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Transmission
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The Seven-Speed SMG
Gearbox: Shifting Gears like in Formula 1
To provide perfect
results, the high-speed engine concept must be combined with an
appropriate transmission. This is the only way to convert the power
coming from the engine into optimum momentum on the road by means of
the right - short - overall transmission ratio.
BMW's Sequential M
Gearbox (SMG) with seven speeds is well suited to conveying the
power of the V10 to the drive wheels. BMW M is the first
manufacturer to offer such a sequential gearbox with seven gears and
Drivelogic, which provides both a manual gearshift with extremely
fast shift times as well as an automatic transmission function for
cruising comfortably in style.
In technical terms, the
gearbox is conceived for torque of up to 405 lb-ft and engine speeds
of up to 8,500 rpm. In other words, it offers adequate reserves for
consistent reliability throughout the car's complete running life,
with additional back-up being provided by a separate oil cooler for
the high-performance transmission.
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Even smaller gear
increments than with BMW's six-speed gearbox
Seven gears keep the
gaps between engine speeds and torque levels when shifting gears
even smaller than with a six-speed gearbox. And since the power
actually conveyed to the wheels depends on high engine speeds, such
smaller increments are the best guarantee for truly dynamic
acceleration.
SMG transmission for the
pure joy of shifting gears
The seven-speed SMG
transmission offers all the benefits of the sequential gearbox
concept: The driver is able to shift gears either via the selector
lever in the center console or from paddles on the steering wheel,
without having to press a clutch pedal. Instead, the driver can even
keep his foot on the accelerator while shifting gears. And unlike
automatic transmission, the Sequential SMG Gearbox does not need a
torque converter taking up energy and reducing the car's
performance.
The SMG transmission shifts all gears electrohydraulically with all
control units operating by wire, that is, without any mechanical
connections. Both the SMG hydraulic unit and the gearshift actuators
are integrated in the transmission housing. Whenever the driver
wishes to shift gears, the control unit activates the appropriate
solenoid valves within thousandths of a second, setting the
hydraulic system as required. Now the hydraulic fluid under a high
level of system pressure of up to 90 bar is able to flow into the
clutch master cylinder within fractions of a second, opening the
clutch in the process. This, in turn, serves to activate four
hydraulic cylinders in the gearshift actuator controlled by solenoid
valves in the hydraulic unit. The four hydraulic cylinders then
serve ultimately to shift the gears by way of four separate
gearshift rods. And when down-shifting, the engine automatically
"blips" the throttle between gears.
New SMG 20 per cent
faster than before
The third generation of
SMG transmission now featured in the BMW M6 speeds up the gearshift
process by no less than 20 per cent. Gears are shifted in a
"flowing" process much faster than even an experienced driver would
be able to. The interruption of power when shifting gears is barely
perceptible. The BMW M6 therefore accelerates from standstill to top
speed in a virtually ongoing surge of power and torque, as if there
were no interruption whatsoever. SMG offers an almost incomparable
Formula1 experience.
A further advantage of
the SMG gearshift is the increase in traffic safety:
With gears shifting at the same persistent speed and in the same
precise, absolutely reproducible process, the driver no longer has
to concentrate on the gearshift as such. The result is an even more
precise, safer and relaxed style of motoring.
Drivelogic: The driver
chooses his particular SMG gearshift
The Drivelogic function
gives the driver a total of 11 gearshift options individually
adjusting the SMG gearshift to the driver's particular style of
motoring. The first and most significant distinction between these
driving programs is the pre-determined gearshift speed: The higher
the program, the engine speed and load, the quicker the gearshift.
Six of these 11 gearshift options come with the sequential manual
gearshift function (S-mode) ranging from smooth and dynamic all the
way to high-performance. And in the S-mode the driver always shifts
gears by hand.
Launch control:
Accelerating to top speed with full power all the way
The launch control
function in the S-mode supplements the purist and sporting M6
driving program, enabling the less experienced driver to accelerate
perfectly from a standstill, using all of the car's power and
acceleration in the process. In this case you switch off DSC in
advance.
Launch control serves to
relieve the driver of the usual chore of shifting gears himself. So
with the car at a standstill, all the driver has to do is push
forward the selector lever and keep it there. Now, pressing the gas
pedal, he automatically sets the engine to its optimum start-off
speed. Then letting go of the selector lever, the driver enables his
M6 to accelerate with ideal wheel spin management, provided the
driver's foot remains fully on the gas pedal. There is subsequently
no need to shift gears all the way to the car's top speed, SMG with
Drivelogic shifting gears automatically in each case shortly before
maximum engine speed and thus moving up smoothly from first to
seventh gear.
As in the S and D modes,
a display in the cockpit activated during launch control informs the
driver of the gear currently engaged.
Automatic transmission
straight from the race track
Five of the 11
Drivelogic programs are available in the so-called automated
D-mode in which the transmission shifts the 7 gears automatically.
This it does as a function of the driving program currently in use,
the respective situation on the road, the speed of the car, and the
position of the gas pedal. Driving program D1, for example, sets off
in second gear and ensures particularly sensitive operation of the
clutch for smooth motoring and acceleration on, say, snowbound roads
or quite generally in winter. The driver is able to influence this
automatic gearshift by slowly taking back the gas pedal to shift up
in the D-mode, too. Conversely, he is able to shift back quickly by
pressing the gas pedal all the way down. Both in the S- and D-mode,
the transmission automatically shifts back to first gear as soon as
the car comes to a standstill. Then, to set off again, all the
driver has to do is press the gas pedal.
Special functions for
extra safety and comfort
The seven-speed SMG
transmission in the BMW M6 supports the driver
not only in terms of optimum motorsport performance, but also by way
of many safety features. In a critical situation, for example when
shifting back on a slippery road, SMG opens up the clutch within
fractions of a second to prevent high engine forces being
transmitted to the drive wheels and causing them to lose traction.
An intelligent
transmission on grades
Hill Detection modifies
the gearshift points on uphill and downhill grades: Driving uphill,
this avoids a constant shift of gears up and down; driving downhill
the function keeps lower gears in mesh for a longer period in order
to capitalize on the engine's braking effect. And in the D-mode the
Hill Detection function sets the gear chosen to the actual grade
encountered at any given point in time.
These functions are only
possible thanks to the close link between the SMG control unit and
the engine management system communicating directly with one
another. This communication is provided by a high-performance CAN
data bus connecting the MS S65 engine control unit with the SMG
control unit networked to 12 redundant SMG sensors. The SMG control
unit therefore receives all relevant data from the MS S65 "brain" on
the current position of the gas pedal, wheel and engine speed,
temperatures, the steering angle, and Key Memory settings. And last
but not least, SMG and DSC also communicate directly with one
another.
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