U.S. patent number RE37,895 [Application Number 08/620,299] was granted by the patent office on 2002-10-29 for evaporative fuel-processing system for internal combustion engines.
This patent grant is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Masataka Chikamatsu, Shigetaka Kuroda, Hiroshi Maruyama, Shoichi Nemoto, Kazutomo Sawamura, Takeshi Suzuki, Masayoshi Yamanaka.
United States Patent |
RE37,895 |
Kuroda , et al. |
October 29, 2002 |
Evaporative fuel-processing system for internal combustion
engines
Abstract
An evaporative fuel processing system adapted to be capable of
detecting abnormality of an evaporative emission control system for
storing, in a canister, evaporative fuel from a fuel tank for
holding fuel to be supplied to an internal combustion engine, and
purging evaporative fuel into the intake system of the engine. A
first control valve is arranged across a passage extending between
the fuel tank and the canister. A second control valve is arranged
across a passage extending between the canister and the intake
system of the engine. A third control valve is provided for an air
inlet part of the canister communicatable with the atmosphere.
Through operating these control valves to open and close them, the
evaporative emission control system is negatively pressurized, and
abnormality of this system is detected based on the pressure
detected in this negatively pressurized state thereof. Timing for
carrying out abnormality determination is determined depending on
conditions of the fuel tank. Before starting the whole process for
abnormality diagnosis of the system evaporative fuel stored in the
canister is allowed to be purged for a predetermined time period.
When the temperature of fuel in the fuel tank exceeds a
predetermined value, the abnormality determination is
inhibited.
Inventors: |
Kuroda; Shigetaka (Wako,
JP), Sawamura; Kazutomo (Wako, JP),
Yamanaka; Masayoshi (Wako, JP), Maruyama; Hiroshi
(Wako, JP), Chikamatsu; Masataka (Wako,
JP), Nemoto; Shoichi (Wako, JP), Suzuki;
Takeshi (Wako, JP) |
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
27457623 |
Appl.
No.: |
08/620,299 |
Filed: |
March 22, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
942875 |
Sep 10, 1992 |
05299545 |
Apr 5, 1994 |
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Foreign Application Priority Data
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Sep 13, 1991 [JP] |
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3-262857 |
Dec 27, 1991 [JP] |
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3-360629 |
Dec 27, 1991 [JP] |
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3-360630 |
Jan 10, 1992 [JP] |
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4-021711 |
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Current U.S.
Class: |
123/520;
123/198D |
Current CPC
Class: |
F02D
41/003 (20130101); F02M 25/0809 (20130101); F02D
41/1454 (20130101); F02D 2041/225 (20130101); F02D
2200/0406 (20130101); F02D 2200/0414 (20130101); F02D
2200/0606 (20130101); F02D 2200/703 (20130101); F02M
2025/0845 (20130101) |
Current International
Class: |
F02D
41/22 (20060101); F02D 41/00 (20060101); F02M
25/08 (20060101); F02M 033/02 () |
Field of
Search: |
;123/520,521,518,519,516,198D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; Carl S.
Attorney, Agent or Firm: Arent Fox Kintner Plotkin &
Kahn, PLLC
Claims
What is claimed is:
1. An evaporative fuel-processing system for an internal combustion
engine having an intake system, including an evaporative emission
control system having a fuel tank, a canister containing an
adsorbent, said canister having an air inlet port communicatable
with the atmosphere, an evaporative fuel-guiding passage extending
between said canister and said fuel tank, a first control valve
arranged across said evaporative fuel guiding passage, an
evaporative fuel-purging passage extending between said canister
and said intake system, and a second control valve arranged across
said evaporative fuel-purging passage, said evaporative
fuel-processing system having an abnormality-determining system in
which comprises: pressure-detecting means for detecting pressure
within said evaporative emission control system;
negatively-pressurizing means for negatively pressurizing said
evaporative emission control system; and abnormality-determining
means for determining abnormality of said evaporative emission
control system based on the pressure within said fuel tank detected
after said evaporative emission control system has been negatively
pressurized by said negatively-pressurizing means.
2. An evaporative fuel-processing system according to claim 1,
wherein said abnormality-determining means determines the
abnormality of said evaporative emission control system based on a
rate of change in the pressure within said fuel tank occurring
before said evaporative emission control system is set to a
predetermined negatively-pressurized condition by said
negatively-pressurizing means and a rate of change in the pressure
within said fuel tank occurring after said predetermined
negatively-pressurized condition of said evaporative emission
control system has been established.
3. An evaporative fuel-processing system according to claim 1,
including tank condition-detecting means for detecting conditions
of said fuel tank, wherein said abnormality-determining means
carries out abnormality determination when a predetermined time
period has elapsed after said evaporative emission control system
was negatively pressed said predetermined time period being
corrected by a correcting time period set in response to said
conditions of said fuel tank detected by said tank
condition-detecting means.
4. An evaporative fuel-processing system according to claim 2,
including tank condition-detecting means for detecting conditions
of said fuel tank, wherein said abnormality-determining means
carries out abnormality determination when a time period has
elapsed after said evaporative emission control system was
negatively pressurized, said predetermined time period being
corrected by a correcting time period set in response to said
conditions of said fuel tank detected by said tank
conditioned-detecting means.
5. An evaporative fuel-processing system according to claim 1,
wherein said abnormality-determining means determines abnormality
of said evaporative emission control system by comparing a value of
a parameter indicative a rate of change in the pressure within said
fuel tank detected after said evaporative emission control system
has been negatively pressurized by said negatively-pressurizing
means with a predetermined reference value, said predetermined
reference value being determined according to a time period
required for setting said evaporative emission control system to
said predetermined negatively-pressurized condition by said
negatively-pressurizing means.
6. An evaporative fuel-processing system according to claim 1,
including means for purging evaporative fuel stored in said
canister for a predetermined time period before the
abnormality-determining process is started by said
abnormality-determining system.
7. An evaporative fuel-processing system according to claim 1,
including fuel temperature-detecting means for detecting the
temperature of fuel contained in said fuel tank and
determination-inhibiting means for inhibiting execution of
abnormality-determining process by said abnormality-determining
system when said fuel temperature detected exceeds a predetermined
value.
8. An evaporative fuel-processing system for an internal combustion
engine having an intake system, including an evaporative emission
control system having a fuel tank a canister containing an
adsorbent, said canister having an air inlet port communicatable
with the atmosphere, an evaporative fuel-guiding passage extending
between said canister and said fuel tank, a first control valve
arranged across said evaporative fuel-guiding passage, an
evaporative fuel-purging passage extending between said canister
and said intake system and a second control valve arranged across
said evaporative fuel-purging passage, said evaporative
fuel-processing system having an abnormality-determining system
which comprises: engine operating condition-detecting means for
detecting operating conditions of said engine; a third control
valve for effecting and cutting off the communication of said air
inlet port of said canister with the atmosphere; tank internal
pressure-detecting means for detecting pressure within said fuel
tank; negatively-pressurizing means for setting said evaporative
emission control system to a predetermined negatively-pressurized
condition by controlling said first to third control valves when it
is detected by said said engine operating condition-detecting means
that said engine is in operation; a first rate of change-detecting
means for detecting a rate of change in the pressure within said
fuel tank caused by controlling opening and closing of said fast
control valve; a second rate of change-detecting means for
detecting a rate of change in the pressure within said fuel tank
caused by closing said second control valve after said
negatively-pressurized condition of said evaporative emission
control system has been established; and abnormality-determining
means for determining abnormality of said evaporative emission
control system based on results of detection by said first and
second rate of change-detecting means.
9. An evaporative fuel-processing system according to claim 8,
including tank condition-detecting means for detecting conditions
of said fuel tank wherein said abnormality-determining means
carries out abnormality determination when a predetermined time
period has elapsed after said evaporative emission control system
was negatively pressurized said predetermined time period being
corrected by a correcting time period set in response to said
conditions of said fuel tank detected by said tank
condition-detecting means.
10. An evaporative fuel-processing system according to claim 8,
wherein said abnormality-determining means determines abnormality
of said evaporative emission control system by comparing a value of
a parameter indicative of a rate of change in the pressure within
the said fuel tank detected after said evaporative emission control
system has been negatively pressurized by said
negatively-pressurizing means with a predetermined preference value
during the negatively pressurizing, said predetermined reference
value being determined according to a time period required for
setting said evaporative emission control system to said
predetermined negatively-pressurized condition by said
negatively-pressurizing means.
11. An evaporative fuel-processing system according to claim 9,
wherein said abnormality-determining means determines abnormality
of said evaporative emission control system by comparing a value of
a parameter indicative of a rate of change in the pressure within
the aid fuel tank detected after said evaporative emission control
system has been negatively pressurized by said
negatively-pressurizing means with a predetermined reference value
during the negatively pressurizing, said predetermined reference
value being determined according to a time period required for
setting said evaporative emission control system to said
predetermined negatively-pressurized condition by said
negatively-pressurizing means.
12. An evaporative fuel-processing system according to claim 8,
wherein said abnormality-determining system includes fuel
amount-detecting means for detecting an amount of fuel contained in
said fuel tank, said abnormality-determining means determines the
abnormality of said evaporative emission control system based on
results of detection by said first and second rate of
change-detecting means and said fuel amount-detecting means.
13. An evaporative fuel-processing system according to claim 8,
including means for purging evaporative fuel stored in said
canister for a predetermined time period before the
abnormality-determining process is started by said
abnormality-determining system.
14. An evaporative fuel-processing system according to claim 8,
including fuel temperature-determining means for detecting the
temperature of fuel contained in said fuel tank, and
determination-inhibiting means for inhibiting execution of
abnormality-determining process by said abnormality-determining
system when said fuel temperature detected exceeds a predetermined
value.
15. An evaporative fuel-processing system for an internal
combustion engine having an intake system, including an evaporative
emission control system having a fuel tank, a canister containing
an adsorbent, said canister having an air inlet port communicatable
with the atmosphere, an evaporative fuel-guiding passage extending
between said canister and said fuel tank, a first control valve
arranged across said evaporative fuel-guiding passage, an
evaporative fuel-purging passage extending between said canister
and said intake system, and a second control valve arranged across
said evaporative fuel-purging passage, said evaporative
fuel-processing system having an abnormality-determining system
which comprises: engine operating condition-detecting means for
detecting operating conditions of said engine, a third control
valve for effecting and cutting off the communication of said air
inlet port of said canister with the atmosphere, tank internal
pressure-detecting means for detecting pressure within said fuel
tank; negatively-pressurizing means for setting said evaporative
emission control system to a predetermined negatively-pressurized
condition by controlling said first to third control valves when it
is detected by said said engine operating condition-detecting means
that said engine is in operation; and abnormality-determining means
for effecting a determination as to whether or not said evaporative
emission control system is abnormally functioning, when a
predetermined time period has elapsed during the
negatively-pressurizing by said negatively-pressurizing means.
