Types of automatic transmissions explained
Automatic transmissions can be confusing. Firstly, there are a number of different technologies to make a car an ‘automatic’, from AMTs to DCTs and more recently iMTs, it can get confusing. Manufacturers don’t help the confusion by christening their transmissions with names like S-Tronic, Steptronic and DSG. Fret not. At evo India, we’re here to clear up any confusion you may have had around automatic gearboxes – right from the type of technology they use, to the various names given to these technologies by different manufacturers.
The automatic transmissions that are on offer with various cars today can be categorised into five broad groups – AMTs, CVTs, DCTs, iMTs, and torque converters. Let’s kick things off with one of the most common types of automatic transmissions, as far as the more affordable-end of the market is concerned –the AMT.
Automated Manual Transmission (AMT)
Automated Manual Transmission, or AMT, is the most commonly used version of automatic transmission in India. Similar in mechanism to the manual transmission, the AMT has sensors and actuators performing the work of clutch and shifting gears. Also known as an automated manual, the AMT uses hydraulics, linked to the electronic control unit (ECU) of the car, to complete a gearshift. A pre-programmed gear shift pattern is recorded and stored in the ECU. As the car revs to a certain RPM level the ECU takes the charge from the actuators and operates both the clutch and gearbox in transition. Since, automatic transmission variants of the cars are pricier than the standard manual variants, an AMT instead allows manufacturers to offer them at an affordable price. Maruti Suzuki has been offering the AMT in the automatic variants of S-Presso, Celerio or Ignis while Renault adopted the use of AMT in its cars since 2010, which can be seen in the Kwid and the Triber. A lot of other companies, like Tata and Mahindra also use AMTs in their cars.
Continuously Variable Transmission (CVT)
Continuously Variable Transmission or CVT is a single speed automatic gearbox, compact in size and simple in construction. The CVT box involves two cone shaped pulleys, connected via V-shaped drive belt, where one pulley is connected to the engine and the other to the wheel. The cone shaped pulleys move according to the engine revs as per the power inputs and the drive belt maintains the same tension according to it. The two cones have an independent movement, thus having infinite gear ratios. CVT, as it has a simple mechanism, is more fuel-efficient and is smoother compared to conventional automatics. They are also very reliable, which is why manufacturers like Nissan and Toyota use CVTs in their cars.
Dual Clutch Transmission (DCT)
Dual Clutch transmission or DCT works with two clutch packs. One clutch controls the odd numbered gears while the other controls the even numbered gears. For example, when first gear is engaged, the odd clutch is in use, and the even clutch pre-selects the second gear, which allows continuous shifts without interrupting the power flow from engine to the transmission. The lightning quick shifts urged manufacturers to start using DCTs for supercars and sportscars, but since the DCTs can be tuned for seamless shifts while helping economy, they started to offer it on mass-market cars. However, due to their complex mechanism, DCTs aren’t the most reliable types of transmission and cost a lot when things go wrong.
Intelligent Manual Transmission (iMT)
Hyundai introduced Intelligent Manual Transmission or the iMT transmission with one of the variants of the Venue. The iMT is a clutchless manual, where the driver has to manually operate the gear lever in the event of an upshift or downshift while the clutch is operated automatically. The gear lever in an iMT is called the transmission gear shift lever (TGS) which is joined to the intention sensor, actuator and an (electronic) transmission control unit. When a driver wants to upshift or downshift, the TGS sends a signal to the transmission control unit, which in turn engages the hydraulic actuator to generate the hydraulic pressure which is then directed to a slave cylinder through a clutch tube. The cylinder then operates the clutch plate and pressure plate using the hydraulic pressure, which engages and disengages the clutch. The iMT transmission is on offer with the Hyundai i20, Venue and Kia Sonet in their turbo-petrol variants in India. However, the iMT wasn’t the first clutchless manual, there was the Manumatic and the Saab Sensonic too. The Hyundai Venue was the first car to get an iMT in India. Hyundai smartly pitched the iMT as an alternative to a manual and demanded only a premium of Rs 20,000 over its manual variant, which is not a bad deal as you get the best of both the worlds. For city traffic and highway cruising the iMT still serves as a better pick over a manual variant, as the absence of a clutch pedal allows you to think about one less thing while driving and even helps you achieve similar fuel-efficiency figures as the manual variant.
Torque Convertor Auto
A torque convertor automatic is the most commonly used automatic transmission, as they offer good performance and fuel efficiency without being too expensive to manufacture. A torque convertor auto involves a torque convertor that has two oppositely faced fans, a transmission fluid flows in the space of the torque convertor which helps transmit power from the engine to the transmission. A pump attached to the torque convertor sends the transmission fluid around the torque convertor, spinning the fan and transmitting the torque into the transmission. Due to this fluid-driven mechanism, the torque convertor has the leverage of more torque at lower-revs.
Since now you have a basic idea about the different types of automatic transmissions on offer, let us dig a little deeper into the names that various manufacturers have given them, and why.
Auto-Gear Shift (AGS)
Auto Gear Shift technology or AGS technology was introduced in India by Maruti Suzuki in 2014. In cars with AGS, the automated manual transmission (AMT) box has an Intelligent Shift Control Actuator operated by an electronic transmission control unit. The AGS transmission system has an ability to assess the driving conditions and adjusts the gear shifts accordingly and delivers better performance and efficiency. Since the actuator and control unit are mounted on the transmission unit, a synchronized movement of clutch and gear shift takes place which accounts for improved fuel efficiency and as a result, the engine remains in its powerband increasing its performance. Cars equipped with AGS tech are the automatic variants of Maruti Suzuki S-Presso, WagonR, Celerio, Ignis, Swift and Dzire.
