Engine control unit

An engine control unit includes an anomaly judging section for judging whether or not there is any anomaly in throttle sensors based on the output of the throttle sensors, a throttle motor driving section for controlling the driving of a throttle motor, and a fuel injection control section for controlling the amount of fuel injection at the time of starting an engine by using the fuel injection map for starting. The throttle motor driving section stops the driving of the throttle motor if the throttle sensors are judged to be anomalous, and the fuel injection control section switches the fuel injection map for starting in a normal state into the fuel injection map for starting in an anomalous state at the time of restarting the engine after stopping the engine in a state wherein the throttle sensors are judged to be anomalous.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2010-075089 filed on Mar. 29, 2010 the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine control unit to control the engine of a motorcycle having the drive wire system.

2. Description of Background Art

Several methods are known for controlling a throttle valve opening of an vehicle engine electrically by motors through the drive-by-wire system. One of such methods is disclosed in Japanese Patent Laid-Open No. Hei 5-79354. This disclosure is concerned with an electronic accelerator system or electronic throttle system which is provided with a mechanism wherein the throttle valve is mechanically moved a certain amount toward its open side as the accelerator pedal is pressed down. This mechanism is intended to prevent the throttle valve from being moved by the return spring to the closed position (which disables the operation of the engine) in case of a failure in the electronic system. Therefore, this mechanism permits a certain amount of intake air to flow into the engine, thereby to start the engine, even when an anomaly occurs in the electronic throttle system.

However, the mechanical structure disclosed in Japanese Patent Laid-Open No. Hei 5-79354, which is designed to keep the throttle valve slightly open in case of an anomaly, has the disadvantage of requiring a complex mechanism in and around the throttle body in spite of the electronic throttle system. Consequently, it is inevitably large in size, which prevents its adoption into a motorcycle which does not have sufficient space to accommodate additional parts.

Moreover, if the structure disclosed in Japanese Patent Laid-Open No. Hei 5-79354 is not adopted, the throttle valve is moved to the close position by the return spring in case of an anomaly. The result is that the engine which has stopped in the anomalous state does not suck in as much intake air as necessary for restarting but sucks in overrich intake air, because the throttle valve remains closed. This makes the engine hard to restart and prevents reverse driving. The engine incapable of restarting is particularly undesirable for comparatively large motorcycles equipped with a reverse system which permits the motorcycle to move backward while the engine is running.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention addresses the foregoing problem with conventional engines. It is an object of an embodiment of the present invention to provide an engine control unit which permits easy starting of the engine when the throttle valve is returned to the close position as the result of an anomaly.

To achieve the foregoing objects, according to an embodiment of the present invention, there is provided an engine control unit including a drive system (80) capable of driving a motorcycle backward while an engine (22) is running, a throttle valve (162) which is energized toward its closed position by a return spring, and a drive-by-wire system (150) which detects the amount of operation of an accelerator by accelerator opening sensors (152,154) and drives the throttle valve (162) by a throttle motor (166) in response to the amount of operation, thereby controlling the opening of the throttle valve (162) and detecting the opening by throttle opening sensors (168,170), wherein the engine control unit has an anomaly judging section (204) which judges whether or not there is an anomaly in the throttle valve opening sensors (168,170) based on the output of the throttle valve opening sensors (168,170), a throttle motor driving section (206) which controls the driving of the throttle motor (166), and a fuel injection control section (210) which controls the amount of fuel injection at the time of starting the engine (22) by using the fuel injection map for starting, the throttle motor driving section (206) suspends the driving of the throttle motor (166) if the throttle valve opening sensors (168,170) are judged to be anomalous by the anomaly judging section (204). Thus, the throttle valve (162) is caused to be returned to the closed position by the return spring. The fuel injection control section (210) has the fuel injection map for starting when the throttle valve opening sensors (168,170) are in a normal state and the fuel injection map for starting in an anomalous state in which the amount of injection is set to be smaller than that in the fuel injection map for starting in a normal state. In addition, the fuel injection control section (210) also switches the fuel injection map for starting in a normal state into the fuel injection map for starting in an anomalous state, at the time of restarting the engine (22) after the engine (22) stops in a state that the throttle valve opening sensors (168,170) are judged to be anomalous by the anomaly judging section (204), thereby enabling the engine to start and allowing the motorcycle to be moved backward by the drive system (80).

According to an embodiment of the present invention, there is provided an engine control unit wherein the fuel injection control section (210) determines the amount of injection from the engine negative pressure and the number of engine revolutions after the engine (22) is started and also determines the amount of injection from the water temperature of the engine (22) at the time of starting the engine (22), and the fuel injection map for starting in an anomalous state is established such that the amount of injection decreases as the water temperature of the engine (22) rises.

According to an embodiment of the present invention, there is provided an engine control unit wherein the fuel injection control section (210) determines the basic amount of injection from the engine negative pressure and the number of engine revolutions after the engine (22) is started and also determines the amount of fuel injection after the engine (22) is started by performing temperature correction on the basic amount of injection in response to the water temperature of the engine (22) by using the temperature correction map. The fuel injection control section (210) further includes the temperature correction map when the throttle valve opening sensors (168,170) are in a normal state and the temperature correction map in an anomalous state in which the amount of correction is set to be smaller than that of the temperature correction map in a normal state, and switches the temperature correction map applicable in a normal state into the temperature correction map applicable in an anomalous state when the engine (22) is restarted in a state that the anomaly judging section (204) judges to be anomalous.

