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CONTINUOUS GEAR RATIO VARIATOR FOR MOTOR VEHICLES, MACHINE TOOLS AND OTHER APPLICATIONS
A car engine generates a force which cannot be transferred directly to wheels. To run, for instance, the rest of the mechanical parts must be isolated by the clutch and, during running, this needs a device which adapts the rotation speed to the one necessary to the wheels to face the infinite needs of the road. This device is the gearbox which can be regarded, to all the extents, as a torque multiplier and a speed reducer.
The traditional hand-operated mechanical gearbox receiving the motion from the engine through the clutch and reducing, together with the differential unit, a high number of revolutions to lower values, schematically comprises a number of toothed gears with different diameter suitably engaged one with the other through the selection by a special lever with respect to the actual driving needs.
Differently from the mechanical type, the automatic gearboxes allow to change the speed without compelling the driver to depress the clutch pedal and to shift the gearbox lever as they have no clutch and are equipped with a hydraulic torque converter used as wheel and clutch. The most suitable ratio to the use conditions of the car is automatically selected by an electronic power unit which decides the most suitable speed to engage by dialoguing step by step with the engine power unit and produces as a result a greater comfort and a lower consumption.
There is also an automatic gearbox with continuous variation of the transmission ratio which enables to pass from a high gear to a low gear through an infinite range of intermediate ratios and which consists of two V-shaped pulleys and a V-belt of steel or aluminium which slides from the narrowest diameter to the widest end of each pulley and changes the transmission ratio in a continuous way and without jerks. The weak point of the CTV is represented by the fact that such gradual ratio variation causes an unpleasant noise of the engine similar to the one of a slipping clutch without a real change of speed. Sometimes ago, there were also CTV suitable for the modest torque of small power displacements due to problems encountered while transferring high torques using the transmission with belts and pulleys. These problems could be partially be solved if larger metal belts or special chains were used or if engines were set up in such a way not to privilege power supply at a high rpm since this compels the CTV to pass to lower ratios as soon as the driver fully depressed the gas pedal causing the noise mentioned above.
Since the aforesaid problems are connected to the intrinsic nature of the CTV using belts and pulleys, the design of the proposed continuous torque variator is much more than convincing since, differently from the known technique, it envisages the transmission of the movement through a couple of elements, both convex or one convex and the other concave, preferably coated with suitable composite materials (ceramics or equivalent) which move simultaneously along the respective incident rotation axes to always remain engaged.
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