Patent Publication Number: US-8977458-B2

Title: Twin clutch controlling apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2012-216985 filed Sep. 28, 2012 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a twin clutch controlling apparatus. More particularly, to a twin clutch controlling apparatus that applies automatic control and manual operation of a clutch in a complex manner. 
     2. Description of Background Art 
     A clutch controlling apparatus is known that controls a clutch of a transmission incorporated in a power source of a vehicle between a connection state and a disconnection state by an actuator. The configuration includes manual operation means such as a clutch lever to allow application of both of automatic control and manual operation of the clutch. 
     Japanese Patent Laid-Open No. 2011-112094 discloses a configuration of a transmission of the constant mesh type for a motorcycle that includes a twin clutch configured from a first clutch that takes charge of odd number stage side gears and a second clutch that takes charge of even number stage side gears. According to the configuration, the twin clutch is automatically controlled by an actuator, while an interposition of a manual operation according to an operation of a clutch lever is permitted. 
     In such a twin clutch type transmission as described above, it is recommended to provide a manual control mode (manual mode) and an automatic control mode (auto mode) for an operation mode for the clutch and the transmission and arbitrarily change over the operation mode between the two modes. However, if a manual operation means such as a clutch lever is operated during selection of the auto mode for the transmission and then the vehicle speed changes during disconnection of the clutch. Then, if shift control suitable for the vehicle speed is not executed, then there is the possibility that a sense of discomfort may be given to the occupant. In contrast, if a shift control suitable for the vehicle speed is executed, then there is the possibility that a variation in driving force upon re-connection of the clutch may give a sense of discomfort to the occupant. In the technology disclosed in Japanese Patent Laid-Open No. 2011-112094, particular control upon such interposition of the clutch manual operation means as just described is not investigated. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The object of the an embodiment of the present invention resides in the provision of a twin clutch controlling apparatus that can solve the problem of the related art described above and wherein an interposition of a manual operation into an automatic control clutch can be carried out smoothly. 
     In order to achieve the above object, an embodiment of the present invention includes a twin clutch controlling apparatus with a multi-speed transmission (TM) having a plurality of gear trains between a main shaft ( 6 ,  7 ) on the input side and a countershaft ( 9 ) on the output side. A shift actuator ( 21 ) is provided for carrying out changeover of a shift stage of the multi-speed transmission (TM). A twin clutch (TCL) is configured from an odd number stage side clutch (CL 1 ) and an even number stage side clutch (CL 2 ) for connecting and disconnecting power transmission between the transmission (TM) and an engine ( 100 ). A clutch actuator ( 107 ) is provided for controlling the twin clutch (TCL). A manual operation clutch capacity arithmetic operation section ( 185 ) is provided for converting an operational amount of a clutch manual operation means (L) to arithmetically operate a manual operation clutch capacity arithmetic operation value (tqc1tmt) corresponding to the manual operation. The twin clutch controlling apparatus includes a control section ( 120 ) for controlling the shift actuator ( 21 ) and the clutch actuator ( 107 ), wherein an auto mode (Auto) in which the twin clutch (TCL) is automatically controlled by the control section ( 120 ) and a manual mode (Manual) in which the twin clutch (TCL) is manually controlled in response to the manual operation clutch capacity arithmetic operation value (tqc1tmt) are provided for a control mode for the twin clutch (TCL). An automatic shift mode (AT) and a manual shift mode (MT) are provided for a control mode for the multi-speed transmission (TM). The control section ( 120 ) is configured such that, when the clutch manual operation means (L) is operated during a deceleration operation in which the automatic shift mode (AT) is selected, the control section ( 120 ) carries out a shift down action in response to an operation of the clutch manual operation means (L). 
     According to an embodiment of the present invention, the shift down action is an action for changing the gear position from a gear position at which driving power transmission can be carried out only by one of the odd number stage side clutch (CL 1 ) and the even number stage side clutch (CL 2 ) to another gear position at which the transmission gear which transmits a driving force is switched in response to the switching control of the clutch. 
     Further, the present invention has a third characteristic wherein when re-connection of the clutch is carried out by the clutch manual operation means (L) after a shift down action is carried out in response to an operation of the clutch manual operation means (L), the control section ( 120 ) determines the odd number stage side clutch (CL 1 ) and the even number stage side clutch (CL 2 ), which are to be driven in response to the manual operation clutch capacity arithmetic operation amount (tqc1tmt), in response to a vehicle speed (V) of a vehicle ( 10 ) in which the engine ( 100 ) is incorporated. 
     According to an embodiment of the present invention, the vehicle speed (V) is a predetermined value (a) set as a shift down vehicle speed during deceleration in response to an off state of the throttle to a shift map (M) in advance. 
     According to an embodiment of the present invention, when re-connection of the clutch is carried out by the clutch manual operation means (L) after a shift down action is carried out in response to an operation of the clutch manual operation means (L), the control section ( 120 ) drives the odd number stage side clutch (CL 1 ) and the even number stage side clutch (CL 2 ) so that a negative driving force generated upon re-connection becomes equal to an engine brake by the gear stage before the shifting. 
     According to an embodiment of the present invention, the twin clutch controlling apparatus includes a clutch control mode changeover switch ( 118 ) that carries out a changeover between the auto mode (Auto) and the manual mode (Manual), wherein the control section ( 120 ) is configured such that, even if the clutch control mode changeover switch ( 118 ) is operated when the auto mode (Auto) is selected, when the odd number stage side clutch (CL 1 ) or the even number stage side clutch (CL 2 ) is in a half clutch state by the automatic control thereof, the changeover to the manual mode (Manual) is inhibited. 
     According to an embodiment of the present invention, a temporary manual mode (Temp. Manual) is provided for the control mode of the twin clutch (TCL) with an automatic shift mode (AT) and a manual shift mode (MT) being provided for the control mode of the multi-speed transmission (TM). If the control mode of the twin clutch (TCL) is set to the manual mode (Manual), then the control mode for the multi-speed transmission (TM) is set to the manual shift mode (MT). 
     According to an embodiment of the present invention, the twin clutch controlling apparatus includes the control section for controlling the shift actuator and the clutch actuator. Further, the auto mode in which the twin clutch is automatically controlled by the control section and the manual mode in which the twin clutch is manually controlled in response to the manual operation clutch capacity arithmetic operation amount are provided for a control mode for the twin clutch. Further, the automatic shift mode and the manual shift mode are provided for the control mode for the multi-speed transmission. Furthermore, the control section is configured such that, when the clutch manual operation means is operated during a deceleration operation in which the automatic shift mode is selected, the control section carries out a shift down action in response to an operation of the clutch manual operation means. Thus, if a clutch operation of the clutch manual operation means is carried out during deceleration operation, then it is determined that the occupant has a will to change over the driving force transmission gear to a gear lower by one stage. Thus, it is possible to rapidly make preparations for the changeover. 
     According to an embodiment of the present invention, the shift down action is an action for changing the gear position from a gear position at which driving power transmission can be carried out only by one of the odd number stage side clutch and the even number stage side clutch to another gear position at which the transmission gear which transmits driving force is switched in response to the switching control of the clutch. Thus, a change to a gear position at which the driving force transmission gear can be changed over to a gear lower by one stage is executed in response to a clutch operation during deceleration operation. Thus, it is possible to rapidly make preparations for the changeover. 
     According to an embodiment of the present invention, when re-connection of the clutch is carried out by the clutch manual operation means after a shift down action carried out in response to an operation of the clutch manual operation means, the control section determines the odd number stage side clutch and the even number stage side clutch, which are to be driven in response to the manual operation clutch capacity arithmetic operation amount, in response to a vehicle speed of the vehicle in which the engine is incorporated. Consequently, for example, when the clutch is disconnected and then re-connected by the clutch lever during a deceleration operation in which the third speed is selected, it is possible to change whether the even number stage side clutch is to be connected to transmit driving force by the second speed or the odd number stage side clutch is to be connected to return to the third speed in response to the vehicle speed. As a result, it is possible to smoothly execute interposition of the clutch manual operation means such as a clutch lever into the automatic control. 
     According to an embodiment of the present invention, the vehicle speed is the predetermined value set as a shift down vehicle speed during deceleration in response to an off state of the throttle to the shift map in advance. Consequently, the selection of the clutch upon re-connection of the clutch can be executed based on a definite parameter which is detected by a sensor. 
     According to an embodiment of the present invention, when re-connection of the clutch is carried out by the clutch manual operation means after a shift down action is carried out in response to an operation of the clutch manual operation means, the control section drives the odd number stage side clutch and the even number stage side clutch so that negative driving force generated upon re-connection becomes equal to an engine brake by the gear stage before the shifting. Therefore, it is possible to avoid an engine brake from increasing suddenly upon re-connection of the clutch thereby to achieve a smooth deceleration. 
     According to an embodiment of the present invention, the twin clutch controlling apparatus includes the clutch control mode changeover switch that carries out changeover between the auto mode and the manual mode. Further, the control section is configured such that, even if the clutch control mode changeover switch is operated when the auto mode is selected, when the odd number stage side clutch or the even number stage side clutch is in a half clutch state by the automatic control thereof, the changeover to the manual mode is inhibited. Consequently, such a situation wherein the clutch capacity changes suddenly to cause a variation of the driving force in response to an operation of the clutch control mode changeover switch while the auto mode is selected can be avoided. 
