CA1210834A - Method and apparatus for controlling fuel injection timing in a compression ignition engine - Google Patents

Abstract

Abstract The method and apparatus for generating start of combustion signals associated with the combustion events in a diesel engine (10), and for using such signals to control the timing of fuel delivery to the engine. The combustion event is sensed, as by an electrostatic (230, 330) or optical (130, 430) sensor, and signal conditioning circuitry (32) pro-vides a start-of-combustion (SOC) signal (34) which is directly and precisely indicative of the time of the onset of combustion. The sensors (130, 230) in-clude self-cleaning capabilities (48, 248) for ex-tended operating life on an engine. The sensors may be incorporated in the structure of a glow plug (330, 430).
The SOC signal (34) is advantageously supplied to a timing control circuit (26) which delivers a timing control signal (28) to a fuel delivery device, such as the controller (16') associated with a fuel pump (16). The control circuit (26) stores (65) one or more start of combustion values (SOC*) which indi-cate the desired timing, relative to an engine cycle (24), for the start of the combustion event as a function of speed (25) and load (27). One or more adjustment signals (.DELTA.SOC) are stored (75) and applied (67, 68) as a function of speed and load to adjust the desired signal (SOC*) such that the control sig-nal (28, SOCc) is corrected for delays. The actual SOC signal (34) is compared (71) with the desired signal (66) to generate an error signal (72) which may be used to finely adjust the stored (75) .DELTA.SOC
signal for particular speed and load conditions.

Description

~L2~
, ,, This application is a divi~ion of Application Serial ~o. 406,641, filed on July 5~ 1982.
Technical ~ield This invention relates to ~he control of fuel in-jection timing in compression ignition engines and more particularly to the control of such fuel injection tim-ing based on the measured timing of the onset of com-bustion. The invention additionally relates to the development of timing signals which are accurately and directly representative of the onset of combustion in a co~bustion chamber of the engine.

Background Art Continuing requirements to achieve improved fuel efficiency and reduced exhaust gas emissions of com-pression ignition engines, hereinafter referred to as diesel engines, has stimulated the development of elec-tronically controlled fueling systems offering the potential for providing more precise engine control.
The gains achievable in diesel engine performance through the introduction of electronic fuel controls depend to a great extent on the control strategy imple-mented, the accuracy to which specific engine operating parameters can be measured and controlled and tne abili~
ty to maintain such control throughout the operat-ional life of the engine.
In compression ignition engines, one of the most critical operating parameters is fuel injection timing.
Presently, control of the time of injection is deter-mined mechanically and/or hydraulically. The ti~ing ;~

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-2-function has typically relied only upon measurements of mechanical timing points, such as crank angle, flywheel position, piston posi.tion and/or injector actuation to provide the requisite timing control. While such con-trol was historically effected mechanically and/orelectromechanically, recent developments have placed increasing emphasi~ on the utilization of electronics.
Representative of these timing techniques and imple-mentations ar~ U.S. Patents 4,033,310 and 4,265,~00 which sense injector actuation to provide corrective feedback information to electronic controls which de-termine and control ~he timing of fuel delivery, or injection, by fuel delive.ry apparatus.
Those systems, however, fail to provide for the lS fact that in diesel engines, unlike spark ignition en-gines, the start of combustion within the cylinder does not directly relate under most circumstances to the mechanical timing point, such as injector actuation.
Engine operating conditions such as cylinder wa]l temperature, air inlet temperature, engine load and speed and fuel quality all influence the specific point or time in the engine cycle at which combustion takes place within the cylinder. An additional complication is the contemplated introduction of a broad spectrum of new fuels, fuel blends (i.e. alcohol and water emulsions), and synthetic fuels widely ranging in cetane rating. These factors combine to introduce a variable delay between the time of fuel injection and the start of combustion which may typically be 5-20 of crank angle. To accommodate such variations in the onset of combustion introduced by the above factors, the purely mechanical timing system must be augmented with precise information on the aforementioned engine operating parameters, as well as with a direct

3--measurement of fuel quality (cetane ratingl and fuel density. From this information, it then becomes pos-sible to estimate the instant at which combustion be-gins. Obviously, the complexity of this approach along with the large number of required sensor inputs limits accuracy and practicability. Furthermore, this ap-pro~ch can, at best, provide only an estimate of the onset of combustion and cannot provide compensation for engine variables.
While the introduction of electronic control sys tems to diesel engines is relatively new, considerable development has occurred with spark ignition gasoline engines. Specifically, efforts have been made to im-prove spark ignition engine performance via the elec-tronic controls associated with engines. For instance, in U~S. Patent 4,181,944, which in turn refers to a different Japanese patent application KoKai (laid-open~
No. 4903/72, there is a general discussion of using combustion pressure sensors for ~onitoring the pres-sure in one or more engine cylinders and for modify-ing a previously-stored spark igniticn timing scheme if the sensed pressure indicates deterioration of the cylinder pressure. Mention is also made of sensing the ion current in the spark plugs in lieu of a pres-sure measurement. These techniques, however, are in-tended for use with spark ignition engines and do not sense the timing of the combustion event, but rather its quality.
Various techniques other than an analysis of pres-sure have also exlsted for irdicating some combustion-related characteristics of an engine. Two such examples, U S. Patents 2,523,017 and 4,232,545, utilize an ionic current detector to detect knocking or "detonation" in , 3~

a spark ignited engine, either for analytical or cor-rective control purposes. U.~. Patent 3,051,035 de~
scribes an optical combustion monitoring device for detecting a flame-out condition in aircraft jet engines.
However, these patents are not concerned with the tim-ing of the onset of combustion nor with the development of a timing signal for a diesel engine, nor specifically with control of fuel injection timing based on a direct measurement of the onset of combustion.
Accordingly, it is a principal ob~ect of the pre-sent invention to provide improved control of the tim-ing of fuel delivery in diesel engines. Included with-in this object is the provision of a method and appa-ratus for controlling such fuel delivery in an accurate and precise manner as a function of the onset of com-bustion in the engine.
It is a further object of the invention to provide apparatus ~or accurately sensing the onset of combustion and generating corresponding start-of-combustion timing signals there~rom. Included within this object is the provision of such apparatus which is relatively durable and long lived, yet relatively inexpensive.
In accordance with the invention, there is pro-vided an improvement in a fuel control system for a diesel engine. The system includes means for delivering fuel to the engine for combustion therein, the fuel delivery means being responsive to at least a timing control signal for controlling the timing of the de-livery of the fuel to a combustion chamber of the engine for combustion therein. The system also in-cludes means for providing signals indicati~e of cer-tain engine operating conditions and means responsive to the signals~indicative of certain engine operating conditions for providing the timing controI signal.
In accoxdance with the invention~ the improvemen~

, . ., - ~a -comprises means insertable through a wall of the com-bustion chamber of the engine for sensing a property of combustion which is directly representative of the onset of combustion therein and for providing a signal indicative thereof. The sensing means additionally is so structured as to provide self-cleaning thereof during and substantiall~ only as a direct consequence of operation in the combustion chamber. The onset of combustion indicating signal being one of the sig-nals indicative of certain engine operating conditionsto which the timing control signal providing means responds.
Further in accordance with the invention, there is provided a fuel timing system Eor a compression ignition engine, the system including means for de-liverinc~ fuel to the engine for combustion, the fuel delivery means being responsive to a timing control signal for controlling the timing of fuel delivery by the fuel delivery means. A first signal generator includes means for sensing a phenomenon in a combustion chamber of th~ engine which is directly representative of the onset of combustion therein and providing a representative signal thereof and means for conditioning the representative signal to provide an electrical signal precisely indicative of the actual instant of the onset of combustion. The sensing means is so structured as to provide a self-cleaning thereof during and substantially only as a direct conse~uence of operation in the combustion chamber to facilitate con-tinuous operation. Second signal generating meansprovide an electrical signal indicative of engine timing. Third signal generating means provide an electrical signal indicative of engine speed. Fourth signal generating means provide an electrical signal indicative of engine load. Control circuit means are ~F~

