JP4508123B2 - Element impedance detector - Google Patents

Description

  The present invention relates to an element impedance detection device that detects an element impedance of a gas concentration sensor element that detects a concentration of a specific gas component in a gas to be detected.

  Conventionally, as an apparatus for detecting the impedance of a gas concentration sensor element formed with a solid electrolyte body, the element impedance is detected based on the amount of voltage change when a detection current is applied to the gas concentration sensor element. An apparatus is known (see Patent Document 1 and Patent Document 2).

  And since element impedance has the characteristic which changes according to the temperature of a gas concentration sensor element, the detected element impedance can be used for temperature control of a gas concentration sensor element (refer patent document 3).

  Note that, when noise is superimposed on an electrical signal for detecting element impedance, the detection accuracy of the element impedance is lowered, and therefore, filter means may be used to reduce the influence of noise. In particular, when a device for detecting element impedance is mounted on a vehicle, the vehicle is equipped with many electrical devices (ignition coils, generators, etc.) that are sources of noise. It is important to detect the impedance.

The filter means includes a filter circuit that removes the same frequency component as noise, a filter means that removes the noise component by performing software filtering on the signal after A / D conversion of the voltage change amount signal, and the like. Can be mentioned. For example, in the element impedance detection device (element resistance detection device) described in Patent Document 1, a signal (a peak of a voltage change amount output from the peak hold circuit 31) in a subsequent stage of the voltage change amount holding means (peak hold circuit 31) is used. The influence of noise superimposed on the value signal) is reduced by the low-pass filter 41 (see FIG. 5).
JP 2000-081414 A (Claim 1, FIG. 5) JP 2000-329730 A (Claim 1) JP-A-10-048180 (Claim 1)

  However, in the configuration in which a filter is provided at the subsequent stage of the voltage change amount holding means as in the conventional element impedance detection device, although the influence of noise superimposed on the hold value signal of the voltage change amount can be reduced, the voltage change amount There is a problem that it is not possible to reduce the influence of noise superimposed on the signal in the previous stage for detecting the hold value of the first.

  In other words, if noise is superimposed on the voltage change amount signal in the previous stage of detecting the hold value, the voltage change signal changes to a large value due to the noise, and the voltage change hold value is It is erroneously detected as a value larger than the actual value. Thus, if the hold value of the voltage change amount is erroneously detected, the detection accuracy of the element impedance is lowered.

  Therefore, the present invention has been made in view of these problems, and an object of the present invention is to provide an element impedance detection device capable of suppressing a decrease in detection accuracy of element impedance caused by erroneous detection of a hold value of a voltage change amount. .

  The invention according to claim 1, which has been made to achieve the above object, is an element impedance detection device for detecting an element impedance of a gas concentration sensor element made of a solid electrolyte body, wherein the element impedance relative to the gas concentration sensor element is Detection current energizing means for energizing a detection current for detecting the first constant period, and voltage change amount detecting means for detecting a voltage change amount at both ends of the gas concentration sensor element due to energization of the detection current; A voltage change amount holding means for holding the voltage change amount detected by the voltage change amount detecting means as a voltage change amount hold value; and a signal output means for outputting the voltage change amount hold value held in the voltage change amount holding means; The signal path from the voltage change amount detection means to the voltage change amount holding means is higher than a predetermined boundary frequency before holding. And holding before filter means for removing frequency band, an element impedance detection device, characterized in that it comprises a.

  In this element impedance detection device, the pre-hold filter means is provided to remove noise components (frequency band components higher than a predetermined pre-hold boundary frequency) superimposed on the signal path upstream of the pre-hold filter means. it can.

As a result, it is possible to suppress the noise component from being superimposed on the voltage change amount input to the voltage change amount holding means, and the hold value of the voltage change amount detected by the voltage change amount holding means is erroneous due to noise. It can suppress being detected.
Therefore, according to the present invention, it is possible to suppress erroneous detection of the hold value of the voltage change amount, and it is possible to suppress a decrease in detection accuracy of the element impedance.

  Here, the circuit configuration of the voltage change amount holding unit is not particularly limited. However, as a mode, the voltage change amount detecting unit is charged to a voltage value corresponding to the voltage change amount detected by the voltage change amount detecting unit, and the voltage value is held in the voltage change amount holding unit. A voltage holding capacitor for holding as a value, a charge allowable switching means for allowing the output voltage from the voltage change detection means to charge the voltage holding capacitor by being turned on, and the charge allowable switching means It is good to comprise from the switching control part which controls switching on / off state. This is because the function as the voltage change amount detecting means can be obtained with a relatively simple circuit configuration.

  In the voltage change amount holding means having such a circuit configuration, for example, in order to charge the output voltage from the voltage change amount detecting means to the voltage holding capacitor and hold it as a voltage change amount hold value, for example, start of energization of the detection current The charging permission switching means is switched from the OFF state to the ON state immediately before the start of energization, and the charging permission switching means is switched to the OFF state at a certain timing within a certain period in which the detection current is supplied.

  By the way, when the voltage holding amount holding value is held in the voltage holding capacitor, when the charge allowable switching means is switched from the OFF state to the ON state in synchronization with the start of energization of the detection current or immediately before the energization start as described above. The voltage variation under the voltage change amount detecting means is substantially caused by the start of energization of the detection current, and the charge charged in the voltage holding capacitor is discharged to the voltage change amount detecting means side. The change amount hold value drops to almost 0V. Then, the output voltage from the voltage change detection means is charged in a state where the voltage change hold value of the voltage holding capacitor is substantially 0V. However, in the configuration including the pre-holding filter means as in the present invention, the output voltage from the voltage change detecting means is charged and charged to the voltage holding capacitor, so that the output voltage change from the voltage change detecting means is changed. Is particularly large, the voltage change amount may be held as a voltage change amount hold value before it reaches a true value (a voltage value corresponding to a voltage change amount that can be originally taken).

  Therefore, in the element impedance detection device described above, the voltage change amount holding means is charged to a voltage value corresponding to the voltage change amount detected by the voltage change amount detection means, and the voltage value is held as a voltage change hold value. A voltage holding capacitor for charging, a charge allowable switching means that allows the voltage holding capacitor to charge the output voltage from the voltage change amount detecting means by being turned on, and a gas concentration sensor by means of a detection current energizing means The charge-acceptable switching means is switched from the off-state to the on-state after a lapse of a second fixed time shorter than the first fixed time after starting energization of the element and for a specific period within the first fixed time. And a switching control unit for controlling.

