JP2009042242A - Control device for gas concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately control a gas concentration by detected element resistance. <P>SOLUTION: An oxygen concentration sensor, as an example of the gas concentration sensor, can suppress a processing load of a micro computer by smoothing so as to execute other element resistance detection processing and element heater control processing at different processing timings with a reference of oxygen concentration detection processing which is necessary to be executed at the fastest processing timing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a gas concentration sensor, for example, when detecting or using an element resistance using a gas concentration sensor for detecting a gas concentration in exhaust gas of an on-vehicle internal combustion engine. .

  2. Description of the Related Art In recent years, for example, an oxygen concentration sensor control device for detecting an oxygen concentration has been proposed as a gas concentration sensor using a gas concentration sensor for detecting a gas concentration, including application to automobiles.

  In recent air-fuel ratio control of in-vehicle internal combustion engines, for example, there is a demand for improving control accuracy and a demand for lean burn, and in order to meet these demands, the air-fuel ratio of the air-fuel mixture sucked into the internal combustion engine A linear air-fuel ratio sensor (oxygen concentration sensor) that detects (A / F: calculated corresponding to the oxygen concentration in the exhaust gas) in a wide area and linearly is embodied. In such an air-fuel ratio sensor, it is indispensable to keep the air-fuel ratio sensor in an active state in order to maintain this detection accuracy. In general, the sensor element (empty sensor) is controlled by energizing the heater attached to the air-fuel ratio sensor. The element of the fuel ratio sensor is heated to maintain the active state.

  By the way, in the energization control of such a heater, a technique for detecting the temperature of the sensor element (element temperature) and performing feedback control so that the element temperature becomes a desired activation temperature (for example, about 700 ° C.) has been conventionally used. More disclosed. In this case, in order to detect the element temperature at that time, it is conceivable to attach a temperature sensor to the sensor element and derive it from the detection result. However, this increases the cost because it is necessary to add the temperature sensor. Therefore, it has been proposed to detect the element resistance using the fact that the resistance of the sensor element (element resistance) has a predetermined correspondence with the element temperature, and to derive the element temperature from the detected element resistance. . The element resistance detection result is also used, for example, for determining the degree of deterioration of the air-fuel ratio sensor.

  FIG. 34 is a waveform diagram for explaining element resistance detection that has been used conventionally, and shows an example in which a limiting current type oxygen concentration sensor is used as an air-fuel ratio sensor for controlling an internal combustion engine. That is, before time t011 in FIG. 34, a predetermined voltage (positive applied voltage Vpos) for air-fuel ratio detection is applied to the sensor element, and the air-fuel ratio (from the sensor current Ipos output corresponding to the applied voltage Vpos) A / F) is required. Further, at time t011 to t012, a negative applied voltage Vneg for detecting element resistance is applied, and the sensor current Ineg at that time is detected. Then, the element resistance (element impedance) ZDC is obtained by dividing the negative applied voltage Vneg by the sensor current Ineg at that time (ZDC = Vneg / Ineg). The above method is generally known as a method for detecting element resistance using the DC characteristics of an air-fuel ratio sensor.

  In the prior art, a DC voltage is applied to the sensor element to detect element resistance (DC impedance). On the other hand, Japanese Patent Publication No. 4-24657 applies an AC voltage to the sensor element to detect the element resistance. A technique for detecting resistance (AC impedance) is disclosed. In such a technique, AC is continuously applied to the air-fuel ratio sensor, the sensor output is passed through a low-pass filter (LPF) to detect the air-fuel ratio, and the sensor output is also averaged after passing through the high-pass filter (HPF). The AC impedance is detected. The above-described method is generally known as a method for detecting element resistance using the AC characteristics of an air-fuel ratio sensor.

  By the way, in the case of an oxygen concentration sensor as a gas concentration sensor, for example, according to the above-described DC impedance method, the sensor current Ineg when applying a square wave negative voltage application Vneg is steep as shown in FIG. In this case, there is a problem that if the oxygen concentration is detected, the true oxygen concentration cannot be detected.

  Further, for example, in the case of an oxygen concentration sensor as a gas concentration sensor, according to the AC impedance method disclosed in Japanese Examined Patent Publication No. 4-24657, the sensor output is passed through a low-pass filter to detect the air-fuel ratio. Phase lag occurs, and AC noise is easily superimposed on the air-fuel ratio output. In particular, the above problem is remarkable when the operating state of the internal combustion engine is in a transient state.

  In the microcomputer, as the gas concentration sensor, for example, the more the processing executed at the same timing among the air-fuel ratio detection processing, the element resistance detection processing, and the element heater control processing for the oxygen concentration sensor, the processing load of this time As a result, the processing time exceeds the processing cycle and the next processing timing is shifted.

  Furthermore, for example, in the case of an oxygen concentration sensor as a gas concentration sensor, there is a problem that when the element resistance is detected, the sensor signal is a minute signal, so that the obtained element resistance value is greatly different from the true value when noise is superimposed. .

  In addition, for example, in the case of an oxygen concentration sensor as a gas concentration sensor, there is a problem in that, when noise is superimposed on the sensor signal when the element resistance is detected and a voltage to be applied is selected for map selection, the map selection becomes unstable.

  Accordingly, the present invention has been made to solve such a problem, and an object thereof is to provide a control device for a gas concentration sensor capable of performing accurate gas concentration control based on the detected element resistance.

  According to the control device for the gas concentration sensor of the first aspect, the control device for the gas concentration sensor outputs a signal corresponding to the gas concentration in the gas to be detected. The control device is used in the air-fuel ratio detection device. Smoothing is performed so that other processes can be executed at different process timings based on the process that needs to be executed at the earliest process timing.

  According to the gas concentration sensor control device of claim 2, the gas concentration sensor control device outputs a signal corresponding to the gas concentration in the gas to be detected, and the gas concentration sensor controls the gas based on a voltage change and a current change. The execution timing of the process for detecting the element resistance of the concentration sensor and the process for increasing the temperature of the gas concentration sensor are distributed.

  As described above, according to the control device of the gas concentration sensor of the first or second aspect, for example, in the case of an oxygen concentration sensor as the gas concentration sensor, the execution timings of a plurality of processes are distributed. Can reduce the processing load.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the sensor current is changed by changing the applied voltage in order to detect the element resistance. Since the signal also changes, the oxygen concentration signal at this time is not a true oxygen concentration signal. Therefore, when detecting the element resistance using the oxygen concentration sensor, the current change in the oxygen concentration sensor is interrupted, and the oxygen concentration signal before the voltage change is held for detecting the element resistance. As a result, when the element resistance is detected, since the oxygen concentration signal before the element resistance detection timing is held, an erroneous oxygen concentration signal is prevented from being used.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the sensor current is changed by changing the applied voltage in order to detect the element resistance. Since the signal also changes, the oxygen concentration signal at this time is not a true oxygen concentration signal. Therefore, when the element resistance is detected using the oxygen concentration sensor, the use of the oxygen concentration signal is prohibited. Thereby, since the use of the oxygen concentration signal is prohibited at the time of detecting the element resistance, it is possible to prevent an erroneous oxygen concentration signal from being used.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the sensor current is changed by changing the applied voltage in order to detect the element resistance. Since the signal also changes, the oxygen concentration signal at this time is not a true oxygen concentration signal. Therefore, when detecting the element resistance using the oxygen concentration sensor, the current change in the oxygen concentration sensor is cut off, and the oxygen concentration signal before the voltage change is held for detecting the element resistance, and matches the actual oxygen concentration signal. The use of oxygen concentration signals during this period is prohibited. As a result, when the element resistance is detected, the oxygen concentration signal is retained before the element resistance detection timing, and the use of the oxygen concentration signal during element resistance detection is prohibited in consideration of the smoothing of the signal by a low-pass filter or the like. As a result, an erroneous oxygen concentration signal is prevented from being used.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the change in element resistance is limited to an allowable range of change, and the execution range of control by the oxygen concentration sensor is limited. Can be within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Is greatly different from That is, the element resistance change of the oxygen concentration sensor is limited to a predetermined amount of change, so that it does not deviate from the normal control range. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  In the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor as the gas concentration sensor, the element resistance can be rounded by an appropriate variation amount allowable range according to the element use state. For this reason, it is possible to execute stable control on the oxygen concentration sensor by changing the change amount limit of the element resistance based on a predetermined condition.

  Further, in the gas concentration sensor control device, for example, in the case of an oxygen concentration sensor, the oxygen concentration sensor is required to change the element resistance change amount limit during and after the temperature increase. Stable control can be executed while realizing early activation.

