JP2004116457A - Egr control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR control device capable of stabilizing engine rotation even when engine torque is lowered in EGR controlling. <P>SOLUTION: In the EGR control device 6, when instruction for tuning an external load 7 on is inputted, EGR controlling is started, and it is determined whether engine rotation is stable or not. When the engine rotation is determined as unstable, the external load is controlled not to be turned on. Therefore, the external load is not added when the rotation is unstable, engine stalling is prevented. The opening of an EGR valve 5 is finely adjusted so as to decrease the flow rate of EGR gas when negative pressure of an intake system 3 becomes strong during EGR controlling. Therefore, the flow rate of the EGR gas can be kept to be suitable amount under normal conditions and even when engine rotation is unstable. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EGR control device for an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art EGR control for reducing harmful components (NOx) is performed by extracting a part of exhaust gas (EGR gas) of an internal combustion engine from an exhaust system and recirculating the exhaust gas to an intake system (EGR: Exhaust Gas Recirculation Exhaust). Gas recirculation). This EGR control reduces combustion efficiency by adding an inert gas called EGR gas to the air-fuel mixture to reduce NOx.
[0003]
[Problems to be solved by the invention]
The EGR control can reduce NOx, but the engine efficiency becomes unstable due to a decrease in combustion efficiency, and the engine torque decreases. Therefore, if an external load (an engine accessory such as an air conditioner or an alternator) is turned on after the start of the EGR control and before the engine rotation is stabilized, an engine stall will occur.
[0004]
Further, in the EGR control, when the negative pressure of the intake system is high, such as during idling, a larger amount of EGR gas is introduced into the intake system than during normal control. Also in this case, a similar problem occurs due to a decrease in engine torque.
To cope with these problems, in the actual EGR control, the amount of EGR gas introduced is suppressed by tuning so that the engine rotation does not become unstable when the external load increases or during idling. However, if the amount of EGR gas is suppressed in this way, the original effect of suppressing NOx becomes insufficient.
[0005]
An object of the present invention is to provide an EGR control device that can stably maintain engine rotation even when engine torque is reduced during EGR control.
[0006]
[Means for Solving the Problems]
The present invention has been made to achieve the above object. In the EGR control device according to the present invention, when the EGR detection means detects the start of the EGR control and the determination means determines that the engine rotation is unstable, the external load switching means receives an instruction to turn on the external load. Also, control is performed so that the external load is not turned on. In this way, by prohibiting turning on the external load when the engine rotation is unstable, engine stall can be prevented.
[0007]
In another aspect of the present invention, when the EGR detecting means detects the start of the EGR control and the negative pressure detecting means for detecting the negative pressure of the intake system detects a negative pressure exceeding a predetermined value, the open state is determined. The degree adjusting means finely adjusts the opening degree of the EGR valve so as to reduce the flow rate of the EGR gas.
As a result, even if the negative pressure of the intake system increases, the amount of EGR gas introduced into the intake system is maintained at about the same level as during normal operation, so that the engine torque does not decrease.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
The configuration of an EGR control device to which the present invention is applied will be described with reference to FIG.
A gas flow path 4 is provided for extracting a part of the exhaust gas from the exhaust system 2 of the engine 1 and recirculating the exhaust gas to the intake system 3 as EGR gas. An EGR valve 5 for controlling the flow rate of the EGR gas is disposed in the gas flow path 4.
[0009]
The EGR control device 6 controls the opening of the EGR valve 5. The EGR control device 6 is incorporated in an EFI / ECU (electronic control device for an electronically controlled fuel injection device).
In addition, the EGR control device 6 performs an on / off operation of the air conditioner 7 according to an operation of the air conditioner switch. In this example, an example in which the air conditioner 7 is used as an external load is described, but the present invention is also applicable to other engine accessories such as an alternator.
[0010]
(Embodiment 1)
The first operation of the EGR control device 6 will be described with reference to the flowcharts of FIGS.
FIG. 2 shows a process for determining whether the EGR control is stable. This process is a process that has also been executed in the conventional EGR control device.
FIG. 3 shows an external load on / off control process based on the result of the determination in FIG. The operation in FIG. 2 is executed at predetermined time intervals.
[0011]
In step S1 of FIG. 2, it is determined whether EGR control has been started. This determination is made by checking a flag (under control) in the EFI / ECU. If No in step 1, the memory 8 stores that the EGR control is stable in step S4. If Yes, proceed to Step S2.
[0012]
In step 2, it is determined whether the engine rotation is stable. Although the details of this determination will be described later, the determination is made based on the elapsed time from the start of the EGR control, a change in the engine speed, and the like. If “Yes” in the step S2, the process proceeds to a step S4, and it is stored in the memory 8 that the EGR control is stable. If No, the process proceeds to step S3, where the EGR control is stored in the memory 8 if it is not stable.
[0013]
When the air conditioner switch is turned on and a signal is input to the EGR control device 6, the process in FIG. 3 starts.
In step S21, it is determined whether the EGR control is stable. If it is stored in the memory 8 as being stable (Yes), an ON signal is sent to the air conditioner 7 to start driving the air conditioner (step S22). If unstable (No), no ON signal is sent to the air conditioner 7 (step S23).
[0014]
As described above, while the EGR control is started and the engine rotation is not stabilized, even if an operation for turning on the air conditioner 7 is performed, the compressor of the air conditioner 7 does not start operating. Therefore, no extra load is applied to the engine 1 while the rotation is not stable, and no engine stall occurs. Further, since the amount of the EGR gas introduced at the start of the EGR control can be sufficiently obtained, the generation of NOx, which is the original purpose of the EGR control, can be suppressed, and the emission can be improved.
[0015]
In addition, even if it is determined in step S21 that the EGR control is not stable and the air conditioner 7 is not turned on, it is determined that the EGR control is stable while the processing of FIGS. 2 and 3 is repeated. An ON signal is sent to the air conditioner 7.
When the on / off control of the external load is performed by another ECU, the off signal of the external load may be transmitted from the EGR control device 6 to the ECU.
[0016]
Here, a specific method for determining whether or not the engine rotation in step S2 in FIG. 2 is stable will be described.
First, the stability of the engine rotation is determined by time. In this case, when the EGR control is started, the timer 9 is started. When a predetermined time has elapsed from the start of the EGR control, it is determined that the engine rotation has been stabilized.
[0017]
The above-mentioned predetermined time may be a fixed time. However, if the predetermined time is determined by using the engine speed NE and the EGR gas amount as parameters, finer adjustment is possible. In this case, when the engine speed NE increases, the predetermined time also increases. When the EGR gas amount increases, the predetermined time also increases.
In addition, the gas amount can be seen from the opening degree of the EGR valve 5 (output of EFI / ECU) and the air flow rate.
[0018]
Further, the above-mentioned predetermined time can be determined using the engine generated torque as a parameter. In this case, when the engine torque becomes small, the predetermined time is made long.
The engine generated torque is obtained from the engine speed NE and the throttle opening. These pieces of information can be those originally input to the EFI / ECU.
[0019]
The second method for determining the stability of the engine speed is based on the magnitude of the fluctuation of the engine speed NE. The engine speed NE signal enters the EFI / ECU as a rectangular wave. What is necessary is just to look at the variation of the width (pulse length) of this rectangular wave. Specifically, a change every n seconds is detected, and when the amount of change becomes equal to or less than a predetermined value, it is determined that the engine rotation is stabilized.
[0020]
With reference to FIG. 4, a modified example of the process for determining the stability of the EGR control of FIG. 2 will be described. Steps S1-S4 are the same as in FIG. Step S5 is added after Yes in step S1, and it is determined whether or not the vehicle is idling. During idling, the engine generated torque decreases. Therefore, if it is determined that the engine is idling (Yes), the process proceeds to step S3, and it is determined whether the engine rotation is stable.
[0021]
If it is determined that the engine is not idling (No), the engine generated torque has not decreased, and the process proceeds to step S4, where EGR control stability is stored. As described above, when the torque generated by the engine is sufficient, it is immediately determined that the EGR control is stable, whereby the on-control of the external load can be quickly performed. The determination as to whether the vehicle is idling can be made based on the amount of depression of the accelerator pedal.
[0022]
Step S5 may be detection of the N range state instead of detection of the idle state. The N range has a small effect on the engine generated torque and is strong against load fluctuations. Therefore, in step S5, it is determined whether or not the vehicle is in the N range. If not in the N range (Yes), the process proceeds to step S3, and in the case of the N range (No), the process proceeds to step S4.
[0023]
(Embodiment 2)
The second operation of the EGR control device 6 will be described with reference to the flowchart of FIG.
In the process of FIG. 5, steps S41 and S43 are processes that have been executed in the conventional EGR control device. That is, when the EGR control is started (step S41), the opening control (normal control) of the EGR valve 5 is started (step S43).
[0024]
In the present embodiment, step S42 is inserted between steps S41 and S43, and it is determined whether the negative pressure of the intake system 3 is strong. Here, if the negative pressure is equal to or less than the predetermined value (No), the process proceeds to step S43 to start the normal control. If the negative pressure is equal to or more than the predetermined value (Yes), fine adjustment of the opening of the EGR valve 5 is started in step S44 so that the gas flow rate of the EGR gas is reduced.
[0025]
When the negative pressure of the intake system 3 increases, the flow rate of the EGR gas flowing into the exhaust system 2 increases even if the opening degree of the EGR valve 5 is the same. As a result, the engine generated torque is reduced. On the other hand, according to the processing of this example, when the negative pressure of the intake system 3 increases at the start of the EGR control, the opening of the EGR valve 5 is finely adjusted so that the flow rate of the EGR gas decreases.
