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Claims  |
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We claim:
1. An ignition transformer for firing a spark plug of a spark ignition internal combustion engine, said ignition transformer comprising:
a substantially cylindrical core constructed of a material having magnetic properties, said core being hollow, having a pair of ends and including portions defining an air gap therein;
a primary winding of wire having ends, said primary winding located about said core in a series of turns which extend longitudinally generally along an inner surface of said core, about one of said ends of said core, longitudinally generally
along an exterior surface of said core and about the other of said ends of said core;
a secondary winding of wire having ends, said secondary winding located about said core in a series of turns which extend longitudinally generally along an inner surface of said core, about one of said ends of said core, longitudinally generally
along an exterior surface of said core and about the other of said ends of said core, said series of turns of said secondary winding being greater in number than said series of turns of said primary winding;
a housing substantially enclosing said core and said primary and said secondary windings;
mounting means connected to said housing for mounting said ignition transformer to a spark plug;
a first pair of terminals electrically connected to said ends of said primary winding and adapted to be coupled to an electrical power supply; and
a second pair of terminals electrically connected to said ends of said secondary winding and adapted to be coupled to the terminals of a spark plug.
2. An ignition transformer as set forth in claim 1 wherein said ignition transformer is a flyback ignition transformer.
3. An ignition transformer as set forth in claim 1 wherein said air gap extends longitudinally relative to said core.
4. An ignition transformer as set forth in claim 1 wherein said air gap extends the entire length of said core.
5. An ignition transformer as set forth in claim 1 wherein said primary winding is wound about said core so as to substantially overlie said air gap.
6. An ignition transformer as set forth in claim 1 wherein said primary winding is toroidally wound about said core.
7. An ignition transformer as set forth in claim 1 wherein said secondary winding is toroidally wound about said core.
8. An ignition transformer as set forth in claim 1 wherein said housing is constructed from a dielectric material.
9. An ignition transformer as set forth in claim 1 wherein said mounting means is metal and forms a portion of said second pair of terminals.
10. An ignition transformer as set forth in claim 1 wherein the retentivity of said material forming said core is within the range of 500 to 1000 Gausses.
11. An ignition transformer as set forth in claim 1 wherein said material forming said core ferrous alloy.
12. An ignition transformer as set forth in claim 1 wherein the retentivity of said material forming said core is less than ten percent of its maximum flux density.
13. An ignition transformer as set forth in claim 1 wherein said material forming said core is capable of experiencing changes in flux of about 900 Gauss.
14. An ignition transformer as set forth in claim 1 wherein said material forming said core is capable of experiencing a change in flux from about 14,000 to 500 Gauss.
15. A low impedance ignition transformer capable of rapidly charging and performing multiple refirings of a spark plug during a single combustion cycle in a spark ignition internal combustion engine thereby allowing the spark plug to be used as
a feedback element of the engine control system to perform various engine diagnostic procedures, said ignition transformer comprising:
a substantially cylindrical core constructed of a material having magnetic properties, said core having a central bore therethrough and including portions defining an air gap extending substantially the length thereof;
a primary winding of wire having ends, said primary winding located about said core and in a series of turns which extend longitudinally generally along an inner surface of said core, about one end of said core, longitudinally generally along an
exterior surface of said core and about another end of said core;
a secondary winding of wire having ends, said secondary winding located about said core in a series of turns which extend longitudinally generally along an inner surface of said core, about one end of said core, longitudinally generally along an
exterior surface of said core and about another end of said core, said series of turns of said secondary winding being greater in number than said series of turns of said primary winding;
a housing generally defining a cavity for receiving and generally enclosing said core, said primary winding and said secondary winding therein; a solid dielectric material located within said cavity and substantially filling the remainder of
said cavity other than said core, said primary winding and said secondary winding;
mounting means connected to said housing for mounting said ignition transformer to a spark plug;
a first pair of terminals electrically connected to said ends of said primary winding and adapted to be coupled to an externally located power supply; and
a second pair of terminals electrically connected to said ends of said secondary winding and adapted to be coupled to the terminals of a spark plug.
