JP2006113081A - Heater controller device for gas concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater controller device of gas concentration sensor, capable of enhancing detection accuracy by inhibiting the false detection of element resistance. <P>SOLUTION: The heater controller device for gas concentration sensor comprises a sensor element using a solid electrolyte; a gas concentration sensor having a heater for heating the sensor element concerned to active status; an element resistance detecting means for detecting element resistance of the gas concentration sensor from the change in current or change in voltage, when the impressed voltage or the current to the sensor element is temporarily switched to the value for element resistive detecting means, a heater controller means for making power distribution to the heater turn on/off periodically; while when the detecting period of element resistance by the element resistance detecting means overlaps the timing of switching on/off at the power distribution to the heater. either each timing is forcibly shifted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heater control device for a gas concentration sensor.

  For example, in an automobile engine, air-fuel ratio control is generally performed based on a detection result by a gas concentration sensor such as an A / F sensor. A gas concentration sensor has a sensor element using a solid electrolyte body made of zirconia, and in order to accurately detect an air-fuel ratio (oxygen concentration) with this sensor element, it is necessary to maintain the temperature of the sensor element at a predetermined activation temperature. is there. Normally, a heater is built in the sensor and the energization amount (duty ratio) of the heater is controlled. As such a heater control method, for example, a method of controlling power supplied to the heater or feedback controlling the element resistance to a target value corresponding to the activation temperature of the sensor element is known.

  In the gas concentration sensor, a change in the power supply voltage of the heater or a voltage change due to the harness occurs, and the power fluctuates due to the change. As a result, there arises a problem that the controllability of heater energization is lowered.

  Further, when controlling the heater energization, the heater energization is periodically switched ON or OFF by duty ratio control. In this case, noise is generated in the electrical path of the sensor element at the time of ON / OFF switching. Therefore, if the element resistance detection period overlaps with the heater energization ON / OFF switching timing, noise due to heater energization ON / OFF switching will occur. There is a possibility that the element resistance is erroneously detected due to the influence of the above. In particular, when the sensor element harness and the heater harness are bundled together, such a problem is likely to occur.

  The present invention has been made paying attention to the above problems, and its object is to provide a heater control device for a gas concentration sensor that can suppress erroneous detection of element resistance and improve its detection accuracy. It is.

  In the first aspect of the present invention, the applied voltage or current to the sensor element is temporarily switched to a value for detecting the element resistance by the element resistance detecting means, and the current concentration or voltage change of the gas concentration sensor is changed from the current change or voltage change at that time. Element resistance is detected. The heater control means periodically turns on / off the power to the heater. In particular, when the element resistance detection period by the element resistance detection means overlaps with the heater energization ON / OFF switching timing, any one of the timings is forcibly shifted.

  If the element resistance detection period and the heater energization ON / OFF switching timing overlap, the element resistance may be erroneously detected due to the influence of noise caused by heater energization ON / OFF switching. On the other hand, according to the present invention, erroneous detection of element resistance can be suppressed and the detection accuracy can be improved.

  Specifically, as described in claim 2, when detecting the element resistance, it is estimated whether or not the heater energization ON / OFF switching overlaps in the element resistance detection period. It is preferable to change the energization switching timing before the start or after the end of detection. At this time, as described in claim 3, when it is estimated that the ON / OFF switching of the heater energization overlaps the element resistance detection period, the heater energization time before the start of the element resistance detection or after the end of the detection. It is better to change the timing of power switching to the one with less change.

  According to the second and third aspects of the invention, the element resistance detection period and the heater energization ON / OFF switching timing do not overlap each other, and the desired effect described above can be obtained. In particular, in claim 3, there is little influence on the heater energization time, and the heater controllability can be maintained well.

  According to the fourth aspect of the present invention, in detecting the element resistance, it is estimated whether the ON / OFF switching of the heater energization overlaps in the element resistance detection period. Wait for detection to start. This is a method of shifting the element resistance detection period, and in this case as well, the element resistance detection period and the heater ON / OFF switching timing can be prevented from overlapping.

  According to a fifth aspect of the present invention, the heater control means sets a duty ratio at a constant predetermined cycle and energizes the heater for an ON time corresponding to the duty ratio, and the heater energization ON / OFF When the switching overlaps the element resistance detection period, the predetermined period is lengthened or shortened. Similarly, in this case, it is possible to prevent the element resistance detection period and the heater energization ON / OFF switching timing from overlapping.

  In the invention according to claim 6, when the heater energization period and the element resistance detection period are synchronized, the maximum value or the minimum value is specified for the duty ratio of the heater energization so as not to overlap with the element resistance detection period. . Similarly, in this case, it is possible to prevent the element resistance detection period and the heater energization ON / OFF switching timing from overlapping.

  In some cases, the gas concentration sensor has a plurality of cells in the solid electrolyte body, and the element resistance detecting means detects the element resistance in each cell. In this case, as described in claim 7, any one of the cells In the element resistance detection period, it is preferable not to overlap the heater energization ON / OFF switching timing.

  Further, in a system having a plurality of gas concentration sensors, as described in claim 8, it is preferable not to overlap all ON / OFF switching timings of heater energization in the element resistance detection period of any gas concentration sensor. good.

  In each of the above inventions, it has been explained that the detection period of the element resistance and the heater energization ON / OFF switching timing do not overlap. However, the element resistance is obtained from the measurement result of the current change or the voltage change. When measuring current change and voltage change, it is good if it is not affected by noise. Therefore, as described in claim 20, the element resistance detection period can be the peak hold period of the peak hold circuit. Alternatively, the element resistance detection period may be a period including at least A / D conversion timing. According to the ninth and tenth aspects, the period during which the energization switching should not overlap is narrowed in a limited manner, so that the influence on the original element resistance detection and heater energization can be minimized.

(First embodiment)
A first embodiment in which the present invention is embodied as an air-fuel ratio detection device will be described with reference to the drawings. The air-fuel ratio detection apparatus in the present embodiment is applied to a gasoline engine mounted on an automobile. In the air-fuel ratio control system, the fuel injection amount to the engine is determined based on the detection result by the air-fuel ratio detection apparatus. Control at a desired air-fuel ratio. In the air-fuel ratio control apparatus, the air-fuel ratio is detected from the oxygen concentration in the exhaust gas using the detection result of the limiting current air-fuel ratio sensor (A / F sensor), and the A / F sensor is activated. In order to maintain it, the element impedance (element resistance) is detected, and the heater built in the sensor is energized. Details will be described below.

  FIG. 1 is an overall configuration diagram showing an outline of an air-fuel ratio detection apparatus according to the present embodiment. In FIG. 1, the air-fuel ratio detection device 15 includes a microcomputer (hereinafter referred to as a microcomputer 20) that forms the center of the internal calculation. The microcomputer 20 controls an engine control ECU 16 for realizing fuel injection control, ignition control, and the like. So that they can communicate with each other. The A / F sensor 30 is attached to an exhaust pipe 12 extending from the engine main body 11 of the engine 10, and a linear air-fuel ratio detection signal proportional to the oxygen concentration in the exhaust gas in accordance with the application of a voltage commanded from the microcomputer 20. (Sensor current signal) is output.

  The microcomputer 20 is configured by a well-known CPU, ROM, RAM, and the like for executing various arithmetic processes, and controls a bias control circuit 24 and a heater control circuit 26 described later according to a predetermined control program. The microcomputer 20 operates by receiving power from the battery power source + B.

  The A / F sensor 30 is configured by a so-called multilayer sensor in which a heater is stacked on a sensor element made of a solid electrolyte body, and the solid electrolyte body and the heater are integrated. Hereinafter, the sensor element structure of the A / F sensor 30 will be described with reference to FIG. The sensor element has a long shape, and FIG. 2 shows a cross-sectional structure in a direction orthogonal to the longitudinal direction.

  In the A / F sensor 30, the oxygen ion conductive solid electrolyte body 31 made of partially stabilized zirconia has a rectangular plate shape, and an exhaust gas side electrode 32 is provided on one surface thereof, and the other surface thereof is provided on the other surface. A reference gas side electrode 33 facing the reference gas chamber 37 is provided. The solid electrolyte body 31 is laminated with a porous diffusion resistance layer 34 made of alumina ceramic having a porosity of about 10% and a gas shielding layer 35 made of dense and gas-sealing alumina ceramic.

  The solid electrolyte body 31 is laminated with a spacer 36 made of alumina ceramic that is electrically insulating and dense and does not transmit gas. The spacer 36 is provided with a groove 36 a that functions as a reference gas chamber 37. It has been. A heater substrate 38 is laminated on the spacer 36, and a heater (heating element) 39 that generates heat when energized is provided on the heater substrate 38.

  Returning to the description of FIG. In FIG. 1, a bias command 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 converted into an analog signal V1 by the D / A converter 21. Thereafter, the signal is input to an LPF (low-pass filter) 22. The output voltage V2 from which the high-frequency component of the analog signal V1 has been removed by the LPF 22 is input to the bias control circuit 24. In the bias control circuit 24, a voltage corresponding to the A / F value at that time is applied to the A / F sensor 30 based on a predetermined applied voltage characteristic at the time of A / F detection, and a single-shot signal composed of a predetermined frequency signal at the time of detecting the element impedance. In addition, a voltage having a predetermined time constant is applied to the A / F sensor 30.

  The current detection circuit 25 in the bias control circuit 24 detects the current value that flows along with the voltage applied to the A / F sensor 30. An analog signal having a current value detected by the current detection circuit 25 is input to the microcomputer 20 via the A / D converter 23.

  The operation of the heater 39 of the A / F sensor 30 is controlled by the heater control circuit 26. That is, the heater control circuit 26 duty-controls energization to the heater 39 according to the element impedance of the A / F sensor 30 in accordance with a command from the microcomputer 20. In this case, the duty frequency of the heater control signal is about 10 Hz, and when the heater is energized, the ON time (energization time) of the heater 39 in one cycle of about 100 ms is controlled.

  FIG. 3 is a circuit diagram showing a configuration of the heater control circuit 26. In FIG. 3, one end of the heater 39 is connected to the battery power source + B, and the other end is connected to the collector of the transistor 26a. The emitter of the transistor 26a is grounded through a heater current detection resistor 26b. The heater voltage Vhe is detected by the potential difference between both ends of the heater 39, and the detection result is input to the microcomputer 20 via the operational amplifier 26c and the A / D converter 27. The heater current Ihe is detected by a potential difference between both ends of the heater current detection resistor 26b, and the detection result is input to the microcomputer 20 via the operational amplifier 26d and the A / D converter 28.

  Incidentally, when the heater control signal is switched from OFF to ON, an interrupt process is started by the microcomputer 20, and the detection timing of the heater voltage Vhe and the heater current Ihe is set by the interrupt process. In this case, when the heater energization is switched ON, a hardware delay occurs in the rise of the heater current Ihe, and thus the heater voltage Vhe and the heater current Ihe are detected at a timing that takes the delay into consideration.

  Next, the operation of the air-fuel ratio detection device 15 configured as described above will be described. FIG. 4 is a flowchart showing an outline of a main routine executed by the microcomputer 20, and this routine is started when the microcomputer 20 is turned on.

  In FIG. 4, first, in step 100, it is determined whether or not a predetermined time Ta has elapsed since the previous A / F detection. The predetermined time Ta is a time corresponding to the detection period of the A / F value, and is set to about Ta = 4 msec, for example. Then, on the condition that step 100 is YES, the process proceeds to step 110, and A / F value detection processing is performed. In this A / F value detection process, an applied voltage corresponding to the sensor current at that time is set, and the voltage is applied between the electrodes 32 and 33 of the A / F sensor 30, and the sensor current at that time is detected as a current. Detection is performed by the circuit 25. Then, the detected sensor current is converted into an A / F value.

  After detecting the A / F value, in step 120, it is determined whether or not a predetermined time Tb has elapsed since the previous element impedance detection. The predetermined time Tb is a time corresponding to the detection cycle of the element impedance ZAC, and for example, a time such as 128 msec or 2 sec is selectively set according to the engine operating state. Then, on the condition that step 120 is YES, the element impedance ZAC is detected in step 130, and heater energization control is performed in the subsequent step 140. The element impedance ZAC detection process and heater energization control will be described in detail later.

  Next, the detection procedure of the element impedance ZAC in step 130 of FIG. 4 will be described with reference to FIG. In the present embodiment, when detecting the element impedance ZAC, a so-called “alternating current impedance” is obtained using a sweep method.

  In FIG. 5, first, in step 131, a heater control signal confirmation process is performed so that the heater 39 is not switched ON / OFF within the detection period of the element impedance ZAC.

