Title: Hydrocarbon adsorbent state monitoring device
Abstract: A characteristic change of a humidity sensor 19 is detected based on the transitional characteristics of output data of the humidity sensor 19 with respect to integrated moisture quantity data representative of an integrated amount of moisture that is supplied to an HG adsorbent 7 by an exhaust gas after an engine 1 has started to operate. A parameter for grasping a state of the HC adsorbent 7 is corrected. The state, such as a deteriorated state or the like, of a hydrocarbon adsorbent (HC adsorbent) is properly monitored while compensating for the effect of the characteristic change of the humidity sensor and the effect of variations of the characteristics of individual units of the humidity sensor.
Patent Number: 6,928,805 Issued on 08/16/2005 to Yamazaki, et al.
| Inventors:
|
Yamazaki; Hideharu (Wako, JP);
Sato; Masahiro (Wako, JP);
Machida; Kei (Wako, JP);
Endo; Tetsuo (Wako, JP);
Ueno; Masaki (Wako, JP)
|
| Assignee:
|
Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
490392 |
| Filed:
|
October 21, 2002 |
| PCT Filed:
|
October 21, 2002
|
| PCT NO:
|
PCT/JP02/10876
|
| 371 Date:
|
April 6, 2004
|
| 102(e) Date:
|
April 6, 2004
|
| PCT PUB.NO.:
|
WO03/03605 |
| PCT PUB. Date:
|
May 1, 2003 |
Foreign Application Priority Data
| Oct 19, 2001[JP] | 2001-321730 |
| Dec 28, 2001[JP] | 2001-400902 |
| Current U.S. Class: |
60/277; 60/276; 60/286; 60/287; 60/297; 60/300 |
| Intern'l Class: |
F01N 003/00 |
| Field of Search: |
60/276,277,284,286,287,288,289,292,295,297,278,300,303
|
References Cited [Referenced By]
U.S. Patent Documents
| 5595060 | Jan., 1997 | Togai et al.
| |
| 6357227 | Mar., 2002 | Neufert.
| |
| 6422006 | Jul., 2002 | Ohmori et al.
| |
| 6477830 | Nov., 2002 | Takakura et al.
| |
| 6581370 | Jun., 2003 | Sato et al.
| |
| 6769417 | Aug., 2004 | Ueno et al.
| |
| Foreign Patent Documents |
| 1132589 | Sep., 2001 | EP.
| |
| 61-294350 | Dec., 1986 | JP.
| |
| 5-256124 | Oct., 1993 | JP.
| |
| 405256124 | Oct., 1993 | JP.
| |
| 2001-33412 | Feb., 2001 | JP.
| |
Other References
European Search Report dated Nov. 22, 2004.
|
Primary Examiner: Tran; Binh Q.
Attorney, Agent or Firm: Armstrong, Kratz, Quintos, Hanson, & Brooks, LLP.
Claims
1. An apparatus for monitoring a state of a hydrocarbon adsorbent disposed in
an exhaust passage of an internal combustion engine for adsorbing hydrocarbons
in an exhaust gas emitted from the internal combustion engine, using output data
of a humidity sensor disposed near the hydrocarbon adsorbent, characterized by:
characteristic change detecting means for detecting a characteristic change of
the humidity sensor based on output data of the humidity sensor under a predetermined
condition, and characteristic change compensating means for correcting a parameter
to grasp the state of the hydrocarbon adsorbent using the output data of the humidity
sensor, based on the characteristic change detected by said characteristic change
detecting means.
2. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 1, characterized by:
integrated moisture quantity data generating means for sequentially generating
data of an integrated amount of moisture supplied to said hydrocarbon adsorbent
by the exhaust gas emitted from the internal combustion engine after the internal
combustion engine has started to operate, wherein said characteristic change detecting
means detects the characteristic change of the humidity sensor based on a change
due to the characteristic change of the humidity sensor, of changes of transitional
characteristics of the output data of the humidity sensor with respect to the data
generated by said integrated moisture quantity data generating means after the
internal combustion engine has started to operate.
3. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 2, characterized in that said characteristic change detecting means detects
the characteristic change of the humidity sensor based on a change from a predetermined
reference value of characteristic change detecting output data which comprises
the output data of the humidity sensor at the time when the data generated by said
integrated moisture quantity data generating means has reached a predetermined
value after the internal combustion engine has started to operate.
4. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 1, characterized in that said characteristic change detecting means detects
the characteristic change of the humidity sensor based on a change due to the characteristic
change of the humidity sensor, of changes of transitional characteristics of the
output data of the humidity sensor with respect to a period of time that has elapsed
after the internal combustion engine has started to operate.
5. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 4, characterized in that said characteristic change detecting means detects
the characteristic change of the humidity sensor based on a change from a predetermined
reference value of characteristic change detecting output data which comprises
the output data of the humidity sensor at the time when the period of time that
has elapsed after the internal combustion engine has started to operate has reached
a predetermined value.
6. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to 3, characterized in that the state of said hydrocarbon adsorbent to be monitored
comprises a deteriorated state of said hydrocarbon adsorbent, and said humidity
sensor is disposed downstream of said hydrocarbon adsorbent, wherein a changing
timing at which a humidity represented by the output data of said humidity sensor
changes to a tendency to increase monotonously from a low humidity level to a high
humidity level after the internal combustion engine has started to operate is detected,
and the data generated by said integrated moisture quantity data generating means
at the detected changing timing is used as said parameter for grasping the deteriorated
state of said hydrocarbon adsorbent.
7. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to any one of claims
1,
4 and
5, characterized in that the
state of said hydrocarbon adsorbent to be monitored comprises a deteriorated state
of said hydrocarbon adsorbent, and said humidity sensor is disposed downstream
of said hydrocarbon adsorbent, further comprising:
integrated moisture quantity data generating means for sequentially generating
data of an integrated amount of moisture supplied to said hydrocarbon adsorbent
by the exhaust gas emitted from the internal combustion engine after the internal
combustion engine has started to operate, and changing timing detecting means for
detecting a changing timing at which a humidity represented by the output data
of said humidity sensor changes to a tendency to increase monotonously from a low
humidity level to a high humidity level after the internal combustion engine has
started to operate, wherein the data generated by said integrated moisture quantity
data generating means at the changing timing detected by said changing timing detecting
means is used as said parameter for grasping the deteriorated state of said hydrocarbon
adsorbent.
8. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to any one of claims
1 through
5, characterized in that the state
of said hydrocarbon adsorbent to be monitored comprises a deteriorated state of
said hydrocarbon adsorbent, and the output data of said humidity sensor before
a humidity represented by the output data of said humidity sensor is converged
to a humidity outside of said exhaust passage after said internal combustion engine
has stopped operating is used as said parameter for grasping the deteriorated state
of said hydrocarbon adsorbent.
9. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 8, characterized in that the output data of said humidity sensor within
a period of time in which the humidity represented by the output data of said humidity
sensor is maintained at a substantially constant level after said internal combustion
engine has stopped operating is used as said parameter for grasping the deteriorated
state of said hydrocarbon adsorbent.
10. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 8, characterized in that the deteriorated state of said hydrocarbon adsorbent
is grasped based on said parameter after said internal combustion engine has stopped
operating under a predetermined condition.
11. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 1, characterized in that said characteristic change compensating means
corrects said parameter when the characteristic change of said humidity sensor
which is detected by said characteristic change detecting means exceeds a predetermined quantity.
12. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 1, characterized in that the deteriorated state of said hydrocarbon adsorbent
is prohibited from being grasped based on said parameter when the characteristic
change of said humidity sensor which is detected by said characteristic change
detecting means exceeds a predetermined upper limit quantity.
13. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 1, characterized in that said humidity sensor has characteristic data
holding means for holding, in advance, data of characteristics of an individual
unit of said humidity sensor, and said characteristic change detecting means detects
the characteristic change of the humidity sensor based on the output data of said
humidity sensor and the data held by said characteristic data holding means.
14. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 3, characterized in that said humidity sensor has characteristic data
holding means for holding, in advance, data specifying said predetermined value
relative to the data generated by said integrated moisture quantity data generating
means, as the data of the characteristics of the individual unit of said humidity
sensor, and said characteristic change detecting means acquires the characteristic
change detecting output data of said humidity sensor using said predetermined value
which is specified by the data held by said characteristic data holding means.
15. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to 5, characterized in that said humidity sensor has characteristic data holding
means for holding, in advance, data specifying said reference value relative to
said characteristic change detecting output data as the data of the characteristics
of the individual unit of said humidity sensor, and said characteristic change
detecting means acquires the characteristic change detecting output data of said
humidity sensor using said reference value which is specified by the data held
by said characteristic data holding means.
16. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to 14, characterized in that said characteristic data holding means comprises a
resistive element having a resistance depending on the value of the data of the
characteristics of the individual unit of said humidity sensor.
17. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 15, characterized in that said characteristic data holding means comprises
a resistive element having a resistance depending on the value of the data of the
characteristics of the individual unit of said humidity sensor.
18. An apparatus for monitoring a state of a hydrocarbon adsorbent disposed in
an exhaust passage of an internal combustion engine for adsorbing hydrocarbons
in an exhaust gas emitted from the internal combustion engine, using output data
of a plurality of humidity sensors disposed at different locations near the hydrocarbon
adsorbent, characterized by:
characteristic change detecting means for detecting characteristic changes of
the humidity sensors based on output data of the respective humidity sensors under
a predetermined condition, and characteristic change compensating means for correcting
a parameter to grasp the state of the hydrocarbon adsorbent using the output data
of the humidity sensors, based on the characteristic changes of the humidity sensors
detected by said characteristic change detecting means.
19. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 18, characterized by:
integrated moisture quantity data generating means for sequentially generating
data of an integrated amount of moisture supplied to said hydrocarbon adsorbent
by the exhaust gas emitted from the internal combustion engine after the internal
combustion engine has started to operate, wherein said characteristic change detecting
means detects the characteristic changes of the humidity sensors based on a change
due to the characteristic changes of the humidity sensors, of changes of transitional
characteristics of the output data of the humidity sensors with respect to the
data generated by said integrated moisture quantity data generating means after
the internal combustion engine has started to operate.
20. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 19, characterized in that said characteristic change detecting means detects
the characteristic changes of the humidity sensors based on a change from a predetermined
reference value of characteristic change detecting output data which comprises
the output data of the humidity sensors at the time when the data generated by
said integrated moisture quantity data generating means has reached predetermined
values for the respective humidity sensors after the internal combustion engine
has started to operate.
21. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 18, characterized in that said characteristic change detecting means detects
the characteristic changes of the humidity sensors based on a change due to the
characteristic changes of the humidity sensors, of changes of transitional characteristics
of the output data of the humidity sensors with respect to a period of time that
has elapsed after the internal combustion engine has started to operate.
22. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 21, characterized in that said characteristic change detecting means detects
the characteristic changes of the humidity sensors based on a change from predetermined
reference values of characteristic change detecting output data of the humidity
sensors which comprises the output data of the humidity sensors at the time when
the period of time that has elapsed after the internal combustion engine has started
to operate has reached predetermined values for the respective humidity sensors.
23. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to 20, characterized in that the state of said hydrocarbon adsorbent to be monitored
comprises a deteriorated state of said hydrocarbon adsorbent, and said humidity
sensors comprise a downstream humidity sensor disposed downstream of said hydrocarbon
adsorbent and an upstream humidity sensor disposed upstream of said hydrocarbon
adsorbent, further comprising:
upstream changing timing detecting means for detecting a changing timing at which
a humidity represented by the output data of said upstream humidity sensor changes
to a tendency to increase monotonously from a low humidity level to a high humidity
level after the internal combustion engine has started to operate, and downstream
changing timing detecting means for detecting a changing timing at which a humidity
represented by the output data of said downstream humidity sensor changes to a
tendency to increase monotonously from a low humidity level to a high humidity
level after the internal combustion engine has started to operate, wherein the
difference between the data generated by said integrated moisture quantity data
generating means at the changing timing detected by said upstream changing timing
detecting means and the data generated by said integrated moisture quantity data
generating means at the changing timing detected by said downstream changing timing
detecting means is used as said parameter for grasping the deteriorated state of
said hydrocarbon adsorbent.
24. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to any one of claims
18,
21, and
22, characterized in that
the state of said hydrocarbon adsorbent to be monitored comprises a deteriorated
state of said hydrocarbon adsorbent, and said humidity sensors comprise a downstream
humidity sensor disposed downstream of said hydrocarbon adsorbent and an upstream
humidity sensor disposed upstream of said hydrocarbon adsorbent, further comprising:
upstream changing timing detecting means for detecting a changing timing at which
a humidity represented by the output data of said upstream humidity sensor changes
to a tendency to increase monotonously from a low humidity level to a high humidity
level after the internal combustion engine has started to operate, downstream changing
timing detecting means for detecting a changing timing at which a humidity represented
by the output data of said downstream humidity sensor changes to a tendency to
increase monotonously from a low humidity level to a high humidity level after
the internal combustion engine has started to operate, and integrated moisture
quantity data generating means for generating data of an integrated amount of moisture
supplied to said hydrocarbon adsorbent by the exhaust gas emitted from the internal
combustion engine from the changing timing detected by said upstream changing timing
detecting means to the changing timing detected by said downstream changing timing
detecting means, wherein the data generated by said integrated moisture quantity
data generating means is used as said parameter for grasping the deteriorated state
of said hydrocarbon adsorbent.
25. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 18, characterized in that said characteristic change compensating means
corrects said parameter when either one of the characteristic changes of said humidity
sensors which are detected by said characteristic change detecting means exceeds
a predetermined quantity.
26. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 18, characterized in that said characteristic change compensating means
compares the characteristic changes of the respective humidity sensors detected
by said characteristic change detecting means with a predetermined upper limit
quantity, and prohibits the deteriorated state of said hydrocarbon adsorbent from
being grasped based on said parameter when the characteristic change of at least
one of said humidity sensors exceeds said upper limit quantity.
27. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 18, characterized in that said humidity sensors have respective characteristic
data holding means for holding, in advance, data of characteristics of individual
units of said humidity sensors, and said characteristic change detecting means
detects the characteristic changes of the humidity sensors based on the output
data of said humidity sensors and the data held by said characteristic data holding means.
28. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to 22, characterized in that said humidity sensors have respective characteristic
data holding means for holding, in advance, data specifying said reference values
relative to said characteristic change detecting output data of the humidity sensors
as the data of the characteristics of the individual units of said humidity sensors,
and said characteristic change detecting means acquires the characteristic change
detecting output data of said humidity sensors using said reference values of the
respective humidity sensors which are specified by the data held by said characteristic
data holding means.
29. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 27, characterized in that said characteristic data holding means comprises
resistive elements having resistances depending on the value of the data of the
characteristics of the individual units of said humidity sensors.
30. An apparatus for monitoring the state of the hydrocarbon adsorbent according
to claim 28, characterized in that said characteristic data holding means comprises
resistive elements having resistances depending on the value of the data of the
characteristics of the individual units of said humidity sensors.
31. A method of monitoring a state of a hydrocarbon adsorbent disposed in an
exhaust passage of an internal combustion engine for adsorbing hydrocarbons in
an exhaust gas emitted from the internal combustion engine, using output data of
a humidity sensor disposed near the hydrocarbon adsorbent, comprising the steps of:
detecting a characteristic change of the humidity sensor based on output data
of the humidity sensor under a predetermined condition; and
correcting a parameter to grasp the state of the hydrocarbon adsorbent using
the output data of the humidity sensor, based on the detected characteristic change.
