Cars

AMT v/s CVT gear type vehicle : which is better?

The recent evolution in gear shifting technology has taken the automotive world by storm. Gone are the days when changing the gear while driving used to be a serious affair as with the advent of the revolutionary automatic engine transmission technology things are looking the other way and the sun is shinier than ever for the automobile industry.

The transmission in a car (or any motorized wheeled vehicle) is a system of gears that literally “transmits” the power generated by the engine to the wheels that drive the vehicle forward. Figuratively and often physically located between the engine and the wheels, it’s a sort of middleman in the process that makes a car move, and it’s a complicated piece of machinery.

Last updated on 31-12-2021

Types of transmissions

Manual Transmission:

 Also known as a “standard” transmission or “stick shift” as noted above. This type requires you to push down on a clutch pedal and then change gears by hand with a shifter in the center of the car. Most modern cars with a manual transmission have five speeds but some now have six, not counting reverse. In the early days of automobiles, all cars had manual transmissions. Overall, the design is fairly simple, efficient and it gives drivers very direct control over the car, something driving enthusiasts like. On the down side, it takes a hand off the steering wheel to operate and using one in stop-and-go traffic can be a mini-workout. It also takes skill and practice to proficiently master a manual transmission.

Automatic Transmission

Also known as an “Auto” , most cars sold today come with an automatic transmission. And it’s easy to see why: there’s really no beating the convenience. Just put it in drive put your foot on the accelerator and off you go while the transmission picks the right gear for you no matter what the situation. But automatic transmissions are extremely complicated (albeit proven) and can cost you some miles-per-gallon due to their extra weight and slightly increased inefficiency when compared to a manual.

In the past, most automatic transmissions had three gears (plus reverse) and if it had four gears, you had a real hot rod – or a luxury barge. Now, automatic transmissions have up to eight gears, either to placate performance drivers or to give cars optimal gearing for fuel efficiency – or both.

Differences

In a conventional manual gearbox, a set of cables or a link usually operates the gearbox in a two-step process. If the gearbox is cable operated like for example in a Tata Nano, two cables do the process of selection and engagement of the gears. The selection cable is actuated when one moves the gearshift lever from left to right or vice versa. The engagement cable is actuated when one actually shifts into one of the gates to engage a gear. Simplifying the shifter process, an Automatic Manual Transmission, or AMT essentially negates these mechanical linkages by replacing them with electromechanical individual devices that work off the engine management and transmission management control units.

AMT (Automated Manual Transmissions)

It is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press a clutch pedal at the same time as changing gears. It uses electronic sensors, pneumatics, processors and actuators to execute gear shifts on the command of the driver or by a computer. This removes the need for a clutch pedal which the driver otherwise needs to depress before making a gear change, since the clutch itself is actuated by electronic equipment which can synchronize the timing and torque required to make quick, smooth gear shifts. The system was designed by automobile manufacturers to provide a better driving experience through fast overtaking maneuvers on highways.

CVT (Continuous Variable Transmission)

 It is a transmission that can change seamlessly through an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios. The flexibility of a CVT allows the input shaft to maintain a constant angular velocity.

Alternatively, it can be used to maximize the performance of a vehicle by allowing the engine to turn at the RPM at which it produces peak power. This is typically higher than the RPM that achieves peak efficiency. Finally, a CVT does not strictly require the presence of a clutch. Nevertheless, in some vehicles a centrifugal clutch is added, to facilitate a “neutral” stance, which is useful when idling or manually reversing into a parking space.

Brownie points

While drawbacks in terms of responsiveness are usually noted by driving “enthusiasts”, Continuously Variable Transmissions have one key advantage over their automatic and manual counterparts. When driving up hills, where traditional automatics can struggle, a CVT can seamlessly provide power without shifting. Even-speed hill driving can prove to be a tough endeavor for novice manual transmission drivers. 

CVTs are incredibly efficient in terms of fuel mileage because they keep the engine within its most efficient operating range. A conventional automatic transmission is much less efficient because it uses a fluid coupling called a torque converter in place of a clutch to transfer power from the engine, which is always turning, to the gears.

This prevents the engine from stalling when the vehicle is stopped when in gear, but creates an inefficient connection between engine and drive wheels. This is addressed in the higher gears by “locking up” the converter and passing power directly from engine to drive system.

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Last modified: December 31, 2021
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