Abstract:
A transmission for an internal combustion apparatus is provided in which a parking lock mechanism is commonly formed with an upstream side portion of a power transmission system of a shift change mechanism, whereby the number of parts is reduced and the parking lock mechanism is compactly incorporated therein to achieve miniaturization of the internal combustion engine. The transmission in which a shift change mechanism performs a shift change in response to an operation of a gear selecting apparatus is configured to include a parking lock mechanism which is driven in an interlocking relationship with a working portion of the shift change mechanism, and if the shift change mechanism is set to the parking position, then a rotary shaft of the transmission is locked against rotation by the parking lock mechanism thereby restricting rotation of the rotary shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2006-004091, filed on Jan. 11, 2006. The subject matter of this priority document is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a transmission for use with an internal combustion engine, in which the transmission includes a parking lock mechanism, and to a vehicle including the locking transmission.  
         [0004]     2. Description of the Background Art  
         [0005]     Various examples of transmissions for internal combustion engines have been proposed, in which a parking position of the transmission can be selected in response to an operation of a shift lever, and in which the transmission includes a parking lock mechanism for restricting rotation of a drive shaft. Such restriction takes place when the vehicle is stopped, the parking position is selected, and then the internal combustion engine is stopped.  
         [0006]     One example of a known transmission including such a parking lock mechanism is disclosed in Japanese Laid-Open Patent No. 2004-353739. In the transmission described in this reference, a parking actuator, that is separate from a gear shift actuator, is controlled and driven by a control device to activate the parking lock mechanism.  
         [0007]     As an embodiment in Japanese Laid-Open Patent No. 2004-353739, a configuration is disclosed wherein, if an electric motor which forms a parking actuator is driven, an engaging member is caused to project through a pinion-rack mechanism and a coil spring, whereupon a tooth at an end of the engaging member is engaged with a parking gear fitted on an input power shaft of a speed change gear. As a result, rotation of the input power shaft is restricted.  
         [0008]     Since the conventional parking lock mechanism is configured such that a power transmission system is formed as an independent apparatus which is separate from a shift change mechanism, and is driven by an actuator provided for exclusive use by the independent apparatus, it includes a great number of parts and increases the size of the internal combustion engine.  
         [0009]     The present invention has been made in view of the above described situation, and it is an object of the present invention to provide a transmission for use with an internal combustion engine, wherein a parking lock mechanism is formed commonly with an upstream side portion of a power transmission system of a shift change mechanism, to reduce the number of parts required, and which can be incorporated compactly in the shift change mechanism to reduce the size of the internal combustion engine.  
       SUMMARY  
       [0010]     In order to achieve the object described above, in a first aspect of the invention, a transmission is provided for use with an internal combustion engine in which a shift change mechanism is operable to perform a shift change, including movement to a parking position, in response to an operation of a gear selection device. The transmission includes a parking lock mechanism that is driven in an interlocking relationship with a working portion of the shift change mechanism, and is configured such that if the shift change mechanism is set to the parking position, then a rotary shaft of the transmission is locked against rotation by the parking lock mechanism. As a result, rotation of the rotary shaft is restricted.  
         [0011]     According to the first aspect of the invention, the parking lock mechanism is driven in an interlocking relationship with the working portion of the shift change mechanism. Therefore, the parking lock mechanism is commonly formed with an upstream side portion of a power transmission system of the shift change mechanism, and is driven making use of an operation means of the shift change mechanism, actuator and so forth as well as the working portion. Consequently, the parking lock mechanism is compactly incorporated in the shift change mechanism without requiring operation means, an actuator and so forth dedicated for exclusive use for parking gear locking. Consequently, the overall size of the internal combustion engine is reduced.  
         [0012]     Further, if the shift change mechanism is set to the parking position, then the rotary shaft of the transmission is locked by the parking lock mechanism, thereby restricting rotation of the rotary shaft. Consequently, the operation thereof is simplified and convenient, and the operability is good.  
         [0013]     In a second aspect of the invention, the transmission for an internal combustion engine according to the first aspect thereof is further configured such that the parking lock mechanism includes a locking member. The locking member is driven in an interlocking relationship with the working portion of the shift change mechanism, and has a pawl portion which is engaged with a locking portion provided integrally on an output power shaft, which is the rotary shaft of the transmission. As a result, rotation of the output power shaft is restricted.  
