DE102009001840A1 - Method for operating a sensor element and sensor element - Google Patents

Abstract

A method for operating a sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines, in particular a lambda probe, is characterized by the following steps: the internal resistance of the sensor element is determined; - It is the pump voltage of the reference electrode at decreasing with increasing temperature internal resistance readjusted such that the control point of the sensor element does not change and a predetermined minimum pumping current is not exceeded.

Description

The The invention relates to a method for operating a sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines and a sensor element for determining the concentration of gas components in Exhaust gas from internal combustion engines.

object The present invention also relates to a computer program and a Computer program product used to carry out the method are suitable.

State of the art

Such sensors, which are also referred to as lambda probes, go for example from the book publication "Bosch Automotive Handbook" 25th edition, pages 133 ff out. A sensor for determining gas components and / or the concentration of gas components in gas mixtures, in particular in exhaust gases of internal combustion engines, with a reference electrode, which is acted upon by a reference gas channel with a reference gas, in particular air or an oxygen-containing gas, is further from the DE 100 43 089 C2 known.

sensor elements for lambda probes, which are usually planar are, have a reference gas channel, in which a reference electrode arranged is. These sensors are used for example as jump probes. The term "jump probe" is of the characteristic derived lambda sensors, which at an air ratio λ = 1 a "jump" from a first voltage value in the range of about 900 mV to a second voltage value in the range of a few mV. This jump is detected and for determining the correct air-fuel mixture at λ = 1, where optimal, stoichiometric combustion is present, evaluated.

About that In addition, these sensors are also pumped with a so-called Reference or with a reference applied to a pump voltage reference operated in the case of an imprinted anodic Power supplies the reference electrode from the exhaust gas with oxygen becomes.

At the Operation of such lambda probes now the problem arises that unburned at the reference electrode or in an adjacent reference gas volume Hydrocarbons occur, for example, from polluted and / or overheated components or a leaking package originate from the probe. By these unburned hydrocarbons becomes a non-negligible part of the reference electrode supplied oxygen consumed, so that the oxygen concentration lowered at the reference electrode and thus the probe function is disturbed. This phenomenon is called CSD behavior ("Characteristic-Shift-Down") known. In this It is further disturbing that the unburned Hydrocarbons preferably in the hot, catalytic active areas, d. H. in particular at the reference electrode oxidized in the hot area of the probe ("hot spot area") become. In addition, the unburned hydrocarbons diffuse in the reference gas channel, although usually slower than oxygen, however typically uses a single hydrocarbon molecule more than a single oxygen molecule, so that the effective oxygen consumption rate by diffused unburned Hydrocarbons is greater than the diffusion rate for pure oxygen. This is what happens at the reference electrode to a relative enrichment of unburned hydrocarbons or to a relative lack of oxygen. Finally is due to the explained mechanisms the danger of the CSD Behavior in the reference gas channel significantly larger as in the inner volume in the probe housing, which is connected to the reference gas channel in Connection stands.

the CSD behavior can now be counteracted by the fact that the Sensor element by applying an electrical voltage with a Electron current is applied, thereby an oxygen ion stream drives. The oxygen ion current goes to the reference electrode into an oxygen flow and overflows the reference channel in the outer area of the Sensorelemen tes. In this case, a sufficient oxygen partial pressure is generated to Oxidize or remove fatty gas components, so that the CSD behavior is actively eliminated.

Of the Internal resistance of such lambda probes is beyond temperature dependent. If such probes with a pumping current operated, a pumping current leads to a voltage drop on the internal resistance and thus to a displacement of the measuring signal. With constant supply voltage and constant internal resistance (the due to a constant temperature) is also the voltage drop constant and can thus be considered in advance in the control unit become. For unheated sensors, however, the internal resistance depending on the exhaust gas temperature. This can cause it a temperature-dependent voltage drop across the internal resistance come, which corresponds to a signal delay. This is proportional to the pumping current.

