BMW is bringing a mild hybrid electric vehicle (MHEV) drivetrain with a diesel combustion engine to the X5 and X6 families, which promises both power and parsimony in equal measure.
Packs 340hp and 700Nm
The new SUV models will carry the 'xDrive40d' nomenclature, which slots them in between the 265hp/620Nm xDrive30d versions and the monster quad-turbo, 400hp/760Nm M50d M Performance variants.
BMW says the xDrive40d twins use a newly developed 3.0-litre, straight-six twin-turbodiesel engine, with low- and high-pressure blowers both featuring variable turbo geometry. With common-rail piezo direct fuel injection operating at 2,700bar, the outputs of this unit are pretty much right in the zone you'd expect them to be, when looking at the 30d and M50d's numbers: the xDrive40d powertrain delivers 340hp at 4,400rpm, with 700Nm on tap from 1,750-2,250rpm.
MHEV tech
Of course, some of that power and torque is provided for by the hybrid system, although this is only an MHEV diesel-electric. Therefore a 48-volt electrical system controls an 8kW (11hp) starter generator, which provides torque infill and acceleration back-up under the guise of 'electric boost' - meaning both the new X5 and X6 models can hit 100km/h from rest in a mere 5.5 seconds. The onboard 48-volt battery pack which powers the starter generator also provides current to other electric driving functions via the vehicles' standard 12-volt electrical system.
The electric power is there primarily to help the eco-stats, however, rather than the performance, and so at cruising speeds the combustion engine can run within an 'efficiency-optimised load range' thanks to the 48-volt system, which reduces excessive fuel consumption. It can also 'sail' on a trailing throttle, with the engine disconnected from the driveline, or it can switch the engine off entirely and coast to further save fuel. The whole drivetrain is fitted with two-stage NOx exhaust gas treatment, made up of an oxidation catalytic converter and a Selective Catalytic Reduction (SCR) coating on the diesel particulate filter. That means both new SUVs meet the mandatory Euro 6d emissions standard, which comes into force at the start of 2021.
Economy in the high 40s
Both models of BMW's prestigious SUVs come with an eight-speed Steptronic automatic transmission and BMW xDrive intelligent four-wheel-drive technology, which has a rear bias for sporty handling characteristics. Expect between 5.9-6.4 litres/100km (47.9-44.1mpg) and CO2 emissions from 154-167g/km for the X5 xDrive40d, and 5.8-6.2 litres/100km (48.7-45.6mpg) with 153-164g/km CO2 from the X6 xDrive40d.