MOTORS & DRIVES & CONTROLS
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3D-model for shaft has an infl uence of interference fi t for bearings
housings are usually stiff , with minor infl uence. But for automotive gearboxes, wind turbines or other applications with optimisation for weight, the infl uence might be important to consider. T e face load factor for gears according to methods A and B of ISO 6336 requires the consideration of deformations of housings and gear bodies, possibly calculated based on 3D-FEA. Planet carriers will deform under torsion. T is deformation will also aff ect the contact pattern of gears and a simple cylindrical shaft model for the carrier might not be suffi cient. If the thickness of housings around bearing seats is small and varies around the circumference, this
Housing deformations aff ect the load distribution within bearings
can also aff ect the load distribution in bearings and therefore the reference rating life according to ISO/TS 16281. Some programs simply import a
reduced stiff ness matrix for housings or
other elastic parts like planet carriers. Basic items like diff erent orientations of coordinate systems can quickly lead to errors. In addition, the deformation of the housing cannot be evaluated. It is less error prone if the geometry of the housing and its deformation can be evaluated together with the system - this also helps to understand the deformed states. T ermal elongations regarding
the preload of bearings must also be considered. Often only uniform temperatures are considered, which is preferable to no thermal expansion. Some programmes can also support non- uniform thermal states. In case of 3D-FEA calculations of high-speed rotating parts, the consideration of centrifugal expansion could be helpful, too.
Another use case of 3D-FEA can
be improved stresses compared to analytical methods. Examples would be the infl uence of two notch eff ects being close to each other, like a shaft shoulder combined with a keyway or simply the strength assessment of housings or planet carriers. As the FEA-meshes are often designed for the evaluation of stiff ness, they might be too coarse for a proper strength assessment. In this case, a full FEA program might be the better choice. However, stresses available in a programme for machine element calculations can serve as a fi rst estimate. FEA is commonly used in mechanical,
aerospace, automotive and civil engineering applications, as well as biomechanics.
Gear body deformations aff ect the contact pattern between gears
Markus Raabe is the Managing Director at Mesys.
www.mesys.ag
www.engineerlive.com 45
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