DE102014223066A1 - Method and control unit for detecting an armature stop of an electromechanical actuator - Google Patents

Abstract

The invention relates to a method for detecting an armature stop of an electromechanical actuator after driving a solenoid driving the actuator, wherein the armature stop of the actuator by means of evaluation of a time derivative of the current _waveform i _{pmp is} determined by the magnetic coil. It is provided that a minimum of the first time derivative i _{grad of} the current _waveform i _{pmp is} determined and that the time of the minimum is assigned to the anchor stop when the minimum is greater than or equal to zero.
The invention further relates to a control unit for carrying out the method.
The method makes it possible to detect an armature stop of an electromagnetic actuator even under unfavorable operating conditions.

Description

State of the art

The invention relates to a method for detecting an armature stop of an electromechanical actuator after driving a solenoid driving the actuator, wherein the armature stop of the actuator is determined by evaluating a time derivative of the current waveform through the magnetic coil.

The invention further relates to a device for carrying out the method.

The font DE 10 2013 200 540 A1 discloses a method for detecting a start of movement of an electromechanical actuator, which is driven by means of at least one magnetic coil. In this case, a release time of the actuator is determined by evaluating a current flowing through the magnetic coil, and its time derivatives. It is envisaged that, for determining the start-up time, a relative inductance is determined from a temporal inductance curve and a time profile of the relative inductance is evaluated.

Accordingly, it is known to determine a stop of the actuator (magnetic stop point MSP) on the basis of the Induktivitätsverlaufs. The disadvantage here is the required high computational effort to determine the inductance, since the inductance can be different for each actuator. For evaluation, the inductance must be normalized. The high computational complexity leads to high required resources. Another disadvantage results from the fact that under certain operating conditions of the actuator, for example at low temperatures and consequent low speeds of the actuator, the armature stop can not be clearly detected by the Induktivitätsverlaufs.

The DE 10 2011 088 701 A1 discloses a method for monitoring the armature movement of a Hubkolbenmagnetpumpe, especially in the delivery module of an SCR catalyst system. For this purpose, a local minimum in the course of the current is sought through the magnetic coil of Hubkolbenmagnetpumpe and recognized as MSP. To determine the local minimum, a zero crossing of the first time derivative of the current waveform can be used.

The disadvantage here is that under unfavorable operating conditions of the actuator at low speeds of the armature movement no minimum in the course of the current is formed. Such unfavorable operating conditions may be present, for example, at low temperatures and high friction.

It is therefore an object of the invention to provide a method with which an improved detection of the armature stop of an electromechanical actuator can be made possible.

It is a further object of the invention to provide a device for carrying out the method.

Disclosure of the invention

The object of the invention relating to the method is achieved by determining a minimum of the first time derivative i _{grad of} the current _waveform i _pmp , and _assigning the time of the minimum to the armature stop if the minimum is greater than or equal to zero. If there is a slowed movement of the armature, for example at low temperatures, no minimum in the current _profile i _pmp forms at the armature _stop and thus no zero crossing of the first time derivative i _{grad of} the current _profile i _pmp . At the time of the anchor stop, however, there is a sudden change in the armature movement and thus the monotonically increasing course of the current flowing through the solenoid current i _pmp . Before the armature stop, the rate of rise of the current i _{pmp decreases} , while it rises again after the armature stop. The first time derivative i _grad therefore forms at the anchor stop a minimum, which is detected according to the invention. The armature stop can thus be reliably detected even under operating conditions which lead to a slower movement of the armature.

If there is a sufficiently fast armature movement, the current i _pmp by the solenoid first increases, but then drops again and forms a minimum before it rises again. The first time derivative i _grad of such a current _waveform i _pmp thus forms a minimum less than zero and two zero crossings. To ensure safe operation even under operating conditions that lead to a fast armature movement Detecting the armature stop can be provided that the armature stop is the time of a second zero crossing of the first time derivative i _{grad of} the current _waveform i _pmp assigned when the first time derivative i _{grad has} zero crossings. By determining the minimum or, if present, the second zero crossing of the first time derivative i _grad , the armature stop can be reliably detected both during slow and fast armature movements.

