As an important module of automotive passive safety system, Airbag ECU is used to detect the collision acceleration signal and control the initiation time of airbag, which plays an important role in protecting the personal safety of passengers. However, if the airbag explodes by mistake, the airbag will not only fail to protect the passengers, but also cause serious injury to the passengers. In order to prevent the airbag from misfiring due to resonance, the ECU mounting bracket must meet certain dynamic stiffness design requirements. In the conceptual design stage, simulation analysis can effectively improve the efficiency and accuracy of the design of Airbag ECU mounting bracket.
2 ECU support resonance analysis principle
The dynamic stiffness design requirements of the Airbag ECU mounting bracket are reflected by the acoustic inertia curve of the ECU fixed point on the mounting bracket. The calculation formula of the acoustic inertia curve is as follows:
The acoustic inertia curve must meet the evaluation criteria shown in Figure 1, in which the slash area is a good area, the blank area is an acceptable area, and the grid area is an unacceptable area. In order to meet the dynamic stiffness design requirements of the mounting bracket, the acoustic inertia curve at the ECU fixed point on the mounting bracket must fall within the acceptable area and the good area.
3.1 preliminary design of ECU mounting bracket of a certain vehicle model
The ECU mounting bracket of a vehicle model is located in the middle of the front floor. During the analysis, the ECU bracket and nearby structures are taken as the analysis object. The structural finite element model is established by using Altair / HyperMesh software. The shell element with basic size of 5mm is selected for meshing, the XYZ three-dimensional degrees of freedom of the longitudinal beam under the floor are constrained, and the structural boundary is simulated. Apply a three-way dynamic unit excitation force to the ECU fixed point on the mounting bracket. The frequency domain is 1-1000hz. Calculate through the radioss solver to output the three-way acceleration response of the ECU fixed point.
3.2 optimization analysis of ECU mounting bracket
Since the ECU mounting bracket structure designed in the early stage has certain resonance risk, the following two optimization schemes are considered to improve the dynamic stiffness of the ECU mounting bracket.
1. Add an L-shaped mounting plate above the floor;
2. Add an arched reinforcing plate under the floor
Comparing the acoustic inertia curve of ECU fixed point position before and after optimization, it shows that the acoustic inertia curve of ECU fixed point position after optimization is significantly improved compared with that before optimization, and meets the dynamic stiffness design requirements of ECU mounting bracket. The acoustic inertia curve of ECU fixed point before and after optimization is shown in Figure 4.
