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BACKGROUND OF THE INVENTION
The present invention relates to a diagnosis device for determining whether
or not an internal combustion engine exhaust gas recycling device used in
a vehicle such as an automobile is functioning correctly, and particularly
relates to a diagnosis device which carries out reliable fault diagnosis
regardless of changes in the environmental conditions.
In an internal combustion engine used in a vehicle such as an automobile,
in order to reduce the NOx in the exhaust gas, conventionally various
types of exhaust gas recycling devices have been incorporated to recycle
the exhaust gas. Such an exhaust gas recycling device is disclosed in for
example Japanese Utility Model Laying Open Publication Sho No. 54-121116
(1979), Japanese Patent Laying Open Publication Sho No. 58-88450 (1983),
and Japanese Patent Publication Sho No. 60-24303 (1985).
Generally an exhaust gas recycling device incorporates an exhaust gas
recycling control valve for controlling the recycling flow rate of the
exhaust gas, a vacuum control valve for controlling the background
pressure, a temperature sensing valve, and so forth, and if there is a
fault in any of these structural components, the exhaust gas recycling
will no longer be carried out and there is a danger of the internal
combustion engine beeing operated in a state where the reduction in NOx in
the exhaust gas is not carried out. Even if the exhaust gas recycling is
not carried out because of a failure, the internal combustion engine will
still operate without failing, and may therefore be driven for a long time
without the driver realizing; this gives rise to atmospheric pollution
problems. Additionally, in certain operating conditions, if exhaust gas
recycling is not carried out then there is a danger of knocking occurring,
and also it is possible for the fuel consumption to be worsened by pump
loss from the intake of the internal combustion engine itself.
In view of the above situation, a failure alarm device has already been
proposed constructed such that when the exhaust gas recycling has stopped
because of a failure of the exhaust gas recycling device the user is
informed and given an opportunity for repair, and this is disclosed in for
example Japanese Utility Model Laying Open No. Publication Sho 49-64623
(1974) (Japanese Utility Model Publication Sho No. 52-9471 (1977), in
Japanese Utility Model Laying Open Publication Sho No. 50-67220 (1975),
and also in Japanese Utility Model Application Sho No. 60-163288 (1985)
(Japanese Utility Model Laying Open Publication Sho No. 62-7163 (1987) by
the same applicant as the applicant in the present application.
Fault diagnosis of the exhaust gas recycling device may be carried out
basically by, under conditions in which exhaust gas recycling should be
carried out, determining whether or not, for example, the temperature
within an exhaust gas recycling passage is at least a certain value, in
other words by determining that if that temperature is not more than a
cetain value exhaust gas is not flowing in the exhaust gas recycling
passage, and thus determining that the exhaust gas recycling device has
failed, but if it is simply supposed that exhaust gas recycling should be
carried out when various parameters indicating operating conditions such
as the intake pressure or intake flow rate of the internal combustion
engine or the engine rotation speed, have certain values, then when the
atmospheric pressure fluctuates because of for example high altitude
driving, since the intake pressure will fluctuate correspondingly, the
conditions for exhaust gas recycling will not be determined appropriately,
and there is a danger that the fault diagnosis of the exhaust gas
recycling device will not be carried out correctly. Particularly when the
exhaust gas recycling control is carried out from the intake pressure, the
ranges of intake pressure and engine revolution rates in which exhaust gas
recycling are carried out will fluctuate according to the atmospheric
pressure fluctuation.
Fault diagnosis of the exhaust gas recycling device may be carried out
basically by, under conditions such that exhaust gas recycling should be
carried out, determining whether or not, for example, the temperature
within an exhaust gas recycling passage is at least a certain value, in
other words by determining that when the exhaust gas recycling passage
temperature is not more than a certain value exhaust gas is not flowing in
the exhaust gas recycling passage, and thus determining that the exhaust
gas recycling device has filed, but when the exhaust gas recycling is
started the temperature within the exhaust gas recycling passage does not
rise rapidly, and moreover this temperature rise is further delayed the
lower the outside temperature. Therefore a false diagnosis may easily be
made if the fault diagnosis is carried out simply by determining if the
exhaust gas recycling passage temperature is at least a certain value
under conditions in which exhaust gas recycling should be carried out.
