JP4165411B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor that detects a specific gas component in a gas to be measured, for example, a gas sensor used for an air-fuel ratio sensor that detects an air-fuel ratio from an oxygen concentration contained in engine exhaust gas.

  Conventionally, in a vehicle, an oxygen concentration sensor is attached to an exhaust pipe in order to detect an oxygen concentration contained in exhaust gas from an engine. The detection output of the oxygen concentration sensor is taken into the electronic control unit, and the air-fuel ratio is calculated from this oxygen concentration. Then, the engine is controlled so that the air-fuel ratio matches a target value (for example, the theoretical air-fuel ratio).

  The gas sensor includes a rod-shaped detection element having a detection surface near the tip and a protective cover having a double-pipe structure covering the detection element. With such a configuration, the detection element is protected from exhaust gas dirt, condensed water, and the like, and deterioration of detection accuracy due to adhesion of the detection element to the sensor detection surface is prevented.

JP 2000-171430 A JP-A-1-296159 Japanese Patent Laid-Open No. 10-253576 JP 2003-43002 A JP-A-10-10084

  However, when the protective cover has a double tube structure as described above, sufficient exhaust gas may not be supplied to the sensor detection surface. For example, when the gas sensor is attached to a position where the flow of exhaust gas is weak in the exhaust pipe, or when the exhaust gas flows backward due to exhaust pulsation and the negative pressure near the exhaust gas intake varies greatly. Thus, when sufficient exhaust gas is not supplied to the sensor detection surface, the responsiveness and output characteristics of the gas sensor are deteriorated.

  The present invention has been made in view of the above-described circumstances, and sufficiently supplies a gas to be measured to the detection surface of the gas sensor without depending on the external environment where the gas sensor is placed, and has stable response and output characteristics. The purpose is to obtain.

  In order to achieve the above-described object, the present invention configures a gas sensor as described below.

  A gas sensor according to the present invention includes a detection element having a detection surface and a protective cover that covers the detection element, and the protective cover includes an inner cover having a vent hole at a position facing the detection surface, and a tip. And a gap formed between the inner cover and the outer cover in a direction in which the vent hole of the inner cover is arranged from other directions. Is also widened.

  With such a configuration, the gas to be measured introduced from the tip of the outer cover is supplied to the detection surface from the vent hole of the inner cover via the widened gap. Therefore, even when the measurement gas introduced from the tip is small, the measurement gas is preferentially guided to the sensor detection surface, so that stable response and output characteristics of the gas sensor can be obtained.

  Said gas sensor is comprised by the following aspect, for example. That is, by offsetting the axis of the inner cover and the axis of the outer cover, the gap formed between the inner cover and the outer cover is different in the direction in which the vent holes of the inner cover are arranged. It is wider than the direction.

  Moreover, you may comprise said gas sensor with the following aspect. In other words, the inner cover has a circular tube shape, and a part of the circular tube shape is formed into a flat shape so that the air gap formed between the inner cover and the outer cover is disposed in the air hole of the inner cover. In the direction to be performed, the width is wider than the other directions.

  In the gas sensor described above, it is preferable that a vent hole formed at a position facing the detection surface of the inner cover is disposed close to the detection surface. Thereby, more stable sensor response and output characteristics can be obtained.

  Hereinafter, a gas sensor according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a gas sensor that detects the oxygen concentration in the exhaust gas is taken as an example.

  First, the gas sensor according to the first embodiment will be described. FIG. 1A shows a longitudinal sectional view of the gas sensor, and FIG. 1B shows a transverse sectional view. In addition, although the base end of the gas sensor is fixed to the exhaust pipe in the upper part of FIG.

  The gas sensor mainly includes a rod-shaped detection element 10 and protective covers 20 and 40 covering the detection element 10. The protective cover has a double tube structure including the inner cover 20 and the outer cover 40.

  The detection element 10 extends downward from a base end fixed to the exhaust pipe, and a detection surface 12 for detecting the oxygen concentration in the exhaust gas is formed in the vicinity of the lower front end portion thereof. In a general oxygen sensor, a pair of electrodes is provided in a sensor element portion formed of a fixed electrolyte such as zirconia, and a detection signal corresponding to the oxygen concentration of a detection gas in contact with the sensor element portion is output from these electrodes. Is done.

  The protective cover having a double-pipe structure includes an inner cover 20 and an outer cover 40. Each of the inner cover 20 and the outer cover 40 has a circular tube shape, and extends downward around the detection element 10. The outer cover 40 does not change in cross-sectional shape from the proximal end to the distal end. Near the tip of the side surface 42, a plurality of (six in this embodiment) vent holes 46 are formed at predetermined angles, and a vent hole 48 is also formed at the center of the tip surface 44.

  Further, the base end side 22 of the inner cover 20 has a circular tube shape having substantially the same diameter as the outer cover 40 and is fixed in contact with the inner periphery of the side surface of the outer cover 40. The distal end side 24 has a radius smaller than that of the outer cover 40 (in this embodiment, about two-thirds) and has a circular tube shape whose axis is offset in the horizontal direction with respect to the outer cover 40. A gap is formed between the inner periphery of the side surfaces. A plurality of (six in this embodiment) vent holes 30 are formed around the sensor detection surface 12 at predetermined angles on the side surface 26 of the inner cover 20, and one vent hole is formed at the center of the front end surface 28. 32 is formed.

  In the gas sensor having the structure described above, the exhaust gas flowing in the exhaust pipe flows into an intermediate chamber formed between the inner cover front end surface 28 and the outer cover front end surface 44 at the front end of the protective cover. The exhaust gas flows in from the upstream side vent hole 46A, flows through the intermediate chamber, and flows out from the downstream side vent hole 46B. Due to the flow of the exhaust gas outside the gas sensor, a negative pressure is generated in the vicinity of the vent hole 48 in the outer cover front end surface 44 in the intermediate chamber, and a part of the exhaust gas in the intermediate chamber flows out from the vent hole 48. Also, due to this flow, a negative pressure is generated in the vicinity of the vent hole 32 of the inner cover front end face 28 in the inner cover, and the exhaust gas in the inner cover 20 flows out into the intermediate chamber.

  Further, the remaining part of the exhaust gas that has not flowed out of the vent holes 46B, 48 flows from the distal end toward the proximal end in the gap formed between the inner cover side surface 26 and the outer cover side surface 42, and the inner cover side surface 26 The plurality of vent holes 30 are reached. At this time, since the gap between the inner cover side surface 26 and the outer cover side surface 42 is particularly widened in the direction in which the sensor detection surface 12 faces, there is little resistance and the flow rate of exhaust gas is large. Therefore, a large amount of exhaust gas flows into the inner cover 20 through the two vent holes 30 at the positions where the sensor detection surface 12 faces. The inflowing exhaust gas then flows toward the front end and flows out from the vent hole 32 of the inner cover front end surface 28 to the intermediate chamber.

  The characteristic feature of the gas sensor according to the first embodiment described above is that the axial center of the outer cover 40 and the inner cover 20 is offset in the horizontal direction, so that the side gap is widened in the direction in which the sensor detection surface 12 faces. In other words, the exhaust gas is sufficiently supplied to the sensor detection surface 12 through the vent hole 30 facing the sensor detection surface 12. As a result, even when the amount of exhaust gas flowing into the intermediate chamber is small, the exhaust gas can be preferentially guided to the sensor detection surface 12 to obtain stable sensor response and output characteristics. As a result, the detection accuracy of the air-fuel ratio of the engine is improved, and the control accuracy to the theoretical air-fuel ratio is also improved.

  In the present embodiment, the sensor detection surface 12 and the inner cover side surface 26 are brought closer to each other by offsetting the axis of the inner cover 20 while keeping the axis of the outer cover 40 aligned with the axis of the detection element 10. I am letting. Thereby, the sensor detection surface 12 is close to the vent hole 30, and a large amount of exhaust gas is supplied to the sensor detection surface 12, so that more stable sensor response and output characteristics can be obtained.

  Next, a gas sensor according to a second embodiment will be described. FIG. 2A shows a longitudinal sectional view of the gas sensor, and FIG. 2B shows a transverse sectional view of the gas sensor. The gas sensor of the second embodiment has a structure similar to that of the first embodiment, but the shape of the tip side of the inner cover is different from that of the first embodiment.

  In the second embodiment, the axial center of the inner cover front end side coincides with the axial center of the detection element 10, and the circular inner cover side surface 62 is planar in the direction in which the sensor detection surface 12 faces. As a result, the gap between the inner cover side surface 62 and the outer cover side surface 42 is widened. A vent hole 64 is formed at a position facing the sensor detection surface 12 of the flat inner cover side surface 62. Also in this embodiment, since exhaust gas is sufficiently supplied to the sensor detection surface 12 through the widened side gap, stable sensor response and output characteristics can be obtained.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made within an equivalent range.

  For example, in the embodiment described above, the exhaust gas is the gas to be measured, but the gas to be measured is not limited to the exhaust gas but may be other types of gases. In the embodiment described above, the gas sensor detects the oxygen concentration, but may detect other types of gases such as NOx.

It is the longitudinal direction sectional view and transverse direction sectional view showing the gas sensor concerning a first embodiment. It is the longitudinal direction sectional view and transverse direction sectional view showing the gas sensor concerning a second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Detection element, 12 Sensor detection surface, 20 Inner cover, 22 Base end side, 24 Front end side, 26 Side surface, 28 Front end surface, 30, 32 Vent hole, 40 Outer cover, 42 Side surface, 44 Front end surface, 46, 48 Pores.

Claims (3)

A gas sensor comprising a detection element having a detection surface and a protective cover covering the detection element,
The protective cover has a double tube structure including an inner cover having a vent hole at a position facing the detection surface, and an outer cover for introducing a gas to be measured from the tip.
The gap formed between the inner cover and the outer cover is wider than the other direction in the direction in which the vent holes of the inner cover are arranged,
A gas sensor, wherein a gas to be measured introduced from a tip of the outer cover is supplied to the detection surface from a vent hole of the inner cover via the widened gap. The gas sensor according to claim 1,
By offsetting the shaft center of the inner cover and the shaft center of the outer cover, the gap formed between the inner cover and the outer cover is larger than the other direction in the direction in which the vent hole of the inner cover is arranged. The gas sensor is also widened. The gas sensor according to claim 1,
The inner cover has a circular tube shape, and a part of the circular tube shape is formed into a flat shape so that a gap formed between the inner cover and the outer cover is provided with a vent hole of the inner cover. A gas sensor that is wider in the direction than in other directions.

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