US3237620A - Semiconductor ignition system - Google Patents

Description

March 1, 1966 L. R. HETZLER ETAL 3,237,620

SEMICONDUCTOR IGNITION SYSTEM Filed Aug. 28, 1963 INVENTOR5 LEWIS R. HETZLER BROOKS H.5H RT THEIR ATTORNEY United States Patent 3,237,620 SEMICONDUCTOR IGNITION SYSTEM Lewis R. Hetzl-er and Brooks H. Short, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Aug. 28, 1963, Ser. No. 305,098 14 Claims. (Cl. 123-148) This invention relates to a semiconductor ignition system and more particularly to a semiconductor ignition system which has the feature of reducing the amount of power required to operate it.

In certain types of semiconductor ignition systems, it has been well known practice to connect a semiconductor such as a transistor in series with the primary winding of an ignition coil. The conduction of the semiconductor is controlled in synchronism with operation of the engine by breaker contacts, magnetic pick-ups or by other suitable means. In some of these ignition systems, the semiconductor such as the transistor is normally biased to conduct by the battery and is only turned off for short periods of time when ignition is required.

Although these systems provide good ignition timing, they have the dis-advantage that the on time of the transistor is such that a considerable amount of current may be wasted. Thus when the engine is operating at low speed, the transistor or semiconductor may be turned on for a length of time that is greater than that required for proper build-up of magnetic flux in the ignition coil with a consequent waste of power.

In contrast to the above described ignition systems, it is an object of this invention to provide an ignition system wherein the interval of time that the primary circuit of the ignition coil is energized is maintained substantially constant at both high and low speeds of the engine.

Still another object of this invention is to provide a semiconductor ignition system wherein a semiconductor such as a transistor controls the current flow through the primary winding of an ignition coil and wherein means are provided for maintaining the on time of the semiconductor or transistor substantially constant at different engine speeds.

A further object of this invention is to provide a semiconductor ignition system wherein a semiconductor such as a transistor controls primary winding current and wherein this transistor or semiconductor is switched on by an engine driven timing device and is switched off by an electric timing circuit which maintains a predetermined constant time interval between the turn-on and turn-off of the semiconductor.

Still another object of this invention is to provide a semiconductor ignition system wherein a semiconductor such as a transistor controls primary winding current and wherein the semiconductor is triggered into conduction by a magnetic pick-up device and is switched off at a predetermined time interval following its beginning of conduction by an RC timing circuit which provides a constant time interval of turn-on regardless of the speed that the magnetic pick-up is driven.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

The single figure drawing is a schematic circuit diagram of a semiconductor system made in accordance with this invention.

Referring now to the drawing, the reference numeral generally designates an ignition coil which is used to provide ignition pulses for an internal combustion engine. The ignition coil 10 has a primary winding 12 "ice and a secondary winding 14 which are magnetically coupled in the usual manner. One side of the secondary winding 14 is connected directly to ground as shown. The opposite side of the secondary winding 14 is connected with a rotor contact 16 which cooperates with the electrodes 18 of a conventional distributor cap 20.

The rotor contact 16 is driven by the engine 22. The electrodes 18 of the distributor cap 20 are connected respectively with one side of the spark plugs 24 which are used to ignite the combustible mixture of the internal combustion engine 22. In the drawing, a four cylinder engine has been shown but it will be appreciated that this invention can be used with engines having six, eight or more cylinders.

The ignition system of this invention employs a semiconductor switch means which in this case takes the form of an NPN transistor 26. The collector electrode of transistor 26 is connected with junction 28 which is also connected to one side of the primary winding 12. The emitter electrode of transistor 26 is connected with junction 30. A diode 32 is connected between junction 30 and ground and it is seen that a capacitor 34 connects the junctions 28 and 30 and is therefore connected across the emitter and collector electrodes of the transistor 26.

The ignition system has another semiconductor switch means which takes the form of an NPN transistor 36. The collector electrode of transistor 36 is connected with junction 38. A resistor 40 is connected between junctions 38 and 42. The junction 42 is connected with the base electrode of transistor 26 and a resistor 44 is connected between junction 42 and ground.

The emitter electrode of transistor 36 is connected directly to ground as shown. The base electrode of transistor 36 is connected with junction 46. The junction 46 is connected with junction 48 via the conductor 50. A capacitor 52 is connected between the junctions 48 and 28.

