JPH10206374A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the response delay and the defective output by arranging a heat conduction improving material at least on an inner surface of a protective cover to effectively transmit the heat of a heater to the protective cover, and burning and removing a deposit of the protective cover to suppress the clogging of an oxygen sensor. SOLUTION: The dark powder 12 of small specific heat is coated with the organic adhesive, or sintered and arranged as a heat conduction improving material on inner and outer surfaces of a stainless steel inner cover 3 and an inner surface of an outer cover 2 to constitute a protective cover. The powder 12 is preferably small in specific heat, and is not affected by high temperature or high humidity, and does not affect a sensor element 1 even in the condition of high temperature and high humidity, for example, Fe3 O4 , Si3 N4 , Fe2 N3 , or FeO2 . The heat of the sensor element 1 heated by a ceramic heater 6 is efficiently transferred to the inner cover 3 and the outer cover 2, and the adhered unburnt part and unburnt oil part are burned and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxygen sensor mounted on an intake system or an exhaust system of an internal combustion engine.

[0002]

2. Description of the Related Art An oxygen sensor is attached to an exhaust system of an internal combustion engine, detects oxygen concentration in exhaust gas discharged from the internal combustion engine, and performs feedback control of an air-fuel ratio of an air-fuel mixture. So-called exhaust gas recirculation (EGR), which is attached to the system and detects oxygen concentration in fresh air or air-fuel mixture introduced into the internal combustion engine and recirculates part of exhaust gas discharged from the internal combustion engine to the intake system. : Exhaust Ga
s Recirculation) is used for a system that controls the amount of feedback.

As an oxygen sensor as described above, Japanese Utility Model Laid-Open No.
An oxygen concentration sensor described in 4-48664 is known. The oxygen concentration sensor removes a sensor element, a protective tube that covers the periphery of the sensor element at a predetermined interval, an exhaust intake hole formed in the protective tube, and carbon attached to the exhaust intake hole. Removing means. As the removing means, a ceramic heater built in a protective tube is exemplified.

The oxygen concentration sensor heats a protective tube by a ceramic heater when carbon (particulate) contained in exhaust gas discharged from an internal combustion engine adheres to the exhaust intake hole. It is intended to burn and remove carbon adhering to the surface.

[0005]

However, the protective tube of the conventional oxygen concentration sensor as described above is generally formed of iron as a base material and has a metallic luster on its surface, so that it has low thermal conductivity. Low, it is difficult for the heat of the heater to be transmitted.
For this reason, carbon or the like attached to the exhaust intake hole of the protection tube may be fixed without being completely burned, which may cause clogging of the exhaust intake hole, which may cause a delay in response of the oxygen sensor or output failure.

In particular, when the oxygen sensor is attached to the intake system of the internal combustion engine, the mist-like unburned oil component is formed by the so-called positive crankcase ventilation that recirculates the blow-by gas in the crankcase of the internal combustion engine to the intake system. And unburned fuel components circulate through the intake system and adhere to the protection tube. And exhaust gas recirculation (EGR)
When the exhaust gas circulates through the intake system, carbon and the like in the exhaust gas adhere to the unburned oil component and the unburned fuel component. And the oxygen sensor is likely to be clogged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and enhances the thermal conductivity of a protective cover for covering a sensor element to effectively transfer heat of a heater to the protective cover, thereby providing a protective cover. It is an object of the present invention to combust and remove kimono, suppress clogging of an oxygen sensor, and prevent response delay and output failure of the sensor.

