KAYABA TECHNICAL REVIEW No. 64 APR. 2022

KAYABAKAYABATECHNICAL APR. 2022
64
REVIEWNo.

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KAYABA TECHNICAL REVIEW
No. 64 APR. 2022
CONTENTS
Foreword
Future of High Value ManufacturingKURIYAGAWA Tsunemoto

1

HIRATSUKA Sadato3

YUBUKI Kento

8

Editorial
Microstructure and Mechanical Properties of Cast Iron
Technology Explanation
Building the Foundation for MES Services in the New Era

GABURIELLA Anak Magin

Research on Technology to Control Air Bubble Content in Hydraulic Fluid

KITAMURA Yoshiaki



KODERA Yasuhiro

17

Technical Article
Research on Particle Assemblage Damper

TOYOUCHI Atsushi

24

ITOU Yuusuke

38

TANAKA Shin42

NOMURA Norifumi

48

TAKINO Shinsuke

53

NAGASHIMA Midori

54

Technology Introduction
Construction of Case Machining Line for Piston Pump
Product Introduction
Development of Shock Absorbers for Snowmobile Racing
Essay
Account of Residence in Czech RepublicGlossary(1) KYB-IoT Platform
(2) Cavitation
Editors Script

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Foreword

Future of High Value Manufacturing(Evolution from Ultimate Form Generation to Function Generation)
KURIYAGAWA Tsunemoto*1. Introduction
In Japan, it is important to discuss a vision for Monozukuri (creative design and manufacturing), which is thecountry's industrial base.
However, Monozukuri that has long contributed to theprosperity of Japan with mass production and volume
consumption is almost coming to an end. We will facecircumstances that require us to develop another type ofMonozukuri responding to various senses of values in the
future.
For example, we need to take measures for achievingcarbon neutral or supporting super-aging of society. It isbeing internationally discussed to develop novel technologies to accomplish these goals as an urgent challenge.
Besides technological innovation, economic and societal innovations are also indispensable. For these ends, weshould have a broad range of knowledge and insight covering areas from human and social sciences to naturalscience. In recent years, some attempts have been actively
made to establish a cross-sectional innovation and eco
systems in which industry, academia and government cantalk together through coalition. Then, what the Monozukuri field can do to help them achieve the ends. One is todevelop even higher-accuracy, even higher-value-added
products that cannot be achieved with foreign technologies. What is significant to achieve this is not only theexisting simple Form Generation, but also Function Generation that creates a structure for expressing functions on
the surface or internally. The author named this "Function
Generation Machining" and has promoted its research anddevelopment to be one of the technologies for "High
Value Manufacturing".
2. What Is Function Generation Machining?
Machined parts are normally evaluated for their machining accuracy with two criteria: form accuracy and surface
roughness. Requirements for machining accuracy haverecently become more intense with some of them exceeding nano order to reach pico order. To achieve such ultimate machining accuracy, comprehensive research and*Professor, Tohoku University

development has already been started covering machining
principles, tooling, machine tools, evaluation and measurement methodologies, materials, assembly methods,
and design theory. Function Generation Machining produces microscopic structures on an ultra-precision
machined surface achieved with these techniques or controls crystal structures in the proximity of the machined
surface, thereby expressing new functions.
In this way, a combination of form generation and function generation is used to try to achieve high-value-added
generation. This type of Monozukuri is called Function
Generation Machining. In other words, the conventional
simple form generation should be merged with function
generation into a new style of Monozukuri.
To achieve this, it is indispensable to scientifically makeclear how the machining works in the molecular or atomic
level and to establish a new machining process for realizing pico-precision machining. Specifically, this comprehensive technology to be established must leverage pico/nano/micro/macro or so-called multi-scale mechanicalsystem design theory that supports pico-precision machining to complete a device or even a system, and tool design
engineering, pico-level in-situ measurement and evaluation techniques, cooperation of machining simulators andsystems, pico-level implementation for precision assembly of microscopic structures, and material generation andstrength reliability evaluation for ensuring safety andsecurity.
3. The Keyword Is “Hybrid”
Many function generation products have a hybrid structure. For example, μm-order diffraction grating is formedon an aspherical lens surface, and furthermore a several
hundred nm-pitch moth-eye structure is superimposed to
be a high-function hybrid refraction-diffraction opticaldevice with nonreflective function. Such a hybrid structure can often be fabricated by combining different
machining methods, not using them independently, toexpress significantly higher efficiency and/or special
functions. These examples include ultrasonic-assisted
grinding that combines ultrasonic machining and grinding, laser-assisted micro machining that combines laser
cutting and grinding, and ultrasonic vibration assisted―1―Future of High Value Manufacturing

electrochemical grinding that combines three techniques:
ultrasonic machining, grinding and electrolysis. In addition, one of the technologies recently developed is one
that uses ultrafine bubble (UFB) machining fluid to simultaneously achieve improved machinability and surface
modification. In this type of machining, the chip removal
mechanism will be greatly affected by chemical factors
because chips are as fine as nano order. Particularly where
electrolysis, discharge, laser and UFB-assisted process
are combined, nano-order physico-chemical phenomena
must be understood not only from the mechanical engineering aspect, but also from the chemical and quantum
aspects.
4. In Closing
This paper has introduced Function Generation Machining for achieving high-value-added Monozukuri that may
be significant in discussing future Monozukuri. To implement a machining technique for future Monozukuri, scientific and rational Monozukuri based on understandingof what's really happening in the nano-order world is
indispensable.
It is also important not to heavily depend on development of innovative mechanical solutions, namely,
advanced hardware. Of course, hardware development isimportant, but software development is also essential inthat hardware items cannot be combined and used efficiently without quality software. Furthermore, Monozukuri must essentially take into account production,
disposal and recycling (including reuse) to be a recyclingbased technology. In the life stream of "materials" (thesyllable "mono" of Mono-zukuri literally means "material" in Japanese), greenhouse gases including CO2 are
generated. Therefore, it is also needed to design andaccomplish life cycle assessment to minimize the greenhouse gases.
Finally, needless to say, it is important to develop humanresources with capability and spirit to overcome various
difficulties in societally implementing novel technologies,
the so-called Devil River, Valley of Death, and DarwinianSea. It is strongly desired to establish a corporate environment for such human resources development to be realized in house as well. Simultaneously, I expect young
engineers to develop and deliver entrepreneurship themselves for jumping into a world they have never seen
before. I am really looking forward to seeing how Monozukuri (creative design and manufacturing) will evolve infuture.

―2―

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Editorial

Microstructure and Mechanical Propertiesof Cast Iron
HIRATSUKA Sadato*

1. Introduction
Cast iron is an important structural material of castings.
Japan produced about 3 million tons of cast iron in 2020.
Of the annual production, 63.7% was used for transportation machinery (including automobiles, railroads andships), 23.7% for general or electric machinery (including
industrial machinery and equipment, construction
machinery, metal working tools & machine tools, andelectric machinery), 7.8% for cast iron pipes, and theremaining 4.7% for other applications (including couplings, kitchen appliances and craftwork) 1).
Fig. 1 shows an example of hydraulic equipment for
regular/compact excavators manufactured by Kayaba
Industry Co., Ltd. 2) The compact hydraulic excavator has
control valves whose body is made of cast iron.
Both cast iron and steel are classified into iron-carbon(Fe-C) alloys. They are differentiated from each other by
carbon content. Steel has a carbon content of not morethan approximately 2 mass% (hereinafter expressed in"%" only) while cast iron has a higher carbon content thanthe level. Practical cast iron is usually considered as
Fe-C-Si alloys because of its carbon content as high as 3%
to 4% and its silicon (Si) content of around 1% to 3%.
With a higher percentage of carbon than 2%, carbide
forms in iron (Fe) in the cast iron. In this sense, cast ironmay be considered as a composite material consisting ofsteel and graphite in various forms.
Boom Cylinder
Arm Cylinder
Piston Pump
Double-acting Cylinder
BucketCylinder
Variable Displacement
Travering Motor Piston Pump

Control Valve

Swing Motor

Tractional Motor (with Reducer)

Sectional Valves for
Compact Excavators

Monoblock Valves for
Excavators
Swing Motor (with Reducer)

Fig. 1

Example of hydraulic equipment for regular/
compact excavators*Professor, Research Center for Casting Technology, Iwate University

The lower carbon content of cast iron compared to steel
results in a substantially low solidifying (or melting) temperature and good fluidity. Cast iron also features good
castability because of its low solidification shrinkage orless shrinkage cavities attributable to volume expansion
taking place when the graphite is crystallized duringsolidification. In addition, the presence of graphite and thehigh silicone content give cast iron excellent industrial
properties including vibration absorption, machineability,
wear resistance, thermal conductivity, corrosion resistance and oxidization resistance.
This paper describes the microstructure and mechanicalproperties of cast iron that may affect its characteristics.
2. Microstructure of Cast Iron
The microstructure of cast iron greatly varies by thechemical composition of the molten iron, the solidification condition, and heat treatment given. What microstructure the solidified cast iron will have is a critical issue
because cast iron is used in the as-cast condition in mostcases; however, this does not matter a lot for steel because
it is subjected to deformation processing, such as rolling,and heat treatment after solidification. The microstructureof cast iron can be roughly divided into graphite andmatrix microstructures. The combination of these two
microstructures greatly affects the mechanical, physicaland chemical properties of the cast iron.
2.1 Graphite Microstructure
Fig. 2 shows how graphite can appear in iron castings.
This classification was proposed by the technical committee in the World Foundry Congress held in 1962 in the
U.S. 3)Form I is flake graphite. Cast iron with graphite flakes isclassified by the Japanese Industrial Standard (JIS) G5501
into gray cast iron. Form II is spheroidal graphite withpointed ends that is likely to appear when a spheroidizing
agent such as magnesium (Mg) is added in an excessive
amount during production of nodular graphite cast iron.
Form III is quasi-flake graphite that may appear with alack of graphite spheroidizing agent. This type of graphite
forms in CV graphite cast iron. Form IV is massive graphite that may appear in malleable cast iron or graphite steel.
Form V is quasi-spheroidal graphite. Form VI is com-―3―

Microstructure and Mechanical Properties of Cast Iron

Fig. 2

Classification of graphite forms

pletely spheroidal graphite that often appears in nodular
graphite cast iron. Among these, the forms II to VI are
uniform graphite in a random distribution in most cases.
However, form I, namely, flake graphite, changes in formand distribution depending on the chemical compositionof the cast iron, its melting history and/or cooling rateduring solidification. American Society for Testing Materials (ASTM) A247 classifies this category of graphite
into Types A to E by distribution as shown in Fig. 3. TypeA shows random flake graphite in a uniform distribution,
which is the most optimally distributed flake graphite.
Type B is called rosette flake graphite. Type C shows
hypereutectic cast iron with coarse pro-eutectic graphite.
Type D is called eutectic graphite that is likely to appear
in titan (Ti)-added or undercooled molten iron. Type E iscalled interdendritic flake graphite.

having a body-centered cubic crystal structure with adensity of 7.9, a tensile strength of 200 MPa to 400 MPa,
and a Brinell hardness of 90 HB to 150 HB. Ferrite in ironcastings is called silico-ferrite because silicon (Si) incorporates into the ferrite to form a solid solution. The ferrite
matrix with more silicon offers higher tensile strength andhigher hardness.
(ii) Cementite
Cementite is a rhombic composition consisting of three
Fe atoms and a C atom with a density of 7.7 and a Brinell
hardness of 550 HB. This is the hardest and brittlest
among all the cast iron microstructures.
(iii) Pearlite
Austenite breaks down (transforms) into ferrite andcementite during metastable eutectoid transformation.
These two phases are generated in the form of a stack ofsheets alternately overlayed with each other. They can be
identified as a layered or banded structure under an optical
microscope. It is a very tough microstructure with adensity of 7.8, a tensile strength of 800 MPa to 900 MPa,
and a Brinell hardness of 200 HB to 240 HB.
Nodular graphite cast iron normally has a so-called
bull's-eye microstructure in which ferrite and pearlite
coexist as shown in Fig. 4.

FerritePearliteFig. 4

Fig. 3

Types of flake graphite by distribution[ASTM A247]

2.2 Matrix Microstructure
The matrix microstructure of cast iron varies by thecooling rate during solidification, the alloy element
content, and/or heat treatment given. This section introduces three typical matrices:(i) Ferrite
The ferrite matrix, which is also known as α-Fe or αsolid solution, is soft iron with a trace quantity of carbon

GraphiteBull's eye microstructure of
nodular graphite cast iron

3. Mechanical Properties of Cast Iron
Mechanical properties of material including tensile
strength, hardness, elongation and fatigue strength arecollectively called generalized strength. Any of theseproperties is a measure of resistance to deformation or
fracture.
The strength of a metallic material is decided by its
microstructure. In the case of cast iron, the strength isgoverned by the graphite, matrix and other microstructures.
3.1 Strength of Flake Graphite Cast Iron
As compared to the matrix, the graphite microstructure―4―

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

(a) Ductile matrix(b) Brittle matrix

Fig. 5

Plastic deformation andductile cracks in matrix
connections

Brittle cracks at theends of graphite
flakesStress α, MPa

can easily fracture with a substantially lower force becauseof its tensile strength of around as low as 20 MPa. Therefore, the strength of cast iron is decided by the strength,
form, and continuity of the matrix except graphite particles.
In other words, cast iron with fine graphite (Type A orE) may offer a high strength. Those with long-type graphite (Type A, B or C) usually have a low strength becauseof their low continuity of the matrix.
Fig. 5 illustrates how two types of flake graphite castiron can fracture when they are applied with a tensile
force: one has a ductile matrix (a) and the other a brittle
matrix (b). 4) The former (a) with a ductile matrix will havea number of ductile cracks and partial ruptures. These will
be connected with each other along the graphite flakes,
thereby accelerating rupture.
The latter (b) with a brittle matrix in turn will accelerate
rupture when brittle cracks occurring at the ends of thegraphite flakes propagate.

Strain ε, %Fig. 6

Stress-strain curves of flake graphite cast iron(a) Ductile matrix

Voids in the matrix due
to plastic deformation

Voids grow and merge tocause ductile fracture(b) Brittle matrix

Cleavage cracks aroundgraphite particles

Cracks propagate andmerge to cause a brittle
fracture

Accumulated ruptures inmatrix connections leadto final rupture

Cracks propagate to beconnected with eachother, resulting in a brittle
fracture

Fig. 7

How flake graphite cast iron fails withtensile fracture

Fig. 6 shows stress-strain curves of flake graphite castiron. 5) The continuously warped curves include no
obvious yield behavior. Determining the 0.2% yield point(or yield strength) will not make sense to flake graphite
cast iron. Rather, it is necessary to define the yield strength
against a small distortion as low as 0.05% or even smaller.
3.2 Strength of Nodular Graphite Cast Iron
Nodular graphite cast iron has a matrix with substantially higher continuity than that of the flake graphite type.
The extent of continuity hardly varies by minor changes
in form (the degree of spheroidization) or particle size ofgraphite as long as the degree of spheroidization is higher
than a certain level (generally 0.7).
Fig. 7 illustrates how two types of nodular graphite castiron can fracture when they are applied with a tensile
force: one has a ductile matrix (a) and the other a brittle
matrix (b). 6)

How nodular graphite cast iron fails withtensile fracture

The former (a) with a ductile matrix involves sufficient
plastic deformation. Many cracks occurring around thegraphite particles merge into voids as deformation progresses. Voids also occur in the grain boundaries andinclusions within the matrix. These voids are connectedwith each other and merge into bigger voids, resulting in a
rupture.
In this rupture development process, cracks tend todevelop in a zigzag manner bridging the closest graphite
particles or the weakest parts of the largest graphite particles.
For the latter (b) with a brittle matrix in turn, cleavage
cracks occurring around the graphite particles will growto cause rapid crack propagation, resulting in a rupture.
Fig. 8 shows the relationship between the tensile
strength and the carbon equivalent (CE) value of nodular,
compacted and flake graphite cast iron. 7) According to thefigure, the strength of flake graphite cast iron greatly
varies by the CE value while that of nodular graphite cast―5―Microstructure and Mechanical Properties of Cast Iron

Tensile strength

Fig. 10 R elationship among pearlite area, tensile strengthand elongation of nodular graphite cast ironCE, mass%

Effect of CE value on the tensile strengthof a variety of cast ironFig. 9 shows stress-strain curves of four types of nodular
graphite cast iron with different matrix microstructures. 8)
Specifically, these curves indicate the stress-strain relationship of austempered ductile irons (ADI) with ferrite
matrix (curve 1), with ferrite and pearlite matrix (bull's
eye microstructure) (curve 2), with pearlite matrix (curve3), and with bainite matrix (curve 4). The curve 1 forStress α, MPa

3. FCD700, Pearlite
2. FCD500,
Ferrite + Pearlite

1. FCD350, Ferrite

Strain ε, %Fig. 9Stress-strain curves of nodular graphite cast ironElongation

Pearlite area, %Flake graphite

4. ADI (FCAD900)

Nakamura

NakamuraCompacted graphite

Fig. 8Combined type

Elongation, %Tensile strength, MPa

Nodular graphite(FCD 500 equivalent)

ferrite matrix shows high elongation. As pearlite occupies
a larger area of the matrix in order of the curves 2, 3, thestress-strain curve tends to show higher stress.
Fig. 10 shows the correlation among pearlite area,
tensile strength and elongation of nodular graphite castiron. 9) As the pearlite area increases, the tensile strength
goes up. By contrast, as the pearlite area slightly increases,
elongation rapidly decreases and then tends to decrease
gradually.

Tensile strength, MPa

iron seldom depends on the CE value. The figure also
implies that compacted graphite cast iron is almost
midway between the two. This is because the strength offlake graphite cast iron heavily depends on the matrix
continuity (i.e., to what extent the matrix among graphite
flakes is sound with no break), in other words, the formand distribution of graphite flakes. For nodular graphite
cast iron consisting of distributed independent spheroidal
graphite particles (approximately 10 vol%) and a matrix(approximately 90 vol%) in turn, the matrix shows considerably higher continuity than for flake graphite castiron. Naturally, the strength of nodular graphite cast ironheavily depends on the matrix microstructure and is
seldom affected by the CE value.

4. In Closing
Cast iron can be considered as a composite material
consisting of graphite and steel. Its strength is governedby the graphite, matrix and other microstructures.
The strength of flake graphite cast iron is primarily
affected by the form of graphite flakes, namely, the matrix
continuity between graphite flakes, and secondarily by thematrix microstructure.
In nodular graphite cast iron in turn, the matrix continuity is substantially higher than for flake graphite cast iron.
This means that the strength of nodular graphite cast ironheavily depends on the matrix microstructure.
Iron castings can deliver excellent mechanical, physicaland chemical properties when their graphite and matrix
microstructures are properly controlled. High-strength,
high-function cast iron whose microstructure has been
suitably controlled can be expected to be applied to avariety of industrial applications. I hope this paper will
help manufacturers achieve this.

References
1) SOKEIZAI Annual Industrial Report: SOKEIZAI Vol.62 (2021)
8.
2) KYB Hydraulics Products Guide (Construction equipment,
industrial vehicles, agricultural equipment, and other industrial
equipment).
3) A.B. Everest: Trans. Amer. Foundrym. Soc., 70 (1962) 210.

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KAYABA TECHNICAL REVIEW No. 64 APR. 2022

4) NOGUCHI Toru: Journal of Japan Foundry Engineering Society,7) Japan Foundry Engineering Society (editor): Foundry Engineering

Volume 77 (2005) 794.

Handbook (Maruzen Publishing Co., Ltd.) (2002) 254.

5) NOGUCHI Toru: Journal of Japan Foundry Engineering Society,8) HARADA Shoji, NOGUCHI Toru: Evaluation of strength ofVolume 76 (2004) 333.

nodular graphite cast iron, AGNE Gijutsu Center Inc. (1999) 50.

