Abstract:
An apparatus for producing an ignition spark in an internal combustion engine. The apparatus comprises an inductive ignition device having a primary coil and a secondary coil, flow of current through the primary coil being controlled by an electronic switching element (e.g., a transistor) responsive to a triggering signal. A rotatable body (e.g., the engine flywheel) having detectable features on a periphery thereof is also provided. A sensor device is located adjacent to the rotatable body at a fixed position and is operative to produce an output in response to the detectable features. The apparatus also includes a controller operative to receive an output from the sensor device and responsively produce the triggering signal so as to have a selected dwell time and ignition position.

Description:
PRIORITY CLAIM  
       [0001]     This application is based upon and claims the benefit of provisional application Ser. No. 60/663,004, filed Mar. 18, 2005, which is relied upon and incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to ignition systems for internal combustion engines. More specifically, the invention relates to an ignition system of the inductive type having certain novel features.  
         [0003]     Inductive ignition systems are well-known in the art. Conventionally, such systems use a primary coil and a secondary or ignition coil. The primary coil is connected such that a current can flow through it. At a predetermined point in the piston&#39;s stroke, a transistor in series with the primary coil circuit opens. As a result, the current through the primary coil quickly goes to zero.  
         [0004]     This rapid change in current through the primary coil induces a voltage across the secondary coil sufficient to arc across a spark plug gap on a spark plug attached to the secondary coil circuit. The number of windings in the primary and secondary coils is such that the voltage induced in the secondary coil is high enough to arc across the spark plug gap.  
         [0005]     An example of a conventional inductive ignition system is disclosed in U.S. Pat. No. 4,487,191, the disclosure of which is incorporated herein by reference.  
         [0006]     While conventional inductive ignition systems have been successful at firing a spark plug at approximately the same time during successive rotations of a piston-cylinder engine, there is a need for more precise control over the exact time of firing and the duration/intensity of the spark. Such a new ignition system would have the further benefit of reducing emissions and reducing wear on the engine due to combustion at a non-ideal time in the engine cycle.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention recognizes the foregoing and other disadvantages of prior art systems and methods.  
         [0008]     In accordance with one aspect, the present invention provides an apparatus for producing an ignition spark in an internal combustion engine. The apparatus comprises an inductive ignition device having a primary coil and a secondary coil, flow of current through the primary coil being controlled by an electronic switching element (e.g., a transistor) responsive to a triggering signal. A rotatable body (e.g., the engine flywheel) having detectable features on a periphery thereof is also provided. A sensor device is located adjacent to the rotatable body at a fixed position and is operative to produce an output in response to the detectable features. The apparatus also includes a controller operative to receive an output from the sensor device and responsively produce the triggering signal so as to have a selected dwell time and ignition position.  
         [0009]     In some exemplary embodiments, the detectable features comprise a plurality of projections located on the periphery of the rotatable body. In this regard, the projections are preferably located at a plurality of index positions evenly spaced such that one of the index positions is without a corresponding projection. For example, the projections may be teeth situated on the periphery of the rotatable body.  
         [0010]     It will often be desirable for the controller to synchronize against the detectable features in order to chronologically locate the ignition position. Preferably, the controller may be further operative to ascertain engine speed and mechanical position by sensing the detectable features and then determine the dwell time and ignition position based thereon. The controller may chronologically locate the ignition position by predicting engine position between two of the detectable features.  
         [0011]     In may preferred embodiments, the dwell time is determined at least in part based on average engine speed. The controller may also samples battery voltage as a factor in determination of the dwell time. If the internal combustion engine is a four stroke engine, the controller may be operative not to produce a triggering signal during the power/exhaust stroke thereof.  
         [0012]     Other aspects of the present invention are provided by a method for determining time at which an ignition spark will be produced in an internal combustion engine. One step of the method involves providing a rotatable body that turns in synchronism with operation of the engine, the rotatable body having detectable features on a periphery thereof. According to a further step, the detectable features on said rotatable body are sensed so as to ascertain a mechanical position of the engine. A triggering signal is produced so as to yield the ignition spark at a selected ignition position. For example, the ignition spark may be produced on a trailing edge of the triggering signal. In addition, a dwell time of the triggering signal may be varied.  
