Patent Publication Number: US-8983744-B2

Title: Automatic shift apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2013-017261, filed on Jan. 31, 2013, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure generally relates to an automatic shift apparatus. 
     BACKGROUND DISCUSSION 
     An automatic shift apparatus disclosed in JP2012-225436A, hereinafter referred to as Reference 1, for example, includes a first clutch ring, a second clutch ring, a sleeve arranged between the first clutch ring and the second clutch ring to be movable in an axial direction, a shaft moving apparatus for moving the sleeve in the axial direction, and a control unit driving the shaft moving apparatus. The first clutch ring and the second clutch ring are fixed gears. The sleeve is a movable gear. The control unit controls the sleeve, which is in an engaged state with the first clutch ring by a dog clutch portion of the sleeve and a dog clutch portion of the first clutch ring being engaged, to move toward a neutral position defined at a position between the first clutch ring and the second clutch ring. More specifically, the sleeve is made to stop at the neutral position by exerting a force in the opposite direction relative to a direction of movement of the sleeve after the dog clutch portions of the sleeve and the first clutch ring are disengaged. 
     In recent years, automatic shift apparatuses with a separation distance reduced between the first clutch ring and the second clutch ring are developed. In the automatic shift apparatus disclosed in Reference 1, in a state where a mechanism includes looseness, the sleeve may contact the second clutch ring by swinging movement in the axial direction at a time at which movement of the sleeve is made to stop at the neutral position. In a state where rotational speed of the second clutch ring is high, a shift shock and a contact noise are generated as a result of the sleeve making contact with the second clutch ring, which are considered as disadvantages. The sleeve making contact with the second clutch ring may be avoided by moving the sleeve in a low speed, however, a shift time becomes longer, which is considered as a disadvantage. 
     A need thus exists for an automatic shift apparatus, which is not susceptible to the drawbacks mentioned above. 
     SUMMARY 
     An automatic shift apparatus includes a rotation shaft axially supported to be rotatable about an axis of the rotation shaft, the rotation shaft configured to be in rotary engagement with one of an input shaft and an output shaft of the automatic shift apparatus, a dog clutch gear shift mechanism including a first clutch ring and a second clutch ring supported on the rotation shaft to be rotatable about the rotation shaft, the first clutch ring providing a first gear ratio, the first clutch ring configured to be in rotary engagement with the other one of the input shaft and the output shaft, the second clutch ring providing a second gear ratio, the second clutch ring configured to be in rotary engagement with the other one of the input shaft and the output shaft, a hub fixed on the rotation shaft at a position between the first clutch ring and the second clutch ring, the position adjacent to the first clutch ring and the second clutch ring, a sleeve fitted to the hub, the sleeve restrained from rotating relative to the hub, the sleeve allowed to move in a direction of the axis of the rotation shaft, a first dog clutch portion protrudingly arranged on a side of the first clutch ring in a direction of the sleeve and a second dog clutch portion protrudingly arranged on a side of the second clutch ring in a direction of the sleeve, the first dog clutch portion and the second dog clutch portion selectively meshing with a spline formed on the sleeve in response to axial movement of the sleeve, a shaft moving apparatus moving the sleeve in the direction of the axis of the rotation shaft, and a sensor detecting a position of the sleeve in accordance with movement of the sleeve in the direction of the axis of the rotation shaft, and a control unit controlling an operation of the shaft moving apparatus based on a detected position of the sleeve detected by the sensor. The control unit controls first moving speed to be faster than second moving speed on moving the sleeve in an engaged state engaged with one of the first clutch ring and the second clutch ring to a neutral position defined at a position between the first clutch ring and the second clutch ring where the first moving speed is a speed of moving the sleeve in the engaged state to a target position defined between the neutral position and the mentioned one of the first clutch ring and the second clutch ring the sleeve is engaged with and where the second moving speed is a speed of moving the sleeve from the target position to the neutral position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic drawing illustrating components of a vehicle including an automatic shift apparatus according to an embodiment; 
         FIG. 2  is a skeleton drawing illustrating components of the automatic shift apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a drawing illustrating components of the automatic shift apparatus illustrated in  FIG. 2  in part in detail; 
         FIG. 4  is a perspective view drawing illustrating a first gear, a clutch hub, and a sleeve forming a dog clutch gear shift mechanism illustrated in  FIG. 2 ; 
         FIG. 5A  is a plan view drawing illustrating the first gear illustrated in  FIG. 4 ; 
         FIG. 5B  is a side view drawing illustrating the first gear illustrated in  FIG. 4 ; 
         FIG. 6  is a plan view drawing illustrating the clutch hub illustrated in  FIG. 4 ; 
         FIG. 7  is a plan view drawing illustrating the sleeve illustrated in  FIG. 4 ; 
         FIG. 8A  is a cross-sectional drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  in a state where the dog clutch gear shift mechanism is before shifted; 
         FIG. 8B  is a cross-sectional drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where a high tooth has come into contact with a clutch front tooth; 
         FIG. 8C  is a cross-sectional drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where each of the high tooth and a low tooth has come into contact with a clutch rear tooth; 
         FIG. 8D  is a cross-sectional drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where each of the high tooth and the low tooth has meshed with the clutch rear tooth; 
         FIG. 9A  is an expanded drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where the high tooth has come into contact with the clutch front tooth; 
         FIG. 9B  is an expanded drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where the high tooth has come into contact with a slanted surface of the clutch front tooth; 
         FIG. 9C  is an expanded drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where each of the high tooth and the low tooth has come into contact with a contact surface of the clutch rear tooth; 
         FIG. 9D  is an expanded drawing illustrating the dog clutch gear shift mechanism illustrated in  FIG. 4  illustrating a state where each of the high tooth and the low tooth has meshed with the clutch rear tooth; 
         FIG. 10A  is a drawing illustrating an operation at a second gear on gear shift from second speed to third speed controlled by a shift control unit; 
         FIG. 10B  is a drawing illustrating an operation at a third counter gear on gear shift from second speed to third speed controlled by the shift control unit; 
         FIG. 11  is a drawing illustrating a sleeve disengagement operation controlled by the shift control unit; 
         FIG. 12  is a block diagram illustrating functional portions of the shift control unit; 
         FIG. 13  is a main flow chart illustrating an overall process of moving the sleeve controlled by the shift control unit; 
         FIG. 14  is a flow chart illustrating a process of disengaging the sleeve controlled by the shift control unit, the process referred to as a disengagement control; 
         FIG. 15  is a flow chart illustrating a process of initially moving the sleeve controlled by the shift control unit, the process referred to as an initial feedback control; 
         FIG. 16  is a flow chart illustrating a process of terminally moving the sleeve controlled by the shift control unit, the process referred to as a terminal feed back control; 
         FIG. 17  is a flow chart illustrating a process of maintaining the sleeve in an idle state controlled by the shift control unit, the process referred to as an idle control; 
         FIG. 18  is a flow chart illustrating a process of disengaging a separate sleeve controlled by the shift control unit; and 
         FIG. 19  is a drawing illustrating sleeve position and change of electric current supplied to a linear actuator with elapse of time during a period during which the sleeve moves controlled by the shift control unit. 
