JP2009156869A - Method and device for determining physical characteristic of gas in measurement gas chamber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method whose measurement flow is easier than that in a conventionally known method, and a device whose sensor structure is extremely simplified. <P>SOLUTION: In this method of determining a physical characteristic of gas in a measurement gas chamber, a sensor element having at least one pump cell is used. A first electrode of this pump cell is exposed to the gas in the measurement gas chamber, a second electrode is arranged in a cavity separated from the measurement gas chamber and sealed air-tightly. At time t<SB>0</SB>, pump voltage U<SB>p</SB>is applied to the pump cell to operate the pump, and pump current flowing through this pump cell is measured. Here, it is determined whether variation characteristic occurs in Nernst counter voltage generated between the first electrode and second electrode occurs. When variation characteristic of Nernst counter voltage is identified, the physical characteristic of the gas is estimated after time t<SB>0</SB>based on the time Δt when this characteristic variation occurs. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention starts from guiding a predetermined ion by a known sensor element based on the electrolyte characteristics of a predetermined solid, that is, a known sensor element resulting from the properties of the solid.

Such sensor elements are used, for example, in automobiles for measuring the air / fuel mixture composition. For example, this type of sensor element is used in so-called “lambda sensors” and plays an important role in reducing harmful substances in exhaust gases, both in gasoline internal combustion engines and in diesel technology. However, the present invention is also applicable to other types of sensor elements including the solid electrolyte as described above. That is, the present invention is, in addition to the bistable sensor (Sprungsonde) and broadband sensor (Breitbandsonde), for example, it is applied to a sensor of similar form having a particle sensor or a solid electrolyte, for example CO, and NO _x or NH ₃ It is also possible to measure. In the following, the present invention will be described by way of example of a lambda sensor without limiting the scope of rights protection, but in view of the above description, other types of sensor elements, for example, other gas components, such as oxygen, may be included. A sensor element that determines the concentration of the gas component can also be produced. The present invention relates to a sensor element, a method for producing a sensor element, for example a sensor element of the present invention, and a method for operating a sensor element.

  In internal combustion engine technology, the so-called air quantity “lambda” (λ) is generally the ratio between the actual air mass supplied and the theoretically required (ie stoichiometric) air mass for combustion. is there. Here, this amount of air is measured by one or more sensors, often at one or more locations in the exhaust gas line of the internal combustion engine. Correspondingly, a “rich” mixture (ie, a fuel-rich mixture) has an air quantity λ <1, while a “lean” mixture (ie, a fuel-less mixture) has an air quantity λ. > 1. In addition to the automotive field, such sensor elements and similar sensor elements control burners in other fields of industrial technology (especially in combustion technology), for example in aircraft technology, or in heating systems or power systems, for example. Used when. Many different embodiments of the above sensor elements are known from the prior art, and for example, “Sensoren im Kraftfahrzeug” by Robert Bosch, June 2001, pages 112 to 117 or “Sauberes by T. Baunach et al.” Abgas durch Keramiksensoren ", Physikjournal 5 (2006), pages 5, 33-38.

  Lambda sensors are known in various forms. The first embodiment is a so-called “vistable sensor” whose measurement principle is based on measuring the electrochemical potential difference between the reference gas and the mixture to be measured. The reference electrode and the measurement electrode are connected to each other via a solid electrolyte. As the solid electrolyte, zircon dioxide (eg, yttria stabilized zircon dioxide, YSZ) or similar ceramic is usually used due to its good oxygen ion conductivity. A so-called “pump cell” can also be used as an alternative or in addition to the bistable sensor, where an electrical “pump voltage” is applied to the two electrodes connected to the solid electrolyte, The “pump current” passing through the pump cell is measured. The sensor principles of the above bistable cell and pump cell can also be used advantageously in combination in a so-called “multicellular” manner.

  However, known sensor elements, in particular broadband sensor elements, actually have some drawbacks and challenging elements. For example, the structure of a typical broadband sensor element is relatively complex. This is because a large number of electrodes and a relatively complicated layer structure are required. Another disadvantage is that the known sensor elements use a reference electrode which is very sensitive to contamination and must be shielded accordingly.

  From DE 102 19 881 A1, a measuring sensor for determining the partial pressure of a measuring gas in a measuring gas chamber is known, which measuring sensor has an ionic conductor (Ioneneleiter) to which a plurality of pump electrodes are attached. One of these pump electrodes is hermetically sealed by a cover. The partial pressure of the measurement gas in the measurement gas chamber can be determined by measuring the Nernst voltage at these pump electrodes or by measuring the amount of charge measured between the pump electrodes.

