CA1183238A - Method and means for controlling air-to-fuel ratio - Google Patents
Method and means for controlling air-to-fuel ratioInfo
- Publication number
- CA1183238A CA1183238A CA000396127A CA396127A CA1183238A CA 1183238 A CA1183238 A CA 1183238A CA 000396127 A CA000396127 A CA 000396127A CA 396127 A CA396127 A CA 396127A CA 1183238 A CA1183238 A CA 1183238A
- Authority
- CA
- Canada
- Prior art keywords
- air
- fuel
- fuel ratio
- sensor
- value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2451—Methods of calibrating or learning characterised by what is learned or calibrated
- F02D41/2454—Learning of the air-fuel ratio control
- F02D41/2458—Learning of the air-fuel ratio control with an additional dither signal
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
- F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Exhaust Gas After Treatment (AREA)
Abstract
Abstract of the Disclosure A method for controlling the air-to-fuel ratio fed to an engine or other combustion device provides for periodically adjusting the air-to-fuel ratio to stoichiometric or near stoichiometric, within the response range of the conventional exhaust gas sensor employed. This establishes a reference point from which the setting of an air-to-fuel ratio propor-tioning device (e.g., carburetor) is established by moving its adjustment means a selected distance from its setting at the reference point. The selected value may be outside the normal response range of the sensor, either rich or lean of stoichio-metric. The apparatus may include a sensor which generates an output signal which is compared against a reference signal by a comparator. When the output signal exceeds (or falls below) the reference signal, a timer to operate the proportioning device adjustment means in the desired direction for a stated interval of time is actuated. A separate timer operates the adjustment means towards stoichiometric at selected intervals to periodically establish the reference point.
Description
METHOD AND MEA~S FOR CONT~LLIMG
- AIR-To-FUEL RATIO
Background o~ the Invention . . .
The present invention relates to a means and me~hod for controlling the air-to-fuel ratio of a combustible mixture fed to a eombustion device. The invention is broadly applicable to sueh purpose and is speeifically useful in adjusting the air-to-fuel ratio of the eombustible mixture fed to an internal eoinbustion engine or to a catalytie combustor.
The prior art is replete with schemes for controlling air-to-fuel ratios, in particular for controlling the air-to-fuel ratio of the com~ustible mixture fed to an internal combustion engine. Often, the purpose of controlling the air-to-fuel ratio is to enhanee the operation of a catalytic exhaust gas purification deviee while maintaining aeceptable levels of engine performanee and efficiency. U.S. Patent 4,202,301, assigned to the assignee of this application, diseloses an air-to-fuel ratio control meehanism which operate~ in partial response to a eontrol circuit whieh, in turn, is responsive to the output of an oxygen sensor mounted in the exhaust line of the engine. This type of arrangement is well-known in the art, and is often referred to as a "elosed-loop" operation in which the carburetor or other air-fuel metering device is regulated by a eon-trol means which receives, as an input to it, a signal eorres-ponding to the presenee of oxygen in the engine exhaust gas, as sensed by the sensor.
U.S. Patent 4,019,474 discloses apparatus which comprises a detector for detecting the density of one component, for example oxygen, in the exhaus-t gases from an internal cornbustion engine for the purpose of regulating the air-to-fuel ratio.
The regulation is basecl on the detected value of the component in such a manner that the air-to-fuel ratio approximates the theoretically correct air-to-fuel ratio, i.e., the stoichiome~ric ratio.
U.S. Patent 3,986,352 discloses a fuel control for an engine equipped with a catalytic conver-tor which engine is normally operated "closed-loop" with a feedback signal from an air-fuel ratio sensor in the engine exhaust. As illustrated in the figure of the patent, an exhaust gas sensor produces an output voltage which exhibits a great rate of change in response to composition changes when operation is in the vicinity of the stoichiometric air-fuel ratio. The signal generated by the sensor passes through a control unit and ultimately influences the air-fuel ratio con-trol means of a carburetor. A relatively inexpensive and commercially available zirconia-type oxygen sensor displays this characteristic of showing, in the vicinity of a stoichiometric air-to-fuel ratio, a large change in the voltage of the output signal with change in the air-to-fuel ratio. ~owever, its sensitivity to chanye in the air-to-fuel ratio diminishes rapidly as -the air-to-fuel ratio moves away from stoichiometric, , -2-B
either to the lean or -the rich side. For this rPaSon/ if it is desired to run either rich or lean a significant distance away from stoichiometric i~ is not feasible, with a ~irconia type oxygen sensor, to control the air-to-fuel ratio at a selected value dif~ering significantly from stoichiometric.
This inherent limitation of oxygen (or other gas component) sensors is not a problem with conventional internal combustion engines, such as automobile engines, which are e~ui~ped with the so-called three-way conversion catalysts utilized to purify the exhaust gas. Three-way conversion catalysts of the type disclosed in U.~. Patent 4,157,316, assigned to the assignee of this application, are typically used to treat exhaust gases by substantially simultaneously o~idizing carbon monoxide and unburned hydrocarbons and reducing nitrogen oxides to nitrogen. ~or most efficient operation of these catalysts, the engine should be operated at or very close to stoichiometric air-to-fuel conditionsn Accordingly, a conventional zirconia or other sensor is useful since it is sensitive to changes in the air-fuel ratio range about stoichiometric conditions. Accordingly, the reference signal generated by the sensor can be utilized to make adjustments to the air-to-fuel ratio control of the carburetor or fuel injection device so as to hold operation at or very close to stoichiometric.
~lowever, for certain applications, it is desired to run either on the rich or on the lean side of stoichiometric at an air-to-fuel ratio which is outside the sensitivity or -esponse range of available oxycJen or other ~as component sensors. For example, it is believed tha-t fuel economy can be increased or maximized under lean air-to~fuel ra~:io conditions, generally about 1 to 3 a:ir-to-~uel ra~ios lean of stoichiometric. Operation in this range would pr~clude the use of a closed loop system using an exhaust gas sensor which is sensitive only within a limited range about stoichiornetric.
In certain other applications it is desirable -to operate on the rich side of stoichiometrlc, outside the response range of conventional sensors. For example, na-tural gas fueled internal combustion engines such as the type utilized ln pipelir.es and oil fields, require maintenance of a rich A/F
ratio which lies outside the limited range of available, reasonable cost sensors.
While means exist for determining exhaust gas component concentration levels resulting from air-to-fuel ratios which lie outside the conventional sensor response range, such eclulpment is either very expensive, complicated or delicate, or all three, as cornpared -to sensors of the type described above, and therefore are not practical for utiliza-tion in rnost internal combustion engine or cataly-tic combus-tor appl:lcations. Whether used in a motor vehicle or in stationary e~uipment, such as a stationary internal combustion engine or a catalytic combustor, it would be desirable to be able to use the less expensive and relatively rugged sensor in lieu of more complicated, delicate and/or expens:ive sensors or analytical ec~uipment.
mC3t'' - ~ ~
It is accordingly an object of the presen~ invention to provide a method and means for controlling the air-to-fuel ratio at a selected value or values which may, but not necessarily are, ou-tside the responsiveness range of the conventional oxygen or other gas component sensor, w~ile nevertheless employing such a sensor as the exnaust gas sensing means.
It is a further object of the present invention to provide a method and means utilizing an exhaust gas component sensor for controlling the air-to-fuel ratio fed to a combustion device, such as an internal combustion engine or a catalytic combustor, without necessity of rapidly oscillating between rich and lean operation.
It is a further object of the present invention to utilize the signal generated from a conventional oxygen (or other gas component) sensor to operate a combustion device, eg., a natural gas fuel engine, at an air-to-fuel ratio dis-placed from stoichiometric; eg., rich of s-toichiometric, while reducing to a minimum or substantially eliminating "wrong side", eg., to lean of stoichiometric, excursions.
Yet another object oE the present invention is to provide a control system which opera-tes "open loop" for a proportion of operating time, i.e., ~ithout continuous adjustment of the air-to-fuel ratio.
Other objects and advan-tages of the invention will become apparent from the following description.
~`
Summar~ of the Invention .
In accordance wlth the present invention there is provided the comblnation of an air-to-fuel rati.o control system and a fuel burning mechanism, the fuel burning mechanism having an adjustable air-fuel proportioning device, a combustion chamber and an exhaust conduit se.rially inter-connected in flow communication whereby a selectively proportioned air-fuel mixture may be introduced from the proportioning device into the combustion chamber for com-bustion therein, and exhaust gases may be withdrawn therefrom through the exhaust conduitO The air-to-fuel ratio control system comprises sensor means positioned in the exhaust gas conduit and having a limited ranse of response to the level of a gaseous component in the exha~st gas to produce a reference signal corresponding to the level. Reset means are operatively connected -to the air-fuel proportioning device Eor periodically adjusting the air-to-fuel ratio -to a first value selected so as to result in a level of the component in -the exhaust gas, which level lies within -the response ~ ranye of the sensor, there~y periodically triggering a reEerence signal generated by the sensor means.
Positioning means are operatively connected to the pro-portioning device and are responsive to the reference signal to adjust the air-to-fuel ratio to a second value which deviates from the first value by a selected amount and which , _ 33~8 may, but does not necessarily, result in a level of the component in the exhaust gas lying outside the response range, whereby the air-to-fuel ratio is periodicall~ adjusted to the second value. The positioning means may be configured to adjust the air-to-fuel ratio -to either rich or lean of stoichiometric.
In one aspect of the invention, the sen~or rneans may ~e an oxygen sensor means, such as a ~irconia sensor, responsive to a range of oxygen level in the exhaust gas corresponding to operation about the stoichiometric air-to-fuel ratio and, the positioning means may be adjustable to enable selection of the amount of deviation from the first selec-ted value which is imposed on the air-fuel metering means by the positioning means.
In other aspects of the invention, the fuel burning mechanism may comprise a catalytic combustor or an in-ternal combustion engine and, in the latter case, an exhaust gas purification catalyst may be positioned in the exhaust conduit downstream of the sensor means.
~0 In accor~ance with another aspect of the invention, there is provided a method for controlling -the air-to-fuel ratio of a :Euel burning mechanism by utilizing the sensed level o.~ a component in the exhaust gas which permi-ts maintenance of the ratio at values which result in exhaust gas levels of the component outside the response range o~ sensor means employed to sense the component level, the combustion mechanism 31~
is one having an adjustable air-fuel proportioning device, a combustion chamber and an exhaust conduit seriall~ interconnected in flow cor~nunication whereh~ a select:ively proportioned ai.r-fuel mixture may be introduced from said proportioning device into said combustion chamber for combustion therein, and exhaust gases may be withdrawn therefrom through the exhaust conduit. The method comprises the following steps.
Periodically, the air-to-fuel ratio is adjusted to a first value selected to result in a level of said component in the exhaust gas which lies within the response range of sensor~
thereby periodically triggering a response range-reference signal generated by the sensor. The air-to-fuel ratio is adjus-ted in response to the reference signal in a direction o~posite to that employed to at-tain the first value and in an amount to attain a second value of the air-to-fuel ratio which deviates from the first value by a selected amount and which results in a level of the component in the exhaust gas wh:Lch i5 outside the sensor response range. As a result, the ~lir~to-fuel ratio is periodically adjusted to -the.second ~0 value in response to the periodic triggering of the reference slgnal.
