JP2011179425A - Exhaust recirculation device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique that an exhaust recirculation device of an internal combustion engine controls an EGR gas having an accurate EGR gas ratio, even when the accuracy of evaluating a front-and-back differential pressure between an inlet and an outlet of a low pressure EGR device is reduced. <P>SOLUTION: When the front-and-back differential pressure between the inlet and the outlet of the low pressure EGR device is lower than a predetermined differential pressure which is a threshold whether the accuracy of evaluating the differential pressure is reduced: an amount of HC in an exhaust is estimated from an engine speed, a fuel injection amount of the internal combustion engine, and an exhaust flow rate; a heating value of an oxidation catalyst is estimated from an exhaust temperature on the upstream of the oxidation catalyst and the amount of HC; a purifying rate of the oxidation catalyst is estimated from the heating value; SV ratio is estimated from the exhaust temperature on the upstream and the purifying rate of the oxidation catalyst; a gas flow rate of passing through the oxidation catalyst is calculated from the SV ratio; and an amount of recirculation of the low pressure EGR gas and a high pressure EGR gas are controlled according to a relationship between the gas flow rate of passing through the oxidation catalyst and a target flow rate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  A low-pressure EGR device that takes in a part of the exhaust gas as low-pressure EGR gas from the exhaust passage downstream of the turbine of the turbocharger and recirculates the low-pressure EGR gas to the intake passage upstream of the compressor of the turbocharger, and exhausts from the exhaust passage upstream of the turbine Is provided with a high-pressure EGR device that takes in a part of the gas as high-pressure EGR gas and recirculates the high-pressure EGR gas to the intake passage downstream of the compressor. And the technique which calculates the EGR gas ratio of low pressure EGR gas and high pressure EGR gas from the differential pressure before and behind the low pressure EGR device is known (refer to patent documents 1).

JP 2008-038627 A

By the way, in the technique of Patent Document 1, in order to acquire the differential pressure between the inlet and the outlet of the low pressure EGR device, pressure sensors are arranged at the inlet and the outlet of the low pressure EGR device to detect the respective pressures. The pressure difference between the front and rear is obtained from the pressure difference.
However, when the operating state of the internal combustion engine is a low load, the pressure in the low pressure EGR device becomes too low, so that the accuracy of obtaining the differential pressure across the front is lowered, and the accurate EGR gas ratio cannot be obtained. As a result, deviation in the control of the EGR gas may occur, and exhaust emission may deteriorate.

  The present invention has been made in view of the above circumstances, and the object of the present invention is that in an exhaust gas recirculation device for an internal combustion engine, the accuracy of obtaining the differential pressure across the inlet and outlet of the low pressure EGR device is reduced. However, an object of the present invention is to provide a technique for controlling EGR gas with an accurate EGR gas ratio.

In the present invention, the following configuration is adopted. That is, the present invention
A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An oxidation catalyst disposed in the exhaust passage downstream of the turbine;
A low-pressure EGR device that takes in a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream from the oxidation catalyst and recirculates the low-pressure EGR gas to the intake passage upstream from the compressor;
A high-pressure EGR device that takes in a part of exhaust gas as high-pressure EGR gas from the exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to the intake passage downstream of the compressor;
When the low pressure EGR device and the high pressure EGR device are used together to recirculate both the low pressure EGR gas and the high pressure EGR gas, before and after obtaining the differential pressure across the inlet and outlet of the low pressure EGR device. Differential pressure acquisition means;
The oxidation catalyst passage gas flow rate is calculated when the front-rear differential pressure acquired by the front-rear differential pressure acquisition unit is equal to or lower than a predetermined differential pressure that is a threshold value indicating whether the accuracy for obtaining the differential pressure has decreased or not decreased. An oxidation catalyst passage gas flow rate calculating means;
According to the relationship between the oxidation catalyst passage gas flow rate calculated by the oxidation catalyst passage gas flow rate calculation means and the target flow rate, the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device and the recirculation flow by the high pressure EGR device. Control means for controlling the amount of recirculation of the high pressure EGR gas to be performed;
An exhaust gas recirculation device for an internal combustion engine.
Here, the predetermined differential pressure is a value at which the accuracy for obtaining the differential pressure decreases when the longitudinal differential pressure acquired by the front / rear differential pressure acquisition means is lower than that, and the accuracy for determining the differential pressure is This is a threshold value indicating whether or not the accuracy for obtaining the differential pressure has decreased.
According to this, when the differential pressure across the inlet and outlet of the low pressure EGR device is not accurate, the oxidation catalyst passage gas flow rate is calculated, and both EGRs are determined according to the relationship between the oxidation catalyst passage gas flow rate and the target flow rate. Control the amount of gas reflux. Thereby, the precision of the EGR gas ratio between the low pressure EGR gas and the high pressure EGR gas is improved. Therefore, it becomes difficult for deviation to occur in the control of the EGR gas, and deterioration of exhaust emission can be suppressed. Further, the HC poisoning of the oxidation catalyst that occurs because the oxidation catalyst passage gas flow rate is higher than the target flow rate can be suppressed.

