Abstract:
An improved method and system for the control of an engine system such as the spark timing. The control senses the speed variations either during a portion of a complete cycle and a complete cycle and/or from cycle to cycle in order to determine the load on the engine from preprogrammed maps based upon the engine characteristics. From this load and the speed reading, it is possible to obtain the desired engine control. In addition the timing is set in this method only under certain specified conditions and only in response to certain specific parameters. This not only reduces the costs of the system by reducing the number of sensors, but also permits adjustments to be made more rapidly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of the application of the same title, Ser. No. 09/682,457, filed Sep. 5, 2001, invented by us and another and assigned to the assignee hereof, now U.S. Pat. No. 6,626,145. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates to an engine control method and apparatus and more particularly to an improved, simplified, highly effective and yet low cost arrangement for such control. 
     In internal combustion engines, a wide variety of systems and methodology are employed for engine control. Generally, smaller and lower volume engine applications incorporate generally less sophisticated controls than those employed on larger production volume engines such as automotive engines. Even in the small displacement lower production volume engines, for example those used in motorcycles, the engine control can become quite complicated. 
     For example and as shown in FIG. 1, the spark control for a motorcycle engine is shown schematically. The control arrangement is intended to control the firing of a spark plug  21  associated with an internal combustion engine  22  that powers the motorcycle, which is not shown in this figure, but which may be of a construction as generally shown in FIG.  3 . An amplified spark voltage is applied to the spark plug  21  from an ignition coil  23 , which, in turn, is controlled by an ignition timing control arrangement, indicated schematically at  24 . This timing control arrangement  24  receives the inputs from a number of engine-associated sensors. These include a crankcase rotational speed sensor  25  which may comprise a pulser coil and a throttle position sensor  26 , which is coupled to the throttle control mechanism for the engine  22  and inputs a signal to the control  24  indicative of engine load and/or operator demand. 
     Electrical power is provided to the ignition control circuit  24  from a battery  27  through a main switch  28 . This battery power is applied to a power source circuit  29  of the control  24  and specifically to an electronic circuit  31  which may comprise a microprocessor. 
     The output from the engine speed sensor  25  is transmitted to a rotational speed detector circuit  32 , which counts the number of pulses generated in a time period so as to determine the rotational speed of the crankshaft of the engine  22 . 
     This outputs a speed signal N to an ignition timing determining circuit, indicated at  33 . In addition, the throttle position sensor  26  inputs a signal to a throttle position detector circuit  34 . This detector circuit  34  outputs a signal “a” to a throttle opening calculating circuit  35 . This, in turn, outputs a throttle angle position θ to the ignition timing determination circuit  33 . 
     From these inputs, the ignition timing determining circuit outputs a signal at a time determined from maps contained in a memory of the circuit  31  to an ignition circuit  36  which may be of the capacitor discharge type so as to output an electrical output “i” to the coil  23  which is stepped up by the coil  23  to a value “I” for firing the spark plug  21  in a well-known manner. 
     FIG. 2 is a graph showing one of the maps which may be incorporated in the circuit  31  and shows how the spark timing is varied in response to engine speed for given load as determined by the throttle opening circuit. There may be a family of such curves so as to vary the ignition timing in response to both throttle position and engine speed. 
     Rather than using a throttle position sensor, load may be sensed by intake manifold vacuum. Either method, however, requires added sensors, transducers and circuitry. 
     It has been found that merely using engine speed and load as detected by something such as a throttle position or intake manifold vacuum sensor does not actually provide as good a control as desired. That is, these two factors by themselves may not be sufficient to provide the desired degree of control. 
     Although systems have been provided for automotive applications wherein more sophisticated controls are employed, this further adds to the cost of the system and does not always provide the optimum results. 
     There have also been other devices than throttle position sensors or vacuum sensors for sensing intake manifold vacuum for determining engine load. It also has been determined that engine load may be found by comparing engine speed from one revolution to another. However, these systems also tend to be complicated and do not lend themselves particularly low production volume, low cost vehicle applications. They also have the disadvantage of requiring a plurality of different types of sensors. 
     Other arrangements have been proposed wherein engine speed is measured for less than one complete revolution of the engine and variations from cycle to cycle have been employed to determine engine load. These systems, however, have for the most part, required multiple sensors and also require some delay from the sensed conditions before adjustment is being made. 
     In the aforenoted co-pending application a system and method is disclosed that measures engine speed for a portion of a revolution and for a complete revolution utilizing a single sensor and makes engine system adjustments in response to the variation of the measured ratios. This permits a more accurate control with a relatively simple system. However, further improvements can be made. 
     It is desirable to keep the system as simple and as low a cost as possible. The inventors have discovered that cycle to cycle adjustments are not always necessary or even desirable. Also the sensitivity of the system can be effectively varied depending on the type of vehicle to which it is applied. 
     It is therefore a principle object of this invention to provide a highly effective, simple and low cost engine control device and method. 
     It is a further object of this invention to provide an engine control device and method that can utilize a relatively simple and compact computer and memory. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in an internal combustion engine control system and a method for operating an engine for controlling a system of the engine. The engine has a driven shaft. A sensor arrangement is associated with the driven shaft for sensing the instantaneous rotational speed of the driven shaft during the rotation of the driven shaft for less than a complete rotation and for sensing the rotational speed of the driven shaft for a complete revolution thereof including the measured less than complete rotation during a first rotation of the driven shaft and for sensing same two rotational speeds of the driven shaft during the immediately succeeding rotation of the driven shaft. A control determines the ratios between the partial and complete revolution measured for each of the two revolutions and the difference between them. The control adjusts the control of the engine system in response to the difference only if the difference is between a pair of predetermined values. In addition the adjustment is only made with certain other parameters to offer further simplification and provide a smoother operation. 
     In accordance with a first feature of the engine, the other parameter is that adjustment is made only in whole integers to minimize the necessary memory. 
     In accordance with a second feature of the engine, the other parameter is that the ratio is utilized to make the adjustment only within a predetermined range of the total expected variation range to avoid excessive calculations. 
     In accordance with a third feature of the invention, the engine powers a vehicle and the other parameter is that the adjustment is made only within a predetermined range of engine loadings to avoid excessive calculations. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a partially schematic view showing a prior art type of engine control system. 
     FIG. 2 is a graphical view showing one of the speed and timing maps for a given engine load utilized in the prior art control system. 
     FIG. 3 is a side elevational view of the type vehicle which the prior art system can be utilized and also which can utilize the invention. 
     FIG. 4 is a partially schematic view, in part similar to FIG. 1, but shows an engine control system embodying the invention. 
     FIG. 5 is a side elevational view showing the sensor and timing mark. 
     FIG. 6 is a timing diagram utilized to explain the importance of choosing the appropriate times for making the speed measurements to optimize the accuracy of the control. 
     FIG. 7 is a block diagram showing a control routine, utilized to practice the invention. 
     FIG. 8 is a graphical view showing the relationship between the VR (speed ratio change) and actual engine load and engine speed. 
     FIG. 9 is a three dimensional map comparing the ignition timing in accordance with the invention with the prior art method. 
     FIG. 10 is a graphical comparison of the fuel efficiency in accordance with the invention and the prior art method and the degree of improvement therebetween. 
     FIG. 11 is graphical view showing the correlation between the value of VR and actual engine load at several different engine speeds. 
     FIG. 12 is a three dimensional map of ignition timing, engine speed and load showing how limiting the magnitude of the adjustment obtains smoother feel to the operator. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and initially to FIG. 3, a motorcycle constructed and operated in accordance with the invention is identified generally by the reference numeral  51 . Also this is the type of vehicle with which the aforenoted prior art constructions are applied. It is to be understood that this specific application for the invention is only a typical one with which the invention may be utilized. A motorcycle is chosen at the exemplary embodiment because the invention, as should be apparent from the foregoing description, has particular utility in conjunction with relatively small, low production volume engines. However, it should also be apparent that the simplicity of the invention lends itself to use with other applications such as automotive application due to the improvement in fuel economy and performance without significant cost penalties. 
     The motorcycle  51  is comprised of a frame assembly, indicated generally by the reference numeral  52 , that dirigibly supports a front wheel  53  on a front fork  54  that is steered by a handle bar assembly  55  in a well-known manner. 
     A rear wheel  56  is supported for suspension movement relative to the frame  52  by means that includes a trailing arm assembly  57 . An engine, indicated generally by the reference numeral  58 , and having a combined crankcase transmission assembly  59  is suitably suspended in the frame  52  and drives the rear wheel  56  through a suitable drive arrangement. 
     The engine  58  has a carburetor  61  to which fuel is supplied from a fuel tank  62  mounted above the engine  58  on the frame assembly  52 . A throttle valve is associated with this carburetor  61  and is operated by a twist grip throttle control  63  mounted on the handle bar  55 . With conventional systems, but not necessary with this invention, a throttle position sensor  64  is associated with the throttle valve shaft of this throttle valve. 
     The engine  58  is provided with one or more spark plugs  65  (FIG. 4) that are fired by the ignition system, which will be described shortly. 
     The combustion gases are discharged from the engine exhaust port through an exhaust pipe  66  and muffler  67 , which has an atmospheric discharge. 
     The engine  58  in accordance with the illustrated embodiment operates on the four stroke principal, but as will become apparent to those skilled in the art, the invention can also be utilized with two cycle engines. 
     A seat  68  is positioned on the frame assembly  52  to the rear of the fuel tank  62  for accommodating the rider in a well-known manner. 
     Refering now primarily to FIGS. 4 and 5, the control system for controlling the engine system, in this case the firing of the spark plug  65  will be described in more detail. The engine  58  has a crankshaft  69  to which a flywheel  71  is affixed for rotation in a known manner. Although the invention is depicted in association with a crankshaft positioned sensor, it may be associated with any other shaft that is driven by the engine in timed relation. 
     A pulser type sensor  72  is associated with the flywheel  71  and specifically with a timing mark  73  affixed to its outer peripheral surface. The timing mark  73  has a leading edge  74  and a trailing edge  75  which, when passing the sensor  72  will output pulses that can be measured so as to measure the time it takes the timing mark  73  to pass the sensor  72 . This constitutes an instantaneous rotational speed for the engine  58  during a portion of a complete rotation. 
     The timing mark  73  is considerably wider, in accordance with the invention, than those normally used. Such widening is not necessarily required, but can improve the control. For example the width of the mark  73  be equal to 60° of crankshaft rotation. 
     The timing mark is set so that it will first trigger a pulse as the engine begins to approach top dead center (TDC) position and another pulse after the crankshaft is at or near top dead center. The specific angles may vary depending upon the particular application. 
     Neverthelss, because of the four-stroke operation, these pulses are generated at the end of the compression and exhaust strokes. Prior art methods may have utilized speed measurements at the power stroke, but it has been found that the compression and exhaust stroke are much more accurate in providing an indication of engine load and this constitutes one of the features of the invention will be described in more detail later, by reference particularly to FIG.  6 . 
     With a two cycle engine the two measurements per revolution will provide adequate information for engine control on the next revolution. 
     As seen in FIG.4, the output from the sensor  72  is delivered to an engine system timing control device  76 , which contains an ignition circuit  77  which can be basically a conventional ignition circuit of the CDI type, which outputs a signal, “i” to a coil  78  that outputs a pulse “I” for firing the spark plug  65  in a known manner. 
     This engine timing control system is powered with electrical power from a battery  79  through a main switch  81 . 
     The output from the sensor  72  is transmitted to a rotational speed detection circuit  82 , which outputs a signal N indicative of the rotational speed of the engine during each complete revolution cycle. In addition, the outputs from the leading and trailing edges  74  and  75  of the timing mark  73  registered on the sensor  72  are transmitted to a degree of rotational variation detector circuit  83 . This circuit  83  selectively outputs a signal indicative of the speed difference to a load calculation circuit  84 . 
     In the described embodiment, the flywheel  71  may be formed of a magnetic material, and the sensor or coil  72  faces the rotational locus of the timing mark  73 . In this case, opposite ends of the timing mark  73  are detected from changes in magnetic resistance in the magnetic path passing through the iron core of the coil  72 . Alternatively the timing mark  73  may be formed from permanent magnets fixed on the flywheel  71  at positions a given angle away from each other, and the sensor may be a magnetic sensor such as a Hall element for detecting passage of the permanent magnets. Alternatively, the mark may be a slit, which may be detected optically with an LED and a light receiving element. 
     The load calculating output circuit operates so as to determine a load factor that is derived from as map as will be described. This output is delivered to an ignition timing determination circuit  85  which operates in accordance with the control routine shown in FIG. 7 so as to output a signal P to the ignition circuit  77  for firing the spark plug  65  at the appropriate time for the engine speed and engine load. 
     The circuit portions  82 ,  83 ,  84  and  85  are all located within a CPU  86  of the engine control system  76 . 
     Refering now primarily to FIG.  6  and later to FIG. 7, the basic control method used in connection with the invention is to measure revolution to revolution changes in speed “R”. From that difference it is possible to determine engine load. Then by consulting a map of ignition control timing and speed, the appropriate ignition timing can be determined in accordance with an important feature of the invention, this specific load determining method is not utilized under all running conditions to simplify the system without significantly decreasing the performance. In fact, in some cases, even smoother operation is possible utilizing the modified methodology. 
     FIG. 6 shows schematically how the output from the rotational sensor, in the specific example the coil  72  outputs its signal to the circuit portions  82  and  83  to determine the degree of rotational variation R. The method to determine the degree of rotational variation R is one in which a ratio (t/T) is determined by measuring the time between the leading and trailing pulses for each of two successive rotations to determine the change in the ratios, referred to as the difference or variation in revolution “VR”. This figure (FIG. 6) will also be utilized to explain the importance of order of the specific strokes that are measured from which the difference VR is obtained. 
     As noted, pulses are generated as the timing mark  73  passes the sensor coil  72 . 
     Therefore, the output waveform of the pulser coil will be a positive (+) pulse at when the leading edge  74  passes at 60° BTDC of the mark and a negative (−) pulse when the trailing end  75  passes at TDC. These pulses are shown in FIG.  6  and two methods are compared in accordance with methods described as “&lt;Method  1 &gt;” and “&lt;Method  2 &gt;”. 
     In accordance with &lt;Method  1 &gt;, the time intervals C, D of the negative (−) pulses including the combustion and the exhaust strokes are taken as cycles of one rotation and the passing time of the projection (mark) in each cycle C, D as B, A to determine the ratio B/C, A/D for each cycle. Then, the absolute value of the difference between these values, B/C−A/D, is determined as the indication of the engine load. 
     However, the present invention finds the engine load by using the “&lt;Method  2 &gt;”, which the time intervals C″, D″ of the positive (+) pulse are assumed as cycles in one rotation and the ratio A/C″, B/D″ is determined for each cycle. The absolute value of the difference between these values, |A/C″−B/D″|, is defined as the VR value. 
     As seen in FIG. 6, effects by the load fluctuation appear such that the time of the exhaust and the intake strokes is relatively longer than the time of the combustion and the compression strokes. As a result, both the numerator and denominator of the ratio (B/C) increase or decrease in reference to the increase or decrease of the load according to the “&lt;Method  1 &gt;”, and both the numerator and denominator of the ratio (A/D) increase or decrease in the same way. Therefore, changes in the difference between two values, |B/C−A/D|, according to the load fluctuation is relatively small. 
     On the other hand, according to the “&lt;Method  2 &gt;”, the ratio (A/C″) becomes such that the denominator C″ decreases and the numerator A increases in reference to the increase of the load, and the ratio (B/D″) becomes such that the denominator increases and the numerator decreases, so that the changes in the difference between two values, |A/C″−B/D″|, according to the load fluctuation become larger. The present invention is to determine the VR value and therefore the engine load by using the “&lt;Method  2 &gt;”. To more effectively determine the engine load because of the larger values obtained by this method. 
     This methodology is utilized in performing the method, which will now be described in detail by reference to FIG.  7 . First, at the Step S 1  it is determined if the engine is running in an idling condition. This may be the condition immediately after a warm start up. In any event, if the engine is operating at an idling speed, the ignition timing α is set to a fixed value α  1  at the step S 2 . Then ignition control is performed at the step S 3 . The program then repeats to the step S 1 . 
     If the engine  58  is found not to be in an idling state at the step S 1 , the degree of rotational variation detection circuit  83  detects the degree of rotational variation VR at the step S 4 . The microcomputer in the electronic circuit  86  determines whether or not the degree of variation VR is within a given range of VR m  VR M  the step S 5 . If the variation is out of this range, the ignition timing is set to a fixed value α  2  or α  3  at either the step S 6  or S 7 . 
     The values of the fixed degrees of advance at idle α 1  is about 10° before top dead center. The values of α 2  α 3  may be in the range of 20° to 30° before top dead center and are set to avoid errors under small deviations in VR to avoid the effects of electrical noise. 
     If at the step S 5  the value of VR is determined to be within this range of VR m -VR M , the load calculation circuit  84  determines load L using engine speed N determined by the rotational speed detection circuit  82  at the step S 8  and looking up the load L from the conversion map of FIG. 8 at the step S 9 . 
     The left hand (A) side of FIG. 8 shows the measurement result of the determination for the relation between the VR value and the engine load determined in accordance with the “&lt;Method  2 &gt;” against different engine speeds n (rpm). The result shows that the engine load is uniquely determined in accordance with the engine speed n and the VR value. The right hand (B) side of FIG. 8 shows the result in the form of a 3-D map. The map shows that the load can be detected without special sensors for detecting the engine load such as a throttle sensor or an intake negative pressure sensor but with the pulser signal only. In addition, it is found that the range of change in the VR value is from 0 to 2.0. 
     FIG. 9 is a 3-D map showing the ignition timing required for obtaining the maximum torque of the engine or the MBT (Minimum Advance for Best Torque) in relation to the load and the engine speed n. This figure also shows why the conventional ignition unit that varies the ignition timing according only to the engine speed n has not been able to make-full use of the engine performance, As seen the deviation from the MBT of the ignition timing becomes larger when the load varies. On the contrary, according to the present invention, the ignition timing is varied along with the MBT in accordance with the engine load, so that the present invention can make full use of the engine performance. 
     Referring back again to FIG. 7, the ignition timing determination circuit  85  then determines ignition timing α at the step S 10  using this load L and engine speed N and looking up this value from the conversion map in FIG.  9 . The ignition timing determination circuit  85  then sends an ignition signal P corresponding to the read ignition timing α to the ignition circuit  77 , causing the ignition plug  65  to be fired. The program then moves to the step S 3  and repeats. 
     A comparison of fuel efficiency between the conventional ignition device and the present embodiment on the same engine is shown in FIG.  10 . It will be seen that the fuel efficiency is improved for 2-12% according to the present embodiment. 
     In the calculation of the VR value, the microcomputer operates to limit the variations in ignition timing so as not to be less than 1° as this will provide a smoother feel to the operator and simplify the system by permitting the use of a simpler computer. As shown in FIG. 11, the minimum variation intervals (minimum increments) of the VR value or resolution to 0.625% of the total variation range of the VR value. The value of 0.625% corresponds to 0.0125 of the VR value (=2.0×0.625/100). The load fluctuation in response to the change in the VR value increases in high engine speed and low load. Thus with a vehicle such as a motorcycle of approximately 100 kgf (kilogram-force, 1 kgf≈9.8N) in the vehicle weight or the like, it is found that the conditions as described above are nearly met if the minimum variation interval of the VR value is determined as the change in an engine load of approximately 7N·m (Newton-meters), also indicated as Nm, 1 kgf·m≈9.8N·m). Thus the resolution (=0.0125) corresponds to approx. 7N·m of the load change in the high engine speed and the low load. 
     Therefore, the fluctuation of the load, 7N·m, approximately corresponds to the change within 1° of the ignition timing as shown in FIG.  12 . It is found that the change within 1° of the ignition timing corresponds to 7N·m of the change in the engine load and the change in that degree does not become significantly apparent to the operator. 
     Thus, from the foregoing description should be readily apparent that the described method and structure provides a very simple and low cost yet highly effective system for controlling an engine. Also, it should be understood although a specific example of engine ignition timing control is disclosed and has been described, other engine systems also may be controlled in a like manner such as fuel control with either fuel injection or other forms of fuel supply and throttle control for fly-by wire throttle systems. Other engine control applications with which the invention may be employed will present themselves to those skilled in art. Also, the system is capable of being used with either two or four cycle engines. Of course, further changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.