JP2010256233A - Sensor controller and sensor unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a preferable abnormal detection by enabling an abnormal pattern to be specified. <P>SOLUTION: A sensor controller 20 is connected to a sensor element 10, and an applied voltage control circuit 21 for applying a voltage to the sensor element 10 is disposed in the sensor controller 20. Element current IL is detected by a shunt resistor 33, and its detection result is outputted to a CPU 50 as an A/F detection voltage AFO via an A/F signal output section 41. The CPU 50 changes a voltage applied state with respect to the sensor element 10 from a first state into a second state. The CPU 50 detects an abnormality about the sensor element 10 on the basis of terminal voltages VS+, VS- and A/F detection voltages AFO before and after the changing operation from the first state to the second state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sensor control device connected to a sensor element of a gas sensor that detects, for example, an oxygen concentration in exhaust gas, and a sensor unit including the sensor control device and a gas sensor.

  For example, a gas sensor is provided in the exhaust pipe of the engine in order to properly control the exhaust emission of the vehicle-mounted engine, and various techniques for detecting an abnormality related to the gas sensor have been proposed. For example, in the gas concentration detection device of Patent Document 1, the positive terminal and the negative terminal of the sensor element are at the same potential, the positive terminal voltage and the negative terminal voltage are within the applied voltage control range, and Since the element current value is an abnormal value, a short circuit abnormality between the positive and negative terminals is detected.

JP-A-2005-331310

  However, it is considered that various abnormalities related to the sensor element may have the same sensor terminal voltage and element current value, although the abnormal forms are different. Therefore, there is a concern that an abnormal form cannot be specified.

  The main object of the present invention is to provide a sensor control device and a sensor unit that can identify an abnormal form and can realize suitable abnormality detection.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The sensor control device of the present invention is connected to a sensor element that has a solid electrolyte body and flows an element current corresponding to the concentration of a predetermined component in a gas to be detected in a voltage application state, and detects the element current. At the same time, the gas concentration is calculated based on the detection result.

  In particular, the voltage / current detection means for detecting at least one of the voltage and the current at a predetermined detection location in the current path through which the element current flows, and the voltage application state to the sensor element from the first state to the second state A switching means for switching, and an abnormality detection means for detecting an abnormality relating to the sensor element based on the detection value by the voltage / current detection means before and after switching from the first state to the second state by the switching means. It is characterized by that.

  In short, if any abnormality related to the sensor element occurs, the voltage and current in the current path through which the element current flows are different from normal values, and it is possible to detect the abnormality by comparing these detected values with normal values. . However, there are multiple forms of abnormality related to sensor elements, such as sensor terminal power supply shorts and sensor terminal shorts. Even if the abnormality form (abnormality type) is different, the detected values may all exhibit the same abnormal value. is there.

  In this regard, in claim 1, the voltage application state for the sensor element is switched from the first state to the second state, and the detection value by the voltage / current detection means before and after the switching (at a predetermined detection location in the current path). Based on the detected values of voltage and current), an abnormality relating to the sensor element is detected, so that different abnormality forms can be distinguished, and suitable abnormality detection can be realized. For example, when the power supply short of the sensor terminal and the short between the sensor terminals are taken as an example, in the former case, even if the voltage application state is switched to the sensor element, the terminal voltage detection value of the sensor element does not change. On the other hand, in the latter case, the terminal voltage detection value is changed by switching the voltage application state with respect to the sensor element. From this, it becomes possible to distinguish the two abnormalities exemplified above. As a result, it is possible to specify an abnormal form, thereby realizing a preferable abnormality detection.

  According to the second aspect of the present invention, the presence or absence of abnormality related to the sensor element is determined based on the detection value by the voltage / current detection means before switching from the first state to the second state by the switching means. If the abnormality is determined to be abnormal, the switching means switches from the first state to the second state, and the abnormality form is specified based on the detected value by the voltage / current detection means after the switching. To do.

  According to claim 2, the voltage application state of the sensor element is switched from the first state to the second state on condition that it is determined that some abnormality relating to the sensor element has occurred, and the voltage current in the second state An abnormal form is specified based on the detection value by the detection means. In this case, the abnormality form can be specified more suitably by performing the two-stage abnormality detection process before and after the switching of the voltage application state. Moreover, since the switching of the voltage application state is limited to the case where it is determined that some abnormality has occurred, the implementation of the switching can be minimized. Therefore, the influence on the gas concentration detection can be suppressed.

  In the invention according to claim 3, the first state is a normal state in which a device current is detected and a gas concentration is calculated based on the detected value, and the switching means changes the voltage application state from the normal state to the normal state. Is temporarily switched to a different second state. In this case, abnormality detection is performed in a voltage application state different from the normal state, so that it is possible to specify an abnormal form that is difficult to specify in the normal state.

  According to the fourth aspect of the present invention, the voltage / current detection means is means for detecting the element current as an element current detection value (A / F detection voltage AFO) by the current detection element, and the terminal voltage of the sensor element is the terminal voltage. Means for detecting as detection values (terminal voltages VS +, VS−), and a change amount of voltage or current generated according to a sweep change of voltage or current when detecting element impedance is detected as an impedance detection value (impedance detection voltage Iout). It is good to have at least one of the means. In any of these cases, suitable abnormality detection can be performed.

  For example, in the circuit configuration of FIG. 1, the element current detection value (A / F detection voltage AFO) is detected as the voltage at both terminals of the shunt resistor 33, and the terminal voltage detection values (terminal voltages VS +, VS−) are the sensor terminals. It is detected as the terminal voltages of S + and S−, and the detected impedance value (impedance detection voltage Iout) is detected as the amount of change in one terminal voltage (point A voltage) of the shunt resistor 33.

  According to a fifth aspect of the present invention, there is provided a voltage application unit that is connected to at least one terminal of the sensor element and applies a voltage to the terminal, and the switching unit is connected to the sensor element by the voltage application unit. By switching off the voltage application, switching from the first state to the second state is performed. And abnormality detection is implemented based on the detection value by the voltage-current detection means before and after interruption of voltage application by the switching means. The voltage applying means applies a voltage other than the ground potential to the terminal of the sensor element, the voltage is applied to one terminal of the sensor element by the applied voltage means, and the other terminal is connected to the ground. Configurations are also included in the configurations of the claims.

  When the voltage application to the sensor element by the voltage application means is interrupted (opened) as described above, the voltage and current (detected value by the voltage / current detection means) in the current path through which the element current flows differ depending on the abnormal form. Change. Taking the sensor power supply short circuit and the sensor terminal short circuit as an example, in the former case, the terminal voltage detection value (terminal voltage VS +, VS-) does not change even if the voltage application to the sensor element is cut off. In the latter case, the terminal voltage detection value changes by cutting off the voltage application to the sensor element. In the case of a short circuit between the sensor terminals, for example, the terminal voltage detection value is the same voltage value as the terminal application voltage that is not interrupted. From this, it becomes possible to distinguish the two abnormalities exemplified above.

  Here, as described in claim 6, a path opening / closing means (switch circuit or the like) is provided in a voltage application path between the voltage applying means and the sensor element, and the switching means opens the path opening / closing means from a closed state. It is preferable to adopt a configuration in which voltage application to the sensor element is cut off by switching to the open state.

  According to the seventh aspect of the invention, there is provided an applied voltage control means which is provided connected to at least one terminal of the sensor element and variably sets a terminal applied voltage applied to the terminal based on the element current. Yes. The applied voltage control means has an upper limit guard function for limiting the terminal applied voltage with a predetermined upper limit value, and the switching means changes the upper limit value to change from the first state to the second state. Switch. And abnormality detection is implemented based on the detection value by the voltage / current detection means before and after the change of the upper limit value by the switching means.

  When the upper limit value of the terminal application voltage is changed as described above, the voltage and current (detected value by the voltage / current detection means) of the current path through which the element current flows change in a different manner depending on the abnormal form. Taking the sensor terminal power supply short and the sensor terminal short as an example, in the former case, the terminal voltage detection value (terminal voltage VS +, VS-) does not change even if the upper limit value of the terminal applied voltage is changed. In the latter case, the terminal voltage detection value changes according to the upper limit value of the terminal application voltage by changing the upper limit value of the terminal application voltage. From this, it becomes possible to distinguish the two abnormalities exemplified above.

  Here, as described in claim 8, the switching means sets the upper limit value to a lower voltage side in a state where the terminal applied voltage set by the applied voltage control means has reached the upper limit value. It should be changed. This makes it possible to clearly grasp the change in the detected terminal voltage value.

  According to the ninth aspect of the present invention, the voltage applied to the terminal is variable based on a control input signal corresponding to each element current. Applied voltage control means for setting is provided. The switching unit switches from the first state to the second state by changing a control input signal input to the applied voltage control unit. And abnormality detection is implemented based on the detection value by the voltage / current detection means before and after the change of the control input signal by the switching means.

  When the control input signal to the applied voltage control means is changed as described above, the voltage or current (detected value by the voltage / current detection means) in the current path through which the element current flows changes in a different manner depending on the abnormal form. Taking the sensor power supply short circuit and the sensor terminal short circuit as an example, in the former case, the terminal voltage detection value (terminal voltage VS +, VS−) does not change even if the control input signal to the applied voltage control means is changed. On the other hand, in the latter case, the terminal applied voltage changes by changing the control input signal to the applied voltage control means. From this, it becomes possible to distinguish the two abnormalities exemplified above.

  Here, as described in claim 10, the switching means may switch the control input signal to an input signal corresponding to an element current flowing in an air-fuel ratio stoichiometric state.

  The difference between before and after switching of the voltage application state as described above is remarkable when a short circuit between the terminals of the sensor element occurs. Therefore, as described in claim 11, when it is detected that a short circuit between the terminals of the sensor element has occurred based on the detection values by the voltage / current detection means before and after the switching of the voltage application state by the switching means. Good.

  It can be considered that the terminal voltage detection values on both the positive and negative sides of the sensor element have the same value due to the occurrence of an abnormality related to the sensor element. For example, when either of the sensor terminal power supply short circuit or the sensor terminal short circuit occurs, if it is known that the terminal voltage detection values (VS +, VS−) on both the positive and negative sides are the same value, the sensor terminal power supply short circuit In addition, it is possible to distinguish between a short-circuit between sensor terminals and other abnormality (see [Voltage value after sensor activation] in FIG. 5). In this case, it is required to distinguish between a power supply short of the sensor terminals and a short between the sensor terminals. Note that the element current detection value (A / F detection voltage AFO) also has the same abnormal value when the sensor terminal is short-circuited to the power supply and between the sensor terminals (see [Voltage value after sensor activation] in FIG. 5).

  In this regard, in the invention described in claim 12, the terminal voltage detection values on both the positive and negative sides of the sensor element are the same value, and the detection value by the voltage / current detection means has changed with the switching of the voltage application state by the switching means. In this case, it is determined that the short circuit between the terminals has occurred. As a result, even if the detection value by the voltage / current detection means exhibits the same abnormal value due to the power supply short of the sensor terminal and the short between the sensor terminals, the detection value by the voltage / current detection means after switching the voltage application state Therefore, it is possible to clearly identify the short circuit between the sensor terminals (for example, refer to [Voltage value after opening the switch] in FIG. 6).

  In the invention according to claim 13, the terminal voltage detection values on both the positive and negative sides of the sensor element are the same value, and the detection value by the voltage / current detection means is a value outside the normal range, and the voltage is applied by the switching means. If the detection value by the voltage / current detection means does not change even when the state is switched, it is determined that a power supply short-circuit has occurred at one of the terminals of the sensor element. As a result, even if the detection value by the voltage / current detection means exhibits the same abnormal value due to the power supply short of the sensor terminal and the short between the sensor terminals, the detection value by the voltage / current detection means after switching the voltage application state Therefore, it is possible to clearly specify that the power supply of the sensor terminal is short-circuited (for example, see [Voltage value after opening the switch] in FIG. 6).

  It is desirable that the sensor unit includes the sensor control device according to any one of claims 1 to 13 and a gas sensor that includes the sensor element and is connected to the sensor control device. In this case, a sensor unit having a suitable abnormality detection function can be provided.

The circuit diagram which shows the structure of the sensor control circuit in 1st Embodiment. Sectional drawing which shows the structure of a sensor element. The figure which shows the output characteristic (VI characteristic) of a sensor element. The figure which shows the relationship between element current IL and terminal voltage VS + of a sensor element, VS-. The figure which shows the measurement result of the voltage value at the time of abnormality of a sensor control system. The figure which shows the measurement result of the voltage value at the time of abnormality of a sensor control system. The flowchart which shows the process sequence of a sensor abnormality detection. The circuit diagram which shows the structure of the sensor control circuit in 2nd Embodiment. The figure which shows the measurement result of the voltage value at the time of abnormality of a sensor control system. The circuit diagram which shows the structure of the sensor control circuit in 3rd Embodiment. The figure which shows the measurement result of the voltage value at the time of abnormality of a sensor control system. The figure which shows the measurement result of the voltage value at the time of abnormality of a sensor control system. The flowchart which shows the process sequence of a sensor abnormality detection in 4th Embodiment. Sectional drawing which shows the structure of the sensor element in 5th Embodiment. The circuit diagram which shows the structure of the sensor control circuit in 5th Embodiment.

(First embodiment)
Hereinafter, a first embodiment of a sensor control device according to the present invention will be described with reference to the drawings. The present embodiment embodies an air-fuel ratio detection device that detects the oxygen concentration (air-fuel ratio: A / F) in the exhaust gas using the exhaust gas (combustion gas) discharged from the vehicle-mounted engine as the detected gas. This detection result is used in an air-fuel ratio control system constituted by an engine ECU or the like. In the air-fuel ratio control system, stoichiometric air-fuel ratio control for feedback control of the air-fuel ratio in the vicinity of the stoichiometric control, lean air-fuel ratio control for feedback control of the air-fuel ratio in a predetermined lean region, and the like are appropriately performed.

  First, the element structure of the A / F sensor will be described with reference to FIG. The A / F sensor includes a sensor element 10 that has a solid electrolyte body and flows an element current in accordance with the oxygen concentration in the exhaust gas in a state where a voltage is applied. 10 shows a cross-sectional configuration. Actually, the sensor element 10 has a long shape extending in the direction orthogonal to the paper surface of FIG. 2, and the entire element is accommodated in a housing or an element cover.

  The sensor element 10 includes a solid electrolyte layer 11, a diffusion resistance layer 12, a shielding layer 13, and an insulating layer 14, which are stacked on the top and bottom of the drawing. A protective layer (not shown) is provided around the element. The rectangular solid electrolyte layer 11 is a partially stabilized zirconia sheet, and a pair of upper and lower electrodes 15 and 16 are disposed opposite to each other with the solid electrolyte layer 11 interposed therebetween. The diffusion resistance layer 12 is made of a porous sheet for introducing exhaust gas to the electrode 15, and the shielding layer 13 is made of a dense layer for suppressing permeation of exhaust gas. The diffusion resistance layer 12 is provided with a mixing chamber 17 so as to surround the electrode 15.

  Both the diffusion resistance layer 12 and the shielding layer 13 are made of a ceramic such as alumina, spinel, zirconia or the like by a sheet molding method or the like, but have different gas permeability due to differences in the average pore diameter and porosity of the porosity. It has become.

  The insulating layer 14 is made of a high thermal conductive ceramic such as alumina, and an air duct 18 is formed at a portion facing the electrode 16. A heater 19 is embedded in the insulating layer 14. The heater 19 is composed of a linear heating element that generates heat when energized from a battery power source, and heats the entire element by the generated heat.

  In the sensor element 10 having the above configuration, the surrounding exhaust gas is introduced from the side portion of the diffusion resistance layer 12 and then flows into the mixing chamber 17 through the diffusion resistance layer 12 and reaches the electrode 15. When the exhaust gas is lean, oxygen in the exhaust gas is decomposed by the electrode 15 and discharged from the electrode 16 to the atmospheric duct 18. On the other hand, when the exhaust is rich, oxygen in the atmospheric duct 18 is decomposed by the electrode 16 and discharged from the electrode 15 to the exhaust side.

  FIG. 3 is a diagram showing output characteristics (VI characteristics) of the sensor element 10. In FIG. 3, the horizontal axis indicates the potential difference between the positive and negative terminals of the sensor element 10 as the applied voltage Vp, and the vertical axis indicates the element current IL. In the characteristic line of FIG. 3, a straight line portion (flat portion) parallel to the Vp axis, which is the horizontal axis, is a limit current region that specifies the element current IL as the limit current, and the increase or decrease in the element current IL is the increase or decrease in the air-fuel ratio. (Ie, the degree of lean / rich). That is, the element current IL increases as the air-fuel ratio becomes leaner, and the element current IL decreases as the air-fuel ratio becomes richer.

  LX in FIG. 3 represents an applied voltage characteristic line for determining the applied voltage Vp to the sensor element 10, and the slope thereof is generally in the resistance dominant region (the slope portion on the lower voltage side than the limit current region). Match. However, for the applied voltage characteristic line LX, an applied voltage characteristic in which the applied voltage Vp decreases as the element current IL increases is set in the region of IL ≧ K1, unlike the region of K1 to K2. Further, in the region of IL ≦ K2, unlike the region of K1 to K2, an applied voltage characteristic is set in which the applied voltage Vp increases as the element current IL decreases. As described above, since the slope of the applied voltage characteristic line LX1 is reversed outside the K1 to K2 region, even when an excessive voltage is applied to the sensor element 10 due to a battery short-circuit or the like, the sensor element 10 It is possible to suppress an excessive current from flowing through.

  Next, the electrical configuration of the sensor control circuit 20 as the main part of the present invention will be described with reference to FIG.

  In FIG. 1, the sensor control circuit 20 variably controls a terminal application voltage applied to one terminal of the sensor element 10 (in this embodiment, the terminal voltage VS + of the positive terminal S + connected to the electrode 16). An applied voltage control circuit 21 is provided. In the configuration of FIG. 1, an applied voltage control circuit 21 is connected to the positive terminal S + of the sensor element 10 via a switch circuit 35 as a path opening / closing means. The switch circuit 35 is a normally closed switch, and is normally closed. The applied voltage control circuit 21 includes a variable setting circuit 22 that variably sets the terminal voltage VS + based on the element current IL, and an applied voltage guard circuit 23 that limits the upper limit and the lower limit of the terminal voltage VS +.

  The variable setting circuit 22 includes a reference power supply 24 and a non-inverting amplifier circuit 25 connected to the reference power supply 24. In the present embodiment, the voltage value of the reference power supply 24 is 2.6V. The non-inverting amplifier circuit 25 has an operational amplifier 25a and a feedback resistor 25b and an input resistor 25c connected to an inverting input terminal (−input terminal) thereof, and a capacitor 26 is connected in parallel to the feedback resistor 25b. Yes. That is, in this configuration, the non-inverting amplifier circuit 25 is provided with an LPF for preventing applied voltage oscillation. The cut-off frequency fc of the LPF is, for example, 2.7 Hz.

  The applied voltage guard circuit 23 is connected to the non-inverting input terminal (+ input terminal) of the operational amplifier 25a. The applied voltage guard circuit 23 gives an upper limit guard and a lower limit guard to the input voltage (+ side input voltage) of the operational amplifier 25a, thereby obtaining the sensor applied voltage (positive side terminal voltage VS +) by the applied voltage control circuit 21. The upper limit guard circuit unit 27 that limits the applied voltage to the upper limit guard and the lower limit guard circuit unit 28 that performs the lower limit guard of the applied voltage. Each of these guard circuit portions 27 and 28 is connected to point B in the figure.

  The upper limit guard circuit unit 27 includes an operational amplifier 27a provided with a negative feedback unit, a diode 27b connected to an output terminal of the operational amplifier 27a, and a first non-inverting input terminal (+ input terminal) connected to the operational amplifier 27a. And a reference power supply 27c. The diode 27b is provided on the output side of the operational amplifier 27a, closer to the operational amplifier side than the connection point with the negative feedback section, and with the cathode as the operational amplifier output side. The lower limit guard circuit unit 28 is connected to an operational amplifier 28a provided with a negative feedback unit, a diode 28b connected to the output terminal of the operational amplifier 28a, and a non-inverting input terminal (+ input terminal) of the operational amplifier 28a. And a second reference power supply 28c. The diode 28b is provided on the output side of the operational amplifier 28a, closer to the operational amplifier than the connection point with the negative feedback section, and with the anode on the operational amplifier output side.

