U.S. patent application number 09/783142 was filed with the patent office on 2001-09-20 for monitoring apparatus for fuel feed system.
Invention is credited to Isobe, Takashi, Iwamoto, Takashi, Niki, Manabu.
Application Number | 20010022177 09/783142 |
Document ID | / |
Family ID | 18569357 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022177 |
Kind Code |
A1 |
Niki, Manabu ; et
al. |
September 20, 2001 |
Monitoring apparatus for fuel feed system
Abstract
A highly stable engine failure diagnosing system free from
influence of purging is presented. A monitoring apparatus for
monitoring a fuel feed system of an internal combustion engine is
provided with an A/F ratio detector and an A/F ratio controller for
performing feedback control of the A/F ratio. An A/F ratio feedback
coefficient is calculated according to the output of the detector.
A malfunction determination parameter is calculated based on the
coefficient. A purging is suspended when the parameter reaches a
first decision value. The monitoring is suspended when the
parameter reaches a second decision value in a purge cutting state.
A value of the malfunction determination parameter it would take if
the purge cut was not carried out is estimated using the value when
the parameter reached the first decision value. The monitoring is
resumed when the estimated value of the malfunction determination
parameter reaches the second decision value.
Inventors: |
Niki, Manabu; (Wako-shi,
JP) ; Isobe, Takashi; (Wako-shi, JP) ;
Iwamoto, Takashi; (Wako-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Family ID: |
18569357 |
Appl. No.: |
09/783142 |
Filed: |
February 15, 2001 |
Current U.S.
Class: |
123/690 ;
123/480; 60/274; 60/285 |
Current CPC
Class: |
F02D 41/0037 20130101;
F02D 41/1495 20130101; Y02T 10/40 20130101; F02D 41/22
20130101 |
Class at
Publication: |
123/690 ;
123/480; 60/285; 60/274 |
International
Class: |
F02D 041/22; F01N
003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2000 |
JP |
2000-047043 |
Claims
What is claimed is:
1. A monitoring apparatus for monitoring a fuel feed system of an
internal combustion engine, comprising: an air fuel ratio detector
provided in an exhaust system of the engine; an A/F ratio
controller for performing feedback control of the A/F ratio based
on an output of said detector; means for calculating an A/F ratio
feedback coefficient based on the output of said detector; means
for calculating a malfunction determination parameter based on the
A/F ratio feedback coefficient; a purge cut controller for
suspending purging when the parameter reaches a first decision
value; a monitor controller for suspending the monitoring when the
parameter reaches a second decision value in a purge cutting state;
and means, responsive to the malfunction determination parameter
reaching the second decision value, for estimating a value of the
malfunction determination parameter it would take if purge cut was
not carried out, an initial value of the estimation being the value
when the parameter reached the first decision value.
2. The monitoring apparatus of claim 1, wherein said monitor
controller resumes monitoring when an estimated value of the
malfunction determination parameter reaches the second decision
value.
3. The monitoring apparatus of claim 2 further comprising means for
determining that the fuel feed system is malfunctioning if the
malfunction determination parameter fails to reach the second
decision value after purge cutting, wherein the parameter is
determined according to an learning value of the A/F ratio feedback
coefficient.
4. A monitoring apparatus for monitoring a fuel feed system of an
internal combustion engine, comprising an electronic control unit
and an air fuel ratio detector provided in an exhaust system of the
engine, said electronic control unit being programmed to: perform
feedback control of the A/F ratio based on an output of the
detector; calculate an A/F ratio feedback coefficient according to
the output of the detector; calculate a malfunction determination
parameter based on the A/F ratio feedback coefficient; suspend
purging when the parameter reaches a first decision value; suspend
monitoring when the parameter reaches a second decision value in a
purge cut state; and to estimate, responsive to the malfunction
determination parameter reaching the second decision value, a value
of the malfunction determination parameter it would take if purge
cut was not carried out, an initial value of the estimation being
the value when the parameter reached the first decision value.
5. The monitoring apparatus of claim 4 wherein said electronic
control unit comprises a microprocessor.
6. The monitoring apparatus of claim 5 wherein the microprocessor
is further programmed to resume the monitoring when an estimated
value of the malfunction determination parameter reaches the second
decision value.
7. The monitoring apparatus of claim 6 wherein the microprocessor
is further programmed to determine that the fuel feed system is
malfunctioning if the malfunction determination parameter fails to
reach the second decision value after purge cutting, wherein the
parameter is determined according to a learning value of the A/F
ratio feedback coefficient.
