The Schaeffler Group’s bearing calculation and simulation program, Bearinx®, now also offers a new friction calculation function. This enables users to calculate the energy efficiency of different bearing supports in a specific application. With Bearinx®, the Schaeffler Group can identify the maximum saving potential of a system at an early design stage. This is an important prerequisite for optimally using friction-optimized bearings and for further increasing the energy efficiency of applications by taking advantage of down¬sizing options.
Friction calculation with Bearinx®
The Schaeffler Group has developed an analytic model for calculating rolling bearing friction and has integrated it into its own bearing calculation program, Bearinx®, which has existed for many years now. In the past, there were two main possibilities for calculating rolling bearing friction – the catalog method on the one hand and highly specialized multibody simulation programs on the other. The catalog method is an empirical approach that enables the quick calculation of the frictional torque, however with low model quality. By comparison, multibody simulation programs render very high model quality, but this requires correspondingly long computing times. The new, physical-based method combines short computing times with high model quality. A large number of parameters are taken into consideration, including for example the real occurring pressure distribution and the internal bearing geometry. In addition to calculating the load distribution and the bearing life, it is also possible to determine the frictional torque and thus the power loss of entire shaft or transmission systems. This enables friction-optimized bearing concepts to be selected even in the early product development stage.
The new friction calculation method takes into consideration both rolling and sliding friction, and both of these under boundary , mixed and full-film lubrication. The method is based on the elastohydrodynamic lubrication theory (EHL), which deals with the formation of lubricant films in heavily loaded contact points of bodies rolling against one another at high speeds. This includes both the formation of a hydrodynamic lubricant film and the elastic deformation of the bodies in contact. Since pressure, sliding speed, viscosity, temperature etc. are not constant over the contact area of a specific contact, every single contact in the bearing is analyzed. As a result, all the frictional forces at the discrete contact area points are available.
Practical example: Friction reduced by over 60 percent
The new friction calculation model in Bearinx® enables engineers to consider various different rolling bearing supports at an early stage in the design process and to assess their friction minimization potential. The solution having the lowest friction can thus be demonstrated to the customer, together with the efficiency potential it offers. A practical example may help to clarify this:
The task is to minimize the overall level of friction in the bearing supports of the compressor (2 shafts), whilst observing the requirements regarding bearing life, rigidity and mounting space. As a first step, the bearing selection and arrangement are optimized. The double-row cylindrical roller bearing on shaft 1, which generates 45 percent of the losses, can be replaced by a single-row cylindrical roller bearing. Moreover, the cylindrical roller bearing on the pressure output side of shaft 1 can be replaced by a more compact one. The cylindrical roller bearing on the intake side of shaft 2 remains unchanged. At the pressure output side, a smaller cylindrical roller bearing is used. The angular contact ball bearing is replaced by two smaller ones without radial release. This ensures that the radial load acts evenly on all the bearings of shaft 2. Friction is reduced due to the use of smaller bearings and the angular contact ball bearings offer a more favorable operating contact angle. At the same time, the required space is 25 percent smaller. All in all, bearing friction can be reduced by 35 percent as a result of the first optimization step.
The osculation of the angular contact ball bearings is optimized for this application as a second step. This results in a further 11 percent reduction in friction. The final step examines the impact of the surface roughness on the frictional torque. In this case, friction can be cut by another 15 percent through surface optimization. Thanks to Bearinx®, the friction level can be decreased by a total of 62 percent compared to the original variant, and the space required for mounting the bearing supports is reduced at the same time.
Conclusion
Rolling bearings and energy efficiency – these terms can be used almost synonymously. After all, it is the purpose of rolling bearings to reduce friction and thus save energy. Energy-efficient solutions provided by the Schaeffler Group are not restricted to the design and production of friction-optimized rolling bearings, but they also involve the development and use of simulation and calculation tools as well as the analysis and understanding of the overall system.
Proven for many years and now further refined, the Schaeffler Group’s Bearinx® calculation program plays a key role for effecting greater efficiency in machines and power units. The lower-friction rolling bearing per se is not necessarily the right solution for all applications. Rather, it is crucial to consider each system as a whole and to take into account all the relevant conditions to ensure optimal design. Only in this way is it possible to select the most appropriate rolling bearing that will then provide the maximum increase in system efficiency. Bearinx® offers the optimal approach to get the most out of efficient bearings. Currently, friction calculation with Bearinx® is available to customers via the advisory service offered by the Schaeffler Group’s qualified field service application engineers and via the application engineering departments.
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