GB1603631A - Internal-combustion engine ignition system - Google Patents

Description

(54) INTERNAL-COMBUSTION ENGINE IGNITION SYSTEM (71) We, PIRANHA IGNITION LIM ITED, a British Company of Dynamo & BR< Electrical Services Limited, Unity Works, Pearson Street, Blackburn, BB2 2ER Lancashire, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to internalcombustion engine inductive ignition systems.

The invention comprises an internal combustion engine inductive ignition system with a battery-powered ignition coil, wherein an engine-driven signal generator is arranged to supply control signals at firing intervals at the engine at moments for the cylinders that are in crankshaft angle advance of the top dead centre moments of the pistons, oscillating means are connected to receive said control signals and are arranged upon the reception of each control signal to commence a limited train of repetitive switching cycles of the ignition coil primary winding circuit, switching the said circuit on at the beginning of the train and off at the end of the train, the repetition frequency of the switching operations within the train being a constant frequency independent of engine speed and considerably higher than the highest ignition frequency in the normal speed range of the engine and such that at least several switching operation cycles of the train take place before the top dead centre moment of the relevant piston, and the ignition coil is ferrite-cored and adapted to enable each train of repetitive switching cycles of the core primary winding circuit to generate a train of repetitive ignition sparks at least several of which are effective before the top dead centre moment of the relevant piston.

The primary current in the winding circuit rises relatively fast when the circuit thereof is closed in each component cycle of a train of switching operations. Thus, at each firing interval of the engine a train of effective spark voltages at high repetitive frequency is generated; at least several of which appear before the top dead centre moment of the relevant piston. The said train can improve the firing of many engines at least at some speeds and at the very least ensures against non-firing. The magnitude of core flux necessary to yield high spark voltages when caused to collapse in each component switching cycle can be attained by using a high magnitude of primary current, which can be taken from the battery power source of a conventional size, e.g. a 12 volt battery, by making the primary windings of low total resistance.The required flux might be attained by a combination of high primary current and low number of primary winding turns. The power source need not usually take a high average power, however, for it Is arranged that no primary current flows in the intervals between successive trains of switching operations while during each train of switching operations there are necessarily cyclic primary current interruptions. For the same reason, the primary winding coil average temperature rise will tend to be low.

The spark voltage will not change with engine speed, for the frequency of switching operations in each train, e.g. at least 20 times any normal ignition frequency demanded by the engine, by reference to which high frequency the circuit constants are now chosen, is independent of engine speed.

The invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a circuit diagram of an opticoelectronically-controlled internalcombustion engine ignition system, Figure 2 shows the form of the rotary shutter of the ignition system, and Figures 3 and 4 are diagrams showing the timing of trains of switching operations at two respective engine speeds.

With reference to Figures 1 and 2 of the drawings, an ignition system for a fourcylinder four-stroke internal-combustion engine has an optico-electronic arrangement for the generation of control signals at the firing intervals of the engine comprising a rotary shutter 1 arranged to be driven by the engine and when so driven alternately to free and to obstruct a radiation path from a radiation source 2 to radiation-responsive means 3; circuitry 4 controlled by the radiation-responsive means is arranged for effecting the generation of spark voltages for ignition in the periods when the radiation path is free; the system also has a distributor 5 for the cyclic allotment of spark voltages to the spark gaps 6 of the spark plugs of the various cylinders.

The circuitry 4 is energized from a positive-voltage line 7 which receives its voltage from the positive terminal 8 of a battery (not shown), which may be a normal battery for the engine, through an on-off ignition switch 9, a diode 10 and a voltage regulator 11 comprising an NPN transistor 12 and a zener diode 13. The radiation source 2 is also energized from the positive line 7 and comprises a light-emitting diode (LED).

With reference to Figure 2, the rotary shutter 1 comprises a disk provided with four-equi-angularly arranged sectoral lobes 21 each extending 26 around the shutter axis of rotation. The shutter is arranged to be rotated by the engine at the valve camshaft speed, that is to say, at half the engine crankshaft speed, and so as to generate the control signals at the moments usual for the engine in crankshaft angle advance of the top dead centre moments of the pistons.

