Luxury, efficiency, perfection: The new generation CL – New engines in the S-Class
Sep 07, 2010
Drive system: New dimension of efficiency
  • About 22 percent lower fuel consumption: CL 500 BlueEFFICIENCY
  • BlueDIRECT technology with third-generation direct petrol injection
  • Multi-spark ignition: up to four ignition sparks per millisecond
  • Energy management: on-demand control of the engine accessories
  • ECO start/stop function: save fuel when stopped at traffic lights
Under the bonnet of the new-generation CL, the most powerful Mercedes-Benz engines do service. The newly developed V8 biturbo engine in the CL 500 BlueEFFICIENCY opens up a new dimension of efficiency in the luxury class through the use of the innovative BlueDIRECT technology, the heart of which is the third-generation spray-guided direct petrol injection system featuring multiple injection. In the CL 600 the proven V12 biturbo engine with 5.5 litres displacement ensures refined and highly enjoyable travel.
CL 500 BlueEFFICIENCY: around 22 percent lower fuel consumption
The new V8 biturbo engine in the CL 500 BlueEFFICIENCY und CL 500 4MATIC BlueEFFICIENCY produces 320 kW (435 hp) with 15 percent less displacement (4663 instead of 5461 cc). It is around 12 percent more powerful than its naturally aspirated predecessor, which had an output of 285 kW (388 hp). Whereas the latter engine got a combined NEDC consumption of 12.3 litres of premium petrol per 100 kilometres in the CL 500, the successor aboard the Mercedes coupé is content with 9.5 litres of fuel. This figure, outstanding in the luxury segment, means fuel savings of 2.8 litres or around 22 percent. CO2 emissions also sink by around 22 percent from 288 grams per kilometre to 224 grams per kilometre – an excellent figure in this output category.
The NEDC fuel consumption of the all-wheel drive variant CL 500 4MATIC BlueEFFICIENCY is 9.9 litres per 100 kilometres (237 g CO2/km). This is 18 percent less than for the preceding model.
At the same time, maximum torque rises from 530 Newton metres to 700 Newton metres – a 32 percent increase. The new V8 also attains top figures for specific output with 68.6 kW and 150 Newton metres per litre displacement.
The maximum torque already is available from 1800 rpm, creating the precondition for an effortlessly superior display of power. This combines with a smoothness and quietness which is exceptional even for an eight-cylinder. The acceleration which the biturbo engine permits is also impressive: CL 500 BlueEFFICIENCY and CL 500 4MATIC BlueEFFICIENCY sprint from zero to 100 km/h in 4.9 seconds (predecessor: 5.4 seconds). Even more impressive is the figure for an 80 to 120 km/h sprint with kickdown – particularly important for safe overtaking on country roads. The CL 500 BlueEFFICIENCY needs 2.7 seconds for this (previously 3.1 seconds) and thus satisfies the condition for an especially relaxed and refined driving experience of a sporty character.
In the sum of its qualities the new BlueDIRECT V8 engine is unique in the luxury segment and plays in a new league. It obtains best values for fuel consumption, emissions and performance.
A hard-charging doubles team: two turbochargers breathe the V8
In the new V8, Mercedes-Benz engineers achieved a high output from a lower displacement primarily by using one turbocharger for each bank of cylinders. The intake air is forced into the eight combustion chambers at an overpressure of up to 0.9 bar, with the turbine blades rotating at up to 190,000 rpm. The turbochargers and their hot gas ducting are accommodated on the outsides of the cylinder heads. This enables the intercooler module with its air/water intercooler and charge-air distributor to be located inside the V of the engine – a solution which Mercedes-Benz engineers found to be advantageous following a long series of tests. This is confirmed by the output and fuel consumption figures achieved in practice.
The Mercedes-Benz engine designers configured the turbochargers to provide high torque even at low engine speeds. Compared to the previous engine, the result is an increase in torque at 2000 rpm by more than 45 percent. An outstanding 700 Nm is available between 1600 and 4750 rpm. The driver therefore perceives no turbo lag, but experiences the same pleasant and effortless performance from the new V8 as that delivered by a mighty, naturally aspirated 7-litre engine.
The engine is based on a diecast aluminium crankcase with aluminium/silicon cylinder liners. The developers adopted the basic and connecting rod journal diameters from the preceding engine, while raising the piston compression height for load reasons by just about 4 millimetres. By reducing the lift and shortening the connecting rod by two millimetres, it was possible to retain the interior height of the crankcase. Showing the high efficiency of the turbocharged V8, which is configured for premium petrol (RON 95), the compression ratio of 10.5:1 remains unchanged versus the naturally aspirated preceding engine.
Key figures for the new V8 engine
Number of cylinders/arrangement
Displacement (cc)
Bore (mm)
Stroke (mm)
Compression ratio
Output (kW) at rpm
320 at 5250 rpm
Torque (Nm) at rpm
700 from 1800-3500 rpm
Great savings potential: innovative technology makes V8 engine fit for the future
The power plant of the CL 500 BlueEFFICIENCY is the representative of a new generation of BlueDIRECT V8 and V6 engines. The previous engine of the CL 500 provides the technical basis for the eight-cylinder. But almost all details were newly developed or intensively revised with the goal of fuel savings and high performance and smoothness. Crankcase, pistons and cylinder head are made of aluminium. Crankshaft, connecting rods and valves are manufactured from a special forged steel. With the new engine Mercedes-Benz clearly shows that uncompromisingly improved internal combustion engines still have great potential. The BlueDIRECT technology package of the new V8 units from Mercedes-Benz includes new developments which are unique in their combination:
  • The third generation spray-guided direct petrol injection system with piezo injectors, in combination with multi-spark ignition, opens up further opportunities for optimising consumption through a homogeneous combustion process.
  • In conjunction with the ECO start/stop function, shift point adjustment and specific friction-reducing measures, improvements in day-to-day fuel consumption by more than 20 percent are possible.
  • The Mercedes designers have selectively reduced the power consumption of engine accessories. Among other things an optimised water pump with second-generation thermal management, a demand-controlled oil pump, a volume-controlled high-pressure fuel pump and an intelligent alternator management system find use.
With lightweight construction techniques and detailed improvements the Mercedes designers have also reduced in-engine friction considerably compared to the previous engine.
High precision: third generation spray-guided direct petrol injection
Spray-guided direct petrol injection, which Mercedes-Benz was the first car manufacturer to introduce in series production, in 2006, has been developed further by the Mercedes-Benz engine designers as a third-generation system in the BlueDIRECT technology package. The system pressure is maximum 180 bar in the V8, the pressure being variably optimised according to the engine's characteristic map. Completely newly developed piezo-electric injectors allow up to five injections per intake stroke for the best possible mixture formation.
The crystalline structure of the piezo-ceramic changes in microseconds under an electric voltage, and with a precision of just a few thousandths of a millimetre. The central component of a piezo-electric injector is the piezo-stack directly arranged in the high-pressure area. It controls the metering needle directly. With a response time of just 0.1 milliseconds, the fuel injection can be very sensitively and precisely adjusted to the current load and engine speed, with a beneficial effect on emissions, fuel consumption and combustion noise.
The multiple injections of smallest fuel quantities made possible by the piezo injection technique have been taken advantage of by the Mercedes-Benz engineers to control a larger useful engine characteristic map with the efficient lean-burn combustion method and to exploit the new "homogeneous split" (HSP) operating mode for the new BlueDIRECT V8 biturbo engine. In this homogeneous combustion process, more than 95 percent of the quantity is injected once or several times during the intake stroke. In addition, a very small ignition-supporting injection takes place to stabilise combustion. This is done in difficult combustion conditions.
Multi-spark ignition: best possible ignition, as need requires
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 optimising the centre 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.
Less is more: low-friction unit
The Mercedes-Benz engine designers paid particular attention to reduced
in-engine friction in the new BlueDIRECT V8 power plant. They achieved their objective primarily by a reduction in flow through the oil and water pumps, low-friction pistons, piston rings and cylinder walls, plus a new thermal management system and a new chain drive.
Intelligent design: cylinder head with new camshaft adjuster
In its basic architecture, i.e. the valve angle, valve disc diameter, valve position, cam follower valve control and combustion chamber configuration, the cylinder head of the new V8 engine is identical to that of the previous engines. Mercedes-Benz engineers have, however, modified the variable, hydraulic vane-type camshaft adjusters for the intake and exhaust sides. These now have a larger adjustment range of 40 degrees with reference to the crankshaft. They were also able to improve the functionality, achieving a 35-percent greater adjustment speed and adjustability at an oil pressure as low as 0.4 bar. Despite the better performance, this new development excels with significantly smaller dimensions and low weight. For this reason the installation space on the longitudinal and vertical axes of the engine was able to be reduced by around 15 millimetres.
The extreme compactness of the camshaft adjusters was achieved by the new, two-stage chain drive. This drives two secondary chains – one per cylinder bank – via a primary chain and an intermediate gear. All three chains can be individually adjusted via a chain tensioner. This results in low tensioning forces and low chain dynamics, ensuring consistent timing and outstanding acoustic properties, with friction reduced even further. In short, the new chain drive is compact and ensures low-noise operation.
