(19) Japan Patent Office (JP)
`
`(12) Japanese Unexamined Patent
`Application Publication (A)
`
`(11) Japanese Unexamined Patent
`Application Publication Number
`H10-37812
`(43) Publication date: February 13, 1998
`
`(51) Int. Cl.6
`F02M 25/08
`
`Identification codes
`
`File Number
`
`Technical indications
`
`311
`
`L
`311 Z
`Request for examination: Not Yet Requested Number of Claims: 3 Floppy disk (Total of 6 Pages)
`
` FI
`F02M 25/08
`
`(21) Application number
`(22) Date of application
`
`H8-213176
`July 23, 1996
`
`(71) Applicant
`
`(72) Inventor
`
`(72) Inventor
`
`(74) Agent
`
`390001177
`Kuraray Chemical Co., Ltd.
`4342 Tsurumi, Bizen City, Okayama Prefecture
`ABE, Susumu
`4125-2 Tsurumi, Bizen City, Okayama Prefecture
`ISHIMURA, Shizuo
`c/o Fujitsu Ltd.
`133-5 Osafune-cho, Oku-gun, Okayama Prefecture
`Patent attorney ODANAKA, TOSHIO
`
`SPECIFICATION
`(54) TITLE OF THE INVENTION
`Fuel Evaporation Preventing Device
`(57) ABSTRACT
`[MEANS FOR RESOLUTION]
`A fuel evaporation preventing device for an automobile,
`wherein: in a canister that adsorbs gasoline vapor produced
`from a fuel tank while an automobile is stopped, and that
`reuses, as fuel, gasoline adsorbed through air intake by an
`engine while running, a second canister is connected in
`series through a pipe or through a similar structure after a
`canister. Here a case wherein an orifice is provided in the
`pipe that connects to the first canister and the second
`canister is also included in the present invention. A
`honeycomb activated carbon is used as the adsorbent of the
`second canister, and the volume thereof is at least 2% and
`not more than 20% of the volume of the first canister.
`[EFFECTS]
`The use of a fuel evaporation preventing device
`according to the present invention causes a significant
`suppression in the speed at which the gasoline that is
`adsorbed in the canister moves due to adsorption
`equilibration to the air discharge port, enabling a reduction
`in the evaporative loss of gasoline to about 1/10, even if an
`automobile is stopped for an extended period of time,
`without increasing the volume of the canister and without
`an increase in the performance of the activated carbon.
`
`BASF-1009
`U.S. Patent No. RE38,844
`
`

`

`[SCOPE OF PATENT CLAIMS]
`[CLAIM 1]
`A fuel evaporation preventing device for an automobile,
`wherein: in a canister that adsorbs gasoline vapor produced
`from a fuel tank while an automobile is stopped, and that
`reuses, as fuel, gasoline adsorbed through air intake by an
`engine while running, a second canister is connected in
`series through a pipe or through a similar structure after a
`canister.
`[CLAIM 2]
`A fuel evaporation preventing device for an automobile,
`wherein: in a canister that adsorbs gasoline vapor produced
`from a fuel tank while an automobile is stopped, and that
`reuses, as fuel, gasoline adsorbed through air intake by an
`engine while running, an orifice and a second canister are
`connected in series by a pipe after a first canister.
`[CLAIM 3]
`A fuel evaporation preventing device for an automobile
`according to Claim 1, wherein:
`the capacity of the second canister is at least 2% and not
`more than 20% of the capacity of the first canister.
`[Detailed Explanation of the Invention]
`[0001]
`[FIELD OF TECHNOLOGY OF THE INVENTION]
`The present invention relates to a so-called canister that
`is a fuel evaporation preventing device for an automobile,
`and to a device that is equipped in an automobile to adsorb,
`recover, and reuse vapor of evaporated gasoline from a fuel
`tank, wherein, through the addition of an orifice or a small-
`volume second canister to an ordinary canister, has the
`effects of significantly reducing the loss of gasoline while
`an automobile is stopped for a long period of time and also
`of preventing pollution.
`[0002]
`[PRIOR ART]
`Vapor that is evaporated from a gasoline tank when the
`engine of an automobile is stopped is conventionally
`released into the atmosphere without being recovered.