The direct current power source for the ignition system of this invention is illustrated as a battery 54. The negative side of the battery is connected to ground whereas the positive side of the battery is connected to one side of a manually operable ignition switch 56. The opposite side of the ignition switch is connected with conductor 58.

A resistor 60 is connected between conductor 58 and the junction 48. Another resistor 62 connects the conductor 58 with the junction 38. A resistor 64 connects the conductor 58 with one side of the primary 12 of the ignition coil 10.

Although the direct current source 54 has been shown as a battery, it will be appreciated that on passenger cars and on certain other vehicles, a generator is provided which supplies ignition power and charges the battery when the engine is being driven at a predetermined speed. When cranking the engine, the battery 54 supplies the ignition power and will supply ignition power when the generator does not develop a voltage sufiicient to charge the battery.

The ignition system of this invention has an engine driven timing device generally designated by reference numeral 70. This ignition timing device includes a rotor 72 which is formed of magnetic material and which is driven by the engine 22. The four arms of the rotor 72 control the flow of magnetic flux through a core element 74 which is formed of magnetic material. A pick-up coil 76 is wound on the core 74 and magnetic flux is caused to flow through the magnetic core 74 by a source of magnetic flux which takes the form of a permanent magnet 78.

In actual practice, the magnetic pick-up 70 and the distributor cap 20 may be built into one unit and rotation of the motor contact 16 is synchronized with the rotation of the rotor 72 and both of these elements are driven by the engine 22.

It will be appreciated that as the rotor 72 rotates, the reluctance of the magnetic circuit is varied depending upon whether or not the arms of the rotor are aligned with the tips 78a and 78b of the core 74. The voltage that is induced in the pick-up coil 76 will therefore vary as the ends of the arms of the rotor 72 become aligned and then go out of alignment with the tips 78a and 78b of the core 74. The voltage that is generated in the pick-up coil 76 will be an alternating voltage due to variation in the reluctance of the magnetic cricuit as the rotor 72 rotates.

One side of the pick-up coil 76 is connected to ground as shown while the opposite side of this pick-up coil is connected to one side of a diode 80. The opposite side of the diode 80 is connected with junction 46.

When the ignition switch 56 is closed, the ignition sys tem of this invention is energized. Current can now flow from conductor 58, through resistor 60, through junction 48, through conductor 50, through junction 46, through diode 80 and then through the pick-up coil 76 to ground. Assuming that there is no voltage generated at this time in the pick-up coil 76, the transistor 36 will be biased to a conductive condition in its emitter-collector circuit because the junction 46 is positive with respect to ground due to' the voltage drop across diode 80 and the pick-up coil 76. When the transistor 36 switches on in its collector-emitter circuit, current flows from conductor 58, through resistor 62, and then through the collector-emitter circuit of the transistor 36 to ground. The resistor 62 limits the current flow to a predetermined value through the transistor 36.

With transistor 36 in a conductive condition, the junction 42 and the base of transistor 26 will be at a potential which biases the emitter and base electrodes of the transistor 26 such that the transistor 26 will be nonconductive in its collector-emitter circuit and no current can flow under this condition through the primary winding 12.

When the transistor 36 is biased to conduct as when the junction 46 is positive with respect to ground, the capacitor 52 will be charged with the polarity indicated on the drawing. The charging circuit for the capacitor is from conductor 58, through resistor 64, through primary winding 12, through the capacitor 52, through junction 48, through conductor 50 and then through the base-emitter circuit of transistor 36. It can be seen from the foregoing that when the transistor 36 is biased to a conductive condition by the battery 54, the capacitor 52 has an opportunity to charge to a potential of the polarity shown on the drawing.

As the rotor 72 rotates, the time will come when a pulse of voltage is generated in the pick-up coil 76 which is positive on its grounded side and negative on its side connected with the cathode of diode 80. A voltage of this :polarity will drive the emitter of transistor 36 positive with respect to its base or at least equal to the potential of its base to cause the transistor 36 to switch off in its emitter-collector circuit. When the transistor 36 switches off in its collector-emitter circuit, current will flow from conductor 58, through resistor 62, through resistor 40 and then through resistor 44 to ground. In effeet, the resistors 62, 40 and 44 are now a voltage divider and a voltage drop will be developed across resis tor 44 which is positive at junction 42. The voltage developed across resistor 44 will bias the transistor 30 to its conductive state between its collector and emitter and current can flow from conductor 58, through resistor 64, through primary 12, through junction 28, through the collector-emitter circuit of transistor 26 and then through the diode 32 to ground.

