Internal combustion engine magneto ignition system of the shunt switch type
United States Patent Haubner et al.  
 1451 Apr. 22, 1975 INTERNAL COMBUSTION ENGINE MAGNETO IGNITION SYSTEM OF THE SHUNT SWITCH TYPE Inventors: Georg I-Iaubner, Berg; Walter Hol&#39;er,  
 Schwabach; Karl-Giinter Schwarz. Altenberg, all of Germany Robert Bosch G.m.b.I-I., Gerlingen-Schillerhohe. Germany Filed: Nov. 19, 1973 Appl. No.: 417,221  
 Assignee:  
 Foreign Application Priority Data Nov 29. I972 Germany 2258288 u.s. c1. l23/l48 1:; 315/209 T; 315/207; 315/218; 310/153 1111. c1. F02p 1/00 mm of Search 123/149 R, 149 A. 148 12; 315/209 r.21s.207;317/14s.s B; 310/153. 70  
 References Cited UNITED STATES PATENTS Minck 315/218 3.484.677 l2/l969 Pitco ..l23/l48E Primary E.raminer--Charles J. Myhre Assistant E.\&#39;aminerRonald B. Cox Attorney, Agent, or Firm-Flynn &amp; Frishauf [57] ABSTRACT The residual voltage drop of a semiconductor switching device in its conducting condition used as a shunt switching element in a magneto ignition system is prevented from diverting a part of the generator current into the primary winding of the spark coil by the provision of a voltage sensitive or voltage-change sensitive switching element, particularly a Zener diode. in series with the primary winding. This auxiliary series switching element is rapidly switched by the voltage build-up produced when the shunt switching element is opened by a control circuit pulsed by a timing pulse generator.  
 16 Claims, 4 Drawing Figures INTERNAL COMBUSTION ENGINE MAGNETO IGNITION SYSTEM OF THE SHUNT SWITCH TYPE This invention relates to a magneto ignition system for an internal combustion engine. and particularly a system in which the primary winding of a spark coil is normally short-circuited by a switching element to build up a heavy current and the switching element is opened at the ignition timing moment to cause a sudden rush of current into the spark coil.  
  When magneto generators are required to supply current for other uses in addition to energizing an igni&#39; tion system for an engine. the spark coil of the ignition system is placed outside of the magneto generator itself in order to make more efficient use of the magneto generator and thus improve its power output for purposes other than the energization of the ignition system. Arrangements of this sort are preferred for application to snow-mobiles and the like. In these ignition systems it is necessary to produce a strong surge of current in the primary circuit at the ignition timing moment. so that a sufficiently high voltage will be induced on the secondary side of the spark coil to excite an ignition spark in the spark plug connected in the secondary circuit.  
  For this purpose it is known to connect the armature winding of the magneto generator directly with the primary winding of the spark coil and to bridge these by a mechanical interruptor controlled by a revolving cam. The armature winding of the generator is shortcircuited when the interruptor is closed. so that a heavy current can flow in the armature winding. At the moment of ignition the interruptor is opened by the cam and the current flowing in the armature winding then shoots into the primary winding of the spark coil and there produces the desired sharp change in current flow.  
  This solution has the disadvantage that the mechanical interruptor is subject to considerable wear and must be attended to and replaced at regular intervals. The interruptor cannot readily be replaced by an electronically controlled switching element of the semiconductor type. because such a switching element even in fully conducting condition has a voltage drop. This voltage drop has the effect that the current of the generator armature winding does not flow exclusively through the switching element. but a part flows through the primary winding of the ignition coil. When the switching element is switched off at the ignition timing moment. the change in the current flow in the primary winding of the spark coil is therefore too small to produce a suffi ciently high ignition voltage in the secondary winding.  
  It is an object of the present invention to provide an ignition system of the shunt switching type in which the mechanical interruptor can be replaced by an electronic switching element without thereby reducing the ignition voltage.  
 SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the electronic switching means. which may be referred to as a semiconductor switching means. because it contains at least semiconductor element. comprises a first switching device of the semiconductor type having a switching path and a control path and also a second switching device connected in series with the primary winding of the spark coil in such a way that when the first switching device. connected in parallel with the armature winding of the generator. becomes non-conducting at the ignition timing moment. the sec ond switching device is switched from its nonconducting condition to its conducting condition.  
  In a plurality advantageous form of the invention the second switching device is of such a type that when the first switching device is turned off. the second switching device is switchable by the voltage built up across the now open switching path of the first switching device. For this purpose switching devices can be used both of the voltage sensitive type and of the voltagechange sensitive device type. In the simplest case this second switching element is a threshold voltage semiconductor element. such as a Zener diode. The invention is further described by way of example with reference to the annexed drawing, in which:  
  FIG. I is a circuit diagram of an ignition system of the magneto and coil type embodying the invention;  
  FIG. 2a is a graph showing the current cycle at a first control element;  
  FIG. 2b is a graph showing the voltage cycle at the magneto generator. and  
  FIG. 3 shows various kinds of second switching devices that may be used in series with the primary winding 30a of the spark coil. utilizing various kinds of elec tronic circuit components.  
  FIG. 1 shows the circuit of a so-called coil ignition system for a single cylinder internal combustion engine. supplied with current by a magneto generator 10. The latter consists of a rotor ll driven by the internal combustion engine comprising a number of permanent magnets I2 describing a circular path and an armature l3 excited by the motor and carrying an armature winding [4 having one terminal connection l4b grounded to the chassis. The other terminal connection of the armature winding 14 is connected through a diode 15 with an output terminal 16 to which various utilization circuits are connected, which are symbolically indicated by the resistor 17 shown in dashed lines. The same end l4a of the armature winding 14 is con nected over another diode 18 which is poled in the direction opposite to that in which the first diode I5 is poled and is connected to the ignition system proper. This last connection is made over a conductor 35 to which a first electronic switching element is connected to provide a circuit in parallel to the armature winding l4 of the magneto generator 10. This first electronic switching element is provided in the form of a semiconductor switching device 19 consisting of a Darlington transistor unit having two npn transistors. 21 and 22. with the emitter of the transistor 21 connected over the diode 18, with the end 14a of the armature winding 14 and the collector of the same transistor 21 connected to the cathode of the diode 20. the anode of which is grounded. The base of the transistor 22 is grounded over a resistor 36 and provides together with the emitter of the transistor 21 a control path in parallel with which the emitter-collector path of an npn control transistor 23 is connected. A magnetic timing pulse generator 24 has its output connected in parallel to the baseemitter path of the control transistor 23 and this mag netic timing pulse generator is connected over a capacitor 25 and a resistor 26 disposed in parallel to the last mentioned capacitor. and further over a diode 27. to the base of the control transistor 23. The base of this control transistor 23 is also connected to ground over a resistor 28. the connection conductor 35 and a resistor 29.  
  In parallel to the semiconductor switching device 19 and the diode 20 in series with it is the primary winding 30a of a spark coil 30 in series with a Zener diode 31 that serves as the second switching element of an ignition system according to the present invention. This Zener diode 31 has a Zener voltage that is greater than the voltage provided by the combination of the remaining voltage drop of the semiconductor switching device 19 in its conducting condition and the small forward voltage across the diode 20 in its conducting condition.  
  The secondary winding 30b of the ignition coil 30 is connected over an ignition cable 32 with a spark plug 33, the other side of which is grounded to the chassis just as one end of the primary and of the secondary windings of the ignition coil 30 are grounded.  
 OPERATION During operation of the internal combustion engine (not shown) the permanent magnets 12 of the rotor II of the magneto generator are moved past the armature winding 14. inducing an alternating current therein. The output voltage of the armature winding I4 is shown in the form ofa graph in FIG. 2a and the current in the switching path of the transistor 21 is plotted in FIG. 2b as a function of the rotation of the rotor 11. The positive half-wave of the generator output voltage U reaches the output terminal in over the diode 15. FIG. 2b shows the course of this voltage in the unloaded condition of the system. The succeeding negative voltage half-wave reaches the face of the transistor 22 over the resistor 36 and switches this transistor by producing a current in its base-emitter path and likewise the transistor 21 by producing a current over its base-emitter path, so that both of these transistors are put into their conducting state. A current 1,, begins to flow over the emitter&#39;collector path of the transistor 21 and over the diode 18, which is driven by the voltage produced in the armature winding 14. This current reaches its highest value at the ignition timing moment t,-. At this moment the timing pulse generator 24 produces a control pulse which reaches the base of the control transistor 23 after passing through the capacitor 25 and the diode 27 and causes the control transistor 23 to be switched into its conducting state. The control path of the semiconductor switching device I9 is thereby shortcircuited and the transistors 21 and 22 are instantaneously blocked. The current I is thereby suddenly interrupted and in consequence a high voltage is built up in the armature winding 14 which soon exceeds the breakdown voltage of the Zener diode 3L In this fashion current l, which previously flowed through the emitter-collector path of the transistor 21 is now diverted over the primary winding a and the Zener diode 3I in series with the winding. The sharp change of current thus produced in the primary wind ing 300 causes the production of a high voltage pulse in the secondary winding 30b of the ignition coil 30, which sets off a spark in the spark plug 33. The diode 20 serves to protect the transistor 2] against reverse operation.  
  The control transistor 23 has its base electrode connected over the resistor 29 to one end of the armature winding 24 in such a way that the voltage pulse produced in the armature winding 24 upon interruption of the current I in the transistor 21 holds the control oil transistor 23 in its fully conducting condition. Only after the control pulse in the timing pulse generator 24 has dropped off and after the voltage pulse in the armature winding l4 has likewise fallen off does the control transistor 23 again go into its non-conducting state and thus again switch the semiconductor switching device I9 into its conducting stage, this switching being accomplished over the resistor 24.  
  During the course of a negative voltage half-wave produced by the magneto generator 10 a number of socalled after-sparks can be produced by a quickly succeeding sequence of corresponding control pulses, because the current of the magneto generator I0 is conducted in the previously described fashion alternatively over the switching path of the transistor 2! and over the primary winding 30a of the ignition coil 30.  
  In order to suppress disturbing voltages produced by the timing pulse generator 24, the capacitor 25 is newly charged with each control pulse. It discharges only gradually over the resistor 26 so that smaller disturbing voltages which form a part of the charging voltage of the capacitor 25 are blocked. Instead of the timing pulse generator 24 a mechanical interruptor 34 actuated by a revolving cam can be used. in which case the interruptor as shown in dashed lines in FIG. 1 is connected in parallel to the base-emitter path of the control transistor 23. When the interruptor 34 opens. the control transistor 23 is switched into its conducting condition by the positive voltage half-wave of the armature winding I3 acting over the resistor 29. whereas upon the subsequent closing of the interruptor 34. the transistor 23 is again blocked.  
  FIG. 3 shows only the ignition coil 30 with the secondary winding 30b and the primary winding 30a and a component referred to above as the second electronic switching device of an ignition system of the type set forth in FIG. I. This electronic switching device is a semiconductor device consisting of a number of diodes connected in series which together have a threshold voltage given by the sum of their forward voltage drops while conducting. As shown by dashed lines, there may be used instead. as a semiconductor element in this position. a semiconductor controlled rectifier 41, the control electrode 41a of which is connected with the anode over a Zener diode 42. When a transistor 43 is used as the second electronic switching device. a voltagedependent control can be effected by providing a Zener diode 44 connected between the base and the collector of the transistor. Similarly a voltagedependent variable resistor (VDR) 45 can be used for this switching device as shown in dashed lines. Finally. it is also possible to use a switching device that is switched into its conducting state by a voltage change. In the simplest case this is as shown in dashed lines. a capacitor 46.  
  Although the invention has been described with reference to a particular embodiment. it is not limited thereto and variations and modifications may be made within the inventive concept. Thus. for example. the Darlington transistor combination shown in FIG. I can be replaced by other electronic switching elements just as the Zener diode 31 can be replaced by other elements as just discussed. What is important from the point of view of the invention is that a first and second electronic component functioning as a switching device operate together to produce a current-diverting arrangement which first allows the current produced by the magneto generator to flow through the circuit connected in parallel to the primary winding and then at the moment of ignition timing this parallel circuit is opened and the current is suddenly directed over the primary winding of the spark coil and thereby excites a spark. Of course. the magneto generator can. without departure from the inventive concept. be equipped with additional power-delivering windings and the ignition system can also be operated with a differently poled winding 14 with corresponding change of the po larity of the various circuit components.  
 We Claim:  
  1. An ignition system for an internal combustion engine comprising:  
 a magneto generator having a permanently magnetized rotor driven by said engine and an armature provided with a generator winding arranged for excitation by said rotor;  
 an ignition coil having primary and secondary windings;  
 at least one spark plug connected in circuit with said secondary winding;  
 said primary winding being connected in circuit with said generator winding at least at the ignition timing moment.  
 semiconductor switching means connected in parallel to said generator winding arranged to be switched from its conducting to its non-conducting state at said ignition timing moment;  
 said semiconductor switching means comprising a first switching device of the semiconductor type (19) having a switching path and a control path and a second switching device (31) connected with said first switching device and said primary winding (a) of said ignition coil (30) in such a way that upon the switching of said first switching device to its non-conducting state said second switching device (31 is switched from its non-conducting to its conducting state.  
  2. An ignition system according to claim I, in which said second switching device (3i) is switchable in dependence upon applied voltage.  
  3. An ignition system according to claim 1, in which said second switching device (31) is switchable in dependence upon rate of change of applied voltage.  
  4. An ignition system according to claim 2, in which said second switching device (3| is a threshold voltage semiconductor device that is put into its conducting state when a voltage equaling or exceeding a threshold voltage is applied thereto.  
  5. An ignition system according to claim 4, in which said second switching device is a Zener diode (31) connected in series with the primary winding (30a of said ignition coil (30).  
  6. An ignition system according to claim 4. in which said threshold voltage semiconductor device comprises a plurality of diodes (40) connected in series.  
  7. An ignition system according to claim 4, in which said threshold voltage semiconductor device comprises a semiconductor controlled rectifier (4i the control electrode (410 of which is connected to its anode over a Zener diode (42).  
  8. An ingnition system according to claim 4. in which said threshold voltage semiconductor device comprises a transistor (43). the base electrode of which is connected to the collector of said transistor over a Zener diode (44).  
  9. An ignition system according to claim 2. in which said second switching device is a voltage-dependent variable resistor (45).  
  10. An ignition system according to claim 3, in which said second switching device is a capacitor (46).  
  H. An ignition system according to claim 1, in which said first switching device is a semiconductor control switch (19) connected in series with a diode (20) com nected in the same direction of conductivity.  
  [2. An ignition system according to claim 11. in which said semiconductor control switch (19) comprises a transistor unit (21. 22) having a control path in parallel with which is connected the emittercollector path of a control transistor (23) and in which means are provided for applying a control voltage to the base of said control transistor (23) for switching said emitter-collector path of said control transistor (23) from non-conducting to conducting condition.  
  13. An ignition system according to claim 12. in which a magnetic timing pulse generator (24) is provided with its output connected in parallel to the baseemitter path of said control transistor (23) for generation of a control voltage therefor at said moment of ignition.  
  14. An ignition system according to claim 12. in which a mechanical interruptor (34) arranged to open at said moment of ignition is connected in parallel to said base emitter path of said control transistor (23).  
  I5. An ignition system according to claim 1, in which said generator winding (14) has one end grounded to the engine chassis and its other end connected in series with a diode (18).  
  I6. An ignition system according to claim 14, in which the ungrounded end of said generator winding (14) is connected with an additional diode (15) poled with its direction of conduction opposite to that of said first diode (l8) and having its other electrode connected with a connection terminal (id) for supply of current to equipment other than the engine ignition equipment.  
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