The “i” in BMW i stands for innovation as exemplified so far by the BMW i3 electric vehicle and the BMW i8 plug-in hybrid sports car. But it really stands for innovation in all aspects of individual mobility, as proven by its patent for a drive unit swing arm that is now going into production at the HNF eBike factory.
When BMW i first developed the drive unit swing arm, it was concentrating on four-wheel vehicles, so the unit was really not planned for use or production within the BMW system. Now BMW has released it for external use and HNF is incorporating it into its Heisenberg XF1 eMountainbike. The unit on the bike will be embossed with the logo and “Concept by BMW i.”
The BMW i patent for the drive unit swing arm integrates a mid-motor, gears, and belt drive into a new type of suspension assembly that no longer needs a conventional belt tensioner. Unlike drive trains that were attached to the main frame as on previous bikes, the HNF Heisenberg XF1, using the BMW i drive unit swing arm will have a drive train that floats freely. For the first time on a full-suspension eBike, the rear suspension can be combined with a durable, maintenance-free carbon belt drive for excellent propulsion and handling.
The HNF Heisenberg XF1’s dynamics-related advantage it derives from the drive unit swing arm is the absence of pedal recoil. Unlike other rear-mounted suspension concepts that are specifically optimized for muscle-powered drive systems, the XF1 experiences no stiffening of the rear swing arm when the electric motor is providing assistance; for example, during acceleration, constant high speeds, or going up hills. As the proportion of human driving force is relatively small, the rider feels no unpleasant rocking motion when accelerating or braking. Especially important for a mountain bike, it is possible to pedal smoothly and efficiently even on uneven terrain.
HNF GmbH started in Biesenthal near Berlin last year, and develops next-generation eBikes under the brand name HNF Heisenberg.
BMW i, as far as we know, will continue to concentrate on four-wheel vehicles. It’s nice to see that deep in the BMW i skunkworks, innovative devices like the drive unit swing arm are being hatched, but we would also like to see innovative devices like an i5 that can bring BMW style, performance, and handling to an electric vehicle with the range and speed to challenge Tesla, which desperately needs challenging. Of course, we have no idea if BMW i is actually working on such a vehicle, but if not, why not?—Scott Blazey
[Photos courtesy of BMW AG.]
