JP2006126032A - Abnormality detector of oxygen sensor and abnormality detecting method of oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detector of an oxygen sensor capable of determining the presence of the small crack formed in a detection element part. <P>SOLUTION: The abnormality detector 1 of the oxygen sensor 2 is constituted so as to detect the abnormality of the oxygen sensor 2 equipped with the detection element part 21 arranged between a first gas and a second gas and outputting the signal corresponding to the oxygen partial pressures of the first and second gases and equipped with a determination means 3 for determining that the crack is formed in the detection element part 21 when the sum total, which is calculated by integrating the change quantity of the output value of the signal during a predetermined period, becomes a predetermined value or above. Since the determination means determines the presence of the crack of the detection element part using the sum total of the change quantity of the output value becoming large when the small crack is formed, the abnormality of the oxygen sensor difficult to detect heretofore can be certainly detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an abnormality detection apparatus for detecting an abnormality of an oxygen sensor, and more particularly to an apparatus for determining the presence or absence of a crack generated in a detection element portion of an oxygen sensor used when detecting an air-fuel ratio.

  An internal combustion engine (hereinafter, simply referred to as an engine) such as a gasoline engine or a diesel engine is provided with an exhaust gas purification system in order to remove harmful components contained in the exhaust gas. In order for this exhaust gas purification system to function effectively, it is important to strictly control the mixing ratio of the atmosphere (air) combusted by the engine and the fuel, that is, the air-fuel ratio. Therefore, in order to detect the oxygen partial pressure of the exhaust gas in the exhaust passage of the engine, for example, an oxygen sensor is installed to perform feedback control so as to obtain an ideal air-fuel ratio (stoichiometric).

FIG. 5A is a diagram showing a detection element portion in a general oxygen sensor. The oxygen sensor 100 includes a cylindrical detection element unit 101 disposed so as to protrude into the exhaust passage 120. The detection element unit 101 is formed so that air (air) Air is introduced to the inner surface side, and the exhaust gas EG that has passed through the sensor cover 102 contacts the outer surface side. FIG. 5B is a diagram showing a cross-sectional structure of the detection element portion 101 in the CR in FIG. As shown in FIG. 5B, the detection element portion 101 has a structure in which a solid electrolyte 107 is interposed and an atmospheric electrode 105 is coated on the inner side and an exhaust electrode 106 is coated on the outer side. The solid electrolyte 107 is formed of a substance that can move inside the state in which oxygen (O ₂ ) is ionized (O ²⁻ ), such as zirconia. In general, the solid electrolyte 107 is not activated unless heated to a high temperature exceeding 500 ° C. Therefore, as shown in FIG. 5A, the detection element unit 101 is provided with a heater 110 for heating.

There is an oxygen partial pressure difference between the atmosphere and exhaust gas, and generally the oxygen partial pressure on the atmosphere side is high. As a result, oxygen is ionized and moves from the atmosphere side to the exhaust gas side via the solid electrolyte 107 so that the oxygen partial pressure difference between the inner atmosphere and the outer exhaust gas is reduced in the oxygen sensor 100. As shown in FIG. 5B, oxygen molecules receive tetravalent electrons (e ⁻ ) in the process of ionization, and emit tetravalent electrons in the process of returning from the ionized state to the molecule. In response to such oxygen movement, electrons move in the electrodes 105 and 106 on the inner and outer surfaces of the detection element unit 101, and an electromotive force is generated in the detection element unit 101. As described above, the oxygen sensor 100 outputs a voltage corresponding to the oxygen partial pressure of the atmosphere and the exhaust gas, and thus has been conventionally used as an air-fuel ratio control sensor.

  However, as shown in FIG. 5A, there is a case where a crack or opening defect (hereinafter simply referred to as a crack) that causes the atmosphere side and the exhaust side to communicate with each other is generated in the detection element portion 101 of the oxygen sensor 100. is there. If there is a crack CK in the detection element unit 101, the oxygen sensor 100 will not function normally.