In one embodiment the air-to-fuel ratio is adjusted in the lean direction to attain the first value and is adjusted in the rich direction to attain said second value; in another embodiment the air-to-fuel ratio is adjusted in the rich direction to attain the first value is adjusted in the lean direction to attain the second value.
/ ! _ ~ ~
,, , Brief Description of the Drawing Figure 1 i8 a graph showing on the vertical axis the output signal in millivolts of an oxygen sensor positioned in the exhaust gas emerging from a combustion chamber, plotted against the air.to-fuel specific ratio (as deflned below) of the combustible mixture fed to the chamber;
Figure 2 i9 a graph showing-on the vertical axis the air-to-fuel specific ratio of a combustible mixture feed to a combustion chamber, plotted against time, illustrating the operation of a prior art control system;
Figure 3 is a schematic electrical and mechanical block di.agram illus-crating one embodiment of the present invention comprising an internal combustion engine equipped with an air-to-fuel ratio con-trol system and utilizing a catalyst to -treat the exhaust from the engine;
Figure 4 is a schematic electrical and mechanical block diagram showing in somewhat greater detail the electrical circuitry portion of the embodiment illustrated in ~igure 3;
Figure 5 is a schematic electrical diagram of one embodiment oE electronic circuitry useable in the present invention; and Figure 6 is a graph showing on the vertical axis the air-to-fuel specific ratio of a combustible mixture fed to a combustion chamber, plotted against time, illustrating the operation of one embodiment of a control system of the B
present inven-tion.
Description of the Preferred Embodiments . _ As above stated, one of the objec-ts of the present invention is to enable the control of the air-to-~uel (sometimes below abbreviated as A/F ~ ratio at a selected setting outside the range of responsiveness of a state of the art oxygen or other gas component sensor. The response range of such a sensor is illustrated by the graph of Fiyure 1, in which there is plot-ted in millivolts on the vertical axis the output signal generated by a conventional zirconia-type oxygen sensor positioned in the untreated e~haust gas emanating f om an internal combustion engine.
On the horizon-tal axis there is plotted the ratio of the actual A/F ratio to the stoichiometric A/F ratio, which will be hereinbelow referred to as the air-to-fuel specific ratio- and is represented by the symbol L in the drawings and specification.
Re~ference to the specific ratio is a conventional usage because it is useful in avoiding con-fusion in making comparisons bctween different operations. For example, an ~/F ratio of ~0 1~.65 (weight of air to weight of fuel) is the stoichiometric ratio corre~ponding to the combustion of a hydrocarbon fuel with an avera~Je Eormula CHl 88. Fuels with differen-t carbon/hydrogen ratios wi~l require different A~F ratios to produce a stoichiometric mixture. The symbol L is thus used to represent the relationship of a par-ticular or actual A/F
rn-J/, - 10 -ratio to the stoichiometric A/F ratio. The actual A/F ratio is divided by the stoichiometric A/F ratio so that in this system L=l is a stoichiometric rnixture, L>l is a fuel-lean mixture and L~1 i9 a fuel-rich mixture. For example, at an S actual A/F ratio of 14.5 for a Clll 88 hydrocarhon fuel, L=14.5/14.65=0.9898 is a fuel-rich mixture.
- Referring now to Figure 1, the vertical axis at L=l.0 represents stoichiometric operation of an internal combustion engine and the graph shows that under these conditions the output of a zirconia type sensor in the exhaust gas stream will have a signal strength of about 400 millivol-ts. As shown by the graph of Figure 1, the curve of the output slgnal from the sensor has a steep slope in a relatively narrow range on either side of the stoichiometric A/F ratio ranging from about 900 millivolts at L=0.985 to somewhat less than 100 millivolts at J.=1.015. The shape of the curve varies somewhat with variations in engine operation. However, in general, the curve may have a very small slope outside the L-0.985 to 1.015 range, and it is readily apparent from the curve that it becomes difficult or impossible to obtain a reliable reading for values of L outside the range.
Conventional control systems of the closed loop type are intended primarily for catalytic exhaust gas purifica-tion using three way conversion catalyst which, as mentioned above, requires operation at s-toichiometric for ~ost e~ecti~Je purification of the e~haust gases. This is accompllshed by manipulating the ~/F ra-tio to rapidly osci]late about stoichio-metric. Such operation requires a precise and sensitive carburetor or fuel in~ection system with a control logic speci~ic ~or the characteristics of the particular engine to which the system is applied. Accordingly, such a control system is rather expensive. Such prior art operation is schematically illustrated in Figure 2, in which the specific ratio L is plotted on the vertical axis agains-t time on the horizontal axis. The horizontal axis L=l.0 represents s-toichiometric operation, with operation above the L=l.0 axis being in the lean region, and operation below the L=l.0 axis being in the rich region. The sensor responsiveness range is indicatecl hy the dashed horizontal lines at, respectively, ~=~.985 and 1.015. The prior art control system is adapted to generate a signal when the AjF ratio crosses stoichiometric at I.=lØ
Because the responsive range is so narrow it is not feasible to malntain conditions within the very narrow band between ~0 I,-0.9~5 and 1.015~ Therefore, it is attempted ;to maintain osclllatincJ rich-lean conditions along opera-ting line 0. The thre~ way conversion catalyst is capable of tolerating limited excursions into the rich and lean regions, which ~verage out to approximately stoichiometric operation.
Thus, it is desired that lean region operation outside a very narrow band around stoichiometric, such as that bounded ~lCJ/: ~ - 12 -by the area abca of Figure 2, will be compensated for by subsecfuent rich area operation in the area bounded by defd.
Since the sensor response range is limited, the conditions as sensed by the sensor are represented by the dashed sensor line S. The system operates as follows. Assume that the carburetor or other air fuel proportioning device is moving in the lean direction along the operating line O and crosses L=l.0 at time to. At points Pl,- P2 and P3, the sensor senses a change between rich and lean. Starting at time tl, the system will initiate a change of the carburetor or other air-fuel proportioning device to move away from lean towards the rich direction for a selected interval of time tb at a selected rate or rates of movement. At time t2 the direction of the carburetor or other fuel proportioning device is reversed, to move in the rich direction for a time interval tc, at a selected rate or rates of movement. At the end of the time interval tc, at time t3, the carburetor or other device is moved back towards the lean condition to repeat the cycle.
This type of control cycle is discussed in SAE (Society of Automotive Engineers) Paper "Development of the Volvo Lambda-Sond System" by Gr~1ne T. Engh ancl Stephen ~allman, Paper 770295, presented at the International Automotive Engineering Con~ress and Exposition, Cobo Hall, Detroit February 28-March 4, 1977. See Figure 23 of the paper.
Wit'n this system, the ex-tent of the respective excursions into the rich and lean regions can not be determined ~y the sensor and conditions may be such as to cause an excursion, for example, along path a'b'c' into the rich region or along d'e'f' into the lean region. Of course, a rich excursion may not necessarily be compensated for by a corresponding lean excursion and extreme excursions may well exceed the excursion tolerance of the three way conversion catalyst.
As a result, noxious components of the exhaust gas will not be as effectively treated.
The rapid oscillating system is nonetheless useful for three way conversion catalysts on engines burning liquid hydrocarbon fuel, i.e., gasoline. ~owever, -the present invention not only permits better control and operation at a selected A/F ratio which may be significantly rich or lean of stoichiometric, but is readily adapted for use with a gaseous fuel device, which lacks the quick fuel-flow response time provided by a liquid fuel device. If the prior art æystem o~ Figure Z were used with a gaseous fuel, larger excursion~ along a'b'c' and d'e'f' of operating line O' wouLd result and detrac-t from efficient catalytic treatment.
In contrast to the oscillating control system, the present invention also permits substantial periods of "open loop"
operation during which the control system is not actively adjusting the A/F ratio.
Referring now to Figure 3, there is shown a schematic rendition of one embodiment of the presen-t invention in which an internal combustion engine 2, which may be an Otto hl~3~
Cycle na-tural gas-fueled internal combustlon enyine, i5 suppli''d with air and natural gas as a fuel through, respectively, lines 4 and 6. ~ fuel contro:L valve 8 is positioned in line 6.
Lines 4 and 6 form part of a carburetor 10, T~lhich comprises an air--fuel proportioning device generally indicated at 12, ~hich :Eeeds a combustible air-fuel mixture at a selected A/F
rat:io via line 14 into engine 2. Engine 2 has an exhaus-t gas li.ne 16 r 16a, 16b through which the combustion exhaust gases pass. A sensor 18, of the type having a limi-ted range of response as illustrated in the graph of Figure 1, is interposed in the exhaust line between segments 16 and 16a. A catalyst 19 is in the exhaust line, to purify the gases before they are discharged via l:ine seyment 16b. Any suitable catalyst may be employed.
The output si~nal of sensor 18 is transmitted via electrical connector 20 to a control unit 22 which comprises a reset means 22a and a positioning means 22b. The electrical output Erom reset means 22a is transmitted via electrical connector ~4a, 26 to operate fuel ccntrol valve 8. The elect.rlcal ou-tput Erom positioni.n~ means 22b is also transmi~ted7 v:la electri:cal connector 24b, 26, to operate fuel control valve 8.
In the embodiment illustrated in Figure 3, fuel control valve 8 serves as the adjusti.ny means of an air-fuel ratio meterin~ device by adjus-ting -the proportion of fuel relative to air which is fed into carburetor 10. Obviously, any m~ 15 -suitable ai.r-fuel ratio proportioning device such as a carhuretor or fuel injection system may be employer.l, and an appropriate drive mechanism may be connected to operate the adjustrnent screws on a carburetor or the controls of a fuel injection device to ad]ust the A/F ratios as taught by the inven-tion.
Before describing the operation of the embodiment illustrated in Figure 3, some additional details of one form o~ construction :in accordance with the invention will be described with re~erence -to the schematic diagram of Figure 4, in which an internal combustion engine 2' is supplied with a combustible air-fuel mixture via line 14' and e~haust gases are discharged through exhaus-t 16', 16'' and 16a', passed through a ca-talyst 19', and finally discharged via line segment 16b'. An oxygen sensor 18' has its probe end disposed within exhaust line 16' and in response to the oxygen level sensed in the exhaust gas generates an output signal Eo which is transmitted through a suitable electrical connector 21 to a comparator 28.
A reEerence signal Rr is also fed through a suitable electrical connector 25 from a reEerence source 30 ~o co~parator 28. In the case illustrated, reference source 30 may be adjusted so that reference signal Er has a value of ~00 m.i:Llivolts, corresponding to stoichiometric operation :Eor the case illustrated in Figure 1. Comparator 28 is connected by an electrical connector 32 to -timer B
which .is in turn connected via electrical connector 3~ to a mcJ/,~ 16 -,,~: . `..
dri.ve rich motor 36 which is opera-tivel~ connected via connector means 38 to air-fuel ratio rneterin~ device 42. A
reset connector 44 connects the output of timer B to a tirne~
which in turn is connected via electrical connector ~6 to a drive lean motor 48. Drive lean motor 48 is opera-tively connected via connector means 50 to air-fuel ratio metering device 42.
