JP2002021645A - Exhaust gas recirculation controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent massive production of NOx in an exhaust gas recirculation controller for an internal combustion engine for feedback-controlling an opening of an exhaust gas recirculation control valve in accordance with a fresh air amount. SOLUTION: The actual fresh air amount introduced inside a cylinder is directly or indirectly detected (Step 103). A minimum opening of the exhaust gas recirculation control valve is limited so as to not come below a minimum exhaust gas recirculation rate preventing massive production of NOx in accordance with this fresh air amount (Steps 112 and 113).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

By recirculating a portion of the Related Art An exhaust gas into the cylinder, to lower the combustion temperature by large heat capacity possessed by the inert gas is a main component of the exhaust gas, to reduce the generation amount of the NO _x exhaust Recirculation is known. In order to realize the exhaust gas recirculation, the internal combustion engine has an exhaust recirculation passage communicating the engine exhaust system and the engine intake system, and an exhaust gas recirculation passage arranged in the exhaust recirculation passage for controlling the amount of recirculated exhaust gas. EG
An R control valve is provided.

The fresh air introduced into the cylinder changes according to the amount of recirculated exhaust gas. That is, when the amount of recirculated exhaust gas increases, the amount of fresh air decreases, and when the amount of recirculated exhaust gas decreases, the amount of fresh air increases. In general, the amount of recirculated exhaust gas introduced into a cylinder is represented by an EGR rate represented by (recirculated exhaust gas amount / gas amount in cylinder (fresh air and recirculated exhaust gas amount)).

A target fresh air amount and EG for each engine operating state
There is a combination with the R rate, and to realize this,
The target opening of the throttle valve and the EGR control valve is mapped for each engine operating state. In the steady engine operating state, the throttle valve and the EG based on such a map are used.
The target fresh air amount and the target EG are controlled by controlling the opening of the R control valve.
Realization of an R rate is possible. However, at the time of engine acceleration, the target fresh air amount is not immediately realized even if the throttle valve and the EGR control valve are each controlled to the target opening. Accordingly, it has been proposed to monitor the fresh air amount using an air flow meter or the like and perform feedback control of the opening of the EGR control valve so as to improve the delay in increasing the fresh air amount.

[0005]

In the feedback control, when a delay in increasing the fresh air amount occurs, the opening degree of the EGR control valve is reduced to reduce the amount of recirculated exhaust gas, thereby reducing the amount of fresh air amount. It promotes the increase. Thereby, at the time of engine acceleration, an increase delay of the fresh air amount is improved, EGR rate becomes very low, so that the NO _x is a large amount of generated.

Further, the target EGR for each engine operating state is simply described.
It has been proposed to feedback-control the opening degree of the EGR control valve so that the rate, that is, the target amount of recirculated exhaust gas is realized, but a delay in increasing the fresh air amount occurs during engine acceleration. Sometimes, when the target recirculated exhaust gas amount is realized, the EGR rate becomes the target, but the absolute value of the new air amount is insufficient, that is, a high target EGR rate after engine acceleration is realized for a small new air amount. Therefore, a large amount of smoke is generated.

Accordingly, a first object of the present invention, in the exhaust gas recirculation control device for an internal combustion engine which feedback control of the opening degree of the EGR control valve in accordance with the fresh air amount, by preventing a large amount occurrence of the NO _x is there.

A second object of the present invention is to prevent a large amount of smoke from being generated in an exhaust gas recirculation control device for an internal combustion engine that performs feedback control of the opening of an EGR control valve according to the amount of recirculated exhaust gas. It is.

[0009]

According to a first aspect of the present invention, there is provided an exhaust gas recirculation control system for an internal combustion engine according to the present invention. in the exhaust recirculation control system for an internal combustion engine feedback control of the actually detected amount of fresh air introduced into the cylinder directly or indirectly, the relative amount of fresh air, preventing the large amount occurrence of the NO _x The minimum opening degree of the EGR control valve is limited so as not to fall below the minimum EGR rate.

