DE102016122956A1 - A method of determining a pressure compensation value for an oxygen sensor and controlling operation of an exhaust gas recirculation internal combustion engine and oxygen sensor - Google Patents

Abstract

The invention relates to a method for determining a pressure compensation value (K) for an oxygen sensor with a Nernst cell and a pumping cell in the intake manifold of an internal combustion engine. According to the invention, for a selected group of electrical resistances of the pumping cell, the respective pumping current (I) is measured, pumping current differences (ΔI) are calculated between the individual electrical resistances of the group and is calculated using a function (f) which determines the dependence of the pressure compensation value ( K) from the pumping current difference (ΔI), the pressure compensation value (K) for the selected group of electrical resistances of the pumping cell determined.

Description

The invention relates to a method for determining a pressure compensation value for an oxygen sensor with a Nernst cell and a pumping cell in the intake manifold of an internal combustion engine, a method for controlling the operation of an internal combustion engine with exhaust gas recirculation and with an oxygen sensor with a Nernst cell and a pumping cell in the intake manifold, wherein the oxygen sensor provides for the oxygen content in the intake manifold characteristic sensor value, on which the control of the engine operation is based inter alia, and an internal combustion engine and a motor vehicle, which are adapted to carry out the method.

Exhaust gas recirculation is used to reduce or limit nitrogen oxide emissions from internal combustion engines, with some of the exhaust gases being returned to the intake manifold. For further emission reduction, it is known to provide a so-called F _MAN sensor in the intake manifold, which provides a sensor value that is characteristic of the oxygen content in the intake manifold and vice versa for the fraction of the burned gas mass in the intake manifold. Based on the F _MAN value supplied by the F _MAN sensor, the fuel quantity to be injected as well as injection or ignition times are set in order to optimize the combustion processes in the cylinders with regard to pollutant emissions.

An F _MAN sensor is an oxygen sensor with a Nernst cell and a pump cell, each containing a zirconium electrolyte that can transport oxygen ions at higher temperatures, creating a voltage across the outer electrodes of the Nernst cell. Since this voltage is jump-shaped, a pumping current can be passed through the pump cell to expand the measuring range, which pumps oxygen ions into or out of the measuring gap between the Nernst cell and the pump cell.

From the DE 10 2010 001 892 B3 It is known that an adjustment or correction of the F _MAN value supplied by the F _MAN sensor is necessary for an accurate F _{MAN control} .

For a fixed pressure and temperature in the vicinity of the F _MAN sensor, the actual concentration of exhaust gas in the exhaust manifold is a nearly linear function of the pumping current. Unfortunately, the pumping current also depends on the temperature and pressure. The influence of temperature can be largely eliminated and therefore neglected by keeping the temperature of the cell in a narrow temperature window by means of a heater in the F _MAN sensor, which is possible by suitable regulation of the heating with high accuracy.

worin P der Druck in der Umgebung des Sauerstoffsensors ist, P₀ ein Referenzdruck ist, K_p ein Druckkompensationswert ist und I_p,cor der korrigierte Pumpstrom ist.Unfortunately, the situation with regard to printing is not so easy. The pressure influence can generally be compensated by a suitable signal correction for the pumping current I _p . This correction generally follows the form: $${\text{I}}_{\text{p}\text{, cor}}=\left({\text{K}}_{\text{p}}+\text{P}\right){\text{/ K}}_{\text{p}}+{\text{P}}_0)\times \left({\text{<figure-callout id="0" label="P" filenames="DE102016122956A1\_0008.png" state="{{state}}">P</figure-callout>}}_0\text{/ P}\right)\times {\text{I}}_{\text{p}}$$

where P is the pressure in the vicinity of the oxygen sensor, P _{0 is} a reference pressure, K _{p is} a pressure compensation value, and I _{p, cor is} the corrected pumping current.

If the pressure compensation value K _p is known very accurately, the pressure-dependent deviations of the pumping current around the reference pressure P _{0 can} be almost completely compensated. However, it has been found that the pressure compensation value K _p required to obtain a correct pumping current can vary greatly from sensor to sensor. If the pressure compensation value K _p varies greatly from sensor to sensor, a pressure level greatly deviating from the level of the reference pressure P ₀ may occur.

