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16-03-2010, 06:59 AM
Post: #1
automatic transmission in cars full report

.doc  AUTOMATIC TRANSMISSION IN CARS.doc (Size: 1.21 MB / Downloads: 1690)

AUTOMATIC TRANSMISSION IN CARS
ABSTRACT
The modern automatic transmission is by far, the most complicated mechanical component in today's automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem. This article will help you understand the basic of the transmission, about automatic transmission, differences between manual and automatic transmission, the concepts behind what goes on inside these technological marvels and what goes into repairing them when they fail
What is a transmission
The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the engine within that range. It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be going in excess of 70 MPH. In addition to the various forward gears, a transmission also has a neutral position, which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing you to back up.


.
Presented BY:-
ARUN K.M. PRADEEP S.V.
VI SEMISTER
DEPARTMENT OF MECHANICAL ENGINEERING
BAPUJI INSTITUTE OF ENGINEERING AND TECHNOLOGY
DAVANAGERE-577004


INTRODUCTION
One of the biggest things that has always separated drivers is whether they prefer an automatic transmission (sometimes known as a "slushbox", because of the characteristic "slushy" feel it creates when shifting between gears) or a standard transmission (often called, for more obvious reasons, a "stick shift").
There are a number of benefits to the standard transmission, but the prevailing reason that most people get them is because they prefer them. Car enthusiasts enjoy the feel of being able to control what gear they're in; it makes them feel closer to the vehicle. People who just want to drive and don't care much about how the car works usually prefer the automatic trannie.
If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and manual transmission:
There is no clutch pedal in an automatic transmission car
There is no gear shift in an automatic transmission car. Once you put the transmission into Drive, everything else is automatic!
The need to shift from manual to automatic transmission
The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission. Driving a manual transmission is especially painful in stop-and-go traffic, where you constantly have to change your gear state. You might also make the case that having to concentrate on shifting your transmission takes some of your attention away from the actual driving, which is dangerous, because you might be concentrating on your tachometer or your gearshift when you really should be focusing on the traffic. An automatic transmission bypasses these problems entirely.
COMPONENTS OF AUTOMATIC TRANSMISSION
When you take apart and look inside an automatic transmission, you find a huge assortment of parts in a fairly small space. Among other things, you see:
Planetary gear sets
The automatic system for current automobiles uses a planetary gear set instead of the traditional manual transmission gear set. The planetary gear set contains four parts: sun gear, planet gears, planet carrier, and ring gear (see Figure 1.) Based on this planetary set design, sun gear, planet carrier, and ring gear spin centrifugally. By locking one of them, the planetary set can generate three different gear ratios, including one reverse gear, without engaging and disengaging the gear set.
Normally an automatic transmission system has two planetary gear sets with different sizes of sun gears with their planet gears inter-meshed (see Figure 2.) Only one planet carrier is used to connect both sets of planet gears. This is called a compound planetary gear set. This design can generate four different gear ratios and one reverse gear.

Figure 1 : Planetary Gear Set Figure 2 : Compound Planetary Gear set
Figure 3 : planetary Gear sets with Band and Clutch
Hydraulic System
It uses a special transmission fluid sent under pressure by an Oil Pump through the Valve Body to control the Clutches and the Bands in order to control the planetary gear sets. Both the band and clutch piston are pressurized by the hydraulic system. The part connecting the band or clutches to the hydraulic system is called the shift valve, while the one connecting the hydraulic system to the output shaft is called the governor (see Figure 4). The governor is a centrifugal sensor with a spring loaded valve. The faster the governor spins, the more the valve opens. The more the valve opens, the more the fluid goes through and the higher the pressure applied on the shift valve. Therefore, each band and clutch can be pushed to lock the gear based on a specific spin speed detected by the governor from the output shaft. To make the hydraulic system work efficiently, a complex maze of passages was designed to replace a large number of tubes (see Figure 5).
Figure 4 Governor
Figure 5 Hydraulic System with maze
¢
¢
Figure 4 :Governor Figure 5 :Hydraulic System with Maze structure

