A Mathematical Method for Eliminating Spin Losses in Toroidal Traction Drives

The efficiency of the original Toroidal continuously variable transmission (CVT) is limited due to the spin losses caused by the different speed distribution in the contact area. To overcome this drawback, this paper replaces the original working surface with a new surface derived from a differential equation and proposes a novel Logarithmic CVT. Equations and ranges of the transmission ratio range, half-cone-angle, and conformity ratio, which are essential geometrical parameters of the Logarithmic CVT, are derived. A set of geometrical parameters is further recommended. With such geometrical parameters, the transmission ratio range of the Logarithmic CVT is as wide as that of the Half-Toroidal CVT. The two types of CVTs are compared with each other in terms of efficiency based on a widely accepted computational model. The results show that efficiency of the Logarithmic CVT is higher than that of Half-Toroidal CVT except for some particular situations because of the thrust bearing losses.

Development of the Sphere-Toroidal Continuously Variable Transmission

This paper describes a new genre of Toroidal-CVT system, called the Sphere-Toroidal Continuously Variable Transmission (STCVT), which is derived from the half-toroidal traction drive (TCVT) and introduces its structure and working principle. The torque transfers from the input shaft to the cross-axle universal shaft coupling connected with the driven shaft. By discussing the difference between the torque-transfer, the paper will show the possibility of the application in the vehicle. To conclude, the system has the potential to implement infinite extension for the CVT theoretically.

Traction and Efficiency Performance of the Double Roller Full-Toroidal Variator: A Comparison With Half- and Full-Toroidal Drives

In this paper, we analyze in terms of efficiency and traction capabilities a recently patented toroidal traction drive variator: the so-called double roller full-toroidal variator (DFTV). By employing a relatively simple model of the elastohydrodynamic contact behavior between the disks and rollers, we compare the performance of the DFTV with classical solutions as the single-roller full-toroidal variator (SFTV) and the single-roller half-toroidal variator (SHTV). Interestingly, the DFTV shows an improvement of the mechanical efficiency over a wide range of transmission ratios, and in particular at the unit speed ratio, as in such conditions the DFTV allows for zero-spin thus strongly enhancing its traction capabilities. The relation between the torque transmission and the operational volume is also investigated for the three toroid geometries. In this case, the better performance is achieved by the SHTV, whereas the other two geometries show a similar behavior.

Time-Accurate Multibody Dynamics Model for Toroidal Traction Drives

A time-accurate multibody dynamics model for predicting the transient response of toroidal traction drives is presented. The model can be used to predict the system’s transient response due to variations in the input speed, variations in the output load, and changing the speed ratio. The model supports half and full-toroidal configurations, multiple transmitters and multiple cavities. The multibody system representing the toroidal drive is modeled using rigid bodies, revolute joints and rotational actuators. A penalty model is used to impose the joint/contact constraints. The contact model detects contact between discrete points on the surface of the transmitter and an analytical surface representation of the input and output shafts’ toroidal surfaces. A recursive bounding sphere contact search algorithm is used to allow fast contact detection. An elasto-hydrodynamic lubrication model is used for the tangential contact traction forces between the transmitter and the toroid. The governing equations of motion are solved along with joint/constraint equations using a time-accurate explicit solution procedure. The model is partially validated by comparing to previously published steady-state models. The model can help improve the design of toroidal continuous-variable transmission systems including increasing the torque capacity and durability.