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Design and Manufacturing Aspects of Magneto-rheological Fluid (MRF) Clutch
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 1525–1534
www.materialstoday.com/proceedings
5th International Conference of Materials Processing and Characterization (ICMPC 2016)
Design and Manufacturing Aspects of Magneto-rheological Fluid (MRF) Clutch a
K. Hema Lathaa
P. Usha Srib
N. Seetharamaiahc
Sr. Assistant Professor, Dept. of Mech. Engg., MJCET, Hyderabad-34, INDIA, [email protected], b
Professor, Dept. of Mech. Engg., UCEOU(A), Hyderabad-7, INDIA, c
Professor, Dept. of Mech. Engg., MJCET. Hyderabad-34, INDIA,
Abstract This paper describes a research work concerned with design method and manufacturing details of a Magneto-rheological Fluid (MRF) Clutch which has a multi-layered disks and micro-size (1 micro meters) gaps of MR fluid for automotive applications. Magneto-rheological Fluid devices are finding a wide variety of applications to meet the new market demand. An MR fluid will be in a free-flowing liquid state in the absence of magnetic field, but under a strong magnetic field its viscosity can be increased by more than two orders of magnitude in a very short time (milliseconds) and it exhibits solid-like characteristics. Various devices working with MR fluids include Clutches, Brakes, Hydraulic valves, dampers, robotic arms. The micro-size gap works for the reduction of magnetic resistance, amount of power supply and size of the total system. The controllability of MR fluids provides an adjustable torque transmission and slippage for the applications. Three-dimensional solid modelling is performed for clutch design and manufactured. The benefits with using MRF are fast response, simple interface between electrical power input and mechanical power output and of course the excellent controllability of the fluid. MRF clutches are known as good Torque transmitting devices. 2214-7853©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016). Keywords:MR Fluid, Magneto-rheological Fluid Clutch, magnetic circuit, magnetic field, Torque transmission.
_____________________________________________________________________________ *Corresponding author. Tel.: +919849138046 E-mail address:[email protected] 2214-7853©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016).
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1. Introduction MRdevices are playing a vital role now a days. Magneto-rheological fluid (MRF) clutches are used in several automotive systems such as auxiliary engine devices, active differentials, and automatic transmissions. MR Fluids are magnetically polarizable particles suspended in viscous fluids. They have the ability to change their rheological properties as shear modulus and viscosity reversibly in milliseconds when subjected to varying magnetic fields. While the magnetic particles are randomly distributed in the liquid when no magnetic field is applied, they form chains in the presence of a magnetic field, and as a result rheological properties of the fluid increase. Typically, the magnetizable particles are metal or metal oxide particles with size of on the order of few microns. Magnetorheological fluids are the suspensions of micron sized, magnetizable particles (iron, iron oxide, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low-carbon steel, silicon steel, nickel, cobalt, and combinations thereofin an appropriate carrier liquid (non-magnetizable) such as mineral oil, synthetic oil, water or ethylene glycol. The carrier liquid serves as a dispersed medium and ensures the homogeneity of particles in the fluid. The purpose of developing the magnetic clutch is to overcome the mechanical friction that happens to the conventional clutch. The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magnetic dipoles are suspended in a non-magnetic fluid, and the applied magnetic field causes these small magnets to line up and form strings that increase the viscosity. 2. MR Fluid Characteristic A typical MR fluid consists of 20-40 percent by volume of relatively pure, 3-10-micron diameter iron particles, suspended in a carrier liquid. MR fluids are field responsive in nature. The magneto-rheological response of these fluids lies in the fact that the polarization is induced in the suspended particles by the application of an external magnetic field. This allows the fluid to transform from freely flowing liquid state to solid-like state within milliseconds, because the magnetically dispersed particles attract each other to form fibril/chain-like structures along the direction of magnetic field. The chain-like structures resist the motion of the fluid and increase its viscous characteristics. Such a behavior of MR fluid is analogous to Bingham plastics - non-Newtonian fluids capable of developing a yield stress. A favorable arrangement consists of particle chains aligned in the direction of the applied field and this, in turn, gives rise to a strong resistance to applied strains as shown in figure 1.
(a)
(b)
(c)
Fig.1: Activation of MR fluid: (a) no magnetic field applied; (b) magnetic field applied ;(c) Ferrous particle chains have formed.
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The viscous fluid can be a non-magnetic liquid, usually oils. Additionally surfactants are used to allow for high particle volume fractions of the MR fluids that can yield higher variations in the rheological properties, and increase the fluid’s stability against sedimentation. Figure 1 illustrates a schematic diagram of MR fluids with and without a magnetic field applied. Depending on the type of the magnetic particles, viscous fluids and their volume rate, the rheological properties of MR fluids vary. The viscosity of MR fluids can vary between 0.2 to 0.3 pascals at 25° C. MR fluids are being considered in variety of energy dissipation and transfer devices such as shock absorbers, clutches, brakes, and engine mounts. The yield stress developed within the MR fluid is a function of the applied magnetic field. However, once this yield stress is exceeded, the behaviour of the MR fluid deviates from that of a Bingham-Plastic. This is attributable to the breakdown of the chains of particles under the forces of the fluid flow, and results in a shear-stress/shear-rate characteristic that is highly non-linear. When used in a damping device, the result is a damper whose force/velocity characteristic is non-linear, but can be changed by the way the magnetic field is applied.They are field responsive in nature and the magneto-rheological response of these Fluids is in the fact that the polarization is induced in the suspended particles by the application of an external magnetic field. This allows the fluid to transform from freely flowing liquid state to solid-like state within milliseconds, because the magnetically dispersed particles attract each other to form fibril/chain-like structures along the direction of magnetic field. The chain-like structures resist the motion of the Fluid and increase viscous characteristics. Such behaviour of MR Fluid is analogous to Bingham plastics (non-Newtonian Fluids) capable of developing yield stress A synthesized MR Fluid contains Carrier Fluid Silicone Oil and Magnetisable particles- Carbonyl Iron of around 8 microns for 40% by the volume concentration of iron particles inclusive of additives. The variation of yield stress with magnetic field strength and also the variation of Magnetic induction with Magnetic flux density are shown in figure2 and figure3.
Fig2..Yield Stress Vs.Magnetic Field strength
Fig.3. Magnetic Induction ( B) Vs.Magnetic Field Density (H)
Having great potential for engineering applications due to their variable rheological behavior, MR fluids find applications in dampers, brakes, shock absorbers, suspensions, clutches and engine mounts. The key defects that affect their applications are sedimentation (gravitational settling), poor dispersion stability and corrosion of the suspended magnetic particles. In order to resolve these, a variety of proprietary additives, similar to those found in commercial lubricants are commonly added to MR fluid to enhance lubricity, modify viscosity and inhibit wear. 3. Magneto Rheological Fluid (MRF)Clutch and its Design Aspects A magneto rheological fluid clutch consists of a input shaft that rotates and which carries an input clutch plate and a housing with front and rear covers. The bearings are provided which support the housing on the input shaft. The Magneto rheological fluid is filled in the gaps between the plates of input and output shaft through which the torque is transferred. An electromagnetic coil is placed radially outside the nonmagnetic spacer, which generates a variable electric current to effect variable magnetic field across the input clutch plate and through the magneto rheological fluid enabling variable torque transmission between input clutch plate and the core. A multi plate torque
transfer device that is a MRF clutch is designed and developed which is shown in the figure 4.
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A uniform magnetic fields is generated from the magnetic circuit in the housing . The output shaft is 79 mm in diameter and fits in the outer disc/housing assembly with a 1 mm gap on either side for the MR fluid. A stationary electromagnetic coil is placed around the clutch with a steel shell enclosure to direct the magnetic field to the active regions of the clutch. The electromagnetic coil has 750 turns.
Fig.4. MRF Clutch Assembly
Fig.6.MRF Clutch Assembly
Fig 5. Solid 3D model of MRF Clutch
Fig. 7 MRF Clutch Assembly
Figure 4 shows a cross section of the MRFclutch and figure 5, shows the 3D model of the MRF clutch. Figure 7 shows the manufactured MRF Clutch Assembly. The gap for MR fluid is 1mm between each plate. Spacers are located in between each set of input and output plates to set the MR fluid thickness fixed and to arrest the disposition of plates. Two alignment bearings are fixed to arrest the off-axis rotation of the clutch pack and also to position the centers of both shafts. The magnetic circuit of the clutch composes of an electromagnetic coil made of copper wire which has 750 windings. The clutch pack and the electromagnet circuit are placed inside a 152.4 mm outer diameter casing, which also acts as a return path for the magnetic field. The total length of the clutch is 119mm.Shaft and the output plates are made to glide on to the spline of the inner casing. 3.1. MR Fluid Used MR fluid MRF-132DG provided by Lord Corporation is used in the device as shown in the figure6.The Properities of the fluid used are shown in the Table 1.LORD MRF-132DG fluid is a hydrocarbon-based magnetorheological (MR) fluid formulated for general use in controllable, energy-dissipating applications such as shocks,
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dampers and brakes.MRF-132DG fluid is a suspension of micron-sized, magnetizable particles in a carrier fluid. When exposed to a magnetic field, the rheology of MRF-132DG fluid reversibly and instantaneously changes from a freeflowing liquid to a semi-solid with controllable yield strength. Altering the strength of the applied magnetic field precisely and proportionally controls the consistency or yield strength of the fluid. MRF-132DG fluid can be used in valve mode(fluid flowing through an orifice) or in shear mode(fluid shearing between two surfaces). In the absence of a magnetic field, MRF-132DG fluid flows freely or allows free movement. Upon application of a magnetic field, the fluid’s particles align with the direction of the field in chain-like fashion, thereby restricting the fluid’s movement within the gap in proportion to the strength of the magnetic field. Table 1.Properities of MRF-132 DG PROPERTY VALUE Appearance Dark Grey liquid Viscosity @ 40°C (104°F)
0.112 ± 0.02 Pas
Density
2.95-3.15 g/cm3
Solids Content by Weight
80.98 %
Flash Point Operating Temperature
>150 (>302) °C (°F) -40 to +130 (-40 to +266) °C (°F)
4. Assembly The following table shows the list of various components of the MRF clutch which forms the Assembly as shown below Table 2. Table 2.Description of the parts for MRF Clutch
S.no
Parts
Radius
Length
Thickness
Numbers
1.a
Input shaft
8.5mm
56mm
25mm
1
1.b
Body holder
39.5mm
7mm
-
1
1.c
Bearing
11mm
7mm
2mm
1
1.d
Hole
M5mm
86pcd
4inch
4
2.
Output shaft plate
39.5mm
10mm
20mm
4
3.
Casing
72.5mm
120mm
56mm
1
4.a
Output shaft
17mm
71.8mm
-
1
4.b
Central output shaft
10mm
62.7mm
-
1
4.c
Output end plate
46.5mm
7mm
8mm
1
5.a
Input shaft plates
46.5mm
10mm
32mm
4
6.a
Input body end plate
46.5mm
26mm
42mm
1
6.b
Bearing
21mm
12mm
10mm
1
6.c
Oil seal
16mm
8mm
3mm
1
7.a
Electromagnet
25mm
95mm
12.5mm
1
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4.1Input shaft and Body Holder The input shaft was selected on the basis for easy coupling to the motor for different application and running on the different input rpm .The shaft is kept according to the load required. Body holder is joint and made with the input shaft such that the body holder adjoins the input shaft plates with the help of the screw. The holes are given according to the standard dimension with M5 hole and 86pcd. The radius of the body holder is made same as that of the plates to be attached to it, fig 8.
Fig.8.Input shaft body and plate holder
4.2.Bearing A step or a indentation is given to allow the bearing to be placed at the centre of the body holder .This bearing is mainly put so that it acts as a gap maintaining device between the input shaft and the output shaft.The holes are given on the body holder according to standard values for attachments of the input shaft plates,fig 9.
Fig.9.Bearing inserted on the input shaft
4.3.Output shaft plate The output shaft plates are made such that there is keyway present at the of length 10mm with the radius 39.5mm.The overall thickness is maintained to be 5mm.The inner diameter is 20mm placed to sit on the central output shaft.Manufactured plates of the input shaft at the top and manufactured plates to be mounted on the output shaft key way, at the right most plate is thicker as it is the end plate of the input shaft consisting of a bearing and oil seal at its centre , fig 10
Fig.10. Output shaft plates
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34.4. Casing The casing houses are electromagnet at the outer part and the clutch centrally. There are 2 bearings fitted at the ends of the casing to hold the input and output shaft. The casing doesn’t rotate and is stationary.It avoids any contact to the environment and acts as a protective case, fig 11.
Fig.11. Casing
4.5. Output shaft with keyway The output shaft is designed such that it is similar to the input shaft and it is made longer in order to come out of the casing. The external loads are applied to this shaft to get the resultant torque output. The shaft is designed in such a way that all the output shaft plates are mounted on it by sliding the plates through the keyway present at it centrally. The keyway is designed according to standard values.The output end plate is designed in such a way that it is attached to the central output shaft and it acts as the first mounting plate to maintain the gap of 1 mm between the output and input shaft plates, fig 12.
Fig.12. Output shaft with keyway
4.6. Bearing and Oil seal It acts as a differentiating part between the input shaft and the output shaft and does not cause any interference between the two and it supports the housing on the input shafts so that the input clutch plate is rotatable on the input shaft relative to the housing. Oil seal acts as a protective device, to avoid any leakage of MR Fluid and it is housed at the end plate of the input shaft which causes a little slip between the two shafts. The magneto rheological fluid settles away from the seal in the cavity due to minimum axial thickness of radial inner portion of the input clutch plate. 4.7. Input shaft plates and Input body end plate These plates are modelled in such a way that they get attached to the body holder of the input shaft with the help of screw. The overall thickness of the plate is maintained at5 mm. Input body end plate acts as the end body cover of the input shaft it is modelled in such a way that when mounted it also maintains a gap of 1mm with the end plate of the output shaft. It acts as the housing for the bearing between the input and the output shafts and the oil seal,fig 13.
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Fig.13. Input shaft plate and Input body end plate
4.8. Electromagnet and Casing Cover Electromagnet is designed specifically to satisfy the amount of magnetic field required to activate the MR fluid present in the gap between the plates of the clutch. It is made by using a soft iron core an high gauge quality single strand wire wound around the soft iron core to about 750 turns. It is housed in the casing and is insulated which does not allow any contact with any metal surface, fig 14 & fig 15.
Fig.14. Electromagnet and casing cover
Electromagnet casing where there is air gap and insulation between the electromagnet casing and the clutch when inserted in it. The electromagnet is made with soft iron core and 750 turns of highly pure copper wire wound around it at the end surface there is a wooden insulation given to prevent the product from any short circuit. Casing cover with bearing placed at centre mounting holes on the outer surface to attach the electromagnet casing and housing at the inner surface there are two major holes for pouring of the fluid. The final assembled MRF cltch is show in the figure 16.
K. Hema Latha et al. / Materials Today: Proceedings 4 (2017) 1525–1534
Fig.15.Casing cover
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Fig.16.MRF Clutch
5. Conclusion In this paper a Magneto rheological fluid Based clutch with detailed description of its design and manufacturing aspects is proposed.Unlike the conventional torque transfer devices which are based on friction a magneto rheological fluid clutch is developed in order to overcome wear, variable loading, engagement, shocks, and temperature variations.The design of the clutch was carried out using Solid works and the torque transfer capacity results were obtained using magneto static analysis in Ansys.To eliminate the wear, engagement, shock and variable loading during operation, a successful magneto rheological fluid based clutch is manufactured. The detailed description of the MRF Clutch comprising of parts likeinput shaft, input body end plates, magnetic core, clutch plates, housing, non magnetic spacers, output shaft with key and casing coveris given. Torque transfer devices are an essential part for a variety of electro-mechanical/robotics systems, in active control of vibrations, optical polishing and inseismic protection. Acknowledgements
This research work is supported and Funded by Research and development Cell-Seed Funds, MuffakhamJah College of Engineering and Technology.
References [1] Naoyuki TAKESUE, Junji FURUSHO, Masamichi SAKAGUCHI, Improvement of Response Properties of MR-Fluid Actuator
by Torque Feedback Control,Proceedings of the 2001 IEEE, Internatonal Conferencce on Robotics and Automation,Seoul, Korea, May 21-26,2001. [2]T Kikuchi, K Ikeda, K Otsuki, T Kakehashi and J Furusho, “Compact MR fluid clutch device for human-friendly actuator”, 11th Conference on Electrorheological Fluids and magnetorheological Suspensions , IOP Publishing Journal of Physics: Conference Series 149 (2009) 012059 doi:10.1088/1742-6596/149/1/012059 [3] D.Torocsik, “Some design issues of multi-plate magnetorheological clutches”, Hungarian Journal of Industrial Chemistry Veszprem, Vol. 39(1) pp. 41-44(2011) [4] A.G.Olabi and A.Grunwald, “Design and Application of Magneto-Rheological Fluid “MRF”,Dublin city University ,School of Mechanical and Manfacturing Engineering,Glasnevin, Dublin9,Ireland. [5] BarkanKavlicogluFaramarzGordaninejad, CahitEvrensel, Alan Fuchs, George Korol, “A Semi-Active, High-Torque, Magnetorheological Fluid Limited Slip Differential Clutch” , ASME 610 /Vol. 128, OCTOBER 2006 [6]Melek Yalcintas,” Magnetorheological Fluid Based Torque Transmission Clutches”, Proceedings of the Ninth (1999) International Offshore and Polar Engineering Conference Brest, France, May 30-June4,1999. [7]Peyman Yadmellat,”Adaptive Modeling of a Magnetorheological Clutch”, IEEE/ASME Transactions on Mechatronics, VOL.19,No.5,October 2014. [8] D.Lampe,R.Grundmann,” Transitional Behaviour of a Magnetorheological Clutch”, TU Dresden, Institut fur Luft- und Raumfahrttechnik, D01062Dresden.
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[9]T.M.Simon,F.Reitich, M.R.Jolly,K.Ito and H.T.Banks,”The Effective Magnetc Properities of Magnetorheological Fluids”, Mathematical and Computer Modelling 33 (2001) 273-284,Elsevier Science Ltd. [10]Josko Deur, Domagoj Libl and Zvonko Herold, Mathew Hancock and Francis Assadian,”Design and experimental characterization of a magnetorheological fluid clutch”, SAE International, 2009. [11] Sadak Ali Khan,A.Suresh,N.Seetharamiah, “Principles,characteristics and Applications of Magneto Rheological Fluid Damper in Flow and Shear Mode”, 3rd International Conference on Materials Processing and characterisation (ICMPC 2014), Procedia Materials Science 6 ( 2014 ) 1547 – 1556 [12]Mr. N. Seetharamaiah, Mr. D.Srinivasrao, Dr. K.Narayanarao and Dr. Suresh Akalla, “Design and Manufacturing aspects of MR Fluid Linear Vibration Damper “, Proc. of the International Conference on Emerging Research and Advances in Mechanical Engineering, ERA 2009, March 2009, Velammal Engineering College, Chennai, Tamil Nadu, India, pp 441-447.
ScienceDirect Materials Today: Proceedings 4 (2017) 1525–1534
www.materialstoday.com/proceedings
5th International Conference of Materials Processing and Characterization (ICMPC 2016)
Design and Manufacturing Aspects of Magneto-rheological Fluid (MRF) Clutch a
K. Hema Lathaa
P. Usha Srib
N. Seetharamaiahc
Sr. Assistant Professor, Dept. of Mech. Engg., MJCET, Hyderabad-34, INDIA, [email protected], b
Professor, Dept. of Mech. Engg., UCEOU(A), Hyderabad-7, INDIA, c
Professor, Dept. of Mech. Engg., MJCET. Hyderabad-34, INDIA,
Abstract This paper describes a research work concerned with design method and manufacturing details of a Magneto-rheological Fluid (MRF) Clutch which has a multi-layered disks and micro-size (1 micro meters) gaps of MR fluid for automotive applications. Magneto-rheological Fluid devices are finding a wide variety of applications to meet the new market demand. An MR fluid will be in a free-flowing liquid state in the absence of magnetic field, but under a strong magnetic field its viscosity can be increased by more than two orders of magnitude in a very short time (milliseconds) and it exhibits solid-like characteristics. Various devices working with MR fluids include Clutches, Brakes, Hydraulic valves, dampers, robotic arms. The micro-size gap works for the reduction of magnetic resistance, amount of power supply and size of the total system. The controllability of MR fluids provides an adjustable torque transmission and slippage for the applications. Three-dimensional solid modelling is performed for clutch design and manufactured. The benefits with using MRF are fast response, simple interface between electrical power input and mechanical power output and of course the excellent controllability of the fluid. MRF clutches are known as good Torque transmitting devices. 2214-7853©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016). Keywords:MR Fluid, Magneto-rheological Fluid Clutch, magnetic circuit, magnetic field, Torque transmission.
_____________________________________________________________________________ *Corresponding author. Tel.: +919849138046 E-mail address:[email protected] 2214-7853©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016).
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1. Introduction MRdevices are playing a vital role now a days. Magneto-rheological fluid (MRF) clutches are used in several automotive systems such as auxiliary engine devices, active differentials, and automatic transmissions. MR Fluids are magnetically polarizable particles suspended in viscous fluids. They have the ability to change their rheological properties as shear modulus and viscosity reversibly in milliseconds when subjected to varying magnetic fields. While the magnetic particles are randomly distributed in the liquid when no magnetic field is applied, they form chains in the presence of a magnetic field, and as a result rheological properties of the fluid increase. Typically, the magnetizable particles are metal or metal oxide particles with size of on the order of few microns. Magnetorheological fluids are the suspensions of micron sized, magnetizable particles (iron, iron oxide, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low-carbon steel, silicon steel, nickel, cobalt, and combinations thereofin an appropriate carrier liquid (non-magnetizable) such as mineral oil, synthetic oil, water or ethylene glycol. The carrier liquid serves as a dispersed medium and ensures the homogeneity of particles in the fluid. The purpose of developing the magnetic clutch is to overcome the mechanical friction that happens to the conventional clutch. The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magnetic dipoles are suspended in a non-magnetic fluid, and the applied magnetic field causes these small magnets to line up and form strings that increase the viscosity. 2. MR Fluid Characteristic A typical MR fluid consists of 20-40 percent by volume of relatively pure, 3-10-micron diameter iron particles, suspended in a carrier liquid. MR fluids are field responsive in nature. The magneto-rheological response of these fluids lies in the fact that the polarization is induced in the suspended particles by the application of an external magnetic field. This allows the fluid to transform from freely flowing liquid state to solid-like state within milliseconds, because the magnetically dispersed particles attract each other to form fibril/chain-like structures along the direction of magnetic field. The chain-like structures resist the motion of the fluid and increase its viscous characteristics. Such a behavior of MR fluid is analogous to Bingham plastics - non-Newtonian fluids capable of developing a yield stress. A favorable arrangement consists of particle chains aligned in the direction of the applied field and this, in turn, gives rise to a strong resistance to applied strains as shown in figure 1.
(a)
(b)
(c)
Fig.1: Activation of MR fluid: (a) no magnetic field applied; (b) magnetic field applied ;(c) Ferrous particle chains have formed.
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The viscous fluid can be a non-magnetic liquid, usually oils. Additionally surfactants are used to allow for high particle volume fractions of the MR fluids that can yield higher variations in the rheological properties, and increase the fluid’s stability against sedimentation. Figure 1 illustrates a schematic diagram of MR fluids with and without a magnetic field applied. Depending on the type of the magnetic particles, viscous fluids and their volume rate, the rheological properties of MR fluids vary. The viscosity of MR fluids can vary between 0.2 to 0.3 pascals at 25° C. MR fluids are being considered in variety of energy dissipation and transfer devices such as shock absorbers, clutches, brakes, and engine mounts. The yield stress developed within the MR fluid is a function of the applied magnetic field. However, once this yield stress is exceeded, the behaviour of the MR fluid deviates from that of a Bingham-Plastic. This is attributable to the breakdown of the chains of particles under the forces of the fluid flow, and results in a shear-stress/shear-rate characteristic that is highly non-linear. When used in a damping device, the result is a damper whose force/velocity characteristic is non-linear, but can be changed by the way the magnetic field is applied.They are field responsive in nature and the magneto-rheological response of these Fluids is in the fact that the polarization is induced in the suspended particles by the application of an external magnetic field. This allows the fluid to transform from freely flowing liquid state to solid-like state within milliseconds, because the magnetically dispersed particles attract each other to form fibril/chain-like structures along the direction of magnetic field. The chain-like structures resist the motion of the Fluid and increase viscous characteristics. Such behaviour of MR Fluid is analogous to Bingham plastics (non-Newtonian Fluids) capable of developing yield stress A synthesized MR Fluid contains Carrier Fluid Silicone Oil and Magnetisable particles- Carbonyl Iron of around 8 microns for 40% by the volume concentration of iron particles inclusive of additives. The variation of yield stress with magnetic field strength and also the variation of Magnetic induction with Magnetic flux density are shown in figure2 and figure3.
Fig2..Yield Stress Vs.Magnetic Field strength
Fig.3. Magnetic Induction ( B) Vs.Magnetic Field Density (H)
Having great potential for engineering applications due to their variable rheological behavior, MR fluids find applications in dampers, brakes, shock absorbers, suspensions, clutches and engine mounts. The key defects that affect their applications are sedimentation (gravitational settling), poor dispersion stability and corrosion of the suspended magnetic particles. In order to resolve these, a variety of proprietary additives, similar to those found in commercial lubricants are commonly added to MR fluid to enhance lubricity, modify viscosity and inhibit wear. 3. Magneto Rheological Fluid (MRF)Clutch and its Design Aspects A magneto rheological fluid clutch consists of a input shaft that rotates and which carries an input clutch plate and a housing with front and rear covers. The bearings are provided which support the housing on the input shaft. The Magneto rheological fluid is filled in the gaps between the plates of input and output shaft through which the torque is transferred. An electromagnetic coil is placed radially outside the nonmagnetic spacer, which generates a variable electric current to effect variable magnetic field across the input clutch plate and through the magneto rheological fluid enabling variable torque transmission between input clutch plate and the core. A multi plate torque
transfer device that is a MRF clutch is designed and developed which is shown in the figure 4.
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A uniform magnetic fields is generated from the magnetic circuit in the housing . The output shaft is 79 mm in diameter and fits in the outer disc/housing assembly with a 1 mm gap on either side for the MR fluid. A stationary electromagnetic coil is placed around the clutch with a steel shell enclosure to direct the magnetic field to the active regions of the clutch. The electromagnetic coil has 750 turns.
Fig.4. MRF Clutch Assembly
Fig.6.MRF Clutch Assembly
Fig 5. Solid 3D model of MRF Clutch
Fig. 7 MRF Clutch Assembly
Figure 4 shows a cross section of the MRFclutch and figure 5, shows the 3D model of the MRF clutch. Figure 7 shows the manufactured MRF Clutch Assembly. The gap for MR fluid is 1mm between each plate. Spacers are located in between each set of input and output plates to set the MR fluid thickness fixed and to arrest the disposition of plates. Two alignment bearings are fixed to arrest the off-axis rotation of the clutch pack and also to position the centers of both shafts. The magnetic circuit of the clutch composes of an electromagnetic coil made of copper wire which has 750 windings. The clutch pack and the electromagnet circuit are placed inside a 152.4 mm outer diameter casing, which also acts as a return path for the magnetic field. The total length of the clutch is 119mm.Shaft and the output plates are made to glide on to the spline of the inner casing. 3.1. MR Fluid Used MR fluid MRF-132DG provided by Lord Corporation is used in the device as shown in the figure6.The Properities of the fluid used are shown in the Table 1.LORD MRF-132DG fluid is a hydrocarbon-based magnetorheological (MR) fluid formulated for general use in controllable, energy-dissipating applications such as shocks,
K. Hema Latha et al. / Materials Today: Proceedings 4 (2017) 1525–1534
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dampers and brakes.MRF-132DG fluid is a suspension of micron-sized, magnetizable particles in a carrier fluid. When exposed to a magnetic field, the rheology of MRF-132DG fluid reversibly and instantaneously changes from a freeflowing liquid to a semi-solid with controllable yield strength. Altering the strength of the applied magnetic field precisely and proportionally controls the consistency or yield strength of the fluid. MRF-132DG fluid can be used in valve mode(fluid flowing through an orifice) or in shear mode(fluid shearing between two surfaces). In the absence of a magnetic field, MRF-132DG fluid flows freely or allows free movement. Upon application of a magnetic field, the fluid’s particles align with the direction of the field in chain-like fashion, thereby restricting the fluid’s movement within the gap in proportion to the strength of the magnetic field. Table 1.Properities of MRF-132 DG PROPERTY VALUE Appearance Dark Grey liquid Viscosity @ 40°C (104°F)
0.112 ± 0.02 Pas
Density
2.95-3.15 g/cm3
Solids Content by Weight
80.98 %
Flash Point Operating Temperature
>150 (>302) °C (°F) -40 to +130 (-40 to +266) °C (°F)
4. Assembly The following table shows the list of various components of the MRF clutch which forms the Assembly as shown below Table 2. Table 2.Description of the parts for MRF Clutch
S.no
Parts
Radius
Length
Thickness
Numbers
1.a
Input shaft
8.5mm
56mm
25mm
1
1.b
Body holder
39.5mm
7mm
-
1
1.c
Bearing
11mm
7mm
2mm
1
1.d
Hole
M5mm
86pcd
4inch
4
2.
Output shaft plate
39.5mm
10mm
20mm
4
3.
Casing
72.5mm
120mm
56mm
1
4.a
Output shaft
17mm
71.8mm
-
1
4.b
Central output shaft
10mm
62.7mm
-
1
4.c
Output end plate
46.5mm
7mm
8mm
1
5.a
Input shaft plates
46.5mm
10mm
32mm
4
6.a
Input body end plate
46.5mm
26mm
42mm
1
6.b
Bearing
21mm
12mm
10mm
1
6.c
Oil seal
16mm
8mm
3mm
1
7.a
Electromagnet
25mm
95mm
12.5mm
1
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4.1Input shaft and Body Holder The input shaft was selected on the basis for easy coupling to the motor for different application and running on the different input rpm .The shaft is kept according to the load required. Body holder is joint and made with the input shaft such that the body holder adjoins the input shaft plates with the help of the screw. The holes are given according to the standard dimension with M5 hole and 86pcd. The radius of the body holder is made same as that of the plates to be attached to it, fig 8.
Fig.8.Input shaft body and plate holder
4.2.Bearing A step or a indentation is given to allow the bearing to be placed at the centre of the body holder .This bearing is mainly put so that it acts as a gap maintaining device between the input shaft and the output shaft.The holes are given on the body holder according to standard values for attachments of the input shaft plates,fig 9.
Fig.9.Bearing inserted on the input shaft
4.3.Output shaft plate The output shaft plates are made such that there is keyway present at the of length 10mm with the radius 39.5mm.The overall thickness is maintained to be 5mm.The inner diameter is 20mm placed to sit on the central output shaft.Manufactured plates of the input shaft at the top and manufactured plates to be mounted on the output shaft key way, at the right most plate is thicker as it is the end plate of the input shaft consisting of a bearing and oil seal at its centre , fig 10
Fig.10. Output shaft plates
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34.4. Casing The casing houses are electromagnet at the outer part and the clutch centrally. There are 2 bearings fitted at the ends of the casing to hold the input and output shaft. The casing doesn’t rotate and is stationary.It avoids any contact to the environment and acts as a protective case, fig 11.
Fig.11. Casing
4.5. Output shaft with keyway The output shaft is designed such that it is similar to the input shaft and it is made longer in order to come out of the casing. The external loads are applied to this shaft to get the resultant torque output. The shaft is designed in such a way that all the output shaft plates are mounted on it by sliding the plates through the keyway present at it centrally. The keyway is designed according to standard values.The output end plate is designed in such a way that it is attached to the central output shaft and it acts as the first mounting plate to maintain the gap of 1 mm between the output and input shaft plates, fig 12.
Fig.12. Output shaft with keyway
4.6. Bearing and Oil seal It acts as a differentiating part between the input shaft and the output shaft and does not cause any interference between the two and it supports the housing on the input shafts so that the input clutch plate is rotatable on the input shaft relative to the housing. Oil seal acts as a protective device, to avoid any leakage of MR Fluid and it is housed at the end plate of the input shaft which causes a little slip between the two shafts. The magneto rheological fluid settles away from the seal in the cavity due to minimum axial thickness of radial inner portion of the input clutch plate. 4.7. Input shaft plates and Input body end plate These plates are modelled in such a way that they get attached to the body holder of the input shaft with the help of screw. The overall thickness of the plate is maintained at5 mm. Input body end plate acts as the end body cover of the input shaft it is modelled in such a way that when mounted it also maintains a gap of 1mm with the end plate of the output shaft. It acts as the housing for the bearing between the input and the output shafts and the oil seal,fig 13.
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Fig.13. Input shaft plate and Input body end plate
4.8. Electromagnet and Casing Cover Electromagnet is designed specifically to satisfy the amount of magnetic field required to activate the MR fluid present in the gap between the plates of the clutch. It is made by using a soft iron core an high gauge quality single strand wire wound around the soft iron core to about 750 turns. It is housed in the casing and is insulated which does not allow any contact with any metal surface, fig 14 & fig 15.
Fig.14. Electromagnet and casing cover
Electromagnet casing where there is air gap and insulation between the electromagnet casing and the clutch when inserted in it. The electromagnet is made with soft iron core and 750 turns of highly pure copper wire wound around it at the end surface there is a wooden insulation given to prevent the product from any short circuit. Casing cover with bearing placed at centre mounting holes on the outer surface to attach the electromagnet casing and housing at the inner surface there are two major holes for pouring of the fluid. The final assembled MRF cltch is show in the figure 16.
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Fig.15.Casing cover
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Fig.16.MRF Clutch
5. Conclusion In this paper a Magneto rheological fluid Based clutch with detailed description of its design and manufacturing aspects is proposed.Unlike the conventional torque transfer devices which are based on friction a magneto rheological fluid clutch is developed in order to overcome wear, variable loading, engagement, shocks, and temperature variations.The design of the clutch was carried out using Solid works and the torque transfer capacity results were obtained using magneto static analysis in Ansys.To eliminate the wear, engagement, shock and variable loading during operation, a successful magneto rheological fluid based clutch is manufactured. The detailed description of the MRF Clutch comprising of parts likeinput shaft, input body end plates, magnetic core, clutch plates, housing, non magnetic spacers, output shaft with key and casing coveris given. Torque transfer devices are an essential part for a variety of electro-mechanical/robotics systems, in active control of vibrations, optical polishing and inseismic protection. Acknowledgements
This research work is supported and Funded by Research and development Cell-Seed Funds, MuffakhamJah College of Engineering and Technology.
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