JP3888024B2 - Exhaust gas recirculation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation device suitable for use in a diesel engine.
[0002]
[Prior art]
Generally, in a diesel engine, exhaust gas recirculation (EGR) is introduced in order to reduce NOx in exhaust gas. However, if the amount of EGR introduced is increased, NOx in the exhaust gas can be reduced, but the particulate matter (PM) in the exhaust gas is increased. That is, regarding the amount of EGR introduced, there is a trade-off relationship between the NOx amount and the PM amount in the exhaust gas.
[0003]
The EGR amount is generally controlled by adjusting the opening degree of the EGR valve. However, in order to efficiently reduce the NOx amount and the PM amount which are in a trade-off relationship as described above, the in-cylinder excess air ratio ( A technique for controlling the opening degree of the EGR valve using λ) as a parameter has been developed. In this technique, the target value (target λ) of the in-cylinder excess air ratio is set according to the operating state of the engine (for example, engine speed and engine load), and the actual in-cylinder (actual λ) becomes this target λ. Thus, the opening degree of the EGR valve is feedback controlled.
[0004]
In this case, the actual λ can be obtained from this sensor output by providing a linear air-fuel ratio sensor (LAFS) in the exhaust passage, but in the case of a diesel engine, the sensor is likely to deteriorate due to the influence of PM or the like in the exhaust, Since the reaction of the LAFS in the exhaust passage is delayed with respect to the change in the excess air ratio (that is, the excess air ratio in the cylinder) in the combustion chamber, an error occurs in the actual λ in a transient state such as during acceleration / deceleration. There is also a possibility that the EGR amount cannot be properly controlled.
[0005]
Therefore, a technique for calculating the actual λ from the intake air amount (fresh air amount), the fuel injection amount, and the EGR amount is proposed in, for example, Japanese Patent Laid-Open No. 10-318047.
[0006]
[Problems to be solved by the invention]
Incidentally, when the actual λ is calculated as described above, it is necessary to obtain the intake air amount, the fuel injection amount, and the EGR amount. Among these, the intake air amount can be grasped by an air flow sensor or a boost pressure sensor, and the fuel injection amount can be grasped as an injector drive command value. Then, the EGR amount is obtained by estimating the EGR flow rate.
[0007]
As shown in FIG. 3, the EGR flow rate is related to the differential pressure and the EGR valve opening. Therefore, the EGR flow rate can be estimated by detecting the differential pressure and the EGR valve opening.
However, in the low load region where EGR demand is high, as shown by region A in FIG. 3, the differential pressure across the EGR valve is very small, for example, about several mmHg, and a large amount of EGR is required) Therefore, the EGR valve opening is almost fully open. Therefore, the change in the EGR flow rate is insensitive to the change in the EGR valve opening, but the change in the EGR flow rate is sensitive to the change in the differential pressure across the EGR valve. Therefore, the EGR flow rate estimated by a slight error in the differential pressure across the EGR valve greatly fluctuates, and the EGR amount cannot be properly grasped, making it difficult to control the EGR with high accuracy.
[0008]
Japanese Patent Laid-Open No. 6-336966 discloses a technique for feedback-controlling the EGR valve opening so that the differential pressure between the exhaust passage and the intake passage downstream of the intake throttle valve becomes a target value. The technology simply uses the differential pressure as a target value and does not focus on the excess cylinder air ratio λ.
The present invention has been devised in view of the above-described problems, and it is possible to control EGR (exhaust gas recirculation) with high accuracy so that the amount of EGR can be accurately grasped even in a low load region where EGR demand is high. An object of the present invention is to provide an exhaust gas recirculation device which can be used.
[0009]
[Means for Solving the Problems]
Therefore, in the exhaust gas recirculation device according to the first aspect of the present invention, the exhaust gas in the exhaust passage of the internal combustion engine is recirculated into the intake passage through the EGR passage by adjusting the opening of the EGR valve. At this time, the target excess air ratio setting means sets the target excess air ratio in the cylinder corresponding to the operation state detected by the operation state detection means. On the other hand, the EGR amount deriving unit derives the EGR amount in the cylinder of the internal combustion engine based on the differential pressure across the EGR valve detected by the differential pressure calculating unit, and the actual excess air rate estimating unit derives the EGR amount deriving unit from the EGR amount deriving unit. The actual excess air ratio in the cylinder is estimated from the EGR amount, the fuel injection amount into the cylinder of the internal combustion engine, and the fresh air intake amount. Then, the target EGR amount setting means sets the target EGR amount based on the target excess air ratio set by the target excess air ratio setting means and the actual excess air ratio estimated by the actual excess air ratio estimation means, and EGR The valve opening control means drives the EGR valve based on the target EGR amount set by the target EGR amount setting means. In particular, when the actual excess air ratio is estimated, the differential pressure increasing means determines that the change in the EGR amount is sensitive to the change in the differential pressure before and after the EGR valve calculated by the differential pressure calculation means. sometimes a predetermined value or less of the region made to increase the differential pressure across the EGR valve.
