JPH04314953A - Exhaust gas recirculation controller - Google Patents

Abstract

PURPOSE:To control an EGR quantity for reducing the NOx generated in an internal combustion engine with high precision. CONSTITUTION:Taking account of the fact that the combustion temperature in a cylinder and the NOx exhaust quantity are correlated, the combustion temperature is obtained from the pressure in the cylinder which is detected by a pressure sensor 7, and the actual EGR rate (NOx quantity) is estimated from the combustion temperature. Feedback control is carried out by increasing or reducing the passage area of an EGR valve 13 by an EGR solenoid 14 through a control unit 15 so that the actual EGR and a previously determined aimed EGR rate accord to each other. Accordingly, the correct recirculation control for exhaust gas which corresponds to a variety of operation states can be performed. In this case, the recirculation control for exhaust gas can be carried out speedily and correctly when an IG switch 16 is turned ON, by memorizing the difference between the actual EGR rate and the aimed EGR rate or the value corresponding to the difference.

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 for recirculating a portion of exhaust gas from an internal combustion engine to the intake pipe of the internal combustion engine.

0002

[Prior Art] Conventionally, NOx in exhaust gas of an internal combustion engine
Exhaust gas recirculation (hereinafter referred to as EGR) is a means to reduce
Exhaust gas recirculation control devices (hereinafter referred to as EGR control devices) are widely used. This EGR control device is B
PT (Back Pressure Transduc)
er) EGR is controlled by an exhaust pressure control method using a valve.

0003

[Problem to be solved by the invention] Such conventional EG
Since the R control device is configured using a BPT valve, etc., it cannot directly detect the amount of exhaust gas recirculation, that is, the amount of EGR.As a result, when the amount of EGR increases due to deterioration of the BPT valve, etc. In addition, when the amount of EGR decreases, the temperature of the engine increases and the NOx component in the exhaust gas increases.

[0004] Furthermore, after turning on the ignition key switch (hereinafter referred to as IG switch) to start the internal combustion engine, the actual EGR rate does not match the target EGR rate for a while due to changes over time, and during this time the exhaust gas deteriorates. There was the problem of inviting the Furthermore, even if the EGR control device becomes abnormal due to deterioration of parts within the device, there is a problem in that it is difficult to detect the abnormality of the device because the amount of EGR cannot be directly detected. In view of the above points, the present invention has been made in order to solve the above problems.
It is an object of the present invention to provide an exhaust gas recirculation control device that can accurately control the amount of EGR that reduces Ox.

[0005]

[Means for Solving the Problems] In order to achieve the above object, an exhaust gas recirculation control device according to the present invention includes a recirculation pipe for recirculating exhaust gas of an internal combustion engine to an intake pipe, and an exhaust gas flowing through the recirculation pipe. a reflux valve that controls the flow rate of the gas; a reflux valve passage area control means that controls the passage area of the reflux valve;
An operating state detecting means for detecting the operating state of the internal combustion engine, a pressure detecting means for detecting the internal cylinder pressure of the internal combustion engine, an intake air amount detected by the operating state detecting means, and an internal cylinder pressure detected by the pressure detecting means. means for calculating the combustion temperature from the combustion temperature and calculating the actual exhaust gas recirculation rate according to the combustion temperature and the detected value from the operating state detecting means, and a target exhaust gas according to the detected value detected by the operating state detecting means. A means for calculating the recirculation rate and a recirculation valve passage area control means based on the deviation between the actual exhaust gas recirculation rate and the target exhaust gas rate, and increasing or decreasing the passage area of the recirculation valve to adjust the actual exhaust gas. The exhaust gas recirculation rate is provided with means for performing feedback control so that the gas recirculation rate and the target exhaust gas recirculation rate match.

[0006] Furthermore, in the exhaust gas recirculation control device according to another aspect of the present invention, in the above device, a deviation between an actual exhaust gas recirculation rate and a target exhaust gas recirculation rate or a value corresponding to this deviation is stored. It is equipped with a storage means. Furthermore, the exhaust gas recirculation control device according to another aspect of the present invention is provided with a failure diagnosis means for detecting a discrepancy between an actual exhaust gas recirculation rate and a target exhaust gas recirculation rate and diagnosing a failure. It is something that

[0007]

[Operation] In the present invention, as shown in FIGS. 4 and 5, the combustion temperature is determined from the cylinder pressure, focusing on the fact that there is a correlation between the combustion gas temperature in the cylinder, that is, the combustion temperature, and the NOx emission amount. Moreover, the actual exhaust gas recirculation rate (NOx amount) is estimated based on the combustion temperature. Then, feedback control is performed by increasing or decreasing the passage area of the recirculation valve so that the actual exhaust gas recirculation rate matches the predetermined target exhaust gas recirculation rate. Thereby, accurate EGR control can be performed according to various operating conditions. Note that FIG. 4 shows the relationship between the NOx emission amount of the exhaust pipe and the combustion gas temperature in the cylinder, and FIG. 5 shows the relationship between the NOx emission amount and the EGR rate.

[0008] In another aspect of the present invention, the deviation between the actual exhaust gas recirculation rate and the target exhaust gas recirculation rate or a value corresponding to this deviation is memorized, so that even immediately after the IG switch is turned on, accurate EGR control can be performed. Furthermore, in another aspect of the present invention, a failure can be determined by detecting a discrepancy between the actual exhaust gas recirculation rate and the target exhaust gas recirculation rate, so that a failure of the apparatus can be directly and accurately detected.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an exhaust gas recirculation control device according to the present invention. In the figure, 1 is the engine, 2 is the air cleaner, and 3 is the intake air amount detector (hereinafter referred to as
4 is an intake pipe, 5 is a throttle valve, 6 is an injector, 7 is a pressure sensor that detects the pressure inside the cylinder of the engine 1, 8 is a spark plug, 9 is an exhaust pipe, 10 is a catalyst, 11 is an engine 1 This is a crank angle sensor that is connected to the crankshaft of the engine and outputs a cylinder identification signal 11a and a crank angle signal 11b. 12 is a recirculation pipe that recirculates a part of the exhaust gas in the exhaust pipe 9 to the intake pipe 4; 13 is an EGR valve as a recirculation valve that controls the flow rate of the exhaust gas flowing through this recirculation pipe 12; and 14 is this EGR valve 13. EG as a reflux valve passage area control means for controlling the passage area of
This is the R solenoid. 15 is an electronic control unit, 16
is the IG switch, 17 is the battery, 18 is the warning lamp,
A throttle opening sensor 19 detects the opening of the throttle valve 5.

Here, the pressure sensor 7 detects the cylinder internal pressure (cylinder pressure) as shown in FIG. 3(a), and the crank angle sensor 11 detects the cylinder pressure as shown in FIG. 3(b).
A cylinder identification signal 11a is output at intervals of 20 degrees (one stroke), and a crank angle signal 11b is output at every unit angle (1 degree) as shown in FIG. 3(c). EGR
The solenoid 14 is connected to a control passage between the diaphragm chamber of the EGR valve 13 and the intake pipe 4, and controls the negative pressure to the diaphragm chamber of the EGR valve 13 in response to a signal from the electronic control unit 15, thereby controlling the valve 13. This allows the area of the passage to be varied.

Further, the electronic control unit 15 inputs signals from the AFS sensor 3, pressure sensor 7, crank angle sensor 11, and throttle opening sensor 19, and controls the AFS.
The combustion temperature is calculated from the intake air amount detected by the sensor 3 and the cylinder pressure detected by the pressure sensor 7, and the actual exhaust gas recirculation rate (hereinafter referred to as Actual EGR rate) is calculated. Then, a target exhaust gas recirculation rate (hereinafter referred to as target EGR rate) is calculated according to the detection value detected by the sensor 3, and the EGR solenoid 14 is controlled based on the deviation between the actual EGR rate and the target EGR rate. By increasing or decreasing the passage area of the EGR valve 13, these actual EGR
Feedback control is performed so that the EGR rate matches the target EGR rate.

FIG. 2 is a detailed block diagram of this electronic control unit 15. In the same figure, 100 is a microcomputer that performs EGR according to a predetermined program.
A CPU 200 that calculates the control amount of the solenoid 14, a free running counter 201 that measures the rotation period of the engine 1, a timer 202 that measures the duty ratio of the drive signal applied to the EGR solenoid 14, and converts analog input signals into digital signals. A/D converter 2 that converts
03, input port 204, RAM 205 used as work memory, ROM 2 where programs are stored
06, an output port 207 that outputs a drive signal, a common bus 208, and the like.

Further, 101 is a first input interface circuit which receives a cylinder identification signal 11 from the crank angle sensor 11.
a, the crank angle signal 11b is waveform-shaped and output to the microcomputer 100 as an interrupt signal. When this interrupt signal is generated, the CPU 200 reads the value of the counter 201, detects the engine rotation speed based on the crank angle signal 11b, calculates the period, and stores it in the RAM 205. 102 is a second input interface circuit, which connects the AFS sensor 3 and the pressure sensor 7.
Input each signal from the throttle opening sensor 19, etc.
/D converter 203, for example, as shown in FIG.
As shown in d), A/D conversion is performed based on the 1 degree crank angle signal, and the intake air amount from each AFS sensor 3 and the cylinder internal pressure from the pressure sensor 7 are detected. 10
4 is an output interface circuit, and output port 20
The drive output from 7 is amplified and output to the EGR solenoid 14. Further, 105 is a first power supply circuit to which power from the battery 17 is supplied via the IG switch 16;
A second power supply circuit 106 is constantly supplied with power from the battery 17, and the control unit 15 including the microcomputer 100 is driven by the power outputs of these power supply circuits 105 and 106.

Next, the operation will be explained. FIG. 6 shows the main routine processing of the CPU 200 of the above embodiment. The CPU 200 first performs other control processing in step 300, and after completing this, calculates the combustion temperature within the cylinder in step 400. After performing EGR control processing for controlling the recirculation of exhaust gas in step 500, the process returns to step 300. Each subroutine will be described with reference to the flowcharts of FIGS. 7 to 9.

FIG. 7 shows the subroutine processing for calculating the combustion temperature in the cylinder. That is, when the engine 1 starts, the CPU 200 first determines the presence or absence of the cylinder identification signal 11a from the crank angle sensor 11 in step 401, and if the signal is present, performs a reset process (0) in step 402.
→ Perform P). Then, in step 403, the sensor 11
When the crank angle signal 11b is received and the rising signal is taken in, in step 404 the cylinder internal pressure Pin obtained from the pressure sensor 7 is detected based on the rising edge of the crank angle signal, and then in step 405 P+
The value p of Pin is determined and stored in the RAM 205. onwards,
This process is repeated until the end of one stroke of the cylinder in step 406, and the total value p of the cylinder internal pressure between the cylinder identification signals is determined.

Next, in step 407, the engine speed Ne is detected based on the crank angle signal, and in step 408, the rotation period t is determined from the engine speed Ne.
After calculating, in step 409, the cylinder average pressure PAVG is determined from the total value p and the rotation period t. Next, in step 410, the intake air amount G is calculated using the sensor output of the AFS sensor 3 and the engine rotation speed, and then, in step 411, the combustion temperature T of the cylinder is calculated using the following equation.

[0017] T∝K・PAVG/G
......(1)

However, K is a constant of V/R, where R is the gas constant and V is the cylinder volume. FIG. 8 shows another example of the cylinder combustion temperature calculation subroutine, and in this example, the maximum value Pmax(
The combustion temperature is determined from the average value of the intake air amount and the cylinder internal pressure up to (see FIG. 3(a)). That is, when the variable for searching for the maximum cylinder pressure is A, the CPU 200 performs a reset process (0→P, A) using that signal when the cylinder identification signal is taken in (steps 450, 451). After detecting the cylinder pressure Pin at the rising edge of the crank angle signal (452,
453), the comparison process is performed until the detected value exceeds the variable A, and the total value p up to the maximum pressure value Pmax is calculated (454 to 457).

Next, the engine rotation speed Ne is detected, and the throttle opening signal θ (or the intake manifold pressure in the intake pipe 4) from the throttle opening sensor 19 is detected, and the intake air amount G is determined based on these Ne and θ. Calculate (same 4
58-460). Then, by calculating the engine rotation period t from this Ne, and further calculating the average pressure PAVG, the combustion temperature T is determined from the intake air amount G up to the maximum value Pmax of the cylinder internal pressure and the average value PAVG of the cylinder internal pressure. (461-463).

After determining the combustion temperature T in this way, C
PU200 performs EGR control processing shown in FIG. That is, in addition to detecting the engine speed Ne, the AFS sensor 3 detects the intake air amount Qa of the intake pipe 4. next,
The EGR operating range is determined from the detected engine speed Ne and intake air amount Qa, and it is determined whether or not it is within the EGR operating range (steps 501 to 504). If it is in the EGR operation region, the target EGR rate TEGR is calculated from the engine speed Ne and the intake air amount Qa, and then the basic EGR control amount kBASE is calculated according to the target EGR rate TEGR (505 to 506). . however,
In step 505, a target combustion temperature may be calculated instead of the target EGR rate TEGR.

[0021] Then, the actual combustion temperature (hereinafter referred to as actual combustion temperature) T obtained in the above combustion temperature calculation process (step 400) is read from the RAM 205, and these actual combustion temperature T, engine speed Ne, and intake air amount Qa are More real EGR
The rate PEGR is calculated, and then the actual EGR rate PEG is calculated from the target EGR rate TEGR based on the graph shown in FIG.
The control gain ΔkEGR is calculated from the value obtained by subtracting R (steps 507 to 509). Note that FIG. 10 is a graph showing the characteristics of the control gain ΔkEGR, and the target EGR
The value obtained by subtracting the actual EGR rate PEGR from the rate TEGR is shown on the horizontal axis, and the value of the control gain ΔkEGR corresponding to this value is shown on the vertical axis.

Then, the EGR control correction value kEGR is calculated by adding the EGR control correction value kEGR before calculation to this control gain ΔkEGR, and then the basic control amount kBASE is added to this EGR control correction value kEGR to calculate the EGR control correction value kEGR.
The control value k is calculated, and the control duty DEGR is calculated from the EGR control value k based on the graph showing the relationship between the EGR control value k and the control duty D in FIG. The solenoid 14 is driven (steps 510 to 514). Through such control, the target EGR rate TEGR and the actual EGR rate PEG
The deviation from R is eliminated, and the target EGR rate TEGR and the actual EGR rate PEGR come to match. Note that FIG. 12 is an explanatory diagram showing the definition of the control duty D. If the on-time is TON and one cycle is Ta, the control duty D is expressed by the following equation.

D=TON/Ta×100(%)
...(2)

Further, if this device is in an idling state and is not in the EGR operation region, and the determination is "N" in step 504, it means that there is no EGR flow rate, and the EGR control value K is set to "K" in step 514.
At the same time, the control duty DEGR is calculated from the EGR control value of "0" in step 512, and the control duty DEGR is set to "0" in step 513.
The EGR solenoid 14 is driven.

FIGS. 13 and 14 are flowcharts illustrating another embodiment of the EGR control device of the present invention, and FIG.
3 shows the main routine with content backup processing, and FIG. 14 similarly shows the EGR control processing subroutine with content backup processing. In this embodiment, in FIG. 13, it is first determined whether the power is turned on for the first time after the battery 17 is installed (step 250). This is determined by detecting that the output voltage of the second power supply circuit 106 connected to the battery 17 changes from a low voltage value to a high voltage value. If this is determined as "Y", the CPU 20
0 is set the EGR control correction value KEGR to "0" (
251), and thereafter, similarly to the above embodiment, other control processes and combustion temperature calculation processes are sequentially executed, and then the EGR control process shown in FIG. 14 is executed.

At this time, if the determination in step 250 as to whether to turn on the power for the first time after the battery 17 is installed is determined to be "N", that is, if the battery 17 is already installed and only the IG switch 16 is turned on. EG
Without setting the R control correction value kEGR to "0",
EGR control correction value kEGR stored in AM205
is used as is in the processing from step 400 onwards.

Next, the flowchart shown in FIG. 14 will be explained. Here, since the processing in steps 550 to 559 is equivalent to the processing in steps 501 to 510 of the flowchart of FIG. 9, detailed explanation thereof will be omitted. That is, in steps 550 to 559, the EGR control correction value kEGR in the EGR operation region is calculated.
R is stored in step 560 and step 5
The EGR control value k is calculated by adding the basic control amount kBASE to the EGR control correction value kEGR obtained in step 59 (step 561), and the control duty DEGR is calculated from the obtained EGR control value k (step 562). The EGR solenoid 14 is driven based on the duty DEGR (step 563).

In this way, the EGR control correction value kEGR
This is stored at the time when it is calculated, and when this device is powered on, if this is not the first power-on after battery 17 is installed, the stored EGR is stored.
Since the control correction value kEGR is used as a correction value before calculation, EGR control can be performed accurately immediately after the IG switch 16 is turned on.

Furthermore, FIGS. 15 and 16 show the EGR of the present invention.
15 is a flow chart showing still another embodiment of the control device, FIG. 15 shows its main routine with failure determination, and FIG. 16 similarly shows its subroutine with failure determination. As shown in FIG. 15, in this embodiment, after sequentially executing other control processing, combustion temperature calculation processing, and EGR control processing, as shown in FIG. The details of the failure determination process will be explained using the flowchart of FIG. 16.

That is, in step 601, it is determined whether the EGR control correction value kEGR is smaller than a predetermined value α that would cause the result of an exhaust gas test to fail, and if it is larger than the predetermined value α, then Step 6
In step 02, it is determined whether the EGR control correction value kEGR is larger than a predetermined value β that would cause the result of an exhaust gas test to fail, and if it is smaller than the predetermined value β, in step 603 this EGR control device is determined to be normal and a flag to that effect is set, and the warning lamp 18 is turned off in step 604.

Further, if the EGR control correction value kEGR is smaller than the predetermined value α and it is determined as “Y” in step 601, or if the EGR control correction value kEGR is larger than the predetermined value α and it is determined as “Y” in step 602. If so, in step 605 this EGR control device is determined to be abnormal and a flag to that effect is set, and in step 606
The warning lamp 18 is lit. As described above, according to this embodiment, the target EGR rate TEGR and the actual EGR rate PEGR
By detecting a discrepancy between the two, it is possible to determine that the EGR control device is malfunctioning.

Next, another embodiment of failure determination for this EGR control device will be described based on the flowchart of FIG. 17. In this embodiment, as shown in FIG. 17, the absolute value of the value obtained by subtracting the actual EGR rate PEGR from the target EGR rate TEGR is set to C (step 650), and this absolute value C is determined as It is determined whether γ is larger than a predetermined value γ that would result in a failure (651). If this absolute value C is smaller than the predetermined value γ, then E
It determines that the GR control device is normal, sets a flag to that effect, and turns off the warning lamp 18 (652-6
53). Further, if the absolute value C is larger than the predetermined value γ, “Y
”, the EGR control device is determined to be abnormal and a flag to that effect is set, and the warning lamp 18 is
(654-655).

In this embodiment, the magnitude of the absolute value C indicating the deviation between the target EGR rate TEGR and the actual EGR rate PEGR is compared with the predetermined value γ, and as a result, it is immediately determined that the device is malfunctioning. I am trying to do this, but the timer is 20
A time measuring means 2 may be introduced to determine whether the device is malfunctioning by confirming that the magnitude relationship between the absolute value C and the predetermined value γ has continued for a certain period of time.

[0034]

As described above, according to the exhaust gas recirculation control device of the present invention, by utilizing the fact that there is a correlation between the combustion temperature of a cylinder and the amount of NOx, the combustion temperature is determined from the cylinder internal pressure, and the combustion The actual EGR rate is calculated from the temperature, the target EGR rate and the actual EGR rate are compared based on this actual EGR rate, and feedback control is performed so that the two match.
Accurate exhaust gas recirculation control can be performed according to various operating conditions.

Further, according to the present invention, since the deviation between the actual EGR rate and the target EGR rate or the value corresponding to this deviation is stored, it is possible to absorb deviations due to changes over time, etc. When turned on, exhaust gas recirculation control can be performed quickly and accurately. Further, according to the present invention, a failure is determined by detecting a discrepancy between the actual EGR rate and the target EGR rate, so there is an effect that a failure of the device can be directly and accurately detected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an exhaust gas recirculation control device of the present invention.

FIG. 2 is a block diagram showing details of the electronic control unit of FIG. 1;

FIG. 3 is a diagram showing the relationship between cylinder pressure and each signal and A/D conversion timing for explaining the above embodiment.

FIG. 4 is a diagram showing the relationship between NOx emissions and combustion gas temperature for explaining the present invention.

FIG. 5 is a diagram showing the relationship between NOx emissions and EGR rate for explaining the present invention.

FIG. 6 is a flowchart showing an example of a main routine of the CPU in the above embodiment.

FIG. 7 is a flowchart showing an example of a cylinder combustion temperature calculation subroutine of the above embodiment.

FIG. 8 is a flowchart showing another example of the in-cylinder combustion temperature calculation subroutine of the above embodiment.

FIG. 9 is a flowchart showing an example of an EGR control subroutine in the above embodiment.

FIG. 10: Integral correction ΔkEG used to explain the above embodiment.
It is a figure showing the characteristic of R.

FIG. 11 is a diagram showing the relationship between the EGR control value k and the control duty D, which is used to explain the above embodiment.

12 is an explanatory diagram showing the definition of control duty D in FIG. 11. FIG.

FIG. 13 is a flowchart of a main routine with content backup processing for explaining another embodiment of the present invention.

FIG. 14 is a flowchart of an EGR control subroutine with content backup processing in the embodiment of FIG. 13;

FIG. 15 is a flowchart of a main routine with failure determination for explaining another embodiment of the present invention.

FIG. 16 is a flowchart showing an example of a subroutine with failure determination in the embodiment of FIG. 15;

FIG. 17 is a flowchart showing another example of the subroutine with failure determination in the embodiment of FIG. 15;

[Explanation of symbols]

1 Engine 3 AFS sensor 4 Intake pipe 5 Throttle valve 7 Pressure sensor 9 Exhaust pipe 11 Crank angle sensor 12 Reflux pipe 13 EGR valve 14 EGR solenoid 15 Control unit 16 IG switch 17 Battery 18 Warning lamp 19 Throttle opening sensor

Claims (3)

[Claims] Claim 1: A recirculation pipe that recirculates exhaust gas from an internal combustion engine to an intake pipe, a recirculation valve that controls the flow rate of the exhaust gas flowing through the recirculation pipe, and a recirculation valve passage area control that controls the passage area of the recirculation valve. means, an operating state detecting means for detecting an operating state of the internal combustion engine, a pressure detecting means for detecting a cylinder pressure of the internal combustion engine, and an intake air amount detected from the operating state detecting means and detected from the pressure detecting means. means for calculating a combustion temperature from the cylinder internal pressure, and calculating an actual exhaust gas recirculation rate according to the combustion temperature and a detected value from the operating state detecting means; means for calculating a target exhaust gas recirculation rate according to the value, and controlling the recirculation valve passage area control means based on the deviation between the actual exhaust gas recirculation rate and the target exhaust gas recirculation rate, and calculating the passage area of the recirculation valve. An exhaust gas recirculation control device characterized by comprising: feedback control means for increasing or decreasing the actual exhaust gas recirculation rate so that the target exhaust gas recirculation rate matches the actual exhaust gas recirculation rate. 2. The exhaust gas recirculation control device according to claim 1, further comprising a storage means for storing a deviation between an actual exhaust gas recirculation rate and a target exhaust gas recirculation rate or a value corresponding to this deviation. Exhaust gas recirculation control device. 3. The exhaust gas recirculation control device according to claim 1, further comprising a failure diagnosis means for diagnosing a failure by detecting a discrepancy between an actual exhaust gas recirculation rate and a target exhaust gas recirculation rate. Exhaust gas recirculation control device.