| As the demand for new energy commercial vehicles expands,the performance requirements are also getting higher and higher.In terms of safety,the improvement of braking performance has an extremely important impact on the safety and comfort of the vehicle,while in terms of braking energy utilization,the mass of the new energy commercial vehicle is larger,and if the braking energy recovery rate can be improved,the economy of the vehicle can be further improved.Due to three-axle vehicles have a larger front and rear wheelbase,which will increase the length of the brake system piping and lead to a slower response of the air-pressure braking force,further causing the slow response of the braking force after the coupling of the wheel electric force and the air-pressure braking force,etc.In response to this problem,how to improve the response of the coupled braking force has become the focus of this paper,through the Uncoupled Brake Energy Recovery System(URBS).Uncoupled Brake Energy Recovery System(URBS)can realize the uncoupling of coupled braking force,which can not only improve the coupling braking force response speed to meet the requirements of the braking performance of the vehicle,but also improve the braking energy recovery rate.During emergency braking,the pneumatic braking force provided by the conventional braking system can meet the performance requirements of the braking system.When braking at low intensity,the participation of the wheel hub electric mechanism power can improve the braking energy recovery rate,therefore,the reasonable distribution of the triaxial braking force,wheel hub electric mechanism power and pneumatic braking force will have a greater impact on the economy and braking safety of the whole vehicle.The main research contents of this paper are as follows:(1)For the whole vehicle configuration of the three-axle new energy commercial vehicle,the wheel motor was matched,and based on the matching result of the wheel motor,the parameters of the composite power supply were matched.The composite power supply includes power battery pack,super capacitor and bi-directional DC/DC converter,and the topology configuration of the composite power supply was determined in order to improve the energy conversion efficiency;and the air pressure braking system was matched,and the parameters of the working volume flow,maximum exhaust pressure and demand power of the air compressor were determined according to the air consumption of the whole vehicle,and the matching principle of the air storage cylinder was studied.(2)Based on the tire model to identify the road adhesion coefficient,the peak adhesion coefficient of the adjacent upper and lower two typical road adhesion coefficient curves was determined according to the current road adhesion coefficient,and the target slip rate was determined by using the equal ratio method,and the logic threshold value-based ABS control strategy was built by using MATLAB/Simulink/Stateflow.Mainly by changing the slope of braking torque change to achieve control of braking pressure,so as to complete the switch of working mode and control the slippage rate near the target slippage rate.Based on the requirements of GB 12676-2014 and the test method,the braking force distribution strategy was developed to realize the distribution of three-axle braking force,wheel electric force and air pressure braking force,in order to recover as much braking energy as possible,the braking energy recovery control strategy was developed based on the operation mode of the composite power supply,and the braking energy recovery evaluation index was studied.(3)For the problems of high energy consumption and slow response of coupled braking force in three-axle new energy commercial vehicle,a uncoupled braking energy recovery system configuration based on superimposed check valve and linear exhaust solenoid valve was proposed,the structure and principle of the composite power supply,tandem double-chamber brake valve,ABS solenoid valve,four-loop protection valve,relay valve and brake air chamber were studied,the internal spool and spring of the pneumatic valve and brake air chamber were analyzed.The force analysis was carried out and the corresponding differential equations of motion were established,the advantages of the composite valve composed of the stacked check valve and linear exhaust solenoid valve were analyzed,and the whole vehicle model,uncoupled brake energy recovery system model and pneumatic brake system model were built based on AMESim.(4)A joint simulation platform based on AMESim and MATLAB/Simulink was built to verify the braking performance and overall vehicle economy of the three-axle new energy commercial vehicle,and the braking force response of the front,middle and rear braking air chambers were studied respectively;the response times of the three-axle braking air chambers to reach 75% of the steady-state pressure were all 0.06 s,while the response times to reach the steady-state pressure were 0.32 s,0.41 s and 0.41 s,in accordance with GB 12676-2014;and the influence factors of brake gas chamber pressure fluctuation were studied;the brake energy recovery control strategy was verified,and the characteristics of ABS solenoid valve pressurization,depressurization,pressure retention,step pressurization and step depressurization were studied,and the decoupled brake energy recovery system with the proposed composite valve was simulated and verified.The brake air chamber braking force response speed was increased by 9.4%,and the control effect of ABS was verified on the road surface with adhesion coefficients of 0.8 and 0.25.The results showed that the control of ABS enabled the vehicle to maintain high longitudinal and lateral adhesion;based on the operating conditions of CCBC,C-WTVC and CHTC-B,the whole vehicle economy was verified,and the URBS was able to improve the whole vehicle economy by the performance of three schemes under different loads,and the hardware-in-the-loop test scheme of the three-axle new energy commercial vehicle pneumatic brake system was investigated. |
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