  Further, according to the control device of the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the change in element resistance is limited to an allowable range of change, and the execution range of control by the oxygen concentration sensor is limited. Can be within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Is greatly different from That is, by passing the low-pass filter having sufficient response to the element resistance change of the oxygen concentration sensor, the element resistance change can be prevented from deviating from the normal control range. Further, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  Further, in the gas concentration sensor control apparatus, for example, in the case of an oxygen concentration sensor as the gas concentration sensor, a low-pass filter is used so that the element resistance has sufficient responsiveness to a normal element resistance change according to the element use state. Change the cutoff frequency. That is, the cutoff frequency of the low-pass filter that is passed through the element resistance detection is changed based on a predetermined condition. Thereby, stable control can be executed on the oxygen concentration sensor.

  In the gas concentration sensor control device, for example, in the case of an oxygen concentration sensor, a low-pass filter having sufficient responsiveness to a change in element resistance during temperature rise and an element after completion of temperature rise of the oxygen concentration sensor By switching a low-pass filter that has sufficient responsiveness to resistance changes during and after temperature rise, stable control can be executed while realizing early activation required for oxygen concentration sensors. it can.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the change in element resistance is limited to an allowable range of change, and the oxygen concentration is low pass filtered. The execution range of the control by the sensor can be kept within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Is greatly different from That is, the element resistance change of the oxygen concentration sensor is limited to a predetermined range of change amount, and low-pass filter processing with sufficient response to the element resistance change can be performed so as not to deviate from the normal control range. . And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  Further, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, a plurality of element resistance values are averaged and the influence of abnormal data is suppressed, so that the control by the oxygen concentration sensor is executed. The range can be kept within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Is greatly different from That is, by averaging a plurality of element resistance values of the oxygen concentration sensor, it is possible not to deviate from the normal control range. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  Also, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the voltage applied to the oxygen concentration sensor when detecting the oxygen concentration changes based on a map using the element resistance as a parameter. However, since the map is fixed as the change in the element resistance is small after the temperature rise is completed, the voltage range applied to the oxygen concentration sensor can be kept within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and the oxygen concentration detection value from being different from the true value. That is, after the temperature rise is finished, a large element resistance change of the oxygen concentration sensor is ignored, so that it does not deviate from the normal control range.

  Also, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the voltage applied to the oxygen concentration sensor when detecting the oxygen concentration changes based on a map using the element resistance as a parameter. However, when selecting this map, the oxygen resistance sensor element resistance gradually decreases as the temperature rises, so that the map selection is not reversed depending on the direction of the element resistance change. The execution range of control by the density sensor can be kept within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and different from the detected oxygen concentration value. In other words, a large element resistance change of the oxygen concentration sensor is ignored, so that it does not deviate from the normal control range.

  Also, according to the control device for the gas concentration sensor, for example, in the case of an oxygen concentration sensor, the voltage applied to the oxygen concentration sensor when detecting the oxygen concentration changes based on a map using the element resistance as a parameter. However, when selecting this map, the element resistance of the oxygen concentration sensor gradually decreases as the temperature rises, so that the map selection is not reversed depending on the direction of change in the element resistance. After completion, the map is fixed on the assumption that the change in element resistance is small, so that the execution range of the control by the oxygen concentration sensor can be kept within the normal range. In other words, when the element resistance of the oxygen concentration sensor is detected, the sensor signal is a minute signal, for example, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc., and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and the oxygen concentration detection value from being different from the true value. That is, the direction of change in element resistance is taken into account during the temperature rise of the oxygen concentration sensor, and a large change in element resistance is ignored after the temperature rise is finished, so that it does not deviate from the normal control range.

Hereinafter, embodiments of the present invention will be described based on examples. In the following embodiments, a specific oxygen concentration sensor control apparatus using an oxygen concentration sensor for detecting the oxygen concentration will be described as a gas concentration sensor for detecting the gas concentration.
<Reference Example 1>
FIG. 1 is a schematic diagram showing a configuration of an air-fuel ratio detection device to which an oxygen concentration sensor control device according to a first example of the embodiment is applied. The air-fuel ratio detection device in this embodiment is employed in an electronically controlled fuel injection system for an internal combustion engine (gasoline engine) mounted on an automobile, and the fuel injection supplied to the internal combustion engine based on the detection result by the air-fuel ratio detection device. Increase or decrease the amount to control to the desired air / fuel ratio. Hereinafter, the air-fuel ratio (A / F) detection procedure using the air-fuel ratio sensor and the element resistance detection procedure using the AC characteristics of the air-fuel ratio sensor will be described in detail.

  In FIG. 1, the air-fuel ratio detection device includes a limiting current type air-fuel ratio sensor (hereinafter referred to as “A / F sensor”) 30 as an oxygen concentration sensor, and this A / F sensor 30 is located downstream of the internal combustion engine 10. The exhaust passage 12 is connected to the exhaust passage 12. The A / F sensor 30 outputs a linear air-fuel ratio detection signal corresponding to the oxygen concentration in the exhaust gas in accordance with the application of a voltage commanded from a microcomputer (hereinafter referred to as “microcomputer”) 20. The microcomputer 20 includes a CPU as a central processing unit that executes various known arithmetic processes, a ROM that stores a control program, a RAM that stores various data, a B / U (backup) RAM, and the like, according to a predetermined control program. A bias control circuit 40, a heater control circuit 60, a sample hold circuit (hereinafter referred to as “S / H circuit”) 70, and an oxygen concentration signal detection permission / prohibition signal, which will be described later, are controlled.

FIG. 2 is a cross-sectional view showing a schematic configuration of the A / F sensor 30. In FIG. 2, the A / F sensor 30 protrudes toward the inside of the exhaust passage 12, and the A / F sensor 30 mainly includes a cover 33, a sensor main body 32, and a heater 31. The cover 33 has a U-shaped cross section, and a plurality of small holes 33 a communicating with the inside and outside of the cover 33 are formed on the peripheral wall thereof. The sensor main body 32 as the sensor element unit has an oxygen concentration in the air-fuel ratio lean region or a gas concentration of carbon monoxide (CO), hydrocarbon (HC), hydrogen (H ₂ ), etc. as an unburned gas in the air-fuel ratio rich region. A limit current corresponding to is generated.

Next, the configuration of the sensor body 32 will be described in detail. In the sensor body 32, an exhaust gas side electrode layer 36 is fixed to the outer surface of the solid electrolyte layer 34 formed in a cup shape in cross section, and an atmosphere side electrode layer 37 is fixed to the inner surface. A diffusion resistance layer 35 is formed outside the exhaust gas side electrode layer 36 by plasma spraying or the like. The solid electrolyte layer 34 is made of an oxygen ion conductive oxide sintered in which CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ or the like is dissolved in ZrO ₂ , HfO ₂ , ThO ₂ , Bi ₂ O ₃ or the like as a stabilizer. The diffusion resistance layer 35 is composed of a heat-resistant inorganic substance such as alumina, magnesia, siliceous material, spinel, mullite or the like. Both the exhaust gas side electrode layer 36 and the atmosphere side electrode layer 37 are made of a noble metal with high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. The area of the exhaust gas side electrode layer 36 is 10 to 100 mm ² and the thickness is about 0.5 to 2.0 μm, while the area of the atmosphere side electrode layer 37 is 10 mm ² or more and the thickness is 0.00. It is about 5 to 2.0 μm.

  The heater 31 is accommodated in the atmosphere-side electrode layer 37, and heats the sensor body 32 (the atmosphere-side electrode layer 37, the solid electrode layer 34, the exhaust gas-side electrode layer 36, and the diffusion resistance layer 35) by the generated heat energy. . The heater 31 has a heat generation capacity sufficient to activate the sensor body 32.

  In the A / F sensor 30 configured as described above, the sensor main body 32 generates a limit current corresponding to the oxygen concentration in the lean region from the theoretical air-fuel ratio point. In this case, the limit current corresponding to the oxygen concentration is determined by the area of the exhaust gas side electrode layer 36, the thickness of the diffusion resistance layer 35, the porosity, and the average pore diameter. The sensor main body 32 can detect the oxygen concentration with a linear characteristic, and a high temperature of about 600 ° C. or higher is required to activate the sensor main body 32. Since the active temperature range is narrow, the element temperature cannot be controlled in the active region by heating only the exhaust gas of the internal combustion engine 10. For this reason, in the present embodiment, the sensor body 32 is heated to the active temperature range by controlling the duty ratio of the power supplied to the heater 31. In the region on the richer side than the stoichiometric air-fuel ratio, the concentration of unburned gas such as carbon monoxide (CO) changes almost linearly with respect to the air-fuel ratio, and the sensor body 32 has carbon monoxide (CO) etc. A limiting current is generated according to the concentration of.

  Next, voltage-current characteristics (VI characteristics) of the A / F sensor 30 will be described with reference to the table of FIG.

