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Introduction of Composite Material Products Used inElectrical Auxiliaries for Automobile

Ken YASUDA *Shinji KOMATSUBARA **The Composite Material Product Division at NTN has developed bearings, mechanical parts, and module
products. These products make full use of tribology and are made of multi materials such as: resins,
sintered metals, magnetic materials. In this article, we mainly introduce products for thermal managementin automobiles.

1. Introduction
In recent years, the automotive industry has been
in development of various technologies focused on
the keyword of CASE. For example, motors and otherpower sources, inverters, and DC-DC converters
are being developed for electrification. Meanwhile,cameras, sensors, and ECUs that integrate and control
these accessories and their parts, are being developed
for autonomous driving. As these accessories become
smaller and lighter to improve the fuel efficiency andpower consumption of automobiles, heat dissipation
has become more difficult to manage due to the risein heat generation of new automobile components.
The addition of electrical and electronic devices thatgenerate large amounts of heat due to high-speed,large-capacity communications (such as 5G) havemade thermal management of the entire automobile
an important theme for ensuring reliability. The shift toelectric vehicles has also created new market demand
for a quiet vehicle interior that offers a recreational
environment free from the noise of a conventional
engine.
This paper introduces examples of applications forcomposite material products and how they contributeto higher efficiency of accessories as they relate
to thermal management of automobiles, and to
improved cabin comfort.

2. Elastomer main shaft seal for electriccompressors
The accessories related to thermal management
are critical to the range and battery life of electricvehicles. This has led to the increased market demandfor energy-saving and high-efficiency performance.

These accessories contain various sliding parts madeof high polymer materials (elastomers and resins) andtheir tribological properties are important.
While conventional internal combustion engine
vehicles use belt-driven compressors powered by theengine, electric vehicles such as HEVs, PHEVs, andEVs use electric compressors. Electric compressors
are used for cooling the cabin in HEVs and PHEVs,
and for temperature control for batteries and othercomponents – in addition to air conditioning in EVs.
There are two types of compressors: scroll type andswash plate type.
Scroll type compressors are used because of theirsuperior quietness. Scroll compressors use a main
shaft seal that seals the refrigerant and refrigeratingmachine oil. NTN has developed a low-torque,
low-leakage, BEAREE TP5300 main shaft seal that
contributes to power savings and higher efficiency.
2.1 Structure of electric scroll compressors
A cross section of an electric scroll compressor isshown in Fig. 1. The refrigerant is compressed by the
gyrating motion of the movable scroll, which is opposedto the fixed scroll. The movable scroll is driven by therotation of the main shaft, and is supported by ballbearings. The main shaft seal has an inner diameterof about 20 mm with lips on both the inner and outercircumference to reduce leakage of refrigerant andrefrigerating machine oil to the rotor side.
In EVs, electric compressors are used not only forheating and cooling, but also for the temperature
management of batteries and other components.
As a result, they operate for longer durations thanin internal combustion engine vehicles. This has
led to the need to improve the durability of electriccompressors.

* Plastics Engineering Dept., Composite Material Product Division** Hydrodynamic Bearing Engineering Dept., Composite Material Product Division

NTN TECHNICAL REVIEW No.89

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Introduction of Composite Material Products Used in Electrical Auxiliaries for Automobile

Stator

Rotor

Fixed scroll

Compression
chamber

Ball bearing

Main shaft

TP5300 and PTFE with filler, on a disc type testingmachine. The BEAREE TP5300 has specific wear ratethat is approximately one-fourth that of PTFE with filler.
0.15

PTFE main shaft seal
(conventional product)
BEAREE TP5300 main
shaft seal

Torque N･m

0.12

Main shaft seal

Cross
sectionLip

Movable scroll

0.09
0.06
0.03

Discharge valve

Fig. 1 Cross section of electric scroll compressors

Table 1 BEAREE TP5300 and PTFE main shaft seal
performance comparison
Item

BEAREE TP5300
main shaft seal

PTFE main shaft seal
(Conventional
product)

