JP2000303917A - Canister - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a canister having high adsorption and desorption performance. SOLUTION: Two or more activated carbon layers 11, 12, and 13 are arranged in series for an inflow of fuel steam from a fuel tank 2. Activated carbon A having a large grain size is used in the activated carbon layer 11 on the side situated upper stream brought into approximate saturated adsorption and activated carbon C is used in the activated carbon layer 13 on the side situated downstream, where fuel steam is apt to flow through voids of activated carbon since only a low boiling point component apt to vaporize flows in, and activated carbon C with a small grain size is used in the activated carbon layer 13 on the side situated downstream having adsorption density lower than that on the side situated upper upstream. Therefore, a pressure loss of a whole of the canister 1 is suppressed to a comparatively low pressure loss by the activated carbon A with a large grain size. Further, purging air is brought into a state to hardly pass the voids of the activated carbon by the activated carbon C with a small grain size, and HC is prevented from remaining on the side situated downstream. Simultaneously, steam fuel hardly passes through to the side situated downstream and adsorption performance of the whole of the canister 1 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a canister in which a container having an evaporative fuel introduction port communicating with a fuel tank and an atmosphere port communicating with the atmosphere is filled with activated carbon capable of absorbing and desorbing fuel vapor. is there.

[0002]

2. Description of the Related Art Activated carbon is sealed as an adsorbent in a canister (evaporated fuel processing device) of an internal combustion engine, and adsorbs and retains fuel vapor evaporated and discharged in a fuel tank.
The adsorbed fuel vapor is desorbed (purged) from the activated carbon by the outside air introduced from the atmospheric port of the canister due to the negative pressure of the intake pipe during operation of the engine, and is led out to the intake pipe and burned together with the fuel injected from the injector.

In 1998, the so-called ORVR regulation, which regulates the emission of HC air during refueling, has begun in the United States.
Due to this regulation, HC staying in the fuel tank space is collected by the canister at the time of refueling, so that the canister was filled with activated carbon having a large particle size and a small variation inevitably to reduce refueling resistance. .

[0004] However, the activated carbon has a high porosity and a low pressure loss. However, when desorbing the adsorbed HC, the purge air easily passes through the air gap and the HC easily remains in the canister. The remaining HC fills the pores involved in the adsorption, and the number of pores effective for the adsorption of new gasoline vapor decreases, resulting in a problem that the adsorption performance is reduced.

[0005] In addition, the H remaining on the canister, particularly on the downstream side,
At the same time, the problem that carbon diffuses toward the exit of the canister while the vehicle is left undisturbed and leaks into the atmosphere has also occurred. In addition, due to the large particle size and low airflow resistance, fuel vapor tends to travel downstream of the canister when adsorbing fuel vapor, and even if the pore surface area and volume are increased, the adsorption performance (the amount of adsorption per unit volume of activated carbon) ) Did not improve.

In a market environment, 80% or more of the HC flowing into the canister from the fuel tank is a component having 4 to 6 carbon atoms (hereinafter referred to as a low boiling component). Since the high-boiling components are easily liquefied, that is, easily adsorbed, the adsorption is completed on the upstream side of the canister.

[0007] For this reason, Japanese Utility Model Publication No. 2-195570 and the like have a structure in which the activated carbon layer on the upstream side of the canister is filled with activated carbon having a large pore diameter in which a high boiling point component is more likely to be adsorbed. Japanese Utility Model Publication No. 19570/1995 is related to the present invention in that an activated carbon layer having a pore diameter suitable for the adsorbed component is arranged, but does not pay any attention to the particle size and material of the activated carbon.

[0008]

SUMMARY OF THE INVENTION The present invention focuses on the difference between the adsorbed density and the fuel evaporation component adsorbed on the upstream and downstream sides of the canister. Activated carbon of a different material is enclosed.

On the upstream side of the canister into which the fuel vapor flows from the fuel tank, there is adsorbed a component having a high boiling point which is relatively easy to liquefy, in addition to a low boiling component occupying 80% or more of the fuel vapor. Further, it is a place where fuel vapor always flows, and the adsorption state of activated carbon is almost saturated adsorption. Focusing on the findings obtained by experiments that the saturated adsorption amount is not related to the size of the particle size (void) if the pore properties (pore surface area and volume) are the same, Enclose activated carbon with a large diameter. The size of the fuel vapor molecules flowing into the canister is about 7 to 20 °, and it is said that there is a correlation (D ≒ 3d) between the size d of the adsorbed molecules and the pore diameter D of the activated carbon. I have. On the upstream side of the canister, 80% of all components in the fuel vapor, especially high-boiling components, have been completely absorbed at this site.
It is preferable to include a large amount in the range of 70 to 70 °, particularly 50 to 70 °.

