JP4910849B2 - EGR system for internal combustion engine - Google Patents

Description

The present invention relates to an EGR system for an internal combustion engine.

As a technique for reducing the amount of NOx emitted from an internal combustion engine, EGR is known in which a part of exhaust gas flows into an intake system and is returned to the combustion chamber of the internal combustion engine. With regard to this technology, in an internal combustion engine equipped with a turbocharger, a part of the exhaust gas is transferred to the internal combustion engine via a first EGR passage that connects an exhaust passage upstream of the turbine of the turbocharger and an intake passage downstream of the compressor of the turbocharger. comprising a first 1EGR means for returning, and the 2EGR means via the first 2EGR passage that connects the intake passage upstream of the exhaust passage downstream of the compressor from the turbine returns a part of the exhaust gas to the internal combustion engine, and operation of the internal combustion engine A technique for performing EGR by using or switching between the first EGR means and the second EGR means according to the state is also known (see, for example, Patent Document 1). The amount of exhaust (the 1EGR gas) that is returned to the internal combustion engine by the 1EGR means, it is adjusted by controlling the opening of the 1EGR valve to change the flow area of the 1EGR passage provided in the 1EGR passage it can. Similarly, the amount of exhaust (the 2EGR gas) that is returned to the internal combustion engine by the 2EGR means adjusted by controlling the opening of the 2EGR valve to change the flow area of the 2EGR passage provided in the 2EGR passage can do.

In addition, a technique for reducing the amount of PM released into the atmosphere by providing a filter having an ability to collect PM in the exhaust in the middle of the exhaust passage is known. In an internal combustion engine equipped with a filter, in order to suitably maintain the PM collecting ability of the filter, the accumulated PM is oxidized by raising the temperature of the filter when the accumulated amount of PM in the filter exceeds a predetermined allowable amount. Processing (hereinafter referred to as PM regeneration processing) may be executed. Regarding the technology of PM regeneration processing, it has been studied to throttle an exhaust throttle valve provided downstream from the filter when performing PM regeneration processing. By doing so, the back pressure rises and the exhaust gas temperature rises, so that the PM oxidation reaction can be promoted.
Japanese Patent Laying-Open No. 2005-076456 JP 2006-183485 A JP 2006-226205 A

By the way, when a filter and a PM regeneration processing system are incorporated in an EGR system provided with the first EGR means and the second EGR means, the filter and the exhaust throttle valve are arranged in the exhaust passage downstream from the turbine and upstream from the connection point of the second EGR passage. Can be considered.

However, in the EGR system configured as described above, when the exhaust throttle valve is throttled as described above when executing the PM regeneration process, the pressure difference between the upstream and the downstream of the first EGR passage is increased due to the back pressure rising. Therefore, it becomes difficult to control the first EGR valve with high accuracy, and there is a possibility that the control accuracy of the first EGR gas amount cannot be sufficiently obtained.

Further, when the back pressure increases, the amount of burned gas discharged from the cylinder to the exhaust passage during the exhaust stroke tends to decrease, and the internal EGR amount tends to increase. Therefore, when the opening control of the first EGR valve and / or the second EGR valve is performed in the same manner as when the exhaust throttle valve is not throttled, the internal EGR amount and the exhaust gas returned to the internal combustion engine by the first EGR means and the second EGR means. The total amount of EGR, which is the sum of the amount of external EGR gas, is larger than expected, and there is a risk of causing a combustion failure such as misfire.

The present invention has been made in view of such problems, and in an EGR system using both the first EGR means and the second EGR means, sufficient EGR can be achieved even when the exhaust throttle valve is throttled at the time of execution of PM regeneration processing or the like. It is an object of the present invention to provide a technique that ensures control accuracy and that can suitably execute EGR.

To achieve the above object, an EGR system for an internal combustion engine according to the present invention includes a turbocharger having a turbine provided in an exhaust passage of the internal combustion engine and a compressor provided in an intake passage of the internal combustion engine, and a downstream of the turbine. an exhaust throttle valve provided in an exhaust passage to change the flow area of the exhaust passage, said provided first 1EGR passage and said second 1EGR passage connecting the intake passage downstream of from the compressor and upstream of the exhaust passage from the turbine a first 1EGR means for directing a portion of the exhaust having a first 1EGR valve to change the flow area through the first 1EGR passage of the 1EGR passage in an internal combustion engine, than the downstream of the exhaust passage compressor than the exhaust throttle valve the 2EG to change the flow area of the 2EGR passage and provided in said first 2EGR passage the first 2EGR passage connecting the intake passage upstream of The amount of exhaust gas returned to the internal combustion engine by controlling a first 2EGR means for directing a portion of the exhaust through the first 2EGR passage has a valve in an internal combustion engine, an opening degree of the first 1EGR valve and said second 2EGR valve and a EGR control means for controlling the EGR control means, if the opening degree of the exhaust throttle valve is throttled in the closing side of the opening than the predetermined exhaust throttle valve opening, the predetermined said first 1EGR valve The first EGR valve opening is substantially fixed, and the amount of exhaust gas returned to the internal combustion engine is controlled by controlling the opening of the second EGR valve.

