JP5428955B2 - Control device for exhaust gas recirculation mechanism - Google Patents

Description

  The present invention relates to a control device for an exhaust gas recirculation mechanism that controls the opening of an EGR valve in accordance with the engine operating state of an internal combustion engine.

As the exhaust gas recirculation mechanism, one that adjusts the EGR amount by controlling the opening of an EGR valve based on the engine load is known (see, for example, Patent Document 1).
In general, the exhaust gas recirculation mechanism sets a target EGR opening based on the intake air amount and the engine speed, and performs control to bring the actual EGR opening closer to the target EGR opening.

Japanese Patent Laid-Open No. 6-249077

  By the way, in the operation region where the ratio of the change amount of the EGR opening is large with respect to the change amount of the intake air amount, the target EGR opening greatly changes with a slight change of the intake air amount GA. As the target EGR opening is changed, the actual EGR opening is changed toward the target EGR opening, so that the actual EGR opening greatly changes. Then, since the EGR flow rate changes greatly due to the change in the actual EGR opening, the intake air amount in the cylinder changes greatly. As a result, as the target EGR opening greatly changes, the actual EGR opening changes greatly again. By repeating such a flow with a very short cycle, the actual EGR opening degree is always repeated with a very short cycle and minute increase / decrease.

  That is, as shown in FIG. 7, the actual EGR opening changes with a very short period and a minute amplitude, unlike the change in the actual EGR opening with a long period and a large amplitude accompanying the accelerator operation. In other words, so-called EGR valve hunting occurs. Incidentally, since the resolution of the step type motor is low, the opening degree of the EGR valve cannot be controlled minutely. Therefore, in an internal combustion engine using a step motor as an actuator for an EGR valve, the occurrence frequency of hunting is higher in the operating region where the ratio of the change amount of the EGR opening is larger than the change amount of the intake air amount. turn into.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an exhaust gas circulation mechanism that can reduce the frequency of hunting of an EGR valve.

In the following, means for achieving the above object and its effects are described.
(1) In the control device for the exhaust gas recirculation mechanism that controls the opening degree of the EGR valve, the invention according to claim 1 uses a parameter for setting the target opening degree of the EGR valve as a target calculation parameter, The ratio of the change amount of the target opening to the change amount of the calculated parameter is defined as an opening change rate, and the control of the EGR valve performed to prevent the change of the EGR flow rate is referred to as a flow rate change reduction control. When the opening degree change value is larger than the opening degree reference value, the degree-of-opening rate of change is controlled to increase the degree to prevent the EGR flow rate from changing in the flow rate change reduction control, compared to when the opening degree change rate is smaller than the opening degree reference value. This is the gist.

  In this invention, when the opening degree change rate is larger than the opening degree reference value, that is, when hunting of the EGR valve is relatively likely to occur, when the opening degree change rate is smaller than the opening degree reference value, that is, for the EGR valve. Compared to the case where hunting is relatively difficult to occur, the degree of hindering the change in the EGR flow rate is increased. As a result, a situation in which the EGR flow rate greatly changes with a slight change in the target calculation parameter is less likely to occur, so that the frequency of hunting of the EGR valve can be reduced.

  (2) The invention according to claim 2 is the exhaust gas recirculation mechanism control device according to claim 1, wherein in the flow rate change reduction control, the absolute difference between the target opening and the actual opening of the EGR valve is determined. By holding the opening degree of the EGR valve when the value is smaller than a predetermined value, the change in the EGR flow rate is hindered. In the reduction degree variable control, the opening degree change rate is higher than the opening degree reference value. Is larger than the predetermined value when the opening degree change rate is smaller than the opening reference value, thereby increasing the degree of obstructing the EGR flow rate change in the flow rate change reduction control. The main point is that

  In this invention, when the opening degree change rate is larger than the opening degree reference value, that is, when hunting of the EGR valve is relatively likely to occur, when the opening degree change rate is smaller than the opening degree reference value, that is, for the EGR valve. Compared to the case where hunting is relatively difficult to occur, the area where flow rate change reduction control is performed is expanded. As a result, the frequency of occurrence of hunting of the EGR valve can be more reliably reduced.

