HUNGARIAN JOURNAL OF INDUSTRY AND CHEMISTRY Vol. 48(1) pp. 77–80 (2020) hjic.mk.uni-pannon.hu DOI: 10.33927/hjic-2020-12 TORQUE TRANSMISSION TIME-CONSTANT EXAMINATION OF A DISK- TYPE MAGNETORHEOLOGICAL CLUTCH SÁNDOR MESTER*1 AND ISTVÁN SZALAI1 1Institute of Mechatronics Engineering and Research, University of Pannonia, Gasparich Márk utca 18/A, Zalaegerszeg, 8900, HUNGARY In this paper, the torque transmission time-constant of a simple disk-type magnetorheological (MR) clutch is investigated. By using MR fluid, controlled torque transmission can be easily implemented, facilitating the widespread use of similar systems. In order to describe the dynamical properties of the system, time constants were measured at different speeds and magnetic inductions. The time constants were derived by fitting an exponential function to the data. Keywords: magnetorheological fluid, clutch, torque transmission 1. Introduction The implementation of intelligent materials has signifi- cantly increased not only in everyday life, but in the in- dustrial environment as well. Magnetorheological fluids are suspensions that consist of at least two phases, whose apparent viscosity changes quickly (within 20 − 30 ms) in the presence of an external magnetic field. The suspen- sion usually consists of small ferromagnetic particles of approximately 10 µm in diameter dispersed in oil. Usu- ally surface active agents are also present in the fluid to prevent the particles from being attracted to each other. In the presence of an external magnetic field, the parti- cles gain an induced dipole moment and form pairs, fol- lowed by chain-like structures. If the fluid is exposed to shearing, these chain-like structures oppose each other leading to an increase in apparent viscosity which can be used in shock absorbers, torque transmission, super- finishing of optical lenses and civil engineering [1–4]. In addition to the rapid change in apparent viscosity, its low power requirement makes MR fluid ideal for use in semi- active shock absorbers and variable torque-transmission clutches. The most basic forms of magnetorheological clutches are the disk and cylindrical types. The differences be- tween the two types are the transmittable torque and the volume of the idling waste. A stream of particles is present in disk-type clutches due to the centrifugal force. In the cylindrical type, the effect is less significant [5, 6]. This study focuses on a disk-type clutch with a well- defined mathematical model [7]. *Correspondence: hollosi.janos@sze.hu 2. Experimental The model of our magnetorheological clutch is shown in Fig. 1. The clutch consisted of the following main compo- nents: 1. DC servomotor with a gearbox; 2. toothed belt drive with 1 : 1 gear ratio; 3. input or drive shaft; 4. in- put shaft bearings; 5. lower disk; 6. upper disk; 7. upper or driven shaft; 8. upper shaft bearings; 9. torque sensor; and 10. toothed belt drive with 4 : 1 gear ratio. The elec- tromagnetic coil, which consisted of approximately 1000 turns, was located around the disks with the coils encir- cling them, providing magnetic field lines parallel to the shafts. The MR fluid was loaded into the lower disk. The diameter of the disks was 116 mm and the gap between them was 1 mm. The input and output signals were read and recorded by an National Instruments (NI) USB-6281 data acquisi- tion device with a sampling rate of 1 kHz. The complete magnetorheological clutch is shown in Fig. 2. For future measurements, a 3-phase AC induction motor with a frequency inverter was installed to serve as an artificial load. 2.1 Samples and Measurements A Hall effect sensor, located at the top of the upper disk, measured the magnetic field. An encoder was located at the bottom of the drive shaft of the clutch to measure the input speed. The control and measurement tasks were car- ried out by a NI USB-6281 data acquisition device con- trolled by LabVIEW software. The input speed and out- put torque were recorded. The MR fluid used was LORD MRF-122EG fluid diluted by 50 m/m% with silicone oil. https://doi.org/10.33927/hjic-2020-12 mailto:hollosi.janos@sze.hu 78 MESTER AND SZALAI Figure 1: Model of a disk-type magnetorheological clutch The output side of the clutch was fixed at the torque sensor with the intention of measuring the torque trans- mission time-constants, so the output speeds at both the sensor and driven shaft were zero. The measurement cy- cles, using a preset magnetic field, consisted of a 3- second-long mixing phase in the absence of a magnetic field, followed by a 6-second-long measurement period with the magnetic field turned on, and finally another 3- second-long mixing phase, all at a constant speed. After the cycle, a new speed was set and a new cycle started. The speeds measured were 11.5, 17.5, 23.5, 29.5, 35.5, 40.5, and 46.5 rpm. The magnetic induction was con- trolled by currents of 1.8, 2.5, 3.3, and 4.4 A applied to the coil, thereafter the corresponding magnetic inductions were 114, 144, 173, and 202 mT. Figure 2: Complete magnetorheological clutch Figure 3: Transmission torque from when the magnetic field was turned on at a speed of n = 11.38 rpm and using different magnetic inductions Figure 4: Transmission torque from when the magnetic field was turned on at a speed of n = 46.5 rpm and using different magnetic inductions 3. Results and Discussion 3.1 Experiments Using the aforementioned method, a series of 12 mea- surements were carried out at each speed and in each magnetic field by taking into consideration the uncer- tainty of the mechanical parts (toothed belts, bearings, etc.). Examples of the measurements can be seen in Fig. 3 (n = 11.38 rpm) and Fig. 4 (n = 46.50 rpm), as well as a periodicity due to the inaccuracies of the mechanical parts. The maximum output torque was M = 0.85 Nm. 3.2 Calculation of time constants Time constants were determined by fitting an exponential function to the measured data: M(t) = A ( 1− e− t τ ) (1) where M denotes the transmission torque, t repre- sents the time, and τ stands for the time constant. The Hungarian Journal of Industry and Chemistry TORQUE TRANSMISSION TIME-CONSTANT OF A DISK-TYPE MAGNETORHEOLOGICAL CLUTCH 79 Figure 5: CFitted curve of measurements at a speed of n = 46.5 rpm and a magnetic induction of B = 202 mT Figure 6: Time constants as a function of magnetic induc- tion at different speeds fitting was carried out according to the measurements. An example of the fitting is shown in Fig. 5. The fitted curve correlates well with the measurement data. The results of the fitting were averaged to obtain the time constants for the applied magnetic inductions and rotational speeds. The time constants are shown in Fig. 6 as a function of magnetic induction. The measured time constants took into account the whole system, including the effects of the MR fluid as well as mechanical parts. By increasing the magnetic field strength, the time constants decreased. In the weakest magnetic field and at the lowest speed, the time constant was extremely high, greater than 1 second to be exact, due to the characteris- tics of the fluid. The time constants as a function of the speeds are shown in Fig. 7. Increasing the speed also resulted in a re- duction in the time constant that was less significant than in stronger magnetic fields. In strong magnetic fields, the influence of the speed on the time constants was insignif- icant, therefore, its effect was almost negligible. Figure 7: Time constants as a function of speed using dif- ferent magnetic inductions 4. Conclusion Based on the measurement results, the torque transmis- sion time-constants for our magnetorheological clutch us- ing the MR fluid were obtained. The time constants dif- fered greatly from the response times of a magnetorheo- logical fluid due to the inertia of the mechanical compo- nents. In the future, the influence of the mechanical parts on the time constants will be measured. Acknowledgements This research was supported by the European Union and co-financed by the European Social Fund under the project EFOP-3.6.2-16-2017-00002. REFERENCES [1] Rankin, P. J.; Ginder, J. M.; Klingenberg, D. J.: Electro- and magneto-rheology. Current Opinion in Colloid & Interface Science, 1998, 3(4), 373–381 DOI: 10.1016/s1359-0294(98)80052-6 [2] Olabi, A. G. ; Grunwald, A.: Design and application of magneto-rheological fluid, Mater. Des., 2007, 28(10), 2658–2664 DOI: 10.1016/j.matdes.2006.10.009 [3] Mazlan, S. A. ; Ekreem, N. B.; Olabi, A. G.: An investigation of the behaviour of magnetorhe- ological fluids in compression mode, J. Mater. Process. Technol., 2008, 201(1–3), 780–785 DOI: 10.1016/j.jmatprotec.2007.11.257 [4] Lampert, S. G. E. ; van Ostayen, R. A. J.: Exper- imental results on a hydrostatic bearing lubricated with a magnetorheological fluid, Curr. Appl. Phys., 2019, 19(12), 1441–1448 DOI: 10.1016/j.cap.2019.09.004 [5] Törőcsik, D.: Some Design Issues of Multi-Plate Magnetorheological Clutches, Hungarian J. Ind. Chem., 2011, 39(1), 41–44 https://mk.uni-pannon. hu/hjic/index.php/hjic/article/view/380 [6] Rabinow, J.: The Magnetic Fluid Clutch, Trans. Am. Inst. Electr. Eng., 1948, 67(2), 1308–1315 DOI: 10.1109/t-aiee.1948.5059821 48(1) pp. 77–80 (2020) https://doi.org/10.1016/s1359-0294(98)80052-6 https://doi.org/10.1016/j.matdes.2006.10.009 https://doi.org/10.1016/j.jmatprotec.2007.11.257 https://doi.org/10.1016/j.jmatprotec.2007.11.257 https://doi.org/10.1016/j.cap.2019.09.004 https://mk.uni-pannon.hu/hjic/index.php/hjic/article/view/380 https://mk.uni-pannon.hu/hjic/index.php/hjic/article/view/380 https://doi.org/10.1109/t-aiee.1948.5059821 https://doi.org/10.1109/t-aiee.1948.5059821 80 MESTER AND SZALAI [7] Decsi, P.; Mester, S.; Szalai, I.: Tárcsás magnetore- ológiai tengelykapcsoló modellezése, a rendszer időbeli viselkedésének vizsgálata, OGÉT XXVI. Nemzetközi Gépészei Konferencia 2018, 91–94 Hungarian Journal of Industry and Chemistry Introduction Experimental Samples and Measurements Results and Discussion Experiments Calculation of time constants Conclusion