Rolling bearings
Bearing stiffness and operating clearance
The calculated bearing stiffness and operating clearance are included in the system calculation, and thus influence the deformation behavior of the entire gearbox. Different deformations may result in the overall system, depending on the type of bearing specified.
Calculation scope
The level of detail of the calculation greatly depends on the availability of the internal geometry data. If the external dimensions and load ratings are known, the service life can be calculated according to DIN/ISO 281.
The extended rolling bearing service life according to DIN/ISO 26281 is based on the internal bearing loads. These are determined taking the installation and operating conditions into account. The load distribution on the individual rolling elements is determined based on the shaft and bearing deformation under load. For line contact, the pressure over the rolling length is solved. As a result, edge carriers can be reliably determined, taking the influence of the profiling of the rolling elements into account.
Defining rolling bearings
The rolling bearing geometry can be specified in several ways in the FVA-Workbench. Various calculations are available, depending on the input method.
The following input types can be selected:
Direct specification of the rolling bearing internal geometry
Import of the rolling bearing internal geometry from an .XML file
Direct specification of the main rolling bearing geometry
Selection of a bearing from the INA/FAG, SKF, TIMKEN manufacturer's catalogs or the FVA catalog
Manual specification of the stiffness
The type of bearing input can be specified in the Editor.
Rolling bearing internal geometry
The contact between the bearing shells and rolling elements significantly influences the calculation of the bearing stiffness and service life. The "internal rolling bearing geometry" input method enables more precise calculation of the bearing stiffness and bearing service life based on the rolling bearing geometry and internal geometry.
The following calculations can be performed if the internal geometry of the bearing is specified:
Calculation of the reference rating life according to DIN/ISO 26281
Calculation of the bearing stiffness based on the specified internal geometry
In addition to the main geometry, the following attributes can be specified:
Reference diameter
Rolling element diameter
Length of the rolling element
Number of rolling elements per row
Distance between the bearing rows (if the bearing contains two bearing rows)
Radius of the inner ring contact surface
Radius of the outer ring contact surface
Pressure angle (if no pressure angle is specified, it is estimated from the specified catalog value e)
Importing bearing data from an XML file
Another input option for rolling bearings is to import an XML bearing file. These files can be obtained from the bearing manufacturer. The characteristic values saved in the XML file include entries for the rolling bearing main geometry as well as the internal geometry.
The following calculations can be performed with XML bearings:
Calculation of the service life according to ISO 281 and catalog methods
Calculation of the reference rating life according to DIN/ISO 26281
Bearing stiffness based on the internal geometry
Structure of an XML bearing file
Download XML bearing file (SKF 6024 deep groove ball bearings)
Rolling bearing geometry
Specifying the "rolling bearing geometry" makes it possible to calculate the bearing stiffness and lifetime without information about the internal geometry of the rolling bearing. An internal calculation is performed which approximates the internal geometry based on the geometry of the rolling bearing. This estimation is used for further calculation of the bearing stiffness and the bearing lifetime.
The following calculations can be performed if the main geometry is specified:
Calculation of the service life according to ISO 281 and catalog methods
Calculation of the bearing stiffness based on the approximate internal geometry
The following attributes can be specified:
Inner diameter
Outer diameter
Bearing width
Pressure angle or catalog value
Number of bearing rows (one or two)
Static load rating
Dynamic load rating
Bearing type
Fixed/floating bearing
Attributes for calculating the service life:
Radial factor X1, X2 and axial factor Y1, Y2 according to manufacturer's catalog
The radial and axial load factors are used to calculate the dynamic equivalent bearing load.
SKF Explorer or X-Life
Selecting the SKF Explorer and X-Life logical variables identifies the bearings as SKF Explorer or INA/FAG X-Life bearings, respectively. This is relevant for more accurately approximating the internal geometry of these bearings.
Catalog bearings
To simplify rolling bearing data entry, bearings can be selected from the INA/FAG, SKF, and TIMKEN manufacturer's catalogs as well as the standardized FVA bearing catalog. Whether the bearing is fixed or floating must be specified manually.
The following calculations can be performed with catalog bearings:
Calculation of the service life according to ISO 281 and catalog methods
Calculation of the reference rating life according to DIN/ISO 26281 for bearings from the FVA catalog
Bearing stiffness based on the approximate internal geometry
To open the bearing selection dialog, select a rolling bearing in the Model Tree and click on the bearing symbol.
FVA Bearing Catalog
The internal geometry of INA/FAG and SKF bearings was estimated based on the load ratings and the main geometry in an FVA research project. The bearing names in the catalog correspond to the manufacturer names. In contrast to the manufacturers' catalogs, these bearings can be used to calculate the reference rating life according to DIN/ISO 281. As the internal geometry is approximated, these bearings are only suitable for preliminary designs. The FVA bearing catalog is not updated; because of this, some information (such as the load ratings) may differ from the current catalog data.
Bearing stiffness
The "bearing stiffness" input field can be used to manually specify the bearing stiffness. The specified bearing stiffness is used in the system calculation. A bearing service life calculation is not performed.
The following parameters can be specified:
Lowering rigidity
Tilting rigidity
Axial stiffness (for locating bearings)
Alternatively, the bearing can be defined as radially stiff with low tilting stiffness.
Advanced bearing determination
Bearing profiling
In the FVA-Workbench, profiling of the bearing rollers along the longitudinal axis can be specified for rolling bearings. In the Editor, separate total profiling of the rolling bodies and the raceway can be specified for rolling element contact on the inner and outer ring. The profiling must be specified for both contacts, even if only the rolling element is profiled. If standard profiling is specified, it is shown in bold in the diagram. 5 pre-defined profiling forms (KF = 1 to KF = 5) can be selected.
Profiling of the inner and outer rings can be specified in the Editor.