U.S. patent application number 09/991519 was filed with the patent office on 2003-05-22 for automotive catalyst state control method.
Invention is credited to Kerns, James Michael, Makki, Imad Hassan.
Application Number | 20030093991 09/991519 |
Document ID | / |
Family ID | 25537293 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030093991 |
Kind Code |
A1 |
Makki, Imad Hassan ; et
al. |
May 22, 2003 |
Automotive catalyst state control method
Abstract
A control system and method for controlling an engine (10) of an
automotive vehicle having a catalyst (34) is set forth herein. The
control system maintains the efficiency of the catalyst by
monitoring the catalyst state and driving the catalyst state to a
target point. A first oxygen sensor (50) generates a first oxygen
signal. A second oxygen sensor (52) downstream of the catalyst
generates a second oxygen signal. A controller (12) is programmed
to perform the steps of determining a catalyst state having a
maximum value, a minimum value, and a target point therebetween;
determining a commanded air-fuel ratio to drive the catalyst state
to the target point; and operating the engine with the commanded
air-fuel ratio.
Inventors: |
Makki, Imad Hassan;
(Dearborn Heights, MI) ; Kerns, James Michael;
(Trenton, MI) |
Correspondence
Address: |
KEVIN G. MIERZWA
ARTZ & ARTZ, P.C.
28333 TELEGRAPH ROAD, SUITE 250
SOUTHFIELD
MI
48034
US
|
Family ID: |
25537293 |
Appl. No.: |
09/991519 |
Filed: |
November 21, 2001 |
Current U.S.
Class: |
60/285 ;
60/277 |
Current CPC
Class: |
Y02T 10/47 20130101;
F02D 2200/0816 20130101; F02D 41/1441 20130101; F02D 41/1456
20130101; F02D 41/0235 20130101; F02D 2200/0802 20130101; F02D
41/0295 20130101; Y02T 10/40 20130101; F01N 2550/02 20130101; F01N
11/007 20130101 |
Class at
Publication: |
60/285 ;
60/277 |
International
Class: |
F01N 003/00; F01N
007/00 |
Claims
What is claimed is:
1. A method for controlling an engine coupled to a catalyst
comprising: determining a catalyst state having maximum value, a
minimum value and a target point therebetween; determining a
commanded air fuel ratio to drive said catalyst state to the target
point; and operating the engine with the commanded air fuel
ratio.
2. A method as recited in claim 1 wherein when the catalyst state
is between said maximum value and said minimum value, determining a
commanded air fuel ratio to drive said catalyst state to the target
point.
3. A method as recited in claim 2 when the catalyst state is not
between said maximum value and said minimum value, determining a
lambda error.
4. A method as recited in claim 3 further comprising adjusting the
commanded air-fuel ratio in response to said lambda error.
5. A method as recited in claim 1 wherein generating said catalyst
state is a function of measured lambda and a reference lambda,
airmass and a current catalyst capacity.
6. A method as recited in claim 1 further comprising the step of
generating a current catalyst capacity as a function of airmass and
catalyst temperature.
7. A method as recited in claim 1 further comprising the step of
generating a reference lambda corresponding to a stoichiometry
value.
8. A method as recited in claim 1 further comprising the step of
when a downstream exhaust gas oxygen sensor value reaches a
predetermined exhaust gas limit value, generating a reference
lambda as a function of a lambda error.
9. A method as recited in claim 1 wherein generating a reference
lambda comprises determining a lambda error in response to airmass,
catalyst state, and a previous catalyst state.
10. A method as recited in claim 1 wherein said minimum value is
about 1, said maximum value is about -1 and said set point is about
zero.
11. A method as recited in claim 1 wherein said target point is a
function of load.
12. A method as recited in claim 1 wherein said step of determining
a commanded air fuel ratio comprises determining the commanded
air-fuel ration as a function of airmass, current catalyst capacity
and said target point.
13. A method for controlling an engine coupled to a catalyst
comprising: determining a rate of change of a catalyst state;
estimating a current catalyst state by integrating the rate of
change of the catalyst state; determining a commanded air fuel
ratio to drive said catalyst state to a target point; and operating
the engine with the commanded air fuel ratio.
14. A method as recited in claim 13 wherein generating said
catalyst state is a function of measured lambda and a reference
lambda, airmass and a current catalyst capacity.
15. A method as recited in claim 13 further comprising the step of
generating a current catalyst capacity as a function of airmass and
catalyst temperature.
