DE102011088701B4 - Method for monitoring the armature movement of a reciprocating magnet pump - Google Patents

Abstract

Method for monitoring the armature movement of a reciprocating magnet pump, in particular a reciprocating diaphragm pump (22) in the delivery module (2) of an SCR catalytic converter system, wherein the pump current profile is measured over time and an end of the armature movement in the stroke direction is detected when the pump current profile reaches a local minimum (C ), whereby the reciprocating magnet pump is a reciprocating diaphragm pump (22) in the delivery module (2) of an SCR catalytic converter system and the time at which the armature movement ends in the stroke direction is used to model the pressure in the SCR catalytic converter system.

Description

The present invention relates to a method for monitoring the armature movement of a reciprocating magnet pump, in particular a reciprocating magnet pump in the delivery module of an SCR catalytic converter system. The invention further relates to a computer program that carries out all steps of the method according to the invention when it runs on a computing device. The invention also relates to a computer program product with program code that is stored on a machine-readable carrier for carrying out the method when the program is executed on a computer or control device.

State of the art

In the SCR process (Selective Catalytic Reduction), the reducing agent AdBlue ^® , which consists of one third urea and two thirds water, is added to the exhaust gas of an internal combustion engine. A nozzle sprays the liquid into the exhaust gas stream immediately before the SCR catalytic converter. There the ammonia necessary for the further reaction is formed from the urea. In the second step, the nitrogen oxides from the exhaust gas and the ammonia combine in the SCR catalytic converter to form water and non-toxic nitrogen.

The DE 10 2005 024 858 A1 relates to a method for operating a metering pump, in particular for conveying fuel for a vehicle heater, which metering pump (14) has a piston (20) that can be moved back and forth between two end positions and an associated piston (20) that can be electrically excited by applying a voltage (U). Drive unit (28, 30), includes the measures: a) applying a voltage to move the piston (20) towards an end position during energization time intervals, b) determining whether the piston (20) has a position at or near a position during an energization time interval has reached the end position, and determining the time during the excitation time interval at which the piston (20) has reached the position at or near the end position, c) comparing the time determined in step b) with a reference, c) when the distance the time at the reference is above a predetermined threshold, applying a changed voltage to shift the time toward the predetermined reference.

The DE 10 2004 002 454 A1 discloses a metering pump system, in particular for metered fuel supply to a vehicle heater, comprising a metering pump (10) with at least one metering pump element (46) movable between two end-of-movement positions and a metering pump element drive (26, 32) assigned to the at least one metering pump element (46), the metering pump element drive ( 26, 32) comprises a coil arrangement (26) and a control device (32), which controls the coil arrangement (26) to generate a magnetic force interaction in order to move the at least one metering pump element (46) in at least one direction of movement, the control device (32) being designed for this purpose is to control the coil arrangement (26) at least in phases in a pulsed manner during a control interval corresponding to a metering pump element movement process.

The DE 100 47 045 A1 discloses a control device for achieving predetermined output pressures of a magnetic pump, which has a pressure chamber equipped with an inlet and an outlet valve, to which a cylinder is connected, a prestressed pressure rod supporting the armature of an electromagnetic pressure magnet being arranged as a piston, and the armature between the two Pole pieces of the pressure magnet that can be excited by its magnetic coil can be moved, should be designed in such a way that at a given delivery height, maximum delivery flows of the pumped oil result and disruptive and energy-sapping hard stops of the anchor or anchors are avoided. For this purpose, it is proposed that the pressure magnet is assigned a displacement sensor which determines the path of its armature and that the magnetic coil of the lifting magnet is acted upon by a control device, the output current of which can be switched on by an oscillator and switched off by a comparator when the actual stroke traveled by the piston is The determined switch-off distance is less than the determined switch-off time or the running time of the piston exceeds the determined switch-off time.

