JP2001152879A - Egr control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control NOX amount exhausted from an engine to the target value, regardless of the operating conditions. SOLUTION: An EGR valve 23 for adjusting the EGR gas amount is installed on an EGR passage 33 of a Diesel engine 1, and an exhaust passage 3 is furnished with a turbo charger, having a variable nozzle 35a and a NOX sensor 71 to sense the NOX concentration in the exhaust gas. An electronic control unit(ECU) of the engine controls the degree of opening of the EGR valve, so that the second NOX concentration becomes the target value decided according to the operating conditions, and performs feedback control of the EGR gas amount. In a condition with the EGR valve fully opened, the ECU makes feedback control of the variable nozzle 35a according to the output of the NOX sensor and thereupon performs feedback control of the EGR gas amount, so that the NOX concentration of the exhaust gas becomes the target value. Thereby it is made practicable to supply a sufficient quantity of EGR gas to the combustion chamber, even in case the exhaust gas pressure is low, and the EGR valve is not solely able to control the EGR gas amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine provided with an EGR device for recirculating a part of exhaust gas from an internal combustion engine to an intake system, and more particularly, to an internal combustion engine for controlling a flow rate of exhaust gas recirculated to the intake system. The present invention relates to an EGR control device.

[0002]

2. Description of the Related Art There is known an exhaust gas recirculation (EGR) device in which a part of exhaust gas of an internal combustion engine is recirculated to an intake system and supplied to a combustion chamber. The exhaust gas of the internal combustion engine has a low oxygen concentration and functions as an inert gas that does not contribute to combustion. Therefore, generation of nitrogen oxides by combustion air excess ratio is lowered combustion engine by supplying the exhaust to the combustion chamber (NO _X) is suppressed.

In general, the amount of exhaust gas (E
_The amount of NO _X generated as GR quantity) increases is reduced, but there is a problem of the lack of oxygen in the combustion chamber and to increase the EGR amount excessively the combustion state deteriorates. In particular, in a diesel engine, when the amount of EGR increases, problems such as an increase in particulates in exhaust gas and generation of exhaust smoke occur.

Therefore, when suppressing NO _X in the exhaust gas by EGR, it is necessary to control the EGR amount so that the effect of suppressing NO _X is maximized within a range where deterioration of combustion and increase of particulates do not occur. is there. Thus, EG to control the EGR amount in order to appropriately suppress the generation amount of the NO _X
Examples of the R control device include, for example, Japanese Patent Application Laid-Open No. 10-2525.
No. 73 is disclosed. The device of the publication is
By placing the NO _X sensor for detecting the concentration of NO _X in the exhaust gas to the engine exhaust passage, calculating the actual of the NO _X generation amount of the engine based on the NO _X concentration detected during the operation. The exhaust gas recirculation control valve (EGR valve) for adjusting the EGR amount is feedback-controlled so that the NO _X generation amount matches a predetermined target NO _X amount according to the operating state of the engine. is there.

[0005]

However, in the device disclosed in Japanese Patent Application Laid-Open No. H10-252573, a problem may occur because the control of the EGR amount is performed only by adjusting the EGR valve opening. That is, in an engine that burns with a high excess air ratio, such as a diesel engine, NO _X
To obtain the effect of reducing the generation amount, it is necessary to supply a relatively large amount of EGR gas to the combustion chamber. On the other hand, an exhaust gas recirculation control valve (EGR valve) that adjusts the EGR amount is generally of the type of a flow control valve provided in an EGR passage that connects the exhaust passage and the intake passage, and throttles the flow of EGR gas flowing through the EGR passage. Thus, the EGR amount is controlled. For this reason,
When the EGR valve is fully opened, the EGR amount cannot be further controlled in the increasing direction. On the other hand, the diesel engine air excess ratio in the combustion the lower the engine load increases, and require a large amount of EGR gas in order to suppress the generation amount of NO _X. However, since the exhaust pressure decreases as the engine load decreases, it is necessary to reduce the pressure difference between the exhaust system and the intake system during low engine load operation, and to return the exhaust gas to the combustion chamber even when the EGR valve is fully opened. EGR that can be done
The gas volume does not increase significantly. For this reason, in the device of the above publication, a sufficient amount of EGR gas cannot be recirculated to the intake system depending on the operating conditions, and the actual NO _X generation amount may not be reduced to the target NO _X amount. .

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention sets the actual NO _X generation amount to the target NO _X regardless of the engine operating state.
It is an object of the present invention to provide an EGR control device for an internal combustion engine that can be reduced to an amount.

