AN INVESTIGATION OF ANTI-LOCK BRAKING STRATEGIES FOR HEAVY GOODS VEHICLES

An articulated lorry was instrumented in order to measure its performa nce in straight-line braking. The trailer was fitted with two intercha ngeable tandem axle sub-chassis, one with an air suspension and the ot her with a steel monoleaf four-spring suspension. The brakes were only applied to the trailer axles, which were fitted with anti-lock brakin g systems (ABS), with the brake torque controlled in response to antic ipated locking of the leading axle of the tandem. The vehicle with the air suspension was observed to have significantly better braking perf ormance than the steel suspension, and to generate smaller inter-axle load transfer and smaller vertical dynamic type forces. Computer model s of the two suspensions were developed, including their brakes and an ti-lock systems. The models were found to reproduce most of the import ant features of the experimental results. It was concluded that the po or braking performance of the steel four-spring suspension was mainly due to interaction between the ABS and inter-axle load transfer effect s. The effect of road roughness was investigated and it was found that vehicle stopping distances can increase significantly with increasing road roughness. Two alternative anti-lock braking control strategies were simulated. It was found that independent sensing and actuation of the ABS system on each wheel greatly reduced the difference in stoppi ng distances between the air and steel suspensions. A control strategy based on limiting wheel slip was least susceptible to the effects of road roughness.