Exhaust manifold stiffening ribs

A manifold assembly for routing an exhaust gas produced by an internal combustion engine to an aftertreatment system, the manifold assembly comprising:

• a plurality of inlet runners in fluid receiving communication with a cylinder head at respective upstream ends thereof, the plurality of inlet runners operatively engaged to and in fluid providing communication with a manifold log at a corresponding plurality of stress points at downstream ends thereof, each of the plurality of inlet runners including a runner wall having a first runner thickness;
• a manifold log in fluid receiving communication with the plurality of inlet runners at the corresponding plurality of stress points and in fluid providing communication with at least one outlet, the manifold log including a log wall having a first log thickness;
• and
• a plurality of stiffening ribs, each of the plurality of stiffening ribs being disposed on an interior surface of at least one of the log wall and the runner wall of a respective one of the plurality of inlet runners at one of the plurality of stress points.

A method of forming an exhaust manifold comprising:

• forming a manifold log including a log wall and a log rib, the log wall having a first log thickness and defining a log bore in fluid communication with a first opening at an upstream end thereof and a second opening at a downstream end thereof, and the log rib being disposed on an interior surface of the log wall and exposed to the log bore in the vicinity of the first opening, wherein the log rib and the log wall in combination provide a second log thickness;
• forming an inlet runner including a runner wall having a first runner thickness and defining a runner bore in fluid communication with a third opening at a downstream end of the inlet runner and a fourth opening at an upstream end of the inlet runner, wherein the third opening is operatively connected to and in fluid communication with the first opening;
• and
• coupling the manifold log to the inlet runner at a stress point, the stress point being defined by a portion of at least one of the log wall and the runner wall at a junction where the first opening of the manifold log is operatively connected to the third opening of the inlet runner, wherein the stress point is subject to greater amounts of heat fatigue than other portions of the log wall and the runner wall.