Although one could determine the pressure compensation value for each sensor in advance and store it in the engine control unit, this would be extremely costly and would also make a possibly necessary replacement of the F _MAN sensor very difficult.

The invention is based on the object of compensating for the influence of pressure on the measured value supplied by an oxygen sensor with a Nernst cell and a pumping cell in a practicable manner.

This object is achieved by the methods and devices specified in the independent patent claims.

Advantageous developments of the invention are specified in the dependent claims.

According to the invention, a pressure compensation value determination procedure is introduced to the vehicle-mounted oxygen sensor, which is preferably downloaded online from a server via a global network, such as a computer. B. the Internet is performed. The online determination procedure makes use of a measurement of the pumping current at different temperatures of the pumping cell. It is assumed that both the pressure and the oxygen concentration in the environment of the pump cell remain constant during the procedure.

Since the temperature of the pumping cell is closely related to its electrical resistance R _vps , measuring the pumping current at different temperatures of the pumping cell is equivalent to measuring the pumping current at various electrical resistances of the pumping cell.

$${\text{K}}_{\text{p}\text{, Gruppe xy}}={\text{f }}_{\text{Gruppe xy}}\left(\mathrm{\Delta }{\text{I}}_{\text{p}\text{,xy}}\right)$$

After the respective pumping current I _{p has been} determined by measurement for a selected group of electrical resistances of the pumping cell, the pumping current difference ΔI _{p, xy} between the individual electrical resistances of the group is calculated. For each combination of electrical resistors of the group, a function is used which describes the pumping current difference ΔI _{p, xy} with respect to the pressure compensation value K _p . Using this function, the pressure compensation value K _p for each group can be found as follows: $$\mathrm{\Delta }{\text{I}}_{\text{p}\text{, xy}}={\text{I}}_{\text{p}\text{, Group x}}-{\text{I}}_{\text{p}\text{, Group y}}$$

$${\text{K}}_{\text{p}\text{, Group xy}}={\text{f}}_{\text{Group xy}}\left(\mathrm{\Delta }{\text{I}}_{\text{p}\text{, xy}}\right)$$

worin A_xy und B_xy Koeffizienten sind, die für die Pumpstromdifferenz zwischen den Gruppen x und y charakteristisch sind.A potential candidate for the function f is: $${\text{K}}_{\text{p}\text{, Group xy}}={\text{A}}_{\text{xy}}\times \text{exp}\left({\text{B}}_{\text{xy}}\times \mathrm{\Delta }{\text{I}}_{\text{p}\text{, xy}}\right)$$

where A _xy and B _{xy are} coefficients characteristic of the pumping current difference between the groups x and y.

The total pressure compensation value K _p can then be found as the mean or a weighted sum of the K _p values determined for each group.

This total pressure compensation value K _p is then used to update the K _p value stored in the EEPROM (Erasable Read Only Memory) of the engine control unit (ECU).

• 1 ein Flussdiagramm einer Prozedur zur Bestimmung eines Druckkompensationswerts;
• 2 die Berechnung von Pumpstromvektoren und des Druckkompensationswerts im letzten Schritt des Flussdiagramms von 1;
• 3 Graphen von beispielhaften funktionalen Zusammenhängen zwischen Pumpstromdifferenz und Druckkompensationswert;
• 4 ein Flussdiagramm einer Prozedur zur Aktualisierung des Druckkompensationswerts; und
• 5 ein Flussdiagramm einer Prozedur für eine verbesserte Druck- und Sauerstoffkompensation für die Pumpstromdifferenz.

The following is a description of embodiments with reference to the drawings. Show:

• 1 a flowchart of a procedure for determining a pressure compensation value;
• 2 the calculation of pumping current vectors and the pressure compensation value in the last step of the flowchart of FIG 1 ;
• 3 Graphs of exemplary functional relationships between pumping current differential and pressure compensation value;
• 4 a flowchart of a procedure for updating the pressure compensation value; and
• 5 a flowchart of a procedure for improved pressure and oxygen compensation for the pumping current difference.

With reference to 1 For example, the procedure for determining a pressure compensation value K _p for a F _MAN sensor is started in step S1. In step S2, a stochastically or deterministically based flow control decides with which steps S3, S4 or S5 it continues.

