ZF 8HP transmission. 8HP is ZF Friedrichshafen AG's trademark name for its 8-speed automatic transmission models  with hydraulic converter and planetary gearsets for longitudinal engine applications. Designed and first built by ZF's subsidiary in Saarbrücken, Germany, it debuted in 2008 on the BMW 7 Series (F01) 760Li sedan fitted with the V12 engine. BMW remains a major customer for the transmission.

Another major customer is Stellantis, who both received a license to produce the transmission and set up a joint-venture plant with ZF. Stellantis has built the transmission at its Kokomo Transmission plant since 2013 under their own brand name, the Torqueflite 8. The joint venture plant in Gray Court, South Carolina opened in 2012.

The 8HP is the first transmission to use this 8-speed gearset concept. In the meantime it has become the new benchmark for automatic transmissions.

The GM 8L transmission is based on the same globally patented gearset concept. While fully retaining the gearset logic, it differs from this only in the patented arrangement of the components with gearsets 1 and 3 swapped.

Specifications

2008: Pilot Series 

The 8HP 70 transmission with the gearset 4 in 23-85-teeth-configuration was the pilot series and therefore without generation designation. It was first used in the BMW 7 Series (F01) 760Li, has a torque handling limit of , and weighs .

2010: 1st Generation 

In addition to the rear-wheel drive variant, two different four-wheel drive versions were available, with a version destined for Volkswagen Group applications using a Torsen centre differential. It is able to encompass a torque range from  to , and is available for use in middle-class cars through to large luxury sport utility vehicles.

Since gearset 4 meshes in almost all gears up to and including 5th gear, large gear wheels are advantageous for durability. As the very high ratio 1st gear is formed exclusively by gearset 4, its sun gear is unusually small. For this reason, this gearset was enlarged by over 20 % when the 1st generation was introduced, even if this advantage had to be given up again immediately when the 2nd generation was introduced in order to increase the total span.

2014: 2nd Generation 

Efficiency improvements over the pilot design and the first generation include a wider ratio span of 7.81, reduced drag torque from the shift elements, reduction in required oil pump pressure, and broadened use of the coasting and start-stop systems. ZF estimated fuel economy improvement over first generation to be 3 %. Refinements were also made with respect to vibration.

2018: 3rd Generation 

Major improvements are total span of 8.59 and a fuel economy improvement of 2.5 % compared to the second generation. There are several options in maximum torque available, also the gearbox is available with mild hybrid and plug in hybrid options: With  and  supporting boosting and recuperation in combination with 48 Volt technology up to  and  for usage with higher voltage.

2022: 4th Generation 

Major improvement is the transition to a versatile modular system that allows vehicle manufacturers to comprehensively and flexibly electrify their models as required. Plug-in Hybrid options with up to  and  are capable of saving up to 70 % of carbon emissions compared with a purely conventional variant of the 8HP according to the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). In addition, a modification to gearset 3 increased the reverse gear ratio, making it less disadvantageous. With this gearset concept, the already disadvantageously large step from 7th to 8th gear is further increased, albeit only slightly.

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). Compared to the 6-speed ZF 6HP transmission it uses 12 % less fuel, and 14 % less than a 5-speed transmission. Due to changes in internal design, the shift times have reduced to 0.2 seconds; additionally, the unit brings the ability to shift in a non-sequential manner – going from gear 8 to gear 2 in extreme situations simply by changing one shift element (actuating brake B and releasing clutch D).

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 patented gearset concept. The resulting progress is reflected in a better ratio of the number of gears to the number of components used compared to existing layouts. The 8HP has become the new reference standard (benchmark) for automatic transmissions.

Layout Quality 

The ratios of the 8 gears are relatively unevenly distributed in all versions. Particularly noticeable are the too small step between 3rd and 4th gear and the too large one between 7th and 8th gear. This cannot be eliminated without affecting all other gear ratios. On the other hand the selected gearset concept offers 2 to 3 gears more than conventional transmissions of comparable manufacturing costs, which more than compensates for the weaknesses.

Applications

See also 
 List of Chrysler transmissions
 List of ZF transmissions

References

External links 
 

8HP
Automatic transmission tradenames
Chrysler transmissions
Chrysler
Auto parts