Getting automotive product design and engineering to meld smoothly is an important required element to ensure market success, so when an OEM hits on a great solution it invariably clings to it for decades.
Mercedes-Benz has done just that, with its two-seat, folding hardtop (vario roof) SLK, and the third generation of the car continues the story. Seen in concept form at the Turin Motor Show and entering production in 1996, it established a genre of push-button transformation from coupe to roadster/convertible that others have followed, albeit with varying degrees of commercial and aesthetic success.
The SLK, though, found immediate success and has maintained a smooth evolution, evolving aesthetics and technology, that has maintained its market position. Sales have totaled more than half a million units.
More recently, the unveiling of the C-Class sedan, which has been a huge commercial success, is following a similar cycle, this year receiving 2000 parts changes, which included the addition of a seven-speed automatic transmission. A coupe version has also been added to the platform.
The third-generation SLK, with front-end styling that reflects that of the gull-wing SLS AMG, may be an evolution of the previous version, but the car looks and feels markedly different. It is, stated Mercedes, “completely newly developed.”
What that means is that just about every aspect of the car has been revisited by styling and engineering teams to see its drag coefficient lowered from 0.32 to 0.30; new four- and six-cylinder engines with stop-start function introduced; suspension changes made; the use of aluminum for hood and fenders; and the application of a wide range of Tier 2 technologies, the most unusual being a panoramic vario roof called, rather quaintly for Mercedes, Magic Sky Control.
The roof uses the physics of a plate capacitor. When an electrical charge is applied, particles in the glass are re-aligned to allow light to penetrate and provide panoramic vision. Without power, the particles are randomly distributed to partially block the light, so darkening the glass. The roof is said by Mercedes to reduce the temperature of some interior fittings by about 10ºC in hot and sunny conditions, when compared to regular green tinted glass. The system is switchable by the driver.
The Magic Sky Control version tops the vario roof types available for the SLK, above the regular, painted version and a panoramic roof with just tinted glass. “Even in transparent mode, the Magic Sky Control system effectively screens out UV and IR light,” said Dr. Uwe Ernstberger, SLK Vice President, Program Management. “In darkened state, it further lowers the heat intensity by up to 80%. A cooler interior lowers the workload of the air-conditioning, which in turn lowers fuel consumption.”
Mercedes is adept at air control for cabin comfort for the SLK. Its Airscarf system, launched in 2004, blows warm air from the head restraints and has an 80% buyer uptake. Now, the new car introduces a pivoting draft-stop called Airguide for roof-down driving. Pivoting, transparent sections are attached to the rear of the roll-over bars. They can be positioned almost out of sight when not required.
Depending on market, there are four-cylinder and V6 gasoline engine choices for the SLK, but later this year a diesel will be added that will use the company’s 2.1-L, 500-N·m (369-lb·ft) 250CDI unit.
Six-speed manual and seven-speed automatic transmissions are used by the SLK. The four-cylinder SLK200 gasoline BlueEfficiency with automatic transmission returns a best fuel consumption of 6.1 L/100 km and the best CO2 of the range at 142 g/km. Its top speed is 237 km/h (147 mph), and acceleration from 0 to 100 km/h (62 mph) takes 7.0 s. The V6 3.5-L SLK 350 BlueEfficiency with 225 kW (302 hp) achieves a combined fuel consumption of 7.1 L/100 km and CO2 of 167 g/km.
Suspension of all versions uses multilink systems front and rear, but there are now three variations offered: conventional steel is standard; a sports setup with stiffer springs and dampers sharpens the car; and thirdly a dynamic handling package embraces electronically controlled automatic damping. The dynamic package also comes with Direct Steer (for enhanced agility and reduced loads at parking speeds) and a torque vectoring brake system that selectively brakes a rear wheel on the inside of bends.
Safety aspects include Attention Assist, which monitors 70 parameters to ensure driver alertness; Active Hood, which improves pedestrian safety and can be reset by the driver; Pre-Safe anticipatory occupant protection; and Intelligent Light System.
At 4134 mm (162.8 in), the new SLK is 31 mm (1.2 in) longer than the second-generation car, 33 mm (1.3 in) wider at 1810 mm (71.3 in), and 5 mm (0.2 in) taller at 1301 mm (51.2 in).
Although it does not have Sky Control as an option, Mercedes’ new C-Class Coupe is available with an opening panoramic glass roof, which gives it an important additional styling cue. The C-Class coupe—which includes the 336-kW (451-hp) 63 AMG version, 358 kW (480 hp) with AMG performance package—completes the C-Class range and is built alongside the sedan, wagon, and GLK versions on a single production line at Bremen, explained Dr. Wolfgang Bernhard, Daimler Board Member for Production and Purchasing. “This gives us the flexibility to respond to changes in the market quickly and efficiently. It is only thanks to the motivation and flexibility of our employees that we can do this with confidence.”
Two large doors, steeply sloping A-pillars, slim C-pillars, and a roofline that stretches beyond the rear axle distinguish the four-seat coupe. It stands 41 mm (1.6 in) lower than the sedan and achieves a Cd figure of 0.26 and CdxA of 0.55 m² (5.9 ft²).
Some 70% of all sheet metal panels use high-strength steel alloys, and ultrahigh-strength steel alloys account for about 20% of the bodyshell’s weight. The hood is aluminum, saving 9.2 kg (20.3 lb) against steel. Front fenders are also aluminum, as is the front assembly including flexible crossmember and crash boxes.
Engine choices include two versions of Mercedes’ 2.1-L diesel, producing 125 kW (168 hp)/400 N·m (295 lb·ft) or 150 kW (201 hp)/500 N·m (369 lb·ft).
The coupe has benefited from the extensive mechanical improvements given to the C-Class sedan, including the 7G-Tronic Plus transmission. Dr. Thomas Weber, Daimler Board member responsible for Group Research and Head of Development for Mercedes-Benz Cars, said that, in terms of efficiency, the company was now making greater leaps forward than ever before. “This becomes clear if you compare our compact (high-performance) top model of 1989, the 190E 2.5-16 Evo 1, with the current C220 CDI (diesel). The performance is virtually identical, and in the space of just 20 years, consumption has been halved, while comfort, safety, and emission characteristics have drastically improved at the same time.”
Described by Mercedes as having undergone a “comprehensive modernization” with 2000 component changes, there is little externally to differentiate the new C-Class sedan and wagon from the model launched in 2007 and which has sold over a million units. Different headlamp design and some detail changes (the coupe now has an aluminum hood) support Mercedes’ philosophy of leaving well enough alone until it is time for a significant update. Again, like the coupe, aerodynamics are impressive, with a best Cd of 0.26 and CdxA of 0.57 m² (6.1 ft²).
Interior changes include an infotainment screen integrated into the dashboard (previously it was a pop-up system), echoing the E-Class’s design. All engine variants are classified as BlueEfficiency, underlining their focus on low fuel consumption; all automatic versions have seven speeds; and final drive ratios have been optimized for economy.
The most economical C-Class is the 220CDI sedan. Depending on version, it can achieve 4.4 L/100 km (NEDC combined) and a best CO2 figure of 117 g/km. Top speed (for the automatic) is 232 km/h (144 mph) and 0-100 km/h time is 8.1 s.
The new C-Class debuts a new telematics generation that will be introduced in other Mercedes model series. It includes larger displays; display of SMS messages; and wireless music streaming via Bluetooth. The multimedia system, COMAND Online, provides Internet access.