The Development of an Automobile Engine Control System

THE DEVELOPMENT OF AN AUTOMOBILE • ENGINE CONTROL SYSTEM Neal Laurance Research Staff, Ford Motor Company, Dearborn, Mz"chz"gan, U. S.A .

AaSTRAcr. ruring the past year, Fbr d i"'lotor Company in troduced tne f HSt multivar ia te control system for automooile eng ine control oased on microprocessor technology. Tnis paper will present an overview of tne development of this system. Two principle areas of effort are descriued, toe development of suitaole ,uicroprocessor technology for the autoootive environment, and the formulation of the engine control proolem in terms suitaole for cQnputer control. The latter area has resulted in the generation of several significant new tools for analysis of tnese systems. These include vehicle sLuulation luooels, engine data acquisition tecnniques, and optimization techniques.

i(Ei\"/ORffi. Automooiles; ComtJUter [-tul tivar iaole control SYSteIil3

control;

Internal

Combustion

Engines;

functlOn of vehicle speed and engine operating conditions, usually engine ~anifold vacuum but also accelerator position. The transmisslOn behavior affects tne speed/torque characteristics of the load a,jainst whiCh tne en::jine ~ust work, ana hence the whole operating regime of tne engine for a ,jiven drive scnedule.

ml'ROoucrION

As conventionally implemented, tne control var iables of an automobile eng ine are determined by several straigntforward control syste,ns. The timing of the spar k is controlled by the distrioutor whicn responds to engine speed, engine manifold vacuum (a signal clooely related to eng ine torque), and other operatlng variables such as tnrottle position an.:! engine coolant temperature. '! he air-fuel ~etering system, usually a carouretor, responds to driver demand througn the accelerator pedal linkage to the throttle, wnich controls the manifold vacuwn, and to toe en,Jine operatin-J regime, most notabl y the eng ine speed and temper a ture. In the years since tne enactment of emission control laws, anotner control element nas a~ared on toe engine, exhaust gas recirculation or EX;R. This system, whici1 was developed to reduce the formation of oxides of nitrogen, takes exhaust gas from the engine output and mixes a small fraction of it wi th the fresn air and fuel at tne eng ine intake. 'D1e amunt of exhaust gas introduced is controlled in a var iety of ways, but it typically is reduced to zero under conditions of engine idle or wide-open throttle operation. Finally in a discussion of engine control we must ine! ude the automatic transnission whiCh is in use on most American cars today. The gear ratio selected is a

The scheduling of these control variables, spark timing, EGR, air-tuel ratio, and transmission gear as a function of engine operating or state variaoles, is called the eng ine cal ior a tion. In conven tional automooiles, each of these systens is operated with an independent control system. As will be shown later, however, the control varlaoles are not independent, and current caliorations represent considerable cOlnpromise in system desi.::jn. Beginning in 1971, Poru ilOtor Com.;any began an advanced research project aimed at developing an integrated control systelu for automotive drivetrains. Ibis progrCl!ll reached its first major milestone with the introduction this year of the first multivariate microprocessor-based automotive control system on a production vehicle. Althou-Jh this first application is restricted to only two of the four control variables described aoove, and nas oeen implemen bed on! y on a sin,Jle low volwlIe model, the extension of this approach to all engine control par~neters is imminent.

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N. Laurance

Various aspects of this program nave been descr ibed ill prev 10 us publ ications (Te.uple and Devlin, 1974; Oswald, Laurance and Devhn, 1975; (-loyer and ['langrulkar, 1975; Oswald, 1977; Blumberg, 1976; Auiler, Zorozek and Bl umber::l, 1976; Baker and Daby, the present paper 1977; Laurance, 1977); will descrlbe tne ~roject in terms of the developnent of toe control system ana provide an overview of its components.

