To provide perfect results, the high-speed engine concept must be com-bined 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 sequen-tial gearbox with seven gears and Drivelogic, which provides both a manual gear-shift with extremely fast shift times as well as an automatic transmission func-tion 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 com-plete running life, with additional back-up being provided by a separate oil cooler for the high-performance transmission.
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
pow-er actually conveyed to the wheels depends on high engine speeds, such smaller increments are the best guarantee for truly dynamic accele-ration.
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 centre 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 pro-cess. This, in turn, serves to activate four hydraulic cylinders in the gearshift actuator controlled by solenoid valves in the hydraulic unit. The four hydrau-lic 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 stand-still to top speed in a virtually ongoing surge of power and torque, as if there were no interruption whatsoever. SMG offers an almost incom-par-able 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 motor-ing. 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 sport-ing M6 driving program, enabling the less experienced driver to ac-celerate perfectly from a standstill, using all of the car’s power and accele-ration 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 si-tu-ation 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 par-tic-ularly sensitive operation of the clutch for smooth motoring and accele-ration 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 pre-vent 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
down-hill 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 De-tec-tion 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 steer-ing angle, and Key Memory settings. And last but not least, SMG and DSC also communicate directly with one another.
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