JP4111169B2 - Gas concentration detector - Google Patents

Description

  The present invention relates to a gas concentration detection device, and more particularly to a technique capable of suitably detecting a short-circuit abnormality between terminals of a gas concentration sensor.

  For example, a limit current type air-fuel ratio sensor (so-called A / F sensor) is known that detects an oxygen concentration (air-fuel ratio) in an exhaust gas discharged from a vehicle engine as a detected gas. That is, the A / F sensor has a sensor element composed of a solid electrolyte body and a pair of electrodes provided on the solid electrolyte body, and an element current corresponding to the oxygen concentration each time a voltage is applied to the sensor element. Is configured to flow. The element current flowing in the sensor element is measured, and the oxygen concentration (air-fuel ratio) is detected from the measurement result.

  If any abnormality occurs in the A / F sensor, the device current cannot be accurately measured, and the oxygen concentration (air-fuel ratio) cannot be detected. Therefore, many techniques for detecting the occurrence of an abnormality in the A / F sensor have been proposed. For example, in the prior art disclosed in Patent Document 1, the element resistance of the A / F sensor is detected, and sensor abnormality detection is performed based on whether or not the element resistance is within a predetermined range. Alternatively, sensor abnormality detection is performed based on the sensor output when the fuel supply amount to the engine is increased or decreased.

However, in recent years, exhaust gas laws and regulations are becoming more and more severe, and it is demanded to detect an abnormality with higher accuracy and to specify details of an abnormal part. In this case, there is a problem that the existing abnormality detection method cannot meet the recent request. In particular, as one of the abnormal forms, when a short circuit occurs between the positive and negative terminals of the A / F sensor, there is no technology that can identify the abnormality.
JP-A-8-271475

  The main object of the present invention is to provide a gas concentration detection device that can identify an abnormal form of a gas concentration sensor, and in particular, can identify a short-circuit abnormality between both positive and negative terminals of the sensor.

  According to the first aspect of the present invention, the element current flowing through the sensor element is measured, and the terminal voltages at both the positive and negative connection terminals connected to the gas concentration sensor are measured. Since the terminal voltage measurement values of the connection terminals on both the positive and negative sides are the same value, the same terminal voltage measurement value is within the applied voltage control range, and the element current measurement value is an abnormal value. A short circuit abnormality is detected between the connection terminals.

  In short, when a short circuit abnormality occurs between the connection terminals on both the positive and negative sides, the element current excessively flows in the element current path for flowing the element current, so that the element current measurement value becomes an abnormal value. However, a voltage is appropriately applied to the gas concentration sensor even if there is a short circuit abnormality. In this case, the terminal voltages of the connection terminals on both the positive and negative sides are almost the same, and the value is within the applied voltage control range. Thereby, it is possible to specify an abnormal form of the gas concentration sensor, and in particular, to specify a short abnormality between the positive and negative terminals of the sensor.

  If a power supply short circuit or ground short circuit occurs at either the positive or negative connection terminal, the terminal voltage measurement value at both the positive and negative connection terminals is the same value and the element current measurement value is an abnormal value, as in the case of a short circuit between terminals. However, the terminal voltage measurement value sticks to the power supply voltage or the ground value, and does not fall within the applied voltage control range. Therefore, it is possible to differentiate from a power supply short circuit and a ground short circuit.

  Here, as described in claim 2, when determining that the measured terminal voltage value is within the applied voltage control range, the measured terminal voltage value is set to a value within the applied voltage control range at the time of lean gas detection. It is good to determine that

  In the inventions of the first and second aspects, as described in the third aspect, a threshold value is set so that at least the applied voltage control range and the other can be distinguished, and the measured terminal voltage value and the threshold value are set. It is preferable to determine that the measured terminal voltage value is within the applied voltage control range by comparing the magnitudes.

  In the invention according to claim 4, the element current flowing through the sensor element is measured, and the terminal voltages of the connection terminals on both the positive and negative sides are measured. Then, before the gas concentration sensor is activated, the terminal voltage measurement value on both the positive and negative connection terminals is the same value and the element current measurement value is an abnormal value, so a short circuit abnormality between the positive and negative connection terminals is detected. Is done.

