U.S. patent application number 09/800721 was filed with the patent office on 2001-07-26 for engine control device.
This patent application is currently assigned to Hitachi Ltd.. Invention is credited to Atago, Takeshi, Kitahara, Yuichi, Suda, Seiji, Takano, Yoshiya.
Application Number | 20010009094 09/800721 |
Document ID | / |
Family ID | 23025681 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009094 |
Kind Code |
A1 |
Takano, Yoshiya ; et
al. |
July 26, 2001 |
Engine control device
Abstract
An engine control device provided with a lean NOx catalyst
comprises means for estimating a condition of the lean NOx
catalyst, means for performing reactivation control of the lean NOx
catalyst based on the result, and means for controlling the
termination of the reactivation control. The lean NOx catalyst is
constantly made usable in a favorable condition.
Inventors: |
Takano, Yoshiya;
(Hitachinaka-shi, JP) ; Atago, Takeshi;
(Hitachinaka-shi, JP) ; Suda, Seiji; (Mito-shi,
JP) ; Kitahara, Yuichi; (Hitachinaka-shi,
JP) |
Correspondence
Address: |
EVENSON, McKEOWN, EDWARDS
& LENAHAN, P.L.L.C.
1200 G Street, N.W., Suite 700
Washington
DC
20005
US
|
Assignee: |
Hitachi Ltd.
|
Family ID: |
23025681 |
Appl. No.: |
09/800721 |
Filed: |
March 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09800721 |
Mar 8, 2001 |
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09269073 |
Mar 19, 1999 |
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6212880 |
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09269073 |
Mar 19, 1999 |
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PCT/JP96/02717 |
Sep 20, 1996 |
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Current U.S.
Class: |
60/277 ; 60/286;
60/301 |
Current CPC
Class: |
F01N 2570/04 20130101;
F01N 3/0842 20130101; F02D 41/028 20130101; F02D 41/1446
20130101 |
Class at
Publication: |
60/277 ; 60/286;
60/301 |
International
Class: |
F01N 003/00; F01N
007/00; F01N 003/10 |
Claims
What is claimed is:
1. An engine control device comprising a means for determining the
amount of air taken into a cylinder of the engine; a means for
calculating the amount of fuel injected so as to achieve a target
air-to-fuel ratio; a means for calculating the amount of time power
must be supplied to an injector, so as to inject said amount of
fuel; an injector for supplying fuel to said engine during the time
power must be supplied obtained by said means for calculating the
time power must be supplied; a means for igniting a combustible
mixture by generating sparks with an ignition plug at a designated
ignition time; and a lean NOx catalyst for cleaning exhaust gas
released from said engine, which further comprises a means for
determining or estimating the deteriorating condition of said lean
NOx catalyst, and a means for reactivating a clean up rate by
reactivating the clean up rate of said lean NOx catalyst based on a
result obtained by said means for determining or estimating the
deteriorating condition of said lean NOx catalyst.
2. An engine control device as claimed in claim 1, wherein said
injector is an in-cylinder-injector for injecting fuel directly
into a combustion chamber of said engine.
3. An engine control device comprising a means for determining the
amount of air taken into a cylinder of the engine; a means for
calculating the amount of fuel injected so as to achieve a target
air-to-fuel ratio; a means for calculating the amount of time power
must be supplied to an injector, so as to inject said amount of
fuel; an injector for supplying fuel to said engine during the time
power must be supplied obtained by said means for calculating the
time power must be supplied; a means for igniting a combustible
mixture by generating sparks with an ignition plug at a designated
ignition time; and a lean NOx catalyst for cleaning exhaust gas
released from said engine, which further comprises means for
reactivating a clean up rate in order to reactivate the clean up
rate of said lean NOx catalyst, wherein said clean up reactivation
is performed by controlling either the temperature of said lean NOx
catalyst or of that of the exhaust gas at the upstream entrance of
said lean NOx catalyst within a range of 500.degree. C. to
900.degree. C.
4. An engine control device comprising a means for determining the
amount of air taken into a cylinder of the engine; a means for
calculating the amount of fuel injected so as to achieve a target
air-to-fuel ratio; a means for calculating the amount of time power
must be supplied to an injector, so as to inject said amount of
fuel, an injector for supplying fuel to said engine during the time
power must be supplied obtained by said means for calculating the
time power must be supplied; a means for igniting a combustible
mixture by generating sparks with an ignition plug at a designated
ignition time; and a lean NOx catalyst for cleaning exhaust gas
released from said engine, which further comprises a means for
reactivating a clean up rate in order to reactivate the clean up
rate of said lean NOx catalyst, wherein said clean up reactivation
is performed by making the continuous unit time of said
reactivation less than 30 seconds, when said temperature of said
lean NOx catalyst or of the exhaust gas at the upstream entrance of
said lean NOx catalyst exceeds 900.degree. C. during said
reactivation.
5. An engine control device as claimed in any one of claims 1 to 4,
wherein said reactivation control is performed by retarding the
ignition time.
6. An engine control device as claimed in any one of claims 1 to 4,
wherein said clean up rate reactivation means comprises a means for
generating an after-burn effect by injecting fuel during an exhaust
stroke.
7. An engine control device as claimed in any one of claims 1 to 3,
wherein the control time for each reactivation of said clean up
rate per once is set so that all subsequent control time is longer
than the first control time.
8. An engine control device as claimed in any one of claims 1 to 3,
wherein the control time of said clean up rate reactivation is set
variably depending on the temperature of the exhaust gas during the
reactivation.
9. An engine control device as claimed in any of claims 1 and 2,
wherein estimation of said deteriorating condition is performed
using, at least, any one of the total amount of fuel supplied to
the engine, the total breadth of fuel injection pulses, the total
amount of air taken in, and the total amount of travel distance or
travel time.
10. An engine control device as claimed in any one of claims 1 to
4, wherein the engine is operated in a stoichiometric air-to-fuel
condition during the reactivation of said clean up rate.
11. An engine control device as claimed in any one of claims 1 to
4, wherein performance of said clean up rate reactivation is
restricted based on, at least, any one of the exhaust gas
temperature, the number of rotations of the engine, and the load to
the engine.
12. An engine control device as claimed in any one of claims 1 to
4, wherein said clean up rate reactivation is performed so that,
when the engine combustion condition is in a lean combustion
condition, said engine combustion condition is transferred once to
said reactivation means via a stoichiometric air-to-fuel ratio
combustion condition.
13. An engine control device as claimed in claim 12, wherein
switching said lean combustion condition to said stoichiometric
air-to-fuel ratio combustion condition is performed such that the
same engine torque as that in said lean combustion condition is
maintained.
14. An engine control device as claimed in claim 13, wherein a
means for maintaining the engine torque includes any one of
throttle opening, fuel injection timing, and ignition timing.
Description
TECHNICAL FIELD
[0001] The present invention relates to an engine control system
for cleaning exhaust gas exhausted from lean-burn combustion
engines, particularly, for suppressing release of NOx, and to an
engine control device for achieving always stable clean up of the
exhaust gas by controlling reactivation of catalyst based on an
estimation of deterioration of the catalyst performance.
BACKGROUND OF THE TECHNOLOGY
[0002] Regarding an improvement on clean-up rates of lean NOx
catalyst, JP-A-5-133260 (1993), for instance, discloses a method
for improving transient clean-up rates by changing a target
air-to-fuel ratio from a rich condition to a lean condition and its
reverse alternately. However, the above prior art does not teach
nor suggest any reactivation (recovery) control of the clean-up
rates to SOx poisoning based on time-elapsing effects of NOx
catalyst by heating utilizing so-called after-burn efficiencies and
the like.
[0003] Regarding conventional in-cylinder-injection engines, a
prior art is described, for instance, in JP-A-4-241753 (1992). The
technology is to make a fuel distribution homogeneous by
controlling fuel injection timing based on a temperature of cooling
water of the engine, in order to achieve stable stratified
combustion in a lean condition of the in-cylinder-injection
engine.
[0004] However, any special countermeasures for the exhaust gas of
the stratified combustion, wherein the combustion is performed in a
lean condition far from the stoichiometric air-to-fuel ratio, has
not been considered. Regarding release of NOx, which is a
particular problem of the lean combustion, no processing nor
controlling has been considered.
DISCLOSURE OF THE INVENTION
[0005] In accordance with the lean-burn engine, particularly lean
combustion (stratified combustion) in the in-cylinder-injection
engine, the combustion is performed by forming a combustible
mixture locally in the vicinity of plugs in a remarkably lean
condition as a whole cylinder.
[0006] Accordingly, its exhaust gas can not be cleaned on all the
components to be removed by conventional three way catalyst,
particularly, a lean NOx catalyst becomes necessary for nitrogen
oxides (NOx).
[0007] Regarding the NOx catalyst, an important point is how to
maintain its performance. In particular, a countermeasure for
gasoline containing sulfur components (S) more than conventional
gasoline becomes necessary in accordance with deregulation on
gasoline and the like.