The present invention considers the above state of affairs, and has as its
object the provision of an improved exhaust gas recycling device diagnosis
device which carries out accurate fault diagnosis always with no erroneous
diagnoses even if the atmospheric pressure fluctuates or the outside air
temperature fluctuates.
SUMMARY OF THE INVENTION
The above objective is achieved according to the present invention by a
diagnosis device for an internal combustion engine exhaust gas recycling
device which carries out fault diagnosis of the exhaust gas recycling
device by determining a time when parameters indicating the operating
condition of the internal combustion engine have certain values as a time
to carry out exhaust gas recycling, and detecting whether or not exhaust
gas recycling is actually being carried out at this time, characterized by
comprising an atmospheric pressure detecting means detecting the
atmospheric pressure, and a correction means correcting certain values of
said parameters according to the atmospheric pressure detected by said
atmospheric pressure detecting means.
According to the above construction, in the operating region in which
exhaust gas recycling should be carried out the comparison values of the
parameters indicating driving conditions such as intake manifold pressure,
intake flow rate or engine revolution rate, which are used to determine
whether or not the operating region is such that exhaust gas recycling
should be carried out, are subject to an atmospheric pressure
compensation, and thereby even if the atmospheric pressure fluctuates the
decision as to whether or not the operating region is such that exhaust
gas recycling should be carried out based on these parameters is carried
out accurately, and thus an accurate diagnosis is carried out.
The diagnosis device according to the present invention may be constructed
so that when the atmospheric pressure detected by the atmospheric pressure
detecting means is not more than a certain value diagnosis is prevented
from occurring.
The parameter or parameters may be at least one of the intake manifold
pressure and the intake flow rate of the internal combustion engine and
the internal combustion engine revolution rate, or may be a combination of
the intake mainfold pressure of the internal combustion engine and the
engine revolution rate.
Again the parameter may be the intake air amount per stroke of the internal
combustion engine derived from the air intake flow rate of the internal
combustion engine and the engine revolution rate, and the construction may
be such that a decision is made that exhaust gas recycling should be
carried out when the intake amount of air per stroke of the internal
combustion engine is within a certain range.
Furthermore the parameters may be the air intake flow rate of the internal
combustion engine and the intake air amount per stroke of the internal
combustion engine calculated from this air intake flow rate and the engine
revolution rate, and the construction may be such that a decision is made
that exhaust gas recycling should be carried out when the air intake flow
is at least a certain value and the air intake flow rate per stroke of the
internal combustion engine is not more than a certain value.
In the diagnosis device according to the present invention, the detection
of the atmospheric pressure may be carried out by an ordinary aneroid type
atmospheric pressure sensor.
Again the diagnosis device according to the present invention may use as an
atmospheric pressure sensor the intake mainfold pressure sensor, by
determining the atmospheric pressure from the value of the intake manifold
pressure detected by this intake manifold pressure sensor immediately
before starting the internal combustion engine.
Alternatively the atmospheric pressure may be determined from an air/fuel
ratio learning high altitude compensation factor for the air/fuel ratio
control of the internal combustion engine.
The detection of whether or not the exhaust gas recycling is actually being
carried out may be based on whether the temperature in an exhaust gas
recycling passage is not more than a certain value over a certain time
interval, and this time interval may be determined depending on the
external temperature.