`However, in consideration in relation to pollution in recent
`years, a method has been adopted in which a collector filled
`with an adsorbent is attached midway in an exhaust pipe to
`the atmosphere to adsorb evaporated gasoline vapors, after
`which air flows in a reverse direction when the engine is
`running to cause desorption, such that the gasoline vapor is
`supplied to the engine and reused. Moreover, activated
`carbon is generally used as the gasoline adsorbent, and a
`single collector filled internally with activated carbon has
`been used.
`[0003]
`To date there have been numerous proposals for reducing
`of the amount of evaporation by improving the adsorption
`performance of the activated carbon or from the perspective
`of the canister structure. However, these ideas have
`primarily focused on improving the "working capacity" (W.
`C.), or in other words, the adsorption and desorption
`capability, as well as the durability so that degradation does
`not occur through use over an extended period of time. As a
`result, these have not always been effective at reducing
`gasoline vapors leaked from the canister when an
`automobile is stopped for a long period.
`[0004]
`
`Japanese Unexamined Patent Application Publication H10-37812
`(2)
`
`In particular, some states of the United States adopted
`new evaporation regulations pertaining to automotive fuel
`beginning in 1995, and in 1996, these new regulations were
`enforced nationwide. According to the new regulations,
`even if there is surplus capability in the W. C. of the
`canister in terms of the 72-hour Diurnal Breathing Loss
`(DBL), envisioning a case in which an automobile is
`stopped for an extended period of time, if the automobile is
`stopped for an extended period of time, there are cases in
`which the amount released into the atmosphere will
`increase to exceed the regulation value, as a result of
`gasoline adsorbed in the canister concentrating and
`diffusing in the adsorption layer as time elapses, and thus,
`countermeasures are needed.
`[0005]
`[PROBLEM SOLVED BY THE PRESENT INVENTION]
`In consideration of the need for Diurnal Breathing Loss
`(DBL) countermeasures, canisters that have conventionally
`used activated carbon as an adsorbent have a problem in
`that the amount of leakage of gasoline vapors increases as
`time elapses when an automobile is stopped for an
`extended period of time. Given this, a new canister able to
`suppress the amount of leakage of gasoline vapor, even
`when an automobile is stopped for an extended period of
`time, by means such as changing the configuration of the
`canister, without increasing the canister volume and
`without increasing the performance of the activated carbon,
`and without a loss of economic efficiency, has been
`developed and provided.
`[0006]
`[MEANS FOR SOLVING THE PROBLEM]
`The canister is a system that recovers and reuses
`evaporated gasoline by adsorbing, in activated carbon,
`gasoline vapors produced from a fuel system, such as a
`gasoline tank, due to the temperature of the outside air
`when an automobile is stopped, and then using a portion of
`the engine intake when the automobile is traveling for
`desorption of the adsorbed gasoline. The inventors have
`focused their attention on the point that, with regard to the
`configuration of the engine, the amount of air that can be
`used for desorption by the canister is quantitatively
`restricted since it is a portion of the air intake, and thus
`approximately half, and in some cases even more, of the
`adsorbed gasoline and is left in the adsorbed state in the
`activated carbon in the activated carbon, rather than being
`desorbed.
`[0007]
`Moreover, the concentration distribution of gasoline
`adsorbed in the activated carbon layer in the canister has a
`gradient with the concentration thereof being high at the
`gasoline vapor entrance side and low at the exhaust side;
`however, because the activated carbon in the canister is a
`single continuous layer of activated carbon, the gas phase
`concentration of the section having a large adsorption
`amount of gasoline vapor at the entrance side is higher than
`at the exit side, and thus, due to adsorption equilibration, as
`time elapses the adsorbed gasoline moves to the exit side
`where the gas phase concentration is low, so that the
`concentration of the gasoline adsorbed in the activated
`carbon layer gradually becomes uniform.
`[0008]
`
`
`
`

`

`The inventors of the present invention discovered that,
`because of the increase in the gas phase concentration at the
`exit side due to this type of mechanism, gasoline vapor
`leakage more readily occurs when an automobile is stopped
`for an extended period of time. Further, the inventors also
`learned that the components of the gasoline vapor that leaks
`from the canister are primarily propane and butane, and
`these components are leaked in small amounts, and thus
`that the provision of a separate small second canister as a
`dedicated leak countermeasure is effective in adsorbing
`these, and arrived at the present invention based thereon.
`[0009]
`That is, this is fuel evaporation preventing device for an
`automobile, wherein, in a canister that adsorbs gasoline
`vapor produced from a fuel tank while an automobile is
`stopped, and that reuses, as fuel, gasoline adsorbed through
`air intake by an engine while running, a second canister is
`connected in series through a pipe or through a similar
`structure after a canister. Here a case wherein an orifice is
`provided in the pipe that connects to the first canister and
`the second canister is also included in the present invention.
`Moreover, with this fuel evaporation preventing device, a
`honeycomb activated carbon is used as the adsorbent of the
`second canister, and the volume thereof is at least 2% and
`not more than 20% of the volume of the first canister.
`[0010]
`Here, the “through a pipe or through a similar structure"
`means having a constricted structure such that when the
`second canister is connected after the canister, the activated
`carbon layer is not in a continuous state, but rather is
`separated, and the gas flow between the two canisters is
`suppressed. As described below, this structure is adopted in
`order to suppress movement of the gasoline in the canister
`to the second canister through adsorption equilibration.
`Hereunder, the present invention is described in detail.
`[0011]
`The fuel evaporation preventing device for an
`automobile of the present invention is an improved
`structure of a canister that is used conventionally, and thus
`particularly has the function of decreasing evaporation loss
`of gasoline when an automobile is stopped for an extended
`period of time.
`[0012]
`In the past, vapors of evaporated gasoline from gasoline
`tanks of automobiles with stopped engines, at gas stations,
`and the like, have been released into the atmosphere rather
`than being recovered. However, recently, photochemical
`smog, oxidants, and other pollution problems have become
`serious, and hydrocarbons found in gasoline that are
`released into the atmosphere are thought to be one of the
`main causes thereof, and thus reducing the amounts
`released has become an important issue. Given this, a
`method is being adopted to recover gasoline vapors
`produced from automobiles by attaching a so-called
`canister, which is a collector filled with an adsorbent,
`midway in an exhaust pipe to the atmosphere to adsorb
`evaporated gasoline, after which air is caused to flow in a
`reverse direction during travel to cause desorption, to
`supply to the engine.
`[0013]
`However, because typically the canister adsorbs and
`desorbs gasoline vapor using a single continuous activated
`
`Japanese Unexamined Patent Application Publication H10-37812
`(3)
`
`carbon layer, when an automobile is stopped for an
`extended period of time, as described above, if there is a
`difference in concentrations of gasoline adsorbed in the
`activated carbon layer, the gasoline vapor will gradually
`move to the exit side, due to adsorption equilibration, to
`thus be released, so an increase in evaporation loss is
`unavoidable. The fuel evaporation preventing device of the
`present invention was developed to resolve this problem,
`wherein a second canister is connected in series through a
`pipe or a similar structure after the ordinary first canister.
`[0014]
`The activated carbon layer of the second canister must be
`connected in series through a pipe or a similar structure in
`order to maintain a separated state without being in a state
`that is continuous with the first canister. When the two
`canisters are separated and connected by a pipe, movement
`of gasoline vapors due to adsorption equilibration is
`significantly inhibited when compared to a single
`continuous activated carbon layer, and even if a small
`volume second canister with a volume that is 10 to 20%
`that of the first canister is used, as illustrated by the
`embodiments described below, results are produced
`wherein the amount of evaporation of the gasoline vapor
`can be decreased sharply to about one-tenth.
`[0015]
`Moreover, the provision of an orifice between the two
`canisters further prevents flow of the gasoline vapors, thus
`enabling a reduction in the amount of evaporation;
`however, there is a drawback in that this increases pressure
`loss. Moreover, more preferably the volume of the second
`canister is no less than 2%, and no greater than 20%, of the
`volume of the first canister. If the volume of the second
`canister were no greater than 2% of the first canister, the
`benefit of newly providing a second canister would
`decrease sharply, and if the volume thereof were 20% or
`greater, the extent of improvement of the effect thereof
`would tend to decrease rapidly.
