Patent Application
20180321099
The present disclosure relates to a measuring device and a method for ascertaining operating parameters at a shaft, for example, the shaft of a bottom bracket bearing arrangement of a bicycle or electric bicycle.
In motor-assisted bicycles, frequently also called pedelecs or electric bicycles, an electric motor contributes force for the forward drive. This force assists at least the pedal force of the rider. The pedal force is introduced into a bottom bracket bearing via a crank and normally varies. Therefore, in order, for example, that a predetermined constant speed can be maintained, the measurement of the torque on the bottom bracket shaft is required for the drive control of the motor.
Even in bicycles without motor assistance, it is frequently of interest, for example, to ascertain and indicate the power introduced by the rider.
EP 0 983 934 B1 discloses a torque sensor with which a torque applied to a bottom bracket shaft, for example a bottom bracket shaft of an electric bicycle, can be ascertained. The torque sensor comprises a pressure sensor element, which is arranged on a sensor carrier and is fitted with a force fit between the bottom bracket shaft and a portion of a bicycle frame that encloses the bottom bracket shaft. The force measurement is therefore carried out substantially on the outer ring of a bearing supporting the bottom bracket shaft. The pressure sensor element registers a value of a force on the bottom bracket shaft, which can be proportional to a torque on the bottom bracket shaft.
Leading on from EP 0 983 934 B1, DE 103 39 304 A1 discloses a sensor carrier for transmitting a force from a bottom bracket shaft to a sensor element. The sensor carrier comprises a radially inner part and a radially outer part, wherein one of the parts has an elevation, for example an element projecting out of the surface of the part, for deforming the other part. When a force acts on the bottom bracket shaft and thus there is a transfer of force to the sensor carrier, the elevation is deformed. Given a known relationship between the deformation and the force on the bottom bracket shaft that effects the deformation, this force can be ascertained from the deformation. The torque can then be ascertained indirectly via the length measurement of the deformation, for example the length measurement by a strain gage.
Also known are torque sensors based on the principle of inverse magnetostriction, see, for example, U.S. Pat. No. 5,351,555 and U.S. Pat. No. 5,520,059. Here, a magnetic field is introduced permanently into a bottom bracket shaft. An action of force on the bottom bracket shaft causes a change in the magnetic field. This change can be measured by appropriate sensors, and thus the torque can be ascertained.
An object of the disclosure is to specify a measuring device for ascertaining operating parameters at a shaft, such as the torque or the power on a bottom bracket shaft of a bicycle or electric bicycle, which structurally and/or functionally improves the measuring devices mentioned at the beginning or provides an alternative thereto. The measuring device is intended to be substantially capable of integration in the standard installation space of such a bottom bracket bearing arrangement. Furthermore, it is an object of the disclosure to permit the components of the motor drive, such as the drive control of the electric motor, an optimal reaction time for the control of the auxiliary force. It is also an object of the disclosure to indicate to the user of a bicycle or electric bicycle their introduced power, for example.
This object may be achieved according to the disclosure by the described measuring device and a method for ascertaining an operating parameter at a shaft. The shaft is supported by at least one bearing and, in particular, can be the shaft of a bottom bracket bearing arrangement of a bicycle or electric bicycle.
Accordingly, the measuring device comprises at least one first sensor element for detecting the absolute angle of the shaft and at least one second sensor element for detecting a change in the distance of the shaft from the aforementioned second sensor element.
A change in the distance of the shaft can occur as a result of a deflection of the shaft, for example on account of a load which acts on one end of the shaft. A change in the distance of the shaft can, however, also occur as a result of a displacement of the shaft. A displacement of the shaft is normally brought about by the bearing operating play or the spring deflection of the shaft in a rolling-contact bearing.
With the disclosure, operating parameters, such as the torque and the power, can thus advantageously be ascertained with two sensor elements. This is because a force F_p introduced via a crank arm can be broken down into a tangential force F_t and a radial force F_r. The radial force F¬_r is frequently also designated as a normal force. The line of action of the radial force F_r is directed toward the center of the shaft and simultaneously forms a right angle with the line of action of the tangential force F_t. The change in the distance that is detected is related directly to the force F_p. Thus, the force F_p can be ascertained from the detected measured value from the at least one second sensor element.
