Mechanical transmissions Introduction

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1. MECHANICAL TRANSMISSIONS Mechanical transmissions are devices suitably designed to transmit motion, as well as torques and forces, from a mechanical component to another component, modifying kinematic and dynamic input parameters – like angular velocity, angular acceleration and torque (or force) – into output parameters having a different magnitude (e.g higher or lower angular speed, higher or lower torque magnitude, etc.). The configurations and morphologies of mechanical transmissions are various. However, in most cases, a transmission has an input and an output shaft. Sometimes the angular velocity of the output shaft is equal, in magnitude and versus, to that of the input shaft. However, in general, the transmission transforms the input angular velocity, ωi, into a different output angular velocity, ωo, with ioω≥ω or ioω<ω. The ratio oiτ=ω ω is commonly used to define the transmission ratio (sometimes the opposite ratio, ioωω, is used to define the parameter τ). The transmission ratio can be constant – like for most transmissions – or variable. Some mechanical transmissions also change the versus of the output angular velocity with respect to that of the input angular velocity (Figures 1.1 and 1.2). Configuration n.1 (disks simulate geared wheels) Configuration n.2 (disks simulate geared wheels) Belt transmission The mutual forces transmitted through some of the mechanical components w hich the transmission is composed of, may cause a not negligible energy dissipation, owing to the presence of friction forces. In many mechanical problems it is not necessary to study and evaluate the local dissipative forces but it is sufficient to obtain an approximate but satisfactory estimate of the energy dissipated by the transmission. This computation can be easily…