According to an embodiment of the present invention, there is provided an engine control unit wherein the temperature correction map applicable in case of anomaly is set such that the amount of correction decreases as the water temperature of the engine (22) rises.

According to an embodiment of the present invention, there is provided an engine control unit wherein the anomaly judging section (204) judges whether or not the accelerator opening sensors (152,154) are anomalous according to the output from the accelerator opening sensors (152,154), and the throttle motor driving section (206) drives the throttle motor (166) to set the opening of the throttle valve (162) to the idle opening in the case where only the accelerator opening sensors (152,154) are judged to be anomalous by the anomaly judging section (204).

According to an embodiment of the present invention, an engine control unit further includes an ignition timing control section (212) for controlling the ignition timing at the time of starting by using the ignition timing map for starting, wherein the ignition timing control section (212) has the ignition timing map for starting when the throttle valve opening sensors (168,170) are normal and the ignition timing map for starting when the throttle valve opening sensors (168,170) are anomalous, and switches the ignition timing map for starting in a normal state into the ignition timing map for starting in an anomalous state, thereby advancing the ignition timing, at the time of restarting the engine (22) after the engine (22) stops in a state that the anomaly judging section judges to be anomalous.

According to an embodiment of the present invention, in the case where the engine is restarted after it is stopped because the throttle valve opening sensors are judged to be anomalous, the fuel injection map for starting, which is used to control the amount of fuel injection, is switched from the fuel injection map for starting in a normal state into the fuel injection map for starting in an anomalous state in which the amount of injection is smaller than that in a normal state. As a result, the amount of fuel injection is reduced even in the case where the throttle valve is closed; this prevents the air-fuel ratio from becoming overrich and permits the engine to start easily. In addition, since it is unnecessary to mechanically move the throttle valve in the open direction in the case of an anomaly, size reduction around the throttle body is achieved. Moreover, this design permits the engine to start easily even in the case where the throttle valve becomes closed owing to an anomaly in the throttle valve opening sensors, and the rider can move the motorcycle backward by the reverse driving system. This improves convenience for the rider.

According to an embodiment of the present invention, the fuel injection map shows the relation between the water temperature and the amount of fuel injection is employed. Thus, it is possible to determine an adequate amount of fuel injection even in the case where the engine is started in a situation unfavorable for detection of an accurate negative pressure of the engine and the like. The fuel injection map for starting is established such that the amount of injection decreases as the water temperature of the engine rises. Therefore, in the case where the water temperature of the engine is low, the amount of fuel injection is increased so that the engine is started easily even in an anomalous state.

According to an embodiment of the present invention, the basic amount of injection is calculated from the negative pressure of the engine and the number of revolutions of the engine after restarting the engine, with the throttle valve opening sensor in an anomalous state. Simultaneously with this calculation, the throttle valve opening sensor switches the temperature correction map to be used to correct the basic amount of injection in response to the temperature from the temperature correction map in a normal state into the temperature correction map in an anomalous state. As a result, fuel injection is performed with a temperature correction corresponding to the closed state even in the case where the throttle valve is closed. This stabilizes the number of revolutions of the engine after the engine is started. This contributes to an easy starting of the engine.

According to an embodiment of the present invention, the temperature correction map is set such that the amount of correction decreases as the water temperature of the engine rises. The effect of this is that when the water temperature of the engine is low, the amount of injection can be increased. This permits the engine to start easily at the time of anomaly.

According to an embodiment of the present invention, the throttle valve is set to the idle opening when only the accelerator opening sensor is judged to be anomalous. This eliminates the necessity of switching the fuel injection map more often than necessary. Thus, this simplifies the control process.

According to an embodiment of the present invention, the ignition timing is advanced by switching to the ignition timing map for starting when the throttle valve opening sensor is anomalous in the case where the engine is restarted while the throttle valve opening sensor is anomalous. As a result, the number of revolutions of the engine can be increased rapidly, thereby permitting easy starting of the engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the engine control unit according to the present invention, which is elaborated with reference to the preferred embodiments and the accompanying drawings.

FIG. 1is a side view showing a motorcycle10equipped with the engine control unit.FIG. 2is a rear perspective view showing the appearance of the motorcycle10shown inFIG. 1. The motorcycle10is equipped with a body frame12, a head pipe14which is attached to the front end of the body frame12, laterally paired front fork16which is rotatably supported by the head pipe14, a steering handle20which is attached to a top bridge18supported at the upper end of a front fork16, the front wheel WF which is attached to the front fork16, an engine22supported on the body frame12, an exhaust muffler24which is connected to the engine22through an exhaust pipe (not shown), a swing arm28which is swingably supported on a pivot shaft26at the rear lower part of the body frame12, and a rear wheel WR attached to the rear end of the swing arm28.