  According to the applied voltage guard circuit 23 described above, when the point B voltage (the + input voltage of the operational amplifier 25a) is higher than the reference voltage V1 of the first reference power supply 27c, the point B voltage is the upper limit guard at the reference voltage V1. Is done. Further, when the point B voltage (the + input voltage of the operational amplifier 25a) becomes lower than the reference voltage V2 of the second reference power supply 28c, the point B voltage is guarded at the lower limit with the reference voltage V2.

  An AC power supply circuit 31, a buffer 32, and a shunt resistor 33 are connected in series to the other terminal of the sensor element 10 (a negative terminal S- connected to the electrode 15). The AC power supply circuit 31 is an AC voltage generating means that outputs an AC voltage of about 10 to 20 kHz, for example, and is configured by an AC voltage generating circuit and an LPF for filtering the AC voltage output of the generating circuit. The AC power supply circuit 31 generates an AC voltage having an amplitude with a predetermined voltage width around a predetermined reference voltage (2.2 V in the present embodiment), and the AC voltage is used as a terminal applied voltage on the S-terminal side. To be applied.

  The shunt resistor 33 for detecting the element current IL is a voltage conversion element, which converts the element current IL into a voltage and outputs it. That is, the shunt resistor 33 is provided on a current path through which the element current IL flows between the AC power supply circuit 31 and the sensor element 10, and the terminal voltage on the opposite side to the sensor element 10 is the reference voltage (AC power supply circuit). 31 of the AC voltage). The element current IL is measured by the terminal voltage of the shunt resistor 33 at an intermediate point A between the shunt resistor 33 and the sensor element 10 (S-terminal).

  Further, an LPF 34 composed of a resistor and a capacitor is connected to an intermediate point A between the shunt resistor 33 and the sensor element 10 (S-terminal). Further, the LPF 34 is non-inverted by the operational amplifier 25a in the applied voltage control circuit 21. It is connected to the input terminal (+ input terminal). In this configuration, an intermediate voltage between the shunt resistor 33 and the sensor element 10 (that is, a voltage divided by the shunt resistor 33 and the sensor element 10) is supplied to the non-inverting amplifier circuit 25 of the applied voltage control circuit 21 via the LPF 34. Is input. Note that the cut-off frequency fc of the LPF 34 is 150 Hz, for example.

  The applied voltage control circuit 21 and the AC power supply circuit 31 correspond to voltage applying means for applying a voltage to both the positive and negative terminals S + and S− of the sensor element 10. From the viewpoint of A / F detection, the AC power supply circuit 31 sets and applies a reference voltage (2.2 V, which is the amplitude center of the AC voltage) as the applied voltage on the S-terminal side. The circuit 21 sets and applies a variable voltage corresponding to the element current IL as an applied voltage on the S + terminal side. The AC power supply circuit 31 is also a voltage applying unit that applies an AC voltage for impedance detection. In this embodiment, the AC power supply circuit 31 outputs an AC voltage that is amplified by 1 V on both positive and negative sides with 2.2 V as a reference. Capacitors 36 and 37 are provided on both the positive and negative terminals (S + terminal, S− terminal) of the sensor element 10 for the purpose of removing noise and the like.

  Here, the relationship between the element current IL and the terminal voltages VS + and VS− of the sensor element 10 will be described with reference to FIG. The negative terminal voltage VS− (point A voltage in FIG. 1) is increased or decreased in proportion to the element current IL, and the VS− value increases as the element current IL increases. On the other hand, the positive terminal voltage VS + is set to increase or decrease in proportion to the element current IL if the element current IL is in the range of K1 to K2, and is set to a predetermined value if the element current IL is K1 or more or K2 or less. Limited. In this case, if IL is in the range of K1 to K2, as the element current IL increases, a voltage that is gradually increased as the applied voltage between the positive and negative terminals is set. For example, when IL = 0 mA, the voltage is 0.4V. The upper limit guard value of the positive terminal voltage VS + is, for example, 4.3V, and the lower limit guard value is, for example, 1.4V.

  On the other hand, at the intermediate point A between the shunt resistor 33 and the sensor element 10 (S-terminal), the intermediate point voltage (that is, the divided voltage by the shunt resistor 33 and the sensor element 10) is individually captured. The two signal output units 41 and 42 are provided. One is an A / F signal output unit 41 for outputting an A / F detection voltage AFO as an A / F detection signal, and the other is an impedance signal for outputting an impedance detection voltage Iout as an impedance detection signal. The output unit 42. The A / F signal output unit 41 includes a differential amplifier circuit in which an operational amplifier 43 and an LPF unit 44 are provided together. In the A / F signal output unit 41, the point A voltage is input to the non-inverting input terminal (+ input terminal) of the operational amplifier 43 via the LPF 34. At this time, the fluctuation of the voltage at the point A, which fluctuates in an AC manner for impedance detection, is removed by the LPF 34. In the present embodiment, in order to simplify the configuration, the LPF 34 provided in the applied voltage feedback path is used in combination to remove AC fluctuations in the A / F signal.

  The A / F signal output unit 41 may be configured to use a non-inverting amplifier circuit. In this case, the point A voltage is input to the non-inverting input terminal (+ input terminal) of the operational amplifier constituting the non-inverting amplifier circuit via the LPF 34, and the reference voltage (2) is input to the inverting input terminal (−input terminal). .2V) is input.

  The impedance signal output unit 42 includes an HPF 45 and a peak hold circuit 46. The peak hold circuit 46 is provided with a signal amplifier. As a result, the amount of change in the voltage at the point A, which accompanies application of the AC voltage (sweep change in applied voltage) by the AC power supply circuit 31, is detected as the impedance detection voltage Iout.

  Both the A / F detection voltage AFO output from the A / F signal output unit 41 and the impedance detection voltage Iout output from the impedance signal output unit 42 are input to the CPU 50 as control means and recognized by the CPU 50. The The CPU 50 is a well-known calculation device including a calculation unit and a storage unit (various memories), and an A / F detection voltage AFO and an impedance detection voltage Iout are input to the AD converter of the CPU 50. . The CPU 50 calculates A / F (oxygen concentration) based on the A / F detection voltage AFO, and calculates the element impedance Zac based on the impedance detection voltage Iout.

  The A / F signal output unit 41 and the impedance signal output unit 42 amplify the voltage signal, but the amplification factors in the output units 41 and 42 are individually set. At this time, the amplification factors in the output units 41 and 42 depend on the voltage levels for the A / F signal and the impedance signal, and the voltage processing range (0 to 5 V here) of the AD converter of the microcomputer 48. In this embodiment, the amplification factor of the A / F signal output unit 41 is 10 to 20 times, and the amplification factor of the impedance signal output unit 42 is five times.

  According to the above configuration, when an AC voltage is applied to the sensor element 10 by the AC power supply circuit 31, the sensor element 10 corresponds to A / F (oxygen concentration in the exhaust gas) in the application state of the AC voltage. A device current in which a current component and a current component corresponding to the device impedance are combined flows. At this time, at the intermediate point between the shunt resistor 33 and the sensor element 10, which is a measurement point of the A / F detection signal (AFO) and the impedance detection signal (Iout), the period of the sensor applied voltage (frequency of the AC voltage) The voltage swings to match. Then, in the LPF 34 and the A / F signal output unit 41, a current component (DC component) corresponding to each A / F is extracted from the element current from the midpoint voltage between the shunt resistor 33 and the sensor element 10. After being amplified at a predetermined amplification factor, it is output to the microcomputer 48 as an A / F detection signal.

  Further, in the impedance signal output unit 42, a current component (AC component) corresponding to each element impedance is extracted from the element current from the midpoint voltage between the shunt resistor 33 and the sensor element 10, and the peak value thereof is further obtained. Is output to the microcomputer 48 as an impedance detection signal. In the microcomputer 48, A / F (oxygen concentration in exhaust gas) is calculated based on the A / F detection signal, and element impedance is calculated based on the impedance detection signal.

  Here, in the voltage signal detected at an intermediate point between the shunt resistor 33 and the sensor element 10, the A / F signal component and the impedance signal component have different voltage levels, but the A / F signal output unit 41 and Since the voltage signal is taken into the impedance signal output unit 42 in a separate system and amplified separately, the decrease in detection accuracy due to the difference in signal level for these two signals is suppressed. . That is, if the amplification for both signals is performed on the basis of the A / F signal, the detection accuracy of the element impedance is reduced. On the other hand, if the amplification for both signals is performed on the basis of the impedance signal, the A / F Although there is a concern that the detection accuracy may be lowered, the inconvenience is solved by the circuit configuration of the present embodiment.

  Incidentally, in the sensor control circuit 20, circuit configurations such as the AC power supply circuit 31, the A / F signal output unit 41, and the applied voltage control circuit 21 (excluding the reference voltage generation unit) are integrated in the IC, and configured as a sensor control IC. Has been. However, the shunt resistor 33 is externally attached to the sensor control IC (IC element), and thus the shunt resistor 33 is externally attached, thereby minimizing the error in the resistance value of the shunt resistor 33 (that is, the shunt resistor 33). A highly accurate shunt resistor 33 can be used), and the detection accuracy of the element current IL can be improved. The switch circuit 35 is also provided integrally with the sensor control IC.

  In addition to the A / F detection voltage AFO and the impedance detection voltage Iout, the CPU 50 includes a positive terminal voltage VS + that is a voltage of the positive terminal S + of the sensor element 10 and a negative terminal voltage that is a voltage of the negative terminal S−. VS− is input through the AD converter as described above. Although not shown, an LPF is provided in the signal path of the terminal voltages VS + and VS−, and the AC component included in the terminal voltages VS + and VS− is removed by the LPF. . In the present embodiment, the CPU 50, the other shunt resistor 33, the A / F signal output unit 41, and the impedance signal output unit 42 constitute a voltage / current detection means.

  Further, the CPU 50 detects an abnormality related to the sensor element 10 (A / F sensor) based on various detection voltages (VS +, VS−, AFO) input from the sensor control circuit 20. In this case, basically, abnormality detection is performed depending on whether or not each detection voltage is a normal value. In the present embodiment, in particular, when an abnormality relating to the sensor element 10 (hereinafter also referred to as an abnormality of the sensor control system) is detected, the voltage application state is changed on the S + terminal side of the sensor element 10 by controlling the opening and closing of the switch circuit 35. In addition to switching, abnormality detection is performed based on changes in the detection voltages before and after switching.

  In the present embodiment, a configuration is adopted in which various abnormalities in the sensor control system can be detected and the abnormal form can be specified, and details thereof will be described below. Each detection voltage differs depending on whether the sensor control system is normal or abnormal. Therefore, whether or not there is an abnormality in the sensor control system is determined based on whether or not each detection voltage is the same as in the normal state, and the abnormality form is specified based on the detection voltage.

The main abnormal forms in the sensor control system are classified into the following (1) to (6) and will be described in order.
(1) Abnormal sensor disconnection (2) VB short of S + terminal (sensor positive terminal) (3) GND short of S + terminal (sensor positive terminal) (4) VB short of S- terminal (sensor negative terminal) ( 5) GND short of S-terminal (sensor negative side terminal) (6) Short between sensor terminals Above (1) is an abnormality caused by disconnection at either S + or S- terminal, (2), (3) Indicates an abnormality in which a battery short and a ground short have occurred at the S + terminal, (4) and (5) indicate an abnormality in which a battery short and a ground short have occurred at the S− terminal, and (6) indicates S + and S−. Refers to an abnormality where the terminals are shorted.

  The inventors measured voltage values of VS +, VS−, and AFO at the time of each abnormality of (1) to (6). The measurement results are shown in FIG. 5, and specific voltage values of VS +, VS−, and AFO at the time of occurrence of each abnormality (1) to (6) will be described with reference to FIG. The lowermost part of FIG. 5 shows the normal voltage value for comparison. FIG. 5 shows the voltage value before the sensor activation and the voltage value after the sensor activation. Here, the voltage value after the sensor activation is mainly described, and the voltage value before the sensor activation is supplementarily described. To do. Note that each voltage value in FIG. 5 is a calculated value (CPU value: 0 to 5 V) by a calculation device, and the pre-activation voltage value is immediately after the sensor is activated (so that it does not become a transient voltage value during sensor activation) ( Immediately after engine start-up, the post-activation voltage value is a value measured when a specified time (for example, about 1 minute) has elapsed after the sensor is started.

(1) Sensor disconnection abnormality When a sensor disconnection abnormality occurs, the element current IL does not flow, and the terminal voltages VS + and VS− respectively have the same voltage value as the reference voltage on each terminal side. That is, the terminal voltage VS + becomes the voltage value (2.6V) of the reference power supply 24, and the terminal voltage VS− becomes the reference voltage (2.2V) of the AC power supply circuit 31. Further, the A / F detection voltage AFO is held at a value (eg, 2.2 V) corresponding to the element current IL = 0 mA (fixed at stoichiometry). The above values are the same before / after sensor activation.

(2) VB short of S + terminal (sensor positive side terminal) When a VB short of S + terminal occurs, battery voltage VB (for example, 14V) is applied to the S + terminal, and a large current flows as element current IL. In this case, the terminal voltage VS + is fixed at the CPU upper limit (5.0V). Further, since the terminal voltage VS− increases as the terminal voltage VS + increases, the VS− value is also fixed at the CPU upper limit (5.0V). Actually, VS− increases to about 10.5 to 6V. The A / F detection voltage AFO is fixed at the CPU upper limit (5.0 V) as the element current IL increases, and becomes a lean abnormal value (lean sticking). Before the sensor activation, VS + = 5.0V and the element impedance Zac is infinite and the element current IL does not flow. Therefore, as in the case of disconnection abnormality, VS− = 2.2V, AFO = 2.2V. Held in.

(3) S + terminal (sensor positive side terminal) GND short When a S + terminal GND short occurs, the S + terminal is fixed at the ground potential (0V), the applied voltage on the S + terminal side is 0V, and the S− terminal side Is applied to the AC power supply circuit 31. In this case, the terminal voltage VS + is fixed at 0V. The terminal voltage VS− and the A / F detection voltage AFO are values that vary according to the oxygen concentration in the exhaust gas. In particular, the AFO value is an air-fuel ratio rich voltage value (0 to 1.0 V). Before the sensor activation, VS + = 0V and the element impedance Zac is infinite and the element current IL does not flow. Therefore, as in the case of the disconnection abnormality, VS− = 2.2V and AFO = 2.2V are maintained. Is done.

(4) VB short of S− terminal (sensor negative side terminal) When VB short of S− terminal occurs, battery voltage VB (for example, 14V) is applied to the S− terminal, and voltage is also applied to S + terminal side accordingly. As the current rises, a large current flows through the shunt resistor 33. In practice, VS + increases to about 10-6V. In this case, the terminal voltages VS + and VS− and the A / F detection voltage AFO are all fixed at 5V.

  Before the sensor activation, VS− = 5 V and AFO = 5 V are obtained as in the sensor activation, and the terminal voltage VS + becomes the control value of the applied voltage control circuit 21. Supplementing the VS + value, the applied voltage control circuit 21 performs the applied voltage control assuming that the point A voltage in FIG. At this time, the applied voltage guard function of the applied voltage guard circuit 23 limits the applied voltage (VS +) on the S + terminal side to the upper limit guard value of 4.3V.

(5) S-terminal (sensor negative side terminal) GND short When a S-terminal GND short occurs, the S-terminal is fixed at the ground potential (0 V), and the applied voltage on the S-terminal side is 0 V. The applied voltage on the S + terminal side is the output voltage of the applied voltage control circuit 21 when the voltage at point A in FIG. In this case, the applied voltage guard function of the applied voltage guard circuit 23 limits the applied voltage (VS +) on the S + terminal side to 1.4 V that is the lower limit guard value. Further, the A / F detection voltage AFO is held at a predetermined rich value (0 V) corresponding to the potential difference across the shunt resistor 33 regardless of the oxygen concentration in the exhaust gas.

  It should be noted that VS + = 1.4V, VS− = 0V, and AFO = 0V before sensor activation as well as after sensor activation.

(6) Short between sensor terminals When a short between sensor terminals occurs, the element current IL flows around the sensor element 10. In this case, since the element current IL increases, the output voltage of the applied voltage control circuit 21 rises to the upper limit guard value (4.3V), and both the terminal voltages VS + and VS− become 4.3V. Further, the A / F detection voltage AFO becomes the maximum value (5.0 V), and becomes a lean side abnormal value (lean sticking).

  Note that, before the sensor activation, VS + = 4.3V, VS− = 4.3V, and AFO = 5V, as in the case after the sensor activation.

  As described above, when the sensor is abnormal, VS +, VS−, and AFO differ from the normal value according to the abnormal form, and become a predetermined abnormal value. Therefore, the abnormal form depends on which abnormal value of VS +, VS−, or AFO. (Abnormality type) can be specified.

However, among the abnormalities (1) to (6) described above, focusing on (2) the VB short of the S + terminal, (4) the VB short of the S− terminal, and (6) the short between the sensor terminals, these (2 ) (4) (6)
-Both positive and negative terminal voltages VS + and VS- have the same value (VS + = VS-),
The A / F detection voltage AFO is an abnormal value, particularly a lean-side abnormal value;
Is common. That is, even if the abnormal form is different, each voltage value has the same abnormal value. Therefore, there is a concern that the distinction between the VB short-circuit abnormality ((2) (4) abnormality) and the sensor-terminal short abnormality ((6) abnormality) is not clear.

  Therefore, in the present embodiment, the voltage application state for the sensor element 10 is temporarily switched, and abnormality detection is performed based on a comparison between each voltage value before the switching and each voltage value after the switching. Specifically, by temporarily opening the switch circuit 35 provided on the output side of the applied voltage control circuit 21, the circuit connection state in the sensor control circuit 20 is different from the normal gas concentration detection state. Change to In this case, when the VB short-circuit of the sensor terminal and the short-circuit between the sensor terminals occur, even if each voltage value is the same voltage value before the state switching, it is different after the state switching. Therefore, the abnormal form can be distinguished. The state in which the switch circuit 35 is closed corresponds to the “first state”, and the state in which the switch circuit 35 is opened corresponds to the “second state”.

FIG.
・ VB short of S + terminal,
・ VB short of S-terminal,
・ Short-circuit between sensor terminals,
For each of these abnormalities, VS +, VS−, and AFO before and after opening when the switch circuit 35 is opened and voltage application by the applied voltage control circuit 21 is cut off (opened) are compared. Note that all numerical values are after sensor activation.

  In FIG. 6, the voltage values (VS +, VS−, AFO) before the switch circuit 35 is opened are as described in FIG. That is, in each abnormality in FIG. 6, VS + = VS− before opening the switch, and the A / F detection voltage AFO is a lean-side abnormal value.

  When the switch circuit 35 is switched to the open state, a difference occurs in the voltage value between the VB short of the sensor terminals (S +, S−) and the short between the sensor terminals. That is, in the case of a VB short of the sensor terminal, the terminal voltages VS + and VS− are held at the maximum value (5V), and the A / F detection voltage AFO is also held at the lean side abnormal value (5V). On the other hand, in the case of a short circuit between the sensor terminals, each voltage value (VS +, VS−, AFO) changes to 2.2V. That is, when the switch circuit 35 is opened and the voltage application on the S + terminal side is cut off (opened), the terminal voltages VS + and VS− are the same as the reference voltage on the S− terminal side (terminal side where the switch is not opened). In addition to the voltage value (2.2 V), the A / F detection voltage AFO becomes a voltage value (2.2 V) equivalent to stoichiometry.

  In the present embodiment, when the abnormal form is different, the abnormal form is identified by utilizing the fact that each voltage value (VS +, VS−, AFO) is different before and after opening the switch circuit 35 as described above. Yes.

  Next, the abnormality detection process executed by the CPU 50 will be described with reference to the flowchart of FIG. The processing in FIG. 7 is repeatedly executed by the CPU 50 at a predetermined time period, for example.