[0008] Even on the conventional gasoline, a decrease of the
clean-up rate by sulfur can be generated based on transient
effects, and it is regarded as a SOx poisoning.
[0009] The SOx poisoning is caused by S components in gasoline, and
depending on how much the catalyst itself is exposed to the exhaust
gas atmosphere.
[0010] FIG. 3 indicates a change of characteristics of the lean NOx
catalyst in accordance with elapsing time, which is indicated on
the abscissa. In accordance with the characteristics, it is
revealed that the change is proportional to the time exposed to the
exhaust gas atmosphere, in other words, proportional to a total
mount of gasoline containing S supplied to the engine.
[0011] Furthermore, in accordance with the mechanism, the S
component in gasoline is changed to SOx (sulfur compounds) by
combustion, released as a part of the exhaust gas, and formed a
compound with an active component for NOx clean-up in the lean NOx
catalyst at surface of the catalyst, as shown in FIG. 4. Due to the
above phenomenon, the function of the active component for NOx
clean-up in the catalyst is decreased, and the catalyst performance
is deteriorated.
[0012] On the other hand, it has been known that the clean-up
performance of the catalyst can be recovered by making its
atmosphere at a designated temperature as indicated by dotted lines
in FIG. 3. In the above case, the higher the temperature in the
atmosphere of reactivation control shown by an arrow is, the higher
the degree of the recovery is.
[0013] The mechanism of recovery is to make the active component of
the catalyst functional as it conventionally is by heating the
catalyst (for instance, at least 500 - 600.degree. C.) for
separating SOx from the active components of the catalyst.
[0014] The problem to be solved by the present invention is to
provide an engine control device provided with lean NOx catalyst,
which is usable of the lean NOx catalyst having the above
characteristics in a preferable condition at all the time, and to
provide an engine control device provided with the lean NOx
catalyst, which can practically perform the reactivation control
indicated by the arrow in FIG. 3 when the clean-up rate is
decreased by sulfur and the like based on change of the lean NOx
catalyst with elapsing time.
[0015] The engine control device provided with the lean NOx
catalyst relating to the present invention solves the above
problems by the following measures.
[0016] First, the engine control device of the present invention
comprises a condition estimating means and a reactivation
controlling means for catalyst itself.
[0017] The condition estimating means for catalyst has practically
a following composition. A deteriorated condition of the catalyst
depends on the elapsing time exposed to the exhaust gas, and the
degree of deterioration depends on the amount of fuel used for the
combustion. This is clear from the previously described mechanism
of deterioration by S components contained in the fuel.
Accordingly, the degree of deterioration is estimated from the
total supplied amount of the fuel and the elapsing time of the
catalyst exposed to the exhaust gas containing the S components.
Furthermore, the degree of deterioration of the catalyst can be
determined by any of the temperature of the catalyst itself,
O.sub.2 sensors arranged at upstream and downstream of the
catalyst, and various exhaust gas sensors such as air-to-fuel ratio
sensors and the like.
[0018] Next, the reactivation control at a high temperature can be
achieved by elevating the exhaust gas temperature forcibly in view
of the fact that the engine is operated routinely in a lean
condition and the exhaust gas temperature is lower than that in a
conventional condition of stoichiometric air-to-fuel ratio.
[0019] Practically, the exhaust gas temperature is elevated by an
ignition timing retardation control. Regarding the
in-cylinder-injection engine, the exhaust gas temperature can be
elevated with an after-burn effect by performing fuel injection
during an exhaust stroke. In accordance with the control, the
exhaust gas temperature can be elevated forcibly to higher than a
routine operation condition, and the reactivation control indicated
in FIG. 3 becomes possible. It is clear that the ignition timing
retardation control is applicable to conventional lean combustion
of a MPI system, and that the reactivation control is effective for
achieving a heating effect for the catalyst atmosphere, because
fuel combustion becomes possible without using a control such as a
special ignition control and the like by injecting fuel into an
atmosphere at a relatively high temperature during exhaust valves
are in an opening condition during an exhaust stroke injection of
the in-cylinder-injection engine.
[0020] Controlling time for the reactivation control is more
effective with a shortened time at a higher temperature as the
dotted line in FIG. 3 indicates. Accordingly, the controlling time
of the reactivation control is regulated based on an estimated
exhaust gas temperature in that condition. The degree of the
heating effect in the reactivation control is the largest at the
first cycle, and is in a tendency to decrease after second cycle
with the same heating time. Therefore, in order to realize the
reactivation control more effective, it is effective to change the
length of the controlling time in consideration of the controlling
cycles such as extending the controlling time after second cycle
longer than the controlling time of the first cycle.