`[0016]
`Note that that while there is no particular limitation on
`the shape of the activated carbon for filling the second
`canister, a honeycomb activated carbon is preferred since
`pressure loss tends to increase with a configuration wherein
`a second canister is added, so this shape is well suited for
`this configuration due to its high adsorption speed.
`[0017]
`[DESCRIPTION OF THE PREFERRED EMBODIMENT]
`One example of a concentration distribution of adsorbed
`gasoline in an ordinary canister is shown in FIG. 1. As
`shown in FIG. 2, the configuration is with a single
`continuous activated carbon layer, and the gasoline
`concentrations were measured at the points represented by
`4 to 8 between the entrance side and the exit side, as
`depicted in the drawings, in order to examine the
`concentration distribution of gasoline adsorbed in the
`activated carbon layer.
`[0018]
`As shown by the distribution curve 1, the concentration
`distribution of gasoline immediately following adsorption
`has a gradient with the concentration being high at the
`gasoline vapor entrance side and low at the exit side.
`[0019]
`
`
`
`

`

`Japanese Unexamined Patent Application Publication H10-37812
`(4)
`
`However, as time elapses, the adsorbed gasoline moves
`to the exit side due to adsorption equilibration based on the
`concentration difference between the entrance side and the
`exit side thereof, with the atmosphere around the adsorbent
`acting as a medium, producing, after 24 hours the state
`represented by distribution curve 2. Furthermore, when the
`engine is started and the automobile begins to travel, the
`gasoline adsorbed in the canister is desorbed by the air
`intake, and when this occurs, the concentration distribution
`shown by the distribution curve 3 results.
`[0020]
`However, while a portion of the air intake of the engine
`is used for the desorption of the adsorbed gasoline, the
`amount of air that can be used is restricted by the
`configuration of the intake and exhaust gas systems of the
`engine. When the volume of activated carbon of the
`canister is about 2 liters, the amount of air that can be used
`is limited to 100 to 300 times the volume of the activated
`carbon, and the extent of desorption thereby is insufficient,
`and thus, as shown by the gasoline concentration
`distribution curve 3 of FIG.1, a state in which the adsorbed
`gasoline is sufficiently desorbed cannot be reached.
`[0021]
`Even with an ordinary canister configuration, the amount
`of gas flowing out from the canister when the automobile is
`in a stopped state for an extended period of time is a small,
`and the main components thereof are propane and butane.
`Accordingly, the object of adsorbing these components can
`be achieved by providing a small second canister to adsorb
`these.
`[0022]
`However, if an activated carbon having the same shape
`as the activated carbon that is filled in the canister were
`used, in the second canister, which has a small volume, the
`inner diameter thereof would generally be small, and thus
`there would be a problem in that the pressure loss would be
`increased because the air flow speed would be increased
`dramatically. Given this, when honeycomb activated
`carbon or activated carbon having large voids is used in the
`second canister, the pressure loss can be reduced to a
`usable range, and leakage of gasoline vapor can be
`significantly reduced.
`[0023]
`Moreover, while the second canister is small in volume,
`the amount of air passing therethrough at the time of
`desorption is the same as that of the first canister, and thus
`desorption can be performed adequately and adsorption
`performance can be maintained with only a small-volume
`second canister.
`[0024]
`An example of the relationship between a purge air
`amount after adsorption by the canister and the gasoline
`leak concentration is shown next. FIG. 3 shows a cross-
`sectional view of a canister having a volume of 1 liter with
`granulated carbon having a particle diameter of 2 mm filled
`into a 127 mm long container with a diameter of 100 mm.
`After gasoline was adsorbed in the canister until
`breakthrough, the respective amounts of air passage were
`changed, and the adsorbed gasoline was purged. After the
`unit was then left in air for 24 hours at a temperature of 30,
`and the concentration of the gasoline leaking from the
`canister was measured with an airflow at a rate of 1
`
`
`
`liter/min. from the gasoline vapor entrance side of the
`canister.
`[0025]
`The resulting relationship between the amount of air
`used in purging and the concentration of gasoline that leaks
`when air is caused to flow from the gasoline vapor entrance
`side after the canister had been left in the air environment is
`shown in Table 1.