DESIG1~ CQ~SIDERATIOl~S

Prior to the enactment of e.ulssion laws, the automobile eng ineer designed his eng ine with three principle oDjectives; ade~uate performance, that is toe torque output required for vehicle acceleration, gooo fuel economy potential as measured by Drake efficiency characteristics, and ther.ual Since engine knock minimal engine knock. limitation is oeing treated outside of the framework of the control system we wish to describe, we will not dlSCUSS it further in the present paper. 'T o meet these objectives, the engL,eer nad several parameters at his dlSfX)sal. witnin the engine proper, he could vary the total displacement, the number of cylinders, combustion chamoer shape, connecting rod length and crankshaft radius, valve area and lift, valve timing, and so forth. Once these parameters were chosen, of course, they remained fixeu over a sizeaole production run. In addition, the engineer specifieu several control paraueters of the engine, values wnich vary dynamically as the engine operates in different regions of power and speed. In the ensuing discussion we will consider toat the characteristics of the transmission are fixed so that we nave three control varlaDles at our disposal, spark tlming, air-fuel ratio and EGR. Although tne exclusion of transmission control does limit the generality of the approach, it is appropriate for the current state of de vel opnen t. with ~ introduction of emission legislation, tne design proDlem oecame consideraoly lI'Qre complex. NOW, in addition to the criteria mentioned above, the engineer was faced with adaitional constraints on of hydrocaroons (rtC) , caroon e.llission monoxide(CJ), and oxiues of nitrogen(l~x). To understand the nature of these constraints, we first must descrlOe the way in wnich trey are measured. '!he Uniteu States Feoeral Goverruuent puolishes a testing procedure (Federal Register, 1972) whicn I will attempt to swrmar lze here. 'lhe automoolle is placed on a cnassis aynamometer whicn has oeen adjusted to the proper 10a.Jing and inertia requirements. '!he rear wheels of

the vehicle rest on dynamometer rollers. (I rear wheel drive vehicles throU8hout this pa~r; appropriate adjustments in the proceuure can easily be made for front wneel drive venicles.) One roller is connected to the loading device; the other roller is instrumented to re
Faced witn these additional constraints on our engine design, some alteration of basic engine design parameters is of course essential. However, equally ilnportant is the control system which controls the engine operating parameters. we will concentrate on the latter aspects of the proolem in the following discussion. '!he next section will describe the oasic Characteristics of each pollutant and toe effects of each control var iaole on its formation. '!he fourth sectlon will describe the system moaelling approach used, and the exper imen tal data required for analysis and design. '!he last section will describe implementation and future direction.

379

Automobile Engine Control System

ElIIISSION SENSITIVrry Of the three polutants, CO is most sensitive to a i r-fuel ratio. It is formed whenever there is insufflcient alr in the ourning mixture for complete comoustion. For average gasoline, approxlmataly 14.7 grams of air are required to ourn 1 gram of .,)asol ine. 'Inis air-fuel ratio, 14 . 7:1 is referred to as the stoicniometric ratio. The emission of CJ increases rapidl y as the mix ture is enr iched (air- fuel ratio less than 14.7) and falls rapidly to low values for air-fuel ratios sligntlyaoove 14.7. Hydrocaroons are present in the exhaust because some of the gasol ine was not burned at all. 'ro a great extent, this lS gasoline WOlcn was very near the wall of the cylinder, so that the fl~ne was extinguished by the (relatively) cold w.:ill uefore this .,)asoline coulu ourn. Calculations show that a rather large amount of HC is contained in this quench layer in the cylinder, out that most of it is oxidizeu eitner in the cylinder or in the hot exnaust after it leaves the cylinder. He is most sensitive to spark tlming, i. e. the posi tion of the pis ton at the tilne at which the spark is fired , since spark timing controls the basic thermodynamlc efficiency of the engine. 'mere is one particular spark timmg for which tne ma~.ilnum ~nount of work per cycle is extracted from the cylinder, all other par~neters being constant. For any other timin.,), the ~1Ount of work decreases , and enaqy oalance requires that the remaining ener.,)y appear as rejected neat. The more heat tnat is rejected to the exhaust , the Inore likely we are to nave the cOIDUustion of those unburned hydrocarbons, and the lower the value of this particular pollutant. Unfortunately, however, this procedure also lowers the fuel economy, sil1ce the availaole work per unit of gasoline expended has decreased. Oxides of ni trogen (referred to as ,-Dx) is a different kind of pollutant; it is formed from the constituents of air alone and is present anytilne the telnperature in air is hi.,)h enough for its formation. mus, oxides of nitrogen are regularly formed in 1 ighthing storms, in arc welding processes, and in automooile engine cylinders at those tLnes when the temperature lS nign. SUCh corditions occur during periOdS of hign load, that is , high power demand . t:xnaustgas recirculation has been developed to control this pollutant. , 'me presence of the exnaust gas in the cylinder tends to dilute toe charge ard to provide an inert element with reasonable specific heat whiCh can prevent the cylinder temperature from rising to the c ritical values necessary for NOx formation.

