United States Patent (19)
`Wakashiro et al.
`
`||||||IIII
`US005456236A
`11
`Patent Number:
`5,456,236
`45) Date of Patent:
`Oct. 10, 1995
`
`(54 EVAPORATIVE EMISSION CONTROL
`SYSTEM FOR INTERNAL COMBUSTION
`ENGINES
`
`I75) Inventors: Teruo Wakashiro; Takeshi Hara;
`Kouichi Hidano, Kazumi Yamazaki,
`all of Wako; Tomoyuki Kawakami,
`Tochigi, all of Japan
`(73) Assignee: Honda Giken Kogyo Kabushiki
`Kaisha, Tokyo, Japan
`
`21 Appl. No.: 335,373
`22 Filed:
`Nov. 3, 1994
`30
`Foreign Application Priority Data
`Nov. 4, 1993 (JP)
`Japan .................................... 5-298.931
`(51
`Int. Cl. ............................. F02M 25/08
`52 U.S. Cl. ........................................................... 123/519
`58) Field of Search ..................................... 123/516, 518,
`123/519, 520
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`1/1982 Hiramatsu et al. ..................... 1231519
`4,308,840
`4,790,283 12/1988 Uranishi et al. ....
`... 1231519
`4,817,576 4/1989 Abe et al. .......
`... 1231519
`4,894,072
`1/1990 Turner et al. ...
`... 1231519
`4,915,643 8/1990 Sato et al........
`... 1231519
`4,919,103 4/1990 Ishiguro et al.
`... 123,519
`5,056,494 10/1991 Kayanuma ............................. 123,519
`5,111,795 5/1992 Thompson .............................. 1231519
`5,143,041
`9/1992 Franzke ................................... 1231516
`
`
`
`5,209,210 5/1993 Ikeda et al. ............................. 1231516
`FOREIGN PATENT DOCUMENTS
`1-159455 6/1989 Japan.
`Primary Examiner-Thomas N. Moulis
`Attorney, Agent, or Firm-Nikaido, Marmelstein, Murray &
`Oram
`ABSTRACT
`57
`An evaporative emission control system for an internal
`combustion engine includes a canister for adsorbing evapo
`rative fuel generated in the fuel tank, a first introducing
`passage for introducing evaporative fuel generated in the
`fuel tank into the canister on an occasion other than at
`refueling, a purging passage for purging evaporative fuel
`adsorbed in the canister into the intake passage of the
`engine, and a first air-inlet passage communicating between
`the canister and the atmosphere. First and second adsorbent
`chambers are formed in the canister and each accommodat
`ing an adsorbent. The first introducing passage and the
`purging passage are connected to the first adsorbent cham
`ber. The first air-inlet passage is connected to the second
`adsorbent chamber. A communication passage communi
`cates between the first adsorbent chamber and the second
`adsorbent chamber. A second introducing passage is con
`nected to the first and second adsorbent chambers, for
`introducing evaporative fuel generated in the fuel tank into
`the canister at refueling. A second air-inlet passage commu
`nicates between the first adsorbent chamber and the atmo
`sphere. An electromagnetic valve is arranged across the
`second introducing passage, for opening the same at refu
`eling.
`
`12 Claims, 9 Drawing Sheets
`
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`U.S. Patent No. RE38,844
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`

`

`U.S. Patent
`
`Oct. 10, 1995
`
`Sheet 1 of 9
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`5,456,236
`
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`U.S. Patent
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`Oct. 10, 1995
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`Sheet 2 of 9
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`5,456,236
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`US. Patent
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`Oct. 10, 1995
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`5,456,236
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`U.S. Patent
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`Oct. 10, 1995
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`Sheet 6 of 9
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`5,456,236
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`Oct. 10, 1995
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`U.S. Patent
`
`Oct. 10, 1995
`
`Sheet 9 of 9
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`5,456,236
`
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`5,456,236
`
`1
`EVAPORATIVE EMISSION CONTROL
`SYSTEM FOR INTERNAL COMBUSTION
`ENGINES
`
`2
`fuel tank into the canister on an occasion other than at
`refueling, a purging passage for purging the evaporative fuel
`adsorbed in the canister into the intake passage of the
`engine, and a first open-to-atmosphere passage connected to
`the canister and communicating with the atmosphere.
