JP2006046253A - Exhaust emission control method and engine provided with dpf device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device and an engine provided with a DPF device preventing unstable combustion in a combustion chamber of the engine and unexpected torque fluctuation even if EGR is performed for reducing NOx emission at a time of regeneration of the DPF device and suppressing deterioration of fuel economy accompanying DPF regeneration. <P>SOLUTION: In a diesel engine of a plurality of cylinders provided with an EGR passage 30 and the DPF device 50, a plurality of the cylinders of the engine 1 are divided into a first cylinder group and a second cylinder group, EGR is performed by EGR gas Ge branched out of only exhaust gas G1 discharged from the first cylinder group at a time of DPF regeneration, fuel injection to the combustion chamber is controlled in at least part of the second cylinder group to raise HC concentration in the exhaust gas G, and collected particulate matter is forcedly burned to regenerate the DPF device 50 from a clogged condition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification method for purifying PM (particulate matter) in exhaust gas using a DPF (diesel particulate filter) device and an engine equipped with the DPF device in an engine that performs EGR (exhaust gas recirculation). Is.

  Regulations for particulate matter (PM), NOx, CO, HC, and the like discharged from an engine (internal combustion engine) such as a diesel engine have been strengthened year by year. Along with this stricter regulation, it has become impossible to meet the regulation value only by improving the engine. Therefore, a technique is adopted in which an exhaust gas aftertreatment device using a catalyst is attached to the engine to reduce these substances discharged from the engine.

  For the removal of PM, a DPF device equipped with a DPF (diesel particulate filter) is used. In normal driving, when the exhaust gas temperature is kept low, PM is collected in the DPF. Therefore, in order to prevent excessive clogging due to this PM deposition, the collected PM is forcibly burned and removed by raising the DPF temperature. DPF regeneration called is performed. As one method for raising the temperature of the DPF, there is a temperature raising method using fuel injection control to the combustion chamber such as post injection or timing retarded injection in the fuel injection control in the cylinder (inside the cylinder).

  This fuel injection control such as post injection is used in a DPF device equipped with an oxidation catalyst such as platinum, and the HC concentration in the exhaust gas is increased by fuel injection control to the combustion chamber. Thereby, HC is supplied to the DPF device, and this HC is oxidized by the catalytic action of the oxidation catalyst, so that the temperature of the DPF device is raised by the heat generated by this oxidation.

  During DPF regeneration using this fuel injection control to the combustion chamber, the HC concentration in the exhaust gas becomes high. Therefore, when EGR is performed, a part of the HC added to the exhaust gas is included in the EGR gas. Since the fuel flows back to the combustion chamber, the amount of fuel at the time of combustion in the combustion chamber deviates from the desired amount of fuel due to the addition of HC in the EGR gas, resulting in unexpected torque changes and unstable combustion. Further, heat exchange performance deteriorates due to adhesion of HC in the EGR gas to the EGR cooler, pressure loss increases, and malfunction of the EGR valve occurs due to adhesion to the EGR valve.

  In addition, HC in the exhaust gas is added to the exhaust gas in order to raise the DPF and perform DPF regeneration by being oxidized by the catalytic action. However, when EGR is performed, a part of the added HC is added. Since the EGR passage returns to the combustion chamber and is used for combustion in the combustion chamber, there is a problem that the temperature rise of the DPF becomes insufficient, the DPF regeneration does not proceed as scheduled, and the fuel consumption also deteriorates.

  Therefore, in the prior art, generally, when the DPF is regenerated, the EGR valve is closed to stop the EGR. However, if EGR is not performed, the concentration of NOx in the exhaust gas increases and the amount of NOx emission increases, which causes a problem that a large amount of NOx is discharged during regeneration of the DPF.

On the other hand, the applicant of the present invention provides an exhaust gas purifying apparatus for an internal combustion engine that includes an EGR and a reduction catalyst, receives HC as a reducing agent for reducing NOx from a fuel tank, and reduces and removes NOx with the reduction catalyst. However, an EGR pipe is provided in an exhaust branch pipe other than the exhaust branch pipe provided with an injector for supplying HC, or an injector is provided downstream of the intake port of the EGR pipe, so that the exhaust gas is supplied into the exhaust passage. An exhaust gas purifying apparatus for an internal combustion engine that prevents HC from entering an EGR pipe and adhering to the inner wall of a pipe line has been proposed (for example, see Patent Document 1).
JP-A-6-74022

  The present invention has been made to solve this problem, and the object of the present invention is to increase the temperature of the DPF device even if EGR is performed to reduce the NOx emission amount during regeneration of the DPF device. Prevents a part of the HC added to the exhaust gas from being recirculated together with the EGR gas, resulting in instability of combustion in the combustion chamber of the engine and occurrence of an unexpected torque change, to the EGR cooler and the EGR valve. Exhaust gas purification method and DPF that can prevent performance deterioration due to HC adhesion, and that can effectively use HC added to exhaust gas to raise catalyst temperature and suppress deterioration in fuel consumption accompanying DPF regeneration It is to provide an engine equipped with the device.

  In order to achieve the above object, an exhaust gas purification method according to the present invention includes an EGR passage provided with an EGR valve, an exhaust passage provided with a DPF (diesel particulate filter) device, and an engine including a plurality of cylinders. By controlling the fuel injection into the combustion chamber and increasing the HC concentration in the exhaust gas, the HC is supplied to the DPF device, and the HC is oxidized by the catalytic action, so that the temperature of the DPF device is increased. In an engine equipped with a DPF device that forcibly burns the particulate matter that has been raised and collected and regenerates the DPF device from the eyes, that is, the forced combustion, when the DPF is regenerated, the plurality of cylinders are The first cylinder group is divided into the second cylinder group, and EGR gas is branched only from the exhaust gas discharged from the first cylinder group to perform EGR, and the second cylinder group At least in part, by controlling the fuel injection into the combustion chamber, a method of increasing the HC concentration in the exhaust gas.

  The first cylinder group on the branch side of the EGR gas and the second cylinder group on the fuel injection control side may be completely fixed, but may change with time, that is, the previous regeneration and the current one. In this regeneration, the cylinder that was the first cylinder group and the cylinder that was the second cylinder group may be interchanged. In addition to the DPF regeneration, EGR may be performed only in the first cylinder group or all cylinders. However, when performing with all cylinders or changing the first cylinder group in time, EGR piping is required accordingly.

  Control of fuel injection for increasing the HC concentration in exhaust gas includes post injection (post injection), timing retarded injection (delayed injection), and the like.

  An engine including a DPF device according to the present invention for achieving the above object includes an EGR passage provided with an EGR valve, an exhaust passage provided with the DPF device, a plurality of cylinders, and a valve of the EGR valve. An engine having an opening degree and a control device for controlling fuel injection control. The control device controls fuel injection into the combustion chamber to increase the HC concentration in the exhaust gas, thereby increasing the DPF device. By supplying HC and oxidizing the HC by a catalytic action, the temperature of the DPF device is raised to forcibly burn the collected particulate matter, and the DPF device is regenerated from the eyes, that is, by the forced combustion. In the engine having the DPF device configured to be configured, the plurality of cylinders are divided into a first cylinder group and a second cylinder group, and an exhaust passage portion connected to the plurality of cylinders is defined as the first cylinder group. And a first exhaust passage that is connected to the second cylinder group, and is divided into a second exhaust passage that is not provided with an EGR passage, and the control device includes the DPF device. At the time of regeneration, at least a part of the second cylinder group performs fuel injection control for increasing the HC concentration in the exhaust gas, and controls opening of the EGR valve provided in the EGR passage. The

  In the engine equipped with the DPF device, a turbocharger turbine is disposed on the downstream side where the first exhaust passage and the second exhaust passage are joined, and the DPF device is disposed on the downstream side of the turbine. Configured.

  As this DPF device, a device in which an oxidation catalyst is arranged on the upstream side of the DPF, a device in which the oxidation catalyst is arranged on the upstream side of the catalyst-carrying DPF, a device in which an oxidation catalyst is carried on the DPF, an oxidation catalyst and a PM oxidation catalyst on the DPF There are devices that carry

  According to the exhaust gas purification method and the engine equipped with the DPF device of the present invention, when regenerating the DPF device, fuel injection control such as post injection and timing retarded injection is performed, and HC in the exhaust gas flowing into the DPF device In the case of increasing the concentration, since the fuel injection control is performed in the second cylinder group not provided with the EGR passage, the HC concentration in the EGR gas does not increase even if the EGR is performed, so that the combustion in each cylinder is stabilized. It is also possible to prevent performance deterioration due to unexpected torque changes and HC adhesion to the EGR cooler and EGR valve.

  Further, since most of the HC added to the exhaust gas by the fuel injection control flows into the DPF device without being introduced into the EGR gas, the temperature of the DPF device can be increased efficiently.

  Therefore, EGR can be performed at the time of DPF regeneration to suppress the generation of NOx in the combustion chamber, so that the amount of NOx emission can be reduced, and the deterioration of fuel consumption accompanying DPF regeneration can be suppressed.