  In short, when a short circuit abnormality occurs between the connection terminals on both the positive and negative sides, the element current excessively flows in the element current path for flowing the element current, so that the element current measurement value becomes an abnormal value. Further, since the internal resistance of the sensor element is infinite before the sensor is activated, the terminal voltages of the positive and negative connection terminals have different values except when a short circuit abnormality occurs between the connection terminals. Therefore, it is possible to identify the abnormal form of the gas concentration sensor, and in particular, to identify a short circuit abnormality between the positive and negative terminals of the sensor.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment embodying a gas concentration detection device of the present invention will be described with reference to the drawings. In the present embodiment, an air-fuel ratio detection device that detects an oxygen concentration (air-fuel ratio, hereinafter also referred to as A / F) in the same gas using exhaust gas (combustion gas) discharged from an on-vehicle engine as a detection gas is embodied. The air-fuel ratio 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 combustion control in which the air-fuel ratio is feedback-controlled in the vicinity of the stoichiometry, lean combustion control in which the air-fuel ratio is feedback-controlled in a predetermined lean region, and the like are appropriately realized.

  First, the configuration of an A / F sensor as a gas concentration sensor will be described with reference to FIG. The A / F sensor has a sensor element 10 having a laminated structure, and FIG. 2 shows a cross-sectional configuration of the sensor element 10. 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 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 10. The rectangular plate-shaped solid electrolyte 11 (solid electrolyte body) is a sheet made of partially stabilized zirconia, and a pair of upper and lower electrodes 15 and 16 are arranged opposite to each other with the solid electrolyte 11 interposed therebetween. The electrodes 15 and 16 are made of platinum Pt or the like. The diffusion resistance layer 12 is made of a porous sheet for introducing exhaust gas into the electrode 15, and the shielding layer 13 is made of a dense layer for suppressing permeation of the exhaust gas. Each of these layers 12 and 13 is formed by molding a ceramic such as alumina or zirconia by a sheet forming method or the like, but the gas permeability varies depending on the difference in the average pore diameter and porosity of the porosity.

  The insulating layer 14 is made of ceramics such as alumina or zirconia, and an air duct 17 is formed at a portion facing the electrode 16. In addition, a heater 18 made of platinum Pt or the like is embedded in the insulating layer 14. The heater 18 is a linear heating element that generates heat when energized by a battery power source, and heats the entire element by the generated heat. In the following description, in some cases, the electrode 15 is also referred to as a diffusion layer side electrode, and the electrode 16 is also referred to as an atmosphere side electrode. In the present embodiment, a terminal connected to the atmosphere side electrode 16 is a positive side terminal (+ terminal), and a terminal connected to the diffusion layer side electrode 15 is a negative side terminal (−terminal).

  In the sensor element 10, the surrounding exhaust gas is introduced from the side portion of the diffusion resistance layer 12 and reaches the diffusion layer side electrode 15. When the exhaust gas is lean, oxygen in the exhaust gas is decomposed by the diffusion layer side electrode 15 by applying a voltage between the electrodes 15 and 16, is ionized and passes through the solid electrolyte 11, and then is discharged from the atmosphere side electrode 16 to the atmosphere duct 17. Is done. At this time, a current (positive current) flows in the direction from the atmosphere side electrode 16 to the diffusion layer side electrode 15. On the other hand, when the exhaust gas is rich, oxygen in the atmosphere duct 17 is decomposed by the atmosphere side electrode 16, is ionized, passes through the solid electrolyte 11, and is then discharged from the diffusion layer side electrode 15. And it reacts with unburned components such as HC and CO in the exhaust gas. At this time, a current (negative current) flows in the direction from the diffusion layer side electrode 15 to the atmosphere side electrode 16.

  FIG. 3 is a drawing showing basic voltage-current characteristics (VI characteristics) of the A / F sensor. In FIG. 3, a flat portion parallel to the voltage axis (horizontal axis) is a limit current region for specifying the element current Ip (limit current) of the sensor element 10, and the increase / decrease in the element current Ip is the increase / decrease in the air / fuel ratio (that is, , Lean and rich). That is, the element current Ip increases as the air-fuel ratio becomes leaner, and the element current Ip decreases as the air-fuel ratio becomes richer.

  In this VI characteristic, the lower voltage side than the limit current region is a resistance dominant region, and the slope of the primary straight line portion in the resistance dominant region is specified by the DC internal resistance Ri of the sensor element 10. The DC internal resistance Ri changes according to the element temperature, and the DC internal resistance Ri increases as the element temperature decreases. That is, at this time, the slope of the primary straight line portion of the resistance dominating region becomes small (the straight line portion lies down). Further, when the element temperature rises, the DC internal resistance Ri decreases. That is, at this time, the slope of the primary straight line portion of the resistance dominating region becomes large (the straight line portion stands up). RG in the drawing represents an applied voltage characteristic (applied voltage line) for determining the applied voltage Vp to the sensor element 10.

  The A / F sensor is controlled by a sensor control unit provided in the engine ECU, and the configuration thereof will be described with reference to FIG.

  In the engine ECU 20, a reference power source 23 is connected to the + terminal T 1 connected to the atmosphere side electrode 16 of the sensor element 10 through an operational amplifier 21 and a current detection resistor 22 as shown in the figure. An applied voltage control circuit 25 is connected to the negative terminal T2 connected to the electrode 15. In this case, the point A at one end of the current detection resistor 22 is held at the same voltage as the reference voltage Ref1 (eg, 2.2 V). The element current Ip flows through the current detection resistor 22, and the voltage at the point B changes according to the element current Ip. When the exhaust gas is lean, the element current Ip flows from the + terminal T1 to the − terminal T2 in the sensor element 10, so that the voltage at the point B rises. Conversely, when the exhaust gas is rich, the sensor element 10 has the + Since the element current Ip flows toward the terminal T1, the B point voltage decreases.

  The applied voltage control circuit 25 monitors the point B voltage and determines the voltage to be applied to the sensor element 10 according to the voltage value. Basically, as shown in the applied voltage characteristic RG shown in FIG. Applied voltage control is performed so as to increase the applied voltage when the element current Ip increases (that is, when the B point voltage increases).

  Further, an operational amplifier (differential amplifier) 26 is connected to the point B and the reference power source 23 in the figure, and the output AFO of the operational amplifier 26 is taken into the A / D port AD1 of the CPU 30 as an A / F output voltage. The CPU 30 calculates an A / F value each time based on each A / F output voltage AFO fetched from the AD1. This A / F value is appropriately used for air-fuel ratio feedback control or the like.

  Further, the CPU 30 commands to temporarily change the applied voltage to the sensor element 10 in an alternating manner, and detects the element impedance Zac as the element internal resistance based on the current change amount at that time. More specifically, at the time of impedance detection, the applied voltage control circuit 25 receives a command from the CPU 30 and changes the applied voltage to the sensor element 10 on both the positive and negative sides with a predetermined width (for example, 0.2 V). At this time, as the sensor applied voltage changes, the B point voltage changes according to the element impedance each time. The voltage change at point B is monitored by the impedance current detection circuit 27, and the output Iout of the impedance current detection circuit 27 is taken into the A / D port AD2 of the CPU 30 as an impedance current signal. The impedance current detection circuit 27 is configured, for example, by connecting a high-pass filter and a peak hold circuit in series. By this high-pass filter and peak hold circuit, at a point B within a predetermined gate-on period corresponding to the impedance detection period. The amount of change in the alternating current is measured. The peak-held point B voltage is reset every time the gate is turned off.

  The CPU 30 calculates the element impedance Zac from the voltage change amount ΔV at the time of impedance detection and the accompanying change amount ΔIout of the impedance current signal. In the impedance detection, the current flowing through the sensor element 10 may be changed in an alternating manner, and the element impedance Zac may be calculated from the current or voltage response change amount.

  The impedance detection is performed every predetermined period (that is, every 128 msec, for example), and a voltage change is commanded from the CPU 30 to the applied voltage control circuit 25 every predetermined period. Further, the CPU 30 controls energization of the heater 18 so that the element impedance Zac is maintained at a predetermined target value. As a result, the temperature of the sensor element 10 is maintained at a predetermined target value (for example, 750 ° C.), and the active state of the sensor element 10 is maintained.

  1, the voltage at the T1 terminal (T1 terminal voltage VS +) is taken into the A / D port AD3 of the CPU 30, and the voltage at the T2 terminal (T2 terminal voltage VS−) is taken as the A / D port AD4 of the CPU 30. It is supposed to be taken in.

