Abstract:
In an automatic transmission includes a main shaft and a counter shaft which are parallel to a crankshaft with the rotation of a torque converter on the crankshaft being transmitted to the main shaft through gears. A two-state speed change is conducted by gears provided on the main shaft and the counter shaft. An oil hydraulic clutch is operatively provided for connection and disconnection between the gear for reducing the spacing between the crankshaft and the transmission and to contrive a reduction in size of a power unit. A tubular auxiliary main shaft rotatable relative to the main shaft is provided at the outer circumference of the main shaft with a first-speed drive gear and a rearward-running drive gear are fixed on the auxiliary main shaft. First and second oil hydraulic clutches are provided for enabling contact and separation between the main shaft and the auxiliary main shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present nonprovisional application claims priority under 35 USC  119  to Japanese Patent Application No. 2002-114432 filed on Apr. 17, 2002 the entire contents thereof is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an automatic transmission for an internal combustion engine-transmission integral type power unit mounted on a four-wheel buggy car (saddle-ride type vehicle for operating on irregular surfaces) or the like.  
           [0004]    2. Description of Background Art  
           [0005]    Japanese Patent Publication No. Sho 57-2953 discloses a conventional crankshaft of an internal combustion engine and a main shaft of a transmission that are disposed on one straight line. Power is transmitted in a series manner from the crankshaft of the internal combustion engine to a torque converter disposed at an end of the main shaft of the transmission. In addition, oil hydraulic clutches are disposed, respectively, on the main shaft and a counter shaft.  
           [0006]    Conventionally, the crankshaft of the internal combustion engine and the main shaft of the transmission have been disposed in series on one straight line, so that the overall length of the power unit is large. This structure is unsuitable for mounting on a four-wheel buggy car or a motorcycle. When the crankshaft and the shaft of the transmission are disposed in parallel to each other in a conventional constitution, for the purpose of obviating the above-mentioned inconvenience and shortening the overall length, the outside diameters of the crankshaft and the clutches will interfere with each other. Therefore, the spacing between the shafts must be enlarged. This approach has a problem in that the power unit becomes large in size and the weight is also increased.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0007]    The present invention solves the above-mentioned problems. The present invention is directed to an automatic transmission including a main shaft and a counter shaft which are disposed parallel to a crankshaft. The rotation of a torque converter is provided on the crankshaft being transmitted to the main shaft through bearings. A two-stage speed change is conducted by gears provided on the main shaft and the counter shaft. An oil hydraulic clutch is provided for connection and disconnection between these gears. A tubular auxiliary main shaft is rotatable relative to the main shaft and is provided at the outer circumference of the main shaft. A first-speed drive gear and a rearward-running drive gear are fixed on the auxiliary main shaft. A first oil hydraulic clutch for enabling contact and separation between the main shaft and the auxiliary main shaft is disposed on the outside of one of a pair of support portions for supporting the main shaft. A second oil hydraulic clutch for enabling contact and separation between a second-speed drive gear which is in loose fit on the main shaft and engaged with a second-speed driven gear fixed on the counter shaft and the main shaft is disposed on the outside of the other of the pair of supporting portions for supporting the main shaft.  
           [0008]    According to the present invention, the crankshaft and the main shaft are thus parallel to each other, so that the overall length of the power unit can be shortened. In addition, since the oil hydraulic clutches are disposed at end portions on the outside of the front and rear support portions for the main shaft, it is possible to obviate interference among the torque converter, a crank, an AC generator and the like on the crankshaft.  