         [0013]     Additional aspects of the present invention are provided by an apparatus for producing an ignition spark in an internal combustion engine. The apparatus comprises an inductive ignition device having a primary coil and a secondary coil, flow of current through the primary coil being controlled by an electronic switching element responsive to a triggering signal. A sensor device is operative to produce an output indicative of engine speed and mechanical position. The apparatus further includes a controller operative to receive an output from the sensor device. The controller produces the triggering signal so as to have variable dwell time and ignition position based on the engine speed and mechanical position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which:  
         [0015]      FIG. 1  is a block diagram of an inductive ignition system constructed in accordance with the present invention;  
         [0016]      FIG. 2  is a block diagram of a controller for use with the ignition system of  FIG. 1 ;  
         [0017]      FIG. 3  diagrammatically shows a sensor adjacent to the engine flywheel so as to detect the mechanical position thereof;  
         [0018]      FIG. 4  is a schematic representation of a typical ignition coil circuit that may be used with the present invention;  
         [0019]      FIG. 5  illustrates a firing signal that may be generated in accordance with the present invention; and  
         [0020]      FIGS. 6 through 15  are flowcharts describing various processes executed by a microprocessor for use with an ignition system of the present invention. 
     
    
       [0021]     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.  
         [0023]     In accordance with one preferred embodiment, an ignition system of the present invention may be used on a single cylinder engine such as are often utilized for small motorcycles. It should be appreciated, however, that principles of the present invention could be used with other types of internal combustion engines.  
         [0024]      FIG. 1  illustrates a schematic diagram of an ignition system  10  in accordance with the present invention. Ignition system  10  includes controller  12 , ignition coil  14 , and spark plug  16 . A 12 VDC power source  18  is connected to both controller  12  and ignition coil  14  by wires  20  and  22 , respectively. Ignition system  10  includes a conventional ignition switch  24 . A second switch  26  optionally is provided in the illustrated embodiment. For example, switch  26  could be a side stand switch or seat pressure switch in a motorcycle application of the present invention.  
         [0025]     A temperature sensor  28  is provided for sensing the temperature of the engine block. Preferably, the temperature sensor is a thermistor that outputs a linearly changing voltage as temperature changes. One skilled in the art will appreciate, however, that any other device for sensing temperature could also be used. The temperature of the engine block is used as an input to the control logic of the system; different timing curves may be used for warm-up and steady state operation of the engine.  
         [0026]     An appropriate transducer  30  is provided to sense the mechanical position of the flywheel, and thus the piston, during operation. Referring now also to  FIG. 3 , transducer  30  (which is a variable reluctance transducer in this embodiment) is positioned adjacent the outer diameter of engine flywheel  29 . Flywheel  29  has a series of teeth positions (e.g., twenty-four) (such as those indicated at  31 ) around its circumference. One of the positions (indicated at G) is missing a tooth, while the remaining positions have a metal tooth. Transducer  30  detects the presence or absence of the teeth as the flywheel turns. This position information is sent from transducer  30  to controller  12 . In this embodiment, the teeth are positioned around the flywheel, but one skilled in the art will appreciate they could also be on the crankshaft or another location that provides a mechanical indication of engine position.  
         [0027]     Referring again to  FIG. 1 , a throttle position sensor  32  also communicates with controller  12 . The throttle position sensor could be a linear variable displacement transducer, a potentiometer (as in the preferred embodiment), or any other suitable sensor. The throttle position determines the load request from the operator. The timing curve utilized by controller  12  may be changed depending on the load request.  
         [0028]     Ground lugs  34  and  36  are provided to connect the controller and ignition coil to vehicle ground. An ignition coil input wire  38  runs from controller  12  to ignition coil  14 . As shown in  FIG. 4 , wire  38  carries a signal to an insulated gate bipolar transistor (IGBT)  35  within the ignition coil  14  and acts as a trigger input to that transistor. The operation of the primary and secondary coils (indicated at  37  and  39 , respectively) within the ignition coil  14  is essentially the same as for traditional inductive ignition systems and should be understood by those of skill in the art.  
