JPH0469565A - Fault decision device for air fuel ratio sensor - Google Patents

Abstract

PURPOSE:To securely decide the fault of the air fuel ratio sensor by providing at least two out of three fault detecting means and outputting a fault signal by at least one of the two fault decision means. CONSTITUTION:A 1st fault decision means constitutes a 1st fault decision means together with detecting circuits 35 and 36 to decide the deterioration and open circuit of a heater and other connecting circuits. A 2nd fault decision means fetches the electromotive force for a sensor cell 20 from a detecting circuit 38 and decides sensor cell fail unless the input value is within a specific permissible width range. A 3rd fault decision means fetches air fuel ratio signals from 1st and 2nd air fuel ratio means and decides pump cell fail unless the input values are within a specific permissible width range. A controller 37 cooperates with a pump cut circuit 39 to function as an in-fault stop processing means and performs feedback control over the amount of injected fuel according to the air fuel ratio signals. Consequently, the fault of the air fuel ratio sensor is securely decided and in case of a fault, the air fuel ratio feedback control is stopped immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a failure determination device for an air-fuel ratio sensor that outputs air-fuel ratio information according to the oxygen concentration in the exhaust gas of an internal combustion engine.

(Prior art) Conventionally, by utilizing the characteristics of zirconia's oxygen concentration battery action and oxygen ion pumping action, the air-fuel ratio (A/F) was determined not only by whether it was lean or rich compared to stoichiometry, but also by what value. However, a linear A/F sensor that performs side-to-side comparison has been proposed. (Refer to Japanese Unexamined Patent Publication No. 63-36140.) As shown in FIG. 12, this linear A/F sensor consists of sensor cells 20 each having a stabilized zirconia element at its base.
and a pump cell 21 are coupled through an insulating layer 22. Cell 1.7 is a diffusion cell through which ILH gas passes.
323. , 24 are formed, and a diffusion t-
A detection chamber 25 is formed to accommodate exhaust gases from +23 and +24, and these constitute a diffusion barrier.

Further, a reference chamber 25a is formed in the absolute 8M22, and is configured to introduce a reference gas, for example, popularity. Furthermore, both cells have platinum electrodes 26.2 that also serve as catalysts.
7, 28, and 29 are provided, and a large number of micro holes are drilled in these. Reference numeral 30 denotes an electric heater, which heats the entire cell to, for example, 800±100° C. to operate each cell in an active state.

The sensor cell 20 has the same principle as the conventional 02 sensor, and has the property of generating an electromotive force when there is a difference in oxygen concentration between the electrodes 26 and 27. On the contrary, the pump cell 21 has the property of generating an electromotive force between the electrodes 211 and 29. It has a property of pumping oxygen from the negative electrode side to the positive electrode side when the pump current IP is applied.

Therefore, the control unit 31 detects the electromotive force VS of the sensor cell 20, and maintains the electromotive force Vs at a constant LJ, that is, the oxygen concentration in the detection chamber 25 or the diffusion hole 23, 24 is maintained at a stoichiometry. ')yo-)1.: Pump current Ip
to control the filled pack. This makes the pump current 1
p is shown in Figure 14 1. Since the air-fuel ratio E9 changes continuously as shown in Figure 1, the air-fuel ratio can be calculated from the pump current p.

The control section 31 and the sensor cell 20 are connected to the comparison circuit 1.
The electromotive force V's is expressed as a reference type high voltage Vre equivalent to stoichiometry.
f, the output of the comparison path 1 is integrated by an integrating amplifier 2 with positive and negative power supplies, and the pump current IP is caused to flow through the pump cell 21 using the integrated output.

A resistor 5 for current detection is added to the pump current Ip circuit.
A pump current Ip is detected by a current detection circuit 3 from the voltage drop across the resistor L2.

Further, the output of the circuit 3 is inputted to the adder circuit 4, and the above formula is processed to obtain a signal V of, for example, 0 to 5 volts. 1. J.T.
As a result, the air-fuel ratio (A/F) is varied.

Vovr=G·Ip+V STP However, G is a current-voltage conversion gain, and vsrp is a step-up voltage.

However, the internal combustion engine does not adjust the air-fuel ratio to the target air-fuel ratio/<<,
Feedback control is performed based on air-fuel ratio information L from the air-fuel ratio sensor. For example, by controlling the air-fuel ratio within a narrow window near the stoichiometry, a two-way catalyst used in the exhaust system is operated efficiently. Alternatively, the exhaust system may be equipped with lean NO, a catalyst, and a three-way catalyst.
- In the case of a combustion engine, feedback control is performed based on air-fuel ratio information from a linear A/F sensor in order to maintain the air-fuel ratio at a predetermined lean side value that is a target value.

(Problems to be Solved by the Invention) In driving an internal combustion engine in this way, accurately controlling the air-fuel ratio to the target value improves fuel efficiency.2) Improves engine output and stabilizes idle rotation. This is extremely important for improving gas efficiency, gas consumption, and drivability. Therefore, it is necessary to control the linear Δ/F sensor from which this air-fuel ratio information is obtained so as not to cause thermal deterioration or brushing damage.

However, the air-fuel ratio sensor, especially the linear A/F sensor, has a complicated structure. In order to function properly, it is necessary to operate the sensor cell in combination with a heater, a sensor cell, and a pump cell.

Therefore, even if a failure occurs in any part of the linear A/F sensor, the reliability of the air-fuel ratio information that is its output will be reduced.

When the linear A/F sensor malfunctions, it is desirable to detect it early, stop feedback control based on the sensor output, and use an alternative control method to control the air-fuel ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio sensor failure determination device that can reliably determine failure of an air-fuel ratio sensor.

(Means for Solving the Problems) In order to achieve the above object, the present invention outputs an electric signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the three mixtures and the oxygen concentration in the reference gas. a sensor cell, a control means for outputting an electrical control signal so that the output from the sensor cell becomes a predetermined value, a pump cell for moving oxygen ions in accordance with the electrical control signal supplied from the control means, and the control means; The air-fuel ratio sensor is attached to an air-fuel ratio sensor that includes an air-fuel ratio detection means that outputs an air-fuel ratio signal according to a control current exchanged with the pump cell, and a heating means that heats the sensor cell and the pump cell to an activation temperature. a first failure detection means that detects a failure of the means; a second failure determination means that determines a failure when this value does not fall within a set range according to the electromotive force of the sensor cell; and a second failure detection means that determines a failure based on the control current. At least two of the three failure detection means are provided with a third failure detection means for determining an abnormality, and when at least one of the two failure determination means outputs a failure signal, The present invention is characterized in that it includes a failure stop processing means for stopping the air-fuel ratio control by the means for performing feedback control based on the air-fuel ratio signal.

(Function) The first failure detection means detects failure of the heating means of the air-fuel ratio sensor, and the second failure detection means determines failure if this value does not fall within the set range according to the electromotive force of the sensor cell of the air-fuel ratio sensor. and a third failure detection means that determines normality or abnormality based on the control current exchanged between the control means and the pump cell. The processing means receives these two
When the failure stop processing means receives a failure signal from at least one of the three failure determination means, the means can reliably stop the air-fuel ratio control by means for performing feedback control based on the air-fuel ratio signal.

(Embodiment) The air-fuel ratio sensor failure determination device shown in FIG. 1 is installed in a control system for a fuel supply system of an internal combustion engine. This fuel supply system calculates the fuel supply amount based on air-fuel ratio (A/F) information obtained from the linear A/F sensor S installed in the exhaust passage, and injects the fuel of the supplied amount into the injection nozzle N. The structure is such that the fuel is injected into the intake passage at a timely manner.

Here, the linear A/F sensor S and the control section 31. connected thereto serve as control means. Current detection circuit 3, addition circuit 4. The resistor 5 for current detection has the same configuration as the conventional device shown in FIG. 13, so a redundant explanation thereof will be omitted.

In FIG. 1, a comparator circuit 1 and an integrating amplifier 2 with positive and negative power supplies constitute a control means, and an electrode 26.2 of a sensor cell 20
The electromotive force Vs between
), the output is integrated by the integrating amplifier 2, a positive or negative control output is applied between the electrodes 28 and 29 of the pump cell 21, and the pump current rp is applied to the pump cell 21 so that V s = Vref. Flow.

The current detection resistor 5 and the current detection circuit 3 constitute a first air-fuel ratio detection means, and the circuit 3 detects the pump current IP from the voltage drop occurring in the resistor 5. Pump current 1p
Although it itself has air-fuel ratio information, the addition circuit 4
The air-fuel ratio signal Vout is converted into a 5-volt air-fuel ratio signal Vout, and the air-fuel ratio signal Vout is output to an engine control unit (hereinafter simply referred to as a controller) 37.

A pump voltage Vρ between electrodes 28 and 29 is applied to a point A of the pump cell 21, and a buffer amplifier 8, a CR filter 10, an operational amplifier 11, and a second air-fuel ratio detecting means are connected thereto. , a resistor 17 and two diodes 15, 16 are connected in sequence.

Here, the voltage at point A is passed through a buffer amplifier 8 to a filter 10, where oscillation prevention, surge countermeasures, and noise removal are performed by feedback of the pump current ρ. Furthermore, it is applied to the inverting input terminal of an operational amplifier (operational amplifier) 11 via a resistor 12, the output of the operational amplifier II is fed back to the inverting input terminal via a resistor 13, and the output of the operational amplifier II is fed back to the inverting input terminal via a resistor voltage divider 14. Provides voltage for shifting. Then, two diodes 15 connected with DC
．． ,．． 16 is connected in reverse bias between a power source of a specific voltage and the ground, and the connection point between the diodes and the output terminal of the operational amplifier 11 are connected by a resistor 17, thereby constructing an amplifier having a clip function.

In this way, the pump voltage VP is basically as shown in Figure 3 (
As shown in b), it has a characteristic of jumping at the stoichiometry point, and if the discontinuous part is detected using a threshold value, the stoichiometric air-fuel ratio λ that differs between the lean side and the rich side with the stoichiometry point as the border becomes a bell. (stoichiometry) signal Vstc can be output to the controller 37. In particular, for the input terminal with the waveform shown in FIG. 3(a), the waveform of the stoichiometric signal V ste changes very smoothly in the vicinity of the stoichiometry, as shown in FIG. 3(1)), so-called λ It has the advantage of having output characteristics comparable to those of sensors.

The heating means attached to the linear A/F sensor S consists of an electric heater 30 (hereinafter simply referred to as heater), a heater drive circuit 2 connected to tt.

The heater control circuit 32 controls the temperature of the heater 30 and the heater resistance R.
, H, the heater switch 1-
It can operate to issue a switching output to the transistor 33, and is composed of a bridge circuit (not shown) including a comparison resistor 34 and a comparator.

This heater parking circuit 32 has a heater applied voltage) E V H
A detection circuit 35 is connected to a detection circuit 36 that detects the heater current based on the voltage drop across the comparison resistor 34. Each detection circuit', 35. :36 is configured as an amplifier circuit using an operational amplifier, and each output is connected to a controller 37.
It is connected to the.

There is a sensor cell electromotive force V between the sensor cell 20 and the control unit 31.
s detection circuit 38 is connected.

A pump current I is connected between the comparator circuit 1 and the integral amplifier 2 with positive and negative power supplies in response to the pump cut power from the controller 37.
A pump cut circuit; 31) for cutting P is connected.

Furthermore, based on the pump current ■, the air-fuel ratio sensor is normal;
A third failure determination means for determining an abnormality is provided, and a portion thereof is constituted by the first and seventh air-fuel ratio determination means.

Note that the reference numeral 40 indicates a starter switch in a combination switch (not shown) of the engine.

The main part of the controller 37 is made up of a microcomputer, and in particular, it receives each output signal, takes in the information in a timely manner, or sends a control signal to the drive circuit 371 in a timely manner.
, 372, etc., the failure determination program shown in FIGS. 4 to 9, the fuel injection amount calculation program shown in FIG. It is composed of a control circuit 375 that calculates a control value according to the following.

Here, the function of this controller 37 will be explained only with regard to the present invention, as shown in FIG.

That is, the controller 37 functions as at least two of the three failure determining means described later, a failure stop processing means to which these are connected, and a means for performing feedback control based on the air-fuel ratio signal.

Here, the first failure determination means constitutes a first failure determination means together with each of the detection circuits 35 and 36.
．． Deterioration or disconnection of the heater and its connection circuit is determined based on the heater applied voltage vH and heater current L+& from 36.

Further, the second failure determining means takes in the electromotive force ■sk of the sensor cell 20 from the detection circuit 38, and if the value is not within a predetermined allowable range φ to ψ, determines that the sensor self-fails.

Furthermore, the third failure determination means takes in the air-fuel ratio signals (Vout, Vsl, C) from the first and second air-fuel ratio detection means, and determines that the value is a normal value and is within a predetermined allowable range. If not, it will be judged as a pump self-ale.

Further, the controller 37 works together with the pump cut circuit 39 to function as a failure determination processing means 2, which, based on the failure signal, sets the output of the comparison circuit to zero, that is, the detection chamber 25
It is possible to output a signal indicating that the stoichiometry is maintained.

Further, the controller 237 also has a function of performing feedback control of the fuel injection amount based on the air-fuel ratio signal.

Here, the controller 37 controls the fuel injection amount.
(Feedback control and oven loop control performed during non-feedback) as well as air-fuel ratio sensor failure determination processing and fuel injection amount calculation processing are shown in Figures 4 to 1.
This will be explained together with the control program shown in FIG.

The controller program starts by turning on the starter switch as shown in FIG. In this case, in the main routine, the heater 30 is turned on,
Subsequently, it is determined whether the starter flag is 1 or not. If the starter flag has not been turned on, the process proceeds to step a8, and if the starter has been turned on, the process proceeds to step a3.

In step a3, the starter flag is cleared, each fail judgment flag Fl, F2 is cleared, and the pump current I
The pump cell activation flag that allows operation of P is cleared. In step a6, the sensor activation timer that regulates the activation timing of the linear A/F sensor S is first reset,
It will then start.

When step a8 is reached, it is determined here whether the count value of the sensor activation timer has exceeded the set value θ (this value is a value corresponding to the waiting time for reliable activation of the air-fuel ratio sensor at the time of activation). do.

If the fuel injection amount is not exceeded, the process proceeds to step a15, where air-fuel ratio feedback is prohibited, and open-loop control of the fuel injection amount is performed. The fuel injection amount is taken into a predetermined area, and the process returns to step a1. Along with this process, a fuel injection routine (not shown) is executed in response to an interrupt timing at a predetermined crank angle, and fuel injection that can achieve a predetermined target air-fuel ratio is performed.

After this, in step a2, since the starter flag is zero, the process proceeds to step a8, and the sensor activation timer is set to θ.
is counted, and when the count value exceeds θ, step a9
reach. Here, if the sensor activation timer is still in operation, its counting operation is stopped at the current value, and the process proceeds to step a10.

At first, if the pump cell activation flag is not 1, the process proceeds to step all, in which the pump cell 21 is activated, the flag is set to 1, the pump cell activation timer is started, and the count of the timer reaches the set value ε (the output of the air-fuel ratio sensor is stable). It is determined whether or not the value has exceeded the waiting time (corresponding to the waiting time for If the reliability is satisfied, the process proceeds to step a17, and if the pump cell operation timer is in operation, the operation is stopped with the count value at that time maintained, and the process proceeds to step a1.
Proceed to step 8.

From step a18 to step a21, the air-fuel ratio sensor S
make a failure determination.

First, in subroutine #1 as step a18,
As shown in FIG. 4, sensor failure is determined based on the air-fuel ratio signal V out. Here, only during feedback control while the fail judgment flag F1 is not 1,
Proceed to step b3, otherwise return to the main routine.

In steps b3 and b4, the value of the target air-fuel ratio A/F corresponding to the driving situation of the current vehicle, which has already been determined in the main routine, is read, and the air-fuel ratio signal V out from the linear A/F sensor S is read. Further, the actual air-fuel ratio according to the air-fuel ratio signal Vout is approximately calculated according to a predetermined air-fuel ratio A/F calculation map (not shown).

In step b6, a deviation ΔA/F between the target air-fuel ratio A/F and the air-fuel ratio detected by the sensor is calculated. And the deviation ΔA/F
It is determined whether or not exceeds the fail judgment value α, and if it does not exceed the fail judgment value α, a return is made, and if it exceeds the fail judgment flag F1 is set to 1 and the return is made.

In subroutine 2 as step a19, as shown in FIG. 5, a sensor failure is determined based on the stoichiometry signal V stc. Here, the fail judgment flag F
2 is not 1 and only during feedback control, step c3
Otherwise, return to the main routine.

In step c3, the value of the target air-fuel ratio A/F according to the driving situation of the vehicle, which has already been determined in the main routine, is read, and the process proceeds to step c4.

Here, the target air-fuel ratio is close to stoichiometry (symbol e in Figure 3).
), the process returns; otherwise, the process proceeds to step C5.

In step c5, if the target air-fuel ratio is rich, the process proceeds to step c6, and if the target air-fuel ratio is lean, the process proceeds to step c8.

In step c6, the current stoichiometry signal V stc is read, and if it is rich, the process returns, and if it is lean, the fail determination flag F2 is set to 1 and the process returns. In step C8, the current stoichiometry signal VstC is read, and if it is lean, the process returns, and if it is rich, the fail judgment flag F2 is set to 1 and the process returns.

In subroutine #3 as step a20, as shown in FIG. 6, a failure of the heater 30 is determined. Here, if the fail determination flag F1 is not 1, step d
Proceed to step 2, otherwise return to the main routine.

In step d2, the heater current ■1 is supplied from the detection circuit 36.
The heater applied voltage V is read from the detection circuit 35, and the heater resistance RI (V) is calculated from I/I.

When step d5 is reached, the heater resistance R, changes to the allowable range ζ〈R
, 〈ξ. This permissible range is determined by adding a predetermined permissible range to the upper and lower heater resistance values according to the active temperature range (700° C. to 900° C.) of the air-fuel ratio sensor. Here, if it is within the allowable range, it returns,
If it is off, it is determined that the heater has failed, the fail determination flag F1 is set to 12, and the process returns.

In subroutine #4 as step a21, as shown in FIG. 7, a failure due to the electromotive force Vs of the sensor cell 25 is determined. Here, the fail judgment flag F1 is 1.
If not, proceed to step e2; otherwise, return.

In step e2, the electromotive force Vs is read from the detection circuit 38, and the process proceeds to step e3. Here, the electromotive force Vs (set to 450 mV, for example) is within the allowable range φ<Vs<
Determine whether it is at ψ or not. Note that an appropriate value for this tolerance range has been experimentally set in advance. Here, if the electromotive force Vs is within the allowable range, a return is made, and if it is outside, it is determined that the sensor cell 20 has failed, and the fail determination flag F1
Returns as 1.

After such a fail determination, step a22 is reached. Here, it is checked whether the fail judgment flag Fl is zero or not, and if it is a failure, the pump cell operation stop output is immediately sent to the pump cut circuit 3 via the drive circuit 372 in step a23 in order to prevent blacking of the pump cell 21.
9, cut the pump current ρ, and proceed to step a1.
Proceed to step 5.

On the other hand, if it is determined that there is no failure in step a22 and the process reaches step a24, it is determined here whether the current operating state satisfies the feedback condition, and if it is not in the feedback permissible determination area, the process proceeds to open loop control in step a15. , is in the determination range, the process reaches step a25. Here, it is determined whether or not the target air-fuel ratio in the current operating state is stoichiometric.

In step a27, the process proceeds to step a2g only when the fail determination flag F2 is not 1, and the stoichiometric signal V s
Feedback control to achieve operation at the stoichiometric air-fuel ratio based on tc is performed in accordance with the fuel injection amount calculation routine shown in FIG. 10, and the process returns to step a1.

In step a27, if the fail determination flag F2 is also 1 and there is an abnormality in the stoichiometry signal Vstc, the process proceeds to step a15, and the process proceeds to open loop control.

On the other hand, in step a25, if the target air-fuel ratio in the current operating state is not stoichiometric but in the lean or rich range,
Step a26 is reached, where the air-fuel ratio signal Vout
Based on this, feedback control that can achieve the target air-fuel ratio (in this case, a value on the high or rich side) is performed in accordance with the fuel injection amount calculation routine shown in FIG. 10, and the process returns to step a1.

In the fuel injection amount calculation routine shown in FIG. 10, first, in step f1, it is determined from the input signal whether the conditions for fuel injection feedback control are satisfied.

If NO, proceed to step f2; if YES, proceed to step f3.

When step f2 is reached, that is, when it is in the stoichiometric operating range in the open loop, the fuel amount correction coefficient KFM is set to 1.
shall be. Then, in step f4, the fuel amount FueQ is calculated. Here, each data is taken in from the engine rotation sensor 41, air flow sensor 42, and atmospheric pressure sensor 43 by one interruption. and.

The basic fuel amount F (A/N, N) is calculated based on the intake air amount A/N and the engine speed N, and this value is multiplied by a correction coefficient KFIl based on the air-fuel ratio, which will be described later. The appropriate fuel amount F is calculated by multiplying by the correction coefficient K based on etc.
Calculate ue Q and return to the main routine.

Note that intake pressure, throttle opening, etc. may be used instead of A/N.

In the case of feedback control that proceeds from step f1 to f3, before calculating the average value Δ■ of the difference ΔV, it is determined in the initial setting whether or not it is necessary to clear this, and if necessary, it is cleared in step f5. , and then proceeds to step f6.

In step f6, the stoichiometric signal Vstc and the air-fuel ratio signal Vout are read.

Next, in step f7, the value of V stc is compared with the value at the time of previous acquisition, and it is determined whether or not there is a change in both. If there is a change due to reaching the stoichiometric air-fuel ratio, the process proceeds to step f8.

In step f8, since the current mixture ratio has reached the stoichiometric air-fuel ratio, the conditions for correcting the average difference value ΔvM (such as whether the change in accelerator opening is less than the reference value or whether it is not immediately after changing the target air-fuel ratio) are determined. If it is appropriate, the process goes to step flo, and if it is unsuitable, it goes directly to step f9.

In step flo, the air-fuel ratio signal Vout is read as the actual value vsT at the time when the stoichiometric air-fuel ratio is reached, and the difference ΔV between the stoichiometric air-fuel ratio signal UST set in advance is calculated. , and the previous or previous difference, and update the difference average value ΔVM.

Then, in step f9, a fuel amount correction coefficient KPM is calculated. Here, the deviation of the air-fuel ratio signal V out at that point is corrected by 67M, for example, (A/F)z=f
The air-fuel ratio is calculated as (Vout-ΔVM).

Next, the value of the target air-fuel ratio A/F according to the driving situation of the current vehicle, which has already been determined in the main routine, is read, and this target air-fuel ratio A/F and the actual air-fuel ratio (A/F),
In addition, the difference ΔE between this value and the previous value is also calculated, and the fuel amount correction coefficient K1-1l based on the air-fuel ratio is calculated.

Here, the proportional term KA of the gain according to the level of the difference ΔE
(i) and the offset amount to prevent response delay of the three-way catalyst are calculated, and further, as a differential term, 0 (Δε),
ΣKr (t + t FB) as an integral term is calculated, and KFB is obtained by adding and subtracting these.

After this, the process proceeds to step f4, and each correction coefficient K F B I
The appropriate fuel supply amount at this point is calculated from Ko and the reference fuel amount F, and the process returns to the main routine.

The value obtained in such a fuel injection amount calculation routine is called in the fuel injection routine that is performed when a predetermined crank angle signal interrupts in the main routine, and the fuel injection nozzle N is activated in the moving circuit for an injection time corresponding to the value. 371, and fuel injection that can achieve a predetermined air-fuel ratio is performed.

In the above, the failure of the heater 30 was determined after calculating the heater resistance R1 from VH/Iu.
Instead of this, the heater applied voltage vl from the detection circuit 35
It is also possible to adopt a configuration that excludes the reading of (.

In this case, as shown in FIG. 11, while the fail determination flag F1 is not 1, the process proceeds to step g2. Here, the heater current flow from the detection circuit 36 is simply explained.

is read, and the process proceeds to step g3. Here, it is determined whether this value A has reached a value corresponding to a disconnection of the heater 30 or the like. If there is a failure such as a disconnection, the process returns with the fail determination flag F1 set to 1, and if it is not a failure, the process returns directly to the main routine. In this case, the device can be simplified.

Furthermore, although the apparatus shown in FIG. 1 was equipped with three failure determination means, it is instead provided with at least two of the three failure determination means, and which receives a failure signal from one of the two means. In this case, the means may be configured to reliably stop the air-fuel ratio control by means for performing feedback control based on the air-fuel ratio signal.

(Effects of the Invention) As described above, the present invention provides that the stop processing means at the time of failure is the third
is connected to at least two failure determination means of the failure detection means, and when a failure signal is received from one of the failure detection means, the means reliably performs air-fuel ratio control by the means for performing feedback control based on the air-fuel ratio signal. Since the air-fuel ratio sensor can be stopped, it is possible to reliably determine whether the air-fuel ratio sensor has failed, and in the event of a failure, the air-fuel ratio feedback control can be immediately stopped and an alternative air-fuel ratio control such as open-loop control can be executed. Deterioration of exhaust gas due to misalignment.

It is possible to prevent or minimize harmful effects such as a decrease in drivability and unstable idling.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a failure determination device for an air-fuel ratio sensor as an embodiment of the present invention, FIG. 2 is a block diagram showing the function of the controller of the same device, and FIG. 3 is a diagram of the stoichiometry signal Vstc in the same device. Characteristic diagrams, Figures 4 to 10
FIG. 11 is a flowchart of the air-fuel ratio sensor failure determination program and fuel injection amount calculation program performed by the controller of the failure determination device of FIG. 1, and FIG. 11 is a flowchart of heater failure detection processing used in another embodiment of the present invention. 1st
Figure 2 is an explanatory diagram of the configuration of the sensor element portion of a conventional air-fuel ratio sensor, Figure 13 is a schematic diagram of the configuration of a conventional air-fuel ratio sensor, Figure 14 is a diagram showing the relationship between pump current and air-fuel ratio, and Figure 15. is a diagram showing the characteristics of a stoichiometric signal based on the direction of pump current. 3... Current detection circuit, 4... Adding circuit, 5... Resistor, 11... Operational amplifier, 2o... Sensor cell,
21...Pump cell, 30...Heater, 31...
・Control unit, 35.36...Detection circuit, 37...Controller, 38...Detection circuit, A...Heater current, Vout...Air-fuel ratio signal, ■,...Pump current, Vs ...Sensor cell electromotive force, S...Air-fuel ratio sensor, N...Fuel injection nozzle, Vstc...Stoichiometry signal, IH...Heater current, ■□...Heater voltage. Line 2 Figure 3 Small section) Figure (t)) Horse/Z diagram

Claims (1)

[Claims] a sensor cell that outputs an electrical signal according to the difference between the oxygen concentration in the exhaust gas after combustion of the air-fuel mixture and the oxygen concentration in the reference gas;
A control means for outputting an electric control signal so that the output from the sensor cell becomes a set value, a pump cell for moving oxygen ions in accordance with the electric control signal supplied from the control means, and a combination of the control means and the pump cell. The air-fuel ratio sensor is attached to an air-fuel ratio sensor that includes an air-fuel ratio detection means that outputs an air-fuel ratio signal according to a control current exchanged between the air-fuel ratio sensor and a heating means that heats the sensor cell and pump cell to an activation temperature. a first failure detection means for detecting the electromotive force of the sensor cell; a second failure determination means for determining a failure when this value does not fall within a set range according to the electromotive force of the sensor cell; and a determination of normality or abnormality based on the control current. At least two of the three failure detection means have a third failure detection means and a third failure detection means, and when at least one of the two failure determination means outputs a failure signal, the air-fuel ratio 1. A failure determination device for an air-fuel ratio sensor, comprising: failure-at-failure stop processing means for stopping air-fuel ratio control by means for performing feedback control based on a signal.