JP6264554B2 - Exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust purification system that reduces nitrogen oxides (NOx) in exhaust gas of an internal combustion engine.

  As a technique for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine (engine), an exhaust purification system using a urea SCR (Selective Catalytic Reduction) system is known. In an exhaust purification system using a urea SCR system, urea water is injected into an exhaust passage provided with a selective reduction catalyst (SCR catalyst), so that urea water is decomposed by the heat of exhaust gas and ammonia is generated. The generated ammonia reacts with NOx in the exhaust gas on the SCR catalyst, and NOx is reduced (purified) to nitrogen and water.

  As a selective reduction catalyst (SCR catalyst) for a urea SCR system, a purification catalyst / particle collection filter in which a flow path of a particle collection filter that collects particulate matter is coated with an SCR catalyst has been known (for example, Patent Document 1). When the purification catalyst / particulate collection filter is used, urea water is injected upstream of the purification catalyst / particulate collection filter.

  By combining the particulate collection filter and the SCR catalyst into a purification catalyst / particulate collection filter, the purification catalyst / particulate collection filter can be mounted close to the engine. For this reason, the fall of exhaust gas temperature is suppressed and the driving | operation area | region which can inject urea water spreads.

  In the purification catalyst / particulate collection filter that combines the particulate collection filter and the SCR catalyst, when ammonia is adsorbed to the purification catalyst / particulate collection filter, the temperature of the purification catalyst / particulate collection filter is increased to the temperature at which ammonia is desorbed. And regenerating by desorbing ammonia.

  By the way, when a catalyst noble metal is included in the SCR catalyst coated on the flow path of the particulate collection filter, the NOx purification performance is lowered. For this reason, it is common that no precious metal is added to the SCR catalyst coated on the flow path in the purification catalyst / particulate collection filter.

  The purification catalyst / particulate collection filter is in a regeneration operation in which particulate matter is burned and forcedly removed by raising the temperature, but no precious metal is generally added to the SCR catalyst. For this reason, even if the regeneration operation is carried out, the burning rate of the particulate matter is lowered, and there is a possibility that unburned residue is generated in the particulate matter.

  From the situation described above, the exhaust purification system in which the purification catalyst / particulate collection filter coated with the SCR catalyst is used in the flow path of the particulate collection filter that collects particulate matter, regenerates by desorbing ammonia. Therefore, there is a demand for a technique capable of accurately performing the treatment to be performed and the regeneration operation for removing the particulate matter.

JP 2013-32706 A

  The present invention has been made in view of the above circumstances, and uses a purification catalyst / particle collection filter coated with an SCR catalyst in the flow path of a particle collection filter that collects particulate matter, and nitrogen oxide (NOx). In an exhaust purification system that supplies urea water to the exhaust passage to reduce the amount of water, the regeneration process that desorbs the product derived from urea water and the regeneration operation that removes particulate matter can be performed accurately. An object of the present invention is to provide an exhaust purification system.

  In order to achieve the above object, an exhaust purification system of the present invention according to claim 1 is provided in an exhaust passage of an internal combustion engine, and a selective reduction catalyst for collecting particulate matter and selectively reducing NOx is provided in the flow path. A coated purification catalyst / particulate collection filter; urea water injection means for injecting urea water into the exhaust passage facing the exhaust passage upstream of the purification catalyst / particulate collection filter in the exhaust flow direction; PM regeneration treatment for removing particulate matter adsorbed on the purification catalyst / fine particle collection filter and product desorption treatment for desorption of urea water-derived product adsorbed on the purification catalyst / fine particle collection filter And an exhaust purification system comprising: a control means for executing the following: the control means when the product is adsorbed by the purification catalyst / particulate collection filter. The first time required for the substance desorption process is compared with the second time required for the PM regeneration process, and the longer one is defined as the filter regeneration time of the purification catalyst / particulate collection filter. And

  In the exhaust gas purification system according to the first aspect of the present invention, urea water is supplied to the exhaust gas so that the temperature is raised by the exhaust gas to produce a product (ammonia), and the ammonia is adsorbed on the purification catalyst / particulate collection filter. Then, ammonia reacts with NOx in the exhaust gas to purify NOx.

