Ignition amplifier circuit
United States Patent [191 Williams IGNITION AMPLIFIER CIRCUIT [75] Inventor: Edward L. Williams, Fort Wayne,  
 Ind.  
 [73] Assignee: International Harvester Company,  
 Chicago, Ill.  
 [22] Filed: Feb. 9, 1973 [21] Appl. No.: 330,917  
 [52] US. Cl..... 123/148 E; 123/148 OC; 315/209 T [51] Int. Cl. F02p 1/00 [58] Field of Search 123/148 E, 148 0CD; 315/209 T [56] References Cited UNITED STATES PATENTS 3.280.809 10/1966 lssler 123/148 E 3,595,212 7/1971 Barnes 123/148 E 3.635.202 l/1972 lssler 123/148 E Primary Examiner-Charles .I. Myhre Assistant ExaminerRonald B. Cox Attorney Agent. or FirmFrederick .1. Krubel; Floyd B. l-larman Apr. 8, 1975 [57] ABSTRACT Ignition amplifier circuit wherein a transistor switch is closed to build up current through a primary winding of an ignition coil and then opened to cause an increase in the voltage of both the primary and secondary windings. A capacitor is charged during closure of the transistor switch and, in response to the increase in voltage of the primary Winding, a SCR is triggered to discharge the capacitor through the primary winding, to generate a short duration high voltage pulse in the secondary winding having a sharp rise time. Thereafter, inductive discharge of the coil continues to produce a secondary voltage of substantial magnitude and a long burn time. The capacitor is charged during closure of the transistor switch through a simple diode connection to the secondary winding.  
 9 Claims, 2 Drawing Figures IGNITION AMPLIFIER CIRCUIT CROSS REFERENCE TO RELATED APPLICATION This application is related to my copending application, Ser. No. 330915 now US. Pat. No. 3,857,376, filed and entitled REGULATED IGNITION AMPLI- FIER CIRCUIT, filed on Feb. 9, 1973.  
  This invention relates to an ignition amplifier circuit and more particularly to a comparatively simple and highly reliable circuit which develops an ignition pulse having a sharp rise time to fire fouled or wetted spark plugs and having a long duration for minimum exhaust emissions.  
 BACKGROUND OF THE PRIOR ART Prior art ignition systems have generally been either of a current interruption type in which the current through a primary winding is interrupted to collapse the magnetic field thereof and to generate a high voltage in a secondary winding, or of a capacitor discharge type in which a capacitor is discharged through the primary winding. Such systems have not been entirely satisfactory in that it has been necessary to compromise between obtaining characteristics necessary for the firing of fouled or wetted plugs and obtaining characteris ties for minimum exhaust emissions, or to sacrifice one characteristic to obtain the other.  
  The Issler Pat. No. 3,280,809 proposes circuits using both current interruption and the discharge ofa capacitor in an attempt to improve performance. As disclosed, the Issler circuits are for the purpose of releasing stored magnetic energy either at substantially the same moment as the release of stored electric energy or after the release of stored electric energy, the theory being that the release of stored electric energy will produce a steep voltage rise while the release of the stored magnetic energy will produce a substantial number of secondary discharges. Such circuits are relatively complex and expensive, requiring either an ignition coil having a pair of separate primary windings, a pair of ignition coils or a tapped primary winding ignition coil and also requiring separate switches or circuits for controlling the release of stored electric and magnetic energy in the time relation as set forth.  
  Other circuits have been proposed in the prior art for producing a plurality of sparks during each power stroke of an engine, but such have not reliably produced optimum results and have generally been quite complex.  
 BRIEF SUMMARY OF THE INVENTION This invention was evolved with the general object of overcoming the disadvantages of prior art circuits and of providing a circuit which will reliably fire wetted or fouled plugs and also reduce exhaust emissions to a minimum.  
  Another object of the invention is to provide a highly effective and reliable ignition circuit which is relatively inexpensive, using a minimum number of component parts.  
  According to the invention, a circuit is provided in which a capacitor is charged while current is built up through a primary winding of an ignition coil, the current being abruptly cut off to generate an increasing voltage in the primary winding and a corresponding increasing voltage in the secondary winding, the capacitor being thereafter discharged through the primary winding to generate a short duration high voltage pulse in the secondary winding. Stored electric energy is thus released after the start of the release of stored magnetic energy rather than at the same moment or before as in the aforementioned Issler patent, but the release of the stored magnetic energy continues after the release of stored electric energy to provide a long burn time.  
  This arrangement has important advantages in that the short duration pulse is reliably generated with a fast rise time, insuring firing of fouled or wetted plugs. At the same time, the magnetic energy is so released as to produce a sustained high voltage and a long burn time to obtain minimum exhaust emissions.  
  The arrangement has the further advantage in that opposing actions-of the current interrupting and capacitor discharge circuits are readily avoided using a simple and straight forward circuit design. In particular and in accordance with a specific feature, the capacitor discharge circuit includes a transistor device, preferably a SCR (silicon controlled rectifier), which conducts in only one direction. The polarity of charge of the capacitor and the direction of conduction through the transistor device are such that the current from the capacitor discharge can only produce a change in magnetic flux in the same direction as that produced by the interruption of the current. With this arrangement and with interruption of current in the primary winding taking place first, the capacitor discharge portion of the circuit cannot oppose the effect of the current interruption portion of the circuit. The capacitor discharge portion becomes effective only after the start of the voltage developed from interruption of current but the voltage developed from interruption of current continues after the end of the capacitor discharge portion.  
  Another advantage is that standard breaker points or any conventional type of pulse generator may be used for controlling current interruption. Preferably and in accordance with a specific feature, a transistor is used for current interruption.  
  A further advantage of the arrangement is that it permits use of a relatively simple and reliable circuit for controlling the capacitor discharge in response to interruption of current. This circuit forms a specific feature of the invention and includes means for responding to the increasing voltage developed across the primary winding in response to the initial portion of the interruption of current therethrough to develop a triggering signal applied to a transistor device of the capacitor discharge circuit, the transistor device being preferably a silicon controlled rectifier.  
  The capacitor may be charged from any suitable source and my aforementioned related application discloses a particular source which can be used advantageously for thispurpose. In the alternative and in accordance with another important feature of the invention, a simple and inexpensive but highly reliable circuit may be provided operative to charge the capacitor from the voltage generated in the secondary winding in response to the build-up of current through the primary winding. This circuit includes a diode and, preferably, a current-limiting resistor, the diode being so poled as to be conductive to charge the capacitor during the build-up of current through the primary winding and non-conductive during generation of the ignition voltage in the secondary winding.  
  This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an ignition amplifier circuit according to the invention, shown connected to an ignition coil and points of an ignition system; and  
  FIG. 2 shows a voltage wave form at the output of the circuit of FIG. 1, for explaining its operation.  
 DESCRIPTION OF A PREFERRED EMBODIMENT Reference numeral generally designates an ignition amplifier circuit constructed in accordance with the principles of this invention. The circuit 10 is shown connected to terminals 11, 12 and 13 of a conventional ignition coil 14 having a primary winding 15 connected between terminals 11 and 12 and having a secondary winding 16 connected between terminals 11 and 13. Circuit 10 is also connected to a ground terminal 18 which is connected to the negative terminal of a battery 19 having a positive terminal connected through a switch 20 to the terminal 11. In the illustrated arrangement, circuit 10 is connected to a breaker point contact 21, a second contact 22 being connected to terminal 11 and being operated by a cam 23 which is ganged to a rotor arm 24 of a conventional distributor 25. Arm 24 is connected to the terminal 13 of the ignition coil 14 and sequentially engages contacts connected to spark plugs, the connection of one contact 26 to a spark plug 27 being shown.  
  In operation, with the switch 20 closed and the engine rotating, the contacts 21 and 22 are closed for a substantial length of time prior to the beginning of each power stroke of the engine and are opened at a time approximately coincident with the beginning of each power stroke at which time a high voltage pulse is developed at the ignition coil terminal 13 and is applied through the distributor to the proper spark plug. With the circuit 10, a high voltage pulse is developed which has a very sharp rise time and which at the same time has a long duration, effective to fire wetted plugs orplugs fouled by carbon deposits and also effective to insure complete burning of the fuel-air mixture and to minimize exhaust emissions.  
