Patent Application
20110210745
This invention generally relates to power circuits for ion sense circuitry, and more particularly to power circuits for integrated ion sense and signal processing circuitry integrated with ignition coils.
In the past it was difficult to determine the performance characteristics of an engine due to the fact that it was difficult to determine what was taking place in the combustion chamber of the engine. With the advent of ion sensing came the ability to determine the characteristics of the combustion within a combustion chamber, allowing one to determine whether a fuel mixture was, for example, too rich or too lean or whether knocking or good combustion was taking place.
Ion sensing relies on the fact that combustion in an engine creates measurable ionized gas. In such an engine an ion sensor may be installed or, with proper circuitry, the ignition spark plug or ignition coil may be used to sense ion current without installing additional sensors. The ion sensor detects a small current that flows through the ionized gas in the combustion chamber, and amplifier circuitry is used to allow analysis of the combustion ion signal to diagnose engine performance characteristics.
To provide enhanced analysis of the ion current signal, electronics are being integrated into ion sensing ignition coils for amplifying the small ion current signal and transmitting a high level analog signal to the Engine Control Unit (ECU) or other engine monitoring systems. Indeed, one such system is disclosed in co-pending application Ser. No. ______, filed on even date herewith, entitled Automatic Variable Gain Amplifier and assigned to the assignee of the instant application, the teachings and disclosure of which are hereby incorporated in their entireties by reference thereto.
One problem that has become apparent in ion sensing, however, relates to powering both the ion sensor, be it the ignition coil (spark plug) or a separate sensor, and the amplifying or signal processing electronics used therewith. In order to generate an ion current, the circuit requires a high voltage bias supply, in the range of 200 to 400 volts DC. The electronics used to amplify this ion signal also requires power, typically +/−5 Vdc.
In order to supply this power to these circuits, additional wires must be included in the system wiring harness. Such additional wires add to the overall cost and complexity of the system and the coil circuitry. Supplying this voltage to the ion sensing ignition coils though requires careful attention to ground loops and wire routing. Additionally, an Electromagnetic Interference (EMI) filter must be present inside each coil to filter any EMI that may be picked up by the system harness. Moreover, the typical voltage available in an engine system is 12 to 24 volts DC.
Further, generating the 200 to 400 volt bias required for the ion current generation is difficult. In the past, the bias would have been created using a flyback DC to DC converter containing a step up transformer. Because the bias current requirements are very low, the DC-DC converter could be small and contained in each coil. However, since the coils operate on the engine, their normal operating temperature is in the range of 90 to 100° C. Transformers of the typical DC-DC converter grade ferrites cannot operate at these high temperatures. Thus, higher cost ferrites, able to operate under the high temperature conditions, would need to be used, but this would drive up cost. Alternatively, the system could utilize a larger single DC-DC converter mounted off the engine to supply voltage to each coil, however this would require additional system harness wiring, again driving up cost and complexity. Moreover, the designer would be required to be cautious so as not to create ground loops, and isolation amplifiers would most likely be required. This, again, would increase cost and complexity.
Therefore, it would be advantageous to provide a system to supply the voltages required by the ion sensing ignition coils and electronics without adding the complexity and cost of additional wiring, high cost DC-DC ferrites, or a DC-DC converter mounted off of the engine. Additionally, it would be advantageous to provide an ignition system with ion sensing ignition coils that does not require EMI filters in the coils and eliminates the risk and complexity associated with possible ground loops created by the harness. Moreover, it would be advantageous to provide ion sensing ignition coil circuitry that is simple, small in size, operable at the high engine temperature.
Embodiments of the present invention provide such a system that provides one or more of the above advantages. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
In view of the above, embodiments of the present invention provide new and improved power supply for ion current sensing circuitry that overcome one or more of the problems existing in the art. More particularly, embodiments of the present invention provide a new and improved power supply for ion current sensing circuitry including ion current sensors and/or use of ignition coils (spark plugs), and amplification or signal processing circuitry that overcome one or more of the problems existing in the art.
In one embodiment, the AC current of the ignition system is rectified during a sparking event and stored in a capacitor to provide the bias voltage required for ion sensing. The ignition current is also rectified and stored on capacitors to power the ion current amplification circuitry. In preferred embodiments, such a power supply is very simple, small in size, utilizes primarily diodes and capacitors, and is able to operate at the high engine temperatures, thus eliminating the need for more expensive ferrites or a separate converter mounted off the engine to supply power to each sensor and to the electronics.
In one embodiment, the power supply utilizes the AC ion sensing ignition coil power during the sparking event for the sparking duration to generate the necessary power to generate the ion current during the combustion event and to power the electronics associated with amplification thereof.
In one aspect, certain embodiment of the present invention provides an ion sensing power supply system to supply the voltages required by the ion sensors or ignition coils used as an ion current sensor without adding the complexity and cost of additional wiring, high cost DC-DC ferrites, or a DC-DC converter mounted off of the engine. In another aspect, certain embodiments eliminate the need for EMI filters in the coils and reduces or eliminates the risk associated with possible ground loops created by wiring that otherwise would be needed in the harness.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.
Turning now to the Drawings, there is illustrated in
As illustrated in
In embodiments that utilize on-engine electronics, such as the variable gain amplifier discusses in the above identified co-pending application, or a low power micro-processor used to process the ion current signal, a sensor circuit power supply of +/−5 Vdc is also provided. To self generate this power requirement the illustrated embodiment includes the sensor power circuit 114 to be discussed in greater detail below.
During the sparking event, which is programmable and may be, e.g., of only 800 microsecond duration, the negative half cycle of AC current flow (see
Once the sparking period has ended, the bias supply capacitor 106 will be fully charged and ready to supply the large bias voltage required by the ion sense circuitry to generate the ion current across the spark gap 110 and sense its flow via resistor 112. During each subsequent sparking event, the AC current flow in the ignition coil secondary circuit 102 will again fully charge the bias supply capacitor 106 through diode 120 to the clamping voltage dictated by zener diode 122.
As introduced above and as described in detail in the above identified co-pending application, the ion sensing circuitry that analyzes the ion current flow may include an amplifier to selectively amplify the ion signal sensed across resistor 112 for use by an ECU. In such systems, power for the amplification circuitry can be self generated by the sensor power circuit 114 illustrated in
This charging cycle is shown by the two waveforms 128, 130 of
In the example simulation particularly suited to generate a 400 Vdc bias voltage and +/−5 Vdc sensor supply voltages during an 800 microsecond sparking event having a minimum triangular AC spark current of approximately 130 milliamperes RMS, the bias supply capacitor 106 is sized at approximately 0.1 μF, while the first and second power circuit capacitors 116, 118 are sized at approximately 5 μF. These small values of capacitance allowed the simulation to show full recharging from an initial condition of zero volts on all capacitors in 800 microseconds or less. Since the AC current flow for the spark generation is current limited by the ignition system, the charging rate of the capacitors 106, 116, 118 is determined by their size. A larger capacitor will charge more slowly, but its voltage will also droop less between recharging sparking events. As such, the capacitors 106, 116, 118 may be sized to provide balance between charge during the duration of the sparking event and droop during the ion measurement event As long as the charge delivered to the capacitors during the spark event is greater than the charge depleted during the ion measurement event, the capacitor voltages will remain in a safe operating area. However, if the charge depleted during the ion measurement event exceeds the charge delivered to the capacitors during the spark event, the capacitor voltages will eventually decrease to near zero and the circuits will cease to operate. Testing of a prototype system showed that it is not necessary to completely recharge the capacitors from zero charge on every spark event, and that on startup several spark events may be required to charge the capacitors sufficiently to be in an acceptable operating voltage range. For prototype testing capacitor 106 was 0.268 μF, and capacitors 116 and 118 were 100 μF. Also, note that as engine RPM increases the recharging spark events occur more frequently and there is therefore more charge available to be depleted by the ion bias and sensor circuits.
In another embodiment with an AC ignition coil diodes 120, 140, and zener 122 can be reversed in polarity to generate positive bias voltage rather than the aforementioned negative bias voltage. In still further embodiments the self power circuit for bias generation or sensor power can be used with either CD (capacitor discharge) or inductive ignition coils, with the limitation that the bias polarity and sensor power polarity options are limited by the unipolar direction of the spark current flow. Furthermore, CD or inductive ignition coils with a negative spark current polarity i.e. current flowing from the ground electrode of the spark gap to the high voltage electrode of the spark gap, can only produce positive bias supply and sensor supply voltages. Inversely, CD or inductive ignition coils with a positive spark current polarity i.e. current flowing from the high voltage electrode of the spark gap to the ground electrode of the spark gap, can only produce negative bias supply and sensor supply voltages.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