     
    
    
     DETAILED DESCRIPTION 
     An automatic shift apparatus  13  according to an embodiment will be described. First, components of a vehicle M including the automatic shift apparatus  13  according to the embodiment will be described referring to  FIG. 1 . The vehicle M includes components, for example, an engine  11 , a clutch  12 , the automatic shift apparatus  13 , a differential apparatus  14 , a control system  15 , and driving wheels Wfl, Wfr, which are left and right front wheels. 
     The engine  11  is an apparatus generating a driving force by combustion of fuel. The driving force from the engine  11  is transmitted to the driving wheels Wfl, Wfr via the clutch  12 , the automatic shift apparatus  13 , and the differential apparatus  14 . In other words, the vehicle M is a vehicle generally referred to as an FF vehicle. The clutch  12  is arranged to automatically connect and disconnect in response to commands from the control system  15 . The automatic shift apparatus  13  automatically selects a gear position from, for example, six positions for forward movement and one position for rearward movement. The differential apparatus  14  includes each of a final gear and a differential gear as components. The differential apparatus  14  is integrally formed with the automatic shift apparatus  13 . 
     Second, components of the automatic shift apparatus  13  will be described. As  FIG. 2  illustrates, the automatic shift apparatus  13  includes, for example, a casing  21 , a drive shaft  22 , a main shaft  23 , a counter shaft  24 , dog clutch gear shift mechanisms  251 ,  252 ,  253 ,  254 , and a shift control unit  26 . The shift control unit  26  is included in the control system  15 . The shift control unit  26  serves as the control unit. Exemplary components of the casing  21  are a main body  21   a  formed in substantially a hollow cylinder, a first wall  21   b , and a second wall  21   c . Each of the first wall  21   b  and the second wall  21   c  partitions a space inside the main body  21   a  into leftward-rightward spaces relative to the first wall  21   b  and the second wall  21   c , where leftward and rightward refer to leftward and rightward in  FIG. 2 . 
     The drive shaft  22  and the main shaft  23  are coaxially arranged. The counter shaft  24  is arranged parallel to the drive shaft  22  and the main shaft  23 . The drive shaft  22 , the main shaft  23 , and the counter shaft  24  are supported on the casing  21  to be rotatable. More specifically, one end of the drive shaft  22 , which is leftward end in  FIG. 2 , is in rotary engagement with an output shaft of the engine  11  via the clutch  12 . The other end of the drive shaft  22 , which is rightward end in  FIG. 2 , is supported with a bearing  271  on the first wall  21   b . As a result, an output from the engine  11  is inputted to the drive shaft  22  while the clutch  12  is connected. 
     One end of the main shaft  23 , which is leftward end in  FIG. 2 , is axially supported on the mentioned other end of the drive shaft  22 , which is rightward end in  FIG. 2 , to be rotatable via the dog clutch gear shift mechanism  251  in a state where the mentioned one end of the main shaft  23  may be in rotary engagement with the mentioned other end of the drive shaft  22 . The dog clutch gear shift mechanism  251  will be described later. The other end of the main shaft  23 , which is rightward end in  FIG. 2 , is supported with a bearing  272  on the second wall  21   c . The main shaft  23  serves as the rotation shaft. The counter shaft  24  may serve as the rotation shaft. One end of the counter shaft  24 , which is leftward end in  FIG. 2 , is supported with a bearing  273  on the first wall  21   b . The other end of the counter shaft  24 , which is rightward end in  FIG. 2 , is supported with a bearing  274  on the second wall  21   c.    
     In order from a direction where the clutch  12  is positioned, the main shaft  23  is arranged with the dog clutch gear shift mechanism  251 , which shifts gears into fifth speed or into reverse, and the dog clutch gear shift mechanism  252 , which shifts gears into second speed or into first speed. In order from the direction where the clutch  12  is positioned, the counter shaft  24  is arranged with the dog clutch gear shift mechanism  253 , which shifts gears into fourth speed or into third speed, and the dog clutch gear shift mechanism  254 , which shifts gears into sixth speed. The dog clutch gear shift mechanisms  251 ,  252 ,  253 ,  254  are provided with gears  281 ,  282 ,  283 ,  284 ,  285 ,  286 ,  28 R for shifting into different speeds, each of which will be described later. 
     Rotational center of a fifth gear  285  is fixed on the mentioned other end of the drive shaft  22 , which is rightward end in  FIG. 2 , for example, by spline fitting. In order from the direction where the clutch  12  is positioned, the main shaft  23  is arranged with a reverse gear  28 R, a fourth gear  284 , a third gear  283 , a second gear  282 , a first gear  281 , and a sixth gear  286 . The reverse gear  28 R is rotatably supported on the main shaft  23 . The fourth gear  284  is fixed on the main shaft  23 , for example, by spline fitting at rotational center of the fourth gear  284 . The third gear  283  is fixed on the main shaft  23 , for example, by spline fitting at rotational center of the third gear  283 . The second gear  282  is rotatably supported on the main shaft  23 . The first gear  281  is rotatably supported on the main shaft  23 . The sixth gear  286  is fixed on the main shaft  23 , for example, by spline fitting at rotational center of the sixth gear  286 . 
     In order from the direction where the clutch  12  is positioned, the counter shaft  24  is arranged with a fifth counter gear  295 , a reverse counter gear  29 R, a fourth counter gear  294 , a third counter gear  293 , a second counter gear  292 , a first counter gear  291 , and a sixth counter gear  296 . The fifth counter gear  295  is a gear that meshes with the fifth gear  285 . The fifth counter gear  295  is fixed on the counter shaft  24 , for example, by spline fitting at rotational center of the fifth counter gear  295 . The reverse counter gear  29 R is a gear that meshes with the reverse gear  28 R via a gear  29   r . The reverse counter gear  29 R is fixed on the counter shaft  24 , for example, by spline fitting at rotational center of the reverse counter gear  29 R. The fourth counter gear  294  is a gear that meshes with the fourth gear  284 . The fourth counter gear  294  is rotatably supported on the counter shaft  24 . The third counter gear  293  is a gear that meshes with the third gear  283 . The third counter gear  293  is rotatably supported on the counter shaft  24 . The second counter gear  292  is a gear that meshes with the second gear  282 . The second counter gear  292  is fixed on the counter shaft  24 , for example, by spline fitting at rotational center of the second counter gear  292 . The first counter gear  291  is a gear that meshes with the first gear  281 . The first counter gear  291  is fixed on the counter shaft  24 , for example, by spline fitting at rotational center of the first counter gear  291 . The sixth counter gear  296  is a gear that meshes with the sixth gear  286 . The sixth counter gear  296  is rotatably supported on the counter shaft  24 . On an outer peripheral surface of the first gear  281  and on an outer peripheral surface of the first counter gear  291 , gears, more specifically helical gears, meshing with each other are formed. Gears are similarly formed between other gears meshing with each other. 