16. A method as recited in claim 13 further comprising the step of
generating a reference lambda corresponding to a stoichiometry
value.
17. A method as recited in claim 13 further comprising the step of
when a downstream exhaust gas oxygen sensor value reaches a
predetermined exhaust gas limit value, generating a reference
lambda as a function of a lambda error.
18. A method as recited in claim 13 wherein generating a reference
lambda comprises determining a lambda error in response to airmass,
catalyst state, and a previous catalyst state.
19. A method as recited in claim 13 wherein said target point is a
function of load.
20. A control system for an engine coupled to an emission catalyst
having: a controller configured to determinr a catalyst state
having maximum value, a minimum value and a target point
therebetween; said controller further configured to determine a
commanded air fuel ratio to drive said catalyst state to the target
point; and said controller further configured to operate the engine
with the commanded air fuel ratio.
21. An article of manufacture comprising a computer storage medium
having a computer program therein for controlling an engine coupled
to a catalyst, said computer storage medium comprising: code for
determining a rate of change of a catalyst state; code for
estimating a current catalyst state by integrating the rate of
change of the catalyst state; code for determining a commanded air
fuel ratio to drive said catalyst state to a target point; and code
for operating the engine with the commanded air fuel ratio.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to an exhaust gas
control system for an internal combustion of an automotive vehicle,
and more particularly, to a method and apparatus for controlling
the catalyst efficiency by monitoring the state of the
catalyst.
BACKGROUND
[0002] Minimizing tailpipe emission is an objective of closed loop
fuel systems. Closed loop fuel systems include a catalytic
converter that is used to treat the exhaust gas of an engine. The
efficiency of a catalytic converter is affected by the ratio of air
to fuel supplied to the engine. At the stoichiometric ratio,
catalytic conversion efficiency is high for both oxidation and
reduction conversions. The air-fuel stoichiometric ratio is defined
as the ratio of air to fuel which in perfect combustion would yield
complete consumption of the fuel. The air-fuel ratio Lambda of an
air-fuel mixture is the ratio of the amount by weight of air
divided by the amount by weight of fuel to the air-fuel
stoichiometric ratio. Closed loop fuel control systems are known
for use in keeping the air-fuel ratio in a narrow range about the
stoichiometric ratio, known as a conversion window of an emission
catalyst.
[0003] The difficulty with known systems is that the catalyst is
very sensitive to errors in the input air fuel mixture that are
less than the resolution of an upstream sensor output signal. Also,
the oxygen storage capability of the catalyst can delay the
response of a downstream sensor making the determination less
accurate due to the time delay. One system estimates the oxygen
mass stored in the catalyst by observing the amount of oxygen
upstream of the catalyst and downstream of the catalyst to infer
the catalyst capacity which may in turn be used to adjust the
air-fuel ratio. Such systems suffer from the drawback mentioned
above.
[0004] Other known systems use a predicted downstream oxygen sensor
voltage to predict the amount of oxygen in the exhaust gas. One
problem with this and other prior known systems is that the storage
capacity of the catalyst will change with temperature and catalyst
age. Therefore, the calculated efficiency in such systems may not
correspond to the actual efficiency of the catalyst, particularly
in older systems.
[0005] It would therefore be desirable to provide a method and
apparatus for maximizing catalyst efficiency that takes into
consideration the state of the catalyst.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method and apparatus for
controlling the operation of an engine of the automotive vehicle in
response to a catalyst state rather than a calculation based on the
amount of oxygen in the exhaust gas.
[0007] In one aspect of the invention, a method for controlling an
engine comprises determining a catalyst state having maximum value,
a minimum value and a target point therebetween. The method further
comprises determining a commanded air fuel ratio to drive said
catalyst state to the target and operating the engine with the
commanded air fuel ratio.
[0008] In a further aspect of the invention, a system for
controlling an engine of an automotive vehicle includes a catalyst
as set forth herein. The control system maintains the efficiency of
the catalyst by monitoring the catalyst state and driving the
catalyst state to a target value. A first oxygen sensor generates a
first oxygen signal. A second oxygen sensor downstream of the
catalyst generates a second oxygen signal. A controller is
programmed to perform the steps of determining a catalyst state
having a maximum value, a minimum value, and a target point
therebetween; determining a commanded air-fuel ratio to drive the
catalyst state to the target; and operating the engine with the
commanded air-fuel ratio.