Efficient: controlled oil pump with two pressure stages
A fourth chain drives a likewise completely newly developed, variable vane-type oil pump. It operates with two pressure stages, depending on the characteristic map. At low engine speeds and loads the pump runs at a low pressure of two bar. At this time the oil-spray nozzles for piston cooling are switched off. The high-pressure stage is activated at the upper load and engine speed levels. Thanks to this control concept, depending on engine load and engine speed the lubrication and cooling points of the engine can be supplied with significantly lower drive energy than would be possible with an uncontrolled pump.
Intelligent: new coolant ducting and 3-phase thermal management
The coolant ducting in the cylinder head is also completely new. The water mantle is of two-piece construction to improve flow. This leads to specific increases in flow speeds and heat dissipation at certain points, accompanied by a rigorous reduction in pressure throughout the coolant circuit. This has made it possible to reduce the power output of the water pump despite an increased engine output.
As it warms up, the flow of coolant is regulated by a 3-phase thermal management system so that it rapidly reaches normal operating temperature. Initially the coolant remains at rest in the engine. It then circulates in the engine circuit, but without the radiator. When a temperature of 105 degrees Celsius has been reached in normal operation (87 degrees Celsius under high load), the vehicle's radiator is included in the circuit. The water supply to the interior heating system is separately controllable.
The Mercedes designers also managed to cut component weights by the concerted replacement of aluminium and steel by plastics in components like the thermostat, belt pulley, impeller, heater valve and hydraulic lines.
Fuel-saving: ECO start/stop function with direct-start
To reduce the fuel consumption of the V8 engine, the CL 500 BlueEFFICIENCY and the CL 500 4MATIC BlueEFFICIENCY get the ECO start/stop function which shuts off the engine when the car stops, for example at traffic lights. The system is a part of the BlueEFFICIENCY package of the V8 variants and is activated as soon as the car comes to a full stop with the driver depressing the brake pedal. When travel is resumed, the engine restarts immediately and almost imperceptibly as soon as the driver takes his foot off the brake pedal or presses the accelerator. Thanks to intelligent control, the heating and entertainment systems remain operating during the stop phase for maximum comfort, as does the automatic climate control. The ECO start/stop function does not switch the engine off if the operating temperature required for proper emission control or the interior temperature desired by the driver have not yet been attained.
In the two dynamic transmission modes "S" (Sport) and "M" (Manual) the ECO start/stop function is always deactivated. But the driver can also actively switch the system off. A yellow "ECO" symbol signals to the driver that though the ECO start/stop function is switched on, one of the mentioned criteria temporarily prevents the stopping of the engine. When all necessary conditions are met,
the colour of the "ECO" symbol changes to green.
The start/stop system of the CL 500 BlueEFFICIENCY operates with starter-supported direct-start. This means that when the engine is switched off, the attitude of the crankshaft is registered by a new crankshaft sensor so that the engine control unit knows the positions of the individual cylinders. On restarting, it can then select the cylinder that is in the most suitable position for first ignition. After the starter has briefly turned over the engine, reliable injection, ignition and combustion is immediately possible in the ideally positioned cylinder.
Energy recuperation: current from braking energy
Efficient alternator management is also a part of the innovative BlueEFFICIENCY package of the CL 500 BlueEFFICIENCY and the CL 500 4MATIC BlueEFFICIENCY. When the battery is charged to more than 80 percent, the alternator is governed to take load off the engine. The energy required in this operating state is supplied by the battery. If the driver removes his foot from the accelerator pedal or applies the brakes in overrun mode, kinetic energy is recovered and fed to the battery. The experts speak of recuperation. In certain situations, for example during acceleration, the alternator is switched to no-load – that saves fuel.
Test marathon: more than seven million kilometres under the harshest conditions
The new Mercedes-Benz BlueDIRECT V8 biturbo engines demonstrated their unlimited suitability for everyday use in extensive tests under most severe conditions. The engine and their accessories spent a total of 52,000 hours on the test bench, including 27,000 hours of endurance runs. The wide-ranging programme comprised simulations of all imaginable driving situations and operating states such as hot and cold starts, stop-and-go traffic and full-throttle operation. Parallel to this the
Mercedes-Benz developers undertook strenuous tests in every climatic zone on earth – in the winter of Northern Europe and the extreme heat of Death Valley (USA), in the thin air of alpine regions and in tropical jungles. Fast laps on the high-speed ovals of Nardo (Italy) and Papenburg (Germany) as well as stop-and-go driving in heavy city traffic completed the marathon testing. On balance, the test vehicles covered more than seven million kilometres under the most adverse conditions at maximum loads with the new V8 engine.
CL 600: high-performance engine with twin turbochargers
The flagship model remains the CL 600 with its 380 kW (517 hp) twelve-cylinder biturbo engine, which accelerates the luxury coupé from a standstill to 100 km/h in impressive 4.6 seconds and in the new generation of the luxury coupé now also complies with the Euro 5 emissions control standard. Maximum torque is 830 Newton metres at 1800 rpm, which makes the 5.5-litre engine one of the world's most powerful series-production car engines. The V12 combines its impressive performance potential with exemplary smoothness and outstanding quiet running – the best possible preconditions for refined and highly enjoyable travel.
The crankcase of the twelve-cylinder engine is made from diecast aluminium, while diecast magnesium is used for the cylinder-head covers. Fracture-split or "cracked" conrods made from high-strength forged-steel alloy, pistons made from a high-quality aluminium alloy, hollow camshafts of induction-hardened forged steel, a weight-optimised forged-steel crankshaft and a diecast aluminium sump feature among the other lightweight components of the engine that were made possible by innovative material technologies.
On both sides, the turbines of the two turbochargers are integrated into the exhaust manifolds to save space, and are therefore in the best position for high efficiency. The compressed air flows through two close-coupled water intercoolers on the cylinder head covers. Depending on the engine load the air is cooled by up to 100 degrees Celsius, achieving just the right temperature and density for the combustion process.
The high-performance coupés CL 63 AMG with 400 kW (544 hp) V8 biturbo engine (5.5 litres displacement) and CL 65 AMG with 463 kW (630 hp) twelve-cylinder (6 litres displacement) are products of Mercedes-AMG. As option, for the CL 63 AMG the AMG Performance package can be ordered, in conjunction with which the output is increased to 420 kW (571 hp).
Transmission: solutions for maximum driving pleasure and low fuel consumption
As standard the eight-cylinder engine is combined with the 7G-TRONIC PLUS seven-speed automatic transmission, which has been further improved in detail, while Mercedes-Benz combines the V12 engine of the CL 600 with a five-speed automatic transmission because of the extremely high torque which is already reached at low engine speeds. The DIRECT-SELECT lever on the steering column enables the driver to select "P", "N", "R" and "D" by nudging the selector. The operating commands are transferred purely electronically, by wire.
In addition, with a switch on the centre console the driver can choose between the driving modes "Sport" (S), "Economy" (E) and "Manual" (M), which alter the transmission characteristics.
  • Economy: the automatic transmission changes gears at low revs; in this switch position the CL starts off in second gear. The ECO program is always active after the engine starts and supplants the previous "Comfort" mode.
  • Sport: the automatic transmission makes the most of the engines' speed range when changing gears. At the same time the accelerator characteristics are changed so that the engine responds more spontaneously to the driver's pressure on the accelerator.
  • Manual: the automatic transmission can be operated manually by steering wheel buttons. The shifting times are distinctly shorter even compared with the "Sport" mode.
Selection of the transmission mode is independent of the spring/damper setting of the suspension so that the driver is freer to determine the overall personality of the luxury coupé.
All in the mood for efficiency: the new 7G-TRONIC PLUS
The 7G-TRONIC seven-speed automatic transmission was improved in detail by the Mercedes engineers. The aim was to further reduce converter slip in the connection with the engine and thus optimise efficiency. In addition, the much increased torque of the V8 biturbo engine in the CL 500 BlueEFFICIENCY raised new demands on the absorption of cyclic irregularities and vibrations in the transmission. The
Mercedes-Benz developers achieved this aim in the new 7G-TRONIC PLUSwith a new torsional vibration damper among other things. It is designed as a double turbo-damper and additionally fitted with a centrifugal pendulum which shifts the mass centre of gravity as a function of engine speed and enables comfortable vehicle operation even at lower engine speeds. Moreover, the optimal damping already makes a distinct reduction in the slip of the torque converter lockup clutch possible at low loads. The result: in ECO mode the engine speed could be reduced, contributing greatly to cut fuel consumption. Plus, it ensures an even quicker response to accelerator commands.
A new hydraulic circuit and optimised torque converter characteristics also help to improve efficiency and drive-away performance. As further consumption-cutting measure a new lower-viscosity automatic transmission fluid (ATF) is used which has a longer life but the same cooling performance. In future, the CL 500 BlueEFFICIENCY only needs a transmission fluid change every 125,000 kilometres.
The optimised electrohydraulic control unit of the transmission and new reduced-friction materials in various parts of the transmission in combination with optimised software result in improved shifting comfort. Owing to a separate ATF pump the 7G-TRONIC PLUS also can feature a start/stop function for the first time. This pump ensures readiness to move off when the fixed-displacement oil pump is not working because the engine is shut off.
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