  According to FIG. 3, it can be seen that the inflow current to the solid electrolyte layer 34 of the sensor body 32 and the applied voltage that are proportional to the detection A / F of the A / F sensor 30 have a linear characteristic. The straight line parallel to the voltage axis V is a limit current detection area for specifying the limit current of the sensor body 32, and the increase / decrease in the limit current (sensor current) corresponds to the increase / decrease in A / F (ie, lean / rich). is doing. That is, the limit current increases as A / F becomes leaner, and the limit current decreases as A / F becomes richer.

  Further, in the voltage-current characteristic of FIG. 3, a voltage region smaller than a linear portion (limit current detection region) parallel to the voltage axis V is a resistance dominant region, and the slope of the primary linear portion in this resistance dominant region is The element resistance (element impedance) ZDC, which is the internal resistance of the solid electrolyte layer 34 in the sensor body 32, is specified. This element resistance ZDC changes with temperature change, and when the temperature of the sensor body 32 decreases, the inclination of the element resistance ZDC decreases due to an increase in the element resistance ZDC.

  On the other hand, in FIG. 1, a bias command signal (digital signal) Vr for applying a voltage to the A / F sensor 30 is input from the microcomputer 20 to the D / A converter 21, and the D / A converter 21 performs analog processing. After being converted to the signal Vb, it is input to an LPF (low-pass filter) 22. The output voltage Vc from which the high-frequency component of the analog signal Vb has been removed by the LPF 22 is input to the bias control circuit 40. From the bias control circuit 40, either the A / F detection voltage or the element resistance detection voltage is applied to the A / F sensor 30. That is, when the A / F is detected from the bias control circuit 40 to the A / F sensor 30, a predetermined voltage Vp corresponding to the A / F at this time is applied using the characteristic line L1 shown in FIG. At the time of resistance detection, a voltage having a predetermined time constant consisting of a predetermined frequency signal is applied.

  Further, the bias control circuit 40 detects a current value flowing along with the application of the voltage to the A / F sensor 30 by the current detection circuit 50, and an analog signal of the current value detected by the current detection circuit 50 is A It is input to the microcomputer 20 via the / D converter 23. The current value detected by the current detection circuit 50 is converted into an oxygen concentration signal and output as an A / F (oxygen concentration) signal via the sample hold circuit 70 and the LPF (low-pass filter) 71. A detailed electrical configuration of the bias control circuit 40 will be described later. The operation of the heater 31 attached to the A / F sensor 30 is controlled by the heater control circuit 60. That is, the heater control circuit 60 performs duty ratio control on the power supplied from the battery power source (not shown) to the heater 31 in accordance with the element temperature of the A / F sensor 30 and the heater temperature, so that the heating control of the heater 31 is executed. Is done.

  Next, the electrical configuration of the bias control circuit 40 will be described based on the circuit diagram of FIG.

  In FIG. 4, the bias control circuit 40 is roughly divided into a reference voltage circuit 44, a first voltage supply circuit 45, a second voltage supply circuit 47, and a current detection circuit 50. In the reference voltage circuit 44, the constant voltage Vcc is divided by the voltage dividing resistors 44a and 44b to generate a constant reference voltage Va.

  The first voltage supply circuit 45 is configured by a voltage follower circuit, and the same voltage Va as the reference voltage Va of the reference voltage circuit 44 is supplied from the first voltage supply circuit 45 to one terminal 42 of the A / F sensor 30. The More specifically, an operational amplifier 45a having a positive input terminal connected to a voltage dividing point of each of the voltage dividing resistors 44a and 44b and a negative input terminal connected to one terminal 42 of the A / F sensor 30; The resistor 45b has one end connected to the output terminal of the operational amplifier 45a, and an NPN transistor 45c and a PNP transistor 45d each having a base connected to the other end of the resistor 45b. The collector of the NPN transistor 45 c is connected to the constant voltage Vcc, and the emitter is connected to one terminal 42 of the A / F sensor 30 through the current detection resistor 50 a constituting the current detection circuit 50. The emitter of the PNP transistor 45d is connected to the emitter of the NPN transistor 45c, and the collector is grounded.

Similarly, the second voltage supply circuit 47 is configured by a voltage follower circuit, and the same voltage Vc as the output voltage Vc of the LPF 22 is supplied to the other terminal 41 of the A / F sensor 30. More specifically, an operational amplifier 47a having a positive input terminal connected to the output of the LPF 22 and a negative input terminal connected to the other terminal 41 of the A / F sensor 30, and an output terminal of the operational amplifier 47a The resistor 47b is connected to one end of the resistor 47b, and the NPN transistor 47c and the PNP transistor 47d are connected to the other end of the resistor 47b. The collector of the NPN transistor 47c is connected to the constant voltage Vcc, and the emitter is connected to the other terminal 41 of the A / F sensor 30 via the resistor 47e. The emitter of the PNP transistor 47d is connected to the emitter of the NPN transistor 47c, and the collector is grounded.
With such a configuration, the constant voltage Va is always supplied to one terminal 42 of the A / F sensor 30. When the voltage Vc lower than the constant voltage Va is applied to the other terminal 41 of the A / F sensor 30 via the LPF 22, the A / F sensor 30 is positively biased. Further, when the voltage Vc higher than the constant voltage Va is applied to the other terminal 41 of the A / F sensor 30 via the LPF 22, the A / F sensor 30 is negatively biased.
The microcomputer 20 controls the S / H circuit 70 and the A / F (oxygen concentration) signal detection permission / prohibition signal to stabilize the A / F signal. That is, the S / H circuit 70 is normally set to a sample state by the microcomputer 20, and the current A / F signal is output from the S / H circuit 70. On the other hand, the S / H circuit 70 is set to the hold state by the microcomputer 20 when the element resistance is detected, and the S / H circuit 70 outputs the A / F signal in the previous sample state. The microcomputer 20 normally outputs an A / F signal detection permission signal, and outputs an A / F signal detection prohibition signal when detecting element resistance.

  Next, the operation of the air-fuel ratio detection apparatus configured as described above will be described.

  FIG. 5 is a flowchart showing a main routine of control in the microcomputer 20 used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first example of the embodiment is applied. Is activated when power supply to the microcomputer 20 is started.

  In FIG. 5, first, in step S100, it is determined whether a predetermined time T1 has elapsed since the previous A / F detection. Here, the predetermined time T1 is a time corresponding to an A / F detection cycle, and is suitably set to about 2 to 4 ms, for example. When the determination condition in step S100 is satisfied and the predetermined time T1 has elapsed since the previous A / F detection, the process proceeds to step S200, and the sensor current Ip (limit current) detected by the current detection circuit 50 is read. The A / F of the internal combustion engine 10 corresponding to the sensor current Ip at that time is detected using a characteristic map stored in advance in the ROM. At this time, the voltage Vp corresponding to the A / F detection result at that time is applied to the A / F sensor 30 using the characteristic line L1 shown in FIG.

  Next, the process proceeds to step S300, and it is determined whether a predetermined time T2 has elapsed since the previous element resistance detection. Here, the predetermined time T2 is a time corresponding to the detection cycle of the element resistance, and is selectively set according to, for example, the operating state of the internal combustion engine 10, and a normal time (A / F change is relatively small). It is set to 2 sec at the time of steady operation and 128 ms at the sudden change of A / F (at the time of transient operation). When the determination condition of step S300 is not satisfied, the processing of step S100 to step S300 is repeated, and the A / F is detected every elapse of the predetermined time T1. On the other hand, when the determination condition in step S300 is satisfied and the predetermined time T2 has elapsed since the previous element resistance detection, the process proceeds to step S400, and after the element resistance detection process is executed, the process returns to step S100 and the same process is performed. Is executed repeatedly.

  Next, FIG. 6 showing a subroutine of element resistance detection processing in step S400 of FIG. 5 will be described.

  In FIG. 6, first, in step S401, it is determined whether the current A / F is lean. When the determination condition in step S401 is satisfied and the A / F is lean, the process proceeds to step S402, and the voltage is changed in the order of the negative side to the positive side with respect to the applied voltage Vp (A / F detection voltage) so far. . On the other hand, when the determination condition in step S401 is not satisfied and the A / F is rich, the process proceeds to step S403, and the voltage is changed in order of positive side → negative side with respect to the applied voltage Vp so far (bias command signal). Vr is manipulated).

  Then, after the applied voltage switching process in step S402 or step S403, the process proceeds to step S404, and the voltage change amount ΔV and the sensor current change amount ΔI detected by the current detection circuit 50 are read. In step S405, the element resistance R is calculated using ΔV and ΔI (R = ΔV / ΔI), and this subroutine is finished.

