The Study On Vehicle Speed Control In The Long Downhill

Serious accidents often occur as the speed of vehicles is out of control when traveling on a long slope. Too much braking time and the sudden temperature increase of brake pads are the main reasons that lead to vehicle brake failure and speeding out of control. In order to providing enough sustained braking ability when go downhill, a combining method of using engine dynamic brake for auxiliary braking, exhaust brake and retarder is commonly used to achieve the purpose of stability. However, this will not only increase the cost and control complexity, but also does not make a full use of engine braking force.Based on the configuration of automatic transmission of vehicle as the research object, using the fuzzy PID control strategy, the suitable automatic transmission gear can be choosed, so that the engine braking torque and car downhill driving torque equilibrium or balance and vehicles in the long downhill running full use of engine braking force speed control, thereby the downhill speed is kept in a safe range.Through a combination of research method of theoretical analysis and simulation study, the engine braking problem of automatic transmission vehicles when during long downhill driving process is researched. Firstly, the control method of engine braking system is studied. Then engine brake fuzzy transmission ratio PID controller is designed. The operating parameters of the automatic transmission vehicles are matched by fuzzy control method. Finally by using of the MATLAB software, an engine brake control system simulation model of automobiles when during long downhill driving process is set up and also an a simulation of braking efficiency under different working conditions is carried out and analyzed.Through theoretical analysis and simulation of engine braking of automatic transmission vehicles, the following conclusions can be drawn:①the engine braking method of real-time changing of the transmission ratio can effectively control the vehicle speed in a relatively stable range in order to avoiding traffic accidents. The control method is scientific and effective;②the fuzzy control method basing on the transmission ratio of a transmission can effectively adjust the output of engine braking force to controlling the vehicle speed in a steady state;③by using engine braking, the vehicle stability can be significantly improved. The speed of vehicles can be effectively dropped to a safe speed in the long downhill. Also the speed of heavy duty truck and the intensity of the work of the service brake can be effectively reduced which improves traffic safety;④the method of engine braking has a certain range of applications. When heavy duty trucks travel in a steep long downhill, by using this method the speed of vehicles can not be reduced under a safe speed. A combination of varieties of braking methods should be adopted in this situation.