JP2006118490A - Sensor abnormality detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor abnormality detection device capable of detecting the abnormality of a detection element part even when an output pattern is not different from that in normal state or the detection element part is not in an active state by the flow of the atmosphere even if a rack occurs. <P>SOLUTION: This sensor abnormality detection device comprises the detection element part 21 disposed between first and second gases and outputting signals according to the oxygen partial pressures of the first and second gases and a heater 22 for heating the detection element part. The device also comprises a temperature detection means 10 detecting the temperature of the detection element part 21 and a determination means 3 determining the presence or absence of the abnormality of the detection element part by using temperature detection data obtained in connection with temperature detection by the temperature detection means and reference temperature data obtained when the normal detection element part is heated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an abnormality detection device for detecting an abnormality of a sensor, and more particularly to an abnormality detection device for a 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. 7A 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. 7B is a diagram showing a cross-sectional structure of the detection element portion 101 in the CR in FIG. As shown in FIG. 7B, 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. 7A, the detection element portion 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. 7B, the oxygen molecule receives tetravalent electrons (e ⁻ ) in the process of ionization and emits 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. 7 (A), an abnormality such as a crack (hereinafter simply referred to as a crack CK) may occur in the detection element portion 101 of the oxygen sensor 100, which causes the atmosphere side and the exhaust side to communicate with each other. . 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 portion based on the output distribution of the detection signal of 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 portion is different from that in the normal state, and compares the output distribution of detection signals to detect cracks in the detection element portion. Whether or not there is. However, since this abnormality diagnosis apparatus makes a determination using an accurate detection signal, the diagnosis is prohibited until the detection element unit is heated to a certain temperature and activated.

JP 2003-14683 A

  The abnormality diagnosis device of Patent Document 1 cannot make a diagnosis unless it waits until the detection element portion of the oxygen sensor is activated. Further, depending on the state of the exhaust gas flowing in the exhaust passage, there may be an air flow that cools the cracked detection element portion. In this case, the output pattern from the oxygen sensor is in a state close to that in the normal state, so there are cases where the abnormality cannot be accurately diagnosed. Further, since no output can be obtained when the oxygen sensor is not activated, conventional output pattern determination cannot be performed. Furthermore, the abnormality diagnosis device of Patent Document 1 cannot accurately diagnose when a lean atmosphere continues depending on the engine operating state.

  A case where an air flow for cooling the detection element portion is generated will be described again with reference to FIG. The gas pressure of the exhaust gas flowing in the exhaust passage 120 varies depending on the state of the engine. For example, when the engine is idle, the gas pressure of the exhaust gas becomes low. When the gas pressure is low, a suction force that sucks out to the exhaust passage 120 side via the crack CK acts on the air Air inside the detection element unit 101. Since the air Air that has received the suction force is sucked out as shown in the drawing, an air flow is generated inside. In such a state, the temperature in the detection element unit 101 decreases and the heating action by the heater 110 also decreases. As a result, since it takes a long time to raise the temperature of the detection element unit, the abnormality diagnosis device of Patent Document 1 that cannot perform diagnosis unless the detection element unit is activated has a longer standby time.

  Accordingly, an object of the present invention is to provide a sensor abnormality detection device capable of detecting an abnormality in a detection element unit even when a crack occurs, even if the output pattern does not differ from the normal state due to the flow of air, or even when the detection element unit is not in an active state. Is to provide.

  The above object is provided between the first gas and the second gas, the detection element unit outputting a signal corresponding to the oxygen partial pressure of the first gas and the second gas, and the detection An apparatus for detecting an abnormality of a sensor including a heater for heating an element unit, the temperature detection unit detecting a temperature of the detection element unit, and obtained in relation to temperature detection by the temperature detection unit By means of an abnormality detection device for a sensor comprising a temperature detection data obtained and a determination means for judging whether or not there is an abnormality in the detection element part using reference temperature data obtained when the normal detection element part is heated Can be achieved.

  According to the present invention, the detection means uses the temperature detection data obtained in association with the temperature detection of the detection element unit and the reference temperature data obtained when the normal detection element unit is heated. Therefore, it is possible to detect an abnormality even when a crack is generated even if the output pattern does not change or the detection element portion is not in an active state.

  The detected temperature data and the reference temperature data include the temperature of the detection element unit detected by the temperature detection unit, and the determination unit detects the temperature of the detection element unit at a predetermined time after the heater is heated. When the temperature based on the detected temperature data is lower than the temperature data and the reference temperature data, it can be determined that the detection element unit is abnormal.

  Further, the detected temperature data and the reference temperature data include a temperature of the detection element unit detected by the temperature detection means and a detection time of the temperature, and the determination means includes the detection temperature data and the reference temperature data. The temperature increase rate per time is obtained and compared from each of them, and when the temperature increase rate based on the detected temperature data is smaller, it can be determined that the detection element unit is abnormal.

  Further, the detected temperature data and the reference temperature data include data relating to a required time until the detection element unit reaches a predetermined temperature, and the determining means determines the required time based on the detected temperature data and the reference temperature data. In comparison, when the required time based on the detected temperature data is longer, it may be determined that the detection element unit is abnormal.

  Further, the detected temperature data and the reference temperature data include data relating to the degree of energization to the heater, and the determination means compares the degree of energization under a predetermined condition with the detected temperature data and the reference temperature data, and When the degree of energization based on the detected temperature data is greater, it may be determined that the detection element unit is abnormal.

  The temperature detection unit includes an impedance calculation circuit that is connected to the detection element unit and calculates an impedance value of the detection element unit, and the determination unit uses the impedance value calculated by the impedance calculation circuit. Judgment can be made.

  Further, the object is to provide a detection element unit that is disposed between the first gas and the second gas and outputs a signal corresponding to the oxygen partial pressure of the first gas and the second gas, A method of detecting an abnormality of a sensor having a heater for heating the detection element unit, which is obtained when the temperature of the detection element unit is detected and the normal detection element unit is heated. This can also be achieved by a sensor abnormality detection method that determines that the detection element unit is abnormal when the temperature increase degree is slower than the temperature increase degree based on the reference temperature data as compared with the reference temperature data. The temperature of the temperature detection means can be detected using the impedance value of the detection element section.

  According to the present invention, since the presence / absence of abnormality is determined using the data related to the temperature of the detection element unit, even when a crack occurs in the detection element unit, the output pattern does not differ from the normal state due to the flow of the atmosphere or the detection element unit It is possible to provide an abnormality detection device capable of detecting an abnormality even when is not in an active state.

  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 connected to an oxygen sensor to be detected. FIG. 2 is a diagram showing an electrical configuration example corresponding to FIG.

  As shown in FIG. 1, the abnormality detection device 1 includes an impedance calculation circuit 10 connected to the detection element unit 21 of the oxygen sensor 2 and a crack in the detection element unit 21 using the impedance value calculated by the impedance calculation circuit 10. CPU (central processing unit) 3 as a determination means for determining the presence or absence of (abnormal).

  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 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 (represented by a battery symbol in FIG. 2) with respect to the ground is generated according to the pressure. In the example shown in FIG. 1, the CPU 3 is configured to also control the oxygen sensor 2. The electromotive force (signal) generated by the oxygen sensor 2 is supplied to the CPU 3 via the electromotive force detection circuit 25.

  FIG. 2 shows the two types of circuits shown in FIG. 1, that is, the impedance calculation circuit 10 and the electromotive force detection circuit 25 in more detail. The electromotive force detection circuit 25 that monitors the electromotive force of the oxygen sensor 2 includes a resistor R1 and is connected to the oxygen sensor 2 via terminals TE1 and TE2. One end of the oxygen sensor 2 is connected to the ground (GND), and the reference voltage is set to 0 (zero). Therefore, the oxygen sensor 2 that has functioned normally generates an electromotive force according to the oxygen partial pressure, so that a positive voltage is supplied to the CPU 3.

