JPH11280525A - Air/fuel ratio control method for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of exhaust emission due to a response delay, by quickening response of air/fuel ratio control when an opening of an EGR (exhaust gas recirculation) valve or an intake throttle valve is large. SOLUTION: In an air/fuel ratio control method for a diesel engine having an EGR valve 42 provided in an EGR passage 41 recirculating part of exhaust gas to the diesel engine 11 by connecting its intake/exhaust passages 16, 24 and an intake throttle valve 25 provided in the intake passage 16 to control air/fuel ratio in the target air/fuel ratio in accordance with an operating condition of the engine, a deviation amount of air/fuel ratio relating to the target air/fuel ratio is corrected by variably changing an opening of the EGR valve 42 when the EGR valve opening is decided less than a prescribed opening, by deciding whether the opening of the EGR valve 42 exceeds the prescribed opening or not. When the EGR valve opening is decided to exceed the prescribed opening, a deviation amount of air/fuel ratio relating to the target air/fuel ratio is corrected by variably changing an opening of the intake throttle valve 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control method for a diesel engine, and more particularly to an air-fuel ratio control method for a diesel engine having an EGR valve and an intake throttle valve.

[0002]

2. Description of the Related Art A conventional diesel engine (hereinafter referred to as a diesel engine)
An EGR (exhaust gas recirculation) control method of an engine includes an EGR passage provided in an EGR passage that communicates an intake passage and an exhaust passage of the engine and recirculates a part of exhaust gas to the engine.
An EGR valve and an intake throttle valve provided in an intake passage of the engine are provided, and the EGR amount and the intake air amount are varied by varying the opening degree of the EGR valve and the intake throttle valve to change the exhaust air-fuel ratio of the engine. Some control the target air-fuel ratio according to the operating state.

However, such a control method has a problem that when the engine is in a transient operation state, the response of the EGR valve and the intake throttle valve is delayed, so that smoke is generated and NOx increases. To solve this problem, Japanese Patent Application No. Hei 9-170562, entitled "Intake throttle valve control device for an engine with EGR control" proposed by the applicant of the present invention, discloses a method of opening an EGR valve and an intake throttle valve in accordance with the operating state of the engine. Controlling the EGR amount to the target amount by cooperatively controlling the degree to the respective target opening degree, that is, the deviation between the actual opening degree of one of the EGR valve and the intake throttle valve and the target opening degree is a predetermined value or more. In this case, the other opening of the EGR valve or the intake throttle valve is controlled to a different target opening according to the operating state of the engine.

[0004]

However, the intake throttle valve control apparatus for an engine with EGR control proposed in Japanese Patent Application No. 9-170562 is designed to change the degree of opening of the EGR valve or the intake throttle valve to thereby reduce the exhaust of the engine. Although the air-fuel ratio control is performed to set the air-fuel ratio to a target air-fuel ratio in accordance with the operating state of the engine, when the opening of both the EGR valve and the intake throttle valve increases, the EGR passage and the intake passage change with respect to a change in the opening. The change in the opening area is reduced, and the response of the air-fuel ratio control is delayed. During this response delay, there is a problem that the exhaust emission deteriorates.

Therefore, the present invention solves the above-mentioned problems, and
An object of the present invention is to provide an air-fuel ratio control method for a diesel engine that avoids both the opening of the GR valve and the intake throttle valve from becoming large, increases the response speed in the air-fuel ratio control, and suppresses the deterioration of exhaust emissions due to a response delay. I do.

[0006]

An air-fuel ratio control method for a diesel engine according to the present invention, which solves the above-mentioned problems, communicates an intake passage and an exhaust passage of a diesel engine to recirculate a part of exhaust gas to the engine. EG provided in the EGR passage
An air-fuel ratio control method for a diesel engine, comprising: an R valve and an intake throttle valve provided in the intake passage of the engine, wherein the air-fuel ratio is controlled to a target air-fuel ratio in accordance with an operation state of the engine. Determine whether the opening exceeds a predetermined opening,
When it is determined that the opening of the EGR valve is less than a predetermined opening, the amount of deviation of the air-fuel ratio from the target air-fuel ratio is corrected by varying the opening of the EGR valve, and
When it is determined that the opening of the R valve exceeds a predetermined opening, the amount of deviation of the air-fuel ratio from the target air-fuel ratio is corrected by varying the opening of the intake throttle valve.

