JP2008261256A - Egr system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique suitably executing EGR by securing EGR control accuracy even when throttling an exhaust throttle valve when executing PM regenerating processing, in an EGR system for simultaneously using an HPL device and an LPL device. <P>SOLUTION: This EGR system has: the exhaust throttle valve arranged in an exhaust passage on the downstream side of a turbine of a turbocharger; the HPL device having an HPL passage for connecting the exhaust passage on the upstream side of the turbine to an intake passage on the downstream side a compressor of the turbocharger and an HPL valve arranged in the HPL passage; the LPL device having an LPL passage for connecting the exhaust passage on the downstream side of the exhaust throttle valve to the intake passage on the upstream side of the compressor and an LPL valve arranged in the LPL passage; and an EGR control means for controlling an EGR gas quantity by con6trolling opening of the HPL valve and the LPL valve. The EGR system controls the EGR gas quantity by controlling the opening of the LPL valve by closing the HPL valve when opening of the exhaust throttle valve is throttled to closing side opening more than predetermined opening. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 technique, in an internal combustion engine equipped with a turbocharger, a part of the exhaust gas is returned to the internal combustion engine via an HPL passage that connects an exhaust passage upstream of the turbocharger turbine and an intake passage downstream of the turbocharger compressor. HPL means, and LPL means for returning part of the exhaust gas to the internal combustion engine via an LPL passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and depending on the operating state of the internal combustion engine A technique for performing EGR by using or switching between HPL means and LPL means is also known (see, for example, Patent Document 1). The amount of exhaust gas (HPL gas) returned to the internal combustion engine by the HPL means can be adjusted by controlling the opening degree of the HPL valve provided in the HPL passage and changing the flow passage area of the HPL passage. Similarly, the amount of exhaust gas (LPL gas) returned to the internal combustion engine by the LPL means can be adjusted by controlling the opening of an LPL valve provided in the LPL passage and changing the flow passage area of the LPL passage.

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 having both HPL means and LPL means, a configuration in which a filter and an exhaust throttle valve are arranged in an exhaust passage downstream from the turbine and upstream from a connection point of the LPL passage is conceivable. .

  However, in the EGR system configured as described above, when the exhaust throttle valve is throttled as described above when the PM regeneration process is performed, the back pressure rises and the pressure difference between the upstream and downstream of the HPL passage is increased. Since it becomes large, it becomes difficult to control the HPL valve with high accuracy, and therefore there is a risk that the control accuracy of the HPL 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 HPL valve and / or the LPL valve is performed in the same manner as when the exhaust throttle valve is not throttled, the internal EGR amount and the external EGR gas that is the exhaust gas returned to the internal combustion engine by the HPL means and the LPL means The total amount of EGR, which is the sum of the amounts, 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 HPL means and LPL means, sufficient EGR control accuracy can be obtained even when the exhaust throttle valve is throttled at the time of PM regeneration processing or the like. It is an object of the present invention to provide a technique for ensuring EGR and preferably enabling execution of 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 that is provided in the exhaust passage and changes the flow passage area of the exhaust passage, an HPL passage that connects an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, and the HPL passage provided in the HPL passage An HPL means having an HPL valve for changing the flow area of the exhaust gas, and an HPL means for guiding part of the exhaust gas to the internal combustion engine through the HPL passage, an exhaust passage downstream from the exhaust throttle valve, and an intake passage upstream from the compressor An LPL passage to be connected and an LPL valve provided in the LPL passage to change the flow area of the LPL passage, and a part of the exhaust gas through the LPL passage LPL means for leading to the internal combustion engine, and EGR control means for controlling the amount of exhaust gas returned to the internal combustion engine by controlling the opening of the HPL valve and the LPL valve, and the EGR control means comprises the exhaust gas When the opening of the throttle valve is throttled to the opening closer to the closing side than the predetermined opening (S), the HPL valve is substantially fixed to the predetermined opening (H) and the opening of the LPL valve is controlled. To control the amount of exhaust gas returned to the internal combustion engine.

