Low voltage ignition control system

Abstract

 Plug is used to realize such a device. Sensors adapted to sense status parameters, such as temperature, pressure, emissions, and the like, may be coupled to the computing circuitry (60), in which case information derived therefrom is factored into the computing circuitry so that appropriate adjustments may be made to the fixed relationship between the synchronizing pulse and the low voltage ignition pulses (58). One embodiment of the invention also permits the computing circuitry to selectively adjust the ratio of fuel to air that is injected into the combustion chamber.

Description

[0001] This invention relates to ignition systems; and more particularly to a low voltage ignition system that distributes a low-voltage signal to the appropriate cylinders of an internal combustion engine, whereat the low voltage signals are converted to an ignition signal or spark of sufficient energy to ignite the fuel/air mixture contained in the cylinder.

[0002] All internal combustion engines utilzied in the prior art employ some sort of ignition system or mechanism to ignite the fuel/air mixture held in the cylinder or other appropriate combustion chamber. Such ignition releases energy from the fuel-air mixture, and this energy is typically used to linearly move a piston. One end of the piston, in turn, is pivotally mounted to a driveshaft (or crankshaft) such that the linear motion of the piston causes the driveshaft to rotate. In a multi-cylinder engine, several pistons are thus connected to the driveshaft or crankshaft, and the ignition of the fuel in each cylinder is carefully controlled, or "timed," so that the energy imparted to the driveshaft or crankshaft optimally adds to, rather than bucks or opposes, the rotational energy already present therein, a flywheel directly coupled to the driveshaft is also typically used to help increase the inertia of the rotating driveshaft or crankshaft.

[0003] Other engine arrangements are known in the art that do not utilize linearly moving pistons, but that rather couple energy released by the ignition of the fuel directly to a rotating member which is connected to the driveshaft (e.g., the "Wankel" engine).

[0004] Regardless of the type of engine mechanism that is employed, an ignition system is required (at least in gasoline engines--as opposed to diesel engines) to distribute a high voltage spark to the appropriate cylinder at the appropriate time. Prior art ignition systems typically include: (1) a battery, or similar power supply from which a primary source of electrical energy is obtained; (2) an ignition coil or transformer to covert the primary source of power, which is a low voltage, to a secondary source of power, which is a high voltage; (3) a set of contact breakers, or "points" connected in series with the primary side of the ignition coil to selectively interrupt the flow of current therethrough, which interruption causes the magnetic field associated with this current to collapse, or otherwise vary, as a function of time, this varying magnetic field, in turn, inducing a high voltage signal in the secondary side of the ignition coil according to well known principles of electromagnetic induction (e.g., Faraday's Law); (4) a capacitor, or condenser, connected across the points to prevent arcing thereacross (which arcing may burn or otherwise damage the points) as the induced secondary voltage collapses and induces a back emf across the primary side of the ignition coil where the points are located; and (5) a mechanical distibutor that selectively distributes this high voltage signal to the spark plug located at the appropriate cylinder, whereat the high voltage causes a spark to arc across the spark.plug electrodes, which spark ignites the fuel/air mixture contained in the cylinder.

[0005] The distributor above referred to typically includes a rotor arm that is mechanically coupled to the drive or crankshaft of the engine. As such, it is driven at a selected and specified ratio of the engine speed (that is the rotational speed of the crankshaft). As the distributor arm rotates, it sequentially comes in contact with one of a plurality of electrodes, each electrode being connected to a desired spark plug. Thus, the high-voltage signal of the secondary side of the ignition coil is sequentially distributed to the spark plugs as the rotor arm rotates and comes in contact with the respective electrodes. The breaker contacts, or "points", are also controlled by means of a cam, or similar mechanism, that is coupled to the shaft that drives the rotor arm of the distributor. The distributor is carefully set with respect to the distributor shaft so that the points are just opening as one of the pistons of an appropriate cylinder nears the top of its compression stroke, and at this same instant the rotor arm affixed to the distributor shaft is just contacting the electrode that is connected to the spark plug about to fire through a heavily insulated cable.

[0006] Numerous problems exist with the ignition system above described, which ignition system is employed on almost all known multi-cylinder gasoline engines known to applicant. The use of the ignition coil, for example, is inefficient, there being typically less than 50% of the energy fed into the primary side thereof that is recoverable in useful form from the secondary side thereof. Further, the transfer of energy through the ignition coil is not instantaneous, there being critical delays (e.g., rise and fall times) associated therewith that vary as a function of several parameters, such as temperature and humidity. These delays are thus very difficult to predict and compensate for. There are also spurious oscillations associated with the use of the ignition coil that dissipate wasted energy. Moreover, these oscillations, coupled with the continual on/off distribution of the high voltage and current signals, creates RFI (radio frequency interference) problems that must be suppressed with appropriate suppression devices, which devices not only represent an added expense, but also reduce the overall efficiency of the engine.

[0007] A further problem exists with properly maintaining the contact breakers or "points". As mentioned above, because of the expanding and collapsing magnetic fields that are associated with the coil, undesirable voltages are continually induced across these points. While the use of a condenser minimizes the impact of such voltages (typically shorting such voltages to ground) the use of such a condenser is not totally effective. Thus, there is always some arcing associated with the points as they close and open. this arcing causes the points to burn, and as they burn their operation is impaired.

[0008] Still an additional problem associated with prior art ignition systems is that all of the high-voltage signals associated with the secondary of the ignition coil or transformer must be carried in heavily insulated cables. These cables, in addition to being expensive, must be carefully routed and secured about the engine. Further, it is not unusual to require an impedance element to be inserted in series with these cables so as to limit the amount of current that can flow therethrough and to minimize RFI and other problems. The use of such impedance elements, of course, represents a significant waste of energy. Further, the longer the cables, the more the energy loss, and the greater RFI problems. Thus, the distributor must be positioned in a central location with respect to the engine, insofar as possible, so that cable lengths are minimized. Such positioning is not always convenient nor possible.

