JPH09151726A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) Abstract: An exhaust gas recirculation amount is prevented from decreasing due to release control of a bypass passage that bypasses exhaust gas. SOLUTION: The presence or absence of a bypass passage release request is determined by a flag FBOPN (S6), and the target opening degree SMTGT of the exhaust gas recirculation valve is determined according to the determination result and engine operating conditions such as engine speed Ne and engine load. Is set (S7, S8). Then, the change amount DSM of the target opening degree
The absolute value of T is compared with the threshold value BDENSL (S
Ten). Here, the absolute value of the change amount DSMT is the threshold value BD.
If it exceeds ENSL, it is determined that the change amount DSMT exceeds the limit response speed of the exhaust gas recirculation valve, and "1" is set to the bypass valve drive prohibition flag FBPDEN to prohibit the release control of the bypass passage (S13). ).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more specifically, the exhaust gas recirculation amount (exhaust gas recirculation rate) changes due to a change in exhaust pressure caused by selectively bypassing an exhaust gas purification catalyst. The present invention relates to a technique for avoiding a decrease in NOx reduction effect.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purifying apparatus for an internal combustion engine, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 57-210116. This system includes two catalysts in series in the exhaust system, and a bypass passage that bypasses the upstream catalyst and directly guides the exhaust gas to the downstream catalyst. Under an operating condition where there is a risk of deterioration, a bypass valve blocks the inflow of exhaust gas into the upstream side catalyst, while opening the bypass passage prevents thermal deterioration of the upstream side catalyst. Is.

By the way, as described above, in the exhaust gas purifying apparatus having the passage for bypassing the catalyst, when the exhaust gas is bypassed and the exhaust gas flow by the catalyst is eliminated, the exhaust resistance due to the catalyst is eliminated and the upstream side of the catalyst is reduced. Exhaust pressure decreases. Therefore, when an exhaust gas recirculation device that recirculates exhaust gas from the catalyst upstream side to the intake passage is provided, the pressure difference between the exhaust gas and the intake side decreases due to the decrease in exhaust pressure, and the exhaust gas recirculation amount decreases. There is a problem that the NOx reduction effect due to the reflux cannot be sufficiently obtained.

On the other hand, in Japanese Unexamined Patent Publication (Kokai) No. 5-44449, an exhaust gas recirculation valve provided in an exhaust gas recirculation passage is opened to cope with a change in exhaust pressure caused by bypassing a catalyst and flowing exhaust gas. Disclosed is an exhaust gas purifying apparatus capable of maintaining a predetermined exhaust gas recirculation amount by correcting the exhaust gas recirculation valve opening degree by correcting the exhaust gas recirculation valve opening degree by an amount corresponding to a decrease in exhaust pressure. Has been done.

[0005]

In the opening / closing control of the exhaust gas recirculation valve, there is a response limit depending on the actuator, and particularly when the step motor is used as the actuator, the response speed is relatively low. For this reason, in particular, when the exhaust valve is switched on and off to selectively cause the exhaust gas to flow through either the catalyst or the bypass passage, and the change in the exhaust pressure due to the switching of the bypass valve is rapid. However, even if an attempt is made to change the opening of the exhaust gas recirculation valve in response to changes in exhaust pressure due to opening and closing of the bypass valve and changes in engine operating conditions, the request for opening change exceeds the response limit and the actual There is a case where the opening degree delays following the change in the required opening degree, and it becomes impossible to secure the exhaust gas recirculation amount necessary for reducing NOx.

[0006] For example, in steady operation in which the actuator can sufficiently respond, or in switching of the bypass valve during slow acceleration, the actual opening can be changed in response to the change in the required opening. Exhaust gas recirculation amount can be secured. However, when the intake air flow rate changes rapidly at the initial stage of sudden acceleration, etc., where the load is high, and the exhaust flow is switched from the catalyst side to the bypass passage side by opening / closing the bypass valve at the same time, the required exhaust gas return The change in the required opening to secure the flow rate exceeds the response limit,
In this case, the actual change in the opening may cause a delay in tracking the required opening, and the exhaust gas recirculation amount may temporarily become insufficient.

Further, an exhaust gas recirculation device (so-called Back Pressure Transducer) having a structure in which the amount of exhaust gas recirculation is mechanically adjusted by a diaphragm valve that uses throttle negative pressure and exhaust pressure as operating sources.
In the case of the er type (BPT type) exhaust gas recirculation device), the exhaust gas recirculation amount (exhaust gas recirculation rate) changes depending on the exhaust pressure change due to the opening / closing switching state of the bypass valve even under the same throttle negative pressure state, and therefore, depending on operating conditions. However, there is a problem in that the exhaust gas recirculation amount (exhaust gas recirculation ratio) is greatly reduced due to the change in the exhaust pressure due to the switching of the bypass valve, and the NOx reduction effect cannot be sufficiently obtained.

The present invention has been made in view of the above problems, and avoids delaying the actual opening change of the exhaust gas recirculation valve in response to a change in engine operating conditions and a request for opening change associated with catalyst bypass control. The purpose is to be able to.
Further, in an engine equipped with an exhaust gas recirculation device that mechanically opens and closes an exhaust gas recirculation valve using throttle negative pressure and exhaust pressure as operating sources, it is possible to avoid large fluctuations in the exhaust gas recirculation rate due to the bypass control. The purpose is to

[0009]

Therefore, the invention according to claim 1 is constructed as shown in FIG. In FIG.
The bypass valve is a valve that switches the flow of exhaust gas to either an exhaust gas purification catalyst or a bypass passage that bypasses the catalyst, and the bypass control means opens and closes the bypass valve according to engine operating conditions to exhaust the exhaust gas. The flow is controlled by switching.

On the other hand, the exhaust gas recirculation valve is interposed in the exhaust gas recirculation passage for recirculating the exhaust gas from the upstream side of the bypass valve to the intake passage, and the exhaust gas recirculation control means sets the target opening degree of the exhaust gas recirculation valve to the engine. The opening degree of the exhaust gas recirculation valve is controlled based on the target opening degree, which is set according to the operating condition and the switching control state by the bypass control means. Here, the switching prohibition unit forcibly prohibits the switching control by the bypass control unit when the change width of the target opening degree is predicted to exceed a predetermined value.

With this configuration, the target opening degree of the exhaust gas recirculation valve is set according to the engine operating conditions and the control state of the bypass valve. Therefore, it is necessary to greatly change the target opening degree from both conditions. If the change exceeds the limit response speed in the opening / closing control of the exhaust gas recirculation valve, the actual opening will change after the target opening. Therefore, in order to prevent the request for opening control of the exhaust gas recirculation valve from exceeding the limit response speed, when the amount of change in the target opening exceeds a predetermined value in response to the request for bypass control, the actual Bypass control is prohibited to suppress changes in the target opening.

The invention according to claim 2 has the same basic structure as the invention according to claim 1 shown in FIG. 1, but in the invention according to claim 2, the exhaust gas recirculation control means is an exhaust gas recirculation valve. While setting the target opening according to the engine operating conditions,
A target opening correction value is set according to the switching control state by the bypass control means, and the opening of the exhaust gas recirculation valve is based on the target opening obtained by correcting the target opening with the target opening correction value. To control.

The switching prohibition means is configured to forcibly prohibit the switching control by the bypass control means in accordance with the target opening correction value corresponding to the bypass valve switching request. According to this structure, the target opening correction value is set to correspond to the change in the exhaust pressure due to the bypass control, and when the change in the exhaust pressure is large, the target opening is largely corrected accordingly. However, if the change in the target opening exceeds the limit response speed, there will be a response delay in the actual change in the opening of the exhaust gas recirculation valve. On the basis of the target opening correction value indicating, the state in which the limit response speed may be exceeded is determined, and if the limit response speed may be exceeded, the actual bypass control is prohibited. The target opening is changed within the limit response speed.

According to a third aspect of the invention, the exhaust gas recirculation control means sets the target opening degree correction value in accordance with the intake air amount of the engine. With this configuration, the change in exhaust pressure due to the bypass control corresponds to the exhaust gas flow rate at that time, and the exhaust gas flow rate corresponds to the intake air amount, so that it is possible to set a correction value that accurately corresponds to the change in exhaust pressure. .

According to a fourth aspect of the invention, the switching prohibition means forcibly prohibits the switching control by the bypass control means for a longer time as the target opening correction value is larger. With this configuration, when the target opening correction value is set to a large value because the exhaust pressure change is large when the bypass switching control is performed, the final opening is combined with the change in the target opening according to the engine operating conditions. Since it is more likely that a change in the target opening will exceed the limit response speed, prohibiting the switching control for a longer time, for example, when accelerating, at a stage where the change in the intake air amount becomes smaller, That is, the actual switching is performed when the change in the target opening degree according to the operating condition becomes sufficiently small.

The invention according to claim 5 is constructed as shown in FIG. In FIG. 2, a bypass valve is a valve that switches the flow of exhaust gas to either an exhaust gas purification catalyst or a bypass passage that bypasses the catalyst, and the bypass control means opens and closes the bypass valve according to engine operating conditions. It is driven to switch and control the flow of exhaust gas.

On the other hand, the exhaust gas recirculation valve is provided in the exhaust gas recirculation passage for recirculating the exhaust gas from the upstream side of the bypass valve to the intake passage, and the exhaust gas recirculation adjusting means operates the exhaust pressure and the throttle negative pressure as operating sources. As a result, the exhaust gas recirculation valve is mechanically opened and closed to adjust the exhaust gas recirculation amount. Here, the exhaust gas recirculation ratio predicting unit predicts the exhaust gas recirculation ratio during steady operation according to the engine operating conditions and the open / close state of the bypass valve.

The switching prohibiting means forcibly prohibits the switching control by the bypass control means when the variation width of the predicted value of the exhaust gas recirculation rate is predicted to exceed a predetermined value. With such a configuration, the exhaust gas recirculation rate is predicted according to the engine operating conditions and the open / close state of the bypass valve, so that the change range of the exhaust gas recirculation rate when bypass control is performed according to the switching request of the bypass valve can be predicted. When is larger than a predetermined value, it is estimated that the NOx reduction effect is reduced. Therefore, the actual bypass control is prohibited to prevent the exhaust gas recirculation rate from largely fluctuating.

According to the sixth aspect of the present invention, when the switching prohibiting means predicts that the change width of the predicted value of the exhaust gas recirculation rate exceeds a predetermined value, the switching control means performs the switching control for a predetermined time. The structure is prohibited. With this configuration, when the predicted change in the exhaust gas recirculation rate is large, the actual bypass valve switching control is delayed with respect to the request for the bypass control, and the effect of the bypass control on the change in the exhaust gas recirculation rate is reduced. At the stage, the actual switching is performed.

