US3842817A

US3842817A - Capacitive discharge ignition system

Info

Publication number: US3842817A
Application number: US00282654A
Authority: US
Inventors: M Mallory
Original assignee: Mallory Electric Corp
Current assignee: Mallory Inc; Mallory Electric Corp
Priority date: 1972-08-22
Filing date: 1972-08-22
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22
Also published as: US4141331A

Abstract

A capacitive discharge ignition system is provided for use in connection with a magneto power supply. A time delay circuit is provided to delay discharge of the capacitor until it is completely charged by a pulse of electrical energy being emitted from the magneto.

Description

1 Wed States Patent 1 32422817 Mallory, Jr. Oct. 22, 1974 [5 1 CAPACITIVE DISCHARGE IGNITION 3,500,809 3/1970 Hohne et a1 123/148 E SYSTEM 3,545,420 12/1970 Foreman 123/148 E 3,612,948 10/1971 Minks 123/148 E Inventor: Marlon o y, J Carson i y, 3,636,936 1/1972 Schuette.. 123/148 E Nev. 3,667,441 6/1972 Cavil 123/148 E [73] Ass gneez Mallory Electric Corporation, 3,704,701 12/1972 Struber 123/148 E Carson Clty Primary Examiner-Charles J. Myhre [22] Filed: Aug. 22, 1972 Assistant ExaminerC0rt Flint [21] A I NO 282 654 Attorney, Agent, or FirmWhittemore, Hulbert &

Belknap [52] US. Cl. 123/148 E, 123/149 R, 123/149 C 57 A S [51] Int. Cl. F02p 3/06 [58] Field of Search 123/149 R 149 D 149 c A P System Pmvded for 123/148E use in connection with a magneto power supply. A time delay circuit is provided to delay discharge of the [56] References Cited capacitor until it is completely charged by a pulse of electrical energy being emitted from the magneto. UNITED STATES PATENTS 3,461,851 8/1969 Stephens 123/148 E 3 2 Drawmg Flgures CAPACITIVE DISCHARGE IGNITION SYSTEM BACKGROUND OF THE INVENTION Magneto ignition systems for internal combustion engines are widely used for motorcycles and snowmobiles. The magneto ignition systems in use are generally adapted to operate in conventional fashion. The magneto, which is a type of generator, induces a voltage in a primary winding which is inductively coupled to a secondary winding to form a step-up transformer. Initially, current is permitted to flow in the primary winding to build up an electrical field thereabout. When the field reaches a certain pre-selected value, the circuit through the primary winding is suddenly opened, resulting in the field collapsing and inducing a sparking voltage in the secondary winding.

More recently, capacitive discharge ignition systems have come into favor. In a capacitive discharge system, a capacitor is charged to a pre-selected voltage. The capacitor is then suddenly discharged through the primary winding of an output coil. A sparking voltage is induced in the secondary winding of the coil upon the build-up of the field about the primary winding as opposed to being induced upon the collapse of the field in the primary winding. One advantage of a capacitive discharge system is that the sparking voltage is obtained more rapidly than is the case in conventional ignition systems. This is advantageous in that by reaching a peak voltage sooner, there is more chance that the spark plug will fire because there is not sufficient time for leakage and dissipation of electrical energy about a fouled spark plug. Additional advantages occur in the permissible range of timing which is realized with a capacitive discharge system.

The present invention permits utilization of the primary circuit of the magneto as the power supply in a capacitive discharge ignition system.

SUMMARY OF THE INVENTION A capacitive discharge ignition system for an internal combustion engine is provided. A capacitor is connected to the primary winding of a magneto and is charged thereby. An ignition coil having a primary winding and a secondary winding is provided. The primary winding of the coil is connected between ground and thecapacitor. A controlled rectifier is connected between the capacitor and ground from a point on the opposite side of the capacitor from the connection of the capacitor to the primary winding of the coil. The controlled rectifier, capacitor and primary winding of the coil form a series circuit. A time delay circuit is connected between the magneto primary winding and the gate electrode of the controlled rectifier. The time delay circuit provides a signal to the gate electrode to trigger ,the controlled rectifier into a conducting state upon a pulse of electrical energy of a selected polarity being emitted from the magneto to charge the capacitor. The signal is delayed for a sufficient time to permit complete charging of the capacitor.