         [0014]     According to the second aspect of the invention, the pawl portion of the locking member is driven in an interlocking relationship with the working portion of the shift change mechanism. In addition, the pawl portion is engaged with the locking portion provided integrally on the output power shaft of the transmission, thereby restricting rotation of the output power shaft. Consequently, rotation of the output power shaft is restricted with certainty with a simple configuration.  
         [0015]     In a third aspect of the invention, the transmission for an internal combustion engine according to the first or second aspects hereof is configured such that the shift change mechanism includes a gear shift arm, fitted with a shift spindle, and a shift drum which meshes with and is rotated by the gear shift arm to perform the shift change. The shift spindle is the working portion which is rotated by the operation of the operation selection device. In addition, the parking lock mechanism is driven in an interlocking relationship with the rotation of the shift spindle to lock the output power shaft which is the rotary shaft. In addition, the gear shift arm forms a sectoral shape having a pivot at the shift spindle, while the output power shaft is disposed outside a range of pivotal motion of the gear shift arm within a maximum diameter of the pivotal motion of the gear shift arm.  
         [0016]     According to the third aspect of the invention, the output power shaft is disposed at a position which is outside the range of pivotal motion of the sectoral gear shift arm which pivots around the shift spindle, and the output power shaft is further disposed so as to overlap with a circle of the maximum diameter of the pivotal motion. Therefore, the shift spindle is positioned in the proximity of the output power shaft, and the parking lock mechanism is compactly incorporated.  
         [0017]     In a fourth aspect of the invention, the transmission for an internal combustion engine according to the second or third aspects thereof is configured such that the locking member of the parking lock mechanism is a lever supported for rocking motion on a fixed support shaft, and has a fulcrum and a point of action at the fixed support shaft and the pawl portion, respectively. In addition, the distance of a power point of the lever from the fulcrum is set to be greater than the distance of the pawl portion, which is the point of action, from the fulcrum.  
         [0018]     According to the fourth aspect of the invention, the distance of the power point of the lever, which is a locking member from the fulcrum, is set greater than the distance of the pawl portion, which is the point of action, from the fulcrum. Therefore, by the principle of the lever, even where the parking lock mechanism is small in size, engagement and disengagement of the pawl portion with and from the locking portion of the output power shaft can be performed smoothly with doubled force.  
         [0019]     In a fifth aspect of the invention, the transmission for an internal combustion engine according to the third or fourth aspects thereof is configured such that the shift spindle, a drum shaft of the shift drum and the output power shaft are disposed in a mutually neighboring relationship so as to form vertices of a triangle when viewed from the rear.  
         [0020]     According to the fifth aspect of the invention, since the shift spindle, the drum shaft of the shift drum and the output power shaft are disposed in a mutually neighboring relationship so as to form the vertices of a triangle, the shift change mechanism is compactly configured.  
         [0021]     In a sixth aspect of the invention, the transmission for an internal combustion engine according to any one of the third to fifth aspects thereof is configured such that an end portion of the shift spindle is formed as a separate removable member, and the parking lock mechanism is connected to the end portion of the shift spindle so as to be interlocked with the shift spindle.  
         [0022]     According to the sixth aspect of the invention, the end portion of the shift spindle is formed as a separate removable member, and the parking lock mechanism is connected to the end portion of the shift spindle so as to be interlocked with the shift spindle. Therefore, by connecting the parking lock mechanism to the end portion so as to form a unit, the assemblage performance is enhanced.  
         [0023]     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  
       [0024]      FIG. 1  is a side elevational view of an entire four-wheel saddle type vehicle on which an internal combustion engine including a transmission according to an embodiment of the present invention is carried.  
         [0025]      FIG. 2  is a perspective view of a transmission gear selecting apparatus.  
         [0026]      FIG. 3  is a schematic rear elevational view of the internal combustion engine of  FIG. 1 , showing the output power shaft disposed leftward and below the crankshaft, and showing the shift drum disposed between the output power shaft and the crankshaft.  
