JP2008196371A - Exhaust gas control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress fluctuation of combustion due to addition of fuel in an exhaust gas control device equipped with an exhaust gas recirculating device for recirculating exhaust gas from downstream of a fuel adding valve provided in an exhaust passage. <P>SOLUTION: An exhaust emission control device such as a DPF or a NOx occlusion reduction catalyst is provided in the exhaust passage of the internal combustion engine. The fuel adding valve is provided on the upstream side of the exhaust emission control device. Further, a low pressure loop EGR device for recirculating exhaust gas from the upstream side of the exhaust emission control device to the intake side, and a high pressure loop EGR device for recirculating exhaust gas from the downstream side of the exhaust emission control device to the intake side are provided. When addition of fuel is performed by the fuel adding valve while the low pressure loop EGR device is operated, the added fuel is returned to the intake side by the low pressure loop EGR device which may cause fluctuation of combustion. Consequently, the adding amount of fuel and an adding cycle are controlled according to the operating state of the EGR devices. Preferably, when the low pressure loop EGR device is operated, the adding amount is reduced and the addition cycle is shortened compared to when only the high pressure loop EGR device is operated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to control of an internal combustion engine including an exhaust gas recirculation passage that recirculates exhaust gas from an exhaust passage to an intake passage.

  2. Description of the Related Art Conventionally, there is known an exhaust purification system for an internal combustion engine that is provided with a fuel addition valve for adding fuel to an exhaust passage and adds fuel for regeneration of an exhaust purification device such as a catalyst or a filter. Specifically, in the case where a nitrogen oxide (NOx) storage reduction catalyst is provided as an exhaust purification device, NOx reduction treatment for reducing NOx in a rich state by adding fuel from a fuel addition valve. Is done. In addition, fuel is added from the fuel addition valve also in the process of removing sulfur oxide (SOx) stored in the NOx storage reduction catalyst (S poisoning regeneration). On the other hand, when a filter (DPF) for processing particulate matter is provided as an exhaust purification device, PM regeneration processing is performed to burn off particulate matter deposited on the filter by adding fuel.

  In the exhaust purification system as described above, if the time during which no fuel is added from the fuel addition valve becomes long, the tip of the fuel addition valve may be carbonized and clogged. Therefore, when fuel addition is not performed for a predetermined time or more for regeneration of the catalyst or the like, forced fuel addition is performed for the purpose of preventing clogging of the fuel addition valve (this is referred to as “clogging prevention addition”). Also called.) An example of such a technique is described in Patent Document 1.

  On the other hand, an exhaust gas recirculation (EGR) device is known in which a part of exhaust gas discharged from an internal combustion engine to the exhaust passage is recirculated to the intake side to lower the combustion temperature and suppress the generation of NOx. In Patent Document 2, in addition to an EGR device that recirculates exhaust gas from a position upstream of the catalyst in the exhaust passage to the intake side, an exhaust gas that includes an EGR device that recirculates exhaust gas from a position downstream of the catalyst to the intake side. A purification system is described.

JP 2005-106047 A JP 2005-264821 A

  As in Patent Document 2, in the case of an exhaust purification system including an EGR device that recirculates exhaust gas from the downstream side to the intake side from the fuel addition valve, part of the fuel added to the exhaust passage due to clogging prevention addition passes through the EGR path. Since the air passes through to the intake type, the combustion of the internal combustion engine may become unstable, for example, by affecting the air-fuel ratio of the air-fuel mixture. As a result, torque fluctuations may occur and problems such as drivability may deteriorate.

  The present invention has been made in view of the above points, and suppresses fluctuations in combustion due to fuel addition in an exhaust gas purification device including an exhaust gas recirculation device that recirculates exhaust gas downstream from a fuel addition valve provided in an exhaust passage. The purpose is to do.

  In one aspect of the present invention, an exhaust control device for an internal combustion engine includes an exhaust purification device provided in an exhaust passage of the internal combustion engine, and fuel addition means provided in an upstream position of the exhaust purification device in the exhaust passage. A first exhaust gas recirculation device that recirculates exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to an intake air side of the internal combustion engine, and an internal combustion engine from a downstream position of the exhaust gas purification device in the exhaust passage. A second exhaust gas recirculation device that recirculates exhaust gas to the intake side of the exhaust gas, and an addition control device that adds fuel to the exhaust gas using the fuel addition device, the addition control device comprising: The amount and period of fuel addition are controlled according to the operating state.

