US3885720A - Method and system for controlling combustion timing of an internal combustion engine - Google Patents

Abstract

The specific disclosure provides for controlling ignition timing of an internal combustion engine by triggering a sawtooth wave generator to generate a sawtooth signal having a frequency equal to the firing frequency of the engine. A feedback network maintains the amplitude of the sawtooth wave signal at a constant level in response to the frequency of the sawtooth wave signal. A voltage detector adjustable to an ignition timing set point detects the set point voltage during the generation of each sawtooth and provides an ignition trigger signal for firing the engine upon each detection of the set point voltage. Another voltage detector may be provided which is adjustable to a fuel injection timing set point for detecting a fuel injection set point voltage during the generation of each sawtooth and for providing a fuel injection trigger signal upon each detection of the fuel injection set point voltage.

Description

United States Pat Brennan 15 1 METHOD AND SYSTEM 170R 4 V CONTROLLING-COMBUSTlON TlMiNG OF AN INTERNAL COMBUSTION ENGINE ent 11 1 111 3,885,720 1451 May 27, 1975 Primary Examiner Char1es J. 'Myhre Assistant Examiner-Cort Flint [75] inventor: William R.;Brennan, Stanford, g-ggxghg or f l'f P l mnuggett; Carl Conn. g 731 Assignee: Mobil 011 Corporation, New York, "[57 y g rAas RAc'r.

The specific disclosureprovides for controlling igni- [22] Filed; Jan. 10, 1973 tion timing of an internal combustion engine by triggermga sawtooth wave generator to generate a saw- 1 PP N94 322,393 tooth signal having a frequency equal to the firing fre- Rcmed Appncafion quency of the engine. A feedback network maintains [63] Cominwion of s" No 09 878 Jan 26 the amplitude of the sawtooth wave signal at a constant level in response to the frequency of the sawtooth wave signal. A voltage detector adjustable to an 23/1 36 53 ignition timing set point detects the set point voltage .[58] ne'ld R E during the generation of each sawtooth and provides 1231i) 7 an ignition trigger signal for firing the engine upon I each detection of the set point voltage. Another voltage detector may be provided which is adjustable to a [56] cued fuel injection timing set point for detecting a fuel in- UNITED STATES PATENTS jection set point voltage during the generation of each 2,670,724 3/1954 Reggio 123/ 140 MC sawtooth and for providing a fuel injection trigger sig- 7 .913 12/1959 Guiot 123/32 EA nal upon each detection of the fuel injection set point 3,020,897 2/1962 Seltine et a1 123/148 5 Velma 3,314,407 4/1967 Schneider 123/148 E 3,592,178 7/1971 Schiif 123 1411 a 14 Claims, 23 Drawing Figures [I ll 1' 111mm mum ime mlms 11mm comm. n'ir' i '1 ,1 ,2 s n ,1 ,s 0

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INVENTOR. W/ll/bm RB/enmn ATTORNEY l METHOD AND SYSTEM FOR CONTROLLING COMBUSTION TIMING OF AN INTERNAL COMBUSTION ENGINE 1 This is a continuation. of a pplication Ser. No. l09.8"l8. filed .lan..26. 197i. 7'

BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to an engine combustion timing control system and method. More particularly. the present invention relates to a method and system for controlling spark ignition and/or fuel injection timing of an internal combustion engine.

2. Description of Prior Art internal combustion engines generally function by mixing fuel and air. compressing the mixture in a chamber, igniting the compressed mixture, and using the expansion of gases resulting from the heat of combustion to drive a piston which, in turn, causes a crankshaft to rotate. it is common to provide an ignition system for generating an electrical impulse which is timed in relation to rotation of the crankshaft to jump a gap inside the combustion chamber and produce a spark which ignites the mixture.

An ignition system supplies electrical energy for lgniting fuel in each engine cylinder at the proper time during the engine cycle. in a conventional ignition system, a storage battery supplies the primary electrical energy which must be amplified to furnish a proper spark at each spark plug gap. The amplification is accomplished in a step-up transformer or coil having a primary winding connected in a primary circuit including the battery, and a secondary winding in which a high voltage is induced by continuous opening and closing of the circuit including the primary winding. The opening and closing of the primary circuit is generally accomplished by cam actuated breaker points. The cam is driven by a camshaft which is generally geared to rotate at one-half engine speed. The cam is customarily located at the lower portion of a distributor. The upper portion of the distributor includes another rotary switch driven by the engine that distributes the high voltage electrical energy induced in the secondary winding to the spark plugs of the engine in a proper engine firing order.

The conventional ignition system has certain characteristics which have become of increasing concern to engine designers as engine power and speed have increased. The secondary voltage output of the coil is limited at high engine speeds as a result of a time element involved in opening and closing the coil circuits. Further, the breaker points are subjected to the full primary current flow, and, therefore, are subject to buming and erosion which will require corrective maintenance from time to time. Transistorized ignition systems were developed to meet this concern. A transistorized ignition system generally acts as an amplifier and a switch.

There are many types of transistorized ignition systems. For example. a contact-controlled ignition system retains the conventional breaker points. in the contact-controlled system. the transistor circuit receives full current from the battery and directs a very'small part as a control medium through the distributor points. The main output of the transistor circuit is applied to the primary of the ignition coil when the breaker points close. The subsequent breaker point 1 opening causes a collapse of the field about the primary of the coil to inducea' high voltage in the secondary of the coil. The subsequent electrical energy distribution to the "engine'spark plugs is the same as in the conventional ignition 'system. A v'ariationof the foregoing contact-controlled transistorized ignition system includesa capacitor which is constantly suppliedby energy from the battery. When the contact points are opened, the transistor circuit causes the capacitor to discharge to the primary of the coil. Since there is no current flow and thus no magnetic field in the coil prior to discharge of the capacitor. the discharge of the capacitor to the primary establishes a magnetic field which induces the required high voltage in the secondary of the coil. Thus, this particular system produces secondary voltage upon the closing of the breaker points rather than upon the opening of the breaker points.

A still further transistorized system is a magneticimpulse system which replaces the breaker points with a small magnetic or pulse generator. in this system, a pole in the shape of a disc is mounted about the lower portion of the distributor and has a number of projections thereupon equal to the number of pistons. The disc is rotated within a stationary pole having an equal number of inwardly directed projections. When the projections of the stationary and rotating'pole pieces are in-llne, a magnetic field is established which induces a voltage in a pickup coil. The induced voltage triggers the transistor circuit to permit the electrical energy of the battery to be applied to the primary of the coil. As the projections separate the field collapses and a small voltage of reverse polarity is again induced in the pickup coil. The voltage having the reverse polarity again triggers the transistor circuit to cause a collapse of the primary coil and thereby develop a high secondary voltage in the secondary of the coil.

An interval of time elapses between the jumping of the gap by the spark and full expansion of the gases with combustion. ignition is therefore timed during each engine cycle to provide for the development of maximum pressure as a result of the expansion of the gases with combustion. By maintaining ignition timing at an optimum setting. the mixture is more completely burned to thereby minimize hydrocarbon emissions from the engine.

ignition timing is commonly called spark advance when the spark is timed to be generated before the top dead center position of the piston, and is commonly called spark retard when the spark is generated after the piston passes through the top dead center position.

ignition timing of an engine will vary with engine design and with engine operation. Specifically, a change in engine speed requires a concurrent change of ignition timing to achieve maximum power output.

it is common to use a device known generally as a "mechanical advance" which balances centrifugal force against spring tension by a series of weights, levers, and springs to provide a device sensitive to engine speed that will vary the ignition timing in response to changes in engine speed. These devices are affected by an alteration of the balance of forces caused by any change in weight due to dirt. grease or wear. and any change in spring tension due to temperature change or wear. They are also affected in their movement by dirt. grease, or the lack of it, and wear, and by any change in consistency of the grease due to a change in temperature.

it is also common to use a device known generally as a vacuum advance" which generally consists of a spring supported diaphragm connected to the intake manifold which will vary the ignition timing in response to the variation of the difierencesbetween the intake manifold pressure and atmospheric pressure. These devices operate on the assumption thata measurement of the variance between intake manifold pressures and atmospheric pressures will accurately reflect, the pressures and temperatures within the combustion chamber. However, since the pressures and temperatures within the combustion chambers are not being measured directly, this provides only an approximation. These devices are furthennore subject to the same problems in moving as are the "mechanical advance" devices, and are additionally affected by leaks in the pressure sensitive system.

