Two-wheeled vehicle control apparatus

Abstract: A two-wheeled vehicle (30) control apparatus comprising: handlebar steering angle computing (32) means for computing the steering angle of the handlebar mounted on a two-wheeled vehicle; vehicle control means (42) for controlling said two-wheeled vehicle in accordance with the velocity of said vehicle and with said handlebar steering angle; vehicle velocity level detecting means (31) for checking to see if the vehicle velocity exceeds a predetermined velocity level; and control stopping means (42) for stopping control operations on said vehicle provided by said vehicle control means if said vehicle velocity is found to exceed said predetermined velocity level.

Description: DETAILED DESCRIPTION OF THE INVENTION: Industrial Field of Utilization: The present invention relates to a two-wheeled vehicle control apparatus and, more particularly, to a two-wheeled vehicle control apparatus which computes the banking angle of the vehicle according to the vehicle's velocity and handlebar steering angle and which controls the vehicle (in terms of light distribution control for the headlight device and of traction control) in accordance with the computed banking angle. Prior Art: The typical prior art headlight device for use with a two-wheeled motor vehicle is required to deliver continuously an appropriate light distribution pattern in front of the vehicle regardless of the vehicle being traveling straight or cornering. This requirement is conventionally met by prior art headlight devices with their light source partially covered with a shade mounted on their opening in front of their reflecting mirror. In operation, the shade partially hides the light source so as to project an appropriate light distribution pattern in front of the vehicle. One such device is disclosed illustratively in Japanese Patent Laid-Open No. 63-158701. To control the headlight device requires detecting the banking angle of the two-wheeled vehicle on which the device is mounted. The prior art device disclosed above uses gimbals, a gyroscope and other related features. One disadvantage of that headlight device is that it complicates the construction of the headlight control apparatus used in conjunction therewith. Moreover, the complicated apparatus construction leads to higher manufacturing costs. To solve the problem, novel techniques are proposed in Japanese Patent Laid-Open No. 1-101245 for detecting the banking angle based on the traveling speed and handlebar steering angle of the two-wheeled vehicle. Also proposed so far is what is known as the traction control apparatus that prevents excessive slippage of the two-wheeled vehicle as it is starting on a slippery road or upon acceleration while traveling. In operation, the traction control apparatus detects the slip ratio of the vehicle from the revolutions of the driving or idle wheel of the vehicle. If the slip ratio is found to be greater than a predetermined value, the traction control apparatus adjusts the ignition timing, the amount of fuel injection, and/or the throttle valve opening so as to reduce the traction of the vehicle. If the above traction control apparatus is supplemented by means for controlling the traction in accordance with the vehicle's velocity and handlebar steering angle, i.e, with the velocity's banking angle, the apparatus will adequately prevent excessive slippage of the vehicle while the latter is executing a cornering run. Problem Intended to Be Solved by the Invention: There are disadvantages of the prior art to be solved by the invention in two areas: (1) The techniques disclosed in Japanese Patent Laid-Open Nos. 63-158701 and 1-101245 are constructed so as to keep providing light distribution control on the headlight device of the two-wheeled vehicle. One disadvantage of this construction is this: that when the two-wheeled vehicle traveling at a relatively high velocity is found to be executing a cornering run through detection of the handlebar steering angle, the cornering radius can be too large for the resulting amount of shade control to affect appreciably the headlight distribution pattern initially set for straight traveling. There is another disadvantage regarding light distribution control: During high velocity traveling, the traction control apparatus is required to compute various control parameters (ignition timing, fuel injection, etc.) on short notice. Where the apparatus doubles as an electronic controller for light distribution control, controlling the light distribution pattern may require the apparatus to delay computations on the other control parameters. Yet another disadvantage is that the control apparatus of the two-wheeled vehicle may dissipate power in dealing with various control parameters that are not currently relevant during the vehicle's run. A further disadvantage is that when the two-wheeled vehicle is traveling on a bumpy road, the repeated, momentary and minute steering of the vehicle's handlebar may cause the control device to control the light distribution pattern accordingly even though the vehicle is traveling straight and the rider's field of vision hardly deviates from the front of the vehicle. When the handlebar is operated abruptly during a ride over a bumpy road, upon a quick change of lanes, or upon a sudden entry into or exit from a cornering run, the change in handlebar steering angle is not the same as that of turns in ordinary arcs. Thus ordinary control based on ordinary arc turns is not appropriate. As described, the prior art techniques for light distribution control on the headlight device tend to deliver the intended control even when such control is hardly needed under the circumstances. As a result, light distribution control can become excessive. (2) The same disadvantages as outlined above also apply when the traction of the two-wheeled vehicle is controlled. It is therefore an object of the present invention to overcome the above-described drawbacks and disadvantages and to provide a two-wheeled vehicle control apparatus which moderates or stops operations on such control parameters as the vehicle's headlight distribution and traction if such controls are liable to become excessive depending on the situation the vehicle is in. Means for Solving the Problem, and Function: In achieving the foregoing and other objects of the present invention and according to one aspect thereof, there is provided a two-wheeled vehicle control apparatus which checks to see if the vehicle is in excess of a predetermined velocity level and, if that predetermined velocity level is found to be exceeded, stops controlling the vehicle in accordance with the vehicle's velocity and handlebar steering angle. According to another aspect of the invention, there is provided a two-wheeled control apparatus which stops controlling the vehicle in accordance with the vehicle's velocity and handlebar steering angle if the amount of vehicle control computed from the vehicle's velocity and handlebar steering angle is below a predetermined level. Cases in which the amount of control is found to be lower than the predetermined level may include a straight run over a bumpy road and other runs that cause the repeated, momentary and minute steering of the handlebar even though the vehicle is traveling straight. According to a further aspect of the invention, there is provided a two-wheeled vehicle control apparatus which computes the amount of change in handlebar steering angle and, if the amount of change is found to exceed a predetermined level, modifies the handlebar steering angle so that the amount of change reaches that predetermined level. The resulting handlebar steering angle and velocity of the vehicle are in turn used to control the latter. Preferred Embodiment: Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. The first to be described is a two-wheeled vehicle headlight control apparatus practiced as a first embodiment of the invention. Fig. 2 is a schematic view of a headlight device to which the first embodiment of the invention is applied. Fig. 3 is a cross-sectional view of the headlight device of Fig. 2. In the two figures, like reference characters designate like or corresponding parts. In Fig. 2, lines H-H and V-V denote a horizontal and a vertical line, respectively. The illustrated headlight device is one for use when, under local traffic law, the two-wheeled vehicle on which it is mounted is supposed to keep to the left while traveling. In Figs. 2 and 3, a headlight device 1 is incorporated in a lamp body, not shown, which in turn is mounted on the two-wheeled vehicle. A reflecting mirror 4 has a spheroidal reflecting surface 3. In front of the reflecting mirror 4 is a convex lens 6, with a connecting member 5 interposed therebetween. The optical axis of the reflecting mirror 4 coincides with that of the convex lens 6 (the optical axis is denoted by X). A bulb 7 has its filament 8 located at a first focal point F1 of an ellipse constituting the reflecting surface 3. A second focal point F2 of the ellipse is located, in this embodiment, on the plane of incidence of the convex lens 6. Reference characters F3 designate the focal point of the convex lens 6. The central point 9C of the upper edge of a shade 9 is located at the focal point F3. Reference characters F3 designate the focal point of the convex lens 6. The central point 9C of the upper edge of a shade 9 is located at the focal point F3. The upper edge of the shade 9 extends crosswise relative to the direction of light irradiation. The upper left edge 9A (viewed from the reflecting mirror 4 toward the convex lens 6; the orientation to be the same hereafter) of the shade 9 extends horizontally at the same height as the central point 9C. The upper right edge 9B of the shade 9 tilts downward from the central point 9C. The lower edge of the shade 9 is integrally equipped with an attachment 9D bent backward, i.e., toward the reflecting mirror 4. The attachment 9D is fixed with a screw 11 to a gear plate 10 in the rear. The gear plate 10 is shaped like a fan large enough to cover the lower half of the cross-sectional area of the headlight device 1. At the center of the upper edge of the gear plate 10 and behind the central point 9C of the shade 9 is a bearing hole 12 whose axis is the optical axis X. Behind the gear plate 10 is a strut 14 whose lower edge is fixedly attached to the lower edge of the opening of the reflecting mirror 4. The upper edge of the strut 14 is located behind a projection 13 of the gear plate 10. In this location is another bearing hole 15 aligned with the bearing hole 12. A pivot shaft 16 penetrates the two bearing holes 12 and 15, forming a bearing section 17 that tiltably supports the gear plate 10 against the strut 14. The gear plate 10 is engaged with a driving gear 19 underneath, the gear being driven by a servo motor 18. Activating the servo motor 18 tilts the gear plate 10 around the axis of the bearing section 17, i.e., around the optical axis X. Correspondingly, the shade 9 is inclined around the optical axis X that passes through the central point 9C of its upper edge. In the above construction, the light irradiated by the bulb 7 forms a light distribution pattern that comprises a dark region 21 and a bright region 22, as depicted in Fig. 2. Boundaries 9a and 9b that distinguish the dark region 21 from the bright region 22 are determined by the upper edges 9A and 9B of the shade 9. Under basic control of the invention, the servo motor 18 rotates the shade 9 so that the boundaries 9a and 9b are turned in a direction L of Fig. 2 when the two-wheeled vehicle performs a leftward cornering run; the servo motor 18 rotates the shade 9 so that the boundaries 9a and 9b are turned in a direction R when the vehicle executes a rightward cornering run. The particular headlight device for use with the invention has been described above only for illustrative purposes. Other alternative headlight devices may also be used in conjunction with the invention. Fig. 4 is a block diagram of the first embodiment of the invention. In Fig. 4, a two-wheeled motor vehicle 30 comprises, in appropriate locations, a vehicle velocity sensor 31 that detects the vehicle's traveling velocity V (i.e., front wheel velocity); a handlebar steering angle sensor 32 that detects the steering angle of the handlebar; the servo motor 18 that rotates the shade 9; and a motor rotation angle sensor 33 that detects the rotation angle of the servo motor 18 (i.e., the rotation angle of the shade 9). In this embodiment, the motor rotation angle sensor 33 is attached to the servo motor 18 via a reduction gear 43 having a suitable reduction ratio. An electronic controller 42 contains a microcomputer for headlight control. The controller 42 also controls, where required, other operational aspects of the vehicle such as ignition timing control and fuel injection control. The vehicle velocity sensor 31 is connected to the electronic controller 42 via an input circuit 34 and a level judging circuit 35. The handlebar steering angle sensor 32 is connected to the electronic controller 42 via an input circuit 36 and an A/D converter 37. The servo motor 18 is connected to the electronic controller 42 via a protective circuit 38 and a driver 39. The motor rotation angle sensor 33 is connected to the electronic controller 42 via an input circuit 40 and an A/D converter 41. The input circuits 34, 36 and 40 protect the level judging circuit 35, the A/D converters 37 and 41, and the electronic controller 42 from the adverse effects of noise, surge voltages, static electricity and electromagnetic waves. Likewise, the protective circuit 38 protects the servo motor 18 from the above-mentioned adverse effects. The vehicle velocity sensor 31 is illustratively a pulse generator that generates pulses (called vehicle velocity detection pulses VP) in accordance with the front wheel revolutions. The handlebar steering angle sensor 32 and the motor rotation angle sensor 33 are each illustratively a potentiometer whose output voltage varies with the steering angle of the handlebar and with the rotation angle of the servo motor 18, respectively. As will be described later in more detail, the level judging circuit 35 judges the voltage value of the vehicle velocity detection pulses VP that are output via the input circuit 34. If the voltage value is not found within a predetermined range of values, the level judging circuit 35 outputs a signal to that effect to the electronic controller 42. Upon receipt of that signal, the electronic controller 42 concludes that the vehicle velocity sensor 31 is disconnected or short-circuited, and stops controlling the shade 9 thereafter. A power supply circuit 45 contains a switching circuit 46 and a constant voltage circuit 47. When a combination switch 49 is turned on, a battery 44 is connected to the constant voltage circuit 47. This supplies a constant voltage (e.g., +5 V) to the electronic controller 42. The turning-on of the combination switch 49 is also detected by the electronic controller 42 by use of a line comprising a resistor 48. Turning off the combination switch 49 changes the state of the switching circuit 46. For a predetermined period of time (e.g., 3 hours) starting from that off-state, the battery 44 stays connected to the power supply circuit 45. This supply of battery power backs up the electronic controller 42. While the battery 44 is being connected to the constant voltage circuit 47, the battery 44 is also connected to a resistor 53, an indicator lamp 50, a protective circuit 51 and a switching element 52, as illustrated. Normally, the switching element 52 remains on to keep the indicator lamp 50 turned off. When something abnormal occurs, the switching element 52 is turned off, which illuminates the indicator lamp 50. Fig. 17 is a function block diagram of the first embodiment showing how it is constructed and how it operates on a two-wheeled vehicle. In both Fig. 17 and Fig. 4, like reference characters designate like or corresponding parts. In Fig. 17, the vehicle velocity detection pulses VP that were output from the vehicle velocity sensor 31 are input to a disconnection/short-circuit detecting means 101. The means 101 detects the voltage value of the pulses VP. If the voltage value is found to be lower or higher than is expected, a short-circuit or a disconnection is recognized, respectively. In either case, a flag Fid is generated by an Fid generating means 102. The function of the disconnection/short-circuit detecting means 101 is achieved in conjunction with the level judging circuit 35 (Fig. 4). A driver 130 normally keeps the switching element 52 on and the indicator lamp 50 off. When the flag Fid is generated, the driver 130 turns off the switching element 52 and illuminates the indicator lamp 50. The indicator lamp 50, when lit, indicates that specific status has occurred on the vehicle. The generation of the flag Fid actuates a switching means 123, to be described later. This in turn connects a motor resetting means 127 to the driver 39. In this setup, the headlight control apparatus stops controlling the shade 9 (i.e., control of the servo motor 18) according to the banking angle, and returns the shade 9 to its center position (ϑ mc). If neither disconnection nor short-circuit of the vehicle velocity sensor 31 is detected, a vehicle velocity detecting means 103 suitably detects the traveling velocity V of the two-wheeled motor vehicle. A velocity range checking means 104 lets the velocity V be output to a banking angle computing means 120 if the velocity V falls within a range of 3 (km/h) ≦ V ≦ 127.5 (km/h) If V < 3 (km/h), then the velocity range checking means 104 considers the velocity V to be 0 (km/h) and outputs zero to the banking angle computing means 120. If 127.5 (km/h) < V, then an Fvo generating means 105 is activated to generate a flag Fvo. The generation of the flag Fvo in turn activates the switching means 123, connecting a second motor control means 126 to the driver 39. While the two-wheeled motor vehicle is traveling at high velocity, the cornering radius thereof is large and the shade 9 need not be controlled. In that case, the second motor control means 126 gradually returns the shade 9 to its center position. A handlebar steering angle signal ϑ ho(n) output by the handlebar steering angle sensor 32 is input to the disconnection/short-circuit detecting means 106 at a predetermined timing. The means 106 detects a voltage value from the signal received. As with the other disconnection/short-circuit detecting means 101, the disconnection/short-circuit detecting means 106 judges the handlebar steering angle sensor 32 to be short-circuited or disconnected if the detected voltage value is less or more than is expected, respectively. In either case, an Fid generating means 107 generates a flag Fid. A Δ ϑ h computing means 116 receives the above-mentioned ϑ ho(n) and computes the deviation Δ ϑ h thereof. Since ϑ ho(n) is detected at the appropriate timing as described, the value Δ ϑ h represents the velocity of handlebar steering angle change. A moving average computing means 108 computes the average of a predetermined sampling number of values of ϑ ho(n), and computes upon acquisition of each average the moving average of a plurality of the averages thus collected so far. Needless to say, the moving average computing means 108 may also be used simply to compute the average of a predetermined sampling number of values of ϑ ho(n). A value ϑ ha is input to a dynamic center value computing means 110. Upon receipt of that value, the means 110 computes dynamic center position data ϑ dcd of the handlebar steering angle sensor 32. The data is represented by a signal ϑ dcd output by the handlebar steering angle sensor 32 when the two-wheeled vehicle is actually traveling straight. The computation of ϑ dcd by the dynamic center value computing means 110 may be performed every time the value ϑ ha is computed; alternatively, the computation may be carried out using a dividing ratio stored in a dividing ratio storing means 112 (that is, every time ϑ ha is computed a predetermined number of times). As will be described later with reference to Fig. 10, the value ϑ dcd is computed with the dynamic center value computing means 110 through the use of the moving average ϑ ha of the handlebar steering angle, a dead zone width R stored in a dead zone width storing means 111, and vehicle velocity detecting pulses VP (i.e., traveled distance data of the vehicle). After being computed, the dynamic center value ϑ dcd is stored as ϑ dc into a dynamic center value storing means 113. A handlebar steering angle computing means 109 computes a true handlebar steering angle ϑ h(n) (relative to the central position of the handlebar) using the handlebar steering angle moving average ϑ ha and the dynamic center value ϑ dc read from the dynamic center value storing means 113. If the handlebar steering angle ϑ h(n) computed this time exceeds the previously computed handlebar steering angle ϑ h(n-1) by more than a predetermined level, a variation limiting means 114 limits the value ϑ h(n) to below that predetermined level. In other words, the variation limiting means 114 checks to see if the variation of the handlebar steering angle exceeds a certain level. If the level is found to be exceeded, the variation limiting means 114 modifies the handlebar steering angle so that the variation will fall below that level. The resulting handlebar steering angle is output to a δ table as well as to the banking angle computing means 120. This moderates the detected banking angle ϑ b in case the handlebar is moved abruptly by the rider. An α table 118, a β table 117 and a δ table 119 are tables or maps containing a first correction factor α , a second correction factor β and a fourth correction factor δ , respectively. The first, the second and the fourth correction factors are read from the tables using, respectively, the vehicle's velocity V, the velocity V as well as the value Δ ϑ h, and the value ϑ h(n). Given the vehicle's velocity V, the handlebar steering angle ϑ h(n), the first correction factor α , the second correction factor β and the fourth correction factor δ , the banking angle computing means 120 computes the banking angle ϑ b (inclination of traveling vehicle) of the two-wheeled motor vehicle using equation (1) below: ϑ b = V x α x ϑ h(n) x δ x β (1) The first correction factor α , the second correction factor β and the fourth correction factor δ will now be described in more detail. The first correction factor α is a factor for determining the banking angle ϑ b by use of the vehicle's velocity V and the handlebar steering angle ϑ h(n). This factor is read out in accordance with the vehicle's velocity V. The second correction factor β is a factor determined by use of the vehicle's velocity V and the handlebar steering angle ϑ h(n) as the parameters. It is assumed here that the second correction factor β is represented by the product of a factor β 1 and a factor β 2, the factor β 1 having Δ ϑ h as its parameter, the factor β 2 having the velocity V as its parameter. In that case, the factors β 1 and β 2 take on the curves depicted in Figs. 18 and 19. That is, the second correction factor β becomes smaller the greater the Δ ϑ h and the higher the velocity V. Upon entry into or exit from a cornering run, the handlebar steering angle does not correspond directly to the banking angle. For example, immediately before making a left turn, the rider momentarily steers the handlebar to the right so as to move his center of gravity to the left-hand side of the two-wheeled vehicle. Only after the momentary steering of the handlebar is made in the opposite direction does the vehicle's rider start executing the intended turn. In that transient state of turn, no direct correspondence exists between the handlebar steering angle and the banking angle. If the banking angle ϑ b is computed directly from the handlebar steering angle in that transient state, the shade 9 may not be controlled appropriately. In such a transient state, i.e., in the state where the value ϑ Δ h abruptly changes, the sudden change in the banking angle computed is minimized by multiplying the second correction factor β , the factor being smaller the greater the value ϑ Δ h. This permits accurate computation of the banking angle and thus provides precise control over the movement of the shade 9. Given the same velocity of handlebar steering angle change, the banking angle is made smaller as the vehicle's velocity V becomes higher. Thus the second correction factor β is minimized as the velocity V is made higher. When both the velocity of handlebar steering angle change and the vehicle's velocity V are higher, the banking angle is judged to be smaller than is expected. In that case, the banking angle data is reduced further for better control on the shade 9. After the two-wheeled vehicle has gone into the turn of a normal arc, the change in ϑ Δ h is reduced. This allows the second correction factor β to be greater so that the banking angle may be accurately computed according to the handlebar steering angle. The fourth correction factor δ is a factor determined in accordance with the handlebar steering angle and with the handlebar being turned right or left. Given the same handlebar steering angle, the fourth correction factor δ in effect when the handlebar is turned right is made smaller than that in effect with the handlebar turned left. Fig. 20 illustrates how the fourth correction factor δ is set depending on the handlebar being turned right or left. The fourth correction factor δ is a factor determined in accordance with the handlebar steering angle and with the handlebar being turned right or left. Given the same handlebar steering angle, the fourth correction factor δ in effect when the handlebar is turned right is made smaller than that in effect with the handlebar turned left. Fig. 20 illustrates how the fourth correction factor δ is set depending on the handlebar being turned right or left. The reason that the fourth correction factor δ is set in the above manner is as follows: When the banking angle is zero, i.e., when the two-wheeled vehicle is traveling upright, the shade 9 is in its central position. On the two-wheeled vehicle that is required by law to keep to the left-hand side on the road, the light distribution pattern projected in front of the vehicle is kept "flat" on the right-hand side and "raised" leftward on the left-hand side. Thus if the rotation angle of the shade 9 is made the same regardless of the handlebar being turned right or left (i.e., regardless of the banking angle being rightward or leftward), the vehicle's rider will perceive a greater amount of controlled light distribution when banking to the right. Since the amount of control of the shade 9 is determined from the banking angle in this embodiment, the fourth correction factor δ is used to minimize that amount of control when the vehicle is banking to the right. A motor control amount computing means 121 multiplies the banking angle ϑ by a third correction factor γ , to be described later, in order to compute the rotation angle (i.e., amount of motor control) ϑ m relative to the motor median ϑ mc of the servo motor 18 (i.e., shade-driving motor rotation angle corresponding to the central position of the shade in effect while the vehicle is traveling straight). The third correction factor γ is lowered based on the data output by the dynamic center value computing means 110. The lowering of the third correction factor γ is performed when the dynamic center value ϑ dc stored in the dynamic center value storing means 113 is found to be still unstable immediately after the vehicle has started traveling. Therefore, the amount of motor control ϑ m is moderated where the reliability of the handlebar steering angle ϑ h(n) is low. If the computed amount of motor control ϑ m falls within a predetermined range of angles, an Fbu generating means 122 is activated, and a flag Fbu is generated thereby. The generation of the flag Fbu causes the second motor control means 126 to be connected to the driver 39. Thus when the amount of motor control ϑ m, i.e., the banking angle ϑ b, is relatively small, the vehicle is judged to be simply changing lanes when traveling straight or to be negligibly inclined as a result of riding on a bumpy road. In such cases, the shade 9 need not be controlled. The second motor control means 126 then returns the shade 9 gradually to its central position without controlling the shade according to the banking angle ϑ b. If the flags Fid, Fvo and Fbu, as well as an Fd, an Fdl and an Fvol (the latter three to be described later) are not generated (i.e., not High), the amount of motor control ϑ m is supplied to a first motor control means 124. The first motor control means 124 computes a motor control angle ϑ m0 by adding to the value ϑ m the motor median data ϑ mc calculated in a manner to be described later. Furthermore, the first motor control means 124 outputs a control signal to the driver 39 using the control angle ϑ m0 and an actual motor rotation angle ϑ m1. The actual motor rotation angle ϑ m1 is output from the motor rotation angle sensor 33 via a disconnection/ short-circuit detecting means 128. The servo motor 18 is thus controlled under this feedback scheme. This feedback control scheme is implemented as follows: A duty ratio corresponding to the difference between the motor control angle ϑ m0 and the actual motor rotation angle ϑ m1 is read from a duty ratio storing means 125 (shown in Fig. 16). The duty ratio is then used to provide chopping control over the servo motor 18. The disconnection/short-circuit detecting means 128 detects the voltage value of the actual motor rotation angle ϑ ml output by the motor rotation angle sensor 33. As with the other disconnection/short-circuit detecting means 101 and 106, the means 128 judges the motor rotation angle sensor 33 to be short-circuited or disconnected when the detected voltage value is less or more than is expected, respectively. In case of a disconnection or short-circuit, an Fid generating means 129 generates a flag Fid. The switching circuit 46 is constructed so that unless the combination switch 49 is turned on, the battery 44 is not connected to the constant voltage circuit 47. When the combination switch 49 is turned on, a current flows in from the battery 44 through the resistor 48. This activates an Fb generating circuit 131 which in turn generates a flag Fb. The generation of the flag Fb resets ci backup timer 133. The flag Fb stops being generated when the combination switch 49 is turned off. When the flag Fb stops being generated, i.e., when the flag is brought Low, an Fhr generating means 132 is activated, and a flag Fhr is generated thereby. The generation of the flag Fhr activates the backup timer 133, turns on the switching circuit 46, and connects the constant voltage circuit 47 directly to the battery 44 without the intermediary of the combination switch 49. Upon elapse of a predetermined period of time (e.g., 3 hours), the backup timer 133 turns off the switching circuit 46 and disconnects the constant voltage circuit 47 from the battery 44. That is, the headlight control apparatus stays connected to the power supply for the predetermined period of time even after the combination switch 49 is turned off. This allows diverse kinds of data (including the dynamic center value ϑ dc stored in the dynamic center value storing means 113) to be held intact in various storing means such as RAMs. Thus if the rider turns off the combination switch 49, takes a break and then resumes traveling on his two-wheeled vehicle, the headlight can be controlled immediately upon departure based on the settings from the previous run. If the combination switch 49 is turned on before the predetermined period of time elapses on the backup timer 133, the flag Fb generated by the Fb generating means 131 resets and stops the backup timer 133. The switching circuit 46 is turned off. Fig. 21 is a timing chart showing the relationship between the status of the combination switch 49, the flag Fb and the backup timer 133 on the one hand, and the supply voltage output by the constant voltage circuit 47 on the other. Referring to Fig. 21, the motor resetting means 127 is activated if the combination switch 49 is found to be on, i.e., if the flag Fb is found to be High. In that case, if the vehicle's velocity V is below a certain level (e.g., 3 km/h), the motor resetting means 127 turns the servo motor 18 fully clockwise and counterclockwise until the shade 9 contacts its right and left stoppers. The actual motor rotation angles in both rotating directions are detected. Then the sum of the detected actual motor rotation angles is halved. If the shade and its stoppers are mounted precisely on the frame of the two-wheeled vehicle, the result of the above computation represents the central position of the handlebar, i.e., a median motor rotation angle ϑ mc that corresponds to the central position of the shade. Thereafter, the servo motor 18 is controlled so that it keeps to the median ϑ mc. When the dynamic center value ϑ dcd computed with the dynamic center value computing means 110 becomes reliable enough to be used for headlight control, i.e., when the two-wheeled vehicle has traveled a relatively long distance so that the dynamic center value ϑ dcd thereof is found to have become dependable, an Fd generating means 115 and an Fd1 generating means 134 generate flags Fd and Fd1, respectively. This aspect of control operation will be described later with reference to Fig. 10. From the time the servo motor 18 is returned to its central position by generation of the flag Fb until the flag Fd is generated, the motor 18 is not controlled. Upon generation of the flag Fd, the switching means 123 is activated so that the first or second motor control means 124 or 126 controls the servo motor 18. With the flag Fd1 generated, control of the servo motor 18 according to the banking angle ϑ b is moderated only when the flag Fd is generated. With the flag Fd generated, the motor rotation angle is gradually made to coincide with the control angle ϑ m0. Thereafter, the flag Fd1 is reset and the first motor control means 124 continues servo motor control. As described, the second motor control means 126 gradually returns the shade 9 to its central position when the flag Fvo is generated (i.e., when 127.5 [km/h] < V). When the vehicle's velocity V becomes equal to or less than 127.5 km/h, i.e., when the Fvol generating means 135 is activated by bringing the flag Fvo Low and by generating the flag Fvol, control of the servo motor 18 according to the banking angle ϑ b is resumed. In this case, the motor rotation angle is made to coincide gradually with the control angle ϑ m0. When the motor rotation angle and the control angle ϑ m0 are found to be matched, the flag Fvol is reset. Thereafter, the first motor control means 124 continues servo motor control. As is evident from the preceding description, although the disconnection/short-circuit detecting means 101, 106 and 128 are functionally similar with one another, only the means 101 is constructed in hardware. (That is, the function of the disconnection/short-circuit detecting means 101 is implemented with the level judging circuit 35.) The function of the disconnection/short-circuit detecting means 106 and that of the means 128 are implemented in software terms with the electronic controller 42 (of Fig. 4). Needless to say, the function of the disconnection/short-circuit detecting means 101 may also be implemented with the electronic controller 42 if so desired. What follows is a detailed description of how the headlight control apparatus of Fig. 17 embodying the invention operates when used in conjunction with a two-wheeled vehicle. Control of the shade 9 with this embodiment is basically accomplished by a main routine of Fig. 5, by an interrupt handling routine of Fig. 7, and by an interrupt handling routine of Fig. 9. The interrupt handling routine of Fig. 7 is carried out at regular intervals while the main routine is being executed. The interrupt handling routine of Fig. 9 is activated using the vehicle velocity detecting pulses during main routine execution. Referring to Fig. 5, step S1 performs initialization. That is, the flag Fb is brought High, and the other flags (Fvo, Fvol, Fbu, Fd, Fdl, Fid and Fhr) are brought Low. Various counter, timer and n value arrangements (to be described later with reference to Fig. 7) are also reset in step S1. A value Ldcmax (to be described later with reference to Fig. 10) is set to zero. In step S2 of Fig. 5, the initial operation of the shade 9 is verified. In this step, the shade 9 (of Figs. 2 and 3) is returned to its central position (i.e., the position in effect when the two-wheeled vehicle 30 is traveling straight). Step S2 will be described in more detail with reference to Fig. 6. In step S20 of Fig. 6, a check is made to see if the flag Fb is High. If the flag Fb is found to be Low, the process of Fig. 6 comes to an end. If the flag Fb is found to be High in step S20, step S21 is reached. In step S21, a check is made to see if the two-wheeled vehicle 30 is traveling at a velocity equal to or lower than 3 km/h. If the vehicle's velocity is found to exceed the 3 km/h threshold, the process of Fig. 6 is terminated. In step S20 of Fig. 6, a check is made to see if the flag Fb is High. If the flag Fb is found to be Low, the process of Fig. 6 comes to an end. If the flag Fb is found to be High in step S20, step S21 is reached. In step S21, a check is made to see if the two-wheeled vehicle 30 is traveling at a velocity equal to or lower than 3 km/h. If the vehicle's velocity is found to exceed the 3 km/h threshold, the process of Fig. 6 is terminated. If the vehicle's velocity is equal to or lower than 3 km/h, step S22 is reached. In step S22; the servo motor 18 is rotated clockwise. The motor rotation continues until the shade 9 is found to come in contact with a stopper, not shown, in step S23. In step S24 of Fig. 6, the rotation angle ϑ m1 of the servo motor 18 is read in as ϑ mrm. In step S25, the servo motor 18 is rotated counter-clockwise. The motor rotation continues until the shade 9 is found to contact the stopper in step S26. In step S27, the rotation angle ϑ m1 is read in as ϑ mlm. In step S28, the rotation angle (median) ϑ mc of the shade-driving motor 18 is computed while the two-wheeled vehicle is traveling straight. The computation is carried out by halving the sum of the values ϑ mrm and ϑ mlm. In step S29 of Fig. 6, the servo motor 18 is driven in such a manner that the rotation angle thereof becomes the median angle ϑ mc. Thereafter, the process of Fig. 6 comes to an end. Although not shown in Fig. 6, there is provided a stage in which a motor lock phenomenon is detected if the servo motor 18 is found to be faulty in rotation in step S22 or S25. In that case, the flag Fid is brought High. The effects of the flag Fid being High will be described later with reference to Fig. 22. Returning to Fig. 5, step S2 is followed by step S3 in which a check is made to see if the flag Fid is High. If the flag Fid is found to be Low in step S3 of Fig. 5, step S5 is reached. In step S5, the switching element 52 is turned on (i.e., the indicator lamp 50 is turned off). Step S5 is followed by step S6. If the flag Fid is found to be High, step S4 is reached in which indicator processing is carried out. Details of the indicator processing are depicted in Fig. 22. The indicator processing may also be executed using an interruption when the flag Fid is brought High. Referring to Fig. 22, step S211 turns off the switching element 52 and turns on the indicator lamp 50. In step S212 of Fig. 22, the servo motor 18 is controlled so that the rotation angle thereof will coincide with ϑ mc. If the flag Fid was found to be High in the process of Fig. 6, that means the value ϑ mc has not been computed. In that case, the servo motor 18 is controlled so that its rotation angle will attain a predetermined value. In step S213, a check is made to see if a reset switch, not shown, is turned on. If the reset switch is found to be on, the process of Fig. 22 comes to an end and step S1 of Fig. 5 is restored. Returning to Fig. 5, step S6 checks to see if the combination switch 49 is turned off. If the combination switch 49 is found to be on, step S7 is reached. Step S7 checks to see if the flag Fhr is Low. If the flag Fhr is found to be Low, step S3 is reached again. If the flag Fhr is found to be High, step S405 is reached. Step S405 resets the switching circuit 45 (of Figs. 4 and 17) and cuts off direction connection between the battery 44 and the constant voltage circuit 47. The above direction connection is established in step S400, to be described later. The flags Fhr and Fb are brought Low and High in steps S8 and S9, respectively. Step S11 resets the backup timer that is set in step S16, to be described later. Thereafter, step S3 is reached again. If the combination switch 49 was found to be off in step S6 of Fig. 5, step S12 is reached in which a check is made to see if the flag Fhr is High. If the Flag Fhr is found to be Low, step S14 is reached. Step S14 brings the flag Fb Low. In step S13, the flag Fhr is brought High. Step S13 is followed by step S400. Step S400 sets the switching circuit 46 and directly connects the battery 44 with the constant voltage circuit 47. In step S16 which follows step S400, the backup timer starts counting time. Thereafter, step S3 is reached again. If the flag Fhr is found to be High in step S12, step S17 is reached. Step S17 checks to see if a predetermined period of time (e.g., 3 hours) has elapsed. If the predetermined period is not found to have elapsed, step S3 is reached again. If the predetermined period is found to have elapsed, step S404 is reached. Step S404 resets the switching circuit 46 and cuts off direction connection between the battery 44 and the constant voltage circuit 47. Because the combination switch 49 is turned off at this time, the headlight control apparatus is not powered, and the process of Fig. 5 comes to an end. Fig. 7 is a flowchart showing how an interruption is carried out at regular intervals (i.e., every 5 msec.) while the main routine is being executed. In step S30 of Fig. 7, the value n is incremented by 1. Step S31 reads the handlebar steering angle signal ϑ h0(n) which is the output signal from the handlebar steering angle sensor 32. Step S32 of Fig. 7 detects a disconnection or short-circuit of the handlebar steering angle sensor 32. Details of what takes place in step S32 are depicted in Fig. 8. The signal output by the handlebar steering angle sensor 32 via the A/D converter 37 (of Fig. 4) normally falls within a range of 0.5 V (handlebar in its full left turn position) to 4.5 V (handlebar in its full right turn position). With the manufacturing and assembly error taken into account, the normal range for the signal is between 0 and 5 V. In step S40 of Fig. 8, a check is made to see if the value ϑ h0(n) is below 0.5 V. If the value ϑ h0(n) is found to be below the 0.5 V threshold, step S42 is reached; if the value ϑ h0(n) is not below the 0.5 V threshold, step S41 is reached. Step S41 checks to see if the value ϑ h0(n) is above 4.5 V. If the value ϑ h0(n) is found to be above the 4.5 V threshold, step S42 is reached; if the value ϑ h0(n) is not above the 4.5 V threshold, step S46 is reached. In step S42, a check is made to see if the vehicle's velocity V is equal to or higher than, say, 30 km/h. If the velocity V is found to be equal to or higher than the 30 km/h threshold, step S43 is reached; if the velocity V is lower than 30 km/h, step S46 is reached. In step S43, a handlebar steering angle counter, not shown, is incremented by 1. Step S44 checks to see if the above count value is equal to or greater than 20. If the count is found to be below 20, the process of Fig. 8 comes to an end; if the count is found to be equal to or higher than 20, a disconnection or short-circuit of the handlebar steering angle sensor 32 is detected, and step S45 is reached in which the flag Fid is brought High. Thereafter, the process of Fig. 8 is terminated. In step S46 of Fig. 8, the count value on the handlebar steering angle counter is reset. That is, the process of Fig. 8 involves detecting a disconnection or short-circuit of the handlebar steering angle sensor 32 based on the fact that when the vehicle is traveling at a relatively high velocity (30 km/h or higher), the handlebar steering angle thereof does not become significantly large (i.e., ϑ h0(n) is not too large or too small). If the handlebar steering angle sensor 32 has no manufacturing or assembly error and if the output thereof always falls within the range of 0.5 V to 4.5 V with no disconnection or short-circuit detected, the threshold value in step S40 is allowed to be higher than 0.5 V and the threshold value in step S41 lower than 4.5 V. Where the threshold value is to be set below the maximum value and above the minimum value of the output from the handlebar steering angle sensor 32, a disconnection or short-circuit of the handlebar steering angle sensor 32 may still be detected even if step S42 is omitted. Returning to Fig. 7 and in step S33, the velocity of handlebar steering angle change Δ ϑ h is computed from equation (1), as follows: A ϑ h = ϑ h0(n) - ϑ h0(n-10) (2) In equation (2) above, the value to be subtracted from the value ϑ h0(n) may alternatively be the value ϑ h0 detected at a timing other than (n-10). In step S34, the moving average (or simply the average) described with reference to Fig. 17 is computed using the value ϑ h0. In step S35, the dynamic center value ϑ dc to be described later