32. A method of monitoring a state of a hydrocarbon adsorbent disposed in an
exhaust passage of an internal combustion engine for adsorbing hydrocarbons in
an exhaust gas emitted from the internal combustion engine, using output data of
a plurality of humidity sensors disposed at different locations near the hydrocarbon
adsorbent, comprising the steps of:
detecting characteristic changes of the humidity sensors based on output data
of the respective humidity sensors under a predetermined condition; and
correcting a parameter to grasp the state of the hydrocarbon absorbent using
the output data of the humidity sensors, based on the characteristic changes of
the humidity sensors detected in said detecting step.
Description
TECHNICAL FIELD
The present invention relates to an apparatus for monitoring the state of a hydrocarbon
adsorbent disposed in the exhaust passage of an internal combustion engine.
BACKGROUND 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.
The applicant of the present application has proposed the following technique
of monitoring a state, e.g., a deteriorated state, of a hydrocarbon adsorbent of
the type described above: The inventors of the present invention have found that
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. Using output data of the humidity sensor, the ability
of the hydrocarbon adsorbent to adsorb moisture and hence the ability of the hydrocarbon
adsorbent to adsorb hydrocarbons are grasped, thus monitoring the deteriorated
state of the hydrocarbon adsorbent.
For adequately evaluating the deteriorated state of the hydrocarbon adsorbent
using output data from the humidity sensor in various many environments that the
internal combustion engine is subject to while in operation, the humidity sensor
that is exposed to high-temperature exhaust gases is 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.
The present invention has been made in view of the above background. It is an
object of the present invention to provide a hydrocarbon adsorbent state monitoring
apparatus for adequately monitoring the deteriorated state or the like of a hydrocarbon
adsorbent by compensating for effects of changes in the characteristics of humidity
sensors that are used and also compensating for effects of characteristic variations
among individual units of the humidity sensors.
DISCLOSURE OF THE INVENTION
To achieve the above object, there is provided in accordance with the present
invention an apparatus for monitoring a state of a hydrocarbon adsorbent disposed
in an exhaust passage of an internal combustion engine for adsorbing hydrocarbons
in an exhaust gas emitted from the internal combustion engine, using output data
of a humidity sensor disposed near the hydrocarbon adsorbent, characterized by
characteristic change detecting means for detecting a characteristic change of
the humidity sensor based on output data of the humidity sensor under a predetermined
condition, and characteristic change compensating means for correcting a parameter
to grasp the state of the hydrocarbon adsorbent using the output data of the humidity
sensor, based on the characteristic change detected by the characteristic change
detecting means (first invention).
According to the above invention, the parameter to grasp the state of the
hydrocarbon adsorbent is corrected based on the characteristic change of the humidity
sensor which is detected based on the output data of the humidity sensor under
a certain condition (e.g., a condition with respect to a timing to acquire the
output data of the humidity sensor, an operating state of the internal combustion
engine, or the like). It is thus possible to obtain a parameter where the effect
of the characteristic change of the humidity sensor has been compensated for. Using
such a parameter, the state of the hydrocarbon adsorbent (a deteriorated state
of the hydrocarbon adsorbent, a state in which moisture is adsorbed by the hydrocarbon
adsorbent, or the like) can appropriately be grasped while compensating for the
effect of the characteristic change of the humidity sensor. As the effect of the
characteristic change of the humidity sensor can be compensated for, the requirements
for the steadiness of the characteristics of the humidity sensor are lessened,
and the humidity sensor is allowed to have certain characteristic changes. Therefore,
the costs needed to develop and manufacture the humidity sensor can be reduced.
According to the present invention, the parameter may be a parameter representative
of the state of the hydrocarbon adsorbent to be grasped, a parameter such as a
threshold to be compared with such a parameter, or an intermediate parameter for
use in a process for determining such parameters. The characteristic change of
the humidity sensor that is detected by the characteristic change detecting means
may, for example, be a characteristic change of the humidity sensor with respect
to desired reference characteristics, such as characteristics of a brand-new humidity sensor.
According to the present invention (first invention), the apparatus has
integrated moisture quantity data generating means for sequentially generating
data of an integrated amount of moisture supplied to the hydrocarbon adsorbent
by the exhaust gas emitted from the internal combustion engine after the internal
combustion engine has started to operate, wherein the characteristic change detecting
means detects the characteristic change of the humidity sensor based on a change
due to the characteristic change of the humidity sensor, of changes of transitional
characteristics of the output data of the humidity sensor with respect to the data
generated by the integrated moisture quantity data generating means after the internal
combustion engine has started to operate (second invention).
Alternatively, the characteristic change detecting means may detect
the characteristic change of the humidity sensor based on a change due to the characteristic
change of the humidity sensor, of changes of transitional characteristics of the
output data of the humidity sensor with respect to a period of time that has elapsed
after the internal combustion engine has started to operate (third invention).
