JP2010190789A - Failure diagnosis device for oxygen sensor - Google Patents

Abstract

A diagnostic accuracy is improved by preventing erroneous determination.
A failure of an oxygen sensor having a detection element (31) arranged in an exhaust passage of an internal combustion engine and having an exhaust electrode (39) facing the exhaust passage and an atmospheric electrode (38) facing an atmospheric chamber inside the detection element. In the diagnostic apparatus, a voltage detection means 40 for detecting the output voltage of the oxygen sensor, a failure determination means for determining that the oxygen sensor is faulty when a negative output voltage is detected by the voltage detection means, an exhaust electrode, an atmospheric electrode, and a voltage There are provided switch means 41 and 42 for switching the connection state with the detection means, and a switch means for setting the connection state to suppress at least the supply of electrons to the atmospheric electrode when the oxygen sensor is inactive.
[Selection] Figure 8

Description

  The present invention relates to an oxygen sensor failure diagnosis device, and more particularly to an oxygen sensor failure diagnosis device that is provided in an exhaust passage of an internal combustion engine and generates an electromotive force according to the oxygen concentration of exhaust gas.

  For air-fuel ratio feedback control and the like, an oxygen sensor that detects the air-fuel ratio based on the oxygen concentration of the exhaust gas is provided in the exhaust passage of the internal combustion engine. The oxygen sensor includes a cylindrical detection element disposed in the exhaust passage, and the detection element is formed of a solid electrolyte having electrodes formed on the inner and outer surfaces. The electrode on the outer surface side is the exhaust electrode facing the exhaust passage, and the electrode on the inner surface side is the atmosphere electrode facing the atmospheric chamber inside the detection element. The oxygen sensor generates an electromotive force according to the difference in oxygen partial pressure of the atmospheric gas of these electrodes. Specifically, the oxygen concentration of the exhaust gas decreases (that is, the air-fuel ratio of the exhaust gas becomes rich). Generates a large electromotive force.

  In this oxygen sensor, when the sensing element is lost and the inside and outside of the sensing element communicate with each other, exhaust gas outside the sensing element enters the inside, and there is no difference in the oxygen partial pressure between the inside and outside, and the sensor generates an electromotive force. No longer. Further, if exhaust gas having a high oxygen concentration (air-fuel ratio lean) is present outside the detection element in a state where the exhaust gas has entered the detection element, an electromotive force in the reverse direction is generated in the oxygen sensor. Accordingly, by detecting the negative (minus) output voltage of the oxygen sensor corresponding to the back electromotive force, it is possible to detect a defect in the detection element of the oxygen sensor, that is, a failure of the oxygen sensor (see, for example, Patent Document 1). ).

JP 2008-121463 A

  By the way, even if the oxygen sensor is not defective as described above and is normal, if the exhaust electrode is poisoned by rich components in the exhaust gas, a negative output voltage may be generated from the oxygen sensor. . Therefore, even in this case, it is erroneously determined that the oxygen sensor has failed, resulting in a decrease in the accuracy of failure diagnosis.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide an oxygen sensor failure diagnosis apparatus that can prevent erroneous determination and improve diagnosis accuracy.

According to one aspect of the invention,
Oxygen having a detection element disposed in an exhaust passage of an internal combustion engine, the detection element having an exhaust electrode facing the exhaust passage and an atmospheric electrode facing an atmospheric chamber inside the detection element In the sensor fault diagnosis device,
Voltage detection means for detecting an output voltage of the oxygen sensor;
Failure determination means for determining that the oxygen sensor is failed when a negative output voltage is detected by the voltage detection means;
Switch means for switching a connection state between the exhaust electrode and the atmosphere electrode and the voltage detection means, and is in a connection state that suppresses at least supply of electrons to the atmosphere electrode when the oxygen sensor is inactive. Switch means;
An oxygen sensor failure diagnosis apparatus is provided.

  According to the present invention, an excellent effect of preventing erroneous determination and improving diagnosis accuracy is exhibited.