`[0026]
`[TABLE 1]
`
`Amount of Purging Air
`(Activated Charcoal
`Volume Ratio)
`(Multiplier）
`100
`
`Leakage Concentration after
`24 Hours
`(Hydrocarbon total: ppm)
`
`25000
`
`200
`300
`1000
`5000
`10000
`
`15000
`12000
`1420
`440
`290
`
`No.
`1
`2
`3
`4
`5
`6
`
`[0027]
`It is understood from these results that when the amount
`of air that is used for purging is 1000 times or greater than
`the volume of the activated carbon, the concentration of the
`gasoline that leaks decreases significantly.
`[0028]
`The fuel evaporation preventing device of the present
`invention has a small-volume second canister that is added
`in series after an ordinary canister. Even when using the
`ordinary amount of air that can be used in purging, which is
`approximately 300 times the first canister, the evaporation
`preventing device of the present invention is able to reduce
`the concentration of gasoline leaked to about the same level
`as when 1000 to 5000 times the amount of air is used with
`an ordinary canister, as shown in Embodiments 2 to 10,
`described below. Accordingly, the amount of gasoline that
`is leaked becomes approximately 1/10 or even less, and an
`extremely significant effect is seen.
`[0029]
`[EMBODIMENTS]
`Hereunder, the present invention is described in more
`detail by way of embodiments.
`[0030]
`FIG. 4 shows a configuration of one embodiment of a
`fuel evaporation preventing device for automobiles of the
`present invention. The first canister shown in the drawing
`has a 127 mm-long container with a diameter of 100 mm
`filled with 1 liter of granulated carbon having a particle
`diameter of 2 mm, and after the first container, a small-
`volume second canister filled with honeycomb activated
`carbon is connected in series by a pipe. Note that the
`spacing between the first canister and the second canister is
`20 mm, and the two canisters are connected by a pipe
`having an inner diameter of 10 mm. Moreover, the shape
`and volume of the activated carbon filled into the second
`canister is shown in Table 2. Instead of the honeycomb
`activated carbon, granulated activated carbon or crushed
`activated carbon, wherein there are large voids and wherein
`the pressure loss is low, can be used in the second canister.
`
`

`

`[0031]
`[TABLE 2]
`
`
`Orifice
`Dia. mm
`
`No. 1 Canister
`Volume mL
`
`Example 1
`
`1000
`
`Example 2
`
`1000
`
`Example 3
`
`1000
`
`Example 4
`
`1000
`
`Example 5
`
`1000
`
`
`
`
`
`
`
`
`
`
`
`
`
`Butane W.C.
`g/canister
`
`Leak Concentration (Hydrocarbon Total ppm) Pressure
`Loss
`After 10
`After 24
`After 48
`After 72
`20 L/min
`minutes
`hours
`hours
`hours
`mmAq
`
`500
`
`48.2
`
`500
`
`48.5
`
`500
`
`48.7
`
`500
`
`49.0
`
`500
`
`48.2
`
`300
`
`270
`
`240
`
`220
`
`450
`
`1030
`
`1150
`
`1500
`
`47
`
`940
`
`1100
`
`1550
`
`47
`
`810
`
`990
`
`1330
`
`47
`
`830
`
`960
`
`1260
`
`47
`
`1900
`
`2500
`
`3600
`
`47
`
`770
`
`950
`
`1280
`
`50
`
`Example 6
`
`1000
`
`Example 7
`
`1000
`
`Example 8
`
`1000
`
`Example 9
`
`1000
`
`Example 10
`
`1000
`
`
`
`2
`
`4
`
`6
`
`1000
`1040
`
`
`
`
`
`None
`
`No. 2
`Canister Size No. of
`
`L x W x H
`Cells
`mm
`45 x 45 x
`20
`40 mL
`65 x 65 x
`20
`84 mL
`45 x 45 x
`40
`81 mL
`65 x 65 x
`10
`126 mL
`45 x 45 x
`10
`20 mL
`Activated carbon
`40 ml
`3 mm granular
`carbon
`Activated carbon
`40 ml
`8/28 mesh crushed
`carbon
`45 x 45 x
`20
`40 mL
`45 x 45 x
`20
`40 mL
`45 x 45 x
`20
`40 mL
`None
`
`500
`
`500
`
`500
`
`Comparative
`Example 1
`Comparative
`Example 2
`
`[0032]
`As shown in Table 2, in Embodiments 1 to 5, the second
`canister is filled with honeycomb activated carbon with
`volumes from 20 to 126 ml, individually, where in
`Embodiment 6, the canister is filled with granular activated
`carbon with a grain size of 3 mm, and in Embodiment 7,
`the canister is filled with crushed activated carbon with a
`mesh of 8 through 28. Moreover, in Embodiments 8
`through 10, filling is with honeycomb activated carbon
`with a value of 40 ml, and orifices with the opening
`diameters shown in Table 2 were inserted at the midpoint
`of the pipes connecting the first canisters to the second
`canisters.