16. An ignition transformer as set forth in claim 15 further comprising a bobbin, said bobbin substantially encasing said core and having a central bore therethrough generally corresponding to said central bore of said core.
17. An ignition transformer as set forth in claim 16 wherein said primary winding is located about both said core and said bobbin in a series of turns, said primary winding being in contact with said bobbin and extending along a longitudinal
inner surface of said bobbin, about one end of said bobbin, longitudinally along an exterior surface of said bobbin and about another end of said bobbin.
18. An ignition transformer as set forth in claim 16 wherein said secondary winding is located about said core and said bobbin in a series of turns, said secondary winding being in contact with said bobbin and extending along a longitudinal
inner surface of said bobbin, about one end of said bobbin, longitudinally along an exterior surface of said bobbin and about another end of said bobbin.
19. An ignition transformer as set forth in claim 16 wherein said bobbin is located within said cavity of said housing.
20. An ignition transformer as set forth in claim 15 wherein said air gap extends the length of said core.
21. An ignition transformer as set forth in claim 15 wherein said primary winding is wound about said core so as to substantially overlie said air gap.
22. An ignition transformer as set forth in claim 15 wherein said primary winding is toroidally wound about said core.
23. An ignition transformer as set forth in claim 15 wherein said secondary winding is toroidally wound about said core.
24. An ignition transformer as set forth in claim 15 wherein said ignition transformer is a flyback ignition transformer.
25. A low impedance ignition transformer capable of rapidly charging and performing multiple refiring of a spark plug during a single combustion cycle in a spark ignition internal combustion engine, said ignition transformer comprising:
a substantially cylindrical core constructed of a material having magnetic properties, said core having a central bore therethrough and including portions defining an air gap extending the length thereof;
a primary winding of wire having ends, said primary winding located about said core and in a series of turns which extend longitudinally generally along an inner surface of said core, about one end of said core, longitudinally generally along an
exterior surface of said core and about another end of said core;
a secondary winding of wire having ends, said secondary winding located about said core in a series of turns which extend longitudinally generally along an inner surface of said core, about one end of said core, longitudinally generally along an
exterior surface of said core and about another end of said core, said series of turns of said secondary winding being greater in number than said series of turns of said primary winding;
a housing generally defining a cavity for receiving and generally enclosing said core, said primary winding and said secondary winding therein;
a dielectric liquid material located within said cavity and substantially filling the remainder of said cavity other than said core, said primary winding and said secondary winding therein;
sealing means for sealing said dielectric liquid within said cavity;
mounting means connected to said housing for mounting said ignition transformer to a spark plug;
a first pair of terminals electrically connected to said ends of said primary winding and adapted to be coupled to an externally located power supply; and
a second pair of terminals electrically connected to said ends of said secondary winding and adapted to be coupled to the terminals of a spark plug.
26. An ignition transformer as set forth in claim 25 further comprising a bobbin, said bobbin substantially encasing said core and having a central bore therethrough generally corresponding to said central bore of said core, said primary winding
being located in a series of turns about both said core and said bobbin.
27. An ignition transformer as set forth in claim 1 wherein said sealing means is an end cap secured to said housing.
28. An ignition transformer as set forth in claim 26 wherein said air gap extends the length of said core.
29. An ignition transformer as set forth in claim 25 wherein said primary winding is wound about said core so as to substantially overlie said air gap.
30. An ignition transformer as set forth in claim 25 wherein said primary winding and said secondary winding are toroidally wound about said core.
31. An ignition transformer as set forth in claim 25 wherein said ignition transformer is a flyback ignition transformer. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention generally relates to a automotive ignition system for an internal combustion engine. More particularly, this invention relates to a coil-on-plug ignition transformer which is capable of being fired according to an algorithm
to perform various engine diagnostic procedures. The spark plug mounted ignition system of the present invention therefore operates as a feedback element of the engine control system.
