21-07-2014, 01:25 PM
AUTOMATIC GEAR TRANSMISSION SYSTEM
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Introduction
Variety of controllers have been developed to improve driving as well as operating conditions of vehicles, such as to provide smooth throttle movement, zero steady state speed error, good speed tracking over rod slopes, and robustness to system variation and operating conditions. The complexity of the speed control algorithms has increased through the years to meet the Growing demands on more stringent automotive performance criteria. Only with the recent availability of inexpensive microprocessors more sophisticated control strategies have been implemented. The clutch-less automatic gear transmission system utilizes a gearbox that automatically changes the gear ratio, which allows the driver to simply select one gear to move or park the vehicle. There are two main types of transmission in cars: manual transmission and 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 but discrete gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission. Manual transmissions can be very tiring to drive in heavy stop and-go traffic. It has the problem of Worn or slipping clutches. In cold weather manual transmissions can become sluggish and hard to shift. Also in the beginning can be difficult to learn.
Types
There are two basic types of automatic transmissions based on whether the vehicle is rear wheel drive or front wheel drive
1. Rear wheel:-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
. Front wheel
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
Parts and operation
Torque converter: A type of fluid coupling, hydraulically connecting the engine to the transmission. It takes the place of a mechanical clutch, allowing the transmission to stay in gear and the engine to remain running while the vehicle is stationary, without stalling. A torque converter differs from a fluid coupling, in that it provides a variable amount of torque multiplication at low engine speeds, increasing breakaway acceleration. This is accomplished with a third member in the coupling assembly known as the stator, and by altering the shapes of the vanes inside the coupling in such a way as to curve the fluid's path into the stator. The stator captures the kinetic energy of the transmission fluid, in effect using the leftover force of it to enhance torque multiplication.
Valve body
hydraulic control center that receives pressurized fluid from the main pump operated by the fluid coupling/torque converter. The pressure coming from this pump is regulated and used to run a network of spring-loaded valves, check balls and servo pistons. The valves use the pump pressure and the pressure from a centrifugal governor on the output side (as well as hydraulic signals from the range selector valves and the throttle valve or modulator) to control which ratio is selected on the gearset; as the vehicle and engine change speed, the difference between the pressures changes, causing different sets of valves to open and close. The hydraulic pressure controlled by these valves drives the various clutch and brake band actuators, thereby controlling the operation of the planetary gearset to select the optimum gear ratio for the current operating conditions. However, in many modern automatic transmissions, the valves are controlled by electro-mechanical servos which are controlled by the electronic engine control unit (ECU) or a separate transmission control unit (TCU, also known as transmission control module (TCM).
Hydraulic & lubricating oil
called automatic transmission fluid (ATF), this component of the transmission provides lubrication, corrosion prevention, and a hydraulic medium to convey mechanical power (for the operation of the transmission). Primarily made from refined petroleum, and processed to provide properties that promote smooth power transmission and increase service life, the ATF is one of the few parts of the automatic transmission that needs routine service as the vehicle ages.
Conclusion
Being able to drive a stick-shift means more than just understanding your gears, however.thats because to shift gears, you usually don’t just move shift lever and be done with it instead you have to press clutch pedal. to eradicate the gear shifting complication this system is implemented in the cars to make and understanding driving easy