JP2017053802A - Gas concentration humidity detection device and gas concentration humidity detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration humidity detection device and a gas concentration humidity detection method capable of suppressing blackening.SOLUTION: A Vs cell 91 and an Ip cell 93 of a whole area air-fuel ratio sensor 9 are used to detect oxygen concentration in a detection target gas, and the Ip cell 93 is used to detect humidity. When the humidity is detected, a first voltage V1 for electrolyzing water in the detection target gas and a second voltage V2 lower in voltage than the first voltage V1 are applied to a pair of second electrodes 77, 79 of the Ip cell 93. Humidity of the detection target gas is detected based on a current difference ΔIp between a first pump current Ip1 flowing through the pair of second electrodes 77, 79 of the Ip cell 93 when the first voltage V1 is applied, and a second pump current Ip2 flowing through the pair of second electrodes 77, 79 of the Ip cell 93 when the second voltage V2 is applied.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a gas concentration / humidity detection device and a gas concentration / humidity detection method for detecting the humidity of a gas to be detected using a gas sensor element for detecting the gas concentration of a specific component in the gas to be detected.

  2. Description of the Related Art Conventionally, an oxygen sensor that is attached to an exhaust passage of an internal combustion engine such as an automobile engine and detects an oxygen concentration in exhaust gas is known as one of sensors used in an automobile. This oxygen sensor detects the oxygen concentration and thus detects the air-fuel ratio of the exhaust gas by utilizing the fact that the magnitude of the current flowing through the gas sensor element changes according to the oxygen concentration in the exhaust gas.

  The sensor control device for controlling the driving of the oxygen sensor has a function of energizing the gas sensor element and converting the current flowing through the gas sensor element into a voltage and outputting it to an electronic control unit (ECU). Based on the output from the controller, the oxygen concentration and air-fuel ratio of the exhaust gas are obtained. The obtained oxygen concentration and air-fuel ratio of the exhaust gas are used for air-fuel ratio feedback control such as adjustment of the fuel injection amount in the ECU.

  Further, when the characteristics of an oxygen sensor mounted on an automobile change due to deterioration with time or durability, sensor output under the same condition may shift. For this reason, it is known to correct the characteristic change that has occurred in the oxygen sensor based on the sensor output in the air atmosphere.

  However, the oxygen sensor exposed to the air atmosphere may change the sensor output under the same conditions due to the influence of humidity in the air atmosphere. Therefore, even if the characteristic change that occurred in the oxygen sensor is corrected based on the sensor output in the air atmosphere, if the humidity at the time of detecting the oxygen concentration is different from the humidity at the time of correction, it is caused by the humidity difference. As a result, the detection accuracy of the sensor output may be reduced.

  As countermeasures, detect the humidity in the atmospheric air, correct the atmospheric condition output according to the humidity to obtain the atmospheric calibration value, and correct the sensor characteristics by making the atmospheric calibration value correspond to the atmospheric oxygen partial pressure. Can be considered. However, in this method, when a humidity sensor for detecting the humidity in the air atmosphere is separately provided, the device configuration becomes complicated and the manufacturing cost increases.

  Therefore, in recent years, it has a gas sensor including an oxygen concentration detection cell (electromotive force cell) having a solid electrolyte body having a pair of first electrodes and an oxygen pump cell having a solid electrolyte body having a pair of second electrodes. A method of detecting the humidity of a gas to be detected using a gas concentration / humidity detection device has been proposed (see Patent Document 1).

  In this technique, the current flowing between the pair of second electrodes of the oxygen pump cell is controlled so that the voltage generated between the pair of first electrodes of the oxygen concentration detection cell becomes the control target voltage. The control target voltage is set to the first voltage, while being set to the second voltage that is higher than the first voltage. The first current (when the first voltage is applied) and the second current (when the second voltage is applied) detected by the oxygen pump cell when the gas to be detected is determined to be the atmosphere. Based on this, the humidity of the gas to be detected is detected.

  Thereby, the humidity when the gas to be detected is in the atmosphere is detected by a simple apparatus configuration using a gas sensor for detecting the gas concentration of the specific component in the gas to be detected without separately providing a humidity sensor. be able to.

JP 2010-281732 A

  In such a gas concentration / humidity detection apparatus, humidity is detected by stepping up the control voltage of the oxygen concentration detection cell. In this case, control between the oxygen concentration detection cell and the oxygen pump cell is performed. A problem sometimes occurs because of the PID control.

  Specifically, when the rate of change when changing the control voltage (Vs) of the oxygen concentration detection cell is large (see FIG. 11A), the voltage of the oxygen pump cell (Vp voltage) or The current flowing through the oxygen pump cell (Ip current) sometimes overshoots (see FIGS. 11B and 11C).

  However, when the Vp voltage overshoots and exceeds a certain voltage as described above, there is a problem that oxygen in the solid electrolyte body of the oxygen pump cell is extracted as a current and blackening occurs.

  This blackening is a phenomenon in which a metal oxide contained in the solid electrolyte body is reduced to generate a metal. When blackening occurs, the characteristics (particularly ion conductivity) of the solid electrolyte body deteriorate.

  The present invention has been made to solve the above problems, and an object thereof is to provide a gas concentration / humidity detection device and a gas concentration / humidity detection method capable of suppressing the occurrence of blackening.

  (1) A gas concentration / humidity detection device according to a first aspect of the present invention includes a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and generates an electromotive force between the first electrodes. An electromotive force cell, and an oxygen pump cell having a second solid electrolyte body and a pair of second electrodes formed on the second solid electrolyte body and capable of pumping oxygen between the second electrodes. Connected to the gas sensor element. In this gas concentration / humidity detection apparatus, a gas concentration of a specific component in a gas to be detected is detected using an electromotive force cell and an oxygen pump cell. In addition to detecting the gas concentration, the humidity of the gas to be detected is detected.

  When detecting the humidity, the voltage application means applies a first voltage for electrolyzing moisture in the gas to be detected to the pair of electrodes of the electromotive force cell or the oxygen pump cell. A second voltage lower than 1 voltage is applied. Then, the humidity detecting means applies a first current flowing between a pair of electrodes of the cell to which the first voltage is applied when the first voltage is applied, and a cell to which the second voltage is applied when the second voltage is applied. The humidity of the gas to be detected is detected based on the difference from the second current flowing between the pair of electrodes.

That is, since the difference between the first current and the second current corresponds to the humidity of the gas to be detected, the humidity can be obtained from the difference between the first current and the second current.
As described above, in the first aspect, the humidity detection is performed by controlling the voltage applied to the electromotive force cell or the oxygen pump cell, instead of performing the humidity detection of the gas to be detected using the PID control as in the prior art. Therefore, overshooting of the Ip current and the Vp voltage due to PID control does not occur, and blackening is unlikely to occur in the solid electrolyte body. As a result, since the characteristics of the solid electrolyte body are not easily deteriorated, there is a remarkable effect that the durability of the gas concentration / humidity detection device is improved.

In the first aspect, not only the humidity of the gas to be detected but also the gas concentration (for example, oxygen concentration) of the specific gas in the gas to be detected can be detected.
Furthermore, for example, when fuel is burned in an internal combustion engine, a combustion point (stoichiometric point) in a stoichiometric state is an optimal combustion point for purifying exhaust gas after combustion (combustion exhaust gas). This stoichiometric point varies depending on the humidity in the atmosphere and the moisture content of impurities in the fuel. Therefore, the optimum stoichiometric point can be estimated by measuring the humidity of the atmosphere or combustion exhaust gas. As a result, feedback control such as the fuel injection amount can be suitably performed based on the estimated stoichiometric point.

Here, the principle of detecting the humidity of the gas to be detected will be briefly described.
When a voltage is applied to an electromotive force cell or oxygen pump cell (hereinafter also referred to as a humidity detection cell) for detecting humidity, when a first voltage for electrolyzing moisture in the gas to be detected is applied to the humidity detection cell There is a difference between a flowing first current and a second current flowing when a second voltage lower than the first voltage (for example, a voltage that does not substantially electrolyze moisture) is applied.

