In an automobile, a fuel tank is sometimes provided under a floor panel, and a vapor storage canister (charcoal canister) is provided adjacent to the fuel tank for the purpose of adsorbing fuel vapor that is generated in the fuel tank. To promptly adsorb the fuel vapor generated in the fuel tank, it is desirable to ensure an adequate storage volume, and place the vapor storage canister (which is referred to simply as “canister” in the following description) as close to the fuel tank as possible. Also, as the space available for installing the canister is limited, various proposals have been made so as to optimize the shape and layout of the canister.
As one such technology, it is known to place a canister between a front end and a rear end of a sub-frame attached to a rear part of a vehicle body frame at a higher elevation than the fuel tank so as to be adjacent or substantially adjacent to the lower surface of the floor panel. See patent document 1.
A known canister comprises a canister casing defining a first adsorption chamber filled with activated charcoal for adsorbing fuel vapor introduced from an inlet port and a second adsorption chamber provided in parallel with the first adsorption chamber and filled with activated charcoal for adsorbing vapor fuel released from the first adsorption chamber. A first space is defined in a part of the second adsorption chamber on the side of the inlet port, and a second space is defined in parallel with the first and second adsorption chambers such that the length of the second space as measured along the direction directed toward the inlet portion is longer than that of the second adsorption chamber, and a communication hole is formed in a wall separating the first space and second space from each other to communicate the first and second chambers to each other. The canister casing is formed with an atmospheric port for communicating the atmosphere with the second space, and is provided with a filter for preventing the intrusion of foreign matters into the second space. See patent document 2.    Patent Document 1: Japanese patent laid open publication No. 2004-143966    Patent Document 2: Japanese patent No. 3951427