborough University
Unit of AssessmentAeronautical, Mechanical, Chemical and Manufacturing Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Mathematical Sciences: Applied Mathematics
Information and Computing Sciences: Artificial Intelligence and Image Processing
Summary of the impact
Drivers of more than 20,000 Jaguar supercharged cars sold worldwide since
2009 are enjoying handling and safety benefits as a direct result of
research at Loughborough University. The active differentials control
system in production on Jaguar's XF, XJ and XK vehicles is controlled by
an algorithm developed at Loughborough. Funded by Jaguar Cars Ltd, the
research from 2002 to 2006 was first adopted, after only minor changes,
into the supercharged Jaguar XF programme released in 2009. The system is
now also in the new F-type and is being extended, in a modified form, to
Range Rovers, starting with the new Range Rover Sport.
Research on techniques to support vehicle stability control has been a
core theme at Loughborough for the past 25 years. The key research here
considered theoretical capabilities and control authority from relatively
expensive, overdriven differentials and also cheaper active limited slip
differentials (ALSD). Although it has a more limited torque transfer
capacity, the ALSD is capable of stabilising the vehicle's handling
response and is the system now in use on Jaguar vehicles.
The research started within an MEng individual student project undertaken
by Matthew Hancock (Loughborough undergraduate 1997 to 2002), sponsored by
Jaguar Cars Ltd and under the supervision of Timothy Gordon, then
Loughborough Professor of Vehicle Dynamics and Control (1985-2002).
Matthew Hancock joined Jaguar Cars' research division after graduation and
pursued the research via a part-time PhD with Loughborough, funded by
Jaguar, under the supervision of Loughborough lecturer Matt Best (employed
1996 to date) and industrial supervisor Robert Williams (JLR). The
resulting 2006 PhD thesis [3.1] includes most of the substantive
elements of research on which the production systems are based. Although
the protection of confidential and commercially sensitive material
restricted publication, the fundamental research has been presented in
respected engineering journals [3.2] and [3.3].
The research required vehicle and differential modelling and validation,
and the development of practicable control algorithms using model
reference and classical control techniques, to regulate continuously the
handling (understeer) behaviour and also maintain vehicle stability and
hence safety. The measure of stability that can be recorded most easily on
the vehicle is the rotation (yaw) rate through the corner. Thus in
developing the techniques for test vehicles, the fundamental research was
modified to use yaw rate alone to determine the control action, with its
magnitude adapted according to vehicle forward speed and road surface
friction. The vehicle development work also included integration and
conflict resolution of the ALSD with a conventional brake-based yaw
stabilisation system that is also invoked in the most extreme cases of
loss of control. The control strategy built on underpinning research at
Loughborough first published in 2000 [3.4] and 2002 [3.5],
where a linear optimal control is designed for a reference vehicle model
and control is applied in two loops, both feedforward and feedback. This
work was by Matt Best, Timothy Gordon and Ayao Komatsu (PhD student at
Loughborough, 1999 to 2003).
References to the research
3.1. Hancock, M.J., `Vehicle Handling Control using Active
Differentials,' PhD Thesis, Loughborough University, April 2006.
Available at https://dspace.lboro.ac.uk/2134/8075
or at request from Loughborough University.
3.2. Hancock, M.J., Williams, R.A., Gordon, T.J., and Best,
M.C.,`Comparison of Braking and Differential Control of Interactive
Yaw-Sideslip Dynamics', Proceedings of the Institution of
Mechanical Engineers, Part D (Journal of Automobile Engineering),
219 [D3] 309-27 (2005). DOI: 10.1243/095440705X6721.
3.3. Hancock, M.J., Williams, R.A., Fina, E. and Best, M.C., `Yaw
motion control via active differentials', Transactions of the
Institute of Measurement and Control, 29 137-57 (2007).
3.4. Komatsu A., Gordon T.J. and Best M.C., `4WS Control of Handling
Dynamics Using a Linear Optimal Reference Model', Proceedings
of the 5 th International
Symposium on Advanced Vehicle Control (AVEC), Ann Arbor,
USA, August 2000, pp 253-260. This output can be made available at
request from Loughborough University.
3.5. Komatsu A., Gordon T.J. and Best M.C., `Vehicle Path Optimisation
using a Time-Variant Linear Optimal Reference Control', Proceedings of
the 6th International Symposium on Advanced
Vehicle Control (AVEC), Hiroshima, Japan, September 2002, pp 93-98.
This output can be made available at request from Loughborough University.
With the exception of R.A. Williams and E. Fina, both of Jaguar Land
Rover, the other authors of the above outputs were affiliated to
Loughborough University at the time of the research.
• Jaguar Land Rover funded part-time PhD, £5,000, Matthew Hancock,
Evidence of Research Quality:
• In 2002, Matthew Hancock won the national SET award for Best Mechanical
Engineering Student for his work on this project.
• Where it has been possible to avoid commercial conflict, aspects of the
algorithm have been published in journals and presented at conferences
that are widely read / attended by both university academics and the
global automotive industry.
