DE102017208458A1 - A method of detecting an occurrence of an open line in a sensor - Google Patents

Abstract

The present invention relates to a method for detecting an occurrence of an open line in a sensor, wherein the sensor has a sensor element for detecting at least one property of a fluid medium, in particular an exhaust gas of an internal combustion engine. The sensor further comprises a heating element which applies a heating power to the sensor element only during at least one time period, the sensor element generating at least one first measuring signal during the period and at least one second measuring signal outside the period. The occurrence of an open line in the sensor is detected by the fact that the at least one second measurement signal (124) within a threshold value (132) corresponds to the at least one first measurement signal (122). The present invention further relates to a computer program which is set up to perform the steps of the method, an electronic storage medium on which such a computer program is stored, and an electronic control unit comprising such an electronic storage medium.

Description

State of the art

The invention relates to a method for detecting an occurrence of an open line in a sensor. The present method is in this case directed to a use in a sensor for detecting at least one property of a fluid medium, in particular an exhaust gas of an internal combustion engine. The present invention further relates to a computer program which is adapted to perform the steps of said method, an electronic storage medium on which such a computer program is stored, and an electronic control unit comprising such an electronic storage medium.

Methods and sensors for detecting at least one property of a fluid medium, in particular for detecting at least a portion of a gas or of particles in a gas mixture, are known from the prior art. The invention will be described below, without limitation of other possible embodiments, essentially with reference to sensors which for quantitative and / or qualitative detection of at least one portion, in particular a partial pressure and / or a volume fraction and / or a mass fraction, a gas or of Serve particles in a gas mixture. The gas can be an exhaust gas of an internal combustion engine, in particular in the automotive sector. In particular, a lambda probe, a NOx sensor, an SOx sensor, a COx sensor or a particle sensor can serve as a sensor for detecting the gas fraction. Such sensors are for example in Reif, K., Deitsche, K.-H. et al., Kraft Paperback, Springer Vieweg, Wiesbaden, 2014, pages 1338-1347 described.

Lambda probes, in particular universal lambda probes, equilibrate two streams, in particular oxygen streams, between two volumes, which may be a gas space outside the device or a cavity in the device. One of the streams is driven by concentration differences through a diffusion barrier. Another stream of material is driven via a solid state electrolyte and two electrodes, in particular two pumping electrodes controlled by an applied pumping current. The pumping current is preferably adjusted so that adjusts a constant and very low oxygen concentration in the cavity. A concentration profile across the diffusion barrier is uniquely determined by a constant control point in the cavity, in particular a constant setpoint voltage resulting in an oxygen concentration, and by an exhaust gas oxygen concentration. An influx of oxygen molecules from the sample gas space to the cavity adjusts according to this unique concentration profile and corresponds to the regulated pumping current. Therefore, the pumping current can serve as a measured value for the oxygen concentration in the measuring gas space, in particular for the oxygen concentration on the exhaust gas side.

Furthermore, methods and sensors for detecting at least a portion of the measured gas component with bound oxygen in a gas mixture, in particular in an exhaust gas of an internal combustion engine, by detecting a proportion of oxygen, by a reduction of the measurement gas component, in particular a nitrogen oxide NO _x , a sulfur oxide SO _x or a carbon oxide CO _x , which generates bound oxygen, in the presence of molecular oxygen. The EP 0769693 A1 discloses a method and an NO _x sensor for detecting at least a portion of the oxygen-bound measurement gas component, particularly the nitrogen oxide NO _x , in a gas mixture by detecting a proportion of oxygen generated by a reduction of the measurement gas component with the bound oxygen Presence of molecular oxygen, in particular by the reduction of the nitrogen oxide NO _x by means of a catalyst suitable for this purpose. The sensor includes a first pumping cell which abuts a first cavity communicating with the sample gas space, the first pumping cell serving to transport oxygen from the first cavity, thereby establishing a lower oxygen partial pressure in the first cavity. The sensor further comprises a reference cell which abuts a reference gas space and which serves to transport oxygen from the second cavity such that an oxygen partial pressure in an atmosphere in the second cavity can be regulated such that the oxygen partial pressure Has value that does not affect the detection of the proportion of the sample gas component. The sensor finally comprises a second pumping cell, which rests against a second cavity, wherein a voltage applied to the second cavity electrode, in particular by a thereto introduced into the electrode catalyst, is adapted to the measured gas component with the bound oxygen, preferably a nitrogen oxide NO _x to reduce or decompose in the atmosphere introduced into the second cavity. The oxygen produced by reduction or degradation of the measurement gas component in the second cavity, which preferably originates from the reduction of the nitrogen oxide NO _x , is converted into the reference gas space by means of the second pumping flow transported and its proportion by means of a value to which the second pumping current is adjusted, demonstrated. Thus, by means of a cascade of at least three pump cells arranged one behind the other, the proportion of nitrogen oxide NO _x in a gas mixture which, in addition to the nitrogen oxide NO _x, also comprises oxygen, can be determined in a measuring gas space.