  In the present embodiment, regarding various abnormalities that occur in the A / F sensor, a configuration that can identify the abnormal form as well as detecting the abnormalities is adopted, and the details will be described below. . For such an abnormality detection, each measurement signal taken into AD1 to AD4 of the CPU 30 is used, and a sensor abnormality occurrence is detected and its abnormality form is specified depending on whether or not these measurement signals are the same as when normal. It has become.

  Here, the values of the A / F output voltage AFO, the change amount ΔIout of the impedance current signal, the T1 terminal voltage VS +, and the T2 terminal voltage VS− before and after the sensor activation will be described. In the present embodiment, the A / F output voltage AFO corresponds to the “element current measurement value”, and the T1 terminal voltage VS + and the T2 terminal voltage VS− correspond to the “terminal voltage measurement value”.

  FIG. 4 is a time chart showing changes in each measurement signal when the A / F sensor is normal. The timing t1 in FIG. 4 indicates the timing of sensor activation completion (for example, the timing at which the element impedance Zac reaches a predetermined activation determination value). The period before t1 is before activation and the period after t1 is after activation.

  In FIG. 4, before the sensor activation, the element impedance Zac is infinite (∞), and no current flows through the sensor element 10. Therefore, the A / F output voltage AFO is held at the same voltage (2.2 V) as the reference voltage Ref1. At this time, even if the applied voltage is changed in an alternating manner at the time of impedance detection, there is no change in the current response, and the change amount ΔIout of the impedance current signal remains zero. The T1 terminal voltage VS + is fixed at 2.2V, which is the same as the reference voltage Ref1, and the T2 terminal voltage VS− is held at a predetermined value (for example, 1.8V) based on the stoichiometric time.

  Then, when the sensor element temperature starts to gradually increase thereafter, the element impedance Zac decreases, and it is determined that sensor activation is completed when Zac reaches the activation determination value at timing t1. Since the element current flows as the sensor is activated, the A / F output voltage AFO converges to a value corresponding to the exhaust gas atmosphere each time. The figure exemplifies the case where the exhaust gas atmosphere is extremely lean (atmosphere), lean (for example, A / F = 18), stoichiometric, and rich (for example, A / F = 12). On the lean side, the A / F output voltage AFO increases on the lean side, and the A / F output voltage AFO decreases on the rich side. When A / F = 12 to the atmosphere is used as the A / F detection range, the A / F output voltage AFO changes in a range of approximately 1.6 to 4.1V.

  The change amount ΔIout of the impedance current signal changes as the element impedance Zac decreases (the sensor element temperature increases), and then converges to a predetermined value by reaching a predetermined active state.

  The T1 terminal voltage VS + is fixed at 2.2 V even after the sensor is activated, whereas the T2 terminal voltage VS− is controlled by the applied voltage control circuit 25 in accordance with the respective element current. In this case, since the sensor applied voltage is increased as the value becomes leaner, the T2 terminal voltage VS− decreases on the lean side and reaches T2 on the rich side, at a predetermined value (for example, 1.8 V) at the time of stoichiometry. The terminal voltage VS− increases.

When the A / F sensor is normal, AFO, ΔIout, VS +, and VS− change as the sensor is activated as shown in FIG. 4, whereas when the A / F sensor is abnormal, the AFO, ΔIout, The change in VS + and VS− is different from that in the normal state. Hereinafter, the abnormality of the A / F sensor is classified into the following (1) to (6) which are typical abnormality forms, and these will be described in order.
(1) Abnormal sensor disconnection (2) VB short of T1 terminal (sensor positive terminal) (3) GND short of T1 terminal (sensor positive terminal) (4) VB short of T2 terminal (sensor negative terminal) (5 ) GND short of T2 terminal (sensor negative side terminal) (6) Short between terminals between T1 and T2 Note that the above (1) is an abnormality caused by disconnection at either T1 or T2 terminal. (3) shows an abnormality in which a battery short and a ground short have occurred at the T1 terminal, (4) and (5) show an abnormality in which a battery short and a ground short have occurred at the T2 terminal, and (6) shows that T1, Each of the abnormalities in which the T2 terminals are short-circuited is indicated.

  The inventors of the present application measured AFO, ΔIout, VS +, and VS− at the time of each of the abnormalities (1) to (6). The measurement results are shown in FIG. 5, and specific numerical values of AFO, ΔIout, VS +, and VS− at the time of each abnormality (1) to (6) will be described with reference to FIG. The lowermost part of FIG. 5 shows normal values for comparison. On the right side of each numerical value, “×” is attached to those that can be determined as abnormal values, and “◯” is attached to the others. Note that the numerical values in FIG. 5 do not become transient values during sensor activation, the values before activation are immediately after the sensor is started (immediately after the engine is started), and the values after activation are the specified time (for example, 1 minute) after the sensor is activated. It is a numerical value measured when the degree) has elapsed.

(1) Abnormal sensor disconnection When an abnormal sensor disconnection occurs, the amount of change ΔIout of the impedance current signal remains 0 before / after sensor activation. In this case, ΔIout before the sensor activation is the same as the normal value, but ΔIout after the sensor activation is different from the normal value. This is the same when an abnormality occurs in (2) to (6) described later, and ΔIout is not touched when the following (2) to (6) are described.

  The A / F output voltage AFO remains unchanged at the reference voltage (2.2 V) through before / after sensor activation. In this case, the AFO before the sensor activation is the same as the normal value, and the AFO after the sensor activation is included in the AFO normal range (1.6 to 4.1 V). Further, the T1 terminal voltage VS + remains unchanged at the reference voltage (2.2V) before / after sensor activation, and the T2 terminal voltage VS− remains unchanged at a predetermined value (1.8V) before / after sensor activation. Become.

(2) VB short of T1 terminal (sensor positive side terminal) When a VB short occurs at T1 terminal, battery voltage VB (for example, 14V) is applied to the T1 terminal, so the A / F output voltage before / after sensor activation The AFO and T1 terminal voltage VS + are fixed at the output upper limit value (5.0 V) of the sensor control unit. In the circuit configuration of FIG. 1, when the T1 terminal is short-circuited by VB, both the point A voltage and the point B voltage of both terminals of the current detection resistor 22 rise. Thereby, AFO and VS + stick to 5.0V. The T2 terminal voltage VS− is held at a predetermined value (1.8V) before the sensor activation, whereas the element impedance Zac decreases after the sensor activation, so that the voltage rises in the same manner as the T1 terminal side. This is the output upper limit (5.0 V) of the sensor control unit.

(3) GND short of T1 terminal (sensor positive side terminal) When a GND short of T1 terminal occurs, the T1 terminal becomes the ground potential (0V), so the T1 terminal voltage VS + is 0V before / after sensor activation. It becomes. In this case, in the circuit configuration of FIG. 1, the point A voltage at one end of the current detection resistor 22 becomes 0V, and the operational amplifier 21 passes the maximum capability current to raise the point A voltage to the reference voltage (2.2V). B point voltage rises. Therefore, the A / F output voltage AFO becomes the output upper limit value (5.0 V) of the sensor control unit before / after sensor activation. The T2 terminal voltage VS− is held at a predetermined value (1.8V) before the sensor activation, whereas the B point voltage in FIG. 1 becomes 5.0V after the sensor activation. It is reduced excessively and becomes the output lower limit value (0.9 V) on the circuit configuration.

(4) VB short of T2 terminal (sensor negative side terminal) When VB short of T2 terminal occurs, battery voltage VB is applied to the T2 terminal, so that T2 terminal voltage VS− is sensor controlled before / after sensor activation. Output upper limit value (5.0V). At this time, since Zac = ∞ before the sensor activation, even if a VB short-circuit occurs on the T2 terminal side, the T1 terminal side is not affected, and the A / F output voltage AFO and the T1 terminal voltage VS + are the reference voltage (2. 2V). On the other hand, since the element impedance Zac decreases after the sensor is activated, the voltage increases on the T1 terminal side as well as on the T2 terminal side, and the A / F output voltage AFO and the T1 terminal voltage VS + are output upper limit values ( 5.0V).

(5) GND short of T2 terminal (sensor negative side terminal) When GND short of T2 terminal occurs, T2 terminal becomes ground potential, so T2 terminal voltage VS- is fixed at 0V before / after sensor activation. Is done. At this time, since Zac = ∞ before sensor activation, even if a GND short circuit occurs on the T2 terminal side, the T1 terminal side is not affected, and the A / F output voltage AFO and the T1 terminal voltage VS + are the reference voltage (2. 2V). In addition, after the sensor is activated, the T1 terminal voltage VS + can be held at the reference voltage (2.2V). However, in the state where VS + = 2.2V and VS− = 0V, the device current increases, and accordingly T1 The terminal voltage VS + becomes the output upper limit value (5.0 V) of the sensor control unit.