At this point we nave described eacn emission component as if one control variaole were responSible for governing its rate of formation. Of course tois is not true and eacn emission component lS sensitive to all control variables. Thus, for example, NJx formation is extremely sensitive to air-fuel ratio. Figures 1, 2 and 3 give basic sensitivlty trends of eacn of the emission components witn tne control variaoles as well as tne sensitivlty of fuel consunption with the control variaoles. (l~ote that all our curves ~isplay fuel consumption , not fuel economy, so that the smaller the numoer is, the oetter.) For ease in cOlnpar ing values of these variaoles at ~ifferent engine operatlng conditions, tne production and consunption rates are nor,nalizeJ oy dividing the value by the power of the en9ine at that cordition. Var iaoles so nor,ual ized are referred to as br aKe spec ific val ues, e.g., BSHC, Bill-Dx, BSCO, and I3SFC . CONS TANT SPEED / LOAD MBT SPARK CONSTAN T EGR

RICH •

• L E AN

AIR/FUEL RATIO 'ri~ical Effi13si0n and Fuel 1. consumption Cnaracteristics vs. Air-Fuel Ratio for tne I.C. t:ngme.

The effect of eacn control var laole also depends on the other control variaoles. For ex~nple, the addition of ~R will cause an increase in fuel consumption at constant SparK advance. mis is because £GR tends to slow toe ourning rate in the cyllOder, thereoy introducing an effective s~rk retard. If , nowever, the spark advance is increased as EGR is aooeLl in a consistent manner, the lUX will oe reduced as before, but the fuel consumption will r~~ain nearly constant. Figure 3 shows the effect of ~R when spark advance is neld constant. In Fig.

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N. Laurance

4, we see the effect of EGR when spark advance is si.Jnultaneously adjusted to its optimum (for fuel consumption) value. This interaction between the control varlaoles is one of the "lost compel! ing reasons for developing a fully integrated control system.

BSNO x

oecome excessively lean during acceleration (thereby promotin~ misfire), current practice is to use an accelerator ~ump whiCh injects extra gasoline to enriCh the mixture during this transient. 'Itlis r icn ,nixture cOnJition and tne riCh mlXtures which are necessary dur ing cold-star tare tne pr incipal mooes whicn generate CO. rlydrocaroon formation occurs, as we have noted, oecause of incolnplete comoustion. Because oxidation in the eXllaus t sys tem is so imFOr tan t for reduction of hydrocaroons, HC elnission is greatest under tnose conditions for whicn there is insufficient nea t or oxygen in the exnaust sys~em. These conditions are present at idle, deceleration, an~ during the first few minutes after a cold-star~.

constant speed / load no EGR

SPARK ADVANCE Fi~.

Fuel

2.

Brake Specific &uissions and vs. Spark tdvance.

Cons~nption

B5FC constant speed Iload MBT spark

Fi~. 4. BraKe ~pecific &nissions and Fuel Consumption vs. E(jR with Spark Advance l-1aintained Optimum (i'lB'r).

constant speed Iload

5A % EGR 3. Brake 3peClfic Emissions anu EGR a t Cons tan t Fuel Consumption vs. Spark Advance (SA). Fi~.

