Patent Publication Number: US-2023144145-A1

Title: Canister

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-181458 filed Nov. 5, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a canister including: a casing internally provided with an adsorbing layer including an adsorbing material capable of adsorbing and desorbing fuel vapor; a tank port provided at one end of the casing and configured to allow the fuel vapor to flow into the casing; a purge port provided at the one end of the casing and configured to allow the fuel vapor to flow out of the casing; and an air port provided at another end of the casing and configured to allow air to flow into and out of the casing. 
     Description of Related Art 
     There is a conventionally-known canister internally provided with an adsorbing layer that is capable of adsorbing and desorbing fuel vapor and is constituted by activated carbon, which is used as an adsorbing material, and a heat storage material including a phase change material that absorbs and releases latent heat according to temperature (see JP 2005-233106M. 
     For example, JP 2001-145832A and JP 2003-311118A disclose, as such a heat storage material including a phase change material, a powdery heat storage material obtained by encapsulating a phase change material such as an aliphatic hydrocarbon, which absorbs and releases latent heat along with a phase change, in microcapsules, and also disclose a latent-heat-storing adsorbing material that is obtained by mixing the powdery heat storage material with an adsorbing material and molding the mixture, or by affixing the powdery heat storage material to a surface of a granular adsorbing material (activated carbon). 
     JP 2005-233106A, JP 2001-145832A, and JP 2003-311118A are examples of related art. 
     In the canister disclosed in JP 2005-233106A, when fuel vapor that has been adsorbed on the activated carbon is to be desorbed, the activated carbon is purged with air that is taken into the canister from ambient air and is used as purge gas to desorb the fuel vapor adsorbed on the activated carbon. At this time, if the adsorbing rate (desorbing rate) of the activated carbon is low, there is a problem in that the concentration of transpired gas (concentration of fuel vapor) in the purge gas cannot be made high. On the other hand, it is possible to increase the concentration of transpired gas in the purge gas with use of activated carbon that has a high adsorbing rate (desorbing rate), but there is a problem in that such activated carbon is expensive, and a desorption amount decreases as a result of a reduction in the temperature due to heat being absorbed through desorption. Also, the concentration of transpired gas in the purge gas sharply decreases as purging progresses, and accordingly, there is a problem in that it is difficult to control the amount of transpired gas sent to the engine through purging. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the above issues, and has an object of providing a canister that can suppress fluctuation of the concentration of transpired gas in purge gas during desorbing operation and improve controllability of purging while maintaining economic efficiency. 
     A canister for achieving the above object is a canister including: 
     a casing internally provided with an adsorbing layer that includes an adsorbing material capable of adsorbing and desorbing fuel vapor; 
     a tank port provided at one end of the casing and configured to allow the fuel vapor to flow into the casing; 
     a purge port provided at the one end of the casing and configured to allow the fuel vapor to flow out of the casing; and 
     an air port provided at another end of the casing and configured to allow air to flow into and out of the casing, the canister being characterized in including: 
     a first adsorbing layer that is provided inside the casing, includes a first adsorbing material as the adsorbing material, and is disposed at a position in contact with the air port at the other end in a flowing direction of the fuel vapor between the one end and the other end; and 
     a second adsorbing layer that is provided inside the casing, includes, as the adsorbing material, a second adsorbing material different from the first adsorbing material, and is disposed closer to the one end than the first adsorbing layer is in the flowing direction, wherein the first adsorbing material adsorbs the fuel vapor at an adsorbing rate that is lower than an adsorbing rate of the second adsorbing material. 
     In order to keep the concentration of transpired gas in purge gas at a certain level or higher during desorbing operation while suppressing an increase in the production cost of the canister, the inventors of the present invention focused on an adsorbing rate at which an adsorbing material constituting an adsorbing layer adsorbs fuel vapor, and completed the present invention. 
     Here, a relationship between an adsorbing rate (desorbing rate) and an adsorption amount of an adsorbing layer K (adsorbing material) including a first adsorbing layer K 1  and a second adsorbing layer K 2  will be described with reference to  FIG.  2   . In  FIG.  2   , the adsorbing layer K is divided into four regions (a region between X0 and X1, a region between X1 and X2, a region between X2 and X3, and a region between X3 and X4) in a flowing direction X in which purge gas PJ (gas containing transpired gas (fuel vapor J: shown in  FIG.  1   )) flows during desorbing operation, and adsorption amounts of the fuel vapor J adsorbed on the adsorbing material in the respective regions are expressed with color depths of triangle marks. A larger adsorption amount is expressed with a deeper color. Furthermore, the vertical axis in  FIG.  2    shows time t, and  FIG.  2    shows a process of desorption of the fuel vapor J from the adsorbing layer K gradually progressing from a time t 0  that is immediately before start of desorption via a time t 1  at which desorption is started, to a time t 2  at which desorption ends. 
     As shown in  FIG.  2   , the fuel vapor J is usually desorbed from the entire adsorbing layer K along the flow of the purge gas PJ in an early stage of purging (e.g., a time near the start t 1  of desorption). Therefore, the concentration of transpired gas in the purge gas PJ is high. On the other hand, in a later stage of purging (e.g., a time immediately before the end t 2  of desorption), desorption of the fuel vapor J from the adsorbing layer K has been completed on the upstream side (the other end side of the casing) in the flowing direction X of the purge gas PJ, and the fuel vapor J is desorbed from the adsorbing layer K on the downstream side (the one end side of the casing), and therefore, the concentration of transpired gas in the purge gas PJ decreases. As described above, the concentration of transpired gas in the purge gas PJ significantly fluctuates through the entire purging process, and controllability of purging is imp aired. 
     According to the characteristic configuration described above, the second adsorbing material on the downstream side (the one end side of the casing) in the flowing direction X of the purge gas PJ adsorbs fuel vapor at an adsorbing rate (desorbing rate) that is higher than the adsorbing rate (desorbing rate) of the first adsorbing material on the upstream side (the other end side of the casing). Accordingly, an amount of the fuel vapor J desorbed from the second adsorbing material can be increased to improve the concentration of transpired gas in the purge gas PJ particularly in the later stage of purging, and thus it is possible to suppress fluctuation of the concentration of transpired gas in the purge gas PJ throughout the entire purging process, and improve controllability of purging. 
     Furthermore, economic efficiency can be improved according to this characteristic configuration because an adsorbing material that has a low adsorbing rate (desorbing rate) and is relatively inexpensive is adopted as the first adsorbing material from which fuel vapor J is completely desorbed in the early stage of purging and that does not contribute to suppressing fluctuation of the concentration of transpired gas in the purge gas PJ. 
     As described above, it is possible to realize a canister that can suppress fluctuation of the concentration of transpired gas in the purge gas during desorbing operation and improve controllability of purging while maintaining economic efficiency. 
     In another characteristic configuration of the canister, the first adsorbing material has an equilibrium adsorption capacity with respect to the fuel vapor that is smaller than an equilibrium adsorption capacity of the second adsorbing material with respect to the fuel vapor. 
     When the equilibrium adsorption capacity of the first adsorbing material with respect to the fuel vapor is smaller than the equilibrium adsorption capacity of the second adsorbing material with respect to the fuel vapor as in this characteristic configuration, economic efficiency can be improved compared with a case where all adsorbing materials used are relatively expensive adsorbing materials having a large equilibrium adsorption capacity. Also, it is possible to effectively suppress a reduction in the concentration of transpired gas in the purge gas in the later stage of purging. 
     In another characteristic configuration of the canister, the first adsorbing material has an average particle diameter that is larger than an average particle diameter of the second adsorbing material. 
