While twin turbos have been used on passenger car petrol motors for some
time, there's never been a sequential twin turbo diesel for use in cars. Until
now.
The new BMW engine is a 3-litre in-line six cylinder. In twin turbo form it
develops 200kW at 4400 rpm and a staggering 560Nm at 2000 rpm. No less than
530Nm is available from 1500 rpm.
The twin overhead cam, iron block and alloy head design uses four valves per
cylinder and weighs only 228kg. BMW state the twin turbo approach has resulted
in a power increase of 20 per cent when compared with existing state of the art
diesel engines.
As is typical with petrol car sequential turbos, two different sized turbos
are used. The smaller operates at low engine speeds, and the larger at higher
speeds.
Three different operating conditions occur:
1. At low engine speeds the intake air flows through the large turbocharger and
is compressed in the smaller turbocharger. This supplies substantial amounts of
air to the power unit, starting without any appreciable delay at idle speed. The 3.0 litre inline six-cylinder diesel develops 530 Nm of torque at as
early as 1,500 rpm.
2. With increasing engine speed, the larger turbocharger becomes more important
- initially as a pre-compressor. The intake air is additionally highly
compressed inside the small turbocharger, the engine reaching its maximum torque
of 560 Nm at 2,000 rpm. By means of a turbine control valve, the flow of exhaust
air is variably distributed to both turbochargers, regulating their
interaction.
3. At high engine speeds work is done primarily by the large turbocharger, the
power unit reaching a maximum output of 200 kW/272 bhp at 4,400 rpm.
With a specific power output of 66.7 kW/l, the new 3.0 litre diesel even
exceeds the rating achieved by the M5 sports saloon (58.8 kW/ltr), production of which ceased at the end of June 2003.
The basic construction of the BMW high-performance diesel is modelled on the
diesel engine already used in Sports Activity Vehicles X5 and X3, or the large 7
Series. While the 2,993 cc capacity remained unchanged, the crankcase
construction was reinforced predominantly within the area of the crankshaft
bearing.
Second-generation Common Rail serves as an injection system, with the flow
characteristic of the fuel-injection nozzles adapted to cope with the new level
of output. The 3.0 litre diesel with
Variable Twin Turbo has in certain driving situations lower specific fuel consumption than the basic
power uni. Injection timing and combustion
process (compression ratio 16.5:1) were adapted to the new parameters.
The Variable Twin Turbo offers the widest useful engine speed range in its
class. In addition to the increase in output, the useful engine speed range was
widened by + 400 rpm. Nominal output of 200 kW/272 bhp is at 4,000 rpm and
maximum engine speed is now 5,000 rpm, which is unusually high for a diesel.
Acid test in the Dakar Rally
At the 2003 Dakar Rally, specialists at the BMW Diesel Competence Centre in
Steyr (Austria) used the new technology with two variable turbochargers in an X5
entered by the independent X-Raid team. During this first appearance, the X5
gained victory in the diesel category. To conclude the final stage of testing,
the BMW X5 was once again entered for the 2004 Dakar Rally. On 17 January, two
BMW X5s, powered by the innovative 3.0 high-performance, near-production diesel,
were the first to cross the finishing line in Dakar.
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When viewed from the side, the upper eye of the engine connecting rod is
shaped like a trapeze. This new technology is used on the internal combustion
engine to create an additional supporting surface for the gudgeon pin within
the lower area of the connecting rod eye for high piston pressures. At the same
time, weight is saved in the upper (narrower) part of the connecting rod eye.
Like all other BMW connecting rods, those installed in the new inline six
engine have also undergone the cracking process. This method entails breaking
the lower connecting rod eye in two. The two parts are then bolted together
again when assembled onto the crankshaft. Due to the uneven surfaces resulting
from the cracking process, the link between the two parts of the connecting rod
has far greater stability than the even surfaces obtained on conventionally sawn
connecting rods.
Thanks to lightweight camshafts, the new R6D has a weight advantage of 1.2 kg
(-25%). The basic component of the new camshaft is a steel tube serving as a
support for the cams prefabricated from high tensile refined steel. The cams
are then joined and finally polished down to an accuracy of 1/1000 mm.
Engine electronics required to control a turbocharged power unit are
significantly more complex. A system comprising two superchargers, turbine
control, bypass and wastegate has to be controlled, not just a turbocharger with
variable turbine geometry. The system elements have to be coordinated with each
other and with the respective operating condition of the engine. The Bosch DDE
6.0 control system provides the required computing power and sufficient storage
capacity to deal with processes adequately.
The exhaust system was specifically designed to cope with the high rate of
air flow. Pipe diameter and silencer were developed independently and the sound was adapted to the sporty character of this high-performance
diesel.
The new BMW high-performance diesel engine with Variable Twin Turbo debuts in
the 535d Saloon and 535d Touring. The saloon sprints from 0 to 62 mph in 6.5
seconds and top speed is limited to 250 km/h (155 mph), using only 8.0 litres of
diesel fuel over a distance of 100 km in the EU combined cycle (all figures
apply to the automatic transmission supplied as standard).
Full Engine Specifications
|
Configuration |
- |
Inline-six |
|
Maximum output |
kW/bhp |
200/272 at 4,400 rpm |
|
Maximum torque |
Nm |
560 at 2,000 rpm |
|
Combustion process |
- |
Direct-injection Common Rail diesel engine with
multi-stage diesel
turbocharging |
|
Capacity, effective |
cc |
2,992.6 |
|
Compression ratio |
- |
16.5 |
|
Bore/stroke |
mm |
84/90 |
|
Max. combustion chamber pressure |
bar |
180 |
|
Minimum specific consumption |
g/kWh |
208 |
|
Crankcase material |
- |
Grey-cast iron (GG25) with cast-in liners |
|
Cylinder block height |
mm |
285 |
|
Distance between cylinders |
mm |
91 |
|
Top land |
mm |
7 |
|
Main bearing diameter |
mm |
60 |
|
Conrod bearing diameter |
mm |
45 |
|
Conrod length |
mm |
137, crack technology, trapezoidal conrods |
|
Cylinder head material |
- |
Aluminium |
|
Camshafts |
- |
2 chain-driven camshafts (assembled camshafts) running in 7 bearings |
|
Valve drive |
|
Roller-type rocker arms; hydraulic valve play compensation |
|
Valves per cylinder |
|
4 |
|
Valve diameter intake/outlet |
mm |
25.9/25.9 |
|
Valve shaft diameter
intake/outlet |
mm |
6.0/6.0
|
|
max. valve lift intake |
mm |
7.5 |
|
max. valve lift outlet |
mm |
7.5 |
|
Intake system |
- |
Twin turbo technology with 2 turbochargers, infinitely variable control,
intercooling |
|
Engine weight according to BMW standard |
kg |
228 |
|
Engine management/mixture
preparation/ignition |
- |
Bosch DDE6.0/Common Rail 1600 bar system pressure with multiple injection |
|
Fuel |
|
Diesel |
|
Certified emission standard |
- |
EU4 |
|
Exhaust system |
- |
Primary catalytic converter, isolated exhaust routing, diesel particulate
filter (additive-free) |
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