  7A and 7B show the waveform of the voltage applied to the A / F sensor 30 (the output voltage Vc after passing through the LPF 22) and the waveform of the sensor current flowing through the A / F sensor 30 according to the applied voltage. Indicates. Here, when A / F is lean (A / F = 18), as shown in FIG. 7A, the voltage applied to the A / F sensor 30 is changed to the negative side by the change amount ΔV, and this voltage A change amount ΔI to the negative side of the sensor current corresponding to the change is detected. The applied voltage = a [V] and sensor current = b [A] in the figure correspond to points a and b in FIG. When the A / F is rich (A / F = 13), as shown in FIG. 7B, the voltage applied to the A / F sensor 30 is changed to the positive side by the change amount ΔV, and this voltage change A change amount ΔI to the positive side of the sensor current corresponding to is detected. Note that applied voltage = c [V] and sensor current = d [A] in the figure correspond to points c and d in FIG.

  At this time, if it is lean, the voltage changes to the negative side, and if it is rich, the voltage changes to the positive side and the sensor current is obtained. Therefore, the sensor current does not exceed the dynamic range of the current detection circuit 50 (see FIG. 3). Absent.

  On the other hand, the element resistance R thus obtained has the relationship shown in FIG. 8 with respect to the element temperature. In other words, the element resistance R increases dramatically as the element temperature decreases. The element resistance R = 90Ω corresponds to a temperature 600 ° C. at which the A / F sensor 30 is activated to some extent, and the element resistance R = 30Ω corresponds to a temperature 700 ° C. at which the A / F sensor 30 is sufficiently activated. . In heater control, energization of the heater 31 necessary to eliminate a deviation between the calculated element resistance R and a target resistance value (for example, 30Ω) that the A / F sensor 30 is considered to be sufficiently activated. The amount is obtained, and the current supply to the heater 31 is duty ratio controlled. That is, element temperature feedback control is performed.

  Next, the flowchart of FIG. 9 which shows the process sequence of the element resistance detection in control of the microcomputer 20 used with the air fuel ratio detection apparatus to which the control apparatus of the A / F sensor concerning the 1st Example of embodiment is applied. This will be described with reference to the time chart of FIG. In the time charts in the following description of the embodiments, the display of time on the horizontal axis is omitted, and the period Tc in the figure represents the element resistance detection cycle.

  In FIG. 9, first, in step S411, the sample / hold function by the S / H circuit 70 is set from the previous sample state to the hold state, and the current A / F signal is held (time t01 in FIG. 10). Then, the process waits until the predetermined time T01 elapses in step S412 (time t01 to time t02 in FIG. 10), proceeds to step S413, and the element resistance detection process shown in FIG. 6 is executed. Next, in step S414, the process waits until a predetermined time T02 as a time until the output fluctuation of the A / F sensor 30 is settled (time t03 to time t04 in FIG. 10), and then proceeds to step S415, where the S / H circuit After the sample hold function 70 is set from the hold state to the sample state (time t04 in FIG. 10), this routine is terminated.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. When detecting the element resistance R of the A / F sensor 30 based on the current change amount ΔI associated with the amount ΔV, the current change in the A / F sensor 30 is interrupted, and the A / F by the sensor current corresponding to the previous A / F is cut off. Holds the F signal.

That is, in order to detect the element resistance R of the A / F sensor 30, the applied voltage is changed and the sensor current is changed. At this time, the A / F signal also changes. The signal is not a true A / F signal. Therefore, when the element resistance R is detected using the A / F sensor 30, the current change in the A / F sensor 30 is interrupted, and the A / F signal before the voltage change is held for element resistance detection. Thereby, when detecting the element resistance, the A / F signal is held before the element resistance detection timing, so that an erroneous A / F signal is not used.
<Reference Example 2>
Next, a flowchart of FIG. 11 showing a processing procedure of element resistance detection in the control of the microcomputer 20 used in the air-fuel ratio detection device to which the control device for the A / F sensor according to the second example of the embodiment is applied. This will be described with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  In FIG. 11, first, in step S421, the A / F (oxygen concentration) signal detection permission / prohibition signal is set from the permitted state to the prohibited state (time t11 in FIG. 12). And it waits until predetermined time T11 passes in step S422 (time t11-time t12 of FIG. 12), it transfers to step S423, and the element resistance detection process shown in FIG. 6 is performed. Next, in step S424, the process waits until a predetermined time T12 as a time until the output fluctuation of the A / F sensor 30 is settled (time t13 to time t14 in FIG. 12), then proceeds to step S425, and the A / F signal After the detection permission / prohibition signal is set from the prohibition state to the permission state (time t14 in FIG. 12), this routine ends.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. When detecting the element resistance R of the A / F sensor 30 based on the current change amount ΔI associated with the amount ΔV, a signal for prohibiting the use of the A / F signal by the sensor current according to the A / F from the A / F sensor 30 Output.

That is, in order to detect the element resistance R of the A / F sensor 30, the applied voltage is changed and the sensor current is changed. At this time, the A / F signal also changes. The signal is not a true A / F signal. Therefore, when the element resistance R is detected using the A / F sensor 30, use of the A / F signal is prohibited. As a result, when detecting the element resistance, the use of the A / F signal is prohibited, so that an erroneous A / F signal is not used.
<Reference Example 3>
Next, the flowchart of FIG. 13 which shows the process sequence of element resistance detection in control of the microcomputer 20 used with the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the third example of the embodiment is applied. This will be described with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. In this embodiment, only the case where the actual A / F signal changes from the rich side to the lean side (upward to the right) will be described. In this embodiment, as shown in FIG. 1, when an LPF (low-pass filter) 71 is connected to an S / H (sample hold) circuit 70 and an A / F (oxygen concentration) signal is output, This is effective when external reading of the A / F signal is controlled by the F signal detection enable / disable signal.

  That is, as shown in FIG. 15, when the actual A / F signal is changing, the S / H (sample hold) circuit 70 releases the hold state and changes to the sample state. There is a possibility that the A / F signal does not reach the true value. Then, the error due to the LPF 71 is superimposed on the A / F signal, resulting in erroneous detection.

  Further, as shown in FIG. 16, when an A / F signal is detected only by an A / F signal detection enable / disable signal with respect to an A / F signal processed by an externally connected LPF, A / F signal detection is prohibited. There is a possibility that the A / F signal does not reach the true value when the A / F signal detection permission state is entered from the state. Also at this time, an error due to LPF is superimposed on the A / F signal, resulting in erroneous detection.

  In order to deal with such a problem, in FIG. 13, first, in step S431, the sample / hold function by the S / H circuit 70 is set to the hold state from the previous sample state, and the current A / F signal is held. (Time t21 in FIG. 14). Next, the process proceeds to step S432, and the A / F (oxygen concentration) signal detection permission / prohibition signal is set from the permitted state to the prohibited state (time t21 in FIG. 14). And it waits until predetermined time T21 passes by step S433 (time t21-time t22 of FIG. 14), transfers to step S434, and the element resistance detection process shown in FIG. 6 is performed. Next, in step S435, the process waits until a predetermined time T22 as a time until the output fluctuation of the A / F sensor 30 is settled (time t23 to time t24 in FIG. 14), proceeds to step S436, and the S / H circuit. The sample hold function 70 is set from the hold state to the sample state (time t24 in FIG. 14). Next, the process proceeds to step S437 and waits until a predetermined time T23 as a time until the influence of the LPF on the A / F signal is eliminated (time t24 to time t25 in FIG. 14), and then step S438. , The A / F signal detection permission / prohibition signal is set from the prohibition state to the permission state (time t25 in FIG. 14), and this routine ends.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. When detecting the element resistance R of the A / F sensor 30 based on the current change amount ΔI associated with the amount ΔV, the current change in the A / F sensor 30 is interrupted, and the A / F by the sensor current corresponding to the previous A / F is cut off. The F signal is held, and the use of the A / F signal by the sensor current corresponding to the A / F from the A / F sensor 30 is prohibited.

That is, in order to detect the element resistance R of the A / F sensor 30, the applied voltage is changed and the sensor current is changed. At this time, the A / F signal also changes. The signal is not a true A / F signal. Therefore, when the element resistance R is detected using the A / F sensor 30, the current change in the A / F sensor 30 is interrupted, and the A / F signal before the voltage change is held for detecting the element resistance. Use of the A / F signal until it matches the A / F signal is prohibited. As a result, when the element resistance is detected, the A / F signal is held before the element resistance detection timing, and the use of the A / F signal during the element resistance detection is performed in consideration of the smoothing of the signal by LPF or the like. Since it is prohibited, an erroneous A / F signal is not used.
<Example 1>
Next, a diagram showing a process procedure of element resistance detection in the control of the microcomputer 20 used in the air-fuel ratio detection device to which the A / F sensor control device according to the fourth example of the embodiment of the present invention is applied. This will be described based on the flowchart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  First, with reference to FIG. 18, the processing content and load at the processing timing of the microcomputer 20 will be described.