is read out. In step S36, the handlebar steering angle ϑ h(n) (relative to the central position of the handlebar) is computed by use of equation (3) below. ϑ h(n) = ϑ ha - ϑ dc (3) In step S37 of Fig. 7, a check is made to see if the absolute difference between ϑ h(n) and ϑ h(n-1) exceeds a predetermined level of, say, 3 (level 1 denotes the computable unit of the microcomputer, i.e., the resolution thereof; the same applies hereafter). If the absolute difference is not in excess of the predetermined level 3, step S39 is reached; if the level 3 is exceeded, step S38 is reached. In step S38, the absolute value of ϑ h(n) is set to the value ϑ h(n-1) plus level 2. In step S39, the value ϑ h(n) is stored, and the process of Fig. 7 comes to an end. Fig. 9 is a flowchart illustrating how interrupt handling is executed by application of the vehicle velocity detection pulses during main routine execution. In step S51 of Fig. 9, the interval detected between the vehicle velocity detection pulses VP is translated by suitable means into the traveling velocity of the two-wheeled vehicle 30. In step S52, a check is made to see if the vehicle's velocity V is in excess of 127.5 km/h. If the velocity is found to exceed the 127.5 km/h threshold, step S53 is reached. In step S53, the flag Fvo is brought High. Then step S56 is reached. If the vehicle's velocity V does not exceed the 127.5 km/h threshold, step S201 is reached. In step S201, a check is made to see if the flag Fvo is High. If the flag Fvo is not found to be High, step S54 is reached. If the flag Fvo is found to be High, the flag Fvo is brought Low in step S202 and the flag Fvol is brought High in step S203. In step S204, a value ϑ mm, to be described later in connection with step S125 of Fig. 13, is reset. Then step S54 is reached. In step S54 of Fig. 9, a check is made to see if the vehicle's velocity V is lower than 3 km/h. If the velocity V is found to be lower than the 3 km/h threshold, the velocity V is set to 0 (km/h) in step S55 before step S56 is reached. If the velocity V is found to be equal to or higher than the 3 km/h threshold, step S56 is reached without passage through step S55. In step S56, a check is made to see if the timing is right for executing step S57, to be described later. That is, the process of step S57 is illustratively performed every time this interrupt handling routine has been executed a predetermined number of times. Step S57 computes the dynamic center value of the handlebar steering angle sensor 32, i.e., the output signal thereof in effect when the handlebar is in its central position. When the dynamic center value is detected, the output signal of the handlebar steering angle sensor 32 in effect with the handlebar in its central position is accurately known even if the sensor 32 is misaligned on the two-wheeled vehicle. What takes place in step S57 is depicted in more detail in Fig. 10. In step S71 of Fig. 10, the value ϑ ha computed in step S34 of Fig. 7 is read. In step S72, a check is made to see if a dead zone is already set in step S85, to be described later. If the dead zone is not set, step S84 is reached. In step S84, the value ϑ ha is set to ϑ haa. In step S85, the dead zone is set. The dead zone has a predetermined width R (shown in Fig. 15) extending up and down the value ϑ haa. The upper limit ϑ hd1 of the dead zone is the value ϑ haa plus the dead zone width R, and the lower limit ϑ hd2 thereof is the value ϑ haa minus the width R. As will be described later, measured next is the distance Ldc (Fig. 15) traveled by the two-wheeled vehicle from the time the dead zone is set (i.e., after ϑ haa is set) until the value ϑ ha falls out of the dead zone. And as will be described later, when a predetermined condition is met, the value ϑ haa at that time is stored as ϑ haa or ϑ haa(FF). In step S86, the distance Ldc traveled since the dead zone was set starts being measured. When the traveled distance has been measured, the process of Fig. 10 comes to and end. If the dead zone is found to be set in step S72 of Fig. 10, step S73 is reached. In step S73, a check is made to see if the value ϑ ha falls out of the dead zone. That is, step S73 determines whether the value ϑ ha is higher than the upper limit ϑ hd1 or lower than the lower limit ϑ hd2. If the value ϑ ha falls within the dead zone, step S87 is reached. In step S87, a check is made to see if the traveled distance Ldc is equal to or greater than a predetermined distance FF. If the distance Ldc is less than the distance FF, the process of Fig. 10 is terminated. If the value ϑ ha is found in step S73 to be outside the dead zone, step S74 is reached. Step S74 completes the measurement of the traveled distance Ldc and stores the measured distance. In other words, step S74 detects the distance Ldc traveled by the two-wheeled vehicle in stable, upright state from the time the dead zone is set until the value ϑ ha falls out of the dead zone. In step S90, a check is made to see if the traveled distance Ldc is equal to or greater than the value Ldcmax (the maximum value of the Ldc measurements taken so far; the initial value of Ldcmax is 0 as initialized in step S1 of Fig. 5). If the distance Ldc is less than the maximum value Ldcmax, step S75, to be described later, is reached. If the distance Ldc is found to be equal to or greater than the value Ldcmax, step S91 is reached. Step S91 checks to see if the above-mentioned predetermined distance FF has been set as Ldcmax. The setting is carried out in step S95, to be described later. If the distance Ldcmax is found to be set to the distance FF, step S94 is reached. The step S94 sets to the value ϑ haa(FF) the value ϑ haa that was set when the dead zone was established. After this, step S75 is reached. If the distance Ldcmax is not found to have been set to the distance FF, step S92 is reached. Step S92 stores the value ϑ haa as is. In step S93, the distance Ldc stored in step S74 is set to Ldcmax and stored as such. Thereafter, step S75 is reached. If the distance Ldc is found in step S87 to be equal to or greater than the predetermined distance FF, step S95 is reached. Step S95 sets the distance Ldcmax to FF. As discussed in connection with step S90, the value Ldcmax is set consecutively to each of the largest values of Ldc. But if the distance Ldc is found to be equal to or greater than the distance FF, the value Ldcmax is fixedly set to the value FF. In step S96, the value ϑ haa set when the dead zone was established is set to ϑ haa(FF). Thereafter, step S75 is reached. As described, the largest value of Ldc is set to Ldcmax, and the value ϑ haa in effect at that time is stored unchanged. After the value Ldcmax is set to the maximum value FF, the value ϑ haa is set to ϑ haa(FF) and stored as such. In step S75, a check is made to see if the flag Fd is Low. If the flag Fd is found to be High, step S80 is reached. If the flag Fd is found to be low in step S75, step S76 is reached. Step S76 checks to see if the value Ldc (or Ldcmax) exceeds the value Ldcb (< FF). If the value Ldc is not found to be in excess of the value Ldcb, step S80 is reached. If the value Ldc is found to exceed the value Ldcb, step S77 is reached. In step S77, the flags Fd and Fdl are brought High each. Thereafter, step S80 is reached. In step S80, a check is made to see if there are four values of ϑ haa(FF). If four values of ϑ haa(FF) are found to exist, step S81 is reached. Step S81 computes the average of the four values as the dynamic center value ϑ dcd of the handlebar steering angle, and stores that value as ϑ dc. In step S82, the oldest ϑ haa(FF) is erased, and the most recent three values of ϑ haa(FF) are selected. Thereafter, step S83 is reached. If four values of ϑ haa(FF) are not found to exist in step S80, step S88 is reached. Step S88 selects the most recent value of ϑ haa (i.e., ϑ haa stored in step S92, or ϑ haa(FF) stored in step S94 or S96) as the dynamic center value ϑ dcd, and stores that value as ϑ dc. Then step S83 is reached. In step S83, the dead zone is reset. Step S83 is followed by step S84 in which the dead zone is set again. Steps S58 through S60 of Fig. 9 read out the first, the second and the fourth correction factors α , β and δ , respectively. These factors were already described in conjunction with Fig. 17. In step S61, the banking angle ϑ b is computed using equation (1) above. In step S62, the amount of control of the servo motor 18 is computed. What takes place in step S62 is depicted in more detail in Fig. 11. In step S100 of Fig. 11, a check is made to see if at least one value of ϑ haa(FF) (shown in Fig. 10) is stored. If at least one value of ϑ haa(FF) is found to exist, it is judged that the dynamic center value has been correctly computed, and step S101 is reached. Step S101 sets the third correction factor γ to a value ε . As described, the banking angle ϑ b has been computed using the handlebar steering angle ϑ h(n), and the value ϑ h(n) is based on the dynamic center value ϑ dc which was determined as depicted in Fig. 10. The value ϑ dc is deemed highly accrate when at least one value of ϑ haa(FF) is stored (i.e., when at least distance FF is traveled by the two-wheeled vehicle with its handlebar steering angle ϑ ha kept within the dead zone). This is because the handlebar is thought to have been in its central position throughout that distance traveled. In the case above, the third correction factor γ is set to the value ε as is. In case no value of ϑ haa(FF) is found to exist, the reliability of the dynamic center value ϑ dc is deemed low. In this case, the third correction factor γ is set to a value smaller than the value ε , as depicted in connection with step S103 or S105. If not even one value of ϑ haa(FF) is found to exist in step S100, step S102 is reached. In step S102, a check is made to see if at least one value of ϑ haa is stored. If not even one value of ϑ haa is found to exist, it is judged that the dynamic center value has not been computed, and step S103 is reached. Step S103 sets the third correction factor γ to zero. That is, in step S62 to be described later, the amount of motor control ϑ m is set to zero. If at least one value of ϑ haa is found to exist in step S103, step S104 is reached. Step S104 checks to see if the value Ldcmax is in excess of the value Ldcb. If the value Ldcmax is not found to be in excess of the value Ldcb, it is judged that the accuracy of the dynamic center value is low, and step S103 is reached. If the value Ldcmax is found to exceed the value Ldcb, step S105 is reached. In step S105, the third correction factor γ is computed using equation (4) below: As indicated by equation (4) above, the third correction factor γ is set to a value smaller than the value ε . That is, after step S105 is reached, it is judged that the dynamic center value, the reliability of which is not very high, may be used if suitably moderated for computing the amount of motor control ϑ m. The third correction factor γ is thus moderated according to the value Ldc. In equation (4) above, the value Ldc may alternatively be replaced with the value Ldcmax. After the third correction factor γ is set, step S106 is reached. Step S106 computes the amount of control ϑ m of the servo motor 18 (angular difference of the rotation axis of the motor relative to the central position thereof) using equation (5) below: ϑ m = ϑ b x γ (5) The value ε used in steps S101 and S105 is the factor for converting the banking angle ϑ b into the amount of control ϑ m of the servo motor 18. Returning to Fig. 9 and in step S63, a check is made to see if the computed amount of motor control ϑ m is within ± 5 degrees. If this condition is met, step S64 is reached in which the flag Fbu is brought High. Then step S65 is reached. If the computed amount of motor control ϑ m is found to be outside the ± 5 degree range, stem S205 is reached in which the flag Fbu is brought Low. Step S205 is followed by step S206 which resets the value ϑ mm as in step S204. Then step S65 is reached. Step S65 reads the rotation angle ϑ m1 of the servo motor 18, the angle being output by the motor rotation angle sensor 33 through the A/D converter 41 (of Fig. 4). Step S66 checks the motor rotation angle sensor 33 for disconnection or short-circuit. Details of what takes place in step S66 are depicted in Fig. 12. The signal output by the motor rotation angle sensor 33 via the A/D converter 41 usually falls within the range of 0.5 V to 4.5 V. In Fig. 12, step S110 checks to see if the value ϑ m1 is lower than 0.5 V. If this condition is met, step S112 is reached. If the value ϑ m1 is not found to be lower than the 0.5 V threshold, step S111 is reached. In step S111, a check is made to see if the value ϑ m1 is in excess of 4.5 V. If this condition is met, step S112 is reached. If the value ϑ m1 is not found to exceed the 4.5 V threshold, step S113 is reached. In step S112, the count value of a motor rotation angle counter, not shown, is incremented by 1. In step S114, a check is made to see if the count value above is equal to or higher than 20. If this condition is not met, the process of Fig. 12 comes to an end. If the count value is found to be equal to or higher than 20, a disconnection or short-circuit of the motor rotation angle sensor 33 is recognized, and step S115 is reached. Step S115 brings the flag Fid High, and the process of Fig. 12 is terminated. In the above-mentioned step S113, the count value of the motor rotation angle counter is reset. Returning to Fig. 9, step S67 provides control on the servo motor 18. What takes place in step S67 is illustrated in more detail in Fig. 13. In Fig. 13, steps S144 and S145 constitute a feedback process for immediately matching the actual motor rotation angle ϑ m1 with the computed amount of control ϑ m0. Steps S125 through S135 provide a process through which to return gradually the actual rotation angle of the motor to its central position. Steps S136 through S143 make up a process for gradually matching the actual motor rotation angle with the computed amount of control. In step S120 of Fig. 13, a check is made to see if the flag Fd is Low. If this condition is met, i.e., until Ldc > Ldcb after the combination switch is turned on (when the dynamic center value is incorrect or not computed, as described in conjunction with step S104 of Fig. 11), the servo motor 18 is not controlled, and the process of Fig. 13 comes to an end. If the flag Fd is found to be High, step S121 is reached. Step S121 checks to see if the flag Fbu is High. If the flag Fbu is found to be high (i.e., when the amount of motor control ϑ m is within ± 5 degrees, as described in connection with steps S63 and S64 of Fig. 9), step S221 is reached. If the flag Fbu is found to be Low, step S122 is reached. In step S122, a check is made to see if the flag Fvo is High. If the flag Fvo is found to be High (i.e, when the vehicle's velocity V is in excess of 127.5 km/h, as discussed in conjunction with steps S52 and S53 of Fig. 9), step S221 is reached. If the flag Fvo is found to be Low, step S123 is reached. In step S221, the flag Fvol is reset to be Low. In step S222, the lag Fdl is reset to be Low. In step S200, a check is made to see if the amount of motor control ϑ m is zero. If this condition is met, the process of Fig. 13 