JP3129082B2 - Air-fuel ratio control device for engine with EGR device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control of an engine having an exhaust gas recirculation device (EGR device) for recirculating a part of the exhaust gas of the engine to an intake system.

[0002]

2. Description of the Related Art Conventionally, there is an engine equipped with an EGR device for extracting a part of exhaust gas from an exhaust system, controlling appropriate temperature, timing, flow rate, etc. and recirculating the exhaust gas to an intake system. Most of the burned gas is inert gas (H ₂ O,
An N _2, CO _2, etc.), and put it into combustion mixture, for maximum combustion temperature by the heat capacity of the inert gas have decreases, it is possible to reduce the NOx contained in the exhaust gas. Further, the EGR device is provided with a flow control valve (EGR valve) in an exhaust gas recirculation path connecting an intake system and an exhaust system of the engine, and opens and closes the EGR valve according to the operation state of the engine to recirculate exhaust gas. The amount (EGR flow rate) is controlled.

The EGR valve is controlled to open and close (EGR).
Control) is obtained by the following equation. τ = intake air amount per engine revolution QN × FAF × FEGR (1) QN: intake air amount calculated by total air intake amount / engine speed NE FAF: feedback correction coefficient from oxygen sensor FEGR : EGR correction value Here, the total air intake amount detected by the intake pressure sensor detects the total sum of new air taken in from the intake system and a part of exhaust gas taken in from the exhaust system. Further, since the exhaust gas taken in by the EGR device does not burn in the combustion chamber, if the fuel injection amount τ is obtained based on the intake air amount QN, the fuel injection amount τ for new combustible air increases. Therefore, since the air-fuel ratio becomes over-rich, the fuel injection amount τ is corrected by the EGR correction value FEGR so that the air-fuel ratio is not over-rich.

[0004]

[SUMMARY OF THE INVENTION Incidentally, if the EGR flow rate was refluxed by EGR device is correctly controlled, air-fuel ratio is over-rich to accurately correct the fuel injection amount τ by the EGR correction value FEGR Can be avoided. However, it is difficult to directly measure the EGR flow rate recirculated by the EGR device. Therefore, the EGR flow rate is obtained by the following equation using Bernoulli's law.

QEGR = A × (PE−PI) ^1/2 Equation (2) QEGR: Flow rate to be recirculated A: Flow resistance coefficient of exhaust gas recirculation path PE: Exhaust pressure PI: Intake pressure EGR device In the equipped engine, PE and PI in the equation (2) usually do not depend on the state of the EGR device, but change according to the state of the engine by the operation of the driver. A is normally changed and controlled by the EGR device. This is because when the EGR flow rate is introduced by (PE-PI) ^1/2 where A is constant, an appropriate flow rate for the engine is not necessarily obtained.

Since PE (absolute pressure) has a roughly proportional relationship with PI (absolute pressure), a desired EGR flow rate can be controlled by changing A in accordance with PI.
Further, since the EGR flow rate is determined according to PI, EGR for maintaining the exhaust air-fuel ratio at the stoichiometric air-fuel ratio according to PI is performed.
The correction value FEGR can be obtained. But A
Corresponds to PI one-to-one in an environment where there is no trouble in the exhaust gas recirculation path and the EGR valve. Therefore, if any trouble (failure) occurs in the exhaust gas recirculation path and the EGR valve, the correspondence between PI and the EGR flow rate is broken, and the correspondence between PI and the EGR correction value is also broken.