[0021] When the reactivation control becomes necessary in a
stratified combustion condition of a lean condition, the
reactivation control is performed by replacing a fundamental
combustion condition of the engine with an sir-to-fuel ratio
condition. In accordance with the replacement, the reactivation
control is performed in a condition that the basic exhaust gas
temperature is elevated by injecting at an exhaust stroke and
retarding the ignition timing in order to improve its effects, and
concurrently, the basic temperature during the reactivation control
can be made clear by selecting the stoichiometric air-to-fuel
combustion condition as the standard condition of the exhaust gas
temperature. Instead of the estimated exhaust gas temperature, the
exhaust gas temperature determined by temperature sensors arranged
in the lean NOx catalyst or the exhaust gas system including the
lean NOx catalyst can be used.
[0022] FIG. 2 indicates a fundamental portion of the present
invention. A SOx poisoning amount of the catalyst is estimated
based on Qa, i.e. an amount of air flow intake into the engine, or
Ti, i.e. a pulse width for controlling the amount of injection
supplied into the engine. Simultaneously, go or no of the exhaust
gas injection is judged based on the exhaust gas temperature, and
the reactivation control is performed with monitoring the exhaust
gas temperature by fuel and ignition control.
[0023] During the reactivation control, the exhaust gas system
damage (thermal deterioration by a high temperature) including the
lean NOx catalyst by a careless control must be avoided, because
the exhaust gas temperature is increased forcibly.
[0024] The heating condition for recovering the functions of the
active component of the catalyst requires at least 500.degree. C.
as described previously. However, the active component of the
catalyst has a possibility to cause a thermal deterioration if the
heating temperature exceeds approximately 900.degree. C. Therefore,
the reactivation control must be performed so that the lean NOx
catalyst temperature, or the exhaust gas temperature at the
upstream entrance portion of the lean NOx catalyst must be kept
lower than 900.degree. C.
[0025] If an overshoot, wherein the transient temperature exceeds
900.degree. C. in a course of stabilizing the reactivation control,
and the like are generated, an unit continuous control time of the
reactivating over 900.degree. C. is desirably shorter than tens to
30 seconds. If a case when the unit time exceeds tens to 30
seconds, the reactivation control must be stopped, or interrupted
temporarily, and the reactivation control is desirably resumed at a
temperature below 900.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic illustration indicating an example of
in-cylinder-injection engine system, whereto the present invention
can be applied, FIG. 2 is an illustration indicating a composition
of the primary portion of the present invention, FIG. 3 is a graph
for explaining the characteristics of the lean NOx catalyst, FIG. 4
is a flow chart for explaining the reaction of the lean NOx
catalyst, FIG. 5 is an illustration indicating a normal injecting
condition of in-cylinder-injection, FIG. 6 is an illustration
indicating an injecting condition, wherein exhaust stroke
injections are added to the condition shown in FIG. 5, FIG. 7 is an
illustration indicating an injecting condition, wherein stratified
combustion is applied to the in-cylinder-injection, FIG. 8 is an
illustration indicating an injecting condition, wherein the normal
and exhaust stroke injections are performed from the condition
shown in FIG. 7, FIG. 9 is an illustration for explaining
conditions of the reactivation control process, FIG. 10 is a graph
indicating a region of the reactivating condition, FIG. 11 a graph
indicating a characteristics of exhaust gas temperature of engine,
FIG. 12 is a flow chart for estimating a condition of the lean NOx
catalyst, FIG. 13 is an illustration indicating an injecting
condition, FIG. 14 is another embodiment of the step {circle over
(1)} shown in FIG. 12, FIG. 15 is a graph indicating a relationship
between air-to-fuel ratio and exhaust gas temperature, FIG. 16 is
an illustration indicating a map composition of weighting factors,
FIG. 17 is another embodiment of the step {circle over (1)} shown
in FIG. 12, FIG. 18 is a flow chart for transition to reactivation
control, FIG. 19 is a flow chart for judging exemption region, FIG.
20 is a flowchart for switching from stratification, FIG. 21 is a
flowchart for switching from stoichiometric air-to-fuel ratio
combustion, FIG. 22 is a flow chart for reactivation control, FIG.
23 is an illustration indicating exhaust stroke injection timing
and set condition, FIG. 24 is a map indicating breadth of exhaust
stroke injection pulse, and FIG. 25 is a map indicating weighting
factors for judging end of reactivation control.
