JP4214518B2 - Failure diagnosis device for exhaust gas recirculation system - Google Patents

Description

  The present invention is applied to an exhaust gas purification system such as a vehicle engine or a stationary engine, and recirculates EGR (exhaust gas recirculation) gas from the exhaust passage of the engine to the intake passage through the EGR passage, and the flow path of the EGR passage. The present invention relates to a failure diagnosis apparatus for an exhaust gas recirculation system provided with an EGR valve for adjusting the area.

In a stationary engine such as a vehicle engine or a power generation engine, as a means for removing NOx (nitrogen oxide) in exhaust gas, a part of exhaust gas in an exhaust passage, that is, EGR (exhaust gas recirculation) gas is flowed by an EGR valve. Many EGR exhaust gas recirculation systems that recirculate to an intake passage through an EGR passage that can adjust the road area are widely used.
In such an EGR exhaust gas recirculation system (hereinafter referred to as an EGR system), the recirculation of EGR gas is stopped by the failure of the EGR valve or the failure of the EGR system such as the EGR passage being clogged due to the accumulation of carbon in the exhaust gas. In order to avoid that the adjustment of the EGR gas flow rate becomes impossible, various failure diagnosis apparatuses for detecting a failure of the EGR system are provided.

FIG. 6 is a schematic configuration diagram showing an example of an engine with an EGR system provided with such a failure diagnosis apparatus. In the figure, 100 is an engine, 101 is an intake manifold of the engine 100, 102 is an exhaust manifold, 106 is a fresh air passage through which fresh air (air) from a supercharger (not shown) flows, and 103 is the intake manifold. It is the intake passage which leads to.
Reference numeral 104 denotes an EGR (exhaust gas recirculation) passage that connects the exhaust passage including the exhaust manifold 102 and the intake passage 103, and 107 denotes a junction between the fresh air passage 106 and the EGR passage 104. Reference numeral 105 denotes an EGR valve that is installed immediately upstream of the confluence portion 107 of the EGR passage 104 and adjusts the flow area of the EGR passage 104, that is, the recirculation amount of EGR gas. The EGR valve 105 is driven by a motor, air, or the like according to the indicated valve opening of the controller 10.

Reference numeral 2 denotes an intake air temperature detector, which is provided in the intake passage 103 on the downstream side of the merging portion 107, and detects the temperature of intake air in which EGR gas from the EGR passage 104 is mixed with fresh air from the new air passage 106. To detect.
Reference numeral 10 denotes a controller, to which the detected value of the intake air temperature is input from the intake air temperature detector 2, and based on the detected value of the intake air temperature, the intake air temperature is detected when the EGR valve 105 is opened and closed. The temperature difference between the values, that is, the opening / closing temperature difference is calculated. When the opening / closing temperature difference becomes smaller than the preset allowable opening / closing temperature difference, it is determined that a failure has occurred in the EGR system, and an alarm is given to the alarm device 3. It comes to send.

Moreover, there exists an apparatus described in patent document 1 (Unexamined-Japanese-Patent No. 3-115767) as one of the failure diagnosis apparatuses of this exhaust gas recirculation system.
In the technique of Patent Document 1, a fresh air temperature detector that detects the temperature of fresh air is provided in the fresh air passage upstream of the joining portion of the intake passage with the EGR passage, and the joining portion of the intake passage includes the fresh air temperature detector. A partition for guiding EGR gas from the EGR passage to the downstream side is provided, and an intake air temperature detector for detecting the temperature of the intake air in which EGR gas is mixed into the fresh air is provided at the outlet of the passage in the partition, The detected value of the fresh air temperature and the detected value of the intake air temperature are input to the controller.
In the controller, when the temperature difference between the intake air temperature detection value from the intake air temperature detector and the fresh air temperature detection value from the fresh air temperature detector is smaller than a preset allowable temperature difference, the EGR system fails. It is determined that has occurred, and an alarm is transmitted.

