Abstract:
An engine speed control that avoid undesirable transmission conditions such as clutch chattering. This is done by sensing actual conditions, which are likely to result in the undesirable transmission conditions such as clutch chattering 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 
     This invention relates to an engine control method and engine control structure for a vehicle and more particularly to an improved engine control that prevents unwanted transmission action such as clutch chatter. 
     In small vehicles such as scooters, engine revolution is often transmitted to the driven wheel through an automatic transmission. Vehicles with belt type continuously variable transmissions have been widely in use. In such cases, the transmission system is typically provided with a starting centrifugal friction clutch. The centrifugal friction clutch becomes engaged through centrifugal force when the rotational speed rises close to a predetermined value and the friction force increases as the rotational speed rises. This enables a smooth start of the vehicle. 
     However, in the friction clutch, a chattering phenomenon caused by vibrations or oscillation may happen during the engagement of the clutch. If this phenomenon happens, not only may the clutch and the transmission system be damaged, but the rider and passengers may experience an uncomfortable feeling. To avoid or minimize these effects the size and material of the clutch have been improved at some cost disadvantage. 
     As a further or substitute remedy, the engine power is reduced by a given amount in a predetermined speed range near the engine speed at which the clutch is connected. One way this has been done is to retard ignition timing to lower engine output so that vibrations are restricted during clutch connection. Alternatively this may be done by skipping or misfiring of the spark plug. In such methods, the delayed angle or skipping is set to a fixed value. 
     However, the juddering phenomenon doesn&#39;t always occur. The occurrence depends on running conditions such as load on the vehicle; wear conditions of the friction members of the clutch, or other factors. In such cases, there is no need of reducing engine power, but the previous systems do so a predetermined speed range at all times. Therefore not only is engine combustion impaired with decreased fuel efficiency, but also undesirable exhaust emissions are increased. 
     Thus, it is a principle object of this invention to provide an improved engine control method and system for a vehicle capable of preventing the generation of transmission vibrations particularly caused by connection and disconnection of a clutch. 
     SUMMARY OF INVENTION 
     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 likely to cause vibrations from occurring in the transmission, and restricting engine output if the rotational state of the shaft is excessive. 
     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 to avoid vibrations from occurring in the transmission. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side elevational view of a small vehicle having an engine control and system for preventing undesirable transmission conditions. 
         FIG. 2  is a partially schematic cross sectional view of the engine, transmission system and driven wheel of the vehicle. 
         FIG. 3  is a schematic view of an engine control constructed and operated in accordance with an embodiment of the invention. 
         FIG. 4  is a side elevational view showing the timing sensor associated with the engine shaft for the control system. 
         FIG. 5  is a schematic view showing the method of determining shaft acceleration in accordance with the invention. 
         FIG. 6  is a block diagram showing a control routine, which may be utilized to practice the invention. 
         FIG. 7  is a graphical view showing shaft speed (A), spark timing (B) and vehicle speed (C) with respect to time during initial vehicle start up under a condition when the engine is controlled to avoid undesirable transmission system vibrations and/or clutch chattering. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and first to  FIG. 1 , a small type of vehicle with which the invention has particular utility is indicated generally by the reference numeral  11 . Although, this vehicle  11  is a motor scooter, it will be apparent to those skilled in the art how the invention can be utilized with other types of vehicles. The motor scooter has a frame  12  on which a body assembly  13  is mounted in a suitable manner. The frame  12  journals a front fork  14 , which, in turn, rotatably supports a dirigible front wheel  15 . A handlebar assembly  16  at the upper end of the front fork  14  can be steered by a rider seated on a seat  17  of the body assembly  13 . 
     A driven rear wheel  18  is positioned beneath the seat and is suspended by the frame  12  via a suspension element  19 . The rear wheel  18  is driven by a combined engine transmission assembly, indicated generally by the reference numeral  21 . The engine transmission assembly  21  will now be described by principal reference to  FIG. 2 . 
     The engine transmission assembly  21  includes an internal combustion engine, shown partially in section and identified generally by the reference numeral  22 . This engine may have any number of cylinders and may operate on any principal i.e. either two stroke or four stroke or be of the rotary type. Therefore, the engine components will be described only generally and these include a cylinder block  23  that defines a cylinder bore in which a piston  24  reciprocates. A connecting rod  25  connects the piston  14  to a throw of a crankshaft  26  that is journalled in a suitable manner in the crankcase assembly of the engine  22 . 
