Traction is the possibility for a car to accelerate. As a result of the driver pushing the throttle, an engine revs up and puts down all torque onto the rear wheels in order to speed up. In some cases, and especially with the high power today's F1 engines deliver, more torque is given to the wheels causing the wheels to spin and hence reducing acceleration. A traction control system is a device to prevent or limit such spinning in the wheels in order to increase the ability to accelerate.
How it works
Various traction control systems have been developed for either racing or road car purposes, some of them more efficient then others. Such a system always monitors car variables and intercepts if too much power is being applied to the wheels. Usually this is realised by sensors that measure rotational speed of the powered wheels and compare that to the speed of the car, measured with either sensors at the non driven - front, in the case of Formula One - wheels or with a sensor (e.g. a pitot tube) that measures the speed of the car itself. In a few milliseconds after the system detect wheel spin in the rear wheels, power is cut to nullify that spin. The different systems mainly differ in the way of reducing that power output to the wheels:
- Retard or suppress the spark to one or more cylinders
- Reduce fuel supply to one or more cylinders
- Brake one or more wheels
- Close the throttle, if the vehicle is fitted with drive by wire throttle.
Traction control has been around in various guises since the 1980s, and cars like the 1992 Williams FW14B which took Nigel Mansell to his drivers' championship title were even more electronic-packed than the current cars - featuring computer-controlled active suspension in addition. After a long period during which traction control was banned, the FIA decided to re-allow its use at the start of the 2001 season (as of the Spanish GP because the smaller teams requested a delay to get more time for developing their systems) as it was becoming increasingly difficult to prove that ECUs (Engine Control Units) were not being used to replicate traction control functions.
The ban in the mid 1990s was introduced because of safety measures to reduce speed, and motivated by the idea that since traction control is quite easy to achieve it would therefore also be easy to spot. To prevent engine mappings adjusted for traction control, the FIA had to check every teams' software. It appeared an impossible task as the 3 FIA experts were unable to review software written by every team independently and often with up to 10 people working on the system.
A rumour from the time claims that some team had the idea of using the pressure in the airbox as a reference for the car's speed. The FIA experts failed to spot that such a pressure meter was used not for telemetry but rather for traction control. When they worked this out, the FIA banned air pressure compensation but obviously a lot of other possibilities were there for grabs.
Use in Formula One
As mentioned earlier there are various ways to implement traction control. In Formula One, wheel spin is reduced by cutting the engine power. While each engine has its own system, the power output is either reduced by cutting fuel supply or by retarding or suppressing the spark. Obviously, cutting the fuel to one or more cylinders is beneficial for fuel economy. Current F1 systems use a combination of these factors to ensure optimum performance. A traction control system can be heard in operation very clearly when cars launch out of slow corners. The engine produces a rough sound, caused by the misfires (a cylinder's fuel that doesn't get fired).
Though it is said that drivers are extremely good in detecting wheel spin, traction control is an electronic device that speeds up the process of reducing engine power. "When the computer detects wheel spin, it will alter all engine functions" says Denis Chevrier, head of operations at Renault F1. "It will lower engine power by reducing the amount of fuel that is fed to the engine, by modifying the opening angle of the butterflies, by altering the ignition and by other means." In a fraction of a second, the rear wheels stop spinning, providing better traction to the tyres.
According to Renault engineers, an F1 tyre works best under a very slight wheel spin. If there's too much wheel spin, the tyres lose traction and acceleration is greatly reduced. Traction control plays a crucial role in assuring constant acceleration when coming out of the corners. "Wheel speed sensors are attached to the four wheels of the car" says Chevrier. "At any moment, the computer knows the exact speed of the car from the front wheels sensors. By comparing the speed of the front wheels to that of the rear wheels, the computer is able to detect the slightest wheel spin. Wheel spin occurs when the speed of the rear wheels exceeds by a certain value that of the front wheels. We do track testing and set the traction control to come into action when the wheel speed difference reaches 103%. Then, we change that value to 102%, and then to 101%. We then compare those changes to the differences in lap times and see what is most efficient."
It's also considered very important that the driver does push the throttle more then if the car would not posses traction control. By pushing it harder, he makes the computer work. And it doesn't need any explanation that computers are a lot faster" then men. Also because the computer can act on numerous parameters at once, he is actually in "knowledge advantage" of the driver. E.g. the driver cannot detect the exact power generated by the engine, as the computer can on fractions of hp's. The driver can even alter the regulations with a button in the cockpit for rainy or dry conditions.
Compared to the traction control systems found in road cars, the basics are roughly the same. "However, the response of the two systems are very different. A typical passenger car weighs between 1,200 and 1,500 kilos and is powered by a motor that can produce between 100 to 250 horsepower. In comparison, an F1 car weighs just 600 kilos and is powered by an 800 horsepower engine. The response of the traction control system of the F1 car needs to be much quicker."