ANALYSIS OF STEADY-STATE BEHAVIOR IN CONTINUOUSLY VARIABLE TRANSMISSIONS (CVTS) USING THE CMM MODELLING APPROACH

A Continuously Variable Transmission (CVT) is an automatic transmission, mostly found on front wheel drives, that can change seamlessly through a continuous range of effective gear ratios. In this way, an unlimited number of transmission ratios is available. This is a benefit not only for fuel economy, but also for comfort and performance. This is possible only with an accurate control strategy of the transmission in order to regulate the speed ratio and the shifting speed and allow the engine to operate on its economy, without affecting the CVT mechanical efficiency. An appropriate control over clamping force is what makes sure to improve efficiency of transmission by optimizing the clamping forces generally in the quasi-stationary (steady-state) conditions, however, recently, it is also possible advance technology to optimize in transient conditions. To enhance the design of the clamping force control, the steady-state behavior of the CVT is studied in details in this project by deducing the KpKs mapping and the traction curves. In the literature are available different CVT models to describe the belt and/or chain CVT dynamics and all of them lead to a good control strategy of the transmission in order to have a higher value of engine efficiency. The model adopted in this project is the so called CMM model [5], made by G. Carbone, L. Mangialardi and G. Mantriota, that allows to have a very precise overview on the CVT behavior without the necessity of experiments with a relatively low computational cost.