Transmission for a vehicle having at least one driving wheel

A vehicle includes a frame, at least one front wheel, at least one rear wheel, a motor mounted on the frame and operatively connected to drive the front wheel and the wheel rear, and the gearbox connected to the motor and having an output shaft. A front suspension arm operatively supports the front wheel and is pivotally mounted about the output shaft for pivotal movement in the plane of the front wheel. A rear suspension arm operatively supports the rear wheel and is pivotally mounted about the output shaft of the gearbox for pivotal movement in the plane of the rear wheel.

BACKGROUND OF THE INVENTION 
The present invention relates to a vehicle having two wheels, an engine 
which drives at least one of the wheels, a gearbox, a frame connected to 
the engine and two front and rear suspension arms of the pivotal type. 
A vehicle is known which comprises driving wheels capable of being 
uncoupled and a device for adjusting the castor and the castor angle of 
the front wheel and is described in PCT/FR88/00073. 
More particularly, in the case of the described vehicle having two wheels, 
two synchronous and distinct driving shafts are provided, one for rear 
wheel and the other for the front wheel. The suspensions are of the type 
having a pivotal arm and a pivot axis of each of these arms is distinct 
from the axis of the driving shafts. This makes it necessary for example 
in the case of a chain transmission, to require a tightener for 
compensating for the tension of the chain upon movements of the arm. 
Moreover, the weight of the different transmission elements is great. 
Also, reliability is reduced bearing in mind that the number of moving 
parts is large and the useful power may be reduced, in particular by 
losses due to friction. 
Furthermore, the steering unit comprises a steering column driven in 
rotation at one end by a handlebar and connected at its other end to a 
compass system itself articulated to a front steering fork, the latter 
being fixed to an inner hub which is rotatably mounted to be steerable on 
a pin carried by a pivot connected to the pivotal arm. 
In order to facilitate the steering orientation of the front wheel, the 
articulations are of the universal type, but this results in particular in 
an increase in weight, a reduction in handling and reliability, a higher 
cost and increased maintenance. 
SUMMARY OF THE INVENTION 
A vehicle having two wheels according to the invention comprises a 
suspension having pivotal arms which avoids the mounting of a device for 
automatically taking up the differential play in transmissions during 
their movements, while reducing the number of moving parts and which 
allows the mounting of a simple and effective clutch release for the front 
wheels, a multi-use frame, and a steering unit which includes a compass 
system and has a reduced number of parts. 
For this purpose, the invention provides a vehicle comprising at least two 
wheels, a motor which drives at least one of the wheels, a gearbox, a 
frame connected to the motor and two front and rear suspension arms of the 
pivotal type fixed to the motor at respective first ends, characterized in 
that at least one of the pivotal arms is mounted to be pivotable relative 
to the motor about an output shaft of the gearbox. 
Furthermore, the invention is characterized in that the front wheel 
comprises driving means with a clutch release device, in particular of the 
centrifugal type mounted coaxially with the output shaft of the gearbox. 
The vehicle according to the invention is further characterized in that the 
frame comprises at least two tubes interconnected at first ends and 
connected at second ends to the motor so as to form a frame, these tubes 
being capable of being employed as an air supply intake for the motor.

