Saddle type vehicle running on uneven ground
This application is a continuation, of application Ser. No. 934,174, filed Nov. 20, 1986, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     (i) FIELD OF THE INVENTION 
     The present invention relates to a saddle type vehicle for running on uneven ground. 
     (ii) DESCRIPTION OF THE PRIOR ART 
     Small motorcycles use a mechanism in which an engine case is structured in a swing type manner. It is structured that a front end of the engine case is supported by a frame and a rear end of the engine case supports a rear axle. The engine case is supported and connected to the frame through buffer means such as a shock absorber. 
     When the saddle type vehicle for running on an uneven ground adopts the mechanism in which the engine case is structured in the swing type, the engine is susceptible to damage since the engine is not protected by the frame. When the vehicle runs on the uneven ground, it is necessary to protect a lower side of the engine. 
     Further, when the swing type engine unit is mounted in the vehicle, since the engine unit is disposed at the rear portion of the vehicle body, the weight allotment ratio for the front and rear wheels in one-sided so that a larger weight is born on the rear wheel as compared with the front wheel. 
     Accordingly, when such a mechanism is adopted in the vehicle for running on the uneven ground such as a four-wheeled vehicle of the saddle type, the control performance of the vehicle is deteriorated. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to solve the above problems and to provide a saddle type vehicle for running on an uneven ground in which the control performance thereof is improved. 
     Further, it is another object of the present invention to provide a saddle type vehicle in which damage to an engine in running over uneven ground is prevented. 
     In order to solve the above problem, the present invention provides a saddle type vehicle for running over uneven ground comprising a swing type engine unit having a pivotal mounting positioned before a center of the wheel base of the vehicle. 
     Further, the saddle type vehicle, in accordance with the present invention, includes a lower member disposed opposite to a lower surface of the engine unit and a frame structured by coupled between the lower member and an upper member by a bridge member surrounding a main portion of the engine unit. 
     According to the saddle type vehicle for running on the uneven ground constructed above, since the pivot of the engine unit is disposed before the center of the wheel center, the wheel base can be shortened and the minimum diameter of rotation is improved. Further, since the weight allotment ratio of the front wheel can be larger than that of the rear wheel, the handling operation at a slow speed is easy and the controllability of the vehicle and the stability of the vehicle body can be improved. 
     Since the frame of the vehicle is structured so that a lower tube is disposed opposite to a lower surface of the engine unit and the main portion of the engine unit is protected by a bridge tube, the main portion of the engine unit can be prevented from being damaged by stones when running on the uneven ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 show a saddle type vehicle for running on an uneven ground according to an embodiment of the present invention, in which FIG. 1 is a side view thereof and FIG. 2 is a plan view thereof; 
     FIGS. 3 and 4 show an enlarged pivot portion of FIG. 1, in which FIG. 3 is a cross-sectional view taken along line A--A of FIG. 1 and FIG. 4 is a side view of FIG. 3; 
     FIG. 5 shows a lower tube of FIG. 2; 
     FIG. 6 is a cross-sectional view showing an embodiment of an axle housing and a chain case; and 
     FIG. 7 is a perspective view of a front bumper. 
    
    
     DETAIL OF THE INVENTION 
     The present invention is now described in detail with reference to the illustrated embodiment applied to a saddle type vehicle for running on an uneven ground. 
     In FIGS. 1 and 2, numeral 1 denotes a frame to which a swing type engine unit 2 is mounted. The frame 1 comprises a pair of upper tubes (upper members) 3 including a sheet rail 3a formed integrally at a rear end thereof for putting a sheet thereon and a front portion formed at a front end 3b thereof by bending the front end 3b downward with an angle, a pair of lower tubes (lower members) 5 including a front end coupled with a coupling tube 4 which is coupled with the front end of the pair of upper tubes 3 and a rear end extending opposite to a lower surface of the engine unit while maintaining a fixed space between the lower surface of the engine unit and the lower tubes 5, a bridge tube (bridge member) 6 disposed in a vertical plane containing an axis of the vehicle body and including one end coupled commonly with the rear end of the lower tubes 5 and the other end coupled with the upper tubes 3 by extending the other end upward to surround the main portion of the engine unit 2, and a reinforcement bridge tube 7 disposed between the upper tubes 3 and the lower tubes 5, between the upper tubes 3 and between the lower tubes 5. The engine unit 2 is configured by coupling integrally the engine case 8 and an axle housing 9 of a rear axle by a chain case 10. 
     The engine case 8 is formed with a recess 8a at a position thereof corresponding to the bridge tube 6 and the bridge tube 6 runs through the recess 8a without prevention by the engine case 8. 
     A bracket 8b is mounted to a front end of the engine case 8 and is coupled with a crank case bracket 11 through a shaft 12. Numeral 13 denotes a rubber bush for a cushion. 
     The crank case bracket 11 is rotatably supported through a pivot shaft 15 with a bracket 14 mounted to a bridge tube 7 1 . The pivot shaft 15 is inserted in a sleeve 16 which is supported by penetrating the bracket 14. A mounting 17 of the crank case bracket 11 is tightened together to both sides of the sleeve 16. Numeral 18 denotes a rubber bush for a cushion. Numeral 19 denotes a stopper which is engaged in a notch 11a formed at a lower side of the crank case bracket 11 to limit angular movement of the crank case bracket 11. The stopper 19 is formed of rubber 21 mounted to a shaft 20 which penetrates the bracket 14. 
     The crank case bracket 11 which is swingably mounted by the pivot shaft 15 is disposed before a center L of the wheel base in which the pivot shaft 15 is positioned. 
     Numeral 22 denotes a buffer device such as a shock absorber supporting the engine unit 2. 
     Numeral 23 denotes an air cleaner, 24 an inlet pipe for introducing external air for cooling a cylinder, 25 a pipe for exhausting air after cooling the cylinder and 26 a pipe for introducing air cooling a V belt pulley. Cooling air introduced from the pipe 26 is exhausted through the pipe 25. 
     FIG. 6 is a cross-sectional view showing an embodiment of the axle housing and the chain case. 
     The axle housing 9 supports a rear axle 28 through a bearing 27 and is supported to the frame 1 through the buffer device 22. 
     Numerals 29 and 30 denote a sprocket and a brake drum, respectively, disposed at both sides of the axle housing 9. The sprocket 29 and the brake drum 30 are coupled with the rear axle 28 through splines 31 1  and 31 2 . Numerals 32 and 33 denote oil seals disposed at inner end peripheries of both openings of the axle housing 9. Numeral 34 denotes a sleeve disposed between the bearings 27. 
     On the other hand, an ouput shaft 35 of the engine unit 2 is supported to the engine case 8 through a bearing 36. A sprocket 37 mounted to the output shaft 35 is coupled with the sprocket 29 of the rear axle 28 through a chain 38. Numeral 39 denotes an oil seal disposed at an inner end periphery of an opening of the engine case 8. 
     The chain case 10 comprises an inner cover 40 and an outer cover 41 which are integrally coupled with each other through bolts 42 and nuts 43. Reinforcement plates 44 and 45 are integrally mounted at peripheries of penetrating holes of the inner cover 40 through which the output shaft 35 and the rear axle 28 penetrate and both the plates 44 and 45 are formed with holes (not shown) for fixing the plates. Numeral 46 denotes a screw meshed with the engine case 8 and the axle housing 9 through the holes of the plates 44 and 45. Numeral 47 denotes an oil seal disposed at an inner end periphery of an opening of the outer cover 41. 
     The buffer device 22 is fixed at its lower metal fitting 49 to a boss 9a of the axle housing 9 through a bolt 48 and a nut 48a. Numeral 50 denotes a rubber bush disposed between a mounting hole 9b of the boss 9a and the bolt 48. 
     A front bumper 51 provided in order to protect the front portion includes a pipe 52 in the form of a reverse letter of U as shown in FIG. 7, both ends 52a of the pipe 52 being tightly attached to both ends of the pipe 4 through bolts 53 and the U-shaped portion of the pipe 52 being welded to an end of a pipe 56 which is mounted to a suspension bracket 54 by a bolt 55.