  In the present invention according to claim 1, when the product desorption process is performed, any one of the second time required for the PM regeneration process and the first time required for the product desorption process Since the longer time is set as the filter regeneration time, the particulate matter can be removed in a state in which the product can be surely removed during the operation of desorbing the product.

  For this reason, a purification catalyst / particulate collection filter coated with an SCR catalyst is used in the flow path of a particulate collection filter that collects particulate matter, and urea water for reducing nitrogen oxides (NOx) is exhausted through the exhaust passage. In an exhaust gas purification system that supplies water, a regeneration process (ammonia desorption process) that desorbs a product derived from urea water and a regeneration operation (PM regeneration process) that removes particulate matter are performed accurately. Is possible.

  Supercharging means that supercharges intake air in the intake passage by exhausting the exhaust passage of the internal combustion engine, and exhaust gas in the exhaust passage downstream of the supercharging means in the exhaust flow direction upstream of the supercharging means in the intake flow direction When the low pressure EGR means for returning to the intake passage is provided, the product is accurately desorbed, so that the exhaust gas not containing the product can be recirculated.

  The exhaust purification system of the present invention according to claim 2 is the exhaust purification system according to claim 1, wherein the control means includes the amount of the product adsorbed on the purification catalyst / particulate collection filter, The first time is set based on the temperature of the purification catalyst / particulate collection filter.

  In the present invention according to claim 2, the amount of the adsorbed product and the temperature of the purification catalyst / particulate collection filter (for example, the operating temperature of the PM regeneration process that is higher than the operating temperature of the product desorption process) Thus, the first time, which is the product desorption treatment time (ammonia desorption time), is set, so that the first time can be accurately estimated, and the product (ammonia) is removed in an accurate time. Can be desorbed.

  The exhaust purification system of the present invention according to claim 3 is the exhaust purification system according to claim 2, wherein the control means includes an amount of urea water injected by the urea water injection means, the purification catalyst, The amount of the adsorbed product is estimated based on the NOx purification amount purified by the particulate collection filter.

  In the present invention according to claim 3, the amount of the adsorbed product is determined by the amount of urea water injected in the product adsorption temperature region and the NOx purification amount purified by the purification catalyst / particulate collection filter. Since it estimates, 1st time can be estimated more correctly and a product can be desorbed according to an actual driving | operation.

  Further, an exhaust purification system of the present invention according to claim 4 is the exhaust purification system according to claim 3, further comprising NOx detection means for detecting NOx amounts before and after the purification catalyst / particulate collection filter, The control means estimates the NOx purification amount based on detection information of the NOx detection means.

  According to the fourth aspect of the present invention, the NOx purification amount is calculated by detecting the NOx amount before and after the purification catalyst / particulate collection filter by the NOx detection means, so that the NOx purification amount can be accurately calculated. As the NOx detection means, an upstream NOx sensor is provided upstream of the purification catalyst / particulate collection filter, and a downstream NOx sensor is provided downstream, and NOx purification is performed based on the difference between the detected values of the upstream NOx sensor and the downstream NOx sensor. The amount (ammonia adsorption amount) can be calculated.

  Further, the exhaust gas purification system of the present invention according to claim 5 is the exhaust gas purification system according to any one of claims 1 to 4, wherein the control means is configured such that when the filter regeneration time has elapsed, When desorption of the product is confirmed, the filter regeneration time is extended.

  In the present invention according to claim 5, when the filter regeneration time has elapsed, even if the product is desorbed, the filter regeneration time is extended so that the desorption of the product is surely completed. Can do.

