Spatio-temporal heuristic method:a trajectory planning for automatic parking considering obstacle behavior

Purpose–The purpose of this paper is to develop a real-time trajectory planner with optimal maneuver for autonomous vehicles to deal with dynamic obstacles during parallel parking.Design/methodology/approach–To deal with dynamic obstacles for autonomous vehicles during parking,a long-and short-term mixed trajectory planning algorithm is proposed in this paper.In long term,considering obstacle behavior,A-star algorithm was improved by RS curve and potential function via spatio-temporal map to obtain a safe and efficient initial trajectory.In short term,this paper proposes a nonlinear model predictive control trajectory optimizer to smooth and adjust the trajectory online based on the vehicle kinematic model.Moreover,the proposed method is simulated and verified in four common dynamic parking scenarios by ACADO Toolkit and QPOASE solver.Findings–Compared with the spline optimization method,the results show that the proposed method can generate efficient obstacle avoidance strategies,safe parking trajectories and control parameters such as the front wheel angle and velocity in high-efficient central processing units.Originality/value–It is aimed at improving the robustness of automatic parking system and providing a reference for decision-making in a dynamic environment.

Gear downshift control of inverse-automatic mechanical transmission of electric vehicle

In order to improve the driving dynamics and riding comfort of pure electric vehicles,taking a two-speed I-AMT(Inverse-Automatic Mechanical Transmission)with rear friction clutch as the research object,a gear shift strategy,which consists of the open-loop control of the clutch position control and the closed-loop control of the drive motor speed control,is proposed.Considering the inherent time-delay and external disturbances within the motor speed adjustment system,a two DOF(degree-of-freedom)Smith predictor with feedforward input is designed to track the target speed of the drive motor.The feedforward input is used to eliminate the influence of clutch sliding friction on the motor speed control,while the feedback speed tracking controller is applied to realize the speed tracking performance with the existence of time-delay and the external disturbance.In order to verify the effectiveness of the gear shift control strategy and the accuracy of the two DOF Smith controller with feedforward control,simulation results comparison is firstly carried out to illustrate the effectiveness of the control scheme.Then,a light pure electric vehicle equipped with I-AMT was used for downshift experiments under large throttle,which is the most difficult working scenario to control the transmission.The experimental results show that the two DOF Smith controller can eliminate the influence of time-delay on the closed-loop control,and the proposed whole gear shift control strategy can limit the clutch slippage time within 1.5 s,resulting in a smaller shift jerk,thus guarantee the driving dynamics and riding comfort simultaneously.