Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
A HIGH-TORQUE MAGNETO-RHEOLOGICAL
FLUID CLUTCH
B. M. Kavlicoglu 1, F. Gordaninejad 2, C. A. Evrensel 3, N. Cobanoglu 1, Y. Liu 4, A. Fuchs 5
Composite and Intelligent Materials Laboratory
University of Nevada, Reno, NV 89557, USA
and
G. Korol
Visteon Automotive Systems
Dearborne, MI 48126, USA
ABSTRACT
This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch.
The clutch’s torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element
analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates
is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the
clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different
input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated
that the clutch is capable of producing high controllable torques.
1. INTRODUCTION
Magneto-rheological (MR) fluids consist of fine ferromagnetic particles in a carrier fluid. They exhibit a controllable
shear yield stress under a magnetic field. The particles are usually 1-10 µm in diameter [1]. MR fluids are increasingly
being considered in variety of devices such as shock absorbers, vibration insulators, brakes or clutches. The activation
of MRF clutch’s built-in magnetic field causes a fast and dramatic change in the apparent viscosity of the MR fluid
contained in the clutch. The fluid changes state from liquid to semi-solid in about 6 milliseconds. The result is a clutch
with an infinitely variable torque output.
Bansbach [2], proposed a double-plate and a multi-plate MRF torque transfer apparatus with a controller that adjusts the
input current. The apparatus is proposed to be placed between the engine of a car and its differential. Gopalswamy et al.
[3] suggested a MRF clutch to minimize reluctance for fan clutches. Gopalswamy et al. [4] also studied a controllable
multi-plate MR transmission clutch. This clutch was also designed to be placed between the engine and differential.
Hampton [5] described a design of MRF coupling with reduced air gaps and high magnetic flux density. Carlson [6]
proposed a MR brake with an integrated flywheel.
1
Graduate Research Assistant, Mechanical Engineering Department
Professor, Mechanical Engineering Department, contact author: E-mail: faramarz@unr.edu,
http://web.me.unr.edu/ciml, Telephone: 775-784-6990, Fax: 775-784-1701
3
Associate Professor, Mechanical Engineering Department
4
Post-doctoral Fellow
5
Assistant Professor, Chemical Engineering Department
2
1
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
2. DOUBLE-PLATE MRF CLUTCH DESIGN
The main goal of this study is to design, develop and understand the performance of a double-plate prototype MRF
clutch. By varying the input current to the clutch, one can achieve a variable torque range. Other factors such as
geometric constraints and magnetic properties of materials play major roles on the performance of the MRF clutches.
Casing
Electromagnetic Coil
Electromagnet
Core
Input Side Cap
O-Rings
MR Fluid
Output Shaft
and Plate
Input Shaft
and Plate
Output Bearing
Output Side Cap
Input Bearing
Figure 1. A three-dimensional view of the double-plate prototype MR fluid clutch.
Figure 1 shows a three-dimensional view of the double-plate prototype MRF clutch. The MR fluid is located in the gap
between the input and output plates, with the diameter of 51.94 mm. These plates are connected to 30 mm diameter
input and output shafts. The shafts are supported by deep groove ball bearings, which are press-fitted into the side caps.
The electromagnet circuit of this clutch consists of an electromagnetic coil, which is wound around an electromagnetic
core. This assembly is located inside a 152.4 mm outer diameter casing with 6.35 mm wall thickness, which is also
acting as a return path for the magnetic field. Two O-rings are located in the grooves machined on the circumferences of
plates to prevent leakage of MR fluid. The MRF clutch is activated by a power supply connected to two ends of the
electromagnet. The total width of the clutch is 31.75 mm.
2
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
3. ELECTROMAGNETIC FINITE ELEMENT ANALYSIS
Electromagnetic finite element analysis is performed, using Maxwell ANSOFT software [7], to optimize the design of
the double-plate prototype MRF clutch. This is done to determine the material and the dimensions of each individual
element of the clutch. One of the design goals is to increase the magnetic field of the MR fluid as much as possible.
Flux line density, Wb/ m2
Figure 2. Contour plot of flux line density from Maxwell ANSOFT for double plate MRF clutch.
