CommentaryEvolution of Fixed Constant Velocity Joint thatContributes to Environmental Protection

Masashi FUNAHASHI *Teruaki FUJIO *Ritsuki SAKIHARA *In 1963 NTN commercialized the constant velocity joint for the firsttime in Japan. Since then, NTN has continued to develop new products
in order to adapt to the environmental policy which changes with thetimes. This article looks back on the evolution of NTNʼs fixed constantvelocity joints and explains about two types of high efficiency fixed constant velocity joints applied for theevolving EV market of the future.

1. Introduction
Drive shafts used for power transmission in
automobiles can be divided into two types. Fixed
constant velocity joints (“fixed CVJs”) are attachedto the tire side and can take a large angle as the tirerolls. Sliding constant velocity joints (“sliding CVJs”)
are attached to the powertrain unit side and can takean angle and slide with vertical movement of thevehicle body (Fig. 1). NTN has been developing drive
shafts that are compact, lightweight, high-angle, lowvibration, and has made continuous improvements
using tribology, materials, mechanical design andother technologies. On the other hand, as abnormal
weather conditions have occurred due to global
warming caused by increased CO2 emissions, theimpact of human activity on the environment is being
taken up as a social problem making it increasingly
important to find a new approach to environmental
conservation. Since the Kyoto Protocol wasestablished in 1997, the international community has
worked to advance global warming countermeasures.
To achieve the global average temperature
increase target set in the Paris Agreement of 2015,
efforts to realize a decarbonized society by 2050
are accelerating around the world. Against thatbackground, in recent years the use of high-efficiency(low heat generation) drive shafts has been attracting
attention.
This paper focuses on fixed CVJs, for which there
is a greater need for improvement from the market.
We introduce the evolution of CVJs that NTN iscontinuously developing in response to the changes
in automobiles associated with environmentalprotection.

2. Market trends/needs
As the drive toward decarbonization continues,
each year countries around the world are tightening
their standards for CO2 emissions and fuel efficiency
of automobiles. There is a continuing need forlightweighting and higher efficiency of all components
used in automobiles. In addition, the automotive
industry is rapidly shifting from conventional internal
combustion engine vehicles to electric vehicles (EVs)which are expected to have a longer cruising range. In
addition, changes in vehicle layout such as changes in
the position of the powertrain unit and extension of
the wheelbase are expected in order to provide spacefor large capacity batteries. (Fig. 2)
Sliding ty

pe C

VJFixed ty

Drivepe C

VJshaft

Fig. 1 Arrangement of fixed CVJs at the drive shaft* CVJ Development Dept., CVJ Products Unit, Automotive Business Headquarters

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Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection

Powertrain
unit

Extended wheelbase

Powertrain
unit

Side of vehicle
Drive shaft

Drive shaft

Powertrain
unit

Powertrain
unit

Top of vehicle

Fig. 2 Image of EV drive shaft arrangement
In this context, the functions required of drive
shafts are (1) higher efficiency, smaller size, andlighter weight to help reduce fuel consumption andelectricity costs, and (2) a higher operating angle(higher steering angle) to control the increase inturning radius due to an extended wheelbase anda higher working angle due to the need to securebattery space. One particular issue has been that fixed
CVJs are less efficient than sliding CVJs in terms of therequired functions and structure. NTN is continuously
developing fixed CVJs to meet these market trendsand needs.

In 1956, Hardy Spicer (U.K.) developed a fixed CVJ
that could transmit power at constant velocity evenwhen the operating angle was increased. This enabled
the front wheels of a car to have both steeringand driving functions. NTN formed a technology
alliance with Hardy Spicer in 1962, through which
we developed the BJ (maximum operating angle
42.5 degrees) for the Suzulight Van FE (Suzuki MotorCorp., Fig. 4). In 1964, the first vehicle equipped witha fixed CVJ that was successfully mass-produced inJapan was introduced to the market (Fig. 5). This
greatly improved handling stability, which had beena problem for FF and 4WD vehicles, and contributed
greatly to the popularization of automobiles in Japan.
Later, to meet the rapidly expanding demand for
fixed CVJs and the increasing need for higher steering
angles in vehicles, NTN developed BJ-L (Fig. 6), which
expanded the maximum operating angle from 42.5
degrees to 46.5 degrees while maintaining the outer
diameter. NTN achieved this by changing the fixed CVJouter ring material from carburized steel to induction
hardened midcarbon steel, and by making an optimalhigh angle design. Mass production of the BJ-L fixed
CVJ began in 1982, is still used as the basic design
today, and continues to evolve to capture the market
needs of small size, lightweight, high efficiency, andhigh angle.

