Transmission and AMT vs CVT : AutoGyan

This is the third edition of our weekly AutoGyan. Through this initiative we aim to explain mechanisms of your vehicles as simply as we can. This week our topic is Automated Manual Transmission vs Continuously Variable Transmission or AMT vs CVT. Both the transmission options will be explained in detail along with advantages and disadvantages. For understanding these transmissions, it is very important to know the basics of a transmission.

The need of Transmission :

Have you ever wondered why do we need transmission or gears in our cars? Well, transmission transfers the power from the engine to the wheels. But why transmission to do that? Because we cannot create a direct contact between the engine and the wheels as both of them rotate at different speeds. The engine rotates a lot faster than the wheels. For instance, a petrol motor rotates between 600 to 6,000 RPM whereas the wheels rotate zero to 1,500 times a minute. So, the transmission limits the speed of the engine to match that of the wheels.

Also read – Electronic Stability Program (ESC) : AutoGyan

Why different gears ratios?

Now a question comes about the need of multiple gears. Imagine having just one gear, which limits the engine to get to a top speed of 100 km/hr. A normal Manual car gets to 100 km/hr in the third gear. So, our car will only have one gear and that will be the third. Now, have you ever tried to start a car from a halt while you are in the third gear? It is not so convenient, right?. 😉 If you somehow get the car going and reach 100 km/hr, the car engine will be running at the maximum RPM which is again not so pleasant. Also for different road conditions like climbing hills or in ghats sections, car needs more torque to have smooth drive. The basic fundamental of transmission is to match the power and torque generated by the engine in a very efficient way to have comfortable driving in all conditions without negotiating fuel economy.

What does the Clutch do?

The automatic transmissions are preferred for a simple reason and that is the absence of a clutch. But, what does the clutch do? The clutch is the link between the engine and transmission. When we press the clutch pedal, it disengages the transmission from the engine. So, now the engine is running on its own with no interference from the transmission. The transmission too is free and hence another gear can be engaged. Once the gear is changed, we leave the clutch pedal. This again creates a contact with the engine and the engine speed is limited according to the new gear.

Automated Manual Transmission :

AMT unit in Celerio

AMT unit in Celerio

The Automated Manual Transmission or the AMT is very popular now a days. The AMT is very similar to the manual transmission. There is just one simple difference between AMT and Manual transmission and that is we don’t have to use the clutch manually. The clutch is operated by some hydraulics and computer. It uses a computer to disengage the clutch and change gears at optimum RPM. Yes, the working of an AMT is this simple!

This facilitates quick gearshifts with maximum fuel efficiency. The prime advantage of the AMT is the hassle free drive or the no-clutch drive. But, the rides on an AMT car can get jerky at times. This problem arises as the throttle is used even when changing gears. However, this problem can be partially avoided by the use of semi-auto mode, which allows the driver to change gears with just a push to the gear knob or paddles behind the steering while cutting the throttle. In India the first car to offer AMT is Maruti Suzuki Celerio and then everyone else followed the trend which includes Tata Nano and Bolt and Zest too.

Continuously Variable Transmission :

CVT gear stick called X-Tronic in Nissan

CVT gear stick called X-Tronic in Nissan

The Continuously Variable Transmission or the CVT in simple words does not have gears at all! Or we can say that it has infinite gear ratios between the maximum and minimum ratios. This one is a bit difficult to understand. Basically, the CVT has two pulleys connected via a ‘V’ shaped belt. Now, one pulley is driven by the engine and the other one is connected to the wheels. To provide the different gear ratios, the transmission changes the ride height of the belt thereby changing the relation between both the pulley. The CVT can have a clutch and even a torque converter to replace the clutch.

So, the CVT is the most efficient transmission as it makes the engine work in the optimum RPM range. It is a delight for normal drivers due to the unmatched efficiency. However, enthusiasts never prefer CVT’s as putting some extra torque may not make a difference in this case until you step on the gas. It performs very well on tracks and at high speeds, but it equally punishes in heavy traffic conditions. To add on about CVT’s efficient than the regular AMT or Manual transmission, Nissan Micra CVT has ARAI certified fuel efficiency of 19.43kmpl and 18.44 kmpl for manual transmission.

Hope you found the article informative. Don’t forget to share it with your friends. Happy Motoring! 🙂

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