EGR ESTIMATION METHOD FOR AN INTERNAL COMBUSTION ENGINE AND EGR ESTIMATION DEVICE FOR AN INTERNAL COMBUSTION ENGINE

An EGR estimation method for an internal combustion engine that estimates an EGR rate in an intake and exhaust system of an internal combustion engine, the intake and exhaust system of an internal combustion engine including: an intake system including an air cleaner and an intake passage that connects the air cleaner and an internal combustion engine, an exhaust system including an exhaust passage that is connected to the internal combustion engine, and a supercharger that is provided in the intake passage and the exhaust passage, the intake and exhaust system being provided with an EGR device including an EGR passage that connects the intake passage and the exhaust passage and an EGR valve that is provided in the EGR passage, and the intake system including an intake bypass passage that connects an upstream pressure portion and a downstream pressure portion of the supercharger in the intake system and a recirculation valve that is provided in the intake bypass passage, the EGR estimation method includes estimating the EGR rate based on EGR gas flowing back to the air cleaner side by opening the recirculation valve during supercharging.