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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for detecting trouble in an
exhaust-gas recirculation (hereinafter referred to as "EGR") system of an
internal combustion engine, particularly to an apparatus capable of
detecting clogging occurred in the EGR passage provided with an EGR
control valve. More specifically, it relates to an apparatus for detecting
trouble in the EGR system, capable of discriminating whether clogging has
occurred on the upstream side or on the downstream side of the EGR control
valve.
2. Description of the Related Art
To reduce an amount of NOx 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 NOx 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 in
the EGR system is seldom found by the driver.
To solve such a problem, apparatuses for diagnosing trouble in the 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 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 a flow of exhaust gas is not detected when
the negative pressure is supplied to the EGR control valve.
According to this apparatus, however, although trouble in the EGR system
can be detected, there is a problem in that 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, according to the proposed apparatus, pressure-detection means is used
for detecting whether or not the exhaust-gas is introduced into the EGR
passage. However, since the pressure in the exhaust system varies in
accordance with the rotational speeds or loads of the engine, it is not
apparent that the pressure variation has occurred due to the lack of
exhaust gas or due to the variation of the operative condition or of the
environment. Accordingly, there has been a problem in the proposed
apparatus in that a mis-determination of trouble in the EGR system may
occur.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a trouble-detection
apparatus, for an EGR system comprising an EGR control valve in an EGR
passage, which is capable of correctly detecting trouble in the EGR system
by the detection of clogging of the EGR passage, irrespective of the
pressure variation in the intake system in accordance with the rotational
speeds or loads of the engine, the atmospheric pressure and the opening
degree of a throttle valve.
Further, another object of the present invention is to provide a
trouble-detection apparatus capable of determining that clogging in the
EGR passage has occurred on the upstream side of the EGR control valve or
on the downstream side thereof, in addition to the correct determination
of the EGR control valve in the EGR system.
According to a first aspect of the present invention, a trouble-detection
apparatus is proposed for an EGR system comprising an EGR passage for
communicating an exhaust passage of an internal combustion engine with an
intake passage thereof and an EGR control valve for controlling a flow
rate of exhaust-gas recirculating through the EGR passage, wherein the
apparatus comprises pulse-detection means provided in the EGR passage, for
detecting pulses in the exhaust-gas flow, pulse amplitude-detection means
for detecting an amplitude of the pulses in the exhaust-gas flow detected
by the pulse-detection means, operation state-detection means for
detecting the operation state in the internal combustion engine, and
clogging-detection means for detecting clogging in the EGR passage in
accordance with the detected amplitude of the pulses in the exhaust-gas
flow and the detected operation state of the internal combustion engine.
preferably the trouble-detection apparatus of the first aspect wherein the
pulse-detection means is provided in the EGR passage on the upstream side
of the EGR control valve further comprises valve-opening detection means
for detecting the open state of the EGR control valve, first abnormality
detection means for detecting the clogging in the EGR passage on the
upstream side of the EGR control valve in accordance with the detected
amplitude of the pulses in the exhaust-gas flow and the operation state of
the internal combustion engine when the EGR control valve is closed, and
second abnormality detection means for detecting the clogging in the EGR
passage on the downstream side of the EGR control valve in accordance with
the detected amplitude of the pulses in the exhaust-gas flow and the
operation state of the internal combustion engine when no clogging on the
upstream side of the EGR control valve is detected by the first
abnormality detection means.
According to a second aspect of the present invention, a trouble-detection
apparatus is provided for an EGR system of an internal combustion engine
comprising an EGR passage for communicating an exhaust passage of the
internal combustion engine with an intake passage thereof and an EGR
control valve for controlling a flow rate of exhaust-gas recirculating
through the EGR passage, wherein the EGR control valve is controlled by a
negative pressure so that the negative pressure supplied to the EGR
control valve is controlled in a feedback manner in accordance with a lift
amount of the EGR control valve detected by a lift sensor and the
operation state of the engine; the apparatus comprising lift
amplitude-detection means for detecting an amplitude of the detected value
issued by the lift sensor, and clogging-detection means for detecting the
clogging in the EGR passage in accordance with the calculated lift
amplitude and the operation state of the internal engine.
