The powertrain: The most innovative and sporty diesel engine in the world
- World’s most powerful six-cylinder in-line diesel engine, unique technology: M Performance TwinPower Turbo with three turbochargers and further developed common-rail injection system for the first time.
- Maximum output: 280 kW, peak torque:
740 Newton metres, instantaneous, linear power delivery across a wide rev band, maximum revs: 5,400 rpm.
- BMW EfficientDynamics: innovative technical highlights ensure optimised efficiency, BMW M550d xDrive with fuel economy of 6.3 litres/100 km in the EU test cycle.
Impressive statistics headline the enviable regard in which modern diesel engines are held. The output now within their compass, but more significantly the maximum torque they are capable of generating have fuelled their popularity among even performance-minded drivers.
The high efficiency of diesel technology also ensures extremely low fuel consumption and CO2 emissions. BMW has played a major role in the burgeoning appeal of the diesel engine, developing units which have time and again raised the bar in terms of sports performance and efficiency. The company’s record of diesel engine development, which began in 1983 with the launch of its first diesel model, now continues into another fascinating dimension.
The first of the new BMW M Performance Automobiles – founding a product category focusing on sporty driving pleasure – are powered by a diesel engine. The 3.0-litre six-cylinder in-line unit, whose cover bears the M Performance badge, has all the necessary tools to fulfil the brief handed to the new breed: technology without parallel worldwide, the highest output ever achieved by a BMW diesel engine and outstanding levels of efficiency.
Fitted in the BMW M550d xDrive, BMW M550d xDrive Touring, BMW X5 M50d and BMW X6 M50d, the 2,993 cc engine generates maximum output of 280 kW. No less imposing is its peak torque of 740 Newton metres, all of which the driver will find on tap as low down as 2,000 rpm. Instantaneous torque development maintained into the upper reaches of the rev range is the hallmark feature of the new unit, one underpinned by an array of innovative and globally unique technical wizardry. Taking centre stage – for the first time in a BMW – are a trio of turbochargers. Their arrangement and interplay strategy are the key to the engine achieving its exceptionally high efficiency.
More pressure, more output, more torque: world premiere for six-cylinder in-line diesel engine with three turbochargers.
The coordinated interplay of turbochargers of different sizes endows an engine with instantaneous responsiveness at low revs and allows charge pressure to be increased according to need when the engine is placed under greater loads. BMW uses this concept in the six-cylinder in-line diesel engines with BMW TwinPower Turbo technology fitted in models including the BMW 535d, BMW X5 xDrive40d and BMW X6 xDrive40d.
And now the company is set to become the world’s first carmaker to present a diesel engine which expands the principle of multi-stage turbocharging to incorporate a third turbocharger. The engine developed for the BMW M Performance Automobiles will, for the first time, see two comparatively small high-pressure chargers working with a larger low-pressure unit. The integration of an additional high-pressure turbo increases the engine’s capability when it comes to generating charge pressure, a key ingredient in taking the engine’s power output to the next level.
The M Performance TwinPower Turbo technology – including the requisite charge air cooling – is, like its predecessor, integrated into a small space in the main unit. Its compact construction puts the engine in a position to meet future pedestrian protection stipulations, while the arrangement of the three turbochargers is also part of an extremely intelligent system.
Both the exhaust inflow to drive the turbos and the supply of fresh air, plus the channelling of compressed air to the combustion chambers, have been designed to ensure that the three compression units work as a team as effectively as possible at all engine speeds. Efficiency is further optimised by the variable turbine geometry of the two high-pressure chargers, which allows them to react even more precisely to the driver’s power needs.
Instantaneous responsiveness and precisely coordinated interplay.
One of the two small turbos is activated at engine speeds just above idle. Its low moment of inertia allows it to respond without delay to the slightest movements of the accelerator and therefore supply the combustion chambers with compressed air at an early stage. As revs increase, the flow of exhaust gas also reaches the larger turbocharger, which announces its arrival with the engine spinning at just 1,500 rpm. Working together with the small charger, it ensures that the impressive peak torque of 740 Newton metres is generated at this low engine speed and maintained up to 3,000 rpm.
