US3791363A

US3791363A - Electronically controlled reversal-proof magneto ignition system

Info

Publication number: US3791363A
Application number: US00309429A
Authority: US
Inventors: P Schmaldienst; G Gemander
Original assignee: ROSCH R GmbH
Current assignee: Rosch R dt GmbH; ROSCH R GmbH
Priority date: 1972-02-08
Filing date: 1972-11-24
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12
Also published as: SE391006B; DE2205722C2; IT973104B; FR2171762A5; DE2205722A1; JPS4888327A

Abstract

A transistor operating as an AND gate permits a semiconductor controlled rectifier to discharge a condenser through the primary of an ignition coil when the magneto and the motor to which it is coupled are turning in the normal direction but does not allow the SCR to be fired when the motor turns in the other direction. A pulse transmitter is mounted on the armature plate of the magneto so as to provide properly timed pulses in cooperation with a projection revolving on the hub of the device. The disposition of these elements relative to the armature which provides the alternating current to the switching path of the transistor assures the appropriate polarity of the voltages applied to the transistor.

Description

Waited States Patent 1 91 Schmaldienst et al.

ELECT RONICALLY CONTROLLED REVERSAL-PROOF MAGNETO IGNITION SYSTEM lnventors: Peter Schmaldienst; Georg Gernander, both of Nurnberg, Germany Robert Rosch GmbH, Gerlingen-Schillerhohe, Germany Filed: Nov. 24, 1972 Appl. No.: 309,429

Assignee:

us. or. .11 123/148 E, 123/148 MC Field of Search 123/148 E References Cited UNITED STATES PATENTS 8/1971 Sohner 123/148 E 3,554,179 1/1971 Burson 123/148 E Primary Examiner-Laurence M. Goodridge Assistant Exqminer-Rona1d B. Cox Attorney, Agent, or Firm-Flynn & Frishauf A transistor operating as an AND gate permits a semiconductor controlled rectifier to discharge a condenser through the primary of an ignition coil when the magneto and the motor to which it is coupled are turning in the normal direction but does not allow the SCR to be fired when the motor turns in the other direction. A pulse transmitter is mounted on the arma' ture plate of the magneto so as to provide properly timed pulses in cooperation with a projection revolving on the hub of the device. The disposition of these elements relative to the armature which provides the alternating current to the switching path of the transis- ABSTRACT tor assures the appropriate polarity of the voltages ap plied to the transistor.

10 Claims, 4 Drawing Figures Pmmw FEB 1 21m SHEET 2 [IF 2 ELECTRONICALLY CONTROLLED REVERSAL-PROOF MAGNETO IGNITION SYSTEM This invention relates to an electronically switched magneto ignition system for an internal combustion engine and particularly to the type of magneto ignition system in which a capacitor is charged over at least one diode by a magneto generator coupled to the engine and the capacitor is provided with a discharge circuit through the primary winding of the type of transformer known as an ignition coil, the secondary of which is connected to one or more spark plugs. In this type of circuit the discharge is initiated by triggering a semiconductor controlled rectifier (SCR) or some similar device.

In one ignition system of the type just described, the alternating voltage produced by the magneto generator is applied to a rectifier circuit and a smoothing filter connected thereto so as to provide an almost constant d.c. potential to the capacitor. A semiconductor con.- trolled rectifier (SCR) serves as the electronic control switch and is put into its conductive condition by the pulse transmitter at the properly timed moment for ignition. This SCR has its anode connected to a tap on a voltage divider, which is fed with the aforesaid practically constant d.c. potential. When this SCR becomes conducting, it provides the dc. voltage picked off at the voltage divider tap to the control electrode of a second SCR, making the latters switching path conducting. The switching path of the second SCR controls a discharge path of the capacitor and when the capacitor discharges through the primary of the ignition coil, a high voltage is induced in the secondary which produces a spark in the spark plug then connected with the secondary of the coil.

