TECHNICAL PAPER

Development of Third-Generation Electronically Controlled
AWD Coupling with New High-Performance Electromagnetic Clutch
J. ANDO H. ANDO T. TSUDA

K. SUZUKI Y. NIIKAWA

This paper describes the development of the new third-generation electronically controlled all-wheel drive (AWD)
coupling that achieves drastically improved drag torque performance and torque accuracy at low temperaturesand contributes to higher fuel efficiency through weight reduction in the driveline. One issue for electronicallycontrolled AWD couplings is an increase in torque due to higher lubricant viscosity at low temperatures,
especially below 0℃ because of clutch slide with the lubricant sealed inside the couplings. The developed thirdgeneration electronically controlled AWD coupling addresses this issue by focusing on the surface texture of theelectromagnetic clutch. The third-generation coupling also restricts the torque increase by actively utilizing the
dynamic pressure between the clutch plates and increasing the clearance of the clutch plates at low temperatures
where viscosity increases. This enables further weight reduction in the driveline. In order to reduce drag torqueat low temperatures, a macroscopic sliding surface profile in the order of tens of micrometers is provided on theelectromagnetic clutch under fluid lubrication. In addition, to reduce control torque at low temperatures whenelectric current is applied, the microscopic sliding surface profile on the electromagnetic clutch, which is in theorder of several micrometers, was optimized under boundary lubrication. This results in stable torque accuracy atboth low and high temperatures.
Key Words: All-Wheel Drive System, Third-Generation ITCC, Electromagnetic clutch, Surface Texture

1. Introduction
In the field of vehicle driveline components, thedevelopment of new products that contribute to improved
fuel efficiency while maintaining driving stability andsafety has become an urgent need from the standpoint of
helping to protect the global environment. Improving fuelefficiency through weight reduction and higher driveline
efficiency is particularly important for vehicles installedwith an all-wheel drive (AWD) system such as that shownin Fig 1.
Minivans and sports utility vehicles (SUVs) basedon the chassis of passenger cars have become popular
all over the world. Furthermore, AWD systems are
increasingly adopting couplings capable of electronicallycontrolling the transmission torque as shown in Fig. 2.
The Intelligent Torque Controlled Coupling (ITCC) is
an electronically controlled AWD coupling that distributes
optimum torque as needed. This coupling enables
excellent AWD performance and high fuel efficiency,
and also allows for a high degree of matching with othercontrol systems, such as brake and electronic stability
control systems. In addition, ITCC is being further

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

developed to achieve both higher AWD performanceand fuel efficiency. It is important to stabilize torqueespecially under low temperature conditions, andimproving this performance may help to reduce theweight of the driveline. The torque derived from clutch
drag when the ITCC control current is not applied (i.e.,
when the clutch is not pressed) and the control torquewhen the control current is applied (i.e., when the clutch
is pressed) increases in low temperature conditions
due to higher lubricant viscosity. Improving this torquechange may enable further weight reduction in the entire
driveline through reviewing the driveline from the aspectof strength design.
The third-generation ITCC has been developed toachieve this aim by focusing on the surface texture of theelectromagnetic clutch. It expands the clearance between
the clutch plates to restrict excess increases in torque by
actively utilizing the dynamic pressure between the clutch
plates at low temperatures where the viscosity of lubricant
increases. This enables weight reduction of the driveline
and contributes to an improvement in fuel efficiency. This
paper describes the high-performance technology of theelectromagnetic clutch used in the third-generation ITCC.