Figure 2 shows the contour plot of flux line density of the double-plate MRF clutch for an input current of 3 Amps. For
this case magnetic flux density as a function of radius of the clutch in MRF section can be seen in Figure 3. As
explained in the following section results shown in Figure 3 are used in theoretical torque output calculations for a given
input electric current. It can be observed from Figures 2 and 3 that, the magnetic field increases with increasing radial
distance from the rotational axis. This is a desirable outcome since the contribution of the resulting shear yield stress on
the torque transmitted increases with increasing radial distance.
0.650
B (Tesla)
0.600
0.550
0.500
0.450
0.400
0
10
20
30
40
50
3. THEORETICAL TORQUE
MODELING
Radius (mm)
Figure 3. Magnetic field strength as a function of radius in the MRF section.
3
60
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
In order to derive the output torque equation for this clutch, the Bingham Plastic model is used as the constitutive
equation for behavior of the MR fluid. Bingham Plastic model gives the total shear stress, as follows:
τ = τ y ⋅ sgn(
∂u
∂u
) + µp
∂y
∂y
(1)
∂u
is the shear strain rate, µ p and τ y are the plastic viscosity and shear yield stress of the MR fluid,
∂y
respectively. τ y is a function of the magnetic field while µ p is assumed to be constant. The first part of the right hand
where,
side of Equation (1) produces a torque, which is dependent on the magnetic field, and the second term generates a
viscous torque. Therefore, the total output torque can be expressed as:
Tout = TMR + Tvis
Derivation of MR torque,
(2)
TMR , requires the relationship between MRF shear yield stress, τ y , and the applied magnetic
flux density, B. This relationship is obtained experimentally for the fluid designed by our group and from the
manufacturer’s data sheet for the commercial MR fluid.
Since the magnetic field is a function of the radial location, shear yield stress can be determined as function of the plate
radius. For a given yield stress distribution, the output torque can be obtained by:
ro
TMR = 2π ∫ τ y ( r , B) sgn(
0
du 2
) r dr
dy
(3)
where r0 is the radial location of seals. For small gap between the plates one can derive the tangential fluid velocity by
assuming no slip condition and linear velocity distribution as follows:
u (r , y ) =
r ⋅ ∆ω
y + ω2 ⋅ r
g
(4)
where ∆ω = ω1 − ω 2 , is the angular velocity difference between the input and output plates, g is the gap between the
plates, y, is the coordinate axis normal to plate surfaces. Differentiation of Eq. (4) with respect to y gives the shear rate:
∂u r∆ω
=
∂y
g
(5)
The sign of shear rate can be written as:
sign (
∂u
r ∆ω
) = sign (
) = sign (ω1 − ω 2 )
∂y
g
Substituting Equation (6) into Equation (3) gives:
4
(6)
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
ro
TMR = 2π sgn(ω1 − ω 2 ) ∫τ y (r , B )r 2 dr
(7)
0
By numerically integrating Eq. (7), MR torque equation for the yield stress function for a given input current, output
torque versus input current relationship is derived. Similarly, the viscous torque can be derived as:
πµ p ∆ωr04
Tvis =
2g
For the dimensions and material properties used, the viscous torque,
(8)
Tvis , is determined to be very small compared to
MR torque, TMR , therefore, viscous effects can be neglected in the total torque output equation. Then, the total torque
for the MRF clutch can be written as a function of input current as:
Tout ≅ TMR = c1 I C2 sgn(ω1 − ω2 )
(9)
where, C1 and C2 are the constants obtained numerically using electromagnetic FEA.
4. EXPERIMENTAL STUDY
To examine the performance of the MRF clutch, a detailed experimental setup is designed, as shown in Figure 4. In the
design process, the expected performance of the MRF clutch and the given design requirements are considered. The
MRF clutch is driven by a 5-HP Dayton EPACT efficient AC-motor, which is controlled by a General Electric’s AC
adjustable frequency drive AF-300 G11. Adjustable frequency drive can only reduce the motor speed to 1:10,
efficiently. In order to reach the velocity range required for experimental analysis a WinSmith C-Face right angle
gearbox with a 1:15 gear ratio is used. Lovejoy flexible coupling is used to connect the gearbox to the MRF clutch.
Two M12x1-180DSAw digital speed sensors are used for the velocity feedback. For static torque measurement the beltpulley system is replaced by a lever arm connected to the output shaft of the MRF clutch. Force exerted by the lever
arm is measured by a Lebow Load Cell Model 3132.
The experimental study is performed to explore the torque output and velocity response of the prototype MRF clutch. In
this study, a UNR-MRPG (MR polymeric gel based fluid), which is developed at University of Nevada Reno (UNR),
and a commercially available MR fluid, LORD MRF-132LD, are used. Output torque is measured using lever arm
system as described previously. The output torque is determined by multiplying exerted force on the load cell with the
distance from exertion point of the load to the center of the output shaft. The torque output determined by this method is
the maximum torque produced by the clutch, since the static output plate maximizes the shear rate by maximizing the
angular velocity difference. The torque output is measured for input velocities of 30, 60, 90 and 120 rpm and the input
current is varied from 0 Amp to 4 Amps. Figures 5 and 6 present the torque output relations for the UNR-MRPG and
LORD-MRF132LD fluids.
It can be observed from Figures 5 and 6 that the velocity effects are minimal on the torque output. For the UNR-MRPG
fluid the maximum torque obtained is 7.9 Nm at 4 Amps, and for the LORD-MRF132LD fluid the maximum torque is
6.9 Nm at 4 Amps.
5
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
AC Motor
AC Inverter
Gearbox
Coupling
Speed
Sensors
MRF Clutch
Signal Converters
Belt-Pulley System
Load Cell
Figure 4. Experimental setup for the prototype MRF clutch characterization.
9
8
7
Torque(N.m)
6
5
30rpm
60rpm
90rpm
120rpm
Theoretical
4
3
2
1
0
0
0.5
1
1.5
2
2.5
3
3.5
Input Current (A)
Figure 5. Torque output as a function of electric input current for
UNR – MRPG fluid for different input velocities.
6
4
4.5
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
9
8
7
Torque(N.m)
6
5
4
30rpm
60rpm
90rpm
120rpm
Theoretical
3
2
1
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Input Current (A)
Figure 6. Torque output as a function of electric input current for
LORD – MRF – 132LD fluid for different input velocities.
Transient velocity of the input and output plates are measured to determine the response time of the system. These
experiments are performed by initially restraining the rotation of the output shaft by exerting a large enough resistance
torque via the belt-pulley system. At time t0, the power supply for the electromagnet coil is turned on and velocities of
both shafts are recorded. For this case the clutch output plate reaches the input plate velocity in about 20 milliseconds
when the power to the electromagnet is turned on, as demonstrated in Figure 7.
5. CONCLUSIONS AND FUTURE WORK
The performance of a double-plate magneto-rheological fluid limited slip differential clutch, which is designed and
developed at UNR, is studied using two types of MR fluids. Theoretical and experimental analyses have illustrated that
this MR fluid clutch can transfer high controllable torques with a very fast time response. This study provides basic
knowledge of MR fluid torque transfer mechanism for the development of a multi-plate MRF fluid limited slip
differential clutch, which is underway.
6. ACKNOWLEDGEMENTS
The authors would like to thank Visteon Corporation for supporting this research.
7
Kavlicoglu, B., Gordaninejad, F., Evrensel, C. A., Cobanoglu, N., Xin, M., Heine, C., Fuchs, A., and Korol,
G., “A High-Torque Magneto-Rheological Fluid Clutch,” Proceedings of SPIE Conference on Smart
Materials and Structures, San Diego, March 2002.
Figure 7. Velocity response of the MRF clutch.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
Ashour O., Rogers C.A, and Kordonsky W., “ Magnetorheological Fluids; Materials, Characterization and
Devices,” Journal of Intelligent Material systems and Structures, Volume 7- pp 123-130, March 1996.
Bansbach, E. E., “Torque Transfer Apparatus Using Magnetorheological Fluids,” United States Patent Number
5,779,013, 1998.
Gopalswamy ,S., Linzell, S., M., Jones, G.L, “ Magnetorheological Fluid Clutch with Minimized Reluctance,”
United States Patent Number 5,845,752, 1998.
Gopalswamy, S., and Jones G., L., “Magnetorheological Transmission Clutch,” United States Patent Number
5,823,309, 1998.
Hampton, K., “Magnetorheological Fluid Coupling,” United States Patent Number 5,967,273, 1999.
Carlson, J.D., “Magnetorheological Brake with Integrated Flywheel,” United States Patent Number 6, 186,290
B1, 2001.
Ansoft Corporation, Pittsburgh, PA, www.ansoft.com
8