JPH0140047Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oxygen concentration sensor, and more particularly to an oxygen concentration sensor suitable for measuring the oxygen concentration in exhaust gas discharged from a vehicle engine.

This type of oxygen concentration sensor has a cylindrical ceramic tube with one end closed. This ceramic tube usually has zirconium oxide as its main component, and a platinum film is provided on each of its inner and outer surfaces. The ceramic tube is usually arranged so that the outer surface is in contact with the exhaust gas from the engine and the inner surface is in contact with the atmosphere, and a voltage is generated between the inner and outer surfaces according to the ratio of the partial pressure of oxygen in the exhaust gas and the atmosphere. It is.

An example of such an oxygen concentration sensor includes a coaxial electrically insulating isolation bush of a ceramic tube, a conductive plate member interposed between the open end of the ceramic tube and the open end of the isolation bush; There is an oxygen concentration sensor that includes a housing that surrounds the ceramic tube, an isolation bush, and a conductive plate-like member to hold these three members. The electrically insulating isolation bushing is a ceramic member whose main component is aluminum oxide, etc., and the housing is made up of two or three metal cylindrical members arranged coaxially and connected to each other. There is.

When used by being attached to the exhaust pipe of a vehicle engine, the housing may be exposed to water while the vehicle is in operation, or water may enter the housing through connections between multiple members forming the housing. Water may come into direct contact with the isolation bush. Oxygen concentration sensors that come into contact with engine exhaust gas reach high temperatures, but the effect of thermal shock from water, etc. is particularly severe on ceramic isolation bushes. There was a risk that the isolation bushing would crack if it was covered with water.

It is an object of the present invention to provide an oxygen concentration sensor of the above type, which is constructed so that the isolation bushing will not be damaged even if the housing is exposed to water.

For this purpose, in the oxygen concentration sensor of the present invention, a heat insulating material made of, for example, asbestos is interposed between the outer peripheral surface of the isolation bush and the inner surface of the housing.

Next, embodiments of the present invention will be described with reference to the drawings.

The figure is a longitudinal sectional view of an oxygen concentration sensor 1 which is an embodiment of the present invention. This sensor 1 has a cylindrical housing H consisting of a substantially cylindrical holder 2 and a cap 3, which are arranged coaxially with each other.
Ceramic tube whose main component is zirconium oxide 4
is held within the housing H so that its closed end protrudes outside the housing H, and the outer surface of the ceramic tube 4 provided with a platinum film (not shown) is
Hole 6 of louver 5 fixed to one end of housing H
comes into contact with a gas flowing through it. Inside the housing H, a cylindrical electrically insulating isolation bush 7 made of ceramic, such as aluminum oxide, is arranged coaxially with the ceramic tube 4. An electrically conductive plate-like member, ie, a contact plate 8, is interposed between the opposing open ends of the ceramic tube 4 and the isolation bush 7. The contact plate 8 has a ventilation hole 9 that communicates the inside of the ceramic tube 4 and the isolation bush 7 with each other. A rubber tube 10 is fitted into the opening at the other end of the housing H, and a lead wire 11 extends into the housing H through the center hole of the tube 10. A ring-shaped spring 12 is engaged with the outer periphery of the isolation bush 7 near the end that engages with the tube 10. The spring 12 is supported by the shoulder 13 of the housing H and One end is elastically supported. The end of the lead wire 11 extending into the housing H is fastened to one end of a substantially plate-shaped connector 14, and the other end of the connector 14 is connected to the contact plate 8. A platinum film (not shown) provided on the inner surface of the ceramic tube 4 is in contact with a contact plate 8, and the potential of the platinum film is detected via the contact plate 8, the connector 14, and the lead wire 11. On the other hand, the potential of the platinum film on the outer surface of the ceramic tube 4 is detected via the metal housing H that is in contact with the platinum film. Note that the inside of the isolation bush 7 is communicated with the atmosphere outside the housing H via a vent hole (not shown).

This oxygen concentration sensor according to the present invention has a heat insulating material 15 made of, for example, asbestos, interposed between the inner surface of the housing H and the outer peripheral surface of the isolation bush 7. This heat insulating material 15 is arranged to cover almost the entire circumference of the isolation bush 7 to be protected from thermal shock, and blocks heat transfer between the isolation bush 7 and the housing H.

Therefore, according to the present invention, even if the housing H is rapidly cooled down due to the oxygen concentration sensor being covered with water, no thermal shock is applied to the isolation bushing. Furthermore, even if the sensor is covered with water and water enters the housing H from, for example, the connection part C between the holder 2 and the cap 3 forming the housing H, the water will not come into direct contact with the isolation bush 7. Therefore, according to the present invention, damage to the ceramic isolation bushing due to thermal shock can be reliably prevented.

[Brief explanation of the drawing]

The figure is a longitudinal sectional view of an oxygen concentration sensor according to an embodiment of the present invention. Explanation of symbols of main parts, 2, 3... Cylindrical member forming the housing, 4... Ceramic tube, 5
... Louver, 7 ... Isolation button,
8...Contact plate, 15...Insulating material.

Claims (1)

[Scope of utility model registration request] A cylindrical ceramic tube with a closed end and a platinum film provided on the inner and outer surfaces, respectively; an electrically insulating isolation bush;
a conductive plate member interposed between the open end of the ceramic tube and the isolation bush and electrically coupled to the platinum film on the inner surface of the ceramic tube; the ceramic tube; and the conductive plate. and a housing surrounding the isolation bushing and holding the three members, the oxygen concentration sensor including a heat insulating material between the outer peripheral surface of the isolation bushing and the inner surface of the housing. An oxygen concentration sensor characterized by being interposed.