According to a second aspect of the present invention, there is provided an exhaust gas recirculation apparatus for an internal combustion engine, wherein the opening degree of an EGR control valve is feedback-controlled in accordance with the amount of recirculated exhaust gas. In the exhaust gas recirculation control device for an internal combustion engine, the amount of fresh air actually introduced into the cylinder is directly or indirectly detected, and a maximum amount of smoke that does not generate a large amount of smoke with respect to the amount of fresh air is detected. The maximum opening degree of the EGR control valve is limited so as not to exceed the EGR rate.

[0011]

FIG. 1 is a schematic diagram showing an internal combustion engine provided with an exhaust gas recirculation device according to the present invention. In the figure, 1 is a diesel engine main body, 2 is an engine intake system, and 3 is an engine exhaust system. The engine intake system 2 has an intake manifold 2a located at the most downstream side, a surge tank 2b located immediately upstream of the intake manifold 2a, and an intake passage 2c connected to the surge tank 2b.

The engine exhaust system 3 has an exhaust manifold 3a located on the most upstream side and an exhaust passage 3b connected to the exhaust manifold 3a. The intake passage 2c and the exhaust passage 3b are connected by an exhaust gas recirculation passage 4a, and the exhaust gas recirculation passage 4a is provided with an EGR control valve 4b for controlling the amount of recirculated exhaust gas. Thus, the exhaust gas recirculation passage 4a and the EGR control valve 4b
Thus, the exhaust gas recirculation device 4 is configured. A throttle valve 7 driven by, for example, a step motor or the like and not mechanically connected to an accelerator pedal is disposed upstream of a connection portion of the exhaust recirculation passage 4a in the intake passage 2c. The compressor 5a of the turbocharger 5 is located upstream of the throttle valve 7 in the intake passage 2c.
The turbine 5b of the turbocharger 5 is located downstream of a connection portion of the exhaust passage 3b with the exhaust recirculation passage 4a.
Is arranged. Reference numeral 6 denotes a fuel injection valve for injecting fuel into each cylinder.

Reference numeral 20 denotes the EGR in the exhaust gas recirculation device 4.
The control device is in charge of controlling the opening of the control valve 4b and controlling the opening of the throttle valve 7. The control device 20 includes a rotation sensor 21 for detecting an engine speed, an accelerator pedal stroke sensor 22 for detecting an amount of depression of an accelerator pedal, an air flow meter 23 for detecting a fresh air amount, An intake pressure sensor 24 for detecting gas pressure in the surge tank 2b, that is, downstream of a connection of the exhaust recirculation passage 4a in the engine intake system 2, and an intake temperature sensor 25 for detecting gas temperature at the same position. And an exhaust-side pressure sensor 26 for detecting gas pressure upstream of a connection of the exhaust recirculation passage 4a in the engine exhaust system 3 and an exhaust-side temperature sensor 27 for detecting gas temperature at the same position. And are connected.

For controlling the injection amount and the injection timing of each fuel injection valve 6, a general fuel injection pump connected to an accelerator pedal may be used. The injection valves may be communicated with the accumulator, and the opening and closing of each fuel injection valve may be controlled by the control device 20 based on a map set for each engine operating state determined by the output of each sensor described above.

The control of the opening of the EGR control valve 4b and the throttle valve 7 by the control device 20 is performed according to a first flowchart shown in FIG. This will be described below. This flowchart is repeated every predetermined time. First, in step 101, the current engine operating state is detected based on the engine speed detected by the rotation sensor 21 and the depression amount of the accelerator pedal as the engine load detected by the accelerator pedal stroke sensor 22.

Next, at step 102, the target fresh air amount Gt based on the current engine operating state and the basic opening Db of the EGR control valve 4b based on the current engine operating state are calculated or read from a predetermined map. . At this time, the opening of the throttle valve 7 is controlled to be the basic opening calculated based on the current engine operating state or read from a predetermined map.

Next, in step 103, the actual fresh air amount Gn is detected by the air flow meter 23, and in step 104, NO _x
The minimum recirculation exhaust gas amount Amin for realizing the minimum EGR rate for preventing the generation of a large amount of exhaust gas is calculated.

