JP2017090129A - Control device, and control method, for air-fuel ratio sensors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device and a control method for detecting abnormal connection of a gas sensor element and a control device.SOLUTION: A control device for air-fuel ratio sensor 3 is equipped with a mode control unit 19, an abnormality detecting unit 21 and a current detecting unit 14. The mode control unit sets an operation mode matching the activated state of a gas sensor element 2 on the basis of the state of admittance of a detecting cell 5. The abnormality detecting unit detects any abnormal connection to the gas sensor element and, if the mode control unit has altered the operation mode, resets the state of abnormality determination processing by processing abnormality determination. The current detecting unit detects any current flowing between it and the gas sensor element. The mode control unit limits alteration of the operation mode based on the state of admittance on the basis of the current detected by the current detecting unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device and a control method for an air-fuel ratio sensor.

  For the purpose of improving the fuel efficiency of a vehicle, feedback control for bringing the air-fuel ratio, which is the ratio of air and fuel in exhaust gas discharged from an internal combustion engine, close to the target air-fuel ratio is widely known. It is detected by a sensor (A / F sensor).

  As an air-fuel ratio sensor, an air-fuel ratio sensor including a gas sensor element having a pump cell and a detection cell and a control device for controlling the gas sensor element is known. In such an air-fuel ratio sensor, for example, if an abnormality occurs in which the connection between the gas sensor element and the control device is opened, it becomes difficult to accurately detect the air-fuel ratio. Therefore, a technique for detecting that an abnormality has occurred in the connection between the gas sensor element and the control device based on the fluctuation state of the terminal voltage of the control device has been proposed (see, for example, Patent Document 1).

JP 2006-258800 A

  In the air-fuel ratio sensor, for example, the activation state of the gas sensor element is detected based on the admittance state of the detection cell. Based on the activated state of the gas sensor element, the operation mode when the gas sensor element is in an inactive state and the operation mode when the gas sensor element is in an activated state are switched.

  However, for example, if an abnormality occurs in which the connection between the gas sensor element and the control device is released, the admittance of the detection cell may not be detected normally, and the operation mode may be frequently changed. And when it is the structure which resets the state of an abnormality determination process when an operation mode is changed, if an operation mode is changed frequently as mentioned above, reset of the state of an abnormality determination process will be repeated, and a gas sensor element In some cases, it is difficult to accurately detect an abnormal connection between the control device and the control device.

  The present invention has been made in view of the above, and an object of the present invention is to provide a control device and a control method for an air-fuel ratio sensor that can accurately detect an abnormal connection between a gas sensor element and a control device.

  In order to solve the above problems and achieve the object, the present invention comprises a detection cell that generates a voltage according to the oxygen concentration in the gas detection chamber, and a pump cell that pumps oxygen into and out of the gas detection chamber. An air-fuel ratio sensor control device including a gas sensor element having a terminal, an admittance detection unit, a mode control unit, an abnormality detection unit, and a current detection unit. The terminal is connected to one end of the pump cell and one end of the detection cell. The admittance detection unit detects an admittance state of the detection cell. The mode control unit sets an operation mode according to an activation state of the gas sensor element based on an admittance state of the detection cell detected by the admittance detection unit. The abnormality detection unit executes an abnormality determination process for determining an abnormality in connection with the gas sensor element to detect the connection abnormality, and the abnormality determination process is performed when the mode control unit changes the operation mode. Reset the state. The current detection unit detects a current flowing between the terminal and the gas sensor element. The mode control unit limits the change of the operation mode based on the admittance state based on the current detected by the current detection unit.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus and control method of an air fuel ratio sensor which can detect the connection abnormality of a gas sensor element and a control apparatus accurately can be provided.

FIG. 1 is a diagram illustrating an example of a configuration of an air-fuel ratio sensor according to an embodiment of the present invention. FIG. 2 is a diagram showing a specific configuration example of the air-fuel ratio sensor shown in FIG. FIG. 3 is a diagram showing a specific configuration example of the gas sensor element shown in FIG. FIG. 4 is a diagram illustrating another configuration example of the measurement current supply unit. FIG. 5 is a diagram illustrating a configuration example of the abnormality detection unit. FIG. 6 is a diagram (part 1) illustrating an example of a state change of a COM current, a VS voltage, an operation mode, and a counter value. FIG. 7 is a diagram (part 2) illustrating an example of the state change of the COM current, the VS voltage, the operation mode, and the counter value. FIG. 8 is a diagram (part 1) illustrating an example of a state change of a COM current, a VS voltage, a voltage between terminals, an operation mode, and a counter value. FIG. 9 is a diagram (part 2) illustrating an example of a state change of a COM current, a VS voltage, a voltage between terminals, an operation mode, and a counter value. FIG. 10 is a flowchart showing a main processing procedure executed by the mode control unit.

  Embodiments of an air-fuel ratio sensor (A / F sensor) control device and control method according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

[1. Configuration of air-fuel ratio sensor]
FIG. 1 is a diagram illustrating an example of a configuration of an air-fuel ratio sensor according to an embodiment of the present invention. As shown in FIG. 1, the air-fuel ratio sensor 1 includes a gas sensor element 2 and a control device 3.

  A gas sensor element 2 shown in FIG. 1 has a pump cell 4 that pumps oxygen into and out of a gas detection chamber, and a detection cell 5 that generates a voltage corresponding to the oxygen concentration in a gas detection chamber (not shown). For example, the gas sensor element 2 is disposed in an exhaust pipe of an internal combustion engine of a vehicle (not shown) and detects an oxygen concentration (air heat ratio) in the exhaust gas.

