JP2000081414A - Element resistance detecting device for gas concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect element resistance by use of an element resistance detecting device detecting the element resistance from temporary changes in voltage and current. SOLUTION: An A/F(air/fuel ratio) sensor 10 has a sensor element part using a solid electrolyte and outputs a current signal (element current) matching the concentration of oxygen in exhaust gas with the application of a voltage. During the detection of element resistance, the voltage applied to the sensor element part in order to detect air/fuel ratio is temporarily changed to a voltage for detection of the element resistance at a frequency matching sensor characteristics, and the element resistance value is detected from the changes in voltage and current at that time. The detected value of the element current is inputted to an S/H(sample hold) circuit 30 and a P/H(peak hold) circuit 31. The S/H circuit 30 samples the element current and outputs it sequentially during the detection of the air/fuel ratio. The P/H circuit 31 holds the peak of the element current during the detection of the element resistance. An S/H circuit 32 samples the peak value held by the P/H circuit 31 and holds the value until the next detection of the element resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a gas concentration sensor for detecting the concentration of a specific component in a gas to be detected, for example, the concentration of oxygen in the exhaust gas of a vehicle engine. The present invention relates to an element resistance detecting device for detecting an element resistance.

[0002]

2. Description of the Related Art In recent years, in air-fuel ratio control of a vehicle engine, there has been a demand for improving control accuracy and a demand for lean burn, for example.
2. Description of the Related Art A linear air-fuel ratio sensor (oxygen concentration sensor) that linearly detects an air-fuel ratio (oxygen concentration in exhaust gas) of an air-fuel mixture to be taken into an engine over a wide area has been embodied. In such an air-fuel ratio sensor, it is indispensable to keep the sensor in an active state in order to maintain the detection accuracy. Generally, the sensor element is heated by energizing a heater attached to the sensor element. To maintain the active state.

[0003] In controlling the energization of the heater, there is a technique for detecting the temperature of the sensor element (element temperature) and performing feedback control so that the element temperature becomes a desired activation temperature (for example, about 700 ° C). Conventionally disclosed. In this case, the element resistance is detected using the fact that the resistance (element resistance) of the sensor element has a predetermined correspondence with the element temperature (FIG. 13), and the element temperature is derived from the detected element resistance. . According to such an element temperature detection method, it is possible to avoid a problem such as an increase in cost caused by attaching a temperature sensor to the sensor element.

The configuration of an existing air-fuel ratio detecting device using a limiting current type air-fuel ratio sensor will be described with reference to FIG. In FIG. 14, a microcomputer (microcomputer) 81
Outputs an applied voltage command value, and the voltage command value is applied to one terminal of an air-fuel ratio sensor 85 via a D / A converter 82, a low-pass filter (LPF) 83, and a drive circuit 84. A reference voltage Vref is applied to the other terminal of the sensor 85 via a voltage buffer 86. When a voltage is applied to the air-fuel ratio sensor 85, a current (element current) flowing through the sensor 85 is detected by a current detecting resistor 87, and the detected value is taken into a microcomputer 81 via an A / D converter 88. It is.

Japanese Patent Application Laid-Open No. 9-292364 discloses a technique for detecting the element resistance value of a gas concentration sensor. This will be described with reference to FIG. 15. A voltage having a predetermined time constant is applied to the gas concentration sensor spontaneously to measure a peak current value ΔI (current change amount) after a lapse of a predetermined time Ts. The element resistance is detected from the change amount ΔV and the peak current value ΔI (element resistance = ΔV / Δ
I). A primary LPF using a capacitor and a resistor
Creates a time constant. In particular, in the case of a limiting current type sensor using a solid electrolyte such as zirconia, a voltage is applied at a frequency corresponding to the characteristic by utilizing the fact that the impedance characteristic is stabilized in a region where the frequency of the applied voltage is 1 kHz or more. I was

[0006]

In the above prior art, by applying a voltage to the sensor and measuring a peak current value ΔI (current change amount) after a lapse of a predetermined time Ts, an accurate element resistance (element impedance) is obtained. Can be detected. However, when the generation time of the peak current value ΔI changes due to sensor characteristics corresponding to element deterioration or the like, there occurs a problem that an accurate element resistance cannot be detected.

This problem will be described with reference to FIG. FIG.
6, the change in the element current in the normal state with respect to the change in the applied voltage (90) has a waveform as indicated by reference numeral 91,
After elapse of s, the current peak value (point A in the figure) is measured. If the current peak value can be accurately measured in this manner, the element resistance can be accurately detected. However, when the element current changes as indicated by reference numerals 92 and 93 due to individual differences of sensors, electrode deterioration, and the like, the generation time of the peak current value ΔI changes from “A” to “B” and “C”. In this case, if the element current is measured at the timing when the time Ts elapses (actually, at the timing read by the A / D converter 88), the peak current value ΔI is measured at “B1” or “C1”. That is, a current value lower than the actual current peak value measured at the timings B and C is measured, and an accurate element resistance cannot be detected.

The element current waveform also changes due to variations in the circuit such as a capacitor and a resistor used to change the applied voltage with a predetermined time constant. It becomes a waveform. Therefore, the generation time of the peak current value also changes from “A” to “D”,
It changes like "E", and the element resistance cannot be detected accurately as before.

From the above, in order to accurately detect the element resistance, it is necessary to accurately measure the current peak value.
As described above, when the frequency of the applied voltage at the time of detecting the element resistance is 1 kHz or more (about 10 kHz depending on the sensor), the current change is monitored sequentially and the current peak value is measured. There was a possibility that it would increase excessively or adversely affect other controls.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an element resistance detecting device for detecting an element resistance from a temporary voltage change and current change. Is to provide an element resistance detecting device of a gas concentration sensor that can accurately detect the element resistance.

[0011]

The element resistance detecting apparatus of the present invention has a premise that an element section using a solid electrolyte is provided, and a current corresponding to a concentration of a specific component in a gas to be detected is applied as a voltage is applied. The present invention is applied to a gas concentration sensor that outputs a signal (element current), and detects a resistance value of the element unit from a temporary voltage change and a current change during gas concentration detection.

According to the first aspect of the present invention, there is provided a hold circuit for monitoring a current change or a voltage change at the time of detecting the element resistance and holding the monitoring result. By monitoring the current change or voltage change at the time of detecting the element resistance and storing it in the hold circuit, even if the occurrence time of the peak value of the current change or voltage change fluctuates due to factors such as sensor deterioration or circuit variation, the same holds true. The peak value can be easily and accurately measured. As a result, the element resistance can be accurately detected.

