EP2449237A1

EP2449237A1 - Method and diagnostic device for diagnosing a heatable exhaust gas probe of an internal combustion engine

Info

Publication number: EP2449237A1
Application number: EP10726131A
Authority: EP
Inventors: Cyril Verdier; Stefan Klein; Gerhard Lemke; Karsten Glashoff; Peter Brida; Frank Meier; Thomas Seiler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2009-07-01
Filing date: 2010-06-30
Publication date: 2012-05-09
Also published as: KR20120102497A; US20120167656A1; CN102472185A; JP5620483B2; JP2012531603A; WO2011000853A1; US9062623B2; DE102009027378A1; CN102472185B

Abstract

The invention relates to a method (71) for diagnosing a heatable exhaust gas probe (11) of an internal combustion engine, wherein a predetermined temporally varying or constant voltage (U₁, U₂) or a predetermined temporally varying or constant current (I₁, I₂) is generated by means of a voltage source (41, 51), the voltage (U₁, U₂) or the current (I₁, I₂) is applied to terminals (APE, RT, I PN, RE, ALE, I PE, 37) of the exhaust gas probe (11), a current (I₁, I₂) that flows through the voltage source or a voltage (U₁, U₂) that is applied to the voltage source when a voltage (U₁, U₂) or a current (I1, I2) is applied is detected, and the current (I₁, I₂) or the voltage (U₁, U₂) is evaluated for diagnosing the exhaust gas probe (11). In order to provide a method (71) for diagnosing the exhaust gas probe (71), which allows a reliable and accurate diagnosis of the exhaust gas probe (71) and permits information to be derived about the type of error potentially present in the exhaust gas probe (71), according to the invention the method (71) is carried out independently of an open and/or closed loop control unit of the internal combustion engine, wherein an operating temperature of the exhaust gas probe (71) is adjusted to a predetermined temperature value by way of a control element (59) that is separate from the open and/or closed loop control unit.

Description

description

title

Method and diagnostic device for diagnosing a heatable

Exhaust probe of an internal combustion engine

State of the art

The invention relates to a method for diagnosing a heatable exhaust gas probe of an internal combustion engine according to the preamble of claim 1 and to a diagnostic device according to the preamble of claim 15.

It is well known internal combustion engines, in particular

Internal combustion engines for motor vehicles to equip with one or more exhaust probes. The exhaust gas probes are usually connected to a control and / or regulating device of the internal combustion engine, so that the control and / or regulating device can acquire information about the composition of exhaust gases emerging from the combustion chambers of the internal combustion engine. As an exhaust gas probe, at least one lambda probe is usually provided in an internal combustion engine with which an oxygen concentration in the exhaust gas can be detected. This allows a conclusion to an air

Fuel ratio in the combustion chamber, so that the internal combustion engine

For example, can be regulated so that exhaust gas regulations are met. The lambda sensors can be in so-called jump probes and

Divide broadband probes. The broadband probes can in turn be designed as single-cell broadband probes or as two-cell broadband probes. A jumping probe has a fairly high sensitivity for an air ratio of the exhaust gas which is in the range of λ = 1. For air numbers not in the range of about λ = 1, the sensitivity of the jump probes is relatively low.

Therefore, a continuously increasing air ratio in the exhaust gas results Jump of an output signal generated by a jump probe as soon as the air ratio enters the range of about λ = 1. By contrast, broadband lambda probes have a relatively high sensitivity even outside the range of the air ratio lying around the value λ = 1.

Modern internal combustion engines usually have one or two

Lambda sensors, which are used for gasoline engine jump and / or broadband probes. Diesel internal combustion engines have predominantly broadband lambda probes.

During operation of the internal combustion engine, the control and / or regulating unit detects sensor signals generated by the lambda probe or the lambda probes and further sensors of the internal combustion engine and operates the internal combustion engine as a function of these sensor signals. To detect errors in the sensors, the control and / or

Control device during operation of the internal combustion engine, the individual sensor signals. In this case, the signals are usually checked as to whether electrical faults (for example short circuits or interruptions of lines) are present. For this purpose, it can be checked, for example, whether the sensor signals are within admissible value ranges. In addition, the tax and / or

Control device usually, whether system errors exist. A system error is detected, for example, if the variables detected by means of different sensors contradict each other. Recognizes the tax and / or

Control device an electrical fault and / or a system error, then it notes the occurrence of the error in a fault memory.

Known diagnostic methods, for example, for the preparation of

Repairs or maintenance work on the internal combustion engine

or on a motor vehicle, in which the internal combustion engine is installed, carried out, resort to the example in the

Error memory stored information back. As a result, conclusions about the functionality of a lambda probe can be drawn to a certain extent. As in the operation of the internal combustion engine complex

Interactions between different components of the

Internal combustion engine is a sufficiently safe and reliable

However, diagnosis of a single lambda probe is not possible. Becomes For example, detected an electrical fault, then can not be determined with certainty, if the fault is based on a defect of the lambda probe or if the control and / or regulating device, in particular an evaluation circuit for the sensor signals of the lambda probe, is defective.

In addition, in many cases, system errors can not be unambiguously associated with a particular sensor, such as a particular lambda probe. There is a risk that the lambda probe

is erroneously recognized as defective, although in reality another component of the internal combustion engine, in particular another sensor of the internal combustion engine, does not function correctly. If a defect occurs in the

Internal combustion engine, it can therefore lead to a lengthy troubleshooting when using known diagnostic methods, until ultimately the actually defective component is identified. Reliable conclusions about the type of fault of the lambda probe are virtually impossible with known diagnostic methods.

Single-cell and dual-cell broadband lambda probes are known, for example, from DE 10 2006 014 266 A1. Furthermore, from DE 197 16 173 A1 discloses a leakage current between an electrode of the lambda probe and a

To detect heating element of the lambda probe.

Disclosure of the invention

The present invention has for its object to provide a method for diagnosing an exhaust gas probe of an internal combustion engine, which allows a reliable and accurate diagnosis of the exhaust probe and allows a statement about the nature of any existing error on the exhaust probe. With regard to their device aspects, the task consists of specifying one to implement the procedure

Diagnostic device.