From the foregoing, it can be seen that current will begin to flow through the primary winding 12 whenever a voltage is induced in the pick-up coil 76 which is of such a polarity as to switch off the transistor 36 and switch on the transistor 26.

The transistor 36 will continue to be switched off and the transistor 26 will continue to be switched on even though the voltage in the pick-up coil 76 now goes to zero or reverses. The transistor 36 is maintained in a nonconductive condition by the potential accumulated by the capacitor 52 of the polarity shown on the drawing. Thus, the charge on the capacitor 52 is such as to drive the base of transistor 36 negative to maintain it in a nonconductive condition for a predetermined length of time.

The length of time that the transistor 36 can be maintained nonconductive and the transistor 26 conductive is determined by the values of the resistor 60 and the capacitor 52 and is determined by the RC time constant of these two elements. The capacitor 52 discharges through the collector-emitter circuit of transistor 26, through diode 32, through battery 54, through the ignition switch 56 and then through the resistor 60 to the opposite side of the capacitor 52. When the energy stored in the capacitor 52 has been dissipated to the point where the junction 46 goes positive with respect to ground, the transistor 36 will be switched back on causing the transistor 26 to be immediately switched oif. When transistor 26 switches off, a high voltage is induced in the secondary winding 14 which causes one of the spark plugs 24 to be fired through the rotor contact 16 and one of the distributor electrodes 18.

From the foregoing, it will be apparent that transistor 26 is switched on when a voltage of the proper polarity is induced in the pick-up coil 76. The transistor 26 is then not switched oil until the charge accumulated by the capacitor 52 has been reduced to a predetermined value. Since the discharging time of capacitor 52 is constant as determined by the RC time constant of the resistor 60 and the capacitor 52, the time interval that the transistor 26 is switched on will remain constant to provide a constant on time for the primary circuit of the ignition system regardless of engine speed.

It will be appreciated that the switching on of the transistor 26 is initiated by the generation of a voltage in the pick-up coil 76 of the proper polarity and is terminated at a fixed time after initiation as determined by the RC time constant of resistor 60 and capacitor 52. The magnetic pick-up 70 therefore has no etiect in terminating the on time of the transistor 26 since this is accomplished by the electric RC timing circuit.

The output voltage of the magnetic pick-up 70 must have pulses that are spaced a suflicient interval of time which is at least as great as the constant on time of the transistor 26. In other words, once the transistor 26 is switched on, the system should operate to maintain this transistor switched on for a time determined by the RC time constant of resistor 60 and capacitor 52. During this interval of time, it is important that no voltage pulses be induced in the pick-up coil 76 that might switch the transistor 36 off and prolong the time interval that transistor 26 is switched on over and above the time set by resistor 60 and capacitor 52. For this reason, it is important that the pulses developed in pick-up coil 76 which switch transistor 36 off be spaced in time an amount greater than the RC time constant of the resistor 60 and capacitor 52.

The diode 80 being connected in series with the pickup coil 76 prevents voltage pulses which are negative at ground and positive at the cathode of diode 80 from triggering the transistor 36.

While the embodiments of the present invention as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. An ignition control unit adapted to be connected with the primary of an ignition coil, with an engine driven timing device and with a source of direct current comprising, first and second transistors, said first transistor being adapted to be connected in series with the primary winding of an ignition coil, means interconnecting said transistors whereby said first transistor is driven conductive when said second transistor is biased to a nonconductive condition, said second transistor being adapted to be connected with an engine driven timing device which is capable of causing said second transistor to be biased to a nonconductive condition, and a timing circuit connected with said second transistor for causing said second transistor to remain in a nonconductive condition for a predetermined fixed time following the biasing of said second transistor to its nonconductive state.

2. The ignition control unit according to claim 1 wherein the timing circuit includes a resistor and capacitor having apredetermined RC time constant.

3. The ignition control unit according to claim 1 wherein the base electrode of the first transistor is connected with the collector electrode of the second transistor.

