Sensors, systems help keep your car going where it should — but can only do so much
How It Works: Stability control
Drifting a car sideways is great fun for an experienced racer on a closed course, but it’s definitely not something drivers want to do in traffic on the daily commute. To help keep you on a straight path, Transport Canada mandates that every new passenger vehicle sold in Canada, starting with the 2012 model year, must have electronic stability control (ESC).
The system reacts in milliseconds when it determines that the vehicle isn’t going in the same direction as the steering input — in other words, a skid — and immediately takes action to straighten everything out. It’s considered important enough that this safety feature is now also required on new tractor-trailers sold in Canada, and next June, on intercity and school buses as well.
While all ESC systems work the same basic way, there can be minor differences between them, and so automakers will often assign proprietary names to theirs. You may see it advertised by such terms as Vehicle Stability Assist (Acura), AdvanceTrac (Ford), StabiliTrak (General Motors), or Vehicle Dynamic Control (Nissan), among several others.
Stability control uses components and sensors from some of the vehicle’s other safety features, including anti-lock brakes (ABS). Brakes stop the wheels from turning, but it’s the tires gripping the asphalt that actually brings the vehicle to a halt, and even good tires can only do so much. In a vehicle without ABS, jamming on the brakes locks up the wheels, and the tires can slide and turn the vehicle into a giant toboggan.
Before ABS, drivers were taught to pump the brakes on and off, giving the tires a chance to grab the pavement each time the brakes released. Anti-lock brakes do the same thing, but they electronically press and release much faster than any driver can, helping to keep the vehicle stable as it comes to a stop. In a panic stop in a vehicle with ABS, you press the brake hard and keep your foot there, allowing the system to do its thing. When the ABS activates, you’ll feel pulsing in the brake pedal, and you may hear a grinding or groaning sound. Because the tires now have grip, instead of sliding, you can also steer the vehicle if it helps avoid a collision, which isn’t possible if the wheels are locked up and sliding.
Electronic stability control also works with the vehicle’s traction control. This electronic system measures how fast the wheels are turning. If one is spinning faster, which can indicate it’s on a slippery surface, the traction control system will activate the brake on that wheel, and may also momentarily reduce the engine’s power, helping the spinning tire to regain its grip. (Sometimes you want a bit of wheel spin, such as when you’re trying to get out of deep snow, which is why it’s recommended that you turn off the traction control if you’re stuck.)
Both ABS and traction control are primarily meant for going forward. If things start to go sideways, that’s when ESC comes in. It depends primarily on three sensors, which measure yaw, wheel speed, and steering angle.
The yaw sensor is located at the centre of the vehicle and, as the name suggests, measures yaw — how much the vehicle is moving to the left or right of its vertical axis. The system then compares this to the steering angle — the direction of the front wheels, and how far you have them turned. If you’ve turned the wheels to the left, and the car is obediently turning in that direction, then all is good.
But if the sensors realize you have your wheels turned to the left, but the car is heading to the right, it knows you’re skidding sideways. To help get you out of it, it uses some or all of the components from the ABS and traction control systems, including braking specific wheels and reducing engine power to bring everything back in line with the direction of the wheels, and get the driver back in control of the vehicle. It works when either the front or the rear wheels lose traction and the vehicle starts to skid. It continually monitors the vehicle, in all weather conditions, and automatically engages as required. It is possible to temporarily disable it on a few models, but will come back on as the default the next time the engine is started.
The system is very efficient, and Transport Canada’s studies suggest a 29 per cent reduction in crashes caused by drivers’ loss of control because of it. But there’s only so much it can do, and you can only argue so far with the laws of physics. To help ensure safe driving, be sure your tires are in good condition, with enough tread and properly inflated. Make highway lane changes gradually, rather than wrenching the wheel to get over. Accelerate slowly and steadily, rather than hitting the throttle hard, especially in slippery conditions. And if you get into gravel or a soft surface, such as on the road shoulder, don’t hit the brakes. Instead, slowly ease off the throttle, and gradually steer back onto the pavement.