KHOA HOC CONG NGHE IMGHIEIM C l i U B d D I E U KHIEIM IVIIJ CHD H E THDIMG DDIMG LUC TRDIMG IMDIMG IMGHIEP, IMDIMG THDIM Hd Hiru Hai' TOM TAT Trong linh vuc nong nghiep va phat trien nong thon hien dang sir dung phd bien he thdng dong luc gom dong CO dot va truyen luc thuy tinh Dong ca dot co tinh ca dong cao, phii hgp vai cac loai may moc tu hanh nhung co nhugc diem Ion la hieu suit thap va thay doi pham vi Ion tiiy thuoc vao diem lam viec ciia no He thdng truyen luc thuy tinh, cung nhu cac he thdng truyen luc vo cap khac cho phep thay doi lien tuc ty s6 truyen ciia he thong ma khong can ngat dong truyin cong suat Do do, co the dieu khien thay doi ty so truyen ciia he thdng truyen luc mot each lien tuc de dua dong ca ddt vl lam viec tai diem toi uu Bai bao trinh bay ket qua nghien ciru, de xuat bo dieu khien ma tac dong dong thai vao dong ca ddt va he thdng truyin luc nhlm tu dong dieu chinh tdc dp chuyen dong cua xe theo yeu cau de dam bao nang suit cong tac, dong thoi dieu chinh diem lam viec cua dong ca ddt nhlm cai thien suat tieu thu nhien lieu cua no Cac ket qua mo phong su lam viec cua he thdng cho thay co bo dieu khien, diem lam viec cua dong ca dot dugc dua vl diem toi uu, suit tieu thu nhien Ueu rieng giam dang ke tir 4% den 10%, giup giam chi phi van hanh va lugng phat thai chit nhilm cua dong ca Tir khoa: Dieu khien md, he thdng dong luc, suat tieu thu nhien lieu, xe nong - lam nghiep I DAT VAN DE Viet Nam dang giai doan cong nghiep hda hien dai hda dat nude, xe chuyen dung dupe dua vIo su dung de ca gidi hda tit c l d c linh vyc kinh tl, dac biet II linh vue n6ng-lam nghiep, xay dyng vl khai khoing Nhieu xe n6ng - lam nghiep sii dung he thdng ddng lye gdm dong ca ddt (DCDT) vl he thdng truyin lye thuy tinh Thong sd dac trung cho tinh kinh t l cua DCDT II hieu suit hay suit tieu thu nhien lieu rieng cua nd Suit tieu thu nhien lieu rieng II lupng tieu thu nhien lieu eua ddng ca tuong ling vdi mot don vi c6ng dong ea phlt tinh theo kWh Thong sd nly hien dugc diing phd biin de dinh gil tinh kinh t l DCDT vl d c hang sin xuat DCDT thudng cho dac tinh tdc cua dong ca vdi d c dudng ddng miie suit tieu thy nhien lieu rieng (hinh 1) Dac tinh cua DCDT cho thay suit tieu thu rieng cua dong ca thay ddi pham vi rlt ldn toln miln llm viec ciia dong ca vl tdn tai mot tap hgp d c dilm llm viec tdi uu eua ddng ca ( d e diem nlm tren dudng ndi elc diem Al, A2, A12 tren hinh 1) Ung vdi mdi gil tri cong suit phlt cita DCDT cd mot gil tri tdc dp llm viec cua nd (gpi II gil tri tdc dp tdi un hay mong mudn), dd suit tieu hao nhien heu rieng cua nd dat gil tri nhd nhat Van dl dat II vdi mdt c6ng suit yeu clu ddi vdi TS Vien Co Dong luc, Dai hoc Bach khoa Ha Noi 52 DCDT, nlu cd bg dieu khien nIo dd dua dupe nd ve llm viec vung ed suit tieu thy nhien lieu rieng nhd nhlt se giiip giam dugc suit tieu thu nhien lieu cua dong ca, va dd giam dugc ehi phi van hinh va lugng chit nhilm phat thai cua xe Muc tieu ciia bii bio II nghien cim, de xult bp dilu khien tren co sd ling dung 16 gie md d l giai quyet vIn d l tren n [1/min] Hinh Dac tinh ciia dong ea ddt II NDI DUNG VA PHUDNG PHAP NGHIEN CUU Phuong phip nghien cim la m6 hinh hda vl mo phdng he thdng tren mIy tinh Day la mot nhirng phuong phip nghien cuu khoa hgc vl phlt trien san pham phd biin hien vi nd cd the nit ngln thdi gian nghien cim phlt trien san phIm vl giam chi phi nghien ciin Bd dilu khiln dugc tdng hgp tren ca sd ung dung 16 gic md (gpi la bp dilu khien md) Bp dilu khiln ma dugc ung NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2010 KHOA HOC CONG NGHE dung rong rai vi co hai uu dilm Ion: kh6ng d n mo ta chinh xac ciia doi tugng dilu khiln va co the ung dung tryc tilp kiln thiic va kinh nghiem cua d c chuyen gia van hanh he thdng Vin d l nghien ciin img dung dilu khiln md dang ed tinh thoi sy hien Trong img dung 16 gic ma, co nhilu phuong phip giai md khac Trong nghien cim img dung phuong phap giii ma theo trgng tam dien tich Phuong phap nly tuong ddi phiie tap, ddi hdi khdi lupng tinh toln ldn nhung cho gil tri diu chinh xlc hon d c phuong phip khIc Noi dung nghien ciiu tap trung vIo xlc dinh thuat toln dilu khiln he thdng ddng luc ciia xe nhlm tdi thilu hda suit tieu thu nhien lieu ciia xe va dl xult bd dilu khiln md thyc hien thuat toln dd Dilu kien boat dong cua he thdng dong lye canh tic n6ng - lam nghiep rlt da dang vl thay ddi lien tuc mot ca lam viec Khi siie cin chuyin dong thay ddi, cong suit yeu clu ddi voi dong ca ddt cung thay ddi va dilm lam viec cua DCDT thay ddi, klo theo sy thay ddi suit tieu thu nhien lieu rieng ciia nd Hinh cho thIy c6ng suit DCDT thay ddi, nd cd thi thay ddi dilm llm viec tir dilm A din cae dilm Bl, B2 hay B3 , tai dd dong CO tieu thy lupng nhien lieu rlt khIc Bl tieu thu nhien lieu rieng Thuat toln dilu khiln d l giii quylt nhiem vu k h i phirc tap, dac biet m6 tl toln hgc ciia he thdng dong luc rlt phuc tap, khd xlc dinh chinh xlc Viec ung dung cac bp dilu khien truyin thdng theo thuat toan dd rlt khd khan Vi vay, ling dung bp dilu khien md de giii quylt nhiem vu dilu khien he thdng dong luc nhlm muc dich neu tren la rat phii hap III KET QUA N G H I E N CUU Bg dilu khiln md dugc xay dyng d l dilu khiln he thdng dong luc theo sa dd t h i hien nhu tren hinh Bp dilu khien md EC tic dong true tilp vIo DCDT, bom thuy lye (B) va m6 ta thuy lye (M) d l dilu chinh tdc dp mIy c6ng tac (MCT) vl diem llm viec eua DCDT Bp dilu khien md dugc d l xult d l dilu chinh cac thong sd ciia he thdng dong lye nhlm dua dilm llm viec cua DCDT ve dilm llm viec tdi uu cd sa dd clu true gdm thinh phln nhu tren hinh Thinh phln thir nhlt (FCl) dilu chinh mirc tii cua DCDT de dim bio c6ng suit phlt cua DCDT dap img yeu clu cua MCT Thanh phln thu hai (FC2) ddng thoi dilu chinh t h i tich cong tic rieng cua B va M d l dim bio tdc dd cua mIy c6ng tie (dam bio nang suit lam viec cua mIy) Thinh phln thiir ba (FC3) dilu chinh ddng thdi mirc tai cua DCDT, the tich cong tie rieng cua B vl M nhlm dilu chinh tdc dp eua DCDT de dua diem lam viec eua nd ve diem tdi un n [i/min] Hinh Sy thay doi dilm lam viec cua DCDT cong suat thay ddi He thdng truyin thiiy tinh gdm bam thiiy lye vl mo ta thiiy lye CIc mIy thiiy lye nly ed thi dilu chinh the tich rieng mot d c h lien tuc, dp dd cd thi thay ddi lien tuc ty sd truyin