oceedings of the Wold Congess on Engineeing 013 ol III, WCE 013, July 3-5, 013, London, U.K. hysical ototype of an utomotive agnetoheological Diffeential. Lanzotti, F. Renno,. Russo, R. Russo,. ezo bstact he development of an automotive semi-active diffeential is descibed. he device is based on the use of a magnetoheological fluid and allows to contol the locking toque and, consequently, to impove the vehicle handling. In ode to evaluate the effectiveness of the poposed device, a physical pototype was ealized and the fist expeimental tests wee caied out. Index ems agnetoheological fluid, automotive diffeential, vehicle dynamics S I. INRODUCION EERL developments concened the fee diffeential with the aim of solving its limit: if one diving wheel tavels on a low fiction suface, the tye- oad inteaction foce is minimized and a limited toque is tansmitted to the othe one, with the consequence that the vehicle loses the diving stability. Suitable passive devices [1, ] (so called limited slip diffeential) wee ealized in ode to tansmit toque to a wheel, even if the othe one is on a slippey suface. he limited slip diffeentials ae based on a mating between the two side geas with the effect of geneating diffeent diving toques. his diffeential locking effect makes the vehicle capable to move itself also in pesence of a wheel chaacteized by low taction. he locking toque that chaacteizes the limited slip diffeentials is typically depending on the wheel elative speed o on the toque acting on the diffeential case and geneates its effects independently fom the vehicle handling, e.g. undesteeing/ovesteeing. Consequently, in some dynamic conditions, the locking toque can also detemine an undesied vehicle behaviou. hanks to the development of the electonic contol, semi-active and active [3] diffeentials wee ealized: these devices ae chaacteized by a contollable locking toque and typically employ hydaulic o electical actuation systems to engage a clutch [4-6] which detemines issues in tems of wea and NH (noise, vibation and hashness) due to the sliding between the pats that ae in contact. his pape focuses on a contollable limited slip diffeential which advantage consists of the employment of a contactless clutch that is activated by means of the magnetisation of a magnetoheological (R) fluid and, consequently, no hydaulic pump o electic moto ae equested. R fluid ae extensively employed in bake,. Lanzotti, F. Renno,. Russo, R. Russo, and. ezo ae with the Dipatimento di Ingegneia Industiale, Univesità degli Studi di Napoli Fedeico II, 8015, Italy (coesponding autho, phone: +39081768385; fax: +39081394165; e-mail: m.tezo@unina.it). ISN: 978-988-195-9-9 ISSN: 078-0958 (int); ISSN: 078-0966 (Online) clutch and dampe [7-9], but no examples concening the design and the development of R fluid based automotive diffeential ae available in the scientific liteatue. physical pototype was ealized and tested in ode to veify its locking effect. he expeimental esults highlight the functionality of the poposed magnetoheological fluid limited slip diffeential (RF LSD). II. HE GNEORHEOLOGICL FLUID LIIED SLI DIFFERENIL agnetoheological fluids ae suspensions of miconsized and magnetisable paticles in a caie fluid. Nomally, R fluids ae fee-flowing liquids, having a consistency simila to that of lubicant oil. Howeve, when a magnetic field is applied, thei ehology changes to moe a solid-like gel. R fluid ehology is modelled in pe-yield and postyield egimes. In the pe-yield egime, R fluids demonstate a visco-elastic behaviou. Fo visco-elastic mateials, while some of the applied enegy is ecoveed (elastic behaviou), some is dissipated in the fom of heat. he visco-elastic behaviou of the R fluids in the peyield egime is analyzed by linea visco-elastic theoies. On the othe hand, the R fluid post-yield behaviou, in pesence of a magnetic field, is appoximated by the