The trouble-detection apparatus for the EGR system of the second aspect may
further comprise the following elements: first EGR control valve
abnormality determination means for determining that the EGR control valve
has an overlift abnormality when the lift amount detected by the lift
sensor exceeds a maximum target value, and second EGR control valve
abnormality determination means for determining that the EGR control valve
has an underlift abnormality when the lift amount detected by the lift
sensor is lower than a minimum target value.
According to a third aspect of the present invention, a trouble-detection
apparatus is provided for an EGR system of an internal combustion engine
comprising an EGR passage for communicating an exhaust passage of the
internal combustion engine with an intake passage thereof and an EGR
control valve for controlling a flow rate of exhaust-gas recirculating
through the EGR passage, wherein the EGR control valve is controlled by a
negative pressure so that the negative pressure supplied to the EGR
control valve is controlled in a feedback manner in accordance with a lift
amount of the EGR control valve detected by a lift sensor and the
operation state of the engine, the apparatus comprising lift
amplitude-detection means for detecting an amplitude of the detected value
issued from the lift sensor, pulse calculation means for calculating
pulses in an exhaust-gas flow passing over the EGR control valve based on
the detected amplitude of the pulses in the exhaust-gas flow, and
clogging-detection means for detecting clogging in the EGR passage in
accordance with the calculated amplitude of the pulses in the exhaust-gas
flow and the operation state of the internal combustion engine.
The trouble-detection apparatus for the EGR system of the third aspect may
further comprise the following elements: first EGR control valve
abnormality determination means for determining that the EGR control valve
has an overlift abnormality when the lift amount detected by the lift
sensor exceeds a maximum target value, and second EGR control valve
abnormality determination means for determining that the EGR control valve
has an underlift abnormality when the lift amount detected by the lift
sensor is lower than a minimum target value.
According to the trouble-detection apparatus for the EGR system of the
first aspect, it is determined that clogging has occurred in the EGR
passage when the detected amplitude of the pulses in the exhaust-gas flow
is smaller than a threshold value corresponding to the operation state of
the engine. According to the apparatus capable of detecting pulses in the
exhaust-gas flow on the upstream side of the EGR control valve, it is
determined that clogging has occurred on the upstream side of the EGR
control valve if the clogging in the EGR passage is detected when the EGR
control valve is in the close state, while it is determined that clogging
has occurred on the downstream side of the EGR control valve if the
clogging in the EGR passage is detected when the EGR control valve is in
the open state.
According to the trouble-detection apparatus for the EGR system of the
second aspect, wherein a negative pressure for the EGR control valve is
controlled in a feedback manner by a lift amount of a valve body detected
by the lift sensor, a lift amplitude is calculated from the values
detected by the lift sensor, and it is determined that clogging has
occurred in the EGR passage when the calculated lift amplitude is smaller
than a preset amplitude corresponding to a normal operation state of the
engine. Also, it is determined that the EGR control valve has an overlift
amount abnormality when the lift amount detected by the lift sensor
exceeds the maximum target value, while it is determined that the EGR
control valve has an underlift abnormality when the detected lift amount
is smaller than the minimum target value.
In addition, according to the trouble-detection apparatus for the EGR
system of the third aspect, wherein a negative pressure for the EGR
control valve is controlled in a feedback manner by a lift amount of a
valve body detected by the lift sensor, pulses in the exhaust-gas flow
passing over the EGR control valve are calculated from the amplitude of
the lift amount of the lift body detected by the lift sensor, and it is
determined that clogging has occurred in the EGR passage when the
calculated amplitude of the pulses in the exhaust-gas flow is smaller than
a preset amplitude corresponding to the normal operation state of the
internal combustion engine. When the lift amount detected by the lift
sensor exceeds the maximum target value, it is determined that the EGR
control valve has an overlift abnormality, and when it is smaller than the
minimum target value, it is determined that the EGR control valve has an
underlift abnormality.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more clearly understood from the description
as set forth below with reference to the accompanying drawings.