8. A Method for monitoring a fuel feed system of an internal
combustion engine having an electronic control unit and an air fuel
ratio detector provided in an exhaust system of the engine
comprising: performing feedback control of the A/F ratio based on
an output of the detector; calculating an A/F ratio feedback
coefficient according to the output of the detector; calculating a
malfunctioning determination parameter based on the A/F ratio
feedback coefficient; suspending purging when the parameter reaches
a first decision value; suspending monitoring when the parameter
reaches a second decision value in a purge cut state; and
estimating, responsive to the malfunction determination parameter
reaching the second decision value, a value of the malfunction
determination parameter it would take if the purge cut was not
carried out, an initial value of the estimation being the value
when the parameter reached the first decision value.
9. The method of claim 8 further comprising resuming monitoring
when an estimated value of the malfunction determination parameter
reaches the second decision value.
10. The method of claim 9 further comprising determining that the
fuel feed system is malfunctioning if the malfunction determination
parameter fails to reach the second decision value after purge
cutting, wherein the parameter is determined according to a
learning value of the A/F ratio feedback coefficient.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus for detecting
malfunctioning of a fuel feed system of an internal combustion
engine (hereinafter referred to as an "engine"), and more
specifically to an apparatus for detecting malfunctioning of a fuel
feed system based on an output of an air-fuel (A/F) ratio sensor
provided in an exhaust system of the engine.
[0002] The Japanese Laid-Open Patent Application No. 8-121226
describes a scheme for detecting malfunctioning of a fuel feed
system of an engine comprising an O2 sensor for detecting an A/F
ratio in exhaust gas and a purge control valve placed between a
fuel tank and an air intake pipe. According to the scheme, during a
failure monitoring, purging is forced to stop when a malfunction
determination parameter KO2AVE, a learning value of an A/F ratio
feedback coefficient, decreases below a first decision value. Then,
whether or not the decrease is caused by purging is determined. If
it is caused by purging, subsequent failure monitoring is
suspended. When the A/F ratio feedback coefficient rises beyond a
second decision value after a predetermined period has elapsed, a
process determines that purging cannot affect the decision to
resume the failure monitoring.
[0003] According to the scheme described above, the frequency of
the failure monitoring may decrease because the monitoring does not
resume until the predetermined period elapses. In addition, the
monitoring may be resumed even if there is influence of purging
because the monitoring is resumed in accordance with the rise of
the wide-variable A/F ratio feedback coefficient beyond the
predetermined decision value. Therefore, there is a need for a
highly stable failure diagnosing system that is free from influence
of purging.
SUMMARY OF THE INVENTION
[0004] In order to solve the above-mentioned problem, according to
one aspect of the invention, a monitoring apparatus is provided for
monitoring a fuel feed system of an engine having an A/F ratio
controller. The controller carries out feedback control of the A/F
ratio based on an output of an A/F ratio detector provided in an
exhaust system of the engine.
[0005] The monitoring apparatus includes means for calculating an
A/F ratio feedback coefficient based on an output of the detector
and means for calculating a malfunction determination parameter
based on the A/F ratio feedback coefficient. The apparatus also
includes a purge cut controller for cutting purge when the
parameter reaches a first decision value, and a monitor controller
for suspending the monitoring when the parameter reaches a second
decision value in a purge cutting state. The apparatus further
includes means for estimating a value of a malfunction
determination parameter that would be taken if the purge cutting
had not been carried out. The estimation is performed responsive to
the malfunction determination parameter reaching the second
decision value and uses as an initial value the value when the
parameter reached the first decision value. The monitor controller
causes the monitoring to be resumed responsive to the estimated
value of the malfunction determination parameter reaching the
second decision value.
[0006] When the malfunction determination parameter reaches the
second decision value in the purge cutting state, that is, when the
fuel feed system is normally functioning but the malfunction
determination parameter is determined to have decreased below the
first decision value due to the influence of purging, estimation of
the malfunction determination parameter starts. This estimation is
carried out using as a starting value the value of the malfunction
determination parameter at the time the first decision value is
reached. The estimated value of the malfunction determination
parameter simulates the operation of keeping monitoring the
malfunction determination parameter without purge cutting after the
malfunction determination parameter reached the first decision
value.
[0007] When the estimated value of the malfunction determination
parameter reaches the second decision value, it is determined that
the condition is over in which the malfunction determination
parameter decreases below the first decision value due to influence
of the purging, and the failure monitoring of the fuel system is
resumed.