BACKGROUND AND SUMMARY OF THE INVENTION
In order to initiate combustion of an air/fuel mixture within an internal combustion engine, a spark ignition system generates a high voltage arc across the spark plug electrodes at the appropriate time in the engine operating cycle. The onset
of the arc across the spark plug gap is timed to occur at a predetermined number of degrees of crankshaft rotation, usually before the piston has reached top dead center (TDC).
If the spark timing is properly set, the combustion process initiated by the spark plug action will cause a pressure increase to develop within the combustion chamber that will peak just shortly after TDC during the piston's power stroke. If the
spark is initiated too late in the operating cycle (retarded timing), the pressure developed within the combustion chamber will not be efficiently converted by the engine into work. On the other hand, if the spark is initiated too early in the operating
cycle (advanced timing), extremely high and potentially damaging pressures and temperatures may result. The pressure and temperature increases associated with advance timing are also not efficiently converted by the engine into a useful work output.
Excessive advanced timing can also lead to the occurrence of several other types of combustion chamber phenomena. One such phenomena is auto-ignition of the end gases and another is pre-ignition.
Auto-ignition is a condition where the end gases (the unburnt portion of the fuel-air mixture initially ignited by the movement of the flame front) explode spontaneously as a result of the cylinder temperature and pressure becoming too high for
the type of fuel being burned in the engine. In response to the sudden release of energy, the cylinder temperature dramatically increases and the cylinder pressure fluctuates, alternately rising and falling, as a pressure wave travels back and forth
across the combustion chamber. When caused by auto-ignition of the end gases, the rapid pressure and temperature fluctuations are seen to occur after TDC. If the rate at which energy is released through auto-ignition is high enough, the exploding gases
will cause the cylinder walls to vibrate resulting in audible engine noises, including the distinctive sound known as "pinging".
Many engine developers believe that a mild degree of auto-ignition is desirable because it generates turbulence within the combustion chamber, which hastens the combustion process, at a critical time when the normal flame kernal is in the process
of being quenched. Slight auto-ignition has also been found to reduce the amount of unburnt hydrocarbons remaining after the completion of the spark-triggered ignition process. By utilizing the energy released when the hydrocarbons are burned during
mild auto-ignition, it follows that lower hydrocarbon emissions and improved fuel economy can be realized.
Because of the benefits stated above, among others, engine designers often seek to calibrate ignition systems so that the spark advance is close to the threshold of auto-ignition. However, excessive auto-ignition must be avoided since it leads
to higher combustion chamber temperatures and is counter productive. In fact, these elevated temperatures can heat the spark plug electrodes to the point where they will initiate the combustion process independently of the occurrence of a spark. This
phenomena is pre-ignition.
Pre-ignition, which can cause significant engine damage including perforation of the piston, is characterized by the occurrence of extremely high cylinder temperatures and pressures near TDC. The audible sound associated with pre-ignition is
produced by the action of auto-ignition and, when extreme, referred to as "knock". Generally, it can be stated that auto-ignition leads to pre-ignition and, subsequently, that pre-ignition leads to further auto-ignition.
A number of factors influence the spark timing threshold which generates auto-ignition. Some of these factors include, inlet air temperature, engine speed, engine load, air/fuel ratio and fuel characteristics. Because accurate control of the
spark timing is a significant contributor to engine performance, numerous types of engine control systems have been developed. These control systems typically employ a microprocessor based closed-loop spark timing control system which simultaneously
measures a number of parameters, such as exhaust composition, coolant temperature, and the occurrence of spark knock via transducers. The resulting data is then processed to set the engine timing near a predicted auto-ignition threshold.
The knock detectors typically used in engine control systems are piezoelectric transducers which sense the intense vibration caused by spark knock. When used in the environment of an internal combustion engine, however, these transducers may not
be selective enough to distinguish the slight vibration produced by incipient auto-ignition over the normal amount of engine vibration. For this reason, these detectors are typically not capable of sensing, particularly at high engine speeds, the
threshold of auto-ignition. An engine control system is therefore needed which is capable of detecting incipient auto-ignition and which enables more precision in setting the spark timing in a closed-loop system.
