| When vehicles travel down along long slopes, brake need be working for a long time, which causes overheat of brake friction discs. The overheat results in a decline of the brake performance. For driving safety, buses and large trucks need to install auxiliary braking system. As the research object of this writing, hydraulic retarder is discussed comprehensively. Hydraulic transmission theory and Matlab/Simulink simulation model of vehicle with hydraulic retarder are discussed. Using Matlab/Simulink simulation model of vehicle with hydraulic retarder, vehicle braking performance are analyzed under both flat road condition and downhill condition. In this paper, main works are as follows:The types of car auxiliary braking system and their advantages and disadvantages, the development trend of automotive auxiliary braking technology, the research status both home and abroad were introduced. The basic structure, basic principle of hydraulic retarder is introduced in details. The modern design methods for hydraulic retarder are introduced, included similarity theory and reverse design.Based on the beam theory, the mathematical model of braking torque of hydraulic retarder is established. The braking torque of hydraulic retarder came mainly from the impact and the friction of the fluid flow. The concept of capacity factor is introduced into this writing, which reflects the size of the braking capacity hydraulic retarder. The mathematical model of the wheels and vehicle were established based on force analysis. The influence on hydraulic retarder hydraulic retarder coming from the filling ratio was discussed.At last, with Matlab/Simulink software, the hydraulic retarder submodel, engine exhaust brake submodel, the vehicle rolling resistance submodel and vehicle brake submodel were established. All submodels are combined organically together and become a whole vehicle Matlab/Simulink simulation model. The relationship between braking torque and wheel speed is analyzed in different filling ratio. The influence of different filling ratio was discussed, when the vehicle braking on the flat road and on downhill road. So there will be a balanced speed when the vehicle braked downhill with hydraulic retarder. The constant speed control strategy of hydraulic retarder was explained. The typical working conditions of constant speed control of the vehicle braking effect are analyzed in the simulation. Because of the limitation of the test condition, the braking performance of the hydraulic retarder was discussed with the 25% filling ratio. The braking performance was compared with the simulation performance.The mathematical model of hydraulic retarder and the Matlab/Simulink simulation model of whole vehicle in this paper, have vital reference values for braking performance research of hydraulic retarder; Constant speed control strategy and the improvement measure in this paper, are obbligato links of completing control strategy of the hydraulic retarder. |
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