Intake system for an internal combustion engine

An internal combustion engine comprising:

• a variable valve control apparatus for variably controlling a valve lift, operation angle and maximum lift phase of an intake valve thereby variably controlling the amount of intake air supplied to cylinders in accordance with an engine operating condition;
• a collector in the form of a box and having a plurality of opening portions;
• a plurality of intake passages fluidly connecting the opening portions of the collector to the cylinders;
• and
• a pressure control mechanism for producing within the collector a vacuum that varies depending upon a variation of the engine operating condition;
• wherein the pressure control mechanism increases the vacuum continuously with increase of one of the amount of intake air, engine speed and engine load;
• and
• wherein the pressure control mechanism comprises a pressure control valve whose opening degree is controlled by the vacuum within the collector.