CONSTANT-ENERGY IGNITION SYSTEMS
United States Patent 3575154
A constant-energy ignition system controlled by a solid-state circuit having an emitter-follower current sensing unit in accordance with the current flowing through the ignition coil. A flywheel diode is connected between the coil and ground to maintain current through the coil just prior to ignition. Semiconductor switches are connected to the coil which are turned on and off by the current sensing unit to increase current through the coil a predetermined magnitude. Then the coil current source is turned off requiring the flywheel diode to permit current to flow through the coil for maintaining a substantially constant energy in the coil irrespective of engine speed. When the coil current amplitude has decreased to a second predetermined amplitude, coil current is again supplied through the switch.
US Patent References:
Internal combustion engine ignition system
Kirk et al. - July 1962 - 3046447
Transistorized ignition system
Guyton et al. - November 1966 - 3288125
Unit impulse ignition systems
Pahl, Jr. - June 1967 - 3324351
Internal combustion engine ignition system
Kirk et al. - July 1962 - 3046447
Transistorized ignition system
Guyton et al. - November 1966 - 3288125
Unit impulse ignition systems
Pahl, Jr. - June 1967 - 3324351
Application Number:
04/831534
Publication Date:
04/20/1971
Filing Date:
06/09/1969
View Patent Images:
Export Citation:
Assignee:
Motorola, Inc. (Franklin Park, IL)
Primary Class:
Other Classes:
315/209R, 315/209T
International Classes:
F02P3/05; F02P3/02; F02P3/02
Field of Search:
123/148E 315/209,214,219
Primary Examiner:
Goodridge, Laurence M.
Claims:
I claim
1. A control circuit for an ignition system with a current source, an ignition coil having an inductive primary winding having a battery end and a load end and capable of storing ignition energy, timing means for indicating spark time and a time period just preceding spark time, and a chassis ground,
2. The circuit of claim 1 further including pulser means connected to said switch means and responsive to the ignition system timing means to supply a spark indicating signal to said switch means, said sensing means being a portion of said switch means and said switch means being responsive to said spark indicating signal to electrically isolate said sensing means from any coil current.
3. The circuit of claim 2 wherein said inertia means is operative during said spark indicating signal duration to complete a discharge path for ignition current generated by the coil electric field flowing through the ignition system.
4. The circuit of claim 3 wherein said inertia means is connected between the winding battery end and the chassis ground.
5. The circuit of claim 4 wherein said inertia means is a unidirectional current conducting device poled to conduct current with respect to the winding in said first direction.
6. The circuit of claim 2 further including an inductance means in said pulser means receiving current from said switch means every time said switch means selectively supplies current and operative to maintain current flow in said pulser means during periods of nonconduction by said switch means.
7. The circuit of claim 6 wherein said switch means includes a first semiconductor device having first and second primary electrodes and a control electrode with the control electrode connected to said pulser means for receiving signals therefrom,
8. The circuit of claim 7 wherein said switch means includes a second semiconductor device having third and fourth primary electrodes and a control electrode connected to said current control means for receiving said actuating signals,
9. The circuit of claim 6 wherein said pulser means includes a transistor device having a current gain of Beta, and
10. The circuit of claim 6 wherein said inductance means and the primary winding have substantially equal inductance to resistance ratios.
11. The circuit of claim 1 wherein said current sensing means comprises impedance means connected between the coil lead end and chassis ground for developing a voltage thereacross indicative of coil current magnitude,
12. The circuit of claim 11 further including a first semiconductor device electrically interposed between the winding load end and said impedance means and having a first control electrode,
13. The circuit of claim 12 wherein said pulser means comprises inductance means connected to said current switching semiconductor device and a second semiconductor device connected between said inductance means and said first semiconductor device control electrode and having a central electrode connected to the timing means with the timing means electrically effectively connecting chassis ground to said second semiconductor device control electrode during said time period and removing said chassis ground connection at spark time to make said second semiconductor device nonconductive.
