DE102013221298A1 - Method for calibrating sensor element for detecting e.g. gas component of measurement gas in gas measuring chamber, involves determining pitch error of measuring signal based on the comparison of reference value and actual value - Google Patents

Abstract

The method involves determining (101) an offset error of a measurement signal of a sensor element (10) at a first known property of the measurement gas. The property of the measurement gas is altered (102a) into a second property. A reference value of the measuring signal is determined (102b) with the second property of the measurement gas. An actual value of the measurement signal is determined (103a) on the second property of the measurement gas. A pitch error of the measuring signal is determined based on the comparison of reference value and actual value. An independent claim is included for a sensor device.

Description

State of the art

A large number of sensor elements and methods for detecting at least one property of a measurement gas in a measurement gas space are known from the prior art. In principle, these can be any physical and / or chemical properties of the measurement gas, one or more properties being able to be detected. The invention will be described below in particular with reference to a qualitative and / or quantitative detection of a proportion of a gas component of the measurement gas, in particular with reference to a detection of an oxygen content in the measurement gas part. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. Alternatively or additionally, however, other properties of the measuring gas are detectable, such as the temperature.

In particular ceramic sensor elements are known from the prior art, which are based on the use of electrolytic properties of certain solids, that is to ion-conducting properties of these solids. In particular, these solids may be ceramic solid electrolytes, such as zirconia (ZrO ₂ ), in particular yttrium-stabilized zirconia (YSZ) and scandium-doped zirconia (ScSZ), the small amounts of alumina (Al ₂ O ₃ ) and / or or silica (SiO ₂ ).

For example, such sensor elements can be configured as so-called lambda probes, as they are made, for example Konrad Reif (ed.): Sensors in the motor vehicle, 1st edition 2010, pp. 160-165 , are known. With broadband lambda probes, in particular with planar broadband lambda probes, it is possible, for example, to determine the oxygen concentration in the exhaust gas over a large range and thus to deduce the air-fuel ratio in the combustion chamber. Also known are so-called jump probes. The air ratio λ describes this air-fuel ratio.

The characteristic of the broadband lambda probes is that they have a unique, monotonic characteristic over the lambda value and thus allow a determination of the oxygen content over a wide range. The essential measure of the broadband lambda probes is the so-called pumping current, ie the current that must be applied to the probe to pump out the residual oxygen from the probe and thus set the measuring chamber in the probe to λ = 1. The pumping current is directly proportional to the oxygen partial pressure in the exhaust gas.

Despite the advantages of the sensor elements known from the prior art, these still contain room for improvement. Thus, the probes exhibit production-related specimen scattering in the geometric structure. These scattering, in particular the diffusion barrier, are reflected in specimen scattering of the necessary pumping current at the same oxygen content in the exhaust gas. That is, the lambda reading of the probe scatters. For this reason, an adjustment of the sensor element is required. There are different matching methods for this.

The adjustment can be carried out in the production. For example, the broadband lambda probe is tuned by installing a trim resistor in the probe connector that forms a voltage divider along with the measurement shunt in the controller. This trim resistor in the connector is specifically modified at the end of the production line by means of laser cuts for each probe specimen in such a way that a specific pump current is established at a given lambda value. Alternatively, for example, it is adjusted by initially dimensioning the diffusion barrier of the sensor element too large and then rendering it permeable by means of laser cuts until a specific pump current is established here as well for a given lambda value. Both adjustment methods mean additional costly work steps in production. The first-mentioned adjustment method has the additional disadvantage that the probe plug can not be freely selected, but always a plug of the manufacturer, which was used during balancing, must be used.

The balancing may be performed during operation of an internal combustion engine, such as an internal combustion engine of a vehicle. On the one hand, in gasoline engines there is an offset adjustment at λ = 1, which makes use of the high-precision lambda signal of the jump probe downstream of a catalytic converter at an operating point of λ = 1. This adjustment evaluates the control deviations and / or the manipulated variable of the trim control over a longer period of time and adapts therefrom an offset correction value for the broadband lambda probe upstream of the catalytic converter. On the other hand, there is, for example, the so-called "thrust balance", in which the probe signal is compared with an expected value in overrun mode with complete injection suppression. The difference thus determined is interpreted as the slope error of the probe signal. From this, a correction value for the slope of the probe signal is adapted. The "thrust balance" is thus dependent on deceleration phases. Due to the increasing use From automatic transmissions and the increasing hybridization, the overrun phases are usually very rare, so that the thrust balance is less and less available.

Analogous to manufacturing scattering also occur aging effects over the life of the sensor elements, which should also be compensated by the inventive method.

Disclosure of the invention

It is therefore proposed a method for balancing a sensor element for detecting at least one property of a sample gas in a sample gas space, which at least largely avoids the disadvantages of known balancing method, can replace the adjustment during manufacture by an adjustment during operation, which does not like the "thrust balance "relies on the usually very rare deceleration phases, allows cost savings in manufacturing, and on the other hand allows the free choice of plug for a dealer or seller, without losing accuracy of the sensor signal.

