JPH0236116Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen concentration sensor, and particularly to an oxygen concentration sensor suitable for detecting the oxygen concentration in exhaust gas of an internal combustion engine.

This type of sensor generally has a test tube-like ceramic tube, such as a zirconia tube whose main component is zirconium oxide, whose inner and outer surfaces are each coated with a porous platinum film and which is closed at one end. This ceramic tube is usually arranged so that its outer surface is in contact with the exhaust gas in the exhaust pipe and its inner surface is in contact with the atmosphere, and a voltage is generated between the inner and outer surfaces depending on the ratio of the partial pressures of oxygen in the exhaust gas and the atmosphere. In such an oxygen concentration sensor, a rod-shaped heater is provided inside the ceramic tube in order to improve the operability and oxygen partial pressure difference-voltage response characteristics of the oxygen concentration sensor, especially when the exhaust gas temperature is in the low temperature range. There are cases. The present invention particularly relates to an oxygen concentration sensor having such a heater.

A conventional example of such an oxygen concentration sensor will be explained with reference to the drawings. In the illustrated oxygen concentration sensor, a zirconia tube whose main component is zirconium oxide is used as the ceramic tube, but other ceramic tubes having similar characteristics may be used instead of the zirconia tube.

The conventional oxygen concentration sensor 1 shown in FIGS. A test tube-shaped zirconia tube 5 with one end closed is installed inside. A porous platinum film (not shown) is provided on the inner and outer surfaces of the zirconia tube 5, respectively, and the outer surface of the zirconia tube 5 is made to come into contact with gas such as exhaust gas from an internal combustion engine passing through the holes 6 of the louver 4. It's getting old. Inside the housing, a substantially cylindrical metal contact ring 7 and a ceramic isolation bush 8 are arranged coaxially with the open end of the zirconia tube 5 and adjacent to each other. , 8 is a spring 1 by an annular disc spring 10 engaged with an annular flange portion 9 of the cap 3.
The zirconia tube 5 is elastically supported by a pushing force acting in a direction from zero toward the zirconia tube 5. Inside the zirconia tube 5, contact ring 7, and isolation bush 8 that are arranged coaxially, a heater 11 having a rod-like outer shape is arranged substantially coaxially with these members. A metal bushing 14 is fitted inside the isolation bushing 8, and the heater 1
1 is engaged with and supported by the bush 14 via a ring-shaped member 15 fitted to the heater. The heater 11 is composed of a metal wire (not shown) embedded in a suitable electrically insulating material such as ceramic, and the metal wire is connected to a sealing rubber plug 2.
A pair of needle electrodes 13 are connected to a pair of lead wires 12 extending into the isolation bush 8 through the
and is heated by the current supplied through the lead wire 12 and electrode 13. The conductive core wire 12a and electrode 13 exposed from the electrically insulating outer sheath at the end of the lead wire 12 are insulated from the metal bushing 14 by an electrically insulating substantially cylindrical insulating member 16 and an insulating cylinder 17. .

In the bore 18 at the end of the bush 14 remote from the contact ring 7 there is provided a cylindrical body or pipe 1 of preferably metallic, electrically conductive and plastic material.
9 are fitted, and the lead wire 12 extends into the bush 14 via the pipe 19. pipe 1
9 is insulated from the housing consisting of the holder 2, cap 3 and louver 4. The end of the pipe 19 within the bush 14 is formed with an annular flange 20 that flares radially outward.
A spring 21 mounted around the pipe 19 within the bushing 14 engages this flange 20 and a radially inward flange 22 at the outer end of the bush 14 to bias the pipe 19 inwardly. The insulating member 16, insulating cylinder 17, and ring-shaped member 15 engaged with the pipe 19 are urged to close the contact ring 7.
is pressed onto the zirconia tube 5.

The platinum film on the outer surface of the zirconia tube 5 is in contact with the metal holder 2 and is at the same potential, while the platinum film on the inner surface of the zirconia tube is connected to the metal contact ring 7 in contact with the platinum film, and to the member 7. It is electrically connected to the pipe 19 via a metal bush 14 that is in contact with one end and a spring 21 that is in contact with the bush 14. Therefore, the sensor output, that is, the voltage between the platinum films on both the inner and outer surfaces of the zirconia tube is equal to the voltage between the holder 2 and the pipe 19. pipe 19
The potential of is detected via the lead wire 24. The lead wire 24 is preliminarily attached to the pipe 19 by inserting the bare end of the core wire 24a from the insulating outer sheath into the pipe 19 and caulking it by applying force F to the pipe 19 using an appropriate tool. It is fastened to the pipe 19 together with the heater lead wire 12 that was inserted through the pipe 19.

In the conventional oxygen concentration sensor described above, if the force F applied to the pipe 19 is small and the amount of caulking deformation is small, the clamping force of the lead wire 24 to the pipe 19 is weak and there is a risk of the lead wire coming off when a tensile force is applied to the lead wire. On the other hand, if the amount of caulking is increased to ensure a fastening force that can withstand tensile force, the sheath of the lead wire 12 will be destroyed, and the heater energization level will appear in the sensor output. Therefore, an object of the present invention is to provide an oxygen concentration sensor that solves the drawbacks of the conventional oxygen concentration sensors described above.

Hereinafter, an embodiment of the oxygen concentration sensor according to the present invention will be described with reference to FIG. As shown in FIG. 2, in the oxygen concentration sensor according to the present invention, the shape of the pipe 25 is different from that of the conventional example shown in FIG. 1, but the other configurations are exactly the same. The pipe 25 is provided with notches 25a, 25b, 2 to prevent unnecessary plastic deformation from occurring in parts other than the caulking part due to the influence of the caulking force when the pipe 25 is caulked.
5c are provided, and the lead wires are caulked to contact the respective notches 25d, 25e, 25f.
is provided.

A pair of lead wires 12 connected to a heater (not shown) to supply current to the heater are connected to a pipe 25.
The pipes are inserted into the pipe 25 through the opening of the annular flange 20 provided at the end thereof, and guided out one by one from the notch 25b symmetrically with respect to the axis of the pipe 25. In this state, the caulked part 25d
By plastically deforming the lead wire 12, the lead wire 12 is fastened to the inner surface of the pipe 25. Next, a lead wire 24 that is electrically connected to the pipe 25 is connected to an opening 25g provided at the end of the pipe 25 in order to take out the electrical signal emitted by the ceramic pipe to the outside of the oxygen concentration sensor (not shown). It is inserted into the pipe 25. At this time, a conductive core wire portion 24a exposed from the electrically insulating outer sheath is provided at the end of the lead wire 24. By plastically deforming the caulked portion 25e in this state, the core wire portion 24a of the lead wire 24 is electrically joined to the pipe 25, and by plastically deforming the caulked portion 25f, the electrically insulating outer sheath of the lead wire 24 is connected to the pipe 25. It is fastened to the inside.

In the oxygen concentration sensor according to the present invention described above, it is possible to increase the tightening force of the lead wires 12 and 24 to the pipe 25, so that it is possible to prevent the lead wires from falling off when a pulling force is applied to the lead wires.
Moreover, the lead wire 12 and the lead wire 24 in the conventional example
There is no problem that the sheathing of the lead wires may be destroyed, which may occur due to the construction in which the lead wires are caulked and fastened together.

[Brief explanation of the drawing]

FIG. 1a is a diagram showing a cross section including the central axis of a conventional oxygen concentration sensor. FIG. 1b is a sectional view showing a state before caulking of a metal pipe into which end portions of heater lead wires and lead wires for detecting the platinum film potential on the inner surface of the zirconia tube are inserted. Second
The figure shows the conventional metal pipe 19 shown in FIG. 1b.
FIG. 3 is a three-dimensional view showing the state of the metal pipe after caulking according to the present invention; Explanation of symbols of main parts, 5...zirconia tube,
12...Lead wire for heater, 19...Pipe or cylindrical body, 24...Lead wire for detecting the potential of the platinum film on the inner surface of the zirconia tube, 25...Pipe or cylindrical body.

Claims (1)

[Scope of utility model registration request] a housing, a ceramic tube approximately in the shape of a test tube with one end closed, a conductive film coated on the inner and outer surfaces of the ceramic tube, and a conductive film such that at least one end is present inside the ceramic tube. The oxygen concentration sensor includes a rod-shaped heater arranged substantially coaxially with the tube and heated by electricity, the sensor being held in the housing so as to be electrically insulated from the housing so that the conductive film is electrically insulated from the housing. an electrically conductive and plastic cylindrical body coupled to the cylindrical body; A pair of lead wires connected to the heater and each covered with an electrically insulating outer sheath to supply current to the heater, and a portion of the cylindrical body other than the portion to which the pair of lead wires are fastened are made of plastic. An oxygen concentration sensor comprising: a lead wire whose one end is fastened to the inner surface of the cylindrical body by being deformed and which is in electrical contact with the inner surface of the cylindrical body.