Dynamic Modeling And Analysis Of The Braking System Based On Its Characteristics

The braking system performance and safety performance of passenger cars are directlyaffected by that whether the matching of braking system is reasonable or not. The simulationof vehicle performance can be achieved through the existing mainstream vehicle dynamicssimulation software. However, braking systems in the mainstream software are either toosimple or too many parameters in demand. It is not easy for the vehicle factory to use themfor simulation comparison validation in the product design stage. Meanwhile, in order to getthe vehicle braking performance that the subject mainly concerns, a lot of structuralparameters and performance parameters are generally required in the vehicle simulationmodel. It is difficult to achieve such a request for the matching the performance of thebraking system for the vehicle factory.To solve this problem, a simple vehicle dynamics simulation software including thebraking system dynamics simulation model is developed in the subject relying on the projectthat the matching and analysis of the passenger car braking system performance supportedbyChang'an Automobile and Jilin University. Asatisfactory result is gained in the paper viaresearch and analysis, theoretical analysis and modeling, model simulation and experimentalverification. The main contents and conclusions in the paper are as follows:Firstly, do a research at home and abroad about the braking system and vehicle modelrelated to braking system. First of all, put forward a complete set of scheme for brakingsystem modeling. Secondly, derive the braking system simulation model with the principlessuch as the mechanical dynamics, hydraulic system dynamics, and fluid mechanics and so onand achieve the braking system simulation development in the MATLAB environment.Finally, Access to the brake system and vehicle parameters and do the correspondingsoftware debugging and validating taking a car for example with the help of the testexperiment for parts performance characteristics.Secondly, establish a suitable model of the braking system. A mechanical brake pedalStatics steady-state model is established ignoring the pedal inertia and other factors. Thedynamic model of the vacuum booster is approximately express with a step inertial part onthe basis of the vacuum booster steady state input and output characteristics, This reducesthe demand for the dynamic model of the vacuum booster on the structural parameters andperformance parameters. In order to reflect the dynamic characteristics of braking systemhydraulic part better, the inertia of the braking master cylinder and brake wheel cylinder piston and clearance between braking master cylinder and brake is taken into account. At thesame time, the dynamic model is established considering brake pipe capacitive and brakingfluid viscosity. With the help of the KELVIN-VOIGT model, Spring-damper contact modelbetween the brake pads and brake discs is established which can satisfy the needs of themodule division and more accurately reflect the dynamic contact process and the brake paddeformation on the pedal displacement. Finally, the brake torque model expressed with aunified braking efficiency factor is given.Thirdly, through the research and comprehensive analysis to get the demand for vehicledynamics model,14degrees of freedom vehicle dynamics simulation model is establishedaccording to the demand. In the Vehicle dynamics model, the full six degrees of freedom ofthe body as a rigid body is established. This Paper mainly studies the modeling of thebraking system, so in the steering system model the steering angle of steering wheel iscalculated by steering wheel angle and the transmission ratio. Linear stiffness and dampingsystem model is adopted to express flexibility components and shock absorbers in thesuspension. And assume that the wheel only has vertical degree of freedom of the body,regardless of the K&C characteristics caused by the suspension-oriented institutions. In orderto reduce the parameters to apply in the pre-development, UA theoretical tire model isselected.At last, a vehicle simulation interface with the braking system is built in the MATLAB/Simulink software environment. The main point for the simulation interface is the analysis ofthe braking system lag feature. Finally, Verify the accuracy of the braking system model andsimulation model of a simple vehicle making use of the vehicle parameters provided byChang'an Automobile and the test data provided by BOSCH and SABS.Through the research in the paper, the prediction and decomposition of the brakingsystem performance and vehicle braking performance can be achieved by automobilemanufacturers in the early product design stage with only a small amount of parameters ofthe braking systems and vehicle. Shorten the post-test cycles, improve system integrationcapabilities, thus shorten the development time, improve efficiency, and reduce productioncosts.