These tasks are each characterized by the characteristics of the independent

Claims solved. The exhaust gas probe is preferably a lambda probe, in particular a jumping probe, a single-cell wideband probe or a two-cell wideband probe. In the diagnosis of the exhaust gas probe by means of the method according to the invention, various parameters of the Exhaust probe largely independent of other components of the

Internal combustion engine to be checked. In particular, interactions with other sensors of the internal combustion engine are excluded. Access to a fault memory of the control and / or regulating device is not required. By regulating the temperature of the exhaust gas probe, in particular the

Temperature of a sensor element of the exhaust gas probe, the exhaust gas probe is brought to a defined operating point, so that the diagnosis delivers results with high validity and reproducibility. The method is preferably carried out with the internal combustion engine stationary and not in operation. In this case, the exhaust gas probe can remain installed in the internal combustion engine. The diagnosis after the

However, the method according to the invention can also be at one of the

Internal combustion engine exhaust gas probe can be performed.

Overall, a fast and reliable check of the exhaust gas probe for errors is made possible by the inventive method. In addition, a relatively detailed diagnosis of the exhaust gas probe can be made, which can be carried out not only in the context of repair or maintenance work, but also at the end of a manufacturing process of the exhaust gas probe, the internal combustion engine or a motor vehicle in which the internal combustion engine is installed. It is also conceivable that the procedure

is carried out when it has been found that a motor vehicle just produced does not work properly, so that by means of the method according to the invention, the nature of the error can be analyzed more accurately. Such a more detailed analysis is also referred to as a "zero-kilometer reading." Further, lambda probes of motor vehicles that are under the customer's control

Claiming a manufacturer's warranty were complained of be reviewed by means of the method according to the invention.

It is preferred that the voltage to the with electrodes of a cell, in particular a pump cell (in the case of a two-cell probe) or a combined pumping and measuring cell (in the case of a single-cell probe), the

Connected to the exhaust probe connected terminals is detected so that a current flowing with an intact exhaust probe through the cell pumping current. By Evaluating the detected pumping current can then be checked whether the exhaust gas probe is functional or whether the exhaust gas probe has a fault.

In this case, it is particularly preferred that the voltage is varied step by step in alternating direction such that the voltage is successively different

Having voltage values, and that for at least two of these voltage values corresponding current values of the current are detected. It is preferred that the two voltage values for which the associated current values are detected are the same.

It is preferred that by evaluating the current values, preferably by comparing the current values with one another, a hysteresis with respect to the dependence between the applied voltage and the detected current is checked. Be exactly two current values for two equal

Voltage values that are applied at different times, recorded, then can be used as a measure of the hysteresis, a difference between the two current values. If the difference in magnitude is greater than a predetermined threshold value, then a defect, in particular a black color, i. Ceramic reduction due to overload / high voltages, be closed at one of the electrodes of the cell.

Further, it is preferable that the voltage is applied to the terminals connected to a trim resistor of the exhaust probe. As a result, it can be checked on the one hand, whether the trim resistance within the exhaust probe

or via a connection cable of the exhaust gas probe correctly with the

Connections of the exhaust probe, to which the voltage is applied, is connected. If the current is outside a permissible range, then a poor contact of the trim resistor or an interruption of the connection between one of the terminals and the trim resistor or a shunt in parallel with the trim resistor is concluded. In general, a shunt is an unwanted electrically conductive path that runs parallel to a desired main electrically conductive path. If the current is within the permissible range, then the value of the trim resistor can be determined from the current. In this case, preferably as a function of a value of

Trim resistance, a setpoint for the pumping current z. B. be determined in air, as a positive voltage pump voltage are applied and the

Exhaust probe depending on the setpoint and the pumping current to be checked. In this case, a quotient between the pumping current and the desired value is preferably determined. If the quotient is greater in amount than one

predetermined threshold, then, for example, a crack in one

Diffusion barrier or detected in the probe ceramic of the cell or an electrical shunt between the electrodes of the cell. If the quotient is smaller in absolute value than a further threshold value, then preferably

Pollution of the diffusion barrier ("sooting") recognized.

As a further check, it may be provided that a negative pump voltage is applied as the voltage, that an inverted pump current is detected as current, and it is checked whether the current is within a predefined permissible value

Area is located. Too small a current indicates a contamination of one

Protective layer of the exhaust probe or insufficient heating of the exhaust probe out. If the power is too large, then it may be

electrical shunt between the electrodes or damage or absence of the protective layer of the probe.

In order to detect a shunt by soiling, explicitly sooting in a region between a probe element and a housing of the exhaust gas probe, the voltage between an electrode of the cell,

preferably an inner electrode of a pump cell, and an electrically conductive housing part of the exhaust gas probe are applied as a current

Housing current can be detected and checked whether the housing current is less than or equal to a predetermined maximum value. If the current exceeds the maximum value, then the method determines that soot or other, in particular metallic deposits between the probe element and the

Housing, in particular a protective tube of the housing, have deposited.

The above-described exhaust gas probe tests often involve a comparison of the detected current or a variable formed as a function of the detected current with predetermined threshold values or predetermined permissible ranges. Because different types of Exhaust gas sensors are used, the threshold values or the permissible ranges must be specified depending on the type of exhaust gas probe. Furthermore, often the regulation of the operating temperature must be adapted to the type of exhaust gas probe. For this purpose, the type of exhaust gas probe can be determined as a function of manual inputs by a user.

However, it is preferred that at least one measured variable, the one

Cell resistance of at least one cell of the exhaust gas probe, preferably the cell resistance of a measuring cell of the exhaust gas probe is characterized, detected or determined and depending on the measured variable, a type of exhaust gas probe is determined. It has been recognized that the individual types of the exhaust gas probe differ in particular in their cell resistance, so that an assignment of the type to cell resistance is possible. By automatically determining the type of exhaust probe operating errors are largely avoided by the user.

To determine the cell resistance, it can be provided that at least one measuring voltage is applied to the cell as the voltage and the current through the cell is detected as measured quantities for each measuring voltage. As a result, the type of exhaust gas probe can be determined more reliably, since the resistance is determined not only for one voltage, but for several voltages.

In this case, it is particularly preferred that at least two measuring voltages of different polarity are applied to the cell in chronological succession. For example, this can in the first case, a statement about the ohmic

Resistance of the cell ceramic and in the second case, a statement about the diffusion resistance of Sauerstoffantransports be derived to the electrode. As a result, age-related changes in the exhaust gas probe of the same type can be distinguished from differences between exhaust gas probes of different types. In this way, errors in the automatic

Detection of the type of exhaust probe due to the aging or wear of the exhaust gas probe at least largely avoided.

