US 3910246 A
An ignition system which employs an inverter to develop a continuous-wave high-frequency spark signal from a DC supply. The inverter employs a single transformer with a high-voltage output winding and a pair of transistors coupled to an input winding plus a feedback winding. There is a saturable-core inductor also coupled to the transistors for causing a frequency shift in the inverter AC signals under load conditions in the spark-signal output.
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Description (OCR text may contain errors)
U.S.Cl.v 123/148 E; 331/113.1;315/209T Int. Cl. F021 l/OO Field of Search 123/148 E, 148 CD;
References Cited UNITED STATES PATENTS 5/1962 Ruckelshaus 123/148 E 7/1966 Lister 10/1968 Aiken 2/ l 969- Hufton 6/1969 Weiss 7/1973 Canup 123/148 E United States Patent 1 [111 3,910,246
Canup [4 Oct. 7, 1975 CONTINUOUS-WAVE HIGH-FREQUENCY OTHER PUBLICATIONS Transistor Inverters and Converters, T. Roddam, London lliffe Books, Ltd., Princeton, N.J., 1963, pp. 139145.
Primary ExamirierCharles J. Myhre Assistant ExaminerRonald B. Cox
Attorney, Agent, or FirmThomas H. Whaley; Carl G. Ries 57 ABSTRACT An ignition system which employs an inverter to develop a continuous-wave high-frequency spark signal from a DC supply. The inverter employs a single transformer with a high-voltage output winding and a pair of transistors coupled to an input winding plus a feedback winding. There is a saturable-core inductor also coupled to the transistors for causing a frequency shift in the inverter AC signals under load conditions in the spark-signal output.
7 Claims, 1 Drawing Figure US. Patent Oct. 7,1975
CONTINUOUS-WAVE HIGH-FREQUENCY AC IGNITION SYSTEM CROSS-REFERENCES TO RELATED APPLICATIONS This invention concerns subject matter that relates to previous applications by the same applicant, as follows:
Ser. No. 263,803 An Ignition-Control System for Internal Combustion Engines, now US. Pat. No. 3,861,369 filed June 19, 1972 Ser. No. 333,856 Improved High-Frequency Continuous-Wave Ignition System, now US. Pat. No. 3,836,503 filed Feb. 20, 1973 Ser. No. 337,509 Ignition System Utilizing Saturable-Core Square Wave Oscillator Circuit, now US. Pat. No. 3,847,129 filed Mar. 2, 1973 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns ignition systems for internal combustion engines in general, and more specifically relates to such a system that employs high-frequency continuous-wave AC signals to produce a controlled spark duration for each ignition. It particularly employs only a single transformer. And, it includes means for causing a frequency shift as the output circuit of the oscillator changes from no-load to load conditions.
2. Description of the Prior Art Heretofore, there have been a considerable number of proposed arrangements that purportedly would employ AC spark signals for internal combustion engines, and the like. However, in such prior arrangements, there have been difficulties in the practical applications. An important aspect of such difficulties related to the ability of such systems to start the oscillation at the instant when a spark signal is called for. While the applicant has earlier overcome that particular difficulty in some of the inventions described in copending previous applications, they did not provide for a beneficial improvement which was only recognized in connection with a two-transformer type of oscillator or inverter. Such beneficial improvement relates to the ability to increase the initial voltage amplitude along with substantial reduction thereof upon striking a spark. This invention teaches how that concept may be applied to a single-transformer type of inverter.
Consequently, this invention is particularly concerned with a single-transformer, continuous-wave, high-frequency AC ignition system which includes an inverter with means for shifting the oscillation frequency from no-load to load conditions as the spark load appears in the output circuit of the inverterv SUMMARY OF THE INVENTION Briefly, this invention concerns an ignition system for an internal combustion engine which system comprises an inverter including a single transformer having a secondary winding for supplying a continuous-wave high frequency spark-signal output, only during controlled sparking intervals. It also comprises a primary winding with at least one transistor connected in circuit therewith, and a feedback winding connected to said transistor for providing an oscillator having a predetermined load frequency during said sparking intervals. The said load frequency is substantially different from a harmonic frequency of the fundamental resonant frequency of said secondary winding circuit. Also, the inhaving a high-voltage AC spark-signal output winding,
and an input winding on said transformer. It also comprises a feedback winding on said transformer, a control winding on said transformer, and a pair of transistors. It also comprises first circuit means for connecting said transistors to said input and feedback windings to form a square-wave high-frequency oscillator, and second circuit means for connecting a DC source of power to said oscillator. In addition, it comprises a saturable core inductor, and third circuit means for connecting said inductor into said oscillator whereby the no-load frequency equals a harmonic of the fundamental resonant frequency of said output-winding circuit. The said load frequency is substantially different from said harmonic frequency.
DESCRIPTION OF THE DRAWING The foregoing and other objects and benefits of the invention will be more fully set forth below in connec tion with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrations provided in the drawing, wherein:
The FIGURE of drawing illustrates a schematic circuit diagram of an ignition system according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT As indicated above, it should be understood that this invention is similar in basic principles to that shown and described in my above-noted earlier application Ser. No. 337,509, filed Mar. 2, 1973. However, in that case, the inverter circuit employed two transformers, and the parameters of both were adjusted for setting the desired frequency shift conditions. In this invention, the ability to obtain similar results was not subject to mere application of the teachings of the prior art. Thus, while a single-transformer inverter system had the advantages of reduction in cost and a compact structure, the ability to strike a spark by extra high initial voltage without adversely affecting power requirements was lacking.
Referring to the FIGURE of drawings, it will be observed that the schematic circuit diagram illustrates an ignition system. It includes a single transformer 11 that has a high-voltage secondary winding 12 which is connected to a ground or common circuit at one end. The other end is connected to a spark-signal circuit which may be for an internal combustion engine (not shown). This is indicated by the caption HIGH VOLTAGE TO DISTRIBUTOR CAP adjacent to a circuit connection 13.
The transformer 11 also has a center-tapped primary winding 16 and a separate feedback winding 17 as well as a control winding 18 thereon.
There is a source of DC power which may be a bat tery 23, as indicated. This, of course, may be a standard automotive battery, e.g., one providing a 12-volt supply, or it may be a 24-volt type battery. Battery 23 is connected into the circuit with one terminal grounded, as indicated at reference no. 24. The other terminal is connected via circuit connections 27 and 28 to a center tap 29 on the transformer primary winding 16. Also, there is a capacitor 30 that is connected between the circuit connection 28 and ground. It is important that the capacitor 30 be physically located close to the center tap 29. Its principal purpose is to nullify the effects of the impedance of the conductor 28 and the internal impedance of the battery 23.
Connected to the ends of primary winding 16 are the collector electrodes of a pair of transistors 33 and 34. The emitter electrodes of these transistors are each connected to ground, as indicated by reference num bers 35 and 36, respectively. The base electrodes of the transistors 33 and 34 are connected to the ends of the feedback winding 17, via circuit connections 39 and 40, respectively. Included in the foregoing base drive circuit from feedback winding 17, there is a resistor 41 for partially determining the oscillator frequency. Also, it may be noted that connected between each of the base electrodes of transistors 33 and 34 and ground, there are diodes 43 and 44, respectively, which act to protect each transistor against harmful reverse voltage that may be applied between its base electrode and ground. As indicated above, the capacitor 30 acts to supply initial energy to the transistors when they conduct, and this compensates for the voltage drop that develops due to the high current which they draw. Consequently, an output voltage in the secondary winding 12 is of greater magnitude than would otherwise be the case.
In order to control the starting and stopping of oscillation of the foregoing inverter circuit, the control winding 18 is included on the transformer l 1. This type of inverter (oscillator), as applied to ignition systems, has been described in my above-noted application Ser. No. 333,856, filed Feb. 20, 1973. It has a DC bias current applied to the control winding 18 during the nonoscillating periods. Simultaneously, there is a low impedance path connected across the winding 18.