19

−Development of Third-Generation Electronically Controlled AWD Coupling with New High-Performance Electromagnetic Clutch−

Vehicle speed
Steering angle
Throttle angle

・Newly developed electromagnetic clutch
Aim: Improvement in temperature dependence of torque,reduction in drag torque at low temperature

PerformanceElectric current
Electronic
control unit
EngineReardifferential
gear

AWD coupling
Front differential gear

Transmission

Gen2
・DLC coating
Aim: Improvement in durability
・High performance fluid for AWD coupling
Aim: Improvement in durability, reduction in drag torqueat low temperature

Gen1

Transfer

1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017
Start ofdevelopment

Gen1

Electromagnetic clutch (material: steel)
Lattice groove

Main clutch (multi-disk clutch)
Input casing

Electromagnetic
clutch part
Electromagnetic
coil
Cam

When not applying current−1
Rotational speed: 0-300 min

16＊1 : Drag torque of ITCC at eachtemperature compared to dragtorque at 50℃

12
8
4
0
−40

Gen2

−20

0

20
40
60
Temperature, ℃

80

100

120

Fig. 4 Temperature dependence of drag torque of ITCC

accuracy at low temperatures were drastically improvedby modifying the surface texture of the electromagnetic
clutch. The third-generation ITCC is now in production.

Output shaft

Fluid
Armature

Fig. 2 Structure of ITCC

2. History of ITCC development
Figure 3 shows the history of ITCC development. The
first-generation ITCC, an electronically controlled AWD
1)coupling, was developed in 1997 (Gen1) , featuring thefirst use of its distinct structure with an electromagnetic
clutch in the world. The second-generation ITCC wasreleased in 2004 (Gen2). Durability was significantly
improved by the use of diamond-like carbon (DLC)2)-4)
on the electromagnetic clutch and a special
coating5)lubricant . These measures expanded the usable boundary
area of the AWD coupling and greatly enhanced thecompetitiveness of the product. In addition, improving the
durability increased the clutch capacity, thereby reducing
the number of clutch plates and helping to reduce size andcost.
This paper describes the third-generation ITCC
(Gen3), in which the drag torque performance and torque

20

Gen3

20

Inner plate

Proportion of drag torque＊1

Micro groove

Gen2

Fig. 3 History of ITCC

Fig. 1 Example of ITCC application

Outer plate

Gen3

3. High performance technology
3. 1 Reduction in drag torque at low temperatures
As shown in Fig. 4, the drag torque of the ITCC
increases under low temperature conditions. This iscaused by increased lubricant viscosity. The secondgeneration ITCC uses a special lubricant with a synthetic
base oil. This reduces the increase in viscosity under low
temperature conditions compared with a general mineralseries lubricant. However, it was necessary to modify thesliding surface to further reduce the drag torque.
Figure 5 shows the Stribeck curve. The range of
lubrication examined in this study is in the hydrodynamic
lubrication region as shown in Fig. 5. Figure 6 indicatesthe influence of each component on the drag torque of the
ITCC. The electromagnetic clutch alone contributes five
percent of the ITCC drag torque. However, considering
torque amplification by cam mechanism, this is equivalent
to 88 percent of the overall total drag torque. Therefore,
reducing the drag torque depends largely on improving
the electromagnetic clutch.
To reduce the drag torque of the electromagnetic
clutch, this study focused on the surface texture of the

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

−Development of Third-Generation Electronically Controlled AWD Coupling with New High-Performance Electromagnetic Clutch−

Boundary
Hydrodynamic
lubrication
lubrication
Mixedlubrication
Range
examinedv : Sliding velocity
P : Pressureg : Viscosity of lubricant

5%Electromagnetic
clutch (alone)
Torqueamplification byelectromagnetic
clutch(main clutch)Camactuation

Fig. 6 Contribution of ITCC components to drag torque

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

s＝ g

U
h

g : Viscosity of lubricant
U : Relative speed between clutch plates
h : Clutch plate clearance

Fig. 7 Method of reducing drag torque
Macroscopic sliding surface profile in the order of tens of µm
Close-up

Inner plate

Land portion

Cross section of groove portion
Conventional

Add crowning

New technology

GrooveGrooveFig. 8 Reducing drag torque by adopting macroscopic sliding
surface profile (crowning)
Generation of
hydraulic reaction force

Moving direction

Outer plate

Inner plate

Main clutch(alone)83%

Shear stress:(drag torque)A

Fig. 5 Illustration of range examined using Stribeck curve(drag torque)