• – Ermitteln eines Offsetfehlers eines Messsignals des Sensorelements bei einer ersten, bekannten Eigenschaft des Messgases,
• – Ändern der Eigenschaft des Messgases in eine zweite Eigenschaft,
• – Ermitteln eines Sollwerts des Messsignals bei der zweiten Eigenschaft des Messgases,
• – Ermitteln eines Istwertes des Messsignals bei der zweiten Eigenschaft des Messgases, und
• – Ermitteln eines Steigungsfehlers des Messsignals basierend auf einem Vergleich zwischen dem Sollwert und dem Istwert.

An inventive method for adjusting a sensor element for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a proportion of a gas component in the measurement gas or a temperature of the measurement gas, wherein the sensor element comprises a layer structure with at least one solid electrolyte layer and at least two electrodes comprises the following steps:

• Determining an offset error of a measurement signal of the sensor element at a first known property of the measurement gas,
• Changing the property of the sample gas into a second property,
• Determining a nominal value of the measurement signal in the second property of the measurement gas,
• - Determining an actual value of the measurement signal in the second property of the sample gas, and
• - Determining a pitch error of the measurement signal based on a comparison between the setpoint and the actual value.

The second property may be different from the first property. The second property may be kept substantially constant for a predetermined time. The first property can be set by a further sensor element. The sensor element comprises at least one electrochemical cell, wherein the offset error is determined based on a measurement signal of the electrochemical cell in the first property. The measurement signal in the first property may differ from the desired value of the measurement signal in the second property by at least 5%, and preferably by at least 10%. At least one further gradient error can be determined for at least one third property of the measurement gas. Based on the pitch errors, a correction value for the measurement signal can be determined. A correction value for the measurement signal can be determined at the first property. The measurement gas may be an exhaust gas of an internal combustion engine, wherein a pitch error is determined for a lean property of the exhaust gas and / or a rich property of the measurement gas. The offset error and the pitch error can be determined during operation of the internal combustion engine. A jumping probe can be used to determine the first known property. The first known property can be determined at an air ratio λ = 1. The second property can be determined at an air ratio λ of 0.05 to 0.99, and preferably from 0.50 to 0.95, for example 0.90. Alternatively or additionally, the second property can be determined at an air ratio λ of 1.05 to 2.5, and preferably from 1.1 to 2.0, for example 1.2.

A sensor device may include a sensor element comprising a layer structure comprising at least one solid electrolyte layer and at least two electrodes, and a controller arranged to perform a method according to one of the preceding claims.

In the context of the present invention, a sensor element for detecting physical and / or chemical properties of a measuring gas is understood to be any sensor element which is suitable for detecting a qualitative and / or quantitative detection of a gas component of the measuring gas, in particular an oxygen content in the measuring gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. For example, such sensor elements can be configured as so-called lambda probes, as described in the above-mentioned prior art.

In particular, the sensor element can be configured as a broadband lambda probe, in particular as a planar broadband lambda probe, with which, for example, the oxygen concentration in the exhaust gas can be determined over a wide range and thus the air-fuel ratio in the combustion chamber can be concluded. A broadband lambda probe is a planar two-cell limit current probe. Your measuring cell consists for example of a zirconia ceramic as a solid electrolyte. It is the combination of a Nernst concentration cell and an oxygen pump cell that transports oxygen ions. The oxygen pumping cell is arranged to the Nernst concentration cell so that a diffusion gap is formed between the two. Inside are two electrodes: a pumping electrode and a Nernst measuring electrode. The diffusion gap communicates with the exhaust gas through a gas inlet hole. A porous diffusion barrier is intended to limit the flow of oxygen molecules out of the exhaust gas. The Nernst concentration cell is connected on one side by a reference air channel via an opening with the surrounding atmosphere and on the other side it is exposed to the exhaust gas in the diffusion gap. The exhaust gas passes through the gas inlet hole of the pumping cell into the actual measuring space, ie the diffusion gap, the Nernst concentration cell. So that the air ratio λ can be set in the diffusion gap, the Nernst concentration cell compares the gas in the diffusion gap with the ambient air in the reference air channel. Alternatively, it is possible to work with a so-called pumped reference, in which the reference is obtained by impressing a reference pump flow from the exhaust gas.

By applying a pumping voltage to the electrodes of the pumping cell, oxygen can be pumped in or out of the exhaust gas into the diffusion gap. An electronic control in a control unit regulates this voltage applied to the pumping cell by means of the Nernst concentration cell in such a way that the composition of the gas in the diffusion gap is constant at λ = 1. The pumping current is proportional to the oxygen concentration in the exhaust gas and thus a non-linear measure of the air ratio λ.

Training as a so-called jump probe is also possible. Jump probes work on the principle of a galvanic oxygen concentration cell with a solid electrolyte. The ceramic becomes conductive at about 350 ° C for oxygen ions. On the exhaust side, there is a sudden change in the residual oxygen content in the region λ = 1, so that an electrical voltage occurs between the two boundary surfaces because of the different oxygen content on both sides of the jump probe.

In principle, however, other types of gas components are detectable, such as nitrogen oxides, hydrocarbons and / or hydrogen. Alternatively or additionally, however, other properties of the measuring gas can also be detected.

