BMW’s new full ActveHybrid system closely follows but does not entirely mimic the principle laid down by petrol-electric pioneer Toyota with its Synergy Drive set-up, as used by the second-generaton version of the ActiveHybrid X6 rivalling Lexus RX400h.
Both cars rely on a petrol engine as their prime means of performance; a 407bhp twin-turbocharged 4.4-ltire V8 in the BMW and a smaller 244bhp naturally aspirated 3.5-litre V6 for the Lexus.
In both cars the petrol engine is supported by a pair of electric motors mounted within the gearbox, with each capable of electric only start up and propulsion over short distances for zero emission capability.
But while the ActiveHybrid X6’s motors generate 91bhp and 86bhp respectively, the RX400h’s are significantly more powerful at 164bhp and 67bhp.
In each, the motors run on electrical energy created during over run and under braking and stored in a nickel-metal hydride battery pack; in the BMW it is mounted within the floor of the boot, while in the Lexus it is set underneath the rear seat.
The biggest departure, however, concerns the way the reserves of the petrol engine and electric motors is transferred to each wheel. The BMW uses a CVT (continuously variable transmission) that incorporates four fixed mechanical gears and what is described as three virtual gears created via the electrical mapping for a total of seven different gears in all.
This gives the ActiveHybrid X6 a conventional delivery, in which revs rise and fall in concert with throttle openings.
The Toyota, on the other hand, runs a more conventional CVT that always sets the revs according to road speed.