The body frame12has a laterally paired main frame30which branches rightward and leftward and extends backward and obliquely downward from the head pipe14, a laterally paired pivot plate32which is connected to the rear part of the main frame30, and a laterally paired seat frame34which extends backward and obliquely upward from the front and rear parts of the pivot plate32. There is a fuel tank36which is placed over the main frame30. A rider seat38and an occupant seat40are placed over the seat frame34. The occupant seat40has a grab rail42and a trunk box44attached to the rear part thereof.

The pivot plate32of the body frame12has a laterally paired step46for the rider mounting on the rider seat38and also has a laterally paired step48for the occupant mounting on the occupant seat40.

The body frame12has a body cowling50attached thereto. The body cowling50has a front cover52which covers the front part of the body, a laterally paired side cover54which covers the lateral parts of the body, an undercover56which covers the lower part of the body, and a rear seal cowl58which covers the rear part of the body. The rear seat cowl58has a laterally paired saddleback60integrally formed thereon. A front fender62which covers the front wheel WF is attached to the front fork16, and a rear fender64which covers the rear wheel WR is attached to the rear seat cowl58. The front cover52has a head light66attached to the front side thereof, has a windshield68attached to the upper part thereof, and has a side mirrors70attached to the right and left ends thereof.

FIG. 3is a partly enlarged view showing the right steering handle20shown inFIG. 2. The right steering handle20has an accelerator grip72and a switch box74. The switch box74is provided with a starter/reverse switch76to start engine and a reverse shifter switch78to shift a starter motor between starting and reversing.

FIG. 4is a block diagram showing a drive system80having a reverse function for the engine control unit. The engine22is connected to a clutch82and then a transmission84of a multistage gear type, which has its final stage shaft86connected to a power transmission gear88(consisting of sprocket and chain) and then the rear wheel WR. While the engine22is running and the clutch82is connected, the rear wheel rotates in the direction in response to the shift position and also in response to the reduction ratio of the gear of the transmission84.

The engine22has the crankshaft (not shown) which is connected to a starter motor92, with a one-way clutch90interposed between them. The starter motor92is coupled to a shifter gear slide mechanism94and then to the final stage shaft86of the transmission84. The one-way clutch90is intended to transmit starting power from the starter motor92to the engine22in one way.

The shifter gear slide mechanism94is intended to switch the connection of the starter motor92to the final stage shaft86of the transmission84. It is coupled to a shifter motor96that functions as an actuator to control it. The starter motor92is electrically connected to a battery98through the starter/reverse switch76to start the starter motor92. The shifter motor96is electrically connected to the battery98through the reverse shifter switch78which switches the starter motor92between for starting and for reversing. In this example, the starter motor92is used to supply the driving power for reversing, and this permits the motorcycle to be reversed much slower than in the case where the engine22is used for reversing.

FIG. 5is a diagram showing the mechanism of the shifter gear slide mechanism94. The shifter gear slide mechanism94has a shifter gear108attached to a reverse shaft104, which transmits the rotation of a reverse drive gear100being turned by the starter motor92(to start the engine22) to a reverse gear102(to reverse the motorcycle). The reverse gear102is a driven gear fixed to the final stage shaft86of the transmission84.

The shift motor96rotates the revolving shaft110in the normal or reverse direction, and the revolving shaft110is arranged coaxially with the reverse shaft104. The shifter gear slide mechanism94has the reverse shaft104and the lost motion mechanism112which couples the revolving shaft110to the reverse shaft104. In addition, the starter motor92is a motor that rotates only in one way, and it works to start the engine22and also move the motorcycle backward.

The shifter gear108is mounted in such a way that it turns in the circumferential direction of the reverse shaft104and it also slides on the reverse shaft104in its axial direction. The shifter gear108meshes with the reverse drive gear100and the reverse gear102.

The shifter gear slide mechanism94is so designed as to slide the shifter gear108in the axial direction on the reverse shaft104(whose axial direction is fixed) as the shifter motor96turns. The reverse shaft104has a cam114attached to one end thereof. The cam114, which is swingable only in the axial direction, is provided with an arcuate cam hole114a, which is inclined right up with respect to the circumference of the cam surface. The cam hole114ahas a pin116loosely fitted thereto. The pin116projects from and fixes on the reverse shaft104. The shift motor96is mounted such that its revolving shaft110is parallel to a revolving shaft92aof the starter motor92and the final stage shaft86of the transmission84.

The lost motion mechanism112is arranged coaxially with a plate118(which is fixed to the end of the reverse shaft104) and the reverse shaft104. It has a discoid plate120(which is fixed to the end of the revolting shaft110of the shifter motor96) and a coil spring122(which is fixed by its ends between the plate118and the plate120). The reverse shaft104, the revolving shaft110of the shift motor96, and the coil spring122are coaxially arranged. When the revolving shaft110of the shifter motor96and the plate120rotate in one direction, the lost motion mechanism112turns the plate118in the same direction as their rotation. If the plate118does not rotate due to resistance whatsoever, the energy for rotation is stored in the coil spring122.

