ANALYSIS OF FAILSAFE HYDRAULIC ACTUATION SYSTEM USING PASSIVE RELIEF VALVES; APPLICATION FOR POWER ASSISTING DEVICES

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1 ANAYI OF FAIAFE HYDRAUIC ACTUATION YTE UING PAIVE REIEF VAVE; APPICATION FOR POER AITING DEVICE otaro IHIGURI*, isuk HIODA, Yusuk YAANAGA, hogo AOHITA and akoto IHIGE * Railway Tchnical Rsarch Institut Hikari-cho, okubunji-shi, Tokyo, Jaan ( ishiguri@rtri.or.j ABTRACT This ar rsnts a hydraulic circuit to nsur safty actuation mchanically. Th systm includs assiv valvs for safty oration. hn th actuation systm movs toward intndd dirction dischargd hydraulic fluid from um gos through th roosd assiv valvs and flows into th actuator cylindr to assist movmnt of th actuator. Consquntly, sulid rssur from th um is corrctly loadd to th cylindr. On th othr hand, whn th actuation systm movs for unintndd dirction, rlif ort to rliv rssur of th actuator is formd and at th sam tim byass channl from highr rssur sid of th um to lowr rssur sid of th um is formd by th roosd assiv valv. As a rsult, th sulid flow is byassd by th valv and rssur of th cylindr is kt on lowr than th dischargd rssur of th um. imulations ar carrid out to valuat th ffctivnss of th circuit. EY ORD Hydraulic, Actuator, Failsaf systm, Passiv valv NOENCATURE A D, A D, A P : Ara of orific (ool valvs A s : Ara of sool valv nd A c, A c3 : Ara of orific (Chck valvs A : Ara of iston a : Ratio of cylindr ara of rod-sid and had-sid c : Cofficint of discharg c : Daming cofficint of sool valvs c : akag cofficint : Bulk modulus of oil k : ring constant of sool valvs m : ass of sool valvs C, CR, P, P, D, DR, A,, B, BR, a, a : Circuit rssur of ach ort D, D, D, DR, A,, P, P, B, BR, C, CR : Circuit flow of ach ort a, a : Inflow of cylindr c, c, c3, c4 : Circuit flow of chck valvs P : Discharg flow of um : akag flow of iston : Dnsity of oil x : Dislacmnt of iston y, y : Dislacmnt of sool valvs BP : Volum of channl nar th um b, b : Cylindr volum of rod-sid and had-sid : Cylindr volum of had-sid

2 ulidrsurat nutral osition, : Total volum of th channl nar th sring sid of sool valvs with th nd of sool valvs B, BR : Volum of channl nar th sring sid of sool valv B : Volum of byass channl INTRODUCTION Hydraulic and numatic actuators ar usd for controlling owr assisting dvics. Thos ar oftn usd for th art whr safty is scurd by othr mchanism. In automotiv systms, owr assisting actuation mchanism for string whls has bn installd to assist string torqu. In th systm, th string shaft is dirctly connctd with handling shaft to nsur safty driving [], []. For this rason, if th owr assisting systm dos not work corrctly, w can avoid dangr by ovrriding th actuator torqu with th owr of ourslvs. Th systm is an xaml of nsuring safty by mchanical systm and human owr. Howvr, thr ar som systms that cannot b suortd by othr sourc of owr. Considring furthr alications of thos actuators, it is ncssary to nsur safty by itslf. Thrfor, this ar rsnts th hydraulic circuit for owr assisting dvics to nsur safty actuation mchanically. actuator. In th corrct oration, it is ncssary to load rssur constantly to assist motion of th actuator. hn w st ordinary rlif valvs for this actuation systm, it is imossibl to st rlif rssur lowr than th actuation rssur for th corrct oration, bcaus th sulid rssur from th um will b loadd also in th fault oration. For this rason, it is ncssary to st u scial valvs. Th valv has two functions, on is to load hydraulic rssur to th actuator in th corrct oration, and anothr is to rliv rssur from th actuator with byassing hydraulic fluid from dlivring sid to suction sid of th um by th byass channl. Figur shows an actuation systm including roosd assiv valvs for safty oration. Th systm has two assiv valvs and four chck valvs. In addition, Figur 3 shows valv unit of th actuation systm. Th valv unit has six orts for controlling hydraulic flow and rssur. P is a ort for sulying fluid from th um. A is a ort connctd with th actuator cylindr. In th corrct oration, hydraulic fluid flows from th um to th actuator through th ort P and A. D is a ort for byass channl. C and D ar orts to rliv rssur of Cylindr ECHANI This actuation systm has a cylindr for owr assisting. Th actuator is initially movd by xtrnal forc and thn th assisting movmnt is followd by th initial movmnt of th actuator. On th contrary, whn th systm movs for unintndd dirction (fault oration, valvs connct um with byass channl and actuator with rlif channl at th sam tim, thn th owr assisting function is invalidatd. Th systm has an actuator cylindr and a um. Figur shows rlationshis btwn rssur and movmnt of thpassiv valv Pum Passiv valv Figur chmatic configuration of failsaf hydraulic actuation systm Vlocity D P Fault movmnt y D y P Rlivd rssur Vlocity Corrct movmnt Atmoshric rssur ulid rssur d d A D y D B C Figur Prssur of th cylindr Figur 3 Valv unit

