TRNG AI HOC S PHAM KY THUAT TP. HO CH MINH KHOA C KH ONG LC

BO MON KHUNG GAM *************************

GGIIAAOO TTRRNNHH

OO TTOO 22

Ngi bien soan: MSc. ang Quy

TP. HO CH MINH, 1 / 2006

1LI NOI AU

en cong nghiep che tao o to tren the gii ngay cang phat trien manh me. Viet nam,trong thi gian khong lau na t tnh trang lap rap xe hien nay, chung ta se tien en t

che tao o to. Bi vay, viec ao tao oi ngu ky s co trnh o ap ng c nhng oi hoi cua nganhcong nghe va sa cha o to la mot nhiem vu rat quan trong va cap bach. e phuc vu cho muc ch lau dai neu tren va trc mat e ap ng cho chng trnh ao taotheo hng cong nghe o to, khoa C kh ong lc cua trng ai hoc s pham ky thuat a phan congcan bo giang day bien soan giao trnh O to 2 dung cho he ai hoc.

Giao trnh nay co 10 chng, bao gom: Khai quat chung ve o to, cac che o tai trong khi xehoat ong, he thong truyen lc, cac cau xe, cac he thong treo, lai, phanh va khung vo cua o to. giao trnh nay se khong e cap nhieu ve cau tao va nguyen ly hoat ong cua cac bo phantren o to. V phan nay sinh vien a c hoc ky cac mon hoc thc tap xng. O to 2 la mon hoc chuyen nganh quan trong nam cuoi. Bi vay, trc khi hoc mon nay,sinh vien phai hoc trc cac mon sau C ly thuyet, Sc ben vat lieu, Cau tao o to, Nguyen lyong c ot trong va O to 1. Giao trnh nay e cap en nhng van e c ban quan trong cua mon hoc, phu hp vi chngtrnh qui nh cua bo Giao duc va ao tao oi vi nganh Cong nghe o to. Noi dung kien thc giaotrnh nay nham trang b cho sinh vien nhng hieu biet c ban ve ac iem cau tao va nguyen ly lamviec cua cac cum, chi tiet va cac he thong thuoc gam o to, nhng tnh toan c ban ve ong hoc vaong lc hoc cua cac cum va cac he thong. T o lam c s cho nhng hoat ong nghe nghiep thuoclnh vc sa cha, lap rap, kiem nh va thiet ke cai tien nhng mau xe mi. Do trnh o va thi gian co han, bi vay giao trnh nay chac se co cho cha hoan thien vathieu sot. Rat mong cac ong ch va ban oc gop y e lan tai ban sau co chat lng tot hn. Toi xinchan thanh cam n!

Ngi bien soan:

MSc. ang Quy

N

2MUC LUCTrang

Li noi au...................................................................................................................................1Muc luc ........................................................................................................................................2Ky hieu va n v o c ban ........................................................................................................6

CHNG 1: KHAI QUAT CHUNG VE O TO ........................................................................7Muc tieu .......................................................................................................................................71.1. Phan loai o to. .....................................................................................................................81.2. Cac yeu cau oi vi o to .....................................................................................................9

1.2.1. Cac yeu cau ve thiet ke, che tao. ..................................................................................91.2.2. Cac yeu cau ve s dung.................................................................................................91.2.3. Cac yeu cau ve bao dng, sa cha. ...........................................................................9

1.3. Cac thong so cua o to. .........................................................................................................101.3.1. Cac thong so kch thc.................................................................................................101.3.2. Cac thong so trong lng. ..............................................................................................11

1.4. Bo tr chung tren o to...........................................................................................................121.4.1. Bo tr ong c tren o to..................................................................................................121.4.2. Bo tr he thong truyen lc tren o to. ..............................................................................14

CHNG 2: TAI TRONG TAC DUNG LEN CAC CUM VA CHI TIET CUA O TO.........19Muc tieu 19 ...................................................................................................................................2.1. Khai niem ve cac loai tai trong...........................................................................................202.2. Nhng trng hp sinh ra tai trong ong. ............................................................................20

2.2.1. ong ly hp ot ngot. ....................................................................................................202.2.2. Khong m ly hp khi phanh. ..........................................................................................212.2.3. Phanh ot ngot khi xe ang chay bang phanh tay. .........................................................232.2.4. Xe chuyen ong tren ng khong bang phang. ...........................................................25

2.3. Tai trong dung trong tnh toan cac cum va chi tiet cua gam o to. .......................................262.3.1. Tai trong tnh toan dung cho he thong truyen lc. .........................................................262.3.2. Tai trong tnh toan dung cho he thong phanh. ...............................................................272.3.3. Tai trong tnh toan dung cho he thong treo va cau. .......................................................282.3.4. Tai trong tnh toan dung cho he thong lai. .....................................................................29

CHNG 3: LY HP ................................................................................................................30Muc tieu .......................................................................................................................................303.1. Cong dung, phan loai, yeu cau............................................................................................31

3.1.1. Cong dung......................................................................................................................313.1.2. Phan loai. .......................................................................................................................313.1.3. Yeu cau. ........................................................................................................................31

3.2. S o cau tao va nguyen ly lam viec cua ly hp ma sat. ....................................................313.2.1. S o cau tao. ................................................................................................................313.2.2. Nguyen ly lam viec cua ly hp ma sat. .........................................................................32

3.3. Anh hng cua ly hp en s gai so. ..................................................................................323.4. Tac dung cua ly hp khi phanh............................................................................................363.5. Cong trt sinh ra trong qua trnh ong ly hp. ...................................................................38

33.5.1. Qua trnh ong ly hp. ...................................................................................................383.5.2. Tnh toan xac nh cong trt. .......................................................................................40

3.6. Xac nh kch thc c ban, tnh toan hao mon va nhiet o cua ly hp. .............................413.6.1. Xac nh kch thc c ban cua ly hp. .........................................................................413.6.2. Tnh toan o hao mon cua ly hp. .................................................................................443.6.3. Tnh toan nhiet o cua ly hp. .......................................................................................44

3.7. Ly hp thuy ong.................................................................................................................453.7.1.Cau tao va nguyen ly lam viec.........................................................................................453.7.2. Tnh toan ly hp thuy ong. ...........................................................................................463.7.3. ng ac tnh cua ly hp thuy ong. ...........................................................................48

CHNG 4: HOP SO VA HOP PHAN PHOI ..........................................................................49Muc tieu .......................................................................................................................................494.1. Hop so co cap. .....................................................................................................................51

4.1.1. Cong dung, yeu cau, phan loai. .....................................................................................514.1.2. S o ong hoc va nguyen ly lam viec cua cac loai hop so. .........................................524.1.3. Trnh t tnh toan hop so co cap. ...................................................................................534.1.4. Xac nh t so truyen cua hop so. ..................................................................................544.1.5. Tnh toan cac thong so hnh hoc cua banh rang hop so. ................................................554.1.6. Bo ong toc....................................................................................................................58

4.2. Hop so t ong. ..................................................................................................................604.2.1. Cong dung, yeu cau, phan loai. .....................................................................................604.2.2. Khai quat ve hop so t ong..........................................................................................614.2.3. Bien momen thuy lc. ...................................................................................................684.2.4. Hop so hanh tinh. ...........................................................................................................734.2.5. He thong ieu khien hop so t ong..............................................................................85

4.3. Hop phan phoi. ....................................................................................................................894.3.1. Nguyen tac phan phoi cong suat cho cac cau cua xe nhieu cau chu ong. ...................894.3.2. S o ong hoc cua cac loai hop phan phoi. .................................................................94

CHNG 5: TRUYEN ONG CAC ANG............................................................................96Muc tieu .......................................................................................................................................965.1. Cong dung, yeu cau, phan loai. ...........................................................................................97

5.1.1. Cong dung......................................................................................................................975.1.2. Yeu cau. ........................................................................................................................975.1.3. Phan loai........................................................................................................................97

5.2. ong hoc cua c cau cac ang. ...........................................................................................975.2.1. C cau cac ang n......................................................................................................975.2.2. C cau cac ang kep......................................................................................................1005.2.3. Khp cac ang kep ong toc. ........................................................................................1015.2.4. Khp cac ang ong toc loai bi. ....................................................................................101

5.3. ong lc hoc cua c cau cac ang. .....................................................................................1055.4. So vong quay nguy hiem cua truc cac ang. .......................................................................106

CHNG 6: CAU CHU ONG ................................................................................................109Muc tieu .......................................................................................................................................109

46.1. S o ong hoc cua bo truyen lc trong cau chu ong. .......................................................1106.1.1 Cau chu ong khong dan hng. ...................................................................................1106.1.2 Cau chu ong dan hng. ..............................................................................................110

6.2. Truyen lc chnh..................................................................................................................1116.2.1. Cong dung, yeu cau, phan loai. .....................................................................................1116.2.2. Tnh toan kch thc truyen lc chnh............................................................................1116.2.3. o cng vng va o ben cua truyen lc chnh. .............................................................1136.2.4. Truyen lc canh. ............................................................................................................115

6.3. Vi sai. ..................................................................................................................................1186.3.1. Cong dung, yeu cau, phan loai. .....................................................................................1186.3.2. ong hoc va ong lc hoc cua vi sai banh rang non. ....................................................1196.3.3. Anh hng cua vi sai en tnh chat keo cua o to. ..........................................................1216.3.4. S o ong hoc cua mot so loai vi sai khac. ..................................................................125

6.4. Ban truc. ..............................................................................................................................1276.4.1. Cong dung, yeu cau, phan loai. .....................................................................................1276.4.2. Xac nh cac lc tac dung len ban truc..........................................................................1296.4.3. Tnh toan cac ban truc theo ben.....................................................................................133

CHNG 7: HE THONG TREO ..............................................................................................136Muc tieu .......................................................................................................................................1367.1. Cong dung, yeu cau, phan loai. ...........................................................................................137

7.1.1. Cong dung......................................................................................................................1377.1.2. Yeu cau. ........................................................................................................................1387.1.3. Phan loai. .......................................................................................................................138

7.2. Bo phan dan hng..............................................................................................................1387.2.1. Cau tao cac c cau hng cua he thong treo. ................................................................1387.2.2. Tnh toan bo phan dan hng. .......................................................................................143

7.3. Bo phan an hoi. .................................................................................................................1467.3.1. ng ac tnh an hoi cua he thong treo.....................................................................1467.3.2. Tnh toan phan t an hoi kim loai. ...............................................................................149

7.4. Bo phan giam chan. .............................................................................................................1627.4.1. Cong dung, yeu cau, phan loai. .....................................................................................1627.4.2. Nguyen ly lam viec cua cac loai giam chan thuy lc....................................................1637.4.3. ng ac tnh cua giam chan thuy lc.........................................................................165

7.5. La chon ac tnh cua he thong treo theo quan iem em du va ong lc hoc. ..................167

CHNG 8: HE THONG LAI ..................................................................................................170Muc tieu .......................................................................................................................................1708.1. Cong dung, yeu cau, phan loai.............................................................................................171

8.1.1. Cong dung......................................................................................................................1718.1.2. Yeu cau. ........................................................................................................................1718.1.3. Phan loai. .......................................................................................................................171

8.2. S o cau tao he thong lai....................................................................................................1728.3. Cac t so truyen cua he thong lai..........................................................................................173

8.3.1. T so truyen cua c cau lai iw.........................................................................................1738.3.2. T so truyen cua dan ong lai id.....................................................................................173

58.3.3. T so truyen theo goc cua he thong lai ig .......................................................................1738.3.4. T so truyen lc cua he thong lai il ................................................................................174

8.4. Xac nh lc cc ai tac dung len vo lang. ..........................................................................1758.5. Tnh toan hnh thang lai........................................................................................................177

8.5.1. ong hoc cua hnh thang lai. .........................................................................................1778.5.2. Kiem tra hnh thang lai. .................................................................................................1778.5.3. Tnh toan thiet ke hnh thang lai. ...................................................................................178

