20. may Bua dong coc diesel

a. Cau tao chung

May bua dong coc diesel thuong gom ba phan chinh:

- May co so: thuong dung can truc xich hoac may dao mot gau, co khi chi dung toa quay lap tren gia di chuyen bang banh sat dat tren duong ray (hinh 6-2). Hinh 6-2. Cau tao chung cua may dong coc dat tren duong ray

1- Khung duoi; 2- Banh sat; 3- Gia bua; 4,5- Co cau dieu chinh gia bua; 6- Toa quay.

- Gia bua: gom he thanh dan huong cho dau bua trong qua trinh dong coc; thanh xien; thanh ngang; thanh nay co the dieu chinh goc nghieng cua gia (ve phia truoc hay phia sau), thuong khoang 50 khi can dong coc xien. De dieu chinh duoc co the dung tangdo hoac xy lanh thuy luc.

- Dau bua: la bo phan truc tiep gay ra luc de dong coc.

Cac may bua dong coc diesel deu co nguyen ly lam viec chung cua dong co diesel. Loi dung su roi tu do cua bua de nen khong khi toi ap suat va nhiet do cao, nhien lieu duoc phun vao gap nhiet do va ap suat cao tu boc chay, tao ap luc khi lon day bua len cao. Thoi diem bua dap vao dau coc xay ra truoc khi nhien lieu boc chay. Uu diem cua loai may bua nay la cau tao gon, de van chuyen. Nhuoc diem la khoi dong kho, dac biet la khi gap dat mem, cong dong coc nho, toc do dong cham, thuong chi dat 5080 lan/ph, nhien lieu dat tien. Khi dong coc o nen dat yeu va ve mua dong bua kho no, do luc dong coc lon nen dau coc de bi vo gay anh huong toi cong trinh xung quanh. Co ba loai bua dong coc diesel: loai hai coc dan, loai ong dan va loai xylanh dan; trong do loai hai coc dan va loai ong dan duoc dung nhieu hon.

b. Bua dong coc diesel hai coc dan (h.6-3, a):

Hinh 6-3. Bua dong coc diesel

a. Loai hai coc dan; b. Loai ong dan; 1- Be bua; 2- Day bua (duc lien voi pittong 12) ; 3- Lo phun dau; 4- Coc dan huong; 5- Chot; 6- Moc khoi dong; 7- Xa ngang; 8- Cap treo; 9- Don dieu khien moc; 10- Xylanh; 11- Chot (thanh gat); 12- Pittong; 13- Duong dau; 14- Bom dau cao ap; 15- Kep dau coc; 16- Dinh vau; 17- Phan be; 18- Lo thoat khi; 19- Binh dau; 20- Moc keo; 21- Xylanh dan huong; 22- Pittong-dau bua; 23- Don bom.

Gom co hai coc dan huong 4 lien ket voi day 2 duoc duc lien voi pittong 12. Khoi day pittong ty len be bua 1 va kep coc 15. Xylanh 10 truot theo hai coc dong thoi lam nhiem vu dau bua. Phia tren coc la xa ngang 7 co cap treo 8, moc khoi dong 6 va don dieu khien moc 9. Khi tha cap roi xuong doc theo hai coc dan, moc 6 tu dong moc vao chot 5, sau do nang ca xa ngang va xylanh den vi tri tren cung. Giat don 9, chot 5 truot khoi moc 6, xylanh 10 roi tu do theo hai coc dan huong chup vao pittong 12 de dong coc va nen khong khi trong buong xylanh. Khi dat toi ap suat va nhiet do cao, dong thoi chot 11 danh vao don 14, dau duoc phun vao trong buong xy lanh duoi dang suong mu, gap khong khi o nhiet do va ap suat cao tu boc chay (no) sinh ra ap luc lon day tung xylanh len. Khi het da, xylanh - dau bua lai roi xuong tiep tuc nen khi, dong coc, no... Loai bua nay co nang luong tuong doi thap chi phu hop voi dat yeu.

c. Bua dong coc diesel ong dan (h.6-3b):

Gom co phan va dap la pittong - dau bua 22 truot trong xylanh dan huong 21. Phan be 17 nam trong xylanh co lo lom hinh ban cau. Pittong 22 lam nhiem vu dau bua, phia tren co bo phan boi tron tu dong, phia duoi co phan loi ra hinh cau tuong ung voi phan lom o be 17. Bua duoc dinh tam voi coc boi dinh vau 16. Khi khoi dong, cap 8 keo moc 20 dua dau bua

len cao, sau do tha cho pittong 22 roi tu do doc theo xylanh; pittong ep vao don bom 23, mo bom 14 lam dau tu binh dau 19 duoc bom vao xylanh hoa tron voi khong khi chay vao phan lom cua be 17.

Pittong tiep tuc di xuong che kin lo thoat khi 18 lam khong khi bi nen toi ap suat va nhiet do cao. Khi phan lom cua he bua 17 thi thuc hien dong coc dong thoi lam cho dau ban tung toe duoi dang suong mu gap khong khi co ap suat va nhiet do cao no tu boc chay day tung pittong len. Khi chaytrong xylanh duoc thoat ra ngoai qua lo 18. Khi pittong het da thi no tu roi xuong va tiep tuc mot chu ky lam viec moi, moi lan pittong roi la mot lan coc duoc dong sau vao trong nen dat. Qua trinh lam viec cua bua diesel loai ong dan duoc the hien tren hinh 6-4.

Khi dung cac loai bua va dap de dong coc can phai tinh chieu cao roi phu hop voi vat lieu va tiet dien coc:

, m

Trong do:  - Cuong do cua coc, N/m2;

F - Tiet dien coc, m2;

l - Chieu dai coc, m;

E - Modun bien dang cua coc, N/m2;

Q - Trong luong dau bua, N;

Nhung chieu cao cua bua duoc chon theo quan he: H  0,8 Hmax

4. Bua rung

Nguyen ly lam viec cua bua rung la loi dung luc gay rung do truc lech tam hay dia lech tam sinh ra de truyen vao coc. Trong qua trinh dong coc, coc luon rung dong voi mot tan so nao do, vi the ma giam duoc luc ma sat giua coc voi dat. Mat khac do trong luong ban than cua coc va bua lam coc lun sau vao long dat. Bua rung duoc su dung thich hop nhat o moi truong dat cat, pha cat hoac dat it dinh. May bua loai nay co uu diem la cau tao don gian, de di chuyen, trong luong nhe, coc khong bi vo khi dong, khong can gia dong coc, gia thanh dong nho (bang 1/21/3 lan so voi cac loai khac). Ben canh uu diem cung co mot so nhuoc diem nhu khong dong duoc coc theo phuong ngang hoac phuong xien qua lon, khi dat co do dinh lon dong it hieu qua.

Bua rung co cac loai noi cung (tan so thap 300500lan/ph), noi mem (tan so cao 7001500 lan) va loai va rung; So do nguyen li the hien tren hinh 6-5.

Bua rung noi cung (hinh 6-5a) co cau tao don gian. Bo gay rung thuong dung cac dia lech tam 2 lap tren truc quay de tao ra luc rung dong. Co the dieu chinh luc gay rung bang cach dieu chinh vi tri cua dia lech tam va tan so

quay. Tuy theo dieu kien dia chat ma chon che do lam viec toi uu. Khi quay theo cac chieu khac nhau cac dia lech tam se gay ra luc rung.

, N

Trong do: G - trong luong khoi lech tam, N;

g - gia toc trong truong g= 9,81m/s2;

 - Van toc goc truc lap dia lech tam s-1 , ( = .n/30);

n = So vong quay trong mot phut cua truc;

e - do lech tam, m.

o loai noi cung dong co duoc noi cung voi vo.

Bua rung noi mem (hinh 6-5b) khac voi loai noi cung la dong co duoc noi voi bo gay rung qua lo xo 5. Vi vay trong qua trinh lam viec dong co giam duoc anh huong co hai do bo gay rung gay ra, tuoi tho cua dong co duoc nang cao.

Bua va rung (hinh 6-5c) khacvoi hai loai tren la bo phan gay rung 2 lap truc tiep tren hai dau truc cua dong co. Khi truc dong co quay cuc lech tam cung quay tao ra luc gay rung; dong thoi tao ra va dap giua be 3 va be 4 va truyen cho dau coc de dong coc. Co the thay doi luc va dap bang cach thay doi khe ho giua be 3 va be 4.