Nếu bạn đã từng điều khiển một chiếc ôtô số tự động, chắc chắn bạn sẽ nhận ra hai điều khác biệt rõ ràng giữa một chiếc xe số tự động và chiếc xe sử dụng số cơ khí gài bằng tay.Sự khác biệt giữa hộp số tự động và hộp số tayTrên hộp số tự động, bạn sẽ không tìm thấy bàn đạp ly hợp và cũng không có cần chuyển số (1, 2, 3, 4..). Bạn chỉ cần thao tác duy nhất là đưa cần chọn số vào nấc D (drive), sau đó mọi thứ đều là tự động.Cả hộp số tự động (với bộ biến mômen) và hộp số cơ khí (với ly hợp ma sát khô) đều có chức năng giống nhau, nhưng về nguyên lý làm việc lại hoàn toàn khác nhau. Và nếu tìm hiểu sâu, chúng ta sẽ thấy hộp số tự động thực hiện những điều vô cùng kinh ngạc.
AUTOMATIC GEAR TRANSMISSION By : Rohit.S.Kumar (14MD16) CONTENTS • • • • • • Introduction Classification Automatic transmission using planetary gea Continuously variable transmission Conclusion References INTRODUCTION • Device which changes gear ratios automatically • Deliver maximum efficiency • Easier to drive because they not have a clutch pedal or gearshift lever • Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony CLASSIFICATION Automatic transmissions using planetary gears Continuously variable transmission(cvt) AUTOMATIC TRANSMISSIONS USING PLANETARY GEARS Components : • Planetary Gear System • Torque Converter • Hydraulic System • Governor • Computer Controls HOW PLANETARY GEARS WORK • A gear set in which all of the gears are grouped around each other like the planets around the sun • The central gear is called sun gear In mesh with it is a circular grouping of gears, called planet gears, mounted on a rotating carrier • By holding any one of the three gear elements motionless, different ratios can be produced between the other two Planetary gear sets are common in automatic transmissions Input Output Stationary Calculation Gear Ratio A Sun (S) Planet Carrier (C) Ring (R) + R/S 3.4:1 B Planet Carrier (C) Ring (R) Sun (S) / (1 + S/R) 0.71:1 C Sun (S) Ring (R) Planet Carrier (C) -R/S -2.4:1 TORQUE CONVERTOR • • • a b c Takes the place of the clutch found on standard shift vehicles It uses oil or transmission fluid to transmit power Torque converter can be divided into main members: Pump/impeller: It is the driving member and rotates with the engine Turbine: The impeller vanes pick up fluid in the converter housing and direct it toward the turbine Stator: Fluid flow drives the turbine, and the turbine rotates and turns the transmission input shaft TORQUE CONVERTOR THE HYDRAULIC SYSTEM • Complex maze of passages and tubes that sends transmission fluid under pressure to all parts of the transmission and torque converter • It works with some components: • Oil pump • Valve body • Shift valves Oil pump: The oil is then sent, under pressure to the pressure regulator, the valve body and the rest of the components, as required VALVE BODY • The brain of the automatic transmission • Contains a maze of channels and passages that direct hydraulic fluid to the numerous valves • These valves activate the appropriate clutch pack or band servo to smoothly shift to the appropriate gear for each driving situation Shift Valves • Supply hydraulic pressure to the clutches and bands to engage each gear • Determines when to shift from one gear to the next • The to shift valves determines when to shift from first to second gear Continuously variable transmission • A continuosly variable transmission is a transmission which can change steplessly through an infinite number of effective gear ratios between maximum and minimum values • CVTs operate smoothly since there are no gear changes which cause sudden jerks • There are 25% fewer moving parts to a CVT transmission COMPUTER CONTROLLS • • • • Detect such things as throttle position, vehicle speed, engine speed, engine load etc To control exact shift points Downshift automatically when going downhill, to control speed and reduce wear on the brakes Up shift when braking on a slippery surface to reduce the braking torque applied by the engine Inhibit the up shift when going into a turn on a winding road CONCLUSION Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony REFERENCES www.drivetrain.com www.sciencedirect.com www.scribd.co www.youtube.com http://www.gears-gearbox.com/semi automatic transmission.html Google , Wikipedia http://auto.howstuffworks.com