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Performance
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The new V10 Power Unit
in the BMW M6: A Masterpiece in Engine Construction
The ten-cylinder power
unit featured in the BMW M6 may rightly be regarded as the most
fascinating engine you can imagine in a production car. Launched
just half a year ago in the BMW M5, this unique power unit has been
thrilling enthusiasts all over the world ever since, offering a
seemingly never-ending surge of power and performance. Many people
see this engine as the "civilian derivative" of the BMW WilliamsF1
racing unit.
The V10 is reminiscent
of BMW's Formula 1 racing engine also in terms of its sound: A bit
deeper and more muscular than even in the M5, the V10 featured in
the BMW M6 clearly "shouts out" its dedication to motorsport.
Inspired by the
Formula 1
power unit
The V10 featured in the
BMW M6 shares both the number of cylinders as well as its high-speed
concept with BMW's Formula1 power unit. This alone guarantees
enormous thrust and muscle from high engine speeds, a feature
characteristic of all high-performance normal-aspiration power units
developed and built by BMW M GmbH. Reflecting this exclusive
standard, this top-of-the-range engine is equally
impressive in all its specifications: ten cylinders, five liter
capacity, 507 horsepower maximum output, 383 lb-ft maximum torque,
engine speeds up to 8,250 rpm - a power pack in its purest form.
But at the same time
this engine is far more than the sum total of outstanding
performance data: Barely touching the gas pedal, you will
immediately appreciate this high-speed normally-aspirated engine as
a typical sports power unit. And at the same time it is perfectly
civilized in everyday traffic: Sometimes a luxurious coupe,
sometimes a thoroughbred sports car. The M6 offers you the best of
both worlds, setting the benchmark in both categories.
Brand-new and offering
the best of the best
The V10 power unit
created by the engineers at BMW M GmbH for the M5 and M6 is
brand-new from the ground up. In the process of developing this
engine, they were inspired by the BMW WilliamsF1 power unit, one of
the most powerful engines in the highest category of motorsport. As
their second consideration, they focused on M-specific features in
standard production such as double-VANOS, individual throttle
butterflies, top-performance engine electronics, and oil supply with
centrifugal force control.
In principle there are
three options to achieve optimum power and performance in engine
construction: To make the engine larger, obtaining higher torque in
the process, to boost engine output by means of a turbocharger or
compressor, or to increase engine speed by means of the high-speed
engine philosophy.
Power is more than just
a number
This means that on the
road, power and performance is more than just an impressive
horsepower rating. Rather, what really counts is a car's behavior
when accelerating and its driving dynamics. And this depends on the
thrust and muscle actually generated by the drivetrain as well as
the weight of the car. The thrust going to the drive wheels, in
turn, is a result of engine torque and the overall transmission
ratio. The high-speed engine concept, therefore, allows the right
transmission and final drive ratios, guaranteeing impressive
performance also in everyday motoring.
Given these basic laws
of physics, we find huge differences between various engines, even
when on paper they have the same output. A large-volume engine, for
example, has the disadvantage of both extra weight and larger
dimensions leading to higher fuel consumption. A turbocharged engine
likewise consumes more fuel and lacks spontaneity that is the
instantaneous response of the engine to the driver's wishes.
The high-revving concept
- the perfect answer
This leaves the third
option: the compact, fast-revving normal-aspiration
power unit. For traditional reasons alone the engineers at BMW M
acknowledge this concept as the ideal solution, increasing engine
output and performance by an appropriate increase in engine speed.
The fact remains, however, that the high-speed engine concept is far
more demanding in technological terms, making it a greater challenge
requiring more sophisticated solutions. Reaching engine speeds of
8,250 rpm, the V10 enters a speed range until recently reserved to
thoroughbred racing cars alone.