(6) Short-circuit between terminals between T1 and T2 When a short-circuit between terminals between T1 and T2 occurs, excessive current flows through the current detection resistor 22, so that the A / F output voltage AFO is the output upper limit value of the sensor control unit. (5.0V). This is the same both before and after sensor activation. In this case, when the voltage at point B in FIG. 1 increases, the applied voltage control circuit 25 controls the sensor applied voltage to the lean limit value. As a result, the T2 terminal voltage VS− becomes the lean limit value (1.1 V) within the applied voltage control range. Further, the T1 terminal voltage VS + is the same potential (1.1 V) as the T2 terminal voltage VS−.

  It should be noted that the value of VS + and VS− within the applied voltage control range when a short circuit between the terminals T1 and T2 occurs depends on the operational amplifier 21 on the T1 side and the operational amplifier on the T2 side (in the applied voltage control circuit 25). ) Due to the difference in current control capability from In the present embodiment, since the current control capability of the operational amplifier on the T2 side (the operational amplifier in the applied voltage control circuit 25) is superior, VS + and VS− are the control values (lean limit values: 1.1V). However, if the operational amplifier 21 on the T1 side wins, VS + and VS− have voltage values in the range up to 2.2V.

  As described above, when the sensor is abnormal, AFO, ΔIout, VS +, and VS− are different from normal values and have predetermined abnormal values according to the abnormality form. It is possible to specify the type of abnormality.

  In particular, in the present embodiment, (6) the short circuit between the terminals T1 and T2 is detected. Specifically, the CPU 30 follows the processing procedure of the flowchart shown in FIG. Detects short-circuit abnormality between terminals.

  In FIG. 6, in step S101, an abnormality detection execution condition is determined. Specifically, the abnormality detection execution condition is that the battery voltage is in a predetermined normal range (for example, 11 to 16 V), the heater power supply voltage is a predetermined value (for example, 11 V), and a constant voltage that is a driving voltage of the CPU 30. In addition, when all of these conditions are satisfied, including that the ground potential is normally determined, the process proceeds to the subsequent step.

  In step S102, it is determined whether or not the T1 terminal voltage VS + and the T2 terminal voltage VS− are at the same potential. In this case, it is actually determined whether or not the difference between VS + and VS− is equal to or less than a specified value (for example, 0.1 V). In step S103, it is determined whether or not the A / F output voltage AFO is an abnormal value (4.7 V or more).

  In step S104, it is determined whether or not the T2 terminal voltage VS− is an abnormal value (3 V or less). Here, the abnormality determination value (3V) used in step S104 is a threshold value for determining that the T2 terminal voltage VS− is within the applied voltage control range (particularly, within the applied voltage control range at the time of lean gas detection). In the case of the present embodiment, the determination value includes the lean side applied voltage control range (1.1 to 2.2 V) and the VS-value (5.0 V) when the T1 and T2 terminals are shorted to VB. Set between. In step S104, the T1 terminal voltage VS + can be used as a determination parameter instead of the T2 terminal voltage VS−. Note that the determination parameters (VS +, VS−, AFO) in steps S102 to S104 may be measured values before / after sensor activation.

  When all of Steps S102 to S104 are YES, the process proceeds to Step S105, and it is determined that a short circuit between the terminals T1 and T2 is abnormal. However, in this case, the final determination of the occurrence of an abnormality may be performed when a short-circuit abnormality between the terminals T1 and T2 is detected a predetermined number of times. At the final determination of the occurrence of abnormality, measures such as turning on the failure warning lamp, storing abnormality information in the backup RAM, turning off the heater 18 of the A / F sensor, etc. are implemented. To be implemented.

  For each of the abnormalities (1) to (5), it is possible to specify the abnormal type from the abnormal values shown in FIG. However, since it is not a gist in this embodiment, explanation is omitted.

  According to the present embodiment described in detail above, it is possible to preferably detect a short-circuit abnormality between terminals T1 and T2 without making a mistake with a VB short-circuit between the terminals T1 and T2. If the abnormal form can be specified, troubles such as ECU inspection, harness inspection, and sensor inspection can be saved greatly, and maintenance inspection becomes easy.