In step S3, the F _MAN sensor is controlled to low electrical resistance R _{vps of} the pumping cell, and the average associated pumping current I _{p, low is recorded} over x seconds.

In step S4, the F _MAN sensor is controlled to the nominal resistance R _{vps of} the pumping cell, and the average associated pumping current I _{p, nom is recorded} over x seconds.

In step S5, the F _MAN sensor is controlled to high electrical resistance R _{vps of} the pumping cell, and the average associated pumping current I _{p, high is recorded} over x seconds.

In step S6, it is checked whether the pumping current N times has been recorded at each of the various electrical resistances. If not, it returns to step S2 and then to the next of steps S3 to S5. If so, proceed to step S6.

For the example of 1 were selected three groups of electrical resistances of the pump cell, for which the respective pumping current I _{p is} determined by measurement. But fewer or more such groups can be chosen.

2 illustrates the calculation of the pumping current differences ΔI _{p, xy} , in this case three pumping current differences ΔI _{p, low-nom} , ΔI _{p, nom-high} and ΔI _{p, low-high} , as pumping current vectors, resulting in three pressure compensation values, the average value of which Pressure compensation value K _p .

3 shows graphs of three functions f _nom-high , f _low-nom and f _low-high , which represent the exponential relationship between the pumping current difference Δl _p and the pressure compensation value K _p at the respective group of electrical resistors.

A procedure for updating the pressure compensation value in the EEPROM of a motor control unit is shown in FIG 4 illustrated.

After the start of this procedure in step S41, a K _p value determination is made in step S42 as described with reference to FIG 1 and 2 described.

In step S43, it is checked whether an ith-determined pressure compensation value K _{p, i is} within the allowable range. If not, an amount "Faulty K _p values" is increased by 1 in step S44, and if this quantity exceeds a preset maximum value, an error is reported. If so, proceed to step S45.

In step S45, it is checked whether the measurement is the first measurement for the sensor. If so, the K _p value stored in the EEPROM is set to the determined value K _{p, i} in step S46. If not, proceed to step S47.

In step S47, a value K _{p, w} = w × K _{p, eeprom} + ( 1-w ) × K _{p, i} , where w = 0 or 1, and in step S48, the K _p value stored in the EEPROM is set to K _{p, w} , and the magnitude "defective K _p values" is decreased by one , In addition, it is checked that the size "Faulty K _p values" is greater than or equal to 0.

The characteristic functions describing the relationship between the pumping current difference ΔI _p and the pressure compensating value K _p may depend on the oxygen concentration and the pressure in the vicinity of the sensor element.

The oxygen concentration in the air surrounding the sensor element may be determined using the pressure information provided by a pressure sensor, the ambient temperature information provided by a temperature sensor, and the relative humidity information provided by a relative humidity sensor. If a relative humidity sensor is not available, a predictive value can be used instead of a measured value.

The pressure in the vicinity of the sensor element results from the pressure information supplied by the pressure sensor.

Knowing the oxygen concentration and the pressure in the vicinity of the sensor element, its influence on the characteristic functions describing the relationship between the pumping current difference ΔI _p and the pressure compensation value K _{p can} be compensated as follows: $$\Delta I_{p.cOr}=\frac{{\overline{K}}_p+P_{sens}}{{\overline{K}}_p+P_0}\frac{P_0}{P_{sens}}\frac{O_{2.0}}{{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="DE102016122956A1\_0007.png"\; state="\{\{state\}\}">O</figure-callout>}}_{\mathrm{2,}act}}\Delta I_p$$

• Das überstrichene K_p eine Konstante, die einen angenommenen festen Wert für K_p repräsentiert, z. B. den für die Produktion gefundenen mittleren K_p-Wert;
• P_sens der tatsächliche absolute Druck in der Umgebung des Sensorelements;
• P₀ der Referenzdruck, bei dem die charakteristischen Funktionen ΔI_p - K_p gewonnen worden sind;
• O_2,0 die Referenz-Sauerstoffkonzentration, bei der die charakteristischen Funktionen ΔI_p - K_p gewonnen worden sind.
• O_2,act die aktuelle Sauerstoffkonzentration in der Umgebung des Sensorelements, die als die Sauerstoffkonzentration der Umgebungsluft angenommen wird. Dieser Wert wird als eine Funktion des Umgebungsdrucks P, der Temperatur T und der relativen Luftfeuchtigkeit X gefunden, z. B. als O_2,act = f(P_Umgebung, T_Umgebung, X_H20, _Umgebung)
• ΔI_p ist die Pumpstromdifferenz, deren Messung unter Bezugnahme auf 1 und 2 beschrieben worden ist.

