Land Rover to demonstrate ZF 9-speed automatic transmission; up to 16% fuel savings over standard 6-speed automatic
27 February 2013
|The ZF 9HP 9-speed. Source: ZF. Click to enlarge.|
At the upcoming Geneva Motor Show, Land Rover will announce the first 9-speed automatic transmission for a passenger car; Land Rover is the lead partner on the project, working together with ZF. The ZF 9HP transmission (earlier post) is specifically designed for transverse applications and front or four-wheel drive and can thus be installed in 75% of all cars produced worldwide, ZF notes.
Increasing the number of gear ratios from six to nine improves fuel economy and a correspondingly reduces CO2 emissions. (ZF suggests that the 9HP can provide fuel savings up to 16% compared to a standard 6-speed front transverse automatic transmission.) Smaller ratio steps give improved response during acceleration, improved shift quality, drive and refinement. The higher top gear not only reduces fuel consumption but the lower engine revs improve comfort and reduce noise when cruising at high speed.
(ZF says that in real-world testing at a constant speed of 120 km/h (74.5 mph), the 9HP reduced fuel consumption by 12% in a gasoline-powered SUV and by 16% in a diesel-powered SUV.)
Features of the 9HP include:
Planetary gearset with 9 speeds, 4 simple gearsets, and 6 shift elements. Gearsets are nested to save space.
Wide transmission ratio spread (nearly 10) with small ratio steps.
The first use of interlocking dog clutches in a passenger car powershift transmission.
Torque converter with excellent vibration and oscillation isolation for optimal comfort during starting (driveoff) and shifting.
Low engine speeds for increased fuel savings
The lowest ratio in the 9HP is far lower than the existing six-speed transmission and is specifically designed for off-road use, towing and more extreme on-road conditions such as gradients and altitude, giving the driver a heightened sense of control.
ZF describes the fast gear changes as being “below the threshold of perception.” 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.
An adaptive shifting system matches the driver’s needs, sharpening up during brisk driving then slipping into a more economical regime under more relaxed driving. Curve Mode, longitudinal acceleration and pedal position all control upshift prevention.
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 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 innovative design features including a new hydraulic vane-type pump, which also contributes to improved efficiency, two patented dog clutches replacing bulkier conventional clutch packs, and an Intelligently Nested gear set.
Land Rover was chosen by ZF to be the lead partner on the 9HP and Land Rover engineers have worked in partnership with ZF engineers to jointly develop the transmission to suit the brand.
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