In order to determine the minimum of the first time derivative i _{grad of} the current _profile i _pmp by the magnetic coil, it may be provided that for the search of the minimum, the value of a first threshold for the first time derivative i _{grad of} the current waveform, starting from a value zero a predetermined value .DELTA.X is gradually increased, that is checked before increasing the first threshold, whether the first time derivative i _grad in their course is less than or equal to the first threshold and that the minimum in the portion of the current waveform, the smaller or equal the first threshold is searched. For this, the course of the first time derivative i is advantageously _degree stored and compared with the first threshold. If the first threshold has been raised so far that values of the first time derivative i _{grad of} the current _waveform i _{pmp are} below the first threshold, then the searched minimum is also below this first threshold and can be found correspondingly quickly.

In order to avoid that disturbances, for example fluctuations, in the ascertained course of the first derivative i _{grad of} the current _profile i _pmp , can be erroneously scored as a minimum and thus as an anchor stop, it can be provided that the time of the minimum is assigned to the anchor stop when the temporal derivative i _grad after the minimum exceeds a second threshold I _{grad, max} . If this is not the case, the search for the minimum will continue.

Accordingly, it can be provided that the time of the minimum is assigned to the armature stop when the first time derivative i _grad of current _flow i _pmp to the minimum within a predetermined time K _{abs reaches} a value by a predetermined third threshold L above the minimum lies. It is therefore checked whether the first time derivative i _{grad of} the current _waveform i _pmp changes greatly after the minimum, ie whether the second time derivative i _{grad reaches} a value greater than a predetermined value. If this is the case, the determined time of the minimum is considered an anchor stop. If the slope of the course of the first time derivative i _{grad of} the current _waveform i _pmp decreases, the search for the minimum continues.

An unambiguous and error-free determination of the anchor stop, even with slowly moving actuator, can be achieved by assigning the time of the minimum to the armature stop if the time derivative i _grad after the minimum exceeds the second threshold I _{grad, max} and the minimum between zero and a fourth threshold X _thres and / or that the time of the minimum is assigned to the armature stop, when the first time derivative i _grad of current _flow i _pmp to the minimum within a predetermined time K _{abs reaches} a value which is by a predetermined third threshold L is above the minimum and the minimum is between the fourth threshold X _thres and a fifth threshold X _max , and / or that no armature stop is detected when the minimum is above the fifth threshold X _max .

The armature stop both fast and slow moving actuators can be found quickly and with little resources that is stored to detect the anchor stop the time course of the first time derivative i _grad of current _flow i _pmp that, starting from a last memory _value , in a Backward search, the second zero crossing is determined or that, if no zero crossing was determined, the achievement of the first threshold is determined and that, starting from the time of reaching the first threshold, in a further backward search, the minimum is determined. For fast moving armatures, the zero crossings in the first time derivative i _{degrees are} formed. The second zero crossing corresponds to the anchor stop. With comparatively slowly moving anchors, no zero crossings are formed, but the minimum greater than zero, which can be assigned to the anchor stop. Thus, with a test routine, the anchor stop can be determined both for fast-moving anchors and for comparatively slowly moving anchors. The method can thus be used for actuators operated under different operating conditions.

The current _profile i _pmp is preferably determined by a voltage measurement via a shunt resistor. The measurement is advantageously carried out via an analog-to-digital converter (ADC). In order to suppress noise in the calculation of the current _waveform i _pmp from the voltage _values and the first time derivative i _{grad of} the current _waveform i _pmp , it can be provided that the current _waveform i _{pmp is determined} at discrete times and filtered via a low-pass filter and that the first Time derivative i _{degree is determined} from the filtered values of the current _waveform i _pmp and / or that the determined anchor stop is corrected by a time offset caused by the low-pass filter. The low pass filter causes a time offset of the determined course of the first time derivative i _grad . This time offset is known and can be considered accordingly in the determination of the anchor stop.

The object of the invention relating to the control unit is achieved in that the processing _{device is designed} to determine a minimum of the first time derivative i _{grad of} the current _profile i _pmp and to assign the time of the minimum to the armature stop if the minimum is greater than zero, and / or that the processing _{device is adapted} to determine a second zero crossing of the first time derivative i _{grad of} the current _waveform i _pmp and to assign the time of the second zero crossing to the armature stop. With the aid of the control unit, it is thus possible to ensure an armature stop both in the case of a fast-moving armature, which forms a minimum in the determined current _flow i _pmp by the magnet coil, and in the case of a comparatively slowly moving armature, which does not form a minimum in the determined current _flow i _pmp be recognized. Thus, the control unit can detect the anchor stop in different operating conditions, for example at high and low temperatures.

The invention will be explained in more detail below with reference to an embodiment shown in FIGS. Show it:

1 a first diagram of a current _waveform i _pmp in a magnetic coil of an electromagnetic actuator with a fast-moving armature,

2 a second diagram of the course of current i _pmp in a magnetic coil at an armature slowed down with respect to the first diagram,

3 a third diagram for current _flow i _pmp in a magnetic coil at a relative to the second diagram slowed moving armature and

4 a flowchart for detecting an anchor stop.

1 shows a first diagram to a current _waveform i _pmp 20 in a solenoid of an electromagnetic actuator with a fast moving armature. In concrete, also shown in the following figures embodiment, it is the anchor of a solenoid drive in a delivery and metering system for supplying a reducing agent in an exhaust passage of an internal combustion engine.

The current _flow i _pmp 20 is opposite to a current axis i _pmp 11 and a timeline 13 applied. One from the current _flow i _pmp 20 formed first time derivative i _grad 30 is opposite to a gradient axis i _grad 10 and a zero line 12 which have the same time distribution as the time axis 13 has, applied.

Along the course of the current i _pmp 20 are a start time 21 (BMP: Begin Motion Point) of the anchor, a first stop time 22.1 (MSP: Magnet Stop Point) of the anchor and one end 14 marked a data collection.

Along the course of the first time derivative i _grad 30 is a first zero crossing 31 , a first minimum 32.1 and a second zero crossing 33 characterized. measuring points 15 digital measurement data acquisition are schematic and representative of the total current _flow i _pmp 20 and the entire course of the first time derivative i _grad 30 represented by dots.

A time offset 16 between the course of the first time derivative i _grad 30 and the current _waveform i _pmp 20 is indicated by a double arrow.

At a start of control is applied to the Hubmagnetpumpe operating voltage so that the current waveform i _pmp 20 begins to rise. At the time of departure 21 begins the armature of the solenoid drive with its movement, which is due to the mutual induction occurring here, the increase of the current _waveform i _pmp 20 flattens. At the first stop time 22.1 suggests the armature of the solenoid drive at its end position. Here the current _curve shows i _pmp 20 a minimum characteristic of the armature stop, after which it continues to increase until a turn-off time. The minimum in the current _curve i _pmp 20 and thus in the second zero crossing of the first time derivative igrad 30 is evaluated to detect the timing of the anchor stop.

Electrically, the electromechanical actuator can be represented by an equivalent circuit consisting of a series connection of an inductance L and an ohmic resistance R of the circuit. At a drive _voltage U _batt results in the context

zu, wobei τ = L/R die Zeitkonstante des Stromkreises ist. After switching on, the current increases accordingly

to, where τ = L / R is the time constant of the circuit.

mit der Annahme, dass der Strom i_pmp zum betrachteten Zeitpunkt konstant bleibt. L_d ist die differenzielle Induktivität im Arbeitspunkt. Wie Gleichung (3) zeigt, verursacht die sich schnell verändernde Induktivität eine Reduzierung in dem Stromverlauf i_pmp 20. Diese Reduzierung endet zu dem Zeitpunkt, ab dem sich die Induktivität L nicht mehr verändert, so dass der Strom ab diesem Zeitpunkt wieder ansteigt. Das so gebildete Minimum in dem Stromverlauf i_pmp 20 entspricht somit dem ersten Ankeranschlag- Zeitpunkt 22.1. Die erste zeitliche Ableitung i_grad 30 weist an diesem Punkt den einfach nachzuweisenden zweiten Nulldurchgang 33 auf. The current i _pmp 20 generates a magnetic field in the magnetic coil. Is the consequent, acting on the armature magnetic force greater than the sum of the friction and acting on the armature spring force of a return spring, the armature is set in motion. The inductance of the magnetic coil is determined in particular by the winding, the iron core, the geometric structure and the air gap changing as a result of the movement of the armature. For the circuit arises with it

with the assumption that the current i _pmp remains constant at the time considered. L _d is the differential inductance at the operating point. As equation (3) shows, the rapidly changing inductance causes a reduction in the current _waveform i _pmp 20 , This reduction ends at the time from which the inductance L no longer changes, so that the current increases again from this point in time. The minimum so formed in the current profile i _pmp 20 thus corresponds to the first anchor stop time 22.1 , The first time derivative i _grad 30 indicates at this point the easily detectable second zero crossing 33 on.

As equation (3) further shows, the change of the current i _{pmp depends} strongly on the speed of the inductance change and thus on the speed of the movement of the armature. Under unfavorable operating conditions, for example at low temperatures, the friction acting on the armature can be so great as to noticeably slow the movement of the armature. This can lead to a monotonically increasing current _profile i _pmp 20 lead, as in the 2 and 3 is shown.

To determine the current _flow i _pmp 20 For example, a voltage which drops across a shunt resistor arranged in series with the solenoid coil is supplied to the measurement points by means of an analog-to-digital converter 15 certainly. The measurement can be limited to a portion of the current curve in the region of the anchor stop. The discrete voltage values are calculated back into current values and then further processed.

• 1. Zunächst wird der Stromverlauf i_pmp 20 durch einen Tiefpass gefiltert, um Störungen durch Rauschen zu unterdrücken. Vorteilhaft wird hierzu ein FIR-Filter verwendet, der einen linearen Phasenverlauf aufweist.
• 2. Anschließend erfolgt die Bestimmung der ersten zeitlichen Ableitung i_grad 30 aus dem Stromverlauf i_pmp 20.
• 3. Ausgehend von dem letzten Wert der ersten zeitlichen Ableitung i_grad 30 wird der Nulldurchgang zurückgesucht. Die Rückwärtssuche erfordert lediglich einen vergleichsweise geringen Ressourcen-, Berechnungs- und Zeitaufwand.
• 4. Um sicherzustellen, dass der so ermittelte erste Anschlag-Zeitpunkt 22.1 dem tatsächlichen ersten Anschlag-Zeitpunkt 22.1 entspricht, wird ein maximaler Wert i_grad,max der ersten zeitlichen Ableitung i_grad 30 bestimmt.
• 5. Dieser maximale Wert i_grad,max wird mit einer in 2 gezeigten zweiten Schwelle I_grad,max 41 verglichen. Überschreitet der maximale Wert i_grad,max der ersten zeitlichen Ableitung i_grad 30 die zweite Schwelle I_grad,max 41, wird der ermittelte erste Anschlag- Zeitpunkt 22.1 als tatsächlicher erster Anschlag-Zeitpunkt 22.1 bestätigt. Andernfalls wird der ermittelte erste Anschlag-Zeitpunkt 22.1 als Störung verworfen.
• 6. Der an Stelle des zweiten Nulldurchgangs 33 bestimmte erste Anschlag-Zeitpunkt 22.1 wird unter Berücksichtigung der Verzögerung durch den Tiefpassfilter nach vorne verschoben.

For the in 1 shown case of a fast armature movement, the detection of the first stop time takes place 22.1 through the following steps:

• 1. First, the current _waveform i _pmp 20 filtered through a low-pass filter to suppress noise interference. Advantageously, an FIR filter is used for this purpose, which has a linear phase characteristic.
• 2. Subsequently, the determination of the first time derivative i is _grad 30 from the current _flow i _pmp 20 ,
• 3. Starting from the last value of the first time derivative i _grad 30 the zero crossing is searched back. The reverse search requires only a comparatively small amount of resources, calculation and time.
• 4. To ensure that the so determined first stop time 22.1 the actual first stop time 22.1 corresponds, a maximum value i is _{grad, max of} the first time derivative i _grad 30 certainly.
• 5. This maximum value i _{grad, max} is with an in 2 shown second threshold I _{grad, max} 41 compared. Exceeds the maximum value i _{degree, max of} the first time derivative i _grad 30 the second threshold I _{grad, max} 41 , the determined first stop time 22.1 as the actual first stop time 22.1 approved. Otherwise, the determined first stop time 22.1 discarded as a disorder.
• 6. The in place of the second zero crossing 33 certain first stop time 22.1 is shifted forward considering the delay through the low-pass filter.

Preferably, an m-order FIR filter is used for the low-pass filtering. This allows a simple calculation and a linear phase curve.

2 shows a second diagram of the current _waveform i _pmp 20 in a magnetic coil with a slower moving relative to the first diagram anchors. The same diagram parts are correspondingly 1 designated.

The first time derivative i _grad 30 forms a second minimum 32.2 off, which is greater than zero. The second minimum 32.2 is on a first threshold 40 , A second stop time 22.2 of the anchor is due to the time offset 16 before the second minimum 32.2 placed.

Along the gradient _axis i _grad are a fourth threshold X _thres 44 and a fifth threshold X _max 45 marked. The second minimum 32.2 is below the fourth threshold X _thres 44 ,

Due to the comparatively slow armature movement, the current _profile i _pmp 20 no minimum and therefore the first time derivative i _grad 30 no zero crossing. The current increases monotonically up to a saturation range. In order nevertheless to recognize the anchor stop the place is searched, at which a sudden change of the current takes place. The armature stop search algorithm is adjusted according to the invention for such cases. If no zero crossing in the course of the first time derivative i _grad 30 is found, it is after a passage of the first time derivative i _grad 30 through the first threshold 40 searched and assigned this the anchor stop. It is then checked whether the passage is the anchor stop or a fault. If it is a fault, the first threshold becomes 40 increased by a predetermined value .DELTA.X and again to a passage of the course of the first time derivative i _grad 30 through the now raised first threshold 40 searched. Otherwise, the second anchor stop time will be 22.2 taking into account the time lag caused by the low-pass filter 16 determined.

3 shows a third diagram of the current _waveform i _pmp 20 in a magnetic coil at one opposite to the in 2 shown second diagram slows down moving anchor.

In addition to the diagram parts shown in the first and second diagrams, the third diagram shows a third minimum 32.3 greater than zero during the first time derivative i _grad 30 , The third minimum 32.3 is at the height of the first threshold 40 , these being opposite to the illustration in 2 is raised. The third minimum 32.3 is thus between the fourth threshold X _thres 44 and the fifth threshold X _max 45 , A third stop time 22.3 of the anchor is due to the time offset 16 over the third minimum 32.3 time shifted forward. A needed time 43 until the first time derivative i _grad 30 , starting from the third minimum 32.3 to a third threshold L 42 has risen, is marked by a double arrow.

The search for the third stop time 22.3 takes place according to the 2 described search for the second stop time 22.2 ,

• 1. Zunächst erfolgt eine Tiefpassfilterung wie zu 1 beschrieben.
• 2. Ermittlung der ersten zeitlichen Ableitung i_grad 30 wie zu 1 beschrieben.
• 3. Rückwärtssuche nach einem Durchgang x der ersten zeitlichen Ableitung i_grad 30 durch die erste Schwelle 40. a. Wird ein Durchgang x erkannt, wird der Messpunkt k_x gespeichert. b. Wird kein Durchgang x erkannt, wird die erste Schwelle 40 um den vorgegebenen Wert ∆X erhöht und die Rückwärtssuche erneut durchgeführt.
• 4. Rückwärtssuche von dem Messpunkt kx nach dem lokalen Minimum 32.2, 32.3, das größer oder gleich Null ist. Dieses Minimum 32.2, 32.3 wird vorläufig als Anschlag-Zeitpunkt 22.2, 22.3 festgehalten.
• 5. Überprüfung, ob der vorläufige Anschlag-Zeitpunkt 22.2, 22.3 dem tatsächlichen Ankeranschlag entspricht. Die Überprüfung erfolgt an Hand des nachfolgenden Verlaufs der ersten zeitlichen Ableitung i_grad 30 wie folgt: a. Liegt der Durchgang x unterhalb der vierten Schwelle X_thres 44 wird der Durchgang x näherungsweise als Nulldurchgang betrachtet, wie dies in 2 dargestellt ist. i. Daraufhin wird überprüft, ob die erste zeitliche Ableitung i_grad 30 in ihrem dem zweiten Minimum 32.2 nachfolgenden Verlauf die zweite Schwelle I_grad,max 41 überschreitet. Ist dies der Fall, wird der vorläufige zweite Anschlag-Zeitpunkt 22.2 als tatsächlicher zweiter Anschlag-Zeitpunkt 22.2 erkannt. Andernfalls wird die Durchgangssuche mit einer erneut um den vorgegebenen Wert ∆X erhöhten ersten Schwelle 40 fortgesetzt. b. Liegt der Durchgang x oberhalb der vierten Schwelle X_thres 44, bedeutet dies, dass der Stromverlauf i_pmp 20 monoton steigend ist und die Steigung relativ groß ist. In diesem Fall wird der Ankeranschlag erkannt, wenn nach dem dritten Minimum 32.3 eine große Steigung der ersten zeitlichen Ableitung i_grad 30 vorliegt, wie dies zu 3 gezeigt ist. i. Es wird überprüft, ob und wann die erste zeitliche Ableitung i_grad 30 einen Wert W erreicht, der um die dritte Schwelle L 42 über dem Durchgang x liegt. Erreicht die erste zeitliche Ableitung i_grad 30 einen Wert W nicht, wird die Durchgangssuche mit einer erhöhten ersten Schwelle 40 fortgesetzt. Ist der zeitliche Abstand zwischen dem dritten Minimum 32.3 bzw. dem Durchgang x und dem Erreichen des Wertes W kleiner als eine vorgegebene Zeit K_abs, liegt ein starker Anstieg der ersten zeitlichen Ableitung i_grad 30 nach dem vorläufigen dritten Anschlag-Zeitpunkt 22.3 vor. In diesem Fall wird der vorläufige dritte Anschlag-Zeitpunkt 22.3 als tatsächlicher dritter Anschlag- Zeitpunkt 22.3 erkannt. Ist der zeitliche Abstand zwischen dem dritten Minimum 32.3 bzw. dem Durchgang x und dem Erreichen des Wertes W größer als die vorgegebene Zeit K_abs, liegt ein vergleichsweise flacher Anstieg der ersten zeitlichen Ableitung i_grad 30 nach dem vorläufigen dritten Anschlag-Zeitpunkt 22.3 vor und die Durchgangssuche wird mit einer erhöhten ersten Schwelle 40 fortgesetzt
• 6. Steigt die erste Schwelle 40 nach wiederholtem Erhöhen um den vorgegebenen Wert ∆X über die fünfte Schwelle X_max 45, wird der Algorithmus gestoppt. In diesem Fall kann kein Ankeranschlag nachgewiesen werden.

Below is the search for the anchor stop for slow moving anchors, as shown in the 2 and 3 is shown, described according to a possible embodiment.

• 1. First, a low-pass filtering as done 1 described.
• 2. determining the first time derivative i _grade 30 how to 1 described.
• 3. Backward search for a passage x of the first time derivative i _grad 30 through the first threshold 40 , a. If a passage x is detected, the measuring point k _{x is} stored. b. If no passage x is detected, the first threshold becomes 40 increased by the predetermined value .DELTA.X and the backward search again performed.
• 4. Backward search from the measuring point kx to the local minimum 32.2 . 32.3 that is greater than or equal to zero. This minimum 32.2 . 32.3 is provisionally as a stop time 22.2 . 22.3 recorded.
• 5. Check if the provisional stop time 22.2 . 22.3 corresponds to the actual anchor stop. The check is made on the basis of the following course of the first time derivative i _grad 30 as follows: a. If the passage x is below the fourth threshold X _thres 44 the passage x is considered approximately as a zero crossing, as in 2 is shown. i. Then it is checked whether the first time derivative i _grad 30 in their second minimum 32.2 subsequent course, the second threshold I _{degree, max} 41 exceeds. If so, the provisional second stop time 22.2 as the actual second stop time 22.2 recognized. Otherwise, the continuity search will begin with a first threshold again increased by the predetermined value ΔX 40 continued. b. If the passage x is above the fourth threshold X _thres 44 , this means that the current _waveform i _pmp 20 is monotonically increasing and the slope is relatively large. In this case, the anchor stop is detected when after the third minimum 32.3 a large slope of the first time derivative i _grad 30 is present, like this too 3 is shown. i. It will be reviewed if and when the first derivative i _degree 30 reaches a value W which is around the third threshold L 42 lies above the passage x. Achieved the first time derivative i _grad 30 If a value W is not, the throughput search will be at an increased first threshold 40 continued. Is the time interval between the third minimum 32.3 or the passage x and the achievement of the value W less than a predetermined time K _abs , there is a sharp increase of the first time derivative i _grad 30 after the provisional third stop time 22.3 in front. In this case, the provisional third stop time 22.3 as the actual third stop time 22.3 recognized. Is the time interval between the third minimum 32.3 or the passage x and the achievement of the value W greater than the predetermined time K _abs , there is a comparatively flat increase of the first time derivative i _grad 30 after the provisional third stop time 22.3 before and the continuity search comes with a raised first threshold 40 continuing
• 6. Rises the first threshold 40 after repeatedly increasing by the predetermined value ΔX over the fifth threshold X _max 45 , the algorithm is stopped. In this case, no anchor stop can be detected.

4 shows a flow chart for detecting an anchor stop.

In a first block 50 the start of the process takes place. At this time, the current _waveform i _pmp 20 as well as the first time derivative i _grad 30 already determined as described above. In a second block 51 the backward search is carried out after the passage x of the first time derivative i _grad 30 through the first threshold 40 , The backward search begins at a last detected value of the course of the first time derivative i _grad 30 , In a subsequent first branch 60 it is checked whether the passage x has been made. If this is not the case, the procedure follows to a ninth block 58 in which the first threshold 40 is increased by a predetermined value ΔX. In a fourth branch 63 is then checked whether the first threshold thus obtained 40 greater than the fifth threshold X _max 45 is. If this is the case, the process is in a tenth block 59 terminated without an anchor stop being detected. Is the threshold 40 less than the fifth threshold X _max 45 , the process branches back to the second block 51 and a further backward search for a passage x takes place with the first threshold now increased by the predetermined value ΔX 40 , Will be in the first branch 60 such a passage x detected, takes place in a third block 52 a backward search for a local minimum 32.2 . 32.3 the first time derivative i _grad 40 which is greater than or equal to zero. This minimum 32.2 . 32.3 will be in a fourth block 53 as a provisional stop time 22.2 . 22.3 the anchor accepted. In a fifth block 54 takes place, starting from the minimum 32.2 . 32.3 , a forward search. In the following second branch 61 it is checked whether the passage x is smaller than the fourth threshold X _thres 44 is. If so, it will be in a sixth block 55 Checks if the maximum value of the first time derivative i _degrees between the minimum 32.2 . 32.3 and the saturation _{degree of} the second threshold _{I, max} exceeds. If the passage x is greater than the fourth threshold X _thres 44 , will be in a seventh block 56 checks if the first time derivative i is _grad 30 , starting from the minimum 32.2 . 32.3 within a predetermined time K _abs by more than a third threshold L 42 increases. Is the condition in the sixth block 55 or the seventh block 56 is fulfilled by the two blocks 55 . 56 following third branch 62 to a final eighth block 57 forwarded. In the eighth block 57 is then on a recognized anchor stop at the specific stop time 22.2 . 22.3 closed. On the other hand, none is in the sixth block 55 and the seventh block 56 verified conditions, branches the third branch 62 back to the ninth block 58 with the already described further procedure.

The method described makes it possible, both for fast and slow moving anchors of electromagnetic actuators a stop time 22.1 . 22.2 . 22.3 the anchor sure to recognize. For this purpose, a common algorithm can be used, resulting in a simple and inexpensive implementation of the method in a corresponding control unit.

The sampling of the current values by an analog-to-digital converter is to be chosen so finely that the feature for detecting the armature stop is not lost. The number of stored ADC values in a memory must be sufficiently selected.

The low-pass filtering is adapted to the hardware characteristics and sampling frequency to suppress noise without harming the armature stop detection feature. The filtering can be integrated as software in the algorithm or it can be realized by the hardware or settings in a corresponding microcontroller or ADC. The method can be used for example in a solenoid or a solenoid valve.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102013200540 A1 [0003]
• DE 102011088701 A1 [0005]

Claims (9)

Method for detecting an armature stop of an electromechanical actuator after a control of a solenoid driving the actuator, wherein the armature stop of the actuator by means of evaluation of a first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) is determined by the magnetic coil, characterized in that a minimum ( 32.2 . 32.3 ) of the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) and that the time of the minimum ( 32.2 . 32.3 ) is assigned to the anchor stop when the minimum ( 32.2 . 32.3 ) is greater than or equal to zero. A method according to claim 1, characterized in that the anchor stop the time of a second zero crossing ( 33 ) of the first time derivative i _grad ( 30 ) of the current profile ipmp ( 20 Is assigned) when the first time derivative i _grad ( 30 ) Has zero crossings. The method of claim 1 or 2, characterized in that (for the search of the minimum 32.2 . 32.3 ) the value of a first threshold ( 40 ) for the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ), starting from a value zero, by a predetermined value ΔX is incrementally increased, that before an increase of the first threshold ( 40 ) checks whether the first time derivative i _grad ( 30 ) in its course less than or equal to the first threshold ( 40 ) and that the minimum ( 32.2 . 32.3 ) in the portion of the current _waveform i _pmp ( 20 ) which is less than or equal to the first threshold ( 40 ) is searched. Method according to one of claims 1 to 3, characterized in that the time of the minimum ( 32.2 . 32.3 ) is assigned to the anchor stop when the first time derivative i _grad ( 30 ) after the minimum ( 32.2 . 32.3 ) a second threshold I _{grad, max} ( 41 ) exceeds. Method according to one of claims 1 to 4, characterized in that the time of the minimum ( 32.2 . 32.3 ) is assigned to the anchor stop when the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) after the minimum ( 32.2 . 32.3 ) within a predetermined time K _{abs reaches} a value that is around a predetermined third threshold L ( 42 ) above the minimum ( 32.2 . 32.3 ) lies. Method according to one of claims 1 to 5, characterized in that the time of the minimum ( 32.2 . 32.3 ) is assigned to the anchor stop when the first time derivative i _grad ( 30 ) after the minimum ( 32.2 . 32.3 ) the second threshold I _{grad, max} ( 42 ) and the minimum ( 32.2 . 32.3 ) between zero and a fourth threshold X _thres ( 44 ) and / or that the time of the minimum ( 32.2 . 32.3 ) is assigned to the anchor stop when the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) after the minimum ( 32.2 . 32.3 ) within a predetermined time K _{abs reaches} a value that is around a predetermined third threshold L ( 42 ) above the minimum ( 32.2 . 32.3 ) and the minimum ( 32.2 . 32.3 ) between the fourth threshold X _thres ( 44 ) and a fifth threshold X _max ( 45 ) and / or that no anchor stop is detected when the minimum ( 32.2 . 32.3 ) above the fifth threshold X _max ( 45 ) lies. Method according to one of claims 1 to 6, characterized in that for the detection of the anchor stop the time course of the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) is stored, that, starting from a last memory value, in a backward search the second zero crossing ( 33 ) or that if no zero crossing ( 31 . 33 ), the achievement of the first threshold ( 40 ) and that, starting from the time of reaching the first threshold ( 40 ), in a further backward search the minimum ( 32.2 . 32.3 ) is determined. Method according to one of claims 1 to 7, characterized in that the current _waveform i _pmp ( 20 ) is determined at discrete points in time and filtered via a low-pass filter, and that the first time derivative i is _grad ( 30 ) from the filtered values of the current _flow i _pmp ( 20 ) and / or that the determined anchor stop is offset by a time offset caused by the low-pass filter ( 16 ) is corrected. A control unit for controlling an electromagnetic actuator, wherein a processing device of the control unit is supplied with a current flowing through a magnetic coil of the electromagnetic actuator current and wherein the processing means is _adapted from the current _waveform i _pmp ( 20 ) by the solenoid to determine an armature stop of the electromechanical actuator, characterized in that the processing means is adapted to a minimum ( 32.2 . 32.3 ) of the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) and the time of the minimum ( 32.2 . 32.3 ) to the anchor stop when the minimum ( 32.2 . 32.3 ) is greater than zero, and / or that the processing device is designed to perform a second zero crossing ( 33 ) of the first time derivative i _grad ( 30 ) of the current _flow i _pmp ( 20 ) and the time of the second zero crossing ( 33 ) attributable to the anchor stop.

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