JPH10170473A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heating efficiency of a heater set at an element part of an oxygen sensor. SOLUTION: A cover 22 of an oxygen sensor 20 consists of an outer cover 25 having an upper end part fixed to a housing 23 and an inner cover 26 covering a leading end part of an element part 21. The element part 21 has a heater. Recessed parts 36, 37 are formed at side faces of the element part 21. A peripheral edge part of a fitting hole 34 is fitted in each recessed part 36, 37 at the inner cover 26. The inner cover 26 is mounted to the element part 21 in a manner never to drop. The inner cover 26 is in touch with only the element part 21 and not in touch with the outer cover 25 and housing 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes an element portion for detecting oxygen concentration having a heater, and a cover having a double structure provided so as to cover the element portion. The present invention relates to an oxygen sensor which is activated by heating it.

[0002]

2. Description of the Related Art In a general oxygen sensor, a pair of electrodes is provided on an element portion formed of a fixed electrolyte such as zirconia, and detection is performed according to the oxygen concentration of a detection gas coming into contact with the element portion from each electrode. A signal is output. Further, a heater is provided in the element portion, and the element portion is heated by the heat of the heater, and is activated at a predetermined activation temperature (for example, 700 ° C.).
By raising the temperature to, a stable output of the detection signal becomes possible.

[0003] For example, in the air-fuel ratio control of an engine, the oxygen concentration of exhaust gas is detected by an oxygen sensor attached to an exhaust pipe. Then, the electronic control unit of the engine controls the engine such that the air-fuel ratio calculated from the oxygen concentration matches the target value.

[0004] In an engine equipped with an exhaust gas recirculation device (EGR device) or a blow-by gas reduction device (PCV device), an oxygen sensor is also attached to the intake pipe of the engine. A method of improving the control accuracy of the air-fuel ratio control by referring to the concentration and the oxygen concentration of the exhaust gas together has been taken.

By the way, such an oxygen sensor is usually provided with a cover for covering the element portion. The element portion is protected by the cover, thereby preventing the element portion from being damaged. Furthermore, covering the element portion with the cover is effective in improving the heating efficiency of the heater because the heat of the heater can be prevented from being transmitted from the element portion to the outside.

As a configuration relating to the cover for the oxygen sensor as described above, a configuration having a double structure has been conventionally known (for example, "Oxygen sensor" described in Japanese Patent Application Laid-Open No. 5-26842). .

FIG. 4 shows an example of the configuration of an oxygen sensor 100 having a double-structured cover. As shown in the figure,
The cover 101 is composed of an outer cover 102 and an inner cover 103 each having a bottomed cylindrical shape. Outer cover 10
2 is fixed to the housing 104 of the oxygen sensor 100. An inner cover 103 is arranged inside the outer cover 102 so as to cover an element portion 105 having a heater (not shown). The bottom of the inner cover 103 is the outer cover 10
2 is fixed by welding or the like. An air layer 106 is formed between the side walls of the inner cover 103 and the outer cover 102. In such an oxygen sensor 100, the heat insulation of the cover 101 can be further improved by the air layer 106.

[0008]

However, in the conventional oxygen sensor 100, the heat of the inner cover 103, which becomes high in temperature, propagates from the outer cover 102 to the housing 104, and does not contribute to the temperature rise of the element portion 105. Therefore, the heating efficiency of the heater is reduced by the heat loss, and the current consumption of the heater must be increased in order to heat the element portion 105 to the activation temperature. In addition, due to such an increase in current consumption,
There is also a risk that the temperature of the heater becomes high and its useful life is shortened.

For example, in an oxygen sensor attached to an exhaust pipe of an engine, the temperature of the exhaust gas is usually about 600.
The heat loss is relatively small since it reaches ~ 900 ° C. On the other hand, in the oxygen sensor attached to the intake pipe, the heat loss is extremely large because the temperature of the intake air is 200 ° C. or less even if, for example, the EGR gas is mixed. As a result, the current consumption of the heater is significantly increased.

