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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for detecting
trouble in an exhaust-gas recirculation (hereinafter referred to as "EGR")
system of an internal combustion engine, particularly to a method and an
apparatus capable of detecting trouble in an EGR control valve and the
clogging of a passage in the EGR system as well as discriminating whether
the clogging occurs upstream or downstream of the EGR control valve.
2. Description of the Related Art
To reduce an amount of No.sub.x in an exhaust gas, an EGR system, as is
well known, wherein the exhaust gas flowing through an exhaust passage is
recirculated to an intake passage of an internal combustion engine via an
EGR passage is used. In the EGR system of such a type, an EGR control
valve is usually provided in the EGR passage. The amount of EGR gas to be
supplied to the intake passage of the internal combustion engine is
controlled by the opening degree of the EGR control valve. However, the
recirculation of exhaust gas may be continuously interrupted if the EGR
control valve is broken or the EGR passage clogs. If such an inconvenience
is left as it is, a large amount of NO.sub.x is continuously discharged
because no EGR is conducted. In addition, the reduction of the amount of
recirculating exhaust gas or the interruption of EGR due to the trouble of
the EGR system is seldom found by the driver.
To solve such a problem, apparatuses, for diagnosing the trouble of EGR
system, have been proposed wherein the opening degree of EGR control valve
is controlled by the magnitude of a negative pressure introduced into a
diaphragm chamber in the EGR control valve partitioned by a diaphragm. For
example, Japanese Unexamined Patent Publication (Kokai) No. 63-75345
discloses an apparatus for diagnosing the trouble of EGR system of a
diaphragm type comprising a pressure detection means provided upstream of
EGR control valve and means for detecting the supply of negative pressure
to the EGR control valve. According to the trouble detection apparatus
disclosed in the above Patent Publication, "trouble" is determined if no
flow of exhaust gas is detected by the pressure detection means when a
negative pressure is supplied to the EGR control valve. Contrarily,
"trouble" is also determined if the flow of exhaust gas is detected when
no negative pressure is supplied to the EGR control valve.
According to this apparatus, however, although trouble in the EGR system
can be diagnosed, it is impossible to determine whether the trouble is
caused by the malfunction of the EGR control valve or by clogging of the
EGR passage. Also, when the EGR passage is clogged, it is impossible to
determine whether the clogging has occurred upstream or downstream of the
EGR control valve. Accordingly, there is a problem in the above-mentioned
trouble detection apparatus in that a long time is required identify the
trouble in the EGR system, which results in a time-consuming repair
operation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a trouble diagnosing
apparatus for an exhaust-gas recirculation system comprising an EGR
control valve in an EGR passage, which is capable of not only detecting
the malfunction of the EGR control valve in the EGR system but also
determining whether the clogging of the EGR passage occurs upstream or
downstream of the EGR control valve when the EGR control valve is in a
normal state.
To achieve the above object, the trouble diagnosing apparatus for an
exhaust-gas recirculation system according to the present invention is a
trouble diagnosing apparatus for an exhaust-gas recirculation system
comprising an EGR control valve provided in an EGR passage communicating
an exhaust passage with an intake passage of an internal combustion
engine, for controlling a flow rate of recirculating exhaust gas,
characterized in that the apparatus further comprises an orifice provided
in the EGR passage, pressure detection means for detecting a pressure in
the EGR passage between the orifice and the EGR control valve, operation
state detection means for detecting an operation state of the internal
combustion engine, operation zone determination means for determining
whether the operation state of the internal combustion engine is in a
first zone wherein an amount of EGR is larger than a predetermined value
or in a second zone wherein an amount of EGR is smaller than the
predetermined value, value-opening detection means for detecting an open
sate of the EGR control valve, and trouble determination means for
determining whether or not the clogging occurs in the EGR passage and
whether the clogging occurs upstream or downstream of the EGR control
valve, based on the operation zone and the pressure value detected by the
pressure detection means when the EGR control valve is in the open state.
In this regard, a pressure switch; which is capable of changing its ON/OFF
states when the negative pressure exceeds a predetermined value can be
used as the pressure detection means. In this case, if the pressure switch
does not reverse in the first operation zone of the engine wherein the
negative pressure exceeds the predetermined value when the EGR control
valve is normal and in the open state, it can be determined that the
clogging occurs downstream of the EGR control valve, while if the pressure
switch reverses in the second operation zone of the engine wherein the
negative pressure is lower than the predetermined value when the EGR
control valve is normal and in the open state, it can be determined that
the clogging occurs upstream of the EGR control valve.
According to the trouble diagnosing apparatus for an exhaust-gas
recirculation system according to the present invention, an orifice is
provided, in addition to the EGR control valve for controlling a flow rate
of recirculating exhaust gas, in the EGR passage communicating the exhaust
passage to the intake passage of the internal combustion engine, and
pressure detection means is provided for detecting a pressure in the EGR
passage between the orifice and the EGR control valve. When the operation
state of the internal combustion engine is in the first operation zone
wherein an amount of EGR is larger than the predetermined value, the
negative pressure increases in the EGR passage between the orifice and the
EGR control valve in the normal state. Accordingly, if the negative
pressure falls, it can be determined that the clogging occurs downstream
of the EGR control valve. On the other hand, when the operation state is
in the second operation zone wherein an amount of EGR is smaller than the
predetermined value, the negative pressure is maintained at the smaller
value in the EGR passage between the orifice and the EGR control valve in
the normal state. Accordingly, if the negative pressure increases, it can
be determined that the clogging occurs upstream of the EGR control valve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a whole structure of one embodiment of a trouble
diagnosing apparatus for an exhaust-gas recirculation system according to
the present invention;
FIGS. 2A and 2B are a flow-chart illustrating one example of a series of
steps for diagnosing trouble in the exhaust-gas recirculation system in
the embodiment shown in FIG. 1;
FIG. 3 is a chart for explaining zones A and B on the coordinates wherein
the abscissa represents a rotational speed of engine and the ordinate
represents a load;
FIG. 4 is an enlarged view of the part of FIG. 1 when a pressure sensor is
replaced by an ON-OFF switch;
FIG. 5A is a characterized curve illustrating the pressure variation in a
negative pressure chamber of FIG. 4 when clogging on the intake side and
the exhaust side, respectively, is growing;
FIG. 5B is a chart for explaining ON/OFF characteristic of a pressure
switch of FIG. 4;
FIG. 6A is a chart illustrating a zone wherein the pressure switch of FIG.
4 is OFF when there is no clogging in the EGR passage;
FIGS. 6B through 6D are charts illustrating the variation of the zone
wherein the pressure switch of FIG. 4 is OFF when the clogging generated
on the intake side of the EGR passage is growing;
FIGS. 6E through 6G are charts illustrating the variation of the zone
wherein the pressure switch of FIG. 4 is OFF when the clogging generated
on the exhaust side of the EGR passage is growing;
FIGS. 7A and 7B are a flow chart illustrating one example of a series of
steps for diagnosing trouble in the exhaust-gas recirculation system in
the embodiment shown in FIG. 4;
FIGS. 8A and 8B are a flow chart illustrating another example of a series
of steps for diagnosing trouble in the exhaust-gas recirculation system in
the embodiment shown in FIG. 4;
FIGS. 9A and 9B are a flow chart illustrating further example of a series
of steps for diagnosing trouble in the exhaust-gas recirculation system in
the embodiment shown in FIG. 4; and
FIG. 10 is a chart illustrating a shifting zone of a boundary line between
ON/OFF zone of the pressure switch calculated in the steps for diagnosing
trouble in the exhaust-gas recirculation system shown in FIGS. 9A and 9B.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a structure of an internal combustion engine
incorporating an apparatus for diagnosing trouble in an EGR system
according to the present invention. In this drawing, reference numeral 1
denotes an internal combustion engine; 2 an exhaust manifold; 3 an intake
manifold; 4 an intake duct; 5 a throttle valve provided in the intake
duct; 6 a pressure sensor for the intake duct; 7 a fuel-injection valve
attached to a branch of the intake manifold 3; 8 an EGR passage
communicating the exhaust manifold 2 to the intake manifold 3; 9 an EGR
control valve provided in the EGR passage 8; and 10 a control circuit
(engine control unit: ECU). Exhaust gas in the exhaust manifold 2 is
recirculated into the intake manifold 3 via the EGR passage 8 when the EGR
control valve 9 is open.
The control circuit 10 is constituted, for example, by a microcomputer
including a ROM (read-only-memory) 12, a RAM (random-access-memory) 13, a
CPU (central processing unit) 14, an input port 15 and an output port 16,
each connected with the others by a two-way bus. In the EGR control valve
9, a lift sensor 30 is provided for detecting the opening degree of a
valve body. A value detected by the lift sensor 30 is input to the input
port 15 via an A/D converter 18. An intake temperature sensor 19 is
provided in the intake duct 4. A value THA detected by the intake
temperature sensor 19 is input to the input port 15 via an A/D converter
20. A sensor 21 for detecting an opening degree of the throttle valve 5 is
connected to the throttle valve 5. A value TA detected by the throttle
opening degree sensor 21 is input to the input port 15 via an A/D
converter 22.
The pressure sensor 6 is attached to a surge tank (intake manifold 3)
provided downstream of the throttle valve 5. A value PA detected by the
pressure sensor 6 is input to the input port 15 via an A/D converter 29. A
water temperature sensor 23 is attached to the engine body 1, for
detecting the temperature of the water for cooling the engine. A value THW
detected by the water temperature sensor 23 is input to the input port 15
via an A/D converter 24. Further, a rotational speed sensor 25 is
connected to the input port 15, for issuing an output signal representing
a rotational speed NE of the engine. The output port 16 is connected, on
one hand, to the fuel-injection valve 7 and a negative pressure control
valve 50 corresponding thereto via driver circuits 26, 26' and, on the
other hand, to an abnormality lamp 28 via driving circuit 27.
In this embodiment, the negative pressure control valve 50 is a solenoid
valve constituted by a solenoid 51, on-off valves 52, 53 and a negative
pressure introduction duct 54. The negative pressure introduction duct 54
is open to the atmospheric pressure P via the on-off valve 52 and
connected to a source of a negative pressure P3 via the on-off valve 53.
The ON/OFF control of the on-off valves 52, 53 is conducted in accordance
with ON/OFF signals (duty signals) input to the solenoid 51 via the driver
circuit 26. According to the ON-OFF control of the on-off valves 52, 53,
the regulated negative pressure P.sub.2 is introduced into a negative
pressure chamber 90 of the EGR control valve 9.
The interior of the EGR control valve 9 is partitioned by a diaphragm 91
into the negative pressure chamber 90 and an atmospheric pressure chamber
94. A shaft 33 is fixed to the diaphragm 91. In the interior of the
negative chamber 90, a spring 92 is provided for biasing the shaft 33
towards the atmospheric pressure chamber 94. The aforesaid lift sensor 30
is attached this EGR control valve 9 and provided with a variable resistor
31 ad a brush 32 fixed to the shaft 33 to slide together with the shaft
33. When the shaft 33 moves upward and downward by the control of the
negative pressure control valve 50, the position of the variable resistor
31 relative to the brush 32 varies to change the voltage value detected by
the brush 32. An output detected by the brush 32 is sent to the input port
15 via the A/D converter 18.
A valve body 93 is attached to a free end of the shaft 33, for
opening/closing a valve seat 83 provided midway in the EGR passage 8. Also
in this embodiment, a metering orifice 80 is provided in the EGR passage
of the valve seat 83 closer to the exhaust manifold 2, for maintaining the
flow rate of exhaust gas constant. A negative pressure chamber 81 is
defined by the EGR passage 8 between this metering orifice 80 and the
valve seat 83. On the other hand, an intake side EGR passage 82 is defined
by the EGR passage 8 between the valve seat 83 and the intake manifold 3.
Also, a pressure sensor 17 is provided in the negative pressure chamber 81
of this embodiment, and an output side of the pressure sensor 17 is
connected to the input port 15 via an A/D converter 34.
