A Control Strategy of ACC System Considering Fuel Consumption

Transcription

1 Proceedings o AVEC 6 he 8 th Interntionl Symposium on Adnced Vehicle Control, August -4, 6, ipei, iwn AVEC634 A Control Strtegy o ACC System Considering Fuel Consumption LI Shengbo, BIN Yng, LI Keqing Hiroshi Ukw, Dongsheng Bi, Mstoshi Hnd Stte Key Lbortory o Automotie Sety nd Energy singhu Uniersity Beijing, 84, P.R. Chin Phone: Fx: e-mil: lisb4@mils.tsinghu.edu.cn Adnced IS Group3 Isuzu Motors Limited Kngw-Ken, 585, Jpn Phone: Fx: e-mil: hiroshi-ukw@isuzu.co.jp Aiming t hey-duty ehicle, uel optiml ACC system controller using consolidted ction o throttle nd ger is igned in this pper. Bsed on the inestigtion o uel consumption chrcteristics in lower lyer system with inerse model, combined throttle nd ger control lgorithm is proposed to relize engine opertionl points trck optiml uel economic cure, thus minimizing uel consumption rte. Computer simultion with nonliner hey-duty ehicle model is crried out nd its results show tht the proposed control system cn improe the uel economy o ACC ehicle without scriicing its trcking perormnce. opics / Vehicle Dynmics nd Control, Drier Assistnce Systems, IS. INRODUCION In the reserch ield o drier ssistnce system, dptie cruise control system (ACC) hs been widely inestigted due to its potentils or reducing the worklod o driers, enhncing the sety nd conenience, nd incresing the tric cpcity o existing highwys. Currently, most o the ACC products pplicble or ehicles im t trcking the preceding ehicle precisely, howeer, with incresing customer requirements or energy consertion, the optimiztion problem o uel consumption begin to drw the reserchers ttention in the ign o uture ACC control strtegies. By sureying the eects o IS on energy consertion, Sdyuki sugw hs pointed out tht besi rod cpcity the ehicle pltoon hs unction to improe ehicle s uel economy due to mintin smoothing tric nd reduce the ollowing ehicle s erodynmic drg []. On the bsis o this concept, modiied PID type ollowing controller ws igned nd computer simultion in ccelertion condition demonstrted tht the lst ehicle s uel consumption could be sed by 9% in n eight hey truck string []. In order to improe uel economy in ACC system, John Jonsson et l proposed Stop nd Go control method bsed on Dynmic Progrmming theory, in which uel consumption ws optimized by choosing cost unction o ehicle sttes[3]. Becuse the control strtegies boe only depend on throttle control, which implies tht uel consumption o ehicle is directly relent to the ccelertion leel, the trcking perormnce is somewht scriiced ineitbly t the moment uel economy becomes better. o del with this problem, cruise controller using gin scheduling method is igned to regulte engine speed while the optiml ger rtio or uel economy is gien simultneously [4]. Additionlly, bsed on the similr strtegy, cruise control system or motor ehicles with CV ws deeloped nd its improement on uel economy is proed by computer simultion [5]. In the two systems boe, consolidted engine nd trnsmission control method presents its potentil to improe uel economy. But, its ppliction is only limited to cruise control system by now. In order to reduce the uel consumption while mintining good trcking perormnce or ACC system, uel optiml controller is igned in the pper using consolidted ction o throttle nd ger. Aiming t the chrcteristics o hey-duty ehicle s drieline, n inerse longitudinl model bsed lower lyer system is deeloped, ollowed by the inestigtion o its uel consumption chrcteristics. Combined throttle nd ger control lgorithm is proposed to relize engine opertionl points trck optiml uel economic cure s close s possible on the premise o mintining ired engine output. And computer simultion in ccelertion scenrios is crried out to lidte the trcking nd uel-sing perormnce o the proposed ACC control system inlly.. Construction o inerse longitudinl model he undmentl o ACC system is tht ccording to inormtion such s inter-ehicle distnce, reltie speed nd ehiculr elocity mesured by sensors mounted on the ollowing ehicle, n engine nd brke eedbck control lw is employed to keep the ollowing ehicle trcking the preceding one bsed on speciic hedwy policy. Currently, two-lyer control strtegy hs been used widely to implement the ACC controller, in which the upper lyer outputs ired ccelertion nd the lower lyer system relizes the ccelertion trcking [6]. Becuse this pper gies emphsis

