WO2019149403A1

WO2019149403A1 - Method for the protected operation of a closed-loop controlled broadband oxygen sensor

Info

Publication number: WO2019149403A1
Application number: PCT/EP2018/082824
Authority: WO
Inventors: Bernhard Ledermann; Claudius Bevot; Florian Mezger; Thomas Schulz; Christian Koerner; Jens Wagner; Ruediger Fehrmann; Antonio Martucci; Ralf Kraemer
Original assignee: Robert Bosch Gmbh
Priority date: 2018-01-31
Filing date: 2018-11-28
Publication date: 2019-08-08
Also published as: DE102018201479A1

Abstract

The invention relates to a method for operating a closed-loop controlled broadband oxygen sensor in order to determine the oxygen concentration in the exhaust gas of an internal combustion engine operated with a fuel-air mixture, wherein the broadband oxygen sensor has a Nernst cell (110) and a pump cell (120), wherein a pump voltage (Up) or a pump current (Ip) is applied at the pump cell (120), and is adjusted depending on a Nernst voltage (Un) corresponding to the oxygen concentration in the exhaust gas and drawn off at the Nernst cell (110) and using a pumping current closed-loop controller controlling the pump current (Ip), and wherein, according to the invention: current values of the pump voltage (Up) with pump current applied at the pump cell (120) and the internal resistance (Ria) of the pump cell (120) are determined (300); a value of the pump voltage (UpO) without pump current applied is calculated (302) from the determined values of the pump voltage (Up) with pump current applied and the internal resistance (Ria) of the pump cell (120); the calculated (302) value of the pump voltage (UpO) without the pump current applied is compared (325) at least with a first threshold value (305) of the pump voltage (UpO) without the pump current applied for an operating state of the internal combustion engine with a rich fuel-air mixture and/or with a second threshold value of the pump voltage (UpO) without the pump current applied for an operating state of the internal combustion engine with a lean fuel-air mixture; and, if the first threshold value (305) is exceeded and/or if the value falls below the second threshold value of the pump voltage (UpO) without the pump current applied, a protective function is activated (335) for protecting the broadband oxygen sensor against an excessively high pump voltage (Up).

Description

description

title

Method for the protected operation of a regulated broadband lambda probe

The invention relates to a method for operating a regulated broadband lambda probe according to the preamble of independent claim 1.

The present invention also relates to a computer program, a machine-readable data carrier for storing the computer program and an electronic control unit, by means of which the method according to the invention can be carried out.

State of the art

Broadband lambda probes to determine the concentration of

Gas components e.g. In the exhaust gas of an internal combustion engine are widely known and have a composite of solid electrolyte layers, ceramic probe body, in which exposed to the sample gas

Body end section gas sensitive electrodes and a (e) below the

Electrode arrangement lying electrical resistance heater or heater are arranged. The electrode assembly comprises a Nernst or

Measuring electrode and a reference electrode, which form an electrochemical Nernst cell with the solid electrolyte. The reference electrode is in one with a reference gas, e.g. Air, acted upon reference gas channel arranged.

DE 10 201 1 007 068 A1 discloses a method for operating a broadband lambda probe for determining the oxygen concentration in the exhaust gas of an internal combustion engine operated with a fuel / air mixture. The broadband lambda probe has a Nernst cell and a pumping cell, wherein a pumping voltage is applied to the pumping cell which, depending on one of the oxygen concentration in the exhaust gas, corresponds to the Nernst cell

removed Nernst voltage is adjusted by means of a pumping current regulator. The pump voltage is measured at temporarily switched off pumping current and compared with a predetermined maximum threshold. When the threshold value is exceeded, the pumping current regulator is deactivated and either the pumping current is switched off or the pumping current is switched off by means of a separate controller regulated so that the pump voltage is within predeterminable limits.