The Torque Converter
Unlike a manual transmission system, automatic transmission doesnâ„¢t use a clutch to disconnect power from the engine temporarily when shifting gears. Instead, a device called a torque converter was invented to prevent power from being temporarily disconnected from the engine and also to prevent the vehicle from stalling when the transmission is in gear. Consider two fans facing each other: when one of them is turned on and starts spinning, the other one will also start spinning at a lower speed (see Figure 6). Thatâ„¢s because the first fan moves the air to drive the second fan to spin. This is the same idea as the torque converter of an automatic transmission system, except that it uses fluid instead of air as the transportation media.
A torque converter consists of four parts, a pump (impeller), turbine, stator, and transmission fluid (Figure7). The pump is connected to the engine and transfers engine power to the transmission fluid. The fluid causes the turbine, which is connected to the input shaft, to spin. The stator is used to redirect fluid returning from the turbine before it hits the pump, again to increase the efficiency. In this design, even when the vehicle is in gear but not moving (the turbine is forced to stop), the pump can still keep spinning without causing the engine to stall. When the vehicle speed is slow, the turbine is always spinning more slowly than the pump. However, when the vehicle moves at high speed, the turbine can spin at almost the same speed as the pump. Therefore, for modern cars, a lock up will occur between pump and turbine when the vehicle is at high speed in fourth gear, which makes the torque converter work more efficiently.
F
Figure 6 Figure 7: The Structure of a Torque Converter.
Tiptronic transmission is a special type of automatic transmission with a computer controlled automatic shift. The driver can switch the transmission to manual mode, which lets the driver to shift the gear at his wish sequentially up (+) or down (-) (see Figure 8) without disengaging the clutch. This works just like a manual transmission; however, it still uses a torque converter to transfer power from the engine. Unfortunately, this is less efficient than a manual transmission.
Figure 8 : Tiptronic transmission.
Spotting problems before they get worse
Watch for leaks or stains under the car.
Check fluid for color and odor.
Be sensitive to new noises, vibrations and shift behavior.
Precautions and Maintenance
Transmission fluid should be changed periodically.
According to ËœB & Mâ„¢, the optimum operating temperature for automatic transmission fluid is 170 degrees. For every 10 degree increase in operating temperature, the useable life of the fluid is reduced by half.
Advantages of automatic transmission
It's a lot less work because you don't have to worry about juggling the gearshift with the clutch.
You don't need to worry about stripping your gears.
Car will never stall during gear shifting.
Limitations of automatic transmission
Indirect contact of the torque converter causes the power loss during transmission.
The Ëœkillerâ„¢ of automatic transmissions is heat. Excessive heat causes the fluid to lose its ability to lubricate, which leads to higher internal-component friction, all resulting in rapid wear-and-tear and premature transmission failure.
Complicated planetary structure makes the transmission heavy and easily broken.
Conclusion
Being able to drive a stick-shift means more than just understanding your gears, however. That's because to shift gears, you usually don't just move the shift lever and be done with it. (You can do this sometimes, but it's not recommended in day-to-day driving, and we'll get to it later.) Instead, you have to press the clutch pedal while you shift. . Keeping the transmission and its fluid cool, and in the correct operating-temperature range is crucial for long life.
References
http://www.scribd.com
http://www.sciencedirect.com

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08-10-2010, 11:07 AM
Post: #2
RE: automatic transmission in cars full report

.pdf  AT21.pdf (Size: 1.68 MB / Downloads: 787)

automatic transmission basic



if u want more about the information please kinndly visit the above link:=\
10-01-2011, 10:06 PM
Post: #3
RE: automatic transmission in cars full report
Hi,
the full report and the presentation of the topic is available at:
http://www.seminarprojects.com/Thread-au...9#pid33589
23-04-2011, 11:36 AM
Post: #4
RE: automatic transmission in cars full report

