JP2000282958A - Exhaust gas recirculation system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly maintain quantity of NOx generated in an internal combustion engine to be a target NOx quantity by detecting an NOx quantity in exhaust gas, and controlling the EGR gas quantity in the engine so that the NOx quantity in exhaust gas becomes the target NOx quantity. SOLUTION: In an exhaust gas recirculating device, in which one part of exhaust gas is supplied to a surge tank 12 via an EGR passage 29 and is introduced together with intake air into a combustion chamber 5, for reducing the NOx generating quantity of an internal combustion engine, an EGR gas quantity is controlled so that the NOx generating quantity when a smoke generating quantity becomes a prescribed quantity, namely, the upper limit value of an allowable smoke generating quantity (hereafter called maximum allowable value) is the target NOx generated quantity. Namely, the opening of an EGR control valve 31 is controlled by a control unit 40 so that NOx concentration detected by an NOx sensor 60 provided in an exhaust pipe 24 becomes the target NOx concentration. Hereby the NOx concentration in exhaust gas is maintained to be the target value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for an internal combustion engine.

[0002]

2. Description of the Related Art There has been a demand for reducing the amount of nitrogen oxides (hereinafter, NO _x ) in exhaust gas discharged from an internal combustion engine. NO _X is Attempts have been made to lower the combustion temperature as a way of the NO _X reduction since less its emissions lower the combustion temperature in the combustion chamber of an internal combustion engine. As a method of reducing the combustion temperature in this way, there is known an exhaust gas recirculation (hereinafter, EGR) method of causing exhaust gas discharged from an internal combustion engine to flow again into a combustion chamber. Since the exhaust gas contains a substance having a large endothermic effect, for example, carbon dioxide, the combustion temperature is reduced if the exhaust gas is introduced into the combustion chamber.

There is a limit to the amount of EGR gas that can be introduced into the combustion chamber. Therefore, for example, Japanese Patent Laid-Open No. 3-1003
In the EGR device disclosed in Japanese Patent Publication No. 61, the EGR gas amount is controlled using the oxygen concentration in the exhaust gas so that the EGR gas amount becomes the target EGR amount. That is, if the oxygen concentration in the exhaust gas is smaller than the target oxygen concentration, it is determined that the EGR gas amount is larger than the target amount. If the oxygen concentration in the exhaust gas is larger than the target oxygen concentration, the EGR gas amount is smaller than the target amount. Judge,
By controlling the oxygen concentration to be the target oxygen concentration, the amount of EGR gas introduced into the combustion chamber is adjusted to a desired EGR gas amount.

[0004]

[SUMMARY OF THE INVENTION Incidentally EGR device originally amount of the NO _X generated in the combustion chamber (hereinafter, NO _X generation amount) is intended to be reduced. That is, this EGR device is not intended to control the oxygen concentration in the exhaust gas. Of course, although not explicitly shown, in the EGR device disclosed in the above publication, N
Also the O _X generation amount as controlling the oxygen concentration so as to minimize under certain conditions be controlled oxygen concentration unrelated only the NO _X generation amount and indirectly, the ultimately NO _X generation amount There is a possibility that the desired amount of generated NO _X cannot be obtained.

In view of the above problems, an object of the present invention is to accurately set the amount of NO _X generated in an internal combustion engine to a target NO _X amount.

[0006]

According to a first aspect of the present invention, there is provided an exhaust gas recirculation system for an internal combustion engine, wherein exhaust gas discharged from the internal combustion engine is allowed to flow back into the internal combustion engine. , wherein the amount of the NO _X in the exhaust gas with the amount of NO _X detection means for detecting, is caused to flow into again to the internal combustion engine as _the amount of NO _X in the exhaust gas becomes the amount of NO _X in the target exhaust Control the amount of gas.

According to the second invention, in the first invention, the target NO _X amount is determined by the engine speed and the fuel injection amount to the internal combustion engine.

[0008]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11. Be linked. The inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17. A throttle valve 20 driven by a step motor 19 is arranged in the intake duct 13. Further, a mass flow detector 21 for detecting a mass flow of the intake air is disposed in the air suction pipe 17. In the surge tank 12, an intake air temperature sensor 53 for detecting the temperature of the intake air and an intake pressure sensor 54 for detecting the pressure of the intake air are arranged.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
The exhaust turbine 2 of the exhaust turbocharger 15 via the
3 and an outlet of the exhaust turbine 23 is connected to a catalytic converter 2 containing a catalyst 25 via an exhaust pipe 24.
6. The catalyst 25 is for example NO _X in the exhaust gas
To purify. An air-fuel ratio sensor 27 for detecting the air-fuel ratio of the exhaust gas and an exhaust pressure sensor 28 for detecting the pressure of the exhaust gas are arranged in the exhaust manifold 22.
The inlet and outlet of the exhaust turbine 23 are directly connected by a bypass passage 55. A bypass control valve 5 driven by a step motor 56 is provided in the bypass passage 55.
7 are arranged.

