HỘP SỐ TỰ ĐỘNG (Automatic transmission)

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

AUTOMATIC GEAR

TRANSMISSION

By :

Rohit.S.Kumar (14MD16)

• Introduction

• Classification

• Automatic transmission using planetary gears

• Continuously variable transmission

• Conclusion

• References

• Device which changes gear ratios automatically

• Deliver maximum efficiency

• Easier to drive because they do 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

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

Input Output Stationary Calculation Gear Ratio

A Sun (S) Planet Carrier (C) Ring (R) 1 + R/S 3.4:1

B Planet Carrier (C) Ring (R) Sun (S) 1 / (1 + S/R) 0.71:1

C Sun (S) Ring (R) Planet Carrier (C) -R/S -2.4:1

• 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

TORQUE CONVERTOR

• 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 3 main

members:

a Pump/impeller: It is the driving member and rotates

with the engine

b Turbine: The impeller vanes pick up fluid in the

converter housing and direct it toward the turbine

c 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 1 to 2 shift valves determines

when to shift from first to second

gear

• 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

Continuously variable 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

Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony

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