The present invention relates generally to ignition modules and, more particularly, to ignition modules used with capacitive discharge ignition (CDI) systems, such as those employed by lawn, garden, and other outdoor equipment.
Capacitive discharge ignition (CDI) systems are sometimes used with small engines, including light-duty internal combustion engines such as those employed by lawn, garden, and other outdoor equipment. In order to provide sufficient ignition voltages during low speed environments, some CDI systems utilize charge coils with higher inductance and resistance characteristics. Although such an arrangement can be beneficial for producing high voltages at lower engine speeds, it can hinder the CDI system's ability to power electrical devices at higher engine speeds.
According to one aspect, there is provided an ignition module for use with a capacitive discharge ignition (CDI) system. The ignition module comprises: a charge coil, an ignition capacitor, a first switching device, a second switching device, and an electronic processing device coupled to the first and second switching devices. Activation of the first switching device creates a low impedance path between the charge coil and ground.
According to another aspect, there is provided a method of operating an ignition module. The method comprises the steps of: (a) inducing electrical energy in a charge coil, (b) shorting the charge coil during a first stage of a charge cycle, (c) interrupting the short during a second stage of the charge cycle, and (d) charging the ignition capacitor according to a flyback charging technique.
According to another aspect, there is provided a method of operating an ignition module. The method comprises the steps of: (a) inducing electrical energy in a charge coil, (b) using a flyback charging technique to charge an ignition capacitor, wherein the flyback charging technique is used when an engine is operating in a lower speed range, and (c) using a non-flyback charging technique to power an additional electrical device, wherein the non-flyback charging technique is used when the engine is operating in a higher speed range.
Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
The exemplary ignition system described herein is a capacitive discharge ignition (CDI) system that can be used with a variety of light-duty internal combustion engines, including those typically employed by lawn, garden, and other outdoor equipment. According to one embodiment, the ignition system uses an ignition module and a ‘flyback’ charging technique in a manner that can provide a number of positive features. For example, the ignition system can charge an ignition capacitor and additional electric devices with a single charge coil, it can charge across a wide spectrum of engine speeds, it can power both high voltage and high current devices, and it can have a reduced number of parts, weight, and expense, to name but a few possibilities.
Ignition System
With reference to
Ignition module 14 can generate, store, and utilize the electrical energy that is induced by the rotating magnetic elements 32 in order to perform a variety of functions. According to one embodiment, ignition module 14 includes a lamstack 40, a charge coil 42, a trigger coil 44, an ignition circuit 46, a step-up transformer 48, and an ignition module housing 50. Lamstack 40 is preferably a ferromagnetic part that is comprised of a stack of flat, magnetically-permeable, laminate pieces typically made of steel or iron. The lamstack can assist in concentrating or focusing the changing magnetic flux created by the rotating magnetic elements 32 on the flywheel. According to the embodiment shown here, lamstack 40 has a generally U-shaped configuration that includes a pair of legs 60 and 62. Leg 60 is aligned along the central axis of charge coil 42, and leg 62 is aligned along the central axes of trigger coil 44 and transformer 48. When legs 60 and 62 align with magnetic elements 32—this occurs at a specific rotational position of flywheel 12—a closed-loop flux path is created that includes lamstack 40 and magnetic elements 32. Magnetic elements 32 can be implemented as part of the same magnet or as separate magnetic components coupled together to provide a single flux path through flywheel 12, to cite two possibilities. Additional magnetic elements can be added to flywheel 12 at other locations around its periphery to provide additional electromagnetic interaction with ignition module 14.
Charge coil 42 generates electrical energy that can be used by ignition module 14 for a number of different purposes, including charging an ignition capacitor and powering an electronic processing device, to cite two examples. Charge coil 42 includes a bobbin 64 and a winding 66 and, according to one embodiment, is designed to have a relatively low inductance of about 2-10 mH and a relatively low resistance of about 10-50 Ω. In order to achieve these electrical characteristics, winding 66 can be made from 500-1,500 turns of 30-34 gauge copper wire. As a reference, some prior art windings are made from approximately 3,000 turns of 38 gauge wire, giving it an inductance of about 30-100 mH and a resistance of about 150-400 Ω. The electrical characteristics of a particular winding are usually tailored to its specific application. For instance, a charge coil expected to produce high voltage will oftentimes have more turns of finer gauge wire (thus giving it a higher inductance and resistance) so that it can generate a sufficient voltage during startup or other periods of low engine speed. Conversely, a charge coil designed to provide high current will typically have less turns of larger gauge wire (with a corresponding lower inductance and resistance), as this enables it to more efficiently create high current when the engine is running at wide open throttle or during other high engine speed conditions. As will be described in greater detail below, charge coil 42 is used as a sort of universal coil that sufficiently creates both high voltage and high current, and is able to do so across a wide range of engine speeds.
Trigger coil 44 provides ignition module 14 with an engine input signal that is generally representative of the position and/or speed of the engine. According to the particular embodiment shown here, trigger coil 44 is located towards the end of lamstack leg 62 and is adjacent to transformer 48. It could, however, be arranged at a different location on the lamstack. For example, it is possible to arrange both the trigger and charge coils on a single leg of the lamstack, as opposed to arrangement shown here. It is also possible for trigger coil 44 to be omitted and for ignition module 14 to receive an engine input signal from charge coil 42 or some other device.
Transformer 48 uses a pair of closely-coupled windings 68 and 70 to create high voltage ignition pulses that are sent to a spark plug via ignition lead 16. Like the charge and trigger coils described above, the primary and secondary windings of transformer 48 surround one of the legs of lamstack 40, in this case leg 62. As with any step-up transformer, the primary winding 68 has fewer turns of wire than the secondary winding 70, which has more turns of finer gauge wire. The turn ratio between the primary and secondary windings, as well as other characteristics of the transformer, affect the high voltage and are typically selected based on the particular application in which it is used, as is appreciated by those skilled in the art.
Ignition module housing 50 is preferably made from a rigid plastic, metal, or some other material, and is designed to surround and protect the components of ignition module 14. The ignition module housing has several openings to allow lamstack legs 60 and 62, ignition lead 16, and electrical connections 18 to protrude, and are preferably are sealed so that moisture and other contaminants are prevented from damaging the ignition module. It should be appreciated that ignition system 10 is just one example of a capacitive discharge ignition (CDI) system that can utilize ignition module 14, and that numerous other ignition systems and components, in addition to those shown here, could also be used as well.
Ignition Module
Turning now to
Electronic processing device 80 executes various electronic instructions pertaining to a variety of tasks, such as ignition timing control, and can be a microcontroller, a microprocessor, an application specific integrated circuit (ASIC), or any other suitable type of analog or digital processing device known in the art. In the illustrated embodiment, electronic processing device 80 is a microcontroller such as a MSP430 series microcontroller produced by TEXAS INSTRUMENTS, running at 16 MHz with 8 Kb of memory to store information like electronic instructions and variables. The electronic processing device is generally powered by charge coil 42 via various electronic components, including capacitor 98, that smooth or otherwise regulate the energy induced in the charge coil. According to the embodiment shown here, electronic processing device 80 includes the following exemplary input/output arrangement: a power input 90 from charge coil 42, a signal output 92 for providing a charge control signal to first switching device 82, a signal output 94 for providing a discharge control signal to second switching device 84, and a signal input 96 for receiving an engine input signal from trigger coil 44 via a number of signal conditioning circuit components. It should be appreciated that numerous circuit arrangements, including ones other than the exemplary arrangement shown here, could be used to process, condition, or otherwise improve the quality of signals used herein. While the engine input signal on input 96 is schematically shown here as provided in serial fashion on a single input, this and other signals could instead be provided on multiple inputs or according to some other arrangement known in the art. An optional kill switch 88, which acts as a manual override for shutting down the engine, could also be coupled to electronic processing device 80.
First switching device 82 is preferably a high voltage solid state switching device that couples charge coil 42 to ground, and is controlled by the charge control signal sent on output 92. In the embodiment shown here, first switching device 82 is shown as a single bipolar transistor, however, other switching devices could be used. For example, first switching device 82 could instead include a single MOSFET, or a pair of transistors connected in a Darlington arrangement; these are also commercially available as a single integrated circuit (IC) transistor package. In one embodiment, first switching device 82 is designed to handle a voltage of at least 300V and at least 1 Amp of current. When the charge control signal turns ‘on’ first switching device 82 so that it is conductive, charge coil 42 is shorted to ground. Conversely, when the charge control signal turns first switching device 82 ‘off’, the short is removed and charge coil 42 is free to charge ignition capacitor 86. According to one embodiment, first switching device 82 functions as a clamping switch with a minimum voltage rating of 300V-350V and a minimum current rating of about 1 Amp, and ignition capacitor 86 has a similar voltage rating and a capacitance of about 0.47 μF. As will be subsequently described in more detail, electronic processing device 80 controls the charging of ignition capacitor 86 by controlling first switching device 82 to create a flyback-type effect during the charge cycle.
Second switching device 84 is preferably a high current solid state switching device, such as a silicon controlled rectifier (SCR) or some other type of thyristor, and is designed to discharge ignition capacitor 86 in order to create a spark at the spark plug. In this embodiment, second switching device 84 is part of an energy discharge path that also includes primary winding 68, ignition capacitor 86, and ground. Second switching device 84 is controlled at its gate by the discharge control signal sent on output 94, and is preferably designed to accommodate at least 30 Amps of limited duration current during discharge of ignition capacitor 86. During normal charging conditions, second switching device 84 is turned ‘off’ so that electrical energy induced in charge coil 42 can charge ignition capacitor 86.
