JP2013250166A - Gas sensor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor control device capable of reducing a possibility of blackening of a second solid electrolyte.SOLUTION: A gas sensor control device 3 includes temperature determination means of determining whether the temperature T of a sensor part 10f reaches a predetermined temperature Td higher than an activation temperature Ta and equal to or lower than a first target temperature Tj1; and permission means of permitting voltage setting means to set a target voltage Vj to a second target voltage Vj2 when the temperature determination means determines that the temperature T reaches the predetermined temperature Td.

Description

  The present invention relates to a gas sensor control device that controls a gas sensor.

  Conventionally, as one of gas sensors, a gas sensor that is attached to an exhaust passage of an internal combustion engine such as an automobile engine and detects an oxygen concentration in the exhaust gas is known. This gas sensor uses the fact that the magnitude of the current flowing through the sensor element (solid electrolyte body) changes in accordance with the oxygen concentration in the exhaust gas, thereby detecting the oxygen concentration and thus the air-fuel ratio of the exhaust gas. It is.

Patent Document 1 describes a gas sensor including a detection cell having a first solid electrolyte body, a pump cell having a second solid electrolyte body, and a heater for heating them as such a gas sensor. Further, Patent Document 1 describes a technique for detecting the concentration of H ₂ O gas in a gas to be measured when the gas to be measured is the atmosphere by a gas sensor control device that controls the gas sensor.

Specifically, the apparatus described in Patent Document 1 uses a first current (a voltage between first electrodes of a detection cell) that is detected when it is determined that the gas to be detected is the atmosphere. Current flowing between the second electrodes of the pump cell) and a second current (current flowing between the second electrodes when the voltage between the first electrodes is set to a second voltage higher than the first voltage). Based on this, the H ₂ O gas concentration in the gas to be measured is detected. The first voltage is a voltage at which the H ₂ O gas in the measurement gas does not substantially dissociate on the first electrode. On the other hand, the second voltage is a voltage at which the H ₂ O gas in the measurement gas dissociates on the first electrode.

JP 2010-281732 A

However, when the voltage between the first electrodes of the detection cell is increased (set to the second voltage), blackening is likely to occur in the second solid electrolyte body (for example, zirconia) of the pump cell. Here, blackening is a phenomenon in which a metal oxide contained in the solid electrolyte body is reduced and a metal is generated in the solid electrolyte body (for example, ZrO ₂ → Zr + O ₂ ). When blackening occurs in the second solid electrolyte body, the characteristics (ion conductivity) of the second solid electrolyte body deteriorate, and as a result, the concentration of H ₂ O gas in the gas to be measured can be detected appropriately. There was a risk of disappearing.

  By the way, at the start-up stage of the gas sensor (such as a vehicle equipped with the gas sensor), the sensor unit including the detection cell and the pump cell is initially at a low temperature, and the first solid electrolyte body and the second solid electrolyte body are oxygen ion conductive. Is often not indicated. Therefore, in order for the first solid electrolyte body and the second solid electrolyte body to exhibit appropriate oxygen ion conductivity, the sensor section is heated with a heater so that the temperature of the sensor section becomes a target temperature (for example, 830 ° C.). On the other hand, in order to enable oxygen concentration detection at an early stage, when the temperature of the sensor unit reaches the activation temperature (for example, 620 ° C.), the first voltage is applied to the detection cell, and the oxygen concentration is detected by the gas sensor. I'm trying to get started.

Blackening of the solid electrolyte body is more likely to occur as the temperature is lower in the temperature range above the activation temperature.
For this reason, when the temperature of the sensor unit reaches the activation temperature, the voltage between the first electrodes of the detection cell is set to a second voltage higher than the first voltage in order to detect the H ₂ O gas concentration. If it controls to, it will become easy to produce blackening especially.

The present invention has been made in view of the current situation, and provides a gas sensor control device that can reduce the possibility of blackening occurring in a second solid electrolyte body due to detection of the H ₂ O gas concentration. For the purpose.

One embodiment of the present invention includes a first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and one electrode of the pair of first electrodes is a gas to be measured. Is disposed in a measurement chamber in which the other electrode is introduced, 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 pair of second electrodes is disposed in the measurement chamber, and the gas to be measured is introduced into the measurement chamber in response to a pump current flowing between the pair of second electrodes. A gas sensor control device for controlling a gas sensor comprising: a sensor unit having a pump cell that pumps or pumps oxygen contained in the gas sensor; and a heater that heats the sensor unit. The voltage will be the target voltage Current control means for controlling a pump current flowing between the pair of second electrodes, a supply gas of the gas to be measured, and a specified gas in which the oxygen concentration in the gas to be measured is continuously set to a predetermined value Supply status determination means for determining whether or not a supply status is present, heater control means for controlling the heater, wherein the temperature of the sensor unit is higher than an activation temperature at which the sensor unit is activated Heater control means including first heater control means for controlling the heater so as to reach a temperature, and voltage setting means for setting the target voltage, wherein the H ₂ O gas in the measured gas is substantially dissociated. When the gas to be measured is determined to be in the specified gas supply status by the first voltage setting means for setting to the first target voltage and the supply status determination means, the target voltage is set to the first target voltage. Higher than Voltage setting means and a second voltage setting means for the H ₂ O gas in the measurement gas is set to a second target voltage to dissociate the temperature of the sensor portion is higher the first target than the activation temperature When the temperature determining means for determining whether or not the specified temperature equal to or lower than the temperature has been reached, and the temperature determining means determines that the temperature of the sensor unit has reached the specified temperature, the voltage setting means is Permission means for permitting the voltage to be set to the second target voltage, the supply state of the gas to be measured is the specified gas supply state, and the voltage between the pair of first electrodes becomes the first target voltage. A first current detecting means for detecting a first pump current flowing between the pair of second electrodes, the supply state of the gas to be measured is the prescribed gas supply state, and the gap between the pair of first electrodes Voltage is the second target voltage In the state, the second current detection means for detecting the second pump current flowing between the pair of second electrodes, and the measured gas based on the first pump current and the second pump current. the H ₂ O gas concentration detection means for detecting a the H ₂ O gas concentration, a gas sensor control device comprising a.

In the above-described gas sensor control device, the H ₂ O gas concentration in the measurement gas is determined based on the first pump current and the second pump current detected when the measurement gas supply status is the specified gas supply status. Detect. Specifically, for example, the H ₂ O gas concentration in the gas to be measured is detected based on a difference value obtained by subtracting the value of the first pump current from the value of the second pump current.

Here, the first pump current is detected in a state in which the voltage between the first electrodes of the detection cell is the first target voltage (the voltage at which the H ₂ O gas in the gas to be measured is not substantially dissociated). Current flowing between the second electrodes. On the other hand, the second pump current is a current flowing between the second electrodes detected in a state where the voltage between the first electrodes is the second target voltage (the voltage at which the H ₂ O gas in the gas to be measured is dissociated). is there.

Therefore, the first pump current is a current detected in a situation where the H ₂ O gas in the gas to be measured is not dissociated on one electrode of the first electrode. On the other hand, the second pump current was detected in a situation where H ₂ O gas in the gas to be measured was dissociated on one electrode of the first electrode (a situation where oxygen ions derived from H ₂ O gas were generated). Current. That is, the value of the second pump current is larger than the value of the first pump current by the current derived from the H ₂ O gas in the gas to be measured. Therefore, the H ₂ O gas concentration in the gas to be measured can be detected based on the first pump current and the second pump current.

  In the gas sensor control device described above, the temperature determination means causes the temperature of the sensor unit including the first solid electrolyte body and the second solid electrolyte body to reach a specified temperature that is higher than the activation temperature and lower than the first target temperature. If it is determined that the target voltage has been set, the voltage setting means permits the target voltage to be set to the second target voltage. That is, in the present control device, when the temperature of the sensor unit becomes a specified temperature higher than the activation temperature, the voltage between the first electrodes can be increased from the first target voltage to the second target voltage. It becomes.

Thus, even if the voltage between the first electrodes is increased from the first target voltage to the second target voltage in order to detect the H ₂ O gas concentration in the gas to be measured, blackening occurs in the second solid electrolyte body. The possibility can be reduced. In particular, in order to detect the H ₂ O gas concentration in the gas to be measured at a stage where the temperature of the sensor section is low (stage where the temperature is lower than the first target temperature), such as when the gas sensor has just started, Even when the voltage is increased from the first target voltage to the second target voltage, the possibility of blackening occurring in the second solid electrolyte body can be reduced.