The DC bias current is applied via an ignition switch 46 that has a pair of stationary terminals 47 which are A both connected directly to the positive terminal of battery 23 via a circuit connection 48. When the movable switch arm of switch 46 is placed into electrical contact with either of the terminals 47 (for start or run conditions), the battery voltage from battery 23 is connected over the circuit connection 48 and on via a connection 49 to a resistor 50 and a diode 51 to a circuit connection point 52.
From the circuit point 52 the circuit carrying DC bat tery potential continues via illustrated circuit connections 55 and 56 to one end of the control winding 18. The other end of winding 18 is connected via circuit connections 59 and 60 to one diagonal point 58 of a diode bridge 61. An adjacent diagonal 62 is connected via a circuit connection 63 to the collector electrode of a transistor 64 which acts as an electronic switch. The emitter electrode of transistor 64 is connected to ground, as indicated by a reference number 67.
It will be noted that this completes a circuit from the battery 23 for application of a DC bias current through the control winding 18 whenever the transistor 64 is conducting. The latter condition is controlled by enginetimed controls, as indicated by the caption adjacent to the base circuit input to the transistor 64.
Simultaneously with the DC bias current fiow through control winding 18, i.e., when the transistor 64 is conducting, there is a low-impedance AC circuit across the winding that permits induced AC signals (from the oscillator) to load down the oscillator so that it will not oscillate. These nonoscillating conditions are created in between spark-signal intervals so that the oscillator remains shut down, and no high-voltage, sparkproducing signal will be developed until the desired time for each engine-controlled instant that is related to the spark interval for each cylinder of an internal combustion engine.
I As indicated above, this inverter circuit acts as a square-wave oscillator which generates high-voltage continuous-wave spark signals in the secondary winding 12 at desired instants for controlled intervals of time. The intervals are controlled by the control winding 18 which stops the oscillations when a lowimpedance AC circuit is applied across the winding. Such low-impedance AC circuit across control winding 18 includes a diode bridge 61 and also a Zener diode that is connected between the circuit point 52 and a diagonal point 71 on the bridge 61.
In this manner, whenever the transistor 64 is conducting, it provides a low-impedance AC path across the winding 18 which may be traced as follows. Beginning at the lower end (as viewed in the drawing) of winding 18 and going via connections 59 and 60 to the bridge 61, current flowing in such downward direction will have a low-impedance path via the upper left-hand diode of the bridge 61 and the circuit connection 63 to and through the transistor 64 and the ground connection 67. A return circuit continues via two parallel paths. The primary path goes via a ground connection 74, a diagonal point 75, diode 78, diagonal point 71, a conductor 79, Zener diode 70, and then via connections 55 and 56 to the other side of the winding 18. The other return circuit path goes from the ground connection 24 to the battery 23 and then via the circuit connections 27 and 48 to the switch 46 (now closed). Then it continues via the connection 49, the resistor 50, the diode 51, the connections 55 and 56 to the other side of the winding 18.
On the reverse half-cycles of induced voltage in winding 18, the low-impedance path for return current flow in the opposite direction may be traced via connections 56 and 55 to the circuit point 52. The path then continues through the Zener diode 70 (breakdown voltage exceeded) to the diagonal point 71 on the bridge 61 and then through the lower left-hand diode of the bridge 61 to the diagonal point 62. From point 62 it continues over the connection 63 to the transistor 64 and, thence, via the ground connection 67 back through another ground connection 74 to an opposite diagonal point 75 on the bridge 61. From that point it may be traced over a resistor 76 and a diode 77 to the diagonal point 58 and on via the connection 60 and the connection 59 to the other end of winding 18.
It may be noted in passing that there are additional capacitors, e.g., capacitors 80, 81 and 82, provided for radio-frequency by-pass. This is important since the oscillator is a square-wave type which consequently generates substantial amounts of radio-frequency energies.
The details of the operation of a system like that described so far, have been fully set forth in my earlier related application Ser. No. 333,856, filed Feb. 20, 1973 That application explains the action of the control winding in stopping oscillation while setting the core of the transformer so that when the DC bias is removed the oscillator will always start positively and instantaneously. Also, it may be noted that the engine-timed control signals which are applied to the base electrode of the transistor 64, might be derived from various sources. For example, see my copending application Ser. No. 263,803, filed June 19, 1972. This invention is particularly concerned with improved results that are obtained from the use of a saturable-core inductor 85. This inductor 85 is connected into the oscillator circuit and across the feedback winding 17. It is also connected between the base electrodes of transistors 33 and 34.
By determining the particular parameters related to the structure of the core and winding for inductor 85, the frequency of the oscillator may be controlled since the inductor can be made to saturate at a desired frequency. In this manner, the open circuit oscillating frequency of the system may be set to match a harmonic frequency of the fundamental resonant frequency that exists in the output circuit to which winding 12 is connected. At the same time the power rating of the transistors 33 and 34 may be chosen along with the primary-to-secondary turns ratio of the transformer and the primary inductance under load, so that adequate spark-plug current can be supplied.
In the foregoing manner, the no-load or striking voltage at the output of winding 12 is increased a substantial amount by the resonant effect, in the manner that has been explained in my above-mentioned application Ser. No. 337,509, filed Mar. 2, 1973. However, when that concept is applied to a single-transformer system, the ability to obtain adequate power in the spark signal after a spark is struck, is impaired unless a saturable core inductor according to this invention is employed. This is because the adjustment of the primary inductance of the transformer would raise the impedance and, consequently, reduce the power that could be delivered. But such adverse adjustment is not necessary when a saturable-core inductance is employed.
While the invention has been described above in considerable detail and in accordance with the applicable statutes, this is not in any way to be taken as limiting the invention, but merely as being descriptive thereof.
1. Ignition system for an internal combustion engine, comprising an inverter including a single transformer having a secondary winding for supplying a continuouswave, high-frequency spark-signal output only during controlled sparking intervals, a primary wind ing with at least one transistor connected in circuit therewith, and a feedback winding connected to said transistor for providing an oscillator having a predetermined load frequency during said spark intervals,
said load frequency being substantially different from a harmonic frequency of the fundamental resonant frequency of said secondary winding circuit, and
saturable-core inductor means connected in circuit with said feedback winding for determining the noload frequency to be substantially equal to said harmonic frequency.
2. Ignition system according to claim 1, further comprising an oscillator-control winding on said transformer,
means controlled by said engine for connecting a loading circuit to said control winding and for applying a DC bias thereto between said sparking intervals whereby removal of said DC bias and said control winding load causes instantaneous starting of said oscillation.
3. Ignition system according to claim 2, wherein said primary winding is center-tapped with two transistors connected in circuit therewith, and said feedback winding is also connected to said two transistors. 4. Ignition system according to claim 3, wherein each of said two transistors has the collectoreniitter circuit across half of said primary winding, and said feedback winding is connected to the bases of both said transistors.
5. Ignition system according to claim 4, wherein said saturable-core inductor means is connected across said bases.
6. Ignition system according to claim 5, wherein said inverter also includes circuit means for connecting a DC source between said primary winding center tap and said collector-emitter circuits at a point between said transistors.
7. In combination, a continuous-wave highfrequency ignition system, wherein said system comprises a single transformer having a high voltage AC spark signal output winding,
an input winding on said transformer,
a feedback winding on said transformer,
a control winding on said transformer,
21 pair of transistors,
first circuit means for connecting said transistors to said input and feedback windings to form a squarewave high-frequency oscillator,
second circuit means for connecting a DC source of power to said oscillator.
a saturable core inductor,
third circuit means for connecting said inductor into said oscillator whereby the no-load frequency equals a harmonic of the fundamental resonant fre quency of said output winding circuit,
said load frequency being substantially different from said harmonic frequency.