Doctor Diesel

Back to basics: ABS and ESP Systems

Web06In 1985, the Ford Granada and Scorpio were introduced to the European market with a Teves electronic anti-lock braking system (ABS) throughout the range as standard, for which the model was awarded the coveted European Car of the Year award in 1986, after receiving highly favourable praise from motoring journalists.

Ford’s bold initiative encouraged other manufacturers to follow suit and what was groundbreaking became the basis of car safety systems that we now almost take for granted. ABS typically centres around the car’s Central Control Unit, or ECU, a set of wheel speed sensors, a hydraulic fluid pump, and a number of power-operated hydraulic valves. The ECU continuously monitors the rotational speed of each wheel, generally using sensors of either active or passive type. Passive sensors are composed of a permanent magnet around which a copper coil is wound placed in close proximity to a reluctor ring, whose outer diameter is in the form of a set of equally spaced teeth. The passage of each tooth and the space between them creates a small voltage in the coil, which is transmitted to the ECU and interpreted as wheel speed. More accurate and sensitive active sensors have been adopted now and depend on variations created in a standard supply voltage (5 volts or 12 volts) that are generated, again by a permanent magnet, or an ABS ring of multiple north-south magnets, sometimes using magnetised powdered metal applied to the wheel bearing seal. Some manufacturers now use active sensors with small transmitting aerials that avoid hard wiring and transmit their square wave signal direct to the ECU.

In a simple ABS system, if the ECU detects a wheel rotating significantly slower than the others, indicating a condition of impending wheel lock, it will actuate appropriate valves to reduce the hydraulic pressure to the cylinder of the affected wheel, reducing the braking force on that wheel; the wheel will then generally become free to rotate faster again. Conversely, if the ECU detects any wheel turning significantly faster than the others, then brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel. Repeated rapidly and continuously, the process can be detected by the driver via brake pedal pulsation of up to fifteen times per second. Wheels of cars equipped with ABS are practically impossible to lock during panic braking and allow steering input to control the car, which is almost impossible with locked steering wheels.

These days, ABS systems are now fully integrated with their descendents, today’s ESC/ESP safety systems, where additional positional sensors supply the ECU with data on the steering wheel angle, using the technique of anisotropic magnetoresistance, and on the car’s direction and speed of travel using gyroscopic sensors for roll, yaw, and acceleration, similar to those used in space rocket control. When any car instability is detected, the ECU is programmed to apply selective braking, sometimes along with applied engine power control, that will in combination help restore stability and actually drive the car out of the skid, whilst steering it in the desired direction. In traction control systems, the power input and braking power on individual wheels is controlled purely to give optimum traction and maximise effective drive in adverse road grip conditions.

Leave a Reply

Your email address will not be published. Required fields are marked *



and save over 40%

Looks like you're leaving

Subscribe to Diesel&EcoCar for just £5.99 a Month

This website uses cookies to ensure you get the best experience on our website.