In the context of the present invention, a layer structure is generally to be understood as meaning an element which has at least two layers and / or layer planes arranged one above the other. The layers can be made conditionally distinguishable by the production of the layer structure and / or from different materials and / or starting materials. In particular, the layer structure can be designed completely or partially as a ceramic layer structure.

In the context of the present invention, a solid electrolyte layer is to be understood as a body or article having electrolytic properties, that is to say having ion-conducting properties. In particular, it may be a ceramic solid electrolyte. This also includes the raw material of a solid electrolyte and therefore the formation as a so-called green or brown, which only becomes a solid electrolyte after sintering. In particular, the solid electrolyte may be formed as a solid electrolyte layer or from a plurality of solid electrolyte layers. In the context of the present invention, a layer is to be understood as a uniform mass in the areal extent of a certain height which lies above, below or between other elements.

In the context of the present invention, an electrode is generally to be understood as meaning an element which is able to contact the solid electrolyte layer in such a way that a current can be maintained through the solid electrolyte layer and the electrode. Accordingly, the electrode may comprise an element on which the ions can be incorporated into the solid electrolyte layer and / or removed from the solid electrolyte layer. Typically, the electrodes comprise a noble metal electrode which may, for example, be deposited on the solid electrolyte layer as a metal-ceramic electrode or otherwise be in communication with the solid electrolyte layer. Typical electrode materials are platinum cermet electrodes. However, other precious metals, such as gold or palladium, are in principle applicable.

In the context of the present invention, a heating element is to be understood as meaning an element which serves to heat the solid electrolyte layer and the electrodes to at least their functional temperature and preferably to their operating temperature. The functional temperature is the temperature at which the solid electrolyte layer becomes conductive to ions and is about 350 ° C. Of this, the operating temperature is to be distinguished, which is the temperature at which the sensor element is usually operated and which is higher than the operating temperature. The operating temperature may be, for example, from 700 ° C to 950 ° C. The heating element may be formed, for example, as an electrical resistance path and is heated by applying an electrical voltage. The heating element may for example be made of a platinum cermet.

In the context of the present invention, a thickness of a component or element is to be understood as meaning a dimension in the direction of the layer structure and thus perpendicular to the individual layer planes of the layer structure.

For the purposes of the present invention, an adjustment is to be understood as meaning any method that is suitable for comparatively matching a measured value supplied by the sensor element to an expected value. In other words, when specifying a known output quantity, a specific measured value is expected. However, the actual reading may differ from the expected reading. Based on a comparison of the actual measured value with the expected measured value, a deviation of the actual measured value from the expected measured value is reliably and reproducibly determined and the determined deviation in the use of the sensor element for the correction of the delivered values is taken into account.

In the context of the present invention, an offset error of a measuring signal generally means a constant, additive or subtractive systematic error of a measured value supplied by the measuring signal, which is determined with a known and constant characteristic of the measuring gas. The offset error is determined or determined by exposing the sensor element to the measurement gas, the measurement gas having a known property, such as a known oxygen partial pressure. With this known property, the measurement signal would have to deliver an expected measured value. However, the expected measured value may differ from an actual measured value. The offset error is then the difference between the expected reading and the actual reading. For example, in a broadband lambda probe, the offset error is determined at λ = 1. Here, the air-fuel mixture in the stoichiometric equilibrium and an oxygen partial pressure in the exhaust gas is known. In such a broadband lambda probe, the pumping current is used as the measuring signal, that is to say that current which has to be applied to the broadband lambda probe in order to pump out the residual oxygen from the broadband lambda probe and thus set the measuring chamber in the probe to λ = 1. At λ = 1 there is no difference in the oxygen partial pressure between the exhaust gas outside the probe and the oxygen partial pressure in the interior of the probe, so that the pumping current as MS signal would have to be 0 A as the measured value. A deviation from this expected measured value is the offset error. Alternatively, the supplied Nernst voltage can be evaluated as a measurement signal in the case of the broadband lambda probe. The expected measured value at λ = 1 is the Nernst voltage of 450 mV. A deviation from this is the offset error.

Accordingly, a measurement signal in the context of the present invention is to be understood as meaning a measured value supplied by the sensor element, which may be an electrical current or an electrical voltage, in particular a pumping current or a Nernst voltage.

In the context of the present invention, a property of the measuring gas is understood to mean a qualitative and / or quantitative property of a gas component of the measuring gas, that is to say a proportion of a specific gas component, in particular an oxygen content in the measuring gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. In principle, however, other types of gas components are detectable, such as nitrogen oxides, hydrocarbons and / or hydrogen. Alternatively or additionally, however, other properties of the measuring gas can also be detected.

In the context of the present invention, a setpoint value is understood to be that value which the sensor element is to deliver as a measurement signal when a specific output variable, such as, for example, the sensor element is exposed to the measurement gas in a known property. In other words, the setpoint is an expected measurement of the measurement signal.