         [0027]      FIG. 4  is a rear elevational view of the inventive shift change mechanism and a parking lock mechanism, showing the pawl engaged with the teeth of the parking gear wheel when the transmission is set to a parking position.  
         [0028]      FIG. 5  is a sectional view of the inventive shift change mechanism and a parking lock mechanism taken along line V-V of  FIG. 4 .  
         [0029]      FIG. 6  is a sectional view of the inventive shift change mechanism and a parking lock mechanism taken along line VI-VI of  FIG. 4 .  
         [0030]      FIG. 7  is a developed view of a shift drum.  
         [0031]      FIG. 8A  is an explanatory view of the inventive shift change mechanism and a parking lock mechanism illustrating the shift state of the shift change mechanism and the parking lock mechanism corresponding to a parked position of the gear selecting apparatus.  
         [0032]      FIG. 8B  is an explanatory view of the inventive shift change mechanism and a parking lock mechanism illustrating the shift state of the shift change mechanism and the parking lock mechanism corresponding to a reverse position of the gear selecting apparatus.  
         [0033]      FIG. 8C  is an explanatory view of the inventive shift change mechanism and a parking lock mechanism illustrating the shift state of the shift change mechanism and the parking lock mechanism corresponding to a neutral position of the gear selecting apparatus.  
         [0034]      FIG.8D  is an explanatory view of the inventive shift change mechanism and a parking lock mechanism illustrating the shift state of the shift change mechanism and the parking lock mechanism corresponding to a drive position of the gear selecting apparatus.  
         [0035]      FIG. 8E  is an explanatory view of the inventive shift change mechanism and a parking lock mechanism illustrating the shift state of the shift change mechanism and the parking lock mechanism corresponding to a low position of the gear selecting apparatus. 
     
    
     DETAILED DESCRIPTION  
       [0036]     A selected illustrative embodiment of the invention will now be described in some detail, with reference to the drawings. 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. Directional descriptions are provided with respect to the point of view of an operator of the vehicle. For example, a disclosure of “forward” refers to the forward operating direction of the vehicle  
         [0037]     A four-wheel, saddle type all-terrain vehicle (ATV)  1  for traveling on rough or irregular ground, and which incorporates an internal combustion engine including a transmission according to the present embodiment, is shown in  FIG. 1 .  
         [0038]     The vehicle  1  includes a vehicle body frame  2 , with a pair of front wheels  3 ,  3  disposed on opposite sides of a front portion of the vehicle body frame. A pair of rear wheels  4 ,  4  are disposed on opposite sides of a rear portion of the vehicle body frame  2 , and all of the front and rear wheels cooperate to support a vehicle body. A steering handlebar  5  is provided at an upper front portion of the vehicle body, for use in steering the front wheels  3 ,  3 . A fuel tank  6  is disposed in back of the steering handlebar  5 , and a seat  7  is provided behind the fuel tank  6 .  
         [0039]     An internal combustion engine  10  is mounted on the vehicle body frame  2  at a central portion of the vehicle body. A transmission gear selecting apparatus  8  is disposed on the left side of the fuel tank  6  above a left side portion of the internal combustion engine  10 .  
         [0040]     The gear selecting apparatus  8  is formed such that a shift lever  9  is pivoted forwardly or backwardly to perform a shift changing operation, as seen in  FIG. 2 . A parking position P, a reverse position R, a neutral position N, a drive position D and a low position L are indicated in conventional order along the pivoting motion of the shift lever  9 .  
         [0041]     The shift lever  9  is configured to pivot only in the forward and backward direction, and is operated forwardly or backwardly by a driver so as to be selectively positioned to a required position to perform a shift change. The parking position P is positioned most forwardly ( FIG. 2 ). The pivoting motion of the shift lever  9  is transmitted to the transmission through a cable (not shown).  
         [0042]     The internal combustion engine  10  is supported at a central portion of the vehicle body, and is a water-cooled single-cylinder four-stroke cycle internal combustion engine. The engine  10  is carried vertically with a crankshaft  11  thereof directed forwardly and backwardly such that power of the engine  10  is transmitted to the four wheels  3 ,  4 .  
         [0043]      FIG. 3  is a schematic rear elevational view of the internal combustion engine  10 .  