To further increase the performance of the large turbocharger, a greater volume of exhaust gas is required at around 2,700 rpm. If the driver calls up additional power, a vacuum-modulated exhaust flap instantly opens up another supply route, allowing extra exhaust gas to flow past the already active high-pressure charger to the large low-pressure turbo. The third turbocharger – integrated into this bypass line – also has a low moment of inertia and variable compressor geometry, which allow it to spring into action as soon as the exhaust flap opens.
The result is additional charge pressure, generated by two sources at the same time. The large turbocharger is able to deliver its full output, while the second small turbo builds on the effect of its two active colleagues by supplying even more compressed air to the combustion chambers. This arrangement allows the turbocharging system to drive the engine with forceful and sustained thrust to its maximum output of 280 kW, which it notches up between 4,000 and 4,400 rpm. The maximum engine speed of the new diesel powerplant is 5,400 rpm.
In order to ensure that charge pressure is developed as effectively as possible, not to mention efficiently, both the exhaust flow and supply of fresh air to the turbos and the channelling of compressed air into the combustion chambers is regulated with maximum precision. If the large turbocharger is spinning at particularly high speeds, a vacuum regulator opens a wastegate valve to relieve the pressure and so avoid unwanted exhaust backpressure.
The supply of fresh air is also controlled according to need by means of pneumatically activated flaps. For example, at low revs a bypass flap ensures that the air is channelled directly to the high-pressure charger, which spins into action very early. At less than 2,700 rpm a change-over flap keeps the air away from the third turbo, which is not yet active, to prevent unnecessary fluctuations in pressure.
Indirect charge air cooling enables the temperature of the air compressed by the three turbos to be reduced to the optimum level for increasing engine output. Both the main radiator positioned immediately in front of the combustion chambers and the intercooler behind the low-pressure charger are supplied by a low-temperature water circuit with separate electric pump.
Detailed optimisation enables higher combustion pressure, increased output and enhanced efficiency.
The new torquey and high-revving diesel engine also breaks new ground with its specific output of 93.6 kW per litre of displacement. However, the output possible using M Performance TwinPower Turbo technology is generated not in the turbochargers but in the core of the basic engine, which has therefore also been extensively modified. Maximum combustion pressure has risen from the 185 bar of the most powerful diesel engine in the existing BMW line-up to 200 bar.
As part of this development, the crankcase in the new 3.0-litre diesel engine features an innovative tie rod concept for the assembly of the main bearing caps and cylinder head. The sintered main bearing caps are given extra strength by a central screw. Like the crankcase, the cylinder head is also subjected to a special high-pressure compression process. This “HIPen” manufacturing concept sees the aluminium castings heated to solution annealing temperature and the casting pores created during manufacturing welded under high pressure. This process gives the finished component additional strength. A double diagonal bore ensures the interbore bridges have high thermal stability.
The geometry of the crankshaft and connecting rods has been further optimised and they are now made from higher-strength materials. Added to which, hub bushings and bowl rim remelting enhance the effect of the increase in piston compression height.
Higher pressure also raises the efficiency of the injection system.
The injection system of the new six-cylinder in-line diesel engine has also benefited from a rigorous process of further development. The common-rail direct injection system plays its part in enhancing the engine’s efficiency and promoting clean combustion by sending extremely precise quantities of fuel into the cylinders. The upgraded system raises the injection pressure of the piezo injectors to 2,200 bar. During each power stroke, three pre-injections, one main injection and four post-injections of fuel take place.
An ultra-high-performance pump channels the fuel to the combustion chambers through a common rail made from forged stainless steel.
The output and capacity of the cooling system have been given another boost, too. An additional low-temperature circuit supplied by an electric water pump controls the temperature of the intercoolers. The exhaust treatment system includes a diesel particulate filter and oxidation catalytic converter, which is located close to the engine in the same casing. More efficient exhaust cooling, meanwhile, minimises the formation of nitrogen oxides. And standard-fitted BMW BluePerformance technology, which includes a NOX storage catalytic converter, helps the new diesel engine powering
the BMW M550d xDrive to meet the EU6 exhaust standard not due to come into force until 2014.
