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, though production did not start until mid-2013. The transmissions are stop-start, hybrid, and all-wheel-drive capable. They have an unusually wide spread of 9.84 — in short, they have much lower first gears and much higher overdrives, boosting launch performance without highway-mileage penalties. Adding three gears to the usual six provided normal gear steps, 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 Jeep Cherokee is 948TE — 9 forward speeds, 480 Nm, Transverse, Electronic control. Minivans are likely to use the same unit. The 928TE would be used for lighter duty applications. While we have no specific information yet, we believe Chrysler has made changes to these transmissions, as they did with their own version of the HP8 eight-speed automatic for rear-drive vehicles.
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.
Early on, according to “Mopar Sage,” the plan was to build the eight-speed 845RE at the Indiana Transmission Plant (ITP), but ITP did not have the floor space to build both the 65RFE (and its 66/68RFE variants) in high volume and set up the 845RE. The plan was quickly changed to install the new 845RE machinery at Kokomo, which had room when the 42RE/46RE transmissions were dropped; and would have even more when the 42RLE was dropped, for later phases and more volume. Thus, the six-speed rear-drive assembly line is within IPT1 (Indiana Transmission Plant 1), along with the line for the nine-speed automatic. That is dubbed 948TE — nine speeds, 480 Nm (354 lb-ft) of torque capacity, transverse configuration, electronic control.
Currently, the Tipton plant is planned for the second and third phases of 948RE assembly — only assembly — and, eventually, the original first-phase assembly line may be moved to Tipton as well, leaving ITP1 dedicated to machining components for the 948RE. ITP1 will not be doing any aluminum machining, which will be kept at Kokomo and, in future, placed at ITP2 — after the Mercedes five-speed is phased out.
Current observer estimates range up to 1.4 million 928TE and 948TE automatics made per year, when production reaches full swing. Earlier, spokesman Jodi Tinson said that Chrysler expects to build 800,000 ZF transmissions per year under license — around 150,000 8xxREs, and the rest 948TEs, as reported by 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 (the transmission uses two 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 will build these transmissions under license. The transmission is expected to be used by BMW in the Mini, by Land Rover, and by other premium automakers.
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.
First, Kokomo was already set up to build transmissions, with its own tooling and robotics, which are far different from those used by ZF. Some changes were made to accommodate the design of the transmission to the equipment and methods used successfully for many years at Kokomo.
In addition, Chrysler needs far more of the 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. To pump out the number of transmissions Chrysler will need, some changes had to be made.
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 do keep ZF informed. Chrysler can patent any of their changes and methods, including the software and controls, and has some internal motivation to improve the transmissions and their production methods to maintain balance with ZF.
Standards for both manufacturers are high; and both ZF and Chrysler use the same end-of-line test centers, driven by the same software.