DE102005059450A1 - Oxygen sensor e.g. lambda sensor, diagnosing method for internal combustion engine, involves comparing actual oxygen filling level of converter with releasing values, where release of signal takes place based on comparison result - Google Patents

Abstract

The method involves evaluating a signal of a back oxygen sensor (15) arranged downstream of a catalytic converter (19), and determining an actual oxygen filling level of the catalytic converter, where the catalytic converter is formed as a three-way catalytic converter. The actual oxygen filling level is compared with releasing values that contain higher and/or lower threshold of the oxygen filling level. The release of the signal of the back sensor is carried out for evaluation based on the comparison result. An independent claim is also included for a device for diagnosing an oxygen sensor.

Description

The The invention relates to methods and apparatus for diagnosing a arranged in an exhaust system sensor, respectively according to the preamble of corresponding independent Claim.

To Today's state of the art are to ensure the greatest possible Pollutant conversion Oxygen sensors (lambda sensors) in the Exhaust system used by internal combustion engines, with their signals via suitable Regulator the fuel / air ratio of the exhaust gas is regulated so that the catalyst in its optimal Conversion area works. For this purpose, setpoints for the signals the probes set. There are various combinations of Control algorithms and the number and type of lambda probes used and catalysts. To detect a faulty probe, include Systems according to the current state of the art different measures for testing the electrical connections, for example, to detect short circuits in the cable ducts, as well as plausibility checks of the Probe signals themselves.

The execution of such plausibility checks takes place under well-defined boundary conditions. Since it can not be ruled out that due to dynamic conditions of the exhaust gas system or scattering of the system components are detected unfounded on probe errors, several measurements of the faulty behavior generally have to be made up to a false reading. Furthermore, there are different release conditions for such plausibility checks. In systems with a lambda probe installed behind the catalytic converter, it is already known to perform time debounces. It is considered that catalysts have a temporal buffering effect on the exhaust gas composition due to their chemical properties, in particular their ability to inject and remove exhaust gas components. From the EP 0234584 B1 A control system is already known having an error detection means for responding to indications that an oxygen sensor device has become defective and for providing an error signal. By means of a control device, a selective provision of control loop control functions takes place. A delay device sets a delay in the transition from one of the control loop control functions to the other according to the operating capability of the sensor indicated by the error signal.

In the DE 10161901 A1 a correction of the linear sensor characteristic using a second lambda probe is described behind the catalyst. In order to compensate for the offset of the sensor characteristic, it is proposed in this document to release the signal of a reference sensor only if it runs within a tolerance field for a predetermined time interval. As a criterion for releasing a lambda probe installed behind a catalytic converter for correcting the offset, a probe installed in front of the catalytic converter, it is possible, among other criteria, to use a defined exhaust gas mass that has passed through the catalytic converter. After throughput of this exhaust mass is assumed that in the normal case, that is, without offset of the front probe, the catalyst is adjusted in its optimum conversion range and the probe is behind the catalyst at its control setpoint. However, if the signal of the rear probe deviates from the desired value, this deviation is adapted as an offset of the front probe or compared with predetermined threshold values and, if necessary, a maintenance signal is generated if these threshold values are exceeded.

Furthermore, from the EP 0234584 B1 Known a stuck at a constant value signal behind a catalyst arranged probe, thereby recognizing that targeted an adjustment of the engine air / fuel ratio is made when the signal of the rear probe for a predetermined time has not crossed the set value of the lambda control. If the fuel / air ratio is actively adjusted, it is assumed that a signal change is achieved for an undamaged probe at which the rear probe signal crosses the specified setpoint. In contrast, it is assumed for a damaged probe that such a signal change does not occur. However, such adjustments cause undesirable exhaust emissions and more fuel consumption.

The The problem underlying the invention is the diagnosis of a in an exhaust system for an internal combustion engine arranged oxygen sensor by means of a Evaluation of the signal arranged downstream of the catalyst rear sensor to improve.

The The problem underlying the invention is achieved by the methods or devices with the features of the respective independent claims.