2 on ccelertion cse, two ACC controllers only relent to engine control is igned. One is bsed on inerse longitudinl model nd the other is bsed on consolidted ction o throttle nd ger. For the purpose o concision, they re clled controller A nd controller B, respectiely. Figure shows conceptul schemtic digrm o hey duty ehicle s powertrin system. It consists o such ssemblies s diesel engine, clutch, utomtic trnsmission, inl ger nd wheel. A ull order nonliner longitudinl ehicle model hs been constructed beore nd will be used or computer simultion in section 5. Finl Ger Wheel rnsmission Clutch J e ω e e α th Fig. Conceptul Schemtic digrm o powertrin In order to simpliy the inerse longitudinl ehicle model, it is ssumed tht () he engine dynmics due to intke nd combustion dely is neglected; () he enggement nd disenggement o clutch re inished instntneously, s well s the ger switching o utomtic trnsmission; (3) Vehicle runs on dry sphlt rod strightly nd the drien torques cting on let nd right shts equl pproximtely; (4) here is no slip between tyre nd rod. Figure shows the block digrm o the inerse model. F R Rolling resistnce Aerodynmic drg Accelertion drg F ig ωe Inerse / r e α th F x iη Mp Fig. Inerse longitudinl ehicle model According to the ired ccelertion commnd gien by upper lyer system, the ired trction orce cting on drien wheel F x is computed rom the ollowing eqution: F = F F δ m x R = C ρ A mg δ m D, () where F denotes erodynmic drg, F R denotes rolling resistnce, is the ollowing ehicle elocity, m is ehicle mss, δ is mss ctor nd C D ρa, g, re erodynmic coeicient, grity constnt nd riction coeicient, respectiely. Considering the inerse model o wheel, trnsmission nd inl ger, the ired engine torque e is deried rom: e Fxr = i i η g, () where r is eectie rdius o wheel, i g nd i denote rtio o trnsmission nd inl ger, η denotes powertrin eiciency. And the ired throttle ngle, th, or the gien ired engine torque e nd engine speed ω e cn be clculted rom inerse engine mp cribed by eqution(3) nd the inerse longitudinl ehicle model is obtined ultimtely. α = Mp (, ω ). (3) th e e In theory the output o lower lyer system identiies the input completely, howeer, due to prmetric uncertinties nd unmodeled dynmics o ctul ehicle plnts, they re somewht inconsistent nd irst order system is used to model this disgreement: K = s l, where K, l denote the estimted prmeters. Considering the dynmic chrcteristics o lower lyer system, stte spce model or ollowing nd preceding ehicle cn be written s eqution (5) by employing the constnt-time hedwy policy. d& τ h d & = p (5) / l & K / l, where τ h is hedwy time, d is the error between ctul distnce nd ired hedwy, is the reltie speed nd, p denote ccelertion o preceding nd ollowing ehicles, respectiely. By using liner qudrtic optiml control theory, the stte eedbck lw (4) = Kx, (6) is chosen to minimize the cost unction: J = ( x Qx R ) dt (7), where x represents the system sttes, Q nd R re weighting mtrices which gie trdeo between trcking perormnce nd ride comort. 3. Fuel economy nlysis o Controller A Beore nlyzing the uel consumption chrcteristics o ACC ehicle with controller A, let s reiew the undmentl ign process o powertrin. In product ehicle, uel economy nd power perormnce is two o the most concerned issues. o compromise between them, the resonble mtching o engine nd drie line, in prticulr engine nd trnsmission, is necessry. Due to the ollowing resons: () power requirements in such conditions s upgrde nd oertke; () the unknown ccelertion leel in n ctul tric low, the inished powertrin usully he the potentil to proide redundnt trction orce, which results in low engine lod nd consequently increse the uel consumption. his cn be illustrted by igure 3, in which str line represents engine opertionl points o ACC ehicle with controller A nd dotted line represents optiml uel economic cure. he ct tht the ormer keeps wy rom the ltter indictes tht the uel consumption rte is not optiml in ACC ehicle with controller A nd it is possible to

