Research Institutions

Saab and chips

As in every aspect of technology, the microchip is playing an ever-increasing role in the development of the car. Engine technology has advanced in leaps and bounds in the last ten years, and we can expect the chassis to be the next major area of advance.

Having been at the forefront of turbo technology as used in road cars, Saab has more recently been developing a Traction Control System (TCS). Since work started on the project in the autumn of 1986, it has undergone field tests through two winters and two summers, and should become available as an option sometime this year. Apart from an extensive re-mapping of the engine, the only additional items to the ABS equipment as fitted to the 9000 series (and as an option on the 900 series as from now), are a valve block, electronic throttle and two processors which add less than 2kg to the weight.

The function of TCS is to improve mobility at low speed. As anybody who has been stuck in snow knows, once one of the driving wheels loses its grip it spins uselessly while the car remains stationary, even if it is on tarmac or on a dry surface. This happens because the differential’s function into allow the wheels on the inside of a corner to travel more slowly than those on the outside. Very few cars are fitted with a limited-slip differential which would overcome this problem.

Saab’s system uses the ABS sensors which are already located in the wheels, to send messages back to the car’s electronic control unit, or brain, telling it that one wheel is losing its grip and about to spin. This information triggers another message to the brakes of that wheel to apply themselves as little as is necessary to enable the torque load to even up. The power from the engine is then directed through both driveshafts as neither offers a lesser line of resistance allowing the wheel with the grip to revolve. This means that the car starts to move. The idea is simple, the application is complicated and the result is good.

TCS can perform other tricks, too. While moving, if the brake sensors detect that one of the driving wheels has hit a slippery patch, is losing traction and about to spin, it is activated again. At speeds lower than 40 kph it performs the same braking function, but at higher speeds there is a different response.

Instead of applying the brakes, the brain takes over the throttle control and progressively decreases the revs until the spinning wheel begins to revolve at the same pace as the other one. The driver’s foot may be pressed hard down on the accelerator pedal, but until that wheel has caught up, the engine will not obey. The sensitivity of the system decreases at higher speeds so that above 200 kph it is completely cut out.

The electronic throttle cable is an essential part of the equipment: it is more than a linkage as it communicates directly with the management system. The traditional throttle cable will be retained more for the sake of assurance than anything else, but therein no doubt it will be dispensed with once the idea has been generally accepted by the public.

The electronic cable also ensures a smoother ride, as the engine mapping system it communicates with countermands a twitchy right foot. It can also respond to other demands such as increasing the engine speed a millisecond before the air conditioning is activated so that there is no loss of power.

I found the system very impressive when testing a prototype on a Saab 9000 recently. Even when braking at a speed of 100 kph over a section of frozen lake that had strips of rubber laid down alternately to left and right every twenty yards, the car was never thrown off balance. Torque-steer was totally absent on hard acceleration as well.

Naturally, with the system relying so much on the brakes at slower speeds, there is the worry that there will be increased pad wear and, more dangerously, high temperatures will be generated on the move. Saab is adamant that pad-wear will not be significantly increased and that heat will not be a factor except in exceptional circumstances, but when a certain temperature is reached, the system will automatically de-activate and a warning light will flash in front of the driver. Once the pads have cooled down, the system will resume operation again.

Though this development will doubtless become as de rigueur in Scandinavian cars as has ABS, it remains to be seen how significant it is for British motorists. WPK