Vehicle power unit

A vehicle power unit is provided in which a transmission including a gear transmission mechanism and a gear selector mechanism is housed in a transmission case, the gear transmission mechanism having gear trains with a plurality of gear positions that can be established alternatively, the gear selector mechanism being capable of operating s as to alternatively establish the gear trains with the plurality of gear positions, and a plurality of rotational speed sensors individually detecting the rotational speed of a plurality of rotating members forming part of the transmission are mounted on the transmission case, wherein the plurality of rotational speed sensors are disposed in a distributed manner so as to sandwich the plurality of shaft members of the gear selector mechanism in a projection on a plane orthogonal to a central axis of a crankshaft.

TECHNICAL FIELD

The present invention relates to a vehicle power unit in which a transmission is housed in a transmission case mounted on a vehicle body frame, the transmission including a gear transmission mechanism that includes gear trains with a plurality of gear positions that can be established alternatively provided between a main shaft into which power from a crankshaft of an internal combustion engine can be input and a countershaft disposed in parallel to the main shaft at a position offset in a vertical direction with respect to the main shaft and operatively linked to a driven wheel, and a gear selector mechanism that is arranged so as to have a plurality of shaft members disposed in parallel to the main shaft and the countershaft on a side opposite to the crankshaft with respect to a virtual plane that passes through a central axis of the main shaft and a central axis of the countershaft and that is capable of operating so as to alternatively establish the gear trains of the plurality of gear positions, and a plurality of rotational speed sensors are mounted on the transmission case on the side opposite to the crankshaft with respect to the virtual plane, the plurality of rotational speed sensors individually detecting a rotational speed of a plurality of rotating members forming part of the gear transmission mechanism.

BACKGROUND ART

A two-wheeled motor vehicle power unit that carries out automatic speed change based on the vehicle speed obtained from a rotational speed sensor detecting the rotational speed of a gear forming part of a gear transmission is known from Patent Document 1.

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The arrangement disclosed in Patent Document 1 above carries out automatic speed change control based on a measurement value from one rotational speed sensor, but in order to improve the precision of automatic speed change control the use of a plurality of rotational speed sensors could be considered. However, when a plurality of rotational speed sensors are disposed in a power unit, since it is necessary to ensure that there is space for disposing these rotational speed sensors, there is a possibility that the power unit will increase in size, and it becomes necessary to take into consideration interference with the surrounding area.

The present invention has been accomplished in light of such circumstances, and it is an object thereof to provide a vehicle power unit that enables a plurality of rotational speed sensors to be disposed while avoiding any increase in size.

Means for Solving the Problems

In order to attain the above object, according to a first aspect of the present invention, there is provided a vehicle power unit in which a transmission comprising a gear transmission mechanism and a gear selector mechanism is housed in a transmission case mounted on a vehicle body frame, the gear transmission mechanism comprising gear trains with a plurality of gear positions that can be established alternatively provided between a main shaft into which power from a crankshaft of an internal combustion engine can be input and a countershaft disposed in parallel to the main shaft at a position offset in a vertical direction with respect to the main shaft and operatively linked to a driven wheel, the gear selector mechanism being arranged so as to have a plurality of shaft members disposed in parallel to the main shaft and the countershaft and being disposed on a side opposite to the crankshaft with respect to a virtual plane passing through a central axis of the main shaft and a central axis of the countershaft while being capable of operating so as to alternatively establish the gear trains with the plurality of gear positions, and a plurality of rotational speed sensors individually detecting a rotational speed of a plurality of rotating members forming part of the gear transmission mechanism are mounted on the transmission case on the side opposite to the crankshaft with respect to the virtual plane, characterized in that the plurality of rotational speed sensors are disposed in a distributed manner so as to sandwich the plurality of shaft members of the gear selector mechanism in a projection on a plane orthogonal to a central axis of the crankshaft.

Further, according to a second aspect of the present invention, in addition to the first aspect, the central axis of the main shaft is disposed further upward and forward in a vehicle fore-and-aft direction than the central axis of the countershaft so as to extend in a vehicle width direction, at least one of the plurality of rotational speed sensors is mounted on an upper face of the transmission case, and at least one of the remaining rotational speed sensors is mounted on a rear face, along the vehicle fore-and-aft direction, of the transmission case (19).

According to a third aspect of the present invention, in addition to the first or second aspect, at least one of the plurality of rotational speed sensors is mounted on the transmission case so as to oppose an outer periphery of a drive gear provided on the main shaft, and at least one of the remaining rotational speed sensors is mounted on the transmission case so as to oppose an outer periphery of a driven gear provided on the countershaft.

According to a fourth aspect of the present invention, in addition to any one of the first to third aspects, the transmission case is divided into two and formed from an upper case half body and a lower case half body one above the other, the plurality of rotational speed sensors and the plurality of shaft members of the gear selector mechanism being supported on the upper case half body.

According to a fifth aspect of the present invention, in addition to the second aspect, a projection is projectingly provided on a rear end part of the transmission case so as to face rearward along the vehicle fore-and-aft direction, the projection forming a through hole, a support member for supporting the transmission case on the vehicle body frame being inserted through the through hole, and a rotational speed sensor mounted on the rear face of the transmission case is covered from below by the projection.

According to a sixth aspect of the present invention, in addition to any one of the first to fifth aspects, the plurality of rotational speed sensors are disposed so that, among the rotational speed sensors, a central axis of some of the rotational speed sensors and a central axis of the other rotational speed sensor intersect at an acute angle in a projection on a plane orthogonal to the central axis of the crankshaft, the other rotational speed sensor sandwiching a plurality of shaft members of the gear selector mechanism between the other rotational speed sensor and the some of the rotational speed sensors.

According to a seventh aspect of the present invention, in addition to the sixth aspect, the gear selector mechanism comprises a shift drum, a shift fork shaft, and a shift spindle, which correspond to the shaft member, and the shift drum, the shift fork shaft, and the shift spindle are disposed in a range surrounded by the central axis of the some of the rotational speed sensors and the central axis of the other rotational speed sensor in a projection on a plane orthogonal to the central axis of the crankshaft.

According to an eighth aspect of the present invention, in addition to any one of the first to seventh aspects, the central axis of the crankshaft is disposed so as to extend in the vehicle width direction, and an automatic gear change control device that includes a shift actuator is disposed on a face, on one side in the vehicle width direction, of the transmission case to a rear of the virtual plane in the vehicle fore-and-aft direction as seen in a side view of the transmission case, so as to drive the gear selector mechanism.

Moreover, according to a ninth aspect of the present invention, in addition to any one of the first to eighth aspects, the main shaft comprises a first shaft having a first clutch disposed between the first shaft and the crankshaft, and a second shaft coaxially and relatively rotatably surrounding the first shaft so as to have a second clutch disposed between the second shaft and the crankshaft, among the first to third rotational speed sensors the first rotational speed sensor is disposed so as to oppose an outer periphery of a drive gear, which is the rotating member supported on the first shaft so as to rotate at a rotational speed corresponding to a vehicle speed, the second rotational speed sensor is disposed so as to oppose an outer periphery of another drive gear, which is the rotating member provided on the second shaft so as to rotate together with the second shaft, and the third rotational speed sensor is disposed so as to oppose an outer periphery of a driven gear, which is the rotating member relatively rotatably supported on the countershaft so as to rotate synchronously with the first shaft.

A crankcase19of an embodiment corresponds to the transmission case of the present invention, an electric motor106of the embodiment corresponds to the shift actuator of the present invention, a fifth speed drive gear118, a fourth speed drive gear120, and a first speed driven gear121of the embodiment correspond to the rotating member of the present invention, and a rear wheel WR of the embodiment corresponds to the driven wheel of the present invention.

Effects of the Invention

In accordance with the first aspect of the present invention, since the plurality of rotational speed sensors mounted on the transmission case on the side opposite to the crankshaft with respect to the virtual plane passing through the central axes of the main shaft and the countershaft are disposed in a divided manner so as to sandwich the plurality of shaft members of the gear selector mechanism in a projection on a plane orthogonal to the central axis of the crankshaft, it is possible to dispose the gear selector mechanism and the plurality of rotational speed sensors in a concentrated manner while easily avoiding interference between the plurality of rotational speed sensors, thus avoiding any increase in the size of the power unit and enhancing the degree of freedom of the layout of the transmission within the transmission case.

Furthermore, in accordance with the second aspect of the present invention, since the central axis of the main shaft extending in the vehicle width direction is present in front of and above the central axis of the countershaft, at least one rotational speed sensor is mounted on the upper face of the transmission case, and at least one of the other rotational speed sensors is mounted on the rear face of the transmission case, it is possible to dispose the gear selector mechanism and at least some of the rotational speed sensors in a concentrated manner on the rear side upper part of the transmission case, thus enabling the power unit to be made compact.

In accordance with the third aspect of the present invention, since at least one rotational speed sensor opposes the outer periphery of the drive gear, and at least one of the other rotational speed sensors is disposed so as to oppose the outer periphery of the driven gear, it becomes easy to avoid interference between the rotational speed sensors by disposing at least two rotational speed sensors so as to be spaced from each other, and it is possible to ensure that there is space for disposing components of the transmission between the rotational speed sensors, thus enabling the power unit to be made smaller.

In accordance with the fourth aspect of the present invention, since the plurality of rotational speed sensors, the shift drum, the shift fork shaft, and the shift spindle are supported on the upper case half body, which forms the transmission case together with the lower case half body, it is possible to make the power unit more compact by disposing the rotational speed sensors and the gear selector mechanism in a concentrated manner on the upper case half body.

In accordance with the fifth aspect of the present invention, since the rotational speed sensor mounted on the rear face of the transmission case is covered from below by the projection provided on the rear end part of the transmission case and projecting rearward along the vehicle fore-and-aft direction, it is possible to protect the rotational speed sensor from flying stones, grit, etc. scattered by the wheel.

In accordance with the sixth aspect of the present invention, since the central axis of some of the rotational speed sensors and the central axis of the other rotational speed sensor sandwiching the plurality of shaft members of the gear selector mechanism between itself and the some of the rotational speed sensors intersect each other at an acute angle in a projection on a plane orthogonal to the central axis of the crankshaft, it is possible to dispose the shaft member of the gear selector mechanism and the rotation sensor together in a compact manner, thus contributing to making the power unit compact and concentrating the mass.

