Air-intake structure of an engine

An air-intake structure of an engine comprising:

• a duct structure configured to take in air from outside;
• an air cleaner including an air filter configured to clean the air guided to the air cleaner through the duct structure;
• a throttle device including a throttle valve for controlling a flow rate of the air guided to the throttle device through the air cleaner;
• an engine including an intake port configured to suction the air guided to the engine through the throttle device;
• and
• an on-off valve provided in the duct structure;
• the duct structure including:
• a main inlet configured to take in air therethrough from outside by utilizing a ram pressure;
• a main passage extending from the main inlet to the air filter;
• a sub-inlet configured to take in air therethrough from outside;
• and
• a joint section located upstream of the air filter, the air flowing from the sub-inlet being joined to the air in the main passage, at the joint section;
• wherein the on-off valve is configured to permit and inhibit air communication between the sub-inlet and the joint section;
• wherein the on-off valve includes a valve body positioned to permit and inhibit air flow through the sub-inlet of the duct structure;
• and
• wherein the valve body is configured to open by an air pressure directly applied to the valve body during running of the engine.