     When the second adsorbing material has a small particle diameter as in this characteristic configuration, particles of the second adsorbing material have a large external surface area per unit volume, and accordingly, particles of the fuel vapor to be adsorbed are likely to reach the surface of the second adsorbing material. Furthermore, the fuel vapor that has reached the surface of the second adsorbing material moves through the second adsorbing material. When the second adsorbing material has a small particle diameter, the distance by which the fuel vapor moves through the second adsorbing material is short, and accordingly, the fuel vapor is likely to spread throughout the inside of the second adsorbing material. For these reasons, the second adsorbing material has a high adsorbing rate (desorbing rate), and accordingly, it is possible to effectively suppress a reduction in the concentration of transpired gas in the purge gas in the later stage of purging. Furthermore, the first adsorbing material has a relatively large average particle diameter, and accordingly, it is possible to suppress a pressure loss when the fuel vapor and air are passed through the canister. 
     In another characteristic configuration of the canister, 
     the first adsorbing layer and the second adsorbing layer include a heat storage material including a phase change material that absorbs and releases latent heat according to a temperature change, and 
     the heat storage material has an average particle diameter of 0.9 mm or more and 1.6 mm or less, and the adsorbing material is activated carbon having a particle size distribution in which particles having a particle size of 0.71 mm or more and 2.36 mm or less constitute 95 wt % or more. 
     According to this characteristic configuration, the heat storage material having an average particle diameter of 0.9 mm or more and 1.6 mm or less is used, and activated carbon having a particle size distribution in which particles having a particle size of 0.71 mm or more and 2.36 mm or less constitute 95 wt % or more is used as the adsorbing material. Therefore, it is possible to improve purging performance of the adsorbing material having the small particle diameter. Also, average particle diameters of the heat storage material and the adsorbing material are approximate to each other, and therefore, classification can be suppressed. 
     In another characteristic configuration of the canister, the average particle diameter of the heat storage material is 0.6 times or more and 1.3 times or less of an average particle diameter of the adsorbing material. 
     According to this characteristic configuration, the average particle diameters of the heat storage material and the adsorbing material are approximate to each other, and therefore, classification can be favorably suppressed. 
     In another characteristic configuration of the canister, the first adsorbing layer has a content rate of the heat storage material that is higher than a content rate of the heat storage material in the second adsorbing layer. 
     According to this characteristic configuration, the content rate of the heat storage material is high in the first adsorbing layer that is on the upstream side (the other end side of the casing), and therefore, it is possible to reduce the amount of residual fuel that is not desorbed through purging from the first adsorbing layer in the vicinity of the air port, and consequently, it is possible to reduce the amount of fuel vapor leaking to the outside while the vehicle is parked for a long time, and DBL (Diurnal Breathing Loss) performance can be improved. 
     In another characteristic configuration of the canister, the first adsorbing layer and the second adsorbing layer include a heat storage material including a phase change material that absorbs and releases latent heat according to a temperature change, and 
     the heat storage material included in the second adsorbing layer has a melting point that is lower than a melting point of the heat storage material included in the first adsorbing layer. 
     According to this characteristic configuration, cold heat generated along with desorption of the fuel vapor J is transmitted from the upstream side (the other end side of the casing) toward the downstream side (the one end side of the casing) in the flowing direction of the purge gas PJ during purging, and accordingly, the temperature is more likely to decrease on the downstream side. 
     According to this characteristic configuration, in particular, the melting point of the heat storage material included in the second adsorbing layer that is on the downstream side is set low, and accordingly, cooling can be suppressed in the second adsorbing layer whose temperature is likely to decrease, and it is possible to effectively suppress a reduction in the concentration of transpired gas in the purge gas particularly in the later stage of purging. 
     In another characteristic configuration of the canister, the heat storage material included in the first adsorbing layer has a melting point of 36° C. or higher, and the heat storage material included in the second adsorbing layer has a melting point lower than 36° C. 
     Cold heat generated along with desorption of the fuel vapor J is transmitted from the upstream side (the other end side of the casing) toward the downstream side (the one end side of the casing) in the flowing direction of the purge gas PJ during purging, and accordingly, the temperature is more likely to decrease on the downstream side. 