[0007]

According to the first aspect of the present invention, there is provided an EGR control device for an internal combustion engine that recirculates a part of exhaust gas of the internal combustion engine to an engine intake system. an EGR passage for communicating the passage, is disposed in the EGR passage, NO for detecting the EGR valve throttling the flow rate of the exhaust gas recirculated to the intake system flows through the EGR passage, the concentration of NO _X in the disposed in the exhaust passage exhaust _{An X} sensor, exhaust throttle means disposed downstream of a connection portion of the exhaust passage with the EGR passage to reduce an exhaust flow rate flowing through the exhaust passage, and the NO _X
By adjusting the opening degree of the EGR valve in accordance with the output of the sensor, the target NO _X that is concentration of NO _X in the exhaust predetermined
And a control means for controlling the flow rate of the exhaust gas recirculated to the exhaust system to a concentration, said control means, said EGR valve opening is fully open, and the concentration of NO _X in the exhaust gas to the target density If you need to increase the flow rate of the exhaust gas recirculated to the intake system to match performs exhaust throttle by the exhaust throttle means in accordance with the output of the NO _X sensor, an EGR control device for an internal combustion engine is provided .

That is, in the first aspect of the present invention, the EGR valve
NO in both exhaust throttle means and exhaust_XBased on concentration
By performing feedback control, NO in exhaust_XDark
Degree is always target NO_XConcentration. This place
In this case, the control means first sets the EGR valve to NO._XAccording to sensor output
The actual exhaust NO _X
Concentration is target NO_XEGR gas amount to match the concentration
Control. When the EGR valve is fully opened,
Even if it becomes impossible to increase the amount of GR gas
Regardless, exhaust NO_XTarget NO for concentration_XThe concentration
If it is necessary to increase the amount of EGR gas for
NO_XThe exhaust throttle means is controlled according to the sensor output. Exhaustion
When the exhaust is throttled by the air throttle, the exhaust throttle upstream
Exhaust pressure increases. Therefore, exhaust gas to the EGR passage
Supply pressure rises and EGR gas recirculation to intake system increases
Become so. As a result, for example, when the engine is operating at a low load,
Even if the exhaust pressure is low and the EGR valve is fully open,
When it is not possible to supply sufficient EGR gas to the combustion chamber
Also the actual exhaust NO_XAccurate target NO_XOne for concentration
It is possible to match.

According to a second aspect of the present invention, there is provided the EGR control apparatus for an internal combustion engine according to the first aspect, wherein the exhaust throttle means includes an exhaust throttle valve arranged in an engine exhaust passage. . That is, in the invention of claim 2, an exhaust throttle valve is used as the exhaust throttle means. The engine exhaust pressure increases according to the degree of exhaust throttle of the exhaust throttle valve (the opening degree of the exhaust throttle valve). Therefore, by performing feedback control in accordance with the exhaust throttle valve opening in the NO _X sensor output,
Even in a region where the EGR valve is fully opened and the EGR gas amount cannot be controlled with the EGR valve opening, the exhaust NO
_{The X} concentration can be controlled to the target NO _X concentration.

According to a third aspect of the present invention, the internal combustion engine includes a turbocharger having an exhaust turbine with a variable nozzle, and the variable nozzle is used as the exhaust throttle means. An EGR control device for an engine is provided. That is, in the invention of claim 3, a variable nozzle of the turbocharger is used as the exhaust throttle means. The variable nozzle of the turbocharger is usually used to reduce the cross-sectional area of the nozzle flow path of the turbine during low engine load operation, etc., and to increase the flow velocity of exhaust gas flowing into the turbine.
When the engine exhaust pressure decreases during low engine load operation, the flow rate of exhaust gas flowing into the turbine decreases, and the turbine speed decreases.In some cases, the supercharging pressure cannot be maintained high. By using this, even when the exhaust pressure is reduced, the flow velocity of the exhaust gas flowing into the turbine is kept high, so that a decrease in the supercharging pressure due to a decrease in the turbocharger rotation speed is suppressed. On the other hand, since the variable nozzle increases the exhaust flow speed by reducing the nozzle flow area, the exhaust pressure on the upstream side of the turbocharger increases when the variable nozzle operates. For this reason, by performing feedback control of the throttle degree of the variable nozzle of the turbine (opening degree of the variable nozzle) according to the output of the NO _X sensor, the exhaust NO _X concentration can be set to the target value over a wide operating range without using an exhaust throttle valve. It becomes possible to control.

Further, since the turbocharger is usually arranged at a position near the engine body in the exhaust passage, the volume of the exhaust passage on the upstream side of the variable nozzle becomes relatively small. Further, the operating speed of the variable nozzle is higher than that of an exhaust throttle valve or the like. For this reason, by changing the variable nozzle opening, the exhaust passage pressure on the upstream side of the variable nozzle can be changed with good responsiveness. Therefore, by performing feedback control of the variable nozzle opening in response to the NO _X sensor output, it is possible to control a very good response EGR gas amount, so that the concentration of NO _X in the exhaust gas varies by the engine operating conditions change it becomes possible to converge the response good exhaust NO _X concentration to the target concentration if such.