         [0044]     The internal combustion engine  10  includes an engine body which is formed from a cylinder  13  in which a piston is fitted for reciprocating movement, a cylinder head  14  and a head cover  15  placed, in order, on the cylinder  13  and coupled to each other, and a crankcase  12  coupled to a rear end portion of the cylinder  13 .  
         [0045]     The crankcase  12  is a case divided into front and rear members, and the crankshaft  11  is supported for rotation on the front and rear crankcase  12  members and connected to the piston through a connecting rod  16  such that reciprocating movement of the piston is converted into and transmitted as rotation of the crankshaft  11 . A transmission  20  is disposed on the left side of the crankcase  12 .  
         [0046]     A main shaft  21  is disposed leftwardly of the crankshaft  11  at a substantially equal height therewith. A counter shaft  22  is disposed obliquely downwardly on the left side of the main shaft  21  while a reverse shaft  23  is disposed above the counter shaft  22 . An output power shaft  24  is disposed obliquely downwardly of the counter shaft  22  and substantially just below the main shaft  21 .  
         [0047]     A driving gear wheel  11  a connected to the crankshaft  11  through a start clutch is held in meshing engagement with a driven gear wheel  21   a  of the main shaft  21 , and a speed change gear train group  25  is formed between the main shaft  21  and the counter shaft  22 . Upon reversal, reverse gears  26  of the reverse shaft  23  are interposed between the main shaft  21  and the counter shaft  22 .  
         [0048]     A shift drum shaft  31  is disposed rightwardly of the counter shaft  22  and rightwardly upwards of the output power shaft  24 . The shift drum shaft  31  integrally supports a shift drum  32  thereon. Two shift forks  37   a  and  37   b  are supported for pivotal motion on a guide shaft  36  disposed between the shift drum shaft  31  and the counter shaft  22 .  
         [0049]     The shift forks  37   a  and  37   b  engage at ends thereof with a sliding member fitted on the counter shaft  22 , and shift pins  37   ap  and  37   bp  projecting from base end portions of the shift forks  37   a  and  37   b  are fitted in shift grooves  32   a  and  32   b  formed on an outer circumferential face of the shift drum  32  (refer to  FIGS. 5 and 7 ).  
         [0050]     As seen in  FIG. 7  which is a developed view of the shift drum  32 , the two shift grooves  32   a  and  32   b  are formed on the outer circumferential face of the shift drum  32 , and a parking position P, a reverse position R, a neutral position N, a drive position D and a low position L are provided in the order of the angle of rotation of the shift drum  32 .  
         [0051]     Although the parking position P and the neutral position N are same in the axial direction of the shift forks  37   a  and  37   b , since the reverse position R at which the shift groove  32   a  is curved is disposed between the parking position P and the neutral position N, such a situation that the shift forks  37   a  and  37   b  enter the parking position P from the neutral position N although the shift lever  9  is not operated is prevented without increasing the size of the shift drum  32 .  
         [0052]     Referring to  FIG. 3 , an oil strainer  17  is provided along the bottom face of the rear crankcase  12  member and is formed on the inner side (front side) with respect to a mating face  12   a  of the rear crankcase  12  member with a rear crankcase cover (not shown).  
         [0053]     It is to be noted that a drum driven gear wheel  33  and a shift cam  34  are fitted integrally on the shift drum shaft  31  as seen in  FIGS. 4 and 5 . The shift cam  34  is in the form of a star-shaped plate and has trough portions of a predetermined shape formed on an outer periphery thereof in order in the counterclockwise direction for the parking position P, reverse position R, neutral position N, drive position D and low position L. When a stopper roller  35   a  supported for rotation at an end of a stopper arm  35  biased in one pivotal direction is pressed against the outer periphery of the shift cam  34 , the stopper roller  35   a  can be received stably by any of the troughs at the positions thereby to set the shift drum  32  to a predetermined angular position.  
         [0054]     A shift spindle  38  is disposed at a position below the shift drum shaft  31  and rightwardly of the output power shaft  24 , and a gear shift arm  39  is provided and fitted at a base end portion thereof with the shift spindle  38 . The gear shift arm  39  has a sectoral shape having a pivot at the shift spindle  38 , and a shift driving gear  39   a  is formed along an end edge of the developed sectoral shape of the gear shift arm  39 . The shift driving gear  39   a  is held in meshing engagement with the drum driven gear wheel  33  fitted on the shift drum shaft  31 .  
         [0055]     Since the output power shaft  24  is positioned on the left side position of the sectoral gear shift arm  39  outside the range of pivotal motion of the gear shift arm  39 , the output power shaft  24  and the shift spindle  38  are positioned near to each other. In particular, referring to  FIG. 4 , the output power shaft  24  is disposed at a position overlapping with a circle  39   b  of a maximum diameter of pivotal motion of the sectoral gear shift arm  39  which is pivoted around the shift spindle  38  (distance from the shift spindle  38  to a pivotal end edge of the gear shift arm  39 ).  
         [0056]     The shift spindle  38  extends at a front end thereof through the crankcase  12  and a front cover (not shown) of the internal combustion engine  10  and projects forwardly, and motion instruction transmission means such as a cable extending from the shift lever  9  is coupled to a front end portion of the shift spindle  38  so that the shift spindle  38  is rotated by a pivoting movement of the shift lever  9 .  
         [0057]     In a shift change mechanism  30  is formed in such a manner as described above, and when the shift spindle  38  is rotated by an operation of the shift lever  9 , the sectoral gear shift arm  39  is pivoted, whereupon the shift drum shaft  31  is rotated together with the shift drum  32  through the meshing engagement between the shift driving gear  39   a  and the drum driven gear wheel  33 . Then, the shift forks  37   a  and  37   b  are moved in an axial direction under the guidance of the shift grooves  32   a  and  32   b  of the rotated shift drum  32  to slidably move the sliding member of the counter shaft  22  thereby to change meshing gear wheels of the speed change gear train group  25  to perform a shift change.  
         [0058]     When the shift lever  9  is moved to the forwardmost position, it is placed into the parking position P, and as the shift lever  9  is pivoted rearwardly from the parking position P, it successively assumes the reverse position R, neutral position N, drive position D and low position L.  
         [0059]     By such rearward pivoting movement of the shift lever  9 , the shift spindle  38  is rotated in the counterclockwise direction in  FIG. 3  via the cable and so forth, and the shift drum shaft  31  is rotated in the clockwise direction through the meshing engagement between the shift driving gear  39   a  and the drum driven gear wheel  33 . Thereupon, the stopper roller  35   a  is successively fitted into the troughs formed on the outer periphery of the shift cam  34  to successively set the shift drum  32  to a predetermined angular position. Consequently, the meshing engagement of the speed change gear train group  25  can be successively shifted and changed to the parking position P, reverse position R, neutral position N, drive position D and low position L.  
         [0060]     According to the present transmission  20 , a parking lock mechanism  50  is incorporated in the shift change mechanism  30  described above.  
         [0061]     The shift spindle  38  is formed at a rear end portion thereof from a rear end spindle  38   b  of a separate member, and serrations formed on an inner circumferential face of a connecting cylindrical portion  38   bb  of the rear end spindle  38   b  mesh with serrations formed on an outer circumferential face of a rear portion of a body spindle  38   a  so that the body spindle  38   a  and the rear end spindle  38   b  can rotate coaxially and integrally with each other.  
         [0062]     The body spindle  38   a  extends through and projects rearwardly from the rear side crankcase  12  member, and the gear shift arm  39  is serration fitted at a rear end portion thereof with the serrations of the projecting portion of the body spindle  38   a  and is prevented from being pulled off by a stop ring  40 . The rear end spindle  38   b  is serration fitted removably with a further tip end portion of the body spindle  38   a.    
         [0063]     The rear end spindle  38   b  is supported for rotation on a parking lock holder  51 . The parking lock holder  51  is securely mounted on the crankcase  12  by means of a first bolt  52  and a second bolt  53  (refer to  FIG. 6 ). The parking lock holder  51  is assembled to the inner side (front side) with respect to the mating face  12   a  of the crankcase  12  with the rear crankcase cover (not shown). The rear end spindle  38   b  extends at an end thereof through and projects rearwardly from the parking lock holder  51 , and a driving arm  54  is fitted, at a base end portion thereof, to the end of the rear end spindle  38   b , and is prevented from being pulled off by a stop ring  55 . The driving arm  54  is located on the end of the rear end spindle  38   b  at an axial position thereof that substantially aligns with the mating face  12   a  of the crankcase  12 .  
