JPH03138560A - Heat type air/fuel ratio detector - Google Patents

Abstract

PURPOSE:To shorten the heating time of a detection part in starting while preventing the detection part from being overheated by applying a heating body with a voltage higher than a rated voltage required to hold the detection part at specific temperature for a specific time right after the starting. CONSTITUTION:A diffusion resistance means consisting of the gas intake hole 16 and flat space 14 of an oxygen concentration detection part 10 guides combustion exhaust gas to below a specific gas diffusion resistance. An electrochemical sensing cell 8 composed of an electrode 26, an electrode 28, and a solid electrolytic body 12 detects the oxygen concentration in the guided combustion exhaust gas. An electrochemical pumping cell 6 consisting of an electrode 22, an electrode 24, and the solid electrolytic body 12 controls the oxygen concentration in the combustion exhaust gas. Then the heating body 32 is applied with the voltage higher than the rated voltage required to hold the detection part 10 at the specific temperature for the specific time right after the starting. Consequently, while the detection body is prevented from being overheated, the time required for heating up to the specific temperature at which a stable measurement can be taken can be shortened.

Description

Detailed Description of the Invention (Technical Field) The present invention provides a heating element that is suitably used for measuring the air-fuel ratio of combustion exhaust gas in combustion control systems in internal combustion engines of automobiles, various industrial furnaces, etc. The present invention relates to a heated air-fuel ratio detector, and particularly to a heated air-fuel ratio detector that can shorten heating time when starting from a low temperature state and improve measurement accuracy at the initial stage of starting.

(Background technology) Traditionally, exhaust gas (combustion exhaust gas) from automobile internal combustion engines
Concentration cell type and limiting current type oxygen sensors that use zirconia porcelain, etc., which is a solid electrolyte that conducts oxygen ions, are used as oxygen sensors to detect the oxygen concentration in combustion exhaust gas discharged from industrial furnaces, boilers, etc. Also known are oxide semiconductor types using titania, niobium pentoxide, etc. whose resistance value changes due to the adsorption of gas onto the surface. In internal combustion engines, etc., in order to control the air-fuel ratio of the air-fuel mixture composed of air and fuel to a target value with high precision, the above-mentioned sensors are generally used to measure the correlation between the air-fuel ratio and the air-fuel ratio. By detecting the oxygen concentration in the exhaust gas, the air-fuel ratio of the air-fuel mixture is detected, and the amount of fuel supplied to the internal combustion engine or the like is feedback-controlled.

By the way, in order for an air-fuel ratio detector using such an oxygen sensor to operate effectively even when the temperature of the combustion exhaust gas as the gas to be measured is relatively low, at least oxygen in the air-fuel ratio detector is required. It is necessary to heat and maintain the detection section that detects the concentration at a predetermined high temperature using an appropriate heater (heating element).

Therefore, conventionally, for such heating, for example, Japanese Patent Application Laid-Open No. 55-140145 and Japanese Patent Application Laid-open No. 57-14255
As shown in Publication No. 5, etc., an air-fuel ratio detector has been disclosed that has a built-in heating element that heats the oxygen concentration detection section by external power supply, and is also provided integrally with the heating element. . In addition, if the voltage supplied to the heating element is too large, problems such as damage to the oxygen concentration detection section due to overheating will occur, so it is usually necessary to maintain the detection section at a predetermined temperature. the amount of heat required,
It will be set to a certain size (rated voltage) that can be obtained by the heating element.

However, in conventional devices in which the voltage supplied to the heating element is set based on the amount of heat required to keep the oxygen concentration sensor warm, it is difficult to start the device from a low temperature. However, due to such a heating element, it takes a long time to heat up the detection part to a measurable temperature. Therefore, in internal combustion engines, it is difficult to control the operation when starting the engine. The problem was that it was difficult to obtain stability.

In particular, as shown in Japanese Unexamined Patent Publication No. 59-190652, the detection section includes a diffusion resistance means for guiding the combustion exhaust gas under a predetermined gas diffusion resistance, and oxygen concentration detection means for detecting the oxygen concentration in the guided combustion exhaust gas; and oxygen concentration detection means for controlling the oxygen concentration in the combustion exhaust gas guided through the diffusion resistance means based on the detected value by the oxygen concentration detection means. In an air-fuel ratio detector that includes a pump means and measures the air-fuel ratio of combustion exhaust gas by a current flowing through the oxygen pump means, formation of the diffusion resistance means and arrangement of the oxygen pump means are required. As the equipment becomes larger and requires a longer time to heat up, the problem of heating time when starting from a low temperature, as mentioned above, has become an even bigger problem. In addition, at low temperatures,
Since the current conductivity to the oxygen pump means is poor, there is also a problem that the output tends to become unstable at the initial stage of startup.