In a preferred embodiment of the invention, the or each

Measured variable compared with a threshold and in response to this

Comparison of the type of exhaust gas probe determined. That is, for each measure is a result of the comparison is determined and the comparison results logically linked together to determine the type of exhaust gas probe.

Another factor influencing the cell resistance is the

Oxygen content of the gas to which the exhaust gas probe is exposed. An exhaust pipe of a conventional internal combustion engine, in which the exhaust gas probe is installed, is usually sealed so well against the ambient air, that after switching off the engine oxygen-poor exhaust gas in the

Exhaust pipe remains and a gas exchange with the environment takes place relatively slowly. Consequently, it may happen that in carrying out the method, the exhaust gas probe is exposed to a low-oxygen gas (air ratio λ <0). In order to eliminate as far as possible a disturbing influence on the detection of the type of exhaust gas probe, it is preferred that a cell voltage generated by the exhaust gas at the cell is detected before applying the at least one measuring voltage to the cell and at least one measuring voltage as a function of the cell voltage is given. It can be provided that the at least one measurement voltage is increased by the detected cell voltage. As a further solution to the above object, a diagnostic device with the features of claim 14 is proposed. With the help of such a diagnostic device, the exhaust gas probe can be checked very easily. For this purpose, when the engine is stopped, an electrical connection between the exhaust gas probe and the control and / or regulating device of the internal combustion engine is released and the connections of the exhaust gas probe are connected to the diagnostic device. As a result, an isolated diagnosis of the exhaust gas probe is made possible. An error on the exhaust gas probe can either be clearly established or safely excluded. The diagnostic device may be used to carry out the invention

Be established method and thus all the benefits of

realize the inventive method. In particular, the

Diagnostic device having a programmable computer, which is programmed to carry out the method according to the invention. Other features and advantages of the invention will become apparent from the

following description in which exemplary embodiments of the invention are explained in more detail with reference to the drawings. 1 shows a to a two-chamber broadband lambda probe

connected diagnostic device in schematic

Presentation;

Figure 2 is a view similar to Figure 1, wherein it is in the

Lambda probe but a one-chamber broadband

Lambda probe is trading;

FIGS. 3 to 7 each show a part of a flow chart as an exemplary embodiment of a method for the diagnosis of the lambda probe shown in FIGS. 1 and 2; and

8 shows a detailed representation of a step of the method from FIGS. 3 to 7. The schematic representation of FIG. 1 shows a two-cell broadband

Lambda probe 1 1, which has an electrical connection in the form of a

Connector 13 is connected to a diagnostic device 15. The lambda probe 1 1 belongs to an exhaust system of an internal combustion engine (not shown). It can be arranged, for example, in the flow direction in front of or behind an exhaust gas catalytic converter in an exhaust pipe of the exhaust gas system. The

However, lambda probe 1 1 can also be temporarily removed from the internal combustion engine for the purpose of diagnosis. It is also conceivable that the

Lambda probe 1 1 for the first time installation in the internal combustion engine

is provided and for a first functional test to the

Diagnostic device 15 is connected. The first functional test can also be carried out with the lambda probe 1 1 already installed.

The lambda probe 1 1 has a pumping cell 17. The pumping cell 17 comprises an external pumping electrode 19, which is connected to a connection of the connector 13 designated "APE." An internal pumping electrode 21 of the pumping cell

17 is connected to a terminal IPN of the connector 13. Between the Outside pumping electrode 19 and the inner pumping electrode 21 is a first formed of zirconia solid electrolyte 23. In the exhaust system built-Lambdasonde 1 1 is limited by the outer pumping electrode 19 side of the pumping cell 17 faces an interior of the exhaust pipe of the internal combustion engine, whereas a limited by the inner pumping electrode side the pumping cell 17 facing a in the interior of the lambda probe 1 1 existing diffusion gap (not shown). The pumping cell 17 is thus located between a side of the lambda probe 11 facing the interior of the exhaust pipe and the diffusion gap of the lambda probe 11.

Between the diffusion gap and a reference air channel (not shown) of the lambda probe 1 1, which is usually connected to ambient air, a measuring cell, usually designated as Nernst cell 25, is arranged. The Nernst cell 25 has a second solid electrolyte 27, on whose diffusion gap side facing a Nernst electrode 29 is arranged, which is electrically connected to the terminal IPN of the connector 13. At one of the reference air duct side facing the second

Solid electrolyte 27, a reference electrode 31 of the Nernst cell 25 is arranged. The reference electrode 31 is electrically connected to a terminal RE of the connector 13. In addition, the lambda probe 1 1 a

Heating element 33, which is connected to two terminals H + and H- of the connector 13. The heating element 33 and the two cells 17 and 25 are integrated into a sensor element of the lambda probe 1 1, so that the heating element 33 is thermally coupled to the cells 17, 25, in particular to their solid-state electrolytes 23, 27.

The lambda probe 1 1 is constructed according to a suitable manufacturing technology. For example, the lambda probe 1 1 may be formed as a so-called finger probe or manufactured in a planar technology. Regardless of the manufacturing technology used, the

Lambda probe 1 1 a housing 35, which is an electrically conductive

Housing part 37 which may for example consist of metal. The electrically conductive housing part 37 is connected to the diagnostic device 15. Furthermore, a trim resistor 39 is arranged in the lambda probe 1 1, wherein a first terminal of the trim resistor 39 is connected to the terminal APE of the connector 13 and a second terminal of the trim resistor 39 is connected to the terminal RT of the connector 13. The trim resistor 39 may, for example, have a value of about 30 ohms to 300 ohms.

The value of the trim resistor 39 is usually set immediately after the lambda probe is manufactured. For this purpose, the trim resistor 39 is connected in parallel to a measuring resistor in the control electronics. Then the trim resistor is adjusted so that a given current (eg 2.54 mA) results from the measuring resistor when the lambda probe 1 1 a

Gas with the air ratio λ = 1 is exposed. When operating the lambda probe 1 1 39 manufacturing tolerances of the lambda probe 1 1 can thus be at least largely offset by means of the trim resistor. The diagnostic device 15 has a first voltage source 41, which is supplied by a

Control device 43 of the diagnostic device 15 is controlled on. The first voltage source 41 is connected in series with a first current sensor 45. The first current sensor 45 is connected to the control device 43, so that the control device 43 can detect a current I ₁ flowing through the first voltage source 41. A terminal of the first current sensor 45 remote from the voltage source 41 is connected to the terminal APE of the connector 13. A side of the first voltage source 41 facing away from the first current sensor 45 is connected to a terminal of a first switching element 47 and of a second switching element 49. Another terminal of the first switching element 47 is connected to the terminal RT of the connector 13.