Japanese Patent Laid-Open No. 3-115767

In an engine with a supercharger and an intercooler, the temperature of fresh air passing through a fresh air passage changes depending on engine operating conditions such as engine load and engine speed.
However, in the engine with the EGR system provided with the failure diagnosis device shown in FIG. 6, the temperature difference of the intake air temperature detection value from the intake air temperature detector 2 when the EGR valve 105 is opened or closed, that is, the open / close temperature difference is obtained. Since the failure of the EGR system is determined when the opening / closing temperature difference becomes smaller than the preset allowable opening / closing temperature difference, if the fresh air temperature changes as described above, the merge section 107 performs EGR. The change in the intake air temperature after the gas merging portion includes a mixture of the EGR gas and the change in the fresh air temperature, and the controller 10 cannot accurately detect the change in the EGR gas temperature. An erroneous determination occurs, and a situation in which a failure of the EGR system cannot be accurately detected occurs.

In the technique of Patent Document 1, a fresh air temperature on the upstream side of the EGR gas merging portion of the intake passage and an intake air temperature after the EGR gas merging on the downstream side are detected, and the detected intake air temperature value and the new air temperature are detected. Since it is determined that a failure has occurred in the EGR gas when the temperature difference from the air temperature detection value is smaller than a preset allowable temperature difference, it is determined by the change in the fresh air temperature as in the prior art in FIG. Misjudgment of EGR system failure judgment can be avoided.
However, in the technique of Patent Document 1, the absolute value of the fresh air temperature detected by the fresh air temperature detector and the absolute value of the intake air temperature detected by the intake air temperature detector are used for determining the failure of the EGR system. Therefore, when a detection error has occurred in the fresh air temperature detector or the intake air temperature detector, the fresh air temperature detection value or the new air temperature detection value that contains the detection error related to the EGR system failure determination in the controller 10 or The intake air temperature detection value is used, and even in such a conventional technique, an erroneous determination occurs in the failure determination of the EGR system, and a situation in which the failure of the EGR system cannot be accurately detected is likely to occur.
And so on.

  Accordingly, in the present invention, in view of the problems of the prior art, a detection error occurs in a detector (sensor) that detects a change in fresh air temperature due to engine operating conditions and the like, and a fresh air temperature or an intake air temperature after EGR mixing. Another object of the present invention is to provide a fault diagnosis apparatus for an exhaust gas recirculation system that can accurately detect a fault in an EGR system without being affected by the change in the fresh air temperature and the detection error of the detector.

The present invention is intended to achieve the object, while refluxing the EGR (exhaust gas recirculation) gas from the exhaust passage of the engine to the intake passage through the EGR passage, for adjusting the flow passage area of the EGR passage with the EGR passage In a fault diagnosis apparatus for an exhaust gas recirculation system provided with an EGR valve, the temperature of intake air in which EGR gas is mixed into fresh air is detected in an intake passage downstream of the junction of the EGR passage and the intake passage. Temperature difference between the maximum temperature (Tmax) and the minimum temperature (Tmin) in a predetermined sampling period during the opening of the EGR valve from the intake air temperature detector to be detected and the detected value of the intake air temperature input from the intake air temperature detector The minimum temperature difference (ΔTs = Tmax−Tmin) is calculated, and the maximum and minimum temperature difference ΔTs is equal to or less than a preset allowable temperature difference (ΔTsa) (ΔTs ≦ ΔTsa). When, characterized by comprising a controller to determine the condition of failure of the exhaust gas recirculation system.

