|Components of the E-Scooter. Click to enlarge.|
At BMW Motorrad Innovation Day 2011, BMW highlighted its latest concept electric-drive E-Scooter. BMW Motorrad earlier developed an electric study vehicle, the C1-E, as a contribution to the European safety project eSUM. (Earlier post.)
The E-Scooter was conceived as a future-oriented vehicle for commuting between urban areas and the city center—therefore attracting funding from the German Federal Ministry of Transport, Building and Urban Development—and so had two main requirements: performance figures comparable to those of a maxi scooter with a combustion engine and a high range in realistic conditions of use.
The concept vehicle BMW E-Scooter provides the necessary sustained output and maximum speed for safe and reliable overtaking on urban motorways and also when carrying two people. It is also easily capable of managing hill starts on steep slopes with a pillion passenger.
The development study also has the necessary maximum output to be able to achieve acceleration figures within the important 0 - 60 km/h range, which are at the level of current maxi scooters powered by a 600cc combustion engine.
The high storage capacity of the battery allows a daily driving range of more than 100 kilometers (62 miles). With this capability, BMW says, the E-Scooter concept vehicle provides a long-term, zero-emissions urban and suburban travel option which is suitable for everyday use.
Unlike existing maxi scooters with combustion engines, the concept vehicle does not have a main frame. Instead, the aluminium battery casing—which also contains the electronic system required for battery cell monitoring—takes over the function of the frame. The steering head support is connected to it, as is the rear frame and the left-hand mounted single swing arm with directly hinged, horizontally installed shock absorber.
|Electric machine for the E-Scooter. Click to enlarge.|
Due to its high output, the BMW Motorrad development study has no hub motor with direct drive or planetary gearbox. Instead, the high-performance electric machine is mounted behind the battery casing. The secondary drive consists of a toothed belt from the electric machine to the belt pulley mounted coaxially on the swinging fork pivot with drive pinion. From here, power transmission occurs via roller chain to the rear wheel. When the E-Scooter is decelerated in trailing throttle or when braking, the energy released is recuperated, thereby increasing the vehicle’s range by between 10 and 20% depending on driving profile.
The electrical components required for the electric drive are installed on the top of the battery casing. The external battery electronics system permanently collects and monitors data such as the temperature and voltage of the battery cells, both during travel and while charging. The power electronics acts as a control system and controls the electric machine. The charging device includes a charge cable which allows the battery to be recharged at a conventional household power socket.
In addition to the other components such as an ISO insulation monitor, high-voltage indicator and a high-voltage distributor, a DC-DC converter is included. It is required to change high voltage to low voltage power to supply the 12 volt vehicle supply and especially for the control units.
The E-Scooter concept vehicle’s battery is charged at regular household power sockets as found in Europe, the USA, Canada and Japan, so no special charging station is required. When the battery is completely flat, the charging period is less than three hours. However, practical experience has shown that the battery rarely runs out completely, so charging times are generally shorter.
During travel, the electric machine and power electronics are liquid-cooled, as is the charging device during charging. An electric coolant pump ensures coolant circulation through the radiator. While a coolant is commonly used for the battery in electrically powered cars, the E-Scooter concept vehicle uses an air cooling system in order to save space.