         [0064]     The first bolt  52  for securely mounting the parking lock holder  51  on the rear side crankcase  12  member is disposed at a position considerably near to and rightwardly obliquely downwardly of the output power shaft  24 . The first bolt  52  secures the parking lock holder  51  while it supports a parking locking lever  56  for rocking motion.  
         [0065]     In particular, as seen in  FIG. 6 , a washer  57  and a sleeve  58 , on which the parking locking lever  56  is fitted for rocking motion, are provided at an open end of a through-hole of the parking lock holder  51  for the first bolt  52 , and the first bolt  52  extends through the washer  57  and the sleeve  58  and further through the through-hole of the parking lock holder  51 . Further, the parking lock holder  51  is screwed in and fastened to the crankcase  12 , and the parking locking lever  56  is supported for rocking motion on the first bolt  52  via the sleeve  58 .  
         [0066]     The parking locking lever  56  extends leftwardly and rightwardly from the first bolt  52 , and the right side extension  56 R is elongated and is connected at the right end thereof to the driving arm  54  through a link member  59 . The parking locking lever  56  is positioned rearwardly of the driving arm  54  and crosses the driving arm  54  such that it overlaps in an axial direction on the driving arm  54 . The driving arm  54  has a boss portion  54   a  projecting rearwardly from an end thereof such that a rear end of the boss portion  54   a  is positioned in flush with a rear face of the parking locking lever  56 .  
         [0067]     The link member  59  is supported at an end thereof for pivotal motion on the boss portion  54   a  of the driving arm  54  by a pin  60  and supported at the other end thereof for pivotal motion at an end of the parking locking lever  56  by a pin  61  thereby to connect the end of the driving arm  54  and the end of the parking locking lever  56  to each other.  
         [0068]     Meanwhile, the left side extension  56 L of the parking locking lever  56 , which extends leftwardly from the first bolt  52 , is shorter than the right side extension  56 R. A pawl  56   a  projects from an end portion of the left side extension  56 L toward the output power shaft  24 . A parking gear wheel  65  is fitted integrally on the output power shaft  24  such that, if the pawl  56   a  of the parking locking lever  56  is meshed with teeth  65   a  of the parking gear wheel  65 , then rotation of the output power shaft  24  is inhibited. The parking locking lever  56  is biased by a torsion spring  62  in a direction in which the pawl  56   a  of the left side extension  56 L thereof meshes with the teeth  65   a  of the parking gear wheel  65 .  
         [0069]     It is to be noted that the teeth  65   a  of the parking gear wheel  65  have a rectangular cross section, and also a groove between one and another one of the teeth  65   a  has a channel shape. Meanwhile, an end of the pawl  56   a  of the parking locking lever  56  projects with a curved face shaped such that it is fitted in a channel-shaped groove of the parking gear wheel  65  to restrict rotation of the output power shaft  24  with certainty whereas it can be removed readily from the groove.  
         [0070]     A velocity sensor  70  in the form of a magnetic detector is disposed in the proximity of the teeth  65   a  of the parking gear wheel  65  such that it can detect the teeth  65   a  revolving in the proximity of a detection portion of the velocity sensor  70  to detect the velocity of the vehicle based on rotation of the output power shaft  24 .  
         [0071]     While the output power shaft  24  is positioned in an overlapping relationship with the circle  39   b  of the maximum diameter of pivotal motion of the sectoral gear shift arm  39 , which pivots around the shift spindle  38 , the output power shaft  24  is disposed at a position in the proximity of the shift spindle  38 . In particular, the output power shaft  24  is disposed such that the teeth  65   a  of the parking gear wheel  65  approach, or are closely adjacent to, the shift spindle  38  as seen in  FIG. 4 . Accordingly, the parking lock mechanism  50  is compactly incorporated in the shift change mechanism  30 , and this contributes to miniaturization of the internal combustion engine  10 .  
