Semi-Analytical Software for Power Transmissions

GeDy TrAss develops and commercializes an innovative software for the design of mechanical components, with a particular focus on gears. Thanks to the deep know-how developed during the years, GeDy TrAss conducts consulting and training on the dynamic behaviour of mechanical components. The start-up is pre-incubated at I3P and the Politecnico di Torino spin-off recognition is undergoing.

by Carlo Rosso, Fabio Bruzzone, Claudio Marcellini, Tommaso Maggi

The entrepreneurial team GeDy TrAss is composed by four mechanical engineers with specific expertise in the field of power transmission. Since GeDy TrAss members have been working for years in the field of aerospace gearboxes and power transmissions, they have highlighted two main difficulties which companies often suffer from:

• customers require mechanical geared system with high performance in terms of durability, power density and at the same time reduction of weights and Noise, Vibration and Harshness (NVH);
• the design process is a bottleneck, because engineers investigate about a limited number of possible layouts of the transmission. Therefore, if customers change the transmission’s specifications or the proposed final solution does not fit with the required performances, the whole design process must be restarted: for this reason, a more flexible approach is needed. Customers in the field of automotive, industrial and aerospace require gearboxes with constantly increasing performance, which make the actual design procedures obsolescent: a revolution of the design phase is necessary today.

Support from the blank sheet up to detailed analysis of components
GeDy TrAss is a semi-analytical software that helps engineers during the design phase, starting from the blank-sheet earl stages when the optimal layout of the system has to be established, until the detailed analysis of the components, through different tools implemented in the software.
During the pre-design phase, GeDy TrAss provides a first-attempt layout by inserting a limited number of geometrical parameters
and operative constraints imposed by the customer.
With this purpose, this tool is divided into two sub-elements: the first one is an algorithm that defines the macro-geometries of the gears, whereas the second is a procedure that generates and then exports a first-attempt layout into any CAD commercial software.
This tool is powerful because it leaves to the user discretion the possibility to impose the
set of constraints on which the algorithm works to skim through the possible layouts.
This procedure is valid for automotive, aerospace and industrial transmissions and it is completed by the automatic choice of bearings, rough dimensions of the synchronizers and of the shafts.
Figure 1 shows a possible first result obtained by this tool, a 5-speed gearbox with reverse gear, shafts, bearings and synchronizers.
Simply giving a series of input parameters through an intuitive interface, for instance input torque, maximum spin speed of the gears, transmission ratio and center distance with permitted tolerances, material and minimum number of operative hours, the software provides a first-attempt layout in a few minutes. This allows a re-use of the saved time for the optimization of the elements dimensioned by the parametric algorithm, but it also allows to investigate rapidly about the effective dimensions of the elements for different configuration layouts simply varying the input parameters.
Furthermore, GeDy TrAss is not limited to the definition of the macro-geometries (clearances, transmission ratios, gears’ dimensions), but it also provides the best solutions both for durability of the components and dynamic behavior of the transmission. Another tool allows a fast and iterative algorithm for the optimization of the micro-geometry of the gear profiles, guarantying the best compromise in terms of low dynamic overloads, low vibration and therefore noise. The approach that defines the optimal micro-geometry for a specific application of the gears has been patented (IT201800001328A1). In particular, firstly a quasi-static approach solves the contact analysis between the gears, taking into account all the flexibility contributions of the bodies. For this aim, a non-Hertzian contact model detects the real areas of contact due to the different curvatures of the bodies and the edge contacts. Figure 2 shows some images of GeDy TrAss performing contact analyses between different types of gears.
This methodology allows a drastic reduction of the computational time to obtain the real distribution of pressure between bodies of general shape, passing from hours used by the finite element method to a few seconds. The non-Hertzian contact model can be used for a huge variety of bodies in contact, for instance gears and rolling elements and races in bearings (see Picture 3).
Successively, GeDy TrAss performs static and dynamic analyses, considering the varying mesh stiffness, the possibility of contact loss between engaging teeth and torque inversion. The dynamics investigation is an enabling technology that is often neglected by engineers due to prohibitive computational time.
Furthermore, alternatively to the detailed analysis of the optimized model obtained by GeDy TrAss from the beginning, for instance stress detection due to loads or operative temperature, the user has the possibility of validating and improving already existing models. Indeed, by re-creating the transmission rapidly, virtual validation of the model in terms of static and dynamic conditions can be conducted.

A case study quantifies and compares design time savings
Since the market does not provide a technology similar to GeDy TrAss, in order to quantify time savings obtained by the software, a case study has been analysed. The test has compared the time for the design and the simulation spent by a general finite element method software (FEM) and a dedicated software for static and dynamic analyses of gears. With the hypothesis that a company has to design seven gearboxes with ten optimized gears in a year, the time required by GeDy TrAss is about 200 hours; the comparison with other software is shown in table 1, where the amount of time savings in hours and percentage brought by GeDy TrAss are reported.
The opportunities brought by its use are the increase of geared transmission analysable and producible, the enhancement of gears’ quality because of the higher number of detailed analyses that can be conducted.
Furthermore, GeDy TrAss enables to amortize the design costs or reallocate the available resources in a more flexible way.
A further investigation has highlighted that the actual commercial softwares are limited to a validation through literature results or other software that do not guarantee their final results’ truthfulness.
Therefore, GeDy TrAss has designed and produced a test bench that would offer the possibility of testing experimentally the previous code results. The testbed is actually designed for the evaluation of the Transmission Error (TE) in quasi-static conditions for spur, helical, bevel and spiral-bevel gears.
At a later stage, the test bench will be implemented to stress analyses and dynamic overloads at high spin speed.
Nowadays, more and more automotive companies are investing on research and development projects related to hybrid or purely electric powertrain, where the transmission has a much more important role that should avoid power dissipation and noise.

The software is addressed to large enterprises and SMEs
GeDy TrAss software has been developed for all the enterprises that design and use high performance mechanical transmissions, for which even the minimum dispersion of energy can make the difference between a competitive product and a mediocre one. Indeed, GeDy TrAss wants to provide the software both to the large enterprises, through a customized version of the tools, and to the Small and Medium Enterprises (SMEs) that cannot afford an annual license, through the cloud computing.