Automatic Transmission (Gearbox) | The Ultimate Guide

Manual transmission 

It is the primary type of transmission that comes as s standard in most Indian cars (non-luxury) under the 50 lakhs segment. The standard manual transmission also known as a stick shifter is either a 5-speed or 6-speed. Here 5 & 6 denote the number of forward-speed gears (apart from these there is also one reverse gear). These gears have to be engaged to transfer the power generated by the engine to the wheels. The gears are engaged by pressing the clutch pedal. The car moves from a standstill in 1st gear and as the speed increases higher gears are selected. 

Now when driving in the city or on a long drive this frequent gear changing becomes cumbersome and irritating. So to solve this problem car manufacturers have introduced automatic transmissions.

Automatic Transmission

In an automatic transmission, there is no clutch pedal and the gearbox automatically selects the gear based on the speed. Although a gear stick is still provided which allows the driver to select reverse or bring the car in neutral. Apart from these most automatic transmissions also give the option of manual mode. In this driver can choose which gear the gearbox should be in. In the Indian car market, there are mainly four main types of automatic transmission offered in the mass market cars. These are-

1. AMT
2. CVT
3. DCT/DSG
4. Torque Converter

AMT

AMT or automated manual transmission (also known as Auto Gear Shift or AGS) is one of the simplest and cheapest available automatic transmissions in our market. In simple words, you take a conventional gearbox and add to it hydraulic or electronically controlled actuators which take care of the whole gear-shifting process. Due to its simple construction, the AMT are cheap and very close to a manual transmission or even better when it comes to fuel efficiency.

That said, AMT is meant for sedate driving as there is a slight delay between the gearbox perceiving throttle (or accelerator or gas pedal) input and selecting the right gear. Not only this, every gearshift is felt by the driver and there is a head nod whenever a gearshift happens.

CVT

CVT or continuously variable transmission is an outlier here as it doesn't have any gears. Instead, it uses a cone-shaped pulley with a band that can travel between the two ends of the pulley. In this way, the system can theoretically create an infinite gear ratio to suit the power requirement. The upside of this is that the CVT provides smooth and seamless gearshifts. While the downside is that it is not meant for spirited driving. Also, overtakes need to be planned in advance. The culprit behind all this is the rubber band effect. 

Consider this, you want to overtake and smash the accelerator pedal, and the engine rpm goes up but the same doesn't translate into more speed. Instead, you hear loud engine noise ( due to it running at high rpm). This phenomenon is known as the rubber band effect. Modern-day CVTs have come a long way and the rubber band effect is far less pronounced in today's CVT-equipped cars. But the bottom line is that it's there and though less pronounced it still sucks. So if you want a smooth driving experience, better fuel economy, and a reliable gearbox only then CVT should be on top of your consideration list. 

DCT or DSG 

DCT or DSG also known as dual-clutch transmission or direct shift gearbox respectively both work on the same principle. Unlike a normal gearbox with a single clutch, a DCT has two clutches, one for odd gears (1,3,5,7) and one for even gears (2,4,6). That's how it also gets its name. The rationale behind this arrangement is to reduce gearshift time and provide quick performance. As for its working, let's say you have 1st gear engaged, the 2nd gear is already ready and as you increase speed it gets engaged. While in the normal gearbox, the clutch is first engaged and the gear is selected and the same clutch is then released to move to a higher gear. Here the same thing happens but the odd gear clutch disengages while the even gear clutch engages both at the same time. As a result, the gearshifts are fast and very hard to notice.

Coming to its types DCT is available in two forms in India, a dry clutch and a wet clutch type. The former is used in cars with smaller engines (generally less than 2.0-litre or 2000 cc) and producing lesser torque. While the latter is used in high torque-producing engines. That said, both types offer good fuel economy and imperceptible gearshifts. Its cons include higher repair costs and poor reliability. Along with that in bumper-to-bumper traffic gearshifts are jerky and chances of gearbox failure are higher. The latter is due to clutch heating which is generally observed in dry-clutch type DCT.

Torque Converter

The last one on our list is probably the oldest but also one of the most reliable forms of automatic gearbox available right now. This type of gearbox substitutes clutches with two sets of blades having opposite faces. Impeller faces the engine while the turbine faces the transmission side. A working fluid flows from the engine side to the transmission side transferring power from the engine to the wheels. There is also another component stator which moves the fluid from the turbine towards the impeller allowing seamless torque transfer. Now due to the fluid, the gearshift is smooth and seamless but results in some torque loss. Therefore these gearboxes offer less efficiency than manual ones. So, to negate this torque loss companies increase the torque output of their model with the above gearbox. 

Bonus

iMT

 

Simply put it is a clutchless manual transmission. It was recently introduced in India by Hyundai. Here the gear selector has inbuilt actuators/sensors and hydraulics. These work in conjunction to automatically engage the clutch when one moves the gear selector. With the elimination of the clutch and small premium over the manual, the iMT is a choice for most people. That said, the target customer for iMT includes folks who like the old-school charm of stick shifting without the hassle of using a clutch.

We hope this post was able to provide better clarity on the topic. Till then, if you liked what you read then don't forget to share this post with your family and friends. And if you have any feedback or suggestion you can write us at contact@anantraj.co.in.