Abstract:
A connection structure between a plastic gear and a shaft permits easy phase matching relative to a device mounted on the shaft, and easy meshing of a gear provided on the shaft with another gear. The connection structure includes a plastic gear, a shaft, and a set plate. The plastic gear has a geometric recess which receives the correspondingly-shaped set plate therein. The set plate includes a central shaped opening. The shaft is provided with a mating extension extending from a first end, and which fits within the shaped opening. The mating extension is formed such that the plastic gear may be mounted thereon in a first position wherein the plastic gear is not positioned to interact with a mating gear, and the plastic gear can be slidably moved thereon to a second position such that the plastic gear is positioned to interact with the mating gear.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2003-324655, filed on Sep. 13, 2003.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a connection structure between a plastic gear and an oil pump drive shaft for an internal combustion engine.  
         [0004]     2. Background Art  
         [0005]     A known method for connecting an oil pump shaft to a gear that transmits a driving force thereto includes the steps of providing a U-shaped groove across a center hole in the gear; fitting a lock pin into a through hole provided perpendicularly relative to a centerline of the shaft; and pushing the shaft into the center hole in the gear, thereby fitting the lock pin into the groove in the gear (see, for example, Japanese Utility Model Publication No. Hei 3-38470, FIGS. 1 and 2).  
         [0006]     Since, in this known connecting method, the lock pin is mounted in the through hole of the shaft, provided perpendicularly relative to the centerline of the shaft, an axial position of the shaft is fixed relative to an axial position of the gear. This makes it difficult, due to the lock pin coming off position, to perform phase matching of an oil pump rotor when the gear is not in mesh with a mating gear.  
         [0007]     What is needed is an improved connecting structure for connecting a gear to an oil pump drive shaft of an internal combustion engine, which permits easy phase matching relative to a device mounted on the shaft, and easy meshing of a gear, provided on the shaft, with another gear. Preferably, such a connecting structure would non-rotatably fix the position of the gear in relation to the shaft, so that the gear and shaft rotate concurrently together as an integral unit.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to provide an improved connection structure for connecting a plastic driven gear and a shaft. The connection structure hereof is suitable for a plastic oil pump gear, and permits easy phase matching relative to a device mounted on the shaft, and easy meshing of a gear, provided on the shaft, with another gear.  
         [0009]     To achieve the aforementioned object, a connection structure between a plastic gear and a shaft, as presented in a first embodiment of the present invention, connects a plastic gear that meshes with a drive gear or a driven gear to a shaft that rotates integrally with the plastic gear.  
         [0010]     The connection structure according to a first embodiment hereof includes a mortised opeining provided at a central portion of a rectangular set plate. A rectangular recess, in which the set plate fits, is provided on a front surface of a portion of the plastic gear, to which the shaft is connected, and the set plate is mounted thereon. The shaft has an end portion including a tenon, which is configured and dimensioned to fit through the mortised opening provided in the set plate. The tenon has a length such that, when the plastic gear is connected to the shaft, the tenon of the shaft is first aligned with and then inserted in the mortised opening of the set plate. When the mounting of the tenon in the mortise has proceeded a predetermined amount, the plastic gear is meshed with the mating gear.  
         [0011]     The connection structure between a plastic gear and a shaft according to the present invention permits transmission of a driving force through a large area of contact produced between the set plate and the recess. This enhances durability of the plastic gear. The connection structure also allows the plastic gear and the mating gear to be meshed with each other after phase matching of an oil pump rotor is performed with the plastic gear mounted on the shaft but not yet in mesh with the mating gear. This enhances efficiency in phase matching and assembly work.  
         [0012]     For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a longitudinal cross sectional view of an air-cooled internal combustion engine for a motorcycle according to an illustrative embodiment of the present invention, as viewed from a right-hand side that shows, by removing a right case cover of a transmission, positions of a rotating shaft that protrudes to a right-hand side of a right crankcase and a number of different gears.  
         [0014]      FIG. 2  is a cross sectional view of the engine of  FIG. 1 , taken along line II-II therein.  