     According to this characteristic configuration, the melting point of the heat storage material included in the second adsorbing layer that is on the downstream side is as low as less than 36° C., and accordingly, cooling can be suppressed in the second adsorbing layer whose temperature is likely to decrease, and consequently, it is possible to effectively suppress a reduction in the concentration of transpired gas in the purge gas particularly in the later stage of purging. 
     In another characteristic configuration of the canister, the first adsorbing layer and the second adsorbing layer include a molded heat storage material molded from microcapsules in which a phase change material that absorbs and releases latent heat according to a temperature change is encapsulated, the molded heat storage material has a columnar shape and includes a first end surface on a first side of a column axis of the molded heat storage material and a second end surface on a second side of the column axis as viewed in a direction orthogonal to the column axis, and an average value of R 1 /rand R 2 /r is 0.57 or more, where R 1  represents a length of a curved surface of a first edge portion, which connects the first end surface and a circumferential side surface around the column axis, in a radial direction of the first end surface, R 2  represents a length of a curved surface of a second edge portion, which connects the second end surface and the circumferential side surface, in a radial direction of the second end surface, and r represents a radius of a cross section of the molded heat storage material taken along the direction orthogonal to the column axis. 
     According to this characteristic configuration, the molded heat storage material has the columnar shape in which the average value of R 1 /rand R 2 /r is 0.57 or more, i.e., a shape including rounded corners, and therefore, miscibility of the molded heat storage material with the adsorbing material (dispersibility of the molded heat storage material in the adsorbing material) can be improved. 
     In the canister described above, the heat storage material preferably has a latent heat of 150 J/g or more and 200 J/g or less. Also, the heat storage material preferably has a bulk density of 0.40 g/mL or more and 0.60 g/mL or less. 
     According to this characteristic configuration, in particular, even when a relatively large amount of heat of adsorption is generated by the second adsorbing material included in the second adsorbing layer and having the high adsorbing rate, the heat of adsorption is favorably stored in the heat storage material, and accordingly, the adsorption amount during adsorption can be increased, and the heat can be favorably released when the fuel vapor is desorbed from the adsorbing material, and thus purging performance during purging can also be improved. 
     In another characteristic configuration of the canister, a mass ratio of the heat storage material to the first adsorbing material in the first adsorbing layer is 0.15 or more and 0.80 or less, and a mass ratio of the heat storage material to the second adsorbing material in the second adsorbing layer is 0.05 or more and 0.50 or less. 
     According to this characteristic configuration, the mass ratio of the heat storage material to the first adsorbing material is as large as 0.15 or more and 0.80 or less in the first adsorbing layer that is on the upstream side (the other end side of the casing) in the flowing direction of the fuel vapor during fuel supply, for example, and accordingly, the heat generated along with adsorption can be favorably stored in the heat storage material contained at the high mass ratio in the first adsorbing layer, and the first adsorbing material can effectively exhibit its adsorbing ability. 
     Also, the mass ratio of the heat storage material to the second adsorbing material in the second adsorbing layer is as small as 0.05 or more and 0.50 or less, and thus it is possible to improve economic efficiency by reducing the mass ratio of the heat storage material to the second adsorbing material having a high adsorbing rate. 
     Note that according to the characteristic configuration described above, the content rate of the heat storage material is high in the first adsorbing layer that is on the upstream side (the other end side of the casing) as described above, and accordingly, the content of the first adsorbing material can be relatively reduced in the first adsorbing layer in the vicinity of the air port to reduce the adsorption amount in the vicinity of the air port, and consequently, it is possible to reduce the amount of fuel vapor leaking to the outside while the vehicle is parked for a long time, and DBL (Diurnal Breathing Loss) performance can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram of an automotive vehicle including a canister according to an embodiment. 
         FIG.  2    is a conceptual diagram showing a function of the canister according to an embodiment. 