Formula 1 technology for
the road
Featuring qualities of
this kind, the new V10 raises the limits to technology in series
engine production to a higher standard never seen before. A
comparison clearly shows what this means in terms the loads and
forces acting on the various materials: At a speed of 8,000 rpm,
each of the 10 pistons covers a distance of some 20 meters a second.
Revving at 18,000 rpm in the BMW WilliamsF1, piston travel is
actually 25 meters per second. But while durability is merely a
relative factor in motorsport, a BMW M engine must last the same
long life as the car itself - in all kinds of weather, under all
traffic conditions, and with that typical M style of motoring.
507 horsepower for a new
world of driving dynamics
The fast-revving
ten-cylinder develops maximum output of 507 horsepower at 7,750 rpm.
But compared with its output and performance it remains a
lightweight athlete weighing just 240 kg or 529 lb. When it comes to
output per liter, on the other hand, this engine is definitely a
"heavy" player. The ten-cylinder easily achieves the magical limit
of 100 hp per liter, with specific output comparable to that of a
racing machine.
Only engine speed can
really bring out power and torque
Maximum torque of 383
lb-ft comes at 6,100 rpm. But the ten-cylinder develops 332 lb-ft
from just 3,500 rpm, with 80 per cent of the engine's maximum torque
offered consistently throughout a wide range of 5,500 rpm.
This alone places the
BMW M6 with its high-speed engine far above the
competition, with virtually all other models focusing on torque
alone provided by larger engine capacity and/or turbocharging. A
further drawback with other models is that they require a
significantly reinforced and, as a result, very heavy drivetrain to
convey their extremely high torque, thus suffering from extra weight
and mass which consistently has to be accelerated and slowed down.
By contrast, BMW's compact V10 with its high-speed concept benefits
from a far lighter drivetrain with a much faster gearshift.
A good example is that
of a cyclist riding up a hill. Shifting down a gear, the cyclist
will have to turn the pedals faster, but is able, in return, to take
virtually every grade. Should the cyclist remain in the same gear or
even shift up, on the other hand, the choices would be to either put
more strength into the pedals or, quite simply, get off the bicycle.
Taking two cyclists absolutely equal in their strength and stamina,
the winner will always be the cyclist able to turn the pedals more
quickly.
Ten cylinders - the
sports concept
Ten cylinders are the
optimum concept for a high-performance sports engine: An engine of
this kind has exactly the right dimensions, the right number of
components and filling capacities. And displacing 500 cubic
centimeters, each cylinder is of exactly the right size, as defined
by the really demanding engine specialist.
Compact construction for
extra strength and enhanced comfort
As one of the world's
leading engine manufacturers, BMW has become famous above all for
its in-line power units. Now, focusing on the ten-cylinder, the
engineers at BMW M GmbH have placed two rows of five cylinders next
to each other at a V angle of 90° and with displacement between the
two cylinder banks of 17 millimeters or 0.67´´, thus forming a very
compact and dynamic configuration. The 90° angle was chosen for its
vibration-and comfort-oriented mass balance, perfectly solving the
conflict of interests between maximum smoothness free of vibrations
and a high level of component strength.
The cylinder crankcase
is cast in a low-pressure die-casting process using an over-eutectic
aluminum-silicon alloy, in this case with a share of silicon of at
least 17 per cent. The cylinder liners are formed by exposing the
hard silicon crystals, with the iron-coated pistons running directly
in the uncoated bore. Cylinder stroke measures 75.2 millimeters or
2.96´´, cylinder bore is 92.0 millimeters or 3.62´´, adding up to an
overall capacity of 4,999 cc.
Like the engine blocks
for Formula1, the M engine blocks are cast at BMW's light-alloy
foundry in Landshut just north of Munich.
Bedplate construction
like in motorsport
High engine speeds, high
combustion pressure and temperatures subject the crankcase to
extremely tough and demanding conditions. The engineers at BMW
Motorsport have therefore made the crankcase very compact and
unusually stiff in a so-called bedplate structure, a technology
carried over from motorsport. The BMW ten-cylinder is the first
production V engine to feature such a bedplate construction.
