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It is difficult to improve tire cavity noise since the pressure of cavity resonance acts as a compelling force, and its low damping and high gain characteristics dominate the vibration of both the suspension and body. For this reason, the analysis described in this article aimed to clarify the design factors involved and to improve this phenomenon at the source. This was accomplished by investigating the acoustic coupling vibration mode of the wheel, which is the component that transmits the pressure of cavity resonance at first. In addition, the vibration characteristic of suspension was investigated also. A speaker-equipped sound pressure generator inside the tire and wheel assembly was developed and used to infer that wheel vibration under cavity resonance is a forced vibration mode with respect to the cavity resonance pressure distribution, not an eigenvalue mode, and this phenomenon may therefore be improved by optimizing the out-of-plane torsional stiffness of the disk.

Systems already exist that reduce collision damage through collision-danger alarms and by operating such features as pre-tensioning seat belts and collision mitigation brakes when the system has determined the possibility of a collision by using millimeter-wave radar. Conversely, at present, carelessness in observing oncoming traffic accounts for a large percentage of head-on collisions. Timely collision warnings are effective in avoiding accidents and for mitigating the severity of the collision. However, warnings given too early even before the driver has had a chance to carry out normal evasive maneuvers, can annoy the driver. Accordingly, by adding a driver face direction sensor, the authors have developed in the present research a system that will only hasten the timing of warnings when the system has detected the direction of the driver's face and determined that they are not facing the front of the vehicle.