JP5741527B2 - Engine aftertreatment device - Google Patents

Description

  The present invention relates to an aftertreatment device that absorbs and separates NOx components of exhaust gas, and more particularly to an engine aftertreatment device that has NOx absorption and separation ability even in a cold state immediately after the engine is cold-started.

  Engines, in particular, NOx (nitrogen oxide) aftertreatment devices for diesel engines, for example, use a catalyst to reduce NOx to purify NOx components. In this technique, NOx purification cannot be achieved at a temperature lower than the operating temperature (about 200 ° C. or higher) at which the catalyst works, so a technique for realizing this is required.

  In addition, it is necessary to use expensive noble metals such as platinum in the NOx occlusion reduction type and adsorption reduction type catalysts. On the other hand, although the base metal can be used for the selective reduction catalyst, a device for metering and supplying urea water to the exhaust system is required, which is expensive. There is a need for a new type of NOx aftertreatment device that can be implemented at a lower cost.

  In other words, NOx purification is possible even from a low temperature immediately after the engine is cold-started, and no expensive catalyst such as precious metals is used for NOx purification, and it is possible to meet future strict emission regulations. It is desired to have a high purification performance and a NOx purification device that satisfies these requirements.

  In this regard, for example, Patent Document 1 below discloses a technique for exhaust purification by absorbing NOx with an alkaline aqueous solution. The technique described in this document has the advantage that the alkaline aqueous solution is inexpensive and NOx purification is possible even at a relatively low temperature.

JP-A-6-173657

  However, in the technique of Patent Document 1, a cooling means is placed in front of the NOx absorbing liquid to cool it to a temperature at which the NOx absorbing liquid functions optimally. Faced with the following challenges: That is, if the capacity of the cooling means is adjusted to the operating conditions in which the engine exhibits the maximum exhaust temperature and the maximum exhaust flow rate, the engine becomes too large and difficult to mount on the vehicle. Therefore, it is desirable to configure a post-processing device that can be optimally adapted for resource saving and environmental load reduction even when the range of operating conditions is wide, such as a vehicle engine, and to exhibit its performance.

  Further, in the case of the method of Patent Document 1, if a failure occurs in the cooling means, there is a possibility that exhaust gas that is not cooled flows into the NOx absorbing means and induces a secondary failure in which the NOx absorbing liquid is decomposed or deteriorated due to high temperature. is there. Therefore, even when the post-processing device fails, it is desirable to provide a fail-safe function that enables safe traveling and promptly performs repair processing without inducing a secondary failure.

  Further, for example, when a DPF (diesel particulate filter) is disposed upstream of the post-processing device in the method of Patent Document 1, the PM collection rate is obtained when the DPF is regenerated and the amount of accumulated PM on the DPF is small. And a relatively large amount of PM slips downstream. This PM adheres to a part of the post-processing apparatus and degrades the performance of the post-processing apparatus. Therefore, in order not to cause such a problem, it is desired that when the PM collection rate of the DPF is low, the slipped PM does not adhere to the post-processing apparatus or is difficult to do.

  Therefore, in view of the above, the problem to be solved by the present invention is that it can be realized at a low cost, achieves high NOx purification performance even at low temperatures, can be applied to a wide range of engine operating conditions, and has the possibility of secondary failure. It is an object of the present invention to provide an engine aftertreatment device that is suppressed and is not easily affected by PM passing through a DPF.

In order to achieve the above object, an aftertreatment device for an engine according to the present invention cools exhaust gas disposed upstream of the purification means in the exhaust passage and purification means for purifying NOx in the exhaust discharged from the engine. Cooling means, a bypass passage formed in the exhaust passage so as to bypass exhaust gas from upstream of the purification means and cooling means to downstream of the purification means and cooling means, and exhaust gas to the bypass passage An adjusting means for adjusting the flow rate, and a first control means for controlling the adjusting means so as to relieve the exhaust gas to the bypass passage when the purifying capacity of the purifying means is reduced when the exhaust gas is circulated to the purifying means. If, on the upstream of the cooling means in the exhaust passage, and a collector for collecting particulate matter, the first control means, said cooling hand displacement of the engine Second control for controlling the exhaust gas to be relieved in the bypass passage when the amount of exhaust gas exceeds the cooling capacity at the present time or when the collection rate of the collector is reduced from the maximum value. Means are provided . As a result, it is possible to adapt to a wide range of operating conditions of the engine, and the possibility of a secondary failure is suppressed, and an engine post-processing device that is hardly affected by PM passing through the DPF can be realized.

