By Mercedes-Benz

The AMG SPEEDSHIFT MCT 7-speed sports transmission is an innovative power transfer system that made its debut in the high-performance SL 63 AMG Roadster in 2008, and has also been in use in the E 63 AMG since summer 2009. It combines the sporty, direct and agile feedback of a manual transmission with the maximum convenience of an automatic transmission. Featuring seven gears, three driving modes and a double-declutch function, the 7-speed sports transmission offers superb versatility. MCT stands for Multi-Clutch Technology and indicates that only clutch elements are employed to perform gearshifts.

A wet start-up clutch, which runs in an oil bath, replaces the conventional torque converter. Thanks to its low rotational inertia, the transmission responds instantaneously and dynamically without the losses typical of a torque converter transmission – thereby helping to save fuel. The AMG sports transmission also impresses with its low weight of just 80 kilograms, which has been made possible through the use of lightweight magnesium for the transmission housing. Vibrations are effectively eliminated by a new, two-stage torsion damper, with resulting benefits in perceived passenger comfort.

During its development and adaptation to the new AMG 5.5-litre V8 biturbo engine, the AMG engineers paid special attention to the new Controlled Efficiency driving mode (“C”). The emphasis was on delivering minimum engine speed coupled with a reduced number of gearshifts in all driving situations. When moving off in “C”, the MCT transmission always selects second gear and shifts decidedly early to the next higher gears if the driving style permits. At 60 km/h for instance, sixth gear will already be engaged – not only improving fuel consumption but also noise levels. Thanks to its powerful, readily available torque even at low engine speeds, the AMG V8 biturbo unit is absolutely ideal for this style of driving. Controlled Efficiency also means convenient gearshifts and a “soft” accelerator response set-up for outstandingly smooth power transfer.

Controlled Efficiency start/stop function as a new feature at Mercedes-AMG
The Controlled Efficiency start/stop function is also being used in an AMG model for the first time. This system is standard equipment in the new S 63 AMG, and permanently active in the fuel economy driving mode “C”. Once the driver comes to a halt e.g. at a red traffic light, the V8 engine is automatically switched off. Once the brake pedal is released or the accelerator is depressed, the engine is immediately restarted and the car is able to move off quickly. Intelligent techno-logy guarantees a comfortable and immediate starting procedure: a crankshaft sensor which recognises the direction of rotation registers the resting position of all eight pistons. For an automatic engine start, the cylinder with the most favourable piston position receives an injection of fuel into its combustion chamber. The precise piezo-electric injectors greatly assist this process, as they make particularly fast starts possible.

The engine management ensures that the engine is only switched off if certain preconditions are met. The starter battery must have sufficient charge, for example, and the engine must be at the necessary operating temperature for efficient emissions control. The same applies to the interior temperature selected by the driver: if this has not yet been reached, the engine is not switched off when the car comes to a stop. The onboard network management system makes sure that active audio, telephone or video functions are not interrupted by the start/stop function.

A green “ECO” symbol in the AMG main menu shows the driver that the Controlled Efficiency start/stop function is active. Should one of the above criteria be preventing activation of the system, this is shown in the central display by the message “Start/stop inactive” and a yellow “ECO” symbol. In the two more performance-oriented driving modes “S” (Sport) and “M” (Manual), the start/stop function is always deactivated. If required, the driver can also switch it off while in “C” mode as well.

The eight-cylinder biturbo engine also features the generator management system familiar from the E 63 AMG: whenever the engine is on the overrun or when braking, kinetic energy is used to charge the battery rather than being wasted as heat in the usual way. In all other operating modes a combination of onboard network and generator management enables the generator to be kept at a low voltage. This reduces the load on the engine and makes for fuel savings of around 0.15 litres per 100 kilometres according to the NEDC standard, and up to 0.2 l/ 100 km in city traffic with its frequent overrun and braking phases.

Drive modes “S” and “M” for even more driving pleasure and dynamism
The engine and transmission come across as much more agile in the “S” (Sport) mode. Accelerator pedal movements trigger a more direct traction response, making the downshifts more spontaneous. The engine speed is allowed to reach a higher level in each gear, while the gearshifts are around 25 percent faster than in “C”. In the manual shift mode “M”, gearshifts at full throttle take just 100 milliseconds, a reduction of 50 percent compared to “C”. In “S” and “M” modes, the engine management system partially suppresses the cylinders: interrupting ignition and injection under full load leads to even faster gearshifts than before. The highly emotional vocals are an appealing side effect of this lightning-fast process.

Ultra-fast, spontaneous multiple downshifts are another forte of the AMG SPEEDSHIFT MCT 7-speed sports transmission. For instance, kickdown allows gearshifts straight from seventh down to fourth gear, or from fifth to second. In the “S” and “M” driving modes the automatic double-declutching function is active. Every manual or automatic downshift is accompanied by precisely metered double-declutching – incrementally from “S” to “M”. And this not only adds to the driver’s emotional experience: the load-free downshift minimises load-change reactions, which pays particular dividends when braking into bends – and also enhances safety in the wet or on ice.
No automatic downshifts in manual “M” mode