  Here, the “predetermined opening degree (S)” is a pressure at which 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 HPL gas amount by the HPL valve. This is the lower limit value of the opening of the exhaust throttle valve that becomes lower. In other words, if the opening of the exhaust throttle valve is an opening (opening side opening) equal to or greater than the predetermined opening (S), the back pressure in the exhaust passage upstream of the exhaust throttle valve will not be excessively high. Therefore, the pressure difference between the upstream and downstream of the HPL passage does not become excessively large, and the amount of HPL gas can be controlled with sufficient accuracy by controlling the opening of the HPL valve. Conversely, when the opening of the exhaust throttle valve becomes smaller than the predetermined opening (S) (opening on the closing side), the back pressure in the exhaust passage upstream of the exhaust throttle valve becomes excessively high, and the HPL passage The pressure difference between the upstream and downstream becomes excessively large, and it becomes difficult to accurately control the amount of HPL gas by controlling the opening of the HPL valve.

  The “predetermined opening degree (H)” is a predetermined opening degree of the HPL valve.

  According to the above configuration, the HPL 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 opening (S). That is, the amount of HPL gas becomes a substantially constant value. The amount of exhaust gas returned to the internal combustion engine is controlled by controlling the opening of the LPL valve. Even when the exhaust throttle valve is further throttled from the predetermined opening (S), the LPL passage is provided so as to extract exhaust from the exhaust passage downstream of the exhaust throttle valve. The pressure difference does not become excessively large. Therefore, the control accuracy of the LPL gas amount by the opening degree control of the LPL valve can be sufficiently ensured. Therefore, it is possible to accurately supply the required total EGR gas amount to the internal combustion engine as a total amount of the substantially constant amount of HPL gas and the LPL gas controlled with sufficient accuracy.

  In the above configuration, in particular, the predetermined opening (H) 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 opening (S), the required total EGR gas amount is supplied to the internal combustion engine using only the LPL means. It will be. In other words, since the total EGR gas amount can be controlled by adjusting only the opening degree of the LPL valve that can be controlled with high accuracy, the total EGR gas amount when the exhaust throttle valve is throttled can be controlled with higher accuracy. It becomes possible to do.

  When the opening of the exhaust throttle valve is throttled to the opening on the closing side from the predetermined opening (S), 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, when the amount of the external EGR gas, which is the exhaust gas that is returned to the internal combustion engine by the HPL unit and the LPL unit, is not reduced to the opening side closer to the closing side than the predetermined opening degree (S). If the amount is the same, 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 degree of the exhaust throttle valve is throttled to the opening side closer to the closing degree than the predetermined opening degree (S), the amount of external EGR gas is set to the predetermined opening degree of the exhaust throttle valve. The opening degree of the LPL 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 from the degree (S).

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

  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 HPL valve is substantially fixed or fully closed at a predetermined opening (H) as described above, and the LPL valve is opened. The amount of exhaust gas returned to the internal combustion engine may be controlled by controlling the degree.

  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 on the closing side from the predetermined opening (S) 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 Of the LPL valve so that the total EGR gas amount is less than the normal total EGR gas amount where the opening degree of the exhaust throttle valve is not restricted to the opening degree on the closing side from the predetermined opening degree (S). The opening degree 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 side closer to the closing side than the predetermined opening degree (S) so as 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 LPL is calculated so that the EGR rate calculated from the total EGR gas amount is smaller than the normal EGR rate at which the opening of the exhaust throttle valve is not restricted to the opening on the closing side from the predetermined opening (S). The opening degree of the 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. The external EGR gas amount is calculated, for example, based on the differential pressure between the upstream and downstream of the HPL passage and the opening of the HPL valve, the differential pressure between the upstream and downstream of the LPL passage, and the LPL The LPL gas amount can be calculated based on the opening degree of the valve, and can be obtained as the total amount of the calculated HPL gas amount and LPL 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 based on the difference between the intake air amount when the exhaust throttle valve is fully opened and EGR is not performed by the HPL means and the LPL means and the actual intake air amount. It can also be calculated.

  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 value of the intake 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 HPL means and LPL means, it is possible to ensure sufficient EGR control accuracy even when the exhaust throttle valve is throttled at the time of PM regeneration processing, etc., and to perform EGR suitably. become.

  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. An HPL passage 41, which will 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 location of the HPL 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. An LPL 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 of the connection point of the LPL 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 flowing into the intake passage 3 is pressurized after passing through the compressor 11 and then cooled through the intercooler 8 and is also introduced into the intake passage 3 by the LPL device 30 and the HPL device 40 described later. The gas flows into the intake manifold 17 while being mixed with gas, and is distributed to the intake port of each cylinder 2 through 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. An HPL 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 location of the HPL 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. An LPL 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 flowing into the exhaust passage 4 is driven to rotate the turbine 13 to remove harmful substances such as PM contained in the exhaust gas purification device 10, and a part thereof is converted into EGR gas by the LPL device 30 and the HPL device 40 described later. It is guided to the intake passage 3. After being purified by the exhaust purification device 10, the exhaust is released into the atmosphere.

  The internal combustion engine 1 includes an HPL device 40 that guides a part of the exhaust gas flowing through the exhaust passage 4 upstream from the turbine 12 to the intake passage 3 downstream from the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. Yes. The HPL device 40 includes an HPL passage 41 that connects the exhaust passage 4 upstream of the turbine 12 and the intake passage 3 downstream of the second throttle valve 9, and intakes a part of the exhaust through the HPL passage 41. It flows into the passage 3. The exhaust gas returned to the combustion chamber by the HPL device 40 is hereinafter referred to as “HPL gas”. An HPL valve 42 that changes the flow area of the HPL passage 41 is disposed in the HPL passage 41. The amount of HPL gas flowing through the HPL passage 41 is adjusted by adjusting the opening degree of the HPL valve 42.

The internal combustion engine 1 is provided with an LPL device 30 that guides part of the exhaust gas flowing through the exhaust passage 4 downstream of the turbine 12 to the intake passage 3 upstream of the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. Yes. The LPL device 30 has an LPL passage 31 that connects the exhaust passage 4 downstream from the exhaust throttle valve 19 and the intake passage 3 upstream from the compressor 11, and a part of the exhaust is taken into the intake passage via the LPL passage 31. 3 is allowed to flow. The exhaust returned to the combustion chamber by the LPL device 30 is hereinafter referred to as “LPL gas”. An LPL cooler 33 for cooling the LPL gas is disposed in the middle of the LPL passage 31. An LPL valve 32 that changes the flow area of the LPL passage 31 is disposed in the LPL passage 31 on the downstream side (the intake passage 3 side) of the LPL cooler 33. By adjusting the opening degree of the LPL valve 32, the amount of LPL gas flowing through the LPL passage 31 is adjusted.

  When EGR is performed by the HPL device 40 and the LPL 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 NOx generation amount 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. In addition, 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 LPL valve 32, the HPL valve 42, and the fuel addition valve 21. These devices are controlled by the output control signal.

  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 HPL device 40 and the LPL 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, in the EGR control of this embodiment, when the operating state of the internal combustion engine 1 is low load and low rotation, EGR is performed mainly by the HPL device 40, and the HPL device increases as the engine load or the engine speed increases. The EGR amount (HPL gas amount) performed by the engine 40 is decreased and the EGR amount (LPL gas amount) performed by the LPL device 30 is increased. When the operating state of the internal combustion engine 1 is at a high load or high rotation side, the LPL is mainly performed. EGR is performed by the device 30.

  In FIG. 2, an area indicated by “HPL” represents an operating state area where EGR is mainly performed by the HPL device 40. This region is hereinafter referred to as an HPL region. An area indicated by “LPL” represents an operating state area where EGR is performed mainly by the LPL device 30. This region is hereinafter referred to as an LPL region. A medium load or medium rotation region represented by “MIX” between the HPL region and the LPL region represents a region where EGR is performed by using the HPL device 40 and the LPL device 30 together. This area is hereinafter referred to as a MIX area. As described above, in the MIX region, the control is performed to decrease the amount of HPL gas and increase the amount of LPL gas as the operation state becomes higher or higher. In other words, the higher the load or the higher rotation side, the lower the ratio of HPL gas in all EGR gases and the higher the ratio of LPL gas.

  The control target values of the HPL gas amount and the LPL gas amount corresponding to each operation state are the NOx generation amount, smoke generation amount, HC generation amount, fuel consumption rate, etc. 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 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 the control target value of the HPL gas amount and the LPL gas amount corresponding to the operating state from the ROM, and the amount of exhaust gas returned to the combustion chamber by the HPL device 40 and the LPL device 30 is determined. The opening degree of the HPL valve 42, the LPL valve 32, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 19, the nozzle vane 5, etc. is controlled so that the respective control target values are obtained.

  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 HPL 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 executing the PM regeneration process, the back pressure Increases the difference between the pressure on the upstream side of the HPL 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 HPL passage 41 (that is, in the vicinity of the connection portion with the intake passage 3). Become. If the pressure difference between the upstream and downstream of the HPL passage 41 becomes excessively large, it becomes difficult to control the HPL valve 42 with high accuracy, and there is a possibility that the control accuracy of the HPL 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 gas (external EGR gas) returned to the internal combustion engine 1 by the HPL device 40 and the LPL 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 gas amount There is a possibility that the total EGR gas amount obtained by summing the above becomes larger than a prescribed 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 this embodiment, when the exhaust throttle valve 19 is throttled along with the PM regeneration process, the external EGR gas amount is controlled only by the control of the LPL valve 32. In other words, during normal times when PM regeneration processing is not performed, the external EGR gas is supplied to the internal combustion engine 1 by appropriately using or switching the HPL device 40 and the LPL device 30 according to the operating state of the internal combustion engine 1 as described above. When the PM regeneration process is performed by restricting the exhaust throttle valve 19, the HPL valve 42 is temporarily fully closed and the external EGR gas is supplied to the internal combustion engine 1 using only the LPL device 30.

  Since the LPL 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 pressure difference between the upstream and downstream of the LPL passage 31. Don't get too big. Therefore, even when the PM regeneration process is being performed and the exhaust throttle valve 19 is throttled, the control accuracy of the LPL gas amount by the opening degree control of the LPL valve 32 can be sufficiently secured and supplied to the internal combustion engine 1. The amount of external EGR gas to be performed can be accurately controlled.

  At this time, the LPL 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 HPL gas amount according to the operating state of the internal combustion engine 1 and the specified value of the LPL gas amount). The LPL valve 32 is controlled so as to be smaller than the total. 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.

  Furthermore, in this embodiment, at this time, the exhaust Elevator valve 19 is not throttled by the total EGR gas amount that is the sum of the internal EGR gas amount and the external EGR gas amount (equal to the LPL gas amount in this embodiment). Less than the specified value of the total EGR gas amount at the normal time (the sum of the specified value of the HPL gas amount, the specified value of the LPL gas amount, and the specified value of the internal EGR gas amount according to the operating state of the internal combustion engine 1) Thus, the LPL valve 32 is controlled.

  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 LPL valve 32 is controlled so that the total amount of EGR gas during the PM regeneration process becomes smaller than the total amount of EGR gas at the normal time. An excessive increase in the amount of inactive components supplied to the 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 LPL gas amount) can be calculated based on, for example, the differential pressure between the upstream and downstream of the LPL passage 31 and the opening degree of the LPL 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 opening degree S. Here, the predetermined opening degree S means that the back pressure of the exhaust passage 4 when the exhaust throttle valve 19 is throttled is lower than a pressure at which sufficient control accuracy can be secured with respect to the control of the HPL gas amount by the HPL valve 42. This is the lower limit value of the opening of the exhaust throttle valve 19. That is, if the opening of the exhaust throttle valve 19 is an opening greater than the predetermined opening S (opening side opening), the back pressure in the exhaust passage 4 upstream from the exhaust throttle valve 19 will not be excessively high. Therefore, the pressure difference between the upstream and downstream of the HPL passage 41 does not become excessively large, and the amount of HPL gas can be controlled with sufficient accuracy by controlling the opening of the HPL valve 42. Conversely, when the opening of the exhaust throttle valve 19 is smaller than the predetermined opening S (opening on the closing side), the back pressure in the exhaust passage 4 upstream of the exhaust throttle valve 19 becomes excessively high, and the HPL passage The pressure difference between the upstream and downstream of 41 becomes excessively large, and it becomes difficult to accurately control the amount of HPL gas by controlling the opening degree of the HPL 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. When the actual EGR rate EGRa> the target EGR rate EGRtrg, the ECU 20 proceeds to step S108 and corrects the opening degree of the LPL valve 32 to the closed side. On the other hand, if the actual EGR rate EGRa <the target EGR rate EGRtrg, the ECU 20 proceeds to step S109 and corrects the opening of the LPL 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 process is executed as a case where the exhaust throttle valve 19 is throttled to the opening side closer to the closing degree than the predetermined opening degree S is exemplified, but the internal combustion engine 1 is warmed up in the cold state. 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 degree than the predetermined opening degree S, the HPL valve 42 is closed and only the LPL valve 32 is controlled to control the amount of external EGR gas. By controlling, it becomes possible to control EGR with high accuracy.

  Further, in the present embodiment, the configuration in which the HPL valve 42 is fully closed when the exhaust throttle valve 19 is throttled to the opening on the closing side from the predetermined opening S has been described. You may make it fix at a time. In this case, a constant amount of HPL gas is supplied to the internal combustion engine 1 through the HPL valve 42 having a fixed opening degree. However, since the amount of HPL gas is constant, the control of the external EGR gas amount is also performed. Is performed by controlling the opening of the LPL 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.

Explanation of symbols

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 LPL device 31 LPL passage 32 LPL valve 33 LPL cooler 40 HPL device 41 HPL passage 42 HPL 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;
An HPL passage that connects an exhaust passage upstream from the turbine and an intake passage downstream from the compressor, and an HPL valve that is provided in the HPL passage and changes the flow passage area of the HPL passage, are exhausted through the HPL passage. HPL means for guiding a part of the engine to the internal combustion engine;
An LPL passage that connects an exhaust passage downstream of the exhaust throttle valve and an intake passage upstream of the compressor, and an LPL valve that is provided in the LPL passage and changes the flow passage area of the LPL passage, via the LPL passage LPL means for guiding part of the exhaust to the internal combustion engine,
EGR control means for controlling the amount of exhaust gas returned to the internal combustion engine by controlling the opening degree of the HPL valve and the LPL valve;
With
The EGR control means substantially fixes the HPL valve at a predetermined opening (H) and opens the LPL when the opening of the exhaust throttle valve is throttled to an opening closer to the closing side than the predetermined opening (S). An EGR system for an internal combustion engine that controls the amount of exhaust gas returned to the internal combustion engine by controlling the opening of a valve. In claim 1,
The EGR system for an internal combustion engine, wherein the predetermined opening (H) is fully closed. In claim 1 or 2,
The EGR control means is an external exhaust that is returned to the internal combustion engine by the HPL means and the LPL means when the opening degree of the exhaust throttle valve is reduced to an opening degree that is closer to the closing side than the predetermined opening degree (S). The opening degree of the LPL valve is such that the amount of EGR gas is smaller than the normal amount of external EGR gas in which the opening degree of the exhaust throttle valve is not restricted to the opening degree closer to the closing side than the predetermined opening degree (S). System for controlling internal combustion 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 opening (S) is the case where 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 position than the predetermined opening (S) in order to promote the oxidation of PM 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 fuel gas and the amount of external EGR gas, is not throttled to the opening on the closing side of the exhaust throttle valve from the predetermined opening (S). An EGR system for an internal combustion engine that controls the opening of the LPL valve so as to be smaller than the total amount of EGR gas in a normal state. In claim 4,
When the exhaust throttle valve is throttled to an opening closer to the closing position than the predetermined opening (S) in order to promote the oxidation of PM 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 closing side than the predetermined opening (S). An EGR system for an internal combustion engine that controls the opening of the LPL valve so as to be smaller than a normal EGR rate that is not restricted by the opening. In claim 5 or 6,
The total EGR gas amount is calculated based on the difference between the intake air amount and the actual intake air amount when the opening degree of the exhaust throttle valve is fully opened and EGR is not performed by the HPL unit and the LPL unit. EGR system for internal combustion engines.

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