Note that, for example, an internal combustion engine mounted on a vehicle may be used when the gas supply state to be measured corresponds to a specified gas supply state in which the oxygen concentration in the gas to be measured is continuously set to a predetermined value. However, when the vehicle is stopped or the like, the engine is in a stable idling state, and the exhaust gas that is the gas to be measured continuously becomes an exhaust gas having a specified A / F value (for example, the theoretical air-fuel ratio). Mention the situation in which it is supplied. In this case, the exhaust gas corresponds to the gas to be measured in which the oxygen concentration in the gas to be measured becomes a predetermined specified value.
Further, there can be mentioned a situation in which exhaust gas, which is a gas to be measured, is continuously turned into the atmosphere by the fuel cut of the internal combustion engine, and this atmosphere is continuously supplied to the gas sensor. In this case, the atmosphere corresponds to the gas to be measured in which the oxygen concentration in the gas to be measured has a predetermined specified value.

  The activation temperature refers to the temperature at which the sensor unit is activated. Furthermore, the activation means that oxygen ion conductivity occurs in the first solid electrolyte body and the second solid electrolyte body included in the sensor unit, and the element can be used for detecting the oxygen concentration as a gas sensor element. Say.

  Furthermore, the gas sensor control device may be a gas sensor control device in which the specified temperature is set to a temperature equal to or higher than a central temperature in a temperature range from the activation temperature to the first target temperature. .

  In the gas sensor control apparatus described above, the specified temperature (the temperature at which the target voltage is allowed to be changed to the second target voltage) is set to a temperature closer to the first target temperature than the activation temperature. This can reduce the possibility of blackening even when the target voltage is changed to the second target voltage, compared to when the specified temperature is set to a temperature close to the activation temperature.

  For example, when the activation temperature is 620 ° C. and the first target temperature is 830 ° C., the central temperature in the temperature range from the activation temperature to the first target temperature is 725 ° C. (= 620 + (830−620) / 2). In this case, in the present control device, the specified temperature (the temperature higher than the activation temperature and not higher than the first target temperature) is set to a temperature in the range of 725 to 830 ° C.

  Furthermore, in any one of the above gas sensor control devices, the heater control means is in the specified gas supply status, and the temperature of the sensor unit is detected after the first pump current is detected by the first current detection means. Includes a second heater control means for controlling the heater so that the second target temperature is higher than the first target temperature, and the second current detection means is under the control of the heater by the second heater control means. Thus, it is preferable that the gas sensor control device detects the second pump current flowing between the pair of second electrodes in a state where the temperature of the sensor unit becomes the second target temperature.

In the gas sensor control device described above, when the second pump current is detected, the temperature of the sensor unit is set to the second target temperature higher than the first target temperature, so that the target temperature is not changed (however, the first electrode H ₂ O in the measured gas compared to the same second target voltage)
Gas dissociation can be promoted. Furthermore, the second pump current to be detected can be stabilized (the fluctuation range of the second pump current accompanying the fluctuation of the voltage between the first electrodes controlled to the second target voltage can be reduced). Thereby, compared with the case where the second pump current is detected while keeping the target temperature of the sensor unit as the first target temperature (when the target temperature of the sensor unit is not increased), the H ₂ O gas concentration in the gas to be measured. Detection accuracy can be increased.

  Further, in the above-described gas sensor control device, the second pump current is more stable than when the second pump current is detected at the first target temperature by increasing the temperature of the sensor unit (the second target temperature). Thus, the voltage between the first electrodes can be lowered. Therefore, in the gas sensor control device described above, if the detection accuracy is the same as when the second pump current is detected at the first target temperature, the target is higher than that when the second pump current is detected at the first target temperature. The second target voltage, which is a voltage, can be set low. In this way, the possibility of blackening occurring in the second solid electrolyte body can be further reduced.

  Furthermore, in the gas sensor control device described above, the second voltage setting unit is configured to control the heater after the temperature of the sensor unit reaches the second target temperature by the control of the heater by the second heater control unit. A gas sensor control device that sets the voltage to the second target voltage may be used.

Blackening of the solid electrolyte body is less likely to occur at higher temperatures in the temperature range above the activation temperature.
On the other hand, in the above-described gas sensor control device, the target voltage is set to the second target voltage after the temperature of the sensor unit reaches the second target temperature. Thereby, after the temperature of the sensor unit reaches the second target temperature, the voltage between the first electrodes rises from the first target voltage toward the second target voltage. Therefore, compared with the case where the target voltage is set to the second target voltage before the temperature of the sensor unit reaches the second target temperature, the possibility of occurrence of blackening in the second solid electrolyte body can be reduced.

  Furthermore, in any one of the gas sensor control devices described above, the second current detection unit is in a state where the temperature of the sensor unit is stabilized at the second target temperature by the control of the heater by the second heater control unit. A gas sensor control device for detecting the second pump current may be used.

  When the temperature of the sensor unit is raised to the second target temperature by controlling the heater by the second heater control means, hunting (overshoot) occurs, and the temperature of the sensor unit is stably controlled to the second target temperature. It may take some time before For this reason, after raising the temperature of the sensor unit to the second target temperature, it may take time for the second pump current to stabilize.

On the other hand, in the above-described gas sensor control device, the second pump current is detected in a state where the temperature of the sensor unit is stable at the second target temperature. That is, after the temperature of the sensor unit is raised to the second target temperature by controlling the heater by the second heater control means, the second pump current is increased after the temperature of the sensor unit is stabilized at the second target temperature. Detect. Thereby, since the H ₂ O gas concentration in the gas to be measured can be detected based on the stable second pump current, the detection accuracy can be further improved.

  The “state in which the temperature of the sensor unit is stabilized at the second target temperature” refers to a state in which the temperature fluctuation of the sensor unit is within the temperature range of the second target temperature ± 10 (deg).

1 is a schematic view of an internal combustion engine according to first and second embodiments. It is a block diagram of the gas sensor unit concerning Embodiment 1,2. 6 is a flowchart showing a flow of gas sensor control according to the first and second embodiments. 3 is a flowchart of H ₂ O gas concentration detection according to the first embodiment. 6 is a flowchart of H ₂ O gas concentration detection according to the _second embodiment. It is a figure which shows the correlation with the voltage between 1st electrodes, and a pump current.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram of an internal combustion engine 100 according to the first embodiment. The internal combustion engine 100 has an engine 101 for driving an automobile. The engine 101 is connected to an exhaust pipe 102 for discharging exhaust gas EG (corresponding to the gas to be measured) discharged from the engine 101 to the outside of the vehicle. The exhaust pipe 102 is provided with a full-range air-fuel ratio sensor 1 (corresponding to a gas sensor). Exhaust gas EG discharged from the engine 101 is supplied to the entire region air-fuel ratio sensor 1.

  The full-range air-fuel ratio sensor 1 (hereinafter also simply referred to as sensor 1) is a gas sensor that detects the gas concentration of a specific component (oxygen in the first embodiment) in the exhaust gas EG flowing through the exhaust passage of the exhaust pipe 102. . This sensor 1 is electrically connected to a gas sensor control device 3 disposed at a position away from itself through a harness (signal line) 91.

  The gas sensor control device 3 detects the oxygen concentration by energizing the sensor 1. Specifically, the gas sensor control device 3 is driven by receiving power from the battery 80, and outputs a detection signal of the oxygen concentration detected using the sensor 1 to the ECU (engine control device) 5.

  The ECU 5 is a device for electronically controlling driving of the automobile engine 101 and the like. As the ECU 5, a microcomputer equipped with a CPU, ROM, RAM, and the like (not shown) having a known configuration is used. The ECU 5 controls the fuel injection timing and ignition timing in accordance with the execution of the control program. As information for performing such control, the ECU 5 receives a detection signal corresponding to the oxygen concentration in the exhaust gas EG output from the gas sensor control device 3. In addition, 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, a coolant temperature, and a combustion pressure) are input to the ECU 5.

  Such an ECU 5 performs air-fuel ratio feedback control of the engine 101 based on the output of the sensor 1. Further, the ECU 5 determines whether or not the supply state of the exhaust gas EG from the engine 101 to the sensor 1 is a specified gas supply state. When the ECU 5 determines that the specified gas supply status is present, the ECU 5 transmits a signal indicating the “specified gas supply status” to the microcomputer 9 (see FIG. 2) in the control device 3. The microcomputer 9 determines whether or not the specified gas supply status is based on this signal.

