Over the last 37 years, ZF’s transmission plant at Saarbrücken, in Germany, has manufactured a series of planetary automatic transmissions, for use in passenger cars.  First came the 3-speed 3HP in 1973, followed by 4-speed 4HP in 1982, the 5-speed 5HP in 1990 and finally the 6-speed 6HP family in 2001.  More recently, in 2006, ZF launched second generation versions of the 6HP family, which were more efficient than the first generation.  Now Saarbrücken has embarked on the next phase of its life, in which the new 8-speed 8HP family will start to take over, with initial production having started in July of 2009.

The main production hall at Saarbrücken occupies an area of 185,650m2, and at its peak in 2006 and 2007, manufactured more than a million transmissions per year.  Of course, this fell significantly in 2009, to just 723,000 units, although volumes are now ramping up again, as the global economy begins to recover.  In 2010, CSM Worldwide is forecasting that approximately 900,000 transmissions will be manufactured at Saarbrücken, for use in over 50 different vehicles around the world.

The advent of the new 8-speed 8HP marks the beginning of the end, for the current 6-speed 6HP family.  Indeed, by 2014, ZF expects that most of the current 6HP transmissions will have been replaced by 8HP transmissions, in the various applications which use them.  This transition is largely driven by the increasing demand for efficiency, in the form of vehicle CO2 emissions, due to legislation and pure market pressures.  Having said this, there is always going to be an element of one-upmanship, particularly between BMW (supplied by ZF) and Mercedes-Benz, which manufactures its own automatic transmissions.  ZF has always maintained that 8 forward gears was the number that dropped out of its extensive computer analysis, which evaluated millions of possible configurations, to find the most efficient ones.  This is almost certainly true, but is also convenient for BMW, whose competitor Mercedes-Benz has been using a 7-speed automatic for a number of years.

Rather than using a few long production lines, the Saarbrücken plant features smaller production modules, which each cater for different transmission variants.  Currently only a few modules are installed for the 8HP, giving ZF a capacity of 350k units per year, based around a 3-shift system.  Given that the plant is currently full, this means that extra capacity can only be installed (probably required by late 2010 or early 2011) if existing 6HP modules are de-commissioned, which of course can be done one-at-a time, as demand falls.  Ultimately CSM expects to see the 8HP capacity rise to more than 1 million units per year, as existing OEMs switch from the 6HP to the 8HP, and as new OEMs start to use the 8HP.

In addition to being able to phase in the 8HP capacity, ZF has also been careful to design the 8HP variants, such that similar parts for each version can be machined on the same equipment, without any changes being made.  This makes for reduced downtime, when swapping from one variant to another, as the demand fluctuates.

Later this year, ZF will start to manufacture variants of the 8HP with stop-start, for BMW and Audi, to further improve vehicle efficiency.  Because of the pressure that OEMs are under to reduce CO2, it seems probable that the majority of all 8HP transmissions will feature stop-start, within the next few years.  Even more efficiency can be achieved with so called ‘8HP+’ variants, which ZF will supply to BMW from later this year.  Although details of the technology were not disclosed, it is largely software-based, with only minor hardware modifications.  Initially BMW will have exclusive access to this technology, which it helped to develop, after which ZF will be free to offer it to other OEMs.  Whilst ZF is referring to these variants internally as the 8HP+, the official program codes are unlikely to reflect this.

Mild hybrid variants of the 8HP are already in production, for use in the BMW 7-Series.  Meanwhile, full hybrid versions are expected from 2011, although the volumes for these will be highly dependent on the market conditions, at that time.

ZF claims that it has kept the manufacturing costs of the 8HP comparable with the existing 6HP, helped by a similar number of components (e.g. 471 for the 6HP28 and 467 for the 8HP70).  This is despite making them more efficient and lighter, whilst maintaining the same package size – making it easier for OEMs to swap from the 6HP to the 8HP.  Of course, there is no guarantee that this cost stability is reflected in the price to OEMs.  Indeed, data from ZF suggests that the average price of a transmission from Saarbrücken has increased from €1,739 in 2007, to €1822 in 2008 and €1,905 in 2009.

So far we have only talked about the existing longitudinal transmissions, for use in vehicles where the engine is mounted in a ‘North-South’ configuration.  In an interesting new development, ZF is now considering the possibility of transverse automatic transmissions – a layout which is common in front-wheel-drive (FWD) vehicles, but which is largely new to ZF.  Whilst ZF has developed a few transverse automatics in the past, these have mostly been manufactured under license, by GM-Daewoo.  This new venture makes it more of a threat to the other independent transmissions suppliers, such as Aisin and JATCO, who now have a new and well-respected competitor in the market place.  Having said this, ZF will have to work hard to overcome the ‘new-boy’ image, despite having a reputation for high quality products.  It will also need to be careful with pricing, in the more mainstream and cost-sensitive FWD market, but it will be able to offer better efficiency, which is on the mind of every OEM at the moment.

One of the reasons behind ZF’s decision is that BMW is considering converting some of its cars from rear-wheel-drive (RWD) to front-wheel-drive.  This will almost certainly apply to the BMW 1-Series, at some point in the future, and the new so-called ‘UKL1’ vehicles, which may both share a common platform with future Minis.  By having several cars based on the same platform, BMW is hoping to benefit from economies of scale, and from the lower costs associated with this layout.  But of course, ZF does not want to lose the BMW business, so it has taken the decision to develop a multi-speed automatic, to target some or all of these applications, with a planned SOP of 2013.

One key question remains thought – how many gears will it have?  So far ZF has remained tight-lipped about this, but you would have to assume it would be more than the current state-of the art, which is 6 forward gears.  So it seems a safe to say that these new transmissions will have 7, 8 or even more forward gears.  And they will certainly be stop-start and hybrid compatible, using a secondary electric oil pump, to maintain the oil pressure when the engine is switched off.  Or ZF might use a pressure storage system, such as the spring-based reservoir system seen on the new 8HP, or the valve based system used on the 7DT dual clutch transmissions.

ZF has said that, despite the limited space in the main hall at Saarbrücken, the new FWD transmission could be built there, although that decision would ultimately depend on where their customers are located.

So, regardless of how popular the ZF FWD project is, there seems little doubt that the Saarbrücken plant will continue to build on its long history, as a source of automatic transmissions.

Chris Guile is a Senior Powertrain Analyst with CSM Worldwide (now part of IHS).