JPH1019837A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor which is provided with a temperature control function in itself. SOLUTION: An insulating-material thermally sprayed layer 14 is formed to prevent an outside electrode 13 which is installed at the outside of a solid electrolyte 11. An electric heater layer 22 in a prescribed pattern is printed on the outside of the thermally sprayed layer 14. In addition, also a temperature transducer layer 23 is printed on the outside of the thermally sprayed layer 14 so as to be electrically in parallel with the electric heater layer 22. In addition, the electric heater layer 22 and the temperature transducer layer 23 are protected by a coating layer 15. When the electric heater layer 22 is electrified, the temperature of an oxygen sensor is raised, the resistance of the temperature transducer layer 23 is lowered, a current which flows in the electric heater layer 22 is reduced, and it is possible to restrain heat from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxygen sensor, and more particularly, to an oxygen sensor having a temperature adjusting function.

[0002]

2. Description of the Related Art It is known to use a catalytic converter to suppress nitrogen oxides, hydrocarbons and carbon monoxide contained in exhaust gas emitted from an internal combustion engine for automobiles from being emitted into the atmosphere. However, in order to maintain a high purification rate, it is necessary to control the air-fuel mixture supplied to the internal combustion engine to approximately the stoichiometric air-fuel ratio.

[0003] In order to control the air-fuel mixture to the stoichiometric air-fuel ratio, the concentration of oxygen remaining in the exhaust gas correlated with the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is detected, and the fuel supply amount is determined according to the intake air amount. Is generally controlled. An oxygen sensor that is currently widely used is a zirconia oxygen sensor has a structure in which a platinum electrode is coated on the inner and outer surfaces of the zirconia solid electrolyte of cylindrical tip is closed (Z _r O _2).

[0004] This oxygen sensor is inserted into an exhaust pipe to expose the outer surface to exhaust gas having a low oxygen partial pressure, and to introduce an atmosphere having a high oxygen partial pressure to the inner surface, whereby oxygen ions flow through the zirconia solid electrolyte, and the inner and outer surfaces are exposed. A current corresponding to the residual oxygen concentration flows between the platinum electrodes. At present, semiconductor-type oxygen sensors using titania are also being developed.However, in order to function as both an oxygen sensor and an oxygen concentration detection sensor that pumps oxygen in gas, a residual oxygen concentration detection element must be specified. Temperature (for example, 650 ° C)
It is necessary to maintain the above.

In order to maintain the activation temperature of the residual oxygen concentration detecting element after the internal combustion engine is started, it is usual to heat the residual oxygen concentration detecting element with an electric heater (Japanese Patent Application No. Hei.
-22464). FIG. 2 is an external view of a conventional oxygen sensor using a solid electrolyte. An electric heater 22 is inserted into a hollow portion of a cylindrical oxygen sensor 21.

The oxygen sensor 21 is formed of a solid electrolyte having a thickness of several millimeters, and its inner and outer surfaces are coated with platinum electrodes. Then, to protect the outer electrode, a sprayed layer and a coating layer of about 500 micrometers are formed on the outer side of the outer electrode. The oxygen sensor 21 includes an inner cover 23 and an outer cover 24.
Is physically protected by

[0007]

However, if the temperature of the electric heater 22 rises excessively, the electric heater 22 may be deteriorated or damaged. Therefore, it is necessary to appropriately control the electric power supplied to the electric heater 22. FIG. 3 is a configuration diagram of a heater control device used for a conventional oxygen sensor,
Power is supplied from a drive circuit 32 to an electric heater 22 for heating a residual oxygen concentration detection element 21 built in the oxygen sensor installed in the oxygen sensor 1.
21, switching element 322, current detecting resistor 323
And a buffer amplifier 324.

That is, the heater 22, the switching element 322
The current detection resistor 323 is connected in series between the power supply 321 and the ground (vehicle body). The current flowing through the electric heater 22 is detected by measuring the voltage generated across the current detecting resistor 323 via the buffer amplifier 324. Electric heater 22 based on electric heater current
The control unit 13 which is a microcomputer system controls the switching block 3 so as to prevent the temperature of the electric heater 22 from being excessively increased while maintaining the activity of the oxygen sensor 21.
22 on / off time.

That is, in the conventional oxygen sensor, not only the electric heater 22 may be deteriorated or damaged due to the excessive temperature rise, but also an economical problem is caused by providing the drive circuit 32 and the control unit. The present invention has been made to solve the above problems, and has as its object to provide an oxygen sensor in which the oxygen sensor itself has a temperature adjusting function.

[0010]

An oxygen sensor according to the present invention comprises a residual oxygen concentration detecting element for detecting a residual oxygen concentration in exhaust gas of an internal combustion engine, and an insulating material provided outside the residual oxygen concentration detecting element. An electrode protection layer made of: an electric heater layer provided outside the insulating material sprayed layer; a temperature-sensitive element layer provided outside the insulating material sprayed layer and electrically connected in parallel with the electric heater layer; An insulating material coating layer for protecting the heater layer and the temperature-sensitive element layer.

In the present oxygen sensor, when the temperature rises due to the heat generated by the electric heater layer, the resistance of the temperature-sensitive element layer decreases, thereby forming a bypass circuit for the electric heater layer.

[0012]

FIG. 1 is an external view and a partially enlarged cross-sectional view of an oxygen sensor according to the present invention. A substrate 11 is obtained by firing a zirconia solid electrolyte into a cylindrical shape having one end closed. The inner surface and the outer surface of the substrate 11 are plated with platinum that functions as the inner electrode 12 and the outer electrode 13.

A thermal sprayed layer 14 of an insulating material is formed on the outer side of the outer electrode 13 to protect the outer electrode 13 and secure insulation between the outer electrode 13 and an electric heater 22 provided further outside. A conductive material (tungsten, rhenium, platinum) is printed in a predetermined shape on the outer surface of the thermal spray layer 14 to form the electric heater 22.

FIG. 4 is a perspective view of an embodiment of the shape of the electric heater 22 and has a structure in which three layers of ring portions 221 are connected by connecting portions 222 extending in the axial direction of the base material 11. The shape of the electric heater is not limited to the above embodiment, and may be a spiral shape. Further, a thermosensitive element material 23 is printed on the outer surface of the thermal spray layer 14 so as to be electrically parallel to the electric heater 22.

That is, when the electric heater 22 has a ring shape as shown in FIG.
3 is installed. When the electric heater 22 has a spiral shape, the temperature-sensitive element material 23 is spirally disposed so as to fill the space between the electric heaters. The temperature-sensitive element material 23 has a negative temperature coefficient N N whose resistance decreases as the temperature increases.
It is a TC thermistor or a CTR thermistor whose resistance rapidly decreases when a predetermined temperature is reached.

As the NTC thermistor, Mn-N
i oxide, Mn-Co-Ni oxide, ZrO ₂ Y ₂ O ₃
Oxide, CoO—Al ₂ O ₃ —CaSiO ₃ oxide, Mg (Al, Cr, Fe) ₂ O ₄ oxide, Si
A mixture of C, SnSe, TaN, or the like, and a conductive material such as platinum for adjusting the resistance value can be used. As the CTR thermistor, a mixture of a V-based oxide and a conductive material can be used.

Further, the electric heater 22 and the temperature-sensitive element material 2
3 is covered by a coating layer 15. A conductive material forming the electric heater 22 is widely printed on the upper portion of the base 11, and functions as a connection line 24 for supplying electric power to the electric heater 22. FIG. 5 is an equivalent circuit of the oxygen sensor according to the present invention when a CTR thermistor is used as the temperature-sensitive element material 23. FIG.
(B) represents a high temperature state.

That is, in the low temperature state, the electric heater 22
a and CTR thermistor 23 connected in parallel to 22b
The resistance values of a and 23b are sufficiently high that the electric power supplied from the battery is consumed by the electric heaters 22a and 22b. When a predetermined temperature is reached by the heat generated by the electric heaters 22a and 22b, the CTR thermistors 23a and 23b
The resistance value of 3b sharply drops and functions as a bypass circuit for the electric heaters 22a and 22b. Therefore, the current flowing through the electric heaters 22a and 22b bypasses the CTR thermistors 23a and 23b, and the heat generation of the electric heaters 22a and 22b stops.

When the temperature drops below a predetermined temperature, the resistance values of the CTR thermistors 23a and 23b become high and the bypass circuit is cut off, so that the electric heaters 22a and 22b
Is resumed. That is, since the CTR thermistors 23a and 23b function as temperature switches, the temperature of the oxygen sensor is maintained substantially constant.

It is also possible to use an NTC thermistor as the temperature sensing element material 23. In this case, the combined resistance of the electric heaters 22a, 22b and the NTC thermistor is maintained substantially constant, but the ratio of the current flowing through the electric heaters 22a, 22b to the current flowing through the NTC thermistor changes depending on the temperature. It is kept almost constant.

In the above embodiment, an oxygen sensor using a zirconia solid electrolyte has been described. However, the present invention can be applied to an oxygen sensor using a semiconductor.

[0022]

According to the oxygen sensor of the present invention, when the temperature rises due to the heat generated by the electric heater layer, the resistance of the temperature-sensitive element layer decreases and a bypass circuit of the electric heater layer is formed. Therefore, not only can the overheating of the electric heater be prevented, but also the oxygen sensor can be maintained at a substantially constant temperature without using a separate control device.

Further, since the electric heater layer and the temperature-sensitive element layer are electrically connected in parallel, even if one of the electric heater layer and the temperature-sensitive element layer is torn, the function of the electric heater layer is maintained. Can be held.

[Brief description of the drawings]

FIG. 1 is an external view and a partially enlarged sectional view of an oxygen sensor according to the present invention.

FIG. 2 is an external view of a conventional oxygen sensor.

FIG. 3 is a configuration diagram of a heater control device used for a conventional oxygen sensor.

FIG. 4 is a perspective view of one embodiment of the shape of the electric heater.

FIG. 5 is an equivalent circuit of the oxygen sensor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Base material 12 ... Inner electrode 13 ... Outer electrode 14 ... Thermal spray layer 15 ... Coating layer 22 ... Electric heater layer 23 ... Temperature sensitive element layer

Claims (1)

[Claims] 1. A residual oxygen concentration detecting element for detecting a residual oxygen concentration in exhaust gas of an internal combustion engine; an electrode protection layer made of an insulating material provided outside the residual oxygen concentration detecting element; An electric heater layer provided outside the layer; a temperature-sensitive element layer provided outside the insulating material sprayed layer and electrically connected in parallel with the electric heater layer; the electric heater layer and the temperature-sensitive element layer An oxygen sensor, comprising: