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Fielder Air Suspension.
The Fielder rapid air suspension system employs air-bag springs at each
corner but, unlike most air systems which are passive, this one is active
under the control of an Intel 486 micro-processor. In contrast, the Range
Rover (II) air suspension is adjustable for height but is not active. An
experimental Fielder system has been fitted to a John Davis Bushranger 4X4.
The Bushranger uses a Range Rover donor chassis and the suspension on the
special looks deceptively like a standard air-suspension Rangie. The front
end has been modified with a link to the top of the diff' and the bushes on
the radius arms have been modified so that they provide no roll stiffness -
that all comes electronically. There is an air bag for each wheel and they
are off-the-shelf items, although not Range Rover ones. Each radius arm has
a sensor to measure suspension position and these are read by the
microprocessor. In addition, there are accelerometers so that the
microprocessor has full information on the actual dynamics of the vehicle.
The suspension system is active to the extent that it resists cornering,
braking and acceleration forces, responding quickly enough to keep the car
level and improve on-road handling. A substantial compressor is driven
through an electric clutch by the engine and keeps air reservoirs fore and
aft charged to 150 psi. Half inch air lines pressurize the springs through
rapid-acting valves controlled by the 486. It can soften a spring by
venting air. A manual over-ride allows the vehicle to be lowered, raised
and tilted, and to perform other tricks.
Offroad, this drive-by-wire system allows the suspension to effectively
have close to a zero spring-rate. The aim is to allow extreme suspension
travel while maintaining ride height and keeping nearly the same weight on
each tyre at all times. The result is to maintain tyre grip and greatly
reduce the need for differential locks. These effects cannot be achieved
with conventional springs without reducing the load-carrying ability and
the roll-stiffness below acceptable levels.
The prototype suspension has a "black box recorder" which saves the last 3
minutes of data for analysis in the event of a disastrous "incident". (This
feature could come in useful for litigation if it is left in production
units.)
The real worry for the electronic cynic has to be, what happens when the
smoke gets out of the electronics and the system fails? Electronics are now
very reliable indeed but there have been numerous cases of 4x4 engine ECU's
failing after getting wet. Here there are position sensors, accelerometers,
valves and finally the microprocessor to worry about. The latter could be
mounted in the roof but some of the sensors just have to be close to the
dust, mud and wet. That aside, this is a very innovative and capable
suspension.
The army are interested, of course, and a study has been made for fitting
the Fielder system to the 6x6 Perentie, the extra axle providing a new
computer programming challenge.
Plans include making conversion kits for Land Rover and Range Rover
vehicles, possibly before the end of 1997.
- L_A11ison
Fielder follows in the tradition of Kinetic, also of Western Australia