The ignition system just described has the disadvantage that it is reversal-proof (i.e. immune to operation in the wrong direction) only when applied to multicylinder internal combustion engines, which require an ignition distributor. The distributor fixes the firing sequence, so that when the engine turns in the wrong direction, continued running of the machine is prevented. In the case of one or two cylinder internalcombustion engines, which require no distributor, the ignition system is not reversal proof.

In another known arrangement utilizing a capacitor discharge, the SCR in the discharge circuit is directly switched by the voltage pulse provided by a magnetic pulse transmitter. In that case the pulse transmitter is so arranged that when the engine is turning in the proper operating direction, the control voltage pulse is provided at the proper firing time by the steep side of a revolving metal piece that concentrates the magnetic lines of force, whereas in the case of rotation in the wrong direction the forming of a control pulse in the pulse transmitter is suppressed because a slanting side of a magnetic field concentrating projection passes by instead.

This last solution is ineffective at high speeds if, for example, the engine is spun fast in the wrong direction with a kick or snap in the wrong direction. In thatcase so-called disturbance voltages are produced which switch the SCR, thus overcoming the reverse drive safety margin of the engine. These disturbance voltages can of course be limited to low values if a weak pulse transmitter is used, but thatis only practical for an engine with high idling speed, that feature being necessary to provide a sufficiently high control voltage for the SCR in normal operation.

An object of the invention is to provide a magneto ignition system that provides an adequate margin of safety against reverse operation over the whole range of engine speed even when the idling speed of the engine is relatively low.

Subject Matter of the Present Invention Briefly, an electronic control switch, preferably a transistor, is interposed between the pulse transmitter and the control circuit of the SCR that switches the capacitor discharge. The emitter-base circuit of this transistor is connected to the output of the pulse transmitter and its emitter-collector path is fed by an alternating current connection of the magneto generator so arranged that when pulses are received from the pulse transmitter, the switching path of the transistor is always being subjected to a voltage half wave of the same polarity. A particularly advantageous arrangement is provided when the emitter of the transistor is connected to an a.c. output of the magneto generator while the collector electrode is connected to the control electrode of the SCR that has its switching path in the discharge circuit of the capacitor. The magneto generator and the impulse transmitter are so arranged that the a.c. voltage half waves of the magneto generator that are present when the pulses are provided by the pulse transmitter always have positive polarity when the engine is turning in its normal direction and negative polarity when it is turning in the abnormal direction.

It is particularly effective to supply the a.c. voltage to the transistor-emitter from a separate control winding located on the same armature member on which the winding is placed which furnishes theenergy for charging the capacitor. The rotor of the pulse transmitter may be provided by the hub of the pole wheel (rotor) of the magneto generator, the hub being provided with projecting ferromagnetic elements that cooperate with the pole pieces of the fixed part of the pulse transmitter for the purpose of generating the transmitter timing pulses. The magneto rotor may conveniently have four segmental permanent magnets that pass around the ends of the fixed armature that carries the load and control windings.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram of one form of capacitor discharge type magneto ignition system according to the invention; i

' FIG. 2a is a graph illustrating the course of the control voltage and of the pulse transmitter voltage, plotted against angle for normal rotational direction;

FIG. 2b is a corresponding voltage graph for engine rotation in the wrong direction, and

, FIG. 3 is a circuit diagram of another form of capacitor type magneto ignition system according to the invention.

FIG. 1 shows the circuit of a capacitor type ignition system for a one-cylinder two-cycle internal combustion engine. The ignition system is supplied with energy by the magneto generator 10, which is driven by an internal combustion engine, not shown, with which it is mechanically'coupled. A power transfer armature 11 of the magneto generator 10 carries a power winding 12 which develops the power for charging capacitor 15 and is connected at one end by conductor 13 to a diode 14, the other side of which is connected to the capacitor 15. The other end of the power winding 12 and also the other terminal of capacitor 15 are connected to ground, or more precisely, to the frame of the engine. A discharge circuit 16 is connected in parallel to capacitor 15 comprising, in series, the primary winding 17a of a transformer of the type known as an ignition coil and an SCR 18 (although abbreviation SCR is the most commonly used short name for semiconductor controlled rectifier, these devices are sometimes also referred to as thyristors).

One end of the secondary winding 17b of the ignition coil 17 is connected to the end of the primary winding which connects with SCR 18. The other end of the secondary winding 17b is connected to a spark plug 20 by means of an ignition cable 19. The control electrode 18a of SCR 18 is connected to a control conductor 21, the other end of which is connected to the control winding 22, which is located along with power winding 12 on the armature 11 of the magneto generator. The other end of that control winding is grounded.

The emitter-collector path of the PNP transistor 23 is interposed in the control wire 21 of the SCR 18, with its emitter connected to the control winding 22 and its collector connected to the control electrode 18a of SCR 18. The transistor 23 is adapted to be fired into conducting condition from time to time by a magnetically operating pulse transmitter 24, which is connected by

conductors

25 and 26 respectively to the emitter and to the base of transistor 23.

The pulse transmitter 24 is, as shown in dashed lines, provided with a permanent magnet 27, induction winding 28 and two pole pieces 29 lying one behind the other in the axial direction of magneto generator 10. The pole pieces 29 work together with magnetically soft projections 30 which, for distinction from the pole pieces 29,-may be referred to as field concentratingor guiding projections (or elements). The field concentrating elements 30 are mounted on the hub 31 of a pole wheel 32, which constitutes the rotor of magneto generator 10 that is adapted to provide a rotating field for the magneto. The pole wheel 32 is cup shaped and is fixed with its hub 31 on one end of the crankshaft of the gasoline engine. It is provided with four permanent magnets 33 circumferentially disposed internally of the rim and symmetrically distributed around the rim. The permanent magnets produce the necessary changes in flux in the power armature 11 as the rotor 32 revolves. Power winding 1 1 and pulse transmitter 24 are mounted on a common fixed armature plate 34 inside the magneto rotor 32.

The manner of operation of the ignition system shown in FIG. 1 will now be explained with reference to FIGS. 2a and 2b. For this purpose, the voltages that arise are to be considered in relation to the crankshaft position in the engine under rotation in the direction of the arrow shown in FIG. 1. This is plotted in FIG. 2a in terms of the same abscissor as is used in FIG. 2b with the corresponding voltages in the case of rotation in the opposite direction. The control voltage U, induced in the control winding 22 of magneto generator 10 and the negative value (polarity chosen because of the polarity conditions of transistor 23) of the output voltage U, of the electromagnetic pulse transmitter 24 are shown in FIG. 2a for the normal direction of rotation and in FIG. 2b for the opposite direction of rotation, in

each case on the same time scale. The values of they voltage -U, are in this case shown as measured at the base of transistor 23.

When the engine is turning in its normal direction there are produced in the charging winding 12 and in the control winding 22 of the magneto generator 10 two alternating voltages that are either in the same phase or in mutually opposed phase. A speed dependent alternating voltage is produced in the charging winding 12 ofa magnitude around 400 V in such a fashion that for every revolution of the magnet bearing rotor 32, two positive voltage half waves are applied through diode 14 to the capacitor 15 to charge the latter, while the negative half waves are blocked by the diode 14. An alternating voltage of about 3 V is produced in control winding 22 and reaches the normally non-conducting transistor 23 over the connection 21. Transistor 23 remaining nonconducting, SCR 18 receives no control voltage U so that the discharge circuit 16 of capacitor 15 is not yet closed.

