KYB技報

第51号

2015―10

技術解説

Polyalkylene Glycol（PAG）as Environmentally
Acceptable Shock Absorber Oil

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）
Christian SCHOLZ ・ Yoshihiro ITO
クリスティアン ショルツ ・ 伊藤 義浩

要旨
近年の環境負荷低減を目的とした欧州REACH規制や米国Vessel General Permit等の強化に伴い，
環境対応技術はより広い領域の分野で求められている．KYBにおいては多くの製品の作動流体として
油圧作動油を用いており，油圧作動油に対しても環境負荷低減が求められるようになっている．このた
めKYBにおいても，将来想定される環境対応要求
に対し準備する必要性がある．
本報では，環境対応技術として作動油に求められる要件，及び環境対応型作動油（Environmentally
Acceptable Lubricants : EAL）であるポリアルキ
レングリコール（Polyalkylene Glycol : PAG）について解説する．また，PAGを自動車用ショックア
ブソーバの動流体として適用した事例について紹介
し，KYB製品における環境対応技術の可能性につAbstract
Due to restrictions, such as European regulation
E C / 1 9 0 7 / 2 0 0 6 （ R E A C H ）, s u b s t a n c e s f o renvironmentally friendly and biodegradable
lubricants getting more in focus of passenger car
OEM’s and suppliers R&D activities. Eco-tox
properties are now mandatory in the U.S. Vessel
General Permit. Goal of the present investigation
is to characterize the tribological performance ofdifferent shock absorber fluids, including those asenvironmentally acceptable lubricants （EAL）
declared. Therefore, four lubricants differing intheir base oil were tested under laboratory
conditions, in bench tests and finally in vehicle
tests. The oils tested are composed of Group IIImineral base fluid and polyalkylene glycol（PAG）

いて述べる．

based oil, which is classified as readily
biodegradable EAL. All oils are fully formulatedwith standard additives for shock absorbers.
Friction properties under oscillating sliding
conditions and Stribeck-curves were determined
besides damping force in real applications.
Subjective car evaluation and sensor-based
objective data recording on public roads gave
good conclusions how the oil and its tribologicalproperties can influence the driving characteristics（vehicle stability and comfort）.

１

closely linked to the environmental impact of
lubricants such as engine oils and hydraulic fluids.

INTRODUCTION

Biodegradability, toxicity, renewability andbioaccumulation are the key words which are

These issues of bio-no-tox properties are getting
more and more in focus of original equipment― 13 ―

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）

manufacturers OEM’s in automotive, marine andhydraulics sectors. Over the last 30 years

EU Ecolabel regulation, the lubricant has to fulfill
several criterions. The following points listed

European, American and Asian governments
released several regulations which address the
toxicity of chemicals（1907/2007/EC REACH）or

below are valid for hydraulic fluids（listed as2）,3）Category 1 lubricants）:

provide the legal basis for lubricants classifications（EPA Vessel General Permit） and so called
Ecolabels（2005/360/EC）. The European REACH- N
 o R phrase triggering materials（Risk phrases）- C umulative mass percentage ≤ 0.1% of
substances categorized ‘very toxic（G）’ withregulation（Registration, Evaluation, Authorization
and Restriction of Chemicals） communicate
information on chemicals ensuring that
manufacturers and customers are aware of healthacute aquatic toxicity ≤ 1 mg/L
- Readily aerobic biodegradation > 90%- N
 o halogen or nitrite compounds or heavy metals- Renewable carbon content > 50%- I mpact on CO2 emission as outlined in thestandard

and safety characteristics of the products. Many
countries worldwide offer eco-labels for several
industrial product categories including lubricants
and their additives. These labels provide adefinition which product have a low environmental
impact, do not affect aquatic organisms or otheranimals and furthermore consider the aspect of
biodegradability and renewability. Unfortunately
these legislation vary in a wide range fromcountry to country and indicate a lot of “bio andeco” terms such as1）:-

