JPH0515221B2 - - Google Patents

Description

Claim 1: A measuring element made of only a solid substance, a part of which is hermetically surrounded by a tubular metal casing, and a portion of which is exposed to the measurement gas is provided with a pot-shaped protection tube. is fixed to the metal casing at one end thereof and encloses at a distance the part of the measuring element projecting from the metal casing towards the measuring gas side in the other extent, with one hole in the bottom part on the measuring gas side for the measuring gas and a side wall. In a sensor for measuring the oxygen content in a gas, especially in the exhaust gas of an internal combustion engine, which has a large number of holes and is equipped with a bypass device, the end of the protective tube on the measuring gas side is formed as a convex cap, and the area that protrudes far away. A papillary protuberance 22 is provided on the protuberance 22, a hole 23 provided as a measuring gas inlet is provided in the protuberance 22, and a number of holes 25 are provided as a measuring gas outlet.
6 is oriented so as to guide the gas flowing longitudinally through the protection tube 18 outwardly at an acute angle with respect to the longitudinal axis of the protection tube 18. A sensor for measuring the oxygen content in a gas.

2. The sensor according to claim 1, wherein the hole 25 of the protective tube 18 is located near the end of the metal casing 14 on the measuring gas side.

3. The sensor according to claim 1 or 2, wherein the protective tube 18 is made of metal.

4. Sensor according to one of claims 1 to 3, characterized in that the protective tube 18 has a total length of 12 to 30 mm, in particular 18 to 25 mm.

5. According to one of the claims 1 to 4, characterized in that the hole 23 provided as a measuring gas inlet in the bottom 21 of the protective tube 18 has a diameter of 1 to 4 mm, in particular 2 to 3 mm. sensor.

6 The papillary ridge 22 of the protective tube 18 is 0.3 to 2 mm,
6. The sensor according to claim 1, wherein the sensor has a height of between 0.4 and 1.5 mm.

7. The sensor according to claim 6, wherein the protuberance 22 of the protective tube 18 is convex.

8 Protuberance 22 on cap-shaped bottom 21 of protection tube 18
7. The sensor according to claim 6, wherein the sensor has a truncated conical shape.

9 Cap-shaped bottom 21 of protection tube 18 is 2.5 to 6
9. The sensor according to claim 1, wherein the sensor has a height of 3 to 5 mm.

10 The hole 25 serving as an outlet for the measuring gas in the side wall 24 of the protective tube 18 is smaller than 5 mm from the measuring gas side end of the metal casing 14, in particular 1.5 to 3 mm.
The sensor according to one of claims 1 to 9, characterized in that the sensor has a distance of mm.

11 The hole 25 in the side wall 24 of the protection tube 18, which serves as an outlet for the measurement gas, has a diameter of 0.3 to 1 mm (height) x 1 to
Claim 1 characterized in that it has a free cross section of 3 mm (width), in particular 0.5 mm (height) x 2 mm (width).
The sensor according to Items 1 to 10.

12 A bypass device 26 for the hole 25 provided as an outlet for the measuring gas is formed as a tongue-shaped piece cut into the side wall 24 of the protective tube 18 and bent, the free end of which is cut into the side wall 24 of the protective tube 18.
12. The sensor according to claim 1, wherein the sensor projects into the sensor 8 and faces the end of the sensor 10 remote from the measuring gas.

13 The protective tube 18 has in its side wall 24 3 to 9, in particular 4 to 6 holes 25 provided as outlets for the measuring gas, which holes preferably lie in a single plane perpendicular to the longitudinal axis of the protective tube 18. The sensor according to one of claims 1 to 12, characterized in that:

14. According to one of the claims 1 to 13, characterized in that the open end of the protective tube 18 has an outwardly directed fixing flange 19, which flange has, in particular, the profile of a corrugated washer. sensor.

STATE OF THE ART The present invention relates to a sensor for measuring the oxygen content in a gas according to the concept of claim 1. This type of sensor is already known (West German patent no. 2338536
This sensor has a protective tube that remotely surrounds the part of the measuring element (solid electrolyte tube), which is essentially made of ceramic material, and projects from the tubular metal casing toward the measuring gas side. This protective tube has a large number of holes in its side wall as an inlet for the measuring gas, and a small diameter hole as an outlet for the measuring gas at the bottom on the measuring gas side. The holes in the side wall tube of the protection tube are arranged in the protection tube in such a way that the measuring gas is conducted approximately tangentially to the inner surface of the protection tube, thereby sufficiently protecting the measuring element from impact by solid particles contained in the measuring gas. It is formed.

On the contrary, the sensor of the present invention having the features set forth in claim 1 differs in the guidance of the measuring gas to the measuring element, and the special formation of the protective tube prevents contamination or poisoning of the measuring element (reaction with oil or lead). This has the advantage that the amount of metal dust (products, engine valves, etc.) is significantly reduced, which contributes to a significant life extension. Another advantage is that the protective tube prevents false control in the event of non-representative measured gas peaks due to its properties and allows the response time from high to low oxygen content and vice versa to be of the same length. , thereby leading to a simplification of the electronic evaluation circuit. Further energy savings result from this protective tube if the measuring element is equipped with a resistive heating element.

Drawings Embodiments of the invention are shown in the drawings and explained in more detail in the following description. The drawing shows an enlarged side view of the sensor, and the end of the sensor on the measuring gas side is shown as a longitudinal section.

DESCRIPTION OF THE EMBODIMENTS Illustrated sensor 10 for measuring oxygen content in a gas
It is envisaged for use in particular in the exhaust gases of internal combustion engines; the basic construction of such a sensor 10 is already known from German Utility Model No. 8101584. The sensor 10 operates on the known principle of an oxygen concentration cell with an ionically conductive solid electrolyte; a particularly stabilized cubic zirconium dioxide is used as the solid electrolyte. The solid electrolyte is designed in this example as a solid electrolyte tube 11 with a bottom 12 on the measuring gas side. The display of the layered electrodes on the outer and inner surfaces of this solid electrolyte tube 11 and the protective layer of the electrodes exposed to the measurement gas are omitted;
These electrodes are particularly coated as a porous layer on the solid electrolyte tube 11 and are connected in a known manner to electrical connections, at least one of which is connected to the connecting cable 13.
The catalytic electrodes, usually on the outside of the solid electrolyte tube 11, are connected to an electrically grounded metal casing 14. Solid electrolyte tube 11
A rod-shaped resistive heating element 16 protrudes into the internal space 15 of the sensor 10, which substantially fills the internal space 15 and reaches close to the bottom 12 of the solid electrolyte tube 11; however, in many uses of this sensor 10, resistive heating The arrangement of element 16 can be omitted. The interior space 15 of the solid electrolyte tube 11 is exposed to a reference gas (for example air), which is in contact with the aforementioned counter electrode, not shown. The rest of the structure of this sensor 10 essentially corresponds to the structure of the sensor described in German Utility Model No. 81 01 584; only the sealing ring 17, which is securely fastened to the metal casing 14, is additionally shown.

The portion of the solid electrolyte tube 11 that protrudes from the metal casing 14 toward the measuring gas side is surrounded by a pot-shaped protective tube 18 made of a corrosion-resistant steel plate. This protective tube 18 has at its open end an outwardly directed flange 19 which is designed in the form of a corrugated washer and has a folded edge 2 at the end face of the metal casing 14.
Fixed by 0. The protective tube 18 separates from and surrounds the solid electrolyte tube 11 and has a bottom portion 21 formed as a convex cap on the measuring gas side. A papillary-like convex bulge 22 is arranged in the farthest projecting region of this cap-shaped bottom 21, which bulge is preferably shaped like a truncated cone and tapers toward the measuring gas side. This bulge 22 includes a hole 23 provided as an inlet for the measuring gas. Although this hole 23 has a diameter of 2.5 mm,
Depending on the application, they have a diameter of 1 to 4 mm, in particular 2 to 3 mm. The ridge 22 surrounding the hole 23 has a height of 1 mm in this case, but, depending on the application, a height of 0.3 to 2 mm, in particular 0.4 to 1.5 mm.
Although the height of the cap-shaped bottom part 21 is 4 mm,
2.5 to 6 mm, especially 3 to 5 mm depending on the application
It is. The overall length of such a protective tube 18 is 20 mm, but depending on the application it can be between 12 and 30 mm, in particular between 18 and 25 mm.

Six holes 25 are arranged in the side wall 24 of the protection tube 18 as outlets for the measuring gas from the inner space of the protection tube 18, which holes are located close to the measuring gas end of the metal casing 14, in this case the metal casing 1
Less than 5mm from this end of 4, especially 1.5 to 3
with a distance of mm. In this example this distance is 2 mm. The free section of this hole 25 in the side wall 24 of the protective tube 18 has a height of in particular 0.5 mm and a width of 2 mm.
Depending on the case of use, this hole has a free cross section of 0.3 to 1 mm in height and 1 to 3 mm in width.
Can vary between mm. The number of these holes 25 may vary from 3 to 9 depending on the case of use, but in particular from 4 to 9.
It is 6. Preferably, this hole 25 is formed in the side wall 24 of the protection tube 18 in a direction perpendicular to the longitudinal axis of the protection tube 18.
placed in one plane.

A bulge 22 with a hole 23 as a gas inlet in the center
Also important for the advantageous operation of this protective tube 18 is the arrangement and formation of a bypass device 26, which guides the measuring gas exiting from the bore 25 in a circular manner at an acute angle to the longitudinal axis of the protective tube 18. do. This bypass device 26 is preferably cut into the side wall 24 of the protective tube 18 and bent. This tongue-shaped bypass device 26 projects with its free end into the interior space of the protective tube 18 and points approximately toward the end of the sensor 10 facing away from the measuring gas. This diversion device 26 of the hole 25, which serves for the gas outflow, is provided by the ridge 22 on the bottom 21 of the protective tube 18, which serves to prevent solid particles present in the measuring gas from entering the inner space of the protective tube 18.
The small cross-section of the holes 23 and 25 and the resulting small measured gas volume flowing through the protective tube 18 support the advantages of Internal space 2 of solid electrolyte tube 11
The case of a sensor 10 which includes a resistive heating element 16 at 5 also serves to reduce the heating capacity.

The measuring element of the sensor 10 according to the invention is the bottom part 1.
Not only the solid electrolyte tube 11 having 2 etc.
Other forms (e.g. U.S. Pat. No. 4,011,655;
It is also possible to use measuring elements of platelet-like form (as described in US Pat. No. 4,283,261) or of other functions (e.g. resistance or conductivity changes as described in US Pat. No. 4,007,435, US Pat. No. 4,011,655); The measuring element is solid.