Specifically, as described in detail later on, the inventors have found
that the output data of the humidity sensor near the hydrocarbon adsorbent exhibits
a characteristic transition with respect to the data (the data generated by the
integrated moisture quantity data generating means) of the integrated amount of
moisture supplied to the hydrocarbon adsorbent by the exhaust gas emitted from
the internal combustion engine after the internal combustion engine has started
to operate or a period of time that has elapsed after the internal combustion engine
has started to operate. The transitional characteristics change depending on the
characteristic change of the humidity sensor. The transitional characteristics
include a portion which changes due to not only the characteristic change of the
humidity sensor, but also the effect of the state in which the hydrocarbon adsorbent
adsorbs moisture, and also include a portion which changes due to only the characteristic
change of the humidity sensor. Based on a change due to the characteristic change
of the humidity sensor, of changes of the transitional characteristics, therefore,
the characteristic change of the humidity sensor can appropriately be detected.
Since the transitional characteristics are also subject to the effect of the state
in which the hydrocarbon adsorbent adsorbs moisture, it is also possible to grasp
the state in which the hydrocarbon adsorbent adsorbs moisture based on the transitional
characteristics while grasping the characteristic change of the humidity sensor.
The data representative of the integrated amount of moisture may be data of the
integrated amount of moisture itself, but may basically be data substantially proportional
to the integrated amount of moisture. For example, the integrated value of an amount
of fuel or an amount of intake air supplied to the internal combustion engine after
the internal combustion engine has started to operate may be used as the data representative
of the integrated amount of moisture. If the operating state of the internal combustion
engine after the internal combustion engine has started to operate is a substantially
constant operating state, e.g., an idling state, then the period of time that has
elapsed after the internal combustion engine has started to operate may be used
as the data representative of the integrated amount of moisture.
According to the present invention (second invention) wherein the characteristic
change of the humidity sensor is detected based on a change of the transitional
characteristics of the output data of the humidity sensor with respect to the data
representative of the integrated amount of moisture after the internal combustion
engine has started to operate, more specifically, the characteristic change detecting
means may detect the characteristic change of the humidity sensor based on a change
from a predetermined reference value of characteristic change detecting output
data which comprises the output data of the humidity sensor at the time when the
data generated by the integrated moisture quantity data generating means has reached
a predetermined value after the internal combustion engine has started to operate
(fourth invention). Similarly, according to the present invention (third invention)
wherein the characteristic change of the humidity sensor is detected based on a
change of the transitional characteristics of the output data of the humidity sensor
with respect to the period of time that has elapsed after the internal combustion
engine has started to operate, more specifically, the characteristic change detecting
means detects the characteristic change of the humidity sensor based on a change
from a predetermined reference value of characteristic change detecting output
data which comprises the output data of the humidity sensor at the time when the
period of time that has elapsed after the internal combustion engine has started
to operate has reached a predetermined value (fifth invention).
Specifically, as described in detail later on, the inventors have found
that if the humidity sensor is disposed downstream of the hydrocarbon adsorbent,
the humidity at the location of the humidity sensor immediately after the internal
combustion engine has started to operate is of a substantially constant low humidity
level due to the adsorption of moisture in the exhaust gas by the hydrocarbon adsorbent.
When the integrated amount of moisture or the elapsed period of time increases
until the adsorption of moisture by the hydrocarbon adsorbent is saturated, the
humidity at the location of the humidity sensor increases monotonously from a low
humidity level to a high humidity level until finally it reaches the humidity inherent
in the exhaust gas (the humidity of the exhaust gas when the hydrocarbon adsorbent
or the like does not adsorb moisture). The output data of the humidity sensor at
the time when the humidity at the location of the humidity sensor reaches the humidity
inherent in the exhaust gas is of a substantially constant value. When the humidity
sensor suffers a characteristic change due to its deterioration, a timing at which
the output data of the humidity sensor becomes substantially constant or the substantially
constant level changes depending on the characteristic change.
If the humidity sensor is disposed upstream of the hydrocarbon adsorbent, then
since the region near the hydrocarbon adsorbent is dry immediately after the internal
combustion engine has started to operate, the humidity at the location of the humidity
sensor is of a low humidity level for a relatively short period of time, and then
changes quickly to a high humidity level and reaches the humidity inherent in the
exhaust gas. The output data of the humidity sensor at the time when the humidity
at the location of the humidity sensor reaches the humidity inherent in the exhaust
gas is of a substantially constant value, as with the above case. When the humidity
sensor suffers a characteristic change due to its deterioration, a timing at which
the output data of the humidity sensor becomes substantially constant or the substantially
constant level changes depending on the characteristic change.
According to the present invention, the output data of the humidity sensor
at the time when the data generated by the integrated moisture quantity data generating
means (the data representative of the integrated amount of moisture) has reached
a predetermined value or the time when the period of time that has elapsed after
the internal combustion engine has started to operate has reached a predetermined
value is used as the characteristic change detecting output data. The predetermined
value may be determined such that the humidity at the location of the humidity
sensor reaches the inherent humidity of the exhaust gas or a humidity close thereto
when the data representative of the integrated amount of moisture or the elapsed
period of time has reached the predetermined value. According to the present invention,
the characteristic change of the humidity sensor is detected based on a change
from the reference value of the characteristic change detecting output data. Thus,
the characteristic change of the humidity sensor can appropriately be detected.