  Next, an exhaust gas purification method and an engine equipped with a DPF device according to an embodiment of the present invention will be described with reference to the drawings, taking as an example a V-type engine equipped with a DPF device comprising an oxidation catalyst and a catalyst-supported DPF. explain.

  FIG. 1 shows the configuration of an engine 1 equipped with this DPF device. The engine 1 is a V-type engine and has a right bank 2A and a left bank 2B.

  An intake passage 10 in which an air cleaner (not shown), a mass air flow meter (MAF) 11, a compressor 41 of a turbocharger 40, an intercooler 12, and an intake valve (intake throttle) 13 are provided on the intake side of the engine 1. It is done. The intake passage 10 is divided into a first intake passage 16A and a second intake passage 16B which are branched into two at a branch point 15 downstream from the junction 14 with the EGR passage 30, and each of them is a first intake manifold 17A in the right bank 2A. And connected to the second intake manifold 17B of the left bank 2B.

  On the exhaust side, the first exhaust passage 22A is connected to the first exhaust manifold 21A of the first cylinder group of the right bank 2A, and the second exhaust is connected to the second exhaust manifold 21B of the second cylinder group of the left bank 2B. A passage 22B is connected. The EGR passage 30 branches from the first exhaust passage 22A at a branch point 23, and is a downstream side of the intake valve 13 of the intake passage 10 of the engine 1 and an upstream side of the branch point 15 of the intake passage 10. 14. The EGR passage 30 is provided with an EGR cooler 31 for cooling the EGR gas Ge, and an EGR valve 32 for controlling ON / OFF of the EGR and adjusting the amount of EGR gas.

  The first exhaust passage 22A and the second exhaust passage 22B join to the third exhaust passage 25 at the joining portion 24 downstream of the branch point 23. The third exhaust passage 25 is the inlet of the turbine 42 of the turbocharger 40. The fourth exhaust passage 26 is further connected to the outlet side of the turbine 42. A DPF device 50 is disposed in the fourth exhaust passage 26. That is, the turbine 42 of the turbocharger 40 is disposed on the downstream side where the first exhaust passage 22A and the second exhaust passage 22B merge, and the DPF device 50 is disposed on the downstream side of the turbine 42.

  In addition, when the twin entry type with two inlets of the turbine 42 is used for the turbocharger 40, the first exhaust passage 22A and the second exhaust passage 22B can be connected to the respective entry portions. This eliminates the need for piping and simplifies piping.

  The DPF device 50 is formed of an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 51 supporting a noble metal catalyst such as platinum on the upstream side, a ceramic monolith honeycomb type wall flow type filter, and the like, and the surface of the passage is oxidized. It comprises a catalyst-carrying DPF (C-DPF: Catalyst Diesel Particulate Filter) 52 carrying a PM oxidation catalyst such as cerium. The oxidation catalyst 51 is used to oxidize HC added to the exhaust gas by catalytic action during DPF regeneration. The heat generated by oxidation of the HC raises the temperature of the catalyst-supported DPF 52, The catalyst-carrying DPF 52 is regenerated by forcibly burning the PM collected by the catalyst-carrying DPF 52. On the other hand, the catalyst-carrying DPF 52 collects particulate matter (PM) and burns and removes the collected PM during DPF regeneration. In FIG. 1, the noble metal catalyst is supported on a converter 51 formed separately from the DPF 52, but an integrated DPF device in which this noble metal catalyst is also supported on the DPF 52 may be used.

  Then, a control device (not shown) called an engine control unit (ECU) that controls the fuel injection control of the engine 1 and the valve opening of the EGR valve 32 to control the ON / OFF of the EGR, the control of the EGR gas amount, etc. ) Is provided. This control device performs EGR control, DPF regeneration control, and the like in addition to overall engine control. Therefore, various detection values such as engine speed, accelerator opening, cooling water temperature and exhaust gas temperature are input, and control signals are output to the fuel injection valve (not shown), the EGR valve 32, the intake valve 13, and the like.

  Next, the flow of air A, exhaust gases G1, G2, G and EGR gas Ge in the engine 1 equipped with the DPF device having the above-described configuration will be described.

  The air A is compressed and boosted by the compressor 41 through the intake passage 10, cooled by the intercooler 12, adjusted in flow rate by the intake valve 13, and supplied to the cylinders of the right bank 2 </ b> A and the left bank 2 </ b> B.

  Regarding the exhaust gas, the exhaust gas G1 from the first cylinder group passes through the first exhaust manifold 21A and the first exhaust passage 22A, and the exhaust gas G2 from the second cylinder group passes through the second exhaust manifold 21B and the second exhaust gas. After passing through the passage 22B, both exhaust gases G1, G2 join the third exhaust passage 25 at the junction 24, drive the turbine 42 of the turbocharger 40, and then pass through the DPF device 50 of the fourth exhaust passage 26. The PM in the exhaust gas G is removed to become purified exhaust gas Gc, which is released into the atmosphere through a silencer (not shown).

  As for the EGR gas Ge, a part of the exhaust gas G1 discharged from the first exhaust manifold 21A of the first cylinder group to the first exhaust passage 22A is branched to the EGR passage 30 at the branch point 23 to become the EGR gas Ge. The air is cooled by the EGR cooler 31, and the amount thereof is adjusted by the EGR valve 32 and supplied from the junction 14 to the intake passage 10, and at the branch point 15, the first intake passage 16A and the second intake passage 16B are separated. The first intake manifold 17A is supplied to both the first cylinder group and the second intake manifold 17B is supplied to both the second cylinder group.

  Next, DPF regeneration and EGR at the time of DPF regeneration of the engine 1 equipped with the DPF device having the above configuration will be described.

  In this DPF regeneration, when the eyes of the catalyst-carrying DPF 52, that is, the state is detected by a differential pressure before and after the catalyst-carrying DPF 52, etc., and it is determined that DPF regeneration control is necessary, part or all of the second cylinder group That is, at least in part, fuel injection control such as post injection or timing retarded injection is performed to add HC to the exhaust gas G2 to increase the HC concentration in the exhaust. At the same time, the EGR valve 32 is controlled to open and EGR is performed to suppress the generation of NOx in the combustion chamber. With this EGR, it is possible to maintain the same amount of NOx emission as when DPF regeneration is not performed.

  That is, the controller 60 performs fuel injection control for increasing the HC concentration in the exhaust gas in at least a part of the second cylinder group during regeneration of the catalyst-carrying DPF 52, and also provides an EGR valve provided in the EGR passage 30. 32 is configured to perform valve opening control.

  At the time of this DPF regeneration, the exhaust gas G2 of the second cylinder group flows into the DPF device 50 via the second exhaust passage 22B and the turbine 42, so that the HC added for the DPF regeneration becomes the EGR gas Ge. Almost all flows into the DPF device 50 without being included. Accordingly, it is possible to almost eliminate the return of HC to the intake air. Since almost all of the HC added for regeneration of the DPF is oxidized by the oxidation catalyst 51, the temperature of the catalyst-carrying DPF 52 can be efficiently raised by the heat generated by the oxidation of the HC. For this reason, it is possible to suppress the deterioration of fuel consumption associated with DPF regeneration.

  Further, the EGR during the regeneration of the DPF is controlled by controlling the valve opening degree of the EGR valve 32 by the control device 60, so that the ON / OFF and the EGR gas amount are set according to the conditions set in advance for the operating state of the engine 1. The EGR gas Ge that is part of the exhaust gas G1 that is adjusted and discharged from the first cylinder group to the first exhaust passage 22A is supplied to both the first cylinder group and the second cylinder group.

  In this first cylinder group, post-injection (post-injection), timing retarded injection (delayed injection), etc. for DPF regeneration are not performed, so the EGR gas Ge is added to the exhaust gas by the fuel injection control. HC that has been released is not included. Therefore, in order to suppress the generation of NOx, even if EGR is performed during DPF regeneration in each cylinder, HC added to the exhaust gas for DPF regeneration may be recirculated into the combustion chamber and burned. Absent. For this reason, the amount of fuel in the combustion chamber does not become a desired amount of fuel, combustion does not become unstable, unexpected torque change does not occur, and performance deterioration due to HC adhesion to the EGR cooler and EGR valve also occurs. prevent.

  FIG. 2 shows an example of fuel injection control in the engine 1 having the above configuration, and FIG. 6 shows an example of conventional fuel injection control. In the case of this conventional example, as shown in FIG. 5, in the engine 1X, the EGR passage 30 branches from a third exhaust passage 25 downstream from the junction 24 of the first exhaust passage 22A and the second exhaust passage 22B. Branches at a point 23. 5 and 6, the EGR valve 32 is closed and the main injection M and the post injection P are performed in all cylinders during the regeneration of the DPF, whereas in the embodiment of FIG. At the time of regeneration, the EGR valve 32 is opened, and the main injection M and the post injection P are performed in the even-numbered cylinders and not in the odd-numbered cylinders. Note that the post injection amount in each cylinder of this embodiment is double the post injection amount in each cylinder of the conventional example.

