EXHAUST GAS RECIRCULATION DEVICE FOR INTERNAL COMBUSTION ENGINE
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas
recirculation device (abbreviated hereafter to EGR) for an
internal combustion engine, and more particularly to precise
determination of a fault in an EGR control valve.
BACKGROUND ART
[0002] An EGR is conventionally provided to reduce NOx
discharge from an internal combustion engine.
Further, an EGR gas control valve for controlling an EGR
gas amount is conventionally provided in an EGR gas passage that
connects an exhaust gas passage and an intake air passage to
each other, and a valve opening amount of the EGR control valve
is controlled by outputting an EGR control valve opening command
signal to the EGR control valve to realize a target EGR valve
opening determined in accordance with operating conditions of
the internal combustion engine.
[0003] However, when a fault occurs in the EGR control
valve such that an accurate target EGR valve opening is not
obtained in response to the EGR control valve opening command
signal, an exhaust gas purification performance and an output
performance of the internal combustion engine deteriorate.
Therefore, various proposals have been made in the background
art in relation to techniques for diagnosing a fault in an EGR
control valve accurately and precisely.
For example, Japanese Patent Application Publication No.
H10-122058 (Patent Document 1) discloses a technique in which,
when an EGR operation condition according to which a target
opening of an EGR control valve varies by at least a
predetermined amount is established, an actual opening
detection unit detects an actual opening, which varies so as
to follow variation in the target opening, from the start of
the variation in the target opening, and a fault is determined
to have occurred in a device including the EGR control valve
when it is confirmed that the detected actual opening is not
varying so as to follow the target opening.
[0004] Further, Japanese Patent Application Publication
No. 2007-255251 (Patent Document 2) discloses a technique for
a device including an EGR control valve having a valve shaft,
a driving unit which is disposed on an extension line of the
valve shaft and includes a reciprocating drive shaft that
reciprocates in an axial direction, and a control unit, wherein
the reciprocating drive shaft of the driving unit is configured
to open the EGR control valve by pressing a tip end of a central
shaft of the EGR control valve when the driving unit is operative.
In this technique, a determination as to whether or not a fault
has occurred in an EGR control valve is made by determining
2
whether a duty ratio of a control signal issued to the driving
unit from the control unit is within or beyond an allowable
range.
[0005] Patent Document 1: Japanese Patent Application
Publication No. H10-122058
Patent Document 2: Japanese Patent Application
Publication No. 2007-255251
[0006] In many cases, a fault in a control valve is caused
by an increase in sliding friction resistance in a valve driving
unit. Valve sliding friction causes a stick slip phenomenon,
in which catching and sliding occur repeatedly during opening
variation, and so on, and a deviation is particularly likely
to appear in response to minute opening variation. Therefore,
to detect abnormal phenomena early, it is advantageous to focus
on a following error occurring in response to minute opening
variation.
[0007] However, Patent Documents 1 and 2 disclose
techniques of determining an abnormality on the basis of a
deviation from an actual opening and a duty ratio range of a
driving control signal rather than techniques for detecting
abnormal phenomena by focusing on the following error occurring
in response to minute opening variation.
It is therefore necessary to develop a technique for
determining a fault in an EGR control valve with improved
accuracy and precision.
DISCLOSURE OF THE INVENTION
[0008] The present invention has been designed in
consideration of this problem, and an object thereof is to
provide an exhaust gas recirculation device for an internal
combustion engine with which a fault in an EGR control valve
provided in the exhaust gas recirculation device can be
determined with improved precision.
[0009] To achieve this object, the present invention is
an exhaust gas recirculation control device for an internal
combustion engine, having an EGR control valve that is provided
in an EGR gas passage connecting an exhaust passage and an intake
passage in order to control an EGR gas amount, the exhaust gas
recirculation device including: an opening command signal
output unit which outputs an opening command signal in relation
to the EGR control valve on the basis of an operating condition
of the internal combustion engine; a variation component
separation unit which separates the valve opening command
signal from the opening command signal output unit into a basic
component and a variation component generated so as to be
superimposed on the basic component; a variation component
determination unit which determines whether the EGR control
valve is in a steady state or a transient state on the basis
of a magnitude of the variation component separated by the
variation component separation unit; and an EGR control valve
4
diagnosis device that performs an abnormality diagnosis on the
EGR control valve when the variation component determination
unit determines that the EGR control valve is in the steady
state.
[0010] According to this invention, the EGR control valve
diagnosis device that performs an abnormality diagnosis on the
EGR control valve is activated only when the EGR control valve
is in the steady state, and therefore erroneous determinations
occurring when a determination is made on the basis of a
transient state signal can be prevented.
More specifically, in the transient state where an
opening command value of the EGR control valve varies greatly,
a deviation between the opening command signal and an actual
opening signal inevitably appears due to a following delay in
the EGR control valve even if the EGR control valve is sound.
By removing this unavoidable deviation from the abnormality
diagnosis subject, the precision of the abnormality diagnosis
can be improved.
[0011]" Further, a fault in the EGR control valve is often
caused by an increase in sliding friction resistance in a valve
driving unit. Valve sliding friction causes a stick slip
phenomenon, in which catching and sliding occur repeatedly
during opening variation, and so on, and therefore a deviation
is particularly likely to appear in response to minute opening
variation. Therefore, to detect abnormal phenomena early, it
is advantageous to focus on the following error that occurs in
response to minute opening variation.
In the present invention, the opening command signal and
the actual opening signal in the steady state,.i.e. not the
transient state, are used, and therefore a highly precise
abnormality determination focusing on a following error
occurring in response to minute opening variation can be made,
which is advantageous in terms of early detection of abnormal
phenomena.
[0012] Further, in the present invention, the variation
component separation unit preferably includes: a basic
component calculation unit which calculates the basic component
of the valve opening command signal from the valve opening
command signal; and an adder-subtractor which subtracts the
basic component calculated by the basic component calculation
unit from the valve opening command signal, and the variation
component separation unit calculates the valve opening command
signal variation component by subtracting the basic component
from the valve opening command signal using the
adder-subtractor.
[0013] Thus, the variation component separation unit
includes the basic component calculation unit and the
adder-subtractor which subtracts the basic component
calculated by the basic component calculation unit from the
valve opening command signal, and the valve opening command
6
signal variation component is calculated by subtracting the
basic component from the valve opening command signal using the
adder-subtractor.
[0014] Further, the basic component calculation unit
preferably includes: a variation component removal dead zone
device; a correction gain device which corrects an output signal
of the variation component removal dead zone device; and an
integrator which integrates an output signal of the correction
gain device.
Hence, by having the basic component calculation unit
multiply a correction gain by the signal from which the
variation component has been removed by the variation component
removal dead zone device, superior characteristics are obtained
in comparison with noise component removal through simple
filter processing in terms of advancement of a rise time of the
signal and removal of the variation component.
[0015] Further, in the present invention, the variation
component determination unit preferably includes: a steady
state` determination device that determines whether or not a
signal of the valve opening command signal variation component
generated by subtracting the basic component from the valve
opening command signal using the adder-subtractor is within a
threshold; and an on-delay timer that switches ON when an output
within the threshold is continued for a fixed time.
With this configuration, the steady state can be
7
determined accurately, enabling an improvement in the precision
of the abnormality diagnosis.
[0016] Further, in the present invention, the EGR control
valve diagnosis device preferably performs the abnormality
diagnosis on the basis of a valve opening command signal input
into the EGR control valve and an actual opening signal relating
to the EGR control valve, and the valve opening command signal
input into the EGR control valve is preferably the valve opening
command signal from the opening command signal output unit.
With this configuration, the precision of the abnormality
diagnosis performed by the EGR control valve diagnosis device
on the basis of the deviation between the valve opening command
signal input into the EGR control valve and the actual opening
signal of the EGR control valve is improved.
[0017] Further, in the present invention, the EGR control
valve diagnosis device preferably performs the abnormality
diagnosis on the basis of a valve opening command signal input
into the EGR control valve and an actual opening signal relating
to the EGR control valve, and the valve opening command signal
input into the EGR control valve is preferably a signal of the
basic component separated by the variation component separation
unit.
