--- Compact 288 volt battery with high energy density
--- Sophisticated control system calculates most efficient operating mode in real time - 160 times per seconds with up to 50 million computations.
--- Atkinson V6 gasoline engine with 275 hp and optimized fuel economy
--- Classic M-Class benefits remain intact - economy of space, high levels of active and passive safety, driving comfort and 4MATIC permanent all-wheel drive
In the search for the optimum hybrid system for the premium auto sector, one thing was absolutely clear to development engineers right from the very earliest stages of the concept phase – a Mercedes-Benz SUV with a hybrid driveline will have to possess the same brand characteristics as every other vehicle produced by the brand.
Core elements such as the highest possible levels of active and passive safety, the best in driving and user comfort, uncompromising operational safety and reliability over a long period of time and high- quality workmanship with select materials must all be at the same level as a comparable, conventionally-driven series production vehicle - combined with the highest possible efficiency.
At the same time, the hybrid powertrain system should emphasize the innovative strength and leading technological excellence of the company. These objectives necessitated a full vehicle development program – as would be required for an entirely new model range.
In bringing it to production, engineers and technicians covered a total of 2.5 million miles - many of them in regions with extreme variations in climate conditions - in order to guarantee the operational safety of the system in everything from freezing arctic temperatures through the dry heat of the desert to the extreme humidity of the tropics.
This work was complemented by extensive test cell development and detailed simulation using a "digital prototype". One important objective of the development process was the optimum matching of the various sub-systems integrated within the driveline. Thanks to this "system matching" process, the user experience of the different drive modes is seamless and intuitive.
The ML450 HYBRID has a powertrain architecture that enables both purely-electric and purely-combustion engine operation, as well as a combination of both. Its two-mode hybrid technology is based on the fundamental work carried out by the "Global Hybrid Cooperation". This industry grouping brings together the research and development efforts of Daimler AG, the BMW Group, General Motors and Chrysler.
Superior technology – two-mode hybrid is the most efficient driveline
Thanks to its two-mode hybrid technology, the ML450 HYBRID possesses considerable benefits; its performance figures are comparable to those of a classic eight-cylinder SUV with permanent all-wheel drive, while fuel consumption and emissions are up to 60 percent lower.
The ML450 HYBRID, which was conceived specifically for the North American market, achieves city gas mileage of 21 mpg and highway mileage of 24 mpg. Classified as a SULEV (Super Ultra Low Emission Vehicle), the SUV currently complies with the most stringent of all U.S. emissions legislation for vehicles with internal combustion engines.
At the same time, the ML450 HYBRID delivers a system performance of 335 hp and an overall torque of 381 lb-ft to guarantee a refined driving experience combined with increased powertrain comfort. The powertrain is controlled fully automatically, meaning that the driver can concentrate on the traffic and enjoy the driving experience of the ML450 HYBRID without additional operational effort. The functionality of the 4MATIC all-wheel drive also remains fully intact.
At the heart of the two-mode hybrid driveline is the transmission unit with two compact electric motors, three planetary gear sets and four clutches. This configuration enables the drive to be split through one electrical and one mechanical route. Conventional one-mode hybrid systems generally have no mechanical gearing.
These systems must therefore transfer the majority of their power through the electrical driveline with higher electrical output and subsequently reduced efficiency. Their most efficient operation takes place largely at lower loads and speeds. Should power transfer also be required at higher loads and speeds, then a larger electric motor would be required.
This, in turn, would use more energy and take up more space, to the detriment of efficiency. In contrast, as load and speed increases, two-mode hybrid technology transfers drive in a variable fashion from the electrical line to the mechanical driveline. In so doing, the system functions significantly more effectively under all conditions ranging from stop-and-go city traffic to rapid highway driving. It also enables the use of more compact electric motors. The "two-mode" technology also derives its name from its increased efficiency in both city traffic and on the open road.
Through the activation of the four clutches, the electrical and internal combustion engine drive is split between all four wheels of the 4MATIC permanent all-wheel drive via four fixed ratios and two variable electrical ratios in accordance with driving conditions. A range of strategies – defined by traffic conditions or driver preference – deliver the best possible figures in terms of fuel economy and performance.
--- In pulling away or at low speeds up to the second fixed gear, the ML450 HYBRID drives very smoothly in ECVT 1 mode (Electric Continuously Variable Transmission).
--- The ECVT 2 mode takes over at higher speeds starting at the second fixed gear ratio. Depending on the optimum operating point, either a combined or constantly variable mode will be selected.
--- In the first and third fixed gear ratios, both electric motors operate together either to provide additional energy for acceleration (boost) or to store the braking and drive energy (recuperation).
--- In the second and fourth fixed ratio, one of the electric motors is switched off in order to increase efficiency. The other electric motor is used for boost and for recuperation.
Both compact electric motors have a high power density and are fully integrated into the transmission casing. The limited packaging space called for a different set up for each of the two motors.
The first is positioned closer to the internal combustion engine, generates 83 hp and 173 lb-ft of torque and is set up specifically for performance. The motor located at the output end of the transmission generates 80 hp and 192 lb-ft of torque and is dedicated to pulling away under electric power and to provide boost.
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