FORCED FREQUENCY IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE

Abstract

An ignition system for an internal combustion engine has a power source, a transformer having first and second primary windings and a secondary winding, a connector extending from the secondary winding and adapted so as to connect with a terminal of the spark plug of the internal combustion engine, and electronic spark timing circuit cooperative with the transformer so as to activate and deactivate voltage to the first and second primary windings. The first and second primary windings are connected to the power source such that the transformer produces an alternating voltage output from the secondary winding of between 1 kHz and 100 kHz and a voltage of at least 20 kV. A forced push-pull inverter is cooperative with the electronic spark timing circuit so as to fix a frequency of voltage to the first and second primary windings.

Claims

1. An ignition system for an internal combustion engine comprising: a power source; a transformer having a first primary winding and a second primary winding and a secondary winding, said first and second primary windings connected to said power source such that said transformer produces an alternating voltage output from said secondary winding of between 1 kHz and 100 kHz and a voltage of at least 20 kv; a connector extending from said secondary winding, said connector adapted to connect with a terminal of a spark plug of the internal combustion engine; an electronic spark timing circuit cooperative with said transformer so as to activate and deactivate a voltage to said first and second primary windings; and a forced push-pull inverter cooperative with said electronic spark timing circuit so as to directly fix a frequency of voltage to said first and second primary windings.

2. (canceled)

3. The ignition system of claim 1, the fixed frequency being between 1 kHz and 100 kHz.

4. The ignition system of claim 1, said forced push-pull inverter comprising an astable oscillator.

5. The ignition system of claim 1, further comprising: an inverting gate-driver IC cooperative with said electronic spark timing circuit so as to transmit voltage relative to a timing pulse of said electronic spark timing circuit; a first field effect transistor connected to an output of said gate-driver IC, said first field effect transistor being switchable so as to transmit the alternating voltage to said first primary winding; and a second field effect transistor connected to an output of said gate-driver IC, said second field effect transistor being switchable so as to transmit the alternating voltage to said second primary winding.

6. An ignition system for an internal combustion engine comprising: a power source; a transformer having a first primary winding and a second primary winding and a secondary winding, said first and second primary windings connected to said power source such that said transformer produces an alternating voltage output from said secondary winding of between 1 kHz and 100 kHz and a voltage of at least 20 kv; a connector extending from said secondary winding, said connector adapted to connect with a terminal of a spark plug of the internal combustion engine; an electronic spark timing circuit cooperative with said transformer so as to activate and deactivate a voltage to said first and second primary windings, said electronic spark timing circuit passing a square wave of voltage to said electronic spark timing circuit, said electronic spark timing circuit producing a voltage pulse off of a falling edge of the square wave.

7. The ignition system of claim 6, said square wave ranging from 0 volts to 5 volts, a spark being generated to said secondary winding from said electronic spark timing circuit when the square wave falls from 5 volts to 0 volts.

8. The ignition system of claim 1, said alternating voltage output of said secondary winding being a spark having a continuous arc duration of between 0.5 millisecond and 5 milliseconds.

9. The ignition system of claim 1, further comprising: a voltage regulator circuit electrically connected between said power source and said electronic spark timing circuit so as to step down voltage from said power source.

10. The ignition system of claim 9, said voltage regulator establish a reference voltage of approximately 8 volts.

11. The ignition system of claim 5, said gate-driver IC inverting voltage so as to cause said first field effect transistor and said second field effect transistor to bias alternately.

12. The ignition system of claim 1, further comprising: a transient voltage suppressor electrically connected between said power source and said electronic spark timing circuit.

13. The ignition system of claim 1, said power supply comprising: a battery having a voltage between 5 volts and 15 volts.