(Problem to be solved) Here, the present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is:
It is an object of the present invention to provide a heated air-fuel ratio detector that can advantageously shorten the heating time of the oxygen concentration detection section at the time of startup while preventing overheating in the oxygen concentration detection section.

(Solution Means) In order to solve this problem, the present invention includes an oxygen concentration detection section that detects the oxygen concentration in combustion exhaust gas, and a heating element that heats the detection section by external power supply. In the heating type air-fuel ratio detector, a power supply means supplies a voltage higher than a rated voltage required to maintain the detection part at a predetermined temperature to the heating element for a predetermined time immediately after starting. It is characterized by the fact that it has been established.

Further, in one aspect of the present invention, the oxygen concentration detection section includes a diffusion resistance means for guiding the combustion exhaust gas under a predetermined gas diffusion resistance, and a diffusion resistance means for guiding the combustion exhaust gas under a predetermined gas diffusion resistance, and a diffusion resistance means for guiding the combustion exhaust gas under a predetermined gas diffusion resistance. oxygen concentration detection means for detecting oxygen concentration;
and an oxygen pump means for controlling the oxygen concentration in the combustion exhaust gas guided through the diffusion resistance means based on the value detected by the oxygen concentration detection means (Example). In order to clarify the present invention more specifically, the configuration of the present invention will be explained in detail based on embodiments shown in the drawings.

First, FIG. 1 shows one specific form of a heated air-fuel ratio detector according to the present invention. In this figure, 10
1 is a schematic cross-sectional view of the oxygen concentration detection section of the detection element of the oxygen concentration detector. The detection unit 10 includes a plate-like elongated solid electrolyte body 12 obtained by laminating and integrally firing a plurality of oxygen ion conductive solid electrolyte layers such as zirconia porcelain doped with ittria. are doing.

In this solid electrolyte body 12, a narrow circular flat space 14 is provided in the direction of the plate surface, and the center part of this flat space 14 is formed by penetrating the solid electrolyte body 12. It is communicated with an external measurement gas existing space 18 through a gas introduction hole 16 . The combustion exhaust gas as the gas to be measured is introduced into the flat space 14 through the gas introduction hole 16 under a predetermined diffusion resistance. In this embodiment, the gas introduction hole 16 and the flat space 14 constitute a diffusion resistance means.

Furthermore, the solid electrolyte body 12 has a flat space 1
A first electrode 22 is in contact with a surface that is substantially exposed to the atmosphere in the gas-to-be-measured space 18, and a second electrode is in contact with a surface that is substantially directly exposed to the gas in the gas-to-be-measured space 18. 24
are provided facing each other with the solid electrolyte body 12 in between. And these first electrodes 22,
The second electrode 24 and the solid electrolyte body 12 constitute an electrochemical bombing cell 6.

On the other hand, an air passage 20 is formed independently within the solid electrolyte body 12 at a position a predetermined distance apart from the flat space 14 . And such air passage 20
Air as a reference gas having a predetermined oxygen concentration is introduced into the chamber.

Furthermore, the solid electrolyte body 12 has a flat space 1
The third electrode 26 is in contact with the surface substantially exposed to the atmosphere in the air passage 20, and the fourth electrode 28 is in contact with the surface exposed to the air as a reference gas introduced into the air passage 20. They are provided in opposing positions with the solid electrolyte body 12 in between. The third electrode 26, fourth electrode 28, and solid electrolyte body 12 constitute an electrochemical sensing cell 8.

In the oxygen concentration detection section 10 of the detection element having such a structure, the electromotive force generated in the sensing cell 8 is input to the differential amplifier 36. In addition, in the differential amplifier 36, the electromotive force of the sensing cell B is adjusted to be equal to the reference voltage 37 in order to keep the atmosphere in the flat space 14 of the detection unit 10 where the third electrode 26 is exposed always around neutrality. The voltage is compared and a voltage corresponding to the comparison result is output.Furthermore, the output of the differential amplifier 36 is inputted to the V-■ converter 38, thereby converting it into a predetermined positive or negative current. It is now possible to convert it.

Further, the current output from this V-1 converter 38 is caused to flow between the first electrode 22 and the second electrode 24 that constitute the pumping cell 6, and thereby, the pumping cell 6 supplies the flat space. Oxygen ions are transferred to the first electrode 2 so that the atmosphere inside the electrode 14 approaches neutrality.
2 to the second electrode 24 side, or vice versa, to perform an oxygen pumping action.