When the oxidation catalyst passage gas flow rate calculated by the oxidation catalyst passage gas flow rate calculation unit is larger than a target flow rate, the control unit decreases the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device, Increase the recirculation amount of the high pressure EGR gas recirculated by the high pressure EGR device, and increase the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device when the oxidation catalyst passage gas flow rate is lower than the target flow rate. And the amount of high-pressure EGR gas recirculated by the high-pressure EGR device may be reduced.
According to this, the oxidation catalyst passage gas amount can be adjusted to the target flow rate. Thereby, the precision of the EGR gas ratio between the low pressure EGR gas and the high pressure EGR gas is improved.

The oxidation catalyst passage gas flow rate calculating means estimates the HC amount in the exhaust from the engine speed, the fuel injection amount of the internal combustion engine, and the exhaust flow rate, and from the exhaust temperature upstream of the oxidation catalyst and the estimated HC amount. The heat generation amount of the oxidation catalyst is estimated, the purification rate of the oxidation catalyst is estimated from the estimated heat generation amount, the SV ratio is estimated from the exhaust temperature upstream of the oxidation catalyst and the estimated purification rate, and the estimated SV ratio The flow rate of gas passing through the oxidation catalyst may be calculated from the above.
According to this, the calorific value of the oxidation catalyst can be estimated without providing new detection means, and the cost increase can be suppressed.

The oxidation catalyst passage gas flow rate calculating means estimates the heat generation amount of the oxidation catalyst from the exhaust temperatures upstream and downstream of the oxidation catalyst, estimates the purification rate of the oxidation catalyst from the estimated heat generation amount, and The SV ratio may be estimated from the exhaust temperature upstream of the gas and the estimated purification rate, and the oxidation catalyst passage gas flow rate may be calculated from the estimated SV ratio.
According to this, the calorific value of the oxidation catalyst can be estimated accurately and easily.

  According to the present invention, in an exhaust gas recirculation device for an internal combustion engine, even when the accuracy for obtaining the differential pressure across the inlet and outlet of the low pressure EGR device is reduced, the EGR gas with an accurate EGR gas ratio is controlled. Can do.

1 is a diagram showing a schematic configuration of an internal combustion engine and an intake system / exhaust system thereof according to Embodiment 1 of the present invention. FIG. It is a figure which shows the pattern of proper use with the recirculation | reflux of the low pressure EGR gas corresponding to the driving | running state of the internal combustion engine which concerns on Example 1, and the recirculation | reflux of the high pressure EGR gas. 3 is a flowchart showing an EGR control routine using an oxidation catalyst passage gas flow rate according to the first embodiment. It is a figure which shows the map which calculates | requires SV ratio which concerns on Example 1. FIG. FIG. 3 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake system / exhaust system thereof according to another example of the first embodiment.

  Specific examples of the present invention will be described below.