Further, a step motor 5 is provided in the exhaust pipe 24.
An exhaust throttle valve 59 driven by 8 is arranged. Further, N in the exhaust gas is provided in the exhaust pipe 24 downstream of the exhaust throttle valve 59.
The NO _X sensor 60 for detecting the concentration of O _X, the exhaust gas temperature sensor 61 for detecting the temperature of the exhaust gas is disposed. The exhaust manifold 22 and the surge tank 12 are E
The EGR passage 29 is connected to each other through the GR passage 29.
Inside, an EGR control valve 31 driven by a step motor 30 is arranged. In addition, EG
An intercooler 32 for cooling the EGR gas flowing in the R passage 29 is provided. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the air-fuel ratio sensor 27, the exhaust pressure sensor 28, the fuel pressure sensor 36, the intake temperature sensor 53, the intake pressure sensor 54, the output signal of the NO _X sensor 60 and an exhaust temperature sensor 61 via a corresponding AD converter 47 respectively are input to the input port 45. A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50,
The output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. Further, an atmospheric pressure sensor 62 for detecting atmospheric pressure is connected to the input port 45 via a corresponding AD converter 47. On the other hand, the output port 46 is
8, a fuel injection valve 6, a throttle valve control step motor 19, an EGR control valve control step motor 30,
The fuel pump 35 is connected to a bypass control valve control step motor 56 and an exhaust throttle valve control step motor 58.

In this embodiment, the catalyst 25 causes NO
_It purifies _X and reduces the amount of NO _X emitted into the atmosphere. However there is a demand to further reduce the amount of the NO _X discharged into the atmosphere. Therefore, in the present embodiment, the amount of NO _X itself (hereinafter, NO _X generation amount) generated in the combustion chamber 5 is reduced as follows. That exhaust gas discharged from the internal combustion engine in order to reduce the NO _X generation amount is supplied to the surge tank 12 through the EGR passage 29,
It is introduced into the combustion chamber 5 together with the intake air. The exhaust gas contains an inert gas having a large endothermic effect, such as carbon dioxide. Therefore, the combustion temperature in the combustion chamber 5 is reduced by introducing the exhaust gas into the combustion chamber 5. NO _X generation amount is small the lower the combustion temperature. Therefore, according to the present embodiment, the amount of NO _X generated is reduced by introducing exhaust gas into the combustion chamber 5, and as a result, the amount of NO _X discharged to the atmosphere is also reduced.

By the way the amount of exhaust gas introduced into the combustion chamber 5 (hereinafter, EGR gas amount) NO _X generation amount in accordance with the different. More typically the amount EGR gas is large NO _X generation amount is small. Of course, EGR to minimize the NO _X generation amount since it is preferable NO _X generation amount is small as possible
It is preferable to increase the gas amount as much as possible. However, if the amount of EGR gas is large, there is a problem with respect to engine operation. Therefore, in practice, the EGR gas amount is controlled by various parameters so that a problem does not occur with respect to engine operation. Next, the control of the EGR gas amount will be described.

[0015] The ratio of the EGR gas amount to the intake air amount to generally as shown in FIG. 2 (hereinafter, EGR rate) larger the NO _X generation amount decreases, generated by the other hand the combustion chamber 5 The amount of smoke (hereinafter, the amount of generated smoke) increases. Since the amount of smoke generation should also be limited to a certain value or less, in the present embodiment, when the amount of smoke generation becomes a predetermined value, that is, the upper limit value of the allowable amount of smoke generation (hereinafter, maximum allowable value), of the NO _X generation amount target of NO
_The EGR gas amount is controlled as the _X generation amount. NO _X concentration (or NO _X in the exhaust gas ie representing the NO _X generation amount
Amount) is detected by the NO _X sensor 60, and the detected NO _X concentration (hereinafter, detected NO _X concentration) is used as the target NO.
_The EGR gas amount is controlled so as to be _X concentration (hereinafter, target NO _X concentration). Specifically, the detected NO _X concentration is
_{When the} concentration is larger than the _X concentration, the EGR gas amount is controlled to increase, and when the detected NO _X concentration is smaller than the target NO _X concentration, the EGR gas amount is controlled to decrease. As described above, in the present embodiment, E is determined based on the concentration of NO _X to be controlled.
Since the GR gas amount is controlled, it is possible to accurately control the NO _X concentration to the target NO _X concentration, that is, the NO _X generation amount to the target NO _X generation amount. Since the smoke generation amount is determined by the engine speed and the fuel injection amount, the maximum allowable value of the smoke generation amount is made to correspond to the target NO _X concentration via the engine speed and the fuel injection amount, and the target NO _X
Calculate _X concentration. Target NO _X as words shown in FIG. 3
The concentration BCnox is stored in the ROM 42 in the form of a map in advance as a function of the engine speed N and the fuel injection amount Q.

