ZF 9-Speed Automatic Transmission for Chrysler cars: 9HP, 948TE, 928TE
ZF unveiled the world’s first nine-speed transverse automatic transmission in June 2011, starting production in 2013. The transmissions are stop-start, hybrid, and all-wheel-drive capable. They have an unusually wide spread of 9.84, boosting launch performance and highway-mileage alike. Adding three gears to provided normal gear steps, so engines can run in their optimal speed ranges.
There are two model ranges for these transmissions, handling torque up to 280 and 480 Nm (206 to 354 lb-ft); the current Pentastar V6 is rated at 260 lb-ft. Chrysler’s name for the more-capable version is 948TE — 9 forward speeds, 480 Nm, Transverse, Electronic control.
Chrysler is building the transmissions in two plants in Indiana (Kokomo and Tipton), thanks to over $843 million in plant investments and licensing from ZF.
The nine speed is similar in many ways to the rear/all wheel drive 8HP, used by BMW, Audi, Bentley, and Rolls-Royce as well as Chrysler, Dodge, and Jeep.
The transmission can downshift in 450 ms, with a 150 ms response time.
The Tipton plant is to assemble the 948RE assembly, with Indiana Transmission Plant (IPT) 1 doing some assembly (at first) and machining components. Aluminum machining is done at Kokomo and is to move to ITP2 after the Mercedes five-speed is phased out.
Current speculation has Chrysler making up to 1.4 million 928TE and 948TE automatics per year, when production reaches full swing. Spokesman Jodi Tinson said that Chrysler expects to build 800,000 ZF transmissions per year under license: around 150,000 845REs, and the rest 948TEs, as reported by the Kokomo Tribune.
Four gearsets and six shifting elements made it possible to have nine speeds; the transmission is compact because the gearsets were “intelligently nested.” Hydraulically-operated constant-mesh elements increase efficiency without a punishing transmission length. While multidisk shift elements in the open condition create drag, these losses are very low in the two dog clutches.
A torque converter is the standard starting element; a multi-level torsion damper system minimizes hydraulic losses while allowing quick application of the torque converter lock-up clutch. Response and shift times are below the threshold of perception.
Direct multiple gearshifts (e.g. 2nd to 4th) are possible; and shifting points and shifting dynamics are highly programmable. ATSYS, the shifting sequence control, contains all clutch controls, adaptation functions, and transmission protection functions, while ASIS, the driving strategy, ensures that the optimal gear is selected.
With all wheel drive setups, the transmission allows for front wheel drive only, or torque vectoring with front wheels and rear wheels engaged, and power distributed between right and left rear wheels.
To keep costs and space manageable, engineers installed the electronic control unit (EGS) separately from the hydraulic control unit (HSG), on the upper side of the transmission housing. The EGS’s computing performance can be increased by another 30% when needed, so software can control even more in the future.
The 9-speed automatic transmission is stop-start capable, without an additional oil pump. Only one friction shift element needs to be closed on restart, so response times are very fast. It can also be used as a hybrid transmission by replacing the torque converter with an electric motor.
The transmission is expected to be used by BMW in the Mini, by Land Rover, and by other premium automakers.
Note: Some press releases have first gear at 4.71, third at 1.90, sixth at 0.80, sevent at 0.69, and ninth at 0.47.
The Chrysler-ZF partnership
According to Mike Kirk, Chrysler’s director of axle, driveline, and manual transmissions, there were two main reasons for Chrysler’s changes to the ZF automatics.
Kokomo was already set up with its own tooling and robotics; some changes were made to match Kokomo’s equipment and methods.
Chrysler also needs many more transmissions than ZF plans to make. Design choices that make sense for production of 50,000 transmissions a year may not make sense for production of 200,000 per year.
Mr. Kirk said that the partnership with ZF had been mutually productive; while Chrysler owns the intellectual property of any changes they make to the transmissions, they keep ZF informed, and are motivated to improve the transmissions and production methods to maintain balance with ZF.
Standards for both manufacturers are high; both ZF and Chrysler use the same end-of-line test centers, driven by the same software. Numerous firmware upgrades were needed for the nine-speed in the Jeep Cherokee, through May 2014.