Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2003-08-05
2004-08-03
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S520000
Reexamination Certificate
active
06769417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for evaluating the deteriorated state of a hydrocarbon adsorbent that is disposed in the exhaust passage of an internal combustion engine.
2. Description of the Related Art
Some known systems for purifying exhaust gases emitted from internal combustion engines have an exhaust gas purifier disposed in the exhaust passage, which may comprise a hydrocarbon adsorbent such as zeolite or a hydrocarbon adsorbing catalyst comprising a composite combination of a hydrocarbon adsorbent and a three-way catalyst, for adsorbing hydrocarbons (HC) in the exhaust gas while the catalytic converter such as a three-way catalyst or the like is not functioning sufficiently, i.e., while the catalytic converter is not sufficiently activated as when the internal combustion engine starts to operate at a low temperature. The hydrocarbon adsorbent has a function to adsorb hydrocarbons in the exhaust gas at relatively low temperatures below 100° C., for example, and operates to release the adsorbed hydrocarbons when heated to a certain temperature in the range from 100 to 250° C., for example.
It has been desired in the art to evaluate the deteriorated state of a hydrocarbon adsorbent incorporated in an exhaust gas purifier in order to determine when to replace the exhaust gas purifier. The applicant of the present application has proposed the following technique of evaluating the deteriorated state of a hydrocarbon adsorbent: The hydrocarbon adsorbent is capable of adsorbing not only hydrocarbons contained in exhaust gases, but also moisture contained in exhaust gases. The ability of the hydrocarbon adsorbent to adsorb moisture, i.e., the maximum amount of moisture that can be adsorbed by the hydrocarbon adsorbent, is highly correlated to the ability of the hydrocarbon adsorbent to adsorb hydrocarbons, i.e., the maximum amount of hydrocarbons that can be adsorbed by the hydrocarbon adsorbent. As the hydrocarbon adsorbent progressively deteriorates, both the ability to adsorb moisture and the ability to adsorb hydrocarbons are progressively lowered in the same manner. Therefore, when the ability of the hydrocarbon adsorbent to adsorb moisture is evaluated, the ability of the hydrocarbon adsorbent to adsorb hydrocarbons can also be evaluated based on the evaluated ability to adsorb moisture. According to the technique proposed by the applicant, a humidity sensor is disposed downstream of the hydrocarbon adsorbent or humidity sensors are disposed respectively downstream and upstream of the hydrocarbon adsorbent. The deteriorated state of the hydrocarbon adsorbent is evaluated based on the transition of an output signal from the humidity sensor or sensors after the internal combustion engine has started to operate.
For adequately evaluating the deteriorated state of the hydrocarbon adsorbent using output data from the humidity sensor or sensors in various many environments that the internal combustion engine is subject to while in operation, the humidity sensor or sensors that are exposed to high-temperature exhaust gases are required to be highly durable over a long period of time, and also required to have minimum changes in the aging characteristics thereof and to suffer minimum characteristic variations among individual units of humidity sensors.
However, it is generally difficult for humidity sensors to fully satisfy all the above requirements. It would need a large expenditure of money and labor to develop humidity sensors that fully satisfy all the above requirements, and such humidity sensors would be highly expensive to manufacture.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus for adequately evaluating the deteriorated state of a hydrocarbon adsorbent by compensating for changes in the characteristics of humidity sensors that are used and also compensating for characteristic variations among individual units of the humidity sensors.
Basic principles of the present invention will first be described below. The humidity which is present downstream of a hydrocarbon adsorbent disposed in an exhaust passage of an internal combustion engine after the internal combustion engine has started to operate, generally undergoes the following transition: Immediately after the internal combustion engine has started to operate, the humidity which is present downstream of the hydrocarbon adsorbent is of a relatively low level as moisture contained in the exhaust gas is adsorbed by the hydrocarbon adsorbent. When the adsorption of moisture in the exhaust gas by the hydrocarbon adsorbent is saturated, the humidity which is present downstream of the hydrocarbon adsorbent changes to a tendency to monotonously increase from a low humidity to a high humidity and is eventually converged to a substantially constant high humidity level. Therefore, a changing timing at which the humidity downstream of the hydrocarbon adsorbent changes to a tendency to monotonously increase from a low humidity to a high humidity after the internal combustion engine has started to operate corresponds to a timing at which the adsorption of moisture by the hydrocarbon adsorbent is saturated. Consequently, a total amount of moisture supplied to the hydrocarbon adsorbent up to the changing timing after the internal combustion engine has started to operate signifies a maximum quantity of moisture that can be adsorbed by the hydrocarbon adsorbent. Accordingly, if the total amount of moisture or a quantity corresponding thereto is recognized, then it is possible to evaluate the ability of the hydrocarbon adsorbent to adsorb moisture and hence the deteriorated state of the hydrocarbon adsorbent.
For evaluating the deteriorated state of the hydrocarbon adsorbent, it is necessary to detect the changing timing. The changing timing can be recognized based on an appropriate characteristic quantity representing a change in an output signal of a humidity sensor that is disposed downstream of the hydrocarbon adsorbent. For example, after the internal combustion engine has started to operate, the time when a change in the output signal of the humidity sensor from a low humidity level to a high humidity level exceeds a preset value can be detected as the changing timing. However, the transition of the output signal of the humidity sensor is affected by not only the deteriorated state of the hydrocarbon adsorbent, but also a characteristic change of the humidity sensor due to a deterioration thereof. As the humidity sensor is progressively deteriorated, the rate of change of the output signal of the humidity sensor is lowered when the humidity represented by the output signal of the humidity sensor changes to the tendency to monotonously increase. Therefore, providing the preset value for detecting the changing timing is constant, then the detected changing timing varies depending on the deteriorated state of the humidity sensor even if the deteriorated state of the hydrocarbon adsorbent remains constant, and hence the total quantity of moisture supplied to the hydrocarbon adsorbent up to the detected changing timing changes. Therefore, it is preferable to correct the preset value for detecting the changing timing depending on the characteristic change of the humidity sensor due to its deterioration, thereby compensating for the characteristic change of the humidity sensor.
According to a first aspect of the present invention, there is provided an apparatus for evaluating a deteriorated state of a hydrocarbon adsorbent disposed in an exhaust passage of an internal combustion engine for adsorbing hydrocarbons contained in an exhaust gas emitted from the internal combustion engine, based on the transition characteristics of an output signal of a humidity sensor which is disposed in the exhaust passage downstream of the hydrocarbon adsorbent after the internal combustion engine has started to operate, the apparatus comprising changing timing detecting means for detecting a changing timing at which a humidity repres
Endo Tetsuo
Ueno Masaki
Yamazaki Hideharu
Arent & Fox PLLC
Honda Giken Kogyo Kabushiki Kaisha
Mohanty Bibhu
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