US3761779A - Flywheel magneto ignition apparatus operating with capacitive ignition effect - Google Patents

Abstract

A flywheel magneto ignition system includes a generator coil about which a magnetic field rotates, a first diode connecting a capacitor and the primary winding of an ignition coil to said generator coil, a second diode connected across said generator coil for conducting current pulses blocked by said first diode, a spark plug of the surface type connected in circuit with the secondary winding of the ignition coil, and a control member actuated in respnse to flywheel rotation for controlling current flow to the capacitor and primary winding, the control member being synchronized with the rotating field to initiate charging of the capacitor when a voltage pulse conducted by the second diode has just reached its maximum potential.

Description

United States Patent 1191 Carlsson Sept. 25, 11973 [5 1 FLYWHEEL MAGNETO IGNITION 3,065,382 11/1962 Kleine 317/81 x APPARATUS OPERATING WITH 3.500,086 3/1970 Baermann... 310/15 X 3,508,116 4/1970 Burson 317/81 CAPACITIVE IGNITION EFFECT 3,584,929 6/1971 Schuette t t r 315/244 [75] Inventor: Hans Thorsten Henrik Carlsson, 3.5 6.133 /19 1 Warr n t a 315/209 SC Amal, Sweden [73] Assignee: Aktiebolaget Svenska Primary Examlinerfvolodymyr y y El kt t A l S d Attorney-Ben amin H. Sherman et a1. [22] Filed: July 5, 1972 21 Appl. No.: 269,131 1571 ABSTRACT A flywheel magneto ignition system includes a genera- [30 F i Application p i Data tor coil about which a magnetic field rotates, a first July 5 swedfin 8698/71 diode connecting a capacitor and the primary winding of an ignition coil to said generator coil, a second diode [52] U S Cl 317/81 123/149 310/15 connected across said generator coil for conducting .3.l 315/24 317 317/96 current pulses blocked by said first diode, a spark plug I 320/1 336/1 of the surface type connected in circuit with the sec- [51] Int CI g llzsg 3/00 ondary winding of the ignition coil, and a control mem- [58] Field 96 her actuated in respnse to flywheel rotation for controll23/l46 5 3 15/506 ling current flow to the capacitor and primary winding,

' 320/l.336/1 d the control member being synchronized with the rotating field to initiate charging of the capacitor when a [56] References Cited voltage pulse conducted by the second diode has just reached its maximum potential. UNITED STATES PATENTS 2,536.468 1/1951 Russell 317/92 5 Claims, 5 Drawing Figures PATENTED SEP 2 5 I973 sum 10F 2 Fig. 3

PATENTED SEP25 I975 I SHEET 2 BF 2 Fig. 4

lllllllll'l FLYWHEEL MAGNETO IGNITION APPARATUS OPERATING WITH CAPACITIVE IGNITION EFFECT From the very beginning of the internal combustion engine era the common way of producing an ignition spark between the electrodes of the spark plug is characterized in that a low-voltage primary current is stepped up in an ignition coil to an operating voltage of 8 to 9 kilovolts. The source of the primary current may be a battery, a DC generator or a magneto. Magnetos are commonly used in e.g. motor cycle and motor bike motors, outboard motors, small-size stationary or tractor motors for various types of auxiliary implements and the like.

In order to establish the spark-over at exactly the right moment, i.e. when the piston is in a predetermined position short of the end of the compression stroke, systems of this type are provided with a breaker device adapted to rotate on the motor shaft or synchronously in connection therewith, said breaker device being adapted to break the primary current to the ignition coil thereby causing a quick magnetic flux change to take place in the iron core thereof so that an ignition voltage is induced in the secondary winding For this reason ignition systems of this type have been considered as being inductive ignition systems irrespective of the fact that a condenser always is connected across the contacts of the breaker in order to attenuate the spark formation which otherwise always will take place due to the voltage peaks inductively produced at the mo-' ment the contacts close and open. The charge received by the condenser during breaking is again fed to the primary circuit and contributes to the energy conversion in the ignition coil, i.e. to increase the ignition spark.

