EP3935375A1

EP3935375A1 - Method for operating a lambda probe

Info

Publication number: EP3935375A1
Application number: EP20708472.4A
Authority: EP
Inventors: Ruediger Fehrmann; Claudius Bevot; Bernhard Ledermann; Thorsten TREFFON; Thomas Schulz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-03-04
Filing date: 2020-03-02
Publication date: 2022-01-12
Also published as: WO2020178221A1; DE102019202880A1; JP7223158B2; JP2022524183A

Abstract

The invention relates to a method for operating a broadband lambda probe which has a measuring space which communicates with a measuring gas and which has an electrochemical pump cell with which oxygen can be transported into the measuring space and out of the measuring space according to the total pump voltage (Up) which is present at said pump cell and according to a pump current (Ip) which results therefrom, and which has an electrochemical Nernst cell at which the Nernst voltage (Un) is formed according to the ratio of the oxygen content in the measuring space relative to the oxygen content in a reference space of the broadband probe, wherein the method provides a control loop whose actual value is the Nernst voltage (Un), whose setpoint value is a predefined value (UnSet) and whose manipulated variable is the pump current (Ip), wherein in order to protect the pump cell the manipulated variable of the pump current (Ip) is subjected to limitation by another limiting value (L_L) and/or by a lower limiting value(L_R) by means of a further effective loop, wherein the upper limiting value (L_L) and/or the lower limiting value (L_R) are each determined in a variable fashion in accordance with the pump current (Ip), the pump voltage (Up) and the internal resistance (R) of the pump cell.

Description

description

title

Method for operating a lambda probe

State of the art

From the prior art, for example from DE 10 2011 007 068 Al or from the subsequently published DE 10 2018 201 479 Al, methods for operating a lambda probe are already known in which measures are taken to avoid a pump cell of the lambda probe is exposed to inadmissibly high pump voltages.

Advantages of the invention

The inventors have recognized that these previously known solutions are disadvantageous insofar as they provide for a temporary interruption of a control loop for regulating the Nernst voltage when fixed, predetermined threshold values are reached, which can delay the operation of the lambda probe or even damage the lambda probe, in particular with repeated interruptions.

By contrast, the method according to the invention ensures that impermissibly high pump voltages are not even reached, and it is achieved that the

Lambda probe can be operated without delay without being damaged.

The invention relates to a method for operating a broadband lambda probe which has a measuring space communicating with a measuring gas and which has a

having an electrochemical pump cell, with which oxygen can be transported into and out of the measuring space according to the total pumping voltage applied to it according to a pumping current resulting therefrom, and which has an electrochemical Nernst cell on which the Nernst voltage is based on the ratio of the oxygen content in the Forms measuring space relative to the oxygen content in a reference space of the broadband probe. For example, it can be a broadband lambda probe with a total of one, two or more electrochemical cells.

According to the invention it is provided that the method provides a control loop whose actual value is the Nernst voltage, whose setpoint is a predetermined value and whose manipulated variable is the pump current.

According to the invention it is further provided that the manipulated variable pump current to protect the pump cell is subject to a restriction by an upper limit value and / or by a lower limit value by means of a further action loop, the upper limit value and / or the lower limit value each depending on the

Pump current, of the pump voltage and of the internal resistance of the pump cell is determined variably.

The restriction can in particular take place in such a way that the pump current assumes the upper limit value if it otherwise, i.e. solely on the basis of the control loop without the restriction resulting from the further action loop, would be greater than the upper limit value.

The restriction can in particular take place in such a way that the pump current assumes the lower limit value when it otherwise, i.e. solely on the basis of the control loop without the restriction resulting from the further action loop, would be smaller than the lower limit value.

The restriction can in particular provide that the pump current through the

Limitation as long as it is not influenced as long as it assumes values that are greater than the lower limit value and are less than the upper limit value.

It can be provided that in the further action loop, the value of an unpowered pump voltage is first determined as the difference between the pump voltage and the product of the pump current and the internal resistance of the pump cell and that the upper limit value and / or the lower limit value are then determined as a function of only the pump current and the non-energized pump voltage is determined, in particular on the basis of a functional relationship in which the pump current and the non-energized pump voltage are included, but not the pump voltage and not the

Internal resistance of the pump cell. In order to prevent the upper limit value and / or the lower limit value from getting into unwanted oscillations, it can be provided that the upper limit value and / or the lower limit value are each filtered by a transmission element, for example a lag element.

The lower limit value and / or the upper limit value can be given, for example, by a characteristic diagram or a function.

