New Mercedes 4-Cylinder Diesel Engine

Press Release

The next chapter in the Mercedes-Benz diesel success story

This new diesel powerplant is Mercedes-Benz's resounding answer to questions over the future of motoring, and marks yet another milestone in the evolution of diesel technology. At the same time, the Stuttgart-based automotive manufacturer is perpetuating a long-standing tradition. It was as long ago as 1936 that the diesel engine received its world premiere in a passenger car from Mercedes-Benz - the now legendary 260 D. Ever since, Mercedes-Benz has been hard at work advancing and honing the technology it pioneered. There have been many momentous occasions over the years, including the first ever turbodiesel passenger car engine in the Mercedes-Benz 300 SD (1977), the world premiere of four-valve technology (1995), the first diesel-powered saloons with particulate filter system in the US state of California (1985), common-rail direct injection technology (1997), the maintenance-free diesel particulate filter (2003) which has in the meantime become available for all Mercedes-Benz diesel models, as well as the introduction of BlueTec technology (2006) for the cleanest-running diesel engines in the world.

100,000 hours on the test rig and ten million test kilometres

Mercedes-Benz is now adding the latest chapter to this long-running success story with the arrival of its all-new, groundbreaking four-cylinder diesel engine. After a 48-month development period, during which time the design engineers employed the very latest computer technology, the first prototype of the new engine was put into operation in August 2005. Some 100,000 hours on the test rig were required to elicit optimum performance characteristics from the new engine under all conditions and regardless of the intended purpose. The power units were subject to tough endurance testing, including acutely demanding cycles on the test rigs that were designed to truly put them through their paces. Over a distance of ten million test kilometres in a variety of vehicles, the engine had to prove its mettle in the baking heat of the desert and the icy cold of the polar regions, withstanding dust, mud, water and the very harshest treatment in the process.

The new engine celebrates its premiere in autumn 2008, when the first power rating variant will be launched in just the C-Class initially. The power unit is due to be deployed in various model series from Mercedes-Benz, returning outstanding fuel consumption figures in all cases. It can be installed both lengthways and crossways and is envisaged for all-wheel-drive vehicles too. Naturally, the new engine can be supplemented by the cutting-edge BlueTec emissions control system developed by Mercedes-Benz, and it is also earmarked for use as a fuel-efficient internal combustion engine in hybrid vehicles.

Innovative technologies without parallel

The exemplary figures achieved by the new engine for output and torque characteristics, economy, exhaust emissions and smoothness are the result
of a whole raft of innovative technologies. These include a number of new developments, the likes of which cannot currently be found in any other standard-production passenger car diesel engine. The principal features of the new Mercedes diesel engine:

• Two-stage turbocharging ensures high power output and optimum torque delivery.
• Fourth-generation common-rail technology with a rail pressure that has been increased by 400 bar to 2000 bar, plus a new piezoelectric injector concept featuring direct injector needle control creates the ideal basis for more flexible injection timing, leading to smoother engine running, lower fuel consumption and reduced emissions.
• The maximum ignition pressure is 200 bar which also contributes to the high output.
• Both the oil-spray nozzles and the water pump are activated in accordance with requirements to save energy.
• The camshaft drive is positioned at the rear in order to enhance running refinement and satisfy the exacting pedestrian protection requirements.
• The engine block is made from cast iron, the cylinder head from aluminium.
• Two water jackets guarantee maximum cooling even at the points of greatest thermal radiation; it is this that enables a ignition pressure of 200 bar and such a high power-to-displacement ratio.
• The aluminium pistons slide up and down in cast-iron barrels for minimum frictional resistance.
• The connecting rods are made from forged steel, and their weight has been optimised by the Mercedes engineers.
• In the interests of vibrational comfort, the forged crankshaft with its eight counterweights turns supported by five bearings. The radii of the crankpins are rolled for high strength.
• To compensate for the free vibration moments which are inherent to four-cylinder inline engines there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings.
• A two-mass flywheel, featuring a primary flywheel mass fixed to the crankshaft that is connected to the secondary flywheel mass on the transmission by means of springs (technical term: spring-mass system), isolates the crankshaft's vibration stimuli from the drivetrain, thereby contributing to the engine's excellent smoothness.

Injection with the fourth generation of the common-rail principle

The new diesel unit from Mercedes-Benz ushers in the fourth generation of the tried-and-tested common-rail direct injection technology. The distinguishing characteristic of the latest generation is the increase of 400 bar in the maximum rail pressure, which now equals 2000 bar. This rise in pressure potential was of crucial importance for boosting the engine's output to 150 kW/204 hp and its torque to 500 Nm, whilst at the same time bringing about a marked improvement in the engine's untreated emissions.

Piezoelectric injectors which are a completely new development form one of the key components in the fourth-generation CDI technology. They harness the ability of piezoelectric ceramic to alter its crystalline structure with microsecond speed when an electrical voltage is applied. The actual spatial movements produced are tiny however, For this reason, the new injectors are fitted with a piezo stack, which is basically made up of piezoelectric elements connected in series. In contrast to the customary systems used to date, the movement of these elements controls the injector needle directly and enables even greater alterations in volume that are accurate to within a few thousandths of a millimetre. The benefits of this are in increase in the available injection volume as well as particularly fine and fast metering of the injection quantities. This enables the fuel injection process to be adapted to the momentary engine load and rev speed with yet greater exactness - by means of high-precision multiple injections of fuel for example - which has a positive impact on emissions, consumption and combustion noise. Plus, the engine runs even more quietly when idling than its predecessor.

As a result of the innovative actuation concept, injector operation is completely leak free. This dispenses with the need for a leak oil line to return the negligible quantities of fuel that used to accumulate unavoidably in the system on account of the operating principle. This improves the injection system’s thermal circuit to such an extent that, even at a rail pressure of 2000 bar, fuel cooling is super-fluous to requirements. Not only does this save energy, it reduces the high-pressure pump’s operating energy input by around one kilowatt at high engine loads.

In order to continue to deliver optimum injection quantities over the engine’s entire service life, an adaptive learning function is able to compensate for any tolerance deviations that may occur as a result of minimal component wear.

200 bar ignition pressure and optimised combustion chamber

The fuel is injected into a combustion chamber with a meticulously devised geometrical form that includes the precision-calculated recesses in the piston crowns. Compared to the engine it replaces, the combustion chamber has been made flatter and the diameter somewhat larger. The compression ratio was reduced from 17.5 :1 to 16. 2 : 1. This optimises the combustion process by achieving a lasting reduction in untreated emissions - NOx levels in particular have been cut drastically.

One of the determining factors for maximum power output and for fuel consumption at full throttle, from an emissions point of view, is the maximum ignition pressure. With a pressure of 200 bar, the new four-cylinder diesel from Mercedes-Benz is one of the top-ranking passenger car diesel engines in this regard. To guarantee spontaneous starting, the engine is fitted with ceramic glow plugs which attain a temperature approximately 200 degrees Celsius higher than metallic glow plugs (1250°C as opposed to 1050°C) and are virtually wear-free. Mercedes-Benz put these glow plugs into series production for the first time in the predecessor diesel engine.