     According to an embodiment of the present invention, the temporary manual mode is provided for the control mode of the twin clutch, and the automatic shift mode and the manual shift mode are provided for the control mode of the multi-speed transmission. Further, if the control mode of the twin clutch is set to the manual mode, then the control mode for the multi-speed transmission is set to the manual shift mode. Therefore, by executing the three control modes of the twin clutch and the two control modes of the multi-speed transmission cooperatively, a manual operation by the clutch manual operation means such as a clutch lever and the shift manual operation means such as a shift pedal can be interposed into the automatic shift control without a sense of discomfort. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a left side elevational view of a motorcycle to which a transmission control apparatus for a twin clutch type automatic transmission according to an embodiment of the present invention is applied; 
         FIG. 2  is a right side elevational view of an engine as a power source of the motorcycle; 
         FIG. 3  is a system diagram of an AMT and peripheral apparatus; 
         FIG. 4  is an enlarged sectional view of the transmission; 
         FIG. 5  is an enlarged sectional view of a transmission mechanism; 
         FIG. 6  is a developed view showing a shape of guide grooves of a shift drum; 
         FIG. 7  is a table of shift positions defined by the shift drum; 
         FIG. 8  is a graph illustrating a relationship between the operation amount of a clutch lever and an output signal of a clutch operation amount sensor; 
         FIG. 9  is a block diagram showing a configuration of an AMT controlling unit; 
         FIG. 10  is a block diagram illustrating an arithmetic operation procedure of a shift motor driving output value and a clutch capacity output value; 
         FIG. 11  is a state transition diagram illustrating a relationship among three clutch control modes; 
         FIG. 12  is a flow chart illustrating a procedure for deciding a clutch for which a manual operation is to be executed; 
         FIG. 13  is a flow chart illustrating a procedure for deciding an Auto mode connection side clutch; 
         FIG. 14  is a flow chart (1/2) illustrating a procedure of a clutch capacity output value arithmetic operation; 
         FIG. 15  is a flow chart (2/2) illustrating the procedure of the clutch capacity output value arithmetic operation; 
         FIG. 16  is a time chart illustrating a flow upon shifting to the fourth speed during operation in the third speed; 
         FIG. 17  is a time chart illustrating a flow when the clutch control mode is changed over during operation with a predetermined gear; 
         FIG. 18  is a time chart illustrating a flow when a clutch lever operation is carried out during operation in the auto mode; and 
         FIG. 19  is a time chart illustrating a clutch re-connection action when a clutch operation is carried out during deceleration with the third speed gear. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, a preferred embodiment of the present invention is described in detail with reference to the drawings.  FIG. 1  is a left side elevational view of a motorcycle  10  to which a transmission controlling apparatus for a twin clutch type automatic transmission according to an embodiment of the present invention is applied.  FIG. 2  is a right side elevational view of an engine  100  as a power source of the motorcycle  10 . A vehicle body frame  14  of the motorcycle  10  has a pair of left and right main pipes  36 , and a head pipe  15  is provided on the vehicle body front side of the main pipes  36 . A pair of left and right front forks  17  support a front wheel WF for rotation thereon and support a steering handlebar  18 . The front forks  17  are supported for pivotal motion with respect to the head pipe  15 . 
     The engine  100  is suspended below the main pipes  36  and is a V-type four-cylinder engine wherein front and rear cylinders are disposed with a predetermined nip angle formed therebetween. A piston  41 , a valve mechanism and so forth which slidably move in a cylinder block  40  have a similar configuration among the four cylinders. A crankshaft  105 , a main shaft  13  and a countershaft  9  are accommodated in a crankcase  46 . The crankshaft  105  supports connecting rods  41   a  (refer to  FIG. 2 ), on each of which a piston  41  is supported, for rotation thereon. The main shaft  13  and the countershaft  9  have a plurality of gear pairs, which configure a transmission, attached thereto. 
     Between the front and rear cylinder blocks, air funnels  42  are disposed. The air funnels  42  introduce fresh air having passed through an air cleaner box disposed at a lower portion of a fuel tank  19  to intake ports of the cylinders. Each air funnel  42  has a fuel injection valve attached thereto. A muffler  54  is disposed below a seat  53  and exhausts combustion gas introduced to the rear side of the vehicle body by an exhaust pipe  59 . 
     A swing arm  38  is supported for rocking motion at a rear lower portion of the main pipes  36 . The swing arm  38  is suspended by shock units  37  and supports a rear wheel WR for rotation thereon. A drive shaft  58  is disposed inside the swing arms  38  and transmits rotational driving force of the engine  100  outputted from the countershaft  9  to the rear wheel WR. A vehicle speed sensor SEV is provided in the proximity of an axle of the rear wheel WR and detects a rotational speed of the rear wheel WR. 
     A clutch lever L is attached to the left side of the steering handlebar  18  in the vehicle widthwise direction and servers as clutch manual operation means for connecting and disconnecting transmission of a driving force between the engine  100  and the rear wheel WR. A shift pedal P is attached in the proximity of a foot placing step on the left side in the vehicle widthwise direction and serves as shift manual operation means for carrying out a shift change of a transmission TM. 
     Referring to  FIG. 2 , each of a front bank Bf and a rear bank BR which form the engine  100  is configured from a cylinder head  44  attached to the upper side of a cylinder block  40  for accommodating a valve mechanism therein and a head cover  45  that covers an upper end of the cylinder head  44 . A piston  41  slidably moves along an inner circumference of a cylinder  43  formed in the cylinder blocks  40 . The crankcase  46  is configured from an upper case half  46   a  formed integrally with the cylinder blocks  40  and a lower case half  46   b  to which an oil pan  47  is attached. 
     A water pump  49  for pressure feeding cooling water is driven to rotate by an endless chain  48  wrapped around a sprocket wheel  13   a  formed on the main shaft  13 . A clutch cover  50  is attached to a side face on the right side of the crankcase  46  in the vehicle widthwise direction. 
     The engine  100  in the present embodiment applies, as a hydraulic clutch for connection and disconnection of rotational driving force to and from the transmission, a clutch of the twin clutch type configured from a first clutch and a second clutch. The hydraulic pressure to be supplied to the twin clutch can be controlled by an actuator, and a first valve  107   a  and a second valve  107   b  as actuators controlling the two clutches are attached to a right side portion of the engine  100 . The twin clutch TCL is driven to connect and disconnect by a combination of automatic control in response to the engine speed, vehicle speed and so forth and a driving instruction of an occupant by an operation of the clutch lever L. 
       FIG. 3  is a system diagram of an automatic manual transmission (hereinafter referred to as AMT)  1  as an automatic transmission and peripheral apparatus of the AMT  1 . The AMT  1  is a twin clutch type automatic transmission apparatus that connects and disconnects the rotational driving force of the engine by the two clutches disposed on the main shaft. The AMT  1  accommodated in the crankcase  46  is controlled and driven by a clutch hydraulic system  110  and an AMT controlling unit  120 . The AMT controlling unit  120  includes clutch controlling means for controlling the driving of the valve  107  as a clutch actuator configured from the first valve  107   a  and the second valve  107   b . Further, the engine  100  includes a throttle body  102  of the throttle-by-wire type in which a throttle valve motor  104  for opening and closing the throttle valve is provided. 
     The AMT  1  includes a transmission TM of six forward stages, a twin clutch TCL configured from a first clutch CL 1  and a second clutch CL 2 , a shift drum  30 , and a shift motor (shift actuator)  21  for rotating the shift drum  30 . The shift motor  21  is driven to rotate by a combination of automatic control in response to an engine speed, a vehicle speed and so forth and a driving instruction of an occupant by an operation of the shift pedal P. 
     A large number of gears which configure the transmission TM are coupled to or loosely fitted on the main shaft  13  or the countershaft  9 . The main shaft  13  is configured from an inner main shaft  7  and an outer main shaft  6 . The inner main shaft  7  is coupled to the first clutch CL 1  while the outer main shaft  6  is coupled to the second clutch CL 2 . Transmission gears are provided on the main shaft  13  and the countershaft  9  such that they are displaceable in the axial direction of the main shaft  13  and the countershaft  9 . Shift forks  71 ,  72 ,  81  and  82  are engaged at end portions thereof with the transmission gears and a plurality of guide grooves formed on the shift drum  30 . 
     A primary driving gear  106  is coupled to the crankshaft  105  of the engine  100  and is held in mesh with a driven gear  3 . The primary driven gear  3  is connected to the inner main shaft  7  through the first clutch CL 1  and connected to the outer main shaft  6  through the second clutch CL 2 . Further, the AMT  1  includes an inner main shaft rotational speed sensor  131  and an outer main shaft rotational speed sensor  132  that measure the rotational speed of predetermined transmission gears on the countershaft  9  to detect the rotational speed of the inner main shaft  7  and the outer main shaft  6 , respectively. 
     The inner main shaft rotational speed sensor  131  detects the rotational speed of a driven side transmission gear C 3  that is attached for rotation but against sliding movement on the countershaft  9  and is held in meshing engagement with a transmission gear attached against rotation on the inner main shaft  7 . Meanwhile, the outer main shaft rotational speed sensor  132  detects the rotational speed of a driven side transmission gear C 4  that is attached for rotation but against sliding moment on the countershaft  9  and is held in meshing engagement with a transmission gear attached against rotation to the outer main shaft  6 . 
     A bevel gear  56  is coupled to an end portion of the countershaft  9 . The bevel gear  56  meshes with another bevel gear  57  coupled to the drive shaft  58  to transmit the rotational driving force of the countershaft  9  to the rear wheel WR. Further, in the AMT  1 , an engine speed sensor  130 , a gear position sensor  134 , a shifter sensor  27 , and a neutral switch  133  are provided. The engine speed sensor  130  is disposed in an opposing relationship to an outer periphery of the primary driven gear  3 . The gear position sensor  134  detects a gear stage position of the transmission TM based on the rotational position of the shift drum  30 . The shifter sensor  27  detects a pivoted position of a shifter that is driven by the shift motor  21 . The neutral switch  133  detects that the shift drum  30  is at a neutral position. A throttle opening sensor  103  is provided on the throttle body  102  and detects a throttle opening. 
     The clutch hydraulic system  110  is configured such that it uses both the lubricating oil for the engine  100  and hydraulic oil for driving the twin clutch. The clutch hydraulic system  110  includes an oil tank  114 , and a pipe line  108  for feeding oil (hydraulic oil) in the oil tank  114  to the first clutch CL 1  and the second clutch CL 2 . A hydraulic pump  109  as a hydraulic supply source and a valve (electromagnetic control valve)  107  as a clutch actuator are provided on the pipe line  108 . On a return pipe line  112  connected to the pipe line  108 , a regulator  111  is disposed for normally keeping the hydraulic pressure to be supplied to the valve  107  to a fixed value. The valve  107  is configured from the first valve  107   a  and the second valve  107   b  that can supply oil pressure to the first clutch CL 1  and the second clutch CL 2 , respectively. An oil return pipe line  113  is provided for each of the first valve  107   a  and the second valve  107   b.    
     A first hydraulic pressure sensor  63  is provided on a pipe line that connects the first valve  107   a  and the first clutch CL 1  to each other and measures the hydraulic pressure generated in the pipe line, namely, the hydraulic pressure generated in the first clutch CL 1 . Similarly, a second hydraulic pressure sensor  64  is provided on another pipe line that connects the second valve  107   b  and the second clutch CL 2  to each other and measures the hydraulic pressure generated in the second clutch CL 2 . Further, on the pipe line  108  that connects the hydraulic pump  109  and the valve  107  to each other, a main hydraulic pressure sensor  65  and a third hydraulic pressure sensor  66  as oil temperature detection means are provided. 
