JP2016090264A - Gas sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor device dispensing with conventional complicated work that has been executed for preliminarily acquiring a relationship between a moisture concentration corresponding value of a detection object gas and a difference in pump currents for each gas sensor individually.SOLUTION: A gas sensor device 4 comprises: a gas sensor 1 including an oxygen concentration detection cell 50 and an oxygen pump cell 40; and a sensor control device 3 connected to the gas sensor 1. The sensor control device 3 includes a current detection part 36 that detects a pump current flowing to the oxygen pump cell 40, and a moisture concentration detection part 220 that detects a moisture concentration corresponding value corresponding to the moisture concentration of the detection object gas on the basis of the current detected by a current detection part 36, when an atmosphere determination part determines that the detection object gas is an atmosphere. The moisture concentration detection part 220 determines the moisture concentration corresponding value on the basis on a value obtained by multiplying a difference between a second pump current and a first pump current by a fixed coefficient K1 (K1 is a positive value other than 1).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a gas sensor device using various gas sensors such as an oxygen sensor, an air-fuel ratio sensor, and a NOx sensor.

  Patent Document 1 discloses an apparatus capable of detecting the moisture concentration of a gas to be detected using an air-fuel ratio sensor having an oxygen concentration detection cell and an oxygen pump cell. Here, “moisture concentration” means the volume ratio of moisture when the moisture contained in the gas to be detected is regarded as water vapor. In the apparatus disclosed in Patent Document 1, the pump current Ip_primary detected with the voltage Vs of the oxygen concentration detection cell set as the first reference voltage and the voltage Vs of the oxygen concentration detection cell detected with the second reference voltage. Based on the difference ΔIp from the pump current Ip_secondary, the moisture concentration of the gas to be detected is detected.

JP 2010-281732 A

  However, the relationship between the moisture concentration of the gas to be detected and the difference ΔIp between the pump currents has individual differences for each gas sensor as illustrated in FIGS. ΔIp was significantly different. For this reason, conventionally, even if the structure, model, product number, etc. of the gas sensor are the same, the relationship between the moisture concentration of the gas to be detected and the error ΔIp of the pump current is obtained in advance for each gas sensor and There is a problem that complicated work is necessary.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, when a gas sensor having an oxygen concentration detection cell and an oxygen pump cell and a gas concentration of a specific component in the gas to be detected and the gas to be detected connected to the gas sensor are the atmosphere A gas sensor device comprising a sensor control device for detecting the humidity of the gas sensor is provided. The gas sensor has a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and a gas to be detected is introduced into one of the pair of first electrodes. An oxygen concentration detection cell, the other electrode being exposed to a reference oxygen concentration atmosphere, 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 is disposed in the detection chamber, and is included in the gas to be detected introduced into the detection chamber according to a current flowing between the pair of second electrodes. An oxygen pump cell for pumping or pumping oxygen. The sensor control device detects a voltage generated between the pair of first electrodes due to a difference between an oxygen concentration in the detection chamber and an oxygen concentration in the reference oxygen concentration atmosphere, and the pair of first electrodes A current control unit that controls a current flowing between the pair of second electrodes so that a voltage generated between them becomes a control target voltage; an atmosphere determination unit that determines whether or not the detected gas is the atmosphere; and While the control target voltage is set to the first reference voltage, the control target voltage is set to be a second reference voltage larger than the first reference voltage when the detected gas is determined to be the atmosphere by the atmosphere determination unit. And a first pump current flowing between the pair of second electrodes of the oxygen pump cell in a state where the first reference voltage is generated between the pair of first electrodes of the oxygen concentration detection cell. Detect In addition, a current detection unit that detects a second pump current flowing between the pair of second electrodes in a state where the second reference voltage is generated between the pair of first electrodes, and the detected object in the atmosphere determination unit Based on the first pump current and the second pump current detected by the current detector when it is determined that the gas is the atmosphere, a moisture concentration equivalent value corresponding to the moisture concentration of the detected gas is detected. A moisture concentration detection unit. The moisture concentration detection unit is based on a value obtained by multiplying a difference between the second pump current and the first pump current by a constant coefficient K1 (K1 is a positive value other than 1) corresponding to an individual difference of the gas sensor. The moisture concentration equivalent value is determined.
According to this gas sensor device, even when the relationship between the value of the first pump current and the value of the second pump current and the moisture concentration differs according to the individual difference of the gas sensor, the constant coefficient K1 is set to the individual difference of the gas sensor. By setting to an appropriate value according to the above, a moisture concentration equivalent value can be obtained from the first pump current and the second pump current. Accordingly, the conventional troublesome work that has been performed in order to individually obtain the relationship between the value corresponding to the moisture concentration of the gas to be detected and the difference in pump current for each gas sensor becomes unnecessary.

(2) In the gas sensor device, the moisture concentration detection unit is a function or table indicating a relationship between a value obtained by multiplying a difference between the second pump current and the first pump current by the coefficient K1 and the value corresponding to the moisture concentration. As an alternative, a function or table that does not depend on individual differences among the gas sensors may be stored, and the coefficient K1 determined depending on individual differences among the gas sensors may be used.
According to this gas sensor device, by setting the coefficient K1 to an appropriate value according to the individual difference of the gas sensor, the function or table common to a plurality of gas sensors having the same structure, model, and product number is used, and the first pump A moisture concentration equivalent value can be obtained from the current and the second pump current.

(3) In the gas sensor device, the moisture concentration detector divides the voltage value Vip1 indicating the first pump current Ip1, thereby dividing the first pump current equivalent voltage K2 · Vip1 (K2 is a positive constant proportional to K1) A voltage dividing circuit that outputs a second pump current equivalent voltage K2 · Vip2 by dividing the voltage value Vip2 indicating the second pump current Ip2, and the moisture concentration detector The moisture concentration equivalent value may be determined from the difference K2 (Vip2−Vip1) between the second pump current equivalent voltage K2 · Vip2 and the first pump current equivalent voltage K2 · Vip1 output from the pressure circuit.
According to this gas sensor device, the moisture concentration equivalent value can be obtained from the first pump current and the second pump currents Ip1 and Ip2 by setting the value of K2 to an appropriate value according to the individual difference of the gas sensors.

(4) The gas sensor device may further include a zero point calibration unit that performs zero point calibration of the gas sensor using the moisture concentration equivalent value.
According to this gas sensor device, it is possible to perform zero point calibration in consideration of moisture concentration, and it is possible to perform zero point calibration of the gas sensor more accurately.

  The present invention can be realized in various forms such as a gas sensor device, a gas sensor control device, a gas sensor control method, and a gas sensor device manufacturing method.

The figure which shows schematic structure around the exhaust system of an internal combustion engine. The figure which shows the structure of a full range air-fuel ratio sensor. A graph which shows an example of a moisture concentration table used for moisture concentration detection. The graph which shows the proportional relationship between pump current Ip1 and Ip2. The block diagram which shows an example of an internal structure of a water concentration detection part. The flowchart which shows the procedure of the zero point calibration process of the sensor using humidity detection. The graph which shows the relationship between the moisture concentration of air | atmosphere, and a 1st pump electric current. The graph which shows how to obtain | require the zero point calibration value which considered the zero point moisture correction value.

A. Diagram 1 of the apparatus is a diagram showing a schematic configuration of a vehicle 100 equipped with the gas sensor device according to an embodiment of the present invention. The vehicle 100 includes an engine 101 that is an internal combustion engine, and an exhaust pipe 102 for discharging exhaust gas to the outside of the vehicle is connected to the engine 101. A full-range air-fuel ratio sensor 1 is disposed on the path of the exhaust pipe 102. The full-range air-fuel ratio sensor 1 is a gas sensor that detects the gas concentration (oxygen concentration in this example) of a specific component in the exhaust gas flowing through the exhaust passage of the exhaust pipe 102. The full-range air-fuel ratio sensor 1 is electrically connected to a sensor control device 3 disposed at a position away from itself via a harness 91 (signal line), and is controlled by the sensor control device 3 to generate oxygen. Detect concentration. The sensor control device 3 operates by receiving power from the battery 80 and outputs an output signal indicating the oxygen concentration detected using the full-range air-fuel ratio sensor 1 to the engine control device 5 (referred to as “ECU 5”). The ECU 5 performs air-fuel ratio feedback control of the engine 101 based on the output signal of the full-range air-fuel ratio sensor 1.

  When fuel is being supplied to the engine 101, the exhaust gas becomes the gas to be detected by the full-range air-fuel ratio sensor 1. On the other hand, in a state where the fuel supply to the engine 101 is stopped (fuel cut period), the atmosphere flows through the exhaust pipe 102, and therefore the atmosphere flowing through the exhaust pipe 102 is detected gas of the entire region air-fuel ratio sensor 1. It becomes. In this specification, “detected gas” is used as a term including both exhaust gas and the atmosphere. As will be described later, the sensor control device 3 also has a function of determining the moisture concentration in the gas to be detected.

  FIG. 2 is an explanatory diagram showing the internal configuration of the gas sensor device 4 including the full-range air-fuel ratio sensor 1 and the sensor control device 3. The full-range air-fuel ratio sensor 1 has a structure in which a sensor element 10 having an elongated and long plate shape is held in a housing (not shown). The full-range air-fuel ratio sensor 1 is electrically connected to the sensor control device 3 via a harness 91 (FIG. 1). Note that some or all of the functions of the sensor control device 3 may be incorporated in the ECU 5.

  The sensor element 10 of the full-range air-fuel ratio sensor 1 includes solid electrolyte bodies 11 and 13 and insulating bases 12, 17, 18, and 24. These members are laminated in the order of the insulating bases 18 and 17, the solid electrolyte body 13, the insulating base 12, the solid electrolyte body 11, and the insulating base 24 in order from the bottom of FIG. 2. In FIG. 2, since the gas detection chamber 23 provided in the insulating base 12 is drawn, the cross section of the insulating base 12 itself does not appear. A pair of electrodes 19 and 20 are respectively formed on both surfaces of the solid electrolyte body 11. Similarly, a pair of electrodes 21 and 22 are also formed on both surfaces of the solid electrolyte body 13. One of the electrodes 22 is embedded between the solid electrolyte body 13 and the insulating substrate 17. Each of the solid electrolyte bodies 11 and 13 and the insulating bases 12, 17, 18, and 24 is formed in an elongated plate shape, and FIG. 2 shows a cross section orthogonal to the longitudinal direction.

  A hollow gas detection chamber 23 (also simply referred to as “detection chamber 23”) into which a gas to be detected can be introduced is formed on one end side in the longitudinal direction of the insulating substrate 12 while the solid electrolyte bodies 11 and 13 are formed as one wall surface. ing. At both ends of the gas detection chamber 23 in the width direction, porous diffusion rate controlling portions 15 for restricting the amount of inflow when the gas to be detected is introduced into the gas detection chamber 23 are provided. The electrode 20 on the solid electrolyte body 11 and the electrode 21 on the solid electrolyte body 13 are exposed in the gas detection chamber 23, respectively.

  A heating resistor 26 is embedded between the insulating bases 17 and 18. The insulating bases 17 and 18 and the heating resistor 26 function as a heater for heating and activating the solid electrolyte bodies 11 and 13.

  The surface of the electrode 19 on the solid electrolyte body 11 is covered with a porous protective layer 25 made of ceramics (for example, alumina). The protective layer 25 is for protecting the electrode 19 so that the electrode 19 is not deteriorated by poisoning components (for example, silicon) contained in the exhaust gas. The insulating base 24 laminated on the solid electrolyte body 11 has an opening so as not to cover the electrode 19, and the protective layer 25 is disposed in the opening.

