WO2010134167A1

WO2010134167A1 - Abnormality diagnostic apparatus for nox sensor

Info

Publication number: WO2010134167A1
Application number: PCT/JP2009/059227
Authority: WO
Inventors: 小田　富久
Original assignee: トヨタ自動車株式会社
Priority date: 2009-05-19
Filing date: 2009-05-19
Publication date: 2010-11-25

Abstract

An abnormality diagnostic apparatus for an NOx sensor installed in the exhaust passage of an internal combustion engine. The exhaust passage comprises an upstream passage, a downstream passage, and an intermediate passage positioned therebetween. The abnormality diagnostic apparatus comprises a changeover valve changeable between a forward flow position where the upstream passage is connected to one end of the intermediate passage and the other end of the intermediate passage is connected to the downstream passage and a reverse flow position where the upstream passage is connected to the other end of the intermediate passage and one end of the intermediate passage is connected to the downstream passage. An NOx catalyst is installed on the upstream side of the intermediate passage and the NOx sensor is installed on the downstream side of the intermediate passage in the forward flow direction of exhaust gas when the changeover valve is set at the forward flow position. When the NOx sensor is diagnosed for abnormality, the changeover valve is changed to the reverse flow position.

Description

NOx sensor abnormality diagnosis device

The present invention relates to a NOx sensor abnormality diagnosis device, and more particularly to a device for diagnosing abnormality of a NOx sensor provided in an exhaust passage of an internal combustion engine.

Generally, a NOx catalyst for purifying NOx (nitrogen oxide) contained in exhaust gas is known as an exhaust purification device disposed in an exhaust system of an internal combustion engine such as a diesel engine. For example, in order to detect whether or not NOx is purified by the NOx catalyst, a NOx sensor for detecting the NOx concentration of the exhaust gas is provided on the downstream side of the NOx catalyst.

On the other hand, in the field of automobiles, in order to prevent the running of a vehicle whose exhaust emission has deteriorated, it is required by the laws and regulations of each country to diagnose the abnormality of the catalyst or the sensor in the on-board state (onboard). There are already relatively many techniques for diagnosing catalyst abnormalities. However, there are not so many proposals for abnormality diagnosis of the NOx sensor provided on the downstream side of the NOx catalyst. In particular, in the current situation where exhaust gas regulations are becoming stricter, it is necessary to reliably prevent deterioration of exhaust emission due to abnormality of the NOx sensor.

Patent Document 1 describes the NOx sensor abnormality diagnosis of the NOx sensor provided on the downstream side of the selective reduction type NOx catalyst, the exhaust gas NOx concentration upstream of the NOx catalyst and the detected concentration of the NOx sensor during the stop of the addition of the reducing agent to the NOx catalyst. And diagnosing an abnormality in the NOx sensor. In this technique, the addition of the reducing agent is stopped at the time of diagnosis in order to eliminate the influence of the NOx catalyst arranged on the upstream side of the NOx sensor.

JP 2008-133780 A

However, according to the technique described in Patent Document 1, since the addition of the reducing agent is stopped at the time of diagnosis, NOx in the exhaust gas cannot be purified by the NOx catalyst. Therefore, there is a problem that exhaust emission is deteriorated at the time of diagnosis.

Therefore, the present invention has been made in view of such circumstances, and one object of the present invention is to provide a NOx sensor abnormality diagnosis device that can prevent deterioration of exhaust emission at the time of diagnosis.

According to one aspect of the invention,
An apparatus for diagnosing an abnormality in a NOx sensor provided in an exhaust passage of an internal combustion engine,
The exhaust passage has an upstream passage, a downstream passage, and an intermediate passage located between the upstream passage and the downstream passage;
A forward flow position that connects one end of the upstream passage and the intermediate passage and connects the other end of the intermediate passage and the downstream passage, and one end of the intermediate passage that connects the upstream passage and the other end of the intermediate passage A switching valve that can be switched to a backflow position that connects the downstream passage is provided,
In the forward flow direction of the exhaust gas when the switching valve is in the forward flow position, a NOx catalyst is provided upstream of the intermediate passage and the NOx sensor is provided downstream of the intermediate passage,
There is provided a NOx sensor abnormality diagnosis device, characterized in that a switching valve control means for switching the switching valve to the backflow position is provided at the time of abnormality diagnosis of the NOx sensor.