Thus the fault diagnosis time is set according to the outside temperature,
and thereby an erroneous decision to the effect that the exhaust gas
recycling device has failed caused by the fact that the external
temperature is low is avoided, and an accurte fault diagnosis with high
reliability can be carried out.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic structural diagram of one embodiment of an exhaust
gas recycling device incorporating a diagnosis device according to the
present invention;
FIG. 2 is a flowchart showing the operation of the diagnosis device
according to the present invention;
FIG. 3 is a flowchart showing an embodiment of a routine for determining
atmospheric pressure in the exhaust gas recycling device diagnosis device
according to the present invention;
FIG. 4 is a flowchart showing another embodiment of an atmospheric pressure
detection routine in the exhaust gas recycling device diagnosis device
according to the present invention;
FIG. 5 is a graph showing differential pressure characteristics used in the
atmospheric pressure detection routine shown in FIG. 4;
FIG. 6 is a flowchart showing the operation of another embodiment of the
diagnosis device according to the present invention;
FIG. 7 and FIG. 8 are graphs showing decision value characteristics in the
embodiment shown in FIG. 6;
FIG. 9 is a graph showing variations in the EGR operating region and
diagnosis region with fluctuations in atmospheric pressure in the
embodiment shown in FIG. 6;
FIG. 10 is a schematic structural diagram of another embodiment of an
internal combustion engine provided with the exhaust gas recycling device
diagnosis device according to the present invention;
FIG. 11 is a flowchart showing one embodiment of the operation of the
exhaust gas recycling device diagnosis device in an internal combustion
engine shown in FIG. 10;
FIG. 12 is a graph showing upper bound characteristics of the corresponding
intake air amount for one stroke of the engine corresponding to the
atmospheric pressure;
FIG. 13 is a flowchart showing one embodiment of a routine for setting the
decision time of the diagnosis according to the external temperature;
FIG. 14 is a graph showing an example of EGR decision time characteristics
according to the external temperature;
FIG. 15 is a flowchart showing a variant of the diagnosis routine of the
exhaust gas recycling device shown in FIG. 13, and
FIG. 16 is a flowchart showing the operation of yet another embodiment of
the exhaust gas recycling device diagnosis device according to the present
invention; and
FIG. 17 is a graph showing the relationship between atmospheric pressure
and an air/fuel ratio learning high altitude compensation factor.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is now described in detail with reference to the
drawings in respect of embodiments.
FIG. 1 shows one embodiment of an exhaust recycling device in which is
incorporated the diagnosis device according to the present invention. In
the drawing, 1 indicates an internal combustion engine, and this internal
combustion engine takes in mixture to a combustion chamber 5 through a
throttle valve 4 and an intake manifold 3; the combustion products, in
other words the exhaust gases, are expelled to an exhaust manifold 6.
The exhaust manifold 6 is provided with an exhaust gas take-in port 7 for
exhaust gas recycling, and the inlet mainfold 3 is provided with an
exhaust gas introduction port 8; the exhaust gas take-in port 7 and the
exhaust gas introduction port 8 are connected by an exhaust gas recycling
line 9, an exhaust gas recycling control valve 20, and a line 10, in
series.
The exhaust gas recycling control valve 20 is provided with an inlet port
21 and an outlet port 22, the inlet port 21 is connected by the line 9 to
the exhaust gas take-in port 7, and the outlet port 22 is connected by the
line 10 to the exhaust gas introduction port 8. The exhaust gas recycling
control valve 20 is provided with a valve port 23 and a valve element 24;
the valve port 23 is opened and closed by the valve element 24 and the
opening is controlled so that the flow rate of exhaust gas recycling is
controlled. The valve element 24 is connected to a diaphragm 26 of a
diaphragm device 25, and when a negative pressure exceeding a certain
value, for example -70 mmHg, is not present within a diaphragm chamber 27,
it is urged downwards by the spring force of a compression coil spring 28
and closes the valve port 23; when a negative pressure exceeding the
certain value is introduced into the diaphragm chamber 27, then this
negative pressure overcomes the spring force of the compression coil
spring 28 and it rises to open the valve port 23.
