DE102018208317A1 - Method for diagnosis of exhaust gas sensors - Google Patents

Abstract

The invention relates to a diagnostic method for determining whether an exhaust gas sensor is poisoned or not poisoned. For this purpose, a sensor performance is determined. The exhaust gas sensor is rated poisoned if the value of the sensor performance is less than a predetermined limit.

Description

State of the art

From the prior art, for example DE102009027276 A1 , electrochemical exhaust gas sensors are already known.

Advantages of the invention

The present invention is based on the recognition that such exhaust gas sensors can be poisoned by some substances, for example by sulfur, whereby the dynamics of their signal deteriorates. With the method according to the invention it is possible to distinguish poisoned exhaust gas sensors from non-poisoned exhaust gas sensors.

In particular, the method of the invention relates to the diagnosis of an electrochemical exhaust gas sensor, the exhaust gas sensor having a first electrochemical cell having a first electrode which is connected to an exhaust gas, e.g. via a diffusion barrier, and having a second electrode disposed inside the exhaust gas sensor. The first electrochemical cell has a first oxygen ion conductive solid electrolyte disposed between the first and second electrodes. The exhaust gas sensor further has a second electrochemical cell, which has a third electrode which is arranged in the interior of the exhaust gas sensor and communicates there with the second electrode, and is located, for example, with the second electrode in the same gas space. The second electrochemical cell further includes a fourth electrode and includes a second oxygen ion conductive solid electrolyte disposed between the third and fourth electrodes.

In particular, it is provided that the exhaust gas sensor has a third electrochemical cell which has a fifth electrode which is arranged in the interior of the exhaust gas sensor and communicates with the second and third electrodes, and for example with the second electrode and the third electrode in the same gas space located. The third electrochemical pumping cell has a sixth electrode which is arranged in a reference gas and which has a third oxygen ion-conducting solid electrolyte, which is arranged between the fifth and the sixth electrode.

In particular, it is provided that the exhaust gas sensor has an integrated heater.

In particular, it is provided that the method according to the invention provides for a first phase preceding the time, a second phase following the first phase and a third phase subsequent in time to the second phase, the first phase ending at a first instant, the second phase being connected to the first phase The first time begins and ends at a third time, with the third phase beginning at the third time. The first phase may begin at a zero time, the second phase may include a second time, and the third phase may include a fourth time and end at a fifth time.

According to the invention, provision is made in particular for a first pumping voltage to be applied to the first electrochemical cell which, depending on the polarity, pumps oxygen ions out of the interior of the exhaust gas sensor and / or pumps the oxygen ions into the interior of the exhaust gas sensor.

It is inventively provided in particular that the first pumping voltage is varied in time so that in the second phase at least on average more oxygen ions are pumped into the interior of the exhaust gas sensor than in the first phase and that in the second phase at least on average more oxygen ions in the inside of the exhaust gas sensor are pumped into than in the third phase and / or it is provided that the first pumping voltage is varied in time so that in the second phase at least on average less oxygen ions are pumped out of the interior of the exhaust gas sensor than in the first Phase and in the second phase at least on average less oxygen ions are pumped out of the interior of the exhaust gas sensor in the third phase, so that the oxygen concentration in the interior of the exhaust gas sensor in the second phase is greater than in the first phase and larger than in the third phase , Of course, this is also included, and the stated effect is also achieved by pumping oxygen ions into the interior of the exhaust gas sensor in the second phase, while in the first phase and in the third phase, oxygen ions are pumped out of the interior of the exhaust gas sensor.

It is inventively provided in particular that to the second electrochemical cell, a second pumping voltage is applied, which pumps oxygen ions from the interior of the exhaust gas sensor, so that in the supply line to the second electrochemical cell, a second electrical pumping current is measured.

According to the invention, in particular, a value of a sensor performance is formed as a quotient of the integral over the second pumping current from the first time to the second time during the second phase and the integral over the second pumping power from the third time to the fourth time during the third time Phase.

Based on this value, it is provided that the exhaust gas sensor is judged to be poisoned if the value is less than a predetermined limit value and / or the exhaust gas sensor is rated as non-poisoned, if the value is greater than a predetermined limit value.

The method may in particular take place in an environment in which the composition of the exhaust gas does not change or changes only very slowly. Thus, the process may take place while an internal combustion engine, which is associated with the exhaust gas sensor, is in the wake.

