ZF claims that the extra three gear ratios results in a transmission that is only 6 mm longer and weighs 7.5 kg less than the old six-speed transmission it replaces.
Land Rover showed the world’s first 9-speed automatic transmission for a light duty vehicle at the 2013 Geneva Motor Show. The ZF 9HP transmission is said to be specifically designed for transverse mounting applications, and is claimed to be one of the most efficient and technically advanced transmissions ever used in a production vehicle. The first volume production will come later this year in the Range Rover with the 9HP manufactured at ZF’s Gray Court facility in South Carolina.
Increasing the number of gear ratios from the existing six to nine gives an improvement in fuel economy and a corresponding reduction in CO2 emissions. Smaller gear ratio steps provide, in theory, improved response during acceleration, and improved shift quality, which in AutoInformed’s experience is not always accomplished in production calibrations, particularly dual clutch versions with paddle shifters. The higher (numerically lower) ninth gear reduces fuel consumption and lower engine revolutions reduce noise when cruising at high speed. There are stringent EU proposals to reduce CO2 output to 95 grams per kilometer by 2020 for the European new car fleet, which means a fuel consumption of less than 4 liters – across all segments and vehicle classes.
The lowest ratio (numerically higher) 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 higher altitudes where engine output drops, giving the driver better performance.
With extremely fast gear changes alleged by ZF as being “below the threshold of perception,” the 9HP is versatile and responsive. Moreover, the existing six-speed transmission makes shifts sequentially; the 9HP has a ‘skip-shift” function for much swifter downshifting under rapid deceleration or from more aggressive driver demands.
The adaptive shifting system, increasingly in widespread industry use on transmissions with six or more speeds, matches driving style, quickening during brisk driving, then moving to a more economical sooner upshifting calibration if the driver is relaxed with accelerator pedal application. During a so-called Curve Mode, longitudinal acceleration and the accelerator pedal position control upshift prevention.
A so-called Fast-Off mode measures the rate of throttle release, anticipating more requests by the driver for high power, then holds the gear if necessary. If the driver requests a downshift when the vehicle is traveling too fast, the transmission computer overrides the wish, but will remember it and make the shift when the speed drops to an appropriate level, sometimes starling the average driver and upsetting the tire contact patches during AutoInformed’s test drives of other automatic transmission with similar calibrations. Such programming can be problematic in current production use, especially if the driver changes his mind be getting in and out of the throttle.
ZF claims that the extra three gear ratios (6 +3=9) results in a transmission that is only 6 mm longer and weighs 7.5kg less than the older design six-speed transmission. The small package space is achieved with a new hydraulic vane-type pump, which also contributes to improved efficiency, and two, patented, dog clutches replacing bulkier conventional clutch packs.
ZF says the 9HP is modular so that it can be used in as many vehicle applications as possible. With two models, it covers a torque range of between 200 Nm and 480 Nm. In addition, it is “start-stop” capable without the need for an additional oil pump—and it can be used on hybrid designs as well. Based on parallel hybrid architecture, the torque converter is replaced by an electric motor. Moreover, ZF’s 9HP has open software and interface structure and an electronic control unit. This means that it will be possible to use it in a variety of applications.