  In the circuit configuration of FIG. 1, the current detection resistor 22 is connected to the positive terminal (T1 terminal) of the sensor element 10 and the applied voltage control circuit 25 is connected to the negative terminal (T2 terminal). Change the configuration. For example, assume the circuit configuration of FIG. The circuit configuration in FIG. 7 is basically a configuration in which the configuration on the T1 terminal side and the configuration on the T2 terminal side of the sensor control unit are interchanged, and the difference will be mainly described.

  In the engine ECU 40, a reference power source 43 is connected to the T2 terminal via an operational amplifier 41 and a current detection resistor 42 as shown in the figure, and an applied voltage control circuit 45 is connected to the T2 terminal. In this case, the point A at one end of the current detection resistor 42 is held at the same voltage as the reference voltage (eg, 2.2 V) of the reference power supply 43. The element current Ip flows through the current detection resistor 42, and the voltage at the point B changes according to the element current Ip. When the exhaust gas is lean, the element current Ip flows from the T1 terminal to the T2 terminal in the sensor element 10, so that the voltage at the point B decreases. Since the element current Ip flows, the point B voltage rises.

  The applied voltage control circuit 45 monitors the point B voltage and determines the voltage to be applied to the sensor element 10 in accordance with the voltage value. Basically, as shown in the applied voltage characteristic RG shown in FIG. Applied voltage control is performed so as to increase the applied voltage when the element current Ip increases (that is, when the B point voltage decreases).

  Further, an operational amplifier (differential amplifier) 46 is connected to the point B in the figure and the reference power supply 43, and the output AFO of the operational amplifier 46 is taken into the A / D port AD1 of the CPU 50 as an A / F output voltage. The CPU 50 calculates an A / F value for each time based on each A / F output voltage AFO fetched from the AD 1. When detecting the impedance, the applied voltage control circuit 45 receives a command from the CPU 50 and changes the applied voltage to the sensor element 10 on both the positive and negative sides with a predetermined width (for example, 0.2 V). At this time, the voltage change at the point B accompanying the change in the sensor applied voltage is monitored by the impedance current detection circuit 47, and the output Iout of the impedance current detection circuit 47 is taken into the A / D port AD2 of the CPU 50 as an impedance current signal. .

  In addition, in the configuration of FIG. 7, the T1 terminal voltage VS + is taken into the A / D port AD3 of the CPU 50, and the T2 terminal voltage VS− is taken into the A / D port AD4 of the CPU 50.

FIG. 8 is a chart showing how AFO, ΔIout, VS +, and VS− are output when the abnormalities (1) to (6) occur in the circuit configuration of FIG. Since the contents are substantially the same as those in FIG. 5 described above, a detailed description is omitted. However, by using the relationship shown in FIG. 8, various abnormalities in the A / F sensor can be suitably detected as described above. Especially here
-The terminal voltages VS + and VS- of T1 and T2 are the same value,
-VS + or VS- becomes a value within the applied voltage control range,
The A / F output voltage AFO is an abnormal value,
To T1, T2 between terminals can be detected.

  As still another configuration of the sensor control unit, a configuration in which the current detection resistor 22 and the applied voltage control circuit 25 are both provided in one of the T1 terminal and the T2 terminal may be employed.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

In the above embodiment,
-The terminal voltages VS + and VS- of T1 and T2 are the same value,
-VS + or VS- becomes a value within the applied voltage control range,
The A / F output voltage AFO is an abnormal value,
The short-circuit abnormality between terminals T1 and T2 was detected, but this is changed as follows. That is,
Before the sensor activation, the terminal voltages VS + and VS− of T1 and T2 are the same value,
Similarly, the A / F output voltage AFO is an abnormal value before sensor activation.
To T1 and T2 between terminals is detected.

  In short, as can be seen from FIG. 5 or FIG. 8, when the short circuit between the terminals T1 and T2 is abnormal, the A / F output voltage AFO is an abnormal value and VS + = VS− before the sensor activation. This is an output pattern different from other abnormal forms, and a short-to-terminal abnormality between T1 and T2 can be specified from each abnormal form.