FIG. 1 illustrates a whole structure of a first embodiment of a
trouble-detection apparatus for an EGR system according to the present
invention;
FIG. 2 is a flowchart illustrating a series of steps for determining
clogging in the EGR passage of the EGR system of the embodiment shown in
FIG. 1;
FIG. 3A illustrates a wave shape of a drive signal for the EGR control
valve in FIG. 1;
FIG. 3B illustrates a wave shape of a lift signal of the EGR control valve
issued from the lift sensor when the EGR control valve is driven by the
drive signal shown in FIG. 3A while the engine is inoperative;
FIG. 3C illustrates a wave shape of pulses in the exhaust-gas flow in a
normal state wherein no clogging has occurred in the EGR passage;
FIG. 3D illustrates a wave shape of the lift signal of the EGR control
valve due to the pulses of the exhaust-gas flow detected by the lift
sensor, when the EGR control valve is driven by the drive signal shown in
FIG. 3A;
FIG. 3E illustrates a wave shape of the pulses of the exhaust-gas flow when
clogging has occurred in the EGR passage;
FIG. 3F illustrates a wave shape of the lift signal of the EGR control
valve due to the pulses in the exhausted-gas flow, detected by the lift
sensor, when the EGR control valve is driven by the drive signal shown in
FIG. 3A;
FIG. 4 is a flowchart illustrating a series of steps in the embodiment
shown in FIG. 1 for determining that clogging in the EGR passage of the
EGR system has occurred on the upstream or on the downstream side of the
EGR control valve;
FIG. 5 illustrates a whole structure of a second embodiment of a
trouble-detection apparatus for an EGR system according to the present
invention;
FIG. 6 is a flowchart illustrating a series of steps for determining
clogging in the EGR passage of the EGR system of the embodiment shown in
FIG. 5;
FIG. 7 illustrates a whole structure of a third embodiment of a
trouble-detection apparatus for an EGR system according to the present
invention; and
FIG. 8 is a flowchart illustrating a series of steps for determining
clogging in the EGR passage of the EGR system of the embodiment shown in
FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a structure of an internal combustion engine
incorporating a trouble-detection apparatus for an EGR system according to
a first embodiment of the present invention. In this drawing, reference
numeral 1 denotes an engine body of an internal combustion engine of a
four-cylinder type; 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 ROM (read-only-memory) 12, RAM (random-access-memory) 13, CPU
(central processing unit) 14, an input port 15 and an output port 16, each
connected with the others by a tow-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, connected
to the input port 15, issues 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 a 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 to be opened and
closed by the solenoid 51, and three connecting ports 55 through 57
wherein the connecting port 55 is open to the outer air, the connecting
port 56 is connected to a negative pressure chamber 90 via a negative
pressure conduit 54, and the connecting port 57 is coupled to a negative
pressure generating part. The negative pressure control valve 50 is
controlled so that the ON-OFF control of the on-off values 52, 53 is
conducted in accordance with ON/OFF signals (duty signals) input to the
solenoid 51 via the driver circuit 26. A negative pressure P.sub.2
regulated at a predetermined pressure by a negative pressure P.sub.3 input
to the connecting port 57 and an atmospheric pressure P.sub.1 input to the
connecting port 55 is introduced to the negative pressure chamber 90 of
the EGR control valve 9 from the connecting port 56 via the negative
pressure conduit 54.
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 pressure chamber 90, a spring 92 is provided for biasing the
shaft 33 to the atmospheric pressure chamber 94. The aforesaid lift sensor
30 is attached this EGR control valve 9 and provided with a variable
resistor 31 and 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 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 closing the
EGR passage 8 when seated on a valve seat 83 provided midway in the EGR
passage 8 and opening the same when released from the valve seat 83. The
EGR passage 8 is divided into an upstream section 81 (on the exhaust pipe
side) and a downstream section (on the intake pipe side) by the valve seat
83. Also, a pressure sensor 17 is provided in the exhaust pipe side
section 81 of the EGR passage in this embodiment and an output of sensor
17 is connected to the input port 15 via an A/D converter 34.