During recent years the continuously increasing demands regarding stable operation over a large range of number of revolutions comprising a low idling speed, for example 200 revolutions per minute, and high speeds during operation, such as 8000 to 10,000 revolutions per minute, good combustion properties throughout the range of operative speeds and last, but not least, improved starting properties, have initiated an intensive developmen work in the field of so-called condenser igntion systems, i.e. ignition systems based on capacitive spark generation. This development work has been performed in parallel to and in close connection with simultaneously performed investigations regarding the ignition and combustion process proper taking place in the motor as well as with attempts to develop novel and improved types of spark plugs. It has been the purpose of these investigations to arrive at a combination of ignition system and spark plug which yields optimal ignition effect throughout the range of operational speeds, which is practically unaffected by fouling in the spark plug, for example due to carbon bridges, soot, oil, excessively rich fuel mixture and the like, and which in addition yields efficient ignition and combustion also during very low starting speeds, such as 200 revolutions per minute.

For technical and physical reasons these requirements cannot be fully satisfied by the inductive ignition systems, whereas condensor systems have proved to offer practically useful solutions yielding particularly good results. Thus, there arenow on the market both battery and generator or flywheel operated condenser systems in combination with so-called surface spark plugs. This latter type of spark plug which has recently been developed and which is particularly suited for use in connection with condenser ignition igniting systems, is distinguished from spark plugs for inductive systems by the fact that it lacks distinct electrode tips between which spark-over takes place and instead is provided with a central electrode disposed in a state of insulation in the tubular spark plug body so that the spark plug body and the central electrode terminate in approximately the same plane. The spark will flash over at any arbitrary point on the annular surface between the central electrode and the tubular body. As a rule, such surface spark plugs are additionally provided with a preliminary spark gap provided within the plug and adapted to bring about a change of distribution between current and voltage to produce a higher overall voltage during spark-over. This distribution effect appears to be of essential importance in condenser systems.

Capacitive ignition systems are essentially based on the fact that during each ignition a preliminarily charged condenser is discharged over the primary winding to an ignition coil due to the fact that a control member closes the circuit. The control member may comprise a mechanical means corresponding to the breaker switch previously mentioned in connection with inductive ignition systems or it may comprise an electronic circuit including, for example, a thyristor, a diode and a trigger coil which for a flywheel magneto ignition apparatus is disposed in the magnetic field of the flywheel so that a position-determined pulse induced in the trigger coil is rectified by the diode and renders the thyristor conductive for the primary current. The electronic circuit and all the component parts thereof may be completely cast into a block of thermosetting resin, such as epoxy resin, and is thus adapted to be attached as a compact and extremely reliable unit within or outside of the flywheel.

For capacitive ignition systems in combination with surface spark plugs certain basic functional conditions have been established insuring reliable ignition under all operational and starting conditions. Thus, during operation the voltage level must be at 18 20 kilovolts rather than the above mentioned range of 8 9 kilovolts in conventional inductive systems and with normal spark plugs. Moreover, the rising time defined as a time required for arriving at the voltage necessary for spark-over in a surface spark plug must not exceed 10 microseconds and preferably be considerably lower, for example, 2 microseconds. Finally, the burning time of the spark must be at least to microsecond. All these conditions which are based on comprehensive practical tests and which now can be considered to be finally established, involve in turn specific requirements regarding dimensions, construction and choice of components and the like for the ignition system. For example, it is necessary to provide for the operating voltage of 18 20 kilovolts a sufficient voltage range so that a maximum voltage exceeding 30 kilovolts may be obtained. Moreover, consideration must be given to the properties of the condenser as far as discharge time is concerned and to the resistance, i.e. inductance in the primary winding of the igniting coil which is decisive for the discharge speed of the condenser and thus directly influences the rising time. In addition, sufficient energy determined by the prodact: charging voltage x condenser capacity must be produced to enable a sufficient burning time (80 to 100 microseconds) of the spark to be obtained. In addition, it is a basic requirement for the entire combination that the components should be cheap, reliable and compact.

In order to satisfy the energy requirement the charging voltage of the condenser must be on a sufficiently high level. A value of, for example, 1000 volts would be desirable. While such a voltage level is actually obtainable, it entails on the other hand an unpermissible increase of the electronic components (such as the thyristor and diode) and, for this reason, the charging voltage of the condenser in practice must be limited to a maximum of 500 volts.