PREFERRED EMBODIMENT OF THE INVENTION
[0027] Hereinafter, embodiments of the engine control device
provided with the lean NOx catalyst of the present invention are
explained in details referring to the drawings.
[0028] FIG. 1 is a schematic illustration indicating an example of
engine system, whereto the present invention can be applied. In
FIG. 1, intake air to the engine is taken from an entrance portion
2 of an air cleaner 1, flows through an air flow meter 3 and a
throttle body, which contains a throttle valve 5 to control an
amount of the intake air, and enters into a collector 6.
[0029] Then, the intake air is distributed to each of intake pipes
connected to each cylinders of the engine 7, and introduced into
the cylinders.
[0030] On the other hand, fuel such as gasoline and the like are
supplied from a fuel tank 14 to a fuel system, whereto an injector
is connected with a pipe, by pressurizing preliminary with a fuel
pump 10, and secondarily with a fuel pump 11. The pressure of the
preliminary pressurized fuel is controlled to be a designated
pressure (for instance, 3 kg/cm.sup.2) by a fuel pressure regulator
12, and the pressure of the secondarily pressurized fuel, which is
higher than the pressure of the preliminary pressurized fuel, is
controlled to be a designated pressure (for instance, 30
kg/cm.sup.2) by a fuel pressure regulator 13, and the fuel is
injected into the cylinder from the injector 9 provided to each of
the cylinders. Here, the fuel pressure regulator 13 can be any type
of regulating mechanically at a designated pressure, and of
regulating the controlling pressure linearly in accordance with
electrical signals from outside the system, and the types of the
regulator do not restrict the present invention.
[0031] The pressure of the secondarily pressurized fuel is detected
by a fuel pressure sensor 23, and the output from the sensor is
input into a control unit 15.
[0032] Signals indicating the amount of the intake air is output
from the air flow meter 3, and is input into the control unit
15.
[0033] A throttle sensor 4 for detecting the opening of the
throttle valve 5 is provided to the throttle body, and its output
is also input into the control unit 15.
[0034] A crank angle sensor 16 is provided to an axle of cam shaft,
and a reference angle signal REF indicating a rotation position of
the crank axle and an angular signal POS for detecting rotation
signal (number of rotations) are output. These signals are also
input into the control unit 15. The crank angle sensor can be of a
type which detects the rotation of the crank axle directly as
indicated as 21.
[0035] In order to ignite an air-fuel mixture in the cylinder,
electric power is supplied to a coil 22 from the control unit 15,
and when supplying the power is interrupted, a high voltage is
charged to an ignition plug 8 and an ignition energy is supplied to
the air-fuel mixture.
[0036] A pressure-in-cylinder sensor 24 detects the pressure in the
cylinder, converts the pressure in electric signals, and transmits
the signals in the control unit 15.
[0037] An A/F sensor 18 is provided at the exhaust gas pipe, and
its output signals are also input in the control unit 15.
Furthermore, a lean NOx catalyst is provided at the exhaust gas
pipe 19, and hazardous components in the exhaust gas are
removed.
[0038] Main part of the control unit 15, although not shown in the
drawing, is composed of MPU, ROM, RAM, and I/O including A/D
converter, LSI, and the like. The control unit 15 takes in signals
from various sensors detecting the operation condition of the
engine as input, performs various calculating processes, outputs
various control signals which are obtained as the results of the
above calculation, supplies designated control signals to the
injector 9 and the ignition coils 22, and executes fuel supplying
amount control and ignition timing control.
[0039] In accordance with the in-cylinder-injection engine as
described above, fuel supply to the engine varies depending on the
operation condition. In a case when fuel is injected in an intake
stroke and ignited in a following compression stroke as indicated
in FIG. 5, that is, combustion is performed in the stoichiometric
air-to-fuel condition (homogeneous combustion) and in a lean
condition such as air-to-fuel ratio as of 20 - 30. On the other
hand, FIG. 7 indicates the fuel injection in the stratified
combustion, and a lean combustion such as the air-to-fuel ratio of
30 - 40 is performed.
[0040] Fuel supplying conditions at the reactivation control of the
present invention are indicated in FIG. 6 and FIG. 8,
respectively.
[0041] The control condition indicated in FIG. 5 is explained as a
normal control (1) under a stoichiometric air-to-fuel ratio
combustion condition.
[0042] When reactivation control becomes necessary in a condition
indicated in FIG. 5, fuel is injected in an exhaust stroke of each
of the cylinders concurrently with the normal control (1).
