Abstract: A valve plate is formed as a butterfly-type valve plate including a first and a second valve-plate half portions that extend in opposite directions to each other from a valve shaft. When the valve plate is at a first changeover position, the first valve-plate half portion is directed to the downstream side of a first intake passage from the valve shaft and the second valve-plate half portion is directed to the upstream side of the first intake passage from the valve shaft so that a first plate face of the valve plate forms a part of the first intake passage. When the valve plate is at a second changeover position, the first valve-plate half portion is directed to the downstream side of a second intake passage from the valve shaft and the second valve-plate half portion is directed to the upstream side of the second intake passage from the valve shaft so that a second plate face of the valve plate forms a part of the second intake passage.

Abstract: A valve plate is formed as a butterfly-type valve plate including a first and a second valve-plate half portions that extend in opposite directions to each other from a valve shaft. When the valve plate is at a first changeover position, the first valve-plate half portion is directed to the downstream side of a first intake passage from the valve shaft and the second valve-plate half portion is directed to the upstream side of the first intake passage from the valve shaft so that a first plate face of the valve plate forms a part of the first intake passage. When the valve plate is at a second changeover position, the first valve-plate half portion is directed to the downstream side of a second intake passage from the valve shaft and the second valve-plate half portion is directed to the upstream side of the second intake passage from the valve shaft so that a second plate face of the valve plate forms a part of the second intake passage.

Abstract: A noise silencer for reducing noise in an intake passage in an intake system has a parabolic portion for collecting noise, a noise accumulation room communicating with the intake passage through a communication passage and a noise discharge pipe communicating with an outside space. A noise collection valve is provided in the communication passage. When sound pressure in the intake passage is positive, i.e., larger than pressure inside the noise accumulation room, the noise collection valve opens the communication passage. As a result, a positive sound pressure portion of low-frequency noise is collected into the noise accumulation room and is discharged outside the intake system. Thus, the noise silencer effectively reduces low-frequency noise in the intake passage and requires less mounting space.