GB2087483A - Extended duration ignition pulse circuits - Google Patents

Abstract

An ignition timing detector 26 produces an alternating signal at each required ignition instant. A first ignition control 14 receives the detector signal and produces a first high voltage pulse in the secondary circuit 44 of an ignition coil 18. A delay circuit 22 produces a delay signal that lags the timing detector signal by a predetermined period. A second ignition control 16 receives the delay signal and produces a second high voltage pulse in the secondary circuit 46 of another ignition coil 20. High voltage diodes 48, 50 in series with each ignition coil logically OR the high voltage pulses and gate the composite signals to the rotor of a distributor 24 to provide sparks having an extended duration. The circuit also provides increased spark energy during engine cranking by short circuiting ballast resistors in the ignition control. Additional ignition controls and delay circuits may be provided to further increase the spark duration. <IMAGE>

Description

SPECIFICATION Extended spark duration ignition system Field of the Invention This invention relates to an ignition control system for an internal combustion engine. More particularly, the present invention is related to the field of electronic ignition controls for extending the duration of the spark-producing pulse at the ignition plug. More particularly still, the present invention is related to the field of electronic ignition controls for producing an extending duration spark by combining the pulses produced by several ignition control circuits whose output pulses are out of phase.

Description of the Prior Art Engine performance is determined principally by the manner in which combustion progresses in the engine cylinder. Factors that affect combustion include quality of the air-fuel mixture, air-fuel ratio, ignition system characteristics and the effects of exhaust gas recirculation. Engines that burn a lean fuel-air mixture produce reduced amounts of carbon monoxide, nitrogen oxides and unburnt hydrocarbons in the exhaust gas.

Increasing the amount of exhaust gas supplied with the incoming charge of fuel and air mixture further reduces the concentration of these undesirable gases in the products of combustion.

But engine performance is adversely affected by the use of lean mixtures and substantial quantities of exhaust gas recirculated to the engine.

Where combustion properties of the mixture are less than ideal, longer spark time and greater electrical potential are required to produce the spark in the cylinder that initiates combustion.

Frequent attempts have been made to alter conventional ignition technique by inserting two spark plugs in each cylinder or combustion chamber of the engine.

For example, U.S. Patent 3,919,994 describes an ignition system for rotary internal combustion engines that provides a delay between the generation of ignition potential for the leading and trailing spark plugs in response to an alternating current signal that corresponds to engine rotor position. The delay period corresponds to a selectable number of engine crankshaft degrees at all engine speeds.

U.S Patent 3,964,454 describes an ignition system for a reciprocating combustion engine having two spark plugs in each cylinder. A pulse delay of variable duration is provided between the firing of each spark plug.

The ignition system of U.S. Patent 3,972,315 uses an ignition coil having two primary windings that inductively couple an inductive discharge system and a capacitive discharge system to the secondary windings of an ignition coil.

It is preferable to accomplish the object of extending spark time and increasing spark energy with the use of one spark plug for each cylinder.

Furthermore, since spark potential produced in the secondary winding of the ignition coil is most effective when applied without excessive loss at the distributor rotor, it is essential that dual ignition systems electrically isolate the secondary winding of each ignition coil from the other coils. Unless isolation is provided, the resistive and capacitive effect of each coil will operate to attenuate the high voltage pulse that should be applied to the distributor with minimal dissipation.

Summary of the Invention The present invention contemplates the generation of a long, high voltage pulse having a predetermined duration. The output voltage from at least two ignition control circuits, each output delayed with respect to the others, is supplied to an OR gate that generates the extended high voltage pulse. A plurality of identical electronic ignition control circuits manufactured in volume, for example, in intregrated circuit form, at comparatively low cost are used to produce the high voltage pulses induced in the secondary windings of the several ignition coils. the input signal received by each ignition control is derived from an engine position detector signal, which is dealyed in a pulse delay circuit.The output of each pulse delay circuit trails the output of other delay circuits by a predetermined period chosen so that an optimal spark duration is produced when the ignition control signals are combined. The trigger delay circuit includes a position sense amplifier that detects the zero crossing of the engine position detector signal. Two monostable multivibrators connected in series receive the zero crossing detector signal. The second multivibrator produces a pulse whose leading edge occurs delayed by the duration of the predetermined delay period following the zero crossing of the ignition position detector signal. An operational amplifier inverts the output of the second multivibrator to produce a pulse having a leading, rising edge following the requisite delay period.

An OR gate comprising two high voltage diodes, is connected in series with the secondary windings of each ignition coil. The ignition circuits including the diodes are connected in parallel with the distributor rotor. In this way, the high voltage pulses produced in the secondary windings of the ignition coils are electrically isolated from one another and the output of each coil is combined in the OR gate. The overall efficiency of the system is enhanced because the inherent capacitive and resistive effect of each coil of the network is not imposed on the output of a single coil due to the isolation effect of the high voltage diodes.

It is an object of this invention, therefore, to produce an ignition system having a long duration high voltate pulse that may be applied to the rotor of the distributor for producing an extended duration spark pulse at the ignition plugs of an internal combustion engine. This result is realized by combining in parallel several conventional ignition control circuits, preferably such circuits made by integrated circuit means, that are identical to each other with the exception of minor modifications to the input ports determined by the requirements of the ingition network.

By using high voltage diodes, two ignitition systems of conventional design and characteristics can be combined to produce an ignition system having greater spark duration and spark energy. A trigger delay circuit is incorporated so that each ignition control fires out of phase with the other control circuits. The high voltage diodes logically OR the individual voltage pulses produced by the control circuits and operate to produce a composite signal of the several voltage pulses that can be supplied to the ignition plugs.

A plurality of ignition controls whose input is appropriately delayed with respect to that of other control circuits can be combined by the principles of this invention to produce even longer spark periods.

The invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an ignition system having the spark ignition system of the present invention included; Figure 2 is a circuit diagram of the typical ignition control used in the ignition system of Figure 1; Figure 3 is a block diagram of the pulse delay circuit used in the ignition system of Figure 1; and Figure 4 illustrates several waveforms present at various points of the circuits of Figures 2 and 3 and the system of Figure 1. These waveforms have the same time base and illustrate the phase relationship among the various signals.

Description of the Preferred Embodiment Turning first to Figure 1, an automotive ignition system to which the ignition control of the present invention could be applied includes a battery 10, an ignition switch 12, a first ignition control circuit 14, a second ignition control circuit 16, a first ignition coil 18, a second ignition coil 20, a pulse delay circuit 22, a distributor 24, a contactless ignition timing detector 26 and ignition plugs 28, one plug installed in each engine cylinder.

Ignition switch 12 has three terminals: run 32, off 34 and start 36. A fixed terminal 38 of the switch 12 is connected to the positive terminal of battery 1 0.

The contactless ignition timing detector 26 consists of an armature 40 having one gear-like tooth for each engine cylinder mounted on the distributor shaft and a permanent magnet inside a small coil 52. The distributor 24 is electrically connected to the secondary circuit windings 44, 46 of the first and second ignition coils 1 8, 20 through the high voltage diodes 48, 50. The ignition timing detector 26 sends a simple alternating current signal 104 to the ignition controls 14, 1 6. The current waveform varies cyclically from positive to negative each time one of the gear teeth on the rotor 40 passes the permanent magnet in the coil 52. When a gear tooth is exactly opposite the coil, the current waveform is at a zero position going from negative to positive.The ignition control is designed to sense this position and to interrupt the flow of current in the windings of the ignition coils 1 8, 20.

A high voltage induced in the secondary windings 44, 46 when the primary circuit current is interrupted is directed to the ignition plugs 28 through the distributor 24.

Figure 2 shows a circuit diagram of the electrical components that comprise the ignition control 14. With reference to Figure 2, the ignition control includes transistors 58-64, resistors 66-81, diodes 84-90, Zenerdiodes 92-96 and capacitors 98-1 00. Transistors 62, 63 and resistors 77, 78 form the Darlington pair 101.

As the input signal waveform 104 crosses through zero in a positive-going direction, as shown in Figure 4, transistor 58 is turned on and a capacitor 98 begins to discharge through diode 87. As this happens, the base of transistor 60 is reverse biased and transistor 62 is turned off. The time for this to occur is the spark time and is a function of the R70 C98 time constant and the frequency of the input signal from the detector 26.

As transistor 60 is turned off, its collector potential rises to approximately 1.4 volts, which potential is coupled to the base of transistor 59.

This switches transistor 59 on and provides a second path for the discharge from capacitor 98. If transistor 58 should turn off due to noise in the input signal, noise on the incoming lines could turn transistor 58 off and shorten the spark time.

Therefore, a latch action is provided whereby transistor 60 insures sufficient spark time.

As capacitor 98 recharges through resistor 68, the base of transistor 60 becomes positive, thus turning transistor 60 on again. This is the dwell function and its duration is a function of the R68 C98 time constant and the frequency of the input signal A third portion of the circuit, apart from the portions that determine spark time and dwell, functions during the period when transistor 60 is off. When this occurs, transistor 61 is turned on because its base is driven positive by the square wave output from transistor 60. Transistor provides signal inversion and gain needed for the Darlington pair 101. The potential at the base of transistor 62 drops as transistor 61 turns on, thus switching the Darlington pair off. The output of the Darlington is then coupled to the output switching transistor 64. The collector of transistor 64 rises to approximately 360 volts depending on the rating of capacitor 100 and the ignition coil parameters. As the current in the primary coil 54 is switched off, the rate of the voltage rise of the ignition coil primary inductance is the source of the high voltage at the collector of transistor 64.

The point at which transistor 58 turns on is related to the match of the base-emitter voltage of transistor 58 and the forward voltage drop of diode 85. The period between the time when diode 58 switches on and the firing of the spark plug ranges from approximately 8 to 20 microseconds.

During the engine starting condition, resistor 75 is bypassed by current from the battery by applying the positive terminal of the battery to terminal 36, thus increasing the current through the Darlington pair 101 and the current to switching transistor 64. A ballast resistor 81 having a rating of 1.4 ohms is also removed from its series connection with the primary winding 54 of the ignition coil 1 8 during engine starting conditions. By removing resistors 75 and 81 from the circuitry, increased electrical energy at the spark plug is provided during engine cranking to facilitate starting.

Figure 4(a) shows the cyclical input signal waveform 104 that is produced by rotation of rotor tooth 42 into proximity with pickup coil 52.

The collector voltage of switching transistor 64 shown in Figure 4(b) as waveform 105 has a spike occurring when the input signal 104 is zero in a positive going direction. The collector current through transistor 64 appears in Figure 4(c) as waveform 106.

A pulse delay circuit 22 is shown in block diagram form in Figure 3. Circuit 22 includes a zero crossing detector 108, first and second pulse generators 110, 112 and an operational amplifier 114. Conductors 55, 57 carry the ignition timing detector signal to the input port of the zero crossing detector, which produces a square wave pulse 11 6 when the detector pulse passes through zero in a positive sense. The duration of this pulse may be approximately 100 microseconds.

Pulse generators 110, 112, which may be monostable multivibrators, remain in the stable state until a triggering signal causes a transition to the quasi-stable state. Then, after a time, the circuit returns to its stable state; hence a signal pulse is generated. The first multivibrator circuit 110 in the pulse delay circuit 22 delivers a pulse 118 of negative polarity, the width of the pulse being approximately one millisecond. The second multivibrator 112 delivers a negative polarity pulse 120 whose width is also approximately one millisecond. The width of pulse 11 8 extends from the rising edge of pulse 11 6; the width of pulse 120 extends from the rising edge of pulse 11 8.

Operational amplifier 114 acts to change the polarity of the output pulse received from multivibrator 112 and produces waveform 122 whose rising edge 124 is delayed in respect of the rising edge of pulse 116. The output waveform 122 of op amp 114 is carried on conductor 126 to the input of the second ignition control circuit 1 6.

The second ignition control 1 6 has applied to it, also, the potential of the positive pole of battery 10, the connection being made by ignition switch 1 2. The function of ignition control 1 6 is nearly identical to that of the first ignition control 14 except that the output pulse 122 of op amp 114 is supplied as input to the second ignition control 1 6 in place of the signal produced by the ignition timing detector 26 carried on lines 55, 57 to the first ignition control 14.

Figure 4 shows the voltage waveform 128 that is applied across the primary winding 54 of the first ignition coil 1 8 and the voltage waveform 1 30 that is applied across the primary winding 56 of the second ignition coil 20. Voltage pulse 130 is delayed from that of pulse 1 28 by period T, the combined time constant of the multivibrators 110, 112. This delay period is adjusted so that an extended spark duration of 2 to 3 milliseconds is produced. The extended spark period shown in Figure 4(j) is the voltage waveform output of the OR gate formed by high voltage diodes 48, 50 and is supplied to the rotor of the distributor 24.Each spark event, i.e., the duration of the negative potential at the output of ignition controls 14, 1 6 indicated in Figures 4(h) and 4(i) by waveforms 128, 130, is assumed to extend between 1 and 1.5 milliseconds. By combining these signals waveform 132 is produced by the OR gate that is arranged according to the requirements of negative voltage logic. In this way, by adjusting the delay period T to be consistent with the duration of the spark event produced by each ignition control, an extended spark can be produced at the distributor rotor. The diodes 48, 50 that comprise the OR gate may be high voltage diodes H 1712 or H 1712S produced by the Varo Corporation.

The cycle is repeated for each occurrence of the ignition timing detector 26 signal whose waveform 104 appears in Figure 4(a). Using this technique, two or more ignition control circuits can be combined to produce even longer spark periods than that of waveform 132 by connecting the output of the secondary winding of each ignition coil to a diode network connected in parallel, thereby forming an OR gate whose output port is connected to the distributor rotor. For example, a second pulse delay circuit similar to delay circuit 22 could be added to the control system of Figure 1. The additional pulse delay circuit would receive as input the ignition timing detector pulse 104 that is carried to pulse delay 22. In this case, however, the second pulse delay circuit would have a delay period that is perhaps twice as long as period T, thereby producing a third voltage waveform across the primary windings of a third ignition coil. This waveform would be similar to the shapes of waveforms 128, 130, but would trail pulse 130 by period T. In this case, three high voltage signals induced in the secondary windings of the ignition coils are logically ORed through the parallel arrangement of three high voltage diodes to produce a potential at the distributor rotor that is extended in duration beyond period T1 by the period by which the additional pulse delay circuit trails the rising edge 124 of pulse 122.

In conventional fashion, the distributor rotor transmits the high voltage potential of the ignition system sequentially to the ignition plugs 28.

Claims (8)

1. An ignition control system for an internal combustion engine having an ignition plug in each combustion chamber comprising: ignition timing detector means producing an engine position detector signal; first ingition control means producing a first pulse in response to the detector signal; pulse delay means producing a delay signal in response to the position detector signal, which delay signal is delayed with respect to the first pulse; second ignition control means producing a second pulse in response to the delay signal; and gate means operative in response to the first and second pulses for producing an extended duration pulse for actuating the ignition plug.

2. The ignition control system of Claim 1, wherein the pulse delay means comprise: a zero crossing detector responsive to the engine position detector signal for producing a pulse as the detector signal crosses a predetermined value; a first pulse generator for producing a pulse of predetermined width in response to the zero crossing detector pulse; a second pulse generator operative for producing a pulse in response to the trailing edge of the first pulse generator pulse and; inverter means operative for inverting the pulse produced by the second pulse generator, whereby the pulse produced by the inverter means is delayed with respect to the pulse of the zero crossing detector by a period approximately equal to the width of the pulse produced by the first pulse generator.

3. The ignition control system of Claim 2 wherein the first and second pulse generators are monostable multivibrators.

4. The ignition control system of Claim 1 wherein the gate means include an OR gate producing a pulse that is a combination of the first and second pulses.

5. The ignition control system of Claim 1, wherein the pulse produced by the second ignition control means is delayed with respect to the pulse of the first ignition control means and wherein the gate means includes an OR gate that produces an output pulse in response to the first and second pulses.

6. The ignition control system of Claim 1, wherein the pulses produced by the first and second ignition control means are high voltage pulses and wherein said gate means includes first and second high voltage diodes connected in series with the first and second ignition control means, respectively, the series connections being arranged in parallel, the parallel arrangement being connected to the ignition plug.

7. An ignition control system for an internal combustion engine having an ignition plug in each combustion chamber comprising: ignition timing detector means producing an engine position detector signal; first ignition control means producing a first pulse in response to the detector signal; pulse delay means producing a plurality of signals in response to the position detector signal, each delay signal being delayed with respect to the first pulse and the other delay signals; a plurality of ignition control means each producing a pulse in response to a delay signal produced by the pulse delay means; and gate means operative in response to the first pulse and the pulses produced by the plurality of ignition control means for producing an extended duration pulse to actuate the ignition plug by combining the first pulse and the phases produced by the plurality of ignition control means.

8. An ignition control system for an internal combustion system substantiaily as hereinbefore described with reference to and as shown in the accompanying drawings.