14. The circuit of claim 12 wherein said inertia means comprises a unidirectional current conducting semiconductor device connected between the winding battery end and chassis ground and poled to conduct current with respect to the winding in the same direction as said selectively supplied current and wherein a circuit loop is formed including the primary winding, said unidirectional current conducting semiconductor device, said impedance means, said second semiconductor device and chassis ground.
15. The circuit of claim 11 wherein said current control circuit comprises first and second semiconductor devices each having one primary electrode connected to chassis ground, a central electrode and another primary electrode,
16. The circuit of claim 15 further including a current sensing control semiconductor device electrically interposed between the winding load end and said impedance means and having a control electrode, and
17. The circuit of claim 16 wherein said pulser means has an energy storing means receiving said selectively supplied current and said pulser means being operative to supply a continuous current to said current sensing central semiconductor device for keeping it continuously current conductive and responsive to the timing means indicating spark time to actuate said current sensing control semiconductor device to current nonconduction.
18. A vehicular ignition system wherein the vehicle has an engine with an ignition means, ignition timing means operative to indicate a time period just before spark time and spark time, a vehicular ground, a current source, an ignition coil connected to the ignition means, and having a primary winding with battery and load ends,
1. A control circuit for an ignition system with a current source, an ignition coil having an inductive primary winding having a battery end and a load end and capable of storing ignition energy, timing means for indicating spark time and a time period just preceding spark time, and a chassis ground,
2. The circuit of claim 1 further including pulser means connected to said switch means and responsive to the ignition system timing means to supply a spark indicating signal to said switch means, said sensing means being a portion of said switch means and said switch means being responsive to said spark indicating signal to electrically isolate said sensing means from any coil current.
3. The circuit of claim 2 wherein said inertia means is operative during said spark indicating signal duration to complete a discharge path for ignition current generated by the coil electric field flowing through the ignition system.
4. The circuit of claim 3 wherein said inertia means is connected between the winding battery end and the chassis ground.
5. The circuit of claim 4 wherein said inertia means is a unidirectional current conducting device poled to conduct current with respect to the winding in said first direction.
6. The circuit of claim 2 further including an inductance means in said pulser means receiving current from said switch means every time said switch means selectively supplies current and operative to maintain current flow in said pulser means during periods of nonconduction by said switch means.
7. The circuit of claim 6 wherein said switch means includes a first semiconductor device having first and second primary electrodes and a control electrode with the control electrode connected to said pulser means for receiving signals therefrom,
8. The circuit of claim 7 wherein said switch means includes a second semiconductor device having third and fourth primary electrodes and a control electrode connected to said current control means for receiving said actuating signals,
9. The circuit of claim 6 wherein said pulser means includes a transistor device having a current gain of Beta, and
10. The circuit of claim 6 wherein said inductance means and the primary winding have substantially equal inductance to resistance ratios.
11. The circuit of claim 1 wherein said current sensing means comprises impedance means connected between the coil lead end and chassis ground for developing a voltage thereacross indicative of coil current magnitude,
12. The circuit of claim 11 further including a first semiconductor device electrically interposed between the winding load end and said impedance means and having a first control electrode,
13. The circuit of claim 12 wherein said pulser means comprises inductance means connected to said current switching semiconductor device and a second semiconductor device connected between said inductance means and said first semiconductor device control electrode and having a central electrode connected to the timing means with the timing means electrically effectively connecting chassis ground to said second semiconductor device control electrode during said time period and removing said chassis ground connection at spark time to make said second semiconductor device nonconductive.
14. The circuit of claim 12 wherein said inertia means comprises a unidirectional current conducting semiconductor device connected between the winding battery end and chassis ground and poled to conduct current with respect to the winding in the same direction as said selectively supplied current and wherein a circuit loop is formed including the primary winding, said unidirectional current conducting semiconductor device, said impedance means, said second semiconductor device and chassis ground.