3 th actuator. In th fault oration, byass channl through ort D and rlif channl through ort C and D work as safty systms. B is for th rload ort to load th sam rssur as th actuator to th sool. Th rload ort works to maintain osition of th sool. Figur 4 shows flow of th actuation systm in th corrct oration. This is an xaml that th actuator movs toward rod-sid. Undr this condition, sulying fluid from th um coms into th ort P, and thn through th ort A R of th sool valv unit to th actuator. In addition, rturnd fluid from oosit sid of th cylindr coms into th ort C of anothr valv, and thn through th ort D of th valv to lowr rssur sid of th um. Consquntly, it is ossibl to load aroriat rssur to th cylindr in th corrct oration. On th othr hand, Figur 5 shows flow of th actuation systm in th fault oration. This is an xaml that th actuator movs toward had-sid. Undr this condition, sulying fluid from th um coms into th ort P, and thn through th ort D R of th sool valv unit to th lowr rssur sid of th um. At that tim, byass channl from highr rssur sid of th um to lowr rssur sid of th um was formd. Consquntly, th actuation systm did not roduc forc for actuation undr th fault condition. IUATION ETTING a a Cylindr c c C D P A D B c 3 c 4 Pum B R A R D R D P C R Passiv valv Figur 6 shows dirction of hydraulic flow and rssur of th actuation systm. Positiv dirction of th fluid flow is indicatd by th arrow in th Figur. orovr, black circls indicat conncting oints of th ath. st dislacmnt of th iston x, and dislacmnt of th assiv valv lmnts y and y, whr th nutral osition of th iston corrsond to x =. And dislacmnt y = and y = corrsond to th osition that srings of sool valvs ar xtndd. Fluid flow at ort D and D ar calculatd from following quations, Figur 4 Flow of th actuation systm in th corrct oration C D D c AD ( y sign C D CR D D c AD ( y sign CR D ( ( a a x a a Cylindr a a c c C A D D CR c c D A A R D D A D C P D B B R D R P C R C y B D BR DR y CR c 3 c 4 P c3 c4 P Pum Passiv valv Figur 5 Flow of th actuation systm in th fault oration Figur 6 Dfinition of hydraulic flow dirction and rssur of th actuation systm

4 whr c is cofficint of discharg, is dnsity, A D (y and A D (y ar th ara of orific rlativ to th dislacmnt of th sool valvs. Fluid flow at ort A and A R ar shown as follows: a c D (4 wt volum at th sring nd of th sool valv ar P A A c AP ( y sign P P c AP ( y sign P A (3. (4 B BR A y (5 A y. (6 ulid rssur from th um and ar hr A P (y and A P (y ar th ara of orific rlativ to th dislacmnt of th sool valvs. By th sam way, fluid flow at ort D and D R ar givn as follows: P D D c AD ( y sign P D P DR DR c AD ( y sign P DR (5.(6 hr A D (y and A D (y ar th ara of orific dnding on th dislacmnt of th sools. Fluid flow at ort P and P ar sum of th fluid flow at ort A and D P A D P DR (7. (8 Chck valvs ar st u from th valv and sring, for this rason, fluid flow of th valv ar calculatd from quations (9 to (. A C c c Ac ( yc (9 CR c c Ac ( yc ( c3 c4 D P c Ac 3( yc3 ( D P c Ac 3( yc4. ( hr A c (y c* and A c3 (y c* ar th ara of orific dnding on th stat of th chck valvs. Inflow of cylindr at rod-sid and had-sid ar as follows: a c D (3 P c (7 3 BP P c R (8 R 4 BP whr is modulus of lasticity of volum, BP is channl volum nar th um; is discharg flow of um. Inflow of byass channl is sam as th fluid flow at ort D and D, C D (9 CR D. ( Acclration of sool valvs ar as follows: A C B c y k y m A CR BR c y k y m y ( y. ( hr m s, c s and k s ar mass, daming cofficint and sring constant of th sool valv. Prssurs of th cylindr ar a a ( x b b ( x a a A x a A x (3. (4 hr a is a ratio btwn rssur rciving ara of rod-sid and had-sid of th cylindr, is lakag flow of th iston du to th ga btwn cylindr and iston c (. (5 a a Volum of th cylindr of rod-sid b, and volum of th cylindr of had-sid b ar shown in quations b ( x a a A x (6

