JP2012237290A - Exhaust gas recirculation flow control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid degradation of adjusting accuracy of an outer EGR quantity fed to a combustion chamber 22 in a concomitant use region of low pressure EGR and high pressure EGR.SOLUTION: A target value of an EGR ratio (hereinafter referred to as hgh pressure EGR ratio) in an after high pressure merging channel 12a and a target value of an EGR ratio (hereinafter referred to as low pressure EGR ratio) in an after low pressure merging channel 12b are set. A high pressure EGR actuator 48a is energized and operated so as to carry out feedback control of the EGR ratio of every time to the target value of the EGR ratio. A high and low pressure harmonized EGR control is carried out for energizing and operating a low pressure EGR actuator 52a so as to carry out feedback control of low pressure EGR ratio of every time to the target value of the low pressure EGR ratio.

Description

  The present invention relates to a supercharger for supercharging intake air supplied to an internal combustion engine, and an intake air connected to the internal combustion engine upstream of an exhaust turbine of the supercharger in an exhaust passage connected to the internal combustion engine. A high-pressure EGR passage that connects a downstream side of the turbocharger compressor in the passage, and a downstream side of the exhaust turbine in the exhaust passage and an upstream side of the compressor in the intake passage. An internal combustion engine comprising a low-pressure EGR passage, and a high-pressure EGR means and a low-pressure EGR means that are energized to adjust the flow rates of the high-pressure EGR and the low-pressure EGR that are recirculated to the intake passage through the high-pressure EGR passage and the low-pressure EGR passage The present invention relates to an exhaust gas recirculation control apparatus for an internal combustion engine that is applied to the combustion control system.

  As this type of control device, as seen in Patent Document 1 below, a part of the exhaust discharged from the internal combustion engine is respectively set as the high pressure EGR and the low pressure EGR via the high pressure EGR passage and the low pressure EGR passage. A device that performs external EGR control for returning to the intake passage is known.

  Specifically, this control device adjusts the low pressure EGR amount so that the flow rate of the low pressure EGR (hereinafter referred to as the low pressure EGR amount) becomes substantially constant regardless of the load of the internal combustion engine in the region where the high pressure EGR and the low pressure EGR are used together. Feed-forward control of the low-pressure EGR valve opening is performed. At the same time, the high pressure EGR valve opening for adjusting the flow rate of the high pressure EGR (hereinafter referred to as the high pressure EGR amount) is feedback-controlled to the target value so that the oxygen concentration in the exhaust gas becomes constant.

  However, in the above control device, there may occur a situation where the actual total EGR amount is insufficient with respect to the total EGR amount (added value of the low pressure EGR amount and the high pressure EGR amount) required to be supplied to the combustion chamber. Such a situation occurs, for example, in a situation where the required total EGR amount increases but the high pressure EGR valve opening is feedback controlled according to the shortage of the total EGR amount and reaches the maximum opening. This may occur in a situation where the forward-controlled low pressure EGR valve opening is not the maximum opening.

JP 2007-315371 A

  In order to solve these problems, the present inventor adjusts the opening degree of each of the high pressure EGR valve and the low pressure EGR valve in order to feedback control the total EGR amount to the target value in the region where the high pressure EGR and the low pressure EGR are used together. Thought to do. However, this has the technical problems described below.

  Due to the low pressure EGR passage being usually longer than the high pressure EGR passage, the low pressure EGR valve is longer than the time from when the high pressure EGR valve opening is changed until the effect appears in the intake air supplied to the combustion chamber. A phenomenon (the response delay of the low pressure EGR) in which the time from when the opening degree is changed until the influence appears in the intake air supplied to the combustion chamber becomes longer occurs. Then, due to the response delay of the low-pressure EGR, so-called hunting occurs in which the total EGR amount periodically fluctuates around the target value, and the adjustment accuracy of the external EGR may be reduced.

  The cause of the occurrence of this hunting will be described. First, in a situation where the total EGR amount is smaller than the target value, the respective opening degrees of the high pressure EGR valve and the low pressure EGR valve are set so as to increase the high pressure EGR amount and the low pressure EGR amount. Adjusted. Then, although the influence of the increase in the high pressure EGR amount appears first and the total EGR amount rises to the target value, the influence of the increase in the low pressure EGR amount appears later due to the response delay of the low pressure EGR described above. As a result, a so-called overshoot in which the total EGR amount exceeds the target value occurs.

  Then, the respective opening degrees of the high pressure EGR valve and the low pressure EGR valve are adjusted so as to decrease the high pressure EGR amount and the low pressure EGR amount. By this adjustment, the influence of the decrease in the high-pressure EGR amount appears first and the total EGR amount decreases to the target value, but thereafter, the influence of the decrease in the low-pressure EGR amount appears delayed due to the response delay of the low-pressure EGR. As a result, a so-called undershoot occurs in which the total EGR amount falls below the target value. Hunting occurs when such overshoot and undershoot are repeated.

  If the adjustment accuracy of the external EGR is reduced due to the occurrence of hunting, the combustion state of the internal combustion engine cannot be made appropriate, and the exhaust characteristics and generated torque of the internal combustion engine cannot be made appropriate. There is.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to suitably avoid a decrease in the adjustment accuracy of the external EGR amount supplied to the combustion chamber in the combined region of the low pressure EGR and the high pressure EGR. An object of the present invention is to provide an exhaust gas recirculation control device for an internal combustion engine.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to a first aspect of the present invention, there is provided a supercharger that is provided between an intake passage and an exhaust passage connected to an internal combustion engine and that supercharges intake air supplied to the internal combustion engine; A high-pressure EGR passage connecting the upstream side of the exhaust turbine of the supercharger and the downstream side of the compressor of the supercharger in the intake passage; and the downstream side of the exhaust turbine and the intake air of the exhaust passage. A low-pressure EGR passage that connects an upstream side of the compressor in the passage, a high-pressure EGR means that is energized to adjust a flow rate of the high-pressure EGR that is recirculated to the intake passage through the high-pressure EGR passage, The present invention is applied to a combustion control system for an internal combustion engine comprising low-pressure EGR means that is energized to adjust the flow rate of low-pressure EGR that is recirculated to the intake passage through a low-pressure EGR passage. Of the passages, the downstream side of the connection portion with the high pressure EGR passage is defined as a high pressure merged passage, and the intake passage is downstream of the connection portion with the low pressure EGR passage and the high pressure EGR passage. Is defined as a post-low pressure merge passage, and the oxygen concentration or EGR rate in the intake air is defined as an intake parameter, based on the operating state of the internal combustion engine, the post-high pressure merge passage and the low pressure Target value setting means for setting each of the target value after the high pressure merge and the target value after the low pressure merge as the target value of the intake parameter in each of the merged passages, and each of the post-high pressure merge passage and the low-pressure merge passages Control value calculation means for calculating each of the control value after high-pressure merging and the control value after low-pressure merging as the value of each intake parameter, and the control value after the high-pressure merging By energizing the high-pressure EGR means to perform feedback control to the target value after the high-pressure merging, and energizing the low-pressure EGR means to feedback control the control value after the low-pressure merging to the target value after the low-pressure merging, The intake passage is provided with control means for recirculating both the high pressure EGR and the low pressure EGR.

