6HP is ZF Friedrichshafen AG's trademark name for its 6-speed automatic transmission models (6-speed transmission with Hydraulic converter and Planetary gearsets) for longitudinal engine applications, designed and built by ZF's subsidiary in Saarbrücken. Released as the 6HP 26 in 2000, it was the first 6-speed automatic transmission in a production passenger car. Other variations of the first generation 6HP in addition to the 6HP 26, were 6HP19, and 6HP 32 having lower and higher torque capacity, respectively. In 2007, the second generation of the 6HP series was introduced, with models 6HP 21 and 6HP 28. A 6HP 34 was planned, but never went into production. It uses a Lepelletier gear mechanism, an epicyclic/planetary gearset, which can provide more gear ratios with significantly fewer components. This means the 6HP 26 is actually lighter than its five-speed 5HP predecessors. The 6HP is the first transmission to use this 6-speed gearset concept. The last 6HP automatic transmission was produced by the Saarbrücken plant in March 2014 after 7,050,232 units were produced. The ZF plant in Shanghai continued to produce the 6HP for the Chinese market. The Ford 6R, GM 6L, and Aisin AWTF-80 SC transmissions are based on the same globally patented gearset concept. The AWTF-80 SC is the only one for transverse engine installation.

Specifications

Layout (Gearset Concept) Progress

The main objective in replacing the predecessor model was to improve vehicle fuel economy with extra speeds and a wider gear span to allow the engine speed level to be lowered (downspeeding). The layout brings the ability to shift in a non-sequential manner – going from gear 6 to gear 2 in extreme situations simply by changing one shift element (actuating clutch E and releasing brake A).

Progress Quality

In order to increase the number of ratios, ZF has abandoned the conventional design method of limiting themselves to pure in-line epicyclic gearing and extended it to a combination with parallel epicyclic gearing. This was only possible thanks to computer-aided design and has resulted in a globally patent for this gearset concept. The 6HP is the first transmission designed according to this new paradigm. After gaining additional gear ratios only with additional components, this time the number of components has to decrease while the number of ratios still increase. The progress is reflected in a much better ratio of the number of gears to the number of components used compared to existing layouts.

Layout Quality

The ratios of the 6 gears are nicely evenly distributed in all versions. Exceptions are the large step from 1st to 2nd gear and the almost geometric steps from 3rd to 4th to 5th gear. They cannot be eliminated without affecting all other gears. As the large step is shifted due to the large span to a lower speed range than with conventional gearboxes, it is less significant. As the gear steps are smaller overall due to the additional gear(s), the geometric gear steps are still smaller than the corresponding gear steps of conventional gearboxes. Overall, therefore, the weaknesses are not overly significant. As the selected gearset concept saves up to 2 components compared to 5-speed transmissions, the advantages clearly outweigh the disadvantages. It has a torque converter lock-up for all 6 forward gears, which can be fully disengage when stationary, largely closing the fuel efficiency gap between vehicles with automatic and manual transmissions. In a Lepelletier gearset, a conventional planetary gearset and a composite Ravigneaux gearset are combined to reduce both the size and weight as well as the manufacturing costs. Like all transmissions realized with Lepelletier transmissions, the 6HP also dispenses with the use of the direct gear ratio and is thus one of the very few automatic transmission concepts without such a ratio.

Imperfections

Problems with this transmission are well known. This transmission locks up the torque converter in all gears, increasing wear. Combined with a sealed transmission pan and "lifetime fluid", some people have experienced catastrophic transmission failure. Owners report shift issues when oil begins breaking down beyond 50K miles, hence shifting issues are common. There are also problems with the valve block and solenoids When this failure starts to occur, shift quality and speed, torque transfer and even loss of ability to engage gears can occur. These problems led Volkswagen Group to extend the warranty on all of their vehicles equipped with this transmission to 100,000 miles or 10 years.

Applications

First Generation · 2000

6HP 19

6HP 19A

The 6HP 19A is a variation of the 6HP 19 for Four-wheel drive applications (Allrad, all wheel).It was used by the Volkswagen Group for some permanent four-wheel drive models.

6HP 26

The 6HP 26 was the initial version and first used by the BMW 7 Series (E65) in 2001. Initially only used by premium brands, it was later available on the 2009 model year V8 Hyundai Genesis. Several versions of the 6HP 26 are available depending on application and brand: 6HP 26, 6HP 26A and 6HP 26X. Ford has developed their own versions (Ford 6R 60 and Ford 6R 80) based on the 6HP 26. Therefore, certain Ford vehicles will not be listed.

6HP 26A

The 6HP 26A is a variation of the 6HP 26 for Four-wheel drive applications (Allrad, all wheel). It was used by the Volkswagen Group for some permanent four-wheel drive models and packages a TORSEN type center differential, and open front differential into the transmission assembly.

6HP 26X & 6HP 26Z

The 6HP 26X and 6HP 26Z is another variation of the 6HP 26, also for Four-wheel drive applications. This transmission is suitable for 4WDs with a separate transfer box (the "X" stands for external 4WD).

6HP 32

6HP 32A

The 6HP 32A is a variation of the 6HP 32 for Four-wheel drive applications (Allrad, all wheel).

Second Generation · 2007

6HP 21

6HP 28

6HP 34

The 6HP 34 was planned for high-output applications. As the successor 8HP was about to be launched and innovations are typically introduced first in the premium segment, the 6HP 34 never went into production.