In accordance with the seventh aspect of the present invention, since the shift drum, the shift fork shaft, and the shift spindle of the gear selector mechanism are disposed in a range that is surrounded by the central axis of some of the rotational speed sensors and the central axis of the other rotational speed sensor sandwiching the plurality of shaft members of the gear selector mechanism between itself and the some of the rotational speed sensors, it is possible to dispose the shift drum, the shift fork shaft, and the shift spindle together in a more compact manner, thus further contributing to making the power unit compact and concentrating the mass.

In accordance with the eighth aspect of the present invention, since the automatic gear change control device for driving the gear selector mechanism is disposed on one side face in the vehicle width direction of the transmission case to the rear, in the vehicle fore-and-aft direction, of the virtual plane passing through the central axes of the main shaft and the countershaft, it is possible to also dispose the automatic gear change control device in a concentrated manner in the rear part of the transmission case when the power unit is viewed from the side, thus making the power unit compact.

Furthermore, in accordance with the ninth aspect of the present invention, since the main shaft includes the first and second shafts coaxially and relatively rotatably disposed so as to each have the clutch disposed between itself and the crankshaft, the first rotational speed sensor is disposed so as to oppose the outer periphery of the drive gear supported on the first shaft so as to rotate at a rotational speed corresponding to the vehicle speed, the second rotational speed sensor is disposed so as to oppose the outer periphery of the other drive gear provided on the second shaft so as to rotate together with the second shaft, and the third rotational speed sensor is disposed so as to oppose the outer periphery of the driven gear relatively rotatably supported on the countershaft so as to rotate synchronously with the first shaft, with regard to the power unit in which the first to third rotational speed sensors are individually opposed to the gears, which have different rotational speeds depending on the running conditions, it is possible, by disposing the three rotational speed sensors together on the side opposite to the crankshaft with respect to the virtual plane passing through the central axes of the main shaft and the countershaft, to make the power unit compact even when there are three rotational speed sensors.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

19Crankcase, which is a transmission case22Support shaft, which is a support member27Crankshaft32Upper case half body32aUpper face of crankcase, which is a transmission case32bRear face of crankcase, which is a transmission case33Lower case half body50Gear transmission mechanism51Gear selector mechanism52Main shaft53Countershaft54First shaft55Second shaft68First clutch69Second clutch81Shift drum, which is a shaft member82,83Shift fork shaft, which is a shaft member84Shift spindle, which is a shaft member105Automatic gear change control device106Electric motor, which is a shift actuator118Fifth speed drive gear, which is a rotating member120Fourth speed drive gear, which is a rotating member121First speed driven gear, which is a rotating member126Through hole127ProjectionC2Central axis of main shaftC3Central axis of countershaftC4Central axis of shift drumC5, C6Central axis of shift fork shaftC7Central axis of shift spindleC8, C9Central axis of some rotational speed sensorsC10Central axis of other rotational speed sensorE Internal combustion engineF Vehicle body frameG1, G2, G3, G4, G5, G6Gear trainM TransmissionP Power unitPL Virtual planeS1, S2, S3Rotational speed sensorWR Rear wheel, which is a driven wheel

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is explained below by reference to the attachedFIG. 1toFIG. 6.

First Embodiment

First, inFIG. 1, a vehicle body frame F of a two-wheeled motor vehicle, which is a saddled vehicle, includes a head pipe12steerably supporting a front fork11axially supporting a front wheel WF, a pair of left and right main frames13extending from the head pipe12downward to the rear, a pair of left and right down frames14extending downward to the rear at a steeper angle than the main frames13, a lower frame15extending from lower ends of the two down frames14to the rear, a pair of left and right center frames16extending from rear ends of the main frames13downward and provided so as to be connected to rear ends of the two lower frames15, a pair of left and right seat rails17extending from the rear ends of the main frame13upward to the rear, and a pair of left and right rear subframes18joining a lower part of the center frame16and a rear part of the seat rail17.

Disposed in a region surrounded by the main frame13, the down frame14, the lower frame15, and the center frame16so as to be supported by the vehicle body frame F is a power unit P that includes a twin cylinder internal combustion engine E and a transmission M (seeFIG. 4), the transmission M being housed in a crankcase19, which is a transmission case of the internal combustion engine E. A front end part of a swing arm20having a rear end part axially supporting a rear wheel WR driven with power exerted by the power unit P is vertically swingably supported on the lower part of the center frame16via a support shaft22, and a rear part of the crankcase19is also supported by the support shaft22. A fuel tank23is mounted on the main frame13above the internal combustion engine E, and a rider's seat24disposed to the rear of the fuel tank23and a pillion seat25disposed to the rear of the rider seat24are supported by the seat rails17.

Referring in addition toFIG. 2andFIG. 3, the internal combustion engine E includes the crankcase19rotatably supporting a crankshaft27having an axis extending in the vehicle width direction, a cylinder block28having a forwardly inclined cylinder axis CC and being joined to the front upper end of the crankcase19, a cylinder head29joined to the upper end of the cylinder block28, and a head cover30joined to the upper end of the cylinder head29, and an oil pan31is joined to a lower part of the crankcase19.