According to the present invention (second invention or fourth invention)
wherein the characteristic change of the humidity sensor is detected based on a
change of the transitional characteristics of the output data of the humidity sensor
with respect to the data representative of the integrated amount of moisture after
the internal combustion engine has started to operate, if the state of the hydrocarbon
adsorbent to be monitored comprises a deteriorated state of the hydrocarbon adsorbent,
then the humidity sensor is disposed downstream of the hydrocarbon adsorbent. A
changing timing at which a humidity represented by the output data of the humidity
sensor changes to a tendency to increase monotonously from a low humidity level
to a high humidity level after the internal combustion engine has started to operate
is detected, and the data generated by the integrated moisture quantity data generating
means at the detected changing timing is used as the parameter for grasping the
deteriorated state of the hydrocarbon adsorbent (sixth invention).
Similarly, according to the present invention (third invention or fifth
invention) wherein the characteristic change of the humidity sensor is detected
based on a change of the transitional characteristics of the output data of the
humidity sensor with respect to the period of time that has elapsed after the internal
combustion engine has started to operate, if the state of the hydrocarbon adsorbent
to be monitored comprises a deteriorated state of the hydrocarbon adsorbent, the
humidity sensor is disposed downstream of the hydrocarbon adsorbent. The apparatus
further comprises integrated moisture quantity data generating means for sequentially
generating data of an integrated amount of moisture supplied to the hydrocarbon
adsorbent by the exhaust gas emitted from the internal combustion engine after
the internal combustion engine has started to operate, and changing timing detecting
means for detecting a changing timing at which a humidity represented by the output
data of the humidity sensor changes to a tendency to increase monotonously from
a low humidity level to a high humidity level after the internal combustion engine
has started to operate. The data generated by the integrated moisture quantity
data generating means at the changing timing detected by the changing timing detecting
means is used as the parameter for grasping the deteriorated state of the hydrocarbon
adsorbent (seventh invention).
Specifically, as described above, if the humidity sensor is disposed
downstream of the hydrocarbon adsorbent, then the humidity at the location of the
humidity sensor immediately after the internal combustion engine has started to
operate is of a substantially constant low humidity level due to the adsorption
of moisture in the exhaust gas by the hydrocarbon adsorbent. When the adsorption
of moisture by the hydrocarbon adsorbent is saturated, the humidity at the location
of the humidity sensor changes to a tendency to increase monotonously from a low
humidity level to a high humidity level. Therefore, a changing timing at which
the humidity represented by the output of the humidity sensor changes to a tendency
to increase monotonously from a low humidity level to a high humidity level signifies
a timing at which the adsorption of moisture by the hydrocarbon adsorbent is saturated
(at this timing, the adsorption of moisture by the hydrocarbon adsorbent is saturated,
the timing may also be referred to as "absorption saturation timing"). The data
generated by the integrated moisture quantity data generating means at the absorption
saturation timing (data of the integrated amount of moisture) corresponds to a
maximum amount of moisture and hydrocarbons that can be adsorbed by the hydrocarbon
adsorbent, and represents a deteriorated state of the hydrocarbon adsorbent. In
this case, the absorption saturation timing (changing timing) at which the humidity
represented by the output of the humidity sensor changes to a tendency to increase
monotonously from a low humidity level to a high humidity level is generally affected
by not only the deteriorated state of the hydrocarbon adsorbent, but also the effect
of the characteristic change of the humidity sensor. The effect of the characteristic
change of the humidity sensor can be compensated for by correcting the data generated
by the integrated moisture quantity data generating means at the absorption saturation
timing depending on the characteristic change of the humidity sensor detected by
the characteristic change detecting means. Therefore, by using the data generated
by the integrated moisture quantity data generating means at the absorption saturation
timing as the parameter for grasping the deteriorated state of the hydrocarbon
adsorbent, the deteriorated state of the hydrocarbon adsorbent can appropriately
be grasped while compensating for the effect of the characteristic change of the
humidity sensor.
According to either one of the first through fifth inventions, if the state
of the hydrocarbon adsorbent to be monitored comprises a deteriorated state of
the hydrocarbon adsorbent, then the output data of the humidity sensor before a
humidity represented by the output data of the humidity sensor is converged to
a humidity outside of the exhaust passage after the internal combustion engine
has stopped operating may be used as the parameter for grasping the deteriorated
state of the hydrocarbon adsorbent (eighth invention).
Specifically, as described in detail later on, the inventors have found
that the humidity near the hydrocarbon adsorbent and hence the output data of the
humidity sensor after the internal combustion engine has stopped operating exhibit
the tendency of a characteristic transition with respect to the deteriorated state
of the hydrocarbon adsorbent. For example, when the temperature of the hydrocarbon
adsorbent drops after the internal combustion engine has stopped operating, the
hydrocarbon adsorbent adsorbs moisture in the exhaust gas around (near) the hydrocarbon
adsorbent. When the adsorption of moisture is saturated, the humidity near the
hydrocarbon adsorbent and hence the output data of the humidity sensor are kept
at a substantially constant level for a relatively long period of time (the humidity
suffers very small time-dependent changes). The amount of moisture that can be
adsorbed by the hydrocarbon adsorbent is smaller as the hydrocarbon adsorbent is
more deteriorated, so that the above constant level depends on the deteriorated
state of the hydrocarbon adsorbent. When a sufficiently long period of time elapses
after the internal combustion engine has stopped operating, since a gas exchange
between the interior of the exhaust pipe including the region around the hydrocarbon
adsorbent and the external atmosphere progresses, the humidity near the hydrocarbon
adsorbent is finally converged to the humidity outside of the exhaust passage.
As described above, because the humidity near the hydrocarbon adsorbent exhibits
a characteristic transition with respect to the deteriorated state of the hydrocarbon
adsorbent after the internal combustion engine has stopped operating, the output
data of the humidity sensor after the internal combustion engine has stopped operating
and before the humidity near the hydrocarbon adsorbent is finally converged to
the humidity outside of the exhaust passage can be used as the parameter to grasp
the deteriorated state of the hydrocarbon adsorbent. Simultaneously, by correcting
the parameter depending on the characteristic change of the humidity sensor, the
deteriorated state of the hydrocarbon adsorbent can appropriately be grasped while
compensating for the effect of the characteristic change of the humidity sensor.
According to the present invention (eighth invention) wherein the output
data of the humidity sensor after the internal combustion engine has stopped operating
is used as the parameter, it is preferable to use the output data of the humidity
sensor in a period of time in which the humidity represented by the output of the
humidity sensor is maintained at a substantially constant level after the internal
combustion engine has stopped operating, as the parameter to grasp the deteriorated
state of the hydrocarbon adsorbent. Specifically, as described above, the output
data (output data having a substantially constant level) of the humidity sensor
in the state wherein the humidity near the hydrocarbon adsorbent is kept substantially
constant after the internal combustion engine has stopped operating depends on
the deteriorated state of the hydrocarbon adsorbent. In the state wherein the humidity
is kept constant, since the output data of the humidity sensor is also stable,
the output data of the humidity sensor is highly reliable as depending on the deteriorated
state of the hydrocarbon adsorbent. Therefore, the deteriorated state of the hydrocarbon
adsorbent can be grasped accurately. Furthermore, inasmuch as the humidity sensor
may be of a type capable of detecting a substantially constant humidity, it is
not required to be highly responsive, but may comprise a relatively inexpensive sensor.
According to the present invention (eighth invention or ninth invention)
wherein the output data of the humidity sensor after the internal combustion engine
has stopped operating is used as the parameter, the deteriorated state of the hydrocarbon
adsorbent is preferably grasped based oh the parameter after the internal combustion
engine has stopped operating under a predetermined condition (tenth invention).
With this arrangement, an exhaust gas state (the humidity state of the exhaust
gas or the like) in the exhaust passage after the internal combustion engine has
stopped operating can be maintained in an optimum state for evaluating the deteriorated
state of the hydrocarbon adsorbent. Therefore, the reliability is increased in
grasping the deteriorated state of the hydrocarbon adsorbent using the output data
of the humidity sensor after the internal combustion engine has stopped operating
as the parameter.
More specifically, the predetermined condition referred to above includes a
condition relative to an air-fuel ratio before the internal combustion engine stops
operating. The deteriorated state of the hydrocarbon adsorbent should preferably
be grasped based on the parameter if the air-fuel ratio immediately before the
internal combustion engine stops operating is continuously maintained at a level
near the stoichiometric air-fuel ratio for a predetermined period of time or longer.
Specifically, if the internal combustion engine stops operating is
operated with its air-fuel ratio (the air-fuel ratio of an air-fuel mixture to
be combusted by the internal combustion engine) maintained at a level near the
stoichiometric air-fuel ratio, the exhaust gas emitted from the internal combustion
engine contains relatively much moisture and the concentration of moisture in the
exhaust gas is substantially constant. Therefore, if the air-fuel ratio immediately
before the internal combustion engine stops operating is continuously maintained
at a level near the stoichiometric air-fuel ratio for a predetermined period of
time or longer, then an exhaust gas containing sufficient moisture at a substantially
constant concentration is present in the vicinity of the hydrocarbon adsorbent
immediately after the combustion engine stops operating. Consequently, the hydrocarbon
adsorbent smoothly adsorbs moisture and is saturated, and the transition of the
moisture in the vicinity of the hydrocarbon adsorbent distinctly depends on the
deteriorated state of the hydrocarbon adsorbent.
If the above predetermined condition includes a condition relative to a warmed-up
state of the internal combustion engine before it stops operating, and the engine
temperature immediately before the internal combustion engine stops operating is
equal to or higher than a predetermined temperature, then the deteriorated state
of the hydrocarbon adsorbent should preferably be evaluated based on the output
of the humidity sensor. With this arrangement, when the internal combustion engine
stops operating while it has sufficiently been warmed up, i.e., while the combustion
of the air-fuel mixture in the internal combustion engine has been stabilized,
and the hydrocarbon adsorbent has sufficiently been heated to release the moisture
adsorbed thereby, the deteriorated state of the hydrocarbon adsorbent is grasped
based on the output data (the parameter) of the humidity sensor after the internal
combustion engine has stopped operating. Therefore, variations in the humidity
of the exhaust gas at the hydrocarbon adsorbent immediately after the internal
combustion engine has stopped operating are reduced, and after the temperature
of the hydrocarbon adsorbent has dropped to a certain extent, the hydrocarbon adsorbent
can smoothly adsorb a maximum amount of moisture depending on the deteriorated
state of the hydrocarbon adsorbent. As a result, the transition of the output of
the humidity sensor after the internal combustion engine has stopped operating
becomes more reliable as corresponding to the deteriorated state of the hydrocarbon
adsorbent, and the accuracy of the deteriorated state of the hydrocarbon adsorbent
as grasped using the parameter is increased.
