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Publication numberUS3923021 A
Publication typeGrant
Publication dateDec 2, 1975
Filing dateAug 12, 1974
Priority dateSep 14, 1973
Also published asDE2346333A1, DE2346333C2
Publication numberUS 3923021 A, US 3923021A, US-A-3923021, US3923021 A, US3923021A
InventorsEberhard Stark
Original AssigneeBosch Gmbh Robert
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Digital circuit providing a trigger signal to trigger an event based on operating functions of moving apparatus elements, particularly to trigger an ignition pulse in an internal combustion engine
US 3923021 A
Abstract
A first transducer provides a sequence of pulses, for example speed-dependent pulses, which cause, sequentially, loading and unloading of more rapidly occurring count pulses. The count pulses may have a count repetition rate depending on an operating condition of the device, for example loading on the engine as determined by inlet manifold vacuum, or fuel/air flow to the engine. The binary number of the count pulses, in a certain interval as determined by the speed or tachometer pulses is compared with the binary number developed, non-linearly, from the function generator as the engine rotates and, upon coincidence of count numbers, a pulse is generated which triggers the ignition of the engine, thereby providing for good approximation of the non-linear spark advance/retard timing with respect to engine speed and loading.
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Description  (OCR text may contain errors)

7 United States Patent Stark 1 Dec. 2, 1975 1 1 DIGITAL CIRCUIT PROVIDING A 3,749,073 7/1973 Asplund 123/117 R TRIGGER SIGNAL T0 TRIGGER AN EVENT P arner BASED ON OPERATING FUNCTIONS OF 3,832,981 9/1974 Wakamatsu et al 123/32 EA MOVING APPARATUS ELEMENTS, PARTICULARLY TO TRIGGER AN IGNITION PULSE IN AN INTERNAL COMBUSTION ENGINE [75] Inventor: Eberhard Stark, Korntal, Germany [73] Assignee: Robert Bosch G.m.b.H.,

Gerlingen-Schillerhoehe, Germany [22] Filed: Aug. 12, 1974 [211 App]. No.: 496,651

[30] Foreign Application Priority Data Sept. 14, 1973 Germany 2346333 [52] US. Cl. 123/117 R; 123/117 D [51] Int. Cl. F02P 3/02 [58] Field of Search 123/117 R, 32 EA [56] References Cited UNITED STATES PATENTS 3,454,871 7/1969 Nolting 123/117 R 3,592,178 7/1971 Schiff 123/117 R 3,738,339 6/1973 Huntzinger et al. 123/117 R Primary ExaminerCharles J. Myhre Assistant Examiner.1oseph A. Cangelosi Attorney, Agent, or Firm-Flynn & Frishauf [57] ABSTRACT A first transducer provides a sequence of pulses, for example speed-dependent pulses, which cause, sequentially, loading and unloading of more rapidly occurring count pulses. The count pulses may have a count repetition rate depending on an operating condition of the device, for example loading on the engine as determined by inlet manifold vacuum, or fuel/air flow to the engine. The binary number of the count pulses, in a certain interval as determined by the speed or tachometer pulses is compared with the binary number developed, non-linearly, from the function generator as the engine rotates and, upon coincidence of count numbers, a pulse is generated which triggers the ignition of the engine, thereby providing for good approximation of the non-linear spark advance/retard timing with respect to engine speed and loading.

27 Claims, 7 Drawing Figures STARTER LlNE START NUMBER STORE ROM] OSCI LLATOR 1 2 21 22 3 I INDUCTION 26 vA c uuM SENSOR 29 l STORAGE I as REFERENCE COUNTER I FULSESWRCE 111m,

37 FUNCTION BINARY GENERATOR J COMPARATOR 1 314 L0 ll 33 FUNCTTII 1| PULSE DOWN L I z COUNTER L 1 WAVE 32 SHAPER l l l 202 START NUMBER 66 A STORE-ROM 2 TURE 7 l.i \LL SENSOR THRESHOLD SWITCH UISQ Patem Dec. 2, 1975 Sheet 1 of4 3,923,021

g 1 1.9 ExHAUST COMPOSITON SPEED PULSE WAVE CONTROL LINE TRANSDUCER SHAPER IIJIO 1 14 c STARTER LINE I 1-7 -I;---- I j I ,K

I I I 16 L8 19 IL I g I ZII$385I 20 II IIIII Z I OSCILLATOR FLINSTANTANEOUS I ENGINE SPEED 27 I DOWN COUNTER IND CTION 3 25 E5 I VA3C8UUM SENSOR 29 STORAGE I/ COUNTER 3s REFERENCE fi PULSE SOURCE I IIf FUNCTION BINARY {l 37 GENERATOR l COMPARATOR 33 3 II I I I II H EI J I I E ES OWN I wAvE/ 32 SHAPER I I I I I IT START NUMBER L2 ENGINE STORE -ROM 2 N TEMPERA- TURE L7 5/ u M, SENSOR THRESHOLD SWITCH Dec. 2, 1975 Sheet 3 of4 3,923,021

U.S. Patent Dec. 2, 1975 Sheet4 0f4 3,923,021

Fig-7 loT DIGITAL CIRCUIT PROVIDING A TRIGGER SIGNAL TO TRIGGER AN EVENT BASED ON OPERATING FUNCTIONS OF MOVING APPARATUS ELEMENTS, PARTICULARLY TO TRIGGER AN IGNITION PULSE IN AN INTERNAL COMBUSTION ENGINE The present invention relates to a digital system to provide a trigger pulse to trigger an operating event in an apparatus, and more particularly to trigger the ignition instant in an internal combustion engine, in which the particular instant of time, with respect to crankshaft position (or other movable element positions of the device) is accurately predetermined.

The ignition timing, that is, the advance or retard angle of ignition with respect to speed and load on the engine, must be changed as the speed and load on the engine, respectively, change; other operating or ambient parameters may, additionally, have to be taken into consideration. Changing the ignition instant is required by the time taken for the combustible mixture to burn. Upon a spark being generated at the gap of the spark plug, only that portion of the combustible air-fuel mixture in the cylinder will ignite which is in immediate vicinity of the spark plug gap. A flame front or wall then passes, with approximately constant speed, throughout the cylinder and ignites the remainder of the combustible mixture therein. This flame front,, or movable wall of flame, requires roughly the same time to pass from the spark plug to the cylinder wall regardless of the speed of the engine.