14. An ignition system for an internal combustion engine comprising: a power source; a transformer having a first primary winding and a second primary winding and a secondary winding, said first and second primary windings connected to said power source such that said transformer produces an alternating voltage output from said secondary winding of between 1 kHz and 100 kHz and a voltage of at least 20 kV; a connector extending from said secondary winding, said connector adapted to connect with a terminal of a spark plug of the internal combustion engine; an electronic spark timing circuit cooperative with said transformer so as to activate and deactivate voltage to said first and second primary windings; a forced push-pull inverter cooperative with said electronic spark timing circuit so as to fix a frequency of voltage to said first and second primary windings, said electronic spark timing circuit passing a square wave of voltage to said electronic spark timing circuit, said electronic spark timing circuit producing a voltage pulse off of a falling edge of the square wave; an inverting gate-driver IC cooperative with said electronic spark timing circuit so as to transmit voltage relative to a timing pulse of said electronic spark timing circuit; a first field effect transistor connected to an output of said inverting gate-driver IC, said first field effect transistor being switchable so as to transmit the alternating voltage to said first primary winding; and a second field effect transistor connected to an output of said inverting gate-driver IC, said second field effect transistor being switchable so as to transmit the alternating voltage to said second primary winding.

15. (canceled)

16. (canceled)

17. The ignition system of claim 14, said alternating voltage output of said secondary winding being a spark having a continuous arc duration of between 0.5 millisecond and 5 milliseconds.

18. The ignition system of claim 14, further comprising: a voltage regulator circuit electrically connected between said power source and said electronic spark timing circuit so as to step down voltage from said power source.

19. The ignition system of claim 16, said gate-driver IC inverting voltage so as to cause said first field effect transistor and said second field effect transistor to bias alternately.

20. The ignition system of claim 14, said power supply comprising: a battery having a voltage of between 5 volts and 15 volts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0045] Referring to FIG. 1, there is shown the ignition system 10 in accordance with the preferred embodiment of the present invention. The ignition system 10 includes a pair of functional groups. The first functional group 12 is the power boost voltage regulator circuit. The second functional group 14 is the output section. The second group 14 produces the high-voltage AC output which is current limited by a ballasting reactance 16. Functional groups 12 and 14 act together so as to appropriately fire the spark plug 18. The functional group 12 is the input power boost voltage regulator. Functional group 12 provides a feedback-controlled regulated DC supply to the second group 14 so as to permit the deployment of the present invention in engine systems with varying input DC supply voltage voltages without adjustment. The input power boost voltage regulator 12 may additionally incorporate suitable means to reduce the output voltage when advisable and go into idle mode to reduce total module current draw from the engine primary DC power supply.

[0046] The second functional group 14 produces the high-voltage AC output supplied to the spark plug 18. The ballasting resistance can be a lumped-element capacitor, a lumped-element conductor, or a distributed inductance comprised of the leakage inductance of the output transformer 22. In each such case, the intent and effect is to limit output current once an arc has been established across the spark plug electrodes 24 permitting the output voltage to develop across the electrodes 24 when the open circuit (no arc) condition occurs.

[0047] One of the important benefits provided by this action is the property of immediately reestablishing the arc (typically within one quarter-cycle of the inverter frequency) should it be interrupted by conditions within the combustion chamber. The second functional group 14 also contains an electronic spark timing pulse timer 25 for controlling the output. The circuit idles the output section when the control input 27 (EST input) is in the idle state and permits operation when the control input 27 is in the active state. The output control 25 can also contain circuitry intended to increase ignition timing accuracy. In the present invention, the second functional group 14 provides a DC-to-AC inverter with high-voltage at the output terminal 28 with output current limiting inherent in the characteristics of the circuit. It provides for sustaining the arc under all normal conditions for minimal electrical wear on the spark plug electrodes 24 within the cylinder. The output of the second functional group 14 (i.e. the oscillator timer) is set in the lower frequency (RF) band (1 kHz to 100 kHz) for the purposes of rapid electrical action and minimization of size. The present invention, by utilizing high frequencies, can provide low mass, compactness, unitary functionality, and rapid buildup of output voltage at turn-on with high electrical efficiency during sustained arcing. The present invention thus serves both distributor-type ignition systems and coil-near-plug systems, or coil-on-plug systems.