  In FIG. 7, in step S11, it is determined whether or not an abnormality detection execution condition is satisfied. Specifically, the abnormality detection execution condition includes that the battery voltage is within a predetermined normal range (for example, 11 to 16 V), that the constant voltage and the ground potential that are the driving voltage of the CPU 50 are normally determined, etc. When all these conditions are satisfied, the process proceeds to the subsequent steps. In addition, it may be included in the execution condition that the sensor element 10 is in the active state.

  In step S12, it is determined whether or not the terminal voltage VS + and the terminal voltage VS− are at the same potential. At this time, it is actually determined whether or not the difference between VS + and VS− is equal to or less than a predetermined value (for example, 0.1 V). If not VS + ≈VS−, the process proceeds to step S13, and if VS + ≈VS−, the process proceeds to step S14. In step S12, in addition to the determination of VS + ≈VS−, it may be determined that both VS + and VS− are abnormal values (for example, an abnormal value on the high voltage side with respect to the normal value).

  In step S13, abnormality detection is executed with an abnormality form (abnormal form other than the above (2), (4), and (6)) that is negated in step S12 among various abnormalities in the sensor control system. At this time, as shown in FIG. 5, each abnormal form is specified by utilizing the fact that the abnormal value is different for each abnormal form. The abnormality detection in step S13 will be briefly described. For example, if each voltage value (VS +, VS−, AFO) is in the normal range but does not change after a predetermined time, it is determined that the sensor is disconnected. The Further, when any one of the terminal voltages VS + and VS− is fixed to 0V, it is determined that the sensor terminal is in a GND short-circuit.

  In step S14, it is determined whether or not the A / F detection voltage AFO is a lean-side abnormal value (4.7 V or higher). And if step S14 is YES, it will progress to subsequent step S15, and if it is NO, this process will be once complete | finished as it is. When a sensor terminal VB short or a short between sensor terminals (abnormalities (2), (4) and (6) above) has occurred with respect to the sensor element 10, VS + ≈VS− and AFO = lean side abnormal value This happens. Therefore, both steps S12 and S14 are YES, and the process proceeds to step S15.

  Steps S12 and S14 correspond to a pre-opening abnormality determination process for determining whether or not there is an abnormality related to the sensor element 10 (particularly, a VB short of sensor terminals or a short between sensor terminals) before the switch is opened. It should be noted that the pre-opening abnormality determination process can be performed by only one of steps S12 and S14.

  Incidentally, in the applied voltage control of the present embodiment, VS + ≈VS− can be obtained in normal operation. For example, at point X in FIG. 4, VS + ≈VS−. In such a case, step S12 is YES and step S14 is NO, and this process is terminated as it is without detecting abnormality after step S15.

  Thereafter, in step S15, the switch circuit 35 is opened, and voltage application from the applied voltage control circuit 21 to the S + terminal side is interrupted. In step S16, the terminal voltages VS + and VS− after the switch is opened are acquired. In subsequent step S17, it is determined whether or not the VS + value and the VS− value have changed from the values before the switch circuit 35 is opened. To do. Here, for example, it is determined whether the VS + value and the VS− value are 2.2V.

  In step S17, if the terminal voltages VS + and VS− have changed from the values before opening the switch, more specifically, the reference on the S− terminal side where the terminal voltages VS + and VS− are opposite to the switch circuit 35. If the voltage is 2.2 V, the process proceeds to step S18 to determine that a short circuit between the sensor terminals has occurred.

  If the terminal voltages VS + and VS− have not changed from the values before opening the switch (VS + and VS− are not 2.2V), the process proceeds to step S19, where the terminal voltage VS + is higher than 4.4V. It is determined whether or not it is an abnormal value. If VS +> 4.4V, the process proceeds to step S20, where it is determined that a VB short circuit of the sensor terminal has occurred. If VS + ≦ 4.4V, the process is terminated as it is, and abnormality detection is performed again.

  It should be noted that the final determination of the occurrence of an abnormality may be performed when a similar abnormality is detected a plurality of times in succession. At the final determination of occurrence of abnormality, measures such as turning on the failure warning lamp, storing abnormality information in the backup RAM, turning off the heater 19 of the A / F sensor, etc. are implemented. To be implemented.

  Incidentally, steps S16 to S20 can be changed as follows. That is, in step S16, the A / F detection voltage AFO after the switch is opened is acquired, and in subsequent step S17, it is determined whether or not the AFO value has changed from the value before the switch circuit 35 is opened. When step S17 is YES (for example, when AFO is changed to 2.2 V), the process proceeds to step S18, and it is determined that a short circuit between the sensor terminals has occurred. If step S17 is NO (if AFO ≠ 2.2V), the process proceeds to step S20, and it is determined that a VB short-circuit has occurred (step S19 is optional).

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  While temporarily switching the voltage application state to the sensor element 10, based on the A / F detection voltage AFO (element current detection value) or the terminal voltage VS +, VS− (terminal voltage detection value) before and after the switching, The abnormality related to the sensor element 10 is detected. Thereby, it is possible to distinguish between different abnormality forms, and it is possible to realize suitable abnormality detection.

  Specifically, the switching of the applied voltage state is performed by opening the switch circuit 35 provided in the voltage application path between the applied voltage control circuit 21 and the S + terminal of the sensor element 10, so that the sensor element by the applied voltage control circuit 21 is opened. The voltage application to 10 was temporarily cut off (opened). In this case, the difference between the terminal voltages VS + and VS− and the A / F detection voltage AFO before and after the switch is opened differs depending on whether the sensor terminal VB is short or between the sensor terminals. Become.

  As a method for switching the applied voltage state, by using a method for cutting off the voltage application to the sensor element 10, it is possible to protect the sensor when an abnormality occurs. That is, for example, when a VB short-circuit abnormality has occurred, by disconnecting the voltage application by opening the switch circuit 35, it is possible to avoid the disadvantage that a large current flows to the sensor element 10 for a long time and the element is broken.

  Further, based on the terminal voltages VS +, VS− and the A / F detection voltage AFO before the switch is opened (before the voltage application state is switched), it is determined whether there is an abnormality in the sensor terminal VB short and the sensor terminal short, When it is determined that there is an abnormality, the switch circuit 35 is opened, and an abnormal form is specified based on the terminal voltage VS +, VS− or the A / F detection voltage AFO after the opening. In such a case, the switch circuit 35 is opened on condition that it is determined that either a VB short circuit of the sensor terminals or a short circuit between the sensor terminals has occurred. In this configuration, the abnormality form can be specified more suitably by performing the two-stage abnormality detection process before and after opening the switch. Further, since the opening of the switch circuit 35 is limited to the case where it is determined that some abnormality has occurred, the implementation of the opening of the switch can be suppressed to the minimum necessary. Therefore, the influence on the gas concentration detection can be suppressed.

  The criterion for determining a short-circuit between sensor terminals is that the terminal voltages VS + and VS− on both the positive and negative sides are the same value, and the terminal voltage VS +, VS− or the A / F detection voltage AFO changed before and after the switch was opened. . Also, the criteria for determining whether the sensor terminal is VB short-circuited is that the terminal voltages VS + and VS− on both the positive and negative sides are the same value, and the A / F detection voltage AFO (VS +, VS− is acceptable) is outside the normal range. Further, the terminal voltage VS +, VS− or the A / F detection voltage AFO is not changed before and after the switch is opened. As described above, even if the terminal voltage VS +, VS− or the A / F detection voltage AFO exhibits the same abnormal value due to the VB short of the sensor terminal and the short between the sensor terminals, it is possible to specify each of the abnormal forms. Become.

  Of the terminals on both the positive and negative sides of the sensor element 10, a switch circuit 35 is provided on the terminal opposite to the shunt resistor 33 to block voltage application. Thereby, in the case where the switch circuit 35 is additionally provided in the sensor control IC (IC element), it is possible to avoid a great design change and complicated manufacturing. Supplementally, in the sensor control circuit 20, as described above, the shunt resistor 33 is externally attached to improve the detection accuracy of the element current IL, and the switch circuit 35 is provided on the same terminal as the shunt resistor 33. In the same way, the switch circuit 35 is also required to be externally attached or the connection port is added to the sensor control IC and the switch circuit 35 is integrally provided in the IC. Incurs complications. On the other hand, by providing the switch circuit 35 at the terminal opposite to the shunt resistor 33, such inconvenience can be avoided.

  Moreover, if it is a structure provided with the sensor control circuit 20 which has the characteristic structure as mentioned above, and the gas sensor (A / F sensor) which has the sensor element 10 and is connected to the sensor control circuit 20, suitable abnormality detection A sensor unit having a function can be realized.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. FIG. 8 is an electrical configuration diagram of the sensor control circuit in the present embodiment.

  In FIG. 8, the switch circuit 35 is deleted and the configuration of the applied voltage guard circuit 23 is partially changed with respect to the configuration of FIG. 1 described above. That is, in the upper limit guard circuit portion 27 of the applied voltage guard circuit 23, the reference voltage switching means is provided at the non-inverting input terminal (+ input terminal) of the operational amplifier 27a. The reference voltage switching means changes the + input voltage (reference voltage) of the operational amplifier 27a by switching between two reference power supplies. Specifically, two reference power supplies 61 and 62 that output different reference voltages V1 and V3 are provided, and the switch circuit 63 can switch which one is connected to the + input terminal of the operational amplifier 27a. ing. For example, V1> V3.

  In the above configuration, the reference power supply 61 is used as the reference power supply for the upper limit guard circuit unit 27 during normal application voltage control. On the other hand, when an abnormality is detected in the sensor control system, the switch circuit 63 is switched by a command signal from the CPU 50, and the reference power supply 61 is changed to the reference power supply 62. Thereby, the upper limit guard value of the applied voltage control circuit 21 is switched from 4.3V to 3V. A state where the upper limit guard value is 4.3 V corresponds to the “first state”, and a state where the upper limit guard value is 3 V corresponds to the “second state”.

FIG.
・ VB short of S + terminal,
・ VB short of S-terminal,
・ Short-circuit between sensor terminals,
For these abnormalities, VS +, VS−, and AFO before and after the switching of the reference voltage for setting the upper limit guard value of the applied voltage control circuit 21 are compared. Note that all numerical values are after sensor activation.

  In FIG. 9, when the reference voltage is V1, each voltage value (VS +, VS−, AFO) is the same as the voltage value described in FIG. Particularly referring to the short circuit between the sensor terminals, since the element current IL increases, the output voltage of the applied voltage control circuit 21 rises to the upper guard value (4.3 V), and the terminal voltages VS + and VS− are both 4 .3V. Further, the A / F detection voltage AFO becomes the maximum value (5.0 V), and becomes a lean side abnormal value (lean sticking).

  On the other hand, when the reference voltage is switched to V3, among the voltage values (VS +, VS−, AFO), the terminal voltages VS + and VS− for the short circuit between the sensor terminals are all changed to 3V. That is, by switching the reference voltage from V1 to V3 smaller than that, the upper limit guard value of the applied voltage control circuit 21 is switched from 4.3V to 3V, and the terminal voltages VS + and VS− are both 3V. The A / F detection voltage AFO is unchanged.

  When the upper limit guard value of the applied voltage control circuit 21 is changed to a voltage value smaller than 3V, the A / F detection voltage AFO changes to the decreasing side. For example, when the upper limit guard value of the applied voltage control circuit 21 is set to 2.2 V (the same voltage value as when stoichiometric detection is performed), the A / F detection voltage AFO changes to 2.2 V.

  In the abnormality detection process (FIG. 7), step S15 is changed to a process for switching the switch circuit 63 (that is, changing the upper limit guard value). Then, based on the terminal voltages VS + and VS− after the switch switching, it is determined whether or not a short circuit between the sensor terminals has occurred. In this case, as described with reference to FIG. 9, if the short circuit between the sensor terminals occurs, the terminal voltages VS + and VS− change before and after the switching. If it occurs, the terminal voltages VS + and VS− do not change before and after switching. This makes it possible to distinguish between a short between sensor terminals and a VB short between sensor terminals.

  As described above, according to the second embodiment, similar to the first embodiment, it is possible to distinguish between different abnormality forms, and it is possible to realize suitable abnormality detection.

  Further, specifically, the upper limit guard value of the applied voltage control circuit 21 is temporarily changed as switching of the applied voltage state. In this case, the difference between the terminal voltage VS +, VS− and the A / F detection voltage AFO before and after the change of the upper limit guard value is different between the sensor terminal VB short and the sensor terminal short. Is possible.

  When either the sensor terminal VB short circuit or the sensor terminal short circuit has occurred, the terminal voltages VS + and VS− have reached the upper limit guard value (4.3 V) of the applied voltage control circuit 21, and in this state, Since the upper limit guard value is changed to a lower voltage side than that, the change in the terminal voltages VS + and VS− after the change of the upper limit guard value can be clearly grasped.

(Third embodiment)
Next, a third embodiment of the present invention will be described focusing on differences from the first embodiment. FIG. 10 is an electrical configuration diagram of the sensor control circuit in the present embodiment.

  10, the switch circuit 35 is deleted and input voltage switching means for switching the voltage input value to the applied voltage control circuit 21 and the A / F signal output unit 41 is added to the configuration of FIG. 1 described above. ing. The voltage input value corresponds to each element current IL, and is a control input signal input to the applied voltage control circuit 21. The input voltage switching means uses the input voltage of the operational amplifier 25 a of the applied voltage control circuit 21 and the input voltage of the operational amplifier 43 of the A / F signal output unit 41 as the terminal voltage on the sensor element 10 side of the both terminal voltages of the shunt resistor 33. The voltage is switched to the voltage on the opposite side (AC power supply circuit 31 side). Specifically, the switching is performed by the switch circuit 65. The switch circuit 65 switches the connection points C and D. If the switch circuit 65 is connected to the C side, the input voltage becomes the sensor-side terminal voltage (point A voltage) of the shunt resistor 33. If the switch circuit 65 is connected to the D side, the input voltage becomes the non-sensor side terminal voltage of the shunt resistor 33.

  The applied voltage control circuit 21 feedback-controls the terminal applied voltage (VS + in this embodiment) of the sensor element 10 based on the element current IL. From this viewpoint, the control input signal is a feedback. Input signal. In this embodiment, the feedback input signal is forcibly changed.

  In the above configuration, during normal application voltage control, the switch circuit 65 is held in a state of being connected to the connection point C, and the application voltage control circuit 21 and the A / F signal output unit 41 include the sensor side terminals of the shunt resistor 33. A voltage (point A voltage) is input. On the other hand, when the switch circuit 65 is switched by the command signal of the CPU 50 and is changed to the state connected to the connection point D when an abnormality is detected in the sensor control system, the applied voltage control circuit 21 and the A / F signal output The anti-sensor side terminal voltage of the shunt resistor 33 is input to the unit 41. Thereby, for example, when the point A voltage (VS-voltage is the same) is held at the maximum value (5 V), the input voltage is switched to the AC value from the maximum value (5 V). The power supply circuit 31 is switched to the reference voltage (2.2 V). The state where the switch circuit 65 is connected to the connection point C corresponds to the “first state”, and the state where the switch circuit 65 is connected to the connection point D corresponds to the “second state”.

FIG.
・ VB short of S + terminal,
・ VB short of S-terminal,
・ Short-circuit between sensor terminals,
VS + and VS− before and after the switching when the input voltage of the applied voltage control circuit 21 and the A / F signal output unit 41 is switched (when the switch circuit 65 is connected to the C side / D side). , AFO. Note that all numerical values are after sensor activation.

  In FIG. 11, when the switch circuit 65 is connected to the C side, each voltage value (VS +, VS−, AFO) is the same as the voltage value described in FIG. Particularly referring to the short circuit between the sensor terminals, since the element current IL increases, the output voltage of the applied voltage control circuit 21 rises to the upper guard value (4.3 V), and the terminal voltages VS + and VS− are both 4 .3V. Further, the A / F detection voltage AFO becomes the maximum value (5.0 V), and becomes a lean side abnormal value (lean sticking).

  On the other hand, when the switch circuit 65 is switched to the D-side connection, among the voltage values (VS +, VS−, AFO), the terminal voltages VS + and VS− for the short circuit between the sensor terminals are all changed to 2.6V. The That is, the input voltage of the applied voltage control circuit 21 and the A / F signal output unit 41 is switched from the abnormal value (5 V) of the point A voltage (VS-voltage is the same) to the reference voltage (2.2 V) of the AC power supply circuit 31. As a result, the operational amplifier 25a of the applied voltage control circuit 21 is supplied with the same voltage as when stoichiometric detection (IL = 0), and the applied voltage control circuit 21 outputs 2.6V that is the applied voltage during stoichiometric detection. To do. Further, the same voltage (2.2V) is input to both the positive and negative input terminals of the operational amplifier 43 of the A / F signal output unit 41, and the A / F detection voltage AFO becomes 2.2V.

  In the abnormality detection process (FIG. 7), step S15 is changed to a process for switching the switch circuit 65 (that is, changing the voltage input value to the applied voltage control circuit 21). Then, based on the terminal voltages VS + and VS− after the switch switching, it is determined whether or not a short circuit between the sensor terminals has occurred. In this case, as described with reference to FIG. 11, the terminal voltages VS + and VS− change before and after the switching if the sensor terminal short circuit occurs, whereas the sensor terminal VB short circuit occurs instead of the sensor terminal short circuit. If it occurs, the terminal voltages VS + and VS− do not change before and after switching. This makes it possible to distinguish between a short between sensor terminals and a VB short between sensor terminals.

  As described above, according to the third embodiment, similar to the first embodiment, it is possible to distinguish between different abnormality forms, and it is possible to realize suitable abnormality detection.

  Further, specifically, the voltage input value (control input signal) for the applied voltage control circuit 21 is temporarily changed as switching of the applied voltage state. In this case, a difference occurs in changes in the terminal voltages VS + and VS− before and after the change of the voltage input value depending on the VB short of the sensor terminal and the short between the sensor terminals. Therefore, it is possible to specify each of these abnormalities.

  When the voltage input value to the applied voltage control circuit 21 is temporarily changed, the voltage input value is changed to a voltage value corresponding to the element current (IL = 0 mA) flowing in the air-fuel ratio stoichiometric state. As a result, after changing the voltage input value to the applied voltage control circuit 21, a short circuit between the sensor terminals occurs based on the fact that each voltage value (VS +, VS−, AFO) is the same voltage value as the stoichiometric detection state. Can be identified.

(Fourth embodiment)
In addition to performing abnormality detection based on the terminal voltages VS +, VS− and the A / F detection voltage AFO as described above, a configuration may be adopted in which abnormality detection is performed based on the impedance detection voltage Iout. Here, as described in the first embodiment, a configuration in which the switch circuit 35 (see FIG. 1) is opened when an abnormality is detected will be described.

FIG.
・ VB short of S + terminal,
・ VB short of S-terminal,
・ Short-circuit between sensor terminals,
1 is compared with Iout before and after opening when the switch circuit 35 of FIG. 1 is opened and voltage application by the applied voltage control circuit 21 is cut off (opened). Note that all numerical values are after sensor activation.

  When the sensor terminal (S +, S−) has a VB short-circuit, in the state where the switch circuit 35 is closed (the state before opening), even if an AC voltage is applied from the AC power supply circuit 31 for impedance detection. The voltage fluctuation hardly occurs on the S-terminal side which is the detection point of the impedance detection voltage. Therefore, the impedance detection voltage Iout is approximately 0V. This state is the same even after the switch circuit 35 is opened. In addition, after the sensor element 10 is activated, the impedance detection voltage Iout corresponding to the respective element impedance (approximately 30Ω) should be originally detected, and Iout = 0V is an abnormal value.

  On the other hand, when a short circuit occurs between the sensor terminals, the impedance detection voltage Iout becomes almost 0 V when the switch circuit 35 is closed (the state before opening), and when the switch circuit 35 is opened, the impedance detection voltage Iout Becomes 5V. This is due to the following reason.