The present invention has been made in view of the above circumstances, and an object thereof is to improve the heating efficiency of a heater provided in an element portion of an oxygen sensor.

[0011]

In order to achieve the above object, the present invention provides an oxygen concentration detecting element having a heater, an inner cover provided to cover the element,
In an oxygen sensor including an outer cover provided on the outer periphery of the inner cover, the inner cover is attached to the element so as to contact only the element.

In the above configuration, the heater generates heat when energized, and the element is heated by the heat to increase the temperature, thereby activating the element. Further, the heat of the heated element portion is transmitted to the inner cover, so that the temperature of the inner cover becomes high. Since the inner cover contacts only the element portion, the amount of heat released from the cover to the outside via other members such as the outer cover is extremely small.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a diesel engine E.
An embodiment embodied in an oxygen sensor used for GR feedback control will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of a diesel engine system according to this embodiment. As shown in FIG. 1, an intake pipe 12 is connected to the diesel engine 11, and intake air is introduced into a combustion chamber (not shown) of the engine 11 through the pipe 12. A throttle valve 13 provided in the intake pipe 12 controls the amount of intake air introduced into the combustion chamber. In the combustion chamber, fuel injected from an injector (not shown) and intake air are mixed, and the air-fuel mixture burns, so that a driving force is obtained for the engine 11. After the combustion, the exhaust gas is introduced into the exhaust pipe 14 from the combustion chamber and then discharged outside through a catalyst or the like (not shown).

The engine 11 is provided with an exhaust gas recirculation device (EGR device) 15. The EGR device 15 includes an EGR passage 16 that communicates the exhaust pipe 14 with the intake pipe 12 downstream of the throttle valve 13, and a flow control valve 17 provided in the passage 16. Part of the exhaust gas in the exhaust pipe 14 passes through the EGR passage 16 and passes through the intake pipe 12
Will be returned within. The flow control valve 17 is controlled by an electronic control unit (not shown) of the engine 11 so that the EG is controlled.
The amount of exhaust gas passing through the R passage 16 is adjusted.

An oxygen sensor 20 is attached to the intake pipe 12 at a position downstream of the opening of the EGR passage 16, and a tip of the oxygen sensor 20 projects into the intake pipe 12. The oxygen sensor 20 detects the oxygen concentration of the intake air including the air that has passed through the throttle valve 13 and the EGR gas introduced into the intake pipe 12 through the EGR passage 16 and outputs a detection signal to the electronic control unit. The electronic control unit executes EGR feedback control of the engine 11 based on a detection signal from the oxygen sensor 20.

FIG. 2 is a sectional view showing the tip side of the oxygen sensor 20. As shown in the figure, the oxygen sensor 20 includes an element portion 21 and a cover 22 having a double pipe structure provided so as to cover the outer periphery of the element portion 21. The element section 21 is fixed to the housing 23 of the oxygen sensor 20.

The cover 22 in the present embodiment comprises an outer cover 25 whose upper end is fixed to the housing 23 and an inner cover 26 provided on the tip side of the element section 21. A plurality of introduction holes 30 and 31 are formed in side and bottom surfaces of the outer cover 25 and the inner cover 26. In the present embodiment, the diameter of the introduction hole 30 of the outer cover 25 is set to be larger than that of the introduction hole 31 of the inner cover 26. On the other hand, the diameter of the introduction hole 31 of the inner cover 26 is set to be small so as to offset a decrease in heat retention due to an increase in the diameter of the introduction hole 30 of the outer cover 25. The intake air flowing through the intake pipe 12 is supplied to the introduction holes 30 and 3.
1 and is introduced into the inside of the inner cover 26 and comes into contact with the front end portion (lower portion in FIG. 2) of the element portion 21.

FIG. 3 is a perspective view showing only the element portion 21 and the inner cover 26. As shown in FIG.
It has a structure in which a substrate 27 made of zirconia, a frame plate 28, and a plate-shaped heater 29 are sequentially stacked, and has a substantially quadrangular prism shape as a whole.

A heating element (not shown) is buried in a tip portion of the heater 29. The heating element generates heat when energized by the electronic control unit, and the heat of the heating element heats the front end portion of the element section 21 to an activation temperature (about 70 ° C.).
0 ° C.).

On the inner and outer surfaces of the substrate 27, platinum electrodes 33 (only the platinum electrodes provided on the outer surface are shown in the figure) are provided. Each electrode 33 is connected to the electronic control unit via a lead (only a lead provided on the outer surface of the substrate 27 is shown) 33a. When the intake air comes into contact with the outer surface of the substrate 27, a detection signal corresponding to the oxygen concentration of the intake air is output from each electrode 33 to the electronic control unit via the lead 33a.

As shown in FIG. 2 and FIG.
Has a hollow box shape, and is formed by joining a pair of half bodies 26a and 26b. The upper surface of the inner cover 26 (FIGS. 2 and 3)
Is formed with a mounting hole 34. In addition, concave portions 36 and 37 are formed on both side surfaces of the element portion 21, respectively. The inner cover 26 is attached to the element portion 21 so as not to fall off by locking the peripheral portion of the mounting hole 34 with the concave portions 36 and 37. The inner cover 26 attached in this manner covers the entire distal end portion of the element section 21 where the heating element is provided.

In the present embodiment, the inner cover 26 is in contact only with the element portion 21 and is not in contact with the outer cover 25 and the housing 23. Also, as shown in FIG.
The element portion 21 does not contact the side surface and the bottom surface of the inner cover 26, and a gap is formed between the two. Similarly,
A gap is formed over the entire circumference between the peripheral portion of the mounting hole 34 in the inner cover 26 and the outer peripheral surface of the element portion 21 where the concave portions 36 and 37 are formed. For this reason, in the present embodiment, even when the element portion 21 thermally expands due to the heat of the heater 29, the thermal expansion is not restricted by the inner cover 26, and the shape change of the element portion 21 is allowed. It has become.

Next, the operation and effects of this embodiment will be described. When the temperature of the distal end portion of the element section 21 rises due to the heat of the heater 29, a large amount of heat is transmitted to the inner cover 26 from the upper portion, and the temperature of the cover 26 becomes high. In the present embodiment, since the inner cover 26 does not contact the outer cover 25 and the housing 23 but only contacts the element portion 21, the inner cover 26 is discharged from the inner cover 26 to the outside via the outer cover 25 and the like. The amount of heat becomes extremely small. Therefore,
Since the heat retention performance of the inner cover 26 is improved and the temperature drop of the element section 21 is suppressed, the heating efficiency of the heater 29 can be improved. As a result, the current consumption of the heater 29 can be reduced, and the activation time of the element section 21 can be shortened and a stable activation state can be maintained.

In this embodiment, as described above,
Even when the element section 21 thermally expands due to the heat of the heater 29, the thermal expansion is not restricted by the inner cover 26. Therefore, it is possible to prevent the thermal stress from acting on the element portion 21 due to the thermal expansion. For this reason, it is possible to prevent the element portion 21 from being damaged, such as a crack, due to the thermal stress.

Further, in this embodiment, since the inner cover 26 is formed in a shape that covers only the tip side portion of the element portion 21, for example, as compared with the conventional inner cover 103 shown in FIG. The miniaturization is achieved. Therefore, the surface area of the inner cover 26 decreases, and the amount of heat radiated from the cover 22 decreases. Therefore, according to the present embodiment, the heating efficiency of the heater 29 can be further improved.

By the way, during intake including EGR gas,
Deposits made of carbon, oil, etc. are included. When the deposits adhere to and accumulate on the surfaces of the outer cover 25 and the inner cover 26, the introduction holes 30 and 31 of the covers 25 and 26 may be clogged. When the temperature of the covers 25 and 26 is high, most of the deposited deposits are burned and removed. Therefore, particularly when the temperature of the covers 25 and 26 is low, the clogging as described above occurs. It is more likely to occur.

In this respect, in the present embodiment, the diameter of the introduction hole 30 of the outer cover 25 is set to be large, and the diameter of the introduction hole 31 of the inner cover 26 is reduced so as to offset the decrease in heat insulation performance. You have set. Therefore, even if the deposit adheres to the low-temperature outer cover 25, the diameter of the introduction hole 30 is increased, so that the hole 30 is not clogged. On the other hand, the inner cover 26 is kept at a high temperature because the amount of heat transfer to the outside is small as described above. Therefore, even if the deposit adheres to the inner cover 26, the deposit is burned and removed, so that the clogging of the introduction hole 31 does not occur like the outer cover 25.

As described above, according to the present embodiment, since the diameters of the introduction holes 30, 31 are set according to the temperatures of the covers 25, 26, clogging of the introduction holes 30, 31 due to the deposit is prevented. be able to.

The present invention can be embodied as other embodiments described below. According to these other embodiments, substantially the same functions and effects as those of the above embodiments can be obtained. (1) In the above embodiment, the concave portions 36 and 37 are formed in the element portion 21.
, And the inner cover 26 is attached to the concave portions 36 and 37. The mounting structure of the cover 26 may be any structure as long as the inner cover 26 does not contact other members other than the element portion 21 and allows the element portion 21 to thermally expand. For example, instead of the concave portions 36 and 37, the element portion 21
May be provided on both side portions of the inner cover 26, and the inner cover 26 may be locked by the convex portions.

(2) In the above embodiment, the present invention is embodied in the oxygen sensor 20 attached to the intake pipe 12 of the diesel engine 11. On the other hand, the present invention can be embodied as an oxygen sensor attached to an exhaust pipe 14 of a diesel engine 11 or an intake pipe or an exhaust pipe of a gasoline engine. Further, the present invention is not limited to an engine, but may be applied to an oxygen sensor used in various combustion devices.

(3) In the above embodiment, the oxygen sensor 20 having the element portion 21 having the laminated structure is used.
1 may for example be of the test tube type. (4) In the above embodiment, the present invention is embodied in the oxygen sensor 20 used in the engine 11 having the EGR device 15, but may be embodied in the oxygen sensor used in the engine having the PCV device described above. it can.

The technical ideas that can be grasped from the above embodiments are described below together with their effects. (A) The oxygen sensor according to the first aspect, wherein the sensor is attached to an intake pipe of an internal combustion engine and detects an oxygen concentration of intake air. In the oxygen sensor attached to the intake pipe of the internal combustion engine, the low temperature intake air comes into contact with the element as described above, so that the power consumption of the heater tends to increase. The above configuration is suitable for improving the heating efficiency of the heating element in the oxygen sensor having such a tendency.

(B) The inner cover and the outer cover each have an introduction hole through which a gas to be detected passes.
In the oxygen sensor described in the above, the diameter of the introduction hole of the outer cover is set larger than that of the introduction hole of the inner cover. According to such a configuration, in addition to the effect of the invention described in the first aspect, it is possible to prevent clogging of each introduction hole due to adhesion of the deposit while maintaining the heat retaining performance of both covers.

[0035]

According to the present invention, the inner cover is attached to the element portion so as to contact only the element portion. Therefore, the amount of heat transmitted to other members such as the outer cover and emitted from the inner cover to the outside is reduced. As a result, according to the present invention, the heating efficiency of the heater can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a diesel engine system.

FIG. 2 is a cross-sectional view showing a tip portion of the oxygen sensor.

FIG. 3 is a perspective view showing an element unit and an inner cover.

FIG. 4 is a cross-sectional view showing a conventional oxygen sensor having a dual structure cover.

[Explanation of symbols]

Reference numeral 20: oxygen sensor, 21: element part, 25: outer cover, 2
6 ... inner cover, 29 ... heater.

Claims (1)

[Claims] 1. An element portion for detecting oxygen concentration having a heater, an inner cover provided to cover the element portion,
An oxygen sensor comprising an outer cover provided on an outer periphery of the inner cover, wherein the inner cover is attached to the element portion so as to contact only the element portion.