[0009] One advantage of the invention is that factors such as
temperature and age may be used in the catalyst state
determination. This results in an improved efficiency calculation
that does not correspond to a particular stored oxygen mass within
the catalyst.
[0010] Other advantages and features of the present invention will
become apparent when viewed in light of the detailed description of
the preferred embodiment when taken in conjunction with the
attached drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of a motor vehicle internal
combustion engine together with apparatus for controlling the
air-fuel ratio to the engine in accordance with the preferred
embodiment of the invention.
[0012] FIG. 2 is a control block diagram of the catalyst state
controller of the present invention.
[0013] FIG. 3 is a control block diagrammatic view of the catalyst
state controller of FIG. 2.
[0014] FIG. 4 is a block diagrammatic view of the integrate state
block of FIG. 3.
[0015] FIG. 5 is a control block diagrammatic view of the upstream
reference block of FIG. 3.
[0016] FIG. 6 is a control block diagrammatic view of the Lambda
control block of FIG. 3.
[0017] FIG. 7 is a block diagrammatic view of the catalyst capacity
block of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] In the following example the same reference numerals and
signal names will be used to identify the respective same
components and the same electrical signals in the various
views.
[0019] The present invention seeks to maximize catalyst efficiency
based on the assumption that the catalyst is most efficient in an
arbitrary state where the active catalyst sites are neither
saturated with nor depleted of oxygen. Also, a high or low
downstream exhaust gas oxygen sensor voltage indicates that the
whole catalyst is effectively saturated rich or lean and is outside
a catalyst state window. When the sensor indicate an intermediate
value, both oxidation and reduction sites are available.
[0020] Referring now to FIG. 1, internal combustion engine 10 is
controlled by electronic controller 12. Engine 10 has a plurality
of cylinders 14, one of which is shown. Each cylinder has a
cylinder wall 16 and a piston 18 positioned therein and connected
to a crankshaft 20. A combustion chamber 22 is defined between
piston 18 and cylinder wall 16. Combustion chamber 22 communicates
between intake manifold 24 and exhaust manifold 26 via a respective
intake valve 28 and an exhaust valve 30. Intake manifold 24 is also
shown having fuel injector 32 coupled thereto for delivering liquid
fuel in proportion to the pulse width of signal (FPW) from
controller 12. The fuel quantity together with the amount of
airmass in the intake manifold 24 defines the air-fuel ratio
directed into combustion chamber 22. Those skilled in the art will
also recognize that engine may be configured such that the fuel is
injected directly into the cylinder of the engine in a direct
injection type system.
[0021] A catalyst 34 is coupled to exhaust manifold 26 through
exhaust system 36 and may comprise a three-way catalytic converter.
Catalyst 34 is used to reduce tail pipe emissions by performing
reduction and oxidation reactions with the combustion gasses
leaving cylinder 22 through exhaust valve 30.
[0022] Controller 12 is shown as a conventional microcomputer 41
including a microprocessing unit (CPU) 38, input/output ports 40,
read-only memory 42, random access memory 44, and a conventional
data bus 46 therebetween.
[0023] Controller 12 is shown receiving various signals from
sensors coupled to engine 10. The various sensors may include a
mass airflow sensor 47 used to provide an airmass signal to
controller 12. An engine speed sensor 48 is used to generate an
engine speed signal corresponding to the rotational speed of the
crankshaft. An exhaust gas oxygen sensor 50 positioned upstream of
catalyst 34 provides a signal corresponding to the amount of oxygen
in the exhaust gas prior to the catalyst. A second exhaust gas
oxygen sensor 52 may be coupled to the exhaust system after
catalyst 34. Sensors 50, 52 may comprise an EGO sensor, an UEGO
sensor, or a HEGO sensor. Catalyst 34 may also have a temperature
sensor 54 coupled thereto. Catalyst temperature sensor 54 provides
an operating temperature signal for the catalyst to controller 12.
Although a physical sensor 54 is illustrated, controller may also
indirectly determine a temperature of the catalyst from other
sensed inputs. The temperature of the catalyst may be estimated
based upon the various engine operating conditions. In particular,
catalyst temperature may be estimated using on a normal estimated
temperature based on engine operating conditions that represent the
catalyst temperature under normal conditions increased by a change
in temperature based on the various operating conditions such as
engine speed or load.