In operation, assume that internal combustion engine 2' is running rich. This would be the normal, desired condition, for example, for a natural gas fueled internal combustion engine. Timer A is running and is set for a preselected interval, say, five minutes, and when the five minute interval is reached, timer A emits a signal through electrical connector 46 which operates drive lean motor 48 to move air-~uel ratio control mechanism 42 to a lean condition. This changes the exhaust gas condition and oxygen sensor 18' generates its output signal E~ as the condition o~ the exhaust gas changes to provide an oxygen level which falls w.~th:in the responsive range of sensor 18'.. When the transmitted output si~nal Eo becomes less than the ~00 milLivolt reference signal Er~ which will occur when L crosses the 1.0 line moving in the lean direction as shown in Figure 1, comparator 28 generates a signal El which is transmitted through electrical connector 32 and triggers an outpu-t signal E2 which operates the drive motor 36 -to drive the air-fue-l mcJ/ - 17 -ratio proportionlng device 42 towards the rich direction for a preselected in-terval of time, say, for :I second. Alternativel~, ins-tead of a timed drive, means -to move the adjustrnent means of such a propor-tioning device, eg., the set scre-" o~ a carburetor, a selected distance as sensed by a location or displacement sensor, may be utilized. Signal E2 is also transmitted through connector 44 to timer A to reset timer A
to 2ero in order to re-start the -Eive minute interval of timer ~. When the five minute interval measured by timer A
has run, the sequence starts over again. Thus, it is seen by periodically, in this case every five minutes, adjusting the air-fuel ratio control mechanism 42 to change the air-fuel ratio towards stoichiometric (in this case, towards a lean condition) a signal is generated when a selected point (in this case, stoichiometric) is reached which causes the air-fuel ratio metering device to be operated a se].ected amount away from -the selec-ted point, in this case, towards the rich condition. Thus, the temporarily and periodically lnduced sto:ichiometric condition serves as a reference point :[rom which, by providing an appropriate drive interval of dr.Lve r:Lch motor 36, a preselected adjustment can be made to an~ deslred rarge within the rich area of operation. Obviously, reference signal Er could conveniently be set at any value between about 100 and 900 millivolts to establish a reference siynal anywhere within the responsive range of the sensor rn~ - - 18 -18'. In this manner, the sensor 18' may be u~ilized to control the air-fuel ratio se-t for any value, rich or lean, even though the value is outside ~he responsiveness ranye of the sensor 18'.
With reference to ~igure 3, it is seen that the output signal Eo will be transmitted from sensor 18 via line ~0 to positioning means 22b and when it exceeds the preselected reference signal positioning means 22b (corresponding to drive motor 36 and its associated initiators) will adjust fuel control valve 8 by opening it a preselected amount to shift the A/F ratio towards the desired, preselected rich condition. Reset means 22a, corresponding to drive ~e~
motor 48 and its associated timer A, will periodically at a selected interval move fuel valve 8 towards the closing direction -to drive the A/F ratio towards the lean direction.
An appropriate setting can be made of reference 30 (Figure 3) to cause comparator 28 to initiate the drive rich sequence ~rom a selected reference point to cause positioning means 22b to operate Euel control valve 8 a preselected amount in the opening direction, thereby re-establishing the desired A/F ratio.
The control unit portion (see Figure 3) of a system ~enerally conforming to that broadly illustrated in Figure 4 is illustrated in some detail in Figure 5. The signal 2S generated frorn oxygen sensor 50 and passed throuyh a buffer amplifier 52 is output signal Eo~ which has a value that is a function of the amount of oxygen in the exhaust gas contacted by sensor 50. ~he strength of sic~nal Eo i5 inversel~ proportiona~
to the oxygen content of the exhaust gases and is applied as one of two inputs -to a comparator circuit generally indicated at 54. A reference circuit 56 applies a reference signal of, for example, 400 millivolts as the second input to ~omparator circuit 54. Obviously, any desired reference signal may be selected. Given the constraints of the conventional oxygen sensor, as described above, a reference signal between about 100 and 900 millivolts would be selected for the reference signal. A different sensor, say a carbon dioxide sensor, which might have a different responsiveness range would require the selection of an appropriate reference signal within its response range.
~ hen the output signal Eo falls below the setting, say 400 millivolts, of the strength of the signal provided by reference circuit 56, as would occur if the engine were to run lean or if the oxygen sensor 50 were to fail, comparator ~0 54 provides an output signal El transi-tion from plu5 12 to 0 volts. The signal El is applied to timer 58, a 0.1 second to 10 second adjustable tirner, and -to nand gate 60 to start a timing cycle of timer 58. The output signal E2 of timer 58, a plu9 12 volt signal, is applied to drive rich relay 62 and to timer 64 through the monostable multivibrator comprised of nand gates 66 and 68 and to tirner 64, through inver'cer 70. The output signal E2, acting through rich drive relay 62, drives the air-fuel ratio proportioning device ~not shown in Figure 4, but corresponding to 42 in Figure 3) towards a rich condition until output signal Rl is 12 volts and timer 58 times out.
When timer 58 times out, and output signal Eo of sensor 50 is greater than 400 millivolts, signifying a rich A-F
ratio engine running condition, signal E2 switches from 12 volts to 0 volts. This transition of signal E2 starts timer 64 through nand gates 66 and 68, connected as a monostable multivibrator, and inverter 70. When signal E2 attains zero, it also serves to turn off rich drive relay 62. Timer 64 is adjustable for a.l to 10 minute time delay and when it is timing, and oxygen sensor 50 output signal Eo indicates a rich enyine operatiny condition, the air-Euel ratio metering device is not being adjusted by the system, i.e., is inactive.
~ fter a set time, timer 64 times out and signal E3 changes ~rom plus 12 volts to 0 volts and passing through n~nd gate9 60, 72 and inverters 74, 76, energizes lean drive relay 7B and prepares timer 58 to start timing. When sensor 50 ~enses lean conditions Erom the oxygen level in the exhaust gas, its output siynal Eo switches from plus 12 volts to 0 volts and -the cycle as described above repeats.
3~
In the specific embodiment illustrated in Figure S, buffer amplifier 52 and comparator 5~ pin number identifications are those of National's quad operational amplifer LM-32~N.
Inverters 70, 74 and 76 are RCA's ~ex Buf~er CD-4049AE, nand gates 66, 6~, 60 and' 72 are RCA's Quad Nand Gate CD-4011A~, and the timers 64 and 58 are RCA's Timers CA-~88G.
The operation of the invention m~y be better understood with reference to Figure 6, which plots on the vertical axis the specific ratio L, against time on the horizontal axis, as in the graph of Figure 2. Thus, the hori'zontal axis is at L=l.~, with operation above this axis line being in the lean region and operation below it in the rich region. The sensor responsiveness range is indicated by the dashed lines at, respec-tively, L=0.985 and 1.015. Assume that it is desired to operate the engine at the rich condition outside the sensor response range, which preselected rich condition is indicated by the dashed line horizontal axis ~-R. Starting at the vertical axis it is seen that the engine is operating at the desired A/F ratio. At the time ta timer A has reached ~ the end of its timing cycle and operates the air-fuel ratio control mechanism towards lean. At time tb stoichiometric conditions have been attained and this actuates timer B to actuate its drive motor and operate the air-fuel ratio control mechanism for a given time in-terval which is calibrated for the particular engine involved, so that at time tc the 3~v~
desired rich ~/F ratio along axis R-R has been atta:ined.
Immediately after time tc, as indicated by the graph of Figure 6, the stoichiometry of the air-fuel mixture rnay change for one or more of a varie-ty of reasons, such as a change in load, a change in fuel composition or any other unexpected or var.iable condition (such as pressure or atmosphere ternperature change, or exhaust back pressure change, etc.).
This causes a drift deeper into the rich range because the actual A/F ratio and/or the stoichiometric ratio is changing.
10 The present invention permits tracking of changes in stoi-chiometric ratio. ~owever, at time t4, timer A has completed its timing sequence and so actuates drive lean motor 48 to adjust the control mechanism 42 towards the lean condition, which it continues to do so until the stoichiometric condition 15 is sensed by the sensor which triggers the sequence as above-described to operate the air-fuel ratio metering device a preselected amount back towards the rich condition along the axis R-R. The next time sequence tl shows steady state operation of the engine with close adherence to -the 20 sclected ~/F ratic~ However, after -the next adjustment cycle ending at td~ due to unforeseen or variable conditions, the engine starts moving in the lean direction, so much so that ~t te it attains stoichiometric condi-tlons. This self-atta.ined stoichiometric condition will trigger the signal E
25 in the same manner as if the stoichiometric condi-tion were imposed by operakion of the ratio control mechanism towards lean, and initiate the sequence of backing off the val~e towards the rich direction a preselected amount until operation 3~
along the A/F axis R-R is attained. Figure 5 shows that t'~e sequence after te resumes normal operation. It will be noted that the normal time interval tl bet~teen operation at the reference points i.s foreshortened in the time interval t2 because the engine attained the lean condition before it would have been imposed by timer A and its associated drive lean motor 48. At time te the sequence also resets timer A
so that the next follo~Jing sequence occurs at the normal preselected time interval tl.
In actual operation, time interval tl may conveniently be selected to be about 1-10 minutes, preferably about 3-5 minutes and the time interval of one half t3, during which the ratio control mechanism is driven into the rich range, may conveniently be selected from about 0.1 to 5 seconds.
Thus, the cumulative time the air-to-fuel ratio is set at the second (imposed by the positioning means) value is about at least twelve times greater than the cumulative time it is set at the first (reset means imposed) value. Obviously, any time per.iods suitable for the particular device involved may be selected. ~y opening a given valve or adjusting screw or other Aevice having a set speed of travel for a set interval in time, the amount of opening (or closing) time necessary to select a desired A/F ratio may readily be determined in each case. Alternatively, displacement or location sensors may be utilized to control the amount of movement. The respective -time intervals tl an~ t3 are not necessarily drawn to scale in Figure 6, and in fact, the time intervals tl are usually relatively much larger than the time intervals t3 illustrated in Figure 6. Thus, if the most efficient mode Qf operation for a given engine or other device is along the axis R-R~ it will be seen that the cumulative time of excursions away from R-R in order to find the stoichiometric reference point in return from it is quite small relative to the cumulative time of operation along the desired axis R-Ro In fact, practical experience with natural gas fired engines has shown that the periodic setting of a stoichiometric or lean reference point does not appreciably affect the overall operation of the engine.
Further, utilization of the invention appears to provide a lS practical fuel savings. This is because natural gas engines often operate for exten~ded periods of time in remote areas, such as pipeline pumping stations, and are not continuously attended. Thus, if the engine requires a certain rich A/F
ratio to continue operating, such an engine, operating without beneEit of -the present invention, will be set by the operator to a condition which is somewhat richer -than the ideal A/F ratio. This is done to allow a safety margin in case transient conditions, load changes or the like cause the engine to drift towards the lean condition. Thus, the engine is normally opera~ing richer than is necessary, with concomitant excess fuel consumption. ~7ith the present invention, the engine may be set to o2erate for the vast majority of its time along precisely the ideal A/F ra-tio with the assurance that the invention will maintain the ratio.
Although the foregoing description has been made speci.ically with reference to operation at a rich A/F, it obviously applies equally to operation a~ a lean A/F. For example, operation could be set along the A/F ratio identified in Figure 5 by horizontal axis ~-L. This could be attained by simply making suitable modifications to the diagram of Figure 4 so that air-fuel ratio control mechanism 42 would periodically be operated in the rich direction from a setting along axis L-L towards stoichiometric~ to find a reference point and then could be reset for a selected drive interval to a lean setting. Obviously, means such as an adjustable timer may be provided to perlnit selec-tion of the duration of the drive interval.
Control oE -the A/F ratio is not only important to maintain engine ef~iciency and smooth running, but is also important to en~ance the efficiency of a ca-talyst which may be utilized in the exhaust gas line to purify the exhaust gas. Such catalysts, which may be used in single or multiple stages, are ernployed to reduce nitrogen oxides to nitrogen and/or to oxidize unburnt hydrocarbons and carbon monoxide to water and carb~n dioxide. r~hus, the selection of a speci~ic A/F ratio will be carried in a manner kno,Jn to those skil1ed in the ar-t -to accommodate not only enyine efficiency but catalyst efEiciency. Oxidation catalysts SllCh as those shown in U.S. Patent 3,565,830, three-way catalysts such as those shown in U.S. Patent 4,157,316 and non-s~lective NO~ abatement ca-talysts such as those shown in U.S. Patent 3,118,727 (all these patents being assigned to the assignee of this application) may be used singly or in combination to treat the exhaust gases.
In order to reduce, by use of a non-selective nitrogen oxides reduction process, the nitrogen oxides (NOX) in the exhaust of a natural gas fired engine, the engine carburetion s~stem must be adjusted so that the engine runs slightly on the rich side of stoichiome-tric. There must be a controlled excess of the natural gas fuel over stoichiometric in the Euel-air mixture fed to the engine so that the NOX in the exhaust can be catalytically reduced.
The exhaust gas emanating from the engine is passed through a catalytic reactor in which the NOX is reduced, ~robably according to the following reactions:
( ) 2 ~52 ~ NO ~ H2O
- AIR-To-FUEL RATIO
Background o~ the Invention . . .
The present invention relates to a means and me~hod for controlling the air-to-fuel ratio of a combustible mixture fed to a eombustion device. The invention is broadly applicable to sueh purpose and is speeifically useful in adjusting the air-to-fuel ratio of the eombustible mixture fed to an internal eoinbustion engine or to a catalytie combustor.
The prior art is replete with schemes for controlling air-to-fuel ratios, in particular for controlling the air-to-fuel ratio of the com~ustible mixture fed to an internal combustion engine. Often, the purpose of controlling the air-to-fuel ratio is to enhanee the operation of a catalytic exhaust gas purification deviee while maintaining aeceptable levels of engine performanee and efficiency. U.S. Patent 4,202,301, assigned to the assignee of this application, diseloses an air-to-fuel ratio control meehanism which operate~ in partial response to a eontrol circuit whieh, in turn, is responsive to the output of an oxygen sensor mounted in the exhaust line of the engine. This type of arrangement is well-known in the art, and is often referred to as a "elosed-loop" operation in which the carburetor or other air-fuel metering device is regulated by a eon-trol means which receives, as an input to it, a signal eorres-ponding to the presenee of oxygen in the engine exhaust gas, as sensed by the sensor.
U.S. Patent 4,019,474 discloses apparatus which comprises a detector for detecting the density of one component, for example oxygen, in the exhaus-t gases from an internal cornbustion engine for the purpose of regulating the air-to-fuel ratio.
The regulation is basecl on the detected value of the component in such a manner that the air-to-fuel ratio approximates the theoretically correct air-to-fuel ratio, i.e., the stoichiome~ric ratio.
U.S. Patent 3,986,352 discloses a fuel control for an engine equipped with a catalytic conver-tor which engine is normally operated "closed-loop" with a feedback signal from an air-fuel ratio sensor in the engine exhaust. As illustrated in the figure of the patent, an exhaust gas sensor produces an output voltage which exhibits a great rate of change in response to composition changes when operation is in the vicinity of the stoichiometric air-fuel ratio. The signal generated by the sensor passes through a control unit and ultimately influences the air-fuel ratio con-trol means of a carburetor. A relatively inexpensive and commercially available zirconia-type oxygen sensor displays this characteristic of showing, in the vicinity of a stoichiometric air-to-fuel ratio, a large change in the voltage of the output signal with change in the air-to-fuel ratio. ~owever, its sensitivity to chanye in the air-to-fuel ratio diminishes rapidly as -the air-to-fuel ratio moves away from stoichiometric, , -2-B
either to the lean or -the rich side. For this rPaSon/ if it is desired to run either rich or lean a significant distance away from stoichiometric i~ is not feasible, with a ~irconia type oxygen sensor, to control the air-to-fuel ratio at a selected value dif~ering significantly from stoichiometric.
This inherent limitation of oxygen (or other gas component) sensors is not a problem with conventional internal combustion engines, such as automobile engines, which are e~ui~ped with the so-called three-way conversion catalysts utilized to purify the exhaust gas. Three-way conversion catalysts of the type disclosed in U.~. Patent 4,157,316, assigned to the assignee of this application, are typically used to treat exhaust gases by substantially simultaneously o~idizing carbon monoxide and unburned hydrocarbons and reducing nitrogen oxides to nitrogen. ~or most efficient operation of these catalysts, the engine should be operated at or very close to stoichiometric air-to-fuel conditionsn Accordingly, a conventional zirconia or other sensor is useful since it is sensitive to changes in the air-fuel ratio range about stoichiometric conditions. Accordingly, the reference signal generated by the sensor can be utilized to make adjustments to the air-to-fuel ratio control of the carburetor or fuel injection device so as to hold operation at or very close to stoichiometric.
~lowever, for certain applications, it is desired to run either on the rich or on the lean side of stoichiometric at an air-to-fuel ratio which is outside the sensitivity or -esponse range of available oxycJen or other ~as component sensors. For example, it is believed tha-t fuel economy can be increased or maximized under lean air-to~fuel ra~:io conditions, generally about 1 to 3 a:ir-to-~uel ra~ios lean of stoichiometric. Operation in this range would pr~clude the use of a closed loop system using an exhaust gas sensor which is sensitive only within a limited range about stoichiornetric.
In certain other applications it is desirable -to operate on the rich side of stoichiometrlc, outside the response range of conventional sensors. For example, na-tural gas fueled internal combustion engines such as the type utilized ln pipelir.es and oil fields, require maintenance of a rich A/F
ratio which lies outside the limited range of available, reasonable cost sensors.
While means exist for determining exhaust gas component concentration levels resulting from air-to-fuel ratios which lie outside the conventional sensor response range, such eclulpment is either very expensive, complicated or delicate, or all three, as cornpared -to sensors of the type described above, and therefore are not practical for utiliza-tion in rnost internal combustion engine or cataly-tic combus-tor appl:lcations. Whether used in a motor vehicle or in stationary e~uipment, such as a stationary internal combustion engine or a catalytic combustor, it would be desirable to be able to use the less expensive and relatively rugged sensor in lieu of more complicated, delicate and/or expens:ive sensors or analytical ec~uipment.
mC3t'' - ~ ~
It is accordingly an object of the presen~ invention to provide a method and means for controlling the air-to-fuel ratio at a selected value or values which may, but not necessarily are, ou-tside the responsiveness range of the conventional oxygen or other gas component sensor, w~ile nevertheless employing such a sensor as the exnaust gas sensing means.
It is a further object of the present invention to provide a method and means utilizing an exhaust gas component sensor for controlling the air-to-fuel ratio fed to a combustion device, such as an internal combustion engine or a catalytic combustor, without necessity of rapidly oscillating between rich and lean operation.
It is a further object of the present invention to utilize the signal generated from a conventional oxygen (or other gas component) sensor to operate a combustion device, eg., a natural gas fuel engine, at an air-to-fuel ratio dis-placed from stoichiometric; eg., rich of s-toichiometric, while reducing to a minimum or substantially eliminating "wrong side", eg., to lean of stoichiometric, excursions.
Yet another object oE the present invention is to provide a control system which opera-tes "open loop" for a proportion of operating time, i.e., ~ithout continuous adjustment of the air-to-fuel ratio.
Other objects and advan-tages of the invention will become apparent from the following description.
~`
Summar~ of the Invention .
In accordance wlth the present invention there is provided the comblnation of an air-to-fuel rati.o control system and a fuel burning mechanism, the fuel burning mechanism having an adjustable air-fuel proportioning device, a combustion chamber and an exhaust conduit se.rially inter-connected in flow communication whereby a selectively proportioned air-fuel mixture may be introduced from the proportioning device into the combustion chamber for com-bustion therein, and exhaust gases may be withdrawn therefrom through the exhaust conduitO The air-to-fuel ratio control system comprises sensor means positioned in the exhaust gas conduit and having a limited ranse of response to the level of a gaseous component in the exha~st gas to produce a reference signal corresponding to the level. Reset means are operatively connected -to the air-fuel proportioning device Eor periodically adjusting the air-to-fuel ratio -to a first value selected so as to result in a level of the component in -the exhaust gas, which level lies within -the response ~ ranye of the sensor, there~y periodically triggering a reEerence signal generated by the sensor means.
Positioning means are operatively connected to the pro-portioning device and are responsive to the reference signal to adjust the air-to-fuel ratio to a second value which deviates from the first value by a selected amount and which , _ 33~8 may, but does not necessarily, result in a level of the component in the exhaust gas lying outside the response range, whereby the air-to-fuel ratio is periodicall~ adjusted to the second value. The positioning means may be configured to adjust the air-to-fuel ratio -to either rich or lean of stoichiometric.
In one aspect of the invention, the sen~or rneans may ~e an oxygen sensor means, such as a ~irconia sensor, responsive to a range of oxygen level in the exhaust gas corresponding to operation about the stoichiometric air-to-fuel ratio and, the positioning means may be adjustable to enable selection of the amount of deviation from the first selec-ted value which is imposed on the air-fuel metering means by the positioning means.
In other aspects of the invention, the fuel burning mechanism may comprise a catalytic combustor or an in-ternal combustion engine and, in the latter case, an exhaust gas purification catalyst may be positioned in the exhaust conduit downstream of the sensor means.
~0 In accor~ance with another aspect of the invention, there is provided a method for controlling -the air-to-fuel ratio of a :Euel burning mechanism by utilizing the sensed level o.~ a component in the exhaust gas which permi-ts maintenance of the ratio at values which result in exhaust gas levels of the component outside the response range o~ sensor means employed to sense the component level, the combustion mechanism 31~
is one having an adjustable air-fuel proportioning device, a combustion chamber and an exhaust conduit seriall~ interconnected in flow cor~nunication whereh~ a select:ively proportioned ai.r-fuel mixture may be introduced from said proportioning device into said combustion chamber for combustion therein, and exhaust gases may be withdrawn therefrom through the exhaust conduit. The method comprises the following steps.
Periodically, the air-to-fuel ratio is adjusted to a first value selected to result in a level of said component in the exhaust gas which lies within the response range of sensor~
thereby periodically triggering a response range-reference signal generated by the sensor. The air-to-fuel ratio is adjus-ted in response to the reference signal in a direction o~posite to that employed to at-tain the first value and in an amount to attain a second value of the air-to-fuel ratio which deviates from the first value by a selected amount and which results in a level of the component in the exhaust gas wh:Lch i5 outside the sensor response range. As a result, the ~lir~to-fuel ratio is periodically adjusted to -the.second ~0 value in response to the periodic triggering of the reference slgnal.
In one embodiment the air-to-fuel ratio is adjusted in the lean direction to attain the first value and is adjusted in the rich direction to attain said second value; in another embodiment the air-to-fuel ratio is adjusted in the rich direction to attain the first value is adjusted in the lean direction to attain the second value.
/ ! _ ~ ~
,, , Brief Description of the Drawing Figure 1 i8 a graph showing on the vertical axis the output signal in millivolts of an oxygen sensor positioned in the exhaust gas emerging from a combustion chamber, plotted against the air.to-fuel specific ratio (as deflned below) of the combustible mixture fed to the chamber;
Figure 2 i9 a graph showing-on the vertical axis the air-to-fuel specific ratio of a combustible mixture feed to a combustion chamber, plotted against time, illustrating the operation of a prior art control system;
Figure 3 is a schematic electrical and mechanical block di.agram illus-crating one embodiment of the present invention comprising an internal combustion engine equipped with an air-to-fuel ratio con-trol system and utilizing a catalyst to -treat the exhaust from the engine;
Figure 4 is a schematic electrical and mechanical block diagram showing in somewhat greater detail the electrical circuitry portion of the embodiment illustrated in ~igure 3;
Figure 5 is a schematic electrical diagram of one embodiment oE electronic circuitry useable in the present invention; and Figure 6 is a graph showing on the vertical axis the air-to-fuel specific ratio of a combustible mixture fed to a combustion chamber, plotted against time, illustrating the operation of one embodiment of a control system of the B
present inven-tion.
Description of the Preferred Embodiments . _ As above stated, one of the objec-ts of the present invention is to enable the control of the air-to-~uel (sometimes below abbreviated as A/F ~ ratio at a selected setting outside the range of responsiveness of a state of the art oxygen or other gas component sensor. The response range of such a sensor is illustrated by the graph of Fiyure 1, in which there is plot-ted in millivolts on the vertical axis the output signal generated by a conventional zirconia-type oxygen sensor positioned in the untreated e~haust gas emanating f om an internal combustion engine.
On the horizon-tal axis there is plotted the ratio of the actual A/F ratio to the stoichiometric A/F ratio, which will be hereinbelow referred to as the air-to-fuel specific ratio- and is represented by the symbol L in the drawings and specification.
Re~ference to the specific ratio is a conventional usage because it is useful in avoiding con-fusion in making comparisons bctween different operations. For example, an ~/F ratio of ~0 1~.65 (weight of air to weight of fuel) is the stoichiometric ratio corre~ponding to the combustion of a hydrocarbon fuel with an avera~Je Eormula CHl 88. Fuels with differen-t carbon/hydrogen ratios wi~l require different A~F ratios to produce a stoichiometric mixture. The symbol L is thus used to represent the relationship of a par-ticular or actual A/F
rn-J/, - 10 -ratio to the stoichiometric A/F ratio. The actual A/F ratio is divided by the stoichiometric A/F ratio so that in this system L=l is a stoichiometric rnixture, L>l is a fuel-lean mixture and L~1 i9 a fuel-rich mixture. For example, at an S actual A/F ratio of 14.5 for a Clll 88 hydrocarhon fuel, L=14.5/14.65=0.9898 is a fuel-rich mixture.
- Referring now to Figure 1, the vertical axis at L=l.0 represents stoichiometric operation of an internal combustion engine and the graph shows that under these conditions the output of a zirconia type sensor in the exhaust gas stream will have a signal strength of about 400 millivol-ts. As shown by the graph of Figure 1, the curve of the output slgnal from the sensor has a steep slope in a relatively narrow range on either side of the stoichiometric A/F ratio ranging from about 900 millivolts at L=0.985 to somewhat less than 100 millivolts at J.=1.015. The shape of the curve varies somewhat with variations in engine operation. However, in general, the curve may have a very small slope outside the L-0.985 to 1.015 range, and it is readily apparent from the curve that it becomes difficult or impossible to obtain a reliable reading for values of L outside the range.
Conventional control systems of the closed loop type are intended primarily for catalytic exhaust gas purifica-tion using three way conversion catalyst which, as mentioned above, requires operation at s-toichiometric for ~ost e~ecti~Je purification of the e~haust gases. This is accompllshed by manipulating the ~/F ra-tio to rapidly osci]late about stoichio-metric. Such operation requires a precise and sensitive carburetor or fuel in~ection system with a control logic speci~ic ~or the characteristics of the particular engine to which the system is applied. Accordingly, such a control system is rather expensive. Such prior art operation is schematically illustrated in Figure 2, in which the specific ratio L is plotted on the vertical axis agains-t time on the horizontal axis. The horizontal axis L=l.0 represents s-toichiometric operation, with operation above the L=l.0 axis being in the lean region, and operation below the L=l.0 axis being in the rich region. The sensor responsiveness range is indicatecl hy the dashed horizontal lines at, respectively, ~=~.985 and 1.015. The prior art control system is adapted to generate a signal when the AjF ratio crosses stoichiometric at I.=lØ
Because the responsive range is so narrow it is not feasible to malntain conditions within the very narrow band between ~0 I,-0.9~5 and 1.015~ Therefore, it is attempted ;to maintain osclllatincJ rich-lean conditions along opera-ting line 0. The thre~ way conversion catalyst is capable of tolerating limited excursions into the rich and lean regions, which ~verage out to approximately stoichiometric operation.
Thus, it is desired that lean region operation outside a very narrow band around stoichiometric, such as that bounded ~lCJ/: ~ - 12 -by the area abca of Figure 2, will be compensated for by subsecfuent rich area operation in the area bounded by defd.
Since the sensor response range is limited, the conditions as sensed by the sensor are represented by the dashed sensor line S. The system operates as follows. Assume that the carburetor or other air fuel proportioning device is moving in the lean direction along the operating line O and crosses L=l.0 at time to. At points Pl,- P2 and P3, the sensor senses a change between rich and lean. Starting at time tl, the system will initiate a change of the carburetor or other air-fuel proportioning device to move away from lean towards the rich direction for a selected interval of time tb at a selected rate or rates of movement. At time t2 the direction of the carburetor or other fuel proportioning device is reversed, to move in the rich direction for a time interval tc, at a selected rate or rates of movement. At the end of the time interval tc, at time t3, the carburetor or other device is moved back towards the lean condition to repeat the cycle.
This type of control cycle is discussed in SAE (Society of Automotive Engineers) Paper "Development of the Volvo Lambda-Sond System" by Gr~1ne T. Engh ancl Stephen ~allman, Paper 770295, presented at the International Automotive Engineering Con~ress and Exposition, Cobo Hall, Detroit February 28-March 4, 1977. See Figure 23 of the paper.
Wit'n this system, the ex-tent of the respective excursions into the rich and lean regions can not be determined ~y the sensor and conditions may be such as to cause an excursion, for example, along path a'b'c' into the rich region or along d'e'f' into the lean region. Of course, a rich excursion may not necessarily be compensated for by a corresponding lean excursion and extreme excursions may well exceed the excursion tolerance of the three way conversion catalyst.
As a result, noxious components of the exhaust gas will not be as effectively treated.
The rapid oscillating system is nonetheless useful for three way conversion catalysts on engines burning liquid hydrocarbon fuel, i.e., gasoline. ~owever, -the present invention not only permits better control and operation at a selected A/F ratio which may be significantly rich or lean of stoichiometric, but is readily adapted for use with a gaseous fuel device, which lacks the quick fuel-flow response time provided by a liquid fuel device. If the prior art æystem o~ Figure Z were used with a gaseous fuel, larger excursion~ along a'b'c' and d'e'f' of operating line O' wouLd result and detrac-t from efficient catalytic treatment.
In contrast to the oscillating control system, the present invention also permits substantial periods of "open loop"
operation during which the control system is not actively adjusting the A/F ratio.
Referring now to Figure 3, there is shown a schematic rendition of one embodiment of the presen-t invention in which an internal combustion engine 2, which may be an Otto hl~3~
Cycle na-tural gas-fueled internal combustlon enyine, i5 suppli''d with air and natural gas as a fuel through, respectively, lines 4 and 6. ~ fuel contro:L valve 8 is positioned in line 6.
Lines 4 and 6 form part of a carburetor 10, T~lhich comprises an air--fuel proportioning device generally indicated at 12, ~hich :Eeeds a combustible air-fuel mixture at a selected A/F
rat:io via line 14 into engine 2. Engine 2 has an exhaus-t gas li.ne 16 r 16a, 16b through which the combustion exhaust gases pass. A sensor 18, of the type having a limi-ted range of response as illustrated in the graph of Figure 1, is interposed in the exhaust line between segments 16 and 16a. A catalyst 19 is in the exhaust line, to purify the gases before they are discharged via l:ine seyment 16b. Any suitable catalyst may be employed.
The output si~nal of sensor 18 is transmitted via electrical connector 20 to a control unit 22 which comprises a reset means 22a and a positioning means 22b. The electrical output Erom reset means 22a is transmitted via electrical connector ~4a, 26 to operate fuel ccntrol valve 8. The elect.rlcal ou-tput Erom positioni.n~ means 22b is also transmi~ted7 v:la electri:cal connector 24b, 26, to operate fuel control valve 8.
In the embodiment illustrated in Figure 3, fuel control valve 8 serves as the adjusti.ny means of an air-fuel ratio meterin~ device by adjus-ting -the proportion of fuel relative to air which is fed into carburetor 10. Obviously, any m~ 15 -suitable ai.r-fuel ratio proportioning device such as a carhuretor or fuel injection system may be employer.l, and an appropriate drive mechanism may be connected to operate the adjustrnent screws on a carburetor or the controls of a fuel injection device to ad]ust the A/F ratios as taught by the inven-tion.
Before describing the operation of the embodiment illustrated in Figure 3, some additional details of one form o~ construction :in accordance with the invention will be described with re~erence -to the schematic diagram of Figure 4, in which an internal combustion engine 2' is supplied with a combustible air-fuel mixture via line 14' and e~haust gases are discharged through exhaus-t 16', 16'' and 16a', passed through a ca-talyst 19', and finally discharged via line segment 16b'. An oxygen sensor 18' has its probe end disposed within exhaust line 16' and in response to the oxygen level sensed in the exhaust gas generates an output signal Eo which is transmitted through a suitable electrical connector 21 to a comparator 28.
A reEerence signal Rr is also fed through a suitable electrical connector 25 from a reEerence source 30 ~o co~parator 28. In the case illustrated, reference source 30 may be adjusted so that reference signal Er has a value of ~00 m.i:Llivolts, corresponding to stoichiometric operation :Eor the case illustrated in Figure 1. Comparator 28 is connected by an electrical connector 32 to -timer B
which .is in turn connected via electrical connector 3~ to a mcJ/,~ 16 -,,~: . `..
dri.ve rich motor 36 which is opera-tivel~ connected via connector means 38 to air-fuel ratio rneterin~ device 42. A
reset connector 44 connects the output of timer B to a tirne~
which in turn is connected via electrical connector ~6 to a drive lean motor 48. Drive lean motor 48 is opera-tively connected via connector means 50 to air-fuel ratio metering device 42.
In operation, assume that internal combustion engine 2' is running rich. This would be the normal, desired condition, for example, for a natural gas fueled internal combustion engine. Timer A is running and is set for a preselected interval, say, five minutes, and when the five minute interval is reached, timer A emits a signal through electrical connector 46 which operates drive lean motor 48 to move air-~uel ratio control mechanism 42 to a lean condition. This changes the exhaust gas condition and oxygen sensor 18' generates its output signal E~ as the condition o~ the exhaust gas changes to provide an oxygen level which falls w.~th:in the responsive range of sensor 18'.. When the transmitted output si~nal Eo becomes less than the ~00 milLivolt reference signal Er~ which will occur when L crosses the 1.0 line moving in the lean direction as shown in Figure 1, comparator 28 generates a signal El which is transmitted through electrical connector 32 and triggers an outpu-t signal E2 which operates the drive motor 36 -to drive the air-fue-l mcJ/ - 17 -ratio proportionlng device 42 towards the rich direction for a preselected in-terval of time, say, for :I second. Alternativel~, ins-tead of a timed drive, means -to move the adjustrnent means of such a propor-tioning device, eg., the set scre-" o~ a carburetor, a selected distance as sensed by a location or displacement sensor, may be utilized. Signal E2 is also transmitted through connector 44 to timer A to reset timer A
to 2ero in order to re-start the -Eive minute interval of timer ~. When the five minute interval measured by timer A
has run, the sequence starts over again. Thus, it is seen by periodically, in this case every five minutes, adjusting the air-fuel ratio control mechanism 42 to change the air-fuel ratio towards stoichiometric (in this case, towards a lean condition) a signal is generated when a selected point (in this case, stoichiometric) is reached which causes the air-fuel ratio metering device to be operated a se].ected amount away from -the selec-ted point, in this case, towards the rich condition. Thus, the temporarily and periodically lnduced sto:ichiometric condition serves as a reference point :[rom which, by providing an appropriate drive interval of dr.Lve r:Lch motor 36, a preselected adjustment can be made to an~ deslred rarge within the rich area of operation. Obviously, reference signal Er could conveniently be set at any value between about 100 and 900 millivolts to establish a reference siynal anywhere within the responsive range of the sensor rn~ - - 18 -18'. In this manner, the sensor 18' may be u~ilized to control the air-fuel ratio se-t for any value, rich or lean, even though the value is outside ~he responsiveness ranye of the sensor 18'.
With reference to ~igure 3, it is seen that the output signal Eo will be transmitted from sensor 18 via line ~0 to positioning means 22b and when it exceeds the preselected reference signal positioning means 22b (corresponding to drive motor 36 and its associated initiators) will adjust fuel control valve 8 by opening it a preselected amount to shift the A/F ratio towards the desired, preselected rich condition. Reset means 22a, corresponding to drive ~e~
motor 48 and its associated timer A, will periodically at a selected interval move fuel valve 8 towards the closing direction -to drive the A/F ratio towards the lean direction.
An appropriate setting can be made of reference 30 (Figure 3) to cause comparator 28 to initiate the drive rich sequence ~rom a selected reference point to cause positioning means 22b to operate Euel control valve 8 a preselected amount in the opening direction, thereby re-establishing the desired A/F ratio.
The control unit portion (see Figure 3) of a system ~enerally conforming to that broadly illustrated in Figure 4 is illustrated in some detail in Figure 5. The signal 2S generated frorn oxygen sensor 50 and passed throuyh a buffer amplifier 52 is output signal Eo~ which has a value that is a function of the amount of oxygen in the exhaust gas contacted by sensor 50. ~he strength of sic~nal Eo i5 inversel~ proportiona~
to the oxygen content of the exhaust gases and is applied as one of two inputs -to a comparator circuit generally indicated at 54. A reference circuit 56 applies a reference signal of, for example, 400 millivolts as the second input to ~omparator circuit 54. Obviously, any desired reference signal may be selected. Given the constraints of the conventional oxygen sensor, as described above, a reference signal between about 100 and 900 millivolts would be selected for the reference signal. A different sensor, say a carbon dioxide sensor, which might have a different responsiveness range would require the selection of an appropriate reference signal within its response range.
~ hen the output signal Eo falls below the setting, say 400 millivolts, of the strength of the signal provided by reference circuit 56, as would occur if the engine were to run lean or if the oxygen sensor 50 were to fail, comparator ~0 54 provides an output signal El transi-tion from plu5 12 to 0 volts. The signal El is applied to timer 58, a 0.1 second to 10 second adjustable tirner, and -to nand gate 60 to start a timing cycle of timer 58. The output signal E2 of timer 58, a plu9 12 volt signal, is applied to drive rich relay 62 and to timer 64 through the monostable multivibrator comprised of nand gates 66 and 68 and to tirner 64, through inver'cer 70. The output signal E2, acting through rich drive relay 62, drives the air-fuel ratio proportioning device ~not shown in Figure 4, but corresponding to 42 in Figure 3) towards a rich condition until output signal Rl is 12 volts and timer 58 times out.
When timer 58 times out, and output signal Eo of sensor 50 is greater than 400 millivolts, signifying a rich A-F
ratio engine running condition, signal E2 switches from 12 volts to 0 volts. This transition of signal E2 starts timer 64 through nand gates 66 and 68, connected as a monostable multivibrator, and inverter 70. When signal E2 attains zero, it also serves to turn off rich drive relay 62. Timer 64 is adjustable for a.l to 10 minute time delay and when it is timing, and oxygen sensor 50 output signal Eo indicates a rich enyine operatiny condition, the air-Euel ratio metering device is not being adjusted by the system, i.e., is inactive.
~ fter a set time, timer 64 times out and signal E3 changes ~rom plus 12 volts to 0 volts and passing through n~nd gate9 60, 72 and inverters 74, 76, energizes lean drive relay 7B and prepares timer 58 to start timing. When sensor 50 ~enses lean conditions Erom the oxygen level in the exhaust gas, its output siynal Eo switches from plus 12 volts to 0 volts and -the cycle as described above repeats.
3~
In the specific embodiment illustrated in Figure S, buffer amplifier 52 and comparator 5~ pin number identifications are those of National's quad operational amplifer LM-32~N.
Inverters 70, 74 and 76 are RCA's ~ex Buf~er CD-4049AE, nand gates 66, 6~, 60 and' 72 are RCA's Quad Nand Gate CD-4011A~, and the timers 64 and 58 are RCA's Timers CA-~88G.
The operation of the invention m~y be better understood with reference to Figure 6, which plots on the vertical axis the specific ratio L, against time on the horizontal axis, as in the graph of Figure 2. Thus, the hori'zontal axis is at L=l.~, with operation above this axis line being in the lean region and operation below it in the rich region. The sensor responsiveness range is indicated by the dashed lines at, respec-tively, L=0.985 and 1.015. Assume that it is desired to operate the engine at the rich condition outside the sensor response range, which preselected rich condition is indicated by the dashed line horizontal axis ~-R. Starting at the vertical axis it is seen that the engine is operating at the desired A/F ratio. At the time ta timer A has reached ~ the end of its timing cycle and operates the air-fuel ratio control mechanism towards lean. At time tb stoichiometric conditions have been attained and this actuates timer B to actuate its drive motor and operate the air-fuel ratio control mechanism for a given time in-terval which is calibrated for the particular engine involved, so that at time tc the 3~v~
desired rich ~/F ratio along axis R-R has been atta:ined.
Immediately after time tc, as indicated by the graph of Figure 6, the stoichiometry of the air-fuel mixture rnay change for one or more of a varie-ty of reasons, such as a change in load, a change in fuel composition or any other unexpected or var.iable condition (such as pressure or atmosphere ternperature change, or exhaust back pressure change, etc.).
This causes a drift deeper into the rich range because the actual A/F ratio and/or the stoichiometric ratio is changing.
10 The present invention permits tracking of changes in stoi-chiometric ratio. ~owever, at time t4, timer A has completed its timing sequence and so actuates drive lean motor 48 to adjust the control mechanism 42 towards the lean condition, which it continues to do so until the stoichiometric condition 15 is sensed by the sensor which triggers the sequence as above-described to operate the air-fuel ratio metering device a preselected amount back towards the rich condition along the axis R-R. The next time sequence tl shows steady state operation of the engine with close adherence to -the 20 sclected ~/F ratic~ However, after -the next adjustment cycle ending at td~ due to unforeseen or variable conditions, the engine starts moving in the lean direction, so much so that ~t te it attains stoichiometric condi-tlons. This self-atta.ined stoichiometric condition will trigger the signal E
25 in the same manner as if the stoichiometric condi-tion were imposed by operakion of the ratio control mechanism towards lean, and initiate the sequence of backing off the val~e towards the rich direction a preselected amount until operation 3~
along the A/F axis R-R is attained. Figure 5 shows that t'~e sequence after te resumes normal operation. It will be noted that the normal time interval tl bet~teen operation at the reference points i.s foreshortened in the time interval t2 because the engine attained the lean condition before it would have been imposed by timer A and its associated drive lean motor 48. At time te the sequence also resets timer A
so that the next follo~Jing sequence occurs at the normal preselected time interval tl.
In actual operation, time interval tl may conveniently be selected to be about 1-10 minutes, preferably about 3-5 minutes and the time interval of one half t3, during which the ratio control mechanism is driven into the rich range, may conveniently be selected from about 0.1 to 5 seconds.
Thus, the cumulative time the air-to-fuel ratio is set at the second (imposed by the positioning means) value is about at least twelve times greater than the cumulative time it is set at the first (reset means imposed) value. Obviously, any time per.iods suitable for the particular device involved may be selected. ~y opening a given valve or adjusting screw or other Aevice having a set speed of travel for a set interval in time, the amount of opening (or closing) time necessary to select a desired A/F ratio may readily be determined in each case. Alternatively, displacement or location sensors may be utilized to control the amount of movement. The respective -time intervals tl an~ t3 are not necessarily drawn to scale in Figure 6, and in fact, the time intervals tl are usually relatively much larger than the time intervals t3 illustrated in Figure 6. Thus, if the most efficient mode Qf operation for a given engine or other device is along the axis R-R~ it will be seen that the cumulative time of excursions away from R-R in order to find the stoichiometric reference point in return from it is quite small relative to the cumulative time of operation along the desired axis R-Ro In fact, practical experience with natural gas fired engines has shown that the periodic setting of a stoichiometric or lean reference point does not appreciably affect the overall operation of the engine.
Further, utilization of the invention appears to provide a lS practical fuel savings. This is because natural gas engines often operate for exten~ded periods of time in remote areas, such as pipeline pumping stations, and are not continuously attended. Thus, if the engine requires a certain rich A/F
ratio to continue operating, such an engine, operating without beneEit of -the present invention, will be set by the operator to a condition which is somewhat richer -than the ideal A/F ratio. This is done to allow a safety margin in case transient conditions, load changes or the like cause the engine to drift towards the lean condition. Thus, the engine is normally opera~ing richer than is necessary, with concomitant excess fuel consumption. ~7ith the present invention, the engine may be set to o2erate for the vast majority of its time along precisely the ideal A/F ra-tio with the assurance that the invention will maintain the ratio.