It is thus true for the ascertainment of the tangential force F_t that:
F_t=F_p*sin(beta), where beta is the detected absolute angle of the shaft from the at least one first sensor element, and the force F_p results from the detected change in the distance.
From the tangential force F_t, it is in turn possible to ascertain the torque or the power on the shaft, for example directly. The disclosure therefore advantageously uses simple and reliable measuring principles, additionally requiring little installation space, in order to draw conclusions about the torque or the power on a shaft. Furthermore, via the continuous measurement of the absolute angle of the shaft, the direction of rotation of the shaft can be ascertained more quickly than in conventional applications with relative angle measurement. For the components of an electric drive, such as the drive control of an electric motor, this permits an optimal reaction time for controlling the auxiliary force to be introduced. Furthermore, the detection of the absolute angle beta of the shaft permits the position of the left-hand and/or the right-hand pedal crank of a bicycle to be ascertained.
In one embodiment, the at least one first sensor element or the at least one second sensor element is formed as an eddy current sensor. Eddy current sensors are non-contacting distance sensors that are substantially insensitive with respect to media such as oil, water and dust in the measuring gap. In one embodiment, both sensor elements are formed as eddy current sensors.
In a further embodiment, the at least one first sensor element and the at least one second sensor element are integrated structurally in one sensor unit. For example, two coils can be arranged on a sensor unit, which, in accordance with the eddy current principle, firstly detect the absolute angle and secondly the change in the distance. A particularly advantageous embodiment of the sensor unit comprises four coils, in order to detect the absolute angle measurement and the change in the distance repeatedly and therefore to be able to carry out a more accurate calculation of the values.
In one embodiment of the measuring device according to the disclosure, for the detection of the absolute angle, an encoder is arranged radially on the shaft or radially on a component rotationally fixedly connected to the shaft, in particular on an extension of an inner ring of the bearing. This embodiment advantageously permits the detection of the absolute angle within the bottom bracket bearing arrangement, that is to say in the protected installation space of the bottom bracket bearing arrangement.
In a further embodiment of the measuring device according to the disclosure, for the detection of the absolute angle, an encoder is arranged axially on the shaft or axially on a component rotationally fixedly connected to the shaft, in particular on an inner ring of the bearing or a seal of the bearing. This embodiment advantageously permits the detection of the absolute angle, for example on an axial surface of the shaft or an inner ring of the bottom bracket bearing arrangement, and can thus be simply retrofitted, such as, for example, in bottom bracket bearings having bearing shells attached to the frame. Furthermore, the axial configuration of the encoder can particularly advantageously be appropriately chosen to be so thin that the encoder is not influenced substantially by effects of the displacement of the shaft. Expressed in other words, the physical detection of the first sensor element can be chosen to be so much wider that the correspondingly thinner configured encoder always remains within the detection range of the first sensor element, despite the displacement effects in the shaft.
The axial or radial encoder can be formed as a central, eccentric or sinusoidal wedge. Binary encoding is also possible. Thus, the two binary values can be formed, for example, by different materials, such as copper and non-copper, or a change in the geometry of the encoder, such as elevation and depression.
In one embodiment of the measuring device according to the disclosure, the at least one bearing has a bearing point, wherein the at least one second sensor element is arranged at the bearing point. An arrangement on or close to the bearing point permits the measurement of the change in the distance which is caused by a displacement of the shaft at the bearing point. Thus, inter-alia, it is possible better to draw conclusions about the operating parameter which is introduced at the bearing point with the corresponding bottom bracket bearing crank.
In a further embodiment of the measuring device according to the disclosure, the at least one bearing has a first and a second bearing point, and the measuring device comprises at least two second sensor elements, wherein one each of the second sensor elements is arranged at the first and the second bearing point. Thus, the operating parameter is introduced at the respective bearing point, that is to say, for example, with the left-hand or right-hand bottom bracket bearing crank of a bicycle, can be ascertained.
In one embodiment of the measuring device according to the disclosure, the at least one bearing has a first and a second bearing point, wherein the at least one second sensor element is arranged between the first and the second bearing point. This permits, for example, the total moment or the total power of a right-hand and left-hand bottom bracket bearing crank to be ascertained. A central arrangement of the at least one second sensor element is particularly advantageous, since the greatest deflection of the shaft occurs here. Furthermore, the at least one second sensor element can be arranged off-center, and oriented at an angle to the shaft in such a way that it is able to detect the greatest shaft deflection.
In one embodiment, the measuring device according to the disclosure comprises at least two second sensor elements, wherein the at least two second sensor elements are arranged to be offset radially by 180 degrees around the shaft. When the shaft is loaded, the one second sensor element thus comes closer to the shaft and the other second sensor element simultaneously moves away from the shaft. This permits the values ascertained to be checked for plausibility.
In one embodiment of the measuring device according to the disclosure, the at least one first sensor element and the at least one second sensor element detect their respective measured variable simultaneously.
The measuring device according to the disclosure further comprises a computing device. The computing device calculates the operating parameter, in particular the torque or the power, with the aid of the detected measured values. The operating parameter can be made available as an electric signal for further applications.
In one embodiment, the measuring device according to the disclosure comprises an energy generating unit. This energy generating unit permits autonomous operation of the measuring device, in particular the computing device. Moreover, with the available energy, it is possible to forward data via a wire-free connection, such as Bluetooth or other radio standards, for example. Thus, the measuring device can be formed to be completely closed and protected well against external environmental influences. An energy generating unit is, for example, a claw-pole generator integrated into the bearing. Alternatively, a power source, for example a rechargeable battery, can also be integrated into the installation space of the bearing or arranged in the physical vicinity.
The previously described embodiments of the measuring device according to the disclosure assume that the sensor elements or sensor units are arranged on a stationary part, for example a bearing housing, and an encoder or the shaft itself are arranged on the rotating part or is the latter itself. Likewise covered by the disclosure is a converse arrangement. The sensor elements or sensor units can therefore also be arranged on the rotating part, such as the shaft. Then, a change in the distance of the shaft from a fixed reference point can likewise be ascertained, or an encoder for the detection of the absolute angle can be arranged fixedly on a non-rotating part. The signals can be transmitted onward, for example by radio.
Also comprised by the disclosure are a bottom bracket bearing arrangement with a measuring device as described above and below, and a bicycle, in particular an electric bicycle, having such a bottom bracket bearing arrangement.
The disclosure also comprises a method for ascertaining an operating parameter, in particular a torque or a power, at a shaft, in particular the shaft of a bottom bracket bearing arrangement of a bicycle or electric bicycle, wherein a force F_p can be introduced into the shaft via at least one pedal crank, wherein the force F_p can be broken down into a tangential force F_t and a radial force F_r, wherein the line of action of the radial force F_r is directed toward the center of the shaft, and wherein the line of action of the tangential force F_t forms a right angle with the line of action of the radial force F_r, comprising: detecting the absolute angle beta of the shaft, detecting a change in the distance of the shaft from a specific part, in particular a sensor element, and calculating the operating parameter at the shaft from the absolute angle beta and the change in the distance, wherein the force F_p can be calculated from the change in the distance, wherein the tangential force F_t can be calculated from the force F_p and the absolute angle beta, and wherein the operating parameter at the shaft is determined by the tangential force F_t.
Further advantages, features and details of the disclosure can be gathered from the example embodiment described below and by using the drawings.
In the following, an example embodiment of the disclosure will be illustrated using the figures. The figures show non-scaled drawings, in which:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 201 455.2 | Feb 2016 | DE | national |
This application is the U.S. National Phase of PCT Appln. No. PCT/DE2017/100062 filed Jan. 31, 2017, which claims priority to DE 102016201455.2 filed Feb. 1, 2016, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2017/100062 | 1/31/2017 | WO | 00 |