The crankcase19is formed by joining an upper case half body32and a lower case half body33that are dividable one above the other via a dividing face34, the cylinder block28being formed integrally with the upper case half body32.

InFIG. 4, the cylinder block28has two cylinder bores36and36disposed side by side in the vehicle width direction, and the crankshaft27, which has a central axis C1extending along the direction in which the cylinder bores36and36are arranged, that is, the vehicle width direction, is rotatably supported on the crankcase19so that the central axis C1is disposed on the dividing face34.

Joined to a left side face of the crankcase19is a left case cover38forming a generator chamber37between itself and the crankcase19, a rotor40of a generator39housed in the generator chamber37being fixed to an end part of the crankshaft27projecting into the generator chamber37, and a stator41of the generator39being fixed to the left case cover38so as to be surrounded by the rotor40.

A starter motor42is fixedly disposed on an upper face of the crankcase19, that is, an upper face32aof the upper case half body32as is clearly shown inFIG. 3, and this starter motor42is covered from the side by an upper end part of the left case cover38. A driven gear44forming part of a reduction gear train43for transmitting power from the starter motor42is linked to the rotor40via a one way clutch45.

A drive gear46is fixed to the crankshaft27at a position approaching the left side wall of the crankcase19from the interior. A balancer shaft47disposed above and in front, in the vehicle fore-and-aft direction, of the crankshaft27is rotatably supported on the upper case half body32of the crankcase19as shown inFIG. 2, the rotational power from the drive gear46being transmitted to the balancer shaft47. Joined to a right side face of the crankcase19is a right case cover49forming a clutch chamber48between itself and the crankcase19.

The transmission M housed within the crankcase19includes a gear transmission mechanism50having gear trains with a plurality of gear positions that can be alternatively established, for example, a first speed gear train G1, a second speed gear train G2, a third speed gear train G3, a fourth speed gear train G4, a fifth speed gear train G5, and a sixth speed gear train G6, and a gear selector mechanism51that can operate so as to alternatively establish the first to sixth speed gear trains G1to G6.

The gear transmission mechanism50is formed by providing the first speed to sixth speed gear trains G1to G6between a main shaft52that has a central axis C2extending in the vehicle width direction and that is rotatably supported on the crankcase19so that the power from the crankshaft27of the internal combustion engine E can be input thereinto, and a countershaft53that is disposed so as to have a central axis C3parallel to the main shaft52and that is operatively linked to the rear wheel WR, which is the driven wheel.

The main shaft52is disposed above and to the rear in the vehicle fore-and-aft direction of the crankshaft27when the crankcase19is viewed from the side, and is formed from a first shaft54and a second shaft55having the first shaft54coaxially and relatively rotatably inserted therethrough. The gear trains with odd-numbered gear positions, that is, the first speed gear train G1, the third speed gear train G3, and the fifth speed gear train G5are provided between the first shaft54and the countershaft53, and the gear trains with even-numbered gear positions, that is, the second speed gear train G2, the fourth speed gear train G4, and the sixth speed gear train G6are provided between the second shaft55and the countershaft53.

The first shaft54is formed so as to have a smaller diameter than that of the second shaft55, one end part of the first shaft54extending rotatably through the upper case half body32of the crankcase19being rotatably supported on the upper case half body32via a ball bearing56, and the other end part of the first shaft54being rotatably supported on the right case cover49via a clutch inner75of a first clutch68and a ball bearing57. An intermediate part in the axial direction of the second shaft55, which has a larger diameter than that of the first shaft54, is rotatably supported on the upper case half body32of the crankcase19via a ball bearing58, an intermediate part of the first shaft54is coaxially and relatively rotatably inserted through the second shaft55, and a plurality of needle bearings59are disposed between the first shaft54and the second shaft55.

The countershaft53is disposed at a position that is offset in the vertical direction with respect to the main shaft52, and in this embodiment the countershaft53is disposed beneath and to the rear, in the vehicle fore-and-aft direction, of the main shaft52so that the central axis C3is disposed on the dividing face34of the crankcase19.

One end part of the countershaft53projects from a left side wall of the crankcase19with a ball bearing61and an annular seal member62disposed between itself and the crankcase19, and the other end part of the countershaft53is rotatably supported on a right side wall of the crankcase19via a needle bearing63.

A drive sprocket64is fixed to the one end part of the countershaft53outside the crankcase19, and the rotational power output from the countershaft53is transmitted to the rear wheel WR via a chain (not illustrated) wound around the drive sprocket64.

Housed in the clutch chamber48formed between the right side wall of the crankcase19and the right case cover49are a primary reduction gear67to which power from the crankshaft27is transmitted and first and second clutches68and69disposed between the primary reduction gear67and the main shaft52.

A transmission tube shaft70that is adjacent to the second shaft55in the axial direction is relatively rotatably fitted onto an intermediate part, close to the other end, of the first shaft54while having a fixed axial position, and power from the crankshaft27is transmitted to the transmission tube shaft70via the primary reduction gear67and a damper spring71. The primary reduction gear67is therefore formed from a drive gear72rotating together with the crankshaft27, and a driven gear73disposed coaxially with the main shaft52so as to mesh with the drive gear72, and the driven gear73is linked to the transmission tube shaft70via the damper spring71.