With the above configuration, when it is determined that the opening of the EGR valve is less than the predetermined opening, the actual exhaust air-fuel ratio λ _R of the engine by varying the opening of the EGR valve is changed according to the operating state of the engine. since the target air-fuel ratio of exhaust gas lambda _T good responsiveness of the air-fuel ratio control for controlling the, by varying the opening degree of the EGR valve, and corrects a shift amount with respect to the target air-fuel ratio of the actual exhaust air-fuel ratio, the opening of the EGR valve When it is determined that the degree exceeds the predetermined opening degree, the response of the air-fuel ratio control by varying the EGR valve opening degree is poor. Therefore, instead of varying the EGR valve opening degree, the opening degree of the intake throttle valve is changed. , The deviation of the actual exhaust air-fuel ratio from the target air-fuel ratio is corrected. Thus the actual exhaust air-fuel ratio lambda _R the air-fuel ratio control of the better the response to control the target exhaust air fuel ratio lambda _T a, can suppress the deterioration of exhaust emission due to the response delay.

[0008]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an air-fuel ratio control device for a diesel engine according to the present invention. A diesel engine (hereinafter simply referred to as an engine) 11 has a plurality of cylinders provided with a combustion chamber 12 at the top. In the intake stroke of the engine 11, the intake port 13 is opened by opening the intake valve 14, so that the intake passage 1
The outside air (intake air) is sucked into the combustion chamber 12 through 6. The fuel injection pump 18 pumps fuel through the fuel line 19 to the fuel injection nozzle 17. Fuel injection nozzle 1
The electronic control unit 7 is driven by an electronic control unit (hereinafter, referred to as an ECU) 20 and directly injects the pumped fuel into the combustion chamber 12. As described above, the air and the fuel supplied into the combustion chamber 12 in the intake stroke of the engine 11 become exhaust gas through the compression stroke and the explosion combustion stroke, and are opened by opening the exhaust valve 23 in the exhaust stroke. Exhaust port 2
2. Discharged from the combustion chamber 12 to the outside air via the exhaust passage 24.

The step motor 26 drives the intake throttle valve 25 based on a control signal from the ECU 20 so that the opening degree of the intake throttle valve 25 becomes a desired value. The fully open switch 58 is turned on when the intake throttle valve 25 is at the fully open position, and is turned off when the intake throttle valve 25 is at any other position. EC
U20 is an intake throttle valve 25 according to the operating state of the engine 11.
Target step amount LSTG calculated from a two-dimensional map (not shown) the opening degree of the rotational speed NE and the fuel injection amount Q _fin
R is adjusted by driving the step motor 26, thereby adjusting the intake air amount.

An EGR (exhaust gas recirculation) device 40 recirculates a part of the exhaust gas discharged from the combustion chamber 12 to the exhaust passage 24 to the intake passage 16 and returns the exhaust gas to the combustion chamber 12. EG
The R device 40 includes an EGR passage 41 communicating the intake passage 16 and the exhaust passage 24 for flowing a part of the exhaust gas from the exhaust passage 24 to the intake passage 16, and an amount of the exhaust gas flowing through the EGR passage 41 (EGR amount). And an EGR valve 42 for adjusting the pressure.

The EGR valve 42 is a diaphragm valve that opens and closes the EGR passage 41 at negative pressure and atmospheric pressure. EG
The R device 40 includes an electronic vacuum control valve (EVRV) 48 for adjusting the negative pressure and the atmospheric pressure introduced into the pressure chamber 46. The EVRV 48 is connected to a negative pressure port 51 connected to the pump 32 and an atmosphere port 53 for taking in the atmosphere, and adjusts the magnitude of the negative pressure supplied to the pressure chamber 46.
The ECU 20 controls the EVRV4 according to the operating state of the engine 11.
8 is a two-dimensional map (not shown) of the rotational speed NE and the fuel injection amount _Qfin with respect to the drive duty ratio ED (= 0 to 100%).
The opening degree of the EGR valve 42 is adjusted by variably controlling the target drive duty ratio ED calculated from Eq. Also, the drive duty ratio ED
Is the operating state of the engine 11, for example, the water temperature THW and the intake pressure P
It is corrected according to M.

FIG. 2 is a block diagram showing the input / output relationship between the inside and outside of the electronic control unit. The electronic control unit (ECU) 20 performs fuel injection amount control of the engine 11, fuel injection timing control, and the like. ECU 20
Perform the method for controlling the air-fuel ratio of a diesel engine according to the present invention. The inside of the ECU 20 is composed of, for example, a digital computer, and the CPU 63, the ROM 64, the RAM 65, the battery backup RAM 66, the input port 67, and the output port 6 interconnected by a bidirectional bus 69.
8 is provided.