In order to produce the charging voltage in flywheel magnetos there is provided, in a previously known way, a generator coil in the rotating field of the flywheel. The alternating voltage generated in the generator coil is rectified in a first diode and the current is fed into the condenser, the control member in the primary circuit being open during this phase of operation. The supplied current has the character of a positive half wave pulse having a voltage proportional to the number of revolutions of the flywheel. In order to relieve the first diode from excessive barrier voltages from the negative half wave of the generator coil a second diode may be provided which is connected in parallel overthe generator coil and which produces a current migration of the negative half wave through the generator coil, this energy being consumed by the inductance and essentially transformed into heat. In this way the voltage amplitude of the negative half wave may be minimized and the voltage charge of the first diode reduced.

In prior systems of this type it has been attempted to rectify only one of these half waves or both of them during charge of the condenser. In other words, the control member has opened in or slightly after the point of cross-over between the negative and the positive half wave to initiate the charge of the condenser. As mentioned previously the applied voltage will be directly proportional to the number of revolutions of the flywheel but will reach maxim'umvalue at-a certain number of revolutions whereafter a voltage reduction will take place due to the increased number of cycles. In order to achieve a sufficient igniting effect during low speeds, i.e. during idling and particularly during starting, it is obviously a matter of paramount interest to bring about as high a charging voltage as possible also during low speeds. However, a limit is established by the mere physical voltage development of the positive half wave which cannot be exceeded and which prevents starting speeds Iower than about 500 revolutions per minute from being achieved.

Through the present invention, which is based on the fact that also the negative half wave yet without rectification is used for charging the condenser, this limitation is eliminated so that a reliable start may be obtained also at, for example, 200 revolutions per minute even if the spark plug should be heavily soiled.

The characterizing features of the invention will appear from the attached claims.

An embodiment of the invention is described hereafter by reference to the enclosed drawings.

current in the form of a mechanical breaking and closing switch. 1

FIG. 2 shows the same circuit diagram as FIG. 1, however, having the control member constructed as an electronic circuit comprising a thyristor and a trigger coil with a diode connected in series.

FIG. 3 shows a diagram indicating the relationship between voltage and number of revolutions from a generator coil of the system as illustrated in respectively FIGS. 1 and 2.

FIG. 4 shows a diagram of the charging voltage from a generator coil belonging to the system according to respectively FIGS. 1 and 2 to a condenser, a negative, diode-controlled half wave and a positive half wave being illustrated.

FIG. 5 is a diagram showing in relation to time the ignition voltage emanating from an ignition coil provided in the system according to respectively FIGS. 1 and 2.

In FIGS. 1 and 2 a generator coil 1 having an iron core 2 is connected by a first terminal to ground at 3 and by another terminal to a branch point 4. From branch point 4 a line extends to a first diode 5 and another line to a second diode 6. This latter diode is connected to ground at 7. The first diode 5 is connected to another branch point 8. Both diodes 5 and 6 are adapted to conduct current in a direction indicated by the arrow in the diode symbols and to block flow of current in the opposite direction. In FIG. 1 a line extending from branch point 8 leads to a mechanical control member generally designated as 9 and comprising a contact arm 10 adapted respectively to open and close a line 11 connected to ground at 12. Contact arm 10 is operated by a cam member 29 provided on the motor shaft and firmly connected thereto and rotating therewith, the construction of the contact arm 10 and cam member being such that for every ignition the cam by means of contact arm 10 brings about a breaking and closing action between branch point 8 and ground connection 12. The closing action in this case takes place in the exact instant when the ignition in the cylinder is to be performed. According to the invention the breaking action is to take place at an instant defined below.

In FIG. 2there is shown an alternative embodiment of the conrol member comprising a thyristor 13 which is connectedto ground at a point 14; Opening and closing of thyristor 13 is determined by a current pulse from a trigger coil 15 provided with an iron core 15' and by means of a terminal connected to ground at 16 and by another terminal connected to a branch point 17 via a diode 17'. In accordance with conventional practice a predetermined resistance 18 is connected between point 17 and the line connecting thyristor l3 and ground connection 14, resistor 18 determining the voltage from trigger coil 15 at which the thyristor 13 will respectively break and close the current in the direction from brach point 8 to ground connection 14.

It is also possible to determine opening and closing of the thyristor by means of two or more trigger coils 15, whereby it is possible to obtain a greater variation of the control action.