  In short, when the impedance is detected by the sweep method, the sensor applied voltage is temporarily manipulated to either positive or negative, but when the heater 39 is switched ON / OFF at that time, noise is generated in the electrical path of the sensor element, and ZAC This may affect the detected value. In particular, when the harness of the sensor element and the harness of the heater 39 are bundled together, such a problem is likely to occur. Therefore, the heater ON / OFF timing is monitored by a counter in the microcomputer 20, and any of the following processes is performed so that the detection period of the element impedance ZAC and the heater ON / OFF timing do not overlap.

  (1) When the heater ON / OFF timing occurs within the element impedance ZAC detection period, the impedance detection is started after the heater ON / OFF timing.

  (2) When the heater ON / OFF timing occurs within the detection period of the element impedance ZAC, the heater ON / OFF switching is made to wait until the impedance detection is completed. In this case, the ON time or OFF time of the heater 39 is temporarily extended (or shortened).

  Thereafter, in step 132, the bias command signal Vr is manipulated to change the voltage to the positive side in a time of about several tens to 100 μsec with respect to the applied voltage for A / F detection up to that time. In step 133, the voltage change amount ΔV at that time and the sensor current change amount ΔI detected by the current detection circuit 25 are read. In the following step 134, the element impedance ZAC is calculated from the ΔV value and ΔI value (ZAC = ΔV / ΔI), and then the process returns to the original routine of FIG.

  According to the above processing, a voltage having a predetermined time constant is applied to the A / F sensor 30 through the LPF 22 and the bias control circuit 24 of FIG. As a result, as shown in FIG. 7, the peak current (current change amount ΔI) is detected after elapse of time t from the application of the voltage, and the element impedance ZAC is detected from the voltage change amount ΔV and the peak current (ΔI) at that time. (ZAC = ΔV / ΔI). In such a case, by applying a single voltage to the A / F sensor 30 via the LPF 22, generation of an excessive peak current is suppressed, and a highly reliable element impedance ZAC can be detected.

  The element impedance ZAC obtained as described above has the relationship shown in FIG. 8 with respect to the element temperature. That is, the lower the element temperature, the greater the element impedance ZAC. In the above configuration, the voltage applied to the sensor is temporarily switched during impedance detection. Instead of this, the current flowing through the sensor element may be switched temporarily. The element impedance is detected from the voltage change amount.

  Next, the heater energization control procedure in step 140 of FIG. 4 will be described with reference to FIG. In the present embodiment, the heater energization is feedback-controlled according to the deviation of the element impedance ZAC so that the sensor element of the A / F sensor 30 is maintained at the target temperature = 700 ° C.

  In FIG. 6, first, in step 141, the execution condition of the heater control at the time of temperature rise is determined. Specifically, the condition for performing the heater control at the time of temperature rise is determined based on whether or not the element impedance ZAC is a predetermined determination value (for example, 50Ω) or more. For example, immediately after the engine is started and the element temperature of the A / F sensor 30 is still low, it is determined that the element impedance ZAC is large and the heater control at the time of temperature increase is performed (YES in step 141).

  When step 141 is YES, it progresses to step 142 and performs heater control at the time of temperature increase. In this heater control at the time of temperature rise, basically all energization control with a duty ratio of 100% is performed. Next, in step 149, after performing duty correction based on the heater power and the like, the process returns to the original routine of FIG. The duty correction in step 149 will be described later.

  If the element temperature rises, step 141 becomes NO. In this case, in step 143, it is determined whether or not the element temperature is less than 720 ° C. based on the element impedance ZAC at that time, and in the subsequent step 144, the element temperature is also 680 ° C. or more based on the element impedance ZAC. It is determined whether or not. That is, the range of ± 20 ° C. around the target value (700 ° C.) of the element temperature is set as the element temperature control range. In steps 143 and 144, the element temperature is within the control range (in this embodiment, 700 ± 20). It is determined whether or not the temperature is within (° C). Then, the process proceeds to step 145 on condition that the element temperature is within the control range, and the control duty ratio Duty is calculated by a known PID control method.

  Specifically, in step 145, the element impedance ZAC at the previous processing is set to the previous value “ZAC0”, and in the subsequent step 146, the current value ZAC of the element impedance (detected value according to FIG. 5) is read. In step 147, the proportional term Gp, the integral term Gi, and the differential term Gd are calculated by the following mathematical formula.

Gp = Kp. (ZAC-ZACref)
Gi = Gi + Ki · (ZAC−ZACref)
Gd = Kd · (ZAC−ZAC0)
In the above equations, “Kp” represents a proportional constant, “Ki” represents an integral constant, and “Kd” represents a differential constant.

  In step 148, the proportional term Gp, integral term Gi, and differential term Gd are added to calculate the control duty ratio Duty (Duty = Gp + Gi + Gd). Return to the routine.

  On the other hand, when the element temperature is not within the control range, the control duty ratio Duty is guarded at steps 150 and 151. That is, when the element temperature is 720 ° C. or higher (when step 143 is NO), the process proceeds to step 150, where the control duty ratio Duty is guarded with a predetermined upper limit value. At this time, for example, the maximum value of Duty is limited so that Duty = 10% or less. When the element temperature is lower than 680 ° C. (when step 144 is NO), the process proceeds to step 151 where the control duty ratio Duty is guarded with a predetermined lower limit value. At this time, for example, the minimum value of Duty is limited so that Duty = 60% or more.

  Incidentally, the upper limit guard set in step 150 corresponds to the “first guard value” described in the claims, and the lower limit guard set in step 151 corresponds to the “second guard value”. According to the value, the duty is limited in the direction in which the change in the element temperature (element impedance) is suppressed. As an example, the guard values are Duty = 10% and 60%. However, the numerical values may be arbitrary, and design values that do not cause defects such as element cracks may be used as appropriate.

  In the present embodiment, the processing of FIG. 5 corresponds to “element resistance detection means” recited in the claims. 6 are the same “determination means”, steps 145 to 148 are the same “control amount calculation means”, step 149 is the same “control amount correction means”, and steps 150 and 151 are the same “ It corresponds to “guard value setting means”.

  Next, the contents of the duty correction at step 149 will be described in detail. This duty correction is performed based on a comparison between a standard heater power defined in advance and a calculated value of the heater power each time. Basically, a quotient of the reference power and the detected power, “ “Reference power / detected power” is used as a correction term, the correction term is multiplied by the control duty ratio Duty, and the product is set as the corrected Duty. In this case, in order to perform correction by power comparison (reference power / detected power), detection values of both the heater voltage and the heater current are required. However, since the processing load increases, the following (a) The correction by the heater voltage and the correction by the heater current will be described in detail.

