DE102011078861A1 - Method for determining absolute position of e.g. crank shaft, of internal combustion engine of motor car, involves determining absolute position of rotatable element based on absolute position of reference pattern - Google Patents

Abstract

The method involves determining predetermined number of segment lengths for detected segments as a segment length pattern. Deviation information is determined based on the pattern and provided reference patterns, where each reference pattern comprises a sequence of predetermined number of segment lengths, and is assigned to an absolute position. An absolute position of a rotatable element i.e. shaft (3), is determined based on the absolute position of the reference pattern, where the deviation information of the reference pattern indicates a slight difference to the segment length pattern. Independent claims are also included for the following: (1) a device for determining an absolute position of rotatable element (2) an arrangement comprising a drive motor (3) a computer program product comprising a set of instructions to perform a method for determining an absolute position of rotatable element.

Description

Technical area

The invention generally relates to the field of position detection of a rotatable element, in particular a position detection of a crankshaft or a camshaft of an internal combustion engine in a motor vehicle.

State of the art

To determine an absolute position of a shaft, z. As a crankshaft of an internal combustion engine, usually a position sensor is used with a donor disk having segments with different segment lengths. The sequence of segments is irregular and unique to the position of the shaft. The encoder disk is read out by means of a sensor element, the passage of the segments past the sensor element being converted into electrical encoder signals upon rotation of the shaft. The course of the encoder signal is due to the different lengths of the segments characteristic of the position of the shaft. By evaluating the encoder signal can therefore be deduced the position of the shaft.

Disclosure of the invention

According to the invention, a method for determining an absolute position of a rotatable element according to claim 1 and a device, an arrangement and a computer program product according to the independent claims are provided.

Further advantageous embodiments of the present invention are specified in the dependent claims.

• – Erfassen eines Gebersignals basierend auf einer Bewegung einer Geberscheibe eines Positionsgebers, wobei die Geberscheibe Segmente unterschiedlicher Länge und einer für die absolute Position charakteristischen Abfolge aufweist;
• – Bestimmen einer vorbestimmten Anzahl von Segmentlängen für aufeinander folgend erfasste Segmente als ein Segmentlängenmuster;
• – Ermitteln jeweils einer Abweichungsangabe abhängig von dem Segmentlängenmuster und einem von mehreren bereitgestellten Referenzmustern, wobei jedes Referenzmuster eine Abfolge der vorbestimmten Anzahl von Segmentlängen umfasst und einer absoluten Position zugeordnet ist;
• – Bestimmen der absoluten Position des drehbaren Elements abhängig von der absoluten Position desjenigen Referenzmusters, dessen Abweichungsangabe den geringsten Unterschied zu dem Segmentlängenmuster angibt.

According to a first aspect, a method for determining an absolute position of a rotatable element is provided. The method comprises the following steps:

• Detecting an encoder signal based on movement of a donor disk of a position sensor, the encoder disk having segments of different lengths and a sequence characteristic of the absolute position;
• Determining a predetermined number of segment lengths for successively detected segments as a segment length pattern;
• - each determining a deviation indication depending on the segment length pattern and one of a plurality of provided reference patterns, each reference pattern comprises a sequence of the predetermined number of segment lengths and is associated with an absolute position;
• Determining the absolute position of the rotatable element as a function of the absolute position of the reference pattern whose deviation indication indicates the smallest difference to the segment length pattern.

The above method is based on pattern recognition by comparing a segment length pattern recorded by moving the rotatable member using the encoder disk with a reference pattern. The segment length pattern results from the transition from one segment to a subsequent segment of the encoder disc resulting signal edges. The segment length pattern can be compared to reference patterns for match and assigned if a certain predetermined position matches, to determine the current position of the rotatable element.

For this purpose, first a segment length pattern is detected and after a predetermined number of segment lengths, preferably a number of segment lengths, after which the segment pattern repeats periodically as the rotatable element advances, a comparison is made with provided reference patterns. The reference patterns, with which the detected segment length pattern is compared, may correspond in number to the number of segments of the reference pattern whose sequence is offset by one position for each reference pattern. If a match or the greatest similarity with a reference pattern is determined, this determines the absolute position of the rotatable element at the time of the last detected signal edge or a specific one of the signal edges.

