JPH08158954A - EGR control device for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] EG when switching intake / exhaust valve lift characteristics of an internal combustion engine
Improves R performance. [Structure] When switching the valve lift characteristics of the intake valve, the switching operation delay time TD2 (TD4) and the operation delay time TD of the EGR valve
3 (TD5) Difference between the external EGR amount that changes by delaying the start of operation of the EGR valve by TD1 and gradually changing the opening of the EGR valve and the internal EGR amount that changes by switching the valve lift characteristic Should be kept approximately constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR control device for an internal combustion engine, in which lift characteristics of intake / exhaust valves are switched according to engine operating conditions, and more particularly to EGR control when switching valve lift characteristics.

[0002]

2. Description of the Related Art As is well known, some internal combustion engines for vehicles are equipped with an EGR device for returning a part of exhaust gas to an intake system in order to reduce NOx emission amount. On the other hand, by switching the valve lift characteristics (characteristics of opening / closing timing and lift amount) of the intake / exhaust valves of the internal combustion engine according to the engine operating state,
For example, there is known one provided with a valve lift characteristic switching device which is designed to improve the stability at idle and the output at high speed while maintaining the operating performance in the normal speed range.

In an internal combustion engine equipped with both the EGR device and the valve lift characteristic switching device, if the presence or absence of EGR is switched at the same time when the valve lift characteristic is switched, there will be a torque change due to the valve lift characteristic switching and a torque change due to the EGR switching. Will overlap and generate a large torque change. Therefore, for example, in the one disclosed in Japanese Unexamined Patent Publication No. 5-163970, a low speed valve is provided while switching from a low speed valve lift characteristic and EGR performing state to a high speed valve lift characteristic and EGR stopping state. It is intended to suppress the torque change across the lift characteristic and the state where EGR is stopped.

[0004]

However, in the conventional switching system as described above, since the EGR is stopped by the low-speed valve lift characteristic which should originally perform the EGR, the NOx emission amount increases, and the other regions are different from each other. By comparison, the difference becomes large, and it becomes difficult to control the air-fuel ratio for reducing exhaust emission.

The present invention has been made in view of the above conventional problems, and suppresses both the torque change and the NOx emission amount change by smoothly changing the EGR rate when switching the valve lift characteristics. EGR of internal combustion engine made possible
An object is to provide a control device.

[0006]

Therefore, according to the invention of claim 1, as shown in FIG. 1, a valve for switching the lift characteristic of the intake / exhaust valve in accordance with the engine operating state detected by the operating state detecting means. In an internal combustion engine provided with a lift characteristic switching means, an EGR means for controlling a flow rate of exhaust gas which is interposed in an EGR passage connecting an exhaust system and an intake system and is recirculated from the exhaust system to the intake system, and the operating state detecting means. The target EGR control amount setting means for setting the target control amount of the EGR means in accordance with the engine operating state detected by the above, and when the valve lift characteristic of the intake / exhaust valve is switched by the valve lift characteristic switching means. EGR control amount correction means for correcting the control amount of the EGR means so that the target control amount set by the target control amount setting means is gradually changed from the value before switching to the value after switching, and the intake / exhaust Characterized by being configured to include a valve lift characteristic switching EGR control means for controlling the EGR device based on the control amount corrected valve lift characteristics switching of the valve, the.

Further, in the invention of claim 2, the valve lift characteristic switching means absorbs or absorbs in accordance with the engine speed and load.
It is characterized in that the valve lift characteristic of the exhaust valve is switched.
Further, the invention of claim 3 is characterized in that the target control amount setting means sets the target control amount of the EGR means according to the rotational speed and the load of the engine. Further, in the invention of claim 4, as shown by the chain line in FIG. 1, the start of the operation of the EGR means is delayed by the amount of time required for the operation switching of the valve lift switching means is larger than the time required for the control switching of the EGR means. It is characterized in that it is configured so as to include an EGR delay means.

[0008]

According to the first aspect of the present invention, when the valve lift characteristic of the intake / exhaust valve is switched by the valve lift characteristic means, the target control amount set by the target control amount setting means corresponds to the switching of the valve lift characteristic. Change. For example, when the valve lift characteristic for low speed is switched to the valve lift characteristic for high speed, the valve overlap amount increases and the cylinder residual exhaust amount, that is, the so-called internal EGR amount increases. Therefore, the EG
The EGR amount (external EGR amount) by the R means is the internal EG
The target control amount is set so as to decrease in proportion to the increase in the R amount, so that the total EGR amount obtained by summing the internal EGR amount and the external EGR amount before and after the switching is set so as not to change.

However, even if the switching of the valve lift characteristic switching means is started, there is a delay in the operation such as a change in the hydraulic pressure for driving, so that the internal EGR amount is gradually switched.
If the GR amount is switched instantaneously, the total EGR amount and thus the EGR rate will change significantly during the switching. Therefore, when the valve lift characteristics are switched, the control amount is corrected so that the target control amount of the EGR means is gradually changed from the value set before the switching to the value set after the switching, so that the internal EGR amount By changing the external EGR amount so as to correspond to the change at the time of switching, it is possible to suppress the change of the total EGR amount and therefore the EGR rate even during the switching, and the air-fuel ratio control for reducing the exhaust emission becomes easy.

According to the second aspect of the present invention, the valve lift characteristic of the intake / exhaust valve can be switched in accordance with the operating condition determined by the engine speed and load. According to the third aspect of the present invention, the target control amount of the EGR means can be set so as to correspond favorably to the operating state determined by the engine speed and the load. Further, according to the invention of claim 4, since the time required for switching the operation of the valve lift switching means is longer than the time required for switching the control of the EGR means, the operation start of the EGR means is delayed, so that the valve lift switching is performed. The switching between the means and the EGR means is completed at substantially the same time, and the EGR rate can be converged to the target value after the switching.
The GR rate can be controlled with high accuracy.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of the present invention. In the figure, a throttle valve 3 is provided in an intake passage 2 of an internal combustion engine 1,
An EGR passage 5 is arranged by connecting the downstream side of the throttle valve 3 of the intake passage 2 and the exhaust passage 4. The EGR passage 5
Is an EGR means for controlling the EGR flow rate.
The valve 6 is interposed. The EGR valve 6 is driven by a step motor, and the opening can be linearly controlled by a control signal from the control unit 7.

Further, a valve lift characteristic switching means 9 for switching the valve lift characteristic of the intake valve 8 of each cylinder according to the engine operating state is provided. The structure of the valve lift characteristic switching means 9 will be described later. Wherein the control unit 7, the battery voltage V _B, the cooling water temperature T _W detected by the water temperature sensor 10, the engine rotational speed N detected by the crank angle sensor 11, the intake air flow rate Q detected by the air flow meter 12, Accelerator opening detected by accelerator opening sensor 13, boost pressure (intake pressure) detected by boost sensor 14, ignition switch (IGN / SW)
ON / OFF of 15, Starter switch 16 ON / OF
Each signal of F is input, and the control unit 7 controls the switching of the valve lift characteristic switching means 9, the control of the EGR valve 6, and the other fuel injection control according to the engine operating state obtained based on these detection signals. Ignition timing control is performed.

As the valve lift characteristic switching means 9,
For example, those disclosed in JP-A-6-123207 can be adopted. Figure 3 shows an overview of this product
~ It demonstrates based on FIG. 3 and 4, a main rocker arm 41 corresponding to the intake valve 8 is swingably supported by the cylinder head via a main rocker shaft 43 common to each cylinder in each cylinder. A roller 48 is rotatably connected to the shaft 46 of the main rocker arm 41, and a low speed cam 49 is brought into rolling contact with the roller 48. A sub-rocker arm 42 is provided on the main rocker arm 41 side by side with the roller 48, and a base end of the sub-rocker arm 42 is connected to the main rocker arm 41 via a sub-rocker shaft 50 so as to be relatively rotatable.

The sub-rocker arm 42 does not have a portion that comes into contact with the intake valve 8, and a cam follower portion 54 that slidably contacts the high-speed cam 53 is formed at the tip of the sub-rocker arm 42. A lost motion spring 39 to be pressed is interposed. Further, as shown in FIGS. 5 and 6, a hole 56 for slidably fitting a plunger 55 is formed in the sub-rocker arm 42, and plungers 57, 58 are slidably fitted in the main rocker arm 41. Holes 59 and 60 are formed to define an oil chamber 61 behind the plunger 57, and a return spring 62 behind the plunger 58.
Is interposed.

The holes 56, 59, 60 are coaxially continuous with each other at a predetermined position and have the same diameter. And the oil chamber 61
The hydraulic oil introduced from the oil pump into the low speed cam is introduced during high speed operation via a cam switching valve 70, which will be described later.
Switching between the high speed cam 53 and the high speed cam 53 is performed smoothly. In addition, a plug 63 is provided at one end of the hole 60 into which the plunger 58 is fitted.
Is press-fitted, and an air vent hole 64 is opened in the plug body 63.