  Here, the “specified gas supply status” refers to a situation in which the supply status of the exhaust gas EG from the engine 101 to the sensor 1 continues and the oxygen concentration in the exhaust gas EG becomes a predetermined specified value. In the first embodiment, while the automobile equipped with the internal combustion engine 100 is stopped, the engine 101 is in a stable idling state, and the exhaust gas EG that is the exhaust gas EG continues to have a prescribed A / F value (for example, The state of being supplied to the sensor 1 as the exhaust gas EG of (theoretical air-fuel ratio) is referred to as “specified gas supply state”. The ECU 5 determines whether or not the supply status of the exhaust gas EG is the “specified gas supply status” as described above based on the input information.

  Next, the sensor 1 and the gas sensor control device 3 will be described in detail with reference to FIG. FIG. 2 is a configuration diagram of the gas sensor unit 4 according to the first embodiment. The gas sensor unit 4 includes a sensor 1 and a gas sensor control device 3.

The sensor 1 has a structure in which a sensor element 10 having an elongated plate shape is held in a housing (not shown).
The sensor element 10 includes a first solid electrolyte body 13 and a second solid electrolyte body 11 mainly composed of zirconia, and insulating bases 12, 17, 18, and 24 mainly composed of alumina. These are laminated in the order of the insulating base 18, the insulating base 17, the first solid electrolyte body 13, the insulating base 12, the second solid electrolyte body 11, and the insulating base 24.

  A pair of second electrodes 19 and 20 mainly composed of platinum are formed on both surfaces of the second solid electrolyte body 11. In addition, a pair of first electrodes 21 and 22 mainly composed of platinum are also formed on both surfaces of the first solid electrolyte body 13. The first electrode 22 is embedded between the first solid electrolyte body 13 and the insulating substrate 17. The first solid electrolyte body 13, the second solid electrolyte body 11, and the insulating bases 12, 17, 18, and 24 are all formed in an elongated plate shape, and in FIG. Show.

  On one end side in the longitudinal direction of the insulating substrate 12 (in the direction orthogonal to the paper surface in FIG. 2), the first solid electrolyte body 13 and the second solid electrolyte body 11 each have a single wall surface, and a hollow in which exhaust gas EG can be introduced. The measurement chamber 23 is formed. At both ends in the width direction (left and right direction in FIG. 2) of the measurement chamber 23, porous diffusion rate controlling portions 15 for restricting the amount of inflow when the exhaust gas EG is introduced into the measurement chamber 23 are provided. It has been. The second electrode 20 on the second solid electrolyte body 11 and the first electrode 21 on the first solid electrolyte body 13 are arranged so as to be exposed in the measurement chamber 23 and are electrically connected to each other. Yes.

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

  The second solid electrolyte body 11 and the pair of second electrodes 19, 20 provided on both surfaces of the second solid electrolyte body 11 pump oxygen into the measurement chamber 23 from the outside according to the pump current Ip flowing between the second electrodes 19, 20. Alternatively, a “pump cell 10 c” is configured to pump out oxygen contained in the exhaust gas EG (exhaust gas EG) introduced into the measurement chamber 23.

The first solid electrolyte body 13 and the pair of first electrodes 21 and 22 provided on both surfaces thereof constitute a “detection cell 10b”. Among these, the 1st electrode 22 functions as an oxygen reference electrode which maintains the oxygen concentration used as the reference | standard for detecting the oxygen concentration in the measurement chamber 23. FIG. The first electrode 22 is exposed to a reference oxygen concentration atmosphere. For this reason, a voltage is generated between the first electrodes 21 and 22 of the detection cell 10b due to the difference between the oxygen ion concentration generated on the first electrode 21 and the oxygen ion concentration generated on the first electrode 22. .
Further, the pump cell 10c and the detection cell 10b constitute a “sensor unit 10f”.

  A heating resistor 26 mainly composed of platinum is embedded between the insulating bases 17 and 18. The insulating substrates 17 and 18 and the heating resistor 26 constitute a “heater 10d” for heating and activating the sensor unit 10f.

Next, the gas sensor control device 3 that controls the sensor 1 (sensor element 10) will be described in detail.
The gas sensor control device 3 includes a microcomputer 9 and an electric circuit unit 30 as constituent entities. The microcomputer 9 is a microcomputer chip on which a CPU 6, a ROM 7, a RAM 8, and the like having a known configuration are mounted. The ROM 7 stores a control program for causing the CPU 6 to execute each process. On the other hand, the electric circuit unit 30 includes a heater control circuit 31, a pump current control circuit 32, a voltage detection circuit 33, a minute current supply circuit 34, a comparison PID circuit 35, a pump current detection circuit 36, and an internal resistance detection circuit 37. The

  Among these, the heater control circuit 31 causes the heating resistor 26 to generate heat by PWM-controlling the voltage Vh supplied to both ends of the heating resistor 26, and the sensor unit 10f (the pump cell 10c including the second solid electrolyte body 11 and the Heating control of the detection cell 10b) including the first solid electrolyte body 13 is performed. Specifically, the heater control circuit 31 controls energization to the heater 10d (the heating resistor 26) so that the temperature T of the sensor unit 10f becomes the target temperature Tj.

The first target temperature Tj1 is a temperature higher than the activation temperature Ta (620 ° C. in the first embodiment) at which the sensor unit 10f is activated. In the first embodiment, the first target temperature Tj1 = 830 ° C. is set.
In addition, “activation” of the sensor unit 10f means that oxygen ion conductivity occurs in the first solid electrolyte body 13 and the second solid electrolyte body 11 constituting the sensor unit 10f, and the oxygen concentration of the sensor 1 element is increased. It means that it can be used for detection.

  In the present embodiment, the temperature T of the sensor unit 10f is controlled by controlling the internal resistance Rs of the first solid electrolyte body 13 included in the sensor unit 10f. Specifically, the first solid electrolyte body 13 has a characteristic that the internal resistance Rs varies according to its own temperature, and the internal resistance Rs of the first solid electrolyte body 13 is correlated with its own temperature. have. Therefore, the internal resistance detection circuit 37 detects the internal resistance Rs of the first solid electrolyte body 13, and based on this (assuming the temperature of the first solid electrolyte body 13 as the temperature T of the sensor section 10f), the sensor section 10f. To control the temperature T.

  The internal resistance Rs of the first solid electrolyte body 13 is detected as follows. First, a constant current I is allowed to flow between the first electrodes 21 and 22 of the detection cell 10b for a certain period of time by a constant current source circuit that constitutes the internal resistance detection circuit 37, and the first electrode 21 and 22 that changes in response thereto is passed. The voltage V is measured by the internal resistance detection circuit 37. The CPU 6 of the microcomputer 9 calculates the value of the internal resistance Rs based on the change amount of the voltage V when the constant current I is applied and the constant current I. More specifically, the voltage between the first electrodes 21 and 22 before the constant current I is supplied to the detection cell 10b by the constant current source circuit included in the internal resistance detection circuit 37, and the constant current I from the constant current source circuit. A voltage between the first electrodes 21 and 22 after a predetermined time has passed after flowing through the detection cell 10 b (for example, after 60 μs has elapsed) is input to the CPU 6 through the internal resistance detection circuit 37. And the value of internal resistance Rs is detected from the difference voltage (change amount) (DELTA) V of two input voltages using the preset formula or map.

Therefore, in the first embodiment, when the control of the sensor 1 by the gas sensor control device 3 is started, the CPU 6 of the microcomputer 9 causes the internal resistance Rs corresponding to the first target temperature Tj1 (the temperature T of the sensor unit 10f to be the first value). The internal resistance Rs of the first solid electrolyte body 13 when the target temperature Tj1 is reached is set as the first target internal resistance Rs1). Then, the heater control circuit 31 controls energization to the heating resistor 26 so that the internal resistance Rs of the first solid electrolyte body 13 becomes the first target internal resistance Rs1. Thereby, the temperature T of the sensor unit 10f is controlled to the first target temperature Tj1. In the first embodiment, this control is referred to as first heater control.
In the first embodiment, the heater control circuit 31 and the microcomputer 9 correspond to heater control means.

  The minute current supply circuit 34 moves oxygen ions from the first electrode 21 side to the first electrode 22 side by causing a minute current Icp to flow from the first electrode 22 to the first electrode 21 side of the detection cell 10b. A reference oxygen concentration atmosphere is generated in the first electrode 22 of the quality. Thus, the first electrode 22 functions as an oxygen reference electrode that serves as a reference for detecting the oxygen concentration in the exhaust gas EG.

