JP2012102684A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely raise a temperature during regeneration of a DPF 8 while suppressing an excessive temperature rise of an SCR catalyst 9.SOLUTION: This exhaust emission control device includes the DPF 8 on an upstream side of an exhaust passage 3, and the SCR catalyst 9 and an urea water injection nozzle 11 on a downstream side. An exhaust throttle valve 13 throttling exhaust during a regeneration request of the DPF 8 is provided on a downstream side of the DPF 8 and on an upstream side of the SCR catalyst 9 and the urea water injection nozzle 11.

Description

  The present invention relates to an exhaust emission control device that removes PM (particulate matter) and NOx (nitrogen oxide) in engine exhaust.

  An engine, particularly a diesel engine, has combustion in a region where the excess air ratio is large. Therefore, CO and HC emissions are small, but PM and NOx are large.

  Therefore, as described in Patent Document 1, in the engine exhaust passage, a filter that collects PM in the exhaust, and a NOx reduction device that reduces NOx using a reducing agent (SCR catalyst and urea water injection nozzle) ) Are arranged in this order, and an exhaust emission control device has been proposed.

JP 2006-342734 A

  By the way, since the PM collection filter collects PM by the porous member, the clogging of the porous member proceeds with an increase in the amount of collected PM, and the exhaust pressure rises above the allowable value. The fuel consumption will be reduced. For this reason, "regeneration processing" that eliminates clogging by burning and burning PM deposited on the filter at an appropriate timing is indispensable.

  Conventionally, for forced regeneration of the filter, the exhaust temperature flowing into the filter is raised by heating means such as fuel injection amount increase, post-injection, exhaust pipe injection, or electric heater. Fuel consumption deteriorates because a large amount of heat is required.

  Therefore, when the intake air amount is reduced by an intake shutter or a variable valve to reduce the exhaust amount during forced regeneration of the filter, oxygen necessary for incineration of PM accumulated on the filter is insufficient, which may cause incomplete combustion. is there.

  Therefore, a method is used in which the exhaust temperature is raised by closing the exhaust throttle valve (exhaust shutter) downstream of the exhaust manifold (or exhaust turbine) and increasing the engine back pressure (and hence the engine load) during forced regeneration of the filter.

  However, in the exhaust emission control device described in Patent Document 1, since the exhaust throttle valve is provided upstream of the filter, the exhaust upstream of the exhaust throttle valve increases in pressure and temperature, but downstream of the exhaust throttle valve. In the filter, since the exhaust gas expands and the pressure and temperature decrease again, the temperature rise effect of the filter is small.

  In view of such a situation, an object of the present invention is to promote an increase in the temperature of a filter during forced regeneration of a filter for collecting PM.

  In order to solve the above-described problems, the present invention is provided with an engine exhaust passage having a filter for collecting PM in exhaust and a NOx reduction device for reducing NOx using a reducing agent in this order. In this exhaust gas purification apparatus, an exhaust throttle means is provided between the filter and the NOx reduction device to throttle the exhaust passage when the regeneration of the filter is requested.

  According to the present invention, it is possible to reliably raise the temperature of the filter upstream from the exhaust throttling position by restricting the exhaust on the downstream side of the filter for collecting PM. On the other hand, on the downstream side of the exhaust throttling position, the temperature can be lowered by the expansion of the exhaust, and the inflow of the high-temperature exhaust to the NOx reduction device can be prevented as much as possible.

FIG. 1 is a system diagram of an engine exhaust system showing a first embodiment of the present invention. Flowchart at the time of playback request in the first embodiment System diagram of engine exhaust system showing second embodiment of the present invention 3 is an enlarged view of the main part of FIG. Flow chart at the time of playback request in the second embodiment

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a system diagram of an engine exhaust system showing a first embodiment of the present invention.

  In order to equip the exhaust passage (exhaust pipe) 3 on the downstream side of the exhaust manifold 2 of the diesel engine (engine body) 1 with an exhaust purification device, the first casing 4 on the upstream side, the second casing 5 on the downstream side, A communication path 6 between the casings 4 and 5 is provided. The first and second casings 4 and 5 have a pipe diameter larger than the exhaust pipe diameter, and the communication path 6 has a pipe diameter equivalent to the exhaust pipe diameter.

  In the first casing 4, a diesel oxidation catalyst (DOC; Diesel Oxidation Catalyst) 7 is accommodated in the front stage, and a diesel particulate filter (hereinafter referred to as “DPF”) 8 is accommodated in the rear stage.

  The DPF 8 is a filter that collects PM (Particulate Matter) that is particulate matter in the exhaust gas. For example, the DPF 8 is made of a porous ceramic honeycomb structure carrier, and has many passages that connect the upstream side and the downstream side. And a wall flow type filter in which the upstream side and the downstream side are alternately sealed in adjacent passages. Therefore, the exhaust gas flows from the passage where the upstream end is open and the downstream end is sealed, passes through the passage wall (its pore), and flows out to the passage where the upstream end is sealed and the downstream end is open. In addition, PM in the exhaust is collected on the passage wall. In such a DPF 8, the exhaust resistance gradually increases due to the accumulation of the collected PM. Therefore, as described later, it is necessary to regenerate the DPF 8 continuously and forcibly.

  The oxidation catalyst 7 oxidizes NO in the exhaust to generate NO2, supplies this NO2 as an oxidant to the DPF 8, and generates oxidation heat to raise the temperature of the downstream DPF 8. By arranging the oxidation catalyst 7 in the preceding stage of the DPF 8 in this way, the PM collected in the DPF 8 reacts with the NO 2 supplied from the oxidation catalyst 7 and is oxidized, so that the continuous regeneration of the DPF 8 is performed. Become.

  In the second casing 5, an SCR catalyst 9 having a function of reducing NOx using ammonia as a reducing agent is accommodated in the front stage, and an ammonia catalyst 10 is accommodated in the rear stage. “SCR” is an abbreviation for Selective Catalytic Reduction.

  A urea aqueous solution (hereinafter referred to as “urea water”) as a reducing agent (ammonia) precursor is injected into the communication passage 6 upstream of the second casing 5 together with the pressurized air toward the SCR catalyst 9. An injection nozzle 11 is provided. The urea water is supplied from a urea water tank (not shown) to the nozzle 11 via the control module 12 for controlling the injection amount, and the control module 12 is controlled by an electronic control unit (ECU) 50.

  The urea water injected from the urea water injection nozzle 11 is hydrolyzed by the heat of the exhaust to become ammonia. The SCR catalyst 9 adsorbs the ammonia thus generated, selectively reduces NOx and ammonia (NH3) using the adsorbed ammonia as a reducing agent, and converts NOx into harmless water (H2O) and nitrogen. Purify to (N2). Here, the SCR catalyst 9 and the urea water injection nozzle 11 constitute a NOx reduction device.

  The ammonia catalyst 10 has a function as an oxidation catalyst that oxidizes ammonia flowing out from the SCR catalyst 9 in the previous stage to make it N2.

  In such an exhaust emission control device for a diesel engine, for forced regeneration of the DPF 8, an exhaust throttle is provided as an exhaust throttle means upstream of the urea water injection nozzle 11 in the communication path 6 between the first and second casings 4 and 5. A valve (butterfly valve) 13 is provided.

  The exhaust throttle valve 13 is configured to be throttled by the electronic control unit 50 in the closing direction when the DPF 8 is forcibly regenerated.

Next, forced regeneration of the DPF 8 will be described.
In the diesel engine, PM contained in the exhaust gas is collected by the DPF 8 and is prevented from being released into the atmosphere.

When the engine load increases and the exhaust temperature becomes high, the PM collected and deposited in the DPF 8 is oxidized and removed by exposure to the high-temperature exhaust, but the engine load is low for a long time. If it continues, PM will not be oxidized and removed in the meantime.
Therefore, the PM accumulation amount of the DPF 8 gradually increases, and the exhaust resistance increases due to the clogging of the DPF 8, and the output of the engine decreases.

  Therefore, the oxidation catalyst 7 is arranged on the upstream side of the DPF 8 so as to achieve combustion removal (continuous regeneration) within a possible range of PM collected and accumulated in the DPF 8, while timely (the amount of PM accumulated in the DPF 8 is increased). When it is determined that the regeneration time is reached (for example, when a predetermined value is reached), the exhaust throttle valve 13 is operated to raise the temperature of the DPF 8 to a temperature at which PM can be combusted, and the DPF 8 is collected and accumulated. Ensure that PM is burnt and removed (forced regeneration).

  The DPF regeneration control by the electronic control unit 50 in this embodiment will be described with reference to the flowchart of FIG.

  In S1, it is determined whether the DPF regeneration condition is satisfied. Specifically, using a differential pressure sensor (not shown) for detecting the differential pressure ΔP before and after the DPF 8, the PM accumulation amount calculated based on the detected differential pressure ΔP before and after the DPF and the regeneration timing determination To determine whether or not it is a regeneration time, and at the same time, determine whether or not the operation condition is reproducible. As a result, when it is the regeneration time and the operation condition is reproducible, it is considered that the DPF regeneration condition is satisfied, and the regeneration is started. Further, after the start of regeneration, the regeneration is continued until the completion of the regeneration, assuming that the DPF regeneration condition is satisfied.