Another connection of the second switching element 49 is connected to the connection IPN of the connector 13.

Between the terminals APE and RE is a voltage sensor 52

arranged, which is so connected to the control device 43 that it can detect a voltage applied between the terminals APE and RE U _M.

Furthermore, the diagnostic device 15 has a second voltage source 51, which is connected in series with a second current sensor 53. The second

Voltage source 51 is controllable and in such a way to the control device 43 connected to this that can set a generated by the second voltage source 51 during operation voltage U ₂ . The second current sensor 53 is coupled to the control device 43 such that the control device 43 can detect a current I ₂ flowing through the second voltage source 51. A remote from the second voltage source 51 terminal of the second

Current sensor 53 is connected to the terminal IPN of the connector 13. A terminal of the second voltage source 51 facing away from the second current sensor 53 is connected to a third switching element 55 and a fourth

Switching element 57 connected. A terminal of the third switching element 55, which is not directly connected to the second voltage source 51, is connected to the housing part 37 of the lambda probe 1 1, and a terminal of the fourth switching element 57, which is not directly connected to the second voltage source 51, is with connected to the terminal RE of the connector 13. Each switching element 47, 49, 55, 57 is coupled to the control device 43, so that the control device 43, the individual switching elements 47,

49, 55, 57 can individually control (corresponding connections are not shown in FIG. 1 for the sake of clarity). Overall, the switching elements 47, 49, 55, 57 form a switching arrangement for connecting the voltage sources 41, 51 and the associated current sensors 45, 53 with the individual terminals APE, RT, IPN, RE of the connector 13 and with the

Casing. In other embodiments of the diagnostic device 15, the switching arrangement is constructed in a different way. The switching elements can at other terminals of the connector 13, for example, between a signal and a heater electrode for checking the internal

Leakage current can be arranged. It can also be a different number

Switching elements are provided. Moreover, it is conceivable to provide only one or more than two voltage sources instead of two voltage sources 41, 51 and to increase or reduce the number of switching elements accordingly. The switching elements 47, 49, 55, 57 can be realized in any desired manner (eg semiconductor switches or switching relays).

Furthermore, the diagnostic device 15 has a control element 59 for regulating a temperature of the lambda probe 1 1 based on an internal resistance of the Nernst cell 25. The control element 59 is connected to the two terminals H + and H- of the connector 13, which is connected to the heating element 33 of the

Lambda probe 1 1 are connected. The control element 59 is connected to the Control means 43 connected, so that the control means 43, the control element 59 can control, for example, to specify a desired value.

In the illustration of FIG. 2, the exhaust gas probe is designed as a single-cell broadband lambda probe 61. Instead of the pumping cell 17 and the Nernst cell

25, single cell broadband lambda probe 61 includes a combined pumping and Nernst cell 63. Therefore, in this probe 61, only the first one

Solid electrolyte 23 is present. An outer electrode 65 is arranged on a side of the first solid electrolyte 23 facing the interior of the exhaust pipe when the probe 61 is installed. On an away from the interior side of the first solid electrolyte 23, an inner electrode 67 is arranged. The outer electrode 65 is electrically connected to a terminal ALE of the connector 13, and the inner electrode 67 is electrically connected to a terminal IPE of the connector 13.

Apart from the fact that only one cell 63 is present in the single-band broadband lambda probe 61, it has the same basic structure as the two-cell broadband lambda probe 1 1 shown in FIG. The

corresponding parts of the single-band wide-band lambda probe 61 are therefore provided with the same reference numerals and will not be explained again in detail. The single-diode broadband lambda probe 61 can be connected to the simplified diagnostic device 15 shown in FIG. In the case of the diagnostic device 15 shown in FIG. 2, the third switching element 55 and the fourth switching element 57 shown in FIG. 1 are not present. It is also possible to use the diagnostic device 15 shown in FIG. 1 in conjunction with the single-cell broadband lambda probe 61. In this case, the terminal RT of the diagnostic device 15 can remain free, and the combined pumping and Nernst cell 63 is connected with its connection ALE to the connection APE of the diagnosis device 15 and with its connection IPE to the connections IPN and RE of the diagnosis device 15 ,

In an embodiment which is not shown, the single-cell broadband lambda probe 61 also has the trim resistor 39. This can for example be between the terminal ALE and the one shown in FIG

Lambda probe 61 non-existent connection RT be arranged. In the following, with reference to the in the figure 3 to 7 shown

Flowchart a method 71 for the diagnosis of an exhaust gas probe,

in particular the two-cell lambda probe 1 1 or the single-cell lambda probe 61, explained in more detail. This method 71 can be carried out by means of the diagnostic device shown in FIGS. 1 and 2 under the control of its control device 43. Deviating from this, the method 71 can also be implemented in other ways, in particular with differently constructed diagnostic devices and / or other, e.g. dynamic, such as sinusoidal, voltage-time programs or current-time programs, are performed.

When using the diagnostic device 15, the lambda probe 1 1 must be electrically disconnected from the control and / or regulating device of the internal combustion engine and connected to the diagnostic device 15. This can be done, for example, by performing before executing the

Method 71 of the connector 13 between the lambda probe 1 1 and the

Manually released control unit and a plug connection between the

Lambda probe 1 1 and the diagnostic device 15 is made manually. The method 71 is executed, for example, when the internal combustion engine is stationary or at a stable operating point. The lambda probe 1 1 can remain installed in the internal combustion engine. However, it is also possible to expand the lambda probe 1 1 before carrying out the method 71 from the internal combustion engine. Since neither the diagnostic device 15 nor the lambda probe 1 1 with the control unit of the internal combustion engine in the

Execution of the method 71 is connected, by means of the method 71 an isolated diagnosis of the lambda probe 1 1 can be performed.

Interactions with the control and / or regulating device of

Internal combustion engine or other parts, in particular sensors and actuators of the internal combustion engine, thereby at least largely

be excluded. Because the process is carried out completely independent of the control and / or regulating device of the internal combustion engine.