[0020]

Embodiments of the present invention will be described below. FIG. 3 is a diagram showing a system configuration of the internal combustion engine in the first embodiment. In FIG. 3, the crank angle sensor 1 measures the engine speed and the position of the crankshaft, the airflow sensor 2 indicates the intake air amount of the engine, the water temperature sensor 3 indicates the cooling water temperature of the engine, and the throttle opening sensor 4
Indicates the throttle opening, and the oxygen sensor 5 measures the oxygen concentration in the exhaust gas.

Detection signals from these various sensors are input to the control unit 6, and the control unit 6 controls the fuel injection amount and the ignition timing based on the detection signals. The control unit 6 includes an I / O port 7, CPU8, ROM9, RA
The CPU 8 is constituted by an M10, and the CPU 8 takes necessary external data from the I / O port 7 according to a program written in the ROM 9 and exchanges data with the RAM 10 to perform necessary processing. I / O port 7 according to the processed data
To output the signal from. The ROM 9 stores a program for controlling the CPU 8, and the ROM 9 stores data used for calculation in the form of a map or the like.

The I / O port 7 receives a signal from the sensor group, and the I / O port 7 outputs a fuel injection signal or an ignition signal to the fuel injection valve 13 or the igniter & coil unit 12. It The fuel injection valve 13
Fuel corresponding to the input pulse width is supplied to the intake port of the engine, and the igniter & coil unit 12 ignites the mixture in the cylinder by sparking the spark plug 14 at the timing corresponding to the pulse input.

On the other hand, the leading catalyst 17 is provided upstream of the main catalyst (underfloor catalyst) 22 provided in the exhaust passage, and
A bypass passage 18 that bypasses the leading catalyst 17 is provided. Further, a bypass valve 19 for opening only one of the side of the leading catalyst 17 and the side of the bypass passage 18 is provided, and the bypass valve 19 is turned on / off by a bypass valve actuator 15 such as a drive solenoid. It is driven to open and close. Then, in order to prevent the leading catalyst 17 from being damaged by high heat in a high load / high rotation operation state, the bypass valve actuator 15 opens and closes the bypass valve 19 to close the leading catalyst 17 side and close the bypass passage 18 side. When released, the leading catalyst 17 can be bypassed and the exhaust gas can be directly guided to the main catalyst 22 through the bypass passage 18. In the following, the opening control of the bypass valve 19 (O
N) indicates that the front catalyst 17 side is closed and the bypass passage 18 is opened.

An exhaust gas recirculation passage 20 for guiding exhaust gas from the upstream side of the bypass passage 18 to the intake passage side is provided, and an exhaust gas recirculation valve 21 is provided in the exhaust gas recirculation passage 20. The opening degree of the exhaust gas recirculation valve (hereinafter also referred to as an EGR valve) 21 is adjusted by an EGR valve actuator 16 such as a step motor. Here, from the I / O port 7, EGR
The valve drive signal and the bypass valve drive signal are output to the EGR valve actuator 16 and the bypass valve actuator 15, respectively.

Next, the control function of this embodiment will be first described in brief. The exhaust gas temperature of the engine generally becomes higher as the engine speed becomes higher and the load becomes higher, that is, when the intake air amount is larger. Therefore, in order to prevent the thermal deterioration of the leading catalyst 17, the exhaust temperature exceeds the allowable catalyst deterioration temperature at high load and high speed. The bypass valve 19 is controlled to open in the area to close the front catalyst 17 side,
It suffices to open the bypass passage 18 side and bypass the leading catalyst 17 so that the exhaust gas flows. At this time, the bypass valve
Since the exhaust pressure decreases with the opening control of 19, the exhaust gas recirculation valve 21
It is necessary to prevent the reduction of the exhaust gas recirculation amount by setting the opening degree on the more open side as the target opening degree.

However, here, for example, when a low rotation and low load condition such as idling, that is, when rapid acceleration is performed from a small intake air amount, the intake air amount rapidly increases and the target opening degree is greatly changed. As the need arises,
Since the operating condition of the engine shifts from the condition that the bypass passage is closed to the condition that it is released, and it becomes necessary to increase the target opening amount by the amount by which the exhaust pressure decreases, the change amount of the target opening amount becomes extremely large and the EGR The limit response speed of the valve actuator 16 is exceeded.

Therefore, the amount of change in the target opening of the exhaust gas recirculation valve 21 is calculated, and the amount of change is constantly compared with a predetermined limit response speed of the actuator to determine the change in target opening exceeding the limit response speed. By prohibiting the opening control switching of the bypass valve, the required exhaust gas recirculation amount can be secured by changing the opening degree of the exhaust gas recirculation valve within the limit response speed.

Inhibiting the bypass valve open control switching delays exhaust control for preventing thermal deterioration of the catalyst, but the actuator delay is about 0.5 sec, so switching is prohibited during this period. Even if this is done, the effect of the heat capacity of the exhaust system is large, so the temperature rise of the catalyst is sufficiently small and there is no practical problem. The first outlined above
The control function in this embodiment will be described in detail with reference to the flowcharts of FIGS. 4 and 5. Bypass control means, exhaust gas recirculation control means, switching prohibition means (see FIG. 1)
The control unit 6 has such a function as software as shown in the flowcharts of FIGS. 4 and 5.

The flowchart of FIG. 4 is a routine for calculating the target opening degree of the exhaust gas recirculation valve 21 and determining the prohibition of the drive of the bypass valve 19 from the variation of the target opening degree.
It is designed to be executed every 10 msec. In the flowchart of FIG. 4, first, in S1, the previous target opening degree SMTGT is set to the previous value SMTGTO.