Such a broadband lambda probe with a corresponding Nernst cell and a pumping cell is regulated by the pumping current to its respective desired value of the Nernst voltage UnO or Un. The voltage value UnO corresponds to an unpowered measurement, whereas the voltage value Un corresponds to an energized measurement. In the case of the aforementioned regulation, it should be noted in particular that the pumping voltage UpO or Up has a certain value

Threshold, otherwise the probe will be destroyed. Because at too high a pumping voltage, it is known to come to a so-called blackening ("blackening") of the probe.

Disclosure of the invention

The invention proposes a method for protecting a regulated broadband lambda probe from excessively high pumping voltage, in which the non-energized pumping voltage applied to a pumping cell is determined taking into account in particular the electrical or ohmic (internal) resistance of the pumping cell.

The proposed method is based on the idea that there are operating phases of the lambda probe in the control units or corresponding ASICs or microcontrollers (pCs) used today for operating such lambda probes, in which the pump cell is not energized. In such an operating situation, the value of the non-energized pump voltage UpO can be determined with relatively little effort or measured directly.

However, the pump cell is continuously supplied with current, future control devices or ASICs / pCs still under development. There is no way to directly measure the required for a protective function, no-current pumping voltage UpO with little effort.

Therefore, the above-mentioned value UpO of the unpowered pump voltage must be determined in a different way.

For the above-mentioned possible damage to the lambda probe also the electrical polarization of the probe is crucial. This polarization will in particular essentially determined or characterized by the non-energized pump voltage UpO.

According to the proposed method, instantaneous values of the energized pump voltage Up and the internal resistance Ria of the pump cell are determined or measured. The determination of the internal resistance Ria may e.g. via a voltage measurement and a calculation in the pC of the control unit. Because the value of the pumping current Ip is the manipulated variable of the

Nernstspannungsreglers ago. The internal resistance Ria of the pumping cell can be determined by detecting a change in voltage caused by a current change at the pumping cell. Predeterminable current pulses can be applied to the pump cell with a parameterizable timing (timing) or impressed on the pump cell.

The value of the non-energized pump voltage UpO can be determined from the variables mentioned, in particular from the pumped-up pumping voltage Up, according to the equation

UpO = Up - Ria ^* Ip are calculated.

In the method, it is generally provided that the thus calculated value UpO of the currentless pumping voltage is used as the voltage to be monitored for the said protective function. So only at

If an empirically predeterminable threshold value Up0_Schw for the pump voltage UpO is exceeded, the protective function is activated or started.

The proposed method for operating a controlled broadband lambda probe for determining the oxygen concentration in the exhaust gas of an internal combustion engine operated with a fuel-air mixture, wherein the broadband lambda probe has a Nernst cell and a pumping cell and wherein the pumping cell, a pumping voltage (Up) or a pumping current (Ip) is applied, which is set as a function of a Nernst voltage (Un), which is taken from the oxygen concentration in the exhaust gas and removed at the Nernst cell, by means of the pump current regulator regulating the pump current (Ip). in that instantaneous values of the energized pumping voltage (Up) and the internal resistance (Ria) of the pumping cell applied to the pumping cell are determined from the values determined for the pumped voltage (Up) and the internal resistance (Ria) of the pumping cell being a value of the unpowered pumping voltage ( UpO) is calculated such that the calculated value of the de-energized pumping voltage (UpO) at least with a first threshold value of the de-energized

Pump voltage (UpO) for an operating condition of the internal combustion engine with a rich fuel-air mixture and / or with a second threshold of the de-energized pumping voltage (UpO) for an operating condition of the internal combustion engine with a lean fuel-air mixture is compared, and that when exceeding the first threshold value and / or falls below the second threshold of the de-energized

Pump voltage (UpO) a protection function to protect the broadband lambda probe from too high a pump voltage (Up) is activated.

It should be noted that the comparison can be performed only with the first threshold of the de-energized pumping voltage (UpO). Additionally or alternatively, the comparison can also be made with the second threshold value, wherein instead of exceeding preferably a possible undershooting is checked and wherein a correspondingly changed sign of the

Pump voltage and the threshold value is based.