DETAILED DESCRIPTION OF THE INVENTION 
The invention having two wheels according to the invention comprises a 
frame 10, two front 12 and rear 14 swing or pivotal arms, a motor 16 
having a gearbox 18, two transmissions 20, 22 respectively driving the 
front wheel 24 and rear wheel 26. 
The rear pivotal arm 14 comprises a rear fork 28 on one of the ends of 
which is mounted a spindle 30 of the rear wheel 26 while the other end is 
rotatably mounted coaxially with an output shaft 32 of the gearbox. The 
transmission 22 is of the type having a chain 34, a chain wheel 36 and a 
gearbox output sprocket 38, as shown in more detail in FIG. 3. The 
suspension of the rear pivotal arm is provided by a deformable articulated 
lever arm or compass system 40 whose movements are controlled by a shock 
absorber 42. The front pivotal arm 12 is of the deformable quadrilateral 
type comprising a lower fork 44 having one end articulated to a pin 45 
relative to the motor 16 and the other end fixed to the ends of a steering 
pivot 46. A shock absorber 48 controls the displacements of lower fork 44 
and is disposed between the lower fork 44 and a reinforcement 52 of a 
strut 50 which will be described subsequently. This arrangement results in 
a progressivity of the shock-absorbing effect, since there is a variation 
in the orientation of the shock absorber when the quadrilateral is 
deformed. 
Lower fork 44 has a special "boomerang" shape defining an obtuse angle, 
facing downwardly so that the rectilinear part of the fork which is fixed 
to the pivot 46 has a length substantially equal to the length of the 
radius of the front wheel 24. 
The front pivotal arm 12 futher comprises the strut 50 with the 
reinforcement or stiffener 52, the strut being employed as a protective 
case for the transmission 20 driving the front wheel. Strut 50 is at one 
of its ends rotatively mounted coaxially with the output shaft 32 of the 
gearbox 18. Transmission 20 is of the type having a chain 54, a chain 
wheel 56 and a sprocket 58. The mounting of the sprocket 58 on the output 
shaft 32 of the gearbox 18 is shown in detail in FIG. 3. 
The other end of the strut 50 is articulated to a steering fork 60 so that 
the latter is free to rotate about an axis 61 and about an axis 65 which 
is the axis of rotation of the chain wheel 56. The chain wheel 56 drives 
through a universal joint 62 a sprocket 64 which cooperates with a chain 
66 engaged on a driving chain wheel 68 connected to an outer part of the 
hub, of wheel 24 that is movable in rotation about an inner hub relative 
to the pivot 46 about a pin 47. 
The steering fork 60 is also fixed at its lower part 70 to the inner hub 
and is articulated at its upper part to an end of a lever arm or compass 
system 72 about a first pin 74. 
Compass system 72 is itself articulated at its other end to a second pin 76 
parallel to the first pin 74 on a steering column 78 surmounted by a 
control handlebar 80. 
Steering column 78 is mounted to be freely rotatable about an axis 82 
relative to the frame 10 on which it is fixed. The dimensions and the 
orientations of the different elements of the steering unit are such that 
the articulation points 76, 74, 65 and 46 respectively of the steering 
column 78, the compass system 72, the front steering fork 60 and the 
steering pivot pin 47 of the front wheel 24 relative to the pivot 46 are 
in alignment. 
The frame 20 comprises at least two tubes 84, 86 interconnected at first 
ends and having second ends connected to the motor so as to form a frame 
88. 
In the upper part of the frame 88 there is provided an air supply intake 90 
surmounted by a filter 92 substantially at the height of the handlebar. 
Each tube 84, 86 comprises an air supply sleeve 94 connecting the tube to 
the motor 16 and more particularly to a carburetor 96. 
The frame 10 further comprises an exhaust pipe 98 which extends up from the 
motor 16, is fixed to the frame 88 at 100 and extends rearwardly to such 
height, relative to the ground, that it is capable of receiving a saddle 
(not shown for the sake of clarity). 
A stiffener 102 is disposed substantially between the end of the exhaust 
pipe and the motor 16 to reinforce the frame. In a known manner, the end 
of the exhaust pipe is completed by a muffler 104. 
The operation of the pivotal arms and the displacements of the principal 
elements of which they are composed is represented diagrammatically in 
FIG. 2. 
The lower fork 44 of the pivotal arm 12 pivots about the pin 45 in a plane 
parallel to the plane containing the wheel and can assume various 
positions represented by dot-dash lines. 
Likewise, the strut 50 pivots about the output shaft 32 of the gearbox and 
can assume various positions represented by dot-dash lines. 
The compass systems 72 compensates for the variations in distance between 
the steering fork 60 and the lower end of the steering column 78. 
The constant alignment of the articulation points 76, 74, 65 and the pin 46 
permits the compass system to be connected directly to the steering colum 
78 without the necessity of providing universal joint assemblies at each 
articulation point. 
Moreover, the strut 50 of the deformable quadrilateral forming the front 
pivotal arm 12 pivots about the shaft 32, and the distance between the 
sprocket 38 and the chain wheel 36 remain constant 36. The position of the 
shaft 32 is defined in accordance with parameters such as wheelbase, 
castor, castor angle. Thus, once the parameters are chosen, the point 32 
is unique. 
FIG. 3 represents a clutch release device 106 for uncoupling the drive of 
the front wheel. Device 106 is disposed coaxially of the shaft 32 and 106 
is of the centrifugal type. 
The sprocket 58, connected to a bell member 108, is mounted to freely 
rotate on the shaft 32 by means of a bearing 110 and is maintained fixed 
in translation relative to the shaft 32 by an elastic ring 112. 
An annular flange 114, mounted with a tight fit on the shaft 32, carries 
shoes 116 which are radially movable relative to flange 114 and are biased 
toward the latter by springs 118. The shoes 116 comprise in the known 
manner a metal weight 120 to the end of which is fixed a friction liner 
122. 
The operation of this clutch device is for example as follows. 
At low speed, the shaft 32 has a low speed of rotation which does not 
enable the centrifugal force imparted to the weights 120 by the speed of 
rotation to overcome the return force exerted by the springs 118. Thus, 
only the rear wheel is driven. 
When the rear wheel loses its adherence and slips, or when the speed of 
rotation of the output shaft of the gearbox increases, the shoes 116 move 
away from the flange 114, the liners 122 come into contact with the bell 
108 and create a sufficient friction to cause driving of the bell and 
simultaneously the driving of sprocket 58. Thus, both the front and rear 
wheels are driven. 
The vehicle according to the invention affords many advantages, in 
particular that of providing a constant adjustment of the tension of the 
chain, which results in an improved chain-sprocket-chain wheel 
cooperation, an improved flexibility in the transmission, an improved 
reliability and an improved efficiency of the transmission. 
The frame is also simplified and lightened owing to the multiple functions 
of certain elements, such as the pivotal arms and the exhaust pipe. The 
frame provides moreover improved air intake which occurs at a greater 
height while remaining easily accessible without requiring a complementary 
assembly element. 
The "boomerang" shape of the fork 44 provides, in combination with the 
simplification of the steering unit by the elimination of universal 
joints, an increased angular movement. 
The movement has been described with regard to a particular embodiment, but 
the invention concept may be applied to vehicles having three or four 
wheels, more commonly called ATC.