Method for determining a rotational speed and / or a movement quantity derived from a rotational speed, computer program product, computer device

Abstract

The invention relates to a method for determining a rotational speed and / or a movement variable derived from a rotational speed, in particular wheel circumferential speed, by means of a rotational speed sensor (1) comprising a plurality of sensor elements (4) and an incremental encoder wheel (2), wherein time intervals between temporally adjacent measurement events of the rotational speed sensor (1) are determined, in particular continuously, wherein, depending on the determined time intervals, at least one estimated value (α̂, β ̂ ) for at least one duty cycle of a period comprising at least two of the measurement events, in particular one or a respective signal curve of the sensor elements (4), wherein, depending on the estimated value (α̂, β ̂ ) at least two of the time intervals are corrected, and the speed and / or the movement quantity are determined as a function of the corrected time intervals.

Description

[0001] The invention relates to a method for determining a rotational speed and / or a movement variable derived from a rotational speed, in particular a wheel circumferential speed, using a rotational speed sensor having multiple sensor elements and an incremental encoder wheel. Furthermore, the invention relates to a computer program product that implements the above-mentioned method when the computer program product is executed on a computer device. Furthermore, the invention relates to a computer device that is specifically configured to execute the computer program product or the above-mentioned method. State of the art

[0002] Methods of the type mentioned above are known from the prior art. For example, such methods are used in the automotive environment. For example, many functions implemented in an ABS / ESP control unit require a wheel circumferential speed (ω r) of a motor vehicle wheel as an input variable. The wheel circumferential speed is typically determined by measuring the rotational speed using a speed sensor.For example, German Patent Application DE 10 2015 213 572 A1 discloses a method for operating such a speed sensor with a signal generator ring having a plurality of magnetic elements evenly distributed over its circumference with alternating magnetic orientations, and with a signal receiver having a plurality of sensor elements for detecting the magnetic fields of the magnets. Information bits are generated as a function of the magnetic field strengths detected by the sensor elements and provided as a speed information signal. To increase the resolution of this speed sensor, output signals from three sensor elements of the speed sensor are linked together. Disclosure of the invention

[0003] The method according to the invention with the features of claim 1 is characterized in that time intervals between temporally adjacent measurement events of the speed sensor are determined, in particular continuously; that, depending on the determined time intervals, at least one estimated value for at least one duty cycle of a period comprising at least two of the measurement events, in particular one or a respective signal curve of the sensor elements, is determined; that, depending on the estimated value, at least two of the time intervals are corrected; and that, depending on the corrected time intervals, the speed and / or the movement variable are determined. This advantageously improves the measurement accuracy of the speed sensor, in particular, as mentioned above, in order to increase the accuracy when detecting a wheel circumferential speed of a wheel of a motor vehicle.The method can be advantageously used with the speed sensors based on the detection of magnetic field strengths mentioned above, but is not limited to them. Rather, it can be used with any type of speed sensor with an incremental encoder. A duty cycle is preferably a value between 0 and 1, related to the length of the period, and describes a relative temporal position of the measurement events or measurement pulses within the respective period. The invention is based on the finding that the duty cycle, as the relative position of the measurement events, deviates from its ideal value in practice, particularly due to non-uniform scanning of the incremental encoder wheel, and that taking its actual value into account through the inventive estimation improves measurement accuracy.As a result of the correction, the corrected time intervals correspond to those of an ideally uniform scanning of the incremental encoder wheel, in particular of a magnetic pole pair, so that systematic measurement errors, for example in the wheel circumferential speed signal derived from it, are minimized. In particular, the estimated value is continuously determined after a predetermined number of measurement events. In particular, the measurement events are generated depending on at least one signal curve of at least one of the sensor elements. In the specific example of a sinusoidal signal, in which zero crossings of the signal curve are recorded as measurement events, the estimated value has a target value of 1 / 2, which is the "average" zero crossing, based on one period of the sinusoidal signal, the position of which is thus described.Preferably, alternatively or additionally, reciprocals of the differences are corrected, and the speed and / or the movement quantity are determined based on the corrected reciprocals. The reciprocal is then a frequency.

[0004] According to a preferred development of the invention, it is provided that a predetermined signal value of a signal curve, in particular a zero crossing of a signal curve, is considered as the measurement event. By considering the signal value, the measurement event is characterized in a particularly advantageous and simple manner. Preferably, at least one, in particular all of the measurement events, are generated when a predetermined signal value of the respective signal curve is reached, for example, a zero crossing event.

[0005] Particularly preferably, a measurement event is determined as a function of the signal profiles of at least two of the sensor elements, in particular as a function of a differential signal profile of at least two of the sensor elements. This allows measurement events to be determined in a particularly robust manner. For example, a zero crossing of the corresponding signal profile is considered as a measurement event.

[0006] According to a preferred development of the invention, at least one deviation value of the duty cycle from a predetermined ideal value and / or at least one reference value characterizing the duty cycle is determined as a function of at least three consecutive time intervals, and the estimated value is determined as a function of the deviation value and / or reference value. By determining and considering the deviation value and / or reference value in this way, a particularly advantageously simple determination of the estimated value is ensured.