For example, if the revolving shaft110of the shift motor96and the plate120turn in the counterclockwise direction, the cam114and the pin116move (rightward inFIG. 5) in such a way that the shifter gear108meshes with the reverse drive gear110and the reverse gear102. However, there may be an instance in which the rightward movement does not occur smoothly depending on the position of the shifter gear108relative to the reverse drive gear100or the reverse gear102(because the gear faces are in contact with each other). In this instance, the coil spring122energizes the plate118in the counterclockwise direction as soon as the cause that prevents the smooth movement disappears, so that the cam114and the shifter gear108move rightward, thereby allowing the gears to mesh with each other.

In addition, a plate118has the projection124formed on the periphery thereof. This projection124has its position detected by the position sensor126. When the plate118turns to a predetermined position, a position sensor126detects the projection124and sends the gear slide detection signal to a control unit128. In this way, the slide movement of the cam114along the reverse shaft104permits the control unit128to detects that the shifter gear108has moved to the reverse position (to mesh with the reverse gear102). When the control unit128detects that the shifter gear108has moved to the reverse position, it turns on an LED arranged in the display unit (not shown) which tells the rider the speed and the engine revolution. Thus the rider is informed that the motorcycle is ready for backward movement. In addition, the control unit128also controls the starter motor92and the shift motor96.

The plate120has a projection130formed on the periphery thereof. Adjacent to the projection130are pins132and134, which regulate the rotation of the plate120which results from the rotation of the revolving shaft110of the shifter motor96.

The shifter motor96is connected to a motor shaft lock detection unit136which detects driving current at all times and also detects the lock current that arises when the rotation of the plate120is restricted and sends the motor lock detection signal to the control unit128. As soon as the control unit128receives the gear slide detection signal from the position sensor126or the motor lock detection signal from the motor shaft lock detection unit136, it works to stop the shifter motor96or rotate the shifter motor96in the normal or reverse direction.

The following is a description of the action of the shifter gear slide mechanism94. When the shifter motor96becomes activated, the revolving shaft110of the shifter motor110rotates in the direction of arrow A1or B1. The rotation of the revolving shaft110and the plate120is transmitted to the plate118through the coil spring122of the lost motion mechanism112, so that the reverse shaft104rotates in the direction of arrow A2or B2. As the reverse shaft104rotates, the cam114moves (relative to the reverse shaft104) linearly in the direction of arrow A3or B3, thereby sliding the shifter gear108.

FIG. 5illustrates in a way that the shifter gear108is being moved to the reverse position for the backward movement of the motorcycle. To be more specific, it shows immediately before the revolving shaft110of the shifter motor96turns in the direction of arrow A1and the cam114displaces in the direction of arrow A3relative to the reverse shaft104, so that the shifter gear108meshes with the reverse gear102of the transmission84.

After that, the shifter gear108moves further to the reverse position so as to mesh with the reverse gear102of the transmission84and the reverse drive gear100. While the shifter gear108is at the reverse position, the starter/reverse switch76may be pressed so as to start the starter motor92. The rotation of the starter motor92is transmitted to the reverse gear102through the reverse drive gear100and the shifter gear108. This action causes the motorcycle to move backward.

On the other hand, the starter motor92can be disengaged from the reverse gear or moved to the neutral position in the following manner. The revolving shaft110of the shifter motor96is turned in the direction of arrow B1so that the cam114displaces in the direction of arrow B3and the shifter gear108is disengaged from the reverse drive gear100and the reverse gear102.

The following is a description of the procedure for moving the motorcycle10backward. In addition, it is assumed that the shifter gear108is at the neutral position in the initial state. After having started the engine22, the rider presses the starter/reverse switch76, thereby causing the starter motor92to rotate and the engine22to start. The engine22generates electric power to be stored in the battery98. The reason why the rider starts the engine22before moving the motorcycle10backward is that the rotation of the starter motor92might reduce the amount of electric power remaining in the battery98, or make the battery98dead in the worst case. Reversing the large-sized motorcycle10by means of the starter motor92would rapidly consume the electric power of the battery98.

After the engine22is started, the rider presses the reverse shift switch78so as to start the shifter motor96. The shifter motor96in action causes the shifter gear108to move in the direction of arrow A3, so that the shifter gear108meshes with the reverse drive gear100and the reverse gear102.

Then, the rider presses the starter/reverse switch76so as to start the starter motor92. The rotation of the starter motor92is transmitted to the reverse gear102so that the motorcycle10moves backward. While the starter/reverse switch76is being pressed, the motorcycle10continues to move backward. When the starter/reverse switch76is released, the motorcycle10stops. Then, the rider presses the starter/reverse switch76again so as to drive the shifter motor96. The rotation of the shifter motor96causes the shifter gear108to disengage from the reverse drive gear100and the reverse gear102and to return the shifter gear108to its neutral position.

In addition, in the example mentioned above, the starter motor92coupled to the revolving shaft92ais used as the power source for the reverse mechanism. However, this example may be modified such that the reverse drive gear100is coupled to the revolving shaft92awhich is turned by the output of the engine22, so that the driving force of the engine22is supplied to the reverse drive gear100. In this case, the engine22is coupled to the transmission84through the shifter gear slide mechanism94as shown inFIG. 4. Thus, the driving force of the engine22is transmitted to the rear wheel WR through the final stage shaft86of the transmission84and the power transmitting unit88, so that the rear wheel WR is driven for backward movement.

