The student Mikel Iricampos Juaristi obtained an EXCELLENT grade
The student Mikel Iricampos Juaristi obtained an EXCELLENT grade
The student Mikel Iricampos Juaristi obtained an EXCELLENT grade
- Thesis title: Effect of independently controlled clamping loads on Toroidal type Continuously Variable Transmissions considering the influence of contact scale and spinning
Court:
- Presidency: Giuseppe Carbone (Politecnico di Bari)
- Vocal: Enrique Chacón Tanarro (Universidad Politécnica de Madrid)
- Vocal: Alberto Porras Vázquez (Shell Global Solutions)
- Vocal: Maider García de Cortázar Aguirrezabal (Tecnalia Research and Innovation)
- Secretary: Iñigo Llavori Osa (Mondragon Unibertsitatea)
Abstract:
To increase the energy efficiency of a system, Continuously Variable Transmissions (CVTs) enable to steadily adapt its transmission ratio in a smooth manner. Among the different existing mechanisms, Toroidal type CVTs (T-CVTs) consist of input and output discs conforming a toroidal-shaped cavity with rollers positioned in between where torque transmission occurs across two contact points: one, between the input disc and the rollers, and the other one, between the rollers and the output disc. For effective power transmission through these contact points, high normal loads are required to increase lubricated traction and to this aim, clamping devices are employed. Despite the differences in geometry and kinematic behaviour of each point, historically both contacts have been subject to equal loads; thus, differences may be expected when loads are adapted to local conditions. Therefore, the main objective of this thesis is to predict and evaluate the efficiency of T-CVTs by independently controlling the clamping loads at the input and the output contact points.
In these transmissions requiring high traction, the occurrence of large-scale interfaces and spinning motion tends to decrease traction. However, the combined impact of these phenomena has not been thoroughly studied. That is why a semi-analytical model to predict traction coefficient at the disc-roller contact points was developed. Results reveal that the traction coefficient increases under low-scale and low-spin velocities, which depicts a favourable scenario for torque transmission.
Moreover, a global analytical model to predict traction equilibrium and efficiency of full T-CVTs has been developed, considering independently controlled clamping loads at each contact point. Results indicate that the efficiency of this transmission decreases under, both, low and high longitudinal sliding conditions. Indeed, clamping loads influence the longitudinal sliding in the contact points while it has been observed that each point behaves differently due to scale effects.
Finally, a T-CVT prototype was designed to validate the proposed models and to measure experimentally the efficiency and longitudinal sliding under variable working conditions; achieving very similar trends to those obtained by previous analytical models. The main innovation of the prototype involves independent control of the input and the output clamping loads. In this way, under low torque conditions, the lowest tested clamping load achieved the highest efficiency, albeit with a lower maximum transmissible torque. Experimental measurements reveal that the input clamping load affects the efficiency of the output point. In other words, overclamping the input point, increases power losses, reducing the energy reaching to the output point. Finally, it is concluded that the transmission efficiency experiences an improvement when the clamping forces are independently controlled in contrast with current equal clamping force control methods.