Mercedes-Benz New Eight-Cylinder CDI Engine

Press Release

State-of-the-art technology for the finest in diesel-powered driving

 

·          World's highest-torque passenger car diesel V8 engine

·          Advanced lightweight aluminium construction

·          Newly developed biturbo system

·          Third-generation common-rail direct injection

·          Maintenance-free particulate filter fitted as standard

 

Developing output of 231 kW/314 hp and maximum torque nudging 730 Newton metres, the V8 diesel engine represents an impressive new chapter in the 70-year history of passenger car diesel engines at Mercedes-Benz. The new unit also underlines in emphatic fashion the expertise of the Stuttgart-based manufacturer in the development and production of state-of-the-art diesel engines. The new eight-cylinder unit is currently the world's highest-torque diesel V8 powerplant for a passenger car.

 

The newly developed V8 celebrates its premiere in the E-Class in autumn 2005 and will also be made available for other Mercedes-Benz passenger car model series in the future.

 

Boasting third-generation common-rail direct injection, piezo injectors, biturbocharging with variable turbine geometry, electrically controlled exhaust gas recirculation with bypass duct, water-cooled intercooler and a selection of other systems besides, the new eight-cylinder engine constitutes a unique package of high-tech innovations. Majestic power development, imposing torque, exemplary smooth running characteristics and low fuel consumption and exhaust emissions are all part of the service. Look no further for diesel-powered driving pleasure of the highest order.

 

A comparison with Mercedes-Benz' previous eight-cylinder CDI engine highlights the main selling points of the V8 under the bonnet of the E 420 CDI:

·          Output: up 20 per cent

·          Torque: up 30 per cent

 

Added to which, the new power unit burns less fuel, despite its higher output, and meets the stringent EU-4 exhaust limits. The E 420 CDI is fitted as standard with a maintenance-free particulate filter system.

 

Aluminium crankcase: power-to-weight ratio cut by 13 per cent

 

A sand-cast aluminium crankcase forms the high-strength and remarkably durable basis for the new CDI engine. This material is a key factor in the engine's impressive power-to-weight ratio of 1.12 kg/kW -- 13 per cent below the value of its predecessor.

 

A bedplate construction ensures that the engine generates very little noise and low vibrations. The bedplate is an aluminium base section with integral grey cast iron inlays for the crankshaft main bearings. It supports the crank mechanism from underneath and provides additional structural rigidity. This helps to reduce longitudinal vibrations on the engine block extremely efficiently.

 

The pistons move along a 86-millimetre stroke in "wet" cylinder liners, which are in direct contact with the coolant and thus ensure that the crankcase is cooled as required. The pistons have also been newly developed, in order to withstand the high firing pressure (175 bar) inside the engine and to improve exhaust efficiency. To this end, a flat recess in the piston crown enhances the combustion process and helps to significantly reduce smoke emissions under full load. The supports for the piston rings have a special cooling duct and are oil-cooled - another new feature for a Mercedes-Benz passenger car diesel engine.

 

In the interests of keeping dimensions compact, the Mercedes engineers have arranged the cylinder banks at an angle of 75 degrees and fitted the eight­cylinder unit with a balancer shaft, which rotates in the opposite direction to the crankshaft and evens out vibrations. Likewise, the square stroke/bore ratio helps to give the new Mercedes diesel engine the smooth-running properties you  would expect from an eight-cylinder unit. At the front end of the balancer shaft is an oil separator, which uses centrifugal force to act as a vent for the engine. The chain­driven device sucks gas containing oil out of the crankcase, before using gravity to filter out the oil. While the oil flows back into the engine, the gases move forwards out of the centrifuge and through a heated vent line into the intake pipe of the V8 engine. A valve takes care of the necessary pressure compensation.

 

The most important data of the new eight-cylinder CDI engine at a glance:

 

 

At 97 millimetres, the distance between the cylinders is the same as that in the previous Mercedes-Benz V8 diesel engine. The outstanding feature of the aluminium cylinder heads are the raised layers in the water jacket, which ensure impressive rigidity. A double-bush timing chain, which is lubricated by a separate oil sprayer, provides the drive for the exhaust camshafts. The distribution of oil over the chain allows it to be spread efficiently over the outer joint surfaces by centrifugal force. The intake and exhaust camshafts are connected by toothed gears, and the high-pressure pump in the common-rail injection system is also driven by toothed gear.

 

Air ducting optimises flow, pressure loss falls by 60 per cent

 

The two exhaust-gas turbochargers, which draw in and compress fresh air through the engine's air filter, are located on the outer sides of the cylinder banks. Integrated hot-film air mass sensors supply the electronics with important basic information for the engine management. Another special feature developed by the Mercedes engineers are hollow inserts integrated into the intake lines, which increase the volume of the air before it enters the turbochargers. This raises torque output at lower engine speeds by up to 15 per cent.

 

The V8 engineers used sophisticated airflow calculations and simulations to reduce the loss of pressure typically experienced in the charge air manifolds of turbochargers and provide a sustained improvement in the supply of air to the new diesel engine. Under full load, the pressure loss is some 30 per cent lower in the charge air manifolds at the entry to the turbochargers than in Mercedes-Benz' previous eight-cylinder CDI engine, and as much as 60 per cent lower in the charge air manifolds at the exit of the turbochargers. This means that an up to 15 per cent greater air mass can flow through the manifolds.

 

Improved VNT turbochargers: higher output coupled with reduced fuel consumption

 

Mercedes-Benz has also made further improvements to the turbochargers. These continue to work according to the proven VNT (Variable Nozzle Turbine) principle and are fitted with variably adjustable guide vanes, which alter their opening angle - and thus the flow area - according to the loads on the engine. This allows them to fully exploit the exhaust energy and create maximum charge pressure. Higher torque, lower exhaust gas backpressure under full load and low smoke output at high speeds are the principal advantages of variable turbochargers.

 

New vane geometry for the compressor and turbine wheels and the guide vanes makes the new engine more efficient than the previous eight-cylinder CDI unit, whilst the maximum permitted turbocharger speed has been further increased.

 

These measures help to raise engine output and reduce fuel consumption, and the durability of the turbochargers under high temperatures has also been improved.

 

Majestic power development: 730 Newton metres as low as 2200 rpm

 

The exhaust-gas turbochargers play a key role in the exceptional torque and output of the new V8 engine. An electronic control system and dual air mass sensor allow the biturbo system to work in synchrony and adapts the supply of combustion air precisely to the output requirement. This enables the engine to develop over 580 Newton metres of torque as low down as some 1600 rpm - that's 80 per cent of the maximum value (see diagram) and higher than the peak torque of its diesel predecessor. The new eight-cylinder unit develops over 700 Newton metres of pulling power at 1950 rpm, with maximum torque hitting 730 Newton metres at 2200 rpm.

 

Which all helps explain how the powerplant under the bonnet of the Mercedes-Benz E 420 CDI is capable of such remarkable performance figures. The Saloon accelerates from 0 to 100 km/h in just 6.1 seconds and completes the third-gear sprint from 60 to 120 km/h in 5.4 seconds. Below is an overview of the engine's performance data:

 

 

*electronically governed