[0009] The rotor shaft of the distributor must, of course, be physically coupled to the driveshaft or crankshaft of the engine. This requires some sort of gearing arrangement. Such arrangement invariably has associated therewith mechanical tolerances that introduce some error into the rotor shaft's position as compared to the driveshaft's position. Further, such rotorshaft represents an additional moving part of the engine that requires continual maintenance and repair. Elimination of the need for such a shaft and gear arrangement would thus represent a significant improvement in the art. However, at present, it is not practical nor feasible to electronically switch such high voltages.

[0010] Dynamically adjusting the timing of a gasoline engine that employs a conventional ignition system as described above is likewise a problem. That is, the precise rotational point of the engine's drive or crankshaft at which the fuel/air mixture needs to be ignited in order to optimally couple energy therto varies as a function of engine speed. Thus, mechanisms that physically alter the point at which the breaker contacts close or open, relative to the rotational position of the distributor's rotor arm, must be employed. Vacuum advance systems, or equivalent mechanical advance systems, are typically employed for this purpose. Such advance systems represent still additional hardware that must be used with the engine. Such hardware is not only expensive, but it must also be kept in good condition and repair if the engine is to operate efficiently. It would, therefore, be an improvement in the art if such hardware could be eliminated.

[0011] A further problem with prior art ignition and fuel delivery systems is.mairitaining the ratio of fuel to air at the most acceptable level for efficient ignition and combustion in light of the temperature, pressure, humidity, emission levels, and other parameters that influence efficient, yet acceptable, engine performance. Furthermore, as with the "timing" adjustments above referred to, the proper ratio of fuel to air is a dynamic parameter that varies as a function of many parameters, such as ambient temperature, engine temperature, humidity, barometric pressure, engine speed, the octane cating of the fuel, and the like.

[0012] From the foregoing, it should be evident that significant improvements could be realized if the mechanical distributor and all the moving parts associated therewith, and the ignition coil, and all the hardware and problems associated therewith, could be eliminated. Unfortunately, as mentioned earlier, due to the significant energy required to ignite a fuel/air mixture (typically around 8_-12 Kvolts, and sometimes as high as 30 Kvolts), it is not presently feasible to distribute such high voltages to the spark plugs through any means other than the mechanical distributor presently used. That is, solid state switching devices cannot, at present, be economically employed to perform the high voltage switching function; and even if they could, the problems associated with generating the high voltage and transferring it over suitable cables (e.g., RFI, unpredictable time delays, etc.) would still be present.

[0013] Accordingly, a main object of the present invention is to provide an ignition system that does not require the use of a mechanical distributor nor the use of a high voltage ignition coil nor any of the elements or hardware typically associated with the use of such devices, such as breaker points_.condensers, RFI suppression devices, and the like.

[0014] A further object of the present invention is to provide an ignition system wherein electronic means are used to selectively distribute a low voltage signal to respective cylinders, at which point the low voltage signal is converted to a high voltage energy of sufficient strength to ignite the fuel/air mixture of the appropriate cylinder.

[0015] An additional object of the present invention is to provide an ignition system as above described wherein the rotational position of the driveshaft is directly sensed without the necessity of mechancially coupling a rotor shaft or similar device thereto.

[0016] Still a further object of the present invention is to provide an ignition system wherein electronic computing means are employed to determine the appropriate "timing" associated with the selective igniting of the fuel/air mixture of a given cylinder relative to the rotation position of the driveshaft.

[0017] Still an additional object of the invention is to provide an ignition system as above described that includes a plurality of sensors adapted to sense environmental and other conditions that may influence the efficient operation of the engine in which the ignition system is used, and wherein electronic computing means are adapted to be responsive to the sensors so as to selectively adjust and compensate the "timing" of the ignition system, thereby realizing a more efficient engine operation.

[0018] It is also an object of the present invention to provide an ignition system that cooperates and controls fuel injection means, thereby making it possible to dynamically control the ratio of fuel-to-air in the fuel/air mixture in order to optimize fuel consumption and engine performance according to the sensed environment in which the engine is used.

[0019] The above and other objects of the invention are realized in an illustrative embodiment of a low voltage ignition system that includes electronic means for generating a low voltage ignition signal having a desired relationship with respect to a synchronizing signal. Distribution means are then used to distribute the low voltage signal to a desired combustion chamber wherein a suitable fuel/air mixture has been inserted. Low-to-high voltage conversion means are next used at the combustion chamber to convert the low voltage signal to a high voltage signal of sufficient energy to ignite the fuel/air mixture contained therein.

[0020] The low-to-high voltage conversion means above referred to is preferrably realized with a piezoelectric spark plug assembly that has associated electrodes placed in direct communication with the combustion chamber wherein the fuel/air mixture is inserted. Such a piezoelectric spark plug assembly is adapted to produce a high voltage spark within the combustion chamber in response to receiving a low voltage ignition signal.

[0021] When the low voltage ignition control system described herein is utilized in a conventional gasoline internal combustion engine, the synchronizing signal above referred to may be readily obtained from optical or magnetic sensors that are directly affixed to the crankshaft or flywheel of the engine, thereby eliminating the need for a distributor shaft that is mechancially geared to the crankshaft of the engine. Further, a sequence of low voltage ignition signals each having a desired relationship with respect to the synchronization signal, may be readily generated using electronic computing circuitry that cannot only be preprogrammed to define the relationship of each low voltage ignition signal to the synchronizing signal, but that also can be used to instantaneously alter or modify this relationship as a function of sensed environmental or engine status conditions. Accordingly, a plurality of sensors may be coupled to the electonic computing means to continually feed information thereinto concerning the status of the engine and the environment in which the engine is operating.