According to the apparatus 1 for diagnosing trouble in the exhaust-gas
recirculation system thus structured, the control circuit 10 drives the
negative pressure control valve 50 in a feedback manner in accordance with
a lift amount of the shaft 33 detected by the lift sensor 30 so that a
target lift value corresponding to the operation state of the internal
combustion engine is obtained. Then, the negative pressure regulated to
P.sub.2 is guided to the EGR control valve 9 in accordance with ON/OFF
signals (duty signals) to the solenoid 51, which causes the valve body 93
to open whereby exhaust gas is guided to the intake manifold 3 via the EGR
passage 8 from the exhaust manifold 2. Thus, EGR is conducted.
In this embodiment, since the metering orifice is provided upstream of the
valve seat 83 in the EGR passage 8, for detecting a flow rate of exhaust
gas, the negative pressure is generated in the negative pressure chamber
81 in accordance with the flow rate of the exhaust gas during EGR when the
EGR control valve 9 is in a normal state, which negative pressure is
detected by the pressure sensor 17.
In this embodiment, it is also possible to detect trouble in the EGR
control valve 9 by monitoring a lift amount of the valve body 93 detected
by the lift sensor 30. When the EGR control valve 9 is normal, it is
possible to detect the clogging of the EGR passage 8 by monitoring the
pressure in the negative pressure chamber 81 detected by the pressure
sensor 17. In addition, according to this embodiment, it is possible to
determine whether this clogging occurs upstream or downstream of the EGR
control valve 9.
The determination whether the clogging of the EGR passage 8 occurs upstream
or downstream of the EGR control valve 9 is conducted as follows. That is,
when the operation state of the internal combustion engine in an operation
zone wherein an amount of EGR is large, the negative pressure in the
negative pressure chamber 81 increases by the metering orifice 80 if the
EGR control valve 9 is normal. Accordingly, the generation of clogging
downstream of the EGR control valve 9 can be detected by the reduction of
negative pressure in the operation zone wherein the amount of EGR is
large.
Centrality, when the internal combustion engine is in the operation zone
wherein the amount of EGR is small, if the EGR control valve 9 is normal,
the negative pressure is maintained at a lower level even if the metering
orifice 80 exists. Accordingly, the generation of clogging upstream of the
negative pressure chamber 81, i.e., upstream of the EGR control valve 9
can be detected by the increase of negative pressure in the operation zone
wherein the amount of EGR is small.
In this regard, if the metering orifice 80 is provided on the exhaust side
of the EGR control valve 9, the pulsation of exhaust gas in the exhaust
manifold 2 is suppressed to minimize the pulsation of pressure in the
negative pressure chamber 81, whereby the pressure in the negative
pressure chamber 81 can be accurately detected.
Next, a procedure for determining trouble in the EGR control valve 9 and
the clogging of the EGR passage 8 will be explained with reference to a
flow chart shown in FIGS. 2A and 2B.
At step 201, the operation state parameters of the engine (for example, an
engine load GN (which can be calculated from an amount of air per one
rotation of engine), an engine rotational speed NE, an opening degree of
throttle TA, a sensor pressure P20, an intake pressure PA and a water
temperature THW) are read. At step 202, it is determined whether or not
determination conditions for the trouble of the EGR control valve 9 and
the clogging of the EGR passage 8 are satisfied. The determination
conditions are as follows (note GN1, GN2, Ne1, Ne2, TA1 and TA2 represent
constants);
(1) the load is in a predetermined range (GN1<GN<GN2),
(2) the rotational speed is in a predetermined range (Ne1<NE<Ne2),
(3) the opening degree of throttle is predetermined range (TA1<TA<TA2),
(4) the engine is not in a transfer state (an acceleration .DELTA.TA of the
opening degree of throttle is less than a predetermined value),
(5) the lift sensor is normal (not broken), and
(6) all of the above conditions are continuously satisfied for at least a
predetermined period.
If these conditions defined by items (1) through (6) are not satisfied at
step 202, the routine is finished, while if they are satisfied, the
control proceeds to step 203.
At step 203, it is determined whether or not the lift amount of the valve
body 93 of the EGR control valve 9 detected by the lift sensor 30 is
larger than a target lift amount La plus a predetermined value .alpha.. In
a case of the lift amount>La+.alpha., the control proceeds to step 212 to
determine the trouble of EGR control valve 9 wherein the lift amount
thereof is too large, then to step 213 at which the abnormality lamp 28 is
lit and thereafter the routine is finished. On the other hand, in a case
of the lift amount.ltoreq.La+.alpha., the control proceeds to step 204.