Maximum combustion pressure should occur in the engine shortly after the piston passes through the upper dead center (UDC) position thereof. This condition, then, requires adjustment of the timing of the ignition spark with respect-to the angular position of the crankshaft of the piston in the respective cylinder in such a manner that the spark is advanced from UDC position as the speed of the machine increases, in order to compensate for the constant propagation time of the flame front in the cylinder upon combustion.

The speed of the flame front depends on the composition of the combustible mixture within the cylinder, that is, on the relative mixture of fuel and air, with respect to stoichiometric values. If the load on the internal combustion is high, and the throttle thereto is wide open so that the inlet manifold will have a low vacuum therein, the cylinder will receive a rich mixture which is readily ignitable. The flame front will propagate with high speed in a rich mixture. Ignition may therefore be retarded. If, however, the loading on the engine is only small and the throttle is essentially closed, the mixture supplied by a carburetor will be on the lean side, which results in a lower propagation speed of the flame front. This condition, then, requires ignition advance. In general, reference is made in this connection to spark advance if the angle ofignition, with respect to crankshaft angle, is well in advance of UDC position; the spark is retarded if the angle of ignition is only slightly in advance of UDC position of the piston, or at, or even after, or behind the UDC position.

The pressure or, rather, the vacuum in the inlet manifold customarily is used as a measure for the load on the internal combustion engine. This vacuum can be measured by means of a diaphragm chamber. Speed of the engine is customarily measured in mechanical ignition control systems by means of centrifugal weights.

Various electronic circuits have been proposed in which the customary mechanical change of angular position of the ignition angle is replaced by electronic circuitry; such electronic circuitry operates without wear and tear. Most such circuits use analog technology. Speed of the engine and inlet vacuum are transformed into d-c voltages of variable amplitude. While satisfactory in many respects, analog technology has the disadvantage that ignition timing circuits require extensive adjustment before the timing circuits can be matched to an engine, and to match the various voltage levels of the various stages of the circuit to each other. Stray fields and possible feedback within the various components of such circuits have to be compensated for. Long-term variations in analog circuits also occur, causing drift, so that the voltage levels of signals in the circuit may slightly shift due to aging of the components in the circuits used.

It has previously been proposed to use digital circuits to adjust and change the ignition angle, in which the speed of the internal combustion engine is sensed by counting in a counter the output pulses from a tachometer generator during a predetermined time. The time itself, during which the pulses are counted, is determined by a monostable multivibrator or flip-flop (FF). The pulse duration, that is, the unstable time of the monostable FF is changed in dependence on inlet manifold vacuum, and may, additionally, be changed in dependence on other operating parameters. This type of circuit is only partially a digital circuit; the monostable FF, providing a predetermined timing period, is actually an analog component which has the disadvantages above. referred to of analog circuitry. lt is, additionally, difficult to control monostable FFs by more than one operating parameter to accurately determine the unstable time thereof.

Circuits of this type, which may be termed composite or semi-digital circuits determine the ignition angle by means of a counting procedure which is sub-divided into two parts or sections. The first section starts, for example, before UDC position. The output pulses of the tachometer generator are counted during the time fixed by the monostable FF. The counting stage increases, with increasing speed. Thereafter, at a predetermined angular position of the crankshaft, for example 45 in advance of UDC position, the counting is continued and terminated at a predetermined time of count pulses, at which time the ignition system is triggered. If more pulses were counted during the first counting portion, then lesser numbers of pulses need be counted in the second portion. As a result, ignition is advanced at high speed.

Such a counting system may introduce a dynamic error if the speed of the internal combustion engine changes rapidly, since speed is determined only once for each revolution of the crankshaft of the engine. If the ignition is then triggered after a subsequent half rotation of the crankshaft, the then instantaneous speed of the engine may already have changed substantially.

It is an object of the present invention to provide a system which is particularly adapted to be useful to trigger an ignition event, and which is entirely based on digital technology, utilizes digital components, and which largely avoids dynamic errors. In general, such a system can provide a pulse representative of a predetermined event in dependence on various parameters.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a first transducer is provided which supplies a sequence of pulses. This transducer may, for example, be a speed signal transducer providing a sequence of pulses representative of engine speed. The time lapse, between pulses, provides a digital number which, as such, preferably is generated by an oscillator; the frequency of this oscillator, which generates pulses which will form a count number may, itself, be variable and controlled by an operating parameter of the engine, for example inlet manifold vacuum. The oscillator will have a frequency which is a high multiple of the frequency of the speed pulse generator, and the count number, between pulses, will then be a binary number representative of speed. This number is stored in a storage counter.

A function generator is provided which provides a sequence of pulses which have a time distribution, with respect to a datum, which is representative of the function of variation of an operating condition as the machine operates, for example, of the function of ignition timing with respect to angular crankshaft position. This function is non-linear and may, for example, be represented by non-linearly distributed marks, or teeth, on a rotating disk, or element, coupled to rotate with the crankshaft of the engine. A second count number will thus be provided, and when the stored count, derived from the pulses of the oscillator and accumulated during subsequent pulses of the speed transducer matches the count number of the count derived from the function generator, a digital comparator provides an output signal indicative of such match, or equality, which output signal is then used to trigger an ignition event.

As applied to an internal combustion engine, the crankshaft of the engine thus drives two pulse sources, namely a pulse source which has output pulses uniformly distributed, angularly, with respect to the crankshaft; and a second pulse source, which operates as a function generator, and which provides pulses in dependence on a desired speed characteristic with respect to crankshaft angle. The speed pulse source, or tachometer generator, may provide a high number of pulses for each full revolution of the crankshaft, so that dynamic errors in measuring speed can be substantially reduced. Each new tachometer generator or speed pulse provides new speed information to the counter, in digital form. The function generator can be so arranged that any desired distribution of speed with respect to ignition advance angle can be simulated, that is, can be matched to a particular internal combustion engine, or to a type of engine. The output derived from the function generator will be a binary number, counted in a function counter which will have a number counted therein which is a measure of the crankshaft angle through which the crankshaft has rotated, after a certain datum level has been passed, that is, after the function generator has started to provide pulses.