In addition to descr ioing the effects of the control var lables on emissions, it is imFOrtant to KOOw the effects of operating conditions on emission rates. As we have already indicated, OOx is forme:] under conditions of nigh FOwer demand. Therefore, l~X prouuction is ~reatest Juring accelerations, followed oy cruise conditions. Caroon mcnoxide generatlOn is practically all associa ted with fuel meter ing practice. If the fuel metering system is adjusted sufficiently lean, steady-state values of CO will be small. In tne case of tne carouretor, however, because most carouretors

In tne description which follows, we shall ignore tne special proolems associated witn cold-star tlng , and shall not incl ude the effects of catalysts. Cold-starting is FOorly enougn understood that it must still oe treated in an ad noc manner. ~~e can include the effect of a catalyst in our system oy Changing the constraint values of emissions upward by a constant factor related to tne average conversion efficiency of tne catalyst. Having described the funu~nental relationship of the pollutants to the control variaoles, we can now formulate tne control proolem we wiSh to sol veFor an arbitrary driving cycle, find the control law whiCh minlffiizes tne fuel consumed subject to fixe:] constraints on tne total amount of clC, CO, and OOx emitted' over the cycle. l~ote

that

no

mention

of

performance

is

Automobile Engine Control System

present in this formulation. Some performance is lndirectly implied by assuming that the venlcle is able to follow the driving scnedule over Which fuel economy is optilnized. In aJdi tion, as men tioned above, we are l.,:;noring octane limitation Which sometimes causes compromises to De made in en.,:;ine calioraClons.

S:iS'.i'tl1 AdAL:iSL:>

To descrioe tne engine in terms amenaole to control analysls, we will list the variables wnich must be accounted for. A. 1. 2. 3. B. 1. 2.

~

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1.

2. 3. D. 1.

2. 3. 4. E. 1. 2. 3. 4.

Engine State Variables Eng ine speed ,-let eng lne torque Intake air flow

En:! ine Input Var iaoles Accelerator positlon Road load engme torque. 'Itlis is value of torque the engine must sUPflly to maintain the venicle in steady state operation. Any excess torque the engine develops is availaole for vehicle acceleration. En:;;ine Control variables SflCirk timing Air-fuel ratlo Exnaust gas reclrculation (&;R)

381

variables. Then, .,:;iven the state variable trajectory in time, we would minimize the integral of the specific fuel consumption suoJect to the constraints on tne integrals of the emission production. The final step in tnis process I>K)Uld be to relate the engine state variables to the engine observables, so tnat control laws could be expressed as a function of tne oDservables. 0f course such a pro.,:;r~n cannot oe carried out in detail. The relationship oetween pollutant production rates and engine var iables cannot be expressed in simple equations, and modelling procedures ailfled at relating these phenomena are still in the developnent stages. Faced wi tn this 1 imitation, we are forced to develop our control strategy in terms of exper~nentally determined quantities. Praonakar, Citron and Goodson(1975) attempted a for,nulatlon of the t?roolem in terms of differential equations related to experimentally determined quantities. However, when tne system had oeen simplified to remove all the exper~nentally unuetermined terlus, most of the dynamlcs of the process had disappeare~. Our aP9roach has been to ignore tne dynamlcs as a first approximation, and formulate tne prOblem completely in terms of steady-state oehavior. It is not obvious at toe outset that sucn an aJProximation will produce resul ts wnicn correlate well with vehicle data; however, extensive use of the procedure togetner with Vehicle measuremen ts nas estaolisned its basic valiaity and quantified the errors introduced oy i':lnoring tne dynamlcs.

EnJine Output Variables fuel conslliilption rate dC emisslon rate CJ emiSSlOn rate l-lOX eluiss ion rate

VAC

J.:L~ ~t::~

CD::line Qbservables En.,:;ine cranksnaft position and speed En':line iilanifold vacuum Exnaust ::Jas flow rate Throttle position

For a complete analYSiS, this list would have to oe augmented with several other var laDles. Al thouJn tne ililplemen ted sys tem does take tnese var laDles into account, we nave ne.,:;lected them here to simplify tne discussion. The next step in tne control syntnesls would oe to write tne differential equations wnicn relate the outtXJt var iaoles to the state var iaDles, the inputs, and the control

,,

T TORQUE

\lAC ...... cuu .. ~To ACCESSORY TORQUE

Fi:l. ::J. ElelilenG and Flow LoglC in tne Computation of the Engine State Trajectory (Olumberg, 1976). The initial step in this proceuure is to relate tne engine state trajectory to that of the venicle. Ihe technique employed here has been described by Blumoeq (1976) . After having assumed a venicle configuration, (i.e. rear axle ratio, transmission, inertia welgnt, etc. ,) the mouell ing procedure relates the velocity-time profile at the rear Wheels to speed/torque requirements at toe ell3 ine output snaft.Ihe process takes

