Chuong5 He Thong Phanh Dieu Khien Bang Dien Tu

7/29/2019 Chuong5 He Thong Phanh Dieu Khien Bang Dien Tu

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He thong ien than xe & ieu khien t ong tren oto Trang 132

CHNG 5: HE THONG PHANH IEU KHIEN BANG IEN T

5.1AI CNG VE HE THONG PHANH CHONG BO CNG BANHXE ABS:

5.1.1 Tong quan:He thong phanh (Brake System) la c cau an toan chu ong cua oto, dung

e giam toc o hay dng va o oto trong nhng trng hp can thiet. No la mottrong nhng cum tong thanh chnh va ong vai tro quan trong trong viec ieukhien oto tren ng.

Chat lng cua mot he thong phanh tren oto c anh gia thong qua tnhhieu qua phanh (the hien qua cac ch tieu nh quang ng phanh, gia toc chamdan, thi gian phanh va lc phanh), ong thi am bao tnh on nh chuyen

ong cua oto khi phanh.Khi oto phanh gap hay phanh tren cac loai ng co he so bam thap nhng trn, ng ong bang, tuyet th de xay ra hien tng sm b ham cngbanh xe, tc hien tng banh xe b trt let tren ng khi phanh. Khi o,quang ng phanh se dai hn, tc hieu qua phanh thap i, ong thi, dan entnh trang mat tnh on nh hng va kha nang ieu khien cua oto. Neu cacbanh xe trc sm b bo cng, xe khong the chuyen hng theo s ieu khiencua tai xe; neu cac banh sau b bo cng, s khac nhau ve he so bam gia banhtrai va banh phai vi mat ng se lam cho uoi xe b lang, xe b trt ngang.

Trong trng hp xe phanh khi ang quay vong, hien tng trt ngang cua cacbanh xe de dan en cac hien tng quay vong thieu hay quay vong tha lammat tnh on nh khi xe quay vong.

e giai quyet van e neu tren, phan ln cac o to hien nay eu c trangb he thong chong ham cng banh xe khi phanh, goi la he thong Anti-lockBraking System - ABS. He thong nay chong hien tng b ham cng cua banhxe bang cach ieu khien thay oi ap suat dau tac dung len cac c cau phanh cac banh xe e ngan khong cho chung b ham cng khi phanh tren ng trn

hay khi phanh gap, am bao tnh hieu qua va tnh on nh cua oto trong quatrnh phanh.Ngay nay, he thong ABS a gi mot vai tro quan trong khong the thieu

trong cac he thong phanh hien ai, a tr thanh tieu chuan bat buoc oi viphan ln cac nc tren the gii.

5.1.2 Lch s phat triene tranh hien tng cac banh xe b ham cng trong qua trnh phanh khi lai

xe tren ng trn, ngi lai xe ap phanh bang cach nhp lien tuc len ban apphanh e duy tr lc bam, ngan khong cho banh xe b trt let va ong thi cothe ieu khien c hng chuyen ong cua xe. Ve c ban, chc nang cua he


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thong phanh ABS cung giong nh vay nhng hieu qua, o chnh xac va an toancao hn.

ABS c s dung lan au tien tren cac may bay thng mai vao nam1949, chong hien tng trt ra khoi ng bang khi may bay ha canh. Tuy

nhien, ket cau cua ABS luc o con cong kenh, hoat ong khong tin cay vakhong tac ong u nhanh trong moi tnh huong. Trong qua trnh phat trien, ABSa c cai tien t loai c kh sang loai ien va hien nay la loai ien t.

Vao thap nien 1960, nh ky thuat ien t phat trien, cac vi mach ien t(microchip) ra i, giup he thong ABS lan au tien c lap tren oto vao nam1969. Sau o, he thong ABS a c nhieu cong ty san xuat oto nghien cu vaa vao ng dung t nhng nam 1970s. Cong ty Toyota s dung lan au tiencho cac xe tai Nhat t nam 1971, ay la he thong ABS 1 kenh ieu khien ongthi hai banh sau. Nhng phai en thap nien 1980s he thong nay mi c phat

trien manh nh he thong ieu khien ky thuat so, vi x ly (digitalmicroprocessors/microcontrollers) thay cho cac he thong ieu khien tng t(analog) n gian trc o.

Luc au he thong ABS ch c lap tren cac xe du lch cao cap, at tien,c trang b theo yeu cau va theo th trng. Dan dan he thong nay c avao s dung rong rai hn, en nay ABS gan nh a tr thanh tieu chuan batbuoc cho tat ca cac loai xe tai, mot so xe du lch va cho phan ln cac loai xehoat ong nhng vung co ng bang, tuyet de trn trt. He thong ABS

khong ch c thiet ke tren cac he thong phanh thuy lc, ma con ng dungrong rai tren cac he thong phanh kh nen cua cac xe tai va xe khach ln.Nham nang cao tnh on nh va tnh an toan cua xe trong moi che o hoat

ong nh khi xe khi hanh hay tang toc ot ngot, khi i vao ng vong vi toco cao, khi phanh trong nhng trng hp khan cap, he thong ABS con cthiet ke ket hp vi nhieu he thong khac:

He thong ABS ket hp vi he thong kiem soat lc keo - Traction control(hay ASR) lam giam bt cong suat ong c va phanh cac banh xe e chong hientng cac banh xe b trt lan tai cho khi xe khi hanh hay tang toc ot ngot,bi ieu nay lam ton hao vo ch mot phan cong suat cua ong c va mat tnh onnh chuyen ong cua oto.

He thong ABS ket hp vi he thong phan phoi lc phanh bang ien tEBD (Electronic Brake force Distribution) nham phan phoi ap suat dau phanhen cac banh xe phu hp vi cac che o tai trong va che o chay cua xe.

He thong ABS ket hp vi he thong ho tr phanh khan cap BAS (BrakeAssist System) lam tang them lc phanh cac banh xe e co quang ngphanh la ngan nhat trong trng hp phanh khan cap. He thong ABS ket hp

vi he thong on nh oto bang ien t (ESP), khong ch co tac dung trong khi


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dng xe, ma con can thiep vao ca qua trnh tang toc va chuyen ong quay vongcua oto, giup nang cao hieu suat chuyen ong cua oto trong moi trng hp.

Ngay nay, vi s phat trien vt bac va ho tr rat ln cua ky thuat ien t,cua nganh ieu khien t ong va cac phan mem tnh toan, lap trnh cc manh a

cho phep nghien cu va a vao ng dung cac phng phap ieu khien mitrong ABS nh ieu khien m, ieu khien thong minh, toi u hoa qua trnh ieukhien ABS.

Cac cong ty nh BOSCH, AISIN, DENSO, BENDIX la nhng cong ty iau trong viec nghien cu, cai tien va che tao cac he thong ABS cho o to.

5.2 PHAN LOAI HE THONG ABS THEO KIEU IEU KHIENABS c ieu khien theo cac phng phap sau:

5.2.1 ieu khien theo ngng trt- ieu khien theo ngng trt thap (slow mode): V du: khi cac banh xe

trai va phai chay tren cac phan ng co he so bam khac nhau. ECU chon thiiem bat au b ham cng cua banh xe co kha nang bam thap, e ieu khien apsuat phanh chung cho ca cau xe. Luc nay, lc phanh cac banh xe la bangnhau, bang chnh gia tr lc phanh cc ai cua banh xe co he so bam thap. Banhxe ben phan ng co he so bam cao van con nam trong vung on nh cuang ac tnh trt va lc phanh cha at cc ai. V vay, cach nay cho tnh onnh cao, nhng hieu qua phanh thap v lc phanh nho.

- ieu khien theo ngng trt cao (high mode): ECU chon thi iembanh xe co kha nang bam cao b ham cng e ieu khien chung cho ca cau xe.Trc o, banh xe phan ng co he so bam thap a b ham cng khi phanh.Cach nay cho hieu qua phanh cao v tan dung het kha nang bam cua cac banhxe, nhng tnh on nh kem.

5.2.2 ieu khien oc lap hay phu thuoc- Trong loai ieu khien oc lap, banh xe nao at ti ngng trt, tc ba t

au co xu hng b bo cng th ieu khien rieng banh o.- Trong loai ieu khien phu thuoc, ABS ieu khien ap suat phanh chung

cho hai banh xe tren mot cau hay ca xe theo mot tn hieu chung, co the theongng trt thap hay ngng trt cao.

5.2.3 ieu khien theo kenh- Loai 1 kenh: Hai banh sau c ieu khien chung (co ABS the he au,

ch trang b ABS cho hai banh sau v de b ham cng hn hai banh trc khiphanh).

- Loai 2 kenh: Mot kenh ieu khien chung cho hai banh xe trc, mot kenhieu khien chung cho hai banh xe sau. Hoac mot kenh ieu khien cho hai banh

cheo nhau.


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- Loai 3 kenh: Hai kenh ieu khien oc lap cho hai banh trc, kenh conlai ieu khien chung cho hai banh sau.

- Loai 4 kenh: Bon kenh ieu khien rieng re cho 4 banh.Hien nay loai ABS ieu khien theo 3 va 4 kenh c s dung rong rai. u

va nhc iem cua tng loai c the hien qua cac phng an bo tr sau.5.3 CAC PHNG AN BO TR HE THONG IEU KHIEN CUA ABS

Viec bo tr s o ieu khien cua ABS phai thoa man ong thi hai yeu to:- Tan dung c kha nang bam cc ai gia banh xe vi mat ng trong

qua trnh phanh, nh vay lam tang hieu qua phanh tc la lam giam quang ngphanh.

- Duy tr kha nang bam ngang trong vung co gia tr u ln nh vay lamtang tnh on nh chuyen ong (driving stability) va on nh quay vong (steering

stability) cua xe khi phanh (xet theo quan iem ve o trt).Ket qua phan tch ly thuyet va thc nghiem cho thay: oi vi ABS, hieu

qua phanh va on nh khi phanh phu thuoc chu yeu vao viec la chon s ophan phoi cac mach ieu khien va mc o oc lap hay phu thuoc cua viec ieukhien lc phanh tai cac banh xe. S thoa man ong thi hai ch tieu hieu quaphanh va tnh on nh phanh cua xe la kha phc tap, tuy theo pham vi va ieukien s dung ma chon cac phng an ieu khien khac nhau.

Hnh 5-1 trnh bay 6 phng an bo tr he thong ieu khien cua ABS tai cac

banh xe va nhng phan tch theo quan iem hieu qua va on nh khi phanh.5.3.1 Phng an 1: ABS co 4 kenh vi cac banh xe c ieu khien oclap.

ABS co 4 cam bien bo tr bon banh xe va 4 van ieu khien oc lap, sdung cho he thong phanh bo tr dang mach thng ( mot mach dan ong cho haibanh xe cau trc, mot mach an ong cho hai banh xe cau sau). Vi phng annay, cac banh xe eu c t ong hieu chnh lc phanh sao cho luon nam trongvung co kha nang bam cc ai nen hieu qua phanh la ln nhat. Tuy nhien khiphanh tren ng co he so bam trai va phai khong eu th moment xoay xe serat ln va kho co the duy tr on nh hng bang cach hieu chnh tay lai. Onnh khi quay vong cung giam nhieu. V vay vi phng an nay can phai bo trthem cam bien gia toc ngang e kp thi hieu chnh lc phanh cac banh xe etang cng tnh on nh chuyen ong va on nh quay vong khi phanh.

