US-12625105-B2 - Gas sensor

US12625105B2US 12625105 B2US12625105 B2US 12625105B2US-12625105-B2

Abstract

Provided is a gas sensor that reduces a possibility that a terminal fitting electrically connecting a sensor element and a lead wire to each other breaks due to vibrations applied to the gas sensor. In the gas sensor according to one aspect of the present invention, a value obtained by dividing a second distance db, which is a distance from a start end that is an end of a reduced diameter portion of a tubular body on a frontmost end side to a positioning fixture of the terminal fitting, by a first distance Da, which is a distance from the start end to a protrusion of the tubular body, is 0.24 or more and 0.39 or less.

Inventors

Shintaro Maki
Kota Katagiri
Kohei Yaita
Yuya Seike
Satoru Shiraishi

Assignees

NGK INSULATORS, LTD.

Dates

Publication Date: 20260512
Application Date: 20240117
Priority Date: 20230220

Claims (6)

1 . A gas sensor capable of detecting a specific gas concentration of a gas to be measured, the gas sensor comprising: a sensor element that extends in an axial direction and includes a detection unit on a front end side and an element electrode on a rear end side; a terminal fitting that extends in the axial direction and includes an element contact portion electrically connected to the element electrode on the front end side; a ceramic housing that houses the element electrode and the element contact portion; a tubular body that has an open end and in which the sensor element, the terminal fitting, and the ceramic housing are disposed; a lead wire, the front side of which is crimped and fixed to a lead wire holder formed in the terminal fitting on the rear end side, and the rear end side of which extends outward from the open end; and an elastic body that is disposed so as to seal the open end and into which the lead wire is inserted, wherein the terminal fitting includes a positioning fixture that is locked to the ceramic housing to fix a position of the terminal fitting with respect to the ceramic housing, the tubular body includes, on the front end side, a protrusion that is in contact with an external member, to which the gas sensor is to be attached, and prevents leakage of the gas to be measured from a space defined by the external member, a reduced diameter portion that caulks a portion of the elastic body that accommodates the lead wire therein and extends in the axial direction from a periphery is formed in the tubular body on the rear end side, and a value obtained by dividing (2) a second distance Db that is a distance in the axial direction from a start end that is an end of the reduced diameter portion on a frontmost end side to the positioning fixture by (1) a first distance Da that is a distance in the axial direction from the start end to the protrusion is 0.24 or more and 0.39 or less.
2 . The gas sensor according to claim 1 , wherein the first distance Da is 51.6 mm or more.
3 . The gas sensor according to claim 1 , wherein the second distance Db is 20.0 mm or less.
4 . The gas sensor according to claim 1 , further comprising a spacer disposed between the ceramic housing and the elastic body in the axial direction.
5 . The gas sensor according to claim 2 , wherein the second distance Db is 20.0 mm or less.
6 . The gas sensor according to claim 2 , further comprising a spacer disposed between the ceramic housing and the elastic body in the axial direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION The present application claims priority from Japanese application JP 2023-024161, filed on Feb. 20, 2023, the contents of which is hereby incorporated by reference into this application. FIELD OF INVENTION The present invention relates to a gas sensor. BACKGROUND Conventionally, a gas sensor that detects a concentration of a specific gas such as oxygen and NOx in a gas to be measured such as an exhaust gas of an automobile is known. For example, JP H02-146365 U discloses a gas sensor that includes a tubular body, an elastic body, a lead wire, and a terminal fitting. The tubular body houses a sensor element. The elastic body seals an opening of the tubular body. The lead wire is inserted into the elastic body. The terminal fitting electrically connects the sensor element and the lead wire to each other. In the gas sensor disclosed in JP H02-146365 U, the elastic body into which the lead wire is inserted is caulked and fixed by the tubular body to seal the tubular body. SUMMARY OF INVENTION The inventors of the present invention have found a problem that when a conventional gas sensor as disclosed in JP H02-146365 U is repeatedly used in an environment where vibrations are applied to the gas sensor, there is a higher possibility that the terminal fitting electrically connecting the sensor element and the lead wire to each other breaks. The inventors of the present invention have conducted studies on the problem, and have identified the following phenomenon as causes of the higher possibility that the terminal fitting breaks by the vibrations applied to the gas sensor. FIG. 4 is a schematic cross-sectional view schematically illustrating a configuration example of a conventional gas sensor. That is, FIG. 4 schematically illustrates a configuration of a cross section of a conventional gas sensor. The cross section is parallel to and in contact with a longitudinal axis (axis line, a line along the left-right direction in the drawing) of the conventional gas sensor. As illustrated in FIG. 4, the conventional gas sensor has an axis and is formed to extend along a longitudinal direction (axial direction). The conventional gas sensor has a front end and a rear end as respective ends in the longitudinal direction. One end in the longitudinal direction is the front end, and the other end is the rear end. In the example in FIG. 4, the conventional gas sensor is disposed such that the front end faces left, and the rear end faces right. That is, the left-right direction in FIG. 4 corresponds to the longitudinal direction (axial direction). The conventional gas sensor illustrated in FIG. 4 includes a tubular body 20, an elastic body 50, lead wires 40, and terminal fittings 30. The tubular body 20 houses a sensor element 10. The elastic body 50 seals an opening of the tubular body 20 on a rear end side. The lead wires 40 are inserted into the elastic body 50. The terminal fittings 30 electrically connect the sensor element 10 and the lead wires 40 to each other. The terminal fitting 30 includes an element contact portion 31 on a front end side and a lead wire holder 32 on the rear end side. The element contact portion 31 is electrically connected to an element electrode of the sensor element 10. The lead wire holder 32 crimps and holds the lead wire 40. The terminal fitting 30 further includes a positioning fixture 33. The positioning fixture 33 is locked to a ceramic housing 60 to fix the position of the terminal fitting 30 with respect to the ceramic housing 60. That is, the positioning fixture 33 is locked to the ceramic housing 60, so that the position of the terminal fitting 30 is fixed with respect to the ceramic housing 60. The tubular body 20 includes a cylindrical metallic shell 21A, a cylindrical inner tube 21B, a cylindrical outer tube 22, and a fixing bolt 23, all of which are formed of a metal member. The metallic shell 21A and the inner tube 21B may be integrally formed, and both may be collectively referred to as a “metallic shell 21”. The sensor element 10, the terminal fittings 30, and the ceramic housing 60 are disposed inside the tubular body 20. The tubular body 20 (metallic shell 21) further includes a protrusion 222 on the front end side. The protrusion 222 is in contact with an external member (for example, an exhaust pipe of an automobile) to which the conventional gas sensor is to be attached, and prevents leakage of a gas to be measured from a space defined by the external member. Furthermore, a reduced diameter portion 221 is formed in the tubular body 20 (outer tube 22) on the rear end side. The reduced diameter portion 221 caulks a “portion of the elastic body 50 that accommodates the lead wires 40 therein and extends in the axial direction” from the periphery. In the example illustrated in FIG. 4, a reduced diameter portion 221(1) and a reduced diameter portion 221(2) are formed. In FIG. 4, “Da” represents a first distance Da that is a distance in the axi