.doc  VIJAY (1)by 3.doc (Size: 613.5 KB / Downloads: 212)
INTRODUCTION :-
Automatic transmission system shifts the gears without assistance from the driver. They start the car moving in first and then shift into higher gears as the car speed increases and engine load decreases. The shifts are produced by hydraulic pressure acting through the transmission fluid.
The control system takes into account the engine load and in general produce changes up when the engine load is light and changes down when the engine load is heavy.
The main components that make up an automatic transmission include:
• The Torque Converter : This acts like a clutch to allow the vehicle to come to a stop in gear while the engine is still running.
• Planetary Gear Sets : They are the mechanical systems that provide the various forward gear ratios as well as reverse.
• The Hydraulic System : It uses a special transmission fluid sent under pressure to control the transmission
Automatic Transmission System
The modern automatic transmission is by far, the most complicated mechanical component in today's automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem.
This is broken down into five sections:
• Transmission?: It breaks down in the simplest terms what the purpose of a transmission is.
• Transmission Components : It describes the general principals behind each system in simple terms to help you understand how an automatic transmission works.
• Spotting problems before they get worse : It shows what to look for to prevent a minor problem from becoming major.
• Maintenance: It talks about preventative maintenance that everyone should know about.
• Transmission repairs : It describes the types of repairs that are typically performed on transmissions from minor adjustments to complete overhauls.
Transmission:-
The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the engine within that range. It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be going in excess of 70 MPH. In addition to the various forward gears, a transmission also has a neutral position which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing you to back up. Finally, there is the Park position. In this position, a latch mechanism (not unlike a deadbolt lock on a door) is inserted into a slot in the output shaft to lock the drive wheels and keep them from turning, thereby preventing the vehicle from rolling.
There are two basic types of automatic transmissions based on whether the vehicle is rear wheel drive or front wheel drive.
On a Rear wheel drive car, the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position. A drive shaft connects the rear of the transmission to the final drive which is located in the rear axle and is used to send power to the rear wheels. Power flow on this system is simple and straight forward going from the engine, through the torque converter, then through the transmission and drive shaft until it reaches the final drive where it is split and sent to the two rear wheels.
On a Front wheel drive car, the transmission is usually combined with the final drive to form what is called a transaxle. The engine on a front wheel drive car is usually mounted sideways in the car with the transaxle tucked under it on the side of the engine facing the rear of the car. Front axles are connected directly to the transaxle and provide power to the front wheels. In this example, power flows from the engine, through the torque converter to a large chain that sends the power through a 180 degree turn to the transmission that is along side the engine. From there, the power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles. There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of sideways and there are other systems that drive all four wheels but the two systems described here are by far the most popular. A much less popular rear drive arrangement has the transmission mounted directly to the final drive at the rear and is connected by a drive shaft to the torque converter which is still mounted on the engine. This system is found on the new Corvette and is used in order to balance the weight evenly between the front and rear wheels for improved performance and handling. Another rear drive system mounts everything, the engine, transmission and final drive in the rear. This rear engine arrangement is popular on the Porsche.
Transmission Components :-
The modern automatic transmission consists of many components and systems that are designed to work together in a symphony of clever mechanical, hydraulic and electrical technology that hasevolved over the years into what many mechanically inclined individuals consider to be an art form.
The main components that make up an automatic transmission include:
• Planetary Gear Sets which are the mechanical systems that provides the various forward gear ratios as well as reverse.
• The Hydraulic System which uses a special transmission fluid sent under pressure by an Oil Pump through the Valve Body to control the Clutches and the Bands in order to control the planetary gear sets.
• Seals and Gaskets are used to keep the oil where it is supposed to be and prevent it from leaking out.
• The Torque Converter which acts like a clutch to allow the vehicle to come to a stop in gear while the engine is still running.
• The Governor and the Modulator or Throttle Cable that monitor speed and throttle position in order to determine when to shift.
• On newer vehicles, shift points are controlled by Computer which directs electrical solenoids to shift oil flow to the appropriate component at the right instant.
Planetary Gear Sets:-
Automatic transmissions contain many gears in various combinations. In a manual transmission, gears slide along shafts as you move the shift lever from one position to another, engaging various sized gears as required in order to provide the correct gear ratio. In an automatic transmission, however, the gears are never physically moved and are always engaged to the same gears. This is accomplished through the use of planetary gear sets.
The basic planetary gear set consists of a sun gear, a ring gear and two or more planet gears, all remaining in constant mesh. The planet gears are connected to each other through a common carrier which allows the gears to spin on shafts called "pinions" which are attached to the carrier. One example of a way that this system can be used is by connecting the ring gear to the input shaft coming from the engine, connecting the planet carrier to the output shaft, and locking the sun gear so that it can't move. In this scenario, when we turn the ring gear, the planets will "walk" along the sun gear (which is held stationary) causing the planet carrier to turn the output shaft in the same direction as the input shaft but at a slower speed causing gear reduction (similar to a car in first gear). If we unlock the sun gear and lock any two elements together, this will cause all three elements to turn at the same speed so that the output shaft will turn at the same rate of speed as the input shaft. This is like a car that is in third or high gear. Another way that we can use a Planetary gear set is by locking the planet carrier from moving, then applying power to the ring gear which will cause the sun gear to turn in the opposite direction giving us reverse gear.
25-04-2011, 12:40 PM
Post: #5
RE: automatic transmission in cars full report
Submitted by:
VIJAY KUMAR