In S2, the cooling water temperature Tw and the idle switch signal are read. In S3 and S4, it is determined whether the exhaust gas recirculation permission condition is satisfied. The permission condition is that the cooling water temperature Tw exceeds the preset EGR permission water temperature (S3) and the idle switch is OFF.
In the non-idle operation state of F (S4), and if any one of these conditions is not satisfied, the process proceeds to S9.

In S9, the target opening SMTGT is set to a preset target opening STPCUT during EGR cutting. On the other hand, when it is determined in S3 and S4 that the permission condition is satisfied, the routine proceeds to S5, where the engine speed Ne, the engine load Tp, and a bypass valve drive state flag FBOPN set / reset in a bypass valve drive routine described later are read. The flag FBOPN is set to "1" when the engine operating condition is the opening condition of the bypass valve 19 (the condition to open the bypass passage), while it is the closing condition (the condition to close the bypass passage). Sometimes "0" is set.

In S6, the bypass valve drive state flag FBOPN is determined. Here, the flag FBOPN
Is "1", the process proceeds to S7, in which the bypass valve opening EGR target opening degree map M is determined by the rotation speed Ne and the load Tp.
The target opening degree SMTGT is searched from APMDO (see FIG. 6). On the other hand, when it is determined in S6 that the flag FBOPN is "0", the process proceeds to S8, in which the target opening from the bypass valve closed EGR target opening map MAPMDC (see FIG. 6) is performed by the rotation speed Ne and the load Tp. Search SMTGT.

That is, two maps, a map for opening the bypass valve and a map for closing the bypass valve, are prepared in advance as the EGR target opening map, and the map for opening the exhaust valve when the bypass passage 18 is opened. A larger target opening is set on the closing map in response to the decrease in pressure. At S10, the latest target opening SMTGT is set.
Target opening SMTG as the deviation between the previous value SMTGTO and
The change amount DSMT of T is calculated.

At S11, the absolute value (change width) of the change amount DSMT and the threshold value B for the bypass valve drive prohibition determination are set.
Compare with DENSL. The threshold value BDENS
L is the execution cycle of this routine and is the change amount DSM.
The limit value (limit response speed) of the opening change that can be driven during 10 msec which is the unit time of T is set. As a result of the comparison in S11, if | DSMT | <BDENSL, the process proceeds to S12, and the bypass valve drive prohibition determination flag FB
Set PDEN to "0" and set | DSMT | ≧ B
If it is DENSL, the flag FBPDEN is set to "1" to forcibly prohibit the opening control of the bypass valve 19.

The flowchart of FIG. 5 is a routine for determining the drive of the bypass valve 19 according to the engine operating condition and outputting the energization / de-energization of the drive solenoid (bypass valve actuator 15). So called background job (BGJ)
Is executed as First, in S21, the engine speed Ne and the engine load Tp are read.

At S22, the bypass valve drive state flag FBOPN is determined. Then, the flag FBOPN
Is "1", that is, when the operating condition requires the open control of the bypass valve 19, the process proceeds to S23.
In S23, the bypass valve drive prohibition determination flag FBPD
If it is determined to be EN, "1" is set in the flag FBPDEN, and the change amount DSMT of the target opening SMTGT exceeds the limit response speed, the process proceeds to S24, and the drive solenoid of the bypass valve 19 is set. Control to OFF (closed state of bypass passage).

On the other hand, at S23, the FBPDEN is set to "0", and the change amount DSM of the target opening SMTGT is set.
When T is within the limit response speed, the process proceeds to S25, and the drive solenoid of the bypass valve 19 is turned on (the bypass passage is released) in accordance with the request from the operating conditions, in other words, the request for preventing the catalyst thermal deterioration. To control. That is, even if there is a request for opening control of the bypass valve 19 from the operating conditions, the target opening SMT when the opening control of the bypass valve 19 is performed according to the opening request.
When the GT change amount DSMT exceeds the limit response speed, it is forcibly prohibited to actually control the opening of the bypass valve 19 so that the target opening degree changes within the limit response speed due to the convergence of the transient operation. Until then, the opening control switching of the bypass valve 19 is postponed.

Therefore, for example, a request for increasing the target opening due to an increase change in the intake air amount during acceleration overlaps with a request for increasing the target opening for responding to a decrease in exhaust pressure due to switching of the open control of the bypass valve 19. In order to secure the required exhaust gas recirculation amount, it is not necessary to increase the opening degree of the exhaust gas recirculation valve 21 beyond the limit response speed of the EGR valve actuator 16, and it is necessary to change the target opening degree within the limit response speed. The exhaust gas recirculation amount can be secured (see FIG. 7).

If it is determined in S22 that the flag FBOPN is "0", there is no open control request for the bypass valve 19 from the operating conditions, so the flow proceeds to S24 to drive the bypass valve 19. The solenoid is controlled to be OFF (the bypass passage is closed). In S26, the engine speed N
e, Bypass valve drive map MAP based on engine load Tp
By referring to BDR, bypass valve drive state flag FBOPN
Search for. Here, the bypass valve on the high rotation and high load side
The opening catalyst 19 is controlled to bypass the leading catalyst 17 to bypass the leading catalyst 17.
In order to avoid the heat deterioration of the above, the flag FBOPN is set to "1", and in other cases, the flag FBOPN is set to "0" so as to perform the exhaust purification by the leading catalyst 17.

In the first embodiment, the target opening degree of the exhaust gas recirculation valve 21 is set at once based on the operating conditions of the engine and the presence / absence of the opening control request for the bypass valve 19. A basic target opening degree set from the engine operating condition may be configured to be corrected and set based on a correction value according to the opening control request of the bypass valve 19 to set the final target opening degree. A second embodiment of the above configuration is shown in the flowcharts of FIGS. The system configuration of the internal combustion engine is the same as that of the first embodiment shown in FIG. Further, also in the second embodiment, the functions of the bypass control means, the exhaust gas recirculation control means, and the switching prohibition means (see FIG. 1) are controlled by the control unit 6 as shown in the flowcharts of FIGS. 8 and 9. Prepared for.

The flow chart of FIG. 8 shows a target opening degree calculation routine of the exhaust gas recirculation valve 21 in the second embodiment, which is executed every 10 msec as in the flow chart of FIG.
In the flowchart of FIG. 8, first, in S31,
The cooling water temperature Tw and the idle switch signal are read. S
At 32, it is determined whether or not the EGR permission condition is satisfied based on the cooling water temperature Tw and the idle switch signal.

If it is determined in S32 that the permission condition is not satisfied, the routine proceeds to S33, where the target opening SMTGT of the exhaust gas recirculation valve 21 is set to the EGR cut target opening STPCUT. Further, in the next S34, the bypass valve drive prohibition timer TMBD
Reset R to zero. On the other hand, if it is determined in S32 that the permission condition is satisfied, the process proceeds to S35, in which the bypass valve drive state flag F is set in addition to the operating conditions such as the engine speed Ne and the engine load Tp.
The intake air amount Qa detected by the BOPN and the air flow sensor 2 is read.

At the next S36, the EGR target opening map MA at the time of bypass valve closing is calculated by the engine speed Ne and the engine load Tp.
The target opening SMTGT is retrieved from PMD. In S37,
The flag FBOPN is determined. Here, when the flag FBOPN is "0", that is, the bypass valve 19
When there is no need to switch the open control, go to 38,
Set the target opening correction value KHSMT to 1.0. Since the target opening correction value KHSMT is a multiplication correction term for the target opening SMTGT, the correction value KHSMT = 1.0
When, the correction is not substantially performed.

On the other hand, if it is determined in S37 that the flag FBOPN is "1", that is, if there is a request for opening control of the bypass valve 19 from the operating conditions, the process proceeds to S39.
The previous value FBOPNO of the flag FBOPN is determined. When the previous value FBOPNO is "0", it is the first time that the engine operating condition has shifted to the open control region of the bypass valve 19, and in this case, the process proceeds to S40 and the prohibit timer is set based on the intake air amount Qa. The initial value of the bypass valve drive prohibition timer TMBDR is set by referring to the initial value table TBLKQ (see FIG. 10).

Here, the timer TMBDR, which is initially set in S40, has a large change in exhaust pressure when the bypass valve 19 is switched to open control, and the target opening value is adjusted by the opening correction value to cope with the change in exhaust pressure. When the change amount of the degree exceeds the limit response speed, the time for forcibly prohibiting the opening control of the bypass valve 19 is measured, and its initial value is that the exhaust pressure change has a large intake air amount Qa. Corresponding to the increase with time, a larger value is set according to the increase of the intake air flow rate Qa. Also,
When the intake air flow rate Qa is sufficiently small and the influence of the exhaust pressure change is negligible, 0 is set as an initial value so that the opening control of the bypass valve is not substantially prohibited.

When it is determined in S39 that the previous value FBOPNO is "1", it means that the opening control region of the bypass valve 19 is continuously maintained. In this case,
Since the initial value of the timer TMBDR has already been set, the process jumps to S41 without proceeding to S40. In S41, the target opening correction value KHSMT is set from the EGR target opening correction table TBLKQ according to the intake air amount Qa.
Here, the target opening degree correction value KHSMT is set to a larger value in accordance with an increase in the intake air flow rate Qa in response to a larger change in the exhaust pressure due to switching as the intake air amount Qa increases. (See Figure 10).

Here, the target opening degree correction value KHSMT is set based on the intake air amount Qa because the amount of change in exhaust pressure due to switching of the open control of the bypass valve 19 is substantially proportional to the exhaust flow rate. Is proportional to the intake air flow rate. S
At 42, the target opening SMTGT is multiplied by the correction value KHSMT, and the multiplication result is set as the final target opening SMTGT.

In S43, the bypass valve drive inhibition time attenuation amount DBDR is subtracted from the timer TMBDR, and the timer TMBDR is set to 0 at the deceleration speed based on the attenuation amount DBDR.
Gradually decrease to. The function Clip (AB, C) described in the flowchart means that the constant B is subtracted from the variable A, and if the subtraction result is the constant C or less, the operation result is held in the constant C. Therefore, the timer TMBD
R is the attenuation value DBD from the initial value for each execution cycle of this routine
It will decrease by R and will eventually be held at zero.

In S44, the value of the present flag FBOPN is set to the previous value FBOPNO. The flowchart of FIG. 9 shows a bypass valve drive routine in the second embodiment, and BGJ is performed in the same manner as the flowchart of FIG.
Is executed as First, in S51, the engine speed Ne,
The engine load Tp is read. In S52, the flag FBO
PN is discriminated, and the flag FBOPN is "0",
If the operating condition that should control the opening of the bypass valve 19 is not satisfied,
As it is, the process proceeds to S54, and the drive solenoid of the bypass valve 19 is controlled to OFF (closed state of the bypass passage).

