Sensor for determination of concentration of gaseous components in exhaust gases of internal combustion engines

IPC classes for russian patent Sensor for determination of concentration of gaseous components in exhaust gases of internal combustion engines (RU 2541702):

G01N27/406 -

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Sensor for determination of concentration of gaseous components in exhaust gases of internal combustion engines / 2541702

Electrolyte layer with thickness of 10 to 50 mcm is located in a sensor under the electrode located on the exhaust gas side; the above layer consists of zirconium oxide stabilised with scandium, and/or a mixture of zirconium oxide stabilised with scandium, and zirconium oxide stabilised with yttrium, and/or zirconium oxide stabilised with a mixture of scandium and yttrium. In order to minimise internal direct-current resistance of the sensor, layers of electrodes are made on the electrolyte so that they have geometrically maximum possible area of the surface.

FIELD: engines and pumps.

SUBSTANCE: electrolyte layer with thickness of 10 to 50 mcm is located in a sensor under the electrode located on the exhaust gas side; the above layer consists of zirconium oxide stabilised with scandium, and/or a mixture of zirconium oxide stabilised with scandium, and zirconium oxide stabilised with yttrium, and/or zirconium oxide stabilised with a mixture of scandium and yttrium. In order to minimise internal direct-current resistance of the sensor, layers of electrodes are made on the electrolyte so that they have geometrically maximum possible area of the surface.

EFFECT: achievement of lower values of internal resistance mainly in low temperature range.

3 cl, 1 dwg

The present invention relates to a sensor for determining the concentration of gaseous components in the exhaust gases of internal combustion engines.

Such sensors, also known as oxygen sensors (sensors oxygen concentration) or lambda probes, are known, for example, from the book "Bosch Kraftfahrtechnisches Taschenbuch" (Pocket automotive Handbook Bosch"), 25th edition, page 133 and forth. In addition, from the publication DE 10043089 C2 is known 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, having a reference electrode (reference electrode) to which the reference gas channel receives the reference gas, in particular air or other oxygen-containing gas.

Sensors for oxygen sensors, which usually are planar (planar technology), have the reference gas channel, which is the reference electrode. These sensors are used, for example, as a switching sensor that outputs a voltage step. The expression "switching sensor" comes from the shape characteristics such oxygen sensors, which when the air excess factor λ=1 makes "the leap" from the first voltage, which is around 900 mV, on the second voltage value, at the order of a few millivolts. This jump is recorded and evaluated to determine the correct fuel / air mixture at λ=1, which is optimal stoichiometric combustion of the fuel.

In addition, such sensors operate with a so-called pumping element or element that is energized pumping when, through the application of the anode current to the electrode is supplied with oxygen from the exhaust gas.

In the operation of such oxygen sensors arises the problem that the electrode or in the adjacent volume of reference gas are unburnt hydrocarbons arising, for example, due to contamination and/or overheating of the structural elements or leaks sealing of the sensor. To transform these unburned hydrocarbons spent a large part of the oxygen supplied to the electrode, resulting in the concentration of oxygen at the reference electrode is reduced, which disrupts the sensor. This phenomenon is known as the offset characteristics of the down or "creep" characteristics (CSD). from the English. "Characteristic Shift Down"). In this regard, interference also creates that unburned hydrocarbons are oxidized, preferably by hot catalytically active surfaces, i.e., in private the tee, the reference electrode in the hottest part of the sensor (in the "hot spot"). In addition, although the unburned hydrocarbons and is diffused into the reference gas channel is basically slower than oxygen, one molecule of a hydrocarbon, typically interacts with more than one oxygen molecule, resulting in an effective rate of oxygen consumption of unburned hydrocarbons, which penetrates by diffusion, larger than the speed of diffusion for pure oxygen. This leads to a relative excess of unburned hydrocarbons at the reference electrode and, accordingly, to the relative lack of oxygen. Finally, in view of the above mechanism, the risk of bias characteristics down clearly higher in the reference gas channel, than in the inner space of the sensor housing, soobshayem with the reference gas channel.