ingham plastic model [10]: d yd ( H ) (1) dt whee, τ is the shea stess, τ yd is the dynamic yield stess due to applied magnetic field (H), is the no- field fluid viscosity, and dγ/dt is the shea ate. When the magnetic field intensity ises, the feomagnetic paticles find an oientation and the yield stess inceases. his popety makes the R fluids functional fo the employment in contollable devices [11 14]. Fig. 1 illustates the RF LSD logical scheme. It consists of a conventional pat and an unconventional one. he side geas ( and ), the planetay geas (G), the diffeential case () and the diffeential gea (R) chaacteize the conventional pat of the RF LSD. he unconventional pat is constituted by a disk housing (C) and a coil (S). he disk housing engages the side gea and the diffeential case, and contains facing plates, altenately integal with the side gea and the diffeential case, that pefom the fiction sufaces. Suitable space elements ceate a gap in which the R fluid is contained. WCE 013
oceedings of the Wold Congess on Engineeing 013 ol III, WCE 013, July 3-5, 013, London, U.K. he powe W l, adopting the convention of positive l, is given by: W (6) l l Consequently: if (7) Fig. 1. Logical scheme of the RF LSD he device is able to tansfe the powe on the diving wheels and, changing the coil cuent, it is possible to bias the toque with diffeent atio. While in a passive limited slip diffeential the locking toque depends on elative sliding o on the toque acting on diffeential case, in the RF LSD it depends on the magnetic field essentially. aking the Willis atio 0 into account, it can be witten: 0 1 () whee and and espectively, and ae otational speed of the side gea is the otational speed of the diffeential case. Fom () it can be obseved that the otational speed of the diffeential case is the aveage of the speed of the side geas: (3) y means of the otational equilibium equation, enegy balance and (3), the expession of the output toque and can be detemined. In steady-state conditions, being the toque acting on the diffeential case and W l the powe due to the locking toque l acting between the diffeential case and the side gea, it can be witten: 0 Wl 0 (4) if (8) y means of a suitable contol system, the locking toque l can be adjusted in ode to enhance the vehicle dynamic behaviou [15]. he device is a semi-active one since it is able to egulate the locking toque value while the toque flux diection is only established by the wheel kinematics: the supplied enegy detemines a contollable toque flux fom the fastest side gea to the slowest one in ode to lock the diffeential in a wide ange of opeating conditions. he diffeential locking toque is given by the following contibutions: the toque due to fiction ( f ), e.g. of the seals and gea, the toque due to the magnetic field ( ) and the toque due to the fluid viscosity ( ). heefoe, it follows: l f (9) aking into account (1), the magnetic and the viscous contibutions ae given by: o n ( ) d (10) i in which n is the numbe of fiction sufaces, i and o ae, espectively, the inne and the oute adius of the fiction suface and the geneic adius. Consequently: 3 3 n y ( H ) o i (11) 3 n d 4 o 4 i (1) he toque and can be expessed as: Wl Wl (5) whee d is the gap between the seveal disks. he no-field viscosity of the R fluid typically allows to conside the viscous contibution negligible espect to the magnetic one. his chaacteistic makes the RF LSD with non-magnetized fluid vey close to a fee diffeential, with the elevant advantage of educing the enegy loss and the undesied toque appotionment. Consequently, the diving ISN: 978-988-195-9-9 ISSN: 078-0958 (int); ISSN: 078-0966 (Online) WCE 013
