Marco Cammalleri

A New Approach to the Design of A Speed-Torque-Controlled Rubber V-Belt Variator

Abstract This paper presents a new model for a torque-speed-sensing rubber V-belt variator. The actuators are of the centrifugal roller kind on the driver side and a helical torque cam plus a compression-torsion spring on the driven side. The equations permit designing the actuator geometry in order to keep the transmissible torque as close as possible to the torque request in the whole operative field. Moreover, a procedure is suggested for the most proper design of an automatic variator of this kind. It permits choosing the required variogram of the transmission, i.e. the matching between the engine and the transmission, and designing the actuators: roller mass, housing shape, contact plate angle for the centrifugal roller actuator, and helical guide slope for the torque cam actuator. Furthermore, the degree of engine transmission matching can be calculated at part load for fixed actuators. Extensive experimental tests were carried out on a proper bench test to validate the procedure.

Approximate Closed-Form Solutions for the Shift Mechanics of Rubber Belt Variators

The mechanical behavior of V-belt variators during the speed ratio shift is different from the steady operation as a gross radial motion of the belt is superimposed to the circumferential motion. The theoretical analysis involves equilibrium equations similar to the steady case, but requires a re-formulation of the mass conservation condition making use of the Reynolds transport theorem. The mathematical model of the belt-pulley coupling implies the repeated numerical solution of a strongly non-linear differential system. Nevertheless, an attentive observation of the numerical diagrams suggests simple and useful closed-form approximations for the four possible working modes of any pulley, opening/closing, driver/driven, whose validity ranges over most practical cases. The present analysis focuses on the development of such simplified solutions, succeeding in an excellent matching with the numerical plots, and on the comparison of the theory with some experimental tests on a motorcycle variator, revealing a very good agreement.Copyright

Dielectric Characterization of Fruit Nectars at Low RF Frequencies

Dielectric properties of apple, apricot, peach, and pear nectars were studied in the frequency range from 15 kHz to 30 MHz and the temperature range from 25 to 60°C. Both the relative dielectric constants and the dielectric loss factors decreased by increasing frequency and increased linearly with increasing temperature with values in the order 104–102 and 105–102, respectively. The power dissipation densities and the power penetration depths were found to increase linearly with temperature. Power dissipation densities remained essentially constant for all the samples while power penetration depths decreased significantly on increasing frequency. The dependence of each of the two dielectric properties on frequency and temperature has been described by two simple equations that proved to be adequate to describe the trend of the relative dielectric constant and dielectric loss factor for all the frequencies temperatures considered. It has been established that the dominant mechanism for the dielectric loss is ionic conductivity.

Helical Shift Mechanics of Rubber V-Belt Variators

A very common configuration of motorcycle V-belt variators allows for the correction of the belt tensioning in dependence on the resistant torque by a suitable helical shape of the tracks that enable the closure/opening of the driven half-pulleys. The theoretical model for the belt-pulley coupling is just complex for this arrangement, where one half-pulley may run in advance and the other is slower than the belt, and requires the repeated numerical solution of a strongly non-linear differential system by a sort of shooting technique, until all boundary conditions are fulfilled (angular contact extent, torque, axial force). After solving the full equations, the present study develops closed-form approximations characterized by an excellent fit with the numerical plots and proposes a simple and practical formulary for the axial thrust in dependence on the torque and the tension level. Then, results of a theoretical-experimental comparison are also reported, revealing a very good agreement of the model with the real operation.

Efficiency of Split-Way CVT’s. A simplified model

ABSTRACT In this paper, a general formula is obtained for the efficiency of all types of Split-Way CVT, consisting of one or two epicyclic trains, a number of fixed ratio gears and one variable speed unit (CVU). It is based on the application of the principle of virtual works and on the simplifying hypothesis that all the dissipation is lumped inside the CVU. The comparison with some experimental results from the literature shows a surprisingly good fit, also in the neighbourhoods of zero speed ratio. INTRODUCTION The possibility of changing the speed ratio continuously between the primary and the secondary shaft of a mechanical transmission is a very interesting topic, mainly in the automotive field. With the aim at overcoming the main drawbacks of mechanical variators, in terms of transmissible power, width of the speed ratio range and efficiency, the idea of using the continuously variable unit (CVU) combined with a differential drive has stimulated the researchers in the last two decades. Although the names of this kind of mechanical transmissions are somewhat different in the literature (Split-Way CVT’s, Split Power CVT’s, Infinitely Variable Transmission IVT, Split Path Transmission, et cetera), they consist always of one or two epicyclic trains, a number of fixed ratio gears and one CVU. Broadly speaking, they can either amplify the overall speed ratio range in comparison with the simple variator, though entailing a higher variator power ratio (i.e. power recirculation in the CVU) and a lower efficiency, or can be designed to get opposite features. Anyway, the combination of a large speed range and a low variator power ratio, with a higher transmission efficiency, can be obtained by using several modes (that is associating two or more split way layouts which commute to each other by brakes or clutches). There are numerous examples of Split-Way CVT (SW-CVT) in literature, also of the multi mode type, but they use only one epicyclic train in general (for example [1] [2] [3] [4] [5], as well as many others). On the contrary, applications with two epicyclic trains are rare, though, the use of a second epicyclic train can improve the variator power ratio substantially, as shown in references [6][7][8][9]. In any case, the theoretical models proposed to describe the kinematical behaviour and to evaluate the performances in terms of power flows and efficiency, are based in general on the knowledge of the structural characteristics of each transmission unit. Nevertheless, assuming ideal working, it has been recently proved, that the overall behaviour of these drives, either with one or two epicyclic trains, depends only on three functional parameters, which can be defined regardless of the drive layout and of its structural components [10]. These three parameters, also named apertures

A theoretical approach to pneumatic muscle mechanics

The mechanical response of pneumatic artificial muscles is analyzed assuming the inextensibility of the sheathing braids and taking into account the stress field inside the rubber bladder, which is regarded as a Mooney-Rivlin hyperelastic material. The end effects are simulated by heuristically profiling the meridian section. After estimating the constitutive parameters by traction tests on rubber specimens, the theoretical results are compared with experiments and a satisfactory accordance may be detected.

On the Birth and Growth of Pendulum Clocks in the Early Modern Era

Measuring the passage of time has intrigued humankind throughout the centuries. Ancient times witnessed the appearance and development of clepsydras and water clocks, whose place was subsequently taken by mechanical clocks in the Middle Ages. It is really surprising how the general architecture of mechanical clocks has remained almost unchanged in practice up to the present time. Yet the foremost mechanical developments in clock-making date from the 17th century, when the discovery of the laws of pendular isochronism by Galilei and Huygens permitted a higher degree of accuracy in the measuring of time.

Effective Linear Friction Welding Machine Redesign through Process Analysis

Linear friction welding is a solid-state joining process developed for non-axisymmetric components in which the joining of the specimens is obtained through reciprocating motion and pressure. In the process, the friction forces work due to the high frequency oscillation and the pressure between the specimens is converted in thermal energy. In order to design an effective machine, relevant issues derive from the high frequency and the large inertial forces involved in the process. In this study, the authors describe the redesign of a preexisting prototypal machine for LFW processes. A machine redesign is needed when welding high resistant materials, i.e. steels or titanium alloys, with high frequencies, up to 72 Hz. The sensors equipping the machine allows in process measurements of key process variables as temperatures of the specimens, tangential forces, accelerations and speeds. At the same time through the acquired data, the main weaknesses of the machine can be highlighted allowing for effective redesign.