The construction of a test bench for studying hybrid lubrication in bearings: simulation and experiments

The project of building a test bench dedicated to hybrid lubricated spherical bearing has begun few years ago, when our research group was involved in a feasibility study on a novel Continuous Variable Transmission (CVT), called Ball Toroidal CVT. The main problem with the BT-CVT consists in how to sustain two transmission balls that rotate inside a spherical socket, in order to avoid direct contacts. In this work the oil film sustaining capability is analyzed in relation to the adopted oil (traction oils), eccentricity, angular velocity, loads, and lubrication regimes (hydrodynamic and/or hydrostatic). A first series of tests has been performed at low velocities (up to 5,000 rpm) and low nominal inlet pressure (0.4 MPa). Simple dependencies between load and minimum film thickness have been detected, as the one represented in Fig. 3. It seems the first results show a lower load carrying capacity than the needed one. However, this result has been obtained without taking advantage of the hydrostatic compensation due to restrictors. Furthermore, the numerical simulator attests that in the real system the load is generally higher than in the test bench. Finally, considering that the angular velocity and inlet pressure in the real system is higher than in the test stand, it can be concluded that the BT-CVT still remains of interest for automotive applications