New freedom
on two wheels

AMPRIO develops high-performance pedelec motor

Riding an e-bike extends your personal radius of action. What’s more, it’s fun, healthy and easy on the environment. Small wonder, then, that the market’s growing at a record pace. This is particularly true of pedelecs, which in Germany don’t require a license plate, liability insurance, a driver’s license or a helmet. AMPRIO, a Rheinmetall startup, has entered the market for electric motors for bicycles with an innovative total system.

When you enter a new field of business, sometimes you have to think laterally. Aiming to put unconventional but promising ideas of its employees into action, Rheinmetall launched a Group-wide ideas contest back in 2015, with the winners receiving an Intrapreneur Award. 

Individuals or teams were given a chance to present their concepts. In the end, five winning contestants gained Group backing for their ideas. The award-winning ideas included a concept for the industrialization of 3D printing, but also a plan for developing a pedelec motor for the growing e-bike market. The latter proposal was put forward by a trio of bicycle enthusiasts who’d already put a lot of thought and effort into e-bike technology in their spare time. Dietmar Greven was one of the inventors: “We’re the perfect team, really. 

One of the first tasks of the new company was to analyze the expectations of the market

Alexander Baumann has a sales background, Thorsten Krill has production experience, while I cover the design engineering side of the business. Together, we were able to put forward a comprehensive concept that not only included development but also production and maintenance aspects. In any case, we were able to convince the jury of the feasibility of our idea.” Today, Greven is in charge of product development for the AMPRIO motor. The startup company was established with the specific aim of developing and marketing the pedelec system. The word pedelec stands for “peddle electric cycle”, by the way. 

A new role in the development process 

For the Rheinmetall Automotive employees involved here, entering the world of the pedelec motor meant a complete rethink. As an auto parts supplier, the company normally gets a specification sheet from the customer listing the main technical and engineering requirements. The challenge then consists of developing and producing the product in accordance with the customer’s wishes. It’s different in the e-bike market, which features a number of large bicycle manufacturers. These companies don’t produce their own specification catalogues, but instead expect the pedelec motor manu-facturer to do this as a sign of their system expertise. One of the startup’s first tasks thus consisted of analyzing the requirements for a motor based on a market study, and then summarizing these in a company specification catalogue. Among the criteria were the load spectrum, dimensions, weight, and of course quality aspects. In addition, optics play a role in visible bicycle components that shouldn’t be underestimated, either. 

Now finalized, the pedelec concept comprises a complete system consisting of a drive unit, a battery, and a control unit. The Neckarsulm-based auto parts supplier specializes in highly sophisticate, top-of-the-line components, which necessarily place the motor in the premium category. As a result, the fast-charging battery unit consists of 21,700 modern, cylindrical cells (individual cell size 21 x 70 mm). Moreover, the control system has been specially developed for AMPRIO, and features an intuitively comprehensible logic and an easy-to-read user interface. And as if this weren’t enough, the startup is entering the market with its own connectivity concept. 

The AMPRIO design team attached special importance to compact dimensions and lightweight solutions

The high-performance motor’s comparatively high torque tops out at 80 Newton meters. For the developers, however, the system’s maximum performance values are less important than its accuracy of control. The support it provides has to kick in in a very sensitive way, subtly adapting to the frequency and force of the rider’s peddling. “As far as we’re concerned, the support the motor provides shouldn’t even be noticeable, resulting in a harmonious riding experience for the bicyclist”, explains Holger Pries, who’s responsible for developing the complete system at AMPRIO.

A small, lightweight drive unit 

The centerpiece of the pedelec system is a drive unit consisting of an electric motor, transmission gearing, control electronics, torque sensor, and a bottom bracket. In line with the young company’s self-imposed specifications, great importance was attached to keeping the system small and light. Among other things, two parameters are decisive in determining the geometric design of pedelec drives. On the one hand, the pedal distance (the so-called Q-factor), and on the other, the total length of the drive unit. A short pedal distance means that the cyclist can maintain his or her natural leg position while peddling. In the AMPRIO system, the bottom bracket shaft is approximately ten millimeters shorter than in most rival designs. This not only results in an extremely low Q-factor, but also creates flexibility when selecting the power transmission to the rear axle.

E-bikes in Germany – a growth market

E-bikes are definitely in. 980,000 pedelecs were sold in Germany alone last year. This corresponds to an increase of 36 percent. The fact that its share in the total market for bicycles has risen to around 23.5 percent in the meantime underscores the growing significance of the e-bike. In the medium term, the German Bicycle Industry Association (ZIV) expects them to account for 30 percent of total annual bike sales, a figure which could reach 35 percent in the long term.

Manufacturers can install the motor in either chain- or toothed belt-driven bicycles with no need for prior modification. The other aspect – the short length of the drive housing – enables a short distance between the bottom bracket and the rear axle. This makes the bike very easy to ride, pretty much the same as a conventional bicycle without an electric motor, resulting in excellent maneuverability and easy, dynamic handling. Particularly with mountain bikes, this is an important factor. “In both these areas, we’re right up there with our leading competitors”, says Greven. 

Meeting goals through Group synergies 

The compact design of the drive unit is due first and foremost to the electromotor used here. Drawing on Group expertise, the company developed it specifically with the special requirements of a pedelec motor in mind. Due to the high degree of winding fullness, it features a very high output density and – thanks to the diameter of the winding wire – very little heat loss. In other areas, too, the Neuss, Germany-based developers took advantage of Group synergies. For example, colleagues from Rheinmetall Automotive lent a hand with test bed studies and help in designing the cast housing. The resulting optimization of the housing components and the use of modern lightweight engineering solutions led to the target to keep the weight of the drive unit under three kilos.

The pedelec system could serve as a basis for the entire micro-electromobility field

Among other things, during the development process the engineers took advantage of the possibilities of innovative 3D printing techniques in order to have prototype components available at short notice for upcoming acoustic and performance tests. Here they cooperated closely with Solidteq, the Rheinmetall Group’s specialist for additive production and another Intrapreneur Award-winning startup. Production of the pedelec system is slated to begin in 2020. The initial focus will be on mountain bikes as well as urban and trekking models.  In the long run, the company could build on this basis to cover the entire micro-electromobility market, including bicycles, tricycles, and urban four-wheelers.

Heinrich Dismon

“Everything a little faster…”

Though he normally focuses his attention on new technologies relating to vehicles with four wheels, Heinrich Dismon, chief technical officer of Rheinmetall Automotive, happens to know a lot about bicycles. Heartbeat spoke with him about the development of the new AMPRIO system.

To what extent did the development of the pedelec motor benefit from know-how from other parts of the Rheinmetall Group?

For the drive unit, we were of course able to draw on expertise from Automotive, especially their special knowledge with regard to electromotors and general mechatronics know-how. Their expertise also proved to be highly useful in configuring the electronics and the motor controls. But in a lot of other areas, when it came to regulating the electromotor, for example, we had to embark on an entirely new course, since – unlike the electronic components in an internal combustion engine – the drive unit interacts directly with the rider. In the pedelec, the torque vectoring is a differenciating characteristic for the end customer. The feeling and performance have to be just right in equal measure. 

What about the other components you developed?

Just like the overarching system concept, things like the HMI and battery system were new to us, which is why we had to draw on external support during development and production. We also hired new people who, along with technical expertise, have an intimate knowledge of the cycling scene. In short, the whole team is making huge strides and doing a great job.

Were there bumps in the road during the development process?

We had to get used to what for us was a completely different business environment. In the pedelec world, everything has to go much faster than in the automotive industry because the product cycles are much shorter. For better or worse, it’s a more volatile environment. But I’m convinced that micro-electromobility is an important market with a bright future, and a great way for Rheinmetall to diversify. 

Conversely, what did other parts of the Group learn from AMPRIO?

As I just mentioned, the general pace is faster in the pedelec business, but the results still need to be highly professional. As I see it, the rest of the automotive world needs to move in this direction, too. In fact, we’re already seeing this. For example, take the speed of implementation newcomers achieve these days in the auto world, especially e-vehicle startups. Connectivity and digitization are other areas where much remains to be done. And here, too, speed is of the essence. I should just mention in this context that connectivity is an important factor for us in the pedelec business, too. 

In the future, do you expect to see changes in the legal regulations covering pedelecs?

It’s safe to assume that legislators in Europe will want to make new rules especially with regard to performance in order to make sure that all pedelecs are equal in this respect. This means product differentiation will have to take other forms. Connectivity, which is relevant for the end customer, is one such area.

Was the electromotor used here specially developed for the purpose and developed in accordance with the relevant specifications?

Yes. The electromotor is a special solution, and so are the gears and even the electronics. A standard motor from our range of existing electromotor products would have worked here only to a certain extent. We’re moving into the pedelec power and sport segment with our new drive unit, which is why we need to push the performance envelope. One example of this is thermal stability in connection with output power, which can break down after just a few minutes when you’re riding in the mountains. Acoustics are another important aspect. Since the rider on a pedelec sits so close to the drive unit, noise from the motor and gearing has to be suppressed to the maximum extent possible. 

The AMPRIO system operates with electrical voltage of 48 volts rather than the 36 volts which a lot of competing systems use. Why did you pick a higher voltage?

As a matter of fact, a number of manufacturers have opted for 48 volts in the meantime, and the same goes for all of the newcomers in the field. There were several reasons why we made this decision. For one thing, a higher voltage level means that we can generate the necessary electricity with lower currents, which also enables smaller wire cross-sections.  Furthermore, it creates added potential for boosting the performance of the motor and electronics for other applications. Finally, it didn’t hurt that 48 volts is the control voltage in the automotive sector for auxiliary units, and that the necessary parts and technical solutions are available on a large scale – and will be. This way, we know we can count on future availability. And of course we also hope that this will have a positive impact on costs. 

You’re a passionate cyclist. What is your current stance on bicycles and e-bikes in particular?

It’s true. I’ve always loved cycling, and own an MTB and a racing bicycle. For the time being, I’m going to try to keep relying on muscle power alone, especially since I can’t imagine riding a bike powered by a competing motor. But if I ever switch to an E-MTB, you can bet it will have an AMPRIO drive unit! I mean, that really ought to go without saying.

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