[0048] The present invention utilizes a DC-to-AC high-voltage, high-frequency inverter which is reactively current limited at the output in which contains a means by which the inverter may be activated and idled by a low voltage signal from the electronic spark timing circuit, such as is to be expected from an engine controller (whether analog or digital). The present invention also utilizes such controllable inverters with the addition of a power boost supply whereby DC power to the controllable inverter may be constant over a specific range of primary supply voltages. The present invention can also include such controllable inverters with regulated power supplies wherein the regulated DC supply to the inverter may be controlled over a specific range of DC output voltages by an external control input to the regulated supply. The present invention can also comprise such controllable inverters with a power supply providing external control inputs wherein the power supply is placed in an idle mode by means of an external control input so as to reduce the power drain from the primary power supply. The present invention also can comprise such controllable inverters with power supplies providing external control inputs for voltage and/or shut down with timers in the inverter controller circuitry such that time delay in the initiation of the arc due to the time required for the inverter to reach full operation is minimized and/or compensated in order to provide accurate ignition timing to the controlled engine. The present invention can also comprise controllable inverters with controllable regulated power supplies and timing-compensated inverter controllers having additional means whereby the voltage across the output terminals and/or the current to the output terminals may be sensed while the inverter is in operation, as desired.

[0049] FIG. 2 is a detailed electrical schematic of the operation of the ignition system of the present invention. It is to be understood that the specific circuit topology shown in FIG. 2, while sufficient to achieve the functionality of the present invention, should not limit, in anyway, the scope of the present invention with respect to the specific circuitry, devices or circuit models contained therein. The present invention is, in each of the functions comprising its whole, is realizable by way of several different circuit topologies, models and theories of operation. It is further understood that the use of several different makes, models, technologies, and types of electronic components in each of the crucial active-device positions in any particular circuit topology chosen can also achieve the desired function.

[0050] Referring generally to FIG. 2, the ignition system 10 of the present invention is shown in schematic form. The ignition system of the present invention includes an output transformer 22. Output transformer 22 can be a gapped magnetic ferrite ceramic core transformer configured so as to provide partial decoupling of the primary and secondary windings. This constitutes the output current limiting reactants in the form of the secondary winding 30 leakage inductance. The primary windings 32 and 33 have a center tap 34 and switching transistors 36 and 38 connected to each end terminal.

[0051] In general, and electronic spark timing (EST) control signal is provided by the engine controller which is conditioned and used to activate an RC-controlled mono-stable oscillator. This mono-stable oscillator 40 is used to control the timing of the electronic spark timing circuit 42 along with the arc duration. The arc duration will be between 0.5 milliseconds to 5 milliseconds. The same timing pulse from the mono-stable oscillator 40 is then used to activate or enable a frequency astable oscillator or timer circuit and enable a buffered FET gate driver integrated circuit. As mentioned above, the second timer is configured as an astable oscillator that is configured to provide about 1 kHz to 100 kHz (a 0 volt to 8 volt signal) and is usesd to provide a first gate drive signal to the inverting input of the gate driver integrated circuit 44. The first output of the gate driver integrated circuit 44 is then used to drive the first FET 36. In addition, this first gate drive output is then connected to the second inverting input of the gate driver integrated circuit 44. This guarantees the necessary out-of-phase gate drive timing to the second FET 38. The combination of these timers and gate driver integrated circuits are used to produce the switching signals to the N channel enhancement mode switching transistors 36 and 38 from the gate drive bias resistors 46 and 48. The primary winding 32 is bridged by a capacitor 50 (external) so as to form a resonant tank circuit. This entire circuit is in the form of a push-pull inverter. The oscillator is disabled by means of the EST mono-stable output returning to 0 volts at the end of the 0.5 millisecond to 5 millisecond desired timing pulse.

[0052] At start-up, the oscillator 40 is commanded on by the engine controller's EST signal. The resonant tank having the capacitor 50 and the primary winding 32 are driven or switched at a commanded frequency to deliver maximum power to the output of the transformer 32. Amplitude oscillation will continue as long as power and bias are available to switching transistors 36 and 38. The push-pull inverter circuit is thus self-starting and self-sustaining. Specifically, referring to FIG. 2, power is initially provided through an EST input 52 toward a resistor 54. Resistor 54 serves to level shift the input for the EST 42. As such, it serves as a voltage divider. Capacitor 56 is a filter capacitor for EST 42. Resistor 58 is for input current sinking to the EST 42. A voltage transient suppression diode 60 is clamped to the eight volt power supply output from the voltage regulator and serves to suppress transients in the voltage being transmitted to the EST 42. An input capacitor 62 is provided along the pathway from the EST input 52 to the trigger terminal of the EST 42. The mono-stable oscillator 40 will extend through pins 1 and 8 of the EST 42. The capacitor 64 and the resistor 66 establish the pulse duration for the alternating voltage for an arc of approximately 1.1 milliseconds. Resistor 68 and diode 70 provide the input threshold trigger. Resistor 72 is a pull-up output resistor to V.sub.dd to provide output drive control. Ultimately, the enable pulse will emanate from the EST input 52 of the engine control module (ECM) so as to be transmitted to the trigger pin of the EST 42. Capacitor and resistors 76, 78 and 80 are used to establish the frequency of the base astable oscillator 82. The astable oscillator 82 provides for a fixed frequency of between 1 kHz and 100 kHz. As such, it serves as a force push-pull inverter so as to force the frequencies of the present invention. The pin 4 of the timer driver IC 84 is provided an enable pulse from pin 3 that passes to the EST 42 output. Capacitor 86 is a filter capacitor that is used to filter V.sub.dd noise spikes. Enable pins 1 and 8 of the gate driver IC 44 are used to wake up the gate-driver IC 44 for about one millisecond pulse. The IC 44 is enabled by the pin 3 output of EST 42. Capacitors 88, 90 and 92 are storage capacitors for the gate driver outputs. The power supply 94 will supply eight volts of power from the voltage regulator circuit. As such, the gate-drive IC 44 can alternately bias the FETs 36 and 38 so as to drive the respective primary windings 32 and 33. The capacitor 50, stated hereinbefore, helps to establish the resonate frequency. Ultimately, the voltage will flow as a sinusoidal voltage to each of the primaries 32 and 33. As a result, the transformer 22 will have the primaries 32 and 34 biased alternately so as to create a high-voltage output from the secondary 30. The system of the present invention assures that the FETs 36 and 38 are not on at the same time. As such, each will have nearly a 50% duty cycle during the arcing of the secondary 30 across the spark plug gap 94.

[0053] The power supply initially comes from the battery 100. An optional power boost voltage regulator 101 can be provided in association with the power supply from battery 100. This power boost voltage regulator is shown in greater detail in FIG. 4. Filter capacitors 102, 104, and 106 are provided so as to filter the transients from the battery voltage. The IC 108 is a voltage regulator that provides power to the timers of the EST 42 into the gate driver IC 44. Diode 110 is a blocking diode for reverse battery protection. Resistors 112 and 114 serve to set the voltage reference to eight volts. Capacitor 116 is a storage capacitor for the voltage regulator. Ultimately, the eight volts created by the voltage regulator will be supplied to 118. Capacitor 120 is a storage/stability capacitor for the primary side voltage. Line 122 will extend to the center tap 34. Line 124 will extend to the secondary 30. The eight volts shown at 118 is supplied to the lower part of the schematic in those areas indicated as 8V.

[0054] In the present invention, a sensing secondary winding can be provided so as to permit feedback to an engine control unit with respect to the voltage on the output secondary winding 30, if desired. The output secondary winding 30, if desired, can have its lower terminal connected to a current sensor, such as a resistor and diode. This will permit feedback to the engine controller unit with respect to the current through the output secondary winding 30.

[0055] The power boost regulator voltage circuit, as shown as functional group 12 of FIG. 1, and in the upper portion of the schematic of FIG. 2, provides a regulated voltage to the inverter in the range of 15 to 50 volts, depending on the integrated circuit chosen and the ratio of the feedback resistors. An input may be provided for reducing the regulated voltage with a proportional positive voltage. The amount of the reduction may be controlled by adjusting the value of the resistors. A control input can be provided to put the switching regulator into an idle mode to the action of a pull-down transistor. The primary power inlet from the battery is protected from load dump surges and spikes by surge-absorbing diode.

[0056] In the present invention, is preferable that the voltage from the battery be boosted so that the 5 to 15 volts from the battery turns into 15 to 50 volts for the push/pull inverter. This would reduce the need for a high turns ratio in the transformer 22. As such, with such increase in voltage, the size of the transformer 22 can be suitably reduced.

[0057] The signal to the spark plugs from the EST 42 is a low voltage square wave that can be configured, as desired, to turn the circuit on when the spark should fire and off when the engine does not require a spark. This can be varied so as to provide longer “arc duration” during cold starting and shorter during normal operation. The circuitry of the present invention can utilize a filter to block radio frequencies from the DC power supply. This can be a small ferrite toroid and a filter capacitor.

[0058] The push-pull inverter used in the present invention, together with the primary windings of the transformer, forms an oscillator with the winding 32 during one-half cycle of the sine wave output and with winding 33 during the other half of the sine wave output. Suitable capacitors can be used so as to help set the desired oscillation frequency, along with the primary inductance and secondary leakage inductance in order to deliver maximum power. The output of the transformer 22 is a high-voltage sine wave that reaches at least +/−20 kV (0-to-peak). The preferred operating frequency is in the range of 10 kHz to 100 kHz.

[0059] The transformer 22 can take various shapes. One preferred type of transformer 22 would include a ferrite core (gapped in the center leg), a primary winding having eight turns center tap of 18 gauge magnet wire, and a section bobbin secondary having approximately 10,000 turns of 40 gauge magnet wire. The transformer 22 can be potted in a high-voltage potting material. The circuit associated with the transformer 22 can be potted in the same shielded enclosure.

[0060] FIG. 3 is a diagrammatic illustration showing the ignition system of the present invention as used directly in association with spark plugs 200 and 202. In FIG. 3, it can be seen that the transformer 204 is directly connected onto the spark plug 200. Similarly, the transformer 206 is directly connected onto the spark plug 202. An electrical line 208 will extend from the controller 210 to the transformer 204. Another electrical line 212 will extend from the controller 210 to the transformer 206. As such, the controller 210 can provide the necessary timing signals to the transformers 204 in 206 for the firing of the spark plugs 200 and 202, respectively.

[0061] Similarly, the transformer 204 includes a sensor line 214 extending back to the controller 210. The transformer 206 also includes a sensor line 216 extending back to the controller 210. As such, controller 210 can receive suitable signals from the transformers 204 in 206 as to the operating conditions of the spark plugs 200 and 202 for a proper monitoring of the output current output voltage of the secondary winding. By providing this information, the controller 210 can be suitably programmed to optimize the firing of the spark plugs 200 and 202 in relation to items such as engine temperature and fuel consumption. The automotive battery 218 is connected by line 220 so as to provide power to the controller 210.

[0062] As can be seen in FIG. 3, unlike conventional ignition coils, the firing of each of the spark plugs 200 and 202 is carried out directly on the spark plugs. The engine controller 210 can be a microprocessor which is programmed with the necessary information for the optimization of the firing of each of the spark plugs. The engine controller 210 can receive inputs from the crankshaft or from the engine as to the specific time at which the firing of the combustion chamber of each of the spark plugs 200 and 202 is necessary. Since each of the transformers 204 and 206 are located directly on the spark plugs 200 and 202, and since they operate at low frequencies, radio interference within the automobile is effectively avoided. Suitable shielding should be applied to each of the transformers 204 and 206 further guard against any RF interference.

[0063] Within the system of the present invention, the 12 volt input is nominally the voltage of battery 218. This can vary from 6 volts at cold cranking to 14.5 or 15 volts during normal operation. The output voltage and energy of the high-voltage transformer is proportional to the input voltage. As such, is necessary to provide enough voltage and energy with 6 volts of input to start the vehicle during low voltage conditions, such as cold starting.

[0064] Referring to FIG. 4, the optional power boost voltage regulator 101, as illustrated in FIG. 2, is illustrated. This power boost voltage regulator 101 includes a switch regulator integrated circuit 266, a switching transistor 268, and energy storage inductor 270, an input filter capacitor 272 and an output filter capacitor 274. The circuit provides a regulated voltage to the inverter in the range of 15 to 50 volts, depending on the integrated circuit 266 that is chosen and the ratio of feedback resistors 276 and 278. An input 280 may be provided for reducing the regulated voltage with a proportional positive voltage. The amount of the reduction may be controlled by adjusting the value of the resistor 282. A control input 284 is provided for putting the switch regulator integrated circuit 266 into an idle mode through the action of pull-down transistor 286. The primary power inlet 288 from the battery is protected from load dump surges and spikes by a surge-absorbing diode 290.

[0065] In the present invention, would be preferable that the voltage from the battery be boosted so that the 5 to 15 volts from the battery turns into 15 to 50 volts for the inverter. This would reduce the need for a high turns ratio in the transformer. As such, with such an increase in voltage, the size of the transformer can be suitably reduced.

[0066] The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.