6) HARADA Shoji, NOGUCHI Toru: Evaluation of strength of
nodular graphite cast iron, AGNE Gijutsu Center Inc. (1999) 52.

9) NAKAMURA Koukichi, SUMIMOTO Haruyoshi: Castings 39(1967) 480.

―7―

Building the Foundation for MES Services in the New Era

Technology
Explanation

Building the Foundation for MES Services in the New Era
YUBUKI Kento, GABRIELLA Anak Magin

Abstract
With the advancement of digital technology, the manufacturing industry is becoming increasingly digitalized.
Companies all over the world are using the Internet ofThings (IoT) to build “smart factories” where each device
in the factory is connected to the Internet to improve theefficiency of the manufacturing process.
Japan’s manufacturing industry has maintained quality
through improvement activities and worker training. For
this reason, there has been little progress in digitalization
efforts. However, in recent years, with the decline in theworking population and rapid changes in the international
market, production systems need to be more productive
and flexible than ever before. This is why MES, whichanalyzes data from manufacturing processes to improve
productivity and support workers, and SCADA, whichmonitors and automatically controls equipment data, areattracting attention.
1

Introduction

With the recent rapid advancement in digital technology, the world's manufacturing industry has changed significantly. Companies are actively introducing digitaltechnology to use the Internet of Things (IoT) Note 1) for
building "smart factories" Note 2) where all devices andequipment are connected with each other via the Internet.
Such a smart factory can collect and accumulate data fromits manufacturing process and analyze it using advanced
technologies including artificial intelligence (AI) Note 3).
This system can be expected to provide the following
effects:
・To identify any inefficient parts of the manufacturing
process and solve problems, achieving higher productivity, higher product quality, and lower cost・To create a database of techniques and expertise ofskilled technicians to allow for automation and transfer of their skills to younger technicians・To use the accumulated data to predict the demandand supply and plan predictive maintenanceHowever, Japan's manufacturing industry has been left
behind on digitalization. Japan's manufacturing (often
called "Monozukuri") has maintained quality throughKYB is also working on MES and SCADA, and has
several systems in operation to acquire and utilize datafrom production lines and equipment. In order to collect,
accumulate, analyze, and utilize data, an analysis platform
called “IoT Platform” has been developed in-house.
However, the systems that have been in operation for along time are not linked to the IoT Platform, so only
limited analysis can be done within the systems, and they
are not being fully utilized.
Therefore, in this development, we have developed a
new service that solves these problems by first linking the
IoT Platform to a single production data collection system.
This system utilizes IoT and cloud technologies to build
its functions. This paper describes the integration with the
IoT Platform and the functions we have developed toutilize data in the manufacturing process.

human efforts including (skilled technicians' improvement activities leveraging their skills and experience andworker training to enforce workplace discipline. Only a
few companies have heavily invested in digitalization
programs. Quality maintenance has mainly been assured
with human-based approaches relying on the expertise oftechnicians. In recent years, however, Japan has failed tosuccessfully deal with the decline in the working population with fewer children and aged adults as well as the
rapid changes in the international market, resulting inlower competitiveness. Owing to such situation, digitalization efforts are attracting attention in the Japanesemanufacturing industry as well.
Today, many systems to promote enterprise digitalization are available. Among them, the following three areconsidered significant in the manufacturing industry:・Enterprise Resource Planning (ERP)・Manufacturing Execution System (MES)・Supervisory Control And Data Acquisition (SCADA)
The ERP is the integrated management of main business processes. The ERP system centralizes managementof business resources including humans, things, money
and information. General systems to collect and control
information necessary for financial, customer, inventory―8―

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

and human resource management are packed in an ERP
system to help companies make decisions.
The MES is used to identify, manage and support manufacturing processes. The system makes use of data on
production equipment, production control and productquality for improving productivity and quality and forsupporting workers. While the ERP system covers management of an entire enterprise, the MES can be said to bea management system tailored to its manufacturing
process. With this difference in mind, the MES can belinked to the higher-order ERP system to allow decision
making based on real-time data collected from the manufacturing process.
The SCADA system monitors and controls manufacturing processes. It monitors how production devices arebeing operated and measured and, if necessary, controls
them. While the MES analyzes and utilizes production
data, the SCADA system monitors what is happening in
the manufacturing process in real time. With this difference in mind, the SCADA system can be linked to thehigher-order MES to allow for management of the manufacturing process and its automatic control in case ofabnormality.
These three systems linked to each other will enable all
employees and management to get a whole grasp of datafrom upstream to downstream and to carry out various
activities based on the data, including decision making,improvement, and new business development.
KYB has also promoted efforts to manage and utilize
data collected from its production lines and devices froman earlier time. The typical systems of this kind include
the Point of Production Information Collection System(POPICS) and the line monitoring system (the details ofthese systems will be described in the following chapter).
These systems that collect and utilize operation data fromproduction lines and devices are considered to be positioned within the production system as shown in Fig. 1.
Our POPICS has certainly achieved data sharing among
the ERP, MES and SCADA regions, but only to a limited
extent. Our line monitoring system is being reviewed toprovide various functions for the SCADA region by introducing new technologies. However, its integration withhigher-order systems such as MES or ERP has not yet
been discussed, resulting in insufficient use of data fromthe manufacturing process.
We have built a foundation to provide new MES services (Fig. 1) using a SCADA collecting data from theline monitoring system linked to an MES that has been
designed to be able to have additional functions. The following describes the details of the foundation and its
related systems.

lected from the devices is analyzed and utilized in a
sophisticated manner to optimize the factory/production
management.
Note 3) An acronym for Artificial Intelligence.

MES services(newly developed)

Equipment

Scheme of systems for MES services (KYB's effort)

Fig. 1

2

Line monitoring system(Data collection
in businesses)

Current Systems in KYB

2.1 POPICS (Fig. 2)
KYB developed and introduced a production line datacollection system called POPICS 20 or more years ago 1).
Via panel computers installed on the production lines,
POPICS transfers production instructions and other datafrom higher-order systems, collects cycle time data using
device I/O, and collects nonconformance reports by
operators and other data from lower-order systems.
POPICS summarizes collected data into KPIs Note 4) such as
productivity and presents them to manager-class personnel using a visualization application program.
Part of POPICS has already been linked to higher-ordersystems so that POPICS data can also be viewed on thesystems that manage cost data and inventory control
information.
A problem is that POPICS only collects data in production lines. Collected data for each line is not sufficient todevelop measures against device failures or conduct
improvement activities, failing to satisfy user needs.

Note 1) An acronym for Internet of Things. The IoT refers togeneral attempts to connect things to the Internet andutilize them.
Note 2) A factory where devices therein are connected with eachother via the Internet to improve the manufacturing
process and enhance the operation efficiency. Data col-―9―Note 4) An acronym for Key Performance Indicator. This major
performance evaluation indicator is intended to evaluateachievements against goals.

Fig. 2

Example of POPICS window (sample data shown)Building the Foundation for MES Services in the New Era

2.2 Line Monitoring System
KYB is promoting Innovative Monozukuri mainly on
the production lines in its factories for manufacturing
shock absorbers, which are one of the company's key
products. This activity aggressively makes use of AI andIoT technologies to recreate a manufacturing system fromdesign to production, with the aim to achieve the following goals:① To double productivity② To halve design-to-production lead time
③ To achieve zero nonconformance
Then, KYB introduced IoT technology to the production lines and developed a new line monitoring system forvisualizing the manufacturing process in an easy-tounderstand way to ensure higher productivity and higher
quality. This system was developed in 2017 as an improved
version of the POPICS described in the previous section
and has been sequentially introduced to KYB facilities.
While the conventional POPICS can only collect data inproduction lines, the new line monitoring system cancollect data in production devices, thereby enabling realtime monitoring of individual devices.
In this line monitoring system, PLCs Note 5) for individual
devices collect operation data, which will be put together
by a general PLC installed on each line and stored in a
database (DB) built on a line server. Furthermore, a visualization software program running on the line server
displays data on a large-sized monitor in an easy-tounderstand way (see section 4.3 for the system configuration).
The monitor displays data as shown in Fig. 3. Production information including KPIs and the operating statusof each device, quality information including measurements, and processing condition information can beviewed on the screen. Note 6) Personnel can easily view
these types of information in real time to identify any
anomaly in each device and take appropriate measures.
However, the current line monitoring system cannot
provide line comparison or long-time data analysis,
posing a challenge of diversified analysis to be available.

Fig. 3

Example of display on the line monitor screen(sample data shown)

Note 5) An acronym for Programmable Logic Controller. This
control device developed as an alternate to a relay circuit
is often used to control production devices.
Note 6) The information includes undisclosed information thathas been intentionally deleted or blurred.

2.3 KYB-IoT Platform (Fig. 4)
In order to analyze and utilize all in-house data, KYB
internally developed a data analysis base called KYB-IoT
Platform Note 7) in 2020. The Platform was developed under
the concept that "anyone can easily analyze and use data
anywhere anytime". Storage of collected data as well as
data analysis and use with AI or BI Note 8) can be started
easily and quickly.
The KYB-IoT Platform has been built on the public
cloud Amazon Web Service (AWS) where the storage andprocessing capability can be scaled up/down depending
on data volume and throughput. The cloud-based platform
can be used anywhere and can easily be deployed throughout the world. Leveraging the abundant cloud services
available on the AWS will efficiently develop new services and provide additional functions.
One of the systems operating on the KYB-IoT platform
is the equipment predictive maintenance system. 2) Thissystem collects data for identifying the equipment status
such as vibration and temperature and then analyze it withAI, thereby enabling prediction of failure signs. The
results are visualized with BI tools to be available to thedepartment users belong to, implementing predictive
maintenance.
In this case example, saving, AI analysis and visualization with BI tools of collected data are all implemented on
the KYB-IoT Platform. Beside these, the platform implements the function that issues an alarm when a failure
exceeds a threshold level and has an improved visualization monitor. The KYB-IoT Platform has thus been addedwith new functions and has been improved as necessary.
Note 7) A system base to collect, visualize, analyze and control
large volume of data from IoT devices connected to the
network.
Note 8) An acronym for Business Intelligence. It refers to collecting, accumulating and analyzing data to support
decision making on enterprise activities.

2.4 Problems with the Current Internal Systems
KYB has different systems shown in Fig. 5. However, itcannot be said that these systems are properly interfaced
to each other so as to optimize the company's total operation. If these systems could share and exchange data, wewould be able to identify more clearly what the company
is actually doing or what we have not noticed so far. The
company should leverage the potential of the systems.
Some production systems have been developed anddeployed recently, including the line monitoring systemdescribed in section 2.2 and the KYB-IoT Platform
described in section 2.3. Unfortunately, these systems
have not been linked to each other, failing to use data
effectively.
― 10 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Collect

Analyze/Visualize

Accumulate

Production info.

Management

Employees

Design info.

Developers

Edge computing

Equipment info.

Products

Users
Process

Automobile

Customers

ManageAgitating truck

Partners
Construction
machineryFig. 4

Cost management system

Overview of IoT Platform

what format, such as the standard data set including "CT
Note 9), MT Note 10) and anomaly time".
In this development, we have built a foundation of a
total system to centralize manufacturing process data in
the KYB-IoT Platform and to link the platform to othersystems. The following sections explain it in detail.

Design management system

No system linkage establishedTypical combinations of linked systems[Design, Cost and Production]

Production
management
system・ To calculate costs and simulate
production using designed CAD
data・ To automatically create process
charts, part list and production
schedules[Production and Quality]

Note 9) An acronym for Cycle Time. It refers to the operation
cycle time from when a task is completed to when a next
task is completed.
Note 10) An acronym for Machine Time. It refers to the machining time of machine tools.

Procurement
management
system・ To strengthen product traceability

3
Maintenance information system

Fig. 5

Quality management system

Current internal systems

In addition to the line monitoring system, the company
has also discussed or developed other data collection
systems to be deployed in internal source locations. Still,these systems have been designed to display and store
data in different ways because they use their own data
formats. This is one of the reasons why the systems canhardly share data.
To overcome these challenges, KYB is discussing tocentralize data in the KYB-IoT Platform. In addition, tosolve the problem that several data collection systems
gather different data items from internal source locations,
it is necessary to decide what data is to be collected in

Requirements

The following shows the requirements for ensuring thatthe total system is operated properly for effective use of
production data:① To standardize data items to be collected so that collected data can be saved in the KYB-IoT Platform② To ensure that all necessary data items are collected
and accumulated in the KYB-IoT Platform③ To enable data analysis in devices and long-time data
analysis④
To link the KYB-IoT Platform to other internal
systems to share design and cost information⑤ To build a total universal system for global use⑥ To ensure that horizontal deployment of and function
addition to the system can easily be done

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Building the Foundation for MES Services in the New Era

4

Development of MES Services

4.1 System Overview
This development has the purpose of building a total
system linking the aforementioned KYB-IoT Platform to
the line monitoring system for analyzing and utilizing
manufacturing process data. The development is underway with another future goal of achieving company-wideand even global deployment of the total system.
Fig. 6 illustrates how the total system is configured. Theline monitoring system collects data from individual
devices and save the data in a predetermined format. All
the collected data is saved in the KYB-IoT Platform forcentralized control of company-wide production data.
Once saved, the data will be immediately visualized to beavailable for analysis.
The KYB-IoT Platform can easily be linked to othersystems because of its collective data management andcan also provide diversified analysis using data from othersystems.
This development roughly covers the following four
major tasks. The details will be explained in the following
sections:・To standardize data to be collected and data format
・To determine how to collect/transfer data・To determine how to save data・To determine how to display and analyze data
4.2 Standardizing Data to Be Collected and Data
FormatWe have standardized data to be collected to ensure thatdata collection systems at various source locations canwrite common data items to the KYB-IoT Platform in thesame data format. This makes it possible to utilize data for
analysis with a unified set of indicators. We have selected
important data items needed by all locations to carry out
improvement activities. These data items can be categorized by data collection timing and data content into fourgroups shown in Table 1. We have specified a data format
for each data group, achieving standardization of data collection.
The first data group is production results (including
actual CT & MT and setup change time) to be stored in the
KYB-IoT Platform. With these types of data available, theuser can find possible causes of lower production while
viewing CT/MT, setup change time and availability dataon the screen.
The second data group is equipment alarm (including
alarm date and time, alarm type and downtime) to be
stored in the KYB-IoT Platform. With these types of data
available, the user can narrow down equipment alarms tobe handled in higher priority and check the equipment
alarm log.
The third one is jig and tool change data (including date
and time of change and the remaining number of times ofuse) to be stored in the KYB-IoT Platform. With thesetypes of data available, user can identify what caused thejigs and tools to be changed.
The fourth one is measurement data (including measurement values and items) to be stored in the KYB-IoT
Platform. With these types of data available, the user canmanage the daily data trend using control charts and findpossible causes of an anomaly in connection with thealarm information. In addition, some devices may measureand save multiple measurement items at the same time.
The style of tables accepting data in this case has beenstandardized to "vertical" Note 11), thereby enabling the user
to easily switch over devices and measurement items or to
analyze data more conveniently.
On the other hand, some source locations may collectdata in a data format other than that stated above in somecases. Then, we, in this development, have decided tosave data collected from individual source locations in acommon file format. In the format, first comes the identification information including production line, production
device, date and time of data collection, and type of datacollected. This general information is followed by sourcespecific data. Although data items to be collected and thenumber of data items vary by target device or object, theKYB-IoT Platform identifies data and executes subsequent processing (including pretreatment and DB storage).
Note 11) A kind of data table structure. It refers to a type of tables
where data is added in the longitudinal (line) direction.

Table 1
Data group
Production

Data to be collected
Data to be collected
・Actual CT
・Actual MT・Setup change time

Equipment alarm

・Date and time of alarm・Type of alarm・Downtime

Jig change

・Date and time of change・Remaining number oftimes of use after change

Measurement data

・Measurement item
・Measurement value

4.3 Data Collection/Transfer
This section explains the line monitoring system,
although several other data collection systems are being
discussed in various sites. It should be noted that any datacollection system could be linked to the KYB-IoT Platform even if the system does not have the same configuration as that of the line monitoring system.
The line monitoring system is generally configured asshown in the Data Collection region in Fig. 6. The line
monitoring system centralizes operation data held by theequipment PLCs to the general PLC and stores data in the
database (DB) built in each line server. By using a visualization software program running on each line server, thesystem displays data on a large monitor in real time. It
also transfers data from the general PLC to the KYB-IoT― 12 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Data Reading
Visualization
softwareData Accumulation

Data Collection
Dashboard Views
FTP server

General PLC

Visualize withvisualization
softwareLine server

Large monitor

Standardized data collection format
Users

Device PLC

Device PLC

Fig. 6

Device PLC

Data
Visualization
and Analysis

Configuration of MES services (overview)

Platform in the following two methods to store data in the
Platform (Fig. 6, ① and ②):① Directly write data from the general PLC into the DB
on the KYB-IoT Platform② Transfer file data in CSV or other format created in
the general PLC by using the file transfer protocol (FTP)
The method ① should be selected for structured data
Note 12)occurring infrequently (in several seconds) that will
be utilized frequently (i.e., accessed) after saved. Specifically, CT, MT and equipment alarms will be transferred inthis method and written into the DB on the Platform one
by one when the equipment cycle is completed or any
alarm is reset. It should be remembered that this method
can only be used with a PLC that supports data writing toa database. It is thus necessary to prepare in advance a
PLC supporting the data writing.
In method ②, the system saves data gathered by thegeneral PLC in a file format and transfers it to an internal
FTP server using the FTP before saving in the storage on
the KYB-IoT Platform. This method should be selected
for data that cannot be accepted by the DB, for example,
data that is generated in a large size per unit time such as

millisecond or non-structured data. Specifically, measurement data and equipment machining condition data
(current and temperature) will be recorded in the general
PLC as required at a certain sampling rate. Several data
sets will be put together to be saved in a file when a setupchange or a production session has been completed. Suchfiles will be periodically transferred using the FTP. In fact,
this type of data saved in files can be viewed at a lower
retrieval speed than that for the DB. Still, our understanding is that no significant problem with system operation
will arise because data utilization (access) has been
assumed to take place infrequently. This method has beenverified to be supported by a wide range of PLCs. How tostore data in these two methods will be described in detailin the following section.
Note 12) "To structure data" means to preliminarily define thetype and sequence of data items and arrange them in a
specified structure.

4.4 Data Storage
As described in the previous section, we have established two different ways of storing data (Fig. 6).
For method ① in Fig. 6, a database (DB) has been

― 13 ―

Building the Foundation for MES Services in the New Era

created on the KYB-IoT Platform (cloud) to store acquired
data. The DB uses an AWS fully managed Note 13) highperformance RDB Note 14) service called "Amazon Aurora"featuring high performance, high expandability, highsafety and high availability. Thanks to its high data reading
performance, Amazon Aurora allows user to quickly
retrieve data by linking multiple data sets using SQL. Note
15)

Method ② in Fig. 6 uses a cloud storage service called"Amazon S3" (hereinafter "S3") to store data saved by thegeneral PLC in files. This service features high durability,
high safety and high availability. Furthermore, S3 canoffer many other benefits including virtually infinite
storage capacity and lower cost than Amazon Aurora. One
disadvantage is that the data retrieval service for S3 is notdesigned to allow the user to easily retrieve data in anadvanced way, resulting in lower retrieval speed than for
RDB.
Furthermore, it costs more for S3 to store large amountsof data than for Aurora as shown in Table 2. The data
storage cost may be reduced by changing where to store
data depending on the data use frequency. It is vital toselect a better one from these two destinations with consideration given to frequency of data occurrence and frequency of data use.
Table 2shows how these screens are configured. All the screensshown in Fig. 7 are standard views for all the sites. A totalof 18 screens are available at this moment. Some of thesescreens cover two or more types of data to allow for diversified analysis. The screens are linked with each other sothat the user can view several screens to find more detailed
analysis screens for deeper analysis. This section will
explain some of these screens we have developed.
Note 18) This industry’s leading BI tool allows the user to easily
visualize and analyze data. KYB is also introducing
and deploying the tool.
Within each of the screens
enclosed with a title ended by theword "Analysis", the user canfreely navigate through sheets bypressing the tab key.
Production Results
CT/MT Analysis
Today’s CT/MT
CT variations
Analysis of manual process
CT histogram
MT variations
MT-error_distribution

Production
progressanalysis

MT-error_time-series
MT histogram

Comparison of data storage

Operation analysis
Set-up change log

AuroraS3

Set-up change analysis

Data volume

Low

High

Frequency of use

High

Low

GeneralProduction
ScreenEquipment Alarm

Storage cost Note 16)

0.12 USD/GB/month

0.025 USD/GB Note 17)(Top page)

Error analysis

Note 13) AWS undergoes server/operating system (OS) management and failure correction for users. Users can focus
on their use of service, leading to higher development
efficiency and lower operation cost.
Note 14) An acronym for Relational Data Base. An RDB
manages data in multiple tables and defines the relationships among the tables to be able to handle therelation among complex data sets.
Note 15) An acronym for Structured Query Language. SQL is aninternationally standardized database language used tooperate and control the RDB management software.
Note 16) The figure shows the price in Tokyo Region as ofDecember 21, 2021. The figure for Aurora only indicates the data storage cost.
Note 17) The price for S3 becomes lower in stages as the datacapacity becomes lower. The figures shown in the tableindicate the service fee for 50 TB/month.