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- 4b operatively connected with and are responsive to each of the on et of combustion signal, the engine timing signal, the engine speed si~nal and the engine load signal for providing the timing control signal. The circuit control means includes means for providi.ng a signal representative of a desired timing of the onset of combustion as a function of the engine speed and the engine load and further means responsive to the desired timing of onset of combustion signal and to the actual instant of onset of combustion signal each referenced to the engine timing signal adaptively provide the timing control signal such that the subse-quent actual start of combustion substantially coincides with the timing of the desired start of combustion.
Still further in accordance with the invention, there is provided a signal generator for use with a compression igniti.on engine to provide electrical sig-nals ~irectly and precisely indicative oE the instant o.E onset of combustion. The signal generator includes means adapted to be mounted in operative communication with a combustion chamber of the compression ignition engine to sense a direct property of the combustion process within the combustion chamber and to provide an electrical signal representative thereof. The sen-sing means is so structured as to be substantiallyself-cleaning during and substantially only as a direct consequence of the operative communication with a combustion chamber whereby substantially continuous operation with the combustion chamber is afforded.
Amplification means, responsive to the electrical sig-nal indicative of the combustion process substantially increases the magnitude of at least the leading edge of the signal indicati.ve of tne combustion process.
Threshold means responsive to the magnitude increased signal exceeding a predetermined relatively low mag-133~
- 4c -nitude threshold level provide an electrical output signal having a leading edge which is substantially vertical relative to the time base of interest in a compression ignition engine. The signal leading edge is precisely indicative of the instant of actual onset of combustion.
In accordance with one aspect oE the invention, there is provided the method of and apparatus for con-trolling fuel delivery in a compression ignition engine at least partly as a function of the onset of combustion in the engine. Command signals indicative of the de-sired start-of-combustion timlng are provided as a function of engine operating parameters and are uti-lized in open-loop manner to control the timing of fuel delivery. The command signals are modified or trimmed as necessary to correct for the variable delays which generally occur between the time (i.e. engine crank angle) of the fuel delivery and the start of combustion.

-~' '?i' The appropriate correction of those control signals is achieved by detecting the actual instant of the start-of-combustion in a respective combustion chamber, com-paring that actual time ti.e. crank angle) with the time which was desired, thereby to detect any error, and correcting the original control signal by an amount equal to or proportional to the error. The desired start of combustion values may be previously determined and stored for a full range of engine speeds and loads.
The correction signals may also be stored as a function of engine speeds and loads and may be periodically up-dated by the determined error values. The processing of error values is done in a manner providing dynamic and accurate correction fcr the control signal even though non-monitored engine operating conditions may chan~e. ~rovision is made for a cold-starting advance.
In accordance with another aspect of the inventi.on, a signal generator is provided for responding to a di~
rect property of the coTnbustion occurring in a cylinder to generate a timing signal indicative of the onset of combustion. A sensor in communication with a cylinder combustion chamber detects the particular property of combustion being monitored, the level OL .hat detected property normally changing at a rapid rate, typically increasing, at the onset of combustion. The sensed property is then converted, as by signal conditioning means, to an electrical timing signal which accurately indicates the onset of combustion.
In one embodimentS the sensor is optical in char-acter and senses electromagnetic radiation~ i.e. lightof some frequency or frequency range, emitted by the combustion event. A photodiode provides an electrical analog of the sensed light. Signal conditioning cir-cuitry then squares the leading edge of the electrical analog, which leading edge then is indicative of the onset of combustion and is used in controlling the 33~

timing of fuel delivery in the diesel engine. The com-bustion radiation may be sensed by a heat-resistant optical element and coupled, as by a fiber optical cable, to the photodiode.
In another embodiment of the lnvention, the sensor detects the level of ionization in the combustion cham ber. An electrical current is developed and, following the type of signal conditioning described in the preced-ing paragraph, provides an electrical signal accurately indicative of the onset of combustion. The sensor in-clu2es one or more electrodes mounted in a cexamic insulator.
For certain engines, either type of sensor may assume the general form of a glow plug for mounting in the precombustion chamber of the engine. A heating ele-.lS ment may be included in the gross sensor structure.
The start of combustion signal generator is em-ployed in combination with khe fuel delivery control system of the engine throughout operation of the system to provide dynamic control.

Brief Description of the Drawings Fig. 1 is a block diagram illustrating the dieseI
engine fuel control system including the signal genera-tor for indicatin~ the start of combustion;
Fig. 2 is a functional block diagram oE the timing control circuitry of the fuel control system of Fig. l;
Fig. 3 is a diagrammatic sectional view illustrat-ing the sensor of the start of combustion indicating signal generato~r positioned in operative relation with a combustion chamber of the diesel engine;
Fig. 4 illustrates one embodiment of a start-of-combustion signal generator;
Fig. 5 illustrates an embodiment of an electrosta-tic start-of-combustion signal generator;
Fig. 6 illustrates a modified embodiment o~ the Fig. 5 signal gen~rator with the sensor combined wi~th a glow plug and positioned in a prechamberi and 3~2~33~

Fig. 7 illustrates a portion of a modified embodi-ment of the Fig. 4 si~nal generator in which the sensor is combined with a glow plug.

Best Mode for Carrying Out the Invention The onset of combustion in the cylinder of a diesel engine is accompanied by a rapid change in several pheno-mena within or near the combustion chamber, including a pressure rise, the production of charged particles, the emission of photons/ a rise in temperature, an increase in the acoustic noise level and the like.- On an experi-mental basis, as in a laboratory, the pressure xise can be employed to determine the point in the engine cycle at which combustion commences. However, the large change in pressure produced by the compression stroke may to some extent mask the change in pressure resulting from the combustion process. Additionally, pressuxe trans-ducers having sufficient life expectancy for mass-market utilization on diesel engines are relatively expensive at present for that particular application. Furthermo~e, engine designers in an effort to reduce diesel engine noise are attempting to minimize in more modern engine designs the rate of pressure rise produced by the com-bustion process~ Accordingly, at least at present, some of the other mentioned physical phenomena appear to pre-sent equal or better opportunity ~or detecting the onsetof combustion. Those phenomena should, ~nd generally do, exhibit a rapid and substantial level change at the onset of combustion., By using one or more of such phenomena, a signal herein designated 'istart of combustion" can be ob-tained and deve~oped, which signal is indicative of theactual beginning of combustio~ in the combustion chamber.
Typically, this signal determines the start of combus-tion to an accuracy of less than one engine crank angle degree.
To such phenomena accompanying the onset of combus-tion and serving to illustrate the principles of the in-vention are the production of significant levels o~

