JP3511639B2 - Exhaust gas recirculation control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device equipped with a self-diagnosis device.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation device (hereinafter, referred to as EGR) that recirculates a part of exhaust gas of an internal combustion engine to an intake pipe of the internal combustion engine is a nitrogen oxide (NO) in the exhaust gas.
It is widely used as a means for reducing _X ) in internal combustion engines for automobiles. By the way, when a malfunction occurs in the EGR due to a malfunction of the EGR valve or a malfunction of the EGR piping, NO _X is likely to increase remarkably. But EG
Since the failure of R has little influence on the driving performance itself, it is difficult for the driver to notice the abnormality. Therefore, a large amount of NO _X may be emitted and pollute the atmosphere.

As a measure against this, conventionally, as a means for detecting a failure of the EGR, for example, there is a means for providing a flow rate sensor or the like in the EGR pipe as described in JP-A-56-60912. However, in the above-mentioned conventional technique, there is a problem that the structure is complicated because a flow rate sensor is required and further the cost is increased. In order to solve this, the amount of change in intake pipe pressure (ΔP = P _ON − when EGR is switched from on to off during steady operation)
JP-A-62 / 62 discloses that P _OFF ) is determined, and when the amount of change in the pressure is less than a predetermined value, it is determined to be abnormal and this result is warned.
It is proposed in Japanese Patent Laid-Open No. 51746.

[0004]

However, in the above method, since the EGR valve is changed from the fully open state to the fully closed state, the emission temporarily deteriorates. further,
When the above method is used for EGR that controls the opening degree of the EGR valve, the internal combustion engine is often operated at a low EGR rate during steady operation, so even if the EGR valve is turned on or off for abnormality determination. Since the amount of change ΔP in the intake pipe pressure is small, it is possible to erroneously detect that the EGR is abnormal.

It is an object of the present invention to provide an EGR control device which can prevent erroneous detection while minimizing the deterioration of emission and which is simple in structure and inexpensive in cost.

[0006]

Therefore, according to the present invention, as shown in FIG. 7, a recirculation pipe for recirculating exhaust gas of an internal combustion engine to an intake pipe, an opening / closing means for opening and closing the recirculation pipe, and an inside of the intake pipe. Intake state detecting means for detecting a state of air flowing through the opening and closing means, and first control means for changing the opening / closing means to a first opening and a second opening on the closing side of the first opening. First change amount detection means for detecting the change amount of the state of the air flowing in the intake pipe when the opening / closing means is changed by the first control means, and detection by the first change amount detection means A first determining means for determining whether the result is less than a predetermined value, and when the first determining means determines that the change amount detected by the first change amount detecting means is less than the predetermined value. , Larger than the opening difference changed by the first control means Second control means for changing the opening degree of the opening / closing means by a degree difference, and detecting a change amount of the state of the air flowing in the intake pipe when the opening / closing means is changed by the second control means. Second change amount detecting means,
An exhaust gas recirculation control device comprising: a second determination unit that determines an abnormality if the detection result of the second change amount detection unit is less than a predetermined value.

[0007]

The recirculation pipe for recirculating the exhaust gas of the internal combustion engine to the intake pipe is provided with an opening / closing means for opening and closing the recirculation pipe. Further, the intake pipe is provided with intake state detecting means for detecting a state of air flowing therein. Then, the first control means changes the opening / closing means to a first opening degree and a second opening degree on the closing side of the first opening degree. At this time, the first change amount detecting means detects the change amount of the state of the air flowing in the intake pipe. Further, the first determination means determines whether the detection result of the first change amount detection means is less than a predetermined value.