  The CPU 3 is connected to the ROM 5 and the RAM 6 by the bidirectional bus 4. The ROM 5 stores various programs and data executed by the CPU 3 such as a program for determining whether or not the detection element unit 21 is cracked based on the impedance value. The RAM 6 provides a processing area for the CPU 3 to execute the program.

  As shown in FIG. 1, the oxygen sensor 2 includes a heater 22. The heater 22 is arranged to heat and activate the detection element unit 21 to an extent exceeding 500 ° C. When the ambient temperature of the detection element unit 21 increases, the impedance value Imp decreases. On the contrary, when the ambient temperature of the detection element unit 21 decreases, the impedance value Imp increases. Based on the correlation between the temperature and the impedance, the temperature of the detection element unit 21 can be confirmed from the impedance value. Therefore, the CPU 3 confirms the temperature of the detection element unit 21 from the impedance value calculated from the impedance calculation circuit 10 and uses it to determine the presence or absence of a crack. Therefore, in the abnormality detection apparatus 1, the impedance calculation circuit 10 functions as a temperature detection unit.

  The impedance calculation circuit 10 is connected to the detection element unit 21 of the oxygen sensor 2 and calculates an impedance value. The impedance calculation circuit 10 includes two switching elements (transistors) Tr1 and Tr2, a resistor R2, a capacitor C1, and a shunt resistor Rs for current measurement. When the internal impedance Imp of the detection element portion 21 is small, a large current flows. Conversely, when the internal impedance Imp is large, a small current flows. The internal impedance Imp can be calculated based on the voltage detected at both ends (N1 and N2) of the shunt resistor Rs. Specifically, when the impedance is measured, the CPU 3 applies the battery voltage Vp from the battery 26, turns on the switching element Tr1, turns off the switching element Tr2, and turns off the switching element Tr1 thereafter. (OFF), an operation to turn on the switching element Tr2 is performed. The internal impedance Imp is calculated based on the voltage change before and after this operation.

  In FIG. 2, when an ECU (electronic control unit) 7 for the oxygen sensor 2 is formed including the impedance calculation circuit 10, the electromotive force detection circuit 25, the CPU 3, the ROM 5, the RAM 6, and the like, The abnormality detection device 1 can be realized by a part of the ECU 7. In this case, a program for detecting an abnormality of the oxygen sensor 2 may be stored in the ROM 5 connected to the CPU 3. The impedance value calculated from the impedance calculation circuit 10 is used for temperature control in order to maintain the activity of the detection element unit 21. That is, in this case, the impedance value calculated from the impedance calculation circuit 10 is used for temperature control of the detection element unit 21 and determination of the presence or absence of cracks in the detection element unit 21.

  FIG. 3 shows a comparison of data obtained when a normal sensor and a sensor having a crack in the detection element portion are installed in the exhaust passage when the engine is stably driven in a low load state such as an idle state. FIG. However, since the gas pressure in the exhaust passage in the low load state is low, the atmosphere with the cracked (abnormal) sensor is being sucked out to the exhaust side. The upper part of FIG. 3 shows the output of the oxygen sensor, and the lower part shows the impedance value Imp of the detection element at this time. In addition, the horizontal axis indicates time (elapsed time).

  As can be seen from FIG. 3, in the state where the atmosphere is sucked out to the exhaust side, the exhaust gas does not enter the detection element portion, so that an output waveform close to a normal sensor is obtained even though there is a crack. However, when looking at the impedance value shown in the lower stage, the output waveform of the impedance value of the sensor having a crack is on the upper side of the output waveform of the normal sensor impedance value (hereinafter referred to as the reference impedance waveform). The reference impedance waveform reflects the temperature change of a normal sensor and can be regarded as reference temperature data. Further, since the impedance value and the time when the impedance value is output can be confirmed from the reference impedance waveform, the reference impedance waveform becomes reference temperature data including information on the temperature of the detection element unit 21 and the detection time.

  As is clear from the above description, an increase in the impedance value indicates that the temperature of the detection element unit is low. Further, in a sensor having a crack (having an abnormality), when the atmosphere on the atmosphere electrode side is sucked out to the exhaust side and cooled, the temperature rise degree becomes slow. If this is seen from an impedance value, it is that the fall degree of an impedance is slow. Therefore, the impedance value reflecting the temperature of the detection element portion can be used for determination of the occurrence of cracks by comparing with the reference impedance waveform. The abnormality detection apparatus 1 determines whether or not there is a crack in the detection element unit based on such a viewpoint.

  The CPU 3 of the abnormality detection device 1 uses the temperature detection data obtained in association with the calculation of the impedance value of the detection element portion temperature (temperature detection) and the crack of the crack using the reference impedance waveform (reference temperature data). Judgment is made. As temperature detection data, for example, data related to the impedance value (temperature) of the detection element unit 21, data related to the calculation (detection) time, and data related to the time required until the detection element unit reaches a predetermined impedance (temperature) are used. it can. When the CPU 3 receives an output signal from the impedance calculation circuit 10, data that can be acquired by checking the impedance value and the calculation time using an internal clock or the like is included in the temperature detection data here. May be. Next, a specific determination method performed by the CPU 3 will be described with reference to FIG.

  The first method by the CPU 3 compares the impedance value Imp calculated by the impedance calculation circuit 10 at a predetermined time T1 after heating the heater and the reference impedance value Simp at the same time T1 in the reference impedance waveform. Then, the CPU 3 determines that there is a crack when the impedance value Imp is not less than or equal to the reference impedance value Simp. A plurality of predetermined times T may be set so that the determination of the presence or absence of cracks can be performed more reliably. For example, ten predetermined times T1 to T10 may be set, and it may be determined that there is a crack when the impedance value Imp does not fall below the reference impedance value Simp at all these times. Here, the predetermined time T may be a predetermined time (for example, a predetermined time from the heater heating) without being associated with the impedance calculation time, or may be, for example, the N-th time calculation using the data related to the calculation time. Also good.

  Moreover, since the temperature rise rate tends to become slow in the detection element part with a crack, the temperature rise rate is low. From the viewpoint of the impedance value, this means that the change in the impedance value within a predetermined time is small in the detection element portion having a crack. Therefore, the second method uses the data relating to the impedance value and the data relating to the calculation time, as shown in FIG. 3, the rate of decrease in the impedance value between the predetermined time t1 and the predetermined time t2 (that is, the temperature rise). The CPU 3 determines whether or not there is a crack from the rate. The CPU 3 compares the impedance value difference ΔSimp between the predetermined time t1 and the predetermined time t2 with respect to the reference impedance waveform and the impedance value difference ΔImp obtained from the impedance value Imp calculated (output) by the impedance calculation circuit 10, If the impedance value difference ΔImp is smaller than the impedance value difference ΔSImp, it is determined that there is a crack.

  In the third method, the CPU 3 determines the presence or absence of a crack based on the length of time required to reach a predetermined temperature. In the third method, the time required to reach a predetermined impedance value PImp (that is, a predetermined temperature) after heating the heater is determined by an impedance value Imp calculated by the impedance calculation circuit 10 and a reference impedance value SImp obtained from the reference impedance waveform. Compare. The CPU 3 determines that there is a crack when the required time Ti of the impedance value Imp is longer than the reference required time Ts of the reference impedance value Simp. As described above, a sensor with a crack tends to have a slower temperature rise, so that such a method can also be used for determination. The abnormality detection apparatus 1 can determine whether or not there is a crack in the detection element portion using any of the above methods. A series of data relating to the reference impedance waveform is stored in the ROM 5, and is read out and used when the CPU 3 determines whether or not there is a 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. The temperature increase (that is, the impedance value decrease) of the detection element unit 21 is easily affected by the temperature change of the exhaust gas in contact with the heater 22 and the oxygen sensor disposed therein. Therefore, here, after “engine warm-up end”, “oxygen sensor warm-up end”, and “heater performance check end” as preconditions, there is a state where air is sucked out when there is a crack in the detection element section. An example in which the CPU 3 determines whether or not the detection element unit 21 is cracked is based on the assumption that the engine is easily idle.

  This routine is started, for example, when the engine is started, and the CPU 3 checks whether or not the precondition is satisfied (S101), and whether a predetermined time X1 (sec) or more has elapsed since the engine became idle. Is confirmed (S102). Thereafter, energization of the heater 22 is forcibly turned on (S103) and maintained for a predetermined time X2 (sec) (S104). The CPU 3 confirms that the conditions for determining the presence / absence of cracks have been met by confirming up to step 104.

  In the next step 105 (S105), the impedance value Imp calculated from the impedance calculation circuit 10 is compared with the reference impedance value SImp read from the ROM 5. If the calculated impedance value Imp is larger than the reference impedance value SImp, it can be determined that there is a crack because the temperature of the detection element portion is lower than in the normal state. Therefore, in this case, the CPU 3 determines that there is an abnormality in the oxygen sensor 2 (S106), and ends the processing by this routine. On the contrary, when the calculated impedance value Imp is equal to or lower than the reference impedance value SImp, it can be estimated that the temperature of the detection element unit is sufficiently increased. Therefore, the CPU 3 assumes that the oxygen sensor 2 is normal in this case (S107), and repeats the processing according to this flowchart.

  The determination of the presence / absence of cracks by the CPU 3 of the abnormality detection apparatus 1 executed as described above is based on the impedance value reflecting the temperature of the detection element unit 21, so that even if there is a crack, an oxygen sensor or detection that outputs in the same manner as normal Even if the oxygen sensor is not in an active state, the presence or absence of cracks can be determined. The flowchart shown in FIG. 4 is an example in which a technique (first technique) for determining the presence or absence of cracks based on the impedance value at a predetermined time is adopted. Even if the second method or the third method is adopted, the abnormality of the oxygen sensor 2 can be detected in the same manner. Further, the presence / absence of cracks may be determined with higher accuracy by combining the above three methods.

  Furthermore, the 4th method of judging the presence or absence of a crack using an impedance is demonstrated. This technique is an efficient technique when the CPU 3 also performs temperature control of the oxygen sensor 2 in order to maintain the activity of the detection element unit 21 using impedance. As described above, in order for the oxygen sensor 2 to function, it is necessary to maintain the detection element unit 21 at a predetermined temperature or higher. In order to maintain the temperature of the detection element unit 21, the CPU 3 performs control to increase the temperature by energizing the heater 22 when the temperature of the detection element unit 21 decreases. For example, a target impedance value MImp corresponding to the optimum temperature (temperature required for activation) of the detection element unit 21 is stored in the ROM 5 in advance, and the impedance value detected by the impedance calculation circuit 10 by the CPU 3 is compared with the target impedance value MImp. Then, the energization to the heater 22 is controlled to maintain the temperature of the detection element unit 21.

  More specifically, when the impedance value detected by the impedance calculation circuit 10 is larger than the target impedance value MImp, the CPU 3 energizes the heater 22 assuming that the temperature of the detection element unit 21 is low. On the contrary, when the detected impedance value is smaller than the target impedance value MImp, the CPU 3 interrupts the energization to the heater 22 on the assumption that the detection element portion 21 has sufficiently heated. Therefore, the state of the detection element unit 21 can be known by checking the degree of energization to the heater 22.

  FIG. 5 is a diagram comparing the temperature control by the CPU 3 with respect to a normal oxygen sensor having no crack in the detection element portion and an abnormal oxygen sensor having a crack in the detection element portion. (A) shows the normal oxygen sensor 2 with no cracks in the detection element portion 21, and (B) shows the abnormal oxygen sensor 2 with cracks in the detection element portion 21. In each figure, the impedance value changes on the upper side, and the heater on / off timings on the lower side.

