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high capacity planet BEAring Technology for High Efficiency gearbox

Periodic Reporting for period 1 - BrEATHE (high capacity planet BEAring Technology for High Efficiency gearbox)

Reporting period: 2019-01-01 to 2020-06-30

The development of Ultra High Propulsive Efficiency (UHPE) engines is a promising challenge to fulfil the objectives of CleanSky 2 ITD ENGINES program and the potential for significant reduction in fuel burn, emissions and perceived noise to the level defined by “ACARE 2035”. Current engine designs are indeed reaching their limits in terms of efficiency (i.e. conventional bypass ratio (BPR) is about 9-10, future UHBR target is 12-15). This is mainly the reason why innovative architectures like the geared turbofan concept are the promising enablers for UHPE engine success. The development of such Integral Drive System raises different technological challenges at the system and component scales. BrEATHE project, standing for BEAring Technology for High Efficiency, will focus on the planet component, the central module of the transmission system of the high power gearbox, where the bearings are key elements. The specificity of the BrEATHE bearing remains in functional integration: a gear with integrated bearing outer raceway.

BrEATHE project objectives can be divided in these main steps:
1. Design of a bearing to be mounted in a high-power gearbox
2. Low TRL evaluation of high-performance steels.
3. Production of the prototype bearings
4. Testing of the bearings
5. Model correlation based on test results

The main impact of BrEATHE is to provide key bearing technologies (material and design) and advanced computational models enabling the development of the innovative power gearbox of the future UHPE engine and other next generation engines to meet the objectives of the Clean Sky 2 programme in terms of environmental benefits and European competitiveness such as the reduction of aircraft CO2 & NOx emissions, the validation of innovative engine technology and employment.
"1/ Design, manufacturing and start-up of the test platform for BrEATHE project

Based in the European Testing Centre of Excellence in Valence, the main objective of SKF Aerospace with this test platform is to reproduce as close as possible the operating conditions of an aeronautic application. This test platform is a common platform on which will be used multiple test head such as the one for BrEATHE project. An associated data acquisition system will bring value for test campaigns lasting from a few hours for a phenomenological test campaign to hundreds of hours for a performance test campaign such as the ones that will be performed in BrEATHE;

The test platform consists in:

- A mechanical transmission for the bearing rotation

- A mechanical load device for the tested bearing in the test head

- A power unit mainframe with its DSP and HMI

- A Lubrication Unit and its network for the bearings in the test head

- A global safety strategy of men, tested product and facility

- A way for environmental protection / pollution: noise, liquid, gas

- Instrumentation and monitoring equipment to realize data acquisition of the test

The robustness, the safety, the precision, the automatization, the assembly and use easiness are the major characteristics of the test platform.

The test platform complies with EN9100 standard.

At this date, the test platform is fully operational and ready to welcome BrEATHE test head.

2/ Advanced raceway steels pre-selection: comparative properties matrix for ""Gear/Rolling bearing"" use

In partnership with the Topic Manager, 6 over 15 advanced steels materials have been selected through a weighted multi-criteria decision matrix. Each of the material candidates have faced criteria representative of the Gear/Rolling bearing use: the functional integration of a gear with integrated bearing outer raceway pushes for a different prioritization in optimal metallurgical properties. While the gear needs toughness and shock resistance properties, the raceway needs high hardness and a fine microstructure: the properties seem opposite at first look, but the decision matrix allow to find the best compromise to create innovation. The properties that have been looked at are for instance hardness, toughness, corrosion resistance, fatigue limit etc.

The materials have been ordered to manufacture small test coupons to validate these properties and for the manufacture of the full bearing by the end of the project."
The expected results of BrEATHE projects are potentially huge, because of the several major advances/innovations necessary to achieve the project technological objectives as well as the next generation UHPE engines. The BrEATHE bearing technology and modelling solution will lead to:

- the increase of design compactness and the reduction in bearing weight while keeping the same load level in comparison with the current state of the art; this will lead to a reduction in the engine size (mass saving) and therefore a direct reduction of fuel consumption and CO2/NOX emissions.

- the decrease of the power loss of the PGB bearings (-30%), by using advanced design for lubrication and roller, thermal mapping and low friction materials/coatings.

- run at higher rotational speeds (>9,000 rpm) for the planetary bearing using low density material, advanced lubrication system and high surface resistance raceways leading to a significant reduction in fuel burn, noise (-30%) and emissions (-25%) while allowing a reasonable core and engine size.

- bring substantial advantages in terms of bearing/system reliability using a high accuracy dynamic modelling of the whole PGB.

Other environmental/economic/social impacts include:

- The possibility offered by BrEATHE project technologies to develop and implement new environmentally friendly aero-engines (such as a UHPE engine).

- A full exploitation of components with increased lifecycle.

- The reduction of the bearing heat generation is also a way to reduce the whole lubrication system (pump, tank, pipe…), which leads to an indirect weight saving.

- Employment of highly skilled personnel in the aerospace industry as the development of bearing design based on dynamic and thermal models will demand high skills and expertise for both design and production in the next 10 years.