Powertrain: Sublime power in velvet gloves

Nov 21, 2019
Stuttgart/Guangzhou

The new Mercedes-Maybach GLS 600 4MATIC (combined fuel consumption: 12.0-11.7 l/100 km; combined CO2 emissions: 273-266 g/km)[1] is driven exclusively by the powerful and discreet M 177 – a new, electrified variant of the V8 petrol engine with a displacement of 3982 cc, 48-volt on-board electrical system and integrated starter-alternator (ISG). ISG is responsible for hybrid functions such as EQ Boost or energy recovery, while allowing fuel savings that were previously reserved for high-voltage hybrid technology. The development focused on the long-term improvement of the consumption and emissions figures. At the same time, the customers' power expectations need to be met. As a result, the engine produces an output of 410 kW (558 hp) and 730 Nm of torque. An additional 250 Nm of torque and 16 kW/22 hp output are available temporarily via EQ Boost. Power is transmitted by the 9G-TRONIC automatic transmission. The wide spread of ratios for gears one to nine ensures a significant reduction in the engine speed and is a decisive factor behind the high levels of drive and ride comfort. Likewise standard is the transfer case with variable transfer of the drive torque from 0-100 percent (Torque on Demand) between the axles.

The new biturbo is configured for high drive comfort and, at the same time, high efficiency and effective emissions reduction. Stand-out features of the V8 in this engine family include the cylinder shut-off in the part-load range. The variable valve control system CAMTRONIC shuts off four cylinders at once. This reduces the gas exchange losses while improving the overall efficiency of the remaining four cylinders in combustion mode by shifting the operating point towards higher loads.

In the Mercedes-Maybach GLS 600 4MATIC, the cylinder shut-off is active in the DYNAMIC SELECT Comfort drive program in the 800 – 3250 rpm speed range. Above that engine speed or when the driver strongly presses the accelerator pedal, cylinders 2, 3, 5 and 8 are switched on within milliseconds. The transition between the two operating modes is seamless and with no loss of comfort for the occupants. A pendulum-type absorber reduces both fourth-order vibrations in eight-cylinder mode as well as second-order vibrations in four-cylinder mode.

The two cylinder heads have particularly high thermal resistance and are thermally conductive thanks to a zirconium alloy. Their intake and exhaust ducts form the tumble, the movement of the air mass during cylinder charging, for particularly efficient and low-emission mixture formation and combustion. A third-generation spray-guided direct petrol injection system with piezo injectors also ensures multiple injections as needed with 100 to 200 bar. The two instantly responding twin-scroll turbochargers are positioned in the "hot inside V" between the cylinder banks to save space. Their boost pressure is adapted to the demand in real time by a control valve. These measures are intertwined and improve the thermal efficiency and the emissions level.

To keep the mechanical losses low, the cylinder surfaces feature NANOSLIDE® coating. Another measure implemented to reduce friction and therefore consumption is "spectacle honing", which prevents unwanted distortion during machining of the cylinder surfaces and thus reduces in-engine friction subsequently.

Saving without compromising: EQ Boost

EQ Boost through the ISG offers great potential for fuel saving and added comfort due to the load point transfer during which the combustion engine is used at a more efficient operating point due to precisely measured additional torque of the ISG. During deceleration, the kinetic energy from the starter-generator is converted into electric power ("recuperated") as appropriate to the driving situation and used to charge the battery.

Knowing where to send the power: 9G-TRONIC and Torque on Demand

Power is sent to the road via the 9G-TRONIC automatic transmission, which has been enhanced to handle the V8 engine's high torque. The particularly good gear-shifting comfort of the nine-speed automatic transmission is the result of extensive measures. These include the novel direct control system which enables short, barely perceptible gear changes. The combination of twin-turbine torsional damper and centrifugal pendulum technology in the torque converter ensures outstanding drive comfort. An additional, electric transmission oil pump is activated in start/stop operation, ensuring a basic supply to the control elements and actuators. The delay between the desire to move off and the vehicle's actual movement is reduced by the electric transmission oil pump.

The 9G-TRONIC's output shaft goes straight through to the transfer case. Its electronically controlled multiplate clutch allows a variable transfer of the drive torque from 0-100 percent (Torque on Demand) between the axles. This takes into account the driver's wishes and the selected drive program, and physical factors such as the current yaw rate or actual traction are also considered. These are used to continuously calculate the most favourable torque distribution, so as to transfer correspondingly more drive torque to the front axle via the multiplate clutch in the transfer case. The result is reliable and stable handling.

When moving off either forwards or in reverse, Torque on Demand ensures the best possible traction even on ice and snow. Here the controlled clutch acts like the centre differential lock in a traditional cross-country vehicle and distributes torque consistently to both axles. During dynamic driving manoeuvres such as driving slaloms, evasive action or cornering, on the other hand, the drive torque at the front axle is reduced to increase lateral stability at the front wheels. The new transfer case also has a positive effect on longitudinal dynamics and ride comfort, as the engine torque no longer needs to be reduced for the purposes of load reversal damping.

Character at the touch of a button: DYNAMIC SELECT

Like the suspension, the powertrain of the Mercedes-Maybach GLS can be adapted to the driver's requirements by selecting a drive program using the DYNAMIC SELECT switch. Here, too, the exclusive Maybach drive program has the task of optimising comfort in terms of noise and vibration levels. The program's settings focus on the engine and transmission and have been configured specifically for the chauffeur mode:

  • Very flat accelerator curve for starting off smoothly
  • Transmission tuning with fewer gearshifts for smooth driving
  • Starting off in second gear
  • No stop/start function.

The smooth control strategies used for the drive system here are also exceptionally energy-efficient. The Off-Road drive program is designed to provide excellent traction when driving off-road, e.g. on farm tracks, gravel, sand or similar. There is also a Sport program, which adapts the dynamic handling control and gearshift points for dynamic driving.

[1]Figures for fuel consumption and CO2 emissions are provisional and were determined by the Technical Service for the certification process in accordance with the WLTP test method and correlated into NEDC figures. EC type approval and a certificate of conformity with official figures are not yet available. Differences between the stated figures and the official figures are possible.

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