In this way, the pumping current = 1p flowing between the first electrode 22 and the second electrode 24 constituting the pumping cell 6 is measured. As is well known, the pumping current has a certain relationship with the air-fuel ratio of the combustion exhaust gas, which is the gas to be measured. The air-fuel ratio can be detected.

On the other hand, a second electrode 2 is provided on the solid electrolyte body 12 constituting the oxygen concentration detection section 10 of the detection element as described above.
A predetermined electrically insulating ceramic layer 30 is integrally provided on the side where 4 is not provided, and a heater element 32 as a heating element is embedded inside this ceramic layer 30. It is arranged in

The heater element 32 is supplied with power from an external power source 34 connected through its connection terminal to generate heat, so that the detection section 10 can be heated and maintained at a predetermined effective operating temperature. It has become.

Therefore, when the external power source 34 is connected to the heater element 32, the heater element 32 can generate enough heat to maintain the detection section 10 at a measurable predetermined temperature. By being connected to the heater element 32 and the rated power supply 44 that supplies the rated voltage (8 V in this example), a voltage that is higher than the rated voltage by a predetermined amount (12V in this example) is generated. The rated power source 44 and the heating power source 46 are selectively connected to the heater element 32 based on the switching operation by the switching mechanism 48. It has become.

Further, in the switching mechanism 48, the switching operation thereof is controlled by a control mechanism 50 which is activated temporally by a timer circuit or the like, so that the switching mechanism 48 performs a so-called time switch-like operation. . More specifically, when measuring the air-fuel ratio in the detection unit 10 as described above, when raising the temperature of the detection unit 10 to a predetermined temperature at which the detection unit 10 can be measured, at the initial stage of startup, heating is applied to the heater element 32. The power supply 46 is connected,
After a predetermined period of time has elapsed, the switching mechanism 48 is operated to switch the rated power supply 44 to the heater element 32.
will be connected.

Note that this switching mechanism 48 allows the startup (initial stage of heating)
The time it takes for the power to be switched from 1 to 2 varies depending on the installation environment and initial temperature of the air-fuel ratio sensor, its structure and size, etc., but for a standard type double cell type like the structure of this example, In the case of an air-fuel ratio detection device for an automobile engine, when the initial starting temperature is room temperature, the time period is normally set to about 5 to 60 seconds. However, if the sensor is connected to a heating power source for too long, it may cause damage to the sensor due to overheating.
This is because if the heating time is too short, it is difficult to obtain sufficient effects.

Incidentally, an air-fuel ratio detector having the above-described structure is installed in a 2000cc automobile gasoline engine, and at the same time when the engine is started from room temperature, the heater element 32
In contrast, the heating situation in the detection unit 10 was actually measured when the heating power source 46 was connected for 10 seconds at the beginning of startup, and then the rated power source 44 was connected. In this measurement, the temperature of the detection unit 10 was measured at a portion located between the facing surfaces of the first electrode 22 and the second electrode 24 (section a in FIG. 1). The results are shown in FIG. In addition, at the same time as this measurement, we actually measured the heating status in the detection unit 10 when only the rated power source 44 or the heating power source 46 was connected to the heater element 32 continuously from the initial stage of startup, and reported the results. , is also shown in FIG. 2 as a comparative example.

As is clear from these actual measurement results, the external power supply 3 that supplies voltage to the heater element 32 as described above
4 is an air-fuel ratio detector having a structure that can be switched between the rated power source 44 and the heating power source 46, compared to the conventional one having a structure in which only the rated voltage is supplied to the heater element (32). In comparison, the warm-up time required to heat the oxygen concentration detection section 10 to a measurable temperature can be advantageously shortened while preventing the oxygen concentration detection section 10 from overheating.

As a result, even when setting the air-fuel ratio when starting from a low temperature state, stable output can be obtained quickly and the internal combustion engine can be controlled well. be.

Furthermore, in the air-fuel ratio detector as described above, the air-fuel ratio is detected after the external power supply 34 connected to the heater element 32 is switched to the rated power supply 44, thereby making it possible to detect the air-fuel ratio at startup. It also has the advantage that initially unstable output can be removed easily and effectively.

In particular, in double-cell air-fuel ratio detectors that include an electrochemical sensing cell as an oxygen concentration detection means and an electrochemical bombing cell, conventionally, the device is large and requires a long time to heat. In addition,
In order to easily apply current to the bombing cell 6, it is necessary for the solid electrolyte body 12 to be at a certain temperature or higher (generally 600°C or higher). However, as mentioned above, by switching the external power supply 34 connected to the heater element 32, these problems can be alleviated very effectively. Or, it can be resolved.

In addition, in the explanation of the air-fuel ratio detector in the embodiment described in (G),
Although not specifically described, the present invention can also be advantageously applied to a heated air-fuel ratio detector having an oxygen sensor structure without the electrochemical pumping cell 6.

In addition, the structure of the oxygen concentration detection means constituting the oxygen concentration detection section may be of various known structures, such as a concentration cell type as illustrated, an oxide semiconductor type, or a limiting current type. However, any of them can be adopted.

Furthermore, since the above embodiment has been described with reference to an air-fuel ratio detector used in an automobile gasoline engine, the heating power source 46 is a 12-inch power source that is normally used as an automobile battery power source. However, the voltage of the heating power source 46 is not particularly limited.

The voltage of the heating power source 46 and the time required to switch from the heating power source 46 to the rated power source 44 are determined as appropriate depending on the required performance of the air-fuel ratio detector, etc. It is also possible to perform control such that the heating power source is switched to the rated power source before the temperature reaches a temperature that allows good measurement in the concentration 5 6 detection unit.

In addition, means for directly or indirectly detecting the temperature of the oxygen concentration detection section 10 or the temperature of the atmosphere to which the oxygen concentration detection section 10 is exposed, such as the heat resistance of a heated air-fuel ratio detector, the water temperature or oil temperature of the engine, may be used. , engine speed, battery voltage,
By determining or measuring a predetermined time for supplying a voltage higher than the rated voltage based on the intake air temperature, etc., and ensuring that only the rated voltage is supplied from the beginning when starting under high temperature, for example, the detection unit 10 can be It is also possible to prevent overheating.

In addition, although the above specific example shows an example in which the present invention is applied to an air-fuel ratio detector used for controlling an automobile engine, the present invention is also applicable to combustion in various industrial furnaces, etc. Of course, the present invention can also be advantageously applied to an air-fuel ratio detector that measures the air-fuel ratio by detecting the oxygen concentration in exhaust gas.

Although the configuration of the present invention has been described above in detail based on one specific example of the present invention, the present invention is by no means to be interpreted as being limited only to such specific example and the above specific description.
Without departing from the spirit of the present invention, the present invention may be implemented with various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art, and such embodiments may overcome the spirit of the present invention. It goes without saying that all of these are included within the scope of the present invention as long as they do not deviate from them.

(Effects of the Invention) As is clear from the above description, in the air-fuel ratio detector according to the present invention, heating of the oxygen concentration detection section at the initial stage of startup causes a voltage higher than the rated voltage to be applied to the heating element. ,
Since this is done by supplying electricity for a predetermined period of time, the time required to heat up to a predetermined temperature that allows stable measurements can be advantageously shortened while preventing overheating, thereby improving the responsiveness of the detector and The stability of the output at the initial stage of startup can also be advantageously improved.

Furthermore, by applying the present invention to a double-cell type air-fuel ratio detector that is equipped with an oxygen pumping cell as well as a sensing cell that detects oxygen concentration, it is possible to solve the problems that conventionally existed with such double-cell type air-fuel ratio detectors. It was said that
It is possible to effectively reduce or eliminate the long heating time required due to the large size, or the instability of output caused by poor conductivity to the oxygen pumping cell at the initial stage of startup. It is.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram showing one embodiment of a heated air-fuel ratio detector according to the present invention. In addition, Figure 2 shows the actual heating state of the detection part at the initial stage of startup when measuring the air-fuel ratio of a gasoline engine using a heated air-fuel ratio detector having the structure shown in Figure 1. It is a graph showing the results together with comparative examples. 6: Electrochemical pumping cell 9 Electrochemical sensing cell detection section 12: Solid electrolyte body flat space
16: Gas introduction hole Measured gas presence space Air passage 22 Second electrode 26 Fourth electrode 30 Heater element 34 Rated power supply 46 Switching mechanism 50 First electrode Third electrode Ceramic layer External power supply Heating power supply control mechanism

Claims (2)

[Claims] (1) In a heated air-fuel ratio detector that includes an oxygen concentration detection section that detects the oxygen concentration in combustion exhaust gas and a heating element that heats the detection section by external power supply, the detection is performed for a predetermined period of time immediately after startup. A heating type air-fuel ratio detector, characterized in that a heating type air-fuel ratio detector is provided with a power supply means for supplying a voltage higher than a rated voltage required for maintaining the heating element at a predetermined temperature to the heating element. (2) The oxygen concentration detection unit includes a diffusion resistance means for guiding the combustion exhaust gas under a predetermined gas diffusion resistance, and oxygen concentration detection for detecting the oxygen concentration in the combustion exhaust gas guided through the diffusion resistance means. Claim (1) comprising means for controlling the oxygen concentration in the combustion exhaust gas guided through the diffusion resistance means based on the detected value by the oxygen concentration detection means. The heated air-fuel ratio detector described.