The first clutch68is a hydraulic multi-plate clutch formed by relatively non-rotatably linking, in response to the action of oil pressure, a clutch outer74relatively non-rotatably joined to the transmission tube shaft70and the clutch inner75relatively non-rotatably joined to the first shaft54of the main shaft52, and the second clutch69is a hydraulic multi-plate clutch formed by relatively non-rotatably linking, in response to the action of oil pressure, a clutch outer76relatively non-rotatably joined to the transmission tube shaft70and a clutch inner77relatively non-rotatably joined to the second shaft55of the main shaft52.

That is, when the first clutch68attains a power transmission state rotational power from the crankshaft27is transmitted to the first shaft54via the primary reduction gear67, the damper spring71, the first clutch68, and the transmission tube shaft70, and when the second clutch69attains a power transmission state rotational power from the crankshaft27is transmitted to the second shaft55via the primary reduction gear67, the damper spring71, the second clutch69, and the transmission tube shaft70.

When the first clutch68is in a power transmission state and power is being transmitted from the crankshaft27to the first shaft54it is possible to transmit power from the first shaft54to the countershaft53via the gear train among the first, third, and fifth speed gear trains G1, G3, and G5that has been alternatively established, and when the second clutch69is in a power transmission state and power is being transmitted from the crankshaft27from the second shaft55it is possible to transmit power from the second shaft55to the countershaft53via the gear train among the second, fourth, and sixth speed gear trains G2, G4, and G6that has been alternatively established.

Referring in addition toFIG. 5, the gear selector mechanism51is formed so as to have a plurality of shaft members disposed in parallel to the main shaft52and the countershaft53. In this embodiment, the gear selector mechanism51is formed so as to have a shift drum81, first and second shift fork shafts82and83, and a shift spindle84as the shaft members; a central axis C4of the shift drum81, central axes C5and C6of the first and second shift fork shafts82and83, and a central axis C7of the shift spindle84are parallel to the central axis C2of the main shaft52and the central axis C3of the countershaft53and, moreover, the shift drum81, the first and second shift fork shafts82and83, and the shift spindle84are disposed on the side opposite to the crankshaft27with respect to a virtual plane PL passing through the central axis C2of the main shaft52and the central axis C3of the countershaft53, in this embodiment to the rear in the vehicle fore-and-aft direction.

First and second shift forks85and86are axially slidably supported on the first shift fork shaft82, which is supported on the upper case half body32of the crankcase19, and third and fourth shift forks87and88are axially slidably supported on the second shift fork shaft83, which is supported on the upper case half body32of the crankcase19.

Furthermore, the shift drum81is pivotably supported on the upper case half body32of the crankcase19, and the first to fourth shift forks85to88respectively engage with four engagement grooves89,90,91, and92provided in an outer face of the shift drum81. These engagement grooves89to92are formed so as to determine the positions of the first to fourth shift forks85to88on the first and second shift fork shafts82and83depending on the position to which the shift drum81is pivoted, and due to the shift drum81pivoting, one of the first to sixth speed gear trains G1to G6is selectively established depending on the position to which it is pivoted.

A shaft93coaxially fixed to one end part of the shift drum81is rotatably supported on a left side wall of the upper case half body32of the crankcase19via a needle bearing94. A shift drum center95is coaxially fixed to the other end part of the shift drum81, and the shift drum center95and the other end part of the shift drum81are pivotably supported on a right side wall of the upper case half body32via a ball bearing96.

The shift drum81is stepwise pivoted by the operation of shift position change drive means97coaxially linked to the other end part of the shift drum81so as to be operated by means of the input of a driving force; the shift position change drive means97is conventionally known and has a drum shifter98of which part is disposed within the shift drum center95so that it can pivot around the same axis as that of the shift drum81, a plurality of pawls99that are fitted symmetrically to the drum shifter98so as to rise and fall in the radial direction of the drum shifter98and that are urged in the direction in which they rise and engage with a plurality of locations in the peripheral direction of the inner periphery of the drum shifter98, and a fixed guide plate100that guides the rise and fall states of the pawl99in response to pivoting of the drum shifter98.

The shift spindle84is pivotably supported on the upper case half body32of the crankcase19, and an arm101fixed to an end part of the shift spindle84projecting from the right side wall of the upper case half body32is linked to a pin98aprojectingly provided at a position displaced from the pivot axis of the drum shifter98in the shift position change drive means97. Furthermore, a lost motion spring102is provided between the shift spindle84and the upper case half body32.

An automatic gear change control device105is disposed on one side face, in the vehicle width direction, of the upper case half body32in the crankcase19, in this embodiment on the left side face of the upper case half body32, the automatic gear change control device105being positioned to the rear in the vehicle fore-and-aft direction of the virtual plane PL when the crankcase19is viewed from the side, and this automatic gear change control device105is formed so as to include an electric motor106, which is a shift actuator.

A cover member107covering, from the side, a rear upper part of the left side wall of the upper case half body32is mounted on the upper case half body32via a plurality of bolts108, and the electric motor106is mounted on the cover member107.

