SENSOR SYSTEM FOR A VEHICLE

Abstract

A sensor system for a bicycle. The system system includes a magnetic field sensor and an acceleration sensor unit having at least one acceleration sensor, and an evaluation unit that is designed to acquire signals from the magnetic field sensor and the acceleration sensor unit. The magnetic field sensor and the acceleration sensor unit are designed for attachment to a wheel of the bicycle. The magnetic field sensor and the acceleration sensor unit are fixed relative to each other and are situated at a predefined distance with respect to an axis of rotation. The evaluation unit is designed to evaluate the signals of the magnetic field sensor and the acceleration sensor unit to ascertain a rotational speed and/or orientation of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation.

Claims

1. A sensor system for a bicycle. comprising: a magnetic field sensor, and an acceleration sensor unit having at least one acceleration sensor; and an evaluation unit configured to acquire signals from the magnetic field sensor and the acceleration sensor unit; wherein the magnetic field sensor and the acceleration sensor unit are configured for attachment to a wheel of the bicycle, the magnetic field sensor and the acceleration sensor unit being fixed relative to each other and being situated at a predefined distance with respect to an axis of rotation; and wherein the evaluation unit is configured to evaluate the signals of the magnetic field sensor and the acceleration sensor unit to ascertain: (i) a rotational speed, and/or (ii) orientation, of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation.

2. The sensor system as recited in claim 1, wherein the acceleration sensor unit has a first acceleration sensor and a second acceleration sensor that are stationary relative to each other and are situated in different angular positions with respect to the axis of rotation.

3. The sensor system as recited in claim 2, wherein the first acceleration sensor and the second acceleration sensor are configured mirror-symmetrically with respect to the axis of rotation.

4. The sensor system as recited in claim 1, further comprising: an additional acceleration sensor situated in stationary fashion with respect to the axis of rotation, the evaluation unit being configured to ascertain a centrifugal acceleration from the signals of the acceleration sensor unit based on signals of the additional acceleration sensor.

5. The sensor system as recited in claim 1, wherein the evaluation unit has a fusion unit, including a Kalman filter, configured to fuse the signals of the magnetic field sensor and the acceleration sensor unit to ascertain, from the fused signals: (i) the rotational speed, and/or (ii) the orientation, of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation.

6. The sensor system as recited in claim 1, wherein the evaluation unit is configured to carry out a first velocity ascertainment based on signals of the magnetic field sensor, and a second velocity ascertainment based on signals of the acceleration sensor unit, and to output an error message when results of the first velocity ascertainment and second velocity ascertainment differ by more than a predefined tolerance.

7. The sensor system as recited in claim 1, wherein the evaluation unit is configured to: when the rotational speed is below a predefined speed threshold, fuse the signals of the magnetic field sensor and of the acceleration sensor unit using a fusion unit including a Kalman filter, to ascertain from the fused signals: (i) the rotational speed, and/or (ii) the orientation of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation, and when the rotational speed is above the predefined speed threshold, carry out a first speed ascertainment based on signals of the magnetic field sensor, and a second speed ascertainment based on signals of the acceleration sensor unit, and output an error message when results of the first speed ascertainment and second speed ascertainment differ by more than a predefined tolerance.

8. The sensor system as recited in claim 1, wherein the magnetic field sensor is configured for at least biaxial ascertaining of magnetic fields and/or the acceleration sensor unit is configured for at least biaxial ascertaining of accelerations.

9. The sensor system as recited in claim 8, wherein: i) the magnetic field sensor is configured to acquire at least two components of the earth's magnetic field in a coordinate system rotating about the axis of rotation as follows, the components m.sub.x and m.sub.y being oriented perpendicular to the axis of rotation:
m.sub.x=A(ψ)×cos(2πft+φ.sub.1)
m.sub.y=A(ψ)×sin(2πft+φ.sub.1) wherein A(ψ) is an absolute value of a magnetic field for direction of travel ψ and mounting angle φ.sub.1 of the magnetic field sensor, and wherein the evaluation unit is configured to ascertain the frequency f from the components m.sub.x and m.sub.y and from the frequency, to ascertain the rotational speed ω according to the following relationship:
ω=2λπ×f and/or (ii) the acceleration sensor unit is configured to acquire accelerations in a coordinate system (xyz) rotating about the axis of rotation as follows:
a.sub.x=a.sub.centr−g′×cos(ωt+φ.sub.2)
a.sub.y=−g′×sin(ωt+φ.sub.2) wherein the centrifugal acceleration a.sub.centr=ω.sup.2r, r is a distance between the axis of rotation and the acceleration sensor unit, and a component g′ of the acceleration due to gravity g in a plane orthogonal to the axis of rotation, the evaluation unit being configured to ascertain the rotational speed w from the accelerations a.sub.x and a.sub.y.

10. A bicycle, comprising: at least one wheel rotatable about an axis of rotation; and a sensor system, including: a magnetic field sensor, and an acceleration sensor unit having at least one acceleration sensor; and an evaluation unit configured to acquire signals from the magnetic field sensor and the acceleration sensor unit; wherein the magnetic field sensor and the acceleration sensor unit are configured for attachment to a wheel of the bicycle, the magnetic field sensor and the acceleration sensor unit being fixed relative to each other and being situated at a predefined distance with respect to an axis of rotation; and wherein the evaluation unit is configured to evaluate the signals of the magnetic field sensor and the acceleration sensor unit to ascertain: (i) a rotational speed, and/or (ii) orientation, of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation; wherein each of the magnetic field sensor and the acceleration sensor unit is attached to the same wheel of the bicycle, and the axis of rotation corresponding to the axis of rotation of the same wheel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the following, exemplary embodiments of the present invention are described in detail with reference to the figures.

[0024] FIG. 1 shows a bicycle according to an exemplary embodiment of the present invention, having a sensor system.

[0025] FIG. 2 shows a schematic view of a sensor system according to a first exemplary embodiment of the present invention.

[0026] FIG. 3 shows a schematic overview of the sensor system according to the first exemplary embodiment of the present invention.

[0027] FIG. 4 shows a schematic view of a sensor system according to a second exemplary embodiment of the present invention.

[0028] FIG. 5 shows a schematic overview of the sensor system according to the second exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0029] FIG. 1 shows a bicycle 10 according to an exemplary embodiment of the present invention. Bicycle 10 has a first wheel 11a and a second wheel 11b, one of the wheels 11a, 11b preferably being drivable both by muscular force of a user and by an electric drive 9. Bicycle 10 is thus preferably an e-bike. Bicycle 10 further has a sensor system 1 for ascertaining a speed of bicycle 10.

[0030] First wheel 11a is rotatable about a first axis of rotation 100a, and second wheel 11b is rotatable about a second axis of rotation 100b. Sensor system 1 has a magnetic field sensor 2 (cf. FIGS. 2 to 5) and an acceleration sensor unit 3 (cf. FIGS. 2 to 5) having at least one acceleration sensor 3a, 3b. Magnetic field sensor 2 and acceleration sensor unit 3 are fixed relative to each other and are situated at a predefined distance r.sub.1, r.sub.2, r.sub.3 with respect to an axis of rotation 100 (cf. FIG. 2 and FIG. 5). Thus, magnetic field sensor 2 and acceleration sensor unit 3 are rotatable about axis of rotation 100. It is preferably provided that magnetic field sensor 2 and acceleration sensor unit 3 are situated on a hub of the first wheel 11a and/or second wheel 11b, so that axis of rotation 100 corresponds to the respective axis of rotation 100a, 100b of the wheel 11a, 11b.

[0031] Due to this configuration, on the one hand there is a magnetic field sensor 2 that rotates relative to the earth's magnetic field m, while on the other hand there is at least one acceleration sensor 3a, 3b that rotates relative to the earth's gravitation g and on which a centrifugal acceleration acts. On the basis of these sensors, the speed of bicycle 10 can be optimally determined.

[0032] In all exemplary embodiments, it is shown that magnetic field sensor 2 and acceleration sensor unit 3 are situated on first wheel 11a. Alternatively, magnetic field sensor 2 and acceleration sensor unit 3 can also be situated on second wheel 11b, or on different wheels 11a, 11b. All the Figures use the same coordinate system. Here, the z-axis is axis of rotation 100. The x-axis is oriented orthogonal to the z-axis, and the y-axis is oriented orthogonal to the z-axis and to the x-axis, the coordinate system being moved and rotated together with the wheel 11a, 11b.

[0033] FIG. 2 schematically shows a sensor system 1 according to a first exemplary embodiment of the present invention, FIG. 2 additionally showing its situation on a wheel 11a, 11b of bicycle 10. Sensor system 1 according to the exemplary embodiment of the present invention can be used as a sensor system 1 as shown in FIG. 1.

[0034] As described above, sensor system 1 has a magnetic field sensor 2 and an acceleration sensor unit 3, which in the first exemplary embodiment has a single acceleration sensor 3a. Magnetic field sensor 2 and acceleration sensor 3 are rotatable about axis of rotation 100, or about axis of rotation 100a, 100b of wheel 11a, 11b. A first distance r.sub.1 of acceleration sensor 3a to axis of rotation 100 and a third distance r.sub.3 of magnetic field sensor 2 to axis of rotation 100 are preferably the same, but can also be different.

[0035] Furthermore, sensor system 1 has an evaluation unit 4 that is designed to detect signals from magnetic field sensor 2 and acceleration sensor unit 3, i.e. acceleration sensor 3a. Advantageously, this is done via a wireless connection if the evaluation unit 4—as shown in the first exemplary embodiment—does not rotate with the wheel 11a, 11b, but is situated fixedly on bicycle 10. Alternatively, evaluation unit 4 can also be fastened on wheel 11a, 11b so as to rotate with it. In this case, a permanent wired connection of magnetic field sensor 2 and acceleration sensor unit 3 to the evaluation unit is preferably provided.

[0036] Evaluation unit 4 is thus set up to ascertain, using magnetic field sensor 2, at least those individual components m.sub.x, m.sub.y of the earth's magnetic field m that are oriented perpendicular to axis of rotation 100, and in particular also the component m.sub.z parallel to axis of rotation 100, in the co-rotating coordinate system xyz, as follows:

m.sub.x=A(ψ)×cos(2πft+φ.sub.1)

m.sub.y=A(ψ)×sin(2πft+φ.sub.1)

m.sub.z=B(ψ)

[0037] Here, A(ψ) and B(ψ) represent absolute values of the magnetic field in the direction of travel ψ. In addition, the components m.sub.x and m.sub.y are functions of a first mounting angle φ.sub.1 of magnetic field sensor 2.

[0038] The signals m.sub.x and m.sub.y thus represent oscillations, where a frequency f of these oscillations is a function of the rotational speed ω=2×n×f of the wheel 11a, 11b. This oscillation is measured because the magnetic field sensor, which is fixed to the wheel 11a, 11b, rotates within the earth's magnetic field m. The oscillations also have the amplitude A(ψ), which is a function of the direction of travel ψ of the wheel 11a, 11b. Since the z-axis represents the axis of rotation 100, m.sub.z is approximately constant B(ψ) but is also a function of the direction of travel ψ. The amplitudes A(ψ) and B(ψ) are, in addition to the direction of travel, also a function of the position of the wheel 11a, 11b on the earth, because both the amplitude and the vertical component of the earth's magnetic field m are a function of the position. The absolute values of the amplitudes A(ψ) and B(ψ) are not relevant for the further course.

[0039] The evaluation unit 4 is thus made able to ascertain the rotational speed ω of the wheel 11a, 11b on the basis of the magnetic field sensor 2, and a speed of bicycle 10 can also be calculated if the wheel circumference of the wheel 11a, 11b is known.

[0040] As a further possibility for ascertaining the rotational speed ω,acceleration sensor 3a is provided. Due to the mounting on the wheel 11a, 11b, for example on the wheel hub, a centrifugal acceleration a.sub.centr acts on the acceleration sensor 3a during a rotation, which acceleration is a function of the rotational speed ω of the wheel 11a, 11b. In the first exemplary embodiment, acceleration sensor 3a is located at a position with coordinates (r.sub.1,0,0). Here, r.sub.1 represents the distance of acceleration sensor 3a to the axis of rotation 100, as described.

[0041] This centrifugal acceleration a.sub.centr is described by the following equation:

a.sub.centr=ω.sup.2r.sub.1

[0042] The centrifugal acceleration a.sub.centr acts exclusively in the direction of the co-rotating x-axis.

[0043] Furthermore, acceleration sensor 3a is additionally acted upon by the component g′ of the acceleration due to gravity g in the plane orthogonal to the axis of rotation. In the co-rotating coordinate system xyz, the component g′ of the acceleration due to gravity g is divided into two components:

a.sub.x,g=−g′×cos(ωt+φ.sub.2)

a.sub.y,g=−g′×sin(ωt+φ.sub.2)

[0044] Here, φ.sub.2 is an angular offset of acceleration sensor 3a due to its mounting, and t is continuous time. The component g′ of the acceleration due to gravity g is a function of an angle of inclination of the bicycle.

[0045] In addition, other components are included in the measured values of acceleration sensor 3a. These are the longitudinal acceleration a.sub.d of bicycle 10 in the direction of travel, for example due to braking or accelerating, as well as the vertical acceleration a.sub.u in the vertical direction, for example due to impacts caused by an uneven ground surface. These additional accelerations are also divided into two components:

a.sub.x,f=a.sub.d×cos(ωt+φ.sub.2)−a.sub.u×sin(ωt+φ.sub.2)

a.sub.y,f=a.sub.d×sin(ωt+φ.sub.2)+a.sub.u×cos(ωt+φ.sub.2)

[0046] For a rotational speed ω there then results, for the signals a.sub.x1 and a.sub.y1 of acceleration sensor 3a:

a.sub.x1=a.sub.centr+a.sub.x,g+a.sub.x,f

a.sub.y1=a.sub.y,g+a.sub.y,f

[0047] The components a.sub.x,f and a.sub.y,f are small compared to the useful signal a.sub.centr∓a.sub.x,g or a.sub.y,g. The useful signal in turn represents an oscillation that is a function of the rotational speed w of the wheel 11a, 11b. For known r.sub.1, from the two signals a.sub.x1 and a.sub.y1 the rotational speed w can be estimated.

[0048] The rotational speed ω can thus be asceratined using two independent measurement principles. This enables several advantages, which are described below:

[0049] At low speed, the direction of travel ψ of bicycle 10 can change quickly. The functional dependence of the signals of magnetic field sensor 2 on the direction of travel ψ thus makes it difficult to determine the current position or speed. Using a suitable fusion algorithm, such as a Kalman filter, which advantageously combines the signals of magnetic field sensor 2 with those of acceleration sensor 3a, not only the speed of bicycle 10 per revolution of the wheel 11a, 11b but also the angular position of the wheel 11a, 11b at any time within a wheel revolution can be better estimated. In this way the instantaneous speed can be better determined, in addition to the average speed. At low speed, the accelerations a.sub.u and a.sub.d and also the centrifugal acceleration a.sub.centr are small compared to the component g′ of the acceleration due to gravity g in the plane orthogonal to the axis of rotation, so that approximately the following holds:

a.sub.x1=a.sub.x,g

a.sub.y1=a.sub.y,g

[0050] From this approximation it is then easy to determine the rotational speed ω of the wheel 11a, 11b, and thus the speed of bicycle 10.

[0051] At higher speeds, it is advantageously provided to acquire the acceleration components a.sub.d and a.sub.u with the aid of an additional non-rotating additional acceleration sensor 5 (see FIG. 1). The latter is already often included in the drive unit of the e-bike in order to realize various support functions. For known a.sub.d and a.sub.u, the rotational speed w can thus be determined from a.sub.x1 and a.sub.y1, sensor system 1 itself not requiring any further acceleration sensor.

[0052] FIG. 4 and FIG. 5 show sensor system 1 according to a second exemplary embodiment of the present invention. In contrast to the first exemplary embodiment of the present invention, two acceleration sensors 3a, 3b are provided. Both a first acceleration sensor 3a and a second acceleration sensor 3b are attached to wheel 11a, 11b so as to rotate along with it. Here, magnetic field sensor 2, first acceleration sensor 3a, and second acceleration sensor 3b are stationary relative to each other. First acceleration sensor 3a and second acceleration sensor 3b have an angular offset to each other.

[0053] At higher speeds, the above approximation no longer holds; i.e., the components a.sub.d and a.sub.u can no longer be disregarded. Using the second acceleration sensor 3b, these components can also be ascertained or taken into account in the calculation of the rotational speed w of the wheel 11a, 11b.

[0054] It is particularly advantageously provided that first acceleration sensor 3a and second acceleration sensor 3b are configured in mirror-symmetrical fashion with respect to axis of rotation 100, as shown in FIG. 5. In this case, a first distance r.sub.1 of first acceleration sensor 3a to axis of rotation 100 is the same as a second distance r.sub.2 of second acceleration sensor 3b to axis of rotation 100. A third distance r.sub.3 of magnetic field sensor 2 to axis of rotation 100 can also be the same, but can also be different. For the acceleration measured by the second acceleration sensor 3b, this results in:

a.sub.x2=a.sub.centr−a.sub.x,g−a.sub.x,f

a.sub.y2=−a.sub.y,g−a.sub.y,f

[0055] Then the rotational speed ω of the wheel 11a, 11b can be estimated using a.sub.x1 and a.sub.x2 without the influence of an external acceleration, because

a.sub.x1+a.sub.x2=2a.sub.centr

[0056] In other words, all measured components of the acceleration with the exception of the centrifugal acceleration a.sub.centr are averaged out when acceleration sensor unit 3 is constructed as in the second exemplary embodiment. This simplifies the ascertaining of the speed by the acceleration sensor unit 3.

[0057] For both the first exemplary embodiment and the second exemplary embodiment, the following holds:

[0058] If, at higher speeds, the speed of bicycle 10 is ascertained on the basis of acceleration sensor unit 3 (either by an additional stationary or co-rotating acceleration sensor), then the speed that was ascertained on the basis of magnetic field sensor 2 can be plausibilized. In the event of a deliberate disturbance of the magnetic field, for example with the aim of influencing the speed measurement, a discrepancy arises between the two ascertained speeds, since the speed ascertained on the basis of acceleration sensor unit 3 is not influenced by the disturbance of the magnetic field. This discrepancy can be recognized by evaluation unit 4 and used to initiate appropriate measures, such as interrupting the motorized support of the e-bike.

[0059] In case of a random disturbance of the earth's magnetic field m, evaluation unit 4 can use the speed ascertained by acceleration sensor unit 3 as a temporary fallback solution to achieve a fail-safe ascertaining of the speed.