According to the trouble-detection apparatus for the EGR system thus
structured, the feedback control of the negative pressure control valve 50
is executed by the control circuit 10. That is, the negative pressure
control valve 50 is driven in a feedback manner to attain a target lift
value corresponding to the operation state of the internal combustion
engine by detecting a lift amount of the shaft 33 through the lift sensor
30. Then, the negative pressure regulated to the pressure P.sub.2 in
accordance with the ON/OFF signal (duty signal) to the solenoid 51 is
introduced to the EGR control valve 9, which lifts the valve body 93 from
the valve seat 83 whereby the exhaust-gas from the exhaust manifold 2 is
introduced to the intake manifold 3 to execute the EGR operation.
Next, the steps for determining clogging in the EGR passage 8 of the first
embodiment will be explained with reference to a flowchart shown in FIG.
2.
At step 201, operation state parameters of the engine (such as an engine
load GN calculated by an air amount per one rotation of the engine, an
engine rotational speed NE, an opening degree of throttle TA, a sensor
pressure P.sub.2, an intake pressure PA or a water temperature THW) are
read. At step 202, it is determined from the operation state parameters
that whether or not conditions are satisfied for representing clogging in
the EGR passage 8. The determination conditions are as follows, wherein
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 in a predetermined range
(TA1<TA<TA2),
(4) the engine is not in a transfer state (a change .DELTA.TA of the
opening degree of the 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 the conditions defined by items (1) through (6) are all satisfied, the
engine is in a stable operation state wherein the EGR flow rate is proper
and the amplitude of pulses in the exhaust-gas flow is stable. In this
embodiment, since such pulses in the exhaust-gas flow are detected by the
pressure sensor 17 which senses the same by the pressure propagation, the
response delay is very small and the pulses can be detected even when the
EGR flow rate is small.
If the above conditions defined by item (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, the period F of the pulses in the exhaust-gas flow of the
four-cylinder type internal combustion engine is calculated based on the
engine rotational speed NE. And, at step 204, a sampling period T is
calculated in accordance with the period of pulses in the exhaust-gas flow
by the following equation:
T=F.times.a
The reason why the sampling period T is calculated in such a manner is
that, since the pulses in the exhaust-gas flow vary with the engine
rotational speed NE when the same are detected by the pressure sensor 17,
it is necessary to synchronize the timing of A/D conversion with the
frequency of the pulses for the purpose of obtaining a correct A/D
conversion. Accordingly, the period F of the pulses in the exhaust-gas
flow is obtained by the engine rotational speed NE at step 203, and the
sampling period T is obtained by multiplying a coefficient a thereto at
step 204. In this embodiment, the A/D conversion is executed at the
sampling period T.
At the next step 205, noise is removed from the values detected by the
pressure sensor 17. The noise removal can be executed by cutting a
frequency component which could not possibly be generated in a normal
engine operation state; for example, frequencies in a range between
F-.alpha.<F+.alpha. are extracted from the detected value, wherein .alpha.
is a predetermined frequency and F is the frequency of the values detected
by the pressure sensor 17. More specifically, the values detected by the
pressure sensor 17 are made to pass through a bandpass filter having a
frequency band in a range between F-.alpha.<F+.alpha..
Next, at step 206, the amplitude P of the pulses in the exhaust-gas flow is
calculated by the values detected by the pressure sensor 17. The pulse
amplitude P is obtainable by a difference between a maximum value
P.sub.max and a minimum value P.sub.min which are detected by the pressure
sensor 17 during a period longer than one cycle of the pulses in the
exhaust-gas flow.
