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. The 8HP is the first transmission to use this 8-speed gearset concept. Thanks to its economical design, consisting of only 9 components, it became established as the standard version of an automatic transmission with a torque converter. The uneven distribution of the gears apparently posed no problem.
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.
Key data
+ Gear ratios Model Gear Total Span Avg.Step Components Nomenclature R 1 2 3 4 5 6 7 8 Nomi-nal Effec-tive Cen-ter Total perGear GearsCount Cou-pling Gear-sets Maximum Input Torque 2008: Pilot series 4 Gearsets2Brakes3Clutches 8 H P 2008 8HP 70 2010: 1st generation 2010 8HP 30/I · 8HP 45 · 8HP 55 · 8HP 708HP 65 · 8HP 90 · · 2014: 2nd generation 2014 8HP 75/I 2nd generation and 3rd generation 8HP 30/II · 8HP 50 · 8HP 75/II · 8HP 95 · 2018: 3rd generation 2018 8HP 76/I 8HP 30/III · 8HP 51 · 8HP 76/II 2022: 4th generation 2022 8HP 100 8HP 80 2016: Racing cars 2016 8P 45R TBD TBD TBD TBD TBD TBD 1.000 TBD TBD TBD TBD — P – 2017: Commercial vehicles 2017 8AP 600 T · 8AP 1000 T8AP 800 T · 8AP 1200 T A P – – 8AP 1200 S
History
Designed and first built by ZF's subsidiary in Saarbrücken, Germany, it first was introduced in 2008 on the BMW 7 Series (F01) 760Li sedan fitted with the V12 engine. BMW remains a major customer for the transmission. It is now in its fourth generation and has been adopted by more than 20 brands from BMW to Ram; by 2023 over 15 million units have been produced.
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.
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.
Planetary gearset concept
Improved fuel economy
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), which is a decisive factor in improving energy efficiency and thus reducing fuel consumption. In addition, the lower engine speed level improves the noise-vibration-harshness comfort and the exterior noise is reduced. 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.
Reduced manufacturing complexity
In order to avoid a further increase in manufacturing complexity while expanding the number of gear ratios, ZF switched from the conventional design method—in which the planetary gearset concept was limited to a purely serial or in-line power flow—to a more modern design method that utilizes a planetary gearset concept with combined parallel and serial power flow. 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.
+ Planetary gearset concept: manufacturing complexity WithAssessment Output:GearRatios InnovationElasticityΔ Output : Δ Input Input: Main Components Total Gearsets Brakes Clutches 8HPRef. Object Topic Δ Number Relative Δ Δ Output Δ Input 8HP6HP 86 Progress 98 43 22 33 Δ Number 2 1 1 0 0 Relative Δ 8HP3-Speed 83 Market Position 97 42 23 32 Δ Number 5 2 2 -1 1 Relative Δ
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 step 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.
Additionally, the gearset 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).