E
 AL for Environmentally Acceptable Lubricants
 CL for Environmentally Considerable LubricantsEE FL for Environmentally Friendly Lubricants
Hydraulic fluids for environmental impact
Biodegradable fire resistant hydraulics fluids
Eco-evaluated/eco-friendly fluids-

Oil respectful of the environment
Eco lubricants

In comparison to other existing national ecolabels, such as the Blue Angel（Germany）, the Eco
Mark（Japan）and the Nordic Swan（northern
European countries）, the EU Ecolabel intensified
the criteria for an approval as environmental
friendly lubricant. In order to get the approval by
Table 1-

ISO 15380 standards for technical performance
criteria

Environmentally acceptable lubricants arecommonly classified according the type of basefluid used in the formulation. Beside vegetable oils,
produced by use of canola, soybeans or sunflower
crops, synthetic esters and polyalkylene glycols（PAG）represent the major share of these basefluids. Group I, II, III and IV base oils which aremainly related to mineral base oils cannot beclassified as EAL or environmentally friendly
lubricants due to their high toxicity againstorganisms, inherently low range of biodegradation
or not given renewability. The United States
Environmental Protection Agency （EPA）
summarizes the major factors of different base oiltypes regarding their biodegradation, toxicity andbioaccumulation potential. Comparing these factors
the majority of currently used lubricant base oils
have a low grade of biodegradation, a highpotential for bioaccumulation and a measurable
toxicity towards marine organisms4）. PAGs, esters,and vegetable oils are candidate base stock for
lubricants with low environmental impact（seeComparative environmental behavior of lubricants base oil type. 4）

Base OilBase Oil Source

Biodegradation

Bioaccumulation

Toxicity

Mineral Oil

Petroleum

Persistent/Inherently

Yes

High

PAG

Petroleum – synthesized hydrocarbon

ReadilyNo

Low

Synthetic Ester

Biological sources

Readily

No

Low

Vegetable Oil

Naturally occuring vegetable oils

ReadilyNo

Low― 14 ―

KYB技報第51号

2015―10

Fig. 1 P olymerization process of different polyalkylene glycol base oil types. Red colored atoms represent oxygen.

Table 1）.
Polyalkylene glycols offer an attractive

PAG polymer is an oxygen atom（see Fig. 1）
which results in a high affinity to metal surfaces.

alternative to conventional hydraulic fluids due toseveral special oil characteristics described in thefollowing context. The long history of PAGs goesback to the early 1940s where it was developed as
one of the first synthetic base oils. The big
advantage of PAGs is that they can be chemicallydesigned to meet a wide range of performance
characteristics in industrial applications. There isno other base available on the market which offers
such versatility.
The manufacturing process of PAGs includes
the reaction of an initiator（for example butanol）
with one or more alkylene oxides（EO – ethyleneoxide, PO – propylene oxide or BO – butyleneoxide）under alkaline conditions and elevatedThis feature contributes moreover mild antiwear
and extreme pressure properties 5）. Typical oil
characteristics of PAGs are:temperatures（see Fig. 1）. It is possible to add theoxides as single oxides forming a homopolymer
such as polyethylene glycol（PEG）or as random
oxides creating a copolymer of ethylene – andpropylene oxide（EO/PO copolymer）for example.
The choice of initiator and alkylene oxides andtheir different ways to react gives PAGs a wide
range of intrinsic properties and makes thecreation of tailor-made products possible.
Additionally, PAGs have excellent lubricant film
forming characteristics. The reason for this is theoxygen rich chemical structure of PAG（highpolarity）.
In comparison to PAG, mineral base oil,produced from crude oil or by synthetizing
petroleum components, consists of a long chain（backbone）of hydrocarbon molecules without any
oxygen. Every third atom along the backbone the-Wide viscosity range（ISO VG 7 to 10000）
High viscosity index（up to 300）
Water solubility and oil tolerance
Hydrolytic stability
Oxidative and thermal stability
High flash point and low volatility
Good additive compatibility
Biodegradability and low toxicity