q u i trinh llm viec cua xe Bing elch dilu khiln thay ddi tai trpng (mue ga) cita DCDT vl ty sd truyin cua he thdng truyin lye, cd thi thay ddi dugc dilm llm viec cita dong ca ddt vl vimg llm viec tdi uu nhlm gilm suit Hmh So dd he thdng dieu khiln Mdi thinh phan cua bd dilu khien md FC diu cd sa dd clu trite chung nhu tren hinh Ddi tugng dilu khiln (DTDK) tilp nhan cle diu vao la th6ng sd dilu khien u (tii bd dilu khien md), th6ng sd nhilu m6i trudng tie ddng vIo dva llm viec vdi d e diu la cle thong sd y So sanh gia tri th6ng sd diu y voi d c gia tri mong mudn w, bp dilu khiln cd dupe diu vIo II gia tri sai lech dilu khien e NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2010 53 KHOA HOC CONG NGHE "A/ CO sd kiln thirc chuyen gia vl DCDT va he thong truyin lye thuy tinh Cac he sd danh nghia hda va hien thyc boa cac dai lugng vao ciia bp dieu khien dupe xlc dinh th6ng qua m6 phdng vIo khao sat he thdng ^ ^ Cam bien FC Cam bien miic tai FC2 : & ^ A0 Cam bien toe 05 Sai lech tdc DCDT d Toe DC - FC3 Cam bien the tich 20 10 60 T h i tich e6ng tac bom Miic tai DCDT thuy luc Hinh So dd eau tnic bg dilu khiln e bd dilu khien md u _, i" + V DTDK •) 1 Tdc dp bien thien sai lech tdc DCDT, mo ta thuy lye dt Cam bien theCam r¥ IT.k- Danli ngliTa Hien tlurc hnn ; IJ Giai 1110 U— Luat dieu khien Ma lioa K 02 01 05 08 ,0 05 The tich eong tac dong Cle bien dau ra: dp gia •u' tang miic tai DCDT, ^ ,-,, ca thuy luc gia tang the tich lam vice eua B va M J Hmh Cac ham thugc cac bien vao cua FC3 Kien lliirc cliuyen gia FCl cd biin dau vIo v l hiln diu bien diu vIo gdm sai lech tdc dp cua dong ca thuy luc so vdi gil tri mong mudn (e_/2,,,/), tde dp hiln thien sai Tinh toan _ ^ lech dd {Ae_nJ, miie dp tai (tinh theo % dp mdga) Tiiong tin — ^ cita DCDT (a,,), tdc dp cua DCDT {n^c), vl th6ng sd dilu chinh t h i tich llm viec cua bom thuy luc (fir)Hinh So dd clu tnic cua bp dilu khien mo Cac biin diu gdm dd gia tang mue tii cua DCDT {AaJ va dp gia tang th6ng sd dilu chinh the tich Trong bp dilu khien md, gil tri e dugc danh nghia hda vl md hda Sau dd bp dilu khiln md Ip lam viec cua bom thuy luc {Afi^jj) FC2 gdm bien dung bp luat dilu khien tinh toln duge gil tri dilu diu vIo vl hiln diu CIc biin diu vao gdm sai khiln dang md, giii md vl hien thyc hda gil tri dieu lech tdc dp cua dong ca thuy lye so voi gia tri mong mudn dinh trudc {e_nM), tde dd bien thien eua sai khien u trudc dua vIo DTDK lech tdc dd {Ae_nJ, th6ng sd dilu chinh the tich CIc ngi dung chinh thilt k l bg dieu khien c6ng tic cita bom (fir), th6ng sd dilu chinh the tich nly II xlc dinh d c h i m thudc cua d c biin diu vIo e c6ng tic eua dong ca thuy lye (fijj ciia bp dilu khien, xlc dinh cle luat dilu khiln tren 54 NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2011 KHOA HOC CONG NGHE Cac biin diu gdm gia tang thong sd dilu chinh the tich c6ng tac cua bom (A/?