  In FIG. 18, in order to execute the element resistance detection process and the element heater control process in addition to the original limit current (A / F) detection process using the A / F sensor 30 by the microcomputer 20, predetermined processes are performed. I need time. In other words, as shown as “0”, the “limit current (A / F) detection process”, “element resistance detection process”, and “element heater control process” are executed at the same processing timing. A load of 20 is the largest.

  On the other hand, when [limit current (A / F) detection processing] and [element resistance detection processing] shown as processing content “2” are executed at the same processing timing, or shown as processing content “3” The load of the microcomputer 20 when the [limit current (A / F) detection process] and the [element heater control process] are executed at the same processing timing is indicated as the processing content “1” [limit current (A / F ) Detection processing] is naturally larger than the case where only the processing is executed, but can be smaller than the case where the processing content is “0”. In this way, the microcomputer 20 is smoothed so that other processes can be executed at different process timings based on the processes that need to be executed at the earliest process timing in the microcomputer 20 used in the air-fuel ratio detection apparatus. Can reduce the processing load.

  Specifically, in FIG. 17, first, predetermined times T32 and T33 at the beginning of control are set in step S1100. Next, the process proceeds to step S1200, where it is determined whether a predetermined time T31 has elapsed since the previous A / F detection. The predetermined time T31 is a time corresponding to the A / F detection cycle, and is, for example, about 4 ms at the earliest processing timing. When the predetermined time T31 elapses in step S1200, the process proceeds to step S1300, and the sensor current Ip (limit current) detected by the current detection circuit 50 is detected as the limit current (A / F) detection process similar to step S200 in FIG. The A / F of the internal combustion engine 10 corresponding to the sensor current Ip at that time is detected using a characteristic map that is read and stored in advance in the ROM. At this time, the voltage Vp corresponding to the A / F detection result at that time is applied to the A / F sensor 30 using the characteristic line L1 shown in FIG.

  Next, the process proceeds to step S1400, and it is determined whether the predetermined time T32 has elapsed. This predetermined time T32 is a time corresponding to the detection cycle of the element resistance, and is set to the same time as the predetermined time T31 at the beginning of control start, and set to, for example, 128 ms after the temperature increase activation of the A / F sensor 30. The When the predetermined time T32 has elapsed in step S1400, the process proceeds to step S1500, and the element resistance detection process shown in FIG. 6 is executed. If the predetermined time T32 has not elapsed in step S1400, step S1500 is skipped. Next, the process proceeds to step S1600, and it is determined whether the predetermined time T33 has elapsed. This predetermined time T33 is a time corresponding to the control cycle of the element heater, and is set to twice the predetermined time T31 at the beginning of the control, and is set to, for example, 128 ms after the temperature increase activation of the A / F sensor 30. Is set. The predetermined time T32 and the predetermined time T33 are the same 128 ms, but are slightly shifted in advance so that the element resistance detection process and the element heater control process do not have the same processing timing. When the predetermined time T33 has elapsed in step S1600, the process proceeds to step S1700, and an element heater control process for controlling the power supplied to the heater 31 in order to maintain the A / F sensor 30 at the activation temperature is executed. When the predetermined time T33 has not elapsed in step S1600, step S1700 is skipped, and then the process returns to step S1200 and the same process is repeatedly executed.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. The execution timing of the process for detecting the element resistance R of the A / F sensor 30 and the process for raising the temperature of the A / F sensor 30 is distributed based on the current change amount ΔI accompanying the amount ΔV.

Therefore, the microcomputer 20 is smoothed so that other element resistance detection processes and element heater control processes can be executed at different process timings based on the A / F detection process that needs to be executed at the earliest process timing. Processing load can be reduced.
<Reference Example 4>
Next, the flowchart of FIG. 19 which shows the process sequence of element resistance detection in control of the microcomputer 20 used with the air fuel ratio detection apparatus to which the control apparatus of the A / F sensor concerning the 5th Example of embodiment is applied. This will be described with reference to the time chart of FIG. 20A shows the operation of this embodiment, and FIG. 20B is a comparative example showing the case where the change amount limitation of this embodiment is not added. The schematic configuration of the air-fuel ratio detection device of this embodiment is the same as that shown in FIGS. 1 to 4, and a detailed description thereof will be omitted.

  In FIG. 19, first, the element resistance detection process shown in FIG. 6 is executed in step S441, and the element resistance R is calculated. Next, the process proceeds to step S442, and it is determined whether the temperature of the A / F sensor 30 is increasing. When the determination condition in step S442 is satisfied and the temperature of the A / F sensor 30 is increasing, the process proceeds to step S443, and the change amount limit value dR of the element resistance detection value is set to dR0 (for example, 50Ω) (FIG. 20 (a)). On the other hand, the determination condition in step S442 is not satisfied, and after the temperature rise of the A / F sensor 30 is completed, that is, when the A / F sensor 30 has reached the activation temperature, the process proceeds to step S444, where the element resistance detection value The change amount limit value dR is set to dR1 (for example, 10Ω) smaller than dR0 during temperature rise (see FIG. 20A). After the processing of step S443 or step S444, the process proceeds to step S445, and it is determined whether the absolute value of the value obtained by subtracting the current element resistance R calculated in step S441 from the previous element resistance is equal to or less than the variation limit value dR. Is done. When the determination condition in step S445 is not satisfied and the absolute value exceeds the variation limit value dR, the process proceeds to step S446, and when the current element resistance R is larger than the variation limit value dR from the previous element resistance. When the resistance value obtained by adding the variation limit value dR to the previous element resistance is replaced with the current element resistance R, and when the current element resistance R is smaller than the variation limit value dR from the previous element resistance, After the resistance value obtained by subtracting the variation limit value dR from the previous element resistance is replaced with the current element resistance R, this routine is terminated. On the other hand, when the determination condition in step S445 is satisfied and the absolute value is equal to or smaller than the change amount limit value dR, step S446 is skipped, and the current element resistance R calculated in step S441 is left as it is, and this routine is terminated.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. The change amount with respect to the element resistance R detected by the A / F sensor 30 is limited based on the current change amount ΔI accompanying the amount ΔV.

  Accordingly, the change in the element resistance R of the A / F sensor 30 is limited as shown in FIG. 20B to FIG. 20A, and the control of the A / F sensor 30 is controlled. The execution range can be kept within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Is greatly different from That is, the change in the element resistance of the A / F sensor 30 is limited to a change amount within a predetermined range, so that it does not deviate from the normal control range. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  In the present embodiment, the change amount limit value dR is changed based on a predetermined condition. Therefore, the element resistance R of the A / F sensor 30 can be rounded by an appropriate variation amount allowable range according to the element use state. For this reason, the change amount limit values dR0 and dR1 of the element resistance R are not limited to the temperature raising operation of the A / F sensor 30, but are changed depending on the operating state of the internal combustion engine 10, for example, and stabilized with respect to the A / F sensor 30. Control can be executed.

In this embodiment, the variation limit value dR is set to be large during the temperature increase of the A / F sensor 30, and is set to be small after the temperature increase of the A / F sensor 30 is completed. In other words, by changing the allowable range of the change amount with respect to the element resistance R of the A / F sensor 30 during the temperature rise and after the temperature rise is completed, the early activation required for the A / F sensor 30 is realized and stabilized. Control can be executed.
<Reference Example 5>
Next, the flowchart of FIG. 21 which shows the process sequence of the element resistance detection in control of the microcomputer 20 used with the air fuel ratio detection apparatus to which the control apparatus of the A / F sensor concerning the 6th Example of embodiment is applied. This will be described with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  In FIG. 21, first, the element resistance detection process shown in FIG. 6 is executed in step S451, and the element resistance R is calculated. Next, the process proceeds to step S452, and it is determined whether the temperature of the A / F sensor 30 is being increased. When the determination condition in step S452 is satisfied and the temperature of the A / F sensor 30 is increasing, the process proceeds to step S453, where the cut-off frequency dfc of the LPF (low-pass filter) is set to dfc0 (temperature increase shown in FIG. (Refer to the somewhat large fluctuation of the element resistance R in the inside). On the other hand, after the determination condition of step S452 is not satisfied and the temperature increase of the A / F sensor 30 is completed, that is, when the A / F sensor 30 has reached the activation temperature, the process proceeds to step S454 and the cutoff frequency of the LPF. dfc is set to dfc1 (refer to the small variation in element resistance R after the temperature rise shown in FIG. 22). After the process of step S453 or step S454, the process proceeds to step S455. After the element resistance R calculated in step S451 is replaced with the element resistance R after the LPF process, this routine is finished.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. An LPF (low-pass filter) is passed through the element resistance R detected by the A / F sensor 30 based on the current change amount ΔI accompanying the amount ΔV.