Further, the second control means, when the first determination means determines that the variation detected by the first variation detection means is less than a predetermined value, the first control means
The opening degree of the opening / closing means is changed with an opening difference larger than the opening difference changed by the control means. The second change amount detection means detects the change amount of the state of the air flowing in the intake pipe when the valve opening degree is changed by the second control means. As a result, if the detection result of the second change amount detecting means is less than the predetermined value, the second determining means determines that it is abnormal.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an internal combustion engine (engine) and its control system applied to an embodiment of the present invention. In FIG. 1, 1 is one cylinder of a 6-cylinder vehicle engine, 2 is an intake pipe pressure sensor that detects the pressure in an intake manifold 3 connected to the cylinder, and is composed of a semiconductor type pressure sensor. . Four
Is an electromagnetically-operated fuel injection valve provided near each cylinder intake port of the intake manifold 3, and 6 is a distributor. The rotor of the distributor 6 is rotationally driven at 1/2 the engine speed, and a rotation sensor 7 that outputs a signal indicating the engine speed and fuel injection timing and a cylinder discrimination signal is provided inside.

Reference numeral 9 is a throttle valve, 10 is a throttle position sensor, 11 is a thermistor type water temperature sensor for detecting an engine cooling water temperature, and 12 is an intake air temperature sensor for detecting an intake air temperature. Reference numeral 13 denotes an exhaust gas recirculation control valve (hereinafter referred to as an EGR valve) mounted on an exhaust gas circulation path 17 connected between the intake manifold 3 and the exhaust manifold 16, and 15
Adjusts the opening of the EGR valve 13
A step motor as an actuator for controlling the rate, and a warning lamp 30 for warning the abnormality of EGR.

The EGR rate is appropriately controlled by obtaining a basic step from the engine rotation and the engine load, rotating the step motor by the number of steps corresponding to the operating state of the engine, and adjusting the opening degree of the EGR valve. To be done. FIG. 2 shows a block diagram of an electronic control circuit 8 for controlling the fuel injection amount of the engine to control the air-fuel ratio, each sensor, etc. The electronic control circuit 8 and a microcomputer are mainly configured.

The control circuit 8 takes in each detection signal from the intake pipe pressure sensor 2, the rotation sensor 7, the throttle position sensor 10, the water temperature sensor 11, and the intake temperature sensor 12, and determines the fuel injection amount based on these detection data. The air-fuel ratio is calculated by controlling the valve opening time of the fuel injection valve 4. Reference numeral 100 denotes an MPU (microprocessor unit) that executes arithmetic processing according to a predetermined program, 101 denotes an interrupt control unit that outputs an interrupt signal to the MPU 100, and 102 counts a rotation angle signal from the rotation sensor 7 to calculate an engine rotation speed. Counter section, 104
Is an A / D converter for selectively inputting detection signals (analog signals) from the intake pipe pressure sensor 2, the water temperature sensor 11, and the intake temperature sensor 12 and converting them into digital signals. 105
Is a ROM which is a read-only memory in which programs and map data used for calculation are stored in advance, and 106 is a RAM which is a writable and readable nonvolatile memory, and retains the stored contents even after the key switch is turned off.

Reference numeral 107 denotes an output port connected to the step motor 15, reference numeral 108 denotes an output counter section for outputting a fuel injection amount (time) control signal including a register, which is an MPU.
The fuel injection amount data sent from 100 is input, the duty ratio of the control pulse signal for controlling the valve opening time of the fuel injection valve 4 is determined based on this data, and the injection amount control signal is output. The control signal output from the output counter unit 108 is applied to the fuel injection valve 4 for each cylinder via the power amplifier 110. Further, in the control circuit 8, the MPU 100 and the interrupt counter unit 108 are Each of them is connected to the common bus 111, and necessary data is transferred according to a command from the MPU 100.

The EGR abnormality detection processing executed in the control circuit 8 in the above configuration will be described with reference to the flowchart shown in FIG. This flowchart is executed every predetermined time. First, in step 301, it is determined whether the EGR abnormality detection condition is satisfied. The determination of this abnormality detection condition is executed based on the flowchart shown in FIG. Details will be described later. When the condition is not satisfied in step 301, this routine is exited. Step 3 if the conditions are met
Go to 02.

In step 302, EGR at this time is performed.
The first variation amount ΔP ₁ of the intake pipe pressure that occurs when the EGR control is stopped is obtained from the rate from the flowchart shown in FIG. FIG. 5 will be described later. Next step 303
Then, it is determined whether the first variation ΔP ₁ obtained in step 302 is equal to or larger than the predetermined value k. Here, if the first variation amount ΔP ₁ is equal to or larger than the predetermined value k, the process proceeds to step 308, and the EGR is determined to be normal, and this routine is exited.