• The system has been adopted for implementation on all Jaguar
supercharged vehicles and will also be adopted in future Land Rover
• Patents issued: Vehicle yaw control with tyre road friction
estimator (GB2428754), Vehicle traction control using active
limited slip differential (GB2428755).
Details of the impact
Electronic Stability Control (ESC) systems have been in use since around
2000 and have widely publicised benefits to the user. Since 2005 their
impact has been measurable and Garrot [5.1] notes that single
vehicle accidents have been reduced by 30-40%, whilst for `loss of
control' fatal accidents the reduction is up to 67%. With such obvious
benefits to consumers, many manufacturers are fitting ESC systems as
standard. EU legislation has required all HGVs and coaches to be fitted
with ESC since 2010 and all cars must have ESC by 2014. Critically, most
ESC systems use the Antilock Brake System (ABS) brake actuators already
fitted to vehicles. These act discretely, at or near the point of loss of
control of the vehicle, braking the vehicle as well as correcting its yaw
rate but producing a noticeable intervention to the driver. Whilst the
statistics prove the accident prevention benefits of these systems, the
motoring press dislike the intervention and in most cases the system can
be turned off by the driver.
The advantage of ALSD is that yaw rate control is provided continuously,
and imperceptibly, to the driver. The yaw correction is provided by
left/right drive torque redistribution at the rear wheels, so no braking
is applied in most driving scenarios. The torque transfer capacity is
limited and the Jaguar system is implemented in conjunction with a
brake-based system that intervenes in the most extreme scenarios. For
drivers of the very powerful supercharged cars that adopt this system,
however, maintaining continuous control over the wider range of yaw
behaviour of the car is seen as a significant advantage, making the
potentially fatal consequences of the driver turning off the ESC less
Following the vehicle and simulation based research carried out by
Matthew Hancock within his PhD research, the system was adopted on
Jaguar's X250 programme for the 2009 XFR (the supercharged variant of the
XF) [5.2]. The control software passed through company
homologation, quality and reliability processes to satisfy BS EN
ISO9001:2008 and therefore attracted rigorous scrutiny and some
modification for mass production.
ALSD does not operate independently of other software on the vehicle. For
example, vehicle speed and yaw rate sensing software and road friction
estimation are required for its use; these were not developed as part of
this research. However, the vehicle and differential system modelling,
supporting simulation work and subsequent structural design of the
controller is specifically relevant. The fundamental operation of Jaguar's
control software is substantially that which appears in Hancock's PhD. The
research is now in production and contributes very substantially to the
overall success of the ALSD on the production vehicle, providing "a major
contribution to the handling performance and stability control refinement
of these vehicles" [5.2].
Since the XFR was launched to critical acclaim (What Car voted the
XF car of the year in 2008, and best executive car in 2011), Jaguar has
introduced the ALSD system onto all new supercharged variants of its range
(XF, XK and XJ). To date approximately 20,000 of these vehicles have been
Jaguar is not the only car company offering differential control (BMW
offer a similar system on the M5) and, as stated, not all of the ESC
benefits of Jaguar's supercharged cars pertain to the ALSD system.
However, the system does introduce benefits for drivers that users have
praised. Press reviews note the beneficial handling qualities as well as
stability of the ALSD. Comments have included:
"The diff control can shunt torque across the axle, promoting better
stability, better response". [5.3]
"Putting the power to the ground further than ever is the new Active
Differential Control (ADC), which is an electronically controlled
alternative to the traditional mechanical limited-slip differential, with
far more subtle control strategies ... Its subtle control strategies
optimize traction at each wheel, improving acceleration on low-grip
surfaces but also potentially improving stability when required." [5.4]
"Active Differential Control technology ... uses a multiplate clutch to
vector torque to the driven wheel with the most grip. Allied to the ABS
and stability control, this allows for the ultimate in traction and
precision both mid-corner and at its exit." [5.5]
"Grip is barnacle-like, and when the driver exceeds the car's limits —
which requires determination — he'll feel the diff helping to keep the
front of the vehicle ahead of the stern." [5.6]
The system is now being used on the new F-type (unveiled at the Paris
Motor Show in September 2012) and is in the process of being extended to
Range Rovers, starting with the new Range Rover Sport.
When assessing domestic economic impact, it is useful to know that all
Jaguar Land Rover vehicles are built in the UK.
Sources to corroborate the impact
To corroborate the impact the following sources can be made available to
the panel at request:
5.1. Garrot, R. 2005, `The Status of NHTSA's ESC Research'
5.2. Signed statement from Head of Vehicle Dynamics, Jaguar Land Rover is
available from Loughborough University at request.
5.3. EVO magazine, March 2009, `Review of Jaguar XFR and XKR'
5.4. Automotive Addicts, September 2009, `2010 Jaguar XKR Supercharged
Convertible Review and Test Drive'
5.5. Auto Spectator, November 2011, ' 2012 Jaguar XK & XKR Coupe
& Convertible Review'
5.6. Car and Driver, September 2011, `2012 Jaguar XKR-S'