時に If the switching valve is switched to the backflow position at the time of abnormality diagnosis, the exhaust gas flows in the reverse flow direction opposite to the forward flow direction. That is, the exhaust gas flowing through the upstream passage flows into the intermediate passage from the other end of the intermediate passage, and first passes through the NOx sensor and then passes through the NOx catalyst, contrary to the forward flow direction. Then, it flows out from one end of the intermediate passage to the downstream passage. At this time, since the exhaust gas before passing through the NOx catalyst is supplied to the NOx sensor, the influence of the NOx catalyst can be eliminated. On the other hand, NOx in the exhaust gas is purified by the NOx catalyst after passing through the NOx sensor. Thereby, it is possible to prevent the exhaust emission from deteriorating at the time of diagnosis.

Preferably, the NOx catalyst is a selective reduction type NOx catalyst, and an addition valve for adding a reducing agent is provided upstream of the NOx catalyst in the forward flow direction. The addition valve may be provided in the upstream passage, or alternatively in the intermediate passage.

Preferably, an addition valve control means for controlling the addition valve is provided, and the addition valve control means stops the addition of the reducing agent from the addition valve when diagnosing abnormality of the NOx sensor.

By stopping the addition of the reducing agent at the time of abnormality diagnosis, the supply of the reducing agent to the NOx sensor can be prevented, and the NOx sensor can be prevented from generating an output corresponding to the reducing agent. Therefore, the diagnostic accuracy can be improved.

Alternatively, the NOx catalyst may be an NOx storage reduction catalyst.

Preferably, the intermediate passage is formed in an annular shape where one portion is divided, the intermediate passage is connected to the upstream passage and the downstream passage at the divided portion, and the switching valve is provided at the connection portion.

This makes it possible to switch between the forward flow direction and the reverse flow direction using a single switching valve.

Preferably, upstream concentration acquisition means for detecting or estimating the NOx concentration of the exhaust gas upstream of the NOx catalyst in the forward flow direction;
A determination unit that determines whether the NOx sensor is normal or abnormal by comparing the NOx concentration detected or estimated by the upstream concentration acquisition unit with the NOx concentration detected by the NOx sensor during abnormality diagnosis of the NOx sensor. And are provided.

Preferably, the upstream concentration acquisition means includes at least one of an estimation means for estimating the NOx concentration of the exhaust gas based on an operating state of the internal combustion engine and an upstream NOx sensor for detecting the NOx concentration of the exhaust gas.

Preferably, the upstream concentration acquisition means includes both the estimation means and the upstream NOx sensor,
The determination unit compares the detected value of the NOx concentration by the NOx sensor, the detected value of the NOx concentration by the upstream NOx sensor, and the estimated value of the NOx concentration by the estimation unit, and compares the NOx sensor, the upstream NOx sensor, and the Judgment is made by distinguishing whether the internal combustion engine is normal or abnormal.

Preferably, the estimation means estimates the NOx concentration from a predetermined map, and when the internal combustion engine is determined to be abnormal by the determination means, at least a detection value of the NOx sensor and a detection value of the upstream NOx sensor Based on one, the map data is modified.

According to the present invention, an excellent effect is exhibited that it is possible to prevent deterioration of exhaust emission at the time of diagnosis.

FIG. 1 is a diagram schematically showing an internal combustion engine according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part when the switching valve is in the backflow position. FIG. 3 is a flowchart of a second example of the abnormality diagnosis process.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

FIG. 1 schematically shows an internal combustion engine according to an embodiment of the present invention. In the figure, 1 is a compression ignition type internal combustion engine or diesel engine for automobiles, 2 is an intake manifold communicated with an intake port, 3 is an exhaust manifold communicated with an exhaust port, and 4 is a combustion chamber. In the present embodiment, fuel supplied from a fuel tank (not shown) to the high pressure pump 5 is pumped to the common rail 6 by the high pressure pump 5 and accumulated in a high pressure state. The high pressure fuel in the common rail 6 is transferred from the injector 7 to the combustion chamber. 4 is directly supplied by injection.