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~29~3~

excita~ion and ioni~ation. The excitation manifests it-self in the emission of electromagnetic radiation~ such as light~ Direct measurements of either the emitted light or ionization levels re~ulting from the in-cylinder S combustion process have been found to provide highly ac-curate and repeatable indications of the onset of combus-tion within the cylinder. Furthexmore, the output signal levels from either optical or electrostatic detectors have been found to be more than adequate formeasurement purposes under a wide range of engine operating conditions.
Referxing to Fig. 1, there is diagrammatically il-lustrated a multicylinder internal combustion engine 10 of the compression ignition, or diesPl, type. Fuel ls delivered in a predetermined sequence to the respective combustion chambers 12 of the respective cylinders 14 by a fuel delivery system including fuel delivary apparatus 16 and suitable injectors 18~ The fuel is injected into the respective combustion chambers 12 by means of the in-jectors 18. As used herein, the term "combustioncham~er"
is intended to also include the prechamber on some die-selengines where combustion "first" begins, such engines being of the "indirect" injection type.
Some cyclically moving portion of engine 10, as for instance flywheel 20, is monitored, as-by engine timing transducer 22, to provide periodic ~ignals indicative of the position of certain parts of the engine. More speci-fically, transducer 22 generates a pulse each time a ref-erence mark 23 on flywheel 20 passes. The reference mark typically indicates some crank angle, as for instance zero, when one specific piston is at a known position such as its top dead center position, and provision may be made for responding onIy to top-dead center indications at the completion of a respective compression stroke. More-over, that engine timing si,gnal might be generated at a predetermined angle, e.g. 120 beore top dead center.
It will be appreciat~d that some other moving component of the engine or fuel pump migh~ he monitored to provide :~2~L~839L

the engine timing signal 24 provided by transducer 22.
Engine timing signal 24 is a principal input signal to on-board control circuitry 26 which provides a timing control signal 28 to the fuel delivery apparatus 16 as will be described. Control circuitry 26 also receives other inputs representative of other engine operating conditions as derived from suitable sensors of known design, such asinput 25 repreSentative of engine speed and input 27 representative of engine load (i.e.
throttle rack position). The fuel delivery apparatus 16 is also responsive to fuel quantity control signals ~not shown)to deliver a controlled q~lantity of fuel.
The fuel quantity control signals are functions of foot pedal position and engine governor characteristics, and their development can be provided mechanicall~ or elec-tronically in a known manner not forming part of the present invention.
~ uel delivery apparatus 16 may typically be a diesel fuel înjection pump, such as the Model lO0 in-~ection pump manufactured by American Bosch and dis-closed in U.S. Patent 3,726,608, capable of delivering a pressuri~ed charge of fuel to each of the injectors lg at the appropriate time and in sequence for injec-tion into the respective combustion chambers 12. The fuel pump is mechanically driven by the engine and de-rives its basic, or xeference, timing in that manner~
However, the timing of the delivery of those fuel charges to and through the injectors and into the com-bustion chamber 12 may be varied by advancing or re-tarding the timing cam of the fuel pump in response toengine operating parameter of speed and load.
The advance/retard timing mechanism of the fuel delivery apparatus typically comprises a piston and cylinder arrangement in which displacement of the ~231Lg~
~10-piston acts either directly or indirectly to azimuthally rotate a ring on which one or more timing cams is posi-ti.oned. The displacement of the piston may be done hydraulically, in the general manner of U.S. Patents

4,265,200 and 4,033,310. Some type of actuator 16', as for instance a stepper motor, a torque motor or the like, responds to control signal 28 from control circuit 26 fox controlling the advance/retard mechanismO
Finally, if the fuel injectors are of the solenoid~
actuated t~pe, fuel delivery timing is done directly at the injector solenoid in response to control signal 28 which then must be expressed and utilized as a time signal, relative to some crank angle, rather ~han a cam angle displacement sisnal. In such instance, the in-jector solenoid is analogous to controller 16' insofaras it e~fects the desired timing of fuel delivery.
In accordance with the invention, a further signal is provided in addition to engine timing signal 24, engine speed signal 25 and engine load signal 27, which is indicative of the response Gf a specific cylinder 14 to the injection of fuel. More particularly, one or more sensors 30 responsive to some sensible phenomenon coincident with and chansing sufficiently rapidly to be accurately indicative of the onset of co~ustion in re-spective combustion chambers 12, for instance, theelectromagnetic radiation or the ioniæation accompany-ing the onset of combustion, operate in conjunction with signal developing circuitry 32 to provide respec-tive start-of-çombustion ~hereinafter referred to as SOC) timing signals 34.
SOC timing signal 34 is applied as an input to control circuitry 26 for precisely and accurately in-dicating the instant of the actual onset of combustion within a respecLive combustion chamber 12 for successive ~Q~

combustion cycles of the respective cylinder 14. The sensor 30 provides SOC timing signals 34 to on~board control circuitry 26 throughout the operation of engine 10 in a vehicle and is thus able t:o provide a con-tinuous dynamic control function. The SOC timing signal34 is utilized for the development: of an error signal which may then be used in various ways, depending upon the control strategy of control circuit 26, to provide and/or modify dynamically the fuel delivery timing control signal 28.
The aforementioned U. SO Patent 4,265,200, discloses one possible configuration for the present control circuitry broadly represented by block 26 in F:ig. 1 herein, subject to the ~ollowing modifications.
1~ Firstly, and most importantly, the engine performance curves stored in memory are predicated on the desired timing (i.e. angle) of the start of combustion as a function of engine operating conditions. Correspond-ingly, the parameter sensed and fed back for comparison is the timing of the start of combustion, i.e. the present SOC signal 34, rather than an indication of the start of injection. Additionally, because the combustion event in a cylinder is statistical in nature, suitable numerical processing is preferably employed to derive a tim.ing signal. This can be accom-plished directly by employing, for example, a first order numerical filter or by utiliæing a running numerical average of the SOC signal. Also appropriate signal processing is employed to accommodate the situa-tion when no combustion occurs in cylinder, as ex-perienced when operating a vehicle with a closed fuel rack.
The aforementioned U. S. Patent 4,033,310, discloses another possible ,.. .

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configuration for the present control circuitry of block 26, subject to the following modifications. The generated signal which is proportional to engine speed and load would in the present instance represent the desired timing of the start of combustion and the sensed parameter for error signal generation would now be the start of combustion rather ~han the injector-actua~ion. I'he resultant signal will con~rol the actu-;ator motor to effect a pump timing which satisfies the desired start of combustiol1 characteristics. As in theabove paragraph, suita~le means for filtering or aver-aging the SOC signal or the error signal would normally be provided.
Each of the aforedescribed control circuits, while being generally suitable for the implementation of the present invention, pos~esses certain limitations. For instance, in U.S. 4,265,200, the coarse control signal is supplied hydraulically and is a function of engine speed only, and only a trim signal is prcvided via the closed-loop circuitry illustrated. That trim control is inherently slow in its response in order to avoid jinstability. In U.S. 4,033,310, the pump timing is ¦provided as a function of multiple engine operating Iconditions, thereby enabling the timing actua~or motor j25 to more rapidly respond to changes in multiple engine !operating conditions. However, the correction signal which is added to the ~asic command or control signal is a proportional value of the error such that the error can neve~ go to zero so long as any correction 130 is needed. In either case, because the correction !value is developed only as a function of the error resulting during the immediately past operating cycle, it may not adequately correct during intervals of rapidly changing operating condition if the correction i!33~