  In the sensor element 10, the solid electrolyte body 11 and the pair of electrodes 19 and 20 provided on both surfaces of the sensor element 10 pump oxygen into the gas detection chamber 23 from the outside, or pump oxygen from the gas detection chamber 23 to the outside. It functions as an oxygen pump cell 40 (also referred to as “Ip cell 40”). Further, the solid electrolyte body 13 and the pair of electrodes 21 and 22 provided on both surfaces thereof are used as an oxygen concentration detection cell 50 (also referred to as “Vs cell 50”) that generates an electromotive force in accordance with the oxygen concentration between both electrodes. Function. The electrode 22 functions as an oxygen reference electrode that maintains an oxygen concentration serving as a reference for detecting the oxygen concentration in the gas detection chamber 23. Detailed functions of the Ip cell 40 and the Vs cell 50 will be described later.

  The sensor control device 3 includes a control unit 9 and an electric circuit unit 30. The control unit 9 includes a gas concentration detection unit 200 that detects the gas concentration (oxygen concentration) of the gas to be detected, an atmosphere determination unit 210 that determines whether or not the gas to be detected is the atmosphere, and moisture that detects the water concentration. It includes a density detection unit 220 and a zero point calibration unit 230 that performs zero point calibration of the sensor. The moisture concentration detection unit 220 includes a voltage setting unit 225 that sets a reference voltage (described later) used in the reference voltage comparison circuit 35. However, the voltage setting unit 225 may be provided outside the moisture concentration detection unit 220. The functions of these parts will be described later. Part and all elements of the control unit 9 may be configured as a hardware circuit, or may be configured as a microcomputer having a CPU, a ROM, and a RAM. In the latter case, a part or all of the functions of the control unit 9 are realized by the CPU executing a computer program stored in a non-volatile storage medium such as a ROM.

  The electric circuit unit 30 includes a heater energization control circuit 31, a pump current drive circuit 32, a voltage detection circuit 33, a minute current supply circuit 34, a reference voltage comparison circuit 35, and a pump current detection circuit 36. .

  The heater energization control circuit 31 heats the heating resistor 26 by PWM energizing the voltage Vh supplied to both ends of the heating resistor 26 and heats the Ip cell 40 and the Vs cell 50. The minute current supply circuit 34 causes a minute current Icp to flow from the electrode 22 of the Vs cell 50 to the electrode 21 side, moves oxygen ions to the electrode 22 side, and generates a reference oxygen concentration atmosphere. Thereby, the electrode 22 functions as an oxygen reference electrode that serves as a reference for detecting the oxygen concentration in the gas to be detected. The voltage detection circuit 33 detects an electromotive force Vs generated between the electrodes 21 and 22 of the Vs cell 50. The reference voltage comparison circuit 35 obtains a comparison result (for example, a difference) between a predetermined reference voltage and the electromotive force Vs detected by the voltage detection circuit 33 and feeds back the comparison result to the pump current drive circuit 32. The pump current drive circuit 32 controls the magnitude and direction of the pump current Ip that flows between the electrodes 19 and 20 of the Ip cell 40 based on the comparison result obtained from the reference voltage comparison circuit 35. As a result, feedback control is performed such that the electromotive force Vs generated between the electrodes 21 and 22 becomes the reference voltage. By this feedback control, oxygen is pumped into the gas detection chamber 23 by the Ip cell 40 and oxygen is pumped out from the gas detection chamber 23. The pump current detection circuit 36 converts the pump current Ip flowing between the electrodes 19 and 20 of the Ip cell 40 into a voltage, and uses a voltage value representing the pump current Ip (also referred to as “pump current equivalent voltage”) as a detection signal as a control unit. Output to 9. The pump current detection circuit 36 corresponds to the “current detection unit” of the present invention.

In the present embodiment, the following two reference voltages Vr1 and Vr2 are used as reference voltages compared with the electromotive force Vs by the reference voltage comparison circuit 35.
(1) First reference voltage Vr1
The first reference voltage Vr1 was introduced into the gas detection chamber 23 when the comparison result of the voltage detection circuit 33 was fed back to the pump current drive circuit 32 to control the oxygen concentration in the atmosphere in the gas detection chamber 23. The voltage value is set such that moisture (H ₂ O) in the gas to be detected does not substantially dissociate. Here, “dissociation of moisture” means dissociation into hydrogen ions and oxygen ions. Whether or not the first reference voltage Vr1 is “a voltage value such that water (H ₂ O) in the gas to be detected is not substantially dissociated” is determined by, for example, detecting the atmosphere with a water concentration of 2% by volume. The pump current Ip obtained at a reference voltage 1.1Vr1 that is 10% larger than the first reference voltage Vr1 hardly changes from the pump current Ip1 obtained at the first reference voltage Vr1 (the amount of change is ± 5%). Or less). The first reference voltage Vr1 is preferably set to a value in the range of 400 mV to 600 mV (particularly 450 mV), for example.
(2) Second reference voltage Vr2
The second reference voltage Vr2 was introduced into the gas detection chamber 23 when the comparison result of the voltage detection circuit 33 was fed back to the pump current drive circuit 32 to control the oxygen concentration in the atmosphere in the gas detection chamber 23. The voltage value is set such that moisture (H ₂ O) in the gas to be detected is dissociated. Whether or not the second reference voltage Vr2 is “a voltage value at which water (H ₂ O) in the gas to be detected is dissociated” is determined by using, for example, the atmosphere having a water concentration of 2% by volume as the gas to be detected. It is possible to determine whether the pump current Ip2 obtained with the second reference voltage Vr2 is significantly larger (greater than 5%) than the pump current Ip1 obtained with the first reference voltage Vr1. The second reference voltage Vr2 is higher than the first reference voltage Vr1, and is preferably set to a value in the range of 1000 mV to 1200 mV, for example.