At step 204, it is determined whether or not the lift amount of the valve
body 93 of the EGR control valve 9 detected by the lift sensor 30 is
smaller than the target lift amount La minus a predetermined value .beta..
In a case of the lift amount<La-.beta., the control proceeds to step 214
to determine the trouble in the ERG control valve 9 due to a cause other
than the clogging of the EGR passage, then to step 215 at which the
abnormality lamp 28 is lit and the routine is finished. On the other hand,
in a case of the lift amount.gtoreq.La-.beta., the control proceeds to
step 205.
At step 205, it is determined whether or not the operation state of the
engine is in zone A. In the zone A, the flow rate of EGR (not the EGR
ratio) is relatively large and the pressure P20 in the negative pressure
chamber 81 is lower (i.e., larger as a negative pressure) than the
predetermined pressure (preset negative pressure) if the EGR system is
normal. The zone A is shown by hatching in the operation state map of
engine in FIG. 3, and represents the rotational speed of engine NE and the
engine load GN. Contrarily thereto, in another zone B, shown by hatching
in FIG. 3, the flow rate of EGR is relatively small and the pressure P20
in the negative pressure chamber 81 is higher (i.e., smaller as a negative
pressure) than the predetermined pressure (preset negative pressure) if
the EGR system is normal.
If it is determined that the operation state of engine is in the zone A at
step 205, the control proceeds to step 206 at which it is determined
whether or not the pressure P20 in the negative pressure chamber 81
detected by the pressure sensor 17 is smaller than the abovementioned
preset negative pressure. If P20 is larger than or equal to the preset
negative pressure, the control proceeds to step 207 at which it is
determined that the EGR system is normal and the routine is finished. On
the other hand, if P20 is smaller than the preset negative pressure, the
control proceeds to step 208 to determine that the clogging occurs in the
intake side EGR passage 82 and finish the routine.
If it is determined that the operation state of engine is not in the zone A
at step 205, the control proceeds to step 209 to determine whether or not
the operation state of engine is in the zone B. If it is determined that
the operation state of engine is into in the zone B at step 209, the
routine is finished without the determination of trouble of the EGR
system. On the other hand, if it is determined that the operation state of
engine is in the zone B at step 209, the control proceeds to step 210 at
which it is determined whether or not the pressure P20 in the negative
pressure chamber 81 detected by the pressure sensor 17 is smaller than the
above-mentioned preset negative pressure. If P20 is smaller than the
preset negative pressure, the control proceeds to step 207 at which it is
determined that the EGR system is normal and the routine is finished. On
the other hand, if P20 is larger than or equal to the preset negative
pressure, the control proceeds to step 211 at which it is determined that
the clogging occurs in the exhaust side EGR passage 8 and the routine is
finished.
In this regard, when the detected pressures are determined to be larger or
smaller than the preset value in steps 212 and 214, respectively, the
abnormality lamp 28 is lit to warn the driver and the code of the
abnormality in the EGR system due to the larger or smaller pressure is
memorized. Also, when the clogging of EGR passage 8 is detected, the
abnormality lamp 28 may be lit and the portion clogged may be memorized by
a specified code.
According to the embodiment of an apparatus for diagnosing the trouble of
an exhaust-gas recirculation system described above, since the flow rate
of EGR in the EGR passage is directly detected, it is possible to more
accurately conduct the trouble detection compared to that using the
exhaust gas temperature.
In the embodiment described above, to detect the clogging of EGR passage 8,
the negative pressure in the negative pressure chamber 81 of the EGR
passage 8 is detected by the pressure sensor 17. However, it is possible
to use a pressure switch, instead of this pressure sensor 17, which is
capable of being switched between ON/OFF states while using the
above-mentioned preset pressure as a neutral point. FIG. 4 illustrates an
embodiment wherein an pressure switch 70 is connected to the negative
pressure chamber 81 of the EGR passage 8.
In the embodiment shown in FIG. 4, the pressure switch 70 is connected via
a pressure introduction pipe 77 to the negative pressure chamber 81
defined by the metering orifice 80 in the EGR passage 8. The pressure
switch 70 is partitioned by a diaphragm 72 into two chambers; a negative
pressure chamber 70A and an atmospheric pressure chamber 70B. The negative
pressure chamber 70A is connected to the negative pressure chamber 81 via
the pressure introduction pipe 77 and has an orifice 75 at an entrance
thereof. In the interior of the negative pressure chamber 70A, a spring 71
is provided to bias the diaphragm 72 toward the atmospheric pressure
chamber 70B. The atmospheric pressure chamber 70B is open to the
atmosphere through a vent 76, and it has, in the interior thereof, a first
conductive piece 73A and a second conductive piece 73B normally connected
to the first conductive piece 73A, which pieces are connected to the
control circuit 10 already described in relation to FIG. 1 via lead wires
74, respectively.
In this embodiment, the pressure switch 70 is normally in ON state wherein
the pieces 73A and 73B are connected to each other, while being in OFF
state if the diaphragm 72 shifts toward the negative pressure chamber 70A
by a distance longer than a predetermined length against the spring 71
when the negative pressure in the negative pressure chamber 81 increases
to exceed the preset negative pressure. FIG. 5B shows the ON/OFF
characteristic of this pressure switch 70, which has a hysteresis wherein
the pressure switch 70 is switched from ON to OFF when the negative
pressure in the negative pressure chamber 81 exceeds the preset negative
pressure, and switched from OFF to ON when the negative pressure in the
negative pressure chamber 81 falls to a value smaller than the preset
negative pressure.
The preset negative pressure at which the pressure switch 70 is switched
from ON to OFF can be determined by selecting the spring 71. FIG. 5A shows
the variation of pressure (negative pressure) in the negative pressure
chamber 81 when the clogging occurs in the EGR passage 8. As described
before, when the EGR system is normal, the negative pressure in the
negative pressure chamber 81 is relatively large, as shown by small
circles, if the operation state of the engine is in the zone A; while the
negative pressure in the negative pressure chamber 81 is relatively small,
as shown by circular dots, if the operation state of engine is in the zone
B. When the clogging occurs in the EGR passage 8 downstream of the EGR
control valve 9 (closer to the intake side), the negative pressure in the
negative pressure chamber 81 falls as the clogging degree becomes larger.
Contrarily, if the clogging occurs in the EGR passage 8 upstream of the
EGR control valve 9 (closer to the exhaust side), the negative pressure in
the negative pressure chamber 81 increases as the clogging degree becomes
larger.
Accordingly, a negative pressure to be preset in the pressure switch 70
(determination value) may be selected as a value corresponding to a
pressure in the negative pressure chamber 81 in the vicinity of a point in
FIG. 5A at which a magnitude relationship between the pressure in the
negative pressure chamber when the operation state of engine is in the
zone A and that when the operation state of engine is in the zone B is
reversed.
FIGS. 6A to 6G explain the variation of OFF state of the pressure switch 70
which is switched from ON state to OFF state as stated above, in
accordance with the degree of clogging of the EGR passage 8. In the normal
state when no clogging occurs in the EGR passage 8, the pressure switch 70
is substantially in the OFF state in the zone A and in the ON sate in the
zone B as shown in FIG. 6A. When the clogging occurs in the EGR passage 8
closer to the intake side which has been maintained in the normal state,
an OFF zone of the pressure switch 70 in the zone A is narrowed as shown
in FIG. 6B, and the more the degree of clogging in the EGR passage 8
closer to the intake side, the narrower the OFF zone in the zone A as
shown in FIGS. 6C and 6D. While, if the clogging occurs in the EGR passage
8 closer to the exhaust side which has been maintained in the normal
state, an OFF zone of the pressure switch 70 extends to the zone B, as
shown in FIG. 6E, and the more the degree of clogging in the EGR passage 8
closer to the exhaust side, the narrower the OFF zone in the zone B as
shown in FIGS. 6F and 6G.
Accordingly, by detecting the variation of the OFF zone of the pressure
switch 70 in the zone A, it is possible to detect the degree of clogging
in the EGR passage 8 closer to the intake side, and, on the other hand, by
detecting the variation of the OFF zone of the pressure switch 70 in the
zone B, it is possible to detect the degree of clogging in the EGR passage
8 closer to the exhaust side.
