JP5618092B2 - Failure determination device for air-fuel ratio detection device - Google Patents

Description

  The present invention relates to a failure determination technique for an air-fuel ratio detection device arranged downstream of a catalyst provided in an exhaust system of an internal combustion engine.

In order to purify exhaust, an exhaust system of an engine (internal combustion engine) is usually provided with a catalyst such as a three-way catalyst or a NOx storage catalyst. Some of these catalysts are provided with an air-fuel ratio detection device for detecting an air-fuel ratio, such as an oxygen concentration sensor, in order to perform air-fuel ratio control downstream of the catalyst.
A technique for switching the fuel injection mode of an internal combustion engine according to a load or the like is also known. The fuel injection mode is, for example, a normal operation mode in which operation is performed in a stoichiometric or lean state while feeding back the air-fuel ratio of exhaust gas, an enrichment operation mode in which the air-fuel ratio is open-loop controlled to be enriched when the load is heavy, etc. There is a fuel cut mode in which fuel injection is stopped when there is no load such as time.

In order to determine the failure of the air-fuel ratio detection device provided downstream of the catalyst, the air-fuel ratio detection device detects that the exhaust gas is rich after a predetermined time has elapsed since the start of the fuel cut mode (start of fuel cut). In such a case, a technique for determining that the air-fuel ratio detection device is malfunctioning is disclosed (Patent Document 1).
Further, when performing the failure determination of the air-fuel ratio detection device on the downstream side of the catalyst in this way, if the rich operation is continued in the enrich operation mode before the fuel cut, hydrocarbons and carbon monoxide in the exhaust increase, and these When the fuel cut is started with a large amount of the components adsorbed on the catalyst, the exhaust gas flowing out from the catalyst becomes rich until the hydrocarbons and carbon monoxide adsorbed on the catalyst are oxidized, and the exhaust gas is exhausted over a predetermined time. There is a possibility that it is erroneously determined that the air-fuel ratio detection device has failed by detecting that the fuel-fuel ratio detection device is rich.

  On the other hand, Patent Document 1 proposes a technique for changing a predetermined time from the start of the fuel cut mode, that is, a threshold for failure determination, based on the duration of the open loop operation before the fuel cut.

Japanese Patent No. 40642765

  However, in Patent Document 1, since the failure determination condition is changed based on the duration of the open loop operation before the fuel cut, depending on the state of the open loop operation before the fuel cut, even if the duration is the same The amounts of hydrocarbons and carbon monoxide adsorbed on the catalyst are different, and a failure determination threshold value cannot be set accurately, making it difficult to perform failure determination with high accuracy.

  An object of the present invention is to provide a failure determination apparatus capable of accurately grasping the influence of hydrocarbons and carbon monoxide adsorbed on a catalyst during open-loop operation and performing highly accurate failure determination. .

In order to achieve the above object, a failure determination device for an air-fuel ratio detection device according to claim 1 is a failure determination device for an air-fuel ratio detection device disposed downstream of a catalyst provided in an exhaust system of an internal combustion engine, Determining failure of the air-fuel ratio detection device based on the time required for the air-fuel ratio of the exhaust gas detected by the air-fuel ratio detection device after the fuel supply to stop to change within a predetermined range after stopping the fuel supply Failure determination means for performing the operation, intake air amount integration means for integrating the intake air amount of the internal combustion engine in the first operation mode in which the air-fuel ratio is made rich before the fuel supply is stopped, and intake air amount integration means A failure determination limiting means for limiting failure determination of the air-fuel ratio detection device by the failure determination means when the integrated value exceeds a predetermined value based on the integrated value of the intake air amount calculated by Features.

According to a second aspect of the present invention, there is provided a failure determination device for an air-fuel ratio detection device according to the first aspect, wherein the intake air amount integrating means operates in a stoichiometric or lean state of the air-fuel ratio before stopping the fuel supply. The intake air amount of the internal combustion engine in at least one of the third operation modes in which the fuel supply is stopped is subtracted from the integrated value of the intake air amount in the first operation mode, and the intake in the first operation mode is subtracted. In the subtraction from the integrated value of the air amount, the subtraction value of the intake air amount of the internal combustion engine in the third operation mode is made larger than the subtraction value of the intake air amount of the internal combustion engine in the second operation mode, so The limiting means prohibits the failure determination of the air-fuel ratio detection device when the integrated value of the intake air amount exceeds a predetermined value , and cancels the prohibition of the failure determination when the integrated value decreases to zero or less. With features That.
According to a third aspect of the present invention, there is provided the failure determination device according to the first aspect, wherein the failure determination limiting means is based on the integrated value of the intake air amount calculated by the intake air amount integration means. It is characterized in that the threshold value for failure determination of the air-fuel ratio detection device is changed.

Also, the failure determination device for an air-fuel ratio detecting device according to claim 4, in any one of claims 1 to 3, failure determining means is empty from the stop of the fuel supply of the detected exhaust gas by the air-fuel ratio detecting device The failure determination of the air-fuel ratio detection device is performed based on the time required until the fuel ratio reaches a predetermined air-fuel ratio.

According to the failure determination device for an air-fuel ratio detection apparatus of claim 1 of the present invention , for example, the required time is determined based on the required time for the air-fuel ratio of the exhaust gas after the fuel supply is stopped to change within a predetermined range by the failure determination means. By exceeding the predetermined time, it is considered that the decrease in the air-fuel ratio in the predetermined range due to the stop of fuel supply has not been accurately detected, and it is possible to determine that the air-fuel ratio detection device is malfunctioning.
Further, the intake air amount of the internal combustion engine in the first operation mode in which the air-fuel ratio is operated in a rich state before the fuel supply is stopped is integrated , and the integrated value exceeds a predetermined value based on the integrated value. In this case, failure determination is limited, so that erroneous determination of failure of the air-fuel ratio detection device in failure determination means due to the fact that a large amount of hydrocarbons or carbon monoxide is adsorbed to the catalyst when the fuel supply is stopped is avoided. It becomes possible to do.

  In particular, the intake air amount integrating means integrates the intake air amount of the internal combustion engine during the rich state operation before stopping the fuel supply, thereby adsorbing hydrocarbons and carbon monoxide on the catalyst when the fuel supply is stopped. By estimating the amount, it is possible to accurately grasp the influence at the time of failure determination. As a result, failure determination can be accurately restricted, and highly accurate failure determination can be performed.

According to the failure determination device for the air-fuel ratio detection apparatus of the second aspect of the present invention, the second operation mode in which the air-fuel ratio is operated in the stoichiometric or lean state before the fuel supply is stopped, and the third fuel supply is stopped. The intake air amount of the internal combustion engine in the operation mode is subtracted from the integrated value of the intake air amount in the first operation mode, and the subtraction value of the intake air amount of the internal combustion engine in the third operation mode is the second operation. Since it is larger than the subtraction value of the intake air amount of the internal combustion engine in the mode, the fuel supply is stopped reflecting the decrease in the adsorption amount of hydrocarbons and carbon monoxide on the catalyst in the second and third operation modes. It is possible to more accurately estimate the amount of adsorption of hydrocarbons and carbon monoxide of the catalyst over time.
Since the failure determination of the air-fuel ratio detection device is prohibited when the integrated value of the intake air amount of the internal combustion engine in the first operation mode before the stop of fuel supply exceeds a predetermined value, an erroneous determination can be made. Thus, it is possible to avoid failure determination in a highly reliable state and perform failure determination with high accuracy.
According to the failure determination device for an air-fuel ratio detection device of claim 3 of the present invention, the failure determination means in the failure determination means based on the integrated value of the intake air amount of the internal combustion engine in the first operation mode before the fuel supply is stopped. Therefore, the failure determination means can correctly determine the failure of the air-fuel ratio detection device by accurately reflecting the effect of a large amount of hydrocarbons and carbon monoxide adsorbed on the catalyst when the fuel supply is stopped. Can be performed with high accuracy.

According to the failure determination device for an air-fuel ratio detection device of claim 4 of the present invention, for example, the required time is set to a predetermined time based on the required time from the stop of fuel supply until the air-fuel ratio of the exhaust reaches a predetermined air-fuel ratio. By exceeding this, it is considered that the air-fuel ratio that decreases due to the stop of fuel supply cannot be accurately detected, and it can be determined that the air-fuel ratio detection device is malfunctioning.