`The evaporative emission control system according to the
`invention is characterized by comprising:
`a first adsorbent chamber formed in the canister and
`accommodating an adsorbent, the first introducing pas
`sage and the purging passage being connected to the
`first adsorbent chamber;
`a second adsorbent chamber formed in the canister and
`accommodating an adsorbent, the first open-to-atmo
`sphere passage being connected to the second adsor
`bent chamber;
`a communication passage formed in the canister and
`communicating between the first adsorbent chamber
`and the second adsorbent chamber,
`a second introducing passage connected to the first and
`second adsorbent chambers, for introducing the evapo
`rative fuel generated in the fuel tank into the canister at
`refueling;
`a second open-to-atmosphere passage connected to the
`first adsorbent chamber and communicating with the
`atmosphere; and
`valve means arranged across the second introducing pas
`sage, for opening the same at refueling.
`The adsorbent accommodated in the first adsorbent cham
`ber and the adsorbent accommodated in the second adsor
`bent chamber may be of substantially the same kind.
`Alternatively, the adsorbent accommodated in the first
`adsorbent chamber and the adsorbent accommodated in the
`second adsorbent chamber have different adsorption char
`acteristics from each other.
`Advantageously, the evaporative emission control system
`may further includes heater means for heating the adsorbent
`accommodated in the first adsorbent chamber.
`Also advantageously, the evaporative emission control
`system includes second valve means arranged across the
`second air-inlet passage, for opening the same at refueling.
`In a preferred embodiment of the invention, the first and
`second open-to-atmosphere passages have ends thereof con
`nected, respectively, to the second and first adsorbent cham
`bers at one side of the canister, the communication passage
`being arranged at another side of the canister opposite the
`one side, the second introducing passage having an end
`thereof opening into the communication passage.
`In another embodiment of the invention, the evaporative
`emission control system is characterized by comprising:
`a first adsorbent chamber formed in the canister and
`accommodating an adsorbent, the first introducing pas
`Sage and the purging passage being connected to the
`first adsorbent chamber,
`a second adsorbent chamber formed in the canister and
`accommodating an adsorbent, the first open-to-atmo
`sphere passage being connected to the second adsor
`bent chamber;
`a third adsorbent chamber formed in the canister and
`accommodating an adsorbent, the third adsorbent
`chamber being interposed between the first adsorbent
`chamber and the second adsorbent chamber;
`a first communication passage formed in the canister and
`communicating between the second adsorbent chamber
`and the third adsorbent chamber;
`a second communication passage formed in the canister
`
`BACKGROUND OF THE INVENTION
`
`Field of the Invention
`This invention relates to an evaporative emission control
`system for internal combustion engines, which prevents
`emission of evaporative fuel generated in a fuel tank of the
`engine into the atmosphere.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`Prior Art
`An evaporative emission control system of this kind has
`been proposed, e.g. by Japanese Provisional Patent Publi
`cation (Kokai) No. 1-159455, which includes not only an
`ordinary canister which adsorbs evaporative fuel generated
`in a fuel tank of the engine during parking of a vehicle in
`which the engine is installed or during operation of the
`engine, but also a canister for exclusive use in refueling,
`which adsorbs evaporative fuel generated during refueling
`into the fuel tank. According to the proposed evaporative
`emission control system, to overcome the disadvantage with
`conventional canisters that they have an insufficient adsorb
`ing efficiency due to a high flow velocity of evaporative fuel
`generated during refueling, the canister for exclusive use in
`refueling has a plurality of layers of adsorbents formed of
`activated carbon defined therein by one or more partitions,
`wherein the flow path of evaporative fuel is deflected so as
`to enhance the adsorbing efficiency without increasing the
`size (ratio L/D(length/diameter)) of the canister.