  When measuring the oxygen concentration in the gas to be detected, the reference voltage comparison circuit 35 uses the first reference voltage Vr1 as a reference voltage to be compared with the electromotive force Vs. On the other hand, when detecting the moisture concentration of the gas to be detected, both the first reference voltage Vr1 and the second reference voltage Vr2 are used. The method for detecting the moisture concentration will be described later. The pump current drive circuit 32, the voltage detection circuit 33, and the reference voltage comparison circuit 35 correspond to the “current control unit” of the present invention. Further, the reference voltages Vr1 and Vr2 compared with the electromotive force Vs in the reference voltage comparison circuit 35 correspond to the “control target voltage” of the present invention.

  The ECU 5 is a device for controlling the engine 101 of the vehicle 100. The ECU 5 uses a microcomputer chip having a known configuration of CPU, ROM, RAM, etc., 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 signal corresponding to the oxygen concentration in the detected gas and an output signal corresponding to the humidity in the detected gas are input from the sensor control device 3. 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 101 can be detected, coolant temperature, combustion pressure, etc.) are also input.

  When the oxygen concentration (exhaust gas air-fuel ratio) of the gas to be detected is detected using the full-range air-fuel ratio sensor 1, the first reference voltage Vr1 (for example, as a reference voltage to be compared by the reference voltage comparison circuit 35) 450 mV) is set. At this time, a minute current Icp is first caused to flow from the electrode 22 to the electrode 21 of the Vs cell 50 by the minute current supply circuit 34. By this energization, oxygen in the gas to be detected is pumped from the electrode 21 side to the electrode 22 side through the solid electrolyte body 13, and the electrode 22 functions as an oxygen reference electrode. Then, the electromotive force Vs generated between the electrodes 21 and 22 is detected by the voltage detection circuit 33, and the electromotive force Vs is compared with the first reference voltage Vr 1 by the reference voltage comparison circuit 35. In the pump current drive circuit 32, the magnitude of the pump current Ip that flows between the electrodes 19 and 20 of the Ip cell 40 so that the electromotive force Vs becomes equal to the first reference voltage Vr 1 based on the comparison result by the reference voltage comparison circuit 35. Control the orientation.

  For example, when the air-fuel ratio of the exhaust gas that has flowed into the gas detection chamber 23 is richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is thin, so that oxygen is introduced into the gas detection chamber 23 from the outside in the Ip cell 40. So that the pump current Ip flowing between the electrodes 19 and 20 is controlled. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the gas detection chamber 23 is leaner than the stoichiometric air-fuel ratio, a large amount of oxygen is present in the exhaust gas. The pump current Ip flowing between the electrodes 19 and 20 is controlled so as to pump out oxygen. The pump current Ip at this time is converted into a voltage in the pump current detection circuit 36 and output to the control unit 9 as an output signal (detection signal) of the full-range air-fuel ratio sensor 1. The gas concentration detection unit 200 of the control unit 9 includes oxygen contained in the detected gas based on the magnitude and direction of the pump current Ip (exactly “pump current equivalent voltage”) output from the full-range air-fuel ratio sensor 1. Determine the concentration, and thus the air-fuel ratio of the exhaust gas.

  As will be described below, the sensor control device 3 can detect the moisture concentration when the gas to be detected is the atmosphere using the full-range air-fuel ratio sensor 1. Further, the zero point calibration of the sensor output of the full-range air-fuel ratio sensor 1 can be executed using the moisture concentration in the atmosphere.

B. Water Concentration Detection Method FIG. 3 is a graph showing an example of the relationship used for detecting the water concentration. This graph represents the relationship of the following equation (1).
Hm = a × (ΔIp) ² + b × (ΔIp) + c (1)
Here, Hm is a moisture concentration (volume% of water vapor), a, b, c are constant coefficients, ΔIp = (Ip2−Ip1), and Ip1 is obtained when the above-described first reference voltage Vr1 is used. The value of the pump current Ip, Ip2, is the value of the pump current Ip obtained when the above-described second reference voltage Vr2 is used. In the example of FIG. 3, a = −1.083, b = 8.968, and c = −0.084.

According to the above equation (1), the water concentration Hm can be expressed as a quadratic function of the difference (Ip2-Ip1) between the second pump current value Ip2 and the first pump current value Ip1. Incidentally, R ² in the figure is the square of the correlation coefficient R when the measured points are plotted is approximated by equation (1). Since R ² is close to 1, it can be seen that sufficiently good approximation is satisfied.

  If you want to determine the humidity of the gas to be detected, measure the temperature of the gas to be detected using a temperature sensor (not shown), and detect the humidity by referring to the saturated water vapor table from the measured temperature and moisture concentration Hm. It is possible to determine the humidity of the gas.

  If the relationship as shown in FIG. 3 is used, it is possible to detect the water concentration Hm by measuring the pump currents Ip1 and Ip2. However, as described in the prior art, the pump currents Ip1 and Ip2 have individual differences among sensors, and even if the sensor structure, model, product number, and the like are the same, there are variations among the individual sensors. Conventionally, as shown in FIG. 5 and FIG. 7 of Patent Document 1, a different relationship is measured in advance for each of the full-range air-fuel ratio sensors 1, and the relationship is stored in the control device. However, as will be described below, the inventor of the present application makes it easier for the proportional relationship to be established between the first pump current Ip1 and the second pump current Ip2 and to use this proportional relationship. It was found that the relationship for detection of moisture concentration can be set.

FIG. 4 is a graph showing a proportional relationship established between the first pump current Ip1 and the second pump current Ip2. The points in FIG. 4 are plots of pump currents Ip1 and Ip2 obtained by a plurality of individuals of the full-range air-fuel ratio sensor 1. In this example, the proportional relationship of the following equation (2) is established.
Ip2 = α × Ip1
= 1.329 · Ip1 (2)
Here, α is a constant coefficient.