  The control device 3 includes an IP terminal Tip, a COM terminal Tcom, a VS terminal Tvs, a voltage control unit 10, a terminal voltage detection unit 11, a feedback control unit 12, a current supply unit 13, and a current detection unit 14. The air-fuel ratio calculation unit 15, the measurement current supply unit 16, the admittance detection unit 17, the mode control unit 19, and the abnormality detection unit 21 are provided.

  The voltage control unit 10 controls the voltage Vcom (hereinafter referred to as the COM voltage Vcom) of the COM terminal Tcom to which one end of the detection cell 5 and one end of the pump cell 4 are connected to be a constant voltage. The terminal voltage detector 11 detects a voltage Vs (hereinafter referred to as VS voltage Vs) of the VS terminal Tvs.

  The feedback control unit 12 outputs a control voltage Vcnt corresponding to the VS voltage Vs detected by the terminal voltage detection unit 11 to the current supply unit 13. The current supply unit 13 supplies a current corresponding to the control voltage Vcnt from the IP terminal Tip to the pump cell 4 of the gas sensor element 2.

  The current detector 14 detects a current flowing between the COM terminal Tcom and the gas sensor element 2 (hereinafter referred to as a COM current Icom). The air-fuel ratio calculation unit 15 calculates an air-fuel ratio (hereinafter sometimes referred to as an A / F value) based on the COM current Icom.

  The measurement current supply unit 16 supplies the measurement current Im for detecting the state of the admittance Ys of the detection cell 5 between the VS terminal Tvs and the COM terminal Tcom, so that the measurement current Im is detected by the detection cell 5. To supply. The admittance detection unit 17 determines the admittance Ys of the detection cell 5 based on a change amount ΔVs of the VS voltage Vs generated by supplying the measurement current Im to the detection cell 5 (hereinafter, may be referred to as a voltage change amount ΔVs). Detect the state of.

  The mode control unit 19 sets an operation mode according to the activation state of the gas sensor element 2 based on the admittance Ys of the detection cell 5. For example, the mode control unit 19 sets the first mode M1 when, for example, the admittance Ys is less than the threshold Yth1, and sets the second mode M2 when the admittance Ys is greater than or equal to the threshold Yth1. The first mode M1 is an operation mode when the gas sensor element 2 is in an inactive state, and is an operation mode in which the gas sensor element 2 is activated. The second mode M2 is an operation mode when the gas sensor element 2 is in an active state, and is an operation mode for detecting an A / F value.

  The abnormality detection unit 21 performs an abnormality determination process for determining a connection abnormality between the gas sensor element 2 and the control device 3 (hereinafter sometimes simply referred to as a connection abnormality). An abnormal connection with the gas sensor element 2 means a state in which the connection between the gas sensor element 2 and the control device 3 is not normal. Such a connection abnormality includes, for example, an open abnormality in which the connection between the terminal T2 of the gas sensor element 2 and the COM terminal Tcom is in an open (open) state (hereinafter, sometimes referred to as a COM open abnormality).

  The abnormality detection unit 21 resets the state of the abnormality determination process when the operation mode is changed by the mode control unit 19. This is because the operation of the air-fuel ratio sensor 1 is not stable immediately after the change of the operation mode (immediately after the mode transition), so that there is a possibility that it is erroneously detected as a connection abnormality although there is no connection abnormality. .

  As described above, the abnormality determination unit 60 resets the state of the abnormality determination process when the operation mode is changed. Therefore, when an abnormality in which the operation mode is frequently switched occurs, the state of the abnormality determination process (for example, an error counter) is frequent. In some cases, it is difficult to detect an abnormality in connection with the gas sensor element 2.

  When the COM open abnormality has occurred, the reference voltage COM voltage Vcom is lost in the feedback path of the feedback control described above, and the VS voltage Vs oscillates. In this case, the admittance Ys detected by the admittance detection unit 17 varies. For this reason, the operation mode is frequently changed by the mode control unit 19, and in the abnormality determination unit 60, connection abnormality with the gas sensor element 2 may be difficult.

  Therefore, the mode control unit 19 restricts the mode change process based on the admittance Ys of the detection cell 5 based on the COM current Icom detected by the current detection unit 14. For example, when the change amount ΔIcom of the COM current Icom is equal to or smaller than the threshold value Ith1, the mode control unit 19 fixes the operation mode to the first mode M1 or the second mode M2 and prohibits the change of the operation mode. Thereby, frequent change of the operation mode is suppressed, and abnormality in connection with the gas sensor element 2 can be detected with high accuracy.

[2. Specific configuration example of air-fuel ratio sensor 1]
Next, an example of a specific configuration of the air-fuel ratio sensor 1 will be described. FIG. 2 is a diagram illustrating a specific configuration example of the air-fuel ratio sensor 1 according to the embodiment, and FIG. 3 is a diagram illustrating a specific configuration example of the gas sensor element 2. The control device 3 of the air-fuel ratio sensor 1 is provided, for example, in an ECU (Electronic Control Unit) provided in the vehicle.

[2.1. Specific configuration example of gas sensor element 2]
First, a specific configuration example of the gas sensor element 2 will be described with reference to FIG. As shown in FIG. 3, the gas sensor element 2 is, for example, a full-range air-fuel ratio gas sensor element, and has a configuration in which a solid electrolyte body 81, an insulating base 85, and solid electrolyte bodies 87 and 89 are sequentially stacked.

  The solid electrolyte bodies 81, 87, and 89 are, for example, solid electrolyte bodies having oxygen ion conductivity, and are configured by adding yttria (Y2O3) to zirconia (ZrO2), for example. The insulating base 85 is made of alumina, for example.