15. The circuit of claim 11 wherein said current control circuit comprises first and second semiconductor devices each having one primary electrode connected to chassis ground, a central electrode and another primary electrode,
16. The circuit of claim 15 further including a current sensing control semiconductor device electrically interposed between the winding load end and said impedance means and having a control electrode, and
17. The circuit of claim 16 wherein said pulser means has an energy storing means receiving said selectively supplied current and said pulser means being operative to supply a continuous current to said current sensing central semiconductor device for keeping it continuously current conductive and responsive to the timing means indicating spark time to actuate said current sensing control semiconductor device to current nonconduction.
18. A vehicular ignition system wherein the vehicle has an engine with an ignition means, ignition timing means operative to indicate a time period just before spark time and spark time, a vehicular ground, a current source, an ignition coil connected to the ignition means, and having a primary winding with battery and load ends,
Description:
BACKGROUND OF THE INVENTION
This invention relates to ignition systems and particularly to a solid-state constant-energy ignition system having a controlled current through the ignition coil.
Many forms of solid-state ignition systems have been constructed. Several such systems require a starting ballast for protecting semiconductor units. Also, some of the ignition systems are quite expensive to implement. A problem occurs in automotive ignition systems in that at the higher speeds a reduced spark potential is generated due to capacitive and inductive delays in the ignition system. SUch reduced ignition voltage reduces the efficiency of the engine. Further, at idle speeds the alternator output may be marginal causing reduced ignition voltage and engine starting difficulties. In conventional ballast resistor approaches to ignition systems there are required undesirably high currents under hot start conditions. Such design problems have been the subject of many sophisticated compromises and each of those mentioned above create problems of practical significance in a particular design. Such problems stem from the fact that the energy stored in the ignition coil varies with operating conditions.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a vehicular constant-energy ignition system.
It is a further object of this invention to provide a constant-energy controlled current ignition system.
A feature of this invention includes a constant-energy semiconductor-type constant-energy switching circuit connected to the primary winding of an ignition coil. The switching circuit or switch is under control of a current sensor which senses the current magnitude in the ignition primary coil and turns the constant-energy switch on and off in accordance with the magnitude through the coil. A flywheel diode is connected between the coil and ground such that when the constant-energy switch is turned off, current may still flow through the primary winding.
After a given magnitude of current is flowing through the ignition primary coil, the constant-energy switch is turned off. As a result, the current through the coil decays to a minimum value at which time the current sensor turns the switch back on for supplying coil current.
At the appropriate time for ignition, the breaker points are closed in the usual manner which disconnects the constant energy circuit from the coil with the energy stored in the coil being discharged through the distributor and ignition system of the engine and through the flywheel diode.
THE DRAWING
FIG. 1 is a combined block in schematic form of one embodiment of the present invention.
FIG. 2 is a graph illustrating typical waveforms used to explain the operating of the FIG. 1 embodiment.
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
Referring now to FIG. 1, there is illustrated in block-schematic form an engine 10 which synchronously drives a distributor 11 and a timing mechanism, such as breaker points 12, as indicated by the dotted lines 13 and 14, respectively. Lines 15, 16, 17, and 18 represent the ignition wires from the distributor to the engine, the engine being shown as a four-cylinder engine, no limitation thereto intended. The usual ignition coil 19 having a primary winding 20 and a secondary winding 21 is shown connected to distributor 11 in the usual manner. Vehicular battery 22 is the current source for the ignition system; the battery being selectively connected thereto by ignition switch 23. The control circuits illustrating the present invention include the constant energy switch 24 having a pair of switching semiconductor devices 25 and 26 connected respectively on opposite ends of the primary winding 20. The constant energy switch is turned on and off by current control circuit 27 which receives coil 20 current magnitude indicating signal over line 28 from current-sensing emitter-follower resistor 29 connected to the emitter electrode of transistor 26. Transistor 26 provides two functions, one, permitting current flow in winding 20, and two, providing a path for coil current to current sensing resistor 29. It is understood that all switching control may be accomplished at one end of the ignition primary.
