Mercedes-Benz Power transmission
Dynamic, variable and efficient
- Performance-oriented AMG 4MATIC all-wheel drive
- 3-stage ESP® with ESP® Curve Dynamic Assist
- AMG SPEEDSHIFT DCT 7-speed sports transmission
- Three modes, double-declutching function and RACE START
- "Momentary M mode" for further enhanced dynamic spirit and
- Mercedes-Benz A-Class
Performance, dynamic spirit and efficiency – Mercedes-AMG meets the highest standards when it comes to power transmission as well as engine technology. The A 45 AMG is equipped with performance-oriented AMG 4MATIC all-wheel drive as standard. Further AMG models with all-wheel drive will follow.
Compact, weight-saving design
Perfect traction: the performance-oriented AMG 4MATIC all-wheel drive is an ideal means of transferring the engine power to the road – regardless of the weather conditions. Furthermore, it raises the dynamic handling of the A 45 AMG to the highest level. In developing this all-wheel drive system, the focus was firmly on performance and dynamic spirit. The power transfer to the rear powertrain is provided by a compact power take-off unit (PTU) which is fully integrated into the AMG SPEEDSHIFT DCT 7-speed sports transmission and is supplied with lubricant from the latter's oil circuit. This configuration gives rise to substantial weight advantages in comparison to rival systems which branch off power by means of an add-on component with its own oil circuit. Together with the friction-minimised tapered roller bearings, the PTU achieves an excellent level of efficiency. As an additional bonus, the system weight of the AMG 4MATIC all-wheel drive is up to 25 per cent lighter than the all-wheel drive versions offered by the competition.
As is always the case with all-wheel-drive systems incorporating a transversely mounted drive unit at the front, the power needs to be diverted by 90 degrees. On the AMG 4MATIC all-wheel drive, this is achieved by quite simple means: the differential gearwheel of the main transmission drives the spur gear of the PTU and a compact bevel gear stage diverts the power. The rear axle is driven via an output flange and a propeller shaft.
A two-part propeller shaft transfers the power from the AMG 2.0-litre four-cylinder turbo engine to the rear axle. In order to minimise crash-induced stress for passengers in a head-on or rear-end collision, the propeller shaft is fitted with a crash joint. In the interests of favourable weight distribution, an electrohydraulically controlled multiple-disc clutch is integrated with the rear axle differential. The multiple-disc clutch control detects slip at the front axle. A hydraulic pump instantaneously presses the discs together and channels the engine torque to the rear wheels as necessary. All this takes place virtually without the driver noticing. To enable particularly fast response, the pump is always active and does not require to be started up each time it is needed, as is customary with other systems. The pump is activated automatically even if there is only a small speed differential between the front and rear axle, with the pressure being regulated by a proportional valve controlled by the 3-stage ESP®.
Torque on demand: fully variable drive torque distribution
The drive torque can be shifted in fully variable mode between front and rear axle according to the given situation (torque on demand): in normal driving, the A 45 AMG uses front-wheel drive in the interests of optimum efficiency. When the dynamic handling so requires, the variable AMG 4MATIC all-wheel drive splits the torque between front and rear axle up to a ratio of 50:50 per cent. When there is a so-called friction jump, i.e. when only the front wheels briefly lose grip on an icy surface, the entire torque is transferred to the rear wheels almost instantaneously. The reverse process takes place just as quickly: as soon as additional drive torque is no longer expedient at the rear axle – e.g. in case of heavy braking manoeuvres with ABS intervention – the rear powertrain is deactivated and torque is reduced to zero. With this strategy, the developers have managed to combine two key requirements defined in the performance specifications: optimum energy efficiency coupled with maximum dynamic handling and driving safety. The variables influencing the power distribution ratio are vehicle speed, lateral and longitudinal acceleration, steering angle, speed difference between the individual wheels, selected gear and accelerator position.
Another feature of the 4MATIC system results in a further increase in dynamic handling, guaranteeing even greater driving enjoyment without compromising driving
safety. In case of impending understeer or oversteer under load, the drive torque is first of all distributed in a way that stabilises the vehicle. This ensures that traction and driving enjoyment are fully maintained in swift driving on winding stretches of road. Only if these measures fail to have a stabilising effect do the control systems adapted to 4MATIC conditions, such as 3-stage ESP® or 4ETS, intervene to keep the car stable.
The 4ETS electronic traction system forms part of the 3-stage ESP® and brakes the driven wheels individually when they go into spin. This provides for a high level of traction on slippery surfaces, on roads which are icy on one side or in continually changing conditions. In a nutshell: while 4ETS is responsible for maintaining the highest possible traction in all conditions, 3-stage ESP® serves as the higher-level control instance to ensure optimum driving stability.
3-stage ESP® with ESP® Curve Dynamic Assist
An exclusive feature is the interaction of the AMG 4MATIC all-wheel drive with the 3-stage ESP® and the ESP® Curve Dynamic Assist. The three ESP® stages enable the driver to vary the dynamics of the A 45 AMG according to his individual wishes at the push of a button. The safety-oriented "ESP ON" mode supports the driver in maintaining neutral handling characteristics. The system initiates braking intervention on one or more wheels and reduces the engine torque on detecting that the operating conditions are becoming unstable.
Briefly pressing the ESP® button activates "SPORT Handling" mode. This dynamically oriented driving mode applies appropriate control strategies for later ESP® intervention and increased drive torque at the rear axle. This means more fun at the wheel for drivers who are keen to exploit the vehicle's dynamic potential. Pressing the ESP® button longer activates "ESP OFF". In this mode, the ESP® functions are not available. ESP OFF should only be used by experienced drivers on cordoned-off racetracks. If the driver steps on the brake pedal in "SPORT Handling" mode or "ESP OFF" mode, all the safety functions of the ESP® system become available during braking.
ESP® Curve Dynamic Assist complements this system to perfection: during dynamic cornering, imperceptible braking intervention on an inside wheel gives rise to a defined yaw moment around the vertical axis, resulting in precise cornering and ensuring that the vehicle remains under control at all times. Depending on the selected ESP® mode, ESP® Curve Dynamic Assist is adapted accordingly. In "ESP SPORT Handling" mode and "ESP OFF" mode it supports the driver's wish for increased agility and dynamic handling. The ESP® Curve Dynamic Assist is an additional function of the 3-stage ESP® which noticeably improves not only agility, but also active driving safety in critical conditions.
AMG SPEEDSHIFT DCT 7-speed sports transmission with RACE START
The AMG SPEEDSHIFT DCT 7-speed sports transmission transfers the engine power to all four wheels. The dual clutch transmission is flange-mounted on the transversely installed AMG 2.0-litre four-cylinder turbo engine and features seven gears, three modes, a double-declutching function and RACE START for optimum acceleration. It also boasts compact dimensions, low weight, high efficiency, exemplary variability, spontaneous gear changes without any interruption in tractive power, a tailor-made control strategy and smooth, easy gear shifting. Key software modules have been adopted from the SLS AMG GT and SLS AMG Coupé Black Series with their inspirational power transmission concepts. Reinforced gear wheels provide for maximum stability. Synchroniser rings with carbon-fibre friction linings improve durability while also optimising the response time during manual gear-changing – the ideal basis for ambitious laps on cordoned-off racetracks.
The three transmission modes - Controlled Efficiency ("C"), Sport ("S") and Manual ("M") - allow the driver to define the character of the car, including its sound, according to individual taste and requirements. In Controlled Efficiency mode, low engine speeds are available in the highest possible gears in all driving situations. When driving in "C" mode, the AMG SPEEDSHIFT DCT 7-speed sports transmission always selects the most fuel-efficient gear, allowing an ecologically oriented driving style without forsaking superior performance. This mode also reduces noise levels. The AMG 2.0-litre four-cylinder turbo engine's favourable torque curve, with plenty of power even at low engine speeds, is ideal for this style of driving. Furthermore, the ECO start/stop function is activated in "C" mode. Controlled Efficiency also means smooth gear changes and a "soft" accelerator pedal curve for a smooth driving style.
The shift times in manual mode "M" and in Sport mode "S" are similarly sporty in character to those of the SLS AMG GT super sports car. Briefly and precisely interrupting ignition and injection under full load leads to even faster gearshifts in "M" and "S", with a more emotional sound. In Manual mode "M", the AMG SPEEDSHIFT DCT 7-speed sports transmission does not change down automatically, neither at full load nor if kickdown is used, allowing the driver to make ideal use of the AMG turbo engine's pulling power and select the ideal gear using the steering-wheel shift paddles. The automatic double-declutching function is active in all modes – although its characteristics vary according to the selected mode. The desired mode is selected by pressing a button on the AMG DRIVE UNIT.
"Momentary M mode" for further enhanced dynamic spirit and driving enjoyment
One special feature here that has already appeared in the SLS AMG Coupé Black Series is "Momentary M mode", which allows drivers of the A 45 AMG to activate Manual mode in "C" and "S" mode by pressing the "up" or "down" shift paddle once - without having to take their hands off the steering wheel. In Momentary M mode the driver experiences full dynamic spirit and performance in the automatic modes - including the kickdown function and automatic upshifting when the rpm limit is reached into the bargain. This allows the driver to enjoy the vehicle's impressive performance to the full. The system deactivates Momentary M mode and reverts to the mode last activated ("C" or "S") fully automatically based on the current driving situation and driving style.
Best acceleration times with RACE START
The RACE START function is used for accelerating in the shortest time: while the car is stationary, the driver first has to activate "SPORT Handling Mode" and manual mode "M" in the 3-stage ESP® and then press the brake pedal with their left foot. Then both steering-wheel shift paddles must be pulled at the same time. Finally, the accelerator must be pressed fully with the right foot, while the left foot must come off the brake pedal. The "RACE START active" message then appears on the central display. The system determines the optimum starting revs fully automatically, and the car accelerates with optimum traction – thanks to the AMG 4MATIC all-wheel drive and the 4ETS electronic traction system. Manual upshifting is not necessary in RACE START mode as the AMG dual clutch transmission changes gear in the quickest possible time for maximum acceleration.