  Specifically, when the first voltage is applied, a larger amount of current (second current) flows than the second current according to the amount of moisture (and hence humidity) as the moisture decomposes. The difference in current has a corresponding relationship with the humidity of the gas to be detected. Therefore, the humidity of the gas to be detected can be obtained based on the difference in current.

  (2) In the second aspect of the present invention, the apparatus includes a control determination unit that determines whether a condition for determining whether to perform gas concentration detection or humidity detection is satisfied, and based on a determination result by the control determination unit, Control that satisfies the above conditions is performed.

In the second aspect, gas concentration detection can be performed when a condition for performing gas concentration detection is satisfied, and humidity detection can be performed when a condition for performing humidity detection is satisfied.
(3) In the third aspect of the present invention, the control determination means uses the result of gas concentration detection as a condition for switching from gas concentration detection to humidity detection.

In the third aspect, switching from gas concentration detection to humidity detection can be performed according to the result of gas concentration detection.
For example, when the gas concentration corresponds to a state in which the fuel is cut (for example, the atmosphere), the gas concentration detection can be switched to the humidity detection.

  (4) In the fourth aspect of the present invention, the electromotive force cell includes a detection chamber in which a gas to be detected is introduced into the gas sensor element, and the electromotive force cell has one of the pair of first electrodes in the detection chamber. The other first electrode is disposed and exposed to an oxygen concentration atmosphere serving as a reference. Furthermore, an oxygen concentration detection means is provided for detecting the oxygen concentration of the gas to be detected in the detection chamber by the electromotive force cell during humidity detection. The control determination unit uses the detection result of the oxygen concentration detected by the oxygen concentration detection unit as a condition for switching from the humidity detection to the gas concentration detection.

  In the fourth aspect, when performing humidity detection, the oxygen concentration of the gas to be detected in the detection chamber can be detected, and switching from humidity detection to gas concentration detection is performed based on this oxygen concentration. Can do.

  (5) In the fifth aspect of the present invention, the detected gas is a gas discharged from the internal combustion engine, and the state of detecting the humidity of the detected gas is an exhaust gas in the atmosphere or stoichiometric state. Detects the humidity of the gas to be detected in either or both cases.

In the fifth aspect, the humidity of the gas to be detected can be detected when the gas to be detected is exhaust gas in the atmosphere or stoichiometric (theoretical air-fuel ratio) state.
Accordingly, for example, the output of the oxygen sensor can be accurately corrected based on the humidity detected in each state, and therefore, for example, the operation of the engine performed based on the output of the oxygen sensor can be suitably controlled. .

  (6) In the gas concentration / humidity detection method according to the sixth aspect of the present invention, the first solid electrolyte body and the pair of first electrodes formed on the first solid electrolyte body have an electromotive force generated between the first electrodes. An electromotive force cell, and an oxygen pump cell having a second solid electrolyte body and a pair of second electrodes formed on the second solid electrolyte body and capable of pumping oxygen between the second electrodes. A gas sensor element is used. In this gas concentration / humidity detection method, the gas concentration of a specific component in the gas to be detected is detected using an electromotive force cell and an oxygen pump cell. In addition to detecting the gas concentration, the humidity of the gas to be detected is detected.

  When detecting the humidity, in the voltage application step, the first voltage for electrolyzing moisture in the gas to be detected is applied to the pair of electrodes of the electromotive force cell or the oxygen pump cell, and the first voltage lower than the first voltage. Two voltages are applied. In the humidity detection step, the pair of electrodes of the cell to which the second voltage is applied when the first current and the second voltage that are applied between the pair of electrodes of the cell to which the first voltage is applied when the first voltage is applied The humidity of the gas to be detected is detected based on the difference from the second current flowing therebetween.

The sixth aspect has the same effects as the first aspect.
Here, each structure of this invention is demonstrated.
As described above, the gas concentration / humidity detection device and the gas concentration / humidity detection method are devices that detect the gas concentration and humidity of a specific component of a gas to be detected using a gas sensor element including an electromotive force cell and an oxygen pump cell. And method.

The gas detection element is an element that includes an electromotive force cell and an oxygen pump cell and is used for detecting the gas concentration and humidity of a specific component of the gas to be detected.
The solid electrolyte body is a member having characteristics as a solid electrolyte (characteristic that can move ions (for example, oxygen ions) by an electric field applied from the outside: ion conductivity). Examples of the material for the solid electrolyte include zirconia (particularly yttria partially stabilized zirconia and magnesia partially stabilized zirconia), ceria (particularly gadolinium-doped ceria and samarium-doped ceria), and the like.

  An electromotive force cell is a cell in which an electromotive force is generated according to the gas concentration of a specific component between a pair of first electrodes when detecting the gas concentration. An oxygen pump cell is a cell that pumps oxygen (oxygen ions) between a pair of second electrodes when detecting a gas concentration.

  In addition, when detecting humidity using an electromotive force cell or an oxygen pump cell, a first voltage and a second voltage are applied between a pair of electrodes of a cell used for humidity detection, and the first voltage flowing at that time is applied. The current and the second current are measured.

  As the pumping operation of the oxygen pump cell, there is an operation of moving oxygen (oxygen ions) from one second electrode of the oxygen pump cell to the other second electrode side (an operation for pumping or pumping oxygen).

Examples of the gas to be detected include exhaust gas discharged from an internal combustion engine, exhaust gas discharged from a fuel cell system, and the like.
-As specific gas, oxygen, NOx, etc. are mentioned.

  In addition, as a basic configuration as a premise of the gas concentration / humidity detection device, “a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and the pair of first electrodes” One of the electrodes is disposed in a detection chamber into which the gas to be detected is introduced, and the other electrode is exposed to a reference oxygen concentration atmosphere (oxygen concentration detection cell), and a second solid electrolyte body And a pair of second electrodes formed on the second solid electrolyte body, one electrode of the pair of second electrodes being disposed in the detection chamber, and a current flowing between the pair of second electrodes In response to the above, the gas sensor element comprising an oxygen pump cell that pumps or pumps oxygen contained in the gas to be detected introduced into the detection chamber, and is to be detected using the electromotive force cell and the oxygen pump cell. Gas of specific component in gas And detection of the concentration, detection and humidity of the gas to be detected, the configuration of the gas concentration humidity detection device "that performs can be employed.

It is a figure which shows the schematic structure around the exhaust system of an internal combustion engine. FIG. 3 is a diagram showing a schematic structure of a full-range air-fuel ratio sensor 9; It is a figure which shows the sensor control apparatus of 1st Embodiment, the sensor unit provided with the gas sensor, etc. with the circuit state in the case of oxygen concentration detection (2 cell control). It is a figure which shows the sensor control apparatus of 1st Embodiment, the sensor unit provided with the gas sensor, etc. with the circuit state in the case of humidity detection (1 cell control). It is a flowchart of the control processing performed with the sensor control apparatus of 1st Embodiment. It is a figure which shows the sensor unit etc. provided with the sensor control apparatus of 2nd Embodiment, and a gas sensor with the circuit state in the case of humidity detection (1 cell control). It is a flowchart of the control processing performed with the sensor control apparatus of 2nd Embodiment. It is a flowchart of the control processing performed with the sensor control apparatus of 3rd Embodiment. It is a flowchart of the control processing performed with the sensor control apparatus of 4th Embodiment. It is a figure which shows the sensor control apparatus of 5th Embodiment, the sensor unit provided with the gas sensor, etc. with the circuit state in the case of humidity detection (1 cell control). It is a graph for demonstrating a prior art.

Hereinafter, embodiments of a gas concentration / humidity detection apparatus and a gas concentration / humidity detection method embodying the present invention will be described with reference to the drawings.
In the following, as an example of the gas concentration / humidity detection device according to the present invention, a sensor control device capable of detecting the oxygen concentration in the gas to be detected and the humidity of the gas to be detected based on the detection signal output from the gas sensor. Will be described as an example. As a gas sensor, a full-range air-fuel ratio sensor in which the sensor current changes linearly according to the oxygen concentration will be described as an example.

