CA1038444A - Ignition system employing controlled-duration continuous-wave high-frequency spark energy - Google Patents

Abstract

IGNITION SYSTEM EMPLOYING CONTROLLED-DURATION CONTINUOUS-WAVE HIGH-FREQUENCY
SPARK ENERGY

(D#73,508-F) ABSTRACT OF THE DISCLOSURE
An ignition system for internal combustion en-gines. It generates a controlled-duration continuous-wave high-frequency spark, and employs an output transformer in an oscillator which includes a control winding for starting and stopping the oscillator. There is an electronic switch in series with the control winding; and the spark inter-vals, including duration thereof, are determined by photo-electric engine-timed means that employ a phototransistor.
There is a control circuit for the electronic switch, which circuit includes means for minimizing the response time of the phototransistor.

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Description

CROSS-REFERENCES TO RELA~ED APP~ICATIONS
This invention is related to the following prior applications which define inventions by the same inventor:
S.N. 157,608 filed 11/27/72 S.N. 165,988 filed 03/13/73 now Pat. 997,824 09/28/76 S.N. 169,583 filed 04/26/73 now Pat. 1,000,501 11/30/76 S.N. 191,913 filed 02/06/74 now Pat. 1,010,946 0~/27/77 BACKGROUND OF THE INVENTION
Field of the Invention This invention concerns ignition systems in gen-eral. More specifically, it relates to an improved ignition system for internal combustion engines, which employs a continuous-wave high-frequency spark generator. The in-vention is particularly related to improvements for the ~
foregoing type of high-frequency spark-generating system. ~-Description of the Prior Art : .
While there are a considerable number of known systems for developing continuous-wave spark signals that are for use in internal combustion engines, and such sys-tems sometimes include the use of photoelectric engine-timed controls for introducing the spark signals, they have been found to have a drawback in that the photo-electric control introduces a substantial time delay in the initial response. Such a time delay is especially detrimental as high speeds are introduced in the engine, because the delay is relatively constant and, consequently, involves greater crank-angle engine-timing delays as the speed is increased.
Consequently, it is an object of this invention to provide an improvement for the control portion of a -high-frequency sparks system that involves photoelectric , 3~ : . -,',,- 1 ` , ~' .. :

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1~3~444 engine-timed controls. The improvement acts to greatly reduce delays caused by response o~ the photoelectric ele-; ments.
Another ob~ect of the invention is to provide asystem for use with high-frequency continuous-wave spark generators, particularly of the type that employs square-wave oscillators. Such a system has been found to gene-rate large amounts of radio-frequency signals~ and since theæe tend to cause spurious actions in the control sys-tem, the elimination of radio-frequency energies from the control system becomes an important feature.
SoUMA~Y OF THE INVENTION
Briefly, the invention relates to an improve-ment that is part of a combination with an ignition sys-tem for internal combustion engines, wherein said system employs controlled-du~ation continuous-wave high-frequency spark energy. me said spark ener~y is generated by an oscillator having an output transformer, and having a con-trol winding thereon for starting and stopping the oscil- -20 lator at the beginning and end of each spark interval. me ~ -combination also includes electronic switch means connected in series with said control winding for breaking and maklng a loading circuit which includes said control winding. The - said spark intervals are determined by photoelectric engine-timed means including a phototransistor, and the said elec-tronic switch means has a control circult therefor, in-cluding said photoelectric engine-timed means. In rela-tion to the foregoing combination, the invention concerns an improvement which comprises means incorporated with said control circult for minimizing the response time of said phototransistor.

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~ 038444 Again, briefly, the invention concerns an im-provement related to a combination with an ignltion system for an internal combustion engine, wherein sald system em-ploys controlled-duration continuous-wave high-frequency spark energy. me said spark energy is created by a square-wave oscillator having an output transformer, and having a control winding thereon for starting and stopping oscll-lation of said oscillator at the beginning and end of each spark interval. me combination also comprises electronic switch means connected in series with said control winding for breaking and making a loading circuit which includes said control winding. me said spark intervals are de-termined by photoelectric engine-timed means compriqing a light-emitting diode and a phototransistor. The said elec-tronlc switch means has a control circuit therefor which includes said phototranslstor. In combination with the foregoing system, this invention concerns the improvement which comprises first circuit means for connecting said phototransistor in a common collector con~iguration rela- - -tive to said control circuit, and second circuit means for connecting the emitter of said phototransistor to the emit-ter of an input transistor of said control unit. me said second circuit means includes a radio-frequency ~ er for blocking radio-frequency signals generated by said spark energy. The improvement also comprises third circuit means including a temperature-sensitive resistor for energizing said light-emitting diode, in order to compensate for changes in ambient temperature at the engine-timed means.
It also comprises fourth circuit means including saidlight-emitting diode having a predetermined forward voltage drop, and connecting said diode to the base of said input `~-

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'~ 1038q44 transistor, all whereby said ignition system has improved response to the engine-timed spark-control means in giving temperature compensation and radio-frequency signal rejection.

BRIEF DESCRIPTION OF THE DR~WINGS

The foregoing and other objects and benefits of the invention will be more fully set forth below in Z connection with the best mode contemplated by the in-ventor of carrying out the invention, and in connection with which there are illustrations provided in the drawings, wherein:
Figure 1 is a schematic circuit diagram illustrat-ing a complete system according to one modification of the invention;
Figure 2 is another circuit diagram illustrating a different modification of the control-circuit portion of a system like that illustrated in Figure l; and Figure 3 is yet another circuit diagram illustrat-ing only the engine-timed photoelectric portion of a third modification of the system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 1, it will be noted that the complete ignition system illustrated includes the basic elements like those shown in one or more of the above-noted copending applications. It will be suf-ficient to note that the system illustrated in Figure 1 includes an oscillator 11 that is enclosed within a dashed-line box 12, and which employs an output trans-former 13 with a control winding 14 thereon.

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`` 1038444 Similarly, the system includes a conventional ignition switch 17 which is shown in a dashed-line box 18 that includes a battery 19 therein. It will be under-stood that the physical locations of the battery and ignition switch are usually quite widely separated on an automobile. The battery 19 supplies power to the oscillator 11 via a permanent circuit connection 22. Also, when the ignition switch 17 is turned on, the battery 19 supplies DC power (via a circuit connection 23) to parallel circuits. One includes a connection 24 for energizing the control winding 14, and the other includes a connection 25 that is for energizing a relay 26 that is shown enclosed in a dashed-line box carrying that re_ ference number.
The control winding 14 is in series with an electronic switch, i.e., a transistor 29, which deter-mines whether the winding 14 is AC-short-circuited or not. At the same time, when the transistor 29 is con-ducting, the circuits include application of a DC bias for creating a core set on the transformer 13. The transistor 29 is controlled for determining whether it is conducting or nonconducting by means of a control circuit 32 that includes all of the circuit elements between the base connection of transistor 29 and the output circuit of a control-circuit-input transistor 35.
The input transistor 35 is controlled by a photoelectric engine-timed unit 38 that includes a light-emitting diode 39 and a phototransistor 40. It .. . ~. . ... .. . , ~: :

will be appreciated that in the system as illustrated in Figure l, the unit 38 will be physically located on the distributor unit of the engine, and there will -~
be included a shutter (not shown) which is driven by a timing shaft (not shown) from the engine so as to determine the engine-timed intervals for producing spark energy.
It will be observed that the phototransistor 40 is connected in a common collector configuration relative to the control circuit 32. Thus, while a "common collector" circuit designation often connotes a grounded collector, in this instance the common cir- :~
cuit to which the collector of phototransistor 40 is connected, is a positive DC circuit that is a common circuit of the control circuit 32. On the other hand, the emitter of phototransistor 40 is connected via a circuit connection 43 to the base of the transistor 35.
Transistor 35 has a DC bias applied to it such that it is just below the cut-off point in the absence of any signal from the emitter of phototransistor 40. Such bias is obtained by having a pair of resistors 46 and 47 connected in series from the common DC supply (DC
potential on a circuit connection 50) to ground. The midpoint between resistors 46 and 47 (which, together, : act as a potentiometer1 is connected to the base of the transistor 35. In this manner, the response time of tran-sistor 40 to the receipt of radiant energy from the light-emitting diode 39, is greatly reduced since only a small voltage rise is needed to cause transistor 35 to conduct.