`However, the canister for exclusive use in refueling is not
`used on occasions other than at refueling, and becomes
`empty after evaporative fuel adsorbed therein is discharged
`or purged into the engine. Thus, the utilization factor of the
`activated carbon is low. Further, two batches of activated
`carbon have to be provided as adsorbents, one for the
`canister for exclusive use in refueling, and the other for the
`ordinary canister, leading to use of a large amount of
`activated carbon and hence an increased cost. Moreover, at
`least two purging passages connecting between the respec
`tive canisters and the intake passage of the engine have to be
`provided to discharge evaporative fuel adsorbed in the
`canisters, resulting in that the evaporative emission control
`system has a complicated construction.
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`SUMMARY OF THE INVENTION
`It is an object of the invention to provide an evaporative
`emission control system for internal combustion engines,
`which is capable of enhancing the utilization factor of
`adsorbents employed therein and hence curtailing the
`amount of adsorbents used.
`Another object of the invention is to provide an evapo
`rative emission control system for internal combustion
`engines, which has a simplified construction involving a
`purging passage connecting between a canister and the
`intake system of the engine.
`To attain the above objects, the present invention provides
`an evaporative emission control system for an internal
`combustion engine having an intake passage, and a fuel
`tank, the system including a canister for adsorbing evapo
`rative fuel generated in the fuel tank, a first introducing
`passage for introducing the evaporative fuel generated in the
`
`65
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`5,456,236
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`3
`and communicating between the first adsorbent cham
`ber and the third adsorbent chamber;
`a second introducing passage connected to the second and
`third adsorbent chambers, for introducing the evapora
`tive fuel generated in the fuel tank into the canister at
`refueling;
`a second open-to-atmosphere passage connected to the
`first adsorbent chamber and communicating with the
`atmosphere; and
`valve means arranged across the second introducing pas
`sage, for opening the same at refueling.
`The above and other objects, features, and advantages of
`the invention will be more apparent from the following
`detailed description taken in conjunction with the accom
`panying drawings.
`
`10
`
`15
`
`4
`23 of an internal combustion engine 1 provided with a filler
`cap 22 which is opened in refueling, a canister 26 accom
`modating adsorbents 24 and 24' which are formed of acti
`wated carbon, a first charging passage (first introducing
`passage) 27 for operation on ordinary occasions, connecting
`between the canister 26 and the fuel tank 23, with an end
`thereof opening into an upper space within the fuel tank 23,
`a two-way valve 52 arranged across the first charging
`passage 27, a second charging passage (second introducing
`passage) 33 for operation at refueling, connecting between
`the canister 26 and the fuel tank 23, with an end thereof
`opening into a space within the fuel tank 23 in the vicinity
`of the filler cap 22, an electromagnetic valve 34 arranged
`across the second charging passage 33 for selectively open
`ing and closing the same, a purging passage 10 connecting
`between the canister 26 and an intake pipe 2 of the engine
`1, with an end thereof opening into the intake pipe 2 at a
`location downstream of a throttle valve 3, and a purge
`control valve 36 arranged across the purging passage 10 for
`selectively opening and closing the same. The electromag
`netic valve 34 and the purge control valve 36 are controlled
`by control signals from an electronic control unit (ECU), not
`shown.
`The canister 26 has a first activated carbon chamber (first
`adsorbent chamber) 42 and a second activated carbon cham
`ber (second adsorbent chamber) 43 formed therein and
`partitioned from each other by a partition 41. The first and
`second activated carbon chambers 42,43 are each defined by
`a canister casing 26a, upper and lower retainer plates 46 and
`47, and the partition 41. The upper and lower retainer plates
`46, 47 are formed of a porous material and have filters 48
`and 49 applied over respective inner side surfaces thereof.
`The first and second activated carbon chambers 42, 43 are
`densely charged, respectively, with the adsorbents 24, 24
`which are formed of almost the same kind of activated
`carbon and in almost the same amount as each other. The
`canister 26 has an inlet port 27a for use on ordinary
`occasions, an air-inlet port 28a, and a discharge port 10a,
`which are provided in an upper portion of the canister 26 in
`or above the first activated carbon chamber 42, and con
`nected, respectively, to the first charging passage 27, an
`air-inlet passage (second air-inlet passage) 28 communicat
`ing with the atmosphere, and the purging passage 10. The
`inlet port. 27a for use on ordinary occasions extends through
`the upper retainer plate 46 and the filter 48 to directly open
`into the activated carbon adsorbent 24. Further, the canister
`26 has an air-inlet port 25a provided in an upper portion of
`the canister 26 above the second activated carbon chamber
`43 and opening into a gap defined between the casing 26a
`and the upper retainer plate 46. The air-inlet port 25a is
`connected to an air-inlet passage (first air-inlet passage) 25
`communicating with the atmosphere. A gap (communication
`passage) 50 is defined between the casing 26a and the lower
`retainer plate 47 at a location just below a lower end of the
`partition 41, and through which the first and second acti
`wated carbon chambers 42, 43 are communicated with each
`other. Another inlet port 33a is connected to the canister 26
`in a fashion directly opening into the gap 50 at a lengthwise
`middle point thereof. The port 33a is connected to a second
`charging passage 33 for operation at refueling. A normally
`open electromagnetic valve 25b and a one-way valve 28b
`are arranged across the first and second air-inlet passages 25,
`28 for opening and closing the same, respectively.
`Mounted in the intake pipe 2 at locations downstream of
`an end of the purging passage 10 opening into the intake
`pipe 2 are fuel injection valves 6 which are connected to the
`fuel tank 23 through a fuel supply pipe 7 and a fuel pump 8
`
`20
`
`25
`
`30
`
`35
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram showing the whole arrange
`ment of an evaporative emission control system for an
`internal combustion engine according to a first embodiment
`of the invention;
`FIG. 2 is a sectional view of a canister appearing in FIG.
`1, useful in explaining how there occurs in the canister a
`flow of evaporative fuel normally generated in a fuel tank,
`e.g. during parking of a vehicle in which the engine is
`installed, with the engine in stoppage, or during operation of
`the engine;
`FIG. 3 is a similar view to FIG. 2, useful in explaining
`how there occurs in the canister a flow of evaporative fuel
`generated in the fuel tank during refueling;
`FIG. 4 is a similar view to FIG. 2, useful in explaining
`how there occurs a flow of evaporative fuel in the canister
`during purging;
`FIG. 5 is a schematic diagram showing the whole arrange
`ment of an evaporative emission control system for internal
`combustion engine according to a second embodiment of the
`invention;
`FIG. 6 is a sectional view of a canister appearing in FIG.
`5, useful in explaining how there occurs in the canister a
`flow of evaporative fuel normally generated in a fuel tank,
`e.g. during parking of the vehicle with the engine in stop
`page, or during operation of the engine;
`FIG. 7 is a similar view to FIG. 6, useful in explaining
`how there occurs in the canister a flow of evaporative fuel
`generated in the fuel tank during refueling;
`FIG. 8 is a similar view to FIG. 6, useful in explaining
`how there occurs a flow of evaporative fuel in the canister
`during purging; and
`FIG. 9 is a sectional view of a canister according to a
`variation of the invention, which is provided with a heater.
`
`40
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`45
`
`50
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`55
`
`60
`
`65
`
`DETAILED DESCRIPTION
`The invention will now be described in detail with refer
`ence to the drawings showing preferred embodiments
`thereof.
`Referring first to FIG. 1, there is illustrated the whole
`arrangement of an internal combustion engine and an evapo
`rative emission control system therefor, according to a first
`embodiment of the invention. In the figure, reference
`numeral 11 designates an evaporative emission control sys
`tem which operates to prevent emission of evaporative fuel
`generated in a fuel tank into the atmosphere. The evapora
`tive emission control system 11 is comprised of a fuel tank
`
`

`

`S
`arranged across the pipe 7. The fuel tank 23 is provided with
`a tank internal pressure sensor 29 and a fuel amount sensor
`30, both mounted in an upper portion of the fuel tank 23 for
`sensing pressure within the fuel tank 23 and an amount of
`fuel within the fuel tank 23, respectively, as well as a fuel
`temperature sensor 31 mounted in a lateral side wall of the
`fuel tank 23 for sensing the temperature of fuel within the
`fuel tank 23.