The exhaust gas from the engine 1 passes through the turbocharger 8 from the exhaust manifold 3 and then flows into the exhaust passage 9 downstream thereof, and after being purified as described later, is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device. It is also optional to include other exhaust purification devices such as EGR devices.

On the other hand, the intake air introduced from the air cleaner 10 into the intake passage 11 passes through the air flow meter 12, the turbocharger 8, the intercooler 13, and the throttle valve 14 in order to reach the intake manifold 2. The air flow meter 12 is a sensor for detecting the intake air amount, and specifically outputs a signal corresponding to the flow rate of the intake air. The throttle valve 14 is an electronically controlled type.

In the exhaust passage 9, in order from the upstream side, an oxidation catalyst 20 that oxidizes and purifies unburned components (especially HC) in the exhaust gas, and particulate matter (PM) in the exhaust gas is collected and removed by combustion. A DPR (Diesel Particulate Reduction) catalyst 22 is provided in series.

Further, on the downstream side of the DPR catalyst 22, the exhaust passage 9 includes an upstream passage 91, a downstream passage 93, and an intermediate passage 92 positioned between the upstream passage 91 and the downstream passage 93. In the present embodiment, the upstream passage 91 and the downstream passage 93 are formed in a straight shape or a straight tube shape, but the intermediate passage 92 is formed in an annular shape, particularly in an annular shape where one portion is divided. In the intermediate passage 92, one end 92A and the other end 92B are formed. The intermediate passage 92 is provided with a NOx catalyst for reducing and purifying NOx in the exhaust gas, particularly a selective reduction type NOx catalyst 24.

The intermediate passage 92 is connected to the upstream passage 91 and the downstream passage 93 at the part where the intermediate passage 92 is divided. That is, the downstream end (right end) of the upstream passage 91 and the upstream end (left end) of the downstream passage 93 are connected in a coaxial state, and one end 92A and the other end 92B of the intermediate passage 92 are connected to these connecting portions from the orthogonal direction. The As shown in the drawing, these four end portions are connected at the same place, and the upstream passage 91, the intermediate passage 92, and the downstream passage 93 cross each other at right angles.

And a switching valve 26 is provided at the connection or intersection. The switching valve 26 can be switched between a forward flow position as shown in FIG. 1 and a backflow position as shown in FIG.

As shown in FIG. 1, when the switching valve 26 is switched to the forward flow position, the upstream passage 91 and the one end 92A of the intermediate passage are connected or communicated, and the other end 92B of the intermediate passage and the downstream passage 93 are connected or communicated. . As a result, as shown by the arrow, the exhaust gas flows from the upstream passage 91 to the one end 92A of the intermediate passage, flows through the intermediate passage 92, and then flows out from the other end 92B of the intermediate passage to the downstream passage 93. Such a flow direction of the exhaust gas is referred to as a forward flow direction.

On the other hand, as shown in FIG. 2, when the switching valve 26 is switched to the backflow position, the upstream passage 91 and the other end 92B of the intermediate passage are connected or communicated, and the one end 92A of the intermediate passage and the downstream passage 93 are connected or communicated. Is done. As a result, as shown by the arrow, the exhaust gas flows from the upstream passage 91 into the other end 92B of the intermediate passage, and flows through the intermediate passage 92 in the direction opposite to that in the forward flow direction. The gas flows out of 92A into the downstream passage 93. Such a flow direction of the exhaust gas is referred to as a reverse flow direction.

According to this configuration, it is possible to switch between the forward flow direction and the reverse flow direction by the single switching valve 26, and advantages such as simplicity and low cost can be obtained.

In the present embodiment, a butterfly valve that rotates about a rotation axis is used as the switching valve 26. Then, the switching valve 26 is rotated about 90 ° counterclockwise from the forward flow position to the reverse flow position, and is rotated about 90 ° clockwise from the reverse flow position to the forward flow position. However, the structure and type of the switching valve 26 are arbitrary, and a spool valve or the like may be used. The switching valve 26 is an electronic control type, and is controlled by an electronic control unit (hereinafter referred to as ECU) 100 as a control means for controlling the entire engine.

Referring back to FIG. 1, the upstream passage 91 is provided with a NOx sensor 30 for detecting the NOx concentration of the exhaust gas. Hereinafter, this NOx sensor 30 is referred to as an upstream NOx sensor 30. The upstream passage 91 is provided with an addition valve 40 for adding a reducing agent downstream of the upstream NOx sensor 30. In this embodiment, urea is used as the reducing agent, but other reducing agents such as ammonia may be used.

The intermediate passage 92 is provided with a NOx sensor 32 for detecting the NOx concentration of the exhaust gas downstream of the NOx catalyst 24 in the forward flow direction of the exhaust gas as shown in FIG. Hereinafter, this NOx sensor 32 is referred to as a downstream NOx sensor 32. The downstream NOx sensor 32 is a sensor that is mainly a diagnosis target in the present embodiment. An upstream exhaust temperature sensor 50 and a downstream exhaust temperature sensor 52 for detecting the temperature of the exhaust gas are provided on the upstream and downstream sides of the NOx catalyst 24, respectively.

ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 controls the injector 7, the high-pressure pump 5, the throttle valve 14 and the like so that desired engine control is executed based on detection values and the like of various sensors. The ECU 100 also controls the addition valve 40 to control the urea addition amount. The ECU 100 is connected to the air flow meter 12, the upstream NOx sensor 30, the downstream NOx sensor 32, the upstream exhaust temperature sensor 50, and the downstream exhaust temperature sensor 52 as sensors.

Further, a crank angle sensor 15 and an accelerator opening sensor 16 are connected to the ECU 100. The crank angle sensor 15 outputs a crank pulse signal to the ECU 100 when the crank angle rotates, and the ECU 100 detects the crank angle of the engine 1 based on the crank pulse signal and calculates the rotational speed of the engine 1. The accelerator opening sensor 16 outputs a signal corresponding to the accelerator pedal opening (accelerator opening) operated by the user to the ECU 100.

Selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) 24 is supported by supporting a noble metal such as Pt on the surface of a substrate such as zeolite or alumina, or a transition metal such as Cu on the surface of the substrate by ion exchange. Examples thereof include those obtained by carrying a titania / vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) on the surface of the substrate. The selective reduction type NOx catalyst 24 can continuously reduce and purify NOx when the catalyst temperature is in a predetermined operating temperature range (for example, 200 to 400 ° C.) and urea as a reducing agent is added. is there. The added urea is hydrolyzed to produce ammonia, and this ammonia reacts with NOx on the catalyst to reduce NOx.

The temperature of the NOx catalyst 24 can be directly detected by a temperature sensor embedded in the catalyst, but in the present embodiment, it is estimated. Specifically, ECU 100 estimates the catalyst temperature based on the exhaust temperatures detected by upstream exhaust temperature sensor 50 and downstream exhaust temperature sensor 52, respectively. Note that the estimation method is not limited to such an example.

In this embodiment, the switching valve 26 is switched to the forward flow position as shown in FIG. 1 during normal operation, and the exhaust gas flows in the forward flow direction. At this time, urea added from the addition valve 40 flows into the intermediate passage 92 from one end 92 </ b> A of the intermediate passage and is supplied to the NOx catalyst 24. Further, the downstream NOx sensor 32 detects the NOx concentration of the exhaust gas downstream of the NOx catalyst 24, in other words, the exhaust gas discharged from the NOx catalyst 24.

On the other hand, at the time of abnormality diagnosis of the downstream NOx sensor 32, the switching valve 26 is switched to the backflow position as shown in FIG. 2, and the exhaust gas flows in the backflow direction. This point will be described in detail later.

During normal operation, the amount of urea added from the addition valve 40 is controlled by the ECU 100 so that the detected concentration of the downstream NOx sensor 32 is always below a predetermined value. Here, the downstream NOx sensor 32 can detect ammonia NH ₃ in addition to NOx, and outputs a signal corresponding to the total concentration of NOx and ammonia. This also applies to the upstream NOx sensor 30. Further, the NOx catalyst 24 can adsorb ammonia within a predetermined limit determined by the catalyst temperature, and if the urea addition amount is excessive, ammonia that cannot be adsorbed by the NOx catalyst 24 is discharged (so-called ammonia slip). This ammonia slip needs to be prevented because it causes a strange odor. Therefore, the amount of urea added so that the NOx catalyst 24 can adsorb a predetermined target amount of ammonia that does not cause ammonia slip and the NOx catalyst 24 can sufficiently purify NOx is based on the detected value of the upstream NOx sensor 30 and the like. Determined by. The addition valve 40 is controlled by the ECU 100 so that the determined urea addition amount is added from the addition valve 40.

The detected concentration of the downstream NOx sensor 32 increases both when the urea addition amount is insufficient and NOx is discharged from the NOx catalyst 24 and when the urea addition amount is excessive and ammonia is discharged from the NOx catalyst 24. . Therefore, the urea addition amount is controlled so that the detected concentration of the downstream NOx sensor 32 is always below a predetermined value (preferably near zero).

On the other hand, the execution / stop of urea addition is controlled according to the catalyst temperature of the NOx catalyst 24. That is, urea addition is executed when the estimated catalyst temperature of the NOx catalyst 24 is within a predetermined operating temperature range (for example, 200 to 400 ° C.), and urea addition is performed when the estimated catalyst temperature of the NOx catalyst 24 is outside the operating temperature range. Stopped.

The DPR catalyst 22 is a kind of diesel particulate filter (Diesel Particulate Filter; DPF), has a filter structure and has a noble metal on the surface, and continuously collects particulate matter collected by the filter using the noble metal. It is a continuous regeneration type that oxidizes (combusts). The DPF is not limited to such a DPR catalyst 22, and any type of DPF can be used.

Next, the abnormality diagnosis of the downstream NOx sensor 32 will be described.

As described above, at the time of abnormality diagnosis of the downstream NOx sensor 32, the switching valve 26 is switched to the backflow position as shown in FIG. 2, and the exhaust gas flows in the backflow direction. Further, urea addition from the addition valve 40 is stopped. Exhaust gas that has flowed through the upstream passage 91 flows into the intermediate passage 92 from the other end 92B of the intermediate passage, and first passes through the downstream NOx sensor 32, and then the NOx catalyst 24, contrary to the forward flow direction. Pass through. Then, it flows out from the one end 92 </ b> A of the intermediate passage to the downstream passage 93 and is discharged to the atmosphere through the downstream passage 93.

At this time, the exhaust gas before passing through the NOx catalyst 24 flows to the downstream NOx sensor 32, and the same exhaust gas is supplied to the upstream NOx sensor 30 and the downstream NOx sensor 32. Therefore, the NOx concentrations detected by the upstream NOx sensor 30 and the downstream NOx sensor 32 should be equal. Accordingly, the detected concentration of the downstream NOx sensor 32 is compared with the detected concentration of the upstream NOx sensor 30, and normality or abnormality of the downstream NOx sensor 32 is diagnosed.

Further, NOx in the exhaust gas at the time of diagnosis is reduced and purified by ammonia already adsorbed on the NOx catalyst 24. That is, when exhaust gas flowing in the reverse flow direction through the intermediate passage 92 passes through the NOx catalyst 24, a reduction reaction occurs between NOx in the exhaust gas and ammonia adsorbed on the NOx catalyst 24, thereby purifying NOx. The Therefore, it is possible to prevent NOx from being released into the atmosphere, and to prevent deterioration of exhaust emission at the time of diagnosis.

Furthermore, since urea addition is stopped at the time of diagnosis, the supply of urea to the downstream NOx sensor 32 can be prevented, and the downstream NOx sensor 32 can be prevented from generating an output corresponding to ammonia generated from urea. Therefore, the diagnostic accuracy can be improved.

Incidentally, as a comparison target of the detected concentration of the downstream NOx sensor 32, the NOx concentration of the exhaust gas estimated by the ECU 100 can be used instead of the detected concentration of the upstream NOx sensor 30. In this case, the ECU 100 determines the NOx concentration of the exhaust gas upstream of the NOx catalyst 24 in the forward flow direction according to a predetermined map based on the detected values of the parameters representing the engine operating state (for example, the engine rotational speed NE and the accelerator opening degree AC). Specifically, the NOx concentration of the exhaust gas discharged from the combustion chamber 4 of the engine 1 is estimated.