  The present invention can be applied not only to an A / F sensor having a 1-cell structure but also to an A / F sensor having a 2-cell or 3-cell structure. Further, the present invention can be applied not only to an A / F sensor having a stacked structure but also to an A / F sensor having a cup structure. The present invention can also be applied to a so-called O2 sensor in which an electromotive force is generated between the electrodes of the sensor element in accordance with the oxygen concentration in the exhaust gas.

  In addition to an A / F sensor whose oxygen concentration is a detection target, the present invention can be applied to a gas concentration sensor whose detection target is another component concentration. For example, a composite type gas concentration sensor has a plurality of cells formed of a solid electrolyte body, of which a pump cell discharges or draws oxygen in a detection gas introduced into the chamber and detects the oxygen concentration. In the sensor cell, the specific component concentration is detected from the gas after the oxygen is discharged. In addition, a gas concentration sensor having a monitor cell that outputs an electromotive force signal according to the residual oxygen concentration in the chamber may be used. This gas concentration sensor is embodied as, for example, a NOx sensor that detects the NOx concentration in the exhaust gas. By applying the present invention, it is possible to detect a sensor abnormality suitable for the NOx sensor.

  In addition to the gas concentration sensor capable of detecting the NOx concentration, the present invention can also be applied to a gas concentration sensor capable of detecting the HC concentration and the CO concentration as the specific component concentration. 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. Furthermore, it can be used for gas concentration detection devices other than those for automobiles, and gases other than exhaust gas can be used as gas to be detected.

It is a circuit diagram which shows the electrical structure of the sensor control part in engine ECU. It is sectional drawing which shows the structure of a sensor element. It is a figure which shows the output characteristic of an A / F sensor. It is a time chart which shows the change of the various signals of an A / F sensor. It is a figure which shows the measured value in each abnormal form of an A / F sensor. It is a flowchart which shows a sensor abnormality detection process. It is a circuit diagram which shows the electrical structure of the sensor control part in engine ECU. It is a figure which shows the measured value in each abnormal form of an A / F sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Sensor element, 11 ... Solid electrolyte, 15, 16 ... Electrode, 22 ... Current detection resistance, 30 ... CPU, 42 ... Current detection resistance, 50 ... CPU, T1 ... + terminal, T2 ...-terminal.

Claims (4)

Applied to a gas concentration sensor having a sensor element composed of a solid electrolyte body and at least a pair of electrodes, and a pair of electrodes arranged opposite to each other with the solid electrolyte body sandwiched in the sensor element via connection terminals on both positive and negative sides In a gas concentration detection device that is connected and applies a voltage to the sensor element and detects a gas concentration from an element current flowing along with the voltage application,
Element current measuring means for measuring element current flowing in the sensor element;
Terminal voltage measuring means for measuring terminal voltages of the connection terminals on both the positive and negative sides,
Since the terminal voltage measurement value of the connection terminal on both the positive and negative sides is the same value, the same terminal voltage measurement value is a value within the applied voltage control range, and the element current measurement value is an abnormal value. An abnormality detection means for detecting a short abnormality between the connection terminals;
A gas concentration detection device comprising: The abnormality detecting means, when determining that the terminal voltage measurement value becomes a value in the applied voltage control range, claim determines that the terminal voltage measurement value becomes a value of the applied voltage control within the limits during lean gas detection The gas concentration detection apparatus according to 1.   A threshold value is set so that at least the applied voltage control range can be distinguished from the others, and the abnormality detection means applies the terminal voltage measurement value by comparing the terminal voltage measurement value with the threshold value. The gas concentration detection device according to claim 1, wherein it is determined that the value is within a voltage control range. Applied to a gas concentration sensor having a sensor element composed of a solid electrolyte body and at least a pair of electrodes, and a pair of electrodes arranged opposite to each other with the solid electrolyte body sandwiched in the sensor element via connection terminals on both positive and negative sides In a gas concentration detection device that is connected and applies a voltage to the sensor element and detects a gas concentration from an element current flowing along with the voltage application,
Element current measuring means for measuring element current flowing in the sensor element;
Terminal voltage measuring means for measuring terminal voltages of the connection terminals on both the positive and negative sides,
Prior to activation of the gas concentration sensor, the terminal voltage measurement values of the connection terminals on both the positive and negative sides are the same value and the element current measurement value is an abnormal value, so that a short abnormality between the connection terminals on both the positive and negative sides is detected. Anomaly detection means to
A gas concentration detection device comprising:

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