[0008]

The present invention employs the following means in order to solve the above-mentioned problems. That is,
An oxygen sensor according to the present invention is an oxygen sensor including a sensor element for detecting an oxygen concentration, a protective cover for covering the sensor element, and a heating unit for heating the sensor element to a temperature at which the sensor element operates effectively. A heat conductivity improving material is disposed on at least the inner surface of the protective cover. In the oxygen sensor configured as described above, when the heating element heats the sensor element, the heated sensor element emits heat. This radiant heat is absorbed by the thermal conductivity enhancer disposed on the inner surface of the protective cover, and then transmitted from the thermal conductivity enhancer to the protective cover.
As a result, the temperature of the protective cover becomes high, and the deposits on the protective cover are burned and removed. The thermal conductivity improving material disposed on the protective cover is, for example, a powder having a small specific heat,
It is a dark powder with a large surface area. As a method of arranging such powder on at least the inner surface of the protective cover,
Examples of the method include sintering or applying the powder to the inner surface of the protective cover, and forming the protective cover itself from the powder by sintering the powder into the shape of the protective cover. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The oxygen sensor according to the present embodiment is, as shown in FIG.
3, a sensor element 1 formed in a cylindrical shape with a bottom, a housing 5 supporting the sensor element 1, and attached to the housing 5 to surround a distal end of the sensor element 1. It includes a protective cover 4 and a ceramic heater 6 built in the sensor element 1.

The sensor element 1 is made of zirconia (ZrO).
The solid electrolyte portion 14 is formed by baking the solid electrolyte portion 2 into a cylindrical shape with a bottom, an outer platinum electrode 15 covering the outer surface of the solid electrolyte portion 14, and an inner platinum electrode 16 covering the inner surface of the solid electrolyte portion 14.

Then, air is introduced into the interior 9 of the sensor element 1 so as to come into contact with the inner platinum electrode 16. Further, an outer platinum electrode 1 of the sensor element 1
5 is exposed to fresh air or air-fuel mixture sucked into the internal combustion engine.

As a result, when there is a difference between the oxygen concentration of the atmosphere in contact with the inner platinum electrode 16 and the oxygen concentration of the fresh air or air-fuel mixture in contact with the outer platinum electrode 15, the oxygen concentration in the solid electrolyte portion 14 is increased. Oxygen ions flow from the high side to the low side to generate an electromotive force, and the oxygen concentration of the fresh air or the air-fuel mixture is determined according to the magnitude of the electromotive force.

Next, the ceramic heater 6 realizes the heating means according to the present invention, is energized through a lead wire (not shown), and operates at a temperature (400 ° C. to 900 ° C.) at which the sensor element 1 operates effectively. Heat the sensor element 1 up to (°).

The protective cover 4 includes an inner cover 3 surrounding the tip of the sensor element 1 and an outer cover 2 enclosing the inner cover 3. The inner cover 3 is formed by molding a metal plate of stainless steel or the like into a cylindrical shape with a bottom whose inner diameter is larger than the outer diameter of the tip of the sensor element, and forming holes 7 at a plurality of locations on the peripheral wall of the bottomed cylindrical body. It becomes. The hole 7 is a hole for introducing fresh air or air-fuel mixture into the inside 11 of the inner cover 3 and discharging fresh air or air-fuel mixture existing inside the inner cover 3 to the outside of the inner cover 3.

On the inner surface and the outer surface of the inner cover 3, dark powder 12 having a small specific heat is disposed as a thermal conductivity improving material of the present invention. This powder 12
It is preferable that the sensor element 1 has a small specific heat, is not affected by high temperature or high humidity, and does not affect the sensor element 1 even under high temperature or high humidity conditions. As such a powder,
Examples include Fe3 O4, Si3 N4, Fe2 N3, and FeO2. As a method of arranging the powder 12 on the inner surface and the outer surface of the inner cover 3, a method of applying the powder 12 with an organic adhesive or a method of sintering the powder 12 can be exemplified. .

Subsequently, the outer cover 2 is formed by molding a metal plate of stainless steel or the like into a bottomed cylindrical shape whose inner diameter is larger than the outer diameter of the inner cover 3, similarly to the inner cover 3. Holes 8 are formed at a plurality of locations on the peripheral wall. The hole 8 is provided with a space 10 formed between the outer cover 2 and the inner cover 3 for supplying fresh air or air-fuel mixture.
And a hole for discharging fresh air or air-fuel mixture existing in the space 10 to the outside of the outer cover 2.

Then, on the inner surface of the outer cover 2,
As the thermal conductivity improving material of the present invention, Fe3O4, Si3N4,
Powder 12 having a small specific heat, such as Fe2N3 or FeO2, is applied or sintered. Hereinafter, the function and effect of the oxygen sensor according to the present embodiment will be described.

When detecting the oxygen concentration of fresh air or air-fuel mixture sucked into the internal combustion engine, first, the ceramic heater 6
And heats the sensor element 1, and changes the temperature of the sensor element 1 to a temperature (400) at which the sensor element 1 operates effectively.
C ° to 900 ° C.).

When the sensor element 1 heated by the ceramic heater 6 radiates heat, the radiated heat is absorbed by the powder 12 on the inner surface of the inner cover, and then the heat absorbed by the powder 12 is transferred to the inner Since the power is transmitted to the cover 3, the temperature of the inner cover 3 increases.

Subsequently, when the temperature of the inner cover 3 becomes high, the heat of the inner cover 3 is radiated from the powder 12 on the outer surface of the inner cover, and the powder 1 on the inner surface of the outer cover is dried.
Absorbed in 2. Then, the heat absorbed by the powder 12 on the inner surface of the outer cover is transmitted to the outer cover 2 to increase the temperature of the outer cover 2.

As described above, by applying or sintering the powder 12 having a small specific heat to the outer cover 2 and the inner cover 3, the heat radiated from the sensor element 1 is efficiently transmitted to the inner cover 3 and the outer cover 2. Therefore, the temperatures of the inner cover 3 and the outer cover 2 become high. As a result, the intake pipe 1 is controlled by exhaust gas recirculation (EGR) and positive crankcase ventilation.
Even if the carbon, unburned fuel component, or unburned oil component introduced to the outer cover 2 adheres to the outer cover 2 or the inner cover 3, they are burned by the heat of the outer cover 2 or the inner cover 3, and the outer cover 2 2 or removed from the inner cover 3. Therefore, according to the present embodiment, the thermal conductivity of the protective cover is increased by disposing the powder having a small specific heat on the protective cover, and the radiation heat of the sensor element is effectively transmitted to the protective cover. The deposits on the protective cover can be burned and removed, and the response delay and output failure of the sensor element due to clogging of the holes of the protective cover can be prevented.

Further, according to the present embodiment, since the surface roughness of the protective cover is increased by disposing the powder on the protective cover, the carbon contained in the exhaust gas, fresh air, air-fuel mixture, etc. The fuel component, the oil component, and the like can be efficiently trapped, and the carbon, the fuel component, the oil component, and the like can be prevented from adhering to the sensor element.

[0023]

According to the oxygen sensor of the present invention, when the sensor element is heated by the heating means and the heated sensor element radiates heat, the radiated heat is absorbed by the thermal conductivity improving material of the protective cover. Then, since the heat conductivity improving material is transmitted to the protective cover, the heat of the heating means can be effectively transmitted to the protective cover. As a result, the temperature of the protective cover becomes high, and the deposits on the protective cover are burned and removed.

Therefore, according to the oxygen sensor of the present invention, clogging of the oxygen sensor can be suppressed, and a response delay of the sensor element, an output failure, and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an oxygen sensor attached to an intake pipe of an internal combustion engine.

FIG. 2 is an enlarged cross-sectional view of a tip portion of an oxygen sensor.

[Explanation of symbols]

 1. Sensor element 2. Outer cover 3. Inner cover 4. Protective cover 5. Housing 6. Ceramic heater 7. Hole 8. Hole 12. Powder 14. Solid electrolyte part 15. Outer platinum electrode 16. Inner platinum electrode

Claims (1)

[Claims] 1. An oxygen sensor comprising: a sensor element for detecting an oxygen concentration; a protective cover for covering the sensor element; and heating means for heating the sensor element to a temperature at which the sensor element operates effectively. An oxygen sensor, wherein a thermal conductivity improving material is disposed on at least an inner surface of a protective cover.