In this case, it is necessary if the sensor element arranged in the sensor has already reached the operating temperature, which in the case of a NOx sensor assumes a value of 600 ° C. to 800 ° C., during the recording of a measured value, since in the case where the operating temperature has not been reached for the sensor in question or can not be kept within predetermined limits, in particular the accuracy of the measured values detected by the sensor element is partially severely impaired. Therefore, the sensor preferably has at least one controllable heating element which is adapted to bring the sensor element to the operating temperature and to keep the temperature of the sensor element within the predetermined limits.

Legislation requires that such sensors, which serve to quantitatively and / or qualitatively detect at least a portion of a gas or particles in the exhaust gas of an internal combustion engine, be subjected to continuous monitoring. In this case, the monitoring must in particular be set up in order to be able to detect a short circuit and / or an open circuit in electrical connections between the sensor element on the one hand and the battery or the ground on the other hand , In this case, it is prescribed in particular that the monitoring takes place, as far as technically possible, with a sampling rate of at least 2 Hz.

Especially in the case of NOx sensors and particle sensors, this legal requirement poses a great technical challenge, since the sensor in this type of sensor typically indicates a very low sensor signal close to zero, since in a purified exhaust gas neither NO _x molecules nor particles in one significant proportion are present. As a result of this fact, the very small sensor signal is practically indistinguishable from an open line. Therefore, in NOx sensors, detection of occurrence of an open line is usually made by once forcing current flow through the sensor at the start of the sensor. If a current flow can be detected, an open line can be excluded. However, in this way, the above-mentioned legal requirement that the sensor is monitored at a sampling rate of at least 2 Hz can not be met. Forcing a flow of current through the sensor during operation of the sensor is also disadvantageous in that a measurement capability of the sensor is impaired and also a longer time, which can typically be 20 s, until the sensor can be used again in a defined range. Since the NOx sensor is designed to be able to detect very small changes in the gas component very sensitive, this disadvantage remains even if the forced current flow is kept very low.

Disclosure of the invention

The present invention therefore relates to a method for detecting an occurrence of an open line in a sensor, a computer program, which is adapted to perform the steps of the method, an electronic storage medium, on which such a computer program is stored, and an electronic control unit, which comprises such an electronic storage medium, having the features of the independent claims. The dependent claims describe advantageous developments of the present method.

The sensor used for carrying out the present method comprises a sensor element which is set up to detect at least one property of a fluid medium, in particular an exhaust gas of an internal combustion engine, preferably with the properties described above. In this case, the sensor element is in particular configured to generate a plurality of measurement signals from which the at least one property of the fluid medium can be determined. The sensor is in particular a lambda probe, a NOx sensor, an SOx sensor, a COx sensor or a particle sensor, the NOx sensor and the particle sensor being particularly preferred. For further details with respect to the respective sensor element, reference is made to the above description and the prior art.

The sensor used for carrying out the present method further comprises at least one controllable heating element, which is set up to apply a selected heating power to the sensor element during at least one period of time. The heating element therefore serves, in particular, to bring the sensor element to an operating temperature which, in the case of a NOx sensor, can reach a value of 600 ° C. to 800 ° C. by application of the heating power and the temperature of the sensor element at the operating temperature within to be kept within predetermined limits. This way you can the highest possible accuracy of the measured values detected by the sensor element is made possible.

