Title:
BREAKERLESS IGNITION SYSTEM
United States Patent 3646926
Abstract:
The breakerless ignition system is designed for use in connection with an internal combustion engine. A multistage transistor amplifier circuit is provided. The first stage of the amplifier includes a transistor which is biased to conduct when a photocell is energized. The photocell is energized by means of a light source in timed relation to engine operation. A capacitor is provided across the base collector of the first stage transistor to prevent inadvertent biasing thereof to conduct. The final stage of amplification includes a transistor which is normally biased to conduct. The primary winding of a step-up transformer is placed in the collector-emitter circuit of the final stage of amplification. When the transistor of the first stage of amplification is biased to conduct, the transistor of the final stage of amplification is placed in a nonconducting state to thereby cause collapse of the field in the primary winding with a resultant induced voltage in the secondary winding sufficient to fire the spark plugs of an internal combustion engine.


Inventors:
PLUME ALFRED JR
Application Number:
04/874509
Publication Date:
03/07/1972
Filing Date:
11/06/1969
Assignee:
Mallory Electric Corporation (Detroit, MI)
Primary Class:
Other Classes:
123/613, 123/652, 315/209R, 315/209T
International Classes:
F02P3/04; F02P3/045; F02P7/073; (IPC1-7): F02P3/02
Field of Search:
123/148E
View Patent Images:
US Patent References:
3422804IGNITION SYSTEM1969-01-21Van Mastrigt
3406672Spark ignition systems1968-10-22Phillips et al.
3390668Electronic ignition system1968-07-02Hufton
3324351Unit impulse ignition systems1967-06-06Pahl
3291110High voltage circuit for automobile engine ignition1966-12-13Peters
Primary Examiner:
Goodridge, Laurence M.
Assistant Examiner:
Flint, Cort
Claims:
What I claim as my invention is

1. A breakerless ignition system for an internal combustion engine comprising a DC power source, a multistage transistor amplifier circuit, the collector-emitter circuits of the transistors being in parallel across said power source, means interconnecting the base of each transistor after the first state transistor to the collector-emitter circuit of the preceding stage transistor whereby conduction of a transistor at one stage will place the base of the succeeding stage transistor at substantially ground potential to prevent conduction thereof, the number of stages being even whereby the final stage transistor and first stage transistor conduct alternately, a step-up transformer having a primary winding and a secondary winding, the primary winding being in the collector-emitter circuit of the final stage transistor, a voltage dividing network connected to the power source and to the base of the first stage transistor, the voltage available to said base via the network being insufficient to bias the first stage transistor to conduct, a photocell between the voltage dividing network and the base of the first stage transistor, said voltage dividing network comprising a resistor and a continuously conducting diode, in that order, in series between the power source and ground, the base of the first stage transistor being connected between the resistor and diode, a light source, means to repetitively impinge light from said light source onto the photocell in timed relation to engine operation to energize the photocell whereby the photocell will develop a voltage which is added to the voltage of the voltage dividing network to bias the first stage transistor to conduct, conduction of the first stage transistor resulting in cutoff of the final stage transistor and collapse of the magnetic field in said primary winding to induce a voltage in the secondary winding sufficient to fire a spark plug of an internal combustion engine.

2. The breakerless ignition system defined in claim 1, and further characterized in that a capacitor is provided across the base and collector of the first stage transistor to prevent application of stray voltages thereto and insure that the biasing voltage will be only that provided by the voltage dividing network and photocell.

3. A breakerless ignition system as defined in claim 1, and further characterized in the provision of a second diode connected between the base of the first stage transistor and a point between the voltage dividing network diode and ground, said second diode being arranged to conduct in an opposite direction from the voltage dividing network diode whereby to dissipate stray voltages which may be present in the circuitry of the first stage transistor.

4. A breakerless ignition system as defined in claim 1, and further characterized in that the biasing voltage for the base of the first stage transistor is substantially 0.67 volts, the voltage drop across the voltage dividing network diode being substantially 0.25 volts, and the voltage drop across the conducting photocell being substantially 0.45 volts.

Description:
BACKGROUND OF THE INVENTION

It has long been desired to provide a satisfactory breakerless ignition system for an internal combustion engine. The most commonly used ignition system in the past has been an electromechanical system which has been operated on the Kettering principle. This ignition system includes the familiar induction coil, the primary of which is connected to the vehicle battery and builds up a magnetic field. Power to the primary winding has been repetitively cut off, causing a collapse of the magnetic field with the result that a voltage of high magnitude has been developed in the secondary winding for firing of the spark plugs. Cutting off of the current to the primary winding has involved the use of a set of contact points with a capacitor placed across them to extend life by reducing flash between the points. The contacts have been opened and closed mechanically in order to interrupt the circuit of the primary winding of the transformer.

This system has had two basic faults. Firstly, it has been difficult to properly time the firing of the spark plugs and secondly repair and maintenance of such a system has been expensive.