The use of the unpowered pumping voltage UpO for said monitoring also has the advantage that the voltage dropping across the internal resistance Ria and / or to the supply or contact resistance

Voltage components no longer occur or have no effect on the method or the mentioned, the method underlying measurement results, and thus in particular also on the monitoring result.

It should be noted, however, that by means of the proposed method either either the no-current pumping voltage UpO or the energized one Pump voltage Up can be used for the protection function. In this case, the value of Ria = 0 W can be set in the above equation. The selection of which of the two pumping voltages is used may be made by means of a register implemented in a said ASIC.

In addition, it is ensured by the proposed method that, if the pump voltage threshold mentioned above is again undershot for the lambda probe, the lambda control can be automatically re-established.

The proposed method can be used in a control unit for controlling a broadband lambda probe of an exhaust aftertreatment system

Internal combustion engine, in particular an internal combustion engine of a

Motor vehicle with an exhaust gas catalyst, in which the size to be controlled, the residual oxygen content in the exhaust gas of the internal combustion engine, are used.

The computer program according to the invention is set up to carry out each step of the method, in particular if it runs on a computing device or a control device. It allows the implementation of the

inventive method on an electronic control unit, without having to make structural changes to this. For this purpose, the machine-readable data carrier is provided on which the computer program according to the invention is stored. By loading the computer program according to the invention on an electronic control unit is the

receive electronic control device according to the invention, which is adapted to a broadband lambda probe affected here a

To operate the exhaust aftertreatment system of an internal combustion engine by means of the method according to the invention.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. Brief description of the drawings

FIG. 1 schematically shows a broadband lambda probe known from the prior art for explaining its operating principle.

FIG. 2 schematically shows an equivalent circuit diagram of that shown in FIG

Broadband lambda probe for explaining the method according to the invention.

FIG. 3 shows an exemplary embodiment of the method according to the invention for protecting a regulated broadband lambda probe from too high a pump voltage on the basis of a flow chart.

FIG. 4 shows a measurement diagram in which, in the method according to FIG

Figure 3 typically resulting voltage values U and current values I over the time t are shown.

Description of exemplary embodiments

FIG. 1 schematically shows the structure of a broadband lambda probe which is concerned here. This has a Nernst concentration probe

1 10 and an oxygen pump cell 120, wherein the oxygen pump cell 120 by an outer pumping electrode (APE) 131 and an inner

Pump electrode (I PE) 132 is formed.

The outer pumping electrode 131 is the exhaust gas A of a (not shown)

Internal combustion engine exposed and the inner, annular pumping electrode 132 is disposed in a cavity 133 which is connected via a channel 134 and a diffusion gap, in which a diffusion barrier 130 is disposed, with the exhaust gas A. The Nernst cell 110 is defined by the inner pump electrode 132 and a reference electrode (RE) 141, which in an inner

Reference air channel 140 is arranged formed. The probe is brought to operating temperature by a heater 150, at which a heating voltage UH is applied.

A control circuit 160, formed for example by a

Operational amplifier, at whose non-inverting input a Reference voltage U _ref of particular 450 mV is applied and at its inverting input, the output signal of the reference electrode 141 is applied, generates a pumping current IR, with which the outer pumping electrode 131

is charged. The inner pumping electrode 132 is connected to ground. The pumping current IP can be tapped by means of connection terminals 161, 162. He forms a measure of the

Oxygen concentration, as briefly described below.

