May 17, 2000

ZF Presents the First 6-speed Automatic Transmission
Text and Photos by Neil McGarry

The Car Transmission Division of ZF has released information about the first 6-speed automatic transmission. The 6 HP 26 is rated for torque capacity up to 444 lb./ft. It is smaller and lighter than it's 5-speed automatic predecessor (the 5 HP 24) which is currently fitted to the S4 and A6 2.7T. This transmission is the cornerstone of a new range which will replace today's 5-speed generation and will be manufactured at ZF Getriebe GmbH, Saarbrücken. ZF has been producing 5-speed transmissions since 1990. Presently they make up 80 percent of ZF's automatic transmission production for passenger cars.

With its new and innovative automatic transmission generation, ZF has obtained the best ratings in all major evaluation criteria of transmissions:

  • Higher Torque capacity
  • Reduced length
  • Reduced weight
  • Less fuel consumption
  • Better acceleration

    The sixth gear

    In the 90s a major design goal of vehicle and engine developers was to further reduce fuel consumption.

    ZF is now counting on an extra sixth gear. Using the Lepelletier gear set concept, ZF has succeeded in making this 6th gear come true with less technical complexity than used in previous 5-speed automatic transmissions. The transmission has improved efficiency and ratio spread, along with an improved power/weight ratio.

    Looking inside the new six-speed transmissions, you will find space-saving planet gear sets for combined action during shifts via a highly efficient control logic of the shift elements. The new concept allows a reduced weight of the transmission by about 13% and a substantial raise in torque capacity.

    Torque converter with novel actuation

    In automatic transmissions the torque converter is mainly used to move off the line. Part of the new electronic control system for the transmission is the Stand-by Control /SBC. Instead of having the converter running against the engine with the vehicle standing still (foot on the brake pedal), as was previously the case, the converter is now disconnected from the powertrain so that there is only minimal residual load. This further reduces fuel consumption.

    Low fuel use and sporty acceleration

    The ratio spread of the new six-speed has been designed in such a manner that in the "long" range, there is an extra gear which lowers internal speeds and simultaneously reduces noise and fuel consumption.

    ZF has designed the smallest gear in such a way that it is even more powerful and permits better acceleration parameters than the previous five-speed transmissions.

    The Mechatronic module

    The transmission is controlled by a mechatronics module, a hydraulic shift unit combined with an integrated electronics module. Both electronic and hydraulic systems are found in the transmission housing and they are specifically geared to each other. In this way, signals and pressures can be realized with the lowest-possible tolerances and gearshifts can be performed even more precisely. This means optimized shift quality and better drive comfort. Use of the mechatronic module not only markedly simplifies logistics and assembly, it provides a number of other benefits. These include weight reductions, as well as raised reliability resulting from a reduction in the number of plugged contacts and fewer interfaces.

    Transmission control

    The electronic transmission control system is based on the newly developed Adaptive ShIft Strategy /ASIS.

    The electronic system is constantly fed with data on the condition of the transmission, operating condition, operator behavior and operator requests. Comprehensive evaluation of these sensor signals permits complex functional structures of the control system. As a result it can react to spontaneous driver action or sudden topographical changes and immediately transmit the optimized shifting points to the attached hydraulic shift unit. In this process, the control system covers innumerable variations of driving style, from very sporty to very economical, derived from the incoming signals.

    Practically unnoticed by the driver, the electronic system also adjusts its drive strategies to special conditions, such a city traffic and different load conditions.

    Model range

    ZF is planning to offer a 6-speed range for various drive solutions with torque ranges from 222 to 555 lb./ft.

    Unlike the predecessor, the 6 HP 26 boasts an expanded ratio spread of 6.04. On top of that, the transmission is 50mm shorter and about 13% lighter than the 5 HP 24. Its acceleration values were increased by 1-5% and fuel consumption was lowered by 5-7%. The 6 HP 26 transmits a maximum input torque of 444 lb./ft.

    6-speed Tiptronics

    Although neither ZF or Audi would confirm the new 6-speed transmission in a specific model range, the new transmission will replace the current 5 HP 24 on the assembly line at ZF sometime in 2001.

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