<Example 1>
(Internal combustion engine)
FIG. 1 shows a schematic configuration of an internal combustion engine to which an exhaust gas recirculation apparatus for an internal combustion engine according to Embodiment 1 of the present invention is applied, and an intake system and an exhaust system thereof. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders 2 that form a combustion chamber together with a piston. The internal combustion engine 1 is mounted on a vehicle. Each cylinder 2 is provided with a fuel injection valve 3 that is supplied with light oil as fuel and injects the light oil into the cylinder 2 at an appropriate amount and at an appropriate timing. An intake passage 4 and an exhaust passage 5 are connected to the internal combustion engine 1.

(Intake system)
In the middle of the intake passage 4 connected to the internal combustion engine 1, a compressor 6a of a turbocharger that operates using exhaust energy as a drive source is disposed. A first throttle valve 7 that adjusts the flow rate of intake air flowing through the intake passage 4 is disposed in the intake passage 4 upstream of the compressor 6a. The first throttle valve 7 is opened and closed by an electric actuator. An air flow meter 8 that outputs a signal corresponding to the flow rate of fresh air flowing in the intake passage 4 is disposed in the intake passage 4 upstream of the first throttle valve 7. The air flow meter 8 measures the amount of intake air (fresh air flow rate) taken into the internal combustion engine 1.
An intercooler 9 that performs heat exchange between the intake air and the outside air is arranged in the intake passage 4 downstream of the compressor 6a. A second throttle valve 10 that adjusts the flow rate of the intake air flowing through the intake passage 4 is disposed in the intake passage 4 downstream of the intercooler 9. The second throttle valve 10 is opened and closed by an electric actuator.
These intake passages 4 and the devices arranged in the intake passages 4 constitute an intake system for taking intake air into the internal combustion engine 1.

(Exhaust system)
On the other hand, a turbocharger turbine 6 b is disposed in the middle of the exhaust passage 5 connected to the internal combustion engine 1. An exhaust purification device 11 is arranged in the exhaust passage 5 downstream of the turbine 6b. The exhaust emission control device 11 includes an oxidation catalyst 11a and a diesel particulate filter (hereinafter simply referred to as a filter) 11b disposed at a subsequent stage of the oxidation catalyst 11a. The filter 11b carries an NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst).
The exhaust passage 5 and the devices arranged in the exhaust passage 5 constitute an exhaust system for exhausting exhaust gas from the internal combustion engine 1.

(Low pressure EGR device)
The internal combustion engine 1 is provided with a low pressure EGR device 30 that recirculates (recirculates) part of the exhaust gas flowing through the exhaust passage 5 to the intake passage 4 at a low pressure. In this embodiment, the exhaust gas recirculated by the low pressure EGR device 30 is referred to as low pressure EGR gas.
The low pressure EGR device 30 includes a low pressure EGR passage 31 through which the low pressure EGR gas flows, a low pressure EGR valve 32 that controls a recirculation amount of the low pressure EGR gas through the low pressure EGR passage 31, and a low pressure EGR cooler 33 that cools the low pressure EGR gas. And having.
The low pressure EGR passage 31 connects the exhaust passage 5 downstream of the exhaust purification device 11 having the oxidation catalyst 11a and the intake passage 4 upstream of the compressor 6a and downstream of the first throttle valve 7. . Through this low-pressure EGR passage 31, the exhaust is sent to the internal combustion engine 1 at low pressure as low-pressure EGR gas.
The low-pressure EGR valve 32 is disposed in the low-pressure EGR passage 31 downstream of the low-pressure EGR cooler 33, and adjusts the passage cross-sectional area of the low-pressure EGR passage 31, whereby the flow rate (return of the low-pressure EGR gas) Adjust the flow rate. The low pressure EGR valve 32 is opened and closed by an electric actuator.
The flow rate of the low pressure EGR gas can be adjusted by a method other than the adjustment of the opening degree of the low pressure EGR valve 32. For example, by adjusting the opening of the first throttle valve 7 or by adjusting the opening of an exhaust throttle valve (not shown), the differential pressure between the upstream and downstream of the low pressure EGR passage 31 is changed. The flow rate of the low pressure EGR gas can be adjusted.
The low pressure EGR cooler 33 is disposed in the middle of the low pressure EGR passage 31. The low-pressure EGR cooler 33 exchanges heat between the low-pressure EGR gas passing through the low-pressure EGR cooler 33 and the engine cooling water, and lowers the temperature of the low-pressure EGR gas.

