Notice in the 8 speed picture from the New 5 series (F10) press release:
1. The multiple disc lock-up clutch (far left) inside the torque converter.
2. The addition of the torque converter provides additional torque multiplication under acceleration.
3. There are two overdrive ratios.
This is from the BMW F10 Press release:
"Playing a supporting role: innovative new 8-speed automatic transmission.
All new BMW 5 Series models will feature an 8-speed automatic transmission, which brings smooth shifting, sportiness and efficiency to new levels of perfection. Compared to the exemplary 6-speed automatic offered in past BMW models, the 8-speed’s “taller” cruising gears make a significant contribution to reduced fuel consumption and emissions, as well as quietness. And its wider spread of ratios from lowest to highest gear enhances acceleration and response across the range of driving speeds.
Technically speaking, this new automatic’s attributes have been achieved via an innovative concept that provides the two additional ratios (7 and 8) with no increase in bulk or weight. In an arrangement not heretofore employed in an 8-speed automatic, four planetary gearsets and five clutch packs are controlled in a way that no more than two of the five clutch packs are freewheeling at any given time. The modest increase in the number of mechanical elements allows the new transmission to achieve unusually high efficiency: the so-called “gearing efficiency” is higher than 98% in all eight gears. In 6th gear, it’s highest of all because that is direct drive, with no gearing reduction at all. Combine this with reduced friction and the ability to keep the torque converter “locked up” more of the total driving time, and the transmission becomes very much a part of the new 5 Series’ overall efficiency concept.
Two additional gears mean threefold progress: quicker shifts, greater smoothness, enhanced efficiency.
The wider spread of ratios allows the engine to run at lower speeds, mainly in the “tallest” gear, 8th. Yet even with this wider spread, the steps between adjacent gears are reduced; in turn this means a stronger, smoother flow of power during acceleration.
And for the same reason, faster shifts are a further benefit because only one clutch pack is disengaged to shift up or down by one or two gears. On the other hand, downshifting more than two gears is accomplished as a direct shift. For example, a downshift from 8th to 2nd gear is made with only one clutch pack disengagement, and thus occurs without stepping down through the intermediate gears. Thus at one instant the driver can be enjoying the quiet, fuel-efficient low rpm of 8th gear, and in the next instant getting maximum acceleration.
Manual Transmissions: Continuing a BMW tradition
BMW continues as the only manufacturer to offer manual transmissions in the 5 Series’ competitive set, underlining the sporty nature of the car, as well as BMW’s commitment to driving enthusiasts.
The 535i and 550i Sedans will be offered with a 6-speed manual transmission in the United States, providing a level of driver involvement unique in the segment."
This looks like a great combination.