According to the above invention, by employing the hold circuit, an element resistance detecting device can be realized with a circuit configuration that does not use a microcomputer, and cost reduction and size reduction can be achieved. In this case, the frequency of the applied voltage is not limited by the limit of the processing capability of the microcomputer. In addition, it is possible to avoid such a problem that the operation load of the microcomputer is excessively increased and other controls are adversely affected. If a microcomputer is used, the change in current or voltage is monitored as described above, and the result of the monitoring is input to the microcomputer, whereby the calculation load on the microcomputer can be significantly reduced. That is,
Since the current value and the voltage value used for calculating the element resistance are already held, a low-speed A / D converter can be used. Further, since it is not necessary to consider the A / D conversion time, the detection time of the element resistance can be shortened, and the non-detection time of the gas concentration can be shortened.

In order to obtain the data of the current change and the voltage change at the time of detecting the element resistance, a method of temporarily changing the voltage applied to the element section and a method of temporarily changing the current value flowing through the element section A method is considered, and specifically, the configurations of claims 2 and 3 can be applied.

According to the second aspect of the invention, the voltage applied to the element portion for detecting the gas concentration is temporarily switched to a voltage for detecting the element resistance at a frequency corresponding to the sensor characteristic, and the voltage change at that time is performed. In the device resistance detecting device for detecting the resistance value of the element portion from the current and the current change, the hold circuit is a peak hold circuit for holding a peak value of the current change at the time of detecting the device resistance.

According to the third aspect of the present invention, the value of the current flowing through the element section when the gas concentration is detected is temporarily switched to a predetermined value, and the resistance of the element section is determined based on the voltage change and the current change at that time. In the element resistance detecting device for detecting a value, the hold circuit is a peak hold circuit or a sample hold circuit for monitoring a voltage change at the time of detecting the element resistance.

Also in the second and third aspects of the present invention, the peak value of the current change or the voltage change can be easily and accurately measured irrespective of factors such as sensor deterioration and circuit variation. As a result, an element resistance can be accurately detected in an element resistance detection device that detects element resistance from temporary voltage changes and current changes.

In particular, in the invention of claim 2, the frequency of the applied voltage is 1 kHz or more (about 10 kHz depending on the sensor).
When the current is changed, the current change at that time can be monitored successively to measure the current peak value. Therefore, the present invention can be suitably applied to a device that switches the voltage at a frequency according to the sensor characteristics when detecting the element resistance. If the element resistance detecting device is realized with a circuit configuration that does not use a microcomputer, the frequency of the applied voltage is not limited by the limit of the processing capability of the microcomputer.

The third aspect of the present invention provides the following fourth to fourth aspects.
The embodiment according to claim 7 is desirable. In other words, in the invention according to claim 4, when the element resistance is detected, after one terminal of the element section is temporarily opened, a constant current source for flowing a constant current to the element section is provided. A hold circuit that holds a terminal voltage of one of the element sections; and a hold circuit that holds a result of monitoring the terminal voltage when a constant current flows, and an element is provided based on a difference between the voltage values held by the respective hold circuits. Find the resistance value. According to claim 4, the value of the constant current by the constant current source is the current change amount at the time of detecting the element resistance,
The difference between the outputs of the hold circuits is the amount of voltage change. Therefore, the element resistance value can be calculated from the current change amount and the voltage change amount.

According to the fifth aspect of the present invention, a constant current source for supplying a predetermined constant current to the element portion when the element resistance is detected, and a voltage between both terminals of the element portion before the current change by the constant current source is held. And a hold circuit for holding a monitoring result of the voltage between both terminals of the element section after the current change, and obtains an element resistance value based on a difference between the voltage values held by the respective hold circuits. According to the fifth aspect, the difference between the current values before and after the flow of the constant current is the current change amount at the time of detecting the element resistance, and the difference between the outputs of the respective hold circuits is the voltage change amount.
Therefore, the element resistance value can be calculated from the current change amount and the voltage change amount.

According to the fifth aspect of the present invention, as described in the sixth aspect, when switching from the gas concentration detection state to the element resistance detection state, the constant current having the same value as the current value flowing through the element section immediately before the switching is applied. After that, it is desirable to change the current value by a predetermined value.

When the voltage peak value is continuously detected after the current change at the time of detecting the element resistance,
The element resistance value obtained from the voltage change amount at that time becomes the value of the DC resistance of the element portion (the slope of the resistance dominant region on the VI characteristic). On the other hand, if the peak value in a predetermined minute time is stored and held in the hold circuit after the current change at the time of detecting the element resistance, the AC impedance can be detected as the element resistance value. become.

The monitoring result of the current change or the voltage change held by the hold circuit needs to be updated every time the element resistance is detected, and thus is cleared before the next element resistance detection. At this time, if the detection value is cleared (when 0 V is output), the detection value of the element resistance temporarily disappears. Therefore, there is an adverse effect on heater control and self-diagnosis (diagnosis processing) using the detected value of the element resistance. Therefore, in the present invention, the adverse effects on various controls are suppressed by adopting the configurations of claims 8 to 11 described below.

According to the present invention, the sample and hold circuit for holding the monitoring result of the current change or the voltage change at the time of detecting the element resistance held by the hold circuit until the next detection of the element resistance is further provided. Prepare. In this case, since the sample and hold circuit holds and outputs the element resistance output even after the monitoring result of the current change or the voltage change is cleared, there is no detected value of the element resistance, which adversely affects various controls. The problem is avoided.

According to a ninth aspect of the present invention, there is provided a low-pass filter for capturing a monitoring result of a current change or a voltage change when detecting the element resistance held by the hold circuit. In this case, it is desirable that the hold value of the hold circuit be cleared immediately before element resistance detection.

According to the ninth and tenth aspects, even if the output of the hold circuit changes due to the setting / resetting of the hold circuit, the change in the output is smoothed by the low-pass filter.
Therefore, it is possible to continuously use the output of the hold circuit as the element current detection value. Therefore, the above-described problem that the detected value of the element resistance is not provided and various controls are adversely affected is avoided.

According to the eleventh aspect of the present invention, when monitoring the current change or the voltage change at the time of detecting the element resistance in the hold circuit, a signal indicating that the use of the monitoring result at that time is temporarily not permitted is output. . In this case, it is possible to prevent the monitoring result from being used for various controls when the element current detection value is uncertain, thereby avoiding a problem that various controls are adversely affected.

According to a twelfth aspect of the present invention, there is provided a gas concentration detecting sample and hold circuit for taking in an element current at the time of gas concentration detection, and the gas concentration detecting sample and hold circuit is the same during the element resistance detecting period. The detected value of the element current immediately before the detection period is held. According to this configuration, the element resistance detection value is updated while the previous detection value for gas concentration detection (previous value of the element current) is held at the time of element resistance detection, and the element resistance detection value at the time of gas concentration detection is updated. The gas concentration detection value is updated while maintaining the previous detection value (the previous value of the element current). Therefore, the detection of the gas concentration and the detection of the element resistance can be continuously performed, and even when one of the values is detected, the other value can be appropriately managed and held. In addition, a problem that the gas concentration detection value fluctuates due to a change in the element current when the element resistance is detected is prevented beforehand.