  That is, in the circuit configuration of FIG. 1, the detection point (point A) of the impedance detection voltage Iout is an intermediate point voltage between the shunt resistor 33 and the sensor element 10 (the voltage dividing point of the shunt resistor 33 and the sensor element 10). At point A, the impedance detection voltage Iout is detected as a divided voltage by the shunt resistor 33 and the sensor element 10. In this case, if a short circuit between the sensor terminals occurs and the switch circuit 35 is closed, the element impedance is almost the same as 0Ω, and is detected as a divided voltage of the shunt resistor 33 and the sensor element 10. The detected impedance voltage Iout is approximately 0V (at this time, the S + terminal side is approximately 0V in terms of AC). Further, when a short circuit between the sensor terminals occurs and the switch circuit 35 is opened, the element impedance becomes infinite, which is detected as a divided voltage of the shunt resistor 33 and the sensor element 10. The impedance detection voltage Iout is about 5V.

  In the present embodiment, the CPU 50 executes the abnormality detection process shown in FIG. In FIG. 13, in step S21, it is determined whether or not an abnormality detection execution condition is satisfied (similar to S11 in FIG. 7). If the execution condition is satisfied, the process proceeds to subsequent step 22 to determine whether or not the impedance detection voltage Iout is an abnormal value. At this time, when an abnormality occurs, Iout becomes an abnormal value, and the processing after step S23 is performed. Here, if the abnormality form to be detected is limited to the VB short of the sensor terminals and the short between the sensor terminals, at least one of VS + ≈VS− and AFO = lean side abnormal value. It is recommended to set other conditions.

  Step S22 corresponds to an abnormality determination process before opening that determines whether or not there is an abnormality related to the sensor element 10 (particularly, VB short of sensor terminals or short between sensor terminals) before the switch is opened.

  Thereafter, in step S23, the switch circuit 35 is opened, and voltage application from the applied voltage control circuit 21 to the S + terminal side is interrupted. In step S24, the impedance detection voltage Iout after the switch is opened is acquired. In subsequent step S25, it is determined whether or not the impedance detection voltage Iout has changed from the value before the switch circuit 35 is opened.

  In step S25, if the impedance detection voltage Iout has changed from the value before opening the switch, more specifically, if the impedance detection voltage Iout has changed from 0V to 5V, the process proceeds to step S26, and the sensor terminals are short-circuited. It is determined that has occurred. If the impedance detection voltage Iout has not changed from the value before opening the switch (if Iout = 0V), the process proceeds to step S27, and it is determined that a sensor terminal VB short-circuit has occurred.

  As described above, according to the fourth embodiment, similar to the first embodiment, it is possible to distinguish between different abnormality forms, and it is possible to realize suitable abnormality detection.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described focusing on differences from the first embodiment. In the present embodiment, the structure of the sensor element of the A / F sensor is changed. First, the element structure will be described with reference to FIG.

  In FIG. 14, the sensor element 80 has two solid electrolyte layers 81, 82. A pair of electrodes 83, 84 are disposed opposite to one solid electrolyte layer 81, and the other solid electrolyte layer 82 is disposed on the other solid electrolyte layer 82. A pair of electrodes 85 and 86 are arranged to face each other. In addition, although the electrodes 83 to 85 are seen at two places on the left and right objects in the figure, they are the same member connected at any part of the front and back of the paper. In the present sensor element 80, the solid electrolyte layer 81 and the electrodes 83, 84 constitute a pump cell 91 as a first cell, and the solid electrolyte layer 82 and the electrodes 85, 86 constitute a monitor cell 92 as a second cell. Each of the electrodes 83 to 86 is connected to the sensor control circuit 100. The sensor element 80 has a laminated structure, which is the same as the sensor element 10 described above. In the figure, reference numeral 87 denotes a gas introduction hole, reference numeral 88 denotes a porous diffusion layer, reference numeral 89 denotes an air duct, and reference numeral 90 denotes a heater. The monitor cell 92 is generally called an electromotive force cell or an oxygen concentration detection cell.

  In the above configuration, the monitor cell 92 generates a binary (0 V or 0.9 V) electromotive force output depending on whether the exhaust gas is lean or rich with respect to the stoichiometry. For example, in the case of lean, the electromotive force output of the monitor cell 92 is reduced, and conversely, in the case of being rich, the electromotive force output of the monitor cell 92 is increased. In such a case, the applied voltage of the pump cell 91 is controlled so that the electromotive force output of the monitor cell 92 becomes the stoichiometric value (0.45 V).

  In the sensor element 80 configured as described above, the limit current region at the time of lean appears in the positive voltage region, and the limit current region at the time of rich appears in the negative voltage region. Therefore, the pump cell applied voltage at the time of lean is determined in the positive voltage range, and the pump cell applied voltage at the time of rich is determined in the negative voltage range.

  FIG. 15 is a circuit diagram showing a configuration of the sensor control circuit 100 applied to the sensor element 80 having the above configuration. In FIG. 15, VM is a common terminal of the pump cell 91 and the monitor cell 92, and the reference power supply 101 is connected to the common terminal VM. The reference voltage of the reference power supply 101 is, for example, 2.5V. IP is a pump cell terminal connected to the electrode 83 of the pump cell 91, and UN is a monitor cell terminal connected to the electrode 86 of the monitor cell 92. Each of these terminals IP and UN is provided with a voltage application circuit including an operational amplifier 102 and a shunt resistor 103. A monitor cell terminal UN is connected to an inverting input terminal (−input terminal) of the operational amplifier 102. A reference power source 104 that generates a reference voltage (3.0 V) is connected to the non-inverting input terminal (+ input terminal).

  The operational amplifier 102 constitutes an inverting amplifier circuit, and a pump cell 91 and a monitor cell 92 are provided in its feedback path. In this case, the operational amplifier 102 variably sets the applied voltage (IP terminal voltage) of the pump cell 91 according to the electromotive force of the monitor cell 92.

  Further, a switch circuit 105 as a path opening / closing means is provided between the pump cell terminal IP and the shunt resistor 103 (that is, the voltage application path of the pump cell 91). The switch circuit 105 is a normally closed switch that is normally closed and is opened based on a command signal from a CPU (not shown). In addition, a pull-up circuit 106 that uses a constant voltage Vcc (5 V) as a power source is connected to an inverting input terminal (−input terminal) of the operational amplifier 102. For example, the pull-up circuit 106 includes a resistor having a resistance value = 1 MΩ.

  When lean, a current flows through the shunt resistor 103 in the direction of B → A. Conversely, when rich, a current flows through the shunt resistor 103 in the direction of A → B. In such a case, the pump cell 91 is feedback-controlled so that the output voltage of the monitor cell 92 becomes a predetermined value (the feedback control circuit is well known, and illustration and detailed description thereof are omitted here).

  A differential amplifier circuit 107 constituting an A / F signal output unit is connected to both ends (point A and point B) of the shunt resistor 103. The differential amplifier circuit 107 has an operational amplifier 108 as an amplification element, and the voltage across the shunt resistor 103 is input to both positive and negative input terminals of the operational amplifier 108. The output of the differential amplifier circuit 107 (the operational amplifier 108) is an A / F detection voltage AFO. The voltage at the IP terminal is output as the pump cell terminal voltage Vip. The A / F detection voltage AFO and the pump cell terminal voltage Vip are respectively input to a CPU (not shown). In the present embodiment, the shunt resistor 103 and the differential amplifier circuit 107 constitute current detection means.

  Further, the element impedance is detected for the monitor cell 92, and the impedance detection circuit 109 changes the voltage applied to the monitor cell 92 in an alternating manner and detects the voltage waveform in response thereto. The detection result is output to the CPU (not shown) as the impedance detection voltage Vz.

In the sensor control circuit 100 described above, the pump cell terminal voltage Vip, the impedance detection voltage Vz, and the A / F detection are detected as abnormal forms such as VB short, GND short, disconnection, and short between terminals of the terminals UN, VM, and IP. Abnormality detection is performed based on the voltage AFO. However, in this embodiment, among the abnormal forms,
(1) UN-VM short circuit between terminals,
(2) VM terminal disconnection,
Only will be described.

  Here, it will be described that the pump cell terminal voltage Vip changes before and after the switch circuit 105 is opened when the abnormalities (1) and (2) occur.

  When the terminal-to-terminal short between (1) and UN-VM occurs, the pump cell terminal voltage Vip changes following the reference voltage (2.5 V) of the VM terminal before the switch circuit 105 is opened. 2.5V. At this time, the voltage values Vip, Vz, and AFO are all balanced at the same 2.5V. On the other hand, when the switch circuit 105 is switched to the open state, the voltage balance (balance) is lost. At this time, since the feedback loop of the applied voltage is interrupted by opening the switch, the comparator operation of the operational amplifier 102 is performed. Since the input voltage of the inverting input terminal of the operational amplifier 102 is 2.5V and the input voltage of the non-inverting input terminal is 3V, the operational amplifier output is 5V (upper limit) and the pump cell terminal voltage Vip is 5V. That is, when the switch circuit 105 is opened, the pump cell terminal voltage Vip changes from 2.5V to 5V.

  When the VM disconnection (2) occurs, both the UN terminal and the IP terminal become 3V due to the voltage feedback loop of the feedback path composed of the pump cell 91 and the monitor cell 92. On the other hand, when the switch circuit 105 is switched to the open state, the UN terminal is not controlled to 3V. The pull-up circuit 106 connected to the inverting input terminal of the operational amplifier 102 functions, and the negative input signal of the operational amplifier 102 becomes the Vcc voltage (5 V). At this time, since the + input signal of the operational amplifier 102 is 3V, the operational amplifier output becomes 0V (lower limit), and the pump cell terminal voltage Vip becomes 0V. That is, when the switch circuit 105 is opened, the pump cell terminal voltage Vip changes from 3V to 0V.

  As described above, the pump cell terminal voltage Vip changes before and after the opening of the switch circuit 105 in each abnormality of the terminal-to-terminal short between the UN and VM and the disconnection of the VM terminal, and the change modes thereof are different from each other. Therefore, the abnormal form can be specified.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the first embodiment, as shown in FIG. 1, the switch circuit 35 is provided on the S + terminal side (applied voltage control circuit 21 side) of the sensor element 10, and the switch circuit 35 is opened when an abnormality is detected. However, this may be changed, and the switch circuit 35 may be provided on the S-terminal side (AC power supply circuit 31 side) opposite to this, and the switch circuit 35 may be opened when an abnormality is detected. In this case, when the short circuit between the sensor terminals occurs, the terminal voltages VS + and VS− are changed from 4.3 V to 2.6 V as the switch circuit 35 is opened (that is, the applied voltage on the side opposite to the voltage cutoff side). To change. Thereby, a short circuit between the sensor terminals can be detected by a voltage change before and after the opening.

  In the sensor control circuit 20, a variable voltage (set voltage of the applied voltage control circuit 21) is applied to the S + terminal side, and a reference voltage (reference voltage of the AC power supply circuit 31: 2.2V) is applied to the S-terminal side. Although it was configured, it is possible to change this and apply a variable voltage to both the S + terminal side and the S− terminal side, or to apply a reference voltage to both the S + terminal side and the S− terminal side. Is possible.

  In the above embodiment, the AC power supply circuit 31 is used and the AC voltage is applied to one terminal of the sensor element 10. However, the AC power supply circuit 31 may not be used. For example, a reference voltage setting circuit that outputs a fixed reference voltage (2.2 V fixed) may be connected to the sensor terminal opposite to the applied voltage control circuit 21.

  A plurality of “second states” may be set, and the voltage application state may be switched to any one of the plurality of second states when an abnormality is detected. In this case, the values of the A / F detection voltage AFO and the terminal voltages VS + and VS− differ depending on which of the plurality of second states is switched to. Therefore, it is possible to increase identifiable (distinguishable) abnormal forms. For example, in the second embodiment, three or more upper limit guard values of the applied voltage control circuit 21 may be switched.

  When the voltage application state for the sensor element is switched from the first state to the second state, the amount of change in various detection values (AFO, VS +, VS−, Iout) before and after the state switching is calculated, and the amount of change is calculated It is good also as a structure which detects abnormality regarding a sensor element based on. Specifically, for example, it is determined that a short circuit between the sensor terminals has occurred based on the amount of change in various detection values before and after the state switching being greater than or equal to a predetermined value.

  In the above-described embodiment, as a method for acquiring the impedance detection value, the change amount of the A point voltage that amplitudes with the application of the AC voltage (sweep change of the applied voltage) by the AC power supply circuit 31 in the sensor control circuit 20 is determined as the impedance detection voltage. Although the configuration of detecting as Iout is adopted, this may be changed. Any known method may be used as a method for acquiring the impedance detection value, as long as the amount of change in voltage or current that occurs in response to the sweep change in voltage or current during impedance detection can be acquired as the impedance detection value. Good.

  When the voltage application state for the sensor element is switched from the first state to the second state, the offset value of the sensor control circuit 20 is calculated based on various detection voltages (VS +, VS−, AFO) before and after the state switching. It is good also as composition to do. The offset value is a steady output error in the sensor control circuit 20 of FIG. Specifically, for example, in the sensor control circuit 20 of FIG. 1, as described above, the switch circuit 35 is opened and the voltage application on the S + terminal side is cut off (opened), so that the terminal voltages VS + and VS− are inherently changed. The voltage value (2.2V) is the same as the reference voltage on the S-terminal side (terminal side where the switch is not opened), and the A / F detection voltage AFO has a voltage value (2.2V) equivalent to stoichiometry. In this case, if an offset error (deviation from the initial setting value) occurs in the sensor control circuit 20, the terminal voltages VS +, VS− and the A / F detection voltage AFO deviate from the initial setting values (2.2 V each). Therefore, the deviation from the initial setting value is calculated as an offset value. Then, correction (offset correction) of the A / F detection voltage AFO or the like is performed using this offset value.

  In addition to the A / F sensor whose oxygen concentration is a detection target, the present invention can also be applied to a gas sensor whose detection target is another gas concentration component. For example, a composite gas sensor has a plurality of cells formed of a solid electrolyte body. Among them, a first cell (pump cell) discharges or draws out oxygen in a gas to be detected and detects an oxygen concentration, In the two cells (sensor cell), the gas concentration of the specific component is detected from the gas after the oxygen is discharged. This gas sensor is embodied as a NOx sensor for detecting NOx concentration in exhaust gas, for example. Further, in addition to the first cell and the second cell, a gas sensor having a plurality of cells such as a third cell (monitor cell or second pump cell) for detecting a residual oxygen concentration after oxygen discharge may be used.

  -It is applicable also to the gas sensor which enables detection of HC concentration and CO concentration as a gas concentration component. In this case, surplus oxygen in the gas to be detected is discharged by the pump cell, and HC and CO are decomposed from the gas after the surplus oxygen is discharged by the sensor cell to detect the HC concentration and the CO concentration.

  The sensor control device of the present invention can be applied not only to a gas sensor (sensor element) used for a gasoline engine but also to a gas sensor (sensor element) used for another type of engine such as a diesel engine. It can be used as a sensor control device for applications other than automobiles, or a gas other than exhaust can be used as a gas to be detected.

  DESCRIPTION OF SYMBOLS 10 ... Sensor element, 11 ... Solid electrolyte layer (solid electrolyte body), 20 ... Sensor control circuit, 21 ... Applied voltage control circuit (voltage application means, applied voltage control means), 22 ... Variable setting circuit, 23 ... Applied voltage guard Circuit: 24: Reference power supply: 25: Non-inverting amplifier circuit: 25a: Operational amplifier: 27: Upper limit guard circuit unit: 31: AC power supply circuit (voltage applying means), 33: Shunt resistor (current detecting element, voltage current detecting means) , 35... Switch circuit (path opening / closing means), 41... A / F signal output section (voltage / current detection means), 42... Impedance signal output section (voltage / current detection means), 50. , Abnormality detection means), 63, 65... Switch circuit, 80... Sensor element, 81... Solid electrolyte layer (solid electrolyte body), 100. Means, abnormality detection means), 103 ... shunt resistor (current detecting element, the voltage current detection means), 105 ... switching circuit (path switching means).

Claims (14)

A solid electrolyte body is connected to a sensor element that flows an element current corresponding to the concentration of a predetermined component in a gas to be detected in a state where a voltage is applied, and detects the element current and gas concentration based on the detection result A sensor control device for calculating
Voltage current detection means for detecting at least one of a voltage and a current at a predetermined detection position in a current path through which the element current flows;
Switching means for switching the voltage application state to the sensor element from the first state to the second state;
An abnormality detecting means for detecting an abnormality relating to the sensor element based on a detection value by the voltage / current detection means before and after switching from the first state to the second state by the switching means;
A sensor control device comprising:   The abnormality detection means determines the presence or absence of an abnormality related to the sensor element based on a detection value by the voltage / current detection means before switching from the first state to the second state by the switching means, and by the abnormality determination The abnormality mode is specified based on a detection value obtained by the voltage / current detection unit after the switching when the switching unit switches from the first state to the second state when there is an abnormality. The sensor control apparatus according to 1. The first state is a normal state in which the element current is detected and a gas concentration is calculated based on the detected value.
The sensor control device according to claim 1, wherein the switching unit is configured to temporarily switch the voltage application state from the normal state to the second state different from the normal state.   The voltage / current detection means is a means for detecting the element current as an element current detection value by a current detection element, a means for detecting a terminal voltage of the sensor element as a terminal voltage detection value, and a voltage or current at the time of detecting an element impedance. The sensor control device according to any one of claims 1 to 3, further comprising at least one of means for detecting, as an impedance detection value, a change in voltage or current that occurs in response to a sweep change. Provided with being connected to at least one terminal of the sensor element, and comprising voltage applying means for applying a voltage to the terminal;
The switching unit is configured to switch from the first state to the second state by interrupting voltage application to the sensor element by the voltage applying unit,
5. The sensor control according to claim 1, wherein the abnormality detection unit performs abnormality detection based on a detection value by the voltage / current detection unit before and after the voltage application is cut off by the switching unit. apparatus. A path opening / closing means is provided in a voltage application path between the voltage applying means and the sensor element,
The sensor control apparatus according to claim 5, wherein the switching unit blocks voltage application to the sensor element by switching the path opening / closing unit from a closed state to an open state. Provided with an applied voltage control means that is connected to at least one terminal of the sensor element and variably sets a terminal applied voltage applied to the terminal based on the element current;
The applied voltage control means has an upper limit guard function for limiting the terminal applied voltage with a predetermined upper limit value,
The switching means is configured to switch from the first state to the second state by changing the upper limit value,
5. The sensor according to claim 1, wherein the abnormality detection unit performs abnormality detection based on detection values of the voltage / current detection unit before and after the upper limit value is changed by the switching unit. Control device.   The sensor according to claim 7, wherein the switching unit changes the upper limit value to a lower voltage side in a state where the terminal applied voltage set by the applied voltage control unit has reached the upper limit value. Control device. Provided with an applied voltage control means that is connected to at least one terminal of the sensor element and variably sets a terminal applied voltage applied to the terminal based on a control input signal corresponding to each element current;
The switching means performs switching from the first state to the second state by changing the control input signal input to the applied voltage control means,
5. The abnormality detection unit according to claim 1, wherein the abnormality detection unit performs abnormality detection based on detection values of the voltage / current detection unit before and after the change of the control input signal by the switching unit. Sensor control device.   The sensor control device according to claim 9, wherein the switching means switches the control input signal to an input signal corresponding to an element current flowing in an air-fuel ratio stoichiometric state.   The abnormality detection unit detects that a short circuit between terminals of the sensor element has occurred based on detection values by the voltage / current detection unit before and after switching of the voltage application state by the switching unit. The sensor control apparatus as described in any one of thru | or 10.   The abnormality detection means has the same terminal voltage detection value on both positive and negative sides of the sensor element, and when the detection value by the voltage / current detection means is changed in accordance with the switching of the voltage application state by the switching means. The sensor control device according to claim 11, wherein it is determined that a short circuit between the terminals has occurred.   The abnormality detection means has the same terminal voltage detection value on both positive and negative sides of the sensor element, the detection value by the voltage current detection means is a value outside the normal range, and further switches the voltage application state by the switching means. The sensor control according to any one of claims 1 to 12, wherein when the detection value by the voltage / current detection means does not change, it is determined that a power supply short-circuit has occurred at any of the terminals of the sensor element. apparatus.   A sensor unit comprising: the sensor control device according to claim 1; and a gas sensor having the sensor element and connected to the sensor control device.

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