At time of ignition, the breaker points 12 open which actuates pulser 30 to effectively electrically open the electrical path, including circuit 24 and primary winding 20. At this time distributor 11 has made electrical connection to one of the ignition wires 15, 16, 17, or 18 and the energy in ignition coil 19 rapidly discharges therethrough causing an ignition spark in the ignition means (not shown) of engine 10. The discharge circuit from coil 19 is through distributor 11, thence over one of the ignition wires 15, 16, 17, or 18; through the ignition means of engine 10 to vehicular ground. The other end of the ignition coil 19 is connected through circuit inertia or flywheel diode 31 to complete the circuit to chassis ground. It is understood that other semiconductor units may be substituted for the flywheel diode 31, such as a silicon control rectifier or transistor, and the like, so long as it is a unidirectional current conducting device operating as described herein.
The control circuits 24, 27, 30, and 31 cooperate with the ignition means of engine 10 to provide a constant energy for each spark discharge. The operation of the circuit is best understood by reference to FIG. 2 in which winding 20 coil current typical waveforms are shown. The above-referenced control circuits are operative upon the closure of breaker points 12 to cause current to flow through primary coil 20 as indicated by waveform 32. Current amplitude increases to a predetermined amplitude. Upon reaching that amplitude, a voltage is generated by the coil current flowing through current sensing resistor 29, such voltage being supplied over line 28 to current control circuit 27. Current control circuit 27 responds to such voltage indicating the desired maximum coil current amplitude to supply a switching control signal over line 33 to turn constant energy switch 24 off, i.e., nonconductive. At this time current stops flowing from battery current source 22 to coil 20. It is desired to keep current flowing through coil 20; therefore, current inertia diode 31 is connected to the battery end 34 of primary winding 20. Upon cessation of battery 22 current, the field of ignition coil 19 starts to collapse causing a circulatory current to flow from primary winding 20 through transistor switch 26, current sensing resistor 29, and thence returning to coil 20 through current or circuit inertia diode 31 via vehicular chassis ground. As the field collapses, the current amplitude is reduced as indicated by the decreasing amplitudes 35 of wave 32. Upon reaching a predetermined lower amplitude, as indicated by the dotted line 36 of FIG. 2, the voltage on line 28 reactuates current control circuit 27 to supply an actuating signal over line 33 to rapidly turn constant energy switch 24 back on to again supply current to primary coil 20. As a result, the current in winding 20 then begins to increase until the maximum current amplitude is again reached, whereupon the just-described cycle is repeated. Such repetition results in the sawtooth waveform at the upper portion of waveforms 32 of FIG. 2 with winding 20 current amplitude oscillating in a zone of current amplitudes between lines 36 and 38. Such control of winding 20 current provides storage of a constant energy in coil 19. It is preferred that points 12 open upon current 32 amplitude reaching maximum amplitude 38, such as indicated at 39 in FIG. 2.
At the appropriate time, the breaker points 12 are opened by engine 10 which deactivates pulser 30 such that transistor 26 of circuit 24 becomes nonconductive. At this time, the predetermined constant energy stored in the coil 19 field collapses to provide the ignition spark through the above-described circuit.
By keeping the oscillating or chopping action of the constant energy switch 24 to be of relatively small magnitude, as indicated in FIG. 2, the energy stored in coil 19 can be kept substantially constant irrespective of the engine speed or battery voltage.
For example, the dwell time of breaker points can vary over a substantial duration without adversely affecting the supply of controlled current in winding 20. Further, the energy stored in coil 19 may be selected such that the battery voltage 22 will not adversely affect the energy stored therein.