`[0033]
`Furthermore, for comparison with Embodiments 1 to 5,
`the fuel evaporation preventing devices of Comparative
`Examples 1 and 2 were not provided with the second
`canister, and the gas at the exit of the first canister was
`released directly.
`
`50.0
`
`190
`
`50.1
`
`180
`
`720
`
`970
`
`1200
`
`52
`
`48.2
`
`48.2
`
`48.2
`
`48.0
`
`49.5
`
`300
`
`320
`
`380
`
`820
`850
`
`990
`
`1130
`
`1680
`
`2000
`
`2600
`
`4200
`
`6000
`
`200
`
`4200
`
`7300
`
`14000
`
`100
`
`12000
`13000
`
`18000
`20000
`
`24000
`
`27000
`
`47
`
`48
`
`[0034]
`Gasoline vapors were adsorbed in these fuel evaporation
`preventing devices until the breakthrough point, after which
`300 liters of air (300 times the volume of the activated
`carbon of the first canister) were passed through, and the
`gasoline adsorbed by these devices was purged. The
`devices were then left in air for 24 hours at a temperature of
`30°C, and after a state was reached in which the residual
`gasoline had moved within the fuel evaporation preventing
`device due to adsorption equilibration, the concentration of
`gasoline that was leaked when air was flowed at a rate of 1
`liter/min. from the gasoline vapor entrance side of the
`device was measured. The measurement results thereof,
`the butane W. C. (working capacity) of the filled activated
`carbon layer, and the pressure loss of the device when the
`air flow rate was 20 liters/min. are shown together in Table
`2.
`[0035]
`
`

`

`Note that the butane W. C. was measured by the
`following method. A metal canister was filled with 1 liter
`of dried activated carbon, absorption of n-butane of 99.0%
`or higher was caused through down-flow at a temperature
`of 25°C at 1 liter/min., and the process was stopped when
`the butane concentration at the exit reached 5000 ppm. The
`increase in mass due to this butane adsorption was defined
`as Wa(g). Following this, air was caused to flow up through
`the canister for 20 minutes at 15 liters/min. at room
`temperature, to cause desorption of the n-butane. The
`decrease in mass due to n-butane desorption was defined as
`Wd(g). The above-described adsorption and desorption
`operation was repeated six times, and in that process, the
`Wa and Wd values for the fourth, fifth, and sixth times
`were used to calculate the butane W. C. using the
`Expression 1:
`[0036]
`[EXPRESSION 1]
`
`Butane W.C. = [(Wa-4+Wa-5+Wa-6) + (Wd-
`4+Wd-5+Wd-6)]/6
`
`[0037]
`From this result, and from the gasoline concentration of
`the air that was leaked when the volume of the honeycomb
`activated carbon of Embodiments 1 to 5 was varied, a
`significant effect was observed even when the volume of
`the activated carbon of the second canister was just 2% of
`the volume of the first canister, and it was observed that a
`full effect is produced if the volume of the honeycomb
`activated carbon is 4% to 8%, and that there was a tendency
`for a substantial reduction in the amount of increase at 12%
`or more. Moreover, no increase in pressure loss was
`observed even if the amount of honeycomb activated
`carbon that was filled into the second canister was varied
`within this range. No improvement in the butane W. C. of
`the first canister was observed, and the result was the same
`as when a second canister filled with honeycomb activated
`carbon was not used.
`[0038]
`In Embodiment 6, when granulated carbon of a grain size
`of 3 mm was used instead of the honeycomb activated
`carbon, there was slight increase in the pressure loss, but
`there was a tendency for increased butane W. C., and the
`gasoline concentration in the air that was leaked was
`reduced. In Embodiment 7, when crushed carbon of an 8
`through 28 mesh was used instead of the honeycomb
`activated carbon, the butane W. C. was increased and the
`gasoline concentration was reduced, but, conversely, a
`tendency for a substantial increase in pressure loss was
`observed.
`[0039]
`In Embodiments 8 through 10, honeycomb activated
`carbon with a volume of 40 ml was used in the second
`canister, the same as in Embodiment 1, and orifices of
`respective hole diameters of between 2 and 6 mm were
`inserted at the midpoint of the pipe, with an internal
`diameter of 10 mm and a length of 20 mm, that connected
`the first canister and the second canister. In Embodiment 8,
`when the hole diameter was 2 mm, an adequate effect was
`observed in reducing the gasoline concentration in the
`leaked air, but a tendency was observed for the pressure
`loss to be rather high, and in Embodiments 9 and 10, when
`orifices with hole diameters of 4 and 6 mm were used, the
`
`Japanese Unexamined Patent Application Publication H10-37812
`(6)
`
`effect of reducing the gasoline concentration in the leaked
`air was poor.
`[0040]
`In Comparative Example 1, in a case in which a second
`canister is not attached, a sharp increase in the gasoline
`concentration in the air leaked as time elapses was
`observed. Moreover, in Comparative Example 2, in a case
`where instead of attaching a second canister the first
`canister was additionally filled with the same amount of
`granulated carbon as the honeycomb activated carbon of
`the second canister of Embodiment 1, the butane W. C.
`improved, but essentially no effect of decreasing the
`gasoline concentration of the air that is leaked was
`essentially observed. Note that no increase in pressure loss
`was observed either.
`[0041]
`[EFFECTS OF THE INVENTION]
`The fuel evaporation preventing device of the present
`invention is provided with a small-volume second canister
`that is connected in series to an ordinary canister by a pipe,
`and basically an orifice is provided in the pipe that connects
`the first and second canisters. The use of a fuel evaporation
`preventing device having such a configuration causes a
`significant suppression in the speed at which the gasoline
`that is adsorbed in the canister moves due to adsorption
`equilibration to the air discharge port through the
`concentration gradient, enabling a reduction in the
`evaporative loss of gasoline to about 1/10, even if an
`automobile is stopped for an extended period of time,
`without increasing the volume of the canister and without
`an increase in the performance of the activated carbon.
`[BRIEF DESCRIPTIONS OF THE DRAWINGS]
`FIG.1 shows an example of the concentration
`distribution of gasoline adsorbed in an ordinary canister.
`FIG. 2 shows a cross-sectional view of a canister used in
`the measurements of FIG.1.
`FIG. 3 shows a cross-sectional view of one example of a
`canister.
`FIG. 4 shows a configuration diagram of one
`embodiment of the fuel evaporation
`[Explanation of Codes]
`1: Gasoline concentration distribution curve after
`gasoline vapor adsorption
`2: Gasoline concentration distribution curve after resting
`3: Gasoline concentration distribution curve after
`desorption
`4: Location of gasoline concentration measurement in
`the activated carbon layer
`5: Location of gasoline concentration measurement in
`the activated carbon layer
`6: Location of gasoline concentration measurement in
`the activated carbon layer
`7: Location of gasoline concentration measurement in
`the activated carbon layer
`8: Location of gasoline concentration measurement in
`the activated carbon layer
`9: Canister
`10: Gas discharge port of the canister
`11: Activated carbon filled layer
`12: Pipe
`13: Second canister
`14: Honeycomb activated carbon
`
`
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`

`

`[FIG. 1]
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`[FIG. 3]
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`Japanese Unexamined Patent Application Publication H10-37812
`(7)
`
`
`[FIG. 4]
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`[VERTICAL AXIS] Amount of Gasoline Adsorbed (Wt %)
`[HORIZONTAL AXIS] Sampling Position
`
`[FIG. 2]
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