JP3500976B2 - Abnormality diagnosis device for gas concentration sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration sensor for detecting a concentration of a specific component or an air-fuel ratio using a solid electrolyte, and relates to an abnormality diagnostic device for the gas concentration sensor.

[0002]

2. Description of the Related Art For example, in an air-fuel ratio detecting device for detecting an air-fuel ratio of a vehicle engine, an air-fuel ratio sensor of a limiting current type is installed in an engine exhaust pipe, and an air-fuel ratio (oxygen concentration in exhaust gas) is set according to the air-fuel ratio. A continuously changing current output is taken from the air-fuel ratio sensor. An electronic control unit (ECU) that controls the fuel injection into the internal combustion engine feedback-controls the air-fuel ratio based on the current output (actual air-fuel ratio) of the sensor input from the air-fuel ratio detection device.

Further, in the feedback control of the air-fuel ratio, if the air-fuel ratio sensor fails or deteriorates and the characteristics of the sensor output change, the control is hindered. That is, the accuracy of the air-fuel ratio control is reduced, and the exhaust emission may be deteriorated accordingly. Therefore, various techniques have been conventionally proposed for performing abnormality diagnosis based on sensor output (for example, Japanese Patent Laid-Open Nos. 8-177575 and 8-270482).

[0004]

By the way, in the case of the limiting current type air-fuel ratio sensor, performances such as output responsiveness and air-fuel ratio detection range change according to the temperature (element temperature) of the sensor element. Therefore, under the condition that the element temperature is different,
The abnormality diagnosis of the sensor cannot be performed accurately, and there is a possibility that the sensor is erroneously diagnosed as normal but abnormal, or erroneously diagnosed as normal although abnormal.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an abnormality diagnostic device for a gas concentration sensor capable of performing an accurate and highly reliable abnormality diagnosis. Is to provide.

[0006]

In the case of a gas concentration sensor having a sensor element made of a solid electrolyte, the element resistance tends to increase as the sensor element temperature decreases, and the element resistance tends to increase during cold starting of an internal combustion engine, for example. It is very large and gradually decreases as it warms up. Therefore, as shown in FIG. 14, as the element resistance increases, the response time increases (that is, the response decreases), and the reliability of the diagnosis result decreases even if the sensor abnormality diagnosis is performed in that state. Also,
In the case of the air-fuel ratio sensor, as shown in FIG. 15, the air-fuel ratio detection range is narrowed as the element resistance increases.

Therefore, in the invention described in claim 1, in the case where the detecting means for detecting the element temperature or the element resistance of the gas concentration sensor and the element temperature or the element resistance of the gas concentration sensor are within a predetermined active range, the sensor And permitting means for permitting execution of the abnormality diagnosis. In this case, the abnormality diagnosis is always performed under the active state of the gas concentration sensor. Further, even if the active state is temporarily changed to the inactive state, it is possible to prevent false detection of a sensor abnormality by temporarily disabling the abnormality diagnosis. As a result, an accurate and highly reliable abnormality diagnosis can be performed. Also, gas concentration
Sensor element temperature or
Sets the abnormality determination value variably according to the element resistance. this
If the gas concentration sensor is in the process of being activated,
The abnormality diagnosis can be started quickly. Also, the activity status
Even when the state temporarily shifts to the semi-active state,
The abnormality diagnosis can be continued without interruption. One
Therefore, the abnormality judgment value must be adapted to the degree of activity of the sensor.
Thus, it becomes possible to perform abnormality diagnosis in a wide range.

[0008] Particularly as described in claim 3, when determining the detected and the presence or absence of abnormality from the sensor responsive to the response of the output of the gas concentration sensor, the effect becomes remarkable. That is, as described above, by performing the abnormality diagnosis only under the condition that the element temperature or the element resistance is constant, it is possible to avoid the inconvenience that the result of the diagnosis is different due to the difference in the active state, and it is possible to correct the error based on the sensor responsiveness. You can perform various abnormality diagnosis.

By the way, the abnormality diagnosis referred to in this specification is: -The responsiveness of the output decreases as the sensor deteriorates.・ Responsiveness is excessively improved due to element cracking.・ Sensor output will not be output due to disconnection of the internal wiring of the sensor. It is for diagnosing various abnormalities such as.

[0010]

According to a second aspect of the present invention, there is provided a gas concentration detecting device in which a heater is attached to the gas concentration sensor, and the energization control of the heater is performed to maintain the state under the activated state of the sensor. The permitting unit permits execution of the abnormality diagnosis on condition that heater energization control is being performed in a sensor active state. In this case as well, an accurate and highly reliable abnormality diagnosis can be performed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. The air-fuel ratio control system in the present embodiment is applied to a vehicle engine, and in the control system, the fuel injection amount to the engine is set to a desired air-fuel ratio based on the detection result of the air-fuel ratio sensor provided in the engine exhaust pipe. Control. In the following description, an air-fuel ratio (A / F) detection procedure using the air-fuel ratio sensor and an abnormality diagnosis procedure for the sensor will be described in detail.

