Land Rover in technical collaboration with transmission technology leader ZF has developed the world’s first nine-speed automatic gearbox. The 9HP ZF automatic transmission has been designed for front transverse applications such as front wheel drive and all-wheel drive cars.
The idea behind developing a nine-speed gearbox was to improve fuel efficiency throughout the powerband of an engine. The ZF 9HP in essence is a torque converter gearbox with a tall ratio for the ninth gear that allows the engine to maintain low revs while cruising, thereby reducing fuel consumption and emissions. More gears also mean smaller step ratios for improved acceleration in the lower gears. The 9HP ZF autobox is also said to have improved shift quality and refinement.
While higher gears in the 9HP autobox have tall ratios the lowest ratio of the gearbox is far lower than that of the existing six-speed gearbox. This will help better low speed response of the engine during off-roading, towing and scaling steep gradients at high altitudes.
ZF states that the new nine-speed gearbox is capable of extremely fast gear changes that are ‘below the threshold of perception’. The gearbox is even capable of skipping gears while downshifting during rapid deceleration with the ‘skip-shift’ function. The gearbox also incorporates a multi-stage damper system for smoother pulling away and improved refinement.
While refinement and efficiency have been critical in development of the new nine-speed gearbox, the ZF 9HP automatic gearbox features an innovative adaptive shifting system that has the capability of matching the driver’s mood within seconds to sharpen gear changes during brisk acceleration and then settle to a more economical mode when the driver takes to more relaxed driving.
The Fast-Off mode of the gearbox measures the rate of throttle release and anticipates the driver’s acceleration habits for more 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.
The new 9HP gearbox may have three gears more than the six-speed unit but weighs 7.5 kg less and is only 6 mm longer. This has been possible because of a new hydraulic vane-type pump, two patented dog clutches and a cleverly nested gear set.
The new 9HP ZF automatic gearbox is slated to replace the six-speed ZF autobox as it offers more in all the three dynamics of performance, refinement and efficiency.
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