It is a figure which shows the exhaust-gas purification system of the internal combustion engine which concerns on this embodiment. It is a fragmentary sectional view which shows the attachment state of an oxygen sensor. It is an expanded sectional view of the detection element periphery of an oxygen sensor. It is a graph which shows the output characteristic of an oxygen sensor. It is an expanded sectional view when a defective part arises in a detection element of an oxygen sensor. It is a graph which shows the change of the output voltage at the time of failure of an oxygen sensor. It is a graph which shows the change of the output voltage in the warming-up process of a normal oxygen sensor. It is the schematic which shows a switch means. It is the schematic which shows the other connection state of a switch means. It is the schematic which shows the modification of a switch means. It is the schematic which shows the further modification of a switch means. It is a flowchart of a failure diagnosis process.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The configuration of an exhaust gas purification system for a vehicle internal combustion engine to which the present invention is applied will be described with reference to FIG. The intake passage 11 of the internal combustion engine 10 is provided with a throttle valve 15 (in this embodiment, electronically controlled) for adjusting the passage area, and the amount of air taken in through the air cleaner 14 is adjusted by opening degree control. . The amount of air sucked here (intake air amount) is detected by the air flow meter 16. The air sucked into the intake passage 11 is mixed with fuel injected from an injector 17 provided downstream of the throttle valve 15 and then sent to the combustion chamber 12 where it is burned.

  On the other hand, a three-way catalyst 18 for purifying harmful components in the exhaust gas is provided in the exhaust passage 13 through which the exhaust gas generated by the combustion in the combustion chamber 12 is sent. A post-catalyst oxygen sensor 20 is provided on each downstream side.

  The three-way catalyst 18 efficiently purifies all the main harmful components (HC, CO, NOx) in the exhaust gas only when the air-fuel ratio of the air-fuel mixture to be burned is in a narrow range (window) near the theoretical air-fuel ratio. . In order for such a three-way catalyst 18 to function effectively, it is necessary to strictly control the air-fuel ratio of the air-fuel mixture to match the center of the window.

  Such air-fuel ratio control is performed by an electronic control unit (hereinafter referred to as “ECU”) 22. The ECU 22 includes the air flow meter 16, the oxygen sensors 19, 20 or the accelerator sensor 21 for detecting the depression amount of the accelerator pedal, the NE sensor 23 for detecting the engine speed, and the outside air temperature sensor 24 for detecting the outside air temperature. Detection signals from various sensors are input. The throttle valve 15 and the injector 17 are driven and controlled in accordance with the operating conditions of the internal combustion engine 10 and the vehicle ascertained from the detection signals of the sensors, thereby controlling the air-fuel ratio as described above.

  First, the ECU 22 obtains the required amount of intake air that is grasped according to the depression amount of the accelerator pedal and the detection result of the engine speed, and sets the opening of the throttle valve 15 so that the intake air amount corresponding to the required amount can be obtained. adjust. On the other hand, an amount of fuel sufficient to obtain the stoichiometric air-fuel ratio is obtained from the actually measured value of the intake air amount detected by the air flow meter 16, thereby adjusting the fuel injection amount from the injector 17. Thereby, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 12 can be brought close to the stoichiometric air-fuel ratio to some extent. However, that alone is not sufficient for the required highly accurate air-fuel ratio control.

  Accordingly, the ECU 22 feedback corrects the fuel injection amount from the injector 17 based on the actual value of the air-fuel ratio grasped from the detection results of the oxygen sensors 19 and 20, and ensures the required accuracy of the air-fuel ratio control. ing.

  As described above, in this exhaust gas purification system, the so-called air-fuel ratio feedback control that performs feedback correction of the fuel injection amount according to the detection results of the oxygen sensors 19 and 20 is performed, so that the air-fuel ratio of the air-fuel mixture is reduced to the theoretical air-fuel ratio. A high exhaust gas purification rate is secured by maintaining the fuel ratio in the vicinity. In this exhaust gas purification system, the air-fuel ratio feedback control is performed by the two oxygen sensors 19 and 20 as described above, thereby further improving the accuracy of the air-fuel ratio feedback control.

  The two oxygen sensors 19 and 20 have the same configuration, and the failure diagnosis method is also the same. Therefore, the pre-catalyst oxygen sensor 19 will be described below as an example (hereinafter, the pre-catalyst oxygen sensor 19 is simply referred to as “oxygen sensor 19”), and the description of the post-catalyst oxygen sensor 20 will be omitted.

  As shown in FIGS. 2 and 3, the oxygen sensor 19 includes a cylindrical detection element 31 arranged so as to protrude into the exhaust passage 13. The detection element 31 defines an atmospheric chamber 34 inside thereof. The atmospheric chamber 34 communicates with the outside through an atmospheric passage (not shown) provided in the sensor and an atmospheric hole 35 formed in the sensor body, so that the atmosphere (air) can be led out. The outer surface portion of the detection element 31 is exposed in the exhaust passage 13 and exposed to exhaust gas flowing in through the sensor cover 32.

  As shown in FIG. 3, the detection element 31 includes a solid electrolyte 37, an atmospheric electrode 38 that is formed on the inner surface of the solid electrolyte 37 and faces the atmospheric chamber 34, and an outer surface of the solid electrolyte 37. And an exhaust electrode 39 as the other electrode facing the exhaust passage 13. The solid electrolyte 37 is a solid substance that can move inside the oxygen ionized state. For example, zirconia is used as an oxygen sensor. The atmospheric electrode 38 and the exhaust electrode 39 contain, for example, platinum Pt.

  The atmospheric chamber 34 is provided with a heater 36 for heating the detection element 31 and activating it early, and the heater 36 is energized and controlled by the ECU 22. The atmospheric electrode 38 and the exhaust electrode 39 are connected to the ECU 22, particularly a voltage detection circuit thereof, so that the electromotive force generated between the atmospheric electrode 38 and the exhaust electrode 39 can be detected by the ECU 22.

  When a difference in oxygen partial pressure occurs between the atmosphere gas (usually air) at the atmosphere electrode 38 and the atmosphere gas (usually exhaust gas) at the exhaust electrode 39, the oxygen partial pressure is reduced in order to reduce the difference in the partial pressure. The oxygen on the higher side (usually the atmosphere electrode 38 side) is ionized, passes through the solid electrolyte 37, and moves to the side having the lower oxygen partial pressure (usually the exhaust electrode 39 side). Oxygen molecules receive tetravalent electrons in the process of ionization, and emit tetravalent electrons in the process of returning from the ionized state to the molecule. Therefore, movement of electrons occurs between the electrodes 38 and 39 in accordance with the movement of oxygen, and as a result, an electromotive force is generated between the electrodes 38 and 39.

  Thus, the oxygen sensor 19 generates an electromotive force according to the difference in oxygen partial pressure between the atmosphere and the exhaust gas. More specifically, as the oxygen concentration of the exhaust gas decreases (that is, the exhaust gas outside the detection element 31). Larger electromotive force is generated (the richer the air-fuel ratio). Here, since oxygen ions are directed from the inner atmospheric electrode 38 to the outer exhaust electrode 39, the direction of the current is reversed, and the inner atmospheric electrode 38 is the positive electrode and the outer exhaust gas for the ECU 22 connected to both electrodes. The pole 39 becomes the negative electrode.

  Incidentally, there are various types of oxygen sensors such as those using a plate-shaped detection element and those using a material other than zirconia for the detection element. In many cases, a configuration for detecting the oxygen partial pressure of the exhaust gas based on the same detection principle as that of the above-described sensor, that is, a detection element arranged to isolate the reference gas (atmosphere) and the exhaust gas is a reference gas. The electromotive force is generated in accordance with the difference in oxygen partial pressure of the exhaust gas with respect to the exhaust gas.

  The output characteristics of the oxygen sensor 19 are illustrated in FIG. As shown, the output voltage of the oxygen sensor 19 changes transiently with a theoretical air / fuel ratio A / Fs (for example, 14.6) as a boundary, and the air / fuel ratio A / F of the exhaust gas supplied to the oxygen sensor 19 is theoretically changed. A region leaner than the air-fuel ratio A / Fs (A / F> A / Fs, hereinafter also referred to as a lean air-fuel ratio) shows a voltage as small as about 0.1 V, and a region richer than the stoichiometric air-fuel ratio A / Fs (A / F <A / Fs (hereinafter also referred to as a rich air-fuel ratio) indicates a relatively high voltage of about 0.9V. Here, the sensor output of 0.45 V is used as a rich / lean determination threshold value to determine whether the detection result of the sensor 19 is richer or leaner than the stoichiometric air-fuel ratio. Note that the magnitude of the sensor output voltage in each region of the oxygen sensor 19 may vary depending on the temperature state of the detection element 31.

  Note that, as in the present embodiment, in an internal combustion engine that performs air-fuel ratio control only for combustion at stoichiometric air-fuel ratio (stoichiometric combustion), oxygen having characteristics in which the output voltage changes transiently with the stoichiometric air-fuel ratio as a boundary. Sensors are often used. Although these sensors have a relatively low resolution, they are often sufficient to perform only the stoichiometric combustion. On the other hand, in an internal combustion engine that performs combustion at a wider range of air-fuel ratio, such as combustion at a lean air-fuel ratio, the output voltage varies linearly with the air-fuel ratio of exhaust gas, and the resolution is higher. An oxygen sensor may be used. The present invention is also applicable to such an oxygen sensor.

  By the way, due to aged deterioration due to long-term use or the like, the detection element 31 of the oxygen sensor 19 may be cracked or the detection element 31 may be broken, and the oxygen sensor 19 may break down. In the case of a sensor failure due to this defect, as shown in FIG. 5, the inside and outside of the detection element 31 communicate with each other through the defect part A of the detection element 31, and exhaust gas outside the detection element 31 enters the inside. If exhaust gas having a high oxygen concentration (air-fuel ratio lean) exists outside the detection element 31 with the exhaust gas entering the detection element 31, an electromotive force in the reverse direction is generated in the oxygen sensor 19. This may occur, for example, when the air-fuel ratio is switched from rich to lean in a sensor failure state, or when fuel cut is performed. In this case, the potential of the exhaust electrode 39 is higher than the potential of the atmospheric electrode 38, and a negative (minus) electromotive force or output voltage is generated.

  FIG. 6 shows an example of a change in the oxygen sensor output voltage at the time of such a failure. As shown in the circled area, the oxygen sensor 19 often outputs a negative voltage. Therefore, by detecting such a negative output voltage by the ECU 22, it is possible to detect a failure of the oxygen sensor.

  However, as described above, even when the oxygen sensor 19 is not defective and is normal, the exhaust electrode 39 is covered by rich components (specifically, hydrocarbon HC, carbon monoxide CO, etc.) in the exhaust gas. When poisoned (hereinafter referred to as rich poisoning), a negative output voltage may be generated from the oxygen sensor 19. Therefore, in this case as well, it is erroneously determined that the oxygen sensor 19 has failed, resulting in a decrease in the accuracy of failure diagnosis.

  For example, within a predetermined time after the engine is started, the fuel injection amount may be increased more than the theoretical air-fuel ratio and the air-fuel ratio may be controlled to the rich side in order to stabilize the rotation and promote warm-up.

  When such fuel increase control is performed when the oxygen sensor 19 (especially the exhaust electrode 39) is inactive, the exhaust electrode 39 is exposed to rich exhaust gas, and the exhaust electrode 39 is richly poisoned.

  Then, the oxygen ions that have moved from the atmospheric electrode 38 through the solid electrolyte 37 to the exhaust electrode 39 cannot be sufficiently molecularized (that is, electrons are released), and the oxygen ions concentrate on the exhaust electrode 39.

  Thereafter, when the oxygen sensor 19 is activated, the molecularization of oxygen ions concentrated on the exhaust electrode 39 proceeds rapidly, and lean gas based on fuel cut or the like may reach the exhaust electrode 39. A large amount of oxygen is present on the electrode 39, and as a result, the difference in oxygen concentration between the exhaust electrode 39 and the atmospheric electrode 38 is reversed, and a negative output voltage is generated.

  If the concentration of oxygen ions at the exhaust electrode 39 is eliminated for a while, the generation of negative voltage is eliminated.

  In FIG. 7, a change in the oxygen sensor output voltage when the fuel increase control is performed in the normal warm-up process of the oxygen sensor is shown by a solid line. In the figure, the change in the impedance of the detection element of the oxygen sensor (hereinafter also referred to as “element impedance”) is indicated by a broken line. The element impedance is a value that correlates with the temperature of the detection element (hereinafter, also referred to as “element temperature”). As can be seen from the figure, the element temperature gradually increases, and the oxygen sensor gradually changes from the inactive state to the active state.

  As shown in the broken-line circle in the figure, there is a time zone in which the oxygen sensor output voltage is negative. This is because the exhaust electrode 39 is richly poisoned before the sensor is activated, and the effect is after the sensor is activated. This is because it has appeared.

  Therefore, in the present embodiment, a switch for switching the connection state between the exhaust electrode 39 and the atmospheric electrode 37 and the ECU 22 in order to prevent the generation and detection of the negative voltage due to the rich poisoning and the erroneous determination based on the negative voltage. Means are provided. This will be described below.

  FIG. 8 simply shows the detection element 31 and the ECU 22. The ECU 22 includes a voltage detection circuit 40 as voltage detection means for detecting an output voltage from the detection element 31 of the oxygen sensor 19, an atmospheric electrode switch 41 for switching the connection state between the voltage detection circuit 40 and the atmospheric electrode 38, and a voltage detection circuit. 40 and an exhaust electrode switch 42 for switching the connection state of the exhaust electrode 39 and the exhaust electrode 39. The atmospheric electrode switch 41 and the exhaust electrode switch 42 constitute the switch means.

  When the oxygen sensor 19 is inactive, the ECU 22 switches both the atmospheric electrode switch 41 and the exhaust electrode switch 42 to the open side as shown in the figure. Then, even if the fuel increase control is performed at this time, even if the exhaust electrode 39 is richly poisoned, the concentration of oxygen ions at the exhaust electrode 39 is greatly suppressed by the following principle, and the generation of negative voltage due to rich poisoning is substantially reduced. Is prevented.

That is, in the atmospheric electrode 38, the oxygen O ₂ is ionized by receiving free electrons from the atmospheric electrode 38. The oxygen ions O ²⁻ move inside the solid electrolyte 37 and reach the exhaust electrode 39. When the exhaust electrode 39 is richly poisoned and lacks activity, the oxygen ions O ²⁻ Cannot be released sufficiently.

However, since the atmospheric electrode switch 41 is switched to the open side and the atmospheric electrode 38 is opened, oxygen O ₂ is ionized only in an amount corresponding to the number of electrons of the atmospheric electrode 38 in the atmospheric electrode 38. Here, if the atmospheric electrode 38 is connected to the voltage detection circuit 40 or the ground, electrons necessary for ionization are successively supplied to the atmospheric electrode 38 and a large amount of oxygen O ₂ is ionized. Therefore, in such an open state, supply of electrons to the atmospheric electrode 38 is cut off, and ionization of oxygen O ₂ at the atmospheric electrode 38 is greatly suppressed. Since only a small amount of oxygen ion O ²⁻ formed in this way moves to the exhaust electrode 39, the concentration of oxygen ions at the exhaust electrode 39 is greatly suppressed. Even if the oxygen sensor 19 is activated later, since the amount of oxygen at the exhaust electrode 39 is small, the exhaust electrode 39 does not have an oxygen concentration higher than that of the atmospheric electrode 38, thereby preventing the generation of a negative voltage.

  As described above, according to the present embodiment, generation and detection of a negative voltage due to rich poisoning of the exhaust electrode 39 can be prevented, erroneous determination can be prevented, and diagnostic accuracy can be improved.

  The ECU 22 switches the atmospheric electrode switch 41 and the exhaust electrode switch 42 to the connection side after the oxygen sensor 19 is activated. As a result, the exhaust electrode 39 and the atmospheric electrode 37 and the voltage detection circuit 40 are connected as usual, and the ECU 22 can execute the fault diagnosis based on the output voltage detection of the oxygen sensor 19 and the negative voltage.

FIG. 9 shows another connection state. In this example, when the oxygen sensor 19 is inactive, the ECU 22 switches only the atmospheric electrode switch 41 to the open side and keeps the exhaust electrode switch 42 on the connection side. This also cuts off the supply of electrons to the atmospheric electrode 38 and greatly suppresses the ionization of oxygen O ₂ at the atmospheric electrode 38. Then, the movement of oxygen ions O ^{2− to} the exhaust electrode 39, the concentration of oxygen ions at the exhaust electrode 39, and the generation of a negative voltage can be prevented.

  FIG. 10 shows a modification of the switch means. In this example, the exhaust electrode switch 42A can be switched between a connection side for connecting the exhaust electrode 39 to the voltage detection circuit 40 and a ground side for connecting the exhaust electrode 39 to the ground GND as shown in the figure. Other points are the same as above.

In this case as well, since the atmospheric electrode 38 is opened, the supply of electrons to the atmospheric electrode 38 is cut off, and the ionization of oxygen O ₂ at the atmospheric electrode 38 is greatly suppressed. Then, the movement of oxygen ions O ^{2− to} the exhaust electrode 39, the concentration of oxygen ions at the exhaust electrode 39, and the generation of a negative voltage can be prevented. Further, when the exhaust electrode 39 is connected to the ground GND, surplus electrons on the exhaust electrode 39 escape to the ground GND, and the oxygen ions O ²⁻ that have reached the exhaust electrode 39 are gradually molecularized. Oxygen ion concentration at 39 can be further prevented.

  FIG. 11 shows a further modification of the switch means. In this example, the atmospheric electrode switch 41B can be switched between a connection side that connects the atmospheric electrode 38 to the voltage detection circuit 40 and a short circuit side that connects the atmospheric electrode 38 to the short-circuit line 43 as shown. Further, the exhaust electrode switch 42B can be switched between a connection side for connecting the exhaust electrode 39 to the voltage detection circuit 40 and a short circuit side for connecting the exhaust electrode 39 to the short-circuit line 43 as shown. Other points are the same as above.

As shown in the figure, when the atmospheric electrode switch 41B and the exhaust electrode switch 42B are switched to the short circuit side and the atmospheric electrode 38 and the exhaust electrode 39 are short-circuited, only an amount corresponding to the number of electrons of the atmospheric electrode 38 and the exhaust electrode 39 is obtained. Oxygen O ₂ is not ionized. Therefore, as described above, the supply of electrons to the atmospheric electrode 38 is greatly suppressed, and the ionization of oxygen O ₂ at the atmospheric electrode 38 is greatly suppressed. Then, the movement of oxygen ions O ^{2− to} the exhaust electrode 39, the concentration of oxygen ions at the exhaust electrode 39, and the generation of a negative voltage can be prevented.

  Next, the failure diagnosis process of this embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 22 every predetermined calculation cycle (for example, 16 msec).

  First, in step S101, it is determined whether or not the engine has been started. When the engine is not started, the routine is ended. When the engine is started, the process proceeds to step S102.

  In step S102, it is determined whether or not the oxygen sensor 19 is in an inactive state. That is, the ECU 22 constantly detects the element impedance R of the oxygen sensor 19, and when the element impedance R is larger than a predetermined value Rs corresponding to the minimum activation temperature (for example, 300 ° C.) of the oxygen sensor 19, It is determined that the sensor 19 is inactive. On the other hand, the ECU 22 determines that the oxygen sensor 19 is in an active state when the element impedance Rs is equal to or less than the predetermined value Rs.

  If it is determined that the oxygen sensor 19 is in an inactive state, the process proceeds to step S103, where the atmospheric electrode switch 41 (41B) and the exhaust electrode switch 42 (42A, 42B) are in the state as shown in FIGS. Can be switched to. That is, in the configuration of FIGS. 8 and 9, the atmospheric electrode switch 41 is switched to the open side, and the exhaust electrode switch 42 is switched to either the open side or the connection side. In the configuration of FIG. 10, the atmospheric electrode switch 41 is switched to the open side, and the exhaust electrode switch 42 is switched to the ground side. In the configuration of FIG. 11, both the atmospheric electrode switch 41 and the exhaust electrode switch 42 are switched to the short-circuit side. As a result, it is possible to prevent oxygen ions from concentrating on the exhaust electrode 39 before activation of the sensor, and thus negative voltage generation after activation of the sensor. This is the end of the routine.

  On the other hand, when it is determined in step S102 that the oxygen sensor 19 is in the active state, the process proceeds to step S104, and both the atmospheric electrode switch 41 (41B) and the exhaust electrode switch 42 (42A, 42B) are switched to the connection side. . As a result, the exhaust electrode 39 and the atmospheric electrode 37 and the voltage detection circuit 40 are connected as usual, and the failure diagnosis based on the output voltage detection and the negative voltage becomes possible.

  Next, in step S105, it is determined whether or not a precondition for executing the failure diagnosis is satisfied. When this precondition is satisfied, for example, when engine warm-up has been completed to some extent, specifically, the engine coolant temperature detected by a water temperature sensor (not shown) is a predetermined temperature (for example, 40 ° C). However, this precondition can be set arbitrarily.

If the precondition is not satisfied, the routine is terminated. On the other hand, when the precondition is satisfied, the process proceeds to step S106, and it is determined whether or not a negative output voltage from the oxygen sensor 19 is detected.
If a negative output voltage is detected, the process proceeds to step S107, and it is determined that the oxygen sensor 19 is faulty or abnormal. That is, it is determined that a defect such as a crack or a crack has occurred in the detection element 31 of the oxygen sensor 19. This terminates the routine.

  On the other hand, if a negative output voltage is not detected, the sensor is not immediately normal, and in order to improve accuracy, in step S108, it is determined whether or not a condition for normal determination (normal determination condition) is satisfied. The The normal determination condition is a condition in which a negative voltage is always generated when the oxygen sensor 19 is defective, and is, for example, a fuel cut immediately after an operation with a large intake air amount Ga. When the intake air amount Ga is small, the exhaust gas flow rate is also small, and there is a possibility that the exhaust gas does not sufficiently flow into the atmospheric chamber 34 from the defect portion A of the detection element 31. In addition, the exhaust gas sufficiently flows into the atmospheric chamber 34 This is because when the fuel is cut, the outer side of the detection element 31 has a higher oxygen partial pressure than the inner side and a negative voltage is generated.

  If it is determined that the normal determination condition is not satisfied, the routine is terminated without being determined normal. On the other hand, if it is determined that the normal determination condition is satisfied, the oxygen sensor 19 is determined to be normal in step S109, and the routine is terminated.

  As mentioned above, although embodiment of this invention was described in detail, this invention can also take other embodiment. For example, the use, type, type, and the like of the internal combustion engine are not limited, and the internal combustion engine may be other than for a vehicle, a diesel engine, or the like.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 13 Exhaust passage 19, 20 Oxygen sensor 22 Electronic control unit (ECU)
31 detection element 34 atmosphere chamber 38 atmosphere electrode 39 exhaust electrode 40 voltage detection circuit 41, 41B air electrode switch 42, 42A, 42B exhaust electrode switch

Claims (1)

Oxygen having a detection element disposed in an exhaust passage of an internal combustion engine, the detection element having an exhaust electrode facing the exhaust passage and an atmospheric electrode facing an atmospheric chamber inside the detection element In the sensor fault diagnosis device,
Voltage detection means for detecting an output voltage of the oxygen sensor;
Failure determination means for determining that the oxygen sensor is failed when a negative output voltage is detected by the voltage detection means;
Switch means for switching a connection state between the exhaust electrode and the atmosphere electrode and the voltage detection means, and a connection state that suppresses at least supply of electrons to the atmosphere electrode when the oxygen sensor is inactive. Switch means;
An oxygen sensor failure diagnosis apparatus comprising:

Images