Giacomo Mantriota

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.

Performances of a series infinitely variable transmission with type I power flow

Abstract The infinitely variable transmissions (IVT) allow the transmission ratio to vary with continuity, offering the possibility of also reaching zero values for the transmission ratio and the motion inversion. In this work the experimental results related to the performances of an IVT, obtained through the joining of a V-belt continuously variable transmissions (CVT), a planetary gear and a transmission with a constant ratio, are shown. The prototype in examination is a series-IVT with a type I power flow. Using a special test rig, the input and output IVT powers as well as the power circulating in the CVT are measured. The experimental results are compared with those obtained through a theoretical model. The torques and powers of the component CVT and those related the IVT are compared in order to evaluate their potentialities. The IVT efficiency curves, in relation to the torque and the transmission ratio variation, are finally reported and compared with those of an equivalent CVT.

Performances of a parallel infinitely variable transmissions with a type II power flow

In this work the performances of an infinitely variable transmissions (IVT), or rather a split-power CVT System with a infinite ratio range, are appraised. The experimental results reported in this work are obtained through a special test rig, in which a IVT prototype was reproduced by joining a V-belt CVT, a planetary gear train, and a fixed ratio transmission. The IVT has a parallel connection and a type II power flow. Considering the output torque and transmission ratio variation, the input, output, and the circulating CVT powers are measured. The performances in terms of torque, power, and IVT efficiency are compared with those of a traditional CVT. The experimental results are compared with those obtained through a theoretical model. The performances of a series-IVT with flow type I are finally compared with those of a parallel-IVT with flow type II.

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.

Communication on optimal grip points for contact stability

The identification of contact points is a priority in planning grasps. This paper proposes a criterion for the determination of optimal grip points to secure contact stability. The criterion is generally valid, that is, it applies to grasps with any number of contact points on objects having a generic shape (polygonal or curved), and does not require that the external force acting on the object be known. A grasp-quality index, fmin, obtained by minimizing the friction coefficient needed to ensure contact stability in the presence of a generic disturbing external action, has been introduced. The criterion leads to the formulation of an optimization problem with nonlinear constraints that is easy to implement. Finally, some examples are provided which compare the results reported in the literature with the results obtained by applying the criterion proposed in this paper.

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.

Theoretical and experimental study of a power split continuously variable transmission system Part 1

Abstract Continuously variable transmissions (CVTs) have made notable progress, especially in the automotive industry, over the past years. In this paper the results of a theoretical and experimental study of an original power split CVT (PS-CVT) system are obtained. The main advantage of the proposed solution is to improve the efficiency of the CVTs by means of a power flow without recirculation using two separate phases of operation. The kinematic characteristics of the single-component devices are obtained. Using a special test rig, the power flows and the efficiency of the PS-CVT system are experimentally determined in the first operational phase. The results are compared with those obtained by a theoretical model. The advantages are therefore shown, in terms of power and efficiency, of the PS-CVT system proposed in this paper in comparison with the single CVT.

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.

Fuel consumption of a vehicle with power split CVT system

Continuously variable transmissions have made notable progress, especially in the automotive industry, in recent years. In this work, we study the performance of a mid passenger car provided with an original Power Split CVT (PS-CVT) system. The main advantage of the proposed solution is to improve the efficiency of the CVT by means of a power flow without recirculation using two separate phases of operation. By means of a simulation model we evaluate the vehicles fuel consumption with the hypothesis to consider the value of transmission ratio speed that minimises the specific fuel consumption. Furthermore the PS-CVT performance is compared with that of traditional CVT.