Control Strategy Development Of All-Wheel-Steering-by-Wire System Based On In-Wheel-mMotor Vehicle

With the steady improvement of the quality of the national economy,cars have entered the ordinary family and have been widely used in various regions of China.China's car ownership is growing rapidly,and this is like a double-edged sword.On the one hand,it has played a positive role in increasing domestic market demand,solving people's employment problems,and changing urban spatial structure.On the other hand,it has also triggered in urban areas with high car usage rates,there are many negative effects such as urban traffic congestion,parking difficulties,and increasing energy shortages.New energy vehicles have a positive significance for reducing environmental pollution and relieving energy crisis,so it has become a trend for new energy vehicles to replace tradition cars.Meanwhile,based on the advantages of in-wheel-motor vehicles:simple structure,no pollution and easy integration of chassis modules,using the new electronically controlled steering system(steer-by-wire)which removes the mechanical connection between the steering wheel and the vehicle wheel,can freely design the variable transmission ratio in the steering system,also develop electric vehicles with high steering flexibility.This is an effective way to solve the urban traffic congestion and improve not only the utilization rate of road but also parking space.This paper starts with the detail of the technical scheme,the construction of the control framework,joint simulation and the experiment of the real vehicles,which are intended to develop all-wheel-steering-by-wire system,including special steering modes such as diagonal/transverse/spin turning row,conventional steering modes such as front/four-wheel steering.The main research contents are as follows:First of all,the chassis and suspension integration modules of the all-wheel steering system are introduced.Aiming at the front-wheel control mode,the fuzzy control method is used to design the variable transmission ratio,a feedforward algorithm based on gradient equation use the gain factor_sK to adjust the front-wheel corner;Considering the stability and flexibility of four-wheel steering,the optimal control and proportional control are proposed.Comparing the two kinds of algorithm,the optimal control algorithm is more feasible.The principle of multi-mode steering system's conversion mode is described.The corner control module that can achieve a variety of mode steering is constructed according to the whole vehicle parameters.Stateflow was used to set up the mode switch logic control system that can provide protection for drivers to choose a reasonable driving mode.Then according to practical application and theoretical analysis,the relationship between lateral acceleration and road sense is selected as the research basis.The reactive torque is further calculated by estimating the lateral force of the front wheel.Simulation experiments of different road adhesion coefficients were carried out respectively.The result indicated that this method enables the drivers to perceive the saturation of the lateral force of the front tire and to highlight the road sense under different working conditions.Next,the control policy about all-wheel-steering-by-wire system mentioned above is verified by the method of Carsim and Matlab/Simulink joint simulation.The operating conditions include the conventional two-wheel steering and four-wheel steering as well as the special steering modes in diagonal/transverse/spin turning row.The experimental results showed that the all-wheel-steering-by-wire model can realize the steering control of various modes of the vehicle by controlling the steering angle of each wheel and the torque direction of the hub motor.The control strategy can not only improve vehicle maneuverability and stability but also maintain the driver's sensation.Finally,in order to prove the practicability and feasibility of the algorithm,a test vehicle was set up.Clarifying the software section including the control architecture of all-wheel-steering-by-wire system,vehicle control mode,mode switch processing module;Clarifying the hardware part including the power battery of the vehicle,components of its power train which contain hub motor,steering wheel angle sensor,steering motor,actuator and the multifunction steering wheel.Also the whole vehicle communication protocols and the realization method of communication between each system,each sensor and the controller.According to the established control model,the real vehicle is tested.The control strategy of all-wheel-steering-by-wire system was verified by real vehicle test,and the multi-mode steer-by-wire strategy has been realized.