In the context of the present invention, an actual value is to be understood as that value which the sensor element supplies when measuring a specific output variable, such as, for example, the exposure of the sensor element to the measurement gas in the case of a known property as a measurement signal. In other words, the actual value is an actual measured value of the measurement signal.

In the context of the present invention, a pitch error of the measuring signal generally means a constant, additive, subtractive or multiplicative systematic error of a measured value supplied by the measuring signal, which is accompanied by a change in the characteristic of the measuring gas. The slope error is determined or determined by exposing the sensor element to the measurement gas, the measurement gas having a known property, but modified from a first known property, such as, for example, an altered, known oxygen partial pressure. With this changed known property, the measurement signal would have to deliver an expected measured value. However, the expected measured value may differ from an actual measured value. The slope error is then the difference between the expected measured value and the actual measured value plotted against the change in the property of the sample gas. For example, in a broadband lambda probe, the pitch error is determined at λ = 1.1 and or 0.9. The air-fuel mixture is not known in stoichiometric equilibrium and an oxygen partial pressure in the exhaust gas. In such a broadband lambda probe the pump current is used as the measurement signal, that is, the current that must be applied to the broadband lambda probe to pump out the residual oxygen from the broadband lambda probe and thus set the measuring chamber in the probe to λ = 1. At λ = 1.1 and / or 0.9 there is a difference in the oxygen partial pressure between the exhaust gas outside the probe and the oxygen partial pressure in the interior of the probe, so that the pumping current as a measurement signal should be less than 0 A or greater than 0 A as the measured value. A deviation from the respective expected measured value with the change of λ is the slope error, ie the change of the pumping current with the change of λ or the change of the Nernst voltage with the change of λ.

In the context of the present invention, the term "based on a comparison" in relation to the determination of a pitch error is to be understood as the determination of a deviation of the nominal value from the actual value. For example, the deviation is expressed in the form of a difference between the actual value and the nominal value.

A basic idea of the invention is to perform the adjustment of the lambda probe in two steps during ongoing vehicle operation. In a first adaptation step, as already known, the offset error at λ = 1 should be determined with the aid of a jump probe behind the catalytic converter and a corresponding correction value should be adapted. Alternatively, the adjustment at λ = 1 can also be done by evaluating the Nernst voltage of the broadband lambda probe itself. In a further adaptation step, the pitch error is determined at a point apart from λ = 1, but in which no thrust is yet present, and a corresponding correction value is adapted. Advantage of this method is that the adjustment is no longer dependent on the overrun operation, as this is less and less available as explained above. The order of the adaptation steps is arbitrary. It is also initially the linearity error or slope error and then the offset error can be adapted.

According to the invention, the offset error is adapted when the lead control based on the jump probe behind the catalyst has set the mixture to λ = 1. The adaptation takes place over a very slow filter over a longer time. Another requirement is that at this operating point a desired lambda of 1 is driven. According to the invention, in a first adaptation step, the mixture deviations caused by tolerances of the pilot control, i. Tolerances of the injection quantity and the cylinder filling, learned and compensated by a correction value in the fuel path. For this one makes use of the fact that the jump probe behind the catalyst allows a very exact adjustment of the mixture to λ = 1. In the same step, decoupled only over time behavior of the adaptations, the offset error of the broadband lambda probe before the catalyst is also adapted by means of trim control based on the high-precision signal of the jump probe behind the catalyst. Alternatively, the adjustment of the offset error of the broadband lambda probe at λ = 1 can also take place by evaluating the likewise available Nernst voltage of the broadband lambda probe itself.

In a further adaptation step, a lambda value apart from λ = 1, such as 1.1 or 0.9, is then specified, for example by changing the fuel mass supplied to the engine.

It is desirable for the method according to the invention to be able to carry out the fuel mass supplied to the engine and the associated change in the lambda value with the greatest possible accuracy.

This is known per se disturbances, such as the inaccuracy of the pilot control for the injection quantity and / or non-linear behavior of injectors.

For example, dead times and ballistic effects of valve needles may justify a systematic deviation in the behavior of injectors from expected behaviors.

For this reason, there is an advantageous development of the invention in its combination with the example of the DE-102010000872 A1 known methods of CVO (Controlled Valve Operation) and / or in its combination with the example of the DE 102007020964 A1 known methods of MFK (quantity error compensation). An increase in the metering accuracy and the accuracy of the set lambda value is achieved.

In order to improve the accuracy, the method may additionally or alternatively be performed at an operating point of the internal combustion engine at which the injection valves have an increased, preferably maximum, linearity of their characteristic relative to the lambda = 1 point. This is preferably the case in partial load ranges of the internal combustion engine.

However, it is also possible to evaluate a plurality of operating points, it also being possible to average the results in each of these operating points, for example 500 times or more. Although a sufficient accuracy can be achieved even after a single averaging, the relative decreases Inaccuracy in further averaging in general according to the laws of statistics, that is, random fluctuations in the injection quantity are so largely eliminated.

In particular, when carrying out the method in the exhaust gas tract of an internal combustion engine having a plurality of cylinders, it may be provided to maintain a selected lambda value until each cylinder has participated in the combustion at least once at this selected lambda value.

