Abstract:
Two embodiments of engine speed control that avoid undesirable vehicle conditions such as wheel slippage or unintentionally performing a wheelie. This is done by sensing actual conditions, which are likely to result in the undesirable vehicle conditions and only changing the engine output when these exact conditions are found. The conditions sensed are the determination of excessive acceleration in engine speed or in the speed of a shaft associated with the engine or the degree of rotational variation or rotational acceleration.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to an engine control method and engine control structure for a small vehicle and more particularly to an improved engine control that prevents unwanted vehicle performance such as wheel slippage or undue lifting of a vehicle wheel from the ground without adversely affecting performance.  
           [0002]    In certain types of small vehicles such as motorcycles or motor scooters, there has been a problem in that if rapid acceleration occurs, either or both of two undesirable phenomena result. One is slippage of the rear wheel that results in the loss of traction for driving and the other is a condition where there acceleration is so rapid that the front wheel actually may lift from the ground causing a phenomenon referred as to performing a “wheelie”. Neither result is desirable.  
           [0003]    It has been proposed, therefore, to provide an arrangement wherein the engine output is reduced under situations where these conditions are likely to occur. The engine power reduction may be accomplished in a variety of manners such as changing ignition timing, skipping ignition timing or others.  
           [0004]    Normally this condition is determined by sensing when the acceleration of the vehicle or a component of the vehicle exceeds a predetermined value. If this value is exceeded, then the power is reduced and the condition avoided.  
           [0005]    However, the prior art methods of accomplishing this result are based upon acceleration alone and power reduction may occur even though it is not necessary to produce the aforenoted affects. For example, if the vehicle is being accelerated in downhill travel, the acceleration necessary to cause wheel slippage or a wheelie to occur is considerably different than that when traveling on an uphill condition.  
           [0006]    [0006]FIG. 1 is a graphical view showing how these prior art type of systems operate. The top curve of this (A) is the acceleration of the vehicle, which can either be in the form of acceleration of the rotational speed of a shaft of the vehicle as N″ or the angular acceleration of the shaft indicated as ω″.  
           [0007]    If these accelerations exceed a predetermined value indicated at N′ o  or ω′ o  which occurs at the time t  1  as shown in the graphs, then the engine speed or power output is reduced, for example by delaying the spark timing from a normal angle β O to a retarded angle β 1 . This retardation is normally held for a predetermined time period as indicated by the timing period Δ t.  
           [0008]    Then the spark timing is returned to its normal timing either abruptly or gradually as shown in the timing curve B of this figure. The acceleration of the shaft again increases but does not reach the level prior to application of control for some time. However, as noted above, it is found that this results in unnecessary and at times detrimental loss of engine performance.  
           [0009]    In addition to the condition noted above i.e. traveling on a grade, it has been discovered that other conditions may occur when the acceleration exceeds the predetermined degree of acceleration used in the prior art methodology but the aforenoted undesirable driving conditions do not result. For example, if the throttle is moved relatively slowly, as may occur when traveling downhill, the acceleration rate can still exceed that preset and power is unnecessarily reduced with the prior art methods and systems. Also, if the throttle grip is moved rapidly from the closed position to a partially opened position or quickly from the partially opened position to a fully opened position, the acceleration rate of the prior art methods may be exceeded but the running conditions are such that the undesirable vehicle conditions will not occur. Thus, performance is inadvertently and unnecessarily decreased with the prior art methods and systems.  
           [0010]    It is, therefore, a principal object to this invention to provide an improved method for engine control for a vehicle that will reduce the power but only at times when undesirable vehicle conditions will occur.  
           [0011]    It is a further object to this invention to provide an engine control arrangement and method wherein the power is reduced only under certain specific conditions when it will be certain that undesirable vehicle running conditions may occur.  
         SUMMARY OF INVENTION  
         [0012]    A first feature of this invention is adapted to be embodied in an engine control method for a vehicle in which rotation of an internal combustion engine shaft is transmitted to a driven wheel through a transmission. The method comprises the steps of detecting variations in the rotational state of the shaft during engine acceleration, determining if the degree of rotational variation is excessive, and restricting engine output if the rotational state of the shaft is excessive.  
           [0013]    Another feature of the invention is adapted to be embodied in a vehicle engine control. The vehicle has an internal combustion engine, a driven wheel and a transmission for driving the driven wheel from a shaft of the internal combustion engine. An engine control detects variations in the rotational state of the shaft during engine acceleration. If the engine control determines the degree of rotational variation is excessive, the engine output is reduced. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    [0014]FIG. 1 is a graphical view showing a prior art type of vehicle engine control. View A shows time and shaft rotational and angular acceleration. View B shows ignition timing with relation to time. View C shows actual rotational speed and angular velocity with relation to time.  
         [0015]    [0015]FIG. 2 is a schematic view of an engine control constructed and operated in accordance with an embodiment of the invention.  
         [0016]    [0016]FIG. 3 is a view showing the timing sensor associated with the engine shaft for the control system.  