actually required differs at different operating conditions.
In accordance with an aspec~ of the invention, a preferred arrangement of control circuitry 26 is dia-grammatically depicted in functional form in Fig. 2.
Control circuitry 26 typically comprises a micropro-cessor or microcomputer, or a portion thereof, suitably programmed in a known manner for performance in accor-dance with the following functional description. It will be understood that appropriate digital-to-analog and analog-to-digital circuitry (not shown) is included to convert the signals from one form to the other. A
number of digital words, for instance possibly 64 or 256, defining an optimized map of desired combustion angle (or time) settings as functions of engine speed ~S) and load (L) are stored, as in an addressable ROM 65. These combustion angle settings are typically determine~ empirically by ~apping a particular class of engine and fuel system, and reflect the timing of com-bustion which will provide desired fuel economy and re-duction of exhaust emissions. The engine mapping is conducted using the particular start-of-co~bustion phe-nomenon to be sensed by sensors 30 in order to prevent any time disparities that may exist between two differ-ent types of start-of-combustion phenomena. These de-s.ired comhustion angle settings are designated SOC* in the map stored in ROM 65 as depicted in Fis. 2. These SOC* settings identify the desired instant when combus-tion is to begin in a particular combustion chamber, and are expressed either as a timQ, or preferably an engine crank angle, relative to some reference. The reference is typically that of an engine part, normally the top dead center (TDC~ position of a piston in the relevant cylinder. The mechanical linkage of the 3~

engine and Euel delivery apparatus 16 are typically set, as by a keying arrangement or the like, at the time of production and assembly such that fuel delivery at a normal position or status of the advance~retard mechanism coincides with fuel delivery at or near TDC, or possibly at some o~her fixed angular bias of the englne .
Because a significant delay exists from the time of fuel pump ejection until the actual start of combus-tion, typically due to various hydraulic and compressionignition delays, a second set or map of engine crank angle values is stored in additional ROM 90 and is designated ~SOCr as depicted in Fig. 2. Alternatively, the ASOCr values may be established from engine mapping ! 15 as a function of engine load and speed and will typi-cally contain values which correspond either with some suitable nominal speed-load function for such engines or with a speed-load function which is predetermined ! to approximately correct or compensate each of the SOC* values for the predetermined or pre-estimated delays between pump actuation ana the start of com-bustion. While respective SOC* values might be modi-fied by the appropria*e summation with corresponding ~SOCr values, variations of as much as 10-15~ in the actual onset of combustion may occur due to changes in temperature, fuel quality, humidity and the lik.e.
Therefore, in accordance with the invention, provi-sion is made for changing the ~SOCr signal in a dyna-mic fashion to refelct such variations in the delay as determined from a dir~ct measurement of the com-bustion event, .

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In f~nctional operation of the preferred system, the ~SOCr map stored in ROM 90 is transferred to an addressa~le random access memory ~RAM) 75 at each engine st~rt-up, as represented by transfer control circuit 93. Then, during operation of the timing control system, the data stored in RAM 75 generally designated ~SOC and initially comprising only ~SOCr values, is appropriately summed at junction 68 with corresponding SOC* data from ROM 65 as a function 1~ of then-existing engine speed and load conditions to provide a corrected time control signal SOCc, also identified as signal 28, to actuate stepper motor 16' controlling the timing of fuel injection.
Upon the injection of fuel and its subse~uent combustion within a combustion chamber of engine 10, a SGC timing signal 34 from sensor 30 and signal conditioning circuitry 32 is generated. SOC signal 34 is precisely indicative of the instant, and thus impliedly the angle, at which combustion starts.
The SOC signal 34 then comprises an input to cir-cuit 26 to provide feedback data of the response of engine 10 to the timing of the fuel delivery. As suming the SOC*--signal -66 and'the'~corre~cte~d ti'min'g control signal 28 represent angular values, the SOC
timing control signal 34 is converted from a pure time indication to one of angle, rep~esented by the measured SOCm signal 70. The conversion is provided by appropriate circuitry 6~, possibly also compris-ing part of a suitably programmed microprocessor, which considers the timing of SOC signal 34 reIative to a reference event such as the TDC time indicated by signal 24 and in view of the speed of ~he engine indi-cated by signal 25.
The SOCm signal 70 is then compared with the desired SOC* signal 66 to obtain an error signal SOCe identified by reference numeral 72. The com~arison is represented at and by the summation juncti.on 71, and the error signal SOCe represents the magnitude and sense of the error. In the event no SOC signal 34 is provided to circuit 26 within some predetermined moni-toring interval in each operating cycle, either ~ecause of sensor failure or because the fuel rack is closed at no load, the conversion circuitry 69 and summing junction 71 are conditioned to function such that the value of error signal SOCe is zero. The 102d signal 27 is addi-tionally provided as an input to circuit 69, which cir-cuit is additionally conditioned to provide a separate output signal 69' which may be provided to an annuncia-tor if no SOC signal 34 occurs and the load signal 27 isnot zero, thereby indicating failure of the SOC sensor.
Depending upon the duratlon of a SOC* signal on lead 66 to comparing junction 71, it may be desirable to include 2 suitable form of delay, as represented by dotted block 85, to ensure that the SOC* signal appears at junction 71 when the naturally delayed SOC~ signal 70 for that particular SOC~ signal also appears thereat.
This need is particularly emphasized during rapidly changing operating conditions of a multicylinder engine when it is desired to compare the SOC signal with the precise SOC* signal which was responsible for that SOCm response.
The error signal SOCe is then utilized, ei~her di-rectly or preferably as some numerically filtered or time-averaged quantity, to modify the QSOC angle value then stored in RAM 75 for the speed and load conditions which produced the error. The modification of the stored QSOC signal is such as to reduce the error the next time those particular speed and load conditions occur, assuming no further changes arise in the oper-~Z~83~

ating parameters. In the event no SOC signal 34 occurs, due to sensor 30 failure, the input of a zero SOCe value to modify the ~SOC already stored in RAM 75 simply means that no updaté of that data will be made. However, it will be appreciated that the QSOC data already stored in RAM 75, or possibly a reload therein of ~SOCr, will noxmally be sufficient in combination with the SOC*
data to provide a fail-soft fully operational capability.
During operation of the engine, the ~SOC map in RAM 75 is modified or updated by replacing a ~SOC data word stored for a particular speed and load condition with a new data word for those same conditions in the event the error signal SOCe has a value other than zero.
Alternatively, in its simplist configuration, a single correction independent of speed and load may be utilized to correct the ~SOC map when a non-zero error signal SOCe occurs. In the preferred arrangement, that modifica-tion of the stored ~SOC value as a function of the error developed for the same speed and load conditions is made utilizing a n~erical filter represente~ by block 80, which minimizes the effect of the small by finite statistical variation associ~ted wi,h the actual combustion event.
The nu~erical filter 80 may be included in a known manner as part of the program fox a microprocessor.
The value of ~SOC to be newly stored in RAM 75, i. e.
~SOCn, equals the presently stored value of ~SOC, i.e.
~SOCp, and the value of the instant error signal SOCe divided by some numerical constant M, i.e. ~SOCn =
SOCe ~SO~p- M . The value of M will be dictated by the combustion statistics associated with a certain engine design. In practice, it has been found that a value in the range of approximately 3~8 is suitable to provide a sufficiently rapid update of engine operating condi-tions while maintaining a high degree of precision.