         [0072]     The parking lock mechanism  50  is configured in such a manner as described above and is formed as a unit in such a manner that it is held by the parking lock holder  51 . In particular, the driving arm  54  and the parking locking lever  56  extend through and are held by the parking lock holder  51  so as to form a unit in a state wherein the driving arm  54  fitted on the rear end spindle  38   b  of the shift spindle  38  and the parking locking lever  56  supported for rotation on the first bolt  52  are connected to each other by the link member  59 .  
         [0073]     The parking lock mechanism  50 , retained by and forming a unit together with the parking lock holder  51  in this manner, is fitted at the rear end spindle  38   b  thereof with the body spindle  38   a  fitted in advance with the gear shift arm  39  at a predetermined position of the crankcase  12 , and is fastened by the first bolt  52  and the second bolt  53  attached already. Accordingly, the parking lock mechanism  50  is superior in assemblage performance.  
         [0074]     The parking lock mechanism  50  is assembled in such a manner that it is incorporated in the shift change mechanism  30  as described above. In the parking lock mechanism  50 , upon rotation of the shift spindle  38 , which is the upstream side of the power transmission system of the shift change mechanism  30 , the driving arm  54  is pivoted. As a result, the parking locking lever  56  is rocked through the link member  59 . Consequently, the pawl  56   a  of the left side extension  56 L of the parking locking lever  56  is brought into or out of meshing engagement with the teeth  65   a  of the parking gear wheel  65  of the output power shaft  24 .  
         [0075]      FIGS. 8A-8E  illustrate shift states of the transmission  20  in order from the parking position.  FIG. 8A  illustrates a state wherein the shift lever  9  is operated to pivot to the parking position P in order to set the shift state to the parking position P (same as  FIG. 4 ).  
         [0076]     The shift spindle  38  is positioned at an angular position corresponding to a maximum position in the clockwise direction as viewed in rear elevation, and the shift change mechanism  30  is set to the parking position P. Further, the parking locking lever  56  of the parking lock mechanism  50  is positioned at an angular position pivoted most in the clockwise direction, in which the pawl  56   a  of the left side extension  56 L meshes with the teeth  65   a  of the parking gear wheel  65  of the output power shaft  24  to inhibit rotation of the output power shaft  24 .  
         [0077]     Then, if the shift lever  9  is operated to pivot rearwardly to the reverse position R, then the shift spindle  38  is rotated in the counterclockwise direction as seen in  FIG. 8B  and the shift change mechanism  30  sets its shift state to the reverse position R. Consequently, by means of the driving arm  54 , which is pivoted in the counterclockwise direction together with the shift spindle  38 , the parking locking lever  56  is pivoted in the counterclockwise direction through the link member  59  until the pawl  56   a  of the left side extension  56 L is removed from a groove between a tooth  65   a  and an adjacent tooth  65   a  of the parking gear wheel  65 , whereby free rotation of the output power shaft  24  is permitted.  
         [0078]     At the parking position P, depending upon the angular position of the output power shaft  24 , the pawl  56   a  of the left side extension  56 L of the parking locking lever  56  may be meshed firmly with the teeth  65   a  of the parking gear wheel  65  of the output power shaft  24  such that, when a shift change to the reverse position R is performed, the pawl  56   a  may not be removed readily from the groove between a tooth  65   a  and an adjacent tooth  65   a  of the parking gear wheel  65 . However, in the disclosed embodiment, the parking locking lever  56  is configured such that the pin  61 , which serves as a power point, is positioned at an end portion of the elongated right side extension  56 R with respect to the first bolt  52 , serving as a fulcrum, and the pawl  56   a , which serves as a point of action, is positioned at an end portion of the shorter left side extension  56 L. Hence the distance from the fulcrum to the point of action is much shorter than the distance from the fulcrum to the power point, and a doubled acting force acts upon the pawl  56   a  in accordance with the principle of the lever. Consequently, the pawl  56   a  is readily removed from the groove between a tooth  65   a  and an adjacent tooth  65   a  of the parking gear wheel  65 .  
         [0079]     Since the parking lock mechanism  50  has a link structure which makes use of the principle of the lever, it is reduced in size and can be incorporated in the shift change mechanism  30  without occupying a great space.  
