Back in 2017, BMW played an April Fools joke by announcing a hybrid all-wheel drive R1200GS. Dubbed the R1200GS xDrive Hybrid (pictured above), the bike would have incorporated an electric hub motor on the front wheel to deliver traction when needed.

The prank fooled some people, in part because it had an element of truth. BMW did have some patents on a similar system filed in 2015, while noted BMW tuner Wunderlich showcased an actual concept model at EICMA, also in 2015.

The idea of a hybrid BMW motorcycle has largely faded into memory as the company launched its electric C Evolution scooter and the R1200 boxer family evolved into the R1250 line with variable valve technology. However, newly-published patent filings reveal that BMW has continued to tinker with the idea of a hybrid boxer engine motorcycle.

Unlike the previous work, the new patent packages the electric motor with the boxer engine, with both delivering power to the rear wheel. The two are connected by an adapter which houses a planetary gear system, with a torque-limiting slip clutch on the electric motor’s side. Through this assembly, the electric motor can drive the crankshaft, delivering power through a regular clutch and transmission and on to the drive shaft. This also eliminates the need for a separate starter motor. The motor can also function as a generator, converting mechanical power from the engine into electricity.

The adapter is a key part of BMW’s patent. It allows the drive train to be modular, making it easy for BMW to adopt different electric motors. The patent describes the potential of using a motor that produces a maximum torque of 20% of the engine’s maximum, or a more powerful electric motor with 200% of the engine’s peak torque (or anything in between). The adapter also helps keep the overall system compact, and, as the patent notes, makes it easier to employ without needing to redesign much of the rest of the motorcycle.

While the patent confirms that BMW has been working on a hybrid boxer powertrain, it’s unclear whether this will result in a finished product. Though the patent was only published last week, it was originally filed with Germany’s patent office on Aug. 8, 2017. Since that time, BMW has released the R1250 engine with ShiftCam variable valve timing. It’s possible the hybrid patent idea is for the next generation of BMW boxers, but it’s also possible it represents a different evolutionary path that may not pan out. The patent doesn’t address vital concerns, such as the size and positioning of the batteries, that will need to be addressed before we see a hybrid motorcycle enter production. Either way, the patent indicates a hybrid BMW boxer was considered at some point in time. Whether we’ll see an physical example remains to be seen.