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Tests of the SOC sensor 30 on various automotive diesel engines have revealed that the SOC signal 34 provides a timing signal accuracy of better than ~1.5~
with an 80% reliability, based on "long term" operation of approximately 2000 revolutions of the engine. Viewed in another manner, in a test in which a series of 26 samples each comprised of a small number (i.e. 2-4) of consecutive combustion events W25 analyzed, it was de-termined that the arithmetic average for each and every sample was within ~1 of a "most probable" SOC angle determined by a long-term average.
In view ol the foregoing discussion, it will be understood that the correction ~SOC map in RAM 75 is automatically and quickly adjusted as a function of individual engine speed and load operating points to provide ~SOC signals 67 which are used in conjunction with the SOC* signal 66 to provide SOCc signal 28.
Assuming the ~SOC values stored in RAM 75 are positive values representative of the crank angle delay between fuel pump actuation and start of combustion, then the negative sign at summing junction 68 associated with ~SOC lead 67 signifies that the pump actuation timing must be advanced relative to SOC* signal 66 to provide combustion at the desired crank angle, SOC*.
During cranking or start-up of a diesel engine when the combustion chambers are relatively cold, i.e.
at ambient air temperature, it is necessary to advance the timing of fuel delivery as a function of that tem-perature and relative to the combined value stored in the SOC* ROM 65 and the ~SOC RAM 75 for those speed and load conditions to initiate combustion and complete start-up. For instanc~, in one automotive diesel en-gine, the amount of such advance additionally required 83~

may be in the range of 8~ to 15 of cra.nk angle for temperatures ranging from 30C down to -10C respec-tively.
Therefor-e~ in the illustrated embodiment, to p~o-vide the indicated timing of fuel delivery via SOCc signal 28 during cold start-up, a further signal 91, additionally designated ~T , is selectively extended to junction 68 for summing with the SOC* and ~SOC sig-nals, if deemed necessary. ~he ~Tc signal 91 is repre-sentative of the additional angle by which the fueldelivery should be advanced, as represented by the negative sign, at a certain temperature or temperature range of the air, the engine block or, preferably, the fuel. A function generator 92 receives the temperature signal T as an input and provides an appropriate output signal ~Tc. In extreme examples, the function gener-ator 92 miyht generate only a single value for aT~,for all ~uel temperatures T, or it may generate a lar~e number of values each corresponding with a respective different fuel temperature T. In a preferred arrange-ment, only a limited number of ~Tc values are generated, each associated with a respective range of fuel tem-peratures T.
A gating circuit 94 having the ~Tc signal as an input from function generator 92 may be controlled by a gating signal 96 to extend the ~Tc signal to junction 68 only during cranking conditions. The gate control signal 96 is provided by the circuitry 69, or an ad-junct thereto, such that gate 94 is enabled to pass th~ QTc signal only during engine cranking when no SOC
signal is sensed from the.engine. After a sufficient number of compression cycles ha~e occurred to warm the engine and fuel to a level at which combustion begins 383~

and SOC signals are generated, the gate may be dis-abled and the ~Tc correction removed from the SOCc signal 28. It will be recalled tha~ while no SOC
signals are generated, the SOC error signal has a value of zero. Once the SGC sisnals begin and the c correction signal is removed, and before the en-gine is fully warmed to normal operatin~ tempera~ure, the SOC signal may have a relatively large value.
These values of SOCe, somewhat moderated by numerical filter 80, serve to modify the ~SOC values in ~. to permit con~inued warm-up. As an optional alternative, gate 94 might be omitted and the signal Tc decreased as a function of increasing temperature, with the adaptive capability of RAM 75 aiding in this regard.
While the described SOCc timing signal 28 is representative of an engine crank angle, and thus also a pump cam angle, to which the timing of actua-tion of the fuel delivery apparatus 16 should be ad-vanced or retarded and may be analog or digital in form, depending upon the type of signal required tc effect control of the controller 16', that signal might alternatively be representative o a time in the engine cycle at which a solenoid-actua~ed injector is to be actuated to inject fuel into the engine. In this latter instance, the signal would time the injec-tor opening/ and the subse~uent delay until the onset of combustion would be somewhat less than from pump actuation, but the general control concept would be the same.
One major advantage of the present invention is that the need for time-consuming and often complex adjustment of the mechanical interrelationship of the fuel pump a~d the engine at the time of assembIy =o then attain precise timing is generally obviated.
Instead, by establishing a mechanical relationship between the engine and pump which is approximately as desired, as by the aforementioned keying or a similarly simple referencing technique, the open-loop timing command obtained from ROM 65 and RAM 75 is sufficient to provide at least functional timing com-mands and the further adaptive provision for modify-ing or correcting the ~SOC data in RAM 75 ultimately corrects for any inaccuracies or errors contained in the set-up timing.
An optional further feature is a provision for periodically returning the corrected ~SOC map stored .in R~ 7S to memory 90 for use as the QSOC reference at the next engine start-up, assu~ing RAM 75 is of the volatile type in which its contents are lost when power is removed. In such instance, memory 90 would be of the programmable type, such as an EEPROM, and the map from RAM 75 would be entered in it periodical-ly and/or during some brief interval in which poweris maintained at shutdown. This capability would insure that upon successive engine start-ups the timing system would immediately include all correc-tions previously made to the very first ~SOCr map after it was entered in RAM 75, rather than requir-ing those corrections be made again by operation of the engine following each start-up.
Referring to Fig. 3, there is illustrated one general form of the SOC sensor, here designated 130, positioned in operative relationship with the combus-tion chamber 12 of cylinder 14. A piston 15 is illus-trated in cylinder 14 near the TDC position at the moment combustion begins following injection of fuel by injector 18. The combustion chamber 12 is -` ~IL2~ 334 accompanied by the emission of electroma~netic radia-tion, such as photons 17, and by ionization of the air/fuel mi~ture, represented by electrical charges 19, The sensor 130 of Fig. 3 is optical in nature and detects the electromagnetic radiation or emission of photons 17 coincident with combustion. Sensor 130 is mounted in the head 21 of engine 10 such that it is in optical communication with the lig~t~emitting combustion process in combustion chamber 12.
Referring to Fig. 4, the optical SOC sensor 130 is illustrated in greater detail in combination with its signal developing and conditioning circu:itry 32 utilized to generate the start of combustion timing signal 34. The optical sensor 130 includes an optical element, such as a quartz or sapphire rod 40 which acts as a viewing window having a proximal end suitably em-bedded in a metal mounting plug 42 which is adapted to be threadably inserted into the head 21 of en~ine 10.
Optical element 40 is bonded by means of a high-tem pera~ure cement or is brazed to plug 42 to provide a high temperature, high pressure, gas-tight seal.
Optical coupling is provided between the mounted end of optical rod 40 and a suitable transducer, such as photodiode 44. Photodiode 44 also forms part of sensor 130 and convexts the sensed electromagnetic radiation or light into an electrical signal. The photodiode 44 may either be directly housed in or mounted on plug 42 or preferaby, is spaced therefrom to minimiæe the ad-verse effects of heat and is optically coupled with element 40 by means of a fiber optic cable 46. The facing end portion of fiber optic cable 46 is retained in a central bore in mounting plu~ 42 in close facing relationship with optical rod 40 by suitable means not ~L2~3~

specifically ill~stratea, such as a collar clamp.
dust cover, such as a protective boot, may supplement the mounting of fiber optic ca~le 46 to mounting nut 42. The opposite end of fiber cable 46 is mounted and maintained in fixed operative relation with photodi~de 44 in a suitable manner which insures good optical coupling.
The formation and/or accumulation of soot or car-bon on the front face of optical rod 40 is substantially eliminated and the rod is physically protected by locat-ing the distal end of that rod within a circumferential gas plenum 48 formed with plug 42 and by maintaining that end of the rod at an elevated temperature. The plenum 48 surronds the optical rod 40 along its distal end. The diameter of the plenum adjacent the distal end of rod 40 gradually decreases to form a narrow an-nular orifice 50 between the plug 42 and the extreme distal end of rod 40 to increase the gas velocity and thus the cleansing action in that region. The gases within cylinder 14 and combustion chamber 12 ar~ com-pressed into the plenum 48 during the compression stroke and rapidly exit therefrom through the orifice 50 during the power stroke, thereby aiding in the de-sired cleansing of the optical rod 40. The rod 40 is of a material which is a poor thermal conductor and extends about one centimeter or more from its point of mour.ting contact with plug 42 to maintain its dis-tal end, during engine operation, at a temperature su'ficiently high to impede the accumulation of oc-cluding deposits by inhibiting condensation and byproducing dry carbonized material which is easily re-moved by the high velocity gas flow from the plenum.
The temperature at the distal end of rod 40 is typi~
cally about 425C.