Then, as shown in FIG. 6, the plunger 57 is fitted into the holes 59 and 56 and the plunger 55 is fitted into the holes 56 and 60 by the operating hydraulic pressure introduced into the oil chamber 61, whereby the main rocker arm 41. And the sub-rocker arm 42 are integrated. In addition, as shown in FIG. 5, the return spring
When the plunger 57 is in contact with the end wall of the hole 59 by the urging force of 62, the plungers 55, 57, 58 are housed in the holes 56, 59, 60, respectively, so that the swing of the main rocker arm 41 is not restricted. It has become.

Low speed cam 49 and high speed cam adjacent to it
53 is integrally formed on a common camshaft,
They are formed in different shapes (including similar shapes having different sizes) so as to satisfy the valve lift characteristics required at low engine speed and high engine speed. Here, the high speed cam 53 has a profile that increases the valve lift amount as compared with the low speed cam 49, and the valve lift curves of the intake valve 5 by the high speed cam 53 and the low speed cam 49 are shown in FIG. It is as shown in FIG.

Next, the operation of the above configuration will be described.
In a predetermined operating state of the engine, the main rocker arm 41 swings according to the profile of the low speed cam 49 to open / close each intake valve and exhaust valve. At this time, the sub-rocker arm 42 is swung by the high-speed cam 53, but the urging force of the return spring 62 causes the plungers 57, 55, 58 to move.
Does not interfere with the movement of the main rocker arm 41 by fitting in the holes 59, 56, and 60, respectively.

On the other hand, when the operating oil pressure is introduced into the oil chamber 61, the plungers 57, 55 and 58 cause the return spring 62 to move.
The rocker arms 41 and 42 are integrated by the plunger 57 fitting over the holes 59 and 56 and the plunger 58 fitting over the holes 56 and 60. To rock. Here, the high speed cam 53 is the low speed cam 49
Since it is formed so that the lift amount is larger than that of, the roller 48 of the main rocker arm 41 floats up from the low speed cam 49 when swinging integrally with the sub-rocker arm 42, and each intake valve and exhaust valve Is driven to open and close according to the profile of the high speed cam 53, and the lift amount increases.

Next, the control unit 7 sucks
The valve lift characteristic switching control of the exhaust valve and the EGR control are shown in FIGS.
This will be described with reference to the time chart of FIG. 12 according to the flowchart of 11. In step (denoted as S in the figure. The same applies hereinafter) 1, it is determined whether or not the starter switch 16 is on, and at the time of cranking when it is on, the intake valve engages the cam for low speed and the valve for low speed is engaged. Since the lift characteristic is selected, the flag F1 which is reset to 0 when the valve lift characteristic for high speed is switched is set to 1 in step 2, and the timer TD for various measurements is reset to 0 in step 3. However, in step 4, the EGR operation delay time TD with respect to the valve lift characteristic switching set as described later is performed.
After resetting 1 to 0, the process proceeds to step 5, and when it is determined in step 1 that the starter switch 16 is off, the process skips steps 2 to 4 and proceeds to step 5.

In steps 5 to 7, the valve lift characteristic is set.
The switching condition of is determined. That is, in step 5, the water temperature Tw
Is within the range of Tw1 <Tw <Tw2, and the engine speed is
N is in the range of N1 <N <N2 and is a group that represents the engine load.
Main fuel injection amount T_PIs T_P> T _PAll conditions that are 1 are satisfied
If the valve lift characteristic is increased, proceed to step 8 to improve the valve lift characteristics.
Set for high speed, and set the flag F1 to 0 in step 9.
To put. Also, at least one of the above conditions is satisfied.
If not, go to step 10 and set the valve lift characteristic to low speed.
And set the flag F1 to 1 in step 11.
To

In step 12, it is judged whether or not the value of the flag F1 has been inverted. When it is determined that the flag has been inverted, the routine proceeds to step 13, where the timer TD is reset to 0, and at step 14, the value of the flag F1 is discriminated. When it is determined that the value of the flag F1 is 0, that is, when it is determined that the valve lift characteristic has been switched from low speed to high speed, the routine proceeds to step 15, where a signal for switching the valve lift characteristic from low speed to high speed is sent. The operation delay time TD2 from the issuance to the completion of the switching is retrieved from a map previously obtained for the engine rotation speed N that determines the operation delay time TD2, and the low speed of the valve lift characteristic is read. The opening degree is controlled to increase in response to switching from high speed to high speed E
The operation delay time TD3 from the generation of the opening switching signal of the GR valve 16 to the completion of the control is
The basic fuel injection amount T _P for determining is read from a map previously obtained. The operation delay time TD2
Is determined by the engine rotational speed N because the cam switching speed is proportional to the engine rotational speed N, while the operation delay time TD3 is determined by the basic fuel injection amount T _P which is the load of the engine. The operation speed of the EGR valve 16 is substantially constant due to the use of the step motor.
The opening degree reduction amount of 16 is set in proportion to the increase amount of the internal EGR amount increased by switching the valve lift characteristic from low speed to high speed, and the increase amount of the internal EGR amount is proportional to the cylinder intake air amount. This is because it is proportional to the basic fuel injection amount T _P.