comes to an end. If the amount of motor control ϑ m is not found to be zero, step S125 is reached. Step S125 checks to see if the value ϑ m is already set to a value ϑ mm in step S126 or S127, to be described later. The value ϑ mm provides basic data for gradually returning the shade 9 to its central position. If the value ϑ mm is found to have been set, step S127 is reached. If the value ϑ mm is not found to be set, step S126 is reached. Step S126 computes the deviation of the actual rotation angle of the motor from its central position by subtracting from the current motor rotation angle ϑ m1 the median motor rotation angle ϑ mc calculated in step S28 of Fig. 6. After the result of the above computation is set to ϑ mm, step S127 is reached. In step S127, a predetermined level (e.g., level 1) is subtracted from the absolute value of ϑ mm. In step S128, the value ϑ mm is set to the amount of motor control ϑ m. In step S129, the value ϑ m is added to the median ϑ mc. The result of this addition is set to the motor control angle ϑ m0, as indicated by equation (6) below: ϑ m0 = ϑ mc + ϑ m (6) In step S130, control data is output to the driver 39 (of Fig. 4). What takes place in step S130 is depicted in more detail in Fig. 14. Referring to Fig. 14, step S150 detects the difference (angular difference) between motor control angle ϑ m0 and actual motor rotation angle ϑ m1. Step S151 detects the polarity of the current supplied to the servo motor 18 depending on the magnitude of the values ϑ m0 and ϑ m1. In accordance with the angular difference obtained above, step S152 reads the duty ratio of the signal to be output to the driver 39 from a table such as one shown in Fig. 16. The table of Fig. 16 is only an example; it is determined by taking into consideration the characteristics of the servo motor 18 and other relevant factors. In step S153, a control signal is output to the driver 39 according to the polarity and duty ratio acquired. Thereafter, the process of Fig. 14 comes to an end. As evident from the description above, if the acquired duty ratio is less than 100 %, the servo motor 18 is subjected to chopping control. Returning to Fig. 13 and in step S131, a check is made to see if the value ϑ m is zero, i.e., if the rotation angle of the servo motor 18 is back in its central position. If the value ϑ m is not found to be zero, the process of Fig. 13 is terminated. If the value ϑ m is found to be zero, step S135 is reached. Step S135 resets the value ϑ mm, and the process of Fig. 13 comes to an end. This allows the servo motor 18 to return gradually to its central position. If the flag Fvo is found to be Low in step S122, step S123 is reached. Step S123 checks to see if the flag Fvol is High. If the flag Fvol is found to be High (i.e., when the vehicle's velocity V has dropped below 127.5 km/h after exceeding that limit, as described in conjunction with steps S52, S53, S201 and S203 of Fig. 9), step S136 is reached. If the flag Fvol is found to be Low, step S124 is reached. In step S124, a check is made to see if the flag Fdl is High. If this condition is met (i.e., when the value Ldc has exceeded the value Ldcb for the first time since the vehicle started traveling and thus having its dynamic center value computed, as described in connection with steps S76 and S77 of Fig. 10), step S136 is reached. If the flag Fdl is found to be Low, then step S144 is reached. In step S136, as in step S129, equation (6) is performed and the motor control angle ϑ m0 is set thereby. In step S137, a check is made to see if the absolute angular difference between ϑ m0 and ϑ m1 is equal to or higher than level 3. If this condition is not met, step S139 is reached; if this condition is met, step S138 is reached. Step S138 restricts the motor control angle ϑ m0 to within the range of the actual motor rotation angle ϑ m1 through level 2. This moderates motor control in step S139, to be described below. In step S139, as in step S130, control data is output to the driver 39. In step S140, a check is made to see if the motor control angle ϑ m0 has coincided with the actual motor rotation angle ϑ m1. If this condition is not met, the process of Fig. 13 comes to an end; if this condition is met, step S141 is reached. Step S141 checks to see if the flag Fvol is High. The check in step S141 is intended to determine whether the process of steps S136 through S140 is carried out because the flag Fvol is High or because the flag Fdl is High. If the flag Fvol is found to be High, step S142 is reached. Step S142 brings the flag Fvol Low, and the process of Fig. Fig. 13 comes to and end. If the flag Fvol is not found to be High, i.e., if the flag Fdl is High, step S143 is reached. In step S143, the flag Fdl is brought Low, and the process of Fig. 13 is terminated. In the above-mentioned step S124, if the flag Fdl is found to be Low, step S144 is reached. In step S144, as in steps S129 and S136, equation (6) is performed and the motor control angle ϑ m0 is set thereby. In step S145, as in steps S130 and S139, control data is output to the driver 39. Thereafter, the process of Fig. 13 comes to an end. Returning to Fig. 9, step S67 is completed. Then the process of Fig. 9 is terminated. In the above-described first embodiment, the dynamic center value computing means 211 was described to be computing the dynamic center value by use of the technique depicted in Fig. 10. Alternatively, the computing may be carried out using any other suitable technique. The timing for modifying the third correction factor γ (step S105 of Fig. 11) is not limited to what was described with reference to Fig. 11. An alternative timing will do whereby the reliability of the computed dynamic center value is not expected to be very high. Fig. 23 is a flowchart showing another version of the process depicted in Fig. 11. In Fig. 23 as well as in Fig. 11, like reference characters designate like or corresponding steps. Referring to Fig. 23, step S300 checks to see if the dynamic center value stored in the dynamic center value storing means 113 is the average computed from four values of ϑ haa(FF) (i.e., the dynamic center value computed in step S81 of Fig. 10). If the condition of step S300 is met, step S101 is reached. If the condition of step S300 is not met, step S301 is reached. Step S301 checks to see if the dynamic center value stored in the dynamic center value storing means 113 is the one derived from the most recent value of ϑ haa (i.e., the dynamic center value established in step S88 of Fid. 10). If the condition of step S301 is met, step S105 is reached; if this condition is not met, step S103 is reached. The significance of what has taken place in the checks of Fig. 23 so far is this: that the dynamic center value is predicted to be highly accurate if found to be computed in step S81, or not very accurate if computed in step S88. In the latter case, the dynamic center value may be used adequately if the applicable requirements thereof are suitably moderated. Thus according to the result of the above prediction, the third correction factor γ is determined. In the process of step S105 (equation (4)) in Fig. 23, the value Ldc may be replaced with Ldcmax in computing the third correction factor. Fig. 1 is a function block diagram of the first embodiment of the invention. In Fig. 1 as well as in Fig. 17, like reference characters designate like or corresponding parts. In Fig. 1, a vehicle velocity computing means 201 computes the traveling velocity V of the two-wheeled vehicle using the signal output by the vehicle velocity sensor 31. The resulting data is output to a banking angle computing means 203A. A vehicle velocity level detecting means 206 checks to see if the vehicle's velocity V is in excess of 127.5 km/h. If the vehicle's velocity V is found to exceed the 127.5 km/h threshold, the flag Fvo is output to a switching means 209. A handlebar steering angle computing means 202 computes the handlebar steering angle ϑ h (of the handlebar relative to its central position) using the signal output at regular intervals by the handlebar steering angle sensor 32. The resulting data is output to the variation limiting means 114. As described with reference to Fig. 17, the variation limiting means 114 compares the currently input handlebar steering angle with the previously computed handlebar steering angle. If the variation of the currently input handlebar steering angle is equal to or greater than a predetermined level, the current handlebar steering angle is modified so that its variation will remain below the predetermined level. The resulting handlebar steering angle data is output to the banking angle computing means 203A. Using various data, the banking angle computing means 203A computes the banking angle ϑ b of the two-wheeled vehicle. The computation is carried out by at least multiplying the handlebar steering angle ϑ b by the vehicle's velocity V. A motor control amount computing means 204 computes the amount of motor control ϑ m (control angle of the motor relative to its central position) using the banking angle ϑ b. If the computed amount ϑ m is equal to or lower than a predetermined angle (predetermined level), the motor control amount level detecting means 208 outputs the flag Fbu to the switching means 209. A median data storing means 210 stores the median data ϑ mc of the servo motor 18. As described with reference to Fig. 17, the first motor control means 124 computes the motor control angle ϑ m0 by adding the median data ϑ mc and the motor control amount ϑ m output by the motor control amount computing means 204. The first motor control means 124 then outputs a control signal to the driver 39 using the control angle ϑ m0 and the actual motor rotation angle ϑ m1 output by the motor rotation angle sensor 33. In this manner, the servo motor 18 is placed under feedback control. A second motor control means 126A is a means for accomplishing part of the function of the second motor control means 126 shown in Fig. 17. Specifically, when activated, the second motor control means 126A receives the actual motor rotation angle ϑ m1 from the motor rotation angle sensor 33. In doing so, the second motor control means 126A gradually returns the servo motor 18 from the actual motor rotation angle ϑ m1 to its central position (motor median ϑ mc). The switching means 209 usually supplies the first motor control means 124 with the output signal ϑ m of the motor control amount computing means 204 and the output signal ϑ m1 of the motor rotation angle sensor 33. If the flag Fvo or Fbu is input, the switching means 209 feeds the output signal ϑ m1 of the motor rotation angle sensor 33 to the second motor control means 126A and activates the latter. If the input of the flag Fvo or Fbu is terminated, the switching means 209 again connects the first motor control means 124 with the motor control amount computing means 204 and the motor rotation angle sensor 33. In the above first embodiment, control of the servo motor 18 is switched from the first motor control means 124 to the second motor control means 126A upon output of the flag Fvo or Fbu. Alternatively, control of the servo motor 18 by the first motor control means 124 may be simply stopped. As described, the first embodiment comprises the vehicle velocity level detecting means 206, the motor control amount level detecting means 208 and the variation limiting means 114. Alternatively, only one of these three means may be provided. If the vehicle velocity level detecting means 206 and the motor control amount level detecting means 208 are not provided, the second motor control means 126A and the switching means 209 naturally become unnecessary. In that case, the output signal lines of the motor control amount computing means 204 and motor rotation angle sensor 33 are directly connected to the first motor control means 124. In connection with the first embodiment above, it was stated that the vehicle velocity level detecting means 206 checks to see if the vehicle's velocity V is in excess of 127.5 km/h. Needless to say, that velocity benchmark is cited only as an example. What follows is a description of how the present invention is illustratively applied to a traction control apparatus for use with a two-wheeled motor vehicle. Fig. 24 is a side view of a two-wheeled vehicle to which a second embodiment of the invention is applied. Fig. 25 is a plan view of the two-wheeled vehicle shown in Fig. 24. In Figs. 24 and 25, like reference characters designate like or corresponding parts. Referring to Figs. 24 and 25, an engine 1005 of the two-wheeled vehicle 1001 comprises a pair of pulsers for detecting engine revolutions, i.e., a first pulser 1002A and a second pulser 1002B. The first pulser 1002A generates a pulse signal PC1 every time the crank shaft of the vehicle rotates a certain degree. The second pulser 1002B generates a pulse signal PC2 every time the crank shaft reaches a predetermined angle. The front wheel (idle wheel) and the rear wheel (driving wheel) of the two-wheeled vehicle 1001 contain a front wheel velocity sensor 1003 and a rear wheel velocity sensor 1004, respectively. The sensors 1003 and 1004 each generate a pulse signal every time the front and rear wheels rotate a certain angle each. An ignition control ECU 1031 is located behind a meter panel 1020 (opposite to the side where various meters are provided). As will be described later, the ignition control ECU 1031 controls the ignition timing (ignition angle) of an ignition coil 1008 using output signals from the front and rear wheel velocity sensors 1003 and 1004. The ignition control ECU 1031 comprises an ignition control CPU and a traction control CPU. The ignition control CPU computes the standard ignition timing of the two-wheeled vehicle. The traction control CPU computes the vehicle's ignition timing for traction control over wheel slippage primarily upon acceleration. The banking angle of the two-wheeled vehicle 1001 is computed using the output signal of the handlebar steering angle sensor 32. This computation is illustratively controlled with the ignition control CPU. An ALB ECU 1032, though not directly related to the workings of the invention, controls the braking action effected with a front caliper 1037 and a rear caliper 1038 if the two-wheeled vehicle's slip ratio or slip amount has exceeded a predetermined level during braking. Reference numerals 1033, 1034, 1035 and 1036 denote respectively a front modulator, a rear modulator, a front brake master cylinder and a rear master cylinder involved in the braking action. A meter panel 1020 contains a speedometer 1021, a tachometer 1022, a fuel meter 1023, a water temperature gauge 1024, a left turn lamp 1025 and a right turn lamp 1026. Above the meter panel 1020 is an indicator panel 1010. Fig. 26 is a detailed plan view of the indicator panel 1010. In Fig. 26, a frame 1010A comprises: an OFF lamp 1011 indicating that traction control is turned off when glowing; an ON 1012 lamp indicating that traction control is turned on; a side stand lamp 1013 indicating that the side stand is spread out; an ALB lamp 1014 and ALB fail LED 1094 indicating that the brake control (ALB) system activated by the above-mentioned ALB ECU 1032 has failed; an oil lamp 1015 indicating that oil is being