Torque, Speed and Direction Measurement for Light Electric Vehicles
Methode was approached to develop a solution for the Light Electric Vehicle (LEV) bike market that enhances the quality of torque measurement and adds the ability to measure speed and direction into a single sensing device.
We developed a custom sensor that has the capability to measure all three elements by incorporating speed sensors in the wheel shaft, allowing the system to measure torque and sense direction.
Approached by an LEV bike manufacturer, Methode was asked to create a single device that enhanced the quality of torque measurement, while adding the ability to measure speed and direction accurately. The limited space available to enclose this sensing device in the bracket that houses the crankshaft further complicated the solution. Previously, the market has used a strain gauge device mounted on the bike frame that could only project the applied torque, not actual torque. Additionally, changes in rider weight and the impact realized by the frame over rough roads compounded the inconsistencies. These inconsistencies, which were enrolled into the monitor and control system to alert the electronic assist, meant riders were not being provided with an effortless riding experience. Lastly, in terms of measurements, the signal needed to be accurate and repeatable, so that a mathematical compensating controller used with older approaches would not be required.
Methode provided a custom designed sensor that enrolled torque, speed and direction in a commercially acceptable framework. The sensor performs at a narrowly defined torque range and has the ability of a "three X" torque overload condition without any residual degrading of the sensor. Therefore, as the rider pedals the bike, an absolute torque measurement is made and sent to the control system to engage the electric motor assist when necessary. As the sensor sends an analog signal, the controller can read changes at the crankshaft at a sub 1.0 ms level in any road and weather condition. Because the speed sensor does not require a target wheel on the shaft, it can be incorporated within a single package that includes the torque and direction sensing, even in the limited space available within the lower bracket of a bicycle. This speed signal is then presented in a digital-signal format to the controller for processing. A side benefit of the use of speed in the control scheme is, when used with the torque measurement, the system can provide the rider with horsepower or calorie burn. The direction is a simple digital signal, which provides the controller with the information to determine the level of any electric assistance.