[0043] FIG. 7 indicates a condition, wherein a condition of the
stratified combustion is taken as a normal control (2). When
reactivation control becomes necessary in a condition indicated in
FIG. 7, fuel supply relating to engine power is performed by the
normal control (1), and the same control as FIG. 7 is performed in
FIG. 8.
[0044] When exhaust stroke injection is performed with
in-cylinder-injection, fuel is injected to an exhaust gas in a
condition at a high temperature soon after burnt in the combustion
chambers and injected fuel is burnt in the route from the
combustion chamber to the lean NOx catalyst 20. Therefore, a high
temperature condition higher than the exhaust gas temperature
generated by the normal control (1) can be generated.
[0045] FIG. 9 indicates various control parameters and changes in
conditions accompanied with operation. The abscissa indicates
elapsing time. At the point A, the estimated result of the
condition of the lean catalyst becomes to necessitate the
reactivation control. Details of the reactivation control will be
described later. At this time, the engine is in a stratified
combustion condition, and transferring to a homogeneous combustion
condition, that is a base condition of the reactivation control, is
performed as a transfer from the point A to the point B. The
air-to-fuel ratio in the stratified condition is a lean condition,
and the operating condition is in a condition wherein the exhaust
gas is being cleaning by the lean NOx catalyst 20. When the
reactivation control becomes necessary at the point A, the
homogeneous combustion at the point B is made possible by operating
target air-to-fuel ratio, throttle opening, fuel injection timing,
and ignition timing. The exhaust gas temperature at this time is
elevated in accordance with transferring from the air excess
condition of the stratified condition to the homogeneous
combustion. The exhaust gas temperature is elevated by performing
fuel injection in the exhaust stroke, which is the reactivation
control of the present invention, after forming this condition, and
retardation control of the ignition timing. Then, the reactivation
control is performed. The diagonally shaded area of the exhaust gas
temperature in FIG. 9 indicates the exhaust gas temperature rise
based on the effect of the reactivation control.
[0046] Regarding the change of cleaning ratio of the lean NOx
catalyst 20, the cleaning ratio is recovered gradually by making
the atmosphere in a high temperature condition, and the control is
finished at the point G.
[0047] The control time from the point B to the point G is
explained referring to FIG. 10 and FIG. 11.
[0048] That is, there is a range in the recovery of cleaning ratio
by the reactivation and the reactivation control, and a
controllable range is indicated by the diagonally shaded area in
FIG. 10. At the low temperature side, the atmosphere temperature is
low such as in a temperature range lower than the temperature,
whereat SOx and the active components of the catalyst is separable.
At the high temperature side, a restriction not to allow the
execution of the reactivation control by the injection at the
exhaust stroke and retarding the ignition timing, or to interrupt
the reactivation control immediately and the like, is required in a
case, when the heat resistance of the catalyst causes a problem,
that is, when the catalyst temperature exceeds 1000 - 1100.degree.
C. However, if the heat resistance is ensured, the restriction at
the high temperature side becomes unnecessary.
[0049] The effects of the reactivation control varies depending on
the temperature of the exhaust gas at the moment. Accordingly, the
control unit 15 has a temperature map such as shown in FIG. 15
inside, and an upper limit control, furthermore, the reactivation
control time can be managed by knowing the condition executing the
reactivation control at the moment and the estimated exhaust gas
temperature (a relationship between number of rotations of the
engine and engine load).
[0050] The above explanation describes all the operation and
effects of the engine control device provided with the lean NOx
catalyst, whereto the present invention is applied. Hereinafter,
details of the reactivation control is explained referring to
figures after FIG. 11.
[0051] FIG. 12 is a flow chart indicating a part of condition
estimation of the lean NOx catalyst in an embodiment of the present
invention, and the flow is executed actually as a program in the
control unit.
[0052] As explained previously on FIG. 3, some conditions of the
lean NOx catalyst 20 vary depending on the environment exposed to
the exhaust gas. Factors reflecting the effects are such as a total
amount of fuel supplied to the engine (.SIGMA.Q.sub.f) , a total
number of fuel injection pulses (.SIGMA.T.sub.p) a total amount of
intake air (.SIGMA.Q.sub.a), travel distance and travel time, and
others. Particularly, because the condition of the catalyst depends
on the amount of fuel burnt in the engine, an example of judging
the condition of the catalyst based on the total amount of fuel
supplied to the engine is taken as an embodiment of the present
invention.
