| Brake system is one of the most important security components in the vehicle and it greatly contributes to the performance of the vehicle. This paper mainly concerns modeling of flexible multibody of vehicle braking system with MSC.ADAMS, and how some parameters contribute to brake lock and vibration while braking.Combined with the research on a cooperative project between ASCL (State Key Laboratory of Automotive Dynamic Simulation) and Chassis Factory of FAW Bus Company——Research of abnormal wearing, self-locking and whistle on brake system of bus chassis, concerning with abnormal braking behavior of bus brake system like: self-lock, wedge effect arose by elliptical contact between drum and shoe, stuck and vibration, this paper have built dynamic simulation models of braking system including components of drake drum, brake shoe and lining and their elastic characteristic, and have analyzed the effect that structure parameters contribute to these problems.This paper use MSC.Nastran to analyze modes of components, and use ADAMS to load analysis result (mode coordinate, modes conversion matrix, modes stiffness matrix and modes frequency) combined with mechanical model to build flexible multibody model of brake system.The method of modeling flexible multiby in this paper is different with others that it concern not only the elastic deformation among components of brake system, but also revolution inertia of wheel and rear axle, as well as stiffness and damp between rear axle and chassis frame.Concerning with the bus brake system, this paper quest some key technologies of modeling flexible multibody with MSC.Nastran and ADAMS including: modeling three-dimensional geometry entry, FEA analysis of with MSC.Nastran, dynamical analysis with ADAMS, modeling flexible multibody of brake system with both software. Among these, the paper pays much attention on flexible contact friction between drum and shoe. By simulation of braking process, components' characteristic of force, deformation, speed and acceleration relative to time can be achieved.As a result of dynamical simulation and analysis of the flexible multibody models, we have some conclusions below:1. The flexible multibody models built in this paper are proven to be accordant with the actual process by and large.2. The friction increase along with the dynamic friction coefficient. But there will be great instantaneous amplitude that would cause vibration of brake system and worsen the stability. On the contrary, with a lower dynamic friction coefficient, the vibration will be restrained but the capacity of brake system will be too low. When selecting brake shoe, the dynamic friction coefficient must fulfill the request of both brake capability and stability.3. To increase self-lock angle of the brake shoe or decrease the cover angle will lower the brake capability and the selection also should fulfill the request of both brake capability and stability. At the same time, it should pay attention on precision of production and assemble.4. Because of insufficient time, this paper does not implement switch between dynamical friction coefficient and a static one, then no harsh can be simulated. At the same time, no stuck was simulated either. It shows that it's not sufficient only concerning elastic characteristic of components while analyzing stuck problem, but other factors like: temperature of brake system, components of suspension and steering, have to be included. This paper applies an elementary research on modeling flexible multibody of brake system, and provides a feasible solution and reference about analysis of complex braking process. This certainly needs more work to make it more and more capable and precise.The solution of modeling flexible multibody in this paper is universal to apply to other friction studies that only need to change some of the parts. It's very convenient to analyze brake system with other structure or some other contact models with it.This paper only applies an elementary analysis on dynamic characteristic o... |
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