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Traction Control
By Scott Memmer
Some of the biggest advances in automotive technology in the past 10 years have come in the area of safety. Spurred by improvements in microprocessor speed, miniaturization, and software development, the automobile continues to evolve. In addition to telematics-based services like OnStar, digital satellite radio and in-car e-mail, recent advances in braking technology have led to shorter stopping distances and increased control while driving in inclement conditions.
Traction control is yet another safety development that has reached the automobile during this period. A popular feature on many vehicles, traction control offers drivers the benefit of space-age electronics that improve a car's contact with the road.
But what is traction control, and how does it work?
In this month's Focus on Safety, we'll take a look at the inner workings of this cutting-edge technology and also discuss the ways it improves your driving experience and enhances safety.
When you first hear the term "traction control," you might think it has something to do with traction and control. "Duh," you're saying; "isn't that a little obvious?" Well, maybe, maybe not. The word traction refers, in general, to your car's ability to maintain adhesive friction between the vehicle (specifically, your tires) and the pavement. And yet there are different kinds of traction. For instance, there's one kind of traction when we brake, another when we accelerate, and still another when we turn. Which kind of traction are we referring to here?
Traction control deals specifically with lateral (front-to-back) loss of friction during acceleration. In other words, when your car accelerates from a dead stop, or speeds up while passing another vehicle, traction control works to ensure maximum contact between the road surface and your tires, even under less-than-ideal road conditions. For example, a wet or icy road surface will significantly reduce the friction (traction) between your tires and the pavement. And since your tires are the only part of your car that actually touches the ground, any resulting loss of friction can have serious consequences.
Traction control is part of a series of three braking technology developments that began appearing in vehicles in the mid-eighties. (Note: Many German vehicle manufacturers call traction control by its original German name: ASR traction control. ASR stands for "Acceleration Slip Regulation." It's the same technology we're talking about here, but with a fancier name that most Americans have never heard of.) In chronological order, these developments are: anti-lock brakes, aka ABS (1978), traction control (1985), and stability control (1995). All three technologies come from the laboratories of Robert Bosch Company in Germany, and all address the issue of improving contact (traction) between your car's tires and the road.
Traction control works at the opposite end of the scale from ABS -- dealing with acceleration rather than deceleration. Still, since many of the same principles apply to both systems, it might be best to visualize it as sort of ABS in reverse. ABS works by sensing slippage at the wheels during braking, and continually adjusting braking pressure to ensure maximum contact between the tires and the road. You can actually hear the system working (a grinding sound) and feel it (the pedal pulsing).
For a more in-depth view of ABS, please read:
Fixing Antilock Brakes
The Attack on Anti-Lock Brakes
As we mentioned above, ABS and traction control operate similarly. In fact, the ABS control unit is the basic "building block" for traction control and stability control. By adding modules and sensors, the system can be expanded to include these newer technologies.
In the case of traction control, the basic ABS system -- as well as other components in the vehicle -- requires some modification. To begin with, the old-style accelerator cable is typically replaced by an electronic drive-by-wire connection (although some older systems still use a mechanical accelerator cable), meaning the mechanical hook-up between the accelerator pedal and the throttle ceases to exist. Instead, a sensor converts the position of the accelerator pedal into an electrical signal, which the control unit (similar to the one used in ABS) uses to generate a control voltage. The standard ABS hydraulic modulator is also expanded to include a traction control component.
All these parts work together to activate the traction control system.
Let's say you're at a stoplight on wet pavement. The light turns green and you press too firmly on the accelerator pedal. There is slick asphalt under your tires and the wheels begin to spin. The traction control system instantaneously kicks in, sensing that the wheels have begun to slip. Within a fraction of a second, this data is fed back to the control unit, which adjusts throttle input and applies braking force to slow the wheels (some older systems also retarded engine spark). The wheels are thus prevented from spinning and the car maintains maximum traction.
It's really that simple. Again, think of it as ABS in reverse.
Traction control is available on a wide selection of vehicles, including some economy cars like the Chevy Cavalier, Saturn S Series and the Ford Focus. Virtually all the major makers, including DaimlerChrysler, BMW, Ford, GM, Saab, Volvo, Lexus, Infiniti, Volkswagen, Audi and Porsche, offer traction control on one or more models. You can check the vehicle detail pages on Edmunds.com to see if traction control is offered on a vehicle you're considering buying.
. There's one inch of ice on the back alley. The alley goes slightly upwards making it fairly easy to spin the tires. The "low traction" light goes on but that's it. No improvement!