[0022] The low voltage signals may advantageously be distributed to the desired combustion chambers in almost any desired fashion, without concern for cable length, high voltage insulation, generation of RFI, and the like.

[0023] Finally, where modern electronic fuel injection means are employed to inject a controlled amount of fuel into the combustion chambers (thereby eliminating the need for a conventional carburetor), the electronic computing means above referred to may also be coupled to the fuel injection means in order to control such fuel injection. Such control not only includes the timing of the fuel injection, but also includes a control of the quantity of fuel delivered to each cylinder, thereby providing a controlled means of dynamically adjusting the fuel-to-air ratio.

[0024] In the drawings:

The above and other objects, features, and advantages of the present invention will be more apparent from the following description of the accompanying drawings, in which:

FIG. 1 is a schematic representation of a conventional prior art ignition system;

FIG. 2 is a schematic block diagram of the low voltage ignition control system of the present invention;

FIG. 3 is a more detailed schematic block diagram of the present invention;

FIG. 4 is an electrical schematic diagram of a suitable buffer circuit shown in FIG. 3;

FIG. 5 is an electrical schematic/block diagram showing an alternate method of distributing the low voltage ignition signals to the desired combustion chambers;

FIG. 6 is a side, cross-sectional view of a low voltage peizoelectric spark plug that may be utilized with the present invention; and

FIG. 7 is a block diagram of the control circuitry shown in FIG. 3.

[0025] Referring now to the drawings:

The advantages and featurs of the present invention are best understood by comparing the invention with prior art ignition systems. Thus, in FIG. 1, there is shown a schematic representation of a prior art ignition system 12. The system includes a source of electrical power, or battery 14, which connects the power through an ignition switch 16 to the primary side of an ignition coil 18. A set of contact breakers or points P is connected in series with the primary of the coil 18 so as to selectively control the current that flows therethrough. A condensor or capacitor C is connected in parallel across the points P.

[0026] The secondary side of the ignition coil 18 is connected via high voltage cable 20 to the rotor 22 of a distributor 24. The representation shown in FIG. 1 contemplates an eight cylinder engine; therefore, the rotor 22 of the distributor 24 is adapted to sequentially come in contact with one of eight terminals 26, each of which is connected via a high voltage cable 28 to a respective spark plug 30. the spark plug 30 is directly connected to a combustion chamber 32 wherein a fuel/air mixture, represented symbolically in FIG. 1 as 34, has been injected.

[0027] The internal combustion engine in which the ignition system 12 is employed includes a drive or crankshaft 36 to which a flywheel 38 is directly connected. A suitable gearing arrangement, represented in FIG. 1 as the gearbox 40, couples a rotor shaft 42 to the rotor 22 of the distributor 24. Also coupled to the rotor shaft 42, typically through a suitable cam arrangement, is a means for opening and closing the points P as a function of the rotational position of the rotor shaft 42.

[0028] In operation, the gearing mechanism 40 typically includes a 2 to 1 reduction so that the rotor shaft 42 makes one complete revolution for every two revolutions of the flywheel 38. A cam (not shown) is placed on the rotor shaft 42 and causes the breaker points P to just begin to open as one of the pistons (not shown) nears the top of its compression stroke. At this same point in time, the rotor 22, carried on top of the rotor shaft 42, is opposite one of the electrodes in the distributor 24.

[0029] When the points P are closed, a current of typically between 3 or 4 amps flows through the primary winding of the ignition coil 18. This primary winding will usually consist of a few hundred turns of heavy gauge insulated copper wire, and a magnetic field is accordingly generated in a laminated iron core 44 of the coil 18. As the rotor shaft 42 turns, the cam mounted thereon opens the points P, interrupting the primary winding current. The magnetic field then "collapses", causing a high voltage of up to 30 Kvolts to be induced in the secondary winding of the coil 18, which secondary winding is typically made up of between 15,000 to 30,000 turns of very fine insulated copper wire wound around the iron core 44.

[0030] As mentioned previously, the magnetic field associated with the induced secondary voltage will, in turn, induce a voltage (referred to as the back emf) in the primary winding. This back emf voltage can be as high as 500 volts. Because this voltage can arc across the opening contacts of the points P, dissipating some of the stored energy in the coil and burning the points, the capacitor C is connected across the points to minimize the impact of such arcing.

[0031] The induced high voltage of the secondary flows through the heavily insulated cable 20 and 28 to the spark plug 30 at the appropriate time, where a spark is produced between the electrodes, at 46. This spark ignites the fuel/air mixture 34 in the combustion chamber 32 and the very rapid burning of this fuel/air mixture releases energy, shown symbolically in FIG. 1 as the arrow 48, that is used to rotate the crankshaft 36 through the use of pistons (not shown) or equivalent mechanisms.

[0032] While the above description of the prior art ignition system 12 is very simplified, it suffices to illustrate that the point in time when the high voltage signal reaches the sparkplug to ignite the fuel is very critical for proper engine performance. As indicated, this timing is controlled by the opening of the points P and the rotational position of the rotor 22. In turn, each of these events are controlled by the rotational position of the rotor shaft 42, which rotational position is determined by the gearing arrangement 40 that is coupled to the crankshaft 36. Each of these elements in this critical timing chain represent moving mechanical parts that are subject to maintenance and repair, a fault in any one of which would prevent the engine from performing properly. Further problems exist with the ignition system 12 as discussed previously, such as the RFI problems that result from having to distribute such a high voltage impulse over the cables 20 and 28 to the appropriate spark plugs. Moreover, much energy can be wasted when undesirable arcing occurs at the points P.