(High pressure EGR device)
On the other hand, the internal combustion engine 1 is provided with a high pressure EGR device 40 that recirculates (recirculates) a part of the exhaust gas flowing in the exhaust passage 5 to the intake passage 4 at a high pressure. In the present embodiment, the exhaust gas recirculated by the high pressure EGR device 40 is referred to as high pressure EGR gas.
The high-pressure EGR device 40 includes a high-pressure EGR passage 41 through which high-pressure EGR gas flows, and a high-pressure EGR valve 42 that controls the recirculation amount of the high-pressure EGR gas through the high-pressure EGR passage 41.
The high pressure EGR passage 41 connects the exhaust passage 5 upstream of the turbine 6 b and the intake passage 4 downstream of the second throttle valve 10. Exhaust gas is sent to the internal combustion engine 1 at high pressure as high pressure EGR gas through the high pressure EGR passage 41.
The high-pressure EGR valve 42 is disposed in the high-pressure EGR passage 41, and adjusts the flow cross-sectional area of the high-pressure EGR passage 41 to adjust the flow rate (reflux amount) of the high-pressure EGR gas flowing through the high-pressure EGR passage 41. The high pressure EGR valve 42 is opened and closed by an electric actuator.
The flow rate of the high pressure EGR gas can be adjusted by a method other than the adjustment of the opening degree of the high pressure EGR valve 42. For example, by adjusting the opening degree of the second throttle valve 10, the differential pressure between the upstream and downstream of the high pressure EGR passage 41 can be changed, thereby adjusting the flow rate of the high pressure EGR gas. Further, when the turbine 6b of the turbocharger is of a variable capacity type, the amount of high-pressure EGR gas can be adjusted also by adjusting the opening degree of the nozzle vane that changes the flow rate characteristics of the turbine 6b.

(ECU)
The internal combustion engine 1 configured as described above is provided with an ECU 12 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 12 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.
The ECU 12 receives the low pressure EGR gas from the low pressure EGR device 30 at the outlet of the low pressure EGR device 30 and the first pressure sensor 13 that detects the pressure of the exhaust gas flowing into the low pressure EGR device 30 at the inlet of the air flow meter 8 and the low pressure EGR device 30. A second pressure sensor 14 that detects the pressure of the intake air immediately after flowing out, a first exhaust temperature sensor 15 that detects the temperature of the exhaust upstream of the oxidation catalyst 11a, a crank position sensor 16 that detects the engine speed, and a driver An accelerator opening sensor 18 capable of detecting an engine load that determines the fuel injection amount of the internal combustion engine 1 by outputting an electric signal corresponding to the amount of depression of the accelerator pedal 17 is connected via electric wiring, and output signals of these various sensors. Is input to the ECU 12.
On the other hand, the ECU 12 is connected with actuators of the fuel injection valve 3, the first throttle valve 7, the second throttle valve 10, the low pressure EGR valve 32, and the high pressure EGR valve 42 through electric wiring. These devices are controlled.

