Our mechanical engineer explains how anti-skid technology helps to keep your car on a straight and safe path.
ELECTRONIC driving aids in one form or another are now standard on all modern cars. First of these was ABS, or Anti-lock Braking System. Using wheel-speed sensors, the ABS modulates hydraulic pressure in the brake lines to prevent wheel lockup that leads to skidding. The ability of ABS to monitor individual wheel speed , and apply the brakes on any one wheel if necessary, has allowed engineers to incorporate individual wheel braking for the purpose of altering the dynamic characteristics of the car – at all speeds and in a variety of driving situations. The first extension of ABS was traction control, which measures the speed of the driven wheels, and then either applies braking or overrides the driver’s throttle input to alleviate wheelspin. Said wheelspin could cause oversteer or understeer, depending on which end the wheels are driven.
ESP, or Electronic Stability Programme, is built on the “ABS plus” principle of vehicular traction control. ESP adds a yaw sensor (to measure the angular moment about the car’s central vertical axis), lateral and longitudinal acceleration sensors, and a steering angle sensor. The data is continuously collected by an Electronic Control Unit (ECU), which compares the measurements against the pre-programmed “ideal situation”. Any deviation means a skid is imminent.
Long before the driver can react to the problem, the ECU commands either the traction control or the ABS, or both in unison, to brake the appropriate wheel, so as to counter excessive yaw or acceleration in either axis. The ECU also cuts the engine power simultaneously. For example, in a right-hand curve, ESP brakes the front left wheel if oversteer is detected, or the rear right wheel if the condition is determined to be understeer (see diagram).
In slippery conditions, when the driver applies excessive pressure on the accelerator pedal, causing the driven wheels to break traction, the ECU takes charge of the electronic throttle to reduce torque to the wheels. The current state of electronic processors makes it possible for ESP to function at incredible speeds. In most cases, the driver never realises how ESP has intervened to counter a potentially hazardous situation.
The system is one of the most critical driving aids in modern cars. It has proven to be highly eff ective in preventing accidents due to driver error, and in maintaining vehicular stability if a sudden, unforeseen evasive manoeuvre becomes necessary. If your new car does not have “ESP” on its specs sheet, that’s probably because it is called something else by the manufacturer of your vehicle – for example, ESC, DSC, VSC, VDC, DTC, ASC, MSP, VSA, VSM and PSM. These are all essentially the same anti-skid system/technology.
For many high-performance cars, selectable ESP modes give skilled drivers the option to take charge of the machine’s dynamics. This is useful on racetracks, but on public roads and particularly in the wet, ESP (or its equivalent by another name) is best left to its own devices. At the end of the day, all drivers should bear in mind that even ESP has its limitations. A safety-conscious driving style, coupled with good road sense and your instinct for self preservation, is still the ultimate anti-skid driving aid. No kidding
