Research On The Parameters Of Steering-by-Wire System Matching With The Whole Car

Steering-by-Wire (SBW) is a supreme form during steering system developing at present,in which lots of advanced electronic technology,information technology and control theory have been adopted now .It is a kind of brand-new concept for the design of steering system. Steering manipulation is detected by corner sensor and torque sensor ,then these signals are transferred to the central controller, which uses these signals and the other sensor's signals to control the rotational angle of front wheel and steering wheel torque. Since there is no conflict between the desirable steering ratio and steering wheel torque. we can freely control the rotational angle of front wheel and design the steering wheel torque characteristic. That could greatly improve the security of vehicle system and make drivers feel more comfortable during driving courses. With these new technologies adopted widely such as the computer aided design and simulation, the virtual prototype has already become the dominating means of vehicle design . In order to accelerate the research and application of Steering-by-wire system in our country, an useful design method is brought forward about Steering-by-Wire system in this paper. It could not only confirm the optimum parameters of SBW by matching with the whole car , but also can evaluate the handling and stability of vehicle . All in all , in the thesis we mainly went into researching the following respects: Firstly, we built up a driver-vehicle-road closed-loop model of 21 DOF .It is well-known that the ideal variable steering ratio should be decided by the ideal gain of yaw rate which could keep up the excellent handling and stability of vehicle at any velocity. As a result, we must match it with the whole car system at different velocities . The model could supply us with a convenient way to analyze the influence on the stability of vehicle when we chose different parameters of SBW . The result of simulation indicated that we could get some variational courses of useful parameters, which told us how to improve the handling and stability of vehicle . Secondly, we completed the matching of ideal gain of yaw rate with the vehicle system .After having explained the principle of parameter optimization design of automobile in detail , the ideal gain of yaw rate was be optimized at each concrete velocity with the evaluation index of handling and stability as the goal function .Through statistical analysis, we took the optimum value from them as the ideal gain of yaw rate ,which can enhance handling and stability of vehicle at any velocity. After having analyzed the result of simulating utilized the ideal gain of yaw rate , we can arrive at such following conclusions: 1) The gain of yaw rate has a serious compact on the handling and stability of vehicle, so the ideal one can better it very much. At the same time , the result also showed the validity of the flexible tolerance method as the optimizing method ; 2) The yaw rate and acceleration are increasing with corresponding accretion of the gain of yaw rate. 3) With the speed of vehicle going up, the variable steering ratio increases too. Moreover, it increases faster at a low speed than it at a high speed. 4) Adopted the ideal gain of yaw rate, cars can complete the double lane task sharply well at different speeds. Thirdly, this paper provided the PID control strategy of front wheel for us, in which we took the error between ideal yaw rate and real yaw rate as the input of PID Controller. The outcomes of emluator indicated that SBW system with PID control strategy could reduce the lag of vehicle response during steering manipulation in that it could eliminate the non-linear disturbing caused by road condition. Therefore, SBW system enables the vehicle to carry out driver's order accurately. By the simulation and analyzing, the conclusions could be obtained as the followings: 1) With the velocity of vehicle increasing ,the variable steering ratio is mounting up faster than it without the PID control strategy. At a result , the variable steering ratio can not only heighten the sensitivity of steering at low speeds ,but also heighten the initiative security of the vehicle at high speeds. 2) At each velocity of vehicle, the PID control strategy could keep on the...