CommentaryDevelopment of Technical Calculation Systems forRolling Bearings

Tomomi ISHIKAWA *Mariko IZUMI *Hiroyasu HIRUKAWA *Cedric BURNET **The performance requirements for rolling bearings are diverse, and the pace of this diversification has
accelerated in recent years due to environmental concerns and other factors. The use of Computer-Aided
Engineering (CAE) technology is indispensable for NTN to respond quickly to these requirements. Twotechnical calculation systems developed by NTN to improve the efficiency and sophistication of rolling
bearing design will be introduced in this technical review.

1. Introduction
Introduce a wide variety of competitive bearing
products to the market that consider market trends
and customer needs in a timely manner, it is necessary
to improve the sophistication and efficiency of productdevelopment work. To this end, NTN is promoting theuse of Computer-Aided Engineering (CAE) technology.
In October 2018, NTN established the CAE Researchand Development Center1) to accelerate our researchand development of CAE technology.
In the past, NTN used both commercial softwareand the NTN-proprietary CAE system for bearing
product development work. There were several
challenges for efficient design, such that engineers
were required to select and use multiple, unlinked
subsystems repeatedly based on their specificapplications to derive design values that met thedesign requirements. Furthermore, even routine Finite
Element Method (FEM) analysis had to be carried out
by a Computer-Aided Engineering (CAE) specialists.
To improve the efficiency of the entire development
process, NTN developed two systems: SharcNT, anintegrated technical calculation system for rolling
bearings that consolidates existing calculation systems
with additional features, and ABICS, an integratedcalculation automation system that automates thedesign work of third-generation (GEN3) hub bearings.
This paper describes an overview of these systems.

2. Integrated technical calculation system
for rolling bearings
2.1 Background
Rolling bearings are an essential machine element
used in mechanical systems. They require a long
operating life, low torque, high stiffness, highprecision, and other performance capabilities. In
recent years, energy saving and decarbonization havebeen advanced to achieve carbon neutrality. This
has led to greater diversity in rolling bearing designto meet required specifications and performanceneeds. For example, electrified automobiles andvarious industrial machines require smaller, lighter
bearings with ultra-high speed specifications, whilewind power generation requires larger bearings withlong operating lives as wind turbines become larger
and are used offshore. NTN must adapt to thesemarket trends and customer needs; there are strong
demands for highly reliable, high-performance bearing
designs and shorter design lead times. The use of CAE
technology is essential to meet these demands.
In the initial stage of designing rolling bearings,
life and internal bearing load calculations basedon theoretical calculations are used as the primaryperformance evaluation. In recent years, calculation
models have become larger, more complex, and moresophisticated. Calculations of entire applications,
including power transmission mechanisms, andcalculations considering elastic deformation aroundthe bearing are essential.
NTN developed SharcNT (Shaft, Housing and Roller
Coupling with NTN Technology), NTNʼs proprietary
integrated technical calculation system for rolling
bearings, to enable designers to design reliable,
high-performance bearings quickly using CAEtechnology.
2.2 Global integration of calculation systems
In the past, NTN conducted design studies byutilizing multiple calculation systems according to
the design requirements of rolling bearings. However,making full use of multiple systems required a certain
level of experience. Therefore, SharcNT was developedby combining the main calculation functions of NTNʼsconventional calculation systems (Fig. 1) based ona system developed and used by NTN subsidiarycompany NTN-SNR.

* CAE R&D Center** NTN-SNR ROULEMENTS Research, Innovation & Development

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Development of Technical Calculation Systems for Rolling Bearings
In addition to the calculation functions required for
performance evaluation such as bearing operating life,
bearing load, load distribution, contact stress, bearing
stiffness, and bearing torque, SharcNT can constructa multi-axis calculation model in which bearings arearranged using an intuitive graphical user interface(GUI) (Fig. 2).
Integration of multiple systems made it possible fordesigners to perform a wide variety of calculations
within a single system and acquire skills andexperience more easily.