16. An evaporative fuel-processing system according to claim 15,
wherein said abnormality-determining system includes evaporative
fuel generation rate-detecting means for detecting a parameter of
an amount of evaporative fuel generated per unit time within said
fuel tank, said abnormality-determining means determining that said
evaporative emission control system is abnormal on condition that
said parameter indicative of said amount of evaporative fuel
generated per unit time within said fuel tank is smaller than a
predetermined value.
17. An evaporative fuel-pressing system according to claim 15,
including means for purging evaporative fuel stored in said
canister for a predetermined time period before the
abnormality-determining process is started by said
abnormality-determining system.
18. An evaporative fuel-processing system according to claim 15,
including fuel temperature-detecting means for detecting the
temperature of fuel contained in said fuel tank, and
determination-inhibiting means for inhibiting execution of
abnormality-determining process by said abnormality-determining
system when said fuel temperature detected exceeds a predetermined
value.
19. An evaporative fuel-processing system for an internal
combustion engine having an intake system, including an evaporative
emission control system having a fuel tank, a canister containing
an adsorbent, said canister having an air inlet port communicatable
with the atmosphere, an evaporative fuel-guiding passage extending
between said canister and said fuel tank, an evaporative
fuel-purging passage extending between said canister and said
intake system, and a purge control valve arranged across said
evaporative fuel-purging passage, said evaporative emission control
system comprising: a drain shut valve disposed to establish and
shut off communication between said air inlet port of said canister
and the atmosphere; pressure-detecting means for detecting pressure
within said evaporative emission control system;
negatively-pressurizing means for negatively pressurizing said
evaporative emission control system; and abnormality-determining
means for determining abnormality of said evaporative emission
control system based on an extent to which the pressure is
maintained within said evaporative emission control system, said
extent being detected based on the pressure within said evaporative
emission control system detected by said pressure-detecting means,
after said evaporative emission control system has been negatively
pressured by sad negatively-pressurizing means.
20. An evaporative fuel processing system according to claim 19,
wherein said abnormality-determining means includes
pressure-holding means for holding the pressure within said
evaporative emission control system after said evaporative emission
control system has been negatively pressurized by said
negatively-pressurizing means, said abnormality-determining means
detecting the extent to which the pressure is maintained within
said evaporative emission control system based on the pressure
within said evaporative emission control system detected by said
pressure-detecting means, while the pressure within said
evaporative emission control system is held by said
pressure-holding means.
21. An evaporative fuel-processing system according to claim 20,
wherein said negatively-pressurizing means opens said purge control
valve and at the same time closes said drain shut valve to
negatively pressurize said evaporative emission control system, and
said pressure-holding means closes said purge control valve and at
the same time closes said drain shut valve to hold the pressure
within said evaporative emission control valve.
22. An evaporative fuel-processing system according to claim 20,
wherein said abnormality-determining means determines the extent to
which the pressure is maintained within said evaporative emission
control means, by detecting a change in the pressure within said
evaporative emission control system detected by said
pressure-detecting means over a predetermined time period, and
determines that there is an abnormality in said evaporative
emission control system, when the detected change exceeds a
predetermined value..Iadd.
23. In an abnormality-determining system of an evaporative
fuel-processing system of a vehicle for supplying and controlling
an evaporative fuel adsorbed and held in a canister to an internal
combustion engine in accordance with an operating condition of the
internal combustion engine, comprising an improvement wherein said
abnormality determining system includes: first engine coolant
temperature determining means for determining whether engine
coolant temperature is lower than a first predetermined value at an
initial start-up of said internal combustion engine; second engine
coolant temperature determining means for determining when said
engine coolant temperature is above a second predetermined value
only if said first engine coolant temperature determining means
initially determines said engine coolant temperature is lower than
said first predetermined value; engine-operating
condition-detecting means for detecting one or more predetermined
engine operating conditions and/or vehicle running conditions when
said second engine coolant temperature determining means determines
said engine coolant temperature is above said second predetermined
value; and abnormality-determining means for determining an
abnormality of said evaporative fuel-processing system when said
engine operating condition detecting means determines one or more
predetermined engine operating conditions and/or vehicle running
conditions are satisfied..Iaddend..Iadd.
24. In an abnormality-determining system of an evaporative
fuel-processing system of a vehicle for supplying and controlling
an evaporative fuel adsorbed and held in a canister to an internal
combustion engine in accordance with operating conditions of said
internal combustion engine, comprising an improvement wherein said
abnormality determining system includes: abnormality determining
means for determining an abnormality of said evaporative
fuel-processing system only when engine coolant temperature is
greater than a first predetermined value; and means for activating
said abnormality-determining means at engine start-up only when
said engine coolant temperature is less than a second predetermined
value which is less than said first predetermined
value..Iaddend..Iadd.
25. An abnormality-determining system for an evaporative
fuel-processing system of a vehicle, the evaporative
fuel-processing system including a fuel tank coupled to an intake
passage of an internal combustion engine via an evaporative
fuel-purging passage, a canister disposed in line with said
evaporative fuel-purging passage for adsorbing and holding
evaporative fuel from said fuel tank, said canister having an air
inlet port for introducing outside air into said evaporative
fuel-processing system, and check valve means disposed between said
fuel tank and said canister for maintaining a predetermined
pressure in said fuel tank, said abnormality-determining system
comprising: pressure-determining means for determining pressure
within said evaporative fuel processing system; first control valve
means, arranged across an evaporative fuel guiding passage which is
between said fuel tank and said canister, for opening and closing
said evaporative fuel passage in response to a first control
signal; second control valve means, arranged across said
evaporative fuel-purging passage between said canister and said
intake passage, for opening and closing the evaporative
fuel-purging passage in response to a second control signal; a
third control valve means for effecting and cutting off
communication with said air inlet port of said canister with the
atmosphere in response to a third control signal; and an
abnormality-determining means for determining presence or absence
of evaporative fuel leakage in said evaporative fuel-processing
system when one or more predetermined engine operating conditions
and/or vehicle running conditions are satisfied, said abnormality
determining means selectively generating said first, second and
third control signals to determined presence or absence of
evaporative fuel leakage..Iaddend..Iadd.
26. An abnormality determining system according to claim 23,
wherein said second predetermined value is greater than said first
predetermined value..Iaddend..Iadd.
27. An abnormality determining system according to claim 23,
wherein said one or more conditions comprise a vehicle velocity
state or an engine rotational speed state..Iaddend..Iadd.
28. An abnormality determining system according to claim 27,
wherein said one or more conditions further comprise one of a
vehicle velocity fluctuation over time, intake pipe pressure, and
throttle opening degree..Iaddend..Iadd.
29. An abnormality determining system according to claim 25,
wherein said one or more conditions include an engine coolant
temperature being greater than a predetermined
value..Iaddend..Iadd.
30. An abnormality determining system according to claim 29,
wherein said one or more conditions comprise a vehicle velocity
state or an engine rotational speed state..Iaddend..Iadd.
31. An abnormality determining system according to claim 30,
wherein said one or more conditions further comprise one of vehicle
velocity fluctuation over time, intake pipe pressure, and throttle
opening degree..Iaddend..Iadd.
32. An abnormality determining system according to claim 24,
wherein said abnormality-determining means includes
engine-operating condition-detecting means for detecting one or
more predetermined engine operating conditions and/or vehicle
running conditions before executing said abnormality-determining
means, said one or more predetermined engine operating conditions
and/or vehicle running conditions being from a group including a
vehicle velocity state, an engine rotational speed state, a vehicle
velocity fluctuation over time, an engine rotational speed, and a
throttle opening degree..Iaddend..Iadd.
33. An abnormality determining system for detecting an abnormality
in an evaporative fuel processing system having a fuel tank storing
an amount of fuel, an evaporative fuel-guiding passage extending
between said fuel tank and a canister, an evaporative fuel-purging
passage through which fuel vapor stored in said canister is purged
into an intake passage of an internal combustion engine and a purge
control valve arranged across said evaporative fuel-purging passage
to allow a purge operation by opening of said purge control valve,
said abnormality-determining system comprising:
negatively-pressurizing means for introducing a negative pressure
from said intake passage of said internal combustion engine into
said evaporative fuel processing system; pressure-detecting means
for detecting pressure within said evaporative fuel processing
system when negative pressure is introduce therein by said
negatively-pressurizing means; abnormality-determining means for
determining an abnormality in said evaporative fuel processing
system based upon pressure in said evaporative fuel processing
system, said determination using values supplied by said
pressure-detecting means; and negative pressure controlling means
for controlling said negatively-pressurizing means so as to
prohibit negatively-pressurizing of said negatively-pressurizing
means while said abnormality-determining means is determining the
abnormality, when said negative pressure is introduced into said
evaporative fuel processing system by said negatively-pressurizing
means wherein suctioning of said fuel vapor collected in the fuel
tank with air into the engine results in fluctuation of an air-fuel
ratio..Iaddend..Iadd.
34. An abnormality-determining system according to claim 33,
further comprising a control valve for effecting and cutting off
communication of an air inlet port of said canister with the
atmosphere wherein; said negatively-pressurizing means comprises
controlling means for controlling said purge control valve and
control valve, negative pressure inside said intake passage being
introduced into said evaporative fuel processing system by closing
said control valve and opening said purge control
valve..Iaddend..Iadd.
35. An abnormality determining system for detecting an abnormality
in an evaporative fuel processing system having a fuel tank storing
an amount of fuel, an evaporative fuel-guiding passage extending
between said fuel tank and a canister, an evaporative fuel-purging
passage through which fuel vapor stored in said canister is purged
into an intake passage of an internal combustion engine and a purge
control valve arranged across said evaporative fuel-purging passage
to allow a purge operation by opening of said purge control valve,
said abnormality-determining system comprising:
negatively-pressurizing means for introducing a negative pressure
from said intake passage of said internal combustion engine into
said evaporative fuel processing system; pressure-detecting means
for detecting pressure within said evaporative fuel processing
system when negative pressure is introduce therein by said
negatively-pressurizing means; negative pressure controlling means
for controlling said negatively-pressurizing when said negative
pressure is introduced into said evaporative fuel processing system
by said negatively-pressurizing means wherein suctioning of said
fuel vapor collected in the fuel tank with air into the engine
results in fluctuation of an air-fuel ratio; and
abnormality-determining means for determining an abnormality in
said evaporative fuel processing system based upon pressure in said
evaporative fuel processing system, said determination using values
supplied by said pressure-detecting means, said system further
comprising means for determining a fuel amount stored in said
canister and said negatively-pressurizing means is activated based
upon said fuel amount stored in said canister..Iaddend..Iadd.
36. An abnormality determining system according to claim 35, said
fuel amount stored in said canister is determined by time elapsed
since said purge control valve was opened..Iaddend..Iadd.
37. An abnormality determining system according to claim 36,
wherein said opening and closing of said purge control valve is
controlled to be linearly changed..Iaddend..Iadd.
