On-Center Steering Wheel Torque Characteristics Modeling And Analysis

With the development of highway and the quickening of vehicle speed, people pay more and more attention to the safety of vehicle in high speed, the high speed on-center"road sense"is very important factor that influence the safety of vehicle in high speed area. Thus, how to design the handling stability and the road sense of high speed vehicle are important urgencies at present. This paper mainly does the research on the model-building,the simulation,the evaluation and the analysis of steering wheel torque characteristics in high speed, and the steering wheel torque characteristics versus different vehicle velocity and lateral acceleration.As known to all, the vehicle handling stability depends on three factors: driver,vehicle and road. Constrained by physiology,gender,age and so on, driver is a factor which is most difficult to change in the closed-loop system of"driver-vehicle-road". As a result, the strategy which makes vehicle adapt to driver is an ultimate method to solve the vehicle handling stability problem, this strategy also reflects the thought of vehicle active-safety design. The feeling of driver is a subjective criterion discovering and detecting the vehicle handling stability, and it is also a very important factor when we do the research on road sense characteristics, while road sense is obtained through the force on steering wheel by driver, so the research on steering wheel torque characteristics is also essential content of the research to improve the road sense characteristics.The main tasks of this paper are as followed: Based on the comprehension of the structure of steering system, building up the dynamic model of steering system using Matlab-Simulink and the dynamic model of vehicle handling stability; Putting forward an easy method to select the power-assistance characteristics in order to obtain steering wheel torque characteristics; Simulating and analyzing the vehicle on-center handling stability, especially the steering wheel torque characteristics, and doing the evaluation using the objective evaluating criterion.The detailed work and conclusions are as follows:1 Building up the dynamic model of steering system based on Matlab-Simulink. First according to the thought of falling rank, converting a complicated real steering system to a easy physics model, then separating the easy physics model into several components, do force research on every component, building up kinematics equation of each of them using Newton kinematics law, simultaneous these equations to obtain the dynamic differential equation of the whole steering system, then compiling the structure chart of the Simulink model according to the dynamic differential equation. We add dynamic,static dry friction,the moment of inertia of every component,rate,damp and some other factors to the model, which provides a solid basis to the precise analysis of the on-center handling characteristics.2 Building up the whole vehicle dynamic parameterized model using CarSim software. During the process of building up the model, first giving a brief introduction to CarSim software, then introduce the process of building up the front and rear suspension models which have a close relationship with vehicle handling characteristics and outer Simulink steering system model. As a vehicle parameterized model building software, CarSim provides interfaces to Matlab software to allow user build up complete vehicle dynamic models by using these two software and do combined simulation to get the result, which can avoid the shortage of CarSim model and meet the require of some particular research. The writer connects the Simulink steering system model to CarSim vehicle model and do combined simulation using the interface to Matlab software. After building up the model, compare the simulation results under slalom test and static circular test with real vehicle tests, which insure the precise of the model.3 The analysis of on-center steering wheel torque characteristic model. The main contents are as follows:1)Introducing the definition and evaluation of steering handiness and road sense, indicating that steering handiness and road sense are conflicting during cornering, analyzing ideal steering wheel torque characteristics. 2)Putting forward an easy method to chose the power-assistance to get the steering wheel torque characteristics needed. According to the present research result, steering assistance ratio has a linear relationship with lateral acceleration. Based on this, through some calculation we can get an easy power assistance chosen method, to determine the characteristics the gradient factor and degressivity factor are needed. The initial rise of the steering wheel torque versus the lateral acceleration is determined by the gradient factor, the degressivity factor describes the subsequent curvature of the characteristics. Then select the steering wheel torque characteristics which are suitable to the driver model developed by the Jilin University vehicle dynamic simulation national key lab to chose power assistance.3)Analyzing on-center steering wheel torque characteristics, and validating the effectiveness of the power assistance chosen method in this paper.