Next, at step 16, the value obtained by subtracting the operation delay time TD3 of the EGR valve 16 from the operation delay time TD2 of the valve lift characteristic switching is set as the operation start delay time TD1 for delaying the operation start of the EGR valve 16. To do. On the other hand, when it is determined in step 14 that the value of the flag F1 is 1, that is, when it is determined that the valve lift characteristic is switched from high speed to low speed, in step 17 the valve lift characteristic is changed from high speed to low speed. The operation delay time TD4 required for switching to the operation mode and the operation delay time TD5 until completion of control of the EGR valve 16 whose opening is controlled to increase corresponding to the switching of the valve lift characteristic from high speed to low speed. , TD4 to TD5 in step 18 after searching and loading from each map
The value obtained by decreasing is the delay time TD for starting the operation of the EGR valve 16.
Set as 1.

Thus, step 16 or step 18
After setting the operation start delay time TD1 with
Proceeding to step 19, the current target step position (corresponding to the target control amount) EGSTPD of the EGR valve 16 is set as EGSTPD0, and then the routine proceeds to step 21. Also, step 12
When it is determined that the value of the flag F1 is not inverted,
That is, if it is not immediately after the switching signal of the valve lift characteristic is issued, it is judged in step 20 whether TD> TD1, and after that, TD1 is reset to 0 in step 21 'and then the process proceeds to step 21.

At step 21, it is judged whether or not the value of the timer TD for measuring the elapsed time after the generation of the valve lift characteristic switching signal has reached the operation start delay time TD1. If not, the routine proceeds to step 22. , The execution cycle D of the routine
Measurement is performed by adding T, and in step 23, the target step position EGSTPD of the step motor is set to EGSTPD0. That is, during this period, the EGR valve 16 is not moved and is maintained at the opening degree before the valve lift characteristic is switched to stand by.

In step 24, a drive signal is output to the step motor so as to match the set target step position EGSTPD. After that, when the measured value of the timer TD reaches the operation start delay time TD1 of the EGR valve 16, the process proceeds to step 25, where it is determined whether or not the condition for stopping the EGR is reached. When it is determined that the EGR stop condition is satisfied, after the EGR damper coefficient EGRDMP used in the calculation of the target opening area EGRAR of the EGR valve 16 described later in step 26 is set to 0,
Go to step 27.

In step 27, the target opening area EGRAR of the EGR valve 16 is calculated by the following equation. EGRR = EGRQ0 + (EGRQ × KPB-EGR
Q0) × EGRDMP where EGRQ is the target EGR flow rate, the engine speed N and the basic fuel injection amount T _P (the load equivalent value, K · Q /
(Calculated as N)), and a map set for each operating region divided by N and T _P is searched. This is because the EGR rate (EGR
The flow rate / intake air flow rate Q) is set to a value that can be obtained. Further, KPB is a differential pressure correction coefficient and is obtained by interpolating the value retrieved from the map based on the engine speed N and the throttle valve opening TVO. At high load, the required EGR flow rate also increases as the intake air flow rate Q increases,
At high load, the difference between the exhaust pressure and the intake pressure (boost pressure) decreases due to the increase of the throttle valve opening.
If the opening area is set in proportion to the flow rate, the EGR flow rate becomes insufficient due to the decrease in differential pressure. Therefore, the differential pressure correction coefficient KPB is set to correct the decrease in the differential pressure. Also, EG
The R damper coefficient EGRDMP is set to increase from 0 to 1 with the lapse of time, whereby the target opening area EGRAR gradually changes from the value EGRQ at the start of switching to the value EGRQ × KPB at the end of switching. .

In step 28, the target step position EGSTPD of the step motor for driving the EGR valve 16 for obtaining the target opening area EGRAR of the EGR valve 16 is set to EGSTPD.
-The EGRAR conversion table is used for conversion to obtain the value, and the routine proceeds to step 24, where the step motor is driven and controlled to the target step position EGSTPD. With such a configuration, when the valve lift characteristics of the intake / exhaust valve are switched, the opening degree of the EGR valve is controlled according to the change in the internal EGR amount before and after the switching so that the external EGR amount is gradually changed. Therefore, as shown in FIG. 13, it is possible to suppress the fluctuation of the total EGR amount and thus the EGR rate during the switching, which can suppress the increase of the NOx emission amount by itself, and the air-fuel ratio control for reducing the exhaust emission is also easy. And NO, CO, H in addition to NOx
Exhaust emissions can be effectively reduced comprehensively including C.