An idea of the above method is now to compare the individual segment lengths of the detected segment pattern with the segment lengths of the respective reference pattern and, depending on a difference specification, the deviations between the detected segment pattern and the reference pattern for each segment, to identify the reference pattern as being hit by the detected segment pattern to which the detected segment pattern has the least deviation indication. In this way, it is possible to carry out the assignment of the detected segment pattern to the respective applicable reference pattern with a few calculation steps and thereby to determine the absolute position of the rotatable element.

Furthermore, it can be provided that the predetermined number of segment lengths for successively detected segments is determined by first segment durations for successively detected segments are detected as a segment duration pattern and using a speed indication of the rotatable element for each segment duration, a segment length is determined. Since the segment lengths are often recorded as a time variable, for example as a time period between two consecutive edges, but the reference pattern may be in the form of a sequence of angle and distance indications, it is necessary to convert the segment duration into a segment specification for each segment , For this purpose, a speed indication can be determined, which indicates the speed of the rotatable element in the unit of the position information divided by the unit of the segment number.

According to one embodiment, the deviation indication may be determined depending on the segment length pattern and one of a plurality of provided reference patterns by determining a difference indication based on the difference of each segment length of the segment length pattern and the associated segment length of the reference pattern and determining the deviation indication for each reference pattern depending on the differences.

In particular, the ratios between each segment length of the segment length pattern and the associated segment length of the reference pattern can be determined as the difference.

It can be provided that the reciprocal value is formed before determining the deviation from the ratios whose value is smaller than 1, or wherein the reciprocal value is formed before determining the deviation indication from those ratios whose value is greater than 1.

Furthermore, the deviation statement for each reference pattern can be determined as a product or as a sum of the ratios.

The absolute position of the rotatable element may be determined as the sum of the absolute position of the reference pattern whose deviation indication indicates the least difference from the segment length pattern and a position difference which depends on a speed of the rotatable element and a time since the detection of the last signal edge of the encoder signal ,

Since the pattern recognition can be started only after the last signal edge, the time for determining the deviation indication which indicates the greatest possible similarity between the reference pattern and the segment length pattern is critical because the rotatable element can continue to move during the execution of the pattern recognition. An estimation of the instantaneous position of the rotatable element from the last determined absolute position is the more accurate, the shorter the elapsed time since the last edge time to the determination of the absolute position during the last edge.

According to one embodiment, the predetermined number of segment lengths of the segment length pattern and the segment lengths of the provided reference patterns can each be provided with alternating signs, whereby only the reference patterns of the several provided reference patterns whose segment lengths have the same sign as the associated segment lengths of the reference are taken into account for determining the deviation specifications segment length pattern.

• – einen Positionsgeber zum Erfassen eines Gebersignals basierend auf einer Bewegung einer Geberscheibe, wobei die Geberscheibe Segmente unterschiedlicher Länge und einer für die absolute Position charakteristischen Abfolge aufweist; und
• – eine Auswerteeinheit, die ausgebildet ist, um • eine vorbestimmte Anzahl von Segmentlängen für aufeinander folgend erfasste Segmente als ein Segmentlängenmuster zu bestimmen; • jeweils eine Abweichungsangabe abhängig von dem Segmentlängenmuster und einem von mehreren bereitgestellten Referenzmustern zu ermitteln, wobei jedes Referenzmuster eine Abfolge der vorbestimmten Anzahl von Segmentlängen umfasst und einer absoluten Position zugeordnet ist; und • die absolute Position des drehbaren Elements abhängig von der absoluten Position desjenigen Referenzmusters zu bestimmen, dessen Abweichungsangabe den geringsten Unterschied zu dem Segmentlängenmuster angibt.

In another aspect, an apparatus for determining an absolute position of a rotatable member is provided. The device comprises:

• A position sensor for detecting a sensor signal based on a movement of a sensor disk, the encoder disk having segments of different lengths and a sequence characteristic of the absolute position; and
• An evaluation unit configured to: determine a predetermined number of segment lengths for successively detected segments as a segment length pattern; • to determine a deviation indication in each case depending on the segment length pattern and one of a plurality of provided reference patterns, each reference pattern comprising a sequence of the predetermined number of segment lengths and associated with an absolute position; and • to determine the absolute position of the rotatable element as a function of the absolute position of the reference pattern whose deviation indication indicates the least difference from the segment length pattern.

In another aspect, an arrangement with a motor and the above device is provided.

According to a further aspect, there is provided a computer program product having a program code which, when executed on a data processing device, performs the above method.

