JP2012215083A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely carry out the regeneration of a filter 13 while preventing the worsening of fuel economy in an exhaust emission control device for an engine with an NOx catalyst 11, an oxidation catalyst 12 and the filter 13 arranged in this order from the exhaust upstream side toward the downstream side.SOLUTION: An exhaust passage of the engine 2 is branched upstream of the NOx catalyst 11 into a first passage 27 that leads exhaust to the NOx catalyst and into a second passage 28 that leads exhaust to the oxidation catalyst 12 without passing through the NOx catalyst 11. A control valve 29 is provided in the exhaust passage, and the flow rate ratio of the flow rate of exhaust flowing into the first passage 27 to the flow rate of exhaust flowing into the second passage 28 can be changed by the control valve 29.

Description

  The present invention belongs to a technical field related to an engine exhaust purification device.

  Conventionally, as an exhaust purification device disposed in an exhaust passage of an engine, a device in which a NOx catalyst portion, an oxidation catalyst portion, and a filter are sequentially arranged from the exhaust upstream side to the exhaust downstream side is known (for example, , See FIG. 6 of Patent Document 1). This exhaust purification device reacts the added fuel with NOx by adding fuel (HC component) into the exhaust from the fuel addition device provided upstream of the NOx catalyst unit (HC-SCR catalyst), It is configured to purify NOx in the exhaust.

  In the above exhaust purification device, there is a problem that exhaust particulate collection (PM) accumulates on the filter, resulting in a decrease in the collection efficiency of exhaust particulates. To solve this problem, various filter regeneration technologies have been developed so far. Has been proposed. For example, in the one disclosed in Patent Document 2, post-injection is performed in the combustion chamber of the engine at the time of filter regeneration, thereby increasing the HC component in the exhaust and promoting the oxidation reaction of the HC component in the oxidation catalyst unit. The filter is regenerated by raising the filter temperature (exhaust temperature supplied to the filter) by the reaction heat.

JP 2008-75610 A JP 2010-265754 A

  However, in the above-described exhaust purification device in which the oxidation catalyst unit is disposed downstream of the NOx catalyst unit, the HC component in the exhaust gas flowing into the oxidation catalyst unit is increased by performing post injection during filter regeneration. Even if the exhaust gas passes through the NOx catalyst part, the NOx in the exhaust gas reacts with the HC component, so that the HC component flowing into the oxidation catalyst part is reduced by the amount of the reaction, and the oxidation of the HC component is performed. In some cases, the filter temperature rise effect (exhaust temperature rise effect) utilizing the reaction cannot be sufficiently obtained. For this reason, exhaust particulates accumulated on the filter cannot be sufficiently removed by combustion, and there is a problem that the pressure loss of the exhaust gas passing through the filter increases or the effect of collecting the exhaust particulates by the filter decreases. .

  On the other hand, it is conceivable to increase the fuel injection amount by post injection in advance by the amount corresponding to the reaction with NOx. However, since the reaction amount between NOx and the HC component depends on the temperature of the NOx catalyst section and the like, it is difficult to accurately predict this reaction amount. Therefore, for example, if the actual reaction amount between NOx and HC components is larger than the predicted value, the amount of HC supplied to the oxidation catalyst section is insufficient, and the regeneration temperature of the filter (exhaust temperature supplied to the filter) is the target. There is a problem that the temperature falls below. Conversely, if the actual reaction amount between NOx and HC components is less than the predicted value, more HC components are supplied to the oxidation catalyst unit than necessary, leading to a deterioration in fuel consumption. There is.

  The present invention has been made in view of such points, and an object of the present invention is an engine in which a NOx catalyst part, an oxidation catalyst part, and a filter are arranged in this order from the exhaust upstream side to the downstream side. An object of the exhaust purification device is to regenerate the filter reliably while preventing the deterioration of fuel consumption by devising the configuration.

  In order to achieve the above object, according to the present invention, the exhaust passage of the engine is arranged on the upstream side of the NOx catalyst portion, the first passage for leading the exhaust to the NOx catalyst portion, and the exhaust catalyst without the NOx catalyst portion. And a control valve is provided in the exhaust passage, and the flow rate of the exhaust gas flowing into the first passage and the flow rate of the exhaust gas flowing into the second passage are controlled by the control valve. The flow rate ratio can be changed.

  Specifically, in the first aspect of the present invention, the NOx catalyst part is disposed in the exhaust passage of the engine and reduces NOx in the exhaust gas using HC as a reducing agent, and disposed downstream of the NOx catalyst part. An exhaust purification device including an oxidation catalyst unit and a filter that is disposed downstream of the oxidation catalyst unit and collects exhaust particulates contained in the exhaust gas is intended.

  The exhaust passage leads the exhaust from the engine to the NOx catalyst portion on the upstream side of the NOx catalyst portion, and the exhaust passage from the engine to the oxidation catalyst portion without passing through the NOx catalyst portion. A control valve that is branched to the second passage and that can change a flow rate ratio between the flow rate of the exhaust gas flowing into the first passage and the flow rate of the exhaust gas flowing into the second passage. Is provided.

  According to a second aspect of the present invention, in the first aspect of the present invention, a determination unit that determines whether or not the filter needs to be regenerated, and a valve control that controls the operation of the control valve based on a determination result by the determination unit. Means.

  According to the first and second aspects of the present invention, when the filter needs to be regenerated, the operation (position) of the control valve is controlled so that a part (or all) of the exhaust from the engine is reduced. It can be made to flow into two passages. The exhaust gas flowing into the second passage is directly supplied to the oxidation catalyst unit without passing through the NOx catalyst unit. In the oxidation catalyst section, the oxidation reaction of the HC component in the exhaust gas supplied from the second passage is promoted, and the temperature of the exhaust gas is raised by the reaction heat generated at this time. The heated exhaust gas is supplied to the filter, so that the filter temperature rises to the target temperature and the exhaust particulates deposited on the filter are burned and removed. As described above, in the present invention, the HC component necessary for the temperature rise of the filter (filter regeneration) can be directly supplied from the second passage to the oxidation catalyst unit without passing through the NOx catalyst unit. Accordingly, it is possible to accurately control the amount of HC supplied to the oxidation catalyst unit during filter regeneration. Thereby, the regeneration of the filter can be reliably performed while preventing the deterioration of the fuel consumption.

  According to a third aspect of the invention, in the second aspect of the invention, the valve control means causes the control valve to exhaust the exhaust from the engine when the judgment means judges that the regeneration of the filter is not necessary. When the determination means determines that regeneration of the filter is necessary while the flow is allowed to flow into only one of the first and second passages, the control valve causes exhaust from the engine to be discharged from the first and second passages. It shall be comprised so that it may flow into both of a channel | path.

  According to this configuration, when it is determined by the determining means that the regeneration of the filter is not necessary, the control valve blocks the flow of the exhaust gas into the second passage, whereby the exhaust from the engine is all exhausted. It can be discharged into the atmosphere from one passage through the NOx catalyst section. Therefore, when it is not necessary to regenerate the filter, NOx in the exhaust can be sufficiently reduced by the NOx catalyst unit, and the purification efficiency of NOx in the exhaust can be improved.

  On the other hand, when the determination means determines that the filter needs to be regenerated, the control valve allows the exhaust to flow into both the first and second passages. The NOx catalyst can be directly supplied from the second passage without passing through the NOx catalyst, whereby the same effect as that of the first aspect of the invention can be obtained.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the apparatus further comprises a deposit amount detecting means for detecting the amount of exhaust particulate deposited on the filter, and the valve control means needs to regenerate the filter by the determining means. When the determination is made, the operation of the control valve is controlled to increase the flow rate of the exhaust gas flowing into the second passage as the accumulation amount of the exhaust particulates detected by the accumulation amount detection means increases.

  According to this configuration, the larger the amount of exhaust particulate deposited on the filter, the higher the flow rate of the exhaust gas flowing from the second passage into the oxidation catalyst unit, and the HC flowing into the oxidation catalyst unit together with the exhaust gas. The amount can be increased. Therefore, the larger the amount of exhaust particulate deposited on the filter, the more the oxidation reaction of the HC component in the oxidation catalyst unit can be promoted, and the temperature of the exhaust gas supplied to the filter through the oxidation catalyst unit can be increased. Therefore, the exhaust particulate deposited on the filter can be efficiently and reliably burned and removed according to the amount of deposition.

  According to a fifth aspect of the present invention, in any one of the second to fourth aspects of the present invention, the apparatus further comprises NOx concentration detecting means that is disposed downstream of the NOx catalyst section and detects the NOx concentration in the exhaust gas. The valve control means is configured to control the control valve based on the NOx concentration detected by the NOx concentration detection means.