In particular, when the relationship is broken in the direction in which the EGR flow rate with respect to the PI increases, the EGR correction value is determined according to the PI value and does not increase in spite of the large EGR flow rate. On the other hand, the fuel injection amount τ increases. Therefore, the air-fuel ratio becomes over-rich, and a large amount of HC and CO flows out to the exhaust system. For this reason, the exhaust emission deteriorates, and in some cases, the afterburning (afterburn) may damage the exhaust system.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to determine whether an exhaust system has exceeded an exhaust regulation or an exhaust system based on an output value output from an existing sensor mounted on an engine. An increase in the EGR flow rate that may cause damage is detected, and a sufficient amount of fuel is reduced to suppress the increase to prevent damage to the exhaust system in the event of a failure of the EGR device and to exceed the HC, CO regulated values. An object of the present invention is to provide an air-fuel ratio control device for an engine with an EGR device, which is prevented by a simple configuration.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 is provided in an exhaust recirculation path connecting an exhaust system and an intake system of an engine. A flow control valve for recirculating the part to the intake system, a rotational speed detecting means for detecting the rotational speed of the engine, an intake air pressure detecting means for detecting the intake air pressure sucked into the intake system, and based on the engine rotational speed and the intake air pressure. a flow control valve as well as opening control Te, the air-fuel ratio control apparatus for an EGR apparatus with an engine having an EGR basic control means for reduction of the amount of fuel injection based on the intake air pressure, the flow control valve by the ERG basic control unit when control is your, and excess flow rate determining means for determining based on whether the exhaust gas recirculated to the intake system from the exhaust recirculation path becomes excessive to the intake air pressure,
If it is determined by the flow rate excess determining means that the exhaust gas is excessively recirculated to the intake system, the fuel injection amount is further reduced to prevent the air-fuel ratio from being over-rich due to excessive exhaust gas recirculation to the intake system. Weight loss correction means for correcting,
Operating state detecting means for detecting an operating state of the engine;
Engine base based on the detection signal from the
Ignition timing calculating means for calculating a main ignition timing;
Excessive exhaust gas is recirculated back to the intake system by excessive judgment means.
Is determined by the ignition timing calculation means.
Retard correction means for retarding the basic ignition timing of a damaged engine
The gist is to have a step .

[0010] The invention according to claim 2 is the invention according to claim 1,
In the air-fuel ratio control device of the engine with the GR device, the flow rate excess determining means determines that the exhaust gas is excessive when the rate of change per hour of the intake air pressure detected by the intake air pressure detecting means is large. Make a summary.

[0011] According to a third aspect, claim 1, wherein the E
An air-fuel ratio control device for an engine with a GR device , comprising an opening detecting means for detecting an opening of a throttle valve of an intake system, wherein the flow rate excess judging means detects a flow rate based on an engine speed and an opening of a throttle valve. Turkey be judged and the reference suction pressure when the control valve is normally controlled, whether the exhaust gas based on the pressure difference between the intake air pressure detected by the intake air pressure detecting means at that time it is in excess And the summary.

[0012]

According to a fourth aspect of the present invention, there is provided the first aspect of the present invention.
In the air-fuel ratio control device of the engine with the GR device,
Correcting means, on condition that the engine based on the detection signal from the operating condition detecting means high load region or the exhaust gas is determined not to become hot, but to perform a retard correction of the basic ignition timing The gist is that there is.

The invention according to claim 5 is the invention according to claims 1 to 4.
Air-fuel ratio control for an engine with an EGR device according to any one of the above.
In the device, NOx detecting means for detecting the NOx emission amount of the exhaust system, and when the NOx emission amount detected by the NOx detecting means is equal to or less than a predetermined value, retard correction of the basic ignition timing by retard correction means The gist of the present invention is to provide an invalidating means for invalidating.

[0015]

According to the first aspect of the present invention, the EGR basic control means controls the flow rate control valve based on the engine speed detected by the speed detection means and the intake air pressure detected by the intake air pressure detection means (EGR control). ) And a part of the exhaust gas is returned to the intake system. Further, the EGR basic control means reduces the fuel injection amount based on the intake air pressure. Therefore, EGR
When the EGR control is being performed by the basic control means, the air-fuel ratio is controlled so as not to be over-rich.

The flow rate excess determining means determines whether or not the exhaust gas is excessively recirculated to the intake system when the EGR control is performed. If the flow rate excess determining means determines that the exhaust gas is excessively recirculated to the intake system, the decrease correction means sets the EG to EG.
The fuel injection amount corrected to be reduced by the R basic control means is further reduced and corrected so that the air-fuel ratio does not become over-rich.

Therefore, even if the flow control valve or the like fails and the exhaust gas is excessively recirculated to the intake system, the fuel injection amount is further reduced and corrected by the reduction correction means, so that the air-fuel ratio is not over-rich. . Therefore, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust system. In addition, the occurrence of misfire or afterburn due to over-rich air-fuel ratio can be suppressed. Furthermore, by reducing the fuel injection amount
Even if the air-fuel ratio becomes lean, the basic ignition timing is retarded.
Correction can suppress the generation of NOx
You.