The high hydrolytic stability of PAGs makes
them a good choice for industrial equipment usedaround waterways. This is caused by the ability to
act as polymeric sponges binding the water, which
entered the system, through hydrogen bonding
and rendering it inert even at levels of up to
20,000 ppm（mineral base oil <500 ppm）.
KYB is one of the world largest manufacturer ofshock absorbers and hydraulic systems. Therefore
a huge interest in improving these system isalways given. By definition shock absorber are
hydraulic or mechanical devices attached to car
chassis and car body structure. The main functionof the device is to damp the kinetic energy of roadshocks, caused by road conditions or severe
impacts, by converting it into another form ofenergy（heat）6）. Beside a high level of comfort ford r i v e r a n d p a s s e n g e r s a s we l l a s d r iv i n g
performance and stability, car shock absorbers
make a significant contribution to driving safety― 15 ―

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）- N
 BR-polymer（oil seal）- Cr6+-plating（steel
piston rod）
- PTFE/Pb covered bronze（bushing）- Cr6+plating（steel piston rod）

（braking distance）. A typical passenger car shock
absorber undergoes 75 million shaft cycles inapproximately 80,000 kilometers, which means 900
cycles per kilometer at various sliding speeds ofpiston and piston rod. Using the shock absorberlonger than recommended by the passenger car
OEM several problems could occur and influence
the car security. Poor steering responsiveness,lack of control, noises and a significant increase in
braking distance are the results of bad shock
absorber performance related to mileage and wear
reasons. Nowadays, a large number of shock
absorber is designed as so called ‘twin-tube’ shock
absorber, which means that it consists of two- P TFE（piston ring）– steel（inner surface ofworking cylinder）
Thus, the damping force itself consists of two
influencing forces, the hydraulic force（oil flow）
and the friction force of sliding parts. Since theshock absorber fluid affects the damping
characteristics by its viscometric properties andthe lubricating properties of various sliding parts,
it has a huge influence on vehicles driving, comfort

cylinders（working or inner cylinder and outercylinder）. Fig. 2 shows a sectional view of atypical passenger car twin-tube shock absorberincluding piston, bushing, and oil seal as mainand stability characteristics.

sliding parts.

Aim of the present study was to investigate
influences of a PAG-based hydraulic oil on the
single tribological interacting parts of the shock
absorber in comparison to fluids with mineral baseoil. Therefore, four different types of shock
absorber oils with specific adjusted tribologicalproperties were selected. The lubricant is one of
the major influencing factor of the shock absorber
performance. For this reason several bench test at
KYB Basic Technology R&D Center wereconducted to evaluate the interaction of the main
sliding parts and oil, mentioned before. Bench testof assembled shock absorbers（ASSY）by use of a
servo-hydraulic test machine should show
differences in damping force curves. Finally, the２

DEVELOPMENT AIM AND BACKGROUND

oils selected were tested on a public road circuit
in a 3 liter rear-wheel drive car. Main target of theFig. 2

Sectional view of a twin-tube shock absorber.

The outer cylinder serves as a reservoir for thehydraulic fluid（approximately 300 ml per shock
absorber）. The fluid valves in the piston and in
the stationary bottom valve control fluid flow
between both cylinders and regulate the damping
force. The valves in the piston have the highest
proportion of shock absorber damping
performance. The material combinations of themain sliding parts in a shock absorber, which aremainly influencing the friction force, are thefollowing:

test series was to analyze the influence of the oils
on driving performance （car stability） andcomfort during driving. Currently the influence ofshock absorber oil properties, friction between themain sliding parts and the resulting car
performance is hardly understood and underrated.

