JPH02684Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen concentration sensor, and more particularly to a type of sensor mounted on an automobile and used for measuring oxygen concentration in engine exhaust gas.

This type of oxygen concentration sensor generally has a test tube-shaped zirconia tube whose main component is zirconium oxide and whose inner and outer surfaces are provided with platinum films, respectively, with one end closed. This zirconia tube is usually arranged so that its outer surface is exposed to the exhaust gas in the exhaust pipe, and generates a voltage between the inner and outer surfaces depending on the difference in oxygen partial pressure between the exhaust gas and the atmosphere. As is well known, this voltage is detected by suitable means and processed as a parameter for feedback control of the air/fuel ratio.

An example of this type of oxygen concentration sensor is an electrically insulating isolation bushing coaxial with a zirconia tube, and a metal plate interposed between the open end of the zirconia tube and the open end of the isolation bushing. Some have a buffer member. The isolation bush, the buffer member, and the zirconia tube are held inside a cylindrical body having openings at both ends, and the zirconia tube hermetically closes one opening of the cylindrical body. The above-mentioned buffer member is electrically coupled to the platinum film on the inner surface of the zirconia tube, and functions as an electrode for detecting the potential of the platinum film, and is usually an isolation bush made of extremely hard ceramic. It acts as a buffer between the zirconia tube and the zirconia tube.

When installed in the exhaust pipe of a vehicle engine, the oxygen concentration sensor may also be subjected to severe vibrations. Therefore, although a sensor is normally provided with a buffer means including the above-mentioned buffer member for buffering mechanical shock, cracks may occur in the isolation bushing. Since the isolation bushing is a single member made of hard and brittle ceramic or the like, cracks may directly lead to the destruction of the entire bushing.

The present invention aims to eliminate this drawback of the above-mentioned type of oxygen concentration sensor.

To this end, in the oxygen concentration sensor according to the present invention, the isolation bushing is comprised of a plurality of electrically insulating columnar members that are assembled side by side to define an axial hole inside thereof.

Embodiments of the present invention will be described below with reference to the drawings.

Oxygen concentration sensor 1 which is an embodiment of the present invention
has a cylindrical body 4 made up of two metallic approximately cylindrical members, namely a holder 2 and a cap 3, which are partially fitted together. The holder 2 is fitted into a hole 6 formed in the wall of the exhaust pipe 5.

A zirconia tube 7 and an electrically insulating isolation bush 8 are housed inside the cylindrical body 4. The zirconia tube 7 closes the shaft hole of the holder 2 and protrudes outside the cylindrical body 4, and the outer surface of the zirconia tube provided with a platinum film (not shown) is connected to the hole 10 of the louver 9 engaged with the holder 2. exposed to exhaust air passing through. A ceramic isolation bushing 8 made of magnesium oxide or the like is arranged coaxially with the zirconia tube 7, and between the isolation bushing 8 and the open end of the zirconia tube 7,
A buffer member 12 made of a plate-shaped conductive material such as metal and electrically bonded to the platinum film on the inner surface of the zirconia tube.
is interposed. The buffer member 12 has a vent hole 13 formed therein for communicating the inside of the zirconia tube with the atmosphere, and a columnar connector 14 is coupled thereto.

At the end of the cap 3 remote from the holder 2, an opening is formed coaxially with the isolation bush 8, and a rubber tube 15 is fitted into this opening. A lead wire 16 extends into the isolation bush 8 through the shaft hole of the tube 15. The potential of the platinum film on the inner surface of the zirconia tube is determined by the conductive buffer member 12, the columnar connector 14, the bifurcated plug-in connector 17 engaged with the columnar connector 14, and the lead wire fastened to the end of the plug-in connector 17. This is the structure detected through 16. The shaft hole of the isolation bush 8 communicates with the atmosphere through a vent hole (not shown).

The buffer member 12, the columnar connector 14, and the plug-in connector 17 are fixed to each other by, for example, spot welding to form an integral member.

A ring-shaped spring 18 engages the end of the isolation bush 8 which engages the rubber tube 15. This spring 18 is connected to the shoulder 1 of the cap 3.
9 and is elastically deformable in the axial direction of the bush 8, and cooperates with the buffer member 12 within the cylindrical body 4 to form a buffer means for buffering mechanical shocks.

In this embodiment, the isolation bush 8 consists of two electrically insulating columnar members 20,21. As shown in FIG. 2, the two members 20, 21 are formed completely symmetrically and flank each other to define an axial bore 22 therein.

As is clear from the above, even if a crack occurs in a part of the isolation bush due to vibration or thermal shock, in the oxygen concentration sensor according to the present invention, since the bush is made of multiple members, The crack does not immediately spread to the entire bushing, and the sensor can be easily repaired by replacing only the damaged part.

[Brief explanation of drawings]

FIG. 1 is an axial cross-sectional view showing an oxygen concentration sensor according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an isolation bush of the sensor. Explanation of symbols of main parts, 2...Holder, 3...
... Cap, 7 ... Zirconia tube, 8 ... Isolation bushing, 9 ... Louver, 12 ... Buffer member.

Claims (1)

[Scope of utility model registration request] A cylindrical zirconia tube whose main component is zirconium oxide with a platinum film provided on its inner and outer surfaces, which is closed at one end, and an electrically insulating tube whose both ends are open and arranged approximately coaxially with the zirconia tube. and an isolation bush having a hole that communicates the inside of the zirconia tube with the isolation bush, and electrically coupled to the platinum film provided on the inner surface of the zirconia tube. a plate-shaped conductive buffer member interposed between the open end and the isolation bush; and a plate-shaped conductive buffer member having openings at both ends to surround the zirconia tube, the buffer member, and the isolation bush. a cylindrical body that holds the three members, the zirconia tube closes one opening of the cylindrical body, and the isolation bushes are assembled with their sides in contact with each other and the inside thereof is closed. An oxygen concentration sensor comprising a plurality of electrically insulating columnar members each having an axial hole defined therein.