Base system

To understand the internal load of the bearing
obtained by calculation, it is necessary to confirm
how the shaft displaces with deformation due toconditions such as gear load and bearing position.
Depending on the structure, it may be extremely
difficult to verify the calculation results using only thenumerical information shown for each power flow.
Fig. 3 shows an example of a calculation for thegearbox. The calculation model is displayed in a
3D model, and the vector of the internal load andthe displacement of the axis on the model can be
confirmed visually. In addition, detailed resultsfor each bearing are output as various graphs andnumerical data. These improvements make it easierfor the user to grasp the characteristics of thecalculation conditions.

All calculation functions

Fig. 1 Integration of calculation systems

Fig. 3 Calculation for entire applications
Fig. 2 Integrated technical calculation system SharcNT
2.3 Calculation for entire applications
In recent years, gearbox manufacturers havediversified their products to cater the wider needsof the markets, for example to meet the varyingrequirements of the automobile market which
provides gasoline vehicles, hybrid vehicles, andelectric vehicles, ranging from simple structures tomulti-stage and complex structures. When bearings
used in more complex structures are examinedthroughout their application, the calculation model
becomes complex. It is not only difficult to understandand verify the calculation results, but it is also difficult
to do so in a short period of time. Even in the case ofcomplex structures, one must accurately and quickly
grasp the bearing characteristics.
To enable complex gearbox construction, SharcNT
makes it possible to create a calculation modelwith many parallel and orthogonal axes to analyze
the bearing in detail while taking into account thepower flow (power transmission path). In addition,
the overall life of the bearing can be determined by
setting the duration of time that the bearing spends
at each operating condition. In addition, advanced
calculations that consider elastic deformation aroundthe bearing, which will be discussed in the next
section, can be completed in a short time.

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2.4 Calculation that considers bearing elastic
deformation
Normally, the internal bearing loads are calculatedon the assumption that the contact between
the rolling element and the raceway surface willcause infinitesimal deformation. However, in some
applications, the stiffness of the housing is low (due tothin thickness, aluminum alloy, etc.), and the internalload of the bearing cannot be accurately determined
unless the elastic deformation of the outer ring andthe housing is considered. In this case, although it
is possible to use FEM to perform calculations thatconsider the elastic deformation of the outer ring andhousing, high-precision calculations demand expertiseand involve a series of calculations, which takes time.
SharcNT has a function2) that can consider elastic
deformation of the outer ring and the entire housing
as a contracted stiffness matrix (“virtual spring”),
which can be combined with the contact calculation
between each rolling element and a raceway with
relevant degrees of freedom. This function allows
calculation that takes elastic deformation of the outerring and housing into account at higher calculation
speeds when compared to FEM.
Calculations can also be performed that consider
elastic deformation of the inner ring and shaft using
the “virtual spring”. However, the fit between theinner ring and the shaft is usually highly rigid whencompared to the fit between the outer ring and thehousing, and it is often sufficient to consider only thedeflection of the shaft. In such cases, the calculation
time can be shortened by modeling the shaft with thebeam element3).

3. Integrated calculation automation
system for hub bearings
3.1 Background to development
Hub bearings are used in automobile undercarriages
to support the rotation of the vehicleʼs wheels. Since
the late 1970s, hub bearings have evolved into unit
products incorporating peripheral components.4)
This was done in response to market demands
for easier bearing assembly into vehicles, bearing
downsizing, reducing bearing weight, and higher
bearing performance (load-carrying capacity,
low-torque performance, resistance against muddy
water, stiffness, strength, etc.). Currently, thepredominant hub bearing is the 3-generation hub
bearing called GEN3 shown in Fig. 4.
Hub bolt

