JPH11125126A - Egr control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly avoid a surge by adjusting internal exhaust gas reflux(EGR). SOLUTION: In a high load region with a basic fuel injection amount Tp is being in a prescribed value Tpo or more, ignition timing control in accordance with a knocking level is performed (S1 to S3), a delay angle correction amount αat the time of this ignition timing control is compared with a threshold value αi set by an operating region and water temperature (S4, S5), when a comparison result is α>αi, it is judged that the state has entered a surge generation region, a valve overlap amount O/L of a suction/exhaust valve is decreased by a decrease amount θt set by the operating region and water temperature, an internal EGR amount is decreased (S6, S7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR (Exhaust Gas Recirculation) control device for an internal combustion engine which reduces NOx emissions while improving fuel efficiency.

[0002]

2. Description of the Related Art Conventionally, NOx is reduced by recirculating a part of exhaust gas to an intake system, and pumping loss is reduced by increasing a throttle valve opening to improve fuel efficiency. . By the way, in the knock control operation region in which the ignition timing is corrected in accordance with the knocking level and control is performed to maintain the knocking level at an appropriate level, as shown in FIG. There is a disadvantage that the ignition timing is also restricted by the EGR rate and the knock limit. Also, considering the change of knock limit range due to environmental conditions such as cooling water temperature, the variation of ignition timing, the characteristics of EGR control valve, etc., the EGR rate is set with a margin for the surge generation range and knock generation range. And the EGR rate cannot be set sufficiently high.

In view of this point, it is detected whether or not the vehicle has entered the surge generating region based on the ignition timing correction amount corresponding to the knocking level, and when the vehicle enters the surge generating region, the EGR is reduced (including stopping. The same applies hereinafter). (See Japanese Unexamined Patent Publication (Kokai) No. 4-325,752) to improve fuel economy and exhaust emission while avoiding knocking and surge.
No.).

[0004]

However, in the above-mentioned conventional surge avoidance system, the EG is required to reduce the EGR.
EGR remaining in the intake system even if the R control valve opening is reduced
The EGR reduction effect is not immediately exhibited by the gas, and the transient operation performance is reduced. If the set EGR rate is reduced in advance to avoid this, there is a problem that the fuel consumption effect is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and has a configuration in which EGR is rapidly reduced when a surge enters a surge generating region. It is an object of the present invention to provide an internal combustion engine EGR control device capable of sufficiently improving the EGR.

[0006]

According to the first aspect of the present invention, as shown in FIG. 1, an E-line connecting an exhaust system and an intake system is provided.
The EGR control valve disposed in the GR passage controls the amount of EGR from the exhaust system to the intake system, and the valve overlap amount of the intake and exhaust valves is reduced by relatively changing the lift characteristics of the intake and exhaust valves. In an EGR control device for an internal combustion engine capable of controlling and adjusting an internal EGR amount, a knocking occurrence area determining means for determining a predetermined operating area in which knocking is likely to occur based on an operating state of the engine; Knocking detection means for detecting knocking in the operation range of the engine, ignition timing correction means for correcting the ignition timing according to the detected knocking level, and a surge generation area based on a correction amount of the ignition timing according to the knocking level. Surge determination means for determining whether or not
An internal EGR amount control means for controlling the valve overlap amount of the intake / exhaust valve to adjust the internal EGR amount in a direction to avoid the surge when it is determined that the intake / exhaust valve is in the surge generating region. It is characterized by comprising.

According to the first aspect of the present invention, the knocking detection means detects the knocking level in a predetermined operating region where knocking is likely to occur, which is determined by the knocking occurrence area determination means, and the ignition timing correction means detects the knocking level. Correct the ignition timing to maintain it properly. The surge occurrence region determining means determines whether or not the vehicle is in the surge occurrence region based on the correction amount of the ignition timing. By controlling the valve overlap amount of the exhaust valve,
Adjust the GR amount. As a result, surge can be quickly avoided by adjusting the responsiveness with the internal EGR amount.