38. An abnormality determining system according to claim 35,
wherein said abnormality determining means determines the existence
or non-existence of a malfunction of said evaporative fuel
processing system by comparing a rate of pressure change inside
said evaporative fuel processing system over a predetermined period
of time with a predetermined value, said rate of pressure change
being obtained by using pressure values detected and supplied by
said pressure detecting means..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an evaporative fuel-processing system for
internal combustion engines, and more particularly to an
evaporative fuel-processing system for internal combustion engines,
which is capable of performing abnormality diagnosis of an
evaporative emission control system for purging evaporative fuel
generated from a fuel tank of the engine into an intake system of
same.
2. Prior Art
Conventionally, there has been widely used an evaporative
fuel-processing system for internal combustion engines, which
comprises a fuel tank, a canister having an air inlet port provided
therein, a first control valve arranged across an evaporative
fuel-guiding passage extending from the fuel tank to the canister,
and a second control valve arranged across a purging passage
extending from the canister to the intake system of the engine.
A system of this kind temporarily stores evaporative fuel in the
canister, which is then purged into the intake system of the
engine.
Whether a system of this kind is normally operating can be checked,
for example, by comparing a first value of an air-fuel ratio
correction coefficient assumed when purging of evaporative fuel
into the intake system is stopped and a second value of the
air-fuel ratio correction coefficient assumed when purging of
evaporative fuel is effected, after completion of warming-up of the
engine. That is, when the evaporative fuel-processing system is
normally functioning to purge evaporative fuel into the intake
system, an air-fuel mixture supplied to the engine is enriched by
the evaporative fuel purged. The enriched air-fuel mixture is
detected by an air-fuel ratio sensor, e.g. an O.sub.2 sensor, and
hence the air-fuel ratio correction coefficient calculated for
feedback control of the air-fuel ratio assumes a smaller value.
Therefore, monitoring of the manner of decrease in the air-fuel
ratio correction coefficient enables to determine abnormality of
the evaporative fuel-processing system. This abnormality diagnosis
method is disclosed in U.S. Pat. No. 5,085,194.
However, the above abnormality diagnosis method using the air-fuel
ratio correction coefficient suffers from a problem that in the
case where a leak of evaporative fuel occurs from defective seals
provided at piping connections, valves, the fuel tank, etc. of the
system, (e.g. a seal at a filler cap of the fuel tank), it is
impossible to detect the leak by the above method, which can result
in emission of a large amount of evaporative fuel into the air.
SUMMARY OF THE INVENTION
It is the object of the invention to provide an evaporative
fuel-processing system for an internal combustion engine, which is
capable of detecting abnormality of an evaporative emission control
system, by detecting whether there occurs a leak of evaporative
fuel from seals provided at piping connections, etc. of the
system.
To attain the above object, according to a first aspect of the
invention, there is provided an evaporative fuel-processing system
for an internal combustion engine having an intake system including
an evaporative emission control system, having a fuel tank a
canister containing an adsorbent, the canister having an air inlet
port communicatable with the atmosphere, an evaporative
fuel-guiding passage extending between the canister and the fuel
tank, a first control valve arranged across the evaporative
fuel-guiding passage, an evaporative fuel-purging passage extending
between the canister and the intake system, and a second control
valve arranged across the evaporative fuel-purging passage.
The evaporative fuel-processing system according to the first
aspect of the invention is characterized by having an
abnormality-determining system which comprises: tank internal
pressure-detecting means for detecting pressure within the fuel
tank; negatively-pressurizing means for negatively pressurizing the
evaporative emission control system; and abnormality-determining
means for determining abnormality of the evaporative emission
control system based on the pressure within the fuel tank detected
after the evaporative emission control system has been negatively
pressurized by the negatively-pressuring means.
Preferably, the abnormality-determining means determines the
abnormality of the evaporative emission control system based on a
rate of change in the pressure within the fuel tank occurring
before the evaporative emission control system is set to a
predetermined negatively-pressurized condition by the
negatively-pressurizing means and a rate of change in the pressure
within the fuel tank occurring after the predetermined
negatively-pressurized condition of the evaporative emission
control system has been established.
Preferably, the evaporative fuel-processing system includes tank
condition-detecting means for detecting conditions of the fuel
tank, wherein the abnormality-determining means carries out
abnormality determination when a predetermined time period has
elapsed after the evaporative emission control system was
negatively pressurized the predetermined time period being
corrected by a correcting time period set in response to the
conditions of the fuel tank detected by the tank
condition-detecting means.
Preferably, the abnormality-determining means determines
abnormality of the evaporative emission control system by comparing
a value of a parameter indicative a rate of change in the pressure
within the fuel tank detected after the evaporative emission
control system has been negatively pressurized by the
negatively-pressurizing means with a predetermined reference value,
the predetermined reference value being determined according to a
time period required for setting the evaporative emission control
system to the predetermined negatively-pressurized condition by the
negatively-pressurizing means.
Preferably, the evaporative fuel-processing system includes means
for purging evaporative fuel stored in the canister for a
predetermined time period before the abnormality-determining
process is started by the abnormality-determining system.
Preferably, the evaporative fuel-processing system includes fuel
temperature-detecting means for detecting the temperature of fuel
contained in the fuel tank, and determination-inhibiting means for
inhibiting execution of abnormality-determining process by the
abnormality-determining system when the fuel temperature detected
exceeds a predetermined value.
According to a second aspect of the invention, the evaporative
fuel-processing system is characterized by having an
abnormality-determining system which comprises: engine operating
condition-detecting means for detecting operating conditions of the
engine; a third control valve for effecting and cutting off the
communication of the air inlet port of the canister with the
atmosphere; tank internal pressure-detecting means for detecting
pressure within the fuel tank; negatively-pressurizing means for
setting the evaporative emission control system to a predetermined
negatively-pressurized condition by controlling the first to third
control valves when it is detected by the the engine operating
condition-detecting means that the engine is in operation; a first
rate of change-detecting means for detecting a rate of change in
the pressure within the fuel tank caused by controlling opening and
closing of the first control valve; a second rate of
change-detecting means for detecting a rate of change in the
pressure within the fuel tank caused by closing the second control
valve after the negatively-pressurized condition of the evaporative
emission control system has been established; and
abnormality-determining means for determining abnormality of the
evaporative emission control system based on results of detection
by the first and second rate of change-detecting means.
Preferably, the evaporative fuel-processing system of the second
aspect of the invention also includes tank condition-detecting
means for detecting conditions of the fuel tank, wherein the
abnormality-determining means carries out abnormality determination
when a predetermined time period has elapsed after the evaporative
emission control system was negatively pressurized, the
predetermined time period being corrected by a correcting time
period set in response to the conditions of the fuel tank detected
by the tank condition-detecting means.
Preferably, also in the evaporative fuel-processing system of the
second aspect of the invention, the abnormality-determining means
determines abnormality of the evaporative emission control system
by comparing a value of a parameter indicative of a rate of change
in the pressure within the the fuel tank detected after the
evaporative emission control system has been negatively pressurized
by the negatively-pressurizing means. With a predetermined
reference value during the negatively pressurizing, the
predetermined reference value being determined according to a time
period required for setting the evaporative emission control system
to the predetermined negatively-pressurized condition by the
negatively-pressurizing means.
Preferably, the abnormality-determining system includes fuel
amount-detecting means for detecting an amount of fuel contained in
the fuel tank, the abnormality-determining means determines the
abnormality of the evaporative emission control system based on
results of detection by the first and second rate of
change-detecting means and the fuel amount-detecting means.
Preferably, the evaporative fuel-processing system according to the
second aspect of the invention also includes means for purging
evaporative fuel stored in the canister for a predetermined time
period before the abnormality-determining process is started by the
abnormality-determining system.
Preferably, the evaporative fuel-processing system according to the
second aspect of the invention also includes fuel
temperature-detecting means for detecting the temperature of fuel
contained in the fuel tank, and determination-inhibiting means for
inhibiting execution of abnormality-determining process by the
abnormality-determining system when the fuel temperature detected
exceeds a predetermined value.
According to a third aspect of the invention, the evaporative
fuel-processing system is characterized by having an
abnormality-determining system which comprises: engine operating
condition-detecting means for detecting operating conditions of the
engine; a third control valve for effecting and cutting off the
communication of the air inlet port of the canister with the
atmosphere; tank internal pressure-detecting means for detecting
pressure within the fuel tank; negatively-pressurizing means for
setting the evaporative emission control system to a predetermined
negatively-pressurized condition by controlling the first to third
control valves when it is detected by the the engine operating
condition-detecting means that the engine is in operation; and
abnormality-determining means for effecting a determination as to
whether or not the evaporative emission control system is
abnormally functioning, when a predetermined time period has
elapsed during the negatively-pressurizing process by the
negatively-pressurizing means.
Preferably, the abnormality-determining system includes evaporative
fuel generation rate-detecting means for detecting a parameter of
an amount of evaporative fuel generated per unit time within the
fuel tank, the abnormality-determining means determining that the
evaporative emission control system is abnormal on condition that
the parameter indicative of the amount of evaporative fuel
generated per unit time within the fuel tank is smaller than a
predetermined value.
The above and other objects, features, and advantages of the
invention will become more apparent from the ensuing detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing the whole arrangement of an
internal combustion engine and an evaporative fuel-processing
system therefor according to an embodiment of the invention;
FIG. 2 is a graph showing test data obtained when there occurs no
leak of evaporative fuel from the system;
FIG. 3 is a graph showing test data obtained when there occurs a
leak of evaporative fuel from the system;
FIG. 4 is a timing chart showing operation of first and second
electromagnetic valves, a drain shut valve, and a second control
valve, and changes in pressure within a fuel tank (tank internal
pressure), all appearing in FIG. 1;
FIG. 5 is a flowchart of a routine for determining whether
monitoring conditions are satisfied;
FIG. 6 is a flowchart of a program for carrying out abnormality
diagnosis of an evaporative emission control system in FIG. 1;
FIG. 7 shows a table for calculating a parameter (fuel
temperature-dependent correcting time period .DELTA.TTF) used for
the abnormality diagnosis;
FIG. 8 shows a table for calculating a parameter (fuel
amount-dependent correcting time period .DELTA.TVF) used for the
abnormality diagnosis;
FIG. 9 shows a table for calculating a parameter (tank internal
pressure-dependent correcting time period .DELTA.TPTO) used for the
abnormality diagnosis;
FIG. 10 shows a table for calculating a parameter
(negatively-pressurizing time period-dependent correcting time
period .DELTA.TtmPT) used for the abnormality diagnosis;
FIG. 11 is a flowchart of an abnormality-determining routine
carried out by the program of FIG. 6,
FIG. 12 is a flowchart of another abnormality-determining routine
carried out by the program of FIG. 6;
FIG. 13 is a timing chart showing operation of first and second
electromagnetic valves, a drain shut valve, and a second control
valve, and changes in the tank internal pressure;
FIG. 14 is a flowchart showing a manner of carrying out an
abnormality diagnosis of the evaporative emission control
system;
FIG. 15 is a flowchart of a routine for determining whether
monitoring conditions are satisfied;
FIG. 16 is a flowchart of a routine for checking tank internal
pressure when the interior of the fuel tank is open to the air;
FIG. 17 is a flowchart of a routine for checking changes in the
tank internal pressure;
FIG. 18 is a flowchart of a routine for reducing the tank internal
pressure;
FIG. 19 is a flowchart of a leak down check routine for checking a
change rate in the tank internal pressure when the evaporative
emission control system is isolated from the intake pipe;
FIG. 20 is a flowchart of a routine for determining conditions of
the system;
FIG. 21 is a flowchart of a routine for determining occurrence of
an abnormality;
FIG. 22 shows a map used by the routine of FIG. 20 for determining
abnormality;
FIG. 23 is a flowchart of another example of the routine for
determining occurrence of abnormality,
FIG. 24 (I), (II), and (III) show maps used by the routine of FIG.