[0033] A simplified block diagram of the present invention is shown in FIG. 2. The primary object of the invention is, of course, to produce an ignition spark, represented symbolically as the wavy arrow 52, at the appropriate time in a combustion chamber 50 that has been filled with a suitable fuel/air mixture, represented by the lines 54. The time at which the ignition spark 52 occurs is determined by the time at which a low voltage ignition signal arrives at a low voltage ignition device 56 over a low voltage signal line 58. The time at which the low voltage ignition signal is generated is determined, in turn, by control circuitry 60 that generates the low voltage ignition signal a predetermined time after receipt of a position over signal line 62. In the preferred embodiment, the control circuitry 60 actually includes computing means whereby the timing between the position signal and the low voltage ignition signal may be selectively adjusted.

[0034] When the low voltage ignition control system of the present invention is employed with a conventional internal combustion engine, the reference signal may be derived from a sensor 64 that is adapted to sense the rotational position of the flywheel 66. The flywheel 66, of course, is directly coupled to the driveshaft or crankshaft 68, thereby providing a means whereby the control circuitry 60 is continually updated with a reference signal that indicates the exact rotational position of the crankshaft 68. Armed with this information, the control circuitry 60 may generate the low voltage ignition signals to selectively occur at precisely the appropriate time so that the energy resulting from the ignition of the fuel/air mixture in the combustion chamber . can be optimally coupled to the crankshaft 68.

[0035] The control circuitry 60 may further provide a signal over signal line 70 to a fuel/air ratio control device 72. This ratio control unit 72 appropriately sets the fuel-to-air ratio of the fuel/air mixture 54 so as to insure optimum engine performance. Thus, the control circuitry 60 may be used not only to control the timing of the ignition of the fuel/air mixture, but also to set the ratio of fuel-to-air contained therein.

[0036] It is to be noted that the low voltage ignition device 56 is coupled to a source of electrical power 74 through ignition switch 76 over signal line 78. Power from the power source 74 is also used to energize the control circuitry 60. In the preferred embodiment, the power source 74 may advantageously be a conventional automobile battery (typically 12 volts).

[0037] In FIG. 3, a more detailed block diagram schematic of a preferred embodiment of the invention is shown. In FIG. 3, like numerals are used to designate like parts from the more general block diagram of FIG. 2.

[0038] It is seen in FIG. 3 that the low voltage ignition device 56 of FIG. 2 includes a piezoelectric spark plug 80 and a buffer circuit 82. the buffer circuit 82 receives the low voltage ignition signal over signal line 58 and converts it to a signal suitable for driving the piezoelectric crystal spark plug 80 that is received over signal line 84. The signal on signal line 84 is still a low voltage signal, but it has been buffered so as to present the proper drive levels required by the piezoelectric crystal spark plug 80. By using the buffer circuit 82 in this fashion, the low voltage ignition signal appearing on signal line 58 may be a very low level signal, such as is commonly employed in low power digital circuitry. Further details of the buffer circuit 82 and the piezoelectric spark plug 80 are discussed below.

[0039] As is evident from FIG. 3, the preferred embodiment contemplates additional buffer circuits 86a and 86b, and corresponding low voltage ignition signal lines 88a and 88b, as well as other low voltage spark plugs (not shown) to be used as part of the invention. That is, each cylinder of the engine will have associated therewith its respective peizeolectric crystal spark plug, such as 80, buffer circuit, such as 82 (or 86a or 86b), and low voltage ignition signal line, such as 58 (or 88a or 88b).

[0040] The control circuitry 60 is adapted to place a low voltage ignition signal on the respective low voltage ignition line connected to the cylinder to be ignited. The timing of this low voltage ignition signal is determined relative to a reference signal recieved over signal line 62 from the rotational position sensor 64.

[0041] Sensors 90a, .90b, 90c, ... 90n are also coupled to the control circuitry 60 over respective signal lines. Each of these sensors is adapted to sense a particular parameter associated with the environment in which the engine is operating. For example, the sensor 90a may sense engine temperature, while the sensor 90b may sense ambient temperature. The sensor 90c could sense barometric pressure, while other sensors could sense parameters such as emissions (exited into the atmosphere through the engine's exhaust system), humidity, altitude, and the like. Each of these variables could, in some way, impact the operation of the engine. Thus, by feeding all this information into the control circuitry 60, appropriate adjustments to the timing of the low voltage ignition signals can be made in order to compensate for the environmental factors.

[0042] Additional compensation may be realized using a feedback sensing circuit 92 that is coupled between the buffer circuit and the piezoelectric spark plug associated with each cylinder. As will be explained in more detail below, the piezoelectric spark plug 80 is a transducer that converts the low voltage ignition signal recieved over signal line 84 to a mechanical stress within a crystal element. This mechanical stress is then converted to a high voltage electrical signal through another piezoelectric element. This high voltage electrical signal then causes a spark to arc between the electrodes 94 and 96 thereof. This spark, in turn, ignites the fuel/air mixture 54, and the resulting combustion produces the energy that is used to rotate the crankshaft 68 in conventional fashion. However, this process also functions, to a limited degree, in reverse. That is, as the rapid combustion of the fuel/air mixture in the combustion chamber occurs, a mechanical stress is sensed in the piezoelectric spark plug 80 that is reflected as a voltage impulse on the signal line 84. This voltage impulse gives an indication of the duration and magnitude of the combustion process that has just taken place within the combustion chamber. A suitable feedback sensing circuit 92 can then be used to direct this magnitude and time duration information back into the control circuitry 60. The control circuitry 60 may then act upon this information and make any adjustments that need to be made in subsequent firings of that particular cylinder. The buffer circuit 82 (or other buffer circuits, such as 86a or 86b) serves the additional function of protecting the control circuitry 60 from this reflective voltage pulse.

[0043] The low voltage ignition system of the present invention may also employ indicators and displays 91 that are coupled to the control circuitry 60. Those displays and indicators are adapted to display numerous parameters, such as the information sensed by the engine sensors 90a, 90b, ... 90n. The particular information displayed may be controlled by manual means, such as a simple keyboard, as indicated by the manual control 93. This manual control 93 may also be used to give specific commands to the control circuitry 60 in order to have it perform a desired function, or to alter the internal programs it uses to compute delay times and the like.