[0018] Hence, the valve opening command signal input into
the EGR control valve is the signal of the basic component of
the valve opening command signal separated by the variation
8
component separation unit, and therefore the EGR control valve
is not affected by the variation component included in the valve
opening command signal. Accordingly, the EGR control valve can
be prevented from moving in small motions due to the variation
component, and therefore unnecessary movement of the EGR
control valve can be prevented, leading to improvements in the
durability and lifespan thereof.
[0019] Fig. 9 shows an operating characteristic of the EGR
control valve and a characteristic of a valve flow rate relative
to the valve opening.
When the valve opening increases to or above a certain
opening, a dead zone region R in which the valve flow rate
exhibits substantially no variation relative to the valve
opening exists. In this region, a valve opening b must be varied
greatly in response to even small flow rate variation a, and
since valve opening variation is required in response to minute
flow rate variation, the EGR control valve opens and closes
frequently in small motions. By providing a hysteresis
characteristic to differentiate valve openings during opening
and closing operations in order to prevent these small motions,
unnecessary small motions of the EGR control valve are
suppressed.
[0020] When hysteresis is provided, however, the opening
command signal of the EGR control valve at which the hysteresis
characteristic switches ON and the opening command signal at
which the hysteresis characteristic switches OFF are fixed, and
therefore a steady state deviation occurs between the actual
valve opening command signal and the valve opening command
signal following application of the hysteresis characteristic
when seen as a time average. When the steady state deviation
is generated, the valve opening may oscillate constantly.
In the present invention, the opening command signal
input into the EGR control valve is the signal of the basic
component separated by the variation component separation unit,
and therefore these small motions and oscillation based on an
action of the hysteresis characteristic can be suppressed,
enabling improvements in durability and lifespan.
[0021] According to the present invention, an exhaust gas
recirculation device for an internal combustion engine
includes: an opening command signal output unit which outputs
an opening command signal in relation to an EGR control valve
on the basis of an operating condition of the internal
combustion engine; a variation component separation unit which
separates the valve opening command signal from the opening
command signal output unit into a basic component and a
variation component generated so as to be superimposed on the
basic component; a variation component determination unit which
determines whether the EGR control valve is in a steady state
or a transient state on the basis of a magnitude of the variation
component separated by the variation component separation unit;
10
and an EGR control valve diagnosis device that performs an
abnormality diagnosis on the EGR control valve when the
variation component determination unit determines that the EGR
control valve is in the steady state. Therefore, in the
transient state where the opening command value of the EGR
control valve varies greatly, a deviation between the opening
command signal and the actual opening signal inevitably occurs
due to a following delay in the EGR control valve even if the
EGR control valve is sound. By removing this unavoidable
deviation from the abnormality diagnosis subject, the precision
of the abnormality diagnosis can be improved.
[0022] Further, a fault in the EGR control valve is often
caused by an increase in sliding friction resistance in the
valve driving unit. Valve sliding friction causes a stick slip
phenomenon, in which catching and sliding occur repeatedly
during opening variation, and so on, and therefore a deviation
is particularly likely to appear in response to minute opening
variation. Hence, to detect abnormal phenomena early, it is
advantageous to focus on the following error that occurs in
response to minute opening variation. In the present invention,
the valve opening command signal and the actual opening signal
in the steady state, i.e. not the transient state, are used,
and therefore an abnormality determination focusing on the
following error generated in response to minute opening
variation can be made, which is advantageous in terms of early
11
detection of abnormal phenomena.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Fig. 1 is a view showing an overall configuration
of an exhaust gas recirculation device for an internal
combustion engine according to an embodiment of the present
invention;
Fig. 2 is a block diagram showing a configuration of an
EGR control device according to a first embodiment;
Fig. 3 is a block diagram showing a configuration of an
EGR control device according to a second embodiment;
Fig. 4 is an illustrative view illustrating an operation
of a variation component removal dead zone device;
Fig. 5 is an illustrative view showing a basic component
wave in a numerical value simulation verification test;
Fig. 6 is an illustrative view showing results of the
numerical value simulation verification test;
Fig. 7 is an enlarged view of an E portion of Fig. 6;
Fig. 8 is an enlarged view of an F portion of Fig. 6;
Fig. 9 is an illustrative view showing valve opening and
valve flow rate characteristics of an EGR control valve;
Fig. 10 is a characteristic diagram of a variation
component removal dead zone device according to a third
embodiment; and
Fig. 11 is a characteristic diagram of a variation
12
component removal dead zone device according to a fourth
embodiment.
