The Study On Collaborative Optimization Of Vehicle Frontal Impact Safety In Multiple Typical Situations

In recent years, great economic boom and perfection of highway network promote the rapid development of automobile industry in China. Meanwhile, the terrible accident problem is also brought to the whole society. For different crashes, frontal impact is the crash type that caused most frequently and resulted into most fatality, however the vehicle safety design is based on100%overlap frontal rigidwall impact and40%overlap offset impact. In order to further enhance the protection of occupants in frontal crash, based on the features of frontal crash situations caused by different crash environments, three typical frontal impact situations including the vehicle to rigidwall impact, vehicle to vehicle impact and vehicle to pole impact were studied. The collaborative optimization of vehicle impact safety in three typical situations was performed to meet the safety requirements in three impact situations at the same time.The main content and innovation of this dissertation are shown as following:1. In vehicle to rigidwall impact, the acceleration pulse is the key of safety design. Through analyzing the three ideal acceleration pulses and mechanism of energy absorbing of thin-wall structure, an octagonal step by step energy absorbing structure was designed to improve the energy absorption of longitudinal rail and acceleration pulse. The optimal design was obtained through optimization, and was used to improve the frame of SUV in frontal rigidwall impact test. The frame impact test shows that the energy absorption ability of frontal structure and acceleration shape of vehicle body could be improved obviously.2. The fullengagement and offset frontal vehicle to vehicle impacts are more frequent in different frontal crashes. The mass and stiffness were isolated through changing the FE model of a mid-size sedan, thus three ideal FE models with mass reduction, stiffness increase and both mass reduction and stiffness increase were obtained. The full factorial experimental design method was adopted to analyze the influence of mass and stiffness to the vehicle body deformation and acceleration pulse in the mid-size sedan to SUV, mid-size sedan and small size sedan100%and50%overlap frontal crashes. The result shows that the stiffness increase and mass reduction of passenger vehicle is the main cause to the increase of driver injury risk in100%overlap crash; while in50%overlap crash, the collapse of compartment caused by stiffness difference is the main reason. The stiffness matching of the two vehicles was studied by adjusting the stiffness of longitudinal rail of SUV and compartment strength of passenger car; the result shows that enhancing the compartment strength of passenger car is more important than decreasing the stiffness of longitudinal rail of SUV to improve its intrusion in vehicle to vehicle offset crash.3. Aiming to higher injury risk of occupant in vehicle to column object crash, the mid-size sedan Taurus was taken as an example to study driver injury risk in vehicle to center pole impact. Through parameterizing the acceleration, it’s found that lower acceleration in earlier stage, higher slope of acceleration in rising stage and higer later stage acceleration would cause the increase of driver injury risk. After that, the optimal TTF (time to fire) of airbag was obtained by adjusting TTF. The method of raising the acceleration in earlier stage in center pole crash was proposed to decrease the occupant injury risk, and the bumper beam was strengthened to achieve it.4. Through changing cross-section and trigging structure of energy absorbing box, the crush box with good energy absorbing abilibty in three impact situations was abtained. Combining the safety design requirements of frontal rigidwall impact,40%overlap offset impact and centerpole impact, by taking the ratio of second stage and first stage acceleration in rigidwall impact, the intrusion of lower A pillar in40%overlap offset impact and acceleration of earlier stage in centerpole impact as design objects, the collaborative optimization strategy, uniform design and simulate anneal arithmetic were adopted to optimize the thickness of frontal main energy absorbing structures of Taurus to obtain the comprehensive design with better crashworthiness in three typical impact situations. The optimal design could improve the acceleration in rigidwall impact, the intrusion in40%overlap offset crash and the earlier stage acceleration in center pole crash at the same time.5. Owing to the traditional sled impact test could regenerate the X acceleration of vehicle body in frontal impact test, but could not simulate the Y and Z acceleration. One new impact sled with passenger car body was designed to simulate the real vehicle to rigidwall impact and40%overlap offset impact test through changing the wheelbase, tire tread, height of center of gravity and parameters of frontal energy absorbing structure. Through the sled frontal impact simulation, the influence of parameters of frontal energy absorbing structure and height of CG to X, Y and Z acceleration; and X, Y and Z acceleration of real vehicle in frontal impact offset were regenerated more accurately by sled impact. Sled frontal impact test result shows that this sled can reproduce both acceleration and the kinematics of vehicle precisely at the same time.