The generic method for the diagnosis of a front oxygen sensor arranged in an exhaust system for an internal combustion engine upstream of a catalytic converter is characterized in that a current oxygen filling of the catalytic converter is determined and compared with the release values of an associated release condition and a release of the signal of the sensor as a function of the comparison result rear sensor for evaluation. As a release condition is in the present context, a set of release values of the oxygen filling of the catalyst, with which a current oxygen filling of the catalyst is compared, wherein an approval of the signal for evaluation requires that the comparison result indicates a deviation between release values and the current oxygen filling, which is smaller than a predetermined Threshold is. If the result of the comparison shows that the current oxygen filling is not close enough to the release values, the signal is not released. If the current oxygen filling of the catalyst is sufficiently close to the release values, it is assumed according to the invention that the catalyst is loaded with a sufficient amount of oxygen in order to ensure that the catalyst is regulated in its optimum conversion range. In this case, it can be assumed that the sensor arranged behind the catalytic converter emits a signal which is at its desired control value. Compared to a method which operates as a release condition with an exhaust mass set through the catalyst within a time interval, according to the invention, the time to release the signal of the rear sensor can be shortened, at least on average, and the diagnostic reliability as well as the diagnosis frequency can be increased.

When Oxygen loading level becomes the relative loading of the catalyst with oxygen, that is the loading of the catalyst with oxygen based on an absolute Oxygen loading amount, called.

In dependence From the interpretation of the exhaust system, it is useful if the clearance values an upper and / or lower threshold of the current oxygen occupancy level include. Preferably, when the upper threshold is 50%, 60%, 70 %, 80%, 90% or 100%. Furthermore, it is preferred if the lower threshold is 40%, 30%, 20%, 10% or 0%.

It It is understood that the upper threshold and the lower threshold respectively so chosen be that an oxygen loading of the catalyst in one area is in the optimum conversion of exhaust gas pollutants guaranteed or to be expected.

In a further embodiment of the invention, it is provided that the exhaust system has a front lambda control loop and a rear lambda control loop with at least one rear oxygen sensor arranged downstream of the catalytic converter. An output signal of the rear oxygen sensor is processed by the rear lambda control loop, a difference value to a rear desired lambda value is formed, and a manipulated variable acting on the desired lambda value of the front lambda control loop is output. For the diagnosis of the rear oxygen sensor, the time period t is determined in which there is no sign change of the difference value and if the time t reaches a value t _max , an active adjustment of the engine air / fuel ratio for functional testing of the rear oxygen sensor. According to the invention, a current oxygen loading state of the catalyst is determined and compared with release values of an associated release condition for said active adjustment. Depending on the result of the comparison, the active adjustment is released. The release of the active adjustment as a function of the comparison result ensures that the diagnosis of the rear sensor takes place only if the oxygen filling state of the catalyst can be expected optimal conversion of pollutants and a certain magnitude of fluctuations of the sensor signal with associated sign changes of the difference value on statement the functionality of the sensor allows. Preferably, the time t _{max can be} increased or it can be completely dispensed with the active adjustment.

It is useful if the oxygen loading of the catalyst within one by one upper and / or lower position defined range, if one Release of the active adjustment should take place. Furthermore, it is useful if no Enable the active adjustment, if the signal of the rear Probe below and / or above predetermined thresholds. According to the currently common built sensor types, it is preferred when the amplitude of the rear Sensor is within a range between 500 and 750 mV.

The actual oxygen loading of the catalyst can be determined in various ways. It is preferred in this case if the determination of the amount of oxygen introduced and discharged into the catalyst in a time interval takes place, as described, for example, in US Pat DE 10231331 A1 or DE 10339063 have been described. However, other methods for determining the actual oxygen loading of the invention are also included. A particularly simple method is to determine the current oxygen load from a balanced amount of oxygen determined within a predetermined time interval.

It is expedient to use the signal of the rear sensor when releasing for offset correction of the front sensor. It is understood that additional release conditions may be provided which are associated with one or more operating parameters of the exhaust system. Preference is given to operating parameters such as exhaust gas mass, exhaust gas mass flow, air mass flow, exhaust gas temperature, lambda value of the exhaust gas.

The The invention also includes a device for diagnosing one in one Exhaust system for an internal combustion engine arranged upstream of a catalyst front oxygen sensor. There is an evaluation of the Signal of a downstream of the catalyst arranged rear sensor. The Device comprises a device for determining a current oxygen filling of the catalyst, wherein the actual oxygen filling degree of the Catalyst determined and with the release values of an assigned Release condition and depending on the comparison result a release of the rear sensor for evaluation takes place.

Further The invention includes a device for diagnosis in an exhaust system downstream of a catalyst arranged rear oxygen sensor as shown in connection with the corresponding method has been. The device comprises a device for determining a current one Oxygen loading of the catalyst and it is envisaged that a current oxygen loading of the catalyst is determined and with enable values of an associated release condition for an active Adjustment of the engine air / fuel ratio compared and in dependence from the comparison result, a release of said active adjustment he follows.

