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Global

Technology

Electric Mobility. NOW.
#emobility

8-Speed Automatic Transmission: Hybrid as Standard

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The fourth generation of the 8HP bestseller marks a paradigm shift: ZF has systematically designed its automatic passenger car transmission for hybrid vehicles. As a result, the efficient drive solution supports the mobility turnaround.
Andreas Neemann, August 26, 2021
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Andreas Neemann wrote his first ZF text in 2001 about 6HP transmissions. Since then, the automotive writer has filled many publications for internal and external readers, showcasing his passion for the Group's more complex subjects.
The market for electric vehicles is booming. In Europe alone, 1.4 million vehicles with electric drives were newly registered in 2020 – 138 percent more than in the previous year. 623,000 of these – almost half of them – are plug-in hybrid vehicles (PHEVs ). There are two limiting factors why purely battery electric vehicles (BEVs) are not better represented: On the one hand, the expansion of the charging infrastructure is not able to stand the pace of the sudden increase in BEVs. On the other hand, the supply of electricity from renewable power sources in many countries is not growing with the current rapid demand. However, the electricity mix is vital when it comes to mobility turnaround. When coal-fired electricity is used to charge the BEV battery, the long-term better energy balance of electric vehicles compared to vehicles with economical combustion engines is no longer present.

Modern PHEVs are preparing the transition to the pure e-mobility age: Even though they still have a combustion engine on board, it is only rarely used. Thanks to a powerful battery, a PHEV has sufficient electric range for a majority of drivers to cover all their daily trips. For the more occasional long trips, on vacation or a weekend excursion, the combustion engine comes into play. With its EVplus concept vehicle, ZF is demonstrating the potential of current PHEVs: The test vehicle featuring suitable software to operate in E-mode as often as possible, has an electric range of 150 kilometers.
Target use case for the fourth-generation 8-speed automatic transmission is an electrified passenger car drive. It is the technical basis for the next generation of plug-in hybrids (PHEVs) with high purely electric ranges, as anticipated by ZF in its EVplus concept. They can cover the everyday mobility requirements of most people purely electrically.

Fourth-generation 8HP: Consistently hybrid

Fourth-generation 8HP: Consistently hybrid

The ZF EVPlus also comes with the 8HP 8-speed automatic transmission. Next year, the fourth generation of this ZF bestseller will enter volume production – systematically designed for hybrid drives. "When volume production started in 2009, the 8HP was designed for use with torque converters in conventional combustion engines, and the hybrid variants were derived from this. We are now turning hybrid into the standard," says Dr. Michael Ebenhoch, Head of Development for electrified drivelines at ZF.
"We systematically designed the fourth generation of the 8HP for mild and plug-in hybrids."
Dr. Michael Ebenhoch, Head of Development for electrified drivelines

Thanks to a modular system, the technology company can offer the 8HP as a mild, full and plug-in hybrid drive with a peak electric performance of 24 to 160 kilowatts. Numerous optimizations show what ZF can achieve by integrating systems: The power electronics are now completely inside the transmission housing – previously, they were located separately in the vehicle and required a corresponding high-voltage wiring. The power electronics are now more compact, with their weight cut in half. The fourth-generation 8HP is also a bit lighter than the third generation. The outer dimensions of the new transmission are just like the predecessor's: ideal for ZF customers who will use the new 8HP in the same model ranges as the third generation. "With every generation of our automatic passenger car transmissions, we made drives more efficient in all aspects – electrically and mechanically. With the 8HP, we further reduced losses with every generation – thereby cutting emissions," says Ebenhoch. The ZF engineers were able to increase efficiency once again.
ZF systematically designed the new generation of its 8-speed automatic transmission as a modular kit for hybrids. As a result, the efficient drive solution supports electrification and the mobility turnaround.

PHEV and mild hybrid: Every efficiency gain counts

PHEV and mild hybrid: Every efficiency gain counts

The fact that the strongest efficiency gains are possible with the electrified 8HP variants is no coincidence – after all, the Group has developed and optimized the new transmission generation for this application. With the plug-in version of the new 8-speed automatic transmission, ZF is laying the foundation for an electric vehicle suitable for everyday use: With a maximum output of 160 kilowatts, the electric motor integrated into the transmission is much stronger than in the previous version (with 90 kilowatts). The transmission reaches its maximum torque of 450 newton meters without switching on the combustion engine. Fast overtaking in pure E-mode? No problem. This power boost is home-grown: ZF relies on a new generation of in-house developed power electronics as well as electric motors. For PHEVs, these are manufactured industrially according to the "hairpin process". They are the decisive factor for the higher power-to-weight ratio. At 300 volts, ZF's PHEV operates at a voltage similar to that of pure electric vehicles with 400 volts.

Mild hybrids with 48 volts are well below that. "They can also play an important role in preventing emissions immediately. We therefore designed our new 8HP modular kit for several types of mild hybrids," explains Ebenhoch. Their essential effect: When braking, the electric motor recuperates energy which is later used for the drive, for example when starting or accelerating. These are the operating points where conventional combustion engines consume quite a lot of fuel and consequently emit more carbon dioxide. 8HP mild hybrid drives of the fourth generation reduce greenhouse gases by approximately 15 grams per kilometer compared to a purely combustion engine-powered 8HP of the third generation.

New transmission generation about to start volume production

New transmission generation about to start volume production

Saarbrücken will be the first production location to be converted to the new 8HP generation. The highly automated final assembly line is already in place, currently producing the first pre-production transmissions. In parallel, the teams in Saarbrücken are cooperating with internal and external suppliers to achieve the maturity level required for volume production, which is to start in summer 2022. In the following years, the 8HP plants in Shanghai (China) and Gray Court (USA) will also change to the new generation. The current call-off figures from Saarbrücken already indicate that the paradigm shift was worthwhile: Slightly more than 50 percent of customer call-offs refer to hybrid variants. This effect is expected to increase even more throughout the entire product life cycle. After all, ZF has already received long-term major orders for the new 8HP generation from several manufacturers worth an amount in the two-digit billion range.

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