Research On Driving Stability Of Tractor-semitrailer Based On Closed Loop Control

With the rapid development of road transportation,at the background of the energy crisis and the global economic recession, when the "green transportation","low-carbon transport" putted forward by the government, road transportation are developing in the direction towards high efficiency and intensification. Developing trends of transport vehicles is bound to high-speed, professional and heavy-duty. As the number of tractor-semitrailer is increasing year by year, the traffic accidents caused by tractor-semitrailers are also increasing rapidly. The loss caused by the accidents is more and more serious. The security issue of tractor-semitrailer transportation is highly important and got more and more attention.As the structure is relatively complex, tractor-semitrailer's driving stability is poor. So the "roll", "jack-knifing", " yawing" and "swing" and other dangerous operating conditions easily happen and result in traffic accidents. Therefore, the tractor-semitrailer's traffic safety study has great significance. Tractor-semitrailer's driving safety is not only relate to the vehicle's own characteristics and traffic environment, but also relate to the driver's control. Most previous studies just focused on the characteristics of the vehicle itself, the role of the driver is few take into account. In the study field of tractor-semitrailer stability, taking the driver's impact into account, the study of tractor-semitrailer closed-loop system stability is a very important research direction. Study result in this area will greatly enhance the tractor-semitrailer's driving safety and give a solution to improve tractor-semitrailer's driving safety. Around the tractor-semitrailer's driving stability of the closed-loop system, this paper carried out the following work:First of all, the approaches of modeling tractor-semitrailer dynamics were comprehensive analyze and the main degrees of freedom and parameters of tractor-semitrailer were tackled. According to research needs, the system was simplify reasonably and non-linear 9-DOF and linear 5-DOF tractor-semitrailer mathematical model were established respectively. This work offered a good tool for analysis of driving stability of tractor-semitrailers.In order to study driving stability of the tractor-semitrailers more real and more effective and improve the tractor-semitrailer's driving safety, a tractor-semitrailer closed-loop system is established in this paper. The system model couple the dirver modeling with time-delay and linear 3-DOF tractor-semitrailer model. Quasi-Newton algorithm was used to determine the optimal parameters of the driver model.Closed-loop system tractor-semitrailer was used to study the driver's response delay time, vehicle's load and speed's impact on straight driving stability of the tractor-semitrailer. A numerical algorithm is used for analysis the system's critical speed and the characteristics of the system in frequency domain range. The results show that: suitable load, appropriate travel speed and driver's good mental state can significantly improve the driving stability the driving safety of tractor-semitrailer.Taking closed-loop system model of tractor-semitrailer as the research object, two kinds of tractor-semitrailer steering control strategy, braking and steering control strategy and non-braking steering control strategy were used to study the driving stability of tractor-semitrailer driving on the bending road. In the braking and steering control strategy, the front wheel steering angle and system braking force were used as control input to control vehicle's motion state. The multivariable backstepping design method was utilized to braking and steering control strategy. The results show that the braking and steering control strategy can more effectively reduce the tractor and the trailer's yawing angle error and increase the stability of the vehicle.In order to verify the correctness of the models and the rationality of analysis in this paper, tractor-semitrailer model was established by TruckSim and ADAMS software respectively. Using the models established by two kinds of software, we analyzed the system's straight driving stability and cornering stability. The results are in well agreement with the result from this paper's model. This confirms that the model established in thia paper is right and the result is reasonable. In addition, the reasons why the software models' analysis results and the calculation results have little differences were also analyzed.