As is known per se, the rear sensor may be preferred as a broadband lambda sensor and / or be formed as part of a NOX sensor.

The inventive method and devices allow effective diagnosis of sensors of exhaust systems where the catalyst is a three-way catalyst or is designed as a NOX catalyst.

Further Benefits arise from the rest Dependent claims, the drawing and the associated Description. In the following the invention with reference to a drawing explained in more detail.

1 shows a device for diagnosing an arranged in an exhaust system for an internal combustion engine oxygen sensor.

1 shows a block diagram of a device 1 for diagnosing an oxygen sensor arranged in an exhaust system for an internal combustion engine. Signal connections and their direction are indicated by arrows 4 characterized. The device 1 has a front loop 5 with a front regulator 7 and a rear loop 9 with a rear regulator 11 on. The rear regulator 11 is input side with a modeling unit 13 and a rear oxygen sensor 15 connected. The rear oxygen sensor 15 is located in an exhaust system 17 of the internal combustion engine 3 downstream of a catalyst 19 , The catalyst 19 may be a 3-way catalyst or a NOx storage catalyst. Downstream of the internal combustion engine 3 and upstream of the catalyst 19 is located in the exhaust system 17 a front oxygen sensor 21 , With the oxygen sensors 15 . 21 they may be, for example, jump and / or broadband sensors. The output signal of these sensors can optionally directly a device explained in more detail below 13 be fed, as from the arrows 31 and 31 ' is apparent. In another, but in the 1 not shown embodiment is not a lambda sensor 21 installed in the front lambda control circuit. Instead, a modeled lambda value is provided which, for example, is determined from engine variables such as fuel injection quantity and air quantity as well as adapted setting values and / or more complex models and is used instead of a measured lambda value. Furthermore, in a further embodiment of the invention, the output of the regulator 11 not with an entrance of the facility 13 connected.

According to the invention for the diagnosis of the front and / or the rear sensor 21 . 15 Release values of an oxygen loading of the catalyst used. It can also be provided additional release conditions associated with one or more operating parameters of the exhaust system. In this case, operating parameters such as exhaust gas mass, exhaust gas mass flow, air mass flow, exhaust gas temperature, lambda value of the exhaust gas are preferred.

The device 1 or the front loop 5 has a setpoint path 23 with a setpoint input 25 on. In the setpoint path 23 is an addition point 27 connected. The addition point 27 the setpoint path 23 on the input side is the setpoint input 25 and the rear regulator 11 assigned. Consequently, by the addition point 27 the manipulated variable of the rear regulator 11 added to the setpoint of the lambda control.

The front loop 5 works independently, is only of the control value of the rear loop 9 and contains the setpoint path 23 , a subtraction point 29 to form the control deviation from the via the setpoint path 23 supplied setpoint and the output signal of the front oxygen sensor 21 , the front regulator 7 , the internal combustion engine 3 as well as its exhaust system 17 with the front oxygen sensor 21 , The rear loop 9 works as a parent Reg and thus includes the entire front loop 5 and also the catalyst 19 , the downstream rear oxygen sensor 19 as well as the decor 13 ,

The device 13 Determines the current oxygen loading of the catalyst 19 , preferably from the catalyst 19 Registered and discharged oxygen amount, the balanced amount of oxygen since a sign change of the difference value between the actual value of the rear oxygen sensor 19 and the desired lambda value. The current oxygen loading is compared with clearance values and, depending on the result of the comparison, the signal from the rear sensor is released. Preferably, an oxygen loading level is determined. The device preferably forms 13 and an evaluation variable as a function of the balanced amount of oxygen for determining a weighted degree of oxygen loading which is used instead of the unweighted degree of loading. It is understood that other methods for determining the oxygen loading of the catalyst 19 to be covered by the invention.

To diagnose the front sensor is a current oxygen loading of the catalyst 19 determined and compared with the clearance values of an assigned release condition. Depending on the result of the comparison, the signal of the rear sensor is released 15 to the results. If the result of the comparison shows that the current oxygen filling is not close enough to the release values, the signal is not released. Is the current oxygen filling of the catalyst 19 sufficiently close to the clearance values, it is assumed according to the invention that the catalyst 19 loaded with a sufficient amount of oxygen to ensure that the catalyst 19 is adjusted in its optimum conversion range. In this case, it can be assumed that the behind the catalyst 19 arranged sensor 15 gives a signal that is at its control setpoint.

