THE INFLUENCE OF EIGENTONES IN INTAKE AND EXHAUST MANIFOLDS ON INTAKEAND EXHAUST NOISE RADIATION

Natural oscillation modes in intake and exhaust manifolds of multi-cyl inder internal combustion engines (mainly car four-cylinder engines) a re considered. The engine with manifolds is considered as the source o f the sound waves in the intake and the exhaust systems. The basic rul es governing the spectrum formation of the manifold eigenmodes are inv estigated. It is shown that some of the natural modes do not depend ve ry much on the intake and exhaust systems after thr manifolds. The sou nd increase (particularly for an asymmetrical excitation) caused by th ese modes depends on the degree of the asymmetry of the manifold and o n the energy dissipation in the manifold. Under some conditions this i ncrease creates a resonance sound radiation. The tendency for resonanc e excitation at the branch of intake (exhaust) pipes with mufflers, wi th unfavourable and arbitrary combinations of their characteristics, i s considered as one of the criteria for the quality of manifold constr uction. Special attention is paid to the intake manifold of modern fou r cylinder engines equipped with airbox. It is shown that a good desig n of the manifold of these engines allows decreasing their intake nois e by 4-6 dB(A) in a wide range of crankshaft RPM.