12%

Clutch plate clearance: hFlow oflubricantA
Increase in clutch
plate clearance

GrooveMoving direction

Fig. 9 Mechanism of drag torque reduction at low
temperature with crowning
20
Proportion of drag torque＊2

gv
P

Outer plate
Inner plate

Velocity: U

Crowning amount

Friction coefficient µ

clutch. Figure 7 shows a general equation of shear stress,
which indicates how to reduce the drag torque. The
drag torque increases due to higher lubricant viscosity
especially under low temperature conditions, but can be
reduced by expanding the clearance between the clutch
plates. Therefore, crowning of several tens of micrometers(μm) was provided on each land portion of the innerplate surface as shown in Figs. 8 and 9. As a result,it was found that the drag torque at −40℃ decreases
linearly with the increase in the amount of crowning
as indicated in Fig. 10. This has a remarkable effect,
especially when lubricant viscosity increases under low
temperature conditions. The crowning allows the active
use of high-viscosity lubricant to effectively leverage thehydraulic reaction force in the direction that expands theclearance between the clutch plates. In contrast, in abovenormal temperatures, this hydraulic reaction force isadjusted to prevent a trade-off relationship. Without thisadjustment, an excess increase in the hydraulic reaction
force due to greater slip velocity would create a negative
l-v characteristic slope (index of vibration resistance:
dependence of friction coefficient on velocity) andgenerate shudder.
Figure 11 compares the drag torque of the second andthird generation ITCC units. Especially below 0℃, thedrag torque of the third-generation ITCC is approximately
50 percent lower than the second-generation ITCC.
The crowning provided on the inner plate surface
allows for a significant reduction in the drag torque.

16

When not applying current
Temperature: −40℃
Rotational speed: 0−300 min−1

12
8
4
0

＊2: Drag torque of ITCC at −40℃ comparedto drag torque of Gen2 at 50℃(see Fig. 4)
Crowning amountFig. 10 Effect of crowning on reduction in drag torque at
low temperature21

−Development of Third-Generation Electronically Controlled AWD Coupling with New High-Performance Electromagnetic Clutch−

Stribeck curve

When not applying current
Rotational speed: 0−300min−1＊3: Drag torque of ITCC at eachtemperature compared todrag torque at Gen2 at 50℃

16
12Friction coefficient µ

Proportion of drag torque＊3

20

Decrease
Gen2

8
4
Gen3
0
−40 −20

Range
examined

Mixedlubrication
Hydrodynamic
lubricationv : Sliding velocity
P : Pressureg : Viscosity of lubricant

gv
P
0

20
40
60
Temperature, ℃

80

100

120

Fig. 11 Temperature dependence of proportion of drag torquein actual ITCC units

3. 2 Improvement in torque accuracy at low
temperatures
The range of lubrication examined in this study liesin the boundary lubrication region on the Stribeck curveas shown in Fig. 12. In order to control this boundary
friction, the optimization of the microscopic sliding
surface profile of the electromagnetic clutch was
examined theoretically and experimentally. Figure 13
illustrates the friction between the sliding materials(i.e., the inner and outer plates) in oil. The friction isconsidered to be a mixture of fluid friction due to theshearing resistance of the lubricant and boundary friction
6)
due to solid contact .
Figures 14 and 15 show the simplified models of thefriction interface between the outer and inner plates used
for theoretical analysis.
The normal force F 1 of the boundary friction area
caused by the clutch pressing force F 0 is represented in
Equation (1)F1 ＝ F0 − ∫∫ Pdrd h⑴where, P is the hydraulic reaction force of the lubricant,and r and h indicate the radial direction to the sliding
direction, and the circumferential direction (the sliding
direction), respectively, as shown in Fig. 14.
The torque T F caused by solid friction is expressed in
Equation (2)TF ＝ ∫

Boundary
lubrication

2pr 2 F 1 lb
drA

Fig. 12 Illustration of range examined using Stribeck curve(control torque)

Microscopic sliding surface profile in the order of several µm
Hydraulic reaction F 0 : Pressing force
force PU : Velocity Outer plate