[0008] According to the present invention, whether purging causes a
decrease in the malfunction determination parameter below the first
decision value is determined based on the malfunction determination
parameter in accordance with the real flow of time. In addition,
whether failure monitoring of the fuel system is to be resumed is
determined based on the estimated value of the malfunction
determination parameter which is a value of the parameter if the
purge cutting is not carried out. Since the actual malfunction
determination parameter is a value resulting from the purge
cutting, the parameter would require a considerable period to
return to a value unaffected by the purge cutting after the
resumption of purging. By using the estimated value of the
malfunction determination parameter, the invention allows to
quickly determine whether the failure monitoring of the fuel system
can be resumed. Furthermore, since the resumption of the failure
monitoring is decided on the malfunction determination parameter,
which is more stable than the A/F ratio feedback coefficient and
its learning value, the system can operate in a stable manner.
[0009] According to another aspect of the invention, the
malfunctioning determination parameter is decided in accordance
with an average of the A/F ratio feedback coefficient. In addition,
the monitoring apparatus further includes a determining unit, which
determines that the fuel system is malfunctioning if the
malfunction determination parameter fails to reach the second
decision value after the purge cutting.
[0010] Since the malfunction determination parameter is decided
according to the average of the A/F ratio feedback coefficient, the
parameter becomes more stable than the feedback coefficient and its
learning value. Therefore, stability of system control based on the
malfunction determination parameter is enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block diagram illustrating the general
configuration of an engine system to which the present invention is
applied.
[0012] FIG. 2 is a block diagram illustrating the general
configuration of a failure monitoring apparatus for a fuel feed
system in a preferred embodiment of the invention.
[0013] FIGS. 3(a) and 3(b) are waveform diagrams illustrating the
relationships between KO2, KAV and KO2AVE.
[0014] FIG. 4 is a flow chart illustrating the process of
calculating the malfunction determination parameter KO2AVE.
[0015] FIG. 5 is a timing chart of actions in the preferred
embodiment of the invention.
[0016] FIG. 6 is a flow chart illustrating the process of a failure
monitoring on the fuel feed system of the preferred embodiment of
the invention.
[0017] FIG. 7 is a flow chart illustrating the process of judging
whether the conditions for the implementation of the monitoring are
satisfied in the preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A preferred embodiment of the present invention will be
described with reference to the accompanying drawings. FIG. 1 is a
block diagram illustrating the general configuration of a fuel feed
system of an engine to which the invention is applied. An engine 1
is, for example, a six-cylinder four-stroke engine provided with a
throttle body 3 at a point in an air intake pipe 2, and a throttle
valve 3' is placed in the throttle body 3. To the throttle valve 3'
is connected a throttle valve opening angle (.theta.TH) sensor 4,
which sends an output signal corresponding to the opening angle of
the throttle valve 3' to an electronic control unit (ECU) 5.
[0019] Each cylinder of the engine is provided with a fuel
injection valve 6, which is connected to a fuel tank 8 via each
fuel pump 7. The opening of the fuel injection valve 6 is
controlled with signals sent from the ECU 5.
[0020] Downstream from the throttle valve 3' is provided an air
intake pipe pressure (PBA) sensor 10 via a pipe 9, and output
signal of the sensor 10 is sent to the ECU 5. Further, downstream
from the air intake pipe pressure sensor 10 is an air intake
temperature (TA) sensor 11, whose output signal is sent to the ECU
5.
[0021] An engine water temperature (TW) sensor 12, comprising a
thermistor or the like, is fixed to the cylinder block of the
engine 1 to send its output signal to the ECU 5. An engine
revolution (NE) sensor 13 and a cylinder-identifying (CYL) sensor
14 are fixed to camshafts or crankshafts of the engine 1. The
engine revolution sensor 13 generates a signal pulse (TDC signal
pulse) at a predetermined crank angle position every 120-degree
turn of the crankshaft of the engine 1, which is sent to the ECU 5.
The cylinder-identifying sensor 14 generates a signal pulse at a
predetermined crank angle position of a specified cylinder, which
is sent to the ECU 5.
[0022] A ternary catalyst 15 is placed on an exhaust manifold 17 of
exhaust pipes 16L and 16R, each provided for left and right
cylinder groups of the engine 1. The catalyst 15 eliminates such
ingredients as HC, CO and NOx of the exhaust gas. O2 sensors 18L
and 18R, A/F ratio detectors, are provided in the exhaust pipes
16L, and 16R, and generate outputs whose values change
substantially in a digital manner across the boundary of the
stoichiometry or theoretical A/F ratio. This output is sent to the
ECU 5 and used for the feedback control of the A/F ratio.
[0023] A vehicle speed sensor 23 detects the velocity V of the
vehicle on which the engine 1 is mounted, and sends its output to
the ECU 5. An indicator 19, comprising a light emitting diode or
the like, is turned on when the ECU 5 detects the abnormal fuel
feed system.
[0024] The top of the sealed fuel tank 8 is connected to the air
intake pipe 2 via a two-way valve 20, a canister 21 and a purge
control valve 22. The ECU 5 controls opening and closing of the
purge control valve 22. The vaporized gas generated in the fuel
tank 8 pushes and opens the positive pressure valve of the two-way
valve 20 when it reaches a predetermined pressure. Then the gas
flows into the canister 21, where the gas is absorbed and stored in
activated carbon. When the purge control valve 22 is opened in
response to a signal from the ECU 5, the vaporized gas stored in
the canister 21 is sucked into the air intake pipe 2 by negative
pressure along with the external air taken in through an air intake
port provided in the canister 21.
[0025] When the fuel tank 8 is cooled by the external atmosphere or
the like and the pressure in the tank decreases, the negative
pressure valve of the two-way valve opens and the vaporized gas
stored in the canister 21 is returned to the tank 8. Thus, the
vaporized fuel generated in the fuel tank 8 is prevented from being
released into the atmosphere.
[0026] The ECU 5 is provided with an input interface 5a and a
central processing unit (CPU) 5b having such functions as shaping
input signals sent from various sensors and to converting analog
signals into digital. The CPU 5b carries out various operations to
control the engine system in accordance with programs stored in a
read only memory (ROM) or in a random access memory (RAM) with a
back-up function which may be a part of a storage unit (memory) 5c.
The memory 5c includes a regular RAM, which provides a primary
storage area for various data and operation results.
[0027] An output interface 5d sends control signals based on the
results of the operation by the CPU 5b to the fuel injection valve
6, the purge control valve 22, the indicator 19, spark plugs and
other elements.
[0028] FIG. 2 is a block diagram illustrating the general
configuration of the failure monitoring apparatus on the fuel feed
system according to one preferred embodiment of the invention. The
functional blocks illustrated herein are realized with the CPU 5b,
the memory 5c comprising RAM and ROM, and the program and data
tables stored in the ROM for use with various operations.
[0029] An droving conditions detecting unit 31 receives outputs
from the sensors in various parts of the engine system via the
input interface 5a. The detecting unit determines whether A/F ratio
feedback-controlled operation or open loop-controlled operation is
to be selected according to the state of operation, and sends to a
fuel injection rate control unit 33 a signal indicating the
operation mode along with such information as engine revolution NE
and air intake pipe pressure PB. Since the present invention
concerns the engine operated in the A/F ratio feedback-controlled
mode, the following description relates to operation in the A/F
ratio feedback-controlled mode.
[0030] The fuel injection rate control unit 33 calculates the
injection time TOUT of the fuel injection valve according to the
following equation;
TOUT=Ti.times.K1.times.KO2+K2. (1)
[0031] Ti is a reference value for the injection time TOUT, and is
read out from a Ti map (stored in the ROM of the ECU 5) having the
engine revolution NE and the air intake pipe pressure PB as
parameters. K1 and K2 are respectively a correction coefficient and
a correction variable calculated according to various engine
parameters, and set so as to optimize the fuel consumption
characteristics, the acceleration characteristics or the like
according to the droving conditions of the engine.
[0032] KO2 is a feedback correction coefficient for the A/F ratio,
and is calculated by a KO2 calculating unit 32 based on the output
from the O2 sensor. KO2 varies as illustrated in FIG. 3(a). When
the output level of the O2 sensor changes from one level to the
other, for example, from rich to lean, KO2 is set so that the A/F
ratio moves to the opposite direction, i.e. to become rich, by
adding a proportional term (P term). Subsequently KO2 is set to
gradually become rich by adding an integral term (I term) until the
O2 sensor senses rich. When the output level of the O2 sensor
changes from lean to rich, KO2 is set so that the operation stated
above is done the other way round (to become lean). This setting
scheme is well known, and in this embodiment the proportional term
and the integral term are read out from a table whose parameters
are engine revolution NE and air intake pipe pressure PB.
[0033] A KAV calculating unit 35 calculates KAV, the learning value
of the A/F ratio feedback coefficient KO2. KAV is calculated
according to the following equation every time the proportional
term is added to KO2, and varies as indicated by a dotted line in
FIG. 3(a).
KAV=KO2.times.CO2/100+KAV'.times.(1-CO2/100) (2)
[0034] CO2 is a variable for setting conformity of KAV with respect
to variations of the correction coefficient (A/F ratio feedback
coefficient) KO2, and is set to a relatively large value within a
range of 1 to 100. KAV' is a preceding value of KAV, and its
initial value is set according to the value of the feedback
coefficient KO2 at the time of entering a specific operation
range.
[0035] A KO2AVE calculating unit 36 calculates a malfunction
determination parameter KO2AVE following the flow shown in FIG. 4.
First, whether the learning value KAV of KO2 is greater than a sum
of the malfunction determination parameter KO2AVE plus a deviation
for determining the secular change .DELTA.KO2AVE (e.g. 0.0078) is
determined (401). If greater, the value of KO2AVE is updated
according to the following equation;
KO2AVE=KO2AVE+.DELTA.KO2AVE/2. (3)
[0036] If the determination at step 401 is NO, the process proceeds
to step 402, where whether the learning value KAV is smaller than
the balance of the value of KO2AVE minus the deviation
.DELTA.KO2AVE is determined. If smaller, the value of KO2AVE is
updated according to the following equation. If the determination
at step 402 is NO, the process ends.
KO2AVE=KO2AVE-.DELTA.KO2AVE/2 (4)
[0037] The process described above holds the value of the
malfunction determination parameter KO2AVE as its preceding value
if the learning value KAV is within the range of
KO2AVE.+-..DELTA.KO2AVE, and updates the parameter KO2AVE according
to above-stated Equation (3) or (4) if KAV is out of the range.
FIG. 3(b) shows the relationship between the value of KAV and that
of KO2AVE.
[0038] Next, function of a KO2AVE monitoring unit 42 (FIG. 2) will
be described with reference to FIG. 5. The KO2AVE monitoring unit
42 monitors whether the value of KO2AVE becomes smaller than a
first decision value (e.g. 0.813). When KO2AVE becomes smaller, the
unit stores the value of KO2AVE at that time into a KO2AVE holding
memory area (in the memory 5c). FIG. 5(d) shows the timing of
holding the value of KO2AVE. At the same time, the unit 42 sends a
purge cut request signal to a purge cut control unit 41 to close
the purge control valve 22 to suspend purging. FIG. 5(f) shows the
timing of purge cutting.
[0039] As the fuel fed to the air intake pipe decreases when
purging is suspended, KO2 begins to rise. The KO2AVE monitoring
unit 42 sends a signal to a monitoring condition judging unit 43
almost simultaneously with the purge cutting. The signal causes the
calculation of KAV and KO2AVE to be stopped by resetting a monitor
permit flag to suspend failure monitoring for a stabilizing period,
which is a duration for the KO2 to become stable after increase of
KO2 is stopped by purge cutting, and is, for example, about six
seconds. The timing of the above operation is shown in FIGS. 5(a)
and 5(g). After the stabilizing period elapses, the failure
monitoring is resumed and the value of KO2AVE is updated and rises
in accordance with the above-mentioned updating scheme for KAV and
KO2AVE. When KO2AVE becomes greater than a second decision value
(e.g. 0.828), the KO2AVE monitoring unit 42 sets a PGOK flag, which
indicates that the purging causes KO2AVE to decrease below the
first decision value and the fuel feed system is normal. The timing
of the above operation is shown in FIG. 5(e).
[0040] If KO2AVE has not become greater than the second decision
value when a predetermined period, e.g. 30 seconds, elapses after
the purge cutting (FIG. 5(f)), a malfunction determining unit 45
determines that the fuel feed system failed and displays a failure
indication on the indicator 19 (FIG. 1).
[0041] If the influence of purging is great, the KO2AVE monitoring
unit 42 resets the purge cut request signal to the purge cut
control unit 41 and sets the PGOK flag to resume purging (FIG.
5(f)). Approximately simultaneously, the monitoring condition
judging unit 43 prohibits the failure monitoring on the fuel feed
system in response to a signal from the KO2AVE monitoring unit 42.
The timing of the above operation is shown in FIG. 5(a). Otherwise
if the failure monitoring is continued, purge cutting might be
requested again when the KO2AVE become smaller than the first
decision value by the resumption of purging. The prohibition of
failure monitoring is intended to prevent the further request.
[0042] The KO2AVE monitoring unit 42 sets a KMCND flag allowing to
estimate a value of the malfunction determination parameter KO2AVES
during the prohibition of failure monitoring after the lapse of a
stabilizing period. The stabilizing period is from the time
immediately after the failure monitoring is prohibited as described
above to the time the KO2 stops decreasing as purging is resumed
and is stabilized. It is, for example, about five seconds. The
timing of the above operation is shown in FIG. 5(b).
[0043] Then the KO2AVE monitoring unit 42 sends a signal to a
KO2AVES estimating unit 37, and start calculation of the estimated
value KO2AVES using the earlier held value of KO2AVE as an initial
value. The calculation of KO2AVES is carried out along the flow
shown in FIG. 4, wherein an initial value of KAV is the value of
KO2 when the aforementioned stabilizing period elapses after the
resumption of purging.
[0044] The monitoring condition judging unit 43 resumes the failure
monitoring on the fuel feed system if the value of KO2AVES
estimated and updated in aforementioned manner becomes greater than
the second decision value. The timing of the above operation is
shown in FIG. 5(a). This means that the influence of purging is
regarded as being decreased when the estimated value of the
malfunction determination parameter KO2AVES becomes greater than
the second decision value.
[0045] In one embodiment of the invention, when a predetermined
period, e.g. five minutes, elapses after the failure monitoring on
the fuel feed system is prohibited at the timing of FIG. 5(a), the
monitoring condition judging unit 43 allows the failure monitoring
even if the estimated value of the malfunction determination
parameter KO2AVES has not become greater than the second decision
value. This enables quick resumption of failure monitoring even if
the influence of purging is relatively great.
[0046] Although KO2 is illustrated as a schematic linear waveform
in FIG. 5, KO2 actually varies finely as shown in FIG. 3(a). The
waveform of KO2 in FIG. 5 shows that it varies faster than those of
KAV and KO2AVE, and varies abruptly by purge cutting. KAV follows
KO2 as the learning value of KO2, and KO2AVE modestly follows KAV
in accordance with the relationships represented by the
above-mentioned two equations.
[0047] Next, the flow of the monitoring on the fuel feed system in
one embodiment of the invention will be described with reference to
FIG. 6. The process of FIG. 6 is carried out every 10 milliseconds,
for example. First, whether the condition for monitoring is
satisfied is determined (101) . This determination of the
monitoring condition is established in a flow of determining
whether the monitoring condition is satisfied, which will be
described below with reference to FIG. 7. If the failure monitoring
is prohibited at step 101, the process proceeds to step 102 to
determine whether the KMCND flag is set. As stated above, this flag
indicates a permission to calculate the estimated value of the
malfunction determination parameter KO2AVES during the prohibition
of the failure monitoring after the resumption of purging. The flag
is set at step 224 and reset at steps 203 or 225 in FIG. 7.
[0048] If at step 102 the KMCND flag is set, the process proceeds
to step 103. If the KMCND flag is not set, a KAV calculation timer
is set (136) and the operation exits this process.
[0049] On the other hand, if the monitoring permission flag is set
at step 101, whether the learning value KAV of KO2 is initialized
is determined according to a KAV flag (103). If initialized, the
process directly proceeds to step 107. If not initialized, the
current A/F ratio feedback coefficient (correction coefficient) KO2
is set as an initial value and the KAV flag is set to 1 at step
106, and then the process proceeds to step 107.
[0050] If the output of the O2 sensor is determined to have
reversed at step 107, the learning value KAV of KO2 is calculated
in accordance with Equation (2) stated above as well as setting the
KAV flag (110). If the output of the O2 sensor does not reverse at
step 107, the process proceeds to step 111. At step 111, whether
the KAV calculation period set at step 136 has elapsed is
determined. This period is set to two seconds for example, and
consequently the process from step 113 onward is carried out
according to the KAV averaged and updated for two seconds. If the
set period has not elapsed, the operation exits this process.
[0051] If the KAV calculation period has elapsed, whether the PGOK
flag is set to 1 is determined (113). As this flag will be set to 1
at step 127 but is initially 0, the process proceeds to a
malfunction determination parameter KO2AVE calculation routine 115.
The routine 115 calculates the malfunction determination parameter
KO2AVE in accordance with above-stated Equations (3) and (4). Then,
whether the purge cut request flag PGREQ explained with reference
to FIG. 5(f) is set to 1 is determined (116). If it is not set, the
current value of KO2AVE is held in the memory as an initial value
of the estimated value of the malfunction determination parameter
KO2AVES (117), and the process proceeds to step 118. If the purge
cut request flag PGREQ is set to 1, the process directly proceeds
to step 118.
