| Electric power steering system not only can provide steering power and lighten theburden of the driver’s manipulation, but also can improve vehicle steering performance anddriving comfort, thus improving vehicle active safety. Currently, EPS system at home andabroad has been standard configuration on many cars. However, in the process of EPSsystem development, the determination of EPS control parameters mainly depends ondebugging personnel’s real vehicle subjective feeling. Meanwhile, the influence of multipleparameters and performance may exist between steering performance and EPS controlparameters. And matched control parameters in one working condition may be not applicablein another one, which lead to a long period of real vehicle debugging and calibration for EPScontrol parameters, and the effect may not be ideal either. Therefore, clarifying influencebetween steering performance and EPS control parameters, getting EPS control parametervalues meeting the performance requirements can provide theoretical guidance for realvehicle debugging and calibration of EPS control parameters, effectively accelerate thematching progress and reduce the development cycle of EPS system.Combined with the national high technology research and development project (863Program)―Research on Key Technologies of Chassis and Vehicle Control for Electricvehicle‖(Project number：2012AA110904) and major projects in Jilin Province―Researchon Key Technologies of selection and Development for Electric Power Steering System Base on Pentium Hybrid Car‖（Project number：：51105165）, the co-simulation platform of theEPS system and vehicle model is built in this paper and the sensitivity analysis of EPScontrol parameters and steering performance by means of model simulation is discussed.Then the sensitivity relationship between EPS control parameters and steering performanceis clarified and the EPS control parameters are choosed to be optimized based on theresearch results of the sensitivity analysis. Finally, the EPS control parameters are confirmedunder ideal steering performance. Meanwhile, considering that EPS can actively exporttorque, additional control functions are developed with full use of signals of EPS systemexisting sensor on the basis of traditional control function, which can effectively improvesteering performance without any increasement in the hardware cost.The specific contents of this dissertation are as follows:(1) A co-simulation platform of EPS system and vehicle model is builtThrough the aspect of promoting vehicle steering performance, research on the EPSsystem is conducted by means of model simulation. So EPS system can be developed basedon the prediction of vehicle steering performance, which can effectively save thedevelopment cost and decrease the development period of the EPS system. Vehicle model isan important part of the co-simulation platform, and commercial software named Carsim isused to accurately describe the vehicle system. Meanwhile, in order to make research on EPSsystem convenient, the EPS system is constructed based on Matlab/Simulink. Finally, theco-simulation platform of the EPS system and vehicle model is built. Considering thatparameters source of the co-simulation platform is also an important part to ensure the modelaccuracy, the parameters of vehicle and EPS assembly characteristics for one certain car aretested based on K&C test bench, and the testing method is also described in this paper.(2) Sensitivity analysis of EPS control parameters based on steering performanceAs the product of electronic technology combined with steering system, EPS systemhas a great potential in improving steering performance. However, during the developmentprocess of EPS system, the influence relationship between EPS control parameters andsteering performance is not clearly. And the determination of EPS control parameters are mainly depended on debugging personnel’s real vehicle subjective feeling, which increasethe development periodof EPS system. Therefore, clarify the sensitivity relationship betweensteering performance and the EPS control parameters, and grasp the effect of EPS controlparameters on the evaluation indexes of steering performance, which can provide theoreticalevidence and guidance for the regulation and calibration of EPS control parameters. Whensensitivity analysis of EPS control parameters and steering performance is conducted, firstly,steering performance and its specific evaluation indexes are determined. Secondly, EPScontrol parameters and their variation values are determined. Finally, the sensitivityrelationship between steering performance and EPS control parameters is clarified base onIsight software.