JP6379000B2 - Gas sensor system - Google Patents

Description

  The present invention relates to a gas sensor system including a gas sensor having an oxygen pump cell and an oxygen concentration detection cell, and a sensor control unit that controls the gas sensor.

  Conventionally, gas sensors such as an all-region air-fuel ratio sensor having two cells, an oxygen pump cell and an oxygen concentration detection cell, and a NOx sensor having three cells in which a cell for detecting NOx gas concentration is added to the above two cells, are available. A gas sensor system is configured together with a sensor control unit that controls the gas sensor system and is mounted on a vehicle or the like.

By the way, in such a gas sensor system, when an excessive voltage is applied to the oxygen pump cell or the oxygen concentration detection cell when the gas sensor is energized, the cell blackening phenomenon due to the loss of oxygen ions from the solid electrolyte ceramic (zirconia) ( In some cases, so-called blackening) or the like occurs and the characteristics of the gas sensor deteriorate. In particular, such a phenomenon is likely to occur before the gas sensor is activated.
For this reason, conventionally, until the gas sensor is activated, the energization state for the gas sensor is set to the energization state before the predetermined activation, and after activation, the energization state is switched to measure the gas concentration. A state is performed (for example, Patent Document 1).

JP 2008-70194 A

  However, in the initial stage before the gas sensor is activated, the temperature of the gas sensor is low, and the element impedance (internal resistance) of the oxygen concentration detection cell and the oxygen pump cell is high. Therefore, a large potential difference is generated between both ends of the cell only by passing a minute current through the cell or generating charges. In particular, there is a problem that blackening is likely to occur when an oxygen pump cell continues to pass a current in a state where a large potential difference is generated between both ends of the cell.

  The present invention has been made in view of such problems, and provides a gas sensor system capable of suppressing the occurrence of blackening of an oxygen pump cell of a gas sensor before the gas sensor is activated.

One aspect thereof includes an oxygen pump cell electrically connected to the first terminal and the second terminal, a gas sensor having an oxygen concentration detection cell electrically connected to the second terminal and the third terminal, and the first terminal. A gas sensor system comprising: a sensor control unit that controls the gas sensor through the second terminal and the third terminal, wherein the sensor control unit is capable of intermittently connecting between the first terminal and the second terminal. connected to said oxygen pump cell rather smaller than the internal resistance of the oxygen pump cell in a state in which the oxygen ion conductivity is not expressed, the first having a higher resistance than the internal resistance of the oxygen pump cell in the active state of the gas sensor One circuit and the first terminal and the second terminal are connected via the first circuit within an activation waiting period until the gas sensor is activated. It includes -2 and the inter-terminal connection unit, wherein the gas sensor has a measuring chamber in which the measurement gas is introduced into said oxygen pump cell includes a first conductive to the first terminal is arranged in the measuring outdoor 1 pump electrode and a second pump electrode arranged facing the measurement chamber and conducting to the second terminal, and the sensor control unit supplies a pump current to the oxygen pump cell through the first terminal. A pump current output circuit for flowing, a pump current switch for turning on and off the pump current flowing from the pump current output circuit to the oxygen pump cell through the first terminal, and the connection terminal between the 1-2 terminals in the active waiting period the while the first terminal and a said second terminal is connected via the first circuit, the gas sensor cis Ru comprising a first shut-off means for turning off the pump current switch, the It is a non.

  In this gas sensor system, the first terminal and the second terminal are connected via the first circuit within the activation waiting period until the gas sensor is activated. During this time, the electrodes (between the first terminal and the second terminal) at both ends of the oxygen pump cell are connected via the first circuit.

The resistance value of the first circuit is smaller than the internal resistance of the oxygen pump cell in a state where oxygen ion conductivity is not expressed in the oxygen pump cell.
The internal resistance of the oxygen pump cell in a state where the cell temperature is low and oxygen ion conductivity is not expressed is, for example, a high resistance of 100 kΩ or more. Therefore, if the resistance value of the first circuit is, for example, about 1 kΩ to 10 kΩ, electric charge is generated in the oxygen pump cell when the internal resistance of the oxygen pump cell is larger than the resistance value of the first circuit during the activation waiting period. Even so, the generated charge is discharged through the first circuit. For this reason, the charge generated in the oxygen pump cell can be discharged through the first circuit during the activation waiting period.
In addition, in a state where the internal resistance of the oxygen pump cell is larger than the resistance value of the first circuit, even if a current is passed through the oxygen pump cell, most of the current flows through the first circuit, and the voltage drop generated in the oxygen pump cell is reduced.
Thereby, the voltage difference produced between the both ends of an oxygen pump cell becomes small, and generation | occurrence | production of the blackening of an oxygen pump cell can be suppressed.
On the other hand, when the internal resistance of the oxygen pump cell is equal to or smaller than the resistance value of the first circuit, the charge generated in the oxygen pump cell is discharged by the internal resistance of the oxygen pump cell and the first circuit. For this reason, the charge generated in the oxygen pump cell can be discharged through the internal resistance of the oxygen pump cell or the first circuit during the activation waiting period.
In addition, in this gas sensor system, the pump current flowing to the oxygen pump cell is interrupted while the first terminal and the second terminal are connected via the first circuit during the activation waiting period. For this reason, the voltage drop due to the pump current does not occur in the oxygen pump cell during the activation waiting period, so that the blackening of the oxygen pump cell can be more reliably suppressed.