oceedings of the Wold Congess on Engineeing 013 ol III, WCE 013, July 3-5, 013, London, U.K. toque can be split in a contolled manne only when it geneates a vehicle dynamics impovement. he vitual pototype of the RF LSD coss section is illustated in Fig. and the seveal components ae listed in able 1. mong the listed components, the coil and its housing only ae motionless espect to the gea box in ode to avoid tavelling electical contacts. he diffeential gea was designed (n 5 in Fig. ) in ode to contain the unconventional pat, constituted by the disk housing and the coil. s egads the conventional pat of the RF LSD, it is based on the mophology and dimensions of the common open diffeential that equipped a middle class vehicle. Fig. 3. hysical pototype of the RF LSD III. EXERIENL ELUION test ig (Fig. 4) was set up in ode to cay out the expeimental investigations. It includes the RF LSD, an invete diven C moto and a eduction unit. Suitable couplings wee adopted to link the seveal components. he measued quantities ae: - otational speed of the C moto by phonic wheel and poximity pick up - input cuent to the RF LSD by Hall effect closed loop cuent senso - tansmitted toque by high stiffness stain gauge load cell. Fig.. RF LSD coss section LE I COONENS OF HE RF LSD No Desciption ateial 1 Side gea Standad steel Side gea Standad steel 3 lanetay gea Standad steel 4 Diffeential case Low cabon steel (ISI 1008) 5 Diffeential gea Low cabon steel (ISI 1008) 6 Inne disk Low cabon steel (ISI 1008) 7 Oute disk Low cabon steel (ISI 1008) 8 Space elements ustenitic stainless steel (ISI 304) 9 Disk shaft ustenitic stainless steel (ISI 304) 10 Disk housing ustenitic stainless steel (ISI 304) 11 Coil oute housing Low cabon steel (ISI 1008) 1 Coil inne housing ustenitic stainless steel (ISI 304) 13 Coil Coppe 14 Sealing Steel 15 Sealing Steel s an example, Fig. 4 shows a fist physical pototype of the RF LSD. he diffeential gea was not completely efined since this featue was not necessay fo the testing pocedue that will be descibed afte. Fig. 4. RF LSD coss section Cuent input was povided by an adjustable 3kW DC powe supply. ll measued quantities wee acquied and stoed by National Instuments Copoation boad and softwae (LabIEW ). he expeimental test ig allows to measue the locking toque l : with efeence to Fig. 5, suitable beaings () sustain the diffeential case that was made integal with the load cell by means of the shaft () and the leve am indicated in Fig. 4. In this way, the locking toque is tansmitted to the diffeential case, by means of the magnetic and the viscous effects, and its value is measued by the load cell. he coil housing (C) was made fixed on a fame. ISN: 978-988-195-9-9 ISSN: 078-0958 (int); ISSN: 078-0966 (Online) WCE 013
oceedings of the Wold Congess on Engineeing 013 ol III, WCE 013, July 3-5, 013, London, U.K. compatible with the peak values of the moden automotive altenatos [16]. Fig. 5. est ig details In ode to evaluate the effectiveness of the manufactued RF LSD, fist esults concening static and dynamic popeties ae pesented. he tests wee conducted at a elative otational velocity of 5 pm. his constitutes a high value eachable in handling manoeuves and consequently was functional to evaluate the viscous contibution on the locking toque. Fig. 6 illustates the static toque-cuent cuve. It can be obseved that the RF LSD is chaacteized by a limited zeo cuent toque ( f ) that makes the device simila to a common fee diffeential. his allows to avoid not equested locking effects and undesiable vehicle dynamic behavious [15]. t the same time, the RF LSD exhibits a significant locking toque in pesence of a educed supply cuent and shows a substantially linea tendency that allows an easie feedback contolle design pocedue. he magnetic toque can be obtained subtacting the zeo cuent toque fom the total one: in this way a /i gain of 6.8 Nm/ was estimated. Fig. 6. Locking toque vs supply cuent he tansient esponse of the device was obtained adopting as input an up-step down-step sequence in tems of supply cuent with an amplitude of 7. In any case, the linea