Why ZF's Eight-Speed Is the Best Automatic Transmission
https://www.caranddriver.com/features/a ... ght-speed/
My RAM has the ZF 8HP and, I must say, it's the best automatic I've ever driven.Two words: shift quality. The 8HP transmission from German supplier ZF is quick enough to serve sports cars and graceful enough for large luxury sedans, and it combines those elements of speed and smoothness whether it’s installed in an Aston Martin, a Rolls-Royce, or a Jeep.
Albert Dick, vice president of car powertrain technology at ZF, says the 8HP’s deeply satisfying shifts are rooted in factors ranging from the quality of the solenoids to the manufacturing methods to the control software. They’re also a product of a fundamental design that determines how the four planetary gearsets, three clutches, and two brakes in every 8HP gearbox are parsed into eight forward ratios. All one-gear and two-gear shifts use just two shifting elements: one opens, another closes. The 8HP also executes certain multigear shifts in this manner; witness the leaps from sixth gear to third and even eighth to second.
The 8HP transmission comes only in longitudinal form for rear- or all-wheel-drive vehicles, and we prefer it immensely to ZF's transverse alternative, a nine-speed. In 2017, some 3.5 million 8HP transmissions were built for a laundry list of manufacturers that includes Aston Martin, BMW, Fiat Chrysler, Jaguar Land Rover, and the Volkswagen Group. Beyond performance, the eight-speed’s appeal is rooted in its versatile modular design. It can accommodate a maximum torque output from as low as 162 pound-feet up to 770. It is compatible with a variety of all- and four-wheel-drive systems, such as an integrated center differential or a two-speed transfer case. The ability to swap the torque converter for an electric motor, as BMW has done, allows automakers to develop hybrid variants with minimal changes to the drivetrain. And the commonalities among all 8HP gearboxes allow companies to share core elements between vehicles as different as the Dodge Demon and the Ram 1500, minimizing development costs. “We keep the same power flow through all of those applications, so we can carry over the calibrations, the software, all of those tools that keep that transmission shifting smoothly,” says Eric Burnett, chief engineer for eight-speed, rear-wheel-drive transmissions at Fiat Chrysler.
Has the dual-clutch transmission met its match, then? You might think that’s the case, given the recent defections by the Audi RS5 and the BMW M5, which switched from dual-clutch transmissions to ZF’s 8HP torque-converter automatics. That’s also the opinion of Andy Palmer, CEO of Aston Martin, who claims ZF’s 8HP is lighter, cheaper, and quicker than a dual-clutch transmission. “Ten years ago, [the dual-clutch] still looked like the transmission of the future. Now it is starting to look like the transmission of the past,” he tells us. But the DCT finds refuge in supercars. The added length of a torque converter can be prohibitive in a mid-engine architecture, and precise launch-control programs provide an advantage in acceleration. And engineers maintain that a good dual-clutch ’box does shift quicker. “For our kind of product, it’s about a really fast shift, which the pre-engagement element of a dual-clutch gearbox helps us with. We think that’s still got a decent speed advantage,” says Marcus Waite, chief engineer of the McLaren Senna.
But for just about every other vehicle, though, it's hard to argue that anything can do the job better than the ZF eight-speed.
I still believe in #SaveTheManuals, but if you need an auto, the ZF is top notch!