JPH10142189A - Oxygen sensor cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor cover which can limit the adhesion of water drops to an element of an oxygen sensor. SOLUTION: An oxygen sensor 11 is mounted to an exhaust pipe of a diesel engine in a manner that a leading end part thereof projects inside the exhaust pipe. The oxygen sensor 11 has a housing 12, an element 13 fixed to the housing 12 and a cover 14. The cover 14 is formed of a stainless thin sheet (thickness: 0.4mm) of a large thermal expansion coefficient into a bottomed cylindrical shape as a whole. A bellows deformation part 15 is formed at a circumferential wall of the cover 14. An introduction hole 20 is formed at each top part A projecting at the deformation part 15 towards the element 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover for an oxygen sensor used in an internal combustion engine, and more particularly, to a cover for an oxygen sensor having an opening through which exhaust gas of the engine flows.

[0002]

2. Description of the Related Art An oxygen sensor generally includes an element formed of a solid electrolyte (zirconia or the like) having an internal space, and a pair of electrodes provided on the inner and outer surfaces of the element. It is a target. A cover for protecting the element is provided on the outer periphery of the element, and the cover has an opening formed therein for introducing a gas to be detected.

In such an oxygen sensor, when a reference gas having a known oxygen concentration is supplied to the internal space of the element, the inner surface of the element comes into contact with the reference gas. On the other hand, by disposing the oxygen sensor in the atmosphere of the detection gas to be detected, the outer surface of the element comes into contact with the detection gas that has passed through the opening of the cover. As described above, when the gas having different oxygen concentrations comes into contact with the inner and outer surfaces of the element provided with each electrode, a detection signal corresponding to the oxygen concentration difference between both gases is output from both electrodes. Therefore,
The oxygen concentration of the detection gas can be known from the magnitude of the detection signal.

In the air-fuel ratio control of an internal combustion engine using an oxygen sensor as described above, an oxygen sensor is provided in an exhaust passage of the internal combustion engine, and the sensor detects the oxygen concentration of exhaust gas. Then, the actual air-fuel ratio is calculated based on the oxygen concentration of the exhaust gas, and the actual air-fuel ratio is calculated based on the target air-fuel ratio (usually,
Feedback control is performed so as to achieve the stoichiometric air-fuel ratio.

[0005]

The exhaust gas from the internal combustion engine contains water vapor. For this reason,
When the operation of the internal combustion engine is stopped, this water vapor may adhere to the inner wall of the exhaust pipe as water droplets and remain in the pipe.
As described above, when the internal combustion engine is restarted with water droplets remaining in the exhaust pipe, the water droplets may pass through the opening of the cover together with the exhaust gas and adhere to the element of the oxygen sensor. The oxygen sensor element is 300
Although the temperature rises to at least ° C., if the temperature rises while water droplets adhere to the element as described above, a large difference in thermal expansion occurs in the element, which may cause damage such as cracks.

In particular, in an internal combustion engine mounted on a vehicle, a bent portion is often provided in an exhaust pipe in order to save space, and water tends to accumulate at the bottom of the bent portion. For this reason, the element is likely to be damaged due to the adhesion of the water droplet as described above.

[0007] In addition to the oxygen sensor provided in the exhaust passage of the internal combustion engine, such a situation is generally common to an oxygen sensor used in an environment having a large temperature difference.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oxygen sensor cover that can suitably prevent water droplets from adhering to an oxygen sensor element.

[0009]

According to a first aspect of the present invention, there is provided an oxygen sensor cover having an opening through which gas flows to cover an oxygen sensor element. The cover is formed of a metal material that changes its shape by heat, and its purpose is to increase the opening area from a substantially closed state at a low temperature as the shape of the metal material changes due to heating.

