Abstract:
A gearshift position detector, for a transmission component of a powertrain unit including an engine and a transmission, includes first and second actuator arms for cooperatively interacting with neutral and reverse indicator switches. The neutral and reverse indicator switches are mounted to a crankcase or a crankcase cover of the engine. The acutator arms are selectively operable to trip the respective switches, and thereby, to generate signals for alerting a vehicle operator that the transmission is in neutral or reverse. The actuator arms are operatively attached to a shift drum skip-turn-prevention plate which, in turn, is secured to an axial end surface of a shift drum. The indicator switches are, respectively, capable of being energized upon interaction between the corresponding actuator arm and the switch. In this configuration, the main components of the detector are housed within the crankcase, thereby saving space in the vicinity of the engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-280860, filed on Sep. 28, 2004. The subject matter of this priority document is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gearshift position detector for a manual transmission used in motorcycles and other vehicles. 
   2. Description of the Background Art 
   Gearshift position detectors are well known, and include one or more detectors for detecting a neutral gear position, a reverse gear position, and/or an engaged gear position. An example of the conventional technology related to the neutral position detector is as follows: A neutral position detector is mounted on the outer wall of a lower crankcase of an engine. A detecting pin, located at the end of the detector, is directed in the direction of the centerline of a shift drum. In addition, a cam face structure portion provided with a cam adapted to detect a neutral position is provided on the outer circumferential surface of the shift drum. The detecting pin is disposed to face the cam face structure portion with a small gap therebetween, or to be in contact with the same with a pressing force. With this configuration, as the shift drum turns, the detection cam of the cam face structure portion presses the detecting pin. Thus, the neutral position is detected at the time of speed-change. This type of structure is disclosed, for example, in FIG. 3 of Japanese Laid-open Patent document No. 2004-203313. 
   In Japanese Laid-open Patent document No. 2004-203313, the neutral position detector has been provided on the outer circumferential surface of the crankcase, in a radial direction of the shift drum. Therefore, the main body of the detector protrudes externally from the crankcase. This configuration creates difficulties in positioning the engine, and in arranging other components around the engine. In addition, in some cases it is difficult to route wiring in the vicinity of the mounted engine. The present invention eliminates the above problems by creating a compact configuration of components, effectively using the space around the shift drum in the axial direction of the shift drum. 
   SUMMARY OF THE INVENTION 
   The present invention improves upon the problems described above. A first aspect of the present invention relates to a gearshift position detector for a vehicular transmission, characterized in that an actuator member (switch plate), adapted to detect a neutral position and a reverse position of a shift drum, is operatively attached to a shift drum skip-turn-prevention plate secured to an end of the shift drum. In addition, a neutral indicator switch and a reverse indicator switch are operatively mounted to a crankcase or a crankcase cover, and these indicator switches become energized upon contact with the actuator member. 
   According to the first aspect of the invention, since the actuator member or the switch plate is operatively attached to the shift drum skip-turn-prevention plate, the length of time required for attachment of the detector is reduced, attachment accuracy is improved and space-saving is achieved. 
   A second aspect of the present invention is characterized in that, in the gearshift position detector for a vehicular transmission as recited in the first aspect of the invention, a neutral switch actuator arm and a reverse switch actuator arm of the actuator member are disposed opposite to each other with respect to an axis of the shift drum. 
   According to the second aspect of the invention, since the neutral switch actuator arm and a reverse switch actuator arm of the actuator member are disposed opposite to each other with respect to an axis of the shift drum, space-saving within and about the crankcase is achieved. 
   Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal cross-sectional view of an internal combustion engine according to a selected illustrative embodiment of the present invention, showing the location and orientation of the shift drum and its turning mechanism within the crankcase. 
       FIG. 2  is a transverse cross-sectional view of a main shaft and a countershaft of a gear transmission of the engine of  FIG. 1 , showing a clutch mounted on one end of the main shaft, and interaction between gears on the main shaft and the countershaft. 