`Description will be made as to how evaporative fuel is
`adsorbed into the canister 26 and purged therefrom in the
`evaporative emission control system constructed as above.
`First, during parking of a vehicle in which the engine 1 is
`installed, with the engine in stoppage, or during operation of
`the engine, no driving signal from the ECU, not shown, is
`supplied to the electromagnetic valve 34 to keep the same
`closed. Then, evaporative fuel generated in the fuel tank 23
`is guided through the first charging passage 27 for use on
`ordinary occasions and the inlet port 27a into the first
`activated carbon chamber 42 within the canister 26. FIG. 2
`shows how evaporative fuel generated in the fuel tank 23
`flows on an ordinary occasion such as during parking of the
`vehicle with the engine in stoppage, or during operation of
`the engine. As shown in the figure, evaporative fuel from the
`chamber 42 first forcibly opens and passes the two-way
`valve 52 arranged across he first charging passage 27 to be
`adsorbed by the activated carbon adsorbent 24 within the
`first activated carbon chamber 42. Then, an overflow of
`evaporative fuel from the chamber 42 is guided through the
`communication passage 50 below the partition 41 into the
`second activated carbon chamber 43 where it is adsorbed by
`the activated carbon adsorbent 24'. Since on this occasion no
`driving signal from the ECU is supplied to the magnetic
`valve 34 to keep it closed as mentioned before, there occurs
`no backflow of evaporative fuel from the canister 26 to the
`fuel tank 23 through the second charging passage 33.
`Further, on this occasion the one-way valve 28b remains
`closed to close the second air-inlet passage 28a so that there
`positively occurs a serial flow of evaporative fuel through
`the canister 26. Since evaporative fuel thus flows serially
`through the first activated carbon chamber 42, the commu
`40
`nication passage 50, and the second activated carbon cham
`ber 43 on an ordinary occasion, the substantial size ratio L/D
`of the canister 26 can be increased, whereby it is prevented
`that evaporative fuel passes through the canister 26 without
`being adsorbed thereby.
`Next how evaporative fuel generated in the fuel tank 23
`at refueling flows will be described with reference to FIG.3.
`At refueling, the electromagnetic valve 34 is opened by a
`driving signal from the ECU. Then, evaporative fuel vigor
`ously generated in large quantities in the fuel tank 23 at
`refueling is guided through the second charging passage 33
`for operation at refueling with an end thereof opening into
`the fuel tank 23 in the vicinity of the filler cap 22, to the
`evaporative-fuel introducing port 33a at the bottom of the
`canister 26, wherefrom it is bifurcated into two flows, which
`enter the first and second activated carbon chambers 42,43,
`respectively, to be adsorbed by the respective adsorbents 24,
`24'. Overflows of evaporative fuel from the chambers 42, 43
`rush toward the respective air-inlet ports 25a, 28a to be
`discharged therethrough. On this occasion, increased pres
`sure within the first activated carbon chamber 42 due to
`vigorously flowing evaporative fuel forces the one-way
`valve 28b to open so that the two flows of evaporative fuel
`are formed in the canister 26. Thus, at refueling there occur
`two flows of evaporative fuel running parallel with each
`other such that the substantial size ratio L/D of the canister
`26 can be reduced to thereby decrease the flow resistance
`
`50
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`5,456,236
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`10
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`15
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`20
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`6
`and hence prevent increased pressure within the fuel tank 23
`which impedes smooth refueling.
`Next, how evaporative fuel is desorbed from the canister
`26 and purged into the engine will be described. FIG. 4
`shows a flow of evaporative fuel occurring in the canister
`during purging from the canister 26. To start purging, a
`driving signal from the ECU is supplied to the purge control
`valve 36 arranged across the purging passage 10 to open the
`valve. Purging of evaporative fuel is carried out when the
`engine 1 is in a predetermined operating condition. When
`the engine 1 is in such a predetermined operating condition,
`there is developed vacuum in the intake pipe 2, which is
`transmitted through the purging passage 10 with the purge
`control valve 36 being open, into the first activated carbon
`chamber 42 within the canister 26, and then into the second
`activated carbon chamber 43 through the communication
`passage 50. Consequently, fresh air is introduced from the
`outside into the second activated carbon chamber 43 through
`the first air-inlet passage 25 and the air-inlet port 25a,
`whereby evaporative fuel is desorbed from the adsorbent 24
`due to the flowing-in air, and a mixture of the desorbed
`evaporative fuel and the air flows through the communica
`tion passage 50 into the first activated carbon chamber 42.
