Study Of PS By Driving Force For Electric Motorized Vehicle

Nowadays, confronting with the stresses of the environmental pollution and the energy consumption, vehicles propelled by the green energy are in urgent need. Because the traditional vehicles with internal combustion engine could not cover the problems concerned above, it is the absolute trend of vehicle industry to develop and apply electric vehicles for the society's sustainable development. The motorized-wheels-driving system is an excellent driving platform which could bring with many predominant advancements for EVs(Electric Vehicles) and realize lots of performances that would not be completed on the traditional vehicles. By now, motorized-wheels-driving system has already become one of the hottest researching focus for vehicle manufactures in domestic and abroad, at the same time, under the impelling of market need, serious environmental pollution and the enormous energy consumption, many companies have promote their electric motorized products which perform well in every aspects. The dissertation makes an in-depth research on the steering department of motorized-wheels-driving platform. Power steering system plays a vital role in the driving system, which could not only reduce the steering torque on steering wheel, as a result, prevent the driver from unnecessary fatigue, but also provide enough road information for drivers at proper time.First and foremost, the dissertation introduces the background of EV, and gives a brief statement about the researching and applying situation of in-wheel motor and motorized-wheels-driving system. Accordingly, puts forward the conception of powering steering by driving force and represent the theory and advancement compared with the EPS(Electrical Power Steering System). In this conception, independent powering steering motor and its relative power steering modules on electric motorized vehicles are replaced by the in-wheel motors which give both the driving torque and the power steering torque. This view is put forward for the first time in the world.The dynamic and computer-simulation model of the steering system are constructed firstly. Because steering system is a complicated mechanical structure which is made up of several linkage structures and rotating,shifting masses, it is really difficult to make an precise module. This dissertation simplifies the complicated steering system into four parts of physical modules, including rotating subassembly of steering wheel,shifting subassembly of pinion and left, right front wheel rotating subassembly. After conducting the dynamic analysis, with the knowledge of Math and Physics, dynamics model and computer-simulation model are made up using the MATLAB/Simulink software.Respectively, the resistance of traveling steering process and pivot steering process are analyzed. The resistance of traveling steering system is consistent of three parts: aligning torque of wheels, frictional torque of kingpin and pinion-rack, aligning torque of tires. On traditional vehicles, because of the function of differential, aligning torque caused by longitudinal force of front wheels will counteract. However, for the special structure of the researching object in the dissertation, which is that four wheels' driving torque could be controlled independently, aligning torque is caused by gravity, lateral force and longitudinal force. The friction model of Academician Konghui Guo is used to construct the dynamic model of friction resistance in steering system, and the "Magic Formula" model is used in the tire model. Pivot steering is a special process in which vehicle velocity is zero, and rotating resistance is replaced by sliding resistance, as a result, the resistance value increases sharply. The dissertation analyzes the resistance and makes up the math model of resistance torque in pivot steering. At last, according with the differential equation, the dissertation constructs the dynamic-simulation model and paves ways for the simulation analysis.Proper control strategy of steering system is analyzed and fixed before controller is set up. Firstly, the dissertation takes ideal drivers" steering torque curve as the control target, which depict the most drivers' preference steering torque along with enough road information, at the same time avoids the drivers to feel oppressiveness when steering. This curve, according to the parameter of the future experimental vehicle, after checking many relative literatures, is established based on enormous experiments and the evaluations from many experienced drivers. Additionally, PID controlling arithmetic is chosen for the fundamental calculating arithmetic of the controller for its simplicity, reliability and stability. It is proper for earlier researches when establishing controller. Finally, takes the torque difference of In-Wheel Motor as the controlling parameter of the power steering controller. This difference is easy to obtain and has a direct effect on the drivers' steering torque.By combining the simulation model of steering system with vehicle simulation platform, Computer simulation is conducted to testify the authenticity of steer model and the validity of control strategy. From the simulation result, we could see that the steer model constructed in this dissertation could reflect the movement and stressing of every part in steering system. Moreover, PID control arithmetic fundamentally satisfies the demand of power assistant controller and could truly perform an efficient power assistant in both steady state and transient state during steering process, as a result, reduce the drivers' steering torque and achieve the desired purpose of the study.