Other characteristics found in ignition systems and considered to be undesirable include, but are not limited to: excessive spark plug electrode wear; the inability to fire fouled spark plugs; poor cold weather starting; poor exhaust emissions
during cold engine starting and running; the remote generation of high voltages in the engine compartment by the ignition system; the routing and distribution of high voltages over considerable lengths of ignition wire; and the generation of significant
amounts of electro-magnetic radiation within and around the ignition system, as well as the vehicle, during operation of the engine.
It is therefore an object of the present invention to provide an engine control and ignition system which overcomes the limitations and disadvantages of known systems.
It is also an object of this invention to provide an ignition system which is capable of performing various engine diagnostic procedures so as to operate as a feedback element of the engine control system. In particular, the invention operates
as a non-invasive combustion chamber monitor through the utilization of the ignition transformer and the spark plug as the feedback elements.
The present invention has as further objects the providing of a method for determining engine load, a method for detecting engine misfire and a method for detecting auto-ignition of the end gases.
Another object of the invention is to provide a coil-on-plug ignition transformer which is capable of charging, firing and retiring the spark plug at short, repeatable intervals as programmed into the engine control system.
One feature of this invention is that it eliminates the various problems associated with the distribution of high voltages throughout the ignition system. Another feature of the present invention is that it reduces the amount of electro-magnetic
radiation generated by the ignition system around the engine and the vehicle itself.
Reduced spark plug electrode wear is another feature as well as the ability to fire badly fouled spark plugs.
A still further feature of the invention is enhanced cold weather starting capabilities of an internal combustion engine and the minimization of exhaust emissions which occur during cold starting and running. A related feature is the extension
of the air/fuel ration toward the lean limit which helps to further reduce emissions and improve fuel economy during normal engine operation.
SUMMARY OF THE INVENTION
Recent research, some of which has been performed by the assignee of the present invention, has indicated that combustion within an internal combustion engine can be improved by initiating the burning process with a spark of the type known as a
breakdown discharge. The breakdown spark has characteristics quite different from those generated by conventional automotive ignition systems and responds differently to different conditions within the combustion chamber. This realization has led to
the development of the present invention, an ignition control system having components which are capable of exploiting the characteristics of the breakdown spark so as to enable the performance of various engine diagnostic procedures using the spark plug
itself as a feedback element of the engine control system.
The ignition process has been characterized as consisting of three distinct phases; the breakdown phase; the arc phase and the glow phase. The initial phase, the breakdown phase, is characterized by high current (typically 50-200 amperes (A))
which results from the energy stored in the spark plug capacitance (typically 10-15 picofarad (pF)) discharging through the arc. The breakdown phase typically lasts less about a nanosecond (ns). The second phase, the arc phase, occurs when the arc
current is between 0.1 and 1.0 A and the arc voltage is about 180 volts (v). The discharge current remains in the arc phase for approximately 100 .mu.s. The glow phase occurs when the arc current drops below 0.1 milliamperes (mA) and the voltage across
the spark plug electrodes goes to 500.gamma..
These three phases, the breakdown, arc and glow phases, have been found to reliably initiate combustion of the air/fuel mixture when the air/fuel ratio is respectively twenty-one to one, eighteen to one and sixteen to one. If the breakdown phase
is exploited, it follows that the lean limit can be extended and numerous benefits realized.
As mentioned above, the present invention details an ignition and engine control system which is not only capable of firing the spark plug, but which is also capable of performing diagnostic functions. Specifically, one aspect of the present
invention details the ignition and engine control system itself. Another aspect details the methods for performing various diagnostic procedures. A further aspect of this invention is a low impedance ignition transformer, mounted directly on the spark
plug, which enables both of the above. The transformer's low impedance augments the capabilities of the engine control system's microprocessor unit (MPU) making it possible for the MPU to use the spark plug to monitor a number of engine conditions
including misfire, auto-ignition and engine load.
The ignition and engine control system of the present invention includes six principal components not counting the engine itself. These are an engine controller (which has inputs that monitors various engine parameters), a MPU (which is
programmed to carry out various routines based on the inputs to the engine controller), ignition or coil driver circuit, an ignition transformer, a spark plug and current discharge detection circuitry, all of which are described in greater detail below.