The device described in DE 102 19 881 A1 has the advantage that the above-mentioned hermetically sealed pump electrode is better shielded against ambient influences and dirt compared to conventional broadband sensors. However, the measurement method described here assumes some ideal assumptions. That is, for example, it is assumed that there is always an unambiguous and known relationship between the amount of charge that has flowed and the current. However, this relationship is in fact a variable nature, or the measurement of the above quantities can be difficult due to measurement technical contingencies, which increases the accuracy and reliability of the measurement. It may be significantly reduced.
DE 102 19 881 A1 "Sensoren im Kraftfahrzeug" by Robert Bosch, June 2001, pages 112-117 "Sauberes Abgas durch Keramiksensoren" by T. Baunach et al., Physikjournal 5 (2006), pp. 33-38.

  It is an object of the present invention to provide a method with a simpler measurement flow and a device with a greatly simplified sensor structure than a conventionally known method.

According to claim 1 of the present invention, there is provided a method for determining a physical property of a gas in at least one measurement gas chamber, in particular a method for determining an oxygen concentration in an exhaust gas of an internal combustion engine, The method uses a sensor element having at least one pump cell, the pump cell comprising at least one first electrode, at least one second electrode, and at least one connecting the first electrode and the second electrode. The first electrode is exposed to the gas in the measurement gas chamber, and the second electrode is disposed in a hermetically sealed space away from the measurement gas chamber. are, determined added pump voltage U _p to said pump cell at time t ₀ is the pump operated, in the form of measuring the pump current flowing through the pump cell, the physical properties of the gas Determining whether or not a characteristic change has occurred in the Nernst counter voltage formed between the first electrode and the second electrode, and identifying the characteristic change in the Nernst counter voltage In this case, the problem can be solved by estimating the physical characteristics of the gas from the time Δt when the characteristic change occurs after the time t ₀ .

  According to claim 12 of the present invention, there is provided a device for determining a physical property of a gas in at least one measurement gas chamber, in particular, a device for determining an oxygen concentration in an exhaust gas of an internal combustion engine. The device includes a sensor element, the sensor element including at least one pump cell, the pump cell including at least one first electrode, at least one second electrode, and the second electrode. 1 electrode and at least one solid electrolyte connecting the second electrode, the first electrode is exposed to the gas in the measurement gas chamber, and the second electrode is the measurement gas Located in a hermetically sealed space away from the chamber, the device further includes an electrical control, which is configured to implement the method described above. It is solved by a device for characteristics and.

The invention relates to a method for determining at least one physical property of a gas in at least one measuring gas chamber. In the following description, emphasis is placed on determining the partial pressure in the measurement gas chamber of the gas component to be detected. By the method of the present invention, at least the above-mentioned drawbacks in the conventionally known methods are largely avoided. The above method is used, for example, to determine the oxygen concentration in the exhaust gas of an internal combustion engine. However, as an alternative, this method can also be used to determine the concentration of other gases such as NO _x , CO, for example.

  The present invention uses a relatively simple sensor element, wherein the sensor element has at least one pump cell, the pump cell having at least one first electrode, at least one second electrode, and a second one. It has at least 1 solid electrolyte which connects 1 electrode and 2nd electrode. Here, the first electrode is exposed to the gas in the measurement gas chamber (eg directly or via a gas permeable protective layer, eg via a porous protective layer). Hereinafter, the first electrode is also referred to as “external electrode” (ASE). On the other hand, the second electrode is disposed in a space separated from the measurement gas chamber and hermetically sealed. This second electrode is hereinafter also referred to as “internal electrode” (ISE).

  Here, the “air-tightly sealed” space is a space that is substantially shielded from the measurement gas chamber. Here, it is preferably completely hermetically shielded, so that the gas exchange with the measuring gas chamber can only take place via the solid electrolyte. However, there can be negligible connections between the void and the measurement gas chamber, where this connection allows a gas flow between the two spaces. This gas flow is a gas flow that is less than the gas flow that flows through the solid electrolyte during operation of the sensor element (e.g. at least one order of magnitude, preferably several orders of magnitude less).

  In the description so far, the sensor elements used in the method according to the invention are similar or the same as, for example, the measurement sensors described in DE 102 19 881 A1. With the configuration of the sensor element described above, there is an advantage that the number of electrodes can be remarkably reduced as compared with a conventionally known sensor element, for example, compared with a conventionally known broadband sensor. As a result, the above structure can be greatly simplified and the cost can be reduced. Furthermore, since the structure proposed here is also compatible with, for example, a conventional bistable sensor and a lean sensor (Magersonde), for example, a synergistic effect can be obtained in manufacturing.

