Research On Dynamics Of Heavy Truck Brake System Based On The Multi-domain Modeling

The dynamic brake systems are used in the vehicle which is more than 8000 kilograms, and :he air brake system is widely used in the heavy trucke for its simple structure and larger brake force. The capacity of brake is not determined by the brake system only, and it is affected by the vehicle parameters. Thus, to research the brake capacity precislier, not only the brake system need to be studied, but also orther systems of vehicle need to be analized.The traditional simulation methods and theories of vehicle are researched on one-domain. The different theories are supported by different softwares, which lead to some troubles. If we research the different theories in a same software platform, the effectivness would be elevated much and the numerical problem caused by the data commutation among different softwares would be avoided.The brake capacity of heavy truck is mainly be researched in this thesis. Firstly, the evaluation indexes are studied, and then the brake system and vehicle model of heavy truck are built in the multi-domain modeling software, lastly the optimization of the brake capacity of heavy truck is completed.Several aspects which were discussed in detail in this thesis are listed as follows:Firstly, research the multi-domain modeling theory, and build and extend the model libiary. The the non-causal modeling theory and the characteristics of Modelica modeling language for multi-domain modeling are presented. The description theory and modeling principle of multibody system under the multi-domain modeling platform are analyzed. The hydrodynamics and thermodynamics theory effecting on the pneumatic transmision are summarized, and the pneumatic transmison library which provides the basic components to the vehicle brake system is built.Secondly, construct the brake system dynamic model. Analyze the structure and work of the key components in detail. Build the model of key components of air brake system on the multi-domain modeling platform MWorks, containing reserivor, brake valve, relay valve, brake chamber, and the assemebely mechanical subsystem of brake system, and then construct the integrate brake system model based on these components. The brake system can simulate the air pressure and brake torque varing with time, which is more accurate than traditional emprical formulas.Thirdly, construct the vehicle dynamic model of heavy truck, and simulate the brake performance combined with brake system model. Decompose the vehicle to several subsystems containing front leaf spring suspension, middle and rear air spring suspension, steering subsystem, and tire model, and then build these subsystems on the same platform MWorks. The leaf spring suspension is based on the beam element model; the air spring suspension is built through the experiments curve fitting of stiffness; tire employs the classic Magic Formula to achieve the model. Simulate the vehicle deceleration, velocity, and brake distance using the combined model of vehicle and brake system. Because the vehicle model and brake system model are built on the same platform, some problems induced by data exchange and solver difference between the different softwares can be avoided.Lastly, the optimization is conducted to enhance the performance of braking system. The static characteristic optimization is carried out as a basis to satisfy the basic rules of braking system. Then, the dynamic characteristic is optimaized through the straight-line brake simulation to decrease the delay time and braking distance. Finally, brake in-turn is simulated to analyze the handling stability during braking. After the optimization, the vehicle not only confirms the brake laws, elevate the brake efficiency, but also reduce the brake distance, and estimate the vehicle steering stability through the simulation of steering brake, which can replace some road test.