AUTOMATIC GEAR TRANSMISSION

By :

Rohit.S.Kumar (14MD16)

CONTENTS

• Introduction• Classification• Automatic transmission using planetary gears • Continuously variable transmission• Conclusion• References

INTRODUCTION

• 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.

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

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 valvesOil 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.

CONCLUSION

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

REFERENCESwww.drivetrain.com www.sciencedirect.comwww.scribd.cowww.youtube.comhttp://www.gears-gearbox.com/semi-automatic transmission.html Google , Wikipedia.http://auto.howstuffworks.com