The aluminum bedplate with grey-cast-iron inlays guarantees very
precise crankshaft bearing - in particular, it keeps main bearing
tolerance within close limits throughout the entire range of
operating temperature. The grey-cast-iron inlays reduce thermal
expansion of the aluminum housing and feature special openings to
provide a positive connection with the surrounding aluminum frame.
At the same time this construction serves to fulfill the acoustic
requirements made of the engine.
Specially designed for a
high level of stiffness and finely balanced for
optimum precision, the crankshaft made of forged, high-strength
steel runs in six bearings and weighs just 21.8 kg or 48.1lb.
Designed for minimum mass inertia, the crankshaft offers a very high
standard of torsional stiffness. In each case two connecting rods
interact with one of the five crank journals displaced from one
another at an angle of 72°. The small distance between cylinders of
just 98 millimeters or 3.86´´ and the short crankshaft made possible
as a result interact with one another for a very high level of
flexural and torsional stiffness on very low weight.
Lightweight engineering
watching out for every gram
The weight-optimized
box-type pistons are cast out of a high temperature-resistant
aluminum alloy and are iron-coated on the surface, weighing just
481.7 grams including their piston pins and rings. Compression
height is 27.4 millimeters or 1.08´´, with a compression ratio of
12.0:1. The pistons are cooled by oil spray nozzles connected to the
main oil duct. The trapezoidal connecting rods, in turn, measuring
140.7 millimeters or 5.54´´ in length, are weight-optimized,
manufactured in cracked technology, and come in high-strength steel.
This effectively reduces oscillating masses within the engine, each
of the connecting rods forged from 70MnVS4 weighing just 623 grams
including the bearing shell.
The single-piece
aluminum cylinder heads on the V10 power unit are also cast by BMW
at the light-alloy foundry in Landshut. As an important contribution
to the appropriate temperature of the catalyst with the catalytic
converter warming up quickly, the cylinder heads come with
integrated air ducts for secondary air injection. A further feature
is the typical configuration with four valves per cylinder
characteristic of a BMW engine. The valves themselves are operated
by ball-shaped cup tappets with hydraulic valve play compensation.
Tappet diameter is just 28 millimeters or 1.10´´, tappet weight 31
grams. The intake valves, in turn, measure 35 millimeters or 1.38´´
in diameter, the outlet valves 30.5 millimeters or 1.20´´.
Special innovations
reducing the cost of maintenance
The intake valves are
made exclusively for the V10. Measuring only
5.0 millimeters or 0.20´´ in diameter, they come with particularly
thin shafts hardly impairing flow conditions in the intake duct.
Valve clearance is automatically maintained at exactly the right
point by hydraulic valve play compensation elements, helping to
reduce the cost of ownership.
More power from the
engine means a greater need for efficient cooling,
particularly near the combustion chambers. With its crossflow
cooling concept, the V10 power unit significantly reduces pressure
losses in the cooling system compared with a conventional cooling
configuration, guaranteeing a consistent distribution of
temperatures in the cylinder head and reducing temperature peaks at
all critical points.
Each cylinder is cooled
consistently by an optimum amount of coolant flowing smoothly around
the cylinders. To achieve this effect, the coolant flows from the
crankcase via the outlet side of the engine through the cylinder
head and over the collector rail on the intake side all the way to
the thermostat and, respectively, the radiator itself.
High-pressure double-VANOS
for an optimum cylinder charge.
Variable double-VANOS
camshaft management ensures an optimum charge cycle within the
ten-cylinder. This, in turn, helps to keep valve timing extremely
short and fast - which in practice means more power, an even better
torque curve, optimum responsiveness, greater fuel economy, and
cleaner emissions.