[0010] On the other hand, only low-boiling components, which are more likely to be vaporized, flow in the downstream of the canister, so that the pores of the activated carbon are easily removed, and the adsorption density is lower than that in the upstream. In addition, if the adsorbed fuel vapor remains on the downstream side, it may cause the fuel vapor to leak to the atmosphere port side. Therefore, it is necessary to desorb the adsorbed fuel vapor as efficiently as possible. ORV
Due to the regulation of R, it is necessary to adsorb fuel vapor remaining in the fuel tank at the time of refueling with the canister, and it is essential to reduce the pressure loss of the canister.

Therefore, in the present invention, in order to solve these problems, activated carbon having a larger particle size than the current size is used on the upstream side where almost saturated adsorption is performed, and conversely, activated carbon having a smaller particle size than the current size is used on the downstream side. Activated carbon is used to make it difficult for purge air to pass through the air gap and to prevent HC from remaining downstream. At the same time, the use of activated carbon having a particle size smaller than that of the current type on the downstream side makes it difficult for fuel vapor to pass therethrough, thereby improving the adsorption performance.

[0012] In short, an object of the present invention is to provide a canister in which fuel vapor is less likely to escape to the atmosphere port side than in the past, while obtaining efficient adsorption and desorption performance.

[0013]

According to the present invention, in order to solve the above-mentioned problems, the technical means described in claims 1 to 6 are employed.

According to the first aspect of the present invention, two or more activated carbon layers are provided in series with respect to the fuel vapor inflow from the fuel tank, and the activated carbon layer on the upstream side, which is almost saturated, has a large particle size. Activated carbon is used, and only low-boiling components that are easy to vaporize flow in, so the activated carbon layer on the downstream side, where the adsorption density is lower than that on the upstream side because it easily escapes the voids of the activated carbon, uses activated carbon with a small particle size. With activated carbon of large particle size,
The pressure loss of the entire canister can be suppressed to a relatively low pressure loss, and the activated carbon having a small particle size makes it difficult for purge air to pass through the gap of the activated carbon, thereby preventing HC from remaining on the downstream side, and at the same time, preventing the purge air from remaining on the downstream side. It becomes difficult for fuel vapor to pass through, and the adsorption performance of the entire canister can be improved.

According to the second aspect of the present invention, since the downstream layer in the canister contains a larger number of small pores, the size of the low boiling component, which accounts for 80% or more of the fuel vapor, is 7 to 10 °. The fuel vapor is efficiently adsorbed by the small pores contained in the downstream layer.

According to the third aspect of the present invention, the canister has an activated carbon layer whose particle diameter gradually decreases from the upstream side to the downstream side with respect to the inflow of fuel vapor from the fuel tank. The effect of the present invention can be obtained continuously rather than stepwise, thereby increasing the efficiency.

According to the fourth aspect of the present invention, the canister has an activated carbon layer containing many pores whose pore diameter gradually decreases from the upstream side to the downstream side with respect to the inflow of fuel vapor from the fuel tank. Since the effect of the invention described in claim 2 can be obtained continuously rather than stepwise, there is an effect of increasing efficiency.

According to the fifth aspect of the present invention, in the canister, the columnar coal is filled on the upstream side and the crushed coal is filled on the downstream side. Has the effect of increasing the charging efficiency and improving the adsorption performance by making it difficult for the fuel vapor to pass through the voids of the activated carbon, and at the same time improving the desorption performance because the purge air easily hits the inside of the pores.

According to the sixth aspect of the present invention, in the canister, wood-based activated carbon is filled on the upstream side, and coal-based activated carbon is filled on the downstream side. FIG. 3 is a graph showing the relationship between the pore surface area and the pore volume of commonly used wood-based and coal-based activated carbon. From FIG. 3, it can be seen that wood-based activated carbon tends to have a small surface area and a large volume. This means that woody activated carbon has many pores with large pore diameters. Although the pore surface area and pore volume can be changed to some extent depending on the activation conditions when producing activated carbon, the above tendencies tend to occur depending on the material. In other words, the fuel vapor flowing into the upstream side, particularly high-boiling components, is adsorbed on the woody activated carbon having a large pore diameter on the upstream side, and the low-molecular-weight, low-molecular-weight activated carbon having a relatively small pore diameter on the downstream side is adsorbed. Boiling point components are adsorbed efficiently.

[0020]

FIG. 1 is a system diagram showing a configuration of an embodiment of the present invention. In FIG. 1, a canister 1 communicates with a fuel tank 2 via a tank port 3 serving as an evaporative fuel introduction port, and an intermediate pressure valve 4 is provided in the middle of the tank port 3 to communicate with the both by the internal pressure of the fuel tank. Activated carbon is sealed inside the canister 1 as an adsorbent,
The activated carbon in this example was obtained from the same raw material, but the activated carbons A, B, and C differed in the pore size distribution and the particle size.
Are vertically and equally distributed in three layers, 11, 12, and 13 from the upstream side with respect to the steam inflow from the fuel tank.

FIG. 2 is a graph showing the pore size distribution of the activated carbons A, B and C. In FIG. 2, activated carbon A has a large pore diameter range of 20 to 70 °, activated carbon B has a large range of 20 to 50 °, and activated carbon C has a large range of 20 to 30 °. Table 1 shows the average particle size, material, and shape of the activated carbon in each layer of the canister 1.

The activated carbon is filled between a pair of upper and lower perforated plates 51 and 52 and is sandwiched between stoppers 6 disposed between the perforated plates 51 and 52 and the container. Filters 71 and 72 are provided between the perforated plates 51 and 52 and the activated carbon to prevent the activated carbon C from falling off. A purge port 8 is provided on the same end surface as the tank port 3 and communicates with the intake pipe via a purge valve 9. An air port 10 is provided on the opposite side of the activated carbon layer, and serves as a communication point between the canister and the atmosphere.

[0023] Next, the operation of the embodiment configured as described above will be described.

During running of the vehicle, the fuel vapor generated in the fuel tank 2 first flows into the activated carbon layer 11 from the tank port 3. Most of the high-boiling components contained in the fuel vapor, which are slightly less than 20%, are easily liquefied, and are mostly adsorbed by the activated carbon layer 11. Among the high-boiling components that could not be adsorbed by the activated carbon layer 11, although small amounts, the components having boiling points close to the low-boiling components and the low-boiling components that could not be adsorbed by the activated carbon layer 11 flow into the activated carbon layer 12. Activated carbon layer 13 adsorbs low-boiling components that could not be adsorbed up to activated carbon layer 12. During traveling of the vehicle, at the same time as the adsorption, air is introduced from the atmospheric port 10 by the intake negative pressure, and a purge for desorbing the adsorbed HC and leading it to the intake pipe together with the air is also performed.

Conventionally, HC adsorbed on the downstream side of the canister, in the vicinity of the activated carbon layer 13, is easily purged by the purge air because of the activated carbon having a large particle size used for reducing the pressure drop of the canister. However, in the present embodiment, the filling efficiency was increased by reducing the particle size of the activated carbon layer 13 and the shape of the activated carbon to be crushed carbon, and the downstream HC was efficiently removed. It can be desorbed and the remaining HC can be reduced. As a result, the emission of HC into the atmosphere when the vehicle is left after the vehicle has traveled can be significantly reduced as compared with the related art.

The size of the fuel vapor molecules flowing into the canister is about 7 to 20 °, and the size d of the adsorbed molecules and the pore diameter D of the activated carbon are correlated (D ≒ 3).
d) is said to be present. Only the low-boiling components flow into the activated carbon layer 13 and the molecular size thereof is about 7 to 10 °.
Therefore, the activated carbon C of the activated carbon layer 13 has a pore diameter of 2
It had pores containing a large range of 0 to 30 °.
Further, if the material is made of a coal based on the above-described characteristics of the pore diameter, activated carbon containing a large range of the pore diameter can be easily obtained.

It is necessary to reduce the pressure loss of the canister according to the ORVR regulations, and it is necessary to reduce the pressure loss to the same level as that of the conventional product. The activated carbon layer 13 is made of activated carbon having a smaller particle size than the conventional one, and the pressure loss is increased. Therefore, it is necessary to reduce the pressure loss in the other layers as compared with the conventional case. In the present invention, the size of the activated carbon A of the activated carbon layer 11 is made larger than that of the conventional activated carbon.

This is the location where the fuel vapor always flows in the upstream part of the canister. The adsorption state of the activated carbon is almost saturated adsorption, and the saturated adsorption amount is the same regardless of the pore characteristics (pore surface area and volume). This is based on the finding that there is no relation to the size of the particle size (void). Although the HC adsorbed on activated carbon is less likely to be desorbed by increasing the particle size than before, high boiling components are mainly adsorbed in the upstream of the canister, and the low boiling point is diffused and released to the atmosphere compared to the downstream. Since the component is adsorbed at an extremely low ratio, it can be sufficiently desorbed even if the particle size is increased. The pore diameter of the activated carbon A in the activated carbon layer 11 needs to have a wide range of 20 to 70 ° in order to correspond to the size of all the fuel vapor molecules flowing into the canister. It is desirable to have a large pore diameter of 50-70 °. In addition, when the activated carbon A is made of wood-based activated carbon, contrary to the activated carbon C, activated carbon containing a large pore diameter range can be easily obtained.

In this embodiment, the properties of the activated carbon filled in the upstream and downstream sides of the canister are controlled, and the activated carbon B of the activated carbon layer 12 is equivalent to the conventional one and has no problem. However, as described above, among the high-boiling components that were not adsorbed by the activated carbon layer 11 in a small amount into the activated carbon layer 12, components having a boiling point close to the low-boiling component and low-boiling components that could not be adsorbed by the activated carbon layer 11 flowed into the activated carbon layer 12. Therefore, it is desirable that the activated carbon B contains a large pore diameter of 20 to 50 ° smaller than the activated carbon A of the activated carbon layer 11. In the present embodiment, the activated carbon layer is divided equally, but it is not always necessary to divide the activated carbon layer into equal parts by matching the particle diameters of the activated carbons A and C with the pressure loss.

At the time of refueling, HC is not purged because the engine is stopped, and the HC remaining in the space in the fuel tank before refueling flows into the canister in a form of being pushed out by refueling fuel. At this time, if activated carbon with a large particle size is sealed downstream of the canister as in the conventional case, low-boiling components that are difficult to be liquefied and flow into the downstream can easily pass through the voids of the activated carbon, so that adsorption per unit volume of activated carbon can be achieved. The amount (adsorption performance) decreases. In the present embodiment, the high-boiling components that are easily liquefied, that is, easily adsorbed, are almost adsorbed, and the particle size is larger than the conventional one on the upstream side where the adsorption performance is close to the saturated adsorption amount of activated carbon and the adsorption performance is not so much affected by the particle size. The activated carbon layer 11 is disposed, and the portion having a reduced pressure loss is filled with activated carbon C having a smaller particle size than the conventional one in the activated carbon layer 13 on the downstream side, so that the low boiling point component is less likely to pass through the voids of the activated carbon. To prevent the adsorption performance from decreasing. After refueling, purging is performed again when the engine is operating, and HC adsorbed on the canister during refueling, especially low-boiling components adsorbed on the downstream side, is efficiently purged to prevent the emission of HC into the atmosphere when the vehicle is stopped. I do.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a graph showing the pore size distribution of activated carbons A, B and C.

FIG. 3 is a graph showing the relationship between the pore surface area and the pore volume of commonly used wood-based and coal-based activated carbons.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Canister 2 Fuel tank 3 Evaporated fuel introduction port (tank port) 10 Atmospheric port 11, 12, 13 Activated carbon layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Naoya Kato 14 Iwatani, Shimowasukamachi, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Kuki Ota 14th Iwatani, Shimotsukamachi, Nishio City, Aichi Prefecture Stock Company Inside the Japan Auto Parts Research Institute, Inc. (72) Noriyo Amano 14th Iwatani, Shimoba Kakumachi, Nishio City, Aichi Prefecture Inside the Japan Auto Parts Research Institute, Inc. (72) Inventor Yoshihiko Budo 1st Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd.

Claims (6)

[Claims] 1. A canister having a container having an evaporative fuel introduction port communicating with a fuel tank and an atmosphere port communicating with the atmosphere filled with activated carbon capable of adsorbing and desorbing fuel vapor. It has two or more activated carbon layers in series with respect to the inflow, and uses activated carbon having a large particle diameter for the activated carbon layer on the upstream side and activated carbon having a small particle diameter for the activated carbon layer on the downstream side. A canister characterized by the following. 2. The canister according to claim 1, wherein, in the canister, the activated carbon layer on the downstream side includes a smaller pore diameter. 3. A canister having a single activated carbon layer in which the activated carbon layer is not divided, the activated carbon layer having a particle diameter gradually decreasing from upstream to downstream with respect to the inflow of fuel vapor from the fuel tank. A canister characterized by the following: 4. The activated carbon layer in which the canister has a gradually increasing number of small pores from upstream to downstream with respect to fuel vapor inflow from the fuel tank. 3. The canister according to 3. 5. The canister according to claim 1, wherein the canister is filled with columnar coal on the upstream side and crushed coal on the downstream side. 6. The canister according to claim 1, wherein an upstream side is filled with woody activated carbon and a downstream side is filled with coal-based activated carbon. Canister.