IN THE DRAWING:

FIG. 1 is an electrical schematic view of one embodiment of a capacitive discharge ignition system in accordance with the present invention; and

FIG. 2 is a partial electrical schematic view of a modified version of the right hand portion of the circuitry shown in FIG. 1.

Referring to FIG. 1, it will be noted that the capacitive discharge ignition system 10 is adapted for use in connection with a magneto 12 power supply. A magneto is a generator having a permanent magnet 14 supplying the magnetic field. The magnet 14 is a rotating member. A stationary, generally horseshoe-shaped ar- 0 mature 16 which surrounds the magnet 14 is fabricated of soft steel laminations. It is possible to provide a magneto with the stationary member being a magnet and having an armature of soft iron as the rotating member. A two-pole magnet has been illustrated. However, a four or six-pole rotor may be used as desired.

In the magneto 12, the north and south are the poles of a permanent-magnet rotating field. In the position shown, lines of flux pass from the north pole through the frame laminations 17 of the armature 16 and the core 18 of winding 20, thence through the frame lamination 22 and back to the south pole. The internal magnetic circuit is completed within the field from the south pole to the north pole. Rotation of the rotor results in inducing an emf in the winding 20 which varies from a maximum value to zero and then from zero to a maximum value with a reversal of direction every 180. The emf induced in the winding 20 is thus of a sinusoidal nature.

Normally, in operation of a magneto in a vehicle ignition system, a secondary winding is also provided on the core 18. The secondary winding is connected to spark plugs of an internal combustion engine via a distributor. A voltage is introduced into the secondary winding for firing of the spark plugs. The means for inducing a high spraking voltage in the normal magneto includes switching structure in the circuit of the primary winding 20. As will be noted, one side of the winding 20 is grounded via lead 24. The other side of winding 20 is connected, via lead 25, to a capacitor 26 and breaker points 28 which, via

leads

30, 32, are connected to ground and arranged in parallel. A manual switch 34 is connected from lead 25 to ground via lead 36. The function of switch 34 is to shunt the winding 20 to ground and thereby stop operation of the internal combustion engine.

In the normal operation of the magneto, the magneto armature 14 is driven via the internal combustion engine for which it is to supply sparking voltage. The engine is started either by manual or motorized cranking. Once the engine is started, it will continue operation until the switch 34 is closed.

The points 28 are repetitively opened and closed by means of a cam 38 which is driven in timed relationship to engine operation. Normally, the points 28 are maintained closed until the rotor poles have passed beyond the position as illustrated in FIG. 1. At this time the current rises rapidly to a maximum in winding 20. When the current is close to a maximum, the points 28 are opened by the cam 38, interrupting the circuit suddenly and causing a high emf to be induced in the secondary winding as a result of the collapsing field in the winding 20. This is sufficient for sparking purposes. The capacitor 26 across the points 28 absorbs, with little loss, the spark energy that otherwise appears at the points causing undesirable arcing of the points. The electrical energy absorbed by the capacitor 26 is fed back to the winding as a harmless oscillatory discharge.

The secondary winding usually provided on core 18 has not been shown in FIG. 1 because this winding is not used in accordance with the circuitry of the present invention. In the present invention, the energy created by the collapsing field of the winding 20 is stored in a capacitor 40 and then subsequently discharged rapidly through the primary winding 42 of a step-up output coil 44 to induce a high voltage in the secondary winding 46 for the purpose of providing a voltage at spark plug 48 sufficient for sparking purposes. In the coil 44, the high voltage in the secondary winding is created by the sudden surge of current upon discharge of capacitor 40 through the primary winding 42 which results in a rapidly developing field around the primary as opposed to the usual ignition system as above-described wherein the high voltage in the secondary is induced as a consequence of a collapsing field in a primary winding.

It is possible to obtain high voltage in a shorter time period by use of a capacitive discharge system as compared to a conventional system. Such is desirable from the standpoint of operation of spark plugs as, for example, it will cause the firing of even fouled spark plugs as a consequence of providing the high voltage in a short period of time to thus prevent leakage of electrical energy around the surfaces of the plugs which dissipates energy which otherwise would be available for sparking purposes.

The circuit to be described assumes that operation of the points 28 is such as to provide a positive pulse to the capacitor 26 upon opening. The circuit of FIG. 1 will work in connection with a system which receives both positive and negative pulses as where the points 28 are operated to open and close on both halves of rotation of the rotor or in a system wherein a sinusoidal output is achieved from a magneto without the use of points. However, the system of FIG. 1 is not designed to be used where only the negative pulse is available. The use of the term positive and negative is relative, it being appreciated that the circuit could be adapted for the use ofopposite polarity by substitution of appropriate circuit components.

A lead 50 is connected to lead at a point between the switch 34 and winding 20. The lead 50 extends to the capacitor 40. A diode 52 is provided in lead 50 before the capacitor 40. The function of diode 52 is to rectify the output of the winding 20 permitting only positive pulses to pass to the capacitor 40. As will be appreciated, if it were decided to have negative pulses only pass to the capacitor 40, the diode 52 could be reversed. The positive pulses which pass diode 52 charge the capacitor to the desired level. However, it is not desired to have the capacitor 40 discharge to primary winding 42 until such time as the complete charge is present thereon. Therefore, a time delay circuit is provided.

A small transformer 54 and controlled rectifier 62 are provided for this purpose. The primary winding 56 of the transformer is connected by lead 57 from the lead to ground at a point before the diode 52. The secondary winding 58 of the transformer is connected from ground to the gate 60 of controlled rectifier 62 via lead 76.

The controlled rectifier 62 is a solid state four-layer NPNP semi-conductor. In its normal state, the controlled rectifier acts as an open circuit that will not pass current. When an appropriate voltage or current pulse is applied to the gate electrode 60, it will cause the controlled rectifier to be forward biased to permit current flow. Application of the proper polarity voltage to the controlled rectifier will allow electrons to flow from the cathode 68 to anode 72. Reversal of the voltage polarity will result in the controlled rectifier being an open circuit. With the controlled rectifier conducting, application of reverse polarity to the gate electrode 60 will place the controlled rectifier in its original state of an open circuit. Thus, the controlled rectifier in the present circuit acts as a switching diode, capable of being switched on or off by appropriate pulses at the gate electrode 60.

As will be noted, the cathode 68 of the controlled rectifier is connected to lead 50 via lead 70 at a point between diode 52 and capacitor 40. The anode 72 is connected to ground via lead 74. As previously mentioned, the gate 60 is connected to one side of secondary winding 58 via lead 76. One side of primary winding 42 is connected to ground via lead 78. One side of the capacitor 40 is connected to the other side of winding 42 via lead 80. The secondary winding 46 of the coil 44 has a common connection via lead 82 to one side of the primary winding 42. The other side of winding 46 is connected to spark plug 48 via lead 84. The other side of the spark plug is connected to ground via lead 86.

In operation of the circuit, with the engine running, the points 28 open thus resulting in a collapsing field about the winding 20. The emf induced in winding 20 causes current to flow through lead 50, assuming a positive pulse, via diode 52 to charge capacitor 40. At the same time, a portion of the current flows through primary winding 56 of the small transformer 54. This results in a developing field about winding 56, which induces an emf in secondary winding 58. When this induced voltage is of sifficient value, it will pulse the gate 60 of controlled rectifier 62 to cause conduction of the controlled rectifier. The capacitor 40 will then have a complete circuit to ground and will discharge through the primary winding 42 of coil 44 thus inducing a high voltage in secondary winding 46 to cause sparking of spark plug 48.

The small time delay caused as a result of the time required for the rising field in primary winding 56 of transformer 54 to induce the necessary voltage in secondary winding 58 is sufficient to permit capacitor 40 to assume its full charge before being discharged. The controlled rectifier 62 is thus not triggered to conduct until such time as the proper charge has been placed on capacitor 40. The automatic nature of operation of transformer 54 is of great value in that its operation is inherent in its original design and therefore does not need adjustment during use of the ignition system.

As will be appreciated, the circuitry illustrated in FIG. 1 could be modified to permit utilization of the opposite sign pulse from the magneto 12. However, as a matter of convenience and commercial practicability, the circuit of FIG. 2 has been developed to permit usage of the circuit of FIG. 1 for negative pulses with minor modifications only. The only changes in the FIG. 2 circuit from that of FIG. 1 consists of providing a diode 88 in lead 74 beyond the connecting point of lead 78 and in switching the connections of

leads

78 and 80 to the opposite ends of primary winding 42. In the system shown in FIG. 2, it is desired to have an induced emf in secondary winding 46 of opposite polarity from that which would be attained in the FIG. 1 circuit. Consequently, reducing the connections of the primary winding 42 will result in reversing the polarity of the field developed about winding 42 to thus provide the induced emf of opposite polarity in winding 46. The diode 88 is provided as a protective device for the coil 44 which has been hooked up in a manner opposite from that originally intended. It is, of course, necessary to change the setting of points ,28 to provide for a positive pulse from magneto 12.

What I claim as my invention is:

l. A capacitive discharge ignition system for an internal combustion engine comprising a magneto including a winding, a capacitor having one side connected to the magneto winding to be charged thereby, an ignition coil having a primary winding and a secondary winding, the primary winding of the coil being connected between ground and the other side of the capacitor, a controlled rectifier connected between the capacitor and ground from a point on said one side of the capacitor whereby the controlled rectifier, capacitor and primary winding of the coil form a series circuit, a time delay circuit comprising a transformer including primary and secondary windings, said transformer primary winding being connected to the magneto winding, the transformer secondary winding be connected to the gate electrode of the controlled rectifier, the output of said magneto acting to charge the capacitor and pass through the transformer primary winding to develop an electrical field therearound, switch means to start the flow of current from the magneto through the transformer primary winding at a selected point in the operation of the magneto whereby the electrical field thereabout will induce an emf in the transformer secondary winding which will provide a signal to the gate electrode to trigger the controlled rectifier into a conducting state, thereby causing the capacitor to discharge through the primary winding of the coil to induce an emf in the coil secondary winding for ignition purposes, the creation of the signal from the transformer secondary winding being delayed a sufficient time as a consequence of the time necessary for it to be induced to permit desired additional charging of the capacitor after actuation of said switch means.

2. A capacitive discharge ignition system for an internal combustion engine as defined in claim 1, further characterized by the addition of a diode in the circuit between the primary winding of the coil and ground and reversal of the connections to the primary winding of the coil to alter the output of the coil secondary so as to provide a coil output of opposite polarity.

3. A capacitive discharge ignition system as defined in claim 1, further characterized in the provision of a diode between the capacitor and winding of the magneto to insure that only pulses of the selected polarity are passed to the capacitor.

Claims

1. A capacitive discharge ignition system for an internal combustion engine comprising a magneto including a winding, a capacitor having one side connected to the magneto winding to be charged thereby, an ignition coil having a primary winding and a secondary winding, the primary winding of the coil being connected between ground and the other side of the capacitor, a controlled rectifier connected between the capacitor and ground from a point on said one side of the capacitor whereby the controlled rectifier, capacitor and primary winding of the coil form a series circuit, a time delay circuit comprising a transformer including primary and secondary windings, said transformer primary winding being connected to the magneto winding, the transformer secondary winding be connected to the gate electrode of the controlled rectifier, tHe output of said magneto acting to charge the capacitor and pass through the transformer primary winding to develop an electrical field therearound, switch means to start the flow of current from the magneto through the transformer primary winding at a selected point in the operation of the magneto whereby the electrical field thereabout will induce an emf in the transformer secondary winding which will provide a signal to the gate electrode to trigger the controlled rectifier into a conducting state, thereby causing the capacitor to discharge through the primary winding of the coil to induce an emf in the coil secondary winding for ignition purposes, the creation of the signal from the transformer secondary winding being delayed a sufficient time as a consequence of the time necessary for it to be induced to permit desired additional charging of the capacitor after actuation of said switch means.