In both FIGS. 1 and 2 a condenser 19 is connected on the one hand to branch point 8 and on the other hand to a branch point 20. An ignition coil generally designated as 23 and having an iron core 24 is attached by means of one terminal from a primary winding 21 and one terminal from a secondary winding 22 to branch point 20. Another terminal from primary winding 21 is connected to ground at 25 and another terminal from secondary winding 22 is connected to an electrode 26 insulated in relation to ground and belonging to a surface spark plug generally designated as 27 the other electrode 28 of which is connected to ground.

It appears from FIGS. 1 and 2 that the exemplary systems shown are identical except as far as the control members are concerned. In both cases the generator coil 1 is so disposed in the rotating field emanating from a flywheel conventionally comprising permanent magnets, that an alternating current is produced in the generator coil 1. In the alternative embodiment according to FIG. 2 trigger coil 5 must be suitably disposed in the rotating field of the flywheel in such a way that the required voltage change acting respectively to open and to close the thyristor is obtained in the exactly correct instance of time required by the invention.

The voltage generated in the generator coil 1 is dependent on the number of revolutions of the flywheel in a way fundamentally shown in FIG. 3 in which a curve A indicates the voltage along an axis V independence of the number of revolutions along an axis n. Within a first range of numbers of revolutions -n, the voltage quickly goes up to a maximum value V, of for example 500 volts and thereafter decreases slightly due to the increase of the inductance in the coil circuit caused-by the increased cycle number.

The voltage wave which is generated upon every complete magnetic field passage in the generator coil is illustrated in FIG. 4 by a curve generally designated as B, the time T being indicated on an x-axis and the voltage being plotted on a y-axis. A negative half wave is designated as B, and a positive half wave as B, the provision being made as far as the negative half wave B, is concerned that the second diode 6 is completely disconnected from the circuit of the generator coil ll. In such a case the two half waves B, and B, will be fully congruent but inverted. By the current-directing effect from the other diode 6, provided this diode is connected as shown in respectively FIGS. 1 and 2, the circuit comprising the second diode 6 and the generator coil l is closed, the negative half wave B, producing a current via the diode through the generator coil ll causing the voltage to be reduced as fundamentally indicated by curve B in FIG. 4. This current and the voltage reduction produced are dependent on the windings of the coil, the dimensions of the wire, the iron core etc. and may be varied within certain limits. It is also possible to achieve by outer resistors or similar devices such an adaptation that the most appropriate course of curve B in respect to the invention is obtained.

It appears from respectively FIGS. 1 and 2 that the charging of condenser 19, irrespective of the course of the voltage according to curves B, and B, respectively, will start only in the instant when control member 9 and 13 respectively will be opened, for when the control member is closed a current passes through the first diode 5 directly to ground connection 12. Another condition which must be fulfilled in order that charging shall take place is of course that the change of voltage for curves B and B, respectively has the right direction for diode 5, i.e. increases with time (and thus has a positive slope according to FIG. 4).

According to the invention the control member 9 and 13 respectively open at or immediately after the instant when curve B has arrived at its negative maximum, i.e.

point P, in FIG. 41. The charging voltage to condenser 19 will then obtain a voltage contribution V, which is added to the maximum voltage V, of the positive half wave. Moreover, the interval of time between the opening point P, and the ensueing closing of the control member is so chosen that condenser 19 is enabled to receive the total voltage sum V V When the control member 9 and 13 respectively again closes discharge of the condenser 19 takes place via control member 9 and ll3 respectively, ground connection 12 and 14 respectively and ground connection 25 through the primary winding 21 to ignition coil 23 via branch point 20. This discharge generates a voltage pulse in the secondary windng 22 and produces a spark in surface spark plug 27 having the properties as described previously.

The voltage development during discharge is illustrated in FIG. 5 as a function of time, the voltage V being plotted along an y-axis and time T along a x-axis. A solid line curve 13;, represents a normal voltage development during a spark-over in the spark plug, a maximum value V,,possibly being found at 18 to 20 kilovolts. A broken curve B indicates the voltage marginally present with a voltage top V of for example 30 kilovolts.

Dueto the fact that according to the invention the charging of the condenser 19 is started within the range of the negtive half wave B FIG. 4, the above mentioned, particularly desirable technical features effects effects, as far as reliable ignition at low idling speeds and low starting speeds are realized. This is shown in FIG. 3 by a curve A, representing the charge voltage of condenser 19 in the arrangement according to the invention, whereas curve A, indicates the charging voltage in conventional systems. Voltage curve A increases more quickly than voltage curve A, to such an extent that the required charging voltage V, is obtained at a starting speed n, in curve A, which may be less than half the starting speed n for curve A,.