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According to inventions that written, by the inertia of the thermal inertia and the exhaust gas temperature detector, misalignment occurs between the operation of the intake air temperature changes and the EGR valve, by using the intake air temperature detection value by the temperature detector By using the maximum and minimum temperature difference (ΔTs = T _max −T _min ) during a predetermined sampling period while the EGR valve is open, even in a situation where an erroneous determination is made in the failure determination of the exhaust gas recirculation system of It is possible to avoid the detection error of the intake air temperature change due to the deviation between the intake air temperature change and the operation of the EGR valve due to the thermal inertia of the temperature detector and the exhaust gas inertia, and the actual operation during the EGR valve opening The intake air temperature change can be accurately detected, and an erroneous determination can be prevented in the failure determination of the exhaust gas recirculation system accompanying the detection error of the intake air temperature change.

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According to the present invention, the temperature difference (ΔT) between the fresh air and the fresh air temperature in two states in the intake air after mixing the EGR gas into the fresh air, that is, the state when the EGR valve is opened and the state when the EGR valve is closed. ₁ ) and the temperature difference (ΔT ₂ ) between the intake air temperatures, and using the fresh air temperature difference (ΔT ₁ ) and the intake air temperature difference (ΔT ₂ ) in the _two states, fresh air and EGR to the fresh air The temperature difference before and after EGR (ΔT = ΔT ₂ −ΔT ₁ ) or the temperature ratio before and after EGR (C _t = ΔT ₂ / ΔT ₁ ) with the intake air after gas mixing is equal to or less than the allowable temperature difference (ΔTa) (ΔT ≦ ΔTa) or Even when the EGR system determines that the EGR system is normal when the allowable temperature ratio (C _ta ) or less (C _t ≦ C _ta ), the determination condition for determining that a failure of the exhaust gas recirculation system has occurred , In a predetermined sampling period during the EGR valve opening When a high minimum temperature difference .DELTA.Ts becomes less than the allowable temperature difference ΔTsa (ΔTs ≦ ΔTsa), by the judgment condition of failure of the exhaust gas recirculation system, it can be reliably avoided failure detection leakage of the EGR system.
As a result, the failure determination accuracy of the exhaust gas recirculation system is improved.

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  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

FIG. 1 is an overall configuration diagram of a failure diagnosis apparatus for an exhaust gas recirculation system in a vehicle engine according to an embodiment of the present invention. Figure 2 is a control block diagram of a first reference example of fault diagnosis system, a control block diagram of a second reference example of FIG. 3 is fault diagnostic apparatus, a control block of the real施例the fault diagnosis apparatus shown in FIG. 4 is the invention FIG. Figure 5 (A), (B) is an operation explanatory diagram of the front you施例.

In FIG. 1 showing the overall configuration of an embodiment of the present invention, 100 is an engine, 101 is an intake manifold of the engine 100, 102 is an exhaust manifold, and 106 is fresh air (air) from a supercharger (not shown). A flowing fresh air passage 103 is an intake passage communicating with the intake manifold 101.
Reference numeral 104 denotes an EGR (exhaust gas recirculation) passage that connects the exhaust passage including the exhaust manifold 102 and the intake passage 103, and 107 denotes a junction between the fresh air passage 106 and the EGR passage 104.
Reference numeral 10 denotes a controller, 105 denotes an EGR valve, and 108 denotes an EGR valve drive unit. The EGR valve drive unit 108 is driven according to the EGR instruction valve opening calculated by the controller 10, and the flow area of the EGR passage 104, that is, EGR gas Adjust the amount of reflux.
The basic configuration of the exhaust gas recirculation system in the vehicle engine described above is the same as that of the prior art as shown in FIG.

In FIG. 1, reference numeral 1 denotes a fresh air temperature detector, which is provided in a fresh air passage 106 upstream of the junction 107 between the EGR passage 104 and the intake passage 103 and flows through the fresh air passage 106. The temperature of fresh air (air) from (not shown) is detected. An intake air temperature detector 2 is provided in the intake passage 103 on the downstream side of the merging portion 107, and detects the temperature of intake air in which EGR gas from the EGR passage 104 is mixed into the fresh air.
The fresh air temperature detection value from the fresh air temperature detector 1 and the intake air temperature detection value from the intake air temperature detector 2 are input to the controller 10, and the fresh air temperature detection value, the intake air temperature detection value, and the EGR indicator valve are input. Based on the opening, a control operation as described later is performed to determine whether or not there is a failure in the EGR system (exhaust gas recirculation system) such as the EGR valve 105 and the EGR passage 104, and the determination result is displayed on the display device 4. At the same time, the alarm is transmitted to the alarm device 3 and an alarm is transmitted to the alarm device 3.

Next, the operation of the fault diagnosis apparatus for the exhaust gas recirculation system will be described with reference to FIGS.
In the first reference example of the failure diagnosis apparatus shown in FIG. 2, the fresh air temperature detection value T ₁ from the fresh air temperature detector ₁ and the EGR instruction valve opening degree U from the EGR valve opening calculation unit 5 are The fresh air temperature difference calculation unit 11 of the controller 10 is input to the intake air temperature detection value T ₂ from the intake air temperature detector ₂ and the EGR instruction valve opening degree U from the EGR valve opening calculation unit 5 is the intake air of the controller 10. Input to the temperature difference calculator 12.

The fresh air temperature difference calculation unit 11 closes the fresh air temperature T ₁₁ and the EGR valve 105 when the EGR valve 105 is opened based on the EGR instruction valve opening degree U based on the fresh air temperature detection value T _1. after calculating the fresh air temperature _{T 12} at the time of the valve, the temperature difference [Delta] T ₁ i.e. fresh air and fresh air temperature _{T 12} at the time of closing of the fresh air temperature _{T 11} and the EGR valve 105 at the time of opening of the EGR valve 105 The temperature difference ΔT ₁ = T ₁₁ −T ₁₂ is calculated.
The intake air temperature difference calculation unit 12 calculates the intake air temperature T ₂₁ when the EGR valve 105 is opened and the intake air temperature T ₂₂ when the EGR valve 105 is closed based on the intake temperature detection value T _2. After that, the temperature difference ΔT ₂ between the intake air temperature T ₂₁ when the EGR valve 105 is opened and the intake air temperature T ₂₂ when the EGR valve 105 is closed, that is, the EGR intake air temperature difference ΔT ₂ = T ₂₁ −T ₂₂ is calculated. To do.
The fresh air temperature difference ΔT ₁ and the EGR intake air temperature difference ΔT ₂ are input to the EGR front-rear temperature difference calculation unit 13.

The EGR front-rear temperature difference calculation unit 13 calculates the EGR front-rear temperature difference ΔT = ΔT ₂ −ΔT ₁ , which is the difference between the EGR intake air temperature difference ΔT ₂ and the fresh air temperature difference ΔT _1, and sends it to the temperature difference determination unit 15. input.
When the temperature difference ΔT before and after EGR (ΔT = ΔT ₂ −ΔT ₁ ) becomes a certain value or less, failure of the EGR system (exhaust gas recirculation system) such as the EGR valve 105 and the EGR passage 104 has occurred. Therefore, the allowable temperature difference setting unit 14 uses the minimum value of the temperature difference ΔT before and after EGR that is a failure occurrence limit of the EGR system, that is, the allowable temperature difference ΔTa as a failure determination condition, and determines the engine operating condition (engine load or It is set for each engine speed.
The temperature difference determination unit 15 compares the temperature difference ΔT before and after EGR (ΔT ₂ −ΔT ₁ ) with the allowable temperature difference ΔTa, and the first determination condition is that the temperature difference ΔT before and after EGR is the allowable temperature difference. When ΔTa or less, that is, ΔT ≦ ΔTa, it is determined that a failure of the EGR system has occurred.
The first determination result in the temperature difference determination unit 15 is displayed on the display device 4, and when the determination result indicates that a failure of the EGR system has occurred, an alarm device is provided for indicating the occurrence of the failure. 3 to send an alarm.

Therefore, according to the first reference example, the temperature difference ΔT (ΔT before and after EGR), which is the temperature difference between the EGR intake air temperature difference ΔT ₂ and the fresh air temperature difference ΔT ₁ between the opening time and the closing time of the EGR valve 105. ₂₋ ΔT ₁ ) and the allowable temperature difference ΔTa of the temperature difference before and after the EGR, and by determining whether the comparison result satisfies the first determination condition ΔT ≦ ΔTa, the EGR system Can be reliably detected.

In this reference example, in order to further increase the accuracy of detecting the occurrence of a failure in the EGR system, the occurrence of a failure in the EGR system is detected based on the following second determination condition in addition to the first determination condition. .
That is, in the temperature difference determination unit 15, the determination based on the first determination condition, that is, the determination whether the temperature difference ΔT before and after EGR is equal to or less than the allowable temperature difference ΔTa (ΔT ≦ ΔTa) is continuous or constant. The measurement is performed at time intervals, and the result is input to the abnormal temperature difference frequency calculation unit 17.
The abnormal temperature difference frequency calculation unit 17 calculates the occurrence frequency N ₁ per fixed time when the temperature difference ΔT before and after EGR is equal to or less than the allowable temperature difference ΔTa (ΔT ≦ ΔTa), and inputs it to the EGR abnormality determination unit 18. .

16 is a permissible frequency setting unit, the failure limit of the EGR system, the EGR downstream temperature difference [Delta] T is less than or equal to the allowable temperature difference ΔTa (ΔT ≦ ΔTa) minimum value or allowable frequency N ₁ per fixed time frequency N ₁₀ is set for each engine operating condition (engine load, or engine speed).
Abnormality in the determination unit 18, as a second determination condition, when the occurrence frequency N ₁ of the EGR downstream temperature difference [Delta] T is the state of the allowable temperature difference .DELTA.Ta below (ΔT ≦ ΔTa) exceeds the allowable frequency N ₁₀ ( N ₁ > N ₁₀ ), it is determined that a failure of the EGR system has occurred.
The second determination result in the abnormality determination unit 18 is displayed on the display device 4, and when it is determined that a failure of the EGR system has occurred according to the determination result, the alarm device 3 detects the failure occurrence. Send an alarm to send an alarm.
Therefore, in addition to the failure determination of the EGR system using the first determination condition, that is, the temperature difference ΔT before and after the EGR, by detecting the occurrence frequency of the second determination condition, that is, the failure condition due to the temperature difference, The failure determination accuracy of the EGR system is further improved.

In the second reference example shown in FIG. 3, a temperature ratio C _t before and after EGR (C _t = ΔT ₂ / ΔT ₁ ) is used instead of the temperature difference ΔT before and after EGR in the first reference example.
That is, in FIG. 3, reference numeral 23 denotes an EGR front-rear temperature ratio calculation unit, which is based on the fresh air temperature difference ΔT ₁ from the fresh air temperature difference calculation unit 11 and the EGR intake air temperature difference ΔT ₂ from the intake air temperature difference calculation unit 12. The temperature ratio C _t before and after EGR (C _t = ΔT ₂ / ΔT ₁ ) is calculated and input to the temperature ratio determination unit 25.
24 at the permissive temperature ratio setting unit, at the permissive temperature ratio setting unit 24, a minimum value i.e. failure determination condition allowable temperature ratio C _{t a} before and after EGR becomes failure limit of the EGR system temperature ratio C _t, It is set for each engine operating condition (engine load or engine speed).

Then, the temperature ratio determination unit 25 compares the temperature ratio C _t before and after EGR (C _t = ΔT ₂ / ΔT ₁ ) with the allowable temperature ratio C _ta and sets the temperature before and after EGR as a first determination condition. When the ratio C _t is equal to or less than the allowable temperature ratio C _ta , that is, C _t ≦ C _ta, it is determined that a failure of the EGR system has occurred.
The first determination result in the temperature difference determination unit 25 is displayed on the display device 4 and, if the determination result indicates that a failure of the EGR system has occurred, the failure occurrence is indicated by an alarm device. 3 to send an alarm.

Therefore, according to the second reference example, the temperature ratio C _t before and after EGR, which is the temperature ratio between the EGR intake air temperature difference ΔT ₂ and the fresh air temperature difference ΔT ₁ during the opening time to the closing time of the EGR valve 105. C _t = ΔT ₂ / ΔT ₁ ) and the allowable temperature ratio C _{ta of the} temperature ratio before and after the EGR, and whether the comparison result corresponds to the first determination condition C _t ≦ C _t a Therefore, it is possible to reliably detect the occurrence of a failure in the EGR system.

In the second reference example, as in the first reference example, in order to further increase the detection accuracy of the occurrence of a failure in the EGR system, the following second determination is made in addition to the first determination condition. The occurrence of a failure in the EGR system is detected according to a condition.
That is, in the temperature ratio determination unit 25, the determination by the first determination condition, i.e. the EGR longitudinal temperature ratio _{C t} is or less than the allowable temperature ratio _{C t} a _{(C t} ≦ _C t a) whether the The determination is performed continuously or at regular time intervals, and the result is input to the abnormal temperature ratio frequency calculation unit 27.
In the different ambient temperature of ratio frequency calculation unit 27, the EGR longitudinal temperature ratio _{C t} is equal to or less than the allowable temperature ratio _{C t} a _{(C t} ≦ _C t a) EGR abnormality by calculating the occurrence frequency _{N 2} per fixed time Input to the determination unit 28.

26 is a permissible frequency setting unit, the failure limit of the EGR system, the EGR longitudinal temperature ratio _{C t} is equal to or less than the allowable temperature ratio _{C t} a _{(C t} ≦ _C t a) frequency per fixed time N minimum value or allowable frequency N ₂₀ of ₂ is set for each engine operating condition (engine load, or engine speed).
In the abnormality determination unit 28, a second determination condition, the EGR longitudinal temperature ratio _{C t} is more than the allowable temperature ratio _{C t} a _{(C t} ≦ _C t a) frequency _{N 2} is the allowable frequency of the state When N ₂₀ is exceeded (N ₂ > N ₂₀ ), it is determined that a failure of the EGR system has occurred.
The second determination result in the abnormality determination unit 28 is displayed on the display device 4 as in the case of the first reference example, and when the EGR system has failed due to the determination result. Transmits the occurrence of the failure to the alarm device 3 to transmit an alarm.
Thus, by addition to the failure determination of the first determination condition i.e. EGR system using the EGR longitudinal temperature ratio C _t, detects the frequency of occurrence of such second determination condition ie fault condition by said temperature ratio Further, the failure determination accuracy of the EGR system is further improved.

In the embodiment of the present invention shown in FIG. 4, the detected value of the intake air temperature by the intake air temperature detector 2 is input to the maximum / lowest temperature detector 31 of the controller 10. Further, the EGR instructs valve opening U from the previous SL E GR valve opening degree calculating section 5 is inputted to the sampling time setting unit 32 of the controller 10, at the sampling time setting unit 32, the opening and closing timing of the EGR valve 105 A sampling time for calculating the maximum and minimum temperature of the intake air temperature is set and input to the maximum and minimum temperature calculation unit 33.

In highest-lowest temperature detecting unit 31, as shown in FIG. 5 (A), the temperature difference i.e. maximum and minimum temperature difference between the maximum temperature _{T max} and the minimum temperature _{T min} in a predetermined sampling period of the EGR valve 105 in the open ΔTs (T _max −T _min ) is calculated, compared with the allowable temperature difference ΔTsa preset in the allowable temperature difference setting unit 34, and the comparison result is input to the EGR abnormality determination unit 35.
In the EGR abnormality determination unit 35, when the maximum / minimum temperature difference ΔTs is equal to or less than the allowable temperature difference ΔTsa (ΔTs ≦ ΔTsa) based on the comparison result in the maximum / minimum temperature calculation unit 33, a failure of the EGR system occurs. The determination result is transmitted to the display device 4.

As shown in FIG. 5B, a deviation occurs between the change in the intake air temperature and the operation of the EGR valve 105 due to the thermal inertia of the temperature detector such as the intake air temperature detector 2 and the inertia of the exhaust gas. There is a time lag Δt between the intake air temperature A and the temperature sensor instruction intake air temperature B by the intake air temperature detector 2, and the EGR valve 105 is opened and closed as shown in FIG. and the temperature difference T ₂ becomes small between, causing error in the failure determination according to the temperature difference T _2.
However, according to the actual施例that written, as described above, the situations causing erroneous determination on the failure determination of the EGR system using the intake air temperature value detected by the temperature detector, such as the intake air temperature detector 2 Even in this case, by using the maximum and minimum temperature difference ΔTs during a predetermined sampling period during the opening of the EGR valve 105, the change in the intake air temperature due to the thermal inertia of the temperature detector and the inertia of the exhaust gas as described above and the EGR valve 105 This makes it possible to avoid an error in detecting an intake air temperature change due to the occurrence of a deviation from the operation.

In the first reference example or the second reference example, the EGR system does not satisfy the first determination condition for failure of the EGR system and does not satisfy the second determination condition for failure of the EGR system. even when it is judged to be normal, as in real施例that written, the maximum and minimum temperature difference .DELTA.Ts the allowable temperature difference DerutaTsa less when the (ΔTs ≦ ΔTsa), the third failure of the exhaust gas recirculating system By making this determination condition, it is possible to reliably avoid a failure detection leak of the EGR system.

  According to the present invention, the EGR system is not affected by a change in the fresh air temperature due to an engine operating condition or the like, and a detection error of a detector (sensor) that detects the fresh air temperature or the intake air temperature after EGR mixing. It is possible to provide a fault diagnosis device for an exhaust gas recirculation system that can accurately detect a fault in the exhaust gas.

1 is an overall configuration diagram of a failure diagnosis device for an exhaust gas recirculation system in a vehicle engine according to an embodiment of the present invention. It is a control block diagram of a first reference example of fault diagnosis system. It is a control block diagram of a second reference example of fault diagnosis system. It is a control block diagram of a real施例failure diagnosis apparatus of the present invention. (A), (B) is an operation explanatory diagram of the front you施例. It is a figure corresponding to FIG. 1 which shows a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fresh air temperature detector 2 Intake air temperature detector 3 Cover 3 Alarm device 4 Display device 5 EGR valve opening calculation part 10 Controller 100 Engine 101 Intake manifold 102 Exhaust manifold 103 Intake passage 104 EGR (exhaust gas recirculation) passage 105 EGR valve 106 New air passage 107 Confluence

Claims (1)

Failure diagnosis of an exhaust gas recirculation system in which EGR (exhaust gas recirculation) gas from the exhaust passage of the engine is recirculated to the intake passage through the EGR passage and an EGR valve is provided in the EGR passage to adjust the flow area of the EGR passage. In the device
An intake air temperature detector that is provided in an intake passage downstream of the joining portion of the EGR passage and the intake passage and detects the temperature of intake air in which EGR gas is mixed into fresh air, and an input from the intake air temperature detector The temperature difference between the maximum temperature (Tmax) and the minimum temperature (Tmin) during a predetermined sampling period during the opening of the EGR valve, that is, the maximum / minimum temperature difference (ΔTs = Tmax−Tmin) is calculated from the detected value of the intake air temperature. An exhaust gas recirculation system comprising: a controller for determining a failure condition of the exhaust gas recirculation system when the maximum and minimum temperature difference ΔTs is equal to or less than a preset allowable temperature difference (ΔTsa) (ΔTs ≦ ΔTsa) Fault diagnosis device.

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