The voltage detection circuit 33 detects the voltage Vs between the first electrodes 21 and 22 of the detection cell 10b.
The comparison PID circuit 35 compares the target voltage Vj set by the CPU 6 of the microcomputer 9 with the voltage Vs detected by the voltage detection circuit 33. Then, based on the comparison result, the pump current Ip flowing between the second electrodes 19 and 20 of the pump cell 10c is increased by the PID control method so that the voltage Vs between the first electrodes 21 and 22 becomes the target voltage Vj. In order to control the sheath direction, a control instruction value is input to the pump current control circuit 32.

  The pump current control circuit 32 changes the magnitude and direction of the pump current Ip based on an instruction from the comparison PID circuit 35, pumps oxygen into the measurement chamber 23 by the pump cell 10c, and supplies oxygen from the measurement chamber 23. Pump out. The pump current detection circuit 36 detects a pump current Ip flowing between the second electrodes 19 and 20 of the pump cell 10c.

  In the first embodiment, the target voltage Vj compared with the voltage Vs by the comparison PID circuit 35 can be set to two target voltages (a first target voltage Vj1 and a second target voltage Vj2). Specifically, the electric circuit unit 30 includes a first reference power supply 38 and a second reference power supply 39 connected to the comparison PID circuit 35 through the switch SW1. The voltage of the first reference power supply 38 is the first target voltage Vj1, and the voltage of the second reference power supply 39 is the second target voltage Vj2. For this reason, the target voltage Vj can be set to the first target voltage Vj1 by connecting the switch SW1 to the first reference power supply 38 side. On the other hand, the target voltage Vj can be set to the second target voltage Vj2 by switching the switch SW1 to the second reference power supply 39 side.

The first target voltage Vj1 is such that when the voltage Vs becomes the first target voltage Vj1, the oxygen gas contained in the exhaust gas EG in the measurement chamber 23 is dissociated on the first electrode 21, but the exhaust gas EG The H ₂ O gas contained in is set to a voltage value that does not substantially dissociate on the first electrode 21 (450 mV in the first embodiment).
On the other hand, when the voltage Vs becomes the second target voltage Vj2, the second target voltage Vj2 includes not only oxygen gas contained in the exhaust gas EG in the measurement chamber 23 but also H ₂ O gas from the first electrode 21. The voltage value dissociates above (1000 mV in the first embodiment).

  In the first embodiment, when the control of the sensor 1 by the gas sensor control device 3 is started, the first heater control described above is started. Thereafter, when it is determined that the temperature T of the sensor unit 10f has reached the activation temperature Ta (620 ° C. in the first embodiment), the microcomputer 9 sets the first target voltage Vj1 as the target voltage Vj, The electric circuit unit 30 starts the control (feedback control) of the pump current Ip so that the voltage Vs between the first electrodes 21 and 22 becomes the first target voltage Vj1. Thereby, detection of the oxygen concentration in the exhaust gas EG based on the pump current Ip is started.

  Whether or not the temperature T of the sensor unit 10f has reached the activation temperature Ta (620 ° C. in the first embodiment) is determined based on the internal resistance of the first solid electrolyte body 13 detected by the electric circuit unit 30. This is performed by the microcomputer 9 based on Rs. The internal resistance Rs of the first solid electrolyte body 13 is a value corresponding to the activation temperature Ta (620 ° C.) (the internal resistance of the first solid electrolyte body 13 when the temperature T of the sensor unit 10f becomes the activation temperature Ta). The microcomputer 9 determines that the temperature T of the sensor unit 10f has reached the activation temperature Ta.

  Further, the microcomputer 9 determines whether or not the temperature T of the sensor unit 10f has reached the specified temperature Td based on the internal resistance Rs of the first solid electrolyte body 13 detected by the electric circuit unit 30. When it is determined that the temperature T has reached the specified temperature Td, the microcomputer 9 allows the target voltage Vj to be changed from the first target voltage Vj1 to the second target voltage Vj2. On the other hand, when it is determined that the temperature T has not reached the specified temperature Td, the microcomputer 9 disables the target voltage Vj from being changed from the first target voltage Vj1 to the second target voltage Vj2.

  The specified temperature Td is a temperature that is higher than the activation temperature Ta and lower than or equal to the first target temperature Tj1. In the first embodiment, the specified temperature Td is set to the center temperature (that is, 725 ° C.) between the activation temperature Ta (620 ° C.) and the first target temperature Tj1 (830 ° C.).

  In the pump current detection circuit 36, the supply status of the exhaust gas EG is the specified gas supply status, and the voltage Vs between the first electrodes 21 and 22 is the first target voltage Vj1, and the pump current Ip is The pump current Ip1 is detected. The microcomputer 9 reads this first pump current Ip1.

  Furthermore, when it is permitted to change the target voltage Vj from the first target voltage Vj1 to the second target voltage Vj2, the microcomputer 9 changes the target voltage Vj to the second target voltage Vj2. Thereafter, in a state where the voltage Vs becomes the second target voltage Vj2, the pump current detection circuit 36 detects the second pump current Ip2 as the pump current Ip. The microcomputer 9 reads this second pump current Ip2.

Further, the microcomputer 9 detects the H ₂ O gas concentration in the exhaust gas EG based on the first pump current Ip1 and the second pump current Ip2. Specifically, the H ₂ O gas concentration in the exhaust gas EG is detected based on a difference value ΔIp (mA) obtained by subtracting the first pump current Ip1 from the second pump current Ip2.
In the first embodiment, the pump current control circuit 32, the voltage detection circuit 33, and the comparison PID circuit 35 constitute a “current control unit”.

Next, the control flow of the sensor 1 according to the first embodiment will be described below.
As shown in FIG. 2, in the sensor 1, the minute current supply circuit 34 causes the minute current Icp to flow from the first electrode 22 of the detection cell 10 b toward the first electrode 21. Oxygen in the exhaust gas EG is pumped into the first electrode 22 side through the solid electrolyte body 13, and the first electrode 22 functions as an oxygen reference electrode.

  As shown in FIG. 3, when the control of the sensor 1 by the gas sensor control device 3 is started together with the start of the engine 101, the first heater control is started in step S1. Specifically, first, the CPU 6 of the microcomputer 9 sets the first target internal resistance Rs1 as the target internal resistance Rsj of the heater control circuit 31. Then, the heater control circuit 31 starts energization control (first heater control) to the heating resistor 26 so that the internal resistance Rs of the first solid electrolyte body 13 becomes the first target internal resistance Rs1.

Next, it progresses to step S2 and it is judged whether the temperature T of the sensor part 10f reached the activation temperature Ta (620 degreeC).
If it is determined that the activation temperature Ta has been reached (YES), the process proceeds to step S3, and the microcomputer 9 sets the first target voltage Vj1 (450 mV) as the target voltage Vj to be compared in the comparison PID circuit 35. Set. Specifically, the switch SW1 is connected to the first reference power supply 38 side, and the target voltage Vj is set to the first target voltage Vj1.

  Subsequently, it progresses to step S4 and the feedback control of the pump current Ip is started. Specifically, the voltage detection circuit 33 detects the voltage Vs between the first electrodes 21 and 22. Thereafter, the comparison PID circuit 35 compares the detected voltage Vs with the first target voltage Vj1. Further, based on the comparison result, the magnitude of the pump current Ip that flows between the second electrodes 19 and 20 of the pump cell 10c so that the voltage Vs between the first electrodes 21 and 22 becomes the target voltage Vj by the PID control method. In order to control the sheath direction, a control instruction value is input to the pump current control circuit 32. The pump current control circuit 32 changes the magnitude and direction of the pump current Ip based on an instruction from the comparison PID circuit 35, pumps oxygen into the measurement chamber 23 by the pump cell 10c, and supplies oxygen from the measurement chamber 23. Pump out.

When the air-fuel ratio of the exhaust gas EG introduced into the measurement chamber 23 is rich, the oxygen concentration in the exhaust gas EG is low, so that oxygen is pumped into the measurement chamber 23 from the outside in the pump cell 10c. The pump current Ip flowing between the second electrodes 19 and 20 is controlled.
On the other hand, when the air-fuel ratio of the exhaust gas EG introduced into the measurement chamber 23 is lean, a large amount of oxygen is present in the exhaust gas EG, so that oxygen is pumped from the measurement chamber 23 to the outside in the pump cell 10c. As described above, the pump current Ip flowing between the second electrodes 19 and 20 is controlled.

