Patent Publication Number: US-3874354-A

Title: Ignition adapter circuit

Description:
Umted States Patent 1 {111 3,874,354 Crouch Apr. 1, 1975 1 IGNITION ADAPTER CIRCUIT 3.134.333 121372 Crouch 123/148 E 3,7 4.7 l l 72 Wcsemeyc 123/148 E [751 Invent: Cmch, Lemme&#34; 3.704.101 12/l972 Strubcr 123/148 E [73] Assignee: Syncro Corporation, Oxford, Mich. [22] Filed: Dec. 14, 1972 Primary Examiner-Charles J. Myhre Assistant Examiner-Ronald B. Cox  
  Appl- 315,139 Attorney, Agent, or Firm-Harness, Dickey &amp; Pierce [52] U.S. Cl. 123/148 E, 123/148 OC, 123/148 MC [51] Int. Cl. F02p 1/00 ABSTRACT [58] new of g&#39; &#39;gfi&#39; 3 6; An electrical ignition system for adapting a conventional magneto spark ignition system of a single- [56] References Cited cylinder engine to a capacitor discharge ignition sys- UNITED STATES PATENTS 3.484.677 12/1969 Piteo .v 123/148 E 9 Claims, 2 Drawing Figures IGNITION ADAPTER CIRCUIT BACKGROUND SUMMARY OF THE INVENTION The present invention relates to an adapter circuit for adapting the conventional magneto spark ignition system of a single-cylinder engine to a capacitor discharge ignition system.  
  The well known advantages of a capacitor discharge ignition (CDI) system often render the conversion of an existing conventional magneto spark ignition system to a CDI system desirable. In a prior U.S. Pat. application, Ser. No. 207,261, filed Dec. 13, l97l, now U.S. Pat. No. 3.704.397 and assigned to the same assignee as the present application. there is disclosed an ignition adapter circuit for converting a conventional magneto spark ignition system of a two-cylinder, two-cycle engine to a CDI system. In that type of engine, a pair of breaker points are individually associated one each with each of the cylinders. and the proper operation of the adapter circuit requires the use of both sets of breaker points.  
  In contrast to a two-cylinder, two-cycle engine, a single-cylinder engine having a conventional magneto spark ignition system utilizes only a single set of breaker points. The present invention provides an adapter circuit which is suitable for use with a singlecylinder engine and which obtains a desired objective of eliminating any need for mechanical revision or modification of the existing ignition hardware when installing the adapter circuit. In other words, the adapter circuit of this invention is installable by simply mounting the adapter on the engine and remaking at most a few simple electrical connections.  
  Important features. advantages and benefits of the invention will be seen in the ensuing description and claims which are to be taken in conjunction with the accompanying drawing.  
 BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a preferred embodiment of the invention in accordance with the best mode presently contemplated for carrying out the invention.  
  FIG. 1 is an electrical schematic diagram of an ignition adapter circuit according to the present invention coupled with a pre-existing magneto spark ignition system of a single-cylinder engine to render it a CDI systern.  
  FIG. 2 is an electrical schematic diagram of another ignition adapter circuit according to the present invention coupled with a pre-existing magneto spark ignition system of a single-cylinder engine to render it a CDI system.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, an ignition adapter circuit according to the present invention is coupled with a magneto ignition section 12 and an ignition coil and plug section 14. In the pre-existing conventional system for a singlecylinder engine. section 12 is directly coupled with section I4.  
  Section 12 comprises a magneto coil 16, a capacitor 18, and a set of breaker points 20. Magneto 16 is mounted on the engine typically in fixed position on a stator (not shown). The stator is in proximity to a flywheel (not shown) which rotates with the engine. Magneto I6 is energized by one or more sets of magnetic pole pairs (not shown) which rotate with the flywheel. In this way as the flywheel turns, an alternating magnetic flux is developed in magneto 16 which causes magneto 16 to supply an alternating polarity output to its load. Magneto l6, capacitor 18, and points 20 are connected in parallel with each other across an output terminal and ground G. Breaker points 20 are mounted on the engine for actuation in timed relation with the rotation of the engine to achieve proper timed engine firing. Capacitor I8 is conventionally provided to minimize arcing across points 20.  
  Section I4 comprises an ignition coil 22 and a spark plug 24. Coil 22 comprises a primary winding 26 and a secondary winding 28 which are connected to a common grounded terminal 14b. Spark plug 24 is connected directly across secondary winding 28. In the pre-existing conventional ignition system, primary winding 26 is connected in parallel with points 20, capacitor 18, and magneto 16 via an input terminal and ground G, terminal 140 being directly connected to terminal 12a. In the conventional system, the opening of points 20 causes the output of magneto coil 16 to be supplied to primary winding 26, the opening of points 20 occurring when the output of magneto coil I6 is of positive polarity. The electrical energy delivered to primary winding 26 in turn causes a rapid change in the magnetic flux linking windings 26 and 28 and hence a voltage to be developed across secondary winding 28 for firing spark plug 24. Thus, plug 24 fires in timed relation with the opening of points 20 to produce desired fuel ignition within the engine cylinder.  
