JP2000002158A - Egr control device of internal-combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increase in smokes from a diesel engine, etc., by suppressing variation of the EGR rate at the time of idling. SOLUTION: At the time of low-speed idling (S31-S32), four types of load conditions are judged in accordance with automatic transmission neutral, drive changeover, air-conditioner On-Off changeover (S32), and excessive increment of the target EGR rate STEPDM is restricted by the upper limit values L1-L4 of EGR rate set according to the respective load conditions (S33-S36).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR for an internal combustion engine.
(Exhaust gas recirculation) The present invention relates to a control device, and more particularly, to a technique for optimizing an EGR rate during idling operation in a diesel engine or the like.

[0002]

2. Description of the Related Art There is known an EGR control device for lowering a combustion temperature by recirculating a part of exhaust gas into intake air for the purpose of reducing NOx (nitrogen oxide) exhausted from an internal combustion engine (Japanese Patent Application Laid-open No. Sho. No. 60-230555). This EG
R is effective in reducing NOx, but if the EGR amount is not controlled to an appropriate amount according to the operating state, the operability deteriorates, such as deterioration of combustion and a decrease in output.

For this reason, in recent years, highly accurate EGR control has been required. In the case of a diesel engine, NOx can be reduced by increasing the EGR rate, and combustion noise can be reduced by lowering the combustion speed. However, smoke increases due to a relative decrease in intake air amount and a decrease in excess air rate, thereby increasing smoke. Therefore, it is necessary to balance these factors and control the EGR rate to an appropriate value.

During idling operation, the load varies greatly depending on whether the automatic transmission is in the neutral range and the drive, and whether the air conditioner is on or off, and the rate of change in the fuel injection amount due to the change in load conditions is large. Since the rate of change is large, it is necessary to have a characteristic in which the target EGR rate rapidly changes in accordance with this (see FIGS. 6 and 7).

[0005]

However, if the EGR control during the idling operation is performed based on the characteristic of rapidly changing the target EGR rate with respect to the fuel injection amount as described above, feedback control of the idling rotational speed and the like are performed. The target EGR rate fluctuates in response to excessive fluctuations due to the fuel injection amount caused by the above, and particularly when the EGR rate fluctuates to an excessively higher side than an appropriate value, adversely affects engine stability, smoke, and the like. .

In recent years, the actual intake air amount is detected and the target EGR ratio is corrected based on the actual intake air amount for the purpose of, for example, avoiding a shift in the EGR rate due to a change in the atmospheric density during traveling at high altitude. There has also been proposed a device which performs such a process (see JP-A-59-74364). The feedback correction of the target EGR rate based on the detected value of the intake air amount is performed by changing the intake air amount due to the adhesion of combustion products, which are likely to be generated in the diesel engine, to the EGR control valve and the fluctuation of the opening degree of the throttle valve for EGR control. Also, particularly, the supercharged engine also has a function of maintaining a desired EGR rate against a supercharging delay during acceleration.

However, when such feedback correction is performed, the fluctuation of the EGR rate due to the fluctuation of the fuel injection amount during the idling operation becomes larger. For example, when the fuel injection amount is switched to the increase (decrease) side by switching the load conditions during the idling operation, first, the EGR rate is controlled to decrease (increase) by the decrease (increase) of the target EGR rate. Since the intake air amount increases (decreases) in response, the EGR rate is increased (decreased) in response to the increase (decrease) of the intake air amount.

If the feedback correction of the EGR rate based on the detection of the intake air amount is stopped, the occurrence of hunting is considerably suppressed. However, when the intake air amount decreases due to a decrease in the atmospheric density during high altitude traveling or clogging of the air cleaner. In this case, an unfavorable state such as an increase in smoke due to the EGR rate being fixed on the increase side from the appropriate value continues. Goal E
A method in which the GR rate is fixed for each load condition also causes the same problem as described above.

The present invention has been made in view of such a conventional problem, and an internal combustion engine in which fluctuations in the EGR rate during idling operation are suppressed and at least the EGR rate is prevented from becoming excessive on the increasing side. It is an object of the present invention to provide an EGR control device.

[0010]

According to the present invention, an EGR control apparatus for an internal combustion engine that recirculates a part of exhaust gas to an intake system under a predetermined operating condition is set based on an operating state of the engine. At least a limit value for increasing the EGR rate is provided for each of different load conditions during idling operation with respect to the target EGR rate, and EGR control is performed while limiting the target EGR rate with the limit value.

With this configuration, the appropriate range of the target EGR rate is different for each different load condition during the idling operation.
A limit value on the rate increasing side is provided, and even if the target EGR rate fluctuates due to a change in the fuel injection amount or the like, the EGR control is performed while being limited by the limit value at least on the increasing side.

According to a second aspect of the present invention, there is provided an EGR control apparatus for an internal combustion engine which recirculates a part of exhaust gas to an intake system under predetermined operating conditions, as shown in FIG. State detecting means, target EGR rate setting means for setting a target EGR rate based on the detected operating state, and at least E for each different load condition during idling operation.
A limit value setting means for setting a limit value on a GR rate increasing side; and an EGR control means for performing EGR control while limiting the target EGR rate with the limit value during idling operation. I do.

According to this configuration, the target EGR rate is set on the basis of the operating state such as the engine speed and the load detected by the operating state detecting means. At least a limit value on the increasing side of the target EGR rate is set according to the appropriate range of the target EGR rate. Then, even if the target EGR rate fluctuates due to a fluctuation in the fuel injection amount or the like, the EGR control means performs the EGR control while being limited at least on the increasing side by the limit value.

According to a third aspect of the present invention, the amount of intake air is detected during the EGR control, and the detected amount of intake air is
The present invention is characterized in that a function is provided for comparing the intake air amount estimated based on the operating state of the engine with a feedback correction of the target EGR rate. The invention according to claim 4 is characterized in that a limit value on the EGR rate decreasing side with respect to the target EGR rate is set for each different load condition during the idling operation.

According to this configuration, based on the appropriate range of the target EGR rate for each different load condition at the time of idling,
The limit value on the EGR rate decreasing side is also set. Further, the invention according to claim 5 is characterized in that the different load conditions at the time of idling include four types of combined conditions of neutral of the automatic transmission range or ON / OFF of the drive and the air conditioner.

According to this configuration, since the load of the automatic transmission range neutral or on / off of the drive and the air conditioner has a large difference, the appropriate range of the target EGR rate under the four types of load conditions in which these are combined greatly differs. Therefore, a limit value is provided for each.

[0017]

According to the first and second aspects of the present invention, at least the fluctuation on the increasing side of the target EGR rate due to the fluctuation of the fuel injection amount during the idling operation is set for each of the load conditions. Since it is limited by the limit value, the increase in smoke can be suppressed while maintaining the stability of the engine. Further, even if only the increase side is limited, the amplification of the fluctuation is suppressed, and there is an effect that the increase in the fluctuation to the decrease side is simultaneously suppressed and the hunting is converged.

According to the third aspect of the present invention, in the apparatus having the function of feedback-correcting the EGR rate according to the amount of intake air, the target EGR rate fluctuates more greatly during idling, and hunting is likely to occur. The effect of limiting the target EGR rate with the limit value is greater, and the effect of correcting the deviation of the EGR rate corresponding to the change in the atmospheric density during high altitude traveling by the feedback correction can be enjoyed as it is.

According to the fourth aspect of the present invention, when the EGR rate fluctuates excessively on the decreasing side, NOx increases and the combustion noise increases, but the excessive decrease of the EGR rate is prevented by the limit value on the decreasing side. Can be reliably restricted, which allows N
Ox and combustion noise can be prevented from increasing. According to the fifth aspect of the present invention, the appropriate range of the target EGR rate is greatly different.
By setting limit values for each of the load conditions,
The EGR rate can be appropriately limited for each load condition.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a schematic configuration of a diesel engine provided with the EGR control device according to the present invention. In the figure, an intake passage 12 and an exhaust passage 13 of an engine 11
The EGR passage 14 is connected through the R passage 14.
An EGR control valve 15 is provided halfway. The EGR
The opening of the valve 15 is controlled substantially continuously from a fully closed position to a fully opened position by an actuator 16.

A throttle valve 17 is provided in the intake passage 12 upstream of the outlet of the EGR passage 14 and an actuator 18 for driving the throttle valve 17 to open and close is provided. The driving of each of the actuators 16 and 18 is controlled by the control unit 19 based on the detection results of various operating states. Under operating conditions requiring a relatively large amount of EGR, the throttle valve 17 is closed and adjusted to adjust the downstream position. The opening of the EGR valve 15 is controlled in a state where a negative pressure is generated on the side. When the EGR amount is small or E
When GR is not performed, the throttle valve 17 is controlled to the fully open position.

A control unit 19 for controlling the actuators 16 and 18 is constituted by a microcomputer having an input / output circuit and a memory, and has a function of various arithmetic means according to the present invention. The control unit 19 receives the engine speed N and the target fuel injection amount Tp as a load representative value as basic operating state parameters for determining the fuel injection amount and the fuel injection timing. It is also used to determine and correct the EGR rate. Also, to correct the target EGR rate,
The cooling water temperature Tw from the water temperature sensor 20 and the intake air amount QAC from the air flow meter 21 are input. The air flow meter 21 is provided upstream of the throttle valve 17 in the intake passage 12 and detects a flow rate of fresh air sucked into the engine 1. In addition, an idle switch 22 that is added to an accelerator sensor or the like to detect idle operation of the engine, a neutral switch 23 that determines whether the automatic transmission is in a neutral range (drive range),
An air conditioner switch 24, a vehicle speed sensor 25, and the like are input to the control unit 19.

FIGS. 3 and 4 show a control routine of the EGR control valve opening according to the present invention in an engine equipped with such an EGR control device. This routine is periodically repeated by the microcomputer in the control unit 19 every several milliseconds to several tens of milliseconds. In FIG. 3, a step (referred to as S in the figure, the same applies hereinafter) In step 1, first, the engine speed N, the fuel injection amount Tp, and the intake air amount QA
C, the cooling water temperature Tw is detected.

In step 2, based on the detection results, it is determined whether or not the engine is in an operation range in which EGR is to be performed by collation with a preset table or the like. This allows
For example, in a low load range, a low rotation range, at the time of starting, at the time of warming-up, etc., the process proceeds to step 3, where the throttle valve 17 is fully opened and the EGR
The control valve 15 is fully closed to stop EGR.

On the other hand, if it is determined that the operating range is such that the EGR is performed, then in steps 4 and 5, the opening of the throttle valve 17 and the opening of the EGR control valve 15 are sequentially calculated, and each actuator 18 is operated. , 16 are controlled so as to have a predetermined opening. FIG. 4 shows a flowchart of a routine for controlling the opening of the EGR control valve 15 in step 5 described above.

First, at step 11, the engine speed N
The target EGR rate MEGRM is calculated by a search from a three-dimensional map based on and the basic fuel injection amount Tp.
Next, at step 12, a first correction amount KEGR1 for the target EGR rate MEGRM is calculated based on the cooling water temperature Tw detected by the water temperature sensor 20. In general, the first correction amount KEGR1 has a characteristic of reducing the EGR amount in consideration of the fact that NOx is less likely to be generated as the engine temperature is lower and the cylinder wall is more likely to be worn by carbon whose generation amount is increased by EGR. It is set to have. In the present embodiment, the first correction amount KEGR1
Is set as a coefficient by which the basic value MEGRM is multiplied, as will be described later. As the first correction amount KEGR1, a correction based on the fuel injection timing, the atmospheric pressure, and the like may be included.

Next, at step 13, in order to correct the change in the intake air amount accompanying the change in the EGR rate by the first correction amount KEGR1, first, the total intake gas amount to the cylinder (intake air amount + EGR gas amount) ), The basic correction amount A as the rate of change of the intake air amount is calculated by the following equation based on the target EGR rate MEGRM and the first correction amount KEGR1. However, it is calculated in two ways according to the difference in the setting of the EGR rate.