N. Laurance

382

account of tire losses, rear axle eff1ciency, transmission ;lear oox losses and torque converter losses. In addition, losses due to certa1n accessories are accounted for (see Fig. 5). The result of this procedure is a ti.ne trajectory of engine speed and engine tor~ue required for this particular vehicle in order to meet t~ Jr1ving sChedule. l~otice that we nave not prescr ibed any of the control variaoles necessary to achieve this result. From this ~ata we can construct a two-dimensional hiatogram which relates the a.nount of tilne that the engine spends in the vicinity of any speed/load point (Fig. 6).

fuel consuned subject to the constraints that the emissions produced are less tnan stated values. A little reflection will reveal that we are tal king abOut a very large quanti ty of exper lffiental data. At each of the speed/load points it is not uncomnon to measure the engine behavior at Cl values of spark auvance, at 5 values of EGR flow, and at Cl values of air-fuel ratio. In order to make the exper imen tal program more manageable, var 10US approximations nave been made in the approach. Ihese experiments, wnich have come to De called eng ine mapping, are descr ioed extensively by Baker am Daby(1977).

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Formulating the oata in this way is tantaJrount to approximating the engine trajectory oy a series of steady-state values. l~OW, by measurin-j the SpeCif1C fuel consumption am emission rates at eacn of the speed/load points, we can sum these val ues usill3 the time values of the histogram as weigntin~ factors to obtain an estimate of the engine oehav1or during the vehicle test. l~ote that this is a ~eneral projection technique and can oe used with any specified values of the control variables at each speed/load point. 'I'he trend prediction capaoil ities of this procedure are very gOOd, and the aosolute accuracy of toe tecnnique varies from good for fuel consumption and NOx to poor for CO. This is understamaole since CO is greatly affected by accelerator p~np air-fuel enrichment, a transient effect whicl1 is not covered in this procedure. For our orig inal proolem, that of specifying toe opt~nun values of the control variables, we can now transform our vehicle opti.nization proulem in to an eng ine proolem. For each of the speed/load points in the nisto~ram for which the time value is non-zero, we measure the fuel conswnption and emission production rates as a function of all the control variaoles throughOut their Jomain. Then using the tLne weignted sUlmation technique descr lDed aoove, we must find the set of control var iables whicn min~lze the total

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~peed/Load

'Ihe technique we use for findin.,l the optilnum calibration nas been described by Auiler, Zorozek and Bl umber~ (1977) . A complete description of tne approacn is beyond the scope of this paper. Basically, nowever, dynamic progra.rming is used to search for the optilnum fuel economy as a function of one of the emission var iables. 1'0 extend the method to two emission constraints, a Lagrange mul tipl ier tecllJ1ique is employed to factor the second emission variable into the objective function. 'Ihe Lagrange multiplier is varie~ systematically until the optimum is found at the correct constra1nt level. In principle th1S process can be extended to incluc.e toe thiru emission variable, CO. In practice, however, CO is usually found to fall witnin its constraint (at least insofar as steady-state values are concerned) after OC and OOx are accounted for. An alternative tecnnigue for finding the optimum calibration has been described oy Rishavy and coworkers (1977) . 'D'1e resul ts of the procedure per formed on an e.1g ine data base for 8 speed/load points at each of three emission constraint levels 1S shown in Fi~. 7. Note especially tne variation in the control variaoles necessary as the emission constr ain ts are var ied. The compromise necessary to achieve optimum fuel economy is

Automobile Engine Control System

evident in this data. Repeating the process at various em1ssion levels, we can predict fuel economy as a function of em1ssion constraints. Sane tYP1Cal resul ts of this k1nd are ShOwn 10 Fig. d. CYS-H NO. IeftAMS'MIL£l

