It’s time for the Mercedes-Benz S-Class to settle down a bit. If Benz’s flagship wants to earn some green cred, then it’s going to need much more than just stop-start technology to balance out the beastly (and fun) S63 AMG 4Matic and S65 AMG. That’s where the 2015 Mercedes-Benz S550 Plug-In Hybrid comes in. We recently headed to Germany for the 2016 Mercedes-AMG GT’s world premiere, which was a look-but-don’t-drive affair, but Benz did hand us the keys to the hybridized S-Class for a short drive in and around Stuttgart.
Mercedes says the goal for the 2015 S550 PHEV could be summed up in three numbers: 8, 4, and 0. Specifically, it should provide eight-cylinder performance, four-cylinder efficiency, and zero-emission capability.
Those numbers sound promising, especially compared to the last-generation S400 Hybrid. That car combined a 3.5-liter V-6 (275 hp and 258 lb-ft of torque) with a tiny electric motor (20 hp and 118 lb-ft) housed within the seven-speed auto. Acceleration was decent at 7.0 seconds flat and its EPA rating of 19/25 mpg city/highway wasn’t a significant improvement over its gas-only counterpart. Additionally, the S400 was more of a mild hybrid that could run on a pure electric mode. To be fair, this was Benz’s early effort into hybridization, and the lessons learned from that car were applied to the much improved sedan we get today.
For starters, the 2015 Mercedes S550 PHEV features the automaker’s new 3.0-liter twin-turbo V-6 that’s already making its way into the Benz lineup. Here, it makes 329 hp and 354 lb-ft. The S550 PHEV also gets a bigger and more robust electric motor rated at 114 hp and 251 lb-ft that is still fitted within the transmission, but can now operate on its own thanks to the addition of a clutch between it and the engine. According to Benz, the S550 PHEV will have a zero-emissions range of 20 miles, with top speed limited at around 54 mph. (Top speed with the engine is 130 mph.)
So how does it deliver on the promise of eight-cylinder performance? Pretty well. As expected, the electric motor provides a fair amount of thrust off the line. Moments later the V-6 steps in seamlessly, with both providing plenty of steam well above highway speeds. A short jaunt on an unrestricted portion of the Autobahn further solidified the powertrain’s strength, with the sedan eagerly reaching its top speed in no time. Benz provides a 0-62 mph estimate of 5.2 seconds, which sounds about right and isn’t too far behind the last S550 we tested (0-60 mph in 4.7 seconds). We’ll have to wait a bit to find out if it delivers on its four-cylinder-like fuel economy. The official European Union test results returned a very optimistic combined rating of 100.9 mph.
Overall, the system is impressively smooth. The sedan is library quiet in EV mode and the transitions between the motor and gas engine are very smooth, especially compared to the last S400 Hybrid. Better yet, the twin-turbo V-6 sounds good when it’s working hard, though its sporty note is fairly muted (this is an S-Class, after all). The brakes can be a bit touchy and sensitive, especially under light braking during the initial overlap of the recuperative braking system and the mechanical brakes.
Drivers can select among four operating modes. Hybrid is essentially the default mode, making the best use of the gas and electric motor. It also optimizes the hybrid system based on the routing entered into the navigation system (i.e., looking for opportunities to recuperate energy). E-Mode depends on the motor as much as possible, while selecting E-Save mode will maintain the battery’s current charge level. Finally, Charge mode will rely mainly on the engine to replenish the battery.
The 2015 S550 Plug-In Hybrid also debuts Benz’s new haptic accelerator pedal. This fancy pedal essentially coaches you to drive more efficiently and operates in Hybrid mode and when the transmission is set to E+ mode (Economy +). Here, the system relies on radar sensors to detect cars in front of you and will double-tap the pedal, encouraging you to take your foot off the pedal to allow the car to coast and recuperate energy. The haptic pedal also operates in E-Mode, providing resistance at the point before the gas engine kicks in. (No more squinting at the E-Mode indicator in the instrument panel.)
The 8.7 kW-hr lithium-ion battery sits above the rear axle and is water-cooled. Weighing in at 251 pounds, the battery pack occupies 3.4 cubic feet of space above the rear axle, reducing the trunk capacity to 12.2 cubic feet, compared to 16.3 cubic feet in non-hybrid models. The hybridized S-Class features a 3.6 kW on-board charger with the connection for the cable located in the rear bumper on the passenger side. Mercedes says charging the battery should take approximately two hours and 45 minutes using a level 2 charger, and wireless charging is on the way.
The S550 PHEV proves that Mercedes is finally getting serious about hybridization. The powertrain was developed and built to be a modular system, which means it’ll eventually make its way into other models including the C-Class and SUVs such as the M and GL-Class. Pricing and official fuel figures should be announced closer to its debut, perhaps at the upcoming Los Angeles or Detroit auto show.
Images of the European-spec Mercedes-Benz S500 Plug-In Hybrid are shown below.