Gas sensor and casing for containing sensor element

A sensor element containment casing for containing a sensor element and a connector while securing the sensor element therein, the sensor element including, on a side of one end portion thereof, a sensing part for sensing a predetermined gas component contained in a measurement gas, the connector electrically connecting the sensor element to an outside, the sensor element containment casing comprising:

• an outer tube including a main portion in which a reference gas is included and a sealing portion being an end portion having a smaller diameter than the main portion, another end portion of the sensor element protruding to the main portion,
• a rubber seal member fitted into the sealing portion to seal the outer tube, and
• a ceramic spacer intervening between the seal member and the connector in the outer tube, wherein
• a predetermined position on a lateral side of the sealing portion is a swaging portion swaged from an outside, and the outer tube is sealed with reduction in a diameter of the seal member in the swaging portion,
• the spacer includes:
• a first end surface on a side of one end portion thereof being flat and having contact with the connector, and
• a second end surface on a side of other end portion thereof being flat and having contact with the seal member,
• and, the spacer is secured by being sandwiched between the connector and the seal member due to friction force between the spacer and the seal member acting on the second end surface which occurs by that predetermined load acts on the spacer from the seal member in accordance with reduction in the diameter of the seal member in the swaging portion,
• wherein
• when an outer diameter of the seal member in a portion other than the swaging portion is A, an outer diameter of the seal member in the swaging portion is B, a distance from a contact surface of the seal member having contact with the second end surface to the swaging portion is C, a width of the swaging portion is D, k is a proportional constant, and the predetermined load is F,
• F=k·(A−B)D/C is satisfied, and
• when a minimum value of the predetermined load for sandwiching and securing the spacer by the connector and the seal member is Fmin, and a value of the predetermined load in a case where a contact point deviation occurring between the connector and the sensor element coincides with a maximum allowable range is Fmax,
• Fmin/k≤(A−B)D/C≤Fmax/k is satisfied.