[0024] A throttle body 56 having a throttle plate 58 and a throttle
position sensor 60 is illustrated. Throttle position sensor 60
provides controller 12 with an electrical signal corresponding to
the desired driver demand.
[0025] Referring now to FIG. 2, a simplified block diagrammatic
view of a portion of controller 12 is illustrated coupled to
various blocks and illustrate various signals provided from the
sensors to the controller 12. Block 70 is the catalyst state
controller which is used to generate an air-fuel ratio lambse based
upon the various inputs. The air-fuel ratio lambse is used to
measure a catalyst state (CatState). The catalyst state is a
normalized number between 1 and -1 indicative of a drift in the
downstream oxygen level. That is, when the catalyst state is
between 1 and -1, both reduction and oxidation sites in the
catalyst are available. At 1 and -1, neither oxidation nor
reduction sites are available. Lambse is a signal that averages to
unity when the engine operates at stoichiometry with no air-fuel
errors or offsets. Typically, lambse ranges between 0.75 and 1.25.
A commanded state output (Out2) may also be provided from block 70
corresponding to the commanded state of the catalyst. Engine 12
receives the lambse signal and the airmass signal that controls the
fuel injector as described above to provide an air-fuel ratio
output to the engine (AirFuelOut). The combustion gasses are
coupled to catalyst 54 and are output through the exhaust system at
output one (Out1).
[0026] Inputs to block 70 include the output from exhaust gas
sensor 50 upstream of catalyst 54 (UEGOLambda). The output of
downstream exhaust gas sensor 52 is coupled to block 70 as DSHEGO
volts. The airmass (AM) from throttle body 56 is also coupled to
block 70. The catalyst temperature (CatTemp) is also coupled to
block 70.
[0027] Referring now to FIG. 3, block 70 is illustrated in further
detail. As described in FIG. 2, the outputs of block 70 are the
catalyst state (CatState), lambse, and commanded state. The
catalyst state (CatState) is determined in the IntegrateState block
72. The IntegrateState block 72 integrates the rate of the state
change that results in an estimated catalyst state (CatState)
between 1 and -1. The estimated catalyst state may actually extend
beyond -1 and 1 due to estimation and measurement errors. Further
details of the IntegrateState block 72 will be further described in
FIG. 4 below. The IntegrateState block 72 has various inputs
including airmass, lambda, lambda1KAM, current capacity,
CatSaturated, and DSHEGOState inputs. The airmass is generated from
the mass airflow sensor 47 in FIG. 1. Lambda is derived from the
upstream exhaust gas sensor 50. Lambda1KAM is derived in upstream
reference block 74. The current capacity of the catalyst is
determined by catalyst capacity block 76. The catalyst saturated
signal (CatSaturated) and the DSHEGOState signal are provided from
state limits block 78. A lambda control block 80 receives the
catalyst state output from IntegrateState block 72 and generates
the CommandedState and lambse signals as will be further described
below.
[0028] Block 76 receives the airmass signal and the catalyst
temperature signal and determines a catalyst capacity
(BaseCapacity). The units of capacity may, for example, be termed
as delta lambda times the pounds of air.
[0029] Block 78 enables the IntegrateState in block 72 by
monitoring the output of the downstream exhaust gas sensor 52 shown
in FIG. 1. An Enable Integrate (Enab_Integrate) signal and a state
reset value (StateResetVal) are generated. By monitoring the
exhaust gas sensor 52, the determination whether or not the
catalyst is saturated rich or lean may be determined. When the
voltages exceed the predetermined limits, block 78 resets the
states to 1 or -1 using the state reset value. Both sensor and
stoichiometric chemistry errors are compensated for in block 74.
The details of block 74 will be further described below.
[0030] Block 80 is coupled to the airmass signal and current
capacity signal generated from block 76. Also, the target state is
provided from a target state block 81. In the present example, the
target state is set at zero. That is, between the catalyst states 1
and -1. Target state zero corresponds to the target state which
will drive the catalyst to the most efficient state. Although zero
is used, various numbers could be used and the number may also be
adjustable based on load or other engine operating conditions.