Base resin

Thermoplastic
elastomer

PTFE

Processing
methodInjection molding

Compression molding+ machining

Flexibility ofshapedesign◎△Torque

◎

〇

Leak

〇

〇

Durability

◎

△

Cost

◎

△

◎ : Excellent 〇 : Good △ : Acceptable

2.3 Friction and wear characteristics
Fig. 2 shows the torque measurement results of the
shaft seal in refrigerating machine oil. The torque of the
BEAREE TP5300 shaft seal is 15 % to 25 % lower thanthat of the PTFE shaft seal, and the TP5300 seal has
lower oil leakage. The oil leakage of the TP5300 seal isequivalent to the PTFE seal (less than 1 mL/min).
Fig. 3 shows the results of a wear test for BEAREE

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NTN TECHNICAL REVIEW No.89

0

0.2

0.4

0.6

0.8

1

Oil hydraulics MPa<Test conditions>
PAG oil, Oil temperature 100 °C
Oil hydraulics 0.3 to 0.8 MPa
Rotation speed 7 500 min-1, Steel main shaft

Fig. 2 Torque measurement results
15

Specific wear rate

×10-8 mm3/(N･m)

2.2 Features of the BEAREE TP5300 main shaft seal
NTNʼs BEAREE TP5300 main shaft seal is madeof a composite material that is formulated with afilling material in a thermoplastic elastomer – offering
excellent friction and wear characteristics. Its flexibility(low elasticity) offers advantages such as low torqueand low leakage. The lip reaction force caused by theinterference with the shaft is small, and the lip tip (innerand outer sides) easily follow the shaft and housing.
Further torque reduction is achieved by optimizing thelip design (thickness, angle, length, etc.).
Table 1 shows a performance comparison with aconventional polytetrafluoroethylene resin (PTFE) shaft
seal. While conventional PTFE shaft seals are machined,
the BEAREE TP5300 shaft seals can be injection
molded, offering better design flexibility and reduction
in manufacturing costs.

0.00

10

5

-75 ％
0

BEAREE TP5300

PTFE with filler<Test conditions>
Ring on disc type testing machine, PAG oil, Room temperature
Surface pressure 0.3 MPa, Speed 1 m/s
Opposing material SUJ2, 50 hFig. 3 Wear test results

3. Low torque plastic sliding bearings forelectric water pump
Electric vehicles are equipped with an electric water
pump that circulates cooling water, and an electriccompressor for thermal management. Sliding bearings
used in these pumps require even lower friction
coefficients for lower fuel and power consumption.
NTN has developed a low torque plastic bearing
with a significantly reduced friction coefficient incooling water. This bearing features special lubrication
grooves on the thrust surface of a PPS sliding bearing.
This bearing is made of a proprietary composite
material1)2) that combines materials such as
polyphenylenesulfide (PPS), polytetrafluoroethylene
resin (PTFE), and carbon fiber (CF).

3.1 Role and structure of electric water pump
Electric water pumps are classified by high-flow,
medium-flow, and low-flow types, with each type
having a different purpose in a vehicle. The highflow type electric water pump is used for engine
cooling, the medium-flow type is used for cooling thebatteries, motors, and inverters, while the low-flow
type is used for cooling and heating intercoolers andexhaust gas recirculation equipment.
Fig. 4 shows a cross section of a typical electricwater pump. The rotor includes: the impeller, magnet,
and sliding bearing, and is found in the pump housing.
Meanwhile, the stator is arranged opposite themagnet and is freely supported by the shaft throughthe sliding bearing. The magnetic field generated
by the energization of the stator causes the rotor torotate about the shaft. Since the impeller is integrated
with the rotor, the impeller rotates as the rotor
rotates, and the cooling water is sucked into the pumphousing.
The inner diameter of the sliding bearing is about 4
to 10 mm. During rotor rotation, radial and axial loads
are generated. This causes the inner diameter surface
and shaft of the sliding bearing, and the thrust surface
and the thrust pad, to slide in the cooling water. The
sliding bearing is pressed against the thrust pad on
the impeller side, and the axial load is larger than
the radial load. The frictional resistance of the thrustsurface is thus greater than that of the inner diametersurface. To reduce the frictional resistance of thesliding bearing, it is therefore necessary to reduce thefrictional resistance of the thrust surface.
Cooling water OUT
StatorThrust pad
Thrust pad
Pump chamber
Shaft (fixed)
Cooling water
IN