(A) Correction by heater voltage When the heater power is W, the heater voltage is V, the heater current is I, and the heater resistance is R, W = V · I = V ^ 2 / R. Indicates power.) In this case, if the heater resistance R is assumed to be constant, the correction term “reference power / detection power” is obtained by “reference voltage ^ 2 / detection voltage ^ 2”. That is, if the reference voltage is defined in advance, the correction term can be calculated from the detection voltage of the heater 39. Then, the duty value is multiplied by the correction term to correct the duty.

  On the other hand, if W = V · I and the heater current I is considered to be constant, the correction term “reference power / detection power” is obtained by “reference voltage / detection voltage”. Also in this case, if the reference voltage is defined in advance, the correction term can be calculated from the detection voltage of the heater 39. Then, the duty value is multiplied by the correction term to correct the duty.

(B) Correction by heater current When W = V · I = I ^ 2 · R and the heater resistance R is considered to be constant, the correction term “reference power / detection power” is “reference current ^ 2 / detection current”. ^ 2 ". That is, if the reference current is defined in advance, the correction term can be calculated from the detected current of the heater 39. Then, the duty value is multiplied by the correction term to correct the duty.

  On the other hand, if W = V · I and the heater voltage V is considered to be constant, the correction term “reference power / detected power” is obtained by “reference current / detected current”. Also in this case, if the reference current is defined in advance, the correction term can be calculated from the detected current of the heater 39. Then, the duty value is multiplied by the correction term to correct the duty.

  According to the above-described correction by (a) heater voltage and (b) correction by heater current, duty correction for voltage change or current change can be easily performed. In particular, when the correction by the heater current is performed, since the current flowing through the energization path of the heater 39 is the same everywhere, the correction can be performed including the variation of the harness resistance.

  It is also possible to use a predefined map as correction by the heater voltage or heater current. Specifically, the correction amount is calculated according to the detected value of the heater voltage using the relationship of FIG. According to FIG. 9, as the heater voltage (detected value) increases with respect to the reference voltage, a smaller correction term is set. Further, the same operation may be performed at the time of correction by the heater current. In this case, if the voltage drop due to the harness is reflected as the map value, the system can be easily adapted.

  FIG. 10 is a time chart showing how the heater energization control is performed as described above, particularly when the element temperature rapidly increases or decreases. Here, (a) in FIG. 10 shows a case where the element temperature rises (ie, ZAC falls) due to factors such as heating of the exhaust gas and falls outside the control range, and (b) in FIG. 10 shows a fuel cut. The case where the element temperature falls due to factors such as (ZAC increases) and falls outside the control range is shown. In the figure, symbol ▽ indicates the timing at which heater energization control is performed at intervals of, for example, 128 msec.

  In FIG. 10A, the element temperature is feedback-controlled near the target value (700 ° C.) before the timing t1. When the element temperature rapidly rises at the timing of t1 and the element temperature at the timing of t2 deviates to the high temperature side of the control range (when it becomes 720 ° C. or more), the control duty ratio Duty is guarded at the maximum value of 10%. In this case, if normal feedback control (PID control) is continued after t2, the duty changes as shown by a two-dot chain line in the figure, and the duty cannot be immediately controlled to a low value. On the other hand, the control delay is eliminated by guarding the duty with the maximum value as described above.

  In FIG. 10B, the element temperature is feedback-controlled near the target value (700 ° C.) before the timing t11. Then, when the element temperature suddenly falls at the timing of t11 and the element temperature at the timing of t12 deviates to the low temperature side of the control range (below 680 ° C.), the control duty ratio Duty is guarded at the minimum value of 60%. In this case as well, the control delay is eliminated as described above.

  According to the embodiment described in detail above, the following effects can be obtained. Since the control duty ratio Duty (heater control amount) is corrected based on a comparison between a predetermined standard heater power and the actual heater power in each case, a change in the power supply voltage of the heater 39 or a voltage caused by the harness Even if power changes due to a change, the control duty ratio Duty can be set in correspondence with the change. As a result, it is possible to appropriately set the control duty ratio Duty and thus improve the controllability of the heater energization.

  In this case, the duty correction is performed by a simple method by correcting the duty by comparing the reference value of the heater voltage with the detected value or by correcting the duty by comparing the reference value of the heater current with the detected value. Can be realized.

  Since the upper limit guard and the lower limit guard of the control duty ratio Duty are set and the duty is limited in such a direction as to suppress the change in the element temperature (element impedance), even if the element temperature changes suddenly due to a rise in exhaust temperature, fuel cut, etc. The heater control can be performed by following the change quickly. In particular, when calculating Duty while reflecting an integral term by PID control, a control delay occurs when the temperature changes suddenly. However, according to the present embodiment, the control delay is eliminated. Therefore, early activation of the sensor element at a low temperature and prevention of problems such as element cracking at a high temperature can be realized.

  Since the duty correction is performed on the upper limit guard and the lower limit guard of the control duty ratio Duty in the same manner as in normal feedback control, the control accuracy of heater energization using the guard value is improved.

  Since each timing is adjusted so that the detection period of the element impedance ZAC does not overlap with the heater ON / OFF timing, erroneous detection of the element impedance ZAC is suppressed, and the detection accuracy is improved.

(Second Embodiment)
Next, a second embodiment will be described. In the first embodiment, the heater control signal confirmation process (step 131 in FIG. 5) is briefly described so that the heater 39 is not turned ON / OFF within the detection period of the element impedance ZAC. In this embodiment, a detailed configuration will be described.

  In the present embodiment, the present invention is embodied in a gas concentration detection device capable of detecting NOx concentration in exhaust gas, and FIG. 11 is a configuration diagram showing an outline of the gas concentration detection device. FIG. 12 is a sectional view showing details of the gas concentration sensor. First, the configuration of the gas concentration sensor 100 will be described with reference to FIG. The gas concentration sensor 100 has a three-cell structure including a pump cell, a sensor cell, and a monitor cell, and is embodied as a so-called composite gas sensor that can simultaneously detect the oxygen concentration and NOx concentration in the exhaust gas. 12A is a cross-sectional view showing the tip portion structure of the sensor element, and FIG. 12B is a cross-sectional view taken along line AA of FIG. 12A.

  In the gas concentration sensor 100, solid electrolytes (solid electrolyte elements) 141, 142 made of an oxygen ion conductive material have a plate shape, and are spaced apart from each other by a predetermined interval via a spacer 143 made of an insulating material such as alumina. Are stacked. Among these, a pinhole 141a is formed in the solid electrolyte 141 on the upper side of the figure, and exhaust gas around the sensor is introduced into the first chamber 144 through the pinhole 141a. The first chamber 144 communicates with the second chamber 146 through the throttle unit 145. Reference numeral 147 denotes a porous diffusion layer.

  The solid electrolyte 142 on the lower side of the figure is provided with a pump cell 110 so as to face the first chamber 144, and the pump cell 110 discharges or pumps oxygen in the exhaust gas introduced into the first chamber 144. At the same time, it detects the oxygen concentration in the exhaust gas. Here, the pump cell 110 has a pair of upper and lower electrodes 111 and 112 with a solid electrolyte 142 interposed therebetween, and in particular, the electrode 111 on the first chamber 144 side is a NOx inert electrode (an electrode that is difficult to decompose NOx gas). . The pump cell 110 decomposes oxygen present in the first chamber 144 and discharges it from the electrode 112 to the atmosphere passage 150 side.

  Further, a monitor cell 120 and a sensor cell 130 are provided on the solid electrolyte 141 on the upper side of the drawing so as to face the second chamber 146. The monitor cell 120 generates a current output in accordance with the electromotive force or voltage application according to the residual oxygen concentration in the second chamber 146. The sensor cell 130 detects the NOx concentration from the gas that has passed through the pump cell 110.

  In particular, in the present embodiment, as shown in FIG. 12B, the monitor cell 120 and the sensor cell 130 are arranged in parallel so as to be in the same position with respect to the flow direction of the exhaust gas. The electrode on the atmosphere passage 148 side is a common electrode 122. That is, the monitor cell 120 includes a solid electrolyte 141 and an electrode 121 and a common electrode 122 arranged to face each other, and the sensor cell 130 similarly includes the solid electrolyte 141 and an electrode 131 and a common electrode arranged to face each other. 122. The electrode 121 (electrode on the second chamber 146 side) of the monitor cell 120 is made of a noble metal such as Au—Pt inert to NOx gas, whereas the electrode 131 (electrode on the second chamber 146 side) of the sensor cell 130 is It consists of noble metals such as Pt that are active in NOx gas.

  An insulating layer 149 is provided on the lower surface of the solid electrolyte 142 in the figure, and an atmospheric passage 150 is formed by the insulating layer 149. In addition, a heater 151 for heating the entire sensor is embedded in the insulating layer 149. The heater 151 generates heat energy by supplying power from the outside in order to activate the entire sensor including the pump cell 110, the monitor cell 120, and the sensor cell 130.

  In the gas concentration sensor 100 having the above configuration, the exhaust gas is introduced into the first chamber 144 through the porous diffusion layer 147 and the pinhole 141a. When the exhaust gas passes through the vicinity of the pump cell 110, a decomposition reaction occurs by applying a voltage between the electrodes 111 and 112 of the pump cell 110, and oxygen flows through the pump cell 110 according to the oxygen concentration in the first chamber 144. Is put in and out. At this time, since the electrode 111 on the first chamber 144 side is a NOx inactive electrode, NOx in the exhaust gas is not decomposed in the pump cell 110, but only oxygen is decomposed and discharged to the atmospheric passage 150. Then, the oxygen concentration contained in the exhaust gas is detected by the current flowing through the pump cell 110.

  Thereafter, the exhaust gas that has passed in the vicinity of the pump cell 110 flows into the second chamber 146, and the monitor cell 120 generates an output corresponding to the residual oxygen concentration in the gas. The output of the monitor cell 120 is detected as a monitor cell current by applying a predetermined voltage between the electrodes 121 and 122 of the monitor cell 120. Further, by applying a predetermined voltage between the electrodes 131 and 122 of the sensor cell 130, NOx in the gas is reduced and decomposed, and oxygen generated at that time is discharged to the atmospheric passage 148. At that time, the concentration of NOx contained in the exhaust gas is detected by the current flowing through the sensor cell 130.

  Next, the electrical configuration of the gas concentration detection device will be described with reference to FIG. FIG. 11 shows a gas concentration detection apparatus using the gas concentration sensor 100 described above, but the electrode arrangement of the monitor cell 120 and the sensor cell 130 is shown in a side-by-side state for convenience.

  In FIG. 11, the control circuit 200 is configured by a known microcomputer including a CPU, an A / D converter, a D / A converter, an I / O port, and the like, and applies an applied voltage to each of the cells 110 to 130 as a D / A. Output as appropriate from the converter (D / A0 to D / A2). In addition, the control circuit 200 uses the A / D converter (A / D0 to A / D5) to set the voltages of the terminals Vc, Ve, Vd, Vb, Vg, and Vh to measure the current flowing through the cells 110 to 130. Enter each. The control circuit 200 detects the oxygen concentration and NOx concentration in the exhaust gas based on the current measured by the pump cell 110 and the sensor cell 130, and outputs the detected value to the outside from the D / A converter (D / A4, D / A3). To do.

  For details of the circuit configuration, in the pump cell 110, the reference voltage Va is applied to one electrode 112 by the reference power supply 201 and the operational amplifier 202, and the control circuit 200 is connected to the other electrode 111 via the operational amplifier 203 and the current detection resistor 204. Command voltage (Vb) is applied. When a current flows through the pump cell 110 according to the oxygen concentration in the exhaust gas when applying Vb, the current is detected by the current detection resistor 204. That is, the Vb voltage and the Vd voltage, which are both terminal voltages of the current detection resistor 204, are taken into the control circuit 200, and the pump cell current Ip is calculated from the Vb voltage and the Vd voltage.

  A reference voltage Vf is applied to the common electrode 122 of the monitor cell 120 and the sensor cell 130 by the reference power source 205 and the operational amplifier 206, and an operational amplifier 207 and a current detection resistor 208 are provided to the sensor cell electrode 131 different from the common electrode 122. The command voltage (Vg) of the control circuit 200 is applied through the via. When a current flows through the sensor cell 130 according to the NOx concentration in the exhaust gas when applying Vg, the current is detected by the current detection resistor 208. That is, the Vg voltage and the Vh voltage that are both terminal voltages of the current detection resistor 208 are taken into the control circuit 200, and the sensor cell current Is is calculated from the Vg voltage and the Vh voltage.

  Further, the command voltage (Vc) of the control circuit 200 is applied to the monitor cell electrode 121 different from the common electrode 122 via an LPF (low-pass filter) 209, an operational amplifier 210 and a current detection resistor 211. When a current flows through the monitor cell 120 according to the residual oxygen concentration in the exhaust gas when applying Vc, the current is detected by the current detection resistor 211. That is, the Vc voltage and the Ve voltage that are both terminal voltages of the current detection resistor 211 are taken into the control circuit 200, and the monitor cell current Im is calculated from the Vc voltage and the Ve voltage. The LPF 209 is realized by a primary filter made up of a resistor and a capacitor, for example.

  In the present embodiment, the element impedance is detected for the monitor cell 120 using the sweep method. That is, when the impedance of the monitor cell 120 is detected, the control circuit 200 instantaneously switches the monitor cell applied voltage (command voltage Vc) to at least one of the positive side and the negative side. This applied voltage is applied to the monitor cell 120 while being sinusoidally processed by the LPF 209. The frequency of the AC voltage is desirably 10 kHz or more, and the time constant of the LPF 209 is set at about 5 μsec. Then, the element impedance of the monitor cell 120 is calculated from the voltage change amount and current change amount at that time.

  Incidentally, in the monitor cell 120 and the sensor cell 130, since one electrode is the common electrode 122, there is an advantage that the drive circuit on the reference voltage side can be reduced and the advantage that the number of lead wires taken out from the gas concentration sensor 100 can be reduced. It is done. In addition, since the monitor cell 120 and the sensor cell 130 are formed adjacent to each other with the same solid electrolyte 141, there is a concern that the current flows to the adjacent electrode during the sweep and the impedance detection accuracy deteriorates. By providing, one electrode becomes the same electric potential, and this influence can be reduced.

  Incidentally, in the monitor cell 120, only a current of about several μA flows when detecting residual oxygen, whereas a current of about several mA flows during sweeping for impedance detection. If currents with different orders are detected by the same detection resistor, overrange may occur or detection accuracy may deteriorate. Therefore, in the present embodiment, the current detection resistor is switched between the residual oxygen detection by the monitor cell 120 and the impedance detection.

  Specifically, another current detection resistor 212 and a switch circuit 213 (for example, a semiconductor switch) are provided in parallel with the current detection resistor 211. The switch circuit 213 is configured to be turned on / off by an output from the I / O port of the control circuit 200. In this case, at the time of normal gas concentration detection, the switch circuit 213 is turned off (opened), and the monitor cell current Im is detected by a resistance of about several hundred kΩ by the current detection resistor 211. On the other hand, at the time of impedance detection, the switch circuit 213 is turned on (closed), and the monitor cell current Im is detected by a resistance of about several hundred Ω by the current detection resistors 211 and 212.

  The Ve voltage is input to the control circuit 200 through the P / H circuit (peak hold circuit) 220. In this case, in the P / H circuit 220, the P / H period is set and canceled by the control circuit 200, and the P / H period is temporarily set in the vicinity of the voltage change reaching the peak value when the impedance is detected. ing.

  The CPU in the control circuit 200 drives the MOSFET driver 251 by outputting the control duty ratio Duty from the I / O port. At this time, the power supplied from the power source 253 (for example, battery power source) to the heater 151 by the MOSFET 252 is PWM-controlled. In the present embodiment, the control circuit 200 constitutes “element resistance detection means” and “heater control means” described in the claims.

  FIG. 13 is a time chart showing an outline of heater energization. As shown in FIG. 13, the PWM counter is configured to repeat counting up at a constant time period. In this embodiment, 128 msec is one period of the PWM counter. Incidentally, this time is the same as the detection cycle of the element impedance ZAC.

  Each time the control duty ratio Duty is calculated, the heater ON set time is set in a register or the like according to the Duty, and when the PWM counter reaches the ON set time, the heater energization is switched from ON to OFF. The heater energization is turned on again at the timing when the PWM counter is reset.

  For example, when the impedance detection period is set in the Ti period in the figure and the Ti period overlaps with ON / OFF switching of the heater energization (ON to OFF in the figure), noise is detected in the electrical path of the sensor element as described above. This is considered to affect the detection value of ZAC. Specifically, as shown in FIG. 20, an error ΔIa occurs in the waveform of the sweep current that accompanies the sweep of the applied voltage, and an incorrect peak value is stored when the P / H circuit 220 is used. Therefore, in the present embodiment, it is proposed to forcibly change the timing of either ON or OFF of the heater energization when the heater energization is switched ON / OFF within the impedance detection period.

  That is, in FIG. 14 showing the details, the timings a and b are the impedance detection period Ti, and the sweep waveform is given to the sensor terminal voltage (or sensor current) within the period Ti. In this case, since the energization OFF timing c occurs within the impedance detection period Ti, the energization OFF timing c is set earlier or later so that the heater energization does not occur during the impedance detection period Ti.

  Actually, it is the voltage change amount ΔV (or equivalent current change) that is desired to be detected accurately within the impedance detection period Ti, and the heater energization is turned on during the period from the start of the change of the sensor voltage to the peak value. It is good if / OFF does not occur. In particular, in this configuration in which the peak value of the voltage change is taken into the control circuit 200 via the P / H circuit 220, the heater energization is turned ON / OFF in the P / H period (periods a to d in the figure) by the P / H circuit 220. If it does not occur, it is good. Therefore, when the energization OFF timing is advanced, the energization OFF timing is changed to timing a, and the energization waveform is changed to “1 after change” in the figure. Further, in order to delay the energization OFF timing, the energization OFF timing is changed to timing d, and the energization waveform is set to “2 after change” in the figure. Incidentally, the duty becomes small after the change 1 and becomes large after the change 2.

  In order to force the heater energization ON / OFF timing earlier or later, the actual heater control signal may be controlled by manipulating the port output. Specifically, as shown in FIG. 15, when the impedance detection period Ti and the energization OFF timing overlap, the port output is temporarily turned OFF, thereby changing the heater energization from the state before the change shown in the figure. Switch to a later state. In addition, it is also possible to change the ON setting time of the PWM counter to the increase side or the decrease side, thereby making the energization switching timing earlier or later.

  FIG. 16 is a flowchart showing a ZAC detection routine in the present embodiment, and this processing is performed by the control circuit 200 at a predetermined time period (in this embodiment, 128 msec period). The process of FIG. 16 corresponds to the process of FIG. 5 in the first embodiment. In practice, the control circuit 200 performs the process corresponding to FIGS. 4 and 6 in addition to this ZAC detection routine. . Although illustration is omitted, in the case of the present embodiment, the NOx concentration is detected in addition to the detection of A / F in the process corresponding to FIG.

The heater energization ON / OFF switching is basically performed separately from the element impedance detection process (the process of FIG. 16), but in this embodiment, the impedance detection period and the heater energization ON / OFF switching timing are performed. Only when and overlap, the switching of the energization is performed within the element impedance detection process.
In FIG. 16, first, at step 301, the current PWM counter value is read, and at the next step 302, the current switching timing is confirmed from the current PWM counter, the ON setting time, and the required time of the P / H period. Then, it is estimated whether the ON / OFF switching of heater energization is performed redundantly during the current impedance detection period (P / H period). Further, at this time, when it is estimated that the energization switching is duplicated, it is determined whether the energization switching is made earlier or later. For this, it is sufficient to select the one with less change of the duty.

  Thereafter, in step 303, it is determined whether or not the heater energization switching should be performed now. When it is assumed that the energization switching is duplicated and the energization switching is accelerated, the step is set to YES, and the heater energization is immediately switched on / off in step 304.

  Thereafter, in step 305, P / H by the P / H circuit 220 is started, and in the subsequent step 306, the applied voltage is changed (swept) once. In step 307, voltage change and current change at that time are measured, and in step 308, P / H by the P / H circuit 220 is terminated.

  In step 309, it is determined whether or not the heater energization switching should be performed now. When it is estimated that the energization switching is duplicated and the energization switching is delayed, the corresponding step is set to YES, and the heater energization is immediately switched on / off in step 310. Finally, in step 311, the element impedance ZAC is calculated from the measured voltage change and current change.

  As described above, according to the present embodiment, when the impedance detection period overlaps with the heater energization ON / OFF switching timing, any one of the timings is forcibly shifted back and forth, so that the element impedance ZAC is erroneously detected. And the detection accuracy can be improved.

  When the heater energization ON / OFF switching overlaps with the impedance detection period, the energization switching timing is changed to the one with less change in the heater energization time (Duty) before the impedance detection starts or after the detection ends. There is little influence on heater energization time, and heater controllability can be maintained well.

  In particular, since the heater energization switching timing is changed so as not to overlap the P / H period, the period during which the energization switching should not overlap is limited and the change in heater energization time can be minimized. Incidentally, by taking in the peak value of the voltage change via the P / H circuit 220, the peak value can be detected correctly even if the timing of the voltage peak varies back and forth.

  When A / D conversion is performed at a predetermined timing and a peak voltage or the like is thereby acquired, the switching timing is changed so that the heater energization switching is not performed at least at the A / D conversion timing. It ’s fine.

  In order to prevent the impedance detection period and the heater energization ON / OFF switching timing from overlapping, a method other than the above can be used, and another mode will be described below.

  First, in FIG. 17, when the heater energization switching timing and the impedance detection period Ti overlap, the start of impedance detection (actually the start of P / H) is waited until the energization switching ends. In the case of FIG. 17, the impedance detection period is changed from Ti to Tia. Similarly, even when the impedance detection period is shifted, it is possible to prevent the impedance detection period and the heater ON / OFF switching timing from overlapping.

  Next, in FIG. 18, when the heater energization switching timing and the impedance detection period Ti overlap, the PWM cycle is lengthened or shortened to change the heater control state. In the example of FIG. 18, the PWM cycle is changed from Tα to Tβ. In this case, if the period of PWM and the period of impedance detection are synchronized, it is only necessary to change to Tβ once and then return to Tα. Here, the period of PWM and the period of impedance detection are in synchronism with each other when the period is the same, or when the period of impedance detection is n times or 1 / n times the period of PWM. Say. Similarly, even when the heater control state is changed, it is possible to prevent the impedance detection period and the heater ON / OFF switching timing from overlapping.

  In FIG. 19, when the PWM period and the impedance detection period are synchronized, the heater energization duty ratio (ON setting time) is maximized so that the heater energization switching timing and the impedance detection period Ti do not overlap. Or it defines the minimum value. In the example of FIG. 19, an upper limit guard value is set so that the ON setting time does not exceed the upper limit guard value. In such a case as well, the effects described above can be obtained. If there is an impedance detection period immediately after the heater energization is ON, a lower limit guard value for the ON setting time may be set.

  In the above description, the element impedance is detected for the monitor cell 120 of the gas concentration sensor 100, but the case where the element impedance is also detected for other cells (pump cell 100, sensor cell 130) is conceivable. In this case, it is preferable not to overlap the heater energization switching timing in the impedance detection period of any cell.

  Also, in a system having a plurality of gas concentration sensors, such as when a plurality of gas concentration sensors are provided in the exhaust pipe of an engine, the timing for switching ON / OFF all heater energization during the impedance detection period of any gas concentration sensor. It is good not to overlap.

  In addition to the above, the present invention can be embodied in the following forms. In FIG. 6, when the duty is limited by the guard value in steps 150 and 151, the duty correction for the guard value may be relatively loose. Therefore, the correction execution time interval is expanded only when the duty is limited by the guard value. In this case, the processing frequency relating to correction is reduced, and the processing load on the microcomputer 20 can be reduced.

  Further, the detection of the heater voltage and the heater current is permitted only when the ON time of the control duty ratio Duty is longer than a predetermined value. Actually, detection of the heater voltage and the heater current is permitted only when Duty ≧ 50%. That is, the heater voltage and heater current are detected when the heater energization is turned on, but if the ON time is too short, it becomes difficult to detect the heater voltage and heater current. On the other hand, according to this configuration, the detection of the heater voltage and the heater current can be reliably performed. In this case, the calculation load on the microcomputer 20 can be reduced, and the heater voltage and heater current can be detected with a simple detection circuit.

  As duty correction, it is also possible to correct the control duty ratio Duty based on a comparison between the heater voltage or heater current detected each time and the heater voltage or heater current detected before that. Specifically, correction is performed using the following equation.