     As  FIG. 3  illustrates, the dog clutch gear shift mechanism  252  includes, as exemplary components, the first gear  281 , which serves as a first clutch ring, the second gear  282 , which serves as a second clutch ring, a clutch hub  311 , which serves as a hub, a sleeve  312 , a shaft moving apparatus  313 , and a position detection sensor  314 , which serves as a sensor. The dog clutch gear shift mechanism  253 , which serves as a separate dog clutch gear shift mechanism, includes, as exemplary components, the third counter gear  293  and the fourth counter gear  294 , each of which serves as a separate clutch ring, a clutch hub  321 , which serves as a separate hub, a sleeve  322 , which serves as a separate sleeve, a shaft moving apparatus  323 , which serves as a separate shaft moving apparatus, and a position detection sensor  324 , which serves as a separate sensor. The dog clutch gear shift mechanism  251 , which serves as the separate dog clutch gear shift mechanism, is composed similarly to the dog clutch gear shift mechanism  253 . Each of the reverse gear  28 R and the fifth gear  285  in the dog clutch gear shift mechanism  251  serves as the separate clutch ring. The dog clutch gear shift mechanism  254 , which serves as the separate dog clutch gear shift mechanism, includes the sixth counter gear  296  alone, the sixth counter gear  296  that serves as the separate clutch ring that serves similarly to the first clutch ring in the dog clutch gear shift mechanism  252 . The dog clutch gear shift mechanism  254  does not include a component that serves similarly to the second clutch ring in the dog clutch gear shift mechanism  252 . An arrangement of the dog clutch gear shift mechanism  252  will be described in detail next. 
     The clutch hub  311  is fixed on the main shaft  23 , for example, by spline fitting at a position between the first gear  281  and the second gear  282 , the position adjacent to the first gear  281  and the second gear  282 . On a side surface of the first gear  281 , the surface in a direction of the clutch hub  311 , a first dog clutch portion  281   a  is formed. The first dog clutch portion  281   a  engages with a spline  312   a  formed on the sleeve  312 , which is illustrated in  FIG. 4 . Similarly, on a side surface of the second gear  282 , the surface in a direction of the clutch hub  311 , a second dog clutch portion  282   a  is formed. The second dog clutch portion  282   a  engages with the spline  312   a  formed on the sleeve  312 . The first dog clutch portion  281   a  of the first gear  281  and the second dog clutch portion  282   a  of the second gear  282  are identically formed. Accordingly, the first gear  281 , the clutch hub  311 , and the sleeve  312  are selected for description in detail referring to  FIGS. 4 to 7 . 
     As  FIG. 4 ,  FIG. 5A , and  FIG. 5B  illustrate, the first dog clutch portion  281   a  includes a protruding portion  281   a   1 , two clutch front teeth  281   b   1 , and clutch rear teeth  281   c   1 . The protruding portion  281   a   1  is formed in a ring form. The clutch front teeth  281   b   1  are arranged on an outer peripheral portion of the protruding portion  281   a   1  at 180 degrees interval. The clutch rear teeth  281   c   1  are arranged on the outer peripheral portion of the protruding portion  281   a   1  between the two clutch front teeth  281   b   1 . More specifically, five clutch rear teeth  281   c   1  are arranged at equally distanced intervals between the two clutch front teeth  281   b   1  in each circumferential direction. The clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1  are formed on the outer peripheral portion of the protruding portion  281   a   1  separated by a clutch tooth recess  281   d   1  between each of the clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1 . Each of the clutch teeth recesses  281   d   1  is provided with a unique width in the circumferential direction. 
     The protruding portion  281   a   1  is formed such that the outer diameter of the protruding portion  281   a   1  is smaller than the inner diameter of high teeth  312   a   1  of the spline  312   a . The clutch front teeth  281   b   1  are formed such that the outer diameter of the clutch front teeth  281   b   1  is larger than the inner diameter of the high teeth  312   a   1  of the spline  312   a  and is smaller than the inner diameter of low teeth  312   b   1  of the spline  312   a . The clutch rear teeth  281   c   1  are formed to be engageable with spline tooth recesses  312   c   1  of the spline  312   a . In other words, the clutch front teeth  281   b   1  are formed not to mesh with the low teeth  312   b   1  and formed to be able to mesh with the high teeth  312   a   1 . The clutch rear teeth  281   c   1  are formed to be able to mesh with the high teeth  312   a   1  and the low teeth  312   b   1 . 
     Number of the clutch front teeth  281   b   1  formed equals the number of the high teeth  312   a   1  formed. In the automatic shift apparatus  13  according to the embodiment, two clutch front teeth  281   b   1  are formed and equally two high teeth  312   a   1  are formed. The clutch front teeth  281   b   1  are formed short so that two high teeth  312   a   1  may easily make entry into a space between two clutch front teeth  281   b   1  even in a state where rotational speed difference between the sleeve  312  and the first gear  281  is large. Each of the clutch front teeth  281   b   1  is formed to extend from a front end surface  281   a   2  of the protruding portion  281   a   1  to a rear end position Pe of the first dog clutch portion  281   a . Each of the clutch front teeth  281   b   1  extends at a position corresponding to the high tooth  312   a   1 . Each of the clutch rear teeth  281   c   1  is formed to extend from a position recessed from the front end surface  281   a   2  of the protruding portion  281   a   1  by a first predetermined amount d1 to the rear end position Pe of the first dog clutch portion  281   a.    
     A contact surface  281   b   4  that may make contact with the high teeth  312   a   1  is formed at a front end portion of each of the clutch front teeth  281   b   1 , the front end portion facing the high tooth  312   a   1 . Furthermore, from each side in the circumferential direction of the contact surface  281   b   4 , a slanted surface  281   b   2  slanting toward the rear end position Pe of the first dog clutch portion  281   a  is formed. The contact surface  281   b   4  of the clutch front tooth  281   b   1  is formed on a same plane as the front end surface  281   a   2  of the protruding portion  281   a   1  or, alternatively, on a plane parallel to the front end surface  281   a   2  of the protruding portion  281   a   1 . 
     A contact surface  281   c   2  that may make contact with the high teeth  312   a   1  and the low teeth  312   b   1  is formed on each of the clutch rear teeth  281   c   1 . Furthermore, a side slanted surface  281   c   4  is formed to extend from each side in the circumferential direction of the contact surface  281   c   2  to each of side surfaces  281   c   3  of the clutch rear tooth  281   c   1 . The slanted surface  281   b   2  of the clutch front tooth  281   b   1  and a side surface  281   b   3  of the clutch front tooth  281   b   1  intersect at a position Pc. The slanted surface  281   b   2  of the clutch front tooth  281   b   1  is formed so that the position Pc is defined at a position in a direction of the front end surface  281   a   2  of the protruding portion  281   a   1  relative to the contact surface  281   c   2  of the clutch rear tooth  281   c   1 . Portions where the contact surface  281   b   4  at the front end portion of the clutch front tooth  281   b  and the slanted surfaces  281   b   2  intersect are chamfered and rounded in a typical R-form. 
     As  FIGS. 4 and 6  illustrate, a spline  311   a  is formed on an outer peripheral surface of the clutch hub  311 . The spline  312   a  is formed on an inner peripheral surface of the sleeve  312 . The spline  311   a  engages with the spline  312   a  to be slidable in the direction of the axis of the main shaft  23 . The spline  311   a  is formed with a multiple number of recesses  311   a   1 , for example, two recesses  311   a   1 , having recessed deeper than the rest of the recesses. The mentioned multiple number of recesses  311   a   1  are recesses corresponding to a multiple number of high teeth  312   a   1 . 
     As  FIGS. 4 and 7  illustrate, the sleeve  312  is formed in a ring form. The sleeve  312  integrally rotates with the clutch hub  311 . Furthermore, the sleeve  312  is arranged to be slidable in an axial direction relative to the clutch hub  311 . The spline  312   a  is formed on an inner peripheral surface of the sleeve  312 . The spline  312   a  engages with the spline  311   a  formed on the outer peripheral surface of the clutch hub  311  to be slidable in the axial direction. 
     The spline  312   a  is formed with a multiple number of high teeth  312   a   1 , for example, two high teeth  312   a   1 , protruding higher than the rest of low teeth  312   b   1 , Edge portions of each of the high teeth  312   a   1  and each of the low teeth  312   b   1 , which are the edge portions at the front end surface in the direction of the first gear  281 , are chamfered in 45 degrees angle to form a typical C-form in order to protect the high teeth  312   a   1  and the low teeth  312   b   1  from being damaged by a shock at a time at which the high teeth  312   a   1  and the low teeth  312   b   1  make contact with the clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1 . Furthermore, on an outer peripheral surface of the sleeve  312 , an outer peripheral recess  312   d  is formed in a direction conforming to a circumferential direction of the sleeve  312 . An arc form portion at an end of the fork  313   a  engages with the outer peripheral recess  312   d  to be slidable in the circumferential direction. 
     As  FIG. 3  illustrates, the shaft moving apparatus  313  is an apparatus making the sleeve  312  to move back and forth in a direction that conforms to the axial direction of the sleeve  312 . The shaft moving apparatus  313  is arranged such that the shaft moving apparatus  313  allows the sleeve  312  to move by a reaction force exerted from the first gear  281  or the second gear  282  at a time at which the sleeve  312  is pushed on the first gear  281  or the second gear  282 . The shaft moving apparatus  323  is similarly arranged. 
     The shaft moving apparatus  313  includes, as exemplary components, a fork  313   a , a fork shaft  313   b , a detent mechanism  313   c , and a linear actuator  313   d . Similarly, the shaft moving apparatus  323  includes, as exemplary components, a fork  323   a , a fork shaft  323   b , a detent mechanism  323   c , and a linear actuator  323   d . The shaft moving apparatus  313  will be described in detail next. 
     An end portion of the fork  313   a  is formed to fit to an outer peripheral form of the outer peripheral recess  312   d  of the sleeve  312 . A base end portion of the fork  313   a  is fixed on the fork shaft  313   b . The fork shaft  313   b  is supported on the casing  21  to be slidable in a direction conforming to the axial direction of the fork shaft  313   b . More specifically, one end of the fork shaft  313   b , which is rightward end in  FIG. 3 , is supported with a bearing  313   e  on the second wall  21   c . The other end of the fork shaft  313   b , which is leftward end in  FIG. 3 , is fixed on a bracket  313   f . The bracket  313   f  is arranged to be slidable on a guide member  313   g  protruding from the first wall  21   b  in the axial direction of the fork shaft  313   b . The guide member  313   g  is a member that restrains the bracket  313   f  from rotating. At the same time, the bracket  313   f  is fixed on a nut member  313   h  in a state where the bracket  313   f  is restrained from rotating relative to the nut member  313   h . The nut member  313   h  is threadably mounted on a driving shaft  313   i  to be movable, the driving shaft  313   i  including the linear actuator  313   d . The driving shaft  313   i  supported with a bearing  313   j  on the first wall  21   b.    
     The detent mechanism  313   c  is a mechanism that controls position of the sleeve  312  by controlling slide position of the fork shaft  313   b  in the axial direction. The detent mechanism  313   c  includes a stopper  313   c   1 , which is biased in a perpendicular direction relative to an axis of the fork shaft  313   b  by a spring. The stopper  313   c   1  fits into triangular grooves s1, sn, s2 formed on the fork shaft  313   b  by a spring force so that the detent mechanism  313   c  may control slide position of the fork shaft  313   b  in the axial direction. 
     More specifically, the stopper  313   c   1  fits into the triangular groove s1 when the spline  312   a  of the sleeve  312  and the first dog clutch portion  281   a  of the first gear  281  are engaged. The stopper  313   c   1  fits into the triangular groove sn when the sleeve  312  is positioned at a neutral position Na. The neutral position Na, which is illustrated in  FIG. 10A , is defined at a position in an intermediate portion between the first gear  281  and the second gear  282 . The stopper  313   c   1  fits into the triangular groove s2 when the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  are engaged. 
     An exemplary type of a linear actuator  313   d  is a ball screw type linear actuator. The linear actuator  313   d , as exemplary components, includes a casing, a rotor, a driving shaft  313   i , and a nut member  313   h . The casing is formed in a hollow cylinder and includes a multiple number of coils serving as a stator arranged in a direction of the inner circumference of the casing. The rotor is arranged relative to the stator to be rotatable. The rotor includes a multiple number of N-pole magnets and a multiple number of S-pole magnets alternately arranged on the outer periphery of the rotor. The magnets are arranged to face the stator with a magnetic clearance defined between the magnets and the stator. The driving shaft  313   i , which is a ball screw shaft, integrally rotates with the rotor with rotational axis of the stator as rotational center. The nut member  313   h  includes a ball nut to be threadably mounted on the driving shaft  313   i.    
     The driving shaft  313   i  is screwed into the nut member  313   h  to be rotatable relative to the nut member  313   h  via a multiple number of balls. By controlling electricity supply to each coil of the stator, the driving shaft  313   i  rotates in positive direction or negative direction, whichever selected. Accordingly, the nut member  313   h  and the fork shaft  313   b  are moved back and forth on the driving shaft  313   i  and are retained at a selected position. Furthermore, in the linear actuator  313   d , a long lead is formed on the driving shaft  313   i  so that the sleeve  312  is allowed to move by a reaction force from the first gear  281  or the second gear  282 . As a result, for example, the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  may be reliably put into engagement. 
     In the automatic shift apparatus  13  according to the embodiment, the linear actuator  313   d  is a ball screw type linear actuator. Nevertheless, the linear actuator  313   d  may be replaced by other types of an actuator, for example, a solenoid type actuator or an oil pressure type actuator, on condition that the actuator is arranged such that the actuator allows movement of the sleeve  312  by a reaction force from the first gear  281  or the second gear  282  while the sleeve  312  is pushed on the first gear  281  or the second gear  282 . The position detection sensor  314  is a sensor for detecting position of the sleeve  312  while the sleeve  312  is operated to move. The position detection sensor  314  uses various types of position sensor, for example, an optical position sensor and a linear encoder. 
