Past shapes the future: Shaft drive isn’t just for looks on BMW’s upcoming electric models
BMW are already established as early adopters in electric bikes but they’re on the verge of a much more concerted push in that field as technology previewed in 2019’s Vision DC concept is set to debut in a new range of high-performance electric bikes.
With the C Evolution scooter, on sale since 2013, BMW proved electric bikes could be more than just low-speed runabouts for short, inner city hops. Now, that bike’s replacement – the CE 04 – is on the verge of production and BMW are also looking towards more ambitious, motorcycle-style electric bikes.
Related articles on MCN
- Kawasaki hybrid technology
- Best electric motorbikes available right now
- Synthetic petrol in development
As well as the ‘CE’ title that will be adopted across a range of battery-powered scooters, BMW have gained the trademark to the ‘DC’ title – followed by numbers ranging from 01 to 09 – for larger electric bikes, have built prototypes and also filed patents that show how these newcomers might look.
The latest patent illustrates one of the key differences between BMW’s electric motorcycle plans and those of their main rivals – the use of a longitudinal motor allied to a shaft drive.
It’s a layout that clearly fits BMW’s heritage. The German company’s tradition of shaft-drive and engines with crankshafts running lengthways goes back to their earliest days and is exemplified by the classic boxer twin. Copying that layout for an electric bike adds tangible benefits compared to more conventional designs which have the motor mounted transversely across the bike.
Most electric bikes mount a motor transversely, near the swingarm pivot, and usually drive the front sprocket via a reduction gearset, amplifying torque and reducing revs. A final drive with a large rear sprocket is usually chosen to further reduce the rear wheel’s speed in comparison to the motor. These designs offer relatively little choice of where to mount the motor – it’s got to be near the front sprocket, which itself must be close to the swingarm pivot.
BMW’s design, with the motor turned 90 degrees, allows a longer motor without increasing bike width. A shaft with constant velocity joints at each end connects the motor to the front of the final drive shaft that’s integrated into the swingarm and gives designers freedom to move the motor around, in turn giving additional freedom for altering weight distribution or packaging for the batteries and electronics.
The firm’s Vision DC concept bike used exactly this layout and given BMW’s decision to turn the similarly futuristic- looking Concept Link scooter – first shown in 2017 – into the production CE 04 that’s due to be launched this summer, it’s looking increasingly likely that it will directly influence a production electric BMW in the near future.
Shaft drive technology explored:
- Perfectly aligned: The longitudinal placement means that BMW can use a planetary gearset as a reduction gearbox. This means the input and output shafts are aligned. With a normal reduction gear there would be a second, offset shaft to hold the output gear.
- Longitudinal mount: BMW’s patent shows a particularly large electric motor, which might be awkward to package – along with a reduction gearbox – if it had to sit transversely near the swingarm pivot.
- Cooler mimics boxer: The Vision DC, shown in 2019, hid its electrics behind bodywork but used a longitudinal motor, as did the firm’s E-Power Roadster technology demonstrator. The Vision DC’s side- mounted coolers mimic the cylinders of a boxer as a further nod to BMW heritage.
- Shaft drive can stay: The shaft drive system is also a benefit. Most electric bikes use belts (chain drives are too noisy when there’s no exhaust to drown them out), but shafts can transmit more power and torque, in near silence, while the bevel gear at the rear wheel provides an additional reduction gear ratio.
- Shaft gives flexibility: The CV-jointed shaft between the motor and the final shaft drive could be made longer or shorter, moving the motor forward or back. It also means the motor can be moved side- to-side or up and down as the designer pleases.
BMW reveal Vision DC Roadster electric concept
First published on 25 June 2019 by Jordan Gibbons
BMW have unveiled the Vision DC Roadster – a naked electric concept bike that moves the electric boxer story on once again after the radical Vision Next 100 bike shown three years ago. This shock move comes as BMW press the accelerator on their program of electrification, promising 25 models across the business by 2023.
In a standard bike everything pretty much starts with the engine as it’s pretty much the biggest thing to accommodate. On an electric bike the biggest parts are the batteries, while the motor itself is relatively compact.
For the DC Roadster a huge block of longitudinal batteries replace the typical boxer engine block, with the electric motor slung underneath. The two ‘cylinders’ are actually radiators with cooling fans (that retract when the bike is parked), not only giving the bike the appearance of a classic boxer but also retaining that ‘air-cooled cylinders in the wind’ vibe of the original 1932 onward machines.
Old dog, new tricks
Despite its modern features BMW have kept some elements of a traditional design. Up front there’s a Duolever fork, with the ‘tank’ shape flowing back from that.
Out back the tail unit has a typical racing slant, while power is delivered to the ground through a thoroughly BMW shaft drive. Even the lights are sculpted and stylised LEDs that echo existing bikes. The whole bike is everything you expect a BMW to be – but reimagined for the electric age.
The frame itself is milled from aluminium, with huge cut outs giving the bike a lightweight appearance while also echoing the finned cylinders of yesteryear. The rest of the bike is built around the centrepiece of the battery, supported on beams that BMW say make it appear like the extra elements are floating.
Function and fashion
Outside of the core bike everything has been designed for both style and safety. The tyres for instance have been made by Metzeler to include fluorescent elements that, just like the frame itself, glow in the dark.
BMW have also designed a riding suit, with near invisible protection as well as light emitting elements to catch the eye of other road users. There’s even a magnetic backpack, naturally.
Now obviously the whole thing is just a concept for now but with BMW’s determination to bring us plenty of new models in the near future, it’s possible that the core battery and motor might well find their way onto a production machine in short order.
BMW’s plan for the future
Electrification is sweeping the world and in an effort to stay ahead of the curve, BMW have unveiled their plans two years early. They say that within four years 25 of their models (across bikes and cars) will be electric, that sales of electric vehicles will more than double by 2021 and will jump by more than 30% within the next six years.
As well as big leaps forward for the hardware, BMW are also planning new jumps in technology unveiling the next generation of autonomous driving for their cars as well as a new ‘digital ecosystem’ that will connect together all your vehicles.
Looking at it from a purely two-wheeled perspective it looks like BMW are keen to take on Harley-Davidson in the competition of who can be the first legacy manufacturer to break the electric market. We imagine there’s a few nervous glances in a Milwaukee boardroom this morning.
Edgar Heinrich, Head of Design BMW Motorrad
“The boxer engine is the heart of BMW Motorrad – an absolute stalwart of its character. But BMW Motorrad stands for visionary zero-emissions vehicle concepts, too.
“In view of this, one question that arises is: what would happen if we were to replace the boxer engine with an electric motor and the required battery? The Vision Bike shows how we’re able to retain the identity and iconic appearance of BMW Motorrad in distinctive form while at the same time presenting an exciting new type of riding pleasure.
“After all: anyone who’s ever tried it out in practice knows very well that riding on two wheels is just as exciting when its electrically powered! The high level of torque right at set-off makes for breath taking acceleration.
“This almost brutal power delivery creates a whole new experience of dynamic performance. And the BMW Motorrad Vision DC Roadster puts a face to this experience.”