At the proper time T, the field concentrating element 30 turning the rotor 32, arrives under the pole piece 29 of the pulse transmitter 24. A voltage pulse is then produced in the induction winding 28 which causes the base of transistor 23 to become negative with respect to its emitter. When the firing control voltages U, of transistor 23 is reached, the latter is switched into the conducting condition and the control voltage U is now supplied to the control electrode 18a of SCR 18 over the switching path of transistor 23. As shown in FIG. 2a, at this time a positive half wave of the control voltage U is being induced in the control winding 22, the magnitude of which has just at this very time reached the firing control voltage U,, of SCR 18. The control voltage U accordingly immediately switches SCR 18 into conducting condition to discharge capacitor 15 through the primary winding 17a of ignition coil 17 and the switching path of SCR 18. The high voltage thereby induced in secondary coil winding 17b strikes a spark in spark plug 20.

When the pulse voltage U falls away at the base of transistor 23, the transistor becomes nonconducting again and the control voltage U that was being applied to the SCR control electrode 18a is interrupted. The SCR 18 accordingly remains conducting only until the discharge current drops to zero. When SCR 18 becomes nonconducting at this point, capacitor 15 can immediately begin to charge again through diode 14.

Because the magnetic field concentrating element 30 extends over a circumferential angle of about 10 on the hub 31, the crankshaft 35, as it continues to turn, causes the pulse transmitter 24 to produce a pulse of opposite polarity shortly after the event just described. This pulse, however, has no effect on transistor 23, which remains nonconducting. The sequence of events just described is repeated for every full revolution of magneto generator 10.

Suitable location of impulse transmitter 24 on the armature mounting plate 34 assures that for every revolution of the rotor 32, the pair of oppositely polarized pulses produced by the pulse transmitter occurs within a single voltage half wave of the alternating voltage U produced in the control winding 22 of magneto generator 10 and of course also that the half wave in question is of the appropriate polarity. As shown in FIG. 2, the half wave of the control voltage U during which the pulse pair is generated has positive polarity in the case When the gasoline engine is turning in the wrong direction, the transistor 23 is still put into its conducting condition briefly when the firing voltage U, is reached at its base electrode, but at this moment the control voltage U, applied to its emitter is negative, so that it is not transmitted through the switching path of transistor 23 to the control electrode 18a of the SCR. The negative control voltage U is hence of no effect on the SCR18, which remains non-conducting, keeping the discharge circuit 16 open. When the control voltage U reaches the positive firing voltage U, of transistor 18 about 90 later, the transistor 23 has already in the meanwhile returned to its nonconducting state. The control voltage U, then still fails to get to the control electrode 18a. The SCR 18 thus continues to remain in its nonconducting state. In this manner a discharge of capacitor 15 and the consequent striking of a spark in spark plug 20 is prevented. The gasoline engine is therefore protected against running backwards.

in FIG. 3 the capacitor type ignition system that is shown which corresponds largely in constitution and manner of operation to the ignition system shown in FIG. 1 and described above. The corresponding components of the ignition systems of FIG. 1 and FIG. 3 are accordingly provided with the same reference numerals. The difference between these two systems is simply that magneto generator a of FlG. 3 which supplies the ignition energy is made without a control winding. in its place, avoltage divider 42 consisting of two series-connected resistors 40 and 41' is connected in parallel to the charging winding 12, which charges capacitor over diode 14. The tap 43 of thevoltage divider 42, at the common connection point of resistors 40 and 41, is connected to the control wire 21 so that the control voltage U produced on the wire 21 has a smaller amplitude but the same wave form as the alternating voltage of the charging winding 12.

Also in this form of ignition system, the magneto generator 10a and the pulse transmitter 24 are so relatively disposed and coupled that the ignition system operates in the manner shown in FIGS. 2a and 217V and above described for the respective cases of normal and abnormal rotational direction.

Although the invention has been described with respect to two particular illustrative examples, it is to be understood that other forms and modifications of the invention are possible within the inventive concept. For example, in place of the hub controlled pulse transmitter 24 it is possible to use a pulse transmitter at some other location of the gasoline engine or of the magneto generator, thus for example on the circumference of the rotor 32. Furthermore, in a four pole magneto generator the magnetic field concentrating element may extend over an arc of 1 80 since in the normal direction of engine rotation, the first pulse of the pulse transmitter would still always occur during the first positive half wave of the magneto generator and assure the provision of a spark for the engine. The second and oppositely polarized pulse would then occur during the second positive half wave of the alternating voltage. When the engine turns in the wrong direction, these pulses in each case occur during a negative half wave of the alternating voltage and a discharge of capacitor '15 is thus prevented.

By appropriate design of the charging current armature 11 and the pulse transmitter 24, a retarding of the timing of the moment when the control voltage U reaches the firing voltage U, of SCR 18 can be produced at high rates of rotation by the effect of armature reaction. in this fashion, by the use of an ignition system according to this invention, a rotational speed limitation can be provided in the normal rotational direction since at high speeds the control voltage U, will then reach the SCR firing voltage U, only after the pulse of the pulse transmitter 24 is over and the transistor 23 is again nonconducting. Since in this case the SCR 18 is no longer turned on and the capacitor 15 is not further discharged, the ignition system is disabled when a maximum permissible speed of the gasoline engine is exceeded.

As already mentioned, the inventive concept is by no means limited to the two illustrative examples here described. Rather, in view of the fact that the transistor 23 in both examples has the function of an AND gate, any other circuit components and circuits may be used in place of the transistor 23 which operate as an AND gate that gives an output signal for turning-on the SCR 18 when both the control voltage U and the pulse transistor voltage U have positive values; Transistor 23, moreover, which in the circuit described is a'PNP type, could naturally be replaced by an NPN transistor in a correspondingly modified circuit.

Other forms of electronically controlled switches could also be used instead of the SCR 18, preferably a switch that continues to conduct until the discharge current falls to zero regardless whether the control voltage that initiated the discharge remains that long on the control electrode of the switch.

We claim:

1. A magneto ignition system for an internal combustion engine comprising:

a magneto generator (10) mechanically coupledto said engine;

a capacitor (15) electrically connected to said magneto generator through at least one diode (14); an ignition transformer (17) having a primary winding connected to said capacitor and a secondary winding connected to at least one spark plug (20');

an electronic switching device (18) connected so that its switching path and said primary winding of said transformer provide a discharge path for said capacitor;

means including a pulse transmitter (24) mechanically coupled to said engine and an electronic control switch (23) in the control circuit of said electronic switching device (18) for timed operationof said electronic control switch, the switching path of said electronic control switch being connected (21) to an alternating current output connection of said magneto generator such that pulses produced in the" switching path of said electronic control switch in response to pulses applied to the control path of said electronic control switch by said pulse transmitter occur during half waves of the a.c. output voltage of said magnetic generator. I

2. A magneto ignition system as defined in claim 1 in which the particular half wave of the alternating current output voltage of said magneto generator which is present during transmission of a pulse by said pulse transmitter is always positive in the case of a normal rotationai direction and always negative in the case of the opposite direction of rotation.

3. A magneto ignition system as defined in claim 2 in which said electronic control switch (18) is a semiconductor controlled rectifier (SCR), said electronic control switch (23) is a transistor, and said transistor has its emitter-collector path connected in series with a winding of said magneto generator and with the control path of said semiconductor controlled rectifier (18') and has its emitter-base path connected (25,26) with the electrical path (28) of said pulse transmitter (29).

4. A magneto ignition system as defined in claim 3 in which said transistor (23) has its emitter connected (21) with an alternating voltage output of said magneto generator and its collector connected with the control electrode (18a) of said semiconductor controlled rectifier (18).

S. A magneto ignition system as defined in claim 1 in which said a.c. output connection of said magneto generator to which the switching path of said electronic control switch (23) is connected is a control winding (22) which is provided on the same armature (11) of said magneto generator (10) as a second longer winding (12) connected to charge said capacitor (15) through said diode (14).

6. A magneto ignition system as defined in claim 1 in which said pulse transmitter (24) is provided with a permanent magnet (27) and induction winding (28) and pole pieces (29) which are adapted to cooperate with magnetic field concentrating pieces (30) fixed on the hub (31) of the magnet-carrying rotor (32) of said magneto generator (10), said armature (11) and said pulse transmitter (24) being mounted on a fixed common armature plate (34).

7. A magneto ignition system as defined in claim 6 in which each said magnetic field concentration piece (30) extends over a circumferential angle corresponding to about 10 of the rotation of said engine.

8. A magneto ignition system as defined in claim 6 in which each said magnetic field concentration piece (30) extends over a circumferential angle corresponding to not more than of the rotation of said engine.

9. A magneto ignition system as defined in claim 1 in which for every revolution of said magneto generator (10) a pair of pulses is produced in said pulse transmitter (24) consisting of two pulses of opposite polarity occurring within a single voltage half wave of the alternating voltage (U produced in said magneto generator (10).

10. A magneto ignition system as defined in claim 1 in which a voltage divider (42) is provided across the load winding (11) of said magneto generator (10a) which energizes said capacitor (15) over said diode or diodes (14), and in which the tap (43) of said voltage divider is connected to supply energy to the switching path of said electronic control switch (23).

Claims

1. A magneto ignition system for an internal combustion engine comprising: a magneto generator (10) mechanically coupled to said engine; a capacitor (15) electrically connected to said magneto generator through at least one diode (14); an ignition transformer (17) having a primary winding connected to said capacitor and a secondary winding connected to at least one spark plug (20); an electronic switching device (18) connected so that its switching path and said primary winding of said transformer provide a discharge path for said capacitor; means including a pulse transmitter (24) mechanically coupled to said engine and an electronic control switch (23) in the control circuit of said electronic switching device (18) for timed operation of said electronic control switch, the switching path of said electronic control switch being connected (21) to an alternating current output connection of said magneto generator such that pulses produced in the switching path of said electronic control switch in response to pulses applied to the control path of said electronic control switch by said pulse transmitter occur during half waves of the a.c. output voltage of said magnetic generator.

2. A magneto ignition system as defined in claim 1 in which the particular half wave of the alternating current output voltage of said magneto generator which is present during transmission of a pulse by said pulse transmitter is always positive in the case of a normal rotational direction and always negative in the case of the opposite direction of rotation.

3. A magneto ignition system as defined in claim 2 in which said electronic control switch (18) is a semiconductor controlled rectifier (SCR), said electronic control switch (23) is a transistor, and said transistor has its emitter-collector path connected in series with a winding of said magneto generator and with the control path of said semiconductor controlled rectifier (18) and has its emitter-base path connected (25,26) with the electrical path (28) of said pulse transmitter (29).

4. A magneto ignition system as defined in claim 3 in which said transistor (23) has its emitter connected (21) with an alternating voltage output of said magneto generator (10) and its collector connected with the control electrode (18a) of said semiconductor controlled rectifier (18).

5. A magneto ignition system as defined in claim 1 in which said a.c. output connection of said magneto generator to which the switching path of said electronic control switch (23) is connected is a control winding (22) which is provided on the same armature (11) of said magneto generator (10) as a second longer winding (12) connected to charge said capacitor (15) through said diode (14).

7. A magnEto ignition system as defined in claim 6 in which each said magnetic field concentration piece (30) extends over a circumferential angle corresponding to about 10* of the rotation of said engine.

8. A magneto ignition system as defined in claim 6 in which each said magnetic field concentration piece (30) extends over a circumferential angle corresponding to not more than 180* of the rotation of said engine.

9. A magneto ignition system as defined in claim 1 in which for every revolution of said magneto generator (10) a pair of pulses is produced in said pulse transmitter (24) consisting of two pulses of opposite polarity occurring within a single voltage half wave of the alternating voltage (Uc) produced in said magneto generator (10).