FIG. 1 is a configuration diagram showing an outline of an air-fuel ratio control system in the present embodiment. In FIG. 1, the engine 10 is configured as a multi-cylinder 4-cycle internal combustion engine. The intake pipe 11 is provided with an injector 12 for injecting and supplying fuel to each cylinder of the engine 10. Further, the exhaust pipe 13 is provided with an A / F sensor 30 composed of a limiting current type air-fuel ratio sensor, and the sensor 30 is provided with the oxygen concentration in the exhaust gas (or the concentration of carbon monoxide or the like in the unburned gas). ), A wide-area and linear air-fuel ratio signal is output.

The A / F sensor 30 includes a solid electrolyte 31 and a diffusion resistance layer 32, which form a sensor element, and a solid electrolyte 3.
Electrodes 33 provided inside and outside 1 (atmosphere side and exhaust side),
34 and a heater 35 for heating the sensor element. Here, the solid electrolyte 31 is made of an oxygen ion conductive oxide sintered body, and the diffusion resistance layer 32 is made of a heat resistant inorganic substance. The electrodes 33 and 34 are both made of a noble metal having a high catalytic activity such as platinum, and the surfaces thereof are subjected to porous chemical plating or the like.

The voltage-current characteristic (V-
I characteristic) is shown in FIG. According to FIG. 2, the A / F sensor 3
It can be seen that the inflow current to the solid electrolyte 31 proportional to the detection A / F of 0 and the voltage applied to the solid electrolyte 31 have linear characteristics. In such a case, the straight line portion parallel to the voltage axis V is the limiting current detection region that specifies the limiting current,
The increase / decrease in the limit current (sensor output) corresponds to the increase / decrease in the air-fuel ratio (that is, the degree of lean rich). That is, the limit current increases as the air-fuel ratio becomes leaner, and the limit current decreases as the air-fuel ratio becomes richer.

In this VI characteristic, a voltage region smaller than the straight line portion (limit current detection region) parallel to the voltage axis V is the resistance governing region, and the slope of the primary straight line portion in the resistance governing region is solid. It is specified by the internal resistance of the electrolyte 31 (hereinafter referred to as element resistance Ri). The element resistance Ri changes with a change in temperature, and when the element temperature decreases, the inclination decreases as the element resistance Ri increases.

On the other hand, in FIG. 1, the ECU 15 includes an engine control microcomputer 16 for optimally controlling the fuel injection amount of the injector 12. The engine control microcomputer 16 fetches various engine operation information from a sensor group (not shown), and detects engine operation states such as engine speed, intake pressure, water temperature, throttle opening, etc. from the detection results of these sensors.

The air-fuel ratio detecting microcomputer 20 is connected to the engine controlling microcomputer 16 so that they can communicate with each other. The air-fuel ratio detection microcomputer 20 operates the heater drive circuit 25 and the bias control circuit 40 according to a predetermined control program, and measures the value of the current flowing through the A / F sensor 30 as the voltage is applied. Then, the air-fuel ratio is detected from the measured current value, and the detection result is output to the engine control microcomputer 16. Further, the microcomputer 20 uses the heater drive circuit 2 so that the A / F sensor 30 is maintained in an active state.
5 is operated, and the heater 35 is energized as needed.

Here, the bias command signal Vr for applying a voltage to the A / F sensor 30 is input from the air-fuel ratio detecting microcomputer 20 to the D / A converter 21 and is analogized by the D / A converter 21. After being converted into the signal Vb, it is input to the LPF (low pass filter) 22. In addition, LPF22
The output voltage Vc from which the high frequency component of the analog signal Vb has been removed is input to the bias control circuit 40. The bias control circuit 40 applies a voltage for air-fuel ratio detection or element resistance detection to the A / F sensor 30. In this case, at the time of detecting the air-fuel ratio, the applied voltage Vp corresponding to the air-fuel ratio at that time is set by using the characteristic line L1 of FIG. A voltage having a predetermined time constant is applied.

The output of the A / F sensor 30 corresponding to the air-fuel ratio (oxygen concentration) at each time is detected by the current detection circuit 50 in the bias control circuit 40, and the detected value is detected by the A / D converter 23. It is input to the air-fuel ratio detecting microcomputer 20 via the. The heater control circuit 25 duty-controls the energization amount to the heater 35 according to the element temperature of the A / F sensor 30 and the heater temperature, and controls the heating of the heater 35.

The air-fuel ratio F / B control by the engine control microcomputer 16 is not the gist of the present invention and its control contents are well known, so a detailed description thereof will be omitted here, but a brief description will be given. The engine control microcomputer 16 takes in the detection result (voltage signal) of the air-fuel ratio by the A / F sensor 30 and other detection results of various sensors, and based on these detection results, implements a control algorithm such as modern control or PI control. Accordingly, the air-fuel ratio F / B control is carried out. That is, the amount of fuel injected and supplied from the injector 12 to each cylinder of the engine 10 is controlled so that the air-fuel ratio at each time matches the target air-fuel ratio.

Next, the operation of the air-fuel ratio control system configured as described above will be described. First, the main routine executed by the air-fuel ratio detecting microcomputer 20 will be described with reference to the flowchart of FIG.

In FIG. 3, first in step 100,
It is determined whether or not a predetermined time Ta has elapsed since the previous detection of the air-fuel ratio. The predetermined time Ta is a time corresponding to the detection cycle of the air-fuel ratio, and is set to Ta = 4 ms, for example. If the predetermined time Ta has passed since the previous detection of the air-fuel ratio (YES in step 100), the routine proceeds to step 110, where the air-fuel ratio detection processing is executed. Step 100 is NO
If so, this routine is temporarily terminated.

At the time of detecting the air-fuel ratio in step 110, the air-fuel ratio detecting microcomputer 20 reads the value of the current flowing through the solid electrolyte 31 due to the voltage application, that is, the sensor output Ip detected by the current detecting circuit 50, and outputs the sensor output. Ip is output to the engine control microcomputer 16.
Further, for the next air-fuel ratio detection, a voltage corresponding to the air-fuel ratio (sensor output Ip) at each time is applied to both electrodes 33, 34 of the A / F sensor 30.

After that, in step 120, it is judged whether or not a predetermined time Tb has elapsed since the previous element resistance detection. The predetermined time Tb is a time corresponding to the detection cycle of the element resistance Ri, and is selectively set according to the engine operating state, for example. In the present embodiment, when the air-fuel ratio change is relatively small (normal operation of the engine 10), T
b = 2 s (seconds), Tb = 128 ms (milliseconds) when the air-fuel ratio suddenly changes (when the engine 10 is started or during transient operation)
The predetermined time Tb is set to be variable.

If step 120 is YES, the element resistance Ri is detected in step 130, and energization control of the heater 35 is executed in step 140. The processes of steps 130 and 140 are respectively described in FIG.
It is performed according to FIG. If step 120 is NO, this routine is once terminated.

Next, the procedure for detecting the element resistance Ri in step 130 of FIG. 3 will be described with reference to FIG. In the present embodiment, when detecting the element resistance Ri, the “AC element impedance” is obtained by using the sweep method.

In FIG. 4, in step 131, the bias command signal Vr is manipulated to change the applied voltage Vp (voltage for air-fuel ratio detection) up to that point to change the voltage to the positive side. The application time of the element resistance detection voltage is set to about several tens to 100 μs in consideration of the frequency characteristic of the A / F sensor 30. After that, in step 132, the voltage change amount ΔV and the sensor output change amount ΔI detected by the current detection circuit 50 at that time are read. Also, the following step 13
In 3, the element resistance Ri is calculated from ΔV and ΔI (R
i = ΔV / ΔI), and then this routine is terminated and the original routine of FIG. 3 is returned to.

According to the above processing, the LPF 2 shown in FIG.
2 and the bias control circuit 40, a voltage having a predetermined time constant is applied to the A / F sensor 30 in a one-shot manner. As a result, as shown in FIG. 6, the peak current ΔI (current change amount) is detected after t time has elapsed from the application of the voltage, and the element resistance Ri is detected from the voltage change amount ΔV and the peak current ΔI at that time. (Ri = ΔV / ΔI). In such a case, by applying a sporadic voltage to the A / F sensor 30 via the LPF 22, generation of an excessive peak current is suppressed, and the detection accuracy of the element resistance Ri is improved.

The element resistance Ri obtained as described above has the relationship shown in FIG. 7 with respect to the element temperature. That is, the lower the element temperature, the greater the element resistance Ri. Incidentally, the activation temperature (about 700 ° C.) of the A / F sensor 30 corresponds to the element resistance Ri≈90Ω.

Next, the control procedure of the heater energization in step 140 of FIG. 3 will be described with reference to FIG. In step 141 in FIG. 5, it is determined whether or not the element resistance Ri is equal to or less than a predetermined determination value (about 200Ω in this embodiment) for determining the semi-active state of the solid electrolyte 31 (sensor element). To do. For example, when the element temperature is low, such as when the engine 10 is started at a low temperature, Ri> 200Ω, and the routine proceeds to step 142, where "100% energization control" of the heater 35 is performed, and thereafter, this routine is ended and the original FIG. Return to the routine. The 100% energization control is control for maintaining the duty ratio control signal to the heater 35 at 100%, and the element resistance Ri becomes 200Ω or less.
Will continue to be implemented until a positive determination is made.

Then, when the element temperature rises due to the heating action of the heater 35 and an affirmative decision is made in step 141, the routine proceeds to step 143, where the element resistance Ri is a predetermined decision value for starting the element resistance F / B control. (In this embodiment, 4
It is determined whether it is less than or equal to 0Ω). Step 14
The determination value of 3 is set as a value of about “+ 10Ω” with respect to the target element resistance RiTG (30Ω in the present embodiment).

If the determination is negative in step 143 before the sensor is activated, the process proceeds to step 144 to control the energization of the heater 35 by "power control", and then this routine is ended to return to the original state of FIG. Return to routine. At this time, the larger the element resistance Ri, the larger the power command value is determined, and the control duty ratio for energizing the heater is calculated according to the power command value.

When the sensor activation is completed, step 14
When the determination of 3 is affirmative, the routine proceeds to step 145, where "element resistance F / B control" is executed. In this element resistance F / B control, the duty ratio Duty for energizing the heater is calculated in the following procedure. In the present embodiment, the PID control procedure is used as an example.

That is, the proportional term GP, the integral term GI, and the differential term GD are calculated by the following equations (1) to (3). GP = KP. (Ri-RiTG) (1) GI = GIi-1 + KI. (Ri-RiTG) (2) GD = KD. (Ri-Rii-1) (3) However, in the above formula, “KP” is a proportional constant, “KI” is an integral constant, “KD” is a differential constant, and the subscript “i-1” is used.
Indicates the value at the time of the previous processing.

Then, the duty ratio DUTY is calculated by adding the proportional term GP, the integral term GI, and the differential term GD (D
UTY = GP + GI + GD), and the heater 35 is energized by the calculated duty ratio DUTY. The heater control procedure is not limited to the PID control described above, and PI control or P control may be performed.

Then, in step 146, the element resistance F
The / B flag XFB is set to "1", after which this routine is terminated and the original routine of FIG. 3 is returned to. Although omitted in FIG. 5, if the element resistance Ri increases and the F / B control is interrupted during the element resistance F / B control (for example, the element temperature decreases and the power control in step 144 is performed). If so, the element resistance F / B flag XFB at that time
Is cleared to "0".

Next, the arithmetic processing executed by the engine control microcomputer 16 will be described. That is, the engine control microcomputer 16 appropriately performs the fuel cut according to the fuel cut determination routine shown in FIG.
A / F sensor 3 according to the sensor abnormality diagnosis routine shown in
The abnormality diagnosis of 0 is executed. 8 and 9 is executed each time a main routine (not shown) is executed (for example, every 8 ms). The processing of FIGS. 8 and 9 will be described in detail below.

In FIG. 8, in step 201, it is judged whether or not the throttle fully closed state has continued for a predetermined time T0. When the step 201 is affirmative, in step 202 the engine speed NE starts fuel cut. Number of revolutions N
It is determined whether it is higher than FC. The fuel cut start rotational speed NFC is preferably set so as not to enter the fuel cut in the idle state, and is set to a higher value as the cooling water temperature is lower, for example.

When either of the steps 201 and 202 is negatively determined, the routine proceeds to step 203, where it is determined whether or not the fuel cut is executed in the previous processing. When the fuel cut is not started and all the determinations in steps 201 to 203 are negative, the routine proceeds to step 205, where normal fuel injection is performed, and then this routine is once ended. That is, the fuel cut execution flag XFC for indicating the execution of the fuel cut.
Is held as "0".

On the other hand, when both steps 201 and 202 are positively determined, the routine proceeds to step 206, where the fuel cut execution flag XFC is set to "1" and the fuel cut is executed. By setting step 201 as the fuel cut execution condition, shock during deceleration due to fuel cut is reduced.

After that, when the fuel cut is executed, the engine speed NE gradually decreases, and when step 202 becomes NO and step 203 becomes YES, the routine proceeds to step 204, where the engine speed NE is higher than the fuel cut return speed NRT. It is determined whether or not it has decreased (however, NRT <NFC). Then, when the engine speed NE becomes lower than the fuel cut return speed NRT, the routine proceeds to step 205, where the fuel cut execution flag XFC is cleared to "0".
As a result, the fuel cut is restored and normal fuel injection is resumed.

Although not shown, even if the throttle is operated to the open side during the fuel cut, the fuel is immediately returned from the fuel cut and the normal fuel injection is restarted.

Next, the sensor abnormality diagnosis routine of FIG. 9 will be described with reference to the time chart of FIG. In the time chart of FIG. 10, the fuel cut is executed before the time t1, and at the time t1, normal fuel injection is restarted by the return of the fuel cut accompanying the decrease of the engine speed NE. In FIG. 10, the chain double-dashed line shows the movement when normal, and the solid line shows the movement when abnormality occurs.

In FIG. 9, first in step 301,
It is determined whether or not the element resistance Ri is within a predetermined range representing the sensor active state. The determination in the same step is performed using the detection value of the element resistance Ri by the air-fuel ratio detection microcomputer 20. Then, on the condition that the affirmative determination is made in step 301, the process proceeds to step 302. That is, step 3
When 01 is affirmatively determined, execution of the abnormality diagnosis after step 302 is permitted, whereas when negative determination is made at step 301, execution of the abnormality diagnosis is prohibited.

After that, in step 302, it is judged whether or not the fuel cut is returned (fuel injection is restarted), and if it is not the fuel cut return, this routine is finished as it is. Whether or not the fuel cut is returned is determined according to the state of the fuel cut execution flag XFC. In FIG. 10, step 302 is negatively determined before the time t1 (however, in FIG. 10, the step 301 is performed for the entire period. A positive determination shall be made).

After that, if the affirmative decision is made at step 302 at the time when the fuel cut is restored (time t1 in FIG. 10), the routine proceeds to step 303, where the detection value (sensor of the A / F sensor 30 at the time of fuel cut restoration (sensor The output Ip) is read, the value is stored as “I1”, and the timer is operated to count the elapsed time after the fuel cut is returned. In the following step 304, it is determined whether or not the sensor output Ip has decreased to the predetermined value I2 with the restart of fuel injection, and the process waits until the sensor output Ip decreases to the predetermined value I2.

After that, when the sensor output Ip decreases to the predetermined value I2, the routine proceeds to step 305, where the elapsed time T1 from the fuel cut recovery to the decrease of the sensor output Ip to the predetermined value I2 is read from the count value of the above-mentioned timer. Remember. In this case, if the A / F sensor 30 is normal,
When the sensor output Ip reaches the predetermined value I2 at time t2 in FIG. 10, but the A / F sensor 30 is abnormal,
At time t3 of 0, the sensor output Ip reaches the predetermined value I2.

Subsequently, at step 306, the change rate ΔIp of the sensor output is calculated by the following equation. ΔIp = (I2−I1) / T1 Further, in step 307, the calculated change rate ΔIp (absolute value) of the sensor output is compared with a predetermined abnormality determination value Ifr. If | ΔIp | ≧ Ifr, it is considered that the A / F sensor 30 has not deteriorated and the sensor output Ip is normal, and this routine is ended.

However, as the A / F sensor 30 deteriorates, the responsiveness of the sensor output deteriorates.
When ΔIp | <Ifr, it is determined that the A / F sensor 30 is abnormal. In this case, the process proceeds to step 308 and the sensor abnormality is stored in the memory, and the warning lamp is turned on to warn the driver of the occurrence of the abnormality. In the present embodiment, step 130 of FIG. 3 corresponds to the detecting means described in the claims, and step 301 of FIG. 9 corresponds to the permitting means.

According to this embodiment described in detail above, the following effects can be obtained. In the present embodiment, the execution of the abnormality diagnosis of the A / F sensor 30 is allowed only when the element resistance Ri of the A / F sensor 30 is within a predetermined active range. In this case, the abnormality diagnosis is always performed under the active state of the A / F sensor 30. Further, even if the active state is temporarily changed to the inactive state, it is possible to prevent false detection of a sensor abnormality by temporarily disabling the abnormality diagnosis. As a result, an accurate and highly reliable abnormality diagnosis can be performed.

In particular, when the responsiveness of the output of the A / F sensor 30 is detected and whether or not there is an abnormality is determined from the responsiveness of the sensor, the effect becomes remarkable. That is, as described above, by performing the abnormality diagnosis only under the condition that the element resistance Ri is constant, it is possible to avoid the inconvenience that the diagnosis result is different due to the difference in the active state, and the accurate abnormality based on the sensor responsiveness is avoided. Diagnosis can be performed.

Since highly reliable abnormality diagnosis can be performed as described above, accurate air-fuel ratio F / B control can be performed. In this case, the inconvenience that the F / B correction amount becomes excessive or deficient due to the deterioration or excessive improvement of the sensor response is also eliminated.

According to the abnormality diagnosis shown in FIG. 9, even if the sensor output Ip at the beginning of the diagnosis is changed depending on the state of the air-fuel ratio before the diagnosis is started (before the fuel cut), the sensor output after the diagnosis is started. The change rate ΔIp of is almost unaffected by the air-fuel ratio before the start of diagnosis. Therefore, the abnormality diagnosis can be performed without being affected by the state of the air-fuel ratio before the start of the diagnosis, and the erroneous diagnosis of the abnormality is eliminated.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. 11 and 12. However, in the configuration of the second embodiment, the same components as those in the above-described first embodiment will be denoted by the same reference symbols in the drawings and the description thereof will be simplified. And
The differences from the first embodiment will be mainly described below.

In the present embodiment, the sensor abnormality diagnosis routine is changed as shown in FIG. 11, and the processing of FIG. 11 is replaced with the processing of FIG. FIG. 12 is a time chart showing the process of FIG. 11 more specifically.

In FIG. 11, in step 401, it is judged whether or not the element resistance Ri is within a predetermined range indicating the sensor active state. Then, when the affirmative determination is made in step 401, it is determined that the subsequent abnormality diagnosis is permitted, and the process proceeds to step 402. In step 402, it is determined whether or not the fuel cut has started, and if the fuel cut has not started, this routine ends as it is. In FIG. 12, a negative determination is made in step 402 before time t11.

Thereafter, if the affirmative determination is made at step 402 at the time when the fuel cut is started (time t11 in FIG. 12), the routine proceeds to step 403, where the detection value of the A / F sensor 30 at the start of the fuel cut (sensor output Ip) is read, the value is stored as "I3", and the timer is activated to count the elapsed time after the start of fuel cut. In the following step 404, it is determined from the count value of the timer described above whether or not a predetermined time T2 has elapsed after the start of fuel cut, and the process waits until the predetermined time T2 has elapsed.

After that, in step 405, the sensor output Ip when a predetermined time T2 has elapsed after the start of fuel cut is read and the value is stored as "I4" (time t12 in FIG. 12). In this case, although the sensor output Ip responds to the lean side with the start of the fuel cut, the A / F sensor 30
Is abnormal, the sensor responsiveness is low, and therefore the amount of change in the sensor output Ip is small.

Subsequently, in step 406, the change rate ΔIp of the sensor output is calculated by the following equation. ΔIp = (I4−I3) / T2 Furthermore, in step 407, the calculated change rate ΔIp (absolute value) of the sensor output is compared with a predetermined abnormality determination value Ifc. If | ΔIp | ≧ Ifc, it is considered that the A / F sensor 30 is not deteriorated and the sensor output Ip is normal, and this routine is ended.

However, as the A / F sensor 30 deteriorates, the responsiveness of the sensor output deteriorates.
If ΔIp | <Ifc, it is determined that the A / F sensor 30 is abnormal. In this case, the process proceeds to step 408, and the sensor abnormality is stored in the memory, and the warning lamp is turned on to warn the driver of the abnormality.

As described above, according to the second embodiment, the first
Similar to the embodiment described above, the abnormality diagnosis can be performed without being affected by the state of the air-fuel ratio before the diagnosis is started, and the erroneous diagnosis of the abnormality is eliminated. Further, in this case, since the abnormality diagnosis of the A / F sensor 30 is permitted to be performed only when the element resistance Ri of the element resistance Ri is within a predetermined active range, accurate and highly reliable abnormality diagnosis can be performed.

The embodiment of the present invention can be embodied in the following forms other than the above. When the abnormality diagnosis of the A / F sensor 30 is performed, the abnormality determination value is variably set according to the element resistance Ri of the sensor 30. That is, for example, the abnormality determination value Ifr in step 307 of FIG. 9 is set according to the element resistance Ri using the relationship of FIG. In the case of the A / F sensor 30, as can be seen from FIG. 14, the element resistance R
Since the responsiveness decreases as i increases, in FIG. 13, the abnormality determination value Ifr is set to a smaller value as the element resistance Ri increases. Alternatively, step 407 of FIG.
In the same manner, the abnormality determination value I depending on the element resistance Ri
fc is set to be variable. In this case, the larger the element resistance Ri, the smaller the abnormality determination value Ifc may be set.

According to the above configuration, even if the A / F sensor 30 is in the process of being activated, the abnormality diagnosis can be started quickly. Further, even when the active state is temporarily changed to the semi-active state, the abnormality diagnosis can be continuously performed without interruption. That is, the abnormality determination value is A / F
By adapting to the degree of activity of the sensor 30, it becomes possible to perform abnormality diagnosis in a wide range.

In FIG. 9 and FIG. 11, it is determined whether or not the element resistance Ri is within a predetermined range indicating the active state (steps 301 and 401), but this is changed. For example, it is determined whether or not "1" is set in the element resistance F / B flag XFB, and on the condition that XFB = 1, that is, the element resistance F / B control is executed by the air-fuel ratio detection microcomputer 20. However, the subsequent abnormality diagnosis processing is permitted. That is, between the air-fuel ratio detecting microcomputer 20 and the engine controlling microcomputer 16 shown in FIG. 1, in the case where only the flag information is transmitted from the former microcomputer 20 to the latter microcomputer 16,
The abnormality diagnosis is permitted or prohibited according to the state of the element resistance F / B flag XFB. As a result, accurate and highly reliable abnormality diagnosis can be performed as in the above-described embodiments.

In the first embodiment, a sensor abnormality is diagnosed based on the sensor output change rate ΔIp when the fuel cut is restored, and in the second embodiment, the sensor output change rate ΔIp when the fuel cut is started. Although the sensor abnormality was diagnosed from the above, it is changed as follows. (A) At the start of fuel cut, the rate of change when the sensor output Ip rises to a predetermined lean value is obtained, and the sensor abnormality is determined based on the rate of change. (B) At the start of fuel cut, the response delay time until the amount of change in the sensor output Ip reaches a predetermined lean value is measured, and if the response delay time becomes long, it is determined that the sensor is abnormal. (C) At the start of fuel cut, the measurement of the change rate of the sensor output Ip is started after the elapse of a predetermined response delay time, and the sensor abnormality is judged based on the change rate at that time.

In addition, the sensor abnormality is diagnosed by the following procedure (d). (D) In the air-fuel ratio F / B control, when the target air-fuel ratio AFTG suddenly changes due to a change in the engine operating state, the amount of change Δ
Amount of change ΔF between AFTG and feedback correction coefficient FAF
The abnormality of the A / F sensor 30 is diagnosed based on the comparison result with AF. That is, it is determined whether or not the ratio between the absolute value of “ΔFAF” and the absolute value of “ΔAFTG” is within a predetermined range. Specifically, it is determined whether or not α <(ΔFAF / ΔAFTG) <β is satisfied (however, for example, α = 0.
9, β = 1.1). In this case, the target air-fuel ratio AFTG
If the feedback correction coefficient FAF is changing in response to the change of, that is, if the A / F sensor 30 outputs a normal signal with the change of the target air-fuel ratio AFTG, the output result is reflected. Feedback correction factor FA
F changes. Therefore, the above inequality is satisfied and the A / F sensor 30 is considered to be normal. On the other hand, the feedback correction coefficient FAF for changes in the target air-fuel ratio AFTG
If is too large or too small, the above inequality is not established and the A / F sensor 30 is considered to be abnormal.

When any one of the above-mentioned methods (a) to (d) is used to carry out the abnormality diagnosis, since the abnormality diagnosis is permitted only under the condition that the element resistance is constant, it is accurate and accurate. A highly reliable abnormality diagnosis can be realized.

As a method for calculating the element resistance, a method other than that shown in FIG. 4 is used. For example, the voltage applied to the A / F sensor 30 is changed to both the positive and negative sides while adjusting to the frequency characteristic of the A / F sensor 30, and the element resistance is detected based on the voltage change amount and the current change amount on both the positive and negative sides. Alternatively, it is also possible to apply a negative applied voltage Vneg (voltage in the resistance control region) to the A / F sensor 30 and detect the element resistance from the sensor current Ineg at that time (element resistance = Vneg / Ine).
g).

In each of the above embodiments, the A / F sensor 30
The element resistance Ri of is determined and whether or not the sensor abnormality diagnosis is performed is determined based on the Ri value, but this is changed. For example, the element resistance Ri is converted into the element temperature by using the relationship of FIG. 7, and it is determined whether or not the sensor abnormality diagnosis is performed at the element temperature. When using the relationship shown in FIG. 13, the abnormality determination value may be variably set according to the element temperature. In this case, the smaller the element temperature, the smaller the abnormality determination value is set.

In each of the above embodiments, the air-fuel ratio control system is constructed by using the two microcomputers 16 and 20 for controlling the engine and for detecting the air-fuel ratio, but the microcomputer may be one. In this case, the same microcomputer is provided with the function of detecting the element temperature or the element resistance of the A / F sensor and the function of permitting the execution of the abnormality diagnosis when the element temperature or the element resistance is within a predetermined activation range. It

The present invention can be applied to other than the air-fuel ratio detecting device using the A / F sensor. That is, NOx, HC, C
A gas concentration sensor that can detect a gas concentration component such as O is used, and the present invention can be applied to a device that detects the gas concentration from the detection result of the sensor. By using the same method as that of the above-described embodiment when applied to the other gas concentration sensor, it is possible to perform accurate and highly reliable abnormality diagnosis.