According to the element impedance detection device of the present invention, the charging allowable switching unit is changed from the off state to the on state while the detection current is started and the voltage change is occurring under the voltage change amount detection unit. Can be switched. As a result, even if the charge allowable switching means is switched to the ON state, the voltage change amount hold value held in the voltage holding capacitor does not drop to 0 V, and the output voltage that starts to be input to the pre-holding filter means is somewhat Therefore, the value held as the voltage change amount hold value (voltage change amount) indicates a true value or a value close to the true value.
Therefore, according to the element impedance detection device of the present invention, even when the pre-holding filter means for suppressing the noise component from being superimposed on the voltage change amount input to the voltage holding capacitor is provided, the voltage holding The voltage change amount hold value held by the capacitor can be made close to the true value or the true value, and the detection accuracy of the element impedance can be improved.

  The invention according to claim 3 made to achieve the above object is an element impedance detection device for detecting an element impedance of a gas concentration sensor element made of a solid electrolyte body. Detection current supply means for supplying a detection current for detecting element impedance, voltage change amount detection means for detecting a voltage change amount at both ends of the gas concentration sensor element due to supply of the detection current, and voltage change amount detection Voltage change amount holding means for holding the voltage change amount detected by the means as a voltage change amount hold value, and signal output means for outputting the voltage change amount hold value held in the voltage change amount holding means. The voltage change amount holding means is charged to a voltage value corresponding to the voltage change amount detected by the voltage change amount detecting means, and the voltage value is changed to the voltage change amount. A voltage holding capacitor for holding as a hold value is provided. The voltage holding capacitor includes a resistance element that forms a low-pass filter. The low-pass filter configured by the voltage holding capacitor and the resistance element has a predetermined pre-holding boundary. An element impedance detection apparatus comprising: removing a frequency band higher than the frequency.

  In this element impedance detection device, a noise component (predetermined in advance) is provided by providing a low-pass filter composed of a voltage holding capacitor and a resistance element. Frequency band components higher than the pre-holding boundary frequency) can be removed.

  As a result, it is possible to suppress the noise component from being superimposed on the voltage change amount input to the voltage change amount holding means, and the hold value of the voltage change amount detected by the voltage change amount holding means is erroneous due to noise. It can suppress being detected.

  Therefore, according to the present invention, it is possible to suppress erroneous detection of the hold value of the voltage change amount, and it is possible to suppress a decrease in detection accuracy of the element impedance. Furthermore, in the element impedance detection device of the present invention, the voltage holding capacitor constituting the voltage change amount holding means is also used as a capacitor for constituting the low-pass filter, so that the number of capacitors to be used can be reduced. There is also an advantage that the configuration is not complicated and the cost is reduced.

  Further, in the above-described element impedance detection device, the voltage change amount holding unit is turned on in addition to the voltage holding capacitor to charge the output voltage from the voltage change amount detection unit to the voltage holding capacitor. The first constant time after the elapse of a second fixed time shorter than the first fixed time from the start of energization of the gas concentration sensor element by the permissible charge switching means and the detection current supply means. It is preferable to provide a switching control unit that switches the charge-permissible switching means from the OFF state to the ON state over a specific period.

According to the element impedance detection device of the present invention, the charging allowable switching unit is changed from the off state to the on state while the detection current is started and the voltage change is occurring under the voltage change amount detection unit. Can be switched. Thereby, even if the charge allowable switching means is switched to the on state, the voltage change amount hold value held in the voltage holding capacitor does not drop to 0V, and the low-pass filter configured by the voltage holding capacitor and the resistance element Since the output voltage that starts to be input reaches a certain value, the value held as the voltage change amount hold value (voltage change amount) indicates a true value or a value close to the true value.
Therefore, according to the element impedance detection device of the present invention, even when the low-pass filter for suppressing the noise component from being superimposed on the voltage change amount input to the voltage holding capacitor is provided, The voltage change amount hold value held in (1) can be made close to the true value or the true value, and the detection accuracy of the element impedance can be improved.

  Here, the noise component superimposed on the voltage change amount may have a different frequency band depending on the installation environment of the element impedance detection device (such as the type of external device disposed in the surroundings). What is necessary is just to set a value according to an installation environment so that a noise component may be removed.

  In addition, if specific frequency component removal (filtering) by pre-holding filter means or low-pass filter (low-pass filter composed of voltage holding capacitor and resistance element) affects not only noise component but also detection of voltage change, voltage change The detection accuracy of the quantity hold value may be adversely affected.

Therefore, in the element impedance detection device described above, the boundary frequency before holding is preferably 3 [kHz] or more.
That is, the pre-holding filter means or the low-pass filter (low-pass filter composed of a voltage holding capacitor and a resistance element) in which the pre-holding boundary frequency is set in this way does not remove at least components in the frequency band of 3 [kHz] or less. Therefore, the voltage change amount included in this frequency band is input to the voltage change amount holding means without being removed by the pre-holding filter means or the low-pass filter.

  Thereby, it is possible to prevent the filtering by the pre-holding filter means or the low-pass filter from affecting the detection of the voltage change amount, and it is possible to suppress the deterioration of the detection accuracy of the element impedance.

  Further, the gas concentration sensor element to be detected by the element impedance is not limited to the one having a single solid electrolyte body (so-called one cell type), and has a plurality of cells formed by the solid electrolyte body. It may be configured.

  When detecting the element impedance of a gas concentration sensor element having a plurality of cells, a detection current is applied to at least one cell, and a voltage change amount at both ends of the cell through which the detection current is passed is detected. What should I do?

  A specific example of the gas concentration sensor element having a plurality of cells is a two-cell type gas concentration sensor element having an electromotive force cell and a pump cell. In this two-cell type gas concentration sensor element, the pump cell is stacked on the electromotive force cell through a diffusion chamber capable of introducing a gas to be detected between the pump cell and the diffusion chamber according to the pump current. It is provided as a cell for taking in and out oxygen. The cell through which the detection current is passed may be a pump cell or an electromotive force cell. Another gas concentration sensor element includes a three-cell type gas concentration sensor element having an electromotive force cell, a first pump cell, and a second pump cell. In this three-cell type gas concentration sensor element, the first pump cell is stacked on the surface side of the electromotive force cell through the first diffusion chamber into which the gas to be detected can be introduced, and the second pump cell is the first pump cell. The thing of the structure laminated | stacked on the back surface side of an electromotive force cell through the 2nd diffusion chamber connected with a diffusion chamber can be illustrated.

