Join Date: Nov 2004
Mercedes-Benz 4MATIC Winter Experience
Fun fact: Mercedes-Benz is celebrating the 25th anniversary of its all-wheel-drive system -- marketed as 4MATIC -- this year. In human years, that's well within the quarter-life crisis window. But unlike the self-doubt manifested in humans during our quarterly crisis, 4MATIC is more focused than ever, and Mercedes was determined to show and tell us all about its system in the wintry clutches of Jackson, Wyoming. Before we get to the slip-sliding, here's a history refresher.
Before 4MATIC, and even before the folkloric Unimog and Gelaendewagen, there was the Daimler Dernburg Wagen. Paul Daimler, engineer and son of company founder Gottlieb Daimler, fashioned together his first four-wheel-drive vehicle in 1903, paving the way for additional all-wheel-drive development. The one-off Dernburg Wagen was built in 1907, and starting in 1908, it served as German Colonial Office Secretary of State Bernhard Dernburg's (hence the name) personal transport in then-German South-West Africa (modern-day Namibia).
It's unclear whether the Dernburg Wagen weighed 3.6 tons or 3.6 tonnes (there's a couple hundred pounds difference between the two), but it was powered by a 6.8-liter four-cylinder delivering 35 horsepower and featured (needed) four-wheel steering. The Wagen had a top speed of 25 mph but could scale challenging grades and negotiate loose surfaces like few vehicles of its time. From today's perspective, the truck is rudimentary yet effective. In 1907, it was remarkable.
The Dernburg Wagen cost 34,750 German marks. After converting long-obsolete marks to U.S. dollars and playing with the U.S. Consumer Price Index to adjust for inflation, you get a value of about $217,000 in 2012 currency.
Decades later, the first generation of 4MATIC took a bow at the 1985 Frankfurt Auto Show before entering production in 1987 pinned to the W124 E-Class (the first 4MATIC was available in the U.S. in 1989). First-gen 4MATIC was a part-time AWD setup consisting of automatic locking differentials and a traction-aid program christened Acceleration Skid Control. In all, this 4MATIC system tipped the scales at more than 300 pounds. Gen 1 was first and foremost rear-wheel-driven, with torque sent to the front only when the back wheels started to slip.
The second iteration of 4MATIC surfaced in 1997 for passenger cars on the W210 E-Class. Mercedes ran with a simpler full-time AWD system, doing away with the automatic locking diffs. It also introduced 4ETS -- 4-wheel Electronic Traction System -- which electronically applies the brakes to limit wheelspin and maximize grip. A few years later, the W211 E-Class hosted the third-gen 4MATIC. Enhanced 4ETS and quicker AWD actuation times helped maintain effectiveness across a greater range of speeds and pushed 4MATIC farther technologically. Then the fourth-gen came along.
Today's 4MATIC branches into two subsets: 4MATIC for passenger cars and 4MATIC for SUVs. There are two key differences between the passenger car (C-, E-, S-, CL-, CLS-, and GLK-Class) and SUV (M-, G-, GL-, R-Class) 4MATIC systems:
1) The passenger car setup employs a fixed torque split of 45 percent to the front wheels and 55 percent to the back, whereas the SUV system goes 50/50.
2) 4MATIC for cars packages the requisite transfer case and center differential directly into the 7G-TRONIC seven-speed automatic transmission. Gen 4 4MATIC first launched on the S550 4MATIC in 2006 as a 2007 model.
Designed, produced, and manufactured completely in-house, the highly modular 4MATIC now weighs between 99 and 154 pounds depending on the vehicle, shedding up to 25 pounds over the Gen 3 system.
Mercedes settled on its passenger cars' 45/55 front/rear torque distribution (having moved from 40/60 front/rear on past five-speed models) for specific reasons. Rival torque-on-demand-style AWD systems can vary and swing engine output between the front and rear axles at any ratio the manufacturer or supplier wishes, which may lead to more thrilling and dynamic performance but result in erratic handling behavior. Locking the distribution at 45/55 front/rear means predictability. Differentials, half-shafts, and propeller shafts can be built to exact specification, saving valuable pounds where torque-on-demand AWD would necessitate components at both ends prepared for maximum output at any time.
Integrating 4MATIC's transfer case and planetary-type center diff into the transmission centralizes mass, exploiting the full benefit of Mercedes' longitudinally mounted engines. A double-plate "breakaway" clutch in the C-, E-, and S-Class 4MATIC transfer cases acts as a pseudo limited-slip diff, capable of changing front to rear load distribution (up to 70 percent frontwards or backwards) when there's less traction available. After the clutch, electronics like 4ETS and stability control can intervene when necessary. Improving the driveline's NVH characteristics and reducing friction was a top priority, too.
In Wyoming, we met the two newest members of the 4MATIC family: the C350 4MATIC Coupe ($45,245 starting MSRP, $2000 more than RWD C350 Coupe) and the E350 4MATIC Coupe ($53,175 MSRP, $2500 more than RWD E350 Coupe). Both go on sale in April, and both proved unflappable in limited driving around snowy Jackson. The advantage of lightweight AWD: Mercedes touts an uncertified 22 combined mpg for both -- identical to the EPA rating of their RWD counterparts.
In addition to the new coupes, a CLS550 4MATIC and S350 BlueTEC 4MATIC took to a restricted handling course with ease. All test cars wore winter tires, of course.
To get a feel for what Mercedes might have up its sleeve for the next 4MATIC, we fired a few items of interest over to Rolf Schroeder, manager of 4MATIC development for passenger cars, to get his take on where the system may go in the future.
On uncovering further efficiency on AWD systems: There's no magic bullet (yet). Weight and friction reduction continue to be seminal areas where efficiency can be unearthed. Unsexy but critical foci include further refinement of gears' tapered roller-bearing microgeometry, formulating low-friction lubrication, and making sure CV joints are located and assembled properly.
On incorporating exotic lightweight materials into the driveline: Keeping 4MATIC as lightweight as possible has meant keeping a close eye on tolerances and minimizing waste, and Mercedes hasn't even resorted to tapping pricier materials like magnesium on a broad scale. It's examined individual component possibilities like carbon-fiber prop shafts, but while serialized implementation isn't in the cards yet, the potential is there.
On axle-disconnect technology: After studying current axle-disconnect arrangements, Mercedes determined the additional complexity (re: weight gain courtesy of more clutches and electronic controls) wasn't worth the minor fuel savings. Chrysler Group employs an axle-disconnect feature on several of its vehicles, which the automaker says leads to a 5-percent fuel economy improvement.
On non-planetary-type center differentials for future vehicles: Mercedes is always exploring different technology but no beans were spilled. We were told a torque-on-demand AWD system might be a more appropriate strategy for transversely mounted engines, which may require a different center diff. Food for thought for future FWD-based Mercedes...
On twin-clutch automatic transmissions: Schroeder assures us there's still room in the future for more efficient conventional automatics, and a mass-market shift to dual-clutch transmissions isn't the golden answer to the fuel economy problem some believe it to be. Drivability and refinement concerns always manifest themselves, and Mercedes aims for a polished, customer-centric driving experience. Currently, dual-clutch autos might offer packaging benefits on smaller displacement, transverse-mounted engines, and have a more noticeable effect on muscular, high-revving powerplants.