New-generation ZF-transmission in BMW 520d

The new 8HP entered volume production at the start of July in the BMW 520d as the 8HP50 version that is designed for torques of up to 500 Nm. In the future, the 8HP75 will be part of the ZF portfolio for drives with even higher torque of up to 750 Nm. Gradually, all further automotive manufacturers to whom ZF has already supplied the 8HP in over 1,000 vehicle applications will utilize the latest generation of the 8-speed automatic transmission.We shall see these transmissions in India too.

The new 8-speed automatic transmission combines many technological advances: Above all, ZF has further optimized the new transmission generation for the requirements of modern engine technology. This is due to the fact that, in order to meet the forthcoming CO2 emission specifications without losses in terms of torque and performance, there are two central trends when it comes to combustion units: Downsizing, which means turbocharged engines with fewer cylinders and less engine displacement and downspeeding, which is the reduction of the engine speeds combined with a maximum torque that is applied at a very early stage.

It is the reduction of the speeds in particular that demands transmissions with a higher spread which is the reason why ZF has increased it from 7.0 to 7.8 on the new 8HP by means of optimized gearsets. "This measure alone reduces the speed across all gears by 50 revolutions per minute on average and reduces fuel consumption by almost one percent," explains Jürgen Greiner. Furthermore, the ZF developers have succeeded in once again reducing the internal transmission losses. This is primarily ensured by the new multidisk separation: Additional springs integrated into the multidisk packages of the shift elements ensure that the friction shift elements are almost fully opened and, consequently, cause less drag torque.

Furthermore, the objective was to take the changing vibration behavior of the increasingly economical yet, at the same time, more powerful downsizing units into account. Therefore, all 8HP automatic transmissions feature particularly advanced torsional vibration dampers: These dampers eliminate the vibrations that occur on the engine side in a particularly effective manner so that they are unable to move further along and into the driveline and the body. The newly developed torque converter contributes to downspeeding because the hydrodynamic transmission of power can be bridged even more quickly – this enables traveling with a closed lock-up clutch at an early stage and at an extremely low engine speed.