BMW to broaden use of eight-speed gearbox

BMW has confirmed that the ZF 8HP eight-speed automatic gearbox that debuted in the F01-series 760Li last year is destined for its entire range of rear-drive and 4WD vehicles over the next few years.

This will include Rolls-Royce models beyond the new Ghost, and will filter right down to the next 1 Series to be introduced during 2011.

Future M-cars such as the next M5 (2011) and M6 (2012) might even offer the eight-speeder.

To be fitted standard throughout the F10 5 Series when the range is released in Australia on June 3, the ZF 8HP transmission will also be included in the F07 5 GT Gran Turismo model launched in Australia this month.

Furthermore, it will central to the upcoming 5 Series ActiveHybrid model that is expected to arrive sometime within the next 12 to 18 months.

BMW has already announced that the ActiveHybrid 7 Series will feature the eight-speed automatic.

Lastly, the ZF 8HP is destined for BMW’s next crop of vehicles with idle-stop technology, beginning with the F10 520d Stop Start model in the middle of this year.

The current generation of BMWs available right now with this technology – namely the 120d and Mini Cooper D – are only paired to a six-speed manual transmission.

However, the eight-speeder will not spell the end of the dual-clutch gearbox (known as DKG in BMW speak) as currently fitted to models like the M3, 335i and 135i.

Instead, both are expected to co-exist to give BMW and Rolls-Royce customers the best possible gearbox applications, according to one BMW insider.

Designed and developed by BMW in conjunction with ZF Friedrichshafen AG, the ZF 8HP is a complete redesign of the ZF 6HP six-speed automatic unit the two companies co-developed in the late 1990s for the previous-generation E65 7 Series unveiled in 2001.

It will be made available in three varieties according to the amount of torque that can be handled – 500Nm, 700Nm and 900Nm.

In contrast, the strongest DKG BMW currently offers can only handle a maximum of between 500Nm and 600Nm, limiting its application across the BMW and Rolls-Royce ranges.

This raises doubts over reports suggesting that the next-generation M5 (and M6) – reportedly to be powered by a 400kW-plus 4.4-litre V8 producing in excess of 650Nm – will use a development of the M3’s DKG transmission.

The ZF 8HP may step in instead as the replacement for the existing models’ outmoded SMG II gearbox, although a second-generation DKG with greater torque capabilities has also been mooted.

According to BMW’S head of development for this gearbox, Oliver Frank, the eight-speed automatic is at the very least in the same performance and efficiency class as the DKG.

“The potential is the same with the eight-speed automatic as it is with the DKG,” he told GoAuto at the F10 5 Series launch in Portugal this week.

“The eight-speed has a little more spread in terms of the comfort side of possibilities compared to the DKG, so its band is a little broader.” Despite the extra ratios, BMW engineers have decreased the number of mechanical and structural components compared to the old six-speed ZF gearbox, for a weight saving of around 2.5kg.

Mr Frank also revealed that BMW considered upping the forward ratio count to 10 speeds before rejecting the proposition, while a CVT continuously variable transmission was also contemplated for a time before also being discarded.

The aim was to achieve new heights of driveability, economy and emissions progress, which are core to BMW’s ‘EfficientDynamics’ mantra.

However, the resulting weight and bulk increases that were necessary with the extra hardware required for the planetary gears not only cancelled out the potential gains of having a greater spread of gear ratios, but also actually brought in inefficiencies not existent in the eight-speed transmission.

“BMW looked at nine- or 10-speed automatics but these were rejected because they required more processes fitted to them which significantly reduced their efficiencies,” Mr Frank said.

“As soon as you add one more planetary gearset you add more gears but you add some losses since you get more parts running through the oil.

“And CVTs suffer losses in efficiency due to the huge pressures needed inside to transmit all the torque – so again it ended up being less efficient than the actual eight-speed automatic.” Mr Frank was asked if BMW and ZF looked at going down the same development route as Toyota did with the Aisin-AW AA80E eight-speed automatic gearbox it launched in the fourth-generation Lexus LS series in 2006 as well as in the GS460 and IS F.

“Toyota went another way – they adapted an existing six-speed gearbox by putting in additional gears and additional parts inside. And to our opinion it is not optimised in terms of efficiency.” BMW said it would include the eight-speed automatic as either an option to a conventional manual or as the standard transmission because it is a completely new design with every part optimised for ultimate gearbox efficiency.

“It’s really the most advanced transmission on the market, and it’s my favourite transmission,” Mr Frank said.

“Since we are preparing it for the whole BMW fleet … it has to serve the top sporting potential as well as the most comfort orientated like the Rolls-Royce Ghost – so its (spectrum) band is complete.

“Its functionality even works well on the racetrack … we have been getting lots of feedback from the professional drivers here at Estoril … one of the guys who races here says he really hates automatic transmissions but says this is the first one that really performs and handles the racetrack well.

“I have been in transmission development for over 12 years now, and there has been quite a lot of evolution (in that time) … and it is all in this eight-speed automatic.

“It is currently the most efficient transmission of its type available anywhere in the world, and will probably remain so for the foreseeable future.” Other manufacturers will also be able to use the ZF 8HP gearbox soon, although there are BMW-specific elements to the transmission that will not be made available for others, a BMW spokesman said.