  Furthermore, in the gas sensor system described above, the sensor control unit is connected to the second terminal and applies a predetermined reference potential, and between the 1-2 terminals in the activation waiting period. Pre-activation reference potential applying means for applying the reference potential to the second terminal by the reference potential circuit while the first terminal and the second terminal are connected via the first circuit by the connecting means; A gas sensor system comprising

  In this gas sensor system, the reference potential is applied to the second terminal while the first terminal and the second terminal are connected via the first circuit by the 1-2 terminal connecting means during the activation waiting period. Thereby, the potential of each terminal of the gas sensor can be held at a stable potential while protecting the oxygen pump cell from blackening.

  Furthermore, in any one of the gas sensor systems described above, the gas sensor includes therein a measurement chamber into which a gas to be measured is introduced and a reference oxygen chamber in which a reference oxygen atmosphere is provided, and the oxygen concentration detection cell includes A first sensing electrode disposed in the reference oxygen chamber and conducting to the third terminal; and a second sensing electrode disposed facing the measurement chamber and conducting to the second terminal; The control unit includes a constant current output circuit for supplying a constant current for pumping oxygen into the reference oxygen chamber to the oxygen concentration detection cell through the third terminal, and the oxygen concentration by the constant current output circuit during the activation waiting period. Preferably, the gas sensor system comprises a pre-activation constant current output means for supplying oxygen to the reference oxygen chamber by supplying the constant current to the detection cell.

  In this gas sensor system, since the constant current is supplied to the oxygen concentration detection cell and oxygen is supplied to the reference oxygen chamber during the activation waiting period before the gas sensor is activated, the gas concentration is quickly supplied after the gas sensor is activated. Measurement can be started.

  Furthermore, in the gas sensor system described above, the sensor control unit causes a temporary change in the constant current flowing through the oxygen concentration detection cell, and in response to the change, the first detection electrode and the first detection electrode. A change amount detecting means for detecting a response change amount of a voltage generated between the two sensing electrodes, an internal resistance detecting means for detecting an internal resistance of the oxygen concentration detection cell based on the response change amount, and the internal resistance Preferably, the gas sensor system includes an activation determination unit that determines whether or not the gas sensor is activated.

  In this gas sensor system, the internal resistance of the oxygen concentration detection cell is detected by causing a temporary change in the constant current while flowing a constant current through the oxygen concentration detection cell. Based on the detected internal resistance, it is determined whether or not the gas sensor is activated. Thereby, it can be determined appropriately whether or not the gas sensor is activated.

  Further, in the gas sensor system described above, the gas sensor has a heater unit for heating a sensor element unit including the oxygen pump cell and the oxygen concentration detection cell, and the sensor control unit is detected by the internal resistance detection unit. It is preferable that the gas sensor system includes a heater energization control unit that feedback-controls energization to the heater unit so that the internal resistance becomes a target resistance value.

  In this gas sensor system, it is possible to maintain the sensor element portion of the gas sensor at a constant element temperature by feedback control of energization to the heater portion.

It is explanatory drawing which shows the whole structure at the time of using the gas sensor system which concerns on embodiment for control of the internal combustion engine of a vehicle. It is explanatory drawing which shows schematic structure of the gas sensor system which concerns on embodiment. It is a schematic sectional drawing which shows the structure of a gas sensor among the gas sensor systems which concern on embodiment. It is a flowchart which shows the flow of the whole process of the gas sensor system which concerns on embodiment. It is a flowchart which shows the processing operation in the active waiting process of a digital signal processor among the gas sensor systems which concern on embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration when a gas sensor system 1 according to the present embodiment is used for controlling an internal combustion engine of a vehicle. FIG. 2 is a diagram showing a schematic configuration of the gas sensor system 1.
The gas sensor system 1 includes a gas sensor 2 mounted on an exhaust pipe EP of an internal combustion engine ENG (engine) of a vehicle (not shown), and a sensor control unit 40 that controls the gas sensor 2.
The gas sensor 2 is an air-fuel ratio sensor (full-range air-fuel ratio sensor) used for air-fuel ratio feedback control in an internal combustion engine by linearly detecting the oxygen concentration (air-fuel ratio) in the exhaust gas EG (measured gas). . As shown in FIG. 2, the gas sensor 2 includes a sensor element unit 3 that detects an oxygen concentration and a heater unit 80 that heats the sensor element unit 3.
The sensor control unit 40 is connected to the gas sensor 2 and controls it. The gas sensor system 1 is connected to the CAN bus 102 of the vehicle via the connection bus 101, and can transmit and receive data to and from the ECU 100. The sensor control unit 40 is configured by an ASIC (Application Specific IC), in addition to a circuit for controlling the sensor element unit 3 of the gas sensor 2, a digital signal processor 30, a heater unit control circuit 70 for controlling the heater unit 80, and the like. It has.