  A gas detection chamber 90 is formed in the insulating base 85, and porous diffusion rate limiting portions 84 that restrict the amount of exhaust gas flowing into the gas detection chamber 90 are provided at both ends of the gas detection chamber 90.

  The pump cell 4 includes a solid electrolyte body 81 and electrodes 82 and 83 formed of porous platinum or the like on both surfaces of the solid electrolyte body 81, and the magnitude and direction of the current supplied between the electrodes 82 and 83. In response to this, oxygen is pumped into and pumped out from the gas detection chamber 90. The electrode 82 is protected by, for example, a porous protective layer 80.

  The detection cell 5 includes a solid electrolyte body 87 and electrodes 86 and 88 formed of porous platinum or the like on both surfaces of the solid electrolyte body 87. By supplying a constant current Icp between the electrodes 86 and 88, an electromotive force corresponding to the oxygen concentration in the gas detection chamber 90 is generated between the electrodes 86 and 88.

  Although not shown in FIG. 3, the gas sensor element 2 is provided with a heater 6 (see FIG. 2), and the gas sensor element 2 is activated by the heating of the heater 6. The heater 6 is, for example, a ceramic heater, and heater wiring is provided inside.

[2.2. Specific configuration example of control device 3]
Next, a specific configuration example of the control device 3 shown in FIG. 2 will be described. The control device 3 is realized by an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control device 3 may be configured to execute part or all of the arithmetic processing by a CPU (Central Processing Unit).

  As shown in FIG. 2, the control device 3 includes an IP terminal Tip, a COM terminal Tcom, a VS terminal Tvs, a voltage control unit 10, a terminal voltage detection unit 11, a feedback control unit 12, and a current supply unit 13. A current detection unit 14, an air-fuel ratio calculation unit 15, a measurement current supply unit 16, an admittance detection unit 17, a heater control unit 18, a mode control unit 19, and an abnormality detection unit 21 (of the abnormality detection device). An example).

  A terminal T2 to which one end of the pump cell 4 and one end of the detection cell 5 are commonly connected is connected to the COM terminal Tcom, and a terminal T1 to be connected to the other end of the pump cell 4 is connected to the IP terminal Tip. A terminal T3 connected to the other end of the detection cell 5 is connected to the VS terminal Tvs.

[2.2.1. Voltage control unit 10]
The voltage control unit 10 outputs a voltage so that the voltage at the terminal T2 of the gas sensor element 2 becomes a constant voltage Va (for example, 3.3 [V]). The voltage control unit 10 includes an operational amplifier OP1 and resistors R1 and R2. The voltage controller 10 operates so that the connection point between the resistor R1 and the resistor R2 becomes a constant voltage Va, and the constant voltage Va is supplied to the terminal Tcom via the resistor R1. Supply.

[2.2.2. Terminal voltage detector 11]
The terminal voltage detection unit 11 includes a current source 40 and a voltage follower 41. The current source 40 supplies a constant current Icp to the detection cell 5. The voltage follower 41 detects a VS voltage Vs that is a voltage of the VS terminal Tvs.

  The constant current Icp from the current source 40 flows from the electrode 88 to the electrode 86 of the gas sensor element 2 shown in FIG. As a result, an electromotive force according to the oxygen concentration between the electrodes 86 and 88 is generated between the electrodes 86 and 88 and appears as a voltage between the terminals T2 and T3.

[2.2.3. Feedback Control Unit 12]
When the operation mode is the second mode, the feedback control unit 12 generates a control voltage according to the VS voltage Vs detected by the terminal voltage detection unit 11 and outputs the control voltage Vcnt to the current supply unit 13.

  The feedback control unit 12 responds to the difference between the VS voltage Vs and a predetermined reference voltage value Vref (for example, 0.45 [V]) by PI (proportional integral) control or PID (proportional integral derivative) control, for example. The control voltage Vcnt is output to the current supply unit 13 so that the current Ip having the same direction and magnitude is supplied from the current supply unit 13 to the terminal T1 of the gas sensor element 2.

[2.2.4. Current supply unit 13]
The current supply unit 13 includes resistors R3 to R7 and an operational amplifier OP2. A current Ip having a direction and magnitude corresponding to the difference between the control voltage output from the feedback control unit 12 and the reference voltage Vb is output from the IP terminal Tip. Supply to the pump cell 4 of the gas sensor element 2. The current supply unit 13 is not limited to the circuit shown in FIG. 2, and may be any configuration that can supply the current Ip according to the control of the feedback control unit 12 to the terminal T1.

[2.2.5. Current detection unit 14]
The current detection unit 14 includes a voltage follower 49 that inputs the output voltage of the operational amplifier OP1, and detects the COM current Icom supplied from the voltage control unit 10 to the terminal T2 of the gas sensor element 2 via the COM terminal Tcom.

  The value of the COM current Icom detected by the current detection unit 14 shown in FIG. 2 is based on the value of the voltage Va as a positive / negative reference. The air-fuel ratio calculation unit 15, the mode control unit 19, and the abnormality detection unit 21 The COM current Icom detected by the current detection unit 14 is used after being converted into a value using, for example, zero as a positive / negative reference. The current detection unit 14 may be configured to detect the COM current Icom using zero as a positive / negative reference based on the voltage across the resistor R2.

  Although not shown in FIG. 2, constant current sources for supplying a constant current Icp are provided at the VS terminal Tvs and the COM terminal Tcom, respectively. The constant current Icp is a COM current detected by the current detection unit 14. It is not included in Icom. Therefore, when the current Id is not supplied by the measurement current supply unit 16, the current detection unit 14 can detect the current Ip flowing through the pump cell 4 (hereinafter referred to as the IP current Ip) as the COM current Icom. .