This lambda variation can be adjusted in particular by operating conditions that occur in any case, such as enrichment for component protection, for example, and therefore does not necessarily have to be active. The operating point for the adaptation must remain as constant as possible depending on operating point for a certain time, so that sets a stable exhaust gas concentration at the broadband lambda probe before the catalyst. The resulting lambda differences between the nominal value and measured value of the broadband lambda probe are interpreted as pitch errors of the broadband lambda probe, and a corresponding correction value for the measuring signal of the broadband lambda probe is adapted. The change in the lambda setpoint by the precontrol can take place either only in the direction of lean or only in the direction of grease or one after the other in both directions.

The prerequisite for the method is that the operating point and the lambda variation are selected so that when setting the second lambda value, the pilot control tolerances, i. the tolerances of the injection quantity and the cylinder filling, change as little as possible, while the probe signal already has a significant stroke.

The order of the adaptation steps is arbitrary. It is also initially the linearity error or slope error and then the offset error can be adapted.

The adaptation of the pitch error of the broadband probe is carried out by one or ideally several measuring operations successively at one or more different operating points. The actual correction value for compensating for the pitch error of the probe signal is then determined using statistical methods from the individual measurement results.

It may be advantageous to determine a separate correction value for the measurement signal for the rich and lean measuring range of the broadband lambda probe. As a result, the otherwise high scattering of the probe characteristic in the rich measuring range can be even better reduced.

The determination of separate correction values for the rich and lean measuring range of the broadband lambda probe also makes it possible to deduce the type of oxidizable constituents contained in the exhaust gas and thus the fuel used for the operation of an internal combustion engine.

For example, in combustion with oxygen deficiency or excess fuel in the exhaust depending on the type of fuel specific ratios of different hydrocarbons, hydrogen and carbon monoxide before. For all these types of gas, the sensor sensitivity is different, that is, with the same actual oxygen deficiency different measurement signals are generated by the sensor. Consequently, different characteristics or correction values result depending on the type of fuel. From these characteristics or correction values in the rich measuring range, in particular taking into account the characteristic curves or correction values in the lean measuring range, it is again possible to deduce the type of fuel used, for example the presence and / or the height of an ethanol component in the fuel.

Brief description of the drawings

Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figure.

It shows:

1 a cross-sectional view of a sensor element according to the invention.

2 a flow chart of the inventive method

3 a representation of the measurement signal at different gas concentrations

Embodiments of the invention

This in 1 illustrated sensor element 10 can be used to detect physical and / or chemical properties of a sample gas, wherein one or more properties can be detected. The invention will be described below in particular with reference to a qualitative and / or quantitative detection of a gas component of the measurement gas, in particular with reference to a detection of an oxygen content in the measurement gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. In principle, however, other types of gas components are detectable, such as nitrogen oxides, hydrocarbons and / or Hydrogen. Alternatively or additionally, however, other properties of the measuring gas can also be detected. The invention can be used in particular in the field of motor vehicle technology, so that the measuring gas chamber can be, in particular, an exhaust gas tract of an internal combustion engine, with the measuring gas in particular being an exhaust gas. This in 1 shown sensor element 10 is designed as a broadband lambda probe, as will be explained in more detail below.

The sensor element 10 has a layer structure 12 on which a solid electrolyte layer 14 and at least two electrodes 16 . 18 includes. The solid electrolyte layer 14 can be composed of several solid electrolyte layers or comprise several solid electrolyte layers. The electrodes 16 . 18 are hereinafter also referred to as the first electrode 16 and second electrode 18 but without giving a weighting of their meaning, but merely to distinguish them conceptually. The first electrode 16 and the second electrode 18 are through the solid electrolyte layer 14 interconnected, in particular electrically connected to each other.

The sensor element 10 also has a gas access path 20 on. The gas access route 20 includes a gas access hole 22 extending from a surface of the solid electrolyte layer 14 into the interior of the layer structure 12 extends. In the solid electrolyte layer 14 can be an electrode cavity 24 be provided, which is the gas access hole 22 surrounds, for example, surrounds annular. The electrode cavity 24 is part of the gas access route 20 and can via the gas entry hole 22 communicate with the sample gas space. For example, the gas access hole extends 22 as a cylindrical blind hole perpendicular to the surface of the solid electrolyte layer 14 into the interior of the layer structure 12 , In particular, the electrode cavity 24 formed substantially annular and from three sides of the solid electrolyte layer 14 limited. Between the gas access hole 22 and the electrode cavity 24 is a channel 26 arranged, which is also part of the Gaszutrittswegs 20 is. In this channel 26 is a diffusion barrier 28 arranged, which a subsequent flow of gas from the sample gas space into the electrode cavity 24 diminished or even prevented and only allows diffusion. About this diffusion barrier 28 can be a limiting current of a pump cell 30 to adjust. The pump cell 30 includes one on the surface of the solid electrolyte layer 14 arranged third electrode 32 that the gas entry hole 22 can surround annular and from the sample gas space, for example, by an optional gas-permeable protective layer 34 can be separated. Furthermore, the pump cell includes 30 a fourth electrode 36 in the electrode cavity 24 is arranged. The fourth electrode 36 can also be designed annular and rotationally symmetrical about the gas inlet hole 22 be arranged. For example, the third electrode 32 and the fourth electrode 36 coaxial with the gas inlet hole 22 arranged. The above-mentioned limiting current thus provides a current flow between the third electrode 32 and the fourth electrode 36 over the solid electrolyte layer 14 In the extension of the extension direction of the gas access hole is a heating element 38 in the layer structure 12 arranged.

Furthermore, the layer structure comprises 12 an insulation layer 40 , The insulation layer 40 extends perpendicular to an extension direction of the gas inlet hole 22 into the interior of the solid electrolyte layer 14 , As mentioned above, the gas entry hole is 22 cylindrically shaped, so that the extension direction of the gas inlet hole 22 parallel to a cylinder axis of the gas inlet hole 22 runs. In this case, the insulation layer extends 40 within the solid electrolyte layer 14 perpendicular to the cylinder axis of the gas inlet hole 22 , The insulation layer 40 may, for example, be parallel to the channel 26 extend. In the direction of the cylinder axis of the gas access hole 22 seen, is the isolation layer 40 substantially at the same axial height as the end of the gas inlet hole 22 inside the solid electrolyte layer 14 , It is expressly mentioned that, as an alternative to the pumped reference, an air reference channel can be provided, in which a gas with known properties, such as, for example, an oxygen partial pressure, can be present. Such an air reference channel can, for example, in an imaginary extension of the gas inlet hole 22 and thus further inside the solid electrolyte layer 14 can be arranged.

The first electrode 16 is in the electrode cavity 24 arranged. For example, the first electrode is located 16 the fourth electrode 36 across from. The second electrode 18 lies above the insulation layer 40 , The first electrode 16 , the second electrode 18 and the part of the solid electrolyte layer 14 between the first electrode 16 and the second electrode 18 form an electrochemical cell, such as a Nernst cell 42 , By means of the pumping cell 30 For example, a pumping current through the pumping cell 30 be adjusted so that in the electrode cavity 24 the condition λ = 1 or another known composition prevails. This composition in turn is from the Nernst cell 42 detected by applying a Nernst voltage between the first electrode 16 and the second electrode 18 is measured. The second electrode 18 may be arranged to be at the sensor element 10 to work with a pumped reference, in which the reference is obtained by impressing a reference pumping current from the exhaust gas. Because at the second electrode 18 , which is used as a reference electrode, an excess of oxygen, may be based on the measured voltage on the composition in the electrode cavity 24 getting closed.

Well, with respect to the 2 and 3 the inventive method for adjusting the sensor element 10 described in more detail. The method may be performed by a controller and / or controller not shown in detail. The control and / or regulation can be integrated in the control and / or regulation of the internal combustion engine or be separate components. First, an offset error 201 a measuring signal of the sensor element 10 determined at a first, known property of the sample gas.

The determination of the offset error 201 takes place in the first process step 101 and can be performed in particular during operation of the internal combustion engine. The first known property is, for example, a property of the measurement gas in the form of the exhaust gas in an air-fuel mixture at λ = 1 of the internal combustion engine. For example, the property is the oxygen partial pressure in the exhaust gas. This mixing ratio can be adjusted, for example, by means of a jumping probe not shown in detail behind or downstream of a catalyst not shown in detail. Downstream is to be seen in the flow direction of the exhaust gas, coming from the internal combustion engine initially to the sensor element 10 flows, then passes through the catalyst, then passes the jumping probe and finally leaves the exhaust tract in the environment, so that downstream indicates a position that the exhaust laterally reaches a reference position referred to in the context, here the catalyst. The measuring signal of the sensor element 10 is in this case the pumping current of the pumping cell 30 which should be a reading of about 0 A at λ = 1. A deviating measured value of the measuring signal of the sensor element 10 is the offset error 201 , This offset error 201 then becomes for further operation of the sensor element 10 adapted or taken into account. In other words, the offset error becomes 201 a correction value is determined, for example in the form of the amount by which the actual measured value 202 from the expected reading 203 differs. Alternatively, the offset error 201 by evaluating the also available Nernst voltage of the Nernst cell 42 of the sensor element 10 be adjusted or determined. The Nernst voltage of the Nernst cell 42 should be a reading of 450 mV at λ = 1. A deviating measured value of the measuring signal of the sensor element 10 is the offset error 201 ,

In a second process step 102 . 102 the property of the sample gas is changed to a second property. The second property is different from the first property. For example, an air-fuel mixture is given unequal to λ = 1, such as λ = 1.1 or λ = 0.9. The default can be achieved, for example, by changing the fuel mass supplied to the engine. The default can be done for example in the feedforward control of the fuel path, for example by imposing a specific amplitude at a fixed frequency or by means of a natural frequency control or an oxygen-balancing fuel quantity modulation based on the signal of the jump probe. The jump probe downstream of the catalytic converter determines whether the specification for the air-fuel mixture is fulfilled. This change in the air ratio λ can be due to operating conditions that occur in any case, such as enrichment for component protection, and therefore does not necessarily have to be active. The second property is maintained substantially constant for a predetermined time to provide a stable exhaust gas concentration at the sensor element 10 upstream or upstream of the catalyst. The exhaust gas concentration must remain stable for a few seconds, on the one hand on the sensor element 10 a stable measurement signal is applied and, on the other hand, the determined pitch error can settle via a filter. The exact times depend on the operating point and the actual exhaust gas mass flow. For example, in the partial load, the predetermined time is about 5 seconds.

