CVT PROTOTYPE

The CVT (Continuos Variable Transmission) devised by Girotto starts from the known concept of exploiting the properties of a two coaxial rotor free-wheel to transfer power and RPM from one rotor to the other in a controlled manner. Between the two coaxial rotors or sleeves (shown in gray) some balls or rollers are placed (shown in red). Depending on the imposed eccentricity for the two rotors, the RPM transferred from one rotor to the other varies continuously.

Sundry inventions by Girotto involved this transmission.

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n the drawings you can see two special ring nuts (shown in cyan) cooperating with two rings (shown in yellow), each couple being arranged on the rotors'sides. In the grooves provided in the ring nuts pins integral with the rollers are inserted and able to slide.

The engagement in the grooves assures the constant contact between the rollers and the rotors, in every phase of the rotary cicle. A simple idea, but one alleviating the great problem of the accidental detachment between rollers and rotors, leading to loss of torque at the output.

Another invention regards the mechanism for imposing the desired eccentricity between the rotors, i.e. for establishing the transmission ratio. Girotto's solution involves a pneumatic piston acting radially upon a rotor, in order to move it. The main benefit, absolutely not discernible at first sight, is that the piston retracts whenever the engine is too much overloaded and, therefore, the torque fed to the output decreses but the engine does NOT turn off.

However, the more relevant idea widening the application field of these transmissions, is probably the cascade of free-wheels. The worst and more limiting problem with these CVTs is the narrow variation in the achievable transmission ratio.

Girotto solves the problem arranging coaxially side by side several free-wheels and coupling them in pairs with a common rotor (see European patent application EP1688645A1), thereby setting them in cascade-connection. In this way any transmission ratio is, theoretically, achievable from a very compact and simply adjustable CVT, now being needed only to design the number of cascaded free-wheels.