Monday, 28 October 2013

A Look at ZF’s 9-speed Automatic gearbox

Credit :
ZF, a leading global supplier of automobile transmissions, says it is looking to set an industry benchmark after becoming the first to develop a modern nine-speed automatic for passenger cars.

It’s a nine-speed transaxle for transverse applications sporting a 9.8 ratio spread and it promises 10-percent better fuel economy when compared to a six-speed slushbox. In a market that goes full frenzy by one-percent here and two-percent there, 10 can’t be ignored.

The trouble with engineering a transmission for a transverse application is packaging. The gearbox, along with the engine, has to fit between the shock towers. According to ZF, which announced it will initially supply the 9HP to the Jeep Cherokee and the Land Rover Range Rover Evoque with more customers to come, the maximum width for such a transmission is about 14.6 inches. It’s no surprise, then, that the 9HP is 14.4 inches wide. With four planetary gear sets and six shifting elements (brakes and clutches) that’s a very dense 14.4 inches.

Of those four planetary gearsets, two of them are nested. In this nested pair, the annulus, or ring gear, of the smaller planetary doubles as the sun gear of the larger set. This arrangement trims some width from the four-gearset tranny.

Speaking at the sidelines of the news conference, ZF board member Michael Hankel expressed confidence that the 9HP would receive a good response from the market worldwide.

"The worldwide penetration of front-drive compact cars, smaller cars, is that the market share in total is roughly 75 per cent worldwide," he said. "A lot of cars have this dimension, so they would potentially need a nine-speed automatic transmission."

Again, that’s according to ZF. If a 10-percent improvement isn’t enough, chew on this: at a steady 75 mph, the 9HP delivers 16-percent better fuel economy than a six-speed.