Study On The Coordinated Control Algrithm Of Braking Force For HEV Bus

With the rapid growth of oil price and the increasingly serious problems of environment pollution, HEV(hybrid electric vehicle) are especially important to urban traffic. One of the means to improve fuel economy for HEV is that motor equipped on HEV can convert braking energy of vehicle to electrical energy to be stored in the battery. During braking,the basic requirements for HEV is to recover as much as braking energy on the basis of maintaining stability of vehicle and meeting the driver's demands, to improve vehicle's fuel economy. Nowadays, people are mainly concerned in the braking force distribution control strategies between the friction braking force and motor braking force. For there are two braking system, there are several braking modes in a HEV. During the switch of braking modes, the target values of motor braking force and fiction braking force from distribution control algorithm will change greatly or suddenly. In the process of switch of modes, we should consider how to coordinate motor an mechanical braking system to work to ensure that the total braking force between motor an fiction force can meet driver's demands and also enable the torque fluctuations as small as possible to avoid passengers in the vehicle feel discomfortable, which is a dynamic coordination control problem.This paper is to study the coordinate control strategy of braking system for HEV bus. To study this issue, the following work are made in this paper:1.For there are motor braking force and pneumatic braking force on the driving wheel, we analyze the dynamic characteristics of regenerative torque and pneumatic braking torque. Then braking modes which to enter is decided by a special strategy for HEV bus are classified and switch between modes are analyzed. After all the analysis above, the reason of dynamic coordination problems is concluded, which make a basis for the dynamic coordinated control strategy.2.According to hierarchical control theory, the braking system for HEV buses are stratification. The dynamic coordinated control strategy which are designed on the basis of braking force distribution control algorithm control pneumatic braking system and motor braking system., so we first study the distribution control algorithm. Aimed at keeping the total braking force of friction and regenerative braking force under small fluctuation when braking mode switch, we design a coordinated controller on the forward-feedback algorithm to control the pneumatic braking system to compensate for error of the motor braking force.3.Adopting forward modeling for vehicles, the paper builds HEV bus and its components math models used as a platform for simulating braking system, which consists vehicle dynamic model, component model and controller model. After translating the math model to Matlab/Simulink and Matlab/Stateflow, this paper simulates the model to validate the coordinated algorithm off-line. Then the results of simulation on the conditions under coordination control and not using coordination control are compared to validate the feasibility of control strategy and achieve its control objectives.4.After the building of off-line simulation platform, ABS+RBS hardware in the loop test platform is built on the basis of Matlab/xPC,on which the dynamic coordination control algorithm is further validated. The braking force coordinated control algorithm can effectively control the braking torque fluctuations during mode-swich according to the tests.