FIG. 6is a diagram showing the construction of a drive-by-wire system150for the engine control unit. The switch box74on the right steering handle20contains a first accelerator opening sensor152and a second accelerator opening sensor154, which detect the opening of the accelerator grip72(or how much the accelerator is turned by the rider). The values of opening detected by the first accelerator opening sensor152and the second accelerator opening sensor154are sent to a control unit (ECU)156. If the first and second accelerator opening sensors152and154are normal, the values of opening detected by them are approximately identical. In addition, the foregoing description is based on an assumption that the first and second accelerator opening sensors152and154are placed in the switch box74; however, they may be placed at any other places (such as the body frame).

An injector158injects fuel into the air, which is sucked through a throttle valve162attached to an intake pipe160, thereby forming the air-fuel mixture. The throttle valve162adjusts the amount of air to be introduced into the combustion chamber (not shown) of the engine22. In addition, the throttle valve162has the return spring (not shown) to return it to its closed position. This return spring energizes the throttle valve162toward the closed position. The mixture formed by the injector158flows into the combustion chamber (not shown) of the engine22and is ignited by an ignition plug164, thereby exploding. The energy of explosion is converted into the driving force by the engine22.

A throttle motor166adjusts the opening of the throttle valve162in response to control by the control unit156. A first throttle valve opening sensor168and a second throttle valve opening sensor170detect the angle of rotation of the throttle valve162, thereby detecting the opening of the throttle valve162. The value of opening detected by the first throttle valve opening sensor168and the second throttle valve opening sensor170are sent to the control unit156. If the first and second throttle valve opening sensors168and170are normal, the detected values of opening are approximately identical. The engine22is provided with an exhaust pipe172through which exhaust gas (arising from combustion of the mixture) is discharged.

So long as the first and second accelerator opening sensors152and154and the first and second throttle valve opening sensors168and170are normal, the control unit156drives the throttle motor166, thereby adjusting the opening of the throttle valve162, based on the opening value detected by at least either of the first accelerator opening sensor152or the second accelerator opening sensor154. The embodiment mentioned herein is assumed (for the sake of easy understanding) that the throttle valve162is controlled so that the throttle valve162opens large in proportion to the opening of the accelerator grip72detected by the first and second accelerator opening sensors152and154, and the larger the opening of the throttle valve162, the larger the output of the engine22.

The first accelerator opening sensor152and the second accelerator opening sensor154(which will be collectively referred to as the accelerator sensors) are regarded as anomalous if there is a difference larger than a predetermined absolute value between the value of opening detected by the first accelerator opening sensor152and the value of opening detected by the second accelerator opening sensor154, there exists a short circuit between the first accelerator opening sensor152and the second accelerator opening sensor154, or there is no change for a fixed period of time in the value of opening detected by the first accelerator opening sensor152and/or the value of opening detected by the second accelerator opening sensor154. In such cases, it is considered that at least either of the first accelerator opening sensor152or the second accelerator opening sensor154is defective.

The first throttle valve opening sensor168and the second throttle valve opening sensor170(which will be collectively referred to as the throttle sensors) are regarded as anomalous if there is a difference larger than a predetermined absolute value between the value of opening detected by the first throttle valve opening sensor168and the value of opening detected by the second throttle valve opening sensor170, there exists a short circuit between the first throttle valve opening sensor168and the second throttle valve opening sensor170, or there is a blank longer than a fixed period of time in which the value of opening detected by the first throttle valve opening sensor168and/or the value of opening detected by the second throttle valve opening sensor170do not follow the target value. In such cases, it is considered that at least either of the first throttle valve opening sensor168or the second throttle valve opening sensor170is defective.

FIG. 7is a functional block diagram for the control unit156. The control unit156has a throttle valve control section200and an engine control section202. The throttle valve control section200has an anomaly judging section204and a throttle motor driving section206. The engine control section202has a fuel injection control section210and an ignition timing control section212. The fuel injection control section210has a first recording section214(which records the fuel injection map at the time of starting) and a second recording section216(which records the temperature correction map). The ignition timing control section212has a third recording section218(which records the ignition timing map at the time of starting).

The first recording section214records the fuel injection map for starting which is used when the throttle sensors are normal and also records the fuel injection map for starting which is used when the throttle sensors are anomalous. The second recording section216records the temperature correction map which is used when the throttle sensors are normal and also records the temperature correction map which is used when the throttle sensors are anomalous. The third recording section218records the ignition timing map for starting which is used when the throttle sensors are normal and also records the ignition timing map for starting which is used when the throttle sensors are anomalous.

The anomaly judging section204judges whether or not the accelerator sensors are anomalous from the values of opening detected by the first accelerator opening sensor152and the second accelerator opening sensor154. The anomaly judging section204also judges whether or not the throttle sensors are anomalous from the values of opening detected by the first throttle valve opening sensor168and the second throttle valve opening sensor170.

The throttle motor driving section206sets up the target opening of the throttle valve162according to the result of judgment by the anomaly judging section204. The throttle motor driving section206also sets, according to need, the target opening value according to the value of opening detected by the first and second accelerator opening sensors152and154. The throttle motor driving section206drives the throttle motor166according to the value of opening set above.

The fuel injection control section210controls the amount of fuel to be injected by the injector158according to the result of judgment by the anomaly judging section204. The ignition timing control section212controls the timing for ignition by the ignition plug164according to the result of judgment by the anomaly judging section204.

FIG. 8is a flowchart showing the control action for the throttle valve162which takes place while the engine22is running. First, the control unit156acquires the value of opening of the accelerator grip72detected by the first and second accelerator opening sensors152and154and also acquires the value of opening of the throttle valve162detected by the first and second throttle valve opening sensors168and170(Step S1and Step S2).

Then, the anomaly judging section204judges whether or not there is anomaly in the first and second accelerator opening sensors152and154and the first and second throttle valve opening sensors168and170(Step3). To be more specific, the anomaly judging section204judges that the accelerator sensors are anomalous in the case where there is a difference larger than a predetermined absolute value between the value of opening detected by the first accelerator opening sensor152and the value of opening detected by the second accelerator opening sensor154, there exists a short circuit between the first accelerator opening sensor152and the second accelerator opening sensor154, and there is a blank longer than a fixed period of time in which the value of opening detected by the first accelerator opening sensor152and/or the value of opening detected by the second accelerator opening sensor154remain unchanged.

Also, the anomaly judging section204judges that the throttle sensors are anomalous in the case where there is a difference larger than a predetermined absolute value between the value of opening detected by the first throttle valve opening sensor168and the value of opening detected by the second throttle valve opening sensor170, there exists a short circuit between the first throttle valve opening sensor168and the second throttle valve opening sensor170, and there is a blank longer than a fixed period of time in which the value of opening detected by the first throttle valve opening sensor168and/or the value of opening detected by the second throttle valve opening sensor170remain unchanged.

Then, the throttle motor driving section206judges whether or not the throttle sensors are judged to be anomalous in Step S3(Step S4). If the throttle sensors are judged to be anomalous in Step S4, the throttle motor driving section206stops the driving of the throttle motor166(Step S5). Thus, the throttle valve162is returned to its closed position by the spring mentioned above (returned to a closed state).

It should be noted that the “closed position” does not necessarily mean that the throttle valve162completely prevents air from flowing from the intake valve160into the combustion chamber of the engine22. In other words, even though the throttle valve162becomes closed, a very small amount of air enters the combustion chamber of the engine22from the intake pipe160through the throttle valve162. As the throttle valve162becomes closed, the amount of air entering the combustion chamber of the engine22decreases, resulting in a low air/fuel ratio in the combustion chamber and hence resulting in an overrich mixture. This situation tends to bring about engine stall. The flowchart shown inFIG. 8is based on an assumption that when the throttle motor166stops, the mixture becomes overrich, with engine stall occurring.

On the other hand, if the throttle sensors are judged to be normal in Step S4, the throttle motor driving section206judges whether or not the accelerator sensors are judged to be anomalous in Step3(Step S6). If the accelerator sensors are judged to be anomalous in Step S6, the throttle motor driving section206sets the target value of opening for the throttle valve162at the value of idle opening (Step7). The value of idle opening denotes a situation in which the throttle valve162is open more than the closed state. It is the value of opening that permits the engine22to run at the minimum speed of revolution. The minimum speed of revolution is a speed of revolution at which the engine22does not stall or is a predetermined established speed of revolution).

Then, the throttle motor driving section206controls the throttle motor166such that the predetermined target value of opening is attained and drives the throttle valve162(Step S8), which is followed by Step S10. At this time, the throttle motor driving section206controls the throttle motor166such that the value of opening of the throttle valve162becomes equal to the target value of opening while watching the value of opening of the throttle valve162detected by the first and second throttle valve opening sensors168and170.

On the other hand, if it is judged that there is not anomaly in the first and second accelerator opening sensors152and154, the throttle motor driving section206carries out ordinary running control (Step S9), which is followed by Step S10. The ordinary running control means that the throttle motor driving section206sets the target value of opening for the throttle valve162which corresponds to the value of opening of the accelerator grip72detected by the first and second accelerator opening sensors152and154. Then, the throttle motor driving section206controls the throttle motor166such that the value of opening of the throttle valve162becomes the predetermined value of opening. At this time, the throttle motor driving section206controls the throttle motor166while watching the value of opening of the throttle valve162detected by the first and second throttle valve opening sensors168and170.

In Step S10, the control unit156judges whether or not the engine22is stopped. The engine22is stopped as the rider turns off the ignition key not shown, or the engine22may be stopped due to engine stall. If the result of judgment in Step S10is that the engine is not at a stop, then Step S10returns to Step S1.

FIG. 9is a flowchart showing the action of controlling the engine22in the case where the engine22is restarted after the engine22is stalled, with the throttle sensors being judged to be anomalous.

As the starter/reverse switch76is pressed, with the shifter gear108being at the neutral position, the revolution of the starter motor92is transmitted to the crankshaft of the engine22(so that the engine22starts). At this time, the fuel injecting control section210switches the fuel injection map for starting from the one in a normal state to the one in an anomalous state (Step S21).

Then, the fuel injection control section210acquires the water temperature of the engine22detected by a water temperature sensor220(Step S22). Then, it determines the amount of fuel injection in response to the water temperature of the engine22acquired as mentioned above and the fuel injection map in an anomalous state (Step S23).

FIG. 10is a diagram showing the fuel injection map for starting. A line300represents the fuel injection map for starting in a normal state. A line302represents the fuel injection map for starting in an anomalous state. The abscissa represents the water temperature of the engine22, and the ordinate represents the duration of injection. The injector158injects fuel at a predetermined pressure; therefore, the amount of injection increases in proportion to the duration of injection. In other words, the duration of injection indirectly represents the amount of injection.

It is noted fromFIG. 10that the fuel injection map for starting in an anomalous state is set such that the amount of injection is less than that in the fuel injection map for starting in a normal state. When the first and second throttle valve opening sensors168and170are judged to be anomalous, the throttle valve162is returned to the closed state. Consequently, the amount of air entering the engine22through the intake pipe160in this case is much smaller than in the case where they are judged to be normal. If the same amount of fuel as in the normal state is injected, there is a high possibility of engine stall due to overrich air/fuel ratio. Thus, it is possible to adjust an adequate air/fuel ratio by decreasing the amount of injection in an anomalous state as compared with that in a normal state.

Usually it is impossible to calculate the amount of injection at the time of starting the engine when the negative pressure of the engine22and the like cannot be detected. However, it is possible to determine an adequate amount of injection only from the water temperature of the engine22if the fuel injection map for starting is employed.

The fuel injection map is designed such that the amount of injection increases as the water temperature of the engine22becomes low. When the water temperature of the engine22is low, the temperature of the engine oil is also low, and the engine oil is viscous at a low temperature. Therefore, the engine oil produces a large resistance when the water temperature of the engine22is low. This makes the crankshaft (not shown) of the engine22difficult to rotate. Thus, the amount of injection is increased as the water temperature of the engine22becomes low, so that the crankshaft produces a large torque.

Thus, when there is an anomaly in the throttle sensors, the fuel injection map in a normal state is switched into the one in an anomalous state. In this way, it is possible to start the engine22easily at all times.

As soon as the amount of injection is determined in Step S23, the fuel injection control section210controls the injector158so that the injector158injects fuel in the thus determined amount (Step S24).

Next, the ignition timing control section212switches the ignition timing map for starting from the one in a normal state into the one in an anomalous state (Step S25).

Next, the ignition timing control section212acquires the number of revolutions of the engine22detected by a revolution sensor222(Step S26) and then determines the ignition timing from the thus acquired number of revolutions of the engine22and the ignition timing map in an anomalous state (Step S27).

FIG. 11is a diagram showing the ignition timing map for starting. A line304represents the ignition timing map in a normal state, and a line306represents the ignition timing map in an anomalous state. The abscissa represents the number of revolutions of the engine and the ordinate represents the ignition timing, in terms of the angle of the crankshaft of the engine22. The ignition timing at zero degrees denotes the ignition timing at the top dead center (without advance or lag). The ignition timing advances in proportion to the angle.

It is noted fromFIG. 11that the ignition timing advances more in the ignition timing map in an anomalous state than in the ignition timing map in a normal state. The advanced ignition timing helps the engine22to produce a larger power because a short time is required for the flame to propagate after ignition and for air to flow in after valve opening.

As mentioned above, the throttle valve162is returned to its closed position in an anomalous state and hence only very little air flows into the engine22through the intake pipe160and the amount of fuel injected is also small accordingly. As a result, the output of the engine22is so small that the engine22would stop. So, it is necessary to advance the ignition timing in an anomalous state more than the ignition timing in a normal state, so that the engine22produces a larger output and increases rapidly the number of revolutions. In this way, it is possible to prevent the engine22from stopping or it is possible to start the engine22easily.

The angle of advance should be larger when the engine22is running slow than when the engine22is running fast. The reason for this is that engine stall tends to occur when the engine22is running slow. In addition, the number of revolutions of the engine22is acquired in Step S26; however, this step may be omitted. In this case, Step S27determines the ignition timing for starting the engine from the predetermined number of revolution and the ignition timing map for starting.

After determining the ignition timing in Step S27, the ignition timing control section212controls the ignition plug so that ignition takes place at the previously determined ignition timing. (Step S28)

Next, the control unit156judges whether or not the number of revolutions of the engine22has reached a predetermined number of revolutions (Step S29). The predetermined number of revolutions may be altered according to the rider's discretion. In this embodiment, it is assumed that the number of revolutions is 500 rpm. Needless to say, the control unit156makes a judgment based on the number of revolutions acquired from the revolution sensor222. If it judges in Step S29that the predetermined number of revolutions is not yet reached, it returns to Step S22and repeats the foregoing actions. The engine starting time lasts until it judges in Step S29that the predetermined number of revolutions is reached.