4.5 Data Visualization and Analysis
We have developed a data display system using a BI
tool called Tableau Note 18) to visualize and analyze collected
data.
This visualization and analysis system reads data on the
KYB-IoT Platform. Once data is saved in the system, thedata immediately becomes available on the screens. Fig. 7

Today's error
Error results
Error log
Intensive error countermeasures

Jig Change Results
Jig Analysis
List of remaining number of times of jig changes

Event log
(appears
every hour on
top page)

Measurement Data
Quality Analysis
Control chart (under development)

Fig. 7

Linkage of visualization and analysis screens

4.5.1 General Production Screen (Top Page)
Fig. 8 shows the general production screen where theuser can view actual results of production. Views showing
CT, MT, setup change, availability, alarm and jig changes
for each device are tiled on the screen, enabling the user tonarrow down possible causes of any lower productivity
from various angles. Note 19) This screen displays how dailycompiled data changes day by day. The user can look at
the graphs on the screen to be able to easily identify any― 14 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

data showing an anomaly (for example, longer CT or
more errors than the criteria). If this is the case, the user
can move on to another analysis screen linked to the top
page for deeper investigation.
Note 19) The information on the screen includes undisclosed
information that has been intentionally deleted or
blurred.

Error occurrences

Availability

Set-up change time

Jig change

Fig. 84.5.3 Alarm Screen for Intensive Measures
Fig. 10 shows the alarm screen for intensive measures
where the user can identify device alarms in the form of
Pareto charts. The Pareto charts are intended to show theoccurrences of device alarms (the left chart on the screen)
and their downtime (the right chart on the screen). If adevice has an alarm of frequent occurrence involving
short downtime, the device should have been frequently
stopped. If a device has an alarm of non-frequent occurrence involving long downtime, the device should havebeen troubled with major stoppages. As a general rule,focusing frequent alarms involving long downtime will
relatively easily improve productivity. First, it is good tonarrow down device alarms into those involving poor
productivity. Once this is done, you can now tackle
improvement activities including device adjustment andwork improvement.

General production screen (Top page)

4.5.2 CT Histogram Screen
Fig. 9 shows the CT histogram screen that displays the
CT results over a specified period of time in the form of atime-series two-dimensional histogram. The upper half ofthe screen provides the CT histogram over a specified
period with the X-axis showing CT bins in the unit of one
second and with the Y-axis showing the magnitude. The
lower half of the screen indicates how CT changes by
each day in light and dark in color. A dark colored cell
represents a high magnitude. The Y-axis shows the date inunits of one day (time elapses from top to bottom with the
top oldest and the bottom newest), representing daily CT
variations (distribution in a day). User can first identify
normal CT on the histogram over the entire period andthen check variations for each day to determine whether
any worse CT than the normal level is attributable to a
spontaneous or chronic cause. If spontaneous, it is advisable to narrow down possible causes on the screen statedin the previous section and take appropriate measures. For
chronic ones, it is effective to review the work andmachining programs and check any other chronic error.

CT histogram over a specified time

Daily histogram expressedin light and dark in color

Pareto chart of error countPareto chart of error timeError list

Fig. 10

Alarm screen for intensive measures

4.5.4 Screen Customization
The visualization screen system we have developed
provide standard screens for all sites. Only using thesestandard screens allows for basic data analysis, but somesites may have to carry out more detailed analysis. For
such sites, an environment is available for users to be able
to create their own necessary visualization screens using
Tableau. Once having created a visualization screen, theuser can easily share it with personnel from other departments via the Internet or easily download any screenscreated by personnel from other departments and thencustomize them so that they can easily use within theirown department.
The screen creation procedure (how to use Tableau) has
been designed so that users can build programs as they
like as a scheme of developing human capital Note 20) is
established to promote evolvement of this system.
Note 20) KYB uses the term "human capital", instead of "humanresources".

Fig. 9CT histogram screen― 15 ―

Building the Foundation for MES Services in the New Era

5

Future Prospects

Through this development, we have built the foundation of a system that utilizes manufacturing process data.
We are now improving the system and adding functions to
it based on user feedback on the lines whose data is savedon the KYB-IoT Platform. We are also promoting thelinkage between the system and other data collection
systems than the line monitoring system, thereby enabling
us to collect data from existing devices that have long
been operated and then to utilize the data.
From now on, we will further improve the system andadd functions to it while promoting its global deployment.
In promoting the global deployment, we are facing somechallenges. As the global deployment progresses, data
will be saved more frequently, which will require us toreview the processing capacity and the way of writing
data from data collection terminals. The visualization
screen system is also anticipated to have lower display
speed and lower operability as it handles more data. Thesepossible problems will have to be discussed as required.
We are also going to discuss establishing a linkage
between the system and other systems. The systems thathave already been put into service and have collected data
should be put together to collectively save their data on
the KYB-IoT Platform. For systems to be built and introduced in future, we will sequentially develop their linkage
mechanisms.
Our final goal is to establish a comprehensive scheme tocentrally control data sets from different functions of thecompany, closely link these data sets, and allow the user
to utilize the data as necessary and make decisions basedon the data. Through the scheme, we will aim at strengthening the engineering chain including strengthening theinter-functional connection and reducing the production
lead time as well as at strengthening the supply chain
including enhancing the product reliability and making
the production scheme flexible.

6

Concluding Remarks

Through this development, we have successfully established a scheme to utilize manufacturing process data.
MES can connect upstream systems and downstream
devices in promoting digitalization of manufacturingindustry. The function we have developed is part of the
MES in the production management system. With this inmind, we will continue promoting the system improvement and function addition and the linkage with othersystems, contributing to the higher productivity andhigher quality.
Finally, we would like to take this opportunity to sincerely thank all those concerned from internal related
functions who extended great support and cooperation tothis development project.

References
1) YAMAMOTO: Establishment of a Process Management
System, KYB Technical Review No. 14 (April 1997).
2) FURUKAWA, ISASHI: Development of an Equipment
Predictive Maintenance System, KYB Technical Review No. 63(October 2021).

Author YUBUKI Kento

GABURIELLA Anak Magin

Joined the company in 2016.
DX Dept., Engineering Div.
Engaged in development of analysis
screen systems using BI tools

Joined the company in 2015.
Group 2, Production Engineering
Sect. No. 2, SA Production
Engineering Dept., Automotive
Components Operations.
Engaged in production preparation― 16 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Technology
Explanation

Research on Technology to Control Air Bubble
Content in Hydraulic Fluid
KITAMURA Yoshiaki, KODERA Yasuhiro
Abstract
In hydraulic pumps used in Continuously Variable
Transmission (CVT) of automobiles, air is mixed from thesurface of hydraulic fluid due to vibration of the hydrauliccircuit, and also the dissolved the air appears in theworking oil due to the cavitation. In CVT pumps, 10% tomore than 30% of air bubbles are contained in the hydraulic fluid in the hydraulic circuit under the operating environment. These bubbles cause many problems such as
pump discharge performance reduction, as well as degradation related to vibration, noise, and durability.
Therefore, when developing a pump, it is necessary toevaluate its performance under actual operating conditions, taking into account the bubble content. However, ingeneral, there are no devices or methods to stably adjust
the bubble content.
1

Introduction

A hydraulic fluid usually contains several percentagesof air dissolved therein under atmospheric pressure. Insidea hydraulic pump like the one shown in Photo 1, thehydraulic circuit may have a local decrease in pressure tocause cavitation, generating voids or air bubbles (Fig. 1).
Tiny bubbles appearing in this way will stay in the fluidfor a certain period of time and may need considerable
time to be dissolved in the fluid again or float up to collapse. The air can also be mixed into the hydraulic fluid
from the outside of the fluid due to entrainment (sloshing)that occurs when the hydraulic circuit or the oil tankvibrates. The hydraulic circuit for continuously variabletransmissions (hereinafter "the CVT") of automobiles is atypical example of those exposed to frequent opportunities for air intrusion in this mechanism. It is said that thistype of hydraulic fluid contains 10% to, in some case,even more than 30% bubbles. The fluid with a high bubble
content looks whitish as shown in Photo 2 compared towhen it has a low bubble content. These bubbles containedin the fluid are often known as the third contaminant 2) ofmachinery, next to the particulates and water, and may
cause the machinery to have vibration, noise or mechanical failure. The presence of air bubbles in the hydraulicfluid reduces the apparent elasticity of the fluid to impair

To solve this problem, KYB has developed a device andmethod to control the bubble content in the hydraulicfluid. First, we focused on a method using a swirling flow
as a technique for removing bubbles from oil, and fabricated a bubble separation device. Second, we analyticallyand experimentally confirmed that the bubble separation
effect of this device was sufficient.
Furthermore, we installed the bubble separator in theactual pump test equipment and verified whether the
bubble removal effect could be obtained. Finally, to automatically control the bubble content, we verified it waspossible to obtain the desired bubble content ratio bycontrolling the opening and closing of the valve on theoutlet side of the bubble separator. In this report, theresults of the above verification are described.

the responsivity of the system. Research 3) has verified that
aggressively decreasing the bubble content of the fluid
will eventually lower the amount of air dissolved in thefluid to reduce cavitation. Taking into account the fact that― 17 ―

Photo 1

Example of KYB hydraulic pump

Cavitation

OUT

Fig. 1IN

How cavitation occurs (example)

Research on Technology to Control Air Bubble Content in Hydraulic Fluid

operation (closing/opening) can be controlled to adjust
the bubble content of the fluid leaving the separator. Furthermore, the report explains the adequacy of this methodby introducing the results of an experimental verification
test.

Design and Fabrication of a Bubble
Separator

2(a) 0% bubble content(b) 10% bubble content
Photo 2

Bubbles in a tank in a hydraulic circuit

one of the major causes of failures of hydraulic machinery
elements is erosion caused by cavitation, reducing the
bubble content of the hydraulic fluid will definitely help
prevent machinery failures.
A question: what is the fluid's bubble content that
degrades the machinery performance to eventually causea failure? Such a quantitative indication has not yet been
determined. This is because you can barely measure or
adjust the bubble content of the fluid in real time at a highaccuracy under the present circumstances. Conventionally, the bubbles in the fluid have been removed predominantly by negative methods, such as spontaneous air purgeof the oil tank or addition of anti-foam agent to the fluid.
In such situation, modern automobiles are required tohave intermittent runs or stops of their engine more frequently for higher fuel efficiency. Accordingly, hydraulicpumps connected to the engines need to be started or
stopped frequently as well. Air bubbles contained in thehydraulic oil are likely to stay or merge in various locations within the hydraulic circuit, which may cause theautomobiles to generate noise or may make the hydraulicsystem unstable during the initial stage of the start-up
process. The need to determine the effect of the bubble
content of the fluid and to take measures has become
urgent.
To respond to the need, we first tackled technical development to implement techniques for stable adjustment of
the bubble content of the fluid. This report proposes a
bubble separation device using a swirling flow and amethod to control the bubble content of the fluid entering
the separator. The separator has an air purge valve whose

2.1 Bubble Separator Using a Swirling Flow
Fig. 2 shows the operating principle and structure of abubble separation device that uses a swirling flow to draw
bubbles, which are distributed throughout the hydraulicfluid, and puts them together to be separated and removed
by a simple mechanism. Using a swirling flow, the separator can draw bubbles distributed in the fluid and build
them up around the central axis in a time as short asapproximately 100 msec. The separator can remove anddischarge these collected bubbles from a purge outlet tothe outside by utilizing a slight difference in pressure
between the fluid outlet and the purge outlet. 4) To implement this, a control valve should be installed downstreamof the purge outlet to adjust the air purge by valve opening/closing. Controlling the period of time for the valve to beopen or closed and/or the operation timing will adjust thevolume of bubbles to be separated from the fluid. In thisdevelopment, we began to fabricate the separator forbuilding a system that can control the bubble content of
the fluid at the fluid outlet of the separator.
Bubbles + Fluid

Fluid outlet

Tapered pipe

Fluid inlet
Purge outlet

Fluid

Bubbles

Fluid inlet
Fluid

Bubbles
Bubbles + Fluid

Fig. 2

Operating principle and structure of bubble separator

2.2 Simulation of Bubble Separation
For the method to be verified in this research, we set up
a target range of the bubble content between 1% and 40%.
To achieve this goal, the bubble separator must provide
adequate bubble removal performance within the range.
Since the performance of the separator heavily depends
on the geometry of the fluid inlet and the diameter of thepurge outlet, 5) it is very important to select appropriate
parameters for flow conditions in designing the separator.
To verify the operating principle and select optimal
geometry parameters, we used the computational fluid
dynamics (CFD) to simulate and verify the bubble separation. For the purpose of CFD, we used a fluid duct shownin Fig. 3 and simulation conditions listed in Table 1.
Within the target range, 20%, 30% and 40% bubble― 18 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

content levels were selected as examples for analysis
purpose.
Fluid inlet

Air purge outlet

L2

L1

φD3

h
L3

w

φD1

φD2

Fluid outlet

D

L

Fig. 3

Fluid duct for computational simulation

Table 1

Computational simulation conditions

Item
Fluid flow at inlet (L/min)
Size of bubble particles (mm)Density (g/cm3)
Physicalproperties ofDynamic viscosity
hydraulic fluid(mm2/sec.)
Bubble content (%)

Value
30
0.1
0.8474
9.189
20, 30, 40

the center of the duct for any of the bubble content levels
as shown in Fig. 4(b). It was verified that the bubbles
flowed towards the purge outlet efficiently to be separated
and removed from the fluid.
As a result of the CFD, an optimal set of geometry
parameters for the bubble separator was obtained asshown in Table 2. Fig. 5 shows the resultant bubble
removal rate of the separator with its fluid inlet sized tobe 2.18 mm (width) x 4.35 mm (height), its air purge
outlet sized to have an inside diameter of φ4.4 mm, andits fluid outlet sized to have an inside diameter of φ16 mm
for the bubble content cases of 20%, 30% and 40%. Notethat the bubble removal rate here refers to what percentage of the bubbles have been removed from the fluid thatis discharged from the fluid outlet, not from the air purge
outlet. The CFD proved that the simulated bubble separator with the optimal geometry parameters delivered abubble removal performance as high as 90% or more forall the cases. These results were used as design parameters for an experimental bubble separation device.
Table 2The bubbles entering the separator via the fluid inlet
has a higher flow rate around the perimeter of the inlet
port and a lower flow rate in the center of the same asshown in Fig. 4(a). The figure represents how a swirling
flow occurs. The volume fraction of the bubbles for the
bubble content levels of 20%, 30% and 40% is higher in

Bubble flow rate (m/sec.)

Optimal geometry parameters for bubble separator
Geometry parameter

Value [mm]Inside diameter of tapered pipe section φD1
Inside diameter of fluid outlet φD2
Inside diameter of air purge outlet φD3
Total Length L
Length of fluid inlet pipe L1
Length of tapered pipe section L2
Length of fluid outlet pipe L3
Width of fluid inlet w
Height of fluid inlet h

30.0
16.0
4.4
150.0
20.0
30.0
100.0
2.18
4.35

40

Bubble removal rate [%]

32
24
16
8
0

(a) Distribution of bubble flow rate(for fluid with 40% bubble content)

120
100

99.8

60
40
20
0

40%
Fig. 540%
bubblecontent

0.0

0.2

0.4

0.6

0.8

1.0

(b) Volume fraction of bubbles
Fig. 4 Computational simulation of bubble flow

90.2

80

20%
bubblecontent
30%
bubblecontent

94.8

30%
20%
Bubble content [%]Results of simulation of bubble separation

2.3 Separator Design and Fabrication
Based on the results of the CFD analysis stated in theprevious section, we designed and fabricated a bubble
separation device to be used in experiments of controllingthe bubble content of the hydraulic fluid. Fig. 6 shows the
bubble separator. The separator was designed in modulars
so that the geometry parameters including the fluid inlet― 19 ―

Research on Technology to Control Air Bubble Content in Hydraulic Fluid

size, the fluid outlet size and the air purge outlet size canbe adjusted later to be suited to the test conditions. Piecesof this modular device can be first inserted into a casing
and then fixed together from both sides to be a one-piece
structure. The peripheral casing and inserts are made oftransparent acrylic.

test made it difficult to achieve precise control of the flowrate at the purge outlet by varying the degree of openingof the valve. Unfortunately, just slightly opening the valve
at the purge outlet actually caused the separator to deliver
the bubble removal effect more than expected, resulting ina substantially lower bubble content of the fluid at thefluid outlet. However, it was verified that the bubble
content of the fluid at the fluid outlet can be controlled bychanging the degree of opening of a valve installed at thepurge outlet.

Peripheral
casing(Air purge outlet)

Fluid outlet(Fluid outlet)

Purge outlet

Bubble separator

InsertNeedle valve

Fluid inlet

Fig. 6

Design and fabrication of bubble separator

Bubble mixing

Evaluation of Performance of Bubble
Separator

Hydraulic circuit for testing of manual control of
bubble content(Purge outlet)

Fig. 7(Fluid outlet)(a) Purge outlet closed(Purge outlet)

To verify the bubble separation performance of thefabricated separator, a preliminary test was first conducted.
Fig. 7 shows the hydraulic circuit used in the preliminary test. The bubble separator was installed on the fluid
circuit. A manually operated needle valve was mounted
on the circuit line of the purge outlet side of the separator
and a Coriolis-type flowmeter was on the circuit line of
the fluid outlet side of the separator. The hydraulic fluid
was forcefully mixed with bubbles from the air blown by
an air compressor located on the discharge side of thepump. While the air was being blown into the fluid, theneedle valve was manually controlled to deliver the fluid
from the separator at different bubble content levels. The
bubble content of the fluid was determined by measuring
the density of the fluid at the fluid outlet against the degreeof opening of the needle valve. 6) The fluid pressure at thefluid inlet of the separator was maintained at 0.5 MPa.
Photo 3 shows what happened inside the bubble separator during the preliminary test. With the purge outlet fully
closed, the fluid looks whitish with great amounts of air
bubbles over the entire duct in the separator as shown in
Photo 3 (a) (Bubble separation with the purge outlet
closed). With the purge outlet fully open, the air bubbles
flowing into the separator from the fluid inlet quickly
flowed toward the purge outlet. Few bubbles stayed in theseparator for a while and then flowed toward the fluid
outlet as shown in Photo 3 (b) (Bubble separation with thepurge outlet open).
Fig. 8 shows the results of the preliminary test: therelationship between the degree of opening of the needle
valve and the bubble content of the fluid at the fluid outlet.
In fact, the specifications of the needle valve used in the

M(Fluid outlet)

3

Manualcontrol

Coriolis-type flowmeter― 20 ―(b) Purge outlet open
Photo 3Inside the bubble separator

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Now we have verified that using the bubble separator in
the actual pump test unit enables quick, stable adjustmentof the bubble content of the fluid in the circuit.

40
30

Cooler

20
Bubble separator

1000

Fig. 8Return line

Bubble content
at fluid outlet [%]50

HeaterDrain line

51015
Degree of opening of needle valve
at the purge outlet [%]Reservetank

Manually controlled bubble content

Bubble content
measuring device

Tank
Suction line

Evaluation of Performance of Bubble
Separator on Actual Machine

To verify that the bubble separator developed can also
be applied to evaluation of actual pumps, we carried out
an experimental test on the bubble separator installed onan actual pump test unit. Note that the bubble separator
used for this test was another unit made of metal, not theoriginal separator.
Fig. 9 shows the hydraulic circuit of the actual machine
test equipment. In order to determine the effect of the
bubble content of the hydraulic fluid on the pump, adevice to mix the air into the hydraulic fluid in a tankupstream of the target pump to be evaluated was provided
to increase the bubble content of the fluid. This air mixing
device was designed to be able to control the air discharge
rate for mixing. The bubble separator was installed downstream of the target pump. On the purge outlet line aneedle valve was provided to be able to be opened orclosed freely in the same manner as for the preliminary
test. On the fluid outlet side an orifice of any round shape
was inserted as a back pressure control. Further downstream, an inline impedance-type bubble content measuring device was installed to measure the bubble content inreal time. The oil temperature was maintained at 100°C bya cooler and a heater provided on the circuit.
As an example of verification of the bubble removal
effect, Fig. 10 shows changes in bubble content of thefluid over time for the case of a constant mixing rate of
bubbles in the tank, a fluid outlet size of φ10, and a pumpdischarge rate of 18 L/min. At the time point of 0 seconds,
the separator has its purge outlet closed and the duct contains the fluid with bubbles mixed in as sufficient asaround 30% with the mixing tank being operated. Whenthe purge outlet is opened, the bubble content immediately
dropped and became stable at around 10% about 4 minutes
later.
This bubble content level was obtained when the bubble
mixing device in the tank and the bubble separator wereboth operated. The air content of the hydraulic fluid may
be adjusted to any given level by controlling the air mixing
rate and/or the air purge rate of the bubble separator.

Target pump

Hydraulic circuit of actual machine test equipment

Fig. 940

Start bubble removal
Bubble content [%]4

Air mixing

30

Stable air content

20

10

0

0

120

240

360

480

600

Time [sec.]

Fig. 10 Bubble content of hydraulic fluid on actual machine

5

Evaluation of Performance of Automatic
Bubble Content Control

After verifying that controlling the degree of opening of
the purge outlet of the bubble separator can adjust the
bubble content of the hydraulic fluid in the circuit, we
further tried to determine the possibility of automaticallycontrolling the bubble content to any given level. To thisend, we installed an on-off control solenoid at the purge
outlet and carried out a test to control the bubble content
of the fluid at the fluid outlet by adjusting the on/off timeor the switching timing of the solenoid.
Fig. 11 shows the hydraulic circuit used in the control
test. The bubble separator was installed on the fluid circuit
similar to the one shown in Fig. 7. A Coriolis-type flowmeter was installed at the fluid inlet and a bubble content
measuring device installed at the fluid outlet. Then, thebubble content of the fluid was measured in real time forvarious cases. Air mixing into the fluid was attained bykeeping the suction port of the pump open to the atmosphere. An on-off control solenoid was installed at the― 21 ―

Research on Technology to Control Air Bubble Content in Hydraulic Fluid

purge outlet of the separator. The solenoid control(opening/closing) was implemented by a sequencer using
a relay according to the deviation of bubble content measurements at the fluid outlet from the target level.
Fig. 12 shows an example of the results of the bubble
content control tests. When the incoming fluid had about
29% bubble content, the outgoing fluid had about 28%
bubble content with the purge outlet closed. Then, thetarget bubble content was set to 18%. With the on-off
control solenoid operation frequency 1s and the duty ratio
between 10% and 100%, the bubble separator automatically controlled the duty ratio to attain the target level as
indicated by the figure. Table 3 shows the average bubble
content for each duty ratio and its relative deviation fromthe target bubble content for a certain period of time (19.2
seconds to 25 seconds) after the bubble content became
stable at around the target level. In general, the smaller the
duty ratio is, the lower the control accuracy and responsivity are. However, this test demonstrated that the relative deviation from the target level was within 9.4% forsmall duty ratios, proving a certain level of control accuracy.
For some duty ratio settings, however, the bubble
content may fail to be stable at around the target level andmay continue fluctuating in some cases. This is because
the on-off solenoid at the purge outlet can only deliver
low responsivity while the bubble separator has highly
Data logger
Bubble separator

Bubble content
measuring device

Relay

Coriolis-type flowmeter

Sequencer

M

Fig. 11

Average [%]Relative deviation [%]

10

19.7

9.4

20

18.8

4.4

30

17.9

0.5

40

16.8

6.7

50

17.3

3.9

60

18.0

0.0

70

18.6

3.3

80

18.6

3.3

90

18.6

3.3

100

18.6

3.3

responsive bubble removal performance. This can beprobably improved by using a more responsive proportional valve.

6

Future Prospects

We will apply the technology that controls the bubble
content of the hydraulic fluid developed in this research toevaluation of our pumps under actual operating conditions, thereby developing high-function and high-quality
products, although the control stability is still a challenge.
On the other hand, we aim to deploy the technology insuch a manner that our pump products including CVT
could be improved in performance by focusing the featureof the technology that can remove the bubbles containedin the fluid, which may be called "the third contamination" as stated in the beginning of this report.
By improving our capability of technical development
like this, we will be able to offer even-higher-efficiency
pumps that could improve the fuel efficiency of automobiles for instance. These products will help create a carbon
neutral society or achieve the sustainable development
goals (SDGs).

7

Duty ratio
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%

29
27
25
23
21
19

Target17
15

Duty ratio [%]Bubble content for various duty ratios

Hydraulic circuit for automatic bubble control test

Start control

Bubble content [%]Target bubble
content

Table 30

Fig. 125

1015Time [s]20

25

Automatically controlled bubble content

Concluding Remarks

This report has introduced the verification of the methodthat freely controls the bubble content of the hydraulicfluid with the bubble removal technology using a swirling
flow, toward establishment of such a bubble content
control system. The verification has produced the following conclusions:(1) A bubble separator has been developed and fabricatedthat can adequately remove air bubbles from thehydraulic circuit to obtain a bubble content between
1% and 40%.
(2) It has been verified that the bubble separator mounted
on the actual pump test unit can control the bubble
content in the hydraulic circuit quickly and stably.

― 22 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022(3) Testing has proven that adjusting the flow rate at thepurge outlet of the bubble separator can control the
bubble content of the fluid at the fluid outlet of theseparator.
This research was carried out in cooperation with Professor TANAKA Yutaka, Hosei University, who designed
the bubble separation device using a swirling flow, andAssociate Professor SAKAMA Sayako, Aoyama Gakuin
University (currently belonging to National Institute ofAdvanced Industrial Science and Technology), whocarried out various element tests. Finally, we would like totake this opportunity to sincerely thank them.

References
1) SAKAMA S, et.al: Air Bubble Separation and Elimination fromWorking Fluids for Performance Improvement of Hydraulic
Systems, Proc. IFPE 2014, Paper No. 27.1 (2014).

2) SEKIDO Makiko, MIZUMURA Atsushi: How to select and use
filters and their trouble cases, Basic Hydraulic Technology Class- How to select and use peripheral equipment, Japan Industrial
Publishing Co., Ltd. (2016).
3) GOTO H, SAKAMA S, SUZUKI R, TANAKA Y: Reduction of
Cavitation Damage by Elimination of Bubbles in Oil Reservoir,
Proc. FLUCOME2013, OSI-02-4. (2013).
4) TANAKA Y, et.al.: Visualization of Flow Fields in a Bubble
Eliminator, J. of Visualization, Vol. 4, No. 1, pp. 81-90. (2001).
5) SAKAMA Sayako, TANAKA Yutaka, SUZUKI Ryushi:
Research on design and evaluation of bubble separation devices(Report #2), Transactions of The Japan Fluid Power System
Society Vol. 45, No. 5, pp. 79-84. (2014).
6) GOTO Hiroyuki, SAKAMA Sayako, TANAKA Yutaka:
Measurement of bubble content of hydraulic oil using Coriolistype flowmeter, Transactions of FY2015 Annual Assembly
Lectures of the Japan Society of Mechanical Engineers (JSME),
No.15-1, S1150302, (2015).

Author 
KITAMURA Yoshiaki

KODERA Yasuhiro

Joined the company in 2013.
Mechanical Component Engineering
Sect., Basic Technology R&D
Center, Engineering Div.
Engaged in research anddevelopment of hydraulic pumps andpower steering

Joined the company in 2009.
Developmental Experiment Sect.,
Developmental Center, Engineering
Headquarters, Automotive
Components Operations
Engaged in development of hydraulicpumps― 23 ―

Research on Particle Assemblage Damper

Technical
ArticleResearch on Particle Assemblage Damper
TOYOUCHI Atsushi

Abstract
Dampers are devices which suppress vibrations thatcause harm to vehicles, buildings, and the like. There arevarious types of dampers, depending upon the application.
However, each type of damper comes with its own problems. Typical examples of such problems are that in thecase of oil dampers, liquid leakage may occur, and thedamping force may be dependent on temperature. Particle
dampers suppress vibrations by generating resistanceforce through the use of particles in place of oil or the like.
These dampers can be exemplified as a possible solution
to the abovementioned problems. In this study, an investigation and examination were carried out in order to clarify
the generative force characteristics and force generation
factors of a separated dual chamber single rod-type particle damper which employs a particulate elastomer*. This
type of damper holds the possibility of solving these
problems by means of a simple structure.
With regard to the damper used in this study, a particle
chamber within the cylinder was divided in two by apiston. It was found that when one chamber of the damper
was filled with particles, the generative force had thecharacteristic of being gradually hardening with hysteresis, with great influence exerted by elastic force in thenormal direction and frictional force in the tangential
1

Introduction

The particle assemblage damper is a damper filled withsmall steel or elastomer balls in place of a fluid such as oil
as in oil dampers. These spherical particles that fill thedamper are fluidized by the movement of a piston to yielda resistive force. (1, 2) The existing oil damper involves
problems including liquid leakage and temperaturedependent damping force. One of the possible solutions to
the problems is the use of particle dampers. A particle
damper using particles of a larger size than the clearanceof the sliding part of the damper is free from leakage. For
a particle damper using small elastomer balls (hereinafter"elastomer particles"), using elastomer material withexcellent heat/cold resistance whose glass transition temperature is low can reduce the temperature dependence ofthe generative force.

direction. The elastic force in this case was mainly
accounted for by repulsion force under compression generated by the compression of the particles, and the frictional force was generated by sliding friction between thecylinder and the particles. Furthermore, it was found thatin particular, the packing fraction and Young’s modulus,
which affects the material, exerted a large effect on the
maximum generative force and the hysteresis.
When both chambers were filled with particles, contrary
to the findings of single-chamber filling, it was found thatthe frictional force was generated by the sliding friction
between the cylinder and rod and the particles, whereby,
due to the friction of the rod, a waveform of the generative
force was asymmetrical with respect to the origin.
These results were demonstrated by means of simulations of generative force and particle behavior using thedistinct element method, as well as by experiments. The
simulation results and the experimental results were ingood agreement with one another both qualitatively andquantitatively, and it was confirmed that the simulations
were able to reliably reproduce the phenomena which
occurred in the experiments.
*“Elastomer” is a generic term for a polymer having elasticity. Rubber and the like correspond to this term.

This study used a separated dual chamber single rodtype particle damper which had two chambers divided bya piston and employed elastomer particles. An investigation was carried out to clarify the generative force characteristics and force generation factors or mechanism fortwo different cases: with particles filling only one of thetwo chambers and with particles filling both chambers.
Elastomer particles were selected with an aim at delivering a high generative force by densely filling them, which
was possible thanks to their high elastic deformation. The
investigation used two approaches: one is to develop a
damping theory based on the distinct element method andthe other to simulate generative force and particle behavior. The simulation results were compared with thoseobtained from experiments using an actual machine todetermine the generative force characteristics and mechanism and to verify the adequacy of the developed theory.

― 24 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Please note that this damper generates a combinedelastic and viscous force, although the term "damper"
might cause you to imagine a damper that can suppress
vibration by exerting a damping force attributable to apressure loss or viscous resistance of the fluid used. That's
why the force generated by this damper is called a "generative force", not a damping force, for clarification purposes.
2

Generative Force Characteristics of Particle
Damper with One of the Chambers Filled

2.1 Damper Structure
Fig. 1 shows the general structure of the damper used insimulations and experiments. The internal void of thedamper is divided into two chambers by a piston and only
the chamber without the rod is filled with spherical particles. The clearance between the piston perimeter and thecylinder bore is very small so that no particles can movefreely between the chambers. Friction in the sliding part isnegligible as it is considerably smaller than the generative
force of the damper. The piston displacement of thisdamper described in the following sections refers to the
movement of the piston in the direction of the z-axis
shown in Fig. 1.

d 2r i
(1)
m
＝Fi
i
dt 2
dΩi
Ii
＝Ti
(2)
dt
where:
i is particle number;t is time;
mi is particle mass;ri is position vector of the particle;
Fi is the sum total of contact forces;
Ii is inertia moment;
Ωi is angular velocity vector of the particle, and;Ti is the sum total of torques applied to the particle.
Fi, Ti and Ii can be expressed in Equations (3) to (5)below:
Fi＝Fcn＋Fct＋mi g(3)Ti＝ri×Fct(4)
8
(5)
Ii＝
ρπr 5
15
In the equations above, the subscript n indicates thenormal direction at the point of contact and the subscript t
the tangential direction at the point of contact. Fcn and Fct
are the contact force in the normal and tangential directions, respectively. mi is particle mass, g is gravitational
acceleration, p is particle density, and r is particle radius.
The concept of contact force was proposed by Cundall
and Strack (3). They used an analysis model consisting of
three elements shown in Fig. 2: a spring, a dashpot and afriction slider. The model can be expressed in Equations(6) and (7). Fig. 3 shows a conceptual rendering of theforce applied in the normal direction and the force appliedin the tangential direction.

Section A-A

Fig. 1 Damper structure
1. Cylinder, 2. End cover, 3. Bearing, 4. Rod, 5. Piston,
6. Elastomer particles, Unit: mm

2.2 Simulations and Experiments
2.2.1 Distinct Element Method
Simulations were conducted by using the distinct
element method (hereinafter "DEM") to clarify the particle
behavior, generative force characteristics, and components of the force. DEM is a method for computing the
behavior of particles by sequentially calculating the equation of the motion of particles for their translationalmotion and rotation at individual time points, with consideration given to contact interactions of particles.
2.2.2 Primitive Equation
DEM can be used to determine the velocity and positionof a particle by solving the equation of motion expressedin Equation (1) and the equation of angular motion
expressed in Equation (2) by taking into account thecontact force of each particle.
― 25 ―（）

Fcn＝ －Knδn1.5－CnVij・ni ni(6)Fct＝－Ktδt－CtVfij(7)Friction slider

(a)

(b)

Fig. 2 Contact model(a) Normal direction, (b) Tangential direction

Research on Particle Assemblage Damper

elastic modulus Kn of the particles during their contact.
Kniw indicates the elastic modulus Kn of the particle when
it makes contact with the cylinder wall. Ei and Ew are themodulus of longitudinal elasticity of the particle and thewall, respectively. vi and vw are Poisson ratios of the particle and the wall, respectively. The elastic modulus in thetangential direction is based on an assumption that noslide occurs at the point of contact and can be expressed in
Equations (15) and (16) in accordance with the Mindlin (4)theory:➡Normal direction, ➡Tangential direction

Fig. 3

Conceptual rendering of forces in the normal andtangential directions

In the equations above, Kn and Kt indicate elastic
modulus in the normal and tangential directions, respectively, and Cn and Ct are viscosity coefficients in thenormal and tangential directions, respectively. δn is displacement in the normal direction at the point of contactand δt displacement vector in the tangential direction at
the point of contact between the particles i and j. ni is theunit vector in the normal direction from the particle i tothe particle j at their contact point. Vij is the relative velocity vector of the particle i against the particle j. vi and vj arevelocity vectors of the particles i and j, respectively. Vfij is
the relative velocity vector in the tangential direction of
the particle i against the particle j at their contact point.
Vij, Vfij and δt can be expressed in Equations (8) to (10):

2 2a Gi 0.5
(15)
Ktij＝
δn
2－νi
8 a Gi 0.5
(16)
Ktiw＝
δ
2－νj nIn the equations above, Ktij is the elastic modulus of theparticles during their contact. Ktiw is the elastic modulus of
the particle and the wall during their contact. Gi is themodulus of transverse elasticity of the particle and can be
expressed in Equation (17):Vij＝νi－νj(8)

Ei
G
(17)
i＝
2（1＋vi）

Vfij＝Vij－(Vij・ni)ni＋2a(ωi－ωj)×ni(9)Cn and Ct can be expressed in Equations (18) and (19):δt＝Δt－Vfij(10)(18)C
mi Kn δn0.25
n＝α

In the equations above, a is the particle radius, and ωiand ωj are angular velocity vectors of the particles i and j.
Elastic modulus in the tangential direction can be
expressed in Equations (11) to (14) using the Hertziancontact theory:

（ ）

aδn
4 1
(11)
Knij＝
2
3π 2δi

（

）

4
1
(12)
aδn
Kniw＝
3π δi＋δw
1－vi2
δi＝
(13)
Eiπ
1－vw2
(14)
δw＝
Ewπ

(19)
Ct＝α mi Kt δct0.25
2
ln（e）
(20)
α＝2.2
2
ln（e）＋π

α is a dimensionless constant that decides the magnitudeof viscous force and can be expressed in Equation (20). e
in Equation (20) is the repulsion coefficient of the particle.
If the relative velocity vector in the tangential direction of
the particle on the contact surface is more than zero (0) or
the contact force in the tangential direction is higher than
the frictional force, it is considered that particle sliding
has occurred along the contact surface. The phenomenon
can be expressed in Equations (21) to (23):In the equations above, the subscript w indicates that therelevant amount is related to the wall surface of the cylinder bore (hereinafter "the cylinder wall"). Knij indicates the― 26 ―

If ｜Vfij｜＝0 and Fct≦μf｜Fcn｜,
Fct＝Fct(21)KAYABA TECHNICAL REVIEW No. 64 APR. 2022

If Fct＞μf｜Fcn｜,

Table 2

Fct＝－μf｜Fcn｜ti(22)
If |Vfij｜＞0,
Fct＝－μf｜Fcn｜ti(23)
Vfij
ti＝
(24)
|Vfij|
ti is unit vector in the Vfij direction of the particle and canbe expressed in Equation (24). μf is the friction coefficientof the particle.
Thus, the analysis model was designed to consider
elastic and viscous forces in the normal direction and, in
addition to these forces, frictional force as well in thetangential direction. This analysis also applied the secondorder accurate Adams-Bashforth method to time-steppingof displacement, velocity and angular velocity.
2.2.3 Simulation and Experimental Conditions
The overview of the experiment equipment is shown in
Fig. 4. The simulation conditions are shown in Table 1
and the experimental conditions are shown in Table 2. The
particles used in the experiments are shown in Photo 1.
Table 1

Simulation conditions

Particle material

Silicone rubber(TSE 3466 made by
Momentive Performance
Materials),
nitrile rubber (NBR madeby Inaba Rubber)Particle size [mm]3, 5Packing fraction [-]0.60, 0.70

Number of particles

1,339, 1,562

Stroke [mm]10

Excitation frequency [Hz]1, 5Time increments [sec.]

