Press Release
Compact dimensions thanks to a new "one-box concept"
Thanks to a newly developed "one-box concept", the V6 engine is among the most compact diesel power units in its displacement class worldwide. "One-box concept" means that the engine forms a single, compact entity with its components and ancillary units. The complete air filter system is directly attached to the engine and therefore occupies no additional installation space. This also simplifies the installation and use of the engine in Mercedes model series anf 4MATIC variants where no six-cylinder diesel engine was previously offered. In other words, the new V6 is even more compact than the previous 5-cylinder inline unit.In addition to lightweight construction, compact dimensions and low-friction valve gear, the new CDI six-cylinder would not be a Mercedes engine if it did not also meet the strict standards of the brand in terms of rigidity, vibration characteristics and long-term durability. Calculations and computer simulations provided the engineers in Stuttgart with valuable data and helped them achieve the demanding specifications. A look at the interior of the V6 engine:
- The forged crankshaft rotates in four bearings which have been enlarged by Page 6 five millimetres versus the in-line six-cylinder engine in the interests of vibration comfort. The radii of the crank pins have been rolled to achieve high strength. The flexural and torsional rigidity of the crankshaft is more than twice that of the preceding engines.
- The connecting rods are also of forged steel. Mercedes engineers have further optimised their weight by using a new alloy and improving their geometry.
- Careful design of the combustion chamber geometry, which includes the precisely calculated recesses in the piston crowns, optimises the combustion process and helps to achieve a lasting reduction in untreated emissions.
- The free vibrations which are inherent to a V6 engine are compensated by a balancer shaft between the cylinder banks. This counter-rotates at the same speed as the crankshaft.
Heat exchangers for oil cooling, heating and exhaust gas recirculation
A separate roller chain is used to drive the oil pump. Via a large full-flow oil filter, the efficient and quiet external-gear pump delivers the oil to the oil-water heat exchanger located between the cylinder banks. The high 15-kW output of the heat exchanger ensures that even under extreme engine loads, the oil temperature does not rise above 130 degrees Celsius. The tunnel of the balancer shaft also serves as the main oil duct from which the oil flows to the main bearings, into the cylinder heads and to the piston-cooling spray units, which automatically open at a certain oil pressure and cool the pistons.The mainstay of the water cooling system is a belt-driven pump on the crankcase. This is a double-helix pump which forces the coolant into the cylinder banks within the crankcase from the front, where it mainly flows to the exhaust side via special holes bored in the cylinder head gasket. Cooling is thermostatcontrolled on the cross-flow principle.
The flow of coolant for the oil-water heat exchanger comes from the crankcase on the right, while the exhaust gas recirculation cooler and the heat exchanger for the heating system are supplied with coolant from the left cylinder head. The coolant circuit is therefore designed to ensure adequate heat dissipation under any load and engine speed conditions. Particularly high rates of flow are achieved at the valve lands, around the injector ducts in the cylinder heads, in the oil-water heat exchanger and in the exhaust gas recirculation cooler, enabling an efficient heat transfer to take place.
Turbocharger with variable turbine geometry
The new V6 diesel engine is aspirated by a VNT turbocharger (Variable Nozzle Turbine). This technology already enables high levels of output and torque to be achieved at low engine speeds. Thanks to electric control, VNT turbochargers are able to vary the angle of their turbine blades rapidly and precisely to suit the operating status of the engine, and can therefore use the largest possible volume of exhaust gas to compress the intake air and build up charge pressure. At low engine speeds the turbine blades reduce the flow cross-section to increase the charge pressure, while the cross-section is enlarged at high engine speeds to reduce the speed of the turbocharger. More efficient cylinder charging and therefore higher torque are the results of variable, demand-related turbocharger control. Moreover, electric VNT technology allows a precise interaction with other units which are responsible for reducing untreated emissions and exhaust gas aftertreatment.The turbocharger is combined with a downstream intercooler which reduces the temperature of the compressed, heated air by up to 95 degrees Celsius, allowing a larger volume of air to reach the combustion chambers. Behind the intercooler there is an electrically controlled flap which enables the V6 engine to be throttled back precisely when the exhaust gas recirculation is in operation. This electrically regulated control flap allows the volume and mix of the exhaust gases added to the combustion air to be very precisely metered. To optimise the volume of recirculated exhaust gas, it is cooled down considerably in a high-performance heat exchanger. Acting in conjunction with the hot-film air flow sensors integrated into the intake air ducts, which provide the engine control unit with precise information about the current volume of intake air, this greatly reduces nitrogen oxide emissions.
The combustion air then flows into the charge air distribution module, which supplies each cylinder in equal measure. The distribution module features an integral, electrically controlled intake port shut-off function with which the intake port cross-section for each cylinder can be finely reduced. This modifies the swirl of the combustion air, ensuring that the charge flow to the cylinders is adjusted for the best possible combustion and exhaust emissions in any load and engine speed conditions.
Piezo ceramics for precisely metered injection within microseconds
The third generation of the well-proven common-rail direct injection system is entering series production at Mercedes-Benz with the new V6 diesel engine. This means that the injectors, high-pressure pump and electronic engine management system will operate even more efficiently, with a further reduction in fuel consumption, exhaust emissions and combustion noise.Instead of the previous solenoid valves, the injectors are equipped with piezoceramics whose crystalline structure changes within milliseconds under an electric voltage. The engine developers have used this effect, which was discovered in 1880 by the brothers Pierre and Jacques Curie, to lift the needle jet at the tip of the injector with a precision of only thousandths of a millimetre and thereby achieve an extremely fine jet of fuel. Moreover, piezo injectors are considerably lighter and operate at twice the speed of conventional solenoid valves. With a response time of only 0.1 milliseconds, the fuel injection process can be even more precisely suited to the current load and engine speed situation, with favourable effects on emissions, fuel consumption and combustion noise. The number of fuel injections per power stroke is increased from three to five thanks to this piezo technology.
This efficient exhaust gas aftertreatment combined with the complex in engine measures already enables the V6 diesel engine to meet the stringent EU4 exhaust limits.
To lower exhaust emissions even further, Mercedes-Benz combines the new sixcylinder engine with a maintenance-free particulate filter system as standard for the German, Austrian, Swiss and Dutch markets, producing a further significant reduction in particulate emissions. The filter purges itself without the use of additives and remains effective over a very high operating mileage.
Like the catalytic converters, the diesel particulate filter features numerous longitudinal, rectangular ducts. In contrast to the catalytic converter ducts, these are however closed at the ends so that the incoming exhaust gases are obliged to find their way through the porous walls between the ducts. In doing so the particulates carried in the exhaust gas accumulate in the filter and are retained by the filter material.
As only a limited quantity of these tiny carbon particles can be taken up, the particulate filter needs to be purged from time to time. The necessary exhaust temperature of more than 550 degrees Celsius is achieved by heating the stream of exhaust gases at higher engine speeds, or by adjusting various engine functions to suit the pressure and temperature of the exhaust gases at the particulate filter. The variable, third-generation common-rail technology considerably assists this process, for depending on the engine operating status and filter condition it allows brief post-injections of fuel for specific increases in the exhaust gas temperature. As a result the particulates accumulating in the filter are burned off in a controlled manner, and unnoticed by the driver or other road users.
Latest-generation electronic engine management
The combustion process is managed by a newly developed electronic control unit which is in constant contact with other microprocessors via a databus and therefore always fully informed about the current driving situation. The range of tasks performed by the engine control unit includes the following functions:
A separate data network links the engine management system with the generator and the glow control unit, which lies at the heart of an innovative quick-start glow system. This shortens the preheating time for the engine to just a moment, so that the diesel is now also the equal of a petrol engine in this respect.Emission control with two catalytic converters and a particulate filter as standard
Two oxidising catalytic converters clean the exhaust gases of the new Mercedes diesel engine. One acts as what is called a light-off converter, and is ready for action very soon after a cold start thanks to its position close to the engine. This unit is accompanied by a downstream main catalytic converter. The purpose of the oxidation-type catalytic converters is to convert carbon monoxide and unburned hydrocarbons by combining them with oxygen (oxidation).