  As can be understood from FIG. 4, the pump currents Ip1 and Ip2 show considerably different values depending on the individual difference of the whole-range air-fuel ratio sensor 1, but both values show a good proportional relationship. The example of FIG. 4 shows the case where the water concentration Hm is 5%, but it has been found that the same proportional relationship can be obtained even with other water concentrations.

If this proportional relationship is used, instead of separately obtaining a different relationship for each individual full-range air-fuel ratio sensor 1, the same relationship for all-range air-fuel ratio sensors 1 having the same structure, the same model, and the same product number (see FIG. 3), the water concentration can be obtained using the following equation (3).
Hm = a × (K1 · ΔIp) ² + b × (K1 · ΔIp) + c (3)
Here, the coefficients a, b, and c are constant values, and the coefficient K1 is a positive constant value. As the coefficients a, b, and c, the same values as in the above equation (1) can be used.

  The value of the coefficient K1 is obtained by measuring the first pump current Ip1 using an atmosphere having a specific moisture concentration (for example, Hm = 5 vol%) as a detection gas, and K1 · Ip1 is a predetermined value (for example, K1 · Ip1 = 3). .8 mA). The coefficient K1 usually takes a value other than 1.0, but may be K1 = 1.0 depending on the individual sensor. However, K1 is not 1.0 for all sensors having the same structure, model, and product number. In this specification, the meaning of “K1 is a positive value other than 1” means that K1 = 1.0 is not satisfied for all sensors of the same structure, model, and product number.

  When determining the coefficient K1, it is only necessary to measure the first pump current Ip1 when using the first reference voltage Vr1, and it is necessary to measure the second pump current Ip2 when using the second reference voltage Vr2. There is no. This is because, as shown in FIG. 4, a proportional relationship is established between the first pump current Ip1 and the second pump current Ip2. Further, as the relationship between the pump current Ip and the moisture concentration Hm, the relationship of the above equation (3) can be used in common if the sensors have the same structure, model, and product number. At this time, in the equation (3), only the coefficient K1 changes depending on the individual difference of the sensor, and the other coefficients a, b, and c are constant values that do not depend on the individual sensor. Therefore, a relationship (for example, the above formula (3)) for determining the moisture concentration is set by a simple setting operation as compared with the conventional case where both the first pump current Ip1 and the second pump current Ip2 are measured. Is possible.

  The moisture concentration detector 220 (FIG. 2) is a value K1 obtained by multiplying a difference ΔIp = (Ip2−Ip1) between the second pump current Ip2 and the first pump current Ip1 by a constant coefficient K1 (K1 is a positive value other than 1). It is possible to determine the moisture concentration based on ΔIp. At this time, for example, a function or a table representing the relationship of the above expression (3) is used.

The water concentration Hm may be determined using a linear function (linear relationship) such as the following expression (4) or (5) instead of the quadratic function of the above expression (3).
Hm = d × (K1 · ΔIp) + e (4)
Hm = K1 (f × ΔIp + g) (5)
Here, d and f are constant coefficients that are not zero, and e and g are constant coefficients.

  Which of the above-described equations (3) to (5) is used is arbitrarily selected according to the structure, model, and product number of the sensor. Various coefficients a to g and K1 are experimentally determined. In any case, the same values are used for the coefficients a to g as long as the sensor structure, model, and product number are the same. Set to Moreover, the relationship of (3)-(5) Formula can be mounted in the sensor control apparatus 3 as a function or a table.

  FIG. 5 is a block diagram showing an example of the internal configuration of the moisture concentration detector 220 (FIG. 2). The moisture concentration detection unit 220 includes a voltage dividing circuit 222, a moisture concentration determination unit 224, and a moisture concentration table 226. The voltage dividing circuit 222 is a circuit that outputs the divided voltage value K2 · Vip by dividing the output voltage Vip of the pump current detection circuit 36 using the resistors R1 and R2. The output voltage Vip of the pump current detection circuit 36 is a voltage value representing the pump current Ip. The voltage dividing ratio K2 (= R2 / (R1 + R2)) of the resistors R1 and R2 is a value proportional to the coefficient K1 used in the above equations (3) to (5). The voltage dividing ratio K2 is equal to a value obtained by multiplying the coefficient K1 by a conversion coefficient when the current value of the pump current Ip is converted into the voltage value Vip. The voltage dividing ratio K2 of the voltage dividing circuit 222 is, for example, an output voltage Vip1 corresponding to the first pump current Ip1 (“the voltage corresponding to the first pump current”) using the atmosphere with a specific moisture concentration (for example, Hm = 5%) as the detection gas. Vp1 ") is measured, and K2 · Vip1 is determined to be equal to a predetermined value (for example, K2 · Vip1 = 2.4V). When the voltage dividing circuit 222 is used, when the output voltage Vip2 (also referred to as “first pump current equivalent voltage Vip1”) corresponding to the second pump current Ip2 is input from the pump current detection circuit 36 to the voltage dividing circuit 222. The voltage K2 · Vip2 multiplied by the voltage dividing ratio K2 is output. The first pump current equivalent voltage K 2 · Vip 1 and the second pump current equivalent voltage K 2 · Vip 2 are supplied from the voltage dividing circuit 222 to the moisture concentration determination unit 224.

The moisture concentration determination unit 224 calculates the difference K2 · ΔVip between the voltages K2 · Vip1 and K2 · Vip2 supplied from the voltage dividing circuit 222 and uses the difference K2 · ΔVip to equalize the above equation (3). The water concentration Hm is determined according to the following equation (3a).
Hm = a × (K 2 · ΔVip) ² + b × (K 2 · ΔVip) + c (3a)
Here, the coefficients a, b, and c are constant values, ΔVip = Vip2−Vip1.