Outside the period under which the sensor element is not exposed to the selected heating power. Without limiting the generality may be stated as a reason for this, in particular that NOx sensors and particle sensors are equipped as so-called "high-Z sensors" usually with high insulation resistance of the sensor line. However, since the measured signals detected by the sensor element are very small, despite the high insulation resistances, a crosstalk of the heating voltage applied to the heating element to the measured signals detected by the sensor element can occur. By means of the heating element and an associated operation of the heating element, a disturbance of the measuring signals of the sensors, in particular of the NOx sensors and the particle sensors, can thus be generated. This phenomenon is usually summarized under the term heater input (HEK). In some cases, the heater coupling can take on such an extent that the measuring signal can no longer fulfill specified specifications. In order to prevent such effects, therefore, in a preferred embodiment, only those measurement signals are evaluated, which are outside the said period, i. while the charging of the sensor element with the selected heating power is omitted, be detected.

In a preferred embodiment, the heating element can be operated by means of a selected heating cycle, particularly preferably by means of a pulse-width-modulated control. However, other types of heating cycles are also possible. Here, the term "pulse width modulation", or "PWM" for short, denotes a type of drive which defines a cycle having a multiplicity of successive first time periods and second time durations. On the one hand, for this purpose, the sensor element is supplied with heating power by the heating element during the first time periods, which may also be referred to as "PWN = ON" in the present cycle; on the other hand, however, during the second periods of time, which may also be referred to as "PWN = OFF" in the present cycle, an application of the heating power to the sensor element is omitted. The pulse width modulation can be set up in particular by applying the heating element with full battery voltage during the first time periods and not applying a voltage during the second time periods so that the heating element can apply the heating power to the sensor element only during the first time periods.

For the pulse width modulated drive, a repetition rate between the respective first time periods, i. when the associated cycle enters an area with "PWN = ON". In particular, in order to meet the above-mentioned requirements for detecting the occurrence of an open line in the sensor, the repetition rate may preferably be set to a value of at least 2 Hz. However, other values for the repetition rate are conceivable; typical values for the pulse-width-modulated actuation are in a range from 20 Hz to 300 Hz.

The present method makes it possible to perform detection of occurrence of an open line in the sensor as described below. For this purpose, the sensor can have a plurality of electrical lines, in particular in each case an electrical line which is connected to the sensor element with a voltage source, in particular a battery or an accumulator, and with a mass, in particular the mass of the motor vehicle. Other lines can be used, for example, to control the sensor element or parts thereof and / or read out measured values from the sensor element. The term "open line", which may also be referred to as a "broken line", refers here to an electrical line which may have been interrupted at any point and therefore can not form a closed circuit. When an open line occurs, therefore, the sensor, depending on the nature and / or location of the interruption of the relevant electrical line, a measuring task assigned to him not, inadequate or perform at least partially incorrect manner. The term "occurrence" here refers to an actual presence or absence of open conduction in the sensor. The term "detection" here refers to a process which can prove the occurrence or non-occurrence of an open line in the sensor as clearly as possible. In a preferred embodiment, in this case the occurrence of an open line in the sensor can be output to an electronic control unit and / or a user, whereby in particular countermeasures can be triggered.

In order to determine the occurrence of an open line in the sensor, it is first proposed that the sensor element generates at least a first sensor signal and at least one second sensor signal. In this case, the at least one first sensor signal is detected during the period, in particular during the at least one first time period in which the associated cycle of the pulse-width-modulated actuation of the heating element is in an area with "PWN = ON". In contrast, the at least one second sensor signal is outside the period, in particular during the at least one second Period in which the associated cycle in the pulse width modulated control of the heating element is in an area with "PWN = OFF" detected.

Furthermore, it is proposed to detect the occurrence of an open line in the sensor in that the at least one second sensor signal within a threshold value corresponds to the at least one first sensor signal. For this purpose, a difference between the at least one first sensor signal and the at least one second sensor signal can preferably be formed and checked as to whether the difference lies below the threshold value, which corresponds to the occurrence of an open line in the sensor. However, if the difference is above the threshold, no occurrence of open conduction in the sensor can be detected. Other types of comparison between the two types of measurement signals are possible, however. In addition, the measurement signals can first be subjected to a treatment, in particular a filtering, before the difference formation, for example in order to enable an improved suppression of noise. The term "threshold value" here denotes a specified value, below or above which a defined consequence occurs. In the present case, an undershooting of the threshold by said difference corresponds to an occurrence of an open line in the sensor, while exceeding the threshold by the difference detects a non-occurrence of an open line in the sensor. In this case, the threshold value can have a height that the person skilled in the art can determine on the basis of simple tests without any special instructions. For example, the threshold may assume a value of 50 to 100 nA.

The proposed method can be understood by applying the above diagram of the operation of the sensor. When a disturbance occurs through the heater input, it can be assumed that the measurement signals generated by the sensor element during the period, i. in the cycle at PWM = ON, at least on average higher. However, the disturbance by the heater input can only occur if the line is functional, i. there is no open position on the lines in the sensor. In contrast, the heater coupling in an open line cause no disturbance of the measurement signal, so that the measurement signal in this case can not change within and outside the period due to the heater input.

In a particular embodiment, the said difference between a plurality of first measurement signals and a plurality of second measurement signals can be formed. For this purpose, in particular during each period, i. in the cycle at PWM = ON, a plurality of first measurement signals are recorded. Likewise, especially outside of the time period, i. in the cycle at PWM = OFF, a plurality of second measurement signals are recorded. In this case, an average value can be created from the plurality of the respective measured values and compared with one another. Other types of evaluation are possible.

In a particular embodiment, a plurality of differences between exactly one first measurement signal and exactly one second measurement signal can be formed, wherein the exactly one second measurement signal outside the time period can follow in time to exactly one first measurement signal within the time period. From the plurality of differences, a common average value can be determined, wherein, in the event that the common mean value of the differences lies below the threshold value, the occurrence of an open line in the sensor can be detected.

Regardless of the configuration of the present method, this can afford a detection of the occurrence of an open line in a sensor with a very high repetition rate, wherein in principle a quasi-continuous detection is possible, which can depend only on a measurement rate of the sensor element. In addition, independent detection according to the above-described method may also be performed by forcing a current flow through the sensor, in particular at the start of the sensor or between two measurement phases of the sensor, which can be used in particular to detect a possible misdetection based on exclusive use of the present method.

In another aspect, the present invention includes a computer program configured to perform the steps of the described method.

In a further aspect, the present invention comprises an electronic storage medium adapted to store a computer program thus equipped.

In another aspect, the present invention includes an electronic control unit configured to include an electronic storage medium having stored thereon a computer program configured to perform the steps of the described method.

list of figures

• 1 eine schematische Darstellung eines Verhaltens eines Sensors in Abhängigkeit von einem Heizzyklus (1C) für einen Sensor mit funktionalen Leitungen (1A) bzw. für einen Sensor mit mindestens einer offenen Leitung (1B);
• 2 eine schematische Darstellung eines Verlaufs eines gefilterten Messsignals aus einem NOx-Sensor;
• 3 ein bevorzugtes Ausführungsbeispiel zur Durchführung des vorliegenden Verfahrens;
• 4 eine schematische Darstellung eines zweiten von zwei aufeinander folgenden Messsignalen in einem Sensor bei einem Wechsel im Heizzyklus zwischen den beiden Messsignalen; und
• 5 ein weiteres bevorzugtes Ausführungsbeispiel zur Durchführung des vorliegenden Verfahrens.

Preferred embodiments of the present invention are illustrated in the figures and will be explained in more detail in the following description. Hereby show:

• 1 2 is a schematic representation of a behavior of a sensor as a function of a heating cycle (FIG. 1C ) for a sensor with functional lines ( 1A ) or for a sensor with at least one open line ( 1B );
• 2 a schematic representation of a course of a filtered measurement signal from a NOx sensor;
• 3 a preferred embodiment for carrying out the present method;
• 4 a schematic representation of a second of two consecutive measurement signals in a sensor at a change in the heating cycle between the two measurement signals; and
• 5 another preferred embodiment for carrying out the present method.

Embodiments of the invention

1 shows a preferred embodiment of an implementation of the present method using the example of a NOx sensor, which has a sensor element for detecting at least one property of a fluid medium, in particular an exhaust gas of an internal combustion engine, and at least one heating element. However, other types of sensors are also possible, in particular particle sensors.

As in 1 C shown, the sensor element by means of a heating cycle 110 acted upon, wherein the heating cycle shown schematically here 110 a pulse width modulation (PWN) 112 corresponds to the control of the heating element. However, other types of heating cycles are also possible. For the pulse width modulation used here 112 becomes the sensor element during first time periods 114 , also referred to as "PWN = ON", is supplied with heating power from the heating element, during second periods of time 116 , which are also referred to as "PWN = OFF", the loading of the sensor element with the heating power is omitted. The pulse width modulation 112 In particular, it can be set up by the heating element during the first time periods 114 full battery voltage, here 12 V, is applied during the second time periods 116 but not with voltage, ie with 0 V, is applied. For the pulse width modulation 112 can by choosing a time interval 118 between two consecutive first periods of time 114 a repetition rate can be set, in particular to meet the above-mentioned requirements for detecting the occurrence of an open line in the sensor, at most 2 Hz. However, other values for the repetition rate are conceivable, up to a quasi-continuous acquisition of measurement signals.

1A shows for a sensor with functional lines, ie for a sensor which has no open line, a first time course 120 of measuring signals. This will be the first measurement signals 122 which within the first time periods 114 with PWN = ON, denoted by an "o", while second measurement signals 124 which are within the second time periods 116 with PWN = OFF, are denoted by an "x". It can be clearly seen that a first signal level 126 the first measurement signals 122 , which is approximately at a value of 10 ppm NO _x , and a second signal level 128 the second measurement signals 124 , which is approximately at a value of 0 ppm NO _x , to clearly distinguish a difference Δ. As shown above, this difference can be between the first signal level 126 and the second signal level 128 to a crosstalk of the heating voltage applied to the heating element to be attributed to the detected by the sensor element measurement signals, whereby a disturbance of the measurement signals of the NOx sensors can be generated, which is commonly referred to as Heizereinkopplung (HEK).

In contrast, shows 1 B an exemplary second time course 130 for a faulty sensor in which an open line is present. It can be seen that the at least one second measurement signal 124 within a threshold 132 the at least one first measurement signal 122 corresponds; this in 1A recognizable phenomenon of Heizereinkopplung is not recognizable here. For example, the threshold value may assume a value of 50 to 100 nA.

2 shows a schematic representation of the time course of filtered first measurement signals 122 from a NOx sensor, which has functional lines, over the time t. Here are the measuring signals after a first curve 136 which only the first measuring signals 122 with PWN = ON, and after a second turn 138 which only the second measuring signals 124 with PWN = OFF, separated from each other, whereby also in this type of representation, the first signal levels 126 by the difference Δ clearly from the second signal height height 128 differ.

The difference between the first course 120 according to 1A and the second course 130 according to 1B can be used according to the present method to detect the occurrence of an open line in a sensor.

In a first embodiment according to a first flowchart 138 can, like out 3 shows a variety of measurement signals 140 recorded and after a decision 142 in which part of the pulse width modulation 112 the heating cycle 110 is located, ie at PWN = ON or PWN = OFF, each associated with a cohort and this preferably each one filtering 144 be subjected. As shown above, only the second measurement signals recorded at PWN = OFF will be used 124 as sensor signals 146 used. Between the measuring signals 140 The two cohorts for PWN = ON and PWN = OFF result in the difference Δ between the measuring signals 140 , The difference Δ obtained in this way can be used in a comparison unit 148 with the threshold 132 be compared. This can be a diagnostic result 150 determined and output, for a first case in which the difference Δ below the threshold 132 can say that the sensor has at least one open line, and a second case in which the difference Δ above the threshold 132 indicates that the sensor has functional lines. Depending on a measuring rate of the sensor element, the detection of the occurrence of an open line in the sensor can thus be carried out with a very high repetition rate, wherein in principle a quasi-continuous output of the diagnosis result 150 is possible.

4 schematically shows a representation of a second of two consecutive measurement signals in a NOx sensor, wherein between the two measurement signals, a change in the heating cycle 110 from PWN = ON to PWN = OFF. For the first case in which the sensor has at least one open line, there is a later recorded measurement signal 152 in the same place as a previously recorded measurement signal 154 , while in the second case, in which the sensor has functional lines, a later recorded measurement signal 156 a signal value which is higher by the difference Δ 158 as the previously recorded measurement signal 154 accepts.

Based on the illustration according to 4 can in a second embodiment according to 5 to detect the occurrence of an open line in a sensor, two consecutive separate measurement signals 140 according to a second flowchart 160 be detected, taking between the two measurement signals 140 a change 162 in the heating cycle 110 from PWN = ON to PWN = OFF. Following this, the difference Δ between the two consecutive measurement signals 140 educated. From a plurality of differences Δ thus formed, an average value 164 to be determined, which in the comparison unit 148 with the threshold 132 can be compared. Again, the diagnostic result 150 for the first case in which the difference Δ is below the threshold value 132 can say that the sensor has at least one open line, and for the second case in which the difference Δ above the threshold value 132 is that the sensor has functional lines. Thus, the detection of the occurrence of an open line in the sensor can also be done here with a very high repetition rate.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0769693 A1 [0004]

Cited non-patent literature

• K., Deitsche, K.-H. et al., Automotive Handbook, Springer Vieweg, Wiesbaden, 2014, pages 1338-1347 [0002]

Claims (12)

A method for detecting an occurrence of an open line in a sensor, wherein the sensor comprises a sensor element for detecting at least one property of a fluid medium, in particular an exhaust gas of an internal combustion engine, and at least one heating element, wherein the heating element with only one period of time Heating power applied, characterized in that the sensor element during the period at least a first measurement signal (122) and outside the period at least one second measurement signal (124), wherein the occurrence of an open line in the sensor is detected by the fact that the at least one second Measuring signal (124) within a threshold value (132) corresponds to the at least one first measurement signal (122). Method according to the preceding claim, characterized in that a difference (Δ) is formed between the at least one first measuring signal (122) and the at least one second measuring signal (124) and the difference (Δ) is below the threshold value (132). Method according to the preceding claim, characterized in that the at least one first measuring signal (122) and the at least one second measuring signal (124) are first subjected to filtering (144) and then the difference (Δ) between the at least one first measuring signal (122 ) and the at least one second measurement signal (124) is formed. Method according to one of the two preceding claims, characterized in that the difference (Δ) between a plurality of first measurement signals (122) and a plurality of second measurement signals (124) is formed. Method according to one of the three preceding claims, characterized in that a plurality of differences (Δ) are formed between exactly one first measurement signal (122) and exactly one second measurement signal (124), and an average value (Δ 4) is calculated from the plurality of differences (Δ) ), wherein the mean value (164) of the differences (Δ) is below the threshold value (132). Method according to one of the preceding claims, characterized in that the heating element is controlled by means of a heating cycle (110), wherein the heating cycle (110) comprises a pulse width modulated drive, which defines a plurality of successive first periods (114) and second periods (116) wherein the heating element during the first periods (114), the heating element applied to the sensor element and wherein the heating element during the second periods (116) does not act on the sensor element with the heating power. Method according to the preceding claim, characterized in that the pulse width modulated drive has a repetition rate of at least 2 Hz. Method according to one of the preceding claims, characterized in that the sensor element is connected via at least one electrical line to a voltage source and to a ground in combination. Method according to one of the preceding claims, characterized in that the occurrence of an open line in the sensor is output to an electronic control unit and / or a user. Computer program adapted to perform the steps of the method of any one of the preceding claims. An electronic storage medium on which a computer program according to the preceding claim is stored. An electronic control unit comprising an electronic storage medium according to the preceding claim.

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