According to a thirteenth aspect of the present invention, there is provided a timing adjusting circuit for switching between gas concentration detection and element resistance detection at a predetermined timing to selectively execute the switching.
By adjusting various timings by the timing adjustment circuit, variations in various timings can be reduced as compared with a case where timings are managed by a microcomputer that executes various arithmetic programs (interrupt processing).

Conventionally, a method of oscillating the voltage applied to the gas concentration sensor and detecting the element resistance from the voltage change amount and the current change amount at that time has been known. According to the invention described above, the value of the current flowing through the element unit when the gas concentration is detected is temporarily switched to a predetermined value, and the resistance value of the element unit is detected from the voltage change and the current change at that time. Also in such a detection method, the element resistance can be accurately detected. The voltage change when the current is temporarily switched may be measured using the hold circuit as described above, or may be measured using a microcomputer.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention embodied in an air-fuel ratio detecting device will be described below with reference to the drawings. The air-fuel ratio detection device according to the present embodiment is applied to an electronically controlled gasoline injection engine mounted on an automobile. In the air-fuel ratio control system of the engine, the engine is controlled based on the detection result by the air-fuel ratio detection device. Is controlled to a desired air-fuel ratio. In the following description, a procedure for detecting an air-fuel ratio (A / F) using an air-fuel ratio sensor and a procedure for detecting an element resistance using an AC characteristic of the sensor will be described in detail.

FIG. 1 is a block diagram showing an outline of the air-fuel ratio detecting device according to the present embodiment. In FIG. 1, the air-fuel ratio detecting device includes a limiting current type air-fuel ratio sensor (hereinafter, referred to as an A / F sensor) 10. The A / F sensor 10 includes a sensor element unit 10a having a solid electrolyte (see FIG. 2), and detects an oxygen concentration in exhaust gas discharged from an engine. That is, the A / F sensor 10 includes the sensor element 1
A limit current (element current) corresponding to the oxygen concentration in the exhaust gas is output with the application of the voltage to 0a.

Here, the configuration of the sensor element section 10a is shown in FIG.
This will be described with reference to FIG. The sensor element portion 10a is roughly divided into a solid electrolyte 11, a gas diffusion resistance layer 12, and an air introduction duct 1.
3 and a heater 14, and each of these members is laminated. Further, a protective layer 15 is provided around each member.

The rectangular plate-shaped solid electrolyte 11 is a sheet made of partially stabilized zirconia, and a porous measurement electrode 16 made of platinum or the like is formed on the upper surface (gas diffusion resistance layer 12 side) by a screen printing method or the like. At the same time, on the lower surface (at the side of the air introduction duct 13), a porous air side electrode 17 also made of platinum or the like is formed by a screen printing method or the like.

The gas diffusion resistance layer 12 has a gas permeable layer 12a made of a porous sheet for introducing exhaust gas to the measurement electrode 16, and a gas shielding layer 12b made of a dense layer for suppressing the transmission of exhaust gas. . Each of the gas permeable layer 12a and the gas shielding layer 12b is formed by molding a ceramic such as alumina, spinel, or zirconia by a sheet molding method or the like. It has become something.

The air introduction duct 13 is made of a ceramic having a high thermal conductivity such as alumina, and an air chamber 18 is formed by the duct 13. The air introduction duct 13 plays a role of introducing air to the atmosphere-side electrode 17 in the atmosphere chamber 18.

A heater 14 is provided on the lower surface of the air introduction duct 13.
Is attached. The heater 14 includes a heating element 14a that generates heat when energized by a battery power supply, and an insulating sheet 14b that covers the heating element 14a. However, in addition to the configuration of FIG.
The heating element 14a may be embedded in the solid electrolyte 11,
A configuration in which 4a is embedded in the gas diffusion resistance layer 12 is also possible.

In the sensor element section 10a, the exhaust gas reaching the measurement electrode 16 does not enter the gas permeable layer 12a in the vertical direction (up and down direction in the figure).
Intrudes from the side of a. That is, since the surface of the gas permeable layer 12a is covered with the gas shielding layer 12b, the exhaust gas cannot enter from the vertical direction in the figure, but enter the inside of the permeable layer 12a from the side surface perpendicular to the direction. In such a case, the gas diffusion amount of the gas permeable layer 12a is
Depends on the left-right dimension (actually, the distance between the side surface of the gas-permeable layer 12a and the measurement electrode 16), but since this dimension can be easily and freely set, the gas-permeable layer 12a
Even if the hole diameter varies, a uniform and stable sensor output can be obtained.

In the A / F sensor 10 having the above configuration, the sensor element 10a generates a limit current corresponding to the oxygen concentration in a lean region from the stoichiometric air-fuel ratio point. In this case, the sensor element portion 10a (solid electrolyte 11) can detect the oxygen concentration with linear characteristics, but a high temperature of about 600 ° C. or more is required to activate the sensor element portion 10a. In addition, since the activation temperature range of the sensor element portion 10a is narrow, the activation state cannot be maintained by heating only the exhaust gas of the engine. Therefore, in the present embodiment, the sensor element section 10a is maintained in the active temperature range by controlling the heating of the heater 14 (the heating element 14a). In the region richer than the stoichiometric air-fuel ratio, the concentration of unburned gas such as carbon monoxide (CO) changes almost linearly with respect to the air-fuel ratio.
0a generates a limit current corresponding to the concentration of CO or the like.

The voltage-current characteristics of the A / F sensor 10 will be described with reference to FIG. In FIG. 3, a straight line portion parallel to the voltage axis V (horizontal axis) specifies a limit current flowing through the sensor element unit 10a. Lean-rich). That is, the limit current increases as the air-fuel ratio becomes leaner, and decreases as the air-fuel ratio becomes richer.

In this voltage-current characteristic, the voltage region smaller than the linear portion parallel to the voltage axis V is the resistance dominating region, and the slope of the primary linear portion in the resistance dominating region is the solid state in the sensor element portion 10a. It is specified by the internal resistance of the electrolyte 11 (this is called element resistance). The element resistance changes with a change in temperature. For example, when the temperature of the sensor element section 10a decreases, the slope decreases due to an increase in element resistance.

On the other hand, the switch circuit 21 shown in FIG.
A circuit for switching the voltage applied to the / F sensor 10 between a voltage for detecting the air-fuel ratio and a voltage for detecting the element resistance, and is selectively connected to any of the contacts a, b, and c in the figure. You. Power supplies 22, 23, and 24 are connected to contacts a, b, and c, respectively.
Is connected. In this case, any one of the power supplies 22 to 24 becomes the applied voltage Vp of the A / F sensor 10 according to the switching position of the switch circuit 21.

Here, when the air-fuel ratio is detected, the voltage of the power source 22 is changed via the contact a of the switch circuit 21 to the A / F sensor 1.
0 is applied. According to the power supply 22, for example, the voltage on the characteristic line L1 in FIG. 3, that is, the voltage corresponding to the air-fuel ratio at each time is applied to the A / F sensor 10 as the applied voltage Vp (however, when the air-fuel ratio is detected). Vp fixed configuration is also possible).