8.6. Phoi hp ong hoc gia he thong treo va he thong lai.........................................................181

CHNG 9: HE THONG PHANH ...........................................................................................183Muc tieu .......................................................................................................................................1839.1. Cong dung, yeu cau, phan loai. ...........................................................................................184

9.1.1. Cong dung......................................................................................................................1849.1.2. Yeu cau. ........................................................................................................................1849.1.3. Phan loai. .......................................................................................................................184

9.2. S o cau tao cac he thong phanh. ......................................................................................1859.2.1. S o cau tao he thong phanh dau. ................................................................................1859.2.2. S o cau tao he thong phanh kh..................................................................................1869.2.3 S o cau tao he thong phanh thuy kh..........................................................................189

9.3. Tnh toan mo men phanh can thiet tai cac c cau phanh. ....................................................1909.4. Tnh toan c cau phanh guoc. ..............................................................................................191

9.4.1. Quy luat phan bo ap suat tren ma phanh. ......................................................................1919.4.2. Tnh toan c cau phanh. .................................................................................................1939.4.3. Phanh em du va on nh cua o to khi phanh .................................................................202

9.5. Tnh toan truyen ong phanh...............................................................................................2039.5.1. Truyen ong phanh bang c kh.....................................................................................2039.5.2. Truyen ong phanh bang chat long (dau). .....................................................................2069.5.3. Truyen ong phanh bang kh nen. .................................................................................208

9.6. He thong phanh chong ham cng ABS. ...............................................................................2119.6.1. Nguyen ly lam viec. ......................................................................................................2119.6.2. S o cau tao cum van phan phoi ap suat dau...............................................................212

CHNG 10: KHUNG VA VO O TO......................................................................................218Muc tieu .......................................................................................................................................21810.1. Cong dung, yeu cau, phan loai. ........................................................................................219

10.1.1. Cong dung...................................................................................................................21910.1.2. Yeu cau.......................................................................................................................21910.1.3. Phan loai. ....................................................................................................................219

10.2. Tnh toan khung theo ben. ................................................................................................21910.3. Tnh toan khung theo xoan. ..............................................................................................22110.4. Phan tch ket cau vo o to. .................................................................................................222

10.4.1. Vo xe khach. ...............................................................................................................22210.4.2. Vo xe du lch...............................................................................................................22310.4.3. Vo xe tai. ....................................................................................................................223

Tai lieu tham khao .......................................................................................................................224

6KY HIEU VA N V O C BAN

ai lng Ky hieu n v He so chuyen oi gia nv c ban va n v cu

Chieu dai l m 1 inch = 2,54 cm = 0,0254 m

Van toc dai v m / s 1m / s = 3,6 km / h

Van toc goc w rad / s

So vong quay n vg / ph

Gia toc j m / s2

Gia toc goc e rad / s2

Lc P N 1N 0,1kG

Trong lng G N 10 3N 10 2kG 0,1tan

Khoi lng m kg

Ap suat q N / m2 1N / m2 = 1Pa = 10 -5kG / cm2

ng suat s N / m2 1MN / m2 10 kG / cm2

Momen quay M N m 1Nm 10 kGcm 0,1 kGm

Cong L J 1J = 1Nm 0,1 kGm

Cong suat N W 1W = 1J/s 0,1 kGm/s1W 1/736 m.l (ma lc)

Nhiet o T 0K T = t + 2730

(T: o Kenvin, t: o Xenxiut)

Nhiet lng Q J 1J 2,4.10-3 kcal

Nhiet dung rieng C J / kgo 1J/kgo 2,4.10-3kcal/kgo

Thi gian t s

7CHNG 1

KHAI QUAT CHUNG VE O TO

Muc tieu:

Sau khi hoc xong chng nay cac sinh vien co kha nang:1. Trnh bay c cac phng an phan loai o to.2. Neu ra c cac yeu cau oi vi o to.3. Trnh bay c cac thong so cua o to.4. anh gia c cac u iem va nhc iem cua tng phng an bo tr ong c.5. Trnh bay c cac phng an bo tr he thong truyen lc tren o to.

81.1. PHAN LOAI O TO:

Nhu cau ve van chuyen hang hoa va khach hang bang cac phng tien van tai o to rat ln. eap ng ay u cac yeu cau van chuyen o, o to co rat nhieu chung loai khac nhau, c tap hptheo s o phan loai (hnh 1.1).

Hnh 1.1: S o phan loai o to

91.2. CAC YEU CAU OI VI O TO:

1.2.1. Cac yeu cau ve thiet ke, che tao:

- Xe o to phai mang tnh hien ai, cac tong thanh tren xe co ket cau hien ai, kch thc nhogon, bo tr hp ly phu hp vi cac ieu kien ng xa va kh hau.

- Vo xe phai ep, phu hp vi yeu cau ve tham my cong nghiep.- Vat lieu che tao cac chi tiet co o ben cao, o chong mon, chong g cao, nham nang cao

tnh tin cay va tuoi tho cua xe. Nen tang loai vat lieu nhe e giam t trong cua xe.- Ket cau cua cac chi tiet phai co tnh cong nghe cao, de gia cong, so lng cac nguyen cong

trong qui trnh cong nghe che tao t.

1.2.2. Cac yeu cau ve s dung:

- Xe phai co cac tnh nang ong lc cao nh: toc o trung bnh cao nham quay vong xe nhanh,nang cao nang suat van chuyen, thi gian gia toc va quang ng gia toc ngan, xe khi ong dedang.

- Xe phai co tnh an toan cao, ac biet oi vi he thong phanh va he thong lai.- Xe phai am bao tnh tien nghi cho lai xe va hanh khach, thao tac nhe va de dang, am bao

tam nhn tot.- Mc tieu hao nhien lieu, dau m boi trn, sam lop va cac vat lieu chay xe t.- Kch thc thung xe phai phu hp vi trong tai e nang cao he so s dung trong tai.- Kch thc va hnh dang xe phai am bao cho cong tac xep d hang hoa c thuan tien va

nhanh chong.- Xe chay phai em, khong on, giam lng oc hai trong kh thai.

1.2.3. Cac yeu cau ve bao dng, sa cha:

- Gi cong bao dng va sa cha xe so vi che tao rat ln, so vi ca i xe thng gap 30 50 lan gi cong che tao.

- Neu moi chi ph cho i xe t khi che tao en khi thanh ly la 100%, cac phan c phan bonh sau (so lieu cua nha may GAZ CHLB Nga):

Thiet ke che tao o to 1,4%Bao dng o to 45,4%Sa cha thng xuyen 46,0%Sa cha ln 7,2%

Qua o, chung ta thay gi cong bao dng, sa cha rat ln. e giam khoi lng cong viec,keo dai chu ky bao dng, o to phai am bao cac yeu cau sau:

- So lng cac iem boi trn phai t e giam gi cong bm dau m, thay the cac iem boitrn co vu m bang vat lieu boi trn vnh cu. Cac vu m phai bo tr thang hang, cung pha thuan licho cong tac bao dng.

- Giam gi cong kiem tra xiet chat bang cach s dung cac bulong, vt cay, ai oc co tnh tham cao, ung tieu chuan va t chung loai e phai thay oi dung cu thao lap.

- Giam gi cong ieu chnh bang cach thay cac khau ieu chnh bang tay bang ieu chnh tong, hoac de ieu chnh.

10

- Ket cau cua xe phai am bao cho cong tac thao lap c de dang, thuan tien cho cong tacsa cha thay the phu tung.

- Ket cau cung nh vat lieu che tao cua cac chi tiet co o hao mon ln phai u ben sau khiphuc hoi, sa cha. Cac mat chuan (cong nghe, nh v ) cua chi tiet phai c bao toan, tao ieukien cho gia cong c kh sa cha ap ng c cac yeu cau ky thuat.

1.3. CAC THONG SO CUA O TO:

1.3.1. Cac thong so kch thc:

Kch thc va hnh dang xe phai phu hp vi chc nang s dung. Theo GOST 9314 - 59 cuaCHLB Nga qui nh chieu rong cua xe khong qua 2,5 m, chieu cao khong qua 3,8 m, dai khong qua12m, trng hp keo na mooc dai khong qua 20m, keo hai mooc th chieu dai tong cong khong qua24m (Hnh 1.2).

20m

3,8m

24m12m

2,5m

Hnh 1.2: Kch thc gii han cua o to (GOST9314 59)

Cac thong so am bao tnh c ong cua xe c the hien bang 1.1.

Bang 1.1: Cac thong so hnh hoc am bao tnh c ong cua o to (hnh 1.3)

Cac goc vat (o)Loai xe

Khoangsang gamxe C (mm) Trc g1 Sau g2

Ban knhthong qua

doc Rm (m)1. Xe con

2. Xe tai: Trong tai 1,5 5 TTrong tai 8,012 T va co tnhnang thong qua cao.

3. Xe khach (dai t 7,0 16,5m)

160 210

200 260270 300250 400240 270

30 3545*

35 6530 4040 5010 20

15 2535*

20 3020 3530 458 13

2,0 4,5

1,5 3,03,0 5,01,5 3,54,0 8,0

* Xe co tnh nang thong qua cao.

11

2gg

Rm

c1

Hnh 1.3: Cac thong so hnh hoc cua tnh nang c ong

1.3.2. Cac thong so trong lng:

Hoi ong tng tr kinh te gia cac nc xa hoi chu ngha a thong nhat dai trong tai cua xetai thung go nh sau: 0,5 T 1 T 1,5 T 3,0 T 5 T 8 T 13 T. Giam t trong cua xe la mot trongnhng phng hng nghien cu che tao o to. T le gia t trong cua xe va trong tai la he so chat taiK.

K =h

0

qm

Trong o: m0 - T trong cua xe.qh - Trong tai cua xe.

He so K c the hien nh sau:

qh 1,5 3,0 5,0 8,0 12,0K 1,15 0,8 0,7 0,65

Tai trong cho phep tac dung len cau chu ong cua cac xe do CHLB Nga che tao c qui nhtrong GOST 9314-59 (bang 1.2).

Bang 1.2

Khoang cach gia hai truc (m)

> 3 m < 3 mLoai ng

KN KNI II

Cac loai xe10060

9055

12

1.4. BO TR CHUNG TREN O TO:

Bo tr chung tren o to bao gom bo tr ong c va he thong truyen lc. Tuy thuoc vao muc chs dung, cong dung va tnh kinh te ma moi loai xe co cach bo tr rieng. Nhn chung, khi chon phngphap bo tr chung cho xe, chung ta phai can nhac e chon ra phng an toi u, nham ap ng cac yeucau sau ay:

- Kch thc cua xe nho, bo tr hp ly phu hp vi cac ieu kien ng xa va kh hau.- Xe phai am bao tnh tien nghi cho lai xe va hanh khach, am bao tam nhn thoang va tot.- Xe phai co tnh kinh te cao, c the hien qua he so s dung chieu dai l cua xe.Khi he so l cang ln th tnh kinh te cua xe cang tang.

Ll

=?

ay : l Chieu dai thung cha hang (xe tai) hoac chieu dai buong cha hanh khach (xe ch khach). L Chieu dai toan bo cua o to.- am bao khong gian can thiet cho tai xe de thao tac, ieu khien xe va cho ngoi phai am

bao an toan.- De sa cha, bao dng ong c, he thong truyen lc va cac bo phan con lai.- am bao s phan bo tai trong len cac cau xe hp ly, lam tang kha nang keo, bam on nh,

em duv.v cua xe khi chuyen ong.