Outer seal
Inner seal
Rolling
element

InnerringHub ring

Outerring

Fig. 4 GEN3 hub bearing
In the design of unitized GEN3 hub bearings,
automobile manufacturers require a balance between
long bearing operating life and high stiffness on theone hand and compactness and light weight on theother. While a larger bearing size is required to reduce
contact stress and increase stiffness to improve
bearing life and steering stability, smaller bearing sizeand lighter weight is optimal for vehicle fuel efficiency.
In addition to these bearing design optimization tasks,
CAD and FEM analyses are also required in the design
process. All of these tasks are performed by humanworkers and required a long time to complete.
To solve these problems, NTN developed an
integrated calculation automation system Axle
Bearing Integrated Calculation System (ABICS) for hub
bearings that automates each area of design work andshortens the design and lead time.
3.2 System overview
To automate the various tasks required for thedesign study of hub bearings, NTN developed theABICS (Fig. 5), which has the following four primaryfunctions.
• Search function for optimal bearing specifications• Automatic creation of 3D shape models• Automatic execution of FEM analysis• Data management

The use of this system enables designers to performtasks that were previously performed by separate
people in charge of each task. This further reduces
design and lead time through automation. Details ofeach function are described in the following sections.

Obtaincustomerrequirement

Bearing
specification
design3D modelcreationStress andstiffness FEM
analysis

Search function for
optimal bearing
specifications

Automatic creation of
3D shape models

Optimal value search
programBearingcharacteristic
calculation program

Bearingcharacteristic
calculation program

Automated creationof 3D shape models
programDesignreview
completion

Reportcreation

Automatic execution of FEM analysis
Automated pre-processing
program

Automated post-processing
program

FEM analysis job management
Program system

User interface & data management“ABICS”: Integrated calculation automation system for axle bearings

Fig. 5 ABICS system overview
3.3 Search function for optimal bearing
specifications
In the past, when determining the bearing
characteristics of a hub bearing, the NTN designer
would repeatedly change each parameter andcalculate the characteristics until the required
characteristics (life, internal mass (mass within acertain area around the rolling element), internal
stiffness, torque, etc.) had been met (Fig. 6 left).
Multiple calculation tools for each characteristic wereused for the characteristic calculation. The human
work therefore required time for both the search for
optimal results and the calculations.
In ABICS, NTN has created a bearing characteristic
calculation program that combines these calculation
tools. An optimal value search function (Fig. 6, right)
has been developed to automatically select desired
values for specifications.
Conventional

This system

Bearing specification
assumptions

Optimal value search program

Various bearing characteristic
calculations

Bearing characteristic
calculation program

Fig. 6 Optimization of bearing specifications
The optimal value search program employs agenetic algorithm (GA), which is classified as AI. For
the search, the desired bearing characteristics to be
optimized are set as the objective function and thedesign parameters that affect the characteristicsof the objective function are set as explanatory
variables. Under these conditions, the explanatory
variables selected by the GA are sent from the optimalNTN TECHNICAL REVIEW No.89

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Development of Technical Calculation Systems for Rolling Bearings

Operating life

value search program to the bearing characteristic
calculation program, where bearing characteristics arecalculated. The characteristic values are returned tothe optimal value search program, and the GA selects
new explanatory variables. This iterative process
results in optimal values.
An example of an optimal value search is shown inFig. 7. The objective function is set to the conflicting
properties of life and internal mass, and theexplanatory variables are the three design parameters
related to these two properties. Fig. 7 shows theresults of the search. The Pareto solution for thebearing life relative to the mass (marked in red)determines the candidates of optimal values. Basedon the results, the designer selects the value thatmeets the customerʼs required characteristics. In thisexample, about 34 000 calculations are required tofind the optimal value by exhaustive search, where thesearch for the optimal value is completed in about 300
calculations (marked in blue) with GA. In addition tothe computational cost, automation of the search also
reduced the work time required of personnel.

Internal mass

Fig. 7 Example of optimal value search
3.4 Automatic creation of 3D shape models
In the past, a CAD specialist created the 3D shapemodel required for FEM analysis and drawing(Fig. 8, top) based on previously-determined bearing
specifications. Since CAD work was done manually
by dedicated personnel, model creation was timeconsuming. In addition, there was time spent waitingfor preliminary meetings with designers and for thecompletion of work in progress.
In the ABICS, an automatic 3D shape model creation
program has been developed to automate this model
creation process (Fig. 8, bottom). The program
has a variety of shape templates and automaticallycreates a 3D shape model by automatically inputting
dimensions derived from bearing characteristics
obtained from the optimal value search function
and the bearing characteristic calculation program
described in the previous section. In the case ofshapes for which it is difficult to create templates, theprogram automatically creates a similar shape andthen allows manual modification.