According to the second aspect of the present invention, when the flow rate control valve is under EGR control by the EGR basic control means, the flow rate excess determining means changes the intake air pressure detected by the intake air pressure detecting means per unit time. When the rate is large, it is determined that the exhaust gas is excessive. And
When the flow rate excess determining means determines that the exhaust gas is excessive, the reducing correction means further reduces the fuel injection amount corrected by the EGR basic control means so that the air-fuel ratio does not become over-rich.

Therefore, even if the flow control valve or the like fails and the exhaust gas is excessively recirculated to the intake system, the fuel injection amount is further reduced and corrected by the reduction correction means, so that the air-fuel ratio is not over-rich. . Therefore, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust system. or,
It is not necessary to install a special detection means for determining whether or not the exhaust gas is excessively recirculated to the exhaust system, and the above-described reduction of the fuel injection amount is corrected by the existing detection means mounted on the engine. It can be carried out. Moreover, it is possible to prevent the occurrence of misfire or afterburn due to over-rich air-fuel ratio.

According to the third aspect of the invention, the opening detecting means detects the opening of the throttle valve. Then, the flow rate excess determining means increases the pressure difference between the reference suction pressure when the flow control valve is normally EGR controlled based on the engine speed and the opening of the throttle valve, and the suction air pressure at that time. When it is determined that the exhaust gas is excessive. Then, when it is determined that the exhaust gas is excessive, the decrease correction means further reduces the fuel injection amount corrected by the EGR basic control means so that the air-fuel ratio does not become over-rich.

Therefore, even if the flow control valve or the like fails and the exhaust gas is excessively recirculated to the intake system, the fuel injection amount is further reduced and corrected by the reduction correction means, so that the air-fuel ratio is not over-rich. . Therefore, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust system. or,
There is no need to install special detection means for determining whether or not the exhaust gas is excessively recirculated to the exhaust system, and the above-described air-fuel ratio reduction correction is performed by the existing detection means mounted on the engine. be able to. Moreover, no misfire or afterburn due to over-rich air-fuel ratio occurs.

[0022]

According to the fourth aspect of the present invention, the ignition timing computing means based on a detection signal from the operating condition detecting means for detecting an operating condition of the engine, calculates the basic ignition timing of the engine. When the flow rate control valve is EGR controlled by the EGR basic control means and the excess flow rate determination means determines that the exhaust gas is excessively recirculated to the intake system, the retard correction means determines whether or not the operation state detection means Based on the detection signal, the engine determines whether the engine is in a high load region or the exhaust gas is at a high temperature, and calculates the ignition timing on condition that the engine determines that the engine is not in the high load region or the exhaust gas is at a high temperature. The basic ignition timing of the engine obtained by the means is retarded. Therefore, the temperature of the high-load region and the exhaust gas engine are not to retard correction until the time of high temperature to prevent heat loss of the exhaust system.

According to the fifth aspect of the invention, the NOx detecting means detects the NOx emission amount of the exhaust system, and if the NOx emission amount is equal to or less than a predetermined value, the invalidating means sets the basic ignition by the retard correction means. The retard correction of the timing is invalidated, and the ignition control of the engine is performed based on the basic ignition timing. Therefore, NOx
Since the basic ignition timing is retarded only when the emission is large,
The temperature of the exhaust gas is not increased until the time when NOx purification is not necessary. Therefore, heat loss of the exhaust system can be prevented.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIGS.
This will be described in detail with reference to FIG. As shown in FIG. 1, the engine 1 has a piston 3 in a cylinder 2, and a combustion chamber 4 formed above the piston 3 has an intake passage 5 and an exhaust system which constitute a part of an intake system. And an exhaust passage 6 which constitutes a part thereof. Combustion chamber 4 and intake passage 5
And the communication between the combustion chamber 4 and the exhaust passage 6 are opened and closed by an intake valve 7 and an exhaust valve 8.

The engine 1 introduces an air-fuel mixture consisting of intake air from an intake passage 5 and fuel injected from a fuel injection valve 9 into a combustion chamber 4 via an intake valve 7.
An ignition plug 11 is mounted on the engine 1, and an ignition voltage distributed by a distributor 12 is applied to the ignition plug 11. The distributor 12 distributes the high voltage output from the igniter 13 to each of the ignition plugs 11 in synchronization with the crank angle of the engine 1. The ignition timing of each of the ignition plugs 11 is determined by the high voltage from the igniter 13. It is determined by the output timing. Then, the engine 1 explodes the air-fuel mixture in the combustion chamber 4 by the ignition plug 11 to obtain a driving force, and then discharges the exhaust gas to the exhaust passage 6 through the exhaust valve 8.

