Skip to main content

Automatic transmission


Automatic transmission
There are two types of automatic transmission (gear box), namely, semi-automatic transmission and transmission and fully automatic transmission. These are distinguished according to their effect on vehicle handling dynamics.
Semi-automatic transmissions are the gear boxes on which all operations normally performed by the driver when changing gear are carried out by electronically controlled actuator systems. This implies that a gear change always involves disengagement of the clutch and hence of the drive to the driving wheels. Semi-automatic transmissions are found on long distance haulage trucks, passenger coaches and more recently on small cars and sports cars.

Fully automatic transmissions (normally called automatic transmission) change gear under load. This means, the power continues to flow to the driving wheels even during a gear shift operation. In this system, the drive engagement and gear ratio selection operations are performed with no additional driver input.
The main components of the automatic transmission are as follows
(1) Hydrodynamic torque converter.
(2) A number of planetary gear sets located downstream the hydrodynamic torque converter.
(3) Hydraulically actuated multiplate clutches, plate or band brakes, assigned to the individual elements within the planetary gear sets.
(4) One way clutches with shift elements.
(5) Transmission control system.
(6) An engine driven hydraulic fluid pump.
Fully automatic transmissions are used in situation where disengagement of power transmission may cause a significant reduction in comfort (particularly in cars with powerful accelerations) or where power flow interruption cannot be accepted for reasons of vehicle handling dynamics (ie. on-off road vehicles).
Mercedes Benz has introduced a seven speed automatic transmission unit, which would make future Mercedes models more economical apart from performance and driveability. This unit employs seven gear rations: These allow the automatic transmission to retain the small increases in engine speed which are important in ensuring optimum gear ratios, while at the same time offering a larger ratio spread between the lowest and highest gear.
An outstanding feature of the new seven speed transmission is the lockup clutch in the hydrodynamic torque converter, which largely eliminates slip between the pump and turbine rotor. Unlike conventional automatic transmissions where the torque converter lock-up is only possible is higher gears, the lock-up clutch in the new seven speed automatic transmission is active from the first gear up.
Electronic transmission control


Automatic gear boxes are controlled by electronically operated hydraulic sysems. Hydraulic system actuates the clutches. Electronic units do gear selection and adapt the hydraulic pressure in accordance with the torque flow.
Sensors detect the transmission output shaft speed, engine load and speed, gear selector lever position and positions of the program selector and kick down switch. The control signal processes this information according to a predefined program and uses the results to determine the control variables which are to be transmitted to the gear box.
Electrohydraulic converter elements form the link between the electronic and hydraulic circults. Solenoid valves activate and disengage the clutches; Pressure regulators control the pressure levels at the friction surfaces, which influence on shift quality.
Intelligent shift programs supplement the standard transmission control data wih additional parameters such as forward and lateral acceleration, and the speed with which the accelerator and brake pedals are pressed. This improves driveability.
Automatic transmission is found in the vehicles namely, Honda Accord (five speed), Mercedez Benz C200K (5 speed) and Mitsubishi Pajero (5 speed).
Labels:

Comments

Post a Comment

Popular posts from this blog

Competitions for mechanical engineers

There are various competitions in which you can participate during your graduation. SAE (society of automative engineers) organize three major events every year :  1. BAJA SAE- design and build an all terrain vehicle 2. SUPRA SAE- design and build a formula type race car 3. EffiCycle- design and build a hybrid cycle ASME  ( american society of mechanical engineers) organize human powered vehicle challenge HPVC. ISNE - It organizes go karting championship. If you have interest in automobiles then these competitions will definitely helps you to improve your skills.I was participated in SUPRA SAE (2016).It was a cool experience for me and helps me to improve my basic knowledge. Please like ,share and comment. Subscribe for more updates. Saurabh_savy 
Post a Comment
Read more

Turbines

You all know about turbines, here is a brief view of turbines. What actually turbine is :   A  turbine  is a turbo machine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. A windmill is the simplest kind of turbine: a machine designed to capture some of the  energy  from a moving fluid (a liquid or a gas) so it can be put to use. As the wind blows past a windmill's sails, they rotate, removing some of the wind's  kinetic energy  (energy of movement) and converting it into mechanical energy that turns heavy, rotating stones inside the mill. The faster the wind blows, the more energy it contains; the faster the sails spin, the more energy is supplied to the mill. Adding more sails to the windmill or changing their design so they catch the wind better can also help to capture more of the wind's energy....
Post a Comment
Read more

IC Engine

You all are aware from this word IC Engine, but still don't know what exactly it is. "An  internal combustion engine  (ICE) is a heat  engine  where the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit." The  internal combustion engine  is an engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself. This contrasts with external combustion engines, such as steam engines, which use the combustion process to heat ...
Post a Comment
Read more