4. An ignition system for an internal combustion engine comprising, an ignition coil having a primary winding and a secondary winding,.a source of direct current, a first transistor having emitter, collector and base electrodes, means connecting the emitter and collector electrodes of said first transistor in series with said primary winding of said ignition coil and in series with said source of direct current, a second transistor having emitter, collector and base electrodes, an engine driven timing device connected with the base electrode of said second transistor and operative to cause said second transistor to be biased to a nonconductive condition, an RC timing circuit energized from said source of direct current when said second transistor is biased to a conductive state, said RC timing circuit being connected with the base electrode of said second transistor whereby said second transistor is maintained in a nonconductive condition for a predetermined length of time once it is switched to this condition by said engne driven timing devce, and means connecting the collector electrode of said second transistor with the base electrode of said first transistor.

5. An ignition system for an internal combustion engine comprising, first and second transistors, an ignition coil having a primary winding and a secondary winding, a source of direct current, means connecting the emitter and collector electrodes of said first transistor in series with said source of direct current and in series with said primary winding of said ignition coil, an engine drven timing device, means connecting the emitter and base electrodes of said second transistor with said engine driven timing device, a first circuit connected across said source of direct current including the emitter and collector electrodes of said second transistor, a second circuit connected in parallel with the emitter and collector electrodes of said second transistor, means connecting the base electrodes of said first transistor with said second circuit, and an RC timing circuit connected with the base electrode of said second transistor for maintaining said second transistor in a nonconductive condition for a time corresponding to the RC time constant of said RC timing circuit and following the biasing of said second transistor to its nonconductive state by said engine driven timing device.

6. An ignition system for an internal combustion engine, first and second transistors each having emitter, collector and base electrodes, an ignition coil having a primary winding and a secondary winding, a source of direct current, means connecting said primary winding and the emitter and collector electrodes of said first transistor in series with said source of direct current, an engine driven magnetic timing device having an output coil, a diode, a first current path connected across said source of direct current including the collector and emitter electrodes of said second transistor, a second current path connected across said source of direct current including in a series connection said diode and said output coil, said diode and output coil being connected across said base and Q emitter electrodes of said second transistor, means connecting the collector electrode of said second transistor with the base electrode of said first transistor, and a capacitor connecting the base electrode of said second transistor and the collector electrode of said first transistor, said capacitor being charged through the primary winding of said ignition coil and through the emitter and base circuit of said second transistor when said second transistor is biased to a conductive condition by the voltage generated in said output coil, the voltage accumulated by said capacitor maintaining said second transistor in a nonconductive condition for a predetermined fixed time following the biasing of said second transistor to its nonconductive condition by the voltage generated in said output coil.

7. An ignition system for an internal combustion engine comprising, first and second transistors, an ignition coil having a primary winding and a secondary winding, a source of direct current, a magnetic pick-up device having an output coil driven by said engine, means connecting said primary winding, the emitter and collector electrodes ofsaid first transistor and said source of direct current in a series circuit, means connecting said first and second transistors in such a manner that said first transistor is switched to a conductive state when said second transistor is switched to a nonconductive state, means connecting said output coil with said second transistor, and an electric timing circuit for maintaining said second transistor in its nonconductive state after it has been switched to this state by a voltage generated in said output coil, said timing circuit maintaining said second transistor in its nonconductive state for a fixed time which is independent of engine speed.

8. The ignition system according to claim 7 wherein the electric timing circuit is an RC network.

9. The ignition system according to claim 7 wherein the electric timing circuit includes a capacitor which is connected between the base electrode of said second transistor and a circuit that connects the collector electrode of the first transistor and one side of the primary winding of said ignition coil.

10. The ignition system according to claim 7 wherein a diode and said output coil are connected across said emitter and base electrodes of said second transistor.

11. An ignition system for an internal combustion engine comprising, first and second conductor means adapted to be connected with a source of direct current, an ignition coil having a primary winding and a secondary winding, a semiconductor switching device, means connecting said primary winding and said semiconductor switching in series across said conductors, an engine driven control means, a bias circuit controlled in synchronism with operation of said engine driven control means connected with said semiconductor switching device, said bias circuit being operative to bias said semiconductor switching device to a conductive condition when said engine driven control means is in a pre determined position, and a timing circuit coupled to said bias circuit, said timing circuit being operative through said bias circuit to maintain said semiconductor switching device in a conductive condition for a predetermined fixed length of time following the initiation of its conduction and independently of engine speed.