Here, the “ predetermined exhaust throttle valve opening degree ” means that the back pressure of the exhaust passage when the exhaust throttle valve is throttled can ensure sufficient control accuracy with respect to the control of the first EGR gas amount by the first EGR valve . This is the lower limit value of the opening degree of the exhaust throttle valve that is lower than the normal pressure. That is, if the opening of the exhaust throttle valve is an opening larger than the predetermined exhaust throttle valve opening (opening side opening), the back pressure in the exhaust passage upstream from the exhaust throttle valve will not become excessively high. Therefore, the pressure difference between the upstream and downstream of the first EGR passage does not become excessively large, and the first EGR gas amount can be controlled with sufficient accuracy by controlling the opening degree of the first EGR valve. On the contrary, when the opening of the exhaust throttle valve becomes smaller than the predetermined exhaust throttle valve opening (opening on the closing side), the back pressure in the exhaust passage upstream from the exhaust throttle valve becomes excessively high, and the first EGR passage The pressure difference between upstream and downstream becomes excessively large, and it becomes difficult to accurately control the first EGR gas amount by controlling the opening degree of the first EGR valve.

The “ predetermined first EGR valve opening” is a predetermined opening of the first EGR valve.

According to the above configuration, the first EGR valve opening is substantially fixed when the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening . That is, the first EGR gas amount has a substantially constant value. Then, the amount of exhaust gas returned to the internal combustion engine is controlled by controlling the opening degree of the second EGR valve. Even when the exhaust throttle valve is throttled further than the predetermined exhaust throttle valve opening , the second EGR passage is provided so as to extract exhaust from the exhaust passage downstream of the exhaust throttle valve, so that the upstream of the second EGR passage and The downstream pressure difference does not become excessively large. Therefore, the control accuracy of the second EGR gas amount by the opening degree control of the second EGR valve can be sufficiently ensured. Therefore, a substantially constant amount of the 1EGR gas, the total amount of the first 2EGR gas controlled with sufficient accuracy, so the total EGR gas amount that is required can be supplied to accurately engine.

In the above configuration, in particular, the predetermined first EGR valve opening may be fully closed. In this case, when the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening , the required total EGR gas amount is supplied to the internal combustion engine using only the second EGR means. Will do. In other words, since the total EGR gas amount can be controlled by adjusting only the opening degree of the second EGR valve that can be controlled with high accuracy, the total EGR gas amount when the exhaust throttle valve is throttled can be more accurately determined. It becomes possible to control.

When the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening, the back pressure in the exhaust passage upstream from the exhaust throttle valve increases as described above, so that the exhaust stroke to the intake stroke There is a tendency that the amount of burned gas discharged from the cylinder into the exhaust passage decreases. That is, the amount of burnt gas (internal EGR gas) remaining in the cylinder tends to increase. Therefore, the amount of the external EGR gas, which is the exhaust gas that is returned to the internal combustion engine by the first EGR means and the second EGR means, is reduced so that the opening degree of the exhaust throttle valve is closer to the closing side than the predetermined exhaust throttle valve opening degree. If the amount is the same as the case where there is not, the total amount of EGR gas supplied to the internal combustion engine may be excessive. In that case, there is a risk of causing a combustion failure such as misfire.

Therefore, in the present invention, when the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening , the amount of the external EGR gas is set so that the opening of the exhaust throttle valve is the predetermined exhaust. Open throttle valve
The opening degree of the second EGR valve may be controlled so as to be smaller than the normal external EGR gas amount that is not restricted to the opening degree on the closing side.

By doing so, even when the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening, it is possible to suppress an excessive amount of EGR gas from being supplied to the internal combustion engine.

The present invention provides a filter that is provided in an exhaust passage downstream from the turbine and upstream from the exhaust throttle valve, and that collects PM accumulated in the filter so as to maintain the PM collection capability of the filter. The present invention can be applied to an internal combustion engine further provided with PM regeneration means for oxidizing.

In this case, when the exhaust throttle valve is throttled to promote the oxidation of PM by the PM regeneration means, the first EGR valve is substantially fixed or fully closed at the predetermined first EGR valve opening as described above, and the second EGR valve is closed. The amount of exhaust gas returned to the internal combustion engine may be controlled by controlling the degree of opening.

By doing so, EGR can be executed with high accuracy even during the process of oxidizing the PM deposited on the filter by the PM regeneration means.

When a process for oxidizing PM (PM regeneration process) is performed by the PM regeneration means, oxygen in the exhaust is consumed as a result of the oxidation reaction of PM in the filter, and carbon dioxide is generated and exhausted in the exhaust. The carbon dioxide concentration tends to increase. For this reason, if the same amount of all EGR gas as that when the PM regeneration process is not performed is supplied to the internal combustion engine, the amount of inert gas in the cylinder becomes excessive, which may lead to poor combustion such as misfire.

Therefore, in the present invention, when the exhaust throttle valve is throttled to the opening side closer to the closing side than the predetermined exhaust throttle valve opening in order to promote the oxidation of PM by the PM regeneration means, the internal EGR gas amount and the external EGR gas amount are The second EGR valve so that the total EGR gas amount is less than the normal total EGR gas amount in which the opening degree of the exhaust throttle valve is not restricted to the opening side closer to the closing side than the predetermined exhaust throttle valve opening degree. The degree of opening may be controlled.

By doing so, it is possible to prevent the amount of the inert gas in the cylinder from becoming excessive even when the PM regeneration process is being performed.

In the above configuration, when the exhaust throttle valve is throttled to the opening on the closed side with respect to the predetermined exhaust throttle valve opening in order to promote the oxidation of PM by the PM regeneration means, the internal EGR gas amount and the external EGR gas amount are summed up. The EGR rate calculated from the total EGR gas amount is smaller than the normal EGR rate where the opening of the exhaust throttle valve is not throttled to the opening on the closing side from the predetermined exhaust throttle valve opening . The opening degree of the 2EGR valve may be controlled.

Here, the total EGR gas amount can be obtained by separately calculating the external EGR gas amount and the internal EGR gas amount and summing them. External EGR gas amount is, for example, the differential pressure between the upstream and the downstream of the 1EGR passage, calculates the opening of the 1EGR valve, the first 1EGR gas amount based on a difference between the upstream and the downstream of the 2EGR passage The second EGR gas amount is calculated based on the pressure and the opening degree of the second EGR valve, and can be obtained as the total amount of the calculated first EGR gas amount and second EGR gas amount. Further, the internal EGR gas amount can be obtained by mapping or functioning the relationship between the back pressure and the internal EGR gas amount through experiments or the like in advance, and determining the internal EGR gas amount from the measured value of the back pressure based on the relationship. it can.

The total EGR gas amount is such that the opening of the exhaust throttle valve is fully opened and the first EGR means and the
It can also be calculated based on the difference between the intake air amount when EGR is not performed by the second EGR means and the actual intake air amount.

Even if the intake pressure is equal, the intake air amount in the state where EGR is performed or the exhaust throttle valve is throttled is compared to the intake air amount in the non-EGR state where the exhaust throttle valve is not throttled and EGR is not performed. The total amount of EGR gas supplied to the engine is reduced. Accordingly, the total EGR gas amount can be estimated based on the difference between the actual intake air amount and the intake air amount in the non-EGR state. For example, the relationship between the intake pressure and the intake air amount in the non-EGR state is obtained in advance through experiments or the like, mapped or functioned, and based on the measured intake air pressure, the intake air amount in the non-EGR state (no EGR intake In addition to calculating the air amount), the actual intake air amount (actual intake air amount) is measured, and the total EGR gas amount can be obtained as the difference between the non-EGR intake air amount and the actual intake air amount.

In addition, said each structure can be employ | adopted combining as much as possible.

According to the present invention, in an EGR system using both the first EGR means and the second EGR means, sufficient EGR control accuracy is ensured even when the exhaust throttle valve is throttled at the time of executing the PM regeneration process, and the EGR is suitably executed. Is possible.

The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

FIG. 1 is a diagram schematically showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

The intake ports (not shown) of the respective cylinders 2 gather in the intake manifold 17 and communicate with the intake passage 3. The intake manifold 17 is provided with an intake pressure sensor 22 for measuring the pressure of intake air. A first EGR passage 41 (to be described later) is connected in the vicinity of the connection portion between the intake manifold 17 and the intake passage 3. A second throttle valve 9 that adjusts the amount of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream from the connection point of the first EGR passage 41. An intercooler 8 for cooling the intake air is disposed in the intake passage 3 upstream of the second throttle valve 9. A compressor 11 of a turbocharger 13 is disposed in the intake passage 3 upstream from the intercooler 8. A second EGR passage 31 described later is connected to the intake passage 3 upstream of the compressor 11. A first throttle valve 6 that adjusts the amount of fresh air flowing into the intake passage 3 is disposed in the intake pipe 3 upstream from the connection point of the second EGR passage 31. An air flow meter 7 that measures the amount of fresh air flowing into the intake passage 3 is provided in the intake passage 3 upstream of the first throttle valve 6. An air cleaner (not shown) is connected to the intake passage 3 further upstream. Hereinafter, the intake passage 3, the intake manifold 17, the intercooler 8, the compressor 11, and the like arranged in these may be collectively referred to as “intake system”.

In the intake system configured as described above, the air from which dust or dust has been removed through the air cleaner flows into the intake passage 3. The air that has flowed into the intake passage 3 is pressurized through the compressor 11 and then cooled through the intercooler 8, and is guided to the intake passage 3 by the second EGR device 30 and the first EGR device 40 described later . Then, it flows into the intake manifold 17 while being mixed with the EGR gas, and is distributed to the intake port of each cylinder 2 via each branch pipe of the intake manifold 17. The intake air distributed to the intake port is drawn into the combustion chamber of each cylinder 2 when an intake valve (not shown) is opened.

