Automatic Transmission: Fourth-Generation Efficiency
Since 2022, ZF has been producing a new 8-speed automatic transmission for passenger cars with mild hybrid and plug-in hybrid drives as well as for pure combustion engines. Never before has top electric performance been packaged so compactly.
Even the longest journey starts with a first step. In the case of the fourth-generation 8-speed automatic transmission, 8HP Gen4 for short, industrialization began with two mild hybrid variants at the ZF plant in Saarbrücken in April 2022. By mid-December of the same year, the workers celebrated a first, small milestone: the 50,000th 8HP transmission, including the brand-new plug-in hybrid variant. By the summer of 2025, a fourth production line will be active at the Saarbrücken plant, where the 8-speed transmission will be produced for combustion engine passenger cars. All transmission variants share a modular system that allows vehicle manufacturers to comprehensively and flexibly electrify their models according to demand.
The plug-in hybrid variant in particular contributes to massively reducing CO2 emissions by making it possible to cover common routes, such as the commute to work, purely electrically. This results in a CO2 reduction of more than 70 percent in the overall system according to WLTC, compared to current conventional transmissions.
With the fourth generation, ZF has fundamentally modernized its automatic transmission. The goal is to enable the comprehensive electrification of passenger car model fleets with a modular drive solution for the front-longitudinal driveline. "For about two years now, we have been proving with our current 8-speed automatic transmission that performance, driving pleasure and CO2 savings through a full-fledged electric drive are not mutually exclusive," explains Sebastian Schmitt, Head of the Electrified Powertrain Systems product line at ZF.
Every Millimeter Counts
In order to offer the OEMs as many advantages as possible, ZF engineers have once again significantly increased the degree of integration and optimally utilized every millimeter of installation space. This is particularly evident in the mild hybrid and plug-in hybrid variants (PHEV). With the PHEV version, a powerful electric motor integrated into the transmission housing enables a purely electric driving performance of up to 160 kilowatts and a torque of 450 Nm – nearly double that of the previous generation. This puts PHEV vehicles with the new 8HP on a par with purely electric vehicles: Depending on the manufacturer and the battery size used, purely electric ranges of over 120 kilometers are possible.
Higher Performance, Less Weight
ZF has now also integrated the power electronics into the transmission housing of the hybrid variants. This simplifies installation considerably for vehicle manufacturers, as external cable connectors or special housing elements are no longer necessary. Advantageous for installation flexibility and system weight: This PHEV variant is 6.5 kilograms lighter than its predecessor. In addition, the volume and weight of the power electronics have fallen by almost 50 percent, compared to 42 percent in mechatronics. At the same time, the performance data of the new transmission generation shows an upward trend and, with an overall performance of 550 kilowatts and a torque of 1,000 Nm, also exceeds the predecessor versions.
Flexible drive solution for the transition to electric mobility: ZF‘s fourth generation 8HP
The transmission was developed in Friedrichshafen, with assembly taking place in Saarbrücken right from the start. Components and systems will be supplied by other German ZF locations, with the electric motors coming from Schweinfurt and the power electronics and transmission control from Auerbach. From 2025, the ZF Grey Court plant in South Carolina, USA, will also produce the new, electrified, fourth-generation 8-speed automatic transmissions.