  However, unlike DE 102 19 881 A1, the following measurement method is proposed here. That is, this method is at least a method of substantially measuring the time until a predetermined characteristic event occurs, rather than only relating to quantitative current measurement. Such a time (hereinafter referred to as Δt) can often be detected more easily in terms of measurement technology than the integral value of the current required in DE 102 19 881 A1. The characteristic event used here is that the gas composition in the measuring gas chamber usually does not change or is only insignificant in the proper pump operation, whereas the above-mentioned airtight sealing is used. The fact is that the gas composition in the stopped space changes. When this change is made so that the point λ = 1 is obtained, the above Nernst counter voltage, that is, the electrochemical potential difference between the first and second electrodes, is jumping or obvious. It changes to be identifiable. Such changes in Nernst counter voltage can be directly identified by voltage measurement or can be recorded in the form of characteristic changes in the measured pump current. Here, the pump current is determined by the effective pump voltage (that is, the superposition of the Nernst counter voltage and the pump voltage applied from the outside).

  From the time between the application of the pump voltage and the occurrence of a characteristic event, the physical characteristics of the gas, for example, the gas composition (for example, the partial pressure of the gas component in the measurement gas chamber) can be estimated. This relationship can be created empirically, semi-empirically or analytically.

  Therefore, the above method is superior to the conventionally known method because the measurement flow becomes extremely simple. In the simplest case, it is only necessary to apply the pump voltage, record characteristic events, and estimate the gas composition from time. Furthermore, as already explained, the sensor structure can be greatly simplified.

  Further details and developments of the method of the invention that can be implemented alone or in combination are described in detail within the framework of the following examples. Here, in addition to the method described above, a further device is proposed. The apparatus further includes an electronic control unit in addition to the sensor element having the characteristics described at the beginning, and the electronic control unit is a book in one of the embodiments described above or below. It is configured to carry out the inventive method.

  Embodiments of the invention are illustrated in the drawings and will be described in detail in the following description.

  FIG. 1 shows an example of a prior art sensor element 110 that is used as a broadband lambda sensor and measures the oxygen partial pressure in the measurement gas chamber 112. The sensor element 110 has an external pump electrode (APE) 114 and an internal pump electrode (SPE) 116, which are separated by a first solid electrolyte 118. The external pump electrode 114 is connected to the measuring gas chamber 112 directly or through a gas permeable protective layer, whereas the internal electrode 116 is arranged in the pump chamber 120, and this pump chamber It is connected to the measuring gas chamber 112 via a diffusion barrier 122 that limits the wake (Nachstroemen).

  In this embodiment, the internal pump electrode 116 is composed of two pieces and has a second electrode portion disposed on the second solid electrolyte 124. A reference electrode 126 is disposed on the opposite side of the internal pump electrode 116 and is disposed in the air reference channel 127.

  Further, the sensor element 110 includes a heating element 128 including a heater 130 and a heater insulator 132.

By applying a voltage (pump voltage) between the external pump electrode 114 and the internal electrode 116, oxygen ions can be moved from the internal pump electrode 116 to the external pump electrode 114 or vice versa. The pump voltage between the external pump electrode 114 and the internal pump electrode 116 is controlled so that a constant voltage is applied to the Nernst cell 134 constituted by the reference electrode 126, the second solid electrolyte 124, and the internal electrode 116. Adjusted. In principle, the pump voltage can be positive or negative. When the pump voltage is positive, oxygen is pumped out of the pump chamber 120, while the negative pump voltage forces oxygen to move into the pump chamber 120 where it diffuses through the diffusion barrier 122. Reduced by reacting with rich gas. These oxygen ions are obtained by the decomposition of CO ₂ and / or water at the external pump electrode 114.

For the above control, different cases of system state can occur:
1. U _Nernst <U _Soll (lean mixed gas composition):
The pump voltage between the pump electrodes 114 and 116 is increased. The oxygen partial pressure is reduced in the pump chamber 120 until a new equilibrium is adjusted by the Nernst voltage U _Nernst = U _Soll between the air reference electrode 126 and the internal pump electrode 116.

2. U _Nernst > U _Soll (rich mixed gas composition):
The controller reduces the pump voltage (possibly to a negative value) and increases the equilibrium oxygen partial pressure in the pump chamber 120 until the target value of U _Nernst = U _Soll is achieved.

