Patent ID: 9188095
Filing Date: 2015-11-17
Classification: F01N,F02B,F02D,F02M,Y02T

Abstract:
1. An intake and exhaust system for a multi-cylinder engine having a plurality of cylinders each provided with 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, the intake and exhaust system comprising: a plurality of independent exhaust passages each connected to the exhaust port in a respective one of the plurality of cylinders, or the exhaust ports in two or more of the plurality of cylinders, whose exhaust strokes are not successive with respect to each other; a collecting pipe connected to downstream ends of the plurality of independent exhaust passages to allow exhaust gas passing through the plurality of independent exhaust passages to be collected together; a volume-enlarged portion provided downstream with respect to the collecting pipe; and valve drivers capable of driving the intake valve and the exhaust valve in each of the plurality of cylinders, wherein: among the plurality of independent exhaust passages, at least two connected to respective ones of two of the plurality of cylinders, whose exhaust strokes are successive with respect to each other, are connected to the collecting pipe at mutually adjacent positions; the valve drivers are operable, at least in a low engine speed region where engine speed is equal to or less than a preset reference engine speed, to drive the intake valve and the exhaust valve in each of the plurality of cylinders in such a manner that a valve opening period of the intake valve and a valve opening period of the exhaust valve in each of the plurality of cylinders overlap with each other for a predetermined overlap period, and the exhaust valve in a certain one of the plurality of cylinders starts opening during the overlap period in a preceding one of the remaining cylinders, whose exhaust stroke immediately precedes that of the certain cylinder; each of at least an upstream portion of the collecting pipe and at least a downstream portion of each of the plurality of independent exhaust passages is formed such that a cross-sectional area thereof gradually decreases toward a downstream direction; the volume-enlarged portion is formed such that a cross-sectional area thereof is increased as compared to a passage upstream with respect to the volume-enlarged portion, so as to cause a positive pressure wave of exhaust gas which reaches the volume-enlarged portion after being discharged from each of the plurality of cylinders, to be reflected and converted to a negative pressure wave; and a length between an upstream end of the collecting pipe and an upstream end of the volume-enlarged portion is set to a dimension which allows a negative pressure wave generated through a phenomenon that a positive pressure wave of exhaust gas discharged from a certain one of the plurality of cylinders is reflected by the volume-enlarged portion at least at a predetermined engine speed equal to or less than the preset reference engine speed, to reach the exhaust port in a preceding one of the remaining cylinders, whose exhaust stroke immediately precedes that of the certain cylinder, during the overlap period in the preceding cylinder.