  If the DPF regeneration condition is determined in S1, the process proceeds to S2, and the exhaust throttle valve 13 is operated in the closing direction. Thereby, by restricting the exhaust passage by the exhaust throttle valve 13 on the downstream side of the DPF 8, it is possible to reliably raise the temperature of the DPF 8 upstream from the exhaust throttle position. On the other hand, on the downstream side of the exhaust throttling position, the temperature can be lowered by the expansion of the exhaust, and the inflow of the high-temperature exhaust to the SCR catalyst 9 that is the NOx reduction device can be prevented as much as possible.

  Thus, by providing the exhaust throttle valve 13 on the downstream side of the DPF 8, the temperature increase of the DPF 8 is promoted during the forced regeneration of the DPF 8 to improve the regeneration efficiency, and at the same time, the SCR installed on the downstream side of the exhaust throttle valve 13. An excessive temperature rise of the catalyst 9 is prevented, and deterioration of the SCR catalyst 9 is suppressed.

  If the DPF regeneration condition is not determined in S1, the process proceeds to S3 and the exhaust throttle valve 13 is operated in the opening direction. As a result, an excessive increase in exhaust temperature due to the exhaust throttle can be prevented.

  According to this embodiment, the passage sectional area of the exhaust passage is changed between the DPF 8 and the NOx reduction device (SCR catalyst 9 and urea water injection nozzle 11) as an exhaust throttle means for restricting the exhaust passage when the regeneration of the DPF 8 is requested. By providing the exhaust throttle valve (butterfly valve) 13 to be operated, a necessary exhaust throttle effect can be obtained with a simple configuration.

Next, a second embodiment of the present invention will be described.
FIG. 3 is a system diagram of an engine exhaust system showing a second embodiment of the present invention, and FIG. 4 is an enlarged view of a main part of FIG. In FIG. 3, the same elements as those in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and different elements will be described.

  In this embodiment, for forced regeneration of the DPF 8, a venturi 21 is provided as exhaust throttling means at a position upstream of the urea water injection nozzle 11 in the communication path 6 between the first and second casings 4 and 5.

Further, the communication passage 6 is an inner cylinder, and an outer cylinder 22 having the same diameter as the cylinder portions of the first and second casings 4 and 5 is provided on the outer side thereof to form an inner / outer double cylinder structure.
And the opening 23 which connects an inner cylinder and an outer cylinder is provided in the diameter-reduction taper part of the exit side of the 1st casing 4, and an inner cylinder and an outer cylinder are provided in the diameter-expansion taper part of the inlet side of the 2nd casing 5. An opening 24 that communicates is provided, and a bypass passage 25 that bypasses the venturi 21 is formed in the outer cylinder 22.

  Then, bypass valves 26 and 27 for opening and closing the opening 23 on the inlet side and the opening 24 on the outlet side of the bypass passage 25 are provided. These bypass valves 26 and 27 are configured to be opened and closed by an electronic control unit 50.

An annular space 28 is provided so as to surround the outside of the throat portion forming surface of the venturi 21, and an air introduction pipe 29 from an air supply source (for example, an air cleaner) is connected to the annular space 28 via an air control valve 30. To do.
A plurality of air jets 31 are provided on the throat portion forming surface of the venturi 21 at equal intervals in the circumferential direction. Accordingly, the air outlet 31 communicates with the annular space 28 and is connected to the air supply source via the air control valve 30.

  The DPF regeneration control by the electronic control unit 50 in this embodiment will be described with reference to the flowchart of FIG.

  In S11, as in S1 (FIG. 2) described above, it is determined whether or not the DPF regeneration condition is satisfied. Specifically, using a differential pressure sensor (not shown) for detecting the differential pressure ΔP before and after the DPF 8, the PM accumulation amount calculated based on the detected differential pressure ΔP before and after the DPF and the regeneration timing determination To determine whether or not it is a regeneration time, and at the same time, determine whether or not the operation condition is reproducible. As a result, when it is the regeneration time and the operation condition is reproducible, it is considered that the DPF regeneration condition is satisfied, and the regeneration is started. Further, after the start of regeneration, the regeneration is continued until the completion of the regeneration, assuming that the DPF regeneration condition is satisfied.

If the DPF regeneration condition is determined in S11, the process proceeds to S12 to close the bypass valves 26 and 27, and further proceeds to S13 to open the air control valve 30.
In this way, by bypassing the bypass passage 25 by the bypass valves 26 and 27 and restricting the exhaust passage by the venturi 21 on the downstream side of the DPF 8, the temperature of the DPF 8 upstream from the exhaust throttling position can be reliably raised.
On the other hand, on the downstream side of the exhaust throttling position, the temperature can be lowered by the expansion of the exhaust, and the inflow of the high-temperature exhaust to the SCR catalyst 9 that is the NOx reduction device can be prevented as much as possible.