The figure which shows one Embodiment of the engine post-processing apparatus in this invention. The figure which shows the example at the time of valve closing in the 1st Example of a relief valve servo mechanism. The figure which shows the example at the time of valve opening in 1st Embodiment of a relief valve servo mechanism. The figure which shows 2nd Embodiment of a relief valve servo mechanism. The figure which shows the Example of a flow-path cutoff valve servo mechanism. The flowchart which shows the example of the control processing procedure of a relief valve servo mechanism. The flowchart which shows the example of the control processing procedure of a flow-path cutoff valve servo mechanism. The figure which shows the example of the relationship between PM deposition amount and PM collection rate in DPF. The flowchart which shows the example of the control processing procedure of the relief valve servo mechanism according to the DPF collection rate.

(First embodiment)
FIG. 1 shows a first embodiment. A DPF (diesel particulate filter) 3 is arranged in the middle of the exhaust pipe 2 of the engine 1, and an exhaust branch pipe 4 is arranged in parallel to the exhaust pipe 2 downstream thereof. A cooling means 5 and a NOx absorbing means 6 are arranged in the exhaust branch pipe 4 in the order of the exhaust flow. Further, a flow path shutoff valve 15 is disposed in the middle of the exhaust pipe 2 downstream of the exhaust branch pipe 4 and in the middle of the relief valve 14 and the exhaust branch pipe 4 and upstream of the cooling means 5.

  The engine 1 takes in air from the intake inlet 7. The air is pressurized by the compressor 8 of the turbocharger, and the air that has become hot due to the pressurization is cooled by the intercooler 9, then sent to the intake manifold 10, and taken into the combustion chamber of the engine 1 from each port. In the combustion chamber of the engine 1, air and fuel are mixed and burned. The piston of the engine 1 is pushed down by the combustion, and power is generated as the rotational force of the engine shaft 11.

  The exhaust after the combustion is exhausted from the combustion chamber of the engine 1 to the exhaust manifold 12. Thereafter, the exhaust gas is discharged into the exhaust pipe 2 after rotating the turbine 13 directly connected to the compressor 8 of the turbocharger to pressurize the air. The exhaust gas passes through the DPF 3 here, and particulate matter (PM, particulate matter) in the exhaust gas is collected by filtration with the DPF. At the same time, the HC component and the CO component are also purified by the oxidation catalyst coated on the DPF surface through which the exhaust passes. Thereafter, in a normal case, the relief valve 14 is closed and the flow path shut-off valve 15 is open, so that the exhaust gas flows through the exhaust branch pipe 4 and passes through the cooling means 5 and is cooled, and normally the exhaust temperature is 100. It falls between ℃ and 180 ℃.

  The cooled exhaust gas further passes through the NOx absorption means 6. Here, NOx contained in the exhaust is absorbed in contact with the NOx absorbing liquid in the NOx absorbing means 6. Up to this point, PM, HC, CO, and NOx are removed, and the exhaust gas is cleaned and discharged from the exhaust pipe outlet 16 into the atmosphere.

  The DPF 3 used here is a known wall flow type exhaust filter in which a porous wall formed of ceramic works as a filter.

  The exhaust cooling means 5 is a Rankine cycle exhaust heat recovery system using engine cooling water or the like as a working fluid disclosed in, for example, JP-A-2002-115573. As described in this document, in this system, an evaporator that generates high-temperature and high-pressure steam using exhaust as a heat source is disposed in the middle of an exhaust pipe. As can be easily understood, the evaporator serves to cool the exhaust gas by converting the water into high-temperature and high-pressure steam.

  Further, by operating the Rankine cycle, the high temperature and high pressure steam operates the expander generating the shaft output to generate the shaft output, and the generator directly connected to the expander and the output shaft is operated to generate electric power. To store electricity. Alternatively, the generator motor 18 directly connected to the output shaft of the engine is driven to assist the engine power. In this way, the amount of heat recovered from the exhaust can be used again as regenerative energy, contributing to improved fuel consumption of the engine and reduced CO2 emissions. The cooling means 5 in FIG. 1 includes an evaporator, an expander, a power generator and the like constituting the Rankine cycle.

  Although a patent application example applied to a hybrid vehicle has been described as a publicly known example, it is applied to a normal engine instead of a hybrid vehicle, and the generated power is stored exclusively in the capacitor 17 so as to reduce the load for operating the engine charging system. May be.

  Next, the NOx absorption means 6 is disclosed in, for example, Patent Document 1 described above. In this method, an alkaline aqueous solution is used as the NOx absorbent, a reducing agent is added as necessary, and a corona discharge field is created to efficiently absorb NOx as nitric acid. It is stated that the outer wall of the reaction tube that absorbs NOx from the exhaust gas by the corona discharge is preferably cooled so that the inner wall surface in contact with the exhaust gas is 20 to 50 ° C. It is also stated that a sufficient NOx purification function can be obtained even if the exhaust temperature is as high as 250 ° C. From these descriptions, it can be seen that a sufficient NOx purification function can be obtained in the exhaust temperature range of 20 ° C. to 250 ° C. That is, the known NOx occlusion reduction type catalyst and urea addition selective reduction type catalyst do not exhibit the NOx purification function unless the exhaust temperature is 150 ° C. to 200 ° C. or higher. And the problems of the known NOx catalyst device can be solved.

  As another example of the NOx absorbing means 6, an ionic liquid that chemisorbs NOx may be used as the NOx absorbing liquid. The ionic liquid is stored in the storage means. The ionic liquid is sent to a gas-liquid contact means provided in the middle of the exhaust pipe and brought into contact with the exhaust to chemically adsorb NOx. Thereafter, the liquid recovery means separates and recovers the ionic liquid from the exhaust and returns it to the storage means again. According to the inventor's knowledge, in this method, NOx in the exhaust gas can be purified without being affected by the exhaust gas temperature, so that a known NOx occlusion reduction catalyst or urea addition selective reduction catalyst does not work. It can be used even when the exhaust temperature is low during light load operation.

  As described above, the cooling device is placed in front to cool the exhaust temperature to a temperature at which the NOx absorbing liquid is optimally operated. The cooling device takes out the exhaust heat recovered by the Rankine cycle as regenerative energy to improve the fuel efficiency of the engine. The concept of improving and removing NOx in the exhaust using an absorbing solution having NOx absorption ability from room temperature solves the problem that the conventional catalyst type method cannot be purified at 150 ° C. to 200 ° C. or lower. This is an excellent technology.

(Exhaust relief function added)
However, when this concept is applied to an automobile engine with a wide engine operating range, if the capacity of the cooling means is adjusted to the operating conditions in which the engine exhibits the maximum exhaust temperature and the maximum exhaust flow rate, it becomes too large, We face the problem that it becomes difficult to install in vehicles.

  In order to solve this problem, in the present invention, the maximum value of the operating condition frequently encountered by the engine (approximately about 1/3 to 1/2 of the engine maximum exhaust flow rate) is set as the rated capacity of the cooling means, and is exceeded. Provides an exhaust passage that bypasses the cooling means and the NOx absorption means that follows, and operates a relief valve that controls the passage of this passage to bypass the amount exceeding the capacity of the cooling means. As a result, cooling and NOx purification can be performed for the flow rate in the defense range of the cooling means, so that it is possible to reduce the environmental burden due to NOx air pollution as much as possible without making excessive resource investment in the cooling means. A solution can be obtained.

  In order to achieve the above object, the embodiment of FIG. 1 specifically includes a relief valve 14. The opening and closing of this valve is controlled by a relief valve servo mechanism 19. When controlled by the electromagnetic valve and the negative pressure servo mechanism, the control is performed by controlling the electromagnetic valve in the relief valve servo mechanism 19 from a known control unit 20 using a microcomputer. A known control unit 20 is input with a temperature sensor 21 for detecting the exhaust gas temperature downstream of the cooling means and other necessary engine information, and performs control according to a flowchart shown later.