The diaphragm chamber 27 of the exhaust gas recycling control valve 20 is
connected by a line 29, a negative pressure control valve 30 for
background pressure control, a line 31, a temperature sensitive valve 32,
and a line 33 to an inlet manifold negative pressure take-out port 34. The
inlet manifold negative pressure take-out port 34 is, as shown in the
diagram, provided in such a position as to be upstream of the throttle
valve 4 when in the fully closed position, but downstream of the throttle
valve 4 when it is opened more than a relatively small amount.
The negative pressure control valve 30 has a valve element 36 which opens
and closes a valve port 35, and a diaphragm 37 which supports this valve
element, and the diaphragm 37 delineates an atmospheric chamber 38 which
is open to the atmosphere on the upper side in the drawing, and a
idaphragm chamber 39 on the lower side in the drawing; when a pressure
(positive pressure) of at least a certain value is not present in the
diaphragm chamber 39 the diaphragm pulls the valve element 36 away from
the value port 35 under the effect of the compression coil spring 40, and
is in the position to open this valve port, whereas when the pressure of
at least a certain value is introduced into the diaphragm chamber 39, the
force of the compression coil spring 40 is overcome, the diaphragm moves
upwards in the drawing, and the valve element 36 is held against the valve
port 35 so that the position is such as to close the valve port.
The diaphragm chamber 39 of the negative pressure control valve 30 is
connected by a line 41 to a pressure chamber 43 between the valve port 23
of the exhaust gas recycling control valve 20 and an orifice 42 provided
downstream thereof, and thus has the exhaust gas pressure within the
pressure chamber admitted to it.
The construction thus described of the negative pressure control valve 30
and the orifice 42 is a well known background pressure control
construction, and in the exhaust gas recycling operating range in which
the inlet mainfold negative pressure is applied to the exhaust gas
recycling control valve 20 the negative pressure supplied to the diaphragm
chamber 27 of the exhaust gas recyling control valve 20 is adjusted so as
to maintain at a substantially constant value the exhaust gas pressure in
the pressure chamber 43, or in other words the opening of the valve port
23 is adjusted, and thereby the ratio of the exhaust gas recycling flow
rate to the intake air flow rate, or in other words the EGR ratio, is
maintained at a substantially constant value.
The temperature sensitive valve 32 responds to the coolant temperature of
the internal combustion engine 1, and when the engine is warming up and
the coolant temperature is not more than a certain value, for example 60
degress C., then the value is closed and the connection between the lines
31 and 33 is shut off; on the other hand when the coolant temperature is
at least a certain temperature a connection between the lines 31 and 33 is
established.
According to the above construction, the exhaust gas recycling control
valve 20 is opened when a negative pressure exceeding a certain value, for
example -70 mmHg, is supplied to the line 29, and the coolant temperature
of the internal combustion engine 1 is at least a certain value, for
example 60 degrees C., so that the temperature sensitive valve 32 is open;
the exhaust gas recycling is carried out with a flow rate corresponding to
this degree of opening.
In the drawings, 50 indicates a microcomputer which carries out the
diagnosis of the exhaust gas recycling device. The microcomputer 50 is of
an ordinary construction, and has a central processing unit (CPU) 51, a
memory 52, an input port 53, and an output port 54; it receives
information relating to the revolution rate of the internal combustion
engine 1 from a revolution rate sensor 56 provided on a distributor 55 of
the internal combustion engine 1, information relating to the coolant
temperature of the internal combustion engine 1 from a coolant temperature
sensor 57, information relating to the intake manifold pressure from an
intake manifold pressure sensor 58, and information relating to the
temperature in the line 10 from a temperature sensor 59 provided at an
intermediate point of the exhaust gas recycling line 10; based on this
information, a diagnosis is made as to whether or not the exhaust gas
recycling device is operating normally, according to the flowchart shown
in FIG. 2 and FIG. 3, and when a decision is made that the exhaust gas
recycling device is not operating normally, an indicator lamp 62 is
illuminated.
The operation of the diagnosis device according to the present invention is
now described with reference to the flowchart shown in FIG. 2.