  The control device of the exhaust purification system of the present invention uses a purification catalyst / particulate collection filter coated with an SCR catalyst in the flow path of a particulate collection filter that collects particulate matter, and reduces nitrogen oxide (NOx). In an exhaust purification system for supplying urea water to the exhaust passage, a regeneration process (ammonia desorption process) that desorbs products derived from urea water and a regeneration operation (PM regeneration process) that removes particulate matter ) Can be accurately implemented.

It is a schematic block diagram showing the system | strain of the exhaust gas purification system which concerns on one Example of this invention. It is a flowchart of the filter regeneration process of a purification catalyst and particulate collection filter.

  The exhaust purification system of the present embodiment is an exhaust purification system using a urea SCR (Selective Catalytic Reduction) system. That is, as a selective reduction catalyst (SCR catalyst) of the urea SCR system, a purification catalyst / particle collection filter coated with an SCR catalyst is provided in the flow path of a particle collection filter that collects particulate matter. A urea water injection valve is provided upstream of the particulate collection filter, and urea water is injected into the exhaust passage from the urea water injection valve.

  As urea water is injected from the urea water injection valve, the urea water is decomposed by the heat of the exhaust gas to generate ammonia (product), and the generated ammonia is placed on the SCR catalyst of the purification catalyst / particulate collection filter. The system reacts with NOx in the exhaust gas and NOx is reduced (purified) to nitrogen and water.

  Then, when a condition for performing a regeneration process (ammonia desorption process) for desorbing ammonia from the purification catalyst / particulate collection filter is established, a regeneration operation (PM regeneration process) for removing particulate matter is performed. . That is, when performing the ammonia desorption process, the time necessary for the PM regeneration process (PM regeneration process time: second time) is grasped, and the time necessary for the ammonia desorption process (ammonia desorption time: first time) The longer one of (time) and PM regeneration processing time (second time) is defined as the filter regeneration time.

  For this reason, at the time of operation of ammonia desorption treatment, particulate regeneration can be performed by performing PM regeneration processing in a state where ammonia desorption can be reliably performed.

  Therefore, a purification catalyst / particulate collection filter coated with an SCR catalyst is used in the flow path of the particulate collection filter that collects particulate matter, and urea water for reducing nitrogen oxide (NOx) is supplied to the exhaust passage. In the exhaust purification system to be supplied, it is possible to accurately carry out the regeneration process (ammonia desorption process) for desorbing ammonia derived from urea water and the regeneration operation (PM regeneration process) for removing particulate matter. become.

  An embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows a schematic configuration representing a system of an exhaust purification system according to an embodiment of the present invention. The exhaust purification system will be described with reference to FIG.

  As shown in the figure, an exhaust purification device 3 is provided in an exhaust pipe 2 as an exhaust passage of a multi-cylinder diesel engine (engine) 1 as an internal combustion engine mounted on a vehicle. A piston 5 is provided in the bore of the cylinder block 4 of the engine 1 so as to be able to reciprocate. A combustion chamber 7 is formed between the piston 5 and the cylinder head 6. The piston 5 is connected to the crankshaft 9 via a connecting rod 8, and the crankshaft 9 is driven by the reciprocating motion of the piston 5.

  An intake pipe 12 including an intake manifold 11 is connected to the cylinder head 6 via an intake port. The intake port is opened and closed by an intake valve. Further, an exhaust pipe (exhaust passage) 2 including an exhaust manifold 13 is connected to the cylinder head 6 through an exhaust port. The exhaust port is opened and closed by an exhaust valve.

  The cylinder head 6 is provided with an electronically controlled fuel injection valve 10 that directly injects fuel into the combustion chamber 7 of each cylinder. The fuel injection valve 10 is supplied with fuel from a common rail (not shown). In the common rail, the fuel is adjusted to a predetermined fuel pressure, and high pressure fuel controlled to the predetermined fuel pressure is supplied to the fuel injection valve 10.

  A turbocharger 15 is provided in the middle of the intake pipe 12 and the exhaust pipe 2 as a turbocharger. The turbocharger 15 is provided with a turbine on the exhaust pipe 2 side, and a compressor connected to the turbine is provided on the intake pipe 12 side. It has been. When the exhaust gas of the engine 1 is sent from the exhaust pipe 2 to the turbocharger 15, the turbine rotates by the flow of the exhaust gas, and the compressor rotates with the rotation of the turbine to supercharge the intake air in the intake pipe 12. .

  An intercooler 16 is disposed in the intake pipe 12 on the downstream side of the turbocharger 15, and the supercharged intake air is cooled by the intercooler 16 and sent to the combustion chamber 7. A throttle valve 17 for opening and closing the intake pipe 12 is provided in the intake pipe 12 on the downstream side of the intercooler 16. Although not shown, the intake pipe 12 on the downstream side of the throttle valve 17 is provided with an intake air temperature sensor for detecting the intake air temperature and an intake manifold pressure sensor for detecting the pressure in the intake manifold 11.

  One end of a high-pressure EGR pipe 31 is connected to the exhaust pipe 2 upstream of the turbocharger 15, and the other end of the high-pressure EGR pipe 31 communicates with the intake pipe 12 downstream of the throttle valve 17 (downstream of the turbocharger 15). doing. A high pressure EGR cooler 32 is provided in the high pressure EGR pipe 31, and a high pressure EGR valve 33 is provided in a connection portion of the high pressure EGR pipe 31 with the intake pipe 12.

  By opening the high pressure EGR valve 33, a part of the exhaust gas flowing through the exhaust pipe 2 upstream of the turbocharger 15 is introduced into the high pressure EGR pipe 31, and the exhaust gas introduced into the high pressure EGR pipe 31 is introduced into the high pressure EGR cooler 32. And is supplied to the intake pipe 12 on the downstream side of the turbocharger 15. By recirculating a part of the exhaust gas to the intake air, the combustion temperature in the combustion chamber 7 of the engine 1 can be lowered and the amount of NOx emission can be reduced.

The exhaust pipe 2 on the downstream side of the turbocharger 15 is provided with a diesel oxidation catalyst (oxidation catalyst) 21 and a purification device 23 for exhaust purification. When exhaust gas flows into the oxidation catalyst 21, nitrogen monoxide (NO) in the exhaust gas is oxidized to generate nitrogen dioxide (NO ₂ ).

  The purification device 23 includes a purification catalyst / particle collection filter 22 in which a selective reduction catalyst (SCR catalyst) is coated on a flow path of a diesel particle collection filter that collects particulate matter. The exhaust pipe 2 between the oxidation catalyst 21 and the purification catalyst / particulate collection filter 22 is provided with a urea water injection valve 28 as urea water injection means.

  The SCR catalyst coated on the purification catalyst / particulate collection filter 22 has a weak acid point and a low ammonia adsorption performance.

Particulate matter (PM) in the exhaust gas is collected by the purification catalyst / particulate collection filter 22. The PM collected by the purification catalyst / particulate collection filter 22 is oxidized (combusted) by NO ₂ in the exhaust gas and discharged as CO _{2. The} NO ₂ remaining in the purification catalyst / particulate collection filter 22 is N _2. It is decomposed and discharged.

  The exhaust pipe 2 on the front side of the purification catalyst / particulate collection filter 22 is provided with a mixer 29, and urea water injected from the urea water injection valve 28 is diffused by the mixer 29 to be purified catalyst / particulate collection filter 22. Contact evenly.

  The urea water is injected into the exhaust pipe 2 from the urea water injection valve 28, whereby the urea water is decomposed by the heat of the exhaust gas to generate ammonia, and the generated ammonia is passed through the purification catalyst / particulate collection filter 22. It reacts with NOx in the exhaust gas on the SCR catalyst, and NOx is reduced (purified) to nitrogen and water.

  The temperature at which urea water is hydrolyzed to produce ammonia is, for example, 200 ° C. or higher. In order to reduce the adsorption amount of ammonia as much as possible, the temperature range for injecting the urea water is set to, for example, 300 ° C. or higher.