After a start 73 of the method 71, a type of lambda probe 1 1 is determined in a probe detection step 75. Individual lambda probes used in internal combustion engines for motor vehicles, even with identical basic structure (single-cell probe or two-cell probe) significantly different geometries, in particular of the individual cells 17, 25, 63 on. This results in significant differences in terms of electrical

Properties of lambda probes 1 1 of different types. The

Probe detection 75 determines the type of probe by electrical measurements, so that the subsequent steps of the method 71 can be carried out in dependence on the determined type of lambda probe 1 1.

In a step 76, the control device 43 adjusts the control element 59 in such a way that it regulates a temperature of the sensor element of the lambda probe to a predetermined desired value. As a controlled variable here is one of the

Temperature of the sensor element dependent internal resistance of the Nernst cell

25 or the combined pump and Nernst cell 63. As a manipulated variable is a heating power of the heating element 33, which may influence the control element 59, for example by changing the heating voltage U _H. The control device 43 determines from the predetermined setpoint value of the temperature and a type of lambda probe identified by step 75 a setpoint value for the

Internal resistance, which then sets the control element 59. Depending on the exact configuration of the diagnostic device 15, the desired value of the temperature of the sensor element can be specified either as a constant, or the desired value of the temperature can be specified depending on the type of lambda probe. It can also be provided that the

Control device 43, the target value of the internal resistance directly in

Depending on the type of lambda probe 1 1, for example, based on a stored in the controller 43 table determined. Subsequently, it is checked in a step 77 whether the trim resistor 39 is correctly connected to the terminals APE and RT. For this purpose, the control device 43 controls the first switching element 47 and the second switching element 49 so that only the first switching element 47 is closed. Of

Furthermore, the control device controls the first voltage source 41 such that a predetermined voltage URT is applied to the voltage source 41 and thus also between the terminals APE and RT. Subsequently, the control device 43 detects the current I ₁ by means of the first current sensor 45, which corresponds to a current through the trim resistor 39 when the lambda probe 1 1 is intact. Subsequently, it is checked in a branch 79, whether the current I _RT within a by a minimum value Im-. _m i _n and a maximum Im-. _max limited Area lies. If this is not the case (N), an error is detected in a step 81. The control device 43 can determine the error in step 81 and / or log. If the current is smaller than the minimum value l _{RT, max} , then a poor contact of the trim resistor 39 or a

Interruption detected between a terminal of the trim resistor 39 and one of the terminals APE or RT of the connector 13. If the detected current I _{RT is} greater than the maximum value I _{RT, max} , then a shunt parallel to the trim resistor 39 is detected. If the detected current is within the allowable range (Y), then branching is made to a next test step 83. Notwithstanding the embodiment shown, depending on the predetermined voltage U _RT and the detected current I _RT , the resistance between the terminals APE and RT can first be calculated and the calculated resistance compared with a permissible resistance range. Depending on this comparison, it is then possible in step 81 again to indicate a bad contact or interruption or a

Shunt be closed.

Subsequently, a hysteresis within a relationship between a positive pump voltage U _P > 0 and a pump current I _{P is} checked (see FIG. 4). For this purpose, in step 83 of the voltage source 41 is a constant

Voltage Ui = U _P > 0 and applied to the terminal APE and via the closed second switching element 49 to the port IPN of the pumping cell 17. In the case of the single-cell probe 61, the voltage U _{P is applied} to the terminals ALE and IPE.

The value of the pumping voltage U _P is varied stepwise. Initially, no or only a low voltage is applied to the pump cell 17 or the pumping and Nernst cell 63, after which a relatively small value U _P ¹ , which can be, for example, 800 mV, is applied and an associated current I _P ^{1 is applied} of the first current sensor 45 is measured. Subsequently, a higher

Pumping voltage U _P ² , which may for example be 1200 mV, to the

Terminals APE and IPN or ALE and IPE applied and an associated current I _P ² measured. After a certain time, the smaller pumping voltage U _P ¹ is again applied and an associated current I _P ^{3 is} detected. Subsequently, a branch 85 checks whether the two current values I _P ¹ and Ip ^{2 are} zero. If this is the case (Y), in a step 87, a defect of

Lines between the terminal APE and / or IPN or ALE and / or IPE and the cell 17 or 63 detected. Otherwise (N) is checked in a branch 89, whether a difference between the current I _P ³ and I _P ¹ amount is greater than a maximum value .DELTA.I _{P, max} . If this is the case (Y), a defect in at least one of the electrodes 19, 21 or 65, 67 of the cells 17 and 63 is detected in a step 91. If the difference between the currents is smaller than the maximum value ΔI _{P max} (branch N of the branch 89), then the hysteresis is sufficiently low and a branch is made to a step 93.

In addition, in the case of a two-cell broadband probe during the two pumping voltages U _P ¹ and U _P ² with the Ip, the Nernst voltages between U _N ¹ and U _N ² between IPN and RE can be measured. Both of them

Absolute values as well as the difference between them can be used as a diagnostic criterion. This improves the sensitivity to defective IPN and, in combination with the results of the Ip hysteresis study, allows a clear distinction as to which of the two pumping electrodes is the defective one.

In the following steps of the method 71, which are shown in Figure 5, it is checked whether the pumping current I _{P is} within an allowable range. For this purpose, first in a step 93 a defined constant voltage URT2 by appropriate driving of the first voltage source 41 and the

Switching elements 47 and 49 applied and the current I ₁ detected as a current I _RT2 . From the detected current I _RT2 , a desired value IP _{, SO is} determined for the pumping current (step 95). Subsequently, in a step 97, a predetermined constant positive pump voltage U _P > 0 is applied to the terminals APE and IPN. For this purpose, the control device 43 controls the switching elements 47, 49 and the first

Voltage source 41 accordingly (Ui = U _P > 0). The resulting

Pumping current I _P is detected by means of the first current sensor 45.