  (3) In the control device for the exhaust gas recirculation mechanism that controls the opening degree of the EGR valve, the invention according to claim 3 uses a parameter for setting the target opening degree of the EGR valve as a target calculation parameter, The ratio of the change amount of the target opening to the change amount of the calculated parameter is defined as an opening change rate, and the control of the EGR valve performed to prevent the change of the EGR flow rate is referred to as a flow rate change reduction control. The gist is to carry out reduction degree variable control for increasing the degree of hindering the change in the EGR flow rate in the flow rate change reduction control as it increases.

  In this invention, when the opening degree change rate is larger than the opening degree reference value, that is, when hunting of the EGR valve is relatively likely to occur, when the opening degree change rate is smaller than the opening degree reference value, that is, for the EGR valve. Compared to the case where hunting is relatively difficult to occur, the degree of hindering the change in the EGR flow rate is increased. As a result, a situation in which the EGR flow rate greatly changes with a slight change in the target calculation parameter is less likely to occur, so that the frequency of hunting of the EGR valve can be reduced.

  (4) The invention according to claim 4 is the exhaust gas recirculation mechanism control device according to claim 3, wherein in the flow rate change reduction control, the absolute difference between the target opening and the actual opening of the EGR valve is determined. By holding the opening of the EGR valve when the value is smaller than a predetermined value, the EGR flow rate is prevented from changing. In the reduction degree variable control, the predetermined value increases as the opening change rate increases. The gist is that the degree of hindering the change in the EGR flow rate in the flow rate change reduction control is increased by increasing.

  In this invention, when the opening degree change rate is larger than the opening degree reference value, that is, when hunting of the EGR valve is relatively likely to occur, when the opening degree change rate is smaller than the opening degree reference value, that is, for the EGR valve. Compared to the case where hunting is relatively difficult to occur, the area where flow rate change reduction control is performed is expanded. As a result, the frequency of occurrence of hunting of the EGR valve can be more reliably reduced.

  (5) The gist of the fifth aspect of the invention is that, in the control device for the exhaust gas recirculation mechanism according to any one of the first to fourth aspects, an intake air amount is used as the target calculation parameter.

  (6) The invention according to claim 6 is the control device for the exhaust gas recirculation mechanism according to any one of claims 1 to 5, wherein the change amount of the EGR flow rate with respect to the change amount of the target opening degree of the EGR valve. When the flow rate change rate is larger than the flow rate reference value, the operating speed of the EGR valve is reduced compared to when the flow rate change rate is smaller than the flow rate reference value. The gist.

  In the present invention, when the flow rate change rate is larger than the flow rate reference value, that is, when hunting of the EGR valve is relatively likely to occur, when the flow rate change rate is smaller than the flow rate reference value, that is, when the EGR valve hunting is relatively The operation speed of the EGR valve is reduced compared to when it is difficult to occur. As a result, when the hunting of the EGR valve is likely to occur, the change in the EGR flow rate becomes small, so that the frequency of hunting of the EGR valve can be more reliably reduced.

The schematic diagram which shows the whole structure of an internal combustion engine provided with the control apparatus about one Embodiment which actualized the control apparatus of the exhaust gas recirculation mechanism of this invention. The map which shows the relationship between the engine speed used for EGR valve control of the embodiment, the amount of intake air, and the target EGR opening degree. The graph which shows the relationship between the opening degree change rate used for EGR valve control of the embodiment, and a dead zone width | variety. The graph which shows the relationship between the flow rate change rate used for EGR valve control of the embodiment, and the operating speed of an EGR valve. The flowchart which shows the procedure of the "EGR opening degree control process" performed by the electronic controller in the same embodiment. The timing chart which shows an example of the execution aspect of the EGR opening degree control process of the embodiment. The graph which shows an example of the change aspect of the EGR opening degree with respect to the operation time of an internal combustion engine.

1 to 6, an embodiment in which the control device for an exhaust gas recirculation mechanism of the present invention is embodied as a control device for an EGR device of a gasoline engine will be described.
As shown in FIG. 1, in the combustion chamber 11 of the engine 10, a spark plug 15 is provided for an air-fuel mixture of air supplied via a throttle valve 13 in an intake passage 12 and injected fuel injected by a fuel injection valve 14. Ignition is performed. The piston 16 reciprocates due to the combustion of the air-fuel mixture, and this reciprocating motion is converted into the rotational motion of the crankshaft 17. The air-fuel mixture after combustion is sent out from the combustion chamber 11 to the exhaust passage 18 as exhaust.

  The engine 10 is provided with an EGR device 20 that recirculates exhaust gas into the intake passage 12. The EGR device 20 is provided with an EGR passage 21 that connects the exhaust passage 18 and the downstream of the throttle valve 13 in the intake passage 12, and an EGR valve 22 that adjusts the flow rate of the exhaust gas flowing through the EGR passage 21. Yes. The opening / closing operation of the EGR valve 22 is controlled by a step type motor 23.

  Various sensors are connected to the input port of the electronic control unit 30. As these sensors, for example, a throttle sensor 31, a crank sensor 32, an intake air amount sensor 33, and an EGR sensor 34 are provided. The throttle sensor 31 detects the opening of the throttle valve 13 (hereinafter referred to as “throttle opening STA”). The crank sensor 32 detects the rotational speed of the crankshaft 17 (hereinafter, “engine rotational speed NE”) and the rotational angle. The intake air amount sensor 33 detects the flow rate of air passing through the intake passage 12 (hereinafter referred to as “intake air amount GA”). The EGR sensor 34 detects the opening degree of the EGR valve 22 (hereinafter, “actual EGR opening degree ETAR”).

  The electronic control unit 30 grasps the engine operating state such as the engine speed NE and the engine load KL based on the output signals of the sensors. The engine load KL is calculated based on the intake air amount GA and the engine rotational speed NE. The electronic control unit 30 outputs command signals to various drive circuits connected to the output port in accordance with the operating state of the engine 10 grasped as described above. The control performed by such an electronic control unit 30 includes throttle control for adjusting the throttle valve opening STA, fuel injection control for adjusting the injection amount of the fuel injection valve 14, and EGR valve for adjusting the actual EGR opening ETAR. Control etc. are mentioned.

In the EGR valve control, the EGR valve is basically controlled as follows.
That is, as shown in FIG. 2, from the map showing the relationship between the intake air amount GA, the engine rotational speed NE, and the target EGR opening EDAT, the target EGR opening EDAT from the intake air amount GA and the engine rotational speed NE at that time. Is calculated. Then, the EGR valve 22 is controlled so that the actual EGR opening degree ETAR becomes the calculated target EGR opening degree EDAT.

In the graph of FIG. 2, the vertical axis is the engine speed NE, and the horizontal axis is the intake air amount GA.
Of the engine rotation speed NE, the engine rotation speed NE1 indicates the value of the engine rotation speed when the operation region is idle operation. The engine speed NE13 indicates the highest engine speed value in the normal operation region. The engine rotation speeds NE2 to NE12 indicate values that increase in order at regular intervals.

  Of the intake air amount GA, the intake air amount GA1 indicates the value of the intake air amount when the operation region is idle operation. The intake air amount GA18 indicates the maximum intake air amount in the normal operation region. The intake air amounts GA2 to GA17 show values that increase in order at regular intervals.

  An operation region R is defined by the engine speeds NE1 to NE13 and the intake air amounts GA1 to GA18. In each operation region R, a target EGR opening EDAT is set.

  In this map, the target EGR opening EDAT is larger than “0” in accordance with the region A in the operating region R where the target EGR opening EDAT is “0” and the engine speed NE and the intake air amount GA. A region B to be changed in the range is provided. Region B corresponds to a region of low engine rotation speed and low intake air amount, a region of medium engine rotation speed and medium intake air amount, and a region of high engine rotation speed and high intake air amount.

Next, the contents of control for controlling hunting of the EGR valve 22 will be described.
Further, the ratio of the change amount of the target EGR opening EDAT per unit change amount of the intake air amount GA (that is, the absolute value of the difference between the target EGR opening EDAT and the actual EGR opening ETA) is expressed as “opening change rate VR”. And

For example, when the engine operation state changes from the operation region R1 to the operation region R2 in the figure, the opening degree change rate VR is calculated by the following formula.

VR = | ETA2-ETA1 | / | GA10-GA4 |

Is required.