  First, the gas sensor 2 will be described. FIG. 3 is a schematic configuration diagram showing the configuration of the gas sensor 2. In the gas sensor 2, the sensor element unit 3 is a stacked body in which the oxygen pump cell 14, the porous layer 18, and the oxygen concentration detection cell 24 are stacked in this order. A heater unit 80 is further stacked on the sensor element unit 3.

The oxygen pump cell 14 has a plate-like electrolyte layer 14c made of a solid electrolyte body mainly composed of zirconia and having oxygen ion conductivity, and a pair of electrodes 12, 16 (porous) mainly composed of porous platinum on both surfaces thereof. Electrode). Specifically, the first pump electrode 12 is formed on the outer surface 14E which is one surface (upper in the drawing) of the electrolyte layer 14c, and the second pump electrode 16 is formed on the inner surface 14I which is the other surface (lower in the drawing). , Each is formed.
Similarly, the oxygen concentration detection cell 24 has a plate-like electrolyte layer 24c made of a solid electrolyte body mainly composed of zirconia and having oxygen ion conductivity, and a pair of electrodes mainly composed of porous platinum on both surfaces thereof. 22 and 28 (porous electrodes) are formed. Specifically, the first detection electrode 28 is formed on the outer surface 24E which is one surface (lower side in the drawing) of the electrolyte layer 24c, and the second detection electrode 22 is formed on the inner surface 24I which is the other surface (upper side in the drawing). , Each is formed.

  The inner surface 14I of the electrolyte layer 14c of the oxygen pump cell 14 faces the inner surface 24I of the electrolyte layer 24c of the oxygen concentration detection cell 24, and the porous layer 18 is sandwiched between the electrolyte layer 14c and the electrolyte layer 24c. The porous layer 18 has a porous wall portion 18c along the edge of the inner surface 14I of the electrolyte layer 14c and the inner surface 24I of the electrolyte layer 24c, and the inside of the porous layer 18 includes the porous wall portion 18c and the electrolyte. A hollow measurement chamber 20 is formed which is surrounded by the layer 14c and the electrolyte layer 24c and into which the exhaust gas EG can be introduced. The porous layer 18 allows the exhaust gas EG to flow into the measurement chamber 20 and restricts the flow rate thereof.

  In the measurement chamber 20, the second pump electrode 16 of the oxygen pump cell 14 and the second detection electrode 22 of the oxygen concentration detection cell 24 are exposed. These electrodes 16 and 22 are electrically connected to each other and connected to the COM terminal of the sensor element unit 3. The first pump electrode 12 of the oxygen pump cell 14 is connected to the Ip + terminal of the sensor element unit 3, and the first detection electrode 28 of the oxygen concentration detection cell 24 is connected to the Vs + terminal of the sensor element unit 3.

  The entire first pump electrode 12 of the oxygen pump cell 14 is covered with a protective layer 15 that suppresses poisoning of the first pump electrode 12. The protective layer 15 is made of porous ceramic or the like, and is disposed in the flow path through which the exhaust gas EG flows. The exhaust gas EG can reach the first pump electrode 12 through the protective layer 15.

  The heater unit 80 is laminated on the outer surface 24E of the electrolyte layer 24c of the oxygen concentration detection cell 24, and has a configuration in which a heater resistor 87 formed of a conductor is sandwiched between a pair of alumina sheets 83 and 85. By increasing the temperature of the sensor element unit 3 with the heater unit 80, the electrolyte layers 14c and 24c of the sensor element unit 3 are activated. Thereby, oxygen ions can move in the electrolyte layers 14c and 24c.

  In addition, the alumina sheet 83 of the heater unit 80 seals the first detection electrode 28 by covering the entire first detection electrode 28 of the oxygen concentration detection cell 24. A space (hole) inside the first detection electrode 28 (porous electrode) constitutes a reference oxygen chamber 26 and functions as an internal oxygen reference source, as will be described later.

  Next, the gas sensor system 1 will be described with reference to FIG. As described above, the sensor control unit 40 is configured by an ASIC having a built-in digital signal processor 30 (hereinafter also simply referred to as the processor 30). The sensor control unit 40 includes a first terminal T1, a second terminal T2, and a third terminal T3, and controls the sensor element unit 3 of the gas sensor 2 through these terminals. The first terminal T1 is connected to the Ip + terminal of the sensor element unit 3 via the first wiring L1. The second terminal T2 is connected to the COM terminal of the sensor element unit 3 through the second wiring L2. The third terminal T3 is connected to the Vs + terminal of the sensor element unit 3 through the third wiring L3.

In addition, the sensor control unit 40 includes A / D converters 41, 42, and 43 connected to the first terminal T1, the second terminal T2, and the third terminal T3, respectively.
The A / D converter 41 detects the first terminal potential V <b> 1 of the first terminal T <b> 1, A / D converts this, and inputs it to the processor 30. Similarly, the A / D converter 42 detects the second terminal potential V <b> 2 of the second terminal T <b> 2, A / D converts this, and inputs it to the processor 30. Further, the A / D converter 43 detects the third terminal potential V3 of the third terminal T3, performs A / D conversion on this, and inputs it to the processor 30.
The A / D converters 41, 42, and 43 are used not only for PID control of the pump current Ip, which will be described later, but also for diagnosing a short circuit abnormality or disconnection abnormality of the gas sensor 2. Further, as will be described later, it is also used when detecting the internal resistance Rpvs of the oxygen concentration detection cell 24.

Further, a first circuit 45 including a first resistor R1 and a first switch SW1 is connected between the first terminal T1 and the second terminal T2. The first resistance value R1r of the first resistor R1 is R1r = 1 kΩ, and the first switch SW1 interrupts the connection between the first terminal T1 and the second terminal T2 via the first resistor R1. . The resistance value (ON resistance) of the first switch SW1 is negligible with respect to the first resistance value R1r. In this embodiment, the resistance value R1c of the first circuit 45 = the first resistance value R1r = 1 kΩ. Then, the first circuit 45 having the resistance value R1c (= first resistance value R1r) connects the first terminal T1 and the second terminal T2 in an intermittent manner.
Further, a second circuit 46 including a second resistor R2 and a second switch SW2 is connected between the second terminal T2 and the third terminal T3. The second resistance value R2r of the second resistor R2 is R2r = 1 kΩ, and the second switch SW2 disconnects the connection through the second resistor R2 between the second terminal T2 and the third terminal T3. . Note that the resistance value (ON resistance) of the second switch SW2 is negligible with respect to the second resistance value R2r. Like the first circuit 45, in this embodiment, the resistance value of the second circuit 46 is set. R2c = second resistance value R2r = 1 kΩ.
The first circuit 45 and the second circuit 46 are circuits used for diagnosing a short circuit abnormality of the gas sensor 2, and turn on the first switch SW1 and the second switch SW2 when diagnosing the short circuit abnormality of the gas sensor 2. . On the other hand, as described later, in the activation waiting process of the gas sensor 2, the first switch SW1 is turned on, but the second switch SW2 is turned off, and the second circuit 46 is not used. Further, when diagnosing disconnection abnormality of the gas sensor 2 or during normal use of the gas sensor 2, both the first switch SW1 and the second switch SW2 are turned off, and the first circuit 45 and the second circuit 46 are not used. Note that the description of the short-circuit abnormality and the disconnection abnormality performed using the first circuit 45 and the second circuit 46 is omitted.

An output of a D / A converter (hereinafter referred to as “current DAC”) 47 that supplies a pump current Ip to the oxygen pump cell 14 in accordance with an instruction from the processor 30 is connected to the first terminal T1 via the third switch SW3. Yes. The third switch SW3 turns on and off the pump current Ip that flows from the current DAC 47 to the oxygen pump cell 14 through the first terminal T1.
Furthermore, the output of the operational amplifier 44 as a reference potential circuit that outputs a reference potential Vref of +2.5 V is connected to the second terminal T2 via the fourth switch SW4. The fourth switch SW4 turns on / off the application of the reference potential Vref from the operational amplifier 44 to the second terminal T2.
In addition, the third terminal T3 detects a constant minute current Icp (= 20 μA) and an internal resistance Rpvs described later in the oxygen concentration detection cell 24 according to an instruction from the processor 30 via the fifth switch SW5. The output of the D / A converter (current DAC) 48 that flows the internal resistance detection current Irpvs is connected. The fifth switch SW5 turns on and off the minute current Icp that flows from the current DAC 48 to the oxygen concentration detection cell 24 through the third terminal T3.
During normal use of the gas sensor 2, the third switch SW3 to the fifth switch SW5 are turned on. However, after the initial setting or when a short circuit abnormality or disconnection abnormality of the gas sensor 2 is detected, the third switch SW3. -Turn off the fifth switch SW5.

Further, the minute current Icp that flows to the oxygen concentration detection cell 24 acts to pump the oxygen in the measurement chamber 20 into the first detection electrode 28 (porous electrode) with respect to the oxygen concentration detection cell 24. Thereby, the reference oxygen chamber 26 functions as an internal oxygen reference source.
Further, the processor 30 supplies such a constant minute current Icp to the oxygen concentration detection cell 24 and detects the detection cell voltage Vs generated at both ends of the oxygen concentration detection cell 24 (a third terminal detected by the A / D converter 43). A so-called digital PID control is performed to control the pump current Ip flowing through the oxygen pump cell 14 so that the difference between the potential V3 and the second terminal potential V2 detected by the A / D converter 42 becomes a predetermined voltage. Thereby, oxygen in the exhaust gas EG introduced into the measurement chamber 20 through the porous layer 18 is pumped and pumped out.

  Then, the current value and direction of the pump current Ip flowing through the oxygen pump cell 14 controlled by the PID control of the processor 30 is determined by the oxygen concentration (empty air) in the exhaust gas EG introduced into the measurement chamber 20 through the porous layer 18. It changes according to the fuel ratio. Thus, the oxygen concentration in the exhaust gas EG can be detected based on the pump current Ip. That is, the sensor control unit 40 controls the driving of the gas sensor 2 by feedback controlling the pump current Ip flowing through the oxygen pump cell 14 so that the detection cell voltage Vs generated in the oxygen concentration detection cell 24 becomes a predetermined voltage. Do.

The sensor control unit 40 includes a fourth terminal T4 and a fifth terminal T5 connected to the heater unit control circuit 70. The fourth terminal T4 and the fifth terminal T5 are the fourth wiring L4 and the fifth wiring. It is connected to the heater part 80 of the gas sensor 2 via L5. Further, the heater unit control circuit 70 is connected to the processor 30, and on / off of energization to the heater unit 80 is PWM-controlled by an instruction from the processor 30. Further, in energization control to the heater unit 80, an internal resistance (an internal resistance Rpvs based on a response change amount ΔVs described later) of the oxygen concentration detection cell 24 is detected, and feedback is performed so that the internal resistance becomes a target resistance value. Control is performed.
Here, the details of the digital PID control of the pump current Ip by the processor 30 and the PWM control of the heater unit 80 are omitted.

  In the gas sensor system 1, before the gas sensor 2 is heated by the heater unit 80, a short circuit abnormality of the gas sensor 2 is diagnosed. And when there is no short circuit abnormality, electricity supply to the heater part 80 is started, the gas sensor 2 is heated up, and the disconnection abnormality of the gas sensor 2 is diagnosed in the stage of the activation of the gas sensor 2. Furthermore, when there is no disconnection abnormality, the process of waiting for activation is performed until the gas sensor 2 is activated.

In this active waiting process, the third switch SW3 is turned off, the PID control of the pump current Ip is not yet performed, and the pump current Ip is not supplied to the oxygen pump cell 14. On the other hand, a constant minute current Icp is supplied to the oxygen concentration detection cell 24 to supply oxygen to the reference oxygen chamber 26.
Further, the internal resistance of the oxygen concentration detection cell 24 is detected by causing a temporary change in the minute current Icp every time a predetermined timing elapses, and this is used to control feedback of energization to the heater unit 80. I do.

FIG. 4 is a flowchart showing the overall processing flow of the gas sensor system 1. As shown in FIG. 4, in the gas sensor system 1, when the system 1 is activated, first, a diagnosis of a short circuit abnormality (step SA) is performed. Next, a disconnection abnormality diagnosis (step SB) is performed, and an activation waiting process (step SC) is performed. After activation, the process proceeds to an oxygen concentration detection process (step SD). In the diagnosis of disconnection abnormality (step SB), energization of the heater unit 80, that is, heating of the sensor element unit 3 (the oxygen pump cell 14 and the oxygen concentration detection cell 24) of the gas sensor 2 is started midway.
In this specification, the details of the diagnosis of the short circuit abnormality and the disconnection abnormality of the gas sensor 2 (step SA and step SB in FIG. 4) are omitted, and the process of waiting for the activation of the gas sensor 2 by the sensor control unit 40 (in FIG. 4). Step SC) will be described with reference to the flowchart showing the processing operation of the processor 30 in FIG. 5 in addition to FIG.

In the diagnosis of disconnection abnormality (step SB in FIG. 4), when there is no disconnection abnormality, the activation waiting process (step SC in FIG. 4) is started, and the process proceeds to step S1 (see FIG. 5).
In step S1, the second switch SW2 and the third switch SW3 are turned off, while the first switch SW1, the fourth switch SW4, and the fifth switch SW5 are turned on. Note that the reference potential Vref (= + 2.5 V) is applied from the operational amplifier 44 to the second terminal T2 by turning on the fourth switch SW4. Also, by turning on the fifth switch SW5, the output of the current DAC 48 is input to the third terminal T3.

In addition, by turning on the first switch SW1, the first circuit 45 (the first resistor) is connected between the first terminal T1 and the second terminal T2, and therefore between the electrodes 12 and 16 at both ends of the oxygen pump cell 14. Connected via the device R1).
The resistance value R1c (= first resistance value R1r) of the first circuit 45 is 1 kΩ, and this value is the internal resistance of the oxygen pump cell 14 in a state where the oxygen ion conductivity is not expressed in the oxygen pump cell 14 ( Less than 100 kΩ). The resistance value R1c (= first resistance value R1r = 1 kΩ) of the first circuit 45 is also larger than the internal resistance (450Ω or less) of the oxygen pump cell 14 in the active state of the gas sensor 2.