 In order to convert the pre-existing conventional ignition to CDI. the connection between terminal 120 and terminal 14a is broken and adapter circuit 10 is connected therebetween. An input terminal 100 of adapter 10 is connected to terminal 120, an output terminal 10b to terminal 14a, and a third terminal 10c to ground G. Adapter circuit 10 comprises a capacitor 30 and a diode 32 connected in series between terminals 10a and 10c. Plate 300 of capacitor 30 is connected to terminal 100, plate 30b of capacitor 30 to the anode terminal 320 of diode 32, and the cathode terminal 32b of diode 32 to terminal 100. Circuit 10 further comprises an SCR 34 having an anode terminal 34a connected to terminal 10b, a cathode terminal 34b connected to the junction of capacitor 30 and diode 32, and a gate terminal 34c connected through the series combination ofa resistor 36 and a diode 38 to terminal 10a. One terminal of resistor 36 is connected to terminal 34c, the other terminal of resistor 36 to the cathode terminal 38a of diode 30a, and the anode terminal 38b of diode 38 to terminal 100. A diode 40 has its anode terminal 40a connected to the junction of capacitor 30. diode 32 and SCR 34 and its cathode terminal 40b to the junction of SCR 34 and primary winding 26. Adapter circuit 10 is desirably packaged as a compact unit having terminals 10a, 10b and IOCavailable for connection. It will be observed that in order to install adapter circuit 10 on the engine, all that is required is breaking the connection between terminals I2a and 14a, and making the connections to terminals 10a, 10b and 10c. Thus the installation is simple and straightforward, requiring no mechanical modification or revision to pre-existing ignition hardware.  
  With adapter circuit 10 installed, the CDI system operates as follows. For the illustrated embodiment of FIG. I, it will be remembered that points 20 open when the output waveform of magneto coil 16 is positive. The timing of points 20 is such that the points remain open during an initial portion of the immediately succeeding negative polarity portion of the magneto output waveform. Accordingly, during this initial portion of the negative polarity portion, current flows from coil 16 via diode 32 to charge capacitor 30 such that plate 30b becomes negative with respect to plate 30a. Thus, voltage of the illustrated polarity is developed across capacitor 30 before the next positive polarity portion of the magneto output waveform during which points 20 will again open. It will be observed that capacitor 30 also forms a series circuit with primary winding 26 and SCR 34. SCR 34 is arranged to permit capacitor 30 to discharge into primary winding 26. However, to render SCR 34 conductive, it is necessary that a suitable gating signal be applied to terminal 34c. So long as points 20 remain closed, magneto 16 supplies no input to adapter circuit 10, and hence cannot provide the necessary gating signal to render SCR 34 conductive. However, when points 20 open (which is when the output of magneto 16 is positive) the magneto output is applied to terminal 100, and in turn to SCR terminal 34c via diode 38 and resistor 36. This is sufficient to develop the necessary gating signal at terminal 34c for rendering SCR 34 conductive. Thus with SCR 34 becoming conductive in response to the opening of points 20, capacitor 30 immediately discharges into primary winding 26. This in turn causes a rapid change in the magnetic flux linking windings 26 and 28 and hence a voltage to be developed across secondary winding 28 for firing spark plug 24. Since the discharge of capacitor 30 into pri* mary winding 26 tends to be oscillatory, diode 40 permits conduction of current in the opposite direction from that of the current flow through SCR 34. When current flows through diode 40, a reverse voltage is developed across SCR 34 and this reverse voltage is advantageously used to positively turn off SCR 34 and thereby prevent energization of primary winding 26 by magneto coil 16 when capacitor 30 is being charged. In this way, the invention provides a CDI system in which the firing of the spark plug is initiated by the opening of points 20 as was the case for the pre-existing conventional ignition system. Thus, the invention achieves the desired objective of being capable of installation in a pre-existing single-cylinder engine without modifica tion or revision of preexisting ignition hardware.  
  FIG. 2 illustrates another form of the invention which is useful in singlecylinder engines wherein the breaker points open when the polarity of the magneto output is negative. In FIG. 2 like numerals are used to indicate iike components, and the only differences between the circuits of FIGS. 1 and 2 are as follows. Since breaker points 20 open during the negative polarity output of magneto l6, diodes 32 and 38 are connected in opposite fashion from their connection in FIG. 1. SCR 34 is replaced by a triac 42 which comprises terminals 42a, 42b and 42c. Diode 40 is not required.  
  The circuit of FIG. 2 operates with respect to negative polarity magneto output in the same way that the circuit of FIG. 1 operates with respect to positive polarity magneto output. In other words. during an initial portion of the positive portion of the magneto output waveform, capacitor 30 is charged via diode 32 to make plate 30b positive with respect to plate 300. Dur ing the immediately succeeding negative portion of the magneto output, breaker points 20 open to provide a gating signal to triac 42 and this renders triac 42 conductive. Capacitor 30 discharges into primary winding 26 causing spark plug 24 to fire. Since triac 42, once triggered, can conduct current flow in both directions, diode 40 is not required. Triac 42 later becomes nonconductive to prevent energization of primary winding 26 by magneto 16 when capacitor 30 is being charged and triac 42 remains non-conductive until again triggered by points 20 opening. Thus in the circuit of FIG. 2, the firing of plug 24 is initiated by the opening of points 20 as in the conventional system. Accordingly, the adapter circuit of FIG. 2 also can be used without modification or revision of pre-existing ignition hardware.  
  While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fuifill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.  
 I claim:  
  1. For a single-cylinder engine having an existing magneto spark ignition system which comprises a magneto coil for supplying alternating polarity output waveform, an ignition coil having primary and secondary windings. a spark plug operatively coupled with the secondary winding and means operatively coupling the magneto coil with the primary winding comprising a single set of breaker points actuatable between open and closed conditions in timed relation with operation of the engine for causing the spark plug to fire, an adapter assembly for converting the existing magneto spark ignition system to a capacitor discharge ignition system and interconnectable between the set of breaker points and the primary winding of the ignition coil, said adapter assembly comprising a capacitor, input circuit means for operatively coupling said capacitor with the points and the magneto, said input circuit means comprising means for causing said capacitor to be charged by at least a portion of one polarity of the alternating output waveform of the magneto when the set of breaker points is in one condition and output circuit means for operatively coupling said capacitor with the primary winding, said output circuit means comprising means responsive to the actuation of the set of breaker points to the other condition for causing said capacitor to discharge through the primary winding and thereby cause the spark plug to tire.  
  2. The adapter assembly of claim I wherein said input circuit means comprises a diode operatively coupling the points and the magneto with said capacitor, said diode being arranged to conduct charging current to said capacitor from the magneto.  
  3. The adapter assembly of claim 1 wherein said output circuit means comprises a solid state switch operatively coupling said capacitor with the primary winding and means operatively coupling said solid state switch with the breaker points for initiating conduction of said solid state switch when the set of breaker points is actuated to the other condition and causing said capacitor to discharge through the primary winding and fire the spark plug.  
  4. the adapter assembly of claim 3 wherein said solid state switch is an SCR.  
  5. The adapter assembly of claim 3 wherein said solid state switch is a triac.  
  6. The adapter assembly of claim 1 wherein said means responsive to the actuation of the set of breaker points to the other condition comprises means responsive to the opening of the set of breaker points for causing said capacitor to discharge through the primary winding.  
  7. For a single-cylinder engine having an existing magneto spark ignition system which comprises a magneto coil for supplying alternating polarity output waveform relative to a ground potential, an ignition coil having primary and secondary windings a spark plug operatively coupled with the secondary winding and means operatively coupling the magneto coil with the primary winding comprising a single set of breaker points actuatable between open and closed conditions in timed relation with operation of the engine for caus ing the spark plug to fire. an adapter assembly for converting the existing magneto spark ignition system to a capacitor discharge ignition system and interconnectable between the set of breaker points and the primary winding of the ignition coil, said adapter assembly comprising a capacitor, input circuit means for operatively coupling said capacitor with the set of breaker points and the magneto, said input circuit means comprising means for causing said capacitor to be charged by at least a portion of one polarity of the alternating output of the magneto such that one terminal of said capacitor is charged to a potential of said one polarity relative to ground potential when the set of breaker points is in one condition and output circuit means for operatively coupling said capacitor with the primary winding. said output circuit means comprising a thyristor having an anode and a cathode defining a principal conduction path through the thyristor and a gate for establishing conduction through the principal conduction path between said anode and said cathode, means connecting said cathode with said one terminal of said capacitor, and means connecting said gate with the set of breaker points when the set of breaker points is actuated to the other condition so that said thyristor is triggered into conduction by the difference between the respective potentials applied to said cathode and said gate whereby said capacitor discharges through said thyristor and into the primary winding and thereby causes the spark plug to tire.  
  8. The adapter assembly of claim 7 wherein said thyristor is an SCRv 9. The adapter assembly of claim 77 wherein said thyristor is a triac.