ABS, also known as anti-lock braking system, is an automotive safety systems which avoid the wheels from locking and then maintain the adhesive force between wheel and road in maximum value. ABS can calculate the speed, wheel angular deceleration and wheel slip ratio according to wheel angular speed signal. ABS wheel speed sensor magnets are a typical application of AlNiCo magnets in the sensor area.
ABS is consists of the wheel speed sensor, hydraulic control unit, and electronic control unit. Electrical control unit will determine to start anti-lock brake according to the wheel speed which tested by wheel speed sensor. Wheel speed sensor can be divided into electromagnetic-type and hall-type. Electromagnetic-type wheel speed sensor is still widely applied in ABS due to its simple structure and low cost. For electromagnetic-type wheel speed sensor, ABS wheel speed sensor magnets are an essential component. Addendum and backlash of the trigger wheel will face to pole pin alternately during the rotating of the trigger wheel and thus generate the induced electromotive force due to alternative variation of magnetic flux inside the inductive coil. This induced electromotive force will be input to the electronic control unit as a signal. The frequency of the induced electromotive force will be changed with the wheel speed, therefore, vehicle speed can be measured by the electronic control unit.