`Then, also evaporative fuel adsorbed by the adsorbent 24 in
`the first activated carbon chamber 42 is desorbed from the
`latter, and the resulting mixture of evaporative fuel and air
`is guided through the purging passage 10 into the intake pipe
`2 to be drawn into the engine 1. In this way, evaporative fuel
`is supplied from the canister 26 to the engine 1 such that
`evaporative fuel adsorbed by portions of the adsorbents
`closer to the air-inlet port 25a is first supplied to the engine,
`followed by one adsorbed by portions of the adsorbents
`remote from the port 25a being supplied to the engine.
`As described above, according to the present embodi
`ment, both on ordinary occasions and at refueling, evapo
`rative fuel generated in the fuel tank 23 is adsorbed by the
`activated carbon adsorbents 24, 24' in the first and second
`activated carbon chambers 42, 43 of the canister 26. As a
`result, the utilization factor of the adsorbents 24, 24' can be
`increased. Therefore, as compared with the conventional
`arrangement wherein activated carbon adsorbents are
`accommodated in separate canisters for operation, respec
`tively, at refueling and on ordinary occasions, the amount of
`activated carbon to be used can be curtailed. Further, accord
`ing to the embodiment, the single purging passage 10 is
`provided, which simplifies the construction, as compared
`with the conventional arrangement wherein two or more
`purging passages are provided. Still further, on an-ordinary
`occasion the activated carbon adsorbents 24, 24' are sub
`stantially arranged in series for a flow of evaporative fuel in
`the canister 26 to be adsorbed thereby, whereas at refueling
`they are substantially arranged in parallel with each other for
`a flow of evaporative fuel in the canister 26 to be adsorbed
`thereby, whereby passing of evaporative fuel through the
`canister 26 without being adsorbed therein can be prevented
`and also refueling can be carried out in a smooth manner.
`Next, a second embodiment of the invention will be
`described with reference to FIGS. 5-8. Referring to FIG. 5,
`there is illustrated the whole arrangement of an internal
`combustion engine and an evaporative emission control
`system therefor, according to the second embodiment. In
`FIGS. 5-8, corresponding elements and parts to those in
`FIGS. 1-4 are designated by identical reference numerals.
`The evaporative emission control system according to the
`second embodiment is distinguished from the first embodi
`ment described above only in the construction of the can
`ister, and other elements and parts are substantially identical
`
`

`

`7
`in arrangement and function with those of the first embodi
`ment. In the second embodiment, a canister 56 is connected
`to a first charging passage 27 for operation on ordinary
`occasions, a second charging passage 33 for operation at
`refueling, the purging passage 10, and first and second
`air-inlet passages 25, 28, similarly to the first embodiment.
`The canister 56 has first to third activated carbon chambers
`58, 59 and 60 formed therein and partitioned from each other
`by partitions 55 and 57. The first and second activated
`carbon chambers 58, 59 are communicated with each other
`at allower portion of the canister 56, as hereinafter described
`and in this sense they can be considered as a single activated
`carbon chamber. The first, second and third activated carbon
`chambers 58, 59, 60 are densely charged with adsorbents
`64a, 64b, and 64c which are formed of almost the same kind
`of activated carbon. The first and second activated carbon
`chambers 58,59 are communicated with each other through
`a gap defined between a lower end off the partition 55 and
`an inner surface of a canister casing 56a. An inlet port 27a
`for use on ordinary occasions, a second air-inlet port 28a,
`and a discharge port 10a connected, respectively, to a first
`charging passage 27 for use on ordinary occasions, a second
`air-inlet passage 28, and a purging passage 10 are provided
`in an upper portion of the canister 56 in or above the first
`activated carbon chamber 58. The inlet port 27a for use on
`ordinary occasions extends through an upper retainer plate
`66 and a filter 68 to directly open into the activated carbon
`adsorbent 64a. Further, the canister 56 has an air-inlet port
`25a provided in an upper portion of the canister 56 below the
`third activated carbon chamber 60 and opening into a gap
`defined between the casing 56a and a lower retainer plate 67.