  FIG. 2 shows an embodiment of the relief valve servo mechanism. The relief valve 14 placed in the exhaust passage 2 has a butterfly valve configuration. The shaft of the butterfly valve is connected to the link 23 outside the pipe. Further, the shaft 25 extending from the central boss portion 26 of the diaphragm 29 of the negative pressure servo mechanism is slidably supported by a sliding bearing 27, and the other end is bent at 90 ° and inserted into the hole 24 of the link 23. Has been. Diaphragm 29 has a circular outer periphery fixed by diaphragm chamber body 30 to divide the upper chamber and lower chamber of the diaphragm. The diaphragm 29 is pushed downward by a spring 28. Air is introduced into the upper chamber of the diaphragm through the opening 32, and upstream pressure of the relief valve 14 of the exhaust pipe 2 is introduced into the lower chamber of the diaphragm through the communication pipe 31.

  In this configuration, when the exhaust pipe pressure becomes equal to or higher than a predetermined pressure, the spring 28 is pushed up by the force generated by the differential pressure across the diaphragm 29, resulting in the state shown in FIG. As the diaphragm central boss portion 26 is raised, the relief valve 14 is opened, so that an excess exhaust gas flow rate can flow through the relief valve. The opening of the relief valve can be balanced when the force of the spring 28 and the force generated by the exhaust pressure are balanced. That is, in this embodiment, the excess exhaust flow rate can be automatically discharged by the mechanical mechanism as described above.

  FIG. 4 shows another embodiment of the relief valve servo mechanism. In addition to the configuration of the first embodiment shown in FIG. 1, a mechanism capable of controlling the pressure in the diaphragm upper chamber by a negative pressure is added. A pipe connected to the opening 32 of the diaphragm chamber body 30 is provided, and a negative pressure introduction port 33 for introducing a negative pressure is provided on the left side. As the negative pressure, a negative pressure generated by a vacuum pump (not shown) is introduced. Above the piping, there is an air inlet 34 including a throttle for taking in the air, and the air flows from the air inlet 34 to the negative pressure inlet 33. A solenoid valve 35 is arranged on the way to the negative pressure inlet 33. The electromagnetic valve 35 works to open and close the passage by turning on and off. An ON-OFF pulse selected from 5 to 50 Hz is given to the electromagnetic valve 35, and the opening of the relief valve 14 is controlled by controlling the negative pressure level applied to the upper chamber of the diaphragm by changing the ON-OFF duty ratio. . The electromagnetic valve 35 generates and controls an ON-OFF pulse having a desired duty ratio by the control unit 20 shown in FIG.

  In the embodiment of the relief valve servo mechanism shown in FIG. 4, FIG. 6 shows a flowchart of operations to be executed by the microcomputer of the control unit 20 when driving using the control unit 20. As an example when applied to a 2L engine used for automobiles.

  When this routine is started, the process proceeds to determination S36, and it is determined whether or not the state where the intake air flow rate of the engine is 60 g / s or more continues for 10 seconds or more. Since the intake air flow rate is substantially proportional to the exhaust gas flow rate, the intake air flow rate generally used in engine control is used. When this condition is not satisfied (in the case of NO), the process proceeds to determination S37, and it is determined whether or not the state where the exhaust gas temperature is 180 ° C. or higher continues for 15 seconds or longer. If this condition is not satisfied (in the case of NO), the routine proceeds to step S38, and the routine exits this routine so that the relief valve 14 is not operated, that is, the opening is at the fully closed position. If the intake air flow rate of 60 g / s or more continues for 10 s or more, or if the exhaust temperature is 180 ° C. or more for 15 s or more (in the case of YES), the process proceeds to step S39 and the relief valve is activated. In step S40, the pulse duty ratio applied to the electromagnetic valve 35 is determined according to engine operating conditions, and an ON-OFF pulse signal having the determined duty ratio is sent to the electromagnetic valve. The determination according to the engine operating condition means that, for example, a surplus flow rate with an intake air flow rate exceeding 60 g / s is obtained, a relief valve opening degree is obtained so that the flow rate passes through the relief valve, and based on the opening degree. And determining the duty ratio.