Hereinafter, the NOx concentration detected by the downstream NOx sensor 32 is referred to as downstream detection concentration Cd, the NOx concentration detected by the upstream NOx sensor 30 is referred to as upstream detection concentration Cu, and the NOx concentration estimated by the ECU 100 is referred to as upstream estimated concentration Ce. The comparison target of the downstream detection concentration Cd can be at least one of the upstream detection concentration Cu and the upstream estimated concentration Ce.

Here, to describe a first example of specific diagnostic processing, the ECU 100 detects the downstream detection concentration Cd when the switching valve 26 is switched to the backflow position and urea addition from the addition valve 40 is stopped, For example, the upstream detection concentration Cu is acquired, and the concentration difference ΔC = | Cu−Cd | is calculated. When the concentration difference ΔC is equal to or smaller than the predetermined value ΔCs, the ECU 100 regards the downstream detection concentration Cd as substantially equal to the upstream detection concentration Cu, and determines that the downstream NOx sensor 32 is normal. On the other hand, when the concentration difference ΔC is larger than the predetermined value ΔCs, the ECU 100 regards the downstream detected concentration Cd as being relatively large from the upstream detected concentration Cu, and determines that the downstream NOx sensor 32 is abnormal.

Next, a second example of diagnostic processing will be described. In the example described here, the downstream detection concentration Cd, the upstream detection concentration Cu, and the upstream estimated concentration Ce are compared with each other, and normality or abnormality of the downstream NOx sensor 32, the upstream NOx sensor 30, and the engine 1 is determined and distinguished. .

Since the downstream detection concentration Cd is compared with both the upstream detection concentration Cu and the upstream estimated concentration Ce, the reliability of abnormality diagnosis of the downstream NOx sensor 32 is improved. For example, if only the downstream detection concentration Cd is compared with the upstream detection concentration Cu, if the downstream detection concentration Cd is greatly deviated from the upstream detection concentration Cu, the downstream NOx sensor 32 is abnormal or the upstream NOx sensor 30 is abnormal. It is not possible to distinguish and specify. According to this example, since the upstream estimated concentration Ce is also added to the comparison target, for example, when the upstream detected concentration Cu and the upstream estimated concentration Ce are substantially equal and only the downstream detected concentration Cd is deviated, the downstream NOx sensor 32. Can be determined as abnormal. In the same manner, the abnormality of the upstream NOx sensor 30 and the engine 1 can be diagnosed. Only one that shows an outlier is diagnosed as abnormal.

Eventually, it is possible to diagnose not only the downstream NOx sensor 32 but also the upstream NOx sensor 30 and the engine 1. Therefore, it is possible to expand the range of abnormality diagnosis.

FIG. 3 shows the procedure of the diagnostic processing according to the second example. First, in step S101, the ECU 100 determines whether or not a predetermined condition suitable for making a diagnosis is satisfied. For example, (a) the upstream NOx sensor 30 and the downstream NOx sensor 32 have reached a predetermined activation temperature, (b) the engine 1 is in a steady operation state, and (c) the engine 1 has been warmed up. When all the conditions are satisfied, the condition is satisfied.

Note that the ECU 100 detects the element impedances of the upstream NOx sensor 30 and the downstream NOx sensor 32 to obtain the element temperature with respect to the condition (a), and determines whether or not the element temperature has reached a predetermined activation temperature. Further, regarding the condition (b), the ECU 100 determines that the engine 1 is in a steady operation state when, for example, the fluctuation amount of the intake air amount GA detected by the air flow meter 12 is within a predetermined range. Furthermore, regarding condition (c), ECU 100 determines that warm-up of engine 1 has ended when the coolant temperature detected by a water temperature sensor (not shown) is equal to or higher than a predetermined value.

The predetermined condition preferably further includes (d) a condition that the estimated catalyst temperature of the NOx catalyst 24 is within a predetermined operating temperature range.

ECU100 will be in a standby state, when it is judged that predetermined conditions are not satisfied. On the other hand, when ECU 100 determines that the predetermined condition is satisfied, urea addition from addition valve 40 is stopped in step S102, and switching valve 26 is switched to the backflow position in step S103.

Next, in step S104, the ECU 100 acquires the downstream detection concentration Cd, the upstream detection concentration Cu, and the upstream estimated concentration Ce.

Thereafter, in step S105, the ECU 100 calculates the concentration difference between the downstream detection concentration Cd, the upstream detection concentration Cu, and the upstream estimated concentration Ce, that is, the first concentration difference ΔC1, the second concentration difference ΔC2, and the third concentration difference ΔC3 by the following equations. calculate.
ΔC1 = | Ce-Cu |
ΔC2 = | Ce−Cd |
ΔC3 = | Cu-Cd |

Next, the ECU 100 compares the first to third concentration differences ΔC1 to ΔC3 with the first to third predetermined values ΔC1s to ΔC3s, respectively. First, in step S106, the ECU 100 compares the first concentration difference ΔC1 with a first predetermined value ΔC1s, and compares the second concentration difference ΔC2 with a second predetermined value ΔC2s.

When the first concentration difference ΔC1 is greater than the first predetermined value ΔC1s and the second concentration difference ΔC2 is greater than the second predetermined value ΔC2s (ΔC1> ΔC1s & ΔC2> ΔC2s), the ECU 100 determines that only the upstream estimated concentration Ce is the other two. It is assumed that there is a deviation from the two values, that is, the upstream detection concentration Cu and the downstream detection concentration Cd, and the engine 1 is determined to be abnormal in step S107.

After the abnormality determination of the engine 1, the ECU 100 corrects or updates the map for calculating the upstream estimated concentration Ce in step S108. That is, since the optimal value of the map data may change from when it is new due to aging, etc., the NOx concentration value actually obtained at present is learned in the map.

Specifically, the values on the map corresponding to the engine parameters (for example, the rotation speed and the accelerator opening) when the upstream estimated concentration Ce is acquired in step S104 are the upstream detection concentration Cu and downstream detection acquired in step S104. The value is replaced with a value based on at least one of the concentrations Cd (either one value or an average value of both).

On the other hand, if the relationship of ΔC1> ΔC1s and ΔC2> ΔC2s is not satisfied in step S106, the ECU 100 compares the first concentration difference ΔC1 with the first predetermined value ΔC1s in step S109 and compares the third concentration difference ΔC3 with The third predetermined value ΔC3s is compared.

When the first concentration difference ΔC1 is larger than the first predetermined value ΔC1s and the third concentration difference ΔC3 is larger than the third predetermined value ΔC3s (ΔC1> ΔC1s & ΔC3> ΔC3s), the ECU 100 determines that only the upstream detected concentration Cu is the other two. The upstream NOx sensor 30 is determined to be abnormal in step S110, assuming that there is a deviation from the two values, that is, the upstream estimated concentration Ce and the downstream detected concentration Cd.

On the other hand, if the relationship of ΔC1> ΔC1s and ΔC3> ΔC3s is not satisfied in step S109, the ECU 100 compares the second concentration difference ΔC2 with the second predetermined value ΔC2s in step S111 and compares the third concentration difference ΔC3 with The third predetermined value ΔC3s is compared.

When the second concentration difference ΔC2 is larger than the second predetermined value ΔC2s and the third concentration difference ΔC3 is larger than the third predetermined value ΔC3s (ΔC2> ΔC2s & ΔC3> ΔC3s), the ECU 100 determines that only the downstream detected concentration Cd is the other two. The downstream NOx sensor 32 is determined to be abnormal in step S112, assuming that there is a deviation from the two values, that is, the upstream estimated concentration Ce and the upstream detected concentration Cu.

On the other hand, if the relationship of ΔC2> ΔC2s and ΔC3> ΔC3s is not satisfied in step S111, ECU 100 determines that all of engine 1, upstream NOx sensor 30, and downstream NOx sensor 32 are normal in step S113.

As mentioned above, although embodiment of this invention was described, this invention can also take other embodiment.

For example, although the addition valve 40 is provided in the upstream passage 91 in the above embodiment, the addition valve 40 may be provided in the intermediate passage 92 upstream of the NOx catalyst 24 in the forward flow direction.

The comparison between the downstream detection concentration and at least one of the upstream detection concentration and the upstream estimated concentration was performed based on the difference between the two in the above embodiment, but the comparison method is not limited to this, for example, based on the ratio between the two. You may go. The internal combustion engine may be other than the compression ignition type, for example, a spark ignition type internal combustion engine, particularly a direct injection lean burn gasoline engine.

An NOx storage reduction (NSR: NOx Storage Reduction) catalyst may be used as the NOx catalyst. The NOx storage reduction catalyst stores NOx in the exhaust gas in the form of nitrate when the air-fuel ratio of the exhaust gas supplied thereto is leaner than the stoichiometric air-fuel ratio (that is, an oxygen-excess atmosphere), and the exhaust gas empty When the fuel ratio is the stoichiometric air-fuel ratio or richer (that is, in an oxygen-deficient atmosphere), the stored NOx is released and reduced to N ₂ , which has an NOx absorption / release action. In this case, the addition valve for adding the reducing agent can be omitted. At the time of abnormality diagnosis, the exhaust gas flowing in the reverse flow direction in the intermediate passage is supplied to the NOx catalyst after passing through the downstream NOx sensor. Then, NOx in the exhaust gas is stored in the NOx catalyst and purified.

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.

Claims

An apparatus for diagnosing an abnormality in a NOx sensor provided in an exhaust passage of an internal combustion engine,
The exhaust passage has an upstream passage, a downstream passage, and an intermediate passage located between the upstream passage and the downstream passage;
A forward flow position that connects one end of the upstream passage and the intermediate passage and connects the other end of the intermediate passage and the downstream passage, and one end of the intermediate passage that connects the upstream passage and the other end of the intermediate passage A switching valve that can be switched to a backflow position that connects the downstream passage is provided,
In the forward flow direction of the exhaust gas when the switching valve is in the forward flow position, a NOx catalyst is provided upstream of the intermediate passage and the NOx sensor is provided downstream of the intermediate passage,
A NOx sensor abnormality diagnosis device, comprising: a switching valve control means for switching the switching valve to the backflow position during abnormality diagnosis of the NOx sensor.
2. The NOx sensor according to claim 1, wherein the NOx catalyst is a selective reduction type NOx catalyst, and an addition valve for adding a reducing agent is provided upstream of the NOx catalyst in the forward flow direction. Abnormality diagnosis device.
The addition valve control means for controlling the addition valve is provided, and the addition valve control means stops addition of the reducing agent from the addition valve at the time of abnormality diagnosis of the NOx sensor. The abnormality diagnosis device for the NOx sensor as described.
The abnormality diagnosis apparatus for a NOx sensor according to claim 1, wherein the NOx catalyst is an NOx storage reduction catalyst.
The intermediate passage is formed in an annular shape divided at one location, the intermediate passage is connected to the upstream passage and the downstream passage at the division location, and the switching valve is provided at the connection location. The abnormality diagnosis apparatus for a NOx sensor according to any one of claims 1 to 4.
Upstream concentration acquisition means for detecting or estimating the NOx concentration of the exhaust gas upstream of the NOx catalyst in the forward flow direction;
A determination unit that determines whether the NOx sensor is normal or abnormal by comparing the NOx concentration detected or estimated by the upstream concentration acquisition unit with the NOx concentration detected by the NOx sensor during abnormality diagnosis of the NOx sensor. The NOx sensor abnormality diagnosis device according to any one of claims 1 to 5, wherein the abnormality diagnosis device is provided.
The upstream concentration acquisition means comprises at least one of an estimation means for estimating the NOx concentration of exhaust gas based on an operating state of the internal combustion engine and an upstream NOx sensor for detecting the NOx concentration of the exhaust gas. Item 7. The NOx sensor abnormality diagnosis device according to Item 6.
The upstream concentration acquisition means comprises both the estimation means and the upstream NOx sensor;
The determination unit compares the detected value of the NOx concentration by the NOx sensor, the detected value of the NOx concentration by the upstream NOx sensor, and the estimated value of the NOx concentration by the estimation unit, and compares the NOx sensor, the upstream NOx sensor, and the The NOx sensor abnormality diagnosis device according to claim 7, wherein the determination is made by distinguishing whether the internal combustion engine is normal or abnormal.
The estimating means estimates the NOx concentration from a predetermined map, and based on at least one of the detected value of the NOx sensor and the detected value of the upstream NOx sensor when the internal combustion engine is determined to be abnormal by the determining means. The NOx sensor abnormality diagnosis apparatus according to claim 8, wherein the map data is corrected.