JP2000065781A - Apparatus for detecting element temperature of oxygen concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make accurately detectable the element temperature by using an impedance value and admittance value as parameters for judging the element temp. of an oxygen concentration sensor. SOLUTION: The sub-microcomputer 18 of a sensor control circuit 16 controls a sensor element 14 so as to hold the applied voltage thereof to be a desired voltage and starts air/fuel ratio feedback when the sensor element 14 is raised in temp. from an in active state to a semi-active state to perform control in an active state. The sub-microcomputer 18 changes over the applied voltage from a reference voltage to a sweep voltage and an impedance value and an admittance value are calculated by respective calculation means. Since the control of the heater 15 at the temp. (element temp.) of the sensor element 14 is possible in the active state, admittance is calculated and the supply of a current to the heater 15 is subjected to feedback control so as to coincide with the objective admittance of the sensor element 14. However, the accurate detection of the element temp. is performed only in a high temp. region from admittance and the element temp. in the unactive state is accurately detected from impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration sensor element temperature detecting device having a function of detecting an element resistance value of an oxygen concentration sensor and judging an element temperature from the element resistance value.

[0002]

2. Description of the Related Art In recent years, for example, in an air-fuel ratio control system of an automobile, the oxygen concentration in exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of an air-fuel mixture taken into an engine is detected based on the detected value of the oxygen concentration sensor. Is controlled in a feedback manner to enhance the exhaust gas purification performance of the three-way catalyst and the like. In general, an oxygen concentration sensor has a large temperature dependency of its output voltage. Therefore, it is necessary to maintain the element temperature at an appropriate temperature (active temperature) in order to maintain good oxygen concentration detection accuracy. Therefore, a heater is attached to the oxygen concentration sensor, and the power supply to the heater is feedback-controlled so that the element temperature is maintained at an active temperature (in this active state, for example, about 700 ° C. or more) by the heat generated by the heater. . In this system, it is necessary to detect the element temperature in order to feedback-control the energization of the heater. However, if a temperature sensor is provided in the oxygen concentration sensor, the size of the oxygen concentration sensor increases and the cost increases.

Therefore, as shown in FIG. 2, attention is paid to the fact that the element impedance (element resistance value) of the oxygen concentration sensor changes according to the element temperature, the element impedance is detected, and the element temperature is calculated from the element impedance. It has been proposed to. As a method for detecting the element impedance, as shown in Japanese Patent Application Laid-Open No. 9-292364, the element applied voltage is switched from the voltage at the time of detecting the oxygen concentration to the voltage for detecting the element impedance, and the voltage change ΔV at that time, A current change ΔI caused by the voltage change ΔV is detected, and the element impedance Z (= ΔV / Δ
There is one that calculates I).

[0004]

As shown in FIG. 2, the temperature characteristic of the element impedance is such that as the element temperature of the oxygen concentration sensor increases, the element impedance decreases. It decreases as the temperature increases. For this reason, in a high-temperature region where a semi-active state (for example, about 600 to 700 ° C.) or a main active state (for example, about 700 ° C. or more), the element temperature change 1
The amount of change in element impedance per ° C is extremely small, in other words, the amount of change in element temperature per 1Ω change in element impedance is very large. Is enlarged, resulting in a large temperature error, and the accuracy of detecting the element temperature is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to provide an element temperature detecting device for an oxygen concentration sensor capable of accurately detecting the element temperature of the oxygen concentration sensor. It is in.

[0006]

Means for determining the element resistance of an oxygen concentration sensor include admittance, which is the reciprocal of impedance, in addition to impedance. The temperature characteristic of the impedance, as shown in FIG.
Since the rate of change decreases as the element temperature increases,
When the element temperature is detected from the impedance, the detection accuracy of the element temperature is reduced in a high temperature area, but is detected in a low temperature area.
The element temperature can be accurately detected. On the other hand, as shown in FIG. 3, the rate of change of the admittance temperature characteristic increases as the element temperature increases. Therefore, when the element temperature is detected from the admittance, the element temperature can be accurately detected in a high temperature region. In the low temperature region, the accuracy of detecting the element temperature is reduced. Therefore, in the low temperature region, the device temperature can be detected more accurately by detecting the device temperature from the impedance, while in the high temperature region, the device temperature can be detected more accurately by detecting the device temperature from the admittance.

Focusing on this point, an element temperature detecting device for an oxygen concentration sensor according to claim 1 of the present invention comprises: impedance calculating means for calculating an element resistance value as an impedance value;
Admittance calculation means for calculating an element resistance value as an admittance value, wherein at least one of the impedance value calculated by the impedance calculation means and the admittance value calculated by the admittance calculation means is used as a parameter for determining the element temperature. It was made. In this case, the element resistance can be calculated as either the impedance value or the admittance value. Therefore, if the element temperature is detected by appropriately using the impedance value and the admittance value in consideration of the change characteristics, the element temperature can be calculated accurately. It can be detected well.

In this case, it is preferable to determine whether to use the impedance value or the admittance value depending on the state of the oxygen concentration sensor, and to switch between the impedance calculation means and the admittance calculation means. This makes it possible to optimize the switching timing of the impedance / admittance calculation means.

