Evaporative-emission-control system and straddled vehicle equipped with evaporative-emission-control system

An evaporative-emission-control system, comprising:

• a canister configured to recover an evaporated fuel generated in a fuel tank that stores a fuel of an engine;
• a fuel-tank-purge passage configured to guide the evaporated fuel into the canister;
• an ambient-air-introduction passage configured to introduce an ambient air into the canister;
• a first purge passage and a second purge passage, configured to purge a gas from the canister into an intake passage of the engine, the gas from the canister containing at least one of the recovered evaporated fuel or the ambient air introduced via the ambient-air-introduction passage;
• a first opening/closing valve configured to switch between a closed position in which the first purge passage is blocked and an open position in which the first purge passage is open;
• a second opening/closing valve configured to switch between a closed position in which the second purge passage is blocked and an open position in which the second purge passage is open;
• an engine-information-acquisition device configured to acquire at least one of an engine speed of the engine or a throttle-valve-opening degree of the engine;
• a purge-amount-calculation device configured to determine whether each of the first opening/closing valve and the second opening/closing valve is in the open position thereof or the closed position thereof;
• and
• a valve control device configured to control opening and closing of each of the first opening/closing valve and the second opening/closing valve, to thereby form a plurality of purge passages through which the gas passes in the evaporative-emission-control system, wherein
• each of the plurality of purge passages has an effective-cross-sectional area,
• the plurality of purge passages includes the first purge passage and the second purge passage,
• the effective-cross-sectional area of the first purge passage is a first effective-cross-sectional area, which is smallest among the effective-cross-sectional areas of the plurality of purge passages,
• the effective-cross-sectional area of the second purge passage is a second effective-cross-sectional area, which is obtained by subtracting the first effective-cross-sectional area from a third effective-cross-sectional area, the third effective-cross-sectional area being a sum of the effective-cross-sectional areas of the plurality of the purge passages, wherein
• the purge-amount-calculation device is configured to select, based on at least one of the engine speed or the throttle-valve-opening degree acquired by the engine-information-acquisition device, a mode among:
• a recovery mode in which the first opening/closing valve is switched to, and remains in, the closed position, and the second opening/closing valve is switched to, and remains in, the closed position, to thereby recover the evaporated fuel by the canister without supplying the evaporated fuel to the engine,
• a first purge mode in which the first opening/closing valve is switched to, and remains in, the open position, and the second opening/closing valve is switched to, and remains in, the closed position, to thereby supply the gas to the engine through the first purge passage,
• a second purge mode in which the first opening/closing valve is switched to, and remains in, the closed position, and the second opening/closing valve is switched to, and remains in, the open position, to thereby supply the gas to the engine through the second purge passage, and
• a third purge mode in which the first opening/closing valve is switched to, and remains in, the open position, and the second opening/closing valve is switched to, and remains in, the open position, to thereby supply the gas to the engine through the first purge passage and the second purge passage, and
• the valve control device is configured to control the opening and closing of the first opening/closing valve and the second opening/closing valve in accordance with the selected mode.