The exhaust ports (not shown) of the respective cylinders 2 are gathered in the exhaust manifold 18 and communicate with the exhaust passage 4. The exhaust manifold 18 is provided with a fuel addition valve 21 for adding fuel as a reducing agent to the exhaust. A first EGR passage 41 is connected in the vicinity of the connection portion between the exhaust manifold 18 and the exhaust passage 4. A turbine 12 of the turbocharger 13 is disposed in the exhaust passage 4 downstream from the connection point of the first EGR passage 41. The turbocharger 13 is a variable capacity turbocharger including a nozzle vane 5 that makes the flow area of exhaust gas passing through the turbine 12 variable. An exhaust purification device 10 is disposed in the exhaust passage 4 downstream from the turbine 12. The exhaust purification device 10 is configured to include an oxidation catalyst and a particulate filter (hereinafter referred to as a filter) that is disposed downstream of the oxidation catalyst and collects PM in the exhaust and deposits it inside. The configuration of the exhaust purification device 10 is not limited to this example, and for example, an NOx storage reduction catalyst may be further provided. An exhaust throttle valve 19 that adjusts the amount of exhaust gas flowing through the exhaust passage 4 is disposed in the exhaust passage 4 downstream of the exhaust purification device 10. A second EGR passage 31 is connected to the exhaust passage 4 downstream from the exhaust throttle valve 19. Hereinafter, the exhaust passage 4, the exhaust manifold 18, and the turbine 12, the exhaust purification device 10, and the like arranged in these may be collectively referred to as “exhaust system”.

In the exhaust system configured as described above, the burned gas burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 through the exhaust port and flows into the exhaust passage 4. Exhaust gas that has flowed into the exhaust passage 4 is driven to rotate the turbine 13 and then the harmful substances such as PM contained in the exhaust gas purification device 10 are purified, and a part thereof is EGRed by the second EGR device 30 and the first EGR device 40 described later . It is led to the intake passage 3 as gas. After being purified by the exhaust purification device 10, the exhaust is released into the atmosphere.

The internal combustion engine 1 is provided with a first EGR device 40 that guides part of the exhaust gas flowing through the exhaust passage 4 upstream of the turbine 12 to the intake passage 3 downstream of the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. ing. The 1EGR apparatus 40 includes an upstream exhaust passage 4 from the turbine 12 the second 1EGR passage 41 which connects the downstream of the intake passage 3 from the second throttle valve 9, the exhaust through the first 1EGR passage 41 one The portion is caused to flow into the intake passage 3. The exhaust returned to the combustion chamber by the first EGR device 40 is hereinafter referred to as “ first EGR gas”. The first EGR passage 41 is provided with a first EGR valve 42 that changes the flow area of the first EGR passage 41. The amount of the first EGR gas flowing through the first EGR passage 41 is adjusted by adjusting the opening degree of the first EGR valve 42.

The internal combustion engine 1 is provided with a second EGR device 30 that guides part of the exhaust gas flowing through the exhaust passage 4 downstream from the turbine 12 to the intake passage 3 upstream from the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. ing. The 2EGR device 30 has a first 2EGR passage 31 connecting upstream of the intake passage 3 downstream of the exhaust passage 4 and the compressor 11 of the exhaust throttle valve 19, a portion of the exhaust through the first 2EGR passage 31 Into the intake passage 3. The exhaust gas returned to the combustion chamber by the second EGR device 30 is hereinafter referred to as “ second EGR gas”. A second EGR cooler 33 that cools the second EGR gas is disposed in the middle of the second EGR passage 31. A second EGR valve 32 that changes the flow area of the second EGR passage 31 is disposed in the second EGR passage 31 on the downstream side (the intake passage 3 side) of the second EGR cooler 33. By adjusting the opening degree of the second EGR valve 32, the amount of the second EGR gas flowing through the second EGR passage 31 is adjusted.

When EGR is performed by the first EGR device 40 and the second EGR device 30 configured as described above, incombustible and endothermic inert gas components such as water and carbon dioxide are mixed in the intake air. As a result, the combustion temperature of the fuel decreases, and the amount of NOx generated decreases.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the internal combustion engine 1. The ECU 20 is a microcomputer provided with a CPU, a ROM, a RAM, an input / output port, and the like. In addition to the air flow meter 7 and the intake pressure sensor 22 described above, the ECU 20 corresponds to the water temperature sensor 14 that outputs an electrical signal corresponding to the temperature of the cooling water circulating in the water jacket of the internal combustion engine 1 and the operation amount of the accelerator pedal. An accelerator opening sensor 15 that outputs an electrical signal and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are electrically connected. Is output to the ECU 20. Further, the ECU 20 is electrically connected to devices such as the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, the exhaust throttle valve 19, the second EGR valve 32, the first EGR valve 42, the fuel addition valve 21, and the like. These devices are controlled by a control signal output from the ECU 20.

ECU20 acquires the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the signal input from each said sensor. For example, the ECU 20 calculates the engine speed based on the signal input from the crank position sensor 16 and calculates the requested engine load based on the signal input from the accelerator opening sensor 15. Then, fuel injection and EGR are controlled by controlling each of the above devices in accordance with the calculated engine load and engine speed.

Here, the EGR control performed in the EGR system of the present embodiment will be described.

