JP3757569B2 - EGR control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EGR control device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust system is regarded as the actual air-fuel ratio of the engine, then the target air-fuel ratio is calculated from the engine speed and the required fuel injection amount, and further detected There is known an EGR control device for an internal combustion engine that feedback-controls the EGR valve opening so that the air-fuel ratio thus made matches the target air-fuel ratio. This EGR control device can control the flow rate (EGR amount) of the exhaust gas recirculated from the exhaust system to the intake system by controlling the EGR valve opening degree. An example of this type of EGR control device for an internal combustion engine is disclosed in, for example, Japanese Patent Laid-Open No. 58-140461.
[0003]
[Problems to be solved by the invention]
The air-fuel ratio sensor of the EGR control device for an internal combustion engine described in the above publication is provided in the exhaust system downstream of the engine. Therefore, the air-fuel ratio detected by the air-fuel ratio sensor during steady engine operation is equal to the actual air-fuel ratio of the engine, but the air-fuel ratio detected by the air-fuel ratio sensor during transient engine operation is the actual air-fuel ratio of the engine. Different from fuel ratio. However, the EGR control device for an internal combustion engine disclosed in the above publication incorrectly sets the air-fuel ratio detected by the air-fuel ratio sensor, which is different from the actual air-fuel ratio of the engine, to be different from the actual air-fuel ratio of the engine. I consider it. Therefore, the EGR valve opening is controlled so that the air-fuel ratio detected by the air-fuel ratio sensor, which is mistakenly regarded as the actual air-fuel ratio of the engine, matches the target air-fuel ratio, and the EGR amount is appropriately set. I can't control it. As a result, emissions will deteriorate.
[0004]
In addition, when the dimensions of the parts of the fuel injection device such as a pump, an injector, etc. vary during manufacturing or change due to deterioration over time, the required fuel injection amount is actually injected. The actual fuel injection amount is different. However, since the EGR control device for an internal combustion engine in the above publication calculates the target air-fuel ratio based on the required fuel injection amount instead of the actual fuel injection amount, the target air-fuel ratio becomes inaccurate. Therefore, the EGR valve opening is controlled so that the air-fuel ratio detected by the air-fuel ratio sensor matches the inaccurate target air-fuel ratio, and the EGR amount cannot be controlled appropriately. As a result, emissions will deteriorate.
[0005]
In view of the above problems, an object of the present invention is to provide an EGR control device for an internal combustion engine that can accurately calculate the actual air-fuel ratio of the engine even during transient operation of the engine.
[0006]
A further object of the present invention is to provide an EGR control device for an internal combustion engine that can accurately calculate a target air-fuel ratio, which is a control target of the EGR valve opening, regardless of the deterioration of the fuel injection device with time. .
[0007]
[Means for Solving the Problems]
According to the first aspect of the present invention, the intake system that communicates with the internal combustion engine is provided with the new amount detection means, and the exhaust system that extends from the internal combustion engine is provided with the air-fuel ratio detection means, and further the exhaust gas In an EGR control device for an internal combustion engine having an EGR valve in an EGR passage communicating the intake system and the intake system, during steady operation of the internal combustion engine, the internal combustion engine is controlled based on a detection value of the air-fuel ratio detection means. An actual air-fuel ratio is calculated, and an actual fuel injection amount actually injected into the internal combustion engine is calculated on the basis of the detection value of the new amount detection means and the detection value of the air-fuel ratio detection means. Calculating a target air-fuel ratio of the internal combustion engine based on the injection amount, and further calculating a difference obtained by subtracting the required fuel injection amount at the time of steady operation determined according to the operation state of the internal combustion engine from the actual fuel injection amount; Of the internal combustion engine During the transfer operation, the actual air-fuel ratio of the internal combustion engine is calculated based on the detection value of the new amount detection means, and the difference is calculated to the required fuel injection amount during the transient operation determined according to the operation state of the internal combustion engine. Is calculated, the target air-fuel ratio of the internal combustion engine is calculated based on the corrected required injection amount, and the opening degree of the EGR valve is adjusted so that the actual air-fuel ratio matches the target air-fuel ratio. An EGR control device for an internal combustion engine is provided.
[0008]
The EGR control device for an internal combustion engine according to claim 1 is supplied to the internal combustion engine instead of the detection value of the air-fuel ratio detection means provided in the exhaust system downstream of the internal combustion engine during the transient operation of the internal combustion engine. The actual air-fuel ratio of the internal combustion engine is calculated based on the detected value of the fresh air amount detecting means for detecting the fresh air amount. Further, even during the transient operation of the internal combustion engine, the fresh air amount detected by the fresh air amount detecting means is substantially equal to the fresh air amount actually supplied to the internal combustion engine. Therefore, the actual air-fuel ratio of the internal combustion engine can be accurately calculated even during transient operation of the internal combustion engine.