^^) dp gia tang th6ng sd dilu chinh the tich c6ng tac ciia m6 to thuy luc (A/?,/^ Cac phln FCl va FC2 dupe trinh bIy chi tilt tai lieu tham khIo [1] va se khong dupe trinh bay chi tilt d day FC3 gdm cd biin diu vao va biin dau Cac hiln diu vIo gdm sai lech tdc dp cita DCDT so vdi gia trj mong mudn - tai dd DCDT lam viec voi suit tieu thu nhien lieu rieng nhd nhlt {e_nf)r), tdc dp biin thien ciia sai lech tdc do {Ae_n[,c), mue dp tai cita DCDT (a,), th6ng sd dilu chinh thi tich c6ng tic cua bom (fir), th6ng sd dilu chinh thi tich c6ng tac cua m6 ta thuy lye (Afiy^ va tdc dp biin thien cua sai lech tdc dp dong ca thiiy lye so voi gil tri mong mudn dinh trudc {Ae_n^j) Cac biin diu cita FC3 gdm dp gia tang miic tii DCDT (Aa^r.j^, dp gia tang thi tich bom (Afi^^ va dp gia tang thi tich mo ta thuy lye (Ap^,^ CIc biin dau vIo e_ni,c, Ae_ni)c va Ae_72,/ duge md hda theo ba biin ng6n ngu (gdm „am", „khdn^' vl „duon^' va dugc ky hieu lln lugt \a N, Z va P), d c biin diu vIo cdn lai duge md hda theo hai bien ng6n ngu (gdm „nhd' va ,Jdif va dugc ky hieu tuong img II S va L) Cac biin diu duge md hda theo biin ng6n ngir {„am ldn", „ain nhd', „khdn^', „duong nhd' va „duong ldn", dugc ky hieu lln lugt II NL, NS, Z, PS vl PT) CIc him thupc d c biin vIo cua FC dugc xlc dinh nhu tren hinh De tang tinh dn dinh ciia he thdng, thinh phln FC3 chi tic dong dilu chinh chi tdc dd cita m6 to thiiy lye tuong ddi dn dinh Ndi d c h khIc, chi gil tri ciia biin diu vao thir cua nd (tdc dp biin thien sai lech tdc dp dong co thuy lye) bing „khdn^' thi FC3 mdi cho d c gil tri diu khIc „khdng' Cung d l tang tinh dn dinh ciia he thdng, FC3 se dieu chinh the tich llm viec ciia bom vl m6 to thuy lye trude dilu chinh mirc tii eua DCDT CIc luat dilu khien eua FC3 nly duge tdm tit ve mat 16 gic thinh nhdm sau day: Nhdm luat Nlu e_/7£,c = Z v l Ae_n[)c = Z, thi he thdng dang can bing tai dilm tdi uu, kh6ng can tac dong dilu chinh: Aa^s = Z, l^Pr.s = Z, A/9,,/j = Z, Nlu e_/7^^ = A^vl Ae_ni)c = P, thi he thdng dang ehuyin din vl dilm tdi uu, khong d n tic ddng dilu chinh: Aa^3=Z, ^p^s = Zva ^PM3 = Z\ Nlu e_nDc =Pva Ae_nBc = A^ thi he thdng dang chuyin din vl dilm tdi uu, kh6ng cin tic dong dilu chinh: Aa^.j = Z va h[ir,3= Z, ^P.\i3 = ^ Nhdm luat Nlu e_nf,c = Nva Ae_nf)c ^ Pva [ir, = S, thi chi tang the tich bom Aot^.j, = Z, APr,3 = PhoacPLva A/3v/j =Z Nlu e_n{,c = A''vl Ae_/7^^ T^PvaPr,=L"^^P.\i = L thi chi dieu chinh giam thi tich dong ca thiiy luc: Aai,.=Z, ^Pr,3 =Zva A/5.,/^ =NS hoac NL Nlu e_nf,c = A^va Ae_npc ^ PvaPc = Lva/?,/ = S va tti, = L, thi chi giam miie dp tii dong co ddt trong: Aa^.j = NS hoac NLva APrs = Zva A/?,,/y = Z Nhom luat Nlu e_nf,c =Pva Ae_ni,c = Pva Pa = L, thi chi giam thi tich bom: Aa^^ = Z, APr.s = A'5' hoac NL va ^PMS=Z Nlu e_ngc = >^vl Ae_n0c = P^a PQ = Sva p^j = S, thi chi tang the tich mo fa thuy lye: Aa^.j = Z, APr,3 = Zva APyj = PS hoac PL Nlu e_n{)c = Pva Ae_nBr = P^a Pr, = Sva /?.,/ = L va a^ = 5, thi chi tang miic tai dong ca ddt trong: Aai,3 = PS hoac PL, APas = Zva A^.,/^ = Z Bd dilu khiln md dugc hieu chinh thong qua m6 phdng, khIo sit q u i trinh lam viec ciia he thdng tren co sd m6 hinh mo phdng DCDT vl he thdng truyin dong thiiy lye thity tinh da duge trinh bIy d c tii lieu tham khao [1], [2] Sau bd dilu khien dugc hieu chinh de he thdng llm viec dn dinh, dip ling nhanh va chinh xlc, he thdng duge m6 phdng khIo sit d c trudng hgp llm viec dien hinh: tang/gilm