1 shows the metering system for an SCR catalyst according to the prior art. This includes a reducing agent tank unit 1 with a fill level sensor, filter and heater, a delivery module 2, for example the DNOx5.1 system from Bosch, a dosing module 3 and a control device 4. The reducing agent solution is transported from the tank unit 1 into the delivery module 2. Here it passes through a suction valve 21 and is sucked into a reciprocating piston diaphragm pump 22. This comprises a membrane 221 for volumetric conveying of the reducing agent solution, a reciprocating piston 222, whose oscillating movement is transmitted to the membrane 221, a lifting magnet 223 with a magnet armature (not shown), which causes the reciprocating piston 222 to be raised when it is energized, and a compression spring 224, which presses the reciprocating piston 222 back into its seat when the solenoid 223 is no longer energized. When the reciprocating piston 222 pumps, the suction valve 21 opens so that the reducing agent can flow into the reciprocating piston diaphragm pump 22. Everyone The pump stroke therefore delivers a certain amount of urea solution. When the reciprocating piston 222 returns to its seat, the suction valve 21 closes and the reducing agent solution is pressed out of the reciprocating diaphragm pump 22 through a pressure valve 23, which at the same time serves as flood protection for the reciprocating diaphragm pump 22. The solution is then conveyed through a pulsation damper 24 and out of the delivery module 2 into the metering module 3, from which it is metered into the exhaust system. The reducing agent solution can be sucked back through a suck-back module 25 in the delivery module 2. The resuction module 25 includes a suction valve 251, a resuction pump 252 and a pressure valve 253. Reducing agent solution that leaves the resuction module can be sucked back into the tank unit 1 through an ice pressure damper 26.

As part of on-board diagnostics (OBD), it is necessary to determine the pressure in the hydraulics of an SCR catalytic converter system, which requires the use of a pressure sensor.

The task is solved by the features of the independent patent claims. Advantageous developments of the invention are described in the subclaims.

Disclosure of the invention

The method according to the invention for monitoring the armature movement in the reciprocating magnet pump, in particular a reciprocating magnet pump in the delivery module of an SCR catalytic converter system, includes measuring the pump current curve over time. An end to the armature movement in the lifting direction is recognized when the pump current curve reaches a local minimum. According to the invention, the presence of the local minimum can be recognized in particular by forming the first derivative of the pump current curve, the local minimum being present when this first derivative is equal to 0. The determination of the armature movement according to the invention enables the system pressure to be modulated. This is achieved by taking into account that a back pressure, for example when using a reciprocating diaphragm pump, the back pressure on the pump membrane, which in turn is in direct connection with the magnet armature of the reciprocating diaphragm pump, ensures that the armature of the lifting magnet of the reciprocating diaphragm pump slowly moves between its two movement points. If the back pressure in the system is higher, a larger magnetic force is required to initially move the armature. Furthermore, the armature requires a longer period of time for a pump stroke because its movement is strongly damped by the counter pressure. In this case, the magnetic field must also be larger than in a system with lower pressure.

When using this method, it should be noted that a reciprocating piston pump is influenced by a number of peripheral factors. Striking variables here are the on-board electrical system voltage, which is measured in the control unit, and the coil temperature of the solenoid. The coil temperature is converted into a temperature by using a pulse width modulation control (PWM) and by measuring the coil current that arises using computer models. The temperature as well as the voltage applied to the solenoid causes a change in the coil current. At a higher voltage, the solenoid is charged faster and the energy level for moving the gas tanker is reached more quickly. At a higher temperature, the internal coil resistance of the coil winding material used increases and the energy level for moving the armature is reached later. Using calculation models, the time at which the armature stops (pumping movement), taking into account the internal coil resistance (the coil temperature), is converted from the on-board electrical system voltage into a pressure, which counteracts the movement of the magnet armature and thus the pump membrane. Using this calculation, the system is regulated to a constant pressure by the control unit. This pressure is required to enable good spray formation in the dosing module and also to comply with the on-board diagnostic guidelines (dosage quantity derivation, consumption model, etc.).

In order to prevent artifacts in the pump current curve from being incorrectly interpreted as an indication of an end to the armature movement of the reciprocating piston magnet pump, it is preferred according to the invention to make the end point of the armature movement plausible. This can be done by determining the first derivative of the current curve between the local minimum and a local maximum preceding it and detecting the end of the armature movement in the lifting direction as reliable if the pump current intensity is in a specified range before and after the point in time of the maximum value of the first derivative of the current curve exceeds a specified threshold value. Furthermore, a plausibility check can be carried out by determining analog-digital converter values at the local minimum and a local maximum of the pump current curve preceding it and recognizing the end of the armature movement in the stroke direction as reliable, while the magnitude of the difference between these two values reaches a fixed threshold value exceeds.

To determine not only the end of the anchor movement, but also the beginning of the anchor movement In order to be able to do this, it is preferred according to the invention that the first derivative of the current curve is determined before a local maximum preceding the local minimum, the course of the first derivative is extrapolated and a start of the armature movement in the lifting direction is recognized as soon as the first derivative according to the pump current curve deviates from the extrapolated value of the first derivative by at least a specified value. In particular, the first derivative is extrapolated as an e-function. Knowing the time at which the anchor movement starts enables an even better representation of the pressure model. This allows the connection between the magnetic field and counterpressure to be worked out more precisely. When solely considering the end point of the armature movement, factors such as friction, spring force, viscosity of the medium to be compressed, deformability of the pump membrane and temperature play a significant role. These factors can be eliminated if the time at which the anchor movement starts is known, thereby increasing the significance of the assessment.

According to the invention, the presence of a local maximum in the pump current curve can be recognized by the fact that the first derivative of the pump current curve is equal to 0. The distinction between a local minimum and a local maximum is possible using the first derivative of the pump current curve, since the first derivative changes from a positive to a negative value at a local maximum in its zero crossing and from a negative to a value at the local minimum in its zero crossing positive value changes.

If the pump current curve does not reach a local minimum within a specified period of time, it is recognized according to the invention that there is a blockage of the magnet armature of the reciprocating piston pump.

The computer program according to the invention can carry out all steps of the method according to the invention if it runs on a control device or computing device. This enables, for example, the implementation of the method according to the invention in an existing SCR catalyst system without having to make any structural changes. The computer program product according to the invention with program code that is stored on a machine-readable carrier is used to carry out the method according to the invention when the program is executed on a control device or computing device.

Brief description of the drawings

• 1 zeigt ein SCR-Katalysatorsystem gemäß dem Stand der Technik.
• 2 zeigt den Pumpenstromverlauf einer Hubkolbenmagnetpumpe.
• 3 zeigt einen Detailausschnitt aus 2.
• 4 zeigt, wie durch Extrapolieren der ersten Ableitung des der Analog-Digital-Wandlerwerte des Stromverlaufs einer Hubkolbenmagnetpumpe der Beginn der Magnetankerbewegung ermittelt werden kann.
• 5 ist eine Darstellung der Analog-Digital-Wandlerwerte des Stromverlaufs einer Hubkolbenmagnetpumpe sowie deren erster Ableitung.
• 6 ist eine andere Darstellung der Analog-Digital-Wandlerwerte des Stromverlaufs einer Hubkolbenmagnetpumpe sowie deren erster Ableitung.
• 7 ist eine Darstellung der Analog-Digital-Wandlerwerte des Stromverlaufs einer Hubkolbenmagnetpumpe mit blockiertem und mit unblockiertem Anker sowie deren erster Ableitung.
• 8 stellt die Stromstärken des Pumpenstroms am Endpunkt der Ankerbewegung einer Hubkolbenmagnetpumpe unter verschiedenen Umgebungsbedingungen dar.
• 9 stellt die Steigungen zwischen lokalem Minimum und lokalem Maximum im Pumpenstromverlauf einer Hubkolbenmagnetpumpe unter verschiedenen Bedingungen dar.

Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description.

• 1 shows an SCR catalyst system according to the prior art.
• 2 shows the pump current curve of a reciprocating piston magnet pump.
• 3 shows a detailed section 2 .
• 4 shows how the start of the magnet armature movement can be determined by extrapolating the first derivative of the analog-digital converter values of the current curve of a reciprocating piston magnet pump.
• 5 is a representation of the analog-digital converter values of the current curve of a reciprocating piston magnetic pump and its first derivative.
• 6 is another representation of the analog-digital converter values of the current curve of a reciprocating piston magnetic pump and its first derivative.
• 7 is a representation of the analog-digital converter values of the current curve of a reciprocating piston magnetic pump with a blocked and unblocked armature as well as their first derivative.
• 8th represents the current strengths of the pump current at the end point of the armature movement of a reciprocating piston magnetic pump under various environmental conditions.
• 9 represents the gradients between local minimum and local maximum in the pump current curve of a reciprocating piston magnetic pump under different conditions.

Embodiments of the invention

In 2 and 3 is the current curve of the pump current of a reciprocating diaphragm pump 22 in an SCR catalytic converter system 1 shown. The changes in the current signal curve are caused by the inductance of the armature movement when the pumping process begins or when the magnet armature of the lifting magnet 223 has hit a residual air gap. In area A the current curve increases steadily. Point B represents the local maximum of the pump current curve at which the first derivative of the pump current curve is equal to 0. Point C represents a local minimum of the pump current curve at which the first derivative of the pump current curve is 0. This is the end point of the armature movement of the magnet armature of the lifting magnet 223. In area D, the current curve increases steadily. At the turning point E there is a maximum negative slope between the two extreme points B and C. The distance F reflects the difference in the current level between the two local extreme points B and C. The distance G corresponds to the time difference between the two local extreme points B and C.

4 shows how the start of the armature movement of the lifting magnet can be determined. The first derivative ADC' of an analog-digital converter signal curve ADC on the magnet armature is determined before the local maximum B. The course of the first derivative is extrapolated as an e-function ADC' _ex and a start of the armature movement in the stroke direction is recognized as soon as the first derivative deviates from the extrapolated value of the first derivative by at least a specified value according to the pump current curve at point H.

To check the plausibility of the detection of the end point of the armature movement, you can check, for example, 300 µs before and 300 µs after point E whether the change in the pump current is greater than 17.5 mA. This corresponds to 29.2 A/s. In a further plausibility check step, it can be checked whether the difference F in the pump current between the two extreme points B and C is greater than 26.2 mA. To check plausibility, according to the invention, the local negative extreme point E of the first derivative can also be evaluated between the two recognized zero crossings B and C in the first derivative of the pump current curve. This means that the largest negative value of this derivative (in digits of the analog-to-digital converter signal) must be greater than an applicable variable. This evaluates whether there was a sufficient negative slope of the derivative and whether the desired extreme points were actually found and not just noise. The current itself must fall sufficiently quickly. The values determined are classified as more reliable the faster the current falls over time. If the requirements of the first plausibility check step have been met, it is checked whether the digitized “raw electricity values” are also within a plausible range. For this purpose, it is evaluated whether the current value of an analog-digital converter between the local maximum B of the current curve and the end point C of the magnet armature movement and the current value of this point C itself have a minimum distance from an applied variable. This evaluates whether the current curve between the local maximum B before the end point of the armature movement C and at the end point C of the armature movement has a pronounced difference in height. The greater the height difference, the more reliable the values are.

5 shows how, according to the invention, the two extreme points B and C in the raw signal can be recognized by the first derivative ADC 'of the analog-digital converter signal curve ADC on the magnet armature. For each of the points B and C, a region from 300 µs before to 300 µs after this point is highlighted, which serves to determine whether a zero crossing of the first derivative ADC 'at this point occurs from positive to negative or from negative to positive. Since the signal curve of the magnet for the first zero crossing of the first derivative is relatively flat and can also contain noise, the first mathematical zero crossing B (positive to negative) of the first derivative ADC' is used at this point for further evaluation. After recording the first derivation, the first plausibility function is applied. A local maximum E of the first derivative ADC' is sought between the two zero crossings. For example, if this maximum is at least 20 digits high (applicable variable in the software of the control unit 4), the derivation ADC' is accepted as correct. This is the difference in the first derivative ADC' between points B and E in 4 has a height of 88 digits and therefore fulfills this condition.

6 shows how the current signal curve of the magnet armature of the solenoid 223 can be checked for plausibility using the values obtained for ADC 'if the first plausibility check function has confirmed the result. In the first derivative ADC' of the current signal curve, both zero points are determined and the position of the two extreme points B and C in the raw signal curve is thereby obtained. The analog-digital converter values ADC are then considered at these two points in the second plausibility check function. The minimum distance between the associated values should be at least 30 digits, for example. The diagram according to 5 was recorded at a temperature of 0 ° C, a supply voltage of the reciprocating piston pump 22 (on-board electrical system voltage) of 16 V and 0 Pa pressure. This chart has a flat but fast signal progression. It can be seen that a flat current signal ADC also flattens the value propagation of the first derivative ADC'. The first plausibility check function only results in a value of 44 digits. However, the applicable value of at least 20 digits is still maintained. The second plausibility check function results in a value of 72 digits. This also ensures that the applicable value of 30 digits is maintained. The best quality of the first derivative results from a very high negative slope in the raw signal between the local maximum and the local minimum in the raw signal.

In 7 the signal curve of the pump current of a reciprocating magnet pump 22 with an unblocked stomach tank is compared with the signal curve of the pump current of two reciprocating magnet pumps 22 with a blocked stomach tanker. Detecting whether an armature is blocked should, according to the invention, ensure under all operating conditions that no error interpretation of the coil current is incorrectly displayed as the end of the armature movement. For this purpose, the magnet mechanics must be designed in such a way that the coil current of the magnet in this case represents reliably recognizable differences to the signal curve of a correct end point of the armature movement.

For the blockage investigation, a lifting magnet 223 was manipulated in such a way that it was possible to push the magnet armature into its rest position and also into its end stop position. The investigations were carried out at a temperature of 25°C and a voltage of 16 V. The signal curve ADC ₁ , in which a local minimum can be seen, corresponds to the current curve of an intact reciprocating diaphragm pump 22. In the other two cases described, ADC ₂ and ADC ₃ , the magnet armature of the reciprocating diaphragm pump 22 is blocked. It can be seen that in the method according to the invention, only the first derivative ADC' ₁ of the signal curve on the unblocked solenoid 223 is evaluated correctly and the signal curves of the blocked solenoids do not have zero crossings of the first derivative ADC' ₂ and ADC' ₃ .

The need to monitor the armature movement of a reciprocating magnet pump 22 results from the 8th and 9 . In 8th Typical current strengths I(msp) are plotted at the end point of the armature movement of the reciprocating piston magnet pump 22 for three different vehicle electrical system voltages (10 V, 13.5 V and 16 V). The variables in the series of measurements were also the ambient temperature (0 ° C, 23 ° C, 40 ° C, 60 ° C) and the pressure built up by the reciprocating piston membrane pump 22 (0 Pa, 200 kPa, 400 kPa, 600 kPa, 800 kPa). These measurements were carried out with the same pump. The pump had an SV3 anchor.

In 9 the amount of the slope S of the pump current curve between the local maximum B and the local minimum C is shown for four different temperatures (0°C, 23°C, 40°C, 60°C), ie the slope of a straight line with which this both points are connected. 60 measurements were carried out. The measurement number is shown on the ordinate. The variables in the series of measurements continued to be the vehicle electrical system voltage (10 V, 13.5 V and 16 V) and the pressure built up by the reciprocating piston diaphragm pump 22 (0 Pa, 200 kPa, 400 kPa, 600 kPa, 800 kPa).

Out of 8th and 9 The result is that the values t(msp), I(msp) and S not only correlate with the pressure in the SCR catalytic converter system, but also depend on the vehicle electrical system voltage and temperature. Fluctuations in these variables can lead to signal noise, which can be taken into account when monitoring the armature movement using the plausibility check steps according to the invention.

Claims (9)

Method for monitoring the armature movement of a reciprocating magnet pump, in particular a reciprocating diaphragm pump (22) in the delivery module (2) of an SCR catalytic converter system, wherein the pump current profile is measured over time and an end of the armature movement in the stroke direction is detected when the pump current profile reaches a local minimum (C ), whereby the reciprocating magnet pump is a reciprocating diaphragm pump (22) in the delivery module (2) of an SCR catalytic converter system and the time at which the armature movement ends in the stroke direction is used to model the pressure in the SCR catalytic converter system. Procedure according to Claim 1 , characterized in that the first derivative of the pump current curve is formed and the presence of the local minimum is recognized when this first derivative is equal to zero. Procedure according to one of the Claims 1 until 2 , characterized in that the first derivative of the current curve between the local minimum (C) and a local maximum (B) preceding it is determined and the detection of the end of the armature movement in the lifting direction is recognized as reliable if the current intensity of the pump current is in a specified range The area before and after the time of the maximum value of the first derivative exceeds a specified threshold. Procedure according to one of the Claims 1 until 3 , characterized in that the first derivative of the current curve is determined before a local maximum (B) preceding the local minimum (C), the course of the first derivative is extrapolated and a start of the armature movement (H) in the lifting direction is recognized as soon as the first Derivation of the measured pump current curve deviates from the extrapolated value of the first derivative by at least a specified value. Procedure according to one of the Claims 1 until 4 , characterized in that at the local minimum (C) and a preceding local maximum (B) of the pump current curve, analogue Digital converter values are determined and the detection of the end of the armature movement in the stroke direction is recognized as reliable if the amount of the difference between these two values exceeds a specified threshold value. Procedure according to one of the Claims 3 until 5 , characterized in that the presence of the local maximum is recognized when the first derivative of the pump current curve is equal to zero. Procedure according to one of the Claims 3 until 5 , characterized in that a blockage of the armature of the reciprocating piston pump (22) is detected if the pump current curve does not reach a local minimum within a specified period of time. Computer program that carries out all the steps of a procedure according to one of the Claims 1 until 7 executes if it runs on a control device (4) or computing device. Computer program product with program code stored on a machine-readable medium for carrying out the method according to one of the Claims 1 until 7 if the program is executed on a control device (4) or computing device.

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