| The Electronic Braking System of commercial vehicles controls the motion of braking valves by electrical signals,which reduces the response time of the braking system.The braking force can be dynamically distributed according to vehicle load,brake lining wear state and other factors,and it has ABS function under emergency conditions.To make the auxiliary braking system work together with the main braking system can improve the braking performance of vehicles.Aiming at real-time estimation system of vehicle mass and road slope and the braking force distribution of the integrated braking system,by reading references the related literatures which is at home and abroad and considering various questions such as the braking efficiency,braking safety and brake comfort,the united estimation of vehicle mass and road slope is carried out firstly.The estimation method is based on the recursive least squares estimation method with variable forgetting factors.The results of estimation can well reflect the change of actual parameters.Secondly,the braking force distribution algorithm based on brake lining wear control and traction pin force control is proposed.Finally,the braking force distribution control algorithm is verified by computer simulation and HIL test.This paper mainly contains the following work:(1)The longitudinal dynamics model of commercial vehicles suitable for the recursive least squares estimation method with forgetting factors is established.The model considers the driving resistance of vehicles,including the driving dynamic model on the flat road and the braking dynamic model of on slope road.Using the model,the vehicle mass and road slope can be estimated in real time.To figure out that vehicle mass and road slope change inconsistently,different forgetting factors are selected in this paper to represent the changes of different parameters.Meanwhile,to improve the estimation effect,a fuzzy controller is designed to dynamically adjust the value of forgetting factors.To verify the effectiveness of the estimation algorithm,TruckSim was used to set different road conditions and vehicle loads for simulation verification.(2)The braking torque model of the auxiliary braking system is established.The composition of the auxiliary braking system selected in this paper is as follows: engine drag braking system,engine exhaust braking system and eddy current retarder braking system.Mathematical models of different auxiliary braking systems were established according to the principles of thermodynamics and electromagnetism.The model is compared with the test results of engine test bench and eddy current retarder test bench to verify the accuracy of the model.Based on the basic theory of braking force distribution,this paper analyzes the influence of auxiliary braking system on braking force distribution.(3)A braking force distribution algorithm,based on an integrated braking system consisting of auxiliary braking systems and main braking system,is proposed under non-emergency braking conditions.In the algorithm,different brake lining wear states and traction pin force are considered.The control objective is to ensure the vehicle braking safety under different lining wear states,which meaning is the braking distance remains changeless.Meanwhile,by controlling the tractor and trailer with the same braking deceleration,the force on the traction pin is minimized to ensure the braking comfort.By adjusting the pressure of each axis brake air chamber under different brake lining wear conditions,the wear of brake lining is equal to ensure the braking economy.Compared with the traditional vehicle,the proposed braking force distribution algorithm is more effective.(4)Commercial vehicle simulator based on semi-trailer is built,in which the braking part of the driving simulator can be used for the HIL test of the braking integration system.The test bench consists of braking parts,vehicle model software,real-time controller system and signal sending and receiving system.On the basis of bench,the braking force distribution control algorithm which aims at brake lining wear control and traction pin force control under different road conditions is verified on test bench. |
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