[0044] The feedback sensing circuit 92 may be realized in numerous ways. Preferrably, a simple differentiating circuit realized with passive components, such as resistors and capacitors, will be used that allows the required timing information to be sensed at the control circuitry 60. This timing information would include an indication of the width of the reflected voltage pulse, as well as an indication of when the reflected pulse was received relative to when the low voltage ignition signal was sent. The width of the timing pulse would, therefore, give some indication of the magnitude thereof. A simple feedback sensing circuit 92 could be realized using a resistor and capacitor in series, although more sophisticated types of feedback sensing circuits could be readily employed by those skilled in the art.

[0045] The sensor 64 could be realized using any of a wide variety of position sensors that are currently available on the market. Alternatively, a simple optical sensor could be realized using an LED (light emitting diode) and photosensitive transistor juxtaposed so as to be in selective light communication with each other as a function of the rotational position of the flywheel. For example. a plurality of holes could be placed in known locations around the circumference of the flywheel 66 and the LED and photosensitive transistor could be placed so as to allow light from the LED to pass through the holes to the transistor. At least one such hole would be required in order to generate at least one reference signal for each revolution of the flywheel 66. However, additional reference signals could be generated during each revolution of the flywheel 66 so that continuous angular or rotational information is fed into the control circuitry 60, which information defines the precise rotational position of the crankshaft 68.

[0046] If desired, rather than employ an optical sensor for the sensor 64, a magnetic sensor could be employed that could sense, for example, the passing of a permanent magnet thereby. Such permanent magnets could be selectively imbedded into the flywheel 66. The use of a magnetic sensor may be preferred over a light sensor due to the accumulations of oil or other lubricants that may find their way onto the periphery of the flywheel 66, and tend to retard or inhibit the transmission or reflection of light.

[0047] In FIG. 4, there is shown an electrical schematic diagram of a simple buffer circuit 82. As shown, the circuit merely includes a transistor Q₁ and a resistor R. The base of the transistor is connected to signal line 58 and the collector thereof is connected to the power line 78. The resistor R connects the emitter of the transistor to a suitable ground reference, and the signal line 84 is also connected to the emitter. Those skilled in the art will readily recognize that the buffer circuit 82 is thus nothing more than an emitter follower, a circuit which provides current gain but not voltage gain.

[0048] In FIG. 5, an alternative embodiment for distributing the low voltage ignition signals to the various signals is shown. In this embodiment, a control chip 100 performs the same function of the control circuitry 60 of FIGS. 2 and 3. However, in this instance, the control chip 100 is adapted to generate a digital word each time a cylinder is to be ignited. Included within this digital word are appropriate address bits that direct it to a specific cylinder. For example, if a cylinder 112 is to be ignited, and this cylinder has a piezoelectric crystal spark plug 110 coupled thereto, then a buffer circuit 106 connects the piezoelectric crystal spark plug 110 to the signal line 98. Included within the buffer circuit 106 is selection logic 102. The selection logic 102 monitors all of the data words that pass by on signal line 98. Only when a correct address is sensed, will the selection logic 102 allow the low voltage signal to pass through the remainder of the buffer circuit to the low voltage spark plug 110. In a similar fashion, a cylinder 114 having a low voltage spark plug 116 and buffer circuit 108, including selection logic 104, directs only those signals to the plug 116 that the selection logic 104 allows to pass through the buffer circuit 108. By using an addressing scheme as thus described, a single wire bus 98 may be used to interconnect all of the low voltage spark plugs and associated buffer circuits to the control chip 100.

[0049] FIG. 6 shows a piezoelectric crystal spark plug that could be employed with the present invention. The features of this spark plug, as well as various embodiments thereof, are more fully disclosed in my co-pending EPO application, No. 81106866.7, filed September 2, 1981, which application is hereby incorporated into this disclosure by reference. Basically, the piezoelectric crystal spark plug may be realized with a high voltage piezoelectric crystal 120 formed in the shape of a long, hollow cylinder. The crystal 120 is confined within a hollow sleeve 122. The sleeve 122 and crystal 120 are, in turn, disposed in the hollow of an insulator 124 which is seated in a conventional spark plug body 126. The body 126 includes a ground electrode 128 extending from the lower portion of the body over a hollow 130 formed in the bottom of the body.

[0050] Positioned above the crystal 120 and sleeve 122 and mechanically coupled to the crystal 120 are a stack of low voltage piezoelectric crystals 132. The crystals 132 are secured together in a stack as shown with the top surface of each crystal being connected to a conductor 134 which is coupled to a threaded bolt 136 at the top of the spark plug. A conventional connecting nut 138 is screwed onto the top of the threaded bolt 136. The bottom of each crystal in the stack 132 is connected by conductor 140 to the spark plug body 126 to complete the circuit for the crystal stack 132. The top of the high voltage piezoelectric crystal 120 is also coupled by way of conductor 140 to the spark plug body 126.

[0051] Disposed below the crystal 120 and electrically coupled thereto is a central electrode 142. The central electrode 142 extends from the bottom of the crystal 120 into the cavity 130 of the spark plug body 126 to a point close to, but spaced from, the ground electrode 128, as in a conventional spark plug.

[0052] In operation, the buffered low voltage ignition signal is supplied by way of conductor 84 to the bolt 136 and from there conducted to the crystal stack 132 to cause the crystal stack to deform. Deformation of the crystal stack 132, in turn, causes crystal 120 to deform (e.g., by compression), to thereby produce a high voltage electrical signal which is supplied to the central electrode 142. This high voltage electrical signal is of significant magnitude to cause a spark to be produced between the central electrode 142 and the ground electrode 128. The spark, in turn, ignites the fuel/air mixture contained in the combustion chamber to which the electrodes 128 and 142 are exposed.