The automatic gear change control device105includes, in addition to the electric motor106, a reduction mechanism109provided between the electric motor106and the shift spindle84, and this reduction mechanism109is housed in a reduction chamber110formed between the cover member107and the upper case half body32.

The reduction mechanism109is formed from a drive gear112provided on a motor shaft111of the electric motor106, a first idle gear113meshing with the drive gear112, a second idle gear114rotating together with the first idle gear113, a third idle gear115meshing with the second idle gear114, a fourth idle gear116rotating together with the third idle gear115, and a driven gear117meshing with the fourth idle gear116. The first and second idle gears113and114are formed as a unit and are rotatably supported by the cover member107and the upper case half body32. The third and fourth idle gears115and116are formed as a unit and are rotatably supported by the cover member107and the upper case half body32. Moreover, the third idle gear115and the driven gear117are sector gears.

The driven gear117of the reduction mechanism109is relatively non-pivotably linked to an end part, projecting from the left side wall of the upper case half body32, of the shift spindle84pivotably supported by the upper case half body32of the crankcase19.

In order to control the operation of the electric motor106of the automatic gear change control device105and connection-disconnection switching timing of the first and second clutches68and69, a plurality of rotational speed sensors that individually detect the rotational speed of a plurality of rotating members forming part of the gear transmission mechanism50of the transmission M are mounted on the crankcase19so as to be disposed on the side opposite to the crankshaft27with respect to the virtual plane PL, in this embodiment to the rear in the vehicle fore-and-aft direction of the virtual plane PL. In this embodiment, a first rotational speed sensor S1for detecting the vehicle speed, a second rotational speed sensor S2for detecting the rotational speed of the second shaft55of the main shaft52, and a third rotational speed sensor S3for detecting the rotational speed of the first shaft54of the main shaft52are mounted on the crankcase19so as to be disposed to the rear, in the vehicle fore-and-aft direction, of the virtual plane PL.

The first rotational speed sensor S1is disposed so as to detect the rotational speed of a fifth speed drive gear118, which is a drive gear as a rotating member forming part of the gear transmission mechanism50. The fifth speed drive gear118is relatively rotatably supported on the first shaft54of the main shaft52while always meshing with a fifth speed driven gear119relatively non-rotatably provided on the countershaft53so as to form, together with the fifth speed drive gear118, the fifth speed gear train G5, and always rotates at a rotational speed corresponding to the vehicle speed when the two-wheeled motor vehicle is running.

Furthermore, the second rotational speed sensor S2is disposed so as to detect the rotational speed of a fourth speed drive gear120, which is another drive gear as a rotating member forming part of the gear transmission mechanism50, and the fourth speed drive gear120is relatively non-rotatably provided on the second shaft55of the main shaft52and rotates together with the second shaft55.

Furthermore, the third rotational speed sensor S3is disposed so as to detect the rotational speed of the first speed driven gear121, which is a rotating member forming part of the transmission M; the first speed driven gear121is relatively rotatably provided on the countershaft53while always meshing with a first speed drive gear122provided integrally with the first shaft54of the main shaft52so as to form, together with the first speed driven gear121, the first speed gear train G1, and rotates synchronously with the first shaft54.

The first, second, and third rotational speed sensors S1, S2, and S3are disposed in a divided manner so as to sandwich the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51in a projection on a plane orthogonal to the central axis of the crankshaft27. In this embodiment the first and second rotational speed sensors S1and S2, which are some of the first to third rotational speed sensors S1to S3, are mounted on the upper case half body32of the crankcase19in front, in the vehicle fore-and-aft direction, of the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84, and the third rotational speed sensor S3, which is the remainder of the first to third rotational speed sensors S1, S2, and S3, is mounted on the upper case half body32of the crankcase19to the rear, in the vehicle fore-and-aft direction, of the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84.

Moreover, at least one of the first to third rotational speed sensors S1to S3, in this embodiment the first and second rotational speed sensors S1and S2, are mounted on the upper face of the crankcase19, that is, the upper face32aof the upper case half body32, and the third rotational speed sensor S3, which corresponds to at least one of the remaining rotational speed sensors, is mounted on the rear face of the crankcase19along the vehicle fore-and-aft direction, that is, on a rear face32bof the upper case half body32.

At least one of the first to third rotational speed sensors S1to S3is mounted on the crankcase19so as to oppose the outer periphery of a drive gear provided on the main shaft52, and in this embodiment the first rotational speed sensor S1is mounted on the upper face32aof the upper case half body32by means of a pair of bolts123and123so as to oppose the outer periphery of the fifth speed drive gear118, and the second rotational speed sensor S2is mounted on the upper face32aof the upper case half body32by means of a bolt124so as to oppose the outer periphery of the fourth speed drive gear120. Furthermore, at least one of the remaining rotational speed sensors is mounted on the crankcase19so as to oppose the outer periphery of a driven gear provided on the countershaft53, and in this embodiment the third rotational speed sensor S3is mounted on the rear face32bof the upper case half body32by means of a pair of bolts125and125so as to oppose the outer periphery of the first speed driven gear121.

Projectingly provided on a rear end part of the crankcase19as clearly shown inFIG. 2so as to project rearward along the vehicle fore-and-aft direction is a projection127for forming a through hole126for the support shaft22, which is the support member for supporting the crankcase19on the center frame16of the vehicle body frame F, to be inserted through. The third rotational speed sensor S3, which is mounted on the rear face32bof the crankcase19, is covered from below by the projection127.

Furthermore, central axes C8and C9of the first and second rotational speed sensors S1and S2, which are some of the first to third rotational speed sensors S1to S3, and a central axis C10of the third rotational speed sensor S3that sandwiches, between itself and the first and second rotational speed sensors S1and S2, the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51intersect each other at an acute angle in a projection on a plane orthogonal to the central axis C1of the crankshaft27. In this embodiment, since the first and second rotational speed sensors S1and S2are at the same position in the vehicle fore-and-aft direction, an angle α formed by the central axes C8and C9of the first and second rotational speed sensor S1and the central axis C10of the third rotational speed sensor S3on the projection is an acute angle.

Moreover, the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84are disposed, in the projection, in a range surrounded by the central axes C8and C9of the first and second rotational speed sensors S1and S2and the central axis C10of the third rotational speed sensor S3.

Furthermore, a neutral sensor S4opposing the outer periphery of the shift drum81is mounted at a position, adjacent to the third rotational speed sensor S3, on the rear face32bof the upper case half body32, so as to detect a neutral position of the shift drum81.

InFIG. 6, the operation of hydraulic switching means130for switching the connection/disconnection of the first and second clutches68and69and the operation of the electric motor106of the automatic gear change control device105are controlled by a control unit131. Input into this control unit131are detection signals from the first to third rotational speed sensors S1to S3, the neutral sensor S4, an engine rotational speed sensor132, a throttle degree of opening sensor133, a gear position sensor134that detects a gear position based on the position to which the shift drum81is pivoted, and a shifter switch135that detects the position to which the shift spindle84is pivoted.

The control unit131includes a speed change control command section136in which a speed change map137is stored, a dog clutch state determination section138, a main shaft speed difference calculation section139, a gear position modification section140, and a shift drum neutral position determination section141.

The speed change control command section136outputs a signal for controlling the operation of the hydraulic switching means130and the electric motor106in accordance with the speed change map based on the vehicle speed input from the first rotational speed sensor S1, the engine rotational speed input from the engine rotational speed sensor132, the throttle degree of opening input from the throttle degree of opening sensor133, and the gear position input from the gear position sensor134.

The main shaft speed difference calculation section139calculates the difference in rotational speed between the first and second shafts54and55of the main shaft52based on the values detected by the second and third rotational speed sensors S2and S3. The dog clutch state determination section138determines whether or not the dog clutch that can alternatively switch the first to sixth speed gear trains G1to G6of the gear transmission mechanism50is in a properly meshed state or an unmeshed state based on information from the main shaft speed difference calculation section139and the gear position sensor134. The gear position modification section140has a modifying function so that the dog clutch attains a properly meshed state or an unmeshed state by operating the hydraulic switching means130and the electric motor106by means of the speed change control command section136when the dog clutch state determination section138determines that there is neither a properly meshed state nor an unmeshed state. Furthermore, the shift drum neutral position determination section141determines whether or not the transmission M is in a reliably neutral state based on information from the shifter switch135and the neutral switch S4.

The operation of this embodiment is now explained; the first to third rotational speed sensors S1, S2, and S3, which individually detect the rotational speed of the fifth speed drive gear118, the fourth speed drive gear120, and the first speed driven gear121forming part of the gear transmission mechanism50having the first to sixth speed gear trains G1to G6, which can be alternatively established, provided between the main shaft52and the countershaft53, are mounted on the crankcase19so as to be disposed on the side opposite to the crankshaft27with respect to the virtual plane PL passing through the central axes C2and C3of the main shaft52and the countershaft53, and in this embodiment to the rear, in the vehicle fore-and-aft direction, of the virtual plane PL. Since the first and second rotational speed sensors S1and S2, which are some of the first to third rotational speed sensors S1to S3, are mounted on the crankcase19in front, in the vehicle fore-and-aft direction, of the central axes C4to C7of the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51and are also disposed in a divided manner so as to sandwich the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84, which are a plurality of the shaft members of the gear selector mechanism51, in the projection on the plane orthogonal to the central axis C1of the crankshaft27, it is possible to dispose the gear selector mechanism51and the first to third rotational speed sensors S1to S3in a concentrated manner while easily avoiding interference between the first to third rotational speed sensors S1to S3, thus avoiding any increase in the size of the power unit P and enhancing the degree of freedom of the layout of the transmission M within the crankcase19.

Furthermore, since the central axis C2of the main shaft52extending in the vehicle width direction is disposed above and in front, in the vehicle fore-and-aft direction, of the central axis C3of the countershaft53when the crankcase19is viewed from the side, the first and second rotational speed sensors S1and S2, which correspond to at least one of the first to third rotational speed sensors S1to S3, are mounted on the upper face32aof the crankcase19, and the third rotational speed sensor S3, which corresponds to at least one of the remaining rotational speed sensors, is mounted on the rear face32bof the crankcase19along the vehicle fore-and-aft direction, it is possible to dispose the gear selector mechanism51and at least some, that is, S1and S2of the rotational speed sensors S1to S3in a concentrated manner on the rear upper part of the crankcase19, thus enabling the power unit P to be made compact.

Moreover, since the first and second rotational speed sensors S1and S2, which correspond to at least one of the first to third rotational speed sensors S1to S3, are mounted on the crankcase19so as to oppose the outer peripheries of the fifth speed drive gear118and the fourth speed drive gear120provided on the main shaft52, and the third rotational speed sensor S3, which corresponds to at least one of the remaining rotational speed sensors, is mounted on the crankcase19so as to oppose the outer periphery of the first speed driven gear121provided on the countershaft53, it becomes easy to avoid interference between the first and second rotational speed sensors S1and S2and the third rotational speed sensor S3by disposing the first and second rotational speed sensors S1and S2and the third rotational speed sensor S3so that they are spaced from each other, and it is possible to ensure that there is space for disposing components of the transmission M between the first and second rotational speed sensors S1and S2and the third rotational speed sensor S3, thus enabling the power unit P to be made smaller.

Furthermore, since the crankcase19is divided into two and formed from the upper case half body32and the lower case half body33one above the other, and the first to third rotational speed sensors S1to S3and the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51are supported on the upper case half body32, it is possible to make the power unit P more compact by disposing the first to third rotational speed sensors S1to S3and the gear selector mechanism51in a concentrated manner on the upper case half body32.

Moreover, since the projection127, in which the through hole126for the support shaft22supporting the crankcase19on the center frame16of the vehicle body frame F to be inserted through is formed, is projectingly provided on the rear end part of the crankcase19so as to face rearward along the vehicle fore-and-aft direction, and the third rotational speed sensor S3mounted on the rear face32bof the crankcase19is covered from below by the projection127, it is possible to protect the third rotational speed sensor S3from flying stones, grit, etc. scattered by the front wheel WF or the rear wheel WR.

Furthermore, since the first to third rotational speed sensors S1to S3are disposed so that the central axes C8and C9of the first and second rotational speed sensors S1and S2, which correspond to some of the rotational speed sensors S1to S3, and the central axis C10of the third rotational speed sensor S3that sandwiches, between itself and the first and second rotational speed sensors S1and S2, the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51intersect each other at an acute angle in the projection on the plane orthogonal to the central axis C1of the crankshaft27, it is possible to dispose the shift drum81, the first shift fork shaft82, the second shift fork shaft83, and the shift spindle84of the gear selector mechanism51and the first to third rotation sensors S1to S3together in a compact manner, thus contributing to making the power unit P compact and concentrating the mass.

Moreover, since the shift drum81, the first and second shift fork shafts82and83, and the shift spindle84of the gear selector mechanism51are disposed in a range surrounded by the central axes C8and C9of the first and second rotational speed sensors S1and S2, and the central axis C10of the third rotational speed sensor S3in the projection on the plane orthogonal to the central axis C1of the crankshaft27, it is possible to dispose the shift drum81, the first and second shift fork shafts82and83, the shift spindle84together in a more compact manner, thus further contributing to making the power unit P compact and concentrating the mass.

Furthermore, since the central axis C1of the crankshaft27is disposed so as to extend in the vehicle width direction, and the automatic gear change control device105, which includes the electric motor106, is disposed on one side face (on the left side face in this embodiment), in the vehicle width direction, of the crankcase19to the rear of the virtual plane PL in the vehicle fore-and-aft direction when the crankcase19is viewed from the side, so as to drive the gear selector mechanism51, it is possible to also dispose the automatic gear change control device105in a concentrated manner in the rear part of the crankcase19when the power unit P is viewed from the side, thus making the power unit P compact.

Moreover, since the main shaft52includes the first shaft54having the first clutch68disposed between itself and the crankshaft27, and the second shaft55coaxially and relatively rotatably surrounding the first shaft54so as to have the second clutch69disposed between itself and the crankshaft27, among the first to third rotational speed sensors S1to S3the first rotational speed sensor S1is disposed so as to oppose the outer periphery of the fifth speed drive gear118supported on the first shaft54so as to rotate at a rotational speed corresponding to the vehicle speed, the second rotational speed sensor S2is disposed so as to oppose the outer periphery of the fourth speed drive gear120provided on the second shaft55so as to rotate together with the second shaft55, and the third rotational speed sensor S3is disposed so as to oppose the outer periphery of the first speed driven gear121relatively rotatably supported on the countershaft53so as to rotate synchronously with the first shaft54, with regard to the power unit P in which the first to third rotational speed sensors S1to S3are individually opposed to the gears118,120, and121, which have different rotational speeds depending on the running conditions, it is possible, by disposing the three rotational speed sensors S1to S3closer to the side opposite to the crankshaft27with respect to the virtual plane PL passing through the central axes C2and C3of the main shaft52and the countershaft53, to make the power unit P compact even when there are the three rotational speed sensors S1to S3.

An embodiment of the present invention is explained above, but the present invention is not limited to the above embodiment and may be modified in a variety of ways as long as the modifications do not depart from the spirit and scope thereof.