かかる場合にも、既述の実施の形態と同様に、制御デューティ比Ｄｕｔｙを適正に設定し、ひいてはヒータ通電の制御性を向上させることができる。なお、上記数式において、「前回の検出電圧／今回の検出電圧」の項を、「前回の検出電圧＾２／今回の検出電圧＾２」に変更したり、「前回の検出電流／今回の検出電流」や「前回の検出電流＾２／今回の検出電流＾２」に変更したりしても良い。因みに、電圧又は電流は２乗の値を用いた方が補正の精度が向上する。また、比較の対象は、今回値と前回値とに限らず、今回値とそれ以前の値との比較であれば良い。

Even in such a case, the control duty ratio Duty can be set appropriately and the controllability of the heater energization can be improved as in the above-described embodiment. In the above equation, the term “previous detection voltage / current detection voltage” is changed to “previous detection voltage ^ 2 / current detection voltage ^ 2” or “previous detection current / current detection voltage”. The current may be changed to “current” or “previous detection current ^ 2 / current detection current ^ 2.” Incidentally, the accuracy of correction is improved when the voltage or current is a square value. The comparison target is not limited to the current value and the previous value, but may be a comparison between the current value and the previous value.

  In the above embodiment, both the duty correction process and the upper limit and lower limit guard processes are performed in the heater energization control routine of FIG. 6, but this routine is realized by incorporating at least the duty correction. It ’s fine. Further, at least one of the upper limit guard on the high temperature side (step 150 in FIG. 6) and the lower limit guard on the low temperature side (step 151 in FIG. 6) may be performed. As a configuration for guarding the control duty ratio Duty, basically, the higher the detected value of the element impedance, the higher the guard value of the element impedance so that the sensor element can be activated at a low temperature and the element can be prevented from cracking at a high temperature. Anything can be realized as long as the value is set to be large.

  As element resistance of the gas concentration sensor, instead of impedance, admittance that is the reciprocal thereof may be calculated. In this case, it is also possible to switch between impedance and admittance depending on the element temperature (sensor active state).

  As the gas concentration sensor, in addition to the aforementioned A / F sensor for detecting the oxygen concentration in the exhaust gas, for example, a NOx sensor for detecting the NOx concentration, an HC sensor for detecting the HC concentration, a CO sensor for detecting the CO concentration, etc. Applicable. In that case, a plurality of detection cells may be provided. Furthermore, a gas other than the exhaust gas can be used as the measurement gas. As the gas concentration detection device, applications other than the air-fuel ratio detection device can be applied.

The block diagram which shows the outline | summary of the air fuel ratio detection apparatus in embodiment of invention. Sectional drawing of the principal part of a sensor element. The circuit diagram which shows the structure of a heater control circuit. The flowchart which shows the main routine by a microcomputer. The flowchart which shows the detection procedure of element impedance. The flowchart which shows the control procedure of heater energization. The wave form diagram which shows the voltage change and current change at the time of an impedance detection. The figure which shows the relationship between element impedance and element temperature. The figure which shows the relationship between a heater voltage and a correction | amendment term. The time chart which shows a mode that heater energization control is implemented. The block diagram which shows the outline | summary of the gas concentration detection apparatus in 2nd Embodiment. Sectional drawing which shows the structure of a gas concentration sensor. The time chart which shows operation of heater energization. The time chart which shows the detail of heater energization switching. The time chart which shows operation of heater energization. The flowchart which shows the detection procedure of element impedance. The time chart which shows operation of heater energization. The time chart which shows operation of heater energization. The time chart which shows operation of heater energization. The time chart which shows the current waveform at the time of heater energization switching.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 15 Air-fuel ratio detection apparatus 20 Microcomputer 30 A / F sensor 31 Solid electrolyte body 39 Heater 100 Gas concentration sensor 110 Pump cell 120 Monitor cell 130 Sensor cell 141, 142 Solid electrolyte 151 Heater 200 Control circuit 220 P / H circuit

Claims (10)

A gas concentration sensor having a sensor element using a solid electrolyte body and a heater for heating the sensor element to an active state;
An element resistance detecting means for temporarily switching the applied voltage or current to the sensor element to a value for detecting the element resistance, and detecting the element resistance of the gas concentration sensor from the current change or voltage change at that time;
Heater control means for periodically turning ON / OFF the energization of the heater,
The heater of the gas concentration sensor, wherein when the element resistance detection period by the element resistance detection means and the heater energization ON / OFF switching timing overlap, any one of the timings is forcibly shifted. Control device. When detecting the element resistance by the element resistance detecting means, it is estimated whether the ON / OFF switching of the heater energization overlaps the element resistance detection period, and when it is estimated that it overlaps, the energization switching is performed before the detection starts or after the detection ends. The heater control device for a gas concentration sensor according to claim 1, wherein the timing is changed. When it is estimated that ON / OFF switching of heater energization overlaps in the element resistance detection period, the timing of switching energization is changed to the one with less change in heater energization time before the start of element resistance detection or after the end of detection. The heater control apparatus of the gas concentration sensor of Claim 2. When detecting the element resistance by the element resistance detection means, it is estimated whether the ON / OFF switching of heater energization overlaps with the element resistance detection period. The heater control device for a gas concentration sensor according to claim 1, wherein The heater control means sets a duty ratio at a constant predetermined cycle, and energizes the heater with an ON time corresponding to the duty ratio, and the heater energization ON / OFF switching overlaps the element resistance detection period. The heater control apparatus for a gas concentration sensor according to claim 1, wherein the predetermined period is lengthened or shortened. The gas concentration sensor according to claim 1, wherein when the heater energization period and the element resistance detection period are synchronized, a maximum value or a minimum value is specified for the duty ratio of the heater energization so as not to overlap with the element resistance detection period. Heater control device. The gas concentration sensor has a plurality of cells in the solid electrolyte body, and the element resistance detection means detects element resistance in each cell, and the heater energization is turned on in the element resistance detection period of any cell. The heater control device for a gas concentration sensor according to any one of claims 1 to 6, wherein the heater control device does not overlap with the timing of switching off / off. The system having a plurality of the gas concentration sensors, wherein any heater energization ON / OFF switching timing is not overlapped in an element resistance detection period of any gas concentration sensor. The heater control apparatus of the gas concentration sensor as described in 2. 9. The configuration according to claim 1, wherein a current change or a voltage change at the time of detecting the element resistance is captured via a peak hold circuit, and the detection period of the element resistance is a peak hold period of the peak hold circuit. Heater control device for gas concentration sensor. 2. A configuration in which a current change or a voltage change at the time of element resistance detection is taken in via an A / D converter at a predetermined timing, and the element resistance detection period is a period including at least an A / D conversion timing. The heater control apparatus of the gas concentration sensor in any one of -8.

Images