     To the AMT controlling unit  120 , a shift mode changeover switch  116 , a shift switch  115 , a neutral select switch  117  and a clutch control mode changeover switch  118  are connected. The shift mode changeover switch  116  carries out changeover between an automatic shift (AT) mode and a manual shift (MT) mode of the transmission TM. The shift switch  115  serves as shift manual operation means that carries out shift instruction for shift up (UP) or shift down (DN). The neutral select switch  117  carries out a changeover between the neutral (N) position and the drive (D) position. The clutch control mode changeover switch  118  carries out a changeover of a control mode for clutch operation. The clutch control mode changeover switch  118  is a push type switch that exhibits an on state from an off state only when it is pushed. The clutch control mode changeover switch  118  can arbitrarily carry out a changeover between an Auto mode in which clutch control is carried out automatically and a Manual mode in which the clutch is driven in response to an operation of the clutch lever L, under a predetermined condition. The switches are provided on handlebar switches of the steering handlebar  18 . 
     It is to be noted that the shift pedal P does not have a mechanical connection to the shift drum  30  but functions as a switch that sends a shifting request signal to the AMT controlling unit  120  similarly to the shift switch  115 . Further, the clutch lever L does not have a mechanical connection to the twin clutch but functions as a switch that sends a clutch operation request signal to the AMT controlling unit  120 . 
     The AMT controlling unit  120  includes a central processing unit (CPU) and controls the valve (clutch actuator)  107  and the shift motor (shift actuator)  21  in response to output signals of the sensors and the switches described above to change the shift position of the AMT  1  automatically or semi-automatically. Upon selection of the AT mode, the shift position is changed over automatically in response to information of the vehicle speed, engine speed, throttle opening and so forth. In contrast, upon selection of the MT mode, the transmission TM is shifted up or down in response to an operation of the shift switch  115  or the shift pedal P. It is to be noted that, also upon selection of the MT mode, auxiliary automatic shift control for preventing an overspeed, installation and so forth of the engine can be executed. 
     In the clutch hydraulic system  110 , a hydraulic pressure is applied to the valve  107  by the hydraulic pump  109  and is controlled by the regulator  111  so that it does not exceed an upper limit value. If the valve  107  is opened in accordance with an instruction from the AMT controlling unit  120 , then the hydraulic pressure is applied to the first clutch CL 1  or the second clutch CL 2  to connect the primary driven gear  3  to the inner main shaft  7  or the outer main shaft  6  through the first clutch CL 1  or the second clutch CL 2 . In particular, both of the first clutch CL 1  and the second clutch CL 2  are normally open type hydraulic clutches. If the valve  107  is closed to stop the application of the hydraulic pressure, then the first clutch CL 1  or the second clutch CL 2  is urged in a direction in which the connection between the inner main shaft  7  and the outer main shaft  6  is cut by a return spring (not shown) built therein. 
     The valve  107  which opens and closes the pipe lines that connect the pipe line  108  and the two clutches to each other to drive the clutches is configured such that the AMT controlling unit  120  adjusts the driving signal so that the time and so forth required to place the pipe lines from a fully closed state to a fully open state can be changed arbitrarily. 
     The shift motor  21  rotates the shift drum  30  in accordance with an instruction from the AMT controlling unit  120 . When the shift drum  30  rotates, the shift forks  71 ,  72 ,  81  and  82  are displaced in an axial direction of the shift drum  30  in accordance with the shape of guide grooves formed on the outer periphery of the shift drum  30 , whereupon the meshing relationship between the gears on the countershaft  9  and the main shaft  13  changes. 
     The AMT  1  according to the present embodiment is configured such that the inner main shaft  7  coupled to the first clutch CL 1  supports odd number stage side gears (first, third and fifth stages) and the outer main shaft  6  coupled to the second clutch CL 2  supports even number stage side gears (second, fourth and sixth stages). Accordingly, for example, while the motorcycle runs with an odd number stage side gear, supply of the pressure oil to the first clutch CL 1  continues and the connection state is maintained. Then, upon a shift change, the transmission gear that transmits a driving force is changed over by carrying out a clutch switching operation in a state in which the transmission gears before and after the shift change remain in a meshing state. 
       FIG. 4  is an enlarged sectional view of the transmission TM. Like reference characters to those used in the foregoing description denote like or equivalent portions. A rotational driving force is transmitted from the crankshaft  105  of the engine  100  to the primary driven gear  3  having a shock absorption mechanism  5  thereon through the primary driving gear  106 . Then, the rotational driving force is transmitted from the twin clutch TCL to the countershaft  9  to which the bevel gear  56  is attached through the outer main shaft  6  and the inner main shaft  7  supported for rotation in the outer main shaft  6  and further through the six gear pairs provided between the main shaft  13  (outer main shaft  6  and inner main shaft  7 ) and the countershaft  9 . The rotational driving force transmitted to the bevel gear  56  is transmitted to the drive shaft  58  with the rotational direction thereof being changed to the vehicle body rear side by the bevel gear  57  with which the bevel gear  56  meshes. 
     The transmission TM has six transmission gear pairs between the main shaft and the countershaft and can select which gear pair should be used to output the rotational driving force depending upon a combination of the position of a slidably movable gear attached for sliding movement in an axial direction of each shaft and the connection or disconnection state of the first clutch CL 1  and the second clutch CL 2 . The twin clutch TCL is disposed in the inside of a clutch case  4  that rotates integrally with the primary driven gear  3 . The first clutch CL 1  is attached against rotation on the inner main shaft  7  while the second clutch CL 2  is attached against rotation to the outer main shaft  6 . A clutch plate  12  is disposed between the clutch case  4  and each of the two clutches. The clutch plate  12  is configured from four driving friction plates supported against rotation on the clutch case  4  and four driven friction plates supported against rotation on each of the two clutches. 
     The first clutch CL 1  and the second clutch CL 2  are configured such that, if oil pressure is supplied thereto from the hydraulic pump  109  (refer to  FIG. 3 ), then a friction force is generated on the clutch plate  12  so that the first clutch CL 1  or the second clutch CL 2  is placed into a connection state. A distributor  8  is embedded in a wall face of the clutch cover  50  attached to the crankcase  46  and forms two hydraulic paths of a double pipe shape in the inside of the inner main shaft  7 . If a hydraulic pressure is supplied to the distributor  8  through the first valve  107   a  and a hydraulic pressure is supplied into an oil path A 1  formed in the inner main shaft  7 , then a piston B 1  is slidably moved in a direction indicated in  FIG. 4  against the biasing force of an elastic member  11  such as a spring so that the first clutch CL 1  is changed over into a connection state. On the other hand, if a hydraulic pressure is supplied into another oil path A 2 , then a piston B 2  is slidably moved to the left in  FIG. 4  to change over the second clutch CL 2  into a connection state. The pistons B 1  and B 2  of the clutches CL 1  and CL 2  are configured such that, if the application of the hydraulic pressure stops, then they return to their initial position by the biasing force of the elastic member  11 . 
     By such a configuration as described above, a rotational driving force of the primary driven gear  3  rotates the clutch case  4  unless a hydraulic pressure is supplied to the first clutch CL 1  or the second clutch CL 2 . However, if a hydraulic pressure is supplied, then the outer main shaft  6  or the inner main shaft  7  is driven to rotate integrally with the clutch case  4 . At this time, by adjusting the magnitude of the supplied hydraulic pressure, an arbitrary half clutch state can be obtained. 
     The inner main shaft  7  connected to the first clutch CL 1  supports driving gears M 1 , M 3  and M 5  for the odd number stages (first, third and fifth speeds). The first speed driving gear M 1  is formed integrally with the inner main shaft  7 . The third speed driving gear M 3  is attached for sliding movement in an axial direction but against rotation in a circumferential direction to the inner main shaft  7  through a spline meshing engagement therebetween. The fifth speed driving gear M 5  is attached against sliding movement in an axial direction and for rotation in a circumferential direction to the inner main shaft  7 . 
     Meanwhile, the outer main shaft  6  connected to the second clutch CL 2  supports driving gears M 2 , M 4  and M 6  for the even number stages (second, fourth and sixth speeds). The second speed driving gear M 2  is formed integrally with the outer main shaft  6 . The fourth speed driving gear M 4  is attached for sliding movement in an axial direction but against rotation in a circumferential direction to the outer main shaft  6  through spline meshing engagement therebetween. The sixth speed driving gear M 6  is attached against sliding movement in the axial direction but for rotation in a circumferential direction to the outer main shaft  6 . 
     The countershaft  9  supports drive gears C 1  to C 6  for meshing with the driving gears M 1  to M 6 . The first to fourth speed driven gears C 1  to C 4  are attached against sliding movement in an axial direction but for rotation in a circumferential direction to the countershaft  9 . The fifth and sixth speed driven gears C 5  and C 6  are attached for sliding movement in the axial direction but against rotation in a circumferential direction to the countershaft  9 . 
     Of the gear trains described above, the driving gears M 3  and M 4  and the driven gears C 5  and C 6 , namely, the “slidably movable gears” which can slidably move in the axial direction, are configured so as to be slidably moved by a movement of a shift fork hereinafter described. Each of the slidably movable gears has an engaging groove  51 ,  52 ,  61  or  62  formed therein for engagement by a pawl portion of the shift fork. It is to be noted that the inner main shaft rotational speed sensor  131  (refer to  FIG. 3 ) detects the rotational speed of the third speed driven gear C 3  and the outer main shaft rotational speed sensor  132  detects the rotational speed of the speed fourth driven gear C 4  as described hereinabove. 
     Meanwhile, the transmission gears (driving gears M 1 , M 2 , M 5  and M 6  and driven gears C 1  to C 4 ) other than the slidably movable gears described above, namely, the “slidably immovable gears” which cannot slidably move in the axial direction, are configured such that they carry out connection and disconnection of the rotational driving force to and from an adjacent slidably movable gear. By the configuration described above, the AMT  1  according to the present embodiment can arbitrarily select one gear pair for transmitting the rotational driving force depending upon the position of the slidably movable gears and the connection or disconnection state of the clutches CL 1  and CL 2 . 
     In the present embodiment, a dog clutch mechanism is applied for the transmission of the rotational driving force between a slidably movable gear and a slidably immovable gear. The dog clutch mechanism makes low-loss transmission of the rotational driving force through meshing engagement between concave and convex shapes configured from dog teeth and dog holes. In the present embodiment, the dog clutch mechanism is configured such that, for example, four dog teeth  55  formed on the sixth speed driven gear C 6  mesh with four dog holes  35  formed on the second speed driven gear C 2 . 