     Third, an operation of the dog clutch gear shift mechanism  252  will be described. More specifically, operations of the high teeth  312   a   1  and the low teeth  312   b   1  of the sleeve  312  and of clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1  of the first gear  281  will be described referring to  FIGS. 8A through 8D  and  FIGS. 9A through 9D . In a case where, for example, the sleeve  312  is meshed with the second gear  282  and is rotating in high speed and the first gear is rotating in low speed, a speed of the sleeve  312  decreases when the sleeve  312  is shifted to mesh with the first gear  281 . On the other hand, in a case where the sleeve  312  is meshed with the first gear and is rotating in low speed and the second gear  282  is rotating in high speed, the speed of the sleeve  312  increases when the sleeve  312  is shifted to mesh with the second gear  282 . An operation where the speed of the sleeve  312  decreases will be described. 
     As  FIG. 8A  illustrates, the sleeve  312  is at a distance from the first gear  281  with a clearance between the sleeve  312  and the first gear  281  before the automatic shift apparatus  13  initiates shifting operation. When the shaft moving apparatus  313  moves the sleeve  312  in the axial direction toward the first gear  281 , front end surfaces  312   a   2  of the high teeth  312   a   1  come into contact with the contact surfaces  281   b   4  of the clutch front teeth  281   b   1 . At this moment, nothing is in contact with the low teeth  312   b   1 . As a result, the speed of the sleeve  312  slightly decreases. 
     When the shaft moving apparatus  313  further moves the sleeve  312  in the axial direction, as  FIG. 9B  illustrates, the front end surfaces  312   a   2  of the high teeth  312   a   1 , which are chamfered portions, make contact with the slanted surfaces  281   b   2  of the clutch front teeth  281   b   1 . At this moment, nothing is in contact with the low teeth  312   b   1 . As a result, the speed of the sleeve  312  significantly decreases. 
     When the shaft moving apparatus  313  moves the sleeve  312  more in the axial direction, as  FIGS. 8C and 9C  illustrate, the front end surfaces  312   a   2  of the high teeth  312   a   1  and the front end surfaces  312   b   2  of the low teeth  312   b   1  make contact with the contact surfaces  281   c   2  of the clutch rear teeth  281   c   1 . As a result, the speed of the sleeve  312  slightly decreases. 
     When the shaft moving apparatus  313  further moves the sleeve  312  in the axial direction, the front end surfaces  312   a   2  of the high teeth  312   a   1 , which are chamfered portions, and the front end surfaces  312   b   2  of the low teeth  312   b   1 , which are chamfered portions, make contact with the side slanted surfaces  281   c   4  of the clutch rear teeth  281   c   1 . Each of the high teeth  312   a   1  and the low teeth  312   b   1  may enter nearby clutch tooth recess  281   d   1  in a short period of time because the clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1  are formed spaced apart on the outer peripheral portion of the protruding portion  281   a   1  by the clutch teeth recess  281   d   1  having a unique width formed between each of the clutch front teeth  281   b   1  and the clutch rear teeth  281   c   1 . As a result, the speed of the sleeve  312  significantly decreases. 
     When the shaft moving apparatus  313  moves the sleeve  312  more in the axial direction, as  FIGS. 8D and 9D  illustrate, the high teeth  312   a   1  and the low teeth  312   b   1  completely mesh with the clutch rear teeth  281   c   1 . As a result, the sleeve  312  and the first gear  281  synchronously rotate and the shift operation ends. 
     Fourth, a control operation by the shift control unit  26  will be described. More specifically a control operation by the shift control unit  26  when shifting from second speed to third speed will be described. As  FIG. 10A  illustrates, the shift control unit  26  controls the shaft moving apparatus  313  to move the sleeve  312  that is in an engaged state engaged with the second gear  282  to the neutral position Na, which is defined at a position between the first gear  281  and the second gear  282 , and stops the sleeve  312  at the neutral position Na. Furthermore, as  FIG. 10B  illustrates, the shift control unit  26  controls the shaft moving apparatus  323  to move the sleeve  322  that is in a stopped state at a neutral position Nb, which is defined at a position between the third counter gear  293  and the fourth counter gear  294 , toward the third counter gear  293  and makes the sleeve  322  engage with the third counter gear  293 . The neutral position Nb serves as a separate neutral position. 
     In the automatic shift apparatus  13  according to the embodiment, each of separation distances between the first gear  281  and the second gear  282  and between the third counter gear  293  and the fourth counter gear  294  are formed in a short distance for making the shift time short. Nevertheless, for example, in a state where mechanisms for shifting gears include looseness, the sleeve  312  may contact the first gear  281  by swinging movement in the axial direction at a time at which movement of the sleeve  312  is made to stop at the neutral position Na. In a state where rotational speed of the first gear  281  is high, a shift shock and a contact noise are generated as a result of the sleeve  312  making contact with the first gear  281 , which are considered as disadvantages. 
     Accordingly, as  FIG. 11  illustrates, in the shift control unit  26  of the automatic shift apparatus  13  according to the embodiment, a target position Pa is defined at a position between the neutral position Na and the second gear  282  in an engaged state engaged with the sleeve  312 . The target position Pa is defined at a position where the sleeve  312  and the second gear  282  disengage, the position where the sleeve  312  does not make contact with the first gear  281  as a result of swinging movement of the sleeve  312  in the axial direction at a time at which movement of the sleeve  312  is made to stop at the target position Pa, the position close to the neutral position Na. As a result, a speed to move the sleeve  312  to the target position Pa may be increased. From the target position Pa to the neutral position Na, the sleeve  312  is moved at a speed that does not cause the sleeve  312  to contact the first gear  281  even in a state where the first gear  281  swings in the axial direction. In other words, the shift control unit  26  controls a moving speed Va of the sleeve  312  for moving the sleeve  312  in the engaged state to the target position Pa to be faster than a moving speed Vb of the sleeve  312  for moving the sleeve  312  from the target position Pa to the neutral position Na. As a result, shift time may be shortened. The moving speed Va serves as the first moving speed and the moving speed Vb serves as the second moving speed. 
     Fifth, an arrangement of the shift control unit  26  will be described. As  FIG. 12  illustrates, the shift control unit  26  includes a position setting portion  261 , a low pass filter portion  262 , an I-control portion  263 , an FF-control portion  264 , a PD-control portion  265 , a P-control portion  266 , and a PI-control portion  267 . The shift control unit  26  performs known proportional-integral-derivative control (PID control) and feed forward control to generate a control electric current based on information of position of the sleeve  312  and supplies the control electric current to the linear actuator  313   d . More specifically, the position setting portion  261  selects between the target position Pa and the neutral position Na and defines the target position Pa and the neutral position Na as a position for the sleeve  312  to move to. The low pass filter portion  262  defines and commands targeting positions for the sleeve  312  to smoothly move during a period during which the sleeve  312  moves to the target position Pa and to the neutral position Na, whichever defined in the position setting portion  261 . 