Next, in step S2, a constant minute current Icp (= 20 μA) is supplied from the current DAC 48 to the oxygen concentration detection cell 24 through the third terminal T3.
In the subsequent step S3, feedback control (also referred to as Rpvs control) of energization to the heater unit 80 using the internal resistance of the oxygen concentration detection cell 24 is started. Specifically, a heater energization control routine (not shown) is separately executed, and energization to the heater unit 80 is feedback-controlled so that an internal resistance Rpvs described below becomes a target resistance value. As described above, in the diagnosis of disconnection abnormality (step SB in FIG. 4), heating of the sensor element unit 3 of the gas sensor 2 by energization of the heater unit 80 has already started. For this reason, during the diagnosis of the disconnection abnormality, the oxygen pump cell 14 and the oxygen concentration detection cell 24 exhibit oxygen ion conductivity, and the internal resistances of the oxygen pump cell 14 and the oxygen concentration detection cell 24 are reduced to 100 kΩ or less, respectively. doing.
Further, in the subsequent step S4, a timer for measuring time is started.

  Next, in step S5, it is determined whether or not the current timing is an internal resistance detection timing. If it is the internal resistance detection timing (Yes), the process proceeds to step S6, and if it is not the internal resistance detection timing (No), the process skips steps S6 and S7 and proceeds to step S8.

  In step S6, the minute current Icp flowing in the oxygen concentration detection cell 24 is temporarily changed to the internal resistance detection current Irpvs, and in response to this change, the first detection electrode 28 and the first detection electrode 28 of the oxygen concentration detection cell 24 are changed. The voltage response change amount ΔVs (change amount of the detection cell voltage Vs) generated between the two detection electrodes 22 is detected. In step S7, the internal resistance Rpvs of the oxygen concentration detection cell 24 is detected (calculated) based on the response change amount ΔVs.

  Next, the process proceeds to step S8, and whether the detected internal resistance Rpvs is smaller than a reference resistance value Rref (= 450Ω) that is a reference as to whether or not the gas sensor 2 (oxygen pump cell 14 and oxygen concentration detection cell 24) is activated. Determine whether or not. That is, in step S8, it is determined whether the gas sensor 2 has been activated based on the internal resistance Rpvs. When the internal resistance Rpvs becomes smaller than the reference resistance value Rref (= 450Ω) (Yes), it is determined that the gas sensor 2 is activated, and the process proceeds to step S10. On the other hand, in other cases (No), it is determined that the gas sensor 2 has not been activated yet, and the process proceeds to step S9.

  In step S9, feedback control (Rpvs control) of energization to the heater unit 80 is started in step S3, and it is determined whether or not a predetermined time TM (= 30 seconds) has elapsed since the timer was started in step S4. To do. If the predetermined time TM has not elapsed (No), the process returns to step S5, and steps S5 to S9 are repeated.

It is considered that the internal resistance of the oxygen pump cell 14 changes at substantially the same value as the internal resistance Rpvs of the oxygen concentration detection cell 24. On the other hand, the first resistance value R1r (= 1 kΩ) of the first resistor R1 is selected to be larger than the reference resistance value Rref (= 450Ω).
Even if the predetermined time TM has elapsed, if it is not Yes in step S8, it is Yes in step S9 and proceeds to step S11.

In step S11, all of the first switch SW1 to the fifth switch SW5 are turned off. Next, the process proceeds to step S12, and the feedback control (Rpvs control) of energization to the heater unit 80 is stopped and the energization to the heater unit 80 is turned off.
Furthermore, it progresses to step S13, determines with the active defect of the gas sensor 2, and reports abnormal content (determination result of active defect) to ECU100. Thereafter, the process does not proceed to the activated oxygen concentration detection process (step SD in FIG. 4), and the process of the processor 30 is terminated (system end).

On the other hand, if Yes in step S8, that is, if the gas sensor 2 is activated, the first switch SW1 is turned off and the third switch SW3 is turned on in step S10. Thereby, the first resistor R1 connected between the first terminal T1 and the second terminal T2 is disconnected. Also, by turning on the third switch SW3, the pump current Ip flows from the current DAC 47 to the oxygen pump cell 14 through the first terminal T1.
Thereafter, the process proceeds to an oxygen concentration detection process (step SD in FIG. 4), which is a process after activation.

  In the present embodiment, in the sensor control unit 40, the operational amplifier 44 corresponds to a reference potential circuit, and the fourth switch SW4 corresponds to a reference potential switch. The current DAC 47 corresponds to a pump current output circuit, and the third switch SW3 corresponds to a pump current switch. In addition, a constant minute current Icp flowing through the oxygen concentration detection cell 24 corresponds to a constant current, and a current DAC 48 corresponds to a constant current output circuit.

In addition, in the present embodiment, the processor 30 executing step S1 corresponds to the 1-2 terminal connecting means, the pre-activation reference potential applying means, and the first cutoff means.
The processor 30 executing step S2 corresponds to a pre-activation constant current output unit.
Further, the processor 30 executing step S6 corresponds to the change amount detecting means, and the processor 30 executing step S7 corresponds to the internal resistance detecting means. Further, the processor 30 executing step S8 corresponds to activation determination means.
Further, the heater unit control circuit 70 of the sensor control unit 40 and the processor 30 executing step S3 and a heater energization control routine (not shown) correspond to heater energization control means.

  As described above, in the gas sensor system 1 of the present embodiment, in the diagnosis of the disconnection abnormality, after the oxygen ion conductivity is developed in the oxygen pump cell 14 and the oxygen concentration detection cell 24, the activation wait period until the gas sensor 2 is activated. In the activation waiting process, the first terminal T1 and the second terminal T2 are connected via the first circuit 45 (first resistor R1). During this time, the electrodes 12 and 16 at both ends of the oxygen pump cell 14 (between the first terminal T1 and the second terminal T2) are connected via the first circuit 45 (first resistor R1).

The resistance value R1c (= first resistance value R1r = 1 kΩ) of the first circuit 45 is a value smaller than the internal resistance (100 kΩ or more) of the oxygen pump cell 14 in a state where the oxygen ion conductivity is not expressed in the oxygen pump cell 14. is there. The resistance value R1c (= first resistance value R1r = 1 kΩ) of the first circuit 45 is also larger than the internal resistance (450Ω or less) of the oxygen pump cell 14 in the active state of the gas sensor 2.
As a result, even if electric charge is generated in the oxygen pump cell 14 in the state where the internal resistance of the oxygen pump cell 14 is larger than the resistance value R1c (= first resistance value R1r) of the first circuit 45 during the activation waiting period, The generated electric charge is discharged mainly through the first circuit 45 (first resistor R1). On the other hand, when the internal resistance of the oxygen pump cell 14 is equal to or smaller than the resistance value R1c (= first resistance value R1r) of the first circuit 45, the charge generated in the oxygen pump cell 14 is reduced to the internal resistance of the oxygen pump cell 14. It is discharged by the first circuit 45 (first resistor R1). For this reason, the charge generated in the oxygen pump cell 14 can be discharged via the internal resistance of the oxygen pump cell 14 or the first circuit 45 (first resistor R1) during the activation waiting period.
Further, in a state where the internal resistance of the oxygen pump cell 14 is larger than the resistance value R1c (= first resistance value R1r) of the first circuit 45, many of the first circuit 45 ( The voltage drop generated in the oxygen pump cell 14 through the first resistor R1) is also reduced.
Thereby, the potential difference generated between both ends of the oxygen pump cell 14 is reduced, and the blackening of the oxygen pump cell 14 can be suppressed.

  Further, in the gas sensor system 1 of the present embodiment, during the activation waiting period, the first switch SW1 is turned on by the 1-2 terminal connecting means (step S1), and the first terminal T1 and the second terminal T2 are connected to the first terminal T1. While being connected through the one circuit 45 (first resistor R1), the reference potential Vref is applied to the second terminal T2. Thereby, the potential of each terminal of the gas sensor 2 can be held at a stable potential while protecting the oxygen pump cell 14 from blackening.

  Further, in the gas sensor system 1 of the present embodiment, during the activation waiting period (activation waiting process), the first switch SW1 is turned on to connect the first terminal T1 and the second terminal T2 to the first circuit 45 (first resistor). The third switch SW3 is turned off and the pump current Ip flowing to the oxygen pump cell 14 is shut off while being connected via the device R1) (until the result of step S1 to step S9 becomes Yes). For this reason, since the voltage drop due to the pump current does not occur in the oxygen pump cell during the activation waiting period, the blackening of the oxygen pump cell 14 can be more reliably suppressed.

  Further, in the gas sensor system 1 of the present embodiment, during the activation waiting period before the gas sensor 2 is activated (from the start of the activation waiting process (step S2) to the end (step S10)), a small current is supplied to the oxygen concentration detection cell 24. Since oxygen is supplied to the reference oxygen chamber 26 by flowing Icp (constant current), measurement of the gas concentration can be started immediately after the gas sensor 2 is activated.

  Furthermore, in the gas sensor system 1 of the present embodiment, the microcurrent Icp (constant current) is allowed to flow through the oxygen concentration detection cell 24, and a temporary change is caused in the microcurrent Icp, so that the inside of the oxygen concentration detection cell 24 is increased. The resistance Rpvs is detected. Based on the detected internal resistance Rpvs, it is determined whether or not the gas sensor 2 is activated. Thereby, it can be determined appropriately whether or not the gas sensor 2 is activated.

  Furthermore, in the gas sensor system 1 of the present embodiment, the sensor element unit 3 of the gas sensor 2 can be maintained at a constant element temperature by performing feedback control of energization to the heater unit 80.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, an air-fuel ratio sensor (entire region air-fuel ratio sensor) that detects the oxygen concentration (air-fuel ratio) in the exhaust gas EG is used as the gas sensor 2, but the “gas sensor” is not limited to the air-fuel ratio sensor. Alternatively, a NOx sensor that detects the concentration of nitrogen oxide (NOx) may be used.
Further, the sensor control unit 40 may be provided in a form built in the ECU 100.

Further, in the embodiment, the gas sensor system 1 in which the sensor control unit 40 is configured by an ASIC including the digital signal processor 30 and performs PID control of the pump current Ip by a digital method is shown.
However, the present invention may be applied to a gas sensor system that includes a sensor control unit configured by an ASIC including an analog PID circuit and a separately provided microprocessor and performs PID control in an analog manner.

Further, in the embodiment, a temporary change is generated in the minute current Icp (constant current) flowing through the oxygen concentration detection cell 24 to detect the response change amount ΔVs, and the oxygen concentration detection is performed based on the response change amount ΔVs. The gas sensor system 1 that detects the internal resistance Rpvs of the cell 24 is shown. However, the present invention may be applied to a system that detects the internal resistance of the oxygen concentration detection cell 24 by other methods.
Further, the determination of whether or not the gas sensor 2 is activated is not limited to the one using the internal resistance Rpvs of the oxygen concentration detection cell 24 as in the embodiment, but the internal resistance of the oxygen pump cell 14 or the heater unit 80. The determination may be made by comparing the heater resistance with a reference value for determining the activation, or based on the accumulated energization time of the heater unit 80.

ENG Internal combustion engine
EP Exhaust pipe EG Exhaust gas (measured gas)
100 ECU
DESCRIPTION OF SYMBOLS 1 Gas sensor system 2 Gas sensor 3 Sensor element part 14 Oxygen pump cell 12 1st pump electrode 16 2nd pump electrode 24 Oxygen concentration detection cell 28 1st detection electrode 22 2nd detection electrode 20 Measurement chamber 26 Reference | standard oxygen chamber 80 Heater part Ip Pump current Icp micro current (constant current)
Irpvs internal resistance detection current T1 first terminal T2 second terminal T3 third terminal L1 first wiring L2 second wiring L3 third wiring V1 first terminal potential V2 second terminal potential V3 third terminal potential Vref reference potential Vex inspection potential 30 Digital Signal Processor 40 Sensor Control Unit 41 A / D Converter 42 A / D Converter 43 A / D Converter 44 Operational Amplifier (Reference Potential Circuit)
45 1st circuit R1 1st resistor R1r 1st resistance value R1c 1st circuit resistance value SW1 1st switch 46 2nd circuit R2 2nd resistor R2r 2nd resistance value R2c 2nd circuit resistance value SW2 2nd switch 47 D / A converter (pump current output circuit)
48 D / A converter (constant current output circuit)
SW3 3rd switch (pump current switch)
SW4 Fourth switch SW5 Fifth switch 70 Heater control circuit (heater energization control means)
S1 1-2 terminal connection means, pre-activation reference potential application means, first cutoff means S2 pre-activation constant current output means S3 heater energization control means S6 change amount detection means S7 internal resistance detection means S8 activation discrimination means

Claims (2)

A gas sensor having an oxygen pump cell electrically connected to the first terminal and the second terminal, and an oxygen concentration detection cell electrically connected to the second terminal and the third terminal;
A gas sensor system comprising: a sensor control unit that controls the gas sensor through the first terminal, the second terminal, and the third terminal;
The sensor control unit
An intermittent connection between the first terminal and the second terminal,
The oxygen pump cell rather smaller than the internal resistance of the oxygen pump cell in a state in which the oxygen ion conductivity is not expressed in a first circuit having a larger resistance value than the internal resistance of the oxygen pump cell in the active state of the gas sensor,
A terminal-to-terminal connecting means for connecting the first terminal and the second terminal via the first circuit within an activation waiting period until the gas sensor is activated ,
The gas sensor
Has a measurement chamber into which the gas to be measured is introduced,
The oxygen pump cell is
A first pump electrode arranged outside the measurement chamber and conducting to the first terminal; and a second pump electrode arranged facing the measurement chamber and conducting to the second terminal;
The sensor control unit
A pump current output circuit for passing a pump current to the oxygen pump cell through the first terminal;
A pump current switch for turning on and off the pump current flowing from the pump current output circuit to the oxygen pump cell through the first terminal;
During the activation waiting period, the pump current switch is turned off while the first terminal and the second terminal are connected via the first circuit by the 1-2 terminal connecting means. gas sensor system Ru and a blocking means. The gas sensor system according to claim 1,
The sensor control unit
A reference potential circuit connected to the second terminal and applying a predetermined reference potential;
During the activation waiting period, while the first terminal and the second terminal are connected via the first circuit by the 1-2 terminal connecting means, the reference potential circuit connects the second terminal to the second terminal. A gas sensor system comprising: a pre-activation reference potential applying means for applying the reference potential.

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