The circuit in accordance with the present invention permits a number of possibilities to further consider additional operating parameters in pure digital form. For example, the initial counting state of any one of the counters may be changed. A particularly simple possibility to consider the vacuum in the inlet manifold is to change the operating frequency of the count oscillator,

for example by introducing a variable L/C circuit therein.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a general schematic block circuit diagram of the system in accordance with the present invention;

FIGS. 2-6 are graphs used in explanation of the operation of the circuit in accordance with FIG. 1; and

FIG. 7 is a schematic representation of'a combined optical speed and function generator transducer.

A tachometer generator 10, forming a speed-pulse transducer (FIG. 1) is coupled to a rotating shaft 38 of an internal combustion engine (not shown), for example to the crankshaft, directly or by means of a transmission. Transducer 10 includes a star wheel 11 having ferromagnetic teeth which pass by a magnetic core 12, on which a coil 13 is in inductively coupled relationship. A terminal of coil 13 is connected to chassis or ground; the other terminal forms the output of the speed pulse transducer 10. A wave-shaping circuit 14 is connected to the speed pulse transducer, including a differentiator 15 and a Schmitt trigger l6. Differentiator 15 has a differentiating capacitor 17 which is connected to the output of tachometer generator 10 and has another terminal thereof connected to a resistor 18, which in turn is grounded. The junction of the capacitor 17 and resistor 18 is connected over a diode 19 to the Schmitt trigger 16.

A vacuum diaphragm chamber 20 is connected by means of piping or tubing 21 to the inlet manifold of the internal combustion engine (not shown). A mechanical coupling 22 is connected to chamber 20 to change the position of a ferrite core 23 within a high frequency coil 24. Coil 24, together with a capacitor 25 forms the tank circuit of an oscillator 26; the position of the core 23 within coil 24 determines the frequency of oscillator 26.

The output of oscillator 26 is connected to the count input z of an engine speed counter 27. Counter 27, preferably, is a backward, or down counter, which counts downwardly from a number which can be set therein. The load input 1 of the engine speed counter 27 is connected to the output of the Schmitt trigger l6. Pulses derived from the oscillator 26 are thus counted when a pulse from Schmitt trigger 16 is received until the next pulse, again, is received as will appear in detail below. The binary count state of the engine speed counter 27 which, due to the number of teeth on star wheel 11 is partically an instantaneous speed counter, is transferred to the input of a storage counter 28. Storage counter 28 has a load input 1 which is energized over an inverter 29 connected to the output of the Schmitt trigger 16.

A function generator 30 is connected to the crankshaft or similar rotating element of the engine 38, and, like the speed transducer 10, has a star wheel 31 which is driven from the engine. Star wheel 31 has ferromagnetic teeth which pass the core 32 as the star wheel rotates. In contrast to the star wheel 11, on which the teeth are uniformly distributed over the surface, wheel 31 has the teeth located nonuniformly over the surface thereof. A coil 13 is wound over core 32, grounded at one end, and having its other terminal connected as the output of the function generator 30, directly to the input of a Schmitt trigger 34, which operates as a wave shaper.

The output of Schmitt trigger 34 is connected to the count input 2 of a function pulse counter 35. Function pulse counter 35, preferably, is a down counter which counts downwardly from a predetermined value. The load input 1 of the counter 35 is connected to the output of a reference pulse transducer or source, formed by a switch 36 which is periodically opened and closed by a cam 37 operating in synchronism with crankshaft rotation of the engine. Broken line 38 schematically indicates the synchronous drive of the two star wheels 1 1, 31 and of cam 37 from the crankshaft of the internal combustion engine. The binary output of the function counter 35 and the output of the storage counter 28 are both connected to two corresponding binary inputs of a binary comparator 39. The comparator 39 is connected to an amplifier 40, and provides an energizing pulse thereto upon coincidence of binary count input from the two counters 28, 35.

Two start number, or initial state storage counters 41, 42 are provided, respectively connected to the instantaneous engine speed counter 27 and to the function pulse counter 35, respectively. The two start number storage counters may be read only memories (ROMs) and are, therefore, indicated as ROM-1 and ROM-2; addressing inputs 43, 44, respectively, connected to the counters 41, 42 permit addressing the counters with predetermined numbers to be set therein. The various addressing inputs, collectively indicated as Za and Zb are connected to suitable inputs thereof.

The binary numbers Za and Zb are indicated, schematically, as three-digit binary numbers. One digit of the binary number Zb is determined by the output signal of a threshold switch 45, the input of which is connected to the tap point of a voltage divider formed by a resistor 46 and an NTC-resistor 47 which is a thermally responsive resistor, in thermal contact with the engine block of the internal combustion engine, to sense engine temperature.

One digit of the binary number Za is determined by whether the starter switch 48 is opened or closed; starter switch 48 is connected to the starter line. Another digit of the number Za is determined by the output signal derived from an exhaust gas sensor (not shown) and schematically indicated as switch 49, thus providing a binary signal on the exhaust composition control line. The other digits of the binary numbers Za and Zb may be used, for example, for more accurate determination of the engine block temperature, so that the ignition timing can be adjusted, accurately, in various stages, depending on engine temperature. Other parameters, such as ambient temperature, ambient air pressure, and the like may also be considered and introduced as numbers into the respective start number storage counters 41, 42.

Basic operation: Alternating voltage pulses are induced in coil 13 of tachometer generator as the teeth of the star wheel 11 pass core 12. The frequency of these pulses is proportional to the speed of the internal combustion engine, as transferred to wheel 11 by shaft 38. The differentiator 15 provides steep needle pulses from the undulating alternating voltage pulses of transducer 10; diode 19 passes only the positive steep needle pulses to the Schmitt trigger 16, which transforms these needle pulses into narrow square pulses, as shown. The pulse duration of these square pulses must be small with respect to the time gap between the square pulses.

The function generator also provides undulating voltage pulses which, however, need not be of such narrow width, nor so accurately triggered, so that the Schmitt trigger 34 can be connected directly to the output of the coil 33; if desired, a differentiator similar to differentiator 15 may also be interposed.

Oscillator 26 oscillates in accordance with the circuit parameters of the tank circuit formed of the inductance 24 and the capacitance of capacitor 25. It is an L/C oscillator connected, for example, as a Hartley, or as a Colpitts oscillator. If the inlet manifold vacuum is high, that is, when the throttle is essentially closed, the diaphragm chamber 20 is compressed by the ambient air pressure, thus pulling the ferrite core 23 by link 22 deeply into coil 24. This increases the inductivity of the coil 24 and the oscillation frequency of the oscillator 26 decreases. The oscillation frequency, thus, increases with decrease in vacuum of the inlet manifold, and hence decreases with increasing loading on the internal combustion engine.

The ferrite core 23, as shown in FIG. 1, is conical. This shape provides for non-linear variation of the frequency with respect to change in vacuum of the inlet manifold. By suitably shaping core 23, for example to be slightly bulged, or to be concave (with respect to a strictly conical form) various vacuum-vs.-oscillator frequency characteristics can be obtained.

Counters 27, 35, ROM'-l, and ROM-2, storage counter 28, and binary comparator 39 are standard articles of commerce in the form of integrated components. Counters 27, 35 may, for example, be SN 74191; storage element 28 may be a SN 7475, and binary comparator 29 may be a SN 7485. The start number storage counters 41, 42 may, for example, be SN 7475 (similar to counter 28) if additional correction quantities Za, Zb are not needed, so that it will not have separate address inputs 43, 44. If an initial count state should be considered, that is if, depending on operating conditions, different binary numbers Za, Zb should be entered into the starting state of the counters 27 35, then the counters 41, 42 should be ROMs. If in order to test, or for experimental circuits, or for other uses, the values in the memory counters 41, 42, representative of the binary numbers Za, Zb are to be changed, then a programmable read only memory (PROM) memory element such as Intel 1702 is suitable.

The outputs of the memory counters 41, 42, whether fixed or programmable, provide a binary number, the value of which is determined by the value of the binary number Za, Zb connected to the address input thereof. The digital position of the output binary number can be matched to the digital positions of the counters 27, 35.

Operation of the system as an ignition timing system, with reference to FIGS. 2-6: FIG. 2 illustrates the speed-timing adjustment curve 50 which is obtained from mechanical ignition timing adjustment systems, operating by means of centrifugal weights. The ignition angle is indicated at az at the ordinate of FIG. 2. For ease of explanation, the abscissa has three scales; the upper scale indicates the speed n in rpm; the intermediate scale shows the speed nin revolutions per second, or Hz; the third, and lower scale shows the time, T, necessary for one revolution in milliseconds (ms). As can be seen from FIG. 2, the ignition angle is effectively constant at low speeds up to about 1,000 rpm; the angle then increases up to a speed of about 3,200 rpm at a rather steep rate; above a speed of 3,200 rpm, the rate of increase is less.

The advance angle characteristic 51 of FIG. 3 is derived from the curve 50 of FIG. 2. The ignition angle az is illustrated as a function of time per revolution, or cycling time T, to a linear, increasing scale on the abscissa. As derived from FIG. 2, the characteristic should have a constant value of about 10 above a cycling time of 60 ms. The circuit according to FIG. 1, however, provides for a gradual decrease as shown by the broken line 52. Such a gradual decrease is desirable since, at very low speeds, the ignition angle should be shifted in the direction of spark delay. Centrifugal controllers cannot provide for such increasing spark delay since, at very low speeds, insufficient centrifugal forces arise in the system.

The characteristic 51 or 52, in accordance with FIG. 3, is formed by the circuit according to FIG. 1. The counter 27 counts a value representative of instantaneous engine speed, that is, the cycling time which elapses between two pulses from the speed pulse transducer 10. Angular adjustment of the ignition angle is thus referred to cycling time and not, as in the customary control systems, to the speed of the engine. The label instantaneous engine speed down counter given to counter 27 is thus used only to conform to customary terminology; the counter, actually, measures elapsed time of angular change of the crankshaft or, in other words, the time gap between pulses derived from the transducer 10. The teeth of star wheel 11 are equally spaced about the circumference thereof and thus, if the teeth are close together so that the angle of rotation between teeth is very small, the counter 27 will measure cycling time or, effectively, instantaneous engine speed.

FIGS. 4 and are graphs which illustrate how the cycling time counter, or instantaneous speed counter 27 measures the time gap between pulses from the tachometer generator and, simultaneously, considers inlet manifold vacuum.

The circuit of FIG. 1 is so polarized that the negative pulse flank.of a pulse applied to the load input 1 of counter 27 (or of the storage counter 28, respectively) causes transfer of the number applied to the respective binary number input. The count state of the counter 27 is thus transferred to the storage counter 28 as soon as Schmitt trigger 16 provides a leading pulse edge which is inverted in the inverter 29. The pulse from the trigger 16 is very short. Its trailing flank causes the binary number Z01 stored in the start number store ROM-l 41 to be transferred to the instantaneous engine speed down counter 27. The count state of the counter 27 is indicated by Z in FIG. 4. It starts at Z01 and decreases in steps, since counter 27 is a down, or backward counter.

Tachometer generator 10 provides pulses at the time instants T1, T2, T3, T4 Assuming overall, average engine speed to remain constant initially, the time gap, that is, elapsed time between the first three pulses T1 to T3 remains constant. Let it be assumed that the speed increases, so that the pulse at time T4 occurs earlier, and so that the time gap is decreased. The diagram according to FIG. 5 is drawn to the same scale and the same speed relationships pertain. The difference between the diagram of FIGS. 4 and 5 is that the counting frequency in FIG. 5, as determined by the frequency of oscillator 26 is increased, since the loading on the engine has increased. As seen in FIG. 4, and at the lower counting frequency, the counter 27 counts down from start count Z01 to a relatively high count state Z1 until the next pulse T2, T3 occurs. This count number, Z1, is transferred to the storage counter 28, and counter 27 is reset to its initial state Z01. At the fourth pulse T4, elapsed time is shorter (the time gap is narrower) so that counter 27 will reach only a still higher final state, or count Z3, which is transferred at time T4 into the storage counter 28.

The diagram of FIG. 5 illustrates, as noted, the same relationship at a higher counting frequency. The counter, therefore, reaches a lower count state Z2 after the first three pulses T1, T2, T3; at the fourth pulse, the count state Z4 is reached.

The final count state Z1 to Z4 is, therefore, on the one hand a measure of the elapsed time between subsequent pulses, that is, speed of the engine over the angular range between teeth of the star wheel 11 and, further, a measure of the pressure (or, rather, vacuum) in the inlet manifold. The determination of the ignition or firing angle a is derived from a combination of the count state in the function pulse counter 35 and the count state Z1 to Z4 reached by the counter 27, as illustrated in FIG. 6.