23 for determining abnormality;
FIG. 25 is a flowchart showing a manner of setting the valves for
normal purging;
FIGS. 26a and b are useful in explaining the influence of fuel
temperature on the abnormality diagnosis; and
FIG. 27 is a schematic diagram showing the whole arrangement of an
internal combustion engine and an evaporative fuel-processing
system therefor according to another embodiment of the
invention.
DETAILED DESCRIPTION
The invention will now be described in detail with reference to the
drawings showing embodiments thereof.
Referring first to FIG. 1, there is illustrated the whole
arrangement of an internal combustion engine and an evaporative
fuel-processing system therefor according to an embodiment of the
invention.
In the figure, reference numeral 1 designates an internal
combustion engine hereinafter simply referred to as "the engine")
having four cylinders, not shown, for instance. Connected to the
cylinder block of the engine I is an intake pipe 2 across which is
arranged a throttle body 3 accommodating a throttle valve 3'
therein. A throttle valve opening (.theta.TH) sensor 4 is connected
to the throttle valve 3' for generating an electric signal
indicative of the sensed throttle valve opening and supplying same
to an electronic control unit (hereinafter referred to as "the
ECU") 5.
Fuel injection valves 6, only one of which is shown, are inserted
into the interior of the intake pipe 2 at locations intermediate
between the cylinder block of the engine I and the throttle valve
3' and slightly upstream of respective intake valves not shown. The
fuel injection valves 6 are connected to a fuel pump 8 via a fuel
supply pipe 7, and electrically connected to the ECU 5 to have
their valve opening periods controlled by signals therefrom.
A negative pressure communication passage 9 and a purging passage
10 open into the intake pipe at respective locations downstream of
the throttle valve 3', both of which are connected to an
evaporative emission control system 11, referred to
hereinafter.
Further an intake pipe absolute pressure (PBA) sensor 13 is
provided in communication with the inferior of the intake pipe 2
via a conduit 12 opening into the intake passage 2 at a location
downstream of an end of the purging passage 10 opening into the
intake pipe 2 for supplying an electric signal indicative of the
sensed absolute pressure within the intake pipe 2 to the ECU 5.
An intake air temperature (TA) sensor 14 is inserted into the
intake pipe 2 at a location downstream of the conduit 12 for
supplying an electric signal indicative of the sensed intake air
temperature TA to the ECU 5.
An engine coolant temperature (TW) sensor 15 formed of a thermistor
or the like is inserted into a coolant passage filled with a
coolant and formed in the cylinder block, for supplying an electric
signal indicative of the sensed engine coolant temperature TW to
the ECU 5.
An engine rotational speed (NE) sensor 16 is arranged in facing
relation to a camshaft or a crankshaft of the engine 1, neither of
which is shown. The engine rotational speed sensor 16 generates a
pulse as a TDC signal pulse at each of predetermined crank angles
whenever the crankshaft rotates through 180 degrees, the pulse
being supplied to the ECU 5.
A transmission 17 is interposed between driving wheels, not shown,
and the engine 1, such that the driving wheels are driven by the
engine 1 via the transmission 17.
A vehicle speed (VSP) sensor 18 is provided at the wheels for
supplying an electric signal indicative of the sensed vehicle speed
(VSP) to the ECU 5.
An oxygen concentration sensor (hereinafter referred to as "the
O.sub.2 sensor") 20 is mounted in an exhaust pipe 19 connected to
the cylinder block of the engine 1, for sensing the concentration
of oxygen present in exhaust gases emitted from the engine 1 and
supplying an electric signal indicative of the sensed oxygen
concentration to the ECU 5.
An ignition switch (IGSW) sensor 21 detects an ON (or closed) state
of the ignition switch IGSW, to detect that the engine 1 is in
operation, and supplies an electric signal indicative of the ON
state of the ignition switch IGSW to the ECU 5.
The evaporative emission control system 11 is comprised of a fuel
tank 23 having a filler cap 22 which is removed for refueling, a
canister containing activated carbon 24 as an adsorbent and having
an air inlet port 25 provided in an upper wall thereof, an
evaporative fuel-guiding passage 27 connecting between 5 the
canister 26 and the fuel tank 23, and a first control valve 28
arranged across the evaporative fuel-guiding passage 27.
The fuel tank 23 is connected to fuel injection valves 6 via the
fuel pump 8 and the fuel supply pipe 7, and has tank internal
pressure (PT) sensor (hereinafter referred to as "the PT sensor")
29 and a fuel amount (FV) sensor 30 (hereinafter referred to as
"the FV sensor") both mounted at an upper wall thereof, and a fuel
temperature (TF) sensor (hereinafter referred to as "the TF
sensor") 31 penetrated through a side wall thereof. The PT sensor
29, FV sensor 30, and TF sensor 31 are electrically connected to
the ECU 5. The PT sensor 29 senses the pressure (tank internal
pressure PT) within the fuel tank 23 and supplies an electric
signal indicative of the sensed tank internal pressure PT to the
ECU 5. The FV sensor 30 senses an amount (FV) of fuel within the
fuel tank 23 and supplies an electric signal indicative of the
sensed fuel amount FV to the ECU . The TF sensor 31 senses the fuel
temperature (TF) and supplies an electric signal indicative of the
sensed fuel temperature TF to the ECU 5.
The first control valve 28 comprises a two-way valve 34 formed of a
positive pressure valve 32 and a negative pressure valve 33, and a
first electromagnetic valve 35 formed in one body with the two-way
valve 34. More specifically, the first electromagnetic valve 35 has
a rod 35a a front end of which is fixed to a diaphragm 32a of the
positive pressure valve 32. Further, the first electromagnetic
valve 35 is electrically connected to the ECU 5 to have its
operation controlled by a signal supplied from the ECU 5. When the
first electromagnetic valve 35 is energized, the positive pressure
valve 32 of the two-way valve 34 is forcedly opened to open the
first control valve 28, whereas when the first electromagnetic
valve 35 is deenergized, the valving (opening/closing) operation of
the first control valve 28 is controlled by the two-way valve 34
alone.
A purge control valve 36 (second control valve) is arranged across
the purging passage 10, which has a solenoid, not shown,
electrically connected to the ECU 5. The purge control valve 36 is
controlled by a signal supplied from the ECU 5 to linearly change
the opening thereof. That is, the ECU 5 supplies a desired amount
of control current to the purge control valve 36 to control the
opening thereof.
A hot-wire type flowmeter (mass flowmeter) 37 is mounted across the
purging passage 10 at a location between the canister 26 and the
purge control valve 36. The hot-wire type flowmeter 37 utilizes the
nature of a platinum wire that when the platinum wire is heated by
electric current applied thereto and at the same time exposed to a
flow of gas, the platinum wire looses its heat to decrease in
temperature so that its electric resistance decreases The output
characteristic of the flowmeter 37 varies according to the
concentration and flow rate of evaporative fuel, and a purging flow
rate of a mixture of evaporative fuel and air, and the flowmeter 37
generates and supplies an output signal according to the varying
output characteristic thereof, to the ECU 5.
A drain shut valve 38 is mounted across the negative pressure
communication passage 9 connecting between the air inlet port 25 of
the canister 26 and the intake pipe 2, and a second electromagnetic
valve 39 is mounted across the negative pressure communication
passage 9 at a location downstream of the drain shut valve 38, the
drain shut valve 38 and the second electromagnetic valve 39
constituting a third control valve 40.
The drain shut valve 38 has an air chamber 42 and a negative
pressure chamber 43 defined by a diaphragm 41. Further, the air
chamber 42 is formed of a first chamber 44 accommodating a valve
element 44a, a second chamber 45 formed with an air-introducing
port 45a, and a narrowed communicating passage 47 connecting the
second chamber 45 with the first chamber 44. The valve element 44a
is connected via a rod 48 to the diaphragm 41. The negative
pressure chamber 43 communicates with the second electromagnetic
valve 39 via the communication passage 9, and has a spring 49
arranged therein for resiliently urging the diaphragm 41 and hence
the valve element 44a in the direction indicated by an arrow A.
The second electromagnetic valve 39 is constructed such that when a
solenoid thereof is deenergized, a valve element 39a thereof is in
a seated position to allow air to be introduced into the negative
pressure chamber 43 via an air inlet port 50 and an opening 39b,
and when the solenoid is energized, the valve element 39a is in a
lifted position to close the opening 39b so that the negative
pressure chamber 43 communicates with the intake pipe 2 via the
communication passage 9. In addition, reference numeral 51
indicates a check valve.
The ECU 5 comprises an input circuit having the functions of
shaping the waveforms of input signals from various sensors,
shifting the voltage levels of sensor output signals to a
predetermined level, converting analog signals from analog-output
sensors to digital signals, and so forth, a central processing unit
(hereinafter called "the CPU"), memory means storing programs
executed by the CPU and for storing results of calculations
therefrom, etc., and an output circuit which outputs driving
signals to the fuel injection valves 6, the first and second
electromagnetic valves 35, 39, and the purge control valve 36.
The outline of the manner of detecting abnormality of the
evaporative emission control system 11 in the evaporative
fuel-processing system constructed as above will be described with
reference to FIGS. 2 and 3. FIGS. 2 and 3 show changes in the
pressure within the evaporative emission control system 11 which
will occur as time elapses after negative pressure has been built
within the system 11. FIG. 2 shows such changes in a case where no
evaporative fuel leaks from the evaporative emission control system
11, while FIG. 3 shows such changes in a case where there occurs a
leak of evaporative fuel from the system 11. Further, the symbol of
a indicates a curve obtained when the fuel tank 23 is filled with
the maximum amount of fuel, while the symbols b and c indicate
curves obtained when the fuel tank contains 1/3 and 1/2 of the
maximum amount, respectively.
As is clear from FIG. 2, when the evaporative emission control
system 11 is held in a negatively-pressurized state, the pressure
within the system 11 progressively increases toward the atmospheric
pressure at a slow rate due to an insignificant or inevitably
permitted amount of leak from seals of the valves, etc., even if
the seals have good performance. However, as shown in FIG. 3, the
rate of increase in the pressure within the system 11 in this case
(and hence the rate of leak of evaporative fuel in a normal purging
mode) increases when the sealing of piping connections, etc. of the
system 11 is faulty. Since the pressure within the system 11 can be
detected by the PT sensor 29, it is possible to determine
abnormality of the system 11 based on the output from the PT sensor
29 outputted when the system is in the negatively-pressurized
state.
