Dynamic analysis of a planetary magnetic gear prototype: evaluation of its magneto-mechanical efficiency

The aim of this thesis is the analysis of the dynamic behaviour and performance of an innovative power transmission system, based on the technology of magnetic gears. The magnetic gear has the capability to transmit motion and torque in a contactless way between two coaxial rotors with permanent magnets through the interaction with a modulator element holding ferromagnetic poles. Several potential benefits can be achieved using this technology, as the reduction of noise, wearing and vibrations, and the absence of lubrication, which are typical of mechanical power transmission systems. This transmission device is called planetary magnetic gear (PMG), due to its topological and functional similarity with a planetary mechanical gearing device, from which the same working principles are derived. In previous research works, a test bench for testing the magneto-mechanical efficiency of the PMG prototype has been designed and realised. The PMG can be tested in different configurations, with regards to the input/output power, and using two different transmission gear ratios. The starting point of this thesis was the development of a design of experiment (DOE) of the experimental tests, which have been carried out on the PMG prototype at different loads, different rotational speeds, different transmission ratio and different working conditions (speed reducer or speed amplifier) to prove that the efficiency is practically independent from the power direction, in contrast with the traditional mechanical transmissions. Moreover, a methodology for the evaluation of transmission efficiency has been developed, for a complete characterisation of the magneto-mechanical properties. Tests in load and no engagement condition have been carried out to characterise the mechanical dissipations, due to friction inside the bearings, in order to obtain the two contributions of mechanical and magnetic efficiency. Mechanical and electromagnetic quantities are collected and then analysed in the post-processing phase. For the sake of clarity, the rotational speeds of input and output shafts are acquired using two incremental magnetic encoder, two torque sensors are used to collect the torque values at the two sides of transmission, while an oscilloscope is used to evaluate the magnetic flux inside the device. The LabView software is used to control and manage the experimental tests, allowing the two electric motors to work in speed or torque control, suppling power, or applying a resistive torque. Eventually, the MATLAB software is used for data post-processing. The results of the data analysis and post-processing has helped to gain insight into the operation of the magnetic gear and to draw convergent conclusions for all the different conditions tested, regarding how losses are distributed and how efficiency trends. Starting from this point, and therefore knowing the strengths of this technology, new studies can be performed to even better the performance.