       FIG. 5  is an enlarged sectional view of a transmission mechanism  20 . Meanwhile,  FIG. 6  is a developed view showing a shape of guide groups of the shift drum  30 . The transmission mechanism  20  includes the four shift forks  71 ,  72  and  81 ,  82  attached for sliding movement to two guide shafts  31  and  32 , respectively, in order to drive the four slidably movement gears described hereinabove. The four shift forks have provided thereon guide pawls ( 71   a ,  72   a ,  81   a  and  82   a ) for engaging with the slidably movable gears and cylindrical convex portions ( 71   b ,  72   b ,  81   b  and  82   b ) for engaging with the guide grooves formed on the shift drum  30 . 
     The shift fork  71  for engaging with the third speed driving gear M 3  and the shift fork  72  for engaging with the fourth speed driving gear M 4  are attached to the guide shaft  31 . Meanwhile, the shift fork  81  for engaging with the fifth speed driven gear C 5  and the shift fork  82  for engaging with the sixth speed driven gear C 6  are attached to the guide shaft  32  on the other side. 
     Guide grooves SM 1  and SM 2  for being engaged by the shift forks  71  and  72  on the main shaft side and guide grooves SC 1  and SC 2  for being engaged by the shift forks  81  and  82  on the countershaft side are formed on the surface of the shift drum  30  disposed in parallel to the guide shafts  31  and  32 , respectively. Consequently, the slidably movable gears M 3 , M 4  and C 5 , C 6  are driven along the shape of the four guide grooves upon rotation of the shift drum  30 . 
     The shift drum  30  is driven to rotate to a predetermined position by the shift motor  21 . The rotational driving force of the shift motor  21  is transmitted to a shift drum shaft  29 , that supports the shift drum  30  of a hollow cylindrical shape, through a first gear  23  fixed to a rotary shaft  22  and a second gear  24  meshing with the first gear  23 . The shift drum shaft  29  is connected to the shift drum  30  through a lost motion mechanism  140 . 
     The lost motion mechanism  140  is configured such that the shift drum shaft  29  and the shift drum  30  are connected to each other by a torsion coil spring  150 . The lost motion mechanism  140  is a mechanism wherein, for example, even if the shift drum  30  cannot be rotated in a scheduled manner due to a failure in the meshing engagement of the dog clutch, a motion of the shift motor  21  is temporarily absorbed by the torsion coil spring  150  so that an excessive load is not applied to the shift motor  21 . 
     The lost motion mechanism  140  is configured from a driving rotor  170  attached to an end portion of the shift drum shaft  29 , a driven rotor  160  attached to an end portion of the shift drum  30 , and a torsion coil spring  150  that connects the driving rotor  170  and the driven rotor  160  to each other. Consequently, if the shift drum  30  is placed into a rotatable state in the state in which the motion of the shift motor  21  is temporarily absorbed, then the shift drum  30  is rotated to the predetermined position by the biasing force of the torsion coil spring  150 . 
     In order for the gear position sensor  134  (refer to  FIG. 3 ) to detect an actual rotational angle of the shift drum  30 , it is disposed so as to detect the rotational angle of the shift drum  30  or the driven rotor  160 . The shifter sensor  27  can detect whether or not the shift motor  21  is at a predetermined position based on the position of a cam  28  rotated by a pin  26  planted on a shifter  25  fixed to the shift drum shaft  29 . 
     A positional relationship between the rotational position of the shift drum  30  and the four shift forks is described with reference to the developed view of  FIG. 6 . The guide shafts  31  and  32  are disposed at positions spaced by approximately 90° in a circumferential direction with reference to the rotary shaft of the shift drum  30 . For example, where the rotational position of the shift drum  30  is the neutral (N) position, the shift forks  81  and  82  are positioned at a position indicated by “C N-N” on the left side in  FIG. 6  while the shift forks  71  and  72  are positioned at a position indicated by “M N-N” on the right side in  FIG. 6 . 
     In  FIG. 6 , the position of each cylindrical convex portion ( 71   b ,  72   b ,  81   b ,  82   b ) of the shift forks in the neutral position is indicated by a broken line circle. Meanwhile, predetermined rotational positions represented by indications following the indication “C N-N” on the left side in  FIG. 6  and predetermined rotational positions represented by indications following the indication “M N-N” on the right side in  FIG. 6  are provided at intervals of 30 degrees. It is to be noted that, from among the predetermined rotational angles, a “neutral waiting (N waiting)” position hereinafter described is indicated by a quadrangular shape. 
     The sliding movement positions of the shift forks determined by the guide grooves are configured such that, while the guide grooves SM 1  and SM 2  on the main shaft side have two positions of a “left position” and a “right position,” the guide grooves SC 1  and SC 2  on the countershaft side have three positions of a “left position,” a “mid position” and a “right position.” 
     When the shift drum  30  is at the neutral position, the shift forks are positioned such that the shift fork  81  is at the mid position, the shift fork  82  at the mid position, the shift fork  71  at the right position and the shift fork  72  at the left position. This is a state in which none of the four slidably movable gears which are driven by the shift forks mesh with adjacent slidably immovable gears. Accordingly, even if the first clutch CL 1  or the second clutch CL 2  is connected, the rotational driving force of the primary driven gear  3  is not transmitted to the countershaft  9 . 
     Then, if the shift drum  30  is rotated from the neutral position described hereinabove to the position (“C 1-N” and “M 1-N”) corresponding to the first speed gear, then the shift fork  81  changes over from the mid position to the left position to change over the fifth speed driven gear C 5  from the mid position to the left position. Consequently, the fifth speed driven gear C 5  is brought into meshing engagement with the first speed driven gear C 1  through the dog clutch to establish a state in which the rotational driving force can be transmitted. If, in this state, the first clutch CL 1  is changed over to a connection state, then the rotational driving force is transmitted in order of the inner main shaft  7 , first speed driving gear M 1 , first speed driven gear C 1 , fifth speed driven gear C 5 , and countershaft  9 . 
     Then, if a shift instruction to the second speed is inputted after completion of the speed change to the first gear, then the shift drum  30  is automatically rotated by 30 degrees in a shift up direction. This rotational movement is called “preliminary upshifting” for completing the speed change only by the changeover of the connection state of the twin clutch TCL when the shift instruction to the second speed is issued. By this preliminary upshifting, the two guide shafts move to the positions of the indications “C 1-2” and “M 1-2” on the left and right sides in  FIG. 6 , respectively. 
     The change of the guide grooves involved in this preliminary upshifting is only the changeover of the guide groove SC 2  from the mid position to the right position. By this changeover, the shift fork  82  moves to the right position to bring the sixth speed driven gear C 6  into meshing engagement with the second speed driven gear C 2  through the dog clutch. At a point in time at which the preliminary upshifting is completed, since the second clutch CL 2  is in the disconnected state, the outer main shaft  6  is driven to rotate by the viscosity of the lubricating oil filled between the outer main shaft  6  and the inner main shaft  7 . 
     By the preliminary upshifting described above, the twin clutch TCL becomes ready for transmission of the rotational driving force through the second gear. If a shifting instruction to the second speed is issued in this state, then the first clutch CL 1  is disconnected and the second speed driven gear C 2  is changed over to a connected state. By this switching action of the clutch, the shifting action to the second gear is completed immediately without interruption of the rotational driving force. 
     Then, if a shifting instruction to the third speed is issued after the completion of the shifting action from the first speed to the second speed, then the preliminary upshifting for completing the shifting action from the second speed to the third speed only by switching of the clutch is executed. By the preliminary upshifting from the second speed to the third speed, the guide shaft on the counter shaft side moves from the position of the indication “C 1-2” on the left side in  FIG. 6  to the position of the indication “C 3-2” and the guide shaft of the main shaft side moves from the position of the indication “M 1-2” on the right side in  FIG. 6  to the position of the indication “M 3-2.” The change of the guide grooves involved in the movement is only changeover of the guide groove SC 1  from the left position to the right position. By the changeover, the shift fork  81  moves from the left position to the right position and the fifth speed driven gear C 5  and the speed third driven gear C 3  are brought into meshing engagement with each other through the dog clutch. 
     After the preliminary upshifting from the second speed to the third speed is completed, a state is established in which a shifting action from the second speed to the third speed is completed only by executing an action of changing over the connection state of the twin clutch TCL from the first clutch CL 1  to the second clutch CL 2 , namely, only by executing a switching action of the clutch. This preliminary upshifting is thereafter executed similarly until selection of the fifth speed gear is carried out. 
     Upon the preliminary upshifting from the second speed to the third speed described above, the guide groove SC 1  passes the mid position of the indication “C N-2” on the left side in  FIG. 6 , namely, the position at which meshing engagement through the dog clutch is not carried out. The rotational position of the shift drum  30  is detected by the gear position sensor  134 , and the rotational speed of the shift drum  30  can be finely adjusted by the shift motor  21 . Consequently, it is possible to differentiate between the rotational speed from the position of the indication “C 1-2” to the position of the indication “C N-2” on the left side in  FIG. 6 , namely, the speed when the meshing engagement of the dog clutch is canceled between the drive gears C 1  and C 5 , and the rotational speed from the position of the indication “C N-2” to the position of the indication “C 3-2,” namely, the speed when the dog clutch is placed into meshing engagement between the driven gears C 5  and C 3 . Or, “neutral waiting” wherein the shift drum  30  stops for a predetermined period of time at the position wherein the indication “C N-2” can be carried out. With such a configuration of the AMT  1  as described above, for example, during driving with the second speed gear, the rotational position of the shift drum  30  can be changed arbitrarily among the positions of “1-2,” “N-2” and “3-2.” 
     If the neutral waiting control for temporarily stopping the shift drum  30  at the “neutral waiting” position is executed at a predetermined timing, then a shift shock which is liable to occur upon connection and disconnection of the dog clutch can be reduced. It is to be noted that the driving timing or the driving speed of the shift drum  30  can be adjusted suitably also in response to the number of the shift stage upon shifting, the engine speed and so forth. 
     It is to be noted that, when the shift drum  30  is at the “neutral waiting” position, one shift gear pair on the odd number stage side and the even number stage side is in the neutral state. For example, at the position of “C N-2,” the dog clutch between the driven gears C 2  and C 6  is in a meshing state. On the other hand, the driven gear C 5  is in the neutral state in which it meshes with none of the driven gears C 1  and C 3 . Accordingly, even if the first clutch CL 1  is changed over at this point of time to a connected state, only the inner main shaft  7  is rotated, but there is no influence upon transmission of the rotational driving force to the countershaft  9 . 