The radiation-responsive means 3 comprise an NPN photo-transistor that is conductive under the influence of radiation from the LED 2. The LED and the phototransistor are arranged on opposite sides of the shutter disk and so that the lobes 21 alternately obscure and clear the view of the LED from the photo-transistor as the shutter rotates.

The photo-transistor 3 is energized through the connection of its collector to the line 7 and a point in a resistive connection of its emitter to earth is connected to the input terminal of a negator or reverser 22. If the input signals to the negator are designated in logic circuit terms as 1 or 0 according as the photo-transistor is irradiated or unirradiated by the LED, then the negator output signal is 0 or 1 according as its input signal is 1 or 0. The negator output signal is led to the input terminal of a second negator or reverser 23. If a semi-conductor chip is being used which has only two-input norgates or two-input nand-gates, each of the negators 22 and 23 may consist of such a gate with its two input terminals connected together.

The output of the second negator 23 is applied both to the input terminal of a pulse generator 24, of which the output is led to one input terminal of a two-input nand-gate 25, and to the input terminal of a one-shot monostable 26, of which the output is led to the other input terminal of the two-input nand-gate 25.

The pulse generator 24 is energized from the positive line 7 and is provided with an external time-constant circuit 27 by adjustment of which the pulse width and gap may be set. The pulse generator 24 is arranged so that so long as its input terminal receives a 0 signal it delivers a 0 signal to the first input terminal of the nand-gate 25, whereas so long as its input terminal receives a 1 signal it delivers to the first input terminal of the nand-gate 25 a square pulse wave form comprising alternating values of 1 and 0 each 1200 microseconds long.

The one-shot monostable 26 is energized from the positive line 7 and is provided with an external time-constant circuit 28 by adjustment of which the monostable time constant may be set. The monostable 26 is arranged so that so long as its input terminal receives a 0 signal it delivers a 0 signal to the second input terminal of the nand-gate 25, whereas when its input terminal receives a 1 signal it is triggered to a quasi-stable state for a 7 millisecond period, during which it delivers a 1 signal to the second input terminal of the nand-gate 25, after which period the monostable reverts to its normal stable state in which it again delivers a 0 signal to the nand-gate.

The output terminal of the nand-gate 25 is connected through a resistor 29 to the base of an emitter-earthed NPN transistor 30 of which the collector is connected both to earth through a resistor 31 and to the control electrode of a thyristor 32. The thyristor 32 lies in a circuit leading from the battery terminal 8 in series through a resistor 33, a winding 34 later described, a resistor 35, the thyristor 32 and a resistor 41.

Between earth and the junction between the resistor 33 and the coil 34 a capacitor 42 is connected.

For the generation of spark voltages a ferrite-cored ignition coil 43 is provided of which the primary winding 44 is connected at one end to the battery terminal 8 and at the other end to the collector of an earthedemitter NPN transistor 45. The transistor 45 is shunted by a resistor 46 - capacitor 47 connection which provides protection against transients. The ignition coil 43 has its secondary winding 48 connected to the rotary arm 49 of the distributor 5.

The transistor 45 provides switching means for the circuit of the ignition coil primary winding 44 and its base is connected to the junction point between the thyristor 32 and the resistor 41. The winding 34 in the circuit of the thyristor 32 is tertiary winding on the ignition coil 43 and is so connected in the thyristor circuit that the electrically and magnetically linked primary winding circuit and thyristor circuit constitute a blocking oscillator, designated generally as 50. The values of the components of the blocking oscillator are chosen to yield an oscillatory period of 100 microseconds during which the switching transistor 45 operates to close the ignition coil primary winding circuit for 50 microseconds and to open it for 50 microseconds.The oscillation is permitted so long as a positive signal is applied to the thyristor control electrode but prevented so long as a near-zero signal is applied to said control electrode.

In the operation of the system, so long as the rotary shutter 1 prevents the passage of radiation from the LED 2 to the phototransistor 3 to the negator 22 receives a 0 output signal and therefore the negator 23 receives a 1 input signal and the pulse generator 24 and the monostable 26 both receive 0 input signals. Consequently the nand-gate 25 receives a 0 input signal from the pulse generator 24 and a 0 input signal from the monostable 26, the nand-gate 25 delivers a 1 output signal, the transistor 30 is on, the control electrode of the thyristor 32 receives a near-zero signal and the blocking oscillator 50 does not oscillate; while the blocking oscillator does not oscillate no current flows in the ignition coil primary winding.

When the rotary shutter 1 is angularly positioned to permit the passage of radiation to the photo-transistor 3 the negator 22 receives a 1 input signal, the negator 23 receives a 0 input signal and the pulse generator 24 and the monostable 26 both receive 1 input signals. The nand-gate 25 receives from the pulse generator 24 a continuous alternation between a 1 input signal for 1200 microseconds and a 0 input signal for 1200 microseconds. To start with, the monostable 26 delivers a 1 input signal to the nand-gate 25, which therefore responds to the alternating 1 and 0 signals from the pulse generator 24 to deliver alternating 0 and 1 output signals, causing the transistor 30 to be alternately off and on.

During each 1200 microsecond off period of the transistor 30 the thyristor control electrode receives a positive signal and the blocking oscillator 50 oscillates; during each 1200 microsecond on period of the transistor 30 the blocking oscillator 50 cannot oscillate. The monostable 26, however, reverts after 7 milliseconds to its normal stable state in which, even although it may still receive a 1 input signal from the negator 23, it delivers a 0 input signal to the hand-gate 25, which perforce can then deliver only-a 1 output signal and the blocking oscillator 50 cannot oscillate.

If, while the pulse generator 24 is delivering its alternating signals, the rotary shutter 1 again prevents the passage of radiation to the photo-transistor 3, the 0 input signal then received by the pulse generator 24 from the negator 23 permits the nand-gate 25 to receive then only a 0 input signal from the pulse generator 24, the nand-gate 25 can then deliver only a 1 output and the blocking oscillator 50 cannot oscillate.

With reference to Figure 3, the top line, Figure 3(a), shows the time spacing of adjacent rotary shutter lobes 21 at an engine speed of 3000 r.p.m. The second line, Figure 3(b), shows a train 60 lasting 1200 microseconds of cycles each of 100 microseconds of switching operations for the circuit of the ignition coil primary winding effected by the blocking oscillator, followed by an interval 61 of 1200 microseconds during which the ignition coil primary winding circuit is open, then by a second similar train 62 of switching operations, then by another similar interval 63 and then by a third similar train 64 of switching operations.The third train 64 is not succeeded after another similar interval by another similar train because after 7 milliseconds from the beginning of the first train 60 the monostable reverts to its normal state and ensures that the nand-gate 25 has a steady 1 output signal and the blocking oscillator 50 cannot oscillate.

As the engine speed is increased the time during which radiation can fall on the photo-transistor between the passages of successive rotary shutter lobes is reduced.

When the photo-transistor is obscured the blocking oscillator 50, for the reasons explained, cannot oscillate. Thus as the speed is continually increased the third train 64 of switching operations is curtailed and then completely prevented and later the second train 62 of switching operations also is curtailed. With reference to Figure 4, the top line, Figure 4(a), shows the time spacing of adjacent rotary shutter lobes 21 at top engine speed of 8000 r.p.m.There is an interval of 3.75 milliseconds between the trailing edges of the two lobes but only an interval of 2.7 milliseconds between the trailing edge of the first lobe and the leading edge of the second lobe; the second line, Figure 4(b), shows that there is now time for only the first train 60, lasting 1200 microseconds, of switching operations, together with the interval 61 of 1200 microseconds, and part of the second train 62 of switching operations.

As the engine speed is caused to fall, there progressively increases, up to the fixed time limit of 7 milliseconds, the total time available for the generation of the series of trains 60, 62, 64.

The properties of a ferrite-cored coil make it possible to operate it with fast rises and falls of a large current therein. In the described circuit the properties are exploited to switch an ignition coil primary winding circuit repetitively at a constant repetition frequency very much higher than any ignition frequency demanded by the engine. The circuit constants being chosen by reference to this constant high frequency, the spark voltage will not change with engine speed.

The burning time of an individual spark due to an individual switching operation in a train is relatively short, however, the effective spark burning time to ensure ignition is long in view of the repetition of the sparks.

If, for example in a cold engine, the sparking resulting from the first few switching operations of the first train fails to ignite the mixture, nevertheless the ignition is rendered progressively more probable by reason of the on the average progressive heating of the plug points and the on the average progressive ionization of the spark gap. It might be observed in this connection that capacitor ignition systems do not readily lend themselves to the curing of short spark burning times by the production of similar repetitive spark voltages at frequencies similarly high in relation to the engine ignition frequencies.

The use of generating trains of ignition coil switching operations in the manner described encourages the provision of the second and third trains that are both in operation at the lower engine speeds, as described and illustrated in Figure 3. It is usual in internal-combustion engines to arrange for each cylinder charge to be ignited before top dead centre if possible; at high engine speed the first train of switching operations with the present arrangement extends over top dead centre; at lower speeds the first train may terminate before top dead centre, and at least, the second train of switching operations operates at or after top dead centre.The provision of sparks at or after top dead centre may well be a useful safeguard against the conceivable blowing out of sparks of the first train owing to pressure nses. The third train operating at the lower engine speeds may be useful as an additional precaution to ensure complete combustion and therefore minimum atmospheric pollution.

The arcuate angle of the movable electrode in the distributor and/or the arcuate angle of the fixed electrodes therein must be relatively large to - permit the transfer of spark voltages during relatively large camshaft angles.

It will usually be required that the ignition timing shall advance with engine speed and to this end the rotary shutter 3 and simultaneously the distributor rotary arm 49 may be angularly displaceable in relation to a driving shaft therefore by centrifugallyoperated devices of known kind.

The described switching operation frequency within the trains of 100 microsecond period, i.e. 10 kHz, is 100 times the engine ignition frequency at 300 r.p.m. and 37.5 times the engine ignition frequency at 8000 r.p.m.; at practicable engine speeds the frequency ratio is therefore always high.

Adapted for engines with more than four cylinders, the described system will yield smaller but still high frequency ratios; however, the system may be feasibly modified to operate with still higher switching operation frequencies within the trains.

Generally, with all the more usual automobile engines it will be feasible to arrange that the frequency ratio will always be 20:1 or greater and that, by virtue of the circuit constants being selected by reference to the higher of the two frequencies, the spark voltage will substantially not change with engine speed.

WHAT WE CLAIM IS: 1. An internal-combustion engine inductive ignition system with a batterypowered ignition coil, wherein an enginedriven signal generator is arranged to supply control signals at firing intervals of the engine at moments for the cylinders that are in crankshaft angle advance of the top dead centre moments of the pistons, oscillating means are connected to receive said control signals and are arranged upon the reception of each control signal to commence a limited train of repetitive switching cycles of the ignition coil primary winding circuit, switching the said circuit on at the beginning of the train and off at the end of the train, the repetition frequency of the switching operations within the train being a constant frequency independent of the engine speed and considerably higher than the highest ignition frequency in the normal speed range of the engine and such that at least several switching operation cycles of the train take place before the top dead centre moment of the relevant piston, and the ignition coil is ferrite-cored and adapted to enable each train of repetitive switching cycles of the core primary winding circuit to generate a train of repetitive ignition sparks at least several of which are effective before the top dead centre moment of the relevant piston.

2. A system as claimed in Claim 1, wherein the ratio between the repetition

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. operations. As the engine speed is caused to fall, there progressively increases, up to the fixed time limit of 7 milliseconds, the total time available for the generation of the series of trains 60, 62, 64. The properties of a ferrite-cored coil make it possible to operate it with fast rises and falls of a large current therein. In the described circuit the properties are exploited to switch an ignition coil primary winding circuit repetitively at a constant repetition frequency very much higher than any ignition frequency demanded by the engine. The circuit constants being chosen by reference to this constant high frequency, the spark voltage will not change with engine speed. The burning time of an individual spark due to an individual switching operation in a train is relatively short, however, the effective spark burning time to ensure ignition is long in view of the repetition of the sparks. If, for example in a cold engine, the sparking resulting from the first few switching operations of the first train fails to ignite the mixture, nevertheless the ignition is rendered progressively more probable by reason of the on the average progressive heating of the plug points and the on the average progressive ionization of the spark gap. It might be observed in this connection that capacitor ignition systems do not readily lend themselves to the curing of short spark burning times by the production of similar repetitive spark voltages at frequencies similarly high in relation to the engine ignition frequencies. The use of generating trains of ignition coil switching operations in the manner described encourages the provision of the second and third trains that are both in operation at the lower engine speeds, as described and illustrated in Figure 3. It is usual in internal-combustion engines to arrange for each cylinder charge to be ignited before top dead centre if possible; at high engine speed the first train of switching operations with the present arrangement extends over top dead centre; at lower speeds the first train may terminate before top dead centre, and at least, the second train of switching operations operates at or after top dead centre.The provision of sparks at or after top dead centre may well be a useful safeguard against the conceivable blowing out of sparks of the first train owing to pressure nses. The third train operating at the lower engine speeds may be useful as an additional precaution to ensure complete combustion and therefore minimum atmospheric pollution. The arcuate angle of the movable electrode in the distributor and/or the arcuate angle of the fixed electrodes therein must be relatively large to - permit the transfer of spark voltages during relatively large camshaft angles. It will usually be required that the ignition timing shall advance with engine speed and to this end the rotary shutter 3 and simultaneously the distributor rotary arm 49 may be angularly displaceable in relation to a driving shaft therefore by centrifugallyoperated devices of known kind. The described switching operation frequency within the trains of 100 microsecond period, i.e. 10 kHz, is 100 times the engine ignition frequency at 300 r.p.m. and 37.5 times the engine ignition frequency at 8000 r.p.m.; at practicable engine speeds the frequency ratio is therefore always high. Adapted for engines with more than four cylinders, the described system will yield smaller but still high frequency ratios; however, the system may be feasibly modified to operate with still higher switching operation frequencies within the trains. Generally, with all the more usual automobile engines it will be feasible to arrange that the frequency ratio will always be 20:1 or greater and that, by virtue of the circuit constants being selected by reference to the higher of the two frequencies, the spark voltage will substantially not change with engine speed. WHAT WE CLAIM IS:

1. An internal-combustion engine inductive ignition system with a batterypowered ignition coil, wherein an enginedriven signal generator is arranged to supply control signals at firing intervals of the engine at moments for the cylinders that are in crankshaft angle advance of the top dead centre moments of the pistons, oscillating means are connected to receive said control signals and are arranged upon the reception of each control signal to commence a limited train of repetitive switching cycles of the ignition coil primary winding circuit, switching the said circuit on at the beginning of the train and off at the end of the train, the repetition frequency of the switching operations within the train being a constant frequency independent of the engine speed and considerably higher than the highest ignition frequency in the normal speed range of the engine and such that at least several switching operation cycles of the train take place before the top dead centre moment of the relevant piston, and the ignition coil is ferrite-cored and adapted to enable each train of repetitive switching cycles of the core primary winding circuit to generate a train of repetitive ignition sparks at least several of which are effective before the top dead centre moment of the relevant piston.

2. A system as claimed in Claim 1, wherein the ratio between the repetition

frequency of the switching operations within the train and the highest ignition frequency in the normal speed range of the engine is at least 20:1.

3. A system as claimed in Claim 2, wherein the repetition frequency of the switching operations within the train is 10kHz in the case of a four-cylinder engine.

4. A system as claimed in any of Claims 1 to 3. having means adapted to ensure, when each said control signal is supplied, the generation of a series of similar trains of said switching operations, the trains of the series being separated by equal and constant time intervals, and means for increasing progressively up to a fixed time limit as the engine speed is caused to fall the total time during which the series of trains may be generated.

5. A system as claimed in any of Claims 1 to 4, wherein each train of switching operations is generated with the aid of a blocking oscillator having a winding on the ferrite-cored ignition coil.

6. A system as claimed in Claim 5, wherein the blocking oscillator includes a thyristor connected to the base of a switching transistor in the ignition coil primary winding circuit, through control of the control electrode of which thyristor the oscillations of the blocking oscillator are permitted or prevented.

7. An internal combustion engine inductive ignition system with a battery-powered ferrite-cored ignition coil and means for switching, at each firing interval of the engine, the circuit of the ignition coil primary winding circuit in a train of repetitive switching operations, arranged and adapted to generate a train of repetitive ignition sparks at least several of which are effective before the top dead centre moment of the relevant piston, substantially as hereinbefore described with reference to the accompanying drawings.