BEST MODES FOR CARRYING OUT THE INVENTION
[0024] The present invention will be described in detail
below using embodiments shown in the drawings. Note, however,
that unless specific description is provided to the contrary,
dimensions, materials, shapes, relative arrangements, and so
on of constituent components described in the embodiments are
not intended to limit the scope of the present invention.
[0025] (First Embodiment)
Referring to Fig. 1, an exhaust gas recirculation device
for an internal combustion engine according to a first
embodiment of the present invention will be described.
As shown in Fig. 1, a diesel engine (to be referred to
hereafter as an engine) 1 includes an exhaust gas turbocharger
7 having an exhaust gas turbine 3 and a compressor 5 that is
driven coaxially with the exhaust gas turbine 3. Air discharged
from the compressor 5 of the exhaust gas turbocharger 7 passes
through an air supply passage 9 and enters an intercooler 11
to be cooled. An air supply flow rate is then controlled by
an intake air throttle valve 13, whereupon the air flows through
an intake manifold 15 to an intake port provided in each cylinder,
and flows from the intake port into a combustion chamber via
an intake valve of the engine 1.
13
[0026] The engine 1 is further provided with a fuel
injection control device 19 that injects fuel into the
combustion chamber while controlling an injection timing, an
injection amount, and an injection pressure of the fuel. The
fuel injection control device 19 supplies a fuel injection valve
21 provided for each cylinder with fuel controlled to a
predetermined fuel pressure at a predetermined fuel injection
timing.
[0027] Further, an EGR (Exhaust Gas Recirculation)
passage 25 bifurcates from a midway point of an exhaust passage
23 such that a part of an exhaust gas is cooled by an EGR cooler
27 and introduced into a site downstream of the intake air
throttle valve 13 via an EGR control valve 29. A throttle valve
control device 31 is provided in relation to the intake air
throttle valve 13 to control opening/closing thereof, and an
EGR control device (an exhaust gas recirculation control
device) 33 is provided in relation to the EGR control valve 29
to control opening/closing thereof.
[0028] Combustion gas burned in the combustion chambers
of the engine 1, or in other words exhaust gas 35, passes through
an exhaust manifold 39, where exhaust ports provided for the
respective cylinders converge, and the exhaust passage 23,
drives the exhaust gas turbine 3 of the exhaust gas turbocharger
7, thereby serving as a power supply of the compressor 5, and
then flows into an exhaust gas post-treatment device (not shown)
14
through the exhaust passage 23.
[0029] An engine rotation speed signal from an engine
rotation speed sensor 42 and an engine load signal from an engine
load sensor 44 are respectively input into a control device
(ECU) 41 together with a detection signal from an intake
manifold temperature sensor 46 provided in the intake manifold
15, a detection signal from an intake manifold pressure sensor
48, and a detection signal from an air flow meter 50.
[0030] The EGR control device (exhaust gas recirculation
control device) 33 includes an opening command signal output
unit 52 which calculates an EGR flow rate corresponding to
operating conditions on the basis of the signals from the
respective sensors using a preset EGR amount map or a
calculation formula and outputs an opening command signal
relating to the EGR control valve 29 on the basis of the
calculated EGR amount, a variation component separation unit
54 which separates the valve opening command signal From the
opening command signal output unit 52 into a basic component
and a variation component generated so as to be superimposed
on the basic component, and a variation component determination
unit 56 which determines whether the EGR control valve 29 is
in a steady state or a transient state on the basis of a magnitude
of the variation component of the valve opening command signal
separated by the variation component separation unit.