     The I-control portion  263  calculates a control command value IA for performing a control proportional to an integral of a deviation between the targeting position information obtained from the low pass filter portion  262  and detected position information obtained from the position detection sensor  314 . The FF-control portion  264  outputs a feed forward command value ID for making the sleeve  312  move fast to quickly settle the sleeve  312  at the target position Pa based on information of the target position Pa defined at the position setting portion  261 . The FF-control portion  264  outputs the feed forward command value ID during a period of an initial feedback control performed between a point in time t1 and a point in time t3, which is illustrated in  FIG. 19 . The feed forward command value ID is added to the control command value IA calculated in the I-control portion  263 . 
     The PD-control portion  265  calculates control command values IB, IC for performing a control based on a moving speed of the sleeve  312  calculated from a temporal differentiation of a deviation of the detected position information obtained from the position detection sensor  314 . The control command values IB, IC calculated at the PD-control portion  265  are subtracted from the control command value IA calculated at the I-control portion  263 . The P-control portion  266  calculates a target electric current for performing a control proportional to a deviation between the detected position information obtained from the position detection sensor  314  and the control command values IA, IB, IC, ID from the I-control portion, the FF-control portion  264 , and the PD-control portion  265 , in order to prevent divergence. The PI-control portion  267  makes the actual electric current to match with the target electric current in accordance with a deviation between the target electric current from the P-control portion  266  and the detected electric current from the linear actuator  313   d  and in accordance with an integral of the deviation between the target electric current from the P-control portion  266  and the detected electric current from the linear actuator  313   d.    
     Sixth, processes in the shift control unit  26  will be described referring to flow charts illustrated in  FIGS. 13 through 18  and a time chart illustrated in  FIG. 19 . As  FIG. 13  illustrates, in step S 1 , the shift control unit  26  determines whether or not there is a request to move the sleeve  312  to the neutral position Na. In a case where there is a request to move the sleeve  312  to the neutral position Na, the shift control unit  26  performs a disengagement control to disengage the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  in step S 2 . More specifically, as  FIG. 14  illustrates, in step S 21 , the shift control unit  26  supplies a predetermined electric current Ia to the linear actuator  313   d . On the other hand, in a case where there is no request to move the sleeve  312  to the neutral position Na, the shift control unit  26  waits to perform the disengagement control until there is a request to move the sleeve  312  to the neutral position Na. 
     In a state where the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  are engaged, the sleeve  312  may not be easily moved because coefficient of static friction between the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  is large, however, when the shift control unit  26  starts supplying the predetermined electric current Ia from the point in time t0, the sleeve  312  is exerted with a thrust force in a direction of movement by an amount corresponding to the predetermined electric current Ia and the sleeve  312  gradually moves so that the spline  312   a  of the sleeve  312  starts to disengage from the second dog clutch portion  282   a  of the second gear  282  as  FIG. 19  illustrates. 
     Next, as  FIG. 13  illustrates, the shift control unit  26  determines whether or not the sleeve  312  has started moving in step S 3 . In a case that the shift control unit  26  has determined that the sleeve  312  has started moving, in step S 4 , the shift control unit  26  performs an initial feed back control. More specifically, as  FIG. 15  illustrates, the shift control unit  26  defines the target position Pa in step S 41  and processes low pass filter processing in step  42 . The low pass filter processing is processed to define and command the targeting positions for the sleeve  312  to smoothly move during a period during which the sleeve  312  moves to the target position Pa. On the other hand, in a case where the shift control unit  26  determines that the sleeve  312  has not started moving, the shift control unit  26  returns to the step S 2 . 
     Following the step S 42 , in step S 43 , a deviation between the targeting position for the sleeve  312  and the detected position of the sleeve  312  is calculated and, in step S 44 , a value of integral of the deviation is calculated. After the step S 44 , in step S 45 , the control command value IA is calculated by multiplying the value of integral of the deviation by an integral gain at the I-control portion  263 . At the PD-control portion  265 , the control command value IB is calculated by multiplying the deviation by a proportional gain in step S 46  and the control command value IC is calculated by multiplying a temporal differentiation of the deviation by a derivative gain in step S 47 . 
     In step S 48  following the step S 47 , at the FF-control portion  264 , the feed forward command value ID for making the sleeve  312  move fast and quickly settle at the target position Pa is calculated by multiplying the target position Pa by a proportional gain. In step S 49 , an electric current to be finally supplied to the linear actuator  313   d  for controlling the linear actuator  313   d  to move the sleeve  312  is calculated by adding the feed forward command value ID calculated in the step S 48  to the control command value IA calculated in the step S 45 , then subtracting the control command value IB calculated in the step  346  and the control command value IC calculated in the step S 47 . The electric current to be supplied to the linear actuator  313   d  for controlling the linear actuator  313   d  here may be written as IA−IB−IC+ID, In step S 50  following the step S 49 , upper and lower limit guard of the electric current to be supplied to the linear actuator  313   d  for preventing the linear actuator  313   d  from damaging is calculated. 
     Accordingly, as  FIG. 19  illustrates, between the point in time t1 at which feedback control begins and the point in time t3, the feed forward electric current, which is another way to describe the feed forward command value ID, is supplied to the linear actuator  313   d . The electric current IA−IB−IC+ID, which reduces the electric current supplied to the linear actuator  313   d  at once and then increases toward zero, is supplied from the point in time t1 so that the sleeve  312  moves relatively fast toward the target position Pa. At this time, the shift control unit  26  controls the linear actuator  313   d  to control the sleeve  312  to be at the targeting positions illustrated with a broken line in  FIG. 19  in order to move the sleeve  312  smoothly as illustrated with a solid line in  FIG. 19 . 
     As  FIG. 19  illustrates, the shift control unit  26  performs a control that exerts a braking force on the sleeve  312 , the braking force directed in the opposite direction relative to a direction of movement of the sleeve  312 , before the spline  312   a  of the sleeve  312  engaged with the second dog clutch portion  282   a  of the second gear  282  disengages from the second dog clutch portion  282   a  of the second gear  282 . More specifically, the sleeve  312  is exerted with the braking force before the sleeve  312  reaches a position Pr, which is a position defined at a position closer to the second gear  282  relative to the target position Pa. Favorably, the braking force is exerted on the sleeve  312  immediately before the sleeve  312  reaches the position Pr. As a result, the sleeve  312  may be settled at the target position Pa even in a state where the moving speed of the sleeve  312  is increased by defining the targeting positions for the sleeve  312  at positions that make the sleeve  312  to displace by a large amount. 
     Exerting of the braking force on the sleeve  312  starts at a point where the electric current supplied to the linear actuator  313   d  reaches zero and crosses over zero. In other words, the braking force is exerted on the sleeve  312  when the position of the sleeve  312  reaches a position Pb and moves further in the direction of movement of the sleeve  312  relative to the position Pb. Until the electric current supplied to the linear actuator  313   d  reaches a point that crosses zero from the point in time t1, which is the point in time the feed back control begins, an electric current is supplied to the linear actuator  313   d  for quickly pulling the spline  312   a  of the sleeve  312  from the second dog clutch portion  282   a  of the second gear  282 . As a result, the sleeve  312  is not exerted with the braking force. Note that, a PID control alone may control the sleeve  312  to be exerted with a braking force that is directed in the opposite direction relative to the direction of movement of the sleeve  312 . 
     The feed forward control described earlier may control the sleeve  312  to move faster and to quickly settle at the target position Pa. Furthermore, the PID control described earlier allows exerting of the braking force on the sleeve  312  before the spline  312   a  of the sleeve  312  engaged with the second dog clutch portion  282   a  of the second gear  282  disengages from the second dog clutch portion  282   a  of the second gear  282 . As a result, the sleeve  312  may be swiftly stopped at the target position Pa. 
     In step S 5  following the step S 4 , as  FIG. 13  illustrates, the shift control unit  26  determines whether or not the sleeve has settled at the target position Pa. In a case where the shift control unit  26  determines that the sleeve has not settled at the target position Pa, the shift control unit  26  returns to the previous step S 4 . In a case where the sleeve  312  has settled at the target position Pa in the step S 5 , as  FIG. 19  illustrates, the shift control unit  26  determines that the sleeve  312  has settled at the target position Pa at the point in time t3, which is the point in time where a difference between the targeting position for the sleeve  312  and the actual position of the sleeve  312  becomes smaller than a predetermined value at a point in time t2 and after a predetermined time T has elapsed from the point in time t2. Note that, in  FIG. 19 , the broken line illustrates the targeting position for the sleeve  312  and the solid line illustrates the actual position of the sleeve  312 . As a result of waiting for the predetermined time T to elapse, swinging movement of the sleeve  312  in the axial direction, the sleeve  312  that has moved to the target position Pa, may be dampened. Accordingly, the moving speed of the sleeve  312  from the target point Pa to the neutral point Na may be increased. 
     When the shift control unit  26  determines that the sleeve  312  has settled at the target position Pa, the shift control unit  26  begins control for engaging the spline of the sleeve  322  with the third dog clutch portion  293   a  of the third counter gear  293 . The process illustrated in  FIG. 18  is an interrupt handling routine, which is separate from the process of  FIG. 13 , separately executed at an occurrence of a predetermined condition. More specifically, as  FIG. 18  illustrates, in a state where the sleeve  312  has settled at the target position Pa and the shift control unit  26  determines that the spline  312   a  of the sleeve  312  and the second dog clutch portion  282   a  of the second gear  282  are disengaged in step S 91 , the shift control unit  26  controls the sleeve  322 , which is in a stopped state at a neutral position Nb, to start moving toward the third counter gear  293  to engage the spline of the sleeve  322  with the third dog clutch portion  293   a  of the third counter gear  293  in step S 92 . 
     Meanwhile, as  FIG. 13  illustrates, in step S 6 , the shift control unit  26  performs a terminal feedback control when the shift control unit  26  has determined that the sleeve  312  has settled at the target position Pa. More specifically, as  FIG. 16  illustrates, the shift control unit  26  defines the neutral position Na in step S 61 , which is followed by processes from step S 62  to step S 69 . The processes from the step S 62  to the step S 69  are similar to the processes from the step S 42  to the step S 51 , which are illustrated in  FIG. 15 , however, processes of calculating and adding a feed forward electric current are excluded. In other words, processes similar to the steps S 48  and the step S 49  are excluded, where the step S 48  is the process of calculating the feed forward command value ID and the step S 49  is the process of adding the feed forward command value ID. 
     Accordingly, as  FIG. 19  illustrates, from the point in time t3, an electric current IA−IB−IC, which temporarily increases and then decreases toward zero, is supplied so that the sleeve  312  moves relatively slow toward the neutral position Na. In other words, the sleeve  312  moves toward the neutral position Na with a moving speed, or a velocity, slower than the moving speed the sleeve  312  has moved to reach the target position Pa. At this time, the shift control unit  26  controls the linear actuator  313   d  to control the sleeve  312  to be at the targeting positions illustrated with the broken line in  FIG. 19  in order to move the sleeve  312  smoothly as illustrated with the solid line in  FIG. 19 . 
     In step S 7  following the step S 6 , as  FIG. 13  illustrates, the shift control unit  26  determines whether or not the sleeve has settled at the neutral position Na. In a case where the shift control unit  26  determines that the sleeve has not settled at the neutral position Na, the shift control unit  26  returns to the previous step S 6 . In a case where the sleeve  312  has settled at the target position Na in the step S 7 , as  FIG. 19  illustrates, the shift control unit  26  determines that the sleeve  312  has settled at the neutral position Na at a point in time t4, which is a point in time where a difference between the targeting position for the sleeve  312  and the actual position of the sleeve  312  becomes smaller than a predetermined value. Note that, in  FIG. 19 , the broken line illustrates the targeting position for the sleeve  312  and the solid line illustrates the actual position of the sleeve  312 . 
     As  FIG. 13  illustrates, in step S 8 , the shift control unit  26  performs an idle control in a state where the shift control unit  26  has determined that the sleeve  312  has settled at the neutral position Na. More specifically, as  FIG. 17  illustrates, the shift control unit  26  sets electric current supply to the linear actuator  313   d  at zero in step S 81 . 
     Seventh, alternative processes in the shift control unit  26  will be described. In the shift control unit  26  in the automatic shift apparatus  13  according to the embodiment, the shift control unit  26  determines whether or not the sleeve  312  has settled at the target position Pa at the point in time t3, which is the point in time where the difference between the targeting position for the sleeve  312  and the actual position of the sleeve  312  becomes smaller than the predetermined value at the point in time t2 and after the predetermined time T has elapsed from the point in time t2. Nevertheless, the shift control unit  26  may be arranged such that the shift control unit  26  determines the sleeve  312  has settled at the target position Pa and proceeds to initiate the terminal feedback control at a point in time where the difference between the targeting position for the sleeve  312  and the actual position of the sleeve  312  becomes smaller than the predetermined value and without waiting for the predetermined time T to elapse. Similarly in such case, the sleeve  312  is controlled such that the sleeve  312  moves to the target position Pa in a moving speed faster than the moving speed at a period during which the sleeve  312  moves from the target position Pa to the neutral position Na. 
     In the shift control unit  26  in the automatic shift apparatus  13  according to the embodiment, the feed forward control is performed at the point in time t1 to supply the feed forward electric current, which is another way to describe the feed forward command value ID, to the linear actuator  313   d . As a result, a time constant for the low pass filter processing for a period from the point in time t1 to the point in time t2 may be made to a large value. Alternatively, the time constant for the low pass filter processing for the period from the point in time t1 to the point in time t2 may be made to a small value so that the shift control unit  26  performs a control that is executed solely by the feedback control and without the feed forward control, although shift time may become slightly longer. 