[0026]
Therefore, even if the negative pressure of the intake system 3 increases, the flow rate of the recirculated EGR gas is maintained at an appropriate flow rate. As a result, the amount of EGR gas introduced at the start of the EGR control can be sufficiently obtained, the generation of NOx can be suppressed, and the emission can be improved.
[0027]
The determination of the negative pressure of the intake system in step S42 in FIG. 5 can be made based on whether the engine is idling. Since the negative pressure of the intake system increases during idling, if an idle state is detected, step S42 becomes Yes.
In addition, the signal from the pressure sensor provided in the intake system can be used for the determination of the negative pressure in step S42. This signal is originally input to the EFI / ECU.
[0028]
The details of the fine adjustment in step S44 will be described.
In the normal control of the EGR valve 5 (step S43), the valve takes either the open position or the closed position, and the EGR gas flows when in the open position. In the fine adjustment in step S44, control is performed so that the open position is not 100% open but an intermediate position close to the closed position.
[0029]
A specific example of the fine adjustment will be described with reference to FIG.
(A) is applied when the EGR valve 5 takes only one of the open position and the closed position.
The EGR control is performed at a cycle of 100 ms. In the illustrated example, the on signal is output for a period of 70% of the EGR control cycle, and the output signal is turned off for the remaining 30% of the period. By outputting such a signal, the opening of the EGR valve 5 becomes 70%, and the flow rate of the EGR gas can be finely adjusted to 70% of that when the EGR valve is fully opened.
[0030]
(B) is applied when the EGR valve 5 is controlled by the stepping motor.
In the illustrated example, the opening 5 and the opening 4 of the EGR valve 5 are switched between 60 ms and 40 ms during the EGR control cycle (100 ms). In this case, a flow rate of 4.6 steps of the opening degree of the EGR valve is obtained as a whole. In this way, by hunting the adjacent steps, it is possible to finely adjust to an intermediate step.
[0031]
【The invention's effect】
According to the present invention, it is possible to obtain an EGR control device that can stabilize engine rotation even when engine torque decreases during EGR control.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an engine system to which an EGR control device of the present invention is applied.
FIG. 2 is a flowchart (part 1) illustrating a first operation of the EGR control device of FIG. 1;
FIG. 3 is a flowchart (part 2) illustrating a first operation of the EGR control device of FIG. 1;
FIG. 4 is a flowchart illustrating a modification of the operation in FIG. 2;
FIG. 5 is a flowchart showing a second operation of the EGR control device of FIG. 1;
FIG. 6 is a diagram illustrating fine adjustment of an EGR valve in the process of FIG. 5;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Exhaust system 3 ... Intake system 4 ... Gas flow path 5 ... EGR valve 6 ... EGR control device 7 ... Air conditioner 8 ... Memory 9 ... Timer

Claims (12)

EGR detecting means for detecting that the EGR control has started,
Determining means for determining whether the engine rotation is stable;
External load opening / closing means for turning on / off an external load, wherein when the EGR detection means detects the start of EGR control and the determination means determines that engine rotation is unstable, the external load is not turned on. External load switching means for controlling,
An EGR control device comprising: 2. The EGR control device according to claim 1, wherein the determination unit determines that the engine rotation has been stabilized when an elapsed time after the EGR detection unit detects the start of EGR control exceeds a predetermined value. 3. The EGR control device according to claim 2, wherein the predetermined value is obtained by using an engine speed and an EGR gas amount as parameters. The EGR control device according to claim 2, wherein the predetermined value is obtained by using an engine generated torque as a parameter. 2. The EGR control device according to claim 1, wherein the determination unit determines that the engine rotation is stable when the amount of change in the engine rotation speed is small. An idle detecting means for detecting an idle state is provided,
2. The EGR control device according to claim 1, wherein the external load switching unit performs control not to turn on the external load when the idle detection unit detects an idle state. 3. N range detecting means for detecting the N range,
2. The EGR control device according to claim 1, wherein the external load switching unit performs control not to turn on the external load when the N range detection unit does not detect the N range. 3. EGR detection means for detecting that EGR control has been started;
Negative pressure detecting means for detecting a negative pressure of the intake system;
An opening adjustment means for adjusting the opening of the EGR valve, wherein the EGR detection means detects the start of EGR control, and when the negative pressure detected by the negative pressure detection means exceeds a predetermined value, the EGR gas Opening adjustment means for finely adjusting the opening so as to reduce
An EGR control device comprising: 9. The EGR control device according to claim 8, wherein the EGR valve is an on / off valve, and wherein the opening degree adjustment unit finely adjusts the EGR gas amount by performing duty control on a valve on / off signal. 10. 9. The EGR valve is driven by a stepping motor, and the opening degree adjusting means finely adjusts the EGR gas amount by performing duty control of an opening degree signal designating adjacent steps with time. 2. The EGR control device according to claim 1. The EGR control device according to claim 8, wherein the negative pressure detection unit is an idle detection unit that detects an idle state. The EGR control device according to claim 8, wherein the negative pressure detection unit is a sensor that detects a pressure of an intake system.

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