Steinbeis experts and H+B Hightech develop a sustainable testing rig for bicycle gear hubs
H+B Hightech is a specialist in high-precision engine components used in combustion engines. To open up new fields of business, in 2020 managing director Hilmar Wanner and his team decided to extend their automotive know-how to the bicycle market. The company found professional support in the development and testing of innovative bicycle transmissions at the Steinbeis Transfer Center for Innovative Drive Engineering and Waste Heat Recovery (IAA). The Steinbeis experts developed a rig for testing bicycle transmissions for an innovative internal-gear hub system called 3X3 NINE.
H+B Hightech has developed a gear system that makes riding bicycles even easier and more intuitive, making an important contribution to sustainable mobility. The 3X3 NINE gear system works whether the bicycle is standing still or being pedaled under load. It also needs very little maintenance. Based on so-called planetary gears, it is fully shielded from external influences and even after thousands of miles on the road, it continues to shift gears as precisely as the first day – using a chain or a belt system. The 3X3 NINE gear hub is also so sturdy, it has no problems dealing with powerful electric motors.
When H+B Hightech embarked on development of the 3X3 NINE project, its focus lay heavily in sustainable design. To develop a rig for testing bicycle gear hubs, the firm sought expert help from Innovative Drive Engineering and Waste Heat Recovery (IAA), a Steinbeis Transfer Center specialized in the development and testing of drive units.
The concept behind the testing facility
In the run-up to the project, the team worked together to establish the requirements for the testing rig:
- Ability to test the 3X3 NINE gear hub system and its variations
- Internal-gear hub system can be driven via a belt or chain
- Quick and versatile changing of gearboxes undergoing testing
- No spoking of gears required
- Must allow gear changes during testing
To develop the testing equipment, the experts used drive units, control systems, and a machine bed that already existed. Their concept envisioned the following: A motor drives a belt pulley via a propeller shaft, which is supported by a bearing block. The test gearbox is operated via belts and pulleys attached at the points of input and output. It is also held in place by a fixed axle in the same way as a bicycle. Two measuring flanges are used to determine revolution speeds and torque around the bearing block. Based on this concept, the test rig was then constructed.
Putting bicycle gears through their paces
The next step was to test the 3X3 NINE gear system, as well as comparable bicycle transmissions. “To make testing as realistic as possible, our first step was to draft a schedule to put readings into groups. This was necessary to weight the timing of loads applied to the gear units being tested, according to realistic revolution speeds and torque,” explains Steinbeis Entrepreneur Professor Dr.-Ing. Markus Kley. After research, interviews with experts, and a period of analysis, the following parameters were established:
- Pedal speed (cadence): between 20 and 115 per minute
- Torque on the crankshaft drive: up to 300 newton-meters
- Continuous power: up to max. 500 watts
Based on these parameters and corresponding distribution factors, the revolution and torque levels were grouped into 500 points of load over equal lengths of time. This allowed the duration of testing to be minimized by forming waves. To do this, points of load deemed irrelevant were converted into higher load points of equivalent wear potential at a lower frequency. This had no impact on maximum grouped values, in order not to trigger unrealistic damage to mechanisms.
This reduced the number of collected readings from 500 points to 27 equivalent load points, distributed along the maximum load curve in waves of speeds and torques. With the 3X3 NINE gearbox, this produced three load points in each gear. It also reduced the amount of time required to conduct testing by 70%. To test the gearboxes on the rig, they were first fixed using a quick clamping system mirroring the back end of a bicycle, before being run through the chosen groups of speeds and torque levels.
Actuator design
“The gear unit will be available as both a manual rotary shift system and an electric shift system. For the electric gear shift, an electromechanical shift actuator will need to be developed,” says Hilmar Wanner, Managing Director of H+B Hightech, explaining further plans. In addition to analyzing the durability of the gear system, the Steinbeis experts also conducted studies to determine the force required to shift gears and the level of shift torque. This involved integrating a power sensor into the existing setup for testing gearboxes by using Bowden cables to attach the sensor between the transmission unit and the rotary shift. To examine the forces required to shift gears and the level of shift torque, the experts ran tests under different loads and pedal speeds, looking at upward and downward gear shifts. The aim of these experiments was to determine the maximum possible torque without causing problems while shifting gears. The data this generated was also important for specifications of the electromechanical actuator.
Endurance testing
To test the 3X3 NINE system, the 27 revolution and torque points were run through one gear after the other. Experience with previous testing showed that it makes sense to start by testing in fractions equivalent to 1% of total time taken and repeat this in cycles. As a result, each gear goes through several sequences and corresponding gearshift frequencies are mapped representatively by a factor of 100.
The experts incorporated their insights from the findings of damage caused into several iterations of the development process, and ultimately this provided a basis for developing a robust and reliable 3X3 NINE gearbox that makes it easy to shift gears.