When the EGR rate is set as EGR gas amount / intake air amount, A = (1 + MEGRM) / (KEGR1 × MEGRM +
1) When the EGR rate is set as EGR gas amount / (EGR gas amount + intake air amount), A = (1−KEGR1 × MEGRM) / (1−MEGR)
M) Actually, when the EGR rate changes, the total intake gas amount to the cylinder itself changes, but at least in an operating range in which EGR is used at least in a range where there is no deterioration in combustion or the like, the change rate of the EGR rate is constant. Therefore, based on this tendency, EG using the first correction amount KEGR1 as a parameter
A correction coefficient (volume efficiency correction coefficient) of an intake air amount according to a change in volume efficiency due to a change in the R rate. A characteristic of CQACC is created as a two-dimensional map using only the first correction amount KEGR1. By using the two-dimensional map, the required capacity of the CPU can be minimized.

In step 14, the first correction amount KEGR1
, A volume efficiency correction coefficient CQACC is calculated by searching the two-dimensional map. In step 15, based on the basic correction amount A and the volume efficiency correction coefficient CQACC, a correction amount Z of the intake air amount is calculated by the following equation. Z = A × CQACC In step 16, the operating state parameter used for setting the target EGR rate MEGRM, that is, the engine speed N
And the basic intake air amount BQ based on the basic fuel injection amount Tp
Calculate AC. The calculation of the basic intake air amount BQAC is the intake air amount when EGR is performed at the same engine speed N and the target EGR rate MEGRM at the basic fuel injection amount Tp, and is calculated by a search from a three-dimensional map or the like. I do.

In step 17, the basic intake air amount B
The QAC is corrected according to the following equation based on the correction amount Z calculated in step 15, and the corrected intake air amount BQAC
Calculate K. BQACK = BQAC × Z Next, at step 18, based on the intake air amount QAC detected by the air flow meter 21 and the corrected intake air amount BQACK, a second correction amount K of the target EGR rate is calculated.
EGR2 is calculated. This second correction amount KEGR2 is Q
The setting is made so as to increase in proportion to the ratio between AC and BQACK (QAC / BQACK). This is because when the actual intake air amount exceeds the target value under the condition that the opening degree of the EGR control valve 15 is constant, the EGR rate decreases. Actually, since it is related to the engine speed N, it is calculated by a search from a three-dimensional map based on the QAC / BQACK and the engine speed N.

In step 19, the target EGR rate ME
GRM is divided into a first correction amount KEGR1 and a second correction amount KEGR.
2 and the final target EGR rate MEGR
Is calculated. In step 20, the final target EG
R rate MEGR, engine speed N, and basic fuel injection amount T
Based on p, the opening degree of EGR control valve 15 (the number of steps in the case of stepping motor drive) STEPDM is calculated.

In step 21, for each load condition during idling operation, an excessive increase in the opening degree STEPDM of the EGR control valve 15 corresponding to the target EGR rate MEGR is limited by upper limit values L1 to L4. FIG. 5 shows a flowchart of a routine for limiting the increase in the EGR control valve opening degree, that is, the increase in the EGR rate in step 21.

In step 31, it is determined whether the idling switch 22 is on and the vehicle speed detected by the vehicle speed sensor 25 is lower than a predetermined value. Is determined. If it is determined that the engine is not idling at the time of low rotation, it is determined that the engine is in an operating state in which the EGR rate does not fluctuate greatly, and the restriction on the EGR rate increasing side is not performed.
Go to step 22 of.

In the idling operation state at the time of low rotation,
That is, if it is determined that the driving state is such that the EGR rate is likely to fluctuate greatly, the process proceeds to step 32, and the load condition is determined based on the signals from the neutral switch 23 and the air conditioner switch 24. And, the automatic transmission is in the neutral range, and the first load condition in which the air conditioner is off, the automatic transmission is in the neutral range, and the second load condition in which the air conditioner is on, the automatic transmission is in the drive range, and Four types of load conditions, that is, a third load condition in which the air conditioner is off, a drive range in which the automatic transmission is in the drive range, and a fourth load condition in which the air conditioner is on, are determined. The increase in the opening degree STEPDM of the EGR control valve 15 is limited by the set upper limit values L1 to L4. Specifically, the opening degree STEPDM is compared with the upper limit values L1 to L4, and the smaller value is selected. Here, the upper limit value L1
L4 are set such that L1>L2>L3> L4 in accordance with the characteristic that the EGR rate needs to be reduced as the load increases sequentially from the first load condition to the fourth load condition. ing.