1 is a schematic configuration diagram of an intake / exhaust system of an engine to which a failure determination device of the present invention is applied. It is a time chart which shows an example of transition of the intake air amount integration calculation value before and after the fuel cut and the output value of the oxygen concentration sensor. It is a graph which shows an example of the relationship between intake air amount integrated value and the time required for air-fuel ratio fall. It is a time chart which shows an example of the relationship between an intake air amount integrated value and each determination condition.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an intake / exhaust system of an engine 1 (internal combustion engine) to which a failure determination device of the present invention is applied.
The engine 1 is mounted on a vehicle and is, for example, an in-cylinder fuel injection type gasoline engine that directly injects fuel from an injection valve into a cylinder.

As shown in FIG. 1, an electronically controlled throttle valve 10 that adjusts the intake air flow rate is provided in the intake passage 2 of the engine 1. The throttle valve 10 is provided with a throttle position sensor 11 that detects the degree of opening of the throttle valve 10.
An air flow sensor 12 for detecting the intake air flow rate is provided in the intake passage 2 upstream of the throttle valve 10.

Further, the engine 1 is provided with a crank angle sensor 20 that detects the crank angle, a cam angle sensor (not shown), a water temperature sensor, and other sensors that detect the operating state of the engine 1.
An exhaust purification catalyst 30 such as a three-way catalyst is interposed in the exhaust passage 3 of the engine 1.
An upstream oxygen concentration sensor 31 for detecting the oxygen concentration in the exhaust gas flowing into the exhaust purification catalyst 30 is detected on the upstream side of the exhaust purification catalyst 30, and an oxygen concentration in the exhaust gas after passing through the exhaust purification catalyst 30 is detected on the downstream side. And a downstream oxygen concentration sensor 32 (air-fuel ratio detection device).

The ECU 40 is a control device for performing comprehensive control including operation control of the engine 1, and includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), and the like. It consists of
On the input side of the ECU 40, the throttle position sensor 11, the airflow sensor 12, the crank angle sensor 20, the upstream oxygen concentration sensor 31, the downstream oxygen concentration sensor 32, a water temperature sensor (not shown), and an accelerator for detecting the accelerator opening. Detection information from a position sensor, a vehicle speed sensor, and other sensors for detecting the operating state of the engine 1 and the vehicle is input.

  Various output devices such as the throttle valve 10, the fuel injection valve 4, and the spark plug 5 are connected to the output side of the ECU 40. The ECU 40 calculates a target throttle opening, a fuel injection amount, a fuel injection timing, an ignition timing, and the like based on detection information from various sensors, and outputs them to various output devices. 4 etc. are controlled.

  In particular, the ECU 40 switches the fuel injection mode of the engine 1 according to the load or the like. The fuel injection mode enriches the air-fuel ratio when, for example, the normal operation mode (second operation mode) in which the operation is performed while feeding back the air-fuel ratio of the exhaust so as to be in the stoichiometric state or the lean state, or when the load is large, etc. Thus, there are an enriched operation mode (first operation mode) in which open loop control is performed, and a fuel cut mode (third operation mode) in which fuel injection is stopped at no load such as during deceleration. In the normal operation mode, a feedback operation is performed based on outputs from the upstream oxygen concentration sensor 31 and the downstream oxygen concentration sensor 32, and an open loop operation is performed in the enrich operation mode and the fuel cut mode.

The ECU 40 has a failure determination function for the downstream oxygen concentration sensor 32.
The failure determination of the downstream oxygen concentration sensor 32 is based on the change in the air-fuel ratio of the exhaust gas detected by the downstream oxygen concentration sensor 32 when the fuel injection mode is stopped (fuel cut) by shifting to the fuel cut mode during engine operation. Based on this, failure determination of the downstream oxygen concentration sensor 32 is performed (failure determination means).

FIG. 2 is a time chart showing an example of changes in the intake air amount integrated value Qol and the output value V of the downstream oxygen concentration sensor 32 before and after the fuel cut. The solid line in the figure indicates the case where the normal operation is performed before the fuel cut is started, and the broken line in the figure indicates the case where the enrichment operation is performed before the fuel cut is started.
As shown by a solid line in FIG. 2, for example, when the fuel is cut from the air-fuel ratio feedback operation in the normal operation mode, the output value V of the downstream oxygen concentration sensor 32 starts to fall with a time lag from the start of the fuel cut. The degree of decrease in the output value of the downstream oxygen concentration sensor 32 at this time, specifically, the required time Tslope when the output value V of the downstream oxygen concentration sensor 32 changes within a predetermined range (from V1 to V2) is approximately. It becomes a constant value. The required time Trl from the start of fuel cut until the output value V of the downstream oxygen concentration sensor 32 decreases to the predetermined value V2 is also a substantially constant value.

  The ECU 40 measures the required time Tslope, and determines that the downstream oxygen concentration sensor 32 is normal when this value is equal to or less than a preset threshold Ta, and when the value exceeds the threshold Ta, the downstream oxygen It is determined that the density sensor 32 is malfunctioning. Further, instead of the required time Tslope, the required time Trl is measured. When the required time Trl is less than or equal to the preset threshold value Tb, it is determined that the downstream oxygen concentration sensor 32 is normal, and when the threshold value Tb is exceeded, the downstream time It may be determined that the side oxygen concentration sensor 32 is out of order.

Further, the present embodiment has a function of limiting failure determination of the downstream oxygen concentration sensor 32 when the enrichment operation mode is set before the fuel cut is started.
As shown by the broken line in FIG. 2, for example, when the fuel is cut from the air-fuel ratio open loop operation in the enrich operation mode, the output value V of the downstream oxygen concentration sensor 32 starts to fall with a time lag from the start of the fuel cut. The descending direction is more gradual than when the fuel is cut from the normal operation mode indicated by the solid line in FIG. 2 (required times Tslope 'and Trl' are larger than Tslope and Trl). Therefore, there is a risk of erroneously determining that the downstream oxygen concentration sensor 32 has failed.

  Therefore, the ECU 40 calculates the intake air amount integrated value Qol during open loop operation before the start of fuel cut (intake air amount integration means), and if the intake air amount integrated value Qol exceeds the threshold value Qolh, the ECU 40 The failure determination of the downstream oxygen concentration sensor 32 is prohibited (failure determination prohibiting means). In order to reliably remove the influence of hydrocarbons and carbon monoxide adsorbed on the catalyst on the output value V of the downstream oxygen concentration sensor 32, the prohibition on the failure determination of the downstream oxygen concentration sensor 32 is cancelled. This is performed when the intake air amount integrated value Qol drops below 0. Further, when the ECU 40 is turned on, the prohibition on the failure determination of the downstream oxygen concentration sensor 32 is canceled as an initial setting.

FIG. 3 is a graph showing an example of the relationship between the intake air amount integrated value Qol and the required time Tslope.
As shown in FIG. 3, the required time Tslope tends to exceed the failure determination threshold Ta from when the intake air amount integrated value Qol during open loop operation exceeds Qb in the figure. The Qb is a value determined by the capacity of the exhaust purification catalyst 30 and the adsorption ability of hydrocarbons and carbon monoxide. The Qb may be set as the threshold value Qolh after confirmation in advance.

Next, a method for calculating the intake air amount integrated value Qol during open loop operation will be described.
The ECU 40 integrates or subtracts the intake air amount detected by the airflow sensor 12 every predetermined time (for example, 100 ms) when the respective conditions are satisfied in the priorities (1) to (6) in Table 1 below. The intake air amount integrated value Qol (n) is calculated.

表１に示すように、ＥＣＵ４０電源投入時あるいはドライビングサイクル開始時(優先順位１、２)には、初期値として吸入空気量積算値Ｑolを０とする。エンストモード中、始動モード中、または始動後経過時間所定時間以下である場合(優先順位３)には、吸入空気量積算値Ｑol(n)を前回の演算値Ｑol(n-1)から増減させない。

As shown in Table 1, when the ECU 40 is turned on or when the driving cycle is started (priorities 1 and 2), the intake air amount integrated value Qol is set to 0 as an initial value. When the engine stall mode, the start mode, or the elapsed time after the start is less than the predetermined time (priority order 3), the intake air amount integrated value Qol (n) is not increased or decreased from the previous calculated value Qol (n-1). .