According to a second aspect of the present invention, in an operation region other than the predetermined operation region, the adjustment of the internal EGR amount based on the valve overlap amount of the intake / exhaust valve is canceled, and the surge level is detected. When the surge level is large, the opening of the EGR control valve is reduced to correct the EGR amount to decrease.

According to the second aspect of the present invention, when the operation shifts from the predetermined operation region in which the knock control is performed to an operation region other than the predetermined operation region in which the knock control is not performed, the valve of the intake / exhaust valve is closed. Adjustment of the internal EGR amount based on the lap amount is canceled to control the internal EGR amount to an appropriate value, and a surge level is detected. When the surge level is large, the opening of the EGR control valve is reduced to correct the EGR amount to decrease. So it adapts to driving conditions and
EGR control that can avoid surge can be performed. Further, the invention according to claim 3 is characterized in that the determination as to whether or not the vehicle is in the surge occurrence region is made by comparing the ignition timing retard correction amount with a threshold value set for each operation region. And

According to the third aspect of the invention, when the retard amount of the ignition timing is increased, the surge enters the surge generating region. Therefore, the limit value of the retard amount in the surge generating region is set as the surge generating threshold. However, this value differs depending on the operation region. Therefore, by setting a threshold value for each of the operation regions and comparing the retard correction amount of the ignition timing with the set threshold value, it is possible to determine the surge occurrence region with high accuracy.

Further, the invention according to claim 4 is characterized in that:
The adjustment of the GR amount is performed by reducing the valve overlap amount of the intake and exhaust valves by a reduction amount set for each operation region. According to the fourth aspect of the present invention, the amount of decrease in the valve overlap amount required to avoid the surge, that is, the internal EGR amount differs depending on the operation region. Therefore,
By setting a decrease amount of the valve overlap amount for each of the operation regions, reducing the valve overlap amount by the set decrease amount, and adjusting the internal EGR amount, it is necessary and sufficient to avoid a surge. EGR control can be performed.

According to a fifth aspect of the present invention, at least one of the threshold value for judging the surge occurrence region and the set decrease amount of the valve overlap amount of the intake and exhaust valves is corrected based on the engine coolant temperature. It is characterized by doing. According to the invention according to claim 5, the threshold value for judging the surge occurrence area,
Since the set decrease amount of the valve overlap amount of the exhaust valve also changes depending on the cooling water temperature of the engine in addition to the operation region, by correcting these values based on the cooling water temperature, more accurately. Can be set.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a system configuration according to an embodiment of the present invention. In FIG. 2, an exhaust passage 1 and an intake passage 2 of the engine are communicated by an EGR passage 3, and an EGR passage 3 is provided.
The valve body 5 of the diaphragm type EGR control valve 4 is interposed. Negative pressure air is supplied to the negative pressure chamber 6 of the EGR control valve 4 via a negative pressure control valve 7.

The negative pressure control valve 7 includes a solenoid valve 8
The solenoid valve 8 is driven and controlled by the control device 9 to control the amount of negative pressure supplied to the EGR control valve 4. Further, a variable valve timing control mechanism (VTC) 11 for controlling the opening / closing characteristics (opening / closing timing, phase angle) of the intake valve 10 is provided. The VTC 11 may be any mechanism that can change the opening / closing timing (phase angle) of the intake valve 10. For example, a mechanism used for controlling the opening / closing timing (phase angle) of the exhaust valve in JP-A-7-301106. (That is, a type in which the phase angle between the camshaft and a cam sprocket for transmitting the rotation of the crankshaft to the camshaft is changed), or a fluid as disclosed in JP-A-6-2514. Using a pressure, an electromagnetic solenoid, or the like, a mechanism or the like for opening and closing the intake valve 10 while variably setting the opening and closing timing can be used. Further, a mechanism (VET) that can variably control the lift amount and the operating angle of the intake valve 10 may be used.
At least the opening and closing timing (phase angle) may be variably controlled. Further, a VTC (or VET) for an exhaust valve may be provided instead of or in combination with the VTC (or VET) for the intake valve 10. In short, the valve overlap amount of the intake / exhaust valve may be provided. To control the internal EGR
What is necessary is just to be comprised so that quantity can be adjusted.

