JP2010256241A - Sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor capable of sealing using a simple structure, an interval between an inside protector covering a sensor element, and a main metal fitting. <P>SOLUTION: The sensor 1 includes: the sensor element 10, having a detection part 10a on the tip side and extending to the axial direction; the cylindrical main metal fitting 2, enclosing the outer peripheral surface of the sensor element, while projecting the detection part from the tip; the metal inside protector 3, having an inside cylindrical part 3s, enclosing the outer peripheral surface of the detection part, and an inside bottom part 3u for blocking the tip side of the inside cylindrical part; an outside protector 4, having an outside cylindrical part 4a enclosing its radial direction in the separated state from the inside cylindrical part, and an outside bottom part 4u for blocking the tip side of the outside cylindrical part. The inside bottom part and the outside bottom part are in contact with each other, and the outside cylindrical part is bonded to the main metal fitting; and rear ends 3e, 3e2 of the inside cylindrical part are gradually enlarged or reduced, as going toward the axial direction rear-end side; and the rear ends are in elastic contact with tip-facing surfaces 2u, 2u3 of the main metal fitting which do not contact the outside cylindrical part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sensor including a protector that covers a sensor element that detects the concentration, temperature, and the like of a specific gas component.

As gas sensors that improve fuel consumption and control combustion in an internal combustion engine such as an automobile engine, oxygen sensors and air-fuel ratio sensors that detect the oxygen concentration in exhaust gas are known. As shown in FIG. 5, these (gas) sensors 200 hold the sensor element 10 for detecting the concentration of a specific gas in the metal shell 2 and are provided on the front end side of the sensor element 10. The protruding detection unit 10a is protected by a double protector including a bottomed cylindrical inner protector 30 and an outer protector 40. With this double protector, moisture and poisonous substances in the exhaust gas are prevented from adhering to the detection portion 10a of the sensor element 10.
As a method of attaching the double protector to the sensor body 200, the inner protector 30 and the outer protector are expanded by increasing the diameter of the open end 30e of the inner protector 30 while making the outer diameter of the inner protector 30 smaller than the distal end portion 2f of the metal shell 2. It is described that 40 end edges are fitted to the front end portion 2f of the metal shell 2, and the entire circumference of the fitting portion is laser-welded from the outside to form a welded portion W20 (Patent Document 1).

JP 2008-116273 A

However, if the laser welding of the entire circumference of the fitting portion is to be carried out completely, it may take a long time to reduce the productivity, and it may be necessary to improve the capability of the laser processing machine in order to secure the amount of penetration. .
Therefore, as described in JP-A-2005-114527, the rear end of the outer protector is fitted to the front end of the metal shell 2 while the bottom of the inner protector and the bottom of the outer protector are in contact with each other. A welded portion is also formed by laser welding the entire circumference of the joint from the outside.
However, if the laser welding of the fitting part is insufficient, the protector may drop off, or the gap between the inner protector and the metal shell will not be completely sealed, and exhaust gas will flow into the sensor element from this gap. There is. As a result, the detection accuracy may be lowered due to the cooling of the sensor element, or the sensor element may be cracked due to moisture. In particular, in the case of such NO _x sensor high detection accuracy is required, the detection accuracy cold generated in the sensor element decreases.
Therefore, an object of the present invention is to provide a sensor that can seal the gap between the inner protector that covers the sensor element and the metal shell with a simple structure.

In order to solve the above-described problems, a sensor according to the present invention includes a sensor element having a detection portion on the distal end side and extending in the axial direction, and a cylindrical main body surrounding the outer peripheral surface of the sensor element while protruding the detection portion from the distal end. A metal inner protector having a metal fitting, an inner cylindrical portion surrounding the outer peripheral surface of the detection portion, and an inner bottom portion that closes the distal end side of the inner cylindrical portion, while being spaced apart from the inner cylindrical portion. In a sensor comprising an outer cylindrical portion surrounding a radial direction, and a metal outer protector having an outer bottom portion that closes a distal end side of the outer cylindrical portion, the inner bottom portion and the outer bottom portion are in contact with each other, The outer cylindrical portion is joined to the metal shell, and the rear end portion of the inner cylindrical portion is enlarged or reduced in diameter toward the axial rear end side, and the rear end portion is the outer cylindrical portion. Elastic contact with the end facing surface of the metal shell without contacting It is.
In this case, the rear end portion of the inner cylindrical portion of the inner protector is in elastic contact with the front end surface of the metal shell, so that the rear end portion tries to return to the original position by the elastic force. Will be in close contact. In particular, since the rear end portion is not in contact with the outer tubular portion of the outer protector, the front end surface of the metal shell is not affected by the elastic force that the rear end portion is trying to return to the original without being weakened by the outer tubular portion. It will push, and a rear-end part will closely_contact | adhere to the front end surface of a metal shell. As a result, the gap between the inner protector and the metal shell is completely sealed, preventing exhaust gas from flowing into the sensor element from the gap. It prevents the sensor element from cracking. Further, since the gap is sealed with a simple structure using the elastic force of the upper edge of the inner protector, productivity is improved.
The “elastic contact” can be confirmed by whether the rear end of the inner cylindrical portion is deformed in a state where the inner protector is assembled to the sensor and a state where only the inner protector is taken out. .