As shown in FIG. 2, in the EGR system of the present embodiment, EGR is performed by using or switching the first EGR device 40 and the second EGR device 30 in accordance with the operating state of the internal combustion engine 1. In FIG. 2, the horizontal axis represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1. As shown in FIG. 2, the EGR control in this embodiment performs the EGR primarily by the 1EGR device 40 when the operating state of the internal combustion engine 1 low load and low rotational speed, the higher the engine load or the engine speed is high The EGR amount ( first EGR gas amount) performed by the 1EGR device 40 is decreased and the EGR amount ( second EGR gas amount) performed by the second EGR device 30 is increased, so that the operating state of the internal combustion engine 1 is high load or high rotation side. At this time, EGR is mainly performed by the second EGR device 30.

In FIG. 2, an area indicated by “ first EGR ” represents an operating state area where EGR is performed mainly by the first EGR device 40. This region is hereinafter referred to as a first EGR region. In addition, a region indicated by “ second EGR ” represents a region in an operating state in which EGR is mainly performed by the second EGR device 30. This region is hereinafter referred to as a second EGR region. A medium load or medium rotation region represented by “MIX” between the first EGR region and the second EGR region represents a region where EGR is performed by using the first EGR device 40 and the second EGR device 30 together. This area is hereinafter referred to as a MIX area. As described above, in the MIX region, control is performed such that the first EGR gas amount is decreased and the second EGR gas amount is increased as the operation state becomes higher or higher. In other words, the ratio of the first EGR gas in the total EGR gas is decreased and the ratio of the second EGR gas is increased as the load increases or the rotation speed increases.

The control target values of the first EGR gas amount and the second EGR gas amount corresponding to each operation state are the NOx generation amount, smoke generation amount, HC generation amount, fuel consumption when the internal combustion engine 1 is in steady operation in the operation state. Various characteristics relating to the engine performance and the exhaust performance such as the rate are determined in advance by an adaptation operation so as to achieve a predetermined regulation value and a desired target value, and are stored in the ROM of the ECU 20. Based on the acquired engine operating state, the ECU 20 reads a control target value of the first EGR gas amount and the second EGR gas amount corresponding to the operating state from the ROM, and is returned to the combustion chamber by the first EGR device 40 and the second EGR device 30. The first EG is set so that the amount of exhaust becomes the control target value .
The opening degree of the R valve 42, the second EGR valve 32, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 19, the nozzle vane 5, and the like is controlled.

When the ECU 20 determines that the amount of PM accumulated on the filter exceeds a predetermined allowable value, the ECU 20 throttles the exhaust throttle valve 19 and adds fuel to the exhaust from the fuel addition valve 21. When fuel is added to the exhaust gas from the fuel addition valve 21, the added fuel undergoes an oxidation reaction in the oxidation catalyst in the upstream stage of the filter, and the oxidation reaction of PM deposited on the downstream filter is promoted by the reaction heat at that time, PM accumulated on the filter is removed. Further, by restricting the exhaust throttle valve 19, the back pressure in the exhaust passage 4 upstream from the exhaust throttle valve 19 increases, the temperature of the exhaust discharged from the internal combustion engine 1 increases, and the oxidation catalyst and the filter are heated. Therefore, the oxidation reaction of PM deposited on the filter is promoted.

In this way, the PM collecting ability of the filter is maintained by appropriately removing the PM deposited on the filter by oxidation. The process of oxidizing and removing PM deposited on the filter by adding the fuel into the exhaust gas from the fuel addition valve 21 while restricting the exhaust throttle valve 19 is hereinafter referred to as PM regeneration process. In this embodiment, the ECU 20 that performs PM regeneration processing corresponds to the PM regeneration means in the present invention.

As a method for estimating the amount of PM deposited on the filter, a known PM accumulation amount estimation method can be employed. For example, it can be estimated on the basis of the intake air amount and fuel consumption since the previous PM regeneration process, the travel distance of the vehicle, the differential pressure across the filter, and the like. In addition, the “predetermined allowable amount” is an upper limit value of the PM accumulation amount such that the pressure loss in the filter does not hinder normal operation of the internal combustion engine, or a predetermined margin is expected for the upper limit value. It is a fixed amount.

By the way, in the EGR system in which the first EGR passage 41 is connected to the exhaust passage 4 upstream from the exhaust throttle valve 19 as in the present embodiment, when the exhaust throttle valve 19 is throttled when performing the PM regeneration process, As the pressure increases, the pressure on the upstream side of the first EGR passage 41 (that is, in the vicinity of the connection portion with the exhaust passage 4) and the pressure on the downstream side of the first EGR passage 41 (that is, in the vicinity of the connection portion with the intake passage 3) The difference increases. When the pressure difference between the upstream and downstream of the first EGR passage 41 becomes excessively large, it becomes difficult to control the first EGR valve 42 with high accuracy, and there is a possibility that the control accuracy of the first EGR gas amount cannot be obtained sufficiently. .