  In view of this, Patent Document 1 proposes an abnormality diagnosis apparatus that determines the presence or absence of a detector defect (a crack in the detection element portion) of an oxygen sensor. This diagnosis device diagnoses the abnormality of the oxygen sensor by determining the presence or absence of cracks in the detection element unit based on the output distribution of the signal from the oxygen sensor. The technique proposed in Patent Document 1 focuses on the fact that the output pattern of the oxygen sensor when a crack occurs in the detection element unit is different from the normal output pattern, and compares the output pattern to thereby detect the detection element unit. The presence or absence of cracks that occur is determined.

JP 2003-14683 A

  When the crack generated in the detection element portion has a certain size, the exhaust gas quickly enters the inside through the crack, so that an oxygen partial pressure state different from the normal time is quickly formed. Therefore, the presence or absence of cracks can be determined relatively easily by comparing the pattern of the output signal of the oxygen sensor with that at the normal time. For example, when the pressure of the exhaust gas EG is high, as shown in FIG. 5A, a large amount of the exhaust gas EG enters the inside of the detection element portion 101 via the large crack CK and the oxygen content is reduced. Since the pressure changes, it is possible to easily detect abnormality of the oxygen sensor.

  However, cracks generated in the detection element unit 101 have various sizes. When the crack is small, the exhaust gas EG is difficult to pass. Further, the state of the exhaust gas EG passing through the peripheral portion of the detection element unit 101 is constantly changing in exhaust pressure and temperature according to the driving state of the engine. Even when a small crack is generated, the exhaust gas EG enters and leaves, but the oxygen partial pressure does not change greatly because the amount of passage of the exhaust gas is small. In such a case, since an extreme change does not appear in the output pattern of the oxygen sensor, it is difficult to detect the abnormality of the oxygen sensor, that is, the occurrence of a small crack, with the apparatus of Patent Document 1 described above.

  Accordingly, an object of the present invention is to provide an oxygen sensor abnormality detection device capable of determining the presence or absence of small cracks generated in a detection element section.

  An object of the present invention is to provide an oxygen detector that is disposed between a first gas and a second gas and includes a detection element unit that outputs a signal corresponding to the partial pressure of oxygen between the first gas and the second gas. A device that detects an abnormality of a sensor, and determines that a crack has occurred in the detection element unit when a total sum of changes in the output value of the signal over a predetermined period becomes equal to or greater than a predetermined value. This can be achieved by an oxygen sensor abnormality detection device provided with a determination means.

  According to the present invention, since the determination means determines the presence or absence of cracks in the detection element portion using the sum of the amount of change in the output value that increases when a small crack occurs, an oxygen sensor that has been difficult to detect in the past. Can be reliably detected.

  The determination means periodically checks the output value of the signal, calculates a difference between the checked output values, determines the change amount, and sequentially adds the change amounts to determine the sum. You can do it.

  Further, the above object is provided with a detection element unit that is disposed between the first gas and the second gas and outputs a signal corresponding to the partial pressure of oxygen between the first gas and the second gas. An oxygen sensor abnormality detection method for determining that a crack has occurred in the detection element unit based on the fact that the output waveform of the signal includes a high-frequency part. Can also be achieved. In addition, the high-frequency portion can be confirmed using a sum total obtained by integrating the amount of change in the output value of the signal over a predetermined period.

  ADVANTAGE OF THE INVENTION According to this invention, the abnormality detection apparatus of the oxygen sensor which can judge the presence or absence of the small crack which generate | occur | produces in a detection element part can be provided.

  A sensor abnormality detection device (hereinafter simply referred to as an abnormality detection device) according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an abnormality detection apparatus 1 in a state where it is connected to an oxygen sensor 2 to be detected.

  As shown in FIG. 1, the abnormality detection device 1 includes an electromotive force detection circuit 4 connected to a detection element unit 21 of the oxygen sensor 2, and a detection element unit 21 based on a change in electromotive force detected by the electromotive force detection circuit 4. And a CPU (central processing unit) 3 as a judging means for judging the presence or absence of cracks. The oxygen sensor 2 includes a detection element unit 21 and a heater 22 for heating the detection element unit 21. The detection element unit 21 may have the same structure as the conventional one, and is installed in the exhaust passage of the engine so as to be in contact with the atmosphere (first gas) on the inside and the exhaust gas (second gas) on the outside. An electromotive force corresponding to the oxygen partial pressure is generated.

  The CPU 3 is connected to the ROM 6 and the RAM 7 by the bidirectional bus 5. The ROM 6 stores various programs and data executed by the CPU 3 such as a program for determining the presence or absence of small cracks generated in the detection element unit 21. The RAM 7 provides a processing area for the CPU 3 to execute the program. Note that the electromotive force detection circuit 4 may be configured as a part of the CPU 3.

  Next, a waveform of a signal output from a detection element portion where a small crack has occurred, that is, an output waveform of an electromotive force will be described with reference to FIG. FIG. 2 shows that a normal sensor and an abnormal sensor in which a small crack is formed in the detection element portion are installed in the exhaust passage of the engine when the air-fuel ratio (A / F) is forcibly made lean to rich. The data obtained from time to time are shown in comparison. However, here, an opening having a diameter of about 0.5 mm is formed as a small crack. The minute or small crack in this specification is a defect that does not allow the exhaust gas to pass smoothly, and assumes, for example, an opening having a diameter of less than 2 mm. Such minute cracks are difficult to detect even if the oxygen partial pressure pattern is simply compared with the normal pattern as pointed out as a problem. In FIG. 2, the air-fuel ratio A / F shown in the upper stage is switched from lean to rich at point CP. The lower part shows the output waveform of the electromotive force (V) output from the detection element unit at this time.

  As can be seen from FIG. 2, the output waveform S of the normal oxygen sensor is switched to the rich state, and a large electromotive force (about 0.8 V) is generated in response to the change in the oxygen partial pressure of the exhaust gas. Show. On the other hand, even when the output waveform E of the abnormal oxygen sensor having small cracks is switched to the rich state, an electromotive force (about 0.6 V) is generated. It can be confirmed that the output waveform E of the abnormal oxygen sensor tends to be lower than the output waveform S of the normal oxygen sensor. However, when both output waveforms are switched to the rich state, the waveforms indicate that a larger electromotive force is generated than before. Therefore, it is difficult to detect sensor abnormality by comparing the overall pattern of the output waveform. By the way, the output waveform from the oxygen sensor when a large crack that causes exhaust gas to enter the inside at once is a constant electromotive force when it is switched to the rich state. Since it becomes 0 (zero) (V), an abnormality can be detected relatively easily.

  Here, when attention is paid to the output waveform E of the abnormal oxygen sensor, after the electromotive force (about 0.6 V in FIG. 2) is generated, a portion NP (hereinafter referred to as a high frequency) pulsating at a high frequency clearly different from other portions. A partial NP) appears. The high-frequency portion NP is generated due to the situation where the exhaust gas enters and leaves the crack portion, and the value of the electromotive force (output value) changes in small increments. When the crack is small, the exhaust gas does not enter the detection element (atmosphere electrode side) at a stretch, so there is no significant change in the oxygen partial pressure, but the exhaust gas enters and exits the crack portion in small increments. The pressure changes in this way.

  As described above, the output waveform E of the abnormal oxygen sensor having small cracks is characterized by including a high-frequency portion NP as compared with the output waveform S of the normal oxygen sensor. The waveform of the high-frequency portion NP has a shape as if high-frequency noise is superimposed on the output waveform S of a normal oxygen sensor. In addition, what is called high frequency in this specification is a waveform whose frequency exceeds 10 Hz, for example. The waveform of a signal output from a normal oxygen sensor or an abnormal oxygen sensor having a large crack generally has a frequency of about 1 Hz. Therefore, the presence or absence of small cracks can be confirmed by confirming whether or not the high-frequency portion NP exists in the output waveform of the oxygen sensor.

  Since the output value (electromotive force value) changes in small increments as described above in the high-frequency portion NP, the total sum of the output value change amounts (hereinafter referred to as the change amount summation) becomes extremely large. Therefore, the presence of the high-frequency portion NP can be confirmed by obtaining the total change amount of the output waveform, and it can be determined that a small crack has occurred in the detection element portion. The abnormality detection device 1 determines the presence or absence of cracks in the detection element unit 21 based on such a viewpoint.

  Therefore, the CPU 3 serving as the determination unit of the abnormality detection apparatus 1 checks the high frequency portion NP using the above-described change amount sum and determines whether or not a small crack has occurred in the detection element unit 21. More specifically, the CPU 3 periodically checks the output value of the signal from the detection element unit 21 received via the electromotive force calculation circuit, calculates the difference between the output value checked before and after, and the amount of change ( The absolute value of the difference in electromotive force) is obtained, and the total amount of change is obtained by integrating the amount of change. When the total amount of change exceeds a predetermined threshold value PD, the CPU 3 determines that there is a small crack in the detection element unit. The threshold value PD may be set to be several times the total amount of change obtained from the output waveform of a normal oxygen sensor or an abnormal oxygen sensor having a large crack.

  The total change amount is obtained by integrating the vertical movement changes in the output waveform, and can be regarded as a change locus length. Therefore, hereinafter, the total amount of change will be referred to as a trajectory length. FIG. 3 is a diagram for explaining a method of calculating the trajectory length. FIG. 3 shows an enlarged part of the high-frequency portion NP that appears in the output waveform E of the abnormal oxygen sensor shown in FIG.

  The horizontal axis indicates the period T in which the CPU 3 confirms the output value (V). That is, the CPU 3 confirms the output value (electromotive force value) at the times T0, T1,. Then, the CPU 3 obtains an output difference D1 between the electromotive force V0 at the time T0 and the electromotive force V1 at the next time T1, and then obtains an output difference D2 between the electromotive force V1 at the time T1 and the electromotive force V2 at the next time T2. Ask. Similarly, an output difference D3 between the electromotive force V2 at time T2 and the electromotive force V3 at the next time T3 is obtained. The output difference Dn here is the amount of change described above. At each time T, the CPU 3 confirms the output value and obtains the output difference Dn and repeats the process of obtaining the locus length by adding them in order. Accordingly, the trajectory length is updated to a new trajectory length by sequentially adding the amount of change. When the trajectory length exceeds a preset threshold value PD, the CPU 3 determines that the detection element unit 21 has a small crack.

  FIG. 4 is a flowchart illustrating a routine example when the CPU 3 of the abnormality detection device 1 determines whether or not the detection element unit 21 is cracked. Since the output of the detection element unit 21 fluctuates before the engine warms up or in a region where the load fluctuation is large, the A / F of the exhaust gas is not stable. There is a possibility of misjudgment. Therefore, the abnormality detection by the abnormality detection device 1 is preferably performed in a state where the engine state is stable and the A / F fluctuation of the exhaust gas is small and the fluctuation of the output waveform of the normal oxygen sensor is small. In this example, after the CPU 3 confirms that “engine warm-up end”, “oxygen sensor warm-up end”, “engine speed is within a specified range”, and “intake air intake amount is within a specified range” as preconditions. Then, the process of determining the presence or absence of a small crack generated in the detection element unit 21 using the locus length is entered.

  This routine is started, for example, when the engine is started, and the CPU 3 confirms whether or not the precondition is satisfied (S101), confirms the output value at a predetermined period, and starts accumulating the amount of change (S102). ). The integration process here is as described above with reference to FIG. 3. The output value is confirmed for each period, and the difference is calculated by calculating the difference between the output values between adjacent periods (for example, T1 and T2). Then, add this amount of change. The CPU 3 repeats this process, accumulates the amount of change, and updates the trajectory length.

  When the accumulated time exceeds a predetermined time (X sec) set in advance (S103), the CPU 3 checks whether or not the trajectory length exceeds the threshold value PD (S104). When it is confirmed in step 104 that the trajectory length is equal to or greater than the threshold value PD, it can be determined that a small crack has occurred in the detection element portion. Therefore, in this case, the CPU 3 determines that there is an abnormality in the oxygen sensor 2 (S105), and ends the processing by this routine. On the contrary, if the trajectory length is less than the threshold value PD in step 104, it can be estimated that there is no occurrence of small cracks in the detection element portion. Therefore, the CPU 3 assumes that the oxygen sensor 2 is normal in this case (S106), and repeats the processing according to this flowchart.

  As described above, according to the abnormality detection apparatus 1, since the CPU 3 determines the presence / absence of a crack using the total amount of change that becomes large when a minute crack occurs, the abnormality of the oxygen sensor, which has been difficult to detect in the past, has been detected. Can be detected. In addition, since it is not necessary to confirm the entire pattern of the output waveform as in the conventional case, the presence / absence of cracks here can be determined in a short time. In the flowchart shown in FIG. 4, the integration is performed until the predetermined integration time elapses in Step 103. However, the integration is performed until the predetermined number of integrations is reached, and the determination in Step 104 is performed. May be. In addition, the abnormality detection device 1 accurately detects that a small crack has occurred in the detection element unit 21. Therefore, when combined with a conventional abnormality detection device that can detect the occurrence of a large crack, a more preferable abnormality detection device that can detect the presence or absence of abnormality regardless of the size of the crack can be configured.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

It is the block diagram which showed the abnormality detection apparatus in the state connected to the oxygen sensor used as detection object. Compare the data obtained when installing a normal oxygen sensor and an oxygen sensor with small cracks in the detection element in the engine exhaust passage when the air-fuel ratio is forced from lean to rich. FIG. It is the figure shown in order to demonstrate the method of calculating locus | trajectory length. It is the flowchart which showed the example of a routine when CPU of an abnormality detection apparatus performs the crack presence determination of a detection element part. (A) is the figure which showed the detection element part in a general oxygen sensor, (B) is the figure which showed the cross-section of the detection element part in CR in FIG. (A).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Abnormality detection apparatus 2 Oxygen sensor 3 CPU (judgment means)
4 Electromotive force detection circuit 6 ROM
7 RAM
21 Detection element part 22 Heater

Claims (4)

An abnormality of an oxygen sensor including a detection element unit that is disposed between the first gas and the second gas and outputs a signal corresponding to an oxygen partial pressure of the first gas and the second gas. A device for detecting,
An oxygen device comprising: a determination unit that determines that a crack has occurred in the detection element unit when a total sum of the amount of change in the output value of the signal in a predetermined period is equal to or greater than a predetermined value. Sensor abnormality detection device. The determination means periodically checks the output value of the signal, calculates a difference between the checked output values to determine the amount of change, and sequentially adds the amount of change to determine the sum. The oxygen sensor abnormality detection device according to claim 1. An abnormality of an oxygen sensor including a detection element unit that is disposed between the first gas and the second gas and outputs a signal corresponding to an oxygen partial pressure of the first gas and the second gas. A method of detecting,
An oxygen sensor abnormality detection method, comprising: determining that a crack is generated in the detection element unit based on an output waveform of the signal including a high-frequency portion. The method for detecting an abnormality of an oxygen sensor according to claim 3, wherein the high-frequency portion is confirmed using a sum obtained by integrating the amount of change in the output value of the signal over a predetermined period.

Images