[0053] A comment at this point in the application would be appropriate as to the feasability of using piezoelectric materials for a spark plug device. Piezoelectric materials, of course, are well known in the art. The word "piezo" is derived from the Greek word meaning "press" and the piezoelectric effect is the production of electricity in a material by the applicaion of pressure. This effect occurs in electrical insulators and results in the appearance of electrical charges on the surface of the mechanically deformed material. The converse effect to piezoelectricity also exists. That is, when an electric field is applied to a piezoelectric material, it distorts mechanically. All piezoelectric materials can be used in either way.

[0054] A study of piezoelectric constants associated with prior art piezoelectric crystals shows that practical levels of compression, say up to 7,000 PSI, will produce voltages in the range of 5 to 15 Kvolts per cm. Thus, in theory, such devices could provide the spark for gasoline motor ignition. However, no one has successfully heretofore been able to use piezoelectric crystal devices for spark plugs because the ceramic element, at least those ceramic elements heretofore employed, have depolarized under continuous stress. However, applicant has successfully overcome this problem by properly loading the piezoelectric crystals both mechanically by pre-stress and electrically by proper loading so that depolarization does not occur. Depolarization of ceramic crystals typically occurs because a voltage is reflected back from an improperly loaded crystal. Thus, by properly loading the crystal, which includes making the gap between the electrodes 128 and 146 (FIG. 6) the proper distance, and by properly configuring the stack of low voltage crystals 132 to the high voltage crystal 120 (FIG. 6), the depolarization problem is obviated and surprising, remarkable results are achieved. Moreover, improved manufacturing techniques of modern piezoelectric crystals greatly reduces the tendency of the crystal to depolarize.

[0055] Further, new piezoelectric materials have recently been developed that greatly lend themselves to the type of application herein disclosed. See generally Uchino, Nomura, Cross, and Newnham, "Electrostriction in Perovskite Crystals and its Applications to Transducers," Pennsylvania State University, PA (Thesis, Dec. 1980), which article on electrostriction is hereby incorporated by reference in this application. Such new materials, while not generally being referred to as "crystals," are most assuredly "piezoelectric," and for that reason are ideally suited for a spark plug application as disclosed herein by applicant.

[0056] It should be noted that a specific advantage of using a piezoelectric spark plug for ignition of a gasoline engine is that the voltage is completely independent of the engine speed. This insures not only excellent starting, but also excellent and predictable engine performance.

[0057] Referring next to FIG. 7, there is shown a typical block diagram of the control circuitry 60. It is to be emphasized that FIG. 7 represents only one

[0058] of many configurations that could be employed to achieve the computing function previously described in connection with the control circuitry 60. The embodiment of FIG. 7 is built around a microprocessor of CPU 150. A clock 152 and system controller 154 interface with the CPU 150. A read only memory, or ROM 156, is also coupled to the CPU 150 over a system bus 158. The ROM 156 typically includes the firmware (permanently stored programs and routines) to steer the CPU 150 to perform its desired functions. A read/write memory 160 may also be employed in order to store parameter values sensed from the engine sensors 90a, 90b, ... 90n, for comparison, and similar purposes. A priority interrupt circuit 162 could be used to couple the manual control 93 (FIG. 3) with the system bus 158. Similarly, a communication interface 164 is adapted to receive and interface the timing reference signal over signal line 62 (FIG. 3), the signals from the engine sensors 90a, 90b, ... 90n, and, if used, the feedback from the low voltage spark plugs (such as is received from the feedback sensing circuitry 92 of FIG. 3). These signals are all directed through the communication interface 164 to the system bus 158, from which location they may be directed to any point within the control circuitry 60 under control of the system controller 154. A peripheral interface 166 is also used to receive signals from the signal bus 158 and direct them to desired locations throughout the low voltage ignition control system. Such signals include the low voltage ignition signals directed to the low voltage spark plugs, the signal that controls the fuel/air ratio set by the controller 72, and the signals required by the system indicators in the displays 91 (FIG. 3).

[0059] All of the above described microprocessor-related devices are well known in the art and could be realized by those skilled in microprocessor art. For example, the Intel 8080 system could be used to realize the control circuitry 60. Numerous semi-conductor manufacturers, in addition to Intel, manufacture comparable (and even pin for pin compatible) micro-processor systems. The 8080 system includes commercially available components that those skilled in microprocessor art could easily combine to realize the desired control. For example, the CPU 150 could be realized using an 8080A CPU. The clock 152 could be realized using an 8224, also a commercially available component. The system controller 154 could likewise be realized using a commerically available 8228; while the priority interrupt 162 could be realized using an 8214, the communication interface 164 using an 8251, and the peripheral interface 166 using an 8255. Further, there are numerous commerically available ROM and read/write memories that could be used for the ROM 156 and the memory 160. Using such commerically available parts, the control circuitry 60 could be realized using a small number of commercially available chips mounted on an appropriate circuit board, which circuit board could advantageously be smaller than the size of a standard piece of paper. Such circuit board could be mounted anywhere within the general vicinity of the gasoline engine wherein the low voltage ignition system is to be used.

[0060] It should also be noted that a microprocessor system using commercially available components as above described provides many more functions than are probably needed by the low voltage ignition control system described herein. Accordingly, it is conceivable that a special purpose semi-conductor chip could be manufactured that would be limited to only the needed functions. For example, the read/write memory capacity required by the control circuitry 60 would be very low compared to the memory requirements of other microprocessor systems. Similarly, the programs and routines stored in ROM, are relatively low compared to other microprocessor uses. Accordingly, all of the functions described in FIG. 7 could quite conceivably be combined in a single semi-conductor chip by those skilled in semi-conductor and electronic art. Such simplifications and manufacturing improvements are contemplated as being included in the present invention.