When the element resistance is detected, the voltages of the power supplies 23 and 24 are changed to A / A via the contacts b and c of the switch circuit 21.
It is applied to the F sensor 10 temporarily. According to the power supplies 23 and 24, as seen from time t2 to time t4 in FIG. 4A, the applied voltage Vp of the A / F sensor 10 is temporarily shifted from the previous air-fuel ratio detection voltage to both the positive and negative sides. Change. In this case, based on the frequency characteristics of the A / F sensor 10, the frequency of the applied voltage Vp at the time of detecting the element resistance is set to 1 kHz or more. However, in order to obtain more stable characteristics, the frequency may be set to 3 kHz or more. By increasing the frequency, it is possible to shorten the element resistance detection period, that is, the period during which the air-fuel ratio cannot be detected. .

The switching circuit 21 performs a switching operation in response to a switching signal SG1 from the timing adjustment circuit 25. The timing adjustment circuit 25 outputs the switching signal SG1 to the switch circuit 21 at a predetermined timing so that the applied voltage Vp is temporarily switched during the detection of the air-fuel ratio to detect the element resistance.

The applied voltage Vp is input to an LPF (low-pass filter) 26, from which high-frequency components are removed, and then input to a drive circuit 27. LPF26
The time constant of the sensor element (solid electrolyte 1)
A value suitable for measuring the internal resistance of 1) (for example, 4.5)
kHz). Then, the output of the drive circuit 27 is applied to one terminal of the A / F sensor 10 as a voltage AFV.

The output terminal of the operational amplifier 28 is connected to the other terminal of the A / F sensor 10 via a current detecting resistor 29. The current detection resistor 29 converts the element current flowing through the A / F sensor 10 into a voltage value and detects the voltage. The detected value (the voltage converted value of the element current) is sampled and held (S /
H) Circuit 30 and peak hold (P / H) circuit 31
Is input to

The S / H circuit 30 samples the element current at the time of detecting the air-fuel ratio, and outputs a signal SG from the timing adjustment circuit 25.
The sample value is sequentially updated and output during the period in which 2 is output (in the ON period of SG2). S / H circuit 3
An output of 0 is output as a detected value of the air-fuel ratio to, for example, an engine control ECU (not shown). The detected value of the air-fuel ratio is used for air-fuel ratio feedback control and the like.

The P / H circuit 31 includes a timing adjustment circuit 2
5 during the period during which the signal SG3 is being output (O of SG3
In the N period), the element current at the time of detecting the element resistance is peak-held. Note that the peak-held element current detection value is reset each time the signal SG3 is turned off.

The P / H circuit 31 has a sample hold (S
/ H) circuit 32 is connected, and the S / H circuit 32
In the period during which the signal SG4 is output from the timing adjustment circuit 25 (in the ON period of SG4), the sample value is sequentially updated and output. The output of the S / H circuit 32 is output as a detected value of the element resistance to, for example, an engine control ECU. The element resistance detection value is A / F
It is used for activity determination of the sensor 10, activation control, abnormality diagnosis (diag processing), and the like.

In the activation control of the A / F sensor 10, the temperature of the sensor element 10a (element temperature) is controlled with respect to the element temperature so that the temperature (element temperature) is maintained at a predetermined activation temperature (eg, 700 ° C.). Are controlled by feedback with respect to the target value. This element resistance (element temperature)
The feedback control is realized, for example, by controlling the energization duty ratio to the heater 14.

Next, the operation of the air-fuel ratio detecting device configured as described above will be described with reference to FIG. FIG. 4 shows a state in which the element resistance is temporarily detected (for example, every 128 msec) when the air-fuel ratio is detected. 4A shows a change in the applied voltage Vp, and FIG.
6, (c) shows the change of the element current detected by the current detecting resistor 29, and (d),
(E) shows changes in signals SG2 and SG3, and (f) shows P / H
(G) shows a change in the output of the circuit 31, and (g) shows a change in the signal SG4.

Before time t1, the switch circuit 21 is turned off as shown in FIG.
, And a voltage Vp for detecting the air-fuel ratio is applied to the A / F sensor 10. The element current flowing according to the air-fuel ratio (oxygen concentration in the exhaust gas) with the application of the voltage is detected by the current detection resistor 29. At this time, of the signals SG2 to SG4, only the signal SG2 input to the S / H circuit 30 is ON, and the S / H
The circuit 30 samples the detected value of the element current at each time and outputs it as an air-fuel ratio detected value (A / F value).

At time t1, the signal SG2 falls by the timing adjustment circuit 25 and the signal SG3 rises. When the signal SG2 is switched from ON to OFF, the S / H circuit 30 detects the detection value (A
/ F value). As a result, the A / F output terminal is held in the state of the A / F value output immediately before time t1.
At time t1, the signal SG3 is switched from OFF to ON, so that the P / H circuit 31 starts the peak hold of the element current.

Thereafter, at time t2, the switch circuit 21 is switched by the switching signal SG1 from the timing adjustment circuit 25, and the applied voltage Vp changes in the order of negative side → positive side (time t2 to t4). At this time, the applied voltage Vp is LP
It changes with a predetermined time constant through F26. That is, the AFV waveform changes while the applied voltage Vp is moderated, and the element current flows with the applied voltage. The peak value of the element current after time t2 is held by the P / H circuit 31.

However, the S / H circuit 30 holds the element current value immediately before time t1. Therefore, even when the element current changes with the change of the applied voltage at the time of detecting the element resistance, the A / F output does not change according to the element current waveform.

At time t3 when the signal SG4 is turned on, the signal SG4 rises for a certain period, and the peak value of the element current held by the P / H circuit 31 is changed to the S / H circuit 3.
2 and the element resistance output is updated with the sampled value. Then, an element resistance value is detected based on the updated element resistance output (current peak value) (element resistance = voltage change amount / current change amount). Further, using the detected value of the element resistance, heater energization control or the like by element resistance (element temperature) feedback is performed.

Thereafter, at time t4, the applied voltage Vp is returned to the value for detecting the air-fuel ratio. At time t5, the signal SG2 rises and the signal SG3 falls. Therefore, the element current sampling by the S / H circuit 30 is restarted, and the air-fuel ratio is detected based on the element current. At time t5, the sample / hold value of the P / H circuit 31 is cleared. From time t5 to the next element resistance detection, the previous detection value (detection value when SG4 = ON)
Is output from the S / H circuit 32 as an element resistance output.

Incidentally, for example, when the element temperature rises with the passage of time, the element resistance decreases accordingly. Therefore, if the amount of change in Vp at the time of detecting the element resistance is constant, the amount of change in the element current (the sample and hold value of the P / H circuit 31) increases as the element temperature increases.

According to the above-described embodiment, the following effects can be obtained. (A) A P / H circuit 31 for monitoring a current change at the time of detecting element resistance and holding a peak value at that time is provided. The peak value of the element current at the time of detecting the element resistance is determined by the P / H circuit
By detecting the current value 1, the peak value can be easily and accurately measured even when the generation time of the current peak value fluctuates due to factors such as sensor deterioration and circuit variation. Further, the frequency of the applied voltage is 1 kHz or more (10 kHz depending on the sensor).
Also, in the case of (approximately z), the current peak value can be measured by sequentially monitoring the current change. As a result, the element resistance can be accurately detected in the element resistance detection device that switches the voltage at a frequency according to the sensor characteristics when the element resistance is detected.

(B) An air-fuel ratio detection device can be realized with a circuit configuration that does not use a microcomputer, and cost reduction and size reduction can be achieved. In this case, the frequency of the applied voltage Vp is not limited by the limit of the processing capability of the microcomputer. In addition, it is possible to avoid such a problem that the operation load of the microcomputer is excessively increased and other controls are adversely affected. By switching the voltage Vp at a high frequency, the period during which the air-fuel ratio cannot be detected (the period during which the element resistance is detected) can be reduced.

(C) After the P / H circuit 31, the same circuit 3
An S / H circuit 32 for taking in the peak value held at 1 and holding the value until the next detection of the element resistance is provided. In this case, even after the current peak value is cleared, S / H
Since the circuit 32 holds and outputs the peak value, the problem that the detected value of the element resistance is not provided and various controls are adversely affected is avoided.

(D) When the element resistance is detected, the previous detection value for detecting the air-fuel ratio (the previous value of the element current) is used as the S / H circuit 3
The element resistance output is updated while being held at 0, and at the time of air-fuel ratio detection, the A / F output is held while the S / H circuit 32 holds the previous detection value for element resistance detection (the previous value of the element current). updated. Therefore, the detection of the air-fuel ratio and the detection of the element resistance can be continuously performed, and even when one of the values is detected, the other value can be appropriately managed and held. Further, such a problem that the detected value of the air-fuel ratio fluctuates due to a change in the element current when the element resistance is detected is prevented.

(E) The timing adjusting circuit 25 is provided, and the timing of the output of the signals SG1 to SG4 is adjusted by the circuit 25. As a result, variations in various timings can be reduced as compared with a case where timings are managed by a microcomputer that executes various arithmetic programs (interrupt processing).

(F) The time constant of the LPF 26 is set to a value suitable for measuring the internal resistance of the sensor element (for example, 4.5 kHz).
z). In this case, a sudden change in the voltage applied to the A / F sensor 10 is suppressed. Further, the voltage application time is appropriately set without prolonging the voltage application at the time of detecting the element resistance more than necessary.

(G) If the element resistance value can be detected with high accuracy as described above, activation control (heater energization control) of the A / F sensor 10 and abnormality diagnosis processing using the detection result can be realized with high accuracy. Become.

Next, second to fifth embodiments of the present invention will be described. However, in the configurations of the following embodiments, the same components as those of the above-described first embodiment are denoted by the same reference numerals in the drawings, and the description is simplified. The following description focuses on differences from the first embodiment.

(Second Embodiment) In the first embodiment, the output of the P / H circuit 31 is S / H as shown in FIG.
After the element resistance is detected by the S / H circuit 32 after the element resistance is detected by the S / H circuit 32, the configuration is changed. In the present embodiment, as shown in FIG.
In the subsequent stage of the circuit 31, an LPF (low-pass filter) 41 is provided instead of the S / H circuit 32 of FIG. Changes of various signals in the configuration of FIG. 5 will be described with reference to a time chart of FIG. In FIG. 7, (a) to (g)
Correspond to the operation of the present embodiment, of which (a) to
(D) corresponds to (a) to (d) in FIG.

In FIG. 7, at time t11, the signal SG3 falls, and the output (sample hold value) of the P / H circuit 31 is cleared. At time t12, the signal SG2
Is lowered, and the signal SG3 is raised. As a result, at time t13 immediately after that, the applied voltage Vp
Is observed in the P / H circuit 31 and the peak value is held. P / H circuit 31
Is passed through the LPF 41 to become an element resistance output. The operations at times t14 and t15 correspond to those at times t4 and t4 in FIG.
Since the operation is the same as that at t5, the description is omitted.

In such a case, the output of the P / H circuit 31 becomes LP
By passing through F41, the change of the output value after time t11 is smoothed by a predetermined time constant, and a rapid change of the output value is suppressed. At this time, the LPF output (element resistance output) slightly changes with the reset of the P / H circuit 31, but the amount of the change is very small, and at this time, an approximate value of the element resistance can be measured.

According to the present embodiment, similarly to the first embodiment, in the element resistance detection device (air-fuel ratio detection device) that switches the voltage at a frequency corresponding to the sensor characteristic when detecting the element resistance, Can be accurately detected. In particular, since the LPF 41 is provided at the subsequent stage of the P / H circuit 31, the output of the P / H circuit 31 can be continuously used as the element current detection value, and there is no element resistance detection value, which adversely affects various controls. Is avoided. In this case, the reset value (time t11 to t12 in FIG. 7) of the P / H circuit 31 is shortened by clearing the hold value of the P / H circuit 31 immediately before the element resistance detection, and the element resistance output becomes “ 0V "can be prevented.

(Third Embodiment) In the third embodiment, as shown in FIG. 6, the output of the P / H circuit 31 is used as the element resistance output as it is. Further, the timing adjustment circuit 25 outputs a use permission signal for instructing “use permission” and “use non-permission”. This use permission signal is output to an engine control ECU (not shown) together with the element resistance output.

The operation of the present embodiment will be described with reference to the time chart of FIG. However, in FIG. 7, (h) shows an operation unique to the present embodiment (others are the same as in the above embodiment). That is, the use permission signal is lowered slightly earlier than the time at which the output of the P / H circuit 31 is reset (time t21 in the figure), and the output of the P / H circuit 31 (the element resistance output) is set to "use permission". "" To "Disallowed". After that, at the time when the output of the P / H circuit 31 is almost stabilized after the application of the voltage for detecting the element resistance (time t22 in the drawing), the use permission signal is started, and the output of the P / H circuit 31 (the element resistance output) is changed. Return to "Permission".

According to the present embodiment, similarly to the first embodiment, the element resistance detecting device (air-fuel ratio detecting device) that switches the voltage at a frequency corresponding to the sensor characteristic when detecting the element resistance is used. Can be accurately detected. Particularly, in the present embodiment, when the peak value of the element current is detected by the P / H circuit 31, a signal indicating that the use of the element resistance output is temporarily not permitted is output, so that the element current detection value is uncertain. Sometimes, the output can be prevented from being used for various controls, thereby avoiding a problem that various controls are adversely affected.

(Fourth Embodiment) In each of the above embodiments, the voltage applied to the A / F sensor when detecting the element resistance is temporarily changed from a voltage value for detecting the air-fuel ratio to a voltage value for detecting the element resistance. However, in the present embodiment, the current value flowing through the A / F sensor is temporarily changed when detecting the element resistance.

FIG. 8 is an electric circuit diagram showing the configuration of the air-fuel ratio detecting device. 8, a switch circuit 51 having three contacts a, b, and c is connected to one terminal of the A / F sensor 10. The switch circuit 51 switches between the A / F detection state and the element resistance detection state, and is switched at a predetermined timing by the timing adjustment circuit 52 so that the element resistance can be detected during the air-fuel ratio detection. .

At the time of A / F detection, the contact of the switch circuit 51 is connected to the a side. Then, as in FIG.
2 and the drive circuit 27, the voltage AFV is applied to the A / F sensor 10, and the element current (limit current according to the A / F) at that time is detected by the current detection resistor 29 and S
/ H circuit 30. The signal sampled and held by the S / H circuit 30 is output to the outside as an A / F output.

On the other hand, at the time of detecting the element resistance, the contact of the switch circuit 51 is connected to the b side or the c side. The contact b is open. A constant current circuit 53 is connected to the contact c, and the constant current circuit 53 generates a constant current Icst for detecting an element resistance based on a change in current.

An S / H circuit 54 and a P / H circuit 55 are connected to the terminal of the A / F sensor 10 on the side of the switch circuit 51, respectively. The S / H circuit 54 and the P / H circuit 55
The set / reset timing is controlled by the timing adjustment circuit 52. When the switch circuit 51 is connected to the contact b side, the S / H circuit 54 temporarily enters a sample state, and sequentially updates and outputs a sample value. Also,
The P / H circuit 55 holds and outputs the peak value when the switch circuit 51 is connected to the contact c side. The output of the S / H circuit 54 and the output of the P / H circuit 55 are input to a negative input terminal and a positive input terminal of a differential amplifier 56, respectively.
The differential amplifier 56 receives the voltage held in the S / H circuit 54 and P
The difference from the voltage held in the / H circuit 55 is calculated. The output of the differential amplifier 56 is output to the outside as an element resistance output via the S / H circuit 57. The S / H circuit 57 is configured to hold the previous output of the differential amplifier 56 until the next detection of the element resistance.

The actual operation will be described with reference to FIG. Before time t31, the switch circuit 51 is operated to the contact a side, and the A / F sensor 10
A voltage for detection is applied (A / F detection operation).

At times t31 to t32, the switch circuit 5
1 is operated to the contact b side to open one end of the A / F sensor 10, and the state is maintained for a predetermined time (about 200 μsec). Then, the S / H circuit 54 is temporarily switched from the hold (H) state to the sample (S) state, and the voltage value of Vp at that time is stored and held by the S / H circuit 54.

At time t32, the switch circuit 51 is switched to the contact c side, and the constant current Icst flows from the constant current circuit 53 to the A / F sensor 10. After the current change by the constant current circuit 55, the P / H circuit 5 is turned on for a period of several tens of microseconds (period t32 to t33).
5 peak-holds the voltage value of Vp, and the A / F sensor 1
The peak value of the Vp voltage generated when the constant current Icst flows to 0 is stored and held.

In the present embodiment, the AC impedance is detected as the element resistance value, and the peak value of the Vp voltage is measured in a very short time (several tens of μsec) after the current change. When the state is maintained for a relatively long time after the current change, the element resistance value obtained from the voltage change amount at that time becomes the element DC resistance, which corresponds to the slope of the resistance dominant region on the VI characteristic. I do. The element DC resistance and the AC impedance of the element have a specific relationship, and it is generally known that there is a relationship of “element DC resistance> AC impedance”.

The voltage value held in the S / H circuit 54 and the P / H
The difference from the voltage value held in the circuit 55 is calculated by the differential amplifier 56, and the calculation result is output to the outside as an element resistance output via the S / H circuit 57. Then, at time t3
In 4, the switch circuit 51 is returned to the contact a side, and normal A / F detection is restarted.

In such a case, the element resistance output is converted into element resistance (AC impedance) by a microcomputer or the like (not shown) connected to the outside. At this time, the constant current circuit 5
3, the constant current Icst becomes the current change amount when the element resistance is detected, and the difference between the outputs of the S / H circuit 54 and the P / H circuit 55 (the output of the differential amplifier 56) becomes the voltage change amount.
Assuming that the output of the differential amplifier 56 (S / H circuit 57) is a voltage change amount ΔV, the constant current Icst is a known constant value, so that the element resistance value is calculated based on the ΔV value and the Icst value ( Element resistance = ΔV / Icst).

As described above, according to the fourth embodiment, in a device for measuring the voltage change at the time of detecting the element resistance by changing the element current, the peak value of the voltage change at the time of detecting the element resistance is determined by the P / H circuit. Since it is held at 55, the peak value of the voltage change can be easily and accurately measured regardless of factors such as sensor deterioration and circuit variation. As a result, the element resistance can be accurately detected. Further, since the S / H circuit 57 is provided at the subsequent stage of the differential amplifier 56, the problem that there is no detected value of the element resistance and adversely affects various controls can be avoided.

(Fifth Embodiment) Another method for detecting the element resistance of an A / F sensor by a change in current will be described below.

FIG. 10 is an electric circuit diagram showing the configuration of the air-fuel ratio detecting device. In FIG. 10, a switch circuit 61 having two contacts a and b is connected to one terminal of the A / F sensor 10. The switch circuit 61 switches between the A / F detection state and the element resistance detection state, and is switched at a predetermined timing by the timing adjustment circuit 62 so that the element resistance can be detected during the air-fuel ratio detection. .

At the time of A / F detection, the contact of the switch circuit 61 is connected to the a side. Then, as in FIG.
2 and the drive circuit 27, the voltage AFV is applied to the A / F sensor 10, and the element current (limit current according to the A / F) at that time is detected by the current detection resistor 29 and S
/ H circuit 30. The signal sampled and held by the S / H circuit 30 is output to the outside as an A / F output.

On the other hand, when the element resistance is detected, the contact of the switch circuit 61 is connected to the side b. A constant current circuit 63 for flowing a constant current IL1 corresponding to the output of the S / H circuit 30 is connected to the contact point b. Here, at the time of A / F detection, the element current IL0 flowing through the A / F sensor 10 is sampled and held by the S / H circuit 30, and the constant current circuit 63
Is, based on the hold value of the S / H circuit 30, its own constant current I
Determine the value of L1. According to the constant current circuit 63, the constant current IL having the same value as the element current IL0 immediately before the element resistance detection is performed.
1 flows to the A / F sensor 10.

The contact b of the switch circuit 61 has 3
A switch circuit 64 having two contacts a, b, and c is connected. The switch circuit 64 changes the current supplied to the A / F sensor 10 when the element resistance is detected. The contact a is connected to the constant current circuit 65, the contact b is open, and the contact c is a constant current. It is connected to a circuit 66.
The constant current circuit 65 allows the constant current IL2 to flow in the same direction as the constant current IL1.
The constant current IL3 flows in the reverse direction.