     The crankshaft  26  is coupled to the input shaft of a continuously variable belt type transmission, indicated generally by the reference numeral  27 , and which extends in part through an elongated casing  28  which defines a clearance opening  29  for a drive belt  31 . The driving pulley for the drive belt  31  comprises a first pulley half  32  that is fixed for rotation with the crankshaft  26 . A second, axially moveable pulley half  33  cooperates with flywheel weights  34  to increase the effective diameter of the driving pulley as the engine speed increases. 
     Referring now to the right hand side of  FIG. 2  that shows how the drive is transmitted from the belt  31  to the rear wheel, a driven pulley assembly, indicated generally by the reference numeral  35 , is associated with the wheel  18 . The driven pulley  35  includes an axially fixed sheave portion  36  that is fixed for rotation with an axle  37  that drives the wheel  18 . Also affixed thereto is the drum  38  of a centrifugal clutch, indicated generally by the reference numeral  39 . 
     The driven pulley  35  further includes an axially moveable sheave  41 , which is loaded by a spring  42  so as to normally urge the sheave halves together to increase the effective diameter of the driven pulley  35 . However, when the driving pulley  27  is in a condition of minimum diameter, the diameter of the driven pulley  35  will be at its maximum to provide a lower transmission ratio. 
     The centrifugal clutch  39  includes a plurality of clutch elements that are pivotally supported and have frictional faces. These elements are indicated by the reference numeral  43 . These elements are normally urged inwardly by coil compression springs  44  so as to hold them out of engagement with the inner surface of the drum  38 . 
     In this condition, the system will operate in neutral. That is, the clutch  39  is disengaged. As the engine speed increases, however, the centrifugal force on the clutch shoes  43  will overcome the action of the springs  44  and the clutch will engage so as to transmit drive to the driven wheel  18 . 
     As the engine speed continues to increase, the diameter of the driving pulley  27  will increase and the effective diameter of the driven pulley  35  will decrease so as to increase the speed at which the wheel  18  is driven relative to the crankshaft  26 . As thus far described, the construction may be considered to be conventional. 
     As should be apparent from the foregoing description, the invention relates to a system for controlling the power generated by the engine  22  under certain running conditions so as to void chattering when the centrifugal clutch  39  is engaged. The specific embodiment illustrated, achieves this by controlling the firing of the ignition system of the engine  22 . To this end, the engine  22  is provided with one or more spark plugs  45  associated with each of its cylinders. These spark plugs  45  are fired by an ignition system and the control system for controlling the firing of the spark plug  45  will be described in more detail. 
     The crankshaft  26  engine  22  is affixed to a flywheel  46  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. The flywheel  46  may also function as a permanent magnet AC generator indicated generally at  47 . This includes permanent magnets  48  fixed to its inner surface that cooperate with coils (not shown) in a manner well known in the art. 
     For ignition timing control, a pulser type sensor  49  ( FIGS. 2–5 ) is associated with the flywheel  46  and specifically with a timing mark  51  affixed to its outer peripheral surface. The timing mark  51  has a leading edge  52  and a trailing edge  53  which, when passing the sensor  49  will output pulses that can be measured so as to measure the time it takes the timing mark  51  to pass the sensor  49 . This constitutes an instantaneous rotational speed for the engine  22  during a portion of a complete rotation. 
     The timing mark  51  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  51  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. 
     Nevertheless, if the engine  22  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. 
     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. 3 , the output from the sensor  49  is delivered to an engine system ignition timing control device  54 , which contains an ignition circuit  55  which can be basically a conventional ignition circuit of the CDI type, which outputs a signal, “i” to a coil  56  that outputs a pulse “I” for firing the spark plug  45  in a known manner. 
     This engine timing control device  54  is powered with electrical power from a battery  57  through a main switch  58 . The ignition timing control device  54  includes an electronic circuit  59  constituted by a microcomputer or the like, and the ignition circuit  55  consisting of a CDI (capacitor discharging ignition circuit), and a power circuit  61 . The power circuit  61  is formed by a constant voltage circuit for outputting power source voltages for the ignition circuit  55  and the electronic circuit  59 . 