After limiting the increase in the EGR control valve opening (increase in the EGR rate) for each load condition as described above, the routine proceeds to step 22 in FIG. In step 22, a signal corresponding to the opening degree STEPD of the EGR control valve 15, which is limited as described above under the predetermined operating conditions and is otherwise set without any restriction, is output to the actuator 16 to output the EGR control valve 15 to control the opening degree to be the opening degree STEPD.

With this arrangement, at the time of the predetermined idling operation, the EGR rate fluctuates along with the fluctuation of the fuel injection amount due to the idle speed feedback control and the switching of the load condition, and further, the feedback correction based on the intake air amount is performed. , The fluctuation of the EGR rate is about to be amplified, whereas the fluctuation on the EGR rate increasing side is set to E for each load condition.
Since the EGR rate is limited by the limit value on the GR rate increasing side, it is possible to prevent the EGR rate from excessively increasing, thereby suppressing the increase in smoke while securing the stability of the engine.
It should be noted that the amplification of the fluctuation is suppressed only by limiting the increase side, and the increase of the fluctuation toward the decrease side can be suppressed at the same time.

Also, a lower limit value may be set on the EGR rate decreasing side to limit an excessive decrease in the EGR rate. In this case, the lower limit value is set to a smaller value for each load condition as the load becomes larger, and the larger value is selected by comparing the EGR control valve opening after the limiting process with the upper limit value and the lower limit value. What is necessary is just to be a structure. In this way, an excessive decrease in the EGR rate is also reliably suppressed at the lower limit value, so that the NOx reduction function and the combustion noise reduction function can be sufficiently ensured.

[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 a main routine of an EGR control routine according to the embodiment.

FIG. 4 is a flowchart showing a subroutine for setting an EGR control valve opening degree.

FIG. 5 is a flowchart showing a subroutine for limiting an EGR control valve opening degree.

FIG. 6 is a characteristic diagram of a target EGR rate map.

FIG. 7 is a diagram showing a target EGR characteristic during low-speed idling.

[Description of Signs] 11 Diesel engine 12 Intake passage 13 Exhaust passage 14 EGR passage 15 EGR control valve 16 Actuator 17 Throttle valve 18 Actuator 19 Control unit 20 Water temperature sensor 21 Air flow meter 22 Idle switch 23 Neutral switch 24 Air conditioner switch 25 Vehicle speed sensor

Claims (5)

[Claims] An EGR control device for an internal combustion engine that recirculates a part of exhaust gas to an intake system under a predetermined operation condition, wherein a target EGR rate set based on an operation state of the engine is different for each different load condition during idle operation. At least E
An EGR control device for an internal combustion engine, wherein a limit value on a GR rate increasing side is provided, and EGR control is performed while limiting the target EGR rate by the limit value. 2. An EGR control device for an internal combustion engine that recirculates a part of exhaust gas to an intake system under a predetermined operating condition, comprising: operating condition detecting means for detecting an operating condition of the engine; and a target based on the detected operating condition. A target EGR rate setting means for setting an EGR rate, and at least an EGR for each of different load conditions during idling operation.
Limit value setting means for setting a limit value on the rate increasing side; and EGR control means for performing EGR control while limiting the target EGR rate with the limit value during idling operation. An EGR control device for an internal combustion engine. 3. A function of detecting an intake air amount during the EGR control and comparing the detected intake air amount with an intake air amount estimated based on an operation state of the engine to perform feedback correction of a target EGR rate. The EGR control device for an internal combustion engine according to claim 1 or 2, further comprising: 4. An internal combustion engine according to claim 1, wherein a limit value for decreasing the EGR rate with respect to the target EGR rate is set for each of different load conditions during the idling operation. EGR control device. 5. The different load conditions during the idling operation are as follows:
The EGR control device for an internal combustion engine according to any one of claims 1 to 4, wherein the condition includes four kinds of combined conditions of neutral or drive of an automatic transmission range and ON / OFF of an air conditioner. .