2021 Mercedes E Class Cabriolet Walkaround
65The electrification of the powertrain takes another major step forward with the facelift of the E-Class. The new two-door models also see the top version of the four-cylinder diesel engine (OM 654 M), rated at 195 kW, fitted for the first time with an integrated starter-alternator (ISG). It therefore has a 48-volt on-board partial electrical system. A recuperation function and the ability to "glide" with the engine switched off make the engine even more efficient.
Ongoing development work means that the integrated starter-alternator used here is a second-generation unit that is now part of the transmission (rather than of the engine). This means that it can be more easily combined with different engines. The extra boost that is available right from the first turn of the engine, known as EQ Boost, can deliver as much as 15 kW and 180 Nm, thus ensuring that the driving enjoyment offered by both of the sporty two-door models is even more pronounced.
The 48-volt technology with ISG is also a feature of the in-line six-cylinder petrol engine (M 256), now available for the first time in the E-Class. As with the Saloon, Estate and All-Terrain models, this unit has now been added to the engine line-up for the two-door models. A unit that is already familiar from the CLS, S-Class and GLE, its electrical boost of up to 16 kW and as much as 250 Nm reinforces the sporty character of both the Coupé and the Cabriolet. The standard combination with the all-wheel drive system 4MATIC further accentuates the dynamism of these two models. The systematic electrification of the engine is a major factor in the exceptional efficiency of the powertrain and evidence of the company's forward-looking drive system strategy.
New technical features for the OM 654: on the way to becoming the most powerful four-cylinder diesel
Fundamental further technical development is envisaged for the OM 654 four-cylinder diesel engine introduced in 2016. Leading the way among the measures aimed at further improving efficiency is the new OM 654 M with integrated starter-alternator. Along with electrification, which also includes the use of an electric refrigerant compressor for the air-conditioning system, the following are the most important modifications that allow an output of up to 195 kW plus an additional 15 kW from the EQ Boost system:
A new crankshaft increases the stroke to 94 mm and the displacement to 1993 cc (previously: 92.3 and 1950)
The injection pressure is increased to 2700 bar (previously: 2500)
Particularly fast response times and steady power delivery thanks to two water-cooled turbochargers, both featuring variable turbine geometry
A sodium-filled cooling duct in each of the steel pistons. This helps to dissipate temperature peaks in the piston recess.
Electric refrigerant compressor
In terms of exhaust gas aftertreatment, this most powerful of the four-cylinder diesel engines also takes things a step further. Its components include
a close-coupled NOx storage catalytic converter for reducing the nitrogen oxides
a DPF (diesel particulate filter with special coating for reducing the amount of nitrogen oxides)
an SCR catalyst (selective catalytic reduction; with metered injected quantity of AdBlue®) as well as
an additional SCR catalyst in the underbody of the vehicle with separately metered injected quantity of AdBlue®
The 9G-TRONIC transmission has also been further developed to accommodate the second-generation ISG and is being used, in a first step, with the four-cylinder ISG engine. The electric motor, the power electronics and the transmission cooler have now moved into or onto the transmission. Previously required cables can be eliminated, which offers advantages with regard to installation space and weight. This makes it easy to combine the transmission with the different combustion engines. In addition, the efficiency of the transmission has been increased. Amongst other things, the optimised interplay with the electric auxiliary oil pump reduces the delivery rate of the mechanical pump by 30 percent. A new generation of the fully integrated transmission control with multi-core processor and new construction and joining technology is also used here. In addition to the increased computing power, the number of electric interfaces has been drastically reduced, and the weight of the transmission control has been cut by 30 percent.
The line-up of diesel engines is completed by the in-line six-cylinder unit (OM 656), which is also available for the two-door models in conjunction with the all-wheel drive system 4MATIC.
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