Ma luc thuoc do cong suat dong co

Thứ ba, 28 Tháng ba 2006, 09:02 GMT+7

Trong hang loat thong so, cong suat duoc chu y nhieu nhat boi no dac trung do nhanh cua chiec xe. Co nhieu phuong phap xac dinh cong suat khac nhau nhung chung deu duoc ghi thanh ma luc de khach hang de hinh dung.

Cong suat thuong duoc cac nha san xuat ghi duoi dang ma luc nhung tren thuc te, khong phai ai cung tuong tan ve ma luc. Thuat ngu "ma luc" co ten tieng Anh “horse power” va Jame Watt la nguoi dau tien dua ra khai niem tren vao nam 1782. Luc dau, Jame Watt chua phan chia cac loai ma luc khac nhau nen sau do, cac nha khoa hoc dat ten cho cach goi cua ong la ma luc co hoc (mechanical horsepower). Mot ma luc co hoc co gia tri chinh xac 745,69987158227022 W, nghia la cong suat 1 bong dien 100 W se bang 0,13 ma luc.

De co hinh anh truc quan hon, ma luc co hoc duoc mo ta la cong ma mot chu ngua bo ra de keo 33.000 pound (1 pound = 454 gram) len 1 foot (30,48 cm) trong thoi gian 1 phut (minute).


Hinh mo ta ma luc. (Howstuffworks)
Hinh mo ta ma luc cua Jame Watt. (Howstuffworks)

Sau thoi diem Jame Watt dua ra dinh nghia ma luc, co hang loat don vi cong suat duoc sang tao de phu hop voi dieu kien tung nganh. Tinh den hien tai, co toi 4 loai ma luc khac nhau gom: Ma luc co hoc (trung voi dinh nghia cua Jame Watt), ma luc theo he met (metric horsepower), ma luc dien (electrical horsepower, su dung cho nganh dien) va ma luc noi hoi (boiler horsepower).

Doi voi nganh cong nghiep xe hoi, ma luc co hoc (mechanical horsepower) va ma luc theo he met la pho bien nhat. Ma luc theo he met khai sinh tai Duc trong the ky 19 va mo rong sang chau Au va chau A. Khi du nhap sang cac nuoc, ma luc he met lai duoc ky hieu khac nhau nhu: “PS” o Duc, “CV” o Phap, “PK” o Ha Lan. Ve co ban, cac don vi nay xap xi bang ma luc co hoc (vao khoang 98,6%) do chung duoc do bang cac don vi khac nhau.

Vi co su khac biet nen khi cac hang dua nhau san xuat dong co cong suat lon thi moi chuyen tro nen roi ram. Tham chi, cong suat dong co duoc nang len gap doi khi chuyen doi cac he do luong khac nhau. Vi du, Bugatti luon cho rang chiec sieu xe Veyron 16.4 co cong suat len toi 1.001 ma luc thi o bo kia Dai Tay Duong, cac ky su My khang khang cho rang no chi co 980 ma luc theo he SAE.


Dong co W16 cua Bugatti Veyron 16.4 (Seriouswheels)
Dong co W16 cua Bugatti Veyron 16.4 (Seriouswheels)

Cach xac dinh cong suat theo ma luc cung la cong viec phuc tap va ton kem. Cong suat dong co ma cac nha san xuat ghi trong bang thong so ky thuat xe la cong suat cuc dai, nghia la cong suat lon nhat ma chiec xe co the dat duoc tai vong tua nhat dinh. Duong cong bieu dien cong suat theo so vong tua may luon ton tai mot diem cuc dai, va gia tri cong suat tai diem do la cong suat toi da cua dong co. Cong suat the hien cho kha nang dat van toc toi da cua chiec xe nhung no khong dai dien cho kha nang tang toc. Vi vay, cong suat cao chua chac xe da “boc” ma con phu thuoc vao mo-men xoan va vong tua may.

Gan day, cac nha san xuat thuong ghi cong suat dong co theo chu viet tat la “hp”. Nhung thinh thoang, van co hang ghi “bhp” khien nhieu nguoi phan van. Thuat ngu “bhp” dung de chi gia tri cong suat xac dinh bang luc ke ham (brake horsepower). Luc ke ham duoc gan vao dau truc co, sau do, cac ky su se ham vong quay de do luc xoan cua truc co trong mot khoang thoi gian nhat dinh. Thu nguyen “bhp” van duoc dung rong rai tai Anh, nhung o Bac My thi cach tinh tong cong suat dong co bang ma luc (hp) cua SAE (Hiep hoi Ky su oto My) lai la cach tinh tieu chuan.

Truoc 1972, gia tri cong suat duoc da so cac hang chap nhan la "hp" theo tieu chuan SAE. The nhung, ngay cang co nhieu hang dua ra cach tinh khac nhau de phuc vu loi ich rieng. Co hang nang cao cong suat de "ninh" nguoi mua thich cong suat lon nhung co hang lai giam cong suat de tranh muc bao hiem cao. Giua cac cach do khac nhau cung khien nhieu nguoi ngac nhien. Vi du, chiec Chrysler 426 Hemi nam 1971 co cong suat 425 ma luc nhung khi do lai theo chuan moi chi con 375 ma luc.

Vi vay, cong suat ma nha san xuat dua ra chi la gia tri tham khao, con muon biet suc manh thuc su cua chiec xe, chi con cach lai thu.

Nguyen Nghia



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