Dynamic stresses exist in parts of a catalyst muffler caused by the vibration of
a moving vehicle, and it is important to clarify and predict the vibration
response properties for preventing fatigue failures. Assuming a vibration
isolating installation in the vehicle frame, the vibration transmissibility and
local dynamic stress of the catalyst muffler were examined through a vibration
machine. Based on the measured data and by systematically taking vibration
theories into consideration, a new prediction method of the vibration modes and
parameters was proposed that takes account of vibration isolating and damping. A
lumped vibration model with the six-element and one mass point was set up, and
the vibration response parameters were analyzed accurately from equations of
motion. In the vibration test, resonance peaks from the hanging bracket, rubber
bush, and muffler parts were confirmed in three excitation drives, and local
stress peaks were coordinate with them as well. The first resonance peak caused
by the rubber bush had relatively low frequency, but the transmissibility was
low by damping. The vibration magnitude from other parts was damped several
times more by the rubber bush. The dynamic stress amplitudes from the vibration
corresponded to the resonance of the catalyst muffler, and were proportional to
the vibration accelerations. With an example where the spring coefficient and
damping coefficient of a component in the sample were changed, the resonance
frequency and transmissibility were obtained by calculation using the model
while the dynamic stress was calculated using the stress scale factor,
demonstrating the model’s general versatility and making it possible to predict
the fatigue durability.