According to the present invention (first through tenth inventions), the
characteristic change compensating means should preferably correct the parameter
when the characteristic change of the humidity sensor which is detected by the
characteristic change detecting means exceeds a predetermined quantity (eleventh
invention). With this arrangement, when the parameter does not need to be corrected
as when a characteristic change of the humidity sensor is detected due to a temporary
disturbance, the parameter is prevented from being corrected.
In either one of the first through eleventh inventions, the deteriorated state
of the hydrocarbon adsorbent should preferably be prohibited from being grasped
based on the parameter when the characteristic change of the humidity sensor which
is detected by the characteristic change detecting means exceeds a predetermined
upper limit quantity (twelfth invention). Specifically, if the humidity sensor
suffers an excessive characteristic change, the humidity sensor may possibly be
excessively deteriorated or may possibly suffer a failure. In such a situation,
it is difficult to obtain the parameter capable of appropriately grasping the state
of the hydrocarbon adsorbent. In this case, therefore, the state of the hydrocarbon
adsorbent is prohibited from being grasped based on the parameter, and hence is
prevented from being grasped in error.
According to the present invention (first through twelfth inventions),
the humidity sensor preferably has characteristic data holding means for holding,
in advance, data of characteristics of an individual unit of the humidity sensor,
and the characteristic change detecting means preferably detects the characteristic
change of the humidity sensor based on the output data of the humidity sensor and
the data held by the characteristic data holding means (thirteenth invention).
With the above arrangement, since the characteristic change of the humidity
sensor is detected using the data held by the characteristic data holding means
associated with an individual unit of the humidity sensor, i.e., the data of the
characteristics of an individual unit of the humidity sensor, it is possible to
compensate for not only the effect of the characteristic change of the humidity
sensor, but also the effect of characteristic variations of individual units of
the humidity sensor in grasping the state of the hydrocarbon adsorbent in grasping
the deteriorated state of the hydrocarbon adsorbent. As a result, the requirements
for the uniformity of the characteristics of individual units of the humidity sensor
are lessened, and the costs needed to develop and manufacture the humidity sensor
can be reduced.
If the characteristic change of the humidity sensor is detected based on the
transitional
characteristics of the output data of the humidity sensor with respect to the integrated
amount of moisture after the internal combustion engine has started to operate
(fourth invention), then the humidity sensor preferably has characteristic data
holding means for holding, in advance, data specifying the predetermined value
relative to the data generated by the integrated moisture quantity data generating
means, as the data of the characteristics of the individual unit of the humidity
sensor. The characteristic change detecting means preferably acquires the characteristic
change detecting output data of the humidity sensor using the predetermined value
which is specified by the data held by the characteristic data holding means (fourteenth invention).
With the above arrangement, the predetermined value (the predetermined value
relative to the data representing the integrated amount of moisture) specifying
the timing at which the characteristic change detecting output data of the humidity
sensor is acquired is adjusted so as to match the characteristics of the individual
unit of the humidity sensor. As a consequence, the effect of characteristic variations
of individual units of the humidity sensor can appropriately be compensated for.
If the characteristic change of the humidity sensor is detected based on the
transitional
characteristics of the output data of the humidity sensor with respect to the integrated
amount of moisture after the internal combustion engine has started to operate
or if the characteristic change of the humidity sensor is detected based on the
transitional characteristics with respect to the elapsed period of time (fourth
or fifth invention), then the humidity sensor preferably has characteristic data
holding means for holding, in advance, data specifying the reference value relative
to the characteristic change detecting output data as the data of the characteristics
of the individual unit of the humidity sensor, and the characteristic change detecting
means preferably acquires the characteristic change detecting output data of the
humidity sensor using the reference value which is specified by the data held by
the characteristic data holding means (fifteenth invention).
With the above arrangement, the reference value serving as a reference for detecting
the characteristic change of the humidity sensor is adjusted so as to match the
characteristics of the individual unit of the humidity sensor. As a consequence,
the characteristic change of the humidity sensor can be detected while appropriately
compensating for the effect of characteristic variations of individual units of
the humidity sensor.
According to the present invention (thirteenth through fifteenth inventions)
wherein the effect of characteristic variations of individual units of the humidity
sensor is compensated for, the characteristic data holding means preferably comprises
a resistive element having a resistance depending on the value of the data of the
characteristics of the individual unit of the humidity sensor (sixteenth invention).
With the above arrangement, the characteristic data holding means can be of
an inexpensive and simple structure. Since the resistance of the resistive element
can be detected relatively easily, the data of the characteristics of the individual
unit of the humidity sensor can easily be recognized. The characteristic data holding
means should preferably be associated with a connector by which the humidity sensor
is connected to an electronic circuit unit or the like which processes the output
data of the humidity sensor, for example.
The humidity sensor used for monitoring the state of the hydrocarbon adsorbent
is not limited to a singl