  Next, the process proceeds to step S5, and the microcomputer 9 starts detecting the oxygen concentration in the exhaust gas EG. Specifically, the oxygen concentration contained in the exhaust gas EG is detected based on the magnitude and direction of the pump current Ip detected by the pump current detection circuit 36 in a state where the voltage Vs becomes the first target voltage Vj1. . The detected oxygen concentration detection signal is output to the ECU 5.

Next, in step S6, the microcomputer 9 determines whether or not the temperature T of the sensor unit 10f has reached the specified temperature Td.
If it is determined in step S6 that the temperature T has reached the specified temperature Td (YES), the process proceeds to step S7, and the microcomputer 9 changes the target voltage Vj from the first target voltage Vj1 to the second target voltage Vj2. Allow to do.
On the other hand, if it is determined that the temperature T has not reached the specified temperature Td (NO), the process proceeds to step S8, where it is impossible to change the target voltage Vj from the first target voltage Vj1 to the second target voltage Vj2. .

As described above, when the internal combustion engine 100 is started, the gas sensor control device 3 according to the first embodiment uses the sensor 1 to increase the oxygen concentration of the exhaust gas EG after the temperature T reaches the activation temperature Ta (620 ° C.). Detection is performed.
However, when it is determined that the supply status of the exhaust gas EG is the specified gas supply status, the sensor 1 is used to detect the H ₂ O gas concentration in the exhaust gas EG.

Therefore, the H ₂ O gas concentration detection executed in the gas sensor control device 3 will be described with reference to FIG.
A program for executing each process (H ₂ O gas concentration detection process) shown in FIG. 4 is stored in the ROM 7 (see FIG. 2) of the microcomputer 9 and is executed by the CPU 6.
Note that each process (H ₂ O gas concentration detection process) shown in FIG. 4 continued the process shown in FIG. 3 after the detection of the oxygen concentration in the exhaust gas EG (the process of step S5) was started. Executed in parallel in the state.

  When the above-described detection of the oxygen concentration in the exhaust gas EG is started (step S5), the microcomputer 9 determines in step W1 whether or not the supply status of the exhaust gas EG is the specified gas supply status. Specifically, it is determined whether or not the supply status of the exhaust gas EG (measured gas) from the engine 101 to the sensor 1 is a supply status in which the oxygen concentration in the exhaust gas EG continuously becomes a predetermined specified value. to decide. More specifically, the engine 101 is in a stable idling state, and the exhaust gas EG is continuously supplied to the sensor 1 as an exhaust gas EG having a specified A / F value (for example, a theoretical air-fuel ratio). Determine whether the situation is true.

In the first embodiment, the ECU 5 detects whether or not the supply status of the exhaust gas EG is the “specified gas supply status” based on information input from various sensors or the like. Specifically, for example, when the automobile is parked, the shift range position is set to the D range, and the automobile engine 101 is immediately after being started but is in a stable idling state, the ECU 5 is in the “specified gas supply status”. It is determined that there is a signal, and a signal indicating the “specified gas supply status” is transmitted to the microcomputer 9.
When the microcomputer 9 receives this signal, it determines that it is the specified gas supply status (YES). On the other hand, when it does not receive the signal, it determines that it is not the specified gas supply status (NO).

When it is determined in step W1 that the supply status of the exhaust gas EG is not the specified gas supply status (NO), the process ends without performing the H ₂ O gas concentration detection process.
On the other hand, if it is determined that the supply status of the exhaust gas EG is the specified gas supply status (YES), the process proceeds to step W2, and the microcomputer 9 changes the target voltage Vj from the first target voltage Vj1 to the second target voltage Vj2. It is determined whether or not the change is permitted. If it is determined that it is not permitted (NO), the process returns to step W1 again and the above-described processing is performed.

If it is determined in step W2 that the operation is permitted (YES), the process proceeds to step W3, and the first pump current Ip1 output from the pump current detection circuit 36 is read. The read value of the first pump current Ip1 is stored in the RAM 8.
At this time, the target voltage Vj of the comparison PID circuit 35 is set to the first target voltage Vj1 (450 mV), and the voltage Vs between the first electrodes 21 and 22 is set to the first target voltage Vj1 (450 mV). It has become. Therefore, the first pump current Ip1 is detected in a state where the voltage Vs is the first target voltage Vj1 (450 mV).

  Next, the process proceeds to step W4, and the microcomputer 9 switches the switch SW1 of the electric circuit unit 30 to change the target voltage Vj of the comparison PID circuit 35 from the first target voltage Vj1 to the second target voltage Vj2 (in the first embodiment). , 1000 mV). Thereby, thereafter, the electric circuit unit 30 starts control of the pump current Ip so that the voltage Vs becomes the second target voltage Vj2.

  Thereafter, the process proceeds to step W5, and the microcomputer 9 determines whether or not a specified time has elapsed since the target voltage Vj was changed to the second target voltage Vj2. Here, during the specified time, the voltage Vs between the first electrodes 21 and 22 is changed to the second target voltage by controlling the pump current Ip by the pump current control circuit 32 after changing the target voltage Vj to the second target voltage Vj2. This is the time required to stabilize at Vj2. This specified time is grasped in advance by a test and stored in the ROM 7 of the microcomputer 9.

  If it is determined in step W5 that the specified time has not elapsed (NO), the process proceeds to step W6, and whether or not the supply status of the exhaust gas EG is the specified gas supply status as in the previous step W1. Judging. If it is determined in step W6 that the specified gas supply state is not reached (NO), the process proceeds to step W9, the switch SW1 of the electric circuit unit 30 is switched to the first reference power supply 38 side, and the target voltage Vj is changed to the first target voltage Vj1. After returning to, the series of processing is terminated. On the other hand, if it is determined in step W6 that the specified gas supply status is (YES), the process returns to step W5 again and the above-described processing is performed.

If it is determined in step W5 that the specified time has elapsed (YES), the process proceeds to step W7, and the microcomputer 9 reads the value of the second pump current Ip2 output from the pump current detection circuit 36 and stores it in the RAM 8. Remember.
At this time, the voltage Vs between the first electrodes 21 and 22 is stable at the second target voltage Vj2. Therefore, the second pump current Ip2 is detected in a state where the voltage Vs becomes the second target voltage Vj2 (1000 mV).

Next, the process proceeds to step W8, and the microcomputer 9 detects the H ₂ O gas concentration in the exhaust gas EG based on the first pump current Ip1 and the second pump current Ip2. Specifically, the H ₂ O gas concentration in the exhaust gas EG is detected based on a difference value ΔIp (mA) obtained by subtracting the first pump current Ip1 from the second pump current Ip2.

In the first embodiment, the correlation between the H ₂ O gas concentration (%) in the exhaust gas EG and the difference value ΔIp (mA) is obtained in advance by testing, and the ROM ₂ of the microcomputer 9 stores the H ₂ A correlation function or map between the O gas concentration (%) and the difference value ΔIp (mA) is stored. Therefore, the CPU 6 of the microcomputer 9 can detect the H ₂ O gas concentration in the exhaust gas EG from the difference value ΔIp (mA) using this correlation function or map.
Thereafter, the process proceeds to step W9, and the target voltage Vj is returned to the first target voltage Vj1. Thereby, a series of H ₂ O gas concentration detection processing is completed.

By the way, the first pump current Ip1 is a current detected in a situation where the H ₂ O gas in the exhaust gas EG is not substantially dissociated on the first electrode 21. On the other hand, the second pump current Ip2 is a current detected in a situation where the H ₂ O gas in the exhaust gas EG is dissociated on the first electrode 21 (a situation where oxygen ions derived from the H ₂ O gas are generated). is there. That is, the second pump current Ip2 is larger than the first pump current Ip1 by the current derived from the H ₂ O gas in the exhaust gas EG. Therefore, the H ₂ O gas concentration in the exhaust gas EG can be detected based on the first pump current Ip1 and the second pump current Ip2.

  On the other hand, if the voltage Vs applied between the first electrodes 21 and 22 is increased (changed from the first target voltage Vj1 to the second target voltage Vj2), blackening is likely to occur in the second solid electrolyte body 11. Further, the blackening of the second solid electrolyte body 11 is more likely to occur as the temperature is lower in the temperature range equal to or higher than the activation temperature Ta. That is, the activation temperature Ta is most likely to occur, and the higher the temperature, the less likely it is to occur.