Furthermore, it is preferable that the taper angle of the surface facing the front end of the metal shell is larger than the taper angle of the rear end portion of the inner cylindrical portion.
In this case, the rear end portion of the inner protector rises from the front end facing surface of the metallic shell, so that the rear end portion can be reliably brought into contact with the front end facing surface of the main metallic shell, and the seal is sufficient.

  According to the present invention, the gap between the inner protector covering the sensor element and the metal shell can be sealed with a simple structure.

It is sectional drawing which follows the longitudinal direction of the sensor which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the process of attaching a double protector to a main metal fitting. It is a fragmentary sectional view in alignment with the longitudinal direction of the sensor which concerns on the 2nd Embodiment of this invention. It is an exploded view which respectively shows the taper angle of the lower surface of the front end side of a metal shell, and the upper end edge of an inner side protector. It is sectional drawing in alignment with the longitudinal direction of the conventional sensor.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows a cross-sectional view along the longitudinal direction of a sensor (oxygen sensor) 1 according to a first embodiment of the present invention. In addition, the lower side of FIG. 1 (the front end side positioned at the detection unit 10a of the sensor element 10) is referred to as “front end side”, and the upper side is referred to as “rear end side”.
The sensor (oxygen sensor) 1 is an assembly in which a sensor element 10 is assembled. The sensor 1 includes a plate-like sensor element 10 extending in the axial direction (vertical direction in FIG. 1), and a metal shell 2 fixed to an exhaust pipe of an automobile engine. The metal shell 2 has a substantially cylindrical shape, and a threaded portion 24 for fixing to the exhaust pipe is formed on the outer surface, while a through hole 25 is formed on the inner side and protrudes radially inward of the through hole 25. A locking portion (shelf) 2p is provided on the tip side. The metal shell 2 accommodates the sensor element 10 in the through hole 25, and holds the sensor element 10 in a state where the detection portion 10 a provided on the distal end side of the sensor element 10 protrudes from the metal shell 2. Between the through hole 25 and the outer peripheral surface of the sensor element 10, a metal cup 20 that is locked to the locking portion 2p, an annular ceramic holding member 21 that surrounds the outer peripheral surface of the sensor element 10, and a powder filler (talc ring). ) 22, 23 and a ceramic sleeve 30 are laminated in this order from the tip side. Then, the talc rings 22 and 23 are compressed by crimping the rear end 2a of the metal shell 2 and pressing the sleeve 30 toward the front end side, and the talc rings 22 and 23 are crushed to form the metal cup 20 or the through hole 25. The gap with the sensor element 10 is filled, and the sensor element 10 is firmly fixed at a predetermined position in the metal shell 2.
Examples of the talc rings 22 and 23 include talc (ceramic powder) and glass (silicate compounds such as silicate glass or silicate glass). Further, the talc, glass, or the like may be disposed on the inner and outer surfaces of the holding member 21 and the sleeve 30.

  An outer cylinder 80 is connected to the rear end side of the metal shell 2, and a lead wire 68 connected to the electrode of the sensor element 10 is drawn from the rear end of the outer cylinder 80 through a grommet 77. A terminal fitting 60 is connected to one end of the lead wire 68 and is electrically connected to an electrode terminal (not shown) provided at the rear end of the gas sensor element 10.

On the other hand, at the front end portion 2f of the metal shell 2, a metal (for example, stainless steel) that covers the detection portion 10a of the sensor element 10 and a metal that covers the inner protector 3 while being separated from the inner protector 3 with a bottomed cylindrical shape. A double protector made of a bottomed cylindrical outer protector 4 is attached. The inner diameter of the outer protector 4 is set larger than the outer diameter of the inner protector 3.
The inner protector 3 includes an inner cylindrical portion 3s that surrounds the detection portion 10a and an inner bottom portion 3u that closes the tip of the inner cylindrical portion 3s, and is arranged with an opening edge facing the rear end side. Similarly, the outer protector 4 includes an outer cylindrical portion 4 s that covers the inner cylindrical portion 3 s and an outer bottom portion 4 u that closes the tip of the inner cylindrical portion 4 s, and the inner protector 3 is coaxial with the inner protector 3. Contained. The inner bottom 3u of the inner protector 3 and the outer bottom 4u of the outer protector 4 are overlapped and welded to form a welded portion W1. A discharge hole 5h passes through the center of each inner bottom 3u and outer bottom 4u. Furthermore, a hole 4h through which exhaust gas flows in and out passes through the front end side of the outer cylindrical portion 4s, and a hole 3h through which exhaust gas flows in and out also through the rear end side of the inner cylindrical portion 3s. .