exhausted; a lamp 1016 and a LED 1096 indicating that a traction control system, to be described later, has failed; a fuel lamp 1017 indicating that fuel is being exhausted; a high beam lamp 1018 indicating that the headlight distribution is in high beam state; and a neutral lamp 1019 indicating that the engine transmission is in neutral position. When turned on, the lamps 1011 through 1013 glow in orange; the lamps and LED's 1014 through 1017, 1094 and 1096 in red; the lamp 1018 in blue; and the lamp 1019 in green. Reference characters 1010B designate a hole with which the indicator panel 101 is secured. Referring again to Fig. 24, reference numerals 1028 and 1029 are a horn and a warning buzzer, respectively. In Fig. 25, reference numerals 1027, 1041, 1042, 1043 and 1044 are a traction control system deactivating switch, a throttle grip, a switch case, an ignition key hole, and a handlebar cover, respectively. Fig. 27 is a block diagram of the second embodiment. In Fig. 27 as well as in Figs. 24, 25 and 4, like reference characters designate like or corresponding parts, and any repetitive description thereof is omitted. The signals output by the first pulser 1002A, second pulser 1002B, front wheel velocity sensor 1003 and rear wheel velocity sensor 1004 are sent through waveform rectifying circuits 1301 through 1303, respectively, to an electronic control circuit 1305. The front wheel velocity sensor 1003 corresponds to the vehicle velocity sensor 31 shown in Fig. 4. The electronic control circuit 1305 contains a microcomputer. Using various input signals, the electronic control circuit 1305 with its microcomputer computes ignition timings ϑ ig (Sϑ ig(n) and Cϑ ig(n), to be described later) in a manner to be described later. One of the computed timings is output to a driver 1069 (ignition controller). In turn, the driver 1069 controls the ignition timing of the ignition coil 1008 in accordance with the slip state of the two-wheeled vehicle. The deactivating switch 1027, which is used to determine whether or not to activate traction control with the second embodiment, is connected to the electronic control circuit 1305. When traction control is effected with the second embodiment in accordance with the slip state, the electronic control circuit 1305 illuminates via a driver 1071 the ON lamp 1012 located on the indicator panel 1010. The OFF lamp 1011 and the fail lamp 1016 on the indicator lamp 101 are connected via drivers 1072 and 1207 to the electronic control circuit 1305. The fail LED 1096 is directly connected to the electronic control circuit 1305. The warning buzzer 1029 located inside the meter panel 1020 is connected via a driver 1108 to the electronic control circuit 1305. The electronic control circuit 1305 provides other controls as required on the two-wheeled motor vehicle 1001 such as fuel injection control, exhaust control, transmission gear ratio control for an automatic transmission, brake control upon deceleration, and headlight distribution control. Below is a description of how the second embodiment works in connection with the computations by the ignition control ECU 1031. Fig. 28 is a flowchart depicting how the second embodiment illustratively operates. The process of Fig. 28 is carried out at regular intervals. It is assumed that the detection of the dynamic center value ϑ dc shown in Fig. 10 and the computation of the handlebar steering angle ϑ h(n) in Fig. 7 are each performed at regular intervals as well. Although the handlebar steering angle ϑ h(n) is limited if its variation is greater than is expected (as in steps S37 and S38 o Fig. 7), this limiting action may be omitted from the operation of the second embodiment. In step S501 of Fig. 28, the value n is incremented by 1. Step S502 computes the front wheel revolutions HA (called the front wheel velocity) and the rear wheel revolutions HB (called the rear wheel velocity) with a known method using the signals from the front wheel velocity sensor 1003 and rear wheel velocity sensor 1004 (of Fig. 27). In step S601, a check is made to see if the vehicle's velocity V (i.e., front wheel velocity HA) is equal to or greater than a predetermined value (velocity). If this condition is met, step S605 is reached. Step S605 sets to 1 a banking angle correction factor Kϑ (to be described later in connection with step S607). Step S605 is followed by step S503. If the vehicle's velocity V is found to be below the predetermined value, step S602 is reached. Step S602 detects the first correction factor α , the second correction factor β and the fourth correction factor δ , as described in conjunction with steps S58 through S60 of Fig. 9. Step S603 computes the banking angle ϑ b of the two-wheeled motor vehicle 1001 using equation (1) described earlier. Step S604 reads the banking angle correction factor Kϑ from the banking angle ϑ b using a table such as the one given in Fig. 29. As shown in Fig. 29, the banking angle correction factor Kϑ is set to 1 if the banking angle ϑ b is less than a very small value ϑ bb. If the banking angle ϑ b is equal to or greater than the value ϑ bb, the banking angle correction factor Kϑ is set according to the banking angle ϑ b. In Fig. 29, K1 indicates the largest allowable value of the banking angle correction factor Kϑ . Step S503 computes the actual slip ratio of the two-wheeled vehicle 1001 using the following equation: Sb(n) = (HB - HA)/HB (7) As a result, the slip ratio Sb(n) is computed within the range of 0 to 1. Naturally, if the front wheel is a driving wheel and the rear wheel is an idle wheel, the values of HA and HB are to be switched. Step S504 reads engine revolutions Ne. It is assumed that another process has already computed the engine revolutions Ne with a known method using PC1 and PC2. Step S505 computes the standard engine ignition timing (called the standard ignition timing) Sϑ ig(n) using a known method. In step S506, a check is made to see if the engine is being controlled with the standard ignition timing or with the traction control ignition timing computed in step S509, to be described later. If the engine is found to be under control with the standard ignition timing, step S507 is reached. If the engine is found to be controlled with the traction control ignition timing, step S606 is reached. Step S507 checks to see if the current state requires control with the standard ignition timing to be continued or to be replaced by control with the traction control ignition timing. If the current state requires continuing control with the standard ignition timing, step S508 is reached. If the current state requires-switching to control with the traction control ignition timing, step S606 is reached. What takes place in step S507 is depicted in more detail in Fig. 30. Referring to Fig. 30, step S521 checks to see if the slip ratio Sb(n) is in excess of a predetermined first slip ratio S1 (0.05 or any other value smaller than a target slip ratio S, to be described later). If the slip ratio Sb(n) is found to be equal to or below the first slip ratio S1, step S508 is reached. If the slip ratio Sb(n) is found to exceed the first slip ratio S1, step S522 is reached. Step S522 checks to see if the rear wheel velocity HB is in excess of a predetermined vehicle velocity HBon (e.g., 5 km/h). If the predetermined vehicle velocity HBon is found to be exceeded, step S509 is reached; if the velocity HBon is not found to be exceeded, step S508 is reached. Referring again to Fig. 28, step S508 adopts the standard ignition timing Sϑ ig(n) as the ignition timing ϑ ig(n). Step S508 is then followed by step S512. Step S606 checks to see if the banking angle correction factor Kϑ is 1. If the factor Kϑ is found to be 1, step S509 is reached. If the factor Kϑ is other than 1 (i.e., higher than 1), step S607 is reached. Step S607 modifies or moderates the banking angle correction factor Kϑ . This process is carried out in the steps shown in Fig. 31 or 32. In Figs. 31 and 32 as well as in Figs. 11 and 23, like reference characters designate like or corresponding steps. As illustrated comparatively, if the dynamic center value is found to have a low level of accurcye , step S703 is reached in which a fifth correction factor γ ' is set to 0. If the dynamic center value is found to have a high level of accuracy , step S701 is reached in which the fifth correction factor γ ' is set to 1. If it is judged that the accuracy of the dynamic center value is not very high but that the dynamic center value, when moderated, may be adequately used in computing the traction control ignition timing, then step S705 is reached. In step S705, the fifth correction factor γ ' is moderated according to the value Ldc and is set within the range of 0 < γ ' < 1 The computation of step S705 may also use the value Ldcmax instead of Ldc. Thereafter, using the fifth correction factor γ ', step S706 modifies (moderates) the banking angle correction factor Kϑ . This modification is carried out using a map such as the one shown in Fig. 41 which utilizes the unmodified Kϑ (i.e., as set in step S604) and the fifth correction factor γ ' as its parameters. As described, the fifth correction factor γ ' is modified in accordance with the reliability of the dynamic center value within the range of 1 up to the value set in step S604. Thereafter, the entire process of Fig. 31 or 32 comes to an end. Referring again to Fig. 28, step S509 computes the traction control ignition timing Cϑ ig(n). What takes place in step S509 is depicted in more detail in Fig. 33. In Fig. 33, step S531 computes feedback control terms Tp, Td and Td2 using the following equations (8) through (10): Td = (Δ S(n) - Δ S(n-1)) x Gd (9) Td2 = {(Δ S(n) - Δ S(n-1)) - (Δ S(n-1) - Δ S(n-2))} x Gd2 (10) where, the feedback control terms Tp, Td and Td2 are terms applicable to PID control; S is the target slip ratio (e.g., 0.1); Gp, Gd and Gd2 are predetermined control gains; Δ S(n) is the difference obtained by subtracting S from Sb(n); Δ S(n-1) is the last computed value of Δ S(n); and Δ S(n-2) is the second-last computed value of Δ S(n). Fig. 42 illustrates the relationships among Sb(n), S and Δ S(n). The terms (Sb(n)-S) for computing Tp represent the difference between the currently detected slip ratio and the target slip ratio; the terms (Δ S(n) - Δ S(n-1)) for computing Td denote the variation of the difference above; and the terms {(Δ S(n) - Δ S(n-1)) - (Δ S(n-1) - Δ S(n-2))} for computing Td2 stand for the variation in the above variation. Step S532 computes the total value Ktotal of the control terms using the following equation (11): Ktotal = Tp + Td + Td2 (11) Step S533 sets the basic correction value Δ ϑ ig using Ktotal and the engine revolutions Ne that were read in step S504. As shown in Fig. 34, the basic correction value Δ ϑ ig is read from a map that has Ktotal and Ne as its parameters. The value Δ ϑ ig of this map is set beforehand for Ne in terms of the relationship of Fig. 35 and for Ktotal in terms of the relationship of Fig. 36. In Figs. 34 through 36, the positive values of Δ ϑ ig are advance angle data, and the negative values thereof are lag angle data. In step S534, a check is made to see if a subtraction correction value Z, set in step S537 to be described later, is 0. Step S537 sets the subtraction correction value Z to a positive value. If the value Z is found to be 0, step S535 is reached. Step S535 checks to see if the last computed slip ratio Sb(n-1) is below the sum of the target slip ratio S and a predetermined third slip ratio S3 (shown in Fig. 37). If this condition is not met, step S539 is reached; if this condition is met, step S536 is reached. In step S356, a check is made to see if the currently computed slip ratio Sb(n) is equal to or greater than the sum of the target slip ratio S and the predetermined third slip ratio S3. If this condition is not met, step S539 is reached; if this condition is met, step S537 is reached. Step S537 reads the subtraction correction value Z illustratively in accordance with the front wheel velocity HA (i.e., vehicle's velocity). Step S537 is followed by step S539. In step S539, the higher the vehicle's velocity, the greater the subtraction correction value Z established, as illustratively depicted in Fig. 38. In the same slip state, the traction should preferably be inhibited sooner at high velocity than at low velocity. In the second embodiment above, better traction control is provided by having the subtraction correction value Z set according to the vehicle's velocity. As will be described later, the value Z becomes the lag angle value for the traction control ignition timing. If the value Z is found to be other than 0 in step S534, step S538 is reached. Step S538 subtracts a predetermined lag angle (e.g., 1) from the value Z. Step S538 is followed by step S539. Step S539 reads the standard ignition timing Sϑ ig(n) computed in step S505. Step S540 reads the banking angle correction factor Kϑ set in step S605 or S607. Step S541 computes the gear ratio GR of the transmission of the two-wheeled vehicle using the following equation (12): GR = (HB x 1000)/(Ne x 60) (12) Step S542 sets a gear ratio factor Kg according to the gear ratio GR. As illustrated in Fig. 39, the higher the gear ratio GR, the greater the gear ratio factor Kg. Thus the magnitude of the correction to the value Δ ϑ ig is greater at higher levels of engine torque than at lower engine torque levels, as will be described later in more detail. Step S543 computes the traction control ignition timing Cϑ ig(n) using the following equation (13): Cϑ ig(n) = Sϑ ig(n) + {(Δ ϑ ig x Kg x Kϑ ) - Z} (13) After the traction control ignition timing Cϑ ig(n) is computed in the above manner, the process of Fig. 33 comes to an end. As evident from equation (13), the ignition timing Cϑ ig(n) is delayed considerably more immediately after the subtraction correction value Z is set than when the value Z is not set (i.e., Z = 0). As described, the value Cϑ ig(n) is principally determined by adding to the standard ignition timing Sϑ ig(n) the basic control amount Δ ϑ ig (i.e., variation in ignition timing) according to the slip ratio Sb. This means that with the past state of vehicle travel reflected in the control process, better control is made available than if the absolute angle of the ignition timing is computed conventionally in accordance with the slip ratio Sb. As described, the basic control amount Δ ϑ ig is determined with Δ S(n), Δ S(n-1) and Δ S(n-2) which in turn were determined with previously computed slip ratios. This means that the past state of vehicle travel is reflected in the control process, whereby better control is made available. As described, computing the banking angle correction factor Kϑ set according to the banking angle means that the value Cϑ ig(n) is set according to the banking angle. This makes it possible to effect traction control upon entry into and exit from a cornering run. With the value Kϑ moderated depending on the reliability of the dynamic center value, better control is provided. Referring again to Fig. 28, step S510 checks to see if the current state requires control with the traction control ignition timing to be continued or to be replaced by control with the standard ignition timing. If the current state requires continuing control with the traction control ignition timing, step S511 is reached. If the current state requires switching to control with the standard ignition timing, step S508 is reached. What takes place in step S510 is depicted in more detail in Fig. 40. In Fig. 40, step S551 checks to see if Sb(n) is lower than a predetermined second slip ratio S2 (S2 < S1; see Fig. 37). If this condition is not met, step S511 is reached; if this condition is met, step S552 is reached. Step S552 checks to see if the absolute difference between Cϑ ig(n) and Sϑ ig(n) is equal to or greater than a predetermined angle r. If this condition is not met, step S511 is reached; if this condition is met, step S553 is reached. Step S553 starts a timer to measure the time. Step S554 checks to see if a predetermined time Tn (msec.) has elapsed on the activated timer. If the time Tn is not found to have elapsed, step S511 is reached; if the time Tn is found to have elapsed, step S555 is reached in which the timer is stopped and reset. Step S556 resets the value Z to 0. Step S556 is followed by step S508. Referring again to Fig. 28, step S511 adopts the traction control ignition timing Cϑ ig(n) as the ignition timing ϑ ig(n). Step S511 is followed by step S512. In step S512, a check is made to see if it is time to perform ignition according to the ignition timing ϑ ig(n) determined. If this condition is met, step S513 is reached in which ignition is effected, followed by step S514; if this condition is not met, step S514 is reached immediately. Step S514 checks to see if the traction control ignition timing Cϑ ig(n) is adopted as the ignition timing ϑ ig(n). If the traction control ignition timing Cϑ ig(n) is not found to be adopted, step S517 is reached. Step S517 then turns off the ON lamp (of Fig. 26), and the process of Fig. 28 comes to an end. If step S514 detects the adoption of the traction control ignition timing Cϑ ig(n), step 515 is reached. Step S515 checks to see if the absolute difference between Cϑ ig(n) and Sϑ ig(n) is equal to or greater than a predetermined angle R. If the absolute difference is found to be less than the predetermined angle R, step S517 is reached. If the absolute difference is found to be equal to or greater than the angle R, step S516 is reached. Step S516 turns on the ON lamp 1012. The process of Fig. 28 then comes to an end. How the above-described control scheme proceeds will now be described further with reference to Fig. 37. Fig. 37 is a timing chart of changes in the slip ratio of the two-wheeled vehicle, illustrating how the second embodiment of the invention provides traction control. In Fig. 37, the axis of ordinate stands for the slip ratio Sb and the axis of abscissa for time. Referring to Fig. 37, ignition timing control is started according to the standard ignition timing. It is assumed that the two-wheeled vehicle 1 starts traveling at a time T0. It is also assumed illustratively that the throttle valve is opened excessively, raising the slip ratio Sb abruptly. When the slip ratio Sb exceeds the first slip ratio S1 and when the rear wheel velocity HB exceeds the predetermined vehicle velocity HBon (i.e., at T1 in Fig. 30), ignition timing control according to the traction control ignition timing Cϑ ig(n) computed in step S509 is introduced. The increase in the slip ratio Sb lowers the value of Cϑ ig(n) and thus delays the ignition timing involved. If the slip ratio Sb keeps increasing even after the above phase of control, exceeding the sum of the target slip ratio S and the third slip ratio S3 (i.e., at T2), the subtraction correction value Z is subtracted from the computed Cϑ ig(n) according to the front wheel velocity HA. The value Z is gradually decremented down to 0. While the value Z is above 0, the resetting of the value Z is inhibited (as shown in Fig. 33). Setting the value Z further delays the ignition timing and thus increases constraints on output. After the value Z reaches 0 (at T3), the slip ratio Sb may again exceed the sum of the target slip ratio S and the third slip ratio S3 (at T4). In that case, the value Z is again set in accordance with the front wheel velocity HA. Thereafter, if the two-wheeled vehicle meets various conditions given in Fig. 40 (at T6), ignition timing control based on the timing Cϑ ig(n) will be replaced with standard ignition timing control based on the timing Sϑ ig(n). If the excess opening of the throttle valve persists, the two-wheeled vehicle is controlled so that its slip ratio Sb will coincide with the target slip ratio S, as illustrated with a two-dot chain line in Fig. 37. Fig. 43 is a function block diagram of the second embodiment of the invention. In Fig. 43 as well as in Figs. 1 and 27, like reference characters designate like or corresponding parts. In Fig. 43, an Ne detecting means 1021 detects engine revolutions Ne using the output signals PC1 and PC2 from the first pulser 1002A and the second pulser 1002B. A slip ratio computing means 1024 computes the slip ratio Sb(n) of the two-wheeled vehicle using the velocities HA and HB as well as the equation (7) described above. A control term computing means 1025 computes the feedback control terms Tp, Td and Td2 using equations (8) through (10). A Ktotal computing means 1026 computes the total value Ktotal using equation (11). Using the Ktotal and Ne thus computed, a Δ ϑ ig setting means reads the basic correction value Δ ϑ ig from a basic correction value table such as the one given in Fig. 34. The basic correction value Δ ϑ ig is output to a traction control ignition timing computing means 1034. A status determining means 1028 determines whether or not to set the value Z depending on the currently computed slip ratio Sb(n), on the last computed slip ratio Sb(n-1), and on whether the value Z is 0. A Z setting means 1029 is activated with the status determining means 1028 to set the subtraction correction value Z according to the value HA. The setting is carried out, as shown in Fig. 38, by reading the data of Z from the table in which values of Z corresponding to values of HA are stored beforehand. A decrement control means 1030 decrements the value Z output by the Z setting means 1029. The decrementing is performed at regular intervals (e.g., every time the computing means 1034 carries out its computing). The decremented value is output to the traction control ignition timing computing means 1034. The decrement control means 1030 inhibits the Z setting means 1029 from setting the value Z again until Z reaches 0. A GR computing means 1032 computes the gear ratio GR using the engine revolutions Ne, the rear wheel velocity HB and equation (12). A Kg setting means 1033 sets the gear ratio factor Kg in accordance with the gear ratio GR. The setting is carried out, as depicted in Fig. 39, by reading the data of Kg from the table in which values of Kg corresponding to ratios of GR are stored. The factor Kg thus set is output to the above-described computing means 1034. A standard ignition timing computing means 1035 computes the standard ignition timing Sϑ ig(n) from the engine revolutions Ne using a known method. The result is output to both the traction control ignition timing computing means 1034 and the switching means 36. As described in connection with Fig. 1, the handlebar steering angle computing means 202 computes the handlebar steering angle ϑ h using the signal from the steering wheel sensor 32. The result is output to the variation limiting means 114. If the variation in the currently input handlebar steering angle is found to exceed a predetermined level, the variation limiting means 114 modifies the currently input handlebar steering angle so that the variation will become lower than the predetermined level. In the second embodiment, the variation limiting means 114 may be omitted. The handlebar steering angle data is output to the banking angle computing means 203A. The banking angle computing means 203A computes the banking angle ϑ b using the handlebar steering angle ϑ h and the vehicle's velocity (front wheel velocity). The banking angle ϑ b is output to a Kϑ setting means 1501 through a switching means 1500. Equipped with the table of Fig. 29, the Kϑ setting means 1501 computes the banking angle correction factor Kϑ in accordance with the banking angle ϑ b. The result is output to the traction control ignition timing computing means 1034. If the vehicle's velocity V is found to exceed a predetermined velocity level, the vehicle velocity level detecting means 206 activates the switching means 1500 to cut off the output of the banking angle ϑ b from the banking angle computing means 203A to the Kϑ setting means 1501. This causes the Kϑ setting means to conclude that the input banking angle ϑ b is 0. The traction control ignition timing computing means 1034 computes the traction control ignition timing Cϑ ig(n) using equation (13). The result is output to a switching means 1036. The switching means 1036 usually outputs the timing Sϑ ig(n) to an ignition control means 1040. But upon receipt of a control signal from a first switching control means 1037, the switching means 1036 causes the timing Cϑ ig(n) to be output to the ignition control means 1040. If a second switching control means 1038 outputs a control signal in the above state, the switching means 1036 again causes the timing Sϑ ig(n) to be output to the ignition control means 1040. According to the ignition timing that has been input, the ignition control means 1040 energizes the ignition coil 1008. The first switching control means 1037 has the function depicted in Fig. 30. If the condition in step S522 of Fig. 30 is met, the first switching control means 1037 outputs its control signal to the switching means 1036. The second switching control means 1038 has the function shown in Fig. 40. If the condition in step S554 of Fig. 40 is met and the process of up to step S556 is completed, the second switching control means 1038 outputs its control signal to the switching means 1036. By this time, the value Z has been reset to 0. A comparing means 1041 executes the process of step S515 in Fig. 28. If the condition in step S515 is met, the comparing means 1041 generates an output at one of the input terminals of an AND gate 1042. Where the timing Cϑ ig(n) is selected, the switching means 1036 generates an output at the other input terminal of the AND gate 1042. The ON lamp 1012 is turned on when the AND gate 1042 yields its output. In the description above, the subtraction correction value Z was determined according to the vehicle's velocity. Alternatively, the value Z may remain fixed regardless of the vehicle's velocity. The gear ratio GR was shown to be computed from equation (12). Alternatively, if the two-wheeled vehicle has a manual transmission, the gear ratio GR may be set simply from the gear position of the transmission without recourse to the computation of equation (12). Furthermore, the values Δ ϑ ig, Kg, Z and Kϑ may be set from tables other than those given in Figs. 34 through 36, 39, 38 and 29. Such tables are determined according to the traveling characteristics and other factors relevant to the two-wheeled vehicle in question. In the description above, traction control was effected through the lag angle of the ignition timing. Alternatively, traction control may be provided in the form of thinned-out ignition control, throttle valve opening control, or control over some other engine device. In the above-described step S531 of Fig. 33, equations (8) through (10) were used to compute the feedback control terms Tp, Td and Td2, the results providing the total value Ktotal. Alternatively, the following equations (14) through (16) may be used to compute PID feedback control terms Tp, Ti and Td, and the results may be used to calculate the total value Ktotal: Td = (Δ V(n-1) - Δ V(n)) x Gd (16) where, Gp, Gi and Gd are predetermined control gains; Vb(n) is the current actual slip amount obtained by subtracting the front wheel velocity from the rear wheel velocity; and VT(n) is the target slip amount. Δ V(n) is therefore the difference between the current actual slip amount Vb(n) and the target slip amount VT(n). dtΣ Δ V(n) is the total of values ranging from Δ V(n) computed at the first regular interruption (i.e., Δ V(1)) to Δ V(n) computed upon the current regular interruption. Effects of the Invention: As described, the two-wheeled vehicle control apparatus according to the invention detects any of various parameters such as those for headlight distribution control and traction control if that parameter is found excessive, and moderates or stops the corresponding type of control so that the vehicle will not be controlled excessively. As claimed, the two-wheeled vehicle control apparatus according to the invention provides the following major effects: (1) The two-wheeled vehicle control apparatus according to claim 1 stops such types of control as headlight distribution control and banking angle-based traction control during high velocity travel because these types of control are not needed while the vehicle is traveling at high velocity. Thus the rider of the two-wheeled vehicle traveling at high velocity does not feel uncomfortable about the vehicle getting excessively controlled. With the unnecessary types of control inhibited, other types of control (e.g., ignition timing control, fuel injection control) may be executed on short notice. Another benefit of inhibiting unnecessary types of control is that the two-wheeled vehicle control apparatus does not dissipate unnecessary power. (2) The two-wheeled vehicle control apparatus according to claim 2 stops controlling the vehicle as per vehicle velocity or as per handlebar steering angle if the amount of vehicle control to be set-with any of these parameters is less than a Predetermined level. For example, if the two-wheeled vehicle is traveling on a bumpy road and the rider is manipulating the handlebar in a marginal or minute manner, the control status of the vehicle remains unchanged. Thus the rider does not feel uncomfortable about the vehicle being excessively controlled. (3) The two-wheeled vehicle control apparatus according to claim 3 modifies the handlebar steering angle if the amount of the change in the angle is found to exceed a predetermined level, so that the amount of the angle change will not exceed the predetermined level, the apparatus further performing such types of control as headlight distribution control and traction control on the basis of the resulting handlebar steering angle data and on the vehicle's velocity. Thus the control apparatus prevents the handlebar steering angle change from getting changed excessively when, say, the vehicle is traveling on a bumpy road, making a quick change of lanes, or executing an abrupt handlebar operation for correcting the banking angle during a cornering run. As a result, the rider does not feel uncomfortable about the vehicle getting excessively controlled. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a function block diagram of the first embodiment of the invention; Fig. 2 is a schematic view of the typical headlight device to which the invention may be applied; Fig. 3 is a cross-sectional view of the headlight device for use with the first embodiment; Fig. 4 is a block diagram of the first embodiment; Fig. 5 is a flowchart describing the main routine for the headlight control apparatus which embodies the invention and whose function block diagram is given in Fig. 17; Fig. 6 is a flowchart showing the details of what takes place in step S2; Fig. 7 is a flowchart depicting how fixed-interval interrupt handling is performed with the embodiment; Fig. 8 is a flowchart illustrating the details of the process in step S32; Fig. 9 is a flowchart showing how interrupt handling is performed upon interruption using vehicle velocity detection pulses; Fig. 10 is a flowchart depicting the details of the process in step S57; Fig. 11 is a flowchart describing the details of the process in step S62; Fig. 12 is a flowchart illustrating the details of the process in step S66; Fig. 13 is a flowchart showing in detail what takes place in step S67; Fig. 14 is a flowchart depicting what takes place in step S130 in detail; Fig. 15 is a timing chart illustrating the relationship between the value ϑ ha and the distance traveled by the two-wheeled vehicle; Fig. 16 is a view showing the typical duty ratio table stored in the duty ratio storing means 125; Fig. 17 is a function block diagram of the headlight control apparatus practiced as the first embodiment of the invention, the diagram conceptually illustrating how the first embodiment works; Figs. 18 and 19 are views showing the values β 1 and β 2 constituting the second correction factor β ; Fig. 20 is a view depicting the contents of the fourth correction factor δ ; Fig. 21 is a timing chart illustrating the relationship between the status of the combination switch 49, the flag Fb and the timer 133 on the one hand, and the supply voltage output by the constant voltage circuit 47 on the other; Fig. 22 is a flowchart showing what takes place in step S4 in detail; Fig. 23 is a flowchart illustrating an alternative process of step S62 in Fig. 9, the flowchart corresponding to that of Fig. 11; Fig. 24 is a side view of a two-wheeled motor vehicle to which the second embodiment of the invention is applied; Fig. 25 is a plan view of the two-wheeled motor vehicle shown in Fig. 24; Fig. 26 is a plan view depicting the details of the indicator panel 1010; Fig. 27 is a block diagram of the second embodiment of the invention; Fig. 28 is a flowchart illustrating how the second embodiment works; Fig. 29 is a table showing the contents of the banking angle correction factor Kϑ ; Fig. 30 is a flowchart depicting the details of step S507; Fig. 31 is a flowchart of an alternative series of steps corresponding to step S607, the steps modifying the banking angle correction factor Kϑ ; Fig. 32 is a flowchart of yet another alternative series of steps corresponding to step S607, the steps modifying the banking angle correction factor Kϑ ; Fig. 33 is a flowchart showing the details of computing the traction control ignition timing Cϑ ig(n) in step S509; Fig. 34 is a map depicting the contents of the basic correction value Δ ϑ ig; Fig. 35 is a view illustrating the relationship between Δ ϑ ig and Ne; Fig. 36 is a view showing the relationship between Δ ϑ ig and Ktotal; Fig. 37 is a timing chart depicting typical changes in slip ratio; Fig. 38 is a table showing the contents of the subtraction correction value Z; Fig. 39 is a table describing the contents of the gear ratio factor Kg; Fig. 40 is a flowchart illustrating the details of the process in step S510; Fig. 41 is a map having the fifth correction factor γ ' and the uncorrected Kϑ as its parameters, the fifth correction factor γ ' being used to correct the Kϑ that was set in step S604; Fig. 42 is a view depicting the relationships among Sb(n), S and Δ S(n); and Fig. 43 is a function block diagram of the second embodiment of the invention. In the figures, like reference characters designate like or corresponding parts or steps throughout: 1 headlight device 18 servo motor 31 vehicle velocity sensor 32 handlebar steering angle sensor 33 motor rotation angle sensor 114 variation limiting means 124 first motor control means 126A second motor control means 201 vehicle velocity computing means 202 handlebar steering angle computing means 203A banking angle computing means 204 motor control amount computing means 206 vehicle velocity level detecting means 208 motor control amount level detecting means 209, 1500 switching means 1003 front wheel velocity sensor 1004 rear wheel velocity sensor 1008 ignition coil 1024 slip ratio computing means 1027 Δ ig setting means 1029 Z setting means 1030 decrement control means 1034 traction control ignition timing computing means 1035 standard ignition timing computing means 1036 switching means 1040 ignition control means 1501 Kϑ setting means Fig. 1 31) Vehicle velocity sensor 32) Handlebar steering angle sensor 201) Vehicle velocity computing means 202) Handlebar steering angle computing means 206) Vehicle velocity level detecting means 203A) Banking angle computing means 204) Motor control amount computing means 114) Variation limiting means 208) Motor control amount level detecting means 124) First motor control means 126A) Second motor control means 39) Driver 210) Median data storing means 33) Motor rotation angle sensor Fig. 4 31) Vehicle velocity sensor 34, 36, 40) Input circuit 35) Level judging circuit 32) Handlebar steering angle sensor 37, 41) A/D converter 18) Servo motor 38, 51) Protective circuit 39) Driver 43) Reduction gear 33) Motor rotation angle sensor 42) Electronic controller Fig. 5 START S1) Initialise S2) Verify initial shade operation S4) Perform indicator processing S5) Turn on switching element 52 S6) Combination switch 49 off? S405, S400, S404) Reset switching circuit 46 S11) Reset backup timer S16) Start counting on backup timer S17) 3 hours passed? END Fig. 6 START S22) Turn servo motor 18 clockwise S23, S26) Stopper contacted? S24) Read motor rotation angle ϑ m1 asϑ mrm S25) Turn servo motor 18 counterclockwise S27) Read motor rotation angle ϑ m1 as ϑ mlm S28) Compute median ϑ mc S29) Control servo motor 18 so as to set motor rotation angle to ϑ mc RETURN Fig. 7 FIXED INTERVAL INTERRUPT HANDLING S31) Read ϑ ho(n) S32) Detect disconnection/short-circuit S34) Compute moving average ϑ ha S35) Read dynamic center value ϑ dc S36) Compute handlebar steering angle ϑ h(n) as ϑ h(n) = ϑ ha - ϑ dc S37) ... > level 3 S38) ... + level 2 S39) Store ϑ h(n) RETURN Fig. 8 START S43) Handlebar steering angle counter --> + 1 S44) Count value ≧ 20? S46) Reset handlebar steering angle counter RETURN Fig. 9 INTERRUPT HANDLING USING VEHICLE VELOCITY DETECTION PULSES S51) Compute vehicle's velocity V S204) Reset ϑ mm S56) Time to compute dynamic center value? S57) Compute and store dynamic center value S58) Read first correction factor α S59) Read second correction factor β S60) Read fourth correction factor δ S61) Compute banking angle ϑ b as ϑ b = ... S62) Compute amount of motor control ϑ m as ϑ m = ... S206) Reset ϑ mm S65) Read motor rotation angle ϑ m1 S66) Detect disconnection/short-circuit S67) Control servo motor 18 RETURN Fig. 10 START S71) Read ϑ ha S72) Dead zone set? S73) Value ϑ ha fall out of dead zone? S74) Store Ldc S92) Store ϑ haa S80) Four values of ϑ haa(FF) exist? S81) Average four values into dynamic center value S82) Erase oldest ϑ haa(FF) S83) Reset dead zone S85) Set dead zone S86) Start measuring distance Ldc S88) Use most recent ϑ haa as dynamic center value RETURN Fig. 11 START S100) At least one value of ϑ haa(FF) stored? S102) At least one value of ϑ haa stored? RETURN Fig. 12 START S112) Motor rotation angle counter --> +1 S113) Reset motor rotation angle counter S114) Count value ≧ 20? RETURN Fig. 13 START S125) ϑ mm set? S127) ... - level 1 S130, S139, S145) Output control data S135) Reset ϑ mm S137) ... level 3? S138) Restrict ϑ mo to range of ϑ m1 to level 2 RETURN Fig. 14 START S150) Compute (ϑ m0 - ϑ m1) S151) Judge polarity S152) Read duty ratio S153) Output duty ratio and polarity to servo motor driver 39 RETURN Fig. 15 Distance traveled Fig. 16 Duty ratio Angular difference Fig. 17 31) Vehicle velocity sensor 32) Handlebar steering angle sensor 101, 106, 128) Disconnection/short-circuit detecting means 102, 107, 129) Fid generating means 103) Vehicle velocity detecting means 105) Fvo generating means 135) Fvol generating means 120) Banking angle ϑ b computing means 121) Motor control amount ϑ m computing means 122) Fbu generating means 104) Velocity range checking means 116) Δ ϑ h computing means 117) β map 118) &A table 119) δ table 108) Moving average computing means 109) Handlebar steering angle computing means 114) Variation limiting means 113) Dynamic center value storing means 110) Dynamic center value computing means 115) Fd generating means 134) Fdl generating means 111) Dead zone width storing means 112) Dividing ratio storing means 125) Duty ratio storing means 124) First motor control means 39, 130) Driver 126) Second motor control means 127) Motor resetting means a) Vehicle velocity V 43) Reduction gear 33) Motor rotation angle sensor 47) Constant voltage circuit 132) Fhr generating means 131) Fb generating means 133) Backup timer b) Activated c) Deactivated d) Reset e) Started Fig. 20 Left-hand side Right-hand side. Fig. 21 Supply voltage Combination switch 49 On Off Timer 133 3 hours Reset Fig. 22 START S211) Turn off switching element 52 S212) Control servo motor 18 so that motor rotation angle attains ϑ mc S213) Reset switch on? RETURN Fig. 23 START S300) Dynamic center value derived from average of four values of ϑ haa(FF)? S301) Dynamic center value derived from most recent ϑ haa? RETURN Fig. 27 51) Protective circuit 1305) Electronic control circuit 1301 - 1303) Waveform rectifying circuit 1069, 1108, 1207, 1072, 1071) Driver Fig. 28 (1/2) FIXED INTERVAL INTERRUPT HANDLING S502) Compute front wheel velocity HA and rear wheel velocity HB S503) Compute slip ratio Sb(n) S504) Read engine revolutions Ne S505) Compute standard ignition timing Sϑ ig(n) S506) Control effected with standard ignition timing? S507) Time to switch to control with traction control ignition timing? S508) Adopt Sϑ ig(n) as ϑ ig(n) S509) Compute traction control ignition timing Cϑ ig(n) S510) Time to switch to control with standard ignition timing? S511) Adopt Cϑ ig(n) as ϑ ig(n) S601) Vehicle's velocity (front wheel velocity HA) higher than predetermined level? S602) Read correction factors S603) Compute banking angle ϑ b as ϑ b = V ... S604) Read banking angle correction factor Kϑ S607) Modify (moderate) banking angle correction factor Kϑ Fig. 28 (2/2) S512) Time to perform ignition? S513) Perform ignition S514) Cϑ ig(n) adopted? S516) Turn on ON lamp 1012 S517) Turn off ON lamp 1012 Fig. 29 Banking angle correction factor Banking angle Fig. 30 FROM STEP S506 S521) S1 < Sb(n)? S522) HBon < HB? TO STEP S508 TO STEP S509 Fig. 31 START S100) At least one value of ϑ haa(FF) stored? S102) At least one value of ϑ haa stored? S706) Modify (moderate) Kϑ using γ RETURN Fig. 32 START S300) Dynamic center value derived from average of four values of ϑ haa(FF)? S301) Dynamic center value derived from most recent ϑ haa? S706) Modify (moderate) K0 using γ RETURN Fig. 33 START S531) Compute feedback control terms Tp, Td and Td2 S532) Compute total value Ktotal S533) Set Δ ϑ ig S537) Set Z S539) Read Sϑ ig(n) S540) Read factor Kϑ S541) Compute gear ratio GR S542) Set factor Kg S543) Compute Cϑ ig(n) RETURN Fig. 37 1) Slip ratio 2) Maximum slip ratio 3) Target slip ratio 4) First slip ratio 5) Second slip ratio 6) Standard ignition timing control 7) Z set 8) Region in which slippage upon start of travel is principally controlled 9) Time 10) Z setting inhibited region 11) Traction control ignition timing control Fig. 38 (Vehicle's velocity) Fig. 39 First gear Fig. 40 FROM STEP S9 S551) Sb(n) < S2? S553) Start timer S554) Tn (msec.) passed? S555) Stop and reset timer TO STEP S508 TO STEP S511 Fig. 41 (uncorrected) (corrected) Fig. 42 Slip ratio Time Fig. 43 1002A) First pulser 1002B) Second pulser 1021) Ne detecting means 1004) Rear wheel velocity sensor 1023) Rear wheel velocity computing means 1003) Front wheel velocity sensor 1022) Front wheel velocity computing means 32) Handlebar steering angle sensor 202) Handlebar steering angle computing means 1035) Standard ignition timing computing means 1032) GR computing means 1033) Kg setting means 1024) Slip ratio computing means 1025) control term computing means 1026) Ktotal computing means 1027) Δ ϑ ig setting means 1034) Traction control ignition timing computing means 1028) Status determining means 1029) Z setting means 1030) Decrement control means 206) Vehicle velocity level detecting means 114) Variation limiting means 203) Banking angle computing means 1501) Kϑ setting means a) Standard control ---> Traction control b) Traction control ---> Standard control 1037) First switching control means 1038) Second switching control means 1036) Switching means 1040) Ignition control means 1008) Ignition coil 1041) Comparing means 1012) ON lamp

Claims: A two-wheeled vehicle control apparatus comprising: handlebar steering angle computing means (202) for computing the steering angle of the handlebar mounted on a two-wheeled vehicle; vehicle control means for controlling said two-wheeled vehicle in accordance with the velocity of said vehicle and with said handlebar steering angle; characterised by vehicle velocity level detecting means (206) for checking to see if the vehicle velocity exceeds a predetermined velocity level; and by control stopping means for stopping control operations on said vehicle provided by said vehicle control means if said vehicle velocity is found to exceed said predetermined velocity level. A two-wheeled vehicle control apparatus comprising: handlebar steering angle computing means (202) for computing the steering angle of the handlebar mounted on a two-wheeled vehicle; vehicle control means for controlling said two-wheeled vehicle in accordance with the velocity of said vehicle and with said handlebar steering angle; characterised by control amount level detecting means (208) for checking to see if the amount of control output by said vehicle control means is equal to or lower than a predetermined level; and by control stopping means for stopping control operations on said vehicle provided by said vehicle control means if said amount of control is found to be lower than said predetermined level. A two-wheeled vehicle control apparatus comprising: vehicle velocity computing means (201) for computing the velocity of said two-wheeled vehicle; handlebar steering angle computing means (202) for computing the steering angle of the handlebar mounted on said two-wheeled vehicle; vehicle control means for controlling said two-wheeled vehicle in accordance with the velocity of said vehicle and with said handlebar steering angle; characterised by variation limiting means (114) for computing a variation in the computed handlebar steering angle and, if said variation is equal to or greater than a predetermined level, modifying said handlebar steering angle so that said variation attains said predetermined level.

Inventors: HATANAKA KAORU, IKEGAMI MASAHIKO, HATANAKA, KAORU, IKEGAMI, MASAHIKO
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1991
Main classification: B62K21
IPC codes: B62J6, B62K21, B60Q1