EHL-Squeeze in High Loaded Contacts: The Case of Chain CVT Transmissions

We analyze the lubrication conditions at the pin-pulley interface in a Gear Chain Industrial chain CVT. In particular, we focus on the squeeze of oil which occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to determine what actually is the lubrication regime at the interface. Taking into account that for normal CVT operations the time the pin spends in contact with the pulley groove is of about 0.01 s (traveling time), we show that rms surface roughness less than 0.1 μm and squeezing load of about 1kN acting on the pin, corresponding to values adopted in such systems, guarantee a fully lubricated EHL regime at the interface. We also show that during low-velocity CVT operations, the lubrication regime at the interface is determined by a succession of hydrodynamic and mixed lubrication stages in an order strictly related to the squeezing load history.