Patent ID: 8671670
Filing Date: 2014-03-18
Classification: F02D,Y02T

Abstract:
1. An exhaust system of a multi-cylinder engine including a plurality of cylinders each formed with an intake port and an exhaust port and provided with an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port, comprising: a plurality of independent exhaust passages each of which is connected to an exhaust port of one cylinder or each of a plurality of cylinders for which the exhaust sequence is inconsecutive, and which are respectively separated at least on a downstream side into low velocity-side passages and high velocity-side passages; a low velocity-side collection part which is connected to a downstream end of each of the low velocity-side passages to be in communication with each of the low velocity-side passages and which collects gas that has passed through each of the low velocity-side passages; a high velocity-side collection part which is connected to a downstream end of each of the high velocity-side passages to be in communication with each of the high velocity-side passages and which collects gas that has passed through each of the high velocity-side passages; a flow passage area variable valve which is provided to each of the high velocity-side passages and which is capable of changing a flow passage area of each of the high velocity-side passages; flow passage area variable valve drive means capable of driving the flow passage area variable valve; and valve drive means capable of driving the intake valve and the exhaust valve of each of the cylinders, wherein, in a low velocity region in which a revolution of an engine is lower than a pre-set reference revolution and at least in a high load region where a required torque of the engine is high, the valve drive means drives the intake valve and the exhaust valve of each of the cylinders so that an opening period of the intake valve and an opening period of the exhaust valve of each of the cylinders overlap for a predetermined overlap period and so that between cylinders for which the exhaust sequence is consecutive, the exhaust valve of one cylinder is opened during the overlap period of another cylinder, the flow passage area variable valve drive means drives the flow passage area variable valve so that a flow passage area of each of the high velocity-side passages is smaller than its maximum area at least in the high load region of the low velocity region, and drives the flow passage area variable valve so that the flow passage area of each of the high velocity-side passages is a maximum area in a high velocity region where the revolution of the engine is higher than the reference revolution, the downstream ends of the low velocity-side passages connected to the cylinders for which the exhaust sequence is consecutive among the respective low velocity-side passages are arranged in mutually adjacent positions, the low velocity-side collection part is shaped so that a flow passage area of at least one of its upstream end and its downstream end is a smallest area of the flow passage area of the low velocity-side collection part, and the high velocity-side collection part is shaped so that a flow passage area of at least one of its upstream end and its downstream end is a smallest area of the flow passage area of the high velocity-side collection part, and shaped so that a relationship a