When the steady state is determined by the variation
15
component determination unit 56, a steady state signal is output
to cause an EGR control valve diagnosis device 58 which performs
abnormality diagnoses on the EGR control valve 29 to execute
a diagnosis.
[0031] Referring to Fig. 2, the variation component
separation unit 54 and the variation component determination
unit 56 will be described.
The variation component separation unit 54 includes a
basic component calculation unit 60 which calculates the basic
component of the valve opening command signal output by the
opening command signal output unit 52 from the valve opening
command signal, and an adder-subtractor 62 which subtracts the
basic component calculated by the basic component calculation
unit 60 from the valve opening command signal. The
adder-subtractor 62 calculates the variation component of the
valve opening command signal by subtracting the basic component
from the valve opening command signal.
[0032] Further, the basic component calculation unit 60
includes a variation component removal dead zone device 64, a
,basic component correction gain device (correction gain device)
66 which corrects an output signal from the variation component
removal dead zone device 64, and an integrator 68 which
integrates output signals from the correction gain device 66.
Furthermore, the variation component determination unit
56 includes a steady state determination device 70 that
16
determines whether or not a signal of the valve opening command
signal variation component generated by subtracting the basic
component from the valve opening command signal using the
adder-subtractor 62 is within a threshold, and an on-delay timer
72 that performs output after determining that an output within
the threshold has continued for a fixed time.
[0033] Next, the basic component calculation unit 60 of
the variation component separation unit 54 will be described
in further detail. To describe the basic component calculation
unit 60, u, z1, and y are appended to signals. Note that
denotes a signal.obtained through temporal
differentiation of y.
[0034] It is assumed that the basic component of an EGR
control valve opening command signal u is zero, and varies
irregularly thereabout. When, at this time, a value of a set
threshold d1 of the variation component removal dead zone device
64 is set at 1, an output signal z1 is as shown in Fig. 4. It
can be seen that z1 varies only when a magnitude of u exceeds
l and that a minute variation component included in u is removed.
Hence, the variation component removal dead zone device 64 has
a function for removing the minute variation component included
in u. Note that d1 is adjusted in accordance with the magnitude
of the minute variation component included in u.
17
[0035] Hence, if a time average value of the EGR control
valve opening command signal u were zero, the variation
component of the EGR control valve opening command signal u
could be removed by the variation component removal dead zone
device 64 alone. In reality, however, a basic wave component
of the EGR control valve opening command signal u is not fixed
at zero, and therefore the dead zone is exceeded by only the
basic wave component of the EGR control valve opening command
signal u.
Hence, the variation component cannot be removed, and
therefore, to cause the variation component removal dead zone
device 64 to function effectively, a basic component y of the
EGR control valve opening command signal is estimated and
subtracted from the EGR control valve opening command signal
u such that an input signal input into the variation component
removal dead zone device 64 varies about zero irrespective of
the value of the basic wave component of the EGR control valve
opening command signal u.
[0036] A basic component correction gain k2 of the basic
component correction gain device 66 is a coefficient for
adjusting an estimation speed of the basic component. When the
output signal zl of the variation component removal dead zone
device 64 outputs a positive value, the basic component y is
increased by a value obtained by multiplying this value by k2.
When zl outputs a negative value, the basic component is reduced
18
by a value obtained by multiplying this value by k2. By
performing this operation repeatedly, the EGR control valve
opening command signal u converges on a steady state value.
Convergence is achieved more quickly as the correction gain k2
increases.
[0037] Next, results of a numerical value simulation
confirming the effect of the basic component calculation unit
60 will be described.
In the simulation, white noise is superimposed as a
variation component on a basic wave component shown in Fig. S.
A solid line X in Fig. 6 denotes an EGR control valve opening
command signal used in the simulation, while a solid line Y
denotes the basic component y of the EGR control valve opening
command signal. It is evident from Fig. 7, which is an enlarged
view of an E portion in Fig. 6, that the variation component
has been removed.
