Land Rover has announced that it will demonstrate the world's first nine-speed automatic transmission for a passenger car at the 2013 Geneva Motor Show. The ZF HP9 9-speed gearbox has a higher top gear in a more compact design, in order to fit in the same space as conventional 6-speed transmissions. According to Land Rover, it will also provide smoother gear shifts with improved accelerations and lower fuel consumption.

ZF has been working on the HP9 since 2011, but has been a bit coy as to what car maker it was intended for. Now it’s revealed that Land Rover is both the customer and lead partner for the new gearbox. Intended for use in front-transverse mounted engines, it’s based on ZF control technologies originally developed for the ZF 8HP gearbox.

By increasing the number of gears from the standard six to nine, ZF has produced a ratio spread of 9.3 with small ratio steps. Where a conventional 6-speed gearbox makes downshifts sequentially, Land Rover and ZF claim that the 9HP glides between gear changes almost imperceptibly. In addition, the lowest ratio is lower than that of a 6-speed and is more suitable for off-road use and steep inclines.

Rear and side views of the gearbox

The 9HP uses a modular design and a software-based transmission control unit. The reason for this is to allow the gearbox to fit into transverse engines without significant modifications to the car. Though the 9HP is 0.24 inches (6 mm) longer than a 6-speed gearbox, it weighs 16.5 pounds (7.5kg) less.

It manages this by using a nested planetary gearset with nine speeds, four simple gearsets and six shift elements. It also has a new, compact hydraulic vane-type pump and instead of conventional clutch packs is has two patented interlocking dog clutches – a first for a passenger car. A torque converter reduces vibration and provides oscillation isolation for more comfortable starting and shifting.

The increased gear ratios of the 9HP mean that cruising is possible at low engine speeds, which allows for smoother shifting. According to the partners, the 9HP’s “Fast-Off” mode monitors the rate of throttle release and if it anticipates a driver’s request for high power, it holds the gear shift if necessary. This provides shorter response times “below the threshold of perception” and quick shifts for improved start-up acceleration. It also monitors requests for downshifts and if the car is traveling too fast for the desired gear, it delays shifting until the speed drops.

Land Rover and ZF say that the 9HP reduces acceleration from 0 to 100 km/h (62 mph) by two seconds over conventional 6-speeds and that it reduces fuel consumption by 12 percent for petrol SUVs and 16 percent for diesels, while keeping the engine running 700 rpms lower with corresponding reductions in emissions. The 9HP is also suitable for hybrid systems.

The 2013 Geneva Motor Show runs from March 7th to 17th.

Source: Land Rover