It can be provided, for example, that the lower limit value is given as a function of the pump current and the unpowered pump voltage, and assumes the value 0mA for magnitude reversed pumping voltages with a negative sign and the value Ipmin for magnitude small unpowered pump voltages with a negative sign, with a The transition between the value 0mA and the value Ipmin as a function of the non-energized pump voltage, the more abrupt the greater the amount of the pump current.

There is a transition of a variable as a function of the de-energized pump voltage

in particular, the more abruptly the greater the maximum of the amount of the derivative of this variable according to the de-energized pump voltage.

In particular, it can be provided that the lower limit value is given as a function of the pump current and the non-energized pump voltage by a

Sigmoid function, especially _j _ IpMin

LR - _{1 + e} D * / p * ₍ l / po-l / poÄ-dl /) _* where L _{R is} the lower limit, Ip the

Is pump current and UpO is the de-energized pump voltage; where IpMin, D, UpOR and dU are given parameters.

The same applies to the upper limit value U, with the proviso that IpMax is used instead of IpMin and that Up0L + dU is used instead of Up0R-dU.

The invention also relates to a corresponding computer program, a

corresponding data carrier and a corresponding control unit. drawing

Figure 1 shows an example of a device for performing the

method according to the invention;

Figure 2 shows an exemplary embodiment of the invention

Method based on a flow chart;

Figures 3a, 3b show examples of the upper and lower limit values as

Function of the pump current and the de-energized pump voltage;

Figures 4a, 4b show examples of the course of the pump current and the

Pump voltage in the exemplary embodiment and in a comparative example, according to the prior art.

Description of the exemplary embodiments

Figure 1 shows an example of a device for performing the

method according to the invention. A lambda probe 10 known per se (for details see, for example, the prior art mentioned at the beginning) is only indicated schematically here. It is assigned the pump current Ip as the input variable and the Nernst voltage Un and the pump voltage Up as output variables.

With regard to the functionality of the lambda probe 10, the oxygen content of a

To determine measurement gas, reference is also made to the prior art mentioned at the beginning.

A control unit 20 connected to the lambda probe 10 has an Un controller 21, an UpO calculator 22, a limit value calculator 23, two lag filters 24a, 24b and a difference calculator 25.

In this example, control unit 20 carries out the method according to the invention in that

- The Un controller 21 first outputs the pump current Ip to the lambda probe 10; At the beginning of the method, the pump current Ip can, for example, be an initial value Ipi, for example with the value 0mA. Later the value of the Pump voltage defined as described below (method step S1, see Figure 2),

The difference generator 25 detects the Nernst voltage Un at its inverting input and detects the predetermined value UnSet at its non-inverting input and outputs the control deviation e thus formed to the Un controller

(Method step S2);

- The UpO calculator detects the pump voltage Up and the pump current Ip and, by varying these variables, the internal resistance Rp of the pump cell

Lambda probe determined and the unpowered pump voltage UpO calculated according to the equation UpO = Up - Rp * Ip, and the unpowered pump voltage UpO at the

Outputs limit value calculator 23 (method step S3);

- the limit value calculator calculates the upper limit value LL according to the formula where the parameters have the following fixed values, for example: IpMax = 6.2 mA; D = 60 W ¹ ; UpOL = 1.1 V; dU = 0.05 V; and the limit value calculator calculates the lower limit value LR according to the formula

IpMin

l _e D * Ip * (Upo-UpoR-dU) 'where the parameters have the following fixed values, for example: lpMin = -lpMax; Up0R = 1.4 V (method step S4);

the lag filters 24a, 24b filter the upper limit value and the lower limit value in such a way that oscillations of the upper limit value LL and / or the lower limit value LR are avoided (method step S5).

Otherwise, such vibrations can in principle occur, since the upper limit value LL and the lower limit value LR are fed back as input variables enter the Un controller 21.

The Un controller 21 now initially calculates in accordance with a given

Control gain a preliminary value of the pump current l’p (method step S6). A new value of the pump current Ipn is determined from this and from the upper limit value U and the lower limit value LR, with the proviso that

• Ipn = I_L if l’p> U

• Ipn = LR if l‘p <LR

• Ipn = l’p otherwise (process step S7).

The method is then continued again with the first method step S1, with the proviso that the original pump current is no longer used as the pump current Ip, but the new value of the pump current Ipn determined as described above.

The functions LL and LR used in the example are shown in FIGS. 3a and 3b. Obviously, these are sigmoid functions, with the property that they assume the value 0mA for large, unpowered pump voltages UpO and the value IpMax or Ipmin for small unpowered pump voltages UpO, with a transition between the value 0mA and the value IpMax or Ipmin as a function of the unpowered pump voltage UpO is all the more abrupt, that is to say occurs over a smaller interval of the unpowered pump voltage, the greater the amount of the pump current Ip.