  Next, the element impedance detection apparatus includes pre-output filter means for removing a frequency band higher than a predetermined pre-output boundary frequency in the signal path from the voltage change amount holding means to the signal output means. Also good.

  In other words, in addition to the pre-holding filter means or the low-pass filter (low-pass filter composed of a voltage holding capacitor and a resistance element), the pre-output filter means is provided to hold the voltage change amount output from the signal output means to the outside. The noise component superimposed on the value can be removed.

As a result, the detection error due to the influence of the noise component can be further reduced in the hold value of the voltage change amount output to the outside by the element impedance detection device.
Therefore, according to the present invention, the detection error of the hold value of the voltage change amount due to the influence of the noise component can be further reduced, and the detection accuracy of the element impedance can be further improved.

Embodiments of the present invention will be described below with reference to the drawings.
First, the schematic block diagram of the element impedance detection apparatus 1 to which this invention was applied is shown in FIG.
The element impedance detection device 1 detects the element resistance value signal Rpvs from the gas concentration sensor element 8 provided in the exhaust pipe of the internal combustion engine, and outputs the detected element resistance value signal Rpvs to the heater control circuit 60. In addition to the element resistance value signal Rpvs, the element impedance detection device 1 detects a gas detection signal VIp from the gas concentration sensor element 8, and outputs the detected gas detection signal VIp to the oxygen concentration detection circuit 52. Also have.

Here, a schematic configuration diagram of the gas concentration sensor element 8 is shown in FIG. 2 and the gas concentration sensor element will be briefly described.
The gas concentration sensor element 8 is configured by laminating a pump cell 14, a porous diffusion layer 18, an electromotive force cell 24, and a reinforcing plate 30.

  The pump cell 14 is mainly composed of partially stabilized zirconia (ZrO 2), and is heated and activated to activate a solid electrolyte body 15 that exhibits oxygen ion conductivity. The pump cell 14 is mainly composed of platinum, and includes a front surface and a back surface of the solid electrolyte body 15. It is comprised from the porous electrodes 12 and 16 formed in this. Further, the electromotive force cell 24 is mainly composed of partially stabilized zirconia (ZrO2), and is heated and activated to activate the solid electrolyte body 23 that exhibits oxygen ion conductivity, and mainly includes platinum. It is comprised from the porous electrodes 22 and 28 formed in each of the front surface and the back surface.

  The porous electrode 16 facing the hollow diffusion chamber 20 in the pump cell 14 and the porous electrode 22 facing the hollow diffusion chamber 20 in the electromotive force cell 24 are electrically connected to each other and the gas concentration sensor element 8. Are connected to the common terminal COM. The common terminal COM is connected to the Vcent point of the element impedance detection device 1 via the resistor R (see FIG. 1).

  The porous electrode 12 of the pump cell 14 is connected to the output terminal Ip + of the gas concentration sensor element 8, and the porous electrode 28 of the electromotive force cell 24 is connected to the output terminal Vs + of the gas concentration sensor element 8. The output terminal Ip + is connected to the output terminal of the operational amplifier OP2 in the element impedance detection apparatus 1, and the output terminal Vs + terminal is connected to the constant current source circuit 62 in the element impedance detection apparatus 1 (see FIG. 1).

The reinforcing plate 30 is mainly formed of zirconia, and is laminated on the electromotive force cell 24 so as to form the reference oxygen chamber 26 while closing the porous electrode 28 of the electromotive force cell 24.
A diffusion chamber 20 surrounded by a porous diffusion layer 18 is formed between the pump cell 14 and the electromotive force cell 24. That is, the diffusion chamber 20 is communicated with the measurement gas atmosphere via the porous diffusion layer 18. In this embodiment, the porous diffusion layer 18 filled with a porous material is used, but small holes can be provided instead.

  A heater 70 is disposed in the vicinity of the gas concentration sensor element 8, and the gas concentration sensor element 8 can detect gas when the pump cell 14 and the electromotive force cell 24 are activated by heating by the heater 70. It becomes.

Returning to FIG. 1, the operation of measuring the oxygen concentration in the element impedance detection apparatus 1 will be described. Hereinafter, the operation of the gas concentration sensor element 8 in a state where the pump cell 14 and the electromotive force cell 24 are activated will be described.
In the element impedance detection device 1, the constant current source circuit 62 supplies a constant minute current Icp to the electromotive force cell 24, and the pump current flows to the pump cell 14 so that the voltage Vs generated at both ends of the electromotive force cell 24 becomes 450 mV. By controlling Ip, oxygen is pumped into the diffusion chamber 20 or oxygen is pumped out of the diffusion chamber 20. Since the current value and current direction of the pump current Ip flowing through the pump cell 14 change according to the oxygen concentration (air-fuel ratio) in the exhaust gas, the oxygen concentration in the exhaust gas is detected over a wide area based on the pump current Ip. can do. In addition, the reference | standard oxygen chamber 26 functions as an internal oxygen reference source by flowing the microcurrent Icp to the electromotive force cell 24 in the direction which pumps the oxygen of the diffusion chamber 20 to the porous electrode 28 side.

  1, the element impedance detection apparatus 1 includes an operational amplifier OP1, an operational amplifier OP2, switches SW1 to SW3, and a PID control circuit 69 in addition to a constant current source circuit 62 (element impedance detection apparatus) 1 generally has a configuration other than that shown in the drawing, but is shown here in a range necessary for explanation). The constant current source circuit 62, the electromotive force cell 24, and the resistor R are connected in this order to constitute a current path through which a minute current Icp flows.

  In the operational amplifier OP2, one input terminal (inverted input terminal) is connected to the Vcent point, the other input terminal (non-inverted input terminal) is applied with a reference voltage (virtual ground voltage) + 4V, and the output terminal is a pump cell. 14 Ip + terminals. In the PID control circuit 69, the pump cell 14 is energized so that the potential difference (corresponding to the voltage Vs) between the potential of the Vs + terminal of the electromotive force cell 24 connected via the operational amplifier OP1 and the potential at the Vcent point is 450 mV. The pump current Ip is PID controlled. Specifically, the PID control circuit 69 calculates a deviation ΔVs between the target control voltage (450 mV) and the voltage Vs generated at both ends of the electromotive force cell 24, and feeds back this deviation ΔVs to the output terminal of the operational amplifier OP2. Then, the pump current Ip is supplied to the pump cell 14. The pump current Ip flows into the output terminal of the operational amplifier OP2 via the pump cell 14 or is supplied from the output terminal of the operational amplifier OP2 depending on the sign.