  During the fuel cut mode, more specifically during the all cylinder fuel cut mode, overrun fuel cut mode or single bank fuel cut mode (only applicable to V-type engines) (priority level 4), the previous calculated value Qol (n-1) Then, a value obtained by multiplying the intake air amount Qa by a coefficient A1 (for example, 10) is subtracted to obtain an intake air amount integrated value Qol (n). In the normal operation mode, specifically, in the air-fuel ratio feedback operation mode or the stoichiometric feedback operation mode (priority order 5), the coefficient A2 (for example, 1) is added to the intake air amount Qa from the previous calculated value Qol (n-1). The value multiplied by is subtracted to obtain the intake air amount integrated value Qol (n). Thus, since the air-fuel ratio is changed from rich to lean when the fuel is cut (priority order 4) and during feedback operation (priority order 5), the intake air amount integrated value Qol (n) is calculated from the previous calculation value. Reduced from Qol (n-1). Since the air-fuel ratio is greatly changed from rich to lean when the fuel is cut, the coefficient A1 at the time of the fuel cut for calculating the reduction amount of the intake air amount integrated value Qol (n) is It is set to a value larger than the coefficient A2 during feedback operation.

In open loop operation other than the above (enrich operation mode), the air-fuel ratio is made rich, so the intake air amount integrated value Qol (n) is increased from the previous calculated value Qol (n-1). The intake air amount integrated value Qol has an upper limit value Qh based on the maximum adsorbable amount of hydrocarbons and carbon monoxide of the exhaust purification catalyst 30.
In an engine that controls fuel injection for each bank, such as a V-type engine, the intake air amount integrated value Qol may be calculated for each bank.

FIG. 4 is a time chart showing an example of the relationship between the intake air amount integrated value Qol and each determination state.
In FIG. 4, in the engine 1 controlled as described above, the transition of the intake air amount integrated value Qol in the case where the fuel cut mode is executed twice with time and each operation mode is executed before that. FIG. 5 is a time chart showing a transition of determination statuses of failure determination prohibition and failure determination execution permission associated therewith.

  As shown in FIG. 4, in section 1, since it is an open loop operation excluding fuel cut, the intake air amount integrated value Qol increases (corresponds to the condition of priority 6 in Table 1 above). Here, failure determination is prohibited when the intake air amount integrated value Qol exceeds a predetermined value Qolh (point A). In the section 1, when the intake air amount integrated value Qol reaches the upper limit value Qh, the upper limit value Qh is maintained. In section 2, since the feedback operation is being performed, the intake air amount integrated value Qol decreases (corresponds to the condition of priority 5 in Table 1 above). In section 3, since it is a fuel cut mode (corresponding to the condition of priority 4 in Table 1 above), the intake air amount integrated value Qol decreases. If the intake air amount integrated value becomes 0 or less, the failure determination prohibition is canceled (point B). Since the actual failure determination is impossible when failure determination prohibition is established at the start of fuel cut, failure determination is not performed in the first fuel cut mode in this figure (point C).

Thereafter, the integration of the intake air amount integrated value Qol continues in the same manner. However, as shown in FIG. 3, at the start of the second fuel cut mode, the intake air amount integrated value Qol does not exceed the threshold value Qolh. Judgment prohibition has been lifted. Therefore, failure determination execution is permitted in the second fuel cut mode (point D).
As described above, in the present embodiment, when the failure determination of the downstream oxygen concentration sensor is performed at the time of fuel cut, if the intake air amount integrated value Qol in the open loop operation so far exceeds the threshold value Qolh, The failure judgment is prohibited. As a result, it is possible to avoid erroneous determination of a failure of the downstream oxygen concentration sensor 32 due to a large amount of hydrocarbons and carbon monoxide adsorbed on the exhaust purification catalyst 30.

