Mercedes-Benz is introducing four new diesel and gasoline engines for its luxury S-Class, including the first four-cylinder engine in its almost 60-year history, the S 250 CDI BlueEFFICIENCY diesel.
Developing an output of 150 kW (204 hp), the S 250 CDI BlueEFFICIENCY achieves a fuel consumption of just 5.7 liters per 100 kilometers (41 mpg US) NEDC, corresponding to CO2 emissions of 149 grams per kilometer. The likewise new V6 diesel in the S 350 BlueTEC delivers 190 kW (258 hp) and has a combined consumption of 6.8 L/100 kilometers (35 mpg US, 177 g CO2/km). With 225 kW (306 hp) in the S 350 BlueEFFICIENCY and 320 kW (435 hp) in the S 500 BlueEFFICIENCY, the new BlueDIRECT gasoline engine generation is now entering the lists in the form of V6 and V8 variants. (Earlier post.)
S 250 CDI BlueEFFICIENCY. With peak power output of 150 kW (204 hp) and maximum torque of 500 N&iddot;m (369 lb-ft), the inline four-cylinder CDI accelerates the large sedan from 0 to 100 km/h in 8.2 seconds, and attains a top speed of 240 km/h (149 mph).
The 2143 cc CDI engine delivers its maximum torque of 500 N&iddot;m at 1600 rpm. The high torque at low engine speeds is a result of two-stage turbocharging. This technology, which is employed in a series-production passenger car diesel engine for the first time in the C and E-Class, is predominantly responsible for the high output at the level of a six-cylinder power unit.
The compact module for the two-stage turbocharger consists of a small high-pressure (HP) turbocharger and a large low-pressure (LP) turbocharger. These are connected in series, and each has a turbine and a compressor driven by this turbine. The HP turbine is located directly at the exhaust manifold and initially allows exhaust gas to flow through it; it then rotates at up to 215,000 revolutions per minute.
The HP turbine housing features an integral bypass duct, which can be opened or closed by means of a charge-pressure control flap triggered by a vacuum cell. If the flap is closed, the whole exhaust stream flows through the HP turbine, so that the exhaust-gas energy is available solely for the HP turbine drive. This means that the optimum charge pressure can be built up at low engine revs.
The two compressors are likewise connected in series, and are in addition connected to a bypass duct. The combustion air from the air filter first flows through the low-pressure compressor, where it is compressed as a function of the LP turbine’s output. This pre-compressed air then passes into the high-pressure compressor, which is coupled to the HP turbine, where it undergoes further compression. The result is a genuine two-stage turbocharging process. The major advantage of this demand-related control of the combustion air supply using two turbochargers is improved cylinder charging, and therefore high torque even at low engine speeds. Fuel consumption is also reduced. When the car is driven, this concept makes itself felt by harmonious driving characteristics with no turbo-lag, a favorable torque curve across the entire engine speed range, responsiveness and performance.
The new diesel also features fourth-generation common rail direct injection, with a rail pressure of 2000 bar.
Dynamically controlled engine mounts feature as an innovation in the new S 250 CDI BlueEFFICIENCY. The rigidity and damping of these mounts alter according to engine speed, load and vehicle speed, thus preventing the transmission of unwanted vibrations and noise from the engine to the body.
S 350 BlueTEC. The second new diesel model in the S-Class is the S 350 BlueTEC. Its V6 develops an output of 190 kW (258 hp) from a displacement of 2987 cc—10% more than the previous model, which delivered 173 kW (235 hp). The torque of the V6 diesel has increased by 15% from 540 to 620 N&iddot;m (457 lb-ft). Despite the performance improvements, the S 350 BlueTEC betters the fuel consumption of its predecessor by 0.8 liters (11%). CO2 emissions have likewise fallen by 11%, from 199 to 177 grams per kilometer.
The V6 diesel accelerates from zero to 100 km/h in 7.1 seconds and has a top speed of 250 km/h (155 mph).
The S 350 BlueTEC uses urea-based selective catalytic reduction to comply with coming EU6 emissions standards. The AdBlue tank is installed under the trunk floor and has a capacity of 25.7 liters. The supply is replenished at the regular maintenance intervals, every 25,000 kilometers.
BlueDIRECT V6 and V8 engines. The two BlueDIRECT power plants are representatives of a new generation of BlueDIRECT V6 and V8 engines. The centerpiece of the BlueDIRECT technology package is the improved third-generation direct petrol injection with spray-guided combustion and piezo injectors. In combination with multi-spark ignition it taps further possibilities for improving consumption—in the V8 unit through a further developed homogeneous combustion process (homogeneous split); in the V6 engine through a new stratified combustion method with a much larger useful engine characteristic map and lean-burn combustion for optimum consumption (homogeneous stratified mode).
The HOS method is a combination of homogeneous-lean and conventional stratified combustion. The first injection takes place during the intake stroke so that a homogeneous base mixture is formed. The stratified injection proper takes place during the compression stroke prior to ignition, as map-controlled single or double injection.
The third-generation direct injection system also features rapid multi-spark ignition (MSI). Following the first spark discharge and a brief combustion period, the coil is rapidly recharged and a further spark is discharged. The MSI system enables up to four sparks to be discharged in rapid succession within one millisecond, creating a plasma with a larger spatial expansion than conventional ignition. Controlling this rapid multi-spark ignition enables both the time lapse before the next spark and the combustion duration for the relevant operating point to be optimally adjusted. This provides scope for optimizing the center of combustion and improving residual gas compatibility, especially during stratified charge operation. Fuel consumption can be reduced by roughly two percent in this way.
Depending on the driving cycle, fuel savings of up to four percent are possible alone by the use of piezo-electric injection technology in combination with multi-spark ignition.
S 350 BlueEFFICIENCY. The 3.5-liter V6 engine of the S 350 BlueEFFICIENCY and S 350 4MATIC BlueEFFICIENCY is naturally aspirated, but also suitable for the future use of a turbocharger thanks to the modular design concept. The new V6 unit feature a reduction in the V-angle between the cylinder banks compared to its predecessor from 90 degrees to 60 degrees. This enables the primary balancer shaft to be omitted, and as a result the driver registers a high level of comfort.
The design highlights of the 3.5-liter V6 include a completely new air intake and exhaust system in conjunction with a variable resonance intake manifold and optimized inflow and outflow. With the same displacement, the output compared with the previous 200 kW (272 hp) model is increased by 12.5% to 225 kW (306 hp), while maximum torque has increased by 5.7% to 370 N&iddot;m (273 lb-ft) and now is available over a broad engine speed range from 3500 to 5250 rpm.
The new engine also cuts NEDC fuel consumption compared to the prior unit by 24% (7.6 L/100km, 31 mpg US). CO2 emissions have also fallen by 24% from 234 to 177 grams per kilometer (short wheelbase) and by 23.5% to 179 grams per kilometer (long wheelbase). The S 350 BlueEFFICIENCY accelerates from standstill to 100 km/h in 6.9 seconds. Top speed is 250 km/h (electronically limited).
S 500 BlueEFFICIENCY. The new V8 biturbo engine in the S 500 BlueEFFICIENCY and S 500 4MATIC BlueEFFICIENCY generates 320 kW (435 hp) with 15% less displacement (4663 instead of 5461 cc), and around 12% more output than its 285 kW (388 hp) predecessor. Torque has risen 32% from 530 to 700 N&iddot;m (516 lb-ft).
Despite a considerable increase in power of 35 kW (47 hp), Mercedes developers have been able to reduce the combined fuel consumption of the S 500 BlueEFFICIENCY significantly. At 9.3 liters of premium gasoline per 100 kilometers (25 mpg US), this is 15.5% (short wheelbase) and 16% (long wheelbase) below the figure for the preceding model. This corresponds to CO2 emissions of 219 grams per kilometer.
The S 500 BlueEFFICIENCY sprints from zero to 100 km/h in 5.0 seconds. Top speed is 250 km/h (electronically limited). The increase in output and torque despite the reduced displacement is mainly due to the use of two turbochargers—one for each bank of cylinders. These force the intake air into the eight combustion chambers at a pressure of up to 0.9.
The turbochargers are configured to provide a high torque at low engine speeds, with 600 N&iddot;m (443 lb-ft) already available between 1600 and 4750 rpm.
Demand-controlled ancillary units. In order to improve efficiency, Mercedes-Benz developers have also reduced the power consumption of the ancillary units for the new gasoline and diesel engines. One of these is a newly developed, controlled oil pump. This operates at two pressure levels. At low engine speeds and loads the pump runs at a low pressure. The high-pressure stage is activated at the upper load and engine speed levels. Through this control concept, the lubrication and cooling points of the engine can be supplied with significantly lower drive energy than would be possible with an uncontrolled pump. In this way, the developers have particularly managed to lower fuel consumption in driving modes requiring less power, for example in urban traffic.
Another feature is the switchable water pump. To enable faster engine warm-up, the pump is not activated until the optimum operating temperature is reached. This also contributes to the reduction in fuel consumption.
In the S 350 BlueEFFICIENCY and S 500 BlueEFFICIENCY, there is also intelligent generator management with braking energy recuperation.
The new 7G-TRONIC PLUS. All four new engines are combined with the new 7G-TRONIC PLUS 7-speed automatic transmission, which brings a further reduction in torque converter slip and optimized efficiency. A central role is played by the new torsion damper, which eliminates torsional eccentricities and vibrations in the transmission. The lower the rpm and the lower the number of cylinders, the more severe these can be. This results in a conflict of aims between comfort and fuel-efficient operation.
Mercedes-Benz developers resolved this by using a twin-turbine damper, which is also fitted with a centrifugal pendulum. Depending on the rpm, this moves the center of mass and allows comfortable operation even in the most economical operating range.
The optimized damping allows a marked reduction in the slip of the torque converter lockup clutch even under low loads. In the fuel-efficient ECO transmission mode, this has enabled engine speeds to be lowered without compromising signature S-Class comfort. In addition, the optimized damping of rotational irregularities and vibrations in the transmission allows an even faster response to driver commands via the accelerator pedal.