Abstract
De Novellis et al. 2012 (1) reported on an EHL tribological model and used this to compare the performance of three fundamentally different toroidal CVT’s. These were a full and a half toroid CVT and a new "Double Roller Full Toroidal Variator CVT" (DFTV) as developed by Ultimate Transmissions (UT). The DFTV geometry achieves zero spin at 1:1 ratio and low spin elsewhere. The model predicted exceptional efficiencies and power densities for the new CVT. Ultimate Transmissions has manufactured a test transmission embodying both the double roller variator and a new UT developed mechanical steering system with a 9.6:1 ratio spread referred to as Direct Roller Steering (DRS). Based on a proposed 150 Nm small car transmission the test transmission has been modified from its original design to facilitate independent control of all parameters and measurement of relevant system characteristics. The University of Technology Sydney has undertaken an extensive range of tests of the test transmission using its motoring dynamometer test bed allowing both steady state analysis and data collection during continuous ratio sweeps. Test sequences were established to allow separate identification of efficiency losses associated with thrust bearings and those that are inherent to the CVT traction contact regions. Results demonstrate the dynamic stability of the DRS steering system at varying speeds across its full ratio spread and for varying forward and reverse output torque. With measured thrust bearing losses removed, the central CVT demonstrates efficiencies up to 96% at 1:1 transmission ratio for a traction coefficient of 0.07, compared to 98% efficiency as predicted using a UT design tool calibrated against the work of De Novellis (1). At high and low transmission ratios the decreases in efficiency due to increasing contact spin are generally in line with these same predictions. The results of this experimental investigation demonstrate that the DFTV has excellent efficiency characteristics under a range of operating conditions and exceptional ratio spread in comparison to other transmissions.
KEYWORDS – Continuously variable transmission; Transmission efficiency; Ratio control; Power density