Commercial CVT’s (Continuously Variable Transmission), in the automotive industry in existence currently (push belt CVT’s), are all based on a dynamic friction interface. The dynamic friction interface transmits the power through steel on steel interface in special traction fluid oil.
However the commercial push belt CVT has a number of disadvantages.
• Firstly the mechanical efficiency, if the whole ratio range and variable load conditions, is considered is much lower if compared to the mechanical efficiency of geared transmissions. This is because the inherent dynamic friction interfaces transmitting power in these CVT’s.
• The second disadvantage is that these CVT’s require a complex hydraulic system in order to apply pressure to the dynamic interface in order to establish traction.
• Above together with the fact that that expensive materials and manufacturing methods are needed for the belt and sheaves of the CVT’s make them a heavy and expensive option as automotive automatic or two pedal solutions, especially in the small vehicle market.
The RotorCVT as a ratcheting CVT
In order to address above shortcomings of commercial CVT’s and to provide the small passenger vehicle market with a light cost effective two pedal solution, Varibox CVT Technologies has developed the RotorCVT. The RotorCVT is a type of ratcheting CVT, featuring two stages, each including a one-way clutch, which takes turns to drive the output.
In order to be practically and commercially viable a ratcheting CVT needs to comply with the following two minimum requirements:
• The velocity profile of the intermittently driving stages needs to be constant when the respective stage is driving. Most of existing concept ratcheting CVT have a sinusoidal velocity profile which cause a rippled output which cause unacceptable levels of vibration.
• Since a ratcheting CVT’s by definition include components that undergo cyclic loading, the interfaces of these components with each other need to operate without any backlash. If any backlash exists, impact noise and vibration will result.
The current innovative RotorCVT meets above requirements.
High mechanical efficiency and low fuel consumption
The current demonstrator vehicle, a Chevrolet Spark, fitted with a RotorCVT, confirmed above, with a mechanical efficiency within 3.6% of that of the equivalent manual transmission and with fuel consumption within 3% of the equivalent manual transmission.
Low manufacturing cost and mass
The innovative features of the RotorCVT results in an estimated manufacturing cost which is higher than a manual transmission, but much less that the cheapest automatic (two pedal) solution.
Overall the RotorCVT presents a two pedal solution, with a very small trade-off between driver comfort and fuel consumption if compared to a manual transmission.
The RotorCVT also features a geared neutral which means in its lowest ratio, the wheels are not turning. This feature eliminates the need for a clutch and torque convertor which contributes to the cost and weight saving.
The current RotorCVT prototype as implemented in the demonstrator vehicle has a mass of only 40 kg.
No hydraulic control/system is used, which also contributes to mass and cost saving.