Press Release
New seven-speed transmission
Ultra-fast shifting with Sequential M Gearbox
· Worlds first production car seven speed sequential manual gearbox
· 11 choices of manual or semi-automatic change patterns
· Rapid manual changes, ten times quicker than the hand
· In-house design showcases BMW engineering expertise
The M6 is fast. It covers the 0, 62 mph sprint in just 4.6 seconds, faster than a DB9, a Vanquish, an SL 55 AMG or a 911 Carrera S. And it is the exemplary transmission of over 500 horsepower through the gears that gives the car this phenomenal speed.
Designed to handle torque of up to 550Nm and engine speeds of up to 8,500rpm throughout the Ms entire lifecycle, the seven speed sequential M gearbox (SMG III) is exactly the right gearbox for the BMW M6s new V10 engine. It is completely new and sets BMW up as the first and only manufacturer to offer a seven speed sequential gearbox with Drivelogic.
But why seven speeds?
Its all about thrust
Seven speeds offer closer ratios than six, in other words there are smaller steps between each gear. This reduces dips in torque and power as each higher gear is selected. The transmission, with its short overall transmission ratio, therefore matches the torque to the prodigious power output and translates it into optimum forward thrust, thrust being closely related to high engine speeds.
Changing gear is a sublime pleasure with SMG
The seven-speed SMG is a true manual gearbox but the changes are handled by super-fast electronic programmes. Gears can be changed using the gear lever, forward to change down, backwards to change up, or by using the paddles behind the steering wheel. There is no clutch to press and SMG efficiently matches engine speed, even in the case of full throttle upchanges.
SMG offers all the benefits of a manual gearbox, engine braking and lower fuel consumption for example, and does not require the energy-sapping torque converter of an automatic.
How it works
Gears are shifted electro-hydraulically using shift-by-wire technology, a product of the aerospace industry. This new third generation SMG system has the hydraulic unit and actuators integrated into the gearbox casing. When a change is called for, the control unit actuates magnetic valves controlling the systems hydraulics.
The hydraulic oil, operating under 90 bar pressure, flows via a magnetic valve into the clutch master cylinder to open the clutch. Then, using solenoid valves, four hydraulic cylinders in the actuator are switched effecting the gear change process by means of four rods. When shifting down the engine the transmission double de-clutches automatically, including giving a throttle blip.
Warp speed changes smoothly
The second generation SMG system featured in the current M3 is already a very effective and fast shifting system. The new seven-speed SMG is, however, 20 per cent quicker.
To put this into perspective the new gearbox changes gear in 50 milliseconds. Compare this to even a seasoned driver using a normal manual gearbox who will take ten times that speed - around half a second.
This speed also reduces the jerkiness sometimes felt in earlier systems because the forward thrust is so seamless. It is also safer. Not having to concentrate on matching engine speed to gear changing allows more driver focus on the road, while enthusiastic down changes at overly high engine revs are an impossibility with the SMG system watching over the driver. The driver is also informed of optimal up-change points when the rev band in the Head-up Display flashes.* HUD additionally shows the gear in mesh, a tachometer graphic and road speed.
Drivelogic, a gearbox of many possibilities
An essential feature of the new seven-speed SMG system is Drivelogic. This function offers no less than eleven gear change options that are determined by the driver. Each programme differs from the others in gear change time, the higher the programme selected the shorter are the shift times, and drivers will quickly determine which of the eleven are their preferred settings.
There are six manual gear change programmes (S mode) and five automated (D mode) which, essentially, alter the shift speed of the transmission, one bar indicated on the programme is a slower shift speed than two and changes up a gear earlier, for example. These programmes are selected using the Drivelogic button beside the gear lever. A preferred mode can be permanently programmed via MDrive Manager* and then simply activated by pressing the MDrive button on the multi-function steering wheel.
* See page 5 for more details on Head-up Display and MDrive Manager
Automatic mode
Each of the five automatic programmes will change gears up and down according to the driving situation, car speed and throttle position. For example, with D1 programme selected the gearbox sets off in second gear and ensures smooth clutch engagement. The driver can influence this process by, for example, releasing the throttle to encourage an up-shift. Alternatively, pushing the accelerator hard calls up a down change.
Launch control
The whole idea of a sequential manual gearbox comes from motorsport. Fast, accurate and foolproof changes ensure the best progress from start lights to chequered flag.
So, as an indulgence, BMW M engineers have included launch control within the new SMG gearbox, a system very similar to that which we see at the start of each Grand Prix. The system is honed to ensure that the rear wheels transmit the maximum power to the road without spinning excessively. In other words it provides the absolute optimum in straight-line acceleration.
Launch control is activated by, first, switching off DSC fully and then selecting the S6 manual gear change mode. The driver then needs to push and hold the centre gear lever forward and depress the accelerator pedal fully. When the optimum engine speed for take-off is reached (4,200rpm), releasing the gear lever allows the SMG system to take over. By keeping the accelerator pedal fully depressed the car rapidly accelerates with the gearbox continuing to up-shift and go on to the cars maximum speed. If the accelerator pedal is released, even by a fraction, the launch control function is cancelled.
Launch control is not a function for regular use on the public roads but on a track it is a lot of fun and perfect for the quick get away.
Three more SMG benefits
For safety and comfort, the new SMG transmission offers a hill start assistant that almost completely eradicates roll back when stopping on a gradient. Application of the footbrake activates the system that then holds for 1.5 seconds the car when the brake is released and before the throttle is re-applied.
Hill recognition allows SMG to change gear change points on gradients and descents. It holds lower gears for longer when going downhill to make use of engine braking. Going uphill the system prevents gear hunting. In D automated mode gear selection is adjusted to the steepness of the gradient.
Finally, if the system detects wheel slip it controls clutch operation to stabilise the M6 in the event of high drag torque on the rear axle.
These many functions of the new system are possible because the SMG control unit and the engine management system communicate with each other in a very powerful CAN databus. The SMG system receives data from the sophisticated MS S65 engine management system on the accelerator position, wheel and engine speed, temperatures, steering angle and key memory. SMG and Dynamic Stability Control (DSC) also communicate directly with one another.