Eight-speed Sports automatic transmission with M-specific gearshift dynamics.
The combination of the most powerful diesel engine ever offered for a BMW with an eight-speed Sports automatic transmission ensures that drive is transferred onto the road surface extremely effectively and efficiently.
The configuration of the transmission management system for the BMW M Performance Automobiles promotes dynamic acceleration.
The M-specification gearshift dynamics enable extremely rapid gear changes with an almost uninterrupted flow of power. The eight-speed Sports automatic transmission offers the driver two automated shift programs – D and S modes – as well as the option of changing gear manually (in M mode).
The automatic gearbox is operated using an electronic gearshift lever on the centre console adorned with an M logo. Manual mode allows the driver to change gears sequentially using either the gearshift lever or the paddles on the steering wheel. In customary M fashion, the right-hand paddle changes up a gear and the left-hand paddle is used for downshifts. If the driver activates manual mode using the gearshift lever, the transmission holds the gear selected until the engine’s revs hit the limiter.
By not shifting up automatically in this mode, the gearbox gives the driver maximum control over the car when pushing the dynamic boundaries. The driver can also switch instantaneously from automatic gear changes to M mode with a nudge of one of the gearshift paddles; if M mode is selected in this way, the gearbox’s automatic shift-up function remains active. The transmission also restores automatic mode if the gearshift paddles are not used again following an upshift or downshift.
Enhancing the natural soundtrack inside the car turns driving pleasure up yet another notch.
The performance capability of the diesel engine and the hallmark M driving characteristics of the BMW M Performance Automobiles underpin a new definition of driving pleasure. Imposing torque and a set-up focused squarely on sports performance give drivers a dynamic driving experience they will never have previously sampled in a diesel car.
The BMW M Performance Automobiles also lace this driving pleasure with additional acoustic appeal. Through sound design technology, the natural engine sound is specifically enhanced to suit the driving situation at the time and sent into the interior via the audio system, ensuring an authentic reproduction of the new engine’s unmistakable straight-six soundtrack.
The system’s digital signal processing technology exchanges data directly with the engine management, allowing it to base its precise transmission of the engine’s timbre on the revs at any one time, the amount of torque being produced and the car’s speed over the road.
Accentuating the straight-six diesel’s turbine-like, sporty and sonorous tones adds to the emotional appeal of the driving experience, especially in the BMW M550d xDrive when SPORT or SPORT+ mode is activated using the Driving Experience Control switch. This gives the driver an impressively accurate impression of how hard the engine is currently working and of the power being unleashed, and provides an even clearer window into the car’s responses on the road. Controlling the audio system in this way also ensures that the engine sound can be enjoyed to equal effect from every seat.
New six-cylinder engine with three turbochargers – a milestone in the glittering history of BMW diesel engines.
The engine developed for the BMW M Performance Automobiles represents a new high water mark in the illustrious history of diesel engines at BMW. The premium carmaker has offered customers diesel-powered models since 1983. The BMW 524td that kicked off this fine tradition quickly earned itself the status of the sportiest diesel model on the market. Its engine developed 85 kW and delivered the best performance yet also the lowest fuel consumption of any car in its class.
Since then, diesel BMWs have regularly emerged as the most efficient models in head-to-head tests. A host of prestigious awards – such as the Engine of the Year Award – and the impressive success of diesel-powered BMW models on the track headline the company’s unrivalled expertise in the development of diesel technology.
And so it is entirely in keeping with the company’s proud heritage that the first BMW M Performance Automobiles are now set to line up with a diesel engine under the bonnet. The unit developed to power them fulfils its sporting brief with leading performance in a range of disciplines and, in so doing, dismantles the historic contradiction between driving pleasure and economy even more effortlessly than ever.