Intake system for internal combustion engine

An intake system for an internal combustion engine, comprising:

• an intake air flow control valve that is formed of a valve body that adjusts a flow passage area in an intake pipe and a valve shaft about which the valve body pivots;
• a control unit that adjusts a valve opening amount, which is an opening amount of the intake air flow control valve, to adjust an intensity of a swirl flow, and that adjusts the valve opening amount within a valve opening amount range from a first opening amount to a second opening amount;
• a first rotation restriction portion that contacts the intake air flow control valve when the valve opening amount is the first opening amount to prevent the valve body from moving beyond a first opening position at which the valve opening amount is the first opening amount;
• and
• a second rotation restriction portion that contacts the intake air flow control valve when the valve opening amount is the second opening amount to prevent the valve body from moving beyond a second opening position at which the valve opening amount is the second opening amount, wherein
• the valve body is divided into a long valve portion and a short valve portion by the valve shaft, a length from the valve shaft to a tip of the long valve portion is greater than a length from the valve shaft to a tip of the short valve portion, and the long valve portion is located upstream of the short valve portion;
• when the valve opening amount is the first opening amount, the intake air flow control valve is pushed against the first rotation restriction portion by an intake air flowing through the intake pipe;
• and
• when the valve opening amount is the second opening amount, the intake air flow control valve is pushed against the second rotation restriction portion by the intake air flowing through the intake pipe.