The amount of smoke generated is introduced into the combustion chamber 5.
Depending on the amount of oxygen (hereinafter referred to as oxygen introduction)
You. In other words, the smaller the amount of oxygen introduced, the larger the amount of smoke generated
Become. Here, not only the amount of oxygen introduced but also the EGR rate change.
It changes depending on the atmospheric pressure. That is, the atmospheric pressure is high
The higher the amount of oxygen introduced, the lower the atmospheric pressure
Few. Therefore, in this embodiment, the higher the atmospheric pressure, the more smoke
It is determined that the generation amount is small, and the target NO_XLow concentration
Set. On the other hand, the lower the atmospheric pressure, the greater the amount of smoke generated
And the target NO_XSet the density higher. Like this
NO _XReduce the amount of generation to the lowest possible value
Can be In this embodiment, as shown in FIG.
Target NO_XThe correction value K1 for the density is calculated as a function of the atmospheric pressure P.
3 is stored in the ROM 42 in advance in the form of a map.
The value BCnox calculated from the map is used as the basic target NO.
_XDensity and the correction calculated by the map of FIG.
Multiply the value K1 and set the target NO_XCalculate the concentration TCnox.
In FIG. 4, the value RP is a reference atmospheric pressure, for example, 1 atm.
It is.

Next, the control of the EGR gas amount of the above-described embodiment will be described in detail with reference to the flowchart of FIG.
First target NO _X concentration TCnox _n in the current routine is calculated in step 100. That is, the formula TCn
The target NO _X concentration is calculated according to ox _n = BCnox _mn × K1. Note that BCnox _mn as described above is the basic target NO _X concentration calculated based on the map of FIG. 3, K1 is a correction value that is calculated based on the map of FIG.

Next, at step 101, the EGR control valve 31 calculated at the present time, that is, at the previous routine is calculated.
The correction value K2 for the valve opening amount Degr _n-1 is calculated.
That is, the detected NO _X concentration DCnox detected by the NO _X sensor 60 and the target N calculated in Step 100
The O _X concentration difference between TCnox _n ΔCnox formula DerutaCnox
= Calculated according TCnox _n -DCnox, the difference Δ
The correction value K2 is calculated from the map of FIG. 6 based on Cnox. Here, the larger the difference ΔCnox is, the smaller the correction value K2 is, and the smaller the EGR gas amount is.

Next, at step 102, the opening amount Degr _n of the EGR control valve 31 in this routine is calculated. That is, the opening amount Degr _n of the EGR control valve 31 is calculated according to the equation Degr _n = Degr _n-1 + K2. Next, at step 103, the opening amount Degr _n of the EGR control valve 31 calculated at step 102 is changed to the EGR value.
It is determined whether or not the maximum valve opening amount Degrmax of the control valve 31 is larger than that of the control valve 31, that is, whether Degr _n > Degrmax.

In step 103, Degr _n > De
When it is determined to be grmax, the EGR is no more than this.
It is determined that the opening amount of the control valve 31 cannot be increased, and the routine proceeds to step 104, where the opening amount D of the exhaust throttle valve 59 is determined.
Ex _n is calculated. That is, E calculated in step 102
The opening amount Degr _n and the maximum opening amount Deg of the GR control valve 31
The difference ΔDegr from rmax is calculated by the formula ΔDegr = Degrm.
ax-Degr _n, a correction value K3 for the current opening amount Dex _{n- 1} of the exhaust throttle valve 59 is calculated from the map of FIG. 7 based on the difference ΔDegr, and the equation Dex _n
= Dex _n-1 + K3, and calculates the opening amount Dex _n of the exhaust throttle valve 59 in this routine. Here, as the difference ΔDegr increases, the correction value K3 decreases, and the opening amount of the exhaust throttle valve 59 also decreases. And exhaust throttle valve 5
When the valve opening amount of No. 9 decreases, the EGR gas amount increases. Next, at step 105, the opening amount Degr _n of the EGR control valve 31 calculated at step 102 is corrected to the maximum opening amount Degrmax.

Next, at step 106, the EGR control valve 31 is controlled such that the opening amount of the EGR control valve 31 becomes the opening amount Degr _n calculated at step 105, that is, the maximum opening amount. the amount of opening of the exhaust throttle valve 59 exhaust throttle valve 59 such that the opening amount Dex _n calculated in step 104 is controlled.

In step 103, Degr_n≤De
When it is determined to be grmax, the EGR control valve 31
Is set to the valve opening amount De calculated in step 102.
gr _nJudge that it can be increased to
08, the opening amount Dex of the exhaust throttle valve 59_nThe most
Let it be the large value Dexmax. Then in step 106
The amount of opening of the EGR control valve 31 is calculated in step 102 above.
Discharged valve opening Degr_nEGR control valve 3
1 is controlled, and then at step 107
The valve opening amount of the valve 59 is calculated in the above step 108.
It will be the maximum value Dexmax, that is, it will be fully open
Thus, the exhaust throttle valve 59 is controlled.

[0023]

According to the first and second aspects of the present invention, based on the amount of NO _{X in} the exhaust gas, the NO _X amount is reduced to the target N
The amount of the exhaust gas is caused to flow into again to the internal combustion engine so that the O _X amount is controlled. Here, the exhaust gas amount is controlled based on the parameter to be controlled, that is, the NO _X amount, so that the NO _X amount can be accurately set as the target NO _X amount.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal combustion engine to which an exhaust gas recirculation device of the present invention is applied.

2 is a diagram showing the relationship between the EGR rate and NO _X generation amount and the amount of smoke generated.

FIG. 3 is a diagram showing a map for calculating a basic target NO _X concentration.

FIG. 4 is a diagram showing a map for calculating a correction value for a basic target NO _X concentration.

FIG. 5 is a flowchart showing EGR gas amount control according to the present invention.

FIG. 6 is a view showing a map for calculating a correction value for the opening amount of the EGR control valve.

FIG. 7 is a diagram showing a map for calculating a correction value for an opening amount of an exhaust throttle valve.

[Explanation of symbols]

1 ... engine body 29 ... EGR passage 31 ... EGR control valve 60 ... NO _X sensor 62 ... atmospheric pressure sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 25/07 570 F02M 25/07 570J F02D 9/04 F02D 9/04 C 21/08 301 21/08 301E 41/02 380 41/02 380E 41/04 380 41/04 380F (72) Inventor Shinji Kamoshita 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yasuhiko Otsubo Toyota Town, Toyota City, Aichi Prefecture 1 Toyota Motor Corporation (72) Inventor Shinichi Kusakabe 2-1-1 Toyota-cho, Kariya-shi, Aichi F-term in Toyota Industries Corporation (reference) 3G062 AA01 BA04 BA06 CA06 EA11 FA12 GA05 GA06 GA13 GA15 GA17 GA21 3G065 AA01 AA10 CA12 DA06 FA12 GA01 GA05 GA06 GA08 GA10 GA26 GA27 GA46 JA04 JA09 JA11 KA02 3G092 AA02 AA17 AA18 DB03 DC01 DC09 DC12 DG08 EC01 FA17 HA01Z HA04Z HA05Z HB01Z HB03Z HD01Z HD04Z HD05Z HD07X HD08Z HE01Z HE03Z HF08Z 3G301 HA02 HA13 JA25 LA00 LA03 MA11 NC02 ND01 PA01Z PA07Z PA10Z PB08A PB08Z PD01Z PD03Z PD01Z PD03Z

Claims (2)

[Claims] In an exhaust gas recirculation device for an internal combustion engine, wherein the exhaust gas discharged from the internal combustion engine is caused to flow back into the internal combustion engine, the NO _X amount for detecting the NO _X amount in the exhaust gas is provided. Detecting means for detecting N in the exhaust gas.
An exhaust gas recirculation device for an internal combustion engine, wherein the amount of exhaust gas flowing back into the internal combustion engine is controlled so that the O _X amount becomes a target NO _X amount. 2. The system according to claim 1, wherein the target NO _X amount is determined by an engine speed and a fuel injection amount to the internal combustion engine.
An exhaust gas recirculation device for an internal combustion engine according to claim 1.