  The relationship of the above expression (3a) can be realized, for example, as the moisture concentration table 226 (FIG. 5). For example, the moisture concentration table 226 can be implemented as a lookup table that outputs the moisture concentration Hm when the voltage difference K2 · ΔVip is input. Instead, the function of the above equation (3a) may be stored in the moisture concentration determination unit 224, and the moisture concentration Hm may be calculated using this function.

Instead of the above equation (3a), the following equations (4a) and (5a) equivalent to the above equations (4) and (5) may be used.
Hm = d × (K2 · ΔVip) + e (4a)
Hm = K2 (f × ΔVip + g) (5a)
Here, d and f are constant coefficients that are not zero, and e and g are constant coefficients.

  As described above, the moisture concentration detection unit 220 divides the voltage value Vip2 indicating the first pump current Ip1 and the voltage value Vip2 corresponding to the first pump current Ip2 and the voltage value Vip2 corresponding to the first pump current Ip2. The water concentration Hm can be determined based on the difference K2 (Vip2-Vip1) between the second pump current equivalent voltages K2 and Vip2.

  The moisture concentration Hm is a value representing the volume% of water vapor in the gas to be detected, and can be used as a value corresponding to the humidity of the gas to be detected. The water concentration detection unit 220 typically calculates a digital value proportional to the water concentration Hm, but may generally determine a value that directly or indirectly represents the water concentration Hm. Here, the “value directly representing the moisture concentration Hm” means a value proportional to the moisture concentration Hm, and the “value indirectly representing the moisture concentration Hm” is not proportional to the moisture concentration Hm. It means a value from which the moisture concentration Hm can be calculated. These values correspond to “moisture concentration equivalent values” associated with the moisture concentration of the gas to be detected. In this specification, the “water concentration equivalent value” means a value that directly or indirectly represents the moisture concentration of the gas to be detected.

  As described above, in the present embodiment, the moisture concentration detector 220 adds a constant coefficient K1 (K1 is a positive value other than 1) to the difference (Ip2−Ip1) between the second pump current Ip2 and the first pump current Ip1. Based on the multiplied value K1 (Ip2−Ip1), the moisture concentration equivalent value can be determined. Moreover, if the coefficient K1 is set to an appropriate value according to the individual difference of the gas sensor, the relationship for determining the moisture concentration equivalent value from the difference (Ip2-Ip1) can be appropriately set. Therefore, there is an advantage that the conventional complicated work that has been performed in order to individually obtain the relationship between the value corresponding to the moisture concentration of the gas to be detected and the difference ΔIp of the pump current for each gas sensor becomes unnecessary.

C. Sensor Zero Point Calibration Process FIG. 6 is a flowchart showing the procedure of a sensor zero point calibration process using moisture concentration measurement. Here, the zero point calibration of the full-range air-fuel ratio sensor 1 is executed using the above-described moisture concentration measurement. “Zero point calibration of the full-range air-fuel ratio sensor 1” is a process for performing calibration so as to obtain a correct output by compensating the change with time of the output of the full-range air-fuel ratio sensor 1. This process is periodically executed at predetermined timings while the vehicle 100 is being driven. Note that the drive control of the circuits 31 to 36 in the electric circuit unit 30 is executed as necessary, separately from the processing shown in FIG. Note that after the vehicle 100 is started and before the process shown in FIG. 6 is first executed, the reference voltage (control target voltage) of the reference voltage comparison circuit 35 is set by the moisture concentration detection unit 220 as described above. The reference voltage Vr1 is set.

  In step S1, the atmosphere determination unit 210 (FIG. 2) determines whether or not the gas to be detected by the entire region air-fuel ratio sensor 1 is the atmosphere. For example, it is determined whether or not the gas to be detected is atmospheric based on whether or not a signal indicating that the engine 101 is stopping fuel supply (hereinafter referred to as a “fuel cut signal”) is received. Can do. For example, the atmosphere determination unit 210 receives a signal indicating whether or not fuel is being supplied from the ECU 5 every predetermined time, and stores the received signal in a RAM (not shown) in the control unit 9 as needed. It may be a thing. In this case, it is possible to determine whether or not the gas to be detected is the atmosphere depending on whether or not the fuel cut signal is stored in the RAM in the control unit 9. If the gas to be detected is not in the atmosphere, the process in FIG. 6 is terminated and the process waits until the next process start timing.

  When the gas to be detected is the atmosphere, the engine 101 is stopping the fuel supply, so the exhaust passage of the exhaust pipe 102 is filled with the atmosphere. The length of the period during which the fuel cut signal is continuously received is preferably measured by a separately executed timer and stored in the RAM in the control unit 9. The length of the period during which the fuel cut signal is continuously received can be used as a value indicating the elapsed time from the time when the fuel supply is stopped (that is, at the start of the fuel cut).

  In step S3, the control unit 9 determines whether or not a predetermined time has elapsed since the fuel supply to the engine 101 was stopped. When it is determined that a predetermined time has elapsed since the stop of fuel supply, the exhaust passage of the exhaust pipe 102 is sufficiently filled with air, and the atmosphere around the sensor element 10 is air with a known oxygen concentration. If the predetermined time has not elapsed, the process of FIG. 6 is terminated and the process waits for the next process start timing. On the other hand, if the predetermined time has elapsed, the process proceeds to the next step S5.

  In step S <b> 5, the water concentration detection unit 220 reads the pump current Ip <b> 1 measured using the first reference voltage Vr <b> 1 (for example, 450 mV) from the pump current detection circuit 36. In step S7, the voltage setting unit 225 changes the reference voltage set in the reference voltage comparison circuit 35 from the first reference voltage Vr1 to the second reference voltage Vr2 (for example, 1100 mV).

  In step S <b> 9, the water concentration detection unit 220 reads the pump current Ip <b> 2 measured using the second reference voltage Vr <b> 2 from the pump current detection circuit 36. In step S11, the voltage setting unit 225 changes the reference voltage set in the reference voltage comparison circuit 35 from the second reference voltage Vr2 to the first reference voltage Vr1.

  In step S13, the moisture concentration Hm of the gas to be detected is calculated from the pump currents Ip1 and Ip2 obtained in steps S5 and S9. This calculation is executed using a function or a table representing any one of the above-described equations (3) to (5) and (3a) to (5a).

  In step S15, the zero point calibration unit 230 (FIG. 2) performs zero point calibration of the full-range air-fuel ratio sensor 1 according to the method described in FIGS. 7 and 8 below based on the moisture concentration Hm obtained in step S13. Determine the value.

  FIG. 7 is a graph showing the relationship between the moisture concentration Hm and the first pump current Ip1 when the gas to be detected is air. The horizontal axis of this graph is the moisture concentration Hm, and the vertical axis is a value K1 · Ip1 obtained by multiplying the first pump current Ip1 by the coefficient K1 (a constant value other than 1). As shown in this graph, the first pump current Ip1 measured using the first reference voltage Vr1 tends to decrease as the water concentration Hm increases. This is because the oxygen concentration decreases as the moisture concentration Hm increases. Therefore, when performing zero point calibration, it is preferable to obtain the influence of the moisture concentration Hm on the first pump current Ip1 as the zero point moisture correction value δw. As shown in FIG. 7, the zero point moisture correction value δw is obtained in advance by storing the relationship between Hm and k · Ip1 in the control unit 9, and referring to this relationship, the actual moisture concentration Hm ( can be obtained from t1). Here, Hm (t1) means the moisture concentration obtained at time t1.

  FIG. 8 is a graph showing how to obtain the zero point calibration value δc in consideration of the zero point moisture correction value δw. The horizontal axis of this graph is time, and the vertical axis is a value K1 · Ip1 obtained by multiplying the first pump current Ip1 by the coefficient K1 (a constant value other than 1). The horizontal broken line indicates the initial value K1 · Ip1 (t0) of the value K1 · Ip1 at time t0. The solid line shows how the zero point changes over time when there is no influence of moisture in the gas to be detected (when the moisture in the gas to be detected is zero), and the one-dot chain line shows the influence of moisture Is shown. The difference between the solid line and the alternate long and short dash line corresponds to the zero point moisture correction value δw caused by the moisture concentration Hm. As described with reference to FIG. 7, when the gas to be detected (atmosphere) contains water vapor, the actual measurement values K1 · Ip1 are lower by the zero point moisture correction value δw. The change in the actual measurement values K1 and Ip1 indicated by the one-dot chain line is the sum of this zero point moisture correction value δw and the zero point movement amount (zero point calibration value δc) over time.

  The zero point calibration unit 230 (FIG. 2) calculates the zero point moisture correction obtained in FIG. 7 from the difference between the initial value K1 · Ip1 (t0) at time t0 and the actual value K1 · Ip1 (t1) at time t1. The zero point calibration value δc is obtained by subtracting the value δw. This zero point calibration value δc is a value that compensates for the amount of movement of the zero point of the entire region air-fuel ratio sensor 1 over time. The zero point calibration value δc is supplied from the zero point calibration unit 230 to the gas concentration detection unit 200, and zero point calibration is executed using the zero point calibration value δc. Therefore, the gas concentration detection unit 200 can obtain a correct detection result when detecting the gas concentration (oxygen concentration) when the exhaust gas is the detected gas thereafter.

  6 to 8, the sensor zero point calibration processing is performed based on the moisture concentration Hm. However, a moisture concentration equivalent value such as the moisture concentration Hm may be used for other purposes. . For example, the moisture concentration equivalent value may be supplied to the ECU 5 from the moisture concentration detection unit 220 so that the ECU 5 can use the moisture concentration equivalent value for the control of the engine 101.

Modification Examples The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

・ Modification 1
In the above embodiment, the coefficient K1 or the coefficient K2 used when determining the water concentration Hm (water concentration equivalent value) from the difference ΔIp between the first pump current Ip1 and the second pump current Ip2 is determined for each individual sensor. However, the coefficient K1 or the coefficient K2 may be selected from a predetermined finite number of values. In the latter case, for example, the gas sensor is classified into a plurality of ranks based on the value of the first pump current Ip1 measured at the time of manufacturing the gas sensor, and the coefficient K1 or the coefficient K2 set in advance for the rank is set. It may be used.

  In the above embodiment, as the function or table as shown in FIG. 3, one function or table common to all sensors having the same structure, model, and product number is used. A plurality of functions or tables corresponding to the rank may be prepared, and one function or table may be selected and used according to the rank of the gas sensor.

・ Modification 2
In the above embodiment, the functions and tables given by the above formulas (3) to (5) and the formulas (3a) to (5a) are used as the relationship for obtaining the moisture concentration equivalent value from the pump currents Ip1 and Ip2. Any other function or table may be used. For example, other functions such as a cubic function or a quartic function may be used instead of the quadratic function or the linear function of the difference ΔIp of the pump current. As these functions and tables, it is preferable to use functions or tables that depend only on the value K1 · ΔIp (or K2 · ΔWip) obtained by multiplying the difference ΔIp between the pump currents Ip1 and Ip2 by the coefficient K1. However, when obtaining the humidity of the gas to be detected as the moisture concentration equivalent value, it is preferable to use a function or table that depends only on K1 · ΔIp (or K2 · ΔWip) and the temperature of the gas to be detected.

・ Modification 3
In the above embodiment, an example in which the full-range air-fuel ratio sensor is used as the gas sensor for detecting the gas concentration of the specific component in the gas to be detected has been described, but the present invention can also be applied to other types of gas sensors, for example, The present invention is also applicable to a NOx sensor that detects the NOx concentration in the gas to be detected.