For supplying primary winding 20 coil 19 current, constant energy switch 24 receives current from battery 22 over line 41, thence the current is passed through the semiconductor switch 25 to line 42, thence to the battery end 34 of primary winding 20. Switch 25 has resistors 43 and 44 in the base electrode circuit which are connected to control line 33 for receiving the actuating on-off signals from current control circuit 27. The signal on line 33 may be of the rectangular waveform type for rapidly turning switch 25 on and off to minimize power dissipation therein. The load end 45 of primary winding 20 is connected to the collector electrode of transistor switch 26 which in turn supplies the winding 20 current to sensing resistor 29. Transistor 26 is maintained in a current conducting state the entire period of time that breaker points 12 are closed, i.e., during dwell. Switch 26 breaks the circuit to primary winding 20 when breaker point 12 opens. To this end, pulser 30, later described, is connected to the base or control electrode of transistor 26 over line 46.
At ignition or spark time, when breaker points 12 are opened, semiconductor switch 26 is quickly made current nonconductive which effectively disconnects the constant energy switch circuit 24 from primary winding 20. It should be noted that when switch 26 is nonconductive, ground reference potential is supplied over line 28 to circuit 27 which actuates current control circuit 27 to make switch 25 current conductive.
Current control circuit 27 has a pair of NPN transistors 50 and 51, both in the grounded emitter configuration. Collector supply resistor 52 is connected to the collector of transistor 50 and also to the base electrode of transistor 51. The indicating signal from the current sensing resistor 29 is supplied through resistor 53 to circuit junction 54. The RC current 55, 56 provides a controlled time of response of circuit 27 by introducing an RC delay at junction 54. Diode 57 is connected between the collector electrode of transistor 51 and circuit junction 54. When the voltage on line 28 and thence junction 54 is reduced by the decreasing current through coil 20, diode 57 isolates such voltage from the collector of transistor 51 and biases transistor 50 to current nonconduction. The voltage from battery 22 is supplied through resistor 52, making transistor 51 conductive. The collector load of transistor 51 is through resistors 43 and 44, shown in the constant-energy switch circuit 24, as well as the base electrode of transistor 25. As transistor 51 begins to conduct current, switch 25 is turned on, thereby starting to increase current flow through winding 20 which, in turn, increases the voltage on line 28. As the voltage potential on junction 54 increases (maximum amplitude is limited by diode 57), the conductivity of transistor 50 switches to current conduction, reducing the voltage on its collector to switch transistor 51 to a nonconductive state. At this time, the voltage on the base electrode of transistor 25 is increased, turning that transistor off, whereupon the above-described cycle is repeated.
Pulser 30 includes transistor 60, having a base control circuit, including resistors 61 and 62, connected to the breaker points 12. With breaker points 12 open, the base circuit is also open, with transistor 60 being forced to current nonconduction. When points 12 close, transistor 60 is turned on. The collector load circuit of transistor 60 is the base circuit of transistor 26 in constant energy switch 24. Transistor 60 emitter current is supplied through choke 63 which improves operation of the circuit, as will be later described. Choke 63 is connected over line 65 to the collector electrode of transistor switch 25 and, therefore, receives current only when the primary winding 20 current is increasing. Choke 63 is used to store energy in its field and serves to provide a continuous drive current to the pulser 30 for keeping transistor 26 continuously conductive during dwell time of breaker points 12. Choke 63 is particularly useful when low gain transistors are used in the ignition control circuit. Choke 63 is also used to shape the current from transistor 60 to that of wave 32; that is, the rising waveform of the base drive current of transistor 26 is the same as that of the primary winding 20. Such matching conserves current. Therefore, it is desired that the ratio of the ignition coil primary winding 20 inductance to the choke 63 inductance should be approximately equal to Beta B of the driven transistor 60. Also, the inductance-to-resistance ratio of choke 63 should approximate the inductance-to-resistance ratio of the coil primary winding 20. Diode 64 is provided to clamp oscillations from choke 63 during turn on and turn off of current for voltage protection of the semiconductor devices.