For this reason, the voltage Vs between the first electrodes 21 and 22 is higher than the first target voltage Vj1 in order to detect the H ₂ O gas concentration when the temperature T of the sensor unit 10f reaches the activation temperature Ta. When the control is performed so as to be the second target voltage Vj2, blackening of the second solid electrolyte body 11 is particularly likely to occur. Accordingly, in increasing the voltage Vs between the first electrodes 21 and 22 (to the second target voltage Vj2), the temperature T of the sensor unit 10f is higher than the stage where the activation temperature Ta at which the oxygen concentration detection is started. When the temperature rises at a higher temperature, blackening is less likely to occur.

  Therefore, in the gas sensor control device 3 of the first embodiment, the temperature T of the sensor unit 10f has reached the specified temperature Td (temperature higher than the activation temperature Ta (620 ° C.), 725 ° C. in the first embodiment). If it is determined, the target voltage Vj is allowed to be changed from the first target voltage Vj1 to the second target voltage Vj2. As a result, the voltage Vs between the first electrodes 21 and 22 can be raised from the first target voltage Vj1 to the second target voltage Vj2 after the temperature T becomes equal to or higher than the specified temperature Td higher than the activation temperature Ta. it can.

Thus, in the first embodiment, even if the voltage Vs between the first electrodes 21 and 22 is increased from the first target voltage Vj1 to the second target voltage Vj2 in order to detect the H ₂ O gas concentration in the gas to be measured. The possibility of blackening occurring in the second solid electrolyte body 11 can be reduced. In particular, in the first embodiment, the H ₂ O gas concentration in the measurement gas is detected at a stage where the temperature T of the sensor unit 10f is lower than the first target temperature Tj1, such as when the gas sensor 1 has just started. Therefore, the voltage Vs between the first electrodes 21 and 22 is changed from the first target voltage Vj1 to the second voltage Vs1.
Even when the voltage is raised to the target voltage Vj2, the possibility of blackening occurring in the second solid electrolyte body 11 can be reduced.

  In the first embodiment, the heater control circuit 31 and the microcomputer 9 that performs the process of step S1 correspond to first heater control means. The microcomputer 9 that performs the process of step S6 corresponds to a temperature determination unit. Further, the microcomputer 9 that performs the process of step S7 corresponds to a permission unit. The microcomputer 9 that performs the processes of steps W1 and W6 corresponds to a supply status determination unit.

Further, the comparison PID circuit 35, the switch SW1, the first reference power supply 38, and the microcomputer 9 that performs the processes of steps S3 and W9 correspond to the first voltage setting means. Further, the comparison PID circuit 35, the switch SW1, the second reference power supply 39, and the microcomputer 9 that performs the process of step W4 correspond to the second voltage setting means. The pump current detection circuit 36 and the microcomputer 9 that performs the process of step W3 correspond to the first current detection means. Further, the pump current detection circuit 36 and the microcomputer 9 that performs the process of step W7 correspond to a second current detection unit. Further, the microcomputer 9 that performs the process of step W8 corresponds to the H ₂ O gas concentration detecting means.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described with reference to the drawings. The gas sensor control device 203 constituting the internal combustion engine 200 according to the second embodiment is different from the gas sensor control device 3 according to the first embodiment in the control program stored in the ROM 7 of the microcomputer 9 and is otherwise the same. . Further, the control by the gas sensor control device 203 according to the second embodiment differs from the first embodiment only in part of the H ₂ O gas concentration detection process, and is the same for the other. Therefore, here, the description will focus on the differences from the first embodiment, and the description of the same points will be omitted.

  In the first embodiment, the temperature T of the first solid electrolyte body 13 and the second solid electrolyte body 11 continues to be the first target temperature Tj1 regardless of whether or not the exhaust gas EG is in the specified gas supply status. Thus, the first heater control was performed. Accordingly, the first pump current Ip1 and the second pump current Ip2 are both detected under the first heater control.

On the other hand, in the second embodiment, when the ECU 5 determines that the exhaust gas EG is in the specified gas supply status, after detecting the first pump current Ip1, the microcomputer 9 sets the second target temperature Tj2. Corresponding internal resistance Rs (the internal resistance Rs of the first solid electrolyte body 13 when the temperature T of the sensor unit 10f becomes the second target temperature Tj2 is set as the second target internal resistance Rs2) is set. Then, the heater control circuit 31 controls energization to the heating resistor 26 so that the internal resistance Rs of the first solid electrolyte body 13 becomes the second target internal resistance Rs2. Thereby, the temperature T of the sensor unit 10f is controlled to be the second target temperature Tj2. In the second embodiment, this control is referred to as second heater control.
The second target temperature Tj2 is a temperature (950 ° C. in the second embodiment) higher than the first target temperature Tj1 (830 ° C.).

In the second embodiment, the first pump current Ip1 is detected under the first heater control.
On the other hand, the second pump current Ip2 is detected under the control of the second heater and in a state where the temperature T of the sensor unit 10f is the second target temperature Tj2.

Next, H ₂ O gas concentration detection according to the _second embodiment will be described with reference to FIG.
A program for executing each process (H ₂ O gas concentration detection process) shown in FIG. 5 is stored in the ROM 7 (see FIG. 2) of the microcomputer 9 and is executed by the CPU 6.
Each of the processes illustrated in FIG. 5 (H ₂ O gas concentration detection process), similar to Embodiment 1, the processing of Step S1~S5 shown in FIG. 3 has been performed, and continues the process shown in FIG. 3 Executed in parallel in the state.

  When the above-described detection of the oxygen concentration in the exhaust gas EG is started (the process of step S5 is executed, see FIG. 3), the microcomputer 9 determines in step U1 that the supply status of the exhaust gas EG is the specified gas supply status. Judge whether there is. A specific determination method is the same as step W1 of the first embodiment.

If it is determined that the specified gas supply status is not reached (NO), the process is terminated.
On the other hand, if it is determined that the specified gas supply status is (YES), the process proceeds to step U2, and similarly to step W2 of the first embodiment, the microcomputer 9 changes the target voltage Vj from the first target voltage Vj1 to the second. It is determined whether or not the change to the target voltage Vj2 is permitted. If it is determined that it is not permitted (NO), the process returns to step U1 to perform the above-described processing.

  If it is determined in step U2 that it is permitted (YES), the process proceeds to step U3, and the first pump current Ip1 output from the pump current detection circuit 36 is read. The read value of the first pump current Ip1 is stored in the RAM 8.

  Next, the process proceeds to step U4, and the target internal resistance Rsj of the heater control circuit 31 is changed to the second target internal resistance Rs2. That is, the heater control by the heater control circuit 31 is changed to the second heater control. Thereby, the temperature T of the first solid electrolyte body 13 and the second solid electrolyte body 11 is controlled to the second target temperature Tj2.

  Next, proceeding to step U5, the microcomputer 9 determines whether or not the temperature T of the sensor unit 10f has reached the second target temperature Tj2 (950 ° C.). Specifically, it is determined whether or not the internal resistance Rs of the first solid electrolyte body 13 has decreased to the second target internal resistance Rs2.

  In step U5, when it is determined that the temperature T of the sensor unit 10f has not reached the second target temperature Tj2 (NO), the process proceeds to step UD, and whether or not the supply status of the exhaust gas EG is the specified gas supply status. Determine whether. Specifically, if a signal indicating that “the specified gas supply status” is received continuously from the ECU 5, it is determined that the specified gas supply status is set (YES). On the other hand, if no signal indicating the “specified gas supply status” is received, it is determined that the specified gas supply status is not reached (NO).

  If it is determined that the specified gas supply status is not reached (NO), the process proceeds to step UC, where the target internal resistance Rsj of the heater control circuit 31 is changed to the first target internal resistance Rs1. Thereby, the heater control by the heater control circuit 31 is changed to the first heater control. Thereafter, the series of processing is terminated.

  On the other hand, when it is determined in step UD that the specified gas supply status is (YES), the process returns to step U5 again, and whether or not the temperature T of the sensor unit 10f has reached the second target temperature Tj2 (950 ° C.). Judging. In this way, the process waits for the temperature T of the sensor unit 10f to reach the second target temperature Tj2.

  If it is determined in step U5 that the temperature T has reached the second target temperature Tj2 (YES), the process proceeds to step U6, and the target voltage Vj of the comparison PID circuit 35 is set in the same manner as in step W4 of the first embodiment. The first target voltage Vj1 is changed to the second target voltage Vj2 (1000 mV).