Unheated lambda sensors known in the art are usually operated without pumping current. On the one hand, this leads to the proportionality of the signal delay Pumping current to a disappearance of the temperature-dependent signal delay. On the other hand, in this way no pumping action to eliminate the CSD behavior by flushing the reference channel can be achieved.

Of the The invention is therefore based on the object, a method for operating an unheated sensor element, in particular a lambda probe, and to mediate such a lambda probe in which the CSD behavior eliminated.

Disclosure of the invention

Advantages of the invention

These The object is achieved by a method for operating a sensor element for determining the concentration of gas components in the exhaust gas of Internal combustion engine and a sensor element with the features of independent claims 1 and 4 solved.

The basic idea The invention is the CSD behavior, so a signal delay for unheated lambda probes, thereby minimizing that at first the internal resistance of the sensor element is determined and that the Supply voltage of the sensor element with increasing temperature and As a result, decreasing internal resistance is readjusted such that the control point of the sensor element does not change, that is, in the same place and thereby a predefinable minimum pumping current is not exceeded.

Of the The advantage of this measure is increased pumping at high temperatures, where fat gas also increases from the Pack can evaporate.

By those listed in the dependent claims Measures are advantageous developments and improvements of specified in the independent claims 1 and 4 Method and the sensor element possible.

So For example, in a first embodiment of the method measured the internal resistance of the sensor element.

at In another embodiment of the method, the internal resistance over the temperature of the sensor element based on the operating parameters of Internal combustion engine calculated or taken from a map. It will depend on, for example, the operating point of the Internal combustion engine, also the exhaust gas temperature, the exhaust gas ratio, determines the exhaust gas mass flow, and from these to the temperature and thus closed the internal resistance of the sensor element.

The Sensor element according to the invention for determination the concentration of gas components in the exhaust gas of internal combustion engines with at least one electrolyte layer is characterized by the use scandium-stabilized zirconia instead of yttria-stabilized Zirconia in the area under the outer electrode with a Thickness between 10 microns and 50 microns. hereby Especially in the low temperature range are lower internal resistance values achievable, because the resistance component of the ion incorporation reaction lowered becomes.

Around can produce improved ionic conductivity while local areas with yttria-stabilized zirconia used become. This concerns in particular the layers, over the one or both electrodes connected to the electrolyte are.

Farther is intended to reduce the DC internal resistance, the To maximize electrode areas and the reference electrode close to the outer surface of the probe to position as possible to the interposed electrolyte good to couple with the hot exhaust gas.

A Such lambda probe is moreover with a very operated low pump current, the lowest possible Stress distortion leads and still CSD and shunt resistance guaranteed. The pumping currents are in the Range between 0 μA and 10 μA, preferably between 2 μA and 5 μA.

Short description of the drawing

embodiments The invention are illustrated in the drawing and in the following description explained in more detail.

In the 1 a sensor element according to the invention is shown schematically in section.

embodiments the invention

In 1 schematically a sensor element is shown, which by an electrolyte 100 is formed on a support 105 , Can be applied for example by screen printing. The electrolyte has a thickness of about 500 microns. The printing technique of the invention for the production of the electrolyte in the field 101 under the outer electrode 110 is used to achieve a small layer thickness of about 10 microns to 50 microns of scandium-stabilized zirconia and thereby minimize the internal resistance due to the ion incorporation reaction.

The lambda probe has an outer electrode exposed to the exhaust gas (not shown) 110 on that with a control unit SG with over in the 1 only schematically illustrated electrical line 111 is connected and one in a reference gas volume 130 (Reference gas channel) arranged reference electrode 120 who also have a line 140 connected to the control unit SG. To reduce the DC internal resistance, the electrode surface is in particular the electrode exposed to the exhaust gas 110 chosen as large as possible, ideally it is maximally selected taking into account the structural conditions and the resulting temperature distributions. The reference electrode 120 whose area is that of the electrode exposed to the exhaust gas 110 is positioned as close as possible to the outer surface of the probe to couple the electrolyte therebetween as well as possible to the hot exhaust gas. The probe can be operated with a pump current that is chosen to be as small as possible in order to cause a small voltage delay and still ensure the CSD and shunt capability. The pump currents are in the range between 0 μA and 10 μA, in particular and preferably in the range between 2 μA and 5 μA.