       FIG. 3  is a transverse cross-sectional view of a gear change mechanism of the engine of  FIG. 1 , showing the neutral position detector and a reverse position detector disposed opposite to each other with respect to an axis of the shift drum. 
       FIG. 4  is an enlarged cross-sectional view of a shift drum turning mechanism and a gearshift position detector of the engine of  FIG. 1 . 
       FIG. 5  is a side plan detail view, partially in cross-section, of the shift drum turning mechanism of  FIG. 4  as viewed from the left side, showing the interaction between the change arm, the shifter plate, and the skip turn prevention plate. 
       FIG. 6  is a side plan detail view, partially in cross-section, of a shift drum turning position stabilizer as viewed from the right side of the shift drum; and 
       FIG. 7  is a side plan detail view, partially in cross-section, illustrating the gearshift position detector and the vicinity thereof as viewed from the left side of the shift drum. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   It should be understood that only structures considered necessary for clarifying the present invention are described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art. Referring now to the drawings,  FIG. 1  is a longitudinal cross-sectional view of an internal combustion engine  1 , as viewed from the left side and incorporating a shift position detector according to a selected illustrative embodiment of the present invention. The engine  1  of  FIG. 1  can also be characterized as a powertrain unit, since it incorporates a transmission internally therein, as well as conventional engine components. The engine  1  is intended for use in a motorcycle or other saddle-type vehicle. A directional arrow F in  FIG. 1  indicates the front, or forward driving direction, of the vehicle. In the figure, a cylinder block  3  is joined to the upper portion of a crankcase  2 . A cylinder head (not shown) and a cylinder head cover (not shown) are omitted from the figure for simplicity of illustration. A crankshaft  4  is provided in the front portion of the crankcase  2 . A connecting rod  6  is connected, at its one end, to a crankpin  5  of the crankshaft  4 . The other end of the connecting rod  6  is pivotally connected to a piston  7 . The piston  7  performs reciprocal up-and-down motions within the cylinder block  3 , resulting in the production of power. A balance shaft  8 , gear-driven through the crankshaft  4 , is provided forward of the crankshaft  4  and carries a balancer  9  thereon. 
   A manual transmission  10  is provided in the rear portion of the crankcase  2 . The transmission  10  includes a main shaft  11 , a countershaft  12 , a shift fork shaft  13 , and a shift drum  14 . The main shaft  11  is drivingly rotated from the crankshaft  4 , via gears and a multiple plate clutch. The countershaft  12  is rotationally driven from the main shaft  11  through speed-change gears. A shift drum turning mechanism  30  is located below the transmission  10 . 
     FIG. 2  is a transverse cross-sectional view of a portion of the engine  1 , illustrating the main shaft  11  and countershaft  12  of the transmission  10 . The main shaft  11  and the countershaft  12 , respectively, are supported for rotation by a left-hand crankcase  2 A and a right-hand crankcase  2 B through bearings  16 . A transmission input gear  20  is fitted to a portion near the right end of the main shaft  11 . The transmission input gear  20  is in full-time engagement with an output gear (not shown) of the crankshaft  4 , and is capable of circumferential rotation about the axis thereof. A multiple plate clutch  21  is provided at the right end of the main shaft  11 . The multiple plate clutch  21  is normally engaged, but can be selectively disengaged when operated by an operation mechanism. A clutch outer portion  22  of the clutch  21  is secured to the transmission input gear  20 , whereas a clutch inner portion  23  of the clutch  21  is secured to the main shaft  11 . Rotation of the crankshaft  4  is transmitted to the transmission input gear  20  via a crankshaft output gear (not shown), and further transmitted to the main shaft  11  through the multiple plate clutch  21 . 