Fluid
Severalµm

F1s

Inner plateg : Viscosity of
lubricanth : Clutch plateclearance

F1 lTotal boundary friction force = Solid friction force + Fluid shear force

Fig. 13 Control of boundary friction on microscopic sliding
surface profile

y

U

h

Z (r)
X (h)

Fig. 14 Wedge-shaped clearance

F0 : Pressing force

Outside⑵

Insidewhere, A represents the apparent contact area of thesliding portions, and l b represents the coefficient ofboundary friction between solids.
Next, the torque T f caused by the viscosity of the
lubricant is expressed as follows.

Outer plate

Tf = ∫∫ srdrd h⑶where, s is the shear stress of the lubricant working
on wall surfaces. As the following equations show, P is

22

Inner plate

T 0 : Total torque
Y
r (Z)
h (X)

Fig. 15 Friction surface profile model of electromagnetic
clutchJTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

−Development of Third-Generation Electronically Controlled AWD Coupling with New High-Performance Electromagnetic Clutch−

ing
d

⑸

where, M represents the viscosity of the lubricant andU represents the sliding velocity. The total torque T 0 is asfollows.

T0 ＝ TF ＋ Tf

Slid

Micro-groove
100 µm⑹

Thus, the optimum total friction, including theboundary friction, was examined considering thehydraulic reaction force and the fluid friction due to theshearing resistance of the lubricant.
Under low temperature conditions where the viscosityof the lubricant increases, an excess increase in control
torque is restricted by actively utilizing the hydraulicreaction force and increasing the microscopic oil film.
Figure 16 shows the three-dimensional shape of the
micro-grooves provided on the outer plate. The microgroove is a microscopic surface profile in the order ofseveral μm. This microscopic sliding surface profile
controls the boundary friction.
The optimum micro-groove pitch of the outer plateobtained by the theoretical analysis described above was
examined. Figure 17 indicates the micro-groove pitch
and rate of torque change (i.e., the proportion of thechange in the control torque at −40℃ compared to that at50℃). The solid line shows the calculated values, and thepoints are the experimental values. Both the experimentand analysis were conducted with crowning (fixed)
provided on the inner plate. Figure 17 indicates that thecalculated values accurately simulated the experimental
values. As the micro-groove pitch of the outer plateincreases, the torque change rate decreases and there
exists an optimal pitch where the control torques at 50℃
and −40℃ become equal. If the micro-groove pitch is
expanded further the thickness of the macroscopic oilfilm in accordance with the increase in sliding velocity
become too large, a negative l-v characteristic slope iscreated and eventually shudder occurs. Based on theseresults, the micro-groove pitch is expanded on the thirdgeneration ITCC to adjust the control torque at low
temperatures so as not to increase significantly over thecontrol torque at 50℃. Since the adoption of a DLC-Si
coating in the second-generation ITCC already improved
the wear resistance of the clutch considerably, the microgroove pitch can be expanded.
Figure 18 shows the proportion of control torquechange at each temperature for the second and

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

Fig. 16 Three-dimensional image of micro-groove
80
Rate of torque change, %＊4

h dP
U
s＝
＋M
h
2 dx

⑷

70
60
50

Experiment
Experiment

40
30

Solid line: Calculation

20
10
0
−10

＊4: Change in torque at−40℃ compared to 50℃−20Micro-groove pitch of outer plate

Fig. 17 Effect of micro-groove pitch on rate of torque change
80
Rate of torque change, %＊5

2
∂2 P
dh
3 ∂P
h
＋h
＝ 6 MU
dx
∂x 2
∂z 2
3

irec
tion

expressed by a simplified hydrodynamic motion equationand s is expressed by a Newtonian viscosity equation.

When applying constant current

60
40
Decrease
20

Gen2

0
−20

Gen3

−40
−40

＊5: Change in torque at eachtemperature compared to 50℃

−20

0

20
40
60
Temperature, ℃

80

100

120

Fig. 18 Temperature dependence of rate of torque change inactual ITCC units

third generation ITCC units based on the torque at
50℃. Especially below 0℃ the third-generation ITCC
dramatically reduces the control torque. When bothchange rates are compared at −40℃, the third-generation
ITCC improves by about 85 percent over the secondgeneration unit.

4. Conclusion
Figure 19 summarizes and compares the surface
profiles of the second and third generation clutches. For
the third-generation clutch, the inner plate is provided
with macroscopic crowning in the order of tens of μm,
and on the outer plate, the pitch of the micro-groove withthe microscopic surface profils in the order of several μm
is adjusted. This drastically improves drag torque andtorque accuracy at low temperatures.

23

−Development of Third-Generation Electronically Controlled AWD Coupling with New High-Performance Electromagnetic Clutch−

Therefore, the ITCC performance is enhanced
remarkably by optimizing the surface texture of theelectromagnetic clutch. It is hoped that the thirdgeneration ITCC can further contribute to the protectionof the global environment in the future by helping to
reduce the size and weight of the vehicle driveline.
The major findings from this research and development
are described as follows:(1) By focusing on the hydraulic reaction force derived
from the macroscopic sliding surface profile andproviding crowning on the sliding surface, the dragtorque at low temperatures was reduced by about 50
percent.
(2) By optimizing the micro-groove pitch of the sliding
surface, which controls the boundary friction
force, the temperature dependence of torque was
improved by about 85 percent.
(3) The newly developed third-generation ITCC
drastically improved drag torque performanceand torque accuracy at low temperatures, and cancontribute to higher fuel efficiency and weight
reduction in the driveline.

Inner plate

Appearance

Gen2

Gen3

W/O crowningWith crowning

3)

4)

5)

6)

J. Ando, T. Ohmori, A. Murase, N. Takahashi, T.
Yamaguchi, and K. Hokkirigawa: "Tribological
Properties of Si-Containing Diamond-Like Carbon
Film Under ATF Lubricated Condition," Wear, 266,
(2009)239-247.
T. Yamaguchi, J. Ando, T. Tsuda, N. Takahashi, M.
Tohyama, A. Murase, T. Ohmori, and K. Hokkirigawa:"Sliding Velocity Dependency of Friction Coefficientof Si-Containing Diamond-Like Carbon Film Under
Oil Lubricated Condition," Tribology International,
vol.44(2011)1296-1303.
J. Ando, N. Sakai, K. Nishi, H. Kuwabara, T. Ohmori,A. Murase, Y. Esaki: "Development of Exclusive Fluid
for AWD Coupling," Japanese Society of Automotive
Engineers Review, vol.29, No.1, (2008) 89-95.
M. Eguchi, M. Takei, R. Yamamoto: "Frictional
Characteristics of Wet Clutch Friction Materials,"
Tribologist, vol. 36, No.7(1991)535.

Outer plate

Crowning: Macroscopic profile in theorder of tens of µm

Expansion of micro-groove pitch
Micro-groove: Microscopic profile in theorder of several µm

Fig. 19 Comparison of surface profiles of second and third
generation electromagnetic cluthes

J. ANDO*

H. ANDO**K. SUZUKI**

Y. NIIKAWA**

T. TSUDA**

References
1)

2)

24

H. Takuno, T. Sakai, N. Sakai, A. Ikeda: "Developmentof New Electromagnetic Controlled Coupling for FourWheel Drive Vehicles," Japanese Society of Automotive
Engineers Proceedings, vol.5, (1998)95.
J. Ando, T. Saito, N. Sakai, T. Sakai, H. Fukami,
K. Nakanishi, H. Mori, H. Tachikawa, T. Ohmori:"Development of Compact, High Capacity AWD
Coupling with DLC-Si Coated Electromagnetic Clutch,"
SAE Paper, 2006-01-0820(2006).

***

Driveline System Engineering Dept.2, Automotive
Systems Business Headquarters, Doctor of Engineering
Driveline System Engineering Dept.2, Automotive
Systems Business Headquarters

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)