  As described above, when the exhaust pressure exceeds the predetermined pressure, the capacity of the cooling means 5 is exceeded, and accordingly, the NOx absorbing means 6 does not properly purify NOx. Therefore, in the embodiment of FIGS. 4. In the embodiment of FIG. 6, electrical control is applied to relieve exhaust to the exhaust pipe 2 side. This avoids a decrease in the NOx purification capacity due to an excessive exhaust gas flow rate.

(Second embodiment, addition of flow path blocking function)
Next, a second embodiment will be described. In the following second and third embodiments, unless otherwise specified, the system configuration to be used is the same as that shown in FIG.

  When the cooling means 5 loses its function for some reason, or when the operation is stopped for some reason, uncooled exhaust gas flows into the downstream NOx absorbing means 6 and decomposes the NOx absorbing liquid due to its high temperature. There is a problem of inducing secondary failures such as deterioration and deterioration. In order to prevent this problem, it is desirable to measure the temperature of the exhaust discharged from the cooling means 5 so that the exhaust does not flow into the cooling means 5 when the temperature exceeds a predetermined temperature.

  For this purpose, the embodiment of FIG. 1 comprises a channel shut-off valve 15 that shuts off the channel. Although the flow path shutoff valve 15 is shown as an example set upstream of the cooling means 5, it may be disposed at a position upstream of the NOx absorbing means 6 or a position downstream of the NOx absorbing means 6. This is because the exhaust flow flowing into the NOx absorption means 6 through the cooling means 5 may be blocked, and the desired effect can be exhibited at any position.

  FIG. 5 shows an embodiment of the flow path cutoff valve servo mechanism 50. The flow path cutoff valve 15 placed in the exhaust branch passage 4 has a butterfly valve configuration. The shaft of the butterfly valve is connected to the link 38 outside the pipe. The shaft 41 extending from the central boss 40 of the diaphragm 39 of the negative pressure servomechanism is slidably supported by a sliding bearing 42 including a stopper, the other end is bent at 90 °, and the hole of the link 38 43 is inserted. Diaphragm 39 has a circumferential outer periphery fixed by a diaphragm chamber body 44 and divides the upper chamber and the lower chamber of the diaphragm. The diaphragm 39 is pressed downward by a spring 45. A negative pressure or an atmospheric pressure determined by an atmospheric opening 46 including a throttle, a negative pressure introduction port 47, and a solenoid valve 48 arranged in the passage leading to the diaphragm is introduced into the diaphragm upper chamber. Atmospheric pressure is introduced through the atmosphere communication port 49.

  In this configuration, when the solenoid valve 48 is not energized and closed, the diaphragm upper chamber formed by the diaphragm 39 and the diaphragm chamber body 44 is at atmospheric pressure, and the pressure in the diaphragm lower chamber is also atmospheric pressure. The portion 40 is pushed down by the force of the spring 45 and stops at a position where it abuts against the stopper on the sliding bearing 42. Corresponding to the position, the flow path shutoff valve 15 is fully opened.

  When the solenoid valve 48 is opened by the energization pulse ON signal given by the ECU 20, the atmosphere flows in from the atmosphere opening 46, passes through the solenoid valve 48, passes through the negative pressure inlet 47, and serves as a negative pressure source (not shown). Inflow. As a result, a negative pressure is generated in the upper chamber of the diaphragm, and the upward force acting on the diaphragm 39 by the negative pressure overcomes the force of the spring 45 and pulls up the central boss portion 40 upward. The displacement is transmitted to the flow cutoff valve 15 via the link mechanism, and moves to a fully closed state. In this way, the exhaust branch passage 4 is opened and closed.

  Next, FIG. 7 shows a flowchart of the operation executed by the microcomputer of the control unit 20. When this routine is started, the process proceeds to determination S51, and first, it is determined whether or not the cooling means 5 is abnormal or not operating. In the case of NO, the process proceeds to determination S52, and it is determined whether or not the state in which the exhaust temperature is higher than the temperature 220 ° C. corresponding to the temperature at which the decomposition or deterioration of the NOx absorbing liquid starts is continued for 15 seconds or more. In the case of NO, the process proceeds to process S53, the flow path shutoff valve 15 is fully opened, the process further proceeds to process S54, the operation of the cooling means 5 is maintained, and the process further proceeds to process S55, where the operation of the NOx absorption means 6 is maintained.

