The Research Of Measurement Methods Of Dynamic ABS Performance Testing Bed

Since the 1980's, with the development of the national economy, the automotive industry and road transport has developed, and the total number of vehicles in China increase quickly. Rapid increase in vehicles would inevitably bring about many traffic problems. According to motor vehicle safety performance statistics, in the event of personal injury in road traffic accidents, many accidents is caused by the effectiveness of vehicle braking, specifically on wet road , snow road and ice road.ABS(Anti-lock braking System)is an active safety device to improve the safety performance of vehicle braking system. Whether a vehicle equip ABS or not, becoming a basis of braking performance evaluation. If there is not a good evaluation of braking performance for the vehicle equipped ABS, vehicle detection will lost its significance. There must be a dynamic ABS performance testing system to judge the performance of ABS performance.ABS testing methods include road-testing method and bed-testing method. Road-testing method needs high cost, long term and low precision, and it can be easily affected by the environment and road conditions. Therefore, bed-testing method is used in the ABS performance testing instead for its accurate measurement to avoid the defects of road-testing method.The test on dynamic ABS performance bed testing system should base on effective measurement method and reliable measurement data. Dynamic ABS performance bed testing system is composed of machinery test bed and measurement-control system. So, the research of measurement method to this system relates to many problems, such as evaluation method of total system, measurement theory of machinery test bed, and data processing of measurement-control system, and so on.Firstly, an evaluation method of total system should be established, giving direction to measurement data which we should determined. ABS is a device optimizes braking system of vehicle equipped ABS for higher braking performance and better braking stability. The improvement of braking performance not only relates to the diversity of road, vehicles and ABS products, but also depends on the ABS control principle, and control method. Therefore, a performance evaluation to ABS is needed. There are some evaluation criteria in ECE statute and ISO standard, but many of the statutes applicable to road-testing only. There is a need to establish statutes for bed-testing. According to main evaluation criteria, make braking distance, utilization of attachment coefficient, slip rate and braking force the evaluation methods in bed-testing. And the measurement data include wheel speed, vehicle Body speed and torque data.Secondly, bed-testing is run by simulating the actual braking conditions according to evaluation methods. Dynamic ABS performance bed testing system obtains test data from sensors, and accesses them to computer after processing. Because of the influence of the sensor structure and environmental factors, there are noises with test data. How to eliminate the noises, is the importance of reliable calculation of data.Optical encoder creates two pulse signals with 90°phase difference. Because of the interferences, the phase difference of measured data is not 90°, which brings uncertainty in measured data. In order to design the detection circuit to eliminate these interferences, analyzing the characteristics of abnormal pulse from normal pulse. After elimination, the pulse signal access to computer for calculation with the objective of less error. Use a improved method for its widely scope of application to measure wheel speed. Research shows, effective use of the phase relationship between two pulse signals would form a four frequency multiplication signal, get wheel speed with maximum accuracy. When wheel speed data is obtained, the vehicle body speed could calculate from wheel speed by using a real-time measurement.Torque sensors export a series of analog voltage output according to the torque changing, after analog to digital conversion, digital torque signal access to computer for step processing. Although coupling filter eliminates a part of the noise during transmission, there are still many noises in torque signal. The elimination of noises by software before data calculation is necessary. Because of the non-stationary nature of the torque signal, chose wavelet analysis to process. Wavelet analysis can get high temporal resolution while signal is high frequency, and get high frequency resolution while signal is low frequency. Use wavelet analysis can decompose signal to summation of many high frequency details and low frequency approximation, then eliminate the noise from the details by set a threshold. At last, we can obtain the best approximation of original signal by composing these processed details and the last Approximation.