Development And Verification Of Braking Control Strategies For Articulated Vehicle Based On Electro-pneumatic Braking System

Commercial vehicles are important carriers of highway transportation because of their large capacity.However,traffic accidents they cause are serious.,so the active safety of them is very important.The inefficiency of the braking system will seriously affect the braking performance of commercial semi-trailers.The unreasonable distribution of braking force will cause some wheels to lock or activate the anti-lock braking system prematurely.Wheel-lock may lead to loss of steering ability,trailer spin out or "jack-knifing".Even if the anti-lock braking system can avoid the lock of wheels,the ground braking force may not be fully utilized and the braking distance may be affected.In addition,due to the large inertia and high center of commercial vehicles,spin out or "jack-knifing" may occur on the low-adherence road surface,and large lateral load transfer may occur on the high-adherence road surface,leading to rollover.Based on the above reasons,it is meaningful to improve the braking efficiency and active stability control of commercial vehicles.In Electro-pneumatic Braking System,electronic control units are used to control pneumatic braking circuit components.Compared with traditional braking system,it could shorten response time and achieve flexible adjustment of braking force.In addition,it can integrate more braking functions.In this paper,the braking control strategies of articulated vehicle based on EBS are designed and verified,including braking strength control,braking force distribution,anti-lock braking,stability control,anti-rollover control and autonomous emergency braking strategies.The strategies are modeled based on Simulink,and the model-in-the-loop simulation is carried out with Truck Sim.Because of the non-linearity of the pneumatic braking system,a hardware-in-the-loop simulation test rig is built,in order to verify control strategies under the condition which response ability of the hardware is limited.The specific contents of this paper are as follows:(1)The ideal braking force distribution relationship is obtained by analyzing the longitudinal force of semi-trailer train during braking.And the relationship between braking force,slip ratio and vertical load is studied by analyzing the longitudinal mechanical properties of tires.The hardware layout of 6*4 tractor and three-axle semi-trailer EBS is confirmed,including the layout of wheel speed sensors and pressure regulating modules.The braking force control strategy is designed based on Simulink.The target braking pressure of each axle is calculated by double feedback.The outer feedback is based on the deceleration error to achieve deceleration control.The inner feedback is based on the slip error to make the slip ratio of each axle follow the front axle of the tractor,so as to realize the braking force distribution.Combining with Truck Sim,the simulation is carried out to verify the control strategies under different load states,road slope and adhesion conditions.In addition,the emergency braking performance under the abnormal condition of front axle braking circuit failure is also verified.(2)The linear three-degree-of-freedom model of semi-trailer train is built,so the expected yaw response during steering can be calculated.The mechanism of rollover is studied by lateral force analysis.Based on the analysis of longitudinal and lateral mechanical properties of tires,a method of judging and avoiding rollover of vehicles based on slip ratio is proposed.The active safety control strategies are designed based on Simulink.The adjustment of the asymmetric braking pressure is calculated based on the error between expected and actual yaw response to control the yaw stability.The degree of lateral load transfer is judged according to whether the inner wheels will be locked while braking under higher lateral acceleration.,and rollover can be prevented by braking the vehicle according to the target strength.According to the relative distance and speed between the vehicle and the front vehicle,the target braking strength can be calculated to realize autonomous emergency braking.The stability control strategies are verified by the closed-loop driving condition and the open-loop steering input condition.The autonomous emergency braking strategy is verified by the conditions of driving behind a vehicle at low speed.(3)A hardware-in-the-loop simulation test rig including the pneumatic circuit of EBS,realtime vehicle dynamic model and real-time control strategy is built.NI PXI is used to collect the pressure signals of pneumatic circuit and solve Truck Sim RT vehicle model in real time,so the pneumatic circuit is embedded in vehicle dynamic model to perform as plant model,which fully reflects the hysteresis characteristics of the pneumatic braking system.The control strategy is calculated by d SPACE Micro Auto Box in real time to obtain the target braking pressures and output the control signals to pneumatic circuit components.Finally,based on the hardware-in-theloop simulation test bench,the control strategies are verified through the straight-line braking conditions,steering conditions and following the target vehicle condition.