Investigation Into The Effectiveness Of Reversible Restraint System For Occupant Injury Prevention In Frontal Collisions

Occupant restraint systems is the last protection barrier of vehicle safety systems for saving occupants' lives and reducing injury,which plays a dominant role in preventing the occupant from being thrown out of the car and pretecting the occupant from colliding with the vehicle interior in second collision.In the vast majority of collision accidents,the occupant restraint systems played a significant role in injury protection and saving the lives of numerous occupants.Recently,the rapid development of automotive integrated safety systems aimed at collision avoidance and injury reduction,fundamentally changed the work patterns of conventional restraint systems.The integrated safety systems builded collision warning and collision avoidance systems,and activated the occupant restraint system properly before impact to improve the occupant's seating posture and kinematic state.In this paper,with a view to the problem that the casualties number of car occupants account for a large proportion of the total casualties,a systematic and in-depth investigation of the reversible restraint systems was carried out to explore its effectiveness and importance for reducing the number of occupant casualties under the guidance of the basic theory of integrated safety systems,based on the conbination of lumped mass model,computer simulation,optimization design,and volunteer experiment.The main research work and innovation was carried out and completed in this paper as follows:1.The optimal restraint force of the reversible restraint system.Aimed at revealing the mechanism of reversible restraint system in reducing injury,the lumped mass model was improved firstly which was used to study the response of chest impact,and the optimal restraint forces of the two models with or without reversible restraint system are obtained respectively through the inverse design method,under the conditions of different chest displacement constraints.Results show that the maximum and loading rate of the optimal restraint force of reversible restraint system are significantly reduced in each different constraints,and the chest injury index was reduced correspondingly.The mechanism of reversible restraint system in reducing injury,was interpreted on the level of optimal restraint force thoery.Subsequently the simulation results of reversible restraint system model demonstrated the effectiveness of the optimal restraint force to reduce occupant injury in collision,and the mechanism was interpreted further from the viewpoint of controlling the occupant's displacement and the energy management.2.A method for simulating the whole process of reversible restraint system was presented.The reversible restraint system changed occupants seating position and kinematics in the pre-crash phase under the control of integrated sefety systems,and it had a direct effect on the outcomes of occupant injury in the in-crash phase.Considering the close relationship between these two phases,the whole process simulation model of reversible restraint system was established,the model includes pre-crash emergency braking and active human model with various seating postures.The key parameters of the reversible restraint system are derived from two series of volunteer experimental results.Furthermore,the proposed model was validated by combining the dynamic response of volunteer in emergency braking experiment and dummy injury outcome in frontal collision.3.The improvement of occupant seating posture and the effectiveness of reduced injury by reversible restraint system.Aimed at the out-of-position seating postures and emergency braking in pre-crash phase,the effectiveness of reversible restraint system in improving seating postures and reducing injury was studied with the whole process reversible restraint system simulation model.The results showed that the closer distance between the occupant and the airbag,or improper restraint of seatbelt to the occupant,led to more serious injuries.Furthermore,the emergency braking deteriorated the occupant seating posture during pre-crash phase,and aggravate the injury of occupant.The reversible restraint system can significantly improve the occupant various seating postures and reduce the injury risk.What's more,the effect of the reversible restraint system on the improvement of the occupant seating posture was closely related to the degree of reduced injury risk,which reflects the ability of the reversible restraint system to deal with the different occupant seating posture.This conclusion meant that it was helpful to eliminate the adverse effect of AEB on occupant seating position during pre-crash phase,and the injury prevention effectiveness of occupant restraint system was further improved by the conbination of AEB with reversible restraint system in the vehicle safety systems.4.The optimization of key parameters of reversible restraint system.Considering the possibility of "wrong judgment" or "missing judgments" for potential collision accidents,the reversible restraint system can not be activated in pre-crash phase,the design principle of "two stages" for the optimization of the key parameters of reversible restraint system was proposed innovatively.The optimization of the conventional restraint system was completed in the first stage with the implementation of multi-objective robust optimization for 6 Sigma quality.In the second stage,the optimization of the reversible restraint system was completed through the same optimization method.The results show that the optimized parameters can significantly improve the injury prevention effectiveness of the reversible restraint system.Furthermore,the robustness of the injury prevention effectiveness was investigated under the fluctuation of the key parameters and the collision strength respectively.The conclusion indecated that the reversible restraint system demonstrated excellent robustness under many influence factors.5.Investigation on a reversible restraint system by volunteer experiment.Based on a prototype of reversible pretension seatbelt,the key performance parameters of the reversible pretension seatbelt were verified by dummy and volunteer experiment on static platform experiment,the results show that the key performance parameters of the prototype met expectations.Based on the framework of integrated safety systems,the reversible restraint system was established which consist of FCW and LDW,and the reversible pretension seatbelt,and main functions and control strategies of the system were defined.Combined with the transducer for vehicle body longitudinal acceleration,the brake pedal angle rate,and the seatbelt tension force,an experiment platform based on a real vehicle was established.Through the road test focused on the subjective feeling of volunteer,the results show that more than 50%of the volunteers hold the attitude of "acceptance" and "partial acceptance"to the reversible restraint system.Finally,the acceptability of the volunteers was enhanced by improving the control strategy of FCW emergency warning properly and making all volunteers experienced the AEB and the reversible pretension seatbelt synchronously.The research results laid down the foundation for further research and application of reversible restraint system.