sire can chuyin ddng hay sue d n c6ng tic, tang/giam tdc (nang suit) M6 phdng dugc thyc hien vdi xe ca vira, cong suit cue dai cua dong ca ddt II 41 kW He thdng truyen lye thuy tInh su dung bom vdi the tich llm viec ldn nhat la 56 cmVvdng vl mo fa thuy lye ed the tich llm viec ldn nhat 54,8 c m l M6 hinh mo phdng ciia he thdng gdm dong ca ddt trong, bom vl m6 ta thity lye dugc xay dung moi trudng Matlab-simulink [1], [2] Qui trinh m6 phdng bat diu td hgp xe hoat dong dn dinh d mot e h l dp nIo dd dudi tic dong dilu khien cita bp dilu khiln Sau dd, dilu kien llm viec thay ddi vl he thdng chuyen ve llm viec tai diem can bing mdi D l so sinh, dinh gil dugc tac dung cita bp dilu khien, thinh phln FC3 eua bd dilu khien dupe tich O^hong tie dung) trude dieu kien NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2010 55 KHOA HOC CONG NGHE llm viec thay ddi vl dugc dua vIo (cd tic dung) sau he thdng da dn dinh tai diem llm viec moi Hinh thi hien sy thay ddi diem llm viec ciia DCDT d cic trang thai can bing qui trinh m6 phdng dilu kien llm viec cita xe thay ddi Hinh 7a cho thIy sy thay ddi dilm llm viec sire can chuyin dong cita xe khong ddi vl ngudi dilu khiln tang tdc dp chuyen dong d l tang nang suit Khi dilu kien lam viec thay ddi, nlu khong cd phan bg dilu khien FC3 DCDT chuyin tir dilm A vl lam viec dn dinh tai diem B nlm xa diem llm viec tdi un Khi thinh phln bp dilu khiln FC3 dugc kich boat, he thdng da dugc dilu khien d l dua DCDT vl llm viec dn dinh tai diem C cd suit tieu thy nhien Ueu rieng nhd nhlt tuong img voi cong suit cita dong ca 1500 2000 2500 3000 3500 4000 4500 n „ loKmln] c) Khi tang tdc dp va siie can Tuong ty, sy thay ddi diem lam viec nguoi lai giir nguyen tdc dp chuyen dong sire can chuyin dong gilm xudng dugc thi hien tren hinh 7b Hinh 7c thi hien sy thay ddi diem llm viec ddng thdi tang siie d n chuyin dong vl tang tdc chuyen dong vl hinh 7d cho thIy dilm lam viec thay ddi ddng thoi gilm site d n va tdc dp chuyin dong 2500 3000 n 3500 [ot/min] d) Khi giam siic can v l tde dp Hinh Su- thay doi diem lam viec cua DCDT 1500 2000 2500 3000 3500 4000 4500 n I I/mini a) Khi sire can kh6ng ddi vl tang tdc dp Kit q u i mo phdng t h i hien tren hinh 7a cho thIy DCDT da chuyen tir diem llm viec B vdi suit tieu thy nhien lieu rieng 276 g/kWh vl diem C vdi suit tieu thy nhien lieu rieng 264 g/kWh, giam dupe khoang 4% Tiordng hpp m6 phdng gilm c6ng suit yeu clu tren hinh 7b cho thIy DCDT da chuyin tir diem llm viec tieu thy 307 g/kWh vl dilm llm viec tieu thu 275 g/kWh, giam dupe khoing 10% Tren hinh 7c, nhd bp dilu khiln md, DCDT da chuyin tir dilm llm viec tieu thu 279 g/kWh vl diem ed suit tieu thy 207 g/kWh Hinh 7d cho thIy diem llm viec cua DCDT trudc va sau tac dong eua bo dilu khien md cd suit tieu thy nhien lieu rieng lln lugt II 301 g/kWh vl 282 g/kWh, giam dugc khoang 7% IV KET LUAN VADE XUAT b) Khi tde dp kh6ng ddi va giam sue can 56 Bii bio da d l xult duge bg dilu khien md diing de dilu khiln he thdng dong lye linh vyc san NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2010 KHOA HOC CONG NGHE xult n6ng nghiep nhlm dim bio suit tieu thu nhien lieu rieng