[0010]
Further, the EGR control device for an internal combustion engine according to claim 1 is a fresh air amount detection means, not a supply fuel injection amount at the time of steady operation determined according to an operation state of the internal combustion engine, during steady operation of the internal combustion engine. The target air-fuel ratio of the internal combustion engine is calculated based on the actual fuel injection amount calculated on the basis of the detected value and the detected value of the air-fuel ratio detecting means. Therefore, the target air-fuel ratio of the internal combustion engine can be accurately calculated even when the actual fuel injection amount and the required fuel injection amount are not equal due to deterioration with time of the fuel injection device or the like. On the other hand, at the time of transient operation of the internal combustion engine, the target air-fuel ratio of the internal combustion engine is calculated based on a correction required injection amount that takes into account deterioration with time of the fuel injection device. Therefore, similarly, the target air-fuel ratio of the internal combustion engine can be accurately calculated regardless of the deterioration of the fuel injection device with time.
[0012]
Furthermore, the EGR control apparatus for an internal combustion engine according to claim 1 controls the EGR valve opening so that the accurately calculated actual air-fuel ratio coincides with the accurately calculated target air-fuel ratio. Therefore, the amount of EGR can be appropriately controlled, and emission can be prevented from deteriorating.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0014]
FIG. 1 is a schematic configuration diagram of an embodiment of an EGR control apparatus for an internal combustion engine according to the present invention. In FIG. 1, 1 is an engine, 2 is an intake pipe communicating with the engine 1, and 3 is an air flow meter provided in the intake pipe 2 for detecting the amount of fresh air supplied to the engine 1. Reference numerals 4 and 5 denote an air cleaner and a throttle valve respectively provided in the intake pipe 2. An exhaust pipe 6 extends from the engine 1, and an air-fuel ratio sensor 7 is provided in the exhaust pipe 6 for detecting an air-fuel ratio in the exhaust pipe 6. 8 is an EGR passage communicating the exhaust pipe 6 and the intake pipe 2, 9 is an EGR valve provided in the EGR passage 8, 10 is a negative pressure control valve for driving the EGR valve 9, and 11 is a negative pressure control. This is a negative pressure source for supplying a negative pressure to the valve 10. 12 is an accelerator opening sensor, 13 is an engine speed sensor, and 14 is a fuel injection device. An ECU 15 is electrically connected to the air flow meter 3, the air-fuel ratio sensor 7, the EGR valve 9, the negative pressure control valve 10, the accelerator opening sensor 12, the engine speed sensor 13, and the fuel injection device 14.
[0015]
The ECU 15 injects the fuel injection device 14 based on signals from the air flow meter 3, the air-fuel ratio sensor 7, the accelerator opening sensor 12 and the engine speed sensor 13 and a signal indicating the actual opening of the EGR valve 9. The fuel injection amount and the opening degree of the EGR valve 9 are feedback-controlled. FIG. 2 is a flowchart showing an EGR control method for an internal combustion engine according to this embodiment. Hereinafter, an EGR control method for an internal combustion engine according to the present embodiment will be described with reference to FIGS. 1 and 2.
[0016]
The internal combustion engine EGR control method starts, for example, at the same time as the engine 1 is started. First, in step 101, the accelerator opening degree sensor 12 and the engine speed sensor 13 detect the accelerator opening degree and the engine speed. Subsequently, at step 102, the required fuel injection amount is calculated from the accelerator opening, the engine speed, and the map shown in FIG. FIG. 3 is a map showing the relationship among the accelerator opening, the engine speed, and the required fuel injection amount. As shown in FIG. 3, the required fuel injection amount increases as the engine speed increases and as the accelerator opening increases.
[0017]
In step 103, the engine speed is detected again. Subsequently, at step 104, the engine speed change rate is calculated from the engine speed detected at step 101 and the engine speed detected at step 103. In step 105, the engine speed change rate is compared with a predetermined value stored in the ECU 15 in advance. If the engine speed change rate is equal to or less than the predetermined value, it is determined that the engine 1 is in steady operation. If the engine speed change rate is larger than the predetermined value, it is determined that the engine 1 is in a transient operation, and the process proceeds to step 111.
[0018]
In another embodiment, instead of step 103, the accelerator opening is detected, and instead of step 104, the accelerator opening detected in step 101 and the accelerator opening detected in place of step 103 are It is also possible to calculate the opening degree change rate. Subsequently, instead of step 105, the rate of change of the accelerator opening is compared with a predetermined value stored in the ECU 15 in advance. If the rate of change of the accelerator opening is equal to or less than the predetermined value, the engine 1 is in steady operation. If it is determined that there is an accelerator opening change rate greater than a predetermined value, it may be determined that the engine 1 is in a transient operation and the process may proceed to step 111.
[0019]
Returning to FIG. 2, subsequently, in step 106, the air flow meter 3 and the air-fuel ratio sensor 7 detect the amount of fresh air and the air-fuel ratio in the exhaust pipe 6. In this case, since the engine 1 is in steady operation, the air-fuel ratio in the exhaust pipe 6 is substantially equal to the actual air-fuel ratio in the engine 1. Therefore, in step 107, the air-fuel ratio in the exhaust pipe 6 detected in step 106 is regarded as the actual air-fuel ratio in the engine 1. Subsequently, at step 108, the actual fuel injection that is the fuel injection amount actually injected from the fuel injection device 14 into the engine 1 from the fresh air amount and the actual air-fuel ratio (the air-fuel ratio detected by the air-fuel ratio sensor 7). The amount (= new air amount × constant / actual air-fuel ratio) is calculated.
[0020]
Subsequently, in step 109, in order to confirm the difference between the requested fuel injection amount commanded from the ECU 15 to the fuel injection device 14 and the actual fuel injection amount actually injected into the engine 1 and burned, step 102 is performed. A difference ΔQ (= actual fuel injection amount−required fuel injection amount) is calculated from the required fuel injection amount calculated in step 1 and the actual fuel injection amount calculated in step 108.
[0021]
Subsequently, at step 110, the target air-fuel ratio is calculated from the engine speed detected at step 101, the actual fuel injection amount calculated at step 108, and the map shown in FIG. . FIG. 4 is a map showing the relationship between the engine speed, the actual fuel injection amount (or correction required fuel injection amount described later), and the target air-fuel ratio. As shown in FIG. 4, the target air-fuel ratio increases as the engine speed increases and as the actual fuel injection amount increases. Subsequently, in step 115, the opening degree of the ECU valve 9 is controlled via the negative pressure control valve 10 so that the actual air-fuel ratio calculated in step 107 matches the target air-fuel ratio calculated in step 110. , The process proceeds to step 116.
[0022]
On the other hand, in step 111, the air flow meter 3 detects a fresh air amount. Subsequently, in step 112, a corrected required fuel injection amount (= requested fuel injection amount + difference ΔQ) is calculated from the required fuel injection amount calculated in step 102 and the difference ΔQ calculated in step 109, and the corrected required fuel is calculated. The injection amount is regarded as the actual fuel injection amount. Subsequently, at step 113, the actual air-fuel ratio (= new air amount / correction required fuel) is calculated from the fresh air amount detected at step 111 and the correction required fuel injection amount (actual fuel injection amount) calculated at step 112. (Injection amount) is calculated. Subsequently, at step 114, the target air-fuel ratio is determined from the engine speed detected at step 101, the correction required fuel injection amount (actual fuel injection amount) calculated at step 112, and the map shown in FIG. calculate. Subsequently, in step 115, the opening degree of the ECU valve 9 is controlled via the negative pressure control valve 10 so that the actual air-fuel ratio calculated in step 113 matches the target air-fuel ratio calculated in step 114. , The process proceeds to step 116.
[0023]
In step 116, it is determined whether or not to end the program. For example, when the engine 1 is stopped, the program is ended. When the engine 1 is not stopped, it is determined that the program is not ended. Repeat the steps.
[0024]
As described above, the EGR control device for the internal combustion engine of the present embodiment has the exhaust pipe 6 because the air-fuel ratio in the exhaust pipe 6 and the actual air-fuel ratio in the engine 1 are substantially equal during the steady operation of the engine 1. By considering the air-fuel ratio detected by the air-fuel ratio sensor 7 provided in the engine 1 as the actual air-fuel ratio in the engine 1, the actual air-fuel ratio in the engine 1 can be accurately obtained. On the other hand, since the air-fuel ratio in the exhaust pipe 6 and the actual air-fuel ratio in the engine 1 are different during transient operation of the engine 1, the actual air-fuel ratio in the engine 1 is determined from the air-fuel ratio detected by the air-fuel ratio sensor 7. Is not calculated. Instead, the actual air-fuel ratio in the engine 1 is calculated from the fresh air amount detected by the air flow meter 3 and the correction required fuel injection amount. Therefore, the actual air-fuel ratio in the engine 1 can be accurately calculated even during transient operation of the engine 1. As described above, the correction required fuel injection amount is obtained by correcting the required fuel injection amount calculated by the map of FIG. 3 by the difference ΔQ calculated at the time of steady operation such as idling after the engine is started. This is a calculated value, which is substantially equal to the actual fuel injection amount actually injected into the engine 1. Further, the amount of fresh air detected by the air flow meter 3 is substantially equal to the amount of fresh air actually supplied to the engine 1 even during transient operation of the engine.