In it is:

• The swept K _{p represents} a constant representing an assumed fixed value for K _p , e.g. B. the mean K _p value found for the production;
• P _sens the actual absolute pressure in the vicinity of the sensor element;
• P _{0 is} the reference pressure at which the characteristic functions ΔI _p - K _p have been obtained;
• O _{2.0 is} the reference oxygen concentration at which the characteristic functions ΔI _p - K _p have been obtained.
• O _{2, act} the current oxygen concentration in the vicinity of the sensor element, which is assumed to be the oxygen concentration of the ambient air. This value is found as a function of ambient pressure P, temperature T and relative humidity X, e.g. As O _{2, act} = f (P _environment , T _environment , X _H20 , _environment )
• ΔI _p is the pumping current difference, their measurement with reference to 1 and 2 has been described.

The corrected pumping current difference ΔI _{p, cor} calculated in accordance with the above formula is used in a third step of the K _p determination procedure to improve the pressure and oxygen compensation for ΔI _p , as shown in FIG 5 is illustrated.

After the start in step S51, the corrected pumping current difference ΔI _{p, cor} is calculated in step S52 using ΔI _p and the swept K _p . In step S53, the K _p value is estimated using ΔI _{p, cor} . In step S55 it is checked whether the difference between the swept K _p and the K _p value is smaller in magnitude than a maximum absolute K _p error value. If not, the swept K _{p is set} equal to the K _p value in step S54, and the procedure advances to step S52. If so, in step S56, the stored value in the EEPROM K _p using the _p in step S53 estimated K -value is updated.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010001892 B3 [0004]

Claims (10)

Method for determining a pressure compensation value (K _p ) for an oxygen sensor with a Nernst cell and a pumping cell in the intake manifold of an internal combustion engine, characterized in that for a selected group of electrical resistances of the pumping cell the respective pumping current (I _p ) is measured; Pumping current differences (ΔI _{p, xy} ) between the individual electrical resistances of the group are calculated; and using a function (f) describing the dependence of the pressure compensation value (K _p ) on the pumping current difference (ΔI _{p, xy} ), determining the pressure compensation value (K _p ) for the selected group of pump cell electrical resistances. Method according to Claim 1 , characterized in that the method is carried out for a plurality of different groups of electrical resistances of the pumping cell, wherein the pressure compensation value (K _p ) is determined as the mean or weighted sum of the pressure compensation values (K _p ) determined for the individual groups. Method according to Claim 1 or 2 , characterized in that the method is carried out for three different groups of electrical resistances of the pumping cell, namely for low resistance, nominal resistance and high resistance of the pumping cell. Method according to one of the preceding claims, characterized in that the determined pressure compensation value (K _p ) is used to update a pressure compensation value (K _p ) stored in an EEPROM of an engine control unit of the internal combustion engine. Method according to Claim 4 characterized in that the various electrical resistances of the pumping cell at which the pumping current is measured are adjusted by varying the temperature of the pumping cell. Method according to one of the preceding claims, characterized in that the method is carried out as an online determination procedure. A method of controlling the operation of an exhaust gas recirculation internal combustion engine and having an oxygen sensor with a Nernst cell and an intake manifold pumping cell, the oxygen sensor providing an intake manifold oxygen sensor characteristic value on which the engine operation control is based inter alia, characterized in that the the measured value supplied by the oxygen sensor is corrected with respect to the pressure therein by means of a pressure compensation value (K _p ) determined in accordance with one of the preceding claims. Method according to Claim 7 , characterized in that the pressure influence is compensated by correcting a signal for the pumping current (I _p ) of the pumping cell. Internal combustion engine having exhaust gas recirculation and with an oxygen sensor having a Nernst cell and a pump cell in the intake manifold, characterized in that the internal combustion engine for carrying out a method according to any one of the preceding claims is arranged. Motor vehicle with an internal combustion engine after Claim 9 ,

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