The design of the ignition transformer provides for a short charging time and an intense secondary current of short duration (approximately 0.5-1A, decaying to zero in approximately 100.mu.s) that reliably initiates stable combustion. This is
achieved while deriving energy directly from the vehicle's 12.gamma. power supply and eliminating the need for an expensive 12.gamma. DC to 250.gamma. DC converter.
Because of the intensity and duration spark, as well as the short charging time of the transformer, the present transformer configuration enables the elimination of the ignition system's high voltage distribution system and also makes possible
the rapid, multi-firing of individual spark plugs by the engine control system. Previously, multi-tiring ignition systems have had to rely on a fixed countdown counter or a natural resonance within the ignition circuitry to retrigger the firing. In a
standard ignition system, the charging time for the primary, and therefore the time necessary for re-firing of the spark plug, is about 3000 .mu.s. Relatively slow in terms of the duration of the engine operating cycle. The present invention, however,
is designed to multi-tire based on algorithms programmed into the engine control system itself and has the capability of retiring the spark plugs at 200 .mu.s intervals.
Under hard to ignite conditions, it has been found that the multi-firing of the spark plug during the combustion event is beneficial to the combustion process. According to the present invention, multi-firing is programmed to occur only under
hard-to-ignite mixture conditions such as throttle tip-ins, cold starts, idle and at combinations of light loads and low rpms. By not multi-tiring under other conditions, an extension in the life of the ignition components is realized, particularly in
the spark plug electrodes.
Since spark plug electrode wear is directly proportional to the time over which the arc current flows, electrode wear can be reduced by applying a higher intensity current over a shorter duration. As mentioned above, when current flowing between
the spark plug electrodes is above 100 mA, the voltage is about 180.gamma.. Below 100 mA, however, the voltage rises to about 500.gamma.. When accelerated by a 500.gamma. differential, the electrons and charged particles being exchanged between the
spark plug electrodes penetrate the electrode surfaces more vigorously than when accelerated by a 180.gamma. differential.
In a standard flyback ignition coil system, the electrons and charged particles are driven for well over 1,500 .mu.s at the 500.gamma. differential. This results in significant electrode wear. In the low impedance system of the present
invention, the peak voltage across the spark plug electrodes is intense, about 22 kilovolts (kv), but it is reached approximately 4 .mu.s after the 14 transformer primary has been switched off and the overall time spent above the 500.gamma. differential
is typically less than 20 .mu.s. While the increased intensity of the spark better ensures stable combustion, its significantly shorter duration minimizes spark plug electrode wear. This is beneficial since it makes it possible to reduce the diameter
of the spark plug electrodes themselves. It is well known that spark plug electrodes having a smaller size and mass will minimize quenching of the initial kernel of burning gases and produce more stable combustion. The intensity and short duration of
the spark plug arc current is advantageous and beneficial in several other regards. These benefits include, but are not limited to: more stable combustion; reduced energy consumption by the ignition process; lower overall exhaust emissions; extending
operation of the engine further toward the lean limit; extended catalytic converter life; a reduction in arc current time and spark plug electrode wear; the increased ability to fire fouled spark plugs; enhanced cold weather starting and running
capabilities; a reduction of cold start exhaust emissions; an elimination of high voltage routing about the engine; and a reduction in electromagnetic radiation generation in and around the vehicle.
As mentioned above, the system of the present invention can be used to detect the misfiring of a cylinder in the engine. After the fully charged ignition transformer has been switched off generating a maximum secondary voltage across the spark
plug electrodes and starting the combustion process, while the crankshaft and the combustion cycle are still near TDC, the MPU causes the ignition transformer to develop a predetermined applied voltage at the spark plug gap. If combustion has already
been initiated, the combination of temperature and pressure in the area of the spark plug will enable the applied voltage to conduct across the electrodes. If the cylinder has misfired, the predetermined level of applied voltage at the spark plug gap
will not be high enough to cause the spark plug electrodes to conduct. As a result of the applied voltage not being spent in a secondary current discharge, a negative voltage excursion is reflected back into the primary. The electronic switch of the
primary winding is monitored by the detection circuitry and the engine control system and, if this negative voltage excursion is detected, the system records that misfire has occurred. If the misfire repeats for a successive combustion cycles, the MPU
and engine controller can be programmed to shut the cylinder down preventing unburnt hydrocarbons from being released in the exhaust emissions and reducing fuel consumption. In an attempt to curb exhaust emissions, various states are enacting laws that
require that a misfiring cylinder be shut down. One such law goes into effect in California in 1996.
