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Transmission elements
1. Introduction to the transmissions
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1. INTRODUCTION TO THE TRANSMISSIONS

A mechanical transmission is constituted by the complex of the elements required to transmit power in a mechanical system, thus transferring energy from an engine to a user for a certain period of time:

The transfer of this power from the engine to the transmission takes place generally via the driving shaft. A user shaft (also called driven shaft) allows instead the transfer of this power from the transmission to the user.

The power that reaches the user can never be equal to the one coming out of the engine. In fact, during transmission, part of this power will be dissipated by friction or heat. To evaluate how much power is actually used compared to the one generated, then an efficiency value (η) is used:

where:

  • Driving Power (Pm)= Useful Power (Pu) + Dissipated Power (Pd)
  • Mm and Mr are, respectively, the driving torque and the resistant torque.
  • ωm and ωu are, respectively, the angular speed of the driving shaft and that of the user shaft.

The driving power is generally expressed as:

Where nm is the number of rounds of the driving shaft expressed in revolutions per minute (rpm) and 9.55 is instead the conversion factor for transforming radians per second in rpm.

The characteristic parameter of the transmission is the transmission ratio (τ), the ratio between the angular speed of the driving shaft and that of the driven shaft: