| Because of its high transport efficiency and low cost,the tractor-semitrailer combination has become the main transportation facility in road transportation.In order to improve the fuel economy and power performance of tractor-semitrailer on low-adhesion and high-gradient pavement,the hydraulic accumulator regenerative braking system is installed on the axle of semitrailer.And the hydraulic regenerative braking system can output driving torque or recover braking energy.However,the intervention of regenerative braking system changes the distribution of braking force between axles,which causes wheel lock-in side slip and instability.In addition,the auxiliary driving force of regenerative braking system aggravates the trend of lateral instability of the vehicle.Therefore,this paper mainly studies the braking stability and lateral stability of hydraulic hybrid tractor-semitrailer.The main research works are as follows:(1)Considering the braking energy recovery efficiency and braking stability,a coordinated control strategy between optimal braking energy recovery and ABS is proposed.The mechanical friction force and regenerative force between three axles is allocated according to braking strength,accumulator energy storage status and road adhesion condition.In the same time,two strategy schemes of logical threshold and sliding mode variable structure are adopted to adjust the mechanical friction braking force.It will maintain the wheel slip ratio in the optimal range.The co-simulation results on the TruckSim-Matlab/Simulink platform show that the anti-lock braking system controlled by logic threshold value method has rapid response,high control precision and fine braking efficiency.In the contrast,the anti-lock braking system controlled by sliding mode variable structure algorithm has lower control precision and higher braking energy recovery efficiency.(2)Considering the short-term driving characteristics of accumulator-motor hydraulic driving system,a hydraulic auxiliary driving method is proposed,which outputs constant torque by phases.The controller can obtain the displacement value of motor according to the accumulator energy storage state and transmission gear ratio.In order to validate the effectiveness of the control algorithm,the simulation model is built by MATLAB/Simulink.The results show that,the hydraulic auxiliary driving method can reduce the longitudinal tension impact of the fifth wheel enforced bysemitrailer.(3)To improve the lateral stability of vehicle,the differential braking control method is adopted.The yaw angular velocity of tractor and semitrailer is selected as the control variation,and the additional yaw moments of vehicle body is calculated by using the fuzzy PID algorithm.The braking forces between each wheel is allocated by according to the coordinated control strategy of regenerative braking and ABS.The simulation is carried on the TruckSim-Matlab/Simulink co-simulation platform.And the results show that,the lateral stability control strategy can reduce lateral stability control variation deviation of tractor-semitrailer effectively,such as yaw angular velocity,center of mass side slip angle,vehicle body rollover angle and articulation angle.The control strategy can directly improve the yaw and jackknife stability of tractor-semitrailer,improve the rollover stability indirectly. |
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