A part of the intake passage 5 is provided with a surge tank 14 for suppressing the pulsation of the intake air. The surge tank 14 is provided with an operating state detecting means for detecting an internal pressure P as an intake air pressure in the intake passage 5 and an intake pressure sensor 16 as an intake air pressure detecting means. On the upstream side of the surge tank 14, a throttle valve 1 that opens and closes in response to operation of an accelerator pedal (not shown)
7 is provided, and the amount of intake air to the intake passage 5 is adjusted by opening and closing the throttle valve 17. In the vicinity of the throttle valve 17, a throttle sensor 18 is provided as opening degree detecting means for detecting the opening degree. An air cleaner 19 is provided upstream of the throttle valve 17.

On the other hand, an oxygen sensor 2 as an operating state detecting means for detecting the oxygen concentration in the exhaust gas is provided in the exhaust passage 6.
Zero or three-way catalytic converter 2 for purifying exhaust gas
1 is attached. An EGR device 23 is provided between the exhaust passage 6 and the intake passage 5 to recirculate exhaust gas in the exhaust passage 6 to the intake passage 5 to recirculate exhaust gas. That is, the EGR pipe 24 as an exhaust recirculation path branches from the exhaust passage 6, and the other end thereof is connected to the surge tank 1.
It is connected to the intake passage 5 between the throttle valve 4 and the throttle valve 17. An EGR valve 25 as a flow control valve is disposed in the EGR pipe 24.

The EGR valve 25 is a so-called step motor type in which a rotor 27 of a step motor 26 rotates in response to a pulse signal, whereby the lift amount of the valve body 28 changes and the opening area of the valve changes. By controlling the opening degree of the EGR valve 25, the amount of exhaust gas (EGR flow rate) recirculated to the intake passage 5 is controlled. E
The opening of the GR valve 25 is controlled based on the operating state of the engine 1, for example, the intake air pressure P and the engine speed NE. Also, the engine speed NE and the throttle valve 1
In some cases, the opening of the EGR valve 25 is controlled based on the opening of FIG.

The engine 1 has an intake pressure sensor 16 and a throttle sensor 1 for detecting its operating state.
8. In addition to the oxygen sensor 20, the rotation speed of the rotor 12a of the
A rotational speed sensor 29 as an operating state detecting means and a rotational speed detecting means for detecting E, and a water temperature sensor 30 as an operating state detecting means for detecting a cooling water temperature TWH of the engine 1 are provided.

Various sensors are input to an electronic control unit (hereinafter, simply referred to as "ECU") 32 as EGR basic control means, decrease correction means, flow rate excess judgment means, retard correction means, ignition timing calculation means and invalidation means. Side is electrically connected. Further, each fuel injection valve 9, igniter 13 and EG
The R valve 25 is electrically connected to the output side of the ECU 32.

The ECU 32 has a central processing unit (hereinafter referred to as a CP).
U) 33 and read-only memory (hereinafter, ROM) 34
, A random access memory (hereinafter, RAM) 35, an input port 37, and an output port 38, which are mutually connected by a bus 39. The CPU 33
Various arithmetic processes are executed according to a preset control program, and a control program and data necessary for the CPU 33 to execute the arithmetic processes are stored in the ROM 34 in advance. The RAM 35 temporarily stores the calculation result of the CPU 33.

Next, the operation based on the air-fuel ratio control program stored in the ROM 34 of the air-fuel ratio control device configured as described above will be described with reference to the flowcharts shown in FIGS.

First, as shown in FIG.
, The CPU 33 determines whether the cooling water temperature TWH is equal to or higher than 35 ° C. based on the detection signal from the water temperature sensor 30. When the CPU 33 determines that the cooling water temperature TWH is equal to or higher than 35 ° C., it is determined that the engine 1 is not in the cold state, and the process proceeds to step 101. If the CPU 33 determines that the cooling water temperature TWH is lower than 35 ° C., the process proceeds to step 102 on the assumption that the engine 1 is in a cold state.