The water temperature sensor 57 provided in the engine 11 is
The temperature THW of the cooling water for cooling the engine 11 is detected, and an analog voltage signal proportional to the water temperature THW is input to the ECU 20. An air flow meter 59 provided on the outside air suction side of the intake passage 16 detects an intake air amount GN to be taken into the combustion chamber 12 of the engine 11 via the intake passage 16, and an analog voltage proportional to the intake air amount GN. Signal of ECU20
Enter An accelerator sensor 61 provided in the vicinity of the accelerator pedal 60 detects the accelerator opening ACCP according to the depression amount of the accelerator pedal, and detects the accelerator opening ACCP.
Is input to the ECU 20. An intake pressure sensor 62 provided in the intake passage 16 detects an intake pressure PM in the intake passage 16 and inputs an analog voltage signal proportional to the intake pressure PM to the ECU 20.
The analog voltage signals of the water temperature THW, the intake air amount GN, the accelerator opening ACCP and the intake pressure PM supplied to the ECU 20 are supplied to the input port 6 via a buffer 70, a multiplexer 71 and an A / D converter 72, respectively.
7 is input.

The crankshaft 21 of the engine 11 rotates a drive shaft 29 of the injection pump 18. Injection pump 18
The rotation speed sensor 56 provided at the sensor detects the rotation speed of the drive shaft 29 to detect the rotation speed of the crankshaft 21, that is, the rotation speed NE of the engine. The rotation speed sensor 56 inputs the output signal to the input port 67 via the waveform shaping circuit 73. Also, a crank angle sensor 55 (not shown in FIG. 1) for detecting the angle of the crankshaft 21 generates an output pulse signal at every predetermined crank angle, for example, every 30 ° CA by converting into a crank angle, and the output signal is shaped into a waveform. The signal is input to the input port 67 via the circuit 73.

The step motor 26 and the electronic vacuum control valve (E
(VRV) 48 is output to the output port 6
8, output via the drive circuit 74, respectively. Hereinafter, the EGR control according to the present invention will be described in detail. FIG. 3 is a diagram showing a relationship between the opening degree of the EGR valve and the opening area of the EGR passage. In FIG. 3, the horizontal axis represents the opening of the EGR valve, and the vertical axis represents the opening area of the EGR passage that changes according to the opening of the EGR valve. As shown in FIG. 3, the opening area of the EGR passage increases as the opening degree of the EGR valve increases. However, the change in the opening area of the EGR passage with respect to the change in the opening degree of the EGR valve depends on the opening degree of the EGR valve. When the opening degree of the EGR valve reaches a predetermined opening degree, for example, 70% or more, the opening area of the EGR passage hardly changes with a change in the opening degree of the EGR valve. The EG shown in FIG.
The 70% opening of the R valve corresponds to about 80% of the opening area of the EGR passage. FIG. 3 shows that when the opening degree of the EGR valve is equal to or more than the predetermined opening degree, the change in the opening area of the EGR passage is small even if the opening degree of the EGR valve is changed, so that the EGR amount does not change with good response.

FIG. 4 shows the relationship between the opening degree of the intake throttle valve and the opening area of the intake passage. In FIG. 4, the horizontal axis represents the opening degree of the intake throttle valve, and the vertical axis represents the opening area of the intake passage that changes according to the opening degree of the intake throttle valve. As shown in FIG. 4, the opening area of the intake passage increases as the opening degree of the intake throttle valve increases, but the change in the opening area of the intake passage with respect to the change in the opening degree of the intake throttle valve depends on the intake throttle valve. When the opening degree of the intake throttle valve becomes a predetermined opening degree, for example, 70% or more, the opening area of the intake passage changes substantially with the change of the opening degree of the intake throttle valve. No longer. Further, the opening degree of 70% of the intake throttle valve shown in FIG. 4 corresponds to about 90% of the opening area of the intake passage. From FIG. 4, it can be seen that when the opening degree of the intake throttle valve is equal to or larger than the predetermined opening degree, even if the opening degree of the intake throttle valve is changed, the change in the opening area of the intake passage is small, so that the intake air amount does not change with good response.

FIG. 5 is a map for calculating the respective opening degrees of the EGR valve and the intake throttle valve according to the operating state of the engine. In FIG. 5, the horizontal axis indicates the engine speed NE (rpm), and the vertical axis indicates the fuel injection amount _Qfin corresponding to the engine load. As shown in FIG. 5, the EGR valve is set to a high opening with a large amount of excess air as the load becomes lighter, and is set to a low opening to suppress the generation of smoke at a high load. You. On the other hand, the intake throttle valve is set to a low opening because the excess air is required to be reduced as the load becomes lighter and the exhaust gas amount is required to be reduced, and is set to a high opening to suppress the generation of smoke at a high load.
In summary, the higher the load of the engine, the lower the opening of the EGR valve and the higher the opening of the intake throttle valve.

Therefore, when executing the air-fuel ratio control for controlling the actual exhaust air-fuel ratio λ _R of the engine to the target exhaust air-fuel ratio λ _T according to the operating state of the engine, the light load region of the engine (the hatched line from upper right to lower left) In the correction region by the intake throttle valve shown in FIG.
Since the opening degree of the GR valve is high, varying the opening degree of the intake throttle valve responds with higher sensitivity than varying the opening degree of the EGR valve, and the engine is in a high load region (shown by oblique lines from upper left to lower right). In the correction region by the EGR valve), since the opening degree of the intake throttle valve is high,
It can be seen that varying the opening of the EGR valve responds with higher sensitivity than varying the opening of the intake throttle valve.

In the air-fuel ratio control for correcting the deviation of the actual exhaust air-fuel ratio from the target air-fuel ratio according to the present invention, the responsiveness of the air-fuel ratio control due to the change in the opening degree of the EGR valve and the opening degree of the intake throttle valve changes the load of the engine. Focusing on the fact that the opening degree of the EGR valve exceeds a predetermined opening degree, for example, 70%, it is determined that the opening degree of the EGR valve exceeds a predetermined opening degree, for example, 70%. By varying the valve opening, the deviation amount of the air-fuel ratio is corrected, and when it is determined that the EGR opening exceeds a predetermined opening, the opening of the intake throttle valve is varied,
The deviation amount of the air-fuel ratio is corrected. According to the present invention, by performing such control, the responsiveness of the air-fuel ratio control is accelerated, and the deterioration of the exhaust emission due to the response delay is suppressed.

Next, an example in which the above-described air-fuel ratio control according to the present invention is executed by the ECU 20 will be described with reference to a flowchart. FIG. 6 is a flowchart of an EGR control routine according to the present invention. This routine is executed at a predetermined cycle, for example, every 8 ms. First, step 60
In 1, the engine 1 detected by the air flow meter 59
The intake air amount GN per revolution, the revolution speed NE and the accelerator opening ACCP are read from the RAM 65. Step 60
In 2, the two-dimensional map injected computed in another routine (not shown) timing stored in advance in the RAM65 according to the rotational speed NE _i and the accelerator opening ACCP _i of read elaborate engine of the current processing cycle in step 601 Fuel injection quantity Q
Calculate _{fin (i)} .

In step 603, the intake air amount GN _i read in step 601 in the current processing cycle is compared with step 60.
Based on the fuel injection amount calculated in 2 Q _{fin (i),} the ratio to the theoretical air-fuel ratio of the actual air-fuel ratio in the exhaust gases of the engine of this processing cycle, that is, the actual lambda value lambda _R, is calculated from the following equation. λ _R = GN _(i) / Q _{fin (i)} / S _to where S _to is λ _R = 1 when the actual air-fuel ratio of the exhaust gas of the engine is the stoichiometric air-fuel ratio (14.5). It is a coefficient.

In step 604, the ratio of the target air-fuel ratio of the exhaust gas of the engine to the stoichiometric air-fuel ratio is calculated from the engine speed NE and the fuel injection amount _Qfin based on a two-dimensional map stored in the ROM 64 in advance as shown in FIG. to calculate a target lambda value λ _T is. In step 605, the current EG
The electronic vacuum control valve (EVR) determines whether the R amount has reached a predetermined amount.
V) The drive duty ratio ED of 48 is K (for example, K = 70).
%), And when the result of the determination is YES, the actual exhaust air-fuel ratio λ _R is controlled to the target exhaust air-fuel ratio λ _T by varying the EGR valve opening to change the EGR amount. Because the control response is poor, proceed to step 611,
By varying the opening of the intake throttle valve, the actual exhaust air-fuel ratio λ
Carry out the air-fuel ratio control to adjust the _R to the target exhaust air-fuel ratio λ _T.
On the other hand, when the determination result is NO, the response to the air-fuel ratio control by changing the EGR valve opening amount and changing the EGR amount is good, so the process proceeds to step 606, and the actual exhaust gas is changed by changing the EGR valve opening amount. Change the air-fuel ratio λ _R to the target exhaust air-fuel ratio λ
Perform air-fuel ratio control to match _T.

In steps 606 to 609, the EGR amount is
The correction is made by varying the opening of the EGR valve. Sand
And the actual lambda value λ_RAnd the target value calculated in step 604.
Waste value λ_TAnd λ_RTo λ_TTo get closer to
At step 606, λ_R<Λ _TWhether or not -α holds
Discriminate, and if the discrimination result is YES, step 607.
The electronic vacuum control valve (EVR
V) The drive duty ratio ED of 48 is set to a predetermined amount, for example, 1%
Is increased (ED ← ED + 1), and the determination result of step 606 is made.
If the result is NO, then at step 608_R> Λ_T+ Α is formed
And if the result of the determination is YES
In step 309, the EVRV 48 is driven to reduce the EGR amount.
The duty ratio ED is reduced by a predetermined amount, for example, 1% (ED
← ED-1) When the determination result of step 608 is NO
Ends this routine.

In steps 610 to 613, the EGR amount is corrected by changing the opening of the intake throttle valve 25.
That is, the actual lambda value λ _R is compared with the target lambda value λ _T, and step 610 is performed so that λ _R approaches λ _T.
Then, it is determined whether or not λ _R <λ _T -α is satisfied. If the result of the determination is YES, step 611 of the intake throttle valve 25 is performed in step 611 so as to reduce the intake air amount.
Is reduced by a predetermined amount, for example, 1% (LSTG
R ← LSTGR-1), and the determination result of step 610 is N
If O, it is determined in step 612 whether or not λ _R > λ _T + α is satisfied. If the determination result is YES, 313 is determined.
The step amount LSTGR of the step motor 26 of the intake throttle valve 25 is increased by a predetermined amount, for example, 1% (LSTGR ← LSTGR + 1) so as to increase the intake air amount, and the routine ends when the determination result of step 612 is NO. I do.

[0025]

As described above, according to the diesel engine EGR control method of the present invention, when the opening of the EGR valve is less than the predetermined amount, the actual exhaust of the engine is varied by varying the opening of the EGR valve. The air-fuel ratio is controlled to control the air-fuel ratio to a target exhaust air-fuel ratio according to the operating state of the engine, and when the opening of the EGR valve is larger than a predetermined amount, the opening of the intake throttle valve is varied to obtain the air-fuel ratio. Since the control is performed, the responsiveness of the air-fuel ratio control when the opening degree of the EGR valve or the intake throttle valve is large is improved, and the deterioration of the exhaust emission due to the response delay can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of an air-fuel ratio control device for a diesel engine according to the present invention.

FIG. 2 is a block diagram showing an input / output relationship between the inside and outside of the electronic control unit.

FIG. 3 is a diagram showing a relationship between an opening degree of an EGR valve and an opening area of an EGR passage.

FIG. 4 is a diagram showing a relationship between an opening degree of an intake throttle valve and an opening area of an intake passage.

FIG. 5 is a map for calculating respective opening degrees of an EGR valve and an intake throttle valve in accordance with an operating state of an engine.

FIG. 6 is a flowchart of an air-fuel ratio control routine according to the present invention.

FIG. 7 is a map for calculating a target lambda value λ _T from an engine speed NE and a fuel injection amount Q _fin ;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Diesel engine 12 ... Combustion chamber 16 ... Intake passage 17 ... Fuel injection nozzle 20 ... Electronic control unit (ECU) 25 ... Intake throttle valve 26 ... Step motor 40 ... Exhaust gas recirculation (EGR) device 41 ... EGR passage 42 ... EGR valve 48: electronic vacuum control valve (EVRV) 56: rotational speed sensor 59: air flow meter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 21/08 301 F02D 21/08 301B 43/00 301 43/00 301K 301N 301W F02M 25/07 550 F02M 25/07 550A 570 570J

Claims (1)

[Claims] An EG for communicating an intake passage and an exhaust passage of a diesel engine and recirculating a part of exhaust gas to the engine.
An air-fuel ratio control method for a diesel engine, comprising: an EGR valve provided in an R passage and an intake throttle valve provided in the intake passage of the engine, wherein the air-fuel ratio is controlled to a target air-fuel ratio in accordance with an operation state of the engine. In the above, it is determined whether or not the opening of the EGR valve has exceeded a predetermined opening, and when it is determined that the opening of the EGR valve is less than the predetermined opening, the opening of the EGR valve is varied. The deviation amount of the air-fuel ratio from the target air-fuel ratio is corrected by
When it is determined that the opening of the R valve exceeds a predetermined opening, the deviation amount of the air-fuel ratio from the target air-fuel ratio is corrected by varying the opening of the intake throttle valve. Air-fuel ratio control method.