Rotor
(rotation)

Impeller

MagnetSliding bearing

Slidingbearing

In general, a rectangular lubrication groove shownin Table 2(b) is used as a lubrication groove on thethrust surface in sliding bearings for electric water
pumps. This rectangular lubrication groove penetrates
radially from the bearing bore to the outer diameter.
The cross section has a simple rectangular shape, so it
is conventionally applied to machined products suchas the carbon sliding bearings used in water pumps.
NTNʼs low torque plastic bearings instead havespecial lubrication grooves on the thrust surface of
the PPS sliding bearing, as shown in Table 2(a). These
special lubrication grooves have a shape that enables
material transfer during injection molding. As shownin Fig. 5, the special lubrication grooves are designed
so that the grooves gradually become shallower inthe counter-rotational direction of the bearing. This
causes cooling water to be forced into the shallower
grooves during bearing rotation, and generatepressure by the hydrodynamic effect. As a result, thecooling water can easily penetrate the thrust sliding
surfaces of the bearing.
Fig. 6 shows the dynamic friction coefficient incooling water for three types of PPS sliding bearings
with three shapes of thrust surface: one with special
lubrication grooves, one without lubrication grooves,and one with rectangular lubrication grooves on thethrust surface. The dynamic friction coefficient of the
PPS sliding bearing with special lubrication grooves
is 65 % lower than that without lubrication grooves,and 30 % lower than that with rectangular lubrication
grooves.
Table 2 Shape of lubrication grooves on thrustsurface of each thrust bearing
Item

Thrustsurfacelubrication
grooveshape(a) Special(b) Rectangular (c) No
lubrication
lubrication
lubrication
groovegroovesgrooves
Rotational
directionof bearing

Slidingarea ratio

0.88

0.95

1 (reference)

Pressure,
MPa

1.06

1.00

0.93

Note: Surface pressure is the value in the test (load 128 N)
described below.

Fig. 4 Structure of electric water pump
3.2 Bearing thrust surface lubrication groove shapeSliding bearings in electric water pumps maintainlow friction and low wear under good lubrication
conditions (high speed and low load). However, during
startup, shutdown, and when there is localized water
film loss during operation, the friction coefficientincreases due to contact between the sliding bearing
and the thrust pad – increasing the likelihood of wear.
As a countermeasure, lubrication grooves are included
on the thrust surface of the sliding bearing.

Pressure
高圧
Thrust pad
スラスト受

摺動面
Sliding surface

Bearing

軸受（スラスト面）(thrust surface)
軸受回転方向Rotational directionof bearing

冷却水がDirection of coolingwater being pushed
押し込まれる方向

Special lubrication groove
特殊潤滑溝

Fig. 5 Hydrodynamic effect from special
lubrication grooves
NTN TECHNICAL REVIEW No.89

81

0.03

-30 ％

0.02
0.01
0

0.03

10

0.02

-34 ％
5

0

(a) Special(b) Rectangular (c) No lubrication
lubrication groove lubrication grooves
grooves<Test conditions>
Ring on disc type testing machine cooling water (ethylene
glycol 50 % concentration), Room temperature, 128 N load
(surface pressure approx. 1 MPa), Speed 125 m/min, Opposing
material SUS304

Fig. 6 Relationship between shape of lubrication
grooves on thrust surface and dynamic friction
coefficient
3.3 Friction and wear characteristics
Fig. 7 shows the results of friction and wear tests
in cooling water for a low torque PPS sliding bearing,
and a conventional carbon sliding bearing with threerectangular lubrication grooves as shown in Table 2 (b).
The low-torque plastic bearing (with special lubrication
grooves) had a 34 % lower coefficient of dynamic
friction and 1/10 th the specific wear rate as comparedto the carbon sliding bearing (rectangular lubrication
grooves). This difference in the dynamic friction
coefficient is similar to the results for the rectangularlubrication groove and the special lubrication groove
shown in Fig. 6.
Low torque plastic bearings are made of PPS
composite material with fillers suitable for sliding incooling water. These bearings have special lubrication
grooves on the thrust surface, which provide lower
friction and wear characteristics compared to carbon
sliding bearings (rectangular lubrication grooves).
Low-torque plastic bearings have various otherexcellent properties, as shown in Table 3.

0.01

-90 ％

Low torqueplastic bearing(special
lubrication
groove)Carbon sliding
bearings(rectangularlubrication
groove)0.00

Dynamic friction coefficient

-65 ％

0.04

15

○

0.05

■ Specific wear rate
×10-8 mm3/(N･m)

Dynamic friction coefficientIntroduction of Composite Material Products Used in Electrical Auxiliaries for Automobile<Test conditions>
Ring on disc type testing machine, Cooling water (ethylene
glycol 50 % concentration), Room temperature, 128 N load
(surface pressure approx. 1 MPa), Speed 125 m/min, Opposing
material SUS304, 50 hFig. 7 Friction and wear characteristics of each typeof sliding bearing
Table 3 Comparison of properties of each type of
sliding bearing
Item

Low torque plastic
bearing(special lubrication
groove)Carbon sliding
bearings(rectangularlubrication groove)

Processing
methodInjection molding

Machining

Chemicalresistance◎◎

Impactresistance〇△Flexibility ofshapedesign◎△Friction
properties(in coolingwater)◎〇

Wear
resistance(in coolingwater)

◎

〇

Cost

◎

△

◎ : Excellent 〇 : Good △ : Acceptable

4. Sintered hydrodynamic BEARPHITE
headlight cooling fan
In conventional internal combustion engine vehicles,
the sound from interior accessories is typically lessnoticeable due to the noise of an internal combustion
engine. With no more engine noise, the electrificationof automobiles has led to a growing demand for
quieter interior accessories reliable over a wide rangeof temperatures.
In recent years, energy-saving and long-life LED
lights have entered the mainstream for headlights.

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NTN TECHNICAL REVIEW No.89

These require higher current to provide a visible lightintensity, but subsequently result in a large amountof heat generated in the LED circuit board. The needfor thermal management is therefore increasing,and the cooling fan motor used for heat dissipation(Fig. 8) must have stable performance over a wideC)
temperature range, from low temperatures (- 40 °C).
to high temperatures (100 °NTN has developed a hydrodynamic bearing,
Hydrodynamic BEARPHITE (Fig. 9), that meets theserequirements and is quiet over a wide temperature
range.

Fig. 9 Hydrodynamic BEARPHITE
4.1 Excellent quietness
Hydrodynamic BEARPHITE is a type of oilimpregnated sintered bearing manufactured bypowder metallurgy and has herringbone-shapedhydrodynamic grooves on the bearing inner diameter(Fig. 10). The hydrodynamic effect generated by shaft
rotation forms an oil film in the bearing clearance andsupports the shaft and bearing without contact.
Fig. 11 shows the results of determining thepresence or absence of contact between the shaft andHydrodynamic BEARPHITE by the electrical resistancemethod. This is done to confirm the difference in oilfilm formation depending on the presence or absenceof hydrodynamic grooves. Based on the detectedvoltage, the oil film formation rate was set to 0 % for
the contact state and to 100 % for the non-contact
state. These results indicate that hydrodynamic
grooves can support the shaft without contact.

10 000
8 000
6 000
4 000
2 000
0
10 000
8 000
6 000
4 000
2 000
0

100

Oil film formation rate % Oil film formation rate %Rotational speed r/min

Fig. 8 Cooling fan motor

Fig. 10 Hydrodynamic BEARPHITE inner surface(red outlined areas: hydrodynamic grooves)

Rotational speed r/min

Hydrodynamic BEARPHITE

Oil ﬁlm formation rate

80
60
40
20

Rotational speed

0

100
80

Oil ﬁlm formation rate

60
40
20

Rotational speed

30 s

0

Fig. 11 Difference in oil film formation depending on
presence or absence of hydrodynamic grooves(upper: no hydrodynamic grooves;lower: with hydrodynamic grooves)
Where a drop in oil film pressure is a concern3),
Hydrodynamic BEARPHITE generally remains quiet at
low rotational speeds. This is why it is popularly usedin cooling fan motors for information equipment, suchas thin-type notebook PCs and mobile terminals. It isalso being used in cooling fan motors for headlights
because of its excellent quietness over a wide rangeof rotational speeds, from low to high speeds.
4.2 High reliability over a wide temperature range
In headlights, the bearing performance remains
stable because of the minimum change in lubricant
viscosity expected, over the wide temperature
range required for headlights. A significant drop in
lubricant viscosity at high temperatures reduces thehydrodynamic pressure effect generated by shaft
rotation. However, the Hydrodynamic BEARPHITE,
which applies a less viscous lubricating oil that
decreases at high temperatures, offers excellent
temperature characteristics when compared toconventional products. (Fig. 12)

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Introduction of Composite Material Products Used in Electrical Auxiliaries for Automobile
5. Conclusion

Viscosity

Developed
product
Conventional
product

35 ％ increase

40 ℃
100 ℃
Temperature

Fig. 12 Relationship between lubricating
oil temperature and viscosity

Eccentricity ratio

Fig. 13 shows the eccentricity ratio calculation
C).
results of the shaft at high temperatures (100 °The eccentricity ratio is the ratio of shaft center
displacement to radial clearance, and a lower
eccentricity ratio means a larger minimum film
thickness. The Hydrodynamic BEARPHITE cansignificantly reduce the eccentricity ratio as compared
to conventional products, ensuring better bearing
reliability over a wide range of temperatures.

References

１） Takuya Ishii, Ken Yasuda, The Latest Technology

of Resin for Automobiles and Aircraft, Technical
Information Institute (2016) 167.
２） Ken Yasuda, Technology of Plastic Sliding
Bearings for Electric Water Pumps, Monthly
Tribology, May 2021, No. 405 (2021) 32.
３） Shinji Komatsubara, Hydrodynamic BEARPHITE
Bearings for Thin Cooling Fan Motors, NTN
TECHNICAL REVIEW, No.88 (2021) 44-45.

-37 ％Developed
product

This paper introduces a case in which NTNʼsbearings and elemental parts made of resin, sinteredmetal, and other materials were adopted to saveenergy in automobiles and provide a comfortablecabin interior.
Thermal management has become vital to thedevelopment of vehicle electrification, autonomous
driving, and connected automobiles. The UN-R51
international standard for four-wheeled vehicle noise
has entered Phase 3 and is becoming stricter. In Phase3, tire noise is taken into account, and the noise level
during driving is required to be reduced from the levelof a vacuum cleaner in Phase 2 to that of a washingmachine. In addition, in a future where autonomous
driving frees drivers from driving operations, it isexpected that the demand for a quieter interior space
will rise.
We will continue developing products andtechnologies that are key to improving thermal
management and vehicle interior habitability, thereby
contributing to the development of a mobile society
with vehicles at its core.

Conventional
product

Fig. 13 Eccentricity ratio calculation results
Furthermore, as a feature of the powder metallurgy
process, Hydrodynamic BEARPHITE can retain ample
lubricant in the pores on the bearing surface layer
and inside the pores (Fig. 14). Therefore, even if theassumed operating temperature range is exceeded,
there is an effect of suppressing seizure due to thecontact between the shaft and the Hydrodynamic
BEARPHITE.

Photo of authors

Pore (black area)

0.1 mmFig. 14 Surface condition of Hydrodynamic BEARPHITE84

NTN TECHNICAL REVIEW No.89

Ken YASUDA

Shinji KOMATSUBARA

Plastics Engineering
Dept.,
Composite Material
Product Division

Hydrodynamic
Bearing Engineering
Dept.,
Composite Material
Product Division