(i) Field of the Invention
The present invention relates to the improvement in or relating to a power transmission system for a relatively small vehicle, and more particularly to an improved power transmission system for use with a four-wheeled light vehicle of the type called a saddle wheeler.
(ii) Description of the Prior Art
There is shown in general view a typical four-wheeled light vehicle of saddle type in FIG. 1.
It is generally designed in this saddle type four-wheeled vehicle designated at the reference numeral 1 that there are mounted a pair of balloon tires 2 and 3 of a relatively low pressure adaptable for driving operation on the irregular grounds such as deserts or wilds on the front and rear axles of this vehicle, respectively. It is also known that this saddle type vehicle 1 is generally equipped with a handlebar 4 for its steering operation, and that this handlebar 4 is designed to cause the front axle and hence the front pair of balloon tires 2, 2 to be steered for changing the heading of the vehicle by way of a steering mechanism, for example, the Ackermann steering mechanism, not shown, mounted in the vehicle's body 5. It is also the practice that there is mounted an internal combustion engine 7 in a transversal relationship across a frame 6 of a vehicle's body 5 with its crank axis disposed at the right angle with respect to the direction of heading of the vehicle 1 shown by an arrow A.
FIG. 2 is a plan view of a crank case 8, with main parts cut-away, showing the general construction of a conventional power transmission mechanism for use with the engine 7 to be adapted in the saddle type vehicle as noted above, and more particularly showing a typical construction of the so-called shaft-driving mechanism 9 for the secondary power transmission of the engine.
Now, referring more specifically to the construction of this power transmission system for the engine 7, it is seen that the motive power or rotating power of the crank shaft 10 of the engine 7 generated from the internal combustion is initially transmitted to a counter-shaft 12 through a clutch mechanism 11 incorporated in the engine's crank casing, and the rotating power of the counter-shaft 12 is then transmitted further to a drive shaft 15 by way of driving gears such as a driving gear 13 and a driven gear 14 being meshed with the driving gear 13. Also, the rotating power is further transmitted from the driving shaft 15 through driving gears 17, 18 in a speed change gear or transmission 16, which is disposed on the left-hand extension of the driving shaft 15, and driven gears 19, 20 meshing respectively with the driving gears 17, 18 to a secondary drive shaft 21. It is known that the driving gears 17, 18 are arranged to be shifted to a desired speed ratio by a gear shifting operation. The driving power of this secondary drive shaft 21 is then directed to a shaft-driving mechanism 9 by way of a bevel-gear transmission 24 which is disposed on one end of the secondary drive shaft 21, and in which there are provided a pair of bevel gears 22, 23 in a right-angled transmission relationship. This shaft drive mechanism 9 is known further comprising a propeller shaft and the like not shown, which is adapted to drive either of the front or rear axles, and hence either of the front or rear pair of balloon tires 2, 2 or 3, 3 shown in FIG. 1.
On the other hand, according to the conventional arrangement of power transmission system as adapted to this type vehicle, there may be employed such an alternative design that there are provided a driving sprocket (not shown) on the extension of the secondary drive shaft 21, in place of the bevel-gear transmission 24, and a driving chain (not shown) extending operatively across this sprocket and complementary one mounted on either of the front or rear axle so that either of the front or rear pair of balloon tires 2, 2 or 3, 3 may be driven for rotation.
According to such a typical construction of the conventional power transmission system as reviewed hereinbefore, it is noted that the secondary transmission mechanism from which either of the front or rear pair of balloon tires 2, 2 or 3, 3 shown in FIG. 1 may be driven in rotating motion, and which comprises the bevel-gear transmission 24, the shaft driving mechanism 9 and the like is generally disposed projecting laterally on an either hand of the crank casing 8 (in the illustrated example, the left hand side). Because of such an arrangement of lateral projection, an overall width W across the lateral extension of the engine 7 plus the power transmission casing would then turn out to be extremely greater, thereby resulting in an obstacle to the compact design of the entire engine and power transmission group of parts. More particularly, when adapting to the so-called front-wheel-drive system, in which the motive power of the secondary transmission is taken in the front of the engine 7 or in the direction shown by the arrow A, it would then be required to have the engine 7 mounted in the reverse way to the engine setting position as shown in FIG. 2. With such an engine mount, it is quite natural that the weight distribution of the saddle-type vehicle 1 would likely turn to be shifted towards the rear part thereof, which would then spoil substantially the stability of the light vehicle.
By the way, it is generally the practice in the design of a power transmission system for use with an ordinary automotive vehicle for the so-called on-road uses that the nominal ratio of the reduction gear ratio of a first speed position or a low gear position to the reduction gear ratio of a highest speed position or a top gear position is set to be from 3 to 4.
In contrast, however, it is specifically essential for the vehicles adapted to the operation on irregular ground or the so-called off-road vehicles that an auxiliary transmission is employed in addition to the transmission of ordinary change gear ratio specification, in order to obtain an extraordinarily extensive range of speed changes which is generally required for such uses.
More specifically, according to a typical construction for providing such an extraordinarily wider range of gear ratios, there are generally provided a primary drive shaft 101 and a secondary drive shaft 102 with a further elongated extension thereof, on the elongated extension of which drive shafts four gears 103 through 106 are installed, with two gears on each of the shaft extensions, and there is also provided a sliding wheel 107 which is adapted to switch the engagement between the gears 103 and 104, whereby there is attained an effect of auxiliary shifting in addition to the ordinary gear shift operation, accordingly.
With this construction, however, as there is attained only two steps of gear shifting, and moreover, as it was impossible to make these gears 103 and 104 smaller than the sliding wheel 107 because of the dimensional limit in strength, it was not feasible in practice to obtain a greater gear ratios than desired. In the design of the vehicle adapted to the operation on irregular ground, it is preferred to have a nominal ratio of the reduction gear ratio of the first speed or low gear position to the reduction gear ratio of the highest speed or top gear position being somewhere about 10 or so. However, under such a restriction in the design of an auxiliary transmission of the conventional construction as noted above, there is merely attained a nominal ratio of 4.5 to 6 at the most.
In consideration of such drawbacks particular to the conventional construction of the power transmission system for a light saddle type vehicle as noted above, it would be desirable to attain an efficient resolution for overcoming such inevitable problems particular to the conventional construction.
The present invention is essentially directed to the provision of a due and proper resolution to such inconveniences and difficulties in practice as mentioned above and experienced in the conventional power transmission system which have been left unattended with any effective countermeasures therefor.