[0007] It is particularly preferred that the determined deviation value or reference value is filtered before determining the estimated value, in particular by means of a discrete PT1 filter with a predetermined initialization value and a predetermined gain factor, wherein, for filtering, at least one difference between two consecutive time intervals assigned deviation values ​​or reference values ​​is determined. Such filtering of the deviation value or reference value results in the advantage that the accuracy in determining the estimated value is further improved.

[0008] According to a preferred development of the invention, it is provided that at least one amount, in particular a plurality of amounts, of the difference between two consecutive time intervals assigned estimated values, deviation values ​​and / or reference values ​​is determined, that depending on the amount or the plurality of amounts it is determined whether consecutive estimated values ​​converge, that the time intervals are only corrected if convergence has been detected, and / or that a convergence rate is determined and the time intervals are corrected weighted by the convergence rate. By determining and taking the convergence into account, it is advantageously ensured that the estimated values ​​are determined robustly. If the estimated values ​​do not converge, the method is aborted in particular, or the time intervals are not corrected. Alternatively or additionally, a correction weighted by the convergence rate is carried out.

[0009] It is particularly preferably provided that the amount, the plurality of amounts and / or an average of the plurality of amounts is compared with a predetermined first threshold value to detect convergence, that convergence is detected if the threshold value, in particular of a predetermined number of amounts or averages, is undershot, and / or that a detected convergence is rejected if a second predetermined threshold value, which is higher than the first threshold value, is at least reached, in particular exceeded, by at least one of the amounts and / or averages, and / or a third predetermined threshold value is at least reached, in particular exceeded, by at least one of the time intervals. This results in the advantage that actual convergences are correctly detected.

[0010] According to a preferred development of the invention, at least two signal profiles are generated, in particular from differently calculated sensor signals from at least two sensor elements of the speed sensor, successive measurement events are assigned to different signal profiles, and estimated values ​​for one duty cycle are determined for each of the signal profiles. This advantageously ensures that a reliable distinction is made between the signal profiles and that only estimated values ​​attributable to the respective signal profile are determined.

[0011] Particularly preferably, at least one estimated value is determined for at least one relative offset of two consecutive measurement events associated with different signal waveforms, and the time intervals are corrected as a function of the estimated value. Taking the estimated offset into account results in the advantage of further improving the accuracy of correcting the time intervals. The estimated offset is thus determined in addition to the duty cycle estimated value and taken into account in the correction.

[0012] According to a preferred development of the invention, a convergence rate and / or a deviation value of the respective duty cycle from a predetermined ideal value for the estimated values ​​is determined, and that, depending on the determined convergence rates and / or deviation values, a duty cycle is assigned to one of the at least two different signal profiles. This advantageously ensures that the corresponding estimated values ​​and thus the underlying measurement events are correctly classified, i.e., assigned to the correct signal profile.

[0013] Particularly preferably, the duty cycle associated with the estimated values ​​with the higher convergence rate and / or the smaller deviation value is assigned to a first signal curve, and the respective other duty cycle is assigned to a second signal curve, in particular by swapping the estimated values. This ensures a particularly simple classification of the estimated values ​​and the underlying measurement events.

[0014] According to a preferred development of the invention, measurement events associated with one of the signal curves are discarded if a fourth predetermined threshold value is undershot for at least one of the time intervals. This advantageously ensures that the computational effort of the method is reduced above a certain threshold value, for example, by ignoring corresponding measurement events above a certain vehicle speed, while simultaneously ensuring the required measurement accuracy.

[0015] It is particularly preferred that the incremental encoder wheel is magnetic and that at least three sensor elements, in particular Hall sensors or magnetoresistive sensors, are arranged equidistantly in a row, wherein a difference between sensor signals from two, in particular from the two outer sensor elements, is generated as a first signal profile, and a difference between one of the sensor signals of one, in particular the middle, of the sensor elements and an average value of sensor signals from two other, in particular the two outer, sensor elements is generated as a second signal profile. This results in the advantage that the accuracy in determining the movement variable is further improved. In this respect, virtual additional signals are generated between two measurement events.In particular, a zero-crossing event of a periodic signal curve, in particular a magnetic flux density, corresponding in particular to an arc length of a magnetic pole pair, is specified as the corresponding signal value. For example, Hall sensor elements are used, with zero-crossings of the magnetic flux density curves of the sensor elements being output as measurement events, i.e., two per magnetic pole pair. To increase accuracy, the aforementioned quasi-virtual additional measurement events are then generated, which are based on differential signals from the Hall sensor elements.

[0016] The computer program product according to the invention for execution on a computer device with the features of claim 14 is characterized in that, when used as intended, it executes the method according to the invention. This results in the advantages already mentioned. Preferably, a data carrier with the computer program product according to the invention stored thereon is provided.