Method of Operation
With reference to
Electronic processing device 80 continues to monitor the engine input signal (
At the time that first switching device 82 is turned off, there is a high level of current flowing from charge coil 42, through switching device 82, to ground. The abrupt change or interruption in current flow through charge coil 42 causes a flyback-type event in ignition module 14. Put differently, when first switching device 82 is turned ‘off’ (open circuit), the current flowing through charge coil 42 is interrupted (
Because of this arrangement, a single charge coil 42 can produce both sufficient current at higher engine speeds (this is due to the relatively low-inductance and low-resistance of charge coil 42), and can provide sufficient voltage to capacitor 86 at lower engine speeds (this is primarily due to the high voltage produced during the flyback event). Some prior art ignition modules address the need for high voltage at low engine speeds by simply increasing the number of windings or turns in the coil; however, adding turns usually increases the inductance and resistance of the charge coil and thus makes it less effective for producing current at high engine speeds. Stated differently, the ignition module described herein addresses low engine speed charging concerns without compromising the high speed performance of the charge coil. Throughout the rest of the charging cycle, both of the switching devices 82 and 84 are maintained in an ‘off’ state so that ignition capacitor 86 can fully charge. For purposes of illustration, the period of time between t1 and t2 is referred to as a second stage of the charge cycle, even though it is possible for additional, intermediate stages to exist between it and the first stage.
As ignition capacitor 86 is being charged, electronic processing device 80 utilizes one or more signal inputs, such as the engine input signal, to determine a desired ignition timing, step 108. As those skilled in the art will appreciate, step 108 can utilize one of a number of different methods and techniques for determining ignition timing, including those disclosed in U.S. Pat. No. 7,000,595, the entire contents of which are hereby incorporated by reference. The particular method or technique used to calculate the ignition timing is not imperative. Once the ignition timing is calculated, electronic processing device 80 sends a discharge control signal to second switching device 84 according to the calculated timing (this usually reflects a certain amount of timing advance or retard with respect to the top-dead-center position of the piston), step 110. The discharge control signal (
The above-provided description is simply an illustration of one possible embodiment for implementing method 100. Numerous variations on this exemplary method are possible and could instead be used. For instance, first switching device 82 is particularly useful when it is used as a current clamping switch during periods of low engine speed. During low speed periods of the charge cycle, charge coil 42 may otherwise be unable to produce adequate charging voltage for ignition capacitor 86. Thus, method 100 could be modified to check and see when the engine surpasses a predetermined speed, say 6,000 RPMs, at which time a normal uninterrupted charge cycle (no flyback) could be used. When the engine is operating at speeds greater than the predetermined speed, it is usually unnecessary to create the flyback effect described above, as the charge coil is usually producing enough voltage on its own.
Turning to
As those skilled in the art will appreciate, the arrangement shown in
Referring to
With reference back to
Testing has shown that the ignition system, modules, and methods described herein can significantly increase or otherwise improve the spark ignition voltage at lower engine speeds and the power output at higher engine speeds. A 2-cycle, single cylinder spark ignition engine utilizing the present ignition module is believed to have significantly increased power output in the lower engine speed range of about 300 RPM to 3,500 RPM, and more particularly in the range of about 300 RPM to 2,500 RPM. Likewise, the same ignition module demonstrates improved power output at high engine speeds in the range of 8,000 RPM and greater, and more particularly in the range of about 8,000 RPM to 11,000 RPM. Some of these results are illustrated in
According to
It is believed and will be understood by persons of ordinary skill in the art that a 4-cycle, single cylinder internal combustion engine with the ignition module described above will also have a similar significantly higher power output and similar significantly increased voltage output characteristics. This is particularly true over the RPM range at which such a 4-cycle engine operates, which is about 150 RPM to 5,000 RPM. It is believed this 4-cycle engine will have these significantly increased power and voltage outputs in both the low to moderate speed range of about 150 RPM to 2,000 RPM and high speed range of about 4,000 RPM to 5,000 RPM.
It is to be understood that the foregoing description is not a definition of the invention but is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “for example”, “for instance,” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
This application claims priority to U.S. Provisional Application Ser. No. 60/897,565, filed Jan. 26, 2007, the entire contents of which are incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
4537174 | Nagasawa | Aug 1985 | A |
4722311 | Erhard | Feb 1988 | A |
4949696 | Muller et al. | Aug 1990 | A |
5050553 | Erhard | Sep 1991 | A |
5476082 | Carpenter et al. | Dec 1995 | A |
5531206 | Kitson et al. | Jul 1996 | A |
5584280 | Kinoshita et al. | Dec 1996 | A |
5635801 | Regazzi et al. | Jun 1997 | A |
6138653 | Juffinger | Oct 2000 | A |
6539930 | Inagaki | Apr 2003 | B2 |
6701896 | Kiessling | Mar 2004 | B2 |
6701904 | Lepley | Mar 2004 | B2 |
6779517 | Sakakura | Aug 2004 | B2 |
7121270 | Plotnikov | Oct 2006 | B1 |
7137385 | Newton | Nov 2006 | B2 |
Number | Date | Country |
---|---|---|
601460 | Jun 1994 | EP |
56032075 | Apr 1981 | JP |
58131358 | Aug 1983 | JP |
61255272 | Nov 1986 | JP |
Number | Date | Country | |
---|---|---|---|
20080178841 A1 | Jul 2008 | US |
Number | Date | Country | |
---|---|---|---|
60897565 | Jan 2007 | US |