Controlling to U _Nernst = U _Soll corresponds to adjusting the oxygen partial pressure to a constant small value. When a gradient of the oxygen partial pressure is generated through the diffusion barrier, a particle diffusion current (Diffusionsteilchenstrom) proportional to the difference in the partial pressure is generated. In the target value of the Nernst voltage described above, the pump current passing through the first solid electrolyte 118 must correspond exactly to the determined amount of particles in consideration of the charge number q = 4e.

  When plotting oxygen partial pressure, a linear characteristic curve of the pump current is obtained. For the course of the pump current for the air quantity λ, starting from the oxygen partial pressure measured in the exhaust gas, the air quantity determined only for the region before the combustion reaction has to be calculated back. For further details of the measurement principle of the sensor element 110 according to FIG. 1, for example, the prior art mentioned at the beginning (for example the publication by T. Baunach et al.) Can be mentioned. The illustrated sensor element 110 is relatively complex and requires at least three electrode terminals.

  In the sensor element 110 described in FIG. 1, only one piece of information (measurement amount) is required to determine the oxygen partial pressure (for example, a pump current determined by diffusion). This is because there is only one relevant gas type (eg oxygen, residual oxygen) in the gas to be measured. If there is an associated second type (e.g. hydrocarbons in rich mode), in many cases and in many sensor variants, ambiguous characteristic curves are obtained. Only by extending to two independent measurement points, the absolute value of the partial pressure of the gas type to be detected can be determined. These independent measurement points can usually be realized by a multi-electrode device (for example using the three-electrode device shown in FIG. 1). Therefore, a sensor element having five contacts is obtained together with a heating element incorporated in the sensor element 110. It is also possible here to partially summarize some of these contacts. However, since the number of contacts is increased as described above, the technical cost is increased and the sensor structure is complicated.

  In contrast, FIG. 2 shows an embodiment of a sensor element 110 that can be used within the framework of the present invention. The sensor element 110 and the method of operating the sensor element described here are based on reducing the number of electrodes to be arranged (two-electrode arrangement configuration), and this electrode arrangement results in a closed cavity configuration. The required independent measurement points are realized by the combination of the reference room and the measurement method of a plurality of phases. Corresponding to the minimum number of electrodes (two-electrode arrangement) and with the contact connection of the internal heating element 128 (for example the ground of the heating element 128 and one of the electrodes mentioned above are connected) Only four or three contact wires are required (depending on whether they are present).

  The illustrated sensor element 110 again has a first electrode 136, hereinafter also referred to as an external sensor electrode (ASE), and a second electrode 138, hereinafter also referred to as an internal electrode (ISE). The electrodes 136 and 138 are connected to each other by a solid electrolyte 140. The external sensor electrode 136 is connected to the measuring chamber 112 in which the gas mixture to be measured is present via an optional porous protective layer 142 that may also act to limit diffusion, whereas the internal sensor electrode 138 is disposed in a hermetically closed space 144. In this embodiment as well, this hermetically closed cavity constituted by the fixed electrolyte material can also be completely or partly filled with a porous filling material, which allows gas uptake and release. It becomes possible. Further, in the embodiment shown in FIG. 2, the sensor element 110 again has a heating element 128 that optionally includes a heater 130 and a heater insulator 132.

  The internal sensor electrode 138 functions as a pure oxygen electrode (Nernst electrode) in this case. The external electrode 136 can be similarly implemented as an oxygen electrode. In order to obtain a smooth characteristic curve of the Nernst counter voltage between the two electrodes 136, 138, it is also possible to use a mixed potential electrode (Mischpotentialelektrode) as an alternative to the oxygen electrode (depending on the mode of operation). is there.

  FIG. 3 shows an embodiment of the device 146, in which the sensor element 110 of FIG. 2 can be used. In this embodiment, device 110 is used to determine the oxygen concentration in the exhaust gas. The device 146 includes an electronic control unit 148 in addition to the sensor element 110, which is configured to perform the measurement method of the present invention using the sensor element 110. The electronic control unit includes a trigger device 150, and the trigger device is configured to temporally control a measurement method described below. Further, the electronic control unit 148 includes a pump voltage source 152, which is one or more in the pump cell 154 of the sensor element 110 of FIG. 2 formed from two electrodes 136, 138 and a solid electrolyte 140. Supply multiple voltages. In addition, the electronic control unit 148 includes a voltage measuring device 156, a current measuring unit 158, and preferably a plurality of ohmic resistors 160.

  In the embodiment of FIG. 3, the wiring of the individual elements of the electronic control unit 148 is performed as follows. That is, since the voltage measuring device 156 is connected between the two electrodes 136 and 138 (the latter is provided inside the sensor element 110), the voltage between these electrodes 136 and 138 can be measured. is there. The current measuring device 158 is selectively connected in series with the pump voltage source 152 or one of the plurality of ohmic resistors 160 via the switch 162. The position of the switch 162 is changed and / or temporally controlled by the trigger device 150, for example, via the control line 164.

