2007 Mercedes CLS in Depth

Press Release

Page 1: Short Version
Page 2: Model Range/Equipment
Page 3: Engine (I)
Page 4: Engine (II)
Page 5: Active & Passive Safety
Page 6: Chassis
Page 7: Specifications

Emission control: in-engine measures plus four catalytic converters

As in the previous V6 with port injection, the emission control concept of the new CGI engine has two stages: it is based both on measures within the engine that ensure low untreated emissions and on effective exhaust gas treatment by a total of four catalytic converters.

The measures within the engine specifically include the Mercedes-developed combustion process featuring multiple closely spaced injections on each power stroke. This improves the exhaust quality of the V6 engine in the warm-up phase, as actively controlled injection and combustion using low quantities of fuel ensures higher temperatures in the exhaust manifold and accelerates catalytic converter warm-up. Just ten seconds after a cold start, the direct-injection petrol engine reaches an exhaust temperature of over 700 degrees Celsius. Dual electrically controlled exhaust gas recirculation is also employed, with which up to 40 percent of the exhaust gases can be returned to the combustion chambers. This achieves a considerable reduction in nitrogen oxide emissions.

Emission control begins with two close-coupled three-way catalytic converters, each of them monitored by two oxygen sensors - a control sensor and a diagnostic sensor. This linear oxygen sensor control goes into operation immediately after the engine starts from cold, providing information about the exhaust gas constituents which the electronic control unit of the V6 uses for a controlled warm-up.

As conventional catalytic converters require a ???????????????????????????????????stoichiometric???????????????????????????????? fuel-air mixture (lambda = 1), but stratified charge operation uses a high excess of air (lambda >1), the CLS 350 CGI is equipped with two NOx adsorber converters. Under lean operating conditions these catalytic converters adsorb the nitrogen oxides, then desorb them during brief regeneration pulses so that they react with other exhaust gas constituents to form harmless nitrogen. The NOx adsorber converters are also monitored by sensors - a temperature and a nitrogen oxide sensor.

High-tech innovations for increased comfort, torque and fuel economy

The new direct-injection petrol engine is based on the port-injected V6 powerplant first presented by Mercedes-Benz in 2004. In addition to its pioneering injection process, this engine excels with a number of other technical innovations:

• Variable camshaft timing on the intake and exhaust sides (no other V6 engine has this feature) improves the available output. The camshaft angles are each continuously adjustable by anything up to 40 degrees to ensure that the valves are able to open and close at the most favourable time in any driving situation.

• A variable intake module varies the air supply as required. The length of the intake ducts leading to the cylinders is adjusted by means of flaps: at lower engine speeds the flaps are closed to increase the length of the intake duct. This creates pressure waves which support the intake process and make a significant improvement to the torque yield in the lower engine speed range. As a result, 317 Nm - around 87 percent of the maximum torque - is already available from 1500 rpm.

• The cylinder head and crankcase are of aluminium. The pistons, connecting rods and cylinder liners also follow the latest design principles, not only helping to save weight but also making a positive contribution to responsiveness and smooth running.

• The cylinder liners are surfaced with a low-friction aluminium-silicon alloy which has proved its worth in other Mercedes-Benz car engines. Other advantages include high dimensional stability, exemplary thermal characteristics and low weight. The weight saving compared with conventional grey cast-iron liners is around 500 grams per cylinder.

• A balancer shaft between the two cylinder banks offsets the free vibration moments which are inherent to a V6 engine, ensuring exemplary smooth running. It counter-rotates at the same speed as the crankshaft.

Eight-cylinder powerplant from the S-Class

The new V8 power unit for the CLS-Class develops 285 kW/388 hp from a displacement of 5.5 litres, an increase of more than 26 percent over the previous eight-cylinder engine. The maximum torque is meanwhile boosted to 530 Nm, which is about 15 percent higher than previously.

The most important data of the CLS 500 at a glance:

The eight-cylinder engine also exhibits its dynamic power when the driver is passing another vehicle, as it takes the CLS 500 only 4.8 seconds to accelerate from 60 to 120 km/h in third gear.

Shifting camshafts for a perfect gas cycle and higher torque

Mercedes engineers already use an intelligent valve control system in the V6 engines, achieving remarkable progress that contributes substantially to the unit??????????????????????????????????????s high torque and performance characteristics as well as its low fuel consumption. In addition to four-valve technology, continuously adjustable intake and exhaust camshafts ensure that the cylinders are optimally supplied with a fresh gas mixture. The valves are opened at precisely the right moment in any driving situation, significantly improving the gas cycle in the combustion chambers and reducing energy losses.

In the new eight-cylinder engine the engineers at Mercedes-Benz have optimised the effect of this four-fold, continuous camshaft adjustment by using shifting camshafts. These control the opening of the exhaust valves and improve the engine??????????????????????????????????????s gas cycle even further. The exhaust cams are designed in such a way that the valves open at different times during the exhaust cycle. This reduces the pressure fluctuations in the exhaust tract which are inherent to a V8 engine, and which lead to an inconsistent residual gas content in the cylinders. As a result, the engine achieves a higher torque and runs more smoothly. At 2000 rpm, for example, the effective mean pressure is around six percent (10.3 : 11.0 bar) higher than in a comparable engine without shifting camshafts.

The developers of the new Mercedes eight-cylinder engine have also made a major contribution to fuel economy with a sophisticated heat management system. Coolant circulation is interrupted during the warm-up phase so that the engine reaches its normal operating temperature more quickly. This rapidly heats up the engine oil and considerably reduces friction in the engine. When the engine is warm and under full load, the heat flows are directed in such a way that the engine oil and coolant are always at an optimal temperature. This is ensured by an innovative, electronic map-controlled thermostat which is active in all operating situations and adjusts the coolant temperature according to the style of driving and the prevailing conditions. This also enables the heat supply to the heat exchanger in the heating system to be controlled as needed.

Twin catalytic converters and linear lambda control for low exhaust emissions

The emission control system of the new Mercedes eight-cylinder engine features a two-stage design and is therefore highly effective. In addition to measures within the engine such as continuous camshaft adjustment, need-related combustion control by means of tumble flaps, internal exhaust gas recirculation and secondary air injection, which ensure low untreated emissions, the new CLS 500 is equipped with two close-coupled catalytic converters as standard. These consist of two individual monoliths or bricks, each of which is monitored by two oxygen sensors: a control sensor upstream of the converter and a diagnostic sensor which analyses the exhaust flow in the gap between the two bricks.