BMW Motorrad unveiled a near-production prototype of an e-scooter as it might soon go on the market. Since it was conceived as a future-oriented vehicle for commuting between the urban periphery and the city centre, there were two particular requirements for its development: performance figures comparable to those of a maxi scooter with a combustion engine and a long range in realistic conditions of use.
The "C evolution" draws on the innovative styling of the BMW Motorrad family, offering a thrilling, inspiring design which arouses an emotional response to the new drive technology. As in other BMW motorcycles, the so-called split face runs across the upper trim section, giving the scooter a distinctive and dynamic front view.
BMW Motorrad design style is also reflected in the styling of the twin-tipped spoiler in the front trim and in a boomerang-shaped, aerodynamically formed floating panel in the side trim. The short, sporty rear will have a helmet compartment in the serial production model and emphasises the proactive character of the "C evolution".
The combined effect of the colour "Light white" and the highlight colour "Electric green" reflects the vehicle's specific properties, such as maximum environmental compatibility, supreme dynamic performance and simple handling. What is more, the illuminating "e" inscription on the two battery side trim elements and motor unit bear out the technical character of an electrically powered scooter.
Multifunctional Instrument Cluster and LED Daytime Running Light
The instrument panel of the "C evolution" has a large, easily legible TFT display which is conceptually based on that of the BMW i3. It has the obligatory speed display as well as offering a wealth of other information. This includes display of the battery charge state (SOC = State of Charge) and the energy balance. The latter is displayed by means of a progress bar, indicating to the rider whether energy is currently being converted into forward propulsion or being recuperated. This information helps the rider in his efforts to ride as efficiently as possible.
In addition to the familiar indicators, the instrument cluster of the "C evolution" naturally features all the status displays required by law in electrically powered vehicles. This includes warning lamps to indicate a potential insulation error or power limitation in the event of overload.
The front lighting unit encompasses headlamps with high and low beam. The "C evolution" also features a centrally located daytime running light. At the back there is a rear light in LED technology.
Hybrid Chassis with Agile Handling Due to Low Centre of Gravity
Unlike existing maxi scooters with combustion engine, the "C evolution" does not have a main frame in the usual sense. The aim of chassis development for the "C evolution" was to combine the best possible directional stability at high motorway speeds with agile handling in urban traffic. Engineers also set out to make full use of the advantages provided by an extremely low centre of gravity - due to the low position of the battery.
For this reason, chassis design is based on a torsionally stiff hybrid composite structure made up of a load-bearing, torsionally rigid battery case made of cast light alloy with integrated mounting for the single-sided drivetrain swing arm. Bolted onto this are the steering head support and the rear frame in steel tubing. In urban traffic in particular, the riding experience is characterised by extremely light handling and excellent slow-running properties. The weight of the vehicle is at a level comparable to maxi scooters with a combustion engine.
Wheel control as well as suspension and damping is taken care of at the front by an upside-down fork with a generous fixed fork tube diameter of 40 mm. The rear wheel suspension consists of a single-sided drivetrain swing arm. At the rear, suspension and damping are performed by a spring strut placed on the left-hand side, directly controlled and adjustable at the spring mount. The spring travel is 115 millimetres at front and rear, thereby offering a high degree of comfort.
High Range Due to Large Battery Capacity
At 8 kWh, the storage capacity of the battery is extremely generous and ensures a range of up to 100 kilometers. This means that realistic zero-emissions riding in the big city and in urban environments is no problem at all.
The "C evolution" uses the same lithium-ion storage modules as are installed in the BMW i3. Here, developers paid particular attention to the quality and service life of the storage modules so as to ensure that the range is preserved even after many years of service life and in very cold weather. One of the main technological challenges was optimum cooling of the high-voltage battery. On the one hand it was necessary to avoid excessively low temperatures due to the fact that the interior resistance of the cells is heavily increased as a result, thereby reducing power. On the other hand, the temperatures must not be too high since this would impair the lifetime of the cells.
While in electrically powered cars a cooling agent is normally used to cool the battery, air cooling is used in the "C evolution" in order to save space and weight. The heat of the high-voltage battery is dissipated by means of an aerodynamically optimised cooling air shaft at the centre of the battery casing through which there is a constant flow of air. To ensure optimum heat dissipation, the battery base has longitudinally arranged cooling ribs.
However, the battery casing in die-cast aluminium not only holds the cells with their special architecture but also the entire electronics unit for monitoring the cells. It also acts as a load-bearing chassis element.
The power electronics for the electric drive is installed behind the battery casing. This not only takes care of controlling the alternator within a range of 100 to 150 volts but also responds to rider commands, for example by detecting the position of the throttle grip. The system also processes information from the brake system and decides whether energy should be recuperated and how much recuperation torque is to be applied to the rear wheel if required.
Intelligent Recuperation in Coasting Mode and When Braking
BMW Motorrad has conducted lengthy road tests to develop a form of recuperation which is unique in single-track vehicles and very transparent for the rider. The "C evolution" is ridden in exactly the same way as a scooter with combustion engine. The rider does not have to actively initiate energy recuperation since the vehicle does this automatically whenever possible.
For example, energy recuperation commences when the throttle grip is closed and - as in a combustion engine - the generator function of the alternator creates drag torque which depends on the degree of recuperation. The drag torque generated by the alternator is like the familiar "engine brake" that takes effect when removing the accelerator with a combustion engine.
Recuperation is also carried out during braking, converting kinetic energy to electrical energy so as to charge the battery. Here, a system of sensors is used to tap into the brake pressure on the front and rear wheel brake. When the power electronics detects that the rider is braking, the alternator builds up drag torque, thereby supporting the brake manoeuvre and recuperating energy. By regaining energy during coasting or braking, the range of the two-wheeler can be extended by 10 to 20 per cent, depending on riding style.