Running at low loads and
engine speeds, the engine therefore operates
with a greater valve overlap and, as a result, a higher level of
internal exhaust gas recirculation. This, in turn, reduces charge
cycle losses and improves fuel economy accordingly. As a function of
the gas pedal position and engine speed - the parameters crucial to
the power and performance required of the engine - valve increments
are adjusted infinitely and by way of map control.
To ensure such efficient
management, the sprocket connected with the crankshaft by a single
chain is linked to the camshaft by a two-stage helical gearing. With
the adjustment piston being moved along its axis, the helical gear
pattern turns the camshaft relative to the sprocket, allowing
variation of the intake camshaft angle by up to 66° and the outlet
camshaft angle by up to 37°.
M double-VANOS requires
a high level of oil pressure in order to adjust the camshaft at
maximum speed and with maximum precision. Accordingly, engine oil is
compressed to an operating pressure of 80 bar by a radial piston
pump fitted in the crankcase. This map-controlled high-pressure
adjustment guarantees short adjustment times and provides the
optimum spread angle synchronized to ignition timing and the amount
of fuel injected as a function of engine load and speed at all
operating points.
Reliable oil supply even
in extremely fast bends
The oil required for
lubrication is delivered to the engine by a total of four oil pumps.
The reasons for such an unusually elaborate and sophisticated oil
supply system are the high standard of dynamic performance and the
extreme acceleration of the BMW M6. In bends, for example, BMW's
large Coupe is easily able to achieve lateral acceleration of well
over 1g. The centrifugal forces generated in such a process press
the engine oil into the outer row of cylinders to such an extent
that the oil is no longer able to flow back in the usual process
from the cylinder head, possibly leading to a lack of oil in the
sump. And should worst really come to worst, the oil pump might then
draw in air instead of oil.
To rule out such an
eventuality, the engine comes with lateral force-controlled oil
supply where, starting at lateral acceleration of approximately 0.6
g, one of two electrically driven duocentric pumps draws oil out of
the outer cylinder head in a bend and conveys it to the main oil
sump. A lateral acceleration sensor serves as the actuator for
initiating pump action. The oil pump itself is a volume-flow
controlled pendulum slide cell pump delivering exactly the amount of
engine oil actually required by the engine. This is made possible by
the inner rotor of the pump adjustable in its eccentricity versus
the pump housing as a function of current oil pressure in the main
oil duct.
A lubrication film which
does not break when applying the brakes
When applying the brakes
to the extreme, the BMW M6 builds up negative acceleration up to a
staggering 1.3 g. Under such extreme conditions, it is quite
possible that the flow of oil back to the oil sump serving as an
intermediate storage reservoir will no longer be sufficient,
especially as the oil sump for reasons of space is fitted beneath
the front axle subframe. So if worst came to worst, lubrication
might be entirely interrupted. To reliably prevent this eventuality,
the engine of the BMW M6 comes with a so-called "quasi-dry sump
system" incorporating two oil reservoirs: one in front of the front
axle subframe, another behind the subframe.
A reflow pump integrated in the compressed oil pump housing draws
oil out
of the small oil sump at the front and pumps it into the large oil
sump at the back. Both the reflow openings and the compressed oil
pump extraction point are precisely matched to the car's
acceleration and driving forces.
Ten individual throttle
butterflies controlled electronically
Again reflecting the
supreme standard of motorsport, each of the ten cylinders comes with
its own throttle butterfly, each row of cylinders being controlled
by a separate adjuster. While this system is extremely demanding and
sophisticated in mechanical terms, there is no better way to achieve
engine response within split-seconds. To give the engine a
particularly sensitive response at low engine speeds while building
up power just as fast wherever necessary for dynamic performance of
the highest standard, the throttle butterflies are masterminded
electronically by two contact-free Hall potentiometers scanning and
evaluating the position of the gas pedal 200 times a second.
Responding precisely to
any change in running conditions, engine management sets the
position of the ten individual throttle butterflies via the two
adjusters. Naturally, it goes without saying that all this takes
place within fractions of a second. Only 120 milliseconds being
required to open the throttle butterflies in full - roughly the time
a driver takes to press down the gas pedal.