Counter 35 is set to an initial count state, as determined by start number store ROM-2 42 by the negative flank of the reference pulse source 35, applied to terminal 1. FIG. 6 assumes that the counter 35 is loaded at an angle a0 of 42' in advance of UDC position. Function generator 30 provides pulses starting at 40 in advance of UDC position.

In that region of the characteristic 51 (FIG. 3) which is steep, the angle az changes strongly at only small changes of cycling time, or small changes in instantaneous speed. Such large change in the ignition angle az is obtained by spacing the teeth of the star wheel 31 further apart. Conversely, the teeth of the star wheel 31 must be very close together when the characteristic curve 51 (FIG. 3) is flat. The star wheel 31 (FIG. 1) schematically indicates by teeth distribution how the curve of FIG. 3 can be formed. The first three teeth are relatively close together, since they have to generate a curve representative of the flat portion of curve 51 between T 10 ms and T 20 ms. Thereafter, a steeper portion follows and the teeth exhibit greater distance from each other. They then become dense, again, in order to form the portion of the curve to T 60 ms, and then are very closely spaced since the curve should be as flat as possible beyond T 60 ms.

The representation of the star wheel 31 (FIG. 1) is to be considered only schematically, since the teeth, there shown, are distributed over an angular range of more than in the example of FIG. 6, the teeth would be present only in an angular range of from 40 to 10 before UDC position, that is, should cover a range of only about 30. If a high angular resolution is required, the teeth 31 may be distributed over a wide angular range as illustrated, for example, in FIG. 1 if an additional transmission is used to rotate star wheel 31 faster than the crankshaft.

The curve along which the count of counter 35 proceeds see FIG. 6 is steep in that portion where the characteristic of FIG. 3 is flat and vice versa. At high speeds, that is, in short cyclical periods T, the counter 27 reaches count numbers which differ only slightly from the initial count state Z01. In that range, the

count curve of the counter 35 is steep (see FIG. 6). The ignition angle az changes only slightly when the change in cycling time is small, as is apparent from FIG. 3. The counting curve in accordance with FIG. 6 reaches the count condition or state Z1 (FIG. 4) at an ignition angle az of about 18 in advance of UDC position. This is the instant of time in which the two binary numbers applied to the comparator 39 are equal, and comparator 39 thus provides an output pulse, to be amplified in power amplifier 40, to trigger the ignition system.

If the engine is highly loaded, that is, if the vacuum in the intake manifold is low (curves of FIG. 5), a lower count will accumulate in counter 27, corresponding to count number Z2. The speed has not changed. Ignition only occurs when the count state, as derived from the count curve of FIG. 6 has reached the count value Z2, that is, at an angle az of about 11 in advance of UDC. This is as desired since, as above explained, at high loading the mixture introduced into the cylinder is more readily flammable or ignitable, so that the time of ignition of the entire mixture is shorter.

The electromagnetic transducer and 30 may have the difficulty that they permit only a limited resolution of the angles of the crankshaft, during which ignition should be commanded. The circumference of a star wheel 11, or 31, respectively, for tolerable size, may accomodate up to about 120 teeth, or projections, spaced by an angular distance of about 3. The accuracy of resolution of the ignition angle az, in accordance with FIG. 6, is determined by the distance of the teeth of the star wheel 31. Even if a speed transmission of 1 4 is provided with respect to the crankshaft, so that the star wheel 31 rotates four times as fast, and the teeth are located as closely to each other as possible, an angular resolution of only about 0.8" can be obtained. The teeth of star wheel 31 are spaced farther apart in the steeper ranges of the characteristic curve of FIG. 3 so that in those ranges an angular resolution of about 5 can be obtained. This resolution remains, independent of the lifetime, or use of the apparatus, and this constantly, perpetually available resolution is a substantial advance with respect to mechanical ignition timing arrangements. Better accuracy should, however, be possible, and the possibility to obtain high accuracy by digital circuits can be additionally utilized by providing transducers which have even higher resolution. Instead of the electromagnetic transducers 10, 30, photoelectric transducers may be used. Such transducers are known. A light source projects light to a photo cell; a disk is interposed in the path of light between source and cell, the disk having transparent and opaque regions which alternate. Upon rotation of the disk, electrical voltage pulses are generated in the photo cell. It is possible to apply a high number of marks on disks of reasonable sizes, for example 1,2000 opaque marks on the circumference of a disk customarily used in a photo-electric transducer, for example of about 10 15 cm diameter. The accuracy of angular resolution can thus be increased by a factor of about 10 with respect to the resolution of an electromagnetic transducer.

A disk, for use in a photo-electric transducer and function generator is illustrated in FIG. 7. The disk rotates in the direction of the arrow about a shaft 53'. It is formed with three tracks 54, 55, 56. The path of light is directed transversely to the disk at the position shown by circles 57, 58, 59 which, conjointly, represent an optical light generating-receiving transducer system.

The arrangement of the markers on the disk will be explained with respect to an eight-cylinder engine. The first, or inner track 54, cooperating with the optical transducer system 57 functions as a reference pulse source and takes the position of the cam 37 and the switch 36 of FIG. 1. The second, or intermediate track 55, together with photo transducer system 58 forms the speed pulse transducer system, and replaces system 10 of FIG. 1. The third track 54, together with the third photo transducer system 59 forms the function generator, corresponding to generator 30 of FIG. 1.

The third track 56 is formed with two series of markers which take the position of the teeth of the star wheel 31. Both series of markers extend over an angle somewhat greater than and are angularly stretched with respect to the counting characteristics of FIG. 6 by a factor of two. The disk of FIG. 7 thus rotate at twice the speed of the engine. For this reason, the first track 54 is formed with two reference markers, so that four reference pulses are provided to load counter 35. It provides four series of characteristic pulse sequences. Each crankshaft revolution provides four ignition pulses, as is required in an eight-cylinder engine. The two series of characteristic markers of the third track 57 may, of course, be distributed only about an angle of about 40 to 45, the disk then being driven directly from the crankshaft. Other transmission ratios, and angular distribution ranges of the disk may likewise be used. The desired angular resolution available with disks of predetermined size, and the number of cylinders of the engine have to be considered.

