Mercedes-AMG's MCT Transmission: Design Peculiarities and Principle of Operation

For car enthusiasts seeking a car with enhanced performance characteristics, the Mercedes-AMG’s model line-up is certainly one of the first that worth considering. The German brand integrates a lot of advanced performance-oriented features in its models, and some of these cars come with an unusual sports transmission named as AMG SpeedShift MCT. In this article we will consider the main design peculiarities of this unit, its modifications and principle of operation.

Mercedes-AMG, commonly known as AMG, is a division of Mercedes-Benz (subsidiary of Daimler AG), which produces more powerful and sports-oriented car models (or modifications) of the German Auto Giant, powertrain components (engine, transmission), as well as its own racing cars and represents interests of Mercedes-Benz in motorsport.

Learn more about SpeedShift MCT technology

AMG engineers designed the 7-speed semi-automatic SpeedShift MCT (Multi-Clutch Technology) gearbox on the basis of the 7G-Tronic. In contrast to conventional automatics and double-clutch solutions, this product has neither torque converter (TC) nor double-clutch mechanism. Instead of the TC unit, this solution is equipped with a space-saving clutch package, which operates in the oil bath. There are several clutches, which are positioned together, but controlled separately. This nsolution can be easily distinguished from doublel-clutch gearboxes because it has only one input shaft. Now, this transmission technology is available in 7-speed and 9-speed versions.

Seven-speed version

Produced in 2008, the 7-speed MCT unit became the first-of-its-kind technology implemented in a production car. In the same year, this solution was installed in the Mercedes-Benz SL 63 AMG. Owners of this model were impressed with operational characteristics of the gearbox and its responsiveness. AMG engineers wanted to create a product with impressive actuating time charactersitcs and enhanced torque transfer capacity, as a regular double-clutch mechanism could not operate properly with high volumes of torque produced by the V8 engines used in brand’s cars, so this technology had to be developed to gain max performance capacity.

In fact, this gearbox is a unique solution combining a planetary design used in conventional automatics and a clutch similar to that found in manual transmissions. Thanks to the minimum inertia of the rotating masses and higher reaction time, this transmission unit rules out interruptions in torque delivery (in contrast to standard automatics equipped with torque converters), thereby ensuring better fuel economy.

The AMG Speedshift MCT 7 unit is even lighter than the AMG Speedshift 7G-Tronic unit by 18%. The MCT unit weighs 80 kg, and the moment of inertia of rotating parts is reduced by 30%. This unit can operate at engine RPM rate of up to 7,200. This unit is used on quite powerful models of the AMG Series. The MCT unit has four modes of operation (C, S, S+ and M), a Race Start feature, and an automatic double-declutch function. The minimum shifting time is 0.1 of a second (S+ mode).

The whole mechanism is controlled by AMG DRIVE UNIT. Gears can be changed either via the gear shifter or with the help of paddle-shifters on the steering wheel. The newly introduced Race Start function ensures max speed-up capacity and optimal traction of the drive wheels.

Nine-speed version

The AMG Speedshift MCT 9 transmission firstly used in the E63 model became the 1-st in the world 9-speed multi-clutch automatic solution. To add two more gears, AMG engineers had to upgrade some hard parts of the unit. Moreover, they also had to introduce some changes to the software part and calibration adjustments to provide optimal operating characteristics. As a result, this transmission unit guarantees extremely quick gear shifting. As well as its 7-speed analog, the 9-speed Speedshift version can carry out several downshifts at once. Engineers preserved the double-declutch feature, improved RaceStart mode, and introduced a “coasting” function.

Application of Multi-Clutch Technology in different types of vehicles

This transmission technology is usually used in vehicles operating under severe conditions, where an ideal responsiveness is needed, along with the necessity to deal with a maximum level of torque. It should be noted that multi-clutch gearboxes are not the same as multi-plate clutches. The latter term refers to the clutch unit itself, which can be implemented in manuals. Multi-clutch gear shifting solutions find application not only in different types of racing cars, but also in heavy engineering industry. The main advantages of this technology are the following: space-saving design and enhanced transmission capacity when compared to standard automatics. In addition, transmission solutions with multiple clutches are not prone to slippages and they have significantly improved response time to pressing of the gas pedal.

It is not surprising that motorcycles have shifted to usage of multi-plate clutches. With extremely small dimensions, standard transmission units installed in motorcycles cannot handle high volumes of torque, while multi-clutch solutions turn out to be much more efficient. Most motorcycles are equipped with wet clutches, which operate in oil to avoid overheating. But, some motorcycles come with dry clutches, such as Ducati.

When it comes to passenger cars, dry clutches got wider use than the wet clutch technology, as the latter one is much more expensive. But some brands prefer the wet clutch solution because of its operating advantages. This technology found application not only in gearboxes, but also in modern differentials. The design of self-locking differentials includes multiple clutch plates inside, and they can engage or disengage axles depending on load.