Binova Drive Unit – Contactless Torque Sensor

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CASE STUDY: BINOVA DRIVE UNIT

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The German innovator and e-mobility motor manufacturer Binova GmbH were facing a contactless torque sensor dilemma. Its 2nd generation retrofittable motor system needed much better reliability and ride feeling. These two factors were key for the very diverse customers. Behind Binova, there is a team of bike enthusiasts who focus on every single detail to ensure the highest quality standards. As daily cyclists themselves, they understand the changing needs of their customers. And so they created the world’s first gearless mid-drive, the Binova flow. This electric drive unit adapts to every situation, from cycling in the city to going uphill or transporting heavy loads.

Binova needed to optimize the drive unit for high power, maximum torque, and perfect control to guarantee maximum riding fun. A contactless torque sensor was essential as this is the only way to provide optimum ride feeling on an e-bike or other e-assist vehicles. However due to the unique side-mount motor design and the omnipresent cost pressure, no standard torque sensor solution fitted the system and completely integrated into the motor unit.

 

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SOLUTION: A CUSTOM TORQUE SENSOR

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Sensitivus created a fully custom contactless torque sensor solution to meet the mechanical constraints of the system. Being a 2nd generation system, legacy compatibility was essential. The previous system was using 2-phase quadrature outputs for the cadence detector and the existing motor controller was capable of accepting an analog torque input. This all became part of the design requirements for the custom contactless torque sensor solution.

 

 

The mechanical design was done by Binova engineers in parallel with the electronic design provided by Sensitivus. This resulted in a rugged solution fitting into most standard bicycle frames. The contactless torque sensor electronics were designed to provide a 32-steps-per-revolution dual compatible quadrature cadence and direction output signal to feed directly into the existing motor controller. This called for an analog output with minimal latency to provide a quick and accurate torque signal compatible with the motor controller requirements.

Typical options for cadence and torque output are serial data, CAN, or I2C/SPI style interfaces, but in a custom solution most things are possible. The important thing is to create the best solution for the specific project.

 

 

In the custom electronics, the very sensitive analog signal picked up from the torque applied to the shaft by a strain gauge is converted and transmitted in digital form from the ROTOR PCB to the STATOR PCB over the air gap (up to 1.6 mm). The STATOR PCB converts the torque signal back to the analog output while providing wireless power to drive the ROTOR.

 

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CONCLUSION: SUCCESSFUL INTEGRATION

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Binova has managed to integrate the torque sensor solution into this innovative and unique system. As a result, Binova customers can now enjoy natural cycling assistance. They will have better responsiveness in all the different and demanding situations.

For an overview of the different technologies used to make e-bike torque sensors, please see the detailed technology comparison. This will explain why we believe a contactless torque sensor based on strain gauges to be the best solution.