Further, when the back pressure increases, the amount of burned gas discharged from the cylinder 2 to the exhaust passage 4 in the exhaust stroke decreases, and the burnt gas (internal EGR gas) remaining in the cylinder from the exhaust stroke to the intake stroke is reduced. The amount tends to increase. Therefore, if the amount of exhaust (external EGR gas) returned to the internal combustion engine 1 by the first EGR device 40 and the second EGR device 30 is set to the same amount as normal time when the exhaust throttle valve 19 is not throttled, the internal EGR gas amount and the external EGR amount There is a possibility that the total EGR gas amount, which is the sum of the gas amounts, becomes larger than the specified value corresponding to the operating state of the internal combustion engine 1. In that case, there is a risk of causing a combustion failure such as misfire.

On the other hand, in the EGR system of the present embodiment, when the exhaust throttle valve 19 is throttled along with the PM regeneration process, the control of the external EGR gas amount is performed only by the control of the second EGR valve 32. That is, at the normal time when the PM regeneration process is not performed, the external EGR gas is supplied to the internal combustion engine 1 by appropriately using or switching the first EGR device 40 and the second EGR device 30 according to the operating state of the internal combustion engine 1 as described above. On the other hand, when the PM regeneration process is performed by restricting the exhaust throttle valve 19, the first EGR valve 42 is temporarily fully closed and the external EGR gas is supplied to the internal combustion engine 1 using only the second EGR device 30. .

Since the second EGR passage 31 is connected so as to extract exhaust from the exhaust passage 4 downstream of the exhaust throttle valve 19, even when the exhaust throttle valve 19 is throttled, the upstream and downstream of the second EGR passage 31 The pressure difference should not be excessive. Therefore, even when the PM regeneration process is being performed and the exhaust throttle valve 19 is throttled, the control accuracy of the second EGR gas amount by the opening degree control of the second EGR valve 32 can be sufficiently ensured, and the internal combustion engine 1 The amount of external EGR gas supplied to can be controlled with high accuracy.

At this time, the second EGR gas amount is a specified value of the external EGR gas amount at the normal time when the exhaust throttle valve 19 is not throttled (the specified value of the first EGR gas amount and the second EGR gas amount according to the operating state of the internal combustion engine 1). The second EGR valve 32 is controlled so as to be smaller than the total value of the above-mentioned prescribed value. As a result, even when the exhaust throttle valve 19 is throttled and the internal EGR gas amount is increased from the normal time, the total EGR gas amount, which is the sum of the internal EGR gas amount and the external EGR gas amount, is larger than the specified value. It is suppressed. Therefore, even when the exhaust throttle valve 19 is throttled during the PM regeneration process, it is possible to suppress the occurrence of combustion failure such as misfire.

Further, in this embodiment, at this time, the exhaust throttle valve 19 is throttled to the total EGR gas amount that is the sum of the internal EGR gas amount and the external EGR gas amount (equal to the second EGR gas amount in this embodiment). Compared with the specified value of the total EGR gas amount in normal time (the sum of the specified value of the first EGR gas amount, the specified value of the second EGR gas amount, and the specified value of the internal EGR gas amount according to the operating state of the internal combustion engine 1) Therefore, the second EGR valve 32 is controlled so as to decrease.

During the PM regeneration process, oxygen in exhaust gas is consumed by the oxidation reaction of fuel and PM supplied as a reducing agent, so that the oxygen concentration in the exhaust gas is reduced and carbon dioxide is generated by the oxidation reaction. The carbon dioxide concentration in the exhaust increases. That is, during the PM regeneration process, the exhaust gas having a higher inert component concentration than the normal time during which the PM regeneration process is not performed is supplied to the internal combustion engine 1 as EGR gas. Therefore, if the total EGR gas amount during the PM regeneration process is controlled to a value equal to the specified value of the total EGR gas amount at the normal time, an excessive amount of inert components than expected is supplied to the internal combustion engine 1. As a result, there is a risk of causing a combustion failure such as misfire.

On the other hand, according to the present embodiment configured as described above, the second EGR valve 32 is controlled so that the total amount of EGR gas during the PM regeneration process is smaller than the total amount of EGR gas at the normal time. An excessive increase in the amount of inactive components supplied to the internal combustion engine 1 is suppressed, and poor combustion such as misfire can be suppressed.

Here, the total EGR gas amount can be obtained by separately calculating the external EGR gas amount and the internal EGR gas amount and summing them. The external EGR gas amount (that is, the second EGR gas amount) can be calculated based on, for example, the differential pressure between the upstream and downstream of the second EGR passage 31 and the opening degree of the second EGR valve 32. Further, the internal EGR gas amount can be obtained by mapping or functioning the relationship between the back pressure and the internal EGR gas amount through experiments or the like in advance, and determining the internal EGR gas amount from the measured value of the back pressure based on the relationship. it can.

The total EGR gas amount can also be calculated based on the relationship between the intake air amount and the intake pressure when the exhaust throttle valve 19 is not throttled and EGR is not performed. FIG. 3 is a diagram showing the relationship between the intake pressure and the intake air amount. The solid line in FIG. 3 shows the relationship between the intake pressure and the intake air amount when the exhaust throttle valve 19 is not throttled and EGR is not performed. This relationship can be obtained in advance by experiments or the like. Also, the alternate long and short dash line in FIG. 3 shows the relationship between the intake pressure and the intake air amount when EGR is performed.