         FIG.  3    is a schematic configuration diagram of a heat storage material according to an embodiment. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A canister according to an embodiment of the present invention can suppress fluctuation of the concentration of transpired gas in purge gas during desorbing operation and improve controllability of purging while maintaining economic efficiency. 
     The following describes the canister with reference to the drawings. 
     As shown in  FIG.  1   , a canister  100  according to the present embodiment includes a casing  10  that is internally provided with an adsorbing layer K capable of adsorbing fuel vapor J, and the canister  100  can be suitably applied to a commonly-known automotive vehicle. The automotive vehicle according to the present embodiment includes: a fuel tank  12  for storing fuel such as gasoline; the canister  100  configured to adsorb fuel vapor J vaporized in the fuel tank  12  particularly during fuel supply (during ORVR) and introduce the adsorbed fuel vapor J into an engine  11 ; and the engine  11  configured to obtain shaft output by combusting fuel including the fuel vapor J introduced from the canister  100  and combustion air in a combustion chamber (not shown). 
     As shown in  FIG.  1   , the canister  100  includes: the casing  10 ; a tank port  10   c  that communicates with the fuel tank  12  and is configured to receive fuel vapor J from the fuel tank  12 ; a purge port  10   b  configured to send fuel vapor J desorbed in the canister  100  during desorbing operation to the engine  11 ; and an air port  10   a  that communicates with ambient air. The tank port  10   c  and the purge port  10   b  are provided at one end in a flowing direction X, and the air port  10   a  is provided at another end in the flowing direction X. The purge port  10   b  communicates with the engine  11  via a purge flow path  11   a . The engine  11  and the fuel tank  12  communicate with each other via a connecting path  13   a.    
     The adsorbing layer K contains an adsorbing material Q that adsorbs and desorbs the fuel vapor J and a molded heat storage material T that is molded from microcapsules in which a phase change material that absorbs and releases latent heat according to temperature is encapsulated. 
     As shown in  FIG.  1   , the adsorbing layer K includes: a first adsorbing layer K 1  that includes a first adsorbing material Q 1  as the adsorbing material Q and is in contact with the air port  10   a  at the other end in the flowing direction X of purge gas PJ between the one end and the other end; and a second adsorbing layer K 2  that includes a second adsorbing material Q 2  as the adsorbing material Q different from the first adsorbing material Q 1  and that is on the one end side relative to the first adsorbing layer K 1 . Note that in the present embodiment, the second adsorbing layer K 2  is in contact with the purge port  10   b  and the tank port  10   c  at the one end, and the first adsorbing layer K 1  and the second adsorbing layer K 2  are separated by a predetermined separation film or the like. 
     Here, the first adsorbing material Q 1  has a lower adsorbing rate with respect to the fuel vapor J than the second adsorbing material Q 2 . 
     The molded heat storage material T is obtained by molding a heat storage material together with a binder into granules, for example. The heat storage material is obtained by encapsulating a phase change material that absorbs and releases latent heat according to a temperature change in microcapsules. It is possible to use a known heat storage material in the form of microcapsules such as that disclosed in JP 2001-145832A or and JP 2003-311118A. 
     The phase change material is constituted by an organic compound and an inorganic compound having a melting point of 10° C. or higher and 80° C. or lower, for example, and examples of the phase change material include: linear aliphatic hydrocarbons such as tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, henicosane, and docosane; natural wax; petroleum wax; hydrated inorganic compounds such as LiNO 3 .3H 2 , Na 2 SO 4 .10H 2 O, and Na 2 HPO 4 .12H 2 O; fatty acids such as capric acid and lauric acid; higher alcohols having 12 to 15 carbon atoms; and esters such as methyl palmitate and methyl stearate. Two or more compounds selected from the above-listed compounds may be used together as the phase change material. 