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Bearingspecification

CADspecialist

3D shapemodel<This system>

Bearing specification

Shape templates

3D shapemodelFig. 8 Creation of 3D shape model
3.5 Automatic execution of FEM analysis
In the past, based on a previously-created 3D
shape model, a CAE specialist would perform thepre-processing, calculation execution, and postprocessing required for FEM analysis stress andstiffness characterization5) (Fig. 9, top). As withthe other tasks described above, time was required
to complete these tasks due to the skill level ofthe specialist, prior discussions with the design
engineer, and waiting time before starting the work.
A program and system were created to automate
these tasks, and an automatic FEM analysis
execution function (Fig. 9, bottom) was developed.
Details of each program are shown below.
• Automated pre-processing program
Automatically create a mesh for each part of the3D shape model to be analyzed, combine theperipheral components necessary for analysis, andset the boundary conditions.
• Automated post-processing program
The system automatically obtains characteristic
values of stress and stiffness from calculation results,
obtains contour plots, checks calculation logs, etc.
• FEM analysis job management program / system
Computers to execute each of the above programs
and FEM calculation jobs are automaticallyassigned according to the computer utilization
status. Fig. 10 shows this job management
system. Jobs are distributed from the ABICS
server to the job management computer (thecomputer executing this program) based on
the input information of the user computer.
From the job management computer, jobs
are allocated according to the usage status ofmultiple computers prepared for pre-processing,calculation execution, and post-processing.
This system reduces the waiting time for jobs
and improves the availability of computers andsoftware licenses used for FEM analysis.

<Conventional>

3D shape model

Pre-processing

Execution ofcalculation

Postprocessing

In addition, design reports can be automaticallygenerated based on the stored input/output results,
reducing the time spent by designers and shortening
lead times.

4. Conclusion
CAD specialist

CAE expert<This system>

3D shape model

Pre-processing Execution ofcalculation

Postprocessing

Fig. 9 FEM analysis work
Jobtransmission

User PCABICSSystemserver

Returnresults

Job transmission

Pre-processingReturn results

Jobmanagement
PC

Execution ofcalculation

Post-processing

Fig. 10 FEM analysis job management system

This paper introduces the integrated technicalcalculation system SharcNT, which is used toevaluate the performance of rolling bearings, andthe integrated calculation automation system ABICS,
which automates the design work of GEN3 hubbearings.
Going forward, NTN will continue to research,develop, and utilize CAE technology to further
enhance the sophistication and efficiency of productdevelopment operations. As we do so, we will build astructure that will enable us to quickly bring to market
the bearings that the market demands.
References
1) An Introduction to the CAE R&D Center, NTN
TECHNICAL REVIEW, No. 87, (2019) Back cover.
2) Rolling Bearing Theory and Practice Guidebook(Cat. No. 9600/J), NTN, (2022) 254-255.
3) Rolling Bearing Theory and Practice Guidebook(Cat. No. 9600/J), NTN, (2022) 253.
4) Makoto Seki, History of Development of Axle
Bearing Aiming at Low Fuel Consumption, NTN
TECHNICAL REVIEW, No. 87, (2019) 55-58.
5) A. Imoo, FEM Analysis of Hub Bearing, NTN
TECHNICAL REVIEW, No.70, (2002) 70-73.

3.6 Data management function
All ABICS usage information (input/output results,etc.) is stored and managed in a database. Information
designed with ABICS can thus be capitalized on andused effectively. The search function makes it easy toview past design results, while the input data used incalculations can be reused, enabling efficient redesign
when improving products.

Photo of authors

Tomomi ISHIKAWA Hiroyasu HIRUKAWACAE R&D Center

CAE R&D Center

Mariko IZUMICedric BURNET

CAE R&D Center

NTN-SNRROULEMENTS
Research, Innovation& Development

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