Next, the exhaust recirculation passage 4a of the engine intake system
And the exhaust gas pressure Pe upstream from the connection of the exhaust recirculation passage 4a of the engine exhaust system. Intake side pressure sensor 2
The gas pressure Pi ′ and the gas temperature Ti ′ detected by the pressure sensor 4 and the intake-side temperature sensor 25 are the pressure and temperature of the mixed gas of fresh air and recirculated exhaust gas. The gas pressure Pe 'and the gas temperature Te' detected by the exhaust pressure sensor 26 and the exhaust gas temperature sensor 27 are the pressure and temperature of the exhaust gas including the recirculated exhaust gas. The required fresh gas pressure Pi and the exhaust gas pressure Pe are values when the recirculated exhaust gas amount at the current fresh air amount is set to zero (when the EGR control valve 4b is fully closed). As a result, the actually detected gas pressure Pi 'and gas temperature T of the engine intake system are detected.
i ′ and the actually detected gas pressure Pe ′ of the engine exhaust system.
The current gas amount and temperature of the recirculated exhaust gas are estimated based on the gas temperature Te ′ and the fresh air amount detected by the air flow meter 23, and the recirculated exhaust gas in each of the engine intake system and the engine exhaust system is estimated. The partial pressure of the gas is calculated, and the partial pressure in the engine intake system is subtracted from the actually detected gas pressure Pi 'in the engine intake system to calculate the fresh air gas pressure Pi. The exhaust gas pressure Pe is calculated by subtracting the partial pressure in the engine exhaust system from the system gas pressure Pe '.

Next, at step 106, the EGR control valve 4 for realizing the minimum recirculated exhaust gas amount Amin based on the fresh air gas pressure Pi and the exhaust gas pressure Pe.
The minimum opening Dmin of b is calculated by the following equation (1) or (2). Dmin = C · Amin / (Pe−Pi) ^1/2 (1) Dmin = C · Amin / (Pe ^1/2 · Φ) (2) where C is a constant and the specific heat ratio of the gas is k. (Pe / Pi)> (2 / (k + 1))
^{When k / (k−1)} , Φ = (k / (k−1) · ((Pe /
Pi) ^{2 / k-} (Pe / Pi) ^{(k + 1) / k} )) ^1/2
When (Pe / Pi) <(2 / (k + 1)) ^{k / (k−1)} , Φ = (2 / (k + 1)) ^{1 / (k−1)} · (k / (k +
1)) ^1/2 . Equation (1) is a calculation equation when the exhaust gas is an incompressible fluid. In practice, it is preferable to use equation (2) for a compressible fluid, but it is preferable to use equation (2). Equation (1) is very simple, and calculation time can be reduced by using equation (1).

Next, in step 107, a deviation dG between the actual fresh air amount Gn and the target fresh air amount Gt is calculated,
In step 108, the feedback operation amount Da of the EGR control valve 4b is calculated. The feedback manipulated variable Da includes a feedback proportional term Dp = dG · P1 (P1 is a constant) based on the fresh air amount deviation dG and a feedback integral term Di = Di + dG based on the fresh air amount deviation dG.
-It is the sum with I1 (I1 is a constant).

Next, at step 109, EGR
The opening D of the control valve 4b is calculated as the sum of the target opening Db and the feedback operation amount Da. In step 110, it is determined whether or not the target opening Db is zero. When the current engine operation state is a cold state, an idle state, or a high load state, and it is preferable to stop the exhaust gas recirculation, this determination is affirmed and the routine proceeds to step 111,
The opening D of the EGR control valve 4b is set to 0. On the other hand, when the determination in step 110 is negative, that is, when it is preferable to execute the exhaust gas recirculation in the current engine operating state, the process proceeds to step 112 and the EGR control valve 4b calculated in step 109 is operated. Opening D
Is the EGR control valve 4 calculated in step 106.
b is smaller than the minimum opening Dmin, and if the determination is negative, the opening D of the EGR control valve 4b is determined.
Is the value calculated in step 109. However, when the determination in step 112 is affirmative, the opening D of the EGR control valve 4b is equal to the minimum opening Dmin.
It is said.