Subsequently, it is checked in a branching 99 whether a quotient of the detected pumping current I _P and the determined desired value I _{P, SO} ιι is in terms of magnitude in a range bounded by the values Q _mιn and Q _max . This is not the case (N), then in a step 101, an error in the pumping cell 17 is detected. If the quotient is greater than the value Q _max , then a crack in one

Diffusion barrier of the lambda probe 1 1 and / or in a probe ceramic, in particular in the first solid electrolyte 23 detected. Furthermore, too large a value of the quotient indicates an electrical shunt parallel to

Pump cell 17 back. If the quotient is smaller in magnitude than the value Q _mm , then a sooting, ie dirt deposits, on the diffusion barrier is detected. If the quotient lies within the permissible range, then a step 103 is continued. The exact value of Q _mιn or Q _max can _depend on the lambda probe to be tested and on the

Probe to be set during diagnosis present gas. For certain types of lambda probe 1 1 and certain gas environments, e.g. Air, the quotient may deviate up to 14%, that is

for example Q _max = 1, 14. Accordingly, a deviation may also be tolerated downwards by 14%, that is, for example Q _mιn =

0.86 can be selected.

It is conceivable that the steps 93, 95, 97, 99, 101 shown in FIG. 5 for checking the hysteresis are also carried out in single-cell probes and / or probes without the trim resistor 39. In individual probes, the pump voltage U _{P is applied} to the terminals ALE and IPE in step 97. at

Exhaust probes without the trim resistor 39 eliminates the step 93, and in step 95, the setpoint I _{P, SO} ιι the pumping current in other ways, for example, as a constant, which may depend on the type of lambda probe set.

Further, in the method 71 except the pumping current I _P in a

Forward direction also checks an inverted pumping current. Corresponding steps of the method 71 are shown in FIG. In a step 103, a negative voltage -U _{Pn is} generated by the first voltage source 41, that is, Ui <0. The negative voltage is applied to the terminals APE and IPN, and ALE and IPE, respectively. For this purpose, the control device 43 closes the first switching element 47 and opens the second switching element 49. When the negative pump voltage -U _Pn is applied, a pump current I _{P is} detected. A branch 105 following the step 103 checks whether the magnitude of the detected pumping current I _{P is} within a range determined by values I _{P mιn} and I _{P, max} limited area lies. If this is not the case (N), then a fault is detected in the lambda probe 1 1 in a step 107. Otherwise (Y), a branch is made to a step 109. If the detected pumping current I _{P is} less than the minimum value Ip _m i _n , then in step 107 a sooting of one on the

External pumping electrode 19 and the outer electrode 65 attached

Protective layer, too low a temperature of the lambda probe 1 1 and / or detected a defect in the first solid electrolyte 23. If the detected pumping current I _{P is} greater in magnitude than the maximum value lp _{, max} , then too high

Temperature of the lambda probe 1 1 and / or an electrical shunt between the outer pumping electrode 19 and the inner pumping electrode 21 and the outer electrode 65 and the inner electrode 67 or damage or a lack of the protective layer detected. Such a

For example, shedding can occur due to deposits between the

Electrodes 19 and 21 or 65 and 67 or insufficient insulation of the electrodes 19, 21 and 65 and 67 against each other.

As another check shown in Figure 7, the electrical

Conductivity between the port IPN or IPE and the conductive housing part 37 checked. For this purpose, in step 109 a

Voltage U _ge between the port IPN or IPE and the electrically conductive housing part 37 is applied. The voltage U is _ge

preferably positive, U _ge > 0. For this purpose, the control device 43 of the diagnostic device shown in Figure 1 closes the third switching element 55 and holds the fourth switching element 57 open. Further, the controller 43 controls the second one

Voltage source 51 so that it generates the voltage U ₂ = U _ge . The current flowing through the second voltage source 51 current I ₂ is detected as a casing current I = I _ge. ₂ Subsequently, it is checked in a branch 1 1 1 whether the detected housing _current l _{ge is} greater than a critical value l _ge , _knt - If this is the case (Y), in a step 1 13, a shunt between a sensor element of the lambda probe 1 1 and the housing 35 detected. Such a shunt may be due to fouling of the lambda probe 1 1, in particular of a

Soot deposit between the sensor element and an inner side of a protective tube of the housing 35 originate. If the housing _current l _{ge is} not greater than the critical value l _ge , _knt (N), then it is branched to a step 1 15. in the

Step 1 15 will be the test results obtained in the previous steps evaluated. For example, they can be displayed and / or saved. It is also conceivable that, in particular if all tests have individually delivered no error finding, a multi-dimensional feature spectrum is checked. That is, the tolerance ranges of each function variable examined are fixed in a final test of where each of the other functional values lie. This allows for a more sensitive overall diagnosis and also takes into account interactions between individual parameters. Subsequently, the process in step 1 17 is terminated. In the illustrated embodiment of the method 71, in the case where a single check recognizes an error, that is, in case one of the steps 81, 87, 91, 101, 107 or 1 13 is executed, the method 71 is referred to the next review. That is, everyone will

Checks are performed independently of the results of the previous reviews. Here, the control device 43 controls the sequence of the method 71 and evaluates detected variables for the diagnosis of the lambda probe 1 1, 61 from. The control device 43 thus also forms an evaluation unit of the diagnostic device 15. Deviating from this, however, it can also be provided that the method

71 is terminated as soon as one of the checks detects an error. In this case, after execution of the step 81, 87, 91, 101 or 107 immediately branches to step 1 15. The order of the checks shown in each case in Figures 3 to 7 can be varied as desired. In other

Embodiments may also account for any of these reviews.

The step 75 for recognizing the type of lambda probe 1 1 will be explained in more detail below with reference to FIG. In step 75, the control device 43 first controls the control element 59 in such a way that a heating voltage U _{H is applied} between the connection H + and the connection H of the lambda probe 1 1 (step

121). An exact control of the temperature of the lambda probe 1 1 is not required for the detection of the type of lambda probe 1 1. The heating voltage UH only has to be sufficiently high so that a sufficiently high temperature of the solid-state electrolytes 23, 27 is achieved for all types of probes with which the diagnostic device 15 is to be operated

Solid electrolytes 23, 27 can conduct oxygen ions. In one Following step 123, oxygen ions are transported to the diffusion gap of the lambda probe 1 1. If the lambda probe 1 1 is a two-cell probe, then a negative voltage U ₀ <0 is applied to the Nernst cell 25. For this purpose, the control device 43 controls the second voltage source 51 so that the voltage U _{2 has} a negative value, that is, U ₂ = UD <0. After a certain time, the Nernst cell 25 is again disconnected from the voltage U ₀ . For this purpose, the control device 43, the fourth switching element 57 open. In a step 125 following the step 123, by means of the

Voltage sensor 52, a voltage U _M between the terminal APE and the terminal RE, that is, substantially a voltage between the outer pumping electrode 19 and the reference electrode 31 detected. The magnitude of the voltage UM is a measure of the oxygen content in the gas, which is present at the side of the lambda probe 1 1 facing the outer pumping electrode 19.

If this is an oxygen-poor gas, the result is a relatively high value for the voltage U _M , which is typically above 450 mV. The steps 123 and 125 thus serve to detect low-oxygen gas (fat gas detection). Low-oxygen gas may be present in particular when the lambda probe 1 1 during the diagnosis in the exhaust pipe of the

Internal combustion engine remains installed. Because after a shutdown of

Internal combustion engine for the purpose of diagnosis often remains residual exhaust gas in the exhaust pipe, which has a relatively low oxygen content. Since in modern internal combustion engines, the exhaust system, in particular the exhaust pipe in which the lambda probe 1 1 is installed, relatively well compared to the

Ambient air is sealed, the oxygen content in the exhaust pipe increases at most slightly after a longer standstill of the internal combustion engine.

If the lambda probe 1 1 is the single-cell probe 61, then in step 123 the voltage UD is applied to the terminals ALE and IPE. For this purpose, the control device 43 controls the first voltage source 41 such that it generates the positive voltage UD> 0, that is, Ui = UD> 0. In step 125, the voltage U _M by means of the voltage sensor 52 between the

Connections ALE and IPE measured. Subsequently, it is checked in a branch 127 whether the detected voltage UM is greater in magnitude than a critical value U _{M, kπt} - If this is the case (Y), then it is recognized that oxygen-poor, that is rich gas is present, and in one step 129, a correction value ΔU is set to a value corresponding to the magnitude of the voltage U _M. Otherwise (N), in step 131, the

Correction value ΔU set to zero.

Step 129 or 131 is followed by a step 133 in which a negative voltage is applied between the terminal IPN and the terminal RE. This voltage corresponds to a predetermined amount

Value USDI> 0, which is corrected by the correction value ΔU> 0, that is, the second voltage source 51 generates the voltage U ₂ = - U _S DI - ΔU <0.

At the same time, the current I _{2 is} detected as the pumping current I _SD2 . Subsequently, in a step 135, a positive predetermined constant voltage U _S D2> 0 is applied to the terminals IPN and RE, whereby the voltage at the

Terminals IPN and RE is reversed. At the same time, the current I _{2 is} detected as a further pumping current I _S D2. Finally, in a step 137, the type of lambda probe 1 1 is determined as a function of the two detected pump currents I _S DI and I _SD2 . Upon completion of step 137, the method 71 continues with step 76 following step 75.

For example, two types of lambda probe 1 1 can be distinguished on the basis of the detected pump currents I _S DI and ISD 2

Geometry, in particular the size of the air diffusion channel for

Reference electrode 31 or the size and position of the Nernst

Electrode 29 differ. Because of the different geometries namely a resistance of the Nernst cell 25 of the lambda probe 1 1 of these different types is different. This results in the lambda probe 1 1 of the type in which the Nernst cell 25 a small ohmic

Resistance and an open reference air channel, a relatively large value for the detected currents I _S DI and I _S D2- In the lambda probe 1 1 of the type in which the ohmic resistance of the Nernst cell 25 is relatively large and the

Diffusion coefficient of the reference air channel is relatively small, these detected currents I _S DI and ISD2 are relatively low. Thus, it can be provided that in step 137, the type of lambda probe 1 1 is detected, in which the resistance of the Nernst cell 25 and the reference air channel is low, when the detected Currents are both greater than certain predetermined minimum values, that is, if I _S DI> Xi and ISD2> as X2. Accordingly, it may be provided in step 137 that the type of lambda probe 11, in which the resistance of the Nernst cell 25 and the reference air channel is high, is detected when the detected currents are less than certain predetermined minimum values, that is, if I _S DI <as Yi and I _S D2 <as Y ₂ . Other, opposite combinations between the detected currents may also characterize a probe type. The above-described steps 133, 135, 137 for distinguishing types of the lambda probe 1 1 can be applied in a corresponding manner also in conjunction with the single-cell lambda probe 61.

It can be seen that the above-described check is redundant in that two detected streams are checked to match between two

different types of lambda probe to distinguish. This allows a particularly reliable distinction between the types of lambda probe 1 1. In cases where the type of lambda probe 1 1 can not be clearly identified, the method 71 can either be canceled or a user of the diagnostic device 15 for manually entering the type of lambda probe

1 1 be prompted. In step 137, a non-unique

Identifiability of the type of lambda probe 1 1 found if none of the above two conditions with respect to the currents I _S DI and I _S D2 apply. As a result, a false identification of the type of lambda probe 1 1 is avoided when z. B. the resistance of the Nernst cell 25 due to

Abrasion or aging effects (so-called dynamic effects) of the lambda probe 1 1 has changed.

Overall, the present invention provides a method or a diagnostic device, with a detailed review of a

Exhaust probe, in particular a lambda probe, is possible, wherein the

Check isolated from other components of the internal combustion engine can be preferably carried out at a standstill internal combustion engine. As a result, the verification will have distorting effects due to

Interactions between different components of the

Internal combustion engine at least largely excluded. By the automatic detection of the type of lambda probe 11, a simple operation of the diagnostic device 15 is achieved.

Claims

claims

1 . Method (71) for diagnosing an electrochemical sensor,

in particular a heatable exhaust gas probe (1 1) a

Internal combustion engine, in which by means of a voltage source (41, 51) a predetermined time-varying or constant voltage (Ui, U ₂ ) is generated, the voltage (Ui, U ₂ ) to the terminals / electrodes (APE, RT, IPN, RE, ALE, IPE, 37) of the exhaust gas probe (1 1) is applied, a voltage (Ui, U ₂ ) flowing through the voltage source current (I ₁ , I ₂ ) is detected and the current (I ₁ , I ₂ ) for Diagnosis of the exhaust gas probe (1 1) is evaluated, or in which by means of a voltage source (41, 51) a predetermined time-varying or constant current (I ₁ , I ₂ ) is generated, the current (I ₁ , I ₂ ) through the terminals / Electrodes (APE, RT, IPN, RE, ALE, IPE, 37) of the exhaust gas probe (1 1), a voltage applied to the voltage source (41, 51) when the current is fed in (I ₁ , I ₂ ) (U ₁ , U ₂ ) is detected and the voltage (U ₁ , U ₂ ) for the diagnosis of the exhaust gas probe (1 1) is evaluated, characterized in that the method (71) inde pendent ngig of a control and / or regulating device of

Internal combustion engine is executed, wherein an operating temperature of the exhaust gas probe (1 1) is controlled by means of a separate from the control and / or regulating device control element (59) to a predetermined temperature value.

