JPS6110760A - Air/fuel ratio detection sensor - Google Patents

Abstract

PURPOSE:To improve the response of a sensor by a method wherein a cap- shaped protector is enclosed with a gas sensor body and a gas to be measured is introduced into an electrode section through an introduction hole of the protector so that more gas being measured is allowed to be introduced as separated farther from the electrode to keep the gas flow from hitting the electrode. CONSTITUTION:An electrode is provided on both sides of an oxygen ion conductor of an oxygen sensor body 1 and a narrow gap G is formed on an electrode contacting a gas to be measured to build a solid electrolytic pump 4. A sensor body 1 is enclosed with a cap-shaped protector 3. The protector 3 is provided with an introduction hole 13 and a deflection plate is mounted near the introduction hole 13 to introduce the gas being measured. Then, the introduction hole 13 is provided to the tip of the protector 3 from near the head side of the narrow gap G and the number thereof is increased so that more of the gas being measured is introduced as farther from the narrow gap G to adjust the angle theta of mounting the deflection plate 14. Thus, this keeps the sensor body from hitting a rapid gas flow thereby enabling the detection at a high accuracy.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The technical contents described in this specification are related to the improvement of gas sensors, especially oxygen sensors that are increasingly being used in exhaust gas atmospheres of internal combustion engines to detect air-fuel ratios. The aim is to propose the results of research and development aimed at improving responsiveness without the disadvantages associated with cooling the sensor body due to the flow of gas to be measured.
In a non-limiting sense, the field of industry generally includes technology related to the combustion of liquid or gaseous fuels, and in particular to the fueling of motor vehicles.

(Prior art) Japanese Patent Application Laid-Open No. 58-153155 discloses that a pair of elements each having an electrode layer provided on the front side of an oxygen ion conductive solid electrolyte plate is arranged in parallel with a narrow gap in between, and An oxygen sensor that uses a pump element and an oxygen concentration battery element has been developed, but when this sensor is put into practical use, for example, in the exhaust gas atmosphere of an internal combustion engine, it is strongly affected by strong air currents, so we will discuss protective measures for this sensor. It has not been done.

(Problem to be Solved by the Invention) Regarding the influence of airflow depending on the environment of the gas to be measured, generally speaking, even if a multi-hole cylindrical protector with many introduction holes is used, the gas may enter through the introduction holes. It is difficult to prevent the element from being cooled by heat removal due to the gas flow, and there is a problem in that the heat removal effect is undesirably enhanced, especially when an attempt is made to improve responsiveness.

(Means for solving the problem) For the purpose of improving responsiveness without the disadvantages associated with cooling the sensor body, (a) The above element, that is, the sensor body, should be arranged so that the gas flow does not directly hit it. (b) opening an inlet hole in the protector in the direction in which the gas flow circulates around the sensor body; (C) widening the opening of the inlet hole at a position that does not face the sensor body; Particularly advantageous are that (a) suppresses the heat removal effect due to the gas flow, (b) improves responsiveness while preventing heat loss, and (c) helps improve responsiveness. discovered.

FIG. 1 shows an air-fuel ratio detection sensor according to the present invention, where 1 is a sensor body, 2 is a mounting bracket, and 3 is a protector.

The sensor body L has electrodes on both sides of an oxygen ion conductor, and one electrode is placed in contact with the gas atmosphere to be measured within a narrow gap G, and diffusion is restricted by the narrow gap G. A solid electrolyte oxygen pump 4 According to the disclosure of JP-A No. 58-153155, another element having a similar structure is placed opposite to form the narrow gap to connect the narrow gap with the surrounding atmosphere. Preferably, the device is a pair of elements filled with a battery 5 useful for measuring the oxygen concentration ratio, and further includes a heater 6 disposed along the back of the solid electrolyte oxygen pump 4 as shown.

The sensor body 1 is mounted on the base side opposite to the front side of the narrow gap G, and the fastening screw 7 is installed inside the metal fitting 2, with a filling layer 8 made of a heat-resistant inorganic adhesive such as aluminum phosphate cement, It is fixed by a glass seal 9.

The oxygen pump 4 and the battery 5 are both made of, for example, a porous metal membrane containing a metal oxide having oxygen diffusion resistance on both sides of stabilized zirconia porcelain, or a porous refractory film having oxygen diffusion resistance. An electrode is provided with a coating of material.

The base side of the sensor body 1 opposite to the front side of the narrow gap G is buried and integrated in the glass seal 9 together with the connecting conductor 1o as shown in the figure.
For installation, the connecting wire 10 is pulled out to the outside under a waterproof seal with a sealing plug 12 made of heat-resistant rubber, for example, silicone rubber, which is caulked inside the joint pipe 11 fixed to the metal fitting 2.

The sensor body 1 is attached to the end of the fastening screw 7 of the metal fitting 7, communicating with the gas environment to be measured via the gas introduction hole 13.
A cap-shaped protector 3 is placed over the area.

Introductory hole] 3 introduces a swirling flow into the protector 3 near the tip of the narrow gap G, the amount of introduced gas increases as the distance from the tip side to the sensor main body 1 increases, and the deflection piece 14 will be established.

The deflection piece 14 is formed by cutting, bending or cutting by so-called punching in a press process so as to protrude inward in a tangential direction with respect to the inner circumference of the protector 3, which usually has a cylindrical shape. Here, the tip side of the sensor body 1 is in contact with or close to the plane perpendicular to the axis of the protector 3, including the tip side of the sensor body 1. It is important to make the deflection pieces 14 in the arrangement β that are farther away from the end of the protector 3 from the edge of the protector 3 larger. Rather, the cutting angle should be made smaller.

This angle is determined by the surface of the deflection piece 14 facing the introduction hole 13.
Defined by the intersection angle θ with respect to the tangent of the inner circumferential surface at the intersection with the inner circumferential surface of the protector 3 (see the sectional view taken along the line A-A in FIG. 1),
The arrangement α is set at 0 to 45°, and the arrangement β is set at 30 to 90°, so that the relationship is α × β.

For example, the deflection piece 14 has four semicircular introduction holes 13 with a radius of approximately 2 mm for the protector 3 having an inner diameter of about 10 mm, with respect to the arrangement α, in a direction along the generatrix direction of the protector 3, with the limit of the chord. Regarding the arrangement β, it is preferable that about 4 to 8 holes are arranged at equal intervals along the circumference of the protector 3 so that the opening edges of the introduction holes 13 in the arrangements α and β do not overlap. Incidentally, in this case, the overall length of the protector 3 is preferably about twice the height of the protrusion on the metal fitting 2, about 20 mm in the illustrated example, when mounting the sensor main body 1 with a width of about 4 mm.

(Function) The above configuration is installed in a gas environment to be measured, and by applying a negative voltage to the electrode facing the narrow gap of the oxygen pump 4 and a positive voltage to the electrode on the opposite side, oxygen is introduced into the solid electrolyte. The ions move and are pumped out from the narrow gap G, creating a difference in oxygen concentration between the ions and the measured gas environment.

This concentration difference generates an electromotive force in the battery 5, and this electromotive force is caused by the balance between the amount of oxygen flowing in and diffusing from the three open ends of the narrow gap G and the amount of oxygen pumped out by the oxygen pump 4 as described above. When the temperature reaches a constant temperature, the current value of the oxygen pump 4 converges to a constant value, so this equilibrium is maintained. Concentration can be determined.

Note that instead of the battery 5, an oxygen pump 4 may be used in which the narrow gap G is formed using a heat-insulating fire-resistant material with the electrode omitted, for example.
Detection of oxygen concentration using a single element is possible, for example, when a sufficiently high constant voltage is applied to the oxygen pump 4, and the current flowing through the pump at that time, that is, the amount of oxygen pumped out through the narrow gap, determines the oxygen concentration in the gas environment to be measured. The oxygen concentration can be measured by taking advantage of the fact that

In any case, if there is a strong airflow of the gas to be measured flowing in through the introduction hole 13 of the protector 3, the assumption of a constant temperature will collapse due to the heat removal effect.
By creating a swirling flow in the protector 3 through the above-mentioned arrangement of 3 and the appropriate arrangement of the deflection pieces, it is possible to effectively avoid an undesirable heat removal effect on the sensor body 1 due to the severe airflow of the gas to be measured, and to improve response. It makes a significant contribution to improving sexual performance.

(Example) As shown in Fig. 1, introduction holes 13 are arranged in a cap-like protector 3 having an inner diameter of 10 mm and a thin wall of 0.3 non, each having a semicircular opening with a radius of 2 mm and 4 holes for both α and β. are arranged at equal intervals on the circumference, and the bending angle θ of the deflection pieces 14 in the arrangement α is set to 25° (No. 1), and the example in which only the deflection pieces 14 in the arrangement β is changed to θ: 60° (No. ,2)
, and the arrays α and β are the same as No. 2, but an example in which a deflection piece 14 of θ; 10° is added to the array T (No. 3).
), the arrangement α and β are both circular punched holes with a radius of 2 mm, and the reference example (No. 4) without a deflection piece has a height that brings the sensor body l to a position corresponding to the tip side of the narrow gap G. A deflection array α9 surrounded by , and an array β9 sandwiching this above and below.

The TV introduction hole 13 is cut and bent or cut and raised at an angle θ.
: A reference example (No. 5) with a 25° deflection piece 14 and a reference example (No. 5) in which the arrangement α of Nα4 is eliminated and only β is provided.
, 6), and the results of comparing the performance according to the following conditions are summarized in Table 1. The arrangement of the introduction holes on each side is shown in FIGS. 2(a) to 2(e).

Test conditions Temperature measurement: A chromel-alumel thermocouple with a diameter of 0.32 mm was adhered to the electrode surface of the battery 5, and the surface temperature of the battery 5 was measured during the test using the resulting thermoelectromotive force.

Responsiveness + Attached to the exhaust pipe of a 2000cc gasoline injection engine, during operation at an average exhaust gas temperature of 450°C, the heater output is kept constant at 14 (15W), and the excess air ratio λ is set from 1.1 to the air-fuel ratio of the intake mixture. The response time when changing to 1.3 was investigated.

Note that this was derived from the gas flow rate. Regarding the variation in the instructions, the engine is warmed up from 700 to 11,000 rpm, approximately 600 rpm.
Based on the sensor output at low flow rate of j7/min, the exhaust gas flow rate is 3000 to 400, which is approximately 300017mln.
Compare the difference with the sensor output at high flow rate equivalent to 0 rpm,
Examined.

As is clear from this result, Reference Example No. 4. No,
5 has excellent responsiveness compared to Reference Example No. 6 and is within the practical range, but the temperature drop of the sensor body 1 is severe below 800 °C, and the dispersion of indications is large, which is a problem. In the example Nos. 1 to 3, the amount of heat removed from the sensor body 1 is reduced, and the responsiveness is improved.

Figure 3 shows the relationship between the temperature of the sensor body 1 and the temperature of the gas to be measured, which is suitable for oxygen concentration measurement, as shown in the example of Figure 1 (No.
, 1) and (No. 1) in Figure 2(d).
, 5) We compared curves (a) and (b) in the case of example, but since curve (b) is below the stable measurement area indicated by the broken straight line in the figure, the measured gas When the temperature is approximately 400° C. or lower, stable measurement becomes difficult, and the measurable range is narrow, making it difficult to put it into practical use.

In addition to the above, Figures 4 (a) and (b)
As shown in (c), the long slit-shaped introduction hole 13 spanning the arrays α and β is deflected into the protector 3 by a deflection piece 14 whose width increases as the distance from the sensor body 1 increases. In addition, in the case of a modification in which only the arrangement β is a simple circular hole, and in the case of a modification in which the number of introduction holes with semicircular deflection pieces is increased to 8 for the arrangement β, Examples 1 to Functions equivalent to those in 3 could be exhibited.

(Effects of the Invention) It is possible to improve responsiveness while avoiding undesired cooling of the sensor body under intense gas flow in the gas atmosphere to be measured.

[Brief explanation of the drawing]

FIG. 1 is a sectional view, FIG. 2 is an external front view of the main part, FIG. 3 is a graph 1 of the relationship between the sensor body temperature and the measured gas temperature, and FIG. 4 is an external front view of a modified example. G...Gap 1...Sensor body 2...
・Mounting with metal fittings 3...Protector 13...Introduction hole 14...Deflection piece.

Claims (1)

[Claims] 1. Among the electrodes formed on both sides of the oxygen ion conductor, one electrode is placed in contact with the gas to be measured that enters the narrow gap, and the narrow gap is used to restrict diffusion. An air-fuel ratio detection sensor comprising a sensor body that uses a solid electrolyte oxygen pump subjected to the above-mentioned narrow gap, and a mounting bracket that holds and fixes the base side of the sensor body opposite to the front side of the narrow gap, the air-fuel ratio detection sensor comprising: A cap-shaped protector that communicates through the gas introduction hole and surrounds the sensor body is placed over the mounting bracket, and the gas is introduced into the gas introduction hole near the tip of the narrow gap as it becomes farther away from the sensor body from the tip. An air-fuel ratio detection sensor characterized by being provided with a deflection piece that guides a swirling flow that increases the amount of gas into a protector. 2. The deflection piece is cut and bent or cut and raised;
1. The sensor according to 1. 3. The sensor according to 1 or 2, wherein the introduction hole of the protector is arranged to open in contact with or close to a plane including the front side of the narrow gap. 4. The sensor according to any one of 1 to 3, wherein the introduction holes are arranged in alternate double rows. 5. The sensor according to 4, wherein the bending or cutting angle of the deflection piece is such that the angle in contact with a plane including the front side of the narrow gap is minimized, and increases as the distance from the front side to the sensor body increases.