Next, at step 101, the CPU 3
3 determines whether or not the intake air pressure P of the engine 1 is equal to or higher than 35 kPa based on a detection signal from the intake pressure sensor 16. When the CPU 33 determines that the intake air pressure P is equal to or higher than 35 kPa, the CPU 33 determines that the intake air pressure P is in a predetermined area where EGR control for recirculating a part of the exhaust gas from the exhaust passage 6 to the intake passage 5 of the engine 1 may be performed, and proceeds to step 103. move on. If the intake air pressure P is less than 35 kPa, the CP
If U33 determines, the CPU 33 proceeds to step 102 assuming that the engine 1 is in an area where EGR control such as idling should not be performed.

When the conditions of the above steps 100 and 101 are satisfied, in step 103, the CPU 33 executes the optimal opening degree data of the EGR valve 25 based on the intake air pressure P and the engine speed NE in order to perform the EGR control. Read from ROM 34. The optimum opening of the EGR valve 25 based on the intake pipe negative pressure P (load) and the engine speed NE is obtained in advance by a test or the like, and is stored in the ROM 34 as optimum opening data. Based on the optimum opening degree data read from the ROM 34, the CPU 33
The control of the valve 25 proceeds to step 104.

In step 104, the CPU 33
An EGR correction value FEGR for calculating the fuel injection amount TU is obtained by executing the GR control. That is, the CPU 33
From the map of the EGR correction value FEGR corresponding to the intake air pressure P stored in advance in the OM 34, the corresponding EGR correction value FEGR is read out, and the routine proceeds to step 105.

In step 105, the CPU 33
It is determined whether or not the EGR flow is recirculated (excess) to the intake passage 5 in a large amount by the GR control. This determination is made as follows. If the EGR control of the EGR valve 25 continues the desired control state, a new intake passage 5
The relationship between the air sucked into the EGR and the EGR flow rate is kept relatively stable and does not change rapidly. Also, EG
The fluctuation of the intake air pressure P when the R control is being performed is usually within the range of the change caused by operating the accelerator. Here, when the EGR valve 25 fails and is fully opened, new air newly introduced into the intake passage 5 and EGR
The ratio with the flow rate becomes unstable. Therefore, the suction air pressure P
Also, under the influence of the excess of the EGR flow rate, a sudden change which does not occur at the normal time is made. Therefore, the CPU 33 monitors the rate of change of the intake air pressure P per time, and determines that the EGR flow rate is excessive when the rate of change greatly changes.

As another determination, there is the following method. If the desired control state of the EGR control of the EGR valve 25 is maintained, how much intake air pressure P is generated according to the design specifications of the engine 1 when the throttle valve 17 and the engine speed NE are clear. Can be calculated by a known method based on the intake system model of the engine 1. Therefore, when the EGR flow rate becomes excessive, the intake air pressure P affecting the intake passage 5 greatly deviates from an expected value. Therefore, the intake air pressure during the normal control of the EGR valve 25 is experimentally measured in advance from the opening of the throttle valve 17 and the engine speed NE, and the data is used as the reference intake air pressure Pref in the ROM 3.
4 is stored in advance. Then, the CPU 33 compares the reference intake air pressure Pref with the detected intake air pressure P, and determines that the EGR flow rate has exceeded when the pressure difference is large. Here, if the EGR flow rate is exceeded, CP
If U33 determines, the process proceeds to step 107. And
The CPU 33 calculates a decrease correction value KEGR based on the following equation.

KEGR = KFEGR × FEGR (3) KEGR: Reduction correction value for finally correcting the fuel injection amount KEFEGR: EGR correction value FEG when the EGR flow rate is excessive
Coefficient for performing weight loss greater than R. It is a value smaller than 1 and is stored in the ROM 34 as data experimentally determined so as not to cause over-rich after setting a judgment reference value of the EGR flow rate excess in advance.

FEGR: EGR correction value Then, the decrease correction value KEGR is calculated based on the equation (3).
If U33 finds it, it proceeds to step 108. Step 1
At 08, the CPU 33 substitutes each parameter into the following equation for calculating the fuel injection amount TU stored in the ROM 34 in advance, calculates the fuel injection amount TU, and terminates the process once.

TU = QN × FAF × KEGR (Equation (4)) QN: Intake air amount obtained by CPU 33 based on intake air pressure P / intake air amount obtained by engine speed NE FAF: From oxygen sensor Feedback correction coefficient KEGR: Reduction correction value If the CPU 33 determines in step 105 that the EGR flow rate has not exceeded, the routine proceeds to step 106. In step 106, the CPU 33 determines that KEGR =
FEGR.