The crankshaft positions are indicated in FIG. 7 where OT indicates the respective UDC positions, and the horizontal axis is representative of the 45 position with respect to UDC position.

Operation: Upon rotation, a reference pulse is provided by the first reference track 54 at an angular crankshaft position of 45 in advance of UDC position. This reference pulse provides for loading of the function pulse counter 35 (FIG. 1) with the initial state or initial count number Z02. At an angular position of about 43 in advance of UDC position, the markers of the third track will pass before the transducer system 59 to provide counting pulses for the function pulse down counter 35. The distance between markers follows the same functional relationship as the distance of the teeth on star wheel 31. The markers continue beyond the upper dead center position. Such delayed ignition can be used at cold starting. At very low temperatures of the engine block, NTC resistor 47 (FIG. 1) may have such a high value that threshold switch 45, which is a simple Schmitt trigger, changes over and thus changes the binary number Zb entered at the address input 44 of the start number store 42. The start number store 42 then provides a binary number which is substantially higher than Z02. The entire counting curve of FIG. 6 is shifted upwardly, resulting in a shifting of the ignition angle, regardless of speed, in the direction of spark retard. The shift of the characteristic curve of FIG. 6 may be so great that ignition angles az may arise which are after the UDC position. The markers of the third track 56 are, therefore, continued beyond the UDC position.

In some special cases, it is desirable to shift the ignition in the direction of spark retard during starting. The starter switch 48, connected to a starter line, is thus further connected to an address input 43 of the start number store ROM-1 41. When the starter switch 48 is closed, the address input 43 will have an initial binary number Za applied thereto of such magnitude that the initial state Z01 of the cyclical, or instantaneous engine speed counter 27 is shifted to a lower value. This results, necessarily, in a lower counter state Z1 to Z4 (see FIGS. 4 and 5). This lower final counter state of the counter 27, which isthen transferred to storage counter 28 is reached only later by counter 35, counting in accordance with the characteristics of FIG. 6. Thus, again, the angle of ignition is shifted towards retardation as desired. Similarly, switch 49, controlled from an exhaust composition sensor and inserted into an exhaust composition control line, may open, or close, to change the angle of ignition, as desired, in the direction of retardation, or spark advance. It is also possible to shift the angle of ignition in dependence on exhaust composition in steps, by utilizing a plurality of lines and switches corresponding to the switch 49 and the single exhaust composition control line, to set various initial numbers into the start number store 41. Reference is made to U.S. Patent application Ser. No. 267,562, filed May 6, 1972, assigned to the assignee of the present invention, with respect to the effect of changing ignition timing on exhaust gas composition. Electrically evaluating exhaust gas composition and deriving control signals therefrom is described, for example, in U.S. Pat. No. 3,782,347, assigned to the assignee of the present application.

Various other changes and modifications may be made. For example, oscillator 26 may be constructed to have a fixed output frequency; loading on the engine is then sensed by selectively closing switches connected to suitable addressing control lines connected to the respective addressing inputs 43 or 44 of the start number storage memories 41, 42. Inlet manifold pressure then directly influences the binary numbers Za and Zb, respectively, which control the initial count state of counters 27 and 35, respectively. The total requirement of circuit components is somewhat less than when using an oscillator 26 with variable frequency; vacuum in the inlet. manifold cannot, however, then be measured continuously but only in steps and some truncating error will result, depending upon the fineness of the steps with which the initial count numbers can be controlled. Rather than measuring the vacuum of the inlet manifold, flow of air to the engine, or flow of a fuel-air mixture to the engine may also be measured, for example by a suitable air flow meter in the inlet manifold, such as a deflectable flap, disk, or the like which changes a slider position of a potentiometer, or contact positions of connecting lines respectively addressing the start number stores 41, 42.

The frequency of oscillator 26, in the example of FIG. 1, may be placed in the order of about 100 kHz; it may shift, for example, between 80 to 120 kHz. The angular distance of the markers on the disk in accordance with FIG. 7 on the track 55, providing the cycling time (or instantaneous speed) marks is preferably so selected that the oscillator 26 provides about as many pulses, at center frequency, in the time between the occurrence of markers as there are, on the average, markers on the outer track 56. In the example of FIG.

7, the second track 55 has 16 markers. The disk, oper- 6 of 6,000 rpm, the time will be 0.3 ms. At an oscillator frequency of kHz, counter 27 will count the time gaps, or elapsed time periods between markers to 300 pulses at no-load speed, and will count 30 pulses at maximum speed. The initial count state Z01 of the counter 27 thus must be somewhat over 300. A series of characteristic markers on the third, or outer track 56 must then also have about 300 markers. This is readily obtainable with photoelectric transducers of the scanned disk type.

A frequency divider may be connected to oscillator 26 if a smaller number of markers are used for the track of the function generator, or a larger number of markers may be used on the track 55.

The wave-shaping circuit 14 of FIG. 1 is shown, schematically, as an example. Various different types of circuits may be used, for example it is possible to so construct a circuit that the output pulses of coil 13, or of photo cell 58, respectively, are directly converted into square wave pulses, and the pulses are then fitted, as well known, in two different time slots. In any event, the counting state of the counter 27 should be transferred to the storage counter 28 before a new initial number is loaded into counter 27 preferably just in advance of a fixed time effecting such loading.

The circuit, as described, solves the problem initially mentioned. Integrated circuits are used exclusively, operating digitally, so that no specific matching of analog circuits to specific engines is necessary. No effects of aging of components will change the operating characteristics. A particular advantage of the circuit of the present invention is that it permits consideration of further operating or ambient parameters to determine the exact ignition angle, by modifying either the counting frequency of the counter 27 (by variation of the frequency of the oscillator 26), by changing the initial counting state of counter 27, or by changing the initial counting state of the counter 35, that is, three different ways can be used to consider such additional parameters when controlling the ignition instant.

The invention has been described with respect to triggering of an ignition event. The same circuit may also be used to control the injection time, or injection instant in fuel injection systems, or to control the opening time and closing time of electro-hydraulically controlled inlet and outlet valves. The function generating markers on track 56 of the disk of FIG. 7, or the teeth on star-wheel 31 (FIG. 1 respectively, may be suitably distributed to provide suitable functions to compensate for different characteristics of the desired control event, with respect to a predetermined position of a movable element of the engine, for example a specific angular position of the crankshaft of the engine.