       FIG. 7  illustrates a table of shift positions defined by the shift drum  30 . The shift drum  30  changes the shift position by one stage, for example, from the position of N-N to the position 1-N by one shifting action. The shift drum  30  has, on both of the odd number stage side and the even number stage side, a neutral waiting position indicated by “N” between gear stages. For example, at the position “1-N,” while the odd number stage side gears are in a state in which the gear for the first speed can be connected, the even number stage side gears are in a neutral state in which no driving force is transmitted. On the other hand, at any position at which no neutral waiting state is provided, such as at the position “1-2,” one of the first clutch CL 1  and the second clutch CL 2  is connected to carry out transmission of driving force. 
       FIG. 8  is a graph illustrating a relationship between the operational amount of the clutch lever L and the output signal of a clutch operational amount sensor SEL. The clutch lever L (refer to  FIG. 1 ) attached to the steering handlebar  18  is a clutch manual operation means for driving the clutch to the disconnection side in response to the operational amount by the occupant from a clutch connection state in which the clutch lever L is not operated and remains free. The clutch lever L is configured such that it returns to its initial position if it is released by the occupant. 
     The clutch lever operational amount sensor SEL is set such that the output voltage (vcltlevin) thereof increases in response to a release of the lever where the state in which the clutch lever L is operated fully is represented as zero. In the present embodiment, the remaining range when an amount of play of the lever which exists when the lever begins to be gripped and an abutment margin determined taking into consideration that the gripped lever is abutted to a handlebar grip formed from rubber or the like are subtracted from the output voltage is set as a range of an effective voltage. 
     More particularly, the amount of the lever from an operational amount Sa when the lever is released until the abutment margin comes to an end after the gripped state of the lever is established to another operational amount Sb at which the lever play amount starts is set so as to correspond to a range from a lower limit value E 1  to an upper limit value E 2  of the effective voltage. Then, the range from the lower limit value E 1  to the upper limit value E 2  is made corresponding in a proportional relationship to a range of zero to a MAX value of the manual operation clutch capacity arithmetic operation value (tqc1tmt). This can reduce the influence of a mechanical play, sensor dispersion and so forth and enhance the reliability of a clutch driving amount required by a manual operation. 
       FIG. 9  is a block diagram showing a configuration of the AMT controlling unit  120 . Like reference characters to those used in the foregoing description denote like or equivalent portions. A shift controlling section  180  of the AMT controlling unit  120  includes an automatic shift mode AT, a manual shift mode MT, a shift map M, a target gear position decision section  181 , and a stopping state clutch off/starting request decision section  182 . The shift controlling section  180  further includes a manual operation clutch decision section  183 , an Auto mode connection side clutch decision section  184 , a manual operation clutch capacity arithmetic operational section  185 , and a clutch control mode decision section  186 . The shift controlling section  180  further includes a shift motor driving output power arithmetic operational section  187  and a clutch capacity output value arithmetic operational section  188 . 
     Output signals from the clutch lever operational amount sensor SEL for detecting an operational amount of the clutch lever L, the gear position sensor  134 , engine speed sensor  130 , throttle opening sensor  103 , vehicle speed sensor SEV, shift mode changeover SW (switch)  116  and clutch control mode changeover SW (switch)  118  are inputted to the shift controlling section  180 . In addition, output signals from a shift pedal operational amount sensor SEP for detecting an operational amount of the shift pedal P, the shift SW (switch)  115 , main hydraulic pressure sensor  65 , first hydraulic pressure sensor  63 , second hydraulic pressure sensor  64  and third hydraulic pressure sensor  66  are inputted to the shift controlling section  180 . 
     When both of the clutch control mode and the shift mode are set to automatic control, the shift controlling section  180  transmits a driving signal to a shift actuator controlling section  190  and a clutch actuator controlling section  191  in accordance with the shift map M configured from a three-dimensional map or the like based on output signals principally from the engine speed sensor  130 , throttle opening sensor  103 , gear position sensor  134  and vehicle speed sensor SEV. 
     Meanwhile, the AMT controlling unit  120  according to the present embodiment is configured such that a manual operation for driving the twin clutch TCL and the shift drum  30  can be executed in response to an operation of the clutch lever L or an operation of the shift switch  115  or the shift pedal P as manual operation means. Among such manual operations, the operation of the manual operation means can be given priority not only when the manual mode is selected by the shift mode changeover switch  116  and the clutch control mode changeover switch  118  but also when the manual operation means is operated during automatic control. It is to be noted that the AMT controlling unit  120  carries out control also for the throttle valve motor  104  and a fuel injection system and, for example, executes also automatic blipping (racing) control for adjusting the engine speed upon shift down and like control. 
       FIG. 10  is a block diagram illustrating an arithmetic operation procedure of a shift motor driving output value and a clutch capacity output value. Like reference characters to those used in the foregoing description denotes like or equivalent portions. The shift motor driving output value and the clutch capacity output value are arithmetically operated by the shift motor driving output power arithmetic operational section  187  and the clutch capacity output value arithmetic operational section  188 , respectively, in the shift controlling section  180  and transmitted to the shift actuator controlling section  190  and the clutch actuator controlling section  191 . 
     The shift motor driving output value for determining the rotational direction and the rotational amount of the shift drum  30  is calculated by the shift motor driving output power arithmetic operational section  187 . The shift motor driving output power arithmetic operational section  187  calculates, when a difference appears between the gear position (gearpos) at present and a target gear position (gptgt), the shift motor driving output value so that the gear position at present comes to coincide with the target gear position. 
     The target gear position (gptgt) is derived by the target gear position decision section  181  in response to a shifting request based on the shift map M by automatic shift control and a shifting request by a manual operation (shift pedal operation or shift switch operation). Meanwhile, the gear position (gearpos) at present is detected as a 12-stage signal by the gear position sensor  134  (refer to  FIG. 7 ). 
     On the other hand, the clutch capacity output value arithmetic operational section  188  arithmetically operates an odd number stage side clutch capacity output value (tqc1) for determining a driving amount of the odd number stage side clutch (first clutch CL 1 ) and an even number stage side clutch capacity output value (tqc2) for determining a driving amount of the even number stage side clutch (second clutch CL 2 ). In this instance, the clutch capacity output value arithmetic operational section  188  carries out the automatic operation based on a manual operation clutch decision value (cntcltmt), an Auto mode connection clutch decision value (cltcont), a clutch control mode (cltmode), a manual operation clutch capacity arithmetic operation value (tqc1tmt), and information necessary for automatic starting-shift control (vehicle speed, throttle opening, engine speed/engine torque estimated value and so forth). 
     The manual operation clutch decision value (cntcltmt) derived by the manual operation clutch decision section  183  indicates which one of the first clutch CL 1  and the second clutch CL 2  is to be determined as a control target in response to an operation of the clutch lever L. This is calculated based on the target gear position (gptgt), gear position (gearpos) and manual operation clutch capacity arithmetic operation value (tqc1tme): E. The manual operation clutch capacity arithmetic operation value (tqc1tmt) is derived by the manual operation clutch capacity arithmetic operational section  185  based on the clutch operational amount sensor signal (vcltlevin) as described hereinabove with reference to  FIG. 8 . 
     The Auto mode connection clutch decision value (cltcont) derived by the Auto mode connection side clutch decision section  184  indicates which one of the first clutch CL 1  and the second clutch CL 2  is to be connected in the clutch Auto mode. This is derived based on the target gear position (gptgt), the gear position (gearpos) and a stopping state clutch off request (f_cltoff). 
     The stopping state clutch off request (f_cltoff) indicates a clutch disconnection action upon stopping of the vehicle during operation of the engine and is derived by the stopping state clutch off/starting request decision section  182  based on the engine speed Ne, throttle opening TH and vehicle speed V. The stopping state clutch off/starting request decision section  182  carries out also detection of a starting request that depends upon, for example, when the engine speed Ne reaches a predetermined value. 
     The clutch control mode (cltmode) derived by the clutch control mode decision section  186  indicates by which one of automatic control and manual operation the clutch is to be driven. This is derived based on a clutch control mode changeover SW state (cltmodsw) representative of an operational state of the clutch control mode changeover SW  118 , a clutch operational amount sensor signal (vcltlevin), an odd number stage side clutch capacity output value (tqc1), an even number stage side clutch capacity output value (tqc2) and a manual operation clutch capacity arithmetic operation value (tqc1tmt). Accordingly, even if the Manual mode is selected by the clutch control mode changeover SW  118 , the clutch control mode (clmode) may be changed to the Auto mode in response to some other parameter. 
       FIG. 11  is a state transition diagram illustrating a relationship among the three clutch control modes. The three clutch control modes are an Auto mode in which an automatic control is carried out, a Manual mode in which a manual operation is carried out, and a Temp. Manual mode (hereinafter referred to sometimes as Temp mode) in which a temporary manual operation is carried out. 
     The Auto mode is a mode in which a clutch capacity suitable for an operating state is arithmetically operated to control the clutch by automatic starting-shift control. Meanwhile, the Manual mode is a mode in which a clutch capacity is arithmetically operated in response to a clutch operation instruction by the occupant to control the clutch. The Temp mode is a temporary manual operation mode in which a clutch operation instruction from the occupant is accepted in the Auto mode and a clutch capacity is arithmetically operated from the clutch operation instruction to control the clutch. It is to be noted that, if the occupant stops the operation of the clutch lever L (fully releases the clutch lever) in the Temp mode, then the clutch control mode returns to the Auto mode. 
     It is to be noted that the twin clutch type transmission according to the present embodiment has a structure that a pump is driven by rotational driving force of the engine to generate clutch controlling hydraulic pressure. Therefore, upon the starting of the system, it is necessary for the twin clutch type transmission to carry out the starting in a clutch off state (disconnected state) in the Auto mode. Similarly, also upon stopping of the engine, since no clutch operation is required, it is set that a clutch off state is restored in the Auto mode. 
     First, if, in the Auto mode, conditions “that the vehicle is in a stopping state, that the engine is in an operating state, that the manual operation clutch capacity arithmetic operation value (tqc1tmt) is equal to or lower than a clutch off decision threshold value and that the clutch control mode changeover SW changes from an off state to an on state (a depression operation is carried out)” are satisfied, then the clutch control mode transits to the Manual mode. 
     Further, if, in the Auto mode, conditions “that the vehicle is being operated, that the clutch is in a connected state by the automatic control, that the clutch lever L is released (the manual operation clutch capacity arithmetic operation value (tqc1tmt) is equal to the clutch connection capacity) and that the clutch control mode changeover SW changes from an off state to an on state” are satisfied, then the clutch control mode transits to the Manual mode. 
     In contrast, if, in the Manual mode, conditions “that the vehicle is being operated, that the clutch lever L is in a released state (tqc1tmt is equal to the clutch connection capacity) and that the clutch control mode changeover SW changes from an off state to an on state” are satisfied, then the clutch control mode transits to the Auto mode. 
     Further, if, in a Manual type mode (Manual mode or Temp mode), conditions “that the vehicle is in a stopping state, that the engine is in an operating state, that the manual operation clutch capacity arithmetic operation value (tqc1tmt) is equal to or lower than the clutch off decision threshold value, that the automatic starting conditions are not satisfied and that the clutch mode changeover SW changes from an off state to an on state” are satisfied, then the clutch control mode transits to the Auto mode. 
     Furthermore, if, in the Auto mode, conditions “that the engine is in an operating state and that the manual operation clutch capacity arithmetic operation value (tqc1tmt) calculated from the clutch operational amount sensor signal is equal to or lower than a clutch capacity output value (tqc1, tqc2)” are satisfied, then the clutch control mode transits to the Temp. Manual mode. Consequently, a so-called override function of causing the clutch control mode to smoothly transit to the Temp mode if the occupant carries out a clutch operation while the vehicle is operating in the auto mode can be implemented. 
     On the other hand, if, in the Temp. Manual mode, a condition “that the clutch lever L is in a released state (tqc1tmt is equal to the clutch connection capacity)” is satisfied, then the clutch control mode transits to the Manual mode. 
     Further, if, in the Temp. Manual mode, conditions “that the vehicle is in a stopping state, that the engine is in an operating state, that the manual operation clutch capacity arithmetic operation value (tqc1tmt) is equal to or lower than the clutch off decision threshold value and that the clutch mode changeover SW changes from an off state to an on state” are satisfied, then the clutch control mode transits to the Manual mode. 
     Then, if, in a Manual type mode (Manual mode or Temp mode), a condition “that the engine is stopping” is satisfied, then the clutch control mode transits to the Manual mode. 
       FIG. 12  is a flow chart illustrating a procedure for deciding a clutch which is to execute a manual operation. This decision executed by the manual operation clutch decision section  183  decides, when the clutch lever L is operated, which one of the first clutch CL 1  and the second clutch CL 2  is to correspond to the operation based on the gear position at present and the target gear position. 
     At step S 1 , it is decided whether or not an odd number stage side gear is in an in-gear state (not in a neutral state). If an affirmative decision is made at step S 1 , then the processing advances to step S 2 , at which it is decided whether or not an even number stage side gear is in an in-gear state. If an affirmative decision is made at step S 2 , then the processing advances to step S 3 . 
     At step S 3 , it is decided whether or not the value of the |target gear position−odd number stage side gear position| is higher than the |target gear position−even number stage side gear position|. In this instance, if both of an odd number stage side gear and an even number stage side gear are in an in-gear state, for example, the gear position is “3-4” and the target gear position is the fifth gear, then |5−3|&gt;|5−4| is satisfied and the decision at step S 3  becomes an affirmative decision. If this inequality is not satisfied, then a negative decision is made at step S 3 . 
     If a negative decision is made at step S 3 , then the processing advances to step S 4 , at which it is decided whether or not the manual operation clutch decision is the odd number stage side clutch. If a negative decision is made at step S 4 , then the processing advances to step S 5 . At step S 5 , it is decided whether or not the manual operation clutch capacity is equal to or smaller than the clutch off capacity, and if a negative decision is made, then the processing advances to step S 6 . At step S 6 , it is decided whether or not the manual operation clutch capacity has changed to the clutch connection side, and if a negative decision is made, then the processing advances to step S 7 . At step S 7 , the manual operation clutch decision is set to the even number stage side clutch, thereby ending the series of control steps. 
     In contrast, if an affirmative decision is made at step S 4 , S 5  or S 6 , then the processing advances to step S 13 , at which the manual operation clutch decision is set to the odd number stage side clutch, thereby ending the series of control steps. 
     Meanwhile, if an affirmative decision is made at step S 3 , then the processing advances to step S 8 , at which it is decided whether or not the manual operation clutch decision is the even number stage side clutch. Then, if a negative decision is made, then the processing advances to step S 9 . At step S 9 , it is decided whether or not the manual operation clutch capacity is equal to or smaller than the clutch off capacity, and if a negative decision is made, then the processing advances to step S 10 . At step S 10 , it is decided whether or not the manual operation clutch capacity has changed to the clutch connection side, and if a negative decision is made, then the processing advances to step S 11 . At step S 11 , the manual operation clutch decision is set to the odd number stage side clutch, thereby ending the series of control steps. 
     In contrast, if an affirmative decision is made at step S 8 , S 9  or S 10 , then the processing advances to step S 14 , at which the manual operation clutch decision is set to the even number stage side clutch, thereby ending the series of control steps. 
     Returning to the decision at step S 1 , if a negative decision is made at step S 1 , namely, if it is decided that an odd number stage side gear is in a neutral state, then the processing advances to step S 12 , at which it is decided whether or not an even number stage side gear is in an in-gear state. If a negative decision is made at step S 12 , namely, if the gear position is “N-N,” then the manual operation clutch decision is set to the odd number stage side clutch at step S 16  (because the position “1-N” only exists as a next position to the position “N-N”), thereby ending the series of control steps. 
     On the hand, if an affirmative decision is made at step S 12 , namely, if it is decided that only an even number stage side gear is in an in-gear state (position “N-2,” “N-4” or “N-6”), then the manual operation clutch decision is set to the even number stage side clutch at step S 15 , thereby ending the series of control steps. 
     Further, returning to the decision at step S 2 , if a negative decision is made at step S 2 , namely, if an even number stage side gear is in a neutral state and only an odd number stage side gear is in an in-gear state (position “1-N,” “3-N” or “5-N”), then the processing advances to step S 13 . At step S 13 , the manual operation clutch decision is set to the odd number stage side clutch, thereby ending the series of control steps. 
       FIG. 13  is a flow chart illustrating a procedure for deciding a connection side clutch in the Auto mode. This decision is executed by the Auto mode connection side clutch decision section  184  and is made in accordance with the gear position at present and the target gear position which one of the first clutch CL 1  and the second clutch CL 2  is to be connected by automatic control during operation wherein the clutch control mode is the Auto mode. 
     At step S 20 , it is decided whether or not the target gear position is the position “N-N,” and if a negative decision is made, then the processing advances to step S 21 . At step S 21 , it is decided whether or not there is a stopping state clutch off request, and if a negative decision is made, then the processing advances to step S 22 . At step S 22 , it is decided whether or not the gear position at present is “N-N,” and if a negative decision is made, then the processing advances to step S 23 . 
     At step S 23 , it is decided whether or not an odd number stage side gear is in an in-gear state, and if an affirmative decision is made, then the processing advances to step S 24 . At step S 24 , it is decided whether or not an even number stage side gear is an in-gear state, and if an affirmative decision is made, namely, if both of an odd number stage side gear and an even number stage side gear are in an in-gear state, then the processing advances to step S 25 . 
     At step S 25 , it is decided whether or not the value of the |target gear position−odd number stage side gear position| is greater than the |target gear position−even number stage side gear position|. If a negative decision is made at step S 25 , then the processing advances to step S 26 , at which the connection clutch state is set to the odd number stage side clutch on, thereby ending the series of control steps. In contrast, if an affirmative decision is made at step S 25 , then the processing advances to step S 28 , at which the connection clutch state is set to the even number stage side clutch on, thereby ending the series of control steps. 
     Returning to the decision at step S 20 , if an affirmative decision is made at step S 20 , S 21  or S 22 , then the processing advances to step S 29 , at which it is determined that no clutch connection is required and the connection clutch state is set to off, thereby ending the series of control steps. 
     In contrast, if a negative decision is made at step S 23 , then the processing advances to step S 27 , at which it is decided whether or not an even number stage side gear is in an in-gear state. If an affirmative decision is made at step S 27 , namely, if it is decided that an odd number stage side gear is in a neutral state and only an even number stage side gear is in an in-gear state (“N-2,” “N-4” or “N-6”), then the processing advances to step S 28 . At step S 28 , the connection clutch state is set to the even number stage side clutch on, thereby ending the series of control steps. 
     It is to be noted that, if a negative decision is made at step S 27 , namely, if it is decided that none of the odd number stage side gear and the even number stage side gear is in an in-gear state, then the processing advances to step S 29 , at which the connection clutch state is set to an off state, thereby ending the series of control steps. In contrast, if a negative decision is made at step S 24 , then the processing advances to step S 26 , at which the connection clutch state is set to the odd number stage side clutch on, thereby ending the series of control steps. 
       FIGS. 14 and 15  are flow charts (1/2) and (2/2) illustrating a procedure for a clutch capacity output value arithmetic operation. At step S 30 , it is decided whether or not the clutch control mode decision value indicates the Auto mode, and if an affirmative decision is made, then the processing advances to step S 31 . However, if a negative decision is made at step S 30 , then the processing advances to A (refer to  FIG. 15 ). 
     At step S 31 , arithmetic operation of an Auto mode state automatic control odd number stage side clutch capacity (tqc1at) is executed, and then at next step S 32 , arithmetic operation of Auto mode state automatic control even number stage side clutch capacity (tqc2at) is executed. At steps S 31  and S 32 , arithmetic operation is executed so that starting/shifting is carried out smoothly in accordance with the shift map M configured from a three-dimensional map or the like based principally on output signals of the engine speed sensor  130 , throttle opening sensor  103 , gear position sensor  134  and vehicle speed sensor SEV. 
     Then at step S 33 , the odd number stage side clutch capacity output value (tqc1) is set to the automatic control odd number stage side clutch capacity (tqc1at), and then at step S 34 , the even number stage side clutch capacity output value (tqc2) is set to the automatic control even number stage side clutch capacity (tqc2at), thereby ending the series of control steps. 
     Meanwhile, if a negative decision is made at step S 30 , namely, if the clutch control mode decision value indicates the Manual mode or the Temp mode, then the processing advances to step S 40  following A. 
