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At the 2015 North American International Auto Show (NAIAS) in Detroit, German parts manufacturer ZF took the opportunity to showcase the second generation of its acclaimed 8HP eight-speed automatic transmission, promising improved efficiency, a higher spread of gears and reduced torsional vibration.

The main draw of the new 8HP – comprising of eight gears, four gearsets and five shift elements – is better fuel economy – up to 3% more fuel-efficient than the already frugal first-generation unit, which itself saved up to 6% more fuel than the old six-speed ‘box.

Contributing to the longer trips between the pumps is the increased spread of gear ratios – from 7.0 to 7.8 – thanks to optimised gearsets. On average, engine speeds are now reduced by 50 rpm, translating to a reduction of fuel consumption by almost one percent.

Transmission inefficiencies have also been reduced through multidisk separation – the shift elements feature more springs integrated into the multidisk packages, ensuring that the friction shift elements are almost fully opened, reducing drag torque. All in all, power losses have decreased by around two thirds compared to the first-gen 8HP.

Also reduced is the “creep” – the slow forwards motion in Drive without any throttle application. A clutch is fully opened during deceleration and when stationary, meaning that it is no longer necessary to hold the brakes at a stop. System pressure in the oil pump has also been reduced from 5 to 3.5 bar, resulting in less energy used.

Refinement has been improved with the use of torsional vibration dampers that stop engine vibrations from transferring through the drivetrain and into the body. A new torque converter more quickly bridges the hydrodynamic transmission of power from the engine, enabling a earlier engagement of the lock-up clutch at extremely low engine speeds.

Adding to lower fuel consumption is the uncoupling of the transmission, dubbed the “coasting” function, which can now operate at speeds of up to 160 km/h. The operation of the optional auto start-stop functionality has also been improved, shutting the engine down at a stop without any discernible delay, instead of 1.5 seconds previously.

Improvements were also made to facilitate spirited driving, with the ability of conducting nested multple downshifts giving the transmission a more spontaneous and dynamic response when necessary.

The second-generation 8HP went into production last July, slotted into the BMW 520d in 8HP50 guise designed for engines producing up to 500 Nm of torque. Later, an 8HP75 unit will come on stream, capable of handling up to 750 Nm. The new transmission will gradually be phased into by all the manufacturers currently utilising the outgoing unit.