[1. First Embodiment]
[1-1. overall structure]
First, a schematic system configuration of an internal combustion engine 3 to which a sensor control device 1 that is a gas concentration / humidity detection device of the first embodiment is attached will be described with reference to FIG.

  The internal combustion engine 3 has an engine 5 for driving an automobile. The engine 5 is connected to an exhaust pipe 7 for releasing the exhaust gas discharged from the engine 5 to the outside of the vehicle. A full-range air-fuel ratio sensor 9 is disposed on the path of the exhaust pipe 7.

  More specifically, the full-range air-fuel ratio sensor 9 is a gas sensor that detects a gas concentration (oxygen concentration) of a specific component (oxygen in the first embodiment) in the exhaust gas flowing through the exhaust passage of the exhaust pipe 7. The full-range air-fuel ratio sensor 9 is electrically connected to the sensor control device 1 disposed at a position distant from itself through a harness 11 and is energized by the sensor control device 1 to detect the oxygen concentration. To do. As will be described later, in the first embodiment, this all-range air-fuel ratio sensor 9 is used to detect the humidity in the exhaust gas.

  Among these, the sensor unit 13 is configured by the full-range air-fuel ratio sensor 9 and the sensor control device 1 connected by the harness 11. That is, in the sensor unit 13, the full-range air-fuel ratio sensor 9 is electrically connected via the harness 11 to the sensor control device 1 attached at a position away from the full-range air-fuel ratio sensor 9.

  The sensor control device 1 is driven by receiving power from the battery 15, and outputs a detection signal of the oxygen concentration detected using the full-range air-fuel ratio sensor 9 to an engine control device (ECU) 17. In the ECU 17, air-fuel ratio feedback control of the engine 5 is performed based on the output of the full-range air-fuel ratio sensor 9.

  In addition, the arrangement | positioning aspect of the sensor control apparatus 1 can be changed suitably, for example, the sensor control apparatus 1 is integrated in ECU17, and it is good also as a sensor unit by the full range air-fuel ratio sensor 9 and ECU17.

  In the first embodiment, when fuel is being supplied to the engine 5, the exhaust gas becomes a detection target of the entire region air-fuel ratio sensor 9 as described above. On the other hand, in a state where the fuel supply to the engine 5 is stopped (fuel cut period), the atmosphere flows through the exhaust pipe 7, so that the atmosphere flowing through the exhaust pipe 7 is detected by the entire region air-fuel ratio sensor 9. Become. In the following description, it is assumed that the “detected gas” to be detected by the full-range air-fuel ratio sensor 9 includes both exhaust gas and air.

[1-2. Full-range air-fuel ratio sensor 9]
Next, the full-range air-fuel ratio sensor 9 will be briefly described with reference to FIG.
The full-range air-fuel ratio sensor 9 includes a cylindrical metal shell 23, a plate-shaped gas sensor element 25 extending in the direction of the axis O (the vertical direction in FIG. 2), and a cylindrical ceramic sleeve 27 surrounding the gas sensor element 25. A cylindrical first separator 31 surrounding the periphery of the rear end (upper side in FIG. 2) of the gas sensor element 25, and a plurality of connection terminals 33 disposed between the gas sensor element 25 and the first separator 31. , Mainly.

  The gas sensor element 25 includes a detection unit 35 that detects the concentration of oxygen contained in the exhaust gas on the front end side, and a plurality of main surfaces that are in a positional relationship between the front and back sides of the outer surface on the rear end side have a plurality of An electrode pad 37 is formed.

  The connection terminals 33 are electrically connected to the electrode pads 37 of the gas sensor element 25, respectively, and are electrically connected from the outside to a lead wire 39 disposed inside the entire region air-fuel ratio sensor 9. The harness 11 is configured by bundling the lead wires 39.

  The metal shell 23 is configured to hold the gas sensor element 25 inserted through the through hole 41. That is, the ceramic holder 43, the talc rings 45 and 47, and the ceramic sleeve 27 are laminated in the through hole 41 of the metal shell 23 so as to surround the periphery of the gas sensor element 25. A protector 49 is attached to the front end side of the metal shell 23.

  On the other hand, an outer cylinder 51 is fixed to the outer periphery of the rear end side of the metal shell 23, and a grommet 53 is disposed on the rear end side of the outer cylinder 51. Two separators 55 are arranged.

[1-3. Gas sensor element]
Next, the structure of the gas sensor element 25 will be described with reference to FIG.
The gas sensor element 25 includes a first solid electrolyte body 61 and a second solid electrolyte body 63 mainly composed of zirconia, a first insulating base body 65, a second insulating base body 67, a third insulating base body 69, a fourth base body mainly composed of alumina. And an insulating base 71.

  In the gas sensor element 25, the first and second insulating bases 65 and 67, the first solid electrolyte body 61, the third insulating base 69, the second solid electrolyte body 63, and the fifth insulating base 71 are viewed from below in FIG. 3. They are stacked in order.

  A pair of first electrodes 73 and 75 mainly composed of platinum are respectively formed on both surfaces of the first solid electrolyte body 61 (vertical direction in FIG. 3). Similarly, on both surfaces of the second solid electrolyte body 63 Also, a pair of second electrodes 77 and 79 are formed. One of the first electrodes 73 is embedded between the first solid electrolyte body 61 and the second insulating base 67.

  The first and second solid electrolyte bodies 61 and 63 and the first to fifth insulating bases 65 to 71 are all formed in a plate shape elongated in the direction perpendicular to the paper surface of FIG. 3, and in FIG. A cross section orthogonal to the longitudinal direction (that is, a cross section of the detection unit 35) is shown.

  A hollow detection chamber 81 into which exhaust gas can be introduced while the first and second solid electrolyte bodies 61 and 63 are used as one wall surface is formed on one end side in the longitudinal direction of the third insulating substrate 69 (that is, the detection unit 35). ing. At both ends of the detection chamber 81 in the width direction (left-right direction in FIG. 3), porous diffusion rate-limiting portions 83 are provided for regulating the amount of inflow when the exhaust gas is introduced into the detection chamber 81 from the outside. Yes.

The inner first electrode 75 on the first solid electrolyte body 61 and the inner second electrode 77 on the second solid electrolyte body 63 are respectively exposed in the detection chamber 81.
In addition, a heating resistor 85 mainly composed of platinum is embedded between the first and second insulating bases 65 and 67. The first and second insulating bases 65 and 67 and the heating resistor 85 function as a heater for heating and activating the first and second solid electrolyte bodies 61 and 63.

  The outer second electrode 79 on the second solid electrolyte body 63 has a surface covered with a porous protective layer 87 made of ceramics (for example, alumina). That is, the second electrode 79 is protected by the protective layer 87 so as not to be deteriorated by poisoning components such as silicon contained in the exhaust gas. The fifth insulating base 71 laminated on the second solid electrolyte body 63 is provided with an opening 89 so as not to cover the second electrode 79, and the protective layer 87 is disposed in the opening 89. ing.

  In the gas sensor element 25 configured as described above, the first solid electrolyte body 61 and the pair of first electrodes 73 and 75 provided on both surfaces thereof are in accordance with the difference in oxygen concentration between the first electrodes 73 and 75. It functions as an oxygen concentration detection cell (that is, electromotive force cell: hereinafter also referred to as “Vs cell”) 91 that generates electromotive force. One first electrode 73 functions as an oxygen reference electrode that maintains an oxygen concentration serving as a reference for detecting the oxygen concentration in the detection chamber 81.

  Similarly, the second solid electrolyte body 63 and a pair of second electrodes 77 and 79 provided on both surfaces of the second solid electrolyte body 63 pump oxygen into the detection chamber 81 from the outside, or pump oxygen from the detection chamber 81 to the outside. It functions as a pump cell (hereinafter also referred to as “Ip cell”) 93. The detailed functions of the Ip cell 93 and the Vs cell 91 will be described later.