[0053] In accordance with the step {circle over (1)}, the amount of
fuel per one cycle of the engine is calculated by multiplying a
pulse breadth, which is represented by the pulse breadth of the
first cylinder Ti#1, by a constant number K, which is a conversion
factor to convert a pulse breadth to the amount of fuel, and
further multiplying by the number of the cylinders n.
[0054] Then, in accordance with the step {circle over (2)},
weighting of the amount of fuel is performed based on the
combustion condition at the moment. The weighting is performed
based on a level of the air-to-fuel ratio in the operating
condition. In FIG. 15, the air-to-fuel ratio is indicated in the
abscissa, and a relationship between the air-to-fuel ratio and the
exhaust gas temperature is indicated. That is, if the environment
where the lean NOx catalyst is exposed to is only a lean condition,
only the active components and the SOx form a compound as indicated
in FIG. 4. However, if the operation is performed in a rich
condition of the air-to-fuel ratio, the exhaust gas temperature is
elevated, and separation of SOx is performed concurrently with the
formation of the compound. Therefore, even if the fuel is supplied
constantly, the degree of the compound formation varies depending
on the air-to-fuel ratio at the time. The weighting in the step
{circle over (2)} is performed in order to correct the variance in
the degree of the compound formation.
[0055] In accordance with the step {circle over (3)}, the amount of
fuel of only this time is added to the total amount of fuel
hitherto. Then, a judgment whether the total amount of fuel reaches
a limit value or not is performed in the step {circle over (4)}. If
the limit is exceeded, the reactivation is necessary, and a flag
F.sub.saisei for requesting the reactivation control is made
F.sub.saisei=1. The above is the part on the estimation of the
catalyst condition.
[0056] An complementary explanation on the FIG. {circle over (1)}
is performed hereinafter referring to FIG. 13. The fuel injection
is performed in accordance with R.sub.ef signals for each of the
cylinders. However, if summation of the total number of the pulses
and judging the limit are performed every time, the load to the
control unit is increased. Therefore, in accordance with the
present invention, the processing using the pulse breadth of the
representative cylinder is performed as indicated in FIG. 12.
However, this part can be replaced with a method using the pulse
breadth of each of the cylinders indicated in FIG. 14.
[0057] The weighting in the step {circle over (2)} is performed
using the air-to-fuel ratio. However, if more exact control is
required, a method indicated in FIG. 17 can be applied. That is, a
method wherein the weighting factors are applied based on the
number of rotations of the engine and the load to the engine as
indicated in FIG. 16. The air-to-fuel ratio is set by the same map
as FIG. 16, and the factor including the air-to-fuel ratio can be
set.
[0058] Then, FIG. 18 is explained.
[0059] The reactivation control is performed based on the condition
of the condition judgment F.sub.saisei in FIG. 12.
[0060] The reactivation control requirement is judged in the step
{circle over (1)}. Completion of judgment on transfer control is
judged in the step {circle over (2)}. The transfer control means an
judgment whether the control between the point A to the point B is
necessary or not, and is indicated in FIG. 20 and FIG. 21.
[0061] In the step {circle over (3)}, a judgment whether the engine
is in stratified combustion, stoichiometric air-to-fuel combustion,
or an operation in a power region at the moment when the
reactivation requirement is generated is performed, and a flag
setting for appropriate to each of regions is performed in the step
{circle over (4)}. This is because the exhaust stroke injection and
the ignition timing retardation are performed as the reactivation
control, wherein:
[0062] (1) If the engine is during the stratified combustion in a
lean condition, target air-to-fuel ratio, throttle opening, fuel
injection timing, and ignition timing are controlled to transfer
the engine once to a stoichiometric air-to-fuel ratio condition,
and then, transfer the engine to the reactivation control.
[0063] This reason is that the effects of the reactivation control
vary depending on the temperature of the catalyst atmosphere, and
the exhaust gas temperature in the base condition is elevated by
making the combustion condition to the stoichiometric air-to-fuel
ratio condition.
[0064] (2) If the engine is operated in the stoichiometric
air-to-fuel condition, it is well known technology and details are
not explained here. However, an air-to-fuel feed back is
interrupted in order to prevent the feed back system from operating
to feed back the exhaust stroke injection, because if the exhaust
stroke injection is performed in a condition that the air-to-fuel
feed back system is operable, the feed back system operates to feed
back the injection.