3 reduce uel consumption by regulting engine opertionl points skillully. Fig. 3 opertionl points in controller A It hppens tht there is not oertke sitution in n ACC system nd the ired ccelertion is lso known due to the existence o upper lyer system. his indictes tht the required engine output cn be determined in dnce nd redundnt power which results in low engine lod is no more necessry in n ACC-ctited ehicle. For gien engine power, the optiml uel economic cure hs minimum uel consumption rte. I we cn regulte engine to operte round it, uel economy o ACC ehicle is possible to be improed. Moreoer, ehicle s trcking perormnce is still mintined becuse the ired ccelertion required by upper lyer system is gurnteed. Howeer, pure throttle control doesn t suice or the need due to the inluence o the ixed shit schedule o utomtic trnsmission. hereore, prt rom the throttle ctutor, the rel-time djustment o ger rtio is lso necessry so s to deelop uel-sing lower lyer control system. Becuse the ired ccelertion gien by upper lyer system relects the requirement or ACC ehicle rising rom rod tric nd the control o throttle ngle nd ger rtio, een speciic shit schedule or ACC-ctited ehicle, is relent to powertrin, the thought presented boe cn be regrded s the mtching between powertrin nd tric low. As cse in points, lower lyer system bsed on consolidted ction o throttle nd ger is deeloped in the ollowing section. 4. Combined throttle nd ger control lgorithm ign Desired Power Clcultor P e Optiml engine sttes clcultor ω e Assistnt Ger=switch Compenstor α th V Automtic rnsmission i g Wheel Model Fig. 4 Combined throttle nd ger control lgorithm he bsic principle o combined throttle nd ger control lgorithm is to mke the engine opertionl point trck optiml uel economic cure s close s possible while mintining ired engine power. Figure 4 shows its schemtic digrm, which consists o three prts: ired power clcultor, optiml engine sttes clcultor nd ssistnt ger-switch compenstor. he irst prt is used to clculte the ired engine power ccording to control commnd gien by upper lyer system. he second prt is to compute ired throttle ngle nd ired engine speed ccording to optiml uel economic cure. he lst prt is to reduce the error o ired nd ctul ger rtio by djusting the ger-shit o utomtic trnsmission. According to ehicle current sttes nd ired ccelertion commnd gien by upper lyer controller, the ired engine power P e cn be clculted by the ollowing eqution: P = mg C ρa δm 3 e D (8) η Using ormul P e =ω e e, the mthemticl cription o optiml uel economic cure in terms o engine output nd engine speed cn be deried rom igure 3: Pe = ( ωe) (9) In optiml engine sttes clcultor, the ired engine speed ω e cn be clculted rom P e through inerse unction o eqution (9) nd subsequently the ired throttle ngle α th cn be computed by engine MAP ccording to obtined ω e. In the hey-duty ehicle, two-rible shit schedule o A depends on ehicle speed nd throttle ngle, in which the ormer hs stronger eect o the switching o ger. In order to keep engine operting on the ired opertionl points, the ctul engine speed nd throttle ngle should be djusted to pproch the ired lue ω e nd α th s close s possible. o trck ω e, n ssistnt ger-switch compenstor is igned to retune ger switching on the bsis o originl economic mode shit schedule. Figure 5 shows its block digrm. he ired ger rtio i g is deried rom ctul ehicle elocity nd ired engine speed nd its dierence with the ctul ger rtio i g is ed bck to PID controller. he output o PID controller is employed to compenste ctul ehicle elocity, giing irtul signl V to utomtic trnsmission. ω e Desired i g PID V ger rtio Controller clcultor - i g Fig. 5 Assistnt ger-switch compenstor heoreticlly, engine speed would pproch the ired engine speed i the ctul ger rtio equls the ired lue. Considering the input on the throttle, engine will work close to optiml uel economic cure, thus generting minimum uel consumption rte. Moreoer, due to eqution (8), ired ccelertion gien by upper lyer controller is gurnteed, which implies trcking perormnce is not scriiced. Similrly to controller A, the upper lyer controller cn be igned by liner qudrtic optiml control theory nd consequently controller B is chieed.