[0038] A filter such as a first order lag filter is
typically used to remove the variation component. A solid line
Z in Figs. 6, 7, and 8 is an estimated value
of a basic component generated by a first order lag filter.
When the first order lag of the filter is set at a time constant
of 0.2 seconds, for example, an arithmetic expression is
expressed as follows.
19
Y0.2s+1
[0039] Fig. 8 is an enlarged view of an F portion in Fig.
6, and shows a rising part. A rising speed of the estimated
value
of the basic component generated by the first order lag
is clearly lower than that of this embodiment. To obtain an
equal rising speed to that of this simulation, the time constant
of the filter must be reduced, but as shown in Fig. 8, the
variation component remains in the estimated value
of the basic component generated by the first order lag,
and therefore, when the time constant of the filter is reduced,
the variation component becomes even more apparent.
It was possible to confirm from the results of the
simulation that in comparison with a conventional filter method,
the method according to this embodiment exhibits superior
characteristics in terms of both the rise of the signal and
removal of the variation component.
[0040] Next, returning to the overall block diagram of Fi
2, the variation component determination unit 56 will be
described. As described above, the variation component
determination unit 56 includes the steady state determination
20
device 70, and the on-delay timer 72 that performs output after
determining that an output within the threshold has continued
for a fixed time. An EGR control valve opening command signal
variation component (a variation component) e obtained by
removing the basic component y of the EGR control valve opening
command signal from the EGR control valve opening command signal
u is input into the steady state determination device 70, and
a determination is made as to whether or not the resulting signal
is a signal within a set threshold d2 on the basis of whether
or not the input variation component is a variation component
of a transient state or a variation component of a steady state,
i.e. a state that cannot be considered transient.
[0041] Further, the on-delay timer 72 determines that the
output of the steady state determination device 70, or in other
words an output within the set threshold d2, has continued for
a fixed time.
Hence, when an ON signal is output from the on-delay timer
72, the ON signal is output as a signal of a determination result
indicating the steady state.
The steady state is determined by the on-delay timer after
the continuous fixed time, and therefore the steady state can
be determined accurately, enabling an improvement in the
precision of the abnormality diagnosis.
[0042] As shown in Fig. 2, the steady state signal output
by the on-delay timer 72 is output to the EGR control valve
21
diagnosis device 58. To diagnose whether or not the EGR control
valve 29 is operating correctly, the EGR control valve diagnosis
device 58 takes in the signal of the EGR control valve opening
command signal u, or in other words a command value in the steady
state, i.e.not the transient state, and an actually measured
value of the EGR control valve 29, calculates a valve opening
deviation h, and determines whether or not an absolute value
(hI of the deviation h is larger than an allowable value.
The allowable value is an upper limit value of IhI
allowable during use of the EGR control valve 29. Further, the
allowable value is set in advance for each individual EGR
control valve 29.
When I h I is larger than the allowable value and this state
continues for a fixed time, the EGR control valve 29 is
determined to be abnormal and notification of this result is
issued.
[0043] According to the first embodiment, as described
above, the EGR control valve diagnosis device 58 that performs
an abnormality diagnosis on the EGR control valve 29 is
activated only when the EGR control valve is in a steady state,
and therefore an erroneous determination obtained on the basis
of a transient state signal can be prevented.
More specifically, in the transient state where the
opening command value of the EGR control valve 29 varies greatly,
22
the deviation IhI between the opening command signal and the
actual opening signal occurs due to a following delay in the
EGR control valve 29 even if the EGR control valve 29 is sound.
Moreover, the deviation h i is generated as a large deviation,
and therefore an erroneous determination of an abnormality
cannot be avoided. By removing this unavoidable deviation from
the abnormality diagnosis subject, the precision of the
abnormality diagnosis can be improved.
[0044] Further, a fault in the EGR control valve 29 is often
caused by an increase in sliding friction resistance in the
valve driving unit. Valve sliding friction causes a stick slip
phenomenon, in which catching and sliding occur repeatedly
during opening variation, and so on, and therefore a deviation
is particularly likely to appear in response to minute opening
variation. Therefore, to detect abnormal phenomena early, it
is advantageous to focus on the following error that occurs in
response to minute opening variation.