2. Method (71) according to claim 1, characterized in that the

Voltage (U ₁ , U ₂ ) to the terminals connected to electrodes (19, 21, 29, 31, 65, 67) of a cell (17, 25, 63) of the exhaust gas probe (11) (APE, RT, IPN,

RE, ALE, IPE) is applied and as a current (I ₁ ) a pumping current (I _P ) is detected.

3. The method (71) according to claim 2, characterized in that the

Voltage (U ₁ ) is varied stepwise and / or in alternating direction such that the voltage (U ₁ ) successively different voltage values (Up ¹ , Up ² ) and that for at least two of these voltage values (Up ¹ , Up ² ) associated current values (I _P ¹ , l _P ² ) of the current (I ₁ ) are detected.

4. The method according to claim 3, characterized in that by evaluating the current values (I _P ¹ , I _P ² ), preferably by comparing the current values

(Ip ¹ , Ip ² ) with each other, a hysteresis for a relationship between the applied voltage (Ui) and the detected current (I ₁ ) is checked.

5. The method according to claim 3, characterized in that by evaluating the Nernstspannungswerte UN between RE and IPN (UN ¹ , UN ² ),

Preferably, by comparing the Nernstspannungswerte (U _N ¹ , U _N ² ) with each other, a hysteresis with respect to a dependence between the applied voltage (Ui) and the detected Nernst voltage (Ui) is checked.

6. The method (71) according to any one of the preceding claims, characterized

in that the voltage (Ui) is applied to the terminals (APE, RT) connected to a trim resistor (39) of the exhaust gas probe (11).

Method (71) according to claim 6, characterized in that

Preferably, as a function of a value of the trim resistor, a desired value (lp _{, So} iι) for the pumping current (I _P ) is determined as voltage (Ui) a positive pumping voltage (U _P ) is applied and the exhaust gas probe (1 1) in

Depending on the desired value (lp _{, So} iι) and the pumping current (I _P ) is checked.

8. The method (71) according to claim 7, characterized in that as

Voltage (Ui) a negative pump voltage (-U _Pn ) is applied as a current

(I ₁ ) an inverted pumping current (I _P ) is detected and it is checked whether the inverted pumping current (I _P ) is within a predetermined allowable range (lp _{, mm} , Ip.max).

9. The method (71) according to any one of the preceding claims, characterized

characterized in that the voltage (U ₂ ) between a with a Electrode of the cell, preferably with an inner electrode (21, 67) of a pumping cell (17, 63), connected connection (IPN, IPE) of the exhaust gas probe (1 1) and an electrically conductive housing part (37) of the exhaust gas probe (1 1) is applied , as a current (I ₂ ) a housing current (l _ge ) is detected and it is checked whether the housing current (l _ge ) is less than or equal to a predetermined maximum value (l _ge , max).

10. The method (71) according to any one of the preceding claims, characterized

in that at least one measured variable (I _S DI, _ISD2)> the a cell resistance of the at least one cell (25, 63) of the exhaust gas probe (1: 1), preferably the cell resistance of a Nernst cell (25) of the exhaust gas probe (1: 1), is characterized, detected or determined and depending on the measured variable (I _S DI, ISD2), a type of exhaust gas probe (1 1) is determined.

1 1. A method according to claim 10, characterized in that as voltage at least one measuring voltage (-U _S D2, U _S D2) is applied to the cell (25) and as measured quantities for each measuring voltage of the current (I _s DI, ISD2) through the cell (25) is recorded.

12. The method (71) according to claim 1 1, characterized in that

successively at least two measuring voltages (-U _S D2, U _S D2)

be applied to the cell (25) of different polarity.

13. The method (71) according to any one of claims 10 to 12, characterized

characterized in that the or each measured variable (I _S DI, ISD2) with a

Threshold (X ₁ , X ₂ , Yi, Y ₂ ) is compared and in dependence on this comparison, the type of exhaust gas probe (1 1) is determined.

14. The method (71) according to any one of claims 1 1 to 13, characterized

in that prior to application of the measuring voltage (-U _S DI, U _S D2) to the cell (25), a cell voltage (UM) generated by the cell (25) is detected and at least one of said measuring voltages (-USDI-ΔU) is given as a function of the cell voltage (UM).

15. Diagnostic device (15) for checking a heated exhaust gas probe

(1 1) of an internal combustion engine, wherein the diagnostic device (15) comprises: at least one voltage source (41, 51), which is designed to apply a predetermined time-varying or constant voltage (Ui, U ₂ ) to terminals (APE, RT, IPN, RE ₁ ALE, IPE, 37) of the exhaust gas probe (1 1) at least one current sensor (45, 53), which is designed to detect a current (I ₁ , I ₂ ) flowing through the voltage source (41, 51) when the voltage (Ui, U ₂ ) is applied, and to an evaluation unit (43) for Evaluating the current (I ₁ , I ₂ ) for the diagnosis of the exhaust gas probe (1 1), or comprising: at least one voltage source, which is configured to generate a predetermined, time-varying or constant current (I ₁ , I ₂ ), and is adapted to the current (I ₁ , I ₂ ) by

To drive terminals of the exhaust gas probe (1 1), a voltage sensor which is adapted to detect a voltage applied to the voltage source when I fed current (I ₁ , I ₂ ), and an evaluation unit which is adapted to evaluate the voltage to the diagnostic electrochemical sensor , characterized in that the diagnostic device (15) is so separated from a control and / or regulating device of the internal combustion engine that it can check the exhaust gas probe (1 1) independently of a control and / or regulating device, wherein the diagnostic device (15) a control element (59) for regulating an operating temperature of the exhaust gas probe (1 1) to a predetermined value.

16. Diagnostic device (15) according to claim 15, characterized in that the diagnostic device (15) for implementing the method (71) according to one of claims 1 to 14 set up, in particular programmed, is.

17. Diagnostic device (15) according to any one of the preceding claims, characterized in that instead of the predetermined voltage, the current is specified and instead of the evaluated current, the associated voltage is evaluated.