1.4.1. Bo tr ong c tren o to:

Cac phng an sau ay thng c s dung khi bo tr ong c tren oto:

1.4.1.1. ong c at ang trc:

Phng an nay s dung c cho tat ca cac loai xe. Khi bo tr ong c ang trc chung ta laico hai phng phap nh sau:

1.4.1.1.1. ong c at ang trc va nam ngoai buong lai:

Khi ong c at ang trc va nam ngoai buong lai (hnh 1.4a) se tao ieu kien cho cong viecsa cha, bao dng c thuan tien hn. Khi ong c lam viec, nhiet nang do ong c toa ra va srung cua ong c t anh hng en tai xe va hanh khach.

Nhng trong trng hp nay he so s dung chieu dai l cua xe se giam xuong. Ngha la the tchcha hang hoa hoac lng hanh khach se giam. Mat khac, trong trng hp nay tam nhn cua ngilai b han che, anh hng xau en o an toan chung.

13

l

L

a)

b)

d)

e)l

L

lc)h)

L

Hnh 1.4: Bo tr ong c tren o toa Nam trc buong lai. d Nam ang sau.b Nam trong buong lai. e Nam di san xe.c Nam gia buong lai va thung xe. h Buong lai lat.

1.4.1.1.2. ong c at ang trc va nam trong buong lai (hnh 1.4b):

Phng an nay a han che va khac phuc c nhng nhc iem cua phng an va neu tren.Trong trng hp nay he so s dung chieu dai l cua xe tang rat ang ke, tam nhn ngi lai cthoang hn.

Nhng do ong c nam ben trong buong lai, nen the tch buong lai se giam va oi hoi phai cobien phap cach nhiet va cach am tot, nham han che cac anh hng cua ong c oi vi tai xe vahanh khach nh nong va tieng on do ong c phat ra.

Khi ong c nam trong buong lai se kho khan cho viec sa cha va bao dng ong c. Bi vaytrong trng hp nay ngi ta thng dung loai buong lai lat (Hnh 1.4h) e de dang cham soc ongc.

Ngoai ra mot nhc iem can lu y na la phng an nay trong tam cua xe b nang cao, lamcho o on nh cua xe b giam.

1.4.1.2. ong c at ang sau:

Phng an nay thng s dung xe du lch va xe khach.Khi ong c at ang sau (hnh 1.4d) th he so s dung chieu dai l tang, bi vay the tch phan

cha khach cua xe se ln hn so vi trng hp ong c at ang trc neu cung mot chieu dai Lcua ca hai xe nh nhau, nh vay lng hanh khach se nhieu hn.

14

Neu chung ta chon phng an ong c at ang sau, ong thi cau sau la cau chu ong, cautrc b ong, th he thong truyen lc se n gian hn v khong can s dung en truyen ong cacang.

Ngoai ra, neu ong c nam sau xe, th ngi lai nhn rat thoang, hanh khach va ngi lai hoantoan khong b anh hng bi tieng on va sc nong cua ong c.

Nhc iem chu yeu cua phng an nay la van e ieu khien ong c, ly hp, hop so v.vsephc tap hn v cac bo phan noi tren nam cach xa ngi lai.

1.4.1.3. ong c at gia buong lai va thung xe:

Phng an ong c nam gia buong lai va thung xe (hnh 1.4c) co u iem la the tch buong laitang len, ngi lai nhn se thoang va thng ch s dung xe tai va mot so xe chuyen dung trongnganh xay dng.

Trng hp bo tr nay co nhc iem sau:No lam giam he so s dung chieu dai l va lam cho chieu cao trong tam xe tang len, do o tnh

on nh cua xe giam. e trong tam xe nam v tr thap, bat buoc phai thay oi s bo tr thung xe vamot so chi tiet khac.

1.4.1.4. ong c at gia san xe:

Phng an nay c s dung xe khach (hnh 1.4e) va no co c nhng u iem nh trnghp ong c at ang sau.

Nhc iem chnh cua phng an nay la khoang sang gam may b giam, han che pham vi hoatong cua xe va kho sa cha, cham soc ong c.

1.4.2. Bo tr he thong truyen lc tren o to:

He thong truyen lc cua oto bao gom cac bo phan va c cau nham thc hien nhiem vu truyenmomen xoan t ong c en cac banh xe chu ong. He thong truyen lc thng bao gom cac bophan sau :

- Ly hp: ( viet tat LH).- Hop so: (viet tat HS).- Hop phan phoi: (viet tat P).- Truyen ong cac ang : (viet tat C).- Truyen lc chnh: (viet tat TC).- Vi sai : (viet tat VS).- Ban truc (na truc): (viet tat N).

tren xe mot cau chu ong se khong co hop phan phoi. Ngoai ra xe tai vi tai trong ln thtrong he thong truyen lc se co them truyen lc cuoi cung.

Mc o phc tap cua he thong truyen lc mot xe cu the c the hien qua cong thc banh xe.Cong thc banh xe c ky hieu tong quat nh sau:

a x b Trong o :

a la so lng banh xe .b la so lng banh xe chu ong .

15

e n gian va khong b nham lan, vi ky hieu tren chung ta quy c oi vi banh kep cungch coi la mot banh.

Th du cho cac trng hp sau:4 x 2 : xe co mot cau chu ong (co 4 banh xe, trong o co 2 banh xe la chu ong).4 x 4 : xe co hai cau chu ong (co 4 banh xe va ca 4 banh eu chu ong ).6 x 4 : xe co hai cau chu ong, mot cau b ong (co 6 banh xe, trong o 4 banh xe la chu

ong).6 x 6 : xe co 3 cau chu ong (co 6 banh xe va ca 6 banh eu chu ong).8 x 8 : xe co 4 cau chu ong (co 8 banh xe va ca 8 banh eu chu ong).

1.4.2.1. Bo tr he thong truyen lc theo cong thc 4 x 2:

1.4.2.1.1. ong c at trc, cau sau chu ong:

Phng an nay c the hien hnh 1.5, thng c s dung xe du lch va xe tai hang nhe.Phng an bo tr nay rat c ban va a xuat hien t lau.

Hnh 1.5: ong c at trc, cau sau chu ong (4 x 2)

1.4.2.1.2. ong c at sau, cau sau chu ong:

Phng an nay c the hien hnh 1.6 thng c s dung mot so xe du lch va xe khach.Trong trng hp nay he thong truyen lc se gon va n gian v khong can en truyen ong cacang. phng an nay co the bo tr ong c, ly hp, hop so, truyen lc chnh gon thanh mot khoi.

Hnh 1.6: ong c at sau, cau sau chu ong (4 x 2)

HS C

CCLH

HS

TC VS

N

16

Mot v du ien hnh cho phng an nay la he thong truyen lc cho xe du lch VW 1200 (cuaCHDC c) hnh 1.7.

1

Hnh 1.7: He thong truyen lc xe VW 1200

1 Banh rang vanh chau2 Vo bo vi sai3 Banh rang ban truc

(Khong ve so lui tren hnh ve)

1.4.2.1.3. ong c at trc, cau trc chu ong:

Phng an nay c the hien hnh 1.8, thng c s dung mot so xe du lch san xuattrong thi gian gan ay. Cach bo tr nay rat gon va he thong truyen lc n gian v ong c namngang, nen cac banh rang cua truyen lc chnh la cac banh rang tru, che tao n gian hn banh rangnon cac bo truyen lc chnh tren cac xe khac.

C

Hnh 1.8: ong c trc, cau trc chu ong

17

Mot v du ien hnh cho phng an nay la cach bo tr he thong truyen lc cua xe du lchTALBOT SOLARA (CH Phap):

1

2

Hnh 1.9: He thong truyen lc cua xe du lch TALBOT SOLARA1 va 2 : c cau sang so lui (khong the hien het hnh ve).

1.4.2.2. Bo tr he thong truyen lc theo cong thc 4 x 4:

Phng an nay c s dung nhieu xe tai va mot so xe du lch. Tren hnh 1.10 trnh bay hethong truyen lc cua xe du lch VAZ - 2121 (san xuat tai CHLB Nga). ben trong hop phan phoi cobo vi sai gia hai cau va c cau khoa bo vi sai o khi can thiet.

LHC HS

P

C

C

1 2

Hnh 1.10 : He thong truyen lc cua xe VAZ 2121

1 C cau khoa vi sai gia hai cau.2 Vi sai gia hai cau.

18

1.4.2.3. Bo tr he thong truyen lc theo cong thc 6 x 4:

C HS

LHC

TC

C

TC

Hnh 1.11: He thong truyen lc cua xe KAMAZ 5320

Phng an nay c s dung nhieu cac xe tai co tai trong ln. tren hnh 1.11 la he thongtruyen lc 6 x 4 cua xe tai KAMAZ 5320 (san xuat tai CHLB Nga). ac iem c ban cua cach botr nay la khong s dung hop phan phoi cho hai cau sau chu ong, ma ch dung mot bo vi sai gia haicau nen ket cau rat gon.

1.4.2.4. Bo tr he thong truyen lc theo cong thc 6 x 6:

Hnh 1.12 : He thong truyen lc cua xe URAL 375

Phng an nay c s dung hau het cac xe tai co tai trong ln va rat ln. Mot v du cho trnghp nay la he thong truyen lc cua xe tai URAL 375 (san xuat tai CHLB Nga) tren hnh 1.12.

ac iem chnh cua he thong truyen lc nay la trong hop phan phoi co bo vi sai hnh tru e chiacong suat en cac cau trc, cau gia va cau sau. Cong suat dan ra cau gia va cau sau c phanphoi thong qua bo vi sai hnh non (Nh hnh 1.11) .

Ngoai ra co mot so he thong truyen lc mot so xe lai khong s dung bo vi sai gia cac caunh xe ZIL 131 ,ZIL 175 K,

19

CHNG 2

TAI TRONG TAC DUNG LEN CAC CUMVA CHI TIET CUA O TO

Muc tieu:

Sau khi hoc xong chng nay cac sinh vien co kha nang:1. Phan biet c cac loai tai trong tac dung len cac cum va chi tiet cua o to.2. Xac nh c cac trng hp sinh ra tai trong ong.3. Tnh c tai trong tnh toan dung cho he thong truyen lc.4. Tnh c tai trong tnh toan dung cho he thong phanh.5. Tnh c tai trong tnh toan dung cho he thong treo va cau.6. Tnh c tai trong tnh toan dung cho he thong lai.

20

2.1. KHAI NIEM VE CAC LOAI TAI TRONG:

Muc ch cua cong viec tnh toan thiet ke o to la xac nh kch thc toi u cua cac bo phan vachi tiet cua xe. Trong khi o, kch thc cua mot chi tiet phu thuoc vao o ln va ban chat cua ngsuat sinh ra ben trong chi tiet o khi no lam viec. Ma ng suat sinh ra trong cac chi tiet cua o to laiphu thuoc vao che o tai trong tac dung len chung trong cac ieu kien s dung khac nhau. Nh vay,muon xac nh kch thc cua cac chi tiet e u o ben lam viec, can phai xac nh tai trong tacdung len chung khi xe lam viec.

O to la mot he ong lc hoc rat phc tap, khi chuyen ong vi van toc khac nhau, tren cac loaing khac nhau th tnh trang chu tai cua cac chi tiet se thay oi. Khi tnh toan o ben cua cac bophan va chi tiet cua o to, ngoai tai trong tnh chung ta phai xet en tai trong ong. Tai trong ongtac dung len chi tiet trong thi gian ngan, nhng gia tr cua no ln hn tai trong tnh rat nhieu.

Tai trong ong xuat hien trong cac bo phan va chi tiet cua he thong truyen lc khi ong ly hpot ngot, khi gai so trong qua trnh tang toc, khi phanh ot ngot bang phanh tay hoac khi phanh gapma khong m ly hp Con oi vi cac bo phan khong c treo va he thong lai, tai trong ong sexuat hien khi xe chuyen ong tren mat ng khong bang phang.

Nh vay, e xac nh c kch thc cua cac chi tiet am bao u o ben lam viec, th chungta phai xac nh c tai trong ong tac dung len chi tiet o khi xe chuyen ong .

Xac nh chnh xac gia tr tai trong ong tac dung len cac chi tiet cua xe la mot bai toan ratphc tap. Bi v, gia tr tai trong ong co the thay oi do ieu kien mat ng va trang thai chuyenong cua xe thay oi.

oi vi he thong truyen lc cua o to, tai trong tnh tac dung len chi tiet c tnh t momenxoan cc ai cua ong c Memax. Con tai trong ong thng c xac nh theo cong thc kinhnghiem nhan c t hang loat cac th nghiem .

Thong thng tai trong ong c ac trng bang he so tai trong ong k. He so nay bang t socua gia tr tai trong ong tren gia tr tai trong tnh:

tnhtrongtaitrgiaongtrongtaitrgiak = (2.1)

Thong qua s phan tch va tong hp gia tai trong tnh, he so an toan, thong ke xac suat taitrong ong, chung ta se chon ra c mot che o tai trong hp ly e a vao tnh toan thiet ke cacchi tiet cua o to.

Tiep theo sau ay chung ta se nghien cu mot so trng hp sinh ra tai trong ong thng gap.

2.2. NHNG TRNG HP SINH RA TAI TRONG ONG:

2.2.1. ong ly hp ot ngot:

Khi khi ong xe, neu chung ta ong ly hp ot ngot (tha ban ap ly hp qua nhanh) th sephat sinh tai trong ong rat ln, v van toc goc cua phan b ong tang len rat nhanh va bien thientheo thi gian, bi vay se xuat hien gia toc goc va momen cua cac lc quan tnh tac dung len truc bong cua ly hp va cac chi tiet c noi vi truc b ong. Ket qua cua viec ong ly hp ot ngot laxe b giat manh hoac ong c se tat may. Hien tai cha co phng phap chnh xac e tnh toan taitrong ong sinh ra khi ong ly hp ot ngot, nen chung ta chap nhan cong thc kinh nghiem sau aye tnh he so tai trong ong cho trng hp nay:

21

i8ik

+= ? (2.2)

ay : b He so d tr cua ly hp (xem chng 3) . i T so truyen chung cua ca he thong truyen lc ng vi tay so ang tnh toan.

Qua th nghiem, ngi ta nhan thay rang khi ong ly hp ot ngot th momen quay sinh ra trentruc s cap cua hop so co the ln gap 33,5 lan momen quay cc ai cua ong c va banh xe chuong momen xoan co the gap hai lan so vi momen xoan t ong c truyen xuong.

bang 2.1 va 2.2 cho thay he so tai trong ong oi vi he thong truyen lc cua mot so xetrong cac ieu kien tai trong khac nhau:

Bang 2.1: He so tai trong ong cua he thong truyen lc khi ong ly hp ot ngot

Hieu o to

GAZ 51 ZIN - 150 MAZ 200

So truyenmot

So lui So truyenmot

So lui So truyenmot

So lui

He so taitrong ong

Ly thuyetThc nghiem

1,992,2

1,55

1,942,75

1,78

2,172,14

1,97

Bang 2.2: He so tai trong ong oi vi he thong truyen lc cua xe GAZ - 51 cac ieu kientai trong khac nhau

Cac thong so Khi ong tai choTha ban ap ly hp e phanh

bang ong c khi chuyen ongxuong doc.

Sotruyen 2

Sotruyen 3

Sotruyen 4

Sotruyen 2

So truyen3

So truyen4

He so tai trongong

T so momen ongtren momen tnh

cua ly hp

3,0

1,67

3,35

1,82

0,66

2,03

2,93

1,62

3,55

1,98

4,05

2,25

2.2.2. Khong m ly hp khi phanh:

Khi phanh ma khong m ly hp th cac chi tiet quay cua ong c (ang ke nhat la banh a vimo men quan tnh Jb ) phai dng lai trong khoang thi gian rat ngan t va vi gia toc cham dan rat

lndt

d bw .

(wb - Van toc goc cua banh a).

22

Luc nay momen cac lc quan tnh Mj cua banh a se truyen qua ly hp tac dung len he thongtruyen lc, gay nen tai trong ong theo s o tren hnh 2.1.

dt??

JM jb

b = (2.3)

Khi cac banh xe a dng han lai th banh a con quay them mot goc jb va se lam cho cac truccua he thong truyen lc b xoan vi cac goc xoan lien quan vi nhau theo bieu thc sau:

jb = jc.ih + jn.i0.ih (2.4)

ay :jc Goc xoan cua truc cac ang (rad).jn Goc xoan cua mot ban truc (rad).

Hnh 2.1: S o tnh toan tai trong ong khi phanh ma ly hp van ong

Cac goc xoan jc, jn c tnh theo sach Sc ben vat lieu" :

.G.J2.l.i.iM

.GJ.l.iM

n

n0hjn

c

chjc

=

=

j

j

ay :lc, ln chieu dai truc cac ang va ban truc (m).Jc, Jn mo men quan tnh oc cc cua tiet dien truc cac ang va ban truc (m4). G mouyn an hoi dch chuyen (khi xoan).

G = 8.104 MN/m2

Jb

i

Ham

Ham

i0

2

b

j i +j i i ij+c

M 2 bx

c h n 0 h 0n

jb

j jMjM

jM

Jc Jn

lc ln

jn

nj .i0

M j

hh.i

.ih.ih

.ih

M j

0.i

0.i

Jn,ln

c, lJc

j

23

Thay cac gia tr jc, jn vao bieu thc (2.4) ta co:

jb ).G2J.l.ii

.GJ

.li(M

n

n2h

20

c

c2h

j += (2.5)

Neu chung ta at:

G.J2l.i.i

G.Jl.i

1C

n

n2h

20

c

c2h +

=

la o cng chong xoan cua he thong truyen lc (Nmrad-1) khi cac banh xe cung b ham, se nhanc mot bieu thc khac bieu dien momen cac lc quan tnh:

Mj = C.jb (2.6)T 2 bieu thc (2.3) va (2.6) chung ta co :

Jbdt

d b? = C.jb (2.7)

Mat khac ta co :

b

bbb

b

bbb

bb d

Jdt

dJ

jjj w

w=w

=d

Jdd

dtd?

Bi vay:C.jb.djb = Jb.wb.dwb (2.8)

Lay tch phan bieu thc (2.8) vi cac gii han sau: khi bat au phanh jb = 0 va wb = wo enthi iem cuoi cung cua qua trnh phanh jb = jmax va wb = 0

= jjj bb dCmax

0bb

0

b d.J0

www

V chung ta can gia tr tuyet oi nen :

C. j2max = Jb.w02 va jmaxC

J b0?=

Sau cung gia tr Mjmax la gia tr chung ta can tm:Mjmax = C.JC bomax w=j (2.9)

Momen cua cac lc quan tnh tac dung len he thong truyen lc cua xe co gia tr cc ai khiphanh gap so truyen thang cua hop so ( ih=1 ), v luc o o cng C cua he thong truyen lc se cogia tr cc ai. Trng hp nay thng xay ra trong thc te.

Neu chung ta phanh gap xe ang chay vi van toc ln (so vong quay truc khuyu khoang20002500 vong/phut) ma khong m ly hp th momen cua cac lc quan tnh Mj se ln hn momencc ai cua ong c khoang 1520 lan. Momen nay se truyen t banh a qua ly hp en he thongtruyen lc. V Mjmax > Ml la momen ma sat cua ly hp, nen luc nay ly hp se trt va momen xoanma banh a truyen xuong he thong truyen lc ch co the bang momen xoan cc ai ma ly hp co thetruyen c. Nh vay trong trng hp nay ly hp lam nhiem vu cua c cau an toan, nham giup chohe thong truyen lc tranh khong b tac dung bi tai trong qua ln.

2.2.3. Phanh ot ngot khi xe ang chay bang phanh tay:

Chung ta xet trng hp c cau phanh tay bo tr truc th cap cua hop so. Khi xe ang chuyenong, ngi lai khong s dung phanh chan e dng xe, ma s dung phanh tay cho en luc xe dng

24

han lai. Khi truc th cap cua hop so b ham chat, nhng do quan tnh, banh xe con quay i mot goc

jbx roi mi dng han lai. ay la chuyen ong quay cham dan vi gia toc gocdt

d bxw , bi vay lam

xuat hien momen cua lc quan tnh :

dtd

JM bxbxjw

= (2.10)

Momen nay truyen ngc tr lai tac dung len he thong truyen lc theo s o hnh 2.2 va gaynen xoan.

Jc, lc

j

Ham

io

2MioHS

HS BX

j

M j bx

cjjcio

iocj jn

j

io2M

Jc

cl nl

nJjbx

jM

Jbx

Hnh 2.2 : S o tnh toan tai trong ong khi s dung phanh tay ot ngot

T s o 2.2 chung ta co quan he gia cac goc xoan :

no

cbx i

j+j

=j (2.11)

ay:

GJilM2

co

cjc

=j

jnGJlM

n

nj

=

Thay cac gia tr jn , jc vao bieu thc (2.11) ta co:

+

=j

GJl

GJil2

Mn

n

c2o

cjbx

25

Neu chung ta goi:

GJl

GJil2

1C

n

n

c2o

c

+

=

la o cng chong xoan cua he thong truyen lc khi phanh ot ngot bang phanh tay, chung ta nhanc mot bieu thc khac cung bieu th momen cac lc quan tnh:

Mj = C.jbx (2.12)

T bieu thc (2.10) va (2.12) ta nhan c phng trnh vi phan sau ay:

Jbx .dt??bx = C.jbx (2.13)

Giai phng trnh nay bang phng phap tng t nh muc (II 2 ) ta co:

jbx max = wbx0C

J bx (2.14)

Bi vay:CJM bx0bxmaxj w= (2.15)

ay:wbx0 : van toc goc cua banh xe khi bat au phanh.

Thong thng tai trong tac dung len he thong truyen lc khi phanh bang phanh chan ln hnkhi phanh bang phanh tay. Khi tnh toan momen cac lc quan tnh theo cong thc (2.9) va (2.15) canchu y rang o cng thc te cua he thong truyen lc se nho hn khi tnh toan, bi v khi momenphanh tac dung th nhp se bien dang, do o vo cau sau cung b quay i mot t.

2.2.4. Xe chuyen ong tren ng khong bang phang:

Khi xe chuyen ong tren mat ng khong bang phang, hien tng dao ong cua xe se lamxuat hien them tai trong phu. Thng th tai trong ong nay c can nhac va xet en khi tnh toanbo phan van hanh va he thong lai. tren hnh 2.3 la mot mo hnh n gian ve dao ong cua xe vaphng phap tnh toan tai trong cho trng hp nay.

ay chung ta co the xem toan bo xe nh mot he ong lc hoc va moi thanh phan cua he euco gia toc dao ong, do o no se chu them tai trong ong:

m.aP =

Trong o : m - Khoi lng. a - Gia toc dao ong.

26

Hnh 2.3: Mo hnh dao ong cua o to

x&& Gia toc M Khoi lnge - Gia toc goc J Momen quan tnh

Theo (hnh 2.3) th tai trong ong oi vi cac cau xe c tnh nh sau :

11o2

oo1 xMLJ

LLxMP &&&& ++= ?

22o1

oo xML?J

LL

xMP &&&& ++=2

ay :P1 Tai trong ong tac len dung len cau trc.

P2 Tai trong ong tac len dung len cau sau.

2.3. TAI TRONG DUNG TRONG TNH TOAN CAC CUM VA CHI TIET CUA GAM O TO:

2.3.1. Tai trong tnh toan dung cho he thong truyen lc:

Qua phan tch muc 1, chung ta thay rang, e am bao u o ben lam viec, cac bo phan va chitiet cua o to phai c tnh toan thiet ke theo che o tai trong ong. Nhng viec tnh toan gia tr taitrong ong theo ly thuyet la rat phc tap va kho chnh xac, v no thay oi tuy theo ieu kien matng va ieu kien s dung. Bi vay, hien tai cac bo phan va chi tiet cua o to c tnh theo taitrong tnh va co tnh en tai trong ong bang cach chon he so an toan phu hp hoac a vao he sotai trong ong c rut ra t thc nghiem. Sau ay se trnh bay phng phap tnh toan sc ben cacchi tiet cua he thong truyen lc theo tai trong tnh:

Khi tnh toan sc ben cac chi tiet, trc het can tnh momen t ong c va momen theo s bamgia banh xe va mat ng truyen en cac chi tiet o, sau o lay gia tr momen nho hn t hai giatr momen va tm c e a vao tnh toan. Muc ch cua cong viec nay la e chon ra knh thctoi u cho chi tiet o, tranh trng hp tha kch thc, ton nhieu vat lieu che tao, khong kinh te.Neu momen truyen t ong c en chi tiet tnh toan ln hn momen tnh theo ieu

Mo, Jo

Xo..

..X1 X2

..M2M1

L1 L2

L

e

27

kien bam, th chi tiet ay se chu momen co gia tr bang momen tnh theo bam ma thoi, luc naymomen cua ong c tha ch lam quay trn cac banh xe chu ong, ma khong lam tang them gia trmomen xoan tac dung len chi tiet ay .

Ngc lai, neu momen tnh theo ieu kien bam ln hn momen cua ong c truyen xuong chitiet ang tnh toan, th chi tiet ay se chu momen xoan co gia tr bang momen tnh theo momen xoancua ong c truyen xuong. Bi v, thc chat cac tai trong sinh ra trong cac chi tiet cua he thongtruyen lc la do momen xoan cua ong c truyen xuong gay nen.

Momen xoan truyen t ong c xuong chi tiet cua he thong truyen lc trong trng hp tnhtheo ong c la:

h= .i.MM maxeX (2.16) ay:

Memax Momen xoan cc ai cua ong c (N.m). i T so truyen t ong c en chi tiet ang tnh toan.

h Hieu suat truyen lc t ong c en chi tiet tnh toan .

Momen tnh theo ieu kien bam ngc len chi tiet c xac nh nh sau :

?

.

=j

i.rx.Z

M bxbxb (2.17)

ay : x So lng cac banh xe chu ong. Zbx Tai trong thang ng tac dung len banh xe chu ong (N).

j He so bam (j = 0,7 0,8). rbx Ban knh lan cua banh xe chu ong (m). i Ty so truyen gia chi tiet ang tnh va banh chu ong.

h Hieu suat truyen lc t chi tiet ang tnh en banh xe chu ong.

2.3.2. Tai trong tnh toan dung cho he thong phanh:

Khi chon che o tnh toan cho c cau phanh, chung ta phai chon cho trng hp phanh xe vicng o phanh va hieu suat cc ai, ngha la lc phanh bang lc bam cc ai cua banh xe vi matng. Luc o momen phanh Mp cua banh xe co gia tr la:

Mp = Zbx .j .rbx

Trng hp xe co hai cau va c cau phanh at trc tiep tat ca cac banh xe, luc o momenphanh moi c cau phanh cua cau trc se co gia tr la Mp1

..m2

GM 1p

1p1

= j .rbx =2LG (b + j.hg)j .rbx (2.18)

va momen phanh moi c cau cau sau la Mp2 :

..m2

GM 2p

2p2

= j .rbx =2LG (a - j.hg)j .rbx (2.19)

28

ay:G Trong lng toan bo cua xe khi ay tai.G1,G2 Tai trong tac dung len cau trc va sau trang thai tnh tren mat ng

nam ngang.m1p, m2p He so thay oi tai trong len cau trc va cau sau khi phanh.a, b Khoang cach t trong tam xe en cau trc va sau.L Chieu dai c s cua xe.j He so bam doc gia lop va ng (j = 0,7 0,8).

Cac he so m1p, m2p c xac nh bi ly thuyet oto:

ah'

1aghj

1m

bh'

1bghj

1m

ggmax2p

ggmax1p

j

j

-=

-=

+=

+=

ay:hg Chieu cao trong tam cua xe.g Gia toc trong trng.jmax Gia toc cham dan cc ai khi phanh.

j He so ac trng cng o phanh

=j

gj

' max

Khi xac nh o ben cac chi tiet cua c cau phanh va dan ong phanh loai khong t ongthng chon:

Lc ap chan cua ngi lai xe khoang 1500 N, lc tay keo khoang 800 N, oi vi xe du lch chnen chon trong khoang 40 50% cac gia tr neu tren.

oi vi loai dan ong t ong: lc tac dung len cac chi tiet dan ong chon theo tr so cc aitng ng vi ap suat kh nen hoac chat long trong cac xilanh lc.

2.3.3. Tai trong tnh toan dung cho he thong treo va cau:

Cac chi tiet cua he thong treo va dam cau c tnh toan ben theo tai trong cc ai Pmax khi xechuyen ong thong qua tai trong tnh Pt a biet va he so tai trong ong k :

Pmax = k.Pt

Thc nghiem chng to rang k tang khi o cng cua he thong treo va van toc cua xe tang.Khi xe hoat ong trong eu kien bnh thng th tai trong ong cc ai t khi xuat hien.Khi xe chuyen ong tren ng bang phang, tai trong tac dung len dam cau va vo cau chu yeu

la t khoi lng c treo. Khi mat ng khong bang phang,tai trong tac dung len dam cau va vocau chu yeu la tai trong ong t cac khoi lng khong c treo.

Nham muc ch xac nh tai trong do chnh trong lng ban than cua cau xe sinh ra, chung tachia cau xe ra lam nhieu phan (thong thng khoang 812 phan) va xac nh khoi lng cua moiphan. Khi xe dao ong th tai trong ong cua moi phan c xac nh:

dtdvmP ii = (2.20)

29

ay: mi Khoi lng cua tng phan.

dtdv Gia toc dao ong thang ng cua cau xe.

2.3.4. Tai trong tnh toan dung cho he thong lai:

Khi tnh toan ben cho cac chi tiet cua he thong lai, chung ta co the tnh theo cac che o taitrong sau:

* Momen cc ai cua ngi lai tac dung len vo lang:Ml = Plmax .R

ay : Plmax Lc cc ai tac dung len vo lang, oi vi xe tai nang va trung bnh vao

khoang 400500 N, con oi vi xe du lch vao khoang 150200 N. R Ban knh cua vo lang.* Lc phanh cc ai tac dung len hai banh xe dan hng khi phanh xe tren ng co he so

bam j=0,8Cac lc P1, P2 tac dung len cac on dan ong cua he thong lai c xac nh theo s o hnh

2.4.

cmZP

nmZP

bx2

bx1

j

j

=

=

* Tnh theo lc va ap cua mat ng len cac banh xe dan hng khi chuyen ong trenng go ghe. Gia tr lc va ap len cac chi tiet cua he thong lai phu thuoc vao van toc cua xe.

Hnh 2.4: S o cac lc tac dung len he thong lai

30

CHNG 3

LY HP

Muc tieu:

Sau khi hoc xong chng nay cac sinh vien co kha nang:1.Ve c s o cau tao va trnh bay c nguyen ly lam viec cua ly hp ma sat.2.Trnh bay c anh hng cua ly hp ti s gai so.3.Giai thch c tac dung cua ly hp khi phanh.4.Tnh c cong trt sinh ra trong qua trnh ong ly hp.5.Xac nh c kch thc c ban cua ly hp.6.Tnh toan c hao mon va nhiet o cua ly hp.7.Ve c s o cau tao va trnh bay c nguyen ly lam viec cua ly hp thuy lc.8.Trnh bay c ng ac tnh cua ly hp thuy lc.

31

3.1. CONG DUNG, PHAN LOAI, YEU CAU:

3.1.1. Cong dung:

Ly hp dung e noi cot may vi he thong truyen lc, nham e truyen momen quay mot cachem du va e cat truyen ong en he thong truyen lc c nhanh va dt khoat trong nhng trnghp can thiet.

3.1.2. Phan loai:

3.1.2.1 Theo cach truyen momen xoan t cot may en truc cua he thong truyen lc:

- Ly hp ma sat: loai mot a va nhieu a, loai lo xo nen bien, loai lo xo nen trung tam, loaicang tach ly tam va na ly tam.

- Ly hp thuy lc: loai thuy tnh va thuy ong.- Ly hp nam cham ien.- Ly hp lien hp.

3.1.2.2 Theo cach ieu khien:

- ieu khien do lai xe (loai ap chan, loai co tr lc thuy lc hoac kh).- Loai t ong.

Hien nay tren o to c s dung nhieu la loai ly hp ma sat. Ly hp thuy lc cung ang cphat trien o to, v no co u iem can ban la giam c tai trong va ap len he thong truyen lc.

3.1.3 Yeu cau:

- Ly hp phai truyen c momen xoan ln nhat cua ong c ma khong b trt trong moiieu kien, bi vay momen ma sat cua ly hp phai ln hn momen xoan cua ong c.

- Khi ket noi phai em du e khong gay ra va ap he thong truyen lc.- Khi tach phai nhanh va dt khoat e de gai so va tranh gay tai trong ong cho hop so.- Momen quan tnh cua phan b ong phai nho.- Ly hp phai lam nhiem vu cua bo phan an toan do o he so d tr b phai nam trong gii

han.- ieu khien de dang.- Ket cau n gian va gon.- am bao thoat nhiet tot khi ly hp trt.

3.2. S O CAU TAO VA NGUYEN LY LAM VIEC CUA LY HP MA SAT:

3.2.1 S o cau tao:

32

Hnh 3.1: Cau tao ly hp ma sat co lo xo ep trung tam a - Ly hp ong b - Ly hp m

1 - a ep 6 - Ong trt2 - Ban ap 7 - Ong co bi t3 - Vo 8 - Lo xo tach dt khoat4 - Cang tach 9 - a b ong5 - Lo xo trung tam 10 - Banh a

3.2.2 Nguyen ly lam viec cua ly hp ma sat:

Khi ngi tai xe ap chan len ban ap 2, qua he thong on ieu khien, on m t len ong co bit 7 tac dung len ong trt 6 ep len xo xo trung tam 5, lo xo 5 ep len cang tach, lam cho cang tachri khoi vau tren a ep va nh lo xo tach dt khoat 8 keo a ep khoi a b ong cung nh khoibanh a 10.

a b ong quay cung vi banh a, co nhiem vu truyen cong suat vao mat ma sat cua a ep,cho nen no phai noi vi banh a thong qua cac bulong. a ep day, co trong lng ln e nhiet tcac be mat ma sat truyen nhanh vao trong a ep roi thoat ra khong kh. Tren a ep co g danhng e nh v lo xo ep va gi lo xo khong b vang khi quay, gia lo xo ep va a ep co vong cachnhiet e tang tuoi tho cua lo xo. Trong qua trnh ong, ngat ly hp, cac tam ma sat b bao mon, lamkhoang cach gia vong bi t va au cang tach giam i, hanh trnh t do cua ly hp tang, qua trnhong hoc cua ly hp xau i, do o trong ly hp phai co c cau ieu chnh e duy tr khoang cach noitren ung qui nh.

3.3. ANH HNG CUA LY HP EN S GAI SO:

Sau ay chung ta xet anh hng cua ly hp en s gai so trong ca hai trng hp : trng hp lyhp ong va trng hp ly hp m. o to s gai so c thc hien ngay khi xe ang chuyen ongva ong c van ang lam viec.V vay ma xuat hien lc va ap khi cac banh rang khong co

33

cung chung mot van toc goc gai vao nhau. Trang thai ly hp ang noi hoac tach se co anh hng lnen gia tr lc va ap. e thay ro anh hng cua ly hp en cac lc va ap, chung ta se xet qua trnhgai so hop so theo s o n gian nh hnh 3.2. Tren s o nay, cac banh rang khong chu taitrong se khong c ve.

lJ

BaJ

mw wb

we

wa1

2 3

4M

E

A

Jm

Hnh 3.2 : S o e xet anh hng cua ly hp en s gai so

ay :Jm Momen quan tnh cua cac chi tiet chuyen ong cua ong c va cua phan chu ong

cua ly hp [Nms2].Jl Momen quan tnh cua phan b ong cua ly hp va cua cac chi tiet hop so co lien he

ong hoc vi phan b ong cua ly hp c quy dan ve truc cua ly hp [Nms2].Ja Momen quan tnh cua banh a tng trng at tren truc th cap hop so tng ng

vi trong khoi chuyen ong tnh tien cua xe [Nms2].Momen quan tnh nay c xac nh theo ieu kien can bang ong nang cua oto chuyen ong

tnh tien va ong nang cua banh a tng trng chuyen ong quay:

2J

vg2

G 2aa2 w=

V obx

a i.rv

=w

Cho nen 2o

2bx

a ir

gGJ = [Nms2] (3.1)

wa Van toc goc cua truc A [rad/s]. G Trong lng toan bo cua xe [N]. v Van toc chuyen ong cua xe [m/s]. io Ty so truyen cua truyen lc chnh. rbx Ban knh lan cua banh xe [m]. g Gia toc trong trng [9,81 m/s2].

Neu co tnh en anh hng cua trong khoi chuyen ong quay cua cac banh xe th can thay vaocong thc (3.1) trong lng G bang G(1 + d), vi :

2bx

bx

rJ

Gg' S=d (3.2)

ay :Jbx Momen quan tnh cua banh xe [Nms2]

34

Trc het ta xet trng hp gai so khi ly hp van ong tc la wm = wb .Khi chung ta a banh rang 4 tren truc th cap vao gai vi banh rang 3 truc trung gian, lap

tc gia cac banh rang 3 va 4 se xuat hien lc va ap. Ap dung phng trnh xung lng cua momencho chuyen ong quay cua truc A trong thi gian gai hai banh rang 3 va 4 chung ta co :

( )aaa44 .Jt.r.P w-w= (3.3) ay :

P4 Lc tac dung len rang cua banh rang 4 trong thi gian gai so. r4 Ban knh vong tron lan cua banh rang 4. t Thi gian lc P4 tac dung ,trong thi gian o truc A thay oi van toc goc t wa en

aw .wa Toc o goc cua truc A trc khi gai so.

aw Toc o goc cua truc A sau khi gai so.wb Toc o goc cua truc B.

Lap luan tng t, chung ta cung lap c phng trnh xung lng cua momen cho truc trunggian E:

( ) ( )ee2

1

2lm33 'r

rJJtrP w-w

+= (3.4)

ay: P3 Lc tac dung len rang cua banh rang 3 trong thi gian gai so.r1, r2, r3 Ban knh vong tron lan cua cac banh rang 1, 2, 3.

we Van toc goc cua truc E trc khi gai so.ew Van toc goc cua truc E sau khi gai so.

Khi thanh lap cac phng trnh (3.3) va (3.4) chung ta a bo qua momen cua ong c vamomen can chuyen ong cua xe la v khi gai cng (khong tach ly hp) cac banh rang th thi gian trat nho va momen xung kch rat ln, nen anh hng cua momen ong c va momen can chuyenong la khong ang ke.

Phng trnh (3.4) co the viet lai nh sau:

( )

w-w

+=

3

4a

2

1b

2

1

2lm33 r

rrr

.rr

.JJt.r.P (3.5)

De dang thay rang lc P3, P4 tac dung gia cac rang la bang nhau va thi gian gai so t la thigian chung.

Khi gai banh rang 4 vao an khp vi banh rang 3 th ty so truyen cua hop so ih se la:

3

4

1

2h r

rrr

i =

T hai phng trnh (3.3) va (3.5) chung ta se xac nh c toc o goc wa .Trc het ta nhan

hai ve phng trnh (3.5) vi3

4rr :

( )3

4

3

4a

2

1b

2

1

2lm

3

433 r

r.

rr

rr

.rr

.JJrr

t.r.P

w-w

+=

( ) ( ) 2halmhblm43 i..JJi..JJt.r.P w+-w+= (3.6)

V P3 = P4 cho nen P3.r4.t = P4.r4 .t . Bi vay t phng trnh (3.3) va (3.6) ta co:

35

( ) ( ) ( ) 2hlmhblmaa .i.JJ.i.JJJ aa ???? +-+=-

Suy ra :( )

( ) a2hlmaahblm

a Ji.JJ.Ji..JJ

++w+w+

=w (3.7)

Thay gia tr wa vao (3.3) ta co:( )

( )

w-

++w+w+

= aa

2hlm

aahblma44 Ji.JJ

.Ji..JJJt.r.P

( ) ( )( ) a2hlm

habhlma44 Ji.JJ

i.i.JJJt.r.P

++w-w+

= (3.8)

Theo phng trnh (3.8) ta thay lc xung kch tac dung len cap banh rang khi gai so phu thuocvao tong so momen quan tnh (Jm + Jl ). Lc nay co the giam bang cach giam tong (Jm + Jl), muonvay khi gai so ta can m ly hp e gia tr Jm khong con anh hng en o ln cua P4.

V momen quan tnh Jm ln hn Jl rat nhieu, nen khi ly hp tach trong qua trnh gai so th lc P4se giam rat nhieu.

Bay gi chung ta xet trng hp gai so khi ly hp m. Luc o anh hng cua Jm khong conna, bi vay Jm se khong xuat hien trong cac phng trnh va phng trnh (3.8) luc nay se nh sau:

( )ah

2l

habhla44 Ji.J

i..i.J.Jt.r.P

+w-w

= (3.9)

ay :4P Lc tac dung len cap banh rang c gai khi tach ly hp.

T phng trnh (3.9) chung ta thay rang lc 4P phu thuoc momen quan tnh Jl. e cho 4Pgiam, can phai giam Jl, bi vay khi thiet ke ly hp can phai giam momen quan tnh phan b ongxuong mc nho nhat co the c.

T phng trnh (3.8) va (3.9) suy ra rang gia tr P4 hoac 4P ty le thuan vi hieu so (wb - wa.ih).Neu trong hop so co at bo ong toc th se tranh c lc va ap gia cac banh rang khi gai so.

e van toc goc co the ong eu nhanh chong th ly hp phai am bao m dt khoat.So sanh phng trnh (3.8) va (3.9) ta co the ket luan rang khi gai so ma ly hp m th xung

lng cua momen hoac lc xung kch se giam ang ke neu hieu so (wb - wa.ih) nh nhau. Ty so cacxung lng cua lc 4P .t va P4.t c xac nh nh sau:

( ) ( )( ) ( )

( )[ ]( )( ) ( )

++

+

+

=++++

=

=-+

++

+-

=

m

lah

2l

m

ah

2

m

ll

lmah2

l

ah2

lml

habhlma

ah2

lm

ah2

l

habhla

4

4

JJ

1JiJ

JJ

iJJ

1J

JJJiJJiJJJ

iiJJJJiJJ

JiJiiJJ

.tP

.tP??

??

(3.10)

V momen quan tnh Jm ln hn Jl rat nhieu, nen co the xemm

l

JJ

co gia tr rat nho, luc o

chung ta co:

36

l

a2h

m

a2h

4

4

JJ

i

JJ

i

tPtP

+

+=

(3.11)

Xet trng hp cu the xe URAL 355 khi gai so truyen III vi cac so lieu biet trc nhsau:

ih3 = 1,84Jm =1,5 Nms2

Ja = 10,2 Nms2

Jl = 0,022 Nms2

Thay cac so lieu tren vao phng trnh (3.11) ta co:

022,0t.Pt.P

4

4 =

Nh vay nh ly hp trang thai m nen xung lng cua lc va ap giam c gan 50 lan khigai so, do o tang c tuoi tho cua banh rang hop so.

3.4. TAC DUNG CUA LY HP KHI PHANH:

Jm

w m Mli h i 0

bxw

Hnh 3.3: S o he thong truyen lc e xet tac dung cua ly hp khi phanh

Chung ta se nghien cu tac dung cua ly hp khi phanh xe nh s o hnh 3.3.Chung ta xet trng hp phanh gap e dng xe ma ly hp van ong.

Khi phanh xe se co gia toc amdtdv va do ly hp ong nen truc khuyu chuyen ong cham dan

vi gia toc gocdt

d mw

Do truc khuyu chuyen ong co gia toc goc, cho nen se xuat hien momen cac lc quan tnh Mjtruyen t ong c qua ly hp:

dtdJM mmj

w= (3.12)

Momen nay se tac dung len he thong truyen lc, neu trong qua trnh phanh ma ly hp vanong va khong b trt, tc la: Mj < Ml

ay:

37

wm - Van toc goc cua truc khuyu.wbx - Van toc goc cua banh xe. v - Van toc cua xe.

i0 - Ty so truyen cua truyen lc chnh. Ml - Momen ma sat cua ly hp.

Gia toc goc cua truc khuyu ong c c tnh nh sau:

ohbxm ii

dtd

dtd

w

=w

Trong odt

d bxw la gia toc goc cua banh xe:

dtdv

r1

rv

dtd

dtd

bxbx

bx =

=

w

Cuoi cung ta co:

dtdv

ri.i

dtd

bx

h0m =w

Thay gia trdt

d mw va tm c vao (3.12) ta co :

Mj = Jmdtdv

ri.i

bx

h0 (3.13)

De dang thay rang Mj phu thuoc vaodtdv , cho nen :

Mj max = Jmmaxbx

h0

dtdv

ri.i

(3.14)

Lc phanh cc ai Pp max chung ta co the xac nh theo nh luat Niutn nh sau:

maxmaxp dt

dvgGP

d= (3.15)

ay :Pp max - Tong cac lc phanh cc ai cac banh xe.

G - Trong lng toan bo cua xe. g - Gia toc trong trng.

d - He so tnh en anh hng cua cac trong khoi quay cua xe ( xem Ly thuyet oto).

++= 2bxbx

bx2bx

tl2o

2hm

.rGgJ

r??ii

GJ

1? (3.16)

Trong o :ht1 - Hieu suat cua he thong truyen lc.

bxJ - Tong so momen quan tnh cua cac banh xe.Gbx - Trong lng cua banh xe.

Lc phanh cc ai oi vi xe co bo tr c cau phanh tat ca cac banh xe se bang tch so giatrong lng toan bo cua xe G vi he so bam j.

Pp max = j .G (3.17)

38

T phng trnh (3.15) va (3.17) chung ta co:

?

.gdtdv

max

j=

(3.18)

Thay gia trmaxdt

dv

(3.18) vao phng trnh (3.14) chung ta xac nh c momen cc ai

cua cac lc quan tnh truyen qua ly hp:

d=

jg.r

ii.JM

bx

0hmmaxj (3.19)

Momen nay se truyen qua ly hp, neu momen ma sat Ml cua ly hp ln hn no. Neu ngc laith ly hp b trt va he thong truyen lc se chu tai trong vi gia tr ch bang momen ma sat Ml cualy hp.

Neu ly hp co momen ma sat Ml bang hoac ln hn gia tr Mj max, th he thong truyen lc sechu tai trong co gia tr ung bang Mj max.

Bi vay khi phanh gap, e tranh gay tai trong qua ln cho he thong truyen lc, chung ta cantach ly hp.

3.5. CONG TRT SINH RA TRONG QUA TRNH ONG LY HP:

3.5.1. Qua trnh ong ly hp:

Qua trnh ong ly hp xay ra khi phan chu ong cua ly hp quay vi van toc goc wm,va phan b ong quay vi van toc goc wb. Do co s khac biet ve van toc goc wm wb nengia cac a chu ong va b ong cua ly hp se sinh ra s trt. S trt nay cham dt khicac a chu ong va b ong c noi lien thanh mot khoi, tc la wm = wb. Khi khi ong xetai cho, do wb =0 nen s trt se rat ln.

S trt se sinh ra cong ma sat, cong nay se bien thanh nhiet nang lam nung nong cacchi tiet cua ly hp, dan en hau qua la he so ma sat cua ly hp giam va cac lo xo co the matkha nang ep.

Qua trnh ong ly hp co the co hai trng hp sau:

3.5.1.1. ong ly hp nhanh:

Luc nay ong c quay vi van toc cao va tai xe ot ngot tha ban ap ly hp. Khi ong nhvay se co s giat ln, nhat la nhng ly hp co he so d tr b ln.

ong ly hp theo phng phap nay khong co li, v no sinh ra tai trong ong ln cho cac chitiet cua he thong truyen lc, nhng trong thc te mot vai trng hp ngi ta van s dung.

3.5.1.2. ong ly hp t t:

trng hp nay tai xe tha t t ban ap cua ly hp cho xe chuyen ong t t. Do o thi gianong ly hp va cong trt trong trng hp nay se tang.

e xac nh cong trt trong qua trnh ong ly hp, chung ta khao sat o th hnh 3.4:

39

Hnh 3.4: S o e tnh toan cong trta - Mo hnh tnh toan.b - o th bien thien van toc goc.

wm, wb Van toc goc cua truc khuyu va truc ly hp.Jm Momen quan tnh cua banh a va cua cac chi tiet ong c quy dan ve banh a.Jb Momen quan tnh cua xe va rmooc quy dan ve truc cua ly hp.

( )2ophbx

2mo

b iiir.

gGGJ

+=

ay:G0 Trong lng toan bo cua xe.Gm Trong lng toan bo cua rmooc.ih, ip, io Ty so truyen cua hop so, hop so phu va truyen lc chnh.Mb Momen can chuyen ong quy dan ve truc ly hp:

( )[ ]tloph

bx2mob iii

rKFvGGMh

+y+= (3.20)

ay :Y He so can tong cong cua ng.K He so can cua khong kh.htl Hieu suat cua he thong truyen lc.w0 Van toc goc cua khoi lng co momen quan tnh Jm va Jb sau khi ly hp va ket

thuc s trt.F Dien tch mat chnh dien cua xe.v Van toc cua xe.rbx Banh knh lan cua banh xe.

Cong trt cua ly hp c xac nh theo phng trnh :

a

a=0

ldML (3.21)

Trong o: Ml Momen ma sat cua ly hp.a Goc trt cua ly hp.

Do co hai qua trnh ong ly hp khac nhau: ong ly hp nhanh va ong ly hp t t, bi vay seco hai phng phap khac nhau e xac nh cong trt.

w

A Bw

toTrtly h?p

Tangtoc

Toc oon nh

m mMmJ

lMbw

bJbM

0wmw

wb

a) b)

tO

40

3.5.2. Tnh toan xac nh cong trt:

3.5.2.1. Phng phap th nhat:

Chung ta gia thiet qua trnh ong ly hp dien ra rat nhanh ( ot ngot). Bi vay trong thi gianong ly hp, cac gia tr Mm, Mb, Ml khong oi va luc o phng trnh cua he chu ong gom ong c,ly hp (Phan A) la :

( ) 0tMtMJ olomomm =-+w-w (3.22)oi vi phan b ong gom ly hp va he thong truyen lc (Phan B) chung ta co :

0t.M)(Jt.M obbobol =-w-w- (3.23)T hai phng trnh (3.22) va (3.23) chung ta xac nh c gia tr wo cuoi thi ky trt:

)MM(J)MM(J)MM(J)MM(J

mlbblm

mlbbblmmo -+-

-w+-w=w (3.24)

Trong o : wm, wb, wo la cac gia tr van toc goc c trnh bay hnh 3.4bCung t hai phng trnh tren ta xac nh c thi gian trt cua ly hp t0 :

)MM(J)MM(J)(JJt

mlbblm

bmbmo -+-

w-w= (3.25)

Goc trt a c xac nh :a = wtb.to

Trong o :wtb Van toc goc trt trung bnh:

( )2

0bmtb

+w-w=w

Thay gia tr t0 va wtb vao bieu thc a ta co :( )

( ) ( )mlbblm

2bmbm

MMJMMJJJ5,0

-+-w-w

=a (3.26)

Cong trt sinh ra khi ong ly hp ot ngot la:( )

( ) ( )mlbblm

2bmbml

l MMJMMJJJM5,0ML

-+-w-w

=a= (3.27)

Cong trt L va goc trt a tnh theo cac cong thc tren se co gia tr nho hn thc te bi v thigian trt ly hp khi ong ly hp ot ngot se nho.

3.5.2.2. Phng phap th hai:

phng phap nay ngi ta xet en hai giai oan thc te cua qua trnh ong ly hp t t :

* Giai oan 1: Tang momen ma sat cua ly hp Ml t 0 en gia tr bang Mb. Luc o xe batau khi ong tai cho.

* Giai oan 2: Tang momen cua ly hp Ml en gia tr khong con ton tai s trt cua lyhp.

giai oan 1, ly hp b trt hoan toan, bi vay cong cua ong c giai oan nay vi thigian t1 se tieu hao cho s trt va nung nong ly hp. Cong trt cua giai oan nay c tnh:

1bm

l1 t.2.ML w-w=

41

giai oan 2, cong cua ong c vi thi gian t2 dung e tang toc truc b ong cua ly hp va ethang cac sc can chuyen ong cua xe.

Gia tr cong trt cua giai oan nay la :

2bmb2

bmb2 t)(M32)(J

21L w-w+w-w=

Cong trt toan bo L cua ly hp la:

2bmb2

2

1bmb21 )(J2

1t32

tt)(MLLL w-w+

+w-w=+= (3.28)

Thi gian t1 va t2 c tnh nh sau:

kAt

kMt

2

b1

=

=

Trong o :k He so t le, ac trng cho nhp o tang momen cua a ly hp Ml khi ong ly hp.

k = 50 150 Nm/s oi vi xe du lch. k = 150 750 Nm/s oi vi xe tai.

Lay gia tr k ln oi vi xe co cong suat rieng ln.Gia tr cua A c xac nh theo cong thc :

)(J2A bmb w-w=Van toc goc cua truc khuyu khi ong ly hp co the coi la khong oi va bang van toc goc ng

vi momen cc ai cua ong c.Qua cac cong thc tren ta thay rang cong trt se tang, neu gia tr cua hieu so wm - wb tang. e

giam cong suat trt (ngha la giam s mai mon cua cac tam ma sat cua ly hp), tai xe can giam giatr cua hieu so wm - wb . Hieu so nay ln nhat khi khi ong xe tai cho, luc o wb = 0. Neu tang khoilng cua xe hoac cua ca oan xe th cong trt cung tang. Khi khi ong xe tai cho, e giam congtrt tai xe phai khi ong so truyen thap, nh o se giam c gia tr momen can quy dan ve trucly hp.

3.6. XAC NH KCH THC C BAN, TNH TOAN HAO MON VA NHIET O CUA LYHP:

3.6.1. Xac nh kch thc c ban cua ly hp:

C s e xac nh kch thc c ban cua ly hp la ly hp phai co kha nang truyen c momenxoan ln hn momen xoan cc ai cua ong c mot t.

Momen ma sat cua ly hp phai bang momen xoan ln nhat can truyen qua ly hp :maxel MM b= (3.29)

ay : Ml - Momen ma sat cua ly hp (Nm).Me max - Momen xoan cc ai cua ong c (Nm).

42

b - He so d tr cua ly hp.Xe du lch : b = 1,3 1,75Xe tai khong co r mooc b = 1,6 2,25Xe tai co r mooc b = 2 3.

Phng trnh (3.29) cung co the viet di dang sau :

pRP?M?M tbmaxel == (3.30) ay :

m - He so ma sat cua ly hp. p - So lng oi be mat ma sat:

1nmp -+= m - So lng a chu ong. n - So lng a b ong. P - Lc ep len cac a ma sat.Rtb - Ban knh ma sat trung bnh (ban knh cua iem at lc ma sat tong hp).

T phng trnh (3.30) xac nh c lc ep can thiet len cac a e truyen c momen Memax:

pRM

pRM

Ptb

emax

tb

l

m

=m

=? (3.31)

Ban knh Rtb c xac nh theo cong thc sau :

12

22

13

23

tb RRRR

32R

--

=

Hnh 3.5 : S o xac nh Rtb

Gia tr Rtb c xac nh nh sau :Tren hnh 3.5 la mot tam ma sat cua ly hp. Chung ta xet trng hp ly hp co mot oi be mat

ma sat (p = 1).Gia thiet co lc P tac dung len tam ma sat vi ban knh trong la R1, ban knh ngoai R2 bi vay

ap suat sinh ra tren be mat tam ma sat se la :

( )1222 RRP

SPq

-p==

Bay gi ta hay xet mot vong phan t nam cach tam O mot oan bang ban knh R va co chieuday dR. Momen do cac lc ma sat tac dung tren vong phan t o la :

dRqR2RdRR2qdM 2l mp=pm=Momen cac lc ma sat tac dung tren toan vong ma sat la:

D2

2R

R

1R

dR

O

43

( )( )2122

31

32R

R

221

22

R

R

2R

R ll

RRRR

32PdRR

RRP2

dRqR2dMM

2

1

2

1

2

1

--

m=-

m=

=mp==

(3.32)

Mat khac momen cac lc ma sat tac dung tren toan vong ma sat cung bang lc ma sat tong hpmP nhan vi Rtb, tc la :

tbl RPM m= (3.33)T cong thc (3.32) va (3.33) ta suy ra ;

( )( )2122

31

32

tb RRRR

32R

--

= (3.34)

Trong trng hp khong can o chnh xac cao th Rtb co the xac nh theo cong thc gan ungsau:

2RRR 21tb

+= (3.35)

ng knh ngoai D2 cua vong ma sat b khong che bi ng knh ngoai cua banh a ong c.Co the chon ng knh ngoai cua tam ma sat theo cong thc kinh nghiem sau:

CM16,3R2D maxe22 == (3.36)

Trong o : D2 ng knh ngoai cua tam ma sat (cm).

Me max Momen xoan cc ai cua ong c (Nm). C He so kinh nghiem:

oi vi xe du lch C = 4,7 oi vi xe tai s dung trong ieu kien bnh thng C = 3,6

oi vi xe tai o hang va xe tai s dung trong ieu kien nang nhoc C = 1,9Ban knh trong R1 cua tam ma sat co the chon s bo nh sau :

R1 = (0,53 0,75 )R2Gii han di (0,53 R2 ) dung cho ong c co so vong quay thap. Con gii han tren (0,75R2)

dung cho cac ong c co so vong quay cao.He so ma sat m phu thuoc vao tnh chat vat lieu, tnh trang be mat, toc o trt va nhiet o cua

tam ma sat. Khi tnh toan, co the tha nhan he so ma sat ch phu thuoc vao tnh chat vat lieu (xembang 3.1).

Bang 3.1 : Vat lieu che tao tam ma sat cua ly hp.

He so ma sat mNguyen lieu cua cac bemat ma sat Kho Trong dau

Ap suat cho phep( kN/m2 )

Thep vi gangThep vi thepThep vi pheraoGang vi pheraoThep vi pherao caosu

0,15 0,180,15 0,200,25 0,35

0,20,4 0,5

0,03 0,070,07 0,15

0,07 0,15

150 300250 400100 250100 250100 250

So lng oi be mat ma sat p co the t chon da vao ket cau hien co, sau o tm lc ep P canthiet theo cong thc (3.31), sau o can kiem tra ap suat len be mat ma sat theo cong thc sau:

44

( ) [ ]qRR?P

SPq 2

122

-

== (3.37)

ay : [q] Ap suat cho phep lay theo bang 3.1Trong trng hp khong the d kien trc c so lng oi be mat ma sat p th co the xac

nh thong qua cong thc sau:p.q.b?R2?.MM .2tbmaxel m==

Trong o :Memax Momen xoan cc ai cua ong c (Nm).b Chieu rong cua tam ma sat : b = R2 R1q Ap suat cho phep lay theo bang 3.1 (N/m2).

T o co the xac nh so lng oi be mat ma sat:

2tb

maxe

R.b.2?.M

p..q. mp

= (3.38)

3.6.2. Tnh toan o hao mon cua ly hp:

Hien tng trt cua ly hp khi ong ly hp se lam cho cac tam ma sat b hao mon. Va khi btrt se xuat hien cong trt. Nhng chung ta khong the anh gia mc o hao mon thong qua congtrt, bi v neu 2 ly hp co cung gia tr cong trt, nhng ly hp nao co dien tch be mat cac tam masat nho hn se b mon nhieu hn. Cho nen e xet mc o hao mon cua ly hp, chung ta phai tnhcong trt tren n v dien tch be mat cac tam ma sat. o chnh la cong trt rieng L0:

[ ]oo Lp.SLL = (3.39)

Trong o :Lo Cong trt rieng (J/m2).L Cong trt sinh ra khi ly hp trt (J).S Dien tch be mat tam ma sat (m2), ( )2122 RR?.S -= .p So lng oi be mat ma sat.[Lo] Cong trt rieng cho phep tra theo bang 3.2.

Bang 3.2:

Loai oto [L0]

O to tai co trong tai en 50 kNO to tai co trong tai tren 50 kNO to du lch

150.000 250.000 J/m2

400.000 600.000 J/m2

1.000.000 1.200.000 J/m2

3.6.3. Tnh toan nhiet o cua ly hp:

Moi lan ong ly hp, cong trt sinh ra bien thanh nhiet nang va lam nung nong cac chi tietcua ly hp. Bi vay, ngoai viec kiem tra cong trt rieng con can phai kiem tra nhiet o cua cac chitiet b nung nong trong qua trnh trt.

Khi khi hanh xe tai cho, cong trt sinh ra se ln nhat. Bi vay, tnh toan nhiet o cua ly hpcan phai kiem tra luc khi hanh.

45

Nhiet o tang len cua chi tiet tiep xuc trc tiep vi tam ma sat trong thi gian ly hp b trtc xac nh theo cong thc :

mcLT

=? (3.40)

ay:T Nhiet o tang len cua chi tiet (0K).q He so xac nh phan cong trt dung e nung nong chi tiet can tnh, q c xac

nh nh sau:

2n1

=q : oi vi a ep (n so lng a b ong)

n1

=q : oi vi a chu ong trung gian.

L Cong trt sinh ra toan bo khi ong ly hp (J)c Nhiet dung rieng cua cac chi tiet b nung nong, oi vi thep va gang c

500J/kg.o m Khoi lng cua chi tiet b nung nong (kg).

Moi lan khi hanh oto tai cho trong ieu kien s dung ng pho T khongc vt qua 100K.

3.7. LY HP THUY ONG:

3.7.1. Cau tao va nguyen ly lam viec:

3.7.1.1. Cau tao (hnh 3.6):

Ly hp thuy ong gom a bm 1 va a tuocbin 2. Chung c at vao mot vo chung co chadau. a B gan tren truc chu ong cua ly hp va noi vi truc ong c, a T gan tren truc b ong cualy hp. Gia B va T (cung nh gia truc chu ong va b ong cua ly hp) khong co s noi cng naoca. Cong suat truyen t B sang T nh nang lng cua dong chat long. Tren B va T co gan cac canhcong, xep theo chieu hng knh. Cac canh nay hp vi cac mat cong trong va ngoai cua a taothanh cac ranh cong. Chat long c tuan hoan trong cac ranh theo hng mui ten hnh 3.6.

Mb bn bw M tntwt

Hnh 3.6: Cau tao ly hp thuy ong

46

3.7.1.2. Nguyen ly lam viec:

Xet qua trnh lam viec khi khi ong xe:Khi ong c lam viec, a B se quay va chat long hai a bat au chuyen ong. Gia cac

canh cua B chat long chuyen ong t trong ra ngoai ra di tac dung cua lc ly tam. Van toc cuadong chat long khi chuyen ong gia cac canh cua B dan dan tang len do nang lng ma dong chatlong nhan t ong c cung dan dan tang len. Khi chuyen ong t cac canh cua B sang cac canhcuaT, chat long ban vao cac canh cua T, tao thanh lc ep len cac canh cua T. Sau o chat long oihng chuyen ong, van toc giam xuong va chuyen ong t ngoai vao tam gia cac canh cua T.

Lc va ap cua chat long tao ra momen quay bat a T phai quay cung chieu vi a B. Sau ochat long lai t a T tr ve a B va chu ky chuyen ong cua chat long lai lap lai neu ong c vanlam viec.

Khi tang so vong quay cua ong c, lc li tam cua chat long a B cang tang, do o lam tanglc ep cua chat long len cac canh cua T va lam tang momen quay cua a T. Khi momen quay cua Tbang hoac ln hn momen can chuyen ong cua ng quy dan ve truc cua a T th xe bat auchuyen ong.

Khi tai trong len truc cua a T co s thay oi, lap tc van toc goc cua T se thay oi theo, doo lam thay oi s tuan hoan chat long va ket qua la momen cua T se thay oi can bang vi gia trcua momen can chuyen ong. Bi vay, ly hp thuy ong la loai truyen ong t ong ieu chnhmomen xoan.

Cac u iem va nhc iem cua ly hp thuy ong (Xem lai mon Cau tao o to).

3.7.2. Tnh toan ly hp thuy ong:

2

1

u

v

wv

wu

2

2

2

1

1

1bM

wb

2a

a1

r2

1r

Hnh 3.7 : Qu ao chuyen ong

47

Khi chuyen ong gia cac canh cua B va T, cac phan t chat long tham gia ong thi haichuyen ong : Chuyen ong tng oi gia cac phan t chat long va cac canh cua B va T, vi vantoc tng oi la wr .

Chuyen ong theo s quay cua B va T vi van toc theo la ur .Bi vay, phan t chat long se chuyen ong theo vec t van toc tuyet oi vr :

uwv rrv += (3.41)

hnh 3.7 la quy ao chuyen ong cua phan t chat long gia cac canh cua B. iem 1 la iemphan t chat long i vao cac canh cua B vi van toc tuyet oi v 1 , iem 2 la iem i ra khoi cac canhcua B vi van toc tuyet oi la v 2 .V khe h gia B va T vo cung nho, nen ton that nang lng cuadong chay khi i qua khe h nay la khong ang ke.

Bi vay, van toc khi i vao va i ra khoi B cua phan t chat long bang van toc khi i ra va ivao cua a T. Cho nen ch can xet cac thanh phan van toc tai iem 1 va 2:

u1 = wb.r1u2 = wb.r2 (3.42)

Momen quay cua a bm Mb bang hieu so cua cac momen ong lng trong tng giay cuachat long khi i ra va i vao a B. Momen M b nam trong mat phang vuong goc vi truc ly hp:

M ( ) ( )11221122b r.ur.u.gGr.ur.u.m -=-= (3.43)

T hnh (3.7) ta thay:222 cos.vu a=

111 cos.vu a=Cho nen :

M ( )111222b cos.v.rcos.v.r.gG

a-a= (3.44)

ay: m Khoi lng cua chat long chay qua cac canh cua B trong mot giay.Momen quay cua tuoc bin Mt cung c tnh nh tren:

M ( ) ( ) b11222211t Mr.ur.u.gGr.ur.u.

gG

-=--=-= (3.45)

Neu ch quan tam en gia tr tuyet oi th:

bt MM = (3.46)

Khi chat long chuyen ong gia cac canh cua ly hp th mot phan cong suat se mat mat do masat trong dong chay, ma sat gia chat long va cac canh va do va ap khi chuyen t B sang T va t Tsang B Bi vay:

rtb NNN += (3.47)

48

Trong o:bN Cong suat cua B.

tN Cong suat cua T.

rN Cong suat mat mat do ma sat.Hieu suat cua ly hp:

b

t

b

t

bb

tt

b

t

nn

.MM

.?M

.?MNN

? === (3.48)

ay: -t,b nn So vong quay cua a B va a T.V bt MM = nen :

S1n

nn1

nn

?b

tb

b

t -=-

-== (3.49)

Gia trb

tb

nnn

S-

= goi la o trt cua a T so vi a B.

Trong thi gian lay a, so vong quay tn cua a T tang len va tien dan en so vong quay

bn cua a B, do o S cang giam. so vong quay ln S= 2 % 3 %, cho nen hieu suat cua ly hp

at ti 98%.Kch thc cua ly hp thuy ong c tnh toan tren c s xac nh ng knh ln nhat D.Tren c s cua ly thuyet cac may co canh, ta co moi lien he gia momen quay c truyen bi

ly hp vi cac thong so cua ly hp (Xem lai monThuy lc va may thuy lc ).

3.7.3. ng ac tnh cua ly hp thuy ong:

o th bieu dien s phu thuoc cua momen quay M, hieu suat h va o trt S theo t sob

t

nn

(vi nb=const) goi la ng ac tnh ngoai cua ly hp thuy ong.

ng ac tnh h theob

t

nn

la ng thang nghieng vi truc hoanh mot goc la 450 do hieu suat

b

t

nn

=h .

Khi hieu suat at ti hmax = 98 % th no giam ot ngot theo ng net t va gia tr sob

t

nn

=1

th h= 0. Do o hieu suat khong the bang 1.

49

Hnh 3.8 : ng at tnh ngoai cua ly hp vi nb = const

S d co hien tng nay la do khi nt tang en gia tr gan bang nb th momen quay cua ly hp segiam nhieu en mc no ch u e thang ma sat c hoc ly hp, do o momen co ch truc b ongcua ly hp se bang khong va h= 0.

ng ac tnh o trt S cung la ng thang va c xay dng theo cong thc:

b

t

nn

11S -=h-= (3.50)

ng ac tnh momen quay M theob

t

nn

c xay dng t thc nghiem.

T o th ta thay:Khi nt giam (va S tang) th M tang. Khi nt = 0 (tc la S = 1) th momen quay truyen bi ly hp

at gia tr cc ai.Momen quay truyen bi ly hp khi nt = 0 goi la momen quay khi ong.

M, S

M

S

0

98

75

50

25

0,25 0.5 0,75 1

h(%)

n tbn

1

0,75

0.5

0,25

h

450

50

CHNG 4

HOP SO VA HOP PHAN PHOI

Muc tieu:

Sau khi hoc xong chng nay cac sinh vien co kha nang:1. Ve c s o ong hoc va neu c nguyen ly lam viec cua cac loai hop so.2. Trnh bay c trnh t tnh toan hop so co cap.3. Xac nh c cac t so truyen cua hop so.4. Tnh c cac thong so hnh hoc cua banh rang hop so.5. Trnh bay c cau tao va nguyen ly lam viec cua bo ong toc.6. Neu c khai quat ve hop so t ong.7. Trnh bay c s o cau tao, nguyen ly lam viec va cac ng ac tnh cua bien momen

thuy lc.8. Tnh toan c ong hoc va ong lc hoc cua hop so hanh tinh.9. Trnh bay c he thong ieu khien hop so t ong.10. Trnh bay c c nguyen tac phan phoi cong suat cho cac cau cua xe nhieu cau chu

ong.

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4.1. HOP SO CO CAP:

4.1.1. Cong dung, yeu cau, phan loai:

4.1.1.1. Cong dung:

- Nham thay oi ty so truyen va momen xoan t ong c en cac banh xe ch