３

TEST OILS AND -PROCEDURE

Four fluids were selected for the tests. Oils No.
23, No. 26 and No. 33 consists of a Group III
mineral base oil, whereas oil PAG 1-4 uses apolyalkylene glycol as base stock. Additionally, the― 16 ―

KYB技報Table 2

2015―10

Key properties of shock absorber oils tested.
No. 23

No. 26

No. 33

PAG 1-4-

Group III

Group III

Group III

Group V PAG

40°C

cSt

12.66

12.82

12.76

12.83

100°C

cSt

4.43

4.502

4.478

3.637

Base OilKinematic
Viscosity

第51号

Viscosity Index（VI）

-

317

321

320

184

Flash Point

°C

140

140

148

208

Anillin Point

°C

92.4

91.9

91.6

n.m.

Total Acid Number（TAN）

-

2.06

1.74

1.42

1.46

base oil of PAG 1-4 can be classified asenvironmentally acceptable lubricant accordingR e f . 1 ）, 4 ） a n d 7 ） w h i c h m e a n s i t i s r e a d i l ybiodegradable（OECD 301B/F）.
The viscometric properties such as kinematic
viscosity, viscosity index and flash point are listed
in Table 2. Comparing the oils it becomes clearlyvisible that the kinematic viscosity is nearly in thesame range of maximum 12.83 cSt at 40°C. The
shock absorber oils based on Group III mineral oil
all have a viscosity index above 300 whereas PAG
1-4 shows with 184 a much lower value. Reason
for this is that PAG itself has already acomparable higher VI than mineral base oils.
Thus, viscosity index improving additives are notneeded for many application where PAGs areused. Furthermore, due to the chemical structureof PAGs the flash point is much higher at around
200°C. All lubricants contain additive packages
including friction modifiers, antifoaming agents,
antioxidants, metal deactivators and antiwear
additives（for PAG 1-4 approximately 1.8 wt% in
total）.
The oils can also classified by the frictional
impact. No. 33 and PAG 1-4 have very low friction
properties, which will be shown more in detail in
the following context. In comparison to these oil
No. 26 has the characteristic of increased friction
whereas No. 23 oil has the highest friction
properties of all oils tested.
The test procedure for the development oils canbe consists of three testing steps:‌Laboratory tests（pin-on-disc and ball-on­three（1）plates test principles）（2）Bench tests（damping force curves by Assy）
V（3） ehicle tests at KYB Suspensions Europe S.A.（KYBSE）

Laboratory bench tests were conducted bymeans of a self-constructed linear oscillating pinon-disc tribometer at 30°C oil temperature.
Thereby, the pin consists of the same rubbermaterial which is conventionally used for theshock absorber oil seal. The disc counterpart wasmade from a hard-chrome plated（Cr6+）SUJ2 disc
representing the piston rod. The tests run for
approximately 40 minutes whereby the sliding
speed was reduced in eight steps from 30 mm/s
to 0.06 mm/s. This tests support a fast evaluationof the shock absorber oils as well as the oil sealmaterials and their frictional properties.
Additionally, Stribeck-curves were measured withthe tribology cell（T-PTD 200）of Anton Paar
rheometer MCR 302 at 20°C and －20°C（ball-onthree-plates）. Using the material combination
PTFE （plate） and steel （ball） the tests candisplay the characteristics of the shock absorber
piston sliding against the inner surface of theworking cylinder. In these tests the sliding speed
was raised from 4.7E-5 up to 1.4 m/s sliding speed.
Damping force characteristics of the test oils were
determined by use of mass production shock
absorbers with identical setting（valve design）ina servo-hydraulic bench testing machine（Kayaba
System Machinery Co., Ltd.）. These test were
performed with a preconditioned shock absorberat a temperature of 20°C ± 3°C and a stroke ofΔx=±25 mm. A force sensor directly above thepiston rod, placed on the mounting point of themachine in z-direction, detects changes in thedamping characteristics caused by different oils
and increased sliding speed over testing time.
In order to evaluate the oil influence on driving
performance and comfort, the four oils were tested
under authentic road conditions on a public circuit― 17 ―

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）

in Spain. Therefore, a 3 liter rear-wheel drive car
was selected as test vehicle. KYB Suspensions
Europe S.A. currently supplies the front and rearshock absorber for this car. The shock absorberwere disassembled and the standard oil was
replaced by the oils described before for the tests.
During the tests several subjective parameters,such as noise level, harshness, car-, steering- andimpact feeling were evaluated by the tests drivers.
Additionally multiple acceleration sensors and a
microphone inside the vehicle cabin measured
data to compare subjective feelings with analyzed,

friction. Furthermore, the low friction of PAG 1-4
and No. 33 contributes a reduction in sliding
noises. If oil seal material and lubricant are notcompatible a so called stick-slip phenomenon canarise. Stick-slip can be described in that case asalternating between sticking of oil seal and piston
rod to each other and sliding over each other, withbig variations in friction force. This includes inparticular the occurrence of noises in low speed
area of shock absorber movement and needs to beprevented at any time.

objective test results. The sensor position in the
car are illustrated in Fig. 3.

Fig. 4
Fig. 3

S ensor positions inside the test vehicle forshock absorber oil evaluation tests at KYB
Suspensions Europe S.A.

Coefficient of friction over sliding speed ofshock absorber oils tested with KYBs pin-ondisc tribometer.

（1）
Laboratory tests
The test results obtained in KYB pin-on-disc
tribometer（Fig. 4）showed a significant difference

In addition to the pin-on-disc tests, a second
tribometer based on linear sliding principle waschosen to investigate the friction of PTFE-pistonand steel surface of the inner shock absorberworking cylinder. Furthermore, the influence of
reduced temperature on oil friction was evaluateby Stribeck curve recording up to 1.4 m/s sliding

in coefficient of friction between the four oils.

speed（see Fig. 5）.

Oil No. 23（pink graph）showed, as might be
expected due to the additive package, the highest
friction in comparison to the other oils. Especiallyin the low speed area of 0.06 mm/s the friction
value μ of No. 23 is approximately four times

Considering the Stribeck curves the different
friction characteristics at 20°C are not clearlyvisible as in the pin-on-disc tests, but rather thehigh friction oil No. 23 showed comparable low
friction when movement starts. All oils were athigher than of No. 33 （blue） and PAG 1-4（yellow）. PAG 1-4 itself has the lowest friction

nearly same friction level and did not show any
significant difference in Stribeck-curve

up to 30 mm/s sliding speed. The μ-values of PAG
1-4 range between 0.01（at 0.06 mm/s）and 0.11
（at 30 mm/s）, in case of oil No. 33 up to 0.19.
Beside the friction modifier, which is included inprogression. The interaction of piston ring andlubricant is of same high interest as the interactionof seal and piston rod as mentioned before.
Considering the test results obtained in thethe additive package, the higher polarity andtherefore better lubricating film formation

rheometer it became visible that the coefficient offriction at the starting point of movement isproperties of PAG contributes a reduction incomparatively high. Especially fluid No. 26 showed

４

TEST RESULTS AND VEHCILE EVALUATION― 18 ―

KYB技報Fig. 5第51号

Stribeck curves of shock absorber oils at 20°C
and －20°C.

2015―10

Fig. 6this behavior. However, PAG 1-4 offered lowest
friction up to sliding speed of 0.05 m/s. The areaDamping force test results of rebound andcom pression side（ASSY）.

of EHL regime（elastohydrodynamic lubrication）
of Stribeck-curve could not be mapped because ofa sliding speed limitation of the rheometer used
（1.4 m/s）. Significant differences in the frictional
behavior became visible by an oil temperature
reduction to －20°C. Hereby, low the friction oils
PAG 1-4 and No. 33 had by far the lowest friction.
On the other hand the Stribeck curve progressionof PAG 1-4 has a small difference to the curves ofmineral base oil samples. Due to molecularinteractions PAG changes its cold temperature
viscosity faster than mineral oils. This leads to afaster lubricating film formation with increasing
sliding speed. Thus, the transition in lubricating
regimes between solid, boundary andhydrodynamic lubrication occur faster. Result of