(3) The optimization of EPS control parameters based on vehicle steering performanceBased on the sensitivity analysis results of EPS control parameters and steeringperformance, the EPS control parameters of higher sensitivity for steering performance arescreened and chosen as the optimization variables. Then EPS control parameters areoptimized to get the ideal steering performance, which can effectively accelerate thematching process of EPS system and has great significance on EPS system development.When optimization of EPS control parameters is conducted, Optimization object of EPSsteering performance is determined. And then control parameters for optimization areobtained based on the results of the sensitivity analysis. Meanwhile, considered the couplingeffects between steering performance and EPS control parameters, a comprehensiveevaluation index of steering performance is established for multi-objective optimization toget EPS control parameters which meet all the requirements of steering performance.(4) The development of EPS additional control functionsBy making full use of existing sensor signals of EPS system, EPS additional controlfunctions are developed without any increasement of the EPS system hardware cost toimprove steering performance by additional software, which is of great significance tomaster core technology of EPS additional control functions and can greatly narrow thetechnological gap between domestic EPS products with similar foreign products. For the difficult issue of return control for EPS vehicles without angle sensor, an EPS active returncontrol method without angle sensor is proposed. Tire aligning torque is estimated based onKalman Filter and compensation current for return control is determined to improveautomotive returnability. Meanwhile, a control algorithm for EPS vehicles to reduce theimpact torque on steering wheel is proposed by applying high-pass filtering processing todistinguish useful road sense information and road impact torque. Based on the estimateddisturbance torque from road surface, impact compensation control current is determined toimprove the road impact resistance of EPS vehicles so as to improve the driving comfort.(5) EPS real vehicle test platform is built to verify the optimized steering performanceand the developed additional control algorithm of EPS systemThe underlying drive control of permanent magnet synchronous motor is developed,and EPS prototype controller is also developed. Meanwhile, a domestic brand car ismodified and the real vehicle test platform is finally built. Combined with the subjectevaluation results of appraisers, the control parameters of EPS controller are determinedbased on control parameters determined by optimization. Then objective evaluation ofvehicle steering performance is tested to verify the steering performance after optimizationof EPS sample car. As for the developed additional control algorithm of EPS, test conditionsare set and the real vehicle tests are conducted to verify the effective of EPS additionalcontrol algorithm.So in conclusion, several innovative aspects proposed by this dissertation are asfollowed：(1) In EPS system development process, the relationship between EPS controlparameters and steering performance is not clear, and the determination of EPS controlparameters mainly depends on debugging personnel’s subjective feeling, which makes thedebug cycle of EPS control parameters longer. As for this phenomenon, the sensitivityanalysis and optimization for EPS control parameters is reasearched based on objectiveevaluation indexes of vehicle steering performance. So the relationship between EPS controlparameters and the exact evaluation indexes of steering performance can be clearly determined. And on this basis, EPS control parameters with higher sensitivity for vehiclesteering performance are selected to be optimized, and finally the value of EPS controlparameters are determined for ideal steering performance. This research can be usefully forthe debug and calibration of EPS control parameters on real vehicle and can greatly improvethe efficiency of debug and calibration.(2) It is the boost curve that reflects the variation of the EPS assisting magnitude anddirection with the input of drivers and vehicle speed. On the basis of broken line type assistcharacteristic, the assist characteristic of multi-line fitting curve can be realized throughincreasing the numbers of nodes, which has a good practical significance. However, it is verydifficult for the node design of the assist characteristic of multi-line fitting curve. As for thisproblem, the regional breakdown for the assist characteristic of multi-line fitting curve isdetermined, and the sensitivity relationship for the exact torque region of EPS assistcharacteristic and steering performance is finally determined, which can be supplied as theguidance for the design of EPS assist characteristic curve.(3) EPS Additional control algorithm is developed, with the full use of sensor signals ofEPS system. Therefore, vehicle steering performance can be greatly improved based on theform of software without increasing the system components. It is difficult for vehicle withoutangle sensor returning to center, which is also a hot research spot. So a return-to-centercontrol method without angle sensor is proposed to improve return performance. Meanwhile,steering wheel impact torque may be generated by road impact, which brought roughinfluence for driver. So a control method is proposed to reduce the impact torque on thesteering wheel caused by road impact, and to improve driving comfort. |
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