5.0×10-9

Excitation waveform

Sinusoidal

Particle density [kg/m3]

1.10×103

Poisson ratio of particle vi

0.5

Friction coefficient μf(wall-particle)

0.5

Friction coefficient μf(between particles)

0.5

Young's modulus Ew [GPa](wall)

210

Young's modulus Ei [MPa](particle)

4.08 (TSE3466),
17.6 (NBR)

Viscosity coefficient α

0.5311

Experimental conditions

Particle material

Silicone rubber (TSE 3466),
nitrile rubber (NBR)

Young's modulus Ei [MPa](particle)

4.08(TSE3466),
17.6(NBR)

Particle size [mm]3, 5Packing fraction [-]0.60, 0.70

Stroke [mm]10

Excitation frequency [Hz]1, 5Fig. 4 Experiment equipment
1. Controller, 2. Motor, 3. Laser displacement gauge, 4. Rod,5. Damper, 6. Load cell, 7. Dynamic distortion amplifier.
8, Oscilloscope, 9. Displacement gauge amplifier unit

(a)

(b)

(c)

Photo 1 Particles used(a) Silicone rubber, particle size 3 mm(b) Silicone rubber, particle size 5 mm(c) NBR, particle size 3 mm

For simulation purposes, the general coefficient offriction between rubbers of 0.5 was used as shown in
Table 1. (5) In a condition for which two or more parameters
are indicated in Table 1 or 2, the one in red is the reference
conditions. The packing fraction refers to the ratio ofparticles in the particle chamber and has been determinedby dividing the volume of all the particles present in thechamber by the volume of the chamber.
2.2.4 How to Calculate Generative ForceIn the simulations of the particle damper with only oneof the chambers filled, the total generative force can be
determined, as shown in Fig. 5, by adding the compres― 27 ―Research on Particle Assemblage Damper

Generative force

Load cell➡Direction of stroke➡Force applied to cylinder bottom by particle compression
and friction➡Force applied to cylinder wall by particles(a)Generative force

Load cell➡Direction of stroke➡Force applied to cylinder bottom by particle compression
and friction➡Force applied to cylinder wall by particles(b)Fig. 5 Generative force in the z-axis direction(a) Positive displacement, (b) Negative displacement

2.2.5 Generative Force and Its Normal andTangential Components
The results of the simulations are plotted in Fig. 6.
These curves show how the generative force and its component in the normal direction (hereinafter "the normalcomponent") and its component in the tangential direction(hereinafter "the tangential component") change withdisplacement under the reference conditions (i.e., forcedisplacement curves). Fig. 7 shows the force-velocity
curves under the same conditions. All the following
figures of these kinds plot a cycle of data. The displacement refers to the piston displacement. The time development of curves is clockwise for force-displacement curves
and counterclockwise for force-velocity curves.
According to Fig. 6, the generative force shows gradually hardening characteristics that the generative force
increases as the displacement advances in the direction ofparticle compression (hereinafter "the compression

process") and involves hysteresis as the piston travels inthe direction opposite to the direction of particle compression (hereinafter "the retraction process"). The graduallyhardening characteristics may be attributable to elastic
repulsion generated by particle compression. The hysteresis may be attributable to viscosity caused by deformation of elastomer particles and/or friction between
particles or between particles and the wall.
Now, let us move on to discussion about the normal andtangential components of the generative force. The normalcomponent is related to resistance generated primarily
during particle compression and the tangential component
is related to shear force generated between particles or
between particles and the wall as well as resistance
between particles or between particles and the wall generated when particles move around.
In the compression process, both the normal and tangential components show gradually hardening characteristics as shown in Fig. 6. The normal component has ahigher maximum value and lower hysteresis than for thetangential component. Since the normal component peaks
at around the point of 0 m/sec. velocity as shown in Fig. 7,
the effect of the viscosity attributable to compressive
deformation of particles in the normal direction should betrivial, which may result in the gradually hardening characteristics and the lower hysteresis. In other words, thenormal component consists predominantly of the elastic
force of particles due to their compression. The tangential
component also shows gradually hardening characteristics, but has higher hysteresis, resulting in a negativevalue that gradually becomes smaller as the displacement
advances during the retraction process. Since the viscosity
affecting the hysteresis depends on the velocity, the effectof viscosity on the tangential component is probably low
because it peaks at around 0 m/sec. velocity as shown in
Fig. 7. In addition, the force converges to 0 N at a displacement of -5 mm, which is the start point of the compression process. Therefore, the tangential component
consists predominantly of frictional force, to which thenormal component acts as vertical resistance. As the positive/negative sign to friction force is switched overaccording to the direction of displacement, the tangential
Generative force
Normal component
Tangential component
Force [N]sive force applied to the cylinder bottom end surface(hereinafter "the cylinder bottom") in the z-axis during
particle compression by the piston to the frictional forceof particles against the cylinder wall in the z-axis direction. The component of the generative force in the normal
direction is attributable to viscoelasticity of particles dueto their compressive deformation. The component of thegenerative force in the tangential direction is attributableto viscoelasticity of particles due to their shear deformation and sliding friction between particles and the cylinder
wall.

Displacement [mm]Fig. 6― 28 ―

Force-displacement curves of generative force andits normal and tangential components

Force [N]Force [N]KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Generative force
Normal component
Tangential component
Velocity [mm/sec.]

Force-velocity curves of generative force and its normal and tangential components

component takes a negative value with higher hysteresis
during the retraction process. The frictional force generated here refers to the friction of sliding particles against
the cylinder wall.
2.2.6 Elastic and Viscous Forces in Normal/
Tangential Direction
To verify the assumption discussed in the previous
section that the normal component of the generative force
consists predominantly of elastic force and the tangential
component consists predominantly of frictional force, thissection further discusses these components by dividingthem into elastic and viscous forces. Fig. 8 shows theforce-displacement curves of the normal component andits breakdown into elastic and viscous forces. Fig. 9 is anenlarged view of the viscosity curve in Fig. 8. Fig. 10shows the force-displacement curves of the tangential
component and its breakdown into elastic and viscous
forces.
In Fig. 8, the normal component curve generally agrees
with the elasticity curve, which implies that the elastic
repulsion of particles due to their compressive deformation is predominant. However, the viscosity never takes avalue of zero (0). The enlarged view in Fig. 9 reveals thata minute force is always generated. Fig. 10 shows that thetangential component involves no elastic or viscous force
attributable to shear deformation of particles along thecylinder wall. Rather, the tangential component only con-

Force [N]Generative force
Normal component
Tangential component

Displacement [mm]Fig. 8

Force-displacement curves of normal component andits elasticity and viscosity

Fig. 9

Enlarged view of force-displacement curve ofviscosity of normal component

Tangential component
Elastic force
Viscosity
Force [N]Fig. 7

Displacement [mm]Displacement [mm]Fig. 10

Force-displacement curves of tangential component
and its elasticity and viscosity

sists of friction of particles against the cylinder wall,
which implies that particles are always sliding along thewall.
Now, the discussion above has revealed that the generative force is greatly affected by the elastic force of particles
in the normal direction due to their compressive deformation and the friction of particles against the cylinder wallin the tangential direction.
2.2.7 Distribution of Particle Compression
Since the generative force heavily depends on theelastic force in the normal direction, we tried to determine
the effect of the compressive force of particles filled in thedamper under the reference conditions. Fig. 11 (a) to (d)show where the piston and particles are located in thedamper when viewed from the section A-A in Fig. 1 andthe distribution of particle compression. The compressive
force on particles in these diagrams is due to the elasticity
in the normal direction.
In Fig. 11 (a), many of the particles close to the piston
are highly compressed during the compression process,resulting in higher particle repulsion against the piston.
Near the cylinder bottom in turn many particles are not sostrongly compressed. This means that the compression of
the particles close to the piston has not been transferredwell to the cylinder bottom. In Fig. 11 (c) for the retraction
process, many of the particles close to the piston are not sostrongly compressed, resulting in lower particle repulsion
against the piston. However, many of the highly com-― 29 ―

Research on Particle Assemblage Damperpressed particles still remain near the cylinder bottom.
This means that the compression of the particles close to
the cylinder bottom has not been transferred well to thepiston. It can be derived from these facts that there is atime lag between the forced excitation by the piston andthe transfer of forces caused by particle deformation.
In the compression process, the particle-particle compressive force, the force pressing particles against thecylinder wall, and the friction against which these twoforces act as vertical resistance increase, resulting in ahigher force applied to the cylinder bottom. In the retraction process, the particle-particle compressive force andthe force pressing particles against the wall becomeRod

Piston(a)Rod

Piston(b)

Rod

Pistonsmaller, resulting in lower friction. In this case, the force
applied to the cylinder bottom is the sum of the compressive repulsion of particles and the friction. Since the friction is switched from a positive value to a negative one orvice versa between the compression and retraction processes, the generative force at any given displacement
during the compression process is different from that at
the same displacement during the retraction process. The
discussion above has revealed that the delay in the transfer
of forces and the friction are one of the causes of the hysteresis of the generative force.
2.2.8 Comparison Between Experimental and
Simulation Results
To verify the adequacy of the simulations and determine
the generative force characteristics under different conditions, we conducted experiments under different conditions and compared the results with the simulation results.
Figs. 12 to 16 show the generative force-displacement
curves obtained from the experiments under the reference
conditions as well as under another set of conditions
where the packing fraction, excitation frequency, particle
material and particle size were changed from the reference conditions, along with the results of the simulations.
The particle material was changed from the reference
conditions in that only the Young's modulus of particles
was changed.
According to Figs. 12 to 16, the simulation results are ingood agreement with the experimental results both qualitatively and quantitatively. Like under the reference conditions, the generative force shows gradually hardening
characteristics during the compression process or hysteresis after the transition from the compression process to
the retraction process, regardless of the packing fraction,
excitation frequency, particle material or particle size.
Figs. 12 to 16 also show how the generative forcechanges under different conditions. Its peak and hysteresis
substantially change with the packing fraction and theYoung's modulus which affects the particle material. They
do not change so much with the excitation velocity or(c)Force [N]Rod

Experiment
Analysis

Piston(d)Fig. 11 Distribution of particle compression(a) Compression process, z = 0(b) z = 5(c) Retraction process, z = 0(d) z = -5

Displacement [mm]Generative force-displacement curves;
Experiment-simulation comparison
Under reference conditions (packing fraction 0.60, excitation
frequency 1 Hz, Young’s modulus 4.08 MPa, particle size
φ3 mm)
Fig. 12― 30 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Experiment
Analysis

Force [N]Force [N]Experiment
Analysis

Displacement [mm]Displacement [mm]Fig. 13G enerative force-displacement curves; Experimentsimulation comparison
With packing fraction changed (0.70)

Fig. 16Since the generative force characteristics are found to
be qualitatively the same under the different conditions,the particles in the damper should generally behave in asame way. It can now be concluded that the simulations
reliably reproduce the phenomena which occurred in theexperiments.

Force [N]Experiment
Analysis3

Displacement [mm]Fig. 14

Generative force-displacement curves; Experimentsimulation comparison
With particle size changed (φ5 mm)

Generative force-displacement curves; Experimentsimulation comparison
With excitation frequency changed (5 Hz)

Characteristics of Generative Force ofParticle Damper with Both Chambers Filled

3.1 Damper Structure
Fig. 17 shows the general structure of the damper used
for the simulations and experiments. The only difference
from the damper described in Chapter 2 is that both chambers divided by the piston are filled with particles. In thecase where both chambers are filled with particles, thechamber without the rod is called Chamber A and thatwith the rod Chamber B.

Force [N]Experiment
Analysis

Section A-A

Displacement [mm]Generative force-displacement curves; Experimentsimulation comparison
With material changed (Young’s modulus 17.6 MPa)

Fig. 15

particle size. The reason for the minor effect of excitation
velocity is the very small effect of viscosity according to
the simulation results. The reason why the particle size
does not influence so much is that, if larger particles areused, the particles would have larger deformation as thedisplacement advances but would have lower friction ofparticles against the cylinder due to the lower number ofparticles. This lower friction was a probable cause of why
the generative force did not increase so much.

Fig. 17 Damper structure
1. Cylinder, 2. End cover, 3. Bearing, 4. Rod, 5. Piston, 6.
Elastomer particles
Unit: mm

3.2 Simulations and Experiments
3.2.1 Simulation and Experimental Conditions
Table 3 shows the simulation conditions. Table 4 showsthe experimental conditions. The simulation methods,
primitive equations and experimental conditions describedin Chapter 2 were also used in these simulations andexperiments. The simulations and experiments in this
Chapter were conducted only under the reference conditions described in Chapter 2 because the generative force
characteristics have been generally verified in Chapter 2.

― 31 ―

Research on Particle Assemblage Damper

Simulation conditions

Table 3

Load cell

Particle material

Silicone rubber (TSE 3466)Particle size [mm]3

Packing fraction [-]0.60

Number of particles

2533

Stroke [mm]10

Excitation frequency [Hz]1Time increments [sec.]

5.0×10-9

Excitation waveform

Sinusoidal

Particle density [kg/m3]

1.10×103

Poisson ratio of particle vi

0.5

Friction coefficient μf(wall-particles)

0.5

Friction coefficient μf(between particles)

0.5

Young's modulus Ew [GPa](wall)

210

Young's modulus Ei [MPa](particle)

4.08(TSE3466)

Viscosity coefficient α

0.5311

Table 4

➡Direction of stroke➡Force applied to cylinder bottom by particle compression
and friction➡Force applied to cylinder wall by particles(a)Load cell➡Direction of stroke➡Force applied to cylinder bottom by particle compression
and friction➡Force applied to cylinder wall by particles(b)Force applied to cylinder bottom in the z-axis
direction(a) Positive displacement, (b) Negative displacement

Fig. 18

Experimental conditions

Particle material

Silicone rubber (TSE 3466)

Young's modulus Ei [MPa](particles)

4.08(TSE3466)Particle size [mm]3

Packing fraction [-]0.60

Stroke [mm]10

Excitation frequency [Hz]1

3.2.2 How to Calculate Generative ForceIn the simulations of the particle damper with both of its
chambers filled, the force applied to the cylinder bottom
Dz shown in Fig. 18 can be determined by adding thecompressive force applied to the cylinder bottom in thez-axis during particle compression by the piston to thefrictional force of particles against the cylinder wall in thez-axis direction. For simulations of a damper with bothchambers filled with particles, the force applied to the rod
end Rz shown in Fig. 19 can be determined by adding thecompressive repulsion applied to the rod end in the z-axis
during particle compression by the piston to the frictional
force of particles against the rod wall in the z-axis direction. There is a balance between Dz and Rz.
The normal component of the generative force is attributable to Viscoelasticity generated by compressive deformation of particles. The tangential component of the― 32 ―

Load cell➡Direction of stroke➡Force applied to piston by particle compression and friction
as well as friction of particles against cylinder wall
➡Force applied to rod wall by particles(a)Load cell➡Direction of stroke➡Force applied to piston by particle compression and friction
as well as friction of particles against cylinder wall
➡Force applied to rod wall by particles(b)Fig. 19 Force applied to rod end in the z-axis direction(a) Positive displacement, (b) Negative displacement

KAYABA TECHNICAL REVIEW No. 64 APR. 2022

friction of particles against the rod wall, and the tangential
friction of particles against the cylinder wall. The asymmetry of the generative force curve to the origin is attributable to the contact force of particles against the rod
located in Chamber B. This issue will be verified later inthe section discussing the results related to the generative
force Rz.
Fig. 21 shows that the generative force and its normal
and tangential components' peak at a point slightly shiftedfrom the 0 m/sec. velocity. Without the influence of viscosity, the force-displacement curve should peak at the
point of 0 m/sec. velocity. According to Equations (6) and(7), the velocity only affects the normal/tangential viscosity. Therefore, the maximum generative force occurs at apoint slightly shifted from 0 m/sec. probably because of
the effect of viscosity.
Then, another simulation was conducted with a focus
on the force applied to the rod wall as shown in Fig. 19.

Force [N]Generative force
Force applied to cylinder wall
Remaining component

Displacement [mm]Fig. 20

Force-displacement curves of generative force Dz,
force applied to cylinder wall and remaining
component
Generative force
Force applied to cylinder wall
Remaining component

Force [N]generative force is attributable to Viscoelasticity generated by shear deformation of particles and the sliding
friction of particles against the cylinder or rod wall.
Therefore, determining Dz will identify the friction ofparticles against the cylinder wall and determining Rz will
identify the friction of particles against the rod wall.
3.2.3 Generative Force and its Breakdown
As shown in Fig. 18, simulations were conducted with afocus on the force applied to the cylinder wall. The simulations produced the results shown in Figs. 20 and 21. Fig.
20 shows the generative force Dz that changes with displacement under the reference conditions, the tangential
component of Dz applied to the cylinder wall, and theremaining component. Fig. 21 shows the generative force
Dz that changes with velocity under the same conditions.
The remaining component was determined by subtracting
the tangential component applied to the cylinder wallfrom Dz. According to Fig. 20, the generative force shows
hardening characteristics and involves hysteresis after the
direction of displacement changes. In general, themaximum generative force during the negative displacement in which the particles in Chamber B are predominantly compressed is larger than the maximum generative
force during the positive displacement in which the particles in Chamber A are predominantly compressed. The
curve of the generative force is asymmetrical with respect
to the origin. Like the damper with one of the chambers
filled with particles, this damper also delivers the generative force with gradually hardening characteristics probably because of the effect of the elastic repulsion due toparticle compression. The hysteresis is attributable to theviscosity due to deformation of the elastomer particles
and/or the effect of the particle-particle or particle-wall
friction. The generative force has been plotted to be a nonlinear curve probably because, as the piston moves toward
Chamber B where the rod exists to increase the displacement, the particle-rod friction increases.
The next step is to discuss the generative force characteristics based on the force applied to the cylinder walland the remaining component. Fig. 20 indicates that, as
the displacement advances in each direction, both theforce applied to the cylinder wall and the remaining component increase. In this process, the force applied to thecylinder wall abruptly jumps when the direction of displacement changes. After a certain point of displacement,
the force mildly increases to show gradually hardening
characteristics. On the other hand, the remaining component involves this gradually hardening characteristics all
the time. So, the hysteresis is considered to be greatly
influenced by the force applied to the cylinder wall. The
maximum generative force is attributable to the force
applied to the cylinder wall and the remaining component
to almost the same extent. Here again, as in Fig. 18, thegenerative force applied to the cylinder bottom on the side
without the rod consists of the normal compression generated when the piston compresses particles, the tangential

Velocity [mm/sec.]

Fig. 21

Force-velocity curves of generative force Dz, force
applied to cylinder wall, and remaining component

Fig. 22 shows the generative force Rz that changes withdisplacement under the reference conditions, its tangential
component applied to the rod wall, and the remaining
component. The remaining component was determined bysubtracting the tangential component of the force applied
to rod wall from Rz. The only difference from Dz is that theforce applied to the rod wall shows gradually hardening― 33 ―

Research on Particle Assemblage Damper

characteristics during the negative displacement, andincreases until the displacement increases to a certain
positive level and then gradually decreases until it gets
down to about 0 N. The remaining component shows
almost the same characteristics as those of the generative
force however considerably differs from the generative
force in the negative displacement region. The force
applied to the rod wall shows gradually hardening characteristics as the friction of particles against the rod wall,
which acts as vertical resistance, increases due to theincrease in particle compression in Chamber B caused bynegative displacement. During the positive displacement,
the friction of particles against the rod wall decreases
because the particle compression in Chamber B decreases.
Furthermore, this force applied to the rod wall makes thegenerative force asymmetrical with respect to the origin.
The gradually hardening characteristics of the remaining
component is attributable to the compressive repulsion ofparticles and the friction of particles against the cylinderwall, which acts as vertical resistance. The hysteresis is
attributable to the friction of particles against the cylinderwall.
Now the force applied to the cylinder wall shown in Fig.
20 can be compared with the force applied to the rod wallshown in Fig. 22. It is obvious that the force applied to therod wall is smaller. This is because the rod has a smaller
outside diameter than the cylinder bore. In other words,
since the rod perimeter has a smaller surface area, the rod
is affected by particle friction to a smaller degree than thecylinder is affected by the same.
From the above, the discussion about Dz and Rz can besummarized as follows. The generative force in Chamber
A mainly consists of the normal repulsion generated
during particle compression by the piston and the tangential friction of particles against the cylinder. In Chamber
B, the tangential friction of particles against the rod is
added to the forces stated above to constitute the generative force. Furthermore, the generative force, the force
applied to the cylinder wall, and the remaining component
peak at a point shifted from the 0 m/sec. velocity as shownin Fig. 21. This implies that these forces are affected by
the viscous force of elastomer particles.