  An upstream NOx sensor 55 as NOx detection means is provided upstream of the oxidation catalyst 21, and a downstream NOx sensor 56 as NOx detection means is provided downstream of the purification catalyst / particulate collection filter 22. Yes. When the detected value of the NOx amount detected by the downstream NOx sensor 56 is higher than the detected value of the NOx amount detected by the upstream NOx sensor 55, ammonia is discharged from the purification catalyst / particulate collection filter 22. Is detected.

  That is, based on the detected value of the NOx amount detected by the upstream NOx sensor 55 and the downstream NOx sensor 56, the purification amount of NOx is estimated by taking the temperature of the purification catalyst / particulate collection filter 22 into consideration. .

  Although the upstream NOx sensor 55 is provided on the upstream side of the oxidation catalyst 21, the upstream NOx sensor 55 may be provided between the oxidation catalyst 21 and the urea water injection valve 28.

  A first temperature sensor 57 is provided upstream of the oxidation catalyst 21, and a second temperature sensor 58 is provided between the mixer 29 and the purification catalyst / particle collection filter 22, and the purification catalyst / particle collection is performed. A third temperature sensor 59 is provided on the downstream side of the collecting filter 22.

  The temperature of the oxidation catalyst 21 is estimated from the temperature of the exhaust gas detected by the first temperature sensor 57, and the temperature of the purification catalyst / particle collection filter 22 is estimated from the temperature of the exhaust gas detected by the second temperature sensor 58. The temperature of the low-pressure EGR filter described later is estimated from the temperature of the exhaust gas detected by the third temperature sensor 59.

  On the other hand, one end of a low pressure EGR pipe 51 serving as a reflux line is connected to the exhaust pipe 2 downstream of the third temperature sensor 59 or the downstream NOx sensor 56 on the downstream side of the purification device 23, and the low pressure EGR pipe 51. Is connected to the intake pipe 12 on the upstream side of the turbocharger 15. The low pressure EGR pipe 51 is provided with a low pressure EGR cooler 52, and a low pressure EGR valve 53 as an EGR opening / closing means is provided in the vicinity of the connection portion of the low pressure EGR pipe 51 with the exhaust pipe 2.

  A low pressure EGR filter 50 is provided between the low pressure EGR valve 53 and the low pressure EGR cooler 52 of the low pressure EGR pipe 51, and the flow path of the low pressure EGR filter 50 is coated with an oxidation catalyst. When the third temperature sensor 59 measures the state where the temperature of the low pressure EGR filter 50 is higher than the activation temperature of the oxidation catalyst, even if ammonia is mixed into the exhaust gas flowing into the low pressure EGR pipe 51, the oxidation catalyst oxidizes. To be detoxified.

  The low pressure EGR filter 50 can be provided integrally with the low pressure EGR cooler 52. Further, the low-pressure EGR filter 50 can be integrally provided on the outlet side of the purification catalyst / particulate collection filter 22.

  By opening the low pressure EGR valve 53, a part of the exhaust gas flowing through the exhaust pipe 2 on the downstream side of the turbocharger 15 is introduced into the low pressure EGR pipe 51, and the exhaust gas introduced into the low pressure EGR pipe 51 is converted into the low pressure EGR filter. After being purified at 50, it is cooled by the low pressure EGR cooler 52 and supplied to the intake pipe 12 upstream of the turbocharger 15.

  NOx emissions are reduced by lowering the combustion temperature in the combustion chamber 7 of the engine 1 or enriching the combustion gas in the combustion chamber by recirculating a part of the exhaust gas to the intake air by the low pressure EGR device. Can be reduced. Even in the operation state where the turbocharger 15 needs to be supercharged sufficiently (the operation state where it is necessary to secure the air amount), the low-pressure EGR device can be used to reduce the NOx emission amount.

  The vehicle is provided with an electronic control unit (ECU) 40 as a control means, and the ECU 40 is provided with an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, timers and counters. Yes. Information from sensors is input to the ECU 40, and comprehensive control of the engine 1 including the exhaust purification device 3 is performed by the ECU 40 based on the information of the sensors.

