Cycloidal drive design for Rotary Regenerative Shock Absorber

Nowadays, the automotive and transportation industries are changing rapidly. The economic and social needs to create a more eco-sustainable mobility are constantly leading to technological innovations, to improve both vehicles and grid. For road vehicles this not only involves a development of electric propulsion, along with all the electronic associated devices, but also the evolution of all the chassis components. They can be electrified to be better integrated, and to reduce the overall emissions of the vehicle. In this scenario, an electrified suspension would bring several benefits, such as the possibility to have a regenerative and active effect and even predictive control. In this context, the need for an efficient and cost-effective electrified suspension led to the development of Rotary Regenerative Shock Absorber (RRSA). Specifically, the aim of this thesis project is to design a cycloidal speed reducer for it. A current prototype of the shock absorber is taken as reference and starting point of the new design. It has been developed at Center for Automotive Research and Sustainable mobility (C.A.R.S.) at Polytechnic of Turin, and it is operating thanks to a double stage planetary gearbox. The speed reducer is running between a permanent magnet electric motor and a leverage system connected to the vehicle suspension. The latter is needed to achieve the rotary-to-linear conversion. Cycloidal drives are also a good alternative for such application, allowing to obtain high transmission ratios in compact sizes while reducing negative effects, such as noise and backlash, particularly unpleasant for automotive suspensions as they require frequent motion reversals. The purpose is therefore to substitute the present planetary transmission with an equivalent cycloidal one to compare the two solutions, outlining advantages and drawbacks of each. After an in-depth state of the art review, the thesis covers the methodology adopted to design the cycloidal drive. It can be described in three main stages: •??Definition of the 2D geometry of the system, exploiting the working principles of this innovative transmission technology and respecting the main design requirements of the project given from the actual prototype. •??Rigid body modelling and analysis of the system, implementing geometry and equilibrium equations on MATLAB®. The force distribution acting on the gearbox functional components is computed, in order to determine stresses and safety factors and to obtain the required axial size of the drive, completing the three-dimensional design. •??Design and verification, through analytical models and with the aid of finite elements analysis, of all the additional components needed, such as bearings, splined shafts (using KISSsoft®), housing etc. The final design presented in this thesis has been obtained after several iterations and optimization processes to achieve similar sizes and performances as the previous gearbox while maintaining the same electric machine and leverage system of the actual suspension prototype. In the end, a complete CAD assembly and technical drawings of the new shock absorber prototype have been realized on Solidworks® for production purposes. Laboratory tests will follow to better understand the cycloidal drive behaviour compared to the current planetary solution. Future works will cover an integrated design methodology of both the electric machine and the transmission, considering the cycloidal speed reducer as the standard for an automotive RRSA.