By using the opening command signal and the actual opening
signal in the steady state, i.e. not the transient state, a
highly precise abnormality determination focusing on the
following error that occurs in response to minute opening
variation can be made, which is advantageous in terms of early
detection of abnormal phenomena.
[0045] (Second Embodiment)
23
A second embodiment will be described with reference to
a block diagram in Fig. 3. In the second embodiment, the signal
of the basic component of the EGR control valve opening command
signal, which is separated by being passed through the variation
component separation unit 54, is input into the EGR control
valve 29 in place of the EGR control valve opening command signal
u input into the EGR control valve 29 in the first embodiment.
All other configurations are similar to the first embodiment,
and therefore description thereof has been omitted.
As shown in Fig. 3, in the second embodiment, the opening
command signal input into the EGR control valve 29 is the signal
of the basic component of the valve opening command signal
separated by the variation component separation unit 54, and
therefore the EGR control valve 29 is not affected by the
variation component included in the valve opening command
signal. Hence, the EGR control valve 29 can be prevented from
being moved in small motions by the variation component, and
therefore unnecessary movement of the EGR control valve 29 can
be prevented, leading to improvements in the durability and
Jifespan of the EGR control valve 29.
[0046] As shown in Fig. 9, a dead zone region R exists in
the characteristics of the.EGR control valve. In this region,
unnecessary small motions occur, and even when a hysteresis
function is applied to prevent these small motions, constant
oscillation occurs. According to the second embodiment,
24
however, the opening command signal input into the EGR control
valve 29 is the signal corresponding to the basic component of
the valve opening command signal separated by the variation
component separation unit 54, and therefore these small motions
and constant oscillation can be avoided, leading to
improvements in the durability and lifespan of the EGR control
valve 29.
[0047] Further, since the operation of the EGR control
valve 29 is controlled by the signal of the basic component of
the valve opening command signal separated by the variation
component separation unit 54, the valve opening of the EGR
control valve 29 is controlled accurately and reliably.
Moreover, as described above in the first embodiment, in
comparison with the conventional first order lag filter method,
the signal of the basic component of the valve opening command
signal separated by the variation component separation unit 54
has superior characteristics in terms of the rise of the signal
and removal of the variation component, and is therefore also
effective in improving a responsiveness of an operation of the
EGR control valve 29, an exhaust gas performance of the engine,
and an output performance of the engine.
[0048] In other words, according to the second embodiment,
in addition to the action and effects obtained by the first
embodiment in terms of improving the fault determination
precision of the EGR control valve diagnosis device 58 that
25
performs abnormality diagnoses on the EGR control valve 29,
improvements in the durability and lifespan of the EGR control
valve can be obtained, as well as an improvement in an exhaust
gas purification action of the EGR control valve 29 itself.
[0049] (Third Embodiment)
A third embodiment will be described with reference to
Fig. 10. In the first and second embodiments, the variation
component removal dead zone device 64 is used in the basic
component calculation unit 60.
However, the actions and effects of this application are
not limited to a characteristic such as that of a variation
component removal function set by the variation component
removal dead zone device 64, which reaches zero using the set
threshold dl as a threshold. The third embodiment uses a
variation component removal function in which an incline in the
vicinity of an origin, instead of a zero dead zone, is set to
be small, the variation component removal function being set
by a variation component removal dead zone device 74 shown in
Fig. 10.
As a result, similar effects to those of the first and
second embodiments can be obtained.
[0050] (Fourth Embodiment)
A fourth embodiment will be described with reference to
Fig. 11. In the fourth embodiment, as shown in Fig. 11, the
variation component removal function set in a variation
26
,component removal dead zone device 76 rises in step form from
the set threshold dl and then increases on an incline. Likewise
when this variation component removal function is used, similar
effects to those of the first and second embodiments can be
obtained.
[0051] In the first to fourth embodiments, a
characteristic whereby zero is reached or a gradient is reduced
in the vicinity of the origin is essential, and as long as this
characteristic is set, the effects of this application can be
obtained.
INDUSTRIAL APPLICABILITY
[0052] According to the present invention, the precision
with which a fault is determined in an EGR control valve provided
in an exhaust gas recirculation device can be improved, and
therefore the present invention is suitable for use in an
exhaust gas recirculation device for an internal combustion
engine.
27

CLAIMS
1. An exhaust gas recirculation device for an internal
combustion engine, having an EGR control valve that is provided
in an EGR gas passage connecting an exhaust passage and an intake
passage in order to control an EGR gas amount, the exhaust gas
recirculation device comprising:
an opening command signal output unit which outputs an
opening command signal in relation to the EGR control valve on
the basis of an operating condition of the internal combustion
engine;
a variation component separation unit which separates the
valve opening command signal from the opening command signal
output unit into a basic component and a variation component
generated so as to be superimposed on the basic component;
a variation component determination unit which
determines whether the EGR control valve is in a steady state
or a transient state on the basis of a magnitude of the variation
component separated by the variation component separation unit;
and
an EGR control valve diagnosis device that performs an
abnormality diagnosis on the EGR control valve when the
variation component determination unit determines that the EGR
control valve is in the steady state.
2. The exhaust gas recirculation device for an internal
28
combustion engine according to claim 1, wherein the variation
component separation unit comprises:
a basic component calculation unit which calculates the
basic component of the valve opening command signal from the
valve opening command signal; and
an adder-subtractor which subtracts the basic component
calculated by the basic component calculation unit from the
valve opening command signal, and
the variation component separation unit calculates the
valve opening command signal variation component by subtracting
the basic component from the valve opening command signal using
the adder-subtractor.
3. The exhaust gas recirculation device for an internal
combustion engine according to claim 2, wherein the basic
component calculation unit comprises:
a variation component removal dead zone device;
a correction gain device which corrects an output signal
of the variation component removal dead zone device; and
an integrator which integrates an output signal of the
correction gain device.
4. The exhaust gas recirculation device for an internal
combustion engine according to claim 2, wherein the variation
component determination unit comprises:
29
a steady state determination device that determines
whether or not a signal of the valve opening command signal
variation component generated by subtracting the basic
component from the valve opening command signal using the
adder-subtractor is within a threshold; and
an on-delay timer that switches ON when an output within
the threshold is continued for a fixed time.
5. The exhaust gas recirculation device for an internal
combustion engine according to claim 1, wherein the EGR control
valve diagnosis device performs the abnormality diagnosis on
the basis of a valve opening command signal input into the EGR
control valve and an actual opening signal relating to the EGR
control valve, and
the valve opening command signal input into the EGR
control valve is the valve opening command signal from the
opening command signal output unit.
6. The exhaust gas recirculation device for an internal
combustion engine according to claim 1, wherein the EGR control
valve diagnosis device performs the abnormality diagnosis on
the basis of a valve opening command signal input into the EGR
control valve and an actual opening signal relating to the EGR
control valve, and
the valve opening command signal input into the EGR
30
control valve is a'signal of the basic component separated by
the variation component separation unit.
Dated this 30/11/2012
RANJNA MEHTA-DUTT
OF REM RY & SAGAR
ATTORNEY FOR THE APPLICANTS
ABSTRACT
An exhaust gas recirculation device for an internal
combustion engine includes: an opening command signal output
unit 52 which outputs an opening command signal in relation to
an EGR control valve on the basis of an operating condition of
the internal combustion engine; a variation component
separation unit 54 which separates the valve opening command
signal from the opening command signal output unit 52 into a
basic component and a variation component generated so as to
be superimposed on the basic component; a variation component
determination unit 56 which determines whether the EGR control
valve is in a steady state or a transient state on the basis
of a magnitude of the variation component separated by the
variation component separation unit 54; and an EGR control valve
diagnosis device 58 that performs an abnormality diagnosis on
the EGR control valve when the variation component
determination unit determines that the EGR control valve is in
the steady state.