  Next, the ratio of the change amount of the EGR flow rate to the change amount of the target EGR opening degree EDAT is set to “flow rate change rate VQ”. In a region where the target EGR opening EDAT is large (for example, when the EGR valve 22 is fully opened or in the vicinity thereof), the flow rate change rate VQ is larger than in a region where the target EGR opening EDAT is small.

In the present embodiment, the following controls (A) to (C) are performed as control for suppressing hunting of the EGR valve 22.
(A) Opening degree holding control for holding the actual EGR opening degree ETAR when hunting of the EGR valve 22 may occur.
(B) Area change control for changing the size of the opening area of the EGR valve 22 in which the opening degree holding control is performed according to the magnitude of the opening degree change rate VR.
(C) Speed change control for changing the operating speed V of the EGR valve 22 in accordance with the magnitude of the flow rate change rate VQ.

The contents of the opening degree holding control will be described.
In the opening degree holding control, a dead band width H for holding the value of the actual EGR opening degree ETAR is set. By setting the dead zone width H, even if the actual EGR opening degree ETAR deviates from the target EGR opening degree EDAT, the actual EGR opening degree ETAR is held at the opening degree at that time.

  When the difference between the target EGR opening EDAT and the actual EGR opening ETA (hereinafter referred to as “opening difference ETX”) is within the dead band H, the actual EGR opening ETA is changed toward the target EGR opening EDAT. And hunting of the EGR valve 22 may occur. Therefore, when the opening degree difference ETX is within the dead zone width H, the actual EGR opening degree ETAR is held. The dead band width H is set slightly larger than the amplitude when hunting of the EGR valve 22 occurs. Moreover, what was grasped | ascertained by the test is used as an amplitude when hunting of the EGR valve 22 arises.

The contents of the area change control will be described.
Ease of occurrence of hunting of the EGR valve 22 varies depending on the opening change rate VR. That is, in the operating region where the opening degree change rate VR is large, the target EGR opening degree EDAT greatly changes with respect to a minute change in the intake air amount GA. Therefore, the EGR valve 22 is compared with the operating region where the opening degree change rate VR is small. Hunting is likely to occur.

  Therefore, in the area change control, the dead zone width H is changed according to the opening degree change rate VR. That is, the dead zone width H is increased when hunting of the EGR valve 22 is likely to occur. As a result, the control range for maintaining the actual EGR opening degree ETAR is expanded, so that the occurrence of hunting of the EGR valve 22 is suppressed.

The contents of the speed change control will be described.
Ease of hunting of the EGR valve 22 varies depending on the flow rate change rate VQ. That is, in the operation region where the flow rate change rate VQ is large, the EGR flow rate changes greatly with respect to the change in the target EGR opening EDAT, and therefore, hunting of the EGR valve 22 is likely to occur compared to the operation region where the flow rate change rate VQ is small.

Therefore, in the speed change control, the operating speed V of the EGR valve 22 is changed according to the flow rate change rate VQ.
Accordingly, when the flow rate change rate VQ is in a large region, that is, when hunting of the EGR valve 22 is likely to occur, the operating speed V of the EGR valve 22 is decreased. As a result, when the hunting of the EGR valve 22 is likely to occur, the change in the EGR flow rate becomes small, so that the hunting of the EGR valve 22 is suppressed.

With reference to FIG. 3, the contents of the map used in the area change control will be described.
In the graph shown in FIG. 3, the vertical axis is the dead zone width H, and the horizontal axis is the opening degree change rate VR. The opening change rate VR is partitioned at a constant interval, and the dead zone width H is set for each partitioned region.

Specifically, the dead zone width H is set to three values according to the region of the opening degree change rate VR.
In the first region VRX in which the opening change rate VR is a region from the minimum value VR1 of the graph in FIG. 3 to a value VR2 greater than this value VR1, the dead zone width H is set as the smallest value H1.

In the second region VRY in which the opening change rate VR is a region from the value VR2 to a value VR3 larger than the value VR2, the dead zone width H is set as a value H2 larger than the value H1.
In the third region VRZ in which the opening change rate VR is a region from the value VR3 to the maximum value VR4 in the graph in FIG. 3, the dead zone width H is set as the largest value H3 (that is, H1 <H2 <H3 ). Note that each value of the dead band width H is constant in each of the regions VRX to VRZ.

  The dead band width H has a predetermined amount of width equal to each other on both the increase side of the actual EGR opening ETAR and the decrease side of the actual EGR opening ETAR with the actual EGR opening ETAR as the center. That is, the dead zone width H has an upper limit HUL and a lower limit HDL having the same width around the actual EGR opening ETAR, and is defined by a size from the lower limit HDL to the upper limit HUL. Based on the above, it is determined whether the opening degree change rate VR at that time falls into any of the first region VRX to the third region VRZ, and the dead band width H of the region is set to the dead zone width H with respect to the opening degree change rate VR at that time. Set as.

With reference to FIG. 4, the contents of the map used in the speed change control will be described.
In the graph shown in FIG. 4, the vertical axis represents the operating speed V of the EGR valve 22, and the horizontal axis represents the flow rate change rate VQ. The target EGR opening EDAT is partitioned at a constant interval, and the value of the operating speed V of the EGR valve 22 is set for each partitioned region.

Specifically, the operating speed V of the EGR valve 22 is set to three values according to the flow rate change rate VQ.
In the first region VQX where the value of the flow rate change rate VQ is from the minimum value VQ1 of the graph in FIG. 4 to the value VQ2 that is larger than this value VQ1, the operating speed V of the EGR valve 22 is the largest value. V1 is set.

  In the second region VQY in which the value of the flow rate change rate VQ is from the value VQ2 to the value VQ3 that is a value greater than the value VQ2, the operating speed V of the EGR valve 22 is set to a value V2 that is smaller than the value V1. ing.

  In the third region VQZ in which the value of the flow rate change rate VQ is from the value VQ3 to the maximum value VQ4 in the graph of FIG. 4, the operating speed V of the EGR valve 22 is set to the smallest value V3 (that is, V3 <V2 <V1). Note that the value of the operating speed V of the EGR valve 22 is constant in each of the regions VQX to VQZ.

  With reference to FIG. 5, the content of the EGR opening degree control process that defines the procedure for suppressing the hunting of the EGR valve 22 will be described. This process is repeatedly performed every predetermined time by the electronic control unit 30.

  In step S10, the target EGR opening degree EDAT is calculated based on the detected engine speed NE and the intake air amount GA. Specifically, the target EGR opening EDAT is calculated from the relationship between the engine speed NE and the intake air amount GA using the map shown in FIG.

  Next, in step S11, the dead zone width H is calculated based on the region of the opening degree change rate VR. Specifically, the opening degree change rate VR is calculated, and it is determined whether the calculated opening degree change rate VR belongs to one of the regions VRX to VRZ. And the value of the dead zone width H according to each area | region VRX-VRZ is calculated using the graph of FIG. In addition, the process of step S11 is corresponded to reduction degree variable control.

  Next, in step S12, the operating speed V of the EGR valve 22 is calculated based on the flow rate change rate VQ. Specifically, the flow rate change rate VQ is calculated, and it is determined whether the calculated flow rate change rate VQ belongs to one of the regions VQX to VQZ. And the value of the operating speed V of the EGR valve 22 according to each area | region VQX-VQZ is calculated using the graph of FIG.

  Next, in step S13, it is determined whether or not the absolute value of the opening difference ETX, which is the difference between the current actual EGR opening ETAR and the target EGR opening EDAT calculated in the current control cycle, is within the dead band width H. To do. That is, it is determined whether or not the opening degree difference ETX is lower than the lower limit value HDL of the dead band width H and whether the opening degree difference ETX is higher than the upper limit value HUL of the dead band width H.

  Here, when the absolute value of the opening degree difference ETX is within the range of the dead band width H (YES in step S13), that is, the opening degree difference ETX is not less than the lower limit value HDL of the dead band width H and the opening degree difference ETX is the dead band. When it is below the upper limit value HUL of the width H, the current actual EGR opening degree ETAR is maintained in step S14. In addition, the process of step S13 and S14 is corresponded to flow volume change reduction control.

  On the other hand, when the absolute value of the opening difference ETX exceeds the dead band width H (NO in step S13), that is, when the opening difference ETX falls below the lower limit value HDL of the dead band width H, or when the opening difference ETX is the dead band width H. When the value exceeds the upper limit value HUL, in step S15, the target EGR opening EDAT calculated in the current control cycle is set as a new target EGR opening EDAT.