  Furthermore, the element impedance detection device 1 differentially amplifies the detection resistor R1 that converts the pump current Ip into a voltage signal and the voltage across the detection resistor R1 (difference between the potential Vcent and the potential Vpid), thereby detecting the gas detection signal. And a differential amplifier circuit 61 that outputs as a (Vip signal).

These gas detection signals (Vip signals) are output from the gas detection signal output terminal 43 (see FIG. 1) to the external oxygen concentration detection circuit 52.
The oxygen concentration detection circuit 52 includes a microcomputer (not shown), which converts a gas detection signal (Vip signal) into a digital value by an A / D conversion circuit (not shown) and then responds from the map held. The oxygen concentration value to be calculated is calculated. The oxygen concentration detection circuit 52 performs a process for detecting the air-fuel ratio based on the calculated oxygen concentration value and the air-fuel ratio control process so that the target air-fuel ratio is obtained.

Next, the resistance value (temperature) measurement operation of the electromotive force cell 24 in the element impedance detection apparatus 1 will be described.
In the element impedance detection device 1, the operational amplifier OP1 forms a sample hold circuit together with the capacitor C1 and the switch SW1. When the resistance value of the electromotive force cell 24 is measured, the switch SW1 is turned off to turn off the electromotive force cell 24. By holding the voltage Vs generated at both ends of the electromotive force cell 24 immediately before the current application for resistance value measurement, the voltage Vs immediately before the resistance value measurement is input to the PID control circuit 69.

  The operational amplifier OP3 energizes the hold value (the voltage Vs of the electromotive force cell 24 immediately before energizing the current for resistance value measurement) held in the operational amplifier OP1 and the resistance value measuring current -Iconst to the electromotive force cell 24. A voltage change amount ΔVs corresponding to the difference from Vs + potential at the time of output is output. Since this voltage change amount ΔVs is proportional to the bulk resistance value of the electromotive force cell 24, it can be used as the element resistance value signal Rpvs.

  That is, the operational amplifier OP3 outputs an element resistance value signal Rpvs that is proportional to the bulk resistance value of the electromotive force cell 24. The element resistance value signal Rpvs has a characteristic proportional to the bulk resistance value of the electromotive force cell 24 and proportional to the temperature of the electromotive force cell 24 as described above.

  The element resistance value signal Rpvs output from the operational amplifier OP3 is externally transmitted from the element resistance value signal output terminal 41 via the signal inversion circuit 75, the first low-pass filter 71, the signal hold circuit 55, and the second low-pass filter 73. Is output.

  The signal inverting circuit 75 is configured to invert the positive / negative polarity of the element resistance value signal Rpvs output from the operational amplifier OP3, and extract and output a signal having a value of 0 or more among the inverted signals.

  The first low-pass filter 71 is provided in the signal path from the operational amplifier OP3 to the signal hold circuit 55, and is a signal in a frequency band larger than a predetermined pre-holding boundary frequency (10 [kHz] in the present embodiment). The filter circuit is configured to remove the component and pass the signal component in the frequency band equal to or lower than the pre-holding boundary frequency.

  As shown in FIG. 7, the signal hold circuit 55 includes a voltage holding capacitor 57 and a switch SW4. When the switch SW4 is switched from the off state to the on state, the element resistance value signal Rpvs (in detail, output from the operational amplifier OP3). The device resistance value signal Rpvs) inverted and extracted by the signal inverting circuit 75 is started to be sampled and held. That is, when the switch SW4 is switched from the off state to the on state, the voltage holding capacitor 57 starts to be charged with the element resistance value signal Rpvs. The signal hold circuit 55 holds the value of the element resistance value signal Rpvs in the voltage holding capacitor 57 and the held element resistance value when the switch SW4 is turned on after a predetermined period has elapsed since the switch SW4 was turned on. A signal Rpvs (hold value) is output. The on / off switching control of the switch SW4 of the signal hold circuit 55 is executed based on a switching signal output from a microcomputer (not shown) constituting the oxygen concentration detection circuit 52. The switching signal is input to the element impedance detection device 1 via the input terminal 45. In addition to the on / off switching signal of the switch SW4, a switching signal for performing on / off switching control of switches SW1 to SW3 described later is input from the microcomputer of the oxygen concentration detection circuit 52 to the input terminal 45. It has come to be.

  The second low-pass filter 73 is provided in a signal path from the signal hold circuit 55 to the element resistance value signal output terminal 41, removes a signal component in a frequency band larger than a predetermined pre-output boundary frequency, and outputs it. It consists of a filter circuit that passes signal components in a frequency band below the front boundary frequency.

In this way, the element impedance detection apparatus 1 outputs the element resistance value signal Rpvs from the element resistance value signal output terminal 41 to the outside.
In the element impedance detection apparatus 1, the switch SW1 controls the operational amplifier OP1, that is, the sample hold circuit voltage hold operation. The switch SW2 turns on / off a current source 63 for flowing a constant current -Iconst for measuring the resistance value (impedance detection) of the electromotive force cell 24, and the switch SW3 is a resistance value passed by the switch SW2. The current source 64 for supplying a constant current + Iconst having a polarity opposite to that of the measurement current −Iconst is turned on / off.

  Next, FIG. 3 shows the waveform of the voltage Vs generated at both ends of the electromotive force cell 24 together with the timing chart of the switches SW1, SW2, SW3, and SW4. Further, the waveform of the element resistance value signal Rpvs after inversion extraction output from the signal inversion circuit 75 (the waveform is shown as ΔVs in the figure), and the sample hold signal output from the signal hold circuit 55 (held by the signal hold circuit 55). The waveform of the element resistance value signal Rpvs) is also shown.

  The switch SW1 is turned off for an off time T6 (for example, 500 μs) set every predetermined interval T5, thereby enabling the resistance measurement of the electromotive force cell 24 to be performed. During the off time T6, the input value to the PID control circuit 69 is maintained at 0.45 V in the sample hold circuit including the operational amplifier OP1 and the like.