[0017] The computer device with the features of claim 15 is characterized in that the computer device is specifically configured to perform the method according to the invention or to execute the computer program product according to the invention. This also results in the advantages already mentioned above. Preferably, the computer device is a control device associated with a motor vehicle, in particular arranged in the motor vehicle.

[0018] Further preferred features and combinations of features emerge from the above description and from the claims. The invention is explained in more detail below with reference to the drawings. Fig. 1 a speed sensor, Fig. 2 first signal curve diagrams, Fig. 3 a method for determining a speed and / or a movement quantity derived from a speed, and Fig. 4 a second signal curve diagram.

[0019] Fig. 1 shows a previously known speed sensor 1, such as is used, for example, to determine a wheel circumferential speed ω r, which can then, as mentioned above, serve as an input variable for ABS / ESP control. The speed sensor 1 is designed to detect (measurement) events, for example magnetic flux changes, of an encoder or incremental encoder wheel 2 rotating with a wheel and to transmit them to a computer device 3, in this case a control unit. The computer device 3 is in turn designed to determine a time interval Δt(i) between the i-th event and the preceding, i-1-th event, in particular with the aid of a high-frequency counter (typically 10 MHz), and to estimate a current wheel speed and, derived therefrom, the wheel circumferential speed as a function thereof.

[0020] Typically, magnetic multipole wheels are used as encoders or incremental encoder wheels 2. The incremental encoder uses several, in this case three, equidistant in a row (in the Fig. 1 shown one above the other). The sensor elements 4 are designed in particular as Hall sensors, AMR sensors, GMR sensors and / or TMR sensors and are designed to detect the magnetic field emanating from the incremental encoder wheel 2, for example in a tangential direction, and to output a measurement variable dependent thereon, for example a Hall voltage.

[0021] The measurement events transmitted to the computer device 3 are derived from the measured variables of the sensor elements 4. For example, a signal zero crossing of the magnetic flux density is used as a measurement event. When the wheel moves, exactly two events occur for each magnetic pole pair of the incremental encoder wheel 2, along the arc length D. To reduce offset errors of the zero position, for example due to temperature effects, the difference signal of the signals of the two outer sensor elements 4, here referred to as A and B (in the Fig. 1 corresponding to the lower and upper sensor element 4) is considered as a first signal curve. The signal of the middle of the sensor elements 4, here designated as M (in the Fig. 1 corresponding to the middle sensor element 4), is used, for example, to determine the direction of rotation.

[0022] Ideally, the magnetic poles within the pole pair have the same length and the zero position of the differential signal also exhibits no offset error, then the events occur at a spatial distance of D / 2. In practice, the relative position of the events, referred to as duty cycle α, deviates from the ideal value of ½, typically by ±5% (the duty cycle is therefore a value between 0 and 1).

[0023] In an ideal incremental encoder wheel 2, each pole pair has the same arc length D, meaning that all pole pairs are evenly distributed over the encoder circumference. Due to manufacturing reasons, pitch errors occur in practice; typical values ​​here are up to ±5%. The resulting wheel-periodically recurring patterns are learned and compensated for, in particular, by evaluating the sequence of events in the computer device 3. A corresponding method is described, for example, in "Increasing signal accuracy of automotive wheel-speed sensors by on-line learning," R. Schwarz, O. Nelles, P. Scheerer, and R. Isermann in American Control Conference, Albuquerque, New Mexico, 1997. Any such irregularities between the pole pairs of an encoder wheel (pitch errors) are preferably considered non-existent or sufficiently compensated for in the method to be described below.

[0024] Recent developments, especially in the field of automated parking, require higher distance resolution in the sense of a higher number of events per wheel revolution. Encoder wheels with a significantly larger number of pole pairs are not practical for technical and economic reasons. However, it is possible to increase the number of measurement events per pole pair, for example, by considering additional signal curves from combined individual signals. In particular, an additional, second signal curve is derived from the zero crossing of the differential signal of the middle sensor element M and an average signal value of the two outer sensor elements A and B.

[0025] The relative position of the now four events per pole pair can be described using three independent variables. The following are used to describe the existing duty cycle α of the measurement events of the first signal waveform (ideal value ½), the duty cycle β of the measurement events of the second signal waveform (ideal value ½), and the relative shift γ of the measurement events as the offset of the signal waveforms from one another (ideal value ¼). This does not represent a limitation to the invention; differently selected independent variables can always be transformed into the three selected ones.

[0026] In general, the statistical properties of the measurement events of the second waveform as intermediate events differ from those of the measurement events of the first waveform as standard events. For example, the different combination of the measured variables results in a Fig. 2 indicated sensor element distance d to the arc length D, typically smaller amplitude of the difference signal M-(A+B) / 2 and thus for a higher sensitivity in the temporal determination of the position of the corresponding measurement events, for example with regard to offset errors of the zero position and / or a tilting of the incremental encoder with the sensor elements 4 in the magnetic field of the incremental encoder wheel 2 as encoder.