     Microcapsules that are formed by using any of these compounds as a core material through a known method such as a coacervation method or an in-situ method (interfacial reaction method) can be used. A known material such as melamine, gelatin, or glass can be used to form outer shells of the microcapsules. The heat storage material in the form of microcapsules preferably has a particle diameter of about several micrometers to several tens of micrometers. If the microcapsules are too small, the proportion of the outer shells constituting the capsules increases, and the proportion of the phase change material that repeatedly melts and solidifies relatively decreases, and therefore, the amount of heat stored per unit volume of the powdery heat storage material decreases. On the other hand, if the microcapsules are too large, the capsules need to have certain strength, and accordingly, the proportion of the outer shells constituting the capsules increases, and the amount heat stored per unit volume of the powdery heat storage material decreases. 
     The powdery heat storage material is molded together with a binder into a substantially cylindrical shape to obtain a granular molded heat storage material T. Various binders can be used, but a thermosetting resin such as a phenol resin or an acrylic resin is preferably used from the viewpoint of thermal stability, stability against a solvent, and strength, which are required when the binder is used in the canister. The granular molded heat storage material T is mixed with the adsorbing material Q, which also has a granular shape, and the mixture is used to obtain a heat storing effect. 
     The molded heat storage material T preferably has a latent heat of 150 J/g or more and 200 J/g or less. 
     Various known adsorbing materials can be used as the adsorbing material Q. For example, activated carbon can be used as the adsorbing material Q. Granules individually molded or crushed to have predetermined dimensions can be used as the adsorbing material Q. 
     On the other hand, the molded heat storage material T that is molded into a columnar shape through extrusion molding as described above as shown in  FIG.  3   , for example, has a first end surface M 2  on a first side of a column axis P 2  and a second end surface M 3  on a second side of the column axis P 2  as viewed in a direction orthogonal to the column axis P 2 , and an average value of R 1 /rand R 2 /r is 0.57 or more, where R 1  represents the length of a curved surface of a first edge portion M 2   a , which connects the first end surface M 2  and a circumferential side surface M 1  around the column axis P 2 , in a radial direction of the first end surface M 2 , R 2  represents the length of a curved surface of a second edge portion M 3   a , which connects the second end surface M 3  and the circumferential side surface M 1 , in a radial direction of the second end surface M 3 , and r represents the radius of a cross section of the molded heat storage material T taken along the direction orthogonal to the column axis P 2 . 
     By adopting such a shape having rounded corners, it is possible to improve miscibility with the adsorbing material Q (dispersibility of the molded heat storage material T in the adsorbing material Q). 
     Note that the molded heat storage material T is shaped in such a manner that the length of the molded heat storage material T along the column axis P 2  and the diameter of the cross section orthogonal to the column axis P 2  do not differ very much from each other. 
     The molded heat storage material T and the granular adsorbing material Q preferably have the same size as far as possible or have approximately the same size in order to suppress separation of the molded heat storage material T and the adsorbing material Q from each other with the passage of time and appropriately secure a gas flow path. 
     However, the first adsorbing material Q 1  preferably has an average particle diameter that is larger than an average particle diameter of the second adsorbing material Q 2 . Furthermore, the molded heat storage material T preferably has an average particle diameter (diameter  2   r  of the cross section orthogonal to the column axis P 2  of the columnar shape shown in  FIG.  3   ) of 0.9 mm or more and 1.6 mm or less, and the adsorbing material Q preferably has an average particle diameter of 1.0 mm or more and 1.8 mm or less. Furthermore, both the first adsorbing material Q 1  and the second adsorbing material Q 2  used as the adsorbing material Q are preferably activated carbon having a particle size distribution in which particles having a particle size of 0.71 mm or more and 2.36 mm or less constitute 95 wt % or more. 
     Also, the average particle diameter ( 2   r  in  FIG.  3   ) of the molded heat storage material T is preferably 0.6 times or more and 1.3 times or less of the average particle diameter of the adsorbing material Q. 
     Also, the first adsorbing material Q 1  preferably has an equilibrium adsorption capacity with respect to the fuel vapor J that is smaller than an equilibrium adsorption capacity of the second adsorbing material Q 2  with respect to the fuel vapor J, and the first adsorbing layer K 1  preferably has a content rate of the molded heat storage material T that is higher than a content rate of the molded heat storage material T in the second adsorbing layer K 2 . 
     The molded heat storage material T preferably has a bulk density of 0.4 g/mL or more and 0.6 g/mL or less. The adsorbing material Q desirably has a bulk density that is 0.2 times or more and 1.1 times or less of the bulk density of the molded heat storage material T, preferably 0.3 times or more and equal to or less than the bulk density of the molded heat storage material T, and more preferably 0.4 times or more and 0.9 times or less of the bulk density of the molded heat storage material T. If the bulk density of the adsorbing material Q largely differs from the bulk density of the molded heat storage material T, the adsorbing material Q or the molded heat storage material T that is heavier than the other moves downward within the casing when the canister is mounted in a vehicle or the like and vibration is applied to the canister, and separation of the adsorbing material Q and the molded heat storage material T progresses. 
     Furthermore, it is preferable that a mass ratio of the molded heat storage material T to the first adsorbing material Q 1  in the first adsorbing layer K 1  is 0.15 or more and 0.80 or less and a mass ratio of the molded heat storage material T to the second adsorbing material Q 2  in the second adsorbing layer K 2  is 0.05 or more and 0.50 or less. By adopting this configuration in which the mass ratio of the molded heat storage material T to the adsorbing material Q is higher in the first adsorbing layer K 1  than in the second adsorbing layer K 2 , it is possible to suppress a temperature increase on the side of the canister that is close to ambient air and at which the temperature is likely to increase during fuel supply (ORVR) and thus prevent a reduction in adsorptivity. 
     Moreover, since the content rate of the molded heat storage material T is high in the first adsorbing layer K 1  that is on the upstream side (the other end side of the casing), the content of the first adsorbing material Q 1  can be relatively reduced in the first adsorbing layer K 1  in the vicinity of the air port  10   a  to reduce the adsorption amount in the vicinity of the air port  10   a , and consequently, it is possible to reduce the amount of fuel vapor J leaking to the outside due to a temperature difference between the inside and the outside while the vehicle is parked for a long time, and DBL (Diurnal Breathing Loss) performance can be improved. 
     Additionally, the molded heat storage material T included in the second adsorbing layer K 2  preferably has a melting point that is lower than a melting point of the molded heat storage material T included in the first adsorbing layer K 1 , and it is preferable that the melting point of the molded heat storage material T included in the first adsorbing layer K 1  is 36° C. or higher and the melting point of the molded heat storage material T included in the second adsorbing layer K 2  is lower than 36° C. According to this configuration, in particular, the melting point of the molded heat storage material T included in the second adsorbing layer K 2  on the downstream side in the flowing direction X of purge gas PJ during purging is as low as less than 36° C., and accordingly, it is possible to suppress cooling in the second adsorbing layer K 2  whose temperature is likely to decrease, and consequently it is possible to effectively suppress a reduction in the concentration of transpired gas in the purge gas particularly in a later stage of purging. 
     As shown in  FIG.  1   , the casing  10  of the canister  100  preferably has dimensions and a shape designed such that a ratio L/D is 2.5 or less, where L represents the length of the adsorbing layer in the flowing direction X of purge gas PJ (including fuel vapor J) in the casing  10 , and D represents the diameter of a cross section of the casing  10 , which is taken along a direction orthogonal to the flowing direction X of the purge gas PJ and assumed to be a perfect circle. With this configuration, it is possible to suppress a pressure loss to a certain level or less even when the adsorbing material Q and the molded heat storage material T have small average particle diameters. 
     OTHER EMBODIMENTS 
     (1) In the above embodiment, the canister  100  is intended to be used during fuel supply (ORVR), but the canister  100  can be used not only during fuel supply but also while the vehicle is parked, stopped, or traveling. 