Further, by opening the air control valve 30, air is sucked from the air outlet 31 of the throat portion of the venturi 21. Therefore, the temperature of the exhaust gas flowing into the SCR catalyst 9 installed downstream can be reliably lowered by mixing the exhaust gas that has become hot due to the forced regeneration operation and the outside air that has flowed in due to the venturi effect.
If it is difficult to suck the outside air from the air cleaner due to the venturi effect, the outside air may be press-fitted using a turbo.

If it is determined in S11 that the DPF regeneration condition is not satisfied, the process proceeds to S14 and the air control valve 30 is closed.
Then, the process proceeds to S15 to determine whether or not the high load range or the high rotation range is determined. If YES, the process proceeds to S16 to open the bypass valves 26 and 27, and if NO, the bypass valves 26 and 27 are closed. .
In this way, in the operation region (high load region and high rotation region) with a high exhaust flow rate, the bypass valves 26 and 27 are opened and the venturi 21 is bypassed to ensure operability. In addition, an excessive increase in the exhaust temperature due to the exhaust throttle can be prevented.

  According to the present embodiment, the exhaust throttle means includes a venturi 21 provided in the exhaust passage, a bypass passage 25 that bypasses the venturi 21, and bypass valves 26 and 27 that open and close the bypass passage 25. By doing so, exhaust can be reliably throttled by the venturi 21.

  Further, according to the present embodiment, the bypass valves 26 and 27 are configured to be closed at least when the regeneration of the DPF 8 is requested and opened when the engine is operating at a high exhaust flow rate. During exhaust flow operation, the exhaust throttle can be released to ensure operability. In this embodiment, the bypass valves 26 and 27 are closed when not in a high load / high rotation range even during normal operation. However, during normal operation including the high load / high rotation range, The valves 26 and 27 may be opened.

  Further, according to the present embodiment, the venturi 21 has an air outlet 31 at the throat thereof, and the air outlet 31 is connected to the air supply source via the air control valve 30. The venturi 21 sucks and mixes air to cool the exhaust, and the temperature of the exhaust flowing into the SCR catalyst 9 can be reliably reduced.

  In the above embodiment, when the regeneration of the DPF 8 is requested, only the exhaust throttling is performed in order to increase the temperature of the exhaust flowing into the DPF 8, but simultaneously with the exhaust throttling, the fuel injection amount increase, the post-injection, the exhaust pipe interior You may make it use together jetting and the heating by an electric heater. Even when used in this manner, fuel consumption can be prevented from deteriorating as much as the temperature is increased by the exhaust throttle.

  The illustrated embodiments are merely examples of the present invention, and the present invention is not limited to those directly described by the described embodiments, and various improvements and modifications made by those skilled in the art within the scope of the claims. Needless to say, it encompasses changes.

1 Diesel engine (engine body)
2 Exhaust manifold 3 Exhaust passage (exhaust pipe)
4 1st casing 5 2nd casing 6 Communication path (inner cylinder)
7 Diesel oxidation catalyst (DOC)
8 DPF
9 SCR catalyst 10 Ammonia catalyst 11 Urea water injection nozzle 12 Control module 13 Exhaust throttle valve (butterfly valve)
21 Venturi 22 Outer cylinder 23, 24 Open 25 Bypass passage 26, 27 Bypass valve 28 Annular space 29 Air introduction pipe 30 Air control valve 31 Air outlet 50 Electronic control unit (ECU)

Claims (6)

In an engine exhaust gas purification apparatus, comprising an exhaust path of an engine for collecting PM in exhaust gas and a NOx reduction device for reducing NOx using a reducing agent in this order.
An exhaust emission control device for an engine, characterized in that an exhaust throttle means is provided between the filter and the NOx reduction device to throttle an exhaust passage when the regeneration of the filter is requested.   The engine exhaust gas purification apparatus according to claim 1, wherein the exhaust throttle means is a butterfly valve that changes a cross-sectional area of the exhaust passage.   2. The engine according to claim 1, wherein the exhaust throttle means includes a venturi provided in the exhaust passage, a bypass passage that bypasses the venturi, and a bypass valve that opens and closes the bypass passage. Exhaust purification equipment.   The engine exhaust gas purification apparatus according to claim 3, wherein the bypass valve is closed at least when the regeneration of the filter is requested and opened when the engine is operating at a high exhaust flow rate.   The engine according to claim 3 or 4, wherein an air outlet is opened at a throat portion of the venturi, and the air outlet is connected to an air supply source via an air control valve. Exhaust purification device.   The NOx reduction device includes an SCR catalyst that reduces NOx using ammonia as a reducing agent, and a urea water injection nozzle that injects urea water into exhaust gas upstream of the SCR catalyst. The exhaust emission control device for an engine according to any one of claims 1 to 5.