Brief description of the drawings

Preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 a schematic representation of an arrangement with a device for determining an absolute position of a shaft;

2 a representation of a waveform of the encoder signal for a revolution of a shaft and a corresponding encoder disc 5 ; and

3 a flowchart illustrating a method for determining the absolute position of the shaft of the 1 ,

Description of embodiments

1 shows a schematic representation of an arrangement with a drive motor 2 that a wave 3 as a rotatable element drives. At the wave 3 is a position transmitter 4 arranged, which can be based on optical and / or magnetic mechanisms of action. The position transmitter 4 is designed to rotate upon rotation of the shaft 3 to output an electrical encoder signal. The position transmitter 4 is further configured so that the encoder signal depending on the position of the shaft 3 Pulse has different lengths of time.

For this purpose, the position sensor 4 a donor disk 5 having segments of different segment lengths. The encoder disc 5 is stuck to the wave 3 arranged and effected in a sensor element 6 of the position encoder 4 near the donor disk 5 is arranged that a signal edge of the encoder signal is generated when a transition from a segment of the encoder disc 5 to a subsequent segment on the sensor element 6 moved past.

The electrical encoder signal is an evaluation unit 10 supplied, which determines dependent on an absolute position indication. The absolute position specification gives the absolute position of the shaft 3 within a turn.

The evaluation unit 10 includes a timer 11 and a memory 12 , The timer 11 measures the time periods between two successive signal edges of the encoder signal and stores the time periods thus determined as segment durations in the memory 12 , If a number of consecutive segment durations has been detected which corresponds to a predetermined number, an evaluation can be made based on the segment duration pattern formed by the detected sequence of segment durations, from which the absolute position of the shaft 3 at the time of the last detected signal edge. For example, the predetermined number of the number of segments of the encoder disc 5 or a number corresponding to the number of segments after which the segment lengths on the encoder disk 5 to repeat.

The evaluation is based on a pattern recognition method in which the detected segment duration pattern is compared with reference patterns, each of which has a certain absolute position of the shaft 3 assigned.

In 2 is a waveform of the encoder signal for one revolution of the shaft 3 and a corresponding encoder disc 5 shown. The illustrated encoder signal is obtained when the encoder disk is rotated 5 counterclockwise. The used encoder disk 5 has eight segments, numbered SE1 through SE8. The encoder signal comprises at one revolution of the shaft 3 eight signal edges, which are numbered F1 to F8. The segment lengths, ie the segment angles on the encoder disk 5 are selected so that depending on the initial position of a revolution, a unique segment duration pattern corresponding to the segments SE1 to SE8 is output as the encoder signal. For example, corresponds to the position of the shaft 3 After an encoder signal has been detected with the edges F1 to F8 and then F1, an absolute position, which is assigned to the time of the edge F1 fixed. For example, the edge F1 of an absolute position of the shaft 3 be permanently assigned by 0 °. The fixed positions of the individual flanks F1 to F8 result according to the example of 2 from the following table: F1 F2 F3 F4 F5 F6 F7 F8 F1 0 ° 20 ° 90 ° 160 ° 180 ° 250 ° 270 ° 290 ° 360 ° / 0 °

The evaluation unit 10 further comprises a reference pattern memory unit 13 , in which the segment lengths given in the following table are stored in angular degrees: SE1 SE2 SE3 SE4 SE5 SE6 SE7 SE8 SE1 20 ° 70 ° 70 ° 20 ° 70 ° 20 ° 20 ° 70 ° 20 °

Further, in the reference pattern memory unit 13 stored the reference pattern for various recently detected edges and possibly for different directions in a suitable manner. That is, the reference pattern memory unit 13 includes the reference patterns {SE1 to SE8}, {SE8, SE1 to SE7}, {SE7, SE8, SE1 to SE6}, etc., and {SE8 to SE1}, {SE7 to SE1, SE8} {SE6 to SE1, SE8, SE7 } etc. Thus, the reference patterns are offset by one or more positions with respect to another reference pattern.

In 3 FIG. 10 is a flow chart illustrating the method of determining the absolute position of the shaft. FIG 3 shown. In step S1, upon receipt of a signal edge of the encoder signal, that of the timer 11 detected time duration t _sg for the last detected segment of the encoder signal as segment duration t _sg in the memory unit 12 written and the timer 11 is reset, as it does after every signal edge. Alternatively, it is possible that each time a signal edge of the encoder signal is received, the current time value of the timer is stored as a time stamp and the time duration t _{sg is determined} as the difference between two time stamps which were determined on a successive signal edge of the encoder signal.

In step S2, it is checked whether a number of segments of the encoder signal (sequence of segments) has been detected, that of the predetermined number of segments of the encoder disk 5 equivalent. As long as this is not the case (alternative: no), it returns to step S1.

Was detected a number of segments of the position signal, that of the number of segments of the encoder disc 5 corresponds (alternative: Yes), then in step S3 first a velocity G is determined as a quotient of the angular range of a full revolution (360 °) and the sum of the segment durations of all segments of the position signal: G = 360 ° / Σt _sg

For example, an indication with the unit degrees per millisecond is obtained as the speed indication G.

Now, the stored segment durations t _{sg are} respectively multiplied by the velocity indication G to determine segment lengths of the successively detected segments (step S4). The individual segment lengths can be suitably stored in the memory unit 12 are stored as segment length patterns, the segment length pattern indicating the sequence of segment lengths and their values.

Now, in a step S5, the sequence of the individual segment lengths of the detected encoder signal (segment length pattern) is compared with each individual reference pattern and a respective deviation indication is determined. The reference pattern specifies a sequence of segment lengths and their values, that of the sequence of segments beginning at a particular absolute position of the encoder disc 5 equivalent.

The deviation indication can be determined by determining the ratio of the segment length of a respective segment of the detected encoder signal and the corresponding segment of the respective reference pattern. If this ratio is less than 1, then the ratio of the previously determined ratio is assumed as the ratio. For each segment length, a ratio value is obtained which is greater than 1 and whose number corresponds to the predetermined number. Alternatively, it may be provided that, if this ratio is greater than 1, the ratio of the reciprocal of the previously determined ratio is assumed as the ratio. For each segment length, a ratio value is obtained which is smaller than 1 and whose number corresponds to the predetermined number

By multiplying the individual ratios with each other, one obtains the deviation indication which corresponds to a distance value. The closer the distance value to the value 1 is, the more similar the segment length pattern and the respective reference pattern. The distance value thus corresponds to an indication of how similar the detected segment length pattern and the tested reference pattern are, ie how large the distance / difference between the segment length pattern and the corresponding reference pattern is. The distance value is determined for each reference pattern (step S5).

In step S6, that reference pattern is selected as the applicable signal pattern whose distance value is the value 1 comes closest. Since the individual edges of the reference pattern respectively absolute positions of the shaft 3 are assigned, the last edge of the position signal according to the above table of an absolute position of the shaft 3 be assigned.

Alternatively, the deviation indication can be determined using the method of quadratic deviation. This is determined for each reference pattern and the reference pattern with the least square deviation is selected as the applicable reference pattern.

The current position of the shaft 3 can then be determined by addition or subtraction of the time elapsed since the last edge, that of the timer 11 is determined multiplied by the speed indication G (step S8).

The method described above will be explained below on the basis of concrete exemplary values. For example, in steps S1 and S2, the segment durations are recorded in milliseconds as follows:
21.3 ms; 69.1 ms; 72.0 ms; 19.5 ms; 75.2 ms; 18.1 ms; 19.3 ms; 66.7 ms.

The speed indication G then results as described above as G = 360 ° / 361.2 ms = 3.98 ° / ms

Now, according to step S5, the individual segment durations are multiplied by the speed indication G. The following segment lengths result (in angular degrees):
21.23 °; 68.87 °; 71.76 °; 19.43 °; 74.95 °; 18.04 °; 19.23 °; 66.48 °.

From this, the ratios of the segment lengths of the detected position signal and the segment lengths of the reference pattern R1 = {S1 to S8} can be obtained as follows:
1.061; 1.016; 1.025; 1.029; 1.071; 1.109; 1.04; 1.053.

This results in a distance value of 1.479 as the product of all ratio values. If the encoder signal is shifted relative to the reference pattern by one or more segments, the distance value differs to a significantly greater extent from the value 1 than when the position signal coincides with the reference pattern.

In an alternative embodiment, the segment durations or segment lengths of the encoder signal and the reference pattern may be given a positive sign when the signal level is high, and a negative sign when the signal level is a lower level, for example 0. If the encoder signal is then shifted by one segment compared to the reference pattern, the distance value becomes negative. This makes it possible in a simple manner to dispense with the multiplication of the individual values, if it can be recognized from the different signs that the encoder signal and the reference pattern can not match. Thus, it is possible to halve the number of calculations of the distance value, thereby further accelerating the method of determining the absolute position of the shaft.

The above method for determining the absolute position can be used advantageously for internal combustion engines for detecting the absolute position of a crankshaft. In internal combustion engines, the crankshaft is often provided with a crankshaft sensor wheel which provides a constant angular resolution. The camshaft is provided with a camshaft encoder wheel having correspondingly different segment lengths for providing a sensor signal having different segment lengths. In combination of both donor wheels, the absolute position can then be determined in a simple manner by using a corresponding pattern recognition method. The above method, in which the segment duration is converted into segment lengths via the speed indication, must be applied when the position detector that reads out the crankshaft sensor wheel is defective and only the camshaft sensor wheel can be used. The above method is therefore particularly suitable for determining an approximate value for the absolute position in position determination systems with two encoder wheels in the event of failure of the finely resolving transmitter wheel for determining the absolute segment length of a transmitter wheel, which is to provide a signal pattern.

Claims (10)

Method for determining an absolute position of a rotatable element ( 3 ), comprising the following steps: detecting an encoder signal based on a movement of a sensor disk of a position sensor ( 4 ), whereby the encoder disk ( 5 ) Has segments (SE1-SE8) of different lengths in a sequence characteristic of the absolute position; - determining (S2, S3) a predetermined number of segment lengths for consecutively detected segments (SE1-SE8) as a segment length pattern; - determining (S5) each a deviation indication depending on the segment length pattern and one of a plurality of provided reference patterns, each reference pattern comprising a sequence of the predetermined number of segment lengths and associated with an absolute position; Determining the absolute position of the rotatable element ( 3 ) depending on the absolute position of the reference pattern whose deviation indication indicates the smallest difference to the segment length pattern. The method of claim 1, wherein the predetermined number of segment lengths for consecutively detected segments (SE1-SE8) is determined by first detecting segment durations for consecutively detected segments (SE1-SE8) as the segment duration pattern and using a speed indication of the rotatable element for each Segment duration is determined a segment length. The method of claim 1 or 2, wherein the deviation indication is determined depending on the segment length pattern and one of a plurality of provided reference patterns by a difference based on the difference of each segment length of the segment length pattern and the associated segment length of the reference pattern and depending on the differences the deviation indication for each reference pattern is determined. The method of claim 4, wherein as the difference, the ratios between each segment length of the segment length pattern and the associated segment length of the reference pattern are determined. The method of claim 5, wherein prior to determining the deviation indication of the ratios whose value is less than 1, the reciprocal is formed, or wherein prior to determining the deviation indication of those ratios whose value is greater than 1, the reciprocal is formed. Method according to one of claims 3 to 5, wherein the deviation indication for each reference pattern is determined as a product or as a sum of the ratios. Method according to one of claims 1 to 6, wherein the absolute position of the rotatable element ( 3 ) is determined as the sum of the absolute position of the reference pattern whose deviation indication indicates the smallest difference to the segment length pattern and a position difference which depends on a speed of the rotatable element and a time since the detection of the last signal edge of the encoder signal. Method according to one of claims 1 to 7, wherein the predetermined number of segment lengths of the segment length pattern and the segment lengths of the provided reference pattern are each provided with alternating signs, wherein for determining the deviation information only those reference patterns the plurality of provided reference patterns whose segment lengths have the same sign as the associated segment lengths of the segment length pattern. Device for determining an absolute position of a rotatable element ( 3 ), comprising: - a position sensor ( 4 ) for detecting an encoder signal based on a movement of a donor disk ( 5 ), whereby the encoder disk ( 5 ) Has segments (SE1-SE8) of different lengths and a sequence characteristic of the absolute position; and - an evaluation unit ( 10 ) configured to: • determine a predetermined number of segment lengths for successively detected segments as a segment length pattern; • to determine a deviation indication in each case depending on the segment length pattern and one of a plurality of provided reference patterns, each reference pattern comprising a sequence of the predetermined number of segment lengths and associated with an absolute position; and the absolute position of the rotatable element ( 3 ) depending on the absolute position of the reference pattern whose deviation indication indicates the least difference to the segment length pattern. Arrangement with a drive motor ( 2 ) and a device according to claim 9. A computer program product comprising program code which, when executed on a data processing device, performs the method of any one of claims 1 to 8.

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