  It should also be pointed out that the device 146 can be configured differently than the embodiment of FIG. In either case, however, the device described above includes an electronic control unit, which can be switched between the two wires of the sensor element 110, thereby causing time variations. And at least two modes of operation that follow. Up to this point, the switch 162 is provided in any case. In the first wiring state, a pump voltage is applied to the pump cell 154. In this case, the pump voltage source 152 must be provided in addition to the switch 162. Since the pump current is also measured here, a current measuring device 158 should also be included. On the other hand, in the second state, there are a plurality of options. Therefore, first, an equilibrium state can be formed between the measurement gas chamber 112 and the closed space 144 (which cannot be identified in FIG. 3) as follows. That is, forming an equilibrium by shorting the electrodes 136, 138 through an ohmic resistor 160 (this ohmic resistor can advantageously take the value 0 or can be combined from a plurality of ohmic resistors). Can do it. Again, the flowing current is measured via the current measuring device 148. Alternatively or additionally, the Nernst voltage between the electrodes 136 and 138 can be measured via the voltage measuring device 156. In this case, the Nernst voltage measurement unit is an essential component of the electronic control unit 148.

  Furthermore, the electronic control unit 148, such as the trigger device 150, can include one or more microcontrollers, which are configured to perform the measurement method described below. In addition to this, other electronic components can be provided, for example the electronic components already mentioned.

  The device 146 shown in FIG. 3 allows for a multi-phase measurement scheme, which is a voltage sequence and / or a current sequence and / or an actively applied time control or charge control or current control or voltage control. Or it can be switched between passive loads (idling-ohmic load resistance-short circuit).

  The present invention proposes a measurement method in which a pump voltage (constant and / or controlled and / or time-varying) is applied to the pump cell 154 by the pump voltage source 152. Here, the pump current through the pump cell 154 is measured via the current measuring device 148. During this pump operation, it is determined whether one or more characteristic quantities of the pump cell 154 characteristically change continuously or at predetermined intervals (eg, at regular intervals). Here, for example, the following characteristic quantities are used. That is, it is an amount that characterizes a jumping change in the Nernst counter voltage generated by the potential difference between the internal sensor electrode 128 and the external sensor electrode 126. This characteristic change in the Nernst counter voltage indicates that the lambda changes, that is, the amount of air in the closed cavity 144 changes from the rich region to the lean region. This characteristic change can be identified, for example, by a simple electronic component of the electronic controller 148 and / or by pattern identification in the electronic controller 148.

  Such a characteristic change in the Nernst counter voltage can be determined in two possible ways, for example (alternatively or in combination). In the first method, therefore, the pump current passing through the pump cell and recorded by the current measuring device 158 is monitored to check for particularly characteristic jumps (eg jump jumps). Alternatively or additionally, the characteristic change can be determined by directly determining the voltage between the electrodes 136 and 138 by the voltage measuring device 156. Thus, for example, for this voltage measurement, the voltage applied to the pump cell 154 from the pump voltage source 152 can be temporarily interrupted (eg, at a preset, eg, regular repetition interval). This interruption itself can be performed by, for example, the switch 162 (for example, controlled by the trigger device 150). This makes it possible to directly adapt the Nernst counter voltage, in which case the characteristic change represents a characteristic change in the measured voltage.

In either case, the time Δt is used as the measurement quantity. Here, after starting to apply the pump voltage (time point t ₀ ), the characteristic change starts at this time Δt. In addition, for example, the current flowing through the pump cell 154 during the time Δt and / or the charge flowing through the pump cell 154 during the time Δt can be determined and taken into account when evaluating the measurement. This can increase the accuracy of measurement. The above consideration of the current and / or the flow of charge can alternatively be carried out over a time other than the time Δt, for example until equilibrium is reached, ie until the pump current is extinguished. It can be carried out.

  Thus, it can be seen from the above measurements that how many oxygens (or other gas components to be detected) have been pumped out of the space 144 by pumping from the rich to lean lambda change marked by the above changes. It must have been pumped up by this.

  In order to be able to quantitatively estimate the gas mixture composition in the measurement gas chamber 112 from this amount of oxygen up to the lambda change, the void 144 is adjusted to a known oxygen partial pressure before starting this measurement. There must be. This can be done by various means. For one thing, it is possible to adjust the equilibrium between the measuring gas chamber 112 and the closed cavity 144 by shorting the pump cell 154 before applying the pump voltage. This short-circuiting can be performed, for example, by connecting the ohmic resistor 160 in the middle as described above. Such an equilibrium is formed after waiting for a time (eg determined by experience and set eg fixed) and / or when the current measured by the current measuring device 158 asymptotically approximates the value zero. In addition, the partial pressure of oxygen in the space 144 substantially corresponds to the partial pressure of oxygen in the measurement gas chamber 112. Estimate the previous partial pressure from this known starting point if the amount of oxygen that must be pumped or pumped into the space 144 before the lambda change is measured according to the above method. Can do. Here, this partial pressure is equal to the partial pressure in the measurement gas chamber 112. This can be done empirically, for example, by using the stored curve or value (eg, using an electronic table) to determine the lambda value from the total charge flow or time Δt. . However, alternatively or additionally, for example, an analytical or semi-empirical evaluation can be performed using known physical quantities of the sensor element 110, such as the size of the void 144, the conductivity of the solid electrolyte 140, etc. It can also be done.

The above method can be combined with a strategy for pre-establishing an equilibrium state in a suitable sequential measurement scheme, but in an alternative form of this method, a predetermined starting state in the cavity 144 is possible. Is formed by That is, it is formed by first “pumping and emptying” this void so that the oxygen partial pressure in this void 144 is very small. Here, “very small” means that, for example, the partial pressure of oxygen is smaller than 10 ⁻⁷ bar. In order to “pump to empty”, the discharge voltage U _E is applied to the pump cell before the pump voltage is applied. This discharge voltage must be appropriately polarized so that oxygen is pumped out of the cavity 144. For the above-described discharge process, for example, a fixed time can be set in advance, that is, an empirically determined time during which oxygen is substantially completely discharged from the space 144 by pumping. It is possible to monitor the current process itself by means of the current measuring device 158 and to stop the discharge process as soon as it falls below a predetermined limit (the current itself asymptotically approaches zero). In this case as well, a predetermined starting state is formed.

  In the above method, where the lambda change in the space 144 occurs after the pumping up or pumping out of the space 144 is started from a predetermined starting state, the pump voltage is often used. There is still an obstacle that the polarity of is incorrectly selected. Thus, for example, oxygen can be pumped up further in the empty space 144 (λ> 1) already in the lean state. In this case, the air quantity lambda does not move in the direction of λ = 1 but rises further. In other words, the above characteristic change cannot be determined. On the other hand, there may be a case where oxygen is pumped out from the already empty space (λ <1) and the lambda change is not achieved as well.

  There are various ways to solve the above problems. The first strategy is that there is already information about whether the gas mixture in the measurement gas chamber 112 is rich or lean. Therefore, for example, a predetermined engine type is operated so that the exhaust gas composition moves in a lean air amount region in a normal state. This can be used as starting information, whereby the pump voltage is selected so that oxygen is pumped out of the cavity 144 in order to obtain the characteristic changes described above.

  Another strategy that can be implemented in combination with the strategy described at first is to pump in one direction as a test. If this initial pumping direction reveals that no lambda change occurs, the pumping direction can be reversed following this pump pink. This method can also be referred to as a “trial and error” method and can also be performed automatically, for example. For example, it can be identified that a characteristic change in Nernst voltage has not occurred after a preset maximum time and / or according to a preset maximum total charge flow flowing through the pump cell. In this case, this pumping process can be interrupted, for example to reverse the polarity of the pump voltage.

  A predetermined starting state can also be formed here as before before reversing the polarity of the pump voltage. This can be done, for example, again by creating an equilibrium between the cavity 144 and the measuring gas chamber 112 by shorting the pump cell 154 as described above. As an alternative or in addition, as in the above description, the void can be emptied here again by pumping.

  In this way, the above method ensures that lambda changes are identified in any case. If the characteristic change is still not recorded, this can be recorded as well and, for example, a corresponding error notification can be output.

  As described above, the pump voltage applied to the pump cell 154 during the pump operation can be selected to be constant over time, for example. However, it is also possible to use a variable pump voltage with a pump voltage sequence or a preset change course. It is also possible to control the pump voltage so that the pump current is within the preset optimum range.

In the following, a detailed example of the sequence of the method of the invention will be described on the basis of FIGS. To understand this method, the ideal course of the Nernst counter voltage U _N (shown here by reference numeral 166) is first shown in FIG. This voltage is adjusted between the electrodes 136 and 138 of the sensor element 110 when no external voltage is applied to the pump cell 154. Here, from the jump of the Nernst counter voltage at the air amount λ = 1, that is, from the rich gas mixture (indicated by reference numeral 168 in FIG. 4) to the lean (indicated by reference numeral 170 in FIG. 4). The jump of the Nernst counter voltage when changing to a gas mixture can be clearly identified. Also shown in FIG. 4 is the equilibrium partial pressure of oxygen (shown symbolically here by reference numeral 172), which also represents a lean gas mixture from a rich gas mixture 168. When changing to 170, the characteristic jump 172 is similarly performed.

Nernst counter voltage shown by curve 166 in FIG. 4, in some cases superimposed voltage applied from the outside to the electrodes 136 and 138, for example, the pump voltage U _p. Here, an effective pump voltage (U _eff ) is formed, and the pump current is determined by this effective pump voltage. That is,
U _eff = U _P -U _N
It is.

When a characteristic jump occurs in the Nernst counter voltage U _N , this appears in the form of a jump in the effective pump voltage U _eff , and in the form of a pump current jump through the Ohm equation. .

5A-5E show very roughly feature quantities, which are obtained as a function of time in an advantageous embodiment of the invention. Here, FIG. 5A shows the pump voltage Up applied to the pump cell 154 from the outside, FIG. 5B shows the oxygen partial pressure p (O ₂ ) in the space 144, and FIG. 5C shows the Nernst counter voltage U shows the _N, Figure 5D shows the effective pump voltage U _eff synthesized from the pump voltage U _p and Nernst counter voltage U _N, Fig. 5E, flows through the pump cell 154 and for example, a current measuring device 158 The pump current I _p detected by is shown.

  The starting point of this method is an equilibrium between the cavity 144 and the measuring gas chamber 112, which is formed, for example, by a low resistance load or short circuit of the pump cell 154 (see above). This equilibrium state occurs due to oxygen ion migration caused by Nernst voltage or mixed potential voltage (Mischpotentialspannung).

Subsequently, a pump voltage or pump current is applied to the pump cell 154 at time t ₀ , for example, oxygen is pumped into the cavity 144. In this embodiment, a constant pump voltage _Up is used for this purpose, as can be seen from FIG. 5A. Correspondingly, a pump current I _p is generated in this embodiment. This pump current can be ideally constant. Here, a predetermined pumping process is performed, and the amount of oxygen pumped is proportional to the amount of charge pumped. Correspondingly, the oxygen partial pressure in the space 144 shown in FIG. 5B increases with the integral value for the pump current I _{p in} FIG. 5E.

The premise in this embodiment is that the pumping direction is correctly selected, for example starting from a rich starting state in the cavity 144, in which oxygen is pumped up by pumping. Correspondingly, a situation occurs in which the point λ = 1 is reached after a time Δt after the start time t ₀ . This is manifested clearly by a characteristic jump in Nernst against voltage U _N shown in FIG. 5C, this characteristic jump in turn characteristic jump in the effective pump voltage U _eff is generated. In this embodiment, this effective pump voltage drops to a lower value at time t ₀ + Δt. This manifests itself in a characteristic jump in the pump current I _p , which in this case is a sharp drop in the pump current. This jump in pump current is distinguishable. This identification can be performed, for example, by the electronic control unit 148, for example, by monitoring the peak of the derivative of the pump current, by setting a trigger threshold, and / or a pattern that identifies a decrease in the current course of the pump current. This can be done by an identification method. The total amount of oxygen pumped into the space 114 by pumping or the total amount of oxygen exhausted from the space 144 by pumping can be estimated from the time Δt and the current flowing up to that point, or empirical. The air quantity lambda can be directly estimated through the characteristic curve required for the above. This total correlates with the integral for the pump current, where the integral corresponds to the hatched area 174 below the curve shown in FIG. 5E. Since this starting state corresponds to the partial pressure in the measurement gas chamber 112, the oxygen partial pressure in the exhaust gas measurement gas chamber 112 can be further estimated from here.

Instead of detecting a lambda change in the pump current I _p, as described above Alternatively or additionally identifies this characteristic points by measuring the Nernst voltage U _N between the two electrodes 136 and 138 directly It is also possible to do. This can be realized as follows, for example. That is, for example, by using the switch 162 to switch back and forth between the pump operation (applying a pump voltage to the pump cell 154) and the Nernst operation (purely measuring the Nernst counter voltage without applying the pump voltage). It can be realized.

It is a figure which shows the Example of the broadband sensor of a prior art. It is a figure which shows the Example of the sensor element used within the frame of this invention. It is a figure which shows the Example of the apparatus used within the frame of this invention. It is a diagram which shows the rough course of the oxygen partial pressure and the Nernst counter voltage depending on the air quantity λ. FIG. 2 is a diagram showing a schematic course of various physical quantities during execution of an embodiment of the method according to the invention.

Explanation of symbols

  110 sensor element, 112 measuring gas chamber, 114 external pump electrode, 116 internal electrode, 118 solid electrolyte, 120 pump chamber, 122 diffusion barrier, 124 second solid electrolyte, 126 reference electrode, 127 air reference channel, 128 heating element, 130 Heater, 132 heater insulator, 134 Nernst cell, 136 first electrode, 138 second electrode, 140 solid electrolyte, 142 porous protective layer, 144 void, 146 device, 148 electronic control unit, 150 trigger device, 152 pump voltage Source, 154 pump cell, 156 voltage measuring device, 158 current measuring device, 160 ohm resistance, 162 switch, 164 control line, 166 Nernst counter voltage, 168 rich gas mixture, 170 lean Gas mixture, 172 equilibrium partial pressure

Claims (12)

A method for determining the physical properties of a gas in at least one measuring gas chamber (112), in particular a method for determining the oxygen concentration in the exhaust gas of an internal combustion engine,
The method uses a sensor element (110) having at least one pump cell (154),
The pump cell includes at least one first electrode (136), at least one second electrode (138), and at least one solid electrolyte that connects the first electrode (136) and the second electrode (138). 140)
The first electrode (136) is exposed to the gas in the measurement gas chamber (112),
The second electrode (138) is disposed in a hermetically sealed space (144) away from the measurement gas chamber (112),
Is the pump operated by adding pump voltage U _p to said pump cell at time t ₀ (154),
In a method for determining the physical properties of a gas in the form of measuring the pump current flowing through the pump cell (154) of interest.
Determining whether a characteristic change has occurred in the Nernst counter voltage formed between the first electrode (136) and the second electrode (138);
When the characteristic change of the Nernst counter voltage is identified, the physical characteristics of the gas are estimated from the time Δt at which the characteristic change occurs after the time t ₀ .
A method for determining the physical properties of a gas. Distinguishing said characteristic change of the Nernst counter voltage by a characteristic change in the pump current, in particular by a jumping or rising of the pump current,
The method of claim 1. Identifying characteristic changes in the Nernst counter voltage by voltage measurement;
Temporarily interrupting the pump operation for the voltage measurement,
The method according to claim 1 or 2. Additionally detecting the current flowing through said pump cell (154) and / or the charge flowing through said pump cell (154);
Additionally using the current and / or charge in determining the physical properties of the gas,
4. A method according to any one of claims 1 to 3. Before applying the pump voltage, an equilibrium is formed between the measuring gas chamber (112) and the closed cavity (144) by short-circuiting the pump cell (154).
The method according to any one of claims 1 to 4. Performing the short circuit through a resistor (160) connected between the first electrode (136) and the second electrode (138);
6. A method according to any one of claims 1-5. Before applying the pump voltage U _p , the discharge voltage U _E is applied to the pump cell (154),
Here, the discharge voltage is selected to substantially completely remove the gas component to be detected from the closed cavity (144).
7. A method according to any one of claims 1-6. If a characteristic change in the Nernst counter voltage is not identified after a predetermined maximum time and / or after a predetermined maximum total charge flowing through the pump cell (154), Reverse the polarity of the pump voltage,
8. A method according to any one of claims 1-7. Short circuiting the pump cell (154) before reversing the polarity of the pump voltage creates an equilibrium between the measuring gas chamber (112) and the closed cavity (144);
9. A method according to any one of claims 1-8. Before the reversal of the polarity, the discharge voltage U _E is applied to the pump cell (154),
Here, the discharge voltage is selected to substantially completely remove the gas component to be detected from the closed cavity (144).
The method of claim 7. Controlling the pump voltage so that the pump current is within a predetermined optimum range;
11. A method according to any one of claims 1 to 10. An apparatus (146) for determining the physical properties of the gas in at least one measuring gas chamber (112), in particular an apparatus (146) for determining the oxygen concentration in the exhaust gas of an internal combustion engine,
The device (146) includes a sensor element (110) having at least one pump cell (154);
The pump cell (154) includes at least one first electrode (136), at least one second electrode (138), and at least one connecting the first electrode (136) and the second electrode (138). A solid electrolyte (140),
The first electrode (136) is exposed to the gas in the measurement gas chamber (112),
The second electrode (138) is disposed in a hermetically sealed space (144) away from the measurement gas chamber (112),
The device (146) further includes an electrical control (148),
The electrical control unit (148) is configured to implement the method according to any one of claims 1 to 11, characterized in that
A device that determines the physical properties of a gas.

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