Under normal combustion, ignition will cause a rapid progressive burning wherein the flame front spreads out from the igniting spark to the more remote sections of the combustion chamber. As the flame front progresses during the burning period, the temperature and pressure in the combustion chamber rises considerably. The ensuing compression of the unburned part of the mixture by the expansion of the burning gases raises the temperature and pressure of the unburned mixture which may cause auto-ignition. in this phenomenon, the mixture which is ignited spontaneously does not burn progressively, but practically explosively with the result that rapid pressure waves are produced. The colliding wave fronts produce sounds which are generally known as combustion knock or detonation. Combustion knock or detonation generally occurs during rapid acceleration at low to medium speeds.

Combustion knock or detonation is to a large extent controlled by the anti-knock quality or octane number of the fuel. The anti-knock quality or octane number of the fuel may be controlled by adjusting the feed stock and/or control variables in a refinery process, and by the use of additives such as tetraethyl-lead. However, the trend at this time is to minimize or avoid the use of additives such as tetraethyl-lead.

Engine mechanical and operating factors also exert a considerable influence upon combustion knock. The tendency to knock increases slightly at lower speeds and mechanical-transmission cars and at higher speeds in automatic-transmission cars, at higher torque, as the spark timing is advanced. when the engine is overheated, when hot dried intake air is used, and at low altitudes. An increase in compression ratio by combustion-chamber deposit accumulations can also increase knocking tendencies.

Combustion knock or detonation produces inefficient and incomplete combustion of the fuel mixture. and therefore increases hydrocarbon emissions.

SUMMARY'OF THE INVENTION in a preferred embodiment of the invention, the timing of a combustion cycle of an internal combustion engine having a rotatable power shaft is controlled by a system comprising means responsive to the rotation of the power shaft for generating sequential input trigger signals having a frequency proportional to the speed rotation of the shaft. A sawtooth waveform generator responsive to the input trigger signal generates sequential sawtooth waveforms where each of the waveforms has a duration corresponding to a predetermined number of degrees of-power shaft-rotation having an amplitude changing as a function of time. The maximum amplitude of thewaveform is maintained at a substantially constant level for all engine speeds by varying the instantaneous rate of change of the amplitude as a function of engine speed. A set point signal is generated corresponding to a predetermined angle of rotation and the .set pointsignal is'compared to amplitude of the waveform. When the amplitude'of thewavefonn is detectedfas having a level equaito the set point's'ignal so as to correspond toa predetermined angle of rotation of the power shaft, a trigger signal is generated. By adjusting the set point signal, the timing of the engine trigger signal may be adjusted to correspond withdifferent predetermined angles of rotation without adjusting the durationof thesawtooth waveforms corresponding to a predetermined number of degrees.

in accordance with one important aspect of the invention, the amplitude of the waveform is maintained at a substantially constant level at all engine speeds by feedback means which vary the rate of change of amplitude as a function of engine speed.

in accordance with another important aspect of the invention, the instantaneous rate of change in amplitude is varied in response to a control signal having a magnitude representing the speed of the rotation of the power shaft. The control signal is then applied to a semiconductor device to control the current flow path to a charged storage means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in block diagram form a specificenbodiment of the invention for controlling ignition timing of an engine;

P10. 2 shows an output curve of a component of a specific embodiment of the invention which is used as a basis for controlling ignition timing of an engine;

FIG. 3a through 3f show a circuit of a specific embodiment of the invention for adjusting ignition timing of an engine;

FIG. 4 shows in block diagram form the manner in which FIGS. 34 through 3] are arranged;

FIGS. 5a through 50 show curves generated at specific points in the circuit of FIGS. 3a through 3},-

FIG. 6 shows a transistorized ignition system circuit suitable for use in the specific embodiment of FIGS. 30 through 3],-

FIG. 7 shows a circuit suitable for use as a timing control set point generator in another specific embodiment of the invention which provides for automatic ignition timing control of an engine;

FIG. 8 shows circuit components suitable for use as an adjustable voltage detector, a manual or automatic network, and a signal inverter amplifier in the embodiment-for automatic ignition timing control of an engine;

FIG. 9 shows circuit components suitable for use as an engine reference signal generator, detector pulse modifier and a transistor ignition system in the embodiment for automatic ignition timing control of an ens i FIG. 10 showsin block diagram form the arrangement of FIGS. 7, 8 and 9 with3a and M as the embodiment for automatic ignition timing control of an engine;

FIG. II shows an engine-referencesignalgenerator suitable for use in the disclosed embodiments;

FIG. I2 shows a vacuum advancecurve for aspecific vehicle; g "=1 FIG. 13 shows a centrifugal advance curve for the specific vehicle;

FIG. 14 shows in block generator suitable for use in the automatic timing con trol embodiment; 7

FIG. 15 is a circuit suitable for use as a curveshapert' and FIG. 16 shows in block diagram form another specific enbodlment of the present invention wherein the automatic ignition timing control system is used as a basis for generating an input signal for a fuel injection control system. I r

DESCRIPTION OF SPECIFIC EMBODIMENTS I FIG. 1 shows in block diagram form an electronic engine ignition timing control system as a specific embodiment of the present invention. With reference to FIG. I, the engine is started by operating an on-off circuit II to the on position and operating the manual or automatic network to the manual position. The engine is then cranked with any known starter system (not shown). An engine reference signal generator I generates a reference or trigger signal during each engine piston cycle which serves as a basis for firing a spark plug.

In a more specific embodiment a positive square wave reference or trigger signal is generated at the ignition distributor breaker points between each opening and closing of the points. However, a transistor ignition system 14 used in the more specific embodiment requires a negative triggering pulse to generate electrical energy for application through an engine ignition distribution system to fire the spark plugs I6. Consequently, the embodiment of FIG. 1 provides for applying the trigger signal from the engine reference signal generator by a line 50 to a signal inverter amplifier 12 wherein the trigger signals are inverted and applied by a line 51, the manual or automatic network 10 in the manual mode, and a line 52 to a trigger pulse modifier I3. The trigger pulse modifier 13 generates negative trigger pulses in response to the positive trigger signals applied thereto for application to the transistor ignition system 14 which, in turn, acts to fire the spark plugs 16 through the engine ignition distribution system 15.

After the engine is started, the manual or automatic network I0 is moved to the automatic mode. In the automatic mode, the engine reference signal generator 1 applies its reference output signal to an input modifier network 2. The input modifier network 2 generates a peaked trigger pulse in response to a negative excursion of the reference signal applied thereto, and applies the peaked trigger pulse to a sawtooth wave generator 3. The sawtooth wave generator 3 generates a sawtooth wave in response to each trigger pulse applied thereto. The sawtooth wave output of the generator 3 is applied to an emitter follower amplifier 4 wherein the sawtooth wave is current amplified.

The current amplified sawtooth signal is applied to a feedback network 5 wherein the' sawtooth signal is clipped at a predetermined level, and the clipped portion of the sawtooth signal is rectified and fed as an output signal to a sawtooth amplitude control 6. The sawtooth amplitude control 6 acts to control the rate of diagram forma knock signal generation of the sawtooth-by the'sawtooth generator in respons'e to the frequency of the sawtooth such that theioutputofthe sawtooth wave generator 3 is maintained atlaconstant-amplitude. I

"Since-the sawtooth wave generator 3 is triggered as -'each-piston"reaches a predetermined position in its cycle, for example,- when the distributor points close, the length of each sawtooth output'of thesawtooth wave generator 3 is proportional to the time elapsed between successive pistonsinfiring order-reaching the predetermined position,'forexample the time between'successive closing of the distributor points, irrespective of engine speed. Further, since the sawtooth wave generator 3 generates a constant amplitude sawtooth output rcgardless of speed, it is apparent that the engine will fire at the same voltage level during each generation of the sawtooth as determined by the ignition timing of the system. g g

The emitter follower amplifier 4 also applies the current amplified sawtooth to another current amplifier 7 which acts togenerate a sawtooth output sufficiently strong to minimize the possibility of distortion of the signal. The current amplified sawtooth output signal from the amplifier '7 is applied to an adjustable voltage detector 8. The adjustable voltage detector 8 also has applied thereto a signal from a timing control set point generator 9. 1

Since a particular timing setting will cause the engine to fire at the same voltage level on the sawtooth, the sawtooth wave is used as a basis for adjusting the ignition timing control of the engine. This is accomplished by adjusting the timing control set point generator 9 to a particular set point which acts to apply a set point signal to the adjustable voltage detector 8 to determine the voltage level detected by the adjustable voltage detector 8.

In a more specific embodiment, the adjustable voltage detector 8 generates a negative square wave signal upon sensing the voltage level during the generation of each sawtooth as determined by the setting of the timing set point generator 9. The negative square wave output of the adjustable voltage detector 8 is applied through the manual or automatic network 10 which is in the automatic mode to the trigger pulse modifier 13 by way of the line 52. In response to the output of the detector 8, the trigger pulse modifier I3 generates peaked negative trigger signals which are applied to the transistorized ignition system 14 to thereby trigger the ignition system 14 to provide high voltage distribution to the spark plugs I6 through the distributor 15. Thus, the sawtooth-voltage level detected by the detector 8 detennines the ignition timing of the engine.

The embodiment of FIG. I also provides for applying the output of the engine reference signal generator I to an engine speed tachometer 18 for monitoring the speed of the engine. Further, FIG. 1 applies a positive voltage from the battery of the vehicle as indicated by the dashed line leading therefrom to the engine reference signal generator I, the signal inverter amplifier 12, the trigger pulse modifier I3, the adjustable voltagc detector 8, and a regulated power supply 17. The regu lated power supply 17 supplies a suitable regulatct power to the input modifier network 2, the sawtootl wave generator 3, the emitter follower amplifier 4, tht feedback network 5, the sawtooth amplitude control 6 the current amplifier 7, the adjustable voltage detecto 8, and the timing control set point generator 9.

Claims (14)

1. A system for controlling the timing of the combustion cycle in an internal combustion engine having a rotatable power shaft, said system comprising: means responsive to rotation of said power shaft for generating sequential input trigger signals having a frequency proportional to the speed of rotation of said power shaft; a waveform generator responsive to said input trigger signals for generating sequential sawtooth waveforms, each of said sawtooth waveforms having a duration corresponding to a predetermined number of degrees of power shaft rotation and having an amplitude changing as a function of time; feedback means responsive to said waveform generator for maintaining the maximum amplitude of said sawtooth waveforms at a substantially constant level for all engine speeds by varying the rate of change of the amplitude as a function of engine speed such that a given instantaneous magnitude of each sawtooth waveform corresponds to a predetermined angular position of the power shaft regardless of engine speed; means for generating a set point signal corresponding to a predetermined angle of rotation of said power shaft; means for detecting when the amplitude of each of said sawtooth waveforms reaches a level defined by said set point signal so as to correspond to a predetermined angle of rotation of said power shaft; means responsive to said detecting means for generating an engine trigger signal corresponding in time to a predetermined angle of rotation of said power shaft; and means for adjusting said set point signal so as to adjust the timing of said engine trigger signal to correspond with a different predetermined angle of rotation of said power shaft.

2. The system of claim 1, wherein the instantaneous amplitude of each of said wave forms corresponds to a unique angle of rotation.

3. The system of claim 1, wherein said wave form generator comprises: a capacitor means; and a current source for charging said capacitor means during said predetermined number of degrees of power shaft rotation to generate said wave forms.

4. The system of claim 1, wherein said feedback means comprises: means for clipping said signals representing the charge on said capacitor means above a predetermined level; and means responsive to the clipped portions of said signals representing the charge on said capacitor means to control the rate of charge of said capacitor means such that said power shaft rotation signals have a unique instantaneous amplitude for a given instantaneous angle of rotation for all engine speeds.

5. The system of claim 1, wherein said means for adjusting said set point signal is manually adustable.

6. The system of claim 1, wherein said means for adjusting said set point signal is automatically adjustable in response to at least one engine parameter.

7. The system of claim 1, including means for initiating sparking in said engine in response to said engine trigger signal.

8. The system of claim 7, wherein said means for adjusting said set point signal is automatically responsive to combustion knock.

9. The system of claim 8, wherein said means for adjusting said set point signal is automatically responsive to engine speed.

10. The system of claim 7, wherein said means for adjusting said set point signal is manually adjustable.

11. The system of claim 10, further comprising switch means for adjusting The duration of said wave forms to permit the system to be used with engines having different numbers of combustion chambers.

12. The system of claim 10, further comprising means initiating fuel injection into at least one combustion chamber of said engine in response to said engine trigger signal.

13. A system for controlling the timing of the combustion cycle of an internal combustion engine having a rotatable power shaft, said system comprising: means responsive to rotation of said power shaft for generating sequential input trigger signals having a frequency proportional to the speed of rotation of said power shaft; a waveform generator responsive to said input trigger signals for generating sequential sawtooth waveforms, each of said sawtooth waveforms having a duration corresponding to a predetermined number of degrees of power shaft rotation and having an amplitude changing as a function of time such that a given instantaneous magnitude of each sawtooth waveform corresponds to a predetermined angular position of the power shaft regardless of engine speed; means for maintaining the maximum amplitude of said sawtooth waveforms at a substantially constant level for all engine speeds by varying the instantaneous rate of change of the amplitude as a function of engine speed; means for generating a set point signal corresponding to a predetermined angle of rotation; means for detecting when the amplitude of each of said sawtooth waveforms reaches a level defined by said set point signal so as to correspond to a predetermined angle of rotation of said power shaft; means responsive to said detecting means for generating an engine trigger signal corresponding in magnitude to a predetermined angle of rotation of said power shaft; and means for adjusting said set point signal so as to adjust the timing of said engine trigger signals to correspond with a different predetermined angle of rotation without adjusting said duration of said sawtooth waveforms corresponding to said predetermined number of degrees.

14. A system for controlling the timing of the combustion cycle of an internal combustion engine having a rotatable power shaft, said system comprising; means responsive to rotation of said power shaft for generating sequential input trigger signals having a frequency proportional to the speed of rotation of said power shaft; a sawtooth waveform generator comprising charge storage means and a semiconductor device acting as a current flow path for changing the charge on said charge storage means, said waveform generator being responsive to said input trigger signal for generating a series of sequential waveforms at the output of said charge storage means having a duration corresponding to a predetermined number of degrees of power shaft rotation and having an amplitude continuously changing as a function of time such that a given instantaneous magnitude of each sawtooth waveform corresponds to a predetermined angular position of the power shaft regardless of engine speed; sawtooth waveform control means for generating a control signal having a magnitude representing the speed of rotation of said power shaft and applying said control signal to said semiconductor device to control the current flow path for changing the charge of said charge storage means so as to maintain the maximum amplitude of the sawtooth waveforms at a substantially constant level for engine speeds by varying the instantaneous rate of change of charge as a function of engine speed; means for generating a set point signal corresponding to a predetermined angle of rotation; means for detecting when the amplitude of each of said sawtooth waveforms reaches a level defined by said set point signal so as to correspond to a predetermined angle of rotation of said power shaft; means responsive to said detecting means for generating an engine trigger signal corresponding in time to a predetermined angle of rotation of said power shaft; aNd means for adjusting said set point signal so as to adjust the timing of said engine trigger signal to correspond with a different predetermined angle of rotation.

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