Luigi Mangialardi

Power flows and efficiency in infinitely variable transmissions

An infinitely variable transmission (IVT) is a continuously variable transmission with an infinite ratio range, which means that the transmission ratio may achieve zero. This paper compares the efficiency of possible IVT configurations consisting of a conventional CVT (continuously variable transmission) coupled to a planetary gear train and a fixed ratio mechanism. A kinematic analysis has been performed to determine the transmission ratio of the IVT components for two types of power flow. The efficiency of the IVT has been determined considering how the efficiency of the IVT members changes as a function of the operating conditions. The power and efficiency curves for the different functional solutions have been compared.

A three-dimensional criterion for the determination of optimal grip points

Abstract Multifingered grasping has aroused remarkable interest because it makes possible the manipulation of objects of different shapes and sizes. However, manipulating and picking up objects in unstructured environments requires accurate contact-point selection. Generally, such processes are subject to external forces which are difficult to predict and may change during task execution. In this paper, an optimization criterion is proposed which is meant to select the optimal grip points in a three-dimensional problem for any number of contact points. This method may be applied to three-dimensional objects of any shape (curved or polygonal) and does not require that the external forces acting on the object be known. A grasp quality index is presented which has been obtained by minimizing the grasping forces required to balance a generalized external disturbance. The optimization criterion has led to the formulation of a single optimization problem with non-linear constraints. Finally, the paper presents the results obtained in searches for the optimal grip points on some two- and three-dimensional objects.

Dynamic behaviour of wind power systems equipped with automatically regulated continuously variable transmission

High efficiency levels may be attained by wind turbines operating at varying speeds when the machine is made to run at a constant tip speed ratio. Previous papers have suggested incorporating a continuously variable transmission (c.v.t.) to achieve this purpose. Following the general recommendation of using efficient, reliable and economical technologies in wind power systems, one of these papers investigated whether a V-belt c.v.t. with automatically adjustable speed was compatible with a wind power system. The investigations in this case were carried out under steady-state conditions.

Leakage mechanism in flat seals

We present a theoretical approach to estimate the fluid leakage in flat seals. The approach is based on the analogy between the seal-substrate interface and a porous medium. We assume that the interface is constituted of a random distribution of noncontact patches (the pores) and small but numerous contact spots (islands). Leakage may occur only through the pores, of which the lateral size and height are distributed according to a probability density function that we calculate on the basis of a recent theory of contact mechanics. Our theoretical approach is based on a percolation scheme that has never been proposed before and we believe it could be useful to stimulate further theoretical or experimental investigations. Within this percolation scheme we apply critical path analysis to calculate the hydraulic conductivity of the medium and compare our predictions with other calculations very recently presented to the scientific community.

The advantages of using continuously variable transmissions in wind power systems

When connected to appropriate electric power generators, wind turbines may be used to produce electric energy. This may become complicated because wind speed tends to change. Traditionally, electric power was produced by electric generators connected to mechanical devices whose movement could be perfectly controlled and adapted to users needs by special governors. This paper explores the feasibility of incorporating a continuously variable mechanical transmission between a wind turbine and an electric generator. Such a system would allow the turbine to operate at maximum efficiency levels and the generator to produce electric power at a desired frequency without using other devices. A mathematical model has been used to simulate a system formed by a wind turbine connected to an induction generator by means of a continuously variable transmission. The simulation was aimed at assessing whether the system was stable and attempted to adjust the transmission in order to ensure the required power supply.

Quantifying Dynamic Characteristics of Human Walking for Comprehensive Gait Cycle

Normal human walking typically consists of phases during which the body is statically unbalanced while maintaining dynamic stability. Quantifying the dynamic characteristics of human walking can provide better understanding of gait principles. We introduce a novel quantitative index, the dynamic gait measure (DGM), for comprehensive gait cycle. The DGM quantifies the effects of inertia and the static balance instability in terms of zero-moment point and ground projection of center of mass and incorporates the time-varying foot support region (FSR) and the threshold between static and dynamic walking. Also, a framework of determining the DGM from experimental data is introduced, in which the gait cycle segmentation is further refined. A multisegmental foot model is integrated into a biped system to reconstruct the walking motion from experiments, which demonstrates the time-varying FSR for different subphases. The proof-of-concept results of the DGM from a gait experiment are demonstrated. The DGM results are analyzed along with other established features and indices of normal human walking. The DGM provides a measure of static balance instability of biped walking during each (sub)phase as well as the entire gait cycle. The DGM of normal human walking has the potential to provide some scientific insights in understanding biped walking principles, which can also be useful for their engineering and clinical applications.

Automatically regulated C.V.T. in wind power systems

The conversion of wind energy into electric power is particularly problematic owing to the changes in wind speed. Previous papers have considered the feasibility of incorporating a continuously variable transmission (C.V.T.) between a wind turbine and an electric generator and have assessed the advantages of such a system in terms of efficiency. However, these papers did not suggest the type of regulator or control system to be used for the C.V.T. Following the general recommendation of using efficient, reliable and economical technologies in wind power systems, this paper has investigated whether a continuously variable transmission with automatically adjustable speed was compatible with a win power system. The investigation has relied on numerical simulations reproducing the behaviour of a wind power system. The paper also hypothetically sited such turbine-C.V.T.-generator systems in locations with available wind data in order to have tangible proof of the advantages of using the C.V.T. proposed.

Influence of Clearance Between Plates in Metal Pushing V-Belt Dynamics

This paper proposes a one-dimensional continuous model of the steel pushing V-belt, which describes the shifting dynamics of the CVT transmission during rapid speed ratio variations. The model investigates the influence of the clearance among the steel segments on the belt dynamics. The plates and pulleys strain motion is neglected, with respect to their rigid body motion, for the evaluation of the friction forces. The power transmission is assured only if an active arc exists where the plates are pressed against each other and where compressive forces arise among the steel segments. Conversely on the idle arc the steel plates are separated and no longitudinal compressive forces exist among the metal segments. The paper shows a significant difference in dynamical behavior between the drive and the driven pulley. Moreover, differences also exist between the pitch radius increasing phases and pitch radius decreasing phases.

Mechanical Hybrid KERS Based on Toroidal Traction Drives: An Example of Smart Tribological Design to Improve Terrestrial Vehicle Performance

We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller full-toroidal variator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller half-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency performances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant undergoes very severe elastohydrodynamic lubrication regimes. 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 in which the DFTV allows for zero-spin, thus strongly enhancing its traction capabilities. The very high mechanical efficiency and traction performances of the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where the efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost capabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest that the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator.

Continuously variable transmissions with torque-sensing regulators in waterpumping windmills

One widespread application of wind energy is in waterpumping. Usually windmills are coupled to water pumps, though piston pumps are difficult to match to wind turbines. In the first approximation, the piston pump requires a constant torque to the turbine at all rotational speeds. Conversely, if the turbine were to operate at maximum efficiency levels, it would supply a torque proportional to the square of the wind speed. Hence, the combination of windmill and piston pump would be maximally efficient only for a single wind speed.