Further, since the start of the operation of the EGR valve is delayed by the difference between the time required to switch the valve lift characteristic and the time required to switch the EGR valve, and the switching end is synchronized, the switching end is substantially synchronized. The EGR rate can be converged to the target value after switching, and the EGR rate can be controlled with high accuracy. In the present embodiment, only the valve lift characteristic of the intake valve is switched, but it is also applicable to the valve lift characteristic of the exhaust valve, so that both the valve lift characteristics of the intake valve and the exhaust valve are switched. Needless to say, this embodiment is also applicable to the VVL (variable lift) according to the present embodiment, but the lift is fixed and the timing (phase) is fixed.
It is also applicable to the one that changes (VTC).

[0030]

According to the first aspect of the present invention, when the valve lift characteristic is switched, the target control amount of the EGR means is gradually changed from the value set before the switching to the value set after the switching. By making the correction, it is possible to suppress the change in the total EGR amount and thus the EGR rate even during the switching, and the air-fuel ratio control for reducing the exhaust emission becomes easy.

According to the second aspect of the present invention, the valve lift characteristic of the intake / exhaust valve can be switched so as to correspond favorably to the operating state determined by the engine speed and load. According to the third aspect of the present invention, the target control amount of the EGR means can be set so as to correspond favorably to the operating state determined by the engine speed and the load. In the invention of claim 4, the valve lift switching means and E
The switching with the GR means is completed substantially at the same time, the EGR rate can be converged to the target value after the switching, and the EGR rate can be controlled with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view of a valve lift characteristic switching device of the above embodiment.

FIG. 4 is a vertical cross-sectional view of the valve lift characteristic switching unit of the above at another position.

FIG. 5 is a transverse cross-sectional view of a portion related to the valve lift characteristic switching of the valve lift characteristic switching means of the above.

FIG. 6 is a transverse cross-sectional view of a portion related to switching of valve lift characteristics in the same state in another state.

FIG. 7 is a diagram showing a valve lift characteristic for low speed by the valve lift characteristic switching means of the same.

FIG. 8 is a diagram showing a valve lift characteristic for high speed.

FIG. 9 is a flowchart showing a preceding stage portion of the valve lift characteristic switching control and EGR control of the embodiment.

FIG. 10 is a flowchart showing the middle part of the same.

FIG. 11 is a flowchart showing the latter part of the same.

FIG. 12 is a time chart when switching valve lift characteristics according to the embodiment.

FIG. 13 is a diagram showing a characteristic of an EGR rate at the time of switching valve lift characteristics according to the embodiment.

[Explanation of symbols]

 1 internal combustion engine 2 intake passage 4 exhaust passage 5 EGR passage 6 EGR valve 7 control unit 8 intake valve 9 valve lift characteristic switching means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 43/00 301 NZ

Claims (4)

[Claims] 1. An EGR passage connecting an exhaust system and an intake system in an internal combustion engine equipped with valve lift characteristic switching means for switching lift characteristics of intake and exhaust valves in accordance with an engine operating state detected by an operating state detecting means. EGR means for controlling the flow rate of the exhaust gas that is interposed in the exhaust system and recirculated from the exhaust system to the intake system, and a target for setting a target control amount of the EGR means according to the engine operating state detected by the operating state detecting means. When the valve lift characteristic of the intake / exhaust valve is switched by the control amount setting means and the valve lift characteristic switching means, the target control amount set by the target control amount setting means is changed from the value before switching to the value after switching. EG for correcting the control amount of the EGR means so as to gradually change to
R control amount correction means, and valve lift characteristic switching EGR control means for controlling the EGR means on the basis of the control amount corrected when switching the valve lift characteristic of the intake / exhaust valve. And an EGR control device for an internal combustion engine. 2. The E of the internal combustion engine according to claim 1, wherein the valve lift characteristic switching means switches the valve lift characteristic of the intake / exhaust valve according to the rotational speed and load of the engine.
GR control device. 3. The internal combustion engine according to claim 1, wherein the target control amount setting means sets the target control amount of the EGR means according to the rotational speed and load of the engine. EGR control device. 4. An EGR delay means for delaying the operation start of the EGR means by an amount corresponding to a time required for switching the operation of the valve lift switching means to be larger than a time required for switching the control of the EGR means. The EGR control device for an internal combustion engine according to any one of claims 1 to 3.