It can be provided in particular that the time period from the first time to the second time 1 s to 8 s, in particular 3 s; is; and that the time period from the third time to the fourth time is 2 s to 12 s, in particular 5 s; and that the predetermined limit value is between 4 and 9, in particular has the value 6.5.

It can be provided, in particular, that a Nernst voltage forming at the third electrochemical cell is measured and regulated to a predetermined setpoint voltage by varying the first pumping voltage as a function of the difference between the measured Nernst voltage and the setpoint voltage, the setpoint voltage in the second phase is set by a smaller value than in the first phase and the target voltage in the second phase is given by a smaller value than in the third phase. The target voltage in the first and in the third phase may be 425 mV, for example; the target voltage in the second phase may be, for example, 225mV.

If the diagnosis has the result that the exhaust gas sensor is poisoned, then a regeneration measure can be initiated, the aim of which is to obtain an exhaust gas sensor which is to be evaluated as non-poisoned. On the other hand, if the diagnosis already has the result that the exhaust gas sensor is not poisoned, the regeneration measure can be omitted.

list of figures

• 1 shows an example of an exhaust gas sensor in cross section.
• 2 shows by way of example the second pumping current during the process
• 3 shows the sensor performance for differently pretreated exhaust gas sensors

Description of the embodiments

The exhaust gas sensor 100 , which for detecting at least a portion of a measured gas component with bound oxygen, hereinafter referred to as nitrogen oxide NOx, in a gas mixture, for example, an exhaust gas of an internal combustion engine, is arranged, for this purpose comprises a sensor element 110 a first electrochemical cell 112 (Pump cell), which is a first electrode 114 and a second electrode 116 and a first solid electrolyte formed therebetween 117 includes. The first electrode 114 , which by means of a porous aluminum oxide layer 118 from the environment of the sensor 100 is separated, in this case has a first electrically conductive connection 120 over which a first pumping voltage UP1 at the first electrochemical cell 112 can create or a first pumping current IP1 in the first electrochemical cell 112 can generate. The first electrically conductive connection 120 is this with a connection P1 an external electronic control unit 122 connected. To get a complete circuit, has the second electrode 116 also via a second electrically conductive connection 124 leading to a common connection COM of the external electronic control unit 122 leads. The first electrochemical cell 112 lies on a first cavity 126 at the inside of the sensor element 110 is located and in communication with the sample gas. By generating the first pumping current IP1 in the first electrochemical cell 112 a first portion of oxygen ions, which are formed from molecular oxygen from the gas mixture, between the first cavity 126 and the environment of the sensor 100 (For example, the exhaust) transport. In the entryway from the environment to the first cavity 126 is a diffusion barrier 128 available.

The sensor element 110 also has a third electrochemical cell 130 on (Nernst cell), which is a fifth electrode 132 and a sixth electrode 134 having. Between them is the third solid electrolyte 135 arranged. While the fifth electrode 132 over the second electrically conductive connection 124 for example, together with the second electrode 116 connected to the common terminal COM, the sixth electrode 134 a separate electrically conductive connection 136 to a terminal Vs of the external electronic control unit 122 on, so one at the third electrochemical cell 130 Nernst voltage Vs can be determined. The third electrochemical cell 130 is located on a reference gas space 138 on.

The measurement gas component nitrogen oxide NOx contained in the gas mixture passes with the bound oxygen, in particular due to a correspondingly low catalytic activity of the second electrode 116 , largely completely to a second electrochemical cell 140 (NOx cell) of the sensor element 110 , This second electrochemical cell 140 has a third electrode 142 and a fourth electrode 144 and a second solid electrolyte interposed therebetween 143 on and lies on a second cavity 145 inside the sensor element 110 on. At least one of these two electrodes 142 . 144 is designed such that upon application of a voltage by means of catalysis from the sample gas component NOx further molecular oxygen can be generated.

While the fifth electrode 142 an electrically conductive connection 146 which leads to the common terminal COM has the sixth electrode 144 an electrically conductive connection 146 via which a second pumping voltage UP2 to the second electrochemical cell 140 can be created. The electrically conductive connection 146 is this with a connection P2 the external electronic control unit 122 connected. Applying a second pumping voltage UP2 to the second electrochemical cell 140 causes a second pumping current IP2. In normal operation of the exhaust gas sensor, it serves to detect the sample gas component.

The sensor element 110 also has a heating element 148 , which by means of two supply lines 150 with connections HTR + and HTR- of the control unit 122 is connected, via which a heating current in the heating element 148 can be introduced, which by means of generating a heating power, the sensor element 110 can bring to the desired temperature.

Time of the normal operation of the exhaust gas sensor, so the detection of at least a proportion of a sample gas component with bound oxygen, separated, for example, during the wake of an internal combustion engine in the exhaust system of the exhaust gas sensor 100 is arranged, the inventive method for diagnosis of the exhaust gas sensor is carried out 100 that is now related 2 is explained by way of example.

The process begins at the zeroth time t0 with a first phase I. In the first phase I is at the first electrochemical cell 112 via a control loop, the first pumping voltage UP1 tracked such that at the third electrochemical cell 130 measured Nernst voltage Vs constant has the value 425 mV. The inside of the exhaust gas sensor 100 , in the cavities 126 and 145 therefore, the oxygen concentration present is very low, and although at the second electrochemical cell 140 the second pumping voltage UP2 is applied, the resulting second pumping current IP2 equals zero. Is the resulting second pumping current IP2 in the first phase I different from zero, it can be interpreted as an offset and the second pumping current IP2 be corrected accordingly throughout the process so that the corrected value of the second pumping current IP2 resulting in the first phase I is zero.

At the first time t1, it ends the first phase I and the second phase II of the method for the diagnosis of the exhaust gas sensor begins 100 , In the second phase II is at the first electrochemical cell 112 via the control loop the first pumping voltage UP1 so tracked that at the third electrochemical cell 130 measured Nernst voltage Vs constant has the value 225 mV. The oxygen concentration inside the exhaust gas sensor 100 So in the cavities 126 and 145 is correspondingly larger and that through the second electrochemical cell 140 flowing ionic current is correspondingly larger. Like in the 2 can be seen, the second pumping current jumps IP2 at the second time to a high value. After a brief transient, the second pumping current remains IP2 in the second phase II at a high value. In this example, the value of the integral becomes above the second pumping current IP2 between the first time t1 and a second time t2, which is three seconds after the first time t1, integrated and the resulting value I1 detected.

Later, at the third time t3, ends the second phase II and the third phase III starts. At this stage will be at the first electrochemical cell 112 via the control loop, the first pumping voltage UP1 tracked again such that at the third electrochemical cell 130 measured Nernst voltage has a constant value of 425 mV. The oxygen concentration inside the exhaust gas sensor 100 So in the cavities 126 and 145 Therefore, it decreases again to a very low value and following a transient is the second pumping current IP2 (if necessary after deduction of the offset determined in the first phase I) zero. In this example, the value of the integral becomes above the second pumping current IP2 between the third time t3 and a fourth time t4, which is five seconds after the third time t3, integrated and the resulting value I2 detected. The third phase III ends at the fifth time t5, subsequent to the fourth time t4.

There will be a sensor performance SPI as a quotient I1 / I2 calculated, ie as a quotient of the integral I1 over the second pumping current IP2 from the first time t1 to a second time t2 during the second phase II and the integral I2 over the second pumping current IP2 from the third time t3 to a fourth time t3 during the third phase III ,

If the sensor performance SPI is less than or equal to 6.5, the exhaust gas sensor becomes 100 rated as poisoned; otherwise, as not poisoned.

Will the exhaust gas sensor 100 evaluated as poisoned, there is a regeneration measure, the aim of which is to be evaluated as non-poisonous exhaust gas sensor 100 to obtain.

Otherwise, no specific action occurs.

In one experiment, a total of 34 exhaust gas sensors 100 subjected to the diagnostic method according to the invention, see 3 ..

A first group of sensors in the 3 described by the letter A, was in new condition. As described above, values between 7 and 8.5 were measured as sensor performance SPI. It was concluded that these sensors are not poisoned

A second group of sensors in the 3 described by the letter B, was aged for 50 hours in the exhaust system of a regular internal combustion engine. Then, as described above, values between 8 and 10 were measured as sensor performance SPI. It was concluded that these sensors are also not poisoned

A third group of sensors in the 3 described by the letter C was contacted with sulfur-containing compounds for 10 hours. As described above, values between 4 and 5 were then measured as sensor performance SPI. It was concluded that these sensors were poisoned. These sensors could subsequently be regenerated by suitable measures.

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

• DE 102009027276 A1 [0001]

Claims (7)

A method of diagnosing an electrochemical exhaust gas sensor (100), wherein the exhaust gas sensor (100) comprises a first electrochemical cell (112) having a first electrode (114) communicating with an exhaust gas and having a second electrode (116) disposed in Inner (126) of the exhaust gas sensor (100) is arranged, and a first oxygen ion conductive solid electrolyte (117) disposed between the first and the second electrode (114, 116), wherein the exhaust gas sensor (100) is a second electrochemical pumping cell (140) having a third electrode (142) disposed inside the exhaust gas sensor communicating therewith with the second electrode (116) and having a fourth (144) electrode and containing a second oxygen ion conductive solid electrolyte (143). disposed between the third and fourth electrodes (142, 144); wherein the method provides a chronologically preceding first phase (I), a first phase following the first phase second phase (II) and one of the second phase (II) temporally subsequent third phase (III), wherein the first phase (I) to a the first time (t1) ends, the second phase (II) beginning at the first time (t1) and ending at a third time (t3), the third phase (III) beginning at the third time (t3); wherein a first pumping voltage (UP1) is applied to the first electrochemical cell (112) which pumps oxygen ions out of the interior (126) of the exhaust gas sensor (100) and / or the oxygen ions into the interior (126) of the exhaust gas sensor (100) wherein the first pumping voltage (UP1) is varied in time so that in the second phase (II) at least on average more oxygen ions are pumped into the interior (126) of the exhaust gas sensor (100) than in the first phase (I) and in the second phase (II), at least on average, more oxygen ions are pumped into the interior (126) of the exhaust gas sensor (100) than in the third phase (III) and / or the first pumping voltage (UP1) is varied over time, in the second phase (II), at least on average, less oxygen ions are pumped out of the interior (126) of the exhaust gas sensor (100) than in the first phase (I) and in the second phase (II) at least on average less oxygen ions from the latter Inner (126) of the Abg Assensors (100) are pumped out than in the third phase (III), so that the oxygen concentration in the interior (126) of the exhaust gas sensor in the second phase (II) is greater than in the first phase (I) and greater than in the third Phase (III); wherein a second pumping voltage (UP2) is applied to the second electrochemical cell (140), which pumps oxygen ions out of the interior (145) of the exhaust gas sensor (100), so that in the supply line (146) to the second electrochemical cell (140) electrical pumping current (IP2) is measured; wherein a value of a sensor performance (SPI) is formed as the quotient of the integral (I1) over the second pumping current (IP2) from the first time (t1) to a second time (t2) during the second phase (II) and the integral (12) via the second pumping current (IP2) from the third time (t3) to a fourth time (t4) during the third phase (III); wherein the exhaust gas sensor (100) is judged to be poisoned if the value of the sensor performance (SPI) is less than a predetermined limit and / or the exhaust gas sensor (100) is rated as non-poisoned if the value of the sensor performance (SPI) is greater than one predetermined limit. Method according to Claim 1 characterized in that the time period from the first time (t1) to the second time (t2) is 3s, and that the time from the third time (t3) to the fourth time (t4) is 5s, and that the predetermined threshold is 6.5 Method according to Claim 1 or 2 characterized in that the exhaust gas sensor (100) comprises a third electrochemical cell (130) having a fifth electrode (132) disposed inside (145) of the exhaust gas sensor (100) and connected to the second and third electrodes (116 , 142) having a sixth electrode (134) disposed in a reference gas and having a third oxygen ion conductive solid electrolyte (135) interposed between the fifth and sixth electrodes (132, 134), one Nernst voltage (Vs) forming at the third electrochemical cell (130) is measured and regulated to a predetermined target voltage by varying the first pumping voltage (UP1) as a function of the difference of the measured Nernst voltage (Vs) and the nominal voltage, the reference voltage in the second phase (II) is given by a smaller voltage than in the first phase (I) and the target voltage in the second phase (II) by a smaller one e voltage is given as in the third phase (III). Method according to Claim 3 , characterized in that the predetermined target voltage during the first and the third phase (III) is 425 mV and that the predetermined target voltage during the second phase (II) is 225 mV Method according to one of the preceding claims, characterized in that the exhaust gas sensor (100) during the process by means of an integrated heater (148) is heated to an operating temperature. Method according to one of the preceding claims, characterized in that in the case of an exhaust gas sensor (100) assessed as poisoned, a regeneration measure is initiated whose target it is to obtain an exhaust gas sensor (100) to be evaluated as non-poisoned. Method according to one of the preceding claims, characterized in that the poisoning is carried out by sulfur and the regeneration measure is in particular to remove the sulfur from the exhaust gas sensor (100).

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