  When the cooling means 5 is abnormal or inoperative (determination S51 is YES), and the state where the exhaust gas temperature is higher than 220 ° C. corresponding to the temperature at which the NOx absorption liquid starts to decompose or deteriorate continues for 15 seconds or longer (determination S52) YES), the process proceeds to process S56, the flow path shutoff valve 15 is fully closed, the process proceeds to process S57, the operation of the cooling means 5 is stopped, the process proceeds to process S58, and the operation of the NOx absorption means 6 is stopped. And it progresses to judgment S59 and it is determined whether the full closure of the flow-path cutoff valve 15 continued for 100 seconds or more. If NO, do nothing and exit this routine. In the case of YES, the process proceeds to step S60 to notify the driver of the abnormality of the cooling means 5 by lighting a lamp or the like and store the failure state of the cooling means 5.

  As described above, when the cooling capacity of the cooling means 5 decreases due to a failure or the like, the exhaust exceeding the current cooling capacity (for example, all exhaust if the cooling capacity is zero) is relieved to the exhaust pipe 2 side. . Thereby, it is avoided that the exhaust gas which is not cooled flows in and the capacity of the NOx absorption means 5 is reduced (for example, in the long term).

  Although the functions of the relief valve and the flow path shut-off valve can be configured by one bypass valve, in the present embodiment, the function is configured by two valves as described above. The advantages of this configuration are described below.

  A secondary failure that causes the cooling means 5 to fail, whereby hot exhaust gas reaches the NOx absorption means 6 and loses its function, is a high quality fault that should never occur during the lifetime of the equipment used. May require mass production design.

  On the other hand, the cooling means 5 is designed with know-how on the extension line of the in-vehicle air conditioner, and the predicted failure rate may not be suitably reduced. Furthermore, since the relief valve and the flow shut-off valve for opening and closing the exhaust flow path are used in a high temperature environment, it is difficult to provide a sufficient lubrication mechanism to the sliding portion. Therefore, the predicted failure rate may not be suitably reduced. Both the expected failure rate of the cooling means and the expected failure rate of the valve that opens and closes the exhaust passage are not suitably lowered, but when a high-quality design is required as a whole, It is necessary to perform a design that never leads to a secondary failure even if both failures occur simultaneously.

  That is, in the case of one exhaust passage opening / closing valve, the cooling means fails, and the opening / closing valve does not move while the exhaust passage with the cooling means and the NOx absorption means is open and the bypass passage is closed. I have to think about it. In this worst case, it is sufficient to limit the operation so that the exhaust temperature of the engine falls below 200 ° C. However, under such constraints, in the case of a vehicle engine, a gentle slope cannot be climbed, in other words, repair. There arises a problem that even the evacuation to the factory becomes difficult.

  If the relief valve 14 and the flow path shut-off valve 15 are separately designed, the failure mode becomes a triple fault while the relief valve 14 is closed simultaneously with the failure of the cooling means 5 and the flow path shut-off valve 15 is open. It can be eliminated from the double failure mode. Therefore, it is possible to avoid the problem that even the retreating of the engine becomes difficult.

  If the flow shut-off valve 15 is closed, the relief valve 14 is closed. Even if the flow shut-off valve 15 is closed, if the leakage flow rate is not less than four times the leakage flow rate of the flow shut-off valve 15, the main exhaust flow will bypass the bypass side. It can be made to flow. If the relief mechanism as shown in 61 of FIG. 4 is further added, the added relief mechanism opens and most of the exhaust flows to the bypass side, so that high-temperature exhaust flows into the exhaust branch pipe 4 side. There is no.

(Third embodiment: Relief function when the DPF PM collection rate is low)
Next, a third embodiment will be described. In this embodiment, the case where the DPF 3 is provided upstream of the cooling means 5 and the NOx absorption means 6 as shown in FIG. In the regeneration mode, when the PM collected by the exhaust gas temporarily heated to high temperature is burned and removed, the PM collection rate decreases, and a relatively large amount of PM, especially the soot component, is DPF. It slips downstream. The PM is mixed in the NOx absorption liquid in the NOx absorption means 6 in a relatively large amount, obstructs the flow of the absorption liquid. There arises a problem that a certain absorption liquid passage is blocked and the flow is alienated.

