ZF Introduces 9-Speed Transmission
ZF Friedrichshafen AG has announced that it has developed a 9-speed automatic transmission for application in front-wheel-drive vehicles.
Notably, compared with 6-speed automatics, the ZF 9HP provides a fuel savings of up to 16%.
Why? Because the 9-speed has a high total gear ratio spread (9.84, to put a number on it), which means the engine is running in a more-optimal gear depending on conditions. So, for example, when cruising along on a highway at 70 mph, the car is in 9th, and the engine is probably running at <1,900 rpm, rather than ~2,600 rpm, which is where it would be with a 6-speed.
ZF engineers have developed the 9HP so it offers two torque ranges (up to 205 lb-ft and up to 350 lb-ft). The transmission can be upgraded so that it is suitable for all-wheel-drive and even start-stop hybrid applications.
What’s more, they designed the transmission to be compact to address the packaging issues of a front-drive car: it’s one thing to have a longitudinal transmission, which provides plenty of space for those gears and clutches; it is another thing entirely when there is transverse mounting.
How did they do it? There is a “nesting” of the four individual gear sets, and hydraulically operated constant-mesh elements are used.
ZF has developed the transmission control software so that OEMs can tailor the 9HF to their specific requirements, as in tuning it for more aggressive performance rather than fuel-efficiency, but chances are, mpgs are going to trump high rpms.
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