         [0029]     Referring now to  FIG. 2 , a preferred embodiment of controller  12  includes ground fault and transient protector  40 , voltage regulator  42 , input signal conditioner  44 , and main processor  46 . A signal from transducer  30  is provided to signal conditioner  44  at line  48 . In this case, signal conditioner  44  conditions the signal from a variable sine curve into a block-shaped wave form for input into main processor  46 . Ground fault and transient protector  40  and voltage regulator  42  protect the controller&#39;s electronics from voltage spikes in the system. Regulator  42  further provides a stable 5-volt signal to main processor  46  and signal conditioner  44 .  
         [0030]     In this embodiment, resistors  50  and  52  are configured and valued such that the voltage entering main processor  46  through wire  54  is one-third of the voltage at line  20 . In this manner, processor  46  samples the battery voltage as one factor used in the timing calculations. Other inputs to the main processor include throttle position sensor  32 , temperature sensor  28 , and switch  26 .  
         [0000]     General Considerations:  
         [0031]     The controller uses a processor to provide a signal to ignition coil  14  to fire spark plug  16 . Referring now to Figure, this signal (indicated at  55 ) consists of a single digital pulse with prescribed starting and ending positions (relative to the engine crank position) and a duration (referred to as dwell time). The signal timing and position is determined by a number of factors, including engine speed, throttle position, engine temperature, and battery voltage.  
         [0032]     In a preferred embodiment, the instantaneous engine speed of a single-cylinder four cycle motorcycle engine varies considerably within a firing cycle (due to the use of a light flywheel), perhaps up to a 1000-RPM variation. This variation in engine speed makes it very difficult to predict the position of an appropriate ignition pulse. As noted above, a series of gear teeth  31  are used around flywheel  29  to help closer specify the engine position for controller  12 .  
         [0033]     Controller  12 , through the transducer  30 , detects gear teeth  31 , which in a preferred embodiment are spaced 15 degrees apart on the flywheel&#39;s periphery. (While the preferred embodiment uses 15 degrees, but that can be modified, based on accuracy requirements by adding more or less gear teeth). For a 15 degree spacing, there should be 24 teeth around the wheel, but there is one tooth missing (as indicated at G in  FIG. 3 ) for position synchronization. Typically, the first tooth after the missing tooth gap may be located at 120 degrees Before Top Dead Center (BTDC) in the flywheel&#39;s rotation.  
         [0034]     Each gear tooth  31  is sensed as it passes by transducer  30 , which ultimately produces a digital signal that is input to processor  46 . The appropriate edge (either rising or falling) of the digital pulse is used as a timing and position reference for engine speed and rotation, based on the polarity of the sensor.  
         [0035]     Since each tooth represents only 15 degrees of engine rotation and better accuracy is needed for the trigger signal (less than 1 degree), processor  46  uses both engine position and the time between pulses to correctly position the spark pulse. The controller accomplishes this by counting a prescribed number of tooth pulses (i.e. engine position) to get close to a firing position. Then, the controller switches to a time-based routine that interpolates the correct amount of time delay until firing.  
         [0036]     Referring now also to the flowcharts of  FIGS. 6-15 , one methodology of achieving the desired ignition timing and duration will be described. Background Routines:  
         [0037]     The background routines are a set of subroutines which are executed once per engine revolution. They are run after the Top Dead Center engine position is detected, since the spark plug has been fired before this occurs. This is also in a region before the next ignition pulse will be generated.  
         [0038]     These subroutines read the throttle position, battery voltage, and engine temperature, computing the present engine speed in RPM, based on the most current period measurement (the time for one engine revolution). The average engine speed is also calculated, based on the current and the previous revolution&#39;s engine speed, since there can be variations between the intake/compression and the power/exhaust strokes of the engine cycles.  
         [0039]     The desired dwell time is selected from an internal table, based on battery voltage and average engine speed. Also, the desired ignition advance is selected from an internal table, based on throttle position, engine temperature, and average engine speed. Ignition advance is the time between top dead center and the desired firing point. These values are used to compute the correct timing for the next engine cycle.  
         [0040]     Also along with the background routines, an adaptive dwell routine is run to maintain the desired dwell time, and the power and intake/compression cycles of the engine are detected. Separate advance values are maintained for each type of engine cycle because of the wide variation in engine speed between the power and intake/compression strokes.  
         [0000]     Tooth Interrupt Routine:  
         [0041]     The tooth interrupt routine is invoked whenever a pulse is presented at the External Input pin of processor  46 . When this pin is driven to a logic high, the program that is running at that time is suspended, and the tooth interrupt routine is started. When this routine is finished, the interrupted program resumes from where it was stopped.  
         [0042]     The interrupt routine records a time stamp (EDGETIME) at each tooth pulse event. It uses this information to compute the time for the most recent pulsewidth, the previous pulsewidth, and the time difference between these two pulsewidths. It also detects synchronization at startup and continues to check this on each revolution of the engine. If the controller loses synchronization for any reason, it resets and starts over.  
         [0043]     In addition, the routine also maintains a counter which is used to track engine position at each tooth. Since each tooth represents 15 degrees of engine rotation, each count in the counter equals 15 degrees. Spark and dwell advance values are stored as 2-bytes, one representing an integer value in 15-degree “tooth” counts and the other representing a fractional value of a tooth. These integer and fractional values of dwell and spark advance are computed based on the desired advance relative to the actual tooth position on the flywheel. At each interrupt, a tooth counter is incremented and compared to the integer values of each type of advance. When the counter and the integer values are equal, a subroutine is run to either create the leading or trailing edge of the ignition pulse.  
         [0044]     This subroutine (similar for the leading and trailing edges of the ignition pulse) uses the present EDGETIME as a reference time. It also uses the present pulsewidth time and the difference between that pulsewidth and the previous pulsewidth to predict a time in the future at which to create an edge. During the background loop, this computed time is compared to an internal real-time clock. When the times are equal, the appropriate edge is output to create the ignition pulse.  
         [0000]     Adaptive Dwell Routine:  
         [0045]     It is desired to maintain a specified dwell time for each ignition pulse. During this dwell time, the current through the primary coil continues to rise. The dwell time is based on engine speed and battery voltage and defines the actual width of the ignition pulse. As the leading and trailing edges of the ignition pulse are generated, the actual dwell time is computed and is compared to the desired dwell time. If the actual and desired dwell times differ by greater than a small dead-band value, the dwell advance is adjusted by a small amount in the appropriate direction to bring the two dwell times to a value within the dead-band.  
         [0000]     Power and Compression Cycles:  
         [0046]     In a four-cycle engine, a complete engine sequence consists of two engine revolutions. The first one consists of the intake and compression strokes; the second consists of the power and exhaust strokes. In normal operation, the engine will tend to slow down incrementally during the compression stroke, then speed up as the spark is generated and ignites the fuel/air mixture during the power stroke. As the processor is continually monitoring engine speed at each revolution, it can decide whether the engine is running in the compression or the power cycles and adjust the dwell and spark advance values accordingly. This is done because there can be a wide variation in the engine speed and hence instantaneous engine position between the two cycles. Differentiating between the compression and power cycles and adjusting spark and dwell advances independently increases the accuracy.  
         [0047]     As the spark plug only needs to be fired during the intake/compression stroke, it is possible to eliminate the firing of the plug on the power/exhaust stroke (commonly called “waste spark”) by detecting these engine cycles. Also, speed differences between adjacent engine cycles can be used to determine an engine “loading” value. This value can be used to adjust spark advance in relation to throttle position, engine speed, and other factors.  
         [0048]     It can thus be seen that the present invention provides a novel timing control system for an inductive ignition. While one or more preferred embodiments of the invention have been described above, it should be understood that any and all equivalent realizations of the present invention are included within the scope and spirit thereof. The embodiments depicted are presented by way of example and are not intended as limitations upon the present invention. Thus, those of ordinary skill in this art should understand that the present invention is not limited to these embodiments since modifications can be made. Therefore, it is contemplated that any and all such embodiments are included in the present invention as may fall within the scope and spirit of the following appended claims.