Research On Testing Technology Of ABS Hall Wheel Speed Sensor Magnet

The wheel speed sensor is one of the key components in Anti-lock Brake System. Because of having wide measurement range for wheel speed and strong anti-interference ability, hall wheel speed sensor has been substituting traditional electromagnetic induction wheel speed sensor. One of the main parts of the hall wheel speed sensor is permanent magnet. And the uniformity of magnetic field impacts duty cycle of wheel speed signal, exceeding the limit of standard scope. Therefore impacts the accuracy of ABS wheel speed.According to operation principle of the hall differential wheel speed sensor, the factors, wheel speed,gear,air gap,and non-uniform magnetic field, impacting duty cycle of wheel speed signal were analysed. According to ABS algorithm and signal processing method, duty cycle of wheel speed signal that exceeding the limit of standard scope—30%-70%impacting the accuracy and stability of ABS was analysed. According to sensor structure,real material parameters and reasonable hypothesis of non-uniform magnet, the wheel speed sensor simulation modeling was established in ANSYS software. Simulation result showed that non-uniform magnetic field changed original signal of sensor, and therefore made duty cycle of wheel speed changed.According to the ABS hall wheel speed sensor magnet testing requirement. Based on existing methods of measurement magnetic fiel, uniform permanent magnet and non-uniform permanent magnet modelings were established in ANSYS, and the simulation result showed that, at the position arouding middle of permanent magnet, a distance of<2mm to the surface of permanent magnet, the difference of magnetic field distribution was distinct obviously. According to this result, testing scheme of hall wheel speed sensor magnet was and the position of system sensor were designed. Considering the effect of frequency response and eccentricity, the testing speed was designed to be 1400r/min by experiment. According to the testing scheme, experimental system is designed in the light of current laboratory conditions. And the software of experimental system was developed in Labview and VC++. It could realize the function of data acquisition,calculation and saving.The experiment of magnet uniformity was developed by testing system, and turned out that average value of signal was insensitive to non-uniformity of magnetic field, variance,maximum value,peakedness coefficient of signal were sensitive to non-uniformity of magnetic field. The variance of signal was selected as the characteristic value of the testing system because of variance was the most sensitive to non-uniformity of magnetic field, and the lower limit of judging the uniformity of permanent magnetic was 0.16.