JPS585246Y2 - oxygen concentration sensor - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of an oxygen concentration sensor that is used by being attached to an exhaust pipe or the like, for example, to measure the concentration of oxygen contained in the exhaust gas of an automobile.

For example, zirconia (Z
rO2) is used to measure the electromotive force generated due to the difference between the oxygen concentration contained in the exhaust gas and the oxygen concentration in the atmosphere, thereby measuring the oxygen concentration in the exhaust gas.

In this type of conventional oxygen concentration sensor, as shown in FIG. 1, a protective cover 111 covers the heat receiving part 105 of the zirconia ceramic tube 102, which is the oxygen detection element, and has a large number of vent holes 110 for gas circulation. is its base 1
12 is attached in tight contact with the inner circumferential surface of the housing 119, so that the heat of the protective cover 111 is conducted to the housing 119 side and escapes.

Therefore, when the temperature of the exhaust gas is low, such as during warm-up, the temperature rise at or near the heat receiving part 105 of the zirconia ceramic tube 102 is slow due to the poor heat storage effect of the protective cover 111, so the ζ sensor functions. However, there is a drawback that it takes time to correct the air-to-air ratio of the intake air to an appropriate value.

This idea eliminates the drawbacks of the conventional oxygen concentration sensor mentioned above, suppresses heat transfer to the housing side of the protective cover, improves low temperature operation, and enables early function even during warm-up operation with low exhaust gas temperature. The purpose of this invention is to provide an oxygen concentration sensor that has been improved to achieve the desired performance.

This invention will be explained below with reference to illustrated embodiments.

In FIG. 2, the main part of the oxygen concentration sensor 1 is a zirconia ceramic tube 2 that constitutes an oxygen detection element. One end of this tube 2 is a closed end 3, and the other end is an open end 4. ing.

The portion of the zirconia ceramic tube 2, including the closed end 3, that is close to the closed end 3 serves as a heat receiving section 5, and porous platinum is sintered on the inner and outer peripheral surfaces of the inner and outer electrodes. 7, and a boss portion 8 is provided adjacent to the open end portion 4.

A housing 9 serving as a ground electrode is annularly attached to the outside of the boss portion 8 of the zirconia ceramic tube 2 formed as described above.

A bottomed cylindrical protective cover 11 having a number of ventilation holes 10 around the heat receiving part 5 of the zirconia ceramic tube 2
The opening side thereof is fitted into the housing 9, and the flange portion 11a at the opening end is fitted and supported between the housing 9 and the boss portion 8 of the zirconia ceramic tube 2.

As shown in the figure, an appropriate number of elongated holes 13 are vertically provided in the root portion 12 of the protective cover 11 that is in contact with the inner circumferential surface of the housing 9 in parallel. The contact area of the protective cover 11 with the housing 9 is reduced as much as possible without significantly impairing the strength of the housing 9, and the cross-sectional area connecting the closed side and the open side of the protective cover itself is reduced as much as possible for protection. This is provided as a heat transfer suppressing means to suppress the heat of the cover 11 from being transferred to the housing 9 side as much as possible.

A cylindrical center electrode 14 made of stainless steel is inserted inside the open end 4 of the zirconia ceramic tube 2, and one end of the center electrode 14 is connected to an annular taper provided on the inner peripheral surface of the open end 4. It is locked to the surface 4a via a conductive sealing material 15.

Reference numeral 16 denotes a cylindrical atmospheric chamber cover provided outside the center electrode 14. A flange 16a is formed at one end of the cover, and the cover is latched to the annular flange portion 9a of the housing 9. There is a locking portion 16b formed in a ring shape and protruding inward.

Between the flange 16a of the atmospheric chamber cover 16 and the boss portion 8 of the zirconia ceramic tube 2, there is a spacer 17 and two rings 18, 19.

This spacer 17 and rings 18, 19 are attached to the flange 16a.
The boss portion 8 is provided to press the boss portion 8 against the flange portion 11a of the protective cover 11 when the flange portion 9a of the housing 9 is locked.

A conductive sealing material 20 is filled between the outside of the boss portion 8 and the inside of the housing 9, and between the flange portion 11a of the protective cover 11 and the ring 19. Airtightness between and outer electrode 7 of boss part 8
and maintains electrical contact with the housing 9.

A ring-shaped rubber stopper 21 having a semicircular groove 21a on the outer periphery is airtightly attached to the end of the atmospheric chamber cover 16 on the side of the locking part 16b, and a center electrode is installed in the center of the rubber stopper 21. A lead wire 22 connected to 14 passes through it in an airtight manner.

Reference numeral 23 denotes an insulator attached to the inside of the atmospheric chamber cover 16 so as to be in contact with the rubber plug 21 (lower side in the figure), and the step portion 23 a of the insulator is attached to the step portion 14 a of the center electrode 14 . A compression spring 24 is installed between them.

The compression spring 24 presses the center electrode 14 against the tapered surface 4a of the open end 4 via the sealing material 15 to maintain electrical contact between the inner electrode 6 and the center electrode 14.

Reference numeral 25 denotes an air intake port provided in the air chamber cover 16, and the air passing through this air intake port 25 flows into the air chamber A surrounded by the inner electrode 6 of the zirconia ceramic tube 2. There is.

The oxygen concentration sensor 1 of this embodiment is constructed as described above, and is airtight with a gasket 27 interposed so that the heat receiving part 5 is exposed to exhaust gas from the exhaust manifold or exhaust pipe 26 of an automobile engine. Installed.

With respect to the oxygen concentration sensor 1 installed in this manner, exhaust gas enters the protective cover 11 through the ventilation hole 10 and comes into contact with the outer electrode 7 of the heat receiving section 5 .

On the other hand, the atmosphere enters the atmosphere chamber A from the intake port 25 and enters the heat receiving part 5.
Touch the inner electrode 6 of ゛.

At this time, when the temperature of the exhaust gas exceeds about 400° C., the oxygen concentration sensor 1 is activated and oxygen ions pass through the wall of the heat receiving section 5 and are guided from the atmospheric chamber A to the exhaust side chamber B.

As a result, an electromotive force is generated between the inner electrode 6 and the outer electrode 7, so this electromotive force is measured, and the oxygen concentration of the exhaust gas is measured based on the electromotive force.

Therefore, in this embodiment, as described above, an appropriate number of long holes 13 are provided in the base portion 12 of the protective cover 11 to suppress the transfer of heat from the protective cover 11 to the housing 9a side as much as possible. When the engine is warmed up, the protective cover 11 is quickly warmed by the exhaust gas, and as a result, the protective cover 11 acts as a heat mass, and the heat radiation effect from the protective cover 11 causes the temperature of the heat receiving part 5 of the sensor and the atmosphere in its vicinity to decrease. is brought close to the temperature of the exhaust gas flowing within the exhaust manifold or exhaust pipe 26.

Therefore, when the exhaust gas temperature reaches 400° C. or higher, the sensor is activated to measure the oxygen concentration of the exhaust gas.

This can be explained by the graph shown in FIG.

That is, FIG. 4 shows the conventional protective cover 11 shown in FIG.
Zirconia ceramic tube 102 in a comparative experiment using 1 and the protective cover 11 of the embodiment shown in FIG.
．． 2 shows the temperature measurement results of the heat receiving section 105.5 of No. 2.

In FIG. 4, the solid line A is the exhaust gas temperature, and the dashed line B
is the heat receiving part 105 when using the conventional protective cover 111.
, and the broken line C indicates the temperature of the protective cover 11 of this embodiment.
This is the temperature of the heat receiving part 5 when using.

As is clear from this graph, the temperature drop in the heat receiving section when the exhaust gas temperature decreases is smaller in this example than in the conventional case, and the effect of suppressing heat transfer to the housing side is recognized.

In other words, the oxygen concentration sensor of this embodiment has improved operability at low temperatures, and therefore, at low temperatures such as during warm-up operation, the protective cover 11 is reduced by an amount corresponding to the heat transfer inhibiting effect. The temperature rise can be accelerated, and the sensor function can be exerted at an early stage.

FIG. 3 shows another embodiment of the present invention, in which an appropriate number of elongated holes 13 are provided in the root portion 12 of a protective cover 11 in three stages in the vertical direction as means for suppressing heat transfer. They are arranged alternately in parallel to each other, and can produce the same functions and effects as the above-mentioned embodiment.

As explained in detail above, this invention is used in an oxygen concentration sensor for automobile engines that measures the oxygen concentration in exhaust gas based on the difference between the oxygen concentration in exhaust gas and the oxygen concentration in the atmosphere. By providing an appropriate number of elongated holes in the base of the protective cover attached to the housing, which is the contact surface with the housing, as a heat conduction suppressing means, the heat of the protective cover is transferred to the housing side. It is possible to prevent escape as much as possible, improve operability at low temperatures, and enable the sensor to quickly perform its functions during warm-up operation when the exhaust gas temperature is low.

[Brief explanation of drawings]

Figure 1 is a partially cutaway front view of a conventional oxygen concentration sensor;
Figure 3 is a front view of a raw water bath showing one embodiment of this invention, Figure 3 is a front view showing a protective cover of another embodiment of this invention, and Figure 4 shows the protective cover shown in Figure 1 and Figure 2. FIG. 6 is a comparison diagram showing the temperature measurement results of the heat receiving part in a comparative experiment using the protective cover shown in FIG. 1... Oxygen concentration sensor, 2... Zirconia ceramic tube, 5... Heat receiving part, 9...
・・Housing, 11・・Protective cover, 12・
...root, 13...long hole.

Claims (1)

[Scope of utility model registration request] A sensor for an automobile engine that measures the oxygen concentration in exhaust gas based on the difference between the oxygen concentration in the exhaust gas and the oxygen concentration in the atmosphere, and the sensor includes a protective cover for covering the heat receiving part of the oxygen detection element. The protective cover is fitted into the housing so that the outer circumferential surface of one side is in contact with the inner circumferential surface of the housing over almost the entire surface, and the base portion of the protective cover that is the contact surface with the housing is provided with a base portion that allows heat to be transferred from the protective cover to the housing side. An oxygen concentration sensor characterized by having an appropriate number of long holes extending through the sensor to suppress transmission.