The purpose of a transmission is to transmit the power/torque produced by the engine to the wheels of the car. Essentially, the performance of a car depends on how efficient the transmission is. The more efficient the transmission, the less will be the losses in transmitting the power. Apart from the basic function, automatic transmissions also provide a world of convenience. Particularly in the city traffic, it helps a ton if you don’t have to work the clutch and gear repeatedly. That is why automatic transmissions are becoming more and more popular these days. Almost all the cars are getting an automatic transmission option. Let’s look at the working, advantages and disadvantages of each!
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Torque Converter
The torque converter is the most common automatic transmission in cars. It can be used in vehicles of every segment. One can find a torque converter on a regular car for daily use. It also finds application in some of the best performance cars in the world. Let’s understand the working of a torque converter.
Working
Torque Converter consists of an impeller, stator, turbine, working fluid inside a housing. The impeller is connected to the engine and the turbine is connected to the transmission (which is connected to the wheels). The stator is placed between the two. When the engine rotates, the impeller rotates with it. When a car is stationary, the turbine does not move with the impeller. When the car starts to accelerate, torque multiplication takes place because of the stator. The fluid around the impeller starts flowing outward and makes the turbine rotate. Stator also helps in getting the fluid back from the turbine to the impeller. During very high speeds, there is a lock-up clutch that locks the impeller to the turbine and they rotate together. In this scenario, there is no loss of energy. This is how a torque converter works.
Advantages and disadvantages
- The gearshifts are very quick and one does not feel the gear changes.
- Extremely efficient at high speeds because the losses are avoided completed because of the fluid coupling.
- They are used in performance cars because of their characteristics.
- It is a bit expensive compared to the other automatic transmissions.
- Fuel economy is affected negatively.
- Difficult to repair and maintain because of complexity.
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DCT (Dual Clutch Transmission)
Dual Clutch Transmission has also gained popularity because of quick shifts. Volkswagen has made the DSG or DCT transmission very popular by using it in their cars. Now, it is a very common transmission setup for a wide variety of cars across all segments.
Working
Essentially, DCT consists of two manual gear transmissions, one for the odd gears (1,3,5) and one for the even gears (2,4,6). As the name suggests, there are two clutches, one on each gear shaft. The purpose of this is to pre-select the next gear for lightning-quick gearshifts. For example, if you are accelerating in 4th gear, then the other clutch will already select 5th gear on the other transmission. When the speed is right, the other transmission shaft gets connected to the engine and there is no time wasted to press the clutch and select the next gear. Because it is essentially two manual transmissions, the fuel efficiency is higher as compared to the torque converter.
Advantages and disadvantages
- Extremely quick gear changes.
- Relatively simpler construction because there are two manual transmissions.
- Better fuel economy compared to the torque converter.
- DCT is generally an expensive automatic.
- Repairs cost a fortune.
CVT (Continuously Variable Transmissions)
Continuously Variable Transmissions are very unique in terms of the application and working. They essentially have an infinite number of gears and therefore, the power delivery and the entire operation are extremely smooth.
Working
A CVT consists of two pulleys connected to the engine and transmission and a metallic V-belt. The V-belt is rotated by the pulley connected to the engine. This belt, in turn, makes the output pulley rotate. The pulleys can come closer to each other, decreasing the effective diameter. This makes the V-belt broader and the gear ratio changes. It is generally used in smaller engines because the V-belts can’t transmit very high torque.
Advantages and disadvantages
- CVTs are the smoothest automatic transmission because no gears are there.
- They are relatively inexpensive.
- Easy to repair because of less number of components.
- They provide decent mileage.
- Rubber band effect results in a lack of spirited performance
- Quick overtakes are not easy because it isn’t very responsive.
AMT (Automated Manual Transmission)
Automated Manual Transmissions are very common in compact hatchbacks in India. It is a cheaper alternative if you are looking for an automatic as compared to all the other automatic transmissions.
Working
An AMT is nothing but manual transmission, which uses predefined parameters to change gears. You already program the Electronic Control Unit of your car with some data. It takes into account various inputs like the speed and throttle input to keep the car in a particular gear
Advantages and disadvantages
- Cheap transmission as compared tp DCT or Torque Converter
- Easy construction because it is essentially a manual transmission.
- Easy maintenance and repair.
- Fuel economy is similar to the manual.
- Gear changes can feel a bit jerky.
iMT (Intellingent Manual Transmission)
The latest addition in indian car market is the iMT, introduced by Hyundai Motors. This is even simpler than an AMT.
Working
Everything in this transmission is the same as a manual transmission apart from the fact that there is no clutch. When you put your hand on the gear lever to change gear, an actuator presses the clutch for you. You just have to manually switch gears without having to worry about the clutch application. This increases convenience, especially in city traffic.
Advantages and disadvantages
- Cheap in comparison to DCT or CVT.
- Provides control on gearshifts.
- No hassle of a clutch.
- Fuel efficient
Image Credit: ZF