Specifically, the impedance calculating means and the admittance calculating means may be switched according to the impedance value or admittance value of the element of the oxygen concentration sensor. With this configuration, it is possible to switch the impedance / admittance calculating means at an appropriate switching timing in consideration of a change characteristic of the impedance value and the admittance value depending on whether the calculated impedance value or admittance value has reached a predetermined switching value. it can.

[0010] According to another aspect of the present invention, the impedance calculating means and the admittance calculating means may be switched depending on whether the element is in an active state or a semi-active state. By doing so, the element temperature can be detected by switching the impedance value and the admittance value so as to be used in a region where the rate of change with respect to the device temperature is large, and the device temperature can be accurately detected over the entire temperature region. Can be.

When the element temperature is equal to or lower than the predetermined temperature, the device is switched to impedance calculating means to calculate the element resistance value as an impedance value, and when the element temperature is higher than the predetermined temperature, the admittance calculating means is used. Switching may be performed to calculate the element resistance value as the admittance value. Also in this case, the impedance / admittance calculation means can be switched at an appropriate timing in consideration of the change characteristics of the impedance value and the admittance value.

Further, the impedance value and the admittance value are converted so that the minimum value and the maximum value of the two values are substantially the same, and the impedance value and the admittance value become the same. The impedance / admittance calculation means may be switched at the boundary of the region. With this configuration, it is possible to switch between the impedance value and the admittance value, which has a larger rate of change with respect to the element temperature, as the element resistance value used for detecting the element temperature. The admittance calculation means can be switched.

Further, after switching from the impedance calculating means to the admittance calculating means as in claim 8,
Switching to the impedance calculating means may be prohibited by the switching prohibiting means. In other words, once the temperature of the element of the oxygen concentration sensor is raised to the active region, even if the element temperature decreases, the amount of temperature decrease is small,
Since the element returns to the active area immediately, even if the switching to the impedance calculating means is inhibited, the detection accuracy of the element temperature does not decrease much and does not cause much problem. Moreover, if the switching from the admittance calculating means to the impedance calculating means is prohibited, the chattering phenomenon that frequently occurs can be prevented, and the control can be stabilized.

Alternatively, the switching characteristic of the impedance / admittance calculating means may be provided with hysteresis. Even in this case, the chattering phenomenon can be prevented, and the control can be stabilized.

When the control value is learned by the learning means based on the element resistance value calculated by the element resistance value calculation means, the learning value is corrected when the impedance / admittance calculation means is switched. good. In this way, it is possible to correct the learning values before and after the switching so as not to be inconsistent, and to maintain the consistency of the learning values before and after the switching.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment (1)] FIG. 1 shows an embodiment (1) in which the present invention is applied to an air-fuel ratio control system.
A description will be given based on FIGS.

First, a schematic configuration of the system will be described with reference to FIG. An oxygen concentration sensor 13 is provided in an exhaust pipe 12 of the engine 11. This oxygen concentration sensor 13
Is a limiting current type oxygen concentration sensor (air-fuel ratio sensor), which generates a limiting current that is substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas. Since the sensor element 14 of the oxygen concentration sensor 13 has a high activation temperature (this activation state is about 700 ° C. or higher) and has a narrow activation temperature range, the activation temperature range can be maintained only by the heat of the exhaust gas. Have difficulty.
Therefore, the oxygen concentration sensor 13 has a built-in heater 15, and energization of the heater 15 is controlled so that the temperature of the sensor element 14 is maintained in the activation temperature range by the heat generated by the heater 15.

The oxygen concentration sensor 13 is controlled by a sensor control circuit 16. The sensor control circuit 16 is provided with a sub-microcomputer 18 (hereinafter abbreviated as “sub-microcomputer”) that transmits and receives data to and from a host microcomputer (hereinafter abbreviated as “host-microcomputer”) 17. The host microcomputer 17 is a microcomputer that controls the entire engine 11 and converts an ignition command signal and an injection command signal calculated according to an ignition / injection control program stored in a ROM (not shown) of the engine 11 into an ignition device ( (Not shown) and a fuel injection valve (not shown) to control the ignition / injection operation.

On the other hand, the sub-microcomputer 18 includes a CPU 21
A ROM 22 (storage medium), a RAM 23, a backup RAM 24 whose power is backed up by a battery, and the like are built-in. In order to control an applied voltage of the sensor element 14, an applied voltage command signal is applied to the element via a D / A converter 26. The voltage is output to the voltage control circuit 27, and at the time of normal oxygen concentration detection, the element applied voltage control circuit 27 controls the applied voltage of the sensor element 14 (the voltage difference between both ends of the sensor element 14) to be maintained at a predetermined voltage. Element applied voltage control circuit 27
A current detection circuit 2 for detecting an element current (limit current) generated in the sensor element 14 according to the oxygen concentration in the exhaust gas.
A voltage corresponding to the element current detected by the current detection circuit 28 is taken into the sub-microcomputer 18 via the A / D converter 29 as an oxygen concentration detection signal. The voltage applied to the sensor element 14 is also taken into the sub-microcomputer 18 via the A / D converter 29.

Further, the sub-microcomputer 18 inputs the Duty signal to the heater control circuit 30, and controls the duty ratio of the heater 15 by the heater control circuit 30, thereby changing the temperature of the sensor element 14 to the active temperature. To keep.

Here, the active state of the sensor element 14 includes:
There are a semi-active state (for example, about 600 to 700 ° C.) and a main active state (for example, about 700 ° C. or higher). When the temperature of the sensor element 14 rises from an inactive state to a semi-active state, a marginal current starts to be generated slightly due to the oxygen concentration in the exhaust gas. However, since the marginal current is still small, the oxygen concentration (air-fuel ratio) is detected. The accuracy is not so high that it can detect a rough oxygen concentration. In consideration of this point, when the state becomes semi-active, the target air-fuel ratio for the air-fuel ratio feedback is calculated, and the gain is made smaller than usual to start the air-fuel ratio feedback.

Thereafter, when the temperature of the sensor element 14 rises to the main activation state, the limit current increases, and the oxygen concentration can be detected with high accuracy. Therefore, the gain is increased and the air-fuel ratio feedback is performed. Further, in the active state, the element temperature changes following the temperature of the heater 15, and the heater 15 can be controlled by the temperature of the sensor element 14 (hereinafter referred to as “element temperature”). The target resistance value (target admittance) of the sensor element 14 is calculated based on the amount, the sensor deterioration state, and the like. The admittance of the sensor element 14 is calculated as described later, and the heater 1 is set so that the admittance matches the target admittance.
5 is feedback-controlled to maintain the element temperature at the target main activation temperature.

Next, the relationship between element temperature, impedance, and admittance will be described. As shown in FIG. 2, the temperature characteristic of the impedance decreases as the element temperature increases, but the rate of impedance decrease decreases as the element temperature increases. Therefore, in a high temperature region where the semiconductor device is in the semi-active state or the main active state, the amount of change in impedance per 1 ° C. of element temperature change is extremely small. In other words, the amount of change in element temperature per 1 Ω of impedance change is very large. Become.

On the other hand, the temperature characteristic of admittance is
As shown in FIG. 3, since the rate of change increases as the element temperature increases, when the element temperature is detected from admittance, the element temperature can be accurately detected in a high temperature area, but the element temperature detection accuracy can be detected in a low temperature area. Decrease.

From such temperature characteristics of impedance and admittance, in the low temperature region, the device temperature can be accurately detected by detecting the device temperature from the impedance, while in the high temperature region, the device temperature can be detected by the admittance. It can be seen that the element temperature can be accurately detected.

Focusing on this point, the sub-microcomputer 18 has a function of selecting and detecting the impedance Z and the admittance Y of the sensor element 14 according to an element activation determination routine shown in FIG. In the impedance / admittance detection method, the voltage applied to the sensor element is switched from a voltage (reference voltage) at the time of detecting the oxygen concentration to a voltage (sweep voltage) for detecting the impedance / admittance, and the voltage change ΔV at that time and the voltage change ΔV The current change ΔI caused by the above is detected, and the impedance Z,
The admittance Y is calculated. Z = ΔV / ΔI Y = 1 / Z = ΔI / ΔV

In this embodiment (1), the impedance Z
And admittance Y are not calculated at the same time.
The state of the sensor element 14 is switched between the calculation of the impedance Z and the calculation of the admittance Y on the basis of the semi-active boundary region shown in FIGS. That is, the impedance Z is calculated in the non-active region, and the admittance Y is calculated in the semi-active region and the main active region.

The element activation determination routine shown in FIG. 4 is stored in the ROM 22 of the sub-microcomputer 18 and is executed by the CPU 21 at predetermined intervals or at predetermined crank angles. When this routine is started, first, in step 101, it is determined whether or not the admittance switching flag XACN is “1” meaning an admittance calculation area. In this embodiment (1), the admittance calculation area is an area (semi-active area, main active area) equal to or greater than the half-active boundary area where the admittance Y is equal to or greater than Y1 shown in FIGS. Note that the admittance switching flag XACN is set in steps 105 and 11 described later.
It can be switched with 1.

If it is determined in step 101 that the admittance switching flag XACN = 0 (impedance calculation area), the process proceeds to step 102, where the impedance Z (= Δ
V / ΔI) is calculated. The processing of this step 102
It functions as an impedance calculating means (element resistance value calculating means) described in the claims. Then, in the next step 103, it is determined whether or not the impedance Z is the semi-active area or the main active area based on whether or not the impedance Z is smaller than Z1 (see FIGS. 2 and 5) corresponding to the semi-active boundary area. . If Z <Z1, it is the semi-active area or the main active area, so the process proceeds to step 104 and the semi-active flag X
HACT is switched to "1" which means a half-active area or more, and in the next step 105, the admittance switching flag X
The ACN is switched to “1” meaning the admittance calculation area, and the routine ends.

On the other hand, if Z ≧ Z1 in step 103, the inactive area (impedance calculation area) is set, so that the state of the half-active flag XHACT = 0 and the admittance switching flag XACN = 0 are not switched. This routine ends.

If it is determined in step 101 that the admittance switching flag XACN = 1 (admittance calculation area), the process proceeds to step 106, where the admittance Y (=
ΔI / ΔV) is calculated. The processing of step 106 plays a role as an admittance calculating means (element resistance value calculating means) in the claims. Then, in the next step 107, it is determined whether the admittance Y is a semi-active area or an inactive area by determining whether the admittance Y is smaller than Y2 (see FIGS. 3 and 5) corresponding to the main active boundary area. . If Y ≧ Y2 in step 107,
Since this is the active area, the process proceeds to step 112, where the active flag XFACT is switched to “1” meaning the active area, and the routine ends.

On the other hand, in step 107, Y <
If it is Y2, it is not the active region, so that step 10
Proceeding to 8, the activation flag XFACT is switched to "0". Thereafter, in step 109, it is determined whether or not the admittance Y is an inactive area (impedance calculation area) based on whether or not the admittance Y is smaller than Y1 (see FIGS. 3 and 5) corresponding to the half-active boundary area. . If this step 10
If Y <Y1 (inactive area) in step 9, step 11
0, the half-active flag XHACT is switched to "0", and in the next step 111, the admittance switching flag X
The ACN is switched to “0” meaning the impedance calculation area, and this routine ends.

On the other hand, if Y ≧ Y 1 in the above step 109, it is a semi-active area or a main active area (admittance calculation area), so that the state of the half-active flag XHACT = 1 and the admittance switching flag XACN = 1 are set. This routine ends without switching.

An example of the element resistance value calculation control in the embodiment (1) described above will be described with reference to FIG. FIG. 5 is a time chart for explaining a switching characteristic between the impedance Z and the admittance Y when the element temperature rises from the inactive region to the main active region via the semi-active region.

In this embodiment (1), while the element temperature is in the inactive region, the impedance Z is calculated, and the duty ratio of the heater 15 is controlled so that the impedance Z matches the target impedance. To raise the element temperature.

Thereafter, when the element temperature rises to the semi-active region, the calculation is switched to the admittance Y, and after the temperature rises to the main active region, the admittance Y is continuously calculated. Therefore, in the semi-active region and the main active region, the heater 1 is set so that the calculated admittance Y matches the target admittance.
By controlling the duty ratio of 5, the element temperature is raised to the target main activation temperature, and control is performed so as to maintain the temperature. still,
The impedance Z and the admittance Y are each converted into an element temperature, and this element temperature is set to a target temperature (actual activation temperature).
The duty ratio of the heater 15 may be controlled so that

In the embodiment (1) described above, the temperature characteristics of impedance and admittance, that is, in the low temperature region, the device temperature can be detected more accurately by detecting the device temperature from the impedance. Considering the characteristic that detecting the element temperature from admittance can detect the element temperature more accurately, in the inactive region,
Since the impedance is calculated and the admittance is calculated in the semi-active region and the main active region, the device temperature is detected by switching the impedance and the admittance to be used in the region where the rate of change with respect to the device temperature is large, respectively. Accordingly, the element temperature can be accurately detected over the entire temperature range. Thereby, the control accuracy of the element temperature (heater control accuracy) can be improved, the detection accuracy of the oxygen concentration (air-fuel ratio) in the exhaust gas can be improved, and the control accuracy of the air-fuel ratio feedback can be improved.

In the method of detecting the element temperature only by the admittance, the control at the start of the heater control is deteriorated because the detection accuracy of the element temperature is low in a low temperature region (inactive region). In (2), since the element temperature is detected from the impedance in the low-temperature area, the element temperature can be accurately detected even in the low-temperature area, and the control accuracy at the start of the heater control can be improved.

[Embodiment (2)] In the above-described embodiment (1), the impedance Z and the admittance Y are switched depending on whether they are in a semi-active region. However, in the embodiment (2) of the present invention, In the element activation determination routine shown in FIG. 6, the impedance Z and the admittance Y are switched depending on whether or not this is the active region.

That is, in the element activation determination routine of FIG. 6, when the admittance switching flag XACN = 0 (impedance calculation area), the impedance Z (= ΔV / Δ
After calculating I) (steps 201 and 202), the process proceeds to step 203, where whether or not the impedance Z is smaller than Z1 (see FIGS. 2 and 5) corresponding to the semi-active boundary region is determined. It is determined whether or not the area is an active area. If Z ≧ Z1 in step 203,
Since it is an inactive area, the process proceeds to step 216, where the half-active flag XHACT is switched to "0", and this routine ends.

On the other hand, in step 203, Z <
If Z1 is a semi-active region or a main active region,
Proceeding to step 204, the half-active flag XHACT is switched to "1" which means a half-active area or higher, and in the next step 205, the impedance Z is lower than Z2 (see FIGS. 2 and 5) corresponding to the main active boundary area. It is determined whether or not this is the active region based on whether or not it is smaller. If the present active area (Z <Z2), the routine proceeds to step 206, where the present active flag XFACT is switched to "1" which means the present active area. Is switched to "1", which means that the routine ends.

On the other hand, in step 205, if Z ≧ Z2, it is a semi-active area or an inactive area (impedance calculation area).
This routine ends without switching the state of the admittance switching flag XACN = 0.

If the admittance switching flag XACN = 1 (admittance calculation area) in step 201, the admittance Y (= ΔI / ΔV) is calculated (step 208). Is smaller than Y2 (see FIGS. 3 and 5) corresponding to the present active boundary region, it is determined whether the region is a semi-active region or an inactive region. If this step 20
If Y <Y2 at 9, this is not the main active area, so the routine proceeds to step 210 and sets the main active flag XFACT to “0”.
And the admittance switching flag XACN
Is switched to “0” meaning the impedance calculation area, and this routine ends.

On the other hand, if Y ≧ Y2 in the above step 209, this is the active area (admittance calculation area), so that the state of the active flag XFACT = 1 and the state of the admittance switching flag XACN = 1 are not switched. This routine ends.

According to the embodiment (2) described above,
As shown in FIG. 5, while the element temperature is in the non-active area or the semi-active area, the impedance Z is calculated, and the duty ratio of the heater 15 is controlled so that the impedance Z matches the target impedance. To raise the element temperature.

Thereafter, when the element temperature rises to the main active region, the calculation is switched to the calculation of admittance Y. Therefore, in this active region, the duty ratio of the heater 15 is controlled so that the calculated admittance Y matches the target admittance,
Control is performed so that the element temperature is maintained at the target main activation temperature.

[Embodiment (3)] The embodiment (1),
In (2), even after the element temperature rises to the admittance calculation area and is switched to admittance calculation, if the element temperature falls to the impedance calculation area, the calculation is switched to impedance calculation. However, if such switching frequently occurs, the heater control may become unstable.

Therefore, in the embodiment (3) of the present invention, the impedance Z is calculated in the inactive region by executing the element activation determination routine shown in FIG. 7, and the temperature is once increased to the semi-active region. After switching to the calculation of the admittance Y, the switching to the calculation of the impedance Z is prohibited, and the admittance Y is continuously calculated even if the element temperature drops to the inactive region.

That is, in the element activation determination routine shown in FIG. 7, at step 105, the admittance switching flag X
After the ACN is switched to “1” meaning the admittance calculation area, the admittance switching flag XACN is set to “0”.
(Step 111 in FIG. 4), and the switching to the calculation of the impedance Z is prohibited. This function corresponds to the switching prohibiting means described in the claims.

After the main activation flag XFACT is switched in step 107 depending on whether Y <Y2 or not (steps 108 and 112), in the next step 109, the half activation flag XHACT is determined depending on whether Y <Y1 or not. Are switched (steps 110 and 113). The other processing is the same as the processing of each step of the routine of FIG. 4 described above.

In the embodiment (3) described above, after switching from the calculation of impedance to the calculation of admittance, the switching to the calculation of impedance is prohibited. However, the element temperature is temporarily reduced to the semi-active region. When the temperature rises to (admittance calculation area), the amount of temperature decrease is small even after that, even if the element temperature drops, and the temperature immediately returns to the semi-active area. There is little decrease in temperature detection accuracy, and it does not cause much problem. Moreover, if the switching from the calculation of the admittance to the calculation of the impedance is prohibited, the chattering phenomenon that frequently occurs can be prevented, and the heater control can be stabilized.

[Embodiment (4)] In the embodiment (4) of the present invention shown in FIG. 8, as in the embodiment (2) shown in FIG.
Is calculated, and admittance Y is calculated in this active region. Then, similarly to the embodiment (3), once the temperature is raised to the admittance calculation area and switched to the calculation of the admittance Y, thereafter, even if the element temperature decreases to the impedance calculation area, the calculation of the impedance Z is started. Is prohibited, and the admittance Y is continuously calculated.

That is, in the element activation determination routine shown in FIG. 8, in step 207, the admittance switching flag X
After the ACN is switched to “1” meaning the admittance calculation area, the admittance switching flag XACN is set to “0”.
(Step 211 in FIG. 6), and switching to the calculation of the impedance Z is prohibited. This function corresponds to the switching prohibiting means described in the claims.

After the main activation flag XFACT is switched in step 209 depending on whether Y <Y2 or not (steps 210 and 212), in the next step 213, the half activation flag XHACT is determined depending on whether Y <Y1 or not. Is switched (steps 214 and 215). The other processing is the same as the processing of each step of the routine of FIG. 6 described above. In the embodiment (4) described above, the same effect as in the embodiment (3) can be obtained.

[Embodiment (5)] The embodiment (3),
In (4), once the calculation has been switched to the admittance Y, the switching to the calculation of the impedance Z is prohibited, thereby preventing the chattering phenomenon and stabilizing the heater control. In the mode (5), the impedance activation calculation and the admittance Y are performed as shown in FIG. 10 by executing the element activation determination routine shown in FIG.
By giving hysteresis to the switching characteristics with the calculation of
The chattering phenomenon is prevented to stabilize the heater control.

That is, in the element activation determination routine of FIG. 9, the semi-active region and the main active region are set as the admittance calculation regions, and when it is determined whether or not to switch from the calculation of the admittance Y to the calculation of the impedance Z, step 1 is performed.
09a, the admittance Y is changed to a predetermined switching value Y1a (FIG. 10).
It is determined whether or not to switch to the calculation of the impedance Z based on whether it is smaller than the reference value. Here, the switching value Y1a is represented by Y1−α (where α is a constant that determines the degree of hysteresis)
, The switching characteristics have hysteresis. If Y <Y1a, it is determined that the area is the impedance calculation area, and the routine proceeds to step 110, where the half-active flag XHACT is switched to "0".
Then, the admittance switching flag XACN is switched to “0”. The other processing is the same as the processing of each step of the routine of FIG. 4 described above.

[Embodiment (6)] An embodiment (6) of the present invention shown in FIG. 11 is an embodiment corresponding to the embodiment (2) shown in FIG. 6 and calculates impedance Z and admittance Y. By providing hysteresis to the switching characteristics of the above, the chattering phenomenon is prevented and the heater control is stabilized.

That is, in the element activation determination routine of FIG. 11, when only the main active region is set as the admittance calculation region and it is determined whether to switch from the calculation of the admittance Y to the calculation of the impedance Z, it is determined in step 209a.
And the admittance Y is a predetermined switching value Y2a (see FIG. 10).
It is determined whether or not to switch to the calculation of the impedance Z based on whether or not it is smaller than the above. Here, the switching value Y2a is set to Y1−
By setting β (where β is a constant that determines the degree of hysteresis), the switching characteristic has hysteresis.
If Y <Y2a, it is determined that the area is the impedance calculation area, and the routine proceeds to step 210, where the main activation flag XF
ACT is switched to “0”, and in the next step 211, the admittance switching flag XACN is switched to “0”.
The other processing is the same as the processing of each step of the routine of FIG. 6 described above.

[Embodiment (7)] In each of the above embodiments,
Switching between the calculation of the impedance Z and the calculation of the admittance Y is performed at the semi-active boundary area or the main active boundary area. However, in the embodiment (7) of the present invention shown in FIGS. Z and the admittance Y are subjected to LSB conversion so that the minimum value and the maximum value of the two become substantially the same RAM value, and the impedance RAM is divided by a region where the impedance RAM value ZM and the admittance RAM value YM are the same. Calculation of Value ZM and Admittance R
The calculation of the AM value YM is switched.

First, an example of the element resistance value calculation control of the embodiment (7) will be described with reference to FIG. The switching value M for switching from the calculation of the impedance RAM value ZM to the calculation of the admittance RAM value YM is set to an intermediate value between the half-active boundary value ZM1 and the main active boundary value YM2. Impedance R
In an area where the AM value ZM is equal to or larger than the switching value M, the impedance RAM value ZM is calculated. At this time, the impedance RA
When the M value ZM falls below the half-active boundary value ZM1, the half-active flag XHACT is switched to "1".

When the impedance RAM value ZM reaches the switching value M, the admittance switching flag XACN is set to "1".
To the calculation of the admittance RAM value YM. Thereafter, when the admittance RAM value YM becomes equal to or more than the main activation boundary value YM2, the main activation flag XFACT is switched to “1”.

Such control is executed by the element activation determination routine shown in FIG. This routine is also executed every predetermined time or every predetermined crank angle. When this routine is started, first, in step 101, it is determined whether or not an area is an impedance calculation area based on whether or not the following equation is satisfied. ΔV> ΔI × K

Here, ΔV is the amount of voltage change during the sweep (= reference voltage−sweep voltage), and ΔI is the amount of current change caused by the voltage change ΔV. K is a constant. This constant K is
It is set to a value corresponding to the impedance RAM value at the switching point M in FIG. Therefore, if the condition of ΔV> ΔI × K is satisfied, the process proceeds to step 302 because the region is the impedance calculation region, and
The value ZM (= ΔV / ΔI) is calculated and subjected to LSB conversion. Here, the LSB conversion refers to conversion so that the minimum value (for example, 1Ω) of the impedance RAM value ZM becomes the minimum value (1 count) of the RAM value. In the present embodiment (7), the LSB conversion of the impedance RAM value ZM is performed by the following equation, for example. ZM = Z × A Here, Z is an impedance value before LSB conversion, and A is a conversion constant, for example, A = 1. Thereby, the impedance RAM value ZM of the present embodiment (7) is obtained.
Is converted so that 1Ω becomes one count.

In the next step 303, the impedance R
The AM value ZM is compared with the semi-active boundary value ZM1, and ZM ≧ ZM
If it is 1, since it is an inactive area, the process proceeds to step 304, where the half-active flag XHACT is set to "0", and Z
If M <ZM1, the process is in the semi-active area, and the process proceeds to step 305, where the semi-active flag XHACT is switched to "1".

Thereafter, at step 306, it is determined whether or not the previous calculated value is the admittance RAM value YM based on whether or not the admittance switching flag XACN = 1. If XACN = 1, the process proceeds to step 307, where the impedance R calculated in step 302 is calculated.
A correction process (correction coefficient α = −4) for matching the AM value ZM with the previous admittance RAM value YM is performed, and in the next step 308, the admittance switching flag XACN
Is switched to “0” meaning the impedance calculation area, and the process proceeds to step 316 to execute a learning process described later. If XACN = 0 in step 306, the impedance RAM value ZM has been calculated the same as this time, so that the process of step 307 (correction) is not performed, and the state of XACN = 0 is maintained ( Step 30
8).

On the other hand, in step 301, ΔV ≦ ΔI
In the case of × K, since it is the admittance calculation area, the process proceeds to step 309, where the admittance RAM value YM (= Δ
I / ΔV) and perform LSB conversion. By this LSB conversion, the admittance RAM value YM and the impedance R
The conversion is performed so that the minimum value and the maximum value of the AM value ZM become almost the same RAM value. The LSB conversion of the admittance RAM value YM of the embodiment (7) is performed by the following equation. YM = Y × B Here, Y is an admittance value before LSB conversion, and B is a conversion constant, for example, B = 1600. Thereby, the admittance RAM value Y of the embodiment (7) is obtained.
In the LSB conversion of M, 1/10 [1 / Ω] is converted into 160 counts.

In the next step 310, the admittance RA
The M value YM is compared with the main active boundary value YM2, and YM <YM2
If so, the area is an inactive area, so the flow advances to step 311 to set the main active flag XFACT to “0”, and
If ≧ YM2, since this is the active region, step 3
Proceeding to 12, the activation flag XFACT is switched to "0".

Thereafter, in step 313, it is determined whether or not the previous calculated value is the impedance RAM value ZM based on whether or not the admittance switching flag XACN = 0. If XACN = 0, step 314
To admittance R calculated in step 309
A correction process (correction coefficient α = 1) for matching the AM value YM with the previous impedance RAM value ZM is performed, and in the next step 315, the admittance switching flag XACN
Is switched to "1" meaning the admittance calculation area, and the routine proceeds to step 316, where a learning process described later is executed. When XACN = 1 in step 313, the admittance RAM value YM is calculated in the same manner as this time, so that the processing in step 114 (correction) is not performed.
XACN = 1 is maintained (step 315).

As described above, step 308 or 3
At 15, the admittance switching flag XACN is switched or maintained in accordance with the type of the current calculated value.
Proceeding to S16, for example, the following learning process is executed. EV (k) = Target element resistance × α−Current element resistance × α

Here, the current element resistance value is determined in step 30.
The impedance RAM value ZM or the admittance RAM value YM calculated in 2 or 309. Therefore, when the current element resistance is calculated with the impedance RAM value ZM, the target element resistance is the target impedance value. When the current element resistance is calculated with the admittance RAM value YM, the target element resistance is calculated. The value is a target admittance value. Further, the current element resistance value xα is calculated in step 30.
7 or 314. The correction coefficient α is α = −4 for the impedance RAM value ZM and α = 1 for the admittance RAM value YM. As a result, learning results as shown in Table 1 below are obtained.

[0071]

[Table 1]

As described above, by switching the correction coefficient α according to the impedance calculation and the admittance calculation,
Learning value EV calculated from impedance RAM value ZM
(k) and learning value E calculated from admittance RAM value YM
V (k).

Using the learning value EV (k), the variation DD of the duty ratio (heater duty) of the heater 15 is calculated by the following equation.
O (k) and the current heater duty DO (k) are calculated. DDO (k) = K1 × EV (k) + K2 × ｛EV (k) −EV
(k-1)｝ (K1, K2 are smoothing coefficients) DO (k) = DO (k-1) + DDO (k) Here, the subscripts (k) are the current value and (k-1) is the previous value. Is shown.
The processing of step 316 described above plays a role as a learning means in the claims.

When performing the correction processing in steps 307 and 314, the learning processing in step 316 may be performed together. In this case, the processing in step 316 becomes unnecessary. In the learning processing of this routine, the learning value EV is calculated using a value obtained by correcting the element resistance value by the correction coefficient α.
(k), DDO (k) and DO (k) were calculated, but the correction coefficient α
EV (k) = Target element resistance−Current element resistance is calculated using the element resistance not corrected by
After correcting EV (k) by multiplying (k) by a correction coefficient α, D
DO (k) and DO (k) may be calculated. Alternatively, EV (k), DD using the element resistance value not corrected by the correction coefficient α.
After calculating all O (k) and DO (k), DDO (k) and D (k)
O (k) may be corrected.

In the embodiment (7) described above, the impedance RAM value ZM and the admittance RAM value YM are subjected to the LSB conversion so that the minimum value and the maximum value of the impedance RAM value ZM are substantially equal to the RAM value. Calculation of impedance RAM value ZM and admittance RA at switching point M where admittance RAM value YM is the same
Since the calculation of the M value YM is switched, the impedance R is used as the element resistance value used for detecting the element temperature.
It is possible to switch between the AM value ZM and the admittance RAM value YM so as to select the one having a larger rate of change with respect to the element temperature, and to switch between the impedance RAM value ZM and the admittance RAM value YM at the optimum switching timing.

Further, when the impedance RAM value ZM and the admittance RAM value YM are switched, the learning value is corrected by correcting the element resistance values (ZM, YM) with the correction coefficient α. Correction can be made so that the learning values do not become inconsistent, and the consistency of the learning values before and after switching can be maintained.

Incidentally, in the present embodiment (7), the admittance R is temporarily changed in the same manner as in the aforementioned embodiments (3) and (4).
After switching to the calculation of the AM value YM, the impedance R
Switching to the calculation of the AM value ZM may be prohibited, or the switching characteristic between the calculation of the impedance RAM value ZM and the calculation of the admittance RAM value YM as in the above-described embodiments (5) and (6). May be provided with hysteresis. In either case, the chattering phenomenon can be prevented and the heater control can be stabilized.

The switching timing between the calculation of the impedance Z and the calculation of the admittance Y is not limited to the above embodiments. For example, when the elapsed time after starting the engine (or the integrated value of the heater supply power) reaches a predetermined value. Alternatively, it may be determined that the element temperature has risen to the semi-active region or the main active region, and the calculation of impedance Z may be switched to the calculation of admittance Y. Alternatively, when the element temperature calculated from the impedance Z or the admittance Y becomes equal to or higher than a predetermined temperature, the admittance Y is calculated from the calculation of the impedance Z.
May be switched to the calculation.

In each of the above embodiments, either one of the impedance Z and the admittance Y is selected and calculated. However, the impedance Z and the admittance Y are calculated simultaneously, and for example, the impedance Z is calculated. The correction with the admittance Y may improve the detection accuracy of the impedance Z and thus the detection accuracy of the element temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an oxygen concentration detection system according to an embodiment (1).

FIG. 2 is a characteristic diagram showing a relationship between the impedance of the sensor element and the element temperature.

FIG. 3 is a characteristic diagram showing a relationship between admittance of a sensor element and element temperature.

FIG. 4 is a flowchart showing a processing flow of an element activation determination routine according to the embodiment (1).

FIG. 5 is a time chart illustrating control characteristics of the embodiments (1) and (2).

FIG. 6 is a flowchart showing a processing flow of an element activation determination routine according to the embodiment (2).

FIG. 7 is a flowchart showing the flow of processing of an element activation determination routine according to the embodiment (3).

FIG. 8 is a flowchart showing the flow of processing of an element activation determination routine according to the embodiment (4).

FIG. 9 is a flowchart showing the flow of processing of an element activation determination routine according to the embodiment (5).

FIG. 10 is a time chart for explaining control characteristics of the embodiments (5) and (6).

FIG. 11 is a flowchart showing the flow of processing of an element activation determination routine according to the embodiment (6).

FIG. 12 is a flowchart showing the flow of processing of an element activation determination routine according to the embodiment (7).

FIG. 13 is a time chart for explaining control characteristics of the embodiment (7).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Engine, 12 ... Exhaust pipe, 13 ... Oxygen concentration sensor, 14 ... Sensor element, 15 ... Heater, 16 ... Sensor control circuit, 17 ... Host microcomputer, 18 ... Sub-microcomputer (element resistance value calculation means, impedance calculation means, Admittance calculating means, switching prohibiting means, learning means), 27 ...
Element applied voltage control circuit, 28: current detection circuit, 30: heater control circuit.

Claims (10)

[Claims] An oxygen concentration sensor in which a current according to an oxygen concentration in a gas to be detected flows through an element to which a voltage is applied, and an element resistance value is detected from a voltage applied to the element when the oxygen concentration is detected. And a device resistance value calculating means for calculating the device resistance value from the voltage change at that time and the current change caused by the voltage change, and the device resistance value calculated by the device resistance value calculating means is provided. In the device temperature detecting device of the oxygen concentration sensor which is used as a parameter for judging the device temperature, the device resistance value calculating means comprises: an impedance calculating device for calculating the device resistance value as an impedance value; Admittance calculation means for calculating as a value, the impedance value calculated by the impedance calculation means and Serial admittance element temperature detector of the oxygen concentration sensor, characterized in that the at least one used as the parameter for determining the element temperature between the calculated admittance value by calculating means. 2. The element according to claim 1, wherein said element resistance value calculating means switches between said impedance calculating means and said admittance calculating means depending on a state of said oxygen concentration sensor. Temperature detector. 3. The oxygen concentration sensor according to claim 1, wherein said element resistance value calculation means switches between said impedance calculation means and said admittance calculation means according to the impedance value or admittance value of said element. Device temperature detector. 4. The device according to claim 1, wherein the element resistance value calculation means switches between the impedance calculation means and the admittance calculation means depending on whether the state of the element is an active state. Element temperature detection device for oxygen concentration sensor. 5. The device according to claim 1, wherein the element resistance value calculation means switches between the impedance calculation means and the admittance calculation means depending on whether the state of the element is a semi-active state. An element temperature detecting device for the oxygen concentration sensor according to claim 1. 6. The element resistance value calculating means switches to the impedance calculating means to calculate the element resistance value as an impedance value when the element temperature is equal to or lower than a predetermined temperature, and when the element temperature is higher than the predetermined temperature, The device temperature detection device for an oxygen concentration sensor according to claim 1, wherein the device resistance value is calculated as an admittance value by switching to the admittance calculation means. 7. The element resistance value calculating means converts the impedance value and the admittance value so that the minimum value and the maximum value of the two values are substantially equal to each other, and calculates the impedance value and the admittance value. 2. The method according to claim 1, wherein the impedance calculating means and the admittance calculating means are switched between the same areas.
An element temperature detecting device for an oxygen concentration sensor according to claim 1. 8. The apparatus according to claim 1, wherein said element resistance value calculating means has a switching prohibiting means for prohibiting a switching to said impedance calculating means after switching from said impedance calculating means to said admittance calculating means. 8. An element temperature detecting device for an oxygen concentration sensor according to any one of 2 to 7. 9. The oxygen concentration sensor according to claim 2, wherein said element resistance value calculation means has a hysteresis in a characteristic for switching between said impedance calculation means and said admittance calculation means. Device temperature detector. 10. A learning unit for learning a control value based on the element resistance value calculated by the element resistance value calculation unit, the learning unit learning when switching between the impedance calculation unit and the admittance calculation unit. 10. The element temperature detecting device for an oxygen concentration sensor according to claim 2, wherein the value is corrected.