           [0009]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0011]    [0011]FIG. 1 is a side view of a four-wheel buggy car (saddle-ride type vehicle for operating on irregular surfaces) on which a power unit comprising an automatic transmission according to one embodiment of the invention is mounted;  
         [0012]    [0012]FIG. 2 shows a cross section of a crankcase  23  of the power unit, as viewed from the front side;  
         [0013]    [0013]FIG. 3 is a sectional view including a crankshaft  7  and a main shaft  8 ;  
         [0014]    [0014]FIG. 4 is a sectional development including the main shaft  8 , a counter shaft  10 , an output shaft  11  and a shift fork guide shaft  19 ; and  
         [0015]    [0015]FIG. 5 is a sectional development including the main shaft  8 , an intermediate shaft  9 , the counter shaft  10  and the shift fork guide shaft  19 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    [0016]FIG. 1 is a side view of a four-wheel buggy car (saddle-ride type vehicle for operating on irregular surfaces) on which a power unit comprising an automatic transmission according to one embodiment of the present invention is mounted. The buggy car comprises a pair of front wheels  2  and a pair of rear wheels  3  mounted at front and rear portions of a vehicle body frame  1 . A power unit  6  includes an internal combustion engine  4  and a transmission  5  integrated with each other and supported at a central portion of the vehicle body frame  1 . The power unit  6  is disposed with a crankshaft  7  directed in the front-rear direction of the vehicle body. The rotation of the crankshaft  7  is transmitted to an output shaft  11  shown in FIG. 1, through a main shaft  8 , an intermediate shaft  9  and a counter shaft  10  of a transmission which will be described later. Each of these shafts is parallel to the crankshaft and is disposed in the front-rear direction of the vehicle body. The front wheels  2  are driven by a front wheel drive shaft  12  connected to the front end of the output shaft  11 , whereas the rear wheels  3  are driven by a rear wheel drive shaft  13  connected to the rear end of the output shaft  11 . A steering handle  14 , a fuel tank  15  and a saddle type seat  16  are provided, in this order from the front side, at upper portions of the vehicle body.  
         [0017]    [0017]FIG. 2 shows a cross section of a crankcase  23  of the power unit, as viewed from the front side. FIG. 2 illustrates the crankshaft  7 , the main shaft  8 , the intermediate shat  9 , the counter shaft  10 , and the output shaft  11 . In addition, the positions of shift forks  17  and  18 , a shift fork guide shaft  19 , and a shift drum  20  are shown. A balance weight shaft  21  is provided in the vicinity of the crankshaft  7 .  
         [0018]    [0018]FIG. 3 is a sectional view including the crankshaft  7  and the main shaft  8 . FIG. 4 is a sectional development including the main shaft  8 , the counter shaft  10 , the output shaft  11  and the shift fork guide shaft  19 . FIG. 5 is a sectional development including the main shaft  8 , the intermediate shaft  9 , the counter shaft  10  and the shift fork guide shaft  19 . The sectional view and sectional developments including these shafts illustrate a power transmission mechanism, and, particularly, FIGS. 4 and 5 show the parts pertaining to the automatic transmission.  
         [0019]    [0019]FIG. 3 shows the power transmission mechanism relating to the crankshaft  7  and the main shaft  8 . A crankcase portion of the power unit includes a front crankcase cover  24 , a front crankcase  25 , a rear crankcase  26 , and a rear crankcase cover  27 , in this order from the front side. The crankshaft  7  is rotatably supported on the crankcases  25  and  26  through bearings  43  and  44 . A front extension portion of the crankshaft  7  is supported on the front crankcase cover  24  through a bearing  45 . The crankshaft  7  is divided into front and rear portions, which are connected by a crank pin  7   b  at crank web portions  7   a  thereof, and a connecting rod  28  is supported by the crank pin  7   b . An AC generator  29  for generating electric power by the rotation of the crankshaft  7  is mounted on a rear end portion of the crankshaft  7 .  
         [0020]    A torque converter  30  is mounted on a front portion of the crankshaft  7 , and a primary drive gear  34  is in loose fit on the crankshaft  7  adjacently to the torque converter  30 . The torque converter  30  includes a pump impeller  31  fixed to the crankshaft  7 , a turbine runner  32  opposed thereto, and a stator  33 . The turbine runner  32  is connected to the primary drive gear  34 . Working oil for the torque converter  30  is supplied from the front crankcase cover  24  through the gap between an outer pipe  36  and an inner pipe  37  of a double-wall pipe inserted in a central hole of the crankshaft  7 . Lubricating oil for the crank pin  7   b  is supplied through the inside of the inner pipe  37 . The double-wall pipe is elastically supported on the front crankcase cover  24  through an O-ring, whereby eccentricity of the axis is absorbed.  
         [0021]    A tubular auxiliary main shaft  38  is provided at the outer circumference of a front half of the main shaft  8 . The auxiliary main shaft  38  is rotatably supported on the front and rear crankcases  25  and  26  through bearings  46  and  47 . The front half of the main shaft  8  penetrates through the central hole of the auxiliary main shaft  38 , and is rotatably supported by the auxiliary main shaft  38  through a needle bearing  48 . A rear portion of the main shaft  8  is rotatably supported on the rear crankcase  26  through a bearing  49 . The main shaft  8  and the auxiliary main shaft  38  are rotatable relative to each other.  
         [0022]    A primary driven gear  35 , normally meshed with the primary drive gear  34 , is fixed to a front portion of the main shaft  8 . The rotation of the crankshaft  7  is transmitted through the torque converter  30  to the primary drive gear  34 , is further transmitted to the primary driven gear  35  meshed with the primary drive gear  34 , and is transmitted to the main shaft  8  through a primary speed reduction by these gears. The main shaft  8  is normally rotated during operation of the internal combustion engine.  
         [0023]    A first-speed oil hydraulic type multiple disk clutch  39  is provided on the front side of the bearing  46 , at the front end of the auxiliary main shaft  38 . A first-speed drive gear A 1  and a rearward-running drive gear A 2  are fixed on the auxiliary main shaft  38 , on the rear side of the bearing  46 . An inner  39   a  of the first-speed oil hydraulic type multiple disk clutch  39  is integral with the primary driven gear  35  fixed on the main shaft  8 . An outer  39   b  of the clutch  39  is fixed on the auxiliary main shaft  38 . When the first-speed oil hydraulic type multiple disk clutch  39  is connected by oil hydraulic pressure, the main shaft  8  and the auxiliary main shaft  38  are connected to each other through the primary driven gear  35  and the first-speed oil hydraulic type multiple disk clutch  39 . The rotation of the main shaft  8  is transmitted to the first-speed drive gear A 1  and the rearward-running drive gear A 2  on the auxiliary main shaft  38 .  
         [0024]    A second-speed drive gear A 3  larger than the first-speed drive gear A 1  in diameter is in loose fit on a rear end portion of the main shaft  8 , on the rear side of the bearing  49 , and a second-speed oil hydraulic type multiple disk clutch  40  is provided adjacently to the second-speed drive gear A 3 . Of the second-speed oil hydraulic type multiple disk clutch  40 , an inner  40   a  is fixed onto the main shaft  8 , and an outer  40   b  is so connected so that it can be rotated as one body with the second-speed drive gear A 3 . When the second-speed oil hydraulic type multiple disk clutch  40  is connected by an oil hydraulic pressure, the rotation of the main shaft  8  is transmitted to the second-speed drive gear A 3 .  
         [0025]    In connecting the first-speed and second-speed clutches, hydraulic oil is supplied only to either one of the clutches for effecting the connection. Working oil for the first-speed oil hydraulic type multiple disk clutch  39  is supplied through the gap between an outer pipe  50  and an inner pipe  51  of a double-wall pipe inserted from the front crankcase cover  24  into the central hole of the main shaft  8 . Working oil for the second-speed oil hydraulic type multiple disk clutch  40  is supplied through the inner pipe  51  of the double-wall pipe. The changeover of the destination of the hydraulic oil is carried out through a changeover of an oil passage inside a valve body  53  by passing an electric current to a solenoid valve  52 , whereby oil passages  54  and  55  inside the front crankcase cover  24  connected to the double-wall pipe are changed over. The current-passing operation for this changeover is automatically conducted by an instruction signal from an electronic controller based on parameters such as vehicle speed, throttle opening, etc. The double-wall pipe is elastically supported on the front crankcase cover  24  through an O-ring, whereby eccentricity of the axis is absorbed.  
         [0026]    [0026]FIG. 4 shows the power transmission mechanism for transmitting power from the main shaft  8  to the counter shaft  10  and the output shaft  11 . The counter shaft  10  is rotatably supported on the front and rear crankcases  25  and  26  through bearings  56  and  57 , whereas the output shaft  11  is rotatably supported on the front crankcase cover  24 , the rear crankcase  26  and the rear crankcase cover  27  through bearings  58 ,  59  and  60 .  
         [0027]    A first-speed driven gear B 1  and a rearward-running driven gear B 2  are in loose fit on the counter shaft  10  with a forward/rearward selection dog clutch  41  being provided therebetween. Either one of the gears B 1  and B 2  can be fixed to the counter shaft  10  by a selecting operation of the shift fork  17 . Further, a high drive gear B 3 , a low drive gear B 4  and a second-speed driven gear B 5  are fixed on the counter shaft  10 . The high drive gear B 3  is larger than the low drive gear B 4  in diameter.  