   The main shaft  11  carries six gears. The countershaft  12  also carries six gears located at positions corresponding respectively to the six gears of the main shaft  11 , so that one of the latter six gears may be full-time meshed with the corresponding one of the former six gears. The power transmission roles of first to fifth speeds and reverse are respectively assigned to the six pairs of gears constituting the group of gears  24 . Incidentally, the pairing reverse gears are meshed with each other through an intermediate gear (not shown). 
     FIG. 3  is a transverse cross-sectional view of a portion of the engine  1 , showing a gear change mechanism  15 , including the shift fork shaft  13 , the shift drum  14  and a change spindle  31 . The left and right ends of the shift fork shaft  13  are supported by the left-hand crankcase  2 A and the right-hand crankcase  2 B, respectively. The shift fork shaft  13  carries three shift forks F 1 , F 2 , F 3 , which are axially slidable thereon. The fork part of the first shift fork F 1  is engaged with a groove G 1  ( FIG. 2 ) provided on an axially movable gear of the group of gears  24 . The fork part of the second shift fork F 2  is engaged with a groove G 2 , and the fork part of the third shift fork F 3  is engaged with a groove G 3 , the grooves G 2  and G 3  also each provided on an axially movable gear of the group of gears  24 . 
   The shift drum  14  is rotatably supported, at its left and right ends, by the left-hand and right-hand crankcases  2 A and  2 B via a needle bearing  32  and a plain bearing  33 , respectively. The shift drum  14  is provided with a first cam groove D 1 , a second cam groove D 2  and a third cam groove D 3 . The sliding pin P 1  of the first shift fork F 1  is slidably engaged with the first cam groove D 1 , the sliding pin P 2  of the second shift fork F 2  is slidably engaged with the second cam groove D 2 , and the sliding pin P 3  of the third shift fork F 3  is slidably engaged with the third cam groove D 3 . 
   The change spindle  31  is rotatably supported by the right-hand and left-hand crankcases  2 A and  2 B. The shift drum turning mechanism  30  is located between the change spindle  31  and the shift drum  14 . A gearshift position detector  60  is provided at the left end of the shift drum  14 . The shift drum turning mechanism  30  is a mechanism for turning the shift drum  14  on a predetermined angle basis, in accordance with a turn of the change spindle  31 . The turn of the change spindle  31  is achieved by a pressure applied onto a shift pedal (not shown), which is provided at the end of a shift pedal arm  34  welded to the left end of the change spindle  31 . 
   Operation of the shift drum turning mechanism  30  turns the shift drum  14  by a predetermined amount, whereby the cam grooves work to move one of the first, second and third shift forks along the shift fork shaft. An axially movable gear in mesh with the shift fork comes into mesh with the rotatable gear adjacent thereto. Consequently, the pair of gears selected, as above, among the group of gears in mesh with each other, is coupled to the respective shaft. When the pair of gears is meshed, the gear change by the gear change mechanism  15  is effected. Thus, rotation is transmitted from the main shaft  11  to the countershaft  12  at a change gear ratio determined by the pair of meshed gears. A sprocket  25  ( FIG. 2 ) is provided at the left end of the countershaft  12 . A chain  26  ( FIG. 2 ) is wound around the sprocket  25 , to transmit the output of the gear transmission  10  to a rear wheel (not shown) for driving the vehicle. 
     FIG. 4  is an enlarged cross-sectional detail view of the shift drum turning mechanism  30  and the gearshift position detector  60 .  FIG. 5  is a side plan detail view of the shift drum turning mechanism  30 , as viewed from the left side. A change arm  35  is fixedly welded to the change spindle  31  for turning therewith. A shifter plate  36  overlaps the change arm  35  and is carried on the change arm  35  with two guide pins  37 A,  37 B slidably with respect thereto. 
   The change arm  35  and the shifter plate  36  are each respectively provided with medial openings  35   a  and  36   a , slightly different in shape from each other. The shifter plate  36  is slidable in the direction of a centerline C-C of the change arm  35 , within a range defined by the longitudinal hole  36   b  of the shifter plate  36  and the cut-in portion  36   c  of the medial opening  36   a . A guide pin  37 A is inserted into the longitudinal hole  36   b , whereas a guide pin  37 B is inserted into the cut-in portion  36   c . A restriction bolt  38  is provided which passes through the medial opening  35   a  of the change arm  35  and the medial opening  36   a  of the shifter plate  36 . The proximal end of the restriction bolt  38  is threadably fixed to the left-hand crankcase  2 A. The change arm  35  includes a spring-pressing portion  35   b , extending transversely outwardly from the main plane of the change arm, on one side of the medial opening  35   a  thereof. The spring-pressing portion  35   b  is shaped to project in the direction of the central portion of the medial opening  35   a , and then bend into the medial opening  36   a  of the shifter plate  36 . 
   The change arm  35  is turned together with the change spindle  31 . In order for the change arm  35  to return to its original position, a change arm return spring  39  is wound around the change spindle  31 , in such a manner that the restriction bolt  38  and the spring-pressing portion  35   b  of the change arm  35  are put between both the ends of the spring  39 . As stated above, the shifter plate  36  is slidable with respect to the change arm  35 . A shifter plate urging spring  40  is attached between the change spindle  31  and the shifter plate  36 , so as to urge the shifter plate  36  in the direction of the shift drum  14 . A skip-turn-prevention plate  41  is fixedly press-fitted onto an end of the shift drum  14 . As described later, this plate  41  is a member for preventing the shift drum  14  from skip-turning in excess of one stage, for one shift operation. Six engagement rollers  42  are provided between the end of the shift drum  14  and the plate  41 . 
   Referring to  FIG. 5 , when the change spindle  31  is turned by a shift pedal force, the change arm  35 , welded to the change spindle  31 , is turned together with the shifter plate  36 , which is slidably attached to the change arm  35  via the guide pins  37 A,  37 B. One leg of the change arm return spring  39  is pressed and opened by the spring-pressing portion  35   b  of the change arm, whereas the other leg is not moved, because of being blocked by the restriction bolt  38 . The shifter plate  36  is turned along with turning of the change arm  35 , whereby one of a pair of right and left engagement projections  36   d  is brought into engagement with an engagement roller  42 , turning the shift drum  14 . As best seen in  FIG. 5 , the engagement projections  36   d  are projecting top ends of the shifter plate  36 . 
   After the shift drum  14  is turned at a predetermined angle, the change arm  35  and the shifter plate  36  are returned to their original positions by the resilience of the change arm return spring  39 . When the shift drum  14  is turned at the predetermined angle, another engagement roller, next to the engagement roller  42  that has been previously engaged with the engagement projections, occupies the position that has been previously occupied by the previously engaged engagement roller. Therefore, when returned, the engagement projections  36   d  of the shifter plate  36  have to override the engagement roller next to the engagement roller that has been previously engaged with the engagement projections. In this case, since the shifter plate  36 , movable in the range of the longitudinal hole  36   b , moves backward against the urging force of the shifter plate urging spring  40 , the engagement projections  36  can override the next roller. If an excessive force is applied to the change arm  35 , then the shift drum  14  is about to skip-turn over the predetermined angle. In this case, an external projection  41   a  of the skip-turn-prevention plate  41  comes into contact with a contact end  35   c  of the change arm  35 , preventing the potential skip-turn from taking place. 
   Referring to  FIGS. 3 and 6 , a shift drum stabilizer  45  is provided at the right end of the shift drum  14 .  FIG. 6  is a view of the stabilizer  45  as viewed from the right side of the shift drum  14 . The stabilizer  45  includes a star-shaped plate  46 , and a stopper roller assembly  47 . The star-shaped plate  46  is secured to an end of the shift drum  14  with a mounting bolt  48  and a locking pin  49 . The stopper roller assembly  47  includes a sleeve  51 , an arm  52 , a roller shaft  53 , a stopper roller  54 , and a spring  55 . The sleeve  51  is secured to the right-hand crankcase  2 B with a bolt  50 . The arm  52  is held for turning around the sleeve  51 . The stopper roller  54  is held at the free end of the arm  52 , for turning around the roller shaft  53 . The spring  55  is adapted to urge the arm  52  in the direction of the curved arrow in  FIG. 6 , so as to press the stopper roller  55  against the circumferential surface of the star-shaped plate  46 . The turning positions of the shift drum  14 , associated with the respective change gear ratios, are stably maintained by press-fitting the stopper roller  54  into one of the outer circumferential recesses  46   a  associated with the respective change gear ratios. 
   Referring again to  FIG. 4 , the gearshift position detector  60  is located on the left side of the shift drum  14 .  FIG. 7  is a view illustrating the detector  60  and the vicinity thereof as viewed from the left side of the shift drum  14 . The detector  60  is a device for detecting the turning positions of the shift drum  14 , particularly when the transmission is in the neutral or reverse gear position. The detector  60  includes a switch plate  62 , a neutral indicator switch  63 , and a reverse indicator switch  64 . The indicator switches  63 ,  64  may be arranged to switch on indicator lamps (not shown) on the user instrument panel, or alternatively, may generate audible signals to alert the user regarding the selected gear. As shown, the indicator switches  63 ,  64  are disposed separately and independently of each other. 
   The switch plate  62  is secured to the skip-turn-prevention plate  41  with two rivets  61 . The switch plate  62  is fixedly swaged to the skip-turn-prevention plate  41  with the rivets  61  before the skip-turn-prevention plate  62  is attached to the shift drum  14 . The combination of the switch plate  62  and the skip-turn-prevention plate  41  is fixedly press-fitted to the end of the shift drum  14 . The switch plate  62 , the skip-turn-prevention plate  41  and the shift drum  14  are turned in a unified manner, that is, at the same time. The neutral indicator switch  63  and the reverse indicator switch  64 , respectively, are threadably secured to the left-hand crankcase  2 A. 
   The switch plate  62  is a metal plate, and is provided, at opposite ends thereof, with a neutral switch actuator arm  62   a  and a reverse switch actuator arm  62   b . The actuator arms  62   a  and  62   b  are formed extending outwardly, like a cam, by deforming the ends of the metal plate so that the respective contact potions are slightly extended with respect to the middle plane portion of the metal plate (see  FIG. 4 ). On the other hand, the indicator switches  63 ,  64  are each respectively provided with a movable contact  63   a ,  64   a , at their respective inwardly-facing terminal ends ( FIG. 4 ). When the movable contacts  63   a ,  64   a  come into contact with the actuator arms  62   a ,  62   b  of the switch plate  62 , respectively, the movable contacts are pressed slightly inwardly, which turns on the switch for energization, thus achieving detection of the shift positions. The energization from the switch lights a lamp (not shown) located at the mid portion of a steering handlebar in front of an operator. This informs the operator of the neutral state or of the reverse state, at that time. 
   Incidentally, in  FIGS. 4 and 7 , the radial distance from the center of turning of the shift drum to the neutral indicator switch  63 , or the neutral switch actuator arm  62   a , differs from that to the reverse indicator switch  64  or the reverse switch actuator arm  62   b . Therefore, only the corresponding contact therebetween will be established. In other words, the neutral switch actuator arm can only activate the neutral indicator switch, and the reverse switch actuator arm can only activate the reverse indicator switch, because of the different radial distances of the respective switches, and the corresponding actuator arms, from the axis of the shift drum. 
   As described in detail above, in the present embodiment, since the switch plate  62  is attached to skip-turn-prevention plate  41  in a unified manner, the length of time required for attachment is reduced, attachment accuracy is improved and space-saving can be achieved. 
   While a working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.