FIG. 4 shows an example of changeover of operative states of the
first and second electromagnetic valves 35, 39, the drain shut
valve 38, and the second control valve 36 of the system, and
changes in the tank internal pressure PT resulting therefrom.
Specifically, the first electromagnetic valve 35 and the second
electromagnetic valve 39 are both deenergized, when the engine is
under a normal operating condition (i.e. in a normal purging mode),
as indicated by (i) in the figure. When the IGSW sensor 21 detects
the ON (or closed) state of the ignition switch IGSW, i.e. the
engine is in operation, the second control valve 36 is turned on or
opened. In this state, the first control 15 valve 28 is controlled
by the two-way valve 34. More specifically, when the tank internal
pressure PT exceeds a preset value of the positive pressure valve
32 of the two-way valve 34, the positive pressure valve 32 opens to
allow evaporative fuel generated from the fuel tank 23 to flow via
the evaporative fuel-guiding passage 27 into the canister 26, where
it is temporarily adsorbed by the adsorbent 24. As mentioned above,
the second electromagnetic valve 39 is in the deenergized (OFF)
state under the normal operating condition (i.e. in the normal
purging mode), and hence the drain shut valve 38 is open, so that
the outside air is supplied via the air-introducing port 45a to the
canister 26, whereby evaporative fuel flowing into the canister is
purged together with the outside air thus introduced, via the
second control valve 36 through the purging passage 10.
When the fuel tank 23 is cooled by the outside air, etc., to
increase the negative pressure within the tank 23, i.e. reduce the
absolute pressure within the fuel tank 23, the negative pressure
valve 33 of the two-way valve 34 is opened to allow evaporative
fuel stored in the canister to return to the fuel tank 23.
When the engine 1 satisfies predetermined monitoring conditions,
specified below, the first and second electromagnetic valves 35,
39, and the purge control valve 36 are operated in a manner
described below to carry out an abnormality diagnosis of the
evaporative emission control system 11.
First the tank internal pressure PT is relieved to the atmosphere,
over a time period indicated by (ii) in FIG. 4. That is, the first
electromagnetic valve 35 is turned on or energized to force open
the first control valve 28, and at the same time the second
electromagnetic valve 39 is held in the OFF state to keep the drain
shut valve 38 open, further with the second control valve 36 being
held in the energized (ON) state, to thereby relieve the tank
internal pressure PT to the atmosphere.
Then, the pressure within the evaporative emission control system
11 is decreased, over a time period indicated by (iii) in FIG. 4.
More specifically, while the first electromagnetic valve 35 and the
second control valve 36 are held energized (ON), the second
electromagnetic valve 39 is turned on, whereby the drain shut valve
38 is closed by a pulling force acting on the diaphragm 41 created
by negative pressure within the negative pressure communication
passage 9 communicating with the intake pipe 2. In this state, the
evaporative emission control system 11 is negatively pressurized by
a gas-drawing force created by negative pressure within the purging
passage 10 communicating with the intake pipe 2.
Then, the leak down check is performed, over a time period
indicated by (iv) in FIG. 4.
More specifically, the second control valve 36 is closed while the
negative pressurized state established over the preceding time
period 3 is maintained, followed by monitoring changes in the tank
internal pressure PT by means of the PT sensor 29. If the sealing
of the evaporative emission control system 11 is good, and hence
there occurs no significant leakage of evaporative fuel from the
system 11 when the engine is under the aforementioned normal
operating condition, i.e. the normal purging mode, there hardly
occurs a change in the tank internal pressure PT, as indicated by
the two-dot chain line, whereas if the sealing of same is faulty,
and hence there occurs a significant leak of evaporative fuel from
the system 11 when the engine is under the normal operating
condition or the normal purging mode, the tank internal pressure PT
changes at a much larger rate than in the former case as indicated
by the solid line, which enables to determine that the evaporative
emission control system 11 is in an abnormal condition.
Next, there will be described in detail a manner of carrying out an
abnormality diagnosis of the evaporative emission control system
11.
FIG. 5 shows a routine for determining whether the monitoring
conditions are satisfied, which permit to carry out monitoring of
the evaporative emission control system 11 with respect to leakage
of evaporative fuel. The routine is executed as background
processing.
First, at a step S1, it is determined whether or not the coolant
temperature TW detected by the TW sensor 15 falls between a
predetermined lower limit value TWL (e.g. 70.degree. C.) and a
predetermined higher limit value TWH (e.g. 90.degree. C.). If the
answer to this question is affirmative (YES), it is determined at a
step S2 whether or not the intake air temperature TA detected by
the TA sensor 14 falls between a predetermined lower limit value
(e.g. 50.degree. C.) and a predetermined higher limit value (e.g.
90.degree. C.). If the answer to this question is affirmative
(YES), it is judged that the warming-up of the engine 1 has been
completed, and then the program proceeds to a step S3.
At the step S3, it is determined whether or not the engine
rotational speed NE detected by the NE sensor 16 falls between a
predetermined lower limit value NEL (e.g. 2000 rpm) and a
predetermined higher limit value NEH (e.g. 4000 rpm). If the answer
to this question is affirmative (YES), it is determined at a step
S4 whether or not the intake pipe absolute pressure PBA detected by
the PBA sensor 13 falls between a predetermined lower limit value
PBAL (e.g. 350 mmHg) and a predetermined higher limit value PBAH
(e.g. 610 mmHg). If the answer to this question is affirmative
(YES), it is determined at a step S5 whether or not the throttle
valve opening .theta.TH detected by the .theta.TH sensor 4 falls
between a predetermined lower limit value .theta.THL (e.g.
1.degree.) and a higher limit value .theta.THH (e.g. 5.degree.). If
the answer to this question is affirmative (YES), it is determined
at a step S6 whether or not the vehicle speed VSP detected by the
VSP sensor 21 falls between a predetermined lower limit value (eg.
53 Km/h) and a predetermined higher limit value (e.g. 61 Km/h). If
the answer to this question is affirmative (YES), it is judged that
the engine 1 has been warmed up and at the same time is in a stable
operating condition, so that the program proceeds to a step S7.
At the step S7, it is determined whether or not the vehicle on
which the engine 1 is installed is cruising. This determination of
cruising of the vehicle is carried out by determining whether or
not the vehicle has continued to travel with a change in the
vehicle speed being equal to or smaller than a value of .+-.0.8
Km/sec. over two seconds. If the answer to this question is
affirmative (YES), it is determined at a step S8 whether or not the
PT sensor 29, and the first to third control valves 28, 36, 40 are
normally operating. If the answer to this question is affirmative
(YES), it is determined at a step S9, from the output from the
hot-wire type flowmeter 37, whether or not the purging flow rate of
a mixture of evaporative fuel and air flowing through the purging
passage 10 shows a sufficient value. If the answer to this question
is affirmative (YES), it is judged that the monitoring conditions
are satisfied, so that a flag FMON is set to "1" at a step S10,
followed by terminating the program. On the other hand, if at least
one of the answers to the questions of the steps S1 to S9 is
negative (NO), it is judged that the monitoring conditions are not
satisfied, so that the flag FMON is set to "0" at a step S11,
followed by terminating the program.
FIG. 6 shows a program for carrying out the abnormality diagnosis
of the evaporative emission control system 11, which is executed by
the ECU 5 of the evaporative fuel-processing system according to a
first embodiment of the invention. This program is executed as
background processing.
First, at a step S21, it is determined whether or not the flag FMON
has been set to "1" in the monitoring condition-determining routine
described above with reference to FIG. 5. Immediately after the
engine 1 has been started, the monitoring conditions are not
satisfied, and hence the answer to the question of the step S21 is
negative (NO), so that the program proceeds to a step S22, where a
first timer tmPTO, formed of a down-counter, is set to a
predetermined time period T1, and started. The first timer tmPTO is
provided to secure a sufficient time period for stabilizing the
tank internal pressure PT after the tank internal pressure PT is
relieved to the atmosphere, and accordingly the predetermined time
period T1 assumes a value of 30 sec., for example. After the first
timer tmPTO is started, the program proceeds to a step S23, where
the evaporative emission control system 11 is set to the normal
purging mode, i.e. the first and second electromagnetic valves 35,
39 are turned off and at the same time the second control valve 36
is turned on as shown at (i) in FIG. 4, followed by terminating the
program.
If the monitoring conditions are satisfied in a subsequent loop,
the flag FMON is set to "1", and hence the answer to the question
of the step S21 becomes affirmative, so that the program proceeds
to a step S24, where it is determined whether or not the count
value of the first timer tmPTO has become equal to "0" to
determined whether the predetermined time period T1 has elapsed. In
the first execution of the step S24, the answer to this question is
negative (NO), so that the program proceeds to a step S25, where
the system 11 is set to the open-to-atmosphere mode. That is, as
described hereinbefore (at the time period indicated by (ii) in
FIG. 4), the first electromagnetic valve 35 and the second control
valve 36 are held energized, and at the same time the second
electromagnetic valve 39 is held deenergized. Then, a second timer
tmPTD, formed of an up counter, is set to "0" at a step S26. The
second timer tmPTD is provided to measure a time period elapsed
before the negatively-pressurized condition of the evaporative
emission control system 11 is established, as described
hereinafter. The timer tmPTD is initially set to "0". Then, the
tank internal pressure PTO assumed when the system 11 is in the
open-to-atmosphere condition is set to a present value of the tank
internal pressure PT detected by the PT sensor 29 at a step S27,
and a flag FRDC, which is set to "1" when the
negatively-pressurizing process is completed, is set to "0" at a
step S28, followed by terminating the program. That is, the tank
internal pressure PTO in the open-to-atmosphere condition is
renewed to a present value of the PT, and the flag FRDC is reset,
followed by terminating the program.
When the predetermined time period T1 has elapsed to make the count
value of the first timer tmPTO equal to "0", in a subsequent loop,
the answer to the question of the step S24 becomes affirmative
(YES), so that the program proceeds to a step S29, where it is
determined whether or not the flag FRDC is equal to "1". In the
first execution of the step S29, the answer to this question is
negative (NO), so that the program proceeds to a step S30, where it
is determined whether or not the tank internal pressure PT is equal
to or lower than a predetermined reference value PTLVL (e.g. -20
mmHg). In the first execution of the step S30, the evaporative
emission control system 11 is in the open-to-atmosphere condition,
and hence the inside-tank pressure PT is substantially equal to the
atmospheric pressure, so that the answer to the question of the
step S30 is negative (NO), and accordingly the program proceeds to
a step S31 where the evaporative emission control system 11 is
negatively pressurized. More specifically, as described
hereinbefore with reference to FIG. 4 (see the time period (iii) in
FIG. 4), the first and second electromagnetic valves 35, 39 and the
second control valve 36 are all turned on or energized to create
negative pressure within the evaporative emission control system
11. Then, at a step S32, the second timer tmPTD is set to a time
period T2 required to create negative pressure within the system
11, i.e. a time period T2 elapsed after it was set to "0" at the
step S26. The program then proceeds to a step S33, where a third
timer tmPTDC, formed of a down counter, for leak down check is set
to a predetermined time period T3, followed by terminating the
program. The predetermined time period T3 assumes a value of e.g.
30 sec. which will be required for completing the leak down
check.
When the negatively-pressurized condition of the evaporative
emission control system 11 necessary for the leak down check is
established, and hence the answer to the question of the step S30
becomes affirmative (YES), the flag FRDC is set to "1" at a step
S34, and then the program proceeds therefrom to a step S35, where
it is determined whether or not the count value of the third timer
tmPTDC is equal to "0" to judge whether the time period required
for completing the leak down check has elapsed.
In the first execution of the step S35, the answer to the question
of the step S35 is negative (NO), so that the program proceeds to a
step S36, where a fourth timer tmPDTDCS for correcting the leak
down check is set to a predetermined time period T4. The correcting
time period T4 is calculated based on conditions of the fuel tank
23 (fuel amount, fuel temperature, tank internal pressure,
negatively-pressurizing time period), and provided to retard
abnormality diagnosis to be performed at a step S39, described
hereinafter. The reason for retarding the timing for execution of
abnormality diagnosis depending on the conditions of the fuel tank
23 is as follows:
When the fuel tank 23 is substantially fully filled with fuel, the
volume of space above fuel of the fuel tank 23 is small, so that
the tank internal pressure PT increases at a higher speed as is
obvious from FIG. 3, whereas when the amount of fuel contained in
the fuel tank 23 is small, the tank internal pressure PT increases
at a lower speed, after establishment of the negatively-pressurized
condition of the evaporative emission control system 11. Therefore,
depending on the amount of fuel contained in the fuel tank 23,
there can be made an erroneous determination as to abnormality of
the system 11. Further, if a longer time period is required in
establishing the negatively-pressurized condition of the system 11,
it takes a longer time period to complete the leak down check, and
therefore it may be required to modify the manner of determining
abnormality depending on the time period required in establishing
the negatively-pressurized condition of the system 11. Further,
when the fuel temperature is high, the amount of evaporative fuel
generated within the fuel tank 23 is large, so that the tank
internal pressure PT increases at a higher speed, which can lead to
an erroneous detection of abnormality of the system 11. Further,
when the tank internal pressure in the open-to-atmosphere condition
is high, which means the atmospheric pressure outside the system is
high it takes a short time period for the tank internal pressure
PT, after the system has been negatively pressurized, to rise to a
predetermined reference value, mentioned hereinafter, which can
result in an erroneous detection of abnormality of the system 11.
Therefore, in order to prevent such erroneous determinations of
abnormality, the timing for starting the execution of abnormality
determination is corrected depending on the conditions of the fuel
tank 23.
More specifically, the correcting time period T4 is calculated by
the use of the following equation (1):
where .DELTA.TTF represents a fuel temperature-dependent correcting
time period, which is calculated by retrieving a .DELTA.TTF map
stored in the memory means of the ECU 5. The .DELTA.TTF map can be
set, e.g. as shown in FIG. 7, such that predetermined values
.DELTA.TTF0 to .DELTA.TTF3 are provided corresponding,
respectively, to predetermined fuel temperature values TF0 to TF3.
A value of the correcting time period .DELTA.TTF is read from the
.DELTA.TTF map or calculated by interpolation.
.DELTA.TVF represents a fuel amount-dependent correcting time
period, which is calculated by retrieving a .DELTA.TVF map stored
in the memory means of the ECU 5. The .DELTA.TVF map can be set,
e.g. as shown in FIG. 8, such that predetermined values .DELTA.TVF0
to .DELTA.TVF3 are provided corresponding, respectively, to
predetermined fuel amount values VF0 to VF3. A value of the
correcting time period .DELTA.TVF is read from the .DELTA.TVF map
or calculated by interpolation.
.DELTA.TPTO represents a tank internal pressure-dependent
correcting time period, which is calculated by retrieving a
.DELTA.TPTO map stored in the memory means of the ECU 5. The
.DELTA.TPTO map can be set, e.g. as shown in FIG. 9, such that
predetermined values .DELTA.TPTO0 to .DELTA.TPTO3 are provided
corresponding, respectively, to predetermined tank internal
pressure values in the open-to-atmosphere condition PTO0 to PTO3. A
value of the correcting time period .DELTA.TPTO is read from the
.DELTA.TPTO map or calculated by interpolation.
.DELTA.TmPTD represents a negatively-pressurizing time
period-dependent correcting time period, which is calculated by
retrieving a .DELTA.TtmPTD map stored in the memory means of the
ECU 5. The .DELTA.TtmPTD map can be set, e.g. as shown in FIG. 10,
such that predetermined values .DELTA.TtmPTD0 to .DELTA.TtmPTD3 are
provided corresponding, respectively, to predetermined
negatively-pressurizing time periods tmPTD0 to tmPTD3. A value of
the correcting time period .DELTA.TtmPTD is read from the
.DELTA.TtmPTD map or calculated by interpolation
As is clear from FIGS. 7 to 10, the correcting time periods
.DELTA.TTF, .DELTA.TVF and .DELTA.TPTO are set to smaller values as
the fuel temperature TF, the fuel amount FV, and the tank internal
pressure PTO assume higher, larger and higher values, respectively,
while .DELTA.TtmPTD is set to a larger value as
negatively-pressurizing time period tmPTD assumes a larger
value.
Thus, the fourth timer tmPTDCS is set to the correcting time period
T4 calculated by the use of the equation (1), and then the
evaporative emission control system 11 is set to the leak down
check mode at a step S37, followed by terminating the program. More
specifically, as described hereinbefore with reference to FIG. 4
(see the time period 4 in FIG. 4), the first and second
electromagnetic valves 35, 39 are held ON or energized,
respectively, and at the same time the second control valve 36 is
turned off or deenergized, followed by terminating the program. In
this connection, when the negatively-pressurizing process is
completed, the flag FRDC is set to "1", and hence the answer to the
question of the step S29 becomes affirmative (YES), so that the
step S35 is immediately carried out.
When the answer to the question of the step S35 is affirmative
(YES), the program proceeds to a step S38, where it is determined
whether or not the correcting time period T4 has elapsed and hence
the count value of the fourth timer tmPTDCS is equal to "0". If the
answer to this question is negative (NO), the program proceeds to
the step S37, where the leak down check is continued, followed by
terminating the program. On the other hand, if the answer to the
question of the step S38 is affirmative (YES), the program proceeds
to a step S39, where an abnormality-determining routine is
executed, and then the evaporative emission control system 11 is
restored to the normal purging mode at the step S23, followed by
terminating the program.
FIG. 11 shows an example (Abnormal Determination A) of the
abnormality-determining routine executed at the step S39 (in FIG.
6).
At a step S41, it is determined whether or not the internal tank
pressure PT is higher than a reference value PTJDG (e.g. -10 mmHg).
If the answer to this question is affirmative (YES), it is judged
that the evaporative emission control system 11 suffers from a
significant leakage and hence it is determined that the system is
in an abnormal condition, at a step S42, followed by returning to
the main routine of FIG. 6. On the other hand, if the answer to the
question of the step S41 is negative (NO), it is judged that no
leakage occurs in the system 11, and hence it is determined that
the system is in a normal condition, at a step S43, followed by
returning to the main routine of FIG. 6.
FIG. 12 shows another example (Abnormal Determination B) of the
abnormality-determining routine.
First, at a step S51, a calculation is made of a rate of change
.DELTA.PTD in the internal tank pressure PT (hereinafter referred
to as "the pressure reduction rate") occurring when the evaporative
emission control system 11 is negatively-pressurized to a
predetermined value PTLVL, i.e. the negatively-pressurized
condition thereof is established, by the use of the following
equation (2). More specifically, an amount of change in the
internal tank pressure PT in establishing the
negatively-pressurized condition of the evaporative emission
control system 11 is divided by the time period T2 required for the
tank internal pressure to be reduced to the predetermined value
from the tank internal pressure PTO in the open-to-atmosphere
condition, to calculate the pressure reduction rate .DELTA.PTD.
Further, a calculation is made of a rate of change .DELTA.PTL in
the inside-tank pressure PT (hereinafter referred to as "leakage
rate") occurring after the negatively-pressurized condition of the
system has been established by the use of the following equation
(3). More specifically, an amount of change in the inside-tank
pressure PT occurring after the aforementioned condition of the
system 11 has been established is divided by a time period required
for the leak down check (i.e. the sum of the time period T3 and the
correcting time period T4) to obtain the leakage rate
.DELTA.PTL.
Then at a step S52, the ratio of the leakage rate .DELTA.PTL to the
pressure reduction rate .DELTA.PTD is calculated, and it is
determined the ratio calculated is larger than a predetermined
reference value PTRJDG. If the answer to this question is
affirmative (YES), it is judged that the leakage is significant,
and hence is determined that the system 11 is in an abnormal
condition, at a step S53, followed by returning to the main routine
of FIG. 6. On the other hand, if the answer to the question of the
step S52 is negative (NO), it is judged that the leakage is
insignificant, and hence it is determined that the system 11 is in
a normal condition, at a step S54, followed by returning to the
main routine of FIG. 6.
As described above, according to the present embodiment, the
evaporative emission control system 11 is negatively pressurized,
and then in this state, it is determined based the behavior of on
the tank internal pressure PT whether or not the evaporative
emission control system 11 is in a normal condition. Therefore, it
is possible to detect deterioration in the seals provided at the
piping connections, the fuel tank 23, etc., which enables to
prevent evaporative fuel from being emitted into the air.
Further, since the timing for determining abnormality of the system
11 is corrected based on conditions of the fuel tank (fuel amount,
fuel temperature, etc.), it is possible to achieve even more
accurate abnormality determination.
FIG. 13 shows changeovers of operative states of the first and
second electromagnetic valves 35, 39, the drain shut valve 38, and
the second control valve 36 of the system, and changes in the
inside-tank pressure PT resulting therefrom, according to a second
embodiment of the invention. The operative states of the valves are
changed over by respective corresponding signals supplied from the
ECU 5 (CPU).
Under the normal operating condition (in the normal purging mode),
during a time period indicated by (i) in FIG. 13, the first
electromagnetic valve 35 is energized, while the second
electromagnetic valve 39 is deenergized. When the ignition switch
IGSW is closed and the IGSW sensor detects that the engine 1 is in
operation, the purge control valve 36 is turned on or opened.
Evaporative fuel generated in the fuel tank 23 then flows via the
evaporative fuel-guiding passage 27 into the canister 26, where it
is temporarily adsorbed by the adsorbent 24. Further, since the
second electromagnetic valve 39 is in the deenergized state under
the normal operating condition as mentioned above, the drain shut
valve 38 is open to allow the outside air to be supplied to the
canister 26 via the air-introducting port 45a. Accordingly, the
evaporative fuel flowing into the canister 26 is purged together
with the air thus introduced, via the second control valve 36
through the purging passage 10 into the intake pipe 2. In this
connection, if negative pressure within the fuel tank 23 increases
due to cooling thereof caused by the outside air, etc., the
negative pressure valve 33 of the two-way valve 34 is opened to
return evaporative fuel stored in the canister 26 to the fuel tank
3.
When predetermined monitoring conditions, described in detail
hereinafter, are satisfied, the first and second electromagnetic
valves 35, 39, and the purge control valve 36 are operated in the
following manner to carry out an abnormality diagnosis of the
evaporative emission control system 11.
First, the tank internal pressure PT is relieved to the atmosphere,
over a time period indicated by (ii) in FIG. 13. More specifically,
the first electromagnetic valve 35 is held in the energized state
to maintain communication between the fuel tank 23 and the canister
26, and at the same time the second electromagnetic valve 39 is
held in the deenergized state to keep the drain shut valve 38 open.
Further, the purge control valve 36 is held in the energized state
or opened, to relieve the tank internal pressure PT to the
atmosphere.
Then, an amount of change in the tank internal pressure PT is
measured over a time period indicated by (iii) in FIG. 13.
More specifically, the second electromagnetic valve 39 is held in
the deenergized state to keep the drain shut valve 38 open, and at
the same time the purge control valve 36 is kept open. However, the
first electromagnetic valve 35 is turned off into the deenergized
state, to thereby measure an amount of change in the tank internal
pressure PT occurring after the fuel tank 23 has ceased to be open
to the atmosphere for the purpose of checking an amount of
evaporative fuel generated in the fuel tank 23.
Then, the evaporative emission control system 11 is negatively
pressurized over a time period indicated by (iv) in FIG. 13. More
specifically, the first electromagnetic valve 35 and the purge
control valve 36 are held in the energized state, while the second
electromagnetic valve 39 is turned on to close the drain shut valve
38, whereby the evaporative emission control system 11 is
negatively pressurized by a gas-drawing force developed by negative
pressure in the purging passage 10 held in communication with the
intake pipe 2. In the figure, TR represents a time period required
for establishing the negatively-pressurized condition of the
system.
Then, a leak down check is carried out over a time period indicated
by (v) in FIG. 13.
More specifically, after the evaporative emission control system 11
is negatively pressurized to a predetermined degree, i.e. after the
negatively-pressurized condition of the system is established, the
purge control valve 36 is closed, and then a change in the tank
internal pressure PT occurring thereafter is checked by the PT
sensor 29. If the system 11 suffers from no significant leak of
evaporative fuel therefrom, and hence the result of the leak down
check shows that there is substantially no change in the tank
internal pressure PT as indicated by the two-dot-chain line in the
figure, it is judged that the evaporative emission control system
11 is normal, whereas if the system 11 suffers from a significant
leak of evaporative fuel therefrom, and hence the result of the
leak down check shows that there is a significant change in the
tank internal pressure PT toward the atmospheric pressure it is
judged that the system 11 is abnormal. Further, if the evaporative
emission control system 11 cannot attain the negatively-pressurized
condition within a predetermined time period, the leak down check
is not carried out, as described hereinafter.
After determining whether or not the system 11 is normal, the
system 11 returns to the normal purging mode, as indicated by (vi)
in FIG. 13.
More specifically, while the first electromagnetic valve 35 is held
in the energized state, the second electromagnetic valve 39 is
deenergized and the purge control valve 36 is opened, to thereby
perform normal purging of evaporative fuel. In this state, the tank
internal pressure PT is relieved to the atmosphere, and hence is
substantially equal to the atmospheric pressure.
Next, there will be described, with reference to related figures,
the manner of abnormality diagnosis of the evaporative
fuel-processing system according to the second embodiment of the
invention.
FIG. 14 shows a program for carrying out the abnormality diagnosis
of the evaporative emission control system 11, which is executed by
the ECU 5 (CPU).
First at a step S101, a routine of determining permission for
monitoring is carried out, as described hereinafter. Then, at a
step S102, it is determined whether or not the monitoring of the
system 11 for abnormality diagnosis is permitted, i.e. a flag FMON
is set to "1", at the step S101. If the answer to this question is
negative (NO), the first to third control valves 28, 36, 40 are set
to respective operative states for the normal purging mode of the
system, followed by terminating the program, whereas if the answer
to this question is affirmative (YES), the tank internal pressure
PT in the open-to-atmosphere condition of the system is checked at
a step S103, and it is determined at a step S104 whether or not
this check has been completed. If the answer to this question is
negative (NO), the program is immediately terminated, whereas if it
is affirmative (YES), i.e. if it is judged that the above check has
been completed, the first electromagnetic valve 35 is turned off to
check a change in the tank internal pressure PT at a step S105,
followed by determining at a step S106 whether or not this check
has been completed. If the answer to this question is negative
(NO), the program is immediately terminated, whereas if it is
affirmative (YES), the first to third control valves 28, 36, 40 are
operated at a step S107 to establish the negatively-pressurized
condition of the evaporative emission control system 11 including
the fuel tank 23.
Simultaneously with the start of the negatively pressurizing
process at the step S107, a first timer tmPRG incorporated in the
ECU5 is started, and it is determined at a step 108 whether or not
the count value thereof is larger than a value corresponding to a
predetermined time period T5. The predetermined time period T5 is
set to such a value as will ensure that the system 11 is negatively
pressurized to a predetermined pressure value, i.e. the
negatively-pressurized condition of the system 11 is established,
if the system is normal. If the answer to the question of the step
S108 is affirmative (YES), it is judged that the system 11 cannot
be negatively pressurized to the predetermined pressure value due
to a hole formed in the fuel tank 23, etc., the program proceeds to
a step S112. On the other hand, if the answer to the question of
the step S109 is negative (NO), it is determined at a step S109
whether or not the negatively-pressurizing process has been
completed, i.e. the negatively-pressurized condition of the system
11 is established. If the answer to this question is negative (NO),
the program is immediately terminated, whereas if it is affirmative
(YES), a leak down check routine, described in detail hereinafter,
is carried out at a step S110 to check whether or not the system 11
is properly sealed, i.e. it is free from a leak of evaporative fuel
therefrom in the normal operating mode thereof. Then, at a step
S111, it is determined whether or not this check has been
completed.
If the answer to this question is negative (NO), the program is
immediately terminated, whereas if the answer is affirmative (YES),
the program proceeds to a step S112.
At the step S112, a process is carried out for determining whether
or not the system 11 is in a normal condition, followed by
determining at a step S113 whether this process has been completed.
If the answer to this question is negative (NO), the program is
immediately terminated, whereas if it is affirmative (YES), the
system 11 is set to the normal purging mode at a step S114,
followed by terminating the program.
Next, the above steps will be described in detail.
(1) Determination of permission for monitoring (at the step S101 of
FIG. 14)
FIG. 15 shows a routine for determining whether or not monitoring
of the system 11 for abnormality diagnosis thereof is permitted.
This routine is executed as background processing Steps S122 to
S123 of this program are identical to the steps S1 to S7 of the
program of FIG. 6.
At a step S121, it is determined whether or not the engine coolant
temperature TWI is lower than a predetermined value TWX. The
abnormality diagnosis of the present embodiment has only to be
carried out only after the engine has been out of operation for a
long time period (e.g. once per day). First, when the ignition
switch IGSW is closed, the engine coolant temperature TWI at the
start of the engine is detected and read in, and it is determined
at the step S121 in the present routine whether or not the engine
coolant temperature TWI is lower than the predetermined value, e.g.
20.degree. C. If the answer to this question is affirmative (YES),
i.e. if the engine coolant temperature TWI at the start of the
engine is lower than the predetermined value TWX, the program
proceeds to a step S122.
At the steps S122 to S128, determinations identical to those of the
steps S1 to S7 are carried out. If the answer to the question of
the step S128 is affirmative (YES), it is determined at a step S129
whether or not purging of evaporative fuel has been carried out
over a predetermined time period. More specifically, in the case
where a large amount of evaporative fuel is stored in the canister
26, it takes a longer time period to establish the
negatively-pressurized condition of the system 11 due to the
resulting large resistance of the canister 26 to permeation of
gases or there is a fear that unpreferably rich evaporative fuel be
purged into the intake system during the negatively-pressurizing
process. Therefore, in the present embodiment, monitoring of the
evaporative emission control system 11 is carried out only after
the purging of evaporative fuel has been carried over the
predetermined time period, to reduce the amount of evaporative fuel
adsorbed and stored in the canister 26.
If the answer to the question of the step S129 is affirmative
(YES), the program proceeds to a step S130, where it is determined
whether or not the fuel temperature TF of fuel contained in the
tank 23 detected by the TF sensor 31 is lower than a predetermined
value TFH (e.g. 35.degree. C.).
If the answer to this question is affirmative (YES), the flag FMON
is set to "1" at a step S131 for permitting monitoring of the
system 12 for abnormality diagnosis, followed by terminating the
program. On the other hand, if at least one of the answers to the
questions of the steps S121 to S130 is negative (NO), the
conditions for permitting monitoring are not satisfied, so that the
flag FMON is set to "0" at a step S132, followed by terminating the
program.
The step S129 is provided in consideration of the fact that the
abnormality determination, described hereinafter, cannot be
accurately carried out in the case where the fuel temperature TF is
higher than the predetermined value (i.e. 35.degree. C.). By
inhibiting the monitoring when the fuel temperature TF is high, it
is possible to avoid an erroneous determination of abnormality of
the system 11. This will be further explained in detail
hereinafter.
(2) Check of the tank internal pressure in the open-to atmosphere
condition (at the step S103 in FIG. 14)
FIG. 16 shows a routine for carrying out the tank internal pressure
check in the open-to-atmosphere condition, which is also executed
as background processing.
First, at a step S141, the system 11 is set to the
open-to-atmosphere mode, and at the same time, a second timer
tmATMP is started. More specifically, the first electromagnetic
valve 35 is held in the energized state, and at the same time the
second electromagnetic valve 39 is held in the deenergized state to
keep the drain shut valve 38 open. Further, the purge control valve
36 is kept open. Thus, the tank internal pressure PT is relieved to
the atmosphere (See the time period indicated by (ii) in FIG.
13).
Then, at a step S142, it is determined whether or not the count
value of the second timer tmATMP is larger than a value
corresponding to a predetermined time period T6. The predetermined
time period T6 is set to a value, e.g. 4 sec., which ensures that
the pressure within the system 11 has been stabilized upon lapse
thereof. If the answer to this question is negative (NO), the
program is immediately terminated, while if it is affirmative
(YES), the program proceeds to a step S143, where the tank internal
pressure PATM in the open-to-atmosphere condition is detected by
the PT sensor 29 and stored in the ECU 5, and then a checkover flag
is set at a step S144, followed by terminating the program.
