Research Of Wheel Speed Signal Acquisition And Processing Technology Based On FFT/IFFT

The precise wheel speed signal is the basis of the active safety control system, and the system calculates vehicle speed、wheel slip ratio、yaw velocity and other important parameters with wheel speed data. These parameters are the basis of the control system to produce control command. However, when the vehicle in a high speed, the wheel speed signal is influenced by space electromagnetic field、the vibration of the vehicle and accuracy of wheel speed sensor. Finally the wheel speed pulse signal obtained by microcontroller may be distorted. Therefore, in order to get the real wheel speed signal, it is necessary to filter the collected wheel speed signal, eliminate noise interference.This paper analyzes the reasons and characteristics of wheel speed signal noise. It is proved that the frequency domain filtering based on FFT/IFFT curve fitting is best by comparing the filtering effect among the traditional hardware filter circuit, time domain filtering and frequency domain filtering. In order to realize the real-time processing of wheel speed signal, SCM programming is adopted to realize frequency filtering. The algorithms include FFT module, curve fitting module and IFFT module. FFT module converts complicated wheel speed signal to the frequency domain which benefits the analysis of of spectrum characteristics of the noise signal and determination of the signal processing method. Curve fitting module establishs appropriate cutoff frequency and pass band according to the characteristics of broadband low energy of noisy signal while narrowband high energy of normal signal.Thus it can retain the signal within the passband,fit curve of the spectrum beyond the cutoff frequency and recover the spectrum curve of normal signal. IFFT module reverts data in frequency domain to timedomain signal and outputs them for the active safety system controller.The results show that the operation based on FFT/IFFT curve fitting filtering procedure is stable. It can effectively filter out the noise superimposed on the wheel speed signal, restore the real wheel speed pulse signal and meet the precise requirements of the wheel speed signal in active safety control system.