  In the above invention, in the combined region of the high pressure EGR and the low pressure EGR, the post-high pressure target value in the post-high-pressure merge passage in the intake passage and the low-pressure post-merging target value in the post-low-pressure merge passage upstream of the high-pressure merge passage in the intake passage. Set. The control value after high-pressure merging is feedback-controlled to the target value after high-pressure merging, and the control value after low-pressure merging is feedback-controlled to the target value after low-pressure merging.

  For this reason, for example, compared with the case where both the low pressure EGR means and the high pressure EGR means are energized and operated with only the control value after the high pressure merging as the target of feedback control, the low pressure EGR and the high pressure EGR are respectively performed by the low pressure EGR means and the high pressure EGR means. After the respective flow rates are changed, the time until the influence of the flow rate change appears on the respective feedback control targets of these EGR means can be shortened. Thereby, it is possible to suppress the influence of the change in the flow rate of the EGR by one of the high pressure EGR means and the low pressure EGR means on the adjustment of the flow rate of the other, and consequently the adjustment accuracy of the external EGR supplied to the internal combustion engine. The decrease can be preferably avoided.

  According to a second aspect of the present invention, in the first aspect of the invention, the flow rate of EGR required to set the post-high pressure merge control value as the post-high pressure merge target value is set to each of the high pressure EGR and the low pressure EGR. The target value setting means is configured to assign each of the target value after high-pressure merging and the target value after low-pressure merging based on the flow rate of high pressure EGR and the flow rate of low pressure EGR allocated by the allocating unit. It is characterized by setting.

  In the above invention, by providing the allocating means, it is possible to set appropriate post-high-pressure merging target value and low-pressure merging target value for setting the post-high-pressure merging control value as the high-pressure merging target value.

  According to a third aspect of the present invention, in the second aspect of the present invention, the high pressure upper limit value setting means for variably setting a high pressure upper limit value that is an upper limit value of the flow rate of the high pressure EGR based on the operating state of the internal combustion engine is further provided. The allocating means allocates the flow rate of the high pressure EGR as a value equal to or less than the set high pressure upper limit value, and determines the control value after the high pressure merging from the flow rate of EGR required to set the control value after the high pressure merging as the target value after the high pressure merging The flow rate of the low pressure EGR is set based on a value obtained by subtracting the flow rate of the allocated high pressure EGR.

  When the flow rate of the high pressure EGR is increased, the flow rate of the exhaust gas that passes through the exhaust turbine is decreased, so that the exhaust energy for supercharging the intake air is decreased. When the exhaust energy is reduced, the degree of supercharging of the intake air by the supercharger is reduced, so that the amount of fresh air filled in the internal combustion engine is reduced and the generated torque of the internal combustion engine may be reduced.

  In this regard, in the above invention, the flow rate of the high pressure EGR is assigned as a value equal to or less than the high pressure upper limit value. For this reason, it is possible to suitably suppress a decrease in the generated torque of the internal combustion engine while returning the external EGR amount to the intake passage.

  Furthermore, the flow rate of the low pressure EGR is set based on a value obtained by subtracting the flow rate of the high pressure EGR from the flow rate of the EGR required to set the post-high pressure merge control value as the target value after the high pressure merge. For this reason, even when the flow rate of the high pressure EGR is limited by the high pressure upper limit value, it is possible to secure the external EGR necessary for controlling the post-high pressure merge control value to the post-high pressure merge target value as much as possible.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the low pressure upper limit value setting means for variably setting the low pressure upper limit value, which is the upper limit value of the flow rate of the low pressure EGR, is further provided based on the operating state of the internal combustion engine. The sum of the flow rate of the high-pressure EGR and the flow rate of the low-pressure EGR allocated by the allocating means is the sum of the high-pressure upper limit value and the low-pressure upper limit value, and the control value after high-pressure merging is set as the target value after high-pressure merging. When it is determined that the required EGR flow rate exceeds the sum of the high pressure upper limit value and the low pressure upper limit value, the target value after the high pressure merging can be realized by the sum of the high pressure upper limit value and the low pressure upper limit value. And a resetting means for resetting the control value after the high-pressure merge.

  There is usually an upper limit for the flow rate of the low pressure EGR that can be recirculated to the intake passage. Here, when the flow rate of the high pressure EGR is limited by the high pressure upper limit value and the flow rate of the low pressure EGR is limited by the low pressure upper limit value, it is required to set the post-high pressure merge control value as the target value after the high pressure merge. The flow rate of EGR cannot be ensured by the high pressure EGR and the low pressure EGR.

  For this reason, in the above invention, when it is determined that the flow rate of EGR required to set the control value after high-pressure merging as the target value after high-pressure merging exceeds the sum of the high-pressure upper limit value and the low-pressure upper limit value, The value is reset as the post-high pressure merge control value that can be realized by the sum of the high pressure upper limit value and the low pressure upper limit value.

  The invention according to claim 5 is the invention according to claim 3 or 4, wherein the high pressure upper limit value setting means sets the high pressure upper limit value low when it is determined that the required torque of the internal combustion engine increases rapidly. Features.

  The increase in the required torque of the internal combustion engine is usually dealt with by increasing the degree of supercharging of the intake air by the supercharger and increasing the amount of fresh air filled in the combustion chamber. Here, in the above-described invention, the high pressure upper limit value is set low in a situation where it is required to increase the degree of supercharging of the intake air. For this reason, the exhaust gas to be supplied to the exhaust turbine can be ensured appropriately, and a decrease in the generated torque of the internal combustion engine can be suitably suppressed.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the high-pressure EGR means is an electronically controlled type that is provided in the high-pressure EGR passage and adjusts the area of the passage. It is a valve body, and the low-pressure EGR means is an electronically controlled valve body that is provided in the low-pressure EGR passage and adjusts the area of the passage.

1 is a system configuration diagram according to a first embodiment. FIG. The flowchart which shows the procedure of the high-low pressure cooperative EGR control concerning the embodiment. The flowchart which shows the procedure of the high / low pressure cooperative EGR control concerning 2nd Embodiment.

(First embodiment)
DESCRIPTION OF EMBODIMENTS Hereinafter, a first embodiment that embodies an in-vehicle control device according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a system configuration diagram according to the present embodiment.

  The illustrated engine 10 is a compression ignition internal combustion engine (diesel engine). In the intake passage 12 of the engine 10, an air flow meter 14 that detects the amount of air that is sucked (new air amount) in order from the upstream side, an intercooler 18 that cools the intake air supercharged by a turbocharger 16, which will be described later, Is provided with an intake throttle valve 20 whose opening is adjusted by an actuator (intake side actuator 20a) such as a DC motor. The intake side actuator 20a has a function of detecting the opening degree of the intake throttle valve 20.

  A downstream side of the intake throttle valve 20 in the intake passage 12 is connected to a combustion chamber 22 of each cylinder of the engine 10. An intake pressure sensor 24 that detects the pressure (supercharging pressure) of intake air flowing through the intake passage 12 and an intake air flow that flows through the intake passage 12 (intake manifold) are disposed downstream of the intake throttle valve 20 in the intake passage 12. An intake air temperature sensor 26 for detecting the temperature is provided.

  The combustion chamber 22 of each cylinder of the engine 10 is provided with an electromagnetically driven fuel injection valve 28 that projects into the combustion chamber 22. High pressure fuel (light oil) is supplied to the fuel injection valve 28 from a pressure accumulation container (common rail) (not shown), and high pressure fuel is injected and supplied from the fuel injection valve 28 to the combustion chamber 22.

  The intake port and the exhaust port of each cylinder of the engine 10 are opened and closed by an intake valve 30 and an exhaust valve 32, respectively. Here, intake air or the like cooled by the intercooler 18 by opening the intake valve 30 is introduced into the combustion chamber 22, and the introduced intake air and the fuel injected and supplied from the fuel injection valve 28 are used for combustion. . The intake air and fuel that have been used for combustion are discharged into the exhaust passage 34 as exhaust gas by opening the exhaust valve 32. A crank angle sensor 38 that detects the rotation angle of the crankshaft 36 is provided near the output shaft (crankshaft 36) of the engine 10.

  A turbocharger 16 is provided between the intake passage 12 and the exhaust passage 34. The turbocharger 16 includes an intake air compressor 16a provided in the intake passage 12, an exhaust turbine 16b provided in the exhaust passage 34, and a rotating shaft 16c that connects these. Specifically, the exhaust turbine 16b is rotated by the energy of the exhaust gas flowing through the exhaust passage 34, and the rotational energy is transmitted to the intake compressor 16a via the rotary shaft 16c, and the intake air is compressed by the intake compressor 16a. That is, the intake air is supercharged by the turbocharger 16. In the present embodiment, the turbocharger 16 is assumed to be capable of adjusting the supercharging pressure of intake air. Specifically, for example, supercharging is performed by adjusting the opening of a variable vane (not shown) of the turbocharger 16. It is assumed that the pressure can be adjusted.

  In the exhaust passage 34, on the downstream side of the turbocharger 16 (exhaust turbine 16b), a purification device 40 for purifying exhaust and an A / F sensor 42 for detecting oxygen concentration in the exhaust are provided in order from the upstream side. It has been. In the present embodiment, as the purification device 40, a DPF (diesel particulate filter) that collects PM (smoke) in the exhaust, a NOx catalyst that purifies NOx in the exhaust, and an oxidation that purifies HC and CO in the exhaust. A catalyst is assumed.

  A part of the exhaust gas discharged to the exhaust passage 34 is returned to the intake passage 12 via the high pressure EGR passage 44 or the low pressure EGR passage 46 as an exhaust gas recirculation passage. Specifically, in the exhaust passage 34, the upstream side of the exhaust turbine 16 b is connected to the downstream side of the intake throttle valve 20 in the intake passage 12 (upstream side of the intake pressure sensor 24) via the high pressure EGR passage 44. The high pressure EGR passage 44 is provided with a high pressure EGR valve 48 that adjusts the flow passage area of the passage. Specifically, the high-pressure EGR valve 48 is provided in the vicinity of the connection portion with the intake passage 12 in the high-pressure EGR passage 44, and its opening degree (high-pressure EGR opening 48) by an actuator such as a DC motor (high-pressure EGR actuator 48 a). This is an electronically controlled valve body whose degree is adjusted. A part of the exhaust discharged into the exhaust passage 34 is cooled by the high pressure EGR cooler 50 in accordance with the high pressure EGR opening, and then supplied to the intake passage 12 as an external EGR (high pressure EGR). The high pressure EGR actuator 48a has a function of detecting the high pressure EGR opening. Further, an exhaust pressure sensor 51 that detects the pressure of the exhaust gas is provided on the upstream side of the connection portion with the high pressure EGR passage 44 in the exhaust passage 34.

  On the other hand, the downstream side of the exhaust turbine 16 b in the exhaust passage 34 is connected to the upstream side of the intake compressor 16 a in the intake passage 12 via the low pressure EGR passage 46. The low pressure EGR passage 46 is provided with a low pressure EGR valve 52 that adjusts the flow passage area of the passage. Specifically, the low pressure EGR valve 52 is provided in the vicinity of the connection portion with the intake passage 12 in the low pressure EGR passage 46, and its opening (low pressure EGR opening) is achieved by an actuator (low pressure EGR actuator 52a) such as a DC motor. This is an electronically controlled valve body whose degree is adjusted. Depending on the low pressure EGR opening, a part of the exhaust discharged to the exhaust passage 34 is cooled by the low pressure EGR cooler 54 and then supplied to the intake passage 12 as external EGR (low pressure EGR). The low pressure EGR actuator 52a has a function of detecting the low pressure EGR opening. The low pressure EGR passage 46 is provided with a differential pressure sensor 53 that detects a differential pressure across the low pressure EGR valve 52.

  An exhaust throttle valve 56 that adjusts the flow area of the exhaust passage 34 is provided on the downstream side of the connection portion between the passage and the low-pressure EGR passage 46 in the exhaust passage 34. The exhaust throttle valve 56 is an electronically controlled valve body whose opening degree is adjusted by an actuator (exhaust side actuator 56a) such as a DC motor. The exhaust side actuator 56a has a function of detecting the opening degree of the exhaust throttle valve 56.

  In the present embodiment, the downstream side of the connection portion with the high pressure EGR passage 44 in the intake passage 12 (including the intake manifold) is referred to as a high pressure merged passage 12a, and the intake passage 12 is connected to the low pressure EGR passage 46. The downstream side of the part and the upstream side of the connecting part with the high pressure EGR passage 44 will be referred to as a low pressure merged passage 12b. The intake air refers to a gas including fresh air and external EGR.

  An electronic control unit (ECU 58) whose operation target is an engine system is configured mainly by a microcomputer including a known CPU, ROM, RAM, and the like. The ECU 58 includes an accelerator sensor 60 that detects an accelerator operation amount (depression amount) of the driver, an air flow meter 14, an intake pressure sensor 24, an intake air temperature sensor 26, a crank angle sensor 38, an A / F sensor 42, and an exhaust pressure sensor 51. The intake side actuator 20a, the high pressure EGR actuator 48a, the low pressure EGR actuator 52a, the differential pressure sensor 53, and the output signal of the exhaust side actuator 56a are sequentially input. The ECU 58 executes various control programs stored in the ROM on the basis of the input signals from the respective sensors, so that the fuel injection control by the fuel injection valve 28, the supercharging pressure control by the turbocharger 16, and the like are performed. The combustion control is performed.

  The fuel injection control will be described. First, the required torque of the engine 10 (hereinafter referred to as engine required torque) is calculated from the engine rotation speed based on the output value of the crank angle sensor 38 and the accelerator operation amount based on the output value of the accelerator sensor 60. Is calculated. Here, normally, the larger the accelerator operation amount, the larger the engine required torque is set. Then, a command value for the fuel injection valve 28 is calculated based on the set engine required torque, and the fuel injection valve 28 is energized based on the command value. As a result, an amount of fuel corresponding to the command value is injected from the fuel injection valve 28.

  Further, in the supercharging pressure control, the turbocharger 16 is energized so as to control the supercharging pressure based on the output value of the intake pressure sensor 24 to the target value. Here, the target value of the supercharging pressure is a value set in advance based on the intake air amount to be supplied to the combustion chamber 22. Specifically, for example, the boost pressure is set higher as the engine required torque is larger.

  In particular, the ECU 58 performs the exhaust gas recirculation control for energizing the high pressure EGR actuator 48a and the like so as to adjust the flow rate of the low pressure EGR (hereinafter referred to as the low pressure EGR amount) and the flow rate of the high pressure EGR (hereinafter referred to as the high pressure EGR amount). External EGR control) is performed. The external EGR control is performed for the purpose of reducing nitrogen oxide (NOx) or the like in the exhaust discharged from the engine 10.

  In the present embodiment, as external EGR control, high-pressure EGR control (represented as HPL in the figure) for returning only the high-pressure EGR to the intake passage 12 based on the operating state of the engine 10 (engine rotational speed NE and engine required torque Trq). High-low pressure cooperative EGR control (represented as HPL & LPL in the figure) that recirculates both the high-pressure EGR and low-pressure EGR and low-pressure EGR control (represented as LPL in the figure) that recirculates only the low-pressure EGR are selected and executed.

  More specifically, the high pressure EGR control is performed when it is determined that the engine required torque Trq is in a low load region equal to or less than the first specified torque Tr1, and the engine required torque Trq exceeds the first specified torque Tr1. In addition, when it is determined that the intermediate load region is equal to or less than the second specified torque Tr2 larger than the first specified torque Tr1, the high-low pressure cooperative EGR control is performed. Further, when it is determined that the engine required torque Trq is in a high load region where the engine required torque Trq exceeds the second specified torque Tr2, low pressure EGR control is performed.

  Here, the method of selecting one of the high pressure EGR control, the high and low pressure cooperative EGR control, and the low pressure EGR control is adopted while appropriately securing the external EGR to be recirculated to the intake passage 12 in order to reduce NOx and the like. This is to avoid a decrease in the generated torque of the engine 10.

  In other words, in the high load region, the required engine torque becomes large, so that it is required to increase the supercharging pressure in order to increase the amount of fresh air charged in the combustion chamber 22. If the amount of high-pressure EGR is increased here, the amount of exhaust gas supplied to the exhaust turbine 16b decreases, so that the supercharging pressure cannot be increased, and the generated torque of the engine 10 decreases. In order to avoid such a problem, in the high load region, low pressure EGR control is performed to recirculate a part of the exhaust on the downstream side of the exhaust turbine 16b as low pressure EGR.

  In the middle load region, the amount of exhaust to be supplied to the exhaust turbine 16b is usually smaller than that in the high load region. For this reason, high-low pressure cooperative EGR control is performed in order to secure external EGR by refluxing high-pressure EGR together with low-pressure EGR.

  Further, in the low load region, the low pressure EGR is cooled by both the low pressure EGR cooler 54 and the intercooler 18, so that the temperature of the low pressure EGR is low, and the combustion state is deteriorated by the supply of the low pressure EGR. Further, since the differential pressure across the entrance and exit of the low pressure EGR passage 46 is small, the low pressure EGR amount cannot be secured. In view of these, high pressure EGR control is performed.

  Next, the high / low pressure cooperative EGR control according to the present embodiment will be described in detail.

In the present embodiment, first, a target value (hereinafter referred to as a target EGR rate) of an EGR rate (hereinafter referred to as an EGR rate) in the post-high pressure merging passage 12a is set as a target value after high pressure merging (refer to a β portion in FIG. 1). A target value (hereinafter referred to as a target low pressure EGR rate) of an EGR rate (hereinafter referred to as a low pressure EGR rate) in the low-pressure merged passage 12b is set as a post-merging target value (see α part in the figure). Here, the EGR rate is a ratio (percentage) of an added value (total EGR amount) of the high pressure EGR amount and the low pressure EGR amount with respect to the intake air amount (filled intake air amount) supplied to the combustion chamber 22. Specifically, when the low pressure EGR amount is Megrlp, the high pressure EGR amount is Meghrp, and the fresh air amount is Mair, the EGR rate is defined by the following equation (c1).
EGR rate = (Megrlp + Megrhp)
/ (Mair + Megrlp + Megrhp) × 100 (c1)
The low pressure EGR rate is the ratio (percentage) of the low pressure EGR amount to the sum of the fresh air amount and the low pressure EGR amount, and is specifically defined by the following equation (c2).
Low pressure EGR rate = Megrlp / (Mair + Megrlp) × 100 (c2)
Then, the high pressure EGR actuator 48a is energized to feedback control the value (actual EGR rate) of the EGR rate as the post-high pressure merge control value to the target EGR rate, and the low pressure EGR rate as the post-low pressure merge control value The low pressure EGR actuator 52a is energized so as to feedback control the value (actual low pressure EGR rate) to the target low pressure EGR rate. The reason why such a control method is adopted as the high-low pressure cooperative EGR control is to avoid a decrease in the adjustment accuracy of the external EGR amount due to the response delay of the low-pressure EGR.

  Here, the response delay of the low pressure EGR means that the low pressure EGR passage 46 is longer than the high pressure EGR passage 44 and the distance from the connection point between the intake passage 12 and the low pressure EGR passage 46 to the combustion chamber 22 is the intake passage 12. From the change of the high-pressure EGR opening degree to the influence of the change in the intake air supplied to the combustion chamber 22 due to the fact that it is longer than the distance from the connection point between the high-pressure EGR passage 44 and the combustion chamber 22. This is a phenomenon in which the time from when the low pressure EGR opening is changed to when the influence appears in the intake air supplied to the combustion chamber 22 becomes longer than the time.

  Before describing the procedure of the high / low pressure cooperative EGR control process, the calculation process (flow rate concentration calculation process) of various parameter values necessary for the calculation of this process will be described. In the present embodiment, as shown in FIG. 1, as the values of the above parameters, the high-pressure EGR amount Megrhp, the low-pressure EGR amount Megrlp, the intake air amount flowing through the low-pressure merging passage 12b (the low-pressure merging intake air amount Mdth), the charged intake air The amount Mcld, the oxygen concentration in the high pressure EGR (high pressure outlet O2 concentration Cegrhp), the oxygen concentration in the low pressure EGR (low pressure outlet O2 concentration Cegrlp), and the oxygen concentration in the intake air flowing through the post-low pressure merge passage 12b (O2 concentration after low pressure merge) The oxygen concentration in the intake air supplied to the combustion chamber 22 (intake O2 concentration) and the oxygen concentration in the exhaust gas exhausted from the combustion chamber 22 (exhaust O2 concentration) are assumed.

  The flow rate calculation method among these values will be described. Specifically, for example, the high pressure EGR amount Megrhp is determined based on the inlet / outlet differential pressure of the high pressure EGR passage 44 and the high pressure EGR opening (the flow passage area of the high pressure EGR passage 44). What is necessary is just to calculate. Here, the inlet / outlet differential pressure may be calculated as a difference between the exhaust pressure calculated from the output value of the exhaust pressure sensor 51 and the supercharging pressure. The low pressure EGR amount Megrlp may be calculated based on the differential pressure across the low pressure EGR valve 52 calculated from the output value of the differential pressure sensor 53 and the low pressure EGR opening (the flow area of the low pressure EGR passage 46). . Then, the charging intake air amount Mcld may be calculated based on the intake air temperature calculated from the boost pressure and the output value of the intake air temperature sensor 26.

  Here, the low-pressure merged intake air amount Mdth is equal to the added value of the fresh air amount Mail and the low-pressure EGR amount Megarlp, and the low-pressure merged intake air amount Mdth and the high-pressure EGR amount Megarhp are equal to the charged intake air amount Mcld. It is said. Here, the fresh air amount Mail may be calculated based on the output value of the air flow meter 14.

  Next, the calculation method of the O2 concentration will be described. The high-pressure outlet O2 concentration Cegrhp, the low-pressure outlet O2 concentration Cegrlp, the low-pressure merged O2 concentration, the intake O2 concentration, and the exhaust O2 concentration are predetermined values for estimating the values of these parameters. Estimate each time by model.

  Specifically, for example, a process for estimating the exhaust O2 concentration based on the charged intake air amount Mcld, the fuel injection amount (or engine required torque) from the fuel injection valve 28, the intake O2 concentration, and the like, and the exhaust O2 concentration and the high pressure EGR amount Megrhp Processing for estimating the high pressure outlet O2 concentration Cegrp based on the exhaust gas O2 concentration, the low pressure EGR amount Megagrp, etc., the processing for estimating the low pressure outlet O2 concentration Cegrlp, the high pressure EGR amount Megagrp, the high pressure outlet O2 concentration Ceghrp, The process of estimating the intake air O2 concentration based on the intake air amount Mdth and the O2 concentration after low pressure merging, etc., and after the low pressure merging based on the low pressure EGR amount Megrlp, the low pressure outlet O2 concentration Cegrlp, the fresh air amount Mail, the oxygen concentration Cair in the fresh air, etc. The respective O2 concentrations are calculated by processing for estimating the O2 concentration. Here, the oxygen concentration Cair in the fresh air may be a fixed value set in advance, for example, or may be a detection value of a sensor that detects the oxygen concentration. According to such a calculation method, it is possible to calculate each O2 concentration each time while taking into account the effect that the exhaust discharged from the combustion chamber 22 is returned to the intake passage 12 via the high pressure EGR passage 44 and the low pressure EGR passage 46. It becomes.

  Then, the actual EGR rate and the actual low pressure EGR rate are calculated using the flow rate and the O2 concentration.

  FIG. 2 shows a procedure of high / low pressure cooperative EGR control processing according to the present embodiment. This process is executed by the ECU 58 at a predetermined cycle, for example.

  In this series of processing, in step S10, the target EGR rate (0% ≦ target EGR rate ≦ 100%) is variably set based on the engine speed NE and the fuel injection amount Q (or the engine required torque Trq). The target EGR rate may be set using a map that defines the target EGR rate associated with the engine speed NE and the fuel injection amount Q. Here, the target EGR rate of the above map is such that the smoke and NOx emission amount is less than or equal to a prescribed amount in a state where a sufficient amount of time has passed since the control amounts of various actuators for combustion control are fixed (steady state). The EGR rate for improving the combustion state of the engine 10 is adapted in advance through experiments or the like.

In the following step S12, the charged intake air amount Mcld is calculated. In step S14, a target value (target total EGR amount) of the total EGR amount supplied to the combustion chamber 22 is calculated based on the target EGR rate and the charged intake air amount Mcld. Here, the target total EGR amount is a total EGR amount required to set the actual EGR rate (control value after high-pressure merging) as the target EGR rate (target value after high-pressure merging). calculated by c3).
Target total EGR amount = (Target EGR rate / 100) × Mcld (c3)
In the subsequent step S16, the target value (target high pressure EGR amount) of the high pressure EGR amount Megrhp is variably set based on the engine speed NE and the fuel injection amount Q from the fuel injection valve 28. Here, the target high pressure EGR amount is a part of the target total EGR amount, and is set using a map in which the target high pressure EGR amount is related to the engine speed NE and the fuel injection amount Q. To do. Note that the target high pressure EGR amount may be set to decrease as the engine required torque Trq increases, for example.

  In the subsequent step S18, the upper limit value of the high pressure EGR amount (high pressure upper limit value ≧ 0) is variably set. This process is a process for avoiding a decrease in the generated torque of the engine 10 together with the processes of steps S20 and S22 described later. That is, if the amount of high-pressure EGR is increased, the amount of exhaust gas supplied to the exhaust turbine 16b is decreased, so that the supercharging pressure may be lowered. In this case, drivability may be reduced due to a decrease in the generated torque of the engine 10. For this reason, by setting the high pressure upper limit value, a decrease in the supercharging pressure is avoided, and a decrease in the generated torque of the engine 10 is avoided. Here, the high pressure upper limit value may be specifically set using, for example, a map in which the high pressure upper limit value associated with the engine rotational speed NE and the fuel injection amount Q is defined.

  Here, in the present embodiment, when it is determined that the engine required torque Trq has increased rapidly (when the vehicle is accelerating), the setting is made at the time of required torque rapid increase in which the high pressure upper limit value is set low. This is a setting for suppressing a decrease in the generated torque of the engine 10 during a sudden change. That is, since the high pressure upper limit value is determined in a steady state, the high pressure upper limit value set in step S18 may not be an appropriate value in a transient state such as when the engine required torque is suddenly increased. For this reason, according to the required torque sudden change setting, the exhaust to be supplied to the exhaust turbine 16b is appropriately ensured when the engine required torque is rapidly increased. Here, whether or not the engine required torque has rapidly increased may be determined, for example, by whether or not the increasing speed of the accelerator operation amount (or the command value of the fuel injection amount Q) is equal to or higher than a specified speed (> 0).

  In step S20, it is determined whether or not the target high pressure EGR amount is equal to or less than the high pressure upper limit value. If it is determined in step S20 that the target high pressure EGR amount exceeds the high pressure upper limit value, the process proceeds to step S22, where the target high pressure EGR amount is limited by the high pressure upper limit value. That is, the target high pressure EGR amount is set as the high pressure upper limit value.

  When an affirmative determination is made in step S20 or when the process of step S22 is completed, the process proceeds to step S24, where the target value of the low pressure EGR amount (the target low pressure EGR amount) is based on the target total EGR amount and the target high pressure EGR amount. ) Is set. This process is a process for allocating an amount of the target total EGR amount other than the amount allocated to the target high pressure EGR amount to the target low pressure EGR amount. In the present embodiment, the target low pressure EGR amount is set as a value obtained by subtracting the target high pressure EGR amount from the target total EGR amount.

  In the subsequent step S26, an upper limit value of the low pressure EGR that can be supplied to the intake passage 12 (low pressure upper limit value> 0) is set. Here, the low pressure upper limit value may be set using a map in which the low pressure upper limit value associated with the engine speed NE and the fuel injection amount Q is defined.

  In a succeeding step S28, it is determined whether or not the target low pressure EGR amount is equal to or lower than the low pressure upper limit value. If it is determined in step S28 that the target low pressure EGR amount exceeds the low pressure upper limit value, the process proceeds to step S30, where the target low pressure EGR amount is limited by the low pressure upper limit value. That is, the target low pressure EGR amount is set to the low pressure upper limit value.

  When an affirmative determination is made in step S28 or when the process of step S30 is completed, the target low pressure EGR rate is set using the above equation (c2) in step S32. As a result, at least part or all of the target high pressure EGR amount exceeding the high pressure upper limit value is compensated by the low pressure EGR.

  When the target low pressure EGR amount is limited by the low pressure upper limit value in step S30, the target low pressure EGR amount is changed from the initial value. Therefore, the target EGR rate is reset to a target EGR rate that can be realized when the sum of the high pressure EGR amount and the low pressure EGR amount is the sum of the high pressure upper limit value and the low pressure upper limit value. Specifically, the target EGR rate is reset using the above equation (c1).

  In the subsequent step S34, the low pressure EGR actuator 52a is energized to feedback control the actual low pressure EGR rate to the target low pressure EGR rate, and the high pressure EGR actuator 48a is energized to feedback control the actual EGR rate to the target EGR rate. Specifically, for example, the feedback operation amount of these actuators is calculated by proportional-integral control based on these control amounts, and the actuator is energized based on the calculated feedback operation amounts. Thereby, when the actual EGR rate is higher than the target EGR rate, the high-pressure EGR opening is reduced and the amount of high-pressure EGR is reduced. When the actual low-pressure EGR rate is higher than the target low-pressure EGR rate, the low-pressure EGR opening is small. As a result, the amount of low-pressure EGR decreases.

  In addition, when the process of step S34 is completed, this series of processes is once complete | finished.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) A value obtained by subtracting the target high pressure EGR amount from the total target EGR amount is set as the target low pressure EGR amount. Therefore, the target total EGR amount required for making the actual EGR rate the target EGR rate can be appropriately allocated to each of the target high pressure EGR amount and the target low pressure EGR amount.

  (2) In the combined region of high pressure EGR and low pressure EGR, in order to feedback control the actual EGR rate to the target EGR rate, to energize the high pressure EGR actuator 48a, and to feedback control the actual low pressure EGR rate to the target low pressure EGR rate. Then, high-low pressure cooperative EGR control for energizing the low-pressure EGR actuator 52a was performed. Thereby, the fall of the adjustment precision of external EGR supplied to engine 10 can be avoided suitably.

  (3) When it is determined that the target high pressure EGR amount exceeds the high pressure upper limit value, the target high pressure EGR amount is set as the high pressure upper limit value. Thereby, it is possible to suitably suppress a decrease in the generated torque of the engine 10 while returning the external EGR amount to the intake passage 12.

  Moreover, if the high pressure upper limit value is a value corresponding to an opening smaller than the upper limit value of the high pressure EGR opening, the high pressure EGR opening is saturated at the upper limit value in the combined region of the low pressure EGR and the high pressure EGR. It can also be avoided.

  (4) When it is determined that the engine required torque has suddenly increased, a setting is made at the time of required torque rapid increase to set the high pressure upper limit value low. As a result, the exhaust to be supplied to the exhaust turbine 16b can be appropriately ensured under a situation where it is required to increase the supercharging pressure, and a decrease in the generated torque of the engine 10 can be more suitably avoided. it can.

  (5) When it is determined that the target high pressure EGR amount exceeds the high pressure upper limit value, and the target low pressure EGR amount is determined to exceed the low pressure upper limit value, the target EGR rate is set to the target high pressure EGR amount and the target low pressure EGR amount. The target EGR rate that was realizable when the sum was the sum of the high pressure upper limit value and the low pressure upper limit value was reset. For this reason, the target EGR rate can be appropriately set according to the change in the total EGR amount that can be actually supplied to the combustion chamber 22.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the present embodiment, the intake O2 concentration is employed as the target value after high pressure merging, and the O2 concentration after low pressure merging is employed as the target value after low pressure merging (see the α and β parts in FIG. 1 above). Then, the value of each intake O2 concentration (actual intake O2 concentration) is adopted as the control value after the high pressure merge, and the value of each O2 concentration after low pressure merge (the O2 concentration after the actual low pressure merge) is adopted as the control value after the low pressure merge. To do. Here, the intake O2 concentration is adopted in order to control the NOx emission amount with high accuracy in view of the fact that this concentration shows a strong correlation with the NOx emission amount of the engine 10.

  FIG. 3 shows a procedure of external EGR control processing including high / low pressure cooperative EGR control processing according to the present embodiment. This process is executed by the ECU 58 at a predetermined cycle, for example. In FIG. 3, the same steps as those shown in FIG. 2 are given the same step numbers for the sake of convenience.

  In this series of processes, in step S10a, a process of variably setting a target value of intake air O2 concentration (target intake air O2 concentration) based on the engine speed NE and the fuel injection amount Q (or engine required torque Trq) is performed. Here, the target intake O2 concentration may be set using a map in which the target intake O2 concentration associated with the engine rotational speed NE and the fuel injection amount Q is defined. Here, the target intake air O2 concentration in the map may be adapted by a method similar to the method in step S10 of FIG.

  After the process of step S10a is completed, the target high pressure EGR amount is variably set in step S16 via the process of step S12. In this embodiment, the actual intake O2 concentration calculated by the flow rate concentration calculation process using the low-pressure merged O2 concentration, the high-pressure outlet O2 concentration Cegrhp, the high-pressure EGR amount Megrhp, and the low-pressure merged intake air amount Mdth as inputs is used as the target intake O2 concentration. The target high pressure EGR amount is set as a part of the target total EGR amount required for That is, this target high pressure EGR amount is a part of the total EGR amount required to make the actual intake O2 concentration the target intake O2 concentration.

  Thereafter, when an affirmative determination is made in step S20 via step S18, or when the processing in step S22 is completed, the process proceeds to step S36, and after the low-pressure merging based on the charged intake air amount Mcld and the target high pressure EGR amount A target value of the intake air amount Mdth (a target low-pressure merged intake air amount) is calculated. More specifically, the target low-pressure merged intake air amount is calculated as a value obtained by subtracting the target high-pressure EGR amount from the charged intake air amount Mcld.

  In the following step S38, the target post-low pressure merged O2 concentration is set based on the charged intake air amount Mcld, the target intake air O2 concentration, the target high pressure EGR amount, the high pressure outlet O2 concentration Ceghrp, and the target low pressure merged intake air amount. Note that the target O2 concentration after low-pressure merging is set by the same method as in the flow rate concentration calculation process.

  In the subsequent step S24a, a target low pressure EGR amount is set. Specifically, based on the low pressure EGR amount Megrlp, the low pressure outlet O2 concentration Cegrlp, the fresh air amount Air, and the oxygen concentration Cair in the fresh air, the low pressure EGR required to set the O2 concentration after the low pressure merging to the target O2 concentration after the low pressure merging. The amount is set as the target low pressure EGR amount. Considering that the target low-pressure merged O2 concentration is set using the target intake O2 concentration, the target low-pressure EGR amount is the target among the total EGR amount required to make the actual intake O2 concentration the target intake O2 concentration. This is an amount other than the amount allocated to the high pressure EGR amount.

  When the processing of step S24a is completed, after the processing of steps S26 to S30, in step S32a, when the target high pressure EGR amount or the target low pressure EGR amount is changed in step S22 or step S30, after the target low pressure merging Reset the O2 concentration and the target intake O2 concentration. Specifically, the target low-pressure EGR amount, the low-pressure outlet O2 concentration Cegrlp, the fresh air amount Mail, and the oxygen concentration in the fresh air are reset to set the target low-pressure O2 concentration. Further, the target intake O2 concentration is reset based on the target low pressure merged O2 concentration, the high pressure outlet O2 concentration Ceghp, the target high pressure EGR amount, and the target low pressure merged intake air amount.

  In the subsequent step S34a, the high pressure EGR actuator 48a is energized to feedback control the actual intake O2 concentration to the target intake O2 concentration, and the low pressure EGR actuator 52a is feedback controlled to change the O2 concentration after actual low pressure merge to the target low pressure O2 concentration. Turn on the power. Specifically, when the actual intake O2 concentration is higher than the target intake O2 concentration and the high pressure outlet O2 concentration Cegrhp is lower than the O2 concentration after the low pressure merge, the high pressure EGR opening is increased and the high pressure EGR amount increases. When the O2 concentration after actual low-pressure merging is higher than the target O2 concentration after low-pressure merging, the low-pressure EGR opening is increased and the low-pressure EGR amount increases.

  In addition, when the process of step S34a is completed, this series of processes is once complete | finished.

  Thus, in the present embodiment, the external EGR amount can be adjusted using the intake air O2 concentration and the low-pressure merged O2 concentration as control amounts.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  In the first embodiment, when it is determined that the target high-pressure EGR amount exceeds the high-pressure upper limit value, a process of setting the low-pressure upper limit value to be larger may be performed as the amount of increase exceeds the target value. Thereby, if there is a margin for increasing the low pressure EGR amount, the shortage of the high pressure EGR amount can be appropriately compensated by the low pressure EGR.

  The installation positions of the high pressure EGR valve 48 and the low pressure EGR valve 52 are not limited to those illustrated in the above embodiments. For example, the high pressure EGR valve 48 may be provided in the vicinity of the exhaust passage 34 in the high pressure EGR passage 44 or in the middle of the high pressure EGR passage 44. Further, for example, the high pressure EGR passage 44 may be provided near both the intake passage 12 and the exhaust passage 34. The low-pressure EGR valve 52 is the same as the above-described various installation modes of the high-pressure EGR valve 48.

  The calculation method of the low pressure EGR amount Megrlp and the high pressure EGR amount Megrhp is not limited to those exemplified in the above embodiments. For example, a sensor that detects the differential pressure across the high pressure EGR valve 48 in the high pressure EGR passage 44 may be provided, and the sensor may be calculated by a method similar to the method for calculating the low pressure EGR amount Megagrp. Further, for example, the low-pressure EGR amount Megagrp may be calculated using the detection values of the two pressure sensors, similarly to the calculation method of the high-pressure EGR amount Megagrp exemplified in the above embodiments.

  In each of the above embodiments, the oxygen concentration parameter values of the high pressure outlet O2 concentration Cegrhp, the low pressure outlet O2 concentration Cegrlp, the low pressure merged O2 concentration, the intake O2 concentration, and the exhaust O2 concentration are calculated by the flow rate concentration calculation process. Absent. For example, a sensor that detects the values of these parameters may be provided, and calculation may be performed by processing detected by these sensors.

  The method for grasping the high-pressure EGR amount Megrhp, the low-pressure EGR amount Megrlp, and the low-pressure merged intake air amount Mdth is not limited to those exemplified in the above embodiments. For example, a flow sensor that directly detects these flow rates may be provided, and may be grasped based on the detection value of the flow sensor.

  In each of the above embodiments, the high pressure upper limit value is set to a value equal to or greater than the target total EGR amount in the low load region and set to 0 in the high load region, and from the low load region to the medium load region If it is continuously reduced as it shifts from the high pressure range to the high load range, the total EGR amount at the time of switching from the high pressure EGR control to the high / low pressure cooperative EGR control or at the time of switching from the high / low pressure cooperative EGR control to the low pressure EGR control The change can be expected to be smooth.

  In each of the above embodiments, the high pressure EGR amount and the low pressure EGR amount are adjusted only by the high pressure EGR valve 48 and the low pressure EGR valve 52, respectively, but the present invention is not limited to this. For example, in addition to these EGR valves, adjustment may be made by at least one of the exhaust throttle valve 56 and the intake throttle valve 20.

  Specifically, as the opening degree of the exhaust throttle valve 56 is decreased by energization operation of the exhaust side actuator 56a, the pressure on the upstream side of the exhaust throttle valve 56 in the exhaust passage 34 increases, and the low pressure EGR passage 46 and the high pressure EGR are increased. The amount of low pressure EGR and the amount of high pressure EGR supplied to the intake passage 12 via the passage 44 are increased. Further, as the opening degree of the intake throttle valve 20 becomes smaller due to the energization operation of the intake side actuator 20a, the pressure on the downstream side of the intake throttle valve 20 in the intake passage 12 decreases and is supplied to the intake passage 12 via the high pressure EGR passage 44. The amount of high pressure EGR to be increased.

  In each of the above embodiments, the low pressure and high pressure EGR actuators are energized only by feedback control, but this is not limitative. For example, the operation may be performed in consideration of feedforward control. Specifically, the feedforward operation amount may be calculated based on the engine speed and the fuel injection amount, and the energization operation may be performed based on the calculated feedforward operation amount. Even in this case, if the degree of contribution of the feedback manipulated variable to the feedford manipulated variable is large, the actual EGR rate (actual intake O2 concentration) periodically fluctuates greatly around the target EGR rate (target intake O2 concentration). Since the occurrence of the phenomenon (hunting) can be avoided, the application of the present invention is effective.

  In each of the above embodiments, the total EGR amount required for setting the post-high pressure merge control value to the target value after high pressure merge is allocated to each of the high pressure EGR amount and the low pressure EGR amount, and then the high pressure EGR amount is the high pressure upper limit value. When it is determined that the amount exceeds the upper limit value of the high pressure EGR amount, the control logic that compensates the amount exceeding the high pressure upper limit value by the low pressure EGR is employed, but the present invention is not limited to this. For example, in principle, the total EGR amount is covered by the high pressure EGR, and only when the high pressure EGR amount is determined to exceed the high pressure upper limit value, the portion of the high pressure EGR amount that exceeds the high pressure upper limit value is converted to the low pressure EGR. Control logic that compensates for this may be employed.

  The internal combustion engine is not limited to a compression ignition internal combustion engine, and may be a spark ignition internal combustion engine such as a direct injection gasoline engine.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 12 ... Intake passage, 12a ... After high pressure merge passage, 12b ... After low pressure merge passage, 16 ... Turbocharger, 16a ... Intake compressor, 16b ... Exhaust turbine, 22 ... Combustion chamber, 34 ... Exhaust passage, 44 ... High pressure EGR passage, 46 ... low pressure EGR passage, 48a ... high pressure EGR actuator, 52a ... low pressure EGR actuator, 58 ... ECU (an embodiment of an exhaust gas recirculation control device for an internal combustion engine).

Claims (6)

A supercharger that is provided between an intake passage and an exhaust passage connected to the internal combustion engine and supercharges intake air supplied to the internal combustion engine; and an exhaust turbine of the supercharger in the exhaust passage. A high-pressure EGR passage that connects an upstream side and a downstream side of the compressor of the supercharger in the intake passage; a downstream side of the exhaust turbine in the exhaust passage; and an upstream side of the compressor in the intake passage. A low pressure EGR passage connected to the side, high pressure EGR means that is energized to adjust the flow rate of the high pressure EGR that is recirculated to the intake passage through the high pressure EGR passage, and the intake air through the low pressure EGR passage. Applied to a combustion control system for an internal combustion engine comprising low-pressure EGR means that is energized to adjust the flow rate of the low-pressure EGR returned to the passage,
A downstream side of the intake passage with respect to the connection portion with the high-pressure EGR passage is defined as a post-high-pressure merge passage, and a downstream portion of the intake passage with respect to the connection portion with the low-pressure EGR passage and the high-pressure EGR passage. The upstream side of the connection with the passage is defined as a low pressure merged passage, and when the oxygen concentration or EGR rate in the intake air is defined as an intake parameter, based on the operating state of the internal combustion engine, the high pressure merged passage and Target value setting means for setting each of a target value after high-pressure merging and a target value after low-pressure merging as a target value of the intake air parameter in each of the low-pressure merging passages;
Control value calculation means for calculating each of the control value after high-pressure merge and the control value after low-pressure merge as the value of the intake parameter in each of the high-pressure merge passage and the low-pressure merge passage;
The high pressure EGR means is energized to feedback control the high pressure merged control value to the high pressure merged target value, and the low pressure EGR means is feedback controlled of the low pressure merged control value to the low pressure merged target value. An exhaust gas recirculation control device for an internal combustion engine, comprising: control means for recirculating both the high pressure EGR and the low pressure EGR to the intake passage by energizing the engine. Further comprising allocating means for allocating a flow rate of EGR required to set the control value after high-pressure merging as the target value after high-pressure merging to each of the high-pressure EGR and the low-pressure EGR;
The target value setting means sets the post-high pressure target value and the post-low pressure target value, respectively, based on the flow rate of the high pressure EGR and the flow rate of the low pressure EGR allocated by the allocating means. Item 2. An exhaust gas recirculation control device for an internal combustion engine according to Item 1. A high pressure upper limit value setting means for variably setting a high pressure upper limit value, which is an upper limit value of the flow rate of the high pressure EGR, based on an operating state of the internal combustion engine;
The allocating means allocates the flow rate of the high pressure EGR as a value equal to or less than the set high pressure upper limit value, and determines the post-high pressure merging control value from the flow rate of EGR required for the target value after the high pressure merging. 3. The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 2, wherein the flow rate of the low pressure EGR is set based on a value obtained by subtracting the flow rate of the allocated high pressure EGR. Low pressure upper limit value setting means for variably setting a low pressure upper limit value that is an upper limit value of the flow rate of the low pressure EGR based on the operating state of the internal combustion engine;
The sum of the flow rate of the high pressure EGR and the flow rate of the low pressure EGR allocated by the allocating means is the sum of the high pressure upper limit value and the low pressure upper limit value, and the post-high pressure merge control value is the post-high pressure merge target value. When it is determined that the EGR flow rate required for the pressure exceeds the sum of the high pressure upper limit value and the low pressure upper limit value, the target value after high pressure merging can be realized by the sum of the high pressure upper limit value and the low pressure upper limit value. The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 3, further comprising resetting means for resetting the control value after the high-pressure merging.   5. The exhaust gas recirculation control device for an internal combustion engine according to claim 3, wherein the high pressure upper limit value setting means sets the high pressure upper limit value low when it is determined that the required torque of the internal combustion engine increases rapidly. The high-pressure EGR means is an electronically controlled valve body that is provided in the high-pressure EGR passage and adjusts the area of the passage.
6. The internal combustion engine according to claim 1, wherein the low pressure EGR means is an electronically controlled valve body that is provided in the low pressure EGR passage and adjusts an area of the passage. Exhaust gas recirculation control device.

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