[0025]
Further, the EGR control device for an internal combustion engine of the present embodiment is configured so that the amount of fresh air detected by the air flow meter 3 and the air-fuel ratio detected by the air-fuel ratio sensor 7 during actual operation of the engine 1 (actual in the engine 1). The actual fuel injection amount is calculated on the basis of the air-fuel ratio. Subsequently, the target air-fuel ratio is calculated from the map of FIG. 4 based on the actual fuel injection amount instead of the required fuel injection amount calculated by the map of FIG. Therefore, the actual fuel injection amount actually injected from the fuel injection device 14 to the engine 1 is different from the required fuel injection amount calculated by the map of FIG. In addition, the target air-fuel ratio can be accurately calculated. On the other hand, even during the transient operation of the engine 1, the required fuel injection amount calculated by the map of FIG. 3 is not used as it is, but the target air-fuel ratio is calculated, but the required fuel injection amount is corrected by the difference ΔQ. Based on the required fuel injection amount, the target air-fuel ratio is calculated from the map of FIG. Therefore, similarly, the target air-fuel ratio can be accurately calculated regardless of the deterioration with time of the fuel injection device 14 or the like.
[0026]
In addition, the EGR control apparatus for an internal combustion engine according to the present embodiment ensures that the actual air-fuel ratio calculated accurately matches the target air-fuel ratio calculated accurately regardless of whether the engine 1 is in steady operation or transient operation. In addition, the opening degree of the EGR valve 9 is controlled via the negative pressure control valve 10. Therefore, the EGR amount can be appropriately controlled, and the emission can be prevented from deteriorating.
[0027]
【The invention's effect】
According to the first aspect of the present invention, the actual air-fuel ratio of the internal combustion engine can be accurately calculated even during transient operation of the internal combustion engine.
[0028]
According to the second aspect of the present invention, it is possible to accurately calculate the target air-fuel ratio, which is a control target for the EGR valve opening, regardless of the deterioration of the fuel injection device over time.
[0029]
According to the third aspect of the present invention, the EGR amount can be appropriately controlled, and the deterioration of emission can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an EGR control device for an internal combustion engine of the present invention.
FIG. 2 is a flowchart showing an EGR control method for an internal combustion engine.
FIG. 3 is a map showing a relationship among an accelerator opening, an engine speed, and a required fuel injection amount.
FIG. 4 is a map showing the relationship among engine speed, required fuel injection amount, and target air-fuel ratio.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Intake pipe 3 ... Air flow meter 6 ... Exhaust pipe 7 ... Air-fuel ratio sensor 8 ... EGR passage 9 ... EGR valve

Claims (1)

The intake system communicating with the internal combustion engine is provided with a new amount detection means, the exhaust system extending from the internal combustion engine is provided with an air-fuel ratio detection means, and the exhaust system and the intake system are communicated with each other. In an EGR control device for an internal combustion engine having an EGR valve in an EGR passage,
During steady operation of the internal combustion engine, the actual air-fuel ratio of the internal combustion engine is calculated based on the detection value of the air-fuel ratio detection means, and the detected value of the new amount detection means and the detection value of the air-fuel ratio detection means The actual fuel injection amount actually injected into the internal combustion engine is calculated based on the actual fuel injection amount, the target air-fuel ratio of the internal combustion engine is calculated based on the actual fuel injection amount, and is further determined according to the operating state of the internal combustion engine. Calculate the difference obtained by subtracting the required fuel injection amount during steady operation from the actual fuel injection amount,
During the transient operation of the internal combustion engine, the actual air-fuel ratio of the internal combustion engine is calculated based on the detection value of the new amount detection means, and the required fuel injection during the transient operation determined according to the operation state of the internal combustion engine Calculating a correction required injection amount obtained by adding the difference to the amount and calculating a target air-fuel ratio of the internal combustion engine based on the correction required injection amount;
An EGR control device for an internal combustion engine , wherein the opening degree of the EGR valve is controlled so that the actual air-fuel ratio matches the target air-fuel ratio .

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