Various circuits employing solid-state components have been proposed to replace, at least in part, the circuitry of the older ignition systems. Commonly, such transistorized ignition systems have required the use of mechanical contacts and a capacitor. Various magnetic systems have been proposed to eliminate the need for the mechanical breaker points. However, the use of magnetic switching has certain drawbacks such as the high cost of the magnetic pickup which must be used and the high tolerances which must be maintained in the magnetic pickup head.

In accordance with the present invention, a breakerless ignition system is proposed which utilizes the photocell principle. The photocell principle involves utilization of a photocell to bias a transistor to conducting and nonconducting states in a timed sequence. Photocell systems have been proposed in the past. However, none of the past systems has proved to be entirely satisfactory in practice. The present invention provides a photocell system which appears to be satisfactory in service under variable operating conditions.

SUMMARY OF THE INVENTION

A breakerless ignition system for an internal combustion engine is provided. The system includes a DC power source and a multistage transistor amplifier circuit. The collector-emitter circuits of the transistors are in parallel and are placed across the power source. Means interconnect the base of each transistor after the first stage transistor to the collector-emitter circuit of the preceding stage transistor whereby conduction of a transistor at one stage will place the base of the succeeding stage transistor at substantially ground potential to prevent conduction thereof. The number of stages of amplification is even whereby the final stage transistor and the first stage transistor conduct alternately. A step-up transformer having a primary winding and a secondary winding is provided. The primary winding is in the collector-emitter circuit of the final stage transistor. A voltage dividing network is connected to the power source and to the base of the first stage transistor. The voltage available to the base of the first stage transistor via the network is insufficient to bias the first steps transistor to conduct. A photocell is connected between the voltage dividing network and the base of the first stage transistor. A light source is provided to energize the photocell. Means to repetitively impinge light from the light source onto the photocell in timed relation to engine operation to energize the photocell are provided. Energization of the photocell will develop a voltage which is added to the voltage of the voltage dividing network to bias the first stage transistor to conduct. Conduction of the first stage transistor results in cutoff of the final stage transistor and collapse of the magnetic field in the primary of the transformer to induce a voltage in the secondary of the transformer sufficient to fire a spark plug. A capacitor is provided across the base and collector of the first stage transistor to insure that the first stage transistor will be biased to conduct only when the photocell is energized.

IN THE DRAWING

FIG. 1 is a view in perspective of a distributor illustrating one physical embodiment of the breakerless distributor amplifier of the present invention with parts broken away for the purpose of clarity; and

FIG. 2 is a schematic illustration of the breakerless distributor amplifier of the present invention.

Referring first to the circuit illustrated in FIG. 2, it will be noted that DC power for the circuit is provided by means of a battery 10 which may be the usual vehicle battery. One side of the battery 10 is grounded at 12. A lead 14 extends from the other side of the battery. A switch 16 is provided in the lead 14 to open and close the circuit. The switch 16 may be the conventional vehicle ignition switch.

A lead 18 extends from the lead 14 to ground. A lamp 20 is provided in the lead 18. A load resistor 22 is also provided in the lead 18. The function of the lamp 20 is to excite a photocell as will be hereinafter more fully explained.

Four transistors 24, 26, 28, 30 are connected in what may be considered four stages of amplification. Each of the transistors is connected in the common emitter configuration. The transistors are illustratively of the NPN type although PNP-type transistors may be used if desired.

The collector 32 of transistor 24 is connected to the lead 14 via lead 34. A load resistor 36, illustratively one-half watt and 2,200 ohms, is provided in the lead 34. The emitter 38 is connected to ground via lead 40. The base 42 is connected to a lead 44 via a lead 46. A photocell 48, preferably a photovoltaic photodiode, is provided in the lead 46. A load resistor 50, illustratively having a value of 4,700 ohms and one-half watt, is provided in the lead 44 between the lead 14 and the connection of lead 46. A diode 52 is provided in lead 44 between the connection of lead 46 and ground. The diode is connected in a manner to pass current between the lead 14, 44 and ground. A second diode 54 is connected from lead 46 to lead 44 at a point between the diode 52 and ground by means of a lead 56. The diode 54 is connected to pass current in a direction opposite to that of the diode 52. The diode 54 functions to dissipate stray voltages which may be present in the circuitry of the first stage transistor 24. A capacitor 58 is connected between the collector 32 and base 42 by means of a lead 60. The capacitor 58 functions to stabilize operation of the transistor 24.

The collector 62 of the transistor 26 is connected to the lead 14 via a lead 64. A load resistor 66, illustratively having a value of 1,000 ohms and one-half watt, is provided in the lead 64. The emitter 68 of transistor 26 is connected to ground via lead 70. The base 72 is connected to the collector 32 of transistor 24 via lead 74.

The collector 76 of transistor 28 is connected to lead 14 via lead 78. A resistor 80, illustratively having a value of 500 ohms and one-half watt, is provided in the lead 78. The emitter 82 of transistor 28 is connected to ground via lead 84. The base 86 is connected to the collector 62 of transistor 26 via lead 88.

The collector 92 of transistor 30 is connected to lead 14 via lead 94. The primary winding 96 of a step-up transformer 98 is connected in the lead 94. The secondary winding 100 is connected to a sparking device 102, such as the common spark plug of a vehicle engine, via lead 104. A distributor 106 is provided in lead 104 to direct the high voltage output of transformer 98 to the proper spark plug. The emitter 108 is connected to ground via lead 110. The base 112 is connected to the collector 76 of transistor 28 via lead 114.

The components of the circuit illustrated in FIG. 2 are mounted within the housing 116 of the distributor 106. The distributor 106 is of generally conventional design. The circuit illustrated in FIG. 2 is adapted to this design in order to avoid the necessity for provision of a specially designed distributor assembly to thereby permit application of the present invention to existing automotive distributor designs.

The housing 116 includes an enlarged open-ended cylindrical portion 118 which houses a rotor assembly 120 driven by a shaft 122. The shaft 122 extends through an elongated portion 124 wherein it is suitably journaled. A camshaft coupling 126 is provided at the outer end of shaft 122 for driving connection to the engine cam shaft. A centrifugal advance mechanism 128 is provided beneath the rotor 120. Elimination of the usual breaker points and condenser provides the necessary room for the circuit components. The circuit components are conveniently mounted within a housing 130 which is secured within the portion 118 adjacent to the interior periphery thereof. A cup-shaped shutter wheel 132 is mounted centrally of the housing portion 118 on the rotor 120 and rotates therewith. The wheel 132 has downwardly depending sidewall structure 134. A plurality of spaced apart slots 136 equal in number to the number of spark plugs in the vehicle engine are provided in the sidewall structure 134. The lamp 20 is positioned within the wheel 132. The photocell 48 is mounted in the housing 130 but is exteriorly visible so that it may receive light from the lamp 20 when one of the slots 136 is in registry therewith.

A distributor cap (not shown) is normally mounted on top of the housing 116. The cap is made of a plastic material designed to handle the high voltage present at the distributor and fits snugly over the housing 116 to keep moisture and dirt out of the housing interior. Contact terminals that lead to the spark plugs of each cylinder are provided within the housing 116 around the outer edge of the interior thereof. These terminals are connected to high voltage via a central terminal provided on the rotor.

Operation of the invention may now be understood. Referring to FIG. 2, with the switch 16 closed, the battery voltage is applied to leads 18, 44, 34, 64, 78 and 94. The lamp 20 is thus energized. Assuming the shutter wheel 132 to be in a position where one of the slots 136 is not in registry with the photocell 48, the photocell 48 will be deenergized and will not generate a voltage. The resistor 50 and diode 52 define a voltage dividing network with respect to the base 42 of transistor 24. The voltage drop across the diode 52 is insufficient to provide the necessary forward bias for conduction of the transistor 24. The voltage drop represented by the diode 52 is illustratively about 0.25 volts. The necessary voltage to forwardly bias transistor 24 is illustratively 0.67 volts. Therefore, transistor 24 will be in the off condition.

With transistor 24 in a nonconducting state, bias voltage is applied to the base 72 of transistor 26 thus biasing transistor 26 to the conducting condition. When saturation is reached, the voltage drop represented by the collector-emitter circuit of transistor 26 approaches zero. Consequently, virtually the entire voltage drop of the battery occurs across the resistor 66. The lead 88 which extends from base 86 of transistor 28 is at virtual ground potential. There is therefore not sufficient bias to cause conduction of transistor 28 and this transistor will be in the off condition.

With transistor 28 in the nonconducting condition, bias voltage is applied to the base 12 of transistor 30 causing this transistor to conduct. Conduction of transistor 30 causes current to flow through the primary winding 96 of transformer 98 thus establishing a field in the transformer.

When one of the slots 136 moves into registry with the photocell 48, the light impinging upon the photocell 48 excites the photocell and causes it to develop an operating voltage. The voltage developed by photocell 48 is illustratively 0.45 volts. This voltage, added to the voltage of diode 52, is sufficiently high to cause forward biasing of the transistor 24. Conduction of the transistor 24 will cause the transistor 26 to cease conducting because the junction of lead 74 and the lead 34 at a point between the collector 32 and resistor 36 will be at substantially ground potential as soon as the transistor 24 reaches saturation.

When the transistor 26 ceases to conduct, bias voltage is applied to the base 86 of the transistor 28 causing this transistor to conduct. Conduction of transistor 28 will cause cutoff of transistor 30 because the junction of lead 114 and lead 78 will approach ground potential as soon as transistor 28 reaches saturation. When the transistor 30 ceases to conduct, the field developed by the primary winding 96 of transformer 98 will collapse thus inducing a high voltage in the secondary winding 100 sufficient to cause firing of the sparking device 102. This voltage is distributed to the proper spark plug by means of the distributor 106.

In connection with operation of the circuit, it should be noted that the diode 54 functions to permit stray voltages, as from the stabilizing capacitor 58, to be dissipated. The capacitor 58 is important in the circuit in that it assures that the transistor 24 will conduct in exactly the manner required, it being appreciated that the small voltages involved are in delicate balance and misconduction of transistor 24 would cause failure of the entire system.