DE102012103998B4 - Exhaust gas recirculation control device for an internal combustion engine - Google Patents

Abstract

Exhaust gas recirculation control apparatus applied to a combustion control system of an internal combustion engine provided with a turbocharger (16) having a compressor (16a) in an intake passage (12) and a turbine (16b) in an exhaust passage (Fig. 34), a high pressure EGR passage (44) connecting a portion upstream of the turbine (16b) and a portion downstream of the compressor (16a), a low pressure EGR passage (46) which defines a portion downstream of the turbine (16). 16b) and a portion upstream of the compressor (16a), a high-pressure EGR control section (48, 48a) which regulates a high-pressure exhaust gas amount recirculated into the intake passage (12) through the high-pressure EGR passage (44) , and has a low-pressure EGR control section (52, 52a) that controls a low-pressure exhaust gas amount that is returned to the intake passage (12) through the low-pressure EGR passage (46)
a part of the intake passage (12) located downstream of a connection portion with the high pressure EGR passage (44) is defined as a high pressure common passage passage (12a);
a part of the intake passage (12) is defined between a connection part with the low-pressure EGR passage (46) and the connection part with the high-pressure EGR passage (44) as a low-pressure common passage passage (12b); and
an oxygen concentration in an intake air or an exhaust gas recirculation ratio is defined as an intake air parameter; in which
the exhaust gas recirculation control device comprises
a target value setting section (S10, S10a) which sets target values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low-pressure common-flow passage (12b);
a control value calculation section that actually calculates current values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low-pressure common-flow passage (12b); and
a control section (58) that controls the high-pressure EGR control section (48, 48a) and the low-pressure EGR control section (52, 52a) so that the actual values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low pressure makeup flow passage (12b) coincide with the target values of the intake air parameters.

Description

TECHNICAL AREA

The present disclosure relates to an exhaust gas recirculation (EGR) control device for an internal combustion engine. The engine is provided with a turbocharger consisting of a compressor in an intake passage and an intake passage and a turbine in an exhaust passage and an exhaust passage, respectively. The engine is further provided with a high pressure EGR (= exhaust gas recirculation) passage connecting a portion upstream of the turbine and a downstream portion of the compressor and a low pressure EGR passage forming a downstream portion of the engine Turbine and a section upstream of the compressor connects. An amount of exhaust gas recirculated into the intake passage through the high-pressure EGR passage and the low-pressure EGR passage is adjusted by an EGR quantity control device provided for the engine.

BACKGROUND

The JP-2007-315371 A shows an external EGR control system in which a portion of the exhaust gas is recirculated through a high-pressure EGR passage and a low-pressure EGR passage into an intake passage.

Specifically, the EGR amount flowing through the low-pressure EGR passage is forward-feed controlled using a low-pressure EGR valve so as to be constant substantially regardless of an engine load. A high pressure EGR valve is feedback controlled so that the EGR amount flowing through the high pressure EGR passage coincides with a target value, whereby an oxygen concentration in the exhaust gas becomes constant.

In the above control system, however, it is likely that the actual present total EGR amount may be bottlenecked relative to a total amount of EGR needed that should be provided to a combustion chamber. In such a case, although the high-pressure EGR valve is fully opened, the low-pressure EGR valve is not fully opened.

In order to solve the above problem, the present inventor made a control system in which a high-pressure EGR valve and a low-pressure EGR valve are feedback-controlled in such a manner that the total EGR amount agrees with a target value. However, this control system has a technical problem which should be overcome as follows.

Since a low pressure EGR passage is generally longer than a high pressure EGR passage, a low pressure EGR response delay will occur. That is, a period of time from when the low pressure EGR valve is actuated to when the amount of gas provided to the combustion chamber begins to change is longer than a period of time from when the high pressure is on EGR valve is actuated until when the amount of gas supplied to the combustion chamber begins to change. Due to the low-pressure EGR response delay, the entire EGR amount may periodically fluctuate around the target value, which deteriorates a control accuracy of the external EGR control.

In addition, the reveals JP 2008 - 261 300 A an exhaust gas recirculation device that calculates a low pressure EGR rate and a high pressure EGR rate, and these are controlled to corresponding target values.

In addition, the post-published publication discloses DE 10 2010 056 514 A1 a method for reducing nitrogen oxide emission in a diesel engine, in which at least one exhaust gas of internal combustion in a combustion chamber is divided as follows: a first portion of exhaust gas passes as an internal exhaust gas recirculation from the combustion chamber of the diesel engine via an outlet valve associated with the combustion chamber in a subsequent Exhaust tract and is again returned via the exhaust valve from the subsequent exhaust tract in the combustion chamber of the diesel engine, a second part of exhaust gas remains in the combustion chamber and is not ejected, a third part of exhaust gas is returned as external exhaust gas recirculation via an exhaust gas recirculation valve in the combustion chamber, and the respective parts of exhaust gas together form a residual exhaust gas in the combustion chamber for a combustion cycle, wherein the Remaining exhaust gas and / or at least a ratio between parts of the exhaust gas is set in the combustion chamber. Furthermore, an internal combustion engine is proposed which implements this method.

SHORT VERSION

It is an object of the present disclosure to provide an exhaust gas recirculation (EGR) control apparatus for an internal combustion engine capable of avoiding deterioration in the control accuracy of an external EGR amount provided to a combustion chamber when a portion of the exhaust gas is recirculated through a low pressure EGR passage and a high pressure EGR passage.

According to the present disclosure, an exhaust gas recirculation control apparatus is applied to a combustion control system of an internal combustion engine. The engine is provided with a turbocharger having a compressor in an intake passage and a turbine of an exhaust passage, a high pressure EGR passage connecting a portion upstream of the turbine and a downstream portion of the compressor, a low pressure EGR passage having a Section downstream of the turbine and a portion upstream of the compressor connects, a high-pressure EGR control section, which regulates a high-pressure exhaust gas amount, which is returned by the high-pressure EGR passage in the intake passage, and a low-pressure EGR control section, which regulates a low pressure exhaust gas amount which is returned to the intake passage through the low pressure EGR passage.

A part of the intake passage, which is located downstream of a connection portion with the high pressure EGR passage, is defined as a high pressure common passage passage. A part of the intake passage between a low-pressure EGR passage connecting portion and the high-pressure EGR passage connecting portion is defined as a low-pressure common passage passage. An oxygen concentration in the intake air or an exhaust gas recirculation ratio is defined as an intake air parameter.

The exhaust gas recirculation control apparatus includes a target value setting section that sets target values of the intake air parameters in the high-pressure common passage and low-pressure common passage, a control value calculation section that actually calculates current values of the intake air parameters in the high-pressure common passage and the low-pressure common passage, and a control section that stores the High-pressure EGR control section and the low-pressure EGR control section regulate so that the actual values of the intake air parameters in the high-pressure common-flow passage and the low-pressure common flow passage coincide with the target values of the intake air parameters.

Accordingly, it can be avoided that a variation in the amount of exhaust gas flowing through one of the EGR passages affects an amount of exhaust flowing through the other EGR passage. A control accuracy of an external EGR control is not deteriorated.

list of figures

• 1 eine schematische Ansicht, welche eine Gesamtstruktur eines Kraftstoffeinspritzsystems gemäß einer ersten Ausführungsform zeigt;
• 2 ein Flussdiagramm, welches eine Prozedur einer kooperativen Hoch-Nieder-Druck-EGR-Regelung gemäß der ersten Ausführungsform zeigt; und
• 3 ein Flussdiagramm, welches eine Prozedur einer kooperativen Hoch-Nieder-Druck-EGR-Regelung gemäß einer zweiten Ausführungsform zeigt.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings are:

• 1 a schematic view showing an overall structure of a fuel injection system according to a first embodiment;
• 2 FIG. 10 is a flowchart showing a high-low-pressure cooperative EGR control procedure according to the first embodiment; FIG. and
• 3 5 is a flowchart showing a high-low-pressure cooperative EGR control procedure according to a second embodiment.

DETAILED DESCRIPTION

First Embodiment

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

1 Fig. 10 shows an overall structure of a control system in the first embodiment.

A machine 10 is a diesel engine. An air flow meter 14 , which detects an intake air flow rate, a charge air cooler 18 which cools the intake air or intake air, which passes through a turbocharger 16 is charged, and a throttle valve 20 , which by an actuator 20a How a DC motor is driven, for example, are in an intake passage and an intake passage, respectively 12 the machine 10 arranged. The actuator 20a can be a position of the throttle valve 20 to capture.

The intake passage 12 is with a combustion chamber 22 every cylinder of the machine 10 connected. An intake air pressure sensor 24 and an intake air temperature sensor 26 are also in the intake passage 12 downstream of the throttle valve 20 arranged.

A fuel injector or a fuel injection device 28 is at an upper portion of each cylinder of the machine 10 provided to fuel directly into the combustion chamber 22 inject. A high pressure fuel (light oil) becomes the fuel injector 28 from a fuel storage (not shown).

Every cylinder of the machine 10 has an intake port and an exhaust port, respectively, through an intake valve 30 and an exhaust valve 32 be opened or closed. When the inlet valve 30 is opened, the intake air, which passes through the intercooler 18 was cooled, in the combustion chamber 22 introduced. The injector 28 injects the fuel into the combustion chamber 22 one. The burned air-fuel mixture becomes the exhaust passage 34 ejected when the exhaust valve 32 is opened. A crank angle sensor 38 is in a neighborhood of a crankshaft 36 the machine 10 arranged to the rotational speed of the crankshaft 36 capture.

A turbocharger 16 is between the intake passage 12 and the outlet passage 34 intended. The turbocharger 16 has an intake air compressor 16a and an exhaust turbine wheel 16c which are connected by a wave 16c are connected. The exhaust turbine wheel 16c is rotated by the exhaust gas flowing therethrough and the intake air compressor 16a compresses the intake air.

In the outlet passage 34 is a cleaning device 40 such as a Diesel Particulate Filter (DPF), a NOx catalyst and an oxidation catalyst. Further, an air / fuel sensor (A / F) 42 which detects an oxygen concentration in the exhaust gas is provided.

Part of the exhaust gas flowing through the exhaust passage 34 flows, flows into the intake passage 12 through a high pressure EGR passage 44 and a low pressure passage 46 back. Especially, there is a section upstream of the turbine 16b with a portion downstream of the throttle valve 20 through the high pressure EGR passage 44 connected. A high pressure EGR valve 48 is in the high pressure EGR passage 44 arranged to a flow passage area or flow passage area of the passage 44 adapt. The high pressure EGR valve 48 is powered by an electric actuator 48a , such as a DC motor driven. According to an opening degree of the high pressure EGR valve 48 the exhaust gas flows through the high pressure EGR passage 44 and gets through the high-pressure EGR cooler 50 cooled. Then, the exhaust gas flows into the intake passage as an external EGR gas (high-pressure EGR gas) 12 , The high pressure EGR actuator 48a may be the opening degree of the high-pressure EGR valve 48 capture or adapt or change. An exhaust pressure sensor 51 , which detects exhaust pressure, is in the exhaust passage 34 upstream of the high pressure EGR passage 44 intended.

Furthermore, a section is downstream of the turbine 16b with a section upstream of the compressor 16a through a low-pressure EGR passage 46 connected. A low pressure EGR valve 52 is in the low pressure EGR passage 46 arranged to a flow passage area or Flow passage cross section of the passage 46 adapt. The low pressure EGR valve 52 is powered by an electric actuator 52a , such as a DC motor driven. According to an opening degree of the low-pressure EGR valve 52 the exhaust gas flows through the low pressure EGR passage 34 and is powered by the low-pressure EGR cooler 54 cooled. Then, the exhaust gas flows into the intake passage as an internal EGR gas (low-pressure EGR gas) 12 , The low pressure EGR actuator 52a may be the opening degree of the low-pressure EGR valve 52 to capture. A differential pressure sensor 53 is in the low pressure EGR passage 46 for detecting a differential pressure between upstream and downstream of the low pressure EGR valve 52 intended.

An outlet throttle valve 56 is in the outlet passage 34 downstream of the low pressure EGR passage 46 intended. The outlet throttle valve 56 is powered by an electric actuator 56a such as a DC motor driven. The actuator 56a may be a position of the outlet throttle valve 56 to capture.

In the present embodiment, hereinafter, the inlet passage 12 downstream of the high pressure EGR passage 46 Referred to as a high pressure manifold gastric massage 12a , Further, hereinafter, the intake passage will be referred to 12 between the low-pressure EGR passage 46 and the high pressure EGR passage 44 Referred to as a low-pressure bulk flow massage 12b , It should be noted that the intake air includes fresh air and the external EGR gas.

An electronic control unit (ECU) 58 is mainly composed of a microcomputer having a CPU, a ROM and a RAM. The ECU 58 receives detection signals from an accelerator pedal position sensor 60 , the air flow meter or air flow meter 14 , the inlet pressure sensor 24 , the inlet temperature sensor 26 , the crank angle sensor 38 , the A / F sensor 42, the exhaust pressure sensor 51 , the actuators 20a . 48a . 52a and 56a and the differential pressure sensor 53 , The ECU 58 executes control programs stored in the ROM for fuel injection control, charge control, and combustion control of the engine 10 perform.

The fuel injection control will be described in detail. First, the computer calculates a required torque of the machine 10 (required engine torque) based on detection values of the crank angle sensor 38 and the accelerator pedal position sensor 60 , When the depressed amount of the accelerator pedal is larger, the required engine torque is increased. Based on this required engine torque, the fuel injector 28 energized to inject the fuel.

In charge control, the turbocharger 16 controlled, so that the pressure, which by the intake air pressure sensor 24 detected matches a target value. The target boost pressure is determined based on the intake air amount of the combustion chamber 22 should be made available. Especially, as the required engine torque becomes larger, the target boost pressure is set larger.

Especially the ECU leads 58 an external EGR control in which the high-pressure EGR actuator 48a is energized so that the low pressure EGR amount and the high pressure EGR amount are adjusted. The external EGR control is performed to remove NOx from the engine 10 is emitted, decrease.

According to the present embodiment, the ECU performs 58 based on an engine operating condition (engine speed NE and required engine torque Trq), one of high pressure EGR control, cooperative high-low pressure EGR control, and low pressure EGR control. In the high-pressure EGR control, which is represented by "HPL" in 1 is designated, only high-pressure EGR gas is in the intake passage 12 recycled. In the cooperative high-low pressure EGR control, which is designated by "HPL &LPL", the high-pressure EGR gas and the low-pressure EGR gas become the intake passage 12 recycled. In the low-pressure EGR control, which is denoted by "LPL", only the low-pressure EGR gas becomes the intake passage 12 recycled.

Specifically, when the required engine torque Trq is less than or equal to a first reference torque Tr1 (low engine load), the high pressure EGR control is performed. When the required engine torque Trq is greater than the first reference torque Tr1 and less than or equal to a second reference torque Tr2 (average engine load), the cooperative high-low pressure EGR control is executed. When the required engine torque Trq is greater than the second reference torque Tr2 (low engine load), the low pressure EGR control is executed.

The reason why one of the three schemes is selected is that the external EGR is properly ensured to reduce NOx, and deterioration in engine torque is avoided.

That is, when the engine load is high, the required engine torque is increased and the boost pressure is also increased to increase the amount of fresh intake air entering the combustion chamber 22 is introduced. When the high pressure EGR amount is increased, the amount of exhaust gas passing through the turbine becomes 16b flows, thereby reducing the engine torque. To avoid such a problem, when the engine load is high, part of the exhaust gas will be downstream of the turbine 16b in the inlet passage 12 as the low pressure EGR control returned.

When the engine load is medium, the amount of exhaust gas passing through the turbine 16b generally flows less than that in the high load range. Thus, the cooperative high-low-pressure EGR control is performed so that the low-pressure EGR gas and the high-pressure EGR gas are introduced into the intake passage 12 which ensures the external EGR.

When the engine load is low, the low pressure EGR gas passes through the low pressure EGR cooler 54 and the intercooler 18 cooled, so that its temperature is low. Such a low-pressure EGR gas is supplied to the combustion chamber, so that the combustion condition of the fuel is deteriorated. Also, given a differential pressure between an inlet and an outlet of the low-pressure EGR passage 46 is low, the low-pressure EGR amount can not be sufficiently ensured. In view of the above, the high pressure EGR control is executed.

The cooperative high-low pressure EGR control will be described in detail.

wobei die Niederdruck-EGR-Menge durch „Megrlp“ bezeichnet wird, die Hochdruck-EGR-Menge durch „Megrhp“ bezeichnet wird, und die Frischlufteinlassmenge durch „Mair“ bezeichnet wird.First, the computer determines a target high pressure EGR ratio at a point "β" in the high pressure manifold gas passage 12a , Then, the computer determines a target low pressure EGR ratio at a point "α" in the low pressure common stream passage 12b , It should be noted that the high-pressure EGR ratio is a ratio (%) between the intake air amount of the combustion chamber 22 is provided and represents an entire EGR amount. Especially, the high-pressure EGR ratio can be defined by the following formula (1): $$\begin{array}{ll}\text{High-pressure EGR ratio =}\hfill & \left(\text{Megrlp + Megrhp}\right)/\left(\text{Mair + + Megrlp Megrhp}\right)\times \hfill \\ \hfill & 100\hfill \end{array}$$

wherein the low-pressure EGR amount is denoted by "Megrlp", the high-pressure EGR amount is designated by "Megrhp", and the fresh-air intake amount is designated by "Mair".

The low pressure ECR ratio represents a ratio (%) of the low pressure EGR amount relative to a total of the intake air amount and the low pressure EGR amount. In particular, the low pressure EGR ratio can be defined by the following formula (2): $$\text{Low pressure EGR ratio}=\text{Megrlp /}\left(\text{Mair + Megrlp}\right)\times 100$$

The high pressure EGR actuator 48a is energized so that the actual high pressure EGR ratio coincides with the target EGR ratio, and the low pressure EGR actuator 52a is energized so that the actual low pressure EGR ratio matches the target EGR ratio. By executing the cooperative high-low pressure EGR control, it can be avoided that the accuracy of matching the external EGR amount due to a low-pressure EGR response delay is deteriorated.

The low pressure EGR passage 46 is longer than the high pressure EGR passage 44 , A distance from a connection point between the intake passage 12 and the low pressure EGR passage 46 to the combustion chamber 22 is longer than that of a connection point between the intake passage 12 and the high pressure EGR passage 44 to the combustion chamber 22 , Thus, a period of time is when the low pressure EGR valve 52 is pressed until then, when the amount of gas, which of the combustion chamber 22 is made available to change, longer than a period of time from then when the high-pressure EGR valve 48 is pressed until then, when the amount of gas entering the combustion chamber 22 is made available to change. This is referred to as the low pressure EGR response delay.

Cooperative high-low pressure EGR control uses various types of parameters. The calculation processes of these parameters will be described hereinafter. According to the present embodiment, as shown in FIG 1 the following parameters are used: that is, the high-pressure EGR amount "Megrhp", the low-pressure EGR amount "Megrlp", the intake flow rate "Mdth" passing through the low-pressure bypass section 12b an amount of charged air "Mcld", an oxygen concentration "Cegrhp" in the high-pressure EGR gas, an oxygen concentration "Cegrlp" in the low-pressure common-flow passage 12b , an inlet oxygen concentration in the intake air, which is the combustion chamber 22 and an exhaust gas oxygen concentration in the exhaust gas discharged from the combustion chamber 22 is ejected.

Specifically, the high pressure EGR amount "Megrhp" may be based on a differential pressure between the inlet and the outlet of the high pressure EGR passage 44 and a flow passage area of the high pressure EGR passage 44 be calculated. The differential pressure between the inlet and the outlet of the high pressure EGR passage 44 may be based on the detection value of the exhaust pressure sensor 51 and the boost pressure. The low pressure EGR amount "Megrlp" may be calculated based on a detection value of the differential pressure sensor 53 and the flow passage area of the low pressure EGR passage 46 , The amount of charged air "Mcld" may be calculated based on the intake air temperature derived from the boost pressure and the detection value of the intake air temperature sensor 26 ,

It should be noted that "Mdth = Mair + Megrlp" and "Mcld = Mdth + Megrhp".

"Mair" can be based on an output of the air flow meter 14 be calculated.

The oxygen concentration "Cegrhp", the oxygen concentration "Cegrlp" and the oxygen concentration in the low-pressure collecting stream passage 12a , the oxygen concentration in the intake air and the oxygen concentration in the exhaust gas are respectively estimated by using models for estimation.

Specifically, the oxygen concentration in the exhaust gas is estimated based on "Mcld," the fuel injection amount, and the oxygen concentration in the intake air. The oxygen concentration "Cegrhp" is estimated based on the oxygen concentration in the exhaust gas and "Megrhp". The oxygen concentration "Cegrlp" is estimated based on the oxygen concentration in the exhaust gas and "Megrlp". The oxygen concentration in the intake air is determined based on "Megrhp", "Cegrhp", "Mdth" and the oxygen concentration in the low-pressure manifold gas passage 12b estimated. The oxygen concentration in the low pressure bulk flow passage 12b is estimated based on "Megrlp", "Cegrlp", "Mair" and "Cair". The oxygen concentration "Cair" may be a fixed value or a detection value of an oxygen concentration sensor. According to the above method of calculating the oxygen concentration, each oxygen concentration can be calculated accurately.

Then, based on the above air flow rate and the oxygen concentration, the actual present high pressure EGR ratio and the actual present low pressure EGR ratio are calculated.

2 FIG. 12 is a flowchart showing processing of the cooperative high-low pressure EGR control. FIG. This processing is repeated after a certain period of time by the ECU 58 executed.

In step S10, the computer sets a target EGR ratio (0% ≤ target EGR ratio ≤ 100%) based on the engine speed NE and the fuel injection amount Q (or the required engine torque Trq). The target EGR ratio may be established using a map defining a relationship between the target EGR ratio, the engine speed NE, and the fuel injection amount Q. This map is previously defined by experiments to be a good combustion condition of the engine 10 to obtain.

In step S12, the computer calculates "Mcld". In step S14, the computer calculates a target total EGR amount of the combustion chamber 22 provided based on the target EGR Relationship and "Mcld". It should be noted that the target total EGR amount is needed to bring the actual EGR ratio (control value) to the target EGR ratio. Specifically, the target total EGR amount can be calculated according to the following formula (3). $$\text{Target total EGR amount}=\left(\text{Target Egr ratio}/100\right)\times \text{Mcld}$$

In step S16, the computer calculates a target value of the high pressure EGR amount "Megrhp" based on the engine speed NE and the fuel injection amount Q. The target high pressure EGR amount is set using a map indicating a relationship between the engine speed NE, of the fuel injection amount Q and the target high pressure EGR amount. In addition, when the required engine torque Trq is larger, the target high pressure EGR amount is set larger.

In step S18, the computer calculates an upper limit of the high pressure EGR amount. This step and the following steps S20 and S22 are processes for avoiding deterioration in the engine torque. That is, when the high pressure EGR amount is excessively increased, the exhaust gas passing through the turbine becomes 16b flows reduced, so that the boost pressure can be reduced. In order to avoid such a situation, the upper limit of the high-pressure EGR amount is set by using a map.

According to the present embodiment, when the computer determines that the required engine torque Trq is suddenly increased, the upper limit value of the high-pressure EGR amount is set lower. That is, in a case where the required engine torque is abruptly increased, it is likely that the upper limit set in step S18 may be inappropriate. Accordingly, in such a case, the exhaust gas, that of the turbine 16b is provided, adequate to ensure. The computer determines whether the required engine torque is increased abruptly based on a depressed amount of the accelerator pedal.

In step S20, the computer determines whether the target high pressure EGR amount is less than or equal to the upper limit. If the answer is NO in step S20, the procedure proceeds to step S22, in which the target high pressure EGR amount is limited by the upper limit. That is, the target high pressure EGR amount is set to the upper limit.

When the answer in step S20 is YES, the procedure proceeds to step S24, in which the computer sets a target value of the low-pressure EGR amount based on the target total EGR amount and the target high-pressure EGR amount. In the present embodiment, the target high pressure EGR amount is subtracted from the target total EGR amount to obtain the target low pressure EGR amount.

In step S26, the computer calculates an upper limit value of the low-pressure EGR amount, that of the intake passage 12 can be made available. The upper limit of the low pressure EGR amount may be established using a map defining a relationship between the engine speed NE and the fuel injection amount Q.

In step S28, the computer determines whether the target low pressure EGR amount is less than or equal to the upper limit. If the answer is NO in step S28, the procedure proceeds to step S30, in which the target low-pressure EGR amount is limited by the upper limit. That is, the target low pressure EGR amount is set to the upper limit.

If the answer in step S28 is YES, the procedure proceeds to step S32, in which the computer calculates the target low pressure EGR ratio according to the above formula (2). Thus, some or all of the EGR levels that exceed the upper limit are compensated by the low pressure EGR amount.

When the target low pressure EGR amount is limited by the upper limit value in step S30, the target low pressure EGR amount is changed from the initial value. Thus, according to the above formula (1), the target EGR ratio is reset.

In step S34, the low pressure EGR actuator becomes 52a energized, so that the actual current Low pressure EGR ratio coincides with the target low pressure EGR ratio. Furthermore, the high-pressure EGR actuator 48a energized so that the actual high pressure EGR ratio coincides with the target high pressure EGR ratio. In particular, the feedback inputs to the actuators are calculated by the proportional plus integral control. Thereby, when the actual high-pressure EGR ratio is greater than the target high-pressure EGR ratio, the high-pressure EGR amount is reduced. If the actual present low pressure EGR ratio is greater than the target low pressure EGR ratio, the low pressure EGR amount is reduced.

When the processing in step S34 is completed, this processing is ended.

1. (1) Die Ziel-Hochdruck-EGR-Menge wird von der Ziel-Gesamt-EGR-Menge subtrahiert, um die Ziel-Niederdruck-EGR-Menge zu erhalten. Demnach kann die Ziel-Gesamt-EGR-Menge in die Ziel-Hochdruck-EGR-Menge und die Ziel-Niederdruck-EGR-Menge aufgeteilt werden.
2. (2) Die kooperative Hoch-Nieder-Druck-EGR-Regelung wird durch ein Regeln der Aktuatoren 48a und 52a ausgeführt. Demnach kann vermieden werden, dass die Genauigkeit der externen EGR-Menge, welche der Maschine 10 zur Verfügung gestellt wird, verschlechtert wird.
3. (3) Wenn der Computer bestimmt, dass die Ziel-Hochdruck-EGR-Menge den oberen Grenzwert überschreiten wird, wird die Ziel-Hochdruck-EGR-Menge auf den oberen Grenzwert gesetzt. Dadurch kann, während das externe EGR-Gas in die Einlasspassage 12 zirkuliert wird, vermieden werden, dass das Maschinendrehmoment verschlechtert wird.

According to the present embodiment described above, the following advantages can be obtained.

1. (1) The target high-pressure EGR amount is subtracted from the target total EGR amount to obtain the target low-pressure EGR amount. Thus, the target total EGR amount may be divided into the target high pressure EGR amount and the target low pressure EGR amount.
2. (2) The cooperative high-low-pressure EGR control is achieved by controlling the actuators 48a and 52a executed. Accordingly, it can be avoided that the accuracy of the external EGR amount, that of the engine 10 is made worse.
3. (3) If the computer determines that the target high pressure EGR amount will exceed the upper limit, the target high pressure EGR amount is set to the upper limit. This allows, while the external EGR gas enters the intake passage 12 is circulated, it can be avoided that the engine torque is deteriorated.

• (4) Wenn der Computer bestimmt, dass das benötigte Maschinendrehmoment Trq plötzlich erhöht wird, wird der obere Grenzwert der Hochdruck-EGR-Menge niedriger gesetzt. Demnach kann sichergestellt werden,dass die Abgasmenge, welche durch die Turbine 16b strömt, eine Verschlechterung in dem Maschinendrehmoment vermeidet.
• (5) Wenn der Computer bestimmt, dass die Ziel-Hochdruck-EGR-Menge den oberen Hochdruck-Grenzwert überschreiten wird, und dass die Ziel-Niederdruck-EGR-Menge den oberen Niederdruck-Grenzwert überschreiten wird, wird das Ziel-EGR-Verhältnis zurückgesetzt. Demnach kann das Ziel-EGR-Verhältnis gemäß einer Variation in der Gesamt-EGR-Menge, welche der Verbrennungskammer 22 zur Verfügung gestellt werden kann, angemessen aufgestellt werden.

Further, when the upper limit value is set lower than a value corresponding to a maximum fluid passage area of the high-pressure EGR passage, it can be avoided that the opening degree of the high-pressure EGR valve is saturated in the upper limit value.

• (4) When the computer determines that the required engine torque Trq is suddenly increased, the upper limit of the high-pressure EGR amount is set lower. Accordingly, it can be ensured that the amount of exhaust gas passing through the turbine 16b flows, avoids a deterioration in the engine torque.
• (5) When the computer determines that the target high-pressure EGR amount will exceed the high-pressure upper limit, and that the target low-pressure EGR amount will exceed the upper low-pressure threshold, the target EGR ratio becomes reset. Thus, the target EGR ratio may vary according to a variation in the total EGR amount of the combustion chamber 22 can be made available, be placed appropriately.

Second Embodiment

A second embodiment will be described hereinafter which focuses on a difference from the first embodiment.

According to the second embodiment, the oxygen concentrations in the high-pressure manifold gas passage become 12a and low pressure bulk flow massage 12b recorded and these oxygen concentrations are regulated. Since the oxygen concentration in the intake air has a high correlation with the amount of NOx, the oxygen concentration is controlled.

3 FIG. 10 is a flowchart showing processing of external EGR control including cooperative high-low pressure EGR control. FIG. This processing is performed at a predetermined time interval by the ECU 58 repeatedly executed. In 3 be the same processes as those in 2 displayed with the same reference characters. The same descriptions will not be repeated.

In step S10a, the computer sets a target oxygen concentration in the intake air based on the engine speed NE and the fuel injection amount Q (or the required engine torque Trq). The target oxygen concentration may be established using a map defining a relationship between the target oxygen concentration, the engine speed NE, and the fuel injection amount Q.

Then, the procedure proceeds to step S12 and step S16 in which the computer sets up a target high pressure EGR amount. The target high pressure EGR amount is established so that the actual current oxygen concentration matches the target oxygen concentration.

In step S36, the computer calculates a target value of "Mdth" based on "Mcld" and a target high pressure EGR amount. Specifically, the target high pressure EGR amount is subtracted from "Mcld" to obtain the target value of "Mdth".

In step S38, the computer sets a target oxygen concentration in the low pressure common flow passage 12b based on "Mcld", the target intake air-oxygen concentration, the target high-pressure EGR amount, "Cegrhp" and the target intake air flow rate in the low-pressure common-flow passage 12b ,

In step S24a, the computer sets the target low pressure EGR amount. Specifically, the target low pressure EGR amount is established based on "Megrlp", "Cegrlp", "Mair" and "Cair".

In step S32a, the target oxygen concentration in the low-pressure manifold gas passage becomes 12b and reset the target oxygen concentration in the intake air. In particular, the target oxygen concentration in the low pressure bulk flow passage becomes 12b reset based on the target low pressure EGR amount "Cegrlp", "Mair" and "Cair". Also, the target intake air-oxygen concentration is reset based on the target oxygen concentration in the low-pressure common-flow passage 12b , "Cegrhp", the target high pressure EGR amount, and the target intake air flow rate in the low pressure common stream passage.

In step S34a, the high pressure EGR actuator becomes 48a energized so that the actual intake air oxygen concentration coincides with the target intake air oxygen concentration. Furthermore, the low-pressure EGR actuator 52a energized so that the actual current oxygen concentration in the low-pressure bulk flow passage 12b with the target oxygen concentration in the low pressure bulk flow passage 12b matches. Especially, when the actual present intake air-oxygen concentration is higher than the target concentration and the oxygen concentration "Cegrhp" is lower than the oxygen concentration in the low-pressure common-flow passage 12b , the high-pressure EGR amount is increased. When the actual current oxygen concentration in the low-pressure bulk flow passage 12b is higher than the target oxygen concentration, the low pressure EGR amount is increased.

When the processing in step S34a is completed, this processing is ended.

As described above, according to the present embodiment, the external EGR amount based on the intake-air oxygen concentration and the oxygen concentration in the low-pressure common-flow passage 12b be managed.

[Other executing]

The above-mentioned embodiments can be modified as follows:

In the first embodiment, when the computer determines that the target high pressure EGR amount exceeds the high pressure upper limit, the low pressure upper limit may be increased. If it is possible to increase the low-pressure EGR amount, a bottleneck in the high-pressure EGR amount can be adequately compensated by the low-pressure EGR amount.

The high pressure EGR valve 48 can be in a neighborhood of the outlet passage 34 be arranged or at a midpoint of the high-pressure EGR passage 44 , Alternatively, the high pressure EGR valves 48 at both ends of the high pressure EGR passage 44 to be ordered. Regarding the low pressure EGR valve 52 a similar arrangement can be applied.

The calculation method of "Megrlp" and "Megrhp" is not limited to the above-described method. For example, a differential pressure sensor is provided, a differential pressure between upstream and downstream of the high-pressure EGR valve 48 capture. Based on the detection values, "Megrhp" can be calculated. Furthermore, the low pressure EGR amount "Megrlp" may be calculated based on detection values of two pressure sensors.

In the above embodiments, each of the oxygen concentrations is calculated using models. However, the oxygen concentrations can be detected by oxygen sensors.

The amounts "Megrhp", "Megrlp" and "Mdth" can be detected using flow rate sensors.

The high pressure upper limit value can be continuously decreased according to a reduction in engine load. This allows the total amount of EGR to be gently varied.

The high pressure EGR amount and the low pressure EGR amount may be through at least one of the exhaust throttle valve 56 of the intake throttle valve 20 be managed.

Especially when the opening degree of the outlet throttle valve 56 decreases, the low-pressure EGR amount and the high-pressure EGR amount are more increased. Also, when the opening degree of the intake throttle valve becomes 20 decreases, the high-pressure EGR amount increases more.

The low pressure EGR actuator and the high pressure EGR actuator may be controlled by a feedback control and a feedforward control.

Only when the computer determines that the high pressure EGR amount exceeds the high pressure upper limit, the low pressure EGR amount may compensate for the bottleneck in the high pressure EGR amount.

The internal combustion engine is not limited to a diesel engine. A direct injection gasoline engine can be used.

Claims (6)

Exhaust gas recirculation control apparatus applied to a combustion control system of an internal combustion engine provided with a turbocharger (16) having a compressor (16a) in an intake passage (12) and a turbine (16b) in an exhaust passage (Fig. 34), a high pressure EGR passage (44) connecting a portion upstream of the turbine (16b) and a portion downstream of the compressor (16a), a low pressure EGR passage (46) which defines a portion downstream of the turbine (16). 16b) and a portion upstream of the compressor (16a), a high-pressure EGR control section (48, 48a) which regulates a high-pressure exhaust gas amount recirculated into the intake passage (12) through the high-pressure EGR passage (44) , and has a low-pressure EGR control section (52, 52a) that controls a low-pressure exhaust gas amount that is returned to the intake passage (12) through the low-pressure EGR passage (46) a part of the intake passage (12) located downstream of a connection portion with the high pressure EGR passage (44) is defined as a high pressure common passage passage (12a); a part of the intake passage (12) is defined between a connection part with the low-pressure EGR passage (46) and the connection part with the high-pressure EGR passage (44) as a low-pressure common passage passage (12b); and an oxygen concentration in an intake air or an exhaust gas recirculation ratio is defined as an intake air parameter; in which the exhaust gas recirculation control device comprises a target value setting section (S10, S10a) which sets target values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low-pressure common-flow passage (12b); a control value calculation section that actually calculates current values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low-pressure common-flow passage (12b); and a control section (58) that controls the high-pressure EGR control section (48, 48a) and the low-pressure EGR control section (52, 52a) so that the actual values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low pressure makeup flow passage (12b) coincide with the target values of the intake air parameters. Exhaust gas recirculation control device according to Claim 1 , further comprising: a quantity ratio setting section (58) which sets a quantity ratio between an amount of exhaust gas flowing through the high-pressure EGR passage (44) and an amount of exhaust gas flowing through the low-pressure EGR passage (46) that the actual current value of the intake air parameter in the high pressure common passage (12a) coincides with the target value of the intake air parameter in the high pressure common passage (12a); wherein a target value setting section sets target values of the intake air parameters in the high-pressure common-flow passage (12a) and in the low-pressure common flow passage (12b) based on the quantitative ratio. Exhaust gas recirculation control device according to Claim 2 , further comprising: a high-pressure upper limit setting section (S18) which sets a high-pressure upper limit value of an exhaust gas amount flowing through the high-pressure EGR passage (44) according to an operating state of the engine; wherein: the quantity ratio setting section sets the quantitative ratio in such a manner that the amount of exhaust gas flowing through the high-pressure EGR passage does not exceed the high-pressure upper limit value; and the quantity ratio setting section sets the amount of exhaust gas flowing through the low-pressure EGR passage based on the amount of exhaust gas flowing through the high-pressure EGR passage. Exhaust gas recirculation control device according to Claim 3 , further comprising: a low-pressure upper limit setting-up portion (S26) which establishes a low-pressure upper limit value of an exhaust gas amount flowing through the low-pressure EGR passage (46); and a resetting section (S32, S32a) that restarts the target value of the intake air parameter in the high-pressure common passage (12a) when it is determined that a total amount of the exhaust gas passing through the high-pressure EGR passage and the low-pressure EGR passage is equal to a whole of the high pressure upper limit and the upper low pressure limit, and when it is determined that the exhaust gas amount needed for the actual present value of the intake air parameter in the high pressure common passage to coincide with the target value, exceeds a total value of the high-pressure upper limit and the lower-pressure low limit, so that the target value of the intake air parameters in the high-pressure common passage (12a) is reset by adding the high-pressure upper limit and the low-pressure upper limit. Exhaust gas recirculation control device according to Claim 3 or 4 wherein: a high pressure upper limit set-up section (S18) decreases the high pressure upper limit value when it is determined that a required engine torque is suddenly increased. Exhaust gas recirculation control device according to one of Claims 1 to 5 wherein: the high pressure EGR control section (48, 48a) includes an electrically operated valve (48) disposed in the high pressure EGR passage (44) to adjust a flow passage area thereof; and the low pressure EGR control section (52, 52a) includes an electrically operated valve (52) disposed in the low pressure EGR passage (46) to adjust a flow passage area thereof.

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