In the above structure, the cover for the oxygen sensor is formed of a metal material which changes its shape by heat. The opening formed in the cover is substantially closed when the temperature of the cover is low (for example, when the internal combustion engine is stopped or immediately after the engine is started). Therefore, at low temperatures, penetration of water droplets into the cover is suppressed. On the other hand, at high temperatures, the shape of the cover changes due to heat, and the area of the opening increases with the change in shape. Therefore, gas is introduced into the cover through the opening.

According to a second aspect of the present invention, in the oxygen sensor cover according to the first aspect, a bellows portion is formed in the cover, and the opening is formed in the bellows portion. The purpose is to form it.

In the above configuration, the bellows portion formed on the cover changes greatly due to heat. The opening area of the opening that is substantially closed at a low temperature increases in accordance with the shape change of the bellows portion.

In order to achieve the above object, according to a third aspect of the present invention, in the oxygen sensor cover according to the first aspect, the opening spirally extends through a peripheral wall of the cover formed in a cylindrical shape. The purpose is to be a slit.

In the above configuration, the opening area of the slit, which is substantially closed at a low temperature, increases due to a change in the shape of the cover due to heat. In order to achieve the above object, according to a fourth aspect of the present invention, in the oxygen sensor cover according to the first aspect, the cover has a cylindrical shape in which at least a part thereof is slidably overlapped, The purpose is that the opening is a plurality of holes formed in the overlapping portion of the cover with their positions shifted.

In the above configuration, the positions of the holes formed in the overlapping portion of the cover coincide with each other as the diameter of the cover expands due to heat. Thereby, the opening area of the opening increases.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Hereinafter, a first embodiment of the present invention will be described.

FIG. 1 shows an oxygen sensor 11 according to this embodiment.
It is sectional drawing which shows the front-end | tip part. This oxygen sensor 11
It is attached to the exhaust pipe (not shown) of the diesel engine (not shown) so that its tip projects into the exhaust pipe (not shown). The oxygen sensor 11 includes a housing 12, an element 13 fixed to the housing 12, and a cover 14.

The element 13 is formed into a test tube by a solid electrolyte such as a zirconia element, and has an inner electrode and an outer electrode (both not shown) made of platinum on the inner and outer surfaces. An air introduction space (not shown) is formed inside the element 13, and the air having a known oxygen concentration is introduced into the space. Further, a rod-shaped heater (not shown) is built in the air introduction space. The heater generates heat when energized by an electronic control unit (not shown) of the engine, and heats the element 13 to a predetermined activation temperature.

The cover 14 is formed of a stainless steel sheet (thickness: 0.4 mm) having a large coefficient of thermal expansion so as to have a substantially cylindrical shape with a bottom. This cover 1
The peripheral wall 4 is a deformed portion 15 formed in a bellows shape. An introduction hole 20 is formed at the top A of each portion of the deformed portion 15 protruding toward the element 13 side.

FIG. 2A shows the state of the deformed portion 15 when the cover 14 is at room temperature, and FIG. 2B shows the state when the cover 14 is heated by the exhaust gas and the heat of the heater to increase the temperature. The state of the same part 15 is shown. As shown in FIG. 3A, when the operation of the engine is stopped and the temperature of the cover 14 is normal temperature (low temperature), the introduction hole 2
0 has a very small effective opening area,
It is almost closed.

On the other hand, when the engine is started and the temperature of the cover 14 rises due to the heat of the heater and the heat of the exhaust gas, the shape of the deformed portion 15 is shown in FIG. Change to shape. That is, in the present embodiment, since the cover 14 is formed of a stainless steel sheet having a large coefficient of thermal expansion, the shape of the deformed portion 15 changes so as to extend in the vertical direction due to thermal expansion. And the substantial opening area of each introduction hole 20 increases by this shape change. In this embodiment, since the cover 14 has an extremely small plate thickness and a small heat capacity, the deformed portion 1
5 is a comparatively short time (5 to 10) from the state shown in FIG.
Seconds), the shape changes to the shape shown in FIG.

The exhaust gas passing through the exhaust pipe is shown in FIG.
As shown by the arrow in (b), the element 13 introduced into the inside of the cover 14 through each introduction hole 20 having an increased opening area.
Contact the outside surface of the On the other hand, the air introduced into the air introduction space contacts the inner surface of the element 13. in this way,
When the atmosphere and exhaust gas having a difference in oxygen concentration come into contact with the inner and outer surfaces of the element 13, an electromotive force is generated between the internal electrode and the external electrode according to the difference in oxygen concentration. Then, the oxygen concentration of the exhaust gas can be detected from the electromotive force.

In addition, when the operation of the engine is stopped, the energization control of the heater is stopped, and the high-temperature exhaust gas stops flowing through the exhaust pipe, the temperature of the cover 14 starts to decrease. Since the heat capacity of the cover 14 is small, its temperature quickly decreases. When the cover 14 is in a low temperature (normal temperature) state as described above, the deformed portion 15
Returning to the shape shown in (a), each introduction hole 20 is substantially closed again.

Next, the effect of this embodiment will be described. In this embodiment, the cover 14 is made of a stainless steel sheet having a high coefficient of thermal expansion. Accordingly, the introduction hole 20 formed in the deformed portion 15 due to a change in shape due to thermal expansion is substantially closed when the engine is stopped and immediately after starting, and the opening area thereof after a predetermined time has elapsed from the start. Can be changed to an increased state.

As a result, according to the present embodiment, it is possible to suppress the entry of water droplets into the cover 14 through the introduction hole 20 immediately after the start of the engine and the attachment of the water droplets to the element 13. This can prevent the element 13 from being damaged due to a difference in thermal expansion, such as a crack.

By the way, unlike the present embodiment, a method of providing a bimetal on the cover and changing the opening area of the introduction hole by changing the shape of the bimetal is also known (see, for example, Japanese Utility Model Laid-Open No. 61-174666). ). However, in such a configuration, a member such as a bimetal is separately required, resulting in a complicated structure and an increase in manufacturing cost. In order to prevent water droplets from adhering to the element 13, it is conceivable to adopt a cover having a double structure. However, even with such a configuration, the same problem as described above still occurs.

In this respect, in the present embodiment, there is no need to separately provide a member for changing the area of the introduction hole 20, and water droplets on the element 13 are eliminated without using the double-structured cover 14. Can be sufficiently suppressed. For this reason,
According to this embodiment, it is advantageous in simplifying the structure and reducing the cost as compared with the above-described configurations.

Further, according to the present embodiment, since the introduction hole 20 is substantially closed immediately after the start of the engine, the element 13 is efficiently heated by the heater.
As a result, the power consumption of the heater can be reduced. Furthermore, before attaching the oxygen sensor 11 to the exhaust pipe, harmful substances that have entered the inside of the cover 14 through the introduction hole 20 are less likely to adhere to the element 13. As described above, the cover 14 of the present embodiment is useful in performing quality control of the oxygen sensor 11 because it can suppress the adhesion of harmful substances to the element 14.

Next, second to fourth embodiments of the present invention will be described. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

[Second Embodiment] FIG. 3 is a sectional view showing the tip of an oxygen sensor 11 according to the present embodiment. As shown in the figure, the cover 14 in the present embodiment does not have the bellows-like deformed portion 15 and has a substantially bottomed cylindrical shape. The cover 14 is made of a bronze material having a very large coefficient of thermal expansion, and is formed of a thin plate (thickness: 0.4 mm) on which inner and outer surfaces are plated with chromium for improving corrosion resistance. A plurality of introduction holes 20 are formed in the peripheral wall of the cover 14, and exhaust gas can be introduced into the cover 14 through each introduction hole 20.

FIG. 4A shows that the cover 14 is at room temperature (low temperature).
FIG. 4B shows the shapes of the cover 14 and the introduction hole 20 when the cover 14 is heated by the exhaust gas and the heat of the heater and the temperature rises. Is shown.

As shown in FIG. 3A, when the operation of the engine is stopped and the cover 14 is at room temperature, the inlet hole 20
Is substantially closed, and the opening area thereof is extremely small. On the other hand, when the engine is started and the temperature rises due to the heat of the heater and the heat of the exhaust gas, the cover 14 is deformed into a barrel shape as shown in FIG. 4B. With the deformation of the cover 14, the introduction hole 2
The opening area of 0 increases.

Further, when the operation of the engine is stopped, the control of the energization of the heater is stopped, and the high-temperature exhaust gas stops flowing through the exhaust pipe, the cover 14 is turned off again as shown in FIG.
Returning to the shape shown in (a), each introduction hole 20 is substantially closed again.

According to the present embodiment having the above-described configuration, substantially the same operation and effect as those of the first embodiment can be obtained. In particular, in the present embodiment, since the bronze having an extremely large coefficient of thermal expansion is used as the material of the cover 14, the shape deformation of the cover 14 due to the thermal expansion is large. For this reason, it is not necessary to form the bellows-like deformed portion 15 on the cover 14 in order to change the opening area of the introduction hole 20, and the manufacture of the cover 14 can be made relatively easy.

[Third Embodiment] FIG. 5 is a sectional view showing the tip of an oxygen sensor 11 according to this embodiment. As shown in the figure, the cover 14 in the present embodiment does not have the bellows-like deformed portion 15 and has a substantially bottomed cylindrical shape. Like the first embodiment, the cover 14 is made of a stainless steel sheet (thickness: 0.4) having a large coefficient of thermal expansion.
mm). The cover 14 is provided with a slit 21 extending spirally from the upper end to the lower end over the entire circumference. The slit 21 is for introducing the exhaust gas into the cover 14 and has the same function as the introduction hole 20.

FIG. 6A shows that the cover 14 is at room temperature (low temperature).
FIG. 4B shows the shapes of the cover 14 and the slit 21 when the cover 14 is heated by the exhaust gas and the heat of the heater to increase the temperature. I have.

As shown in FIG. 3A, when the operation of the engine is stopped and the cover 14 is at room temperature, the slit 2
The width of 1 is extremely small. On the other hand, when the engine is started and the temperature rises due to the heat of the heater and the heat of the exhaust gas, the cover 14 is deformed so as to increase the width of the slit 21 as shown in FIG. 6B.

Further, when the operation of the engine is stopped and the control of energization of the heater is stopped, and the high-temperature exhaust gas stops flowing through the exhaust pipe, the cover 14 is re-opened as shown in FIG.
Returning to the shape shown in (a), the width of each slit 21 again becomes extremely small.

According to the present embodiment having the above-described configuration, substantially the same operation and effect as those of the first embodiment can be obtained. [Fourth Embodiment] FIGS. 7 and 8 are a front view and a sectional view, respectively, showing the tip of an oxygen sensor 11 according to this embodiment. FIGS. 9A and 9B are cross-sectional views taken along line 9-9 of FIG.

As shown in these figures, the cover 14 in the present embodiment has a substantially cylindrical shape, and a flange 14a is formed at an upper end thereof. FIG. 9 (a),
As shown in (b), the cover 14 is partially overlapped in part. Then, the cover 14 is deformed while expanding its diameter from the state shown in FIG. 3A to the state shown in FIG. 3B so that the overlapped portions are in sliding contact as shown by arrows. Is possible.

As shown in FIG. 8, a cylindrical support 30 is fitted on the outer periphery of the housing 12. A peripheral groove 30 a is formed on the inner peripheral wall surface of the support 30. The flange 14a of the cover 14 is held between the lower end of the housing 12 and the inner wall of the peripheral groove 30a. The flange 14a is slidable with respect to both the lower end portion of the housing 12 and the inner wall of the peripheral groove 30a, so that the cover 14 is allowed to expand and deform as described above. The depth of the peripheral groove 30a is set to a size such that the outer peripheral portion of the flange 14a does not interfere with the inner wall of the peripheral groove 30a when the diameter of the cover 14 is increased.

As shown in FIGS. 7 and 9 (a) and 9 (b), the outer portion 14b and the inner portion 14c which are double overlapped on the cover 14 are provided in the axial direction of the oxygen sensor 11 (up and down in FIG. 7). Pair of introduction holes 2 spaced apart in the direction
0 is formed. In the cover 14 having such a structure, when the operation of the engine is stopped and the cover 14 is at room temperature, as shown in FIG.
The introduction hole 20 formed in the outer portion 14b of the cover 14 is closed by the inner portion 14c, and the introduction hole 20 formed in the inner portion 14c is closed by the outer portion 14b. For this reason, the substantial opening area of each introduction hole 20 is “0”.

On the other hand, when the engine is started,
The temperature of the cover 14 increases due to the heat of the heater and the heat of the exhaust gas. As a result, as shown by arrows in FIG. 9B, the outer portion 14b and the inner portion 14c move while being in contact with each other, and the cover 14 is deformed so as to expand in diameter. Due to the deformation of the cover 14, the outer portion 14b and the inner portion 14c are formed.
The positions of the introduction holes 20 formed in the respective holes coincide with each other, and the exhaust gas can flow through each introduction hole 20.

Further, when the operation of the engine is stopped, the control of the energization of the heater is stopped, and the high-temperature exhaust gas stops flowing through the exhaust pipe, the cover 14 is again closed as shown in FIG.
Returning to the shape shown in (a), each introduction hole 20 is in a closed state.

According to the present embodiment having the above-described configuration, substantially the same operation and effect as those of the first embodiment can be obtained. In the present embodiment, since the lower end side of the cover 14 is open, there is a concern that water droplets that have entered the inside of the cover 14 from this opening will adhere to the element 13. However, the oxygen sensor 11 is attached to the exhaust pipe such that the tip of the oxygen sensor 11 faces downward in the vertical direction (the direction of gravity), and the length of the cover 14 in the axial direction of the oxygen sensor 11 is set slightly longer. Thereby, the adhesion of the water droplet as described above can be easily avoided.

The present invention can be embodied as another embodiment described below in addition to the above embodiments. In these other embodiments, substantially the same operation and effects as those of the above embodiments can be obtained.

(1) In each of the above embodiments, stainless steel or bronze having a high coefficient of thermal expansion is used as a material for forming the cover 14. On the other hand, the cover 14 can be formed of another material as long as the material causes a shape change sufficient to change the opening area of the introduction hole 20 or the width of the slit 21 due to the heat of the exhaust gas.
Similarly, the thickness of the material forming the cover 14 can also be appropriately changed.

(2) In the first embodiment, the deformed portion 1
In 5, an introduction hole 20 was formed at the top A of each portion protruding toward the element 13 side. On the contrary,
The introduction hole 20 may be formed at the top B (shown in FIG. 1) of each portion of the deformation portion 15 protruding toward the outside. Further, the introduction holes 20 can be formed at both the tops A and B.

(3) In each of the above embodiments, the element 13 is covered with one cover 14. On the other hand, by adopting the cover 14 having a double structure, it is possible to surely prevent water droplets from adhering to the element 13.

(4) In the first to third embodiments,
Although the cover 14 is formed in a substantially cylindrical shape with a bottom, the cover 14 may be formed in, for example, a rectangular tube shape. (5) In the fourth embodiment, the cylindrical cover 1
4 were overlapped, and each introduction hole 20 was formed in that portion. On the other hand, the cover 14 may be overlapped over the entire circumference, and the introduction holes 20 may be formed on the entire circumference of the cover 14. According to such a configuration, since the exhaust gas can be introduced into the inside of the cover 14 from any direction, it is not necessary to consider the mounting direction when the oxygen sensor is mounted on the exhaust pipe.

(6) In each of the above embodiments, the present invention is embodied as a cover of an oxygen sensor provided in a diesel engine. On the other hand, the present invention may be embodied as a cover of an oxygen sensor provided in a gasoline engine. In addition, the intended use of the oxygen sensor is
Other than the oxygen sensor of these engines, it is optional. For example, the present invention can be applied as a cover of an oxygen sensor in which water droplets are expected to adhere to an element due to a temperature change or the like.

(7) In each of the above embodiments, the present invention is embodied as a cover of an oxygen sensor having a test tube element. On the other hand, the present invention may be embodied as a cover of an oxygen sensor having a stacked element.

[0053]

According to the first aspect of the present invention, the cover for the oxygen sensor is formed from a metal material that changes its shape by heat, and the opening area of the opening is increased from a substantially closed state by the change in its shape. I have. Therefore, when the temperature of the cover is low, the opening is substantially closed.
For this reason, penetration of water droplets into the cover is suppressed. As a result, it is possible to prevent water droplets from adhering to the element of the oxygen sensor, and it is possible to avoid problems such as cracking of the element due to a difference in thermal expansion.

According to the second aspect of the present invention, the cover is formed with a bellows-like portion, and the opening is formed in the bellows-like portion. With the bellows shape, the shape change due to heat in the portion of the cover where the opening is formed can be increased. As a result, according to the present invention, in addition to the effects of the invention described in claim 1,
The gas can be introduced into the cover by reliably increasing the opening area of the opening.

According to the third aspect of the present invention, the cover is formed in a cylindrical shape, and the peripheral wall of the cover is formed with a slit extending spirally. As a result, according to the present invention, in addition to the effect of the invention described in claim 1, the width of the slit can be increased by a change in the shape of the cover due to heat, and gas is introduced into the cover through the slit. Can be.

According to the fourth aspect of the present invention, the cover is formed in a cylindrical shape in which at least a part thereof is slidably overlapped, and a plurality of holes whose positions are shifted are formed as openings in the overlapping portion of the cover. I have to. Therefore, each overlapping portion of the cover slides so that the position of each hole coincides with the diameter expansion deformation of the cover due to heat. as a result,
According to the present invention, in addition to the effect of the first aspect, the gas can be introduced into the cover by reliably increasing the opening area of the opening.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a distal end portion of an oxygen sensor according to a first embodiment.

FIG. 2 is a sectional view showing a shape change of a deformed portion and an introduction hole.

FIG. 3 is a cross-sectional view showing a tip portion of an oxygen sensor according to a second embodiment.

FIG. 4 is a front view showing a shape change of a cover and an introduction hole.

FIG. 5 is a cross-sectional view showing a tip portion of an oxygen sensor according to a third embodiment.

FIG. 6 is a front view showing a shape change of a cover.

FIG. 7 is a front view showing a tip portion of an oxygen sensor according to a fourth embodiment.

FIG. 8 is a cross-sectional view showing a tip portion of the oxygen sensor.

FIG. 9 is a sectional view taken along line 9-9 in FIG. 7;

[Explanation of symbols]

11: oxygen sensor, 14: cover, 20: introduction hole, 21
…slit.

Claims (4)

[Claims] 1. An oxygen sensor cover having an opening through which a gas flows to cover an element of an oxygen sensor, wherein the cover is formed of a metal material that changes its shape by heat, and the opening is formed at a low temperature. An oxygen sensor cover characterized in that the opening area increases with a change in shape of the metal material due to heating from a substantially closed state. 2. The oxygen sensor cover according to claim 1, wherein a bellows portion is formed in the cover, and the opening is formed in the bellows portion. 3. The oxygen sensor cover according to claim 1, wherein the opening is a slit extending spirally around a peripheral wall of the cover formed in a cylindrical shape. 4. The cover for an oxygen sensor according to claim 1, wherein the cover has a cylindrical shape in which at least a part thereof is slidably overlapped with each other, and the opening is formed in an overlapping portion of the cover. A cover for an oxygen sensor, wherein a plurality of holes are formed in a displaced state.