Vehicle Collision Avoidance System For Vulnerable Road Users

Vulnerable Road Users(VRU)refer to participants who are vulnerable in road traffic due to lack of safety protection,mainly including pedestrians and two-wheeler users.According to relevant statistics,more than half of the fatalities in global traffic accidents are vulnerable road users,and the road safety of VRU has become an urgent problem to be solved.Improving the safety protection of vulnerable road users has become the development trend of the next generation of vehicle collision avoidance system.VRU have flexible movements,random positions,so braking and steering may be the best collision avoidance operations.This paper proposed a vehicle collision avoidance system that combines active braking and active steering operations,focusing on the collision avoidance system test scenarios,safety assessment and autonomous decision rules,and vehicle lateral and longitudinal collision avoidance control.First of all,the domestic and international research status of vehicle collision avoidance technology for vulnerable road users was summarized.Based on the Chinese In-depth Accident Study(CIDAS)database,the functional scenarios of the collision avoidance system were extracted through accident screening,scenarios classification,and type ranking.The characteristic value ranges of the participant’s speed and lighting conditions were determined.Then,the specific characteristic values in the scenario were determined with reference to the relevant test specifications,and the test scenarios of the collision avoidance system for VRU were obtained.Finally,the overall scheme of the collision avoidance system was proposed.Secondly,the safety evaluation method and autonomous decision rules of collision avoidance system were studied.According to the type of road on which the car travels,the positional relationship models between ego car and the object were constructed respectively when driving on straight and curved roads.Three indicators of time to enter(TTE),time to disappear(TTD)and time to collision(TTC)were established to identify dangerous object on the vehicle’s driving path,and then a collision warning and brake safety distance model of the ego car to the dangerous objects was constructed for brake safety assessment.Steering safety assessment was carried out from two aspects of steering dynamics constraint and collision-free path.Finally,the priority order of collision avoidance operations was determined: driver warning-driver assistance-active braking-active left turn-active right turn.Then,the vehicle’s longitudinal and lateral collision avoidance controllers were designed using a layered structure.It was determined that the upper output of the longitudinal collision avoidance controller is the maximum braking deceleration and the lower output is the brake pressure,and the switching logic of the longitudinal drive mode,idle mode,and braking mode was designed.The upper layer of lateral collision avoidance controller was determined to be used for path planning,and the lower layer was used for path tracking.A path planning module based on quintic polynomial fitting was designed.The lower layer model predictive path tracking controller was built based on Model Predictive Control(MPC)theory.Through the joint simulation of CarSim and Matlab / Simulink,the control effect of the MPC path tracking controller under different lateral avoidance displacements and vehicle speeds was verified.Finally,a model-in-the-loop simulation test platform of the collision avoidance system was built by integrating PreScan,CarSim and Matlab / Simulink.The collision avoidance test scenarios for VRU was constructed based on PreScan,and then the decision and execution module was built in Simulink.Finally,a simulation analysis of the test cases for vulnerable road users was carried out to verify the functionality of the vehicle collision avoidance system.