`The air-inlet port 25a is connected to a second air-inlet
`passage 25 communicating with the atmosphere. A nor
`mally-open electromagnetic valve 25b and a one-way valve
`28b are arranged across the first and second air-inlet pas
`Sages 25, 28, respectively, for opening and closing the same.
`A gap (communication passage) 71 is defined between the
`casing 56a an the upper retainer plate 66 at a location above
`the second and third activated carbon chambers 59, 60, and
`through which the second and third activated carbon cham
`bers 59, 60 are communicated with each other. Another inlet
`port 33a is connected to the canister 56 in a fashion directly
`opening into the communication passage 71 at a lengthwise
`middle point thereof. The port 33a is connected to the
`second charging passage 33 for use at refueling. Fuel
`injection valves 6 are mounted in an intake pipe 2 of the
`engine 1 at locations downstream of an end of the purging
`passage 10 opening into the intake pipe 2 and connected to
`a fuel tank 23 through a fuel supply pipe 7 and a fuel pump
`8 arranged across the pipe 7, similarly to the first embodi
`ment.
`Next, description will be made as to how evaporative fuel
`is adsorbed into the canister 56 and purged therefrom in the
`evaporative emission control system according to the second
`embodiment constructed as above. First during parking of a
`vehicle in which the engine 1 is installed, with the engine in
`stoppage, or during operation of the engine, no driving
`signal from the ECU, not shown is supplied to an electro
`magnetic valve 34 arranged across the second charging
`passage 33 to keep the same closed. Evaporative fuel
`generated in the fuel tank 23 forcibly opens the two-way
`valve 52 arranged across the first charging passage 27 to be
`adsorbed by the activated carbon adsorbent 64a within the
`first activated carbon chamber 58 through the inlet port 27a.
`FIG. 6 shows how evaporative fuel generated in the fuel tank
`23 flows on an ordinary occasion such as during parking of
`the vehicle with the engine in stoppage, or during operation
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,456,236
`
`10
`
`15
`
`20
`
`25
`
`8
`of the engine. As shown in the figure, evaporative fuel
`introduced into the first activated carbon chamber 58 is
`adsorbed by the adsorbent 64a, and then an overflow of
`evaporative fuel from the chamber 58 is guided through a
`gap defined between a lower end of the partition 55 and an
`inner surface of the canister casing 56a into the second
`activated carbon chamber 59 where it is adsorbed by the
`activated carbon adsorbent 64b. An overflow of evaporative
`fuel is further guided from the second activated carbon
`chamber 59 and then through the communication passage 71
`into the third activated carbon chamber 60 to be adsorbed by
`the activated carbon adsorbent 64c. Since on this occasion
`the magnetic valve 34 is kept closed as mentioned before,
`there occurs no backflow of evaporative fuel from the
`canister 56 to the fuel tank 23 through the second charging
`passage 33. Further, on this occasion the one-way valve 28b
`remains closed to close the second air-inlet passage 28a, so
`that there positively occurs a serial flow of evaporative fuel
`through the canister 56. Thus, evaporative fuel flows serially
`along a generally S-shaped path on an ordinary occasion, the
`substantial size ratio L/D of the canister 56 can be increased,
`whereby it is prevented that evaporative fuel passes through
`the canister 56 without being adsorbed thereby.
`Next, how evaporative fuel generated in the fuel tank at
`refueling flows will be described with reference to FIG.7. At
`refueling, the electromagnetic valve 34 is opened by a
`driving signal from the ECU. Then, evaporative fuel gen
`erated in large quantities in the fuel tank 23 at refueling is
`guided at a high flow rate through the second charging
`passage 33 for use at refueling with an end thereof openin