According to a fourth aspect of the present invention, there is provided an EGR control device for an internal combustion engine that recirculates a part of exhaust gas of the internal combustion engine to an engine intake system, wherein the EGR control device connects the engine exhaust passage and the intake passage. A passage and an EG disposed in the EGR passage.
EGR for reducing the flow rate of exhaust gas flowing through the R passage and returning to the intake system
A valve, and the NO _X sensor wherein disposed in the exhaust passage for detecting the concentration of NO _X in the exhaust gas, on the intake passage, the EGR
By adjusting the opening degree of the EGR valve according to the output of the NO _X sensor, the NO _X concentration in the exhaust gas is reduced by adjusting the opening degree of the EGR valve in accordance with the output of the NO _X sensor. Control means for controlling the flow rate of exhaust gas recirculated to the exhaust system so as to attain a predetermined target NO _X concentration, wherein the control means is configured so that the EGR valve is fully open and the NO _X If you need to increase the flow rate of the exhaust gas recirculated to the intake system to match the density to the target concentration, the NO _X in accordance with the output of the sensor performs intake throttle by the intake throttle means, the internal combustion engine EGR A control device is provided.

That is, in the invention of claim 4, the EGR amount is increased by restricting the intake air when the EGR valve is fully opened. As the intake throttle means, for example, an intake throttle valve or the like can be used. When the intake throttling is performed by the intake throttling means, the intake passage pressure downstream of the throttling means decreases according to the degree of throttling. For this reason, even when the engine exhaust pressure decreases, the differential pressure between the exhaust system and the intake system becomes sufficiently large, and the amount of EGR gas flowing from the EGR passage into the intake system increases. Therefore, by feedback-controlling the throttle degree of the intake throttle means according to the NO _X sensor output (e.g., the intake throttle valve opening), so that the exhaust gas pressure lower EGR valve not enough EGR gas amount becomes fully opened also in Do operating range, it is possible to accurately control the exhaust NO _X concentration to the target concentration.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel. In FIG. 1, 1 is a diesel engine main body, 2 is an intake passage of the engine 1, 20 is a surge tank provided in the intake passage 2, and 21 is an intake branch pipe connecting the surge tank 20 and an intake port of each cylinder. . In this embodiment, an intake throttle valve 27 for reducing the flow rate of intake air flowing through the intake passage 2 and an intercooler 26 for cooling intake air are provided in the intake passage 2.
Is provided. The intake throttle valve 27 is a stepper motor,
An electronic control unit (EC, described later) is provided with an appropriate type of actuator 27a such as a vacuum actuator.
U) Take an opening in accordance with the control signal from 30. In the present embodiment, the intake throttle valve 27 is used to lower the intake pressure, for example, when the engine is running at a low speed, and to increase the amount of exhaust gas (EGR gas) flowing back to the surge tank 20 through an EGR passage 33 described later. In addition, it is used to restrict the intake air and raise the exhaust gas temperature when burning the particulates collected by the particulate filter 43 (regenerating the particulate filter 43).

In FIG. 1, reference numeral 25 denotes an air flow meter provided near the intake port of the intake passage 2. In the present embodiment, an air flow meter 25 such as a hot wire flow meter that can directly measure the weight flow rate of the intake air flowing through the intake passage 2 is used. The air flowing into the intake passage 2 passes through an air flow meter 25, is pressurized by a compressor of an exhaust supercharger (turbocharger) 35, is cooled by an intercooler 26 provided in the intake passage 2, and It is sucked into each cylinder via the branch pipe 21.

In FIG. 1, reference numeral 111 denotes a fuel injection valve for directly injecting fuel into each cylinder. Fuel injection valve 111
Is a common accumulator (common rail) for storing high-pressure fuel
115. The fuel of the engine 1 is pressurized by the high-pressure fuel pump 113 and supplied to the common rail 115, and is directly injected from the common rail 115 into each cylinder via each fuel injection valve 111.

In FIG. 1, reference numeral 31 denotes an exhaust manifold for connecting an exhaust port of each cylinder to the exhaust passage 3;
Indicated by is a turbocharger. The turbocharger 35 includes an exhaust turbine driven by exhaust gas in the exhaust passage 3 and an intake compressor driven by the exhaust turbine. In this embodiment, a variable nozzle 35a is provided at the exhaust inlet of the exhaust turbine. The variable nozzle 35a is a nozzle whose opening area can be changed. For example, when the exhaust flow rate is low and the load is low, the variable nozzle 35a narrows the nozzle opening area to increase the flow rate of the exhaust gas flowing into the exhaust turbine. The throttle speed of the exhaust turbine is kept high by restricting the variable nozzle 35a during the low load operation of the engine, so that a decrease in the compressor discharge pressure (supercharging pressure) is prevented. When the variable nozzle 35a is throttled, the exhaust flow path resistance increases, and the exhaust back pressure of the engine 1 increases. In the present embodiment, the variable nozzle 35a is a stepper motor (not shown),
Equipped with an actuator such as a vacuum actuator,
The opening is determined according to the control signal from the ECU 30.

In this embodiment, the turbocharger 3
An exhaust throttle valve 37 for reducing the flow rate of exhaust gas flowing through the exhaust passage 3 is disposed on the exhaust passage 3 on the downstream side 5. The exhaust throttle valve 37 includes an actuator 37a similar to the intake throttle valve 27, and takes an opening degree according to a control signal from the ECU 30. In the present embodiment, the exhaust throttle valve 37 is used when adjusting the EGR gas amount and regenerating the particulate filter 43 to raise the exhaust gas temperature, similarly to the intake throttle valve 27.

Further, in this embodiment, an EGR device for recirculating a part of the exhaust gas to the intake system is provided. The EGR device includes an EGR passage 33 that connects the exhaust manifold 31 and the intake surge tank 20, an EGR valve 23 disposed on the EGR passage 33, and an EGR valve 23 upstream of the EGR valve 23.
An EGR cooler 45 provided in the R passage is provided. E
The GR valve 23 includes an appropriate type of actuator such as a stepper motor and a vacuum actuator (not shown).
The opening is determined according to the control signal from the ECU 30, and the EGR
EG returning to the intake surge tank 20 through the passage 33
Control the R gas flow rate. In the present embodiment, a relatively large amount of EGR is used in a wide operating range from a low load range to a high load range.
The EGR valve 23 is controlled so that the gas is recirculated. For this reason, in this embodiment, the intake air drawn into each cylinder contains a relatively large amount of EGR gas. Since the EGR gas is high-temperature exhaust gas discharged from the cylinder, if a large amount of the EGR gas is recirculated to the intake air, the intake air temperature rises, and the intake volume efficiency decreases. In the present embodiment, in order to prevent this, a water-cooled or air-cooled EGR cooler 45 is provided in the EGR passage 33 upstream of the EGR valve 23.
Is provided. In the present embodiment, the EGR cooler 45
By reducing the temperature of the EGR gas that is recirculated to the intake system using, a large amount of EGR gas can be recirculated without lowering the volumetric efficiency of the intake air.

In this embodiment, a known type of exhaust purification catalyst 41 such as a three-way catalyst and a particulate filter (DPF) 4 are disposed downstream of the exhaust throttle valve in the exhaust passage 3.
3 are arranged. The DPF 43 includes, for example, a metal mesh, a ceramic porous filter, and the like, and captures particulates in the exhaust gas. In the present embodiment, the DPF 4
As 3, a well-known type of particulate filter can be used.

Furthermore, in the present embodiment, in the exhaust passage of the turbocharger 35 downstream NO _X sensor 71 for detecting the concentration of NO _X in the exhaust gas are provided. NO _X sensor 7
1 is a crank described in detail later. Reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine 1. The ECU 30 of the present embodiment is configured as a microcomputer having a known configuration, and has a configuration in which a CPU, a RAM, a ROM, an input port, and an output port are mutually connected by a bidirectional bus. In addition to performing basic control such as fuel injection control and rotation speed control of the engine 1, the ECU 30 controls the amount of EGR gas passing through the EGR passage 33 according to the output of a NO _X sensor 59, which will be described later, in this embodiment, and controls the exhaust NO _X performs NO _X control that controls the target NO _X concentration was determined according to a concentration of operating conditions.

In order to perform these controls, a signal corresponding to the engine speed NE is input to an input port of the ECU 30 from a speed sensor 55 disposed near the crankshaft of the engine 1, and an air flow meter 25. And a signal corresponding to the driver's accelerator pedal depression amount (accelerator opening amount) ACCP from the accelerator opening sensor 57 disposed near the engine accelerator pedal. ing. Further, in this embodiment, the exhaust NO _X sensor 71 in the exhaust passage detects the exhaust NO _X
A signal corresponding to the concentration is input to an input port of the ECU 30.

An output port of the ECU 30 is connected to a fuel injection valve 111 of the engine 1 via a fuel injection circuit (not shown), and controls the fuel injection amount and the fuel injection timing from the fuel injection valve 111. Further, an output port of the ECU 30 is connected to actuators of the EGR valve 23, the intake throttle valve 27, and the exhaust throttle valve 37 and an actuator of the variable nozzle 35a of the turbocharger 35 via a drive circuit (not shown) to control the respective valve openings. are doing.

FIG. 2 is a diagram schematically showing the configuration of the NO _X sensor 71 of the present embodiment. In FIG. 2, the NO _x sensor 71 is a solid electrolyte 3 such as zirconia (ZrO ₂ ).
And a first reaction chamber 340 communicating with the exhaust passage through the diffusion control part 335, a second reaction chamber 350 communicating with the first reaction chamber 340 through the diffusion control part 337, and a solid electrolyte. An atmosphere chamber 360 into which the atmosphere as a standard gas is introduced is provided. The diffusion control sections 335 and 337 suppress the inflow of the oxygen component into the first reaction chamber 340 and the second reaction chamber 350 due to the diffusion, respectively.
The reaction chamber can maintain the oxygen concentration difference between the first reaction chamber and the second reaction chamber.

In FIG. 2, reference numeral 341 denotes a first reaction chamber 340.
Reference numeral 342 denotes a platinum electrode (cathode) disposed in the inside, and a similar platinum electrode (anode) provided outside the sensor 71 with the cathode 341 and the solid electrolyte 331 interposed therebetween. Also, the second
The reaction chamber similar platinum electrode 350 is within 350 and NO _X detecting rhodium (Rh) electrode 353, platinum electrode 361 for reference to the air chamber 360 are disposed respectively. An electric heater 370 for heating the solid electrolyte is shown in the figure.

The electrode 341 and the external electrode 342 in the first reaction chamber 340, and the electrode 351 and the external electrode 342 in the second reaction chamber 340.
Function as oxygen pumps for exhausting oxygen in the exhaust gas in the first reaction chamber 340 and the second reaction chamber 350, respectively. When a voltage is applied between the electrodes 341 and 342 and the electrodes 351 and 342 when the solid electrolyte 331 is at a certain temperature or higher, oxygen molecules in the exhaust gas are ionized on the cathodes 341 and 351 and the ionized oxygen molecules are solidified. It moves inside the electrolyte 331 toward the anode 342 and becomes an oxygen molecule again on the anode 342. Therefore, the first reaction chamber 340,
Oxygen in the exhaust gas in the second reaction chamber 350 is exhausted to the outside. In addition, the electrodes 342 and 3
A current proportional to the amount of oxygen molecules moved per unit time flows between 41 and 351. Therefore, by controlling this current, the amount of oxygen discharged from each reaction chamber can be controlled.

In this embodiment, an oxygen battery is formed between the electrode 361 in the atmosphere chamber 360 and the electrodes 341 and 351 in each reaction chamber. Since the exhaust gas in the first and second reaction chambers has a lower oxygen concentration than the atmosphere, there is a difference in oxygen concentration between the air in the atmosphere chamber 360 and the exhaust gas in each reaction chamber. When the temperature of the solid electrolyte separating the atmosphere chamber 360 and each of the reaction chambers 340 and 350 is equal to or higher than a certain temperature, the solid electrolyte 331 flows from the inside of the atmosphere chamber 360 due to a difference in oxygen concentration when no voltage is applied between the electrodes from the outside. Reaction chamber 34
Oxygen moves to 0,350. That is, oxygen molecules in the atmosphere in the atmosphere chamber 360 are ionized on the electrode 361, move in the solid electrolyte 331, and become oxygen molecules again on the electrodes 341 and 351 of the reaction chambers 340 and 350 having a low oxygen concentration. For this reason, the electrode 361 and each electrode 341,
351 generates a voltage corresponding to the difference between the oxygen concentration in the atmosphere and the oxygen concentration in each reaction chamber. Since the oxygen concentration in the atmosphere is constant, the potential differences V0 and V1 (FIG. 2) between the electrode 361 and the electrodes 341 and 351 are respectively set in the first reaction chamber 340.
And the oxygen concentration of the exhaust gas in the second reaction chamber 351.

In this embodiment, as described above, each reaction
Oxygen pump that discharges oxygen from the chamber
342, electrodes 351 and 342) are provided.
The oxygen pumping rate of each oxygen pump is
By adjusting the pump currents Ip0, Ip1 (FIG. 2)
The oxygen concentration of the exhaust gas in each reaction chamber (that is, the voltage V
0, V1) is controlled to be a predetermined constant value. Book
In the embodiment, the oxygen concentration in the first reaction chamber 340 is, for example, 1
ppm, and the oxygen concentration in the second reaction chamber 350.
Is, for example, about 0.01 ppm.
p0 and Ip1 are controlled. Therefore, the second reaction chamber
The inside of 350 is maintained in a reducing atmosphere with extremely low oxygen concentration.
You. On the other hand, NO in exhaust_X(NO, NO_Two) Is an oxygen pump
First and second reaction chambers
NO of exhaust inside_XConcentration is maintained the same as external exhaust
You. However, NO in the second reaction chamber_XThe detection electrode 353 is
Since it is indium (Rh), it functions as a reduction catalyst and reduces
NO under atmosphere_X(NO, NO _Two) To reduce. Also,
Reference electrode 361 in atmospheric chamber 360 and NO_XDetection electrode 35
3 is applied with a voltage, NO_XFor detection
On the electrode 353, NO → (1/2) N_Two+ (1/2) O_TwoMa
Or NO_Two→ (1/2) N_Two+ O_TwoReaction occurs and NO _XReturn of
Oxygen is generated by the origin. This oxygen is
353, the reference electrode 361 of the atmosphere chamber 360 is ionized.
Move through the solid electrolyte 331 toward the reference electrode 36.
1 to form oxygen molecules. Oxygen in second reaction chamber 350
Since the concentration is extremely low, the solid
The total amount of oxygen ions flowing through the electrolyte is NO
_XIs caused by the reduction of That is, solid electrolytic
The amount of oxygen ions flowing per unit time through
NO in reaction chamber_XConcentration (NO of exhaust gas in exhaust passage)_XDark
Degree). Therefore, this oxygen ion transfer
The current value (Ip2 in FIG. 2) generated by
As a result, the exhaust NO in the exhaust passage_XDetect concentration
Can be. NO of this embodiment_XThe sensor 71 detects the current
The value Ip2 is converted to a voltage signal, and the NO_XDepending on the concentration
Output the same voltage signal.

In the present embodiment, the ECU 30_XSen
The concentration in the exhaust gas detected by the
Target NO set according to the situation_XTo match the concentration
Then, the air returns to the surge tank 20 through the EGR passage 33.
To control the amount of EGR gas _XControl. Less than
Below, NO of this embodiment_XThe control will be described.

The exhaust gas (EGR gas) recirculated to the intake surge tank 20 through the EGR passage 33 is an inert gas having a low oxygen concentration. If the amount of the EGR gas is increased, the excess air ratio of combustion decreases and the combustion temperature decreases. Due to the decrease, the NO _X amount generated by combustion decreases. However, when gradually increasing the EGR gas amount, although _the amount of NO _X continues to decrease, increases the particulates in exhaust by a decrease in the excess air ratio, further generates the exhaust smoke amount EGR gas is excessive Become like For this reason, in order to prevent the generation of exhaust smoke and the increase of the particulate exceeding the allowable range, the NO _X generation amount cannot be excessively reduced, and the NO _X generation amount has an allowable minimum value. . Since the allowable minimum value changes according to the engine speed (intake air amount) and the fuel injection amount, it changes according to the operating state of the engine.

In the present embodiment, the actual engine is operated in advance by changing the rotation speed and the fuel injection amount, and the generation of exhaust smoke and the increase in particulates do not occur in the combination of each rotation speed and the fuel injection amount. The allowable minimum value of the exhaust NO _X concentration in the range is obtained. In the present embodiment, these exhaust NO rpm the minimum value of _X concentration NE and the fuel injection amount Q _{fi n}
Is stored in the ROM of the ECU 30 in the form of a numerical table using the above and is used as the target NO _X concentration in the actual operation.

The ECU 30 calculates the engine speed during actual operation.
NE and fuel injection amount Q_finFrom the target exhaust NO_X
Set the concentration, NO_XActual exhaust detected by sensor 71
NO _XConcentration is target NO_XEGR pass to match the concentration
The EGR control valve 23 opening of the road 33 is feedback-controlled.
Thus, the EGR gas amount is adjusted. This allows
Exhaust smoke and particulates are constantly generated in the combustion chamber.
NO within a range that does not cause an increase in_XOnly the amount generated is minimized
Is supplied.

However, as described above, the EGR valve 23
If the EGR gas amount is controlled only by the opening degree of the engine, for example, during idling or low load operation when the exhaust pressure decreases, EGR
After GR valve 23 opening is fully opened can not be increased any more EGR gas amount, is to obtain a target exhaust NO _X concentration becomes impossible to flow just enough amount of EGR gas issues is there.

In this embodiment, after the EGR valve 23 is fully opened, the exhaust throttle valve 37, the turbocharger 35
Of the variable nozzle 35a, solves this problem by feedback control according to the NO _X concentration any one or more was detected in NO _X sensor 71 of the intake throttle valve 27. When the opening degree of the exhaust throttle valve 37 or the turbocharger variable nozzle 35a is reduced, the exhaust pressure in the exhaust manifold 31 increases due to an increase in exhaust resistance. Therefore, the pressure difference between the intake surge tank 20 and the exhaust manifold 31 increases, and the flow rate of the EGR gas passing through the EGR passage 33 increases. Since the pressure in the exhaust manifold 31 to rise enough to decrease the degree of opening of the exhaust throttle valve 37 or the variable nozzle 35a, by feedback-controlling the opening degree of the exhaust throttle valve 37 or the variable nozzle 35a according to the NO _X sensor 71 outputs In addition, it is possible to control the actual exhaust NO _X concentration to the target exhaust NO _X concentration.

When the opening degree of the intake throttle valve 27 is reduced, the pressure loss in the intake passage increases.
The pressure in the surge tank 20 decreases according to the opening. For this reason, the pressure difference between the exhaust manifold 31 and the surge tank 20 increases, and even when the exhaust pressure decreases, the EGR passage 3
3 can be increased.
Further, since the pressure of the surge tank 20 decreases as the opening of the intake throttle valve 27 decreases, the actual exhaust NO _{X is} controlled by feedback controlling the opening of the intake throttle valve 27 in accordance with the output of the NO _X sensor 71. it is possible to control the concentration of target exhaust NO _X concentration.

The exhaust throttle valve 37, the turbocharger variable nozzle 35a, and the intake throttle valve 27 may use one of them to control the amount of EGR gas, or use two or more of them. May be. Hereinafter, taking the case where the turbocharger variable nozzle 35a is used as an example, N
O _X control will be described, it becomes substantially the same control even when using other means.

FIG. 3 shows a turbocharger variable nozzle 35.
6 is a flowchart illustrating a NO _X control operation using a. This operation is performed as a routine executed by the ECU 30 at regular intervals. In the operation of FIG. 3, each time the operation is performed, the engine 1 rotation speed NE is read from the rotation speed sensor 55 in step 301, and the ECU 30
The engine fuel injection amount _Qfin calculated by the fuel injection amount calculation operation executed by the above is read. In the present embodiment, E
CU30 is to calculate the fuel injection amount Q _fin of the engine from a predetermined relationship based on the separate accelerator pedal depression amount of the fuel injection amount calculation operation to be performed with the engine rotational speed NE driver (accelerator opening) ACCP Step 301
Uses the result of this operation.

Next, in step 303, step 30
Using the values of NE and _Qfin read in step 1, ECU3
The value of the target NO _X concentration TNOX corresponding to the current operating condition from a pre-stored foregoing numerical table to 0 of ROM is read. In step 305, the current actual exhaust from NO _X sensor 71 in the exhaust passage 3 NO _X concentration AN
OX is read.

In steps 307 and 319,
Actual exhaust NO read by _XThe concentration ANOX is
Target NO_X± α (α is a positive constant
Value), it is determined whether the value is within the range (T).
If NOX-α <ANOX <TNOX + α),
This operation is completed as it is from step 319. in this case
Means that the opening of the variable nozzle 35a and the EGR valve 23 is
Will always be maintained.

[0040] On the other hand, the current of the NO _X concentration ANOX the target N
O _X higher than alpha than the concentration (ANOX ≧ TNOX + α) in the case, NO _X concentration A by increasing the EGR gas amount from the current
It is necessary to reduce NOX to the target concentration TNOX.
In this case, step 309 is executed to the next step 307, the opening degree VEG current EGR valve 23 whether has reached the maximum opening degree (full open opening) VEG _MAX is determined. When the opening of the EGR valve 23 is not fully opened, the EG is still increased by increasing the opening of the EGR valve 23.
Since it is possible to increase the R gas amount, next, in step 311, the EGR valve opening degree VEG is set to a constant value K ₁ (K ₁ >).
0), and at step 313, the EGR valve opening is set to K ₁
The current operation is terminated by controlling the value to the value that has increased. In this case, the opening of the variable nozzle 35a is not changed.

On the other hand, in step 309, the EGR valve 23
Is fully open (VEG = VEG _MAX ),
By increasing the opening of the EGR valve 23, the EGR gas amount cannot be further increased. Therefore, in this case, the amount of EGR gas is increased by restricting exhaust gas by the variable nozzle 35a. That is, in this case, the process proceeds to step 315, where the variable nozzle 35 of the turbocharger is
In step 317, the variable nozzle opening VVN is changed to the opening reduced as described above, while the opening VVN of a is reduced by a constant value K ₂ (K ₂ > 0). This gives E
Even when the GR valve 23 is fully open, the variable nozzle 3
EGR gas amount is increased by performing the exhaust throttling with 5a, the exhaust NO _X concentration will be lowered.

At step 307, ANOX≤TNOX + α
In step 319, the current exhaust N
O _X concentration ANOX is than the target exhaust NO _X concentration TNOX α
It is determined whether the value is lower than the above. ANOX ≦ TNO
When X-α, the actual exhaust NO _X concentration is considerably lower than the target value, and there is a possibility that the generation of exhaust smoke and the increase of particulates may occur.
It is necessary to reduce the amount of gas. Therefore, in this case, the variable nozzle 35 of the turbocharger is
It is determined whether or not the opening degree VVN of “a” has reached the maximum opening degree VVN _MAX . If VVN <VVN _MAX , the EGR gas amount can be reduced by still increasing the opening of the variable nozzle 35a.
Increasing the variable nozzle opening VVN predetermined value K ₂ at 23,
In step 325, an operation of changing the variable nozzle opening VVN to the increased opening is performed, and the current operation is completed.

On the other hand, in step 321, VVN = VVN
If it is _MAX , the EGR gas amount cannot be reduced by further increasing the variable nozzle opening. Therefore, as possible to reduce the amount of EGR gas by throttling the EGR valve 23 opening in this case, as well as set to a value obtained by reducing the current EGR valve 23 opening by the predetermined value K ₁ processing proceeds to step 327, step E at 329
The degree of opening of the GR valve 23 is controlled to the reduced value, and the current operation ends.

[0044] In this operation, the engine exhaust NO _X concentration ANOX by the will always be accurately controlled to a value of ± alpha with respect to the target NO _X concentration TNOX predetermined according to engine operating conditions. α is an allowable deviation from the target NO _X concentration. Further, the turbocharger 35 to the exhaust concentration of NO _X after the EGR valve 23 is fully opened in this embodiment
Is controlled by controlling the opening degree of the variable nozzle 35a in accordance with the output of the NO _X sensor 71, so that the EGR gas amount can be increased or decreased with good responsiveness to the fluctuation of the exhaust NO _X concentration. It is possible to control the NO _X concentration to be close to the target exhaust NO _X concentration with good responsiveness.

In FIG. 3, the case where the EGR gas amount is controlled by controlling the opening degree of the turbocharger variable nozzle 35a in the region where the EGR valve 23 is fully opened has been described. even if the feedback control in accordance opening of the valve 37, or the opening degree of the intake throttle valve 27 in the NO _X sensor 71 outputs, the same procedure of FIG.

Incidentally, in FIG. 3, the EGR valve 23 opening VE
The G and the opening degree VVN of the variable nozzle 35a may be separately detected by disposing an opening degree sensor for detecting the opening degree. For example, when a stepper motor is used as an actuator, an integrated value of the number of driving steps is used. When a vacuum actuator is used, the duty ratio of a drive pulse for driving a drive solenoid of a negative pressure control valve for controlling a negative pressure supplied to the vacuum actuator (the ratio of an ON signal to one cycle of the drive pulse) is approximated. You may make it use it.

Although the above embodiment has been described by taking the case where the present invention is applied to a diesel engine as an example, it goes without saying that the present invention can be applied to a spark ignition engine as well. .

[0048]

Effects of the Invention According to the invention described in the claims, a common effect can be accurately controlled at all times actual exhaust NO _X concentration regardless of the engine operating state at the target exhaust NO _X concentration Play.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel engine.

FIG. 2 is a diagram schematically showing the structure of a NO _X sensor.

FIG. 3 is a flowchart illustrating one embodiment of the NO _X control operation of the present invention.

[Explanation of symbols]

1 ... diesel engine body 2 ... intake passage 3 ... an exhaust passage 23 ... EGR valve 27 ... throttle valve 30 ... electronic control unit (ECU) 35 ... turbocharger 35a ... variable nozzle 37 ... exhaust throttle valve 71 ... NO _X sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 21/08 301 F02D 21/08 301H 3G301 311 311B 41/02 380 41/02 380E 41/04 360 41 / 04 360C 43/00 301 43/00 301N 301W 301K F02M 25/07 570 F02M 25/07 570J 570P F-term (reference) 3G005 DA02 EA15 GB24 GD13 JA35 JA39 3G062 AA01 AA05 BA00 BA06 ED08 GA04 GA05 GA03 AGAA AA3A CA12 DA02 DA06 FA11 GA05 GA10 GA46 JA04 JA09 JA11 KA02 3G084 AA01 BA05 BA08 BA20 CA03 DA10 EA11 EB08 EB12 EC03 EC07 FA08 FA10 FA13 FA18 FA28 FA33 3G092 AA02 AA06 AA17 AA18 DB03 DC03 DC09 DC13 DE18S DG06 HA08 HD08 HA08 HA13 JA24 JA25 KA08 LA00 LA01 LC04 LC07 NA08 N C02 ND02 PA04Z PA17Z PB03Z PD01Z PD15Z PE01Z PF03Z

Claims (4)

[Claims] 1. An EGR control device for an internal combustion engine that recirculates a part of exhaust gas of the internal combustion engine to an engine intake system, wherein the EGR control device is disposed in the EGR passage that communicates an engine exhaust passage with an intake passage. , an EGR valve for throttling the flow rate of the exhaust gas recirculated to the intake system flows through the EGR passage, a NO _X sensor arranged in the exhaust passage for detecting the concentration of NO _X in the exhaust gas, the exhaust channel, connected between the EGR passage an exhaust throttle means throttling the flow rate of the exhaust gas flowing through the exhaust passage disposed subordinates stream side, by adjusting the opening degree of the EGR valve in accordance with the output of the NO _X sensor, the concentration of NO _X in the exhaust predetermined Control means for controlling the flow rate of exhaust gas recirculated to the exhaust system so as to reach the target NO _X concentration, wherein the control means is such that the EGR valve opening degree is in a fully open state;
When it is necessary to increase the flow rate of the exhaust gas recirculated to the intake system in order to make the NO _X concentration in the exhaust gas equal to the target concentration, the exhaust throttle by the exhaust throttle means is controlled according to the output of the NO _X sensor. An EGR control device for an internal combustion engine. 2. The EGR control device for an internal combustion engine according to claim 1, further comprising an exhaust throttle valve disposed in an engine exhaust passage as said exhaust throttle means. 3. The EGR control device according to claim 1, wherein the internal combustion engine includes a turbocharger having an exhaust turbine with a variable nozzle, and the variable nozzle is used as the exhaust throttle means. 4. An EGR control device for an internal combustion engine that recirculates a part of exhaust gas of the internal combustion engine to an engine intake system, wherein the EGR control device is disposed in the EGR passage that connects an engine exhaust passage and an intake passage. , an EGR valve for throttling the flow rate of the exhaust gas recirculated to the intake system flows through the EGR passage, a NO _X sensor arranged in the exhaust passage for detecting the concentration of NO _X in the exhaust gas, on the intake passage, and said EGR passage an intake throttle means throttling the intake air that is disposed at the connection portion upstream flowing through the intake passage, by adjusting the opening degree of the EGR valve in accordance with the output of the NO _X sensor, the concentration of NO _X in the exhaust predetermined Control means for controlling the flow rate of exhaust gas recirculated to the exhaust system so as to reach the target NO _X concentration, wherein the control means is such that the EGR valve opening degree is in a fully open state;
And when it is necessary to increase the flow rate of the exhaust gas recirculated to the intake system in order to make the NO _X concentration in the exhaust gas equal to the target concentration, the intake throttle by the intake throttle means is controlled according to the output of the NO _X sensor. An EGR control device for an internal combustion engine.