Modification 4
In the above embodiment, it is determined that the detected gas is the atmosphere based on the fuel cut signal that is output when the fuel supply to the engine is stopped. It may be determined whether or not. For example, the entire-range air-fuel ratio sensor 1 is provided with a device that fills the atmosphere around the sensor element 10 with a correction gas having a known oxygen concentration, and the gas to be detected is based on a signal output when the correction gas is filled. May be determined to be atmospheric.

・ Modification 5
In the above embodiment, the sensor control device 3 determines the oxygen concentration, the air-fuel ratio, the moisture concentration in the atmosphere, etc. in the exhaust gas, but instead, various signals such as the pump current Ip from the sensor control device 3. May be output to the ECU 5, and the ECU 5 may determine the oxygen concentration in the exhaust gas, the air-fuel ratio, the moisture concentration in the atmosphere, or the like based on these signals.

DESCRIPTION OF SYMBOLS 1 ... Full range air-fuel ratio sensor 3 ... Sensor control apparatus 4 ... Gas sensor apparatus 5 ... Engine control apparatus (ECU)
DESCRIPTION OF SYMBOLS 9 ... Control part 10 ... Sensor element 11 ... Solid electrolyte body 12 ... Insulation base | substrate 13 ... Solid electrolyte body 15 ... Diffusion control part 17 ... Insulation base | substrate 18 ... Insulation base | substrate 19-22 ... Electrode 23 ... Gas detection chamber (detection chamber)
DESCRIPTION OF SYMBOLS 24 ... Insulating base | substrate 25 ... Protective layer 26 ... Heat-generating resistor 30 ... Electric circuit part 31 ... Heater energization control circuit 32 ... Pump current drive circuit 33 ... Voltage detection circuit 34 ... Minute current supply circuit 35 ... Reference voltage comparison circuit 36 ... Pump Current detection circuit (current detection unit)
DESCRIPTION OF SYMBOLS 40 ... Oxygen pump cell 50 ... Oxygen concentration detection cell 80 ... Battery 91 ... Harness 100 ... Vehicle 101 ... Engine 102 ... Exhaust pipe 200 ... Gas concentration detection part 210 ... Atmosphere discrimination | determination part 220 ... Water concentration detection part 222 ... Divided voltage circuit 224 ... Water concentration determination unit 225 ... Voltage setting unit 226 ... Moisture concentration table 230 ... Zero point calibration unit

Claims (4)

A first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and one of the pair of first electrodes is in a detection chamber into which a gas to be detected is introduced. An oxygen concentration detection cell that is disposed and the other electrode is exposed to a reference oxygen concentration atmosphere; a second solid electrolyte body; and a pair of second electrodes formed on the second solid electrolyte body. One of the second electrodes is arranged in the detection chamber, and pumps out oxygen contained in the detection gas introduced into the detection chamber in accordance with a current flowing between the pair of second electrodes, or A gas sensor including an oxygen pump cell that performs pumping; and a sensor control device that is connected to the gas sensor and detects a gas concentration of a specific component in the gas to be detected and humidity when the gas to be detected is the atmosphere. Gassen with A device, the sensor control apparatus,
The voltage generated between the pair of first electrodes due to the difference between the oxygen concentration in the detection chamber and the oxygen concentration of the reference oxygen concentration atmosphere is detected, and the voltage generated between the pair of first electrodes is controlled. A current control unit that controls a current flowing between the pair of second electrodes so as to be a target voltage;
An atmosphere discriminating unit for discriminating whether or not the gas to be detected is air;
While the control target voltage is set to the first reference voltage, when the detected gas is determined to be the atmosphere by the atmosphere determination unit, the control target voltage is set to a second reference that is greater than the first reference voltage. A voltage setting unit for setting the voltage;
Detecting a first pump current flowing between the pair of second electrodes of the oxygen pump cell in a state where the first reference voltage is generated between the pair of first electrodes of the oxygen concentration detection cell; A current detector for detecting a second pump current flowing between the pair of second electrodes in a state where a reference voltage is generated between the pair of first electrodes;
Based on the first pump current and the second pump current detected by the current detection unit when the detected gas is determined to be the atmosphere by the atmosphere determination unit, the moisture concentration of the detected gas is determined. A gas sensor device comprising a moisture concentration detection unit for detecting a corresponding moisture concentration equivalent value,
The moisture concentration detection unit is based on a value obtained by multiplying a difference between the second pump current and the first pump current by a constant coefficient K1 (K1 is a positive value other than 1) corresponding to an individual difference of the gas sensor. A gas sensor device that determines the moisture concentration equivalent value. The gas sensor device according to claim 1,
The moisture concentration detection unit is configured to calculate a difference between the second pump current and the first pump current by the coefficient K1 and a function or table indicating a relationship between the value corresponding to the moisture concentration and an individual difference of the gas sensors. A gas sensor device characterized by storing an independent function or table and using the coefficient K1 determined depending on an individual difference of the gas sensor. The gas sensor device according to claim 1 or 2,
The moisture concentration detector outputs a first pump current equivalent voltage K2 · Vip1 (K2 is a positive constant value proportional to K1) by dividing the voltage value Vip1 indicating the first pump current Ip1, and A voltage dividing circuit that outputs a second pump current equivalent voltage K2 · Vip2 by dividing a voltage value Vip2 indicating the second pump current Ip2,
The moisture concentration detecting unit is configured to determine the moisture concentration equivalent value from a difference K2 (Vip2−Vip1) between the second pump current equivalent voltage K2 · Vip2 and the first pump current equivalent voltage K2 · Vip1 output from the voltage dividing circuit. Determining a gas sensor device. The gas sensor device according to any one of claims 1 to 3, further comprising a zero point calibration unit that performs zero point calibration of the gas sensor using the moisture concentration equivalent value. .

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