         [0017]    [0017]FIG. 4 is a schematic view showing the method of determining shaft acceleration in accordance with the invention.  
         [0018]    FIG. S is a block diagram showing a control routine, which may be utilized to practice the invention.  
         [0019]    [0019]FIG. 6 is a graphical view in part similar to FIG. 1, but shows the performance in accordance with the invention.  
         [0020]    [0020]FIG. 7 is a schematic view, in part similar to FIG. 2, showing an engine control constructed and operated in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring now in detail to the drawings and initially primarily to FIGS. 2 and 3, these figures illustrate a control system and control method for a vehicle such as a motor scooter or small motorcycle. Although the invention is described in conjunction with such vehicles, it should be readily apparent to those skilled in the art that other vehicular applications of the invention are possible. Also, since the construction of the associated vehicle forms no part of the invention, the complete vehicle is not illustrated. Rather, the drawings illustrate only the engine and the transmission system associated with it, which drives a driven wheel of the vehicle through a suitable drive such as a continuously variable belt type transmission, a change speed transmission or any other type of transmission.  
         [0022]    The internal combustion engine is indicated generally by the reference numeral  11  and includes a cylinder block  12  having one or more cylinders, which are spark, ignited by spark plugs  13 . As is typical in the practice with this type of vehicle, the cylinder block  12  extends from a crankcase assembly  14  in which a transmission may be positioned or, alternatively, an engine flywheel  15  powers the vehicle through an associated transmission system, which is not shown.  
         [0023]    Since the invention deals primarily with the engine control and this engine control can be utilized with a wide variety of types of engines and transmissions, these components are not illustrated in any significant detail or, in fact, may not even be shown.  
         [0024]    The control system for controlling the firing of the spark plug  13  will be described in more detail. The engine  11  has a crankshaft  16  to which the flywheel  15  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.  
         [0025]    A pulser type sensor  17  is associated with the flywheel  15  and specifically with a timing mark  18  affixed to its outer peripheral surface. The timing mark  18  has a leading edge  19  and a trailing edge  21  which, when passing the sensor  17  will output pulses that can be measured so as to measure the time it takes the timing mark  18  to pass the sensor  17 . This constitutes an instantaneous rotational speed for the engine  11  during a portion of a complete rotation.  
         [0026]    The timing mark  18  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  18  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.  
         [0027]    Nevertheless, if the engine  11  operates on a 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.  
         [0028]    With a two cycle engine the two measurements per revolution will provide adequate information for engine control on the next revolution.  
         [0029]    As seen in FIG. 2, the output from the sensor  17  is delivered to an engine system ignition timing control device  22 , which contains an ignition circuit  23  which can be basically a conventional ignition circuit of the CDI type, which outputs a signal, “i” to a coil  24  that outputs a pulse “I” for firing the spark plug  13  in a known manner.  
         [0030]    This engine timing control device  22  is powered with electrical power from a battery  25  through a main switch  26 . The ignition timing control device  22  includes an electronic circuit  27  constituted by a microcomputer or the like, and the ignition circuit  23  consisting of a CDI (capacitor discharging ignition circuit), and a power circuit  28 . The power circuit  28  is formed by a constant voltage circuit for outputting power source voltages for the ignition circuit  23  and the electronic circuit  16 .  
         [0031]    The output from the sensor  17  is transmitted to a rotational speed detection section  29  of the engine system ignition timing control device  22  and specifically the electronic circuit, which outputs a signal N indicative of the rotational speed of the engine  11  during each complete revolution cycle. In addition, the outputs from the leading and trailing edges  19  and  21  of the timing mark  18  registered on the sensor  17  are transmitted to a degree of rotational variation detection section  31 . This rotational variation detection section  31  outputs a signal indicative of the speed difference to an output restriction judgment section  32 .  
         [0032]    In the described embodiment, the flywheel  15  may be formed of a magnetic material, and the sensor or coil  17  faces the rotational locus of the timing mark  18 . In this case, opposite ends of the timing mark  18  are detected from changes in magnetic resistance in the magnetic path passing through the iron core of the coil  17 . Alternatively the timing mark  18  may be formed from permanent magnets fixed on the flywheel  15  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.  
         [0033]    As seen in FIG. 2, the electronic circuit  27  comprises the rotational speed detection section  29 , the degree-of-rotational variation detection section  31  and the output restriction judgment section  32 , as already noted. The electronic circuit  27  further comprises an ignition timing determination section  33 , an output restriction section  34  and other components, some of which will be described. At least one of these circuits  29 ,  31 - 34  can be formed by the software of a microcomputer.  
         [0034]    The output signal of the sensor  17 , that is, the positive or negative pulse outputted after detection of the forward and rearward ends  19 ,  21  of the projection  18 , is inputted into the rotational speed detection section  29 , where a rotational speed N (rpm) is determined from the time interval between successive two positive pulses or two negative pulses. The output pulse of the sensor  17  is inputted into the degree-of-rotational variation detection circuit  31 , where the degree of rotational variation R is determined.  
