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MIRA's quest for MG TF zest

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					                                    MIRA’s quest for MG TF zest
                                    by Richard Adams, MIRA




                                    AN EXERCISE IN MIRA’S CAPABILITY TO                 indicate a strong interest in hybrids but are
                                    design, develop and prove alternative               concerned that these vehicles will lack strong
                                    powertrain systems has opened the door to           performance…”
                                    several production opportunities for vehicle           This confirmed MIRA’s belief that many view
                                    manufacturers.                                      hybrids with the misconception that they
                                       Intrigued by results of a market research        were merely vehicles aimed at pacifying
                                    survey by the J.D. Power organisation in            ecology lobbyists, and therefore offered a
                                    the USA, engineers in MIRA’s Advanced               bland driving experience with uninspiring
                                    Powertrain Group recently saw an opportunity        power delivery. Another relevant finding from
                                    to demonstrate the company’s wide-ranging           the study that MIRA decided should influence
Richard Adams joined MIRA in        engineering expertise by developing a two-          its MG TF 200HPD was that women are
1998 as a graduate trainee          seater sports car with class-beating perfor-        clearly interested in hybrid vehicles, but defer
spending time in various            mance. The survey – Hybrid Vehicle Consumer         their purchase decision due to insecurity over
departments including,              Acceptance Study – was based on responses           their limited knowledge of hybrid technology.
Aerodynamics, Thermo Fluids,
Impact Simulation and Body
                                    from more than 5,200 recent new-vehicle                MIRA’s independent status ensured the
Structures. While in the Fluids     buyers in the US. It showed that hybrid sales       choice of vehicle was approached from a
Group, he was seconded to MG-       are expected to increase dramatically in the        purely technical angle. The final decision
Rover with specific                 next few years and approach at least 500,000        was taken only after an initial design study
responsibilities for thermal        per annum by 2006.                                  showed the potential within the MG TF to
management for current and
future models, and also to the
                                       MIRA’s initial concept – jointly developed       create an AWD sports car. At this point MIRA
Arden International Motorsport      with MG-Rover who supplied an MG TF as the          approached MG-Rover management who
F3000 team part owned by            base vehicle for the project – embraced a           saw the potential to have a technology
Prodrive. Currently he is part of   hybrid powertrain that would bring additional       demonstrator that would “break the mould.”
MIRA’s Business Development         benefits of All Wheel Drive (AWD). It also          And provide a market-conditioning tool.
Team looking after PR.
                                    recognised that, unlike many hybrid vehicles,          The objective for MG TF 200HPD was a
                                    the proposed MG TF 200 Hybrid Performance           petrol/electric powered sports car featuring a
                                    Development (HPD) had to remain an exciting,        combined output of 200PS deployed through
                                    high-performance vehicle. The J.D. Power            all four road wheels. It needed to redefine
                                    survey concluded: “Male new-vehicle buyers          hybrid perceptions by injecting real pace on ®




                                    Figure 1: No compromise between open-road performance and good economy for MIRA’s prototype – as
                                    demonstrated by high-speed and urban-cycle testing on the company’s extensive proving ground




                                                                                         MIRA – NEW TECHNOLOGY 2004                    1
                                 demand, satisfy buyers seeking additional           pedal, ‘pseudo-automatic’ city mode. This
                                 ‘customer delight’ features, and appeal to the      would be ideal for urban driving, in traffic jams,
                                 widest-possible customer base.                      or where constant stop-start driving is more
                                    The decision to turn the production RWD          taxing in three-pedal vehicles.
                                 mid-engined MG TF into a more balanced                 Power generated using the IC engine will
                                 AWD sport car is a departure from conven-           remain the cheapest and most common form
                                 tional ‘hybridisation,’ as most current offerings   of primary energy production for the fore-
                                 tend to transmit all power through the existing     seeable future, this despite stricter controls
                                 driven wheels. Was there danger in departing        placed on its emissions. There are, however,
                                 from the norm?                                      operating conditions under which even this
                                    MIRA says not. Many of the traditional           cornerstone of automotive technology cannot
                                 drawbacks of AWD disappear when you                 meet the desired emissions or performance
                                 consider the technology more closely: no            requirements.
                                 requirement to package a cumbersome                    To resolve this MIRA enhanced the
Figure 2: Under-bonnet view      prop-shaft; none of the traditional frictional      performance of the IC engine using hybrid-
illustrates the front electric
                                 penalties, and the potential to cost-effectively    isation, thus extending the envelope of
drive. This technology
                                 roll out the approach across an entire model        operational performance. This configuration is
demonstrator was packaged
for access. However, MIRA’s      range.                                              known as a ‘parallel hybrid,’ whereby both
expertise in design for niche-      Other benefits include isolation of the front    engine and motor can simultaneously drive
volume production would          electric drive, which permits the internal          the wheels.
guarantee a significantly more   combustion (IC) engine to idle – or even shut          In general, hybrids have been developed
compact production version.      down – while running on electricity in the two      to address environmental issues. The usual
                                                                                     option is to downsize the conventional engine,
                                                                                     and temporarily fill the power deficit with
                                                                                     energy from a battery pack through an electric
                                                                                     motor. The application to enhance perform-
                                                                                     ance has, by and large, been overlooked. For
                                                                                     the MG TF 200HPD, the direction was very
                                                                                     different. Already fitted with the most potent
                                                                                     engine in the range (160 PS), the additional 40
                                                                                     PS from the electric drive system takes the
                                                                                     combined peak power to 200 PS.
                                                                                        The power generation capability of the
                                                                                     combined IC engine and the electric motor
                                                                                     is shown in Figure 1. This hybridisation meets
                                                                                     one of MIRA’s objectives of providing add-
                                                                                     itional ‘punch’ throughout the rev range,
                                                                                     tending to create the feel of a big engine –
                                                                                     something desired by most sports car
                                                                                     drivers. Conventional tuning methods tend not
                                                                                     to bolster the power and torque curves in
                                                                                     such a favourable manner.
                                                                                        The IC engine is excellent at producing
                                                                                     large quantities of power continuously, and
                                                                                     the electric motor is extremely good at reacting
                                                                                     instantaneously to the driver’s transient peak
                                                                                     demands. Hybrids employ an electrical storage
                                                                                     system charged by a generator mounted on
                                                                                     the IC engine to act as a secondary energy
                                                                                     source. Popular storage systems range from
                                                                                     traditional lead-acid, nickel-metal-hydride and
                                                                                     lithium-ion batteries through to super-
                                                                                     capacitors. The choice of storage medium is
                                                                                     dictated by power duration, quantity of power
                                                                                     required, and, of course, cost.
                                                                                        Recognising that the energy density of
                                                                                     super-capacitors and batteries are both less
                                                                                     than gasoline, MIRA needed to make an
                                                                                     informed decision.
                                                                                        Either the secondary storage system is
                                                                                     high-capacity, heavy and difficult to package,
                                                                                     or the system has a power potential that is


