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Knock noise induced by automotive shock absorbers has serious influence on driving comfort and vehicle quality. Some research focusing on knock noise had been introduced in the past. However there is the unidentified phenomenon that has been unnoticed. This paper describes the new theory to clarify one of the unidentified phenomenon and proposes the equation for stability assessment which is useful on designing stage of development. First of all, the characteristics of the unidentified rod vibration of shock absorbers are investigated experimentally. Second, the new theory is established on the basis of the non-linear physical model with friction forces between piston and cylinder. This theory shows that the unstable vibration, so called the Self Excited Vibration, can be induced by not only friction property but also structure of rod and piston. Third, the equation for stability assessment, which is useful on designing stage of development, is proposed on the basis of new theory.

In developing a power-steering system, quietness is one of the important requirements. And a quantitative evaluation of the noise is required to estimate effects of noise reduction practices. Generally, an absolute evaluation based on experienced engineer's audibility is used as an evaluation method of the noise. However, it is difficult to make a detailed evaluation on the noise. Thus, the establishment of the quantitative evaluation technology is required for the detailed evaluation. In this study, we aim to clarify the characteristics of the noise and to establish a quantitative evaluation method for the noise. Sensory evaluation for interior noises of an actual vehicle as well as for artificial noises is conducted by experienced engineers. Then, correlation between the sensory evaluation result and the signal characteristics of interior noises is analyzed, and an evaluation equation for the noise is proposed.