Further, the switch SW4 of the signal hold circuit 55 is switched from the off state to the on state in synchronization with the timing at which the switch SW1 is switched from the on state to the off state. At this time, the sample hold signal (the element resistance value signal Rpvs held by the signal hold circuit 55) flows into the output terminal of the open OP3 and decreases to 0V.
After the time T1 has elapsed since the switch SW1 was turned off, the switch SW2 is turned on for a time T3 (100 μs), and a constant current −Iconst for measuring the resistance value is caused to flow to the electromotive force cell 24 side. The polarity of the current -Iconst is opposite to that of the internal electromotive force generated in the electromotive force cell 24, and the voltage at both ends of the electromotive force cell 24 is decreased by ΔVs by the current -Iconst as shown in the figure.

  Here, after the start of energization of the current -Iconst, when the time T2 (60 μs) elapses, the switch SW4 of the signal hold circuit 55 is switched from the on state to the off state, and the operational amplifier at the time (60 μs elapses after the energization start). The value of the output of OP3 (element resistance value signal Rpvs) is held in the signal hold circuit 55 (voltage holding capacitor 57). The signal hold circuit 55 holds the hold value of the element resistance value signal Rpvs until the next detection timing of the element resistance value signal Rpvs (specifically, when the switch SW1 is switched from on to off). The held element resistance value signal Rpvs (in other words, the sample hold signal) is output.

  Here, the value of 60 μs after the start of energization of the current −Iconst is measured so that the measured resistance value does not include the resistance component at the interface between the porous electrode and the solid electrolyte body. Because. This is because a value including a change in resistance component at the interface due to deterioration of the interface between the porous electrodes 22 and 28 of the electromotive force cell 24 and the solid electrolyte body is detected when measurement is performed with a low-frequency current or voltage. For this reason, accurate measurement cannot be performed by this change. When the viewpoint is changed, the resistance including deterioration can be measured by changing the measurement time and used for detecting deterioration.

  When the time T3 elapses from the time when the switch SW2 is turned on, the switch SW2 is turned off and the switch SW3 is turned on at the same time, and the current for measuring the resistance value− is almost equal to the time when the switch SW2 is turned on. A constant current + Iconst having a polarity opposite to that of Iconst is supplied to the electromotive force cell 24 side. This is because the internal electromotive force is affected by the orientation phenomenon of the oxygen ion conductive solid electrolyte body constituting the electromotive force cell 24, and the normal electromotive force value reflecting the original oxygen concentration difference is not output. This is to shorten the return time until the state is restored, and to restart the oxygen concentration measurement in a short time after the resistance value measurement.

  After the elapse of time T3 for energization of the constant current + Iconst, after the switch SW3 is turned off, the switch SW1 is turned on at the timing when the time T4 elapses, and the voltage Vs of the electromotive force cell 24 is again changed to the operational amplifier OP1. Then, the measurement of the oxygen concentration is resumed in a form in which the pump current is PID controlled. Then, after the elapse of the interval T5, the switch SW1 is turned off, and the resistance value of the electromotive force cell 24 is measured again.

  The element impedance detection device 1 outputs an element resistance value signal Rpvs (specifically, a sample hold signal) to the heater control circuit 60, and the heater control circuit 60 is based on the element resistance value signal Rpvs. The energization to the heater 70 for heating the gas concentration sensor element 8 is controlled so that the value correlated with the bulk resistance value of the electromotive force cell 24 becomes the target value. This temperature control substantially increases the input power when the bulk resistance value of the electromotive force cell 24 is higher than the target value, and decreases the input power when the bulk resistance value is lower than the target value. It functions to keep the temperature at the target temperature (for example, 800 ° C.) accurately.

  Here, noise is superimposed on the input signal to the operational amplifier OP3 (voltage Vs generated at both ends of the electromotive force cell 24), and the element resistance value signal Rpvs (in other words, voltage change amount) output from the operational amplifier OP3. The effect of the first low-pass filter 71 when a noise component is superimposed on the waveform of (ΔVs) will be described with reference to FIG.

  In FIG. 4, the waveform of the voltage Vs generated at both ends of the electromotive force cell 24, the timing chart of the switch SW4, and the waveform of the element resistance value signal Rpvs after inversion extraction output from the signal inversion circuit 75 (in the figure, as ΔVs) A waveform is shown) and a waveform of a sample hold signal (element resistance value signal Rpvs held by the signal hold circuit 55) output from the signal hold circuit 55 is shown.

  As a waveform of the sample hold signal, a waveform when the first low-pass filter 71 is not provided and a waveform when the first low-pass filter 71 is provided are shown. In addition, in the waveform of the sample and hold signal when the first low-pass filter 71 is not provided, the waveform of the sample and hold signal when no noise is superimposed (the same waveform as in FIG. 3) is indicated by a dotted line for comparison.

  As shown in FIG. 4, the waveform of the sample and hold signal when the first low-pass filter 71 is not provided is larger than the waveform (dotted line) of the sample and hold signal when noise is not superimposed. This is because an error occurs in the value of the element resistance value signal Rpvs (voltage change amount ΔVs) due to the influence of the noise component. As a result, a detection error due to the influence of noise occurs in the value of the sample hold signal. .

  On the other hand, the waveform of the sample hold signal when the first low pass filter 71 is provided is similar to the waveform of the sample hold signal when noise is not superimposed because the noise component is removed by the first low pass filter 71. It becomes the waveform. That is, by providing the first low-pass filter 71, it is possible to prevent a detection error due to the influence of noise when detecting the sample hold signal (the element resistance value signal Rpvs held by the signal hold circuit 55).

  In addition, the element impedance detection apparatus 1 includes a second low-pass filter 73 in the subsequent stage of the signal hold circuit 55, and the second low-pass filter 73 is a noise component superimposed on the signal path in the previous stage of the second low-pass filter 73. Remove. That is, it is possible to prevent the noise component from being superimposed on the element resistance value signal Rpvs (sample hold signal held by the signal hold circuit 55) output to the external device (heater control circuit 60).

  In the present embodiment, the current source 63 and the switch SW2 correspond to the detection current supply means described in the claims, and the operational amplifier OP3, the operational amplifier OP1, the capacitor C1, and the switch SW1 serve as the voltage change amount detection means. The signal hold circuit 55 corresponds to voltage change amount holding means, the element resistance value signal output terminal 41 corresponds to signal output means, the first low-pass filter 71 corresponds to pre-holding filter means, and the second low-pass filter. 73 corresponds to pre-output filter means. Further, the switch SW4 corresponds to the charge permission switching means described in the claims, and the microcomputer of the oxygen concentration detection circuit 52 that performs on / off switching control of the switch SW4 corresponds to the switching control unit.

