Fuel Efficient ML 320 CDI Arrives
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8th November, 2005
Boasting fuel consumption below 10 litres per 100 kilometres, thanks to its third-generation common-rail direction injection engine, the diesel M-Class has joined the line-up of engines in the new M-Class range.
The all new V6 diesel-powered ML 320 CDI is now available in Mercedes-Benz showrooms across the country, priced from $82,900, joining the petrol models which first went on sale in September.
The new diesel M-Class will continue the sales success of its predecessor; the well regarded five-cylinder ML 270 CDI. Over a quarter of all M-Class delivered in Australia have had a diesel engine beneath the bonnet, and last year the proportion was closer to 40 per cent.
“Luxury four wheel drive buyers are attuned to the benefits of diesel powered engines with over 3,000 diesel M-Class delivered in Australia since 1999,” said Horst von Sanden, managing director of the Mercedes Car Group in Australia.
“The new ML 320 CDI, which benefits from a new more powerful yet fuel efficient engine package along with a host of critically acclaimed improvements in the new M-Class, will continue to attract luxury four-wheel-drive buyers to the three-pointed star.
“With an operating range between re-fuelling of nearly 1,000 kilometres, the new diesel-powered ML 320 CDI will appeal to a large proportion of M-Class buyers given current fuel prices,” said von Sanden.
The very high levels of standard appointments in the new ML 320 CDI are the same as the petrol V6 ML 350. Highlights include permanent all-wheel drive, 17-inch light-alloy wheels, 7-speed automatic transmission, Electronic Stability Programme (ESP), Downhill Speed Regulation (DSR), 4ETS electronic traction control, PARKTRONIC parking sensors, rain sensor for the windscreen wipers, airbags for driver and front passenger, sidebags in front and rear, windowbags, 6-disc CD changer, cruise control with variable speed limiter, folding rear bench seat, mobile phone pre-installation, multi-function steering wheel, newly developed crash-responsive NECK-PRO head restraints, off-road ABS and ASR, anticipatory occupant protection system PRE-SAFE, automatic climate control and tyre pressure loss warning system.
The ML 320 CDI features third-generation common-rail direct injection and the latest in piezo injectors. The unit delivers 165 kW and places a maximum torque of 510 Newton metres on tap from 1,600 rpm. It consumes just 9.4 litres of fuel per 100 kilometres (combined consumption), making the new M-Class one of the most economical off-roaders in its class.
In 2005, Mercedes-Benz opened a new chapter in its tradition-steeped history of diesel engine development, underlining its leadership in this field with a newly developed V6 power unit. This engine combines all the current and trailblazing technologies in diesel engine development -- from the mechanics and thermal/flow dynamics to the electronic engine management and emissions control. This guarantees outstanding results in terms of output and torque characteristics, economy, exhaust emissions and smooth running.
The new V6 engine replaces the previous in-line five-cylinder unit of the ML 270 CDI. In the new M-Class, the new CDI engine boasts an output rating of 165 kW.
The key features of the new Mercedes diesel engine in brief:
Six cylinders in a V-arrangement
Aluminium crankcase with cast-in grey iron cylinder liners
Third-generation common-rail injection with piezo injectors
Four-valve technology with two camshafts per cylinder bank
Turbocharger with electrically adjustable turbine blades
Peak combustion pressure of up to 180 bar
Exhaust gas recirculation (EGR) with electrically controlled valve
Electrically controlled intake air throttling
Swirl control by electrically controlled intake port shut-off
Quick-start glow system
The world’s first aluminium V6 diesel engine
More output, more torque and lower exhaust emissions – the engineers at Mercedes approached the main objectives of their development work in various ways. Take lightweight construction, for example: owing to an intelligent choice of materials and innovative production methods, the DIN weight of the unit has been reduced to approx. 208 kilogrammes or roughly the level of the in-line five-cylinder. The power-to-weight ratio of the V6 engine is a remarkable 0.79 kW/kg.
As a world first, Mercedes-Benz has developed this diesel engine with an aluminium crankcase and cast-in grey iron cylinder liners. It tips the scales at only 41 kilogrammes and is therefore a prime example of lightweight construction. Aluminium is also used for the cylinder heads, cylinder head covers, pistons, coolant pump, sump and charge pressure distributor. Plastics are also used to save weight. Components in the fresh and charge air ducting systems, silencer and engine shrouding are of plastic.
A likewise newly developed valve control system reduces both friction and moving masses: the 24 intake and exhaust valves are controlled by an overhead camshaft for each cylinder bank, via roller-type rocker arms with hydraulic valve clearance compensation. The camshafts are driven by a tried-and-tested double-bush timing chain system into which the balancer shaft and the high-pressure pump for the fuel injection system are integrated.
Compact dimensions thanks to a new "one-box" design
Thanks to a newly developed "one-box" design, the V6 engine is among the most compact diesel power units in its displacement class worldwide. "One-box" design 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 makes the new V6 even more compact than the previous five-cylinder in-line 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 five millimetres compared with the in-line six-cylinder unit 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 making improvements to 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 drilled in the cylinder head gasket. Cooling is thermostat-controlled 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 (EGR) 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 nozzle turbine
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 abruptly cooled in a high-performance heat exchanger. Acting in conjunction with the hot-film air mass sensors integrated into the intake air ducts, which provide the engine control unit with precise information about the current volume of intake air, this significantly 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 post cross-section for each cylinder can be variably 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 under any load and engine speed conditions.
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 piezo-ceramics whose crystalline structure changes within milliseconds under an electric voltage. The engine developers 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 mere 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.
Mercedes engineers have also made improvements to other components of the common-rail system and the injection process:
The hydraulically optimised injector nozzles have eight holes (previously seven), which ensures even finer distribution of the fuel within the combustion chamber and more efficient mixture formation.
The inlet-metered high-pressure pump operates with a maximum injection pressure of 1600 bar.
The pilot injection process developed by Mercedes-Benz, which ensures a smoother combustion process and thereby audibly reduces the operating noise of the engine, takes place twice in succession in the new V6 engine. Small pilot quantities of fuel are injected within less than a millisecond and preheat the combustion chambers even more efficiently.
To burn off the soot particles in the particulate filter, there is a double post-injection of fuel when required.
Emission control with two catalytic converters
Two oxidising catalytic converters clean the exhaust gases emitted by the new Mercedes diesel engine. One acts as pre-catalytic 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 to form chemical compounds (oxidisation).
This efficient exhaust gas after treatment combined with the complex in-engine measures already enables the V6 diesel engine to meet the stringent EU4 exhaust limits.
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