  Next, the process proceeds to Step U7, and it is determined whether or not a specified time has elapsed since the target voltage Vj was changed to the second target voltage Vj2 as in Step W5 of the first embodiment. If it is determined that the specified time has not elapsed (NO), the process proceeds to step UE, and it is determined whether the supply status of the exhaust gas EG is the specified gas supply status, as in the previous step U1. If it is determined in step UE that the specified gas supply status is not (NO), the process proceeds to step UB, the switch SW1 of the electric circuit unit 30 is switched to the first reference power supply 38 side, and the target voltage Vj is changed to the first target voltage Vj1. Return to. Next, the process proceeds to step UC, where the target internal resistance Rsj of the heater control circuit 31 is changed to the first target internal resistance Rs1, and then a series of processes is terminated. On the other hand, if it is determined in step UE that the specified gas supply status is (YES), the process returns to step U7 again to perform the above-described processing.

  If it is determined in step U7 that the specified time has elapsed (YES), the process proceeds to step U8, and the microcomputer 9 determines whether or not the temperature T of the sensor unit 10f is stable at the second target temperature Tj2. To do. Specifically, it is determined whether or not the internal resistance Rs of the first solid electrolyte body 13 detected by the electric circuit unit 30 is stable at the second target internal resistance Rs2.

  In the second embodiment, the temperature T of the sensor unit 10f remains in the variation within the temperature range of the second target temperature Tj2 ± 10 (deg), and the temperature T of the sensor unit 10f is the second target temperature. The state is stable at Tj2. This state corresponds to a state in which the internal resistance Rs of the first solid electrolyte body 13 remains within the range of the second target internal resistance Rs2 ± 10 (Ω). Therefore, in step U8, it is determined whether or not the internal resistance Rs remains in the range of the second target internal resistance Rs2 ± 10 (Ω).

  If it is determined in step U8 that the temperature T is not stable at the second target temperature Tj2 (NO), the process proceeds to step UF, and the supply status of the exhaust gas EG is the specified gas supply as in step U1. Determine whether the situation is true. If it is determined in step UF that the specified gas supply state is not reached (NO), the process proceeds to step UB, the switch SW1 of the electric circuit unit 30 is switched to the first reference power supply 38 side, and the target voltage Vj is changed to the first target voltage Vj1. Return to. Next, the process proceeds to step UC, where the target internal resistance Rsj of the heater control circuit 31 is changed to the first target internal resistance Rs1, and then a series of processes is terminated. On the other hand, if it is determined in step UF that the specified gas supply status is (YES), the process returns to step U8 again to perform the above-described processing.

If it is determined in step U8 that the temperature T is stable at the second target temperature Tj2 (YES), the process proceeds to step U9, and the microcomputer 9 outputs the second pump current Ip2 output from the pump current detection circuit 36. Is read and stored in the RAM 8.
At this time, the voltage Vs between the first electrodes 21 and 22 is stable at the second target voltage Vj2. Further, the temperature T of the sensor unit 10f is stable at the second target temperature Tj2. Accordingly, the second pump current Ip2 is detected in a state where the temperature T is the second target temperature Tj2 (950 ° C.) and the voltage Vs is the second target voltage Vj2 (1000 mV).

Next, the process proceeds to step UA, and the microcomputer 9 detects the H ₂ O gas concentration in the exhaust gas EG based on the first pump current Ip1 and the second pump current Ip2. Specifically, as in the first embodiment, the H ₂ O gas concentration in the exhaust gas EG is detected based on the difference value ΔIp (mA) obtained by subtracting the first pump current Ip1 from the second pump current Ip2.

Thereafter, the process proceeds to step UB, where the target voltage Vj is returned to the first target voltage Vj1. In step UC, the target internal resistance Rsj of the heater control circuit 31 is returned to the first target internal resistance Rs1. Thereby, the heater control by the heater control circuit 31 is returned to the first heater control. Thereby, a series of H ₂ O gas concentration detection processing is completed.

Incidentally, in the second embodiment, the second pump current Ip2 is detected in a state where the temperature T of the sensor unit 10f is set to the second target temperature Tj2 that is higher than the first target temperature Tj1.
As described above, when the second pump current Ip2 is detected, the temperature T of the sensor unit 10f is set to the second target temperature Tj2 that is higher than the first target temperature Tj1, so that the target temperature is not changed (the target temperature is the first temperature). In the case where the target temperature Tj1 remains unchanged, the voltage Vs between the first electrodes 21 and 22 is set to the same second target voltage Vj2, and the dissociation of the H ₂ O gas in the exhaust gas EG is promoted. be able to. Further, as will be described later, the detected second pump current Ip2 can be stabilized (the fluctuation range of the second pump current Ip2 accompanying the fluctuation of the voltage Vs controlled to the second target voltage Vj2 can be reduced).

  FIG. 6 shows a correlation between the voltage Vs between the first electrodes 21 and 22 and the pump current Ip. In FIG. 6, each measured value in a state where A / F is the theoretical air-fuel ratio and the temperature T of the sensor unit 10f is maintained at 830 ° C. (first target temperature Tj1) in an environment with a relative humidity of 80%. A triangle is shown, and a curve connecting them is shown by a broken line. On the other hand, in an environment where the relative humidity is 80%, A / F is the stoichiometric air-fuel ratio, and each measured value in a state where the temperature T is maintained at 950 ° C. (second target temperature Tj2) is indicated by ○, and these are connected. The curve is shown as a solid line.

  As can be seen from FIG. 6, when the voltage Vs between the first electrodes 21 and 22 is the same 1000 mV (target voltage Vj) (point A and point B in FIG. 6), the temperature T of the sensor unit 10f is 830. When the pump current Ip is detected at a temperature T of 950 ° C. (second target temperature Tj2) (point B) than when the pump current Ip is detected as ° C (first target temperature Tj1) (point A), The slope of the curve (differential coefficient, rate of change) becomes small. Accordingly, even when the voltage Vs is the same 1000 mV (second target voltage Vj2), the temperature T is set to be lower than when the pump current Ip is detected at the temperature T of 830 ° C. (first target temperature Tj1) (point A). When the pump current Ip is detected at 950 ° C. (second target temperature Tj2) (point B), the measured value of the obtained pump current Ip is more stable (the fluctuation range of the pump current Ip accompanying the fluctuation of the voltage Vs is smaller). It can be said.

Therefore, compared with the case where the second pump current Ip2 is detected in addition to the first pump current Ip1 while keeping the target temperature at 830 ° C. (first target temperature Tj1) (when the temperature T is not increased). Thus, when the second pump current Ip2 is detected by raising the target temperature to 950 ° C. (second target temperature Tj2), it can be said that the detection accuracy of the H ₂ O gas concentration in the exhaust gas EG can be improved. . Thus, according to the second embodiment, the H ₂ O gas concentration in the exhaust gas EG can be detected more appropriately.

Further, as described above, it is known that blackening is likely to occur in the second solid electrolyte body 11 when the voltage Vs between the first electrodes 21 and 22 is increased.
In contrast, in the gas sensor control device 203 of the second embodiment, the second pump current Ip2 is detected at the first target temperature Tj1 by increasing the temperature T of the sensor unit 10f (set to the second target temperature Tj2). Compared to the case, the voltage between the first electrodes 21 and 22 at which the second pump current Ip2 is stabilized can be lowered.

  Here, it demonstrates concretely using FIG. According to FIG. 6, when the target temperature is 950 ° C. and the voltage Vs = 1000 mV (point B), the slope (derivative coefficient, rate of change) of the curve is the voltage Vs when the target temperature is 830 ° C. = 1100 mV (point C), the slope (differential coefficient, rate of change) of the curve is the same. Therefore, if the target temperature Tj is set to 830 ° C. (first target temperature Tj1), the target voltage Vj is set to 1100 mV, and the detection accuracy equivalent to the detection of the second pump current Ip2 is obtained, the target temperature Tj is set to 950 ° C. In the case of (second target temperature Tj2), the target voltage Vj (second target voltage Vj2) can be reduced to 1000 mV.

That is, in the gas sensor control device 203 of the second embodiment, if the detection accuracy equivalent to the case of detecting the second pump current Ip2 with the first target temperature Tj1 is good, the temperature T of the sensor unit 10f is increased. By controlling to the temperature (second target temperature Tj2), it is possible to lower the second target voltage Vj2 of the voltage Vs compared to the case where the second pump current Ip2 is detected with the first target temperature Tj1 being maintained. Become. Thereby, the possibility of blackening occurring in the second solid electrolyte body 11 can be reduced. Even in this case, the H ₂ O gas concentration in the exhaust gas EG can be detected more appropriately.