  As described above, the element impedance detection device 1 includes the first low-pass filter 71 so that a noise component caused by ignition noise or the like is superimposed on the element resistance value signal Rpvs input to the signal hold circuit 55. The detection error due to noise can be suppressed from occurring in the hold value of the element resistance value signal Rpvs held by the signal hold circuit 55.

  Further, by providing the second low-pass filter 73 in addition to the first low-pass filter 71, it is possible to prevent noise components from being superimposed on the element resistance value signal Rpvs output to the heater control circuit 60.

  Therefore, the element impedance detection apparatus 1 of the present embodiment can suppress erroneous detection of the hold value of the voltage change amount ΔVs (element resistance value signal Rpvs) by including the first low-pass filter 71, so that the detection accuracy of the element impedance is improved. The decrease can be suppressed. Further, by providing the second low-pass filter 73 in addition to the first low-pass filter 71, it is possible to suppress the noise component from being superimposed on the element resistance value signal Rpvs output to the outside. Reduction can be suppressed.

  In the present embodiment, since the frequency band of the element resistance value signal Rpvs is 10 [kHz] or less, the first low-pass filter 71 removes signal components in a frequency band larger than 10 [kHz], and 10 Since it is configured to pass signal components in a frequency band of [kHz] or less, noise components can be effectively removed. Furthermore, since the first low-pass filter 71 does not remove the signal component of the element resistance value signal Rpvs, it is avoided that filtering by the first low-pass filter 71 affects the detection of the hold value of the element resistance value signal Rpvs. Can do.

  If only the second low-pass filter 73 is provided without providing the first low-pass filter 71, it is possible to suppress the noise component from being superimposed on the voltage change amount signal input to the signal hold circuit 55. Detection error may occur due to the influence of noise components.

Accordingly, FIG. 5 shows waveforms of respective parts when the first low-pass filter 71 is removed from the element impedance detection device 1 shown in FIG.
In FIG. 5, the waveform of the voltage Vs generated at both ends of the electromotive force cell 24, the timing chart of SW4, the sample hold signal output by the signal hold circuit 55 (the element resistance value signal Rpvs held by the signal hold circuit 55). The waveform and the waveform of the element resistance value signal Rpvs in the subsequent stage of the second low-pass filter 73 are shown.

  As shown in FIG. 5, the waveform of the sample and hold signal when the first low-pass filter 71 is not provided is larger than the waveform of the sample and hold signal (dotted line) when the first low-pass filter 71 is provided. . This is because the noise component in the signal input to the signal hold circuit 55 cannot be removed, and the hold value of the element resistance value signal Rpvs (ΔVs) is erroneously detected larger than the actual value due to the influence of the noise component.

  The waveform output from the second low-pass filter 73 to which the sample hold signal including such an error is input shows a waveform that changes more slowly than the waveform of the sample hold signal. It shows the same value as the sample hold signal including.

  Therefore, when only the second low-pass filter 73 is provided without the first low-pass filter 71 (in the case of the prior art), the element resistance value signal Rpvs output to the outside from the element resistance value signal output terminal 41 is used. Includes an error, and it is impossible to suppress a decrease in detection accuracy of the element impedance.

  On the other hand, since the element impedance detection apparatus 1 of the present embodiment includes the first low-pass filter 71, the noise component is superimposed on the voltage change amount signal input to the signal hold circuit 55. Since it can suppress, and it can suppress that an error is contained in element resistance value signal Rpvs, the fall of the detection accuracy of element impedance can be controlled.

(Another embodiment)
Next, an element impedance detection apparatus different from the above-described embodiment will be described. In the second embodiment, a voltage holding capacitor 87 and a resistance element 85 are provided in place of the first low-pass filter 71 and the signal hold circuit 55 in the above embodiment (hereinafter also referred to as the first embodiment). A two-signal hold circuit 77 is provided. Since this other embodiment is the same as the configuration (circuit configuration) of the first embodiment except for the configuration other than the second signal hold circuit 77, the description of the same portion will be omitted.

FIG. 6 shows an internal circuit diagram of the second signal hold circuit 77.
In the second signal hold circuit 77, the switch SW4 and the resistance element 85 are connected in series from the input side terminal 81 to the output side terminal 83, and between the connection path between the resistance element 85 and the output side terminal 83 and the ground line. And a voltage holding capacitor 87 connected to the. The input side terminal 81 is connected to the output side of the signal inverting circuit 75 (see FIG. 1), and the output side terminal 83 is connected to the input side of the second low-pass filter 73 (see FIG. 1).

  Among these, the voltage holding capacitor 87 and the resistance element 85 constitute a low-pass filter, and the electrostatic capacity of the voltage holding capacitor 87 and the resistance value of the resistance element 85 are signals that the low-pass filter has 10 kHz or less. It is set to pass the component and remove the signal component having a frequency higher than 10 [kHz].

  Similarly to the first embodiment, the switch SW4 operates in the same manner as the timing chart of the switch SW4 shown in FIG. 3, so that an externally input signal (element resistance value signal Rpvs) is supplied to the voltage holding capacitor 87. To hold.

  That is, the second signal hold circuit 77 has a function of holding (holding) an externally input signal (element resistance value signal Rpvs) and a function of a low-pass filter for removing noise components.

  For this reason, in the element impedance detection device including the second signal hold circuit 77 instead of the first low pass filter 71 and the signal hold circuit 55 in the first embodiment, the low pass filter including the voltage holding capacitor 87 and the resistance element 85 is provided. The noise component is removed from the element resistance value signal Rpvs input to the second signal hold circuit 77. The second signal hold circuit 77 can hold the element resistance value signal Rpvs from which the noise component has been removed and output the held element resistance value signal Rpvs (hold value).

  That is, even in the element impedance detection device including the second signal hold circuit 77, similarly to the first embodiment, it is possible to suppress a noise component caused by ignition noise or the like from being superimposed on the element resistance value signal Rpvs, It is possible to suppress the occurrence of a detection error due to noise in the hold value of the element resistance value signal Rpvs held by the second signal hold circuit 77.