  As can be confirmed from FIG. 5, the oxygen sensor 2 in which the crack is generated is unstable because the impedance waveform frequently moves up and down. In particular, the time during which the heater 22 is energized is long. That is, in FIG. 5, since the temperature of the detection element portion where the crack is generated is likely to decrease, and even if the heater is energized, it is difficult to increase the temperature. Therefore, the amount of power supplied to the heater is larger than that of a normal oxygen sensor. (The degree of energization increases). When the crack is generated in the detection element unit 21, the temperature is likely to decrease. Therefore, the CPU 3 increases the degree of energization to the heater in order to maintain the activation of the oxygen sensor. Therefore, when the detection element unit 21 is cracked, the energization amount (power supply amount) to the heater 22 within a certain time is increased as compared with a normal detection element unit.

  Therefore, for example, when the energization rate to the heater 22 is greater than or equal to a predetermined value within a predetermined time (monitoring time), it indicates that the degree of energization is high, so that it can be determined that a crack has occurred in the detection element unit 21. When heater control is performed using impedance, the ratio at which the detected impedance value is smaller than the target impedance value MImp corresponds to the energization rate. Therefore, in the fourth method, it can be determined that a crack has occurred in the detection element unit 21 when the integration time during which the impedance value detected within a predetermined time is less than the target impedance value MImp exceeds the reference time. Become.

  Specifically, the time when the impedance value detected by the impedance calculation circuit 10 by the CPU 3 is smaller than the target impedance value MImp is confirmed and integrated. When the accumulated time exceeds a predetermined time set in advance, it is determined that the detection element unit 21 has a crack. In the case of this method, the energization rate, energization time, and the like are included in the heater 22 that heats the detection element unit 21 as the above-described temperature detection data and reference temperature data. The reference time used for crack determination may be set in advance based on the energization rate and stored in the ROM 5.

  Furthermore, conditions and the like regarding the fourth method will be described with reference to FIG. FIG. 6 shows the relationship between the size of the cracks formed in the detection element section 21 (specified by the hole diameter here) and the energization rate and the effect when the oxygen sensor 2 is arranged in the exhaust passage of the engine with different load conditions. ing. It can be seen from FIG. 6 that the energization rate increases as the cracks increase. In addition, the current-carrying rate during continuous running at a low load (for example, 40 km / h) indicated by a white diamond is higher than that during continuous running (for example, 60 km / h) at a medium load indicated by a black square. It is relatively high. Since the exhaust gas temperature increases as the engine load increases, the detection element section is also heated. Therefore, it is difficult to confirm the cooling effect of the detection element portion due to the occurrence of cracks. That is, since it is easier to be affected by cooling due to the occurrence of cracks during low-load running, the presence or absence of cracks in the detection element unit 21 can be accurately determined. Therefore, it is desirable that the crack determination by the fourth method is executed after the sensor warm-up and the engine warm-up are completed, and when the engine is in a relatively low load operation state. For example, from FIG. 6, in the case of low-load running, if it is determined that there is a crack when the energization rate exceeds 70%, even a small crack with a diameter of about 0.1 mm can be detected. In addition, if the data of the electricity supply rate about the driving | running state where an engine is more than medium load is acquired beforehand by a test etc., a crack judgment can be performed also about a medium or high load state. In the above description, the case where the degree of energization is confirmed by the energization rate is described as an example. However, the degree of energization may be confirmed based on the amount of energization to the heater 22, The accumulated energization time may be used.

  Since the abnormality detection device of the present invention detects the temperature of the detection element unit and determines the presence or absence of cracks in the detection element unit in comparison with reference temperature data obtained when the normal detection element unit is heated, Even if there is a sensor that outputs the same as normal or a sensor in which the detection element unit is not activated, the abnormality can be detected. Further, since the abnormality detection device of the present invention determines the presence or absence of cracks based on the temperature change of the detection element portion, it can also make a determination even in the engine operating state where the lean state continues. In the above embodiment, the temperature is detected using the impedance value and the impedance calculation circuit is used as the temperature detecting means. However, the presence or absence of cracks in the detection element unit is detected using a sensor that directly measures the temperature of the detection element unit. You may make it judge. Moreover, although the said embodiment demonstrated the oxygen sensor which generates an electromotive force according to oxygen partial pressure as an example, not only this but a bias voltage is applied to a detection element part, and it is comprised so that oxygen concentration may be known from a limiting current The present invention can also be applied to an air-fuel ratio sensor (also referred to as a full-range air-fuel ratio sensor or a linear air-fuel ratio sensor).

  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. It is the figure which showed the electrical structural example corresponding to FIG. A comparison of data obtained when a normal sensor and a sensor with a crack in the detection element section are installed in the exhaust passage when the engine is driven stably in a low load state such as an idle state. FIG. 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. It is the figure which compared and showed the mode of temperature control by CPU about the normal oxygen sensor without a crack in a detection element part, and the abnormal oxygen sensor with a crack in a detection element part. It is the figure shown about the influence when the oxygen sensor is arrange | positioned to the relationship between the magnitude | size of the crack formed in the detection element part, and an electricity supply rate, and the exhaust passage of an engine from which load conditions differ. 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 figure (A).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Abnormality detection apparatus 2 Oxygen sensor 3 CPU (judgment means)
DESCRIPTION OF SYMBOLS 10 Impedance calculation circuit 21 Detection element part 22 Heater 25 Electromotive force detection circuit

Claims (8)

A detection element unit disposed between the first gas and the second gas and outputting a signal corresponding to an oxygen partial pressure of the first gas and the second gas, and heating the detection element unit An apparatus for detecting abnormality of a sensor provided with a heater for performing,
Temperature detection means for detecting the temperature of the detection element section;
Using temperature detection data obtained in connection with temperature detection by the temperature detection means and reference temperature data obtained when the normal detection element unit is heated, the presence or absence of abnormality of the detection element unit is determined. An abnormality detection device for a sensor, comprising: a determination unit. The detected temperature data and the reference temperature data include the temperature of the detection element unit detected by the temperature detection means,
The determination unit compares the temperature of the detection element unit at a predetermined time after heating the heater with the detected temperature data and the reference temperature data, and when the temperature based on the detected temperature data is lower, The sensor abnormality detection device according to claim 1, wherein it is determined that the detection element unit is abnormal. The detected temperature data and the reference temperature data include a temperature of the detection element unit detected by the temperature detection means and a detection time of the temperature,
The determination means obtains and compares the temperature increase rate per time from each of the detected temperature data and the reference temperature data, and when the temperature increase rate based on the detected temperature data is smaller, the detection element unit The sensor abnormality detection device according to claim 1, wherein it is determined that there is an abnormality in the sensor. The detected temperature data and the reference temperature data include data related to a time required until the detection element unit reaches a predetermined temperature,
The determination unit compares the required time with the detected temperature data and the reference temperature data, and determines that the detection element unit is abnormal when the required time based on the detected temperature data is longer. The sensor abnormality detection device according to claim 1. The detected temperature data and the reference temperature data include data relating to the degree of energization to the heater,
The determination unit compares the degree of energization under a predetermined condition with the detected temperature data and reference temperature data, and when the degree of energization based on the detected temperature data is greater, the detection element unit is abnormal. The sensor abnormality detection device according to claim 1, wherein the determination is performed. The temperature detection means includes an impedance calculation circuit that is connected to the detection element unit and calculates an impedance value of the detection element unit,
6. The sensor abnormality detection device according to claim 1, wherein the determination unit performs the determination using an impedance value calculated by the impedance calculation circuit. A detection element unit disposed between the first gas and the second gas and outputting a signal corresponding to an oxygen partial pressure of the first gas and the second gas, and heating the detection element unit A method of detecting an abnormality of a sensor provided with a heater for performing,
When the temperature of the detection element unit is detected and compared with reference temperature data obtained when the normal detection element unit is heated, the temperature increase degree is slower than the temperature increase degree by the reference temperature data A method for detecting an abnormality of a sensor, comprising: determining that the detection element unit is abnormal. The sensor abnormality detection method according to claim 7, wherein the temperature detection unit detects the temperature using an impedance value of the detection element unit.

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