[1-4. Sensor control device]
Next, the configuration of the sensor control device 1 will be described with reference to FIG.
The sensor control device 1 includes a microcomputer 101 and an electric circuit unit 103 as constituent elements. The microcomputer 101 is a microcomputer chip on which a CPU 101a, a ROM 101b, a RAM 101c, a nonvolatile memory (not shown), and the like having a known configuration are mounted.

  The ROM 101b stores a control program for causing the CPU 101a to execute each process, a table indicating a relationship between a current difference ΔIp and humidity described later, a humidity correction table for performing humidity correction, and the like.

  The electric circuit unit 103 includes a heater voltage supply circuit 105, an electromotive force measurement circuit 107, a minute current supply circuit 109, a voltage output circuit 111, a reference voltage comparison circuit 113, a pump current drive circuit 115, and a pump current detection circuit 117. .

  A first switch 121 is provided between the electromotive force measuring circuit 107 and the first electrode 73 to turn on (connect) and turn off (shut off) the circuit. Is provided with a second switch 123 for turning on and off the circuit. A third switch 127 for turning on / off the circuit is provided between the minute current supply circuit 109 and the first circuit 125, and a third switch 127 for turning on / off the circuit is provided between the voltage output circuit 111 and the first circuit 125. Four switches 129 are provided. Further, the first circuit 125 is provided with a changeover switch 131 that switches a connection between the first circuit 125 and the first electrode 73 and a connection between the first circuit 125 and the second electrode 79.

The heater voltage supply circuit 105 performs PWM control on the voltage Vh supplied to both ends of the heating resistor 85 to cause the heating resistor 85 to generate heat, and heats the Ip cell 93 and the Vs cell 91.
The electromotive force measurement circuit 107 measures the electromotive force Vs generated between the pair of first electrodes 73 and 75 of the Vs cell 91. The measurement result is output to the microcomputer 101. The electromotive force measurement circuit 107 can be used as a circuit for monitoring whether the atmosphere (specifically, the oxygen concentration in the detection chamber 81) has changed during humidity detection. You may omit it.

  The minute current supply circuit 109 causes a minute current Icp to flow from one first electrode 73 of the Vs cell 91 to the other first electrode 75 side, and moves oxygen ions to the first electrode 73 side to serve as a reference oxygen concentration atmosphere. Is generated. Thereby, the 1st electrode 73 functions as an oxygen reference electrode used as a standard for detecting oxygen concentration in gas to be detected.

  The voltage output circuit 111 detects an electromotive force Vs generated between the pair of first electrodes 73 and 75 of the Vs cell 91 when detecting the oxygen concentration. Further, when detecting the humidity, an electromotive force Vp generated between the pair of second electrodes 77 and 79 of the Ip cell 93 is detected. The detection result is output to the reference voltage comparison circuit 113.

  The reference voltage comparison circuit 113 compares a predetermined reference voltage with the electromotive force Vs or electromotive force Vp detected by the voltage output circuit 111 and feeds back the comparison result to the pump current drive circuit 115.

  The pump current drive circuit 115 controls the magnitude and direction of the pump current Ip that flows between the pair of second electrodes 77 and 79 of the Ip cell 93 based on the comparison result obtained from the reference voltage comparison circuit 113. As a result, oxygen is pumped into the detection chamber 81 and oxygen is pumped out of the detection chamber 81 by the Ip cell 93.

  The pump current detection circuit 117 detects the pump current Ip flowing between the pair of second electrodes 77 and 79 of the Ip cell 93, converts the voltage, and outputs it as a detection signal to the microcomputer 101.

  In the first embodiment, two reference voltages (first voltage V1 and second voltage V2: first voltage V1> second) are used as reference voltages to be compared with the electromotive force Vs or the electromotive force Vp by the reference voltage comparison circuit 113. Voltage).

  Among these, the second voltage V2 lower than the first voltage is used when detecting the oxygen concentration and detecting the humidity, as will be described later. The second voltage V2 is used for comparison with the electromotive force Vs in the Vs cell 91 or the electromotive force Vp in the Ip cell 93 detected by the voltage output circuit 111.

That is, when the oxygen concentration is detected, the operation of the pump current drive circuit 115 is controlled so that the electromotive force Vs becomes the second voltage V2. Specifically, the second voltage V2 is normally used as the reference voltage to be compared with the electromotive force Vs, and the oxygen concentration in the exhaust gas is calculated based on the pump current Ip. The second voltage V2 is set to a voltage value (for example, 450 mV) such that moisture (H ₂ O) in the exhaust gas introduced into the detection chamber 81 does not substantially dissociate.

  On the other hand, the first voltage V1 higher than the second voltage, together with the second voltage V2, is a voltage used when detecting humidity, as will be described later, and the Ip cell 93 detected by the voltage output circuit 111. Is used for comparison with the electromotive force Vp at.

  That is, when detecting the humidity, the operation of the pump current drive circuit 115 is controlled so that the electromotive force Vp becomes the first voltage V1, and the pump is made so that the electromotive force Vp becomes the second voltage V2. The operation of the current drive circuit 115 is controlled.

The first voltage V1 is set to a high voltage value (for example, 1000 mV) such that moisture (H ₂ O) in the exhaust gas introduced into the detection chamber 81 is dissociated.
[1-5. ECU]
Next, the configuration of the ECU 17 will be described.

  The ECU 17 is a device for electronically controlling driving of the engine 5 of the automobile. The ECU 17 uses a microcomputer chip having a CPU, ROM, RAM, etc. having a known configuration, and controls the fuel injection timing and ignition timing according to the execution of the control program.

  As information for performing such control, an output (detection signal) corresponding to the oxygen concentration in the exhaust gas is input from the sensor control device 1. Further, as other information, signals from other sensors (for example, information such as a crank angle at which the piston position and the rotation speed of the engine 5 can be detected, a coolant temperature, a combustion pressure, etc.) are also input.

[1-6. Gas concentration / humidity detection method]
Next, a gas concentration / humidity detection method performed by the sensor control device 1, that is, an oxygen concentration detection method and a humidity detection method will be described.

<Method for detecting oxygen concentration>
First, the operation for detecting the oxygen concentration of the exhaust gas (and hence the air-fuel ratio of the exhaust gas) using the full-range air-fuel ratio sensor 9 will be briefly described. When detecting the oxygen concentration of the exhaust gas, as described above, the second voltage V2 (for example, 450 mV) is set as the reference voltage to be compared by the reference voltage comparison circuit 113.

  When detecting the oxygen concentration, a circuit is connected as shown in FIG. That is, the first and second switches 121 and 123 are turned off, the third and fourth switches 127 and 129 are turned on, and the first circuit 125 and the electrode 73 are connected by the changeover switch 131.

  In the connection state of this circuit, first, the minute current supply circuit 109 causes a minute current Icp to flow from one first electrode 73 of the Vs cell 91 to the other first electrode 75. By this energization, oxygen in the exhaust gas is pumped from the other first electrode 75 side to the first electrode 73 side through the first solid electrolyte body 61, and the first electrode 73 functions as an oxygen reference electrode. .

  Then, an electromotive force Vs generated between the first electrodes 73 and 75 is detected by the voltage output circuit 111, and the electromotive force Vs is compared with the second voltage V2 by the reference voltage comparison circuit 113. In the pump current driving circuit 115, the magnitude of the pump current Ip passed between the second electrodes 77 and 79 of the Ip cell 93 so that the electromotive force Vs becomes the second voltage V2 based on the comparison result by the reference voltage comparison circuit 113. Control the orientation.

  If the air-fuel ratio of the exhaust gas flowing into the detection chamber 81 is richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, so that oxygen is pumped into the detection chamber 81 from the outside in the Ip cell 93. In addition, the pump current Ip flowing between the second electrodes 77 and 79 is controlled. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the detection chamber 81 is leaner than the stoichiometric air-fuel ratio, a large amount of oxygen is present in the exhaust gas, so that oxygen is pumped from the detection chamber 81 to the outside in the Ip cell 93. The pump current Ip flowing between the second electrodes 77 and 79 is controlled so as to be output.

  The pump current Ip at this time is converted into a voltage by the pump current detection circuit 117 and output to the microcomputer 101 as the output (detection signal) of the full-range air-fuel ratio sensor 9. The microcomputer 101 can specify the concentration of oxygen contained in the exhaust gas and thus the air-fuel ratio of the exhaust gas based on the magnitude and direction of the pump current Ip output from the full-range air-fuel ratio sensor 9.

  That is, as described above, in the first embodiment, the sensor unit 13 (the entire region air-fuel ratio sensor 9 and the sensor control device 1) has the same configuration as that of the conventional sensor unit, and the oxygen concentration of the exhaust gas. The detection operation of (the exhaust gas air-fuel ratio) is the same as the conventional one.

<Humidity detection method>
In the first embodiment, as will be described in detail below, the humidity of the gas discharged from the engine 5 using, for example, the Ip cell 93 as a single humidity detection cell in the configuration of the entire region air-fuel ratio sensor 9. Is detected.

First, the basic principle of humidity detection will be described in detail.
For example, as disclosed in JP-A-63-85351, when the components of the exhaust gas are water vapor (moisture), oxygen, and nitrogen, the pump current that flows through the Ip cell 93 by the voltage applied to the Ip cell 93 is determined. Ip changes.

Specifically, when only oxygen gas passes through the second solid electrolyte body 63 constituting the Ip cell 93 as oxygen ions, water is electrolyzed as well as oxygen gas, and H ₂ O → H ₂ +1. Oxygen ions represented by / 2O ₂ may also pass through the second solid electrolyte body 63. Therefore, the pump current Ip varies depending on the applied voltage of the Ip cell 93 even if the amount of water contained in the exhaust gas is the same.

  Specifically, when the Ip cell 93 is driven with a first voltage V1 (for example, 1000 mV) that electrolyzes moisture, the first pump current Ip1 flows through the Ip cell 93 and is lower than the first voltage V1 (substantially electrolyze moisture). When the Ip cell 93 is driven with the second voltage V2 (for example, 450 mV) that is not decomposed, a second pump current Ip2 smaller than the first pump current Ip1 flows through the Ip cell 93.

It is known that the partial pressure _PH2O of water vapor at this time is proportional to the current difference ΔIp between the first pump current Ip1 and the second pump current Ip2 in the gas phase equilibrium state.
Therefore, the partial pressure _{PH2O of} water vapor can be obtained from the current difference ΔIp (= Ip1−Ip2) between the first pump current Ip2 and the second pump current Ip1. That is, the humidity of the exhaust gas can be obtained.

  In the first embodiment, when the humidity is detected based on the principle described above, the circuit is connected as shown in FIG. 4 so that only the Ip cell 93 is operated without operating the Vs cell 91. Is done.

  That is, the first, second, and third switches 121, 123, and 127 are turned off, the fourth switch 129 is turned on, and the first circuit 125 and the second electrode 79 are connected by the changeover switch 131.

  In the connection state of this circuit, first, the operation of the pump current drive circuit 115 is controlled so that the second voltage V2 of, for example, 450 mV is applied between the second electrodes 77 and 79 of the Ip cell 93.

  Specifically, the pump current drive circuit 115 causes the pump current Ip to flow between the second electrodes 77 and 79 of the Ip cell 93. At this time, the voltage output circuit 111 causes the second electrodes 77 and 79 of the Ip cell 93 to flow. An electromotive force (pump voltage) Vp generated in the meantime is detected, and this pump voltage Vp is compared with the second voltage V2 by the reference voltage comparison circuit 113.

In addition, since the difference of oxygen concentration arises between both the 2nd electrodes 77 and 79 by flowing pump current Ip, the electromotive force Vp generate | occur | produces by this oxygen concentration difference.
In the pump current driving circuit 115, the pump current Ip flowing between both the second electrodes 77 and 79 of the Ip cell 93 so that the pump voltage Vp becomes the second voltage V 2 based on the comparison result by the reference voltage comparison circuit 113. To control.

The pump current Ip at this time is converted into a voltage by the pump current detection circuit 117 and output to the microcomputer 101 as the second pump current Ip2.
Next, the operation of the pump current drive circuit 115 is controlled so that the first voltage V1 of, for example, 1000 mV is applied between the second electrodes 77 and 79 of the Ip cell 93.

  Specifically, the pump current drive circuit 115 causes the pump current Ip to flow between the second electrodes 77 and 79 of the Ip cell 93. At this time, the voltage output circuit 111 causes the second electrodes 77 and 79 of the Ip cell 93 to flow. An electromotive force (pump voltage) Vp generated in the meantime is detected, and this pump voltage Vp is compared with the first voltage V1 by the reference voltage comparison circuit 113.

  In the pump current driving circuit 115, based on the comparison result by the reference voltage comparison circuit 113, the pump current Ip flowing between the second electrodes 77 and 79 of the Ip cell 93 so that the pump voltage Vp becomes the first voltage V 1. To control.

The pump current Ip at this time is converted into a voltage by the pump current detection circuit 117 and output to the microcomputer 101 as the first pump current Ip1.
In the microcomputer 101, a current difference ΔIp between the first pump current Ip1 and the second pump current Ip2 is obtained. And the humidity of exhaust gas is calculated | required from current difference (DELTA) Ip using the table which shows the relationship between current difference (DELTA) Ip and humidity memorize | stored in ROM101b.

[1-7. Control processing]
Next, the gas concentration / humidity detection processing executed in the sensor control apparatus 1 will be described with reference to FIG. A program for executing each process shown in FIG. 5 is also stored in the ROM 101b described above, and is executed by the CPU 101a.

In this gas concentration / humidity detection process, the humidity is detected when the engine 5 is started, and thereafter the oxygen concentration is detected.
Since the gas discharged from the engine 5 immediately after the start of the engine 5 is neither the atmosphere nor the exhaust gas in the stoichiometric state (combustion exhaust gas), a predetermined time is required so that the exhaust gas becomes stoichiometric after the engine 5 is started. It is preferable to detect the humidity after a while.

  As shown in the flowchart of FIG. 5, when the gas concentration / humidity detection process is started in the sensor control device 1, first, various initial settings are performed in step (S) 100. For example, a process of erasing the atmospheric humidity stored in the nonvolatile memory at the previous execution of humidity detection and the stoichiometric humidity from the nonvolatile memory is performed.

  In the next step 110, it is determined whether or not it is the timing of humidity detection. That is, it is determined whether or not a predetermined time (that is, an initial time until the start of oxygen concentration detection: for example, 300 seconds or more) has elapsed since the engine 5 was started. If an affirmative determination is made here, the process proceeds to step 120, while if a negative determination is made, the process proceeds to step 160.

  In step 120, processing for switching to 1-cell control is performed in order to perform humidity detection. Specifically, in order to detect the humidity using only the Ip cell 93 without using the Vs cell 91, the connection state of each switch as shown in FIG. 4 is set.

  In the subsequent step 130, the humidity is detected by the above-described “humidity detection method” using the sensor unit 13 set in the circuit shown in FIG. 4 and the Ip cell 93 as the humidity detection cell.

  That is, as described above, the pump current Ip flowing between the second electrodes 77 and 79 of the Ip cell 93 is controlled so that the second voltage V2 of 450 mV is obtained between the second electrodes 77 and 79 of the Ip cell 93. Then, the pump current Ip at this time is obtained as the second pump current Ip2. Further, the pump current Ip flowing between the second electrodes 77 and 79 of the Ip cell 93 is controlled so that the first voltage V1 of 1000 mV is established between the second electrodes 77 and 79 of the Ip cell 93. The pump current Ip is obtained as the first pump current Ip1. Then, a current difference ΔIp between the first pump current Ip1 and the second pump current Ip2 is obtained, and the humidity of the exhaust gas is obtained from the current difference ΔIp.

