JP2000171430A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor capable of obtaining uniform response or output characteristics regardless of the flow direction of gas to be measured to a multiple structure protector while employing the protector. SOLUTION: The leading end of the second cylindrical part 6a of a protector 6 is positioned so as to protrude from the leading end of the first cylindrical part 6b of the protector 6 and the gas EG to be measured introduced from second side gas inlets 63 formed to the side wall part of the second cylindrical part 6a flows from the base end side of the first cylindrical part 6b to the leading end side thereof along the outer surface of the diameter contracted part 6t of the first cylindrical part 6b to flow out of a second side gas outlet 64. By forming this flow of the gas, negative pressure is created in the first side gas outlet 62 formed to the leading end of the diameter contracted part 6t to evacuate the interior of the first cylindrical part 6b and the gas EG is almost isotropically sucked into the first cylindrical part 6b from the first side gas inlets 60, 61 in a peripheral direction. As a result, even if the flow of the gas impinges against the protector 6 at any angle around the axial line of the protector 6, since the gas EG is supplied to the detection part D in the protector 6 alamost isotropically, uniform response or output characteristics are obtained regardless of a gas flow direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an oxygen sensor, an HC sensor,
The present invention relates to a gas sensor such as a sensor or a NOx sensor for detecting a component to be detected in a gas to be measured.

[0002]

2. Description of the Related Art As a gas sensor as described above, there is known a gas sensor having a structure in which a rod-shaped or cylindrical detection element having a detection portion for detecting a component to be detected formed at a tip thereof is disposed inside a metal casing. ing. In such a gas sensor, a protector that covers a detection unit located in the measurement atmosphere is provided. A gas flow hole is formed in a side wall of the protector, and a gas to be measured such as an exhaust gas is guided from the gas flow hole into the protector and is brought into contact with the detection unit.

In recent years, various types of gas sensors for automobiles have often been used in which the protector has a double structure comprising two inner and outer cylindrical portions in order to enhance the protection performance of the detecting portion against water drops, oil drops, dirt, and the like. ing. Conventionally, as shown in FIG.
At 06, gas inlets 163 and 161 are formed in the side walls of the inner and outer cylindrical portions 106a and 106b, respectively, and the gas to be measured first passes through the gas inlet 163 of the outer cylindrical portion 106a, and then the inner cylindrical portion. It reaches the detection unit 102 through the gas inlet 161 of the 106b.

[0004]

By the way, in the protector having the double structure as described above, the protection performance of the detecting portion can be enhanced, but the resistance to gas flow increases by the double wall portion, For example, the exchange rate of the gas to be measured between the outside of the protector and the internal space of the protector often decreases. Therefore, when the concentration of the component to be measured in the measurement atmosphere changes rapidly, there is a structural problem that the response is likely to be delayed.

In this case, for example, as shown in FIG.
2, the gas detection surface D is provided only on one surface of the laminate.
When P is formed, the following problem occurs. That is, when the gas to be measured EG, such as exhaust gas, flows into the protector 106 from the gas detection surface DP side, the gas flow relatively directly reaches the gas detection surface DP, and thus the detected component in the gas. The detection responsiveness when the concentration or the like changes becomes relatively good, but, for example, when the detection flow is flowing from the opposite side, the detection response of the detection surface DP of the detection unit 102 is opposite to the surface on which the detection surface DP is formed. Because of the gas flow, detection response delay is likely to occur. As described above, there is a disadvantage that the responsiveness and output characteristics of the sensor are easily changed according to the direction of the gas flow to be measured with respect to the protector.

If the protector has a single structure, the gas exchange rate between the inside and the outside of the protector can be increased, so that the response of the sensor is good. However, the function of protecting the detecting section is naturally deteriorated. In addition, if the gas flow rate rapidly increases or the gas temperature decreases, the temperature of the detection unit decreases. For example, the oxygen concentration cell element becomes inactive, causing a problem that the detection sensitivity is reduced or the detection output is interrupted. . In order to increase the gas exchange rate, there is also a method of increasing the size of the gas inlet of the double-structure protector. It has been difficult to achieve both protection and protection.

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent protection function for a detection element unique to a multi-layer protector, and furthermore, it is difficult for the response characteristic of a sensor to have a direction dependency of a gas flow to be measured. It is an object of the present invention to provide a gas sensor capable of obtaining high responsiveness or output characteristics.

[0008]

Means for Solving the Problems and Functions / Effects In order to solve the above problems, in a gas sensor according to the present invention, a protector for covering a detecting portion formed at a tip portion of a detecting element includes a first cylindrical portion, A second tubular portion disposed outside the first tubular portion, and a tapered diameter-reduced portion is formed on an axial front end of a side wall portion of the first tubular portion, and A second gas inlet is formed at a position corresponding to the reduced diameter portion in the side wall portion of the two cylindrical portions.