As described above, this flow chart shows that when the deviation dG between the actual fresh air amount Gn and the target fresh air amount Gt exists, the opening degree of the EGR control valve 4b is increased or decreased to increase or decrease the recirculated exhaust gas amount. Thus, the target fresh air amount Gt can be achieved at an early stage. However,
For example, when the actual fresh air amount Gn is significantly lower than the target fresh air amount Gt during engine acceleration or the like, the EGR control valve 4
In order to prevent the EGR rate from becoming excessively low due to excessively decreasing the opening degree of b, the opening degree of the EGR control valve 4b is set to a minimum value for realizing the minimum EGR rate with respect to the actual fresh air amount Gn. Guarding is performed at the opening degree Dmin. As a result, NO _x it will not be a large amount generated in order to realize at an early stage target fresh air amount.

FIG. 3 is a second flowchart for controlling the opening of the EGR control valve 4b and the throttle valve 7, which is executed instead of the first flowchart. Only the differences from the first flowchart will be described below. In this flowchart, in step 202, a target recirculation exhaust gas amount At for realizing an optimum EGR rate based on the current engine operating state, and an EGR based on the current engine operating state
The basic opening degree Db of the control valve 4b is calculated or read from a predetermined map. At this time, the opening of the throttle valve 7 is controlled to be the basic opening calculated based on the current engine operating state or read from a predetermined map.

In step 204, the maximum EG which does not generate a large amount of smoke with respect to the actual fresh air amount Gn
A maximum recirculation exhaust gas amount Amax for realizing the R rate is calculated.

In step 206, the maximum opening of the EGR control valve 4b for realizing the maximum recirculated exhaust gas amount Amax based on the fresh gas pressure Pi and the exhaust gas pressure Pe by the same equation as in the first flowchart. The degree Dmax is calculated.

In step 207, the intake side pressure sensor 2
5 and the actual recirculated exhaust gas amount An calculated based on the gas pressure and the gas temperature detected by the intake-side temperature sensor 26 and the fresh air amount detected by the air flow meter 23, and the target recirculated exhaust gas amount The deviation dA from At is calculated, and in step 208, the feedback operation amount Da of the EGR control valve 4b is calculated. The feedback manipulated variable Da includes a feedback proportional term Dp = dA · P2 (P2 is a constant) based on the deviation dA of the recirculated exhaust gas amount and a feedback integral term Di = Di + dA · I2 based on the deviation dA of the recirculated exhaust gas amount. (I2 is a constant).

Next, at step 209, as in the first flowchart, the opening D of the EGR control valve 4b is calculated as the sum of the target opening Db and the feedback operation amount Da. After it is determined in step 210 whether or not the target opening Db is 0, in step 212, the opening D of the EGR control valve 4b calculated in step 209 is changed to the EGR control valve calculated in step 206. It is determined whether or not the opening degree Dmax of the EGR control valve 4b is greater than the maximum opening degree Dmax. If the determination is negative, the opening degree D of the EGR control valve 4b is set to the value calculated in step 209. However, when the determination in step 212 is affirmative, the opening D of the EGR control valve 4b becomes the maximum opening D
max.

As described above, when the deviation dA between the actual amount of recirculated exhaust gas An and the target amount of recirculated exhaust gas At is present, the opening of the EGR control valve 4b is increased or decreased to reduce the amount of recirculated exhaust gas. Is increased or decreased, thereby enabling the target recirculation exhaust gas amount At to be achieved at an early stage. However, for example, at the time of acceleration of the engine or the like, in order to realize an EGR rate suitable for the engine operating state after acceleration, despite the fact that the actual fresh air amount Gn is small, E
When the opening of the GR control valve 4b is increased, the actual fresh air amount G
Since a large amount of exhaust gas is recirculated with respect to n, the opening degree of the EGR control valve 4b is set to the maximum EGR which does not generate a large amount of smoke with respect to the actual fresh air amount Gn.
Guarding is performed at the maximum opening degree Dmax for realizing the rate. Thereby, the target recirculated exhaust gas amount At
A large amount of smoke is not generated in order to achieve the above at an early stage.

In the first and second flowcharts, when calculating the minimum recirculation exhaust gas amount Amin and the maximum recirculation exhaust gas amount Amax with respect to the actual fresh air amount Gn, the current engine temperature, fuel injection timing, etc. It is preferable to consider that the EGR rate must be reduced as the combustion becomes unstable based on the following equation. Further, the minimum recirculated exhaust gas amount Amin with respect to the actual fresh air amount Gn
And the maximum recirculated exhaust gas amount Amax has been an actual lower limit and the upper limit of the recirculated exhaust gas amount range to prevent a large amount occurrence of the NO _x is not a large amount of generated smoke against fresh air amount, for example, , In the first and second flowcharts, the smoke and N
The optimal value for both O _x is determined by the minimum recirculated exhaust gas amount A
min and the maximum recirculated exhaust gas amount Amax may be used.

[0030]

As described above, according to the exhaust gas recirculation control apparatus for an internal combustion engine according to the first aspect of the present invention, the exhaust gas of the internal combustion engine that feedback-controls the opening degree of the EGR control valve according to the fresh air amount. in the recirculation control device, in fact, directly or indirectly detecting the amount of fresh air introduced into the cylinder, against the fresh air amount, the minimum EGR to prevent a large amount occurrence of the NO _x
The minimum opening of the EGR control valve is limited so as not to fall below the rate. Thereby, even if an increase delay of the fresh air amount is generated in the engine during acceleration or the like, at least the minimum EGR rate with respect to the actual fresh air amount is ensured, it is possible to prevent a large amount generation of NO _x.

Further, according to the exhaust gas recirculation apparatus for an internal combustion engine according to the second aspect of the present invention, the exhaust gas recirculation control for the internal combustion engine that feedback-controls the opening of the EGR control valve according to the amount of recirculated exhaust gas. In the device, the amount of fresh air actually introduced into the cylinder is directly or indirectly detected, and the new air amount is not exceeded by a maximum EGR rate at which a large amount of smoke is not generated. The maximum opening of the EGR control valve is limited. As a result, even if a delay in increasing the fresh air amount occurs at the time of engine acceleration or the like, the maximum EGR rate is suppressed even if the amount is larger than the actual fresh air amount, and generation of a large amount of smoke can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view of an internal combustion engine provided with an exhaust gas recirculation device according to the present invention.

FIG. 2 is a first flowchart for controlling the opening of a throttle valve and an EGR control valve.

FIG. 3 is a second flowchart for controlling the opening of a throttle valve and an EGR control valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine main body 2 ... Engine intake system 3 ... Engine exhaust system 4 ... Exhaust recirculation device 4a ... Exhaust recirculation passage 4b ... EGR control valve 7 ... Throttle valve 20 ... Control device

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02M 25/07 570 F02M 25/07 570P

Claims (2)

[Claims] In an exhaust gas recirculation control device for an internal combustion engine that feedback-controls an opening of an EGR control valve according to a new air amount, a new air amount actually introduced into a cylinder is directly or indirectly detected. and, wherein the relative amount of fresh air, a large amount generating the smallest internal combustion engine, characterized in that it falls below the EGR rate limits the minimum opening of the EGR control valve so that no exhaust gas recirculation to prevent of the nO _x Control device. 2. An exhaust gas recirculation control device for an internal combustion engine that feedback-controls an opening of an EGR control valve according to a recirculated exhaust gas amount, wherein a fresh air amount actually introduced into a cylinder is directly or indirectly measured. Wherein the maximum opening of the EGR control valve is limited so as not to exceed a maximum EGR rate that does not generate a large amount of smoke with respect to the fresh air amount. Exhaust recirculation device.