         [0035]    A manner in which the degree of rotational variation can be obtained will now be described by reference to FIG. 4. The degree-of-rotational variation detection section  31  measures the time interval “D” from the forward end  19  to the rear end  21  of the projection  18  as being tn−1 for the compression stroke and tn for the subsequent exhaust stroke. Also determined is a length of time “T” for the crankshaft  16  to makes one revolution by measuring the time interval between successive positive (or negative) pulses. Here, the period on the compression stroke is represented by Tn−1, and the period on the exhaust stroke by Tn.  
         [0036]    A first method of determining the degree of rotational variation R is one in which a ratio t/T of detection time t of the projection to the period T is determined, and the ratio (t/T)=R represents the degree of rotational variation. A second method of determining the degree of rotational variation R is one in which ratios (t/T) obtained by the first method are determined for the compression stroke and the exhaust stroke, and the difference between them represents the degree of rotational variation. That is, a difference (Rn−1 Rn)=D between a ratio (tn−1/Tn−1)=Rn−1 on the compression stroke and a ratio (tn/Tn)=Rn on the exhaust stroke is determined for each compression or exhaust stroke.  
         [0037]    The output restriction judgment section  32  compares the degree of rotational variation R (or D) obtained in the degree-of-rotational variation detection section  31 , with a set value stored in advance. If R (or D) exceeds the set value, an output restriction signal Q is outputted. The output restriction section  34  controls the engine to restrict its output, based on the output restriction signal Q. In this embodiment, since ignition timing is delayed to restrict engine output, delayed angle β is calculated.  
         [0038]    The delayed angle β may be a fixed value or a variable related to the operating conditions such as rotational speed N or some other running condition. For example, the delayed angle β is increased during high speed rotation, and decreased during low speed rotation. The ignition timing determination section  33  determines an ignition timing α at the time of normal operation, subtracts the delayed angle β to obtain (α−β), and outputs an ignition signal P with (α−β) as an ignition timing. The ignition circuit  23  generates ignition sparks based on the ignition signal P at the ignition plug  13 .  
         [0039]    The ignition timing determination section  33  may determine the ignition timing α based on rotational speed N or on a combination of rotational speed and load from a map. The load may be obtained from the amount of rotational movement of a throttle control (lever), that is, throttle valve opening, or based on the degree of rotational variation R (or D).  
         [0040]    The control routine of this embodiment will generally be described with reference to FIG. 5. First, at the step S 1  the degree-of-rotational variation detection circuit  31  detects a degree-of-rotational variation, either D or R as noted above. Then at the step S 2  the output restriction judgment section  32  of the electronic circuit  27  compares this degree of variation D with a set value D0. If D&lt;D0, the output restriction signal Q is not outputted. Thus at the step S 3  the output control section  34  sets the delayed angle β to zero.  
         [0041]    If D is not less than D0, the output restriction signal Q is outputted and at the step S 4  the output restriction section  34  calculates a delayed angle β. Then at the step S 5  the ignition timing determination circuit  33  determines an ignition timing (α−β) using this delayed angle and the rotational speed N. The circuit sends an ignition signal P corresponding to the ignition timing (α−β) to generated ignition sparks at the ignition plug  13  at the step S 6 . The program then repeats until D is less than D0. The effect of this operation is shown in FIG. 6, which should be compared with the prior art method in FIG. 1.  
         [0042]    The rotational acceleration N′0 (angular acceleration ω′) at the time when the degree of rotational variation D (or R) coincides with a set value D0, is stored in a memory, and thereafter, the delayed angle β is feedback controlled such that the rotational acceleration N′0 (ω′0) is constant. Thus, the acceleration is constant during accelerating operation, so that a smooth acceleration feeling can be achieved.  
         [0043]    [0043]FIG. 7 is a block diagram of another embodiment. Where components of this embodiment are the same as those of the first embodiment they are designated by the same reference numerals and will be described again only where necessary to understand and utilize this embodiment. In this embodiment, an ignition timing control  51  employs a timing control circuit  52  having many of the same components as the first embodiment. However an output restriction judgment section  53  judges whether or not output restriction is performed using the degree of rotational variation D (or R) and the rotational acceleration N′. Thus a rotational acceleration detection section  54  is provided for obtaining the rotational acceleration N′ (or angular acceleration ω′) by calculating the derivative of the rotational speed N to time.  
         [0044]    In this embodiment, output restriction is performed, based on a judgment that both the degree of rotational variation D (or R) and the rotational acceleration N′ (or ω′) become larger than the respective set values, so that an operating condition in which engine output restriction is needed, can be judged more exactly. For example, in the case of downward slope starting, the acceleration becomes excessive even if the throttle grip is moved slowly, or moved quickly from the closed position to a half-open position or from a half-open position to the full-open position, but the degree of rotational variation is small because of low load, and thus engine output restriction can be avoided.  
         [0045]    Thus, from the foregoing description it should be readily apparent that the described embodiments provide much more effective engine output control to avoid undesirable vehicle conditions than the prior art methods. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.