[0065] (3) In judging the power region, a high number of rotations
and high load condition is particularly detected. Because, the
exhaust gas temperature in the high number of rotations and high
load condition is already in a fairly high condition, and , if the
exhaust stroke injection is performed in the above condition, the
temperature will exceed the withstand temperature of the catalyst
itself. Therefore, the judgment whether in the exemption region or
not is performed in the step {circle over (5)}. If the engine is in
the exemption region from the high number of rotations and high
load condition, the flag is set as a F.sub.wait condition, and
monitoring of the operation condition is continued. When the
operation condition exceeds the exemption region, the reactivation
control is performed.
[0066] FIG. 20 indicates a process in a case when the step {circle
over (4)} in FIG. 18 determines the stratified combustion. As
previously described, a target throttle opening is set based on the
set of a target A/F {circle over (1)}, then, the engine is
transferred to the stoichiometric air-to-fuel ratio condition by
setting a target injecting timing and ignition timing in the step
{circle over (2)}. The target values here are controls from the
point A to the point B, and each of parameters is not renewed at
once, but stepwise. All the control are set so as to add dampers,
in order not to generate a torque change, and transferred to the
stoichiometric air-to-fuel ratio condition. This is because, any
shock accompanied with the change in condition is prevented, and
any anxiety is not given to the operator accidentally.
[0067] FIG. 21 indicates a case when the judgment {circle over (4)}
in FIG. 18 determines a stoichiometric air-to-fuel ratio condition,
and the air-to-fuel ratio feed back is interrupted in this case as
described previously.
[0068] Hereinafter, details of the reactivation control is
explained referring to FIG. 22 - FIG. 25.
[0069] The reactivation control is performed by setting the exhaust
stroke fuel injection and the ignition timing retardation for the
reactivation control in the step {circle over (1)} in FIG. 22.
[0070] In particular, the exhaust stroke fuel injection is
explained in detail referring to FIG. 23. Normally, in order to
inject the fuel at an intake stroke synchronizing with a R.sub.ef
signal, the pulse breadth T.sub.inj and .theta.1 from the R.sub.ef
rise of #1 to the start of the injection is set (in FIG. 23, set to
#3 cylinder). In accordance with the composition of the present
invention, the exhaust stroke injection of #2, .theta.2, and the
pulse breadth of the exhaust stroke injection, T.sub.fire, are set
simultaneously with setting the #3 at the R.sub.ef rise of #1.
[0071] The pulse breadth of the exhaust stroke injection is defined
by the map indicating number of rotations of the engine and engine
load as shown in FIG. 24. The philosophy of setting the pulse
breadth in the exhaust stroke is to set a same pulse breadth in the
regions indicated by (a) in FIG. 24. This is the characteristics of
same air flow rate, the regions have a same exhaust gas temperature
in a base condition (in stoichiometric air-to-fuel ratio combustion
condition), and the exhaust gas temperature rise due to after
burning by the fuel injection during a same exhaust stroke becomes
almost same. For instance, (b) are regions having a higher exhaust
gas temperature than (a). Regarding the ignition timing, the amount
of retardation is set similarly using a map having the same
composition.
[0072] Next, a check on the operation region indicated by {circle
over (2)} in FIG. 22 is explained hereinafter. After starting the
reactivation control, it is necessary to judge how long should the
control be continued.
[0073] Because, the reactivation of the lean NOx catalyst indicated
in FIG. 3 depends on the exhaust gas temperature and the control
time as indicated in FIG. 10. In accordance with the present
invention, the weighting factor of the region is assigned to the
same composition map as FIG. 24 as indicated in FIG. 25. That is,
the end of the reactivation is determined by a composition, wherein
the number in each region is counted when the reactivation control
is performed in the each region, and when the counted number
exceeds a designated value, the reactivation control is judged as
completed (step {circle over (3)}).
[0074] For instance, when the region judgment is performed per
every cycle, the counted number becomes [1] when one cycle is
passed at a point on the line (a), for instance, in FIG. 25, and,
if the next one cycle is in the (b) region, [5] is added and the
counted number becomes [6].
[0075] Thus, even if the reactivation is performed in any region,
same effects (reactivation time, clean up rate after the
reactivation) are intended.
[0076] The above is the explanation of an embodiment of the present
invention.
[0077] As being understood from the above explanation, the engine
control device provided with the lean NOx catalyst of the present
invention has the following feature:
[0078] (1) The performance of the lean NOx catalyst can be ensured
stably and certainly, and harmful exhaust gas can be suppressed
certainly.
[0079] (2) The suppression of the exhaust gas can be achieved with
adding no special devices and the like, and with a low cost.
[0080] (3) In accordance with applying the present invention, the
reactivation control can be performed certainly in the range, which
does not exceed the heat resistance of the catalyst.
* * * * *