26 24 22 20 18 PROJECTED 16 OPTIMAL 14 CVS-H FUEL 12 ECO 11011 Y 10

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F1-;J. d . Jptimwn Fuel Econolny for a 3000 lb., 2.3L Vehicle at Different Em1ssion Levels (Auiler, lbrozek and t3lumoer-:l, 1977). In uesi-;Jn1ng toe en~ine mapping experiment, care lnust be taken that the data does not defend in too mucn detail on the exact d1str1but1on of time in the speed load histogram . Because of tne ..lay we nave par ti tlOned the proolem, all the en-;J ine char acter istics are now presen t in the experimental :..lata base, wnile all the venicle characteristics are present 1n the histogram. If the eO-;Jine Jata oase is comtJlete enough , we can use this technique to evaluate the effects of many Kinds of vehicle cnan-;Jes merely by Jeveloping a revised tiloe histo-;Jran and applyin-;J it against tne engine data oase . Thus , for example, one could eas1ly evaluate the effect on fuel economy anJ enissions of a change in rear axle rat10. cassidy (1977), on the otoer hand, has developeu an on-line eng ine dynamo'lleter test proceuure for prodUCing the optilnum calioration ny continuously el/al ua ting the exper l.Jnen tal uata and directing the exper l.JOIen tal search. .3ucn techniques .nay be a sizeaole i..nproveH1ent in generatin-;J an optilOlum caliorat1on for a -:llven Vehicle conEi-;Jurat10n. The exper l.Jnental procedure must oe totally repeated, however, for a change in vehicle configuratlon or emlSS10n constralnt.

383

Temple a-rl Oevlln (1974), Oswald , Laurance am Devlln (1975) , cswalu (1977), anJ by Laurance (1977) • In addition to the microprocessor and its memory, the control unit contalOs an analo;) to digital converter and special di~ital circuitry necessary for -:lenerating high frequency timlng marks from the low frequency tilning pulses pickeJ up Tnese hign frequency from the crankshatt. pulse trains are used for control actions WhiCh must oe synchronous with crankshaft intervals. Spark inltiation is controlled through a conventional electronic ignition jnodule wnlcn takes its tilning signal from the microprocessor. &;~ flow control required the develoj:Allent of a special flow control valve. This \'alve COns1StS of a sonic orifice wnose cross sectional area can ne controlleu ny a ,noving j?intle. 'm e pintle position is read by a linear potentiometer and the valve actuating mechanism lS controlleu by the micro processor in a DDC loop. The current production Vehicle implementation does not contain control of air-fuel ratiO, out this feature· will oe introduced 10 suosequent. years . l'he complete characteristics of toe sensors and actuators are descrioed oy Oswald (1977). Tne mlcroprocessor is a custom L.3I design , fabr icateu in l~11a:; . Its archi tecture has oeen descrlocd oy Laurance (1977). ariefly, it is organizeu as a 12 oit minicomputer, with special attention glven to requirements for control algoritnrn implemenc.ation. mus the archit.ec ture contains a nardware 12 nit unsi.gned multlply ana divi:::te instruction wnich are needed for linear interpolation. The control pro;jram in the microprocessor contlnuously reads the eng1ne variaoles and calculates ap!?ropriate values of the control \Tar iaole3 oaseJ on the resJ! ts of the optilOlizat.ion Jrocess. The prvceJure is a cOiooination of taole lOOkup and linear interpolation. The calculation takes between 20 and 30 milllseconds in the current program . Al t.nou-:lh tnis i3 slow compared to the 5 lnillisecond incerval netween spark f1[lOgS in an engine runnlng at 3000 KP,1, it seems sufficient for satlsfactory o~ratlon of me englne. .i:'hat lS, this t.L.1e is still fast cOiU,;:arect Wl th tne tline necessary for sl-;Jnlficant change of tne engine state var iaoles.