  Therefore, since the element impedance detection device including the second signal hold circuit 77 can suppress erroneous detection of the hold value of the voltage change amount ΔVs (element resistance value signal Rpvs) as in the first embodiment, detection of element impedance is possible. A decrease in accuracy can be suppressed.

(Modification)
Next, a modified example in which the timing of the on / off switching control of the switch SW4 of the signal hold circuit 55 is changed in the element impedance detection device 1 having the circuit configuration shown in the above embodiment (first embodiment) will be described. In the above-described embodiment, the example in which the timing at which the switch SW4 of the signal hold circuit 55 is switched from the off state to the on state is synchronized with the timing at which the switch SW1 is switched from the on state to the off state. On the other hand, in the present modification, the timing at which the switch SW4 of the signal hold circuit 55 is switched from the OFF state to the ON state is set after a certain time has elapsed since the switch SW2 for flowing the constant current -Iconst is switched from the OFF state to the ON state. An example is shown.
In the following, the timing chart shown in FIG. 8 in the same format as that of FIG. The switch SW1 shown together with the waveform of the element resistance value signal Rpvs (shown as a waveform as ΔVs) and the waveform of the sample hold signal (element resistance value signal Rpvs held by the signal hold circuit 55) output from the signal hold circuit 55. This modification will be described with reference to the timing charts of SW2, SW3, SW3 and SW4.

  The switch SW1 is turned off over an off time T6 (for example, 500 μs) set every predetermined interval T5, as in the above embodiment, and the resistance of the electromotive force cell 24 can be measured. During the off time T6, the input value to the PID control circuit 69 is maintained at 0.45 V in the sample hold circuit including the operational amplifier OP1 and the like.

  Next, after a time T1 has elapsed since the switch SW1 was turned off, the switch SW2 is turned on for a time T3 (about 100 μs), and a constant current −Iconst for measuring the resistance value is caused to flow to the electromotive force cell 24 side. Due to this current -Iconst, the voltage across the electromotive force cell 24 is lowered by ΔVs as shown in the figure.

  Here, when a time T7 (a time set to a time shorter than the time T1, specifically 30 μs) has elapsed after the switch SW2 is turned on, the switch SW4 of the signal hold circuit 55 changes from the off state to the on state. Switch. When 30 μs elapses after the switch SW4 is turned on (that is, when the switch SW2 is turned on and the energization of the current −Iconst starts and time T2 (about 60 μs elapses)), the switch of the signal hold circuit 55 The SW4 is switched from the on state to the off state, and the value of the output (element resistance value signal Rpvs) of the operational amplifier OP3 at this time (60 μs has elapsed from the start of energization) is held in the signal hold circuit 55 (voltage holding capacitor 57). . The signal hold circuit 55 holds the hold value of the element resistance value signal Rpvs until the next detection timing of the element resistance value signal Rpvs (specifically, when 30 μs elapses after the switch SW2 is switched from the off state to the on state). And the held element resistance value signal Rpvs (in other words, the sample hold signal) is output.

  When the time T3 elapses from the time when the switch SW2 is turned on, the switch SW2 is turned off at the same time as the switch SW3 is turned on. Is applied to the electromotive force cell 24 side with a constant current + Iconst having a reverse polarity. After the elapse of time T3 for energization of the constant current + Iconst, after the switch SW3 is turned off, the switch SW1 is turned on at the timing when the time T4 elapses, and the voltage Vs of the electromotive force cell 24 is again changed to the operational amplifier OP1. Is added to the PID control circuit 69, and the measurement of the oxygen concentration is resumed. Then, after the elapse of the interval T5, the switch SW1 is turned off, and the above-described processing is repeated again.

  According to the element impedance detection device described as the modification, the inversion-extracted element resistance value signal Rpvs (ΔVs) output from the signal inversion circuit 75 is changed while the energization of the current −const is started. That is, the switch SW4 of the signal hold circuit 55 is switched from OFF to ON after 30 μs has elapsed since the switch SW2 was turned ON. As a result, even if the switch SW4 is turned on, the voltage change amount hold value (the waveform of the sample hold signal in FIG. 8) held in the voltage holding capacitor does not drop to 0V, and the first low-pass Since the output (ΔVs) that starts to be input to the filter 71 has reached a certain value, the voltage change amount hold value (sample hold signal) held in the signal hold circuit 55 (voltage hold capacitor 57) is the first low pass. Even when the filter 71 is provided, it shows a true value (a value of ΔVs that can be originally taken) or a value close to the true value.

  Therefore, according to the element impedance detection device of this modification, the first low-pass filter 71 for suppressing the noise component from being superimposed on the voltage change amount input to the signal hold circuit 55 (voltage holding capacitor 57). Even when is set, the voltage change hold value (sample hold signal) held by the voltage holding capacitor 57 can be brought close to the true value or the true value, and the detection accuracy of the element impedance can be further improved.

As mentioned above, although this invention was demonstrated according to the said embodiment, another embodiment, and a modification, this invention is not limited to the said embodiment etc., A various aspect can be taken.
For example, in the above-described embodiment and the like, the gas concentration sensor element 8 including a plurality of cells (pump cell 14 and electromotive force cell 24) formed from a solid electrolyte body has been described as the gas concentration sensor element. The target gas concentration sensor element is not limited to a configuration including a plurality of solid electrolyte bodies, and may be a configuration including a single solid electrolyte body (one cell type).

  Further, in the gas concentration sensor element 8, the detection target of the element impedance may be not the solid electrolyte body of the electromotive force cell 24 but the solid electrolyte body of the pump cell 14, or the solid electrolytes of both the electromotive force cell 24 and the pump cell 14. The element impedance may be detected for the body.

  Further, the pre-holding boundary frequency of the first low-pass filter 71 is not limited to 10 [kHz], and noise components can be removed according to the frequency band of the signal of the voltage change amount ΔVs (element resistance value signal Rpvs). It should be set as follows.

  For example, when detecting an element impedance in a gas concentration sensor element installed in an internal combustion engine, if the gas concentration sensor element is installed in an exhaust manifold or an exhaust pipe immediately thereafter, the gas concentration sensor element is connected to an ignition coil. Since they are arranged close to each other, ignition noise is considered as a cause of noise generation. And since the frequency component of the high voltage part which has a bad influence on the detection of element impedance among ignition noise is about 33 [kHz], the 1st low pass filter 71 removes a frequency component higher than 30 [kHz]. By configuring so, the influence of ignition noise can be removed.