  Further, in the configuration example shown in FIG. 2, a single current detection unit 14 includes a current detection unit that detects a current for air-fuel ratio calculation and a current detection unit that detects a current used for mode change processing restriction determination and abnormality determination. Although shared, it is not limited to such a configuration. For example, in addition to the current detection unit 14, a second current detection unit that detects the COM current Icom is separately provided, and the COM current Icom detected by the second current detection unit is detected by the mode control unit 19 and the abnormality detection unit 21. It can also be used.

[2.2.6. Air-fuel ratio calculation unit 15]
When the operation mode is the second mode, the air-fuel ratio calculation unit 15 is based on the COM current Icom detected as the IP current Ip by the current detection unit 14 when the current Id is not supplied by the measurement current supply unit 16. The air-fuel ratio (A / F value) is calculated.

[2.2.7. Current supply unit for measurement 16]
The measurement current supply unit 16 generates a constant current Id (hereinafter referred to as a measurement current Id) for measuring the admittance Ys state of the detection cell 5 between the current source 42 and the COM terminal Tcom and the VS terminal Tvs. To supply. As a result, the measurement current Id is supplied to the detection cell 5. The measurement current supply unit 16 includes a current source 42 and a switch 43.

  The current source 42 and the switch 43 are arranged and connected in series between the VS terminal Tvs and the ground GND. The switch 43 is intermittently turned on (for example, turned on for a predetermined period TB every predetermined period TA), and the measurement current Id is intermittently supplied from the current source 42 to the detection cell 5.

  The measurement current supply unit 16 is not limited to the configuration shown in FIG. FIG. 4 is a diagram illustrating another configuration example of the measurement current supply unit 16. The measurement current supply unit 16 illustrated in FIG. 4 includes a switch 43, a voltage source 44, and a capacitor 45.

  The switch 43, the voltage source 44, and the capacitor 45 are arranged connected in series between the VS terminal Tvs and the ground GND. The switch 43 is intermittently turned on, and the measurement current Id is intermittently supplied from the voltage source 44 and the capacitor 45 to the detection cell 5.

[2.2.8. Admittance detection unit 17]
The admittance detection unit 17 detects the admittance Ys of the detection cell 5 based on the VS voltage Vs detected by the terminal voltage detection unit 11. For example, the admittance detection unit 17 detects the state of the admittance Ys (= Im / ΔVs) based on the voltage change amount ΔVs generated by supplying the measurement current Im to the detection cell 5.

  The admittance detection unit 17 can also detect the admittance Ys itself as the admittance Ys state, and can also detect a value corresponding to the admittance Ys (for example, the impedance Zp of the detection cell 5).

[2.2.9. Heater control unit 18]
The heater control unit 18 is connected to the heater wiring of the heater 6 provided in the gas sensor element 2 and controls the amount of power supplied from the battery BAT to the heater 6. Thereby, the temperature of the heater 6 is controlled.

  The heater control unit 18 includes, for example, a PWM (Pulse Wide Modulation) control unit and a switching element. The PWM control unit generates a PWM signal having a duty ratio D corresponding to the amount of power supplied to the heater 6. The switching element is turned on / off at a duty ratio D of the PWM signal, and supplies power corresponding to the duty ratio D from the battery BAT to the heater 6.

  The PWM control unit adjusts the duty ratio D so that the admittance Ys becomes the control value Yth2. Thereby, the temperature of the gas sensor element 2 can be raised and the gas sensor element 2 can be made into the activated state.

[2.2.10. Mode control unit 19]
Based on the state of the admittance Ys detected by the admittance detection unit 17, the mode control unit 19 selects one of the first mode M1 that is an inactive state operation mode and the second mode M2 that is an active state operation mode. Set the mode.

  The mode control unit 19 includes an activation determination unit 51, a state determination unit 52, and a mode determination unit 53. The activation determination unit 51 determines the activation state of the gas sensor element 2 based on the admittance Ys. For example, the activation determination unit 51 determines that the gas sensor element 2 is activated when the admittance Ys is equal to or greater than the threshold Yth1, and the gas sensor element 2 is activated when the admittance Ys is less than the threshold Yth1. Judge that there is no.

  For example, the activation determination unit 51 determines that the gas sensor element 2 has changed from the inactive state to the active state when the state in which the admittance Ys is greater than or equal to the threshold Yth1 continues from the state in which the admittance Ys is less than the threshold Yth1. can do. Moreover, when the state where the admittance Ys is less than the threshold Yth1 continues from the state where the admittance Ys is equal to or greater than the threshold Yth1, it can be determined that the gas sensor element 2 has changed from the active state to the inactive state.

  Further, the activation determination unit 51 may be configured to determine the activation state of the gas sensor element 2 based on the voltage change amount ΔVs that is a value corresponding to the admittance Ys instead of the value of the admittance Ys itself. In this case, for example, the activation determination unit 51 determines that the gas sensor element 2 is activated when the voltage change amount ΔVs is less than the threshold value Vth1, and when the voltage change amount ΔVs is equal to or greater than the threshold value Vth1, It is determined that the gas sensor element 2 is not active.

  The state determination unit 52 determines the state of the COM current Icom detected by the current detection unit 14. For example, in the state determination unit 52, the change amount ΔIcom (hereinafter referred to as current change amount ΔIcom) of the COM current Icom caused by the supply of the detection cell 5 to the measurement current Im by the measurement current supply unit 16 has the threshold value Ith1. It is determined whether or not it exceeds.

