The Design And Simulation Of Active Steering System For A Medium Bus

Compared with passenger cars,the medium bus is much bigger and heavier.So,the center of gravity of the bus is higher.In view of the front axle load,the medium usually use circular-ball steering gearbox and steering linkage to drive mechanism.However,compared with the rack and pinion steering system,it has disadvantages in space occupation and daily maintenance.The active front steering system(AFS)is relative to the mechanical front steering system.The mechanical steering system have only one input(from steering wheel)and a output(steering gearbox).AFS have another input,which could be controlled by system.The vehicle steering operation will feedback the response based on the comprehensive parameters of the vehicle.Therefore,the AFS can effectively improve the vehicle’s handling performance,thus reducing the work intensity of the driver and ensuring the safety of driving.This paper will introduce the optimal design of steering system for a medium bus.First,the author designs a new steering system with rack and pinion steering gear.Then,an active steering system is designed based on double planet gear mechanism.Firstly,the author redesigns the overall structure of the steering system on the basis of knowing the vehicle parameters and a coupling mechanism of AFS is designed based on double planetary gear mechanism.The 3d virtual prototype design of the system is completed and the main parameters of the mechanism are determined.Meanwhile,the performance characteristics of the mechanism are analyzed in detail,the variable transmission ratio curve of the active steering system is designed.Secondly,based on CarSim software,a dynamic analysis model of the medium bus(without AFS)is established.At the same time,the differential equations of the system are listed for Simulink modeling.Finally,this paper evaluates the performance of the active steering system based on the co-simulation of CarSim and Simulink.The co-simulation test items are included double lane change test,step input of the steering wheel test and steering wheel angle pulse input test.Test co-simulation results show that: Bus equipped with AFS can improve the response of vehicles at low and medium speeds and reduce response of vehicles when the vehicle is running at high speed.The analysis of this paper shows that it can reduce the driving labor intensity of drivers,improve the convenience of low-speed operation of vehicles,reduce the sensitivity of high-speed operation,and effectively improve the vehicle’s handling performance after installed with the AFS designed in this paper.