Investigation of Crash Impact Induced Oscillatory Response of Elements of Automotive Latch Systems

Vehicle door closure systems often include self-balancing double pendulum mechanisms. For example, the counterweight in the outside handle assembly is used to reduce handle motion under inertia loadings occurring during crash events. The system is configured in such a way that the inertia forces developed during a crash are applying opposite moments to each of the pendulums (i.e., to the handle and the counterweight). Investigation of crash impact induced oscillatory response of such mechanisms is presented in this paper. A comprehensive dynamic model is developed that captures all essential characteristics of the double pendulum mechanism. An important aspect of the model is its discontinuous nature due to potential impacts between both pendulums and between one of the pendulums and the base part. Analytical conditions of self-balancing of the double pendulum system are formulated and used to provide an insight into the principles of self balancing. During dynamic simulations of the system, high frequency / high acceleration amplitude oscillatory motion of the base part provides inertia input to the system. It is shown that the double pendulum systems usually respond to such excitation with irregular motion. A methodology has been developed to study this system behavior and to analyze the resulting motion of the system. The multi-level analysis presented in the paper is used to investigate the conditions under which the system may not respond to external excitations, and to quantify the irregular response of the system when it does. The sensitivity of the solutions of the dynamic model to variation of system parameters and input characteristics is also addressed in the paper.