Thereafter, as described above, the CPU 33 proceeds to step 108, calculates the fuel injection amount TU, and ends this process once. Step 100 and step 10
If the condition 1 is not satisfied, the CPU 33 determines that the EGR control is not performed. Then, the CPU 33 closes the EGR valve 25 and sets the decrease correction value KEGR = 1.
And Thereafter, the CPU 33 proceeds to step 108,
The same processing as above is performed.

Therefore, even if the EGR valve 25 or the like fails and the exhaust gas is excessively recirculated to the intake passage 5 , the normal EGR
Since the fuel injection amount TU obtained at the time of the control is further reduced and corrected, over-rich of the air-fuel ratio is prevented. As a result, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust passage 6. In addition, since it is possible to suppress the occurrence of misfire or afterburn due to over-rich air-fuel ratio, the exhaust passage 6 and the three-way catalyst 21 can be suppressed.
Etc. can be prevented.

Although it is not possible to directly measure whether the EGR flow rate is excessively recirculated to the intake passage 5, the rate of change of the intake air pressure P per unit time and the throttle valve 1
It is determined whether or not the EGR flow rate is excessive (excess) based on the pressure difference between the reference suction pressure Pref and the suction air pressure P based on the opening degree of 7 and the engine speed NE. As a result, the fuel injection amount TU can normally be reduced by the existing sensor mounted on the engine 1 or the like.

Next, based on the flowchart of FIG.
The ignition timing control performed simultaneously with the EGR control based on the flowchart of FIG. 3 will be described. First, step 20
At 0, the CPU 33 determines the intake air amount QN and the engine speed NE at that time from the basic ignition timing map stored in the ROM 34 in advance based on, for example, the intake air amount QN per engine revolution and the engine speed NE. The basic ignition timing ABSE is obtained based on the above, and the routine proceeds to step 201. In step 201, the CPU 33 determines whether or not EGR control is being performed. When the CPU 33 determines that the EGR control is being performed, the process proceeds to step 202.
In step 202, the CPU 33 determines whether or not the EGR flow rate has been exceeded. When the CPU 33 determines that the EGR flow rate has been exceeded, the process proceeds to step 203.
In step 203, the CPU 33 determines whether or not the ignition timing is in a retardable region where the ignition timing can be delayed. CP
U33 is based on the engine speed NE, the water temperature of the water temperature sensor 30 and the like, when the exhaust temperature is originally high in the high load region, in the middle region, when the vehicle has been operating in the high load region for a long time immediately before, When the temperature is high, it is determined that it is not in the retardable region. If the above-described condition is satisfied, the CPU 33 determines that the region is the retardable region and proceeds to step 204.

This is because EGR control is performed and EG
When the R flow rate is exceeded, the fuel injection amount TU is reduced substantially uniformly by the control based on the flowchart of FIG. 3, and no misfire occurs due to the air-fuel ratio over-rich. However, a large amount of NOx is generated due to a lean air-fuel ratio due to a decrease in the fuel injection amount TU depending on the degree of excess of the EGR flow rate. In order to prevent this, it is conceivable that the ignition timing ACAL is delayed from the basic ignition timing ABSE to reduce the generation amount of NOx. However, since the exhaust gas temperature rises due to the retard control,
The retard control is not performed in a region where the original exhaust gas temperature is high and the exhaust system is concerned about heat loss.

In step 204, the CPU 33 preliminarily obtains the amount of retardation, the degree of NOx suppression, the degree of increase in exhaust gas temperature, etc. in a trial manner in order to perform retardation control, and determines an appropriate retardation correction value based on a balance between the two. The AEGR is read from the ROM 34, and the routine proceeds to step 205. In step 205, the CPU 33 adds the basic ignition timing ABSE obtained in step 200 and the retardation correction value AEGR to obtain an ignition timing ACAL, and proceeds to step 206. In step 206, the CPU 33 determines that the ignition timing ACAL
The ignition control based on is performed.

On the other hand, if the conditions of steps 201, 202 and 203 are not satisfied, the process proceeds to step 207,
After setting the retard angle correction value AEGR to 0, the CPU 33 proceeds to step 205. Then, the same processing as described above is performed. In this case, since the retard correction value AEGR is 0, the basic ignition timing AB obtained in step 200 is obtained.
The ignition is controlled based on the SE, and the retard control is not performed.

Therefore, even if the fuel injection amount TU is corrected to be reduced by the CPU 33 of the ECU 32 and the air-fuel ratio becomes lean, the basic ignition timing is retarded and the generation of NOx can be suppressed.

[0051] Moreover, since the temperature of the high-load region and the exhaust gas of the engine 1 it is up to the time of high temperature and so as not to retard the ignition timing, it is possible to prevent the high temperature of the exhaust gas, the exhaust passage 6 and the three-way catalyst 21 can be reliably prevented from heat loss.

In addition, as shown in FIG. 1, a NOx detection sensor 50 as NOx detection means is provided in the exhaust passage 6, and this NOx detection sensor 50 is connected to the input port 37 of the ECU 32. Then, the CPU 33 compares the NOx emission amount detected by the NOx detection sensor 50 with a predetermined value stored in the ROM 34 in advance.
When the condition of step 203 is satisfied and the NOx emission amount is equal to or more than a predetermined value, the CPU 33 retards the basic ignition timing. Even if the conditions of steps 200 to 203 are satisfied, N
When the Ox emission amount is equal to or less than a predetermined value, the ignition control may be performed based on the basic ignition timing.

In this case, only when the NOx emission amount is large, C
Since the PU 33 retards the basic ignition timing, it is possible to prevent the temperature of the exhaust gas from rising until the time when NOx purification is not necessary, and to prevent heat loss of the exhaust passage 6 and the three-way catalyst 21. It can be done reliably.

In this embodiment, the EGR device 23 is constituted by the stepping motor 26, and the exhaust gas is recirculated to the intake passage 5. In addition to this, the pressure regulating valve of the diaphragm type, constructed by combining a plurality of EGR valves and EGR permission valves (e.g., JP 63-10024
26, 28, 30) shown in FIG. 2 of 7 No., to recirculating a part of exhaust gas to the intake passage 5 by utilizing the negative pressure in the intake passage 5 by the switching control of the EGR permission <br/> valves It is also possible to configure.

[0055]

As described above in detail, according to the first aspect of the present invention, even if the flow control valve or the like fails and the exhaust gas excessively recirculates to the intake system, it can be obtained during normal EGR control. Since the reduced fuel injection amount is further reduced, the air-fuel ratio is prevented from being over-rich. As a result, a large amount of HC and CO can be prevented from being discharged from the exhaust system, and furthermore, it is possible to suppress the occurrence of misfire or afterburn due to over-rich air-fuel ratio. Furthermore,
The fuel injection amount is reduced and the air-fuel ratio becomes lean
However, since the basic ignition timing is retarded, NOx
Generation can be suppressed.

According to the second aspect of the present invention, even if the flow control valve or the like fails and the exhaust gas excessively recirculates to the intake system, the fuel injection amount obtained during the normal EGR control is further reduced and corrected. Therefore, over-rich of the air-fuel ratio is prevented.
As a result, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust system, and it is necessary to mount a special detection means for determining whether or not the exhaust gas is excessively recirculated to the exhaust system. Instead, the fuel injection amount can be reduced by the existing detection means mounted on the engine. Further, it is possible to suppress occurrence of misfire or afterburn due to over-rich air-fuel ratio.

According to the third aspect of the present invention, even if the flow control valve or the like fails and the exhaust gas excessively recirculates to the intake system, the fuel injection amount obtained during the normal EGR control is further reduced and corrected. Therefore, over-rich of the air-fuel ratio is prevented.
For this reason, it is possible to prevent a large amount of HC and CO from being discharged from the exhaust system, and it is necessary to mount a special detecting means for determining whether or not the exhaust gas is excessively recirculated to the exhaust system. In addition, the above-described air-fuel ratio reduction correction can be performed by the existing detection means mounted on the engine. Further, it is possible to suppress occurrence of misfire or afterburn due to over-rich air-fuel ratio.

[0058]

[0059] According to the fourth aspect of the invention, it is possible that the temperature of the high-load region and the exhaust gas engine are not to retard correction until the time of high temperature to prevent heat loss of the exhaust system.