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An ignition system according to this invention may be made operative over a full range of te~perature conditions that might be encountered with internal combus-tion engines, by including in the circuit for energizing the light-emitting diode 39 a temperature~sen~itive resis-tor 53. mis is because of the characteristics of light-emitting diodes and phototransistors. mus, the radlant energy emitted by a light-emitting diode is a ~unctlon of the current passed through the ~unction. If too much cur-rent is passed through the ~unction, it will overheat, andthe diode will be destroyed. The safe current level of the diode will be determined by the ability of the ~unction to dissipate heat. merefore, the safe current at high ; ambient temperatures is much lower than when the ambient temperature is low. Also, the light-emittlng efficiency of the light-emitting dlode lncreases as the junction tem-perature decreases, so that at low ambient temperatures more radlation will be emitted for the same ~unction cur-rent than when the ambient temperature is increased. In 20 addition, a phototransistor becomes less sensitive as the ~ ~ -temperature is decreased, and more sensitive as the tem-perature rises, which tends to partially compensate for the opposite changing amount of radiation from the light-emit-ting diode. However, in practice it is found that the total effect is not exactly offsetting, and at low ~mbient temperatures it is necessary to increase the light-emitting diode's output to compensate sufficiently for the lack of sensitivity of the phototransl~tor. Similarly, at high ambient temperatures, the phototransistor increases in gain faster than the light-emltting diode loses efficiency. Con-sequently, the ~unction current of the light-emltting diode :

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may be reduced at higher temperature while still maintain- -ing the total or combined sensitivity. At the same time, the reduced current tends to keep the junction cooler which contributes to maintaining the emitting efficienoy high.
It has been found that the system using the tem-perature-sensitive resistor 53 will operate satisfactorily within an ambient temperature range of ~rom about -45 F.
to about ~237.5 F.
It has been discovered that in the type of con-tinuous-wave high-frequency ignition system according to this invention, largely because the oscillator is square-wave in nature, a large amount of radio-frequency energy is generated at the park gaps during each of the sparking intervals. Such radio-frequency energies are radiated and tend to be applied at various points in the whole circuit.
Consequently, there is a tendency to introduce undesired signals after each starting of the oscillator, and these tend to cause reenergization, or continuation of the 08-cillation beyond the normal stopping thereof. mis tends to cause untimed spark ignitions in additon to overload-ing, and thus tending to burn out various elements of the system, e.g., the electronic switch (transistor) 29.
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In order to avoid the foregoing undesired condi-tions, there is included in the circuits with the input transistor 35 a radio-~requency choke coil 56 located be-tween the emitter of transistor 35 and ground. mis pre-vents radio-frequency signals from reaching the base of a transistor 64. Also, there is a capacitor 68 connected ~rom the collector o~ transistor 35 to ground which shunts radio-frequency signals ard, in addition, there is another 1038~44 ., capacitor 67 connected from the collector of input tran- -sistor 35 to the base thereof, which causes a substantial amount of negative feedback to the radio-frequency signals.
In addition to the radio-frequencv blocking effects, there is a coil 57 connected in the output circuit of the transistor 35, which is designed to improve the response of the control system to the desired signal fre-; quency, e.g., to be resonant at about 20,000 Hertz. There is a resistor 60 connected across the coil 57 so as to critically damp the resonant effects in order to prevent ` any undesired ringing.
Figure 2 illustrates a modification of the con- ;
trol-unit portion of the system, and for the purpose of ade~uate orientation, the same basic control circuit 32 as is illustrated in Figure 1, is shown again in Figure -2. Thus, the transistor 29 is illustrated at the out-put end of the control circuit 32 and, of course, it con~
trols the starting and stopping of the oscillator 11 (see Figure 1) by means of controlling AC-short-circuit conditions for the control winding 14 (see Figure 1) in the same manner as indicated above in connection with Figure 1. Also, the relay 26 and circuit connections 25 and 23 which were indicated in Figure 1, are shown again in Figure 2.
In Figure 2, the fast-reaction circuit related to the phototransistor 40 (see Figure 1) takes a modified form over that illustrated in Figure 1. Thus, in Figure 2, the emitter connection 43 (see Fig. 1) from transistor 40 (Fig.
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1) ls applied to a terminal 71 that has a circuit connec-tion 72 leading therefrom to one end of a radio-frequency choke coil 73. The other end of the coil 73 leads direct-ly to the emitter of a PNP transistor 76. The base of transistor 76 is connected to the midpoint between a re-sistor 77 and a diode 78, which diode is one having a pre-determined forward voltage drop in order to set the voltage on the base of transistor 76 at a desired level. me out-put of transistor 76 goes to the control circuit 32 and, as illustrated, this ls via a circuit connection 81 that goes to the base of another transistor 82.
It has been discovered that by making use of the lllustrated circuit, including the PNP transistor 76, a ; greatly reduced response time from the phototransistor 40 (FIG. 1) may be had. Because of the characteristics of translstors generally, and lncluding phototransistor~, there has been a difficulty encountered in high-frequency applications by reason of the load-dependent frequency re-sp~nse in regard to the phototransistors. Since a photo-transistor is a current ~ource, it is desirable to use a ` large-load resistance to develop maximum output voltage or to have high sensitivity. However, large-load resis-`
tances limit the frequency range which would mean longer response time for an ignition system. Thus, in the past, it has been considered necessary to compromise, i.e., trade voltage for speed, or Yice versa. ~ut, by applying the illustrated circuit to a control ~ystem according to this invention, a deslred reduction in response time ls created.
me coil 73 ls part of a radlo-frequency filter, which includes a parallel re~istor ô5, along with a pair of capacitors 86 and 87, which are connected to ground and to - lM~L~4 the ends of the coil 73 as well as to the ends of resistor 85.
FIG. 3 illustrates a modi~ication o~ the photo-transistor circuit portion o~ the control circuit. It is applicable particularly to a system like tha~ shown in FIG.
2. This arrangement permits elimination o~ a resistor, along with making use of the light-emitting diode for two purposes so that the diode 78 may also be elimin~ted.
mus, in FIG. 3, there is a llght-emitting diode 90 that is connected for energization from a circuit con-nection 91 which corresponds to circult connection of FIGS.
1 and 2. Also, there is a temperature-sensitive reslstor ~: :
94 that corresponds to resistor 53 o~ FIG. l, and the radia- :
tion of light from diode 90 is directed toward a phototran-sistor 95 in the same manner as was described in connectlon with translstor 40 o~ FIG. l.
In this instance, phototransistor 95 has its emit-ter connected directly to the emitter of a PNP transi~tor : 98 that corresponds with transistor 76 of FIG. 2. In the 20 FIG. 3 modlfication, the base of transistor 98 is connected -via a connector 99 to a ~unction between resistor 94 and .
diode 90. me collector of transistor 98 goes directly to the base of another transistor 102 which corresponds to the transistor 82 of FIG. 2.
- By making use of a circuit according to FIG. 3, the resistor 77 (FIG. 2) as well as the diode 78 (FIG. 2) may both be elimlnated slnce resistor 94 and the light~
emlttlng diode 90 take thair place. However, it should be noted that wh~re the circuit as indicated in FIG. 3 i8 em-ployed, the elements shown must be physically located on or at the dlstrlbutor (not shown) o~ the engine, in the manner :. . . . :, . .

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indicated in connection with FIG. 1. In other words, when the FIG. 3 modificatlon is employed, there is a dlstributor- ~
located unlt 105 which i8 indicated by the dashed lines -Y~ around the circuit elements illustrated in FIG. 3.
While the invention has been described above in 3 considerable detail and in accordance with the applicable statutes, this is not to be taken as ln any way limiting the lnvention, but merely as being descriptive thereof.
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Claims (14)

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

1. In combination with an ignition system for an internal combustion engine, wherein said system employs controlled-duration continuous-wave high-frequency spark energy, said spark energy being generated by an oscilla-tor having an output transformer and having a control wind-ing thereon for starting and stopping oscillation of said oscillator at the beginning and end of each spark interval, electronic switch means connected in series with said control winding for breaking and making a loading cir-cuit which includes said control winding, said spark intervals being determined by photo-electric engine-timed means including a phototransistor, said electronic switch means having a control circuit therefor including said photoelectric engine-timed means, the improvement comprising circuit means for connecting said phototransistor in a common-collector configuration relative to said control circuit in order to minimize the response time of said phototransistor.

2. The invention according to claim 1, further including second means incorporated with said control circuit for blocking radio-frequency signals generated by said spark energy.

3. The invention according to claim 1, where-in said improvement means also comprises means for connecting the emitter of said photo-transistor to a prebiased base of an input transistor of said control circuit.

4. The invention according to claim 1, where-in said improvement circuit means also comprises means for connecting the emitter of said photo-transistor to the emitter of an input transistor of said control circuit.

5. The invention according to claim 4, where-in said means for connecting said emitters comprises a radio-frequency filter for blocking radio-frequency signals generated by said spark energy.

6. The invention according to claim 3, where-in said improvement circuit means further comprises reactance means in the output circuit of said input transistor for by-passing and blocking radio-fre-quency signals generated by said spark energy.

7. The invention according to claim 4, where-in said improvement circuit means also comprises diode means in the base circuit of said input transistor, said diode means having a predetermined forward voltage drop in order to provide a desired voltage level to said input transistor.

8. The invention according to claim 1, where-in said photoelectric engine-timed means comprises a light-emitting diode.

9. The invention according to claim 8, where-in said improvement circuit means also comprises means for connecting the emitter of said photo-transistor to the emitter of an input transistor of said control circuit.

10. The invention according to claim 9, wherein said means for connecting said emitters comprises a radio-frequency filter for blocking radio-frequency sig-nals generated by said spark energy.

11. The invention according to claim 9, where-in said improvement circuit means also comprises diode means in the base circuit of said input transistor, said diode means having a predetermined forward voltage drop in order to provide a desired voltage level to said input transistor.

12. The invention according to claim 11, where-in said means for connecting said emitters com-prises radio-frequency filter for blocking radio-frequency signals generated by said spark energy.

13. The invention according to claim 11, where-in said diode means comprises said light-emitting diode.

14. In combination with an ignition system for an internals combustion engine, wherein said system em-ploys controlled-duration, continuous square wave, high-frequency spark energy, said spark energy being generated by a square-wave oscillator having an output transformer, and having a control winding thereon for starting and stopping oscillation of said oscillator at the beginning and end of each spark interval, electronic switch means connected in series with said control winding for breaking and making a load-ing circuit which includes said control winding, said spark intervals being determined by photo-electric engine-timed means comprising a light-emitting diode and a phototransistor, said electronic switch means having a control circuit therefor including said phototransistor, the improvement comprising first circuit means for connecting said phototransistor in a common-collector configuration relative to said control circuit, second circuit means for connecting the emitter of said phototransistor to the emitter of an input transis-tor of said control circuit, said second circuit means including a radio-frequency filter for blocking radio-frequency signals generated by said spark energy, third circuit means including a temperature-sensitive resistor for energizing said light-emitting diode in order to compensate for change in ambient tem-perature at said engine-timed means, fourth circuit means including said light-emitting diode having a predetermined forward voltage drop and connecting said diode to the base of said in-put transistor, all whereby said ignition system has improved response to the engine-timed spark-control means in-cluding temperature compensation and radio-frequency signal rejection.