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Despite the controversy over ‘fly-by-wire’ technology, of the type used
by the Airbus jet which crashed near Strasbourg in January, the Swedish
car maker Saab is continuing work to design such controls for cars. The
company is developing a computer-controlled steering system in which the
driver sends commands to the computer using a joystick – there is no direct
electrical or mechanical connection between the joystick and the wheels.

Many cars already have computers which prevent their brakes locking
or tyres spinning on slippery surfaces. ‘Active steering’ is the next step,
says Saab. This will cut out irrelevant information which the driver does
not need to control the car safely, such as from gusts, crosswinds and irregularities
in the road surface. The result will be less stress for the driver.

Saab’s parent company, the Saab-Scania Group, built the Gripen fighter
aircraft which has fly-by-wire controls. Saab has now adapted some of those
controls for cars: the joystick is the same as that used in the fighter.
The company has built one prototype so far. ‘It’s a real toy to drive,’
says Thomas Schulz of Saab.

The wheels are steered hydraulically by two motors which are controlled
by a microprocessor. The microprocessor takes information from the driver’s
joystick as well as from sensors which register speed, acceleration and
other forces acting on the car.

Much of Saab’s work is involved in simulating the feel of a steering
wheel: when the wheels resist turning, the joystick must also be harder
to turn. The response of the wheels to movements of the joystick also vary
depending on the driving conditions. At motorway speeds the wheels will
move only slightly in response to the driver’s commands, but when parking
the wheels must make much larger movements.

Schulz says that one of the main benefits is safety: there is no steering
wheel for the driver to be crushed against in a crash. The car’s instruments
can also be laid out in a more convenient way without a wheel obstructing
them.

Saab is very aware that drivers may be nervous of entrusting control
of steering to a computer. A large part of the research is involved with
ensuring that every part of the system has a backup. ‘If any part of the
system fails,’ says Schulz, ‘the driver must have enough power and hydraulic
pressure to drive the car to safety.’

The hydraulic controls have a back-up reservoir in case they should
spring a leak and the joystick contains two separate sets of position sensors.
The microprocessor which controls the whole system has two control channels.
If the normal digital channel fails in any way, control is switched to the
second channel which operates using simpler analogue electronics.

Schulz says it will be beyond the year 2000 before any cars fitted with
the system go on sale.