PSI - Issue 57

Karthik Krishnasamy et al. / Procedia Structural Integrity 57 (2024) 793–798 Karthik KRISHNASAMY/ Structural Integrity Procedia 00 (2019) 000 – 000

798

6

99%

90%

Gears

System relia bility

Bearings

Target design life

Fig-5: System Reliability curve.

The graph (Fig-5) shows the system reliability (blue curve) of the complete reducer for a high-end application,in addition with other components reliability curve. In the above design, required life is 6000 hrs @ R(n c ) = 90% and the predicted system reliability R(n c )=90% is 6600 hrs. Even though all the components satisfy its requirement, but the gear seems to be the weakest component. It is true at high mileage lifetime hours (R(n c )>90%), but at low mileage lifetime hours, the bearings are the weakest components. More the individual components are involved, the system reliability curve moves toward left. With the above graph (Fig-5), the system reliability is calculated quickly and easily for the given targets. 5. Summary In VALEO, most sophisticated methods based on Wohler curve are used to analyze each component lifetime in the reducer. These methods determine the achievable life to calculate the reliability using Weibull parameters. These individual reliabilities are further processed to calculate the system reliability using serial structure function in detail. Project team members, who don’t have time to go into deep technical details, will find this method of calculating and displaying the system reliability much easier to understand than achieved safety factor for gears, achievable life of bearings etc. They don’t need to understand in detail about the calculation is done with material 90% (using ISO 281) or 99% (using ISO 6336) standards. All these calculation are used together for the well-balanced reliability statements. References 1. Beermann, S., 2017, “Reliability, Lifetime and Safety Factors,” 2017 Fall Technical Meeting (FTM), American Gear Manufacturer s Association, Columbus, USA. 2. Bernd Bertsche., 2008, “ Reliability in Automotive and Mechanical Engineering ” , Berlin, Heidelberg: Springer Verlag, 2008. 3. ISO 6336:2006. Parts 1 – 6: Calculation of load capacity of spur and helical gears. 4. ISO 281:2007. Rolling Bearings — Dynamic Load Ratings and Rating Life.