  The exhaust control device for the internal combustion engine is provided with an exhaust purification device such as a DPF and a NOx storage reduction catalyst. Fuel addition means such as a fuel addition valve is provided upstream of the exhaust purification device. The fuel addition means can add fuel to the exhaust passage for PM regeneration with respect to the DPF, NOx reduction with respect to the NOx storage reduction catalyst, recovery of S poisoning, and the like. In addition, a first exhaust gas recirculation device that recirculates exhaust gas from the upstream side of the exhaust gas purification device to the intake side and a second exhaust gas recirculation device that recirculates exhaust gas from the downstream side of the exhaust gas purification device to the intake side are provided.

  If fuel addition is performed by the fuel addition means while the second exhaust gas recirculation device is operating, the added fuel may be returned to the intake side by the second exhaust gas recirculation device, causing fluctuations in combustion. In particular, as the amount of fuel added by a single fuel addition increases, the amount of fuel that is returned to the intake side at a time also increases, and the degree of fluctuation in combustion increases. Therefore, the amount and period of fuel addition are controlled in accordance with the operating state of the exhaust gas recirculation device.

  In one aspect of the exhaust gas control apparatus for an internal combustion engine, the control means operates when the second exhaust gas recirculation device is operated, compared to when only the first exhaust gas recirculation device is operated. And the addition period is shortened.

  In this aspect, when the second exhaust gas recirculation device operates, the amount of fuel added at one time is reduced and the addition cycle is shortened by that amount compared to when the second exhaust gas recirculation device does not operate. As a result, the amount of fuel that travels to the intake side at a time is reduced, and the degree of combustion fluctuation can be reduced.

  In another aspect of the exhaust gas control apparatus for an internal combustion engine, when the control means operates both the first and second exhaust gas recirculation apparatuses, the addition amount and the addition cycle are determined by the first control unit. It is a value between when only the exhaust gas recirculation device is operated and when only the second exhaust gas recirculation device is operated. When both the first and second exhaust gas recirculation devices operate, the addition amount and the addition cycle are the same as those when only the first exhaust gas recirculation device operates and when only the second exhaust gas recirculation device operates. By setting the value between, combustion fluctuation can be suppressed.

  In a preferred example, the control means adds fuel to prevent clogging of the fuel addition means. In a particularly preferred example, a means for executing regeneration control for adding fuel to exhaust gas for regeneration of the exhaust gas purification device is provided, and the addition control means is configured to add the fuel when the regeneration control is not executed. Add fuel to prevent clogging. Thereby, when fuel addition is not performed for regeneration of the exhaust purification device, it is possible to effectively prevent clogging of the fuel addition means while suppressing combustion fluctuation of the internal combustion engine.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Device configuration]
FIG. 1 is a block diagram showing a schematic configuration of an exhaust control device for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals.

  In FIG. 1, an exhaust control device 100 for an internal combustion engine includes an in-line four-cylinder internal combustion engine (hereinafter referred to as “engine”) 10 having first to fourth (# 1 to # 4) cylinders. Each cylinder of the engine 10 is connected to an intake manifold 11 and an exhaust manifold 12. The engine 10 includes a fuel injection valve 15 provided in each cylinder, and a common rail 14 that supplies high-pressure fuel to each fuel injection valve 15. The common rail is in a high-pressure state by a fuel pump (not shown). Supplied. The fuel injection amount and injection timing from the fuel injection valve 15 are controlled by a control signal S4 supplied from the ECU 7.

  In the intake passage 20 connected to the intake manifold 11, there are an air flow meter 21 that measures the amount of air flowing into the engine 10, a throttle 22 valve, a compressor 23 a of the turbocharger 23, and an intercooler 24 that cools the intake air. Is provided. The detection signal S1 from the air flow meter 21 is supplied to the ECU 7. The opening degree of the throttle valve 22 is controlled by a control signal S2 supplied from the ECU 7.

  A turbine 23 b of a turbocharger 23 is provided in the exhaust passage 25 connected to the exhaust manifold 12. The upstream position of the turbine 23 b in the exhaust passage 25 and the downstream position from the intercooler 24 in the intake passage 20 are connected by an EGR passage 31. The EGR passage 31 is provided with an EGR valve 33 for controlling the EGR amount. The opening degree of the EGR valve 33 is controlled by a control signal S3 supplied from the ECU 7. The EGR device in which the outlet for EGR gas is located upstream of the turbine of the turbocharger is referred to as a “high pressure loop (HPL) EGR device”.

