JP5170689B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  A urea selective reduction exhaust purification device is known as an exhaust purification device that purifies nitrogen oxides (NOx) contained in exhaust gas discharged from an internal combustion engine (see, for example, Patent Document 1). This exhaust purification device includes a catalytic converter including a selective reduction catalyst (SCR) in an exhaust passage, and a urea water addition valve provided upstream thereof. The selective reduction catalyst carries a catalyst metal such as vanadium oxide on its catalyst carrier. When urea water is added to the exhaust passage, the urea water is hydrolyzed and ammonia is generated by the heat of the exhaust gas, and this ammonia and NOx undergo a denitration reaction with NOx in the selective reduction catalyst to generate nitrogen and water.

JP 2003-301737 A

  By the way, in the urea selective reduction exhaust purification apparatus, it is necessary to constantly monitor that the NOx purification rate is maintained within a certain range. For this reason, for example, when a NOx sensor for detecting the NOx concentration is provided downstream of the catalytic converter in the exhaust passage, the NOx concentration of the exhaust gas after purifying NOx is monitored, and the NOx purification rate decreases, Judge as abnormal.

  However, in the method of detecting an abnormality in the NOx purification rate with the NOx sensor arranged on the downstream side of the catalytic converter as described above, the cause of the abnormality in the NOx purification rate is an abnormality of the selective reduction catalyst, an abnormal concentration of urea water, or urea. It was difficult to individually detect whether the amount of water addition was abnormal (that is, whether the urea addition valve was abnormal).

  The present invention has been made in view of the above problems, and an object thereof is to provide a urea selective reduction type exhaust purification device capable of detecting the cause of abnormality when an abnormality in the NOx purification rate occurs. It is in.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of an internal combustion engine, and selectively reduces NOx contained in exhaust gas selectively using ammonia produced by hydrolysis of urea water as a reducing agent. An exhaust purification device for an internal combustion engine, comprising: a catalyst; and a urea water addition valve that adds urea water toward the selective reduction catalyst from an upstream side of the selective reduction catalyst in the exhaust passage, wherein the NOx of the selective reduction catalyst In order to detect the cause of the abnormality when the purification rate decreases, a NOx sensor is provided downstream of the urea water addition valve in the exhaust passage and upstream of the selective reduction catalyst.

  In the above configuration, it is possible to employ a configuration that further includes abnormality detection means for detecting a decrease in the NOx purification rate of the selective reduction catalyst and the cause of the abnormality using the detection signal of the NOx sensor.

  In the above configuration, the abnormality detection means detects a decrease in the NOx purification rate of the selective reduction catalyst based on the detection signal of the NOx sensor and the detected or estimated NOx concentration downstream of the selective reduction catalyst. The configuration can be adopted.

  In the above configuration, when the abnormality detecting unit detects a decrease in the NOx purification rate of the selective reduction catalyst, the NOx sensor detection signal and the detected or estimated upstream NOx concentration of the urea water addition valve are detected. Based on the above, it is possible to estimate the amount of ammonia supplied to the selective reduction catalyst, and based on the estimated amount of ammonia, detect an abnormality in the urea water addition amount and an abnormality in the concentration of the added urea water. .

  In the above configuration, when the urea water concentration is normal, the abnormality detection means determines whether the urea addition amount is normal based on the estimated ammonia amount. A configuration that corrects the amount of urea water added to the valve can be adopted.

  In the above configuration, when the NOx purification rate is not normalized after correcting the urea water addition amount of the urea water addition valve, it is possible to adopt a configuration in which the selective reduction catalyst is determined to be abnormal.

  In the above configuration, the abnormality detection means determines whether the concentration of urea water is normal based on the estimated ammonia amount when the addition amount of urea water is normal, and when the concentration of urea water is normal Can adopt a configuration in which the selective catalytic reduction catalyst is determined to be abnormal.

  The abnormality detection unit may employ a configuration in which the ammonia amount is estimated when a predetermined condition is satisfied for hydrolysis of urea water to generate ammonia.

  According to the present invention, when an abnormality in the NOx purification rate is detected in the urea selective exhaust purification device, the cause of the abnormality can be detected.

1 is a configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. It is a flowchart which shows an example of the abnormality detection process of the exhaust gas purification apparatus by ECU. 6 is a flowchart showing another example of an abnormality detection process of the exhaust gas purification apparatus by the ECU.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention.
In FIG. 1, the internal combustion engine 1 is, for example, a diesel engine. In the exhaust passage 10 of the internal combustion engine 1, an oxidation catalyst converter 30, a diesel particulate filter (DPF) 40, a urea water addition valve 62, and a selective reduction catalyst converter 50 are provided from the upstream side. The exhaust passage 10 is provided with NOx sensors 70A, 70B and 70C for detecting the concentration of nitrogen oxide (NOx) in the exhaust gas EG. The NOx sensor 70A is provided on the downstream side of the urea water addition valve 62 and on the upstream side of the selective catalytic reduction converter 50. The NOx sensor 70B is provided on the downstream side of the selective catalytic reduction converter 50. The NOx sensor 70 </ b> C is provided on the upstream side of the urea water addition valve 62.

  The oxidation catalyst converter 30 carries an oxidation catalyst made of a catalyst metal or the like that oxidizes unburned fuel or the like in the exhaust gas EG in order to raise the temperature of the exhaust gas EG supplied to the DPF 40 or the like at the subsequent stage.

  The DPF 40 is a filter that collects particulate matter (PM) contained in the exhaust gas EG. As is well known, the structure of the DPF 40 is composed of, for example, a honeycomb body made of metal or ceramics. The DPF 40 needs to be regenerated when a predetermined amount of PM is deposited. Specifically, for example, the oxidation catalyst converter 30 is activated by raising the temperature, and the exhaust gas EG heated by the oxidation action of the oxidation catalyst converter 30 is supplied to the DPF 40. As a result, the collected PM is burned and the filter function is regenerated. The DPF 40 may be configured to carry an oxidation catalyst made of a catalyst metal.

  The urea water addition valve 62 is connected to the urea tank 60 and adds a predetermined concentration of urea water 63 supplied from the urea tank 60 toward the selective reduction catalytic converter 50 to the exhaust passage 10. The urea water addition valve 62 is configured to add an addition amount according to a control command from the electronic control unit (ECU) 100. The urea water added to the exhaust passage 10 is hydrolyzed by the heat of the exhaust gas EG to generate ammonia.

The selective reduction catalytic converter 50 selectively reduces NOx contained in the exhaust gas EG into nitrogen gas and water using ammonia generated from the urea water added from the urea water addition valve 62 as a reducing agent. . This selective reduction catalytic converter 50 has a well-known structure, for example, a material composed of zeolite containing Si, O, and Al as main components and containing Fe ions, or a surface of a base material made of aluminum oxide alumina, for example. In addition, a catalyst on which a catalyst metal such as a vanadium catalyst (V ₂ O ₅ ) is supported can be used, but it is not particularly limited thereto.

  The ECU 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup memory such as an EEPROM (Electronically Erasable and Programmable Read Only Memory), an A / D converter, a buffer, and the like. It comprises hardware including an output interface circuit including an input interface circuit, a drive circuit, etc., and necessary software. The ECU 100 receives detection signals from the three NOx sensors 70 </ b> A to 70 </ b> C and outputs a control signal to the urea water addition valve 62. The processing content of the ECU 100 will be described later.

  Next, an example of the abnormality detection process of the exhaust purification device by the ECU 100 will be described with reference to the flowchart shown in FIG. Note that the processing routine shown in FIG. 2 is executed, for example, every predetermined time after the internal combustion engine 1 is started.

  First, it is determined whether the NOx purification rate of the exhaust gas EG purified by the selective reduction catalytic converter 50 is lower than a predetermined range (step S1). This can be determined, for example, from the detected value of the NOx sensor 70B on the downstream side of the selective catalytic reduction converter 50 and the detected value of the NOx sensor 70A or 70C on the upstream side of the selective catalytic reduction converter 50. That is, by detecting the NOx concentration on the upstream side and downstream side of the selective catalytic reduction converter 50, the NOx purification rate of the exhaust purification device can be calculated, and it can be determined whether this value is within a predetermined range.

  In step S1, when the NOx purification rate is within the predetermined range, the process is terminated, and when it is determined that the NOx purification rate falls and falls outside the predetermined range, it is determined that an abnormality has occurred in the exhaust purification device. In order to detect the cause of the abnormality, first, it is determined whether the concentration of the urea water 63 added from the urea water addition valve 62 is normal (step S2). In order to detect an abnormality in the urea water concentration, for example, a urea water abnormality sensor can be provided in the urea tank 60 or the like. For simplification of the apparatus, for example, immediately after the urea water is replenished in the urea tank 60, urea is added. It can be determined whether or not the urea water concentration is normal by determining whether or not the NOx purification rate has decreased immediately after replacement of the tank 60 or the like.

  If it is determined in step S2 that the urea water concentration is abnormal, the urea water abnormality is detected (step S9). That is, it is determined that the cause of the decrease in the NOx purification rate is an abnormal urea water concentration.

  If it is determined in step S2 that the urea water concentration is normal, the urea water concentration is added to the currently selective catalytic reduction converter 50 using the detection signals of the downstream and upstream NOx sensors 70A and 70C of the urea water addition valve 62. The amount of ammonia present is estimated (step S3). Here, the NOx sensor 70A on the downstream side of the urea water addition valve 62 detects both NOx contained in the exhaust gas EG and ammonia generated by hydrolysis of the urea water. On the other hand, the NOx sensor 70C on the upstream side of the urea water addition valve 62 detects only NOx contained in the exhaust gas EG. Therefore, the amount of ammonia added to the selective catalytic reduction converter 50 can be estimated from the difference between the detected value of the NOx sensor 70A and the detected value of the NOx sensor 70C. In order to estimate the amount of ammonia added to the selective catalytic reduction converter 50 with higher accuracy, it is preferable to use the detection value of the NOx sensor 70A in a state where the hydrolysis of the urea water 63 has sufficiently progressed. The state in which the hydrolysis of the urea water 63 has sufficiently progressed is, for example, a state in which the temperature of the exhaust gas EG exceeds a predetermined temperature necessary for hydrolysis.

  Next, the actual urea water addition amount added from the urea water addition valve 62 is calculated using the ammonia amount estimated in step S3 (step S4). That is, the actual urea water addition amount is calculated based on the estimated ammonia amount and the concentration of the urea water 63.

  Next, the difference between the actual urea water addition amount calculated in step S4 and the addition instruction value from the ECU 100 for the urea water addition valve 62 is calculated, and this difference is compared with a predetermined threshold value (step S5). If the difference between the actual urea water addition amount and the addition instruction value is smaller than the predetermined threshold value, it is determined that the actual urea water addition amount is normal, and the process of step S7 described later is executed.

  In step S5, when the difference between the actual urea water addition amount and the addition instruction value is larger than a predetermined threshold value, it is determined that the urea water 63 addition amount is abnormal. That is, it is determined that an appropriate amount of urea water is not added due to malfunction of the urea water addition valve 62 or the like. Therefore, based on the difference between the actual urea water addition amount and the addition instruction value, the urea water addition instruction value is corrected so that the actual urea water addition amount becomes an appropriate amount (step S6).

  Next, it is determined whether or not the NOx purification rate of the exhaust gas EG purified by the exhaust purification device has been normalized (step S7). This can be determined by the same method as described in step S1. If the NOx purification rate of the exhaust gas EG has been normalized by correcting the actual urea water addition amount in step S6, it can be determined that the abnormality in the urea water addition amount has been resolved, and the processing is terminated.

  If the NOx purification rate of the exhaust gas EG is not normalized in step S7, an abnormality in the selective catalytic reduction converter 50 is detected (step S8). That is, if the concentration of urea water is normal and the amount of urea water added is normal, but the NOx purification rate of the exhaust gas EG does not normalize, there is an abnormality in the selective catalytic reduction converter 50. It can be judged that it exists.

  In the present embodiment, a NOx sensor 70A is disposed downstream of the urea water addition valve 62 and upstream of the selective catalytic reduction converter 50 in order to detect a decrease in the NOx purification rate and the cause of the abnormality. By estimating the amount of ammonia to be supplied, it is possible to identify the cause of the abnormality that reduces the NOx purification rate.

  In the present embodiment, the NOx sensors 70B and 70C are also arranged downstream of the selective catalytic reduction converter 50 and upstream of the urea water addition valve 62. Instead, the ECU 100 constructs a NOx estimation model and selects it. A configuration in which the NOx concentration downstream of the reduction catalytic converter 50 and / or upstream of the urea water addition valve 62 is estimated may be employed.

  Next, another example of the abnormality detection process of the exhaust gas purification apparatus by the ECU 100 will be described with reference to the flowchart shown in FIG. Note that the processing routine shown in FIG. 3 is executed, for example, every predetermined time after the internal combustion engine 1 is started.

  First, it is determined whether the NOx purification rate of the exhaust gas EG purified by the exhaust purification device is lower than a predetermined range (step S11). This can be determined by the same processing as in step S1 described above.

  In step S11, if the NOx purification rate is within the predetermined range, the process is terminated, and if it is determined that the NOx purification rate falls outside the predetermined range, it is determined that an abnormality has occurred in the exhaust purification device. In order to detect the cause of the abnormality, first, it is determined whether the urea water addition valve 62 is normal (step S12). This can be determined, for example, by providing a flow meter in the urea water addition system and measuring the urea addition amount. It can also be determined whether the urea water addition valve 62 is operating normally by measuring the addition pressure at the urea water addition valve 62.

  If it is determined in step S12 that the urea water addition valve 62 is not operating normally, a urea water addition valve abnormality is detected (step S18). If it is determined in step S12 that the urea water addition valve 62 is operating normally, the current selective reduction is performed using the detection signals of the NOx sensors 70A and 70C on the downstream side and the upstream side of the urea water addition valve 62. The amount of ammonia added to the catalytic converter 50 is estimated (step S13). This process is the same process as step S3 described above.

  Next, the concentration of the urea water 63 added from the urea water addition valve 62 is calculated from the estimated amount of addition to the urea water addition valve 62 and the estimated ammonia amount (step S14).

  Next, it is determined whether the concentration of the urea water 63 added from the urea water addition valve 62 calculated in step S14 is within the reference value range (step S15). When it is determined that the concentration of the urea water 63 is within the reference value range, neither the urea water addition amount nor the urea water concentration is abnormal, and thus an abnormality of the selective catalytic reduction converter 50 is detected (step S16). ). Further, when the concentration of the urea water 63 is outside the range of the reference value, it is determined that the urea water concentration is abnormal (station S17).

  According to the present embodiment, the NOx sensor 70A is disposed downstream of the urea water addition valve 62 and upstream of the selective reduction catalytic converter 50, and the amount of ammonia supplied to the selective reduction catalytic converter 50 is estimated, thereby purifying NOx. When an abnormality in which the rate decreases is detected, it is possible to identify the cause of the abnormality in which the NOx purification rate decreases.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 10 ... Exhaust passage 30 ... Oxidation catalytic converter 40 ... DPF
50 ... Selective reduction catalytic converter 60 ... Urea tank 62 ... Urea water addition valve 63 ... Urea water 100 ... ECU
EG ... Exhaust gas

Claims (5)

A selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx contained in the exhaust gas by hydrolysis of urea water using ammonia as a reducing agent; and the selective reduction catalyst in the exhaust passage. An exhaust gas purification apparatus for an internal combustion engine comprising a urea water addition valve for adding urea water toward the selective reduction catalyst from the upstream side,
For NOx purification rate of the selective reduction catalyst for detecting the cause of the abnormality when lowered, NOx sensor is provided on the upstream side of the downstream side a and the selective reduction catalyst of the urea water addition valve of the exhaust passage ,
Using a detection signal of the NOx sensor, further comprising an abnormality detection means for detecting a decrease in the NOx purification rate of the selective reduction catalyst and the cause of the abnormality,
The abnormality detecting means detects a decrease in the NOx purification rate of the selective reduction catalyst based on the detection signal of the NOx sensor and the detected or estimated NOx concentration upstream of the urea water addition valve. Estimating the amount of ammonia supplied to the selective reduction catalyst, and detecting an abnormality in the urea water addition amount or an abnormality in the concentration of the added urea water based on the estimated ammonia amount. An exhaust gas purification apparatus for an internal combustion engine characterized by the above. The abnormality detection means determines whether the urea addition amount is normal based on the estimated ammonia amount when the urea water concentration is normal, and determines that the urea addition amount of the urea water addition valve is abnormal if it is determined to be abnormal. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the amount of addition is corrected. 3. The internal combustion engine according to claim 2 , wherein if the NOx purification rate is not normalized after correcting the urea water addition amount of the urea water addition valve, the selective reduction catalyst is determined to be abnormal. Exhaust purification device. The abnormality detection means determines whether the concentration of urea water is normal based on the estimated ammonia amount when the addition amount of urea water is normal, and if the concentration of urea water is normal, the selection The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the reduction catalyst is determined to be abnormal. The said abnormality detection means estimates the amount of ammonia when satisfy | filling the predetermined condition for urea water to be hydrolyzed and to produce | generate ammonia, The ammonia amount in any one of Claim 1 thru | or 4 characterized by the above-mentioned. An exhaust purification device for an internal combustion engine.

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