The benefit for the
driver is instantaneous engine response with the car "taking off"
without the slightest delay and the driver being able to sensitively
dose the engine power required. At the same time electronic
operation of the throttle butterflies makes the transition from
overrun to part load and vice versa absolutely smooth and
harmonious.
The V10 draws in the air
it needs through ten flow-optimized intake funnels extending into
two air collectors. The funnels and collectors are all made of a
light composite material containing 30 per cent glass fiber.
Twin-chamber
stainless-steel exhaust system
As important as the
intake side may be for giving the power unit of the M6 maximum
output and performance, the exhaust system may not be neglected in
any respect. So here again, only the best meets the demanding
standards of the engineers and other specialists at BMW M.
The two five-in-one
stainless-steel manifolds have been optimized in elaborate computer
processes to provide exactly the same operating length.
To ensure exactly the
right tube diameter, in turn, the stainless-steel pipes, produced as
one unit without a seam in between, are formed from inside in an
internal high-pressure molding process and under a production
pressure of up to 800 bar. And last but not least, the exhaust
manifolds come with walls measuring only about 0.8 millimeters in
thickness - again a clear sign of the utmost care and diligence the
engineers at BMW M have given to each and every detail of this
masterpiece in engine construction.
A high-performance
sports engine clean and compatible with the environment
The exhaust system is
designed consistently for minimum counterpressure, the dynamic gas
flow is optimized for perfect power and torque. The exhaust system
extends back to the silencers in two chambers, leading into the four
striking tailpipes so typical of a BMW M Car. Compared to the M5,
the sound of the exhaust on the M6 is even more muscular and
aggressive.
As is to be expected of
a BMW M Car, two trimetal-coated catalysts on each exhaust pipe
clean emissions from the ten-cylinder in line with the demanding
European EU4 and, respectively, the equally stringent US LEV2
standards. Two catalysts are fitted in the underfloor, one catalyst
each in the exhaust pipe close to the engine. In conjunction with
the thin-walled exhaust manifolds, these catalysts reach their
optimum operating temperature as quickly as possible, a significant
requirement particularly when starting the engine cold.
Particular attributes of the
system are its low pressure loss and high level of mechanical
stiffness.
Engine control unit
unique the world over
The MS S65 engine
management unit is crucial to the outstanding performance and
emission management of the V10. It ensures optimum coordination of
all engine functions, on the one hand, and the car's control units,
on the other. It also controls interaction with the SMG
transmission.
This engine management
system is quite unique in production engine technology worldwide:
Incorporating more than 1,000 components, it has by far the highest
level of package density. The hardware and software, as well as the
specific functions of the system, have all been developed by BMW M.
High engine speed
demands extreme performance
Given the high speed of
the engine and the large number of management and control functions,
the demands made of the engine management system are very
significant indeed. To meet these demands, the MS S65 control unit
comes with no less than three 32-bit processors able to handle more
than 200 million operations per second. Working with absolute
precision, they determine the optimum ignition timing from more than
50 incoming signals individually for each cylinder and operating
cycle, at the same time calculating the ideal cylinder charge,
injection volume and injection point. The system also determines and
sets the optimum camshaft spread, just as it adjusts the individual
throttle butterflies.
Pressing the Power
button, the driver is able activate a high-performance program
calling up all of the engine's power and performance. This program
uses a more progressive map control line relating gas pedal to the
opening of the throttle butterflies and modifying the dynamic engine
management functions for even greater responsiveness.
The more
comfort-oriented of the two programs is called up automatically
as soon as the engine is started. The driver has the option to
configure
the program switch-over function as a feature of the car's MDrive
control. MDrive also offers yet a further sports program for
particularly dynamic motoring.
Engine management with a
wide range of additional functions
Electronic throttle
butterfly control is based on a system of all-round output and
torque management: The potentiometer on the gas pedal measures the
driver's demand for power and performance, translating this signal
into the torque and output required at any given point in time. The
output and torque manager then adjusts this power request by taking
ancillaries and additional equipment such as the a/c compressor or
alternator into account. Functions such as idle speed control,
exhaust gas management and knock control are also coordinated and
compared with the maximum and minimum forces required for Dynamic
Stability Control as well as Engine Drag Force Management. The
desired power and torque calculated in this way is then set within
the engine, focusing in the process on the current ignition angle.
And last but not least, engine management performs a wide range of
additional on-board diagnostic functions with diagnostic routines
for the workshop, additional operating functions, as well as the
efficient management of peripheral units.
A new highlight in engine management: ionic current technology.
Ionic current technology
serving to detect any risk of the engine knocking as well as
misfiring and miscombustion is a new feature of the engine control
unit. "Knocking" is unwanted self-ignition of fuel in the cylinders.
Engines without knock control have a somewhat lower compression
ratio and a somewhat later ignition point, to make sure that none of
the cylinders ever reaches or let alone exceeds the knock limit.
However, this "safety" distance from the knocking limit means a
trade-off in terms of fuel economy, engine output, and torque.
Active knock control, by
contrast, allows the engine to run at its optimum ignition point.
Knock management protects the engine from damage at all points where
knocking is monitored and limited. The result, obviously, is maximum
efficiency on the road.
With conventional
technology knock control receives its knock signal from various body
sound sensors fitted on the outside of the cylinders. On a BMW M Car
there is one sensor for each set of two cylinders. But as
sophisticated and progressive as this technology may otherwise be,
even this is not sufficient on a multi-cylinder, high-speed engine
such as the new V10.
It is not able to
reliably detect the risk of the engine knocking. And since at the
same time a relatively high standard of monitoring accuracy is
essential in the light of high engine speeds in order to guarantee
appropriate combustion quality in the cylinders and, accordingly, a
long service life of all components and appropriate emission
control, the new technology now introduced is ionic current
management.
Spark plugs with additional control functions.
Using this technology,
the engine is able, via the spark plug in each cylinder, not only to
sense and control the risk of knocking, but also to monitor the
ignition process and recognize any tendency of the engine to
misfire. In other words, the spark plug serves both as a sensor
observing the combustion process and as an actuator for the
ignition. This marks the big difference versus a conventional
knocking and ignition sensor fitted outside of the combustion
chamber. Ionic current measurement, by contrast, is conducted
directly within the combustion chamber, the spark plug itself
serving as the sensor.
Measurements right in
the middle of the combustion process.
The temperatures
generated in the combustion chambers of an internal
combustion engine may well be up to 2,500 °C or 4,500 °F. As a
result
of these high temperatures and chemical reactions during the
combustion process, the gasoline/air mixture in the combustion
chambers is partially ionized. Particularly along the flame front,
the gas becomes electrically conductive once ions are formed by the
fission and accumulation of electrons (ionization). By means of the
spark plug electrode electrically insulated from the cylinder head
and connected to a control unit - the ionic current satellite -
affiliated in turn to the engine management unit, the system is able
to measure the ionic current flowing between the electrodes, with
the spark plug electrode itself being kept under direct voltage. The
level of such ionic current flow depends on the degree of gas
ionization between the electrodes.
Ionic current
measurement thus provides information on the combustion process
directly where it counts, that is in the combustion chamber itself.
The ionic current
satellite receives signals from the five spark plugs in each row of
cylinders, amplifies these signals and conveys the data to the
engine management unit. The control unit then analyses the data
received and, where necessary, intervenes on specific cylinders,
adjusting the ignition timing ideally to the combustion process by
way of knock control.
This dual function of
the spark plugs serving, first, as the spark-generating
unit and, second, as a sensor, helps additionally to facilitate
diagnostic procedures in maintenance and service.
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