(EGR control)
In the internal combustion engine 1 in the present embodiment, as shown in FIG. 2, the low pressure EGR gas recirculation and the high pressure EGR gas recirculation are selectively used according to the operating state. FIG. 2 shows different usage patterns of low-pressure EGR gas recirculation and high-pressure EGR gas recirculation corresponding to the operating state of the internal combustion engine 1. The horizontal axis in FIG. 2 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1. In at least one of the operation state of high load and high rotation, only the low pressure EGR gas 30 is recirculated using only the low pressure EGR device 30. The region where only the low pressure EGR gas is recirculated is referred to as an LPL region. In the middle load operation state, the low pressure EGR device 30 and the high pressure EGR device 40 are used together to perform both the low pressure EGR gas recirculation and the high pressure EGR gas recirculation. A region where both the low pressure EGR gas recirculation and the high pressure EGR gas recirculation are referred to as an MPL region. In the low load operation state, only the high pressure EGR gas is recirculated using only the high pressure EGR device 40. A region where only the high pressure EGR gas is refluxed is referred to as an HPL region.
Thereby, in the HPL region, the responsiveness of the EGR operation is ensured by refluxing the high-pressure EGR gas having excellent responsiveness. In the LPL region, the low-temperature low-pressure EGR gas is recirculated to prevent the temperature of the EGR gas from becoming excessively high. As a result, an EGR operation that recirculates exhaust gas in a wider operating state is realized.

(EGR control in the MPL area)
In the MPL region, the low pressure EGR device 30 and the high pressure EGR device 40 are used in combination as described above. Here, in the MPL region, the difference between the pressures detected by the first and second pressure sensors 13, 14, that is, the differential pressure between the inlet and the outlet of the low pressure EGR device 30, and the low pressure EGR gas that is recirculated The ratio of EGR gas to high pressure EGR gas is calculated. Then, the low pressure EGR valve 32, the high pressure EGR valve 42, and the like are controlled so that the EGR gas ratio becomes the target ratio.
If there is too much low-pressure EGR gas in both EGR gases recirculated to the internal combustion engine 1, the exhaust back pressure upstream of the turbine 6b will increase, and the pumping loss of the internal combustion engine 1 will increase. It will occur. On the other hand, if the low pressure EGR gas in both EGR gases is too small, the recirculation amount of the high pressure EGR gas relatively increases, the temperature of the intake air flowing into the internal combustion engine 1 rises, and the amount of smoke and NOx generated increases. Bad effects will occur. In order to avoid these adverse effects, the EGR gas ratio is controlled to be the target ratio.

  However, when the operating state of the internal combustion engine 1 is a low load, the pressure in the low pressure EGR device 30 becomes too low, so that the accuracy of obtaining the differential pressure across the inlet and outlet of the low pressure EGR device 30 is reduced, and accurate EGR The gas ratio cannot be determined. As a result, deviation in the control of the EGR gas may occur, and exhaust emission may deteriorate. Further, if a deviation occurs on the side where the ratio of the low-pressure EGR gas in both EGR gases increases, the oxidation catalyst passage gas flow rate may increase, and HC poisoning of the oxidation catalyst 11a may be promoted.

Therefore, in this embodiment, when the differential pressure across the inlet and outlet of the low-pressure EGR device 30 is not accurate, the oxidation catalyst passage gas flow rate is calculated, and depending on the relationship between the oxidation catalyst passage gas flow rate and the target flow rate. Thus, the reflux amount of both EGR gases is controlled.
Specifically, first, in the case of the MPL region, the differential pressure across the inlet and outlet of the low pressure EGR device 30 is acquired from the detection values of the first and second pressure sensors 13 and 14.
Next, when the acquired front-rear differential pressure is equal to or less than a predetermined differential pressure that is a threshold value indicating whether the accuracy for obtaining the differential pressure has decreased or not, the engine rotational speed and accelerator detected by the crank position sensor 16 The amount of HC in the exhaust gas is estimated from the fuel injection amount of the internal combustion engine 1 obtained from the opening sensor 18 and the exhaust gas flow rate obtained from the fresh air flow rate detected by the air flow meter 8 and the fuel injection amount of the internal combustion engine 1. The heat generation amount of the oxidation catalyst 11a is estimated from the exhaust temperature upstream of the oxidation catalyst 11a detected by the exhaust temperature sensor 15 and the estimated HC amount, the purification rate of the oxidation catalyst 11a is estimated from the estimated heat generation amount, and the oxidation catalyst 11a SV from the exhaust gas temperature upstream and the estimated purification rate
The ratio is estimated, and the oxidation catalyst passage gas flow rate is calculated from the estimated SV ratio.
Here, the predetermined differential pressure is a value at which the accuracy for obtaining the differential pressure is reduced when the previously obtained front-rear differential pressure is less than that. This is a threshold value indicating whether or not the accuracy for obtaining the differential pressure has decreased.
Finally, according to the relationship between the calculated oxidation catalyst passage gas flow rate and the target flow rate, the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device 30 and the high pressure EGR recirculated by the high pressure EGR device 40 The amount of gas reflux is controlled.
As the control at this time, when the calculated oxidation catalyst passage gas flow rate is larger than the target flow rate, the recirculation amount of the low-pressure EGR gas recirculated by the low-pressure EGR device 30 is decreased and recirculated by the high-pressure EGR device 40. Increase the reflux amount of the high-pressure EGR gas. On the other hand, when the calculated oxidation catalyst passage gas flow rate is smaller than the target flow rate, the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device 30 is increased and the high pressure EGR gas recirculated by the high pressure EGR device 40 is increased. Reduce reflux.

  According to this embodiment, the oxidation catalyst passage gas amount can be adjusted to the target flow rate. Thereby, the precision of the EGR gas ratio between the low pressure EGR gas and the high pressure EGR gas is improved. Therefore, it becomes difficult for deviation to occur in the control of the EGR gas, and deterioration of exhaust emission can be suppressed. Further, the HC poisoning of the oxidation catalyst that occurs because the oxidation catalyst passage gas flow rate is higher than the target flow rate can be suppressed.

Further, in this embodiment, the engine speed detected by the crank position sensor 16, the fuel injection amount of the internal combustion engine 1 obtained from the accelerator opening sensor 18, the fresh air flow detected by the air flow meter 8, and the fuel injection of the internal combustion engine 1. The amount of HC in the exhaust is estimated from the exhaust flow rate obtained from the amount, and the heat generation amount of the oxidation catalyst 11a is estimated from the exhaust temperature upstream of the oxidation catalyst 11a detected by the first exhaust temperature sensor 15 and the estimated HC amount. .
According to this, the calorific value of the oxidation catalyst 11a can be estimated without providing a detection means such as a new sensor, and the cost increase can be suppressed.

(EGR control routine using gas flow rate through oxidation catalyst)
An EGR control routine using the oxidation catalyst passage gas flow rate according to this embodiment will be described. FIG. 3 is a flowchart showing an EGR control routine using the oxidation catalyst passage gas flow rate according to this embodiment. This routine is repeatedly executed by the ECU 12 every predetermined time.

In S101, it is determined whether or not the operating state of the internal combustion engine 1 is in the MPL region.
In this determination, the engine rotational speed detected by the crank position sensor 16 and the engine load detected by the accelerator opening sensor 18 are taken in the map shown in FIG. It is determined whether or not EGR control using both the low pressure EGR device 30 and the high pressure EGR device 40 is performed.
If an affirmative determination is made in step S101 that the region is the MPL region, the process proceeds to step S102. If it is determined in S101 that the region is not the MPL region, this routine is temporarily terminated.

In S102, the differential pressure across the inlet and outlet of the low pressure EGR device 30 is acquired from the detected values of the first and second pressure sensors 13, 14.
ECU12 which performs step of S102 respond | corresponds to the front-back differential pressure | voltage acquisition means of this invention.

In S103, it is determined whether or not the differential pressure obtained in S102 is equal to or less than a predetermined differential pressure that is a threshold value indicating whether the differential pressure is inaccurate or accurate.
If a positive determination is made in S103, the process proceeds to S104. If a negative determination is made in S103, this routine is once terminated.

In S104, the engine rotational speed detected by the crank position sensor 16, the fuel injection amount of the internal combustion engine 1 obtained from the accelerator opening sensor 18, the fresh air flow detected by the air flow meter 8 and the fuel injection amount of the internal combustion engine 1 are obtained. The amount of HC in the exhaust is estimated from the exhaust flow rate.
The amount of HC in the exhaust can be estimated by taking the engine speed, the fuel injection amount, and the exhaust flow rate into a predetermined map.

In S105, the heat generation amount of the oxidation catalyst 11a is estimated from the exhaust temperature upstream of the oxidation catalyst 11a detected by the first exhaust temperature sensor 15 and the HC amount estimated in S104.
The calorific value of the oxidation catalyst 11a can be estimated by taking the exhaust temperature upstream of the oxidation catalyst 11a and the estimated amount of HC into a map determined in advance.

In S106, the purification rate of the oxidation catalyst 11a is estimated from the estimated calorific value of the oxidation catalyst 11a.
The purification rate of the oxidation catalyst 11a can be estimated by taking the estimated calorific value of the oxidation catalyst 11a into a predetermined map.

In S107, the SV ratio is estimated from the exhaust temperature upstream of the oxidation catalyst 11a detected by the first exhaust temperature sensor 15 and the purification rate estimated in S106.
Here, the SV ratio is the ratio between the oxidation catalyst passage gas flow rate and the oxidation catalyst capacity. As shown in FIG. 4, the exhaust gas temperature upstream of the oxidation catalyst 11a and the purification rate of the oxidation catalyst 11a are obtained in advance. It can be obtained by importing into a certain map.

In S108, the oxidation catalyst passage gas flow rate is calculated from the SV ratio estimated in S107.
“Oxidation catalyst passage gas flow rate” = “oxidation catalyst capacity” × “SV ratio”. The oxidation catalyst capacity can be determined in advance.
The ECU 12 that executes the steps S104 to S108 corresponds to the oxidation catalyst passage gas flow rate calculation means of the present invention.

In S109, it is determined whether or not the oxidation catalyst passage gas flow rate matches the target flow rate. The target flow rate is determined according to the operating state of the internal combustion engine 1.
If an affirmative determination is made in S109, this routine is once terminated. If a negative determination is made in S109, the process proceeds to S110.

In S110, it is determined whether or not the oxidation catalyst passage gas flow rate is higher than the target flow rate.
If a positive determination is made in S110, the process proceeds to S111. If a negative determination is made in S110, the process proceeds to S112.

In S111, the recirculation amount of the low pressure EGR gas is decreased and the recirculation amount of the high pressure EGR gas is increased. After the processing of this step, this routine is once ended.
The increase or decrease of the reflux amount can be performed by controlling various EGR valves or by controlling the above-described reflux amount. Further, the degree of increase / decrease in the reflux amount may be increased as the difference from the target flow rate increases.

  In S112, the recirculation amount of the low pressure EGR gas is increased and the recirculation amount of the high pressure EGR gas is decreased. After the processing of this step, this routine is once ended.

As described above, according to this routine, even when the accuracy for obtaining the differential pressure across the inlet and outlet of the low pressure EGR device 30 is lowered, it is possible to control the EGR gas with an accurate EGR gas ratio.

The exhaust gas recirculation apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.
In the above-described embodiment, the HC amount in the exhaust gas is estimated from the engine speed, the fuel injection amount of the internal combustion engine, and the exhaust gas flow rate. From the exhaust gas temperature upstream of the oxidation catalyst 11a and the estimated HC amount, the oxidation catalyst 11a The calorific value was estimated. However, it is not limited to this. For example, as shown in FIG. 5, in addition to the first exhaust temperature sensor 15 that detects the exhaust temperature upstream of the oxidation catalyst 11a, a second exhaust temperature sensor 19 that detects the exhaust temperature downstream of the oxidation catalyst 11a is provided, The heat generation amount of the oxidation catalyst 11a may be estimated from the exhaust temperatures upstream and downstream of the oxidation catalyst 11a. In this case, in the routine of FIG. 3, the steps of S104 and S105 may be changed to a step of estimating the heat generation amount of the oxidation catalyst 11a from the exhaust temperatures upstream and downstream of the oxidation catalyst 11a. In this case, the calorific value of the oxidation catalyst 11a can be estimated accurately and easily.

1: internal combustion engine, 2: cylinder, 3: fuel injection valve, 4: intake passage, 5: exhaust passage, 6a: compressor, 6b: turbine, 7: first throttle valve, 8: air flow meter, 9: intercooler, 10: second throttle valve, 11: exhaust purification device, 11a: oxidation catalyst, 11b: filter, 12: ECU, 13: first pressure sensor, 14: second pressure sensor, 15: first exhaust temperature sensor, 16: Crank position sensor, 17: accelerator pedal, 18: accelerator opening sensor, 19: second exhaust temperature sensor, 30: low pressure EGR device, 31: low pressure EGR passage, 32: low pressure EGR valve, 33: low pressure EGR cooler, 40: High pressure EGR device, 41: High pressure EGR passage, 42: High pressure EGR valve

Claims (4)

A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An oxidation catalyst disposed in the exhaust passage downstream of the turbine;
A low-pressure EGR device that takes in a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream from the oxidation catalyst and recirculates the low-pressure EGR gas to the intake passage upstream from the compressor;
A high-pressure EGR device that takes in a part of exhaust gas as high-pressure EGR gas from the exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to the intake passage downstream of the compressor;
When the low pressure EGR device and the high pressure EGR device are used together to recirculate both the low pressure EGR gas and the high pressure EGR gas, before and after obtaining the differential pressure across the inlet and outlet of the low pressure EGR device. Differential pressure acquisition means;
The oxidation catalyst passage gas flow rate is calculated when the front-rear differential pressure acquired by the front-rear differential pressure acquisition unit is equal to or lower than a predetermined differential pressure that is a threshold value indicating whether the accuracy for obtaining the differential pressure has decreased or not decreased. An oxidation catalyst passage gas flow rate calculating means;
According to the relationship between the oxidation catalyst passage gas flow rate calculated by the oxidation catalyst passage gas flow rate calculation means and the target flow rate, the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device and the recirculation flow by the high pressure EGR device. Control means for controlling the amount of recirculation of the high pressure EGR gas to be performed;
An exhaust gas recirculation device for an internal combustion engine. When the oxidation catalyst passage gas flow rate calculated by the oxidation catalyst passage gas flow rate calculation unit is larger than a target flow rate, the control unit decreases the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device, Increasing the amount of high-pressure EGR gas recirculated by the high-pressure EGR device,
When the oxidation catalyst passage gas flow rate is smaller than the target flow rate, the recirculation amount of the low pressure EGR gas recirculated by the low pressure EGR device is increased, and the recirculation amount of the high pressure EGR gas recirculated by the high pressure EGR device is decreased. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, wherein   The oxidation catalyst passage gas flow rate calculating means estimates the HC amount in the exhaust from the engine speed, the fuel injection amount of the internal combustion engine, and the exhaust flow rate, and from the exhaust temperature upstream of the oxidation catalyst and the estimated HC amount. The heat generation amount of the oxidation catalyst is estimated, the purification rate of the oxidation catalyst is estimated from the estimated heat generation amount, the SV ratio is estimated from the exhaust temperature upstream of the oxidation catalyst and the estimated purification rate, and the estimated SV ratio The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein the flow rate of the gas passing through the oxidation catalyst is calculated from the above.   The oxidation catalyst passage gas flow rate calculating means estimates the heat generation amount of the oxidation catalyst from the exhaust temperatures upstream and downstream of the oxidation catalyst, estimates the purification rate of the oxidation catalyst from the estimated heat generation amount, and The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1 or 2, wherein an SV ratio is estimated from an exhaust gas temperature upstream of the exhaust gas and an estimated purification rate, and an oxidation catalyst passage gas flow rate is calculated from the estimated SV ratio.

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