How Automatic Transmission Works in Hindi | Automatic Transmission System कैसे काम करता है ?

An automatic transmission(AT) is a transmission system in which selection of appropriate gear ratio need by the vehicle is an automatic process operated by the accelerator and brake pedal. The lay shaft, main shaft and clutch shaft with parallel gear train arrangement is replaced with an epicyclic or sun and planetary gear train arrangement and also the manual clutch from manual power train is replaced with hydro-coupled clutch or torque converter which in turn removes the clutch pedal from the vehicle.

The automatic transmission usually comes with p-parking, n-neutral, r-reverse, d-drive, s-speed,mode,Each mode is having infinite torque and speed ratios required by vehicle.

Main Parts of Fully Automatic Transmission:

1. Epicyclic gear train- It is also known as the sun and planetary gear arrangement,The parallel shaft gear train from manual transmission is replaced with more compact epicyclic gear train in automatic transmission that consists of –

1. Annular or ring gear- A ring type gear with inner angular cut teethes and is placed at the outermost position in epicyclic gearbox, inner teethes of annular gear is meshed with the the planet gears at the outer point.

2. Sun gear- It is the gear having angular teethes which are in constant mesh with the planet gears at the inner point, The sun gear is connected to the torque convertor shaft.

3. Planet gears – Small pinion gears which not only rotates about their own axis but also revolve around the sun gear.

4. Planet carrier- It is the carrier over which the axis of the planet gears is mounted and is connected with the final output shaft.

5. Brake or clutch bands- Fixing mechanism used to fix any one from the above in order to attain required gear ratio.

2. Hydraulic system- It is the system of automatic transmission that contains oil pumps, governor and hydraulic valves that controls the brake or clutch band by sending pressurised fluid through the valve body in order to control the epicyclic gearbox, The band are connected to the hydraulic system through the shift valve and the output shaft is connected to the hydraulic system through the governor used.

3. Torque convertor– The clutch from the manual transmission is replaced with the torque convertor that uses pressurised fluid for the engagement and disengagement of the engine output, The torque convertor is operated by the accelerator pedal.

The torque convertor has 3 main parts –

1. Impeller – It is the part of torque convertor that is connected with the engine output shaft and causes the pressurised fluid to flow inside the torque convertor when the engine starts.

Impeller has angular cut vanes that causes rotation of the fluid.

2. Turbine – It is the part of torque convertor that is connected to the transmission input shaft and transmits engine’s power to the transmission by the help of rotating pressurised fluid.

Turbine has opposite cut angular vanes that catches the fluid sent by the impeller which in turn causes rotation of the transmission input shaft.

3. Stator – It is the intermediate device having angular cut vanes used to direct the fluid from impeller to the the turbine.

Working :

The working of automatic transmission is totally different from the manual transmission as no clutch pedal and no continuous shifting of gears is required in this transmission system.

Drive mode:

It is the forward drive mode which consists the different gear ratios from high torque to medium speed, When this mode is selected and if the vehicle is in its steady state then by sensing the accelerator pedal by hydraulic system or electronic control unit the input is sent to epicyclic gearbox which in turn locks the annular gear with the help of bands and high torque or first gear ratios are obtained.

When the vehicle starts moving and attaining the accelerator pedal input from the hydraulic system or electronic control device is again sent to the epicyclic gearbox which in turn activates the bands which in turn locks the sun gear and medium speed or second gear ratios are obtained.

Reverse mode:

When reverse mode is selected the accelerator pedal input is sent to the epicyclic gearbox by hydraulic system or ecu which in turn activates the bands and the bands locks the planet gear carrier, Which reverses the direction of the output shaft which in turn reverse the direction of the vehicle.

Parking mode:

When this mode is selected the the latch mechanism locks the drive wheel which in turn prevents the vehicle from moving.

Neutral mode:

When neutral mode is selected the turbine shaft or transmission input shaft is disconnected from the engine output or impeller shaft and the neutral gear is achieved.

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