Engine intake control system

An engine intake control system comprising:

• an intake passage body attached to an engine;
• a first intake passage formed in the intake passage body and having a downstream end connected to an intake port of the engine;
• a second intake passage formed in the intake passage body and having a downstream end connected to the intake port;
• and
• a changeover valve that includes a valve shaft rotatably supported by the intake passage body, and a valve plate attached to the valve shaft, the valve plate being moved rotationally, by a rotational movement of the valve shaft, between a first changeover position, where the valve plate closes the second intake passage and allows the first intake passage to be connected to the intake port for air flow, and a second changeover position, where the valve plate closes the first intake passage and allows the second intake passage to be connected to the intake port for air flow,
• wherein the valve plate is a butterfly-type valve plate including first and second valve-plate half portions that extend in opposite directions to each other from the valve shaft,
• when the valve plate is at the first changeover position, a first plate face, which is at one side of the valve plate, forms a part of the first intake passage, and
• when the valve plate is at the second changeover position, a second plate face, which is at the other side of the valve plate, forms a part of the second intake passage,
• a first valve seat with which a sealing portion located on the second plate face side of the first valve-plate half portion is in contact when the valve plate is at the first changeover position is formed in the intake passage body,
• a second valve seat with which a sealing portion located on the first plate face side of the second valve-plate half portion is in contact when the valve plate is at the first changeover position is formed in the intake passage body,
• a third valve seat with which a sealing portion located on the first plate face side of the first valve-plate half portion is in contact when the valve plate is at the second changeover position is formed in the intake passage body,
• a fourth valve seat with which a sealing portion located on the second plate face side of the second valve-plate half portion is in contact when the valve plate is at the second changeover position is formed in the intake passage body, and
• in at least one of the first valve-plate half portion and the second valve-plate half portion, the sealing portion located on the first plate face side and the sealing portion located on the second plate face side are separated from each other in the thickness direction of the valve plate.