The control device 9 receives signals from a knocking sensor 12, a crank angle sensor 13, a water temperature sensor 14, a key switch 15 and the like as knocking detecting means, and according to the operating state (rotational speed, load) of the engine. Control of fuel injection amount, ignition timing, EGR, etc. is performed. In the ignition timing control, when a predetermined operating region (high load region) in which knocking is likely to occur based on the engine operating state is detected, the knocking level is appropriately maintained based on a signal input from the knocking sensor 12. Correct the ignition timing as follows
Further, when it is detected that the operation region has entered the surge generation region based on the correction amount of the ignition timing, the VTC
11, the internal EGR amount is reduced by correcting the overlap amount of the intake and exhaust valves to decrease. Thereafter, when the vehicle shifts to an operation region (low load region) other than the predetermined operation region, the normal EGR control is performed after the reduction correction of the internal EGR amount is canceled, and the rotational fluctuation rate and the in-cylinder pressure are also reduced. The surge level is detected from the fluctuation rate or the like, and the EGR control valve corrects the decrease in the EGR amount according to the surge level.

The control of the EGR will be described with reference to the flowchart of FIG. In step 1, detection signals from the sensors are input. In step 2, based on the detection signal, it is determined whether or not a predetermined operating region in which knocking is likely to occur, for example, a high load region in which the basic fuel injection amount Tp is equal to or greater than a predetermined value To.

If it is determined in step 2 that the engine is in the predetermined operating range, the process proceeds to step 3 in which ignition timing control is performed in accordance with the knocking level detected by knocking sensor 12. The function of step 3 constitutes ignition timing correction means. Specifically, when the knocking level is less than a predetermined value, the advance angle is corrected little by little, and when the knocking level becomes equal to or more than the predetermined value, the control for making a large retardation is repeated. A control is performed to maintain the power in the vicinity and improve the output as much as possible.

In step 4, a surge occurrence determination threshold value αi is set. Specifically, a basic threshold value αio for determining the occurrence of a surge corresponding to the operation region i determined by the current engine speed N and the basic fuel injection amount Tp representing the load is searched from the map stored in the ROM (FIG. 4), the surge threshold value αi is calculated by multiplying the basic threshold value αio by a water temperature correction coefficient KTW based on the cooling water temperature (water temperature) Tw detected by the water temperature sensor 14. That is, as shown in FIG. 7, when the ignition timing retard amount is increased under the same EGR rate condition, the surge enters the surge generation region, and the limit value of the retard amount entering the surge generation region is set to the surge generation threshold. This value differs depending on the operating region, and the water temperature T
w, the operating region and the water temperature Tw
Is set with high accuracy based on

In step 5, the ignition timing retard correction amount α at the time of knock control is compared with the surge occurrence determination threshold value αi calculated in step 4 to determine whether or not the ignition has entered the surge occurrence range. That is, step 4
And step 5 constitute the surge determination means. When it is determined in step 5 that the vehicle has entered the surge generation region, the process proceeds to step 6 and the valve overlap amount O / L of the intake / exhaust valve is set.
Is set. Specifically, the basic decrease amount θto corresponding to the current operation area i is searched from the map stored in the ROM (see FIG. 5), and the basic decrease amount θt is obtained.
o is multiplied by the water temperature correction coefficient KTW to calculate a decrease amount θt. That is, when entering the surge generation region, the internal EGR amount is reduced to avoid the surge. The decrease amount θt of the valve overlap amount O / L required to avoid the surge also differs depending on the operation region. In addition, since the temperature also changes depending on the water temperature Tw, it is set with high accuracy based on these operating regions and the water temperature Tw.

In step 7, the VTC 11 is driven to reduce the valve overlap amount O / L of the intake / exhaust valve by the decrease amount θt set in step 6. That is, the functions of steps 6 and 7 constitute the internal EGR amount adjusting means. In this manner, when the surge enters the surge generating region due to knock control, the valve overlap amount O / L of the intake / exhaust valve is reduced by a predetermined amount to improve the internal EGR with good responsiveness.
By reducing the amount, surges can be avoided quickly.

When the surge enters the surge generation region by knock control, the opening of the EGR control valve 4 may be reduced and corrected together with the external EGR amount. Then, the insufficient response delay may be covered by the correction for decreasing the internal EGR amount. After this state, when the operation region shifts to an operation region other than the predetermined operation region where knock control is not performed, for example, a low load region in which the basic fuel injection amount Tp is less than the predetermined value Tpo, the process proceeds from step 2 to step 8, The correction for decreasing the valve overlap amount O / L of the intake / exhaust valve is released, and the valve overlap amount is controlled to an appropriate amount according to the operation range.

Then, the process proceeds to a step 9, wherein the opening degree of the EGR control valve 4 set on the map is searched for each of the operating regions classified by the engine speed and the load. In step 10, the surge level β is detected based on the engine speed fluctuation rate and the in-cylinder pressure fluctuation rate. In step 11, the detected surge level β is compared with a predetermined value βo, and when it is determined that the detected surge level β is equal to or more than the predetermined value, the process proceeds to step 12, and the opening degree of the EGR control valve 4 set in step 9 is set to avoid the surge. Is reduced by a fixed amount or a correction amount corresponding to the surge level.

In step 13, the opening degree of the EGR control valve 4 is determined by the opening degree searched in step 10 or the opening degree.
Control is performed so that the opening is reduced and corrected in step 11. This makes it possible to perform EGR control that can adapt to the operating state even when the load is low and can avoid surge.

[Brief description of the 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 according to an embodiment of the present invention.

FIG. 3 is a flowchart showing an EGR control routine in the embodiment.

FIG. 4 is a map of a threshold value of a retard amount used in the embodiment.

FIG. 5 is a map of a reduction amount of a valve overlap used in the embodiment.

FIG. 6 is a diagram showing a relationship between an EGR rate and a surge limit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust passage 2 Intake passage 3 EGR passage 4 EGR control valve 9 Control device 10 Intake valve 11 VTC 12 Knocking sensor 14 Water temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02P 5/152 F02P 5/15 D 5/153

Claims (5)

[Claims] An EGR control valve interposed in an EGR passage connecting an exhaust system and an intake system provides an EGR from the exhaust system to the intake system.
Control of the internal EGR amount by controlling the valve overlap amount of the intake / exhaust valve by controlling the amount of the intake / exhaust valve and by changing the lift characteristic of the intake / exhaust valve relatively.
In the GR control device, a knocking occurrence area determining means for determining a predetermined operating area in which knocking is likely to occur based on an operating state of the engine; a knocking detecting means for detecting knocking in the determined predetermined operating area; Ignition timing correction means for correcting the ignition timing according to the detected knocking level, and surge determination means for determining whether or not the vehicle is in a surge generation range based on a correction amount of the ignition timing according to the knocking level. An internal EGR amount control means for controlling the valve overlap amount of the intake / exhaust valve to adjust the internal EGR amount in a direction to avoid the surge when it is determined that the intake / exhaust valve is in the surge generation region. An EGR control device for an internal combustion engine, comprising: 2. In an operation region other than the predetermined operation region,
Internal EG based on the valve overlap amount of the intake and exhaust valves
Release the adjustment of the R amount, detect the surge level,
2. The EGR control device for an internal combustion engine according to claim 1, wherein when the surge level is high, the opening degree of the EGR control valve is reduced to correct the EGR amount to decrease. 3. The system according to claim 1, wherein the determination as to whether or not the vehicle is in the surge occurrence region is made by comparing the ignition timing retard correction amount with a threshold value set for each operation region. Or an EGR control device for an internal combustion engine according to claim 2. 4. The method according to claim 1, wherein the adjustment of the internal EGR amount is performed by reducing the valve overlap amount of the intake and exhaust valves by a reduction amount set for each operation region. An EGR control device for an internal combustion engine according to any one of the preceding claims. 5. A threshold value for judging said surge occurrence area,
The EG of an internal combustion engine according to claim 3 or 4, wherein at least one of the set reduction amount of the valve overlap amount of the exhaust valve is corrected based on the engine coolant temperature.
R control device.