Patent ID: 8468800

Claim:
A four-stroke engine structured to introduce fresh air and EGR gas into a cylinder, the four-stroke engine comprising: a blowdown supercharging system using a combustion chamber internal pressure when exhaust valves open in an expansion stroke of a first cylinder to generate an exhaust blowdown pressure for introducing EGR gas into a second cylinder from near a bottom dead center of an intake stroke to near a bottom dead center of a compression stroke of the second cylinder which is different from the first cylinder in combustion timing; and a secondary air supply system supplying secondary air to an exhaust port of the second cylinder prior to arrival of the exhaust blowdown pressure at the second cylinder, and wherein the secondary air in the exhaust port and the EGR gas are supercharged into the second cylinder by the exhaust blowdown pressure from the first cylinder and the secondary air supply system comprises a secondary air supply path and secondary air control valves interposed in the secondary air supply path, wherein the secondary air supply path connects an intake system and the exhaust port of each cylinder in a communicative manner, and an auxiliary supercharger interposed upstream of the secondary air control valves in the secondary air supply path and driven by an electric motor or engine output.