| Steering system is one of the key systems which is related to handling stability, riding comfort and driving safety. Electrical Power Aided Steering system is a new-style automotive power aided steering system, which adopts power aided electromotor controlled by Electronic Control Unit to provide power aided torque, so it can adjust power aided torque according to vehicle speed and guarantee automotive steering portably and flexibly at low speed, stably and reliably at high speed. Compared with other Power Aided Steering systems, Electrical Power Aided Steering system with the advantages of advanced technology, lower energy consumption, high driving safety and protecting environment etc. is a new high-tech product which closely follows modern automotive development topic and meets the demand of modern automobile with electronization, intelligence and low carbon, so it has become the researching hotspot of power aided steering technology. This paper took column power aided type Electrical Power Aided Steering system as the studying object and establish dynamical model for it; studied its control method based on H_∞; designed an Electronic Control Unit that matched it and carried out test study on the test-bed.Firstly, simplified dynamical model of Electrical Power Aided Steering system, simplified dynamical model of linear two freedoms vehicle and mechanical model of tire were established; meanwhile, dynamical equations of each mechanical parts in Electrical Power Aided Steering system and linear two freedoms vehicle were also established. Steering resistant moment was analysed combining to simplified dynamical model of linear two freedoms vehicle and mechanical model of tire; sequentially the equation of steering resistant moment which is equivalent to output axes was derived."Road feeling"of Electrical Power Aided Steering system was analysed and the reason of illogicality between steering portability and"Road feeling"was found.Secondly, considering noise of sensor and disturbance from road in Electrical Power Aided Steering system, H_∞based on mixed sensitivity optimization problem was applied to its control. Mixed sensitivity H_∞robust controller was designed and was simulated in MATLAB/Simulink. Compared with the simulation results of without controller and using PID controller, the noise of torque sensor and disturbance from road were effectively contained after using H_∞robust controller. This controller strengthened robustness of the control system.Thirdly, according to the standards of automotive electronics, developed by American Freescale corporation such as MC9S08GB60A Micro Control Unit, power supply management device and predrive device were chose and sequentially hardware circuit and software of Electronic Control Unit were designed. For hardware circuit, the circuits of power supply management, input interface, armature current sampling of power aided electromotor, detection and fail-safe, fault display and drive for power aided electromotor were designed and the principles of these circuits were expounded detailedly. For software, software control flow of Electronic Control Unit was analysed. Overall design of control software was designed and main program, underlying interrupt program and communication program were programed. There was some innovation in how to realize H_∞Robust Control by Algorithm. At the same time, anti-interference measures for designs of hardware circuit and software were discussed.In the end, the test study on the test-bed for the designed Electronic Control Unit was carried out. The programs without adjusting control algorithm, with PID control algorithm and with H_∞robust control algorithm were separately written to the Micro Control Unit to carry out three tests. H_∞robust control can observably strengthen robustness of Electronic Control Unit was got based on comparing and analysing the part of the test results. |
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