Method and device for determining wheel rotation frequency

Abstract

The invention relates to a method for determining the rotation frequency of a wheel, in particular of a motor vehicle, by means of a rotational speed sensor (1) with a sensor wheel (2) associated with the wheel and a sensor element (3) associated with the sensor wheel (2). SOLUTION: The sensor wheel (2) has pulse generators (4) evenly spaced apart around its circumference, the edges (5) of which are detected by sensor elements (3) to determine the rotation frequency of the sensor wheel (2). In order to compensate for modulation of the rotation frequency caused by eccentricity, the sensor wheel (2) is divided into segments (I to IV), the pulse frequencies (f1 to f4) of the signal pulses detected for each segment (I to IV) are determined and averaged, and modulation parameters (AR, AI) for correcting the rotation frequency are determined depending on the averaged pulse frequencies (f1 to f4).

Description

[Technical field]

[0001] The invention relates to a method for determining the rotation frequency of a wheel, in particular of a motor vehicle, by means of a rotation speed sensor with a sensor wheel associated with the wheel and a sensor element associated with the sensor wheel, the sensor wheel having pulse generators arranged uniformly spaced apart over its circumference, which pulse generators protrude, for example radially from the sensor wheel and whose edges are detected in the circumferential direction by the sensor elements in order to determine the rotation frequency of the sensor wheel.

[0002] The invention further relates to an apparatus comprising a control device which, in intended use, implements the method described above. [Background technology]

[0003] In safety braking systems of motor vehicles, the rotational speed or rotational frequency of one or more wheels of a motor vehicle is monitored in order, for example, to be able to recognize and prevent wheel locking. In the control unit of an ABS or ESP system, the rotational frequency is determined with the aid of a rotational speed sensor. The rotational speed sensor has a sensor wheel connected to the wheel and a sensor element associated with the sensor wheel and fixed to the body. The sensor wheel has a number of pulse generators arranged evenly distributed over the circumference, for example protruding radially from the sensor wheel in the form of teeth and / or configured as magnetic poles. The individual pulse generators are arranged at a distance from one another, so that two edges of each pulse generator can be detected by the sensor element. The sensor wheel can then be scanned optically and / or electromagnetically by the sensor element. To determine the rotational frequency, the number of edges detected over a defined measurement interval is correlated with the time difference measured by the control unit between the last edges detected in the previous and current measurement intervals, respectively.

[0004] However, due to the manufacturing technique, the sensor wheels may have eccentricities, which result in an influence of the pitch error modeled as a sinusoidal waveform on the time difference between the respective detected edges. The amplitude and phase position then depend on the individual sensor wheel, but are not speed-dependent. A static imbalance of the sensor wheel may also lead to an eccentricity effect, when this leads to a wheel-periodic radial force which, via the mechanical system of the wheel bearing, leads to a wheel-periodic modulation of the dynamic load radius, which has the same effect as the pitch error modeled as a sinusoidal waveform. However, in this case, unlike the manufacturing technique eccentricity, there are typically also changes in amplitude and phase position depending on the rotation speed.

[0005] Furthermore, from the applicant's not yet published US Pat. No. 5,399,436, a method is known in which an optimal filter is used to compensate for the modulation caused by eccentricity, the modulation parameters of which are adapted by means of a sequential least squares method, which leads to a relatively slow behavior, which may result in a speed-dependent phase lag of the compensation signal during stationary operation and may lead to overcompensation during dynamic passage through the unbalanced resonance region. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent Application No. 102018221713 Summary of the Invention

[0007] The method according to the invention having the features of claim 1 has the advantage that the above-mentioned drawbacks are overcome and an improved method is created for determining the modulation parameters of the rotation-periodic modulations caused by eccentricity or wheel unbalance in a frequency signal scanned at equal intervals in time. This is achieved according to the invention in that the sensor wheel is divided into segments in order to compensate for the modulations of the rotation frequency caused by eccentricity, the pulse frequencies of the detected signal pulses are determined for each segment and averaged, and a modulation parameter for correcting the rotation frequency is determined as a function of the averaged pulse frequencies. In this case, a segment is understood in particular to mean a segment defined or limited by an angle, i.e. an angular segment. Thus, for a given (angular) segment of the sensor wheel, the pulse frequencies resulting from the detected signal pulses generated by the pulse generator or detected by the sensor elements are respectively determined. Furthermore, these pulse frequencies are averaged over time. From the averaged pulse frequencies, the eccentricity of the sensor wheel can be deduced and can thus be used for determining the modulation parameters.

[0008] In a preferred development of the invention, in order to average the pulse frequency of each segment, the pulse frequency is detected a number of times for each segment over a settable time period or over a settable number of revolutions of the sensor wheel and then averaged. It is particularly preferred that the pulse frequency is averaged algorithmically by simple arithmetic averaging, alternatively or additionally weighting or geometric averaging methods can be applied.

[0009] In a preferred embodiment of the invention, the sensor wheel is divided into equal-sized segments. It is particularly preferred to divide the sensor wheel into four equal-sized segments (quadrants), which results in a symmetrical division of the sensor wheel, with two of the segments diametrically opposite each other. Alternatively, the sensor wheel is divided into differently sized segments, for example into four differently sized segments, of which, for example, two of each have equal size. In principle, a smaller number of segments, for example three segments, or even more than four segments, are also possible.

[0010] In a preferred development of the invention, the non-eccentric pulse frequency is determined from the averaged pulse frequencies of diametrically opposite segments, i.e. the assumption is made that the average value of the pulse frequencies of opposite segments or the averaged pulse frequency is considered to be non-eccentric.

[0011] The pulse frequency including eccentricity is preferably determined from the averaged pulse frequencies of adjacent segments, i.e. segments that follow each other in the direction of rotation, in particular assuming a linear acceleration which allows a good estimation of the instantaneous pulse frequency without eccentricity as well as of the pulse frequency including eccentricity.

[0012] It is furthermore preferably provided that the modulation parameter is determined from the ratio of the averaged eccentricity-containing pulse frequency to the averaged eccentricity-free pulse frequency, in particular from the ratio of the averaged eccentricity-containing segment frequency to the averaged eccentricity-free segment frequency or from the ratio of the averaged pulse frequencies, the modulation parameter is estimated segment-by-segment when leaving each segment.

[0013] The modulation parameters preferably describe the value and phase position of the eccentricity of the sensor wheel. Alternatively, the modulation parameters may be complex-valued amplitudes A R +iA I Describe the following.

[0014] Furthermore, it is preferably provided that the modulation parameters are subjected to a smoothing filtering, in particular by means of a PT1 filter, so that it is achieved in particular that the modulation parameters are not entirely re-estimated several times for each rotation, but rather that previous estimates are used and adapted to the current evaluation.

[0015] The device according to the invention having the features of claim 10 is characterized in that the control device is specially set up for carrying out the method according to the invention during intended use, thereby resulting in the advantages already mentioned above.

[0016] The present invention will now be described in detail with reference to the drawings. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a simplified diagram showing a rotation speed sensor for a motor vehicle. [Diagram 2] 2 is a schematic model for explaining a preferred method of operating the rotation speed sensor; [Figure 3A] FIG. 1 is a simplified diagram showing a computational model. [Figure 3B] FIG. 1 is a simplified diagram showing a computational model. [Figure 4] FIG. 1 is a geometric diagram showing a computational model. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] FIG. 1 shows a rotational speed sensor 1 for a motor vehicle in a simplified diagram. The rotational speed sensor 1 has a sensor wheel 2 with an associated sensor element 3. Here, the sensor element 3 is radially associated with the outer circumference of the sensor wheel 2 and is arranged in a housing-fixed manner. The sensor wheel 2 is connected non-rotatably with the shaft of a drive wheel of the motor vehicle, for example. The sensor wheel 2 has a number of pulse generators 4 distributed over its circumference and arranged at equal intervals from one another. In the present example, these are configured as radially projecting ring segments or teeth, each delimited in the circumferential direction by two edges 5. Alternatively, the pulse generators 4 are configured, for example, as poles of a magnetic multi-pole wheel, axial teeth and / or perforated plates. In this example, the sensor wheel 2 has a number of magnetic pole pairs N, which are formed in particular by one or more permanent magnets. P The instantaneous rotational frequency f of the wheel or sensor wheel 2 is determined by a control device, in particular by an ABS / ESP control device, at a time instant n * At time ΔT, the number e of edges 5 of the sensor wheel 2 or pulse generator 4 detected by the sensor element 3 in a defined measurement interval ΔT, for example with ΔT=5 ms, is determined by relating it to the time difference t(n)-t(n-1) measured by the control device between the last detected edges of the previous and current measurement intervals. In the present example, six edges 5_1 to 5_6 are detected by the sensor element 3 within the measurement interval ΔT, while the sensor wheel 2 rotates clockwise on the plane of the drawing, as indicated by the arrow 6.

[0019] The computational model described below, in a simplified form shown in FIG. 2, advantageously compensates for the adverse effects or modulations caused by eccentricity in the time-equidistant frequency signal.

[0020] In this respect, FIG. 2 shows in a simplified manner a model which is implemented in particular by a control device of a speed sensor or by a control device associated with the speed sensor.

[0021] The sensor element 3 determines the pulse frequency f resulting from the edges of the pulse generator 4 and the rotation speed, which is then proportional to the number of encoder wheel poles N P is scaled to angular frequency through:

number

[0022] According to the not-yet-published patent document 1, the modulation generated by imbalance or eccentricity is expressed as the complex amplitude A R +iA I It is already known to compensate for this by a model 12 after estimating , or alternatively by its value and phase position. For this purpose, as described in the above mentioned patent application, the following correction signal g(n) is used:

number

[0023] where the parameter f M represents the time-averaged pulse frequency and s(n) represents the instantaneous wheel angle determined by integrating the number of edges:

number

[0024] In contrast, the method or model shown in a simplified form in Fig. 2 assigns the measured frequency signal to segments or angular segments, in particular to quadrants of the sensor wheel 2, depending on the wheel angle at the time of the measurement, and when leaving the segment, one of the modulation parameters is determined from the relationship of the frequency average values ​​calculated for each segment. This results in only small phase shifts that do not require a time-averaged frequency and therefore react dynamically to speed changes, which improves the compensation of the modulation. At the same time, the cost of the algorithm is reduced.

[0025] The model shown in Fig. 2 will be considered in detail with reference to Fig. 3A and Fig. 3B. The instantaneous pulse frequency is understood to be wheel angle dependent in this example. The pointer 7 rotating at the wheel angular frequency, whose length reflects the pulse frequency f and whose angular position reflects the wheel angular position, describes concentric circles with respect to the coordinate origin 8 as shown in Fig. 3A under a constant speed and concentric sensor wheel 2. Thus, the pointer 7 has the same length independent of the wheel angle.

[0026] However, if the sensor wheel has eccentricity as shown in Figure 3B, the center point of the circle is displaced from the coordinate origin 8, resulting in a change in the length of the pointer 7 depending on the wheel angle and a corresponding rotationally periodic modulation of the measured pulse frequency f. During accelerated motion, the pointer describes a circular spiral. Eccentricity is characterized by the displacement of the spiral center point from the origin 8.

[0027] By accumulating the number of edges, the instantaneous wheel angle s(n) is calculated as already explained above. The measured instantaneous pulse frequency is given by:

number

[0028] Thereby, if the complex pointer in the complex plane is expressed as cos s(n)+I sin s(n), the segment average values ​​are located on the positive real axis, the positive imaginary axis, the negative real axis or the negative imaginary axis. This simplifies the assignment of the segments to the adapted modulation parameters. Whereas in the present embodiment the sensor wheel is divided into four (angular) segments I to IV (quadrants) of equal size, in other embodiments it is intended that the segments are of different sizes or that there is a different number of segments, but at least three, which, however, require weighting in the assignment to the modulation parameters.

[0029] Preferably, an assignment of the average of the pulse frequency to the wheel angle is made, i.e. the above wheel angle calculation at the end of the time interval n is modified as follows:

number

[0030] The instantaneous pulse frequencies f1 to f4 measured after each passage of each segment are preferably averaged. For this purpose, an arithmetic mean is performed, which allows a particularly simple implementation of the algorithm, although other weightings, for example a geometric mean, are also possible. For example, if a segment K (K=1 to 4) is A ,...,n E In that case, at time n E The average frequency f k (n e ) is formed for segment k:

number

[0031] The average pulse frequencies of opposing segments 1,3 and 2,4 can be assumed to be eccentricity-free. For the constant rotation speed assignments given above, (f1+f3) / 2 and (f2+f4) / 2 are both good estimates of the eccentricity-free pulse frequencies.

[0032] Under the assumption of linear acceleration, which is usually well approximated within half a wheel revolution, the average of the pulse frequencies of adjacent segments is a good estimate of the instantaneous pulse frequency without eccentricity, and the instantaneous frequency with eccentricity, f K , the non-eccentric pulse frequency (f k -1+f k +1) / 2 can be assigned.

[0033] Modulation Parameter A R and A I is estimated from the ratio of the averaged pulse frequency with eccentricity to the pulse frequency without eccentricity, preferably alternating between segments and each time leaving one segment.

[0034] [Table 2]

[0035] In this case, the most recently measured averaged pulse frequency is used in each case. As indicated above, the evaluation is preferably delayed by a quarter of a rotation, so that, for example, when leaving segment IV, the averaged pulse frequency of the most recently passed segments II, III and IV is used.

[0036] The method can be described geometrically as shown in FIG. 4. The instantaneous pulse frequency, which is plotted centered on the origin 8, is assigned to one of four segments I to IV, which are represented in FIG. 4 by dashed lines and double arrows. For each segment I to IV, an averaged pulse frequency f1 to f4 is determined. As shown by dashed lines, the secant bisector between the respective averaged pulse frequencies of opposite segments has approximately the length of the circle radius representing the pulse frequency without eccentricity. From the orthogonal lines of the secant bisectors, the center point 9 of the pulse frequency circle can be determined. The displacement of the origin 8 and the circle center point 9 with respect to the circle radius corresponds to the modulation parameters to be estimated in amplitude and phase or in real and imaginary parts.

[0037] The above-described evaluation is preferably followed by a smoothing filtering by a filter 10 as shown in FIG. 2, for example by a PT1 filter with a proportion of 30% for each new evaluation, so that a completely new estimation of the modulation parameters does not have to be performed twice each time the sensor wheel 2 rotates. Instead, the advantage is that the previous estimation is adapted by the evaluation. In this way, a correction signal g is calculated by the model 11 from the estimated modulation parameters and the instantaneously measured pulse frequency, so that the corrected signal f corr The rotational periodic modulation is compensated for by (n) = f(n) - g(n).

[0038] From the thus modulated and corrected signal the velocity v and acceleration a can then be determined in a simple conventional manner. [Explanation of symbols]

[0039] 1 Rotational Speed ​​Sensor 2 Sensor Wheel 3 Sensor element 4 Pulse Generator 5. Edge 10 PT1 Filter I-IV segments f1~f4 pulse frequency

Claims

1. 1. A method for determining the rotational frequency of a wheel by means of a rotational speed sensor (1) with a sensor wheel (2) assigned to the wheel and a sensor element (3) assigned to the sensor wheel (2), the sensor wheel (2) having pulse generators (4) evenly spaced apart over its circumference, the edges (5) of which are detected by the sensor element (3) in order to determine the rotational frequency of the sensor wheel (2), the method comprising: dividing the sensor wheel (2) into segments (I to IV) in order to compensate for a modulation of the rotational frequency caused by eccentricity, averaging the pulse frequencies (f1 to f4) of the signal pulses detected in each of the segments (I to IV) and determining modulation parameters (AR, AI) for correcting the rotational frequency as a function of the averaged pulse frequencies (f1 to f4), determining non-eccentric pulse frequencies (f1-f4) from the averaged pulse frequencies of diametrically opposed segments (I, III; II, IV); determining an eccentric pulse frequency from the averaged pulse frequencies of adjacent segments (I, II, III, IV); A method according to claim 1, characterised in that said modulation parameters (AR, AI) are determined from the ratio of the averaged eccentricity-containing pulse frequency to the eccentricity-free pulse frequency.

2. 2. The method according to claim 1, characterized in that in order to average the pulse frequencies (f1-f4) of each of the segments (I-IV), the pulse frequencies (f1-f4) are detected a number of times for each of the segments (I-IV) over a settable time period or over a set number of revolutions of the sensor wheel and then averaged.

3. 3. The method according to claim 1 or 2, characterized in that the sensor wheel (2) is divided into segments (I-IV) of equal or different size.

4. 4. The method according to claim 1, wherein the sensor wheel (2) is divided into at least three segments (I-IV).

5. 5. A method according to claim 1, wherein said modulation parameters (AR, AI) describe the value and the phase position of the eccentricity of said sensor wheel.

6. A device for determining the rotational frequency of the wheels of a motor vehicle, characterized in that it has a control device set up to carry out the method according to any one of claims 1 to 5.

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