Study On Pop-up Device Of Active Engine Hood Base On Shape Memory Alloy

With the development of automobile electrification and intelligence,more humane,more comprehensive automobile safety performance that considers pedestrians and other disadvantaged groups has gradually attracted people’s attention.In recent years,with the introduction of automobile safety regulations,the survival probability and the degree of injury of drivers and occupants in traffic accidents have been generally improved.In contrast,the development of pedestrian safety technology in automobiles has been slow,and collisions between people and vehicles have become a common concern for researchers all over the world.To reduce and prevent pedestrians from being injured in collision accidents,in addition to introducing collision safety regulations,there is also the development of new technologies for active and passive safety.The current mainstream technologies for pedestrian protection mainly include the modification of the front end of the engine hood,the installation of a pedestrian detection system,and an engine hood pop-up system.As a new type of smart material,Shape Memory Alloy(SMA),with its high power-to-weight ratio,large driving stroke,quiet and no noise,can be directly used for driving without transmission,and is widely used as a driving element in aerospace,Biomedicine,mechanical structure and automotive industry and other fields.In the application of the automotive industry,many scholars use the energy absorption characteristics of SMA to apply it to collision energy absorption for passive protection of pedestrians.Aiming at the disadvantages of the existing pedestrian protection system that needs to modify the car,it cannot be restored after starting,the maintenance cost is high,and the structure is complicated.Based on the shape memory alloy,a hood pop-up mechanism for pedestrian protection is proposed.The mechanism is simple in structure,quick in response,and can be manually restored after being bounced,and can be adapted to various car models.The research content of this article mainly includes:Firstly,the methods and research status of pedestrian protection at home and abroad are studied.According to the current existing engine hood pop-up mechanism,it is classified and its working principle is analyzed.According to the movement trajectory and design requirements of the engine hood,various parameters are calculated and determined,and according to the determined Parameter selection of the structure and design of the three-dimensional model.Then the dynamic response characteristics of SMA and its driving characteristics are studied.The effects of strain rate and strain amplitude on the mechanical properties of SMA were studied,and the maximum recoverable strain and phase transition temperature were measured.The resistance characteristic of SMA is studied,the resistance model is established,and the numerical simulation results show that the higher the resistivity is,the faster the SMA’s response is when the current is the same.The resistivity of SMA is measured in the process of heating and cooling,and the experimental data are fitted to observe the law.It is found that the resistivity of SMA is related to the volume fraction of martensite and austenite in the material,and the overall resistance characteristic is the sum of the resistance characteristics.The relationship between SMA resistivity and response speed was studied,and the response speed and recovery force were experimented.The discharge principle of supercapacitor is studied,and the response speed and restoring force of SMA under the condition of large current and short time are experimentally studied.Finally,the dynamic model of the engine hood lifting mechanism was established and the numerical simulation was carried out to study the relationship between the driving spring stiffness and the lifting height and speed,and the spring stiffness was determined according to the design requirements.Finite element simulation of SMA was carried out to analyze the force relation of the locking part of the bouncing mechanism and to design a simplified mechanism.The finite element simulation and dynamic simulation of the simplified mechanism were carried out to study the influence of different parameters on the response speed and lifting height of the bouncing mechanism.The structure is improved and processed,and the actual experiment of engine hood lifting mechanism is carried out,and the experimental phenomenon is recorded by high-speed camera.By comparing the actual experimental data with the numerical simulation and dynamic simulation,the error range is reasonable,and the influence rule of each parameter on the performance of the bouncing mechanism is observed.