  In the exhaust purification system described above, a regeneration operation (PM regeneration process) for removing particulate matter deposited on the purification catalyst / particulate collection filter 22 is performed at a preset interval. For example, the purification catalyst / particulate collection filter 22 is heated by supplying additional fuel or the like (for example, 400 ° C. or more), and the particulate matter is burned and removed.

  In addition, a regeneration process (ammonia desorption process) is performed to desorb ammonia adsorbed on the purification catalyst / particle collection filter 22 according to the urea water injection status from the urea water injection valve 28. For example, an operation of desorbing ammonia is performed by supplying additional fuel or the like to raise the temperature of the purification catalyst / particulate collection filter 22 (desorption temperature or higher).

  In the ECU 40, the PM regeneration process is performed when a condition for performing the ammonia desorption process is satisfied. That is, when performing the ammonia desorption treatment, the time required for the ammonia desorption treatment (first time: hereinafter referred to as ammonia desorption treatment time) and the time required for the PM regeneration treatment (second time: hereinafter) PM regeneration processing time), and the PM regeneration processing is performed using the longer time as the filter regeneration time.

  The ECU 40 determines the ammonia desorption processing time based on the amount of ammonia adsorbed on the purification catalyst / particulate collection filter 22 and the temperature of the purification catalyst / particulate collection filter 22 (temperature rise during PM regeneration). Set.

  The amount of adsorbed ammonia is estimated from the amount of urea water injected from the urea water injection valve 28 in the ammonia adsorption temperature region and the NOx purification amount purified by the purification catalyst / particle collection filter 22. .

Specifically, first, it was added to the purification catalyst / particulate collection filter 22 based on the amount of urea water injected from the urea water injection valve 28 and the hydrolysis reaction formula of the urea water (the following formula (1)). Calculate the amount of ammonia. At this time, the temperature detected by the second temperature sensor 58 is taken into account.
CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ (1)

Next, the amount of ammonia consumed for NOx purification is determined based on the NOx purification amount purified by the purification catalyst / particulate collection filter 22 and the NOx decomposition reaction formula (the following formula (2)) on the purification catalyst. calculate.
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (2)

  Then, the amount of adsorbed ammonia is calculated by subtracting the amount of ammonia consumed for NOx purification calculated by equation (2) from the amount of ammonia added calculated by equation (1).

  Note that the NOx purification amount is calculated based on the difference between the detected values of the upstream NOx sensor 55 and the downstream NOx sensor 56, taking into account the temperature detected by the second temperature sensor 58.

  That is, the ECU 40 receives information on the detection values of the upstream NOx sensor 55 and the downstream NOx sensor 56 and information on the detection value of the second temperature sensor 58.

  Specific processing of the exhaust purification system will be described based on FIG.

  FIG. 2 shows a flowchart for performing a regeneration process of the purification catalyst / particulate collection filter.

  In step S1, it is determined whether ammonia is adsorbed on the purification catalyst / particulate collection filter 22. That is, it is determined whether urea water is injected in a state where the temperature of the purification catalyst / particulate collection filter 22 is in the ammonia adsorption temperature range. If it is determined in step S1 that ammonia is not adsorbed on the purification catalyst / particulate collection filter 22, the ammonia desorption process is not performed, and the process ends.

  If it is determined in step S1 that ammonia is adsorbed on the purification catalyst / particulate collection filter 22, the amount of ammonia adsorbed is calculated in step S2 to perform ammonia desorption processing, and ammonia desorption in step S3. Time T1 is calculated.

  As described above, the ammonia adsorption amount is detected by the amount of urea water injected from the urea water injection valve 28, the detection values of the upstream NOx sensor 55 and the downstream NOx sensor 56, and the second temperature sensor 58. It is calculated based on the temperature of the purification catalyst / particle collection filter 22. The ammonia desorption time T1 is calculated based on the amount of ammonia adsorbed and the temperature of the purification catalyst / fine particle collection filter 22.

  When executing the ammonia desorption process, the PM regeneration process time is grasped. That is, the deposition amount of the particulates (PM) is calculated in step S4, and the PM regeneration processing time T2 is calculated in step S5 based on the PM deposition amount.

  In step S6, the ammonia desorption time T1 and the PM regeneration processing time T2 are compared. If it is determined in step S6 that the ammonia desorption time T1 is longer than the PM regeneration processing time T2, the filter regeneration time is set to T1 in step S7. Set. If it is determined in step S6 that the ammonia desorption time T1 is not longer than the PM regeneration processing time T2, the filter regeneration time is set to T2 in step S8.

  If it is determined that the ammonia desorption time T1 is equal to the PM regeneration processing time T2, the ammonia desorption time T1 is considered to be longer than the PM regeneration processing time T2, and the process proceeds to step S7. In this case, it is also possible to move to step S8.

  After setting the filter regeneration time, a filter regeneration process is executed in step S9. For example, when the filter regeneration time is set to T1, the PM regeneration process is operated at the ammonia desorption time T1. In step S10, it is determined whether or not the filter regeneration time has elapsed. The process proceeds to step S9 and the determination in step S10 is repeated until the filter regeneration time has elapsed.

  If it is determined in step S10 that the filter regeneration time has elapsed, it is determined in step S11 whether or not ammonia is discharged. More specifically, the detection values of the upstream NOx sensor 55 and the downstream NOx sensor 56 are compared. If the detection value of the downstream NOx sensor 56 is larger, it is determined that ammonia is discharged.

  If it is determined in step S11 that ammonia is not discharged, that is, if the detected value of the upstream NOx sensor 55 is larger than the detected value of the downstream NOx sensor 56, the process ends. If it is determined in step S11 that ammonia is discharged, the filter regeneration time is extended in step S12, and the determination in step S11 is repeated until there is no ammonia discharge.

  That is, when the ammonia regeneration process and PM regeneration process are completed after the filter regeneration time has elapsed, even if ammonia has been exhausted, the filter regeneration time should be extended until no ammonia is exhausted. Filter regeneration processing is executed.

  In the exhaust purification system described above, when the conditions for performing the ammonia desorption treatment are satisfied, the longer operation time of the ammonia desorption time or the PM regeneration treatment time is used as the filter regeneration time at the temperature condition of the PM regeneration treatment. Filter regeneration processing is executed.

  Thereby, the ammonia desorption process can be performed at the temperature of the filter regeneration process (for example, 400 ° C. or more), and the desorption of ammonia can be reliably performed. Then, during the operation of ammonia desorption treatment, particulate matter can be removed by performing PM regeneration processing in a state where ammonia desorption can be reliably performed.

  In other words, when the ammonia desorption process is performed at a frequency higher than the interval of the PM regeneration process, the PM regeneration process can also be performed at the same time. Can be reduced.

  Therefore, the purification catalyst / fine particle collection filter 22 coated with the SCR catalyst is used in the flow path of the fine particle collection filter for collecting the particulate matter, and urea water for reducing nitrogen oxide (NOx) is exhausted through the exhaust passage. In the exhaust gas purification system supplied to the exhaust gas, it is possible to accurately perform an ammonia desorption process for desorbing ammonia derived from urea water and a PM regeneration process for removing particulate matter.

  In addition, since the ammonia desorption time is calculated based on the amount of ammonia adsorbed on the purification catalyst / particle collection filter 22 and the temperature of the purification catalyst / particle collection filter 22, the ammonia desorption treatment is more accurately performed. And PM regeneration processing can be performed.

  The amount of adsorbed ammonia is calculated based on the amount of urea water injected by the urea water injection valve 28 and the NOx purification amount purified by the purification catalyst / particle collection filter 22. For this reason, it is possible to accurately estimate the adsorption amount of ammonia, and it is possible to more accurately estimate the desorption time of ammonia.

  Further, the NOx purification amount is estimated based on the NOx amount detected by the NOx sensors (upstream NOx sensor 55, downstream NOx sensor 56) disposed before and after the purification catalyst / particulate collection filter 22, The amount of ammonia adsorbed on the purification catalyst / particulate collection filter 22 can be estimated more accurately.

  In addition, since the amount of ammonia discharged from the purification catalyst / particulate collection filter 22 is estimated using the detection value of the NOx sensor, inexpensive detection can be performed without providing another detection means for detecting ammonia. A means for detecting ammonia emissions.

  An ammonia sensor that directly detects ammonia can be provided on the downstream side of the purification catalyst / particulate collection filter 22. In that case, the discharge of ammonia from the purification catalyst / particulate collection filter 22 can be easily detected. Further, it is possible to easily estimate the amount of ammonia adsorbed on the purification catalyst / fine particle collection filter 22.

  The present invention can be used in the industrial field of exhaust purification systems that reduce nitrogen oxides (NOx) in exhaust gases of internal combustion engines.

1 Multi-cylinder diesel engine (engine)
2 Exhaust pipe 3 Exhaust gas purification device 4 Cylinder block 5 Piston 6 Cylinder head 7 Combustion chamber 8 Connecting rod 9 Crankshaft 10 Fuel injection valve 11 Intake manifold 12 Intake pipe 13 Exhaust manifold 15 Turbocharger 16 Intercooler 17 Throttle valve 21 Diesel oxidation catalyst ( Oxidation catalyst)
22 Purification catalyst / particulate collection filter 23 Purification device 28 Urea water injection valve 29 Mixer 31 High pressure EGR pipe 32 High pressure EGR cooler 33 High pressure EGR valve 40 Electronic control unit (ECU)
50 Low Pressure EGR Filter 51 Low Pressure EGR Pipe 52 Low Pressure EGR Cooler 53 Low Pressure EGR Valve 55 Upstream NOx Sensor 56 Downstream NOx Sensor 57 First Temperature Sensor 58 Second Temperature Sensor 59 Third Temperature Sensor

Claims (5)

A purification catalyst / particulate collection filter provided in an exhaust passage of an internal combustion engine, which collects particulate matter and selectively reduces NOx, and the flow path is coated with a selective reduction catalyst;
Urea water injection means for injecting urea water into the exhaust in the exhaust passage facing the exhaust passage upstream of the purification catalyst / particulate collection filter in the exhaust flow direction;
PM regeneration treatment for removing particulate matter adsorbed on the purification catalyst / fine particle collection filter and product desorption treatment for desorption of urea water-derived product adsorbed on the purification catalyst / fine particle collection filter Control means for executing
An exhaust purification system comprising:
The control means includes
When the product is adsorbed on the purification catalyst / particulate collection filter, a first time required for the product desorption treatment and a second time required for the PM regeneration treatment are compared, An exhaust purification system characterized in that the longer one is the filter regeneration time of the purification catalyst / particulate collection filter. The exhaust purification system according to claim 1,
The control means includes
The exhaust purification system characterized in that the first time is set based on the amount of the product adsorbed on the purification catalyst / particulate collection filter and the temperature of the purification catalyst / particulate collection filter. . The exhaust purification system according to claim 2,
The control means includes
The amount of the adsorbed product is estimated based on the amount of urea water injected by the urea water injection means and the NOx purification amount purified by the purification catalyst / particulate collection filter. Exhaust purification system. The exhaust purification system according to claim 3,
Further comprising NOx detection means for detecting the amount of NOx before and after the purification catalyst / particulate collection filter,
The control means includes
An exhaust purification system, wherein the NOx purification amount is estimated based on detection information of the NOx detection means. The exhaust gas purification system according to any one of claims 1 to 4,
The control means includes
The exhaust gas purification system is characterized by extending the filter regeneration time when desorption of the product is confirmed when the filter regeneration time has elapsed.

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