  In step S16, the actual EGR opening degree ETAR is changed to approach the new target EGR opening degree EDAT using the operating speed V of the EGR valve 22 calculated in step S12.

  With reference to FIG. 6, an example of a control mode of the opening degree of the EGR valve 22 by the above-described EGR opening degree control process will be described. In FIG. 6, the horizontal axis represents time (t) and the vertical axis represents the EGR opening, and the change of the target EGR opening EDAT and the actual EGR opening ETA over time is shown. Note that the thick line in the graph indicates the actual EGR opening ETA, and the thin line indicates the target EGR opening EDAT. A broken line indicates the dead band width H.

  At time t0 to t2, the engine load KL increases due to the accelerator operation. Along with this, since the target EGR opening EDAT increases and the opening difference ETX exceeds the upper limit value HUL of the dead zone width H, the EGR valve 22 changes so that the actual EGR opening ETER increases.

  Further, at time t0 to t1, the flow rate change rate VQ becomes the first region VQX, so that the operating speed V of the EGR valve 22 is set to the value V1. At time t1 to t2, the flow rate change rate VQ becomes the third region VQZ, so the operating speed V of the EGR valve 22 is set to the value V3.

  From time t2 to t3, the accelerator depression amount is substantially maintained, but the intake air amount GA changes due to a slight change in the accelerator depression amount, a change in the running state of the vehicle, or the like. Accordingly, the target EGR opening EDAT changes. However, since the target EGR opening EDAT is a change within the dead zone width H, the actual EGR opening ETA is maintained. That is, the actual EGR opening degree ETAR is maintained in a state where it is separated from the target EGR opening degree EDAT.

  When the absolute value of the opening difference ETX exceeds the dead zone width H and the target EGR opening EDAT falls below the lower limit HDL (time t3) as the accelerator depression amount changes, the actual EGR opening ETAR is the target at that time It is changed toward the opening ETA which is the EGR opening EDAT (time t4). Then, the dead band width H after time t4 is set based on the value ETAX.

According to the present embodiment, the following effects can be achieved.
(1) In the present embodiment, when the opening degree change rate VR is in the third region VRZ, that is, when hunting of the EGR valve 22 is relatively likely to occur, the opening degree change rate VR is equal to the first region VRX or the second region VRX. The degree of hindering the change in the EGR flow rate is reduced as compared with when it is in the region VRY, that is, when hunting of the EGR valve 22 is relatively difficult to occur. As a result, a situation in which the EGR flow rate greatly changes with a slight change in the intake air amount GA is less likely to occur, and therefore the frequency of hunting of the EGR valve 22 can be reduced. The same applies to the comparison between when the opening degree change rate VR is in the second region VRY and when it is in the first region VRX.

  (2) In this embodiment, when the opening degree change rate VR is in the third region VRZ, that is, when hunting of the EGR valve 22 is relatively likely to occur, the opening degree change rate VR is the first region VRX or the second region VRX. The region where the flow rate change reduction control is performed, that is, the dead zone width H, is made larger than when it is smaller than when it is in the region VRY, that is, when hunting of the EGR valve 22 is relatively difficult to occur. Thereby, the frequency with which hunting of the EGR valve 22 occurs can be more reliably reduced. The same applies to the comparison between when the opening degree change rate VR is in the second region VRY and when it is in the first region VRX.

  (3) According to the present embodiment, since the dead zone width H is set based on the amplitude of the EGR valve when the EGR valve 22 is hunted, the hunting of the EGR valve 22 that actually occurs in each region VRX to VRZ is appropriately performed. Can be suppressed.

  (4) In this embodiment, when the flow rate change rate VQ is in the third region VQZ, that is, when hunting of the EGR valve 22 is relatively likely to occur, the flow rate change rate VQ is the first region VQX or the second region VQY. In other words, the operating speed V of the EGR valve 22 is made smaller than when the hunting of the EGR valve 22 is relatively difficult to occur. As a result, when the hunting of the EGR valve 22 is likely to occur, the change in the EGR flow rate becomes small, so that the frequency of hunting of the EGR valve 22 can be more reliably reduced.

(5) From the viewpoint of improving fuel efficiency, it is conceivable to increase the EGR flow rate by using an EGR valve having a large physique.
However, when the step type motor is used as the actuator for operating the EGR valve having a large physique, the operation amount of the EGR valve per one step of the motor becomes large, so the EGR amount per one step increases. As a result, the amount of change in the EGR flow rate increases. As a result, hunting of the EGR valve 22 is likely to occur.

  In this respect, in the present embodiment, since the actual EGR opening degree ETAR is held based on the dead zone width H, hunting of the EGR valve 22 can be suppressed even when the EGR flow rate per step is large. Therefore, it is possible to achieve both improvement in fuel efficiency by adopting an EGR valve having a large physique and suppression of hunting of the EGR valve 22.

  (6) Since the stepping motor has a low resolution, the opening degree of the EGR valve 22 cannot be controlled minutely. Therefore, in the engine 10 using the step type motor as the actuator of the EGR valve 22, the occurrence frequency of hunting of the EGR valve 22 is higher in the operation region where the opening degree change rate VR is large. In this regard, in the present embodiment, although the step type motor 23 is used as the actuator of the EGR valve 22, since the EGR valve opening degree control process is performed, the operating range in which the opening degree change rate VR is large is used. The occurrence of hunting of the EGR valve 22 can be suppressed.

(Other embodiments)
The specific configuration of the control device for the exhaust gas recirculation mechanism of the present invention is not limited to the configuration illustrated in the above embodiment, and can be changed as follows, for example. The following modifications are not applied only to the above-described embodiment, and different modifications can be combined with each other.

  In the above embodiment, the operating speed V of the EGR valve 22 is set as a different value in each region VQX to VQZ of the flow rate change rate VQ (see FIG. 4), but the operating speed V is set to the entire region of the flow rate change rate VQ. It can also be set as a constant value.

  In the above embodiment, the dead band width H of the EGR valve 22 is set as a value different from each other in the regions VRX to VRZ of the respective opening change rates VR (see FIG. 3), but the dead band width H is the entire opening change rate VR. It can also be set as a constant value over the range.

  In the above embodiment, the dead zone width H is set as a constant value in each of the regions VRX to VRZ (see FIG. 3), but the dead zone width H may be variable in each of the regions VRX to VRZ. Specifically, in each of the regions VRX to VRZ, the value of the dead zone width H can be set so as to continuously increase as the opening degree change rate VR increases.

  In the above embodiment, the operation speed V is set as a constant value in the regions VQX to VQZ (see FIG. 4). However, the operation speed V may be variable in the regions VQX to VQZ. Specifically, the value of the operating speed V can be set to continuously decrease as the opening degree change rate VR increases in each of the regions VQX to VQZ.

  In the above embodiment, it is determined whether or not the actual EGR opening ETAR is maintained by comparing the dead zone width H and the opening difference ETX, but the number of steps of the motor 23 corresponding to the opening difference ETX and the number of steps It is also possible to determine whether or not to hold the actual EGR opening degree ETAR based on the relationship with the dead zone width H adapted to.

  In the above embodiment, the value of the dead band width H is set based on the opening degree change rate VR. However, the dead band width H can also be set based on a parameter different from the opening degree change rate VR. For example, the absolute value of the ratio of the change amount of the target EGR opening EDAT to the change amount of the engine rotational speed NE is calculated as a parameter instead of the opening change rate VR, and the value of the dead zone width H is set based on this parameter. You can also.

  In the above embodiment, three regions are set as the region of the opening degree change rate VR with respect to the dead zone width H, but the method of partitioning the region of the opening degree change rate VR is not limited to this. For example, it can be divided into a first area where the opening degree change rate VR is larger than a predetermined opening degree reference value and a second area where the opening degree change rate VR is less than or equal to the above opening degree reference value. In this case, when the opening change rate VR is in the first region, that is, when it is predicted that hunting of the EGR valve 22 is likely to occur, the actual EGR opening ETAR is held. On the other hand, when the opening change rate VR is in the second region, that is, when it is predicted that hunting of the EGR valve 22 is unlikely to occur, the actual EGR opening ETAR is changed toward the target EGR opening EDAT. .