To the pumping cell 120, a voltage is applied. If the voltage in the present unicellular lambda probe is high enough, a "limiting current" is established, which is proportional to the difference in the oxygen concentration on both sides of the probe. It should be noted, however, that the following is in particular a regulation of a two-line lambda probe means of the manipulated variable pumping current (Ip). With the (border) current

polarity dependent transported oxygen atoms. The control circuit 160 causes the concentration probe 1 10 from the pumping cell 120 via the narrow diffusion gap and the diffusion barrier 130 always exactly as much oxygen is supplied from the exhaust gas A, that at her the state lambda = 1 prevails. With excess air in the exhaust gas (lean area), oxygen is pumped out. At low residual oxygen content of the exhaust gas (rich area), oxygen is supplied by reversing the pumping voltage. The pumping current, which can be picked off via the terminals 161, 162, forms the output signal. It represents a measure of the oxygen concentration and thus of the lambda value. This pumping current regulation is referred to below as "pumping current regulator" for short. By means of this pump current regulator, the pump voltage Up on the

Nernst voltage U _n , which corresponds to the reference voltage regulated.

FIG. 2 schematically shows the equivalent circuit diagram of the broadband lambda probe. The broadband lambda probe includes the internal resistance R, _e 220 and a fictitious voltage source 221 that provides the Nernst voltage U _n o.

The pump cell is replaced by a fictitious voltage source 231, which is the

Pumping voltage Upo provides, and an internal resistance R, _a 230 formed.

Between the outer pumping electrode APE, provided with reference numeral 131 in FIG. 1, and the inner pumping electrode IPE, provided with reference numeral 132 in FIG. 1, the pumping voltage U _p drops. Between the inner pumping electrode IPE and the reference electrode RE, provided with reference numeral 141 in FIG. 1, the Nernst voltage U _n drops. By appropriate terminals, the outer pumping electrode APE and the inner pumping electrode IPE and the

Reference electrode RE with an evaluation having

Circuit unit 270 connected.

The broadband lambda probe is regulated by means of the pumping current regulator to its nominal value, the Nernst voltage U _n . The pumping current I _P required for this purpose generates a pumping voltage U _P which must be within two threshold values, which are described below in more detail, which will be discussed below, so as not to cause the probe to become too large

Destroying pumping voltage. These two threshold values relate to a preferably upper first threshold value of the de-energized pumping voltage (UpO) for an operating state of the internal combustion engine with a relatively rich fuel-air mixture and / or a preferably lower second threshold value of the de-energized pumping voltage (UpO) for an operating state of the engine

Internal combustion engine with a relatively lean fuel-air mixture.

The invention described below with reference to FIG 3, according to the invention

A method for protecting the regulated broadband lambda probe against excessively high pumping voltage now starts from a measured, pumped voltage U _p which has been energized 300, but applies the non-energized pumping voltage U _p o as a decision variable for the protective function mentioned at the outset.

A suitable period or point in time to measure the current-fed pumping voltage U _p in a manner known per se is the period of time shown in FIG. 4 with preset pumping current I _p (see, for example, the signal shown by reference numeral 402 in FIG. 4). It should be noted that the pumping current I _p is calculated by the Nernstspannungsregler, according to a present control difference. This calculation can be performed both in a microcontroller (pC) and in an application-specific integrated circuit (ASIC).

From the variables thus present, namely the preset value of the pumping current IP, the value of the energized pumping voltage UP measured as described above, and the assumption of a constant temperature Ti = const. as a substantially constant value of the

Internal resistance R, _{a of} the lambda probe (substantially equal to the ohmic resistance of the pump cell), the pump voltage U _p o for the de-energized case is measured from the following equation

Pump voltage U _p for the energized case calculated by the pCs 302:

UpO = Up - Ria * lp.

It should be noted here that in the exemplary embodiment shown (see also FIG. 4), the temperature of the lambda probe is constant. However, this condition does not have to be met in real operation, for example in a heating phase of the lambda probe. The temperature can be determined and readjusted with a measuring frequency of more than 10 Hz, for example. It should also be noted that the internal resistance R _a contained in the equation can be calculated by means of the pCs via the voltage drop between the outer pumping electrode (APE) and the inner pumping electrode (I PE) of the lambda probe.

