JP2007321658A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

In an exhaust gas purification apparatus for an internal combustion engine, a technique is provided that can supply EGR gas from a high pressure EGR passage and EGR gas from a low pressure EGR passage at an appropriate ratio.
A low pressure EGR passage that recirculates low pressure EGR gas from an exhaust passage downstream of a turbine of a turbocharger to an intake passage upstream of a compressor, a low pressure EGR valve that adjusts an amount of the low pressure EGR gas, and a turbine. A high pressure EGR passage for recirculating high pressure EGR gas from an upstream exhaust passage to an intake passage downstream of the compressor, a high pressure EGR valve for adjusting the amount of high pressure EGR gas, and a target value of the ratio of EGR gas in the cylinder are determined. A target EGR rate determining means (S101) and an actual EGR rate estimating means (S104) for estimating an actual value of the ratio of EGR gas in the cylinder, and based on the difference in the ratio of the EGR gas between the target and the actual When changing the amount of EGR gas, the time it takes for the target opening to be reached after the high pressure EGR valve starts changing is longer than that for the low pressure EGR valve. To (S113).
[Selection] Figure 2

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  A turbocharger having a turbine in the exhaust passage and a compressor in the intake passage is provided. The exhaust passage downstream of the turbine and the intake passage upstream of the compressor are connected, and a part of the exhaust from the internal combustion engine is used as the intake passage. An exhaust gas recirculation device for an internal combustion engine having a low pressure EGR passage for recirculation is known. Further, there is known an exhaust gas recirculation device for an internal combustion engine having a high-pressure EGR passage that connects an exhaust passage upstream of the turbine and an intake passage downstream of the compressor and recirculates part of the exhaust gas from the internal combustion engine to the intake passage. Yes.

The low pressure EGR passage and the high pressure EGR passage are provided, and when low temperature combustion is performed, the EGR gas flowing in the low pressure EGR passage (hereinafter referred to as the low pressure EGR gas) is supplied during high load operation of the internal combustion engine. A technique for supplying EGR gas (hereinafter referred to as high-pressure EGR gas) that flows through a high-pressure EGR passage during a load operation is known (for example, see Patent Document 1).
JP-A-2005-76456 Japanese Patent Laid-Open No. 9-228899

  Here, in order to set the amount of the low-pressure EGR gas and the amount of the high-pressure EGR gas to appropriate values, it is conceivable to feedback-control them. However, since the low pressure EGR passage is connected to the downstream side of the exhaust passage and to the upstream side of the intake passage rather than the high pressure EGR passage, the distance through which the EGR gas flows is long. Further, the differential pressure between the exhaust passage side and the intake passage side of the low pressure EGR passage is smaller than that of the high pressure EGR passage. Further, the low-pressure EGR gas supplied from the low-pressure EGR passage to the intake passage passes through a large-volume member such as an intercooler. Accordingly, even if the opening degree of the low pressure EGR valve is changed, the time taken for the amount of the low pressure EGR gas and the ratio of the low pressure EGR gas in the total EGR gas to change is longer than that for the high pressure EGR valve. Hereinafter, a long time is referred to as a slow response of the EGR valve, and a short time is referred to as a fast response of the EGR valve. That is, the response of the low pressure EGR valve is slow and the response of the high pressure EGR valve is fast.

  Thus, the low pressure EGR valve and the high pressure EGR valve differ in the time from when the opening degree is changed to the target value during feedback control until the EGR gas amount actually changes to the target value. It is difficult to feedback control the amount of high-pressure EGR gas at the same time.

  Therefore, the amount of EGR gas flowing through one EGR passage may be feedback controlled, and the amount of EGR gas flowing through the other EGR passage may be subjected to open loop control. In such a case, the ratio between the high pressure EGR gas and the low pressure EGR gas may not be an appropriate value.

  The present invention has been made in view of the above-described problems, and in an exhaust gas recirculation apparatus for an internal combustion engine, EGR gas from a high pressure EGR passage and EGR gas from a low pressure EGR passage are supplied at an appropriate ratio. The purpose is to provide technology that can be used.

In order to achieve the above object, an exhaust gas recirculation apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas recirculation device for an internal combustion engine according to the present invention is:
A turbocharger having a turbine in the exhaust passage of the internal combustion engine and a compressor in the intake passage;
A low-pressure EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor and recirculates part of the exhaust from the internal combustion engine to the intake passage;
A low pressure EGR valve that adjusts the amount of low pressure EGR gas flowing through the low pressure EGR passage by opening and closing in the low pressure EGR passage;
A high-pressure EGR passage that connects an exhaust passage upstream of the turbine and an intake passage downstream of the compressor and recirculates part of the exhaust from the internal combustion engine to the intake passage;
A high pressure EGR valve that adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage by opening and closing in the high pressure EGR passage;
Target EGR rate determining means for determining a target value of the ratio of EGR gas in the gas sucked into the internal combustion engine;
An actual EGR rate estimating means for estimating an actual value of the ratio of EGR gas in the gas sucked into the internal combustion engine;
With
Based on the difference between the EGR gas ratio determined by the target EGR rate determining means and the EGR gas ratio estimated by the actual EGR rate estimating means, the target opening of the low pressure EGR valve and the target of the high pressure EGR valve When the EGR gas amount is changed by simultaneously changing the low pressure EGR valve and the high pressure EGR valve toward these target openings, the opening degree is set after the high pressure EGR valve starts changing. The time required until the time is longer than the time required until the target opening degree is reached after the low pressure EGR valve starts changing.

  The target EGR rate determining means determines a target value of the ratio of EGR gas in the total gas sucked into the internal combustion engine (hereinafter also referred to as EGR rate). The EGR gas at this time is the high pressure EGR gas and It is the sum of the low pressure EGR gas. Then, the target EGR rate determining means determines the target value of the EGR rate based on, for example, the operating state of the internal combustion engine, the vehicle state, or the atmosphere state.

  The actual EGR rate estimation means estimates the actual EGR rate, but this may be actually measured.

  “Based on the difference between the ratio of EGR gas determined by the target EGR rate determination means and the ratio of EGR gas estimated by the actual EGR rate estimation means, the target opening degree of the low pressure EGR valve and the high pressure EGR valve “Setting the target opening and changing the EGR gas amount by simultaneously changing the low pressure EGR valve and the high pressure EGR valve toward these target openings” means, for example, the EGR gas determined by the target EGR rate determining means This shows that the EGR gas amount feedback control is performed so that the difference between the ratio and the EGR gas ratio estimated by the actual EGR rate estimating means is eliminated.

  Then, the EGR gas amount can be increased by moving the low pressure EGR valve and the high pressure EGR valve to the open side, and the EGR gas amount can be decreased by moving the low pressure EGR valve and the high pressure EGR valve to the closed side. The time taken from the start to the target opening is set longer than the time taken from the start of the low pressure EGR valve to the target opening.

  In this case, the time required for the target opening to be reached after the high pressure EGR valve starts changing may be lengthened, and the time required for the target opening to be reached after the low pressure EGR valve starts changing. It can be shortened.

By increasing the time it takes for the target opening to reach after the high pressure EGR valve starts changing, the opening of the high pressure EGR valve changes slowly. Originally, the time from when the opening degree of the high pressure EGR valve is changed to the target value during feedback control until the actual amount of the high pressure EGR gas changes to the target value is shorter than that of the low pressure EGR valve, the high pressure EGR valve changes. By increasing the time required from the start until the target opening is reached, the time until the high pressure EGR gas amount reaches the target value can be made closer to the time until the low pressure EGR gas amount reaches the target value. . That is, apparently, the response speed of the high pressure EGR valve can be made closer to the response speed of the low pressure EGR valve.

