Rolling bearing selection method

Abstract

A rolling bearing selection method comprising following steps: Specifying values of at least one energy consumption parameter for various rolling bearing product designations and selecting at least one rolling bearing product designation based on said values in connection with suitabilities for defined operating conditions and application requirements.

Description

[0001] Rolling Bearing Selection Method

[0002] Description

[0003] The invention relates to a rolling bearing selection method and a correlated software program product.

[0004] So far, during the rolling bearing selection process, parameters indicating bearing life, load carrying capacity, temperature and / or maximum speed are taken into consideration to select one or more rolling bearing product designations suitable for the specified application. Usually, these performance parameters are used in the first step of the iterative bearing selection process and are used to pick the first bearing to start the iteration with. In catalogue tables respectively on drawings, the following parameters C (dynamic load rating), Co (static load rating), Pu(fatigue load limit), nref (reference speed) and niim (limiting speed) serve as indicators for engineers on the expected performance of the bearing.

[0005] It is one object of the present invention to improve the rolling bearing selection process.

[0006] The object is solved by the subject of claim 1. Advantageous embodiments are described in the dependent claims.

[0007] According to claim 1 the rolling bearing selection method comprising following steps:

[0008] Specifying values of at least one energy consumption parameter for various rolling bearing product designations and selecting at least one rolling bearing product designation based on said values in connection with suitabilities for defined operating conditions and application requirements.

[0009] Usually the selection method incorporates a translation of the defined operating conditions and application requirements into a type, arrangement, size, lubrication, operating temperature, speed, interfaces, execution, sealing, mounting and / or dismounting of the rolling bearing being subject matter of the selection method. Thereby said interfaces address topics like tolerances for bearing seats and abutments, surface texture of bearing seats, seal tolerances, resultant fits and so on. Said execution addresses internal clearance or preload, bearing tolerance classes, cage design and so on. Details on this, but also on the traditional rolling bearing selection process without said energy consumption parameter are described in more detail e.g. in the online available SKF catalogue „Rolling Bear- ings“ of October 2018.

[0010] Among the cognition of the invention, it was realized that with increasing focus on reduction of direct or indirect CO2 emission of machines to avoid global warming, also rolling bearing arrangements need to be selected reflecting low energy consumption and thus low CO2 emission. According to the invention this is enabled now by the energy consumption parameter as a simple key performance indicator, which correlates with the energy consumption of a bearing over e.g. a certain period. This new performance parameter will help to guide the engineer during the design and selection process to pick an energy efficient bearing, which still fulfils other requirements, like life, operating temperature, etc.. This may be more of earlier importance for certain industries, e.g. electric vehicles, railway or fluid, but it is foreseen that energy consumption becomes a major selection criterium respectively design target in general. In most cases, physically, low friction bearings have a short life, so there is a design conflict to either design for low friction meaning low energy consumption like reducing number of rolling elements, striving for small contacts, etc., or for long life e.g. via increased number of rolling elements, large contacts, etc. - both at the same time is not possible. As consequence, it is now transparent both in the bearing design process and in the bearing selection process, if a bearing is designed for either long life e.g. indicated already by C and Pu, or for low friction respectively low energy consumption indicated by the energy performance parameters according to the invention.

[0011] Thereby the invention is both about the energy performance parameter as such, but especially about the process, how they are determined using models and engineering software.

[0012] The energy consumption parameter of a bearing is defined for at least one reference case over e.g. a number of revolutions resulting in an energy consumption parameter unit of kWh per million revolutions. The definition of at least one, particularly two or more reference cases e.g. reflecting low and high Kappa values is of particular advantage. Thereby Kappa is the ratio of the actual oil viscosity in the application to the oil viscosity required in the application. Higher Kappa values indicate a “thicker” oil film. The Kappa values usually range from 0.1 to 4. Kappa values greater than 4 offer little improvement in fatigue life, and the life reduction effect of kappa values less than 0.10 are not well understood. Advantageously energy consumption parameters are calculated at least for two load reference cases. In a preferred embodiment a first reference load case is based on a medium bearing load and a good, meaning sufficient lubrication film in the rolling contact particularly together with a clean lubricant what altogether correlates to a high Kappa and a second reference load case is based on a high bearing load and a low lubricant film thickness what altogether correlates to a low Kappa. The first case could also be seen as an ideal design load case, the second one as an unavoidable in a real application. For the calculation of assortments of bearings, which may vary by type, size, proportions, etc., it is important to keep other parameters constant to have a fair comparison. The speed used to calculate energy consumption for a reference case should e.g. be scaled with the average bearing diameter dm; or in other words: The n*dmvalue should be the same if the energy consumption parameters are calculated for a population of bearings, thereby n represents the speed respectively more specifically the revolution respectively rotation speed. By looking at the energy consumption parameters for both cases, engineers will get a first order of magnitude, which energy consumption can be expected in their application, which is most probably between these two cases. Of course, also different two and / or more reference load cases are possible.