  The circuit 10 comprises a transistor 30 having an emitter connected to the ground terminal 18, a collector connected to the ignition coil terminal 12 and a base connected through a resistor 31 to the contact 21, transistor 30 being conductive when the contacts 21 and 22 are closed to build up current through the primary coil 15 and being abruptly rendered nonconductive when the contacts 21 and 22 are opened. The magnetic field in the coil 14 then collapses producing an increasing voltage in the primary winding 15 and a corresponding increasing voltage in the secondary winding 16.  
  During the closure of the contacts 21 and 22 and the build-up of current through the primary winding 15, a capacitor 32 is charged with a polarity as indicated. In response to the increasing voltage in the primary winding after the transistor 30 is cut off, the capacitor 32 is discharged through the primary winding 15 by means of a silicon controlled rectifier 33 having an anode connected through capacitor 32 to the terminal 11 and having a cathode connected through a diode 34 to terminal 12, the primary winding 15 being thus connected in series with capacitor 32, rectifier 33 and diode 34.  
 The current in the primary winding 15 from discharge of capacitor 32 produces a short duration high voltage pulse in the secondary winding 16 with a steep rise time for firing of wetted or fouled plugs. Thereafter the voltage developed from release of stored magnetic energy continues for insuring complete burning of fuel and for minimizing exhaust emissions.  
  The capacitor 32 could be charged from a separate voltage source, one advantageous arrangement being disclosed in my aforesaid copending application. In the illustrated circuit, however, and in accordance with a specific feature of the invention, the capacitor 32 is charged from the voltage developed in the secondary winding 16 in response to the build-up of current through the primary winding 15 during conduction of transistor 30. For this purpose, a diode 35 is provided having an anode connected to the terminal 13 and having a cathode connected through a resistor 36 to the capacitor 32. During the build-up of current through the primary winding 15, the terminal 13 is at a positive potential and capacitor 32 is charged to a polarity as indicated in the drawing, through current flow through diode 35 and resistor 36. The high voltage wave form developed at terminal 13 following opening of the contacts 21 and 22, however, is of negative polarity and the diode 35 is then non-conductive, producing no loading effect on the development on the high voltage wave form.  
  Another specific feature relates to the control of the silicon controlled rectifier 33 in a manner such that it is automatically rendered conductive in response to the short duration high voltage pulse. In accordance with this feature, the gate of the rectifier 33 is connected through a resistor 37 to the cathode thereof and through a resistor 38 to the terminal 12 while a capacitor 40 is connected between the cathode of rectifier 33 and ground. When the transistor 30 is rendered nonconductive, the resulting collapse of the magnetic field generates an e.m.f. in the primary winding 15, causing the voltage at terminal 12 to rise and producing a current flow through resistors 37 and 38, charging the capacitor 40. When the voltage across resistor 37 reaches a certain value, from 0.6 volts to 1.0 volts, for example, and when the anode of rectifier 33 is sufficiently positive relative to the cathode thereof, the rectifier 33 is rendered conductive to cause discharge of the capacitor 32 through the primary winding 15 of the ignition coil 14.  
  FIG. 2 illustrates a typical wave form produced at the terminal 13 of the ignition coil 14. At time t contacts 21 and 22 close to cause application of a positive voltage to the base of transistor 30 and to cause conduction of current from the positive terminal of battery 19 through switch 20, the primary winding 15 and transistor 30 and back through ground to the negative terminal of the battery 19. The current through the primary winding 15 then increases, producing an increasing magnetic flux in the coil 14 and generating a positive voltage in the secondary winding 16, causing the voltage of the terminal 13 to be at a positive level approximately equal to the battery voltage times the turns ratio between the secondary and primary windings. By way of example, the voltage may be on the order of 1000 volts. This voltage is applied through the diode 35 and resistor 36 to the capacitor 32 charging the capacitor 32 with a polarity as indicated in the drawing.  
  At time t,, the contacts 21 and 22 are opened and current flow through the transistor 30 is cut off. The magnetic flux of the ignition coil 14 then starts to collapse, producing an increasing voltage in the primary winding 15, in a positive direction at terminal 12, and a corresponding increasing voltage in the secondary winding 16, in a negative direction at terminal 13. As the voltage of the terminal 12 goes in a positive direction, the potential of the gate of the silicon controlled rectifier 33 goes proportionately positive relative to the cathode thereof and a short time after time 1,, the rectifier 33 is triggered into conduction. It is noted that at time t,, capacitor 40 is substantially discharged and its value is sufficiently large for development of the gating or triggering signal for the rectifier 33 through the resistors 37 and 38.  