In the gas sensor of the present invention, the protector has at least a double structure having an inner first cylindrical portion and an outer second cylindrical portion. This allows
Water and oil droplets are less likely to enter the inside of the protector, providing excellent protection for the detector.

In addition, a tapered diameter-reduced portion is formed on the side of the side wall of the first cylindrical portion in the axial direction, and a tapered portion is formed on the side wall of the second cylindrical portion at a position corresponding to the diameter-reduced portion. A two-side gas inlet is formed so that the gas to be measured hitting the reduced diameter portion flows along the outer surface of the side wall portion of the reduced diameter portion. As a result, a negative pressure is generated on the first gas outlet side, and the inside of the first cylindrical portion is depressurized, and the gas to be measured is rapidly sucked, so that sufficient responsiveness can be ensured despite the multi-structure protector. .

In the present invention, the "tapered reduced diameter portion" may be formed such that when the first cylindrical portion is cut along a plane including the axis, the reduced diameter portion has a straight cross section. However, it may be formed in an outward or inward curved surface shape. Further, it is desirable that the reduced diameter portion is formed to have a smaller diameter at the distal end side than at the base end side, in order to generate a negative pressure at the first side gas outlet.

Specifically, the first cylindrical portion may be configured such that a truncated cone-shaped reduced diameter portion is integrated with a tip end side of a cylindrical main body portion. For example, when the entire length of the first cylindrical portion is defined, by adjusting the length of the cylindrical main body portion formed on the base end side, the inclination angle of the outer surface of the reduced diameter portion can be changed, for example, the first side gas. It can be easily set to a value convenient for generating a negative pressure at the outlet.

Therefore, as a specific embodiment of the present invention,
A detection element that detects a component to be detected in the gas to be measured by a detection unit formed at the tip, a tubular element housing that covers the detection element in a state where the detection unit is protruded, and ,
The detector is coupled to the opening end on the side where it protrudes,
A protector that covers the detection unit in a state where the gas to be measured is allowed to flow, the protector is formed in a cylindrical shape surrounding the detection unit in the circumferential direction around the axis of the detection element, and the side wall has a circumferential direction. A plurality of first-side gas inlets are formed at predetermined intervals, while a tapered diameter-reduced portion is formed at the axial end side of the side wall portion, and a first-side gas outlet is formed at the distal end surface of the reduced-diameter portion. Is formed, and an opening is formed at the tip, and is arranged in such a manner that a predetermined amount of gap is formed between the first cylindrical portion and the outside of the first cylindrical portion. When arranged in a gas flow to be measured, the gas to be measured is allowed to flow from its base end side to its tip side along the tapered outer surface of the reduced diameter portion, and The gas to be measured flows directly into the first gas inlet in a direction orthogonal to the axis of the cylindrical portion. And a second cylindrical portion for preventing said,
In the first cylindrical portion, the first side gas outlet is located closer to the base end side in the axial direction than the distal end surface of the second cylindrical portion, or the inner edge of the opening of the second cylindrical portion on the outer surface of the reduced diameter portion. The reduced diameter portion may project from the opening of the second cylindrical portion in the opposed positional relationship.

In this case, the detection unit is, for example, an oxygen concentration cell in which a detection-side porous electrode is formed on one side of a plate-shaped oxygen-ion-conductive solid electrolyte layer, and an oxygen-reference-side porous electrode is formed on the opposite side. An oxygen detector comprising a device and a plate heater laminated on the oxygen reference side porous electrode side of the oxygen concentration cell element, wherein the electrode surface of the detection side porous electrode is a gas detection surface. can do. This configuration can be suitably adopted, for example, for a λ-type oxygen sensor.

Next, in the gas sensor according to the present invention, a plurality of first-side gas inlets are formed in the side wall portion of the first cylindrical portion at predetermined intervals in the circumferential direction, and the first-side gas inlet is formed in the axial direction. , And two of the pairs of holes are arranged such that one of the pairs of holes is opposed to the detection unit, and the other pair of the holes is closer to the tip than the tip of the detection unit. Can be configured. For example, when the first gas inlet has only one row corresponding to the detection unit, if the flow rate of the gas to be measured into the first cylindrical portion increases due to the negative pressure, most of the inflow gas hits the detection unit. Become. If water droplets or the like are mixed with the gas to be measured, the water droplets may hit the detection unit, and the protection function of the protector may be impaired. Therefore, if one or more rows of holes are added on the tip side from the tip of the detection element, the flow of water droplets is dispersed, so that the protection function can be maintained.