In dependence From the interpretation of the exhaust system, it is useful if the clearance values an upper and / or lower threshold of the current oxygen occupancy level include. Preferably, when the upper threshold is 50%, 60%, 70 %, 80%, 90% or 100%. Furthermore, it is preferred if the lower threshold is 40%, 30%, 20%, 10% or 0%.

To calculate in the catalyst 19 registered or discharged amount of oxygen, the output signals of the oxygen probes 21 and 15 be used. Alternatively, but especially not only in the case that the front lambda control loop 3 operating with a modeled lambda actual value is used instead of the signal from the front oxygen sensor 21 a modeled lambda value is used. The device 13 used in the simplest case, a simple integrator to determine the amount of oxygen introduced and removed. Alternatively, more complex oxygen models of the catalyst can be used to calculate the oxygen input and output.

at the evaluation size of the balanced amount of oxygen, it can be an absolute or a relative rating. At a relative evaluation size, will the balanced amount of oxygen to a predefined value of Oxygen storage capacity of the catalyst. The pre-defined value of oxygen storage capacity may be a maximum oxygen storage amount of the catalyst. Furthermore, the defined amount of oxygen depending on from the properties of the catalyst coating in terms of a maximum pollutant conversion to be achieved, for one predetermined pollutant, preferably set a NOX, HC or CO content become.

The rating may be selected depending on the current value of a catalyst characteristic, the latter being the state of the catalyst 19 characterized. Preferably, the current state refers to the operating phase of the internal combustion engine 3 before the sign change of the difference value. This can be taken into account in a simple manner that the catalyst 19 after a previous coasting phase of the internal combustion engine 3 is completely filled with oxygen or after a rich operation phase of the internal combustion engine 3 completely emptied of oxygen. Furthermore, the evaluation variable itself can be selected depending on the current value of the catalyst size.

From the rear loop 11 a difference value of the rear actual lambda value is formed to the rear target lambda value. For the diagnosis of the rear oxygen sensor, the time period t is determined in which there is no sign change of the difference value and, if the time t reaches a value t _max , there is an active adjustment of the engine air / fuel ratio for functional testing of the rear oxygen sensor. In this case, a current oxygen loading of the catalyst is determined and compared with release values of an associated release condition for said active adjustment. Depending on the result of the comparison, the active adjustment is released. The release of the active adjustment as a function of the comparison result ensures that a certain size of fluctuations of the sensor signal with associated sign changes of the Dif value allows a statement about the functionality of the sensor. Preferably, the time t _{max can be} increased or it can be completely dispensed with the active adjustment.

The Oxygen loading of the catalyst is within a through an upper and / or lower threshold defined area, if a release of the active adjustment should take place. Furthermore, no Release of the active adjustment, if the signal of the rear Probe below and / or above predetermined thresholds. According to the currently common Built sensor types, it is preferred if the signal amplitude of the rear sensor within a range between 500 and 750 mV is located. Also with this diagnosis can further release conditions additionally be used.

In one embodiment of the invention, first the diagnosis of the rear sensor 15 carried out. After recognized functionality of the rear sensor 15 becomes a diagnosis of the front sensor 21 carried out. It is preferred after a sign change of the difference value from the device 13 the balanced amount of oxygen determined for a time interval since the sign change. Preferably, it is additionally provided to form a correction value for increasing the regulator stability as a function of the balanced amount of oxygen.

To calculate in the catalyst 19 the amount of oxygen discharged or discharged can be the set value of the rear control loop 9 be used. Thus, the oxygen input or output that results from the control intervention of the rear control loop is balanced. As in 1 is shown here is the output of the controller 11 with an entrance of the facility 13 connected. Advantageously, this embodiment is not exclusive but in particular, if at the same time a forward control for front loop 5 For example, the influence of dynamic disturbances on the compliance with the front reference value is used 25 to compensate. In a forward balance, the oxygen input or discharge is downstream of the engine 3 and upstream of the catalyst 19 For example, in the place of a front oxygen sensor 21 minus the influence of the rear regulation 11 also included in the balance sheet. In this case, for example, the signal of the front oxygen sensor, the control value of the front controller 7 deducted. In this case, the desired value is preferred on average 25 of the front control loop 5 held.

1

contraption

3

internal combustion engine

4

arrow

5

front loop

7

front regulator

9

rear loop

11

rear regulator

13

Facility

15

rear oxygen sensor

17

exhaust system

19

catalyst

21

front oxygen sensor

23

Setpoint path

25

Setpoint input

27

addition site

29

subtraction

31

arrow

31 '

arrow

Claims (15)

A method for diagnosing a front oxygen sensor arranged in an exhaust gas system for an internal combustion engine upstream of a catalytic converter by means of an evaluation of the signal of a rear sensor arranged downstream of the catalytic converter, characterized in that a current oxygen filling of the catalytic converter is determined and compared with the release values of an associated release condition, and Depending on the comparison result, a release of the signal of the rear sensor for evaluation takes place. Method according to claim 1, characterized in that in that the release values are an upper and / or lower threshold of the degree of oxygen filling include, where the upper threshold is 50 percent, 60 percent, 70 Percent, 80 percent, 90 percent or 100 percent, and the lower threshold 40 percent, 30 percent, 20 percent, 10 percent, 0 percent. A method for diagnosing a rear oxygen sensor disposed in an exhaust system, the exhaust system having a front lambda control loop and a rear lambda control circuit having at least one rear oxygen sensor disposed downstream of the catalyst and processing an output signal of the rear oxygen sensor from the rear lambda control circuit, forming a difference value to the rear target lambda value and a manipulated variable acting on the desired lambda value of the front lambda control loop is output, wherein the time period t is determined in which no change in sign of the difference value has taken place, and if the time duration t reaches a value t _max an active adjustment of the engine air / fuel value for functional testing of the rear oxygen sensor takes place, characterized in that a current oxygen loading of the catalyst is determined and compared with release values of an associated release condition for said active adjustment and, depending on the comparison result, a release of said active adjustment. Method according to claim 3, characterized that no release of said active adjustment takes place, if the determined oxygen filling below and / or above predetermined oxygen filling level thresholds especially a lower threshold of 40 percent, 30 percent, 20 percent, 10 percent, or 0 percent, and an upper threshold 50 percent, 60 percent, 70 percent, 80 percent, 90 percent or 100 percent Percent. Method according to claim 3 or 4, characterized that no release of the active adjustment takes place, if the signal the rear sensor below and / or above predetermined thresholds lies, in particular between 500 and 750 mV. Method according to one of the preceding claims, characterized characterized in that the current oxygen loading from the in the amount of oxygen introduced and removed in a time interval is determined. Method according to Claim 6, characterized that the actual oxygen loading is from within a given Time interval determined balanced amount of oxygen is determined. Method according to one of the preceding claims, characterized characterized in that the signal of the rear sensor for an offset correction of front oxygen sensor is used. Method according to one of the preceding claims, characterized characterized in that additional Release conditions are provided, the one or more operating parameters the exhaust system are assigned from the following group: exhaust gas mass, Exhaust gas mass flow, air mass flow, exhaust gas temperature, lambda value of Exhaust gas. Device for the diagnosis of an exhaust system for one Internal combustion engine upstream of a catalyst arranged front Oxygen sensor by means of an evaluation of the signal downstream the catalyst arranged rear sensor, characterized in that in that a device for determining a current oxygen filling of the Catalyst is provided and that a current oxygen filling of Catalyst determined and with the release values of an assigned Release condition and depending on the comparison result a release of the rear sensor for evaluation takes place. Device for diagnosing a rear oxygen sensor arranged downstream of a catalytic converter in an exhaust system, the exhaust system having a front lambda control circuit and at least one rear oxygen sensor arranged downstream of the catalytic converter, wherein an output signal of the rear oxygen sensor processes from the rear lambda control circuit a difference value formed a rear target lambda and a value acting on the desired lambda values of the front lambda control loop control variable is determined and the time t is determined in which no sign change of the difference value takes place and if the time t reaches a value t _max an active adjustment of the engine air / fuel ratio for functional testing the rear oxygen sensor is carried out, characterized in that a device for determining a current oxygen loading of the catalyst is provided and a current Saue determined material loading of the catalyst and compared with release values of an associated release condition for said active adjustment and depending on the result of the comparison, a release of said active adjustment takes place. Device according to claim 10 or 11, characterized the rear sensor is a broadband lambda sensor. Device according to claim 10 or 11, characterized the rear sensor is part of a NOX sensor. Device according to one of claims 10 to 13, characterized that the catalyst is designed as a three-way catalyst. Device according to one of claims 10 to 13, characterized that the catalyst is designed as a NOX catalyst.