Note that the order in which the first voltage V1 and the second voltage V2 are applied, that is, the order in which the first pump current Ip1 and the second pump current Ip2 are detected may be performed first.
In the following step 140, it is determined whether or not the same exhaust gas state (atmosphere) is maintained when the present humidity detection is performed. This is because the driver arbitrarily accelerates and decelerates while the vehicle is traveling, so that fuel injection and fuel cut occur randomly and the exhaust gas is not constant. Then, since there is a possibility that the measurement atmosphere may change during the humidity detection, this determination is added to detect the humidity in the same atmosphere.

  Here, for example, when a fuel cut is made based on a fuel cut (fuel cut signal), it is determined that the atmosphere has changed. If a negative determination is made here, the process returns to step 110. If an affirmative determination is made, the process proceeds to step 150.

In step 150, assuming that humidity is properly detected in the same atmosphere, the humidity is stored in the RAM 101c, and the process returns to step 110.
After that, when humidity is detected a plurality of times by the same process, for example, the average value can be adopted as the humidity.

Here, the detected humidity and the average value of the humidity are also stored in the nonvolatile memory (the same applies hereinafter).
Further, in step 160, which is determined to be negative in step 110, the process of switching to 2-cell control is performed in order to detect the oxygen concentration. Specifically, in order to detect the oxygen concentration as usual using the Vs cell 91 and the Ip cell 93, the connection state of each switch as shown in FIG. 3 is set.

In the subsequent step 170, the oxygen concentration is detected by the above-described “oxygen concentration detection method” using the sensor unit 13 set in the circuit shown in FIG.
That is, as described above, the Vs cell 91 and the Ip cell 93 are used, and the electromotive force Vs of the Vs cell 91 is caused to flow between the second electrodes 77 and 79 of the Ip cell 93 so as to become the second voltage (450 mV). The magnitude and direction of the pump current Ip are controlled, the oxygen concentration is obtained based on the pump current Ip at this time, and this process is temporarily terminated.

[1-8. effect]
In the first embodiment, the full-range air-fuel ratio sensor 9 can be used as the sensor, and the oxygen concentration in the exhaust gas can be detected using the Vs cell 91 and the Ip cell 93, and the Ip cell 93 is used. Humidity can be detected.

  Specifically, after a predetermined time has elapsed from the start of the engine 5, a first voltage V1 of, for example, 1000 mV for electrolyzing moisture in the gas to be detected is applied to the pair of second electrodes 77 and 79 of the Ip cell 93. Further, a second voltage V2 of 450 mV, for example, which is lower than the first voltage V1 is applied. A first pump current Ip1 flowing between the pair of second electrodes 77 and 79 of the Ip cell 93 when the first voltage V1 is applied, and a pair of second of the Ip cell 93 when the second voltage V2 is applied. Based on the current difference ΔIp between the second pump current Ip2 flowing between the electrodes 77 and 79, the humidity of the exhaust gas can be detected.

  That is, in the first embodiment, the Vs cell 91 and the Ip cell 93 are used and the humidity of the exhaust gas is not detected by performing PID control as in the prior art, but the humidity applied by controlling the voltage applied to the Ip cell 93 is controlled. Since the detection is performed, overshoot of the Ip current and the Vp voltage accompanying the PID control does not occur, and the second solid electrolyte body 63 is not easily blackened. As a result, since the characteristics of the second solid electrolyte body 63 are not easily deteriorated, there is a remarkable effect that the durability of the full-range air-fuel ratio sensor 9 is improved.

In the first embodiment, the humidity detection is performed using the Ip cell 93, but the humidity detection may be performed using the Vs cell 91 without using the Ip cell 93.
[2. Second Embodiment]
Next, the second embodiment will be described, but the description of the same contents as the first embodiment will be omitted or simplified. In addition, the same number is attached | subjected and demonstrated to the structure similar to 1st Embodiment.

In the second embodiment, when the humidity detection is performed using the Ip cell 93, simultaneously, the electromotive force (and hence the oxygen concentration) of the Vs cell 91 is measured (monitored) using the Vs cell 91.
[2-1. Configuration and basic operation]
First, the configuration and basic operation in the second embodiment will be described.

  As shown in FIG. 6, the system configuration in the second embodiment includes an entire-range air-fuel ratio sensor 9 and a sensor control device 1 as in the first embodiment. A computer 101 and an electric circuit unit 103 are provided. The electric circuit unit 103 includes the circuits 105 to 117 and the switches 121, 123, 127, 129, and 131 as in the first embodiment.

  In the second embodiment, a circuit is connected as shown in FIG. That is, the first and second switches 121 and 123 are turned on, the third switch 127 is turned off, and the fourth switch 129 is turned on, and the first circuit 125 and the second electrode 79 are connected by the changeover switch 131. .

When the humidity is detected using the Ip cell 93 in the connection state of this circuit, it can be performed in the same manner as in the first embodiment.
That is, a first voltage V1 of 1000 mV, for example, is applied to the pair of second electrodes 77 and 79 of the Ip cell 93, and a second voltage V2 of 450 mV, for example, is applied. The first pump current Ip1 that flows between the second electrodes 77 and 79 of the Ip cell 93 when the first voltage V1 is applied, and the second electrodes 77 and 79 of the Ip cell 93 when the second voltage V2 is applied. The humidity of the exhaust gas is detected based on the current difference ΔIp with the second pump current Ip2 flowing therebetween.

In the second embodiment, the change in the oxygen concentration of the exhaust gas is detected by the Vs cell 91 when the humidity is detected as described above.
Specifically, the voltage Vs between the first electrodes 73 and 75 of the Vs cell 91 is measured using the electromotive force measurement circuit 107. This measurement result is sent to the microcomputer 101, and the microcomputer can detect the oxygen concentration of the exhaust gas from the voltage change.

  Therefore, when the oxygen concentration of the exhaust gas changes, it can be considered that the state (atmosphere: component) of the exhaust gas for which humidity detection is performed has changed. In that case, it is not appropriate to perform humidity detection as it is, and the operation is switched to detection of oxygen concentration by 2-cell control.

  Here, when the exhaust gas is in the atmosphere (for example, in a fuel cut state where no fuel is supplied to the engine 5), the oxygen concentration is high, while when the fuel is supplied to the engine 5 and burning, the exhaust gas The oxygen concentration inside becomes lower than the atmosphere.

  Therefore, for example, the voltage Vs of the Vs cell 91 can be used to determine whether the exhaust gas is air or exhaust gas after combustion (for example, exhaust gas in a stoichiometric state). Therefore, it is possible to determine whether the humidity currently being measured is atmospheric humidity or exhaust gas (for example, stoichiometric) humidity.

[2-2. Control processing]
Next, the gas concentration / humidity detection processing in the second embodiment will be described.
As shown in the flowchart of FIG. 7, when the engine 5 receives fuel supply and burns and operates, when the humidity detection condition is satisfied (for example, when the atmosphere is fuel cut), In order to detect the humidity, in step 200, as in step 120, the one-cell control state shown in FIG. 4 is set.

In the subsequent step 210, the humidity is detected by the one-cell control in the same manner as in step 130.
In the subsequent step 220, as in step 140, it is determined whether or not the same atmosphere is maintained. For example, it is determined whether or not the voltage Vs between the first electrodes 73 and 75 of the Vs cell 91 monitored from the start of humidity detection is maintained within a predetermined range indicating that there is no change in the atmosphere. If an affirmative determination is made here, the process proceeds to step 230. If a negative determination is made, the process returns to step 210.

In step 230, the humidity is stored as in step 150.
In the following step 240, it is determined whether or not the oxygen concentration is detected. For example, when the fuel cut is switched to the fuel supply state (therefore, the oxygen concentration is changed from the atmosphere), whether or not the voltage Vs between the first electrodes 73 and 75 of the Vs cell 91 is out of the predetermined range. Judge by. If an affirmative determination is made here, the process proceeds to step 250, whereas if a negative determination is made, the present process is temporarily terminated.

In step 250, in order to detect the oxygen concentration, the two-cell control state is set as in step 160.
In the subsequent step 260, as in step 170, the oxygen concentration is detected by the two-cell control, and the process is temporarily terminated.

After that, the oxygen concentration is detected until the humidity detection condition is satisfied.
Therefore, in the second embodiment, the same effect as that of the first embodiment is obtained, and when the conditions for detecting the oxygen concentration are satisfied by the above-described control processing, for example, during the detection of atmospheric humidity, By switching to concentration detection, the oxygen concentration can be detected. That is, the atmospheric humidity can be detected with high accuracy.

[3. Third Embodiment]
Next, the third embodiment will be described, but the description of the same contents as the first embodiment will be omitted or simplified. In addition, the same number is attached | subjected and demonstrated to the structure similar to 1st Embodiment.

In the third embodiment, the apparatus configuration and the like are the same as those in the first embodiment, and only the control processing is different. Therefore, only the different control processing will be described.
In the third embodiment, when the oxygen concentration is detected by two-cell control, when the humidity detection condition is satisfied, the oxygen concentration detection is switched to the humidity detection.

  As shown in the flowchart of FIG. 8, when the engine 5 is supplied with fuel and burns and operates, in step 300, the two-cell control shown in FIG. Set to state.

In the subsequent step 310, as in step 170, the oxygen concentration is detected by the two-cell control.
In the subsequent step 320, it is determined whether or not it is time to perform humidity detection. For example, when the humidity detection is performed when the exhaust gas becomes the atmosphere, it is determined that it is the timing to perform the humidity detection when, for example, a fuel cut signal is detected. If an affirmative determination is made here, the process proceeds to step 330, whereas if a negative determination is made, the process returns to step 310 to continue detection of the oxygen concentration.

In step 330, in order to detect the humidity, a state of 1-cell control (using the Ip cell 93) is set as in step 120.
In the subsequent step 340, the humidity is detected by one-cell control, as in step 130.

  In the subsequent step 350, as in step 140, it is determined whether or not the same atmosphere is maintained. For example, it is determined whether a fuel cut is maintained by outputting a fuel cut signal. If an affirmative determination is made here, the process proceeds to step 360. If a negative determination is made on the other hand, the present process is temporarily terminated.

  When the humidity detection is performed using the Ip cell 93, when the oxygen concentration is detected using the Vs cell 91 as in the second embodiment, a change in the atmosphere is determined based on the oxygen concentration. May be.

In step 360, as in step 150, the humidity detected this time is stored, and the process is temporarily terminated.
Even after this process is completed, the same process is repeated again to detect the oxygen concentration.

  Therefore, in the third embodiment, the same effect as that of the first embodiment is obtained, and when the humidity detection condition is satisfied during the detection of the oxygen concentration by the above-described control processing, switching to the humidity detection is performed. The humidity can be detected.

[4. Fourth Embodiment]
Next, the fourth embodiment will be described, but the description of the same contents as the first embodiment will be omitted or simplified. In addition, the same number is attached | subjected and demonstrated to the structure similar to 1st Embodiment.

In the fourth embodiment, the apparatus configuration and the like are the same as those in the first embodiment, and only the control processing is different. Therefore, only the different control processing will be described.
In the fourth embodiment, when the oxygen concentration is detected by the two-cell control, when the condition for detecting the humidity of the atmosphere and the condition for detecting the humidity of the exhaust gas in the stoichiometric condition are satisfied, Is detected.

  As shown in the flowchart of FIG. 9, when the engine 5 is supplied with fuel and burns and operates, in step 400, the two-cell control shown in FIG. Set to state.

In the subsequent step 410, as in step 170, the oxygen concentration is detected by the two-cell control.
In the following step 420, it is determined whether or not it is time to detect humidity in the atmosphere. That is, it is determined whether or not the discharged gas is the atmosphere. If an affirmative determination is made here, the process proceeds to step 420, while if a negative determination is made, the process proceeds to step 470.

  Here, whether or not the gas discharged from the engine 5 is atmospheric can be determined using the oxygen concentration detected in step 410, for example. That is, when the oxygen concentration is a concentration indicating the atmosphere, it can be determined that the atmosphere is the atmosphere. Further, when the fuel is cut (when the fuel cut signal is detected), it may be determined that the atmosphere is air.

In step 430, in order to perform humidity detection, a state of 1-cell control (using the Ip cell 93) is set as in step 120.
In the subsequent step 440, as in step 130, the humidity is detected by one-cell control.

  In the subsequent step 450, as in step 140, it is determined whether or not the same atmosphere is maintained. For example, it is determined whether a fuel cut is maintained by outputting a fuel cut signal. If an affirmative determination is made here, the process proceeds to step 460, whereas if a negative determination is made, the present process is temporarily terminated.

  When the humidity detection is performed using the Ip cell 93, when the oxygen concentration is detected using the Vs cell 91 as in the second embodiment, a change in the atmosphere is determined based on the oxygen concentration. May be.

In step 460, as in step 150, the humidity detected this time is stored as the atmospheric humidity, and the process is temporarily terminated.
Further, in step 470 which proceeds with a negative determination in step 420, it is determined whether or not it is time to detect humidity in the exhaust gas in the stoichiometric state. That is, it is determined whether the exhaust gas is stoichiometric. If an affirmative determination is made here, the process proceeds to step 480, whereas if a negative determination is made, the process proceeds to step 410.

  That is, when the gas discharged from the engine 5 is neither the atmosphere nor the exhaust gas in the stoichiometric state, the detection of the oxygen concentration by the two-cell control is continued assuming that the humidity is not detected.

  Whether the gas discharged from the engine 5 is exhaust gas in a stoichiometric state can be determined using, for example, the oxygen concentration detected in step 410. That is, when the oxygen concentration is a concentration indicating stoichiometry, it can be determined that the exhaust gas is in a stoichiometric state.

In step 480, in order to detect the humidity, a state of 1-cell control (using the Ip cell 93) is set as in step 120.
In the following step 490, the humidity is detected by the one-cell control as in step 130.

  In the subsequent step 500, as in step 140, it is determined whether or not the same atmosphere is maintained. For example, when the humidity detection is performed using the Ip cell 93, when the oxygen concentration is detected using the Vs cell 91 as in the second embodiment, a change in the atmosphere is determined based on the oxygen concentration. be able to.

In step 510, as in step 150, the humidity detected this time is stored as the humidity of the exhaust gas in the stoichiometric state, and the process is temporarily terminated.
Even after this process is completed, the same process is repeated again to detect the oxygen concentration.

  Therefore, in the fourth embodiment, the same effects as in the first embodiment can be obtained, and the humidity of the atmosphere and the exhaust gas in the stoichiometric state can be detected by the control process described above.

[5. Fifth Embodiment]
Next, a fifth embodiment will be described, but the description of the same contents as the first embodiment will be omitted or simplified. In addition, the same number is attached | subjected and demonstrated to the structure similar to 1st Embodiment.

[5-1. Control processing]
In the fifth embodiment, when humidity detection is performed by 1-cell control, the function of the Ip cell is stopped and humidity detection is performed by the Vs cell.

  As shown in FIG. 10, the system configuration in the fifth embodiment includes an all-range air-fuel ratio sensor 9, a sensor control device 1, and the like, as in the first embodiment, and the sensor control device 1 includes a microcomputer. 101 and an electric circuit unit 103. The electric circuit unit 103 includes the circuits 105 and 109 to 117 and the switches 121, 123, 127, 129, and 131 as in the first embodiment.

  In particular, the fifth embodiment includes an Is current drive circuit 106 that controls the current Is that flows between the pair of first electrodes 73 and 75 of the Vs cell 91 in place of the electromotive force measurement circuit of the first embodiment.

  Therefore, here, the first switch 121 is provided between the Is current drive circuit 106 and the first electrode 73, and the second switch 123 is provided between the Is current drive circuit 106 and the first electrode 75. .

  In the fifth embodiment, circuits are connected as shown in FIG. That is, the first and second switches 121 and 123 are turned on, the third switch 127 is turned off, and the fourth switch 129 is turned on, and the first circuit 125 and the second electrode 79 are connected by the changeover switch 131. .