  A DPF (Diesel Particulate Filter) 36 is provided at a position downstream of the turbine 23 b in the exhaust passage 25. The DPF 36 adsorbs particulate matter contained in the exhaust gas. An exhaust throttle valve 41 is provided at a position downstream of the DPF 36 in the exhaust passage 25. The opening degree of the exhaust throttle valve 25 is controlled by a control signal S7 supplied from the ECU 7.

  Further, an EGR passage 35 that connects a position of the exhaust passage 25 downstream of the turbine 23b and a position of the intake passage 20 upstream of the compressor 23a is provided. More specifically, the EGR passage 35 is configured to extract exhaust gas (EGR gas) from a position downstream of the DPF 36 provided in the exhaust passage 35. The EGR passage 35 is provided with an EGR valve 37 for controlling the amount of EGR gas and an EGR cooler 39, and the opening degree of the EGR valve 37 is controlled by a control signal S6 from the ECU 7. An EGR device having an EGR gas outlet on the downstream side of the turbine of the turbocharger is referred to as a “low pressure loop (LPL) EGR device”.

  In addition to the fuel injection valve 15 provided for each cylinder, the exhaust manifold 12 is provided with a fuel addition valve 17 for injecting unburned fuel. The amount of fuel added from the fuel addition valve 17 is controlled by a control signal S5 supplied from the ECU 7. The fuel addition valve 17 adds fuel into the exhaust mainly for PM regeneration processing of the DPF 36 provided in the exhaust passage.

  The ECU 7 includes a CPU, a ROM, a RAM, and the like (not shown), and comprehensively controls each element of the control device 100 for the internal combustion engine as described above.

  In the above configuration, the DPF 36 corresponds to the exhaust purification device in the present invention, and the high-pressure loop EGR device configured by the EGR passage 31 and the like corresponds to the first exhaust gas recirculation device, and the low-pressure loop configured by the EGR passage 35 and the like. The EGR device corresponds to a second exhaust gas recirculation device. The fuel addition valve 17 corresponds to fuel addition means, and the ECU 7 corresponds to addition control means.

  FIG. 2 is an example of a map showing the operation region of the EGR device, and specifically shows the relationship between the engine speed and load and the operation regions of the high-pressure loop EGR device and the low-pressure loop EGR device.

  As shown in the figure, the ECU 7 operates only the high-pressure loop EGR device in a region where the engine speed is low and the engine load is small. On the other hand, in the region where the engine speed is high and the required load is high, the ECU 7 operates only the low-pressure loop EGR device. When the engine speed and the required load are between the operating region of the high-pressure loop EGR device and the operating region of the low-pressure loop EGR device, the ECU 7 operates both the high-pressure loop EGR device and the low-pressure loop EGR device. A region where both the high-pressure loop EGR device and the low-pressure loop EGR device are operated simultaneously is referred to as an “MPL (Mixed Pressure Loop) region”. Specifically, the ECU 7 acquires the engine speed by a crank angle sensor (not shown) or the like, and calculates the engine load based on the output of the accelerator opening sensor, the fuel injection amount, and the like. Then, control signals S3 and S6 are supplied to the EGR valves 33 and 37 to control the operations of the high pressure loop EGR device and the low pressure loop EGR device.

[Clogging prevention addition control]
Next, clogging prevention addition control according to the present invention will be described.

  The clogging prevention addition is performed every predetermined time when fuel addition for catalyst regeneration such as PM regeneration is not performed and fuel addition is not performed from the fuel addition valve 17 for a predetermined time or more. However, if clogging prevention addition is performed by the fuel addition valve 17 while the low-pressure loop EGR device is operating, the added unburned fuel is returned to the intake passage 20 via the EGR passage 35, so that combustion is not performed. May become stable. Normally, as a clogging prevention addition, a constant amount of fuel is added at a constant cycle, so the added fuel is periodically sent to the intake side, and the combustion state fluctuates, for example, the air-fuel ratio becomes rich periodically. . In particular, as the amount of fuel added at one time increases, the temporary fluctuation of the air-fuel ratio increases, and the combustion state greatly fluctuates periodically. Therefore, in order to suppress fluctuations in combustion, it is effective to reduce the fuel addition amount (hereinafter simply referred to as “addition amount”) in the clogging prevention addition and to shorten the addition cycle accordingly. is there.