  Moreover, the opening degree of the low pressure EGR valve can be changed quickly by shortening the time taken from the start of the change of the high pressure EGR valve to the target opening degree. Since the time from when the opening of the low-pressure EGR valve is changed to the target value during feedback control until the actual amount of low-pressure EGR gas changes to the target value is longer than that for the high-pressure EGR valve, the low-pressure EGR valve starts to change. By shortening the time taken for the target opening to reach the target value, the time until the low pressure EGR gas amount reaches the target value can be made closer to the time until the high pressure EGR gas amount reaches the target value. That is, apparently, the response speed of the low pressure EGR valve can be made closer to the response speed of the high pressure EGR valve.

  Thereby, even if high-pressure EGR gas and low-pressure EGR gas are simultaneously feedback-controlled, the ratio of high-pressure EGR gas to low-pressure EGR gas can be quickly converged to an appropriate value. Further, the EGR rate can be set to an appropriate value.

  In the present invention, the opening degree of the high pressure EGR valve can be gradually changed toward the target opening degree. This may incorporate a delay system in the control when changing the opening of the high-pressure EGR valve.

  By gradually changing the opening degree of the high-pressure EGR valve, the amount of high-pressure EGR gas gradually changes, so that the response of the high-pressure EGR valve can be apparently delayed.

  Furthermore, in the present invention, when the opening degree of the low pressure EGR valve is changed toward the target opening degree, the actual opening degree of the low pressure EGR valve can temporarily exceed the target opening degree. That is, you may make it overshoot. As a result, the amount of low-pressure EGR gas changes abruptly, so that the response of the low-pressure EGR valve can be accelerated.

  The exhaust gas recirculation device for an internal combustion engine according to the present invention can supply the EGR gas from the high pressure EGR passage and the EGR gas from the low pressure EGR passage at an appropriate ratio.

  Hereinafter, specific embodiments of an exhaust gas recirculation device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its intake / exhaust system. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

An intake pipe 3 and an exhaust pipe 4 are connected to the internal combustion engine 1. In the middle of the intake pipe 3, a compressor housing 5a of a turbocharger 5 that operates using exhaust energy as a drive source is provided. The intake pipe 3 upstream of the compressor housing 5a is provided with a first throttle 6 for adjusting the flow rate of intake air flowing through the intake pipe 3. The first throttle 6 is opened and closed by an electric actuator. The intake pipe 3 upstream of the first throttle 6 is provided with an air flow meter 7 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake pipe 3. The air flow meter 7 measures the amount of fresh intake air in the internal combustion engine 1.

  The intake pipe 3 downstream of the compressor housing 5a is provided with an intercooler 8 that performs heat exchange between intake air and outside air. The intake pipe 3 downstream of the intercooler 8 is provided with a second throttle 9 that adjusts the flow rate of the intake air flowing through the intake pipe 3. The second throttle 9 is opened and closed by an electric actuator.

On the other hand, a turbine housing 5 b of the turbocharger 5 is provided in the middle of the exhaust pipe 4. Further, a particulate filter (hereinafter simply referred to as a filter) 10 is provided in the exhaust pipe 4 downstream of the turbine housing 5b. The filter 10 carries an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst). This particulate filter collects particulate matter in the exhaust. Further, the NOx catalyst occludes nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high, and on the other hand, when the oxygen concentration of the exhaust flowing into the NOx catalyst decreases. Releases the stored NOx. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, NOx released from the NOx catalyst is reduced.

  An exhaust pressure sensor 11 that detects the pressure in the exhaust pipe 4 is attached to the exhaust pipe 4 upstream of the turbine housing 5b.

  The internal combustion engine 1 is provided with a low pressure EGR device 30 that recirculates a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a low pressure. The low pressure EGR device 30 includes a low pressure EGR passage 31, a low pressure EGR valve 32, and an EGR cooler 33.

  The low pressure EGR passage 31 connects the exhaust pipe 4 downstream of the filter 10 and the intake pipe 3 upstream of the compressor housing 5 a and downstream of the first throttle 6. Through this low pressure EGR passage 31, the exhaust gas is recirculated at a low pressure. In this embodiment, the exhaust gas recirculated through the low pressure EGR passage 31 is referred to as low pressure EGR gas.

  Further, the low pressure EGR valve 32 adjusts the amount of the low pressure EGR gas flowing through the low pressure EGR passage 31 by adjusting the passage sectional area of the low pressure EGR passage 31. Further, the EGR cooler 33 exchanges heat between the low-pressure EGR gas passing through the EGR cooler 33 and the cooling water of the internal combustion engine 1 to lower the temperature of the low-pressure EGR gas.

  Further, the internal combustion engine 1 is provided with a high pressure EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a high pressure. The high pressure EGR device 40 includes a high pressure EGR passage 41 and a high pressure EGR valve 42.

  The high pressure EGR passage 41 connects the exhaust pipe 4 upstream of the turbine housing 5 b and the intake pipe 3 downstream of the second throttle 9. Exhaust gas is recirculated at high pressure through the high pressure EGR passage 41. In this embodiment, the exhaust gas recirculated through the high pressure EGR passage 41 is referred to as high pressure EGR gas.

  Further, the high pressure EGR valve 42 adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage 41 by adjusting the passage sectional area of the high pressure EGR passage 41.

The internal combustion engine 1 configured as described above is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. ECU
20 includes an accelerator opening sensor 15 capable of detecting an engine load by outputting an electric signal corresponding to the amount of depression of the accelerator pedal 14 by the driver, and a crank position sensor 16 for detecting the engine speed. Are connected via electric wiring, and output signals of these various sensors are input to the ECU 20. On the other hand, the ECU 20 is connected to the first throttle 6, the second throttle 9, the low pressure EGR valve 32, and the high pressure EGR valve 42 through electric wiring, and these devices are controlled by the ECU 20.

  In this embodiment, when feedback control of the low pressure EGR gas amount and the high pressure EGR gas amount is performed, when changing the ratio of EGR gas (EGR rate) in the total gas sucked into the cylinder 2, The change amount of the EGR gas is divided into a change amount of the low pressure EGR gas and a change amount of the high pressure EGR gas according to a predetermined ratio.

  On the other hand, when changing the ratio (EGR ratio) between the high pressure EGR gas and the low pressure EGR gas in all the EGR gases, the sum of the low pressure EGR gas amount and the high pressure EGR gas amount is made constant.

  As described above, when the EGR rate or the EGR ratio is changed, the opening degrees of the low pressure EGR valve 32 and the high pressure EGR valve 42 are adjusted in this embodiment. Then, in order to match the EGR rate or EGR ratio to the target value, correction values for the opening degrees of the low pressure EGR valve 32 and the high pressure EGR valve 42 are obtained. And according to this correction value, the opening degree of the low pressure EGR valve 32 and the high pressure EGR valve 42 is changed. At this time, the low pressure EGR valve 32 applies the correction value as it is to set the target opening degree, but the high pressure EGR valve 42 further performs a delay process on the opening degree obtained by applying the correction value to thereby achieve the target opening degree. Set.

  Here, the delay process is a process for reducing the rate of change of the high-pressure EGR valve 42. That is, the low-pressure EGR valve 32 is immediately adjusted to the set corrected opening, but the high-pressure EGR valve 42 is gradually changed toward the set corrected opening.

  By doing in this way, since the time required for changing the high pressure EGR gas amount can be matched with the time required for changing the low pressure EGR gas amount, the high pressure EGR gas and the low pressure EGR gas can be feedback-controlled simultaneously. . Further, the EGR rate can be set to an appropriate value.

  Next, the flow of opening degree control of the low pressure EGR valve 32 and the high pressure EGR valve 42 according to the present embodiment will be described. FIG. 2 is a flowchart showing a flow of opening control of the low pressure EGR valve 32 and the high pressure EGR valve 42 according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, a target EGR rate EGRtrg (hereinafter referred to as a target EGR rate EGRtrg) is calculated. The EGR rate is a ratio of the EGR gas amount to the total gas amount in the cylinder 2. Further, the amount of EGR gas at this time is a total amount of the low pressure EGR gas and the high pressure EGR gas.

  The target EGR rate EGRtrg is determined based on the engine speed and the engine load. The relationship between the target EGR rate EGRtrg, the engine speed and the engine load is obtained in advance through experiments or the like, mapped, and stored in the ECU 20. In this embodiment, the ECU 20 that performs the process of step S101 corresponds to the target EGR rate determining means in the present invention.

In step S102, the basic opening degree Lh of the high pressure EGR valve 42 is calculated. The basic opening degree Lh of the high-pressure EGR valve 42 is an opening degree serving as a reference for the high-pressure EGR valve 42 and is determined based on the engine speed and the engine load. The relationship between the basic opening degree Lh of the high pressure EGR valve 42, the engine speed and the engine load is obtained in advance through experiments or the like, mapped, and stored in the ECU 20.

  In step S103, the basic opening degree L1 of the low pressure EGR valve 32 is calculated. The basic opening Ll of the low-pressure EGR valve 32 is an opening serving as a reference for the low-pressure EGR valve 32, and is determined based on the engine speed and the engine load. The relationship between the basic opening degree Ll of the low pressure EGR valve 32, the engine speed, and the engine load is obtained in advance through experiments or the like, mapped, and stored in the ECU 20.

  In step S104, an actual EGR rate EGRact (hereinafter referred to as an actual EGR rate EGRact) is estimated. For example, the actual EGR rate EGRact is estimated based on the engine speed, the engine load, and the intake fresh air amount. That is, the total gas amount sucked into the cylinder 2 is obtained based on the engine load and the engine speed. This relationship is obtained in advance by experiments or the like. This total gas amount is the sum of the intake fresh air amount and the total EGR gas amount. The total EGR gas amount can be obtained by subtracting the intake fresh air amount from the total gas amount. Then, the actual EGR rate EGRact can be obtained by dividing the total EGR gas amount by the total gas amount. In this embodiment, the ECU 20 that performs the process of step S104 corresponds to the actual EGR rate estimating means in the present invention.

  In step S105, a difference ΔEGR (hereinafter referred to as an EGR rate difference ΔEGR) between the target EGR rate EGRtrg and the actual EGR rate EGRact is calculated. That is, how much the actual EGR rate EGRact is deviated from the target EGR rate EGRtrg is calculated.

  In step S106, the exhaust pressure P4 is detected. The exhaust pressure P4 can be obtained by the exhaust pressure sensor 11.

  In step S107, the flow rate Vh of the high pressure EGR gas (hereinafter referred to as the high pressure EGR gas flow rate Vh) is estimated. Since the high pressure EGR gas flow rate Vh correlates with the opening degree of the high pressure EGR valve 42 and the exhaust pressure P4, it is calculated from the relationship between them.

  In step S108, the flow rate Vl of the low pressure EGR gas (hereinafter referred to as the low pressure EGR gas flow rate Vl) is estimated. The low-pressure EGR gas flow rate Vl correlates with the opening degree of the low-pressure EGR valve 32, the engine speed, and the engine load.

  In step S109, an actual EGR ratio EGRRact (hereinafter referred to as an actual EGR ratio EGRRact) is estimated. The EGR ratio is a ratio between the high pressure EGR gas and the low pressure EGR gas in the total EGR gas supplied into the cylinder 2. The actual EGR ratio EGRRact is obtained by dividing the high pressure EGR gas flow rate Vh calculated in step S107 by the low pressure EGR gas flow rate Vl calculated in step S108.

  In step S110, a target EGR ratio EGRRtrg (hereinafter referred to as a target EGR ratio EGRRtrg) is calculated. The target EGR ratio EGRRtrg is determined based on the engine speed and the engine load. The relationship between the target EGR ratio EGRRtrg, the engine speed and the engine load is obtained in advance through experiments or the like, mapped, and stored in the ECU 20.

  In step S111, a difference ΔEGRR between the target EGR ratio EGRRtrg and the actual EGR ratio EGRRact (hereinafter referred to as EGR ratio difference ΔEGRR) is calculated. That is, how much the actual EGR ratio EGRRact is deviated from the target EGR ratio EGRRtrg is calculated.

In step S112, the opening degree of the high pressure EGR valve 42 is corrected, and in step S113,
Delay processing is performed on the corrected opening degree of the high pressure EGR valve 42, and the opening degree of the low pressure EGR valve 32 is corrected in step S113.

  FIG. 3 is a diagram showing the relationship between the EGR rate difference ΔEGR, the correction value A for the high pressure EGR valve opening, and the correction value B for the low pressure EGR valve opening. This relationship is obtained in advance through experiments or the like and mapped.

  Here, as the EGR rate difference ΔEGR increases with a positive value, the ratio of EGR gas in the gas sucked into the cylinder 2 becomes lower than the target. That is, the sum of the high pressure EGR gas and the low pressure EGR gas is smaller than the target. In such a case, the correction value A for the high pressure EGR valve opening and the correction value B for the low pressure EGR valve opening are determined so as to increase the amounts of the high pressure EGR gas and the low pressure EGR gas. That is, as the EGR rate difference ΔEGR increases with a positive value, the correction value A for the high pressure EGR valve opening and the correction value B for the low pressure EGR valve opening are increased with a positive value. At this time, the correction value A for the high pressure EGR valve opening is set to be larger than the correction value B for the low pressure EGR valve opening. Thereby, the ratio of the high pressure EGR gas and the low pressure EGR gas in the EGR gas that is increased at the time of correction is quickly determined.

  On the other hand, the smaller the EGR rate difference ΔEGR is, the smaller the ratio of EGR gas in the gas sucked into the cylinder 2 becomes higher than the target. That is, the sum of the high pressure EGR gas and the low pressure EGR gas is larger than the target. In such a case, the correction value A for the high pressure EGR valve opening and the correction value B for the low pressure EGR valve opening are determined so as to reduce the amounts of the high pressure EGR gas and the low pressure EGR gas. That is, as the EGR rate difference ΔEGR becomes smaller at a negative value, the correction value A for the high pressure EGR valve opening and the correction value B for the low pressure EGR valve opening are made smaller by a negative value. At this time, the correction value A for the high pressure EGR valve opening is set to be smaller than the correction value B for the low pressure EGR valve opening. Thereby, the ratio of the high pressure EGR gas and the low pressure EGR gas in the EGR gas that is increased at the time of correction is quickly determined.

  Next, FIG. 4 is a diagram showing the relationship between the EGR ratio difference ΔEGRR, the correction value C for the high pressure EGR valve opening, and the correction value D for the low pressure EGR valve opening. This relationship is obtained in advance through experiments or the like and mapped.

  Here, as the EGR ratio difference ΔEGRR increases with a positive value, the ratio between the high-pressure EGR gas and the low-pressure EGR gas becomes lower. That is, the high pressure EGR gas is relatively less than the low pressure EGR gas. In such a case, the correction value C of the high pressure EGR valve opening is determined so as to increase the ratio of the high pressure EGR gas. At the same time, the correction value D of the low pressure EGR valve opening is determined so as to reduce the ratio of the low pressure EGR gas. That is, as the EGR ratio difference ΔEGRR increases with a positive value, the correction value C for the high-pressure EGR valve opening is increased with a positive value, and the correction value D for the low-pressure EGR valve opening is smaller with a negative value. Is done. At this time, the respective correction values are determined so that the sum of the high pressure EGR gas amount and the low pressure EGR gas amount does not change.

  On the other hand, the smaller the EGR ratio difference ΔEGRR becomes a negative value, the higher the ratio between the high pressure EGR gas and the low pressure EGR gas. That is, the high-pressure EGR gas is relatively larger than the low-pressure EGR gas. In such a case, the correction value C of the high pressure EGR valve opening is determined so as to reduce the ratio of the high pressure EGR gas. At the same time, the correction value D of the low pressure EGR valve opening is determined so as to increase the ratio of the low pressure EGR gas. That is, as the EGR ratio difference ΔEGRR becomes smaller at a negative value, the correction value C for the high pressure EGR valve opening is made smaller at a negative value, and the correction value D for the low pressure EGR valve opening is made larger at a positive value. .

The corrected opening degree Lhf of the high pressure EGR valve 42 can be obtained by adding the correction value A and the correction value C to the basic opening degree Lh of the high pressure EGR valve 42. Similarly, low pressure EGR valve 3
The corrected opening degree Llf of 2 can be obtained by adding the correction value B and the correction value D to the basic opening degree L1 of the low pressure EGR valve 32. Then, the target opening degree of the low pressure EGR valve 32 is set to the corrected opening degree Llf.

  Here, FIG. 5 is a diagram showing the relationship between the corrected opening degree Lhf of the high-pressure EGR valve 42 and the opening degree Lhd of the high-pressure EGR valve 42 subjected to further delay processing. As described above, the opening degree Lhd subjected to the delay process in step S113 gradually approaches the corrected opening degree Lhf. Then, the opening degree Lhd after the delay process is performed is set as a new target opening degree. The time constant of the delay process is set so that the time required for the high pressure EGR gas amount to change to the target value is equal to the time required for the low pressure EGR gas amount to change to the target value.

  Thus, when feedback control of the EGR rate and EGR ratio in the cylinder 2 is performed, the response speed of the high pressure EGR valve 42 and the low pressure EGR valve 32 are apparently delayed by slowing the response of the high pressure EGR valve 42. Can be matched with the speed of response. This facilitates feedback control of the EGR rate and EGR ratio, so that the desired EGR rate and EGR ratio can be obtained quickly.

  As described above, according to the present embodiment, the high pressure EGR gas amount and the low pressure EGR gas amount can be simultaneously feedback controlled, so that the EGR rate and the EGR ratio can be quickly adjusted to the target values.

  In the first embodiment, a delay process is performed on the opening degree of the high pressure EGR valve 42, but in this embodiment, a differential operation is incorporated when the opening degree of the low pressure EGR valve 32 is changed. As a result, the amount of low-pressure EGR gas can be quickly changed, so that the response speed of the low-pressure EGR valve 32 can be made closer to the response speed of the high-pressure EGR valve 42.

  Next, the flow of opening degree control of the low pressure EGR valve 32 and the high pressure EGR valve 42 according to the present embodiment will be described. FIG. 6 is a flowchart showing a flow of opening control of the low pressure EGR valve 32 and the high pressure EGR valve 42 according to the present embodiment. This routine is repeatedly executed every predetermined time. This flowchart is different from the flowchart shown in FIG. 2 in that there is no processing in step S113 and there is processing in step S201. Therefore, the steps in which the same processing as that of the flow is performed are denoted by the same reference numerals and description thereof is omitted.

  In step S201, differential processing is performed on the corrected opening degree of the low pressure EGR valve 32.

  Here, FIG. 7 is a diagram showing the relationship between the corrected opening degree Llf of the low pressure EGR valve 32 and the opening degree Llff of the low pressure EGR valve 32 subjected to further differential processing. In this way, by the differential processing, the opening is once made larger than the corrected opening Llf, and then gradually approaches the corrected opening Llf. The opening degree Llff subjected to such differential processing is set as a new target opening degree.

  Thus, when feedback control of the EGR rate and EGR ratio in the cylinder 2 is performed, the response of the low pressure EGR valve 32 is apparently made faster so that the response speed of the high pressure EGR valve 42 and the low pressure EGR valve 32 are increased. Can be matched with the speed of response. This facilitates feedback control of the EGR rate and EGR ratio, so that the desired EGR rate and EGR ratio can be obtained quickly.

As described above, according to the present embodiment, the high pressure EGR gas amount and the low pressure EGR gas amount can be simultaneously feedback controlled, so that the EGR rate and the EGR ratio can be quickly adjusted to the target values.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its intake / exhaust system. 3 is a flowchart illustrating a flow of opening degree control of a low pressure EGR valve and a high pressure EGR valve according to the first embodiment. It is the figure which showed the relationship between EGR rate difference (DELTA) EGR, the correction value A of the high pressure EGR valve opening degree, and the correction value B of the low pressure EGR valve opening degree. It is the figure which showed the relationship between EGR ratio difference (DELTA) EGR, the correction value C of the high pressure EGR valve opening degree, and the correction value D of the low pressure EGR valve opening degree. It is the figure which showed the relationship between the opening degree Lhf after correction | amendment of a high pressure EGR valve, and the opening degree Lhd of the high pressure EGR valve which performed the delay process further to it. It is the flowchart which showed the flow of the opening degree control of the low pressure EGR valve by Example 2, and a high pressure EGR valve. It is the figure which showed the relationship between the opening degree Llf after correction | amendment of a low pressure EGR valve, and the opening degree Llff of the low pressure EGR valve which performed the differentiation process further to it.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake pipe 4 Exhaust pipe 5 Turbocharger 5a Compressor housing 5b Turbine housing 6 1st throttle 7 Air flow meter 8 Intercooler 9 2nd throttle 10 Particulate filter 11 Exhaust pressure sensor 14 Accelerator pedal 15 Accelerator opening sensor 16 Crank position sensor 20 ECU
30 Low pressure EGR device 31 Low pressure EGR passage 32 Low pressure EGR valve 33 EGR cooler 40 High pressure EGR device 41 High pressure EGR passage 42 High pressure EGR valve

Claims (3)

A turbocharger having a turbine in the exhaust passage of the internal combustion engine and a compressor in the intake passage;
A low-pressure EGR passage that connects an exhaust passage downstream of the turbine and an intake passage upstream of the compressor and recirculates part of the exhaust from the internal combustion engine to the intake passage;
A low pressure EGR valve that adjusts the amount of low pressure EGR gas flowing through the low pressure EGR passage by opening and closing in the low pressure EGR passage;
A high-pressure EGR passage that connects an exhaust passage upstream of the turbine and an intake passage downstream of the compressor and recirculates part of the exhaust from the internal combustion engine to the intake passage;
A high pressure EGR valve that adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage by opening and closing in the high pressure EGR passage;
Target EGR rate determining means for determining a target value of the ratio of EGR gas in the gas sucked into the internal combustion engine;
An actual EGR rate estimating means for estimating an actual value of the ratio of EGR gas in the gas sucked into the internal combustion engine;
With
Based on the difference between the EGR gas ratio determined by the target EGR rate determining means and the EGR gas ratio estimated by the actual EGR rate estimating means, the target opening of the low pressure EGR valve and the target of the high pressure EGR valve When the EGR gas amount is changed by simultaneously changing the low pressure EGR valve and the high pressure EGR valve toward these target openings, the opening degree is set after the high pressure EGR valve starts changing. An exhaust gas recirculation device for an internal combustion engine, characterized in that the time required for the internal combustion engine is made longer than the time required for the target opening to be reached after the low-pressure EGR valve starts changing.   The exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein the opening degree of the high pressure EGR valve is gradually changed toward the target opening degree.   The internal combustion engine according to claim 1 or 2, wherein when the opening degree of the low pressure EGR valve is changed toward the target opening degree, the actual opening degree of the low pressure EGR valve temporarily exceeds the target opening degree. Exhaust gas recirculation device.

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