The mentioned threshold values for the energized pump voltage U _p are determined or predetermined empirically. Concretely, corresponding values in the controller 271 are written in a register 270. Separate threshold values can be set for the two operating ranges "rich" and "lean". The two operating areas are also each with an adjustable

Hysteresis behavior (see, e.g., Figure 4, reference numeral 420).

FIG. 3 shows an exemplary embodiment of the method according to the invention for the secure operation of a regulated broadband lambda probe. The voltage and current values typically resulting from the method are illustrated in FIG.

The broadband lambda probe is first, as is known, regulated 304 by means of the Nernst voltage regulator to its nominal value, the so-called "Nernst voltage". The pumping current I _p required for this regulation generates a current-fed pumping voltage U _p . From the current pumped voltage U _p is based on the above equation, a corresponding value of

de-energized pumping voltage U _p o calculated.

In the present exemplary embodiment, the non-energized pump voltage U _p o is in a voltage range between two predefinable threshold values 305, 310 limited to the lambda probe not by a high

Pumping voltage U _p o destroy.

The limitation of the pump voltage U _p o also to low voltage values, ie within a specified voltage range, occurs because, in particular, relatively low voltage values of U _p o would lead to damage to the lambda probe.

It should also be noted that the two threshold values 305, 310 for the maximum permissible pump voltage U _p o for the safe operation of the lambda probe for the two operating ranges of an internal combustion engine, namely for the "rich operation" and for the "lean operation", are preferably separately adjustable ,

In step 304, a predeterminable value of the per se variably adjustable pump current I _p (in reference numeral 402) is set by the controller. In step 320, the resulting instantaneous value of the de-energized pumping voltage U _p o (see reference numeral 400 in FIG. 4) is determined in the manner mentioned. Then it is first checked 325, whether the two

Threshold values 305, 310 (see also FIG. 4, reference numeral 403 for the upper threshold value) are exceeded or undershot, ie, in particular, if the maximum permissible pump voltage U _p o is exceeded or is undershot with a correspondingly opposite sign (see also FIG. 4, reference numeral 404) ).

If test 325 indicates that the stated condition is met, then the Nernst voltage regulator is at least temporarily disabled 330 and a named protection function is activated 335. In this embodiment, the protection function is to set pumping current I _p to zero. However, another suitable current can be selected which is suitable for effectively preventing the destruction of the lambda probe. Otherwise, jump back to step 320 again.

By activating 335 of the protective function, the pumping voltage U _p o or the corresponding value of U _{p will} briefly return to the permissible range within the specified threshold values (see also FIG. 4, reference numeral 410). In the time window 412 shown in FIG. 4, the protective function is then at least temporarily active. On the basis of a further test step 340 performed, for example, in a subsequent run of the routine shown in FIG. 3, the determined value of the no-current pump voltage (UpO) becomes the upper first one

Threshold 305 and / or compared to the lower second threshold 310. If test 340 indicates that the first threshold 305 and / or the second threshold 310 (see also FIG. 4, reference numeral 407) are dependent on the current, non-energized pump voltage U _p o

is exceeded or exceeded, then a counter is started 345. After an adjustable number of clocks, the previously deactivated 330

Nernstspannungs regulator reactivated 350 (see also Figure 4,

Reference numeral 415). As a result of this procedure, the time-dependent hysteresis behavior 420 to be seen in FIG. 4 results overall.

As an alternative to the procedure described, with the method, instead of monitoring the non-energized U _p o, the energized

Pump voltage U _p are monitored in a similar manner by the value of _a = 0 W is set. The selection of which of the two pump voltages is used can be made flexibly by means of a register implemented in the ASIC for this purpose.

As an alternative, the protective function against too high a pump voltage can also be used correspondingly for regulated, single-cell lambda probes.

It should be noted, however, that in the case of a single-cell lambda probe, said electrochemical cell functionally represents both the pump cell and the Nernst cell.