Force [N]Generative force
Force applied to rod wall
Remaining component

Displacement [mm]Fig. 22 F orce-displacement curves of generative force Rz,
force applied to rod wall, and remaining component

3.2.4 Elasticity and Viscosity of Force Applied
to Cylinder or Rod Wall and of Remaining
Component of Generative Force
To verify the effect of viscosity described in the previous section, the force applied to the cylinder or rod walland the remaining component of the generative force weredivided into elasticity and viscosity.
Fig. 23 shows the force-displacement curves of theforce of Dz applied to the cylinder wall and its elasticity
and viscosity. Fig. 24 shows the force-displacement
curves of the remaining component of Dz and its elasticity
and viscosity. Fig. 25 is an enlarged view of Fig. 24
showing the viscosity.
According to Fig. 23, the force applied to the cylinderwall only consists of the friction of particles against thecylinder. No elastic or viscous force is generated due toshear deformation of particles. Like the discussion about
the tangential component of the generative force in theparticle damper with one of the chambers filled, thisdamper also has sliding of particles against the cylinder inthe tangential direction all the time. According to Fig. 24,
the remaining component consists predominantly of elasticity with gradually hardening characteristics and hysteresis. The remaining component is generally in good
agreement with the elasticity. Therefore, like the normalcomponent of the particle damper with one of the chambers filled, this damper also delivers the generative force
whose remaining component consists predominantly ofthe elastic repulsion due to compressive deformation ofparticles. The effect of the viscous force generated during
particle deformation is very small. Unlike the normalcomponent of the particle damper with one of the chambers filled, this damper delivers the generative force
whose elasticity involves hysteresis. This is because theelastic modulus finally formed by the particle groups
filled in chamber A and chamber B are different in eachchambers. Another reason is, according to Fig. 18, that theelastic force of this damper includes the frictional force ofparticles against the rod. Therefore, properly speaking,this is not an elastic force or elasticity, but it is called here
an elastic force or elasticity for convenience purposes.
The viscous force never takes a value of zero (0). Rather,a minute viscous force is generated as shown in Fig. 25.
Fig. 26 shows the force-displacement curves of theforce of Rz applied to the rod wall and its elasticity andviscosity. Fig. 27 shows the remaining component of Rz
and its elasticity and viscosity. Fig. 28 shows an enlarged
view of the viscosity curve in Fig. 27.
According to Fig. 26, like Dz, Rz also comes with theforce applied to the rod wall only consisting of the frictionof particles against the rod. No elastic or viscous force isgenerated by particle deformation. This means that particles around the rod are sliding all the time. According to
Fig. 27, like Dz, Rz also comes with the remaining component consisting predominantly of elasticity with graduallyhardening characteristics and hysteresis. The remaining― 34 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

reason is, according to Fig. 19, that the generative force of
this damper includes the friction between the cylinder andparticles. Like Dz, Rz also includes a minute viscous force
as shown in Fig. 28.
Now it may be useful to compare the generative force
characteristics of this elastomer particle damper with therepulsion characteristics of cylindrical or other-shapedelastomer blocks during compression. When elastomer
cylinders are compressed, many of them produce thegenerative force that depends on the displacement andinvolves viscoelasticity with hysteresis. In this damper inturn, friction of elastomer particles against the cylinder orForce [N]Force applied to cylinder wall
Elasticity
Viscosity

Displacement [mm]Fig. 23 F orce-displacement curves of component ofgenerative force Dz applied to cylinder wall andits elasticity and viscosity

Force [N]Force applied to rod wall
Elasticity
Viscosity

Force [N]Remaining component
Elasticity
Viscosity

Displacement [mm]Fig. 26 F orce-displacement curves of component ofgenerative force Rz applied to rod wall and its
elasticity and viscosity

Displacement [mm]Fig. 24 F
 orce-displacement curves of remaining
component of generative force Dz and its
elasticity and viscosity

Force [N]Force [N]Remaining component
Elasticity
Viscosity

Displacement [mm]Fig. 27 F orce-displacement curves of remaining
component of generative force Rz and its
elasticity and viscosity

Displacement [mm]Enlarged view of force-displacement curve ofviscosity of remaining component (in Fig. 24)component is generally in good agreement with the elasticity. Properly speaking, according to Fig. 19, this is not
an elastic force because the elasticity in Fig. 27 consists ofthe elastic repulsion of particles during compressive
deformation and the friction between the cylinder andparticles, but it is called here an elastic force or elasticity
as in the case of the force applied to the cylinder wall andthe remaining component. The reason why the elastic
force involves hysteresis is that, like Dz, the chambers
show different non-linear Young's modulus values
depending on the presence/absence of the rod. Another

Force [N]Fig. 25

Displacement [mm]Fig. 28― 35 ―

Enlarged view of force-displacement curve ofviscosity of remaining component (in Fig. 27)

Research on Particle Assemblage Damper

Rod

Piston(a)Rod

Piston(b)

Rod

Piston(c)

Rod

Piston(d)Fig. 29 Distribution of particle compression(a) Compression process, z = 0(b) z = 5(c) Retraction process, z = 0(d) z = -5

Experiment
Analysis

Force [N]rod wall occurs to greatly affect the generative force.
Thus, the generative force of this damper shows higher
hysteresis in comparison with the characteristics of theelastomer block of the same volume when it is compressed.
3.2.5 Distribution of Particle Compression
Like the particle damper with one of the chambers
filled, this damper with both chambers filled also produces
the generative force Dz heavily dependent on the othercomponents than that applied to the cylinder wall, that is,particularly the elastic force in the normal direction. Then,
we tried to determine the effect of the compressive force
applied to particles filled in the damper. Fig. 29 (a) to (d)show where the piston and particles are located in thedamper when viewed from section A-A in Fig. 17 and the
distribution of particle compression. The compressive
force applied to particles in these diagrams is due to theelasticity in the normal direction.
In Fig. 29 (a), as the piston travels in the direction of
positive displacement, many of the particles close to thepiston in Chamber A are highly compressed while manyof the particles close to the cylinder bottom are weakly
compressed. In Chamber B, many of the particles close to
the piston are weakly compressed while many of the particles close to the cylinder bottom are highly compressed.
This means that, as the piston travels in the direction of
positive displacement, the force applied to the piston by
the particles in the Chamber A increases while the force
applied to the piston in Chamber B decreases. This phenomenon also takes place when the piston travels in the
opposite direction as shown in Fig. 29 (c). However, acomparison between Figs. 29 (a) and 29 (c) reveals that
Chamber B in Fig. 29 (c) has a greater number of highly
compressed particles than in Chamber A in Fig. 29 (a)while Chamber A in Fig. 29 (c) has a greater number of
weakly compressed particles than in Chamber B in Fig. 29(a). This means that the compressive force applied toparticles in Chamber B during displacement in the negative direction has greater influence. This is probably
because Chamber B has a smaller volume than Chamber
A by the volume of the rod, thereby giving particles
smaller space to escape in Chamber B. As a result, particle
compression in Chamber B is started at a smaller displacement than in Chamber A. In addition, a delay in the transfer of the force due to particle deformation can be foundin Fig. 29 as in the case of the damper with one of thechambers filled.
3.2.6 Comparison Between Experimental and
Simulation Results
To verify the adequacy of the simulations, we conducted
experiments and compared the results with the simulation
results. Fig. 30 shows the generative force-displacement
curves obtained from the experiments and simulations.
According to Fig. 30, the simulation results are in good
agreement with the experimental results both qualitatively
and quantitatively. It can now be concluded that the simu-

Displacement [mm]Fig. 30 G enerative force-displacement curves; Experimentsimulation comparison― 36 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

lations reliably reproduce the phenomena which occurredin the experiments, as in the case of the damper with oneof the chambers filled.

4

Concluding Remarks

In this study, an investigation and discussions wereconducted to clarify the generative force characteristics
and force generation factors of a separated dual chamber
single rod-type damper using elastomer particles for thetwo cases of one of the chambers filled and both chambers
filled.
When only one of the chambers is filled with particles,
the generative force shows gradually hardening characteristics along with hysteresis and is greatly affected by theelasticity in the normal direction and the friction in thetangential direction. This elasticity is mainly attributable
to the compressive repulsion of particles during compression. The friction here indicates the sliding friction ofparticles against the cylinder. Increasing the packing fraction, the excitation frequency, the Young's modulus which
affects the particle material, and the particle size will raise
the maximum generative force and hysteresis. In particular, the packing fraction and Young's modulus strongly
affect the generative force.
With both chambers filled with particles, the generative
force shows gradually hardening characteristics alongwith hysteresis and is affected by the frictional force
applied to the cylinder and rod walls in the tangential
direction and the elasticity included in the remaining
component, as in the case of the damper with one of thechambers filled. The force-displacement curve of thegenerative force is asymmetrical with respect to the origin
because of the frictional force applied to the rod wall.
The results of DEM-based simulations of a damper with
one of the chambers filled and a damper with both chambers filled were in good agreement with the experimental
results both qualitatively and quantitatively. This has
proved that the simulations reliably reproduce the phenomena which occurred in the experiments.

This report has now successfully clarified the generative force characteristics and force generation factors.
A future challenge is to enhance the accuracy of discussions and analyses. This report has mainly discussed thegenerative force based on its force-displacement curves
and distribution of particle compression. Rather, weshould determine the variations in elastic modulus ofparticles and the amount of particle deformation in theanalysis process and then verify them in connection withthe equations used for analysis. Furthermore, when considering to commercialize the damper, we also need todetermine how the generative force changes with the sizeof the piston or the length of the particle chambers and toclarify advantages and disadvantages of this damper compared with other types of dampers.
Note) This report has been prepared by re-editing the FY2020
doctoral dissertation thesis in Nagoya Institute of Technology: Generative Force Characteristics of Separated Dual
Chamber Single Rod-type Particle Damper Using Elastomer Particles.

References
1) IDO Y, HAYASHI K: Damping Force of Damper Utilizing a
Spherical Particle Assemblage, Proceedings of 15th International
Conference on Experimental Mechanics, 2012, Paper ref: 2714.
2) MORISHITA Y, IDO Y, MAEKAWA K, TOYOUCHI A: Basic
Damping Property of a Double Rod Type Damper Utilizing an
Elastomer Particle Assemblage, Advanced Experimental
Mechanics, Vol. 1, 2016, pp. 93-98.
3) P.A. Cundall, O.D.L. Strack: A Discrete Numerical Model for
Granular Assemblies, Géotechnique, Vol. 29, Issue I, 1979, pp.
47-65.
4) R.D. Mindlin: Compliance of Elastic Bodies in Contact,
Transaction of ASME, Series E, Journal of Applied Mechanics,
Vol. 16, 1949, pp. 259-268.
5) The Japan Society of Mechanical Engineers, JSME MechanicalEngineers' Handbook, Vol. 6, 1977, pp. 3-34, Maruzen
Publishing Co., Ltd.

Author 
TOYOUCHI Atsushi
Joined the company in 2009
New Products Development Sect.,
Developmental Center, Engineering
Headquarters, Automotive
Components Operations
Engaged in research anddevelopment of particle assemblage
dampers― 37 ―

Construction of Case Machining Line for Piston Pump

Technology
Introduction

Construction of Case Machining Line for Piston Pump
ITOU Yuusuke

1

Note 1) An abbreviation for piston pump motor
Note 2) A system that controls the pump discharge to supply theflow as much as needed

Introduction

PPM Note 1) products manufactured in KYB Sagami Plant
include piston pumps (Fig. 1). The piston pump is used as
a component of hydraulic excavators. One of the components of the piston pump is a pump case (Photo 1) (hereinafter "the case"), which is the core part of the pump.
With the recent rising market demand for environmental measures and energy saving, the demand for piston
pumps with a load sensing control Note 2) is expected toincrease (Fig. 2). We are thus required to manufacturecompetitive products of this kind. Among the piston pump
manufacturing processes, the one involving the highest
manufacturing cost ratio is case machining. It is therefore
indispensable to reduce the cost. Then, in preparation for
the establishment of a new production line, we have successfully established a level of quality, which had been
hardly accomplished before, to achieve higher availability
and shorter cycle time (hereinafter "CT"). We have finallybuilt a production line that can realize lower manufacturing costs.

Production volume

Fig. 1

Piston pump

Photo 12

2.1 Case Machining LineThe pump case machining line consists of machining
centers (hereinafter "MC"), deburring, rough cleaning,inspection, and jet cleaning (Fig. 3).

Note 3)

Material

Fig. 3

Inspection

Jetcleaning

Finishedproduct

Manufacturing process

2.2 Problems
The MCs can provide an integrated process Note 4). EachMC can deliver finished products by itself. The problem isthat, after products have been machined, they are measured on the same MC, resulting in a long cycle time.
Dimensional correction is conducted as the necessity
arises, which leads to lower availability. In addition, thepump case is a heavy workpiece (18 kg) to be lifted using
a crane. This dangerous work is a factor in the long manual
handling operation.
Note 4) A single MC can support all related processes.

Production 1.4 times
the benchmark

3

PurposeTo improve productivity to build a production line forlower manufacturing costs.

2021 2022 2023 2024 2025 2026
Fiscal year

Fig. 2

DeburringRoughcleaning

Note 3) Machined product

Pump case

BenchmarkLine Overview and Challenges

4

Objective

Table 1 shows the target values.

Estimated production volume of piston pumps― 38 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022
Table 1
Item

Target (from theconventional level)

Production volume

33% upAvailability

6% up

Cycle time

27% down

Personnel

1 person reduced

Case
Spindle180-degree turn
Bore on the front (a)SpindleMisalignment

Bore on the back (b)Overview of front/back machining of caseFig. 4

Requirements

Variations in outside
air temperature

Displacement① The machining accuracy shall be improved to ensure
the required quality without relying on human operation.
② The machining rate shall be increased to reduce themachining time (hereinafter "MT").
③ Work handling shall be achieved without using a crane
to remove dangerous tasks.

Outside air temperature (°C)

5

Target values

Displacement
6

Achievements

Equipment displacement

6.1 No more 100% measurement in MCs
6.1.1 Conventional Quality Problems
The case has two holes as its critical parts: one is on thefront and the other on the back (Photo 2). In fact, alignment of these holes (coaxiality) was difficult to beobtained (Fig. 4), resulting in 100% manual measurementand dimensional adjustment. These additional tasks
degraded the availability and productivity. The casemachining was conducted by turning the machining tableby 180 degrees to machine the front or the back or viceversa. Naturally, the machining quality was affected by
the equipment accuracy. This was found to be attributableto variations in outside air temperature superimposed by
the heat generated during continual machining, whichdisplaced the equipment, resulting in unstable machining
positions (Figs. 5 and 6). To follow any displacement of
the equipment due to temperature variations, temperature
sensors and temperature control systems needed to be
added, which meant even higher capital investment.

(a) Front(b) Back
Photo 2

Bore

Fig. 5External temperature

Equipment displacement due to outside airtemperature
SpindleOrigin ofmachineTable

Center ofrotation

Reference
position
Displacement

Equipment is displaced withoutside air temperature.

Fig. 6

X-axisConceptual rendering of displacement

6.1.2 Internal Measurement using Touch
Sensors
High capital investment leads to high manufacturingcosts. So, a software program has been developed tomeasure displacement or deviation from the reference
position using the touch sensors already mounted on theequipment and compensate for any displacement toachieve the machining target values (Fig. 7).
① Measure the position of holes provided in the jigs andthen establish reference values as initial settings forequipment introduction② Before mass production, measure the position of theholes in the jigs before machining and add any deviation from the reference value to the machining target
value
If the equipment is displaced during mass production,
the hole position in the jig changes. That is, the deviation― 39 ―

Construction of Case Machining Line for Piston Pumpfrom the initially set reference value will be the displacement of the equipment.
This measurement has made it possible to satisfy the
coaxial front and back machining capability. The 100%
measurement during mass production is no longer necessary to achieve shorter CT. The dimensional adjustment
has been also abolished to eliminate any adjustment loss,
thus improving the availability.

Down milling→ Resistance applied in a direction
opposite to the direction of travel
ResistanceResistance

Rotation
Up milling→ Resistance applied in
the direction of travel

Equipment
preparation

Record the position
as reference

ResistanceResistance

Feed

Cutterrotation

Up milling

Resistance

Jig hole(position
sensing)

Measure the positionof jig holes
Massproduction

Down milling

Rotation

Resistance
Measure the positionof jig holes

Path

Feed

Resistance occurs in two directions,which is likely to cause chattering

Work

Fig. 9Calculate deviationfrom the reference

Milling (before change)

Add the deviation to
the coordinate system

Down milling

CutterrotationFig. 7 Program flow and machining jig

Resistance

6.2 MT Reduction with Optimal Milling Path
Among the case machining processes, milling is themost time-consuming one (Fig. 8). In the conventional
milling technique, the milling cutter moves along theshortest path to accomplish the required machining. Since
50% of the perimeter of the cutter was used for milling,
the cutter involves mixed operation of up milling anddown milling. In fact, this resulted in unstable cutting
resistance, which might cause chattering (Fig. 9). The
milling machine eventually machined work at a lower
speed, resulting in a prolonged MT.
To solve the problem, an optimal milling path has beendeveloped to be suited to the complex geometry of thecase (Fig. 10). The cutter has then become able to machine
only with down milling being applied with cutting resistance in a fixed direction, successfully suppressing chattering. The machining speed has been doubled to reduce
the MT.

Path

Constant resistance to suppress chattering

Fig. 10

Milling (after change)

6.3 Reduction of Manual Handling Time by
Improving Jig Installability
The horizontal MC uses cross jigs for machining thecase. Work must be set in position horizontally (Fig. 11).
Lifting the heavy work involves danger tasks. The use ofa crane makes it difficult to accurately position work,
taking more time to complete attaching or detaching. As aresult, the target manual handling time cannot be met.

Work

Jig

Machining time

Install・May drop
・No support

ø100 milling cutterø25 reamer
ø40 milling cutter
ø4.8 drill
M6 formed tool
Touch sensor
ø12.5 reamer
ø16.0 end mill
ø24.97 burnisher
M6 tapø10.3 drill
M12＊1.75 tap
ø32.8 formed toolR-chamfered drill
PF 3/4 formed tool
ø24 T-slot cutter
ø25 formed tool
PF 1/4 formed toolFig. 11

Fig. 8

Machining time of individual processes

Conventional way of setting work

To solve the problem, a jig that can allow the operator to
set heavy work without lifting using a crane has beendeveloped (Photo 3).
When loading, the work is slid into the jig from thecarrier cart and guided by the jig for temporary positioning. The operator can just push the work to the end toaccomplish final positioning with the aid of tapered pins
― 40 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

(Photo 4). With improved operability of jig setting, thework attach/detach time has been reduced by 50% and themanual handling time in the total production line has been
reduced by 20%.

7

Results

The target values have been achieved. The results areshown in Table 2.
Table 2

Fall prevention

Tapered pin(positioning)

Results

Item

Achievements (from theconventional level)

Production volume

36% upAvailability

14.7% up

Cycle time

27% down

Personnel

1 person reduced

Guiding

8

Jig overview

Photo 3A new measurement method has been developed toachieve the process capability for the machining accuracy
that was difficult to be achieved before. A new production
line has been built to no longer involve dangerous tasks or
no longer put a load on operators.
We will deploy this technique to realize new products atlower costs in future.

