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Twin Turbo and EfficientDynamics for 4cyl Petrol and Diesel - 4-cyl Diesel: Fuel Economy and Variable Twin Turbo

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Article Index
Twin Turbo and EfficientDynamics for 4cyl Petrol and Diesel
4-cyl Gasoline: Introduction
4-cyl Gasoline: High Precision Injection
4-cyl Gasoline: Clean and Efficient
4-cyl Gasoline: Specifications
4-cyl Diesel: Introduction
4-cyl Diesel: Fuel Economy and Variable Twin Turbo
4-cyl Diesel: Specifications
All Pages
Efficient combustion for optimum fuel economy.
The cylinder head with its intake ducts is a new design. The intake ducts are positioned at the side and designed as a spiral and tangential manifold.
To reduce emissions to an absolute minimum, the spiral duct serving to fill the cylinder is electronically variable in an infinite process. With their larger diameter, the valves facilitate the gas charge cycle and are now positioned upright, facing vertically into the combustion chambers. This avoids the need for extra cavities on the piston surface, which no longer requires separate valve pockets. The turbulence duct, in turn, gives the fresh air flowing into the engine a swirl motion improving the internal mixture formation process.
While the “basic” engine operates at an injection pressure of 1,600 bar and solenoid valves serve to supply the fuel in appropriate doses, the two more powerful engines inject diesel fuel at a pressure of 1,800 and, respectively, 2,000 bar through four piezo-injectors. The most powerful version of the new diesel is incidentally the first engine ever to use piezo-injectors operating at this high pressure of 2,000 bar.
To make the combustion process even more efficient, both the shape of the combustion chambers and the trough at the bottom of the piston have been modified and the compression ratio reduced to 16 : 1. And since fuel is injected in up to three “doses” for each operating stroke of the engine, the ignition flames spreads in a relatively “gentle” process benefiting in particular the smoothness and refinement of the diesel engine.
Various improvements within the engine itself – reduction of friction, redesigned combustion chambers, optimisation of the mixture formation process, combustion and air guidance – ensure a significant improvement in fuel economy right from the start. This improvement is supplemented by various other technologies and features on the car itself, such as Brake Energy Regeneration, the Auto Start Stop function, the gearshift point indicator, as well as EPS Electrical Power Steering.

Making its debut in the four-cylinder diesel: Variable Twin Turbo technology.
Two-stage turbocharging in the 150 kW/204 hp top version of the new four-cylinder diesel ensures a particularly fast response and even more muscular power. Variable Twin Turbo technology has already been introduced in the world’s most sporting and dynamic six-cylinder diesel featured in the BMW 535d. Today this 3.0-litre straight-six developing maximum output of 210 kW/286 hp is available in several model series. The technology providing this unique, dynamic power and performance is referred to as twin-stage turbocharging, a principle now featured for the first time also in a four-cylinder diesel.
The turbocharger unit in the Variable Twin Turbo is made up of one small and one large exhaust gas turbocharger. Benefiting from its lower inertia, the smaller turbocharger becomes active at low engine speeds just above idling. At higher speeds the larger turbocharger then also cuts in, developing extra power in the process.Thanks to this configuration, the turbocharger effect is built up spontaneously without any time lag, developing noticeable thrust and momentum even when the driver barely presses down the accelerator pedal. A turbine control flap distributes the flow of exhaust gases variably to the two turbochargers.
Specially developed, high-performance engine electronics ensure smooth management in the transition phase between the two turbochargers and optimum interaction of the two units with one another. This sophisticated control concept coordinates the complete system of turbines, the turbine control flap, bypass and wastegate as a function of the engine’s operating conditions.
The most powerful of the three new diesel engines develops its maximum torque of 400 Nm or 295 lb-ft at just 2, 000 rpm. Maximum charge pressure in the system is limited in this engine to 3.0 bar.
Developing maximum output of 150 kW/204 hp, this power unit enters a new dimension of EfficientDynamics. Through its power and performance, it indeed sets new standards not only in the segment of four-cylinder diesels, since this is the first all-aluminium diesel in the world to offer output per litre of more than 100 hp.


Available in two power stages: BMW diesel with variable turbine geometry.
The drive units developing 105 and, respectively, 130 kW (143 and 177 hp) each feature one exhaust gas turbocharger with variable turbine geometry. This technology allows optimum development of power tailored perfectly to all load conditions. An electric step motor serves to adjust the turbine blades with supreme accuracy and minimum delay to the respective operating conditions and running requirements.
This ensures a spontaneous response at low engine speeds as well as high power and superior performance under full load. Maximum charge pressure in the 105 kW/130 hp power unit is 2.5 bar, as opposed to 2.55 bar in the 130 kW/177 hp version. Maximum torque, in turn, is maintained consistently between 1,750 and 2,500 rpm or, in the latter case, between 1,750 and 3,000 rpm.

Compact power pack with carefully conceived solutions.
For reasons of the car’s package and efficiency in production, all ancillaries such as the coolant pump, alternator and climate compressor are on the intake side of the engine. This arrangement serves inter alia to provide ade-quate space for the two exhaust gas turbochargers featured on the top engine. And since all ancillary units are driven by one single belt, there is no need for a second belt level, which again helps to enhance the overall standard of efficiency by avoiding frictional losses.
The design and construction concept of BMW’s new four-cylinder diesels also has a positive effect on the safety standard of future vehicles. To improve pedestrian safety, for example, the chain drive has been moved to the same side as the flywheel. The high-pressure pump, in turn, is driven by a chain from the crankshaft – and then serves itself to drive the camshaft by way of a second chain.
To make the new engines even more compact, the two balance shafts running in needle bearings in the opposite direction to the engine are integrated in the crankcase at the side. This particular arrangement takes the special configuration and space available in an all-wheel-drive vehicle into account. The balance shafts run for the first time in needle bearings to significantly reduce the frictional forces generated in the process. For thanks to their compact dimensions, the new four-cylinder diesels with balance shafts may also be combined with BMW’s intelligent xDrive all-wheel-drive system.
The oil/water heat exchanger is also housed in a very compact arrangement, fully integrated in the oil filter casing assembled directly on the crankcase.
The filter casing, in turn, is designed for maximum operating efficiency without requiring any hoses otherwise used to connect the heat exchanger to the water shell around the crankcase.
The overall height of the engine has also been reduced by moving the vacuum pump for boosting brake power from its usual arrangement on the same side as the flywheel to the oil sump for the engine. The compact starter, finally, is fitted on the same level as the seals beneath the engine.

Exemplary emission control thanks to the diesel particulate filter.
To keep the periphery of the engine as clear-cut and uncluttered as possible, the feed pipe for exhaust gas recirculation (EGR) is integrated in the cylinder head. The EGR valve is positioned on the hot side of the engine, the EGR radiator features a bypass serving to limit the emission of harmful substances while the engine is warming up. A further advantage of this concept is that it ensures smooth and cultured engine refinement at all times.
All versions of this new engine generation come as standard with a diesel particulate filter fitted close to the engine. This ensures optimised emission control and management quite unique in this drive segment. The diesel engine is a core technology used by the BMW Group in its strategy to reduce CO2 emissions. Accordingly, the BMW Group is acting according to the policy agreed by the European Association of Automobile Manufacturers with the EU Commission to reduce CO2 emissions to 140 grams per kilometre in the European car fleet average by the year 2008 – which equals a reduction by 25 per cent versus the level in 1995.
BMW’s newly developed four-cylinder diesel engines are a further step through which the BMW Group is making a clear-cut and decisive contribution in reaching these targets. Indeed, the new BMW 120d already reduces CO2 emissions to 129, the new BMW 118d to an even more impressive 123 grams per kilometre.
A further point is that BMW already fulfils the commitment made by the German automotive industry to fit all new diesel passenger cars with a particulate filter ex works by the year 2008. The diesel particulate filters used by BMW achieve a separation rate already confirmed by the German Federal Office of the Environment of more than 99 per cent, the concentration of particulates in the exhaust emission of a BMW diesel thus reaching a level similar to the concentration in the ambient air – that is in the environment as a whole.

Last Updated on Monday, 09 April 2007 13:58  

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