On the other hand, when the flag FBOPN is "1" in S52 and it is judged that the operating condition is such that the bypass valve 19 should be controlled to be opened, the routine proceeds to S53, in which the timer TMB is set.
It is determined whether DR is 0 or not. The timer TMBD
If R is not 0, the routine proceeds to S54, in which the drive solenoid of the bypass valve 19 is controlled to OFF (closed state of the bypass passage) to forcibly prohibit the open control switching of the bypass valve 19.

When the timer TMBDR is attenuated to 0 by the attenuation control in S43, the process proceeds from S53 to S55 to turn on the drive solenoid of the bypass valve 19.
(Bypass passage open state). In S56, the bypass valve drive map MAPBDR is referred to based on the engine speed Ne and the engine load Tp, and the bypass valve drive state flag FBOPN is searched.

According to this configuration, when the exhaust pressure change due to the opening control of the bypass valve 19 is large and the target opening may exceed the limit response speed due to the correction by the target opening correction value, the actual Since the opening control switching of the bypass valve 19 is prohibited, it is possible to prevent the actual exhaust gas recirculation amount from becoming insufficient due to the generation of a request that exceeds the limit response speed.

Next, the system configuration of the internal combustion engine in the third embodiment will be described with reference to FIG. In FIG. 11 showing the system configuration of the third embodiment, parts other than the exhaust gas recirculation device are the same as those in FIG. 3, so the same elements as those in FIG. 3 are assigned the same reference numerals and explanations thereof are omitted. In FIG. 11, a diaphragm type exhaust gas recirculation valve 30 is provided in the middle of the exhaust gas recirculation passage 20, and this exhaust gas recirculation valve 30 has a negative pressure working chamber 31 in which the throttle negative pressure is partitioned by the diaphragm.
The valve body 32 is lifted upward in the figure against the valve closing urging force of the spring 33 to open the valve.

An electromagnetic switching valve 42 is provided in the negative pressure introducing passage 41 for introducing the throttle negative pressure to the negative pressure operating chamber 31, and the switching valve 42 selectively selects the throttle negative pressure and the atmospheric pressure. Can be led to the negative pressure introduction path 41, for example, under conditions such as exhaust gas recirculation is stopped when the engine is cold, etc., the atmospheric pressure by the switching valve 42 via the negative pressure introduction path 41. By acting on the negative pressure working chamber 31,
The exhaust gas recirculation valve 30 is kept closed. The switching valve 42 may be replaced with a bimetal valve or the like.

Further, in the middle of the negative pressure introducing passage 41, in a state where the throttle negative pressure is introduced by the switching valve 42, the throttle negative pressure is diluted with the atmospheric pressure in accordance with the exhaust pressure, so that the exhaust gas recirculation is performed. BPT (Bac
A k Pressure Transducer) valve 50 is provided. The BP
The T valve 50 is divided by a diaphragm from a negative pressure working chamber 52 facing a negative pressure adjusting passage 51 that branches off from the negative pressure introducing passage 41 and guides a throttle negative pressure, and is separated by a diaphragm to the upstream side of the valve body 32 of the exhaust gas recirculation valve 30. And the pressure working chamber 54 into which the exhaust pressure is introduced via the exhaust pressure introducing passage 53. The negative pressure working chamber 52 is open to the atmosphere, and when the exhaust pressure on the upstream side of the valve body 32 becomes higher than the set pressure of the spring 55, the valve body 56 fixed to the diaphragm lifts upward in the drawing and The negative pressure adjusting passage 51 is closed, and the throttle negative pressure is guided as it is to the negative pressure operating chamber 31 of the exhaust gas recirculation valve 30.
On the other hand, if the exhaust pressure on the upstream side of the valve element 32 is lower than the set pressure,
When the negative pressure adjusting passage 51 is opened, the throttle negative pressure is diluted with the atmosphere and weakens the negative pressure introduced into the negative pressure operating chamber 31, so that the exhaust gas recirculation valve 30 is closed.

That is, when the exhaust pressure near the upstream of the valve body 32 is high, the negative pressure adjusting passage 51 is closed, so that the throttle negative pressure is directly introduced to the negative pressure operating chamber 31 and the exhaust gas recirculation valve 30 is opened. The exhaust gas recirculation is executed. Here, when exhaust gas recirculation is performed, the exhaust pressure near the upstream of the valve element 32 is reduced, and the negative pressure adjusting passage 51 is opened in the BPT valve 50 to dilute the throttle negative pressure with the atmosphere. The recirculation valve 30 is closed to stop the recirculation of exhaust gas. However, by stopping the exhaust gas recirculation, the exhaust pressure near the upstream of the valve body 32 rises again,
In the state where the exhaust gas recirculation is performed again and the throttle valve negative pressure is guided by the switching valve 42 (exhaust gas recirculation region), this operation is always repeated to control the exhaust gas recirculation rate to be constant.

The BPT valve 50 and the diaphragm type exhaust gas recirculation valve 30 correspond to the exhaust gas recirculation adjusting means. The manner of controlling the bypass valve 19 in such a system configuration will be described with reference to the flowcharts of FIGS. 12 and 13. The control unit 6 has the functions of the bypass control means, the exhaust gas recirculation rate prediction means, and the switching prohibition means as software, as shown in the flow charts of FIGS.

In the flowchart of FIG. 12, first, S
At 61, the cooling water temperature Tw and the idle switch signal are read. In S62, it is determined whether or not the EGR permission condition is satisfied based on the cooling water temperature Tw and the idle switch signal.