For this exemplary embodiment, FIG. 4a shows the course of the pump current Ip in response to a relatively large jump in the oxygen content of the measurement gas (p02, dotted line) with a relatively cold lambda probe (Rp = 1000 ohms)

Times t = 0.5 and t = 0.7. While the settlement procedure (gray

solid line) leads to relatively large fluctuations in the pump current Ip

Vibrations and toggling, i.e. too rapid jumps in the signal in

opposite directions, this is not the case with the method according to the invention (black solid line). Instead, the

The method according to the invention quickly and precisely determines a pump current that correlates with the actual oxygen content of the measurement gas. For this exemplary embodiment, FIG. 4b shows the associated profile of the pump voltage Up, according to the method according to the invention and according to a comparison method. It shows a similar characteristic as in Figure 4a.

Claims

Expectations

1. A method for operating a broadband lambda probe which has a measuring chamber communicating with a measuring gas and which has an electrochemical pump cell with which oxygen enters and leaves the measuring chamber in accordance with the total pump voltage (Up) applied to it according to a pump current (Ip) resulting therefrom The measuring room can be transported out, and the one electrochemical

The Nernst cell has the Nernst voltage (Un) according to the ratio of the oxygen content in the measuring space relative to the oxygen content in one

Forms the reference space of the broadband probe,

The method provides a control loop whose actual value is the Nernst voltage (Un), whose setpoint is a predetermined value (UnSet) and whose manipulated variable is the pump current (Ip), the manipulated variable pump current (Ip) to protect the pump cell by means of a further action loop is subject to a restriction by an upper limit value (l_i_) and / or by a lower limit value (LR), the upper limit value (l_i_) and / or the lower limit value (LR) each depending on the pump current (Ip) from which Pump voltage (Up) and the internal resistance (R) of the pump cell is variable.

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

Action loop first the value of a de-energized pump voltage (UpO) is determined as the difference between the pump voltage (Up) and the product

Pump current (Ip) and internal resistance (Rp) of the pump cell and that the upper limit value (Li_) and / or the lower limit value (L _R ) is then determined depending on only the pump current (Ip) and the de-energized pump voltage (UpO).

3. The method according to claim 1 or 2, characterized in that in the further action loop the upper limit value (Li_) and / or the lower limit value (LR) are each transmitted by a transmission element, e.g. a lag element, is filtered so that oscillations of the upper limit value (LL) and / or the lower limit value (LR) are avoided.

4. The method according to any one of the preceding claims, characterized in that the lower limit value (LR) and / or the upper limit value (LL) is given by a map or a function.

5. The method according to any one of the three preceding claims, characterized in that the lower limit value (LR) is given as a function of the pump current (Ip) and the de-energized pump voltage (UpO), and for large amounts of energized pump voltages (UpO) with a negative sign Assumes the value 0mA and assumes the value Ipmin for small, unpowered pump voltages (UpO) with a negative sign, whereby a transition between the value 0mA and the value Ipmin as a function of the unpowered pump voltage (UpO) is the more abrupt, the greater the amount of the pump current ( Ip) is;

and or

that the upper limit value (l_i_) as a function of the pump current (Ip) and the

voltage (UpO) is given, and for magnitude large reversed pump voltages (UpO) with a positive sign assumes the value 0mA and for absolute small unpowered pump voltages (UpO) with a positive sign assumes the value IpMax, with a transition between the value 0mA and the The value of IpMax as a function of the unpowered pump voltage (UpO) is more abrupt, the greater the amount of the pump current.

6. The method according to any one of the four preceding claims, characterized in that the lower limit value (LR) as a function of the pump current (Ip) and the unpowered pump voltage (UpO) is given by a sigmoid function, in particular

j _ IpMin

LR - _{1 + e} D * / p * ₍ l / po-l / poÄ-dl /) _* IP is the pump current (Ip) and UpO is the

7. De-energized pump voltage (UpO) and where IpMin, D, UpOR and dU

default parameters are;

and or

that the upper limit value (Li_) as a function of the pump current (Ip) and the

The unpowered pump voltage (UpO) is given by a sigmoid function, in particular the pump current (Ip) and UpO the

de-energized pump voltage (UpO) and where IpMin, D, UpOR and dU

are given parameters.

8. Computer program for performing a method according to one of the preceding claims.

9. Electronic data carrier on which a computer program after

preceding claim is not stored volatilely.

10. Control device with an electronic data carrier according to the preceding claim.