I claim:

1. Digital system to provide a trigger signal to trigger an operating event in an operated device at a time subsequent to a datum instant, which time depends on operating conditions of the device,

characterized by a. first transducer means (10) coupled to the device and providing a sequence of first pulses representative of an operating condition thereof;

first counter means (27, 28) having said first pulses applied thereto, determining the time gap between pulses, and providing a representation of said time gap in form of a digital number;

b. a function generator (30) providing a second sequence of second pulses, having a time distribution which is representative of the function of variation of an operating condition with respect to the operating condition of said device subsequent to operation with respect to said datum;

second counter means (35) providing a representation of the number of second pulses, derived from said function generator, in the form of a second digital number, arising subsequent to said datum;

c. a digital comparator (39) connected to and comparing the numbers in both said first counter means (27, 28) and said second counter means (35) and providing said trigger signal upon determination of equality of said first and second digital number;

d. a start number storage means (41) connected to at least one of said counter means (27, 28; 35), and providing a predetermined start number to the respective counter means representative of an operating condition of the device; and

e. means (36, 37) coupled to said operated device, providing a datum reference pulse, and providing said pulse at a predetermined operating position of an operating element of said device to form said datum, the load input terminal (a) of said second counter means (35) being controlled by the datum reference pulse from said reference pulse source means.

2. System according to claim 1, wherein said first counter means comprises a first counter (27) and a storage counter (28), the

storage counter storing the digital number representative of said time gap, said storage counter being connected to said digital comparator for comparison of said first digital number with the second digital number in the second counter (35).

3. System according to claim 1, further comprising a count pulse generator means (26) generating a sequence of count pulses having a pulse repetition rate (PRR) which is high with respect to the PRR of the sequence of first pulses, said sequence of count pulses being applied to said first counter means to determine the binary number stored in said first counter means between successive first pulses applied to said first counter means (27, 28).

4. System according to claim 3, further comprising means (20, 21) sensing an operating condition of the device, said sensing means being connected to and controlling the PRR of the count pulse generating means (26) so that the binary number stored in the first counter means will be a function of (a) the time gap between successive pulses and (b) sensed operating conditions of the device.

5. System according to claim 1, wherein the start number storage means comprises at least one start number store (41, 42) having means (43, 44) controlling entry of a number therein;

said at least one start number store being connected to, respectively, at least one of said first and second counter means (27, 28; 35) to provide an initial number to the respective first and second counter means for algebraic combination with the number being entered into said respective first or second counter means.

6. System according to claim 5, further comprising second transducer means (45, 46, 47) sensing a condition of operation of said device, connected to said start number store to enter a start number to said start number store representative of a condition of operation of said device.

7. System according to claim 1, wherein said device is a mechanical apparatus having movable elements including a rotatable shaft (38) rotating in synchronism with movement of said elements, and comprising means (36, 37; 54, 57) responsive to a predetermined angular position of said shaft (38) and providing a datum signal, said predetermined angular position forming said datum, said datum signal being connected to said second counter means (35) to enable the second counter means to counter pulses derived from said function generator (30) upon receipt of said datum signal.

8. System according to claim 1, wherein said device is a movable apparatus having a movable element, and wherein the first transducer means is coupled to said movable element and provides a sequence of pulses representative of change in position of said movable element so that the elapsed time between successive pulses will be a measure of the speed of movement of said element from a first position to a next subsequent position.

9. System according to claim 1, wherein the device is a mechanical apparatus having a rotatable shaft (38), said first transducer means (10) is a speed pulse transducer providing speed signal pulses and said function generator (30) provides a sequence of pulses representative of angular position of the shaft (38) in accordance with a function having a non-linear relationship of accumulated pulse count with respect to angular position, said system comprising a disk rotating in synchronism with said shaft having a first circumferential track (55) carrying marks thereon uniformly spaced about the circumference to provide the speed signal pulses, a second circumferential track (56) having markers thereon located above the circumference thereof and starting from a position corresponding to said datum, said markers of said second circumferential track being distributed about the circumference of the disk in accordance with said non-linear function;

and stationary reading means (58, 59) responsive to said markers and providing a pulse upon passage of a marker before the reading means, said markers on the disk, and said reading means forming, respectively, said transducer and said function generator means.

10. System according to claim 2, wherein the start number storage means (41) has an initial number stored therein representative of an operating condition of the device which has a persistence time which is long with respect to recurrence rate of said pulses;

the first pulse controlling tranfer of the count in the first counter (27) to said storage counter (28) and, immediately thereafter, transferring the count from said start number storage means (41) into said first counter (27).

11. System according to claim 10, wherein the start number storage counter (41) comprises a read-only memory (ROM) (41);

and means (48, 49) applying a digital number to said ROM, the value of which is controlled by conditions of operation of said device.

12. System according to claim 1, further comprising a count pulse oscillator (26) coupled to the device and generating a sequence of count pulses representative of an operating condition of said device other than that sensed by said first transducer means (10), connected to the counting input (2) of said first counter means (27, 28).

13. System according to claim 12, wherein the oscillation frequency of said oscillator is variable and high with respect to said sequence of first pulses,

14. System according to claim 12, wherein the oscillator (26) is an L/C oscillator having a tank circuit (24, including a variable inductance (24) having a movable core (23), said device comprises an internal combustion engine, and the position of said core is variable in accordance with vacuum in the induction system of the engine.

15. System according to claim 14, wherein the core has a conical shape.

16. System according to claim 1, wherein the start number storage means (42) comprises a read-only memory (ROM), and means (46, 47; 45) introducing a start number to said ROM and having a binary value representative of an operating condition of said device.

17. System according to claim 1, wherein at least one of said counter means (27; 35) comprises a down counter.

18. System according to claim 5, wherein said device comprises an internal combustion engine;

a threshold switch (45) is provided, the switching state of said threshold switch being determined by the temperature of said internal combustion engine, said threshold switch being connected to at least one of said start number storage means to provide an initial number to the respective storage means, the value of which depends on the temperature of the engine.

19. System according to claim 1, wherein said device comprises a rotating engine, said transducer means (10) and said function generator (30) comprising electromagnetic transducers including, each, a star wheel (11, 31) having ferromagnetic teeth, and magnetic pick-up means (13, 33) respectively, magnetically coupled to respective star wheels;

the tooth distribution of the star wheel of the transducer being uniform about its circumference, and the tooth distribution of the function generator being non-linearly distributed about the circumference thereof, in accordance with said function.

