JP4209884B2 - Canister - Google Patents

Description

  The present invention relates to a canister for an evaporative fuel processing apparatus of an internal combustion engine, and more particularly to a canister that can suppress the emission of evaporative fuel to the atmosphere.

  Conventionally, evaporative fuel generated from a fuel tank while the engine is stopped is adsorbed to an adsorbent accommodated in a canister vessel, and after the engine is started, the adsorbed evaporative fuel is desorbed (purged) by an intake pipe negative pressure and burned. There is a canister for an evaporative fuel treatment device that burns in a chamber.

  In this canister, when the engine is stopped, the evaporated fuel flowing from the fuel tank cannot be adsorbed, and a so-called blow-through phenomenon occurs in which it is diffused to the atmosphere from the atmosphere port for introducing the atmosphere. This blow-through is caused when the vehicle is left in a high temperature atmosphere for a predetermined time after the engine is stopped after driving the vehicle, so that the evaporated fuel remaining in the adsorbent evaporates and spreads to the adsorbent layer on the downstream atmospheric port side. After the so-called diffusion phenomenon occurs, the vaporized fuel flowing from the fuel tank pushes the diffused vaporized fuel and diffuses it from the atmospheric port to the atmosphere.

  This blow-through frequently occurs in a conventional canister that uses activated carbon A (details will be described later) as an adsorbent, which has a characteristic that a large amount of evaporated fuel is adsorbed in order to make the canister compact. FIG. 7 is a graph showing the blow-through amount with respect to the inflow amount of the evaporated fuel from the fuel tank, and FIG. 8 is a longitudinal sectional view of the canister of the prior art 1. The graph of FIG. 7 is shown as a result of tests performed according to the test sequence shown in the figure. That is, first, the canister 31 in FIG. 8 is purged from the breakthrough state for a predetermined time. By repeating this, the fuel vapor is stabilized and the remaining amount is kept constant. Thereafter, the fuel is left in a high temperature state, and after 36 hours, the evaporated fuel from the fuel tank 9 flowing into the canister 31 is assumed, and 15 g of evaporated fuel per hour is supplied to the tank port 2d of the canister 31. Under these conditions, the blow-through amount from the atmospheric port 2h with respect to the inflow amount is measured. The blow-through amount in the prior art 1 shown in FIG. 8 using only activated carbon A (5a) as the adsorbent is as large as about 140 mg when the inflow amount of evaporated fuel from the fuel tank 9 is 80 g. This is because the low-boiling components in the evaporated fuel that remain without being purged at the back of the pores of the activated carbon evaporate while they are left in the high-temperature atmosphere and fill the downstream adsorbent layer by the diffusion phenomenon. It is considered that the fuel is pushed out by the evaporated fuel flowing from the fuel tank 9 and blown into the atmosphere.

Therefore, a canister as shown in FIG. 9 is known as an improved technique (see Patent Document 1). This is referred to as Conventional Technology 2. This prior art 2 has a plurality of activated carbon layers for adsorbing fuel, activated carbon having a weak fuel adsorbing power and a large effective adsorption amount, on the communication port 25 side of the communication passage 25 to the fuel tank and on the communication port 22 side to the engine intake system. The activated carbon layer 20 is formed, the fuel adsorbing power is strong, the effective adsorption amount of the fuel is small, but the activated carbon hardly causes breakthrough of the fuel before the saturated state of the adsorption action. An activated carbon layer 21 is formed on the side through a wire mesh 24, and most of the fuel vapor provided from the communication passage 25 to the fuel tank is adsorbed by the activated carbon layer 20 on the communication port 25a side. Since only a part of the vapor that broke through the activated carbon layer is adsorbed by the activated carbon layer 21 on the opening 23 side, the fuel vapor is surely adsorbed by the activated carbon layer.
Japanese Utility Model Publication No. 57-68163