Although the foregoing description has been made speci.ically with reference to operation at a rich A/F, it obviously applies equally to operation a~ a lean A/F. For example, operation could be set along the A/F ratio identified in Figure 5 by horizontal axis ~-L. This could be attained by simply making suitable modifications to the diagram of Figure 4 so that air-fuel ratio control mechanism 42 would periodically be operated in the rich direction from a setting along axis L-L towards stoichiometric~ to find a reference point and then could be reset for a selected drive interval to a lean setting. Obviously, means such as an adjustable timer may be provided to perlnit selec-tion of the duration of the drive interval.
Control oE -the A/F ratio is not only important to maintain engine ef~iciency and smooth running, but is also important to en~ance the efficiency of a ca-talyst which may be utilized in the exhaust gas line to purify the exhaust gas. Such catalysts, which may be used in single or multiple stages, are ernployed to reduce nitrogen oxides to nitrogen and/or to oxidize unburnt hydrocarbons and carbon monoxide to water and carb~n dioxide. r~hus, the selection of a speci~ic A/F ratio will be carried in a manner kno,Jn to those skil1ed in the ar-t -to accommodate not only enyine efficiency but catalyst efEiciency. Oxidation catalysts SllCh as those shown in U.S. Patent 3,565,830, three-way catalysts such as those shown in U.S. Patent 4,157,316 and non-s~lective NO~ abatement ca-talysts such as those shown in U.S. Patent 3,118,727 (all these patents being assigned to the assignee of this application) may be used singly or in combination to treat the exhaust gases.
In order to reduce, by use of a non-selective nitrogen oxides reduction process, the nitrogen oxides (NOX) in the exhaust of a natural gas fired engine, the engine carburetion s~stem must be adjusted so that the engine runs slightly on the rich side of stoichiome-tric. There must be a controlled excess of the natural gas fuel over stoichiometric in the Euel-air mixture fed to the engine so that the NOX in the exhaust can be catalytically reduced.
The exhaust gas emanating from the engine is passed through a catalytic reactor in which the NOX is reduced, ~robably according to the following reactions:
( ) 2 ~52 ~ NO ~ H2O
(2) 2NO t 2H2 ~ 2 H2O
(3) NO2 ~ CO and/or > NO -~ CO2
(4) 2NO -~ 2CO _ N2 ~ 2CO2 mcJ/~` - 27 -The control system of the present invention is particularly useful in controlling the air-to-fuel ratio a-t a ric'n level selected to enhance operation of the catalytic abater. Such a system has, as described above, other advantages, such as fuel economy, because an A/F ratio which will optimize MOX
abatement and engine performance can be more closely maintained.
EXAMPLE
The following engine is supplied with an A/F ratio control system in accordance with the present invention:
Engine. Waukesha L7042GU
HP- ~ominal; 1000 Hp at 1200 RPM. Operating:
58Q Hp at 750 RPM.
Exhaust Pipe Connection: 8" or 10"
Fuel Composi-tion: Methane89.37%
Ethane 6.66~
Propane1.48%
Butane .26%
Pentane .04 Hexane .Q3 ~0 Carbon Dioxide .99%
Mitrogen 1.15 Oxygen .01%
Exhaust Gas Flowrate: 1298 SCFM a-t 60DF ambient temperature, at 900 RPM engine operation Exhaust Gas Temperature: 957F
Available Pressur~ Drop: 10 inches w.c.
The exhaust pipe connection leads to a catalytic con~ertor having a honeycomb type monolithic catalyst disposed therein.
The catalys-t is 38 inches in diameter and 3 inches in depth and has 300 rectangular cross-section gas flo~.~ passages per S square inch. The mo~olithic honeycotnb is comrised of cordierite and has an alumina (predominantly gamma alumina) coating on the surface thereof. There is distended upon the alumina coating catalytic metal comprising platinum, rhodium and ruthenium in a weight ratio of 5:2:1. The total precious metal (platinum, rhodium and ruthenium) loading on the catalyst is between 40 and 50 grams of precious metal per cubic foot cataly-tic monolithic honeycomb. The catalyst is housed within a convertor 60 inches long to which the exhaust gas line is connected. Within the convertor housing is a distribution plate to aid in distributing the exhaust gas flow across substantially the entire face of the catalyst.
The monollthic honeycomb catalyst is substantially disc shaped with its gas flow passages extending par~llel to each other from the substantially circular inlet face to the 2~ subst,antially circular outlet face thereof.
The followiny table shows the exhaust gas analysis honeycolnb as Eollows.
Analysis A - Raw exhaust gas upstream of the catalyst.
Analysis B - Treated exhaust gas downstream of the catalyst.
Analysis C - P~aw exhaust gas upstream of the catalyst with the engine operated at a selected A/F ratio maintained by a control system in accordance with khe present invention.
Analysis D - Treated exhaus-t gas downstream of the catalyst with A/F ratio maintained by the same control system as in Analysis C.
.
Volume Percent (~ vol) or Volume Parts Perr~llion (pp~) Spindt* AfF
Analysis Ratio NOx C~ ~drocarbons A ~.0 660 p~mv 3.0% vol 1750 ppmv B 15.0 75 ppmv 2.7% vol 1250 ppmv (88.6~ con- 10% con- (28~ con-version) version) version) C 16.5 2790 ppmv g706 ppmv 1100 ppmv D 16.5 183 p~?nv 870 ppmv 650 ppmv (93% con- (90% con- (41~6 con-version) version) version~
*Spindt P/F ratio is an air-fuel ratio calculated in accordance with the me-thod in the article "Air/Fuel Ratios From Exhaust Gas Analysis"
by R.S. Spindt, SAE Paper 650507. This publication is incorporated by reference herein.
As shown by the above example, -the control system of the present invention permits maintenance of a selected air-to-fuel ratio even at values substantially outside the response range of a conven-tional oxygen sensor, thereby enhancing the operation oE an exhaust gas puriEica-tion catalys-t as well as attaining good engine eEficiency. Note in Analysis C, Eor example, that the unburned hydrocarbons are substantially reduced as compared -to operation at the lower air-to-fuel ratio and that higher-conversion efficiency of the noxious components is obtained at the main-tained higher air-to-~uel ratio. Successful operation has also been attained with an o-therwise iden-tical catalyst con-taining platinum and rhodium 3~
in a weight ratio of 4:1 as the catalytlc metal~.
In addition to internal combustion englnes, the present invention is equally applicable to controlling the air-fuel ratio fed to catalytic combustors. Such catalytic combustors employ a catalyst, such as that shown in U.S. Patent 3,928,961, assigned to the assignee of the present application, to enable combustion of a fuel at a lower temperature than would occur with uncatalyzed combustion. Such operation has the benefit o~ avoiding or minimizing production of nitrogen oxides, which is an increasingly important consideration in maintaining air polluting s-tandards. Such combustors have numerous uses as prime heat sources as described, for example, in U.S. Patent 3,92~,961, assigned to the assignee of the present application.
While the invention has been described wi~h respect to speeific preferred embodiments, it will be apparent to one skilled in the art that numerous variations may be made to the embodiments without departing from the spirit and scope of the invention. For example, the periodic intervals between establishing the reference points in the vicinity of stoiehiometrie operation need not be, although they preferably are, regular i.e., of equal dura-tion. Reference to "a combustion ehamber" in the specification and claims is intet.ded to include a plurality of discrete chambers, such as ~5 the individual cylinders of a multi cylinder internal combustion engine.
abatement and engine performance can be more closely maintained.
EXAMPLE
The following engine is supplied with an A/F ratio control system in accordance with the present invention:
Engine. Waukesha L7042GU
HP- ~ominal; 1000 Hp at 1200 RPM. Operating:
58Q Hp at 750 RPM.
Exhaust Pipe Connection: 8" or 10"
Fuel Composi-tion: Methane89.37%
Ethane 6.66~
Propane1.48%
Butane .26%
Pentane .04 Hexane .Q3 ~0 Carbon Dioxide .99%
Mitrogen 1.15 Oxygen .01%
Exhaust Gas Flowrate: 1298 SCFM a-t 60DF ambient temperature, at 900 RPM engine operation Exhaust Gas Temperature: 957F
Available Pressur~ Drop: 10 inches w.c.
The exhaust pipe connection leads to a catalytic con~ertor having a honeycomb type monolithic catalyst disposed therein.
The catalys-t is 38 inches in diameter and 3 inches in depth and has 300 rectangular cross-section gas flo~.~ passages per S square inch. The mo~olithic honeycotnb is comrised of cordierite and has an alumina (predominantly gamma alumina) coating on the surface thereof. There is distended upon the alumina coating catalytic metal comprising platinum, rhodium and ruthenium in a weight ratio of 5:2:1. The total precious metal (platinum, rhodium and ruthenium) loading on the catalyst is between 40 and 50 grams of precious metal per cubic foot cataly-tic monolithic honeycomb. The catalyst is housed within a convertor 60 inches long to which the exhaust gas line is connected. Within the convertor housing is a distribution plate to aid in distributing the exhaust gas flow across substantially the entire face of the catalyst.
The monollthic honeycomb catalyst is substantially disc shaped with its gas flow passages extending par~llel to each other from the substantially circular inlet face to the 2~ subst,antially circular outlet face thereof.
The followiny table shows the exhaust gas analysis honeycolnb as Eollows.
Analysis A - Raw exhaust gas upstream of the catalyst.
Analysis B - Treated exhaust gas downstream of the catalyst.
Analysis C - P~aw exhaust gas upstream of the catalyst with the engine operated at a selected A/F ratio maintained by a control system in accordance with khe present invention.
Analysis D - Treated exhaus-t gas downstream of the catalyst with A/F ratio maintained by the same control system as in Analysis C.
.
Volume Percent (~ vol) or Volume Parts Perr~llion (pp~) Spindt* AfF
Analysis Ratio NOx C~ ~drocarbons A ~.0 660 p~mv 3.0% vol 1750 ppmv B 15.0 75 ppmv 2.7% vol 1250 ppmv (88.6~ con- 10% con- (28~ con-version) version) version) C 16.5 2790 ppmv g706 ppmv 1100 ppmv D 16.5 183 p~?nv 870 ppmv 650 ppmv (93% con- (90% con- (41~6 con-version) version) version~
*Spindt P/F ratio is an air-fuel ratio calculated in accordance with the me-thod in the article "Air/Fuel Ratios From Exhaust Gas Analysis"
by R.S. Spindt, SAE Paper 650507. This publication is incorporated by reference herein.
As shown by the above example, -the control system of the present invention permits maintenance of a selected air-to-fuel ratio even at values substantially outside the response range of a conven-tional oxygen sensor, thereby enhancing the operation oE an exhaust gas puriEica-tion catalys-t as well as attaining good engine eEficiency. Note in Analysis C, Eor example, that the unburned hydrocarbons are substantially reduced as compared -to operation at the lower air-to-fuel ratio and that higher-conversion efficiency of the noxious components is obtained at the main-tained higher air-to-~uel ratio. Successful operation has also been attained with an o-therwise iden-tical catalyst con-taining platinum and rhodium 3~
in a weight ratio of 4:1 as the catalytlc metal~.