  FIG. 8 shows the relationship between the PM deposition amount per unit volume of the ceramic wall flow type DPF and the PM collection rate. When the PM accumulation amount becomes zero by regeneration, the collection rate is deteriorated to about 85%. After the regeneration, the engine operation is continued to gradually accumulate PM, and when PM becomes 0.2 g / L or more, the collection rate reaches a level exceeding 99%. Since the amount of PM deposited for regeneration is normally in the range of 2 g / L to 6 g / L, assuming that one regeneration travel distance is from regeneration to the next regeneration, one regeneration travel distance is It can be seen that a phenomenon occurs in which the collection rate decreases at a travel distance of 1/10 to 1/30.

  In order to solve the above problem, when the DPF trapping rate decreases immediately after the regeneration immediately before the regeneration ends and a relatively large amount of PM flows downstream, the relief valve 14 is opened, and the exhaust gas containing the PM is absorbed by the NOx absorbing means. 6 is bypassed to flow. In this case, NOx purification of the exhaust that bypasses cannot be performed, but since the travel distance for executing it is short, the average amount of NOx exhausted to the atmosphere while traveling a long travel distance is slightly deteriorated. It can be realized with restraint.

  In order to effectively bypass PM, as shown in FIG. 1, the exhaust passage 2 constituting the bypass is arranged straight, and the exhaust branch pipe 4 in which the cooling means 5 and the NOx absorption means 6 are arranged is bent sideways. Branch. Since PM is a fine particle but has a mass, it does not easily flow into a sharply bent portion and easily flows in a straight direction. Therefore, by selecting such a layout, PM to the NOx absorbing means 6 is selected. Inflow can be reduced.

  Further, in order to reduce the NOx mixing into the NOx absorption means 6, it is only necessary to close the flow passage shut-off valve 15 in accordance with the opening of the relief valve 14 to prevent the PM from flowing into the exhaust branch passage 4.

  FIG. 9 shows a flowchart for carrying out what has been described above. When the routine is started, the process first proceeds to step S62, and the current collection rate of the DPF is estimated. The collection rate is estimated by measuring the differential pressure before and after the DPF. When the differential pressure is small compared to the predetermined exhaust flow rate, the PM accumulation amount is small, and when the differential pressure is large, the PM accumulation amount is large. There is. If this relationship is obtained in advance and stored in the memory of the microcomputer, the amount of accumulated PM can be determined from the flow rate and the differential pressure. Furthermore, if the relationship of FIG. The rate can be determined. Further, the DPF collection rate may be obtained from the elapsed operation time of the engine after regeneration, the travel distance of the vehicle, the elapsed time of regeneration, the travel distance from the start of regeneration, or the like. In addition, the PM discharged from the engine is estimated and accumulated every moment, and the current PM accumulation amount is estimated by estimating and accumulating the PM combustion amount (reduction amount) during regeneration every moment. The DPF collection rate may be obtained.

  Next, it progresses to judgment S63 and it is determined whether the DPF collection rate is 95% or less. 95% is an example of implementation and may be other values in the vicinity. If S63 is YES, the process proceeds to S64 to S68. That is, the flow path shut-off valve 15 is fully closed to stop the inflow of exhaust gas into the exhaust branch pipe 4, the operation of the cooling means 5 and the NOx absorption means 6 is stopped, and the relief valve is opened to meet the engine operating conditions. An ON-OFF signal having a pulse duty ratio determined in this manner is sent to the solenoid valve 35 to be operated.

  If S63 is NO, the process proceeds to steps S69 to S71. The flow passage shut-off valve 15 is opened so that the exhaust gas is guided to the exhaust branch passage 4. Then, the cooling means 5 and the NOx absorption means 6 are operated. Next, it progresses to determination S72 and it is determined whether the travel distance after reproduction | regeneration is more than Akm. I would like to judge whether the DPF collection rate is 98-99% or higher, but this is inferior in numerical resolution, so when I run Akm after the regeneration is finished, the DPF collection rate becomes 98-99%. Akm is obtained from the correspondence relationship. The engine operation time or the estimated PM accumulation amount may be used as a determination index instead of the travel distance. If S72 is YES, the process proceeds to S73, and the relief valve is deactivated (fully closed). If S72 is NO, this routine is exited without performing any processing.

  As described above, when the DPF collection rate is reduced from the maximum value of the DPF collection rate, for example, immediately after regeneration of the DPF 3, the exhaust is relieved to the exhaust pipe 2 side. Thereby, it is possible to appropriately avoid the PM that has passed through the DPF 3 from reducing the ability of the NOx absorbing means.

  The above three embodiments may be implemented in any combination. In addition, the said Example can be suitably changed in the range which does not deviate from the meaning described in the claim. For example, in the embodiment of FIG. 9, the relief valve is fully closed and the flow path shut-off valve is fully opened by independent determination so that more precise control can be realized. However, the same determination may be performed simultaneously. Moreover, you may use the integral valve mechanism which integrated the function of both the relief valve and the flow-path cutoff valve. The engine is not limited and may be a diesel engine, a lean burn gasoline engine, or the like.

1 Engine 2 Exhaust pipe (bypass passage)
3 DPF (collector)
5 Cooling means 6 NOx absorption means (purification means)
14 Relief valve (adjustment means)
15 Channel shutoff valve (adjustment means)

Claims (7)

Purification means (6) for purifying NOx in the exhaust discharged from the engine;
A cooling means (5) for cooling the exhaust gas disposed upstream of the purification means in the exhaust passage;
A bypass passage (2) formed in the exhaust passage so as to bypass exhaust gas from upstream of the purification means and cooling means to downstream of the purification means and cooling means;
Adjusting means (14, 15) for adjusting the flow rate of the exhaust gas to the bypass passage;
First control means (20) for controlling the adjusting means so as to relieve the exhaust gas to the bypass passage when the purification ability of the purification means decreases when exhaust gas is circulated to the purification means;
A collector (3) for collecting particulate matter upstream of the cooling means in the exhaust passage;
The first control means, when the displacement of the engine is a displacement that exceeds the current cooling capacity of the cooling means, or when the collection rate of the collector is reduced from the maximum value, An engine aftertreatment device comprising second control means (20) for controlling the exhaust gas to be relieved in the bypass passage . The said 2nd control means is provided with the 3rd control means (20, S39) which controls so that exhaust may be relieved to the said bypass passage, when the pressure of exhaust gas exceeds predetermined pressure . Engine aftertreatment device. First detection means for detecting a decrease in the cooling function of the cooling means;
The second control means includes fourth control means (20, S56) for controlling the exhaust to be relieved in the bypass passage when the first detection means detects a decrease in the cooling function of the cooling means. The engine aftertreatment device according to claim 1 . A shut-off valve (15) for stopping the inflow of exhaust gas to the cooling means and the purifying means,
4. The rear part for an engine according to claim 3 , wherein the fourth control unit includes a closing unit (S <b> 56) that closes the shut-off valve when the first detection unit detects a decrease in the cooling function of the cooling unit. Processing equipment. The first detection means includes
Second detection means (21) for detecting the temperature of the exhaust gas that has passed through the cooling means;
A first determination unit (S52) that determines that the cooling function of the cooling unit is deteriorated when the temperature detected by the second detection unit exceeds a threshold;
The engine aftertreatment device according to claim 3 or 4 provided with . The second control means includes fifth control means (S64, S67) for controlling the exhaust gas to be relieved in the bypass passage when the collector is within a predetermined period from the start of regeneration to the end of regeneration. The engine aftertreatment device according to claim 1 . The second control means includes
At least one of the pressure difference between the upstream and downstream of the collector, the travel distance from the end of regeneration of the collector, and the estimated value of the amount of particulate matter accumulated in the collector is used to capture the collector. Second determination means (S63) for determining that the collection rate has decreased from the maximum value;
If the second determination means determines that the collection rate of the collector has decreased from the maximum value, sixth control means (S64, S67) for controlling the exhaust to relieve the bypass passage;
The engine aftertreatment device according to claim 1 , comprising:

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