3. Evolution of NTN fixed CVJs1)2)4)5)
3.1 Development of CVJs in Japan
Before the 1960s, automobiles developed mainly
as rear-wheel drive (FR) vehicles, while front-wheel
drive (FF) and four-wheel drive (4WD) vehicles
were also developed to improve comfort and driving
performance, etc. In FF and 4WD vehicles, powerfrom the engine is transmitted to the front wheels.
Drive components are therefore required to be abletransmit power at constant speed even if the tires aresteered. The cardan joint (cross shaft coupling, Fig. 3)
used at that time was an unequal-velocity joint thatcaused large rotational fluctuations between the input
and output shafts when the operating angle increased,resulting in unstable steering operation during driving.

Fig. 4 Suzulight Van FE (Suzuki Motor Corp.)

Fig. 5 Exterior of CVJ mounted on Suzulight Van FE

Fig. 3 Cardan Joint (cross shaft coupling)
Fig. 6 BJ-L exterior74

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3.2 The shift towards more compact, lightweight,
high-efficiency CVJs
The evolution of fixed type CVJs is shown in Fig. 7.
The first evolution was to change the lubricant
sealed inside the CVJ from lithium-based grease
to urea-based grease, thereby achieving a longer
operating life. The fixed CVJ (BJ-L compact) is
4 % smaller and 8 % lighter than the BJ-L while
maintaining the maximum operating angle of 46.5
degrees. Mass production began in 1992.
The next evolution was the E-series fixed CVJ(“EBJ”; Fig. 8), which achieved further downsizing
and weight reduction. To reduce the size while
maintaining the same load carrying capacity as theBJ-L, the outer diameter size was reduced and thenumber of balls was increased from six to eight. The
EBJ is 13 % smaller and 20 % lighter than the BJ-L,
and it improved the torque loss ratio by 30 % (higherefficiency). Mass production of the EBJ began in 1998.
The torque loss ratio was further improved by 20 %with the EBJ-S, by optimizing the internal clearance
and applying low-friction grease to the EBJ. Mass
production of the EBJ-S began in 2020.

Fig. 8 Exterior of EBJ, EBJ-S
In 2022, NTN began mass production of the highefficiency fixed CVJ “CFJ”.3) This was the first CVJ
to adopt NTNʼs proprietary spherical cross groove
structure (the “proprietary structure”) as a further
evolution of the EBJ. The same outer diameter andmass as the EBJ were maintained while the torqueloss ratio was improved by more than 50 %. CFJs will
be introduced in detail in Chapter 4.

Standard typeHigh-angle type

BJ-LBJ-Lcompact

EBJ

EBJ-S

CFJ

UJ

UJ compact

VUJ

DevelopedproductNo. of balls

668886668Maximum
operatingangle

46.5degrees

46.5degrees

47degrees

47degrees

47degrees50
degrees50degrees50
degrees52
degreesStart ofmass
production

1982

1992

1998

2020

2022

1988

1992

2007

ー

Lightweight,
higherefficiency

100 %Efficiency

Function

Developedproduct52 degrees

99 %Compact

Standard
type
Compact

High-angle
type

-10 %

0%

10 %

20 %

30 %

Mass Reduction Rate

Fig. 7 Evolution of fixed type CVJs

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Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection
3.3 Increasing the operating angle of CVJs
As FF vehicles became larger in the 1980s and 4WDvehicles increased in number, the need to reducethe minimum turning radius drove demand for fixed
CVJs with a high operating angle. In 1988, NTN
began mass production of UJ, which has a maximum
operating angle of 50 degrees. To ensure high angle
functionality, mass production of UJ began with a4 % increase in diameter and an 8 % increase inmass compared to BJ-L. In 1992, UJ (small size) was
developed that achieved an outer diameter and massequivalent to BJ-L by applying urea-based long-lifegrease (Fig. 7).
In 2007, NTN began mass production of VUJ,
which has the same six balls as UJ, but is smaller andlighter due to the optimized strength of each partand the application of long-life grease. In 2022, NTN
completed basic development of a 52-degreehigh-angle fixed CVJ [developed product] based on
CFJ technology. Compared to the UJs (compact type)developed since the 1990s, the VUJ is 4 % smallerand 8 % lighter, while the 52-degree high-angle fixed
CVJ [developed product] is 10 % smaller and 16 %lighter, with a torque loss ratio improvement of over
50 % (Fig. 7).

4.1.1 Features(1) Arc-shaped tracks on the inner and outer rings are
inclined in the axial direction, with adjacent tracks
arranged in mirror-image symmetry (Fig. 10).
(2) The slopes of the inner and outer ring tracks
cross each other and the ball is placed at theintersection (Fig. 11).
The torque loss of a CVJ is equivalent to the energy
lost due to the frictional forces that occur between
the parts during torque transmission. In the case ofEBJ, among the internal forces of the CVJ that occur
during torque transmission, the direction of the forceof the ball pushing the cage is the same for all balls.
The cage is pushed in one direction and contacts
the outer and inner rings. On the other hand, theunique structure of the CFJ causes the force of theball pushing the cage to be in the opposite direction
for adjacent balls, which cancels out the force on thecage and significantly reduces the contact force withthe outer ring and inner ring (Fig. 12). This reduces
the frictional force between the cage and the outerand inner rings, resulting in the worldʼs highest level ofefficiency.

Track

4. Helping to reduce environmental impact
with higher efficiency fixed type CVJs
To meet vehicle requirements, NTN offers two typesof fixed CVJs: a standard type and a high-angle typewith different maximum operating angles, as shown inFig. 7.
This chapter introduces the standard high-efficiency
fixed CVJ “CFJ” and the high-angle type 52-degree
fixed CVJ [developed product] to show how
improvements in the efficiency of fixed CVJs can help
to reduce environmental impact.
4.1 High-efficiency fixed CVJ “CFJ”3) (standard type)
The CFJ is a fixed CVJ with a maximum operating
angle of 47 degrees that achieves the worldʼs highest
level of efficiency through the adoption of a uniquestructure (Fig. 9) with the aim of reducing automobile
CO2 emissions and improving fuel efficiency. The
torque loss ratio is reduced by 50 % or more while
maintaining the same outer diameter and mass as theEBJ (conventional product), which has achieved theworldʼs highest levels of compactness and lightweight.

Fig. 10 Image of track shape

Fig. 11 Arrangement of track and ballOuterring
BallCage
Innerring

Fig. 9 Configuration of CFJ

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EBJCFJ

Direction of the force of the ball pushing the cage

Fig. 12 Comparison of internal force

Torque loss ratio %Blue line: conventional product (EBJ)Red line: CFJ
Continuous line: During normal driving
Dotted line: During regenerative driving

036

9Operating angle deg

1215Fig. 13 Comparison of torque loss ratios
4.1.3 Efficiency of Fixed CVJs and Estimated Effects
on Vehicles
The efficiency of the drive shaft, the component thattransfers power from the engine to the tires, directly
affects the fuel efficiency and electricity consumptionof a vehicle. In addition, it has an even greater impact
on hybrid vehicles and EVs that have regenerative
braking for recovering energy during deceleration.
Performing a detailed calculation for CFJ, we findthat in the case of a gasoline vehicle, fuel efficiency
improves by 0.62 % and CO2 emissions decrease by
0.96 g/km compared with EBJ (fuel efficiency: 17.6km/L) when the vehicle weighs approximately 1.5tons and the drive shaft is installed at a 9-degree
angle under the WLTP（Worldwide Harmonized LightVehicle Test Procedure）conditions. BEV (electricpower consumption: 155 Wh/km) improves electric
power consumption by 0.90 % (Table 1).
Table 1 Effects on automobiles (EBJ ratios)
Fuel and electricity
cost Improvement rate