[0061] The sensors 90a, 90b, ... 90n shown in FIG. 3 may also be realized using commercially available components. Such sensors are presently in use on many modern automobile engines to indicate such parameters as temperature, oil pressure, emission levels, and the like. Manufactures of such sensors (and such sensors are constantly being improved) include Ford, General Motors, and Robert Bosch. Such sensors and other similar sensors, could be readily realized by those skilled in the art depending upon the particular parameter that is to be determined.

[0062] While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit of the scope of the present invention. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. An ignition system for use with an internal combustion engine having at least one combustion chamber adapted to receive a fuel/air mixture that may be selectively ignited, said ignition causing a release of energy from said fuel/air mixture that is transferred to rotational energy at a driveshaft of said engine, said igntion system comprising

means for sensing the rotational position of the driveshaft of said engine;

means for generating a low voltage ignition signal when the rotational position of said driveshaft is at a predetermined position;

distribution means for distributing said low voltage ignition signal to a desired combustion chamber; and

low-to-high voltage conversion means for converting said low voltage ignition signal upon its arrival at the appropriate combustion chamber to an ignition energy sufficient to ignite the fuel/air mixture contained therein.

2. An ignition system as defined in Claim 1 wherein said low-to-high voltage conversion comprises a piezoelectric spark plug assembly in direct communication with the combustion chamber, said piezoelectric spark plug assembly being adapted to produce a spark within said combustion chamber in response to receiving the low voltage ignition signal, which spark is adapted to be of sufficient energy to ignite the fuel/air mixture.

3. An ignition system as defined in Claim 2 wherein said piezoelectric spark plug assembly includes:

a first electrode;

a second electrode electrically coupled to a reference potential disposed near but spaced apart from one end of the first electrode;

a piezoelectric crystal, one side of which is electrically coupled to the other end of said electrode, said piezoelectric crystal being adapted to produce a high voltage electrical spark between said first and second electrodes in response to being mechanically deformed; and

deforming means for deforming said piezoelectric crystal in response to said low voltage ignition signal.

4. An ignition system as defined in Claim 1 wherein said means for sensing the rotational position of the driveshaft comprises:

at least one identifying mark coupled to said driveshaft, whereby said identifying mark rotates as said driveshaft rotates;

a sensor adapted to sense and signal the presence of said mark whenever said mark assumes a fixed and known orientation with respect to said sensor, said sensor being adapted to generate a position signal each time said fixed and known orientation is assumed.

5. An ignition system as defined in Claim 4 wherein said identifying mark is placed on a flywheel that is directly coupled to said diveshaft, one revolution of said driveshaft causing one revolution of said flywheel.

6. An ignition system as defined in claim 5 wherein said identifying mark comprises a transmission path through said flywheel through which radiation may pass, and further wherein said sensor comprises a radiation emitter and a radiation receiver juxtaposed on opposite sides of said flywheel, radiation generated by said emitter being received by said receiver only when the rotational position of said flywheel has aligned said radiation transmission path between said emitter and receiver, said receiver being adapted to generate said position signal in response to receipt of the radiation generated by said emitter.

7. An ignition system as defined in Claim 6 wherein said radiation is light and wherein said transmission path comprises an aperture through said flywheel through which a beam of said light may pass.

8. An ignition system as defined in Claim 1 wherein said means for generating a low voltage ignition signal comprises computing circuitry, said circuitry being adapted to compute the rotational position of said driveshaft at all times, said computing circuitry being further adapted to verify and update this computed rotational position at least once for each revolution of said driveshaft by comparing and synchronizing this computed rotational position with the actual rotational position as sensed by said driveshaft rotational position sensing means, said computing circuitry being further adapted to generate said low voltage ignition signal whenever the computed rotational position of said driveshaft has attained a predetermined position.

9. An ignition system as defined in Claim 8 further comprising a plurality of engine status sensors selectively positioned throughout and around said engine, each of said status sensors being adapted to input a status signal to said computing circuitry that indicates a selected engine operating parameter, such as engine temperature, barometric pressure, engine emissions, and the like, said computing circuitry being adapted to adjust the computed rotational position of said driveshaft at which said low voltage ignition signal is generated as a function of the value of the engine operating parameters sensed by said status sensors.

10. An ignition system as defined in Claim 9 further including ratio adjusting means for selectively adjusting the ratio of fuel and air delivered to said combustion chamber as controlled by said computing circuitry, said ratio adjusting means being adapted to optimally adjust the ratio of fuel and air as a function of the value of the engine operating parameters sensed by said status sensors, thereby providing for a more complete and energy efficient combustion of said fuel/air mixture.

11. An ignition system as defined in Claims 9 or 10 further including feedback sensing means coupled to said combustion chamber and connected to said computing circuitry for sensing the time, duration, and quality of the combustion that occurs within said combustion chamber, said computing circuitry being adapted to monitor this combustion information in conjunction with the other engine operating parameters and to selectively adjust the computed rotational position of said driveshaft at which the low voltage ignition signal is generated so as to optimize the operation of said engine.

12. An ignition system as defined in Claim 8 wherein said distribution means comprises a separate conductive element connected between said computing circuitry and the low-to-high voltage conversion means associated with each combustion chamber of said engine, said computing circuitry having a separate output temrinal associated with each of said conducting elements.

13. An ignition system as defined in Claim 12 wherein said distribution means further includes a buffer circuit interposed between said low-to-high voltage conversion means and said conductive element of each combustion chamber of said engine, said buffer circuit being adapted to provide a suitable interface between said computing circuitry and said low-to-high voltage conversion means.

14. An ignition system as defined in Claim 13 wherein said buffer circuit comprises a transistor element that is adapted to increase the current drive capability of said low voltage ignition signal, the transistor elements of each of said buffer circuits being connected in common to a power bus that is connected to a suitable power source.