     According to an aspect of this disclosure, an automatic shift apparatus  13  includes a rotation shaft (a main shaft  23 , a counter shaft  24 ) axially supported to be rotatable about an axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ), the rotation shaft (the main shaft  23 , the counter shaft  24 ) configured to be in rotary engagement with one of an input shaft and an output shaft of the automatic shift apparatus  13 , a dog clutch gear shift mechanism  252  including a first clutch ring (a first gear  281 ) and a second clutch ring (a second gear  282 ) supported on the rotation shaft (the main shaft  23 , the counter shaft  24 ) to be rotatable about the rotation shaft (the main shaft  23 , the counter shaft  24 ), the first clutch ring (the first gear  281 ) providing a first gear ratio, the first clutch ring (the first gear  281 ) configured to be in rotary engagement with the other one of the input shaft and the output shaft, the second clutch ring (the second gear  282 ) providing a second gear ratio, the second clutch ring (the second gear  282 ) configured to be in rotary engagement with the other one of the input shaft and the output shaft, a hub (a clutch hub  311 ) fixed on the rotation shaft (the main shaft  23 , the counter shaft  24 ) at a position between the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ), the position adjacent to the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ), a sleeve  312  fitted to the hub (the clutch hub  311 ), the sleeve  312  restrained from rotating relative to the hub (the clutch hub  311 ), the sleeve  312  allowed to move in a direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ), a first dog clutch portion  281   a  protrudingly arranged on a side of the first clutch ring (the first gear  281 ) in a direction of the sleeve  312  and a second dog clutch portion  282   a  protrudingly arranged on a side of the second clutch ring (the second gear  282 ) in a direction of the sleeve  312 , the first dog clutch portion  281   a  and the second dog clutch portion  282   a  selectively meshing with a spline  312   a  formed on the sleeve  312  in response to axial movement of the sleeve  312 , a shaft moving apparatus  313  moving the sleeve  312  in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ), and a sensor (a position detection sensor  314 ) detecting a position of the sleeve  312  in accordance with movement of the sleeve  312  in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ), and a control unit (a shift control unit  26 ) controlling an operation of the shaft moving apparatus  313  based on a detected position of the sleeve  312  detected by the sensor (the position detection sensor  314 ). The control unit (the shift control unit  26 ) controls first moving speed Va to be faster than second moving speed Vb on moving the sleeve  312  in an engaged state engaged with one of the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ) to a neutral position Na defined at a position between the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ) where the first moving speed Va is a speed of moving the sleeve  312  in the engaged state to a target position Pa defined between the neutral position Na and the mentioned one of the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ) the sleeve  312  is engaged with and where the second moving speed Vb is a speed of moving the sleeve  312  from the target position Pa to the neutral position Na. 
     In a state where the sleeve  312  is moved to the neutral position Na by increasing moving speed of the sleeve  312  in order to reduce a shift time, swinging movement of the sleeve  312  in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ) becomes larger and may cause the sleeve  312  to contact the clutch ring (the first gear  281 , the second gear  282 ) positioned at a position in the direction of movement of the sleeve  312 . Accordingly, the target position Pa is defined at a position between the neutral position Na and the clutch ring (the first gear  281 , the second gear  282 ) in the engaged state engaged with the sleeve  312 , the position where the sleeve  312  does not make contact with the clutch ring (the first gear  281 , the second gear  282 ) positioned at the position in the direction of movement of the sleeve  312  as a result of the swinging movement of the sleeve  312  in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ). As a result, the first moving speed Va of the sleeve  312  for moving the sleeve  312  to the target position Pa may be increased. Furthermore, from the target position Pa to the neutral position Na, the sleeve  312  is moved at the second moving speed Vb that does not cause the sleeve  312  to contact the clutch ring (the first gear  281 , the second gear  282 ) positioned at the position in the direction of movement of the sleeve  312  by swinging in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ). As a result, the shift time may be shortened. 
     According to another aspect of this disclosure, the control unit (the shift control unit  26 ) of the automatic shift apparatus  13  controls the sleeve  312  to start moving from the target position Pa to the neutral position Na after an elapse of a predetermined period T from a point in time where the sleeve  312  reaches the target position Pa. 
     Accordingly, swinging movement in the direction of the axis of the rotation shaft (the main shaft  23 , the counter shaft  24 ) of the sleeve  312  that has moved to the target position Pa may be dampened. As a result, the moving speed of the sleeve  312  from the target position Pa to the neutral position Na may be increased. 
     According to further aspect of this disclosure, the control unit (the shift control unit  26 ) of the automatic shift apparatus  13  performs a control to exert a predetermined force directing in moving direction of the sleeve  312  on the sleeve  312  when the sleeve  312  in the engaged state with one of the first clutch ring (the first gear  281 ) and the second clutch ring (the second gear  282 ) starts moving toward the target position Pa. 
     Upon the arrangement described herewith, the spline  312   a  formed on the sleeve  312  and the dog clutch portion (the first dog clutch portion  281   a , the second dog clutch portion  282   a ) of the clutch ring (the first gear  281 , the second gear  282 ) may be swiftly disengaged so that the shift time may be further shortened. 
     According to another aspect of this disclosure, the automatic shift apparatus  13  further includes a separate dog clutch gear shift mechanism (a dog clutch gear shift mechanism  251 , a dog clutch gear shift mechanism  253 , a dog clutch gear shift mechanism  254 ) including a separate clutch ring (a fifth gear  285 , a reverse gear  28 R, a third counter gear  293 , a fourth counter gear  294 , a sixth counter gear  296 ), a separate hub (a clutch hub  321 ), a separate sleeve (a sleeve  322 ), a separate dog clutch portion (a third dog clutch portion  293   a ), a separate shaft moving apparatus (a shaft moving apparatus  323 ), and a separate sensor (a position detection sensor  324 ). The control unit (the shift control unit  26 ) controls the separate sleeve (the sleeve  322 ) of the separate dog clutch gear shift mechanism (the dog clutch gear shift mechanism  251 , the dog clutch gear shift mechanism  253 , the dog clutch gear shift mechanism  254 ) positioned at a separate neutral position (a neutral position Nb) to start moving from the separate neutral position (the neutral position Nb) to the separate clutch ring (the fifth gear  285 , the reverse gear  28 R, the third counter gear  293 , the fourth counter gear  294 , the sixth counter gear  296 ) when the sleeve  312  of the dog clutch gear shift mechanism  252  reaches the target position Pa. 
     Accordingly, controlling engagement of a separate spline of the separate sleeve (the sleeve  322 ) and the separate dog clutch portion (the third dog clutch portion  293   a ) of the separate clutch ring (the fifth gear  285 , the reverse gear  28 R, the third counter gear  293 , the fourth counter gear  294 , the sixth counter gear  296 ) may be started at an earlier point in time. As a result, a shift time at the separate dog clutch mechanism (the dog clutch gear shift mechanism  251 , the dog clutch gear shift mechanism  253 , the dog clutch gear shift mechanism  254 ) may be shortened. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.