[0027] This manifests itself in the measurement as an increased scatter of β compared to α. Due to the spatial and temporal sampling of the magnetic field, where the spatial component now becomes relevant, the accuracy of the geometric center position of the sensor element M also influences the duty cycle value β of the intermediate events.

[0028] These fundamental relationships are in the Fig. 2. In the Fig. 2, a section of the incremental encoder wheel 2 is projected as an encoder with alternating magnetic north pole N and magnetic south pole S. Each of these pole pairs has the arc length D. Below, in a corresponding diagram, exemplary, correspondingly sinusoidal, curves of the magnetic flux density B in the far field of the encoder at the three sensor elements A, M and B, when the encoder is moved to the right, are plotted against the encoder rotation angle φ. In another corresponding diagram, the described used difference signals AB and M-(A+B) / 2 are plotted against the rotation angle φ. Each arc length D comprises one period of the corresponding signal, and thus two zero-crossing events for each of the signal curves.

[0029] In the following, with reference to Fig. 3 describes an advantageous method for determining a speed and / or a movement quantity derived from a speed using a speed sensor, in particular using the speed sensor 1 described above. Fig. 3 illustrates the method using a flowchart. In particular, the method ensures that the accuracy in determining the corresponding variables is improved by taking into account the deviation of the duty cycles from their corresponding ideal values, as described above. The method is carried out, in particular, using the computer device 3.

[0030] In a step S1, the method begins by determining corresponding time intervals between temporally adjacent measurement events of the speed sensor, in particular continuously. Preferably, a predetermined signal value of a signal curve, in particular a zero crossing of a signal curve, is taken into account as the measurement event. Particularly preferably, a measurement event is determined as a function of the signal curves of at least two of the sensor elements, in particular as a function of a differential signal curve of at least two of the sensor elements. For example, zero crossings of the two are taken into account with reference to the Fig. 1 and Fig. 2, which result from correspondingly linked differential signals of the sensor elements 4. However, for the method according to the invention, it is generally sufficient if only one signal curve, for example the first signal curve as the differential signal of the sensor elements A and B, is taken into account accordingly.

[0031] For example, at least three sensor elements, in particular Hall sensors or magnetoresistive sensors, are arranged equidistantly in a row, as in the Fig. 1 and Fig. 2, wherein a first signal waveform is generated by a difference between sensor signals from two, in particular from the two outer sensor elements, and a second signal waveform is generated by a difference between one of the sensor signals from one, in particular the middle, sensor elements and an average value of sensor signals from two other, in particular the two outer, sensor elements. In particular, but not necessarily, the incremental encoder wheel is magnetic. Thus, the method can also be advantageously applied to optical sensing or another type of event transmission or measurement.

[0032] In a subsequent step S2, at least one estimated value for at least one duty cycle of a period comprising at least two of the measurement events, in particular one or a respective signal curve of the sensor elements, is determined as a function of the determined time intervals.

[0033] Regarding the Fig. 1 and Fig. 2, for example, the relative position within the magnetic pole pair in the form of the duty cycles α and β as well as the relative displacement γ is then estimated from the measured time intervals of all measurement events detected by the speed sensor, and, based on this, the corresponding measurement events are classified based on the duty cycle estimates and their convergence speed, i.e. assigned to their respective signal curve, as will be described in detail below.

[0034] In the Fig. 4 shows a corresponding example of the speed sensor 1 described above with the three sensor elements 4. The Fig. 4 shows the first and second signal curves plotted over a larger range of the rotation angle φ, so that of the four different events per arc length D, two similar measurement events (of two consecutive arc lengths D or periods) are shown, each of which has a distance D 1 , D 2 , D 3 , D 4 from each other. Also shown are the duty cycle α of the measurement events of the first signal waveform, the duty cycle β of the measurement events of the second signal waveform, and the relative offset γ, as described above.

[0035] In the case of the Fig. 1, Fig. 2 and Fig. In the specific embodiment described in Figure 4, the relative position of the events within the arc length D of a magnetic pole pair is estimated from the continuous sequence of measured time intervals between measurement events Δt(i). In the case of doubled resolution, i.e., taking into account the second signal curve, it is assumed that each pole pair is always characterized by four adjacent time intervals, meaning that, in particular, no measurement event is detected too many or too few.

[0036] For this purpose, at least one deviation value of the duty cycle from a predetermined ideal value and / or at least one reference value characterizing the duty cycle is preferably determined as a function of at least three consecutive time intervals, and the estimated value is determined as a function of the deviation value and / or reference value.

[0037] In the simplest case, only one signal curve, for example the first signal curve (AB) from Fig. 2. The estimation of the then one duty cycle value α̂ is carried out in particular (first instance) after every second event (i = 2n with n ∈ ℕ): α^(n)=Δt(2n−1)Δt(2n−1)+Δt(2n)

[0038] Alternatively, the deviations α̃ from the ideal value are first estimated: α˜(n)=Δt(2n−1)Δt(2n−1)+Δt(2n)−12

[0039] Then, depending on this, the estimated values ​​α̂ are determined: α^(n)=12+α˜(n)

[0040] Preferably, at least two signal profiles are generated, in particular from differently offset sensor signals from at least two sensor elements of the speed sensor, as described above, successive measurement events are assigned to different signal profiles, and estimated values ​​for a respective duty cycle are determined for each of the signal profiles. In this case, preferably, at least one estimated value is additionally determined for at least one relative offset of two successive measurement events assigned to different signal profiles.

[0041] In the concrete embodiment, in particular (first instance), the duty cycle α̂ and β̂ and the relative offset γ̂ are estimated after every fourth event (i = 4n with n ∈ ℕ): α^(n)=Δt(4n−3)+Δt(4n−2)∑k=03Δt(4n−k) β^(n)=Δt(4n−2)+Δt(4n−1)∑k=03Δt(4n−k) γ^(n)=Δt(4n−3)∑k=03Δt(4n−k)

[0042] The corresponding procedure can be generalized for further resolution increases. For example, if 8 events per arc length, especially of a magnetic pole pair, are planned, the estimation of the then four duty cycle values α^,β1^,β2^ and β3^ and the relative offset values γ1^,γ2^ and γ3^ after every eighth event (i = 8n with n ∈ ℕ) by: α^(n)=∑k=47Δt(8n−k)∑k=07Δt(8n−k) β1^(n)=∑k=36Δt(8n−k)∑k=07Δt(8n−k) β2^(n)=∑k=25Δt(8n−k)∑k=07Δt(8n−k) β3^(n)=∑k=14Δt(8n−k)∑k=07Δt(8n−k) γ1^(n)=Δt(8n−7)∑k=07Δt(8n−k) γ2^(n)=Δt(8n−6)∑k=07Δt(8n−k) γ3^(n)=Δt(8n−5)∑k=07Δt(8n−k)

[0043] Returning to the concrete example, in an alternative representation the deviations α̃, β ̃, γ̃ are estimated from the respective ideal values ​​(analogously, a generalization is possible, for example, to the 8 events mentioned above): α˜(n)=Δt(4n−3)+Δt(4n−2)∑k=03Δt(4n−k)−12 β˜(n)=Δt(4n−2)+Δt(4n−1)∑k=03Δt(4n−k)−12 γ˜(n)=Δt(4n−3)∑k=03Δt(4n−k)−14

[0044] Then, depending on this, the estimated values ​​â, β ̂ , γ̂ is determined: α^(n)=12+α˜(n) β^(n)=12+β¯(n) γ^(n)=14+γ˜(n) In particular, the determined deviation value or reference value is filtered before the estimated value is determined, in particular by means of a discrete PT1 filter with a predetermined initialization value and a predetermined gain factor, wherein for filtering purposes, in particular at least one difference between two consecutive time intervals of assigned deviation values ​​or reference values ​​is determined.

[0045] In the simplest case, only one signal curve is used, for example the first signal curve (AB) from Fig. 2. The deviations from the ideal values ​​are then preferably filtered (second form), in particular in the form of a discrete PT1 filter with the initialization value α̂(0) = 0 and the gain factor k (for example, k = 3%): Δα˜(n)=Δt(2n−1)Δt(2n−1)+Δt(2n)−12−α˜(n−1) α˜(n)=α˜(n−1)+k⋅Δα˜(n)

[0046] In the concrete embodiment, in particular (second embodiment) the deviations from the ideal values ​​are filtered for both signal curves (analogously, a generalization is possible, for example, to the 8 events mentioned above), in particular in the form of a discrete PT1 filter with the initialization values ​​α̃(0) = β ̃ (0) = γ̃(0) = 0 and the gain factor k (for example k = 3%): Δα˜(n)=Δt(4n−3)+Δt(4n−2)∑k=03Δt(4n−k)−12−α˜(n−1) α˜(n)=α˜(n−1)+k⋅Δα˜(n) Δβ˜(n)=Δt(4n−2)+Δt(4n−1)∑k=03Δt(4n−k)−12−β¯(n−1) β¯(n)=β¯(n−1)+k⋅Δβ˜(n) Δγ˜(n)=Δt(4n−3)∑k=03Δt(4n−k)−14−γ˜(n−1) γ˜(n)=γ˜(n−1)+k⋅Δγ˜(n)

[0047] An advantageously increased estimation quality, in particular when the measured time intervals change due to speed changes, is provided by a further preferred calculation rule (third form), in which a reference value in the denominator is divided in half between those two pole pairs which result from the duration of the measured pole and its predecessor or successor, and based on this, a corresponding filtering is carried out.

[0048] In the simplest case, only one signal curve is used, for example the first signal curve (AB) from Fig. 2. The result is: Δα˜(n)=Δt(2n−1)2⋅(Δt(2n−2)+Δt(2n−1))−Δt(2n)2⋅(Δt(2n−1)+Δt(2n))−α˜(n−1)

[0049] For the concrete example with the consideration of two signal curves, the following results (analogously, a generalization is possible, for example, to the 8 events mentioned above): Δα˜(n)=Δt(4n−3)+Δt(4n−2)2⋅∑k=25Δt(4n−k)−Δt(4n−1)+Δt(4n)2⋅∑k=03Δt(4n−k)−α˜(n−1) Δβ˜(n)=Δt(4n−2)+Δt(4n−1)2⋅∑k=14Δt(4n−k)−Δt(4n−4)+Δt(4n−3)2⋅∑k=36Δt(4n−k)−β˜(n−1) Δγ˜(n)=Δt(4n−3)2⋅∑k=36Δt(4n−k)−Δt(4n−3)2⋅∑k=03Δt(4n−k)−γ˜(n−1)

[0050] Particularly preferably, a convergence rate and / or a deviation value of the respective duty cycle from a predetermined ideal value for the estimated values ​​is determined, and depending on the determined convergence rates and / or deviation values, a duty cycle is assigned to one of the at least two different signal profiles. In particular, the duty cycle assigned to the estimated values ​​with the higher convergence rate and / or the smaller deviation value is assigned to a first signal profile, and the respective other duty cycle is assigned to a second signal profile, in particular by swapping the estimated values.

[0051] For example, if the type of event is unknown in the specific example, the assignment of the estimated duty cycle to the curves is initially arbitrary. If one of the two duty cycle estimates α̂(n) or β ̂(n) is significantly faster than the other, for example, if the number of threshold violations upon detection of convergence is more than twice as high, then this is classified as the duty cycle of the first signal waveform, and the other as that of the second signal waveform. This is based on the assumption of a higher degree of scatter in the temporal determination of the measurement events of the second signal waveform.

[0052] Alternatively or additionally, the duty cycle estimate α̂(n) or β ̂(n), which is closer to the ideal value of 1 / 2, is classified as the duty cycle of the first waveform, and the other as that of the second waveform. This is based on the assumption of poorer offset alignment of the measurement events of the second waveform. The two criteria can be combined in various ways; preferably, classification is based first on the convergence speed and, if unambiguous, subsequently on the convergence value.

[0053] If the initial, arbitrary assignment of the estimated duty cycle to the event types turns out to be incorrect during classification (β ̂ (n) is classified as the duty cycle of the first signal waveform), the estimated values ​​are preferably swapped: α^new(n)=1−β^(n) β^new(n)=α^(n) γ^new(n)=α^(n)−γ^(n)

[0054] Even if the type of events is known, the corresponding classification based on statistical signal properties is still advantageous for plausibility checks and / or monitoring. The classification can be applied analogously to the eight events mentioned above and generalized.

[0055] In particular, measurement events assigned to one of the signal waveforms are discarded if a fourth predefined threshold value is undershot for at least one of the time intervals. In particular, the calculation of the movement quantity can be performed only on the basis of the measurement events of the first signal waveform classified as such, and explicitly without using the measurement events of the second signal waveform. This advantageously reduces computational effort and / or signal noise in the calculated output signal.

[0056] Preferably, the estimation is aborted at very long time intervals, which, for example, are close to a wheel standstill when the speed sensor is used on a motor vehicle wheel, in order to avoid the special case of a reversal of the direction of rotation, in which the assumption of four measurement events per pole pair may not apply. In particular, a temporary pause of the estimation is performed, for example, to temporarily reduce the computational load or under expected poor convergence conditions, such as sharp speed changes or driving on unpaved roads when used in a motor vehicle.

[0057] After an interruption of the estimation, as described above, in particular near wheel standstill, a new initialization preferably takes place in order to achieve a faster convergence of the estimated values ​​in the event of a reversal of the direction of rotation.

[0058] In a step S3, at least two of the time intervals are corrected depending on the estimated value(s), so that the corrected time intervals correspond to those of an ideally uniform scanning of the incremental encoder wheel, in particular with respect to the Fig. 1 and Fig. 2 of a magnetic pole pair, and systematic measurement errors in the resulting wheel circumferential speed signal are minimized.

[0059] In the simplest case, only one signal curve is used, for example the first signal curve (AB) from Fig. 2. Then, in particular, the estimated value α̂ is continuously used to correct the measured time differences Δt(i), so that the corrected time differences Δt˜(i) which correspond to an ideally uniform scanning of the magnetic pole pair: Δt(i)=Δt(i)⋅{12⋅(1−α^),i=2n12⋅α^,i=2n−1

[0060] In the concrete embodiment, the estimated values ​​α̂, β ̂ and γ̂ are preferably used continuously to correct the measured time differences Δt(i) (the following considerations can be applied and generalized analogously, for example, to the 8 events mentioned above): Δt˜(i)=Δt(i)⋅{14⋅(1−β^−γ^),i=4n14⋅(β^−α^+γ^),i=4n−114⋅(α^−γ^),i=4n−214⋅γ^,i=4n−3

[0061] In an alternative approximation for sufficiently small deviations from the ideal values, the correction can also be applied only after the time difference reciprocals have been calculated, so that for the subsequent speed estimation when only considering one signal curve, the following corrected pulse frequency sequence is used: f˜(i)=2Δt(i)⋅{α^,i=2n1−α^,i=2n−1

[0062] Analogously, in the specific embodiment, the following corrected pulse frequency sequence is used when considering the two signal curves: f˜(i)=4Δt(i)⋅{1−β^−γ^,i=4nβ^−α^+γ^,i=4n−1α^−γ^,i=4n−2γ^,i=4n−3

[0063] When it comes to determining the movement quantity, especially wheel speed or wheel circumferential speed, the advantages of higher-resolution incremental encoders are essentially limited to low speeds. Due to the incremental encoder principle, the information age of the speed signal—the time interval between the validity time between two events and the availability time after the second event—increases reciprocally with decreasing speed.

[0064] The doubling of resolution provided in the specific embodiment halves the information age of the speed signal. This is relevant in the speed range of, for example, less than one event per 5 ms. Furthermore, a relative error such as a not yet converged, and therefore uncorrected, duty cycle of the second signal waveform (at low speeds) has only a minor impact on the absolute accuracy of a speed estimate.

[0065] At speeds above this range, the halving of the information age is negligible; here, a possible accuracy disadvantage of the intermediate pulses as measurement events of the second signal curve as well as the disadvantage of a computational effort that increases linearly with the number of events outweighs the disadvantage.

[0066] Preferably, the estimation of the movement quantity is therefore carried out for higher speeds as described above, explicitly without using the intermediate pulses classified as such, i.e., only at every second event and by accumulating the measured time differences over the intermediate pulse with the following alternative pulse frequency sequence: f˜fast(i)=4Δt(i)+Δt(i−1)⋅{1−α^,i=4nα^,i=4n−2

[0067] Particularly preferably, at least one amount, in particular a plurality of amounts, of the difference between two consecutive time intervals associated with estimated values, deviation values, and / or reference values ​​is determined beforehand. In particular, depending on the amount or the plurality of amounts, it is then determined whether consecutive estimated values ​​converge, and the time intervals are only corrected if convergence has been detected. Alternatively or additionally, a convergence rate is determined, and the time intervals are corrected weighted by the convergence rate.

[0068] In this case, the amount, the plurality of amounts and / or an average of the plurality of amounts are preferably compared with a predetermined first threshold value to detect convergence, and convergence is detected when the threshold value, in particular of a predetermined number of amounts or average values, is undershot.

[0069] Alternatively or additionally, a detected convergence is rejected if a second predetermined threshold value, which is higher than the first threshold value, is at least reached, in particular exceeded, by at least one of the amounts and / or mean values, and / or a third predetermined threshold value is at least reached, in particular exceeded, by at least one of the time intervals.

[0070] In the simplest case, only one signal curve is used, for example the first signal curve (AB) from Fig. 2. Then, in particular, the amount of the change in the estimated value |α̂(n) - α̂(n - 1) | or, in the second and third instances, alternatively, the amount of the change difference |Δα˜(n)| concluded that the estimate converges.

[0071] In the concrete embodiment, when considering both signal curves, in particular the amount of the change in the estimated value |α̂(n) - α̂(n - 1)|, |β ̂ (n) - β ̂(n - 1)| or |γ̂(n) - γ̂(n - 1)| or in the second and third form alternatively from the change difference amount |Δα˜(n)|,|Δβ˜(n)|or|Δγ˜(n)| on the convergence of the respective estimate.

[0072] For a particularly low-computational effort implementation, each magnitude is preferably compared with a threshold value of, for example, 0.1%, and convergence is detected if the value continuously falls below the threshold across, for example, 100 multipoles. Alternatively, averaging / filtering of the magnitude values ​​and corresponding threshold comparisons of the mean value are provided.

[0073] Preferably, as described, the measured time intervals are corrected only using converged estimates. Alternatively, a correction weighted by the convergence rate is provided. A detected convergence is rejected, in particular, if, for example, large time differences (near standstill) exist, or if the value exceeds a second, higher threshold of, for example, 0.5%, for example due to increased signal noise when driving on unpaved roads.

[0074] Finally, in a step S4, the rotational speed and / or the movement quantity are determined as a function of the corrected time intervals, for example, the wheel circumferential speed, as described above. The method is preferably carried out continuously.

[0075] In particular, in addition to duty cycle correction, further signal processing steps such as reciprocal value formation, pitch error correction, anti-aliasing filtering, sampling rate conversion, consideration of the number of multipoles per encoder, and wheel circumference are performed to determine the duty cycle. Preferably, the duty cycle correction according to the invention is initially performed in combination with reciprocal value formation; for all subsequent steps, one of the described pulse frequency sequences is preferably used. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2015 213 572 A1

[0002] Zitierte Nicht-Patentliteratur

[0000] Increasing signal accuracy of automotive wheel-speed sensors by on-line learning“, R. Schwarz, O. Nelles, P. Scheerer, and R. Isermann in American Control Conference, Albuquerque, New Mexico, 1997

[0023]

Claims

[1] Method for determining a rotational speed and / or a movement variable derived from a rotational speed, in particular wheel circumferential speed, by means of a rotational speed sensor (1) having a plurality of sensor elements (4) and an incremental encoder wheel (2), - wherein time intervals between temporally adjacent measurement events of the speed sensor (1) are determined, in particular continuously, - where, depending on the determined time intervals, at least one estimated value (α̂, β ̂ ) is determined for at least one duty cycle of a period comprising at least two of the measurement events, in particular one or a respective signal curve of the sensor elements (4), - where depending on the estimated value (α̂, β ̂ ) at least two of the time intervals are corrected, and - whereby the speed and / or the movement quantity are determined depending on the corrected time intervals. [2] Method according to claim 1, characterized by that a given signal value of a signal curve, in particular a zero crossing of a signal curve, is taken into account as a measurement event. [3] Method according to one of the preceding claims, characterized by that a measurement event is determined as a function of the signal curves of at least two of the sensor elements (4), in particular as a function of a difference signal curve of at least two of the sensor elements (4). [4] Method according to one of the preceding claims, characterized by that at least one deviation value (α̃, β ̃ ) of the duty cycle from a predetermined ideal value and / or at least one reference value characterizing the duty cycle is determined as a function of at least three consecutive time intervals, and that the estimated value (α̂, β ̂ ) depending on the deviation value (α̃, β ̃ ) and / or reference value is determined. [5] Method according to claim 4, characterized by that the determined deviation value (α̃, β ̃ ) or reference value before determining the estimated value (α̂, β ̂ ), in particular by means of a discrete PT1 filter with a predetermined initialization value and a predetermined gain factor, wherein for filtering purposes, in particular at least a difference between two successive time intervals associated deviation values ​​(α̃, β ̃ ) or reference values ​​are determined. [6] Method according to one of the preceding claims, characterized by that at least one amount, in particular a plurality of amounts, corresponds to the difference between two consecutive time intervals assigned estimated values ​​(α̂, β ̂ ), deviation values ​​(α̃, β ̃ ) and / or reference values, that depending on the amount or the plurality of amounts it is determined whether successive estimated values ​​(α̂, β ̂) converge, that the time intervals are only corrected when convergence has been detected, and / or that a convergence rate is determined and the time intervals are corrected weighted by the convergence rate. [7] Method according to claim 6, characterized by that the amount, the plurality of amounts and / or an average of the plurality of amounts is compared with a predetermined first threshold value to detect convergence, that convergence is detected when the threshold value, in particular of a predetermined number of amounts or averages, is undershot, and / or that a detected convergence is rejected when a second predetermined threshold value, which is higher than the first threshold value, is at least reached, in particular exceeded, by at least one of the amounts and / or averages, and / or a third predetermined threshold value is at least reached, in particular exceeded, by at least one of the time intervals. [8] Method according to one of the preceding claims, characterized by that at least two signal curves are generated, in particular from differently offset sensor signals from at least two sensor elements (4) of the speed sensor (1), that successive measurement events are each assigned to different signal curves, and that for each of the signal curves estimated values ​​(α̂, β ̂ ) for each duty cycle. [9] Method according to one of the preceding claims, characterized by that at least one estimated value (γ̂) is determined for at least one relative offset of two successive measurement events assigned to different signal curves, and that the time intervals are corrected as a function of the estimated value (γ̂). [10] Method according to one of the preceding claims, characterized by that a convergence rate and / or a deviation value (α̃, β ̃, γ̃) of the respective duty cycle from a given ideal value for the estimated values ​​(α̂, β ̂ , γ̂) is determined, and that depending on the determined convergence rates and / or deviation values ​​(α̃, β ̃ , γ̃) a duty cycle is assigned to one of the at least two different signal curves. [11] Method according to claim 10, characterized by that the estimated values ​​(α̂, β ̂ , γ̂) with the higher convergence rate and / or the smaller deviation value (α̃, β ̃ , γ̃) is assigned to a first signal curve, and the other duty cycle is assigned to a second signal curve, in particular by exchanging the estimated values ​​(α̂, β ̂ , γ̂). [12] Method according to one of the preceding claims, characterized bythat measurement events assigned to one of the signal curves are discarded if a fourth predetermined threshold value is undershot by at least one of the time intervals. [13] Method according to one of the preceding claims, characterized by that the incremental encoder wheel is magnetic and that at least three sensor elements (4), in particular Hall sensors or magnetoresistive sensors, are arranged equidistantly in a row, wherein a difference between sensor signals from two, in particular from the two outer sensor elements (4) is generated as a first signal profile, and a difference between one of the sensor signals of one, in particular the middle, of the sensor elements (4) and an average value of sensor signals from two other, in particular the two outer, sensor elements (4) is generated as a second signal profile. [14] Computer program product for execution on a computer device (3), characterized bythat the computer program product, when used as intended, carries out a method according to one of the preceding claims. [15] Computer device (3), in particular control device for a motor vehicle, characterized by that the computer device (3) is specially adapted to execute the computer program product according to claim 14.

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