On the other hand, if it judges in Step S29that the number of revolutions of the engine22reaches the predetermined number, it judges that the engine22is started, and the fuel injection control section210switches the temperature correction map which is used to correct the basic amount of injection according to temperature after the engine22is started, from the one in a normal state into the one in an anomalous state (Step S30).

Then, the fuel injection control section210acquires a negative pressure of the engine22detected by a negative pressure sensor224and also acquires the number of revolutions of the engine22detected by the revolution sensor222(Step31). Then, it calculates the basic amount of injection from the negative pressure of the engine22and the number of revolutions obtained as mentioned above. (Step S32)

Next, the fuel injection control section210acquires the water temperature of the engine22detected by the water temperature sensor220(Step S33). Then, it corrects the basic amount of injection calculated in Step S32according to the water temperature of the engine22by using the temperature correction map in an anomalous state (Step S34).

FIG. 12is a diagram showing the temperature correction map. A line308represents the temperature correction map in a normal state, and a line310represents the temperature correction map in an anomalous state. The abscissa represents the water temperature and the ordinate represents the increased correction factor. Multiplying the basic amount of injection by the increased correction factor gives the correction of the basic amount of injection according to the temperature. The increased correction factor which is indicated by the temperature correction map in a normal state and the temperature correction map in an anomalous state, should be larger than one.

It is noted fromFIG. 12that the increased correction factor indicated by the temperature correction map in an anomalous state sets up a smaller amount of correction than the increased correction factor indicated by the temperature correction map in a normal state. The reason for this is that, as described above, when the first and second throttle valve sensors168,169are judged to be anomalous, the throttle valve162is returned to its closed state and hence an adequate air-fuel ratio is maintained by keeping the amount of fuel injection low. Moreover, the increased correction factor is established high because the engine oil increases in resistance more as the water temperature of the engine22decreases.

When the temperature correction for the basic amount of injection is made in Step S34, the fuel injection control section210controls the injector158such that the injector158injects fuel according to the basic amount of injection which is temperature-corrected (Step S35).

Next, the control unit156judges whether or not the engine22is stopped (Step S36). If the control unit156judges that the engine22is not stopped, the process returns to Step S31.

In addition, the ignition timing after the engine22is started may be controlled by the action of Steps S27and S28. In other words, the ignition timing for the ignition plug164may be controlled by using the ignition timing map for starting or by any other methods.

What has been mentioned above is about how to control the injector158and the ignition plug164to start the engine22after the engine22is stopped because the throttle sensors are judged to be anomalous. In the case where it is necessary to start the engine22after the engine22is stopped because the accelerator sensors and throttle sensors are judged to be normal, or the accelerator sensors are judged to be anomalous but the throttle sensors are judged to be normal, it is acceptable to control the amount of fuel injection and the ignition timing by using the fuel injection map for starting in a normal state, the ignition timing map for staring in a normal state, and the temperature correction map in a normal state. In other words, at the time of starting the engine22, it is a usual practice to control the injection of fuel in a predetermined amount by employing the fuel injection map for starting in a normal state without switching the fuel injection map for starting to be used when the engine22is started. Also, it is a usual practice to determine the ignition timing to control ignition by employing the ignition timing map for starting in a normal state without switching the ignition timing map for starting to be used when the engine22is started. Also, after the engine22is started, it is a usual practice to perform temperature correction for the basic amount of injection by using the temperature correction map in a normal state without switching the temperature correction map to be used for the temperature correction of the basic amount of injection.

The motorcycle10having the reverse function is designed so as to switch the fuel injection map for starting, which is used to control the amount of fuel injection, from the fuel injection map for starting in a normal state into the fuel injection map for starting in an anomalous state in which the amount of injection is more reduced than that in a normal state in the case where the engine22is started again after it is stopped because the throttle sensors are judged to be anomalous. The effect of this design is that the amount of fuel injection is reduced even in the case where the throttle valve162is closed; this prevents the air-fuel ratio from becoming overrich and permits the engine22to start easily. This design also makes it unnecessary to mechanically move the throttle valve162in the open direction in the case of anomaly, and this contributes to size reduction around the throttle body. Moreover, this design permits the engine22to start easily even in the case where the throttle valve162becomes closed owing to anomaly in the throttle sensors, and the rider can move the motorcycle backward by means of the starter motor92. This is convenient for the rider.

In addition, according to the foregoing embodiment, there are two accelerator opening sensors, such as the first accelerator opening sensor152and the second accelerator opening sensor154. However, one accelerator opening sensor may suffice. Moreover, according to the foregoing embodiment, there are two throttle valve opening sensors, such as the first throttle valve opening sensor168and the second throttle valve opening sensor170. However, one throttle valve opening sensor may suffice.

The present invention has been explained above with reference to its preferred embodiment. However, the technical scope of the present invention is not restricted to the one disclosed in the preferred embodiment. The foregoing embodiment may be variously changed or modified within the scope of the claims of the present invention. In addition, the parenthesized symbols contained in the claims of the present invention are quoted from the accompanying drawings to help understand the present invention easily, and they should not be construed to restrict the scope of the present invention.