Patent ID: 9255503
Filing Date: 2016-02-09
CPC Classification: F01N,F02B,F02D,Y02T

Claim Text:
1. An exhaust device for a multicylinder engine, comprising a plurality of cylinders each including an intake port, an exhaust port, an intake valve capable of opening and closing the intake port, and an exhaust valve capable of opening and closing the exhaust port, wherein the exhaust device comprises a plurality of independent exhaust passages, each of the plurality of independent exhaust passages having at least one upstream end and a downstream end, each upstream end connected to an exhaust port of one cylinder of the plurality of cylinders, which are non-sequential in exhaust order, and a mixing pipe including an upstream end connected to each downstream end of each respective independent exhaust passage and into which exhaust that has passed through the respective independent exhaust passages flows, each downstream end of each respective independent exhaust passage being connected in a bundled form to the upstream end of the mixing pipe to form a bundle of independent exhaust passage downstream ends, a pre-silencer and a main silencer including a space section in which a flow path sectional area is increased are disposed in an exhaust passage downstream from the mixing pipe in such an order that the main silencer is located on a downstream side of the pre-silencer, a first distance from a seating position of the exhaust valve in the exhaust port of each cylinder to an upstream end of the pre-silencer is set to a distance such that, in a first operation region including at least an intermediate speed range in which an engine rotation speed is greater than or equal to a first reference rotation speed set in advance and less than or equal to a second reference rotation speed higher than the first reference rotation speed, a first negative pressure wave is generated due to an exhaust pressure wave generated by opening the exhaust valve reaching and being reflected by the pre-silencer and the first negative pressure wave reaches the exhaust port of the cylinder during a first overlap period in which an open period of the exhaust valve and an open period of the intake valve of the cylinder of which the exhaust valve has been opened overlap for a first predetermined period, a second distance from the seating position of the exhaust valve in the exhaust port of each cylinder to an upstream end of the main silencer is set to a distance such that, in a second operation region including at least a low speed range in which the engine rotation speed is less than the first reference rotation speed, a second negative pressure wave is generated due to an exhaust pressure wave generated by opening the exhaust valve reaching and being reflected by the main silencer and the second negative pressure wave reaches the exhaust port of the cylinder during a second overlap period in which an open period of the exhaust valve and an open period of the intake valve of the cylinder of which the exhaust valve has been opened overlap for a second predetermined period, and a valve driving device configured to open and close the intake valve and the exhaust valve of each cylinder is provided so that an open period of the exhaust valve and an open period of the intake valve of each cylinder overlap for one of the first predetermined period, the second predetermined period, and a third predetermined period different from the first predetermined period and the second predetermined period, and, for cylinders that are sequential in exhaust order, the exhaust valve of a subsequent cylinder opens during an overlap period of a preceding cylinder, in a predetermined operation region including at least low and intermediate speed ranges in which the engine rotation speed is less than or equal to the second reference rotation speed.