5.3.2 Phng an 2: ABS co 4 kenh ieu khien va mach phanh bo tr cheo.S dung cho he thong phanh co dang bo tr mach cheo (mot buong cua xy

lanh chnh phan bocho mot banh trc va mot banh sau cheo nhau). ABS co 4cam bien bo tr cac banh xe va 4 van ieu khien. Trong trng hp nay, 2

banh trc c ieu khien oc lap, 2 banh sau c ieu khien chung theongng trt thap, tc la banh xe nao co kha nang bam thap se quyet nh ap


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lc phanh chung cho ca cau sau. Phng an nay se loai bo c mo men quayvong tren cau sau, tnh on nh tang nhng hieu qua phanh giam bt.

5.3.3 Phng an 3: ABS co 3 kenh ieu khien.

Trong trng hp nay 2 banh xe sau c ieu khien theo ngng trtthap, con cau trc chu ong co the co hai phng an sau:- oi vi nhng xe co chieu dai c s ln va moment quan tnh oi vi truc

ng i qua trong tam xe cao tc la co nhieu kha nang can tr o lech hngkhi phanh, th ch can s dung mot van ieu khien chung cho cau trc va motcam bien toc o at tai vi sai. Lc phanh tren hai banh xe cau trc se bangnhau va c ieu chnh theo ngng trt thap. He thong nh vay cho tnh onnh phanh rat cao nhng hieu qua phanh lai thap.

- oi vi nhng xe co chieu dai c s nho va moment quan tnh thap th e

tang hieu qua phanh ma van am bao tnh on nh, ngi ta e cho hai banhtrc c ieu khien oc lap. Tuy nhien phai s dung bo phan lam cham s giatang moment xoay xe. He thong khi o s dung 4 cam bien toc o at tai 4 banhxe.

a. Phng an 1 b. Phng an 2 c. Phng an 3

d. Phng an 4 e. Phng an 5 f. Phng an 6Hnh 5-1: Cac phng an ieu khien cua ABS.


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5.3.4 Cac phng an 4, 5, 6eu la loai co hai kenh ieu khien. Trong o:- Phng an 4 tng t nh phng an 3. Tuy nhien cau trc chu ong

c ieu khien theo mode chon cao, tc la ap suat phanh c ieu chnh theo

ngng cua banh xe bam tot hn. ieu nay tuy lam tang hieu qua phanh nhngtnh on nh lai kem hn do moment xoay xe kha ln.- Phng an 5, tren moi cau ch co mot cam bien at tai 2 banh xe cheo

nhau e ieu khien ap suat phanh chung cho ca cau. Cau trc c ieu khientheo ngng trt cao, con cau sau c ieu khien theo ngng trt thap.

- Phng an 6 s dung cho loai mach cheo. Vi hai cam bien toc o at taicau sau, ap suat phanh tren cac banh xe cheo nhau se bang nhau. Ngoai ra cacbanh xe cau sau c ieu khien chung theo ngng trt thap. He thong naytao o on nh cao nhng hieu qua phanh se thap.

Qua trnh phanh khi quay vong cung chu anh hng cua viec bo tr cacphng an ieu khien ABS: Neu viec ieu khien phanh tren tat ca cac banh xeoc lap th khi quay vong lc phanh tren cac banh xe ngoai se ln hn do taitrong tren chung tang len khi quay vong. ieu nay tao ra moment xoay xe trenmoi cau va lam tang tnh quay vong thieu. Neu o trt cua cau trc va causau khong nh nhau trong qua trnh phanh (do ket qua cua viec chon ngngtrt thap hay cao tren moi cau, hoac do phan bo tai trong tren cau khi phanh)se tao ra s trt ngang khong ong eu tren moi cau. Neu cau trc trt

ngang nhieu hn se lam tang tnh quay vong thieu, ngc lai khi cau sau trtngang nhieu hn se lam tang tnh quay vong tha.5.3.5 Mot so s o bo tr thc te

Hnh 5.2: S o he thong phanh ABS ieu khien cac banh sau

Cam bien toc o

Cam biengia toc

Xi-lanhbanh sau

Xi-lanh chnh

Hop ccau lai

Bm tr lc laiva bnh cha dau

en bao

Khoa ien

AM1

ALT

MAIN

ABSECU

Rle cuon day

LSP & BV

Bochaphanh


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Hnh 5.3: S o he thong phanh ABS ieu khien tat ca cac banh

Hnh 5.4 : S o he thong phanh ABS van ien 2 v tr

Van ien ba v tr

Cam bien G

ABS ECUCam bien

toc o

Xi lanh banhxe sau phai

Xi lanh banhxe sau trai

Xi lanh banhxe trc phai

Xi lanh banhxe trc trai

Bo chap hanh ABS

Xi lanh chnh

Van 1 chieu

Bm van 1 chieu


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Hnh 5.5: S o he thong phanh ABS van 3 v tr

5.4 CAU TRUC HE THONG PHANH ABSCau truc he thong phanh ABS c trnh bay tren hnh 5.6.

5

3

4

2

22

1

1 1

1

Hnh 5.6: S o he thong phanh ABS trenxe1. Cam bien toc o banh xe 2. Xi lanh 3. Xi lanh chnh va cum thuy lc

4. Hop ieu khien 5. en bao ABS

Nguyen ly lam viec:Khi xe chuyen ong toc o khong oi, toc o cua xe va banh xe lanh nhau (noi cach khac cac banh xe khong trt). Tuy nhien khi ngi lai ap phanh egiam toc o, toc o cua cac banh xe giam t t va khong the bang toc o than xe luc na yang chuyen ong nh quan tnh cua no. S khac nhau gia toc o than xe va toc o banhxe c bieu dien bang mot he sogoi la he so trt.

Toc o xe toc o banh xeHe so trt = x100%

Toc o xe

Vanienba vtr

Cambien

toc obanhxe

Xi lanhbanh xe

trc benphai

Xi lanhbanh xe

trc ben

trai

Xi lanhbanh xesau benphai

Xi lanhbanh xesau ben

trai

Vanienba vtr

Mo tbm


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Hnh 5.7: o th moi quan he gia lc phanh va he so trtHnh 5.7 ch ra cac ng ac tnh trt, the hien moi quan he gia he so bamdoc x va he so bam ngang y theo o trt tng oi cua banh xe ng vicac loai ng khac nhau.

T cac o th tren, chung ta co the rut ra mot so nhan xet nh sau:- Cac he sobam doc xva he so bam ngang y eu thay oi theo o trt

. Luc au, khi tang o trt th he so bam doc xtang len nhanh chong va

at gia tr cc ai trong khoang o trt =10 30%. Neu o trt tiep tuctang th x giam, khi o trt = 100% (lop xe b trt let hoan toan khiphanh) th he so bam doc x giam 20 30% so vi he so bam cc ai. Khing t con co the giam nhieu hn na, en 50 60%. oi vi he so bamngang y, se giam nhanh khi o trt tang, trang thai trt let hoan toan th ygiam xuong gan bang khong.

- He so bam doc at gia tr cc aimaxx

gia tr o trt toi u0 . Thc

nghiem chng to rang ng vi cac loai ng khac nhau th gia tr 0 thngnam chung trong gii han t 10 30 %. gia tr o trt toi u

0nay, khong

nhng am bao he so bam doc xco gia tr cc ai ma he so bam ngang ycung co gia tr kha cao.

- Vung a goi la vung on nh, ng vi khi mi bat au phanh, vung b lavung khong on nh cua ng ac tnh trt. he thong phanh thng, khi otrt tang en gii han b ham cng =100% (vung b), do thc te s dung x

Chuong5 He Thong Phanh Dieu Khien Bang Dien Tu

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