  According to a sixth aspect of the present invention, in the fifth aspect of the invention, the valve control means increases the NOx concentration detected by the NOx concentration detection means when the judgment means judges that regeneration of the filter is necessary. The control valve is controlled so as to increase the flow rate of the exhaust gas flowing into the first passage.

  According to the fifth and sixth aspects of the invention, filter regeneration can be performed efficiently and reliably while preventing a reduction in the NOx purification rate.

  That is, at the time of filter regeneration, as described above, part (or all) of exhaust from the engine flows directly from the second passage into the oxidation catalyst unit without passing through the NOx catalyst unit. For this reason, if the amount of exhaust gas passing through the second passage is too large, the flow rate of exhaust gas supplied from the first passage to the NOx catalyst unit may decrease, and the NOx purification efficiency during filter regeneration may decrease. On the other hand, in the present invention, when the filter is regenerated, the higher the NOx concentration of the exhaust gas detected by the NOx concentration detecting means, the higher the flow rate of the exhaust gas flowing from the first passage into the NOx catalyst unit. As a result, it is possible to efficiently and reliably execute the filter regeneration while suppressing the decrease in the NOx purification performance during the filter regeneration as much as possible.

  According to a seventh aspect of the invention, in any one of the first to sixth aspects, the amount of HC in the exhaust discharged from the engine is controlled by post-injecting or after-injecting fuel into the cylinder of the engine. It is further assumed that HC control means is provided.

  According to this configuration, in order to supply the amount of HC necessary for the reduction reaction of NOx in the exhaust and the amount of HC necessary for the temperature rise of the filter (the amount of HC necessary in the oxidation catalyst unit) into the exhaust, Since it is not necessary to separately provide a fuel (HC) addition device or the like, the entire device can be made compact.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the NOx catalyst part includes a cylindrical NOx catalyst holding body for holding a NOx catalyst, and the oxidation catalyst part is an oxidation catalyst. And the filter is formed in a cylindrical shape, and the NOx catalyst holder, the oxidation catalyst holder, and the filter are arranged in series and coaxially. It shall be.

  According to this configuration, the cylindrical NOx catalyst holding body that holds the NOx catalyst, the cylindrical oxidation catalyst holding body that holds the oxidation catalyst, and the cylindrical filter are arranged in series and coaxially. As a result, the entire apparatus can be made compact.

  As described above, according to the exhaust gas purification apparatus of the present invention, the exhaust passage of the engine is arranged upstream of the NOx catalyst portion, and the first passage for guiding the exhaust to the NOx catalyst portion and the exhaust gas without passing through the NOx catalyst portion. A branch is made to the second passage leading to the oxidation catalyst section, and a control valve is provided in the exhaust passage, and the flow rate of the exhaust gas flowing into the first passage and the exhaust gas flowing into the second passage are controlled by the control valve. By making it possible to change the flow rate ratio with respect to the flow rate, it is possible to reliably regenerate the filter while preventing deterioration in fuel consumption.

It is a schematic plan view which shows apparatus arrangement | positioning in the engine room of the hydraulic excavator carrying the diesel engine to which the exhaust gas purification apparatus which concerns on embodiment of this invention is applied. It is an II directional arrow line view of FIG. It is the schematic which shows the internal structure of an exhaust gas purification apparatus. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is a flowchart which shows an example of normal driving | operation control and filter regeneration control in ECU.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a structure in an upper swing body 101 of a hydraulic excavator 100 including an exhaust purification device 1 according to an embodiment of the present invention. This exhaust purification device 1 (see FIGS. 1 to 3) is applied to an exhaust purification process of a diesel engine 2 (hereinafter simply referred to as an engine) mounted on a hydraulic excavator 100.

  The engine 2 is an in-line four-cylinder engine, for example, and is disposed in an engine room 3 provided in the upper swing body 101 of the excavator 100. In the engine room 3, in addition to the engine 2, a hydraulic pump 4, a radiator 5, an exhaust purification device 1, and the like are accommodated. Exhaust gas discharged from the engine 2 is guided to the exhaust purification device main body 6 via the exhaust manifold (not shown) and the exhaust pipe 7 and is discharged from the exhaust purification device main body 6 to the atmosphere via the tail pipe 8.

  The exhaust purification device main body 6 has a substantially cylindrical shape, and extends substantially horizontally on the side of the engine 2 in a direction orthogonal to the cylinder arrangement direction. An exhaust pipe 7 is connected to one end in the longitudinal direction of the exhaust purification apparatus body 6 from below, and a tail pipe 8 is connected to the other end in the longitudinal direction of the exhaust purification apparatus body 6 from above. The exhaust pipe 7 and the tail pipe 8 are each connected perpendicularly to the exhaust purification device main body 6.

  The exhaust purification apparatus 1 includes a NOx catalyst unit 11 that reduces and purifies NOx contained in exhaust discharged from the engine 2, and an oxidation catalyst unit 12 that purifies harmful substances such as HC and CO contained in the exhaust. And a filter 13 that collects exhaust particulate (PM) such as soot contained in the exhaust, and these NOx catalyst part 11, oxidation catalyst part 12, and filter 13 are the exhaust purification apparatus body 6 The exhaust passage is formed in this order from the upstream side to the downstream side.

  The NOx catalyst unit 11 is a cylindrical honeycomb having an HC selective reduction type NOx catalyst (hereinafter referred to as HC-SCR catalyst) with enhanced reaction selectivity so that NOx can be selectively reacted with HC even in the presence of oxygen. A body (hereinafter referred to as NOx catalyst holder) 14 is held on the cell surface. For this HC-SCR catalyst, for example, a well-known base metal oxidation catalyst such as copper / zeolite, iron / zeolite or the like can be adopted, and the NOx catalyst holding body 14 holding these HC-SCR catalysts can be used. For example, alumina or the like can be used.

The oxidation catalyst portion 12 is a cylindrical honeycomb body (hereinafter referred to as an oxidation catalyst holding body) 15 having a noble metal such as Pt (platinum) coated on the cell surface and coated with a catalyst layer. It is configured to promote an oxidation reaction in which CO and HC are oxidized to produce CO ₂ and H ₂ O.

  The filter 13 is a porous ceramic diesel particulate filter (DPF), and the surface of the cell is coated with a catalyst layer holding a precious metal such as Pt. The filter 13 is formed in a cylindrical shape, and the filter 13, the NOx catalyst holding body 14, and the oxidation catalyst holding body 15 are arranged in series and coaxially with each other. Each of the holding bodies 14 and 15 and the filter 16 are fixed to the tube wall of the exhaust purification device main body 6.

  The upstream side and the downstream side of the filter 13 in the exhaust passage communicate with each other via a differential pressure detection passage 21, and the differential pressure detection passage 21 detects a differential pressure ΔP between the upstream side and the downstream side of the filter. A differential pressure detection sensor 22 is provided. Further, a NOx sensor 23 for detecting the NOx concentration in the exhaust gas is provided on the downstream side of the filter 13. Detection signals of the sensors 22 and 23 are output to an ECU (Engine Control Unit) 25 via an electric connection line (not shown).

  The exhaust passage includes a first passage 27 that guides exhaust from the engine 2 to the NOx catalyst unit 11 on the upstream side of the NOx catalyst unit 11, and an oxidation catalyst unit that does not pass the exhaust from the engine 2 through the NOx catalyst unit 11. 12 and branched into a second passage 28 leading to 12 (see FIG. 3).

  The first passage 27 and the second passage 28 are separated from each other by a partition plate 26 provided at the downstream end of the exhaust pipe 7. The partition plate 26 is disposed at the downstream end of the exhaust pipe 7 so as to divide the passage space in the exhaust pipe 7 into two in the radial direction (see FIG. 4). An end portion on the exhaust gas downstream side of the partition plate 26 is fixed by welding to the outer peripheral surface of the NOx catalyst holding body 14.

  In the portion of the exhaust passage that starts to branch into the first passage 27 and the second passage 28, the ratio between the exhaust flow rate flowing into the first passage 27 and the exhaust flow rate flowing into the second passage 28 is changed. A control valve 29 is provided.

  As shown in FIG. 4, the control valve 29 has a valve body 31 made of a semicircular plate-like member, and a rotation pin 32 fixed to the valve body 31 so as to rotate together. The rotation pin 32 is disposed so as to penetrate the passage space in the exhaust pipe 7 in the radial direction. Both ends of the rotation pin 32 are rotatably supported on the tube wall of the exhaust pipe 7, and are rotated integrally with the valve body 31 by the electric motor 33. The outer peripheral surface of the rotation pin 32 is in contact with the end surface of the partition plate 26 on the exhaust upstream side so as to be able to rotate and slide. The valve body 31 rotates the rotation pin 32 by the electric motor 33 to fully close the first passage fully closed position where the upstream opening of the first passage 27 is fully closed and the upstream opening of the second passage 28. It can be controlled to an arbitrary position between the fully closed position of the second passage (the normal position described later). The electric motor 33 is controlled by an ECU 25 described later.

