Mechanism for gradually and smoothly varying rotational speed between a drive member and a driven member

A mechanism for varying rotational speed between two rotary shafts, namely a drive shaft and a driven shaft. The mechanism is designed to replace gear boxes which are generally used in motor vehicles. The mechanism includes two truncated cones with concave surface generatrices attached to a shaft secured to the engine and to a shaft secured to the transmission members, respectively. A roller made up of an inverted double cone having convex surface generatrices is mounted on an arm via a pin and arranged to rotationally interconnect the truncated cones by means of the adherence caused both by the choice of materials and by the bearing force exerted on the truncated cones by the roller through a suitable pressure member. The roller is translationally movable over the convex surfaces of the truncated cones by means of a suitable position varying system for adapting the drive ratio to the various parameters which influence the operation of the whole mechanism, according to its position. The mechanism is particularly suitable for use in motor vehicles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mechanism for gradually and smoothly 
varying the rotational speed between a driving member and a driven member. 
2. Description of the Related Art 
It is sometimes necessary not to interconnect the driving shaft directly to 
the movement transmission members. This is all the more true when there is 
an internal combustion engine which cannot be started when engaged since 
it provides an appreciable torque only from a certain rotational speed. 
The maximum driving torque available from a given engine is approximately 
constant, while the resistance to be overcome to ensure movement can vary 
continuously. In a motor-car, the propelling power must be equal to the 
repelling power so that it can move at a determined speed. The repelling 
torque varying continuously with the profile of the road, it would be 
desirable that the drive ratio between the rotational speeds of the engine 
and of the propeller shaft be responsive to the profile fluctuations, 
which amounts to having continuous gear shifting. 
To vary the drive ratio, the following are generally used : gear boxes 
having various compound trains which can be activated at will, gearboxes 
having epicycloidal trains, torque converters as well as driving belt 
propeller means. 
The use of these systems requires one to frequently modify the drive ratio 
according to the changes of the repelling power, which causes the engine 
speed to be varied and entails a specific consumption more significant 
than with a constant speed. 
The mechanism according to the invention allows to overcome such drawbacks 
by enabling the speed changes in a continuous and progressive way, while 
enabling the engine to run at a constant speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The mechanism represented in FIG. 1 comprises a truncated cone (3) attached 
to a shaft (2) rotationally driven by a driving member (1), and a 
truncated cone (5) mounted on a shaft (6) attached to the movement 
transmission members. The truncated cones (3, 5), the generatrices of 
which form concave conic frustums, are mounted in an opposite 
configuration so that the narrow end of one can correspond to the wide end 
of the other one. The transmission of the rotational movement from the 
truncated cone (3) to the truncated cone (5) is effected by a roller (4). 
Roller (4) is composed of two inverted truncated cones sharing the same 
axle (a), the generatrices of which form convex conic frustums. 
Adhesion of roller (4) on truncated cones (3, 5) is ensured by the force 
transmitted by a pressure member (7). Roller (4) can move laterally by 
means of a varying system (8) enabling it to slide the length of truncated 
cones (3, 5). 
At the beginning of the start-up phase, roller (4) has one of its frustums 
in contact with the smallest diameter of the driving truncated cone (3) 
while the other one is in contact with the largest diameter of the driven 
truncated cone (5); such a configuration corresponds with the lowest 
ratio. Pressure member (7) must provide a pressure force sufficient to 
obtain an adhesion between roller (4) and truncated cones (3, 5) that is 
at least equal to the driving torque. 
The adhesion is enhanced by use of materials having a high friction 
coefficient on the surface of truncated cones (3, 5) and roller (4). 
The use of truncated cones requires converging vertices for each position 
of roller (4). This is achieved by giving the frustums of each truncated 
cones (3, 5) and roller (4) a particular radius of curvature. 
The use of concave or convex shapes enables the vertex of truncated cones 
(3, 5) to be moved along their respective axles while achieving a perfect 
convergence of the vertices for each position occupied by roller (4). 
When it is desired to increase the rotational speed of the driven shaft 
(6), it is sufficient to vary the roller position (4) by having it slide 
along truncated cones (3, 5) by means of a varying system (8). The drive 
ratio is gradually varying to pass from the lowest ratio to the highest 
ratio and vice versa by tilting roller 4 around its vertical axis, as 
shown in FIG. 2. 
This system allows continuous gear changing without requiring the changes 
in the engine speed which can be used in the range of maximum torque. It 
then becomes worthwhile to use an engine having an important torque for a 
low specific consumption. This configuration allows rapid accelerations 
and high speeds which can be compared to those of more powerful propelling 
systems, all the while keeping the engine speed within a range of use 
favoring low consumption. Accordingly, the longevity of the engine is 
greatly increased. 
Similarly, the controlled variation of the drive ratio by any system allows 
for a powerful engine braking as soon as the accelerator pedal is 
released, which increases the longevity and the efficiency of the brake 
system. This system enables significant safety improvements. 
The mechanism according to the invention is particularly adapted for the 
motor vehicles.