20. System according to claim 1, wherein said device is an internal combustion engine, a reference pulse source (36, 37) is provided comprising a switch (36), opened and closed, periodically, in synchronism with rotation of said engine.

21. System according to claim 1, wherein said device comprises a rotating internal combustion engine, and means are provided to generate a reference pulse at a predetermined angular position of the crankshaft of the internal combustion engine;

wherein said first transducer means, said function generator, and said reference pulse generating means comprises photoelectric transducer means including a disk having alternatingly occuring opaque and transparent zones, and photoelectric means sensing the presence of said respective zones.

22. System according to claim 21, wherein said disk comprises three concentric tracks (54, 55, 56) having opaque markers thereon;

three photoelectric transducer means (57, 58, 59) one, each, associated with said tracks, and reading said markers and forming said transducer means, said function generator means and said reference pulse generator means, respectively. 23. Ignition pulse control system for an internal combustion engine comprising the digital system as claimed in claim 1, wherein said internal combustion engine forms said device and said trigger signal provides the ignition control signal therefor;

said first transducer means (10) provides a sequence of pulses representative of time gap between uniform, predetermined angular displacement of the crankshaft of the engine; said first counter means (27, 28) comprises a first counter (27) and a storage counter (28); count pulse generator means (26) are provided coupled to the engine, and providing count pulses at a repetition rate which is representative of engine loading, which rate is high with respect to the recurrence rate of said first pulses; the count pulse generator means (26) being connected to said first counter (27), said first counter (27) counting a countable number of count pulses in the gaps, or intervals between recurrence of said first pulses, the number of count pulses counted during said gaps being a function of a. the pulse repetition rate of said count pulses as generated by said count pulse generator means (26) and b. the duration of said gaps, or elapsed time between said first pulses,

said function generator (30), providing said second sequence of second pulses being coupled to the crankshaft of the engine and providing said second sequence of pulses at a nonuniform recurrence rate, in dependence on angular position of the crankshaft of the engine, with respect to upper dead center position of the crankshaft;

said first pulses transferring a counted number in said first counter (27) to said storage counter (28), and said digital comparator (30) comparing the stored number in said storage counter (28) with the counted number in said second counter means (35) and providing an ignition trigger pulse upon sensed coincidence of said numbers.

whereby the comparator will compare a first digital number representative of a composite of engine speed and loading with a second digital number representative of a function of crankshaft position, forming a composite of ignition timing with respect to upper dead center crankshaft position.

24. System according to claim 23, further comprising at least one start number storage means (41, 42) having input terminals (43, 44), respectively, to set a predetermined number into said start number storage means;

and means (45, 46, 47; 48; 49) sensing a condition of operation of the engine, connected to a respective input terminal of said at least one start number storage means to enter a start number therein representative of a condition of operation of said engine.

25. Digital system to provide a trigger signal to trigger an operating event in an operated device at a time subsequent to a datum instant, which time depends on operating conditions of the device,

characterized by I M, J

a. first transducer means coupled to the device and providing a sequence of first pulses representative of an operating condition thereof;

first counter means (27, 28) having said first pulses applied thereto, determining the time gap between pulses, and providing a representation of said time gap in form of a digital number;

b, a function generator (30) providing a second sequence of second pulses, having a time distribution which is representative of the function of variation of an operating condition with respect to the operating condition of said device subsequent to operation with respect to said datum;

second counter means (35) providing a representation of the number of second pulses, derived from said function generator, in the form of a second digital number, arising subsequent to said datum;

c. a digital comparator (39) connected to and comparing the numbers in both said first counter means (27, 28) and said second counter means (35) and providing said trigger signal upon determination of equality of said first and second digital numbers;

d. and a count pulse oscillator (26) coupled to said operated device and generating a sequence of count pulses at a repetition rate which is representative of an operating condition of said device, and at a rate which is high with respect to the recurrence rate of said first pulses, the count pulse oscillator (26) being connected to the counting input (2) of said first counter means (27, 28);

whereby the comparator (39) will compare a digital number representative of a composite of the operating conditions sensed by the first transducer means and the count pulse oscillator, with a digital number representative of a function of a variation of an operating condition of said device subsequent to operation of said device with respect to said daturn.

26. Internal combustion engine in ignition trigger pulse control system to provide a trigger signal to initiate ignition, comprising first transducer means (10) coupled to the crankshaft of the engine and providing a sequence of first pulses representative of speed of engine operation;

a count pulse generator (26) coupled to the engine and providing count pulses at a repetition rate which is representative of engine loading;

first counter means having said first pulses representative of engine speed and said count pulses representative of engine loading applied thereto and counting a digital number, the value of which is representative of engine speed at a certain load;

datum signal generating means (36) providing a signal representative of a predetermined angular datum crankshaft position in advance of upper dead center position of a piston of the engine;

a function generator (30) providing a second sequence of second pulses having a time distribution which is representative of the function of variation of ignition timing with respect to instantaneous angular crankshaft position of the engine with respect to said datum;

second counter means (35) providing a digital count number representative of the number of second pulses, derived from said function generator, subsequent to the engine crankshaft passing said datum angular position;

and a digital comparator (39) connected to and comparing the number in both said first counter means (27, 28) representative of a composite of engine speed and engine loading with the number in said second counter means (35) representative of the function of ignition timing with respect to instantaneous angular crankshaft position, and providing said trigger signal upon determination of a predetermined relationship of said first and second digital numbers.

27. System according to claim 26, further comprising means (46, 47; 48, 49) sensing operating conditions of the engine which have a persistence time which is long with respect to the recurrence time of said first and second pulses;

start number storage means (41, 42) connected to said long-time condition sensing means and controlled thereby, the output of said start number storage means (41, 42) being connected to at least one of said counter means (27, 28; 35) to provide a predetermined start number to the respective counter means,

to modify the count in said counter means, for comparison in said comparator (39) in accordance with engine operating conditions independent'of instantaneous angular crankshaft position of the engine.

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Classifications
U.S. Classification123/406.55, 123/406.63
International ClassificationF02P3/045, F02P5/15, G06F7/62
Cooperative ClassificationG06F7/62, Y02T10/46, F02P5/15
European ClassificationF02P5/15, G06F7/62