Here, the front end portion 2f of the metal shell 2 has a cylindrical shape with a diameter smaller than that of the screw portion 24, and the front end facing surface 2u is formed flat. On the other hand, the inner diameter of the outer protector 4 (the inner diameter of the outer cylindrical portion 4s) is substantially the same as the outer diameter of the distal end portion 2f. Then, the rear end portion 4e of the outer protector 4 is fitted to the tip portion 2f, and the outer protector 4 is connected to the tip portion 2f by laser welding the fitting portion from the outside to form the welded portion W2. Yes.
The rear end 3e of the inner protector 3 is radially expanded toward the rear end, and the rear end 3e is connected to the front end 2f while the rear end 3e is connected to the outer protector 4 (outer side). It is in elastic contact with the tip-facing surface 2u of the metal shell 2 without contacting the cylindrical portion 4s). As will be described in detail later, this causes the rear end portion 3e to come into close contact with the tip-facing surface 2u in an attempt to return to the original state by elastic force. Particularly, since the rear end portion 3e is not in contact with the outer cylindrical portion 4S, the elastic force that the rear end portion 3e tries to return to presses the front end facing surface 2u without being weakened by the outer cylindrical portion 4s. Thus, the rear end portion 3e is brought into close contact with the front end facing surface 2u. As a result, the gap between the inner protector 3 and the metal shell 2 is completely sealed, the exhaust gas is prevented from flowing into the sensor element 1 from the gap, and the detection accuracy of the sensor element 1 due to the cooling of the sensor element 1 is improved. This prevents the sensor element 1 from being cracked due to lowering or moisture. Further, since the gap between the inner protector 3 and the metal shell 2 is sealed using the elastic force of the rear end portion 3e, it is not always necessary to weld the entire periphery of the fitting portion between the outer protector 4 and the metal shell 2. Productivity is improved.

  In this example, the sensor element 10 is an oxygen sensor element having an oxygen concentration battery cell and an oxygen pump cell, but a known oxygen sensor can be used. In other words, the oxygen concentration battery cell and the oxygen pump cell of the oxygen sensor each have a configuration in which a pair of electrodes are arranged on the surface of the solid electrolyte layer, and the solid electrolyte layer is used to protect the solid electrolyte layer or to stack the heater. An insulating layer (alumina or the like) is laminated so as to cover the layers.

Next, an example of a process of attaching the double protector to the metal shell 2 will be described with reference to FIG.
First, the double protector in which the inner bottom portion 3u of the inner protector 3 and the outer bottom portion 4u of the outer protector 4 are welded and integrated is fitted to the distal end portion 2f of the metal shell 2 (FIG. 2A). Here, the rear end portion 4e of the outer protector 4 protrudes from the rear end portion 3e of the inner protector 3, and the rear end portion 3e of the inner protector 3 is expanded in diameter.
When the outer protector 4 is fitted to the front end portion 2f, the rear end portion 3e of the inner protector 3 comes into contact with the front end facing surface 2u of the metal shell 2 eventually. Therefore, when the outer protector 4 is further fitted to the back (rear end side) and the rear end portion 4e of the outer protector 4 is brought into contact with the stepped portion of the front end portion 2f of the metal shell 2 and the screw portion 24, the inner protector is provided. 3 is pressed against the front-facing surface 2u of the metal shell 2, and a force Fp is applied to expand outward (arrow Fp in FIG. 2B).

In the state of FIG. 2B, when the fitting portion between the outer protector 4 and the metal shell 2 is welded to form the welded portion w2, and the outer protector 4 is fixed to the metal shell 2, the expansion force Fp is received. A force Fs (spring back) is generated at the rear end portion 3e to return by the elastic force of the metal (arrow Fs in FIG. 2C). As a result, the rear end portion 3e is biased toward the front end facing surface 2u, and the gap between the inner protector 3 and the metal shell 2 is completely sealed.
Here, the rear end 3e and the outer protector 4 are appropriately designed such that the distance between the inner protector 3 and the outer protector 4 and the taper angle (described later) of the rear end 3e are designed so that the rear end 3e does not contact the outer protector 4. A gap G is formed between the outer protector 4 and the outer protector 4. If the gap G is not provided, the rear end portion 3e is brought into contact with the outer protector 4 before sufficiently expanding, and the force Fp becomes weaker and the reaction force Fs becomes weaker. Sealing of the gap with the metal shell 2 is insufficient.

FIG. 3 is a partial cross-sectional view along the longitudinal direction of a sensor (oxygen sensor) according to the second embodiment of the present invention. The sensor according to the second embodiment is the same as the sensor according to the first embodiment except that the contact mode between the inner protector 3 and the metal shell 2 is different. Only the vicinity of the contact portion with the metal shell 2 is shown.
In FIG. 3, the distal end portion 2 f 2 of the metal shell 2 is reduced in diameter from the screw portion 24 toward the distal end, and further, a conical portion 2 u 2 is formed on the distal end side. And the rear end part 3e2 whose diameter of the inner protector 3 is expanded is in contact with the tip-facing surface 2u3 constituting a part of the conical part 2u2 (in the vicinity of the central part of the conical part 2u2 in FIG. 3).

Here, as shown in FIG. 4, the taper angle θ _T2 of the front end facing surface 2u3 is larger than the taper angle θ _T1 of the rear end portion 3e2. In this way, the rear end portion 3e2 rises from the front end facing surface 2u3, so that the rear end portion 3e2 can be reliably brought into elastic contact with the front end facing surface 2u3, and the seal is sufficient.
The “taper angle” is an angle formed by two line segments constituting the tip-facing surface 2u3 and the rear end portion 3e2 in the axial section of the tip-facing surface 2u3 and the rear end portion 3e2, and represents the degree of taper. For example, in the case of the first embodiment, the taper angle of the front-facing surface 2u of the metal shell 2 is 180 degrees, and the taper angle of the rear end portion 3e is less than 180 degrees, so that θ _T2 > θ _{T1 is} also _satisfied . Satisfies the relationship.
In FIG. 4, the taper angle of the rear end 3 e 2 represents the taper angle when the outer protector 4 is fixed to the metal shell 2. Before fitting the outer protector 4 to the metallic shell 2, the rear end portion 3e2 is because it is not pressed against the forward-facing surface 2U3, but the taper angle is further reduced than theta _T1, mainly the outer protector 4 fitting 2 It is important from the viewpoint of sealing performance that the taper angle of the rear end portion 3e2 becomes θ _T2 > θ _T1 even after being fixed to.

It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention. For example, the connection method between the outer protector 4 and the metal shell 2 is not limited. For example, in addition to welding such as laser welding, caulking or the like may be performed. Moreover, the fitting part of the outer protector 4 and the metal shell 2 may be welded all around, or a part of the fitting part may be welded. Further, the rear end portion of the inner protector may be reduced in diameter as compared with the side surface.
Further, the tip-facing surfaces 2u and 2u3 may be not only the tip-facing surfaces formed at the tip portion 2f and the conical portion 2f2 of the metal shell 2, but also any of the surfaces facing the tip side of the metal shell 2.
Examples of the sensor include a temperature sensor in addition to various gas sensors that detect the concentration of a specific gas component.

DESCRIPTION OF SYMBOLS 1 Sensor 2 Main metal fittings 2u, 2u3 Front end direction surface of the main metal fitting 3 Inner protector 3e, 3e2 Rear end part of inner protector 3s Inner cylindrical part of inner protector 3u Inner bottom part of inner protector 4 Outer protector 4e Outer protector Rear end portion 4s Outer cylindrical portion of the outer protector 4u Outer bottom portion of the outer protector θ _T1 Taper angle of the rear end portion of the inner protector θ _T2 Taper angle of the front-facing surface of the metal shell

Claims (2)

A sensor element having a detection portion on the distal end side and extending in the axial direction, a cylindrical metal shell surrounding the outer peripheral surface of the sensor element while projecting the detection portion from the distal end, and an inner cylinder surrounding the outer peripheral surface of the detection portion Metal inner protector having an inner bottom portion that closes the distal end side of the inner cylindrical portion, the outer cylindrical portion surrounding the radial direction while being spaced apart from the inner cylindrical portion, and the outer cylinder In a sensor comprising a metal outer protector having an outer bottom portion that closes the distal end side of the shape portion,
The inner bottom part and the outer bottom part are in contact with each other, and the outer cylindrical part is joined to the metal shell,
The rear end portion of the inner cylindrical portion is enlarged or reduced in diameter toward the rear end side in the axial direction, and the rear end portion does not contact the outer cylindrical portion and faces the front end surface of the metal shell. Sensor in elastic contact.   The sensor according to claim 1, wherein a taper angle of the front-facing surface of the metal shell is larger than a taper angle of a rear end portion of the inner cylindrical portion.

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