Work is slid into position
Jig

Carrier cart

Cart can slide
up to jig

Photo 4

Conclusions

9

In Closing

I would like to take this opportunity to thank all thoseconcerned from related functions who extended cooperation to the building of this production line as well as all
those who gave guidance and support to us.

Work in position

Author 
ITOU Yuusuke
Joined the company in 2017.
Production Engineering Sect.,
Production Engineering Dept.,
Sagami Plant, Hydraulic Components
Operations
Mainly in charge of design of pump
manufacturing process for PPM
products― 41 ―

Development of Shock Absorbers for Snowmobile Racing

Product
Introduction

Development of Shock Absorbers for Snowmobile Racing
TANAKA ShinIntroduction

KYB Motorcycle Suspension (hereinafter "KMS")
designs and manufactures shock absorbers (hereinafter“SA”) for domestic and overseas motorcycle manufacturers. KMS also designs and manufactures shock absorbers
for snowmobiles and ATVs and has been in business withBRP Inc. Note 1) and BRP Finland Oy. Note 2) over 30 years.
They lineup snowmobiles called Ski-Doo and Lynx Note 3)
known as a major brands in North America and Nordic
Countries and they gained to have a majority share of the
global market in 2020. 1) High-performance SA used in thehigh-end snowmobiles of both brands are designed andmanufactured by KMS.
As snowmobiles have become technologically innovative, many state-of-the-art technologies have beenreflected in their SAs. All of these technologies wereoriginally developed for snowmobile racing and they canbe found everywhere in today’s mass-produced SAs forsnowmobiles.
This paper introduces development of technologies thatcan be found in our high performance SAs.
Note 1) BRP Inc. originated with the invention of the first evervehicle that can travel on snow by Joseph-Armand Bombardier at Valcourt in Quebec, Canada. L’Auto-Neige
Bombardier Limité was established in 1942. In 1959, theSki-Doo brand was born. In April 2003, Bombardier Inc.
announced the sale of the Bombardier Recreational
Products division.
Note 2) A forerunner of BRP Finland Oy was Nordtrac, which
was the only snowmobile manufacturer in Nordic countries and became BRP Finland in 2005, it has continuously produced the Lynx brand. Lynx is still the only
snowmobile brand in the Nordic countries.
Note 3) Ski-Doo and Lynx are the trademarks of BRP.

2

Snowmobiles Information

2.1 Vehicle Lineup
Snowmobile manufacturers offer a wide variety ofvehicles that suit riders’ preferences such as sport/utility
models used as heavy duty work horses on snow, comfort-

able touring models, trail models for high-speed aggressive rides on groomed trails, crossover models that shine
both on and off the trails, and deep snow models specifically designed for riding in the steep mountains covered
with deep snow. Many package options are available foreach model and industry’s first semi-active SAs (KADS 2))
can be selected as an option for high-end package of trail
and crossover models in order to have advanced shock
absorption, handling and stability control. Weight savingsare critical for deep snow models so lightweight highperformance SAs are chosen to improve maneuverability
in the mountain terrain with steep slopes. Characteristics
of snowmobile SAs required in various riding conditions
are shown in Fig. 1.

Weight → Light

1

Shock Absorption/Stability Control → High
Fig. 1

Characteristics of snowmobile SAs for each models

2.2 Suspension design
Snowmobiles are quite different from motorcycles or
ATVs because they have skis and track to be able to driveon the snow (Fig. 2).
The skis will float and steer a snowmobile to be able tobe controlled by a handlebar on the snow. Generally, skis
are suspended by double wishbone suspension. This
design makes it possible to have a wider ski stance while
ensuring longer suspension stroke in order to achieve
higher steering stability. The right and left skis are bothsuspended by independent suspensions and front shocks
are mounted on each side.
The track will make it drive forward on snow using its― 42 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Front Shocks

Rail

Track

Ski
Center ShockFig. 2

Rear Shock

Components of snowmobile suspension

lugs while keeping it floating on the snow by enlarging thecontact area. There are many track styles that suit any
riding conditions. Some have studs in order to have traction on hard, icy trail surfaces while some have longer
lugs in the paddle form to be able to run on deep snow.
Center and Rear Shocks will control the movement of therail to keep the track in contact with rough, bumpy trails.
2.3 SA Structure
Snowmobiles are equipped with gas filled shock absorbers (hereinafter “Gas SA”) that use a steel or aluminum
monotube cylinder as a standard package. (hereafter "gasSA"). All Gas SAs have Spring Preload adjuster but also
some have Rebound adjuster to control Rebound Damping
Force. (Fig. 3).
For the high-end package, Remote Gas SAs or Piggyback Gas SAs that have Base Valve with Compression
Adjuster are equipped since much more shock absorption
and stability controls are requested. (Figs. 3 and 4).
Regardless of which package they are used for, all SAs
are using specially developed parts in order to be operated
in specific environment conditions. The examples are in
the following.

Gas-filled valve
Springpreloadadjuster

Compression
adjusterSpringpreloadadjusterGas-filled valve
Aluminium light-weightcylinderRebound adjuster
Rebound adjuster

Fig. 3

Lightweight aluminium single cylinder gas SA (left)
and piggyback gas SA (right)

・ Ice scraper:
Integrated Ice Scraper in the seal head to scrape off
frozen snow on Piston Rod surface (Fig. 5)
・ Oil:
Specially formulated to ensure fluidity in freezing condition
Compression
adjuster

Rebound adjuster
Oil

Base valve

Low Temp Compatible Seal
Ice Scraper

Spring preload adjuster

Fig. 4

Piggybackguide cylinder

Base valve

Components of piggyback gas SA― 43 ―

Development of Shock Absorbers for Snowmobile Racing

・ Low-temperature seal:
Carefully chosen seal material to keep Oil in SA in
freezing condition

Fig. 6

Fig. 5

 rozen ice covered Center Shock at the racingF
paddockFig. 7

3

Ski-Doo MXZx 600RS Note 4)

Types of Snowmobile Racing

Lynx Rave 600RS Note 4)

Note 4) MXZx, Rave and 600RS are trademarks of BRP Inc..

There are various kinds of snowmobile races as in thecase of other motorsports. The following describes major
categories of snowmobile races.
3.1 Snowcross
Snowcross was derived from the sport of motocross.
Like motocross, riders compete with each other on manmade racetracks with tight turns, banked corners, steep
jumps and obstacles.
Today, Snowcross are held are held at many locations inNorth America and Nordic countries. Courses in North
America include consecutive jumps and tight corners,
thereby requiring harder braking and rapid acceleration.
On the other hand, many of the courses in the Nordic
countries make use of original natural terrains. Since thesecourses are usually wide, racers are likely to run at higher
average speeds. The International Series of Champions(ISOC) Snocross, which are held around Great Lakes inNorth America, are participated in by famous competitors
not only from North America but also from the Nordic
countries. The world's premium race riders compete in a
total of 17 races at eight racing venues every year vying
with each other to clinch the championship title.
Both Ski-Doo and Lynx have lineups for the racingready snowmobile specific for Snowcross called 600RS
that is only available for snowcross competitors (Figs. 6
and 7). They are developed based on Trail snowmobiles
but equipped with a fine-tuned 600cc two-stroke engine
and race-proven special suspension system.
KMS has been providing specially designed SAs called“Factory Shocks” to BRP Racing Department and joining
BRP’s Racing program to develop better SAs by supporting them technically.

3.2 Hill Climb
Riders compete on how fast they can climb up ski slopes
with specially modified Deep Snow snowmobiles. The
most famous race is the World Championship Snowmobile Hill Climb that is held at Jackson Hole in March.
3.3 Cross-country
Competitors run a long distance toward a specified
destination with the Crossover snowmobile like Dakar
Rally. The most famous race is the Iron Dog in Alaska.
Competitors race over 4,000 km in a week and may berequired to ride on dirt, grass or skipping over frozen
rivers.
3.4 Others
Oval racing competitors corner on icy oval racetracks at
the highest speed with specially modified, lowered snowmobiles. Drag racing can record the highest speed on ashort, straight course. Snowmobile racing is not only heldin winter; Watercross is getting popular, competitors skip
snowmobiles on a lake to race like snowcross.

4

Development of SA for SnowcrossThe following are the major functions that are required
specially for Snowcross SA.
4.1 Front ShockTo prevent rolling moment during high-speed corneringin order to keep skis in contact on the trail, Front Shocks
need to provide a certain amount of damping force fromlower piston speed range. In addition, Front Shocks have
longer shock strokes to accommodate the larger gaps andjumps found on recent racetracks.

― 44 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

4.2 Center and Rear Shocks
Center and Rear Shocks will stabilize the snowmobile
by controlling the rear suspension system and keep therail tracks on bumpy racetracks. Center Shock attached to
the front of the rail needs to be supple enough to help therail to follow the rough track surface while maintaining acertain amount of Ski pressure to have good handling.
However, it also needs to get stiffer to absorb energy toprevent harsh landing after jumping. Thus its damping
force will have progressive characteristics that can generate less damping force at lower piston speed range but
generate more damping force as it gets higher. Rear Shockis attached on the rear end of snowmobiles to control thevehicle pitching moment during acceleration and braking
by providing a certain amount of damping force at lower
piston speed balancing with Front Shocks. To provide
higher damping force at a higher piston speed range toabsorb landing impacts after jumps, it has the longest
stroke than the other SAs. So it is essential to have higher
rigidity construction to withstand its harsh use condition.
4.3 Adjuster
In Snowcross racing, competitors need to race all day
for several rounds of races; qualifying in daytime and thefinal at nighttime. SAs need to have many kinds of adjusters in order to quickly adapt to any kinds of racetrack
conditions because it changes depending on the weather
moment to moment.
4.4 History of Development of SA for 600RS
4.4.1 Development in the Early 2000s
Before the 2000s, aluminum monotube Gas SAs wereused because of its lightweight construction but they onlyused to have a rebound adjuster. In the early 2000s, riding
style has drastically changed from old-school “sit-on seat”
style to revolutionary “stand-up” style that suits modern
racetracks. To adapt this, a new chassis; REV and front
suspension system; RAS were developed. At that time,
BRP requested to develop new Remote Gas SAs in orderto improve shock absorption by adding Base Valve andFig. 8

 lair Morgan’s racing snowmobile built forB
X-Games in 2006

Compression Adjusters that can generate higher damping
force (Figs. 8 and 9).

Fig. 9Remote Reservoirs of Front Shocks were
fixed in the hood

Later in 2004, piggyback Gas SAs were developed andintroduced in all SAs years later by replacing Remote Gas
SAs. To further improve shock absorption, the piston
diameter got larger from 36 mm to 40 mm and rod diameter was also enlarged for higher strength and rigidity.
These racing technologies developed and validated werelater used in SAs for consumer models and they are stillused in today’s SAs.
4.4.2 Development in recent years
For the Snocross Pro Open; premier class in Snocross,it had been permitted to modify engines, pipes and chassisof racing snowmobiles to gain performance. But in 2018,
the regulations were revised to limit the modification.
This gained even more attention on the development of
the stock racing-ready snowmobile; 600RS. Particularly,
improving the suspension performance was considered asa critical challenge to ride faster on modern racetracks.
To do so, suspension linkage mechanisms were fully
redesigned and more performance improvements of SAs
were strongly requested. As a result, peripheral parts for
suspensions have been improved every year and SAs havealso been improved every year from 2018.
Following technologies were originally developed for
Snocross Factory Shocks and adapted for 600RS.
① Larger diameter piston for Center and Rear Shocks
As stated above, revision of regulations were taken as
an opportunity to improve performance of the rear suspension system. Larger Diameter Pistons were alreadyintroduced for Factory Center and Rear shocks but evaluation swung into high gear to find good setups. Riders
soon highly valued its stability and improved impact
absorption performance to prevent harsh landing after big
jumps. It was adapted for Center shock of 600RS MY2018
first and for Rear shock of MY2019 later.

― 45 ―

Development of Shock Absorbers for Snowmobile Racing② Integral adjuster
An integral adjuster, originally used for motocrossracing shocks, was introduced for Factory shocks to beable to be fine-tuned to rider’s preferences in a tight racing
schedule. It made it possible to adjust high-speed rebounddamping force quickly from outside that used to be hard toadjust via conventional adjusters and normally required
re-valving (Fig. 10). The characteristics of the check valve
were re-calibrated for Snocross after being introduced for
Snocross. As a result, it will settle shock movements tomaintain a good ride height when shock rebounds from afully stroked position which gives better handling whenriders enter corners right after a jump landing. It showed
its value on the racetracks with many jumps and was more
useful than conventional adjusters. Finally, it was adaptedin all SAs from 600RS MY2020.
③ Larger diameter piston for front shocks
Since the larger diameter piston used for center and rearshocks had been highly valued as stated above, a request
arose to apply it for front shocks as well. However, it waseven harder for the front shocks because they had to be fit
in a very limited space around them. To solve this, relatedparts needed to be redesigned from ground up. A brandnew guide cylinder and bearing were designed and firstly
used in 2018-2019 season (Fig. 11) They reduced rider’sarms fatigue by absorbing landing impact after huge consecutive jumps and provided better stability that leads togreat advantage during racing. Development was further
continued to find good setup and the reliability was provedon racetracks. They firstly debut for 600RS MY2021 andalso selected as production shocks for high-end Lynx Trailmodel (Fig. 12).

Gas
chamberHigh Speed
Rebound Damping
AdjusterFig. 10Base valve

Check valve

Rebound Oil flows in the Integral Adjuster andHigh Speed Rebound Damping adjust circuit

Brand new design
guide cylinder

Integral adjuster
optimized for
Snocross

Brand new design
bearing
Large diameter
piston/cylinder

Fig. 11

A brand new Front shocks with large diameter
piston debut in 2018-2019 season

Fig. 12First production trail snowmobile adopted front
shocks with large diameter piston

4.4.3 Current Development
They are equipped with new technologies that are
expected to be adopted for the next generation of SAs for
600RS and production shocks. Our technologies had
already been verified by great racing results as follows.

5

Major Racing Results

2020-2021 Season#200 Elias Ishoel
Three consecutive championship in Pro Class of ISOC
Snocross (Fig. 13)
Won Race 1 and finished 6th overall in FIM SnowcrossWorld Championship 2021

― 46 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Finally, I would like to express my deep respect to ourpredecessors who were involved in the past development
and brought those technologies of racing shocks into production that had built the foundation of today’s technology and cordially thank all those from the internal related
departments who extended their cooperation to us. I am
committed to develop products that are even more attractive to riders all over the world and hopefully our latest
technologies will be their advantage.

References

Fig. 1361) Power Sports Business, 2020 Market Data Book, p.61,
Worldwide Snowmobile Market Share.
2) UEMURA, KOJIMA, SUGAWARA: Development of "KADS"- An Electronically -Controlled Suspension System forMotorcycles, KYB Technical Review No. 63, (October 2021).

Elias Ishoel won the three consecutive
championship along with our technicians;
Tim (left) and Gilles (right)

In Closing

I would like to take this opportunity to thank all theengineers of BRP and BRP Finland who extended theircooperation into the development field as well as thetechnicians from Enzo Canada who have been joining ourracing support program and provided technical support on
our factory shocks for more than 20 years.

Author 
TANAKA Shin
Joined the company in 2015.
Group 2, Design Sect. No.2,
Formerly engaged in design anddevelopment of motocross racing
suspensions and later engaged indesign and development of SAs forsnowmobiles and ATVs

― 47 ―

Account of Residence in Czech Republic

Essay
Account of Residence in Czech Republic
NOMURA Norifumi

1. Introduction
I was assigned to work for KYB Manufacturing Czech
s.r.o (hereinafter "KMCZ") as an expatriate for five years
between April 2016 and April 2021. Before the assignment, I had been involved in the shock absorber (SA)-related quality support operation in Japan for overseas sites
and in charge of ASEAN projects even while I had been
preparing for the assignment. Actually, I had never been
to KMCZ before. Although I had to begin my work for
KMCZ rather suddenly with no specific information
available, home is where you make it. I eventually developed personally thanks to a variety of experiences overthose five years.
Looking back, I will outline my life there. You know
many predecessors who had been sent to the Czech Republic have already talked about tourist attractions andlocal cuisine, but there are still many other interesting
places and stories. I hope you enjoy reading my essay.

2. Information about Czech Republic
Before 1993, the Czech Republic used to be part ofCzechoslovakia along with its current neighbor Slovakia.
I remember in my childhood the Czech ambassador stepping onto the Sumo wrestling ring on the last day of eachtournament (Senshuraku) and read out loud "hyo-sho-jo,
anta-wa-erai !" in Japanese (meaning "congratulations,
you are the winner") while handing a huge Bohemianglass cup to the champion. Bohemian glass is still one of
the famous specialty products of the Czech Republic.
Featuring high transparency and hardness, Bohemianglass used to be used for the stained glass in churches andis popularly used in a wide range of applications including flower vases and drinking glasses.
The Czech Republic is a landlocked country borderedby Germany to the west, Poland to the north, Austria to
the south, and Slovakia to the southeast. Located in thecenter of Europe, the country is at a latitude roughly
equivalent to Hokkaido. It is very cold in winter. In middle February, the temperature is below -10°C for several
consecutive days. When I was in the Czech Republic, I
always stayed indoors on weekends during the winterseason, except going out for shopping, to spend comfortable hours in warm rooms where the temperature wascontrolled by a central heating system. On the contrary,
the summer is comfortable with low humidity. You canspend the season without using air conditioners just by
keeping the windows open.
The summer in the Czech Republic is the best season todrink beer. In front of restaurants on the street you can
see tables, chairs and parasols where people can enjoy
talking with their family and friends with a glass of beerin one hand. Speaking of beer, the Czech Republic isnumber one in the world in per capita beer consumption.
Of course, the small country cannot be top in total beer
consumption, but scores far ahead of others in per capita
consumption. When I walked by a restaurant or bar in theearly morning, I sometimes happened to see a beer tanktruck parked alongside the building supplying more andmore beer to the restaurant or bar. That made me understand how much beer customers drank in the restaurant
last night. I recognized anew that Czechs really loved
beer every time I saw such a scene.
The word Czech may also remind you of some famous
traditional towns including several World Heritage sites.
Not only in Prague, but also near Pardubice where I lived,
there are many famous tourist sites such as Kutna Hora.
The town used to prosper with silver mines and is still
dotted with gorgeous traditional buildings.
Among them, the Church of St. Barbara and the Cathedral of Our Lady at Sedlec are particularly well-known.
The Church of St. Barbara has Gothic architecture fromthe 13th to 15th centuries with various statues and paintings decorated inside the church. The historical building
has three roofs at the center, around which there are several pointed columns.
The Cathedral of Our Lady at Sedlec is internally decorated using the bones of about 10,000 people. When you
step into the cathedral, it is cool even during summer andmay feel a little dusty. On the front of the gate there is anemblem. Inside the cathedral you can see a chandelier
and several decorations on the wall. All of them are madeof bones! You may be astonished by this way of using
human bones, something that never happens in Japan.
Pardubice, where the KMCZ plant is located, is in East
Bohemia and 100 km east of Prague. A famous event inthis city is Velká pardubická, which is a cross-country― 48 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

horserace or steeplechase held in October every year.
Many tourists from everywhere in Europe visit the city toenjoy the race with a glass of wine in hand.
During my expat assignment in the Czech Republic, I
lived in the center of Pardubice. I often ate at the plaza
where the city hall was located or visited old castles nearby. The city hall was in a traditional building that had
been renovated. The building exterior was decorated andlit up at night during seasonal events, which is popularamong the citizens.
In addition, the Czech Republic has many other various
tourist spots. Most Japanese tourists typically enter the
Czech Republic from Prague and then travel to Austria
via Český Krumlov.