     (2) In the above embodiment, a configuration example is described in which the adsorbing layer K includes the first adsorbing layer K 1  and the second adsorbing layer K 2 , but the adsorbing layer K may further include an adsorbing layer other than the first adsorbing layer K 1  and the second adsorbing layer K 2 . 
     Also, a configuration example is described in which the first adsorbing layer K 1  and the second adsorbing layer K 2  are separated from each other by the separation film, but a configuration is also possible in which the separation film is not provided. 
     Furthermore, a configuration is also possible in which the adsorbing material Q is provided between the first adsorbing layer K 1  and the second adsorbing layer K 2  in such a manner that the adsorbing rate increases toward the second adsorbing layer K 2 . 
     (3) In the above embodiment, the average particle diameter of the first adsorbing material Q 1  is larger than the average particle diameter of the second adsorbing material Q 2 . 
     However, the average particle diameter of the first adsorbing material Q 1  may be approximate or equal to, or smaller than the average particle diameter of the second adsorbing material Q 2  as long as the first adsorbing material Q 1  adsorbs the fuel vapor J at a lower adsorbing rate than the second adsorbing material Q 2 . 
     Also, instead of adopting the configuration in which the average particle diameter of the first adsorbing material Q 1  is larger than the average particle diameter of the second adsorbing material Q 2 , it is possible to adopt a configuration in which the first adsorbing material Q 1  has a larger specific surface area than the second adsorbing material Q 2 . 
     (4) In the above embodiment, a configuration is described in which the adsorbing layer K includes the molded heat storage material T, but a configuration is also possible in which the molded heat storage material T is not provided. Also, the molded heat storage material T may have various shapes such as a rectangular tube-like shape, other than the cylindrical shape. 
     (5) In the above embodiment, the equilibrium adsorption capacity of the first adsorbing material Q 1  with respect to the fuel vapor J is smaller than the equilibrium adsorption capacity of the second adsorbing material Q 2  with respect to the fuel vapor J. 
     However, the equilibrium adsorption capacity of the first adsorbing material Q 1  with respect to the fuel vapor J may be approximate or equal to, or larger than the equilibrium adsorption capacity of the second adsorbing material Q 2  with respect to the fuel vapor J as long as the first adsorbing material Q 1  adsorbs the fuel vapor J at a lower adsorbing rate than the second adsorbing material Q 2 . 
     (6) In the above embodiment, the content rate of the molded heat storage material T in the first adsorbing layer K 1  is higher than the content rate of the molded heat storage material T in the second adsorbing layer K 2 . 
     However, the content rate of the molded heat storage material T in the first adsorbing layer K 1  may be equal to or lower than the content rate of the molded heat storage material T in the second adsorbing layer K 2 . 
     Note that the configurations disclosed in the above embodiment (including the other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments as long as no contradiction arises. Also, the embodiments disclosed in the present specification are examples, and embodiments of the present invention are not limited to the disclosed embodiments, and it is possible to modify the embodiments as appropriate within a scope not departing from the object of the present invention. 
     The canister according to the present invention can be effectively used as a canister that can suppress fluctuation of the concentration of transpired gas in purge gas during desorbing operation and improve controllability of purging while maintaining economic efficiency. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
         
           
               10  Casing 
               10   a  Air port 
               10   b  Purge port 
               10   c  Tank port 
               100  Canister 
             J Fuel vapor 
             K Adsorbing layer 
             K 1  First adsorbing layer 
             K 2  Second adsorbing layer 
             M 1  Circumferential side surface 
             M 2  First end surface 
             M 3  Second end surface 
             M 2   a  First edge portion 
             M 3   a  Second edge portion 
             P 2  Column axis 
             PJ Purge gas 
             Q Adsorbing material 
             Q 1  First adsorbing material 
             Q 2  Second adsorbing material 
             T Molded heat storage material 
             X Flowing direction