         [0015]      FIG. 3  is a cross sectional detail view of part of the engine of  FIG. 1 , taken along line III-III thereof, and showing a right-hand half portion inside a crankcase.  
         [0016]      FIG. 4  is a cross sectional detail view of the engine of  FIGS. 1-3 , taken along line IV-IV of  FIG. 3  showing the crankshaft, the main transmission shaft, the balance shaft, and the tenon on the leading end of the oil pump shaft. 
     
    
     DETAILED DESCRIPTION  
       [0017]     It should be understood that only structures considered necessary for explaining and 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.  
         [0018]     Referring to  FIGS. 1 and 2 , a crankcase assembly  50  for an air-cooled internal combustion engine E is illustrated in cross-section, and is provided for installation on a motorcycle (not shown). The crankcase assembly  50  includes a left case cover  1 , a left crankcase  2 , a right crankcase  3 , and a right case cover  4 . A cylinder block  5 , a cylinder head  6 , and a cylinder head cover  7  are connected, in sequence, to an upper portion of the crankcase assembly  50 .  
         [0019]     The crankcase assembly  50  includes a crankshaft  10 , a main transmission shaft  11 , a transmission countershaft  12 , and a kick starter shaft  13 . The reference numeral  14  represents the position of a center of rotation of a shift drum within the crankcase assembly  50 . The crankcase assembly  50  further includes a transmission shifter  15 , a balance shaft  16 , an oil pump shaft  17 , a crankpin  18  and a connecting rod  19  connected to the crankpin  18 . A piston  20  is connected to the connecting rod  19 , and moves reciprocally up and down in the cylinder block  5 .  
         [0020]     Referring to  FIG. 2 , the crankshaft  10  is rotatably supported between the left crankcase  2  and the right crankcase  3  through a ball bearing  21  and a roller bearing  22 , respectively. The main transmission shaft  11  and the transmission countershaft  12  are also each respectively supported between the left crankcase  2  and the right crankcase  3  through respective ball bearings. The kick starter shaft  13  is supported by the right crankcase  3  and the right case cover  4 . The transmission countershaft  12  is an output shaft of this internal combustion engine.  
         [0021]     A drive sprocket  23  is provided on a portion of the transmission countershaft  12  protruding outwardly from the left crankcase  2 , as shown. The drive sprocket  23  thus drives a rear wheel of the motorcycle through a chain  24 . An alternator  39  is provided on a left end portion of the crankshaft  10 .  
         [0022]     A balancer drive gear  25  and a shared drive gear  26  are secured, via a key  27 , to a right-hand portion of the crankshaft  10 . The balancer drive gear  25  meshes with a balancer driven gear  37  ( FIG. 1 ). The shared drive gear  26  meshes with a main shaft driven gear  28  on the main transmission shaft  11  and an oil pump gear  44  on the oil pump shaft  17  ( FIG. 1 ).  
         [0023]     The main shaft driven gear  28  is fitted to a right-side portion of the main transmission shaft  11 . The main shaft driven gear  28  is in constant mesh with the shared drive gear  26 , and is circumferentially rotatable relative to the main transmission shaft  11 . A multiple disc clutch  30  is provided on a right end of the main transmission shaft  11 . The multiple disc clutch  30  is normally engaged, but disengaged when an operating mechanism  29  is operated. A clutch outer section  31  of the multiple disc clutch  30  is secured to the main shaft driven gear  28 . A clutch inner section  32  is secured to the main transmission shaft  11 . Rotation of the crankshaft  10  is transmitted to the main shaft driven gear  28  through the shared drive gear  26 , and to the main transmission shaft  11  through the multiple disc clutch  30 .  
         [0024]     Referring to  FIG. 2 , transmission gears  33  are provided for the main transmission shaft  11  and the countershaft  12 . The transmission gears  33  include five gears provided on the main transmission shaft  11  and another five gears provided on the countershaft  12  and in constant mesh with the five gears on the main transmission shaft  11 . A total of ten of these gears are classified into any of the following three categories: (a) those secured to the shaft; (b) those held in position by the shaft through a plain bearing that are circumferentially rotatable relative to the shaft, but not movable axially; and (c) those held in position by the shaft through a spline that are axially movable, but not circumferentially rotatable relative to the shaft.  
