Drive system: Biturbo engines and 9G-TRONIC: Power and efficiency

Feb 27, 2016
Sophisticated V-engines with twin turbochargers ensure high output and impressive pulling power - transferred to the road smoothly and efficiently by the new 9G-TRONIC automatic transmission.
Now uprated by 25 kW for the SL 400, the V6 biturbo with a displacement of three litres comes from the M276 engine family and features the BlueDIRECT injection and combustion system. Cylinder heads and block are made of aluminium. To reduce friction, the cylinder barrels are coated with the aid of the innovative NANOSLIDE process. Other engine characteristics include four valves per cylinder, a particularly quiet chain drive system with silent chains and two camshaft adjusters each for the intake and exhaust sides. The car is equipped with a direct coil ignition system.
The third-generation direct injection system has a fuel pressure of 200 bar and spray-guided multiple injection with piezo injection nozzles. The on-demand vane-type oil pump cools and lubricates the engine depending on engine load and engine speed. The volume control distinguishes between a low and a high pressure level and adjusts the volume flow as required. The weight of the components of the water circuit was reduced through the specific use of plastic. In an extended temperature range the heating supply for the interior is preferentially served. The desired temperature is thus very quickly reached during the warm-up phase.
Despite the different cylinder angle (90° vs. 60°), the M278 series V8 engine in the SL 500 is closely related to the six-cylinder unit. The crankcase, pistons and cylinder heads are likewise made of aluminium, while the injection and combustion process follow the same principle. Here, too, the Mercedes-Benz engineers have achieved high performance with good drivability, particularly thanks to the use of one exhaust gas turbocharger per cylinder bank.
The key data at a glance:
SL 400
SL 500
Number of cylinders/arrangement
6/V
8/V
V-angle (degrees)
60
90
Bore/stroke (mm)
88.0/82.1
92.9/86.0
Displacement (cc)
2996
4663
Number of turbochargers
2
2
Excess charge pressure at full load (bar)
1.80
0.9
Compression ratio
10.5:1
10.5:1
Engine weight, dry (kg)
179.2
222.5
Injection process
Spray-guided direct petrol injection
Valves per cylinder
4
4
Number of camshafts
4
4
Rated output (kW/hp at rpm)
270 (367) at
5500-6000
335 (455) at 5250
Rated torque (Nm at rpm)
500 at 2000-4200
700 at 1800-3500
Fuel consumption (combined) from (l/100 km)
7.7
9.0
Combined CO2 emissions from (g/km)
175
205
Efficiency class
D
E
Acceleration 0-100 km/h (s)
4.9
4.3
Top speed (km/h)*
250
250
*Electronically limited
 
New 9G-TRONIC nine-speed automatic transmission: comfort and efficiency
The 9G-TRONIC, being used in the SL for the first time, is a highly efficient transmission. The broad ratio spread of 9.15 for gears one to nine allows a clearly perceptible reduction in engine speed and is a decisive factor behind the high level of energy efficiency and ride comfort. Shortened shift and response times ensure optimum immediacy combined with outstanding ease of shifting. In manual mode and S mode in particular, the 9G-TRONIC responds significantly more spontaneously than the previous transmission and enhances driving pleasure. Plus it has a 'sailing' function in E mode.
The particular ease of shifting of new 9G-TRONIC comes courtesy of a comprehensive package of 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. Together with the extended gear ratio spread, higher speeds can now be driven at lower engine speeds for even greater comfort.
A further focus of transmission development was "compact lightweight construction". Despite two additional gears and a maximum transferable torque of up to 1000 newton metres, the new automatic transmission requires as little installation space as its predecessor and is also lighter in weight. The two-piece housing design has been retained: the torque converter housing is made of lightweight aluminium, while the transmission housing with weight-optimised plastic oil pan is made of an even lighter magnesium alloy. Nine gears are implemented with a minimal number of planetary gear sets and shift elements: only four simple planetary gear sets and six shift elements are necessary. Three speed sensors monitor operation and provide the transmission control system with corresponding data for effective shifting. It is possible for several gears to be jumped when accelerating or decelerating, should the driving conditions call for it.
To ensure the reliable and at the same time energy-efficient supply of long-lasting and shear-resistant, second-generation synthetic fuel economy engine oil, the new automatic transmission is equipped with two pumps. The considerably smaller mechanical main pump, featuring an off-axis design, is located next to the main shaft and is chain-driven and fed by a separate electric auxiliary pump. This design enables the flow of lubrication and coolant to be controlled actively on demand and also means that the 9G-TRONIC can benefit from a start/stop system. Thanks to the world's first direct control system in a planetary automatic transmission with nine gears, it has also been possible to significantly increase hydraulic efficiency within the transmission. The higher number of gears and the broader gear ratio spread help to increase drive comfort and allow a significant enhancement to be achieved in terms of engine power conversion.
Mercedes-Benz SL. 9G-TRONIC gear
15C1369_19
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