Electromobility is considered a decisive factor for the energy transition and as a tried and tested means, the CO₂-Brake emissions. The BMW Group is taking this development into account with its electric vehicles and celebrated the premiere of its commercial electric scooter “C Evolution” in April this year. A metric thin section bearing from Rodriguez is built into it. It takes over the storage of the belt pulley in the gear of the scooter.

In the spring of this year, the BMW Group launched the electric scooter C Evolution, the answer to one-lane urban mobility, after its electric vehicle i3. Like the i3, this electric scooter also uses the technology of recuperation for energy recovery. In this way, both the gas release in overrun mode and braking the energy released is made available for further use.

The electric power supplies an air-cooled high-voltage lithium-ion battery with a capacity of 8 kWh. It gives the scooter a range of 100 km and is fully recharged within 4 h on a conventional power outlet. With a rated power of 11 kW (15 PS) and a peak power of 35 kW (47,5 PS), the scooter achieves an electronically controlled maximum speed of 120 km / h. With acceleration from zero to 100 km / h in 6,2 s, the new electric scooters can easily keep up with gasoline-powered maxi scooters.

Storage of the pulley

With all design elements of the C Evolution, attention was paid to keeping the dead weight as low as possible, including the bearing of the belt wheel of the powerful electric drive. This takes the form of a drivetrain swing arm with a liquid-cooled permanent synchronous motor Timing belts and a ring gear.

In this ring gear, the thin section bearing K13008AR0 serves as a bearing for the belt wheel, which in turn transmits the power via a planetary gear transferred to the rear wheel. The hardened, thin-walled, roller bearing from Rodriguez's metric thin-section bearing series serves in this case as the outer support bearing of a pair of bearings that center the pulley/output shaft assembly in the gearbox housing while absorbing all forces introduced by the rear wheel. It weighs only 170g.

That can only be a thin-ring bearing

In addition to the lowest possible weight, the bearing of choice had to meet a number of other requirements. A decisive criterion was the largest possible inner diameter with the smallest possible outer diameter. Only this was a storage within the small available space between the gear housing and rotating unit even possible. With a bore diameter of 130 mm with an outside diameter of 146 mm, the unsealed thin-ring angular contact ball bearings easily meet these requirements.

But not only in terms of the diameter ratio or the bearing size of the special application made high demands on the camp. It had to be able to easily absorb the high lateral speeds and large radial loads occurring at maximum speed as well as the high transverse forces arising from the load changes of the rear wheel when cornering. In addition, a certain shock resistance in all directions was a prerequisite for the installation of this camp. It is required at the latest when the landing gear can no longer completely absorb all loads in extreme cases or on very uneven roadways.

Further application possibilities

Like the entire Rodriguez thin-section bearing range, the bearing used in this application is characterized by its weight-saving design and extra-small cross-section, which remains constant as the bore diameter increases. However, it brings with it the decisive high rigidity and a low starting torque to meet the highest requirements in terms of speed, temperature and loads. The large bore diameter provides space for components such as air or hydraulic lines, electrical wiring or slip rings. Due to these mechanical properties, thin-section bearings are used wherever high demands are placed on weight efficiency, compactness and miniaturization while at the same time offering maximum precision and ease of assembly. Further application examples are the storage of solar cells or radar systems in the aerospace industry as well as rotary unions or robotic modules in the semiconductor industry. Precision rotary indexing tables, tool changers or articulated arm robots are also stored on thin-ring bearings.

More than 250 types - metric and imperial

The Eschweiler drive specialists produce and sell more than 250 metric and imperial thin section bearing types made of roller or stainless steel for every application. In addition to the classic standard bearings, the range also includes hybrid bearings and "ultra-slim" bearings with a particularly small cross-section. All thin section bearings are available as deep groove ball bearings, four-point bearings or angular contact ball bearings. Stainless steel versions are also made with ball cages polyamide, PEEK or stainless steel available. In addition, Rodriguez manufactures complete, ready-to-install assemblies based on the thin-section bearings, which are precisely tailored to the respective application. These customer-specific special solutions fall under the "Value Added Products" business area, which is one of the company's core competencies and not only offers customer-specific complete solutions or the realization of entire assemblies in small quantities, but also comprehensive all-round service for the field of bearing mechanics.

Picture above: The pulley (r.) In the ring gear of the C Evolution is mounted on a Rodriguez metric thin ring bearing.

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