.ppt  Automatic Transmission System ppt.ppt (Size: 1.32 MB / Downloads: 429)
INTRODUCTION
The modern automatic transmission is by far, the most complicated mechanical component in today’s automobile. 
Automatic transmissions contain Mechanical systems, Hydraulic systems, Electrical systems and Computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem.
WHAT IS TRANSMISSION ?
The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels
Purpose of the transmission is to provide high torque at the time of starting the engine, hill climbing , accelerating and pulling a road.
TYPES OF AUTOMATIC TRANSMISSION
Rear wheel drive
Front wheel drive
REAR WHEEL DRIVE
The transmission is usually mounted to the back of the engine.
Power flow on this system is simple and straight forward going from the engine, through the torque converter, then through the transmission and drive shaft until it reaches the final drive where it is split and sent to the two rear wheels.
Example of rear wheel – Alpha Romeo Alfeta in early 70’s
REAR WHEEL DRIVE
FRONT WHEEL DRIVE

On a front wheel drive car, the transmission is usually combined with the final drive to form what is called a transaxle.
Transaxle is a device set up in the transmission gear box, clutch, final drive, combined into a single unit.
. Front-wheel-drive layouts are those in which the front wheels of the vehicle are driven. The most popular layout used in cars today is the front-engine, front-wheel drive, with the engine in front of the front axle, driving the front wheels.
This layout is typically chosen for its compact packaging. 
Front axles are connected directly to the transaxle and provide power to the front wheels. 
FRONT WHEEL DRIVE
TRANSMISSION COMPONENTS

Planetary Gear Sets
Hydraulic System
Oil Pump
Valve Body
Clutches
Band
Seals and Gaskets
Torque Converter
Governor
Computer Controls
PLANETARY GEAR SETS
SIDE VIEW
CLUTCH PACKS
BANDS
A band is a steel strap with friction material bonded to the inside surface. 
One end of the band is anchored against the transmission case while the other end is connected to a servo.
TORQUE CONVERTER
HYDRAULIC SYSTEM

The Hydraulic system is a 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
COMPUTER CONTROLS
The computer uses sensors on the engine and  transmission to detect such things as throttle position, vehicle speed, engine speed, engine load, brake pedal position, etc. to control exact shift points as well as how soft or firm the shift should be.  Once the computer receives this information, it then sends signals to a solenoid pack inside the transmission
NON-COMPUTERIZED TRANSMISSIONS
Governor
Vacuum Modulator
Throttle Cable
Seals and Gaskets
SPOTTING PROBLEMS BEFORE THEY GET WORSE
Watch for leaks or stains under the car.
Check fluid for color and odor.
Be sensitive to new noises, vibrations and shift behavior.
TRANSMISSION REPAIRS
Adjustments and In-Car Repairs
Reseal job
Replace accessible parts
Complete Overhaul
Replacement unit vs. overhaul existing unit
Conclusion
Being able to drive a stick-shift means more than just understanding your gears, however. That's because to shift gears, you usually don't just move the shift lever and be done with it. (You can do this sometimes, but it's not recommended in day-to-day driving, and we'll get to it later.) Instead, you have to press the clutch pedal while you shift. . Keeping the transmission and its fluid cool, and in the correct operating-temperature range is crucial for long life.
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