  FIG. 3 shows the case of EGR only in the right bank and post injection only in the left bank (A), when EGR is performed without performing DPF regeneration (B), and when the EGR valve is closed (C). FIG. 4 shows a comparison of NOx emission amounts for the right bank and the post-injection only for the left bank (A), and the case where EGR is performed without DPF regeneration (B). Fig. 6 shows a comparison of the amount of HC recirculated to the intake passage when post injection is performed (D). 3 and 4, it can be seen that in the case of EGR only in the right bank and post injection only in the left bank (A), the NOx emission amount and the HC amount recirculated to the intake passage are significantly reduced.

  In the above description, the EGR passage 30 is provided on the right bank 2A side and the fuel injection control for DPF regeneration is performed on the left bank 2B side. However, the left and right banks are interchanged to change the left bank 2B side. The EGR passage 30 may be provided in the right bank 2A to perform fuel injection control for DPF regeneration.

  In the above description, the V-type engine is taken as an example. However, the present invention is not limited to the V-type engine. If the EGR gas can be branched from a specific cylinder and returned to the intake side, the in-line engine or the like Can also be applied. In particular, in an in-line 6-cylinder engine, a twin entry type turbocharger is often used. In this case, upstream of the entry part of the first exhaust passage connecting the first cylinder group and one entry part. A branch portion of EGR gas, that is, an intake port for EGR gas is provided, and fuel injection control such as post injection is performed on the second cylinder group connected to the second exhaust passage connected to the other entry portion.

  Further, EGR passages may be provided in both cylinder groups, and during DPF regeneration, EGR may be performed using only one EGR passage alternately in time series.

It is a figure showing composition of an engine provided with a DPF device of an embodiment concerning the present invention. It is a figure which shows the example of the fuel-injection control of embodiment which concerns on this invention. It is a figure which shows NOx discharge | emission amount at the time of DPF regeneration. It is a figure which shows the amount of HC recirculated to the intake passage at the time of DPF regeneration. It is a figure which shows the structure of the engine provided with the DPF apparatus of the prior art example. It is a figure which shows the example of the fuel injection control of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine provided with DPF device 10 Intake passage 20 Exhaust passage 22A First exhaust passage 22B Second exhaust passage 23 Branching portion 24 Merge portion 25 Third exhaust passage 26 Fourth exhaust passage 30 EGR passage 32 EGR valve 40 Turbocharger 42 Turbine 50 DPF equipment 51 Oxidation catalytic converter (DOC)
52 DPF
60 Control device G1, G2, G Exhaust gas Ge EGR gas

Claims (3)

By controlling the fuel injection into the combustion chamber and increasing the HC concentration in the exhaust gas with an engine equipped with an EGR passage provided with an EGR valve, an exhaust passage provided with a DPF device, and a plurality of cylinders, By supplying HC to the DPF device and oxidizing the HC by a catalytic action, the particulate matter collected by raising the temperature of the DPF device is forcibly burned, and the forced combustion causes the eye from being clogged. In an engine equipped with a DPF device for regenerating the DPF device,
At the time of regeneration of the DPF, the plurality of cylinders are divided into a first cylinder group and a second cylinder group, EGR gas is branched only from the exhaust gas discharged from the first cylinder group, and EGR is performed. An exhaust gas purification method characterized in that in at least a part of the second cylinder group, fuel injection into the combustion chamber is controlled to increase the HC concentration in the exhaust gas. An engine comprising an EGR passage provided with an EGR valve, an exhaust passage provided with a DPF device, a plurality of cylinders, and a control device for controlling valve opening and fuel injection control of the EGR valve, wherein the control device comprises: By controlling the fuel injection into the combustion chamber and increasing the HC concentration in the exhaust gas, the HC is supplied to the DPF device, and the HC is oxidized by the catalytic action, so that the temperature of the DPF device is increased. In an engine equipped with a DPF device configured to forcibly burn particulate matter collected by raising, and to regenerate the DPF device from the eyes, that is, by the forced combustion,
The plurality of cylinders are divided into a first cylinder group and a second cylinder group, and an exhaust passage portion connected to the plurality of cylinders is connected to the first cylinder group and provided with an EGR passage. And divided into a second exhaust passage connected to the second cylinder group and not provided with an EGR passage,
The control device performs fuel injection control for increasing the HC concentration in the exhaust gas in at least a part of the second cylinder group during regeneration of the DPF device, and includes an EGR valve provided in the EGR passage. An engine equipped with a DPF device, characterized in that the valve opening control is performed. 3. The DPF according to claim 2, wherein a turbine of a turbocharger is disposed on a downstream side where the first exhaust passage and the second exhaust passage merge, and the DPF device is disposed on a downstream side of the turbine. Engine with equipment.

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