The S / H is connected between both terminals of the A / F sensor 10.
The circuit 67 and the P / H circuit 68 are connected, and these circuits 67 and 68 take in the voltage of both terminals of the A / F sensor 10 and hold the value. The output of the S / H circuit 67 and the output of the P / H circuit 68 are input to a negative input terminal and a positive input terminal of the differential amplifier 69, respectively.
The difference between the voltage held in the circuit 67 and the voltage held in the P / H circuit 68 is calculated. The output of the differential amplifier 69 is S / H
It is output to the outside as an element resistance output via the circuit 70. The S / H circuit 70 is configured to hold the previous output of the differential amplifier 69 until the next detection of the element resistance.

Here, when detecting the element resistance, the element current flowing through the A / F sensor 10 is temporarily changed with reference to the current element current IL0 corresponding to the current A / F as shown in FIG. A) in the figure, and the voltage change (B in the figure) between the sensor terminals at this time is measured. Then, the AC impedance of the sensor element unit is calculated from the change amount of the element current and the change amount of the voltage between the sensor terminals.

Next, the actual operation will be described with reference to FIG. At the time of A / F detection, the switch circuit 61 is operated to the contact a side, and the A / F sensor 10
/ F detection voltage is applied. At this time, A / F
An element current IL0 corresponding to A / F flows through the sensor 10.

At time t41 immediately before the detection of the element resistance, S /
By switching the H circuit 30 from the sample (S) state to the hold (H) state, voltage fluctuation during element resistance detection is prevented from being output to the outside. At time t42, the contact of the switch circuit 61 is connected to the b side, and detection of element resistance starts. At the beginning of element resistance detection,
The switch circuit 64 is connected to the contact b.

The element current at the time of A / F detection is “IL
0 ”at the beginning of the element resistance detection, the constant current IL1 equal to the element current IL0 is supplied from the constant current circuit 63 to the A / F.
It is supplied to the sensor 10 (IL1 = IL0). The value of this constant current IL1 also matches “IL0 (reference value at the time of current change)” shown in FIG.

After time t42, the S / H circuit 67 is temporarily switched from the hold (H) state to the sample (S) state, and the voltage between the sensor terminals before the change in the element current is stored and held in the S / H circuit 67. Is done.

Thereafter, at time t43, the switch circuit 6
4 is connected to the a side so that the constant current circuit 65
Is selected, and “IL1 + IL2” is displayed in the A / F sensor 10.
Current flows. At time t43, the P / H circuit 68
Is temporarily in a peak hold state, and the peak value at the time of the voltage change accompanying the current change of IL2 is stored and held by the P / H circuit 68. Also in this embodiment, the AC impedance is detected as the element resistance value, and the peak value until several tens μsec elapses after the current change is measured by the P / H circuit 68.

During the period from time t44 to time t45, the contact of the switch circuit 64 is connected to the side c, so that the a
The current flows in the opposite direction to the side. That is, the A / F sensor 1
0, a current of “IL1-IL3” flows, and the next A / F
Preparation for detection is performed. Further thereafter, at time t46
Then, the switch circuit 61 is returned to the contact a side, and the normal A
/ F detection is restarted. Immediately after that, the S / H circuit 3
0 is returned to the original sample state.

As described above, when the voltage between the sensor terminals before and after the change in the element current is stored and held in the S / H circuit 67 and the P / H circuit 68, the difference between the voltage values of the two circuits 67 and 68 is determined by the differential. The differential amplification is performed by the amplifier 69, and the operation result is output to the outside as an element resistance output. The element resistance output is converted into element impedance by a microcomputer or the like (not shown) connected to the outside.

In such a case, the constant current IL of the constant current circuit 65
2 is the element current variation ΔI, and the difference between the output voltages of the S / H circuit 67 and the P / H circuit 68 (the output of the differential amplifier 69) is the voltage variation ΔV, and the element resistance is calculated from these ΔI and ΔV. (Element resistance = ΔV / ΔI).

According to the fifth embodiment, in a device for measuring the voltage change at the time of detecting the element resistance by changing the element current at the time of detecting the element resistance, the peak value of the voltage change at the time of detecting the element resistance is determined by the P / H circuit. Since it is held at 55, the peak value of the voltage change can be easily and accurately measured regardless of factors such as sensor deterioration and circuit variation. As a result, the element resistance can be accurately detected.

Further, at the subsequent stage of the differential amplifier 69, an S / H for holding its output until the next detection of the element resistance is provided.
Since the circuit 70 is provided, it is possible to avoid a problem that a detection value of the element resistance is not provided and various controls are adversely affected.

The present invention can be embodied in the following forms other than the above. In the first to third embodiments, a timing adjustment circuit 2 for outputting signals SG1 to SG4
5 is embodied by a microcomputer. In this case, although the cost is increased by using the microcomputer, the peak value can be detected without error by measuring the current peak value when the element resistance is detected by the P / H circuit 31 as described above. As a result, the detection accuracy of the element resistance is improved. Also in this case,
Since there is no need to closely monitor the element current that changes at a frequency corresponding to the sensor characteristics, the calculation load on the microcomputer is greatly reduced. Similarly, in the fourth and fifth embodiments, the timing adjustment circuit may be embodied by a microcomputer.

In the fourth and fifth embodiments, the configuration of the air-fuel ratio detecting device is changed as follows. For example, in FIG. 8, an S / H circuit 57 is provided after the differential amplifier 56.
Is provided instead of the LPF. In FIG. 10, an LPF is provided in a stage subsequent to the differential amplifier 69 instead of the S / H circuit 70. According to this configuration, the change in the output value of the differential amplifier is L
The output value is smoothed by the PF, and the output value can be continuously used as the element current output. Therefore, the above-described problem that the detected value of the element resistance is not provided and various controls are adversely affected is avoided.

In the fourth and fifth embodiments, the use of the differential amplifiers 56 and 69 is temporarily prohibited when the outputs of the differential amplifiers 56 and 69 are not stable, for example, when the current changes for detecting the element resistance. I do. In this case, the uncertain element resistance output is not used for various controls, and the problem that various controls are adversely affected is avoided.

In the fourth and fifth embodiments, the current change at the time of detecting the element resistance is not changed within a unit time (Equation 10).
μsec) to the peak hold circuit (P /
Although the data is stored and held by the H circuits 55 and 68), this configuration is changed. For example, a sample and hold circuit stores and holds a voltage change around a unit time (around several tens of μsec) with respect to a current change at the time of element resistance detection. In such a case, as described above, the peak value of the voltage change can be easily and accurately measured regardless of factors such as sensor deterioration and circuit variation, and as a result, the element resistance can be accurately detected.

