JPH0473100B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) Gas sensors, especially oxygen sensors, are increasingly being used in exhaust gas atmospheres of internal combustion engines to detect air-fuel ratios. The purpose is to propose the results of research and development aimed at improving responsiveness without the disadvantages associated with cooling the sensor body, and in a non-limiting sense, it refers to technologies related to the combustion of liquid or gaseous fuels in general, and to fuel supply for automobiles in particular. It is positioned in an industrial field that includes (Prior art) JP-A-58-153155 discloses a pair of elements each having an electrode layer formed on both sides of the tip side of an oxygen ion-conductive solid electrolyte plate, and a pair of elements arranged between the electrodes facing each other. An oxygen sensor has been developed in which an oxygen pump element and an oxygen concentration battery element are installed parallel to each other with a narrow space between them. There is no mention of protective measures for areas that are strongly affected by this. (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 loss due to the gas flow, and there is a problem in that, in particular, when trying to improve responsiveness, the heat removal effect is undesirably enhanced. (Means for solving the problem) For the purpose of improving the response without the disadvantage of 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; It has been found that (a) is particularly advantageous in that it suppresses the heat removal effect caused by the gas flow, (b) improves responsiveness while preventing heat removal, and (c) helps improve responsiveness. Served. FIG. 1 shows an air-fuel ratio detection sensor according to the present invention, in which 1 is a sensor body, 2 is a mounting bracket, and 3 is a protector. The sensor body 1 consists of a pair of elements each having electrodes formed on both sides of an oxygen ion conductive solid electrolyte plate (hereinafter simply referred to as an ion conductor). In order to make contact with the gas atmosphere to be measured within the narrow G
It is assumed that a solid electrolyte oxygen pump 4 and an oxygen concentration battery 5 whose diffusion is restricted by G are used. Furthermore, it is preferable to include a heater 6 disposed along the back of the solid electrolyte oxygen pump 4 as shown in the figure. The sensor body 1 has a filling layer 8 made of a heat-resistant inorganic adhesive such as aluminum phosphate cement, and glass inside a mounting bracket 2 provided with a fastening screw 7 on the base side opposite to the tip side of the narrow G. It is fixed by a 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 material having oxygen diffusion resistance. The electrode is coated with On the base side of the sensor body 1 opposite to the tip side of the narrow gap G, there is a glass seal 9 along with a connecting conductor 10 as shown in the figure.
Joint pipe 11 embedded in and fixed to mounting bracket 2
The connecting wire 10 is led out under a waterproof seal made of a sealing plug 12 made of heat-resistant rubber, for example, silicone rubber, which is caulked inside. The end of the fastening screw 7 of the mounting fitting 7 is covered with a cap-shaped protector 3 that communicates with the gas environment to be measured through the gas introduction hole 13 and surrounds the sensor body 1. The introduction hole 13 is provided with a deflection piece 14 near the front end of the narrow gap G, which guides a swirling flow into the protector 3 in which the amount of introduced gas increases as the distance from the front end to the sensor main body 1 increases. The deflecting piece 14 is formed by cutting, bending or cutting by so-called punching in a press process so as to protrude inward in the connection direction from the inner periphery of the normally cylindrical protector 3. 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 that of the deflection pieces 14 of the arrangement β larger, which are farther away from the edge of the protector 3 (as in FIG. 2b)
Furthermore, when the deflecting pieces are provided in the array γ surrounding the sensor main body 1, the angle of cutting and bending is rather smaller. This angle is defined as the intersection angle θ of the surface of the deflection piece 14 facing the introduction hole 13 with the tangent to the inner circumferential surface of the protector 3 at the intersection point (see the sectional view taken along the line A-A in FIG. 1). , 5 to 45 degrees for the array α and 30 to 90 degrees for the array β, so that the relationship α<β is established. The deflection piece 14 has a semicircular introduction hole 13 with a radius of about 2 mm for the protector 3 with an inner diameter of about 10 mm, for example.
Assuming that the chord is limited in the direction along the generatrix direction of the protector 3, about 4 strings are set for the array α, and about 4 to 8 strings are set for the array β at equal intervals along the circumference of the protector 3. It is preferable to arrange the opening edges of the introduction holes 13 in the arrays α and β so that they do not overlap. Incidentally, in this case, the total length of the protector 3 is approximately 2 times the protrusion height on the mounting bracket 2 of the sensor body 1, which has a width of approximately 4 mm.
In the illustrated example, it is preferably about 20 mm. (Function) When installed in the gas environment to be measured with the above configuration,
For example, if the electrode facing the narrow gap of the oxygen pump 4 has a negative
By applying a positive voltage to the electrode on the opposite side, oxygen ions move within the solid electrolyte and close the narrow gap G.
There is a difference in oxygen concentration between the gas and the measured gas environment. This concentration difference generates an electromotive force in the battery 5, and this electromotive force is caused by the difference between the amount of oxygen flowing in and diffusing from the three open ends of the narrow gap G and the amount of oxygen being pumped out as described above by the oxygen pump 4. Oxygen pump 4 that maintains this equilibrium because it converges to a constant value when equilibrium is reached.
By adjusting the current, the current value is approximately proportional to the oxygen concentration in the gas environment to be measured at a substantially constant temperature, so the oxygen concentration can be determined. Note that detection of the oxygen concentration using only the oxygen pump 4 as an element in which a heat-insulating refractory material with its electrodes omitted is used to form the narrow gap G instead of the battery 5 is, for example, a sufficiently high constant value for the oxygen pump 4. The oxygen concentration can be measured by applying a voltage of . 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 appropriately arranging the pieces to generate swirling flow within the protector 3, undesirable heat removal effects on the sensor body 1 due to the unreliable airflow of the gas to be measured can be effectively avoided, and responsiveness is improved. makes a significant contribution to (Example) According to Fig. 1, a thin cap-shaped protector 3 with an inner diameter of 10 mm and a wall thickness of 0.3 mm has four arrays for both α and β.
To this end, the introduction holes 13 each having a semicircular shape with a radius of 2 mm are arranged at equal intervals on the circumference, and the bending angle θ of the deflection pieces 14 of the arrangement α is 25°.
Example (No. 1) where the cutting angle θ of 4 is 45°, the arrangement β
An example (No. 2) in which only the deflection piece 14 is changed to θ: 60°, and the arrangement α and β are the same as No. 2, but the arrangement γ is
For the example (No. 3) in which a deflection piece 14 with θ: 10° is added, the arrangement α and β are circular punched holes with a radius of 2 mm, and the reference example (No. 4) without a deflection piece and the sensor The introduction holes 13 of the deflection array α _v that surrounds the main body 1 at a height corresponding to the front side of the narrow gap G and the arrays β _v and γ _v that sandwich this above and below are both bent or cut. Reference example (No. 5) with deflection piece 14 with angle θ: 25°
Table 1 summarizes the results of comparison with Reference Example (No. 6) in which the sequence α and No. 4 were omitted and only β was used, and the performance according to the following conditions was compared. The introduction hole arrangement of each of the above examples is shown in FIGS. 2a to 2e. 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 resulting thermoelectromotive force was used to measure the surface temperature of the battery 5 during the test. Responsiveness: Attached to the exhaust pipe of a 2000c.c. gasoline injection engine, during operation at an average exhaust gas temperature of 450°C, the heater output is constant at 14V and 15W, and the excess air ratio λ is from 1.1 to the air-fuel ratio of the intake mixture. We investigated the response time when changing to 1.3. Regarding the dispersion of the indication due to the gas flow rate, the engine is warmed up from 700 to 1000 rpm, approximately 600 rpm.
/min Based on the sensor output at low flow rate, 3000 to 4000 rpm, where the exhaust gas flow rate is approximately 3000/min.
We compared and investigated the difference with the sensor output at a considerably high flow rate.