[0052] At step 118, whether the malfunction determination parameter
KO2AVE exceeds the upper limit, e.g. 1.190, is determined.
Exceeding the upper limit means that the fuel feed system is
malfunctioning. Therefore, the purge cut request flag PGREQ is set
to 0, a forced purge cut flag FMPG is set to 0 (119), a flag
indicating the fuel system is malfunctioning is set to 1 (120), an
FSDD flag is set to 1 (121), the KAV calculation timer is set
(136), and the operation ends this process. In continuous
monitoring of the fuel system and misfiring, the FSDD flag is
intended to prevent normal failure monitoring from being resumed in
the operation cycle in which malfunctioning fuel feed system has
been detected, even if the fuel feed system is detected normal
afterwards.
[0053] If KO2AVE is the upper limit or less at step 118, the
process proceeds to step 123 to determine whether the forced purge
cut flag FMPG is set to 1. FMPG is set to 1 (229) when the purge
request flag PGREQ is set to 1 in the flow of FIG. 7 to be
explained below (227).
[0054] Since no forced purge cutting is carried out at first, the
process proceeds to step 128 and whether the malfunction
determination parameter KO2AVE is smaller than the first decision
value (see FIG. 5) is determined (128). If smaller, this means that
the fuel feed system may be malfunctioning, and whether the
aforementioned FSDD flag is set to 1 is determined (129). If this
flag is set to 1, this means that malfunction of a fuel system has
already been detected, the operation exits this process after going
through step 119 thereafter. If the FSDD flag is not set to 1, the
purge cut request flag PGREQ is set to 1 (130), the KAV calculation
timer is set (136) and the operation exits this process.
[0055] If KO2AVE is the first decision value or more at step 128,
the fuel feed system is determined to be normal. A fuel system
normal flag is set (131), the KAV calculation timer is set (136)
and the operation exits this process.
[0056] If forced purge cutting is in the execution at step 123, the
process will proceeds to steps 124 and 125 to wait for the lapse of
a predetermined period of around 30 seconds. A counter is
incremented at step 124 and whether the count has reached a value
corresponding to 30 seconds for example is determined at step 125.
If reached, the KAV calculation timer is set to end the process and
the process reaches step 124 again in the next processing cycle.
When a preset period has elapsed in cycles, whether the malfunction
determination parameter KO2AVE has reached or exceeded the second
decision value (see FIG. 5) is determined at step 126. If KO2AVE
has reached or exceeded the second decision value, the decrease of
KO2AVE below the first decision value is determined to be caused by
purging and not by any failure in the fuel feed system, as stated
with reference to FIG. 5.
[0057] Therefore, the process proceeds to step 127, where the PGOK
flag indicating the above-mentioned determination is set to 1, the
counter used at steps 124 and 125 is reset, and the purge cut
request flag PGREQ is set to 0. Then, the process proceeds to step
131, where the fuel system normal flag indicating the normal fuel
feed system is set, and the KAV calculation timer is set (136) and
the operation exits this process.
[0058] Reaching step 113 in the next processing cycle, as the PGOK
flag is set to 1 this time, the process enters into the routine to
calculate the estimated value of malfunction determination
parameter KO2AVES (114). In this routine, the estimated value
KO2AVES is calculated with the malfunction determination parameter
KO2AVE as the initial value in accordance with Equations (3) and
(4) stated above. The parameter KO2AVE is already held in the
memory at step 117 in the immediately preceding processing cycle in
which the purge cut request flag PGREQ was set to 1.
[0059] FIG. 7 illustrates a flow to determine whether the
implementing conditions for the monitoring are satisfied. While the
processing shown in FIG. 6 is carried out every 10 milliseconds,
the processing shown in FIG. 7 is carried out, for example, every
200 milliseconds.
[0060] In the flow of FIG. 7, the monitoring permission flag at
step 201 is a flag to be set when a central management unit of the
ECU 5 permits the monitoring on the fuel feed system through
managing various processes. When the monitoring is permitted,
whether each of the engine revolution NE, air intake pipe pressure
PB, engine water temperature TW and air intake temperature TA or
the like is within each appropriate range is determined (216). If
each parameter is determined to be within each preset appropriate
range, whether the engine is operated in the A/F ratio feedback
control mode is determined according to an A/F ratio feedback
control mode flag (217).
