GB2350684A

GB2350684A - Exhaust gas sensor

Info

Publication number: GB2350684A
Application number: GB0011871A
Authority: GB
Inventors: Cameron Harold Fowler; Donald W Havas
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1999-05-24
Filing date: 2000-05-18
Publication date: 2000-12-06
Anticipated expiration: 2020-05-18
Also published as: GB0011871D0; GB2350684B

Abstract

An exhaust gas sensor for a motor vehicle includes a housing 22 for attachment to an exhaust system of the motor vehicle, an insulator 32 disposed in the housing 22 and a gas sensitive element 80 extending through the insulator 32 and having one end extending past the insulator. The exhaust gas sensor includes a potting compound 82 of ceramic paste disposed between the insulator and the gas sensitive element to cantilever the one end of the gas sensitive element 80 relative to the insulator 32 and allow longitudinal movement of the gas sensitive element 80 relative to the insulator 32 due to thermal expansion.

Description

1 2350684 - 1 EXHAUST GAS SENSOR The present invention relates generally

to sensors for motor vehicles and, more specifically, to an exhaust gas sensor for a motor vehicle.

It is known to provide an exhaust gas sensor for a motor vehicle. The exhaust gas sensor typically includes a gas sensitive element which is disposed in a housing and provides an electrical output signal indicative of the existence of a specific gas or the concentration of that gas in an environmental gas atmosphere. The gas sensitive element is made of a ceramic material that is cantilevered out the end of the exhaust gas sensor. The exhaust gas sensor has a lower support made of a glass material that is disposed between the gas sensitive element and the housing.

Although the above exhaust gas sensors have worked well, they suffer from the disadvantage that the glass material for the lower support adheres strongly to the gas sensitive element which is undesired. Another disadvantage of the exhaust gas sensor is that the glass material for the lower support does not allow for differential thermal expansion, resulting in fractures of the gas sensitive 25 element. According to a first aspect of the invention, there is provided an exhaust gas sensor for a motor vehicle comprising: 30 a housing for attachment to an exhaust system of the motor vehicle; an insulator disposed in said housing; a gas sensitive element disposed in said insulator; and means disposed between said insulator and said gas sensitive element for providing structural support of said gas sensitive element laterally while allowing movement of said gas sensitive element longitudinally.

According to a further aspect of the invention, there is provided an exhaust gas sensor for a motor vehicle comprising:

a housing for attachment to an exhaust system of the motor vehicle; an insulator disposed in said housing; gas sensitive element extending through said insulator and having one end extending past said insulator; and a potting compound disposed between said insulator and said gas sensitive element to cantilever said one end of said gas sensitive element relative to said insulator and allow movement of said gas sensitive element relative to said insulator due to thermal expansion.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of an exhaust gas sensor, according to the present invention, illustrated in operational relationship with a motor vehicle, FIG. 2 is a fragmentary elevational view of the exhaust gas sensor of FIG. 1, and FIG. 3 is an enlarged elevational view of a portion of the exhaust gas sensor of FIG. 2.

Referring to the drawings and in particular FIG. 1, one embodiment of an exhaust gas sensor 10, according to the present invention, is illustrated for a motor vehicle, generally indicated at 12. The motor vehicle 12 includes an engine 14 and an exhaust system 15 connected to the engine 14. The exhaust system 15 includes an exhaust manifold 16 connected to the engine 14, an exhaust pipe 18 connected to the exhaust manifold 16 and a catalytic converter 20 connected to the exhaust pipe 18. In this embodiment, the exhaust gas sensor 10 is connected to the exhaust pipe 18 between the exhaust manifold 16 and catalytic converter 20 to sense oxygen content in the exhaust gases from the engine 14 to the catalytic converter 20. It should be appreciated that, except for the exhaust gas sensor 10, the motor vehicle 12 is conventional and known in the art.

Referring to FIGS. 2 and 3, the exhaust gas sensor 10 includes a housing or shell 22 extending axially for engaging the exhaust pipe 18. The shell 22 is generally cylindrical in shape and has a passageway 24 extending therethrough. The shell 22 has a plurality of exterior threads 26 near one end for threaded engagement with the exhaust pipe 18. The shell 22 has a reduced diameter end 28 adjacent the end of the threads 26 and an enlarged diameter end 30 at the other end for a function to be described. The shell 22 is made of a metal material such as stainless steel. The exhaust gas sensor 10 may include a seal gasket 31 disposed between the shell 22 and the exhaust pipe 18 to prevent exhaust gases from leaking between the exhaust pipe 18 and the shell 22. The seal gasket 31 is made of a metal material.

The exhaust gas sensor 10 also includes a lower insulator 32 disposed in the shell 22 and extending into the passageway 24. The lower insulator 32 is generally cylindrical in shape and extends axially. The lower insulator 32 has a passageway 34 extending axially therethrough. The lower insulator 32 is made of a ceramic material such as alumina having a Type 1 thermal expansion as is known in the art.

The exhaust gas sensor 10 includes matting 36 disposed between the lower insulator 32 and the shell 22 to provide vibration damping and mechanical support. The matting 36 is made of an inorganic material such as mica disposed in the passageway 24 between the shell 22 and the lower insulator 32.

The exhaust gas sensor 10 includes a wedge ring 38 disposed at one end of the lower insulator 32. The wedge ring 38 is generally cylindrical in shape and has an aperture 40 extending axially therethrough. The wedge ring 38 is made of an insulating material such as alumina ceramic. The exhaust gas sensor 10 includes a seal 42 disposed about one end of the lower insulator 32 and wedge ring 38. The seal 42 is generally annular and made of an insulating material such as glass. The seal 42 hard bonds the lower insulator 32 to the wedge ring 38.

The exhaust gas sensor 10 includes an upper insulator 44 disposed at one end of the wedge ring 38. The upper insulator 44 is generally square in shape and has an aperture 46 extending axially therethrough. The upper insulator 44 is made of an insulating material such as steatite ceramic. The exhaust gas sensor 10 includes a support 48 disposed about one end of the upper insulator 44 and wedge ring 38. The support 48 is generally annular and made of an insulating material such as glass.

The exhaust gas sensor 10 includes an upper shield 50 disposed about the lower insulator 32. The upper shield 50 is generally cylindrical and tubular in shape. The upper shield 50 has a flange 52 extending radially at one end and disposed adjacent the matting 36. The upper shield 50 extends axially about the lower insulator 32 and past the wedge ring 38 and upper insulator 44 for a function to be described. The upper shield 50 has a flange 53 extending axially and radially inwardly at one end thereof for a function to be described. The upper shield 50 includes a dimple 54 extending radially inward near the end thereof for a function to be described. The upper shield 50 is made of a metal material such as stainless steel.

The exhaust gas sensor 10 includes an adapter 56 disposed within one end of the upper shield 50. The adapter 56 is generally cylindrical in shape and extends axially. The adapter 56 includes at least one, preferably a plurality of apertures 58 extending axially therethrough for a function to be described. The adapter 56 includes a groove 60 extending axially along an outer periphery thereof to receive the dimple 54 of the upper shield 50. The adapter 56 further includes a recess 62 extending partially axially along the outer periphery thereof to receive a spring clip 64 to be described. The adapter 56 is made of a material such as alumina ceramic. The exhaust gas sensor 10 includes a spring clip 64 disposed between the upper shield 50 and the adapter 56. The spring clip 64 extends axially and is disposed in the recess 62 between the upper shield 50 and the adapter 56. The spring clip 64 is made of a metal material such as steel. It should be appreciated that the dimple 54 of the upper shield 50 and spring clip 64 secure the upper shield 50 to the adapter 56.

The exhaust gas sensor 10 includes at least one, preferably a plurality of male terminals 66 extending axially for a function to be described. Each of the male terminals 66 have one end disposed in one of the apertures 58 of the adapter 56 and the other end disposed in the apertures 46 and 40 of the upper insulator 44 and wedge ring 38, respectively. The exhaust gas sensor 10 includes at least one, preferably a plurality of female terminals 68 disposed in the apertures 58 of the adapter 56 and extending axially. Each of the female terminals 68 have one end connected to-the male terminals 66 and the other end connected to wires 70 extending axially from the apertures 58 and connected to an electronic controller 72 as illustrated in FIG. 1. It should be appreciated that the controller 72 is conventional and known in the art.

As illustrated in FIG. 2, the exhaust gas sensor 10 includes a seal 74 disposed adjacent the adapter 56 and disposed about the wires 70 to prevent contaminants from entering the apertures 58 of the adapter 56. The seal 74 is generally cylindrical in shape and made of an elastomeric material. The exhaust gas sensor 10 also includes a retainer 76 disposed about the seal 74 and the upper shield 50 to secure the seal 74 to the upper shield 50. The retainer 76 has a stepped shape and is made of a metal material such as steel. The exhaust gas sensor 10 further includes a boot 78 disposed about one end of the retainer 76 and the seal 74 and the wires 70. The boot 78 is made of an elastomeric material.

The exhaust gas sensor 10 also includes a heated gas sensitive or sensor element 80 disposed in and extending through the apertures 46 and 40 and the passageway 24. The gas sensitive element 80 is a flat plate having one end connected to the male terminals 66. The gas sensitive element 80 extends axially past the end of the lower insulator 32 and is cantilevered relative thereto. The gas sensitive element 80 is made of a ceramic material such as high temperature co-fired ceramic multi-layer structure having a Type 2 thermal expansion as is known in the art.

It should be appreciated that the Type 1 thermal expansion is different from the Type 2 thermal expansion.

As illustrated in FIGS. 2 and 3, the exhaust gas sensor 10 further includes a cement support 82 disposed in the end of the lower insulator 32 to support the gas sensitive element 80 in a cantilevered manner relative to the lower insulator 32. The cement support 82 is made of a potting compound. The potting compound is made of a ceramic material such as Ceramaboud 668 and 569, which are commercially available from Aremco Corporation. The potting compound is a paste disposed in an enlarged opening 84 of the passageway 34 of the lower insulator 32 between the gas sensitive element 80 and the lower insulator 32. The cement support 82 does not adhere strongly to the gas sensitive element 80. The cement support 82 provides mechanical support of the gas sensitive element 80 in an x-y direction without a rigid attachment while having sufficiently low bonding to allow thermal expansion of the gas sensitive element 80 in the z-direction. The cement support 82 also allows axial movement or flexing of the gas sensitive element 80 when subjected to temperature changes.

Additionally, the exhaust gas sensor 10 may include a lower shield 86 attached to the reduced diameter portion 28 of the shell 22 and disposed about the cantilevered end of the gas sensitive element 80. The lower shield 86 is generally cylindrical and hollow in shape. The lower shield 86 has at least one aperture 88 extending axially and radially therethrough to allow the exhaust gases to enter and contact the gas sensitive element 80. The lower shield 86 is made of a metal material such as inconel. The exhaust gas sensor 10 may also include a protective shield 90 disposed about-the upper shield 50 and the enlarged diameter portion 30 of the shell 22. The protective shield 90 is generally cylindrical and tubular in shape. The protective shield 90 is made of a metal material such as steel.

In operation, exhaust gases from the engine 14 flow past the exhaust gas sensor 10. These gases enter through the aperture 88 in the lower shield 86, heat and envelop the gas sensitive element 80. As a result, a voltage signal is produced based on the oxygen content in the exhaust gases that reacts with the gas sensitive element 80 and sends a signal to the controller 72 via the wires 70. As illustrated in FIG. 3, the end of the lower insulator 32, cement support 82 and gas sensitive element 80 is in a very hot area as indicated by the dotted line A and the other end of the lower insulator 32 and gas sensitive element 80 is in a less hot area as indicated by the dotted line B. Consequently, the gas sensitive element 80 is not thermally stressed by the temperature difference between the two ends nor the thermal expansion of the lower insulator 32 due to the ceramic support 82.

i CILAIMS An exhaust gas sensor for a motor vehicle comprising:

2. An exhaust gas sensor as claimed in claim 1, wherein said gas sensitive element is a flat plate extending axially.

3. An exhaust gas sensor as claimed in claim 1, wherein said potting compound is a ceramic material.

4. An exhaust gas sensor as claimed in claim 1, wherein said potting compound is a paste.

5. An exhaust gas sensor as claimed in any preceding claim, wherein said gas sensitive element is made of a ceramic material.

6. An exhaust gas sensor as claimed in any preceding claim, wherein said insulator is made of a ceramic material.

7. An exhaust gas sensor as claimed in claim 6, including a seal to hard bond another end of said insulator to another member of said exhaust gas sensor.

8. An exhaust gas sensor as claimed in claim 7, wherein said seal is made of a glass material.

9. An exhaust gas sensor as claimed in any preceding claim, wherein said insulator has a recess in one end and said potting compound is disposed in said recess.

10. An exhaust gas sensor as claimed in claim 9, wherein insulator has a passageway extending axially therethrough, said gas sensitive element extending through said passageway.

11. An exhaust gas sensor as claimed in claim 9, including matting disposed between said housing and said insulator.

12. An exhaust gas sensor for a motor vehicle comprising: a housing for attachment to an exhaust system of the motor vehicle; an insulator disposed in said housing; a gas sensitive element disposed in said insulator; and means disposed between said insulator and said gas sensitive element for providing structural support of said gas sensitive element laterally while allowing movement of said gas sensitive element longitudinally.

13. An exhaust gas sensor constructed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.