The technical idea grasped from each of the above-mentioned embodiments and not described in the scope of the claims will be described below together with the effect thereof. (1) The gas concentration sensor abnormality diagnosis device according to claim 1, wherein the gas concentration sensor is applied to an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine according to a detection result of the gas concentration sensor. When performing abnormality diagnosis of the sensor using the detection result of the concentration sensor, the change in the fuel supply amount to the internal combustion engine is detected, and the change rate of the sensor output is obtained after the change in the fuel supply amount. The presence or absence of abnormality is determined based on the rate of change in output.

In this case, even if there is a situation in which the sensor output at the beginning of the diagnosis changes depending on the state of the air-fuel ratio before the start of the diagnosis (before detecting the change in the fuel supply amount), the rate of change in the sensor output after the start of the diagnosis is It is hardly affected by the air-fuel ratio before the start of diagnosis. Therefore, the abnormality diagnosis can be performed without being affected by the state of the air-fuel ratio before the start of the diagnosis, and the erroneous diagnosis of the abnormality is eliminated.

(2) The abnormality diagnosis device for a gas concentration sensor according to claim 1, which is applied to an air-fuel ratio control device for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine according to a detection result of the gas concentration sensor. When performing an abnormality diagnosis of the sensor using the detection result of the gas concentration sensor, while calculating the feedback correction amount according to the deviation between the actual air-fuel ratio corresponding to the sensor output and the target air-fuel ratio,
Whether or not there is an abnormality is determined based on the behavior of the calculated feedback correction amount with respect to the sensor output. In this case, accurate abnormality diagnosis can be performed from the change in the feedback correction amount that follows the change in the air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of an air-fuel ratio control system in an embodiment.

FIG. 2 is a diagram showing a VI characteristic of an A / F sensor.

FIG. 3 is a flowchart showing a main routine executed by an air-fuel ratio detection microcomputer.

FIG. 4 is a flowchart showing a subroutine of element resistance detection.

FIG. 5 is a flowchart showing a subroutine for heater energization control.

FIG. 6 is a waveform diagram showing changes in sensor voltage and sensor current during element resistance detection.

FIG. 7 is a diagram showing the relationship between element temperature and element resistance.

FIG. 8 is a flowchart showing a fuel cut determination routine executed by an engine control microcomputer.

FIG. 9 is a flowchart showing a sensor abnormality diagnosis routine executed by an engine control microcomputer.

FIG. 10 is a time chart showing a process of abnormality diagnosis.

FIG. 11 is a flowchart showing a sensor abnormality diagnosis routine in the second embodiment.

FIG. 12 is a time chart showing a process of abnormality diagnosis.

FIG. 13 is a diagram for setting an abnormality determination value according to element resistance.

FIG. 14 is a diagram showing a relationship between element resistance and sensor responsiveness.

FIG. 15 is a diagram showing a relationship between element resistance and an air-fuel ratio detection range.

[Explanation of symbols]

10 ... Engine (internal combustion engine), 13 ... Exhaust pipe, 15 ... E
CU, 16 ... Engine control microcomputer forming permitting means, 20 ... Air-fuel ratio detecting microcomputer forming detecting means,
30 ... A / F sensor (limit current type air-fuel ratio sensor) as gas concentration sensor, 31 ... Solid electrolyte, 32 ... Diffusion resistance layer, 35 ... Heater.

Claims (3)

(57) [Claims] 1. A gas concentration sensor having a sensor element made of a solid electrolyte for detecting the concentration or air-fuel ratio of a specific component in exhaust gas discharged from an internal combustion engine, and using the detection result of the gas concentration sensor. In the abnormality diagnosis device for performing abnormality diagnosis of the sensor, a detection means for detecting the element temperature or the element resistance of the gas concentration sensor, and if the element temperature or the element resistance of the gas concentration sensor is in a predetermined active range, and a permitting means for permitting the implementation of the abnormality diagnosis, when performing an abnormality diagnosis of the gas concentration sensor, said sensor
The abnormality judgment value can be variably set according to the element temperature or element resistance of
Abnormality diagnosis apparatus for a gas concentration sensor according to claim to Rukoto. 2. A heater is attached to the gas concentration sensor,
To maintain the sensor in its active state
In the gas concentration detector that controls the energization of the heater for
Therefore, the permission means can control the heater energization in the sensor active state.
It is allowed to carry out the above-mentioned abnormality diagnosis on condition that it has been carried out.
An abnormality diagnosis device for a gas concentration sensor according to claim 1, wherein
Place 3. The responsiveness of the output of the gas concentration sensor is detected.
The presence or absence of abnormality is determined from the sensor responsiveness.
An abnormality diagnosis device for a gas concentration sensor according to claim 1 or 2.
Place