  When rectifier 33 is triggered into conduction, the capacitor 32 discharges through the diode 34 and the primary winding 15, rapidly increasing the potential of terminal 12 in a positive direction and producing a short duration high voltage pulse at terminal 13 of negative polarity. The steep rise of the pulse is effective to insure firing of wetted or fouled plugs. A short time after time and before time t the rectifier 33 reverts to a non-conductive state, and the magnetic field of the coil 14 continues to collapse, producing a continuing voltage of negative polarity and of substantial magnitude at terminal 13, thereby producing a long burn time.  
  At time contacts 21 and 22 close, causing transistor 30 to conduct and another cycle is initiated.  
  By way of example and not by way of limitation, the resistor 37 may have a value of 4.7 ohms, resistor 38 may have a value of 100 ohms and capacitor 40 may have a value of 0.1 microfarads. The gate signal required for triggering the rectifier 33 may be from 0.2 to 1.5 volts, depending upon operating conditions. Capacitor 32 may have a value of from 1 to 2 microfarads, its value being limited, essentially, only by the time required for charging thereof. Coil 14 is preferably similar to a standard type of ignition coil but with a secondary winding of lower resistance, on the order of percent that of the secondary winding of a standard type of coil.  
  It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.  
 What is claimed is:  
  1. In an ignition circuit, an ignition coil including inductively coupled primary and secondary winding means, capacitor means, and control means coupled in circuit with said primary winding means and said capacitor means and including means arranged for charging said capacitor means, first switch means for connection in series with said primary winding means to a DC supply and arranged to be closed to build up current through said primary winding means and to be opened to cut off said current through said primary winding means to generate an increasing voltage across said primary winding means and a corresponding increasing voltage across said secondary winding means,  
 and second switch means connected in series with said primary winding means and said capacitor means and arranged to be closed in response to said increasing voltage across said primary winding means to discharge said capacitor means through said primary winding means and to generate a short duration high voltage pulse in said secondary winding means, said second switch means comprising an electronic current control device having first and second power electrodes having a controllable impedance therebetween connected in series with said primary winding means and said capacitor means and having a control electrode for controlling said impedance, and said control means further comprising trigger signal means responsive to said increasing voltage across said primary winding means to apply a trigger signal to said control electrode to initiate conduction of said electronic device to discharge said capacitor means through said primary winding means.  
  2. In a circuit as defined in claim 1, said first switch means having a first terminal connected to one terminal of said primary winding means and a second terminal for connection to said DC supply, said trigger signal means comprising impedance means coupled between said first terminal of said first switch means and said control electrode of said electronic device.  
  3. In a circuit as defined in claim 2, said trigger signal means further comprising second impedance means coupled between said first power electrode of said electronic device and said control electrode.  
  4. In a circuit as defined in claim 3, said control means further including unidirectional conduction means coupled between said first power electrode and said terminal of said first switch means.  
  5. In a circuit as defined in claim 4, by-pass capacitor means coupled between said first power electrode and said second terminal of said first switch means.  
  6. In a circuit as defined in claim 1, said electronic current control device being a silicon-controlled rectifier having cathode and anode electrodes respectively forming said first and second power electrodes and a gate electrode forming said control electrode.  
  7. In a circuit as defined in claim 1, said first switch means being in the form of a transistor.  
  8. In a circuit as defined in claim 1, unidirectional coupling means coupling said secondary winding means to said capacitance means for charging said capacitor means during closure of said first switch means.  
  9. In an ignition circuit, an ignition coil including inductively coupled primary and secondary winding means, capacitor means, unidirectional conduction means coupling said secondary winding means and said capacitance means, means for coupling said primary winding means to a voltage source to build up current through said primary winding means and to generate a voltage in said secondary winding means to charge said capacitor means through said unidirectional conduction means, and means for thereafter discharging said capacitor means through said primary winding means. l= l