At step 207, it is determined that whether or not the pulse amplitude P
calculated from the values detected by the pressure sensor 17 is smaller
than a preset amplitude P.sub.ref in a normal operation state of the
engine. If P is larger than or equal P.sub.ref, the control proceeds to
step 210 at which the routine is finished after the determination that the
EGR passage 8 is normal. On the other hand, if P is smaller than P.sub.ref
at step 207 the control proceeds to step 208. At step 208, it is
determined that clogging has occurred in the EGR passage 8, and the
control proceeds to step 209. At step 209, the abnormality lamp 29 is lit
to warn the driver that clogging has occurred in the EGR passage 8, and
the routine is finished.
FIG. 3 illustrates wave shapes in the respective positions in FIG. 1 in
both the normal and the abnormal states when the determination of clogging
in the EGR passage 8 is conducted in accordance with the steps explained
with reference to FIG. 2. First, FIG. 3A illustrates a wave shape of a
drive signal for a negative pressure control valve (VSV); i.e., the EGR
control valve 9; which is input to the solenoid 51 of the negative
pressure control valve 50 from the controller 10. FIG. 3B illustrates a
wave shape a lift signal representing a lift amount of the valve body 93
in the EGR control valve issued from the lift sensor 30 when the EGR
control valve 9 is driven by supplying the drive signal shown in FIG. 3A
to the solenoid 51 in the negative pressure control valve 50 when the
engine is inoperative. When the pulse signal of 50% duty shown in FIG. 3A
is supplied to the solenoid 51 in the inoperative state of the engine, the
EGR control valve 9 repeats the periodic up-down motion.
The exhaust-gas flowing in the EGR passage 8 pulses as shown in FIG. 3C
when the engine is operated and no clogging has occurred in the EGR
passage 8. Therefore, the amplitude P of the pulses in the exhaust-gas
flow obtained from the values detected by the pressure sensor 17 becomes
larger. Contrarily, the pulses in the exhaust-gas flow flowing in the EGR
passage are smaller as shown in FIG. 3E when the engine is operated and
the clogging has occurred in the EGR passage 8. Accordingly, the amplitude
P of the pulses in the exhaust-gas flow obtained from the values detected
by the pressure sensor 17 becomes smaller. The present amplitude P.sub.ref
used at step 207 is determined to be a value capable of discriminating the
wave shapes shown in FIGS. 3C and 3E, respectively, from each other.
As described above, according to the trouble-detection apparatus of the EGR
system of the first embodiment, since the clogging in the EGR passage 8 is
determined by directly detecting the amplitude of the pulses in the
exhaust-gas flow by the pressure sensor, it is possible to correctly
determine the abnormality irrespective of the variations of the rotational
speed or load of the engine, the atmospheric pressure, the opening degree
of the throttle or others.
In this regard, in the trouble-detection apparatus for the EGR system
explained with reference to FIG. 1, it is also possible to determine that
the clogging has occurred in the EGR passage 8 on the upstream side
(exhaust manifold side 2) or on the downstream side (intake manifold side
3).
One example of the steps will be described with reference to the
flowcharts, shown in FIG. 4, for determining that the clogging in the EGR
passage 8 has occurred on the upstream side of the EGR control valve 9 or
on the downstream side thereof, wherein the same step numbers are used for
denoting the same steps as those of FIG. 2 and the explanation thereof is
omitted.
At step 201, the operation state parameters of the engine are read. At step
401, it is determined whether or not the engine is in an idling state. If
the engine is in the idling state, no EGR is executed and therefore the
EGR control valve 9 is open. According to this embodiment, when the
combustion engine is in the idling state, the clogging in the EGR passage
8 on the upstream side of the EGR control valve 9 can be detected, which
will be first explained.
At step 403, the period F of the pulses in the exhaust-gas flow in the
four-cylinder type internal combustion engine is calculated, and at the
next step 404, the sampling period T (=F.times.a) is calculated in
accordance with the period of the pulses in the exhaust-gas flow. At step
405, the noise removal from the value detected by the pressure sensor 17
is executed by a filter or the like, and at step 406, the amplitude P of
the pulses in the exhaust-gas flow is calculated from the value detected
by the pressure sensor 17.
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