     Referring to  FIG. 15 , at step S 40 , it is decided whether or not the manual operation clutch decision value is the odd number stage side clutch. If an affirmative decision is made at step S 40 , then the processing advances to step S 41 , at which it is decided whether or not the automatic control odd number stage side clutch capacity (tqc1at) has been changed to the manual operation clutch capacity arithmetic operation value (tqc1tmt) already. If a negative decision is made at step S 41 , then the processing advances to step S 42 , at which Manual mode state tqc1at arithmetic operation is executed. At step S 42 , when the automatic control clutch capacity arithmetic operation value is changed to the manual operation clutch capacity, an arithmetic operation of tqc1at is executed so that the influence upon the vehicle body behavior may be minimized together with the even number stage side clutch capacity. 
     At step S 43 , it is decided whether or not tqc1at is equal to or higher than tqc1tmt. If a negative decision is made at step S 43 , then the processing advances to step S 44 , at which tqc1 is set to tqc1at. 
     If an affirmative decision is made at step S 41  or S 43 , then the processing advances to step S 45 , at which tqc1 is set to tqc1tmt, and then at next step S 46 , the tqc1at is set to tqc1mt. Thereafter, the processing advances to step S 47 . 
     At step S 47 , the Manual mode state tqc2 at arithmetic operation is executed. At step S 47 , basically the clutch capacity is set to a value equal to or smaller than a predetermined value (in the present embodiment, zero), and if the clutch capacity is equal to or greater than the predetermined value, then the clutch capacity arithmetic operation value is changed to the predetermined value. At this time, the arithmetic operation is executed so that the influence on the vehicle body behavior may be minimized together with the odd number stage side clutch capacity. Then, after tqc2 is set to tqc2at at step S 48 , the processing returns to B, thereby ending the series of control steps. 
     Returning to the decision at step S 40 , if a negative decision is made at step S 40 , then arithmetic operation similar to those at steps S 41  to S 48  described hereinabove is started in order beginning with the even number stage side clutch. 
     More particularly, if a negative decision is made at step S 40 , then the processing advances to step S 49 , at which it is decided whether or not the automatic control even number stage side clutch capacity (tqc2at) has changed to the manual operation clutch capacity arithmetic operation value (tqc1tmt). If a negative decision is made at step S 49 , then the processing advances to step S 50 , at which Manual mode state tqc2at arithmetic operation is executed. 
     Then at step S 51 , it is decided whether or not tqc2at≧tqc1tmt is satisfied. If a negative decision is made at step S 51 , then the processing advances to step S 52 , at which tqc2 is set to tqc2at. 
     If an affirmative decision is made at step S 49  or S 51 , then the processing advances to step S 53 , at which tqc2 is set to tqc1tmt, and then at step S 54 , tqc2at is set to tqc1tmt. Thereafter, the processing advances to step S 55 . 
     At step S 55 , Manual mode state tqc1at arithmetic operation is carried out. Then, tqc1 is set to tqc1at at step S 56 , and then the processing advances to B. 
     In the following, a flow of clutch control in various settings is described with reference to time charts. The time charts illustrated in  FIGS. 16 ,  17 ,  18 , and  19  include, in an upper half thereof, a table including a total of ten parameters and, in a lower half thereof, three graphs corresponding to the table. 
     The parameter table is configured from items of (a) to (j) give below. 
     (a) Target gear position (gptgt)=one of N, 1, 2, 3, 4, 5 and 6 
     (b) Gear position at present (gearpos)=one of N-N, 1-N, 1-2, N-2, 3-2, 3-N, 3-4, N-4, 5-4, 5-N, 5-6 and N-6 
     (c) Gear shift state=one of STOP (shift drum stopping), UP (shift up side feeding action proceeding) and DOWN (shift down action proceeding) 
     (d) Gear shift control mode (sftmode)=one of Auto (AT shift mode) and Manual (MT shift mode) 
     (e) Clutch control mode changeover SW (clmodsw)=ON or OFF (the switch is on only while the switch is depressed and indicates a changeover will to the clutch Manual mode) 
     (f) Clutch control mode (cltmode)=one of Auto mode, Temp. Manual mode and Manual mode 
     (g) Auto mode connection side clutch decision value (cltcont)=on/off of odd number stage side clutch or on/off of even number stage side clutch 
     (h) Manual operation clutch decision value (cntcltmt)=odd number stage side clutch or even number stage side clutch 
     (i) Odd number stage side clutch capacity output (tqc1)=tqc1 at or tqc1tmt 
     (j) Even number stage side clutch capacity output (tqc2)=tqc2 at or tqc1tmt 
     Meanwhile, the three graphs in the lower half of the time chart indicate the clutch operational amount sensor signal (vcltlevin) and clutch capacity, throttle opening, and engine speed and vehicle speed. In the graph of the clutch capacity sensor, the capacity output (tqc1) of the first clutch CL 1  is indicated by a thick line formed from slanting lines, and the capacity output (tqc2) of the second clutch CL 2  is indicated by a thick line formed from drawing dots. Meanwhile, the clutch operational amount sensor signal (vcltlevin) is indicated by an alternate long and short dashed line, and the manual operation clutch decision value (cntcltmt) is indicated by an alternate long and two short dashed line. Further, a numeral in a round mark in the time chart is represented, in the following description, by the numeral in parentheses like (1), (2) or (3). 
       FIG. 16  is a time chart illustrating a flow upon shifting to the first speed during operation in the second speed, whereafter re-acceleration is carried out. This time chart corresponds to a flow until, while, in a second speed operating state in which the Auto mode is applied to both of the gear shift control mode and the clutch control mode, a shift down operation to the first speed is started by gripping the clutch lever L during deceleration caused by turning off the throttle and a state in which re-acceleration by the first speed is possible is established in response to a clutch release operation by the occupant. 
     First, a rapid fully opening operation of the throttle is executed at time t 1  corresponding to (1) during steady operation at the second speed, and an engine brake begins to operate simultaneously. At this time, the gear position is N-2, the clutch control mode is Auto, the gear shift control mode is Auto, and the second clutch CL 2  is in a connected state. 
     Then, during dropping of the engine speed Ne and the vehicle speed V by this engine brake, a gripping operation of the clutch lever L is started. Then, when the clutch operation amount sensor signal (vcltlevin) becomes lower than the sensor effective voltage upper limit value at time t 2  corresponding to (2), the even number stage side clutch capacity output (tqc2) is changed over to the manual operation clutch capacity arithmetic operation amount (tqc1tmt). Then, the manual operation clutch capacity arithmetic operation amount (tqc1tmt) and the even number stage side clutch capacity output (tqc2) begin to decrease in an interlocking relationship with the movement of the clutch lever L. Further, also at the gear position controlled by the AT (Auto) mode, a shift down action from the “N-2” position to the “1-2” position is started. 
     In particular, in the flow described above, since the clutch lever is gripped and the even number stage side clutch is selected by the manual operation clutch decision, when the manual operation clutch capacity arithmetic operation amount (tqc1tmt) calculated from the clutch lever operation becomes lower than the even number stage side clutch capacity output (tqc2), the clutch control mode is changed over to the Temp mode. Further, when the clutch control mode is the Temp mode, since the even number stage side clutch capacity output (tqc2) exhibits the manual operation clutch capacity arithmetic operation amount (tqc1tmt), clutch capacity control by the clutch lever operation is enabled. 
     On the other hand, in a shift down action from the “N-2” position to the “1-2” position, the clutch lever is gripped during deceleration by an engine brake caused by an off state of the throttle, and the clutch control mode transits to the Temp mode. Further, when the shift control mode is Auto, in order to make it possible to select a gear suitable for re-acceleration, control of automatically selecting a gear position suitable for the vehicle speed V is executed. 
     Then at time t 3  corresponding to (3), in response to the gripping of the clutch lever L, the even number stage side clutch CL 2  is disconnected, and the engine speed Ne drops to an idling speed. Further, the engine brake is cancelled, and also the deceleration of the vehicle speed V is moderated. 
     Then at time t 4  corresponding to (4), the vehicle speed V becomes lower than a predetermined value a, which is prescribed in the shift map M, as a changeover vehicle speed from the second speed to the first speed when the throttle is off. In response to this, the target gear position changes over to the first speed, and as a result, the manual operation clutch decision value (cntcltmt) becomes the odd number stage side clutch. Consequently, the even number stage side clutch capacity output (tqc2) changes over to tqc2at, and simultaneously, the odd number stage side clutch capacity output (tqc1) changes over to the manual operation clutch capacity arithmetic operation amount (tqc1tmt). 
     Within a range indicated by (5), an operation of the clutch lever L to the connection side is carried out while the throttle is opened in order to re-accelerate the vehicle, and the odd number stage side clutch capacity output (tqc1) outputs the manual operation clutch capacity arithmetic operation amount (tqc1tmt). Consequently, clutch re-connection interlocked with the lever operation is executed. 
     Then, at time t 6  corresponding to (6), since the clutch lever L is released, the clutch control mode changes over to the Auto mode and the odd number stage side clutch capacity output (tqc1) outputs the automatic control odd number stage side clutch capacity arithmetic operation value (tqc1at). Further, at time t 6 , in response to the release of the clutch lever L, the clutch control mode returns to the Auto mode, and the gear position begins to be changed over to 1-N which is suitable for operation at the first speed. 
     According to the control method described above, if a clutch disconnection operation by the clutch lever L is carried out during a deceleration operation in which the auto mode is selected for the gear shift control mode, then shift down from the “N-2” position to the “1-2” position is automatically carried out in order to select a gear position suitable for the vehicle speed V. Consequently, when a clutch operation by the clutch lever L is carried out during a deceleration operation, it is determined that the occupant has a will to change over the driving force transmission gear to a speed lower by one stage. Thus, the change to the gear position at which the driving force transmission gear can be changed over to a stage lower by one state is executed, and it is possible to make preparations for the change of the gear position rapidly. 
       FIG. 17  is a time chart illustrating a flow when the clutch control mode is changed over during operation in a predetermined gear. First, in an initial state, the gear position is 1-N, the clutch control mode is Auto, the gear shift mode is Auto, and the twin clutch TCL is in a disconnected state and the vehicle is in a stopping state. 
     Then, at time t 10  corresponding to (1), the throttle opening TH exceeds a predetermined value, and connection of the first clutch CL 1  is started by automatically starting control based on the shift map M. Then, in the present embodiment, at time t 11  corresponding to (2), the clutch control mode changeover switch  118  is operated into an on state by the occupant. However, the clutch control mode maintains the auto mode. 
