Mercedes-Benz is preparing to introduce a new version of its 4Matic all-wheel drive transmission aimed at transverse-engined front-wheel drive powertrain architectures, starting with the 2014 CLA 45 AMG. Featuring fully variable torque distribution, the new gearbox is described by the company as a “completely new development." Its innovative aspects include power take-off (PTO) to the rear axle which is integrated into the company’s established 7G-DCT automated dual-clutch transmission and a rear axle with integrated, electrohydraulically controlled multidisc clutch.
The CLA 45 AMG is a new high-performance A-segment variant based on the automaker's CC architecture that underpins A- and B-segment vehicles. It is due to enter production later this year. At 70 kg (154 lb), Mercedes claims the new 4Matic system is lighter by about 25% compared to systems used by competitors. This is particularly due to the use of a compact PTO unit integrated into the main transmission, which supplies lubricant. Rival systems branch off power via an add-on component with its own oil circuit, states Mercedes. The PTO unit uses tapered roller bearings.
Fully variable torque distribution is achieved via the multidisc clutch positioned in the rear axle gear unit. With the clutch open, the car behaves virtually identically to a front-wheel drive vehicle, with almost all torque sent to the front axle. With the clutch closed, the rear axle is also driven, with torque balance available between axles on demand according to overall conditions.
ABS application sees the rear powertrain deactivated and subsequently no torque delivery. Drive torque to front and rear is used to counter under or oversteer under load, with chassis electronic systems actioned in a secondary role.
System pressure to introduce the rear axle is supplied via a rotor-type pump in the axle’s gear unit with an ESP controlled proportioning valve looking after pressure.
Torque distribution is also dependent on the activated shift program (Eco, Sport, or Manual) of the dual clutch transmission. In Eco, the front axle gets the most torque in normal conditions, while Sport and Manual see activation times reduced and the rear axle receiving more torque, to provide the driver with required rear-biased dynamics. Mercedes states that on AMG versions, adaptation of the 4MATIC controller takes place in accordance with the three-stage ESP.
All CLA models will be available with 4MATIC. The production CLA will look very similar to the Mercedes Concept Style Coupe previously seen at international motor shows.
The high-performance CLA 45 AMG will have a 2.0-L turbocharged gasoline engine capable of producing peak torque in excess of 400 N·m (295 lb·ft).
Although Mercedes has long offered AWD on some models, its application across its entire model range has not been as comprehensive as Audi’s Quattro. The new system for fwd transverse-engine architecture will help redress that situation.
Each of Mercedes’ SUVs and ATVs (all-terrain vehicles) including M-Class, GL, and G-Class, has standard all-wheel drive but use a torque converter system. The only Mercedes models at present offering dual-clutch technology are the A- and B-Classes and the high-performance SLS AMG.