  When the frequency band of the voltage change amount ΔVs signal (element resistance value signal Rpvs) is 3 [kHz] or less, the first low-pass filter 71 is set to suppress the influence on the element resistance value signal Rpvs. It may be configured to remove frequency components higher than 3 [kHz].

  Further, in an environment where there is no influence of noise in the signal path from the signal hold circuit 55 to the element resistance value signal output terminal 41, the element impedance detection device may be configured without the second low-pass filter 73.

  In addition, the installation position of the first low-pass filter 71 can be set to any position in the signal path from the operational amplifier OP3 to the signal hold circuit 55, but the noise component in the signal input to the signal hold circuit 55 is effectively removed. In order to do so, it is desirable to install it at a position close to the signal hold circuit 55.

  Further, the element resistance value signal Rpvs (voltage change amount ΔVs) held in the signal hold circuit 55 or the second signal hold circuit 77 is a hold hold time determined in advance from the start of energization of the constant current for measuring the resistance value −Iconst. The value is not limited to the value at the time when (the above time T2) has elapsed, and may be a peak value in the energization period of the resistance measurement current.

  Further, the on / off switching timing of the switch SW4 in the element impedance detection apparatus described in the modification example is operated in the same manner as the timing chart of the switch SW4 shown in FIG. The input signal (element resistance value signal Rpvs) may be held in the second signal hold circuit 77 (voltage holding capacitor 87). As described above, even when the second signal hold circuit 77 has a function as a low-pass filter by operating the switch SW4 on / off switching timing as shown in FIG. The voltage change amount hold value (sample hold signal) held by the voltage holding capacitor 87 can be brought close to the true value or the true value, and the detection accuracy of the element impedance can be further improved.

It is a schematic block diagram of an element impedance detection apparatus. It is a schematic block diagram of a gas concentration sensor element. It is a timing chart which shows the signal waveform in each part of the element impedance detection apparatus of an embodiment. It is explanatory drawing which shows the effect of a 1st low-pass filter when a noise component is superimposed on the waveform of element resistance value signal Rpvs (voltage change amount (DELTA) Vs). It is a timing chart which shows the waveform of each part at the time of removing the 1st low pass filter from an element impedance detection device. FIG. 6 is an internal circuit diagram of a second signal hold circuit. It is a circuit block diagram of the signal hold circuit with which the element impedance detection apparatus of embodiment is equipped. It is a timing chart which shows the signal waveform in each part of the element impedance detection apparatus of a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Element impedance detection apparatus, 8 ... Gas concentration sensor element, 14 ... Pump cell, 24 ... Electromotive force cell, 41 ... Element resistance value signal output terminal, 52 ... Oxygen concentration detection circuit, 55 ... Signal hold circuit, 63 ... Current source 69 ... PID control circuit, 71 ... first low-pass filter, 73 ... second low-pass filter, 77 ... second signal hold circuit, 85 ... resistive element, 57, 87 ... voltage holding capacitor, OP3 ... op amp, SW2, SW4 …switch.

Claims (7)

An element impedance detection device for detecting an element impedance of a gas concentration sensor element made of a solid electrolyte body,
A detection current supply means for supplying a detection current for detecting an element impedance to the gas concentration sensor element over a first fixed time;
Voltage change amount detecting means for detecting a voltage change amount at both ends of the gas concentration sensor element by energization of the detection current;
Voltage change amount holding means for holding the voltage change amount detected by the voltage change amount detecting means as a voltage change amount hold value;
Signal output means for outputting the voltage change amount hold value held in the voltage change amount holding means;
Pre-holding filter means for removing a frequency band higher than a predetermined pre-holding boundary frequency in a signal path from the voltage change amount detecting means to the voltage change amount holding means;
An element impedance detection apparatus comprising: The voltage change amount holding means is charged to a voltage value corresponding to the voltage change amount detected by the voltage change amount detection means, and a voltage holding capacitor for holding the voltage value as the voltage change amount hold value; The gas concentration sensor element is energized by the charging allowable switching means that allows the voltage holding capacitor to be charged with the output voltage from the voltage change detection means, and the detection current energizing means. Control of switching the charge-acceptable switching means from off to on after a lapse of a second fixed time shorter than the first fixed time from the start and over a specific period within the first fixed time A switching control unit that performs,
The element impedance detection apparatus according to claim 1. An element impedance detection device for detecting an element impedance of a gas concentration sensor element made of a solid electrolyte body,
A detection current supply means for supplying a detection current for detecting an element impedance to the gas concentration sensor element over a first fixed period;
Voltage change amount detecting means for detecting a voltage change amount at both ends of the gas concentration sensor element by energization of the detection current;
Voltage change amount holding means for holding the voltage change amount detected by the voltage change amount detecting means as a voltage change amount hold value;
Signal output means for outputting the voltage change amount hold value held in the voltage change amount holding means;
With
The voltage change amount holding unit is charged with a voltage value corresponding to the voltage change amount detected by the voltage change amount detection unit, and includes a voltage holding capacitor for holding the voltage value as the voltage change amount hold value. And
Comprising a resistance element constituting a low-pass filter together with the voltage holding capacitor;
The low-pass filter constituted by the voltage holding capacitor and the resistance element removes a frequency band higher than a predetermined boundary frequency before holding;
An element impedance detection apparatus comprising: The voltage change amount holding means, in addition to the voltage holding capacitor, by being turned on, charging permission switching means that allows the voltage holding capacitor to charge the output voltage from the voltage change amount detecting means, A specific period within the first constant time after the elapse of a second fixed time shorter than the first fixed time after the gas current sensor is energized by the detection current supply means. The device impedance detection apparatus according to claim 3, further comprising: a switching control unit that controls the charge-accepting switching unit to switch from an off state to an on state. The element impedance detection device according to any one of claims 1 to 4,
The boundary frequency before holding is 3 [kHz] or more,
An element impedance detection device characterized by the above. The gas concentration sensor element has a plurality of cells formed of a solid electrolyte body, and the detection current energizing means energizes the detection current to at least one cell;
The element impedance detection apparatus according to claim 1, wherein: Comprising pre-output filter means for removing a frequency band higher than a predetermined pre-output boundary frequency in a signal path from the voltage change amount holding means to the signal output means;
The element impedance detection apparatus according to claim 1, wherein: