The orientation of the power-producing mechanicals in an automobile or motorcycle chassis is chosen for numerous reasons, many related to which direction the power is to be sent, but also packaging, weight distribution, and even simple tradition. A typical European sports sedan will mount the engine longitudinally, the crankshaft running front-to-back, making it easier to send the power to the rear wheels via a shaft spinning in the same orientation as said crankshaft. Motorcycle inline-fours, with very limited space between the wheels, typically mount their engines transversely, allowing the crankshaft and transmission shafts to be stacked close together, then powering the rear wheel via a chain. A less common layout for motorcycles mimics the sport sedan, with a longitudinal engine driving a shaft to the rear wheel, notably found in BMW twins. While most electric motorcycles have continued the tradition of transverse motors, BMWs latest patents show that they are again not inclined to follow convention, utilizing a longitudinal motor layout and shaft drive.
As reported by Cycle World and Cycle Volta, the longitudinal layout described in BMWs patent filings feature some unique ideas in the form of a planetary gearset for shaft speed reduction on the back of the motor, and an intermediate shaft between the planetary gearset and the shaft final drive. The gearset is simple, compact, and inline with the motor and shaft drive. The intermediate shaft, with CV joints at both ends, allows for the freedom to alter the placement of the motor within the chassis to suit any packaging or weight distribution requirements.
While BMWs electric scooter, the CE 04, follows the more popular transverse motor layout, these patents show that for their bigger electric bikes, the longitudinal layout with shaft drive may be the way forward. The planetary gearbox and intermediate shaft introduces some unique advantages to the layout that go beyond simply using the layout for tradition’s sake. No word yet on production plans.