1!!33~

~2q--Referring to the signal-developing circuitry 32, the light which accompanies combus-~ion within chamker 12 and which is sensed by rod 40 and is converted by pho~
todetector 44 to an electrical signal is represented by the current waveform 52 which comprises arl electrical analog of the intensity of the light detected. The signal 52 comprises the input to circuitry 32. It will be noted that the signal 52, as a function of time, ex-hibits a very rapid inc~ease at the onset of combustion.
The time of this increase is designated TSoc herein.
The magnitude of the signal may continue to increase thereafter, but at a slower rate, and then diminishes as the excitation accompanying combustion diminishes.
The current signal 52 is passed through a current-to-voltage converter 54 which provides the output signalvoltage having the waveform 56. The converter 54 is provided with sufficient gain to dxive it into satura-tio~ and the~reby provide the resulting waveform 56 with a particularly steep wave front at time TSoc. The am-~0 plitude of signal 56 at time Tso~ is relatively largeand that signal is then extended to an input of compa-rator 58 having a much smaller reference voltage 60 ap-plied to its other input. When the signal 56 exceeds the reference voltage 60 at time TSoc, the comparator 58 provides an output signal 34 having a squared, sub-stantially vertical wave front at time TSoc which is utilized as the start OI combustion (SOC) timing signal.
It will be appreciated that additional circuitry ~not shown) may be ~tilized if it is wished to convert the leading edge of the waveform 34 at time TSoc to a single spik~ rather than the leading edge of a square wave pulse. In either event, the very short rise time of the signal at time TSoc provides a precise signal for accurately identifying the onset of combustio~ Ln a combustion ..

.

chamber and is utilized as the SOC timing signal 34 provided to control circuit 26.
Alternate forms of a SOC sensor which rely on the detection of the ionization resulting from combus-tion of the air/fuel mixture are depicted in Figs. 5and 6. Fig. 5 depicts a basic form of ionization or electrostatic type SOC sensor, here designated 230.
The combustion of fuel within diesel engine 10 results in the rapid formation of ions in the combustion cham-ber and/or the precombustion chamber during fuel com-bustion. A rapid increase in the level of ionic charges occurs at the instant co~bustion begins. The electro-static sensor 230 is intended to sense this rapid in-crease in the ionization level and convert it to an electrical SOC timing signal 34.
A center electrode 240 is mounted in a suitable metallic mounting plug 242 via the intermediate sup-porting and electrically insulating structure of cera-mic insulator 241. The electxode 240! insulator 241 and m~unting plug 242 are hermetically bonded to one another, as with a suitable hea~ resis~ant cement, or are brazed to insure the pressure integrity within the combustion chamber. The mounti-ng plug 242-of Fi-g. 5----may be threaded into a threaded opening through the head of engine 10 to place it in communication with the respective combustion chamber 12. The innermost end of electrode 240 may be substantially flush with the inner end of plug 242 and preferably is relatively short such that it remains relatively cool to avoid the emission o~ electrons. The center electrode 240 is spaced from the inner circumference of the mounting nut 242 such that an annular or circumferential plenum 248 is formed therebetween. The insulator 24I includes a tapered surface for increasing the length o that ., : , .

~Z~3~

surface between the plug 2~2 and the center electrode 240 to minimize electrical leakage. The tapered insu-lator 241 ~nd the plenum 248 introduce certain turbu-lences to the gases entering that area to promote the S avoidance or elimination of soot formation on the elec-trode 240 and the surface of the insulator.
The plug 242 is in direct electrical connection with the engine lO, typically at ground potential. A
source 245 of a small finite DC voltage, i.e. 5 volis, is applied to the electrode 240 via an electrical con-necting cable 246 for facilitating the establishment of an electrical current flow through the electrode and the cable as a result of the ionic charges developed by combustion in the combustion chamber 12. The direc-15 tion of current flow is a function of the polarity ofthe applied voltage. The developed current is propor-tional to the level of ionization in the combustion chamber which in turn reflects the level of activity in the ~ombustion process. That electricâl current, appearing in conductor 246, is applied as the input to signal developing circuitry 32 constituted in substan-tially the same manner 2S hereinbefore described.
Since operation of the electrostatic sensor 230 is predicated on electrical charges from the combustion process arriving at electrode 240, the precise location of this sensor within the combustion chamber is impor-tant. Specifically, combustion takes place more nearly in the center of the chamber in a region which varies in size in relation to the engine operating speed and load conditions. Accordingly, the timing and the in-tensity of the ionization signal sensed by sensor ~30 is dependent upon its positioning in the chamber rela-tive to the origin of the com~ustion process. In view of this consideration a~d because there may be little or no additional room available in the head of certain ~23~83~

diesel engines for the installation of additional struc-tural elements, the SOC sensor may be incorporated with other functional engine elements.
Accordingly, referring to Fig. 6, there is illus-trated yet another embodiment of the electrostatic SOCsensor, here designated 330~ In this embodiment, the SoC sensor 330 takes ~he shape of a conventional glow plug heater normally inserted in the prechamber 12' associated with many diesel engines. In certain in-stances, the SOC sensor and glow plug heater may becombined in a single structural element. The prechamber 12' is typically mounted àbove and communicates with the main combustion chamber 12 via an orifice 11. The fuel injector nozzle 18' is mounted so as to inject fuel into the prechamb~r 12' where it undergoes preliminary com-bustion and is expelled via orifice 11 to the main com-bustion chamber 12 for the completion of combustion.
Typically, glow plugs are mounted in each of the pre-chambers 12' to facilitate ignition of the fuel in the prechamber, particularly during start-up and especially cold weather start-up. The structural configuration and positioning of the glow plug structure within prechamber 12l relative to the fuel injection path is known to be critical and has been optimized by various engine manu-facturers. Accordingly, that portion of SOC sensor 330which extends within prechamber 12' has been configured and dimensioned externally and positioned to conform as nearly as possible to the configuration and positionins of that portioh of a con~entional giow plug normally inserted into such prechamber.
The electrostatic SOC sensor 330 operatively posi-tioned in prechamber 12' in Fig. 6 is comprised in the main of a metal mounting plu~ 342, an ionization sens-iny electrode 340 and an insulator 341 which is . ~ ~

