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

An EGR estimation method for estimating an EGR rate in an intake and exhaust system of an internal combustion engine, the intake and exhaust system including: an intake system including an air cleaner and an intake passage that connects the air cleaner and the engine, an exhaust system including an exhaust passage, and a supercharger that is provided in the intake passage and the exhaust passage, the intake and exhaust system including an EGR device including an EGR passage that connects the intake passage and the exhaust passage and an EGR valve, and the intake system including an intake bypass passage that connects an upstream pressure portion and a downstream pressure portion of the supercharger and a recirculation valve. The EGR estimation method includes: opening the recirculation valve during supercharging, and estimating the EGR rate after closing the EGR valve based on the EGR rate before opening the recirculation valve.