Also, in this case, the second cylindrical portion allows the gas to be measured to flow from the base end to the distal end on the outer surface of the tapered reduced diameter portion at the distal end of the first cylindrical portion. Has become. By forming such a gas flow to be measured, a negative pressure is generated at the first gas outlet side formed at the distal end of the reduced diameter portion, and the inside of the first cylindrical portion is sucked, whereby the inside of the first cylindrical portion is sucked. The gas to be measured is substantially isotropically sucked from each of the first gas inlets in the circumferential direction. As a result, a uniform response or output can be obtained regardless of the direction of the gas flow, regardless of the angle at which the gas flow to be measured strikes around the axis of the protector. This is particularly true when the gas detection surface is formed along a part of the outer circumferential surface of the detection unit along the circumferential direction, or when the gas detection surface is formed on one side in a plate shape, It works as a particularly advantageous effect.

Further, in the gas sensor according to the present invention, a first-side gas outlet is formed at a distal end surface of the first cylindrical portion, and a second-side gas outlet is formed at a distal end surface of the second cylindrical portion. The side gas outlet may be configured as being located on the distal end side of the first side gas outlet. In this configuration, the gas to be measured introduced from the second-side gas inlet directly hits the reduced-diameter portion, and the gas flow velocity along the reduced-diameter portion is increased, so that the negative pressure generated at the first-side gas outlet is increased. can do. as a result,
The suction speed of the gas to be measured from the first-side gas inlet, and thus the exchange speed of the gas to be measured in the first cylindrical portion, are improved, and the detection response and the output follow-up to the concentration change are further improved.

Further, in order to effectively draw out the suction effect as described above, the gas sensor of the present invention can be configured such that the second-side gas outlet is formed larger than the first-side gas outlet. In this configuration, the outflow of the gas to be measured from the second-side gas outlet is smooth without being hindered, and the negative pressure fluctuation generated at the first-side gas outlet can be suppressed. Therefore, stable detection responsiveness or output follow-up to a change in density can be obtained.

In this case, the first and second gas outlets can be formed in a concentric positional relationship with each other. With this configuration, the gas to be measured sucked from the first cylindrical portion through the first gas outlet can be smoothly discharged from the second gas outlet together with the gas to be measured flowing along the reduced diameter portion. As a result, it is possible to further improve the detection response of the sensor or the output follow-up to the density change.

Further, in the gas sensor according to the present invention, a first-side gas outlet is formed at a distal end surface of the first cylindrical portion, and a second-side gas outlet is formed at a distal end surface of the second cylindrical portion. The side gas outlet can be configured as being located on the distal end side of the second side gas outlet. In this configuration, the second-side gas outlet is directly opposed to the reduced-diameter portion on the tip side of the first cylindrical portion,
If the gap between the outer surface of the reduced diameter portion and the inner edge of the second gas outlet is reduced, the flow rate of the gas to be measured along the reduced diameter portion is further increased, and the negative pressure generated at the first gas outlet is further increased. can do. Therefore, the exchange speed of the gas to be measured in the first cylindrical portion is further improved, and the detection response and the output follow-up to the concentration change are further improved.

Next, in the gas sensor of the present invention, the second gas inlet forms a curved cut in the side wall portion of the second tubular portion, and the claw-shaped portion formed inside the curved cut is radially inward. It can be configured as being formed by being bent into a. In this configuration, the claw-shaped portion overlaps the second gas inlet in a flap shape, so that water droplets, oil droplets, and the like hardly enter the inside of the protector, and the protection function for the detection unit is further improved. Moreover, the gas to be measured is swirled along the side wall of the second cylindrical portion by the claw-shaped portion formed by being bent inward in the radial direction. Therefore, the flow velocity of the gas along the reduced diameter portion is increased, and the negative pressure generated at the first gas outlet can be further increased. As a result, the exchange speed of the gas to be measured in the first cylindrical portion is improved, and the detection response and the output follow-up to the concentration change are further improved.

Further, in the gas sensor according to the present invention, a pair of holes arranged in the first gas inlet and opposed to the detecting portion form a curved cut in a side wall portion of the first cylindrical portion. The claw-like portion formed inside the curved cut can be formed by being bent inward in the radial direction. In this configuration, since the claw portion overlaps the first gas inlet in a flap shape, it is difficult for water droplets, oil droplets, and the like to enter the inside of the first cylindrical portion, and the protection function for the detection unit is further improved. . In addition, the gas to be measured is sucked substantially isotropically as a swirling flow along the side wall of the first cylindrical portion by the claw-shaped portion formed by bending inward in the radial direction.
As a result, a uniform swirling flow of the gas to be measured is generated around the axis of the protector, and uniform response or output is obtained.

[0023]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows an oxygen sensor 1 for detecting the concentration of oxygen in exhaust gas of an automobile or the like as an embodiment of the gas sensor of the present invention. This oxygen sensor is commonly called a λ-type oxygen sensor, and has a structure in which an elongated plate-like ceramic element 2 (detection element) is fixed to a metal shell 3. Then, the mounting portion 3a formed on the outer peripheral surface of the metal shell 3 is attached so that the detecting portion D on the distal end side is located in the exhaust pipe,
It is exposed to a high-temperature exhaust gas as a gas to be measured flowing in the exhaust pipe.

The ceramic element 2 has a rectangular axial cross section, and as shown in FIG. 2A, an oxygen concentration cell element 21 formed in a horizontally long plate shape, and the oxygen concentration cell element 2
And a heater 22 for heating the heater 1 to a predetermined activation temperature. The oxygen concentration cell element 21 is formed of an oxygen ion conductive solid electrolyte mainly composed of zirconia or the like. On the other hand, the heater 22 is constituted by a known ceramic heater.

In the oxygen concentration cell element 21, the porous electrodes 25 and 26 have electrode lead portions 25a and 26a extending toward the mounting base end of the oxygen sensor 1 along the longitudinal direction.
Are integrated. Among them, the electrode lead portion 25a from the electrode 25 on the side not facing the heater 22 is
The end is used as the electrode terminal portion 7. On the other hand, the electrode lead portion 26a of the electrode 26 on the side facing the heater 22
As shown in FIG. 2C, is connected to the electrode terminal 7 formed on the opposite element surface by a via 26b crossing the oxygen concentration cell element 21 in the thickness direction. That is, the oxygen concentration cell element 21 has a shape in which the electrode terminal portions 7 of the porous electrodes 25 and 26 are formed side by side at the end of the plate surface on the electrode 25 side. Each of the above electrodes, electrode terminal portions and vias is P
It is obtained by forming a pattern by screen printing or the like using a paste of a metal powder having a catalytic activity of an oxygen molecule dissociation reaction such as a t or Pt alloy and firing the paste.

On the other hand, the resistance heating element pattern 2 of the heater 22
The lead portions 23a, 23a for supplying current to
As shown in (d), the oxygen concentration cell element 2 of the heater 22
Electrode terminal portions 7, 7 formed at the end of the plate surface on the side not facing 1 are connected via vias 23b, respectively. The oxygen concentration cell element 21 and the heater 22 are shown in FIG.
As shown in (b), ZrO ₂ based ceramic or A
They are joined together via a ceramic layer 27 such as l ₂ O ₃ ceramic. In the oxygen concentration cell element 21, the bonding-side porous electrode (oxygen reference side porous electrode) 26 functions as an oxygen reference electrode by applying a minute pumping current, while the opposite side porous electrode 25 exhausts. It becomes a detection side electrode which comes into contact with the gas, and the surface thereof becomes a gas detection surface.

Returning to FIG. 1, the ceramic element 2 is inserted through the insertion hole 30 of the insulator 4 disposed inside the metal shell 3, and the detecting portion D at the tip is fixed to the exhaust pipe.
Is fixed in the insulator 4 in a state of protruding from the front end. One end of the insulator 4 communicates with the rear end of the insertion hole 30 in the axial direction, and the other end is open to the rear end surface of the insulator 4 and has a shaft section 31 whose axial cross section is larger in diameter than the insertion hole 30. Are formed. A sealing material layer 3 mainly composed of glass (for example, crystallized zinc silica borate glass) is provided between the inner surface of the cavity 31 and the outer surface of the ceramic element 2.
2 sealed.

A talc ring 36 and a caulking ring 37 are fitted between the insulator 4 and the metal shell 3 so as to be adjacent to each other in the axial direction, and the caulking ring 37 is attached to the outer peripheral portion on the rear end side of the metal shell 3. The insulator 4 and the metal shell 3 are fixed by caulking to the insulator 4 side through the intermediary. Further, in the present specification, in the axial direction of the metal shell 3, the protruding side of the detecting portion D is defined as a front side, and the opposite side is defined as a rear side.

A ceramic separator 16 and a grommet 15 are fitted inside the outer cylinder 18 at the end (upper part in the drawing), and a connector 13 is further provided on the inner side. The rear end side of the lead wire 14 extends to the outside through the ceramic separator 16. On the other hand, the distal end side of the lead wire 14 is electrically connected to each electrode terminal portion 7 (collectively four poles) of the ceramic element 2 shown in FIG.

The tip of the metallic shell 3 has a ceramic element 2
, That is, a protector 6 that covers the detection unit D is attached. The protector 6 has a double structure having an inner first cylindrical portion 6b and an outer second cylindrical portion 6a. As shown in FIG. 3, the first cylindrical portion 6b is formed in a cylindrical shape surrounding the detection portion D around the axis of the detection element 2,
A plurality of first gas inlets 60 and 61 are formed on the side wall at predetermined intervals in the axial direction, and a tapered diameter reducing portion 6t is formed on the side of the side wall in the axial direction to reduce the diameter. Part 6t
A first gas outlet 62 is formed at the tip end surface of the first gas outlet. Specifically, the reduced diameter portion 6t is formed integrally with the distal end side of the cylindrical main body 6s in a truncated cone shape. The first gas inlets 60 and 61 include a plurality of sets (60 and 61) of holes arranged at substantially equal intervals along the circumferential direction of the main body 6s. In this embodiment, a set of holes 6 each including four holes in the form of a circular opening is used.
0 and 61 are formed in two rows in the axial direction of the main body 6s.

The second cylindrical portion 6a has a predetermined gap G between the second cylindrical portion 6a and the first cylindrical portion 6b outside the first cylindrical portion 6b.
Is formed in the form of a cylinder, the tip of which is protruded from the first cylindrical portion 6b, and the second gas outlet 64 is formed on the tip end surface. Then, as shown in FIG. 5, for example, when arranged in the gas flow EG to be measured flowing in a direction perpendicular to the axis of the detection element 2, the gas is introduced from the second gas inlet 63 formed on the side wall thereof. The measured gas EG flows from the base end to the distal end along the tapered outer surface of the reduced diameter portion 6t, and then flows out from the second gas outlet 64.

More specifically, the second cylindrical portion 6a is formed in a cylindrical shape having a bottom portion 6f formed at the front end, and is substantially equal in the circumferential direction at a position corresponding to the reduced diameter portion 6t near the front end of the side wall portion. A plurality of second side gas inlets 63 are provided at intervals (in this embodiment, one
2) are formed. On the other hand, the second side gas outlet 64 is
It is formed in the center of the bottom 6f in a concentric positional relationship with the first gas outlet 62. Here the second gas inlet 63
For both the first gas inlets 60 and 61,
The cylindrical portions 6a and 6b are formed in a positional relationship shifted from each other in the axial direction. Thus, the gas to be measured EG in the direction orthogonal to the axial direction is prevented from flowing directly into the first gas inlets 60 and 61 by the second cylindrical portion 6a.

The two sets of holes 60 and 61 forming the first gas inlet are arranged such that one of the sets (61) is located closer to the tip end in the axial direction than the tip of the detector, and the other set (60). ) Is located on the proximal side. The to-be-measured gas stream may contain poisoning substances such as phosphorus, sulfur, and silicon in addition to water droplets of condensed water. Such water droplets and poisoning substances enter the first cylindrical portion 6b through the row of holes 60 or 61, but those that enter through the row of holes 61 have a high probability of being discharged to the outside in the gas flow as they are, It becomes difficult to adhere to the detection unit. That is, if the first gas inlet is formed to include the two hole rows 60 and 61 sandwiching the tip of the detection unit as described above, the durability of the detection unit against condensed water and poisoning substances can be improved. become able to.

Next, as shown in FIG. 1, the distal end side of the metal shell 3 is slightly reduced in diameter from the mounting screw portion 3a to form a small diameter portion 3b.
Are formed. As shown in FIG. 3, a cylindrical positioning projection 3c projecting from the peripheral edge of the opening is formed on the distal end surface of the small diameter portion 3b. First cylindrical portion 6b
The large diameter portion 6g formed on the opening side is fitted outside the small diameter portion 3b of the metal shell 3 while being positioned by the positioning projection 3c. On the other hand, the second cylindrical portion 6a is fitted into the small-diameter portion 3b of the metallic shell 3 from the outside of the large-diameter portion 6g of the first cylindrical portion 6b at the base end side opening, and
The g is fixed to the small diameter portion 3b by a circumferential weld 65 (for example, a spot weld formed intermittently or a laser weld formed in a continuous ring) together with g.

The oxygen sensor 1 is fixed to a vehicle exhaust pipe at a mounting screw portion 3a. The detection unit D detects the exhaust gas E
G, the porous electrode 2 of the oxygen concentration cell element 21
5 (FIG. 2) comes into contact with the exhaust gas EG, and an oxygen concentration cell electromotive force corresponding to the oxygen concentration in the exhaust gas EG is generated in the oxygen concentration cell element 21. This electromotive force is extracted as a sensor output. Since the protector 6 has the double structure as described above, the protector 6 has an excellent protection function for the detection unit D. On the other hand, as shown in FIG.
The exhaust gas EG introduced into the protector 6 flows from the proximal side to the distal side along the outer surface of the reduced diameter portion 6t of the first cylindrical portion 6b, and then flows out from the second side gas outlet 64. I do.

When such a gas flow is formed, a negative pressure is generated at the first side gas outlet 62 to suck the inside of the first cylindrical portion 6b, and the first side gas inlets 60 and 61 in the circumferential direction are formed. The exhaust gas EG is substantially isotropically sucked from the exhaust gas. As a result, no matter what angle the gas flow to be measured strikes around the axis of the protector, the gas EG is supplied to the detecting portion D substantially isotropically, so that the gas EG is uniformly supplied regardless of the direction of the gas flow. Responsiveness or output characteristics. Further, since the first side gas outlet 62 has a negative pressure, the exhaust gas EG sucked from the first side gas inlets 60 and 61 makes a comparison along the surface (gas detection surface) of the detection side porous electrode 25. Since an extremely large gas flow can be formed, good output followability can be obtained even when the atmosphere changes from a rich atmosphere to a lean atmosphere, and a difference in effect due to the direction of the gas flow with respect to the protector 6 hardly occurs.

An example of the dimensions of each part of the oxygen sensor 1 will be described below with reference to FIGS. 1 and 4 (when the dimensions are shown in a range, specific numerical examples are shown in parentheses. In addition, the code | symbol of each part in FIG. 4 should refer to FIG. 3). The length L2 of the protector 6 is 16.5 mm.・ Nominal diameter D1 of mounting screw portion 3a: M12 × P1.25.
(The above is Figure 1)

The protrusion length L3 of the ceramic element 2 from the front end surface of the metal shell 3 is 5 mm. -Distance L4 from the front end surface of the first cylindrical portion 6b to the inner bottom surface of the second cylindrical portion 6a: 5 mm or less. If L4 exceeds 5 mm, there may be a problem that the response is deteriorated. -Length L5 of the reduced diameter portion 6t: D6 <L5 (3.5 mm). L5
Is out of the range, the response of the sensor 1 is easily affected by the direction of the gas flow. The taper angle θ of the reduced diameter portion 6t: less than 80 ° (45 °).
However, in the section including the axis O of the first cylindrical portion 6b,
An angle θ between the axis O and the outer surface of the reduced diameter portion 6t is defined as a taper angle.

An axial distance L6 from the inner bottom surface of the second cylindrical portion 6a to the center of the second gas inlet 63: L4 <L6 <L4 +
L5 (3 mm). -Distance L7 from the protector base end to the base side first gas inlet 60: L7 <L3 (1.8 mm). Distance L8 from the protector base end to the first side gas inlet 61 on the distal end side: L3 <L8 (6.8 mm).

When the inner diameter of the second cylindrical portion 6a is D2 and the outer diameter of the first cylindrical portion 6b is D3, D2-D3: 0.5 to
10 mm (1.9 mm). If D2-D3 is less than 0.5 mm, the flow of gas from the second gas inlet 63 to the second gas outlet 64 may be hindered, leading to a deterioration in detection response. If it exceeds 10 mm, a problem that the negative pressure effect is lost may occur.

The inner diameter D4 of the second gas outlet 64: D5 <D
4 <D3 (4 mm). When D4 is less than D5, outflow of gas from the second cylindrical portion 6a is hindered, which may lead to deterioration of detection response.・ Inner diameter D5 of first gas outlet 62: 0.5 mm <D5 <D
3 (2 mm). When D5 is less than 0.5 mm, outflow of gas from the first cylindrical portion 6b is hindered, which may cause deterioration of detection response.・ Inner diameter D6 of second gas inlet 63: 0.5 mm <D6 <L
5 (2 mm). When D6 is less than 0.5 mm, the flow of gas into the second cylindrical portion 6a is hindered, which may lead to deterioration of detection response. In addition, when L5 is exceeded, the responsiveness of the sensor 1 is easily affected by the direction of the gas flow.・ Inner diameter D7 of first side gas inlets 60 and 61: 0.5 mm <
D7 <4 mm (1 mm). When D7 is less than 0.5 mm, the flow of gas into the first cylindrical portion 6b is hindered, and the detection response may be deteriorated. If the distance exceeds 4 mm, the responsiveness of the sensor 1 tends to be affected by the direction of the gas flow.

The number n1 of the second gas inlets 63 formed in the circumferential direction: n1 ≧ 2. If the number is less than two, the flow of gas into the second cylindrical portion 6a is hindered, and the detection response is deteriorated. There is. · Number of first gas inlets 60, 61 formed in the circumferential direction: n2
≧ 2. If the number is less than 2, the flow of gas into the first cylindrical portion 6b is hindered, and the detection response may be deteriorated. In addition,
If the number of formed gas inlets is excessively increased, the width of a portion sandwiched between adjacent gas inlets may be too narrow, which may lead to a decrease in strength. To be determined.

Hereinafter, a modified example of the protector 6 will be described. In the protector 6 shown in FIG.
At the position corresponding to t, the second gas inlets are formed in two rows of 63b and 63a. Thereby, the reduced diameter portion 6
The flow of the gas along the outer surface of t becomes smooth, the responsiveness is improved, and the gas flow is less affected by the direction of the gas flow. In FIG. 6A, the circumferential step 6h is shown.
Accordingly, the diameter of the distal end side of the first cylindrical portion 6b is reduced, thereby forming a gap G between the first cylindrical portion 6b and the second cylindrical portion 6a. The base end of the first cylindrical portion 6b is a small-diameter portion 3b of the metal shell 3.
It is fitted in. Then, the base end of the second cylindrical portion 6a is fitted so as to be overlapped on the outside thereof, and is fixed to the small-diameter portion 3b by a welded portion (not shown) together with the first cylindrical portion 6b in the overlapping portion. I have.

In FIG. 6B, a third gas inlet 60 (only one row is formed on the base end side) is formed between the first cylindrical portion 6b and the second cylindrical portion 6a so as to cover the third gas inlet 60 (only one line is formed on the base end side). Has a triple structure provided with the cylindrical portion 6c. This makes it more difficult for water droplets, oil, dirt, and the like to enter the inside of the first cylindrical portion 6b.

In FIG. 6 (c), the third cylindrical portion 6c is arranged outside the second cylindrical portion 6a so as to cover the base end thereof and not to cover the second side gas inlet 63. I have. With this, if the gas flow rate suddenly rises,
The temperature drop of the detection unit D is more effectively prevented. Further, in FIG. 6D, the third cylindrical portion 6c is extended to the position of the second gas inlet 63, and the third gas inlet 66 is formed at a corresponding position. This makes it more difficult for water droplets, oil, dirt, and the like to enter the inside of the first cylindrical portion 6b.

FIG. 7E shows an example in which the airflow guide 6w is formed so as to protrude inward from the inner surface of the second cylindrical portion 6a along the peripheral edge of the second gas inlet 63. Thus, the flow of the exhaust gas toward the reduced diameter portion 6t is less likely to be disturbed, and the effect of the present invention in which the response of the sensor 1 is less likely to be affected by the direction of the gas flow can be further enhanced.

FIG. 7F shows an example in which a reduced diameter portion 6u is also formed on the tip side of the second cylindrical portion 6a. As a result, the effect of sucking the gas flowing into the protector 6 is enhanced, and the effect of the present invention in which the response of the sensor 1 is less affected by the direction of the gas flow can be further enhanced.

Further, as shown in FIG. 7 (g), a cylindrical linear portion 6v may be further formed on the distal end side of the reduced diameter portion 6t of the first cylindrical portion 6b. On the other hand, the second cylindrical portion 6a
As shown in (h), the shaft cross section may be formed in a polygonal shape.

As shown in FIGS. 7 (i) and 7 (j), almost the entire outer surface of the first cylindrical portion 6b is reduced in diameter.
It may be set to t. 7 (i), the cross section of the reduced diameter portion 6t may be substantially linear (in this case, the outer shape of the reduced diameter portion 6t is a truncated cone). As shown in FIG. 7 (j), it may be a curved surface projecting outward (in this case, the outer surface shape of the reduced diameter portion 6t is a spindle shape). Further, as shown in FIG.
At t, the tip side may be made to protrude from the second-side gas outlet 64 (tip-side opening). In this case, the inner edge of the opening of the second gas outlet 64 is positioned so as to face the outer surface of the reduced diameter portion 6t.

FIG. 8 shows still another modification of the protector, in which the following changes are made to the second gas inlet 63 and the first gas inlet 60. The second side gas inlet 63 is
In the side wall portion of the second cylindrical portion 6a, a cut of a curved shape (or a shape extending from one base end portion and changing its direction by the direction changing portion 6a1 and reaching the other base end portion) is a half-moon shape. A cut 6a2 is created, and the cut 6a
2 is formed by bending a claw-shaped portion 6a3 formed inside the inner side 2 inward in the radial direction. The exhaust gas EG introduced into the protector 6 from the second gas inlet 63 flows from the base end side to the distal end side along the outer surface of the reduced diameter portion 6t of the first cylindrical portion 6b, and then flows into the second end portion. It flows out from the side gas outlet 64. At this time, the exhaust gas EG is swirled along the side wall of the second cylindrical portion 6a by the claw-shaped portion 6a3 formed by bending inward in the radial direction. For this reason, since the flow velocity of the gas along the reduced diameter portion 6t is increased, the negative pressure generated at the first gas outlet 62 can be further increased. As a result, the first side gas inlet 6
The suction speed of the exhaust gas EG from 0 and 61, and further, the exchange speed of the exhaust gas EG in the first cylindrical portion 6b is improved, and the detection responsiveness or the output follow-up performance with respect to the concentration change is further improved. Further, the claw-shaped portion 6a3 is connected to the second gas inlet 63.
8 (f) (see FIG. 8 (b)), it is difficult for water droplets, oil droplets, etc. to enter the inside of the protector 6, and the protection function for the detection unit D is excellent.

On the other hand, among the first gas inlets 60 and 61, a pair of holes 60 arranged in a form facing the detection portion D has a curved shape (or a side wall) in the side wall portion of the first cylindrical portion 6b. A half-moon-shaped cut 6b2 is formed as a cut of a shape extending from one base end to reach the other base end after the direction is changed by the direction changing unit 6b1.
Is formed by bending a claw-like portion 6b3 formed inside the inside in the radial direction inward. Due to the negative pressure generated at the first side gas outlet 62, the inside of the first cylindrical portion 6b is sucked, and at this time, the exhaust gas E
G is a claw-shaped portion 6b3 formed by bending inward in the radial direction.
As a result, a swirling flow along the side wall portion of the first cylindrical portion 6b is sucked substantially isotropically. As a result, a uniform swirling flow of the exhaust gas EG is generated around the axis of the protector 6,
Uniform response or output is obtained. In addition, the claw-shaped portion 6
Since b3 overlaps the first gas inlet 60 in a flap shape, water droplets, oil droplets, and the like hardly enter the inside of the first cylindrical portion 6b, and the function of protecting the detection portion D is excellent.

The shape of the cuts 6a2, 6b2 can be changed to a U-shape, a U-shape or the like as appropriate. Also, the break 6a2
The number of 6b2, the position of the bending line, the bending direction, and the like can be changed.

The structure of the sensor of the present invention described above is a gas sensor other than an oxygen sensor, for example, an HC sensor or NOx.
The same can be applied to sensors and the like.

[Brief description of the drawings]

FIG. 1 is a front view and a longitudinal sectional view of an oxygen sensor showing an example of a gas sensor of the present invention.

FIG. 2 is an explanatory view showing a structure of a ceramic element as the detection element.

FIG. 3 is a partial longitudinal sectional view and an AA axis sectional view showing details of the structure of the protector of FIG. 1;

FIG. 4 is a partial longitudinal sectional view and an axial sectional view showing dimensions of each part of the protector of FIG. 1;

FIG. 5 is a partial longitudinal sectional view and a sectional view taken along the line BB showing the operation of the protector of FIG. 1;

FIG. 6 is a longitudinal sectional view showing some modified examples of the protector.

FIG. 7 is a longitudinal sectional view ((e) to (g), (i) to (k)) and an axial sectional view ((h)) showing some other modifications of the protector.

FIG. 8 is a partial longitudinal sectional view, a CC sectional view, and a DD sectional view showing still another modification of the protector.

FIG. 9 is a sectional view showing the structure of a conventional protector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxygen sensor (gas sensor) 2 Ceramic element (detection element) D Detection part 3 Metal shell 6 Protector 6a Second cylindrical part 6b First cylindrical part 6t Reduced diameter part 6s Main part 6a1, 6b1 Direction conversion part 6a2, 6b2 6a3, 6b3 Claw-shaped part 21 Oxygen concentration cell element 22 Heater 25 Porous electrode (porous electrode on detection side) 26 Porous electrode (porous electrode on oxygen reference side) 60, 61 First side gas inlet 62 First side gas outlet 63 Second side gas inlet 64 Second side gas outlet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsutoku Oi 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Japan Specialty Ceramics Co., Ltd. No. 18 Japan Special Ceramics Co., Ltd. (72) Inventor Teppei Okawa 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd.

Claims (5)

[Claims] 1. A protector for covering a detection portion formed at a tip portion of a detection element, comprising: a first cylindrical portion; and a second cylindrical portion disposed outside the first cylindrical portion. A tapered diameter-reduced portion is formed on the axial end side of the side wall portion of the first cylindrical portion, and the second gas is located at a position corresponding to the diameter-reduced portion on the side wall portion of the second cylindrical portion. A gas sensor, wherein an inlet is formed. 2. A plurality of first-side gas inlets are formed in the side wall portion of the first cylindrical portion at predetermined intervals in a circumferential direction, and the first-side gas inlets are two holes separated in an axial direction. Of the two holes, one of the holes is arranged so as to face the detection unit, and the other pair of holes is located closer to the tip than the tip of the detection unit. The gas sensor according to claim 1, wherein 3. A first-side gas outlet is formed at a front end surface of the first cylindrical portion, a second-side gas outlet is formed at a front end surface of the second cylindrical portion, and the second-side gas is provided. The gas sensor according to claim 1, wherein an outlet is located on a distal end side of the first gas outlet. 4. The gas sensor according to claim 3, wherein the second gas outlet is formed larger than the first gas outlet. 5. The first gas outlet is formed at a front end surface of the first cylindrical portion, and the second gas outlet is formed at a front end surface of the second cylindrical portion. The gas sensor according to claim 1, wherein the side gas outlet is located closer to the tip than the second side gas outlet.