(57) In order to provide a filter structure for a canister in which dust or the like in
air is prevented from sticking to the filter and being distributed over the entire
surface thereof, and accordingly, the filter can hardly clogging so as to prevent
lowering of the purge volume of a canister due to an increase in ventilation resistance,
the dust filter 8 is formed in a crescent-like shape, having, at a substantially center
thereof, a pipe hole 8a fitted on a pipe extended to a filter chamber le, the filter
chamber le accommodating the dust filter 8 is formed in a crescent-like shape substantially
identical with that of the dust filter 8 and the atmospheric port 1f is communicated
with the bottom side of the dust filter 8, and accordingly, the atmospheric air flows
by a large volume around the pipe 7a so that the dust or the like is likely to be
accumulated around the pipe 7a, but the opposite ends becoming narrow outward so that
the flow rate of the atmospheric air is become less. As a result, the dust or the
like can hardly be accumulated so as to prevent the ventilation resistance of the
dust filter 8 from increasing, thereby preventing leakage of evaporation fuel into
the atmosphere.
Further, in a canister, in order to aim at restraining the ventilation resistance
of the filter from being increased by dust sucked with air through the atmospheric
port, and at enhancing the mounting ability of the filter for restraining suction
of the dust, the atmospheric port 33 is formed in the upper portion of a canister
casing 31, dust sucked through the atmospheric port 33 being caused to stick to the
lower surface of a dust preventing filter 34 while the sticking dust is allowed to
be dropped by vibration. Further, the dust preventing filter 34 is held by a filter
holding member 35, and is then fitted in a filter mounting chamber 39 defined in the
canister casing 31. Thereafter, an adsorbent side filter 36 is secured. A temporary
holding device A for temporarily holding the filter holding member is provided in
the filter holding member 35 and the filter mounting chamber 39.
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