  In short, the control mode of the degree-of-change change control is a region where the opening degree change rate VR is relatively small, that is, in a region where hunting of the EGR valve 22 is likely to occur, As long as the EGR valve 22 is less likely to cause hunting, the control may be performed to increase the degree to which the change in the EGR flow rate is hindered.

  In the above embodiment, the flow rate change rate VQ is divided into three regions of the first region VQX to the third region VQZ, but the region of the flow rate change rate VQ is not limited to this. For example, when the flow rate change rate VQ when the target EGR opening EDAT is close to full open is the flow rate reference value and the flow rate change rate VQ is larger than the flow rate reference value, the flow rate change rate VQ is smaller than the flow rate reference value. Then, any control that reduces the operating speed V of the EGR valve 22 may be used.

  In the above embodiment, the control for suppressing the hunting of the EGR valve 22 is applied to the gasoline engine, but it can also be applied to a diesel engine.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 11 ... Combustion chamber, 12 ... Intake passage, 13 ... Throttle valve, 14 ... Fuel injection valve, 15 ... Spark plug, 16 ... Piston, 17 ... Crankshaft, 18 ... Exhaust passage, 20 ... Exhaust gas recirculation mechanism, 21 ... EGR passage, 22 ... EGR valve, 23 ... motor, 30 ... electronic control device, 31 ... throttle sensor, 32 ... crank sensor, 33 ... intake air amount sensor, 34 ... EGR sensor.

Claims (6)

In the control device of the exhaust gas recirculation mechanism that controls the opening degree of the EGR valve,
The parameter for setting the target opening of the EGR valve is set as a target calculation parameter, and the ratio of the change amount of the target opening to the change amount of the target calculation parameter is set as the opening change rate, thereby preventing the change in the EGR flow rate. As the flow rate change reduction control, the control of the EGR valve performed at
When the opening degree change rate is larger than the opening degree reference value, the degree of obstructing the EGR flow rate change in the flow rate change reduction control is increased compared to when the opening degree change rate is smaller than the opening degree reference value. A control device for an exhaust gas recirculation mechanism that performs variable reduction control. The control device for the exhaust gas recirculation mechanism according to claim 1,
In the flow rate change reduction control, when the absolute value of the difference between the target opening and the actual opening of the EGR valve is smaller than a predetermined value, the change in the EGR flow rate is prevented by maintaining the opening of the EGR valve. Is,
In the reduction degree variable control, the predetermined value when the opening degree change rate is larger than the opening degree reference value is made larger than the predetermined value when the opening degree change rate is smaller than the opening degree reference value. Accordingly, the degree of hindering the change in the EGR flow rate in the flow rate change reduction control is increased. The control device for the exhaust gas recirculation mechanism. In the control device of the exhaust gas recirculation mechanism that controls the opening degree of the EGR valve,
The parameter for setting the target opening of the EGR valve is set as a target calculation parameter, and the ratio of the change amount of the target opening to the change amount of the target calculation parameter is set as the opening change rate, thereby preventing the change in the EGR flow rate. As the flow rate change reduction control, the control of the EGR valve performed at
A control device for an exhaust gas recirculation mechanism that performs variable reduction degree control that increases the degree of obstructing the change in EGR flow rate in the flow rate change reduction control as the opening degree change rate increases. The control device for the exhaust gas recirculation mechanism according to claim 3,
In the flow rate change reduction control, when the absolute value of the difference between the target opening and the actual opening of the EGR valve is smaller than a predetermined value, the change in the EGR flow rate is prevented by maintaining the opening of the EGR valve. Is,
In the reduction degree variable control, the predetermined value is increased as the opening degree change rate increases, thereby increasing the degree of hindering the change in EGR flow rate in the flow rate change reduction control. Control device for recirculation mechanism. In the control apparatus of the exhaust gas recirculation mechanism according to any one of claims 1 to 4,
A control device for an exhaust gas recirculation mechanism, wherein an intake air amount is used as the target calculation parameter. In the control apparatus of the exhaust gas recirculation mechanism according to any one of claims 1 to 5,
The ratio of the change amount of the EGR flow rate to the change amount of the target opening of the EGR valve is defined as a flow rate change rate.
When the flow rate change rate is larger than the flow rate reference value, the operating speed of the EGR valve is reduced compared to when the flow rate change rate is smaller than the flow rate reference value. Control device.

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