  From this point of view, according to the present invention, the addition amount and the addition cycle in the clogging prevention addition are adjusted according to the operating state of the EGR device, more specifically, according to the operating state of the low-pressure loop EGR device.

  An example is shown in FIG. As shown in the figure, a region where only the high-pressure loop EGR device is operating (hereinafter referred to as “HPL region”), a region where only the MPL region and the low-pressure loop EGR device are operating (hereinafter referred to as “LPL region”). In this order, the amount of fuel added is small and the addition cycle is shortened.

  More specifically, when the addition amount of anti-clogging addition in the HPL region is the reference addition amount and the addition cycle is the reference addition cycle, the addition amount of anti-clogging addition in the LPL region is smaller than the reference addition amount, and The addition cycle is made shorter than the reference addition cycle. In the MPL region, the addition amount is set to be smaller than the reference addition amount but larger than the addition amount in the LPL region, and the addition cycle is shorter than the reference addition cycle but longer than the addition cycle in the LPL region. .

  FIG. 3 shows a control example of the addition amount and the addition period of the clogging prevention addition according to the operation state of the EGR device. In FIG. 3, the horizontal axis indicates time, and the widths WH, WM, and WL of the respective waveforms correspond to the fuel addition amounts QH, QM, and QL. In the HPL region, the addition amount is set to the reference addition amount QH, and the addition period is set to the reference addition period TH. In contrast, in the LPL region, the addition amount is set to an addition amount QL smaller than the reference addition amount QH, and the addition cycle is set to an addition cycle TL shorter than the reference addition cycle TH. Further, in the MPL region, the addition amount is smaller than the reference addition amount QH, but is set to an addition amount QM larger than the addition amount QL in the LPL region. The addition period is set to an addition period TM shorter than the reference addition period TH but longer than the addition period TL in the LPL region.

  Thus, in the present invention, when the low-pressure loop EGR device is operating, the addition amount is reduced and the addition cycle is shortened, so that the unburned fuel added by the clogging prevention addition flows to the intake side and burns. The problem of causing fluctuations can be suppressed.

  In more detail, it is preferable to control the addition amount and the addition cycle in accordance with the operation ratio of the low-pressure loop EGR device. That is, the ECU 7 sets the addition amount and the addition cycle in the HPL region as the reference addition amount and the reference addition cycle, and then determines the reference addition amount and the reference addition cycle according to the operation level of the low-pressure loop EGR device in the MPL region and the LPL region. May be corrected. As the degree of operation of the low-pressure loop EGR device, for example, the EGR rate of the low-pressure loop EGR device or the ratio of the EGR rate of the high-pressure loop EGR device to the EGR rate of the low-pressure loop EGR device can be used. Here, the EGR rate refers to the ratio of the EGR gas amount to the intake air amount of the engine.

  1, the exhaust passage 25 is provided in the vicinity of the # 1 cylinder in the exhaust manifold 12, and the fuel addition valve 17 is located in the vicinity of the # 4 cylinder in the exhaust manifold 12, that is, farthest from the exhaust passage 25. Provided in position. Therefore, the HPL region is basically configured so that the fuel added to prevent clogging does not flow into the intake side by the high-pressure loop EGR device.

  FIG. 4 is a flowchart of clogging prevention addition control according to this embodiment. This process is mainly executed by the ECU 7.

  First, the ECU 7 determines whether or not regeneration control is necessary (step S101). Here, in the present embodiment, PM regeneration of the DPF 36 provided in the exhaust passage 25 corresponds to regeneration control. When the ECU 7 detects or estimates the amount of particulate matter accumulated in the DPF 36 and determines that PM regeneration is necessary (step S101; Yes), the fuel addition valve 17 adds a predetermined amount of fuel, PM regeneration is performed as regeneration control (step S102).

  On the other hand, when it is determined that regeneration control is not necessary (step S101; No), the ECU 7 determines whether or not a predetermined time has elapsed since the previous fuel addition by the fuel addition valve 17 (step S103). The “predetermined time” is a time during which the fuel addition valve 17 can be clogged when fuel is not injected, and is determined in advance based on the characteristics of the fuel injection valve 17 and the like. The “previous fuel addition” includes both fuel addition for catalyst regeneration and fuel addition for preventing clogging.