[0013] The way respectively the procedure of the calculation of the energy consumption parameters are particularly determined using a stress-based or advanced four-sources friction model or a simplified model e.g. as disclosed in the above referenced SKF catalogue and also implemented in publicly available engineering tools like SKF bearing select on SKF.com. In case of a bearings with seals or shields and / or cages, of course, the models need to reflect the influence of these components in addition to rolling bodies and raceway elements. It is another cognition of this invention that also other energy performance parameters, which may be mainly used during the product development process and may not be publicly available in catalogues or in publicly available engineering tools, can be designed from the afore described e.g. as follows:

[0014] - Estimated rating life, divided by calculated energy consumption e.g. in h / kWh or million revolutions per kWh.

[0015] - Calculated energy consumption divided by estimated rating life e.g. in kWh / h or kWh per million revolutions.

[0016] - Total energy consumed of estimated rating life e.g. in kWh.

[0017] With the use of the publicly available and the just internally employed inventive energy consumption parameters in the bearing design process, the rolling bearings are optimized either towards life or energy consumption particularly towards a good balance between these two.

[0018] Further advantages, features and details of the invention result from following exemplary embodiments of the invention according to the figures. Other embodiments result by modifying these among other things in the frame of what is outlined in the claims.

[0019] Figure 1 shows a calculation process for values of an energy consumption parameter, and

[0020] Figure 2 shows a selection table for rolling bearing product designations including energy consumption parameter values.

[0021] As one embodiment of the invention Figure 1 illustrates how values of an energy consumption parameter can be calculated according to following steps: In a first step 1 an existing bearing is selected or a new bearing is designed e.g. via an engineering tool. In a second step 2 at least one reference load case is setup e.g. again in said engineering tool. Thereby different reference load case correlate with different Kappa values. In a third step 3 the friction is calculated on the basis of a simplified or advanced friction model for rolling bearings. Usually, an iteration reverting to the second step 2 from the third step 3 is required to vary the temperature to calculate the required Kappa value according to the at least one reference load case. As soon as the required Kappa value is reached the third step 3 is followed by a final step 4 in which the friction the therewith correlated energy consumption parameter value is calculated.

[0022] Figure 2 shows an example how the inclusion of energy consumption parameter values into a selection table for rolling bearing product designations can look like, whereby the energy consumption parameter values are under the table headline “Energy consumption” for two different reference cases (full film, medium load and low film, high load) in kWh / mioRev (kilowatt-hours per million revolutions). Figure 2 shows a table for single row deep groove ball bearing with the inner ring inner diameter d of 120 mm. The further principal dimensions D (outer ring outer diameter) and B (bearing width), basic load rating C (dynamic) and Co (static), the speed rating, the mass and the designations are as in a conventional catalogue. For some of the bearings with identical principle dimensions different designs are offered, like without seals or shields, with two shields on both sides of the bearing indicated with the abbreviation 2Z as supplementary designation after the minus in the bearing product designation, with contact seals of acrylonitrile butadiene rubber (NBR) on both sides of the bearing indicated with the abbreviation 2RS1 as supplementary designation after the minus in the bearing product designation or with a ball centered or outer ring centered brass cage with the abbreviation M respectively MA after a blank in the bearing product designation (without a specific supplementary designation it is the standard steel cage). This selection table enables the selection of an appropriate rolling bearing designation with the inclusion of its energy consumption, particularly considering the selection of the bearing product designation with the lowest or low energy consumption parameter values.

Claims

Claims1. Rolling bearing selection method comprising following steps:Specifying values of at least one energy consumption parameter for various rolling bearing product designations and selecting at least one rolling bearing product designation based on said values in connection with suitabilities for defined operating conditions and application requirements.

2. Method according to claim 1, whereby the selection method comprises a translation of the defined operating conditions and application requirements into a type, arrangement, size, lubrication, operating temperature, speed, interfaces, execution, sealing, mounting and / or dismounting of the rolling bearing being subject matter of the selection method and correlated rolling bearing product designations.

3. Method according to claim 1 or 2, whereby the at least one energy consumption parameter is specified in kilowatt-hours per revolutions particularly million revolutions.

4. Method according to any of the claims 1 to 3, whereby the at least one energy consumption parameter is defined for a reference case particularly comprising a bearing load definition, a lubrication film thickness definition, a Kappa value and / or a speed respectively a speed as a function of a bearing diameter, particularly comprising at least two of the aforementioned list.

5. Method according to any of the claims 1 to 4, whereby different energy consumption parameters are defined for differently defined reference cases,particularly comprising one reference case with a medium bearing load and a full lubrication film thickness and another reference case with a high bearing load and a low lubrication film thickness.

6. Method according to any of the claims 1 to 5, whereby a rolling bearing product designation with a low or the lowest value of the least one energy consumption parameter or a combination of low or lowest values of energy consumption parameters is selected.

7. Method according to any of the claims 1 to 6, whereby the method comprises the calculation of a bearing rating life for rolling bearings being subject matter to the selection method and the rolling bearing product designation is selected balancing a long bearing rating life with one or more low values of the energy consumption parameters.

8. Method according to any of the claims 1 to 7, whereby values of the energy consumption parameters are calculated on the basis of a friction model.

9. Software program product for supporting execution of the method according to any of the claims 1 to 8 comprising values of at least one energy consumption parameter for various rolling bearing product designations.

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