[Table] As is clear from this result, Reference Examples No. 4 and No. 5
In this case, the response is superior to Reference Example No. 6 and is within the practical range, but the temperature of the sensor body 1 drops significantly below 800℃, and the air-fuel ratio (A/F)
However, in Examples Nos. 1 to 3, there is less heat dissipated from the sensor body 1, and the response 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, in the example (No. 1) in Figure 1 and in the case (No. 5) in Figure 2 d. In the case of the example, curves A and B were compared,
Since curve B is below the stable measurement area shown by the straight line shown in the figure with a broken line, stable measurement becomes difficult when the gas temperature to be measured is approximately 400℃ or less.
The measurable range is narrow and it is difficult to put it into practical use. In addition to the above, as shown in FIGS. 4a, b, and c, the long slit-shaped introduction holes 13 spanning the arrays α and β are deflected so that the width of the holes increases as the distance from the sensor body 1 increases. When guiding the circular flow into the protector 3 with the piece 14, the arrangement β
In the case of a modification in which only a simple circular hole is used for the arrangement β, and in the case of a modification in which the number of introduction holes with semicircular deflection ends is increased to 8 for the arrangement β, the same function as in Examples 1 to 3 is exhibited. could have been done. (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 drawings]

Figure 1 is a sectional view, Figure 2 is a front view of the main parts,
FIG. 3 is a graph showing the relationship between the temperature of the sensor body and the temperature of the gas to be measured, and FIG. 4 is an external front view of a modified example. G...Gap, 1...Sensor body, 2...Mounting bracket, 3...Protector, 13...Introduction hole, 14
...Deflection piece.

Claims (1)

[Claims] 1. Consists of a pair of elements in which electrodes are formed on both sides of an oxygen ion-conducting solid electrolyte plate, a narrow space is provided between the mutually facing electrodes of both elements, and a narrow space is provided within this narrow space. The sensor body, which uses a solid electrolyte oxygen pump and oxygen concentration battery, whose diffusion is restricted by the constriction, is placed in contact with the invading gas to be measured, and the base side of the sensor body opposite to the tip of the constriction is held and fixed. The air-fuel ratio detection sensor is constructed by combining a mounting bracket with a cap-shaped protector that surrounds the sensor body in communication with the gas environment to be measured through an inlet hole for the gas, and covers the mounting bracket. is characterized in that a deflection piece is provided near the tip of the narrow hole to guide the swirling flow from the introduction hole into the protector, the amount of gas being introduced increases as the distance from the tip side to the sensor body increases. Air-fuel ratio detection sensor. 2 The deflection piece is cut and bent or cut and raised. A sensor according to claim 1. 3. The sensor according to claim 1 or 2, wherein the introduction holes of the protector are arranged to open in contact with or in close proximity to a plane including the narrow end side. 4. The sensor according to any one of claims 1 to 3, wherein the introduction holes are arranged in alternate double rows. 5. Claim No. 5, wherein the bending or cutting angle of the deflection piece in contact with a plane including the tip side of the narrow end is minimized, and the angle becomes larger as it moves away from the tip side to the sensor body. The sensor according to item 4.