When the EGR permission condition is not satisfied, the routine proceeds to S67, where the predicted EGR rate TEGRR is set to zero. On the other hand, if the EGR permission condition is satisfied, S
In step 63, the engine speed Ne, the engine load Tp, and the bypass valve drive state flag FBOPN are read. In the next S64, the flag FBOPN is determined. Then, when the flag FBOPN is "1" and the operating condition is such that the bypass valve 19 should be controlled to be opened, the predicted exhaust gas recirculation rate obtained when the bypass valve 19 is switched to open control is set to the engine speed Ne and the load. The retrieved exhaust gas recirculation rate is set in the predicted EGR rate TEGRR by referring to a map MEGEO (see FIG. 14) stored in advance corresponding to Tp.

On the other hand, when the flag FBOPN is "0" and the operating condition is such that the bypass valve 19 should be closed, the predicted exhaust gas recirculation rate obtained when the bypass valve 19 is closed is defined as the rotational speed Ne. The retrieved exhaust gas recirculation rate is set in the predicted EGR rate TEGRR by referring to a map MEGEO (see FIG. 14) stored in advance corresponding to the load Tp.

At S68, the latest predicted EGR rate TEGRR set at any of S65 to S66 and the previous value TEGRR are set.
The difference from O is calculated as the change amount DEGR of the predicted EGR rate TEGRR.
Is calculated as In S69, the absolute value of the change amount DEGR is compared with the bypass valve drive prohibition determination threshold value BDENSL.

If | DEGR | <BDENSL and it is determined that the change in the exhaust gas recirculation rate is sufficiently small, the routine proceeds to S70, where the bypass valve drive prohibition timer TM is used.
Reset BDR to zero. On the other hand, | DEGR | ≧ BD
In the case of ENSL, when it is determined that the change of the exhaust gas recirculation rate exceeds the allowable level and is large, the process proceeds to S71, and the timer TMBDR is set to the drive inhibition initial value KIBDR.

At S72, the predicted EGR rate TE set this time is set.
GRR is set to the previous value TEGRRO, and the timer TMBDR is set to the attenuation amount D for each execution cycle of this routine.
A process of gradually decreasing to 0 based on BDR and holding it at 0 after reaching 0 is performed. The flowchart of FIG. 13 shows the bypass valve drive control in the third embodiment, but since the processing content is the same as the flowchart of FIG. 9 in the second embodiment, it will be described briefly below.

That is, the bypass valve drive state flag FB
Even if the OPN is "1" (S82) and the operating condition is such that the bypass valve 19 should be opened and switched, the timer TM
When BDR is not 0 (S83), the bypass passage 18 is held in the closed state without controlling the opening of the bypass valve 19 (S84). According to the above configuration, it is possible to prevent a change in the control pressure in the BPT valve 50 and a large change in the exhaust gas recirculation rate due to the switching of the opening control of the bypass valve 19, and it is possible to stably reduce NOx (see FIG. 15). ).

That is, when the exhaust pressure is reduced by controlling the opening of the bypass valve 19, the exhaust gas recirculation valve 30 is driven by the BPT valve 50 in the direction of decreasing the exhaust gas recirculation amount (exhaust gas recirculation rate). If the bypass valve 19 is controlled to open when the exhaust gas recirculation rate needs to be increased, the actual exhaust gas recirculation rate will drop significantly relative to the required exhaust gas recirculation rate (see FIG. 15). The opening control of the bypass valve 19 is prohibited in advance by predicting the change in the reflux rate. If the actual switching is executed after the prohibition time by the timer TMBDR has elapsed, the increase change in the required exhaust gas recirculation rate due to acceleration slows down with time, so that the bypass control has less influence on the exhaust gas recirculation rate. The switching can be executed at a different stage.

[0066]

As described above, according to the first aspect of the present invention, when it is predicted that the target opening change amount of the exhaust gas recirculation valve when the bypass control request is met exceeds the limit response speed, the engine is Bypassing the bypass control required from the operating conditions is forcibly prohibited, so that it is possible to avoid a delay in following the change in the opening of the exhaust gas recirculation valve, causing a shortage of the exhaust gas recirculation amount, thus maintaining the NOx reduction effect. The effect is that you can do it.

According to the second aspect of the present invention, the target opening correction value for responding to the change in the exhaust pressure due to the bypass control is large, and the limit response speed may be exceeded in the opening control of the exhaust gas recirculation valve. Since the bypass control is forcibly prohibited at a certain time, it is possible to avoid a shortage of the exhaust gas recirculation amount due to a follow-up delay due to the change in the opening degree of the exhaust gas recirculation valve, thereby reducing the NOx reduction effect. The effect is that it can be maintained.

According to the third aspect of the invention, there is an effect that the target opening correction value for coping with the change in the exhaust pressure due to the bypass control can be accurately set. According to the invention described in claim 4, when it is predicted that the change in exhaust pressure due to the bypass control is large, the change in the target opening according to the engine operating condition and the target opening for responding to the change in the exhaust pressure. There is an effect that it is possible to reliably avoid that the correction overlaps with each other, and thus prevent a response delay from occurring in the opening degree of the exhaust gas recirculation valve.

According to the fifth aspect of the present invention, the variation range of the exhaust gas recirculation rate when the bypass control is performed is predicted and the execution of the bypass control that causes a large fluctuation of the exhaust gas recirculation rate is avoided in advance. This has the effect of stabilizing the reflux rate and maintaining a high NOx reduction effect. According to the sixth aspect of the present invention, when the demand for increasing the exhaust gas recirculation rate in the initial stage of acceleration is high, for example, it is possible to reliably avoid the exhaust gas recirculation rate from being greatly reduced by the bypass control, and the bypass control is performed. There is an effect that the bypass control can be executed at a stage when the influence on the power consumption is sufficiently reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the invention according to claim 1;

FIG. 2 is a block diagram showing a basic configuration of the invention according to claim 5.

FIG. 3 is a system configuration diagram common to the first and second embodiments.

FIG. 4 is a flowchart showing exhaust gas recirculation control according to the first embodiment.

FIG. 5 is a flowchart showing bypass control according to the first embodiment.

FIG. 6 is a diagram showing an outline of a target opening map of an exhaust gas recirculation valve.

FIG. 7 is a time chart showing the actions and effects of the first embodiment.

FIG. 8 is a flowchart showing exhaust gas recirculation control according to the second embodiment.

FIG. 9 is a flowchart showing bypass control according to the second embodiment.

FIG. 10 is a diagram showing characteristics of a target opening correction value or a prohibition timer initial value according to an intake air amount.

FIG. 11 is a system configuration diagram of the third embodiment.

FIG. 12 is a flowchart showing predictive control of an exhaust gas recirculation rate in the third embodiment.

FIG. 13 is a flowchart showing bypass control according to the third embodiment.

FIG. 14 is a diagram showing a map of a predicted value of an exhaust gas recirculation rate.

FIG. 15 is a time chart showing actions and effects according to the third embodiment.

[Explanation of symbols]

 1 crank angle sensor 2 air flow sensor 3 water temperature sensor 4 throttle opening sensor 6 control unit 17 start catalyst 18 bypass passage 19 bypass valve 20 exhaust gas recirculation passage 21 exhaust gas recirculation valve 22 main catalyst 30 exhaust gas recirculation valve 50 BPT valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Matsumoto 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (6)

[Claims] 1. A bypass valve for switching an exhaust flow to either an exhaust purification catalyst or a bypass passage bypassing the catalyst, and an opening / closing drive of the bypass valve according to engine operating conditions to switch the exhaust flow. By-pass control means for controlling, an exhaust gas recirculation valve interposed in an exhaust gas recirculation passage for recirculating exhaust gas from the upstream side of the bypass valve to an intake passage, and a target opening degree of the exhaust gas recirculation valve for engine operating conditions and An exhaust gas purification apparatus for an internal combustion engine, comprising: an exhaust gas recirculation control unit that is set according to a switching control state by a bypass control unit and controls the opening degree of the exhaust gas recirculation valve based on the target opening degree. The internal combustion engine is characterized in that a switching prohibition means for forcibly prohibiting the switching control by the bypass control means is provided when it is predicted that the change width of the degree exceeds a predetermined value. Exhaust gas purification device for engines. 2. A bypass valve for switching an exhaust flow to either one of an exhaust purification catalyst and a bypass passage bypassing the catalyst, and an opening / closing drive of the bypass valve according to engine operating conditions to switch the exhaust flow. By-pass control means for controlling, an exhaust gas recirculation valve interposed in an exhaust gas recirculation passage for recirculating exhaust gas from the upstream side of the bypass valve to an intake passage, and a target opening degree of the exhaust gas recirculation valve depending on engine operating conditions. The target opening correction value is set according to the switching control state by the bypass control means, and the exhaust gas is exhausted based on the target opening obtained by correcting the target opening with the target opening correction value. In an exhaust gas purification apparatus for an internal combustion engine, comprising: an exhaust gas recirculation control unit that controls an opening degree of a recirculation valve, the bypass according to the target opening correction value corresponding to a request for switching the bypass valve. An exhaust emission control device for an internal combustion engine, comprising switching prohibition means for forcibly prohibiting switching control by the control means. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas recirculation control means sets the target opening degree correction value in accordance with an intake air amount of the engine. 4. The switching prohibition means forcibly prohibits the switching control by the bypass control means for a longer time as the target opening correction value is larger. Exhaust gas purification device for internal combustion engine. 5. A bypass valve for switching an exhaust flow to either an exhaust purification catalyst or a bypass passage bypassing the catalyst, and an opening / closing drive of the bypass valve according to engine operating conditions to switch the exhaust flow. By-pass control means for controlling, an exhaust gas recirculation valve interposed in the exhaust gas recirculation passage for recirculating exhaust gas from the upstream side of the bypass valve to the intake passage, and exhaust gas recirculation using exhaust pressure and throttle negative pressure as operating sources. An exhaust gas purification apparatus for an internal combustion engine, comprising: an exhaust gas recirculation adjusting unit that mechanically opens and closes a valve to adjust an exhaust gas recirculation amount, and an exhaust gas during a steady operation according to an engine operating condition and an opening / closing state of the bypass valve. Exhaust gas recirculation rate predicting means for predicting the recirculation rate, and switching control by the bypass control means when it is predicted that the variation width of the predicted value of the exhaust gas recirculation rate exceeds a predetermined value. Exhaust purification system of an internal combustion engine, wherein a switching inhibiting means for forcibly prohibited, that was provided. 6. The switching prohibition means prohibits the switching control by the switching control means for a predetermined time when it is predicted that the change width of the predicted value of the exhaust gas recirculation rate exceeds a predetermined value. The exhaust gas purification device for an internal combustion engine according to claim 5.