58 DYNAMIC LEGENDS
›The TXII can trace its
black cab origins back to
1948, when the Austin
FX3 taxi was introduced,
with more than 7,000 of
the black cabs produced
over a decade. A few
redesigns followed over
the years, the most major
being the familiar FX4,
a workhorse of which
more than 75,000 were
sold between 1958
and 1997. A step change
then came in 1997 when new owner,
London Taxis International (LTI) introduced the TX1,
having brought in Kenneth Grange as designer. Grange was an
appropriate choice for such a quintessentially British vehicle,
having designed items such as parking meters and post boxes,
Kenwood mixers, Parker pens, and the InterCity 125 train.
Further development of the TXI followed, with the
relatively brisk introduction of the TXII in 2002, ‘hailed’ as
the smoothest taxi ever. A team of nine engineers from LTI
focused on improving the ride and handling, with a distinctly
low carbon footprint approach to the development. Indeed the
fl eet selected for benchmarking comfort was sourced from the
company’s car park, with a VW Sharan, Peugeot Partner Combi
and Chrysler Voyager selected, as they were the only vehicles
available that could seat passengers above the rear axle.
The team, led by David Black, LTI Vehicles’ project manager
(and ex-TWR man), carried out subjective engineering
assessments of the three vehicles and looked at specifi c
features such as ride harshness, suspension noise, lateral
and vertical motion, and then plotted the characteristics
that produced a smooth ride. The LTI team also used elastokinematic
modelling in their development work for the
fi rst time, which helped bring down development times and
prototype costs, with just fi ve development prototype TXIIs
built for real-world testing, which was carried out in the
UK at Millbrook, MIRA, and on public roads.
The team investigated optimising the existing setup,
but found that the existing leaf springs and dampers were
outdated and couldn’t handle all
the different loads in all directions
to a suffi ciently high level.
As Black said during the project,
“It’s a heavy beast. If a taxi hits a
speed bump, for example, the heavy
axle will start to travel upwards. Trying
to control axle movement to dampen
those forces while the vehicle is
decelerating is very diffi cult.”
Thus, in a major break from tradition
for the black cab’s underpinnings, the rear
leaf-spring setup was scrapped in favour
of a twin trailing-arm confi guration from
Dana. The variable-rate coil springs and
self-adjusting load-dependent dampers were
designed to control all forces and not transmit
them through the chassis frame or body structure.
A Panhard rod system was also employed to keep lateral
movements of the live rear axle in line during cornering,
braking and acceleration, while double radius arms helped
locate the suspension to the chassis.
Passenger comfort is critical in a taxi, but driver comfort
is also important, especially given that ‘cabbies’ are expected
to remain chirpy and knowledgeable as they spend long
days driving busy city dwellers and tourists around urban
environments – and also since many select and purchase their
own vehicle. Thus, softer dampers were specifi ed at the front,
as well as a 25mm-diameter anti-roll bar, delivering what
Black described us handling “much more like a saloon car”.
Another key feature of the front setup that is unique to
a black cab is the 7.6m turning circle that enables U-turns
in urban streets. Thus the front suspension was designed
specifi cally around the turning circle specifi cation, determined
by the steering geometry and the way the steering linked
into the front suspension, enabling the front wheels to turn
almost 90° – a feature that is used around one million times
a year by London’s taxi drivers alone.
The newest successor to the TXII is the Geely-backed LEVC
TX (previously known as the TX5) plug-in hybrid model,
but the unbeatable packaging and appealing form of its
forebears remain clear.
cab
black TXII INDEX TO ADVERTISERS
A&D Technology .................................................. 23
Altair Engineering .......................... Inside back cover
BorgWarner ......................................................... 5
BWI Group ..........................................................57
Cayman Dynamics ............................................... 40
dSpace ...............................................................15
VehicleDynamicsInternational.com • November/December 2019 Dytran Instruments ............................................. 23
Electric & Hybrid Vehicle Technology International ... 35
Kistler Instrumente ............................................. 39
Mechanical Simulation Corporation ....................... 39
MSC Software ..................................................... 29
MTS Systems Corporation ....................................6+7
MVO ..............................................Inside front cover
Racelogic............................................................13
Sentient ............................................................ 21
Tenneco Automotive ...................... Outside back cover
Vehicle Dynamics International ................... 26, 29, 43
Wabco ................................................................19
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