83~

positioned between and electrically isolates the elec-trode 340 fro~ the mounting plug 342 and thus from the engine 10. The mounting plug 342 is conveniently threaded into the threaded opening in the wall of a prechamber 12' which normally receives 2 glow plug~
The mounting plug 342 typically includes an axial bore therethrough for housing certain electrical elements to be hereinafter described. The longitudinally inner, or distal, end of plug 342 includes an annular seat in which is positioned an annular ceramic insulator 341 hermetically sealed thereto by a suitable heat resis-tant cement. An annular recess in the longitudinally inner, or distal, wall of the insulator 341 provides a seat for the proximal end of the electrode 340 which is hermetically sealed thereto by a suitable heat resis-tant cement. The electrode 340 is provided with a sur-face geometry and configuration which closely conforms to that of the glow plug heater designed for utiliza-tion in the particular prechamber 12'. Typically, the electrode 340 is a tubular metal shell having a blind, or closed, distal end and being open at its proximal end which is in seated engagement with insulator 341.
To provide the re~uisites of an ionization sensor, it is only necessary that an electrical conductor 346 be connected at one end to the electrode 340 and that its other end be led out through the bore in plug 342 to signal conditioning circuitry, as for instance cir-cuit 32 illustrated in Fig. 4. Additionally, a source of signal developing voltage analogous to source 245 in Fig. 5 may be connected to the lead 346.

~34 The structure comprising electxostatic SOC
sensor 330 in Fig. 6 may include additional elements to enable it to operate cooperatively or alternatively as a glow plug for the purpose of facilitating fuel combustion in the prechamber 12' during cold start-up conditions. For instance, the SOC sensor 330 may include an elongated rigid spar 352 mounted thereto and extending coaxially within the central bore in a manner analogous to a conventional glow plug.
The spar 352 may be of heat resistant material and is preferably an elPctrical insulator, as for instance a ceramic. A wire-like h~ating element 350 is wound about the distal end of spar 352 which is positioned within the recess formed by electrode 340. One end of heater wire 350 is placed in electrical connection with the engine 10, as by connection with conductive ring 354 seated in electrical contact with plug 342.
The other end of heater wire 350 may be led out through the rear of the sensor structure for selective connection to a source of electrical power, as for instance the 12 volt supply of an automobile. The proper placement of insulating supports and/or insulating coatings on the respective conductors 346 and 350 insure their electrical isolation from one another and from certain elements of the sensor structure.
The optical SOC sensor 130 described with xeference to Figs. 3 and 4 may also be structured similar to the external structure of ~he electrostatic SOC
~0 sensor 330 of Fig. 6 to provide a sensor configuration which conforms externally to that of a conventional glow plug for introduction to the prechamber 12'.
~oreover, the optical SOC sensor may include a heating element to function as a glow plug. Specifically referring to Fig. 7, a portion of an optical SOC sensor 430 is illustrated in which the base plug or mounting ,, ~

~Z3L5,'~339L

structure includes a tubular extension 442' having an external geometry which substantially conforms to that of a con~entional glow plug and to the electrode 340 of the electrostatic SOC sensor 330 of Fig. 6.
The optical element 440 is generally longer than its counterpart illustrated in Fig~ 4, and a suitable heating element 449 is concentrically disposed about the element 440 within plug extension 442' for providing heat during start-up. An aperture 451 in the distal end of extension 442' is in optical registry with the distal end of optical element 440 to provide the necessary optical path to the combustion site. The aperture 451 is sized and posi~ioned relative to the distal end of the optical element 440 to form a narrow annular orifice 450 therabout for the high speed entry and exhaust of gases to and from the plenum 448 for cleaning the optical element.
It will also be ullderstood that a multicylinder diesel engine may be provided with SOC sensors in one, all, or less than all, of the combustion and/or precombustion chambers of the engine in developing the requisite timing control signals. The utilization of more than one SOC sensor not only improves the precision of tIming control, but also may provide engine diagnostic information. If the engine includes precombustion chambers, each precombustion chamber may be equipped with a SOC sensor having the dual capabilities of generating a signal indicative of the start of combustion and providing heat to facilitate the combustion of fuel in the prechamber during start-up. Alternatively, one prechamber may be provided with a SOC sensor capable only of providing a SOC
timing signal and the remaining prechambers would include conventional glow plugs having no SOC sensing capability. Moreover, the SOC sensor might instead be incorporated in the structure of the injector so as to minimize the number of penetrations of the combustion chamber wall, this being of particular ~alue in direct injection engines which do not have a precombustion chamber and a glow plug entry.
Although this invention has been shown and described with respect to dPtailed embodiments thereof, it will be understood by those skilled in the art that ~arious changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention. It will be appreciated that the invention described herein provides an improved fuel delivery timing control for diesel engines and can be implemented on a fully electronic fuelin~ control or in conjunction with a mechanical or hydraulic-mechanical governor control without departing from the spirit of the invention. Moreover, although detailed discussions of an optical and an electrostatic SOC sensor exist herein, it will be appreciated that SOC sensors which respond to other SOC phenomena are within the ambit of the invention.
For instance, rapid-response temperature sensor, or similarly rapid sound and/or pressure transducers, or the like might also be used.

.

Claims (29)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a fuel control system for a diesel engine, said system including means for delivering fuel to said engine for combustion therein, said fuel delivery means being responsive at least to a timing control signal for controlling the timing of the delivery of fuel to a combustion chamber of the engine for combustion therein, means for providing signals indicative of certain engine operating conditions and means responsive to said signals indicative of certain engine operating conditions for providing said timing control signal, the improvement comprising means insertable through a wall of said combustion chamber of said engine for sensing a property of combustion which is directly representative of the onset of combustion therein and for providing a signal indicative thereof, said sensing means additionally being so structured as to provide self-cleaning thereof during and substantially only as a direct consequence of operation in a said combustion chamber, said onset of combustion indicating signal being one of said signals indicative of certain engine operating conditions and to which said timing control signal providing means responds.

2. A fuel timing system for a compression ignition engine, said system including:
means for delivering fuel to said engine for combustion, said fuel delivery means being responsive to a timing control signal for controlling the timing of fuel delivery by said fuel delivery means;
a first signal generator comprising means for sensing a phenomenon in a combustion chamber of said engine which is directly representative of the onset of combustion therein and providing a representative signal thereof and means for conditioning said representative signal to provide an electrical signal precisely indicative of the actual instant of the onset of combustion, said sensing means being so structured as to provide self-cleaning thereof during and substantially only as a direct consequence of operation in a said combustion chamber to facilitate continuous operation;
second signal generating means for providing an electrical signal indicative of engine timing;
third signal generating means for providing an electrical signal indicative of engine speed;
fourth signal generating means for providing an electrical signal indicative of engine load;
and control circuit means operatively connected with and being responsive to each of said onset of combustion signal, said engine timing signal, said engine speed signal and said engine load signal for providing said timing control signal, said control circuit means including means for providing a signal representative of a desired timing of the onset of combustion as a function of said engine speed and said engine load and further means responsive to said desired timing of onset of combustion signal and to said actual instant of onset of combustion signal each referenced to said engine timing signal, for adaptively providing said timing control signal such that the subsequent actual start of combustion substantially coincides with the timing of said desired start of combustion.

3. The invention of claim 2 wherein said sensed phenomenon is optical electromagnetic radiation emitted by the combustion process.

4. The invention of claim 3 wherein said sensing means comprises a heat resistant optical element adapted for mounting through a wall of said engine combustion chamber.

5. The invention of claim 4 wherein said signal conditioning means includes signal shaping means for sharpening in time the leading edge of said combustion onset representing signal.