12. An ignition system for an internal combustion engine comprising, first and second conductor means adapted to be connected across a source of direct current, an ignition coil having a primary winding, first and second semiconductor switching devices, means connecting said first semiconductor switching device and said primary winding in series and across said source of direct current, a first bias circuit for said first semiconductor switching device connected across said conductor means and operative to bias said first semiconductor switching device to a nonconductive condition, a second biasing circuit for said second semiconductor switching device connected across said conductor means and operative to bias said second semiconductor switching device to a conductive condition, means interconnecting said first semiconductor switching device and said second switching device whereby said first semiconductor switching device is switched to a conductive condition 'when said second semiconductor switching device is biased to a nonconductive condition, means driven in synchronism with said engine for periodically biasing said second semiconductor switching device to a nonconductive condition, and a timing circuit including a capacitor for maintaining said second semiconductor switching device nonconductive for a predetermined length of time following the biasing of said second semiconductor switching device to its nonconductive state.

13. An ignition system for an internal combustion engine comprising, first and second conductor means adapted to be connected across a source of direct current, an ignition coil having a primary winding, first and second transistors, means connecting the emitter and collector of said first transistor and said primary winding of said ignition coil in' series with said conductor means, a biasing circuit connected across said conductor means and with the emitter and base of said first transistor for periodically biasing said first transistor to a nonconductive condition, means connecting the emitter and collector of said second transistor across said conductor means and in parallel with said biasing circuit, said second transistor when conductive shunting said biasing circuit to thereby bias said first transistor to a nonconductive condition, means connected with the emitter and base of said second transistor including means driven in synchronism with said engine 'for controlling the conduction of said second transistor, and a capacitor connected between the base of said second transistor and one of the emitter and collector electrodes of said first transistor, said capacitor being charged across said conductor means by current flow through the emitter-base circuit of said second transistor and being discharged through the emitter-collector circuit of said first transistor, said capacitor when discharging being operative to hold said second transistor in its nonconductive state for a length of time determined by the rate of discharge of said capacitor.

14. An ignition system for an internal combustion engine comprising, a source of direct current, first and second conductor means connected across a source of direct current, a semiconductor switching device, an ignition coil having a primary winding and a secondary winding, means connecting said semiconductor switching device and said primary winding in series across said conductor means, a biasing circuit connected with said conductor means and with said semiconductor switching device for biasing said semiconductor switching device to a nonconductive condition by said source of direct current, engine driven control means, and a control circuit coupling said engine driven control means and said semiconductor switching device, said control circuit being operative to periodically trigger said semiconductor switching device to a conductive condition, and timing means coupled to said control circuit and operative to maintain said semiconductor switching device in a conductive condition for a predetermined fixed time following the beginning of its conductive cycle and independently of engine speed.

References Cited by the Examiner UNITED STATES PATENTS 2,811,672 10/1957 Gilbert 123148 3,087,090 4/1963 Konopa 123148 MARK NEWMAN, Primary Examiner. RICHARD B. WILKINSON, Examiner.

Claims (1)

1. AN IGNITION CONTROL UNIT ADAPTED TO BE CONNECTED WITH THE PLURALITY OF AN IGNITION COIL, WITH AN ENGINE DRIVEN TIMING DEVICE AND WITH A SOURCE OF DIRECT CURRENT COMPRISING, FIRST AND SECOND TRANSISTORS, SAID FIRST TRANSISTOR BEING ADAPTED TO BE CONNECTED IN SERIES WITH THE PRIMARY WINDING OF AN IGNITION COIL, MEANS INTERCONNECTION SAID TRANSISTORS WHEREBY SAID FIRST TRANSISTOR IS DRIVEN CONDUCTIVE WHEN SAID SECOND TRANSISTOR IS BIASED TO A NONCONDUCTIVE CONDITION, SAID SECOND TRANSISTOR BEING ADAPTED TO BE CONNECTED WITH AN ENGINE DRIVEN TIMING DEVICE WHICH IS CAPABLE OF CAUSING SAID SECOND TRANSISTOR TO BE BIASED TO A NONCONDUCTIVE CONDITION, AND A TIMING CIRCUIT CONNECTED WITH SAID SECOND TRANSISTOR FOR CAUSING SAID SECOND TRANSISTOR TO REMAIN IN A NONCONDUCTIVE CONDITION FOR A PREDETERMINED FIXED TIME FOLLOWING THE BIASING OF SAID SECOND TRANSISTOR TO ITS NONCONDUCTIVE STATE.

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