Exhaust gas sensor

Abstract

An exhaust gas sensor has a sensing element having a sensing area that detects certain components in exhaust gas, a holder that supports a base end portion of the sensing element and has a sensor-mounting structure for sensor installation, and a protector that is fixed to the holder and protects the sensing area of the sensing element. To support the sensing element, a sensing element insertion hole for receiving the base end portion of the sensing element is formed at the holder. Then, a clearance between an inner surface of the sensing element insertion hole and a surface of the sensing area is set to be smaller than a clearance between an inner surface of the protector and the surface of the sensing area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a top end portion of an oxygen sensor according to the present invention.

FIG. 2 is a graph showing a relationship between diameter of condensed water (a clearance width) and rate of occurrence of an element crack.

Claims

1. An exhaust gas sensor comprising: a sensing element having a sensing area detecting certain components in exhaust gas;a holder supporting a base end portion of the sensing element and having a sensor-mounting structure for sensor installation; anda protector fixed to the holder and protecting the sensing area of the sensing element, anda clearance between an inner surface of a sensing element insertion hole that is formed at the holder and a surface of the sensing area being set to be smaller than a clearance between an inner surface of the protector and the surface of the sensing area.

2. The exhaust gas sensor as claimed in claim 1, wherein: a gas flow hole is formed at the protector,and wherein:the clearance between the inner surface of the sensing element insertion hole and the surface of the sensing area is applied to a clearance located inside a tubular area that is a top end area of the sensing element insertion hole, located at a top end side of the holder, andthe clearance between the inner surface of the protector and the surface of the sensing area is applied to a clearance located between the closest gas flow hole to the top end portion of the holder and the top end portion of the holder in the protector.

3. The exhaust gas sensor as claimed in claim 2, wherein: an enlarged portion is formed at a top end side of the sensing element,and wherein:a border between the enlarged portion and a non-enlarged portion other than the enlarged portion of the sensing element is positioned inside the tubular area.

4. The exhaust gas sensor as claimed in claim 3, wherein: a clearance between a surface of the non-enlarged portion of the sensing element, which is located from the border to the base end portion of sensing element in the tubular area, and an inner surface of the tubular area is smaller than the clearance between the inner surface of the protector and the surface of the sensing area.

5. The exhaust gas sensor as claimed in claim 1, wherein: a maximum clearance among clearances between the inner surface of the sensing element insertion hole formed at the holder and the surface of the sensing area is set to be smaller than a minimum clearance among clearances between the inner surface of the protector and the surface of the sensing area.

6. The exhaust gas sensor as claimed in claim 1, wherein: a cross section of the clearance between the inner surface of the sensing element insertion hole formed at the holder and the surface of the sensing area and a cross section of the clearance between the inner surface of the protector and the surface of the sensing area are each formed to be substantially constant along an axial direction of the sensor.

7. The exhaust gas sensor as claimed in claim 1, wherein: the clearance between the inner surface of the sensing element insertion hole formed at the holder and the surface of the sensing area is set to less than 0.9 mm.

8. The exhaust gas sensor as claimed in claim 7, wherein: the clearance between the inner surface of the protector and the surface of the sensing area is set to be greater than or equal to 1.4 mm.

9. An exhaust gas sensor comprising: a sensing element having a sensing area detecting certain components in exhaust gas;a holder supporting a base end portion of the sensing element and having a sensor-mounting structure for sensor installation; anda protector fixed to the holder and protecting the sensing area of the sensing element, andboth of a clearance between an inner surface of a sensing element insertion hole that is formed at the holder and a surface of the sensing area and a clearance between an inner surface of the protector and the surface of the sensing area being set to less than 0.9 mm.

10. The exhaust gas sensor as claimed in claim 9, wherein: a gas flow hole is formed at the protector,and wherein:the clearance between the inner surface of the sensing element insertion hole and the surface of the sensing area is applied to a clearance located inside a tubular area that is a top end area of the sensing element insertion hole, located at a top end side of the holder, andthe clearance between the inner surface of the protector and the surface of the sensing area is applied to a clearance located between the closest gas flow hole to the top end portion of the holder and the top end portion of the holder in the protector.

11. The exhaust gas sensor as claimed in claim 10, wherein: an enlarged portion is formed at a top end side of the sensing element,and wherein:a border between the enlarged portion and a non-enlarged portion other than the enlarged portion of the sensing element is positioned inside the tubular area.

12. The exhaust gas sensor as claimed in claim 11, wherein: a clearance between a surface of the non-enlarged portion of the sensing element, which is located from the border to the base end portion of sensing element in the tubular area, and an inner surface of the tubular area is smaller than the clearance between the inner surface of the protector and the surface of the sensing area.

13. The exhaust gas sensor as claimed in claim 9, wherein: both of the clearance between the inner surface of the sensing element insertion hole formed at the holder and the surface of the sensing area and the clearance between the inner surface of the protector and the surface of the sensing area are set to be greater than or equal to 0.1 mm.

14. The exhaust gas sensor as claimed in claim 9, wherein: a cross section of the clearance between the inner surface of the sensing element insertion hole formed at the holder and the surface of the sensing area and a cross section of the clearance between the inner surface of the protector and the surface of the sensing area are each formed to be substantially constant along an axial direction of the sensor.