| In order to carry out the emergency rescue for various natural and sudden disasters and fully guarantee the safety of people’s lives and property,in recent years,the emergency rescue vehicles(such as fire rescue vehicles,special rescue vehicles,ambulance vehicles,etc.)have been developed rapidly with the strong support of the governments around the world.It is difficult for the traditional emergency rescue vehicles to pass through narrow and complicated areas(such as walking streets,urban villages,narrow streets,etc.)quickly,which misses the best time to rescue disasters seriously.How to improve the trafficability and mobility of vehicles effectively in the narrow and complex areas has become an urgent technical demand for the emergency rescue vehicles.This paper is funded by the fourth research topic--“Key technologies of walking device in narrow and complicated areas”(Project Number: 2016YFC0802900)of the National Key Research and Development Program “Research and application of key technologies for high-mobility and multifunctional emergency rescue vehicles”.In this paper,the fire rescue vehicle is taken as the research object based on the multi-mode steer-by-wire technology,and the key control theories including the independent steering control strategy of the electro-hydraulic wheels,the multi-mode steering control method,and the dynamic switch control strategy of steering modes are proposed.Furthermore,the proposed multi-mode steer-by-wire control strategies are tested based on the independently developed test bench and fire rescue prototype vehicle.The main research contents are shown as follows:(1)The hydraulic steering actuator model and dynamic model of the emergency rescue vehicle are built,which lays the foundation for the designs and simulations of the multi-mode steer-by-wire controllers.The mathematical models of the hydraulic steering mechanisms including the proportional amplifier,the electromagnetic proportional servo valve and the screw swing cylinder are constructed.The mathematical model of the road feeling actuator is built by the permanent magnet brushless DC motor.The two linear degrees of freedom vehicle dynamics model,the eight nonlinear degrees of freedom vehicle dynamics model based on the Dugoff tire model and the "preview-follow" driver model are constructed.(2)In order to improve the ability of the emergency rescue vehicles to pass through narrow and complex areas quickly,the multiple steering modes(front wheel steering,rear wheel steering,four wheel steering and in-situ steering)are realized based on the relevant controlalgorithms.The overall architecture of the multi-mode steer-by-wire system of the emergency rescue vehicles is put forward,and then the control logics of the controller module and the hydraulic components are proposed.The independent steering control strategy of the electro-hydraulic wheel is proposed,and the fractional order PID controller based on the Oustaloup filter is designed,and then the parameters of the fractional order PID controller are optimized by the parallel adaptive clonal selection algorithm.The steering angles assignment strategy based on the Ackerman principle is proposed to realize the multiple steering modes of the emergency rescue vehicles.The steering radius and dynamic performances of the vehicles under different steering modes are compared and analyzed to provide decision-making for the driver to switch the steering modes.The relationship among the road feeling torque,the steering resistance and the vehicle speed is constructed by using the road feeling characteristic curve,and the road feeling control strategy based on the fractional order PID algorithm is proposed.The control logic of the four wheel steering system is proposed by tracking the yaw rate of the ideal reference model,and the uncertainties of the control system are analyzed.In order to improve the robustness and dynamic performance of the four wheel steering control system,the four wheel steering controller is designed based on the hybrid H2/H_∞ control strategy,and the weighted functions are built to optimize the hybrid sensitivity of the four wheel steering controller.The simulations under four typical steering conditions(the step input condition,the sinusoidal input condition,the fishhook condition,and the double-lane change condition)are conducted to verify the effectiveness of the proposed hybrid H2/H_∞control strategy.(3)Considering the shortcomings of multi-mode steering vehicles that need to switch steering modes in the parking state,the dynamic switch control method of steering modes for the emergency rescue vehicles without stopping is proposed.In order to ensure the safety of the vehicles in the steering modes switch process,the preconditions of steering modes switch for the emergency rescue vehicles are put forward.Taking the constant vehicle turning radius as the switch control target,the wheels steering angle relationships and the target steering angles are obtained in the steering modes switch process,and then the dynamic switch control strategy of the steering modes is proposed.Based on the B-spline theory,the angle trajectory of the driving wheel is constructed toimprove the smoothness of the steering modes switch.The improved NSGA-II multi-objective optimization algorithm is used to optimize the angle trajectory of the driving wheel,and then the TOPSIS decision model based on the grey correlation method is applid to rank the Pareto optimal solutions to obtain the optimal angle trajectory of the driving wheel.The simulations of two typical steering modes switch conditions are perfomed to demenstrate the effectiveness of the designed switch method of steering modes.(4)Based on the developed test bench and fire rescue prototype vehicle,the effectiveness of the proposed control theories of the multi-mode steer-by-wire system are verified.The overall design and key components’ selections of the test bench are carried out,and then the multi-mode steer-by-wire test bench is built.The electro-hydraulic wheel steering control strategy,the various steering modes control method and the H2/H_∞ control strategy of the four wheel steering system are tested.On the basis of the test bench,the multi-mode steer-by-wire fire rescue prototype vehicle is designed,developed and manufactured by our research team and an enterprise.A data measurement system is built to test the effectiveness of the proposed control theories including the electro-hydraulic wheel steering control strategy,the various steering modes control method,the H2/H_∞ control strategy of the four wheel steering system,and the dynamic switch control method of steering modes.The experimental results of the test bench and fire rescue prototype vehicle verify the effectiveness of the proposed control strategies and the feasibility of the designed controllers.The control strategies and the test methods for the multi-mode steer-by-wire system of the emergency rescue vehicles proposed in this paper not only have high technical reference and important theoretical guidance value for the study of the emergency rescue vehicles’ steering system,but also have obviously practical significance for the application and promotion of the emergency rescue vehicles. |
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