         [0080]     As shown in  FIG. 8C , if the shift lever  9  is further operated to pivot rearwardly to the neutral position N, then the shift spindle  38  is further rotated in the counterclockwise direction. Consequently, the shift change mechanism  30  sets its shift state to the neutral position N, and also the parking locking lever  56  is further rocked in the counterclockwise direction, whereupon the pawl  56   a  of the left side extension  56 L is removed from the teeth  65   a  of the parking gear wheel  65 , whereby free rotation of the output power shaft  24  is permitted.  
         [0081]     A state wherein the shift lever  9  is further pivoted to the drive position D is illustrated in  FIG. 8D , and a state wherein the shift lever  9  is further pivoted to the low position L is illustrated in  FIG. 8E . Since the parking locking lever  56  is further rocked in the counterclockwise direction, the pawl  56   a  of the left side extension  56 L is further spaced away from the teeth  65   a  of the parking gear wheel  65  and the output power shaft  24  can rotate freely.  
         [0082]     It is to be noted that, in a state wherein the parking locking lever  56  is rocked to the utmost in the counterclockwise direction as seen in  FIG. 8E  at the low position L, the parking locking lever  56  is positioned closely to but does not interfere with the mating face  12   a  of the crankcase  12 .  
         [0083]     In this manner, when the shift change mechanism  30  is shifted and set to the parking position P, the pawl  56   a  of the left side extension  56 L of the parking locking lever  56  meshes with the teeth  65   a  of the parking gear wheel  65  to inhibit rotation of the output power shaft  24 . However, when the shift change mechanism  30  is set to any position other than the parking position P, the pawl  56   a  of the left side extension  56 L of the parking locking lever  56  is spaced away from the teeth  65   a  of the parking gear wheel  65  and the output power shaft  24  can rotate freely.  
         [0084]     As described above, since the present parking lock mechanism  50  is configured such that it is driven by rotation of the shift spindle  38  which is on the upstream side of the power transmission system of the shift change mechanism  30 , the parking lock mechanism  50  is compactly incorporated in the shift change mechanism  30  without requiring operation means, an actuator and so forth for exclusive use for parking locking. Consequently, miniaturization of the internal combustion engine is achieved.  
         [0085]     Further, since the parking lock mechanism  50  has a link structure which makes use of the principle of the lever, it is reduced in size, and further miniaturization of the internal combustion engine is anticipated. Still further, engagement and disengagement (removal) of the pawl  56   a  of the parking locking lever  56  of the parking lock mechanism  50  with and from the teeth  65   a  of the parking gear wheel  65  of the output power shaft  24  is smoothly performed.  
         [0086]     The oil strainer  17  is provided at an inlet port for absorbing oil accumulated on the bottom of the crankcase  12 , and is disposed below the parking lock mechanism  50  as shown in  FIG. 3 . However, the oil strainer  17  is formed on the inner side with respect to the mating face  12   a  of the rear crankcase  12  member with the rear crankcase cover (not shown) as described hereinabove, and the oil strainer  17  does not interfere with the driving arm  54  or the parking locking lever  56  which are positioned on the outer side (rear side) with respect to the mating face  12   a  as seen in  FIG. 5 .  
         [0087]     Only if the shift lever  9  is operated to pivot to the parking position P, the parking lock mechanism operates to inhibit rotation of the output power shaft  24  of the transmission  20  thereby to set parking locking. Consequently, the operation is simplified and convenient, and the operability thereof is good.  
         [0088]     The gear shift arm  39  fitted on the shift spindle  38  of the shift change mechanism  30  has a sectoral shape, and the output power shaft  24  is disposed outside the range of pivotal motion of the gear shift arm  39 . In addition, the shift spindle  38  and the output power shaft  24  are disposed near to each other. Consequently, the parking lock mechanism  50  is compactly incorporated.  
         [0089]     Further, since the shift spindle  38 , the drum shaft  31  of the shift drum  32  and the output power shaft  24  are disposed in the proximity of each other at the vertices of a triangle as seen in a rear view of the engine  10 , the shift change mechanism  30  is compactly formed.  
         [0090]     As described hereinabove, the rear end spindle  38   b  of the shift spindle  38  is formed as a separate removable member to form the parking lock mechanism  50  into a unit. Therefore, the assemblage performance of the parking lock mechanism  50  is enhanced.  
         [0091]     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.