In addition the important fact is to be observed that the voltage development of the negative half wave, curve 8,, FIG. 4, only insignificantly is dependent on the number of revolutions which means that the voltage sum V V never can reach values dangerous for diode 5.

The practical adaptation of the invention to the mechanical control member 9 is simple to perform and in volves shaping the cam controlling contact arm in such a way that contact arm 10 will respectively open and close the circuit as described.

In an analogous way, in the electronic control member according to FIG. 2, the trigger coil 15 is arranged so that the diode will respectively open and close at the described moments.

Practical tests performed with a device according to the invention have given excellent results. By deliberate total soiling, such as by application of thick gear box oil or similar material, the spark plug has been brought into such a condition that starting with the aid of ordinary condenser ignition systems has been possible only at 500 to 600 revolutions per minute. With the aid of the device according to the invention, a complety reliable start has been achieved at speeds as low as 200 revolutions per minute. Moreover, fully reliable idling has been achieved at low speeds. Thus, the invention involves an important progress on the field of capaci-' tive ignition as applied to flywheel magneto igniting apparatus.

What is claimed is: 1. A flywheel magneto ignition system for an internal combustion engine, comprising:

a. means on the flywheel having a magnetic field with at least one pole rotatable about the flywheel axis; b. a generator coil disposed in the rotatable magnetic field and inductively responsive thereto to provide at least one negative half-wave and positive halfwave as each said pole passes thereby; c. a first diode connected to said generator coil; d. a second diode connected across said generator coil and oriented to conduct current pulses blocked by said first diode;

rent from said coil as rectified by said first diode;

f. an ignition coil having a primary winding in circuit with the other side of said capacitor, and having a secondary winding;

g. a spark plug of the surface type connected in circuit with said secondary winding; and

h. a control member actuated in response to flywheel rotation for controlling current flow to said capacia capacitor connected at one side to receive cur-.

tor and said primary winding, said control member being synchronized with the rotating field to initiate charging of the capacitor when a voltage pulse conducted by said second diode has just reached its maximum potential.

2. A system according to claim 1 in which said control member is a switch controlled by a cam on the flywheel shaft and synchronously rotating therewith.

3. A system according to claim 2 in which the cam is shaped to open said switch to initiate said charging and to close said switch when said capacitor is fully charged and ignition is to take place.

4. A system according to claim 1 in which said control member comprises:

a. a thyristor,

b. a third diode, and

c. at least one trigger coil disposed in said rotatable field and connected in series with each other.

5. A system according to claim 4 in which said trigger coil is so disposed in the rotatable field as to open said thyristor to initiate said charging and to close said thyristor when said capacitor is fully charged and ignition is to take place.

Claims (5)

1. A flywheel magneto ignition system for an internal combustion engine, comprising: a. means on the flywheel having a magnetic field with at least one pole rotatable about the flywheel axis; b. a generator coil disposed in the rotatable magnetic field and inductively responsive thereto to provide at least one negative half-wave and positive half-wave as each said pole passes thereby; c. a first diode connected to said generator coil; d. a second diode connected across said generator coil and oriented to conduct current pulses blocked by said first diode; e. a capacitor connected at one side to receive current from said coil as rectified by said first diode; f. an ignition coil having a primary winding in circuit with the other side of said capacitor, and having a secondary winding; g. a spark plug of the surface type connected in circuit with said secondary winding; and h. a control member actuated in response to flywheel rotation for controlling current flow to said capacitor and said primary winding, said control member being synchronized with the rotating fiEld to initiate charging of the capacitor when a voltage pulse conducted by said second diode has just reached its maximum potential.

2. A system according to claim 1 in which said control member is a switch controlled by a cam on the flywheel shaft and synchronously rotating therewith.

3. A system according to claim 2 in which the cam is shaped to open said switch to initiate said charging and to close said switch when said capacitor is fully charged and ignition is to take place.

4. A system according to claim 1 in which said control member comprises: a. a thyristor, b. a third diode, and c. at least one trigger coil disposed in said rotatable field and connected in series with each other.

5. A system according to claim 4 in which said trigger coil is so disposed in the rotatable field as to open said thyristor to initiate said charging and to close said thyristor when said capacitor is fully charged and ignition is to take place.

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