CO2 Emission
Reduction

Gasolinevehicle

0.62 % UP-0.96 g/km

HEV

0.76 % UP-1.12 g/km

BEV

0.90 % UP―<Test conditions>
Setting angle: 9 degreesVehicle: fuel efficiency 17.6 km/L; power consumption 155 Wh/km
Vehicle weight: approx. 1.5 tons; driving conditions: WLTP

4.2 52 degrees fixed type CVJ (high-angle type)[developed product]
This product is a high-angle, high-efficiency fixed
CVJ. As well as offering a high operating angle that islarger than the maximum operating angle of the VUJ(maximum operating angle: 50 degrees), it offers highefficiency and is compact and lightweight.
4.2.1 Features
By adopting a unique structure similar to that of theCFJ, it is possible to reduce the force generated inside
the CVJ during torque loading (internal force) and to
improve the load carrying capacity at high operating
angles. In addition, NTN changed the track shape in
the area where the ball moves toward the outer ring
aperture at high operating angles. This secured therolling path length of the ball to align with the contact
point between the ball and the track at operating
angles exceeding 50 degrees. The cage, which is theweakest part of the fixed CVJ at high operating angles,
was made smaller yet higher angle was achievedby optimizing the shape and changing the material.
As a result, a 6 % reduction in size and an 8 %weight reduction were achieved while increasing themaximum operating angle by 2 degrees compared tothe VUJ (Fig. 14).
VUJ

Developed productFig. 14 Design comparison
4.2.2 Function- Efficiency (torque loss ratio)
By adopting a unique structure, the torqueloss ratio was improved by more than 50 % in all
angular regions compared to the VUJ (Fig. 15).

Conventional product (VUJ)

Torque loss ratio %4.1.2 Function
Fig. 13 shows the measurement results of torqueloss ratio. The torque loss ratio was reduced by morethan 50 % compared to the conventional productnot only during normal driving, but also during theregenerative driving that occurs in vehicles such asEVs.

Developed product0369

Operating angle deg

1215Fig. 15 Comparison of torque loss ratios

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Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection

Breakage torque Nm- Strength at high operating angles
By using a unique structure, modifying the trackshape, optimizing the cage shape, and changing
the materials, we achieved a 6 % reduction insize and 9 % reduction in weight compared to theVUJ, while achieving the same strength at highoperating angles (Fig. 16).

Conventional product(VUJ)

DevelopedproductFig. 16 High angle static torsional strength comparison

5. Summary
This paper touched on the evolution of fixed CVJs
that contribute to reducing environmental impact, andintroduced products NTN has developed in responseto the changing times and their effectiveness. To
realize a global decarbonized society, automobiles areundergoing a once-in-a-century transformation. CVJs
are required to provide enhanced functions to respondflexibly to this transformation. As a constant velocity
joint manufacturer, NTN will target demand for EVs,
which will continue to expand going forward so that
we can contribute to the realization of a decarbonizedsociety and reduce environmental impact. We willcontinue to develop CVJs that are small, lightweight,
high-performance, and have excellent quietness
with optimal strength and durability tailored to
the locations of their application and to vehicle
characteristics.

Photo of authors

Masashi FUNAHASHI

Teruaki FUJIO

Ritsuki SAKIHARA

CVJ Development
CVJ Development
CVJ Development
Dept.,
Dept.,
Dept.,CVJ Products Unit,
CVJ Products Unit,
CVJ Products Unit,
Automotive Business Automotive Business Automotive BusinessHeadquarters
Headquarters
Headquarters

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NTN TECHNICAL REVIEW No.89

References

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Automobiles and Recent Technology, NTN
TECHNICAL REVIEW, No. 70, (2002) 8-17.
２） Shin Tomogami, Technical Trends in Constant
Velocity Universal Joints and the Development ofRelated Products, NTN TECHNICAL REVIEW, No.
75, (2007) 10-15.
３） Teruaki Fujio, Next Generation High Efficiency
Fixed Constant Velocity Joint “CFJ”, NTN
TECHNICAL REVIEW, No. 81, (2013) 64-67.
４） Shinichi Takabe, History of Constant Velocity
Joints, NTN TECHNICAL REVIEW, No. 85, (2017)40-45.
５） Tatsuro Sugiyama, History of Developmentof Constant Velocity Joint Aiming at Low FuelConsumption, NTN TECHNICAL REVIEW, No. 87,(2019) 59-62.