Research On Control Strategy Of Electro-hydraulic Coupling Steering System For Commercial Vehicles

With the development of China's economy,China's automobile production and sales in 2016 hit a high record,ranking first in the world,of which commercial vehicles production and sales 3.6881 million and 3.651 million,an increase of 8.01% and 5.80%.At the same time,the "Thirteen Five" plan proposed to further improve the urbanization rate,will promote the integration of urban and rural passenger transport and the strong demand for logistics vehicles.It is clear that the future demand for commercial vehicles is growing,but also put forward higher requirements on the commercial vehicle's driving comfort.Commercial vehicles,mostly used to carry cargo,are different from passenger cars and lag a lot compared to the passenger car in the driving comfort and steering maneuverability.This shortcoming in the domestic commercial vehicle is particularly evident.Facing these shortcomings of commercial vehicles,the long run to the driver will bring about related occupational disease.The European Occupational Safety and Health Organization(EU-OSHA)conducted a study showed that 54% of women in the European transport industry and 37% of men have muscular and skeletal problems.Therefore,it is necessary to design a steering assist system for commercial vehicles to improve steering maneuverability and portability.Based on the relevant technology at domestic and abroad,the mechanical structure of the Electrohydraulic coupling steering system of commercial vehicle was designed,the corresponding hardware in the loop test rig was built,and the basic steering assist,self-aligning and damping control strategies was designed based on the ideal steering wheel torque which based on the test rig.The correctness of the control strategy is verified by simulation and bench experiment.The main contents of this paper are as follows:(1)Designing the steering assist torque curve of commercial vehicle.Analysising the factors that affect driver's ideal steering hand torque factors at different speed,dividing into low-speed and high-speed section to consider the power characteristics.In the case of low speed,the ideal steering torque characteristic is considered as the variable of the steering wheel angle,and in the case of high speed it is considered as the variable of the lateral acceleration.Finally,the steering assist curve torque is designed according to the difference between the ideal steering torque curve and the actual steering hand torque.(2)Designing the basic power control,self-aligning and damping control strategies of commercial vehicles for steering portability and maneuverability.The basic power control is based on the assisting curve torque which is related to the speed,and determines the assist torque according to the vehicle speed and the steering hand torque.The self-aligning and damping controls are based on the PID control of the steering wheel angle,which determines the self-aligning torque and the damping torque.(3)Verifying the control strategy of Electro-hydraulic coupling steering system through software simulation.The AMESim model were established for the hydraulic power system,the electric power system and the steering mechanical system of the Electro-hydraulic coupling steering system respectively.The control strategy model were set up in Simulink.The effectiveness of the steering control strategy is verified by the joint simulation of Simulink,Truck Sim and AMESim.(4)Designing hardware in the loop test rig.The structural characteristics of foreign products were analyzed,and the hardware in the loop test rig for the Electro-hydraulic coupling steering system of the steering column assisted commercial vehicle was designed,Also,the hardware was designed and selected according to the overall design of the test rig.The Lab VIEW-based control procedures of communication between Truck Sim and Lab VIEW RI,steering resistance,signal acquisition,power motor was programmed.(5)Verifying control strategy on the hardware in the loop test rig.In order to verify the effectiveness of the steering control strategy applied in material object,this article build hardware in the loop test rig of Electro-hydraulic coupling steering system for commercial vehicle,relying on the design scheme.Experiments show that the steering control strategy of commercial vehicles can effectively improve the steering portability,self-aligning performance and self-aligning overshoot of commercial vehicles.