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With the goal of improving drivability, this research aimed to clarify the mechanism of vehicle longitudinal acceleration, focusing on tip-in acceleration. Conventional typical analysis methods include experimental modal and model-based analysis. However, since the former requires the measurement of impulses and other input forces while the vehicle is stopped, measurement under actual driving conditions is difficult. The latter requires characteristic values such as the stiffness and damping coefficients to be identified in advance, which cannot be achieved either easily or precisely. Therefore, this paper proposes a new experiment-based analysis method. This method enables the acquisition of engine torque and transmission torque/force by measuring only the acceleration values of some components under driving conditions.

First Order Analysis (FOA) is useful for designing subunits in the mid-frequency range, as the layout and mounting positions can easily be decided at the conceptual design phase. In order to reduce vibration, we propose FOA for Noise and Vibration (NV) with the following characteristics. First, a dynamic beam element is formulated analytically using Euler's beam theory [1], so that a long uniform beam can express one element with high-order vibration. Second, power flow between potential energy and kinetic energy can be expressed as post-processing, so we can examine how to change or cut off the vibration energy path. In this paper, the above analysis is applied to a front subframe for the conceptual design of an automotive body structure.

We have developed new CAE tools in the concept design process based on First Order Analysis (FOA). Joints are often modeled by rotational spring elements. However, it is very difficult to obtain good accuracy. We think that one of the reasons is the influence of the nonlinear behavior due to local elastic buckling. Automotive body structures have the possibility of causing local buckling since they are constructed by thin walled cross sections. In this paper we focus on this behavior. First of all, we present the concept of joint analysis in FOA, using global-local analysis. After that, we research nonlinear behavior in order to construct an accurate joint reduced model. (1) The influence of local buckling is shown using uniform beams. (2) Stiffness decrease of joints due to a local buckling is shown. (3) The way of treating joint modeling considering nonlinear behavior is proposed.