15. An ignition system as defined in Claim 8 wherein said distribution means comprises:

a common conductive element that interconnects said computing circuitry with the low-to-high voltage conversion means associated with each combustion chamber of said engine; and

a buffer circuit interposed between each low-to-high voltage conversion means, said buffer circuit being adapted to receive only those low voltage ignition signals that said computer circuitry respectively directs to a particular low-to-high voltage conversion means over said common conductive element.

16. An ignition system as defined in Claim 15 wherein said buffer circuit comprises:

selection means for selectively receiving only those low voltage ignition signals on said common conductive element that have been directed to said buffer circuit by said computing circuitry; and

a transistor element adapted to increase the current drive capability of said received low voltage ignition signal, said transistor element being coupled to a suitable power source over a power bus that is shared with other buffer circuits.

17. An ignition system as defined in Claim 8, 9 or 10 wherein said computing circuitry comprises:

a central processing unit;

a system controller adapted to control said central processing unit;

a clock for providing timing signals used by said central processing unit and system controller;

a read only memory;

a plurality of interface circuits for interfacing the electrical signals received by and sent from said computing circuitry; and

means for electrically interconnecting said central processing unit, system controller, clock, memory, and interface circuits.

18. An improved low voltage ignition system for sequentially and cyclicly generating an igniting spark at timed intervals in respective combustion chambers into which a desired fuel/air mixture has been placed, said ignition system comprising:

a source of stored electrical power;

timing means coupled to said source of electrical power for generating a synchronizing pulse that defines the beginning of the igniting cycle;

computing circuitry responsive to said synchronizing pulse for generating a sequence of low voltage firing pulses, one firing pulse being generated for each combustion chamber in which the fuel/air mixture is to be ignited, each of said firing pulses assuming a fixed adjustable timed relationship with respect to said synchronizing pulse as computed by said computing circuitry;

low-to-high voltage conversion means attached to each combustion chamber, each of said conversion means being adapted to generate an igniting spark having sufficient energy to ignite the fuel/air mixture; and

low-voltage distribtution means for distributing each low voltage firing pulse to a respective low-to-high voltage conversion means.

19. An ignition system as defined in Claim 18 wherein said low-to-high voltage conversion means comprises a piezoelectric sparkplug assembly adapted to produce a spark inside of said combustion chamber in response to receiving said low voltage firing pulse.

20. An ignition system as defined in Claim 19 further including a plurality of status sensors coupled to said computing means, each of said sensors being adapted to sense a different parameter associated with the operation of said ignition system or the environment in which said ignition system is used, and to generate a sensor signal that is proportional to the valve of the parameter thus sensed, said computing means being adapted to receive said sensor signals and factor them in to the determination of the timed relationship between said firing pulses and said synchronization pulse, said variable timed relationship being used as a mechanism for adjusting the operation of said ignition system.

21. An ignition system as defined in Claim 18 wherein said timing means further generates a plurality of sub-synchronizing pulses having a fixed relationship to said synchronizing pulse, said sub-synchronizing pulses being used by said computing circuitry to further define the timed relationship between each of said firing pulses and said synchronizng pulse.

22. An ignition system as defined in Claim 18 wherein said computing circuitry comprises a microprocessor.

23. A. A method for igniting a fuel/air mixture delivered to a combustion chamber of an internal combustion engine having a driveshaft adapted to be rotated by energy derived from the selective ignition of said fuel/air mixture, said ignition method comprising the steps of:

(a) sensing the rotational position of said driveshaft;

(b) generating a low voltage ignition signal when said driveshaft is in an optimum position, as sensed in step (a), to receive energy derived from the ignition of the fuel/air mixture of a particular combustion chamber;

(c) distributing said low voltage ignition signal to the appropriate combustion chamber; and

(d) converting said low voltage ignition signal upon arrival at the appropriate combustion chamber to an ignition energy sufficient to ignite said fuel/air mixture, whereby energy derived from said ignition is optimumly transferred to said driveshaft.

24. An ignition method as defined in Claim 23 wherein step (a) of sensing the relative position of the driveshaft comprises:

(1) selectively marking the driveshaft with at least one identifying mark;

(2) mounting a driveshaft position sensor in close proximity to said driveshaft, said sensor being adapted to generate an electrical signal each time said identifying mark passes thereby; and

(3) using the receipt of said signal as an indication of the present position of said driveshaft.

25. An ignition method as defined in claim 24 wherein said identifying mark is placed on a flywheel directly coupled to said driveshaft.

26. An ignition method as defined in Claim 24 wherein step (b) of generating a low voltage ignition signal comprises

(1) monitoring the receipt of said electrical signal generated by said driveshaft-position sensor;

(2) using computing circuitry to compute the rotational position of said driveshaft at all times based upon the monitoring of said electrical signal; and

(3) generating said low voltage ignition signal to occur at the same time that said driveshaft has reached a pre-computed rotational position.

27. An ignition method as defined in Claim 26 wherein said computing circuitry is further response to environmental sensors selectively positioned in and around said engine, said environmental sensors being adapted to sense such parameters as engine temperature, barometric pressure, engine emissions, and the like, and to generate output signals as a function thereof, said computing circuitry being adapted to vary the pre-computed rotational position of the driveshaft at which the low voltage ignition signal is generated as a function of the output signals received from said environmental sensors.

28. An ignition method as defined in Claim 28 wherein step (d) comprises connecting a piezoelectric spark plug assembly in direct communication with each combustion chamber, said spark plug assembly including:

a first electrode;

a second electrode electrically coupled to a reference potential disposed near but spaced from one end of the first electrode;

a piezoelectric crystal, one side of which is electrically coupled to the other end of said first electrode, said piezoelectric crystal being adapted to produce a high voltage electrical spark between said first and second electrodes, said spark having sufficient ignition energy associated therewith to ignite the fuel/air mixture in said combustion chamber in response to being mechanically deformed; and

deforming means for mechanically deforming said piezoelectric crystal in response to said low voltage ignition signal.

Drawing