In each of the above embodiments, the air-fuel ratio detecting device is embodied using the stacked A / F sensor shown in FIG.
The sensor may be changed to a cup type A / F sensor. Further, the present invention can be applied to devices other than the air-fuel ratio detecting device using the A / F sensor. That is, the present invention can be applied to a gas concentration detection device using a gas concentration sensor capable of detecting gas concentration components such as NOx, HC, and CO. By using the same method as the above embodiment also in the other gas concentration detection device,
The resistance value of the sensor element can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an outline of an air-fuel ratio detection device according to a first embodiment.

FIG. 2 is a sectional view showing a configuration of a sensor element unit of the A / F sensor.

FIG. 3 is a diagram showing voltage-current characteristics of an A / F sensor.

FIG. 4 is a time chart for explaining the operation of the air-fuel ratio detection device.

FIG. 5 is a diagram showing a part of the configuration of an air-fuel ratio detection device according to a second embodiment.

FIG. 6 is a diagram showing a part of the configuration of an air-fuel ratio detection device according to a third embodiment.

FIG. 7 is a time chart for explaining the operation of the air-fuel ratio detection device in the second and third embodiments.

FIG. 8 is a diagram illustrating a configuration of an air-fuel ratio detection device according to a fourth embodiment.

FIG. 9 is a time chart for explaining an operation of the air-fuel ratio detection device in the fourth embodiment.

FIG. 10 is a diagram showing a configuration of an air-fuel ratio detection device according to a fifth embodiment.

FIG. 11 is a diagram showing changes in current and voltage when element resistance is detected.

FIG. 12 is a time chart for explaining the operation of the air-fuel ratio detection device in the fifth embodiment.

FIG. 13 is a diagram showing a relationship between element resistance and element temperature.

FIG. 14 is a configuration diagram showing an outline of an air-fuel ratio detection device in a conventional technique.

FIG. 15 is a time chart showing changes in applied voltage and element current of the A / F sensor.

FIG. 16 is a time chart for explaining a change in generation time of a current peak value.

[Explanation of symbols]

Reference numeral 10: A / F sensor (limit current type air-fuel ratio sensor) as a gas concentration sensor; 10a: sensor element; 11: solid electrolyte; 25: timing adjustment circuit;
0: sample hold (S / H) circuit, 31: peak hold (P / H) circuit, 32: sample hold (S / H)
H) Circuit, 41 ... LPF, 51 ... Switch circuit, 52 ...
Timing adjustment circuit, 53 ... constant current circuit, 54, 57 ...
S / H circuit, 55: P / H circuit, 56: differential amplifier, 6
1: switch circuit, 62: timing adjustment circuit, 63,
65: constant current circuit, 67, 70: S / H circuit, 68: P
/ H circuit, 69 ... differential amplifier.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Satoshi Haneda 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Tomio Kawase 1-1-1, Showa-cho, Kariya-shi, Aichi Co., Ltd. Inside DENSO

Claims (14)

[Claims] The present invention is applied to a gas concentration sensor having an element portion using a solid electrolyte and outputting a current signal corresponding to the concentration of a specific component in a gas to be detected in response to application of a voltage. An element resistance detection device for detecting a resistance value of the element unit from a temporary voltage change and a current change, wherein a hold circuit for monitoring a current change or a voltage change at the time of detecting the element resistance and holding the monitoring result. An element resistance detecting device for a gas concentration sensor, comprising: 2. The method according to claim 1, wherein a voltage applied to said element portion for detecting a gas concentration is temporarily switched to a voltage for detecting element resistance at a frequency corresponding to a sensor characteristic, and a voltage change and a current change at that time are applied to said element. 2. The element of the gas concentration sensor according to claim 1, wherein the element is a device resistance detection device that detects a resistance value of the unit, and the hold circuit is a peak hold circuit for holding a peak value of a current change at the time of detection of the device resistance. Resistance detector. 3. An element resistance detecting device for temporarily switching a value of a current flowing through the element portion to a predetermined value when detecting a gas concentration, and detecting a resistance value of the element portion from a voltage change and a current change at that time. The device according to claim 1, wherein the hold circuit is a peak hold circuit or a sample hold circuit for monitoring a voltage change at the time of detecting the element resistance. 4. A constant current source for flowing a constant current to the element section after the one terminal of the element section is temporarily opened when detecting the element resistance. ,
A hold circuit that holds one terminal voltage of the element portion in the open state, and a hold circuit that holds a monitoring result of the terminal voltage when a constant current flows, and a voltage value held by each of the hold circuits. An element resistance detecting device of a gas concentration sensor for obtaining an element resistance value based on a difference. 5. The element resistance detecting device according to claim 3, wherein a constant current source for supplying a predetermined constant current to the element portion when detecting the element resistance, and both ends of the element portion before the current is changed by the constant current source. A hold circuit that holds the voltage between the terminals, and a hold circuit that holds the monitoring result of the voltage between both terminals of the element after the current change. Element resistance detection device of a gas concentration sensor for determining 6. The element resistance detecting device according to claim 5, wherein when switching from the gas concentration detection state to the element resistance detection state, a constant current having the same value as the current flowing through the element section immediately before the switching is applied. An element resistance detecting device for a gas concentration sensor that changes a current value by a predetermined value. 7. The device resistance detecting device according to claim 4, wherein the hold circuit for monitoring the voltage change after the current change includes a predetermined minute time after the current change at the time of detecting the element resistance. The element resistance detection device of the gas concentration sensor that stores and holds the peak value at the time. 8. A sample and hold circuit according to claim 1, further comprising a sample and hold circuit for holding a monitoring result of a current change or a voltage change at the time of detecting the element resistance held by said hold circuit until the next detection of the element resistance. An element resistance detection device for a gas concentration sensor according to any one of the above. 9. The gas resistance sensor according to claim 1, further comprising a low-pass filter for capturing a monitoring result of a current change or a voltage change when detecting the element resistance held by the hold circuit. apparatus. 10. The device resistance detecting device according to claim 9, wherein a hold value of the hold circuit is cleared immediately before the device resistance detection. 11. A method according to claim 1, wherein when the hold circuit monitors a current change or a voltage change at the time of detecting an element resistance, a signal indicating that use of the monitoring result at that time is temporarily not permitted is output. An element resistance detection device for a gas concentration sensor according to any one of claims 1 to 3. 12. A gas concentration detecting sample and hold circuit for taking in an element current at the time of gas concentration detection, wherein in the element resistance detection period, the gas concentration detection sample and hold circuit operates immediately before the element current detection period. The element resistance detecting device for a gas concentration sensor according to any one of claims 1 to 11, which holds a detection value of: 13. The element resistance detection of the gas concentration sensor according to claim 1, further comprising a timing adjustment circuit for switching between gas concentration detection and element resistance detection at a predetermined timing and selectively performing the operation. apparatus. 14. A gas concentration sensor which has an element portion using a solid electrolyte and outputs a current signal corresponding to the concentration of a specific component in a gas to be detected in response to application of a voltage, An element resistance detecting device for a gas concentration sensor, wherein a value of a current flowing through an element portion is temporarily switched to a predetermined value, and a resistance value of the element portion is detected from a voltage change and a current change at that time.