Gas separation: apparatus – Solid sorbent apparatus – With control means responsive to sensed condition
Reexamination Certificate
2002-04-12
2004-02-10
Lawrence, Frank M. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
With control means responsive to sensed condition
C096S113000, C096S114000, C096S126000, C096S130000, C096S146000, C123S519000
Reexamination Certificate
active
06689196
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Applications No. 2001-115821 filed on Apr. 13, 2001, No. 2000-312073 filed on Oct. 12, 2000, and No. 11-292499 filed on Oct. 14, 1999 the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel vapor control apparatus having a canister for adsorbing fuel vapors released from a fuel tank.
2. Related Art
A fuel vapor control apparatus is used to adsorb and store fuel vapors evaporated from a fuel tank so as not to be released to the outside of a vehicle during travel of the vehicle or when the vehicle is stopped, and has a canister filled with activated carbon as an adsorbent. The fuel vapor adsorbed by the canister is desorbed and led to an intake pipe by drawing outside air from an atmosphere port of the canister by a negative pressure of an intake pipe when the engine operates, and the fuel vapor is burned along with a fuel injected by an injector.
In recent years, control on release of the fuel vapor to atmosphere is becoming rigorous. For example, in ORVR control of U.S.A. it is requested to capture all of fuel vapors from a fuel tank exhausted during refueling by a canister, not to be released to the atmosphere. Consequently, a large amount of fuel vapors has to be treated by a canister, and a canister having higher performance is demanded. The adsorption/desorption performance of activated carbon is largely influenced by temperature. The lower the temperature is, the more the adsorption amount increases. The higher the temperature is, the more the desorption amount increases. However, in the canister, the temperature changes so as to increase at the time of adsorption and so as to decrease at the time of desorption. There is consequently a problem such that the performance of activated carbon is not fully displayed. For example, in the case where the activated carbon adsorbs the fuel vapors, a capillary condensation phenomenon occurs in fine pores of the activated carbon, and the fuel vapors as gases are liquefied and adsorbed. In this case, together with the phase change from gases to liquid, adsorption heat (condensation latent heat) is generated, and the temperature increases. On the other hand, in the case where the liquefied fuel vapors are desorbed, the fuel adsorbed by purging becomes gases from the liquid while taking heat of evaporation from the surrounding, so that the temperature decreases due to the heat absorption.
In the conventional canister, due to the phenomenon, the temperature in the canister becomes higher than the ambient temperature by tens degrees at the time of adsorption. On the other hand, at the time of desorption, the temperature in the canister drops and may become equal to or below 0° C. Particularly, at the time of desorption, a part in which the activated carbon temperature decreases due to the heat absorption reaction does not easily desorb the fuel vapors due to decrease in temperature. If the fuel vapors adsorbed cannot be completely desorbed, there is the possibility that, while the vehicle is parked, the fuel vapors diffuse in the canister and leak from the atmosphere port.
JP-A-8-42413, JP-A-60-6061, and JP-A-
64-347
and Japanese Unexamined Utility Model Application JP-U-60-27813, JP-U-2-13161, JP-U-5-21158, and JP-U-58-144051 disclose a technique of heating activated carbon in a canister by heating means. The conventional techniques have, however, a problem such that activated carbon cannot be uniformly heated or a problem such that the size of the canister increases. On the other hand, the fuel vapors released from the canister are burned in an internal combustion engine. Consequently, fluctuations in density of fuel vapors or fuel vapor amount may cause poor combustion or deterioration in exhaust emission.
SUMMARY OF THE INVENTION
An object of the invention is to provide a fuel vapor control apparatus with improved performance of desorbing/adsorbing fuel vapors without increasing the capacity of a canister.
Another object of the invention is to provide a fuel vapor control apparatus capable of obtaining desired temperature in the whole area of a fuel adsorption layer in a canister.
Further another object of the invention is to provide a fuel vapor control apparatus in which an amount of heat of heating and the shape of a fuel adsorption layer are set so as to obtain desired temperature in the whole area of a fuel adsorption layer in a canister.
Further another object of the invention is to provide a fuel vapor control apparatus capable of preventing deterioration in combustion state or exhaust emission.
According to a first feature of the present invention, temperature of a fuel adsorption layer is derived by an equation expressing an amount of heat given to an adsorbent by temperature control means and a distance from the temperature control means. The amount of heat given to the adsorbent by the temperature control means and the shape of the fuel adsorption layer (distance to a part which is the farthest from the temperature control means of the fuel adsorption layer) are set so that the temperature is higher than the boiling point of the fuel and lower than the fire point of the fuel in the whole area of the fuel adsorption layer.
Concretely, when an amount of heat given to the adsorbent by the temperature control means for controlling the temperature of the fuel adsorption layer is Q(W), a distance from the temperature control means to a farthest part which is the farthest from the temperature control means of the fuel adsorption layer is X(m), and temperature of the fuel adsorption layer is T(K),
the amount Q of heat and the distance X are specified by the following relational expression (1)
T=−
355
Q×X
2
−815
X+Q+
298 (1)
so that the temperature T satisfies the following condition (2) in the whole area of the fuel adsorption layer.
boiling point of fuel≦
T
<fire point of fuel (2)
The relation between the temperature of the fuel and the evaporation amount is that after the temperature of the fuel exceeds the boiling point, the evaporation amount sharply increases (When the temperature of the fuel becomes equal to or higher than the boiling point, the fuel is vaporized very easily). Consequently, by setting the temperature of the fuel adsorption layer to be higher than the boiling point of the fuel, the fuel vapors liquefied and adsorbed by the adsorbent are easily vaporized and very easily desorbed. Therefore, when the amount Q of heat given to the adsorbent by the temperature control means and the shape of the fuel adsorption layer (the distance from the temperature control means to the farthest part of the fuel adsorption layer) are designed in accordance with the equation (1) so that the temperature T of the fuel adsorption layer is higher than the boiling point of the fuel, the temperature of the whole area of the fuel adsorption layer can be sufficiently controlled.
When the temperature of the fuel adsorption layer is increased too much and exceeds the fire point of the fuel, it is not desirable from the viewpoint of safety. The temperature T of the fuel adsorption layer has to be set lower than the fire point of the fuel. Consequently, by setting the amount of heat given to the adsorbent by the temperature control means and the shape of the fuel adsorption layer (the distance from the temperature control means to the farthest part of the fuel adsorption layer) so that the temperature T in the whole area of the fuel adsorption layer satisfies the condition (2), specifically, the temperature in the portion closest to the temperature control means of the fuel adsorption layer is lower than the fire point of the fuel and the temperature in the portion farthest from the temperature control means of the fuel adsorption layer is higher than the boiling point of the fuel, a canister having high desorption performance can be obtained.
The heat gradient of the canister satisfying the conditio
Amano Noriyasu
Itakura Hideaki
Kato Naoya
Koyama Nobuhiko
Takeyama Masaki
Lawrence Frank M.
Nippon Soken Inc.
Nixon & Vanderhye P.C.
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