Intake silencer of the variable type for use in motor vehicle

A motor vehicle intake silencer having a variable-length resonance chamber, said length being rapidly changeable in response to engine speed by varying the effective length of said resonance chamber, said silencer comprising:

• a side branch resonator tube communicable with a vehicle air intake tube to extend transversely of said air intake tube and constitute a variable length resonance chamber, said resonator tube having an end wall remote from said air intake tube and defining a first effective length of said resonator tube, said resonator tube also having a substantially constant inside cross-sectional profile along said first effective length from said air intake tube to said end wall;
• at least one divider valve disposed in said resonator tube intermediately of said first effective length, said divider valve having a valve element adapted for movement transversely of said resonator tube into a tube-closing position in which said resonator tube has a further effective length shorter than said first effective length wherein an open position of each at least one said divider valve provides a straight-line resonance path between said intake tube and said end wall;
• a valve actuator to operate each said divider valve selectively to close or open it in response to engine speed changes;
• a valve controller coupled to each said valve actuator and including an engine speed detector, said valve controller being operative on each said valve actuator in response to a predetermined engine speed change;
• whereby said first effective length of said resonator tube is selected to provide quarter-wave resonant noise reduction at a first engine speed range and each said further effective length is selected to provide enhanced noise reduction at a further engine speed range.