Photo 1

Currently, on the west side of the KMCZ plant is aloading dock to receive and ship finished products including tubes. Nearby is a storage space for finished products.
To the southwest are tube/rod machining lines and part
warehouses. The expanded area was mainly used as a finished product yard and a preliminary machining space.
To the east of the plant are an internal valve assembly
line, a standard SA assembly line, and a strut SA assembly line. The production system is designed to transfer
finished products to the finished product yard to the west.
KMCZ has about 700 employees. They work in three
shifts for assembly lines and in four shifts for preliminary machining lines. We set up the Open House in summer and held a Christmas party in winter to allow employees to enjoy themselves with smiling faces, while
they worked with their serious faces in daily production.

Photo 2

Pardubice City Hall

KMCZ Open House

4. Entertainment
3. KMCZKMCZ in 2016 finished with a plant expansion to thewest (more than doubling from 15 thousand m 2 to 35
thousand m 2) since 2015 and introduced additional assembly lines. The plant had started to increase production since FY2015. With an economic boom in the Czech
Republic from around that time, the country enjoyed anincrease in capital investment and private consumption
year by year. As the jobless rate decreased and wages increased every year, some of the employees retired from
KMCZ and tried to work at another workplace on slightly
more favorable terms. One of my missions during the assignment was to find substitutes for those who retired.
KMCZ introduced another manual production line forassembling single-cylinder gas SAs and standard SAs in
August 2016. As the third line, an ST welding and assembly line was introduced to steadily improve the production plan in December 2017. The plant shipped 3.70 million pcs/year in 2014 before the plant expansion increased
the level to 5.70 million pcs/year in 2018. Thereafter, production has increased year by year, although shipments
dropped in 2019 and 2020 partly because of the effect of
the novel coronavirus (COVID-19) pandemic.

Czech people really like to do outdoor activities. On
weekends they often go hiking in the mountains, cycling,or inline skating with their family. When I was there, we
also played golf on weekends. On golf courses, we often
found that the husband of a typical Czech family wasplaying golf and his wife and children were walking theirdogs following the husband. I was moved by the fact that
Czechs really loved to be in nature with their family.
Sport is also a Czech favorite. The popularity of tennis
may be well known to Japanese. In particular, in women's
tennis, several Czech players are ranked high in theworld. Many readers may have heard the names Barbora
Krejcikova and Karolina Pliskova. News of their performance was reported by Czech television almost everyday. It reminds me that a Czech woman won the gold
medal in both skiing and snowboarding in the winterOlympics, which was quite before though. The prominence of Czech women in the world of sport is remarkable.

― 49 ―

Account of Residence in Czech Republic

Photo 3Kunětická golf course

Photo 4 A game of ice hockey

5. Ice Hockey

6. Czech FoodIce hockey is very popular among Czechs with multiple
active professional leagues. In Pardubice, where there is a
professional hockey team, the arena is packed for every
game with fans in the team's uniform and they roar on theteam regardless of whether it is winning or losing. It waseasy to figure out when a hockey game was held just by
hearing the chanting on the street. I went to the arena towatch hockey games several times. In these games I saw
players battling with each other for the puck or charging
into each other. They had a fight once in a while. Unfortunately, I could never clearly see the scoring moment
when I was watching a hockey game. Instead, I enjoyed
the scoring scene by noting it with the scoring lamp andbeep sound as an instant fan.
Hockey is a national sport for Czechs. They play hockey on a skate rink from childhood. Even during summer,
they enjoy playing ground hockey using a stick similar tothat used for ice hockey. In the PyeongChang 2018 Winter Olympics, the semifinal game was the Czech Republicagainst Russia. Although the Czech Republic finally lost,
Czech staff members in KMCZ were always checking
what was going on in the game via the Internet or the liketo share information with each other, putting work to one
side.
If you tell a Czech person that you are from Japan, you
may be asked "Which part of Japan?". Since the Czech
national hockey team won the gold medal in the Nagano
1998 Winter Olympics, the word ‘Japan’ reminds them ofNagano. In spite of being a hockey superpower, the Czech
team had only ever won the silver medal, and it had been
beaten by Russia many times. In Nagano in 1998, theCzechs were especially happy when the national teamwon the gold medal by beating Russia in the final. Thisbig event for Czechs did happen at Nagano in Japan. If
you talk about the Nagano Olympics, you can get friendly
with Czechs very quickly.

I am often asked "What is typical Czech food?" One ofthe popular lunchtime dishes in KMCZ was Schnitzel,
thin slices of chicken or pork that are fried. It tastes similar to cutlets in Japan. Japanese expatriates often asked
the kitchen to dress Schnitzel with pork cutlet sauce andenjoyed eating it with rice. Neighboring countries including Austria and Germany also have the same dish. Schnitzel is typically served along with potato in these countries.
A kind of beef stew originating in Hungary called Goulash is another typical lunch dish. When you are in a restaurant anywhere in the Czech Republic, you can always
find Goulash on the menu. This national food is a little bit
salty compared to beef stew in Japan and is often servedwith steamed bread. I privately recommend Goulashsoup in a bowl made of bread.
The next cuisine I want to introduce is Beef Steak Tartare; I do not know if you like it though. Japanese, including me, tend to have difficulty ordering this food at a restaurant because they cannot pronounce it correctly. SteakTartare is like beef yukhoe seasoned with spices and garlic. You can put grated garlic on a piece of well-baked
bread and then add an appropriate portion of Tartare on
the bread before eating. Czechs, whether they are men or
women, cram it into their mouths without caring about
the smell of garlic. I do not know how your stomach will
be next day if you eat Tartare too much.
Typical drinks in the Czech Republic include Kofola, akind of carbonated drink. As the name implies, this is a
Czech version of cola. It is said that Kofola originatedduring the time of Czechoslovakia when people mimicked cola. This slightly carbonated drink smells a little
bit like lemon. I thought at first that it was just cola withlemon that had gone flat, but I gradually became used tothe taste. It is definitely a national drink along with beer.

― 50 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

8. COVID-19 Pandemic in Europe

Photo 5 Steak Tartare

7. Czech Names
I had an opportunity to learn the typical surnames ofCzechs. I want to introduce some of them as their surnames and Japanese counterparts have several things incommon. Some Czech surnames are named after the natural world, such as Kopecky meaning "hill" or "mountain" and Novotony meaning "new". I thought these might
be similar to the popular Japanese surnames Yamamoto(literally meaning "foot of the mountain") and Arai (literally meaning "new well"), respectively. The order ofnames is also common between Czechs and Japanese: thesurname comes first and is followed by the "first name".
This was a story I felt connected me with Czechs.
I almost forgot to say, but Czech surnames for men end
a little bit differently from those for women. Most surnames for men end with "ky" or "y" while those for women end with "a". Kopecky, as mentioned above, will be
Kopecka for women, and Novotony will be Novotona for
women. Many surnames for women add "ova" to the surnames for men.
I found in KMCZ that a popular name for men was Jan.
In Czech, "ja" is pronounced "ya". Many famous heroes
are called Jan, and this should be popular among today's
people too. However, its nickname is a little bit strange.
Jan is nicknamed Honza, which is quite different fromthe original name. I did not get it at all in the early days of
my stay in the Czech Republic. I remember I sometimes
looked around me trying to find what people were called
as I did not understand what the nickname meant. In addition, Anna, Anicka, Eva, and Evicka were also typicalnicknames. I wondered why they were called by a nickname that was longer than the original name.
Another interesting story about names is that peoplecelebrate their name day on the date corresponding totheir own given name on the calendar. So, Czechs have
two birthdays in one year. At first, I did not understand
why they would celebrate their birthday again as they hadcelebrated it the previous month.

COVID-19 first spread as an epidemic in Italy andSpain a couple of months before the news of Japan's first
infection cases on the Diamond Princess Cruise Ship
were reported. Czechs seemed to look upon it as "That's
not my business" in the beginning. However, as Czechs
who had come home back from the designated countries
were infected with the disease, the Czech Republic started to close its borders with neighboring countries and tosuspend air services in March 2020. Various COVID-19
control measures including an entry ban for foreigners
were taken to combat the virus in European countries.
KMCZ also took COVID-19 control measures for its
employees. For example, those who had traveled to Italy
or Croatia during their children's school winter holidays
were recommended to voluntarily isolate. In order tocope with the problem of shortages of masks and disinfectants, the company placed orders for these goods early.
It also changed the scheduled period of business trips of
employees and meant those who had been sent to a foreign country had to come home before the suspension ofinternational air services.
The situation rapidly deteriorated thereafter and was
followed by a lockdown. Some customers planned plant
shutdowns, and KMNA suspended production in April
2020. During the lockdown, all shops except food markets, gas stations and drug stores were closed. With norestaurants open, I had difficulty in getting food as I lived
alone. Other control measures included a night curfew
from 9 o'clock at night to 6 o'clock the next morning. The
lighting in shops on the streets was turned off and nobody was walking on the street. Even the downtown area
was quiet.
After that, the restrictions were relaxed in phases as thenumber of newly infected patients had changed. A cycleof lifting the ban and the spread of infection was repeatedover and over again. During this period, the entry of foreigner tourists was prohibited, greatly impacting the
tourism and food service industries.
I had the opportunity to visit Prague on business during the period of relaxed restrictions. The city, which had
usually been crowded with tourists, was quiet and nobody was on the famous Charles Bridge (Karluv most) oron the road on the other side of the river. It felt strange theway the city was different from usual, but the scenery
was still beautiful.
KMCZ also had a difficult time and struggled to secure
the personnel necessary for production during the pandemic because of the increased number of newly infectedpatients. Some employees were infected and some others
were identified as persons who had close contact with patients and were asked not to report to work. COVID-19
may still be advancing or retreating. I hope the pandemic
will be over soon.

― 51 ―

Account of Residence in Czech Republic

Photo 6

Prague, photographed from Letná Parks

9. In Closing
I returned to Japan after finishing with my five-year
term of residence in the Czech Republic. Now I can see
what difficulties my colleagues may have had during
their expat assignments in foreign countries.

During my assignment in the Czech Republic, I learned
a lot about corporate management as I served as site manager and was involved in management that I had neverexperienced in Japan. The experience of living in anotherculture also gave me a good opportunity to change myway of looking at things that I had never previously
doubted. Particularly as I experienced living in two countries (before living in the Czech Republic, as I had been
assigned to the U.S.A.), I can now compare the people,
culture and economy of those countries with those of Japan, which helps me think I am a better person. I reallyappreciate being given such opportunities.
I would like my colleagues, if they have an opportunity
to work overseas, to absorb another culture while they
live in the country in addition to their daily work in Japan.
Finally, I would like to thank all those who supported
me when I lived overseas. I am committed to continuously doing my best for the development of KMCZ.

Author 
NOMURA Norifumi
Joined the company in 1992.
General Manager of Quality
Management Dept., Quality Div.
Took present post after working in
SA Quality Assurance Dept.,
expatriate in the U.S., Product
Planning Dept., and expatriate in the
Czech Republic.

― 52 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

ary

s
los

G

KYB-IoT Platform
Refer to Building the Foundation for MES Services in the New Era (page 8)

TAKINO Shinsuke
DX Dept.

1

2

Overview of KYB-IoT Platform

Recently, KYB has also become involved in many
projects making use of data and digital technology.
As these projects increase in number, it is necessary tobuild a Data Collection Foundation that continually
collects and accumulates big data and a Data Analysis
Foundation for accelerating data utilization including
Business Intelligence (BI) and Artificial Intelligence (AI).
So, the DX Department is promoting the building of an
IoT Platform as a Data Collection/Analysis Foundation sothat KYB can internally utilize digital technology widelyand correctly. Fig. 1 shows a conceptual illustration of theKYB-IoT Platform.
KYB-IoTGroup
companies

Production

platform
Production info.

Anyone can easily use andanalyze data anytime, anywhere.

④ Provide new values

Equipment info.

Design & Development

To ensure that the KYB-IoT Platform can effectively
deliver in the future, the following three technicalfunctions are important:① Data collection
It is essential to build a system that can quickly andcontinuously collect and store data from individual
departments without consuming too many man-hours toanalyze and utilize the big data.
② Tampering-proof
All accesses to the system should be recorded in a log.
In case of tampering, the system automatically records
the event and transmits alert e-mails. This will ensuretransparency around internal data management andaccess, providing safety and security to customers.

Users
Quality info.

Overseas
sites

Major Functions of KYB-IoT Platform① Higher productivity, ② Higher quality, ③ Higher added-value products
Design info.

Sales info.

Manager・Grasp thecircumstances・Quick decision making

Product info.

Fig. 1

Shop floor・Predictive
maintenance・Quality estimation

R&D
・Smart roadmonitoring・Oil condition sensor

KYB-IoT Platform

The cloud-shaped area in Fig. 1 represents the KYBIoT Platform that has been implemented with the cloudservice available from Amazon Web Services (AWS).
Data from the Production and Design & Development
fields (e.g., plant facilities and products underdevelopment) held by KYB and its affiliates is collected,
processed, analyzed and visualized to provide new values
to external users or customers and to be available tointernal users for improving productivity, quality andadded-value products.

③ Analysis and management
In an AI development project, reproducibility can only
be secured with all of the three elements: source code,
data, and parameters.
Data is changing even during operation. It is essential tobuild a foundation for managing data in sets and forcontinual relearning and remodeling, in order to achieve
long-term operation.
It is also needed to develop human capital for datautilization to ensure that information on the KYB-IoT
Platform is accessible by anybody in the company and canbe viewed in various ways as well as be analyzed in a
simple way on Web browsers during daily work as
standard.

― 53 ―

Cavitation

ary

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Cavitation
Refer to Research on Technology to Control Air Bubble Content in Hydraulic Fluid (page 17)

NAGASHIMA Midori
Mechanical Component Engineering Sect., Basic Technology R&D Center, Engineering Div.

What Is Cavitation?

A hydraulic fluid may contain bubbles for several
reasons, including mixing of the air by agitation, mixingof the air due to vibration of the hydraulic circuit or tank(sloshing), and precipitation of the air dissolved in thefluid when the fluid pressure reduces to a certain level(aeration). Particularly, when the pressure reduces tobelow the saturated vapor pressure due to an increase inflow rate of the fluid in the hydraulic line or machinery,
the fluid may vaporize to generate bubbles. Thisphenomenon is called cavitation (Fig. 1).

Theoretical
Measurements

Discharge

Vapor of the fluid

Saturated vapor
pressure

Fig. 1

2

Pump speed
Fig. 2Pressure down

Atmosphericpressure

Decrease in discharge
due to cavitation

Discharge characteristics

2.2 Shock Absorbers
A shock absorber as a component of an automobile (Fig.
3 (1)) can alleviate the vibration transmitted from thesurface of the road to the vehicle body. This can beachieved by a piston rod (valve) moving backwards andforwards within a cylinder filled with a hydraulic fluid. If
the piston rod abruptly strokes at a higher speed, cavitation
may occur to generate bubbles. When the bubbles affectthe compressibility of the fluid, the intended damping
characteristics may be lost as shown in Fig. 4.

Cavitation

How cavitation occurs

Problems Caused by Cavitation

Seal

Bubbles that have been generated by cavitation rapidly
disappear (collapse) when the fluid pressure increases
again. The collapse generates impact pressure that may
damage the wall of the fluid duct and machinerycomponents, which may cause erosion (cavitation
erosion). Repeated shock waves may also lead tovibration or noise of the piping or machinery.
In addition, cavitation could be a cause of degradedproducts. The following introduces two examples of suchproducts.

Reservoir Piston valve

ExtendBackside

InsideUpperchamberof piston

Lowerchamberof pistonRetract
Piston rod

Fig. 3

CylinderDamping force1

2.1 Hydraulic Pumps
When a hydraulic pump is run at a higher speed, thehydraulic fluid is sucked at a higher flow rate. Once thesuction speed exceeds a certain level, the suction port has
a local decrease in pressure, causing cavitation. When anumber of bubbles are present in the fluid, the fluid
accounts for less percentage of the suction volume by thesame amount as the bubbles. This results in the problem
of a decrease in discharge rate as shown in Fig. 2.

Theoretical
Measurements

Stroke speed

Overview of shock absorber Fig. 4

Damping
characteristics

References
1) SANO Yuta: Development for Analytical Technology of Shock
Absorber Valve Characteristics, KYB Technical Review No. 58(April 2019).

― 54 ―

Editors Script
I wrote three consecutive articles in the middle of the Heisei era. At that time, I had no literary talent so proofread my articles
over and over again in response to comments by editors, while complaining "Why do I have to write consecutive articles?".
Fifteen years have passed since then. When I read the articles of other engineers in this Technical Review, I can recognize anew
the necessity of taking a step forward, creating new things, revealing them to the public, cultivating them, and taking anotherstep forward. It reminds me when my boss told me "A plateau is the same as a slope". He added "The difference in speed of
improvement or development between us and our competitors will be the difference in profits, and you win only when you go
forward faster than competitors". I expect all KYB engineers, including those who contributed to this Technical Review, will dotheir best even in the toughest of situations.
(NOGUCHI)
Our way of living has changed dramatically during the coronavirus pandemic. Many people now take it for granted thatthey can work at home using the Internet and attending web meetings. Meetings of our editorial board are also held online. On
holidays, going camping has become popular because of few chances to have close contact with each other. I am one of thesecamping converts. Still, I felt a little complicated when I learned the demand for enjoying "inconvenience" in a sense while
digitization has improved convenience. KYB Technical Review is also a consequence of responding to a variety of customer andinhouse needs. I would like to continue providing information on KYB technologies and experiences.
(HAYASE)
There is a trend for automobiles and construction machinery to introduce automated driving and remote control. We arealways concerned with how we should cope with or follow such trend as a hydraulic component manufacturer. Against such abackground, I became an editor checking articles for the Technical Review. I sometimes find a lot of helpful hints in recent KYB
Technical Reviews. In spite of the tough circumstances connected to the COVID-19 pandemic, I am very proud of the engineers
who have developed and produced various products in different sites. By leveraging the total engineering prowess of the overall
KYB Group, I would like to further promote technical development.
(KOBAYASHI)

Editorial members◎ ITO Takashi
KABASAWA Ryoichi
HAYASE Tomonori
SUO Shiro
MATSUMURA Ryoichi
OTA Yasuhiro
MIYATANI Osamu
SASAKI Kazuhiro
NOGUCHI Yoichi
SAITO Keiji

Basic Technology R&D Center,
Engineering Div.
Basic Technology R&D Center,
Engineering Div.
Basic Technology R&D Center,
Engineering Div.
Intellectual Property Dept., Engineering
Div.
Management Planning Dept.,
Management Planning Headquarters
Engineering Headquarters, AC
Operations
Engineering Headquarters, AC
Operations
Engineering Headquarters, AC
Operations
Production Engineering Dept., PS
Business Operations, AC Operations
Sagami Hydraulics Engineering Dept.,
HC Operations

NAKANO Tomokazu
MARUYAMA Seiichi
KAWASHIMA Shigeru
OKADA Kiyoshi
OKAMURA Kazunori
KAWANO Yoshihiko
KOBAYASHI Hirotaka○ KOBATA Hiroshi○ OBAYASHI Yoshihiro

Gifu South Hydraulics Engineering,
HC Operations
Engineering Dept., Aircraft Equipment
Business Operations
Engineering Dept., Kumagaya Plant,
Special Purpose Vehicles Div.
Production Engineering Dept., KYB
Motorcycle Suspensions (KMS)
Engineering Dept., KYB Stage
Engineering Co., Ltd.
Development Dept., Engineering Div.,
Takako Industries, Inc.
Design Dept., KYB-YS Corporation
Engineering Planning Dept.,
Engineering Div.
Engineering Planning Dept.,
Engineering Div.

◎ Editorial Chief○ Editorial Secretariat
HC Operations: Hydraulic Components Operations
AC Operations: Automotive Components Operations

Notification regarding website release
KYB TECHNICAL REVIEW No.64[All rights reserved] [NFS]

Published on April 1, 2022
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