5 b x ( A x. (7 Prssur of th channl of sring sid of th roosd valvs ar as follows: ( y B A A B c ( y BR BR c (8 (9 whr and ar total volum of th channl nar th sring sid of sool valvs with th nd of sool valvs ( y A y (3 B BR ( y A y. (3 Prssur of th byass channl is D D D c4 (3 B. D DR hr B is th volum of byass channl. Prssurs of th ort connctd with th byass channl ar th sam as th rssur D c3 D D DR D. (33 Paramtrs for simulation ar listd on Tabl. This stting is usd to vrify fundamntal oration of th roosd assiv valvs undr th corrct oration and th fault oration. IUATION REUT st two conditions for th simulation. On is th corrct oration and anothr is th fault oration. In addition, th tim, w st th actuator forcd to mov toward th corrct and fault dirction to mulat conditions that th actuator movs to th commandd dirction and unintndd dirction. imulation rsults of corrct oration ar shown in Figur 7. Th to Figur shows dislacmnt of th actuator. In this Figur, ositiv dislacmnt mans shrinking. Thrfor th actuator forcd to shrink from two to sconds and to rturn toward nutral osition from 7 to 7 sconds, undr this stting. Th middl Figur shows hydraulic flow from th um. In th Figur, ositiv flow of th um corrsonds to suly hydraulic fluid to had-sid of th actuator. Undr this stting, th um dischargs hydraulic fluid toward rod-sid of th actuator from two to sconds, and thn aftr th 5-scond sto, th um dischargs hydraulic fluid toward had-sid of th actuator from 7 to 7 sconds. Th bottom Figur Tabl Paramtrs for simulation Paramtrs ymbol Valu Unit Atmoshric rssur sa kpa Prssur of discharg sid of um sb 4 kpa Dnsity of oil 86 kg/m 3 Bulk modulus of oil.6 GPa Cofficint of discharg c.7 Diamtr of sool valv d s 7. mm ass of sool valv m s.45 kg ring constant of sool valv k s.98 N/mm Daming cofficint of sool valv c s 3. Ns/m Diamtr of sool ort d d 8. mm Ovrwra of sool ort D y D 6.5 mm Ovrwra of sool ort P y P. mm Ovrwra of sool ort D y D.5 mm Diamtr of actuator iston d 4. mm Ratio of cylindr ara of rod-sid and had-sid a.68 akag cofficint C. (/min/(kgf/cm Volum of channl nar th um BP.6 cm 3 Volum of byass channl B 58.5 cm 3 Volum of channl nar th sring sid of sool valv B 3.7 cm 3

6 mm cm 3 /s Pa 6 4 Actuator dislacmnt Flow from um Prssur of cylindrs Tim s Rod nd Had nd Figur 7 Corrct oration had-sid of th cylindr. As shown in this Figur, dischargd hydraulic fluid gos through th roosd assiv valvs and flows into th actuator cylindr to assist actuator motion. Consquntly, sulid rssur is corrctly loadd to th cylindr undr this condition. On th contrary, simulation rsults of fault oration ar as shown in Figur 8. cifications of lins ar sam as that of th Figur 7. Undr this stting, discharging dirction of th um is sam as th corrct oration. By contrast, dirction of th actuator dislacmnt is oosit from th stting of th corrct oration. Th bottom Figur shows rssur of th actuator cylindr. As shown in this Figur, surging rsons is invitabl at th transition tim instantanously. Howvr, xct for th transitional riod, rssur of th cylindr is kt on lowr than th dischargd rssur of th um at th condition. At that tim, byass channl from highr rssur sid of th um to lowr rssur sid of th um is formd by th roosd assiv valv. As a rsult, th sulid flow is byassd by th valv and rssur of th cylindr is kt on lowr than th dischargd rssur of th um. Consquntly, th actuation systm did not roduc forc for actuation undr th fault condition. In addition, it is ossibl to nsur safty oration by using th roosd assiv rlif valv. mm cm 3 /s Pa 6 4 Actuator dislacmnt Flow from um Prssur of cylindrs Tim s Rod nd Had nd Figur 8 Fault oration shows rssur of th actuator cylindrs. Continuous lin corrsonds to rssur of rod-sid of th cylindr. In addition, dottd lin corrsonds to th rssur of CONCUION In this ar, w studid hydraulic circuit for owr assisting dvics to nsur safty actuation. Two assiv valvs ar installd in this systm. hn th actuation systm movs toward intndd dirction, sulid rssur from th um is corrctly loadd to th cylindr to assist movmnt of th actuator. On th contrary, whn th actuation systm movs for unintndd dirction, th sulid flow is byassd by th valv and rssur of th cylindr is kt on lowr than th dischargd rssur of th um. imulation rsults show that th actuator works just as intndd both in th corrct oration and th fault oration. Consquntly, it is ossibl to nsur safty oration of owr assisting dvics by using th roosd assiv valv. REFERENCE. Baharom,. B., Hussain,. and Day, A. J., Dsign concts and analysis of a smi-activ string systm for a assngr car, Procdings of th Institution of chanical Enginrs, Part : Journal of ulti-body Dynamics, 9, Vol.3, No.4, Nong, Z., and ial,., Dynamic odling of Hydraulic Powr tring ystm with Variabl Ratio Rack and Pinion Gar, JE Intrnational Journal, ris C, 5, Vol.48, No.,.5-6