nhd nhlt ddng thoi giu dugc tdc dd lien hgp may lam viec theo yeu clu Bd dilu khiln vl he thdng dong lye da dugc m6 phdng tren m6 hinh Matlab-Simulnk cac dilu kien lam viec khIc Kit qui m6 phdng cho thIy, dilu kien llm viec thay ddi xe chuyen dung vdi bg dilu khiln dugc dl xult da ty dong dim bao tdc dp cua may cong tic (hay nang suit) theo yeu clu eiia ngudi dilu khiln va DCDT da dugc dua vl lam viec tai diem tdi uu, giiip giam lupng tieu thu nhien lieu ciia DCDT din khoing 10% Bp dilu khiln cd thi dugc nghien cim thyc nghiem trudc cung hda nd bing thief bi dien tir chuyen diing cho d c he thdng dong lye sir dung DCDT va he thdng truyen dong thuy tinh tren d c lien hpp mIy sin xult nong nghiep, xay dung vl thi c6ng khai khoing Kit qua nghien cim eua bii bio cdn cd the llm tu lieu tham khIo nghien ciin dilu khien tdi un hda he thdng ddng lye tren to sir dung he thdng truyin lye CVT vl cac t6 ed k h i nang ghIp vdi d e dong CO khIc TAI UEU THAIVl KHAO Ho H H Rizeni a optimalizace parametru hnaciho ustrojf, Disertacni price; Liberec, 2005 Hd Hiru HIi Xay dung md hinh va md phdng he thdng truyen ddng thuy luc the tich tren xe chuyen dung bing Matlab-SimuIink Tap ehi Khoa hpc vl C6ng nghe elc trudng DH Ky thuat, sd 692009 STUDY TO PROPOSE FUZZY CONTROLER FOR M O T F ^ SYSTEM ON AGRICULTURAL MOBILE WORKING MACHINERY Ho Huu Hai Summary Agricultural mobile working machinery use motive system with internal combustion engine and hydrostatic transmissions Internal combustion engines are appropriate for mobile machinery due to their high mobility, but they also have remarkable disadvantage of low and wide-varied efficiency depending on the working points Hydrostatic transmission has a great advantage that is ability of continuously variable transmission ratio So it is possible to change transmission ratio continuously to move working point of engine to optimal point, where it consumes least fuel This article presents proposal of fuzzy controller for motive transmission of mobile working machines The controller regulates the engine and hydrostatics transmission simultaneously so, that mobile machine works at desirable speed and engine works at optimal point to improve its fuel consumption System simulation shows that working point of engine was moved to optimal point and specific fuel consumption was improved obviously Keywords: Agricultural mobile working machinery, fuel consumption, fuzzy control, motive system Ngudi phan bien: GS TSKH Pham Van Lang NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 4/2010 57 ... d l nghien ciin img dung dilu khiln md dang ed tinh thoi sy hien Trong img dung 16 gic ma, co nhilu phuong phip giai md khac Trong nghien cim img dung phuong phap giii ma theo trgng tam dien... trgng tam dien tich Phuong phap nly tuong ddi phiie tap, ddi hdi khdi lupng tinh toln ldn nhung cho gil tri diu chinh xlc hon d c phuong phip khIc Noi dung nghien ciiu tap trung vIo xlc dinh thuat... dilm lam viec cua DCDT thay ddi, klo theo sy thay ddi suit tieu thu nhien lieu rieng ciia nd Hinh cho thIy c6ng suit DCDT thay ddi, nd cd thi thay ddi dilm llm viec tir dilm A din cae dilm Bl, B2