         [0028]    A high driven gear C 1  and a low driven gear C 2  are in loose fit on the output shaft  11  with a high/low selection dog clutch  42  being provided therebetween. Either one of the gears C 1  and C 2  can be fixed to the output shaft by a selecting operation of the shift fork  18 . Shift forks  17  and  18  are both supported by the guide shaft  19 . Tip ends of shifter pins  17   a  and  18   a  provided in the shift forks  17  and  18  are inserted in cam grooves  20   a  and  20   b  which are provided, as grooves for exclusive use for the respective pins, in the shift drum  20  shown in FIG. 2. Turning of the shift drum  20  is manually effected by the rider, through an operation cable (not shown) connected to a shift lever (not shown) provided at the steering handle  14  of the vehicle.  
         [0029]    The first-speed driven gear B 1  is in loose fit on the counter shaft  10  and is normally meshed with the first-speed drive gear A 1  on the auxiliary main shaft  38 . The rearward-running driven gear B 2  is in loose fit on the counter shaft  10  and is normally meshed with the rearward-running drive gear A 2  through a direction changeover gears M 1  and M 2  which will be described later. The high drive gear B 3  and the low drive gear B 4  fixed on the counter shaft  10  are normally meshed, respectively, with the high driven gear C 1  and the low driven gear C 2  which are in loose fit on the output shaft  11 . The second-speed driven gear B 5  is normally meshed with the second-speed drive gear A 3  on the main shaft  8 .  
         [0030]    [0030]FIG. 5 shows the power transmission mechanism for transmitting power from the main shaft  8  to the counter shaft  10  through the intermediate shaft  9 . The intermediate shaft  9  is supported on the front and rear crankcases  25  and  26 . The direction changeover gears M 1  and M 2  are rotatably supported on the intermediate shaft  9 . The direction changeover gears M 1  and M 2  are idle gears which have a common boss portion. The gear M 2  is smaller than the gear M 1  in diameter. The direction changeover gear M 1  is normally meshed with the rearward-running drive gear A 2  fixed on the auxiliary main shaft  38 , whereas the direction changeover gear M 2  is normally meshed with the rearward-running driven gear B 2  on the counter shaft  10 .  
         [0031]    The automatic transmission according to the present embodiment is constituted as described above. In describing the speed change functions of the automatic transmission, for convenience of description, selection of the first-speed clutch of the first-speed and second-speed oil hydraulic type multiple disk clutches  39  and  40  will be designated as “first speed,” selection of the second-speed clutch will be designated as “second speed,” selection of the first-speed driven gear B 1  side of the forward/rearward selection dog clutch  41  will be designated as “forward,” selection of the rearward-running driven gear B 2  will be designated as “rearward,” selection of the high driven gear C 1  side of the high/low selection dog clutch  42  will be designated as “high gear,” and selection of the low driven gear C 2  side will be designated as “low gear.” 
         [0032]    There are six choices for combinations of the oil hydraulic type clutch and the dog clutch, which can be arranged in the order of increasing vehicle speed as follows. For the individual choices, the gear trains to be operated will also be shown.  
         [0033]    In the case of forward running:  
         [0034]    (a) First speed-Forward-Low gear: A 1 -B 1 -B 4 -C 2 ,  
         [0035]    (b) First speed-Forward-High gear: A 1 -B 1 -B 3 -C 1 ,  
         [0036]    (c) Second speed-Low gear: A 3 -B 5 -B 4 -C 2 ,  
         [0037]    (d) Second speed-High gear: A 3 -B 5 -B 3 -C 1 ,  
         [0038]    In the case of rearward running:  
         [0039]    (a) First speed-Rearward-Low gear: A 2 -M 1 -M 2 -B 2 -B 4 -C 2 ,  
         [0040]    (b) First speed-Rearward-High gear: A 2 -M 1 -M 2 -B 2 -B 3 -C 1 .  
         [0041]    As has been described in detail above, the automatic transmission according to the present invention has a structure in which the crankshaft  7  and the main shaft  8  are parallel to each other, so that the overall length of the power unit can be shortened. In addition, since the oil hydraulic clutches  39  and  40  are disposed at end portions on the outside of the front and rear support portions (the bearing  46  and the bearing  49 ) for the main shaft, interference of the oil hydraulic clutches  39  and  40  with the torque converter  30 , the crank  7   a  and  7   b , the AC generator  29  and the like on the crankshaft  7  can be obviated.  
         [0042]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.