The present invention can also be used to detect auto-ignition of the end gases and set the engine timing at the threshold of auto-ignition. In using the spark plug to detect whether auto-ignition of the end gases is occurring, the MPU causes
the ignition transformer to rapidly duty cycle at a predetermined voltage. This is done at a point in the combustion cycle where knock is expected to occur (typically after top-dead-center (ATDC)). The duty cycle period is calculated from an algorithm
stored in the MPU of the engine controller and is a function of various engine parameters including engine load, engine speed, and charge temperature.
If normal combustion conditions are occurring in the cylinder at the time of duty cycling, the current resulting from the duty cycling will not be transferred across the plug gap, but will instead be reflected back through the primary as a
negative voltage excursion. The negative excursion can again be detected at the high side of the electronic switch by the detection circuitry and the engine controller. If auto-ignition is occurring, the resulting temperature and pressure waves present
within the cylinder will correspond with one or more of the applied duty cycle voltage potentials enabling it to conduct across the electrode gap. As a result, not all of applied voltages will have a corresponding reflected negative voltage excursion.
By monitoring the primary for a missing negative voltage excursion, auto-ignition of the end gases can be recognized and detected by the engine controller. Using this information regarding the occurrence or non-occurrence of auto-ignition, the engine
controller can progressively step the ignition timing so that threshold of auto-ignition is maintained.
Additionally, the uniqueness of the present ignition transformer facilitates the measurement of the spark plug breakdown voltage during the combustion cycle. It is the magnitude of this parameter (which reflects the relationship between the
combustion pressure, temperature and fuel concentration) that provides a non-intrusive indication of the engine's performance or load. By enabling monitoring of the engine load, the ignition and engine control system of the present invention eliminates
the need for expensive manifold absolute pressure (MAP) sensors. Knowing that the cylinder pressure is proportional to the engine load, the spark plug breakdown voltage can be directly correlated to the engine load in view of Paschen's Law. At an
"interrogate" time or crank angle position ATDC, where other variables such as spark advance and the air/fuel ratio are no longer an influence on the cylinder pressure, the breakdown voltage is determined by firing the spark plug and measuring the time
over which the transformer inductive current discharge. In view of the transformer's known characteristics, the discharge time is then correlated by the engine controller into breakdown voltage to determine the cylinder pressure and, ultimately, the
engine load.
All of the above is made possible by the short charging and discharging time of the ignition transformer, the ignition and detection circuitry and the control software programmed into the MPU and engine controller. In the time it takes a
conventional ignition transformer performs a single charge and discharge, the ignition transformer of the present invention is capable of initiating combustion, recharging and refiring a multiple number of times to perform the diagnostic procedures.
Intended to operate within the spark plug well of the engine, the flyback transformer of the present invention incorporates a torodial design that eliminates the flow of magnetic flux inside the cylinder defining the spark plug well. This makes
the present ignition transformer largely insensitive to eddy current loading and is a major reason for the decreased production of electro-magnetic radiation.
Having a restricted diameter, the ignition transformer itself includes a cylindrical core whose length can be varied to provide the necessary cross sectional area in the transformer core. The core is positioned within a dielectric bobbin and the
primary and secondary of the transformer are wound around both the bobbin and the core. The wound core and bobbin is then positioned within a housing whose lower end is configured to receive the high side terminal of a spark plug. The spark plug itself
can be of a standard design or can be modified to reflect the ability to use smaller electrodes with the present invention.
The electronics of the ignition and engine control system are controlled by engine controller which monitors input signals from the cam and crank speed sensors, as well as the vehicle ignition signal. These inputs allow the engine controller and
the MPU to calculate engine speed and position. As a result of these calculations, the MPU calculates and sends output signals at the proper time, based on its programmed algorithm, to coil driver circuits which charge and trigger the ignition
transformer. The MPU utilizes the detection circuitry to monitor the combustion cylinder and determine the engine load and/or whether a knock or misfire condition exists. Depending on the existing conditions, the MPU signals and alerts other circuits
or modules of the engine to take the appropriate measures.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration showing the general components of an ignition and engine control system embodying the principles of the present invention;
FIG. 2 is a perspective view with portions broken away showing the ignition transformer of the present invention positioned on the spark plug of an internal combustion engine;
FIG. 3 is a longitudinal sectional view of a portion of an ignition transformer embodying the principles of the present invention;
FIG. 4 is a perspective view of the core, bobbin, primary and secondary windings as provided by the present invention;
FIG. 5 is a top plan view of the core, bobbin, primary and secondary windings as seen in FIG. 4;
FIG. 6 is a perspective view of the transformer core;
FIG. 7 is a longitudinal sectional view of a second ignition transformer incorporating the principles of the present invention;
FIGS. 8(a and b) is a graphical representation of the primary charging current and the secondary discharge voltage with respect to time;
FIG. 9(a-d) is a graphical illustration of the pressure and temperature at the spark plug during both a normal combustion event and a misfire event, as well as the applied voltages and reflected voltages occurring in the transformer during both
events;
FIG. 10(a-c) graphically illustrates the pressure and temperature in the cylinder during a normal combustion event as well as the applied and reflected voltages in the ignition transformer during knock detection;
FIGS. 11(a-c) is a graphical illustration of the pressure and temperature in the cylinder during auto-ignition of the end gases as well as the applied and reflected voltages in the ignition transformer;
FIG. 12 is a graphical illustration of the cylinder pressure relative to crank angle position for various engine loads;
FIG. 13 is a graphical illustration of the breakdown voltage relative to the inductive current discharge time; and
FIG. 14 is a schematic illustration of the coil driver circuits, ignition transformer and the detection circuits utilized in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, an ignition and engine control system embodying the principles of the present invention is generally illustrated in FIG. 1 and designated at 20. The system includes an engine controller 22 and an MPU 24 which
spends most of its time executing a main program loop that performs various engine functions which are relatively non-critical from an engine timing standpoint. The rate at which these functions must be repeated is also relatively slow in comparison to
the engine cycle itself. This generally means that these "non-critical" functions can be performed asynchronously from the engine combustion events.
Fuel injection and ignition events, however, must be precisely synchronized to the engine cycle. To accomplish this, the engine controller 22 and MPU 24 are programmed to service interrupts that are triggered by timing pickups or speed sensors
26 mounted on the engine 28 relative to a flywheel 30 on the crankshaft and/or a pulley 32 on the camshaft. The interrupts produced by the timing pickups 26 load a timing element of the MPU 24 which creates real time control signals for the fuel
injectors and ignition coil drivers at the correct instant and for the correct duration during the combustion cycle. The engine controller 22 is also be coupled to various other engine parameters including the vehicle ignition signal.
Using the results of the above calculations, the MPU 24 outputs signals at the proper time through an ignition or coil driver circuit 34 causing an ignition coil or transformer 36 to begin charging directly from the vehicle's 12.gamma. power
supply. The ignition transformer 36, which is mounted directly onto a spark plug 38 and is known as a coil-on-plug transformer 36, is charged until its core becomes saturated. At the appropriate number of engine degrees before top dead center (BTDC),
the MPU 24 then causes a high speed switching transistor of the coil driver circuit 34 to open, shutting off the current in the transformer primary. If conditions are right within the engine cylinder, the secondary capacitance of the transformer 36 will
discharge in a high voltage current across the spark plug 38 gap and initiate combustion. After the ignition transformer has been scheduled to fire, the MPU 24 runs through a series of programmed algorithms designed to cause multi-firing of the spark
plug or perform various engine diagnostic procedures. If diagnostic procedures are being performed, the MPU 24 utilizes the detection circuitry 40 as further outlined below.
