New York Auto Show: Mercedes-Benz ML450 Hybrid

Article by Christian Andrei, on February 26, 2009

Every vehicle that Mercedes-Benz releases comes with the usual attributes expected from the brand. This includes offering the best safety features, both passive and active. It should also have maximum ride comfort while ensuring a straightforward operation.

The vehicle should also be reliable with first-class workmanship using selected materials. All of these attributes combined mean that vehicles from Mercedes-Benz offer the best efficiency possible. The challenge however was to make sure that all of these are present in a hybrid car.

This is why when the engineers started working on the SUV with a hybrid drive, they made sure that even from the concept phase it had to have the attributes mentioned. Aside from the characteristics, the company’s drive system is also proof of its strength and use of leading technology.

In order to meet these objectives, the company would need to undergo a complete development cycle like developing a new model from scratch. Even before the Mercedes-Benz ML 450 HYBRID managed to arrive at series-production maturity, certain tests had to be done.

To determine for example if the system was indeed reliable, technicians and engineers had to run a total distance of four million kilometers. These involved different climatic conditions like the humid temperatures in the tropics, sub-zero temperatures of the Arctic Circle, and even the scorching heat of the desert regions.

This work was complemented using the "Digital Prototype" with its detailed simulations and wide-ranging test-rig program. While the ML 450 HYBRID was still being developed, the objective was to ensure that the different subsystems inside its powertrain match.

The importance of system matching is that the different drive modes can be used without difficulty even while the vehicle is being driven. The ML 450 HYBRID has a two-mode hybrid technology with a drive design that can operate using pure electricity, its combustion engine alone, or a combination of both.

This is all due to the fundamental work done by the "Global Hybrid Cooperation". This group is responsible for bringing together all of the research and development performed by different automakers like BMW Group, Chrysler, Daimler AG, and General Motors.

The two-mode hybrid technology exhibits a number of advantages. Fuel consumption and emission for instance have been lowered by as much as 60% yet the performance is similar to your standard all-wheel drive eight-cylinder SUV.

A version has been tailor-made for the U.S. market with a fuel consumption of 21 mpg 'city' and 21 mpg 'highway', figures that can be said as the most efficient in its class. Since this SUV has been classified as a Super Ultra Low Emission Vehicle, it meets even the strictest of emission standards in the U.S. that have been set for vehicles that use combustion engines.

The ML 450 HYBRID delivers 250 kW, around 340 hp, of power with 517 Nm of combined total torque. The result is a driving experience that is unmatched while the level of ride comfort is increased. Since the drive management system of the ML 450 HYBRID is completely automatic, the driver can focus on the road ahead without the need to choose any of the added functions.

Still, the permanent all-wheel drive 4MATIC system continues to retain its functions. At the core of this hybrid drive is the transmission unit that is composed of four clutches, three planetary gear sets, and two electric motors.

The configuration of the transmission allows the power to be transmitted to either an electrical path or a mechanical one. This is the advantage of a two-mode hybrid system as one-mode hybrid systems are unable to have any mechanical ratios.

Thus for one-mode hybrid systems, majority of the power is transmitted through the electrical path using a high electrical output and thereby lowering the efficiency.

Press Release

Mercedes-Benz ML450 Hybrid

In the search for the optimum hybrid system for the premium motor car, the engineers were already sure of one thing right from the concept phase: a Mercedes-Benz SUV with a hybrid drive would have to share the same typical brand attributes as any other Mercedes vehicle. Essential elements such as the greatest possible active and passive safety, optimum ride comfort and ease of operation, uncompromising reliability over a long period and high-quality workmanship with select materials would have to be on a par with a comparable, conventionally powered standard-production vehicle. And all combined with the greatest possible efficiency.

At the same time, the drive system should be testimony to the company's innovative strength and cutting-edge technology. These objectives demanded a complete development cycle -- the kind of process any new model family developed from scratch would undergo. Until the Mercedes-Benz ML 450 HYBRID reached series-production maturity, the engineers and technicians clocked up a total of four million kilometres, taking in some of the world's most extreme climatic conditions to prove the system's reliability, be it in the sub-zero Arctic circle, the searing heat of arid desert regions or in the sweltering, humid temperatures of the tropics. The work was supplemented by an extensive test-rig programme and detailed simulations as part of the "Digital Prototype".

An important aim during development was to optimally match the various subsystems within the powertrain. System matching enables the various drive modes to be easily used while the customer is driving. The two-mode hybrid technology in the ML 450 HYBRID, whose drive architecture supports purely electric operation and purely combustion engine operation or any combination of the two, takes its lead from the fundamental work undertaken by the "Global Hybrid Cooperation". This group brought together research and development work undertaken by the companies Daimler AG, BMW Group, General Motors and Chrysler.

Thanks to two-mode hybrid technology the ML 450 HYBRID boasts tangible benefits: its performance figures are on a par with a conventional eight-cylinder SUV with permanent all-wheel drive while fuel consumption and emissions have been reduced by up to 60%. The vehicle designed specifically for the US market delivers 'city' fuel consumption of 21 mpg and 'highway' consumption of 24 mpg, making it the most efficient vehicle in its segment. With its SULEV (Super Ultra Low Emission Vehicle) classification, the SUV meets the most stringent emissions standard for vehicles with a combustion engine currently applicable in the US. At the same time, the ML 450 HYBRID with a system output of 250 kW (340 hp) and a combined torque of 517 newton metres guarantees a superlative driving experience combined with an enhanced level of ride comfort.

The driver can concentrate fully on the traffic and enjoy the ML 450 HYBRID driving experience without having to select additional functions as the drive management system is fully automatic. The functionality of the 4MATIC permanent all-wheel drive system is also fully retained. At the heart of the two-mode hybrid drive is the transmission unit with two compact electric motors, three planetary gear sets and four clutches. This configuration enables the power to be split into an electrical and a mechanical path. Conventional one-mode hybrid systems tend not to have mechanical ratios. As such, this kind of system transfers the bulk of the power via the electrical path with high electrical output and hence lower efficiency.

It works efficiently principally at lower loads and speeds. If power also needs to be transferred at higher loads and speeds, an accordingly larger electric motor would be required. Having to power and find space for this engine would only be possible at the expense of efficiency. In response to increasing engine loads and higher speeds, two-mode technology, by contrast, variably shifts the power transfer from the electrical path to the mechanical drive path. As a result, the system is much more efficient in all situations, both in inner-city stop-and-go traffic as well as on fast motorway journeys, while also enabling smaller electric motors to be used. The efficiency boost -- both in urban traffic as well as on motorway journeys -- is therefore where "two-mode" technology gets its name from. The four clutches are used to distribute the driving force generated by the electric motor and combustion engine via four fixed ratios and two electric variable ratios to all four wheels on the 4MATIC permanent all-wheel-drive system, depending on the driving situation.

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