EXHAUST MANIFOLD FOR INTERNAL COMBUSTION ENGINE, TO PREVENT DETERIORATION OF MEASUREMENT ACCURACY OF EXHAUST BY AIR FUEL RATIO SENSOR

摘要

PURPOSE: An exhaust manifold for an internal combustion engine is provided to prevent deterioration of precise measurement of exhaust gas passing through the exhaust manifold via an air fuel ratio sensor. CONSTITUTION: An exhaust manifold for an internal combustion engine having four engine cylinders(4) includes four branches(5,6,7,8) for discharging exhaust gas from the engine cylinders; a downstream exhaust pipe(9) connected the branches; a partition(10) partitioning an exhaust path in the downstream exhaust pipe into a first passage(11) and a second passage(12) each having a semi-circular section; an air fuel ratio sensor(16) mounted to the downstream exhaust pipe to project to the first and second passages through an incision part(18) of the partition; and a communicating part(21) formed in the partition in a state of communicating with the first and second passages. In the partition, the incision part is formed a side in a transverse direction perpendicular to an axial direction of the downstream exhaust pipe. The communicating part has a first portion(21A) situated on a side of the partition and a second portion(21B) situated on the opposed side of the partition. The first portion is situated to the lower side than the second portion. Each of the first and second passages is connected to two of the branches connected to two of the engine cylinders ignited in a discontinuous order and the two branches of the four branches each communicate with first and second quadrant areas of the first and second passages.