The ignition transformer 36 of the present invention is a very low impedance device which, by design, is capable of generating a significant secondary voltage (about 25 k.gamma.) which peaks in approximately 2-4 .mu.s and decays to zero in
approximately 100 .mu.s. Since the transformer 36 will fully charge and saturate its core in about 100 .mu.s from the vehicles 12.gamma. power supply, this means the transformer 36 is capable of being retired at 200 .mu.s intervals.
Previously, to create signals for repetitively operating the coil driver circuit 34 or for multi-firing an ignition transformer and spark plug at 200 .mu.s intervals, numerous timing interrupts would have had to been serviced by the engine
controller 22 and MPU 24 for each refiring of the spark plug. This, however, would result in excessive interrupt loading of the MPU 24 and would create a significant number of timing conflicts. With excessive interrupts being present, the main program
the MPU 24 would be disrupted at a high frequency during a large percentage of its execution time resulting in interrupts being nested within one another. The multiple timing conflicts would require the MPU 24 to service more than one interrupt at a
time in order to generate the required control signals. The MPU 24, however, can only execute one interrupt at a time.
In the present invention, the MPU 24 is directed by the engine controller 22 to send signals to the coil driver circuit 34 according to a specific algorithm programmed into the MPU 24. Thus, the need for servicing a multitude of interrupts is
eliminated because of the short time necessary to re-fire the transformer 36.
The ignition and engine control system 20 of the present invention utilizes a specially designed spark plug mounted ignition coil or transformer 36 as a feedback element in the engine control system 20. In addition to its feedback functions, the
ignition transformer 36 provides an intense, short duration (less than 100 .mu.s) secondary current that reliably initiates combustion, even when the spark plug is badly fouled, and promotes spark plug longevity.
The uniqueness of the ignition transformer 36 provides for a non-intrusive indication of engine performance by facilitating the measurement of the spark plug breakdown voltage, a parameter whose magnitude reflects the relationship between the
combustion pressure, temperature, and fuel concentration. In general, the relationship between the pressure, temperature and electrode gap is defined by Paschen's Law which states: ##EQU1## where P is the pressure; d is the electrode spacing; T is the
temperature; and K.sub.1 and K.sub.2 are constants.
The voltage level that is generated by the ignition transformer 36 is directly related to the magnitude of the primary winding current, which is a function of charging time, at the time the ignition transformer is switched. In the present
invention, the primary current that generates the maximum secondary voltage is typically reached in a charge time of 100 .mu.s when the voltage applied to the primary winding is 12.gamma.. A charge time of less than 100 .mu.s will therefore result in a
secondary voltage that is less than the maximum. In other words, the shorter the charge time, the lower the secondary voltage of the ignition transformer 36.
Referring now to FIGS. 2 and 3, the spark plug mounted or coil-on-plug ignition transformer 36 of the present invention is generally illustrated therein. The physical dimensions of the ignition transformer 36 are dictated by the design of the
engine 28 itself. To enable mounting directly on the spark plug 34 itself, the ignition transformer 36 must be able to fit within the diameter of a spark plug well 41 of the engine 28. While this specific design criteria differs from one engine version
to the next, the principles of the present invention will be applicable to the entire range of spark plug well diameters. The length limit of the ignition transform is determined by the clearance between the engine 28 and the hood of the vehicle (not
shown). The length of the ignition transformer 36 can therefore be adjusted to accommodate the required cross sectional area of its core, as determined by the various other transformer parameters.
The ignition transformer 36 of the present invention includes a magnetic core 42 which is received in a dielectric bobbin 44. Perhaps best seen in FIGS. 4-6, the core 42 is substantially cylindrical and includes portions which define an air gap
46 that extends the length of the core 42. In order to provide a very efficient transformer 36, the retentivity of the core is required to be a very small percentage of its maximum flux density. When the magnetizing force (expressed in ampere turns) is
removed from the core 42 of the transform | | |