  Therefore, the change in the element resistance R of the A / F sensor 30 is limited to be within the allowable range, and the execution range of the control by the A / F sensor 30 can be kept within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Is greatly different from That is, by passing an LPF having sufficient responsiveness to the element resistance change of the A / F sensor 30, the element resistance change can be prevented from deviating from the normal control range. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.

  In this embodiment, the cutoff frequency dfc of the LPF (low-pass filter) is changed based on a predetermined condition. Therefore, the cut-off frequency of the LPF is changed so that the element resistance R of the A / F sensor 30 has sufficient responsiveness to a normal element resistance change in accordance with the element use state. That is, the cut-off frequencies dfc0 and dfc1 of the LPF that are passed through the element resistance detection are not limited to the temperature rising state of the A / F sensor 30, but are changed depending on, for example, the operating state of the internal combustion engine 10. Thereby, stable control can be executed on the A / F sensor 30.

In this embodiment, the cutoff frequency dfc of the LPF (low-pass filter) is set high during the temperature rise of the A / F sensor 30 and is set low after the temperature rise of the A / F sensor 30 is completed. That is, an LPF having sufficient responsiveness to a change in element resistance during temperature rise of the A / F sensor 30 and an LPF having sufficient responsiveness to a change in element resistance after the temperature rise of the A / F sensor 30 are obtained. Switching between during the temperature rise and after the temperature rise is completed, it is possible to execute stable control while realizing the early activation required for the A / F sensor 30.
<Reference Example 6>
Next, the flowchart of FIG. 23 which shows the process sequence of the element resistance detection in control of the microcomputer 20 used with the air fuel ratio detection apparatus to which the control apparatus of the A / F sensor concerning 7th Example of embodiment is applied. This will be described with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  In FIG. 23, first, the element resistance detection process shown in FIG. 6 is executed in step S461, and the element resistance R is calculated. Next, the process proceeds to step S462, and it is determined whether the temperature of the A / F sensor 30 is being increased. When the determination condition in step S462 is satisfied and the temperature of the A / F sensor 30 is rising, the process proceeds to step S463, and the change amount limit value dR of the element resistance detection value is set to dR0 (for example, 50Ω) (FIG. (Refer to the somewhat large fluctuation of the element resistance R during the temperature rise shown in 24). On the other hand, the determination condition of step S462 is not satisfied, and after the temperature increase of the A / F sensor 30 is completed, that is, when the A / F sensor 30 has reached the activation temperature, the process proceeds to step S464, and the element resistance detection value The variation limit value dR is set to dR1 (for example, 10Ω) smaller than dR0 during temperature rise (see the small variation in element resistance R during temperature rise shown in FIG. 24). After the process of step S463 or step S464, the process proceeds to step S465, and it is determined whether the absolute value of the value obtained by subtracting the current element resistance R calculated in step S461 from the previous element resistance is equal to or less than the variation limit value dR. Is done. When the determination condition of step S465 is not satisfied and the absolute value exceeds the variation limit value dR, the process proceeds to step S466, and when the current element resistance R is larger than the variation limit value dR from the previous element resistance. When the resistance value obtained by adding the variation limit value dR to the previous element resistance is replaced with the current element resistance R, and when the current element resistance R is smaller than the variation limit value dR from the previous element resistance, The resistance value obtained by subtracting the variation limit value dR from the previous element resistance is replaced with the current element resistance R. On the other hand, when the determination condition in step S465 is satisfied and the absolute value is equal to or less than the change amount limit value dR, step S466 is skipped and the current element resistance R calculated in step S461 is left as it is. Next, the process proceeds to step S467, and after the calculated element resistance R is replaced with the element resistance R after the LPF processing, this routine is finished.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. The amount of change with respect to the element resistance R detected by the A / F sensor 30 is limited based on the amount of current change ΔI accompanying the amount ΔV, and the LPF (low-pass filter) is passed.

Accordingly, since the change in the element resistance R of the A / F sensor 30 is limited to the allowable range, and the LPF process is performed, the execution range of the control by the A / F sensor 30 can be kept within the normal range. . That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Is greatly different from That is, the change in the element resistance of the A / F sensor 30 is limited to a change amount within a predetermined range, and LPF processing with sufficient response to the element resistance change is performed so as not to deviate from the normal control range. it can. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.
<Reference Example 7>
Next, the flowchart of FIG. 25 which shows the process sequence of the element resistance detection in control of the microcomputer 20 used with the air fuel ratio detection apparatus to which the control apparatus of the A / F sensor concerning the 8th Example of embodiment is applied. This will be described with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  25, first, in step S471, the element resistance detection process shown in FIG. 6 is executed, and the element resistance R is calculated. Next, the process proceeds to step S472, and the n element resistances of the element resistance detected this time and the element resistances up to (n−1) times before are averaged (the predetermined width of the element resistance R shown in FIG. 26). See small variations). Next, the process proceeds to step S473, where the element resistance of (n-1) times before is erased, and the element resistance detected this time is stored instead. Next, the process proceeds to step S474, the value obtained by averaging in step S472 is replaced with the element resistance Rx, and this routine is terminated.

  As described above, the present embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with the application of a voltage. A plurality of element resistances R detected by the A / F sensor 30 are averaged based on the current change amount ΔI accompanying the amount ΔV.

Therefore, changes in the element resistance R of the A / F sensor 30 are averaged, and the influence of abnormal data is suppressed, so that the execution range of control by the A / F sensor 30 can be kept within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Is greatly different from That is, the change in the element resistance of the A / F sensor 30 is averaged so that it does not deviate from the normal control range. And, since it is not affected by a minute change, it does not affect the control due to a normal change in element resistance, and the response required by element heater control based on the detected element resistance can be obtained.
<Reference Example 8>
Next, the applied voltage to the A / F sensor 30 after detecting the element resistance in the control of the microcomputer 20 used in the air-fuel ratio detection device to which the A / F sensor control device according to the ninth example of the embodiment is applied. Description will be made with reference to the time chart of FIG. 28 based on the flowchart of FIG. FIG. 28A shows the operation of the present embodiment, and FIG. 28B is a comparative example showing a case where the map selection range of the present embodiment is not limited. The schematic configuration of the air-fuel ratio detection device of this embodiment is the same as that shown in FIGS. 1 to 4, and a detailed description thereof will be omitted.

  In FIG. 27, first, there is a condition that the applied voltage map for calculating the voltage applied when the A / F sensor 30 detects A / F in step S501 and the element resistance at that time as a parameter is fixed. It is determined whether it is established. Here, it is determined whether the element resistance becomes less than 50Ω due to the temperature rise, for example, and the A / F sensor 30 has almost reached the activated state. When the determination condition in step S501 is satisfied, the process proceeds to step S502, and the applied voltage map after the fixed condition is satisfied is selected (refer to FIG. 28 (a) fixed map selection after the temperature rise is completed). On the other hand, when the determination condition of step S501 is not satisfied, the process proceeds to step S503, and the applied voltage map is selected based on the element resistance at that time. After the processing in step S502 or step S503, the process proceeds to step S504, the voltage to be applied to the A / F sensor 30 is calculated based on the selected applied voltage map, and this routine ends.

  As described above, this embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with application of a voltage. When changing the voltage applied to the A / F sensor 30 when detecting F based on a preset map using the element resistance R of the A / F sensor 30 as a parameter, after the temperature increase of the A / F sensor 30 is completed Then, the selection range of the map is limited.

Therefore, when the A / F sensor 30 detects A / F, the voltage applied to the A / F sensor 30 is changed based on a map using the element resistance R as a parameter. Since the map is fixed on the assumption that there is little change, the execution range of control by the A / F sensor 30 can be kept within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and the oxygen concentration detection value from being different from the true value. That is, after the temperature rise is finished, a large change in the element resistance of the A / F sensor 30 is ignored, so that it does not deviate from the normal control range.
<Reference Example 9>
Next, the applied voltage to the A / F sensor 30 after detecting the element resistance in the control of the microcomputer 20 used in the air-fuel ratio detection device to which the A / F sensor control device according to the tenth example of the embodiment is applied. Based on the flowchart of FIG. 29 which shows the processing procedure of a calculation, it demonstrates with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS. 1 to 4 and will not be described in detail.