The measurement gas in the form of the exhaust gas of the internal combustion engine is composed of at least two components, namely oxygen, which was not consumed in the combustion, and other combustion exhaust gases, such as carbon dioxide. The second property differs from the first property with respect to at least one of the components, such as the proportion of oxygen in proportion to the proportion of carbon dioxide. The second property is determined at an air ratio λ of 0.05 to 0.99, and preferably from 0.50 to 0.95, for example 0.9. In the second property of the measurement gas, a desired value of the measurement signal of the sensor element 10 determined, ie an expected measured value of the pumping current of the pumping cell 30 , In the second property, the pumping current of the pumping cell should be 30 at λ = 0.9, be a measured value <0 A. The second property is then the oxygen content in the exhaust, such as the oxygen partial pressure. The measurement signal in the first property differs from the desired value of the measurement signal in the second property by at least 5%, and preferably by at least 10%, such as 12%.

Then in a third process step 103 . 103a an actual value of the measuring signal 204a . 204b determined at the second property of the sample gas, ie an actual measurement of the pumping current of the pumping cell 30 , Then one Slope error of the measurement signal based on a comparison between the setpoint 205a . 205b and the actual value of the measurement signal 204a . 204b determined. For example, a difference 206a . 206b between the actual value of the measuring signal 204a . 204b and the setpoint 205a . 205b determined as pitch error.

The steps of determining the setpoint value and determining the actual value can be repeated as in the present example in order to determine, for example, a plurality of pitch errors. In the example is next to the step 102 , in which a feedforward to λ = 0.9 is the step 102b provided in which a feedforward to λ = 0.9 takes place. The calculation of the associated correction factors takes place in the steps 103a and 103b ,

For example, at least one further pitch error is determined in at least one third property of the measurement gas. The third property is determined at an air ratio λ of 1.05 to 2.5, and preferably 1.1 to 2.0. The third property may be, for example, an oxygen content at an air ratio λ = 1.1. The pumping current of the pump cell should be 30 at λ = 1,1 a measured value> 0 A. Based on the pitch error or the pitch errors, a correction value for the measurement signal is determined. In other words, the measurement signal is corrected based on the pitch errors by a certain value with the change of the property of the measurement gas. Thus, first the slope of the measurement signal is determined with a change in the air ratio λ and then a correction value for the further operation of the sensor element 10 determined by the measuring signal is corrected at a given by the control property of the measurement gas on the change of the property of the measurement gas. The slope of the measurement signal compared to the slope of the expected value is the slope error. More precisely, the slope error is determined from the difference between the measured value and the expected value in relation to the expected value. Both values are filtered in advance. The result of error detection must remain stable for a certain time. The evaluation is based on stability criteria, such as the settling of a filter. The error determination is repeated several times, preferably at different operating points. All results obtained in this way are filtered again, outliers are appropriately eliminated. This results in a stable value for the measurement error. The actual correction value then results from the reciprocal of the error thus determined. For example, if the slope error is 1%, the correction factor for the measurement would be 1 / 1.01 = 0.99. This correction value is then used in the following to permanently multiply all measured values acquired in the future with it. The correction value is continuously adapted whenever the conditions permit. When determining the slope error and the correction value, it must be taken into account that the expected value is correct. Therefore, the injection and filling must be stable and the impressed change in the injection quantity must correspond very precisely to the assigned setpoint value, ie in a range or in an order of magnitude in which the tolerances of the injection are relatively small.

Since the probe error may be different in the lean and rich exhaust gases, it is preferable, as described above, to separately apply the slope error and lean and rich correction method and to determine two separate correction values. It is possible, for example, for a lean property of the exhaust gas and / or a rich property of the measurement gas in each case a pitch error is determined, since the pumping current of the pumping cell 30 does not change linearly with a change in the air ratio λ. The correction value may then be during operation of the sensor element 10 be taken into account for correcting the measurement signal at a change in the air ratio λ.

An optional further development of the method provides for a further method step 110 in front. In this method, following the procedure shown in the example above, the type of oxidizable constituents contained in the exhaust gas and thus the fuel used for the operation of an internal combustion engine are deduced from the determined correction values for the rich and lean measuring range of the broadband lambda probe.

For this, the characteristic curve or the correction value in the rich measuring range is changed 210 in particular taking into account the characteristic curves or correction values in the lean measuring range 211 , in the nature of the fuel used, for example, on the presence and / or the amount of ethanol content in the fuel, inferred. This is possible because in combustion with oxygen deficiency or excess fuel in the exhaust depending on the type of fuel specific ratios of different hydrocarbons, hydrogen and carbon monoxide and present for all these types of gas depending on the speed of transport of this gas through the diffusion barrier 28 there is a different sensor sensitivity.

To optimize the method, the accuracy with which a pilot control of the amount of fuel supplied to the combustion can be improved, so that also an air-fuel mixture with higher accuracy can be adjusted. Here, for example, from the DE-102010000872 A1 known methods of CVO (Controlled Valve Operation) and / or from the example of the DE-102007020964 A1 known methods of MFK (volume error compensation) use.

In the present case, CVO is understood to mean in particular: A method for operating an electromagnetic actuator of a fuel injection valve of an internal combustion engine of a motor vehicle, in which the electromagnetic actuator is actuated during a driving process in order to influence an operating state of the actuator, wherein, in particular at the beginning of the driving process, Condition of a magnetic circuit of the electromagnetic actuator is considered in the control of the electromagnetic actuator.

In the present case, the term MFG is understood in particular as follows: Method for cylinder equalization of an internal combustion engine in which the cylinders are compared with respect to their torque contribution to achieve the best possible smoothness, whereby a running noise signal is evaluated, wherein fuel is injected in at least one injection in a combustion chamber of a cylinder wherein the at least one injection makes a contribution to the torque of the internal combustion engine, characterized in that in a post-injection during a working cycle of the cylinder, fuel is injected into the combustion chamber of the cylinder without torque with respect to the evaluation of the running-rest signal that the post-injection is such that the Exhaust substantially corresponds to a stoichiometric air-fuel mixture.

The invention can be used, for example, in gasoline engines that use a broadband lambda probe in front of a catalyst and a jump probe behind the catalyst. The use of the invention can be detected, for example, by evaluating the electrical signals or the software used in the controller. The detection is also possible by manipulating the signals of the broadband lambda probe and evaluating the real curves of the air ratio λ using an unmanipulated broadband lambda probe or a lambda value determined from the exhaust gas analysis in comparison between identically running tests before and after the manipulation.

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 102010000872 A1 [0037, 0068]
• DE 102007020964 A1 [0037, 0068]

Cited non-patent literature

• Konrad Reif (ed.): Sensors in the motor vehicle, 1st edition 2010, pp. 160-165 [0003]

Claims (15)

Method for adjusting a sensor element ( 10 ) for detecting at least one property of a measurement gas in a measurement gas space, in particular for detecting a portion of a gas component in the measurement gas or a temperature of the measurement gas, wherein the sensor element ( 10 ) a layer structure ( 12 ) with at least one solid electrolyte layer ( 14 ) and at least two electrodes ( 16 . 18 . 32 . 36 ), the method comprising the steps of: - determining an offset error ( 201 ) of a measuring signal of the sensor element ( 10 in a first, known property of the measurement gas, changing the property of the measurement gas into a second property, determining a nominal value of the measurement signal in the second property of the measurement gas, determining an actual value of the measurement signal in the second property of the measurement gas, and determining a pitch error of the measurement signal based on a comparison between the setpoint and the actual value.  A method according to the preceding claim, wherein the second property is different from the first property.  Method according to one of the preceding claims, wherein the second property is kept substantially constant for a predetermined time.  Method according to one of the preceding claims, wherein the first property is set by a further sensor element. Method according to one of the preceding claims, wherein the sensor element ( 10 ) at least one electrochemical cell ( 30 . 42 ), wherein the offset error ( 201 ) based on a measurement signal of the electrochemical cell ( 30 . 43 ) is determined at the first property.  Method according to one of the preceding claims, wherein the measurement signal in the first property differs from the desired value of the measurement signal in the second property by at least 5% and preferably by at least 10%.  Method according to one of the preceding claims, wherein at least one further pitch error is determined in at least one third property of the measurement gas.  Method according to the preceding claim, wherein from the pitch error and the further pitch error on a composition of the sample gas in question property of the measurement gas, in particular a ratio of oxidizable gases contained in the measurement gas is concluded, and / or on a the composition of a fuel from the combustion thereof the measurement gas results as exhaust, property in question, in particular to an ethanol content, is closed.  Method according to one of the two preceding claims, wherein based on the pitch errors, a correction value for the measurement signal is determined.  Method according to one of the preceding claims, wherein a correction value for the measurement signal in the first property is determined.  Method according to one of the preceding claims, wherein the measuring gas is an exhaust gas of an internal combustion engine, wherein for a lean property of the exhaust gas and / or a rich property of the measuring gas, a pitch error is determined.  Method according to the preceding claim, wherein the offset error and the pitch error during operation of the internal combustion engine are determined.  Method according to one of the preceding claims, wherein a jumping probe is used to determine the first, known property of the measuring gas.  Method according to one of the preceding claims, wherein the first known property at an air ratio λ = 1 is determined and the second property at an air ratio λ of 0.05 to 0.99 and / or from 1.05 to 2.5 is determined , Sensor device comprising a sensor element ( 10 ), which has a layer structure ( 12 ) with at least one solid electrolyte layer ( 14 ) and at least two electrodes ( 16 . 18 . 32 . 36 ), and a controller arranged to perform a method according to any one of the preceding claims.

Images