Il>1PLEM&h'ArIOl~

The nasic control strategy developea ny the above methods is implemen ted in a microprocessor based electronic control unit. The electronic system elements have oeen descr ibed from var ious points of view ny

'I'here are, nowever, dyna1l1C proo12ms in the control wnicn are consider&.! in the comfli..lter program. The 31ew rate ot tne &;~ vall/e is qui te slow compared to the other times in the system, while the spark oelivery system is rearly instantareous in its response to

384

N. Laurance

changed input. If the eng ine state var laDles change so as to require a significant change in spark and EGR, it lS possible that in the transition to the new operating point, we coulu be quite far from an optimum settin~ of the control variaoles. To compensate for this, at least in part, the microprocessor modulates tne Change in spark advance based on the actual value of the EGR valve position, rather than on its corrvnand value. For ex~nple, lf we wlshed to change the spark advance from 30 to 40 de~rees and to change the EGR rate from 10% to 20% silnul taneously, the microprocessor would c~nmand the E3R valve to open to tne 20t point. men, JOOnitor ing the opening of the EGR valve through lts DDC loop, it would advance the spark in a 1 inear fashion so that the spark advance reached 40 degress when the EGR valve had assumed its new position. while some minor gain in fuel economy Inay oe real ized oy this tecnnique over independent control, the main advantage appears to oe an improvement in driveability. The "crossed controls" situation in which spark advance and EGR are not changed in concert may well be the cause of sOlne dr iveaoil ity problems such as hesitation or surge, al though tnis point nas yet to oe fully explored.

with the advent of the fully integrated computer-based electronic control system for automooile engines, a new era in the approach to engine control has begun. AlthOugh tne first implementation is devoted completely to satisfying tne emission-fuel economy proolem, the potential for appllcation to problems related to dynamlcs seems obvious. Tne system even as descr ioed in this paper is enorlnousl y complex, anu the incl us ion of all the dynamic terms of importance strains the imagination. Nevertneless, I feel confident that we shall see the more significant dynamic terms identified and added to the control structure in the next few years. A contlnuing proolem lS that of the sensors and actuators. In one sense this is the proolem of producing good quallty, hignly reliable sensors and actuators at reasonable cost for tne automooile enviro~~ent. A deeper proolem, however, is the fact that tne ooservables are not simply related to the constralnt variaoles. The extenslve process of englne mapping must oe used to relate these two, and since this process must preceed the construction of the venicle, the POSSibilities for a~aptive control are greatly Ilmited. Sensors of var laoles whicn are more dlrectly related to emission proauctlon and fuel consumption are sorely

needed for improved control systems. Finally, looking to tne future, the introduction of a computer-based control system whose al~or it~ns are constructed from an extensive data oase has implications which exteoo into the manufacturing process as well as into the area of vehicle service. Full exploitation of tnese possioilities should provide even ITIore challenge in the future.

REF t:REt'JCE.3 Auiler ,J .E., J.D.ZorozeK and P.l~.81wnberg (1977) . Optimlzation of AutOJOOtlve Engwe Cal iorations for Better Fuel Economy: Methods and AfPlica tions. SAE paper 770ft! 7& • BaKer,R.E., and E.~.Daby (1977). Engine Mapping Methodology. '::>AE Paper 7700 17 • 81 umoerg,p.t~. (1976) . flower train Simulation: A Tool for the Design and t::val ua tion of t::ng ine Control Str a t eg ies in Venicles. '::>At:: PAPER 760158. Cassldy,J .F. (1976). A Computerized On-Line ApproaCh to Calculating (ptilnum Engi,1e Caliorations . SAE Paper 770018. Federal Register, Vol 37, No. 221, Part 11. New Motor Vehicles and l'Jew I'Dtor Vehicl es Eng ines. L~ovej(t>er 15, 1972. Laurance,l~.L. (1':177) . A £1icroprocessor Architecture tor Engine Control. IEEE CompCon , ~vashington, D.C. (1975) • f'byer,i).F., and S.f1.l'langrulkar En~ine Control by an On-Board Computer. SAE Paper 750433. Oswald,R.S. (1977). The Ford Electronic Engine Control System. SAt: f'aper 770007. S.S.Devlin Oswald,R.S. , l'J.L.Laurance , and (1975) . Design Considerations for an SAE Paper On-Board Computer System. 750434. praohakar,~., S.J.Citron, and R.E.Goodson, (1975) • cptimization of Automotive Eng ine Fuel Economy arid Emissions. A.;>HE Paper, 7:i-~~A/Aut-19. Rishavy,E.A., S.C.Ha.uil ton, l'i .A.t