Preferably, the internal combustion engine is a diesel engine, and the differential pressure increasing means throttles an intake throttle valve provided in the intake passage to increase the differential pressure across the EGR valve.
The EGR amount deriving means uses the EGR flow to map the opening degree of the EGR valve and the differential pressure across the EGR valve according to a map in which the opening degree of the EGR valve, the differential pressure across the EGR valve and the EGR quantity correspond to each other. It is preferable to derive the EGR amount from the above.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1 to 4 show an exhaust gas recirculation apparatus as an embodiment of the present invention.
First, an engine (internal combustion engine) provided with the exhaust gas recirculation device will be described. As shown in FIG. 1, the engine 1 is a direct injection type diesel engine, and a high pressure injection nozzle 3 is provided above the cylinder 2. The injection port is disposed so as to face the combustion chamber 4, and is directly injected from the high-pressure injection nozzle 3 into the combustion chamber 4.
[0011]
The intake passage 11 is equipped with an air cleaner (not shown) at the upstream end, and from the upstream side, the compressor portion of the turbocharger (supercharger) 30, the intercooler 13, the intake throttle valve 14, the surge tank 15, and the intake valve 16 is interposed. An exhaust valve 22, a turbine part of the turbocharger 30, a diesel oxidation catalyst (not shown), and the like are interposed in the exhaust passage 21 from the upstream side.
[0012]
An exhaust gas recirculation device (EGR) 23 that recirculates exhaust gas is provided between the exhaust passage 21 and the intake passage 11. The EGR 23 is an EGR passage (exhaust gas recirculation) provided from an upstream portion (for example, an exhaust manifold) of the exhaust passage 21 to a downstream portion of the intake passage 11 (here, a portion between the intake throttle valve 14 and the surge tank 15). For use) 24 and an EGR valve 25 for controlling the opening degree of the EGR passage 24.
[0013]
In this embodiment, the EGR valve 25 is configured as a negative pressure type that is opened by the negative pressure from the vacuum pump 26. The opening degree of the EGR valve 25 is adjusted by adjusting the opening degree of the EGR solenoid 27 interposed in the middle of the piping from the vacuum pump 26 (for example, opening degree adjustment by duty control). To do it.
[0014]
The EGR solenoid 27, the high-pressure injection nozzle 3, and the intake throttle valve 14 are controlled by an ECU (engine control unit) 40 as control means. That is, the ECU 40 has an engine speed (rotation speed) Ne detected by the crank angle sensor 61, an accelerator opening (APS) detected by the accelerator position sensor (APS) 62, and a boost detected by the boost sensor 63. The pressure (intake pipe pressure) Pb, the boost temperature (intake pipe temperature) Tb detected by the boost temperature sensor 64, and the EGR valve opening (actual) detected by the EGR position sensor (EPS) 65 as the opening detection means. EPS) and the upstream pressure Pegr of the EGR valve 25 detected by the pressure sensor 66 are input, and the EGR solenoid 26 and the high-pressure injection nozzle 3 are controlled based on the detected information. Note that the crank angle sensor 61 and the accelerator position sensor (APS) 62 correspond to operating state detecting means for detecting the operating state of the internal combustion engine.
[0015]
The function of controlling the EGR solenoid 27 and the intake throttle valve 14 in the ECU 40 will be described. As shown in FIG. 2, the ECU 40 has a target excess air ratio in the cylinder (target excess air ratio in the cylinder, hereinafter referred to as target λ). Target excess air ratio setting means 41 for setting EGR mass (EGR amount) Grcng, and an EGR amount deriving means 42A for deriving (calculating) EGR mass (EGR amount) Grcng; The actual excess air ratio estimating means 42 for estimating the EGR valve basic position setting means 43 for setting the basic position of the EGR valve opening, and the difference between the target λ and the actual λ (actual λ−target λ). PI calculation means 44 for PI calculation, EGR valve target position setting means (target EGR amount setting means) 45 for setting the target position of the EGR valve, and a command signal is output to the EGR valve 25 based on this target position EGR valve command means (EGR valve opening degree control means) 46, differential pressure calculation means 47 for calculating the differential pressure DEP before and after the EGR valve 25, and differential pressure before and after the EGR valve 25 calculated by the differential pressure calculation means 47 A differential pressure increase control means 48 that increases through the intake throttle valve 14 when DEP is equal to or less than a predetermined value is provided.
