【正文】 s of crash sensors are used in airbag systems including mechanical, electromechanical, and electronic sensors. An electromechanical sensor (see Figure 1) consisting of a ball and two springs cased in a plastic housing is discussed in this paper. When the sensor experiences a severe crash pulse, the ball pushes two springs into contact pleting the electric circuit allowing the airbag to fire. The forcedisplacement response of the two springs is critical in designing the sensor to meet various acceleration input requirements. Stresses in the sensor springs must be kept below the yield strength of the spring material to prevent plastic deformation in the springs. Finite element analysis can be used as a predictive engineering tool to optimize the springs for the desired forcedisplacement response while keeping stresses in the springs at acceptable levels. In the past, sensors were designed by building and testing prototype hardware until the forcedisplacement requirements were met. Using finite element analysis, the number of prototypes built and tested can be significantly reduced, ideally to one, which substantially reduces the time required to design a sensor. The analysis procedure discussed in this paper has demonstrated the ability to eliminate months of prototyping effort. MSC/ABAQUS [1] has been used to analyze and design airbag crash sensors. The analysis was geometrically nonlinear due to the large deflections of the springs and the contact between the ball and springs. Various contact elements were used in this analysis including rigid surface interface (IRS) elements, Bezier 3D rigid surface elements, parallel slide line interface (ISL) elements, and slide line elements. The finite element analysis results were in excellent agreement with experimental results for various electromechanical sensors studied in this paper. PROBLEM DEFINITION The key ponents of the electromechanical sensor analyzed are two thin metallic springs (referred to as spring1 and spring2) which are cantilevered from a rigid plastic housing and a solid metallic ball as shown in Figure 1. The plastic housing contains a hollow tube closed at one end which guides the ball in the desired direction. The ball is held in place by spring1 at the open end of the tube. When the sensor is assembled, spring1 is initially displaced by the ball which creates a preload on spring1. The ball is able to travel in one direction only in this sensor and this direction will be referred to as the xdirection (see the global coordinate system shown in Figure 2) in this paper. Once enough acceleration in the xdirection is applied to overe the preload on spring1, the ball displaces the spring. As the acceleration applied continues to increase, spring1 is displaced until it is in contact with spring2. Once Figure 1. Electromechanical automobile crash sensor. contact is made between spring1 and spring2, an electric circuit is pleted allowing the sensor to perform its function within the airbag system. FINITE ELEMENT ANALYSIS METHODOLOGY When creating a finite element representation of the sensor, the following simplifications can be mad