  The mode determination unit 53 sets the operation mode to the first mode M1 or the second mode M2 based on the determination result by the state determination unit 52 and the determination result by the activation determination unit 51. For example, it is assumed that the state determination unit 52 determines that the current change amount ΔIcom exceeds the threshold value Ith1. When the activation determination unit 51 determines that the gas sensor element 2 is not activated, the mode determination unit 53 sets the first mode M1, and the activation determination unit 51 determines that the gas sensor element 2 is activated. If determined, the second mode M2 is set.

  On the other hand, when the state determination unit 52 determines that the current change amount ΔIcom is equal to or less than the threshold value Ith1, the mode determination unit 53 determines whether the first mode M1 or the second mode M2 regardless of the determination result of the activation determination unit 51. The operation mode is fixed to. Thereby, when the current change amount ΔIcom is equal to or less than the threshold value Ith1 by the state determination unit 52, the operation mode is fixed to one of the first mode M1 and the second mode M2.

[2.2.11. Terminal voltage detector 20]
The inter-terminal voltage detector 20 detects a voltage Vic between the IP terminal Tip and the COM terminal Tcom (hereinafter referred to as inter-terminal voltage Vic). The inter-terminal voltage Vic is a voltage between the terminal T1 and the terminal T3 of the gas sensor element 2 when the connection state between the gas sensor element 2 and the control device 3 is normal.

[2.2.12. Abnormality detection unit 21]
The abnormality detection unit 21 performs abnormality determination to determine whether or not a COM open abnormality and an IP-COM short abnormality have occurred.

  The COM open abnormality is an abnormality in which the connection between the terminal T2 of the gas sensor element 2 and the COM terminal Tcom is insufficient, and occurs, for example, when the connection between the terminal T2 and the COM terminal Tcom is disconnected.

  The IP-COM short abnormality is an abnormality in which the IP terminal Tip and the COM terminal Tcom are short-circuited. Such an IP-COM short circuit abnormality occurs, for example, when a first connection line connecting the terminal T1 and the IP terminal Tip contacts a second connection line connecting the terminal T3 and the COM terminal Tcom.

  FIG. 5 is a diagram illustrating a configuration example of the abnormality detection unit 21. As shown in FIG. 5, the abnormality detection unit 21 includes an abnormality determination unit 60 and an edge detection unit 61. The abnormality determination unit 60 determines the connection abnormality based on the COM current Icom and the inter-terminal voltage Vic detected when the measurement current supply unit 16 intermittently supplies the measurement current Im to the detection cell 5. I do. The edge detection unit 61 detects a change in the operation mode by the mode control unit 19.

  The abnormality determination unit 60 includes a first state determination unit 62, a first error counter 63, a first determination unit 64, a second state determination unit 65, a second error counter 66, and a second determination unit 67. Prepare.

  Each time the measurement current Im is supplied to the detection cell 5, the first state determination unit 62 changes the amount of change ΔIcom of the COM current Icom detected by the current detection unit 14 by supplying the measurement current Im to the detection cell 5. Is less than or equal to the threshold value Ith1. The threshold value Ith1, for example, is set to a value larger than the current change amount ΔIcom caused by the measurement current Im when there is an ICOM open abnormality and smaller than the current change amount ΔIcom caused by the measurement current Im when there is no connection abnormality. The

  The first error counter 63 increments the internal counter value Cd1 each time the first state determination unit 62 determines that the current change amount ΔIcom is equal to or less than the threshold value Ith1. The first determination unit 64 determines that a COM open abnormality has occurred when the counter value Cd1 of the first error counter 63 is equal to or greater than the threshold value Cth1.

  On the other hand, the first error counter 63 does not increment the internal counter value Cd1 when the first state determination unit 62 determines that the current change amount ΔIcom exceeds the threshold value Ith1. The counter value Cd1 is reset by the edge detection unit 61 when the first mode M1 is changed to the second mode M2 or when the second mode M2 is changed to the first mode M1.

  The second state determination unit 65 determines that the inter-terminal voltage Vic detected by the inter-terminal voltage detection unit 20 in a state where the measurement current Im is supplied to the detection cell 5 at every timing when the measurement current Im is supplied. It is determined whether or not it is within a range from the threshold value Vth2 to the threshold value Vth3 (hereinafter referred to as a predetermined range S). The predetermined range S is set, for example, to a range that does not include the inter-terminal voltage Vic generated by the measurement current Im during normal operation.

  The second error counter 66 increments the internal counter value Cd2 every time the second state determination unit 65 determines that the inter-terminal voltage Vic is within the predetermined range S. The second determination unit 67 determines that an IP-COM short abnormality has occurred when the counter value Cd2 of the second error counter 66 is greater than or equal to the threshold value Cth2.

  On the other hand, the second error counter 66 does not increment the internal counter value Cd2 when the second state determination unit 65 determines that the inter-terminal voltage Vic is outside the predetermined range S. The counter value Cd2 is reset by the edge detection unit 61 when the first mode M1 is changed to the second mode M2 or when the second mode M2 is changed to the first mode M1.

  The configuration of the abnormality detection unit 21 is not limited to the configuration illustrated in FIG. For example, the abnormality detection unit 21 may be configured to detect a COM open abnormality by determining by a timer whether or not the state where the current change amount ΔIcom is equal to or less than the threshold value Ith1 continues for a predetermined period. The abnormality detection unit 21 is configured to detect an IP-COM short abnormality by determining whether or not the state where the inter-terminal voltage Vic is outside the predetermined range S continues for a predetermined period by measuring with a timer. Also good. In the case of such a configuration, the abnormality detection unit 21 can reset the time count of the timer when the mode is changed by the mode control unit 19.