         [0025]     The axially movable gears classified in category (c) make up a dog-tooth clutch. An axially movable gear is moved axially by a shift fork (not shown) that is in constant engagement therewith. The axially movable gear is thereby engaged with a circumferentially rotatable gear classified into category (b), thus locking the gear in category (b) relative to the shaft. Through the operations described above, one pair of gears capable of transmitting drive is selectively made to enable gearshift from a 1st speed up to a 5th speed.  
         [0026]     A gear  34  on the kick starter shaft  13  can start to rotate the crankshaft  10  through a gear  35  on a right end portion of the countershaft  12 , a gear  36  on a right end portion of the main transmission shaft  11 , the main shaft driven gear  28 , and the shared drive gear  26  on the crankshaft  10 .  
         [0027]      FIG. 3  is a cross sectional view taken along line III-III of  FIG. 1 , showing a right-hand half portion inside the crankcase. The right-hand half portion of the crankshaft  10  is supported on the right crankcase  3  through the roller bearing  22 . A bushing  38  is interposed between the right crankcase  3  and the roller bearing  22 . As described earlier, the balancer drive gear  25  and the shared drive gear  26  are mounted through the shared key  27  to the crankshaft  10 .  
         [0028]     As seen best in  FIG. 3 , an oil pump  40  is provided in the crankcase assembly  50  below the crankshaft  10 . A pump case  41  is mounted on the right crankcase  3  through a steel plate  42 , being secured thereto with a bolt  43 . An oil pump shaft  17  is rotatably supported between the right crankcase  3  and a wall body of the pump case  41 .  
         [0029]     One end of the oil pump shaft  17  passes through the wall body of the pump case  41 , protruding to the right as seen in the drawing of  FIG. 3 , to form a rightward protruding portion. A plastic oil pump gear  44  is secured to the rightward protruding portion of the oil pump shaft  17 , by way of a tenon  17   a  on a leading end of the oil pump shaft  17  and a set plate  45  having a mortised opening  45   a  formed therein, as will be further described. The plastic oil pump gear  44  meshes with the shared drive gear  26  on the crankshaft  10 .  
         [0030]     The set plate  45  is fitted into a set plate mounting recess  44   a  provided on a front surface of the oil pump gear  44 . The tenon  17   a,  on the leading end of the oil pump shaft  17 , is fitted in a mortised opening  45   a  formed in a central portion of the set plate  45 . An oil pump rotor  46  is fitted over the oil pump shaft  17 , on an end of the shaft opposite the tenon.  
         [0031]     As the crankshaft  10  rotates, the oil pump rotor  46  is rotated via the shared drive gear  26 , the oil pump gear  44 , the set plate  45 , the tenon  17   a,  and the oil pump shaft  17 .  
         [0032]      FIG. 4  is a cross sectional view taken along line IV-IV of  FIG. 3 , showing the crankshaft  10 , the main transmission shaft  11 , the balance shaft  16 , and the tenon  17   a  on the leading end of the oil pump shaft  17 . The shared drive gear  26  on the crankshaft  10  meshes with the main shaft driven gear  28  on the main transmission shaft  11 , and also meshes with the plastic oil pump gear  44  on the oil pump shaft  17 . The balancer drive gear  25  on the crankshaft  10  meshes with the balancer driven gear  37  on the balance shaft  16 .  
         [0033]     Still referring to  FIG. 4 , the set plate  45  for inhibiting relative rotation is interposed between the plastic oil pump gear  44  and the oil pump shaft  17 . The set plate  45  is a rectangular metal plate provided at the center thereof with the mortise  45   a  having two faces running in parallel with each other. Steel is a material which is usable to form the set plate  45 .  