  The ECU 25 is composed of a known microcomputer including a CPU, a ROM, a RAM, and the like. The ECU 25 operates the engine 2 and the control valve 29 (electric motor 33) based on detection signals from the NOx sensor 23, the differential pressure detection sensor 22, and various sensors (not shown) attached to the engine 2. Control.

  When the differential pressure ΔP detected by the differential pressure detection sensor 22 is less than a preset first threshold pressure, the ECU 25 determines that regeneration of the filter 13 is not necessary and executes normal operation control. Specifically, when the ECU 25 determines that the regeneration of the filter 13 is not necessary, the ECU 25 moves the control valve 29 to the normal position (the position indicated by the two-dot chain line in FIG. The NOx concentration in the exhaust discharged from the engine 2 based on the operating state of the engine 2 and necessary for NOx reduction in the NOx catalyst unit 11 based on the estimated NOx concentration. The HC amount is calculated, and post injection is performed into the combustion chamber of the engine 2 to supply the calculated HC amount into the exhaust gas. This post-injection is performed in the compression step prior to the main injection near the compression top dead center.

  If the differential pressure ΔP detected by the differential pressure detection sensor 22 is equal to or higher than the first threshold pressure, the ECU 25 determines that regeneration of the filter 13 is necessary and executes filter regeneration control. Specifically, when the ECU 25 determines that the filter regeneration control is necessary, the ECU 25 calculates the amount of exhaust particulates accumulated on the filter 13 based on the differential pressure ΔP detected by the differential pressure detection sensor 22, and calculates the calculation. The temporary target control position of the control valve 29 is calculated based on the exhaust particulate amount. This temporary target control position is an intermediate position between the first passage fully closed position and the second passage fully closed position, and the exhaust flow rate flowing into the second passage 28 increases as the amount of exhaust particulate accumulation increases. The ECU 25 calculates the map data stored in advance.

  Then, the ECU 25 corrects the calculated temporary target control position according to the NOx concentration detected by the NOx sensor 23. In the present embodiment, the ECU 25 corrects the temporary target control position so that the exhaust flow rate flowing into the first passage 27 increases as the NOx concentration detected by the NOx sensor increases, and the corrected temporary target control position is determined. The true target control position of the control valve 29 is set.

  During the filter regeneration control, the ECU 25 calculates the amount of HC necessary for NOx reduction in the NOx catalyst unit 11 and the amount of HC necessary for raising the temperature of the exhaust gas in the oxidation catalyst unit 12, and the calculated HC amount is being exhausted. Post-injection is performed in the combustion chamber of the engine 2 to supply to the engine.

  Next, normal operation control and filter regeneration control in the ECU 25 will be described in detail based on the flowchart of FIG.

  In the first step S1, a concentration signal from the NOx sensor 23, a pressure signal from the differential pressure detection sensor 22, and signals from various sensors attached to the engine 2 are read.

  In step S2, the differential pressure ΔP on the upstream side and downstream side of the filter 13 is calculated based on the pressure signal from the differential pressure detection sensor 22 read in step S1, and the differential pressure ΔP is greater than or equal to the first threshold pressure. If the determination is NO, the process proceeds to step S13. If the determination is YES, the process proceeds to step S3.

  In step S3, a filter regeneration program stored in the ROM of the ECU 25 is executed to start the filter regeneration control.

  In step S4, the accumulation amount (PM accumulation amount) of exhaust particulates deposited on the filter 13 is calculated based on the differential pressure ΔP calculated in step S2.

  In step S5, the temporary target control position of the control valve 29 is calculated based on the accumulated amount of exhaust particulates calculated in step S4.

  In step S6, the NOx concentration on the downstream side of the filter 13 is calculated based on the detection signal from the NOx sensor read in step S1.

  In step S7, the calculated temporary target control position is corrected according to the NOx concentration calculated in step S6, and the target control position of the control valve 29 is determined.

  In step S8, a necessary control signal is output to the electric motor 33 in order to control the control valve 29 to the target control position.

  In step S9, the NOx concentration in the exhaust on the upstream side of the NOx catalyst unit 11 is calculated based on detection signals from various sensors of the engine 2, and the NOx in the NOx catalyst unit 11 is calculated based on the calculated NOx concentration. The amount of HC required for the reduction reaction is calculated. Further, based on the accumulated amount of exhaust particulates calculated in step S4, the amount of HC necessary for the oxidation catalyst unit 12 to burn and remove the exhaust particulates is calculated. The operating state of the engine 2 may be estimated based on signals from each sensor attached to the engine 2 read in step S1.

  In step S10, for the injector (fuel injection valve), the HC amount in the exhaust gas immediately after being discharged from the engine 2 (in the exhaust gas upstream of the NOx catalyst unit 11) becomes the HC amount calculated in step S9. The necessary control signal is output and post injection is executed.

  In step S11, a detection signal from the differential pressure detection sensor 22 is read to calculate the current differential pressure ΔP, and whether or not the calculated differential pressure is equal to or lower than a second threshold pressure (<first threshold pressure). If this determination is NO, the process returns to step S2. If YES, the process proceeds to step S12. In step S12, the filter regeneration control is terminated, and then the process returns.

  In step S13 which proceeds when the determination in step S2 is NO, a necessary control signal is output to the electric motor 33 in order to control the control valve 29 to the above-described normal position (second passage fully closed position).

  In step S14, the NOx concentration in the exhaust discharged from the engine 2 is calculated (estimated) based on the detection signals from the various sensors of the engine 2, and the NOx catalyst unit 11 calculates the NOx concentration based on the calculated NOx concentration. The amount of HC required for the reduction reaction of NOx is calculated.

  In step S15, the post-injection is executed by outputting a necessary control signal to the injector so that the HC amount in the exhaust gas immediately after being discharged from the engine 2 becomes the HC amount calculated in step S9. Return.

  In the exhaust emission control device 1 configured as described above, during normal operation where there is no regeneration request for the filter 13 (when the determination in step S2 is NO), the ECU 25 executes the process of step S13. The control valve 29 is controlled to the normal position (second passage fully closed position). For this reason, the upstream opening of the second passage 28 is fully closed by the control valve 29, and the inflow of exhaust gas into the second passage 28 is blocked. As a result, all exhaust from the engine 2 is discharged from the first passage 27. After being supplied to the NOx catalyst unit 11, it is discharged into the atmosphere via the oxidation catalyst unit 12 and the filter 13. On the other hand, when there is a regeneration request for the filter 13, the ECU 25 executes steps S <b> 3 to S <b> 8 and the control valve 29 is moved between the first passage fully closed position and the second passage fully closed position by the ECU 25. The target control position is controlled. As a result, the exhaust from the engine 2 branches into a flow that flows into the NOx catalyst unit 11 from the first passage 27 and a flow that flows into the oxidation catalyst unit 12 without passing through the NOx catalyst unit 11 from the second passage 28. The HC component in the exhaust gas flowing into the NOx catalyst unit 11 from the first passage 27 is used for the NOx reduction reaction in the NOx catalyst unit 11. The HC component in the exhaust gas flowing into the oxidation catalyst unit 12 from the second passage 28 is used for the oxidation reaction in the oxidation catalyst unit 12, and the temperature of the exhaust gas is raised by the reaction heat generated at this time. Thus, the heated exhaust gas is supplied to the filter 13, so that the temperature of the filter 13 reaches a target temperature (a temperature at which the exhaust particulates can be combusted), and the exhaust particulates accumulated on the filter are removed by combustion. . As described above, in the above embodiment, the HC component necessary in the oxidation catalyst unit 12 at the time of filter regeneration is directly supplied from the second passage 28 to the oxidation catalyst unit 12 without passing through the NOx catalyst unit 11. In addition, the amount of HC supplied to the oxidation catalyst unit 12 during filter regeneration can be accurately controlled, so that the regeneration of the filter 13 can be reliably performed while preventing deterioration in fuel consumption associated with filter regeneration.

  Further, in the above embodiment, when the filter is regenerated, the ECU 25 executes the process of step S5 (and step S8), and the exhaust gas flow rate that flows into the second passage 28 as the amount of exhaust particulates accumulated on the filter 13 increases. The position of the control valve 29 is controlled by the ECU 25 so as to increase. As a result, as the amount of exhaust particulate deposited on the filter 13 increases, the HC component supplied to the oxidation catalyst unit via the second passage 28 can be increased. As a result, the HC component in the oxidation catalyst unit is increased. The temperature of the exhaust gas supplied to the filter 13 can be increased by promoting the oxidation reaction. Therefore, the exhaust particulate deposited on the filter 13 can be efficiently and reliably burned and removed according to the amount of deposition.

  Furthermore, in the above embodiment, at the time of filter regeneration, the ECU 25 executes the process of step S7, and the position of the control valve 29 is controlled according to the NOx concentration on the downstream side of the filter 13. Thereby, the fall of the NOx purification rate during filter regeneration can be suppressed as much as possible. That is, at the time of filter regeneration, as described above, part of the exhaust from the engine 2 flows directly from the second passage 28 into the oxidation catalyst unit 12 without passing through the NOx catalyst unit 11. For this reason, if the amount of exhaust gas passing through the second passage 28 is too large, the amount of exhaust gas supplied from the first passage 27 to the NOx catalyst unit 11 may decrease and the NOx purification efficiency during filter regeneration may decrease. is there. On the other hand, in the above embodiment, at the time of filter regeneration, the higher the NOx concentration on the downstream side of the filter 13 detected by the NOx sensor 23, the higher the flow rate of the exhaust gas flowing into the NOx catalyst unit 11 from the first passage 27. As a result, the reduction reaction of NOx in the exhaust gas is promoted, so that a reduction in NOx purification performance accompanying filter regeneration can be suppressed as much as possible.

  In the above embodiment, the ECU 25 supplies the HC amount necessary for the NOx reduction reaction and the HC amount necessary for increasing the temperature of the filter 13 (HC amount necessary for the oxidation catalyst unit 12) into the exhaust gas. Therefore, post-injection is performed in the combustion chamber of the engine 2 (the processing of step S10 and step S15 is executed). Therefore, it is not necessary to separately provide an HC addition device or the like in order to secure these necessary HC amounts. Therefore, the number of parts can be reduced, and the exhaust purification device 1 can be made compact and low in cost. In addition, since the dedicated piping required when the fuel addition device is provided is not necessary, troubles such as fuel leakage can be prevented and safety can be improved.

  Further, in construction machines such as the excavator 100, the exhaust purification device 1 needs to be housed in the narrow engine room 3 together with the accessory equipment such as the hydraulic pump 4 as described above. Although the space is limited, in the above-described embodiment, as described above, it is not necessary to separately provide the fuel addition device. Therefore, the exhaust purification device 1 can be made compact and efficiently disposed in the narrow engine room 3.

(Other embodiments)
The configuration of the present invention is not limited to the above embodiment, but includes various other configurations. That is, in the above embodiment, at the time of filter regeneration, the control valve 29 is controlled to an intermediate position between the first passage fully closed position and the second passage fully closed position, and the engine is placed in both the first passage 27 and the second passage 28. However, the present invention is not limited to this. For example, the control valve 29 may be controlled to the first passage fully closed position during filter regeneration.

  Moreover, in the said embodiment, although the control valve 29 shall have the one valve body 31, it is not restricted to this, For example, the control valve 29 is the 1st channel | path 27, the 2nd channel | path 28, May have two valve bodies 31 that can be opened and closed independently.

  In the above embodiment, the determination as to whether or not the regeneration of the filter 13 is necessary is performed based on the differential pressure detected by the differential pressure detection sensor 22, but the present invention is not limited to this. The ECU 25 estimates the amount of exhaust particulate deposited on the filter 13 based on the history of the operating state (combustion state etc.) of the engine 2, and whether the filter 13 needs to be regenerated based on the estimated amount of exhaust particulate. Such a determination may be made. Alternatively, the ECU 25 may execute the timer control to determine that the filter 13 needs to be regenerated every predetermined time, and execute the regeneration control of the filter 13.

  In the above embodiment, the NOx sensor 23 is disposed on the downstream side of the filter 13. However, the NOx sensor 23 may be disposed anywhere on the downstream side of the NOx catalyst unit 11. In the above embodiment, the NOx concentration on the downstream side of the filter 13 is detected by the NOx sensor 23. However, the present invention is not limited to this. For example, the ECU 25 is based on detection signals from various sensors. The operating state of the engine 2 may be estimated, and the NOx concentration may be estimated (detected) based on the estimated operating state.

  Further, in the above embodiment, post injection is performed in the combustion chamber of the engine 2 in order to supply the HC amount necessary for NOx reduction and the HC amount necessary for increasing the temperature of the filter 13 into the exhaust gas. However, for example, after injection may be performed instead of post injection, or after injection may be further performed in addition to post injection. In addition, a fuel addition device may be separately provided in order to ensure the necessary amount of HC.

  Moreover, in the said embodiment, although the example which applied the exhaust gas purification apparatus 1 to the diesel engine 2 was shown, you may make it apply not only to this but a gasoline engine, for example. Further, the engine 2 is not limited to an in-line four-cylinder engine, and may be a horizontally opposed type or a V-type engine, and the number of cylinders is not limited to four. For example, the number of cylinders may be three or less or five or more. Good.

  In the above embodiment, the HC-SCR catalyst is used as the catalyst for reducing NOx. However, for example, a NOx storage reduction catalyst may be used. In this case, the engine 2 is preferably a gasoline engine.

  Moreover, although the example which applied the exhaust gas purification apparatus 1 to the engine 2 of the hydraulic excavator was shown in the said embodiment, it is not restricted to this, For example, you may make it apply to the engine 2 of a motor vehicle or a ship. .

  INDUSTRIAL APPLICABILITY The present invention is useful for an engine exhaust purification device, and particularly useful for an engine exhaust purification device mounted on a construction machine such as an excavator.

1 Exhaust gas purification device
2 Engine
11 NOx catalyst section
12 Oxidation catalyst part
13 Filter
14 NOx catalyst holder 15 Oxidation catalyst holder 22 Differential pressure detection sensor (determination means, accumulation amount detection means)
23 NOx sensor (NOx detection means)
25 ECU (valve control means, determination means, HC control means, NOx detection means,
Accumulation amount detection means)
27 First passage
28 Second passage
29 Control valve

Claims (8)

A NOx catalyst portion disposed in an exhaust passage of the engine for reducing NOx in exhaust gas using HC as a reducing agent; an oxidation catalyst portion disposed downstream of the NOx catalyst portion; and a downstream side of the oxidation catalyst portion An exhaust purification device comprising a filter that collects exhaust particulates contained in the exhaust,
The exhaust passage includes a first passage that guides exhaust from the engine to the NOx catalyst on the upstream side of the NOx catalyst, and a second that guides exhaust from the engine to the oxidation catalyst without passing through the NOx catalyst. It is formed by branching to the passage,
The exhaust gas purification apparatus is characterized in that the exhaust passage is provided with a control valve capable of changing a flow rate ratio between the flow rate of the exhaust gas flowing into the first passage and the flow rate of the exhaust gas flowing into the second passage. . The exhaust emission control device according to claim 1,
Determining means for determining whether or not regeneration of the filter is necessary;
An exhaust emission control device comprising: valve control means for controlling the operation of the control valve based on a determination result by the determination means. The exhaust emission control device according to claim 2,
When it is determined by the determination means that the regeneration of the filter is not necessary, the valve control means allows the exhaust from the engine to flow into only the first path of the first and second paths by the control valve. On the other hand, when it is determined by the determination means that the filter needs to be regenerated, the control valve is configured to allow exhaust from the engine to flow into both the first and second passages. An exhaust purification device characterized by the above. The exhaust emission control device according to claim 3,
A deposition amount detecting means for detecting the amount of exhaust particulate deposited on the filter;
In the case where the determination means determines that the filter needs to be regenerated, the valve control means is configured to increase the flow rate of the exhaust gas flowing into the second passage as the accumulation amount of the exhaust particulates detected by the accumulation amount detection means increases. An exhaust emission control device for controlling the operation of the control valve so as to increase the exhaust gas. The exhaust emission control device according to any one of claims 2 to 4,
Further comprising NOx concentration detecting means disposed downstream of the filter and detecting NOx concentration in the exhaust;
The exhaust gas purification apparatus, wherein the valve control means is configured to control the operation of the control valve based on the NOx concentration detected by the NOx concentration detection means. The exhaust emission control device according to claim 5,
The valve control means increases the flow rate of the exhaust gas flowing into the first passage as the NOx concentration detected by the NOx concentration detection means is higher when the judgment means judges that the regeneration of the filter is necessary. An exhaust emission control device for controlling the control valve as described above. The exhaust emission control device according to any one of claims 1 to 6,
An exhaust emission control device, further comprising HC control means for controlling the amount of HC in the exhaust discharged from the engine by post-injecting or after-injecting fuel into the cylinder of the engine. The exhaust emission control device according to any one of claims 1 to 7,
The NOx catalyst part includes a cylindrical NOx catalyst holding body that holds the NOx catalyst,
The oxidation catalyst part includes a cylindrical oxidation catalyst holding body for holding an oxidation catalyst,
The filter is formed in a cylindrical shape,
The exhaust gas purification apparatus, wherein the NOx catalyst holding body, the oxidation catalyst holding body, and the filter are arranged in series and coaxially.

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