[0061] If determined "NO" at steps 201, 216 and 217, a
predetermined period, e.g. two seconds, is set on a TMCND timer
(202). If operated in the feedback control at step 217, the process
proceeds to step 218, where whether the period set at step 202 has
elapsed is determined. This period is the waiting time for the
stabilization of the operating mode.
[0062] If the predetermined period has elapsed at step 218, whether
the PGOK flag is set to 1 is determined (219). The PGOK flag is a
flag set to 1 at step 127 in FIG. 6, and its timing is shown in
FIG. 5(e). As stated above, this flag indicates that the purging
causes the decrease of the malfunction determination parameter
KO2AVE below the first decision value and the fuel feed system
itself is normal. Therefore, when this flag is set, the process
enters into a determining process whether the estimated value of
the malfunction determination parameter KO2AVES becomes greater
than the second decision value.
[0063] If the PGOK flag is set to 0 at step 219, the process
proceeds to step 211. At step 211, the predetermined value
mentioned above is set in the TKMCND timer to be referenced at step
220, and the aforementioned period, e.g. five minutes, is set in
the suspending period timer to be referenced at step 223. These
settings intend to provide for entering into the flow of step 220
from step 219 when the PGOK flag is set in the next and subsequent
processing cycles.
[0064] Then whether the purge cut request flag PGREQ is set to 1 is
determined (227). If it is not set to 1, a post-purge cut
stabilization timer TFMPGS is set (232), a failure monitoring
condition satisfied flag is set (231) and the operation exits this
process. If the purge cut request flag PGREQ is set to 1, the
process proceeds to step 229, and the forced purge cut flag is set
to 1 (229) to suspend purging. Then whether a post-purge cut
stabilization period TFMPGS, e.g. six seconds, has elapsed is
determined at step 230. The monitoring condition is kept
unsatisfied until the post-purge cut stabilization period TFMPGS
elapses. Therefore, the A/F ratio correction coefficient KO2 can
rise by the shifting of the A/F ratio to the lean side because of
the purge cutting. Furthermore, misdiagnosis can be avoided by
suspending various calculations until this rise in KO2 ends and is
stabilized. If the post-purge cut stabilization period TFMPGS has
elapsed, the monitoring condition is set satisfied (231). If it has
not, the monitoring condition is not satisfied (206).
[0065] If the PGOK flag is set to 1 at step 219, the process
proceeds to step 220, and whether a stabilization period, e.g. five
seconds, has elapsed is determined (220). The stabilizing period is
an estimated period for the decrease of KO2 due to the resumption
of purging to stop. As seen in FIG. 5, simultaneously with the
setting of the PGOK flag to 1, the purge cut request flag PGREQ is
set to 0 to resume the purging, and then KO2 decreases by the
resumed purging. Consequently, KAV calculation is suspended until
the decrease stops and misdiagnosis can be avoided. If the
determination at step 220 is "YES", whether KO2AVES becomes the
second decision value (see FIG. 5) or more is determined (222). If
the determination is "YES", the PGOK flag (FIG. 5(e)) is set to 0,
and the aforementioned KMCND flag is set to 0 (225).
[0066] The forced purge cut flag FMPG is set to 0 (205). Setting
the PGOK flag to 0 (225) causes the next processing cycle to enter
into the flow of step 211 from step 219, and the monitoring
condition is satisfied at step 231.
[0067] If the predetermined period has not elapsed at step 220, the
KAV flag is set to 0 (221), and the aforementioned KMCND flag is
set to 0 (203). When the determination at step 222 is "NO", whether
a period set as the maximum permissible duration, e.g. five
minutes, for suspending the fuel feed system monitoring has elapsed
is determined (223). If elapsed, the process proceeds to step 225
and the monitoring condition is satisfied (231) to resume the
failure monitoring on the fuel feed system. If the period for
suspending has not elapsed at step 223, the KMCND flag indicating
the estimation of KO2AVES is set to 1 (224). The process proceeds
to step 205 to set an FMPG flag to 0, the monitoring condition is
determined unsatisfied (206) and the operation exits from this
process.
[0068] Although the preferred embodiments of the present invention
have been described in the foregoing, the invention is not confined
to such embodiments.
[0069] According to one aspect of the invention, a state allowing a
resumption of a failure monitoring on a fuel system can be quickly
determined. Further, according to another aspect of the invention,
a more stable system operation can be achieved because the
resumption of the failure monitoring is decided based on
malfunction determination parameter, which is a more stable factor
than an A/F ratio coefficient and its learning value.
* * * * *