Influence of a bellows-type flexible joint on exhaust system dynamics

Abstract

Most modern cars have a bellows-type flexible joint between the manifold and the catalytic converter to allow for thermal expansion and to decouple large engine movements and vibrations from the rest of the exhaust system. To obtain better understanding of the influence of this joint, the dynamic response of a typical exhaust system is studied when excited via different joint configurations. Measurements show the great order of reduction in vibration transmission to the exhaust system that a bellows joint, with and without an inside liner, gives in comparison with a stiff joint. For the combined bellows and liner joint, vibration transmission is, however, higher than for the bellows alone. Together with some other aspects this makes the choice of including a liner in the exhaust system application complex. For a system in general the possibility of tuning the friction limit of the liner, to minimize overall vibrations through friction-based damping, depends on how close to ideal the excitation source is and its location. Anyhow, the combined bellows and liner joint makes the exhaust system behaviour significantly non-linear, whereas the system behaviour proves to be essentially linear when the bellows has no liner, which imply that the liner needs to be included in theoretical models when present in the real system.

Dynamic Characteristics of a Combined Bellows and Liner Flexible Joint

“…A a damping parameter bellows combined with an inside liner and an outside b damping parameter braid is commonly used for this purpose between the e strain manifold and the rest of the exhaust system. As shown j damping ratio by Wall et al [1], this joint greatly in uences the s stress (Pa) dynamics of the complete system. An understanding of v angular frequency (rad/s) its dynamic characteristics and a modelling method that facilitates simulations of the exhaust system at an early stage of the product development process are therefore…”