ZF 9-Speed Automatic Transmission for Chrysler cars: 9HP
ZF released the world’s first nine-speed automatic transmission for passenger cars in June 2011, months after Sergio Marchionne said Chrysler and Dodge would use them.
The modular transmissions are stop-start, hybrid, and all-wheel-drive capable, and have a surprisingly wide spread of 9.84. This allows lower first gears and higher overdrives at the same time, boosting launch performance without highway-mileage penalties. Using nine speeds allows for normal gear steps between those extremes, so engines can run in their optimal speed ranges.
There are two model ranges for these transmissions, covering a torque range of 280-480 Nm (206 to 354 lb-ft); the current Pentastar V6 is rated at 260 lb-ft in minivans, but direct injection versions are expected to boost their power. The official code for the one going into the Cherokee is 948TE — 9 forward speeds, 480 Nm, Transverse, Electronic control.
Chrysler will build the transmissions in Kokomo, thanks to an $843 million plant investment and licensing from ZF. The German drivetrain maker said the nine-speed would raise gas mileage by 16% versus a current six-speed, which could mean three to four miles per gallon. Actual results will depend on many factors, including how well the gearing is matched to the engine, the controller’s programming, and axle ratios.
The nine speed appears similar to the recently launched 8HP, currently used by BMW, Audi, Bentley, and Rolls-Royce, and set to be used in the 2012 LX cars. Production is expected to start in mid-to-late (calendar year) 2012 at Indiana Transmission Plant I off U.S. 31 in Kokomo — after eight speed production starts.
Chrysler expects to build 800,000 ZF transmissions per year under license, eventually; around 150,000 are to be 8HPs and the rest are to be the 9HPs, according to Jodi Tinson, as quoted in the Kokomo Tribune.
Four individual gearsets and six shifting elements made it possible to have nine speeds; yet the transmission is compact, because the gearsets were “intelligently nested” instead of being distributed on the longitudinal axis. Hydraulically-operated constant-mesh elements were used in order to enable high efficiency without a punishing overall transmission length; while multidisk shift elements in the open condition create drag torques, these losses are very low in dog clutches. Thus, enhanced efficiency generated by small transmission steps is not lost again via drag losses due to the complex design.
A torque converter is used in the 9HP as the standard starting element, for its smooth starting and maneuvering. 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 actually below the threshold of perception.
Direct multiple gearshifts are possible; and shifting points and shifting dynamics are highly programmable – from emphasize given to comfort and optimized fuel consumption up to extremely sporty. 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 for each driving situation, unnoticed by the driver.
With four wheel drive, 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 did not use a fully-integrated mechatronics module for all sensors, actuators, and the electronic control unit (EGS). Instead, the EGS is installed separately from the (reduced-size) hydraulic control unit (HSG), on the upper side of the transmission housing. The oil pump was moved as well.
The EGS's computing performance can be increased by another 30% when needed, so software can control even more in the future; and the EGS’ hardware allows for different automaker requirements to be applied without any problems.
The ZF nine-speed automatic has been designed so that an additional transfer case can be connected for all wheel drive; ZF itself has an all-wheel drive that can be decoupled (AWD Disconnect). It actuates the rear axle drive only when needed and, thus, saves five percent fuel compared to the permanent all-wheel drive (Chrysler already uses a similar system).
The 9-speed automatic transmission is, without an additional oil pump, stop-start capable. Since, in the case of restarting, it is only one friction shift element that needs to be closed, response times are very fast. It can also be used as a hybrid transmission by replacing the torque converter with an electric motor.
Chrysler is expected to build these transmissions under license but may purchase them from ZF, either instead of constructing them or while bringing a new plant up to speed. The transmission is expected to be used by BMW in the Mini, and at least one other buyer has already been lined up.