         [0034]     In the depicted embodiment, the set plate mounting recess  44   a  is formed in a rectangular shape, in which the set plate  45  fits, is provided on the front surface at the portion of the plastic oil pump gear  44 , at which the oil pump shaft  17  is connected. The set plate  45  fits into this set plate mounting recess  44   a.  A driving force from the plastic oil pump gear  44  is transmitted through four faces around the set plate mounting recess  44   a  and edge surfaces of the set plate  45 , on which the four faces of the set plate mounting recess  44   a  abut.  
         [0035]     The oil pump shaft  17  is a shaft made of steel. The tenon  17   a  is provided on the end of the oil pump shaft  17  to be connected to the oil pump gear  44 . The tenon  17   a  is to be fitted into the mortise  45   a  in the set plate  45 . The tenon  17   a  on the end of the shaft has a cross section of the same shape as a cross section of the mortise  45   a  in the set plate  45 . Specifically, the tenon  17   a  includes two surfaces that run in parallel with, and abut on, the two parallel surfaces of the mortise  45   a  in the set plate  45 . A driving force from the set plate  45  is transmitted to the oil pump shaft  17  through these parallel abutment surfaces.  
         [0036]     The tenon  17   a  is set to have such a length that, when the plastic oil pump gear  44  is to be connected to the oil pump shaft  17 , the mortise  45   a  is first aligned with the tenon  17   a,  and then is followed by the step of mounting the tenon  17   a  in the mortise  45   a.  When the mounting of the tenon  17   a  in the mortise  45   a  has proceeded a predetermined amount, the plastic oil pump gear  44  is meshed with the mating shared drive gear  26 .  
         [0037]     The connection structure between the plastic gear and the shaft according to the preferred embodiment of the present invention is arranged as described in the foregoing. The set plate  45  has the four edge surfaces therearound that are in contact with the recess  44   a  of the plastic gear  44 . This allows the driving force of the gear to be transmitted to the set plate  45  through the four edge surfaces. This connection structure has a greater surface area for transferring pressure as compared with the known lock pin assembly. The inventive connection structure allows surface pressure to be reduced, thus resulting in enhanced durability of the plastic gear  44 .  
         [0038]     Assembly steps proceed as follows when assembling the oil pump  40 , the oil pump shaft  17 , and the plastic oil pump gear  44  using the connection structure between the plastic gear and the shaft according to the preferred embodiment of the present invention. Specifically, with the tenon  17   a  aligned with the mortise  45   a  and with the plastic oil pump gear  44  not in mesh with the shared drive gear  26 , the plastic oil pump gear  44  is assembled together with the set plate  45  and the oil pump shaft  17 .  
         [0039]     Then, the plastic oil pump gear  44  is meshed with the shared drive gear  26 . The tenon  17   a  is provided with length that is relatively long as described in the foregoing. This extended length allows phase matching between the oil pump gear and the oil pump shaft to be performed when the plastic oil pump gear  44  is not yet in mesh with the shared drive gear  26 . This enhances efficiency in phase matching work.  
         [0040]     According to the prior art arrangement, the lock pin used as a locking member interposed between the oil pump gear and the oil pump shaft is passed through the oil pump shaft. This makes it difficult to bring gears into mesh with each other after phase matching of the oil pump rotor has been performed.  
         [0041]     In accordance with an embodiment of the present invention, on the other hand, the set plate  45  is used as the locking member and, unlike the prior art arrangement, the oil pump shaft  17  (the tenon  17   a  on the leading end thereof) is passed through the locking member (set plate  45 ). This allows the axial position of the oil pump gear to be freely changed relative to the axial position of the oil pump shaft.  
         [0042]     This makes it possible to first perform phase matching between the oil pump gear and the oil pump shaft, and then to bring the oil pump gear into mesh with the drive gear. This enhances efficiency in pump and gear assembly work.  
         [0043]     Although the present invention has been described herein with respect to a number of specific illustrative embodiments thereof, the foregoing description is intended to be illustrative, and not restrictive. Those skilled in the art will realize that many modifications of the embodiment could be made which would be operable. All such modifications that are within the scope of the claims are intended to be within the scope and spirit of the present invention.