Cambio Corsa is an automated manual transmission, and it was introduced with the Maserati Coupe and Spyder from 2001 to 2007. In the Cambio Corsa transmission, the upshifts and downshifts are done using paddle-shifters, while buttons on the central console engage the reverse gear. It is actually a manual transmission with a computer-controlled clutch. The gearbox here is mounted longitudinally at the rear and contributes to 53/47 per cent weight distribution of the vehicle. Maserati MC20 comes with a Cambio Corsa transmission.
Direct Drive System (DDS)
Christian von Koenigsegg invented the Direct Drive System, a single-speed fixed-gear transmission system for the Regera. The gearbox has been developed in-house by the Koenigsegg Advanced Engineering team. The KDD (Koenigsegg Direct Drive) system eliminates the need for a transmission and allows for a pure EV mode. The DDS transmission has a 2.73:1 reduction ratio, where the crankshaft mounted on the ICE rotates 2.73 times for a single rotation of the output shaft. In cars equipped with the DDS transmission, the electric motor takes care of propulsion below the speed of 48kmph and above 48kmph (or 1000rpm) the hydraulic coupling begins to close and reaches a point where it is completely locked by the virtue of a clutch and provides direct and uninterrupted drive to the wheels. Further technical details about the mechanism behind the DDS are scarce. Also, in reverse gear, the electric motors do the job of propelling the car and the DDS transmission is unique in its way as it is only seen in the Koenigsegg Regera, which can attain a top-speed of 400kmph.
Direct Shift Gearbox
Direct Shift Gearbox, commonly known as DSG, was introduced by Volkswagen. It is an electronically-controlled, dual-clutch, multiple shaft automatic gearbox. The system involves two engine-driven clutch packs, where one shaft is of a larger diameter and the other is of a shorter diameter. The larger or the outer shaft is responsible for driving gear 1, 3, 5 and reverse while the inner or smaller clutch shaft drives 2, 4 and 6. The DSG transmission works similar to a motorcycle’s wet multi-clutch plate. The DSG transmission is licensed under the name of Volkswagen Group and used by vehicles under the group. Manufacturers like Audi, Bugatti, Lamborghini and Volkswagen use their versions of the DSG transmission in most of their cars, like the Audi A4, Bugatti Veyron and Lamborghini Huracan.
Intelligent Variable Transmission (IVT)
Intelligent Variable Transmission or IVT is similar in mechanism to a continuous variable transmission (CVT) but instead of having fixed gear shifts the IVT picks up the virtual gear shifts as per drivers input and driving conditions. The IVT transmission has continuous shifts that help provide better fuel efficiency in comparison to other automatic transmissions. The mechanism of continuous shifts is carried out by modulating the pressure of the pulley system in the transmission and adjusting the pressure based on the inputs by the driver and driving conditions around. Hyundai and Kia cars in India, like the Hyundai Verna, Creta and Kia Seltos, get the IVT transmission.
Porsche Doppelkupplungsgetriebe (PDK)
Porsche Doppelkupplungsgetriebe (PDK) translates to Porsche's dual clutch transmission. It was designed by Porsche in 1980 for motorsport use and is now the most common automatic transmission in Porsche’s lineup. It is in use in the 718 Cayman, 718 Boxster, 911, Panamera and the Macan.
Audi calls its dual-clutch transmission as the S-Tronic. The S-tronic transmission is on offer in Audi cars either with a seven-speed or a nine-speed dual-clutch gearbox. The S-Tronic transmission is available across various models in the company’s lineup like Audi TT, A3, A4, A6, A8, Q2, Q3 and even the R8 Coupe and Spyder.
Steptronic transmission is BMW's way of calling their torque convertor auto box. The Steptronic transmission carries the same torque convertor mechanism but with use of dual clutches. Similar to the DCT box, one clutch controls the odd numbered gears while the other is responsible for even gears. Along with this mixed mechanism of two boxes, the Steptronic transmission gets three modes, one fully automatic drive mode, a manual/sport drive mode that allows high revving before shifts and a fully-manual shift for manual control of gears using paddle shifters and lever. BMWs Steptronic transmission comes on offer with the 3 Series, 5 Series, 7 Series and even the 8 Series Gran Coupe.
9G Tronic and 7G Tronic
Mercedes-Benz trademarked its nine-speed and seven-speed torque convertor auto box as 9G Tronic and 7G Tronic transmission. The 9G Tronic and 7G tronic transmission systems are based on the torque convertor auto gearbox mechanism and are on offer in the C-Class, E-Class and S-Class (except the V12 models).
Another transmission name trademarked by Mercedes-Benz is the AMG Speedshift TCT and AMG Speedshift MCT technology. The TCT carries the similar mechanism of a torque converter auto with a nine speed or a seven speed gearbox while the MCT is a multi-clutch technology, with a wet-clutch setup and, as the name suggests, it is used in AMG variants only.
And that’s it! These are some of the most common types (and names) of automatic transmissions. So, the next time you see a car paired to an automatic transmission with a fancy name, you can impress your friends by dropping some knowledge about it. That is of course until the next quirky automatic transmission is introduced.