[0016]
The EGR amount deriving unit 42A is provided with an EGR flow rate estimating unit 42A ', and the EGR mass Grcng is calculated based on the EGR flow rate Vegr estimated by the EGR flow rate estimating unit 42A'. The EGR flow rate estimating means 42A ′ includes an EGR valve for processing EGR valve opening degree (actual EPS) detection data (EGR valve position sampling data) detected by the EGR position sensor (EPS) 65 prior to estimation of the EGR flow rate. Position data processing means 42B is provided. Further, the intake throttle valve 14 and the differential pressure increase control means 48 constitute a differential pressure increase means 49.
[0017]
In the target excess air ratio setting means 41, the target excess air ratio (target λ) is determined from the engine speed Ne and the fuel injection amount Q into the cylinder (amount corresponding to the engine load) Q according to a target λ setting map prepared in advance. ) Is set.
In the EGR flow rate estimating means 42A, the EGR valve opening degree (actual EPS) detected by the EGR position sensor (EPS) 65 as the opening degree detecting means, and the front and rear of the EGR valve 25 detected by the differential pressure calculating means 47 described later. The EGR flow rate into the cylinder of the engine is estimated from the differential pressure, and the estimation result is output for estimating the actual excess air ratio. However, the value processed by the EGR valve position data processing means 42B is used for the actual EPS (EGR valve position).
[0018]
In this EGR valve position data processing means 42B, all EGR valve position sampling data sampled in the intake stroke immediately before the combustion stroke (explosion stroke) of the cylinder to be estimated is averaged (here, a simple average). Thus, this value is used for estimating the EGR flow rate.
For example, FIG. 4 is a diagram showing the sampling timing of data such as the EGR valve position and the calculation timing of the fuel supply amount in a four-cylinder engine in correspondence with the crank angle (each stroke) of the engine. In FIG. 4, EPS1 to EPS9 indicate EGR valve position data obtained at each sampling timing, and λr1 to λr9 indicate actual λ estimated values obtained when the actual λ is estimated corresponding to each EGR valve position data. Show.
[0019]
In the present apparatus, as indicated by a broken line in FIG. 4, the fuel injection amount is calculated in the compression stroke of a certain target cylinder, here B105 [105 ° before compression top dead center (crank angle)], whereas EGR As the valve position, the intake stroke of the target cylinder, that is, an average value EPS of a plurality of data (three in FIG. 4) sampled in B360 to B180 [360 to 180 ° before compression top dead center (crank angle)]. _AV (= ΣEPS _{n + 1 to} EPS _{n + k} / k) is calculated, and this average value EPS _AV is set as an actual EPS (EGR valve position). FIG. 4 shows the respective mean value EPS _AV1 shown in ～EPS _AV3, the average EPS _AV1, EPS _AV2 real λ calculated in correspondence with at λr _AV1 ~λr _AV.
[0020]
The actual excess air ratio estimating means 42 calculates the actual excess air ratio (actual λ) from the cylinder intake air amount (cylinder intake air amount) Ga and the fuel injection amount Q into the cylinder by the following equation (1). .
Actual λ = Ga / Q / theoretical air-fuel ratio (1)
Here, the fuel injection amount Q can be given as a target value of the fuel injection amount from the high-pressure injection nozzle 3, for example, and the cylinder intake air amount Ga is the EGR mass introduced by EGR from the total intake amount Ge into the cylinder. It can be calculated by subtracting Grcng (Ga = Ge-Grcng).
[0021]
Among these, the total intake air amount Ge to the cylinder can be calculated from the engine speed Ne, the boost pressure Pb, and the boost temperature Tb as in the following equation (2). In the following equation (2), Vh is the engine stroke volume, ηv is volume efficiency, and γb is a specific weight obtained from the boost pressure Pb, the atmospheric pressure Pa, and the boost temperature Tb.
Ge∝ [Ne × Vh × ηv × γb (Pb, Pa, Tb)] (2)
The EGR mass Grcng is calculated by the EGR flow rate estimating means 42A. In the EGR flow rate estimating means 42A, the EGR valve passage flow rate Vegr that can be calculated from the actual EPS and the differential pressure DEP before and after the EGR valve 25, and the fuel injection amount. EGR mass value Gr calculated as the product of EGR gas density ρegr that can be calculated from Q and engine temperature (generally engine coolant temperature) Tw is expressed by the following equation (3): The EGR mass Grcng can be obtained by correcting with the ratio Ra.
[0022]
Grcng = Gr * (1-Ra) (3)
However, Gr = Vegr * ρegr
Here, the EGR valve passage flow rate (EGR flow rate) Vegr is estimated by the EGR flow rate estimation means 42A ′. That is, in the EGR flow rate estimation means 42A ′, the value obtained by averaging the sampling data of the actual EPS detected by the EPS 65 by the EGR valve position data processing means 42B and the front and back of the EGR valve 25 calculated by the differential pressure calculation means 47 From the differential pressure DEP, the EGR flow rate can be estimated by a three-dimensional map of correspondence as shown in FIG.
[0023]
The differential pressure calculation means 47 calculates the difference (= Pegr−Pb) between the boost pressure (intake pipe pressure) Pb detected by the boost sensor 63 and the upstream pressure Pegr of the EGR valve 25 detected by the pressure sensor 66. To do. At this time, the boost pressure Pb and the upstream pressure Pegr of the EGR valve 25 used for the calculation are also obtained by averaging the data obtained in the intake stroke of the target cylinder, as in the sampling data processing of the EGR valve position. To.
[0024]
The EGR gas density ρegr can be calculated from the fuel injection amount Q and the engine temperature (generally the engine coolant temperature) Tw.
On the other hand, the EGR valve basic position setting means 43 uses the EGR valve basic position setting map prepared in advance based on the engine speed Ne and the fuel injection amount Q into the cylinder (an amount corresponding to the engine load) Q. Set the position.
[0025]
Further, the PI calculating means 44 calculates the deviation (= target λ−actual λ) between the target λ set by the target excess air ratio setting means 41 and the actual λ estimated by the actual excess air ratio estimation means 42 as PI. Arithmetic processing.
The EGR valve target position setting means 45 adds the EGR valve basic position set by the EGR valve basic position setting means 43 and the value calculated by the PI calculation means 44 to set the EGR valve target position EPSt. .
[0026]
The EGR valve command means 46 outputs a command signal (= EPSt−ESP) to the EGR valve 25 based on the EGR valve target position EPSt set by the EGR valve target position setting means 45 and the current EGR valve position ESP.
The differential pressure increase control means 48 compares the front-rear differential pressure DEP of the EGR valve 25 calculated by the differential pressure calculation means 47 with a predetermined value, and when the front-rear differential pressure DEP is less than the predetermined value, the intake throttle valve 14 is controlled. The pressure difference is increased to increase the differential pressure across the EGR valve 25. This is because the EGR flow rate can be properly grasped and the EGR can be controlled with high accuracy.
[0027]
That is, in this apparatus, as described above, the EGR flow rate (EGR valve passage flow rate) Vegr is measured by the actual EPS (opening degree of the EGR valve 25) detected by the EPS 65 and the differential pressure calculation means 47 of the EGR valve 25. This is estimated and calculated from the front-to-back differential pressure DEP using a map of correspondence as shown in FIG.
In FIG. 3, ΔPi (that is, ΔP _{1 to} ΔP ₁₁ ) indicates the differential pressure before and after EGR, and ΔP ₁ , ΔP ₂ , ΔP ₂ ... ΔP ₁₁ in this order (as the value of i increases). The front / rear differential pressure is large. As for the pressure difference between adjacent differential pressures, the difference between ΔP ₁ and ΔP ₂ , the difference between ΔP ₂ and ΔP _3, and the difference between ΔP ₃ and ΔP ₄ are all 5 mmHg. , and the a 10mmHg any difference between the difference, the [Delta] P ₆ and [Delta] P ₇ between the difference [Delta] P ₅ and [Delta] P ₆ between the [Delta] P ₄ and [Delta] P _5, before and after difference [Delta] P ₇ after the adjacent The pressure difference between the pressures gradually increases.
[0028]
However, in the low load region where the EGR requirement is high, as shown by region A in FIG. 3, the differential pressure across the EGR valve is very small, for example, about several mmHg, and a large amount of EGR is required. Since the EGR valve opening is almost fully open, changes in the EGR flow rate become sensitive to changes in the differential pressure across the EGR valve, and the EGR flow rate estimated by a slight error in the differential pressure across the EGR valve greatly fluctuates. End up.
[0029]
Therefore, in this case, by using the region where the change in the EGR flow rate is not sensitive to the change in the differential pressure across the EGR valve by restricting the intake throttle valve 14 and increasing the differential pressure across the EGR valve 25, the EGR valve Even if an error occurs in the differential pressure before and after, the estimated EGR flow rate is not greatly deviated so that the EGR flow rate can be properly grasped. The intake throttle valve 14 is originally controlled in a state corresponding to the operating state of the engine, but the differential pressure increase control means 48 corrects the target opening of the intake throttle valve 14 in accordance with the operating state of the engine to the throttle side. By doing so, the differential pressure is increased.
[0030]
Since the exhaust gas recirculation device according to one embodiment of the present invention is configured as described above, the target excess air ratio setting means 41 sets the target λ according to the operating state of the engine, and the actual excess air ratio. When the estimation unit 42 estimates the actual λ, the PI calculation unit 44 performs PI calculation on the difference between the target λ and the actual λ. On the other hand, when the EGR valve basic position setting means 43 sets the EGR valve basic position, the EGR valve target position setting means 45 adds the set EGR valve basic position and the above-mentioned PI calculation processing value to obtain the target value of the EGR valve. The position is set, and the EGR valve command means 46 outputs a command signal to the EGR valve 25 based on the target position and the actual position of the EGR valve.
[0031]
When estimating the actual λ, the EGR flow rate (EGR valve passage flow rate) Vegr is used to determine the EGR amount, and when the EGR flow rate is determined, the EGR valve opening (EGR valve) processed by the EGR valve position data processing means 42B is used. Position) and the differential pressure DEP before and after the EGR valve 25 calculated by the differential pressure calculation means 47 is used.
At this time, the EGR valve position data processing means 42B averages the sampling data obtained in the intake stroke immediately before the combustion stroke (explosion stroke) of the cylinder whose EGR flow is to be estimated, and this value is used as the EGR flow rate. Since it is used for estimation, the EGR valve position data when EGR intake is actually performed in the cylinder (during the intake stroke) is appropriately used.
[0032]
Therefore, the EGR amount can be accurately estimated, an accurate estimated value of actual λ can be obtained, and EGR (exhaust gas recirculation) can be controlled with high accuracy.
Further, in a low load region where EGR demand is high, as shown by region A in FIG. 3, the EGR valve front-rear differential pressure is very small, for example, about several mmHg, and a large amount of EGR is required. Since the valve opening is almost fully open, a slight error in the differential pressure across the EGR valve will greatly deviate the estimated EGR flow rate, but this apparatus is provided with differential pressure increasing means 49. Therefore, there is an effect that such a problem is avoided.
[0033]
That is, when the differential pressure across the EGR valve is equal to or lower than the predetermined pressure, the intake throttle valve 14 is throttled to increase the differential pressure across the EGR valve 25. Therefore, as shown in FIG. The EGR flow rate is estimated along a line with a higher differential pressure.
If, for example, the target EGR flow rate is at a level indicated by the target EGR flow rate in FIG. 3, the actual EGR flow rate normally exists in the vicinity thereof, but by increasing the differential pressure across the EGR valve 25, in FIG. As indicated by an arrow (an arrow heading from the right side ● to the left side ●), the EGR flow rate can be secured while the opening degree of the EGR valve 25 is relatively small.
[0034]
As described above, in the region where the differential pressure across the EGR valve 25 is relatively large and the opening degree of the EGR valve 25 is not so large, the change in the EGR flow rate with respect to the error in the differential pressure across the EGR valve is reduced. Even if there is a slight error in the calculated value of the differential pressure across the valve, the estimated value of the EGR flow rate is little affected and the EGR amount can be properly grasped.
[0035]
As a result, the feedback control of the EGR valve using the in-cylinder excess air ratio λ as a parameter can be performed with high accuracy, and the EGR control can be performed appropriately.
In addition, this invention is not limited to the above-mentioned embodiment, It can apply in various deformation | transformation.
[0036]
For example, in the above-described embodiment, the EGR flow rate is estimated by using simple averaging processing of sampling data obtained in the intake stroke of the estimation target cylinder, but the averaging may be an appropriate weighted average. Moreover, even if the EGR flow rate is estimated using only one representative value of the sampling data obtained in the intake stroke, the estimation accuracy of the EGR flow rate can be improved to some extent.
[0037]
In the above-described embodiment, the intake throttle valve 14 is used as the differential pressure increasing means 49. However, in the case of an engine having a VG turbo, the differential pressure is increased by restricting the variable vane of the VG turbo. can do.
Furthermore, in the above-described embodiment, the intake throttle valve 14 is used as the differential pressure increasing means 49. However, in the case of an engine having a VG turbo, the differential pressure is increased by restricting the variable vane of the VG turbo. can do.
[0038]
It is also conceivable to estimate the EGR flow rate using the upstream pressure of the EGR valve instead of the differential pressure across the EGR valve.
Furthermore, although the above-mentioned embodiment applies this invention to the diesel engine provided with the turbocharger, it is suitable also for a naturally aspirated diesel engine, a lean combustion type gasoline engine, etc. Furthermore, the specific configuration and control procedure of the engine control system can also be changed without departing from the spirit of the present invention.
[0039]
【The invention's effect】
As described in detail above, according to the exhaust gas recirculation device of the present invention, the differential pressure increasing means is arranged before and after the EGR valve calculated by the differential pressure calculating means in estimating the actual excess air ratio. When the differential pressure is in a region below a predetermined value where the change in the EGR amount becomes sensitive to the change in the differential pressure across the EGR valve, the differential pressure in the EGR valve is increased so that the EGR amount can be accurately derived. Thus, the estimation accuracy of the actual excess air ratio is improved, and the EGR control can be performed with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an internal combustion engine provided with an exhaust gas recirculation device according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating control by an exhaust gas recirculation device according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating the relationship between the differential pressure across the EGR valve, the EGR valve opening, and the EGR flow rate for explaining the problem of the present invention and for explaining the operation of the exhaust gas recirculation device according to one embodiment of the present invention. FIG.
FIG. 4 is a time chart for explaining the operation of the exhaust gas recirculation device as one embodiment of the present invention.
[Explanation of symbols]
11 Intake passage 21 Exhaust passage 23 Exhaust gas recirculation system (EGR)
24 EGR passage 25 EGR valve 41 target excess air ratio setting means 42 actual excess air ratio estimation means 42A EGR amount derivation means 42A 'EGR flow rate estimation means 42B EGR valve position data processing means 45 EGR valve target position setting means (target EGR amount setting means) means)
46 EGR valve command means (EGR valve opening control means)
47 Differential pressure calculating means 49 Differential pressure increasing means 61 Crank angle sensor 62 as operating condition detecting means Accelerator position sensor (APS) as operating condition detecting means
65 Opening detection means

Claims (3)

An EGR passage that communicates an exhaust passage and an intake passage of the internal combustion engine to recirculate exhaust gas in the exhaust passage into the intake passage;
An exhaust gas recirculation device having an EGR valve provided in the EGR passage and configured to adjust an amount of exhaust gas recirculated into the intake passage;
Operating state detecting means for detecting the operating state of the internal combustion engine;
Target excess air ratio setting means for setting a target excess air ratio in the cylinder of the internal combustion engine corresponding to the operating condition detected by the operating condition detection means;
Differential pressure calculating means for calculating the differential pressure across the EGR valve;
EGR amount deriving means for deriving an EGR amount in the cylinder of the internal combustion engine based on the front-rear differential pressure detected by the differential pressure calculating means;
An actual excess air ratio estimating means for estimating an actual excess air ratio in the cylinder using the EGR amount derived by the EGR amount deriving means;
Target EGR amount setting means for setting the target EGR amount based on the target excess air ratio set by the target excess air ratio setting means and the actual excess air ratio estimated by the actual excess air ratio estimation means;
EGR valve opening control means for driving the EGR valve based on the target EGR amount set by the target EGR amount setting means,
When the differential pressure of the EGR valve which is calculated by the difference calculating portion is within a predetermined value or less of the area change of the EGR amount is sensitive to changes in the differential pressure of the EGR valve, the EGR valve An exhaust gas recirculation device is provided, wherein differential pressure increasing means for increasing the differential pressure before and after is provided.   The internal combustion engine is a diesel engine,
  The differential pressure increasing means throttles the intake throttle valve provided in the intake passage to increase the differential pressure across the EGR valve.
The exhaust gas recirculation device according to claim 1, wherein:   The EGR amount deriving means uses the EGR flow to map the opening degree of the EGR valve and the differential pressure across the EGR valve according to a map in which the opening degree of the EGR valve and the differential pressure across the EGR valve correspond to the EGR quantity. The EGR amount is derived from
The exhaust gas recirculation device according to claim 1 or 2, characterized by the above.

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