To control the voltage of the load end 45 of winding 20 to ground for the protection of transistors 25 and 26, capacitor 66 is connected thereto as shown. During dwell time of points 12, capacitor 66 is charged to a desired potential; then at spark time when points 12 open, the voltage at load end 45 is limited to the capacitor voltage. Generally, the smaller the capacitor 66 the higher the voltage at end 45.
This invention relates to ignition systems and particularly to a solid-state constant-energy ignition system having a controlled current through the ignition coil.
Many forms of solid-state ignition systems have been constructed. Several such systems require a starting ballast for protecting semiconductor units. Also, some of the ignition systems are quite expensive to implement. A problem occurs in automotive ignition systems in that at the higher speeds a reduced spark potential is generated due to capacitive and inductive delays in the ignition system. SUch reduced ignition voltage reduces the efficiency of the engine. Further, at idle speeds the alternator output may be marginal causing reduced ignition voltage and engine starting difficulties. In conventional ballast resistor approaches to ignition systems there are required undesirably high currents under hot start conditions. Such design problems have been the subject of many sophisticated compromises and each of those mentioned above create problems of practical significance in a particular design. Such problems stem from the fact that the energy stored in the ignition coil varies with operating conditions.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a vehicular constant-energy ignition system.
It is a further object of this invention to provide a constant-energy controlled current ignition system.
A feature of this invention includes a constant-energy semiconductor-type constant-energy switching circuit connected to the primary winding of an ignition coil. The switching circuit or switch is under control of a current sensor which senses the current magnitude in the ignition primary coil and turns the constant-energy switch on and off in accordance with the magnitude through the coil. A flywheel diode is connected between the coil and ground such that when the constant-energy switch is turned off, current may still flow through the primary winding.
After a given magnitude of current is flowing through the ignition primary coil, the constant-energy switch is turned off. As a result, the current through the coil decays to a minimum value at which time the current sensor turns the switch back on for supplying coil current.
At the appropriate time for ignition, the breaker points are closed in the usual manner which disconnects the constant energy circuit from the coil with the energy stored in the coil being discharged through the distributor and ignition system of the engine and through the flywheel diode.
THE DRAWING
FIG. 1 is a combined block in schematic form of one embodiment of the present invention.
FIG. 2 is a graph illustrating typical waveforms used to explain the operating of the FIG. 1 embodiment.
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
Referring now to FIG. 1, there is illustrated in block-schematic form an engine 10 which synchronously drives a distributor 11 and a timing mechanism, such as breaker points 12, as indicated by the dotted lines 13 and 14, respectively. Lines 15, 16, 17, and 18 represent the ignition wires from the distributor to the engine, the engine being shown as a four-cylinder engine, no limitation thereto intended. The usual ignition coil 19 having a primary winding 20 and a secondary winding 21 is shown connected to distributor 11 in the usual manner. Vehicular battery 22 is the current source for the ignition system; the battery being selectively connected thereto by ignition switch 23. The control circuits illustrating the present invention include the constant energy switch 24 having a pair of switching semiconductor devices 25 and 26 connected respectively on opposite ends of the primary winding 20. The constant energy switch is turned on and off by current control circuit 27 which receives coil 20 current magnitude indicating signal over line 28 from current-sensing emitter-follower resistor 29 connected to the emitter electrode of transistor 26. Transistor 26 provides two functions, one, permitting current flow in winding 20, and two, providing a path for coil current to current sensing resistor 29. It is understood that all switching control may be accomplished at one end of the ignition primary.
