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Into the eight-speed upgrade

by David Zatz on

Chrysler is set to upgrade their eight-speed automatics from the first to second generations, but BMW was already there in 2014, according to a ZF press release discovered by “redhed.”

The new ZF 8HP automatic, which will also be made and sold by Chrysler (and made by them), was first used in the BMW 520d. “Comprehensive” changes have lower drag torque, a higher gear spread (distance between first and eighth), and lower vibration.

The changes, which increase efficiency “by up to 3%,” were partly made to deal with small, turbocharged engines, and to work better with engines that reach peak torque early on (such as diesels).  The latter required a higher gear range, so that the eight-speed will move from 7.0 to 7.8 — incidentally beating the eight-speed currently used by General Motors.

Internal losses were cut partly by adding sprints into the multidisk packages of the shift elements, to almost fully open friction shift elements and thereby cause less drag torque. Power losses were cut by over two thirds, according to ZF.

Creep torque has been cut by fully opening a clutch during deceleration and when the vehicle is stopped, so that drivers don’t have to brake to keep the car from moving (which may feel odd to some drivers). The oil pump pressure has been cut in pressure by around 30%.

New torsional vibration dampers eliminate vibrations from the engine, stopping them from moving along the driveline and into the driveline and the body.

The new torque converter allows faster transmission of power and lets lock-up occur much earlier.

Coasting with the transmission uncoupled can now occur at speeds up to around 100 mph, and stop-start systems can now work immediately instead of after 1.5 seconds.

The transmission also improves downshifts, providing nested multiple downshifts for even quicker response times

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