Mercedes-AMG: DCT for 2010 supersports SLS
A seven-speed dual clutch transmission will be one of the key
elements in an all new supersports car to be launched by Mercedes-Benz in 2010.
The SLS, developed jointly by Mercedes and its high-performance division AMG, will take over the
brand's flagship sports car role from the McLaren Mercedes SLR, which ceases production this year.
It is not thought that McLaren has had any involvement in the development of the SLS.
In an a typical move, Mercedes last month (March) released technical details and engineering visuals of the new model, but kept the final external styling under wraps, only issuing photographs of heavily camouflaged prototypes on test. The SLS is of great emotional importance, especially in Germany: with its roof-hinged gullwing doors it is being eagerly anticipated as the spiritual successor to the legendary 300SL Gullwing of 1954.
Trusted industry sources as well as web reports say that the dual clutch transmission has been developed in conjunction with Getrag: on a business level this could be very significant as Mercedes-Benz has done almost all of its transmission development to date - including its seven-speed planetary automatics - in-house.
Mercedes-AMG is in good company: the Ferrari California, launched last year, has a similar mechanical configuration and also uses a Getrag dual-clutch rear transaxle.
Engineering highlights
In contrast to the outgoing carbon-fiber construction McLaren Mercedes SLR, the new SLS uses an aluminum spaceframe and aluminum body panels; even so, at an expected curb weight of 1620kg the new car matches the weight of the exotic McLaren model. The SLS uses a development of the 6.2 liter Mercedes-AMG V8 engine, now giving 571hp at 6800rpm and a peak torque figure of 650Nm at 4750rpm. Changes to the inlet and exhaust system allow faster response as well as improved efficiency, says AMG.
The main change in the engine, however, is the switch to dry-sump lubrication. Without the bulky oil pan the engine can sit much lower in the chassis to keep the center of gravity as low as possible; in addition, the engine can now be positioned in a central position just behind the front axle, aiding front-rear weight distribution.
An essential part of the achieving of this ideal 48:52 front-rear balance is the positioning of the transmission at the rear of the car, linked to the engine unit by a lightweight composite propeller shaft rotating at engine speed in a rigid torque tube.
Dual clutch transaxle
Echoing the arrangement used by the Nissan GT-R and Ferrari California, the SLS balances the mass of its engine at the front - in this case 206kg - with the weight of the rear transaxle unit, which Getrag quotes at 120kg for the 7DCL750 in its mid-engined application.
Importantly, too, much of the transaxle's mass and bulk is concentrated low down or behind the rear axle, allowing Mercedes to give the SLS a short wheelbase for improved handling agility. Drive from the one-piece propshaft is taken to the concentric twin wet mulitplate clutches ahead of and just below the rear axle; this output is then taken rearwards to the seven speed transmission assembly.
The transmission's output shaft, coming forward once more but at a higher level, directly drives the pinion which impinges on the differential crown wheel; an integrated locking mechanism then controls drive to each of the rear half-shafts. Mercedes does not give details of how the system operates other than stating that it is a mechanical lock.
Four different driving modes - ranging from comfortable to "extremely sporty" -- are available for the transmission, as well as a racing start function that optimizes acceleration. The system guarantees fast changes with no loss of tractive force, says the company.
Consumption
The light weight and high efficiency that make a sports car fast and responsive can also make it more economical than one would normally expect. In this context the anticipated provisional fuel consumption figure of 13 liters of super gasoline per 100km (17.4 US mpg) will be seen as a significant achievement for a vehicle capable of 0-100km/h (0-62mph) in 3.8 seconds and a top speed of 315km/h (196mph).
The transmission naturally has an important role to play in this. DCTfacts.com will provide further details as soon as Mercedes-AMG confirms the supplier and the specification of the transaxle.
| Specification | ||||||||
|---|---|---|---|---|---|---|---|---|
Engine: 6.3 liter V8, naturally aspirated |
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Outputs: 571 hp at 6800 rpm, 650 Nm at 4750 rpm |
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Transmission: 7-speed dual clutch, inunit with rear axle |
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Vehicle weight: 1620 kg |
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Performance (provisional): Maximum speed 315 km/h, 0-100 km/h acceleration 3.8 seconds |
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Fuel consumption (provisional): 13 liters/100 km |
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Launch: spring 2010 |
Story Filed: 5/8/2009
By Tony Lewin, managing editor DCTfacts.com