8 and Beyond: A New Generation of Automatic Transmissions
Figure 2 dimensions to the ZF6HP26
This 8-speed transmission has fewer moving parts than the 6HP26 6-speed.
torque ratings of this transmission are also available — the 8HP30, 8HP70 and the 8HP90. A version of this transmission
has been used in flagship Audi, Rolls Royce, BMW, and Bentley models since 2010.
845RE Technical Features • Enhanced planetary gear mesh- ing to reduce noise and friction (figure 2)
• Four planetary gear sets and five clutch elements
• Offset chain driven variable dis- placement pump (figure 3)
• Optional engine stop/start feature. Not used in Chryslers for 2012
• Hybrid technology capable • Two and all wheel drive versions • Non-sequential shifting • Torque range capacity from 300- 1000km, 8HP30-8HP90
• 200 millisecond shift times • Fully electronic shift by wire, no shift cable or linkage
• NIC Neutral idle control allows clutch “B” slippage at stop to reduce load and vehicle creep
• Similar weight and physical 22
• Adaptive strategies: High tem- perature, warm up, cruise control, Winter mode, drag recognition and Neutral idle control
• Air cooled
Fuel Economy This 8-speed transmission has
fewer moving parts than the 6HP26 6-speed. There are only three multi-disc clutch packs and two multi-disc brakes in the transmission geartrain (labeled A, B, C, D and E). Only two of the five clutch elements are open (released) in each gear. The fewer open shift elements
there are, the fewer internal transmis- sion components that’ll be rotating relative to one another. This provides a significant reduction in friction loss and reduces the transmission’s rotating mass. Both qualities will contribute to improving the overall fuel economy and acceleration. By comparison, the Lexus AA80E 8-speed uses four gear sets and seven multi-disc clutch packs.
*Optional Engine Start/ Stop Function This feature is enabled by the
development of the hydraulic impulse oil storage system (HIS). At idle, the engine automatically shuts off. The HIS system supplies the oil pressure needed to keep the transmission’s clutch ele-
Figure 3 According to ZF, when
comparing fuel economy to their 6-speed
transmission, the newly developed 8-speed
automatic transmission
reduces fuel consumption by an additional 11%.
ments engaged while the engine is off. 350 milliseconds after starting, the vehicle is ready to drive. With the start/ stop function, it’s possible to reduce fuel consumption by another 5% and
further reduce CO2 output. *This feature is not reported for
use in Chryslers for 2012 According to ZF, when comparing
fuel economy to their 6-speed trans- mission, the newly developed 8-speed automatic transmission reduces fuel consumption by an additional 11%. The hybrid model will provide even better
fuel economy and further reduced CO2 output.
The HIS system relies on a charged
oil, accumulator-type reserve to main- tain oil pressure with the engine off. There are no additional pumps that would load the system and counteract the fuel savings.
GEARS January/February 2012
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