In principle, it is also possible to switch on a pumping current only at a higher temperature, for example> 500 ° C., which serves to bring about an "abreaction" of the fat gas evaporating from the sealing packing. An outlet 132 of the pumping gas is dimensioned small in order to advance from fat gas to the reference electrode 120 as possible to prevent. However, it must be chosen so large that a pressure equalization with the environment is guaranteed. In this case, porous layers with high flow resistance must be avoided. To prefer is an open channel with a correspondingly small cross-section. The reference channel can be realized by a simple printing layer with a sacrificial layer of thickness 20 to 30 microns and a channel width between 0.5 and 1 mm (not shown). In principle, it is also possible to use a not quite tight printed electrode lead as a reference channel (not shown). In addition, it can be provided with a porous printing layer 133 In the input region of the reference channel further penetration of fat gas components in the reference gas channel 130 to suppress and at the same time adjust the flow resistance and thus the pressure build-up in the reference range.

in the Following is a method for operating such a lambda sensor to compensate for the signal delay caused by the pumping current to suppress CSD behavior. The compensation of the signal delay sets the knowledge of the internal resistance the sensor element, which is first determined. This For example, by measurements or mathematically or for example by means of a map, depending on the operating parameters the internal combustion engine, such as the exhaust gas mass flow, the exhaust gas amount ratio, the exhaust gas temperature and the like. It takes place Now an adjustment of the supply voltage of the probe to the with rising temperature sinking internal resistance such that the Supply voltage is readjusted with increasing temperature, so the control point is always in the same place, that is does not change and thereby a minimal pumping current not fallen below. This is advantageously a Increased pumping is achieved at high temperatures, which also include grease gas can increasingly evaporate from the pack.

By the change in the control point, within a rule software in the control unit SG, CSD-related Signal distortions are compensated.

The The method described above can be used, for example, as a computer program be implemented in the control unit of the internal combustion engine and run out there. The program code may be on a machine-readable Carrier be stored, the control unit SG can read.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10043089 C2 [0003]

Cited non-patent literature

• - "Bosch Automotive Handbook" 25th edition, pages 133 ff [0003]

Claims (9)

Method for operating a sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines, in particular a lambda probe, characterized by the following steps: - the internal resistance of the sensor element is determined; It becomes the pumping voltage of the reference electrode at ( 120 ) With decreasing internal resistance so that the control point of the sensor element does not change and a predeterminable minimum pumping current is not exceeded. Method according to claim 1, characterized in that the internal resistance of the sensor element is determined by a Ri-pulse internal resistance measurement becomes. Method according to claim 1, characterized in that that the internal resistance of the sensor element based on the operating parameters the engine is calculated or a map is removed. Sensor element for determining the concentration of gas components in the exhaust gas of internal combustion engines having at least one electrolyte layer, characterized by an electrolyte layer ( 101 ) under the exhaust gas side electrode between 10 and 50 microns thick, consisting of a. Scandium stabilized zirconia and / or b. a mixture of scandium- and yttrium-stabilized zirconium oxide and / or c. using a mixture of scandium to yttrium stabilized zirconia. Sensor element according to claim 4, characterized in that to minimize the DC internal resistance of the sensor element, the electric denflächen ( 110 . 120 ) are formed on the electrolyte so that they have a geometrically maximum possible surface. Sensor element according to claim 4 or 5, characterized in that the reference electrode ( 120 ) is disposed near the outer surface exposed to the exhaust gas of the sensor element. Sensor element according to one of claims 4 to 6, characterized in that it is acted upon by a pumping current which is between 0 μA and 10 μA, preferably between 2 μA and 5 μA. Computer program that shows all the steps of a procedure according to one of claims 1 to 3 executes when it on a computing device, in particular the control unit an internal combustion engine runs. Computer program product with program code based on a machine-readable carrier is stored for execution The method according to any one of claims 1 to 3, when said Program on a computer or a control unit of a vehicle is performed.