In addition to internal combustion englnes, the present invention is equally applicable to controlling the air-fuel ratio fed to catalytic combustors. Such catalytic combustors employ a catalyst, such as that shown in U.S. Patent 3,928,961, assigned to the assignee of the present application, to enable combustion of a fuel at a lower temperature than would occur with uncatalyzed combustion. Such operation has the benefit o~ avoiding or minimizing production of nitrogen oxides, which is an increasingly important consideration in maintaining air polluting s-tandards. Such combustors have numerous uses as prime heat sources as described, for example, in U.S. Patent 3,92~,961, assigned to the assignee of the present application.
While the invention has been described wi~h respect to speeific preferred embodiments, it will be apparent to one skilled in the art that numerous variations may be made to the embodiments without departing from the spirit and scope of the invention. For example, the periodic intervals between establishing the reference points in the vicinity of stoiehiometrie operation need not be, although they preferably are, regular i.e., of equal dura-tion. Reference to "a combustion ehamber" in the specification and claims is intet.ded to include a plurality of discrete chambers, such as ~5 the individual cylinders of a multi cylinder internal combustion engine.
Claims (11)
1. The combination of an air-to-fuel ratio control system and a fuel burning mechanism, said fuel burning mechanism having an adjustable air-fuel proportioning device, a combus-tion chamber and an exhaust conduit serially interconnected in flow communication whereby a selectively proportioned air-fuel mixture may be introduced from said proportioning device into said combustion chamber for combustion therein, and exhaust gases may be withdrawn therefrom through said exhaust conduit;
said air-to-fuel ratio control system comprising:
sensor means positioned in said exhaust gas conduit and having a limited range of response to the level of a gaseous component in the exhaust gas to produce a reference signal corresponding to said level;
reset means operatively connected to said air-fuel propor-tioning device for periodically adjusting the air-to-fuel ratio to a first value selected to result in a level of said component in the exhaust gas, which level lies within the response range of said sensor means, thereby periodically triggering a response range-reference signal generated by said sensor means; and positioning means operatively connected to said propor-tioning device and responsive to said reference signal to adjust the air-to-fuel ratio to a second value which deviates from the first value by a selected amount, whereby the air-to-fuel ratio is periodically adjusted to said second value in response to the periodic triggering of said reference signal,
said air-to-fuel ratio control system comprising:
sensor means positioned in said exhaust gas conduit and having a limited range of response to the level of a gaseous component in the exhaust gas to produce a reference signal corresponding to said level;
reset means operatively connected to said air-fuel propor-tioning device for periodically adjusting the air-to-fuel ratio to a first value selected to result in a level of said component in the exhaust gas, which level lies within the response range of said sensor means, thereby periodically triggering a response range-reference signal generated by said sensor means; and positioning means operatively connected to said propor-tioning device and responsive to said reference signal to adjust the air-to-fuel ratio to a second value which deviates from the first value by a selected amount, whereby the air-to-fuel ratio is periodically adjusted to said second value in response to the periodic triggering of said reference signal,
2. The combination of claim 1 wherein said sensor means is an oxygen sensor means responsive to a range of oxygen level in the exhaust gas corresponding to operation about the stoichiometric air-to-fuel ratio and said second value of the air-to-fuel ratio results in a level of oxygen in the exhaust gas lying outside the sensor response range.
3. The combination of claim 1 wherein said positioning means is adjustable to enable selection of the amount of deviation from the first selected value which is imposed on said air-fuel metering means by said positioning means.
4. The combination of claim 2 wherein said positioning means is adjustable to enable selection of the amount of deviation from the first selected value which is imposed on said air-fuel metering means by said positioning means.
5. The combination of claim 3 or claim 4 wherein said fuel burning mechanism comprises a natural gas fueled internal combustion engine, the combination further includes an exhaust gas purification catalyst positioned in said exhaust conduit downstream of said sensor means, and said positioning means is configured to adjust the air-to-fuel ratio to a second value which is rich of stoichiometric.
6. The combination of claim 3 or claim 4 wherein said sensor means is an oxygen sensor means comprising zirconia whose responsiveness range embraces an oxygen level in the exhaust gas corresponding to operation about the stoichiometric air-to-fuel ratio, and said positioning means is configured to adjust the air-to-fuel ratio to a second value which is such as to result in an oxygen level in the exhaust gas which is outside the responsiveness range of said sensor.
7. The combination of claim 3 wherein said air fuel metering device includes adjustment means to change the air-to-fuel ratio setting of said metering device, said reset means comprises a firs-t drive means actuated by a resettable first timing means and operatively associated with said adjustment means to periodically drive said adjustment means to change the air-to-fuel setting of said metering device, and means to periodically reset said first timing means, and said positioning means comprises a second drive means activated by a second timing means and operatively associated with said adjustment means to change the air-to-fuel setting of said metering device in a direction opposite to that of said reset means.
8. The combination of claim 7 further including comparator means having input connectors and an output connector, said input connectors being connected, respectively, to a reference signal source and to said sensor to receive, respectively, a reference signal and the output signal of said sensor, and said output connector being connected to said second timing means to provide an actuating signal thereto upon said sensor output signal attaining a selected level relative to said reference signal.
9. A method for controlling the air-to-fuel ratio of a fuel burning mechanism by utilizing the sensed level of oxygen in the exhaust gas, which method permits maintenance of the ratio at values which may result in exhaust gas levels of oxygen outside the response range of sensor means employed to sense the oxygen level, said combustion mechanism having an adjustable air-fuel proportioning device, a combustion chamber and an exhaust conduit serially interconnected in flow communi-cation whereby a selectively proportioned air-fuel mixture may be introduced from said metering device into said combustion chamber for combustion therein, and exhaust gases may be withdrawn therefrom through said exhaust conduit, -the method comprising the steps of:
periodically adjusting the air-to-fuel ratio to a first value selected to result in a level of oxygen in the exhaust gas which lies within the response range of said sensor, thereby periodically triggering a response range-reference signal generated by said sensor;
adjusting the air-to-fuel ratio in response -to said reference signal in a direction opposite to that employed to attain said first value and in an amount to attain a second value of the air-to-fuel ratio which deviates from the first value by a selected amount, whereby the air-to-fuel ratio is periodically adjusted to said second value in response to the periodic triggering of said reference signal.
periodically adjusting the air-to-fuel ratio to a first value selected to result in a level of oxygen in the exhaust gas which lies within the response range of said sensor, thereby periodically triggering a response range-reference signal generated by said sensor;
adjusting the air-to-fuel ratio in response -to said reference signal in a direction opposite to that employed to attain said first value and in an amount to attain a second value of the air-to-fuel ratio which deviates from the first value by a selected amount, whereby the air-to-fuel ratio is periodically adjusted to said second value in response to the periodic triggering of said reference signal.
10. The method of claim wherein the second value results in a level of oxygen in the exhaust gas which is outside the sensor response range.
11. The method of claim 10 wherein the average time interval the air-to-fuel ratio is set at said first value is from about 0.1 to 5 seconds and the average time interval the air-to-fuel ratio is set at said second value is from about one to ten minutes.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US23507181A | 1981-02-13 | 1981-02-13 | |
| US235,071 | 1981-02-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183238A true CA1183238A (en) | 1985-02-26 |
Family
ID=22883985
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000396127A Expired CA1183238A (en) | 1981-02-13 | 1982-02-12 | Method and means for controlling air-to-fuel ratio |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS57151042A (en) |
| BR (1) | BR8200773A (en) |
| CA (1) | CA1183238A (en) |
| DE (1) | DE3204969A1 (en) |
| GB (1) | GB2093228A (en) |
| SE (1) | SE8200867L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4502444A (en) * | 1983-07-19 | 1985-03-05 | Engelhard Corporation | Air-fuel ratio controller |
| DE3920661A1 (en) * | 1989-06-23 | 1991-01-10 | Comuna Metall Vorrichtungs Und | Setting optimum air-fuel ratio for engine with catalytic exhaust unit - using measuring probe in exhaust line having voltage curve with stoichiometric ratio of combustion air-fuel of lambda at unity |
| US6260547B1 (en) * | 2000-02-01 | 2001-07-17 | Michael Spencer-Smith | Apparatus and method for improving the performance of a motor vehicle internal combustion engine |
| US6837233B1 (en) | 2002-11-04 | 2005-01-04 | Michael Spencer-Smith | System for enhancing performance of an internal combustion engine |
| GB201617349D0 (en) * | 2016-10-13 | 2016-11-30 | Johnson Matthey Public Limited Company | Oxidation catalyst for hydrocarbons produced by an internal combustion engine |
-
1982
- 1982-02-10 GB GB8203834A patent/GB2093228A/en not_active Withdrawn
- 1982-02-12 SE SE8200867A patent/SE8200867L/en not_active Application Discontinuation
- 1982-02-12 BR BR8200773A patent/BR8200773A/en unknown
- 1982-02-12 DE DE19823204969 patent/DE3204969A1/en not_active Withdrawn
- 1982-02-12 CA CA000396127A patent/CA1183238A/en not_active Expired
- 1982-02-13 JP JP2194482A patent/JPS57151042A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| BR8200773A (en) | 1982-12-21 |
| SE8200867L (en) | 1982-08-14 |
| GB2093228A (en) | 1982-08-25 |
| DE3204969A1 (en) | 1982-08-19 |
| JPS57151042A (en) | 1982-09-18 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4526001A (en) | Method and means for controlling air-to-fuel ratio | |
| US4024706A (en) | Method of improving the operational capacity of three-way catalysts | |
| US4240389A (en) | Air-fuel ratio control device for an internal combustion engine | |
| US4502444A (en) | Air-fuel ratio controller | |
| US6828156B2 (en) | Evaluating method for NOx eliminating catalyst, an evaluating apparatus therefor, and an efficiency controlling method therefor | |
| US5937634A (en) | Emission control for a gas turbine engine | |
| CA1105116A (en) | Oxygen sensor control system | |
| EP0306983B1 (en) | Electronic air-fuel ratio control apparatus in internal combustion engine | |
| US4072137A (en) | Air-to-fuel ratio adjusting system for an internal combustion engine | |
| US5822976A (en) | Method and system for controlling the amount of secondary air introduced into an internal combustion engine | |
| WO1998027322A1 (en) | METHOD OF DE-SULPHURATING ENGINE EXHAUST NOx TRAPS | |
| CA1183238A (en) | Method and means for controlling air-to-fuel ratio | |
| US5623824A (en) | Air-fuel ratio control system for internal combustion engine | |
| Engh et al. | Development of the Volvo Lambda-sond system | |
| US4793135A (en) | Method of detoxification of exhaust gas from an internal combustion engine using a catalytic system, and apparatus for performing the method | |
| US5243954A (en) | Oxygen sensor deterioration detection | |
| US4364356A (en) | Exhaust emissions control system | |
| JP3272465B2 (en) | Engine exhaust gas purification device | |
| US4030459A (en) | Multicylinder engine | |
| JP2000517022A (en) | Method and apparatus for controlling combustion equipment for catalytically purifying exhaust gas, and combustion equipment | |
| US4655181A (en) | Air-fuel ratio control system | |
| JPS6011663A (en) | Air/fuel ratio controller for internal-combustion engine | |
| CA1175211A (en) | Method for catalytic purification of combustion exhaust gases | |
| GB2169111A (en) | Air-fuel ratio control method for an internal combustion engine | |
| US4110978A (en) | Apparatus for purifying exhaust gas |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |