JP2009209748A - Exhaust gas recirculation device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation device for an engine capable of inhibiting deterioration of travelling by enabling early rise of supercharging pressure while inhibiting deterioration of NOx emission even in acceleration during exhaust emission recirculation control. <P>SOLUTION: This device is provided with an exhaust gas passage, an exhaust gas recirculation quantity control valve disposed in the exhaust gas passage, and an exhaust gas recirculation control means controlling opening of the exhaust gas recirculation quantity control valve with setting oxygen concentration as a target (s4, s13). The exhaust gas recirculation control device maintains opening of the exhaust gas recirculation quantity control valve constant (s7) when oxygen concentration is richer than prescribed value (s5, s6). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas passage, an exhaust gas recirculation amount control valve disposed in the exhaust gas passage, and an exhaust gas recirculation control means for controlling the opening degree of the exhaust gas recirculation amount control valve with the oxygen concentration as a target. It is related with the exhaust-gas recirculation apparatus of the engine provided with.

  2. Description of the Related Art In general, an automobile engine is provided with an exhaust gas recirculation (EGR) device that recirculates a part of exhaust gas to an intake system as EGR gas in order to reduce the amount of NOx (nitrogen oxide) generated or emitted. It is done.

  However, when EGR gas is introduced, the amount of fresh air, that is, the amount of intake air flowing from the atmosphere (new air amount) excluding EGR gas out of the amount of intake air sucked into the combustion chamber is reduced, and the air-fuel ratio (air) There is a problem of affecting the excess rate.

  Specifically, when a large amount of EGR gas is introduced, NOx emission deterioration can be suppressed, but on the other hand, the air-fuel ratio becomes rich, and the combustibility deteriorates to generate smoke.

  Therefore, in recent years, in the EGR device, while setting the target oxygen concentration, the opening degree of the exhaust gas recirculation amount control valve (EGR control valve) is controlled based on the difference between the target oxygen concentration and the actual oxygen concentration, A device for controlling the exhaust gas recirculation amount has been proposed (see Patent Document 1).

In the following Patent Document 1, it is possible to converge the actual air-fuel ratio to the target air-fuel ratio that becomes the particulate generation limit (smoke limit) by this EGR device, thereby reducing the amount of smoke generated and the deterioration of NOx emissions. We are trying to achieve both suppression.
JP-A-11-82183

  By the way, in a diesel engine for automobiles, in order to increase engine output, a turbocharger having a turbine interposed in an exhaust passage and a compressor interposed in an intake passage is usually provided.

  However, at the time of acceleration, there is a problem that a delay in the introduction of fresh air, that is, a delay in the increase in supercharging pressure occurs due to the delay in the rotation of the turbocharger, and the air-fuel ratio becomes rich and smoke is likely to be generated. It was happening.

  Therefore, in order to solve such a problem, for example, when the EGR device as described above is provided, it is conceivable that the EGR control valve is controlled to be fully closed at the time of acceleration so that a large amount of fresh air is introduced quickly. However, such a method causes a significant deterioration in NOx emissions.

  Next, it can be considered that the air-fuel ratio is prevented from becoming rich by reducing the fuel injection amount regardless of the control of the exhaust gas recirculation amount control valve. However, in this case, since sufficient torque cannot be obtained, the acceleration performance is deteriorated, resulting in a problem that the passenger feels stalled.

  Furthermore, when the EGR device controls the EGR control valve based on the difference between the target oxygen concentration and the actual oxygen concentration as in Patent Document 1, if the fuel injection amount is limited, the actual oxygen concentration Changes, the opening degree of the EGR control valve changes, and as a result, the amount of fresh air is changed.

  The change in the fresh air amount causes a change in the fuel injection amount by predetermined feedback control, and causes a further change in the actual oxygen concentration. For this reason, the change in the opening degree of the EGR control valve, the change in the fresh air amount, the change in the fuel injection amount, the change in the actual oxygen concentration, etc. are repeated as described above. (Strangeness) occurs, giving the passenger a sense of incongruity, such as the inability to feel acceleration.

  The present invention provides an exhaust gas recirculation device for an engine that enables an early increase in supercharging pressure while suppressing deterioration in NOx emission even during acceleration during exhaust gas recirculation control, and can suppress deterioration in running performance. The purpose is to provide.

  An exhaust gas recirculation device for an engine according to the present invention includes an exhaust gas passage, an exhaust gas recirculation amount control valve disposed in the exhaust gas passage, and an opening degree of the exhaust gas recirculation amount control valve with an oxygen concentration as a target. And an exhaust gas recirculation control means for controlling the exhaust gas recirculation control means to maintain a constant opening of the exhaust gas recirculation amount control valve when the oxygen concentration is richer than a predetermined value.

  According to this configuration, when the actual oxygen concentration becomes rich during acceleration during exhaust gas recirculation control, the opening degree of the exhaust gas recirculation amount control valve is kept constant regardless of the difference between the actual oxygen concentration and the target oxygen concentration. Therefore, as in the past, the change in the opening degree of the exhaust gas recirculation amount control valve, the change in the fresh air amount, the change in the fuel injection amount, the change in the actual oxygen concentration, the change in the actual oxygen concentration, etc. Hunting can be suppressed, and as a result, deterioration in running performance can be suppressed.

  Further, by setting the exhaust gas recirculation amount control valve to a constant opening degree, it is possible to increase the supercharging pressure early by limiting the EGR introduction amount while suppressing deterioration of NOx emission.

  In one embodiment of the present invention, the exhaust gas recirculation control means is configured to return the exhaust gas when the oxygen concentration is richer than a predetermined value or when the actual supercharging pressure is lower than a predetermined value with respect to the target supercharging pressure. The opening degree of the flow control valve is kept constant.

  For example, even if the actual oxygen concentration is not rich, if the actual supercharging pressure is greatly delayed from the target supercharging pressure, the amount of fresh air is small, so the oxygen concentration is low. It is considered that the probability of becoming rich will increase.

According to this configuration, if the delay of the actual supercharging pressure with respect to the target supercharging pressure becomes large during sudden acceleration due to the control of the exhaust gas recirculation amount control valve based on the supercharging pressure, the point in time when the state is detected The control valve can be immediately opened at a constant opening. Therefore, the control valve can be set to a constant opening at a time earlier than the actual oxygen concentration becomes rich, and the boost pressure increase characteristic can be further improved.
Also, at the time of slow acceleration, since the difference between the actual supercharging pressure and the target supercharging pressure is small, the exhaust gas recirculation amount control valve is controlled based on the state where the actual oxygen concentration is richer than a predetermined value. The opening can be constant.

  In one embodiment of the present invention, the exhaust gas recirculation control means has an opening degree of the exhaust gas recirculation amount control valve at a predetermined opening degree, or immediately before the oxygen concentration is determined to be rich above a predetermined value, or in actual supercharging. The pressure is maintained at the opening just before it is determined that the pressure is lower than a predetermined value with respect to the target boost pressure.

  According to this configuration, the supercharging pressure can be increased quickly by maintaining the exhaust gas recirculation control valve at a predetermined opening or an opening just before.

  In one embodiment of the present invention, the exhaust gas recirculation control means is configured such that the oxygen concentration is richer than a predetermined value after the state in which the opening degree of the exhaust gas recirculation amount control valve is maintained constant for a predetermined period of time. The exhaust gas recirculation amount control valve is controlled to be fully closed.

  According to this configuration, even if the exhaust gas recirculation amount control valve is maintained at a constant opening for a predetermined period of time, when the actual oxygen concentration remains rich due to a shortage of fresh air, the control valve is By controlling the valve fully closed (opening degree 0), it is possible to reliably increase the supercharging pressure.

According to the present invention, when the actual oxygen concentration becomes rich during acceleration during exhaust gas recirculation control, the opening degree of the exhaust gas recirculation amount control valve is kept constant regardless of the difference between the actual oxygen concentration and the target oxygen concentration. Therefore, as in the past, the change in the opening degree of the exhaust gas recirculation amount control valve, the change in the fresh air amount, the change in the fuel injection amount, the change in the actual oxygen concentration, the change in the actual oxygen concentration, etc. Hunting can be suppressed, and as a result, deterioration in running performance can be suppressed.
Further, by setting the exhaust gas recirculation amount control valve to a constant opening degree, it is possible to increase the supercharging pressure early by limiting the EGR introduction amount while suppressing deterioration of NOx emission.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing an overall configuration of a diesel engine provided with an exhaust gas recirculation device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a control system of the diesel engine shown in FIG.

  A diesel engine (hereinafter referred to as an “engine”) according to the present embodiment includes a cylinder block 1 formed with an arrangement in which cylinder bores of each cylinder are arranged in series in the front-rear direction (direction orthogonal to the plane of FIG. 1), and above The engine body is composed of the cylinder head 2 disposed. In each cylinder bore of the cylinder block 1, pistons 3 are slidably arranged, and these pistons 3 are connected to crankshafts 5 that are engine output shafts via connecting rods 4.

  A deep dish-shaped combustion chamber 6 is formed on the top surface of the piston 3. The cylinder head 2 is provided with a fuel injection valve 7 for each cylinder so as to directly inject and supply fuel to the combustion chamber 6. Further, the cylinder head 2 is provided with a cross-flow type intake port 8 and an exhaust port 9 that open to the left and right (left and right directions in FIG. 1) side wall portions for each cylinder. The intake port 8 is connected to a single intake passage 10 upstream of the manifold type, and the exhaust port 9 is connected to a single exhaust passage 11 downstream of the manifold type.

  In the intake passage 10, an air cleaner 12 that purifies intake air, an air flow sensor 13 that detects intake air amount, a blower 14 a of a turbocharger 14 that pressurizes and supplies intake air in order from the intake upstream side to the downstream side. An intercooler 15 that cools the pressurized intake air, an intake control valve 16 that throttles the intake air, an intake air temperature sensor 17 that detects the intake air temperature, and an intake air pressure sensor 18 that detects the intake air pressure are disposed on the downstream side. Is provided with a surge tank 19 at a position branched toward the intake port 8 of each cylinder.

  Further, in the exhaust passage, in order from the exhaust upstream side to the downstream side, there is an oxidation catalyst-carrying filter device 20 including a turbine 14b of the turbocharger 14 and a filter that carries the oxidation catalyst and collects particulates in the exhaust gas. It is arranged.

  An EGR passage (exhaust gas recirculation passage) for returning a part of the exhaust gas to the intake system between the upstream side of the turbine 14b of the exhaust passage 11 and the upstream side of the surge tank 19 downstream of the intake pressure sensor 18 of the intake passage 10 25 is provided. A negative pressure actuator type EGR control valve (exhaust gas recirculation amount control valve) 26 and an EGR cooler 27 that cools the recirculated exhaust gas (EGR gas) with engine coolant are disposed in the middle of the EGR passage 25. ing.

  The engine is driven by the crankshaft 5 to pressurize the fuel supplied from a fuel tank (not shown), and the high pressure fuel discharged from the fuel pump 28 is accumulated, and the fuel supply pipe 29 is connected. And a common rail 30 that is distributed and supplied to each fuel injection valve 7. The fuel injection valve 7 is connected to a fuel return pipe 31 that returns excess fuel after injection to a fuel tank (not shown).

  Further, in this engine, a water temperature sensor 32 for detecting the engine water temperature is arranged in the cylinder head 2, and a crank angle sensor 33 for detecting the engine rotation speed against the end of the crankshaft 5 is provided.

  The fuel injection valve 7, the turbocharger 14, and the EGR control valve 26 are controlled by an ECU 100 (engine control unit) (see FIG. 2) using a microcomputer.

  As shown in FIG. 2, this ECU 100 is detected by an intake air flow detected by an air flow sensor 13, an intake air temperature detected by an intake air temperature sensor 17, an intake air pressure detected by an intake air pressure sensor 18, and an engine water temperature sensor 32. Control information such as the engine water temperature, the engine speed (engine speed) detected by the crank angle sensor (engine speed sensor) 33, and the accelerator position (ie, engine load) detected by the accelerator position sensor 40. It is used for various control of the engine. The ECU 100 estimates the oxygen concentration in the intake passage 10 or the surge tank 19 on the downstream side of the EGR passage 25.

  However, control methods for general engine control (for example, fuel injection control, supercharging capacity change control, particulate combustion control, etc.) are well known to those skilled in the art, and Since control is not the gist of the present invention, description of general control of the engine is omitted. The ECU 100 performs engine control by controlling, for example, the fuel injection valve 7, the intake control valve 16, the EGR control valve 26, and the like.

  In the engine control of the ECU 100, first, the engine speed N and the accelerator opening degree θ are detected (read), and the required torque T of the engine is calculated based on the engine speed N and the accelerator opening degree θ. Further, in this engine control, the required injection amount is determined based on a map defined for the relationship between the engine speed N and the accelerator opening θ and the required fuel injection amount simultaneously with the calculation of the required torque T.

  FIG. 3 shows an operation region (first region) in which EGR (exhaust gas recirculation) is to be executed and an operation region (second region) in which EGR is to be stopped using the engine speed N and the required fuel injection amount as parameters. FIG. As described above, after the required torque T and the required fuel injection amount are obtained, the EGR control valve 26 is opened in the first region, which is the low rotation / low load region, as shown in FIG. EGR is executed. On the other hand, in the second region that is the high rotation region or the high load region, the EGR control valve 26 is controlled to be fully closed to stop the EGR.

  Next, the target oxygen concentration of the intake air supplied to the combustion chamber 6 is calculated based on the engine speed N and the required torque T. Subsequently, the actual oxygen concentration of the intake air supplied to the combustion chamber 6, specifically, for example, the oxygen concentration of the intake air in the surge tank 19 or in the intake passage 10 downstream of the EGR passage 25 is the above-described existing oxygen concentration. It is estimated using various sensors.

  As shown in FIG. 4, the target oxygen concentration is set with the engine speed N and the required torque T as parameters. Specifically, the target oxygen concentration is set such that, for example, the lower the engine speed and the smaller the required torque T (or engine load), the lower the target oxygen concentration. Note that the specific method for estimating the oxygen concentration of the intake air described above is already known, for example, from Japanese Patent Application Laid-Open No. 2008-8181, and the description thereof is omitted here.

  In this embodiment, after the oxygen concentration of the intake air supplied to the combustion chamber 6 is estimated, the supply amount of EGR gas (exhaust gas return) is set so that this oxygen concentration estimated value (actual oxygen concentration) becomes the target oxygen concentration. (Flow rate) is feedback controlled. The control of the supply amount of the EGR gas is performed by the opening degree control of the intake control valve 16 and the opening degree control of the EGR control valve 26 provided in the EGR passage 25.

  For example, when the supply amount of EGR gas (exhaust gas recirculation amount) is insufficient, the intake control valve 16 is controlled in the valve closing direction. That is, the intake control valve 16 is basically fully opened so that when the supply amount of EGR gas is insufficient, the intake pressure of the portion 25a decreases and the supply of EGR gas from the EGR passage 25 increases. It is controlled in the valve closing direction.

  Further, in the present embodiment, during feedback control of the EGR control valve 26 targeting such oxygen concentration, the engine or the vehicle on which the engine is mounted is in an acceleration operation state, and the actual oxygen concentration is a predetermined value or more. When the air-fuel ratio becomes richer than a predetermined value, the ECU 100 keeps the opening degree of the EGR control valve 26 constant.

  Hereinafter, the EGR control executed by the ECU 100 will be described with reference to the flowchart shown in FIG. 5 and the graph shown in FIG. FIG. 5 is a flowchart for explaining the EGR control executed by the ECU 100, and FIG. 6 is a graph showing the change over time in the physical quantity related to the operation of the diesel engine during acceleration. Here, the graphs G1 to G10 shown in FIG. 6 are respectively the engine speed, the accelerator opening, the fuel injection amount limit value based on the smoke limit, the actual fuel injection amount, the boost pressure target value, and the actual boost pressure. , The opening degree of the EGR control valve 26, the oxygen concentration target value, the oxygen concentration limit value based on the smoke limit, and the temporal change of the actual oxygen concentration are shown.

  As shown in FIG. 5, in this engine control, first, in step s1, the intake air amount, intake air temperature, intake pressure, detected engine speed (engine speed), accelerator opening, Control information such as engine water temperature is detected (read). Here, for example, the required torque T of the engine and the required fuel injection amount are determined based on the engine speed N and the accelerator opening θ.

  Next, in step s2, it is determined whether or not it is an operation region (first region) in which EGR (exhaust gas recirculation) should be executed using the engine speed N and the required injection amount as parameters. If the ECU 100 determines that the region is not the first region but the second region (step s2: NO), the ECU 100 proceeds to step s3, controls the EGR control valve 26 to be fully closed (opening degree 0), and returns the process. On the other hand, if it is determined that the region is the first region (step s2: YES), the routine proceeds to step s4, where the so-called EGR control valve 26 feedback control subroutine targeting the oxygen concentration is executed. To do.

  Here, during the execution of the feedback control of the EGR control valve 26 in step s4, the ECU 100 calculates the oxygen concentration estimated value (actual oxygen concentration) and the smoke limit oxygen concentration (oxygen concentration limit value) that serves as a measure of smoke generation. The difference Δα (see FIG. 6) is detected.

  The oxygen concentration limit value is determined by the number of fuel injections at the fuel injection valve 7 and the pressure (fuel pressure) of the common rail 30, and the threshold value for limiting the oxygen concentration is set higher as the number of fuel injections increases. The lower the fuel pressure, the lower the setting. This is because as the number of injections increases, the air-fuel ratio becomes richer and smoke is more likely to be generated, whereas when the fuel pressure is higher, the air-fuel ratio becomes lean and smoke is less likely to be generated. For these reasons, the oxygen concentration limit is set more severely as the number of injections is larger, and the oxygen concentration limit is relaxed as the fuel pressure is higher.

  In step s5, the ECU 100 determines whether or not the oxygen concentration is richer than a predetermined value based on the difference Δα. If it is determined that the oxygen concentration is not richer than the predetermined value (step s5: NO), the process proceeds to step s6 described later. On the other hand, it has been detected that the state where the difference between the actual oxygen concentration and the oxygen concentration limit value is equal to or less than the predetermined value α0, that is, the state where the oxygen concentration (air-fuel ratio) is rich above the predetermined value continues for a predetermined time. Sometimes (step s5: YES), the routine proceeds to step s7 described later.

  Incidentally, in the present embodiment, the ECU 100 detects the difference Δβ (see FIG. 6) between the actual boost pressure and the target boost pressure simultaneously with the difference Δα. If it is determined in step s5 that the actual oxygen concentration is not rich (step s5: NO), in step s6, the state in which the actual boost pressure has decreased by a predetermined value β0 or more compared to the target boost pressure continues for a predetermined time. It is determined whether or not.

  Here, when the ECU 100 detects that the state in which the actual boost pressure has decreased by the predetermined value β0 or more compared to the target boost pressure continues for a predetermined time (step s6: YES), the process proceeds to step s7 described later. If not (step s6: NO), the process is returned.

  In step s7, the ECU 100 maintains the opening of the EGR control valve 26 at a predetermined value (here, 5%) as shown by a graph G7 in FIG.

  Then, ECU 100 determines whether or not a timer means (not shown) has already been set and the time during which EGR control valve 26 is maintained at a constant opening is measured (step s8). The timer means counts down a predetermined time t determined in advance. If the timer means is set (step s8: YES), the ECU 100 decrements the count value of the timer means (step s9). If the timer means is not set (step s8: NO), it is set (step s10).

  Next, the ECU 100 determines whether or not the count value of the timer means has become zero. Here, if the count value is not 0 (step s11: NO), the ECU 100 returns the process, and when the count value becomes 0, that is, the opening degree of the EGR control valve 26 continues for the time t. If it is maintained constant (step s11: YES), the process proceeds to step s12 to determine whether or not the actual oxygen concentration has become lean.

  If the actual oxygen concentration is lean (step s12: YES), the ECU 100 proceeds to step s13, returns to the feedback control subroutine of the EGR control valve 26, and returns the process. On the other hand, if the actual oxygen concentration (air-fuel ratio) does not become lean and remains rich (step s12: NO), the ECU 100 proceeds to step s14 and fully closes the EGR control valve 26 (opening degree). 0).

  In this case, since a large amount of fresh air can be introduced by closing the EGR control valve 26, the oxygen concentration can be made lean anyway. After closing the EGR control valve 26 in step s14, the ECU 100 returns to the process in step s12 and repeats the processes in steps s12 and s14 until the oxygen concentration becomes lean.

  Thus, in this embodiment, when the actual oxygen concentration becomes rich during acceleration during exhaust gas recirculation control, the opening degree of the EGR control valve 26 is set regardless of the difference between the actual oxygen concentration and the target oxygen concentration. Since it is kept constant, the hunting of the fuel injection by repeating the change of the opening degree of the EGR control valve 26, the change of the fresh air amount, the change of the fuel injection amount, the change of the actual oxygen concentration,. As a result, it is possible to suppress deterioration in running performance.

  Further, by setting the EGR control valve 26 to a constant opening degree, it is possible to increase the supercharging pressure early by limiting the EGR introduction amount while suppressing the deterioration of NOx emission.

  In the present embodiment, even if it is determined in step s5 that the actual oxygen concentration is not rich, if the actual boost pressure is reduced compared to the target boost pressure in step s6, the ECU 100 The opening degree of the control valve 26 is kept constant.

  This is because even if the actual oxygen concentration is not rich, if the actual supercharging pressure is greatly delayed from the target supercharging pressure, the fresh air amount is small, so the oxygen concentration If the delay of the actual supercharging pressure with respect to the target supercharging pressure at the time of sudden acceleration increases due to the control of the EGR control valve 26 based on this supercharging pressure, As soon as this state is detected, the EGR control valve 26 can be set to a constant opening. Therefore, the EGR control valve 26 can be set to a constant opening at a time earlier than the actual oxygen concentration becomes rich, and the boost pressure increase characteristic can be further improved.

  Further, at the time of slow acceleration, since the difference between the actual supercharging pressure and the target supercharging pressure is small, the EGR control valve 26 is constantly opened based on a state where the actual oxygen concentration is richer than a predetermined value. Can be degrees.

  In this embodiment, in step s5, the opening of the EGR control valve 26 is maintained at a predetermined value (5%) set in advance, but the present invention is not necessarily limited to this. For example, the EGR control valve 26 immediately before it is determined that the actual oxygen concentration has become richer than the predetermined value α0 or immediately before it is determined that the actual supercharging pressure is lower than the target supercharging pressure by the predetermined value β0 or more. The opening may be maintained.

  As described above, by maintaining the opening degree of the EGR control valve 26 at a predetermined value (5%) set in advance or the opening degree immediately before each of the above determinations, the boost pressure can be increased quickly.

  Further, on a slope with a steep road surface gradient, there is a case where the increase in the boost pressure becomes noticeable when climbing up. As described above, the EGR control valve 26 is maintained at a constant opening for a predetermined period. However, the actual oxygen concentration may remain rich due to a shortage of fresh air. In such a case, as in the present embodiment, the supercharging pressure can be reliably increased by controlling the EGR control valve 26 to be fully closed (opening degree 0) in step s14.

  In the above-described embodiment, the opening degree of the EGR control valve 26 is kept constant for a predetermined time t set in advance by the processing of steps s8 to s11, but is not necessarily limited thereto. For example, when the difference Δα between the target oxygen concentration and the actual oxygen concentration is equal to or greater than a predetermined value, or the difference Δβ between the target boost pressure and the actual boost pressure is equal to or less than a predetermined value, the boost pressure is appropriately increased. Therefore, it is possible to return to the feedback control subroutine of the EGR control valve 26 corresponding to step s13 in FIG.

  In this case, since it is possible to return to the feedback control of the EGR control valve 26 earlier according to the situation, it is possible to more appropriately suppress the NOx emission deterioration.

In the above-described embodiment, the actual oxygen concentration is estimated using an existing sensor. However, the present invention is not necessarily limited to this. For example, a dedicated linear O ₂ sensor is used for the surge tank 19. It may be provided to directly detect the oxygen concentration.

In correspondence between the configuration of the present invention and the above-described embodiment,
The exhaust gas passage of the present invention corresponds to the exhaust passage 11,
Similarly,
The exhaust gas recirculation amount control valve corresponds to the EGR control valve 26,
The exhaust gas recirculation amount control means corresponds to the engine control unit 100 that executes steps s4 to s14.
The present invention is not limited only to the configuration of the above-described embodiment, and many embodiments can be obtained.

The schematic diagram which shows the whole structure of the diesel engine provided with the exhaust-gas recirculation apparatus which concerns on embodiment of this invention. The block diagram which shows the control system of the diesel engine shown in FIG. The figure which shows the operation area | region which performs EGR in the diesel engine of FIG. The figure which shows the rough setting method of the target oxygen concentration of an intake passage. The flowchart for demonstrating EGR control performed by an engine control unit. The graph which shows the time-dependent change of the physical quantity relevant to the driving | operation of a diesel engine at the time of acceleration.

Explanation of symbols

11 ... Exhaust passage 26 ... EGR control valve 100 ... Engine control units s4 to s14 ... Exhaust gas recirculation control means

Claims (4)

An exhaust gas passage;
An exhaust gas recirculation amount control valve disposed in the exhaust gas passage;
An exhaust gas recirculation control means for controlling the opening degree of the exhaust gas recirculation amount control valve with the oxygen concentration as a target;
The exhaust gas recirculation device for an engine maintains the opening of the exhaust gas recirculation amount control valve constant when the oxygen concentration is richer than a predetermined value. The exhaust gas recirculation control means maintains the opening of the exhaust gas recirculation amount control valve constant when the oxygen concentration is richer than a predetermined value or when the actual supercharging pressure is lower than a predetermined value with respect to the target supercharging pressure. The exhaust gas recirculation device for an engine according to claim 1, which is maintained. The exhaust gas recirculation control means is configured such that the exhaust gas recirculation amount control valve is opened at a predetermined opening, immediately before the oxygen concentration is determined to be rich above a predetermined value, or when the actual supercharging pressure is higher than the target supercharging pressure. The exhaust gas recirculation device for an engine according to claim 1, wherein the exhaust gas recirculation device is maintained at an opening immediately before it is determined to be lower than a predetermined value. The exhaust gas recirculation control means controls the exhaust gas recirculation amount control valve when the oxygen concentration is richer than a predetermined value after the state in which the opening degree of the exhaust gas recirculation amount control valve is maintained constant for a predetermined period of time. The exhaust gas recirculation device for an engine according to claim 1, wherein the exhaust gas recirculation device is controlled to be fully closed.

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