Method and device for determining the rotational frequency of a wheel

Abstract

The invention relates to a method for determining the rotational frequency of a wheel, in particular of a motor vehicle, the vehicle having 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), wherein the sensor wheel (2) has, in its circumferential direction, pulse transmitters (4) arranged uniformly spaced from one another, the flanks (5) of which are detected by the sensor element (3) for determining the rotational frequency of the sensor wheel (2). It is provided that, in order to compensate for the modulation of the rotational frequency caused by eccentricity, the sensor wheel (2) is divided into segments (I-IV), the pulse frequency (f1-f4) of the detected signal pulses is determined for each segment (I-IV) and averaged, and a modulation parameter (A R , A I ) for correcting the rotational frequency is determined from the averaged pulse frequency (f1-f4).

Description

Technical Field

[0001] The present invention relates to a method for determining the rotational frequency of a wheel, particularly a wheel of a motor vehicle, the wheel having a rotational speed sensor having a sensing wheel associated with the wheel and a sensor element associated with the sensing wheel, wherein the sensing wheel has pulse transmitters evenly spaced apart from each other in its circumferential direction, the pulse transmitters protruding, for example, radially from the sensing wheel, and the side of the pulse transmitters being detected in the circumferential direction by the sensor element to determine the rotational frequency of the sensing wheel.

[0002] Furthermore, the present invention relates to an apparatus having a controller that performs the above-described method during normal use. Background Technology

[0003] In a motor vehicle's safety braking system, the rotational speed or frequency of one or more wheels is monitored to detect and prevent wheel lock-up, for example. In the controller of an ABS or ESP system, the rotational frequency is determined by means of a speed sensor. The speed sensor has a sensing wheel coupled to the wheel and a sensor element fixed to the vehicle body, the sensor element being associated with the sensing wheel. The sensing wheel has a plurality of pulse transmitters evenly distributed circumferentially, the pulse transmitters being, for example, toothed radially projecting from the sensing wheel and / or configured as magnetic poles. The pulse generators are arranged at intervals such that two sides of each pulse generator can be detected by the sensor element. Here, the sensing wheel can be sampled optically and / or electromagnetically by the sensor element. To determine the rotational frequency, the number of sides detected at defined measurement intervals is referenced to the time difference between the last detected sides in past and current measurement intervals, as measured by the controller.

[0004] However, in manufacturing, the sensing wheel can be eccentric, whereby a sinusoidally modeled indexing error affects the time difference between the detected sides. The amplitude and phase here depend on the individual sensing wheel, but not on speed. Eccentricity also occurs when a static imbalance of the sensing wheel causes a radial force in the wheel cycle, which modulates the wheel cycle of the dynamic rolling radius through the mechanical system supporting the wheel and acts similarly to a sinusoidally modeled indexing error. However, compared to eccentricity in manufacturing, the amplitude and phase here typically vary according to the rotational speed.

[0005] Furthermore, a method is known from the applicant's unpublished patent application DE 10 2018 221 713, in which an optimal filter is used to compensate for modulation caused by eccentricity, and the modulation parameters of the optimal filter are adapted by a sequential least squares method. This method results in relatively inertial behavior, which may lead to a velocity-dependent phase delay of the compensation signal in steady-state operation and overcompensation when dynamically passing through unbalanced resonance regions. Summary of the Invention

[0006] The method according to the invention has the advantage of overcoming the aforementioned disadvantages and providing an improved method for determining modulation parameters for a period of one rotation caused by eccentricity or wheel imbalance in a frequency signal sampled at equal time intervals. According to the invention, this is achieved by dividing the sensing wheel into segments to compensate for the modulation of the rotational frequency caused by eccentricity; for each segment, the pulse frequency of the detected signal pulses is determined and averaged; and modulation parameters for correcting the rotational frequency are determined based on the average pulse frequency. A segment is currently understood, in particular, to be a segment defined or defined by an angle, i.e., an angular segment. Therefore, pulse frequencies are determined for each predetermined (angular) segment of the sensing wheel, the pulse frequencies being derived from the detected signal pulses generated by a pulse generator or detected by a sensor element. Furthermore, these pulse frequencies are averaged over time. The eccentricity of the sensing wheel can be inferred from the average pulse frequencies, and thus these pulse frequencies can be considered for determining the modulation parameters.

[0007] According to a preferred improvement of the invention, in order to average the pulse frequencies of corresponding segments, the pulse frequencies of the corresponding segments are detected multiple times over a pre-given time period or a pre-given number of revolutions on the sensing wheel, and then averaged. Particularly preferably, the pulse frequencies are averaged algorithmically by a simple arithmetic mean, wherein weighted or geometrical means can be used alternatively or additionally.

[0008] According to a preferred embodiment of the invention, the sensing wheel is divided into segments of equal size. Particularly preferably, the sensing wheel is divided into four segments (quadrants) of equal size, such that the symmetrical division of the sensing wheel exists such that two segments in each quadrant are diametrically opposed. Alternatively, the sensing wheel can be divided into segments of different sizes, for example, four segments of different sizes, wherein, for example, two segments each have the same size. In principle, a smaller number of segments, such as three or more than four segments, is also possible.

[0009] According to a preferred improvement of the invention, the unbiased pulse frequency is obtained from the average pulse frequency of segments that are diametrically opposed to each other. Therefore, it is assumed that the average or average pulse frequency of the pulse frequencies of the opposing segments is considered unbiased.

[0010] Preferably, the eccentric pulse frequency is obtained from the average pulse frequency of adjacent segments, i.e., successive segments along the direction of rotation. Here, linear acceleration is particularly assumed, which allows for good estimation of both the instantaneous unectic pulse frequency and the eccentric pulse frequency.

[0011] Furthermore, it is preferably specified that the modulation parameters are determined by the ratio of the eccentric and uneccentric average pulse frequencies. In particular, the modulation parameters are estimated by alternating segments, respectively, by the ratio of the eccentric and uneccentric average segment frequencies or the average pulse frequencies as the segments leave a segment.

[0012] Preferably, the modulation parameters describe the magnitude and phase of the eccentricity of the sensing wheel. Alternatively, the modulation parameters are used as a complex-valued amplitude A. R + iA I describe.

[0013] Furthermore, it is preferred that the modulation parameters undergo smoothing filtering, particularly by means of a PT1 filter. This, in particular, ensures that the modulation parameters do not need to be completely re-estimated multiple times per cycle, but rather are adapted using previous estimates and current evaluations.

[0014] The device according to the invention is characterized in that the controller is specifically configured to execute the method according to the invention during normal use. This results in the advantages already mentioned above. Attached Figure Description

[0015] In the following description, the invention will be explained in more detail with the aid of the accompanying drawings.

[0016] Figure 1 A simplified diagram illustrates a speed sensor used in a motor vehicle. Figure 2 A schematic model is shown to illustrate an advantageous method for operating the speed sensor. Figure 3A and 3B A simplified diagram of the computational model is shown, and Figure 4 A geometric illustration of the computational model is shown. Detailed Implementation

[0017] Figure 1A simplified illustration shows a speed sensor 1 for a motor vehicle. The speed sensor 1 has a sensing wheel 2, with a sensor element 3 disposed on the sensing wheel. Here, the sensor element 3 is radially disposed on the outer periphery of the sensing wheel 2 and fixedly arranged with a housing. The sensing wheel 2 is coupled to, for example, the shaft of a drive wheel of a motor vehicle, in a way that resists relative rotation. The sensing wheel 2 has a plurality of pulse sensors 4 arranged at uniform intervals to each other in its circumferential direction. In the current embodiment, they are constructed as radially projecting circular segments or teeth, each defined by two side surfaces 5 in the circumferential direction. Alternatively, the pulse generator 4 is constructed, for example, as the magnetic poles of a magnetic multipole wheel, axial teeth, and / or a perforated plate. Currently, the sensing wheel 2 is a multipole wheel with multiple pole pairs N. P The pole wheel, in particular, is formed by one or more permanent magnets. The instantaneous rotation frequency f of the wheel or sensing wheel 2 is determined, in particular by means of a controller, especially an ABS / ESP controller, at time point n * ΔT by the number e of sides 5 detected by the sensor element 3 in a determined measurement interval ΔT of, for example, ΔT = 5 ms, with reference to the time difference between the last detected sides in the past and current measurement intervals t(n) - t(n-1), as measured by the controller. In the current embodiment, six sides 5_1 to 5_6 are detected by the sensor element 3 within the measurement interval ΔT, wherein the sensing wheel 2 rotates clockwise in the plane of the paper in accordance with arrow 6.

[0018] As described below and Figure 2 The simplified computational model is used to compensate for the damage caused by eccentricity or to modulate frequency signals into time-equidistant signals in a favorable manner.

[0019] Figure 2 The model is shown in a simplified manner for this purpose, and the model is implemented in particular by a controller of a speed sensor or a controller associated with a speed sensor.

[0020] The pulse frequency f generated by the side and rotation speed of the pulse generator 4 is obtained by the sensor element 3, and this pulse frequency is then transmitted through the encoder wheel pole number N. P Scaling to circular frequency: (1).

[0021] As is known from the unpublished patent application DE 10 2018 221 713, modulation caused by imbalance or eccentricity in estimating its complex-valued amplitude A R + iA I Its magnitude and phase are then compensated using Model 12 or alternatively. For this purpose, as in the aforementioned patent application, the following correction signal g(n) is used: (2).

[0022] In this parameter f M Let s(n) represent the time-averaged pulse frequency and s(n) represent the instantaneous wheel angle determined by the accumulation of side lengths. (3).

[0023] And through Figure 2 The simplified method or model shown in the figure assigns the measured frequency signal to a segment or angle segment at the measurement time point according to the wheel angle, particularly to the quadrant of sensing wheel 2, and obtains one modulation parameter from the relationship of segment-by-segment calculated frequency averages when leaving a segment. This produces only a small phase shift, which does not require time-averaged frequency and thus dynamically responds to speed changes, thereby improving modulation compensation. At the same time, algorithm overhead is reduced.

[0024] according to Figure 3A and 3B This should be discussed in more detail. Figure 2 The model in question. The instantaneous pulse frequency is currently understood to be related to the wheel angle. A pointer 7 rotating at the wheel circle frequency (its length representing the pulse frequency f and its angular position representing the wheel angle position) operates at a constant speed and with concentric sensing wheels 2, as shown in... Figure 3A As shown in the diagram, a circle concentric with the origin 8 is depicted. Therefore, pointer 7 has the same length regardless of the wheel angle.

[0025] However, in the case of eccentric sensor wheel, such as in Figure 3B As shown, the center point of the circle moves from the origin 8, thereby changing the length of the pointer 7 according to the wheel angle, thus periodically modulating the measured pulse frequency f by rotating one revolution. During accelerated motion, the pointer describes a circular spiral. The eccentricity is characterized by the movement of the spiral's center point from the origin 8.

[0026] The instantaneous wheel angle s(n) is calculated by accumulating the side angles, as previously described. The measured instantaneous pulse frequency is derived from the following... (4) And they are respectively assigned to segments I through IV. Preferably, the assignment is carried out as shown in the table below: I II II IV

[0027] This results in the complex pointer cos s(n) + I sin s(n) being represented in the complex plane such that the segment average value lies on the positive real axis, positive imaginary axis, negative real axis, or negative imaginary axis. This simplifies the assignment of segments to the appropriate modulation parameters. According to the current embodiment, the sensing wheel is divided into four segments of the same size (angle) from I to IV (quadrants), while according to another embodiment, the segment sizes may differ or there may be different numbers of segments, but at least three, and these segments then need to be weighted when assigned to the modulation parameters.

[0028] Preferably, the average wheel angle of the pulse frequency is assigned, that is, the above wheel angle calculation is corrected at the end of the time interval n as follows: (6).

[0029] The instantaneous pulse frequencies f1 to f4 measured at each traversal of each segment are preferably averaged. For this purpose, an arithmetic mean is performed, which is particularly simple to implement algorithmically; alternatively, other weighted or, for example, geometric mean is also possible. Thus, for example, segments K (K=1 to 4) at time point n A , …, n E After that, and then at time point n E Upper average frequency f k (n e For segment k formation: (7).

[0030] The average pulse frequencies of the opposite segments 1, 3 and 2, 4 can be assumed to be unbiased. Under the above configuration with constant rotational speed, (f1 + f3) / 2 and (f2 + f4) / 2 are both good estimates of the unbiased pulse frequencies.

[0031] Assuming linear acceleration (which is typically adequately approximated within half a revolution of the wheel), the average pulse frequency of adjacent segments is a good estimate of the unbiased instantaneous pulse frequency (f). k -1 + f k +1) / 2 can be assigned to the eccentric instantaneous frequency f. K .

[0032] Modulation parameter A R and A I The preferred segments are estimated by the ratio of the average pulse frequencies of the eccentric and non-eccentric segments when leaving the segment. Segmental transition IV->I Segmental transition I -> II Segmental transition II -> III Segmental transition III -> IV

[0033] Here, the average pulse frequency of the last measured pulse is used. Preferably, as shown above, the delay of a quarter turn is evaluated, thus using, for example, the average pulse frequency of the last passed segments II, III, and IV when leaving segment IV.

[0034] This method can be explained geometrically, such as in Figure 4 As shown in the diagram. The instantaneous pulse frequency plotted around the origin 8 corresponds to one of the four segments I to IV. Segments I to IV are... Figure 4 The values ​​are indicated by dashed lines and double arrows. For each segment I to IV, the average pulse frequencies f1 to f4 are calculated. The secant segments opposite to the average pulse frequencies, as shown by dashed lines, approximate the length of a circle radius, which represents the unbiased pulse frequency. The center point 9 of the pulse frequency circle can be determined from the orthogonal line bisected by the secant. The shifts of the origin 8 and the center point 9 relative to the circle radius correspond to the modulation parameters to be estimated in amplitude and phase, or real and imaginary parts.

[0035] Preferably, the evaluation described above is also smoothly connected downstream by means of filter 10, such as a PT1 filter, as in Figure 2 As shown, each has a 30% share of the new evaluation, so that the modulation parameters do not need to be completely re-estimated twice per revolution of detector wheel 2. Instead, the previous estimate is adapted in a favorable manner by evaluation. Therefore, the correction signal g is calculated by model 11 from the estimated modulation parameters and the instantaneously measured pulse frequency, such that in the correction signal f corr The modulation with a period of one rotation in (n) = f(n) – g(n) is compensated.

[0036] Then, from the signal that has been modulated and corrected in this way, the velocity v and acceleration a can be determined in a simple and conventional manner.

Claims

1. A method for determining the rotational frequency of a wheel, the wheel having a rotational speed sensor (1), the rotational speed sensor having a sensing wheel (2) associated with the wheel and a sensor element (3) associated with the sensing wheel (2), wherein, The sensing wheel (2) has pulse transmitters (4) evenly spaced apart from each other in its circumference. The sides (5) of the pulse transmitters are detected by sensor elements (3) to determine the rotation frequency of the sensing wheel (2). The characteristic feature is that, in order to compensate for the modulation of the rotation frequency caused by eccentricity, the sensing wheel (2) is divided into segments. For each segment, the pulse frequency (f1-f4) of the detected signal pulse is calculated and averaged. Based on the average pulse frequency (f1-f4), a modulation parameter (A) for correcting the rotation frequency is determined. R A I ), Wherein, the unbiased pulse frequencies (f1-f4) are obtained from the average pulse frequencies of segments that are diametrically opposed to each other, wherein the biased pulse frequencies are obtained from the average pulse frequencies of adjacent segments, and wherein the modulation parameter (A) R A I The ratio is determined by the ratio of the average pulse frequencies of the eccentric and uneccentric pulses.

2. The method according to claim 1, characterized in that, To average the pulse frequencies (f1-f4) of the corresponding segments, the pulse frequencies (f1-f4) of the corresponding segments are detected multiple times over a pre-defined time period or a pre-defined number of revolutions on the sensing wheel, and then averaged.

3. The method according to claim 1 or 2, characterized in that, The sensing wheel (2) is divided into segments of the same or different sizes.

4. The method according to claim 1 or 2, characterized in that, The modulation parameters (A) R A I This describes the magnitude and phase of the eccentricity of the sensing wheel.

5. The method according to claim 1 or 2, characterized in that, The modulation parameters (A) R A I It undergoes smoothing filtering.

6. The method according to claim 1, characterized in that, The method is used to determine the rotation frequency of the wheels of a motor vehicle.

7. The method according to claim 1 or 2, characterized in that, The sensing wheel (2) is divided into exactly four or more segments.

8. The method according to claim 5, characterized in that, The modulation parameters (A) R A I The filter is smoothed by means of PT1 filter (10).

9. A device for determining rotation frequency, comprising a rotation speed sensor (1), the rotation speed sensor having a sensing wheel (2) associated with the wheel and a sensor element (3) associated with the sensing wheel (2), wherein, The sensing wheel (2) has pulse transmitters (4) arranged uniformly or at intervals on its circumference, the sides (5) of which can be detected by the sensor element (3) to determine the rotation frequency, characterized by a controller specifically constructed for performing the method according to any one of claims 1 to 8 in normal use.

10. The apparatus according to claim 9, characterized in that, The device is used to determine the rotation frequency of the wheels of a motor vehicle.

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