  If the predetermined time has not elapsed since the previous fuel addition (step S103; No), the process ends because there is a low possibility that the fuel addition valve 17 is clogged. On the other hand, when the predetermined time has elapsed since the previous fuel addition (step S103; Yes), the ECU 7 performs the clogging prevention addition. Specifically, the ECU 7 determines the reference addition amount and the reference addition period of the fuel using a map prepared in advance based on the fuel injection amount (engine load), the engine speed, the exhaust temperature, and the like. (Step S104). Next, the ECU 7 determines an operating state of the EGR device, that is, an EGR region by referring to the map illustrated in FIG. 2 based on the engine load, the engine speed, and the like (step S105).

  When the EGR area is the LPL area (step S106; Yes), the ECU 7 acquires the addition amount in the LPL area and the correction coefficient for the addition period based on a map prepared in advance, and the reference addition is performed based on the addition coefficient. The amount and the reference addition period are corrected (step S107). In this case, the addition amount QL for the LPL region obtained by the correction is smaller than the reference addition amount QH, and the addition cycle TL for the LPL region is shorter than the reference addition cycle TH.

  On the other hand, when the EGR area is the MPL area (step S108; Yes), the ECU 7 acquires the addition amount and the addition period correction coefficient in the MPL area based on a map prepared in advance, and based on them. The reference addition amount QH and the reference addition cycle TH are corrected (step S109). In this case, the addition amount QM for the MPL region obtained by the correction is smaller than the reference addition amount QH but larger than the addition amount QL for the LPL region. Further, the addition period TL for the LPL region is shorter than the reference addition cycle TH, but is longer than the addition cycle TL for the LPL region.

  When the EGR region is an HPL region, the reference addition amount QH and the reference addition period TH are used as they are. Thus, when the addition amount and the addition cycle are determined based on the EGR region, the ECU 7 sends a control signal S5 to the fuel addition valve 17 to execute fuel addition (step S110).

  As described above, in the present embodiment, when the low-pressure loop EGR device is operated, the amount of one-time addition of clogging prevention is reduced and the addition cycle is shortened compared to the case where the low-pressure loop EGR device is not operated. The degree of fluctuation of the combustion state of the internal combustion engine can be reduced by returning the added fuel to the intake side.

[Modification]
In the above embodiment, the DPF is provided as an exhaust purification device in the exhaust passage, and PM regeneration of the DPF is performed as regeneration control by adding fuel. Instead, when a NOx storage reduction catalyst is provided in the exhaust passage, fuel addition for NOx reduction or S poison regeneration is performed as regeneration control. Even with such a configuration, the present invention can be applied to clogging prevention addition while regeneration control is not performed.

1 is a schematic block diagram of an exhaust control device for an internal combustion engine according to an embodiment. The map of an EGR area | region is shown. An example of controlling the amount and period of fuel addition according to the EGR region will be shown. It is a flowchart of clogging prevention addition control.

Explanation of symbols

7 ECU
10 Engine 15 Fuel injection valve 17 Fuel addition valve 20 Intake passage 23 Turbocharger 25 Exhaust passage 31, 35 EGR passage 36 DPF
33, 37 EGR valve

Claims (5)

An exhaust control device for an internal combustion engine,
An exhaust purification device provided in an exhaust passage of the internal combustion engine;
Fuel addition means provided at an upstream position of the exhaust purification device in the exhaust passage;
A first exhaust gas recirculation device for recirculating exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
A second exhaust gas recirculation device that recirculates exhaust gas from the downstream side position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
Addition control means for adding fuel into the exhaust using the fuel addition means,
The exhaust control device for an internal combustion engine, wherein the addition control means controls an addition amount and an addition cycle of fuel according to an operating state of the exhaust gas recirculation device.   When the second exhaust gas recirculation device is operated, the control means reduces the addition amount and shortens the addition period as compared with the case where only the first exhaust gas recirculation device is operated. The exhaust control device for an internal combustion engine according to claim 1.   When the control means operates both the first and second exhaust gas recirculation devices, the addition amount and the addition period are determined when only the first exhaust gas recirculation device is operated and when the second exhaust gas recirculation device is operated. 3. An exhaust control device for an internal combustion engine according to claim 2, wherein the value is a value during operation of only the device.   The exhaust control device for an internal combustion engine according to any one of claims 1 to 3, wherein the control means adds fuel to prevent clogging of the fuel addition means. Means for performing regeneration control for adding fuel to the exhaust for regeneration of the exhaust purification device;
The internal combustion engine according to any one of claims 1 to 3, wherein the addition control means adds fuel to prevent clogging of the fuel addition means when the regeneration control is not executed. Engine exhaust control device.

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