At time of ignition, the breaker points 12 open which actuates pulser 30 to effectively electrically open the electrical path, including circuit 24 and primary winding 20. At this time distributor 11 has made electrical connection to one of the ignition wires 15, 16, 17, or 18 and the energy in ignition coil 19 rapidly discharges therethrough causing an ignition spark in the ignition means (not shown) of engine 10. The discharge circuit from coil 19 is through distributor 11, thence over one of the ignition wires 15, 16, 17, or 18; through the ignition means of engine 10 to vehicular ground. The other end of the ignition coil 19 is connected through circuit inertia or flywheel diode 31 to complete the circuit to chassis ground. It is understood that other semiconductor units may be substituted for the flywheel diode 31, such as a silicon control rectifier or transistor, and the like, so long as it is a unidirectional current conducting device operating as described herein.
The control circuits 24, 27, 30, and 31 cooperate with the ignition means of engine 10 to provide a constant energy for each spark discharge. The operation of the circuit is best understood by reference to FIG. 2 in which winding 20 coil current typical waveforms are shown. The above-referenced control circuits are operative upon the closure of breaker points 12 to cause current to flow through primary coil 20 as indicated by waveform 32. Current amplitude increases to a predetermined amplitude. Upon reaching that amplitude, a voltage is generated by the coil current flowing through current sensing resistor 29, such voltage being supplied over line 28 to current control circuit 27. Current control circuit 27 responds to such voltage indicating the desired maximum coil current amplitude to supply a switching control signal over line 33 to turn constant energy switch 24 off, i.e., nonconductive. At this time current stops flowing from battery current source 22 to coil 20. It is desired to keep current flowing through coil 20; therefore, current inertia diode 31 is connected to the battery end 34 of primary winding 20. Upon cessation of battery 22 current, the field of ignition coil 19 starts to collapse causing a circulatory current to flow from primary winding 20 through transistor switch 26, current sensing resistor 29, and thence returning to coil 20 through current or circuit inertia diode 31 via vehicular chassis ground. As the field collapses, the current amplitude is reduced as indicated by the decreasing amplitudes 35 of wave 32. Upon reaching a predetermined lower amplitude, as indicated by the dotted line 36 of FIG. 2, the voltage on line 28 reactuates current control circuit 27 to supply an actuating signal over line 33 to rapidly turn constant energy switch 24 back on to again supply current to primary coil 20. As a result, the current in winding 20 then begins to increase until the maximum current amplitude is again reached, whereupon the just-described cycle is repeated. Such repetition results in the sawtooth waveform at the upper portion of waveforms 32 of FIG. 2 with winding 20 current amplitude oscillating in a zone of current amplitudes between lines 36 and 38. Such control of winding 20 current provides storage of a constant energy in coil 19. It is preferred that points 12 open upon current 32 amplitude reaching maximum amplitude 38, such as indicated at 39 in FIG. 2.
At the appropriate time, the breaker points 12 are opened by engine 10 which deactivates pulser 30 such that transistor 26 of circuit 24 becomes nonconductive. At this time, the predetermined constant energy stored in the coil 19 field collapses to provide the ignition spark through the above-described circuit.
By keeping the oscillating or chopping action of the constant energy switch 24 to be of relatively small magnitude, as indicated in FIG. 2, the energy stored in coil 19 can be kept substantially constant irrespective of the engine speed or battery voltage.
For example, the dwell time of breaker points can vary over a substantial duration without adversely affecting the supply of controlled current in winding 20. Further, the energy stored in coil 19 may be selected such that the battery voltage 22 will not adversely affect the energy stored therein.
For supplying primary winding 20 coil 19 current, constant energy switch 24 receives current from battery 22 over line 41, thence the current is passed through the semiconductor switch 25 to line 42, thence to the battery end 34 of primary winding 20. Switch 25 has resistors 43 and 44 in the base electrode circuit which are connected to control line 33 for receiving the actuating on-off signals from current control circuit 27. The signal on line 33 may be of the rectangular waveform type for rapidly turning switch 25 on and off to minimize power dissipation therein. The load end 45 of primary winding 20 is connected to the collector electrode of transistor switch 26 which in turn supplies the winding 20 current to sensing resistor 29. Transistor 26 is maintained in a current conducting state the entire period of time that breaker points 12 are closed, i.e., during dwell. Switch 26 breaks the circuit to primary winding 20 when breaker point 12 opens. To this end, pulser 30, later described, is connected to the base or control electrode of transistor 26 over line 46.