  In FIG. 29, first, in step S511, it is determined whether or not the current element resistance is greater than or equal to the previous element resistance. Here, the element resistance at the time of selecting the previous applied voltage map is compared with the element resistance at the time of selecting the current applied voltage map, and the change direction of the element resistance is determined. When the determination condition of step S511 is satisfied and the element resistance is increasing, the process proceeds to step S512, and the applied voltage map is selected according to the applied voltage map selection criterion when the element resistance is increasing (FIG. 30). Refer to the map selection transition to high temperature side). On the other hand, if the determination condition of step S511 is not satisfied and the element resistance is decreasing, the process proceeds to step S513, and the applied voltage map is selected according to the applied voltage map selection criterion when the element resistance is decreasing ( (See map selection stability shown in FIG. 30). After the applied voltage map selection process in step S512 or step S513, the process proceeds to step S514, and the voltage to be applied to the A / F sensor 30 is calculated based on the selected applied voltage map. Next, the process proceeds to step S515, where the element resistance used for the current applied voltage map selection is stored for use in the next applied voltage map selection, and this routine ends.

  As described above, this embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with application of a voltage. When the voltage applied to the A / F sensor 30 when detecting F is changed based on a preset map using the element resistance R of the A / F sensor 30 as a parameter, the map selection determination has hysteresis. It is something to make.

Therefore, when the A / F sensor 30 detects A / F, the voltage applied to the A / F sensor 30 is changed based on a map using the element resistance R as a parameter. In general, since the element resistance of the A / F sensor 30 gradually decreases as the temperature rises, the map selection is not reversed depending on the direction of change in the element resistance. Can be within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and the oxygen concentration detection value from being different from the true value. That is, a large element resistance change of the A / F sensor 30 is ignored, so that it does not deviate from the normal control range.
<Reference Example 10>
Next, the applied voltage to the A / F sensor 30 after detecting the element resistance in the control of the microcomputer 20 used in the air-fuel ratio detection device to which the A / F sensor control device according to the eleventh example of the embodiment is applied. Based on the flowchart of FIG. 31 which shows the processing procedure of a calculation, it demonstrates with reference to the time chart of FIG. The schematic configuration and the like of the air-fuel ratio detection apparatus according to this embodiment are the same as those shown in FIGS.

  In FIG. 31, first, in step S521, it is determined whether the current element resistance is greater than or equal to the previous element resistance. Here, the element resistance at the time of selecting the previous applied voltage map is compared with the element resistance at the time of selecting the current applied voltage map, and the change direction of the element resistance is determined. When the determination condition of step S521 is satisfied and the element resistance is increasing, the process proceeds to step S522, and the applied voltage map is selected based on the applied voltage map selection criterion when the element resistance is increasing (FIG. 32). Refer to the map selection transition to high temperature side). On the other hand, when the determination condition of step S521 is not satisfied and the element resistance is decreasing, the process proceeds to step S523, and the applied voltage map is selected according to the applied voltage map selection criterion when the element resistance is decreasing ( (See map selection stability shown in FIG. 32).

  After the applied voltage map selection process in step S522 or step S523, the process proceeds to step S524, and the voltage applied when the A / F sensor 30 detects A / F is calculated using the element resistance at that time as a parameter. It is determined whether or not a condition for fixing the applied voltage map is satisfied. Here, it is determined whether the element resistance becomes less than 50Ω due to the temperature rise, for example, and the A / F sensor 30 has almost reached the activated state. When the determination condition of step S524 is satisfied, the process proceeds to step S525, and the applied voltage map after the fixed condition is satisfied is selected (refer to fixed map selection after completion of temperature increase shown in FIG. 32). On the other hand, when the determination condition of step S524 is not satisfied, step S525 is skipped. Next, the process proceeds to step S526, and a voltage to be applied to the A / F sensor 30 is calculated based on the selected applied voltage map. Next, the process proceeds to step S527, where the element resistance used for the current applied voltage map selection is stored for use in the next applied voltage map selection, and this routine ends.

  As described above, this embodiment is a control device for the A / F sensor 30 that outputs a sensor current (current signal) corresponding to A / F (oxygen concentration) in exhaust gas in accordance with application of a voltage. When the voltage applied to the A / F sensor 30 when detecting F is changed based on a preset map using the element resistance R of the A / F sensor 30 as a parameter, the map selection determination has hysteresis. In addition, after the temperature increase of the A / F sensor 30, the selection range of the map is limited.

  Therefore, when the A / F sensor 30 detects A / F, the voltage applied to the A / F sensor 30 is changed based on a map using the element resistance R as a parameter. In general, since the element resistance of the A / F sensor 30 gradually decreases as the temperature rises, the map selection is prevented from going backward depending on the direction of change in the element resistance, and the change in the element resistance R is small after the temperature rise is completed. Since the map is fixed, the execution range of control by the A / F sensor 30 can be kept within the normal range. That is, when the element resistance of the A / F sensor 30 is detected, noise is superimposed from the operating state of the internal combustion engine, the wiring state of the sensor signal, etc. because the sensor signal is a minute signal, and the detected element resistance value is a true value. Therefore, it is possible to prevent the voltage applied to the sensor from becoming abnormal and the oxygen concentration detection value from being different from the true value. That is, the direction of change in element resistance is taken into account during the temperature rise of the A / F sensor 30, and a large change in element resistance is ignored after the temperature rise is completed, so that it does not deviate from the normal control range.

  In the above-described embodiment, the control device for the A / F sensor 30 that detects A / F (air-fuel ratio) as a current signal corresponding to the oxygen concentration has been described. Not only the limiting current type oxygen concentration sensor but also a two-cell type oxygen concentration sensor may be used. Further, not only a cup-type oxygen concentration sensor but also a stacked-type oxygen concentration sensor may be used.

  In the above embodiment, the A / F sensor 30 for detecting the oxygen concentration is described as the gas concentration sensor used in the control device for the gas concentration sensor. However, as another gas concentration sensor, nitrogen oxide ( The NOx concentration sensor 100 for detecting the (NOx) concentration will be described with reference to FIG. FIG. 33 is a schematic cross-sectional view showing the configuration of the main part of the tip of the NOx concentration sensor 100. The NOx concentration sensor 100 is housed in a predetermined cylindrical housing, and the A / F sensor 30 shown in FIG. In the same manner as described above, the exhaust passage 12 is connected to the downstream side of the internal combustion engine 10.

  33, the NOx concentration sensor 100 mainly includes an oxygen pump cell 120 composed of a solid electrolyte SEA and a pair of electrodes 121, 122, an oxygen detection cell 150 composed of a solid electrolyte SEB and a pair of electrodes 151, 152, and a pair of solid electrolyte SEBs. The NOx detection cell 160 is composed of the electrodes 161 and 162. A spacer 130 made of alumina (aluminum oxide) or the like is interposed between the solid electrolyte SEA and the solid electrolyte SEB, and the first internal space 131 and the second An internal space 132 is formed. Further, a spacer 140 made of alumina or the like is interposed on the back surface side of the solid electrolyte SEB, and air that is a reference oxygen concentration gas is introduced into the spacer 140 through a hole extending to the edge in the longitudinal direction. An air passage 141 is formed, and a heater 170 for heating each cell is stacked.

  The oxygen pump cell 120 is for maintaining the oxygen concentration in the first internal space 131 at a predetermined concentration. The oxygen ion cell 120 is screen-printed at opposite positions on both sides of the oxygen ion conductive solid electrolyte SEA formed in a sheet shape. It consists of a pair of electrodes 121 and 122 formed by, for example. For example, yttria-added zirconia is used as the oxygen ion conductive solid electrolyte SEA.

  A pinhole 111 having a predetermined diameter is formed through the solid electrolyte SEA and the pair of electrodes 121 and 122. The diameter dimension of the pinhole 111 is appropriately set so that the diffusion speed of the exhaust gas passing through the pinhole 111 and introduced into the first internal space 131 becomes a predetermined speed. Further, a porous protective layer 113 made of porous alumina or the like is formed so as to cover the exhaust gas-side electrode 121 and the pinhole 111, and the poisoning of the electrode 121 and the pinhole 111 are contained in the exhaust gas. It is possible to prevent clogging with the like.

  The oxygen detection cell 150 detects the oxygen concentration in the first internal space 131, and includes a sheet-like solid electrolyte SEB made of zirconia or the like, and a pair of electrodes 151 formed by screen printing or the like at opposite positions on both sides thereof. , 152. Of the pair of electrodes 151 and 152, the electrode 151 is formed of, for example, a porous Pt (platinum) electrode and exposed to the atmospheric passage 141, and the electrode 152 facing the electrode 151 with the solid electrolyte SEB interposed therebetween is the first electrode 151. The inner space 131 is exposed. Similar to the electrode 122 of the oxygen pump cell 120, the electrode 152 is inactive with respect to the reduction of NOx, and the electrode activity is adjusted so as to be active with respect to the reduction of oxygen.

