It was not a long time ago that 6-speed automatic gearboxes were a privilege largely enjoyed by top of the range models. However, in their quest for efficiency, manufacturers have quickly moved on to 7- and 8-speed boxes which trickle down the line to even the smallest models in the range (e.g. the new BMW 1-Series).
But ZF has outdone them all by launching the world’s first 9-speed automatic transmission for passenger cars in the VDI Conference “Transmissions in Vehicles 2011”. The new gearbox, code-named 9HP and designed for cars with front-transverse drive, is available in two model ranges, can handle torque between 280 and 480 Nm (206.5 – 331.9 lb-ft) and can be combined, according to each manufacturer’s requirements, with different stop-start systems, hybrid and all-wheel drive applications.
According to ZF, the 9HP offers fuel savings up to 16% compared to today’s 6-speed automatic transmissions in front-wheel drive cars thanks to the extremely high total spread of 9.84 and the high number of gears that allow the engine to run in the most fuel-efficient speed range. For example, in 9th speed, you can travel at 120 km/h (75mph) with the engine running at just 1,900 rpm, compared to 2,600 rpm in a 6-speed auto.
But the 9HP offers more than better fuel economy: even though it uses a standard torque converter instead of the double-clutch configuration which has become increasingly popular, ZF states that it has designed all components for faster response and shift times that are “actually below the threshold of (the driver’s) perception”.
ZF’s new gearbox has been developed as a “construction kit”, making it possible to be installed in a variety of configurations. To achieve this, the company has developed a new all-wheel drive system in which the rear axle drive is decoupled under normal driving conditions and is actuated only when required, reducing fuel consumption by 5% compared to permanent all-wheel drive systems.
The 9HP is, by default, compatible with stop-start systems without the need for an additional oil pump, and can also be used in parallel hybrid architectures, in which case the torque converter is replaced by an electric motor.