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High Efficiency ROller Bearing - NTN-SNR hybrid tapered roller bearing solutions for aerospace applications

Periodic Reporting for period 2 - HEROe Bearing (High Efficiency ROller Bearing - NTN-SNR hybrid tapered roller bearing solutions for aerospace applications)

Reporting period: 2019-09-01 to 2021-08-31

Regarding NTN-SNR’s State of the Art, the qualification of the bearings with ceramic rollers needs many research activities. The maturity of hybrid ball bearings is high (TRL5) but there are some differences between the behaviour of a ball bearing and a tapered roller bearing due to the difference in types of contact. (Elliptic contact for ball bearing and linear contact for roller bearing + contact between shoulder and roller face). The Technology Readiness Level (TRL) for hybrid tapered roller bearings at the beginning of the project was around 3. To be able to introduce the hybrid bearing on all the aerospace applications, it is necessary to qualify all types of bearings. The demonstration of a TRL 5 on the technology is also mandatory to be allowed to perform some tests on the complete system.
The innovative test plan will allow to demonstrate the TRL 5 at the end of HEROe Bearing project. These means of demonstration will prove:
- the better behaviour of hybrid tapered roller bearings in comparison with full steel bearings,
- the non-instantaneous failure mode,
- the allowable limit contact pressure,
- the definition of the critical defects
- and the better oil off behaviour.
All these answers will prove that hybrid tapered roller bearings are safe for aerospace applications.
The NTN-SNR objectives for this project are to develop, design, manufacture, test and simulate the new generation of tapered bearings for aerospace applications and especially for the helicopter gearbox bearings. For NTN-SNR, hybrid bearing is a promising solution for aerospace market especially thanks to the weight saving and the potential improvement of the bearing life duration it offers.
To do so, the hybrid bearing prototypes will be designed, calculated, manufactured, and tested to compare steel and hybrid bearing behaviour and to demonstrate the benefits.
For test activity, the objective is to perform the back-to-back assessment under several test conditions (clean environment, contaminated conditions, poor lubrication conditions, oil shut off conditions and tests with defect on rollers) in order to demonstrate the benefits offered by hybrid tapered roller bearings.
In order to start aerospace mass production of hybrid tapered roller bearings, the critical defects (size, shape, location on the rolling element) have to be defined. Hence one of NTN-SNR’s objective is to determine the size of critical defect on tapered roller bearing performance. This critical size will allow to define the efficient quality inspection to be performed and define the methods of inspection.
The last objective is to simulate the hybrid bearing behaviour in order to update NTN-SNR’s handbook and design rules to guarantee the quality, the robustness and the optimization of our bearing designs.
During the first reporting period of HEROe Bearing project, 5 milestones have been achieved. The 7 first delivrables were submitted. One delivrable has been postponed due to the complexity of test rig upgrade. Regarding technical activities, After the functional analysis and the FMEA dedicated to this hybrid tapered roller bearing, the associated risk analysis for the product was performed. Based on these analysis, NTN-SNR defined the mitigation test risk plan. The main criteria for test comparison between HEROe Bearings and RACER LGB bearings have been defined in order to mitigate also the risk for RACER LGB bearing. Thanks to these criteria, NTN-SNR defined the innovative test plan to demonstrate the benefits of hybrid tapered roller bearings.
During this first period, lot of bearing calculations were done using NTN-SNR bearing software. NTN-SNR performed also Finite Element calculation to modelise the ceramic roller behaviour. At the end of this step, the manufacturing drawings were drawn, and the manufacturing process review has been issued.
NTN-SNR developed a new roller process to manufacture the ceramic rollers. This task needs a lot of work especially to adapt the inspection methodology for mass production. This task is achieved at the end of this reporting period. The bearing prototypes need to complete the innovative test plan are manufactured at the end of this period. The test rigs were updated, and mitigation tests were performed to validate the main updates and the good behaviour of the test rig. At the end of this reporting period, some improvements are in progress. All these activities are detailed in the first reporting technical report.
During the second reporting period, the 2 last milestones have been achieved. And the 5 last deliverables have been submitted. All the tests defined in the test plan were performed successfully. More 8200 hours of test were performed. The bearings (more 55 bearings) have been expertized after tests. Thanks to these actions, the analysis and the comparison of full steel bearings and hybrid bearings have been done. In order to increase the benefits of hybrid bearing, an improvement of roller roughness was done, and the evaluation of this improvement was characterized. The thermal and life duration studies were done and compare to the test results. The results obtained during the second reporting period and globally during the whole project are in line with the initial project objectives.
At the end of the project, all the benefits of hybrid tapered roller bearings are demonstrated. Hybrid tapered roller bearing behaviour is similar or better to the one of full steel bearings with the same loads applied. Now, critical failure due to ceramic roller occurred during the test campaign. The roller defects tested are not critical and don’t create bearing failure. In conclusion, this solution can be used on aerospace application with the current monitoring devices.
The expected results concerning the goals of the project are in line with the initial objectives. Thanks to good partnership between NTN-SNR and the Topic Manager, the expected results and the improvement of ceramic roller manufacturing process are more important than the foreseen knowledge. HEROe bearing project allow to demonstrate the benefits of hybrid tapered roller bearings and to qualify this type of solution for aerospace applications and especially for helicopter market. This project allows to have a better understanding of impact of all the supply chain contributors in the performance of the ceramic roller. It is benefit for several players of European aerospace industry in several European countries.
Regarding environmental aspect, the solution developed during the project allows a bearing mass reducing o 15%. Thanks to the weight benefit, the weight of application will be lower. So, the fuel consumption and gas rejects are reducing.
At the end of the project, NTN-SNR can propose to its customers hybrid tapered roller bearings for aerospace application for mass production. NTN-SNR will show scientific results during dedicated international conferences. The competitiveness of NTN-SNR and especially of Argonay plant increases thanks to this project. All the results obtained during the project can also benefit other industries, namely railway and automotive.
HEROe bearing hybrid prototype