Research Of Returnability Character Modeling Method In Vehicle Real-Time Dynamic Simulation

Vehicle virtual prototype technology is the core technology which can shorten product development period, reduce product development cost and development risk. The key of virtual prototype technology is that vehicle dynamic model has high simulation fidelity and simulation condition applicability. Currently, the vehicle handling performance model is relatively mature, a lot of commercial softwares have been used in vehicle industry field successfully. These models'starting point is to describe the vehicle open-loop characters, they can simulate the basic vehicle working performance and can be used in vehicle objective evaluation conveniently. However, when these models are used in driver-vehicle-environment closed-loop simulation to do vehicle subjective evaluation, there are still some deficiencies: model can not accurately describe the vehicle's returnability characters and stability characters, can not fully simulate the vehicle's driving qualities.This dissertation researched the modeling method for vehicle returnability character in vehicle real-time dynamic simulation, focused on the research of key modeling factors for vehicle returnability character. Based on the theory analysis, proposed the effective stick-slip friction state separate modeling method. The steer system model, the wheel dynamic model and the vehicle model had been built, striving to enhance the simulation fidelity and simulate the vehicle working performances and driving qualities. First, the history, the status quo and their respective characteristic of the vehicle dynamic models are summarized. Based on the contrast and analysis, the models'deficiencies in vehicle returnability and stability simulation are pointed out. The intention and the significance of this dissertation are discussed and the key content and method of research are defined.From the perspective of vehicle dynamics real-time simulation, focusing on the research of key modeling factors for returnability character and stability character. The vehicle friction model, the steering system model and the wheel-tire system model are the three main modeling factors.Based on the research of friction modeling theories, the stick-slip friction state separate modeling method is proposed. The whole friction model can be divided into four sections: friction judge logic, stick friction calculation, stick-slip boundary calculation and slip friction calculation. Using a single mass contact friction system as example, the friction model calculation method is elaborated.Face to the gear-rack steering system structure, the steering system model which considering the whole affective factors for vehicle steering performance is established. The model constructed a complete dynamics system including the steering wheel-axle, the steering track rod and the steering rack. At the same time, the steering system dry friction solution algorithm under slip and stick conditions have also been developed, it can simulate the stick and slip friction charactors for steering system.Based on the research of modeling method for wheel-tire system, the wheel dynamic simulation model is developed. The model constructed a dynamics system which is constituted by the carcass and the tire contact patch. Wheel model uses tire carcass dynamics module to calculate the motion state at tire contact center. Considering the flexibility characteristic of tire carcass, model describes the tire's filtering effect and using the stick-slip friction algorithm to calculate the static and dynamic friction force between tire and ground. So the wheel model can be suited for stand-still condition simulation.The solution method of brake torque under braking near zero speed and braking lock condition has been researched and the solution algorithm of slip-stick brake torque was developed. Based on the"roll center"theory, the suspension model according to assembly characters has been built. It uses the K&C experiment characteristic to describe the constraint relationship between suspension and wheel.Some simulation instances including vehicle power performance tests, vehicle brake performance tests, vehicle handing and stability performance tests and vehicle special tests have been simulated by using the vehicle model. Through comparing with the test results, it shows that the modeling method is reasonable, the model has a high accuracy and can be suited well for the vehicle returnability and stability character simulation.The creative works in this dissertation are:1) The vehicle model can realize the simulation for returnability characters, at a certain extent it can simulate the vehicle stability characters. The work of this dissertation drived the vehicle dynamics models from vehicle handling characters simulation to vehicle stability characters simulation. It can enhance the simulation fidelity and simulate the vehicle working performances and driving qualities accurately.2) Proposing the stick-slip friction state separate modeling method and using it in modeling the vehicle friction sections. This method can describe the friction dynamic characteristic preferably, get the exact stick and slip friction force and suit for real-time simulation.3) Build the steering system model which can realize the cooperation between the left and the right wheel. The steering friction model is improved using the stick-slip friction state separate modeling method. Through the steering system elasticity model, the steer wheel torque can be got exactly. So the whole steering model can simulate the vehicle returnability performances and stability performances.4) Build the wheel dynamic model which includes the carcass compliance. It can calculate the motion state at tire contact patch center through carcass dynamic module and realize the cooperation between tire lognitudinal slip and lateral slip. Through the calculation of carcass elasic force, the stick friction force between tire and ground can be got. The wheel dynamic model can enhance the simulation fidelity and can realize the stand-still conditions'simulation.5) Develop a new braking system model. Depending on the state of motion between the brake disc and the brake pliers (brake drum and brake shoe), a solution algorithm of the slip-stick brake torque was established. The model can simulate the conditions of braking on flat road and parking on ramp road.