[0031] Referring now to FIG. 4, IntegrateState block 72 of FIG. 3
is illustrated in further detail. The IntegrateState block 72 has a
calculate state rate (CalcStateRate) block 82 that is used to
determine the rate of change in the catalyst state. Block 82
receives lambda, lambda1KAM, airmass and current capacity signals
as described above. The catalyst state dot (CatStateDot) is
determined in block 82. The difference between lambda and
lambda1KAM is the catalyst input air-fuel ratio error. Thus, the
change in the catalyst state is determined as a function of the
catalyst input air-fuel ratio error. That is,
(CatStateDot)=[am*(Lambda-Lambda1Kam)]/Current Capacity. The output
of block 82 is coupled with the catalyst saturated signal
(CatSaturated) and the DSHEGOState signal. By integrating the
catalyst state dot signal an estimate of the current catalyst state
(CatState) is determined in block 84.
[0032] Referring now to FIG. 5, block 74 of FIG. 3 is illustrated
in further detail. A target downstream voltage block 88 is coupled
to a summing block 90. Summing block 90 is also coupled to the
downstream heated exhaust gas oxygen voltage. The 0.6 value within
the target downstream voltage block 88 represents the desired
operating value of the downstream sensor. This value, of course,
may change based upon a function of the engine operating condition
such as engine speed and load.
[0033] The output of the summing block 90 is the downstream voltage
error. Saturation block 92 receives the downstream voltage error.
Saturation block 92 is used because the downstream voltage error
may be larger in one direction than the other since the target
voltage may not be exactly in the center of the sensor voltage
range. Saturation block 92 limits the signal maximum and minimum
values to provide a symmetric output.
[0034] A gain block 94 receives the downstream voltage error signal
after passing through saturation block 92. The downstream voltage
gain block 94 is coupled to integral controller 96 to calculate the
lambda reference. Of course, those skilled in the art would
recognize that other types of controllers may be used. As an
alternative, the lambda reference may also be stored in a table as
a function of engine load and speed. Other values may also be
coupled to integral controller 96 to allow the proper integration
of the signal and enable the integration. It should also be noted
that the voltage gain of block 94 may be a function of catalyst
capacity.
[0035] The lambda1 reference signal generated by integral
controller 96 refers to the use of one upstream sensor. In various
other applications, such as a "V" style engine, multiple sensors
may be used.
[0036] As can be seen, a lambda reference is used to determine the
measured upstream lambda that corresponds to the desired downstream
heated exhaust gas oxygen voltage.
[0037] Referring now to FIG. 6, the CatState is used as an input to
the fuel control where it is compared to a target catalyst state.
FIG. 6 illustrates block 80 of FIG. 3 in further detail. The target
state and the catalyst state are provided to a summing block 104.
As mentioned above, the catalyst state is preferably between -1 and
+1, while the target state is preferably a value therebetween such
as zero. The difference in the signal is the catalyst state error
(CatStateError) signal. This signal is provided to a proportional
integrator controller (PI) having a proportional block 108 and a
discrete-time integrator block 110. Those skilled in the art will
recognize that other types of controllers could be used to control
the target state and the estimated catalyst state. The PI
controller 106 sums the proportional signal provided by block 106
in block 112. The sum of the proportional and integrated signal is
the commanded state (CommandedState). The commanded state signal is
added together with a constant from block 114 in block 116. The
current capacity, the commanded state signal, and the airmass are
combined together in product block 118 to obtain lambse. That is,
by multiplying the commanded state times the current capacity and
dividing it by the airmass, some limits are provided on the oxygen
in and out rate. The storage reaction rate is limited and the high
deviation from stoichiometric will have a tendency for breaking
through the predefined limit. The commanded rate may therefore be
clipped or limited by constant 114.
[0038] Referring now to FIG. 7, block 76 of FIG. 3 is described in
further detail. In block 76, the capacity estimate of the catalyst
is determined. It should be noted that if the catalyst estimate is
in error the catalyst will not be operating at an optimum state
contrary to the goals of the present invention. Various methods may
be used to estimate the catalyst state. One manner would be to
intrusively sweep the estimated state from one limit to the other
preferably at a light engine loading condition where emissions are
lowest. If the state saturates at opposite values to frequency this
would be an indication that the estimated capacity is too large and
thus the estimated capacity may be reduced. By compensating for the
catalyst capacity, the age of the catalyst may also be taken into
consideration. As the catalyst gets older, the capacity will be
reduced. Thus, by determining the catalyst state having a maximum
value, a minimum value, and a target point therebetween, a
commanded air-fuel ratio may be determined to drive the catalyst to
the target point. The engine is then operated with the commanded
air-fuel ratio.
* * * * *