  In this circuit connection state, when the humidity is detected using the Vs cell 91, the Ip cell 93 used in the first embodiment is replaced with the Vs cell 91, and similarly, the Vs cell 91 is supplied with the first voltage V1. This can be implemented by applying the second voltage V2.

  That is, the first voltage V1 of 1000 mV, for example, and the second voltage V2 of 450 mV, for example, are applied to the pair of first electrodes 73 and 75 of the Vs cell 91 by the Vp current driving circuit 106. When the first voltage V1 is applied, the first pump current Ip1 flowing between the first electrodes 73 and 75 of the Vs cell 91 and between the first electrodes 73 and 75 of the Vs cell 91 when the second voltage V2 is applied. The humidity of the exhaust gas is detected based on a current difference ΔIp with the second pump current Ip2 flowing through

As described above, the fifth embodiment has the same effects as the first embodiment, although the humidity detection cell used is different from that of the first embodiment.
[5-2. Processing after humidity detection]
Here, the process after humidity detection will be briefly described. In addition, about the process after humidity detection, it can apply to the said 1st-4th embodiment.

a) When only atmospheric humidity is used A table (map data) indicating the relationship between atmospheric humidity and the optimal stoichiometric combustion point (stoichiometric point) (and therefore the optimal fuel injection amount) is incorporated in the ECU 17.

Therefore, the optimum fuel injection amount suitable for exhaust gas purification can be obtained from the humidity detected in the atmosphere (during fuel cut) based on the table.
b) When only stoichiometric exhaust gas humidity is used A table (map data) showing the relationship between the stoichiometric exhaust gas humidity and the optimal stoichiometric combustion point (stoichiometric point) (and hence the optimal fuel injection amount) is incorporated in the ECU 17. Yes.

Therefore, the optimum fuel injection amount suitable for exhaust gas purification can be obtained from the humidity detected during stoichiometry based on the table.
c) When using atmospheric humidity and stoichiometric exhaust gas humidity The relationship between the atmospheric humidity and stoichiometric exhaust gas humidity (difference in humidity) and the optimal stoichiometric combustion point (stoichiometric point) (and hence the optimal fuel injection amount) A table (map data) shown is incorporated in the ECU 17.

  Therefore, the humidity difference between the detected atmospheric humidity and the stoichiometric exhaust gas humidity can be obtained, and the optimum fuel injection amount suitable for exhaust gas purification can be obtained from the humidity difference based on the table.

Assuming the case of complete combustion of gasoline CH _1.85 , the relationship between before combustion and after combustion is expressed by the following formula (1).
CH _1.85 + 1.4625 × O ₂ ═CO ₂ + 0.925 × H ₂ O (1)
Further, the ratio of oxygen and nitrogen in the atmosphere is “oxygen: nitrogen = 21: 76”.

Therefore, the optimum fuel injection amount is set in consideration of these relationships.
[3. Correspondence between Embodiments and Claims]
In the above embodiment, the sensor control device that executes S130 and the like corresponds to the “voltage application means (voltage application process)” and “humidity detection means (humidity detection process)” of the present invention, and S240, S320, S420, S470, and the like. The sensor control device that executes the control corresponds to the “control determination means” of the present invention, the electromotive force measurement circuit 107 and the like correspond to the “oxygen concentration detection means” of the present invention, and the CPU 6 that executes the pump current detection circuits 36 and S9. Corresponds to the “second current detection means” of the present invention.

The present invention is not limited to the embodiment described in detail above, and various modifications may be made without departing from the scope of the present invention.
For example, in the above-described embodiment, the case where the full-range air-fuel ratio sensor that detects the oxygen concentration in the detection gas is used as the gas sensor that detects the gas concentration of the specific component in the detection gas is exemplified. Not. For example, even if a NOx sensor that detects the NOx concentration in the gas to be detected is used, humidity correction can be performed in the same manner as described above.

  That is, in the NOx sensor that detects the NOx concentration by driving the electromotive force cell and the oxygen pump cell, such as a known NOx sensor having an electromotive force cell and an oxygen pump cell, as in the above embodiment, the electromotive force cell or oxygen The first voltage and the second voltage may be applied to the pump cell, and the humidity in the gas to be detected may be obtained based on the difference between the currents when the voltages are applied.

DESCRIPTION OF SYMBOLS 1 ... Sensor control apparatus 5 ... Engine 9 ... Whole area air-fuel ratio sensor 13 ... Sensor unit 25 ... Gas sensor element 61 ... 1st solid electrolyte body 63 ... 2nd solid electrolyte body 73, 75 ... 1st electrode 77, 79 ... 2nd Electrode 81 ... Detection chamber 91 ... Oxygen concentration detection cell (electromotive force cell: Vs cell)
93 ... Oxygen pump cell (Ip cell)
101 ... Microcomputer

Claims (6)

An electromotive force cell having a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body and capable of generating an electromotive force between the first electrodes, a second solid electrolyte body, An oxygen pump cell having a pair of second electrodes formed on the second solid electrolyte body and capable of pumping oxygen between the second electrodes, and connected to a gas sensor element;
Gas concentration for performing gas concentration detection corresponding to detection of gas concentration of a specific component in the gas to be detected using the electromotive force cell and the oxygen pump cell, and humidity detection corresponding to detection of humidity of the gas to be detected A humidity detector,
Voltage application means for applying a first voltage for electrolyzing moisture in the gas to be detected and a second voltage lower than the first voltage to a pair of electrodes of the electromotive force cell or the oxygen pump cell;
The pair of cells to which the second voltage is applied when the first current flowing between the pair of electrodes of the cell to which the first voltage is applied and the second voltage are applied when the first voltage is applied Humidity detecting means for detecting the humidity of the gas to be detected based on a difference from a second current flowing between the electrodes;
A gas concentration / humidity detection device comprising: Control determining means for determining whether a condition for determining whether to perform the gas concentration detection or the humidity detection is satisfied,
2. The gas concentration / humidity detection apparatus according to claim 1, wherein control satisfying the condition is performed based on a determination result by the control determination unit.   The gas concentration / humidity detection apparatus according to claim 2, wherein the control determination unit uses a result of the gas concentration detection as a condition for switching from the gas concentration detection to the humidity detection. The gas sensor element includes a detection chamber into which the gas to be detected is introduced, and the electromotive force cell includes one electrode of the pair of first electrodes disposed in the detection chamber, and the other first electrode. Is exposed to the standard oxygen concentration atmosphere,
Furthermore, when performing the humidity detection, the electromotive force cell comprises oxygen concentration detection means for detecting the oxygen concentration of the detected gas in the detection chamber,
The said control determination means uses the detection result of the said oxygen concentration detected by the said oxygen concentration detection means as conditions for switching from the said humidity detection to the said gas concentration detection. Gas concentration humidity detector.   The detected gas is a gas exhausted from an internal combustion engine, and when the detected gas is atmospheric or stoichiometric exhaust gas, the humidity of the detected gas is detected in either or both cases. The gas concentration / humidity detection device according to claim 1, wherein An electromotive force cell having a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body and capable of generating an electromotive force between the first electrodes, a second solid electrolyte body, A gas sensor element comprising a pair of second electrodes formed on the second solid electrolyte body and an oxygen pump cell capable of pumping oxygen between the second electrodes,
Gas concentration for performing gas concentration detection corresponding to detection of gas concentration of a specific component in the gas to be detected using the electromotive force cell and the oxygen pump cell, and humidity detection corresponding to detection of humidity of the gas to be detected A humidity detection method comprising:
A voltage application step of applying a first voltage for electrolyzing moisture in the gas to be detected and a second voltage lower than the first voltage to a pair of electrodes of the electromotive force cell or the oxygen pump cell;
The pair of cells to which the second voltage is applied when the first current flowing between the pair of electrodes of the cell to which the first voltage is applied and the second voltage are applied when the first voltage is applied A humidity detecting step for detecting the humidity of the gas to be detected based on a difference from a second current flowing between the electrodes;
A gas concentration / humidity detection method comprising: