magnetic encoder sensor - e-bike as potential field of application?!

[WU_Student]

Dear all,

In the course of a project headed by the University of Business and Economics Vienna, we are looking for potential application fields of a magnetic encoder.

Basically the technology allows measuring the position of a magnet.

Can you imagine a field, where for instance one or several of the following problems occur;

• Positions have to be measured contactless
• Extreme external conditions (dust, other magnetic fields, temperature, vibrations) have to be passed over
• Maintenance is difficult due to the high complexity of the final product/application
• Linear, rotating or three-dimensional positions have to be measured
• The space is limited and expensive
• It is vivid to avoid/know about malfunctions of position tracking systems
• Easy implementing and catch/use of the signal is necessary
• An energy effective solution is important.

We were able to identify the drive system as a potential field of application. To be precise, the sensors, which control the power of the electro motor, show (according to various interviewees) several weak spots. This could be e.g.: imprecise responding behaviour of the sensors which prevents the driver from controlling the e-motor properly, necessity of calibrating the sensors after change of tyre or chain, sensors which are heavily affected by dirt an therefore have to be cleaned or exchanged regularly, usage of antiquated gearshift equipment…

Please let us know if you experienced any of the above mentioned or other problems in the past. It would be of great help for us!

Thank you very much!

 

[flecc]

Our electric assist bikes use Hall sensors for magnetic sensing in four different ways, but I don't think any of them exhibit the potential problems you mention:

1) Our brushless hub motors often use three Hall sensors to inform the controller of the rotor magnet positions, allowing correct phase current pulsing. No positional error problems are experienced in this function on any motor I've experienced.

2) Our Cycle computers measure speed and distance by detection of a wheel spoke mounted magnet pulsing a Hall sensor at each wheel revolution. The computer has internal user settable correction for wheel size circumference variations or a tyre change.

3) Some of the e-bikes having a motor system that drives though the bicycle's chain (crank drive) use a rear wheel spoke magnet and sensor for the controller to detect when the legal maximum assist speed is reached to facilitate power cut-off. Similar to the cycle computer sensor function, this also has no problems.

4) Many hub motor e-bikes have a disc on the pedal shaft which incorporates a ring of small magnets. An adjacent Hall sensor is thus able to send a stream of pulses to the controller when pedalling is evident, enabling the controller to apply motor power only when the rider is pedalling in accordance with the pedelec law.

None of these areas particularly suffer in the ways you propose as possibilities. There is often considerable dirt and dust contamination on bicycles, but normally never affecting the Hall sensing function. The only item above suffering a problem is with cycle computers that send the pulse signals from the sensor wirelessly, since they can suffer from electro-magnetic interference from adjacent drive motors ot powerful transmitter masts.

I hope this is of some help, but please say if there is any specific e-bike related magnetic sensing problem that you have heard of and would like to examine.

 

[WU_Student]

@flecc
Thank you for your reply.
1) A manufacturer of e-bikes recently mentioned that seniors in e-motors, which determine the position of the rotor face heat issues from time to time. Could this be a potential weak spot of sensors in e-motors?

2) You mention the problem with external magnetic fields...do these electro magnetic fields disturb the sensor itself or does it affect the transfer of the signal to the output device? If the problem occurs directly at the sensor, this could be prevented through applying our magnetic encoders, as they can not be influenced by external magnetic fields.

3) It also helps us a lot when e-bikers simply tell us, that there are no problems. We are, however, still trying to find out, if there are an issues which can be solved by our magnetic encoders.

4) Does this system have any weak spots, e.g. has to be cleaned very often, etc. Can you think of an problems with this system?


@all
Please let us know if you can think of an further problem, concerning the sensors applied in e-bikes.