(3) Check of a change in the tank internal pressure (at the step
S105 in FIG. 14)
FIG. 17 shows a routine for checking a change in the tank internal
pressure, which is executed as background processing.
First, at a step S151, the system 11 is set to a PT change-checking
mode, and at the same time a third timer tmTP is started. More
specifically, while the purge control valve 36 and the drain shut
valve 38 are held open, the first electromagnetic valve 35 is
turned off to thereby set the system to the PT change-checking mode
(See the time period indicated by (iii) in FIG. 13).
Then, at a step S152, it is determined whether or not the count
value of the third timer tmTP is larger than a value corresponding
to a predetermined time period T7, e.g. 10 sec. If the answer to
this question is negative (NO), the program is immediately
terminated, whereas if it is affirmative (YES), the tank internal
pressure PCLS after the lapse of the predetermined time period T7
is detected and stored in the ECU 5 at a step S153, followed by
calculation of a first rate of change PVARIA in the tank internal
pressure by the use of the following equation (4):
Then, the first rate of change PVARIA thus calculated is stored in
the ECU 5 and a check-over flag is set at a step S155, followed by
terminating the program.
(4) Negatively pressurizing process (at the step S107 in FIG.
14)
FIG. 18 shows a routine for carrying out a process of negatively
pressurizing the system 11 to establish the negatively-pressurized
condition of the system, which is executed as by background
processing.
First, at a step S161, the system 11 is set to a
negatively-pressurizing mode. More specifically, the purge control
valve 36 is kept open, and at the same time the first
electromagnetic valve 35 is held in the energized state, and the
second electromagnetic valve is turned on to close the drain shut
valve 38 (see the time period indicated by (iv) in FIG. 13). In
this state, the system 11 is negatively pressurized to a
predetermined value by a gas-drawing force created by operation of
the engine 1. Then, it is determined at a step S162 whether or not
the tank internal pressure PCHK in this mode of the system 11 is
lower than a predetermined value PI (e.g. -20 mmHg). If the answer
to this question is negative (NO), the program is immediately
terminated, whereas if it becomes affirmative (YES), a processor
flag is set at a step S63, followed by terminating the program.
(5) Leak down check (at the step S110 in FIG. 14)
FIG. 19 shows a routine for performing a leak down check of the
system 11, which is executed as background processing.
First, at a step S171, the system 11 is set to a leak down check
mode. More specifically, while the first electromagnetic valve 35
is held in the energized state, and at the same time the drain shut
valve is kept closed, the purge control valve 36 is closed to cut
off the communication between the system 11 and the intake pipe 2
of the engine 1 (see the time period (v) in FIG. 13).
Then, the program proceeds to a step S172, where it is determined
whether or not the tank internal pressure PST at the start of the
leak down check has been detected. In the first execution of this
step S172, the answer to this question is negative (NO), so that
the program proceeds to a step S173, where the tank internal
pressure PST is detected and a fourth timer tmLEAK is started.
Then, it is determined at a step S174 whether or not the count
value of the fourth timer tmLEAK is larger than a value
corresponding to a predetermined time period T8 (e.g. 10 sec.). In
the first execution of this step S172, the answer to this question
is negative (NO), so that the program is immediately
terminated.
In the following loop, the answer to the question of the step S172
becomes affirmative (YES), so that the program jumps over to the
step S174, where it is determined whether or not the count value of
the fourth timer tmLEAK is larger than the value corresponding to
the predetermined time period T8. If the answer to this question is
negative (NO), the program is immediately terminated, whereas if it
becomes affirmative (YES), the present tank internal pressure i.e.
the tank internal pressure PEND at the end of the leak down check
is detected and stored into the ECU 5 at a step S175, followed by
calculation of a second rate of change PVARIB in the tank internal
pressure PT at a step S176 by the use of the following equation
(5):
The second rate of change PVARIB in the tank internal pressure PT
thus calculated is stored into the ECU 5, and a check-over flag is
set at a step S177, followed by terminating the program.
(6) System condition-determining process (at the step S112 in FIG.
14)
FIG. 20 shows a routine for carrying out a process of determining a
condition of the system 11, which is executed as by background
processing.
First, at a step S181, it is determined whether or not the count
value of the first timer tmPRG exceeded the predetermined value T5
during the negatively-pressurizing process. If the answer to this
question is affirmative (YES), it is judged that the system 11 may
suffer from a significant leak of evaporative fuel due to a hole
formed in the fuel tank 23, etc., so that the program proceeds to a
step S182, where it is determined whether or not the first rate of
change PVARIA in the tank internal pressure PT is larger than a
predetermined value P2. If the answer to this question is negative
(NO), which means that evaporative fuel was not generated at a
large rate in the fuel tank 23, and hence the
negatively-pressurized condition of the system 11 could have been
properly established in the negatively-pressurizing process if the
system 11 had been in a normal condition, it is judged that the
system 11 suffers from a significant leak of evaporative fuel from
the fuel tank 23, piping connections, etc., determining that the
evaporative emission control system 11 is abnormal, and then a
process-over flag is set at a step S136, followed by terminating
the program. On the other hand, if the answer to the question of
the step S182 is affirmative (YES), which means that evaporative
fuel was generated at a large rate in the fuel tank 23 to increase
the tank internal pressure PT, which prevented the system 11 from
being negatively pressurized in a proper manner in the
negatively-pressurizing process, the determination of the system
condition is suspended at a step S184, and then the process over
flag is set at the step S186, followed by terminating the
program.
On the other hand, if the answer to the question of the step S181
is negative (NO), i.e. if the system 11 was negatively pressurized
to the predetermined value, an abnormality determining routine is
carried out at a step 185, and then the process-over flag is set at
the step S186, followed by terminating the program.
The abnormality-determining routine carried out at the step S185 is
shown by way of example in FIG. 21.
First, it is determined at a step S191 whether or not the
difference between the second change of rate PVARIB in the tank
internal pressure PT and the first rate of change PVARIA in same is
larger than a predetermined value P3.
More specifically, in order to determine whether a main factor
which has determined the rate of change PVARIB in the tank internal
pressure PT is the faulty scaling of the system 11, which means
that there occurs a significant leak of evaporative fuel from the
system 11 in the normal operating mode thereof, or generation of
evaporative fuel from the fuel tank 23, it is determined whether or
not the difference between the second rate of change PVARIB and the
first rate of change PVARIA is larger than the predetermined value
P3. If the second rate of change PVARIB assumes a large value due
to generation of a large amount of evaporative fuel from the fuel
tank 23, the answer to the question of the step S191 is negative
(NO), whereas if the second rate of change PVARIB assumes a large
value due to the faulty sealing of the system 11, the answer is
affirmative (YES). The predetermined value P3 is set according to
the time period TR required for establishing the
negatively-pressurized condition of the system 11 in a manner as
shown in FIG. 22. More specifically, the predetermined value P3 is
set to a value P31 when the time period TR is longer than a
predetermined value TR1, whereas it is set to a value P32 (>P31)
when the time period TR is shorter than the predetermined value
TR1. If the answer to the question of the step S191 is affirmative
(YES), it is determined at a step S192 that the evaporative
emission control system 11 is abnormal, whereas if the answer is
negative (NO), it is determined at a step S193 that the system 11
is normal, followed by terminating the program.
FIG. 23 shows another example of the abnormality-determining
routine.
First, at a step S201, it is determined whether or not the fuel
amount FV in the fuel tank 23 detected by the FV senor 30 is larger
than a first predetermined value FV1, to determine whether or not
the fuel tank 23 is Substantially fully filled with fuel. If the
answer to this question is affirmative (YES), a map [I] is
selected, whereas if the answer is negative (NO), it is determined
at a step S203 whether or not the fuel amount FV is larger than a
second predetermined value FV2, to determine whether or not the
fuel tank 23 is filled half or more with fuel. If the answer to
this question is affirmative (YES), a map [II] is selected at a
step S204, whereas if the answer is negative (NO), a map [III] is
selected at a step S205.
Then, the abnormality-determination is carried out by the use of a
selected one of the maps [I] to [III], followed by terminating the
program.
More specifically, as shown in FIGS. 24 [I]-[III], the maps [I] to
[III] are each formed such that a normal region and an abnormal
region are defined in a manner depending on the relationship
between the first rate of change PVARIA in the tank internal
pressure PT and the second rate of change PVARIB in the tank
internal pressure PT. By retrieving the selected one of the maps,
it is determined whether or not the system 11 is normal. In the
figures, the hatched sections indicate the abnormal regions.
(7) Normal purging (at the step S114 in FIG. 14)
FIG. 25 shows a routine for restoring the normal purging mode of
the system 11, in which the operative states of the valves are
specified.
More specifically, the first electromagnetic valve 35 is held in
the energized state and the drain shut valve 39 and the purge
control valve 36 are opened to thereby set the system to the normal
purging mode, at a step S211, followed by terminating the
program.
As described heretofore, according to the present embodiment, if
the predetermined time period T5 has elapsed during the process of
negatively-pressurizing the system 11, it is immediately determined
(by jumping-over of the step S108 to S112 in FIG. 14) whether or
not the system 11 is abnormal. Therefore, even if the system 11
cannot be negatively pressurized to the predetermined value, it is
possible to determine whether or not the system 11 is abnormal.
Further, according to the present embodiment, as shown in FIG. 21
or FIG. 23, the abnormality determination of the system is carried
out with reference to the relationship between the first rate of
change PVARIA in PT calculated during the PT change check (at the
step S105 in FIG. 14; and FIG. 17) and the second rate of change
PVARIB in PT calculated during the leak down check (at the step
S110 in FIG. 14; and FIG. 19), it is possible to perform an
accurate abnormality determination even if evaporative fuel is
being generated at a large rate. That is, it can be avoided to
erroneously determine that the system is abnormal when evaporative
fuel is generated at a large rate.
Further, when the fuel temperature TF is at a normal value
(20.degree. C.), the relationship between the first rate of change
PVARIA and the second rate of change PVARIB has a marked border
line between the normal region and the abnormal region as shown in
FIG. 26a depending on whether the system suffers from a leak or
not, and hence, it is possible to effect accurate determination of
abnormality of the system by the use of a reference level indicated
in the figure. However, when the fuel temperature TF is high, e.g.
40.degree. C., the marked border line cannot be discriminated from
the relationship between the first and second rates of changes
resulting from whether the system suffers from a leak of
evaporative fuel or not, making it impossible to effect accurate
abnormality determination. Therefore, by the step S130 in FIG. 15,
the abnormality determination is inhibited when the fuel
temperature TF is high (>TFH), to thereby prevent an erroneous
determination of abnormality, which enhances the accuracy of the
abnormality determination.
Although, in the above embodiments of the invention, the third
control valve 40 is comprised of the drain shut valve 38, the
second electromagnetic valve 39, and the negative pressure
communication passage 9, this is not limitatine, but the third
control valve 40 may be constituted by a single electromagnetic
valve 60 for opening and closing the air inlet port 25 to control
introduction of air into the consister 26. This contributes to
simplification of the construction of the evaporative
fuel-processing system of the invention.
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