     The output from the sensor  49  is transmitted to a rotational speed detection section  62  of the engine system ignition timing control device  54  and specifically the electronic circuit  59 , which outputs a signal N indicative of the rotational speed of the engine  22  during each complete revolution cycle. In addition, the outputs from the leading and trailing edges  52  and  53  of the timing mark  51  registered on the sensor  49  are transmitted to a degree of rotational variation detection section  63 . This rotational variation detection section  63  outputs a signal indicative of the speed difference to an output restriction judgment section  64 . 
     In the described embodiment, the flywheel  46  may be formed of a magnetic material, and the sensor or coil  49  faces the rotational locus of the timing mark  51 . In this case, opposite ends of the timing mark  51  are detected from changes in magnetic resistance in the magnetic path passing through the iron core of the coil  49 . Alternatively the timing mark  51  may be formed from permanent magnets fixed on the flywheel  46  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. 
     As seen in  FIG. 3 , the electronic circuit  59  comprises the rotational speed detection section  62 , the degree-of-rotational variation detection section  63  and the output restriction judgment section  64 , as already noted. The electronic circuit  59  further comprises an ignition timing determination section  65 , an output restriction section  66  and other components, some of which will be described. At least one of these circuits  62 ,  63 – 66  can be formed by the software of a microcomputer. 
     The output signal of the sensor  49 , that is, the positive or negative pulse outputted after detection of the forward and rearward ends  52 ,  53  of the projection  51 , is inputted into the rotational speed detection section  62 , 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  49  is inputted into the degree-of-rotational variation detection circuit  63 , where the degree of rotational variation R is determined. 
     A manner in which the degree of rotational variation can be obtained will now be described by reference to  FIG. 5 . The degree-of-rotational variation detection section  63  measures the time interval “D” from the forward end  52  to the rear end  53  of the projection  51  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. 
     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. 
     The output restriction judgment section  64  compares the degree of rotational variation R (or D) obtained in the degree-of-rotational variation detection section  63 , 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  66  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. 
     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  65  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  55  generates ignition sparks based on the ignition signal P at the ignition plug  45 . 
     The ignition timing determination section  65  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). 
     The control routine of this embodiment will generally be described with reference to  FIG. 6 . First, at the step S 1  the rotational speed detection section outputs a signal indicative of instantaneous engine speed to a clutch operating range section of the circuit  59 . This section determines if the engine speed is in the range when the centrifugal clutch  39  will engage or disengage. This is shown as step S 1  in  FIG. 6  where it is determined if the speed is in the range N 1  to N 2 . If it is not in this range protective action is not required and the program moves to the step S 2  where tie timing adjustment angle β is set to zero and normal ignition timing will result. 
     If the engine speed is in the range where engagement of the centrifugal clutch  39  may change, the program moves to the step S 3  where the circuit degree-of-rotational variation detection circuit  63  detects a degree-of-rotational variation, either D or R as noted above. Then at the step S 4  the output restriction judgment section  64  of the electronic circuit  59  compares this degree of variation D with a set value D 0 . If D–D 0 , the output restriction signal Q is not outputted. Thus at the step S 2  the output control section  66  sets the delayed angle β to zero. 
     If D is not less than D 0 , the output restriction signal Q is outputted and at the step S 5  the output restriction section  66  calculates a delayed angle β. Then at the step S 6  the ignition timing determination circuit  65  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  45  at the step S 7 . The program then repeats until D is less than D 0 . 
     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 D 0 , 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 and lack of clutch chattering can be achieved. 
     This result can be seen by reference to  FIG. 7  which is a graphical view showing rotational speed variations, spark timing and vehicle speed in accordance with the invention in relation to time. It will be seen that when the speed begins to perturbate due to changes in angular acceleration, the spark timing is delayed and as a result the acceleration and engagement of the clutch is smooth. After the clutch is engaged, then the system returns to normal operation and the desired results of the invention are achieved. 
     Thus, from the foregoing description it should be readily apparent that the described embodiment very effectively controls engine acceleration during the time when the clutch is being engaged to avoid chattering of the clutch engagement and other difficulties with the transmission. This has been done by delaying the spark timing but it also should be readily apparent that other ways of controlling the engine power output during this time to reduce acceleration variations can be employed such as cylinder skipping or misfiring of a single cylinder. Of course, the foregoing description is that of preferred forms of the invention and various changes and modifications can be made without departing from the spirit and scope of the invention, as defined by the appended claims.