The method described can also be realized in the form of a control program for an electronic control unit for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs). The described circuit arrangement can be realized in the form of a named, ASIC-based control unit or else constructed from discrete components in a control unit of an internal combustion engine.

Claims

claims

1. A method for operating a controlled broadband lambda probe for the determination of the oxygen concentration in the exhaust one with a

Fuel-air mixture operated internal combustion engine, the

Broadband lambda probe has a Nernst cell (110) and a pumping cell (120) and wherein to the pumping cell (120) a pumping voltage (Up) or a pumping current (Ip) is applied, which depends on one of

Oxygen concentration in the exhaust gas corresponding to the Nernstzelle (1 10) removed Nernst voltage (Un) using the pump current (Ip) regulating pumping current regulator is set, characterized in that instantaneous values of the pump cell (120) applied, energized pumping voltage (Up) and of the internal resistance (Ria) of the pumping cell (120), it is determined (300) that a value of the unpowered pumping voltage (UpO) is calculated from the determined values of the pumped voltage (Up) and the internal resistance (Ria) of the pumping cell (302) in that the calculated (302) value of the de-energized pumping voltage (UpO) is at least equal to a first threshold value (305) of the de-energized pumping voltage (UpO) for an operating state of the engine with a rich fuel-air mixture and / or with a second threshold value (310). the unpowered pump voltage (UpO) for an operating condition of the internal combustion engine with a lean fuel-air mixture is compared (325), and da ss when exceeding the first threshold value (305) and / or falling below the second threshold value (310)

de-energized pump voltage (UpO) a protection function to protect the broadband lambda probe from too high a pump voltage (Up) is activated (335).

2. The method according to claim 1, characterized in that at

Exceeding the first threshold (305) and / or during

Falling below the second threshold (310) of the de-energized pumping voltage (UpO) a Nernstspannungsregler is deactivated (330) and the protection function is activated (335).

3. The method according to claim 1 or 2, characterized in that the

Internal resistance (Ria) of the pumping cell (120) by detecting a caused by a change in current at the pumping cell (120)

Voltage change is determined.

4. The method according to any one of the preceding claims, characterized

characterized in that the value of the de-energized pumping voltage (UpO) according to the equation

UpO = Up - Ria ^* Ip is calculated (302), in which UpO the no-current pump voltage, Up the pump voltage applied, Ria the internal resistance of the pump cell (120) and Ip the pump current.

5. The method according to any one of the preceding claims, characterized

in that the determined value of the currentless pumping voltage (UpO) is compared (340) with the first threshold value (305) and / or with the second threshold value (310) and that when the first threshold value (305) is undershot and / or exceeded second threshold (310) a counter is started (345), wherein after a presettable number of cycles the previously deactivated (330)

Nernstspannungsregler is reactivated (350).

6. The method according to claim 5, characterized in that by the

Deactivation (330) and re-activation (350) of the

Nernstspannungsreglers a temporal hysteresis behavior (420) of the de-energized pumping voltage (UpO) and the pumping current (Ip) is generated.

7. The method according to any one of the preceding claims, characterized

characterized in that, instead of the de-energized pumping voltage (UpO), the energized pump voltage (Up) is compared to the first threshold value (305) and / or to the second threshold value of the pumped current voltage (Up) (325), wherein in the equation UpO = Up - Ria ^* Ip the value of Ria is set equal to zero , and in that when the first and / or falls below the second threshold of the energized pump voltage (Up), the protective function is activated (335).

8. The method according to claim 7, characterized in that the selection of whether the energized pump voltage (Up) or the de-energized pump voltage (UpO) in the comparison (325) is based, carried out by means implemented in an electronic control unit register.

A computer program configured to perform each step of a method according to any one of claims 1 to 8.

10. Machine readable medium on which a computer program

is stored according to claim 9.

1 1. Electronic control device which is adapted to operate a broadband lambda probe, in particular an exhaust aftertreatment system of an internal combustion engine by means of a method according to one of claims 1 to 8.