When the EGR is performed, the intake air amount is reduced by the amount of the introduced EGR gas as compared with the case where the EGR is not performed even when the intake pressure is equal. Therefore, the difference between the intake air amount Gb without EGR corresponding to the intake pressure measured by the intake pressure sensor 22 and the actual intake air amount Ga obtained by measuring with the air flow meter 7 is calculated. If calculated, it can be considered that it is substantially equal to the total amount of EGR gas introduced into the internal combustion engine 1.

Hereinafter, the EGR control performed by the ECU 20 when the exhaust throttle valve 19 is throttled will be described with reference to FIG. FIG. 4 is a flowchart showing a routine for performing EGR control when the exhaust throttle valve 19 is throttled. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

First, in step 101, the ECU 20 determines whether or not the exhaust throttle valve 19 is throttled. Specifically, it is determined whether or not the opening degree of the exhaust throttle valve 19 is closer to the closing side than the predetermined exhaust throttle valve opening degree . Here, the predetermined exhaust throttle valve opening means that the back pressure of the exhaust passage 4 when the exhaust throttle valve 19 is throttled can ensure sufficient control accuracy with respect to the control of the first EGR gas amount by the first EGR valve 42 . This is the lower limit value of the opening degree of the exhaust throttle valve 19 that is lower than a certain pressure. That is, if the opening of the exhaust throttle valve 19 is larger than the predetermined exhaust throttle valve opening (opening side opening), the back pressure of the exhaust passage 4 upstream from the exhaust throttle valve 19 becomes excessively high. Therefore, the pressure difference between the upstream and downstream of the first EGR passage 41 does not become excessively large, and the first EGR gas amount can be controlled with sufficient accuracy by controlling the opening degree of the first EGR valve 42. . Conversely, when the opening of the exhaust throttle valve 19 becomes smaller than the predetermined exhaust throttle valve opening (opening side opening), the back pressure in the exhaust passage 4 upstream from the exhaust throttle valve 19 becomes excessively high, The pressure difference between the upstream and downstream sides of the first EGR passage 41 becomes excessively large, and it becomes difficult to accurately control the first EGR gas amount by controlling the opening degree of the first EGR valve 42. In the present embodiment, the exhaust throttle valve 19 is throttled during the PM regeneration process, so it may be determined in step S101 whether the PM regeneration process is being performed. If an affirmative determination is made in step S101, the ECU 20 proceeds to step S102. If a negative determination is made in step S101, the ECU 20 proceeds to step S110.

In step S <b> 102, the ECU 20 acquires the actual intake air amount Ga by the air flow meter 7.

In step S <b> 103, the ECU 20 acquires the intake pressure Pim by the intake pressure sensor 22.

In step S104, the ECU 20 determines the intake air amount Gb assumed when the intake pressure is Pim when the exhaust throttle valve 19 is not throttled and EGR is not being performed. It is calculated based on the relationship with the quantity (displayed with a solid line).

In step S105, the ECU 20 calculates an actual EGR rate EGRa. Specifically, the actual EGR gas amount is calculated from the difference (Gb−Ga) between the intake air amount Gb without EGR calculated in step S104 and the actual intake air amount acquired in step S102, and the calculated actual EGR gas Based on the quantity, the actual EGR rate is calculated by (Gb-Ga) / Ga.

In step S106, the ECU 20 calculates a target EGR rate EGRtrg. As described above, the target EGR rate EGRtrg is set to a smaller value than the target value of the EGR rate determined according to the operating state of the internal combustion engine 1 when the exhaust throttle valve 19 is not throttled.

In step S107, the ECU 20 determines the magnitude relationship between the actual EGR rate EGRa and the target EGR rate EGRtrg. When the actual EGR rate EGRa matches the target EGR rate EGRtrg, the ECU 20 once ends the execution of this routine. Actual EGR rate EGRa> Target EGR
In the case of the rate EGRtrg, the ECU 20 proceeds to step S108 and corrects the opening degree of the second EGR valve 32 to the closed side. On the other hand, when the actual EGR rate EGRa <the target EGR rate EGRtrg, the ECU 20 proceeds to step S109 and corrects the opening degree of the second EGR valve 32 to the open side.

In step S110, the ECU 20 performs normal EGR control when the exhaust throttle valve 19 is not throttled (that is, control according to the EGR control map shown in FIG. 2).

The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the present embodiment, the case where the PM regeneration processing is executed is illustrated as the case where the exhaust throttle valve 19 is throttled to the opening side closer to the closing side than the predetermined exhaust throttle valve opening degree. In some cases, the opening of the exhaust throttle valve 19 may be throttled. Also in this case, when the exhaust throttle valve 19 is throttled to the opening side closer to the closing side than the predetermined exhaust throttle valve opening degree , the first EGR valve 42 is closed and only the second EGR valve 32 is controlled as in this embodiment. By controlling the amount of external EGR gas, it is possible to control EGR with high accuracy.

Further, if the exhaust throttle valve 19 in this embodiment is squeezed into the closed side of the opening than the predetermined exhaust throttle valve opening, the first 1EGR valve 42 has been described for the fully closed, the opening of the 1EGR valve 42 You may make it fix to a fixed opening degree. In this case, a constant amount of the first EGR gas is supplied to the internal combustion engine 1 through the first EGR valve 42 having a fixed opening degree. However, since the first EGR gas amount is constant, the external EGR gas is also used. The amount is controlled by opening degree control of the second EGR valve 32. Therefore, even when the exhaust throttle valve 19 is throttled, EGR control can be performed with high accuracy.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an EGR system according to a first embodiment is applied, and an intake system and an exhaust system thereof. It is a figure which shows the EGR control map in Example 1. FIG. It is a figure which shows the relationship between the intake pressure in Example 1, and intake air amount. 7 is a flowchart showing an EGR control routine when the exhaust throttle valve in the first embodiment is throttled.

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Nozzle vane 6 First throttle valve 7 Air flow meter 8 Intercooler 9 Second throttle valve 10 Exhaust purification device 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank Position sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
21 Fuel addition valve 22 Intake pressure sensor 30 2nd EGR device 31 2nd EGR passage 32 2nd EGR valve 33 2nd EGR cooler 40 1st EGR device 41 1st EGR passage 42 1st EGR valve

Claims (7)

A turbocharger having a turbine provided in an exhaust passage of the internal combustion engine and a compressor provided in an intake passage of the internal combustion engine;
An exhaust throttle valve that is provided in an exhaust passage downstream from the turbine and changes a flow passage area of the exhaust passage;
The 1EGR passage and said said has a first 1EGR valve to change the flow area of the provided the first 1EGR passage to the 1EGR passage second 1EGR connecting the intake passage downstream of from the exhaust passage upstream of the turbine compressor First EGR means for guiding part of the exhaust gas to the internal combustion engine through the passage;
The has a first 2EGR valve to change the flow area of the first 2EGR passage provided in the 2EGR passage and said second 2EGR passage connecting the intake passage upstream of than the downstream of the exhaust passage compressor than the exhaust throttle valve a first 2EGR means for directing a portion of the exhaust to the engine via the first 2EGR passage,
EGR control means for controlling the amount of exhaust gas returned to the internal combustion engine by controlling the opening degree of the first EGR valve and the second EGR valve;
With
The EGR control means substantially fixes the first EGR valve to a predetermined first EGR valve opening when the opening of the exhaust throttle valve is throttled to an opening closer to the closing side than the predetermined exhaust throttle valve opening , An EGR system for an internal combustion engine, wherein the amount of exhaust gas returned to the internal combustion engine is controlled by controlling the opening degree of the second EGR valve. In claim 1,
The predetermined first EGR valve opening is an EGR system for an internal combustion engine that is fully closed. In claim 1 or 2,
The EGR control means uses the exhaust gas returned to the internal combustion engine by the first EGR means and the second EGR means when the opening degree of the exhaust throttle valve is throttled to a close side of the predetermined exhaust throttle valve opening degree. The second EGR valve is set such that the amount of the external EGR gas is smaller than the amount of the external EGR gas at the normal time when the opening of the exhaust throttle valve is not throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening. System of an internal combustion engine that controls the opening of the engine. In any one of Claims 1-3,
A filter provided in an exhaust passage downstream of the turbine and upstream of the exhaust throttle valve for collecting PM in the exhaust;
PM regeneration means for oxidizing PM deposited on the filter;
Further comprising
The case where the opening of the exhaust throttle valve is throttled to the opening closer to the closing side than the predetermined exhaust throttle valve opening is an internal combustion engine in which the exhaust throttle valve is throttled to promote the oxidation of PM by the PM regeneration means. Institution EGR system. In claim 4,
When the exhaust throttle valve is throttled to an opening closer to the closing side than the predetermined exhaust throttle valve opening in order to promote PM oxidation by the PM regeneration means, the existing exhaust gas remaining in the cylinder from the exhaust stroke to the intake stroke of the internal combustion engine. The total amount of EGR gas, which is the sum of the amount of internal EGR gas that is the fuel gas and the amount of external EGR gas, is not throttled to an opening closer to the closing side than the predetermined exhaust throttle valve opening. An EGR system for an internal combustion engine that controls an opening degree of the second EGR valve so as to be smaller than a total amount of EGR gas at a normal time. In claim 4,
When the exhaust throttle valve is throttled to an opening closer to the closing side than the predetermined exhaust throttle valve opening in order to promote PM oxidation by the PM regeneration means, the existing exhaust gas remaining in the cylinder from the exhaust stroke to the intake stroke of the internal combustion engine. The EGR rate calculated from the total amount of EGR gas, which is the sum of the amount of internal EGR gas that is the fuel gas and the amount of external EGR gas, indicates that the opening of the exhaust throttle valve is closer to the closed side than the predetermined exhaust throttle valve opening . An EGR system for an internal combustion engine that controls an opening degree of the second EGR valve so as to be smaller than a normal EGR rate that is not restricted by the opening degree. In claim 5 or 6,
The total EGR gas amount is determined based on the difference between the intake air amount and the actual intake air amount when the opening of the exhaust throttle valve is fully opened and EGR is not performed by the first EGR means and the second EGR means. EGR system for internal combustion engine to be calculated.

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