Further, the blackening of the second solid electrolyte body 11 is less likely to occur as the temperature is higher in the temperature range equal to or higher than the activation temperature Ta.
On the other hand, in Embodiment 2, after confirming that the temperature T of the sensor unit 10f has reached the second target temperature Tj2 in Step U5, the target voltage Vj is set to the second target voltage Vj2 in Step U6. doing. Accordingly, after the temperature T of the sensor unit 10f reaches the second target temperature Tj2, the voltage Vs between the first electrodes 21 and 22 is increased toward the second target voltage Vj2. Therefore, compared with the case where the target voltage is set to the second target voltage Vj2 before the temperature T of the sensor unit 10f reaches the second target temperature Tj2, the possibility of occurrence of blackening in the second solid electrolyte body 13 is reduced. be able to.

  Further, when the temperature T of the sensor unit 10f is raised to the second target temperature Tj2 by the second heater control after step U4, hunting (overshoot) occurs, and the temperature T of the sensor unit 10f is the second temperature T. There may be a case where time is required until the target temperature Tj2 is stably controlled. Accordingly, it may take time for the second pump current Ip2 to stabilize.

On the other hand, in the second embodiment, after confirming that the temperature T of the sensor unit 10f is stabilized at the second target temperature Tj2 in Step U8, the second pump current Ip2 is detected in Step UB. That is, even after the temperature T is increased to the second target temperature Tj2, the second pump current Ip2 is detected after the temperature T is stabilized at the second target temperature Tj2. Thus, since the H ₂ O gas concentration in the exhaust gas EG can be detected based on the stable second pump current Ip2, the detection accuracy can be further improved.

  In the second embodiment, the microcomputer 9 that performs the processes of steps U1, UD, UE, and UF corresponds to a supply status determination unit. Further, the comparison PID circuit 35, the switch SW1, the first reference power supply 38, and the microcomputer 9 that performs the processes of step S3 and step UB correspond to the first voltage setting means. Further, the comparison PID circuit 35, the switch SW1, the second reference power supply 39, and the microcomputer 9 that performs the process of step U6 correspond to the second voltage setting means. The microcomputer 9 that performs the process of step S6 corresponds to a temperature determination unit. Further, the microcomputer 9 that performs the process of step S7 corresponds to a permission unit.

The heater control circuit 31 and the microcomputer 9 that performs the processes of step S1 and step UC correspond to first heater control means. In addition, the heater control circuit 31 and the microcomputer 9 that performs the process of step U4 correspond to second heater control means. Further, the pump current detection circuit 36 and the microcomputer 9 that performs the process of step U3 correspond to the first current detection means. The pump current detection circuit 36 and the microcomputer 9 that performs the process of step U9 correspond to the second current detection means. Further, the microcomputer 9 that performs the process of step UA corresponds to the H ₂ O gas concentration detecting means.

In the above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to the above-described first and second embodiments, and can be appropriately modified and applied without departing from the gist thereof. Needless to say, it can be done.
For example, in the first and second embodiments, the gas sensor control device 3 is provided between the sensor 1 and the ECU 5, and the gas sensor units 4 and 204 are configured by the sensor 1 and the gas sensor control devices 3 and 203. However, the arrangement of the gas sensor control devices 3 and 203 can be changed as appropriate. For example, the gas sensor control devices 3 and 203 may be incorporated in the ECU 5 and the sensor 1 and the ECU 5 may constitute a gas sensor unit.

  In the first and second embodiments, the specified temperature Td is set to the center temperature (ie, 725 ° C.) in the temperature range from the activation temperature Ta (620 ° C.) to the first target temperature Tj1 (830 ° C.). . However, the specified temperature Td is not limited to this temperature, and may be any value within a range that is higher than the activation temperature and lower than or equal to the first target temperature, and preferably within a temperature range from the activation temperature to the first target temperature. Of these, the temperature is above the center temperature.

  Moreover, in Embodiment 1, 2, the gas sensor (sensor 1) with which an exhaust pipe is mounted | worn was illustrated as a gas sensor. However, the present invention is also applied to, for example, a gas sensor that is mounted on an intake pipe of an engine including an EGR device and detects the concentration of a specific gas (for example, oxygen) in the intake gas, and a gas sensor control device that controls the gas sensor. can do.

1 Full-range air-fuel ratio sensor (gas sensor)
3,203 Gas sensor control device 4,204 Gas sensor unit 5 ECU
9 Microcomputer (supply status judgment means, temperature judgment means, voltage setting means, heater control means, permission means, H ₂ O gas concentration detection means)
DESCRIPTION OF SYMBOLS 10 Sensor element 10b Detection cell 10c Pump cell 10d Heater 10f Sensor part 11 2nd solid electrolyte body 13 1st solid electrolyte body 19,20 2nd electrode 21,22 1st electrode 23 Measurement chamber 26 Heating resistor 30 Electric circuit part 31 Heater Control circuit (heater control means)
32 Pump current control circuit (current control means)
33 Voltage detection circuit (current control means)
35 Comparison PID circuit (current control means)
36 Pump current detection circuit (first current detection means, second current detection means)
37 Internal resistance detection circuit 100, 200 Internal combustion engine EG Exhaust gas (measured gas)
Ip Pump current Ip1 First pump current Ip2 Second pump current Vs Voltage between first electrodes Ta Activation temperature Td Specified temperature Vj Target voltage Vj1 First target voltage Vj2 Second target voltage

Claims (5)

A first solid electrolyte body and a pair of first electrodes formed on the first solid electrolyte body, and one electrode of the pair of first electrodes is in a measurement chamber into which a gas to be measured is introduced. A sensing cell disposed and the other electrode 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, wherein one electrode of the pair of second electrodes is disposed in the measurement chamber; A pump cell that pumps or pumps oxygen contained in the measurement gas introduced into the measurement chamber in response to a pump current flowing between a pair of second electrodes, and a sensor unit; and
A gas sensor control device for controlling a gas sensor comprising a heater for heating the sensor unit,
Current control means for controlling a pump current flowing between the pair of second electrodes so that a voltage between the pair of first electrodes becomes a target voltage;
A supply status determination means for determining whether the supply status of the gas to be measured is a specified gas supply status in which the oxygen concentration in the gas to be measured is continuously a predetermined specified value;
Heater control means for controlling the heater,
Heater control means including first heater control means for controlling the heater so that the temperature of the sensor part becomes a first target temperature higher than an activation temperature at which the sensor part is activated;
Voltage setting means for setting the target voltage,
First voltage setting means for setting to a first target voltage at which H ₂ O gas in the measurement gas does not substantially dissociate;
When the gas to be measured is determined to be in the specified gas supply status by the supply status judging means, the target voltage is set higher than the first target voltage, and the H ₂ O gas in the gas to be measured is dissociated. Voltage setting means including second voltage setting means for setting to a second target voltage
Temperature determining means for determining whether the temperature of the sensor unit has reached a specified temperature higher than the activation temperature and lower than the first target temperature;
Permission means for allowing the voltage setting means to set the target voltage to the second target voltage when the temperature determination means determines that the temperature of the sensor unit has reached the specified temperature;
The first pump current flowing between the pair of second electrodes when the supply state of the gas to be measured is the specified gas supply state and the voltage between the pair of first electrodes is the first target voltage. First current detecting means for detecting
The second pump current that flows between the pair of second electrodes in a state where the supply state of the gas to be measured is the specified gas supply state and the voltage between the pair of first electrodes becomes the second target voltage. Second current detecting means for detecting
Based on the first pumping current and said second pumping current, the H ₂ O gas concentration detection means for detecting H ₂ O gas concentration in the measurement gas, the gas sensor control device comprising a. The gas sensor control device according to claim 1,
The gas sensor control device in which the specified temperature is set to a temperature equal to or higher than a central temperature in a temperature range from the activation temperature to the first target temperature. The gas sensor control device according to claim 1 or 2,
The heater control means includes
The heater is set so that the temperature of the sensor unit is a second target temperature higher than the first target temperature after the first pump current is detected by the first current detection unit in the specified gas supply state. Second heater control means for controlling
The second current detection means includes
Gas sensor control for detecting the second pump current flowing between the pair of second electrodes in a state where the temperature of the sensor unit reaches the second target temperature under the control of the heater by the second heater control means. apparatus. The gas sensor control device according to claim 3,
The second voltage setting means includes
A gas sensor control device that sets the target voltage to the second target voltage after the temperature of the sensor unit reaches the second target temperature by controlling the heater by the second heater control means. The gas sensor control device according to claim 3 or 4, wherein
The second current detection means includes
A gas sensor control device that detects the second pump current in a state where the temperature of the sensor section is stabilized at the second target temperature by the control of the heater by the second heater control means.

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