  The NOx detection cell 160 detects the NOx concentration from the amount of oxygen generated by the NOx reductive decomposition. The NOx detection cell 160 is a solid electrolyte SEB common to the oxygen detection cell 150 and a pair of electrodes formed by screen printing or the like at opposite positions on both sides thereof. 161, 162. A communication hole 112 as a throttle is formed between the first internal space 131 and the second internal space 132 provided by the hole in the spacer 130 adjacent to the solid electrolyte SEB. The gas to be measured in the space 131 is introduced into the second internal space 132 at a predetermined diffusion rate.

  Of the pair of electrodes 161 and 162, the electrode 161 is formed of, for example, a porous Pt electrode and exposed to the atmospheric passage 141, and the electrode 162 facing the electrode 161 with the solid electrolyte SEB interposed therebetween is a second internal space. 132 is exposed. The electrode 162 is made of, for example, a porous Pt electrode that is active against the reduction of NOx. For this reason, NOx in the gas to be measured introduced into the second internal space 132 is reduced and decomposed at the electrode 162 to generate oxygen and nitrogen.

  Further, the heater 170 has a heater electrode 171 formed on the surface of a heater sheet 173 made of alumina or the like. As the heater electrode 171, a Pt electrode is usually used, and an insulating layer 172 made of alumina or the like is formed on the upper surface thereof. A lead (not shown) is connected to the heater electrode 171 and the lead portion of each electrode, and is connected to a terminal of the sensor base.

  The operation of the NOx concentration sensor 100 configured as described above will be described below. Exhaust gas, which is the gas to be measured, is introduced into the first internal space 131 through the pinhole 111. In the oxygen detection cell 150, an electromotive force represented by the Nernst equation is generated based on the difference in oxygen concentration between the electrode 152 facing the first internal space 131 and the electrode 151 facing the air passage 141 into which the atmosphere is introduced. Is done. By measuring the magnitude of this electromotive force, the oxygen concentration in the first internal space 131 can be known.

  In the oxygen pump cell 120, a voltage is applied between the pair of electrodes 121 and 122, and oxygen in the first internal space 131 is taken in and out, so that the oxygen concentration in the first internal space 131 is controlled to a predetermined low concentration. Is done. For example, when a predetermined voltage is applied so that the exhaust gas side electrode 121 becomes a (+) electrode, oxygen is reduced on the electrode 122 on the first internal space 131 side to become oxygen ions, and the electrode is pumped. It is discharged to the 121 side. The energization amount between the pair of electrodes 121 and 122 is feedback-controlled so that the electromotive force generated between the pair of electrodes 151 and 152 of the oxygen detection cell 150 becomes a predetermined constant value. The oxygen concentration is constant. Here, the electrodes 122 and 152 facing the first internal space 131 are active for the reduction of oxygen, but are inactive for the reduction of NOx. NOx decomposition does not occur, and therefore, the operation of the oxygen pump cell 120 does not change the amount of NOx in the first internal space 131.

  The exhaust gas having a constant low oxygen concentration by the oxygen pump cell 120 and the oxygen detection cell 150 is introduced into the second internal space 132 through the communication hole 112. Since the NOx detection cell 160 facing the second internal space 132 is active with respect to NOx, a predetermined voltage is applied between the pair of electrodes 161 and 162 so that the electrode 161 becomes a (+) pole. Then, NOx is reduced and decomposed on the electrode 162, and an oxygen ion current due to oxygen atoms in the NOx molecule flows. By measuring this current value, the concentration of NOx contained in the exhaust gas can be detected.

  In the NOx concentration sensor 100 having the above-described configuration, voltages are applied between the pair of electrodes 121 and 122 of the oxygen pump cell 120, between the pair of electrodes 151 and 152 of the oxygen detection cell 150, and between the electrodes 161 and 162 of the NOx detection cell 160, respectively. By distinguishing the timing for detecting the element resistance and the timing for detecting the element resistance, an abnormality in the detected value of the NOx concentration by the NOx concentration sensor 100 is prevented. That is, as with the A / F sensor 30, the NOx concentration sensor 100 detects the NOx concentration from the sensor current (limit current) that flows along with the application of the voltage. For example, the NOx concentration sensor 100 detects the element resistance. At the time of detection, the current change in the NOx concentration sensor 100 is interrupted, and the NOx concentration signal before the voltage is changed for detecting the element resistance is held, so that an erroneous NOx concentration signal is prevented from being used.

  As described above, the A / F sensor 30 that detects the oxygen concentration and the NOx concentration sensor 100 that detects the nitrogen oxide (NOx) concentration have been described as the gas concentration sensors used in the control device of the gas concentration sensor. In the case of carrying out, it is not limited to these, but also to a control device for a gas concentration sensor using a gas concentration sensor for detecting a gas concentration of hydrocarbon (HC), carbon monoxide (CO) or the like. The same can be applied.

FIG. 1 is a schematic diagram showing a configuration of an air-fuel ratio detection apparatus to which an A / F sensor control apparatus according to first to eleventh examples of an embodiment is applied. FIG. 2 is a cross-sectional view showing a schematic configuration of the A / F sensor in FIG. FIG. 3 is a table showing the voltage-current characteristics of the A / F sensor used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first to eleventh examples of the embodiment is applied. It is. FIG. 4 is a circuit diagram showing an electrical configuration of the bias control circuit in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first to eleventh examples of the embodiment is applied. FIG. 5 is a flowchart showing a main routine of control in the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first example of the embodiment is applied. FIG. 6 is a flowchart showing a subroutine of the element resistance detection process of FIG. FIG. 7 shows a change in voltage applied to the A / F sensor used in the air-fuel ratio detection apparatus to which the control apparatus for the A / F sensor according to the first example of the embodiment is applied, and a change in current associated therewith. FIG. FIG. 8 is a characteristic diagram showing the relationship between the element temperature and the element resistance of the A / F sensor used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first example of the embodiment is applied. It is. FIG. 9 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the first example of the embodiment is applied. FIG. 10 is a time chart specifically showing the operation in FIG. FIG. 11 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the second example of the embodiment is applied. FIG. 12 is a time chart specifically showing the operation in FIG. FIG. 13 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the third example of the embodiment is applied. FIG. 14 is a time chart specifically showing the operation in FIG. FIG. 15 shows only the sample hold function with respect to the change in A / F by the A / F sensor used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the third example of the embodiment is applied. It is a time chart which shows the malfunction when taking into consideration. FIG. 16 shows an A / F signal with respect to a change in A / F by an A / F sensor used in an air-fuel ratio detection device to which an A / F sensor control device according to a third example of the embodiment is applied. It is a time chart which shows the malfunction when only a detection permission / prohibition function is considered. FIG. 17 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the fourth example of the embodiment of the present invention is applied. is there. FIG. 18 is a block diagram for explaining the operation in FIG. FIG. 19 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the fifth example of the embodiment is applied. FIG. 20 is a time chart specifically showing the operation in FIG. FIG. 21 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the sixth example of the embodiment is applied. FIG. 22 is a time chart specifically showing the operation in FIG. FIG. 23 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the seventh example of the embodiment is applied. FIG. 24 is a time chart specifically showing the operation in FIG. FIG. 25 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the eighth example of the embodiment is applied. FIG. 26 is a time chart specifically showing the operation in FIG. FIG. 27 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the ninth example of the embodiment is applied. FIG. 28 is a time chart specifically showing the operation in FIG. FIG. 29 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the tenth example of the embodiment is applied. FIG. 30 is a time chart specifically showing the operation in FIG. FIG. 31 is a flowchart showing a process procedure of element resistance detection in the control of the microcomputer used in the air-fuel ratio detection apparatus to which the A / F sensor control apparatus according to the eleventh example of the embodiment is applied. FIG. 32 is a time chart specifically showing the operation in FIG. FIG. 33 is a schematic cross-sectional view showing the main configuration of the NOx concentration sensor. FIG. 34 is a waveform diagram for explaining conventional element resistance detection.

Explanation of symbols

10 Internal combustion engine 20 Microcomputer
30 A / F sensor (oxygen concentration sensor)
31 Heater 40 Bias control circuit 50 Current detection circuit 60 Heater control circuit 70 S / H circuit (sample hold circuit)

Claims (3)

A control device for a gas concentration sensor that outputs a signal corresponding to a gas concentration in a gas to be detected,
A gas concentration sensor that performs smoothing so that other processing can be executed at different processing timings based on processing that needs to be executed at the earliest processing timing in the control device used in the air-fuel ratio detection device Control device. A control device for a gas concentration sensor that outputs a signal corresponding to a gas concentration in a gas to be detected,
Control of a gas concentration sensor, wherein execution timings of a process for detecting an element resistance of the gas concentration sensor and a process for increasing the temperature of the gas concentration sensor are distributed based on a voltage change and a current change. apparatus.   3. The control device for a gas concentration sensor according to claim 1, wherein the element resistance of the gas concentration sensor is detected based on a current change accompanying a voltage change.

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