At ignition or spark time, when breaker points 12 are opened, semiconductor switch 26 is quickly made current nonconductive which effectively disconnects the constant energy switch circuit 24 from primary winding 20. It should be noted that when switch 26 is nonconductive, ground reference potential is supplied over line 28 to circuit 27 which actuates current control circuit 27 to make switch 25 current conductive.
Current control circuit 27 has a pair of NPN transistors 50 and 51, both in the grounded emitter configuration. Collector supply resistor 52 is connected to the collector of transistor 50 and also to the base electrode of transistor 51. The indicating signal from the current sensing resistor 29 is supplied through resistor 53 to circuit junction 54. The RC current 55, 56 provides a controlled time of response of circuit 27 by introducing an RC delay at junction 54. Diode 57 is connected between the collector electrode of transistor 51 and circuit junction 54. When the voltage on line 28 and thence junction 54 is reduced by the decreasing current through coil 20, diode 57 isolates such voltage from the collector of transistor 51 and biases transistor 50 to current nonconduction. The voltage from battery 22 is supplied through resistor 52, making transistor 51 conductive. The collector load of transistor 51 is through resistors 43 and 44, shown in the constant-energy switch circuit 24, as well as the base electrode of transistor 25. As transistor 51 begins to conduct current, switch 25 is turned on, thereby starting to increase current flow through winding 20 which, in turn, increases the voltage on line 28. As the voltage potential on junction 54 increases (maximum amplitude is limited by diode 57), the conductivity of transistor 50 switches to current conduction, reducing the voltage on its collector to switch transistor 51 to a nonconductive state. At this time, the voltage on the base electrode of transistor 25 is increased, turning that transistor off, whereupon the above-described cycle is repeated.
Pulser 30 includes transistor 60, having a base control circuit, including resistors 61 and 62, connected to the breaker points 12. With breaker points 12 open, the base circuit is also open, with transistor 60 being forced to current nonconduction. When points 12 close, transistor 60 is turned on. The collector load circuit of transistor 60 is the base circuit of transistor 26 in constant energy switch 24. Transistor 60 emitter current is supplied through choke 63 which improves operation of the circuit, as will be later described. Choke 63 is connected over line 65 to the collector electrode of transistor switch 25 and, therefore, receives current only when the primary winding 20 current is increasing. Choke 63 is used to store energy in its field and serves to provide a continuous drive current to the pulser 30 for keeping transistor 26 continuously conductive during dwell time of breaker points 12. Choke 63 is particularly useful when low gain transistors are used in the ignition control circuit. Choke 63 is also used to shape the current from transistor 60 to that of wave 32; that is, the rising waveform of the base drive current of transistor 26 is the same as that of the primary winding 20. Such matching conserves current. Therefore, it is desired that the ratio of the ignition coil primary winding 20 inductance to the choke 63 inductance should be approximately equal to Beta B of the driven transistor 60. Also, the inductance-to-resistance ratio of choke 63 should approximate the inductance-to-resistance ratio of the coil primary winding 20. Diode 64 is provided to clamp oscillations from choke 63 during turn on and turn off of current for voltage protection of the semiconductor devices.
To control the voltage of the load end 45 of winding 20 to ground for the protection of transistors 25 and 26, capacitor 66 is connected thereto as shown. During dwell time of points 12, capacitor 66 is charged to a desired potential; then at spark time when points 12 open, the voltage at load end 45 is limited to the capacitor voltage. Generally, the smaller the capacitor 66 the higher the voltage at end 45.