When the first fluctuation amount ΔP ₁ is smaller than the predetermined value k in step 303, the routine proceeds to step 304, where the basic step amount determined by the engine speed and the engine load is set in order to increase the EGR rate. The step amount offset by step offset is sent to the step motor as a control signal. Then, in the next step 305, the second variation amount ΔP ₂ of the intake pipe pressure that occurs when the EGR control is stopped is detected from the EGR rate at this time by executing the flowchart of FIG.

In the next step 306, step 305
It is determined whether or not the _second variation amount ΔP ₂ obtained in step 3 is greater than or equal to a predetermined value k. The predetermined value used at this time does not necessarily have to be k and may be a value other than k. Where the second
When the change amount ΔP _{2 of} is greater than or equal to the predetermined value k, the process proceeds to step 308, and the EGR is determined to be normal, and this routine is exited. When the second variation ΔP ₂ is less than the predetermined value k, the routine proceeds to step 307, where it is determined that there is an abnormality in EGR, and then this routine is exited.

By the above processing, there is no difference between the intake pipe pressure when the EGR is operating and the intake pipe pressure when the EGR is stopped, and E
When it is not determined that the GR is normal, the EGR
Increase the rate. Then, the difference between the intake pipe pressure when the EGR operation is performed when the EGR rate is increased again and the intake pipe pressure when the EGR is stopped is detected, and when there is no difference between the two, it is determined that the EGR is abnormal. You can

Next, the abnormality detection condition determination processing will be described with reference to the flowchart shown in FIG. First, in step 401, it is determined whether the EGR control is in progress. If the EGR control is in progress, the process proceeds to step 402. In step 402, the engine speed Ne is N ₁ (for example, 1000 rpm in this embodiment) <Ne <N ₂ (2500).
It is determined whether the relationship of is satisfied. Engine speed N
When e satisfies this condition, the process proceeds to step 403.

In step 403, the intake pipe pressure P _m is changed to P
₃ (250 mmHg) <P _m <P ₄ (600 mmHg)
It is determined whether the relationship of is satisfied. When the intake pipe pressure P _m satisfies this condition, the routine proceeds to the next step 404. In step 404, it is determined whether the atmospheric pressure P _A is larger than a predetermined value P ₅ (700 mmHg). If so, go to step 405. Further, in step 405, the variation ΔP _m of the intake pipe pressure within a predetermined period is detected, and it is determined whether this value is smaller than a predetermined value P ₆ (100 mmHg) which is set in advance. If it is smaller, the process proceeds to step 302 of FIG.
Anomaly detection is performed.

Even one of the above conditions is applicable
When there is something that doesn't fit, good detection of EGR abnormality
If the EGR abnormality detection
Exit this routine without doing it. Next, the steps of FIG.
302, Step 304: intake pipe pressure fluctuation amount ΔP
₁, ΔP₂Figure 5 shows the processing executed when
A description will be given according to the flowchart. This flow
The chart shows the abnormality detection condition determination routine shown in FIG.
When it is determined that the abnormality detection condition is satisfied,
It is executed every predetermined time. Furthermore, this flowchart
If the detection conditions are not met during the execution of
Return the opening of the valve 13 to the state before executing this flowchart.
(For example, when the EGR control is stopped, the EG
R control is started), counter C₁After clearing
End the reason.

First, in step 501, it is determined whether the value of the counter C ₁ is a predetermined time t ₁ (0 second in this embodiment). When it is not the predetermined time t ₁ , the process proceeds to step 503. If it is the predetermined time t ₁ , the process proceeds to step 502. Then, in step 502, the intake pipe pressure P _aON at this time is read, and the _routine proceeds to step 503. In step 503, it is determined whether the value of the counter C ₂ is the predetermined time t ₂ (1 second in this embodiment). When it is not the predetermined time t ₂ , the process proceeds to step 505. If it is the predetermined time t ₂ , the process proceeds to step 504. Then, in step 504, the intake pipe pressure P _bON at this time is read, and step 5
Go to 05.

In step 505, it is determined whether P _aON and P _bON are substantially equal. This is to prevent false detection
This is a process for preventing abnormality determination when the intake pipe pressure is changing within a predetermined time. Therefore, if it is determined that they are not equal to each other, the counter C ₁ is cleared in step 506, the process returns to step 501, and the above processes are repeated. If it is determined that they are substantially equal, the process proceeds to step 507 and the subsequent steps.

At step 507, the EGR control is stopped. Then, in step 508, it is determined whether the value of the counter C ₁ is the predetermined time t ₃ (2 seconds in this embodiment).
When it is not the predetermined time t ₃ , the process proceeds to step 511. If it is the predetermined time t ₃ , the process proceeds to step 509. Then, in step 509, the intake pipe pressure P _cOFF at this time is _set.
Is read and the process proceeds to step 510. In step 510, the EGR control is started again, and the process proceeds to step 511.

In step 511, it is determined whether the value of the counter C ₁ is the predetermined time t ₄ (3 seconds in this embodiment). When it is not the predetermined time t ₄ , the routine proceeds to step 515, where the counter C ₁ is incremented by ₁ and this routine is exited. If it is the predetermined time t ₄ , the process proceeds to step 512. Then, at step 512, the intake pipe pressure P _dON at this time is read, and the _routine proceeds to step 513. In step 513, the intake pipe pressure fluctuation amount ΔP ₁ or ΔP ₂ is obtained from the following equation.

[0026]

[Equation 1] Then, the process proceeds to step 514. In step 514, the counter C ₁ is cleared and the routine exits.

Next, the above intake pipe pressure fluctuation amount is detected.
The process will be described according to the time chart shown in FIG.
It In FIG. 6, the EGR abnormality detection condition is satisfied.
When, first, time t₁At intake pipe pressure P_aONDetect
To do. And time t₁A predetermined time (1 second) has passed since
Time t₂At intake pipe pressure P_bONTo detect. P_bON
After detection, P_aONAnd P _bONWhen and are almost equal, EGR system
Stop. Then time t₃(Time t₁2 seconds after
Excess), the intake pipe pressure P_cOFFTo detect. further,
Time t₁A predetermined time (3 seconds) from the time t_Foursmell
And intake pipe pressure P_dONTo detect.

Based on these detection results, the intake pipe pressure fluctuation amount is calculated by the mathematical formula 1. In the present embodiment, the exhaust gas circulation path 17 serves as a recirculation pipe, the EGR valve 13 serves as an opening / closing means, step 507 serves as a first control means, the intake pipe pressure sensor 2 serves as an intake state detecting means, and steps 302 and 1 Step 504, Step 507 to Step 513 executed by the first change amount detecting means, and Step 303
Is executed by the first determining means, step 304 is executed by the second controlling means, and step 305 and step 50 are executed for the second time.
4, step 507 to step 513 correspond to the second change amount detecting means, and step 306 and step 307 correspond to the second determining means, respectively, and function.

In the present embodiment, the execution cycle and the number of executions of the flowchart shown in FIG. 3 are, for example, once every 20 seconds after the engine is started and before the engine is stopped until the EGR abnormality determination is made. The number of execution cycles and the number of executions may be such that they do not affect the operating state of the engine. Further, in this embodiment, as a method of detecting the amount of change in the intake pipe pressure, the difference between the average value of the intake pipe pressure before and after the opening / closing control of the EGR valve 13 and the intake pipe pressure during the closing control of the EGR valve 13 is determined. Detected, but EGR valve 1
It is also possible to detect the difference between the intake pipe pressure at the time of the three-open control (before or after the close control) and at the time of the close control. Further, in the present embodiment, the EGR valve 13 is fully closed when the EGR valve 13 is closed, but the EGR valve 13 may be controlled on the valve closing side so that a predetermined opening difference is produced by the step motor.

Alternatively, any method may be used as long as the difference in intake pipe pressure between the open control and the close control of the EGR valve 13 is detected. For example, when the EGR control is not performed, the EGR valve is opened by a predetermined opening degree. Detect the difference in intake pipe pressure that occurs when the valve is opened and controlled from fully closed. At this time, if the difference is not detected, further increase the opening degree and similarly detect the difference in intake pipe pressure. You may do it.

Further, as another embodiment, in the above embodiment, the intake manifold pressure sensor 4 is provided in the intake manifold 3.
EGR system abnormality detection is performed to detect the EGR of the intake pipe pressure P _m .
The air flow meter for detecting the air amount Q is provided upstream of the throttle valve 9 instead of the intake pipe pressure sensor 4, and the EGR of the air amount Q detected by the air flow meter is provided. The abnormality of the EGR system may be detected by a change based on the change in the operating state of.

Similarly, in a system in which a temperature sensor is provided downstream of the confluence portion of the EGR pipe with the intake pipe, the EGR system changes due to a change in the temperature detected by the temperature sensor based on a change in the operating state of the EGR system. Abnormality detection may be performed.

[0033]

As described above, according to the present invention, when the EGR is operating normally, the first determining means can detect that the EGR is operating normally. However, even though the EGR rate that is being performed when the EGR abnormality is detected is small and normal, the first
When it is determined by the determining means that the condition is not normal, the EGR
The abnormality is detected again by the second determining means after increasing the rate, so that it is determined to be normal at least at this time. As a result, it can be prevented that the EGR is normal but is determined to be abnormal.

When the EGR is abnormal, the second determining means can surely detect the abnormality. Further, in the present invention, the EGR rate is increased and re-determination is performed only when the first determination means does not determine that the engine is normal, so that deterioration of exhaust gas caused by changing the EGR rate unnecessarily is minimized. You can keep it to the limit.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an internal combustion engine and its peripheral equipment used in an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control circuit used in one embodiment of the present invention.

FIG. 3 is a flowchart showing an EGR abnormality detection process executed in a control circuit used in this embodiment.

FIG. 4 is a flowchart showing an EGR abnormality detection condition determination routine executed in the control circuit used in the present embodiment.

FIG. 5 is executed in the control circuit used in this embodiment.
Intake pipe pressure fluctuation amount ΔP₁, ΔP ₂Detecting the flow
It is

FIG. 6 is a time chart showing a process when detecting an intake pipe pressure fluctuation amount in the present embodiment.

FIG. 7 is a diagram corresponding to the claims of the present invention.

[Explanation of symbols]

2 Intake pipe pressure sensor 3 intake manifold 8 control circuit 13 EGR valve 15 step motor 17 Exhaust gas circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-23356 (JP, A) JP-A-4-175450 (JP, A) JP-A-3-267561 (JP, A) JP-A-5- 79405 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02M 25/07 550 F02M 25/07 570 F02D 41/02 301 F02D 43/00 301

Claims (2)

(57) [Claims] 1. A recirculation pipe for recirculating exhaust gas of an internal combustion engine to an intake pipe, an opening / closing means for opening / closing the recirculation pipe, an intake state detecting means for detecting a state of air flowing in the intake pipe, and the opening / closing means. To a first opening degree and a second opening degree on the closing side of the first opening degree, and when the opening / closing means is changed by the first control means, A first change amount detecting means for detecting a change amount of the state of the air flowing through the intake pipe; and a first determining means for determining whether a detection result of the first change amount detecting means is less than a predetermined value. When the first determining means determines that the change amount detected by the first change amount detecting means is less than a predetermined value, the opening amount larger than the opening difference changed by the first control means is set. A second control that changes the opening degree of the opening / closing means by a difference in degree. Control means, second change amount detection means for detecting a change amount of the state of air flowing in the intake pipe when the opening / closing means is changed by the second control means, and the second change amount. An exhaust gas recirculation control device comprising: a second determination unit that determines an abnormality if the detection result of the detection unit is less than a predetermined value. 2. The exhaust gas recirculation control, wherein the intake state detecting means detects at least one of an amount of air flowing through the intake pipe, a pressure inside the intake pipe, and a temperature inside the intake pipe. apparatus.