     More specifically, even if the clutch control mode changeover switch  118  is operated into an on state, if the clutch is in a half clutch state by the automatic starting control, then the AMT controlling unit  120  does not accept the operation of the clutch control mode changeover switch  118  and carries out notification by an indicator or the like. 
     Then, at time t 12 , the clutch connection by the automatic control is completed and the acceleration state by the first speed continues. Then, at time t 13  corresponding to (3), a shift timing in accordance with the shift map M is reached, and the target gear position changes over to the second speed. Consequently, a shift up action is started. 
     Then, at time t 14 , the change from the “1-N” position to the “1-2” position is completed, and a switching action of the clutch is started. In the present embodiment, at time t 15  after the clutch switching action is started, a switching on operation of the clutch control mode changeover switch  118  for the second time is carried out. However, also at this time, no change of the clutch control mode is carried out. 
     This is because, when the clutch is in a half clutch state by the automatic starting control, the setting that, even if the clutch control mode changeover switch  118  is operated into an on state, this operation is not accepted, is applied also to the clutch switching control. It is to be noted that, also in response to an operation of the clutch control mode changeover switch  118  upon clutch switching, notification by an indicator or the like may be carried out. 
     Thereafter, in the present graph, after the second clutch CL 2  is fully connected at time t 16  corresponding to (5), a switching on operation of the clutch control mode changeover switch  118  for the third time is carried out at time t 17  corresponding to (6). Since, at time t 17 , the clutch is in a fully connected state and is not in a half clutch state by the automatic control, the switching on operation of the clutch control mode changeover switch  118  is effective, and the clutch control mode changes over to the manual mode. Further, at time t 18 , the clutch control mode changes over to the auto mode in response to the switching on operation of the clutch control mode changeover switch  118  for the fourth time. 
     It is to be noted that, in the present embodiment, when the clutch control mode is changed over to the auto mode at time t 18 , the gear shift control mode remains in the manual mode. However, the gear shift control mode may otherwise be set such that it is changed over to the auto mode in an interlocking relationship with the clutch control mode. 
     According to the control method described above, even if the clutch control mode changeover switch  118  is operated into an on state, when the clutch is in a half clutch state by the automatic control, changeover of the clutch control mode is inhibited. Thus, it is possible to avoid such a situation that, in response to an operation of the clutch control mode changeover switch  118 , the clutch capacity varies suddenly to cause a variation in the driving force. 
     It is to be noted that, also in the time chart of  FIG. 17 , control for reducing the engine speed by fuel injection control or ignition control upon disconnection of the clutch is executed so that a smooth shift up action can be carried out without closing the throttle opening TH. 
       FIG. 18  is a time chart illustrating a flow when a clutch lever operation is carried out during operating in the auto mode. This time chart corresponds to a flow until, while a shift down operation to the first speed is carried out by gripping the clutch lever L in a second speed operating state in which the Auto mode is applied to both of the gear shift control mode and the clutch control mode, the second speed is restored in response to a clutch release operation by the occupant to continue operating the vehicle. 
     First, during steady operation at the second speed, a rapid fully closing operation of the throttle is executed at time t 30  corresponding to (1), and an engine brake begins to act simultaneously. At this time, the gear position is N-2, the clutch control mode is Auto, the gear shift control mode is Auto, and the second clutch CL 2  is in a connected state. 
     Then, while the engine speed Ne and the vehicle speed V are dropping by the engine brake, a gripping operation of the clutch lever L is started, and at time t 31  corresponding to (2), the clutch operation amount sensor signal (vcltlevin) becomes lower than the sensor effective voltage upper limit value. Thereupon, the manual operation clutch capacity arithmetic operation amount (tqc1tmt) and the even number stage side clutch capacity output (tqc2) begin to decrease and a shift down action from the “N-2” position to the “1-2” position is started in an interlocking relationship with the movement of the clutch lever L. At this time, the target gear position remains the second speed. 
     More specifically, in the flow described above, the clutch lever is gripped, and the odd number stage side clutch is selected by the manual operation clutch decision. Thus, when the manual operation clutch capacity arithmetic operation amount (tqc1tmt) calculated from the clutch lever operation becomes lower than the even number stage side clutch capacity output (tqc2), the clutch control mode changes over to the Temp mode. Further, when the clutch control mode is the Temp mode, the even number stage side clutch capacity output (tqc2) exhibits the manual operation clutch capacity arithmetic operation amount (tqc1tmt). Therefore, clutch capacity control by the clutch lever operation becomes possible. 
     Further, the shift down action from the “N-2” position to the “1-2” position is carried out because, when the clutch lever is gripped during deceleration by an engine brake arising from an off state of the throttle, the clutch control mode changes to the Temp mode, and in addition the shift control mode is Auto, control for establishing a gear position suitable for the vehicle speed in order to make it possible to select an appropriate gear for re-acceleration is executed. 
     Then, at time t 32  corresponding to (3), the even number stage side clutch CL 2  is disconnected as a result of the gripping of the clutch lever L. Consequently, the engine speed Ne drops to an idling speed. Further, the engine brake is canceled, and consequently, also the deceleration of the vehicle speed V is moderated. Then, at time t 33 , the shift down action from the “N-2” position to the “1-2” position is completed. 
     Then, within a range corresponding to (4), an operation of the clutch lever L to the connection side is carried out while the throttle is opened in order to carry out acceleration again. At this time, the AMT controlling unit  120  determines the clutch to be connected in response to the vehicle speed V. In particular, when the vehicle speed V is equal to or lower than a predetermined value, the first clutch CL 1  is connect to carry out a driving force transmission at the first speed. In contrast, as shown in the graph of  FIG. 18 , when the vehicle speed V is equal to or higher than the predetermined value a, the second clutch CL 2  is connected to carry out driving force transmission by the second speed same as that before the operation of the clutch lever L. The predetermined value a is set as a changeover vehicle speed from the second speed to the first speed when the throttle is in an off state during the automatic shift control to the shift map M. 
     Then, at time t 34  corresponding to (5), the clutch lever L is opened. Consequently, the clutch control mode changes over to the Auto mode, and the even number stage side clutch capacity output (tqc2) outputs the automatic control odd number stage side clutch capacity arithmetic operation value (tqc1at). Further, at time t 35 , the clutch lever L is released, and thereupon, the changeover to the “N-2” position suitable for second speed operation is completed. 
     According to the control method described above, when a clutch disconnection operation by the clutch lever L is carried out during a deceleration operation in which the auto mode is selected for the gear shift control mode, shift down from the “N-2” position to the “1-2” position is automatically carried out in order to select a gear position suitable for the vehicle speed V. However, when the deceleration degree is low, it is possible to re-connect the shift gear before the shift down. Consequently, shift control in which the driving force variation is suppressed can be executed in various operating stages. 
       FIG. 19  is a time chart illustrating a clutch re-connection action when a clutch operation is carried out during deceleration by the third speed gear. This time chart corresponds to a flow after the clutch lever L is operated during deceleration in response to an off state of the throttle in a third-speed operating state in which the Auto mode is applied to both of the gear shift control mode and the clutch control mode until operating at the second speed becomes possible in response to a clutch release operation by the occupant. In the present embodiment, starting of a shift down action is set so as to be carried out later than an operation of the clutch lever L. 
     First, during a deceleration operation in the third speed, the gear position is 3-N, the clutch control mode is Auto, the gear shift mode is Auto, and the second clutch CL 2  is in a connected state. Then, if an operation of gripping the clutch lever L is started at time t 40 , then the AMT controlling unit  120  can be set so that, at step t 41  which is a timing earlier than that at a vehicle speed at which the gear position changes to the second speed in the ordinary Auto mode, the gear position is shifted down from the “3-N” position to the “3-2” position. 
     Then, in the example of the graph of  FIG. 19 , re-connection of the clutch by an operation of the clutch lever L is started at time t 43 . At this time, the AMT controlling unit  120  changes over the clutch to be connected in response to whether re-connection of the clutch is started before or after time t 42 . In particular, if re-connection of the clutch is started later than time t 42  at which the vehicle speed V reaches a predetermined value V 1 , then the even number stage side clutch CL 2  is connected to start transmission of the driving force at the second speed. In contrast, if re-connection of the clutch is started prior to time t 42 , then the odd number stage side clutch CL 1  is connected to start transmission of the driving power at the third speed. 
     In the present embodiment, since a re-connection action by the clutch lever L is started at time t 43  later than time t 42 , the even number stage side clutch CL 2  is connected to start the transmission of the driving power in the second speed. Then, at a point in time at which the engine brake at the second speed which increases as a result of clutch connection, namely, negative engine driving force, becomes equal to the engine brake Ta, the connection speed of the even number stage side clutch is lowered irrespective of the release speed of the clutch lever L. This is a characteristic of the twin clutch controlling apparatus of the present embodiment. 
     More particularly, if the connection action of the even number stage side clutch CL 2  started at time t 43  is carried out in response to the clutch operation amount sensor signal (vcltlevin), then the variation to a second-speed engine brake Tb becomes sudden as indicated by a broken line C. Therefore, the clutch capacity at the beginning of re-connection is adjusted so as to become equal to a third speed engine brake, and then the clutch capacity is gradually increased from the adjusted value thereby to moderate the variation of the driving force to achieve a smooth shift down action. Thereafter, at time t 45 , the even number stage side clutch CL 2  is fully connected, and at time t 46 , the gear position is changed to the “N-2” position so that operation in the second speed continues. 
     As described above, the twin clutch controlling apparatus according to the present invention is configured such that, if the clutch lever L is operated during a deceleration operation in which the auto mode is selected, then a shift down action from a gear position (“N-2” or the like) at which driving force transmission can be carried out by only one of the odd number stage side clutch CL 1  and the even number stage side clutch CL 2  to another gear position (“1-2” or the like) at which the shift gear for transmitting driving force is switched in response to switching control of the clutch is carried out in response to an operation of the clutch lever L. Therefore, when a clutch operation by the clutch lever L is carried out during a deceleration operation, it is decided that the occupant has a will to change over the driving force transmission gear to a gear position lower by one stage. Then, a change of a gear position at which the driving force transmission gear is changed over to a gear position lower by one stage can be executed to rapidly make preparations. 
     It is to be noted that the shape and the structure of the twin clutch, multi-speed transmission and engine, the configuration of the control apparatus, the configuration of the manual operation means for the clutch and so forth are not limited to those of the embodiment described above, but various alterations are possible. The twin clutch controlling apparatus according to the present invention can be applied not only to a motorcycle but also to various vehicles such as three/four-wheeled vehicles of the saddle type and so forth. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.