  However, as in the prior art 2 (Patent Document 1), activated carbon (activated carbon A in the present application) having a weak fuel adsorbing power (hereinafter referred to as holding power) and a large effective adsorbing amount of fuel and a strong fuel holding power. In the canister in combination with the activated carbon having a small effective adsorption amount (activated carbon C in the present application), as shown in FIG. 7, the blow-through amount at the inflow amount of evaporated fuel from the tank port is about 65 mg. Although it is greatly reduced, it is still insufficient to reduce the blow-through after being left to the target value (50 mg) or less. As shown in FIG. 6, the characteristics of the activated carbon A and activated carbon C described above are high in the remaining amount (hereinafter abbreviated as “residual amount”) of the low-boiling component in the evaporated fuel after purging because of the high temperature. There is a diffusion phenomenon when left unattended, and it is thought that it will be pushed out by evaporated fuel flowing in from the tank port later and blown into the atmosphere.

  Accordingly, an object of the present invention is to provide a canister that can suppress the diffusion phenomenon in the adsorbent layer of the canister as much as possible, reliably adsorb the evaporated fuel flowing in, and suppress the blow-through to the atmosphere. It is.

In order to solve the above-mentioned problem, the invention according to claim 1 is the canister in which the adsorbent layer is divided into the first adsorbent layer and the second adsorbent layer by the partition walls and arranged in series. The adsorbent layer of the first layer is divided into two by a filter or a plate , and the adsorbed fuel is adsorbed to the first adsorbent layer from the activated carbon of the adsorbent layer on the air port side divided as the second layer. A large amount of activated carbon with the same holding power is filled, and the adsorbent layer on the air port side divided in the second layer has less holding capacity for the evaporated fuel than the activated carbon of the first adsorbent layer. Is a canister characterized by being filled with equivalent activated carbon .

According to a second aspect of the invention of claim 1 Symbol placement, the capacity of the adsorbent layer of the second layer of the divided air port side was less 14.3% volume of the total adsorbent layer It is a canister characterized by this.

According to a third aspect of the present invention, in the mounting according to claim 1 or 2 SL, a canister, characterized in that the removal of the said filter or the plate.

  According to the present invention, the adsorbent layer on the air port side of the second layer is filled with activated carbon B having a characteristic that the remaining amount of evaporated fuel after purging is less than that of the adsorbent of the first layer. Emission of evaporated fuel after being left at high temperature can be suppressed.

According to invention of Claim 2 , the said effect can be heightened further.

According to the invention of claim 3 , since the filter or the plate is removed, the structure becomes simple and it can be manufactured at low cost.

A preferred embodiment of the present invention will be described with reference to FIGS.
First, the adsorbent used in the present invention will be described with reference to FIGS.

  The adsorbent used in the present invention is activated carbon, and there are many pores P as shown in FIG. 5 on the surface of the activated carbon, and gasoline fuel molecules enter and are captured in the pores. In FIG. 5, D represents the pore diameter, and F represents the pore volume.

  Next, the differential pore distribution and residual and adsorption / desorption regions (normal temperature state) of the activated carbon will be described with reference to FIG.

  The area E (pore volume F) in the distribution curve in the adsorption / desorption region G in the differential pore distribution diagram as shown in FIG. 4 is in a proportional relationship.

  Further, the smaller the pore diameter at the peak position in the differential pore distribution diagram, the stronger the retention (adsorption force) of the evaporated fuel. That is, the holding force is inversely proportional to the pore diameter.

  In the residual region H of the differential pore distribution diagram, the area E (pore volume F) in the distribution curve and the residual amount of the low boiling point component in the evaporated fuel are in a proportional relationship.

  Further, the amount of blown fuel vapor is proportional to the size of the pore diameter at the peak position of the differential pore distribution curve when the adsorbed gasoline vapor is diffused within 1 hour (no standing). In addition, when the vapor diffusion is 6 hours or more (with leaving), it is almost proportional to the result of multiplying the residual diameter by the pore diameter at the peak position.

  In view of the characteristics of the activated carbon as described above, the activated carbon used in the present invention is selected from three types of activated carbon having the characteristics shown in FIG.

  In FIG. 4, activated carbon A has a characteristic that the peak position in the differential pore distribution diagram is concentrated on the pore diameter with a good balance of adsorption and desorption of gasoline vapor, and the diameter D is about 2.5 nm. The area E (pore volume) formed by the curve of the activated carbon A in the differential pore distribution diagram and the horizontal axis in the differential pore distribution diagram is larger than that of the activated carbon B.

  Therefore, this activated carbon A has a characteristic that the retention of the evaporated fuel is weak and the amount of adsorption of the evaporated fuel is large.

  Activated carbon B has the same peak position in the differential pore distribution diagram as activated carbon A, but has a smaller pore volume than that of activated carbon A.

  Therefore, this activated carbon B has a weaker retention of evaporated fuel, like the activated carbon A, and the amount of evaporated fuel adsorbed is smaller than that of the activated carbon A.

  Activated carbon C has a characteristic that the peak position in the differential pore distribution concentrates on the pore diameter suitable for the adsorption of low-boiling components (mainly butane) in gasoline vapor, and pores having a diameter D of about 2 nm. And the pore volume is smaller than that of the activated carbons A and B.

  Therefore, the activated carbon C has a smaller amount of evaporated fuel adsorbed than the activated carbons A and B, but the evaporated fuel has a stronger holding power than the activated carbons A and B.

  From the above, when the activated carbons A, B, and C are compared, as shown in the table of FIG. 6, activated carbon A has the largest adsorbed amount of evaporated fuel among activated carbons A, B, and C. Therefore, the residual amount of low boiling point components in the evaporated fuel after purging has a medium characteristic among the activated carbons A, B and C. In the activated carbon B, the adsorption amount of the evaporated fuel is medium among the activated carbons A, B, and C, and the holding power is weak. Therefore, the residual amount of the low boiling point component in the evaporated fuel after the purge is the activated carbon A, B, C. It has the fewest characteristics among them. Activated carbon C has the smallest adsorbed amount of evaporated fuel among activated carbons A, B, and C, but its holding power is stronger than activated carbons A and B. Therefore, the remaining amount of low boiling point components in evaporated fuel after purging is activated carbon. It has the most characteristics among A, B, and C.

  As described above, as the activated carbons A and B, by using activated carbon having a peak position of the curve in the differential pore distribution in the vicinity of the desorption limit line I, the activated fuel A and B can be used for the evaporated fuel after purging. It becomes possible to make activated carbon that can reduce the remaining amount. Further, as the activated carbon C, activated carbon in which the peak position of the curve in the differential pore distribution is significantly shifted from the desorption limit line I toward the remaining region H side is used.

  With respect to the amount of blow-through when evaporative fuel flows from the fuel tank, when the gas is left at a high temperature for a predetermined time after purging, that is, with leaving, the activated carbon A and C have a large amount of blow-through and the activated carbon B has a small amount. This is presumably because the low boiling point component of the evaporated fuel remaining in the activated carbon after purging evaporates during standing at a high temperature, causes a diffusion phenomenon, fills the canister, and is pushed out by the flowing evaporated fuel to cause blow-through. That is, since it is almost proportional to the result obtained by multiplying the residual diameter by the pore diameter at the peak position as described above, when activated carbon A, B, C is compared, activated carbon A, C has a large amount of blow-through and activated carbon B has a small amount. .

  However, when not leaving the high temperature after purging, that is, without leaving, there is little activated carbon A, B, C. This is because even if the low-boiling component remains in the evaporated fuel on the activated carbon, it is not left at a high temperature, so that a diffusion phenomenon due to evaporation of the low-boiling component hardly occurs. Therefore, in order to suppress an increase in the amount of blow-through after being left at a high temperature, it is necessary to select the pore diameter at the peak position and to reduce the residual amount of low-boiling components in the evaporated fuel after purging. In addition, about manufacture of the activated carbon which has each above-mentioned characteristic, it can manufacture easily by the activated carbon manufacturer by showing a characteristic.

  Next, the canister of the first embodiment of the present invention shown in FIG. 1 using the activated carbon will be described.

  In FIG. 1, the inside of the case 2 constituting the canister 1 is divided into two by a partition wall 2a, and one of the adsorbents 5 is sandwiched by filters 3a, 3b, 3c having air permeability and has air permeability, for example, a hole is opened. The first adsorbent layer, that is, the first adsorbent layer 7 is formed by being pressed by the spring 6a through the plate 4a. Similarly, the second adsorbent layer 8 is pressed by the spring 6b through the plate 4b having a hole, for example, the adsorbent 5 sandwiched between the filters 3d and 3e having air permeability. Is forming. The second adsorbent layer 8 has air permeability, for example, is partitioned by a plate 4c or a filter 3f having a hole, and forms a second adsorbent layer 8a and a third adsorbent layer 8b.

  A tank port 2d communicating with the upper portion of the fuel tank 9 is opened in the first space 2c formed by the case 2, the filter 3a, and the partition plate 2b. A purge port 2f communicating with the surge tank 11a of the intake pipe 11 through the flow rate adjusting valve 10 is opened in the second space 2e formed by the case 2, the filter 3b, and the partition plate 2b. An atmosphere port 2h communicating with the atmosphere is opened in the third space 2g formed by the case 2, the filter 3e, and the partition wall 2a. A communication passage 2i is provided at the tip of the partition wall 2a, and a fourth space 2j is formed by the case 2 and the plates 4a and 4b. Thus, each adsorbent layer 7, 8a, 8b is arranged in series with the flow of the evaporated fuel via the fourth space 2j.

  In the first adsorbent layer 7, the activated carbon has a large amount of evaporated fuel adsorbed but has a low holding power, and therefore the activated carbon has a relatively large amount of low-boiling components remaining in the evaporated fuel after purging. A (5a) is filled. In the second adsorbent layer 8a and the third adsorbent layer 8b, the adsorbed amount of the evaporated fuel is medium, that is, less than the activated carbon A, and the holding power is weak as in the activated carbon A. The activated carbon B (5b), in which the remaining amount of low boiling point components in the evaporated fuel later is less than that of the activated carbon A, is filled. The volume of the third adsorbent layer 8b is 300 cc, the volume of the first adsorbent layer 7 is 1400 cc, and the volume of all the adsorbent layers is 2100 cc.

Next, the operation of the first embodiment will be described.
In FIG. 1, the evaporated fuel generated from the fuel tank 9 while the engine is stopped flows in from the tank port 2d of the canister 1, passes through the activated carbon A (5a) in the first adsorbent layer 7, and the second adsorbent layer 8a and the second adsorbent layer 8a. 3 is sequentially adsorbed by the activated carbon B (5b) in the adsorbent layer 8b, and leakage to the atmosphere is suppressed. Next, when the engine 50 is started and a negative pressure is generated in the intake pipe 11, the evaporated fuel adsorbed by the activated carbon A (5a) and B (5b) together with the atmosphere flowing in from the atmosphere port 2h is purged by the negative pressure. Purged from 2f. After purging for a predetermined time, the engine 50 is stopped and the vehicle is left in a room maintained at a predetermined temperature for a predetermined time.

  During this time, the canister 1 is left in the activated carbon A (5a) with a predetermined low boiling point component remaining at a high temperature, so that the remaining fuel evaporates and diffuses and flows downstream on the atmospheric port 2h side of the canister 1. Is adsorbed by the activated carbon B (5b) in the second and third adsorbent layers 8a and 8b with a low residual amount of low-boiling components, and the evaporated fuel flowing from the fuel tank 9 is also adsorbed by the activated carbon B (5b) later. Therefore, the emission of evaporated fuel to the atmosphere is reliably suppressed. In the canister using this activated carbon B, the blow-through amount was measured under the above-mentioned conditions. As a result, the blow-through amount was slightly less than 40 mg in the inflow amount of evaporated fuel from the tank port 2d in FIG. Greatly reduced. The volume of the entire adsorbent layer of the canister used for the measurement of the blow-through amount in FIG. 7 is 2100 cc, the volume of the first adsorbent layer 7 is 1400 cc, and the volume of the third adsorbent layer 8b is 300 cc.

  In the first embodiment, the second layer is divided into two by the filter or the air-permeable plate 4c (3f), so that the second adsorbent layer 8a and the third adsorbent layer 8b are separated. By forming a flow resistance by the filter or the like, it is possible to further suppress the evaporated fuel that is diffused to the atmosphere through the third adsorbent layer 8b.

FIG. 2 shows a second embodiment of the modification of FIG.
In the second embodiment, the plate 4c or the filter 3f that partitions the second adsorbent layer 8a and the third adsorbent layer 8b in the first embodiment is removed, and the second adsorbent layer 8a in the first embodiment is removed. And the third adsorbent layer 8b are integrated, and the second adsorbent layer 8 filled with activated carbon B is integrally formed.

  Since the other structure is the same as that of the first embodiment, the same parts as those described above are denoted by the same reference numerals and the description thereof is omitted.

  Also in the second embodiment, the same functions and effects as those of the first embodiment (except for the functions and effects of the plate 4c or the filter 3f) are exhibited, and further, compared with the first embodiment, the plate 4c or By removing the filter 3f, the structure and manufacturing become simpler and the cost can be reduced.

Next, a third embodiment shown in FIG. 3 will be described.
Only the parts different from the first embodiment will be described, and the description of the same functional parts will be omitted.

FIG. 3 is a longitudinal sectional view of a canister according to a third embodiment of the present invention.
In FIG. 3, the first adsorbent layer 7 is filled with activated carbon A (5a) in the first embodiment, and the second adsorbent layer 8a is filled with activated carbon B (5b) in the first embodiment. However, the third adsorbent layer 8b is filled with the activated carbon C different from the activated carbons A and B.

  The activated carbon C has a smaller amount of evaporated fuel adsorbed than the activated carbons A and B, but the retention of evaporated fuel is stronger than that of the activated carbons A and B. Therefore, the low boiling point of the evaporated fuel after purging is low. This is activated carbon having a characteristic that the remaining amount of components is larger than that of the activated carbons A and B.

The operation of the third embodiment will be described.
Since the process up to the adsorption of the evaporated fuel while the engine is stopped is the same as that in the first embodiment, the description will be omitted, and the description will start from the purge stage after the engine is started.

  In the purge stage after the start of the engine 50, the evaporated fuel adsorbed on the activated carbon C (5c) in the third adsorbent layer 8b is purged by the negative pressure of the intake pipe 11 generated in the purge port 2f. (5c) has a characteristic that there is a large residual amount with respect to the adsorption amount of the low boiling point component in the evaporated fuel after the purge, and in general, a large residual amount exists even after the purge is completed. Since the amount is small and the third adsorbent layer 8b closest to the atmosphere is filled, purging is effectively performed by fresh air introduced from the atmosphere port 2h at the start of the purge, thereby completing the purge. There will still be a small residual amount.

  Thereafter, even if the evaporated fuel from the fuel tank 9 flows into the canister 1, the evaporated fuel is almost adsorbed by the activated carbons A and B of the first and second adsorbent layers 7 and 8a, and is not adsorbed. Since the evaporated fuel is reliably adsorbed by the activated carbon C of the third adsorbent layer 8b having a strong adsorbing power (holding power), there is a sufficient adsorbing amount even if there is a small remaining amount, and the air can be blown into the atmosphere sufficiently. It is suppressed.

  Next, when the volume of the third adsorbent layer 8b is set to 2.3 to 4.8% of the total volume of the adsorbent layer, for example, the total volume of the adsorbent layer is 2100 cc, A case where the volume of 8b is 50 cc will be described.

  Since the process up to the adsorption of the evaporated fuel while the engine is stopped is the same as that in the first embodiment, the description thereof will be omitted, and the description will start from the purge stage after the engine is started.

  In FIG. 3, the evaporated fuel adsorbed on the activated carbon C (5c) in the third adsorbent layer 8b at the purge stage after the start of the engine 50 is almost entirely due to the negative pressure of the intake pipe 11 generated in the purge port 2f. Purged. This is because activated carbon C (5c) has a characteristic that the amount of low-boiling components remaining in the evaporated fuel after purging is large, but the third adsorbent layer 8b has a volume of 50 cc and a total volume of 2100 cc. This is because by reducing the volume to 4%, the purge air amount per unit volume can be increased, and the purge performance is improved. For example, when the purge air flow rate is 2100 cc, the purge air flow rate per unit volume is 2100 cc / 50 cc = 42 cc / cc with a capacity of 50 cc activated carbon C (5c).

  Therefore, at the stage of purging and leaving at high temperature, even if the low boiling point component remaining in the first adsorbent layer 7 evaporates and a diffusion phenomenon occurs, the second adsorbent filled with activated carbon B (5b). Since it is adsorbed by the layer 8a, even if evaporated fuel flows from the fuel tank 9 later, the evaporated fuel is adsorbed by the second adsorbent layer 8a, and the evaporated fuel not adsorbed by the second adsorbent layer 8a is the first. Since the three adsorbent layers 8b are reliably adsorbed, the blow-off to the atmosphere is suppressed. In FIG. 7, the blow-through amount is a little less than 30 mg when the inflow amount of evaporated fuel is 80 g, which is significantly reduced as compared with the prior arts 1 and 2, and is also reduced as compared with the first embodiment described above. Regarding the volume of the third adsorbent layer 8b, the above effect is maintained up to 50 to 100 cc (2.3 to 4.8%) with respect to the total volume of 2100 cc, but the effect is reduced at 200 cc. Has been confirmed.

1 is a longitudinal sectional view of a canister according to a first embodiment of the present invention. It is a longitudinal cross-sectional view of the canister which concerns on the 2nd Example of this invention. It is a longitudinal cross-sectional view of the canister which concerns on the 3rd Example of this invention. It is a characteristic view which shows the change rate of the pore volume with respect to the pore diameter of the activated carbon used in this invention, and a pore diameter. It is an enlarged view which shows the pore of activated carbon. It is a list which shows the characteristic of the activated carbon used for this invention. It is a graph which shows the test result which measured the blow-through amount of the canister which concerns on the past and this invention. 1 is a longitudinal sectional view of a canister showing a conventional technique 1. FIG. It is a longitudinal cross-sectional view of the canister which shows the prior art 2.

Explanation of symbols

1 Canister 2a Bulkhead 3f Filter 4c Plate 5a Activated carbon A
5b Activated carbon B
5c Activated carbon C
7 First adsorbent layer (first adsorbent layer)
8 Second adsorbent layer 8a Second adsorbent layer 8b Third adsorbent layer G Adsorption / desorption region H Remaining region I Desorption limit line

Claims (3)

In a canister in which the adsorbent layer is divided into two first and second adsorbent layers by a partition and arranged in series, the second adsorbent layer is divided into two by a filter or a plate, The first adsorbent layer is filled with activated carbon having a larger amount of evaporated fuel adsorbed than the activated carbon of the adsorbent layer on the air port side divided in the second layer and having the same holding power. A canister characterized in that the divided adsorbent layer on the atmospheric port side is filled with activated carbon having a smaller amount of evaporated fuel adsorbed than the activated carbon of the first adsorbent layer and having the same holding power. The capacity of the adsorbent layer of the second layer of the divided air port side, claim 1 Symbol placement of the canister, characterized in that not more than 14.3% of the volume of all adsorbent layer. Claim 1 or 2 Symbol mounting of the canister, characterized in that removing the filter or the plate.

Images