[2.3. COM open error detection]
The detection of the COM open abnormality will be further described with reference to FIGS. 6 and 7 are diagrams showing examples of state changes of the COM current Icom, the VS voltage Vs, the terminal voltage Vic, the operation mode, and the counter value Cd. FIG. 6 shows an example when it is assumed that the mode determination unit 53 sets the operation mode based only on the determination of the activation determination unit 51 without using the determination result of the state determination unit 52.

  As shown in FIGS. 6 and 7, the measurement current supply unit 16 supplies the measurement current Im to the gas sensor element 2 for a predetermined period TB every predetermined period TA. The abnormality determination process by the abnormality detection unit 21 is executed at each timing when the measurement current Im is supplied (hereinafter referred to as determination timing), and the current change amount ΔIcom is based on whether or not the threshold value Ith1 is equal to or less than the threshold value Ith1. , COM short abnormality is detected. In the example shown in FIGS. 6 and 7, the process start timing is times t1, t2, t3, t4, t6, t7, t8, t9, and t10.

  As shown in FIGS. 6 and 7, when the COM open abnormality occurs (t ≧ t5), the VS voltage Vs enters an oscillation state. If the mode determination unit 53 sets the operation mode based only on the determination of the activation determination unit 51, the admittance Ys detected by the activation determination unit 51 varies, so that as shown in FIG. The mode changes frequently. In this case, since the abnormality detection unit 21 resets the counter value Cd1 of the error counter every time the operation mode is changed, the counter value Cd1 is less likely to be greater than or equal to the threshold value Cth1, and it is difficult to detect the COM open abnormality. There is.

  On the other hand, since the mode determination unit 53 fixes the operation mode based on the determination result of the state determination unit 52, the operation mode is set at the first determination timing t6 after the COM open abnormality occurs, as shown in FIG. The first mode M1 is fixed. The abnormality detection unit 21 increments the counter value Cd1 at the determination timing t6 because the current change amount ΔIcom is equal to or less than the threshold value Ith1, but the operation mode is fixed from the second mode M2 to the first mode M1, and thus the operation is performed. The counter value Cd1 is reset in the abnormality detection unit 21 by changing to the mode.

  As shown in FIG. 7, when the COM open abnormality continues from time t5, the state where the current change amount ΔIcom is equal to or less than the threshold value Ith1 continues. Therefore, the mode control unit 19 keeps the operation mode fixed, and the abnormality detection unit 21 increments the counter value Cd1 at each determination timing. Since the counter value Cd1 exceeds the threshold Cth1 at the determination timing at time t10, the abnormality detection unit 21 determines that a COM open abnormality has occurred.

  Thus, when the current change amount ΔIcom is equal to or less than the threshold value Ith1, the control device 3 according to the embodiment sets the operation mode to one of the first mode M1 and the second mode M2, so that the COM The occurrence of an open abnormality can be detected with high accuracy.

  Note that the mode control unit 19 can also fix the operation mode to the second mode M2 when the current change amount ΔIcom is equal to or less than the threshold value Ith1. In this case, since the counter value Cd1 is not reset, the detection time of the COM open abnormality can be shortened compared to the case where the first mode M1 is fixed. The mode controller 19 can also fix the operation mode by maintaining the operation mode immediately before the COM open abnormality occurs.

[2.4. Detection of IP-COM short abnormality]
The detection of the IP-COM short abnormality will be further described with reference to FIGS. 8 and 9 are diagrams showing examples of state changes of the COM current Icom, the VS voltage Vs, the terminal voltage Vic, the operation mode, and the counter value Cd. FIG. 8 shows an example when it is assumed that the mode determination unit 53 sets the operation mode based only on the determination of the activation determination unit 51 without using the determination result of the state determination unit 52.

  As shown in FIGS. 8 and 9, the measurement current supply unit 16 supplies the measurement current Im to the gas sensor element 2 for a predetermined period TB every predetermined period TA. The abnormality determination process by the abnormality detection unit 21 is performed at each determination timing described above, and detects an IP-COM short abnormality based on whether or not the inter-terminal voltage Vic is outside the predetermined range S.

  As shown in FIGS. 8 and 9, when an IP-COM short abnormality occurs (t ≧ t5), the VS voltage Vs enters an oscillation state. This is because when the IP terminal Tip and the COM terminal Tcom are short-circuited, non-inverted feedback is performed in the feedback path of feedback control.

  If the mode determination unit 53 sets the operation mode based only on the determination of the activation determination unit 51, the admittance Ys detected by the activation determination unit 51 varies when an IP-COM short abnormality occurs. Therefore, the operation mode is frequently changed as shown in FIG. In this case, the abnormality detection unit 21 resets the counter value Cd2 of the error counter every time the operation mode is changed. Therefore, the counter value Cd2 is less likely to be greater than or equal to the threshold value Cth2, and it is difficult to detect an IP-COM short abnormality. There is a case.

  When the IP-COM short abnormality occurs, the measurement current Im flows into the IP terminal Tip, so that the current change amount ΔIcom is reduced compared to the normal time, and the current change amount ΔIcom becomes equal to or less than the threshold value Ith1. Since the mode determination unit 53 fixes the operation mode based on the determination result of the state determination unit 52, the operation mode is set at the first determination timing t6 after the occurrence of the IP-COM short abnormality as shown in FIG. The first mode M1 is fixed.

  Then, the abnormality detection unit 21 increments the counter value Cd1 because the inter-terminal voltage Vic is within the predetermined range S at the determination timing t6, but the operation mode is fixed from the second mode M2 to the first mode M1. Therefore, the counter value Cd2 is reset in the abnormality detection unit 21 by changing to the operation mode.

  When the IP-COM short abnormality continues from time t5, as shown in FIG. 9, the state where the current change amount ΔIcom is equal to or less than the threshold value Ith1 continues. Therefore, the mode control unit 19 keeps the operation mode fixed, and the abnormality detection unit 21 increments the counter value Cd2 at each determination timing. Since the counter value Cd2 exceeds the threshold Cth2 at the determination timing at time t10, the abnormality detection unit 21 determines that an IP-COM short abnormality has occurred.

  Thus, when the IP-COM short abnormality occurs, the control device 3 according to the embodiment continuously sets the operation mode to one of the first mode M1 and the second mode M2, so that the IP-COM The occurrence of a short circuit abnormality can be detected with high accuracy. As in the case of the COM open abnormality, the mode control unit 19 can also fix the operation mode to the second mode M2, and maintain the operation mode immediately before the IP-COM short abnormality occurs. It is also possible to fix the operation mode.

[3. Processing flow of mode control unit 19]
Next, an example of the mode setting process flow of the mode control unit 19 will be described. FIG. 10 is a flowchart showing a main processing procedure executed by the mode control unit 19, and is a process that is repeatedly executed.

  As shown in FIG. 10, the mode control unit 19 determines whether or not the current change amount ΔIcom is equal to or less than a threshold value Ith1 (step S1). If the mode control unit 19 determines that the current change amount ΔIcom is equal to or less than the threshold value Ith1 (step S1; Yes), the mode control unit 19 restricts the change of the operation mode (step S2). If the mode control unit 19 determines that the current change amount ΔIcom is not equal to or less than the threshold value Ith1 (step S1; No), the mode control unit 19 determines whether the admittance Ys is equal to or greater than the threshold value Yth1 (step S3).

  When the admittance Ys is not equal to or greater than the threshold Yth1 (step S3; No), the mode control unit 19 sets the operation mode to the first mode (step S4), and when the admittance Ys is equal to or greater than the threshold Yth1 (step S3; Yes). The operation mode is set to the second mode M2 (step S5). When the processes of steps S2, S4, and S5 are finished, the process shown in FIG. 10 is finished, and is executed from the process of step S1 at the next processing timing.

  As described above, the control device 3 for the air-fuel ratio sensor 1 according to the embodiment includes the mode control unit 19, the abnormality detection unit 21, and the current detection unit 14. The mode control unit 19 sets an operation mode according to the activation state of the gas sensor element 2 based on the state of the admittance Ys of the detection cell 5. The abnormality detection unit 21 sets an operation mode according to the activation state of the gas sensor element 2 based on the state of the admittance Ys of the detection cell 5. The abnormality detection unit 21 executes an abnormality determination process for determining a connection abnormality with the gas sensor element 2 to detect a connection abnormality, and resets the state of the abnormality determination process when the mode control unit 19 changes the operation mode. To do. The current detection unit 14 detects a current flowing between the COM sensor Tcom (an example of a terminal to which one end of the pump cell 4 and one end of the detection cell 5 are connected) and the gas sensor element 2. The mode control unit 19 restricts the change of the operation mode based on the admittance Ys state based on the state of the COM current Icom detected by the current detection unit 14.

  Accordingly, since the operation mode can be fixed regardless of the state of the admittance Ys of the detection cell 5, frequent changes in the operation mode are suppressed, and abnormal connection with the gas sensor element 2 can be accurately detected. . Further, for example, the number of parts, size, cost, etc. can be reduced as compared with the case where an oscillation detection circuit for detecting that the VS voltage Vs is oscillating is provided to detect a COM open abnormality or an IP-COM short abnormality. it can.

  In addition, the control device 3 includes a measurement current supply unit 16 that controls the supply of the measurement current Im for measuring the state of the admittance Ys to the detection cell 5. The mode control unit 19 limits the change of the operation mode based on the admittance Ys based on the change amount ΔIcom of the COM current Icom detected by the current detection unit 14 by supplying the measurement current Im to the detection cell 5.

  Thus, since the change of the operation mode based on the admittance Ys is limited based on the change amount ΔIcom of the COM current Icom, the change of the operation mode is accurately limited when there is a COM open abnormality or an IP-COM short abnormality. be able to.

  The abnormality detection unit 21 includes first and second error counters 63 and 66 (an example of a counter), and first and second determination units 64 and 67 (an example of a determination unit). The first and second error counters 63 and 66 increment counter values Cd1 and Cd2 indicating the state of the abnormality determination process when the state of the air-fuel ratio sensor 1 satisfies the abnormality determination condition. The first and second determination units 64 and 67 determine that there is an abnormality in connection with the gas sensor element 2 when the counter values Cd1 and Cd2 are equal to or greater than a threshold value. The first and second error counters 63 and 66 reset the counter values Cd1 and Cd2 when the mode control unit 19 changes the operation mode.

  With this configuration, it is possible to accurately detect a COM open abnormality and an IP-COM short abnormality, and it is possible to detect an abnormality without adding a component by building a logic by software.

  The abnormality detection unit 21 determines that the state of the air-fuel ratio sensor 1 satisfies the abnormality determination condition when the change amount ΔIcom of the COM current Icom generated by supplying the measurement current Im to the detection cell 5 is equal to or less than the threshold value Ith1. . Thereby, it is possible to accurately detect the COM open abnormality.

  The control device 3 detects the inter-terminal voltage Vic between the IP terminal Tip (an example of a terminal to which the other end of the pump cell is connected) and the VS terminal Tvs (an example of a terminal to which the other end of the detection cell is connected). A terminal voltage detector 20 is provided. The abnormality detection unit 21 determines that the state of the air-fuel ratio sensor 1 is abnormal when the amount of change in the voltage detected by the inter-terminal voltage detection unit 20 by supplying the measurement current Im to the detection cell 5 is within a predetermined range. It is determined that the condition is satisfied. Thereby, an IP-COM short circuit abnormality can be detected with high accuracy.

  The current detection unit 14 is the same as the current detection unit that detects the IP current Ip (an example of an air-fuel ratio calculation current). Thereby, compared with the case where a current detection part is provided separately, the number of parts, size, cost, etc. can be reduced.

  The operation mode according to the activated state of the gas sensor element 2 is a first mode M1 that is an operation mode when the gas sensor element 2 is inactive and a second operation mode when the gas sensor element 2 is active. Mode M2. The mode control unit 19 limits the change of the operation mode by fixing the operation mode to one of the first mode M1 and the second mode M2 based on the COM current Icom detected by the current detection unit 14. Do.

  When the operation mode is fixed to the first mode M1, for example, the operation for detecting the A / F value is not performed, and the IP current Ip does not flow, so that the power consumption can be reduced. Further, when the operation mode is fixed to the second mode M2, an operation for detecting the A / F value is performed, so that an IP-COM short abnormality can be detected with high accuracy.

  The threshold value Ith1 used by the mode control unit 19 and the threshold value Ith1 used by the abnormality detection unit 21 may or may not be the same. For example, by setting the threshold value Ith1 used in the mode control unit 19 to a value higher than the threshold value Ith1 used in the abnormality detection unit 21, the operation mode can be fixed more quickly. The determination can be made with high accuracy.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Air fuel ratio sensor 2 Gas sensor element 3 Control apparatus 4 Pump cell 5 Detection cell 6 Heater 10 Voltage control part 11 Terminal voltage detection part 12 Feedback control part 13 Current supply part 14 Current detection part 15 Air fuel ratio calculation part 16 Current supply part 17 for measurement 17 Admittance detection unit 18 Heater control unit 19 Mode control unit 20 Terminal voltage detection unit 21 Abnormality detection unit 51 Activation determination unit 52 State determination unit 53 Mode determination unit 60 Abnormality determination unit 61 Edge detection unit 62 First state determination unit 63 1 error counter 64 first determination unit 65 second state determination unit 66 second error counter 67 second determination unit

Claims (8)

A control device for an air-fuel ratio sensor comprising a gas sensor element having a detection cell that generates a voltage according to the oxygen concentration in a gas detection chamber and a pump cell that pumps oxygen into and out of the gas detection chamber,
A terminal to which one end of the pump cell and one end of the detection cell are connected in common;
An admittance detection unit for detecting an admittance state of the detection cell;
A mode control unit that sets an operation mode according to an activation state of the gas sensor element based on the admittance state detected by the admittance detection unit;
An abnormality detection that detects an abnormality in connection by executing an abnormality determination process for determining an abnormality in connection with the gas sensor element, and resets the state of the abnormality determination process when the mode control unit changes the operation mode. And
A current detection unit that detects a current flowing between the terminal and the gas sensor element;
The mode control unit
The control device that restricts the change of the operation mode based on the admittance state based on the state of the current detected by the current detection unit. A measurement current supply unit for controlling supply of the measurement current for measuring the admittance state to the detection cell;
The mode control unit
The control device according to claim 1, wherein a change in the operation mode based on the admittance is limited based on a change amount of the current detected by the current detection unit due to the measurement current. The abnormality detection unit
A counter that increments a counter value indicating the state of the abnormality determination process when the state of the air-fuel ratio sensor satisfies an abnormality determination condition;
A determination unit that determines that there is an abnormality in connection with the gas sensor element when the counter value is equal to or greater than a threshold value;
The control apparatus according to claim 2, wherein the counter value is reset when the mode control unit changes the operation mode. The abnormality detection unit
4. The state of the air-fuel ratio sensor is determined to satisfy the abnormality determination condition when a change amount of the current detected by the current detection unit is not more than a predetermined value. The control device described in 1. An inter-terminal voltage detector that detects a voltage between a terminal to which the other end of the pump cell is connected and a terminal to which the other end of the detection cell is connected;
The abnormality detection unit
The state of the air-fuel ratio sensor is determined to satisfy the abnormality determination condition when a change amount of the voltage detected by the inter-terminal voltage detection unit is within a predetermined range. Item 5. The control device according to Item 3 or 4. The current detector is
The control device according to claim 1, wherein the control device is the same as a current detection unit that detects an air-fuel ratio calculation current. The operation mode according to the activation state of the gas sensor element is:
A first mode that is an operation mode when the gas sensor element is in an inactive state and a second mode that is an operation mode when the gas sensor element is in an active state;
The mode control unit
The change of the operation mode is limited by fixing the operation mode to one of the first mode and the second mode based on the current detected by the current detection unit. The control apparatus as described in any one of Claims 1-6. A control method of an air-fuel ratio sensor comprising a gas sensor element having a detection cell that generates a voltage according to the oxygen concentration in a gas detection chamber and a pump cell that pumps oxygen into and out of the gas detection chamber,
An admittance detection step of detecting an admittance state of the detection cell;
A mode control step of setting an operation mode according to the activation state of the gas sensor element based on the admittance state of the detection cell detected by the admittance detection step;
An abnormality that detects the connection abnormality by executing an abnormality determination process for determining an abnormality in connection with the gas sensor element, and resets the state of the abnormality determination process when the operation mode is changed in the mode control step A detection process;
A current detection step of detecting a current flowing between a terminal connected to one end of the pump cell and one end of the detection cell and the gas sensor element,
The mode control step includes
The control method characterized by restricting the change of the operation mode based on the admittance state based on the state of the current detected by the current detection step.

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