4 5. Simultion results In the oregoing sections, the ACC controller A is igned bsed on inerse ehicle model nd controller B is bsed on consolidted ction o throttle nd ger, which is intended to be more uel-sing. In order to lidte the perormnce o those controllers, series o computer simultions in ccelertion scenrios re crried out bsed on ull order nonliner longitudinl hey-duty ehicle model. Additionlly, due to two types o shit schedule ixed with hey-duty ehicle, controller A is simulted under economic mode nd dynmic mode, respectiely. Considering our typicl ccelertion scenrios, ccelertion proiles o preceding ehicle re selected to be sinusoidl signl with prmeters s ble. Figure 6() shows the preceding ehiculr elocity proile. ble Prmeters o ccelertion proiles Scenrio Frequency Amplitude Bis (rd/s) (m/s ) (m/s ) I II III IV he preceding nd ollowing ehicle he the sme initil speed m/s, nd initil distnce is set s 9 m. o compre the perormnce o those controllers, prmeters o upper lyer controller re selected to be identicl, tht is K= [-., -.3, 4.3]. preceding one, the bsolute lue o distnce error increses ineitbly s the elocity error between two ehicles ugments. he simultion results in period [s, 45s] show tht the elocity nd distnce errors re bsiclly the sme, which indictes tht the trcking perormnce o controller B is not reduced compred with controller A. Fig. 7() Ger rtio in scenrio III () Preceding elocity proile (c) Velocity error (b) Accelertion error (d) Distnce error Fig. 7(b) opertionl points in scenrio III Figure 7() shows ger rtio under controller A nd B in scenrio III. Simultion results show tht ctul ger rtio under controller B trcks ired lue more precisely thn controller A, which indictes engine is in higher uel-sing operting re. Additionlly, s shown in igure 7(b), engine opertionl points under controller B re closest to optiml uel economic cure. Controller A with economic mode nd dynmic mode tkes the second nd third plce. his is consistent with the oregoing nlysis. Fig. 6 rcking errors in scenrio III Figure 6(b)(c)(d) shows the trcking errors o ccelertion, elocity nd distnce, which re deined s the dierence between preceding nd ollowing ccelertion, the dierence between preceding nd ollowing elocity, the dierence between ctul nd ired inter-ehicle distnce, respectiely. A-E Mode denotes controller A under economic mode nd A-D Mode denotes controller A under dynmic mode. From t=s to t=5s, ACC controllers regulte the sttes o ollowing ehicle to eliminte the initil clernce error. From t=5s to t=45s, the ollowing ehicle is under stedy ollowing scenrio, howeer, ccelertion error nd elocity error ry in bounded rnges rther thn conergence to zero due to ritionl preceding ehicle. From t=45s to t= 6s, or the limited mximum elocity o the ollowing hey-duty ehicle is smller thn the Fig.8 Fuel consumption o our scenrios Figure 8 shows br grph o uel consumption t the end time o our ccelertion scenrios. Simultion results show tht controller B hs better uel economy thn controller A, een though under economic mode. In order to quntiy the

5 perormnce o uel economy, reltie uel-sing degree (RFD) is deined s LA LB RFD= %, () LA where L A denotes uel consumption o ollowing ehicle with controller A, L B denotes tht o ollowing ehicle with controller B. By simple clcultion, we know tht uel consumption o controller B is reduced by 4.94% in erge compred with controller A under economic mode, by.6% compred with controller A under dynmic mode. From those simultion results, it is conclude tht the ACC controller bsed consolidted ction o throttle nd ger cn improe uel economy o ollowing ehicle while the trcking perormnce is bsiclly not inluenced. 6. CONCLUSION Aiming t the uel economy problem, uel optiml controller using consolidted ction o throttle nd ger is implemented or ACC system in this pper ter inestigting uel consumption chrcteristics o inerse model bsed lower lyer system. heoreticl nlysis nd computer simultion indicte tht: () Due to the considertion o redundnt ccelertion perormnce in shit schedule o utomtic trnsmission, engine lod in lower lyer system with pure throttle control usully is low nd uel consumption rte hs the potentil to be decresed urther; () he proposed lower lyer system bsed on consolidted ction o throttle nd ger cn minimize uel consumption rte by mking engine opertionl points trck optiml uel economic cure. In nture, this method cn be regrded s resonble mtching between tric low nd powertrin. (3) ACC system bsed on consolidted ction o throttle nd ger cn improe uel economy o ACC ehicle while mintining the sme trcking perormnce s tht with inerse longitudinl model. REFERENCES [].Sdyuki sugw. An oeriew on energy consertion in utomobile tric nd trnsporttion with IS. IEEE, pp, 37-4, (). [].Jinlong Zhng, Petros Ionnou. Longitudinl control o hey trucks: Enironmentl nd uel economy considertions. IEEE Intelligent rnsporttion systems conerences, pp , Wshington.D.C, (4). [3].John Jonsson. Fuel optimized predictie ollowing in lower speed conditions. Mster thesis, Linköping Uniersity, (3). [4].Hongyu Huo, Jun Li. Cruise control bsed on gin scheduling PI diesel engine speed controller. Vehicle Electronics Conerence, pp.-5, (999). [5].Wng Hongyn, Qin Dtong. A study on the cruise uzzy control system o ehicles with CV. Automotie ering, Vol., No.4, (). (in chinese) [6].Kyongsu Yi, Ilki Moon nd Young Do Kwon. A ehicle-to-ehicle distnce control lgorithm or stop-nd-go cruise control. IEEE intelligent trnsporttion systems conerence proceedings, pp ,().