According to the fifth aspect of the invention, the basic ignition timing is retarded only when the NOx emission amount is large.
By preventing the temperature of the exhaust gas from rising until the time when the purification of x is not necessary, it is possible to reliably prevent the heat loss of the exhaust system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an air-fuel ratio control device for an engine with an EGR device according to the present invention.

FIG. 2 is a characteristic diagram showing a map for obtaining an EGR correction coefficient FEGR with respect to intake air pressure.

FIG. 3 illustrates a state in which EGR control of an EGR valve is performed.
It is a flowchart figure which performs control at the time of EGR flow exceeding.

FIG. 4 is a flowchart for controlling the ignition timing when the ignition timing can be retarded in a state where the exhaust gas is excessive.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 5 ... Intake passage which comprises an intake system, 6 ... Exhaust passage which constitutes an exhaust system, 12 ... Rotational speed sensor as operation state detection means and rotation detection means, 16 ... Operation state detection means and intake air pressure detection Intake pressure sensor as a means,
18 Throttle sensor as operating state detecting means, 2
0: oxygen sensor as operating state detecting means; 24, EGR pipe as exhaust gas recirculation path; 25, RGR valve as flow control valve; 30, water temperature sensor as operating state detecting means; 32, EGR basic control means; ECU as a first reduction correction control unit, a flow rate excess determination unit, a retard correction unit, an ignition timing calculation unit, and a nullification unit; TU: fuel injection amount;
P: intake air pressure, NE: engine speed, Pref: reference intake air pressure

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 43/00 301 F02D 43/00 301N 45/00 314 45/00 314Z 368 368Z F02P 5/15 F02P 5/15 G Field surveyed (Int.Cl. ⁷ , DB name) F02M 25/07 550 F02D 41/02 330 F02D 43/00 301 F02D 45/00 314 F02D 45/00 368 F02P 5/15

Claims (5)

(57) [Claims] 1. A flow control valve disposed in an exhaust recirculation path connecting an exhaust system and an intake system of an engine to recirculate a part of exhaust gas to an intake system, and a rotational speed for detecting a rotational speed of the engine. Detecting means; intake air pressure detecting means for detecting the intake air pressure sucked into the intake system; opening control of the flow control valve based on the engine speed and the intake air pressure; and reducing the fuel injection amount based on the intake air pressure. the air-fuel ratio control apparatus for the EGR device with engine equipped with an EGR basic control means for, when the flow rate control valve is controlled by ERG basic control means, the excess exhaust gas recirculated to the intake system from the exhaust recirculation path If the exhaust gas is excessively recirculated to the intake system by the excess flow determining means for determining whether or not the exhaust gas is Reduction correction means for further decreasing correction of the fuel injection amount in order to prevent the air-fuel ratio of the over-rich by refluxing the gas is excessively intake system and Effects
Operating state detecting means for detecting an operating state of the engine; and
Exhaust gas is excessively supplied to the intake system by the ignition timing calculating means for calculating the basic ignition timing and the flow rate excess determining means.
When it is determined that the fuel is being recirculated, the ignition timing
Retards the basic ignition timing of the engine calculated
An air-fuel ratio control device for an engine with an EGR device, comprising: a retard correction means . 2. The flow rate excess judging means judges that the exhaust gas is excessive when the rate of change per hour of the intake air pressure detected by the intake air pressure detecting means is large. Control device for an engine with an EGR device. 3. An opening detecting means for detecting an opening of a throttle valve of an intake system, wherein the flow rate excess judging means controls the flow control valve normally based on an engine speed and an opening of the throttle valve. a reference intake pressure when being, billing, wherein the benzalkonium be determined whether the exhaust gas based on the pressure difference between the intake air pressure detected by the intake air pressure detecting means at that time is in excess Item 2. An air-fuel ratio control device for an engine with an EGR device according to Item 1. 4. The operating state detecting means according to claim 1, wherein said retarding angle correcting means is an operating state detecting means.
Engine is in the high load range or
On condition that it is determined that the gas is not hot,
The air-fuel ratio control device for an engine with an EGR device according to claim 1, wherein the basic ignition timing is retarded . 5. A NOx detection system for detecting a NOx emission amount of an exhaust system.
The output means and the NOx emission amount detected by the NOx detection means are predetermined.
If it is equal to or less than the predetermined value, at the time of basic ignition by the retard correction means
Invalidation means for invalidating the delay correction of the period.
An air-fuel ratio control device for an engine with an EGR device according to any one of claims 1 to 4 .