Research On Braking System Integration Of Battery Electric Truck

China’s oil consumption is large,the development of new energy vehicle is an important way to ensure China’s energy transformation.The electrification of truck can help reduce oil consumption,and due to the large mass of battery electric truck,more braking energy can be recovered during braking.Research on braking energy recovery of battery electric truck is conducive to improving vehicle economic benefits.The Electro-mechanical Brake(EMB)can achieve precise adjustment of mechanical braking torque,which meets the demands of the uncoupled braking energy recovery system for the mechanical braking torque.The EMB also has fast braking response,providing better braking performance.However,the braking efficiency of EMB declines when braking slowly for a long time,so it can not meet the needs of slow braking.while the Energy Recovery Retarder(ERR)can meet the requirements of slow braking and recover the energy of slow braking.Besides,the EMB,ERR and drive motor can jointly brake.And the distribution of braking torque during braking affects vehicle economic benefits and braking safety.Based on the above,the main research contents of this paper are as follows:(1)In order to meet the demand of the uncoupling braking energy recovery system for the mechanical braking torque and improve the braking efficiency,a scheme of bidirectional synchronous force-increasing EMB actuator with two-way eccentric was proposed.Through the structural and force analysis of the force increasing mechanism of the EMB actuator,the relationship between the force increasing ratio and the eccentricity of the two-way eccentric was found out.Moreover,the relationship between the compensation amount of the force increasing mechanism for the wear of the brake lining and the eccentricity of the two-way eccentric was determined.In addition,based on the force increasing ratio and the demand of compensating the maximum wear of brake lining,the design of structural parameters such as eccentricity of the two-way eccentric were completed.And the static analysis and kinematic verification of key part of EMB actuator were carried out.An ERR scheme installed on one axle of semi-trailer was proposed,and the ERR parameters were matched.The goal is to make up for the lack of EMB’s inability to meet the needs of retarding braking and meet the national standard requirements.At the same time,it is also targeted to deal with the collision problem between the tractor part and the semi-trailer part of the battery electric truck.(2)The paper analyzed the integrated control process of the braking system.And the integrated control strategies of braking systems such as slow braking control,light braking control and ABS control were studied.In order to obtain the required braking torque,the braking intensity identification and vehicle mass estimation were studied.On the one hand,the identification parameters and algorithms of driver’s braking intention and intensity were selected.Furthurmore,the identification accuracy was verified by using different braking intensity conditions.On the other hand,based on vehicle longitudinal dynamics model and recursive least square method,vehicle mass estimation was studied and verified.Apart from that,based on particle swarm optimization,the optimal distribution of braking torque of the EMB,ERR and drive motor was distributed.This aims to improve the recovery rate of braking energy and reduce the impact force between tractor and semi-trailer.(3)Based on Truck Sim and MATLAB/Simulink,the co-simulation platform for battery electric trucks was built.The tractor model,semi-trailer model,load model and road model of battery electric truck were built through Truck Sim.Moreover,the driver model,drive motor model,EMB model,ERR model and integrated control model of braking system were built through MATLAB/Simulink.In addition,signal interaction was carried out through the data interaction interface to complete the construction of the co-simulation platform.(4)Based on the battery electric truck co-simulation platform,the braking system performance and vehicle economic benefits were verified.First,the EMB braking response time,EMB braking torque adjustment performance and braking system service braking performance were verified.The braking response time of EMB is reduced by 68.8%compared with the specified time,and EMB can precisely adjust the mechanical braking torque,the braking performance of the braking system meets the requirements of the national standard.Secondly,it is verified whether EMB can meet the requirements of ABS for braking torque adjustment.EMB works in coordination with ABS to keep the wheel slip ratio of each axle around 0.2,and EMB meets the requirements of ABS for braking torque adjustment.Finally,under the conditions of retarding braking performance test conditions,China heavy-duty commercial vehicle test cycle for tractor-trailer,and China world transient vehicle cycle,the vehicle economic benefits and braking performance of battery electric trucks integrating EMB and ERR are evaluated.After integrating EMB and ERR,the energy consumption per 100 kilometers of the battery electric truck is reduced,and the greater the vehicle load,the higher the energy saving ratio.During the slow braking,the ERR installed on the semi-trailer can significantly improve the collision problem when the battery electric truck is loaded.Meanwhile,the collision force between the tractor and the semi-trailer is reduced by 84.5% under full load and low-intensity braking.The integration of EMB and ERR is beneficial to improve vehicle economic benefits and braking safety.