JPS587184B2 - high gas school - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring device for determining the amount of oxygen, primarily in the exhaust gas of an internal combustion engine, which has an electrochemical measuring detection end in the form of an oxygen concentration cell with an ionically conductive solid electrolyte.

Automatic combustion engines produce air-polluting substances in their exhaust gases, among others carbon monoxide, nitrogen oxides, and unburned or incompletely burned hydrocarbons.

In order to minimize the air pollution caused by these substances, it is necessary to remove them from the internal combustion engine exhaust gas of motor vehicles as fully as possible.

This must convert carbon monoxide and hydrocarbons as completely as possible to their highest oxidation stage, i.e. carbon dioxide, in the case of hydrocarbons to carbon dioxide and water, or nitrogen oxides to elemental nitrogen. Must be.

Such conversion of the harmful components of the exhaust gas into the harmless substances carbon dioxide, nitrogen and water is carried out, for example, by conducting the exhaust gas to a catalyst at a temperature of about 600 DEG C. or higher and subjecting the exhaust gas to secondary combustion.

However, in order to obtain good results it is prerequisite that the composition of the exhaust gas is adjusted in such a way that almost complete reaction to harmless compounds is possible, i.e. the air-to-fuel ratio is approximately stoichiometric, i.e. close to λ Must have a value.

This means that when λ≦1 with respect to the amount of oxygen in the exhaust gas, there is no excess oxygen that exceeds the equilibrium amount of the various possible reactions, and when λ>1 it indicates that there is an excess of oxygen in the mixture. .

Therefore, at λ=1 the exhaust gas transitions from a reducing to an oxidizing state.

In order to maintain the λ value at 1, it is necessary to insert a measuring device in the exhaust gas channel, which serves, for example, to measure the oxygen content and to correctly adjust the exhaust gas composition by means of a control device.

Known devices of this type are equipped with an electrochemical measurement detection end based on the principle of an oxygen concentration cell with an ionically conductive solid electrolyte.

In this case, it is always required that the measuring device exhibits as sharp potential fluctuations as possible at λ=1.

This is because such sharp fluctuations are particularly advantageous for the operation of the control device.

The required sharp voltage changes can only be achieved if the components of the exhaust gas are in thermodynamic equilibrium, which is not normally the case.

BACKGROUND OF THE INVENTION Measuring devices are already known which have a measuring end which carries on the surface exposed to the exhaust gas an electronically conductive porous layer which serves as a catalyst for regulating the gas balance.

This catalyst layer is likewise covered with an inert protective layer as a porous catalyst, which layer serves to homogenize the exhaust gas before it comes into contact with the catalyst layer.

This increases the reaction rate and thus reduces the response time of the measuring device.

Furthermore, the residence time of the gas on the catalyst surface increases due to the reduction in gas velocity within the protective layer.

Since the electrochemical measurement sensing end with a layered structure in this measuring device comes into direct contact with the exhaust gas, this sensing end is exposed to strong mechanical effects such as thermal shock and particle impact, so the ceramic that forms the sensing end High requirements are placed on the temperature change stability and the adhesion of the overlying layer, which results in a relatively high manufacturing cost for this measuring sensing tip.

It is therefore an object of the present invention to provide an exhaust gas system in which the measurement sensing end is protected against thermal shock and particle bombardment, whose electrochemical properties are not inferior to those of currently known measuring devices, and which therefore can be manufactured simply and inexpensively. The object is to obtain a measuring device for measuring the amount of oxygen in the air.

This purpose is achieved by the present invention, comprising: a tubular ionically conductive solid electrolyte with one end open and the other end closed so as to be exposed to exhaust gas from an internal combustion engine; a first electrode in contact with the outer surface of the tube; and a second electrode in contact with the inner surface of the tube. It has an oxygen detection element consisting of two electrodes, and has a protection and catalyst unit that is a catalyst that adjusts the gas to which the detection element is exposed to an equilibrium state, and that protects the outside of the solid electrolyte and the first electrode, and this unit is a catalyst that controls the gas to which it is exposed. a tubular separator consisting of a mesh material surrounding the solid electrolyte tube away from the solid electrolyte, and a tubular support element surrounding this unit forming a chamber between this element and the tubular separator to remove the exhaust gas. A catalyst consisting of a carrier extending into the flow and coated at least in part with a layer of catalytic material is arranged in this chamber, and at least one hole communicating with the outside air is provided in the upper closure part of the support element for inducing a flow of exhaust gas in the chamber. The measuring device is arranged and the end of the support element protruding into the exhaust gas stream is provided with at least one exhaust gas inlet hole.

The catalyst consists of a spherical, particularly porous carrier whose surface is covered with a catalyst layer.

The support may consist of, for example, aluminum oxide, and the catalyst layer may consist of, for example, platinum or a platinum alloy containing aluminum, cobalt, nickel, chromium or other platinum metals as alloying constituents.

However, the catalyst can also consist of mineral wool whose surface is covered with a catalyst layer.

Mineral wool may in particular be glass or asbestos, the surface of which is coated with the same catalytic material mentioned for the aluminum oxide support.

Next, the present invention will be explained with reference to the drawings.

The measuring device of FIG. 1 is installed in the exhaust gas main stream 1.

The measurement detection end, which is an element of the stagnation device, has a solid electrolyte tube 3 closed on one side, which supports a collar 4 at its open end.

The solid electrolyte tube 3 is made of stabilized cubic zirconium dioxide.

There is an outer electrode 5 on the outer surface of the solid electrolyte tube 3, and an inner electrode 6 in the hollow space of the tube 3, and each of these electrodes has the shape of a strip-shaped conductor.

The two electrodes 5 and 6 are made of platinum and are produced by application of a platinum suspension and subsequent baking.

The electrodes each reach up to the collar 4.

The solid electrolyte tube 3 is fixed by its collar 4 in a correspondingly shaped steel holder 7, which has a thread 8 on the outside for screwing the measuring detection end.

Between the collar 4 of the tube 3 and the holder 7 there is an electrically conductive molten material 9.

This molten material serves for the mechanical connection of the solid electrolyte tube 3 and the holder 7 and at the same time guarantees the electrical contact between the outer electrode 5 and the holder 7.

Furthermore, the molten substance ensures a seal between the solid electrolyte tube and the holder.

At the top of the hollow space of the solid electrolyte tube 3 there is a contact nipple 10, which is mechanically fixed by the same electrically conductive molten substance 9 and at the same time brings the inner electrode 6 and the contact nipple 10 into electrical contact.

Above the electrically conductive molten material 9 are steel rings 11 or 12, which serve as pistons that compress the electrically conductive molten material.

The contact nipple 10 is provided with a hole 13, which allows the ambient air, which is used as a reference value, to freely enter the hollow space of the tube 3.

The part of the measurement detection end 2 projecting into the main stream 1 of the exhaust gas is surrounded by a conical tube 14 made of special steel, the lower end of which is closed by a wire gauze 15 made of special steel.

The conical tube 14 is filled with a catalyst 16, which consists of aluminum oxide spheres having a diameter of about 3 mm and carrying a thin layer of platinum on the surface.

At least one hole 17 is installed in the upper closure of the pipe 14 in one plane with the exhaust gas pipe, which hole is connected to the outside air or to the suction pipe, so that in this way a reflux of the exhaust gas is possible. It is.

By this means, a portion of the exhaust gas can reach the surface of the solid electrolyte tube 3 through the packed catalyst.

A reduction in the response speed of the measuring device due to a significant reduction in the gas velocity and possible dead volumes are thereby avoided.

In order to avoid direct contact between the packed catalyst 16 and the outer surface of the solid electrolyte tube 3, a wire mesh 18 made of special steel is installed at the bottom of the holder 7 to surround the solid electrolyte tube 3.

This wire mesh 18 itself can be provided with a platinum layer, which further enhances the catalytic action, or the catalyst 16
Catalytic adjustment of the gas balance is also ensured if the gas is no longer sufficiently effective.

In the example described, the outer surface of the solid electrolyte tube 3 supports only the outer electrode in the form of a strip conductor.

To support the effectiveness of the catalyst 16, at least part of the outer surface of the electrolyte tube 3 can furthermore be provided with an electronically conductive layer, which acts as a catalyst for gas balance regulation.

Such a catalyst layer, which must be porous so that the exhaust gases can reach the electrolyte surface, consists of platinum or a platinum alloy containing aluminum, cobalt, nickel, chromium or other platinum metals as alloying constituents, or optionally It can consist of oxide systems such as copper monochromium oxide doped with barium oxide or nickel halide or lanthanum-cobalt oxide optionally doped with strontium oxide.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of a measuring device according to the invention arranged in the main stream of exhaust gas. 1... Main stream of exhaust gas, 2... Measurement detection end, 3... Solid electrolyte tube, 4... Collar, 5... Outer electrode , 6...inner electrode,
14... Conical tube, 16... Catalyst.

Claims (1)

[Scope of Claims] 1. A measuring device in combination with a catalyst for emitting an electrical signal indicative of the presence of oxygen in exhaust gas led by a conduit from an internal combustion engine, one end being open and the other end being open to the exhaust gas from the internal combustion engine. It has an oxygen detection element consisting of a tubular ion conductive solid electrolyte 3 closed so as to be exposed to exhaust gas, a first electrode 5 in contact with the outer surface of the tube, and a second electrode 6 in contact with the inner surface of the tube, to which the detection element is exposed. It is a catalyst that adjusts the gas to an equilibrium state, and includes a protection and catalytic unit that protects the outside of the solid electrolyte 3 and the first electrode 5, which unit surrounds the solid electrolyte tube 3 away from the solid electrolyte in order to separate the catalyst from the solid electrolyte. It comprises a tubular isolator 18 made of mesh material which surrounds this unit, into which tubular support elements 14, 15 extend into the exhaust gas stream so as to form a chamber between this element and the tubular isolator 18. A catalyst 16 consisting of a support coated at least in part with a layer of catalytic material is arranged, at least one hole 17 communicating with the outside air is arranged in the upper closing part of the support element, in order to induce a flow of exhaust gas into the chamber;
Measuring device for determining the amount of oxygen in exhaust gas, characterized in that the end of the support element that projects into the exhaust gas stream is provided with at least one exhaust gas inlet hole 15.