The EGR diagnosis routine shown in FIG. 2 is executed as an interrupt
routine at a certain interval, and first in step 10 a test is made as to
whether or not the atmospheric pressure Pa determined as shown in FIG. 3,
is at least a certain value. When Pa is more than Paset control proceeds
to step 12 for the execution of diagnosis, whereas when Pa is not greater
than Paset, diagnosis is not carried out, and the diagnosis interrupt
routine ends.
In step 12, a decision is made as to whether or not the exhaust gas
recycling passage temperature Tegr detected by the temperature sensor 59
exceeds a decision temperature Tset. When Tegr is greater than Tset,
exhaust gas recycling is being carried out, and this being the normal
situation, control proceeds to step 20; on the other hand if Tegr is not
more than Tset, exhaust gas recycling is not being carried out, and
control proceeds to step 14.
In step 14, a decision is made as to whether or not the revolution rate Ne
of the internal combustion engine 1 detected by the revolution rate sensor
56 is at least certain value Neset1 and not more than a second certain
value Neset 2 which is greater than Neset1. When Ne is greater than Neset1
and less than Neset 2, control proceeds to Ne is greater than Neset1 and
less than Neset 2, control proceeds to step 16.
In step 16, a decision is made as to whether or not the intake manifold
pressure Pi of the internal combustion engine 1 detected by the intake
manifold pressure sensor 58 is at least a first certain value Piset1 and
not more than a second certain value Piset2 which is greater than Piset1.
When Pi is greater than Piset1 and less than Piset 2, control proceeds to
step 18.
In step 18, the malfunction determination causes the indicator lamp 62 to
be turned on. By the illumination of this indicator lamp 62, the user can
be made aware that a failure has occurred in the exhaust gas recycling
device.
In step 20, the normal operation decision causes the indicator lamp 62 to
be turned off, or not turned on, and at this time the exhaust gas
recycling device is operating normally.
In the above described embodiment, the atmospheric pressure Pa is
determined as shown in FIG. 3 directly from the intake manifold pressure
Pi detected by the intake manifold pressure sensor 58 immediately before
the engine is started.
The determination of atmospheric pressure may also be carried out according
to the flowchart shown in FIG. 4, and next a description of this method of
atmospheric pressure detection is given with reference to the flowchart
shown in FIG. 4.
The atmospheric pressure detection routine shown in FIG. 4 may be executed
as an interrupt routine at a certain time interval, and initially in step
70, a test is made as to whether or not the engine revolution rate Ne of
the internal combustion engine 1 detected by the revolution rate sensor 56
is at least a third certain value Neset 3 and is not more than a fourth
certain value Neset4 which is greater than Neset 3. When Ne is greater
than Neset3 and less than Neset4, control proceeds to step 72.
In step 72, a decision is made as to whether or not the absolute value of
the rate of change of the intake manifold pressure Pi in a certain time
interval, DELTA Pi, is not more than a certain value DELTA Piset. If the
absolute value of DELTA Pi is less than DELTA Piset, control proceeds to
step 74.
In step 74, a differential pressure Pe is determined according to a control
value map as shown in FIG. 5, depending on the revolution rate Ne of the
internal combustion engine 1 detected by the revolution rate sensor 56.
This differential pressure Pe is the difference between the intake
manifold pressure Pi at the throttle opening such that a throttle switch
60 described later opens and closes, and a standard atmospheric pressure,
and this differntial pressure Pe increases with an increase in the
revolution rate Ne.
After step 74, control proceeds to step 76, and in step 76, a derived value
for atmospheric pressure Pap is calculated by adding the differential
pressure Pe determined in step 74 to the intake manifold pressure Pi
detected by the intake manifold pressure sensor 58. After step 76 control
proceeds to step 78.
In step 78, a decision is made as to whether or not the throttle switch 60
is in the on site. The throttle switch 60 changes to the on state when the
throttle valve 4 is opened to exceed a certain value, and goes to the off
state when the throttle valve 4 is closed beyond the certain opening, and
when the throttle switch 60 is in the on state control goes to step 80,
whereas when the throttle switch 60 is not in the on state control goes to
step 82.
In step 80, a comparison is made between the previously determined
atmospheric pressure Pa and the newly determined derived atmospheric
pressure value Pap, and if Pap is less than Pa, control goes to step 84.
In step 82, again a comparison is made between the previously determined
atmospheric pressure Pa and the newly determined derived value for the
atmospheric pressure Pap, and if Pap is not less than Pa control goes to
step 84.
In step 84, the newly determined derived value of the atmospheric pressure
Pap is determined as the atmospheric pressure Pa. In other words, when the
throttle switch 60 is in the on state the atmospheric pressure Pa is
updated to a smaller value, whereas when the throttle switch 60 is in the
off state, the atmospheric pressure Pa is updated to a larger value.
By carrying out the detection of the atmospheric pressure according to the
above described flowchart, an atmospheric pressure substantially equal to
the actual atmospheric pressure is detected.
In the above described embodiment, when the atmospheric pressure is not
more than a certain value, diagnosis is completely prevented from being
carried out, but in the diagnosis device of the present invention, equally
corrections may be applied to the parameter comparison values for
determining the exhaust gas recycling region, according to the
fluctuations in atmospheric pressure.
Next the operation of another embodiment of the diagnosis device according
to the present invention is described with reference to the flowchart
shown in FIG. 6.
The EGR diagnosis routine shown in FIG. 6 is executed as an interrupt
routine at a certain time interval, and initially in step 100, a decision
is made as to whether or not the exhaust gas recycling passage temperature
Tegr detected by the temperature sensor 59 is higher than a decision
temperature Tset. When Tegr is at least Tset, then exhaust gas recycling
is being carried out, and at this time the situation is regarded as normal
and control goes to step 150, whereas when Tegr is not at least Tset
exhaust gas recycling is not being carried out and at this time control
goes to step 110.
In step 110, depending on the atmospheric pressure Pa, decision values
(comparison values) A, B, C and D are determined from control data maps as
shown in FIG. 7 and FIG. 8. The decision values A and B are decision
values for the engine revolution rate, and decrease with a decrease in the
atmospheric pressure Pa. The decision values C and D are decision values
for the intake manifold pressure Pi, and these also both decrease with a
decrease in the atmospheric pressure Pa. Determination of the atmospheric
pressure Pa may in this embodiment also be carried out by substituting the
intake manifold pressure detected by the intake manifold pressure sensor
58 immediately before starting the engine. After step 110, control goes to
step 120.
In step 120, a decision is made as to whether or not the revolution rate Ne
of the internal combustion engine 1 detected by the revolution rate sensor
56 is least the decision value A and not more than the decision value A+B
which is greater than A. When Ne is greater than A and less than A+B
control goes to step 130.
In step 130, a decision is made as to whether or not the intake manifold
pressure Pi detected by the intake manifold pressure sensor 58 is at least
the decision value C and not more than the decision value C+D which is
greater than C. When Pi is greater than C and less than C+D control goes
to step 140.
In step 140, the malfunction decision causes the indicator lamp 62 to be
turned on. Turning on the indicator lamp 62 allows the user to be made
aware that there is a failure in the exhaust gas recycling device.
In step 150, the normal decision means that the indicator lamp 62 is turned
off, or is not turned on. At this point the exhaust gas recycling device
is operating normally.
As described above, the decision values for the engine revolution rate and
the intake manifold pressure, in other words the comparison values, are
determined according to the atmospheric pressure, whereby as shown in FIG.
9 if the EGR operation region varies with a variation in the atmospheric
pressure the diagnosis region also varies with it, and the diagnosis
region does not go outside the EGR operation region.
By carrying out the exhaust gas recycling device diagnosis as described
above, the exhaust gas recycling device diagnosis is carried out reliably
without erroneous decisions, irrespective of fluctuations in atmospheric
pressure.
Next using FIG. 10 another embodiment of an internal combustion engine
fitted with an exhaust gas recycling device diagnosis device according to
the present invention is described. In this embodiment, the internal
combustion engine 10 takes air into a combustion chamber 5 through an air
cleaner 2, an air flow meter 63, a throttle valve 4 and an intake manifold
3; fuel is supplied by injection from a fuel injector 49 provided in the
intake manifold 3, and the combustion products, in other words the exhaust
gases, are expelled to an exhaust manifold 6.
The microcomputer 50 is constructed so as to carry out fuel injection
amount control of the fuel injector 49 and also the exhaust gas recycling
device disgnosis; it receives information relating to the rotation rate of
the internal combustion engine 1 from a rotation rate sensor 56,
information relating to the coolant temperature of the internal combustion
engine 1 from a coolant temperature sensor 57, information relating to the
intake air flow rate from the air flow meter 63, information relating to
the temperature in the line 10 from a temperature sensor 59 provided at an
intermediate point in the exhaust gas recycling line 10, information
relating to the atmospheric pressure from an aneroid bellows type of
atmospheric pressure sensor 64, and information relating from an oxygen
sensor 61 provided in the exhaust manifold 6; fuel injection amount
control is carried out based on this information and following the
flowchart shown in FIG. 11 a diagnosis is also made as to whether or not
the exhaust gas recycling device is operating normally, and whn a decision
is made that the exhaust gas recycling device is not operating normally,
an indicator lamp 62 is turned on.
The fuel injection amount control is carried out by determining the basic
fuel injection amount Tp based on computing the ratio Q/N of the air
intake flow rate Q detected by the air flow meter 63, and the engine
revolution rate N detected by the revolution rate sensor 56, determining
an engine warm up correction coefficient Ktw based on the coolant
temperature Tw detected by the coolant temperature sensor 57, determining
an air/fuel ratio correction coefficient Kf based on the air/fuel ratio
signal from the oxygen sensor 61, and determining the fuel injection time
by a calculation based on the basic fuel injection amount Tp and the above
correction coefficients Ktw and Kf.
Next the operation of the diagnosis device in this embodiment is described
with reference to the flowchart shown in FIG. 11.
The EGR diagnosis routine shown in FIG. 11 is executed as an interrupt
routine at a regular time interval, and first in step 200 a decision is
made as to whether or not the indicator lamp 62 is on, or in other words
is already illuminated. When the indicator lamp 62 is in the on state,
then a decision has already been made that the exhaust gas recycling
device is functioning abnormally, and at this time the routine terminates,
whereas when the indicator lamp 62 is not on, control proceeds to step
210.
In step 210, a decision is made as to whether or not the coolant
temperature Tw detected by the coolant temperature sensor 57 is at least a
predetermined value Twset, which is for example 60 degrees C. When Tw is
greater than Twset control goes to step 220, and otherwise since exhaust
gas recycling is not being carried out the routine terminates.
In step 220, the intake air amount per stroke of the engine Q/N is
calculated from the intake air flow rate Q detected by the air flow meter
63 and the revolution rate N of the internal combustion engine 1 detected
by the revolution rate sensor 56, and a decision is made as to whether or
not Q/N is at least a lower bound Q/Nmin. When Q/N is greater than Q/Nmin
control goes to step 230, and otherwise the routine terminates.
In step 230, an upper bound Q/Nmax of the intake air amount per one stroke
of the engine Q/N for which exhaust gas recycling should be carried out is
determined according to the atmospheric pressure Pa detected by the
atmospheric pressure sensor 64 according to characteristics as shown in
FIG. 12. The upper bound Q/Nmax decreases with a decrease in the
atmospheric pressure. After step 230, control goes to step 240.
In step 240, a decision is made as to whether or not the intake air amount
per one stroke of the engine Q/N is not more than the upper bound Q/Nmax.
When Q/N is less than Q/Nmax, it is determined to be in the exhaust gas
recycling region, and at this time control goes to step 250, whereas
otherwise the routine terminates.