The offset characteristics of down can be counteracted by submitting to the sensor voltage with the electronic current, causing the current of oxygen ions. This current oxygen ion moves from the reference electrode in the oxygen stream and goes through the reference gas channel in the outer part of the sensor. The created partial pressure of oxygen is sufficient for the oxidation and removal of the hydrocarbon components of the exhaust gas, making actively eliminates the offset of the ha is acteristic down.

In addition, the internal resistance of the oxygen sensors of this type depends on the temperature. If such sensors operate with a pump current, the latter causes a voltage drop at the internal resistance, and hence the displacement of the measuring signal. At constant voltage and constant internal resistance (due to constant temperature), the voltage drop is constant and can be taken into account in advance in the control unit. However, unheated, pressurized sensors internal resistance depends on the temperature of the exhaust gases. Because of this internal resistance can be voltage drop, temperature-dependent and corresponds to a specific shift signal. This shift is proportional to the current pumping.

Known from the prior art unheated, pressurized oxygen sensors usually work without the pump current. On the one hand, this leads, in view of the proportionality shift signal current pump, the disappearance of the temperature-dependent shift of the signal. On the other hand, it is impossible to achieve the effect of pumping to eliminate bias characteristics down by "purging" of the reference gas channel.

The present invention is the task of developing a sensor for determining the concentration of gaseous components, in private the tee oxygen, the exhaust gases of internal combustion engines, which would have eliminated the phenomenon of displacement characteristics down and would be improved connection located between the electrodes of the electrolyte with hot exhaust gases.

Proposed in the invention, the sensor for determining the concentration of gaseous components in the exhaust gases of internal combustion engines has at least one layer of electrolyte, and located under side of the exhaust gas electrode is a layer of electrolyte thickness from 10 to 50 μm, consisting of:

(a) zirconium oxide stabilized with scandium and/or

b) a mixture of zirconium oxide stabilized with scandium, and zirconium oxide stabilized with yttrium, and/or

b) a zirconium oxide stabilized with a mixture of scandium and yttrium,

and to minimize the internal resistance of the sensor DC electrode layers is performed on the electrolyte so that they are geometrically possible surface area.

This ensures achievement, especially in the field of low temperatures, the smaller the values of the internal resistance decreases as the proportion of the resistance caused by the reaction of ion implementation. To improve the ionic conductivity can be used in local areas with stabilized triem the zirconium oxide. This applies, in particular, layers, of which one electrode or both electrodes are connected with the electrolyte. In addition, to reduce the internal DC resistance is provided by maximizing the surface area of the electrodes and the location of the reference electrode near the outer surface of the sensor that provides the best possible connection located between the electrodes of the electrolyte with hot exhaust gases.

In accordance with the invention, the offset characteristics down in unheated, pressurized oxygen sensors, i.e., the shift signal, minimize, first determining the internal resistance of the sensor, and when the temperature rises, and thus decreasing the internal resistance, adjusting the supply voltage of the sensor so that the point of regulation of the sensor is not changed, i.e. it was in that place, and the value of the pump current when it is not reduced below the specified minimum value.

The advantage of this activity is to increase pumping at high temperatures, which may also stronger to leak from the seals exhaust gases from unburned hydrocarbons.

Given in the dependent claims, the event characterized by private and preferred embodiments of the invention.

In addition, similar to sour odny sensor is operated with a very small pump current, which leads to the possible minimum offset voltage and, nevertheless, provides resistance to displacement characteristics down to the leakage current. When the pumping currents are in the area between 0 and 10 m, preferably between 2 and 5 μa.

On a single drawing as an example, schematically illustrates the invention the sensor is discussed in detail below.

The drawing schematically depicts a sensor (sensor element) formed by the electrolyte 100, which may be deposited on a substrate 105, for example, by the method of screen printing. The thickness of the electrolyte is approximately 500 μm. Provided by the invention of the printing technique for the formation of the electrolyte in the region 101 under the outer electrode 110 is applied to achieve the small thickness of the layer of scandium stabilized zirconium oxide constituting from about 10 to 50 μm, and thus to minimize the internal resistance caused by the reaction of ion implementation.

The oxygen sensor has an external electrode 110 in contact with the exhaust gases (not shown) and coupled with a control unit SG electric conductor 111, shown in the drawing only schematically, and the reference electrode 120, located in volume 130 of the reference gas reference gas channel and an associated control unit SG electric is named conductor 140. To reduce the internal DC resistance of the surface area of the electrodes, in particular in contact with the exhaust gases electrode 110, chosen as big as possible, in the ideal case, it selects the maximum, taking into account the design features and the resulting temperature distributions. The reference electrode 120, the surface area is consistent with the electrode 110 in contact with the exhaust gases, is located as close as possible to the outer surface of the sensor to ensure the best possible connection located between the electrolyte with hot exhaust gases. The sensor can be operated with the pump current, the value of which is chosen as low as possible to provide low offset voltage signal and the resistance to displacement characteristics down to the leakage current. Values of the pump current are in the range from 0 to 10 μa, in the particular and preferred embodiment, they comprise from 2 to 5 µa.

In principle, it is also possible to connect the pump current only at a higher temperature, for example >500°C, and the pump current is used to provide exhaust gas aftertreatment with unburned hydrocarbons seeping out of the seal. Outlet 132 for pumped gas has a small size, to a maximum of prepa is to facilitate the penetration of exhaust gases with unburned hydrocarbons to the reference electrode 120. However, the size of the holes should be such as to ensure equalization of pressure with the ambient pressure. This should avoid the use of porous layers with high resistance to flow. Preferred is an open channel with a correspondingly small cross-section. The reference gas channel (not shown) can be implemented by simple printed layer with a sacrificial (removed) with a layer thickness from 20 to 30 μm and a channel width of from 0.5 to 1 mm. In principle, as a reference gas channel can also be used not very tightly sealed power line electrode (not shown). In addition, in the input of a channel region of the reference gas can be provided printed porous layer 133, preventing further penetration into the channel 130 reference gas hydrocarbon components of the exhaust gas and at the same time specifying the flow resistance, and hence the degree of increase of pressure in the reference gas.

The following describes a method of operating such an oxygen sensor, providing compensation of the shift of the signal due to the pump current to suppress displacement characteristics down. Deskew signal assumes the knowledge of the internal resistance of the sensor, which determines the beginning. The internal resistance can be determined, for example, by measurement is s or calculations or for example, by means of multiparameter characteristics, depending on the operating parameters of the internal combustion engine, such as the mass flow rate of exhaust gases, the proportion of the components of the exhaust gas, exhaust gas temperature, etc., Then the supply voltage of the sensor is adjusted in accordance with the decrease in internal resistance with increasing temperature, adjusting the supply voltage with increasing temperature so that the point of regulation is always in the same place, i.e. not changed, and the value of the pump current is not reduced below the minimum value. This is achieved by increasing the pump at high temperatures, which may also stronger to leak from the seals exhaust gases from unburned hydrocarbons.

By changing the point of regulation occurring within regulatory software in the control unit SG, it is possible to compensate for the shifts of the signal caused by the shift of the characteristics of down.

The above method can be implemented, for example, in the form of a computer program in the control unit of the internal combustion engine and can be run in the control unit. Software code may be stored on a machine-readable storage medium that can be read by the unit the Board SG.

1. A sensor for determining the concentration of gaseous components in the exhaust gases of internal combustion engines, having at least one layer of electrolyte, characterized in that located under side of the exhaust gas electrode is a layer (101) of the electrolyte thickness from 10 to 50 μm, consisting of:
(a) zirconium oxide stabilized with scandium and/or
b) a mixture of zirconium oxide stabilized with scandium, and zirconium oxide stabilized with yttrium, and/or
b) a zirconium oxide stabilized with a mixture of scandium and yttrium,
moreover, to minimize the internal resistance of the sensor DC layers of electrodes (110, 120) is implemented in the electrolyte so that they are geometrically possible surface area.

2. The sensor under item 1, characterized in that the electrode (120) is located near the external contact with the exhaust gases of the surface of the sensor.

3. The sensor under item 1 or 2, characterized in that at a pump current of 0 to 10 μa, preferably from 2 to 5 µa.