6. The invention of claim 4 wherein said sensing means further includes a photodetector, said photodetector being spaced a significant distance from said optical element and being optically coupled therewith by a fiber optic cable.

7. The invention of claim 2 wherein said sensed phenomenon comprises the ionization level in the combustion chamber.

8. The invention of claim 7 wherein said sensing means comprises electrode means, said electrode means being supported in electrically insulated relationship with said engine, and additionally including means for cleaning said electrode means during operation in a said combustion chamber to facilitate continuous operation of said electrode means in a said combustion chamber.

9. The invention of claim 8 wherein said sensing and conditioning means includes a source of biasing potential connected between a reference potential and said electrode means for establishing a current representative of the level of ionization sensed.

10. The invention of claim 2 wherein said engine is constructed to mount a conventional glow plug heater extending through an opening in a wall thereof into a portion of the combustion chamber, that portion of a said conventional glow plug heater positioned within said chamber having a characteristic external structure and said combustion sensing means being externally structured for mounting in said engine in substantially identical substitution for said external structure of said conventional heater otherwise positioned within said chamber.

11. The invention of claim 10 wherein the structure of said combustion sensing means additionally includes heating means to retain the heating function of the replaced conventional heater.

12. The invention of claim 10 wherein said sensed phenomenon comprises the ionization level in the combustion chamber, and said sensing means comprises electrode means, said electrode means being supported in electrically insulated relationship with said engine.

13, The invention of claim 4 wherein said optical element cleaning means comprises means defining a gas plenum around and along at least a distal portion of said optical element, said plenum being alternately filled and emptied by changes in the gas pressure within said combustion chamber such that gas is caused to sweep across and thereby clean said distal portion of said optical element.

14. The invention of claim 13 wherein said optical element cleaning means further comprises said optical element being mounted such that the distal, light-sensing end thereof is maintained at a temperature sufficiently high during engine operation that the accumulation of occluding deposits thereon is substantially impeded.

15. The invention of claim 8 wherein said means for cleaning said electrode means comprises means defining a gas plenum around and along at least a portion of said electrode means, said plenum being alternately filled and emptied by changes in the gas pressure within said combustion chamber such that gas is caused to sweep across and thereby clean said portion of said electrode means.

16. The invention of claim 4 wherein said control circuit means for adaptively providing said timing control signal such that the subsequent actual start of combustion substantially coincide with the timing of said desired start of combustion comprises:
means for comparing the signal indicative of the timing of the actual instant of the onset of combustion with said signal representative of a desired timing of the onset of combustion for said engine speed and load to provide an error signal indicative of the timing difference therebetween; and means for automatically correcting said signal representative of a desired timing of the onset of combustion, said corrected timing control being said timing control signal for controlling the timing of fuel delivery by said fuel delivery system to effect said desired timing of said onset of combustion, said means for correcting said predetermined timing control signal including retrievable storage means, means for forming at least one correcting signal and storing said correcting signal in said storage means, and means for combining said correcting signal with said signal representative of a desired timing of the onset of combustion in a manner such that said corrected timing control signal tends to reduce said error signal said means for forming a said correcting signal including means for adding a fraction less than unity of a said error signal to the correcting signal previously stored for the same speed and load conditions such that said correcting signal represents substantially the most probable start of combustion timing under the same speed and load conditions.

17. The invention of claim 6 wherein said means for conditioning said representative signal to provide an electrical signal precisely indicative of the actual instant of the onset of combustion comprises:
amplification means responsive to said electrical signal indicative of the combustion process for substantially increasing the magnitude of at least the leading edge of said signal indicative of the combustion process; and threshold means responsive to said magnitude-increased signal exceeding a predetermined relatively-low magnitude threshold level for providing an electrical output signal having a leading edge which is substantially vertical relative to the time base of interest in a compression ignition engine, said signal leading edge being precisely indicative of the instant of actual onset of combustion.

18. A signal generator for use with a compression ignition engine to provide electrical signals directly and precisely indicative of the instant of the onset of combustion, said signal generator comprising:
means adapted to be mounted in operative communication with a combustion chamber of said compression ignition engine to sense a direct property of the combustion process within said combustion chamber and provide an electrical signal representative thereof, said sensing means being so structured as to be substantially self-cleaning during and substantially only as a direct consequence of said operative communication with a said combustion chamber whereby substantially continuous operation with a said combustion chamber is afforded;
amplification means responsive to said electrical signal indicative of the combustion process for substantially increasing the magnitude of at least the leading edge of said signal indicative of the combustion process; and threshold means responsive to said magnitude-increased signal exceeding a predetermined relatively-low magnitude threshold level for providing an electrical output signal having a leading edge which is substantially vertical relative to the time base of interest in a compression ignition engine, said signal leading edge being precisely indicative of the instant of actual onset of combustion.

19. The signal generator of claim 18 wherein said amplification means is driven into saturation by said signal indicative of the combustion process.

20. The signal generator of claim 19 wherein said threshold level of said threshold means is provided by a reference signal much smaller in magnitude than said mangitude-increased signal.

21. The signal generator of claim 18 wherein said combustion property sensing means comprises optical viewing means adapted to be mounted in optical communication with the combustion chamber of said engine to sense electromagnetic radiation emanating from combustion in said chamber, the level of said electromagnetic radiation being rapidly and substantially increased at the onset of combustion.

22. The signal generator of claim 21 wherein said optical viewing means comprises a heat-resistant optical element adapted for mounting through a wall of said engine combustion chamber, means defining a gas plenum around and along at least a distal portion of said optical element, said plenum being alternately filled and emptied by changes in the gas pressure within said combustion chamber such that gas is caused to sweep across and thereby clean said distal portion of said optical element.

23. The signal generator of claim 22 wherein said sensing means includes a photodetector and a fiber optic cable operatively connecting said optical element and said photodetector.

24. The signal generator of claim 22 wherein said optical element cleaning means further comprises said optical element being mounted such that the distal, light-sensing end thereof is maintained at a temperature sufficiently high during engine operation that the accumulation of occluding deposits thereon is substantially impeded.

25. The signal generator of claim 18 wherein said combustion property sensing means comprises electrode means, said electrode means being supported in electrically insulated relation with said engine for sensing the level of ionization in the combustion chamber and including means defining a gas plenum around and along at least a portion of said electrode means, said plenum being alternately filled and emptied by changes in the gas pressure within said combustion chamber such that gas is caused to sweep across and thereby clean said portion of said electrode means.

26. The signal generator of claim 25 wherein said sensing means includes a source of biasing potential connected between a reference potential and said electrode means for establishing a current representative of the level of ionization sensed.

27. The signal generator of claim 18 wherein said sensing means includes a structure having an elongated tubular outer surface along that portion thereof suited for mounting within the prechamber of a diesel engine, said surface geometry substantially conforming to that of a conventional glow plug heater normally positioned within such prechamber.

28. The signal generator of claim 27 wherein said sensing means structure additionally includes heating means to include the function of a glow plug heater.

29. The signal generator of claim 18 wherein said sensing means includes a sensing element having a distal end adapted for disposition in proximate, direct communication with said engine combustion chamber, and wherein said structuring of said sensing means to effect said self cleaning provides a relatively high temperature at and a gas flow across said distal end of said sensing element during engine operation for substantially impeding the accumulation thereat of occluding deposits.

means to effect said self cleaning provides a relatively high temperature at and a gas flow across said distal end of said sensing element during engine operation for substantially impeding the accumulation thereat of occluding deposits.