low friction has a strong influence on the comfort,
perceived road contact and feeling of vibrations.
By increasing the piston speed, the damping force
increases progressively and the influence ofviscometric oil properties raises.
（3）Vehicle tests at KYBSE
Target of the vehicles tests performed in Spain
was on the one hand to evaluate the stability andcomfort characteristics of the shock absorber oils
and on the other hand to compare this subjective
data with measurement data recorded by various
sensor in the test car. In order to analyze comfort
and stability representative test tracks on thecircuit were selected. These test tracks showedsome clear differences in the cabin noise level
recorded by a microphone and also in the cabin

this behavior is an obviously higher friction over
1.0 m/s sliding speed.

and shock absorber acceleration in z-, y- androlling direction during driving. In total 11 test（2）
Bench tests（ASSY）
Furthermore, low friction properties define also
the damping characteristics of shock absorber intests servohydraulic controlled bench tests（Fig. 6）.

tracks were selected to evaluate several subjective
test parameters and to compare the oils
respectively. Fig. 7 shows the results of one
selected test track with high level of vehicle

A sensor in the test machine measures the force
which is necessary to compress the shock

dynamics and therefore predestinated for stability
analysis. The sensor raw data was prepared byabsorber as well as to rebound. Both force values
together result in the total damping force
depending on damper speed.
Especially the oil behavior in low speed area,

use of LabView and a PSD filter（power spectral
density）. A PSD-spectrum describes the power
variation of a signal over frequency in an
infinitesimal frequency band. Considering thefrom 0.01 to 0.1 m/s sliding speed, is strongly
depending on low or high friction properties of the

diagrams in Fig. 7 and Fig. 8 a lower PSD value
indicates higher stability or lower accelerationoils. Oils with low friction in laboratory tests
revealed also lower damping forces. Here again,

respectively. In the frequency area of 0.4 to 4 Hz,
which is mainly related to greater movements of― 19 ―

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）

the vehicle, the high friction oil No. 23 and PAG
1-4 revealed highest cabin stability（Fig. 7 top）
and less rolling characteristics（Fig. 7 bottom）.
This coincides with the subjective evaluation of
the track. No. 26 and No. 33 oil were less stable.
The diagrams in Fig. 8 are recorded at a test
tracks with very rough and noise-/vibration
producing road conditions. Here, themeasurements allow conclusions to be drawn
about the road contact of the tire. The data
reveals less accelerations of the shock absorber
and thus of the cabin. Due to the higher stability
and low friction characteristics of No. 33 and PAG
1-4 the road contact and therefore steering
response could be improved in comparison to No.
23 and No. 26.
Beside stability and driving performance
comfort characteristics for driver and passenger
are essential. Similar to the car stability evaluation
representative test tracks were selected tomeasure the cabin noise level under different
conditions. Hereby, the influence of a sharp road
impact（bridge expansion joint）on a highway at
120 km/h（Fig. 9）and a test track with roughroad surface at 70 km/h driving speed（Fig. 10）
were chosen.
As the test vehicle passed the sharp, metallic
bridge expansion joint a clear increase in thecabin noise level could be recognized（see Fig. 9）.
However, there was a big difference between thefour test oils. No. 23 and No. 26 oil were nearly inthe same noise range, whereas the oils PAG 1-4
and especially No. 33 could absorb the impact

Fig. 7

Stability characteristics: cabin acceleration inlateral direction（y-direction, top）and rolling（bottom）.

Fig. 8

Vertical acceleration in z-direction of the car:cabin（top）and shock absorber（bottom）.

better. This is reflected in a reduction of the cabinnoise pressure level by 1.5 dB（A）for PAG 1-4
and 2 dB（A）for No. 33 respectively.
Under continuous driving on a road surface
which occurs a high noise level inside the cabin
No. 33 and PAG 1-4 oil showed their benefits once
again（see Fig. 10）. Whereas the noise pressurelevel over time could be reduced by 2.5 dB（A）
with PAG 1-4 in comparison to No. 23 oil, No. 33 oilwere nearly an the same level. This effect became
perceptible in the frequency area of 2000 –
8000 Hz, which is still audible for the human ear.

― 20 ―

KYB技報Fig. 9第51号

2015―10

Bridge expansion joint impact noise（cabinnoise pressure level）at 120 km/h.

Fig. 11

Fig. 10

B ackground noise inside the cabin: Noiseover time（top）and sound power over frequency（bottom）at 70 km/h driving speed.

KYB oil classification regarding stability/controllability and riding comfort.

stability and comfort.
Fig. 11 shows a summarizing comparison of alloils tested, No. 23 as high friction oil, No. 26 as
medium friction oil, No. 33 as low friction oil and
PAG 1-4 as low friction oil with an alternative
base oil. It is clearly visible that the change ofmineral oil based shock absorber oil to PAG 1-4
can have a positive effect especially on the vehicle
stability and controllability. In order to improvethe comfort characteristics of this kind of oil amodification of the shock absorber piston valve
setting would be necessary. However, a very goodcompromise between riding comfort and stability

Aim of the study was to evaluate thetribological performance of a polyalkylene glycol-

could be found. Whereas the other oils could only
be classified as oil with higher comfort or higher
stability, but without improvement in both
directions, PAG 1-4 improves both characteristics.

based oil（PAG）as new type of shock absorber
fluid. Beside of several chemical and viscometricadvantages PAG can be classified as

The range of applications for PAG-based fluids
is manifold. For hydraulic systems with highstability demands or special requirements on theenvironmentally acceptable lubricant, which takes
this oil to a special position on the sales market incomparison to mineral base oils. The laboratory
and bench conducted draw the conclusion thatbase oil（flashpoint, hydrolytic stability）and evenfor shock absorber systems in the motorsports
sector PAG can offer a promising alternative tocommonly used oils. Furthermore, the use of an

PAG 1-4 as fully formulated oil offers very low
friction characteristics in combination with theenvironmentally acceptable oil based on PAG
could in future be a useful sales argument withmain sliding parts of a shock absorber.
Furthermore, the vehicle tests under real driving
conditions at KYBSE（Spain）showed a highly
promising performance with regard to vehicle

regard to the global environmental awareness inmany industrial areas.

５

SUMMARY AND CONCLUSIONS― 21 ―

環境対応型ショックアブソーバ油としてのポリアルキレングリコール（PAG）
REFERENCES‐11‐002.

1） Woydt, M., 2013, “Biolubrifiants”, Encyclopédie5）	Greaves, M., 2013, “Polyalkylene Glycols” in Rudnick, L.,

Techniques de l’Ingénieur, TRI 1 800v2.

“Synthetics, Mineral Oils and Lubricants: Chemistry2）	Lawate, S., 2013, “Environmentally Friendly Hydraulicand Technology”, Taylor & Francis Group, ISBN 978-1-

Fluids” in Rudnick, L., “Synthetics, Mineral Oils andLubricants: Chemistry and Technology”, Taylor &4398-5538-6.
6）	Dixon, J. C., 2007, “The Shock Absorber Handbook”,

Francis Group, ISBN 978-1-4398-5538-6.

Second Edition, John Wiley & Sons Ltd.

3）	The Commission of the European Communities, 2005,7）	L ämmle, P. and Rohrbach, P., 2012, “Application ofCommission Decision 2005/360/EC.

ECLs and Today’s Legislation”, Journal of ASTM

	United States Environmental Protection Agency, 2011,
4）

International, 9（1）.

“Environmentally Acceptable Lubricants”, EPA 800‐R著者 

クリスティアン

ショルツ

伊藤

義浩

2014年入社. 技術本部基盤技術研

2007年入社. 技術本部基盤技術研

究所材料研究室．
博士
（工学）
．
ショッ

究所材料研究室．ショックアブ

クアブソーバ用材料（主に環境対ソーバ用材料の研究開発に従事．

応型作動油）の研究開発に従事．

― 22 ―