Honda’s previous motorcycle airbag system employs a crash detection method to deploy the airbag according to signals the system receives from four accelerometers where two of them installed on each of the front suspension fork legs. However, the system can be used only on models with larger vehicle sizes due to larger area required for the installation of the four sensors.
This paper describes the development of a method to overcome the space limitations of the prior method. In developed method, the crash detection can be carried out by only two sensors where one of them installed on each front suspension fork leg. This makes it possible to apply an airbag system to other motorcycle models as well.
In this developed method, the threshold value, which is used for crash discrimination, is processed as a function of longitudinal displacement of the front suspension. At each time step in the discrimination execution processes, the deceleration value is compared with the threshold processed as described above.
Through the analysis using spectrogram, it was revealed that the accelerometer outputs, when traveling on rough roads, show sinusoidal oscillation waves derived from the natural oscillation of the system composed of the front wheel and the suspensions. Consequently, waveforms of the longitudinal deceleration and the displacement, where the displacement is calculated by the second order integration of the deceleration, show the opposite phase to each other. On the other hand, in a frontal impact, the output of the accelerometer is generally expressed by the approximation of a half sine wave. Accordingly, the displacement from a frontal impact shows a monotonic increase. Utilizing these characteristics, a two-sensor crash detection method has been developed.
The developed method was evaluated using data measured in various tests, including full-scale impact tests and rough roads tests, using large touring motorcycles and large scooters.