Next, the procedure for the determination of trouble in the EGR control
valve 9 and the degree of clogging in the EGR passage 8 closer to the
exhaust side will be explained with reference to a flow chart shown in
FIGS. 7A and 7B. In this regard, the same numbers are used for designating
the same steps as in FIGS. 2A and 2B.
At step 701, operation state parameters of the engine (for example, an
engine load GN (which can be calculated from an amount of air per one
rotation of engine), an engine rotational speed NE, an opening degree of
throttle TA, an intake pressure PA and a water temperature THW) are read.
At step 202, it is determined whether or not determination conditions for
trouble in the EGR control valve 9 and the clogging of the EGR passage 8
are satisfied. The determination conditions are as stated before.
If the determination conditions are not satisfied, the routine is finished.
Contrarily, if the determination conditions are satisfied, it is
determined whether or not the lift amount of the valve body 93 of the EGR
control valve 9 detected by the lift sensor 30 is proper at steps 203 and
204. If the abnormal state of lift amount>La+.alpha. is detected, it is
determined at step 212 that the trouble occurs wherein the lift amount of
the EGR control valve 9 is excessive, and the abnormality lamp 28 is lit
at step 213. While, if the abnormal state of lift amount<LA-.beta. is
detected, the control proceeds to step 214 at which it is determined that
the trouble occurs in the EGR system other than the clogging of EGR
passage 8, and then to step 215 at which the abnormality lamp 28 is lit.
On the other hand, when the lift amount of the EGR control valve 9 is
proper, the control proceeds to step 205 at which it is determined whether
or not the operation state of engine is in the zone A. If it is determined
that the operation state is in the zone A, the control proceeds to step
702 at which it is determined whether or not the pressure switch 70 is
OFF. If it is determined that the pressure switch 70 is OFF, the control
proceeds to step 207 at which the routine is finished after it is
determined that the EGR system is normal. While, if the pressure switch is
maintained in ON state, the control proceeds to step 208 at which the
routine is finished after it is determined that the clogging occurs in the
intake side EGR passage 82.
If it is determined at step 205 that the operation state of the engine is
not in the zone A, the control proceeds to step 209 at which it is
determined whether or not the operation state of engine is in the zone B.
If it is determined at step 209 that the operation state of engine is not
in the zone B, the routine is finished without conducting a determination
of the trouble in the EGR system. While, if it is determined that the
operation state of engine is in the Zone B, the control proceeds to step
703 at which it is determined whether or not the pressure switch 70 is
OFF. If it is determined that the pressure switch 70 is ON, the control
proceeds to step 207 at which the routine is finished after it is
determined that the EGR system is normal. On the other hand, if the
pressure switch 70 is OFF, the control proceeds to step 211 at which the
routine is finished after it is determined that the clogging occurs in the
exhaust side EGR passage 8.
In such a manner, even if the ON/OFF type pressure switch 70 is used
instead of the pressure sensor 17, it is possible to detect whether or not
the trouble occurs in the EGR control valve 9 and whether the clogging
occurs in the EGR passage 8 upstream or downstream of the EGR control
valve 9. When the ON/OFF type pressure switch 70 with a single contact is
used instead of the pressure sensor 17, it is possible to reduce the
production cost of the apparatus for diagnosing trouble in the exhaust-gas
recirculation system because the switch 70 is more inexpensive than the
pressure sensor 17, and the input circuit for the control circuit 10 and
the wire harness can be simplified. The preset pressure of the pressure
switch 70 is adjustable by varying a spring constant of the spring 92, and
the negative pressure value to be generated in the negative pressure
chamber 81 is adjustable by varying a diameter of the metering orifice 80,
which enhances the degree of freedom for adaptation. In addition, when the
ON/OFF characteristic of the pressure switch 70 is defined to be ON on the
atmospheric pressure side (the positive pressure side as in the preceding
embodiment, a separate circuit for exclusively detecting the wire breakage
of the pressure switch 70 is unnecessary and it is possible, immediately
after the electric source is input to the | | |
