10 years ago no one could imagine with which speed electromobility would move forward. Not only the cars and the associated drive technologies are called for by electric mobility, but also „micro-mobility applications“ such as bicycles. The bicycle as a term is used less and less. The new keywords are E-Bike or pedelec. Both terms are often used for the same thing, but there is a big difference. Where an e bike is driven by an electric motor and can only be moved by this additional electric power exclusively, the assistance of an electric motor in a pedelec is controlled by the pedaling power of the driver. The e-bike is subject to completely different legal conditions, than the pedelec. This differentiation between the two electromobility variations continues in the needed electronics and mechanics for the respective functionality.
Pedelecs, unlike E-Bikes, need sensors that can detect the pedaling force and cadence of the driver and process this information in electric regulation. Such sensors are often described as „E-Bike sensors“. In many forums you can read posts about the E-Bike Sensor. It is obvious, that the E-Bike Sensor is the heart of the E-Bike and that its driving behavior is significantly defined by these sensors. The accuracy of the e-bike sensors is thus of great importance for the pedelecs as it influences the electric drive and the handling of the bicycle directly. A malfunction of the e-Bike sensor is noticed by the user immediately. Also uncertainties in the measurement are perceived by the user as a discrepancy in the regulation. The challenge of the developers and manufacturers of pedelec drives is therefore to tune the sensors in a way, that the driving behavior is as similar to a bicycle as possible.
In general, an E-Bike sensor consists of two sensors, a torque sensor for the detection of mechanical work and a cadence sensor for determining the pedaling frequency (cadence). By determining the mechanical work and the cadence, the power applied by the driver can be determined. The regulations of pedelecs are usually designed so that you amplify this applied by a driver performance with a certain gain level. For most systems, this gain level is adjustable – depending on how much the assist mode is desired. The basic principle of the measurement and control is based sounds very simple. The implementation, however, is very difficult.
The big challenge of the first systems was that at that time no torque sensor technologies were available on the market that were cheap enough to be applied in an pedelec. The sensor technologies that have developed due to the need for affordable torque sensors had to overcome many obstacles. One example is the rotating measuring point, which makes a classical contact measurement very difficult. Torque sensors, which are mounted on the rotating shaft can measure the mechanical stresses but require an intelligent solution to be supplied with energy and to transmit the signals to the controller. Non-contact torque sensors have the problem that the measuring position changes due to the rotating shaft, which can affect the measurement.
These challenges have resulted in relatively large measurement errors of the first generation torque sensors which as a consequence can be felt by the users. Many influences of the sensors on the measurement uncertainty could be compensated by good control systems, but not all of them.
Therefore, the development of new technologies for torque sensor aims to significantly improve the measurement performance of the sensor in order to improve in particular the deviation between sensors so that the implementation in the final application does not result in any differences from bike to bike. The Magnetic Sense GmbH has solved the challenge of measurement accuracy by realizing a combination of torque and cadence/angle sensor. This combination enables the compensation of the measurement inaccuracy via the angle information. In this way a „smart sensor“ was developed, which leads to an overall error <1% FS. Thanks to additional information on the pedal position (angle), it is also possible to determine the pedalling speed. Finally, together with the torque information, the power can be determined.
The company Magnetic Sense has managed to develop a torque sensor for pedelecs, which can meet the requirements of the future pedelecs with a high measuring accuracy. The intelligent sensor system also creates new possibilities for using the additional information. The measured angle and the pedal position are output to the driver to be used for training purposes.