  In particular, in this embodiment, the prohibition of failure determination is not determined based on the open loop operation time before the start of the fuel cut mode, but is calculated by calculating the intake air amount integrated value Qol. Thus, it is possible to estimate the amount of adsorption of hydrocarbons and carbon monoxide by the exhaust purification catalyst 30 in the above, and to accurately grasp the influence at the time of failure determination. As a result, failure determination can be accurately prohibited, and highly accurate failure determination can be performed.

Further, when feedback operation is performed in the fuel cut mode and the normal operation mode, the intake air amount integrated value Qol is subtracted, so that it depends on hydrocarbons and carbon monoxide adsorbed on the exhaust purification catalyst 30 at the time of subsequent fuel cut start. The impact can be estimated accurately.
In the present embodiment, the failure determination is prohibited when the intake air amount integrated value Qol exceeds the threshold value Qolh, but the present invention is not limited to this. For example, the failure determination threshold value Ta or Tb of the downstream oxygen concentration sensor 32 may be changed based on the intake air amount integrated value Qol. Specifically, the failure determination threshold value Ta or Tb may be increased as the intake air amount integrated value Qol increases. In this way, as the intake air amount integrated value Qol increases, the change in the detected value of the downstream oxygen concentration sensor 32 becomes smaller due to the influence of hydrocarbons and carbon monoxide adsorbed on the exhaust purification catalyst 30. (The required times Tslope and Trl increase), but it becomes difficult to erroneously determine that there is a failure by increasing the threshold Ta or Tb for failure determination.

  Further, the present invention is applicable not only to an in-cylinder fuel injection type gasoline engine as in the above embodiment, but also to various internal combustion engines, and an air-fuel ratio disposed downstream of various catalysts provided in the exhaust system thereof. It can be widely applied to the failure determination of the detection device.

1 Engine 30 Exhaust purification catalyst 32 Downstream oxygen concentration sensor 40 ECU

Claims (4)

A failure determination device for an air-fuel ratio detection device disposed downstream of a catalyst provided in an exhaust system of an internal combustion engine,
The fuel supply is stopped during the operation of the internal combustion engine, and the air-fuel ratio detection apparatus detects the air-fuel ratio detection apparatus based on the time required for the air-fuel ratio of the exhaust detected by the air-fuel ratio detection apparatus to change within a predetermined range after the fuel supply is stopped. Failure determination means for determining failure;
Intake air amount integration means for integrating the intake air amount of the internal combustion engine in a first operation mode in which the air-fuel ratio is operated in a rich state before stopping the fuel supply;
Based on the integrated value of the intake air amount calculated by the intake air amount integrating means, a failure determination that limits failure determination of the air-fuel ratio detection device by the failure determining means when the integrated value exceeds a predetermined value A failure determination device for an air-fuel ratio detection device. The intake air amount integration means is configured to output at least one of the second operation mode in which the air-fuel ratio is operated in a stoichiometric or lean state before the fuel supply is stopped and the third operation mode in which the fuel supply is stopped. Subtracting the intake air amount of the internal combustion engine from the integrated value of the intake air amount in the first operation mode;
In the subtraction from the integrated value of the intake air amount in the first operation mode, the subtraction value of the intake air amount of the internal combustion engine in the third operation mode is the internal combustion engine in the second operation mode. Is larger than the subtracted value of the intake air amount of
The failure determination limiting means prohibits the failure determination of the air-fuel ratio detection device when the integrated value of the intake air amount exceeds a predetermined value , and cancels the prohibition of the failure determination to reduce the integrated value to zero or less. The failure determination device for an air-fuel ratio detection device according to claim 1, wherein the failure determination device is performed when the air pressure decreases .   The failure determination limiting means changes a failure determination threshold value of the air-fuel ratio detection device in the failure determination means based on the integrated value of the intake air amount calculated by the intake air amount integration means. The failure determination device for an air-fuel ratio detection device according to claim 1. The failure determination means determines a failure of the air-fuel ratio detection device based on a required time from the stop of the fuel supply until the air-fuel ratio of the exhaust gas detected by the air-fuel ratio detection device reaches a predetermined air-fuel ratio. The failure determination device for an air-fuel ratio detection device according to any one of claims 1 to 3 .

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