Variable-geometry resonator for a vehicle engine air intake system, and air intake system featuring such a resonator

A variable-geometry resonator (4) for silencing an air intake system (1) of a vehicle engine, wherein a closed, axially symmetrical casing (8) has two couplings (10,15) communicating hydraulically with the outside, and is divided internally into two variable-volume chambers (11,12) - each connected permanently to one of the couplings (10,15) - by a partition (13) movable axially and cooperating in fluidtight manner with an inner lateral wall (14) of the closed casing (8); the resonator (4) also has means (16) for moving the movable partition (13) axially inside the closed casing (8) in response to a variation in the speed of the engine, and means for connecting the couplings (10,15) hydraulically to two different hydraulically in-series portions (3,3a) of an air intake pipe (2) of the engine.