World’s first nine-speed automatic transmission cuts emissions

Gearbox will be developed by ZF and launched by Jaguar Land Rover

Land Rover is to launch what it claims is the world’s first nine-speed automatic transmission for a passenger car. The gearbox, developed with Tier One supplier ZF, will be unveiled this week at the Geneva motor show.

The technology supports Jaguar Land Rover’s attempts to ensure that its vehicle fleet does not emit more than an average of 130g of CO₂ per kilometre. The Midlands-based firm also wants to be increasingly seen as a technology leader.

The ZF 9HP transmission is specifically designed for transverse applications. Land Rover said that increasing the number of gear ratios from six to nine would bring significant improvements in fuel economy and a corresponding reduction in CO₂ emissions. 

Smaller ratio steps are said to give improved response during acceleration, improved shift quality, drive and refinement. The higher top gear reduces fuel consumption and the lower engine revs improve comfort and reduce noise when cruising at high speed, said Land Rover.

The lowest ratio in the 9HP is far lower than in the existing six-speed transmission and is specifically designed for off-road use, towing and more extreme on-road conditions like gradients and altitude. 

Whereas the existing six-speed transmission makes shifts sequentially, the 9HP has a skip-shift function for much swifter downshifting under rapid deceleration or from greater driver input demands. The torque converter incorporates a multi-stage damper system for smoother pulling away and improved refinement.

Fast-off mode measures the rate of throttle release, anticipates further requests by the driver for high power, then holds the gear if necessary. If the driver requests a downshift when the vehicle is travelling too fast, the transmission will remember the request and make the shift when the speed drops to an appropriate level.

Despite the extra three gear ratios the ZF 9HP is only 6mm longer and weighs 7.5kg less than the outgoing six-speed transmission. The small package space is achieved by a number of design features including a new hydraulic vane-type pump and two patented dog clutches replacing bulkier conventional clutch packs.

The transmission is compatible with stop-start systems and, like the eight-speed ZF unit in the Range Rover, was designed from the outset for hybrid applications.