In step 250, a decision is made as to whether or not the exhaust gas
recycling passage temperatue Tegr detected by the temperature sensor 59 is
not more than a predetermined value Tset. When Tegr is less than Tset,
control goes to step 260, whereas otherwise the routine terminates.
In step 260, the elapsed time since a "yes" decision was made in step 240,
in other words since it was determined to be in the exhaust gas recycling
operation region, or in other words the EGR time Cegr is determined from a
count value. After step 260, control goes to step 280.
In step 270, a decision is made as to whether or not the EGR time Cegr is
greater than a predetermined decision time Cset. When Cegr is greate than
Cset, a decision is made that the exhaust gas recycling device has
malfunctioned, and control goes to step 280, whereas otherwise the routine
terminates.
In step 280, because of the malfunction decision, the indicator lamp 62 is
put in the on state, or in other words turned on.
The predetermined decision time Cset for the EGR time in the above
described embodiment may be constant, but also as shown in FIG. 13 and
FIG. 14, the decision time Cset may be variable according to the external
temperature Tair. This decision time Cset may be set longer the lower the
external temperature Tair, and therefore an erroneous malfunction decision
when the external temperature is low can be avoided.
As the external temperature Tair may be employed the intake air temperature
detected by an intake air temperature sensor 65 provided on the engine
intake system.
In the above described embodiment, the EGR operation region, or in other
words the EGR diagnosis region, is such that the coolant temperature Tw is
at least a set value Twset, the air intake amount per one stroke of the
engine Q/N is at least bound Q/Nmin and at most an upper bound Q/Nmax, but
this EGR diganosis region may be alternatively determined so that the
coolant temperature Tw is at least a certain value Twset, the intake air
flow rate Q detected by the air flow meter 63 is at least a lower bound
Qmin, and the intake air amount per ont stroke of the engine Q/N is at
most an upper bound Q/Nmax, and in this case the diagnosis is carried out
according to the flowchart shown in FIG. 15.
Instead of direct detection of the atmospheric pressure, the atmospheric
pressure may be determined by using learning control in feedback control
of the air/fuel ratio based on an air/fuel ratio signal from the oxygen
sensor 61. This learning control value is termed an air/fuel ratio
learning high altitude correction coefficient. Such an air/fuel ratio
learning high altitude correction coefficient is already in use in high
altitude correction control of the air/fuel ratio, and more detailed
description may be found by making reference to Japanese Patent Laying
Open Publication Sho No. 60-50249 (1985) and Japanese Patent Laying Open
Publication Sho No. 60-53635 (1985).
Next with reference to FIG. 16, an embodiment is described in which
air/fuel ratio learning high altitude correction coefficient is used as an
atmospheric pressure correction for EGR diganosis.
The EGR diagnosis routine shown in FIG. 16 is executed as an interrupt
routine at a certain time interval, and first in step 300 a decision is
made as to whether or not the indicator lamp 62 is in the on state, in
other words is turned on. If the indicator lamp 62 is on, then a decision
has already been made that the exhaust gas recycling device is abnormal,
and at this point the routine terminates, whereas if the indicator lamp 62
is not on, control goes to step 310.
In step 310, a decision is made as to whether or not the coolant
temperature Tw detected by the coolant temperature sensor 57 is at least a
certain value Twset, for example 60 degrees C. When Tw is greater than
Twset, control goes to step 320, whereas otherwise exhaust gas recycling
is not being carried out, and the routine terminates.
In step 320, the intake air amount per one stroke of the engine Q/N is
calculated from the intake air flow rate Q detected by the air flow meter
63 and the rotation rate N of the internal combustion engine 1 detected by
the rotation rate sensor 56, and a decision is made as to whether or not
Q/N is at least a predetermined lower bound Q/Nmin. When Q/N is greater
than Q/Nmin, control goes to step 330, whereas otherwise the routine
terminates.
In step 330, a decision is made as to whether the intake air amount per one
stroke of the engine Q/N is not more than a predetermined upper bound
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