Research Of Vehicle Dynamics Real-Time Simulation Method Based On Assembly Structure

Vehicle virtual prototype technology can shorten design periods, save R&C expenses and debase the risk of exploitation. As a key of vehicle virtual prototype technology, vehicle performance simulator is widely used for active security performance evaluation and matching. At present, large-scale auto manufactories have adopted simulator technology in succession as a substitute for the field test to optimize the full vehicle performance and ultimately upgrade the exploitation ability.The key of the simulator technique is that vehicle dynamic model has RTS (real time simulation) and high fidelity. So far at home, most of the vehicle dynamic model is based on Roll-Center theory. This kind of model has only one point to transfer tire forces to car body because of no consideration of suspension structure, so the forces acting on suspension and vehicle body do not fit well with the real condition. And much more tests must be done to define the model's parameter while suspension's parameter is changed, which does not meet with the request of lower exploitation periods and saving expenses.Using commercial software such as ADAMS and DADS, the full vehicle dynamic model can be built based on structures. Multi-body programs can be commonly used and also have high precision, but the disadvantage is that the computing is so slow as not to meet the demand of real-time simulation.Considering that neither does the present vehicle model meet with the request of fidelity nor the commercial multi-body dynamic softwares suit for RTS, this dissertation tried to explore a RTS method based on assembly real structure, and build a vehicle dynamic simulation model which could be applied to the driver simulator of ASCL of Jilin University. This vehicle model can not only meet with the request of general use and high fidelity but also realize RTS on high performance computers. The work presented in this paper would be a good basement for vehicle dynamic simulation, design and optimization. Making a comprehensive view, there are several parts in the dissertation.1,The history, the status quo and their respective characteristic of the vehicle dynamic models are summarized. According to the updating request of the driver simulator of ASCL, the intention and the significance of the dissertation are discussed and the key content and method of research are defined.2,Contraposing to the fixed step size characteristic of integration for real time simulation, a new method for vehicle real-time dynamic simulation based on assembly structure, that is, composite constraints separating and uncoupling method is introduced. The process and realization of the uncoupling method would be proposed. The solution process of this method can be divided into three process, which are, kinematics phase, statics phase and dynamics phase. The basic theories, on which the kinematics constraints equations, statics analysis equations and subsystems dynamics equations based, are discussed. After the summary of the solution process of modeling method, the meanings of separation and uncoupling of the system are analyzed. Meanwhile, the influence on simplifying modeling and enhancing solution efficiency by adopting this conception are all put forward.Comparing to commercial software such as ADAMS and DADS, the method proposed in this paper has the following characteristics:Those components which have little mass and inertia are viewed as massless composite constraints, and they only have constraints effect on adjoining rigid bodies. Because of only considering kinematics and statics of the composite constraints, the mass differences of rigid-bodies which status are needed to be solved by dynamic equations are decreased, the stiffness ratio of whole system would be decreased dramatically, this would be very useful for improving the ODES numerical integration speed .With composite constraints, the system can be isolated into some independent subsystems, there will be one or a few bodies in each subsystem. The simpleness of subsystem structure can simplify dynamic formulae deducing, and will be useful for model equations establishing and solving.The kinematics, statics and dynamics model correspond with three stages of model sovling progress can be sovled independently, this will be helpful for high-performance parallel computation.3,Following a comprehensive structure analysis of the target vehicle, based on the concept of composite constraints, some component of suspension which has a relatively small mass can be considered as massless part, such as the damper slide column and the low-arm, which are all defined as composite constraints. By using composite constraints, the vehicle system is uncoupled into six independent dynamics subsystems such as vehicle body, steering rack and four wheel-axle systems.Considering the advantage of recursive dynamics method for kinematics analysis such as less number of solving equations and higher computation speed, suspension kinematics analysis model in this dissertation is established based on recursive dynamics method. From the process of analysis, we can see that comparing to Cartesian coordinate method, the number of equations for solving the state of suspension's movement is decreased greatly and the computation efficency improved enormously.Using vector analysis mehtod, the elasticity force between bodies is obtained, and the suspension static analysis model is built.Through the force analysis of each dynamics subsystems, the vehicle body, steering rack and four wheel-axle systems'dynamics equations can be established based on Newton-Euler's method. In wheel-axle dynamics equations, the gyroscope moment caused by wheel rotation is also considered.4,Some instances including steady-state cornering, transient cornering, cornering release and braking inline have been simulated by using the vehicle model and compared to the test results. It shows that the model has a high accuracy and can be suited well for the vehicle dynamics simulation. Comparing with multi-body dynamic softwares such as ADAMS and DADS, the computation speed can be accelerated dramatically, and it may realize RTS by using this method with the high performance computer and parallel computation method.The creative works in this dissertation are:1) According to the characteristics of real-time simulation, a new method-Composite Constraints Separating and Uncoupling Method, is proposed to build the real-time vehicle dynamic simulation model based on assembly structure. This method can avoid rigid differential-algebraic equations which the traditional multi-body dynamics vehicle models often face to and quicken the computation speed.2) Based on the recursive dynamics, and with the joints relative movement analysis, the kinematics model based on the suspension structure has been built by analysing of the relative movement of rigid bodies. This model greatly quickens the computation speed because of solving less differential equations and suits well for the vehicle real-time simulation.