behaviou allows to conside the dynamic popeties of the RF LSD independent fom the cuent input. Fig. 7 shows the output toque of the RF LSD nomalized by the espective maximum value. he input-output elationship can be well appoximated by a fist ode linea timeinvaiant system and consequently a time constant of 0.03 s was detemined, satisfying the typical dynamic equiements of the vehicle handling contol systems. complete demagnetization is obtained afte the downstep, allowing to pevent a esidual activation of the device and, futhemoe, the equested electical powe is fully ISN: 978-988-195-9-9 ISSN: 078-0958 (int); ISSN: 078-0966 (Online) Fig. 7. Step esponse of the RF LSD I. CONCLUSION magnetoheological semi-active diffeential was descibed and a fist physical pototype was illustated and tested. he expeimental esults highlight the static and the dynamic pefomances of the RF LSD, showing its inclination to be a useful tool to contol yaw moment and, consequently, to impove vehicle handling. REFERENCES [1] I.H. aueg, J. Host, Induced toque amplification in viscous couplings, SE ape 900557, 1990. []. Gassmann, J. alage, isco-lok: a speed-sensing limited-slip device with high toque pogessive engagement, SE ape 960718, 1996. [3]. Canale, L. Fagiano,. ilanese,. oodani, Robust vehicle yaw contol using an active diffeential and IC techniques, Contol Engineeing actice, vol. 15, no. 18, pp. 93 941, 007. [4] G. Naito, E. Yaguchi,. atuda,. sahi,. Nakata, I. Inokuchi, New electonically contolled toque split 4WD system fo impoving coneing pefomance, SE ape 900556, 1990. [5]. eaoka, Development of the electo-magnetic contolled limited slip diffeential unit (ECD), SE ape 93103, 1993. [6] J. sgai, D. Hovat, On-demand fou wheel-dive tansfe case modeling, SE ape 970969, 1997. [7] K. Kaakoc, E.J. ak,. Suleman, Design consideations fo an automotive magnetoheological bake, echatonics, vol. 18, no. 8, pp. 434-447, 008. [8]. Kavlicoglu, N. Kavlicoglu, Y. Liu, C. Evensel,. Fuchs, Kool G and F. Godaninejad, Response time and pefomance of a high-toque magneto-heological fluid limited slip diffeential clutch, Smat ateials and Stuctues, vol. 16, pp. 149-159, 007. [9] G.Z. Yao, F.F. Yap, G. Chen, W.H. Li, S.H. Yeo, R dampe and its application fo semi-active contol of vehicle suspension system, echatonics, vol. 1, no. 7, pp. 963 973, 00. [10] J. n, D.S. Kwon, odeling of a magnetoheological actuato including magnetic hysteesis, J Intel ate Syst Stuct, vol. 14, no. 9, pp. 541 550, 003. [11] E.J. ak, D. Stoikov, L. Falcao da Luz,. Suleman, pefomance evaluation of an automotive magnetoheological bake design with a sliding mode contolle, echatonics, vol. 16, no. 7, pp. 405 416, 006. [1] R. Russo,. ezo, odelling, paamete identification, and contol of a shea mode magnetoheological device, in oc IechE at I: Jounal of Systems and Contol Engineeing, vol. 5, no. 5, pp. 549 56, 011. [13] R. Russo,. ezo, Design of an adaptive contol fo a magnetoheological fluid bake with model paametes depending on tempeatue and speed, Smat ateials and Stuctues, vol. 0, no. 11, 115003 (9pp), 011. [14] R. Russo,. ezo, F. impone, Softwae-in-the-loop development and expeimental testing of a semi-active magnetoheological coupling fo 4WD on demand vehicles, in oc. of the ini Confeence on ehicle System Dynamics, Identification and nomalies, pp. 73 8, 008. [15] R. De Rosa,. Russo, R. Russo,. ezo, Optimisation of handling and taction in a ea wheel dive vehicle by means of magneto- WCE 013
oceedings of the Wold Congess on Engineeing 013 ol III, WCE 013, July 3-5, 013, London, U.K. heological semi-active diffeential, ehicle System Dynamics, vol. 47, no. 5, pp. 533 550, 009. [16] D.J. eeault,. Caliskan, utomotive powe geneation and contol, IEEE ansactions on owe Geneation and Contol, vol. 19, no. 3, pp. 618 630, 004. ISN: 978-988-195-9-9 ISSN: 078-0958 (int); ISSN: 078-0966 (Online) WCE 013