2      MIRA – NEW TECHNOLOGY 2004
mild or short-lived. However, it is important
to note that the reality of driving on today’s
road systems plays to the strengths of the
finite peak power potential of hybrids. It is
impossible to maintain wide-open throttle
(WOT) for more than a few seconds at a time.
Once drivers have reached their desired
velocity, or overtaken the car in front, they are
required to back off the throttle.
   MIRA’s extensive experience collecting
data, including usage profiles, across all
segments of the market, provided the platform
for calculating how long the additional
power of the electric drive would reasonably
be required before a period of part throttle
operation would ensue. Part-throttle driving
provides the opportunity to recharge the
batteries in preparation for the next burst.
   MIRA is at the forefront of vehicle safety,
particularly in the field of complex electrical/
electronic systems. This allowed the design
team to design-in the required levels of safe
operation demanded by the global market.               With the application of an in-house control     Figure 3: AWD Active Torque
   The application of hybrid technologies has       strategy, the hybrid drive has been tuned to       Distribution bestows fine
implications far beyond motive power. New           give an enjoyable driving experience, and          dynamic control
                                                                                                       demonstrated on MIRA’s
approaches are made possible for vehicle            employs active torque distribution to maintain
                                                                                                       specialised wet grip facility
cooling, weight distribution, radical packaging     vehicle control.
and innovative styling concepts.                       Despite the J. D. Power report indicating
   Under-bonnet packaging alterations pro-          that, in the short term, there is a greater
vided the opportunity to re-consider the            willingness in the market to pay more for a
powertrain cooling flow field. Skilfully revised    hybrid than was previously believed, a major
intake ducting in concert with a redirection of     factor when comparing a standard vehicle and
the exit-flow through the bonnet significantly      a hybrid must remain higher cost. The
reduced the front-end lift coefficient to the       increased purchase price of the hybrid vehicle
ideal. Zero front-end lift is a key element in      could be prohibitive to some consumers.
high-speed feel and vehicle stability. MIRA         However, higher costs need to be considered
achieved zero-lift without recourse to ungainly     in the light of the list of features that
aerodynamic add-ons that increase drag and,         consumers desire, coupled with lower
in some territories, adversely affect sales         operating costs. For example, the MG TF
(because buyers perceive an earlier problem         200HPD’s less-costly road fund license and
that has been corrected by add-on aero-             exemption from city congestion charges in the
dynamic aids). Together, these measures also        UK (as well as some other territories) and, of
reduced drag by 10 per cent, a further comp-        course, effectively superior fuel economy with
lementary influence on emissions and fuel           more performance for the same mpg.
economy.                                               Another big advantage of the MIRA concept
   The team realised a further advantage by         is that despite the availability of ‘big-engine’
downsizing the radiator, a move afforded by         performance, urban driving sees the MG TF
the improvements to the cooling airflow.            200HPD able to return excellent fuel economy       Figure 3: HPD – the thinking
   Careful packaging of the front electric          since its IC engine is ‘as produced’ by MG         man’s GTI
drive train and associated battery pack also        and not tuned up. Its
gave the 200HPD a perfect 50/50 weight              emissions, as measured on
distribution not found on the production MG         the EU drive-cycle, are as
TF.                                                 standard. Consequently, in
   This holistic approach enabled the car to be     the UK – where there are
designed to achieve 0-60mph in under 6              swingeing company car tax
seconds compared with the standard vehicle’s        rules to encourage the use
6.9 seconds – a clear answer to male buyers’        of smaller-engined vehicles
concerns over tardy performance. In-gear            – the car does not attract
acceleration is particularly crisp, as the          additional      tax  liability
delivery characteristics of the electric motor      despite        its    added
have been tailored to provide most assistance       performance              and
early in the rev range.                             functionality. s


                                                                                 MIRA – NEW TECHNOLOGY 2004                           3

				
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