JP6607138B2 - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation control device for an internal combustion engine.

  In an internal combustion engine, EGR is known that realizes NOx reduction of exhaust gas and improvement of fuel consumption by providing an exhaust gas recirculation pipe that recirculates exhaust gas as exhaust gas recirculation (EGR) gas to the intake side.

  In EGR, variations between cylinders in EGR gas distribution and variations in EGR gas flow rate due to deposit accumulation occur between cylinders, leading to variations in combustion between cylinders.

  In Patent Document 1, an intake air temperature sensor is arranged in each intake branch passage connected to each cylinder, the variation in the EGR gas distribution between the cylinders is determined from the variation in the intake air temperature of each cylinder, and the EGR valve provided in front of the intake manifold is The variation is eliminated by reducing the valve opening.

  In Patent Document 2, a cylinder in which an air-fuel ratio deviation abnormality has occurred is determined by a pre-catalyst sensor, and based on a knock index value before and after the occurrence of the abnormality, whether the air-fuel ratio deviation abnormality is due to variations in EGR gas distribution or fuel injection amount It is judged whether it is due to the variation of the.

JP-A-11-257162 Japanese Patent No. 5234143

  However, since the thing of patent document 1 is eliminating the dispersion | variation by reducing the valve opening degree of an EGR valve and reducing the amount of EGR gas, when it determines with there being dispersion | variation between cylinders of EGR gas distribution, A decrease in the EGR rate leads to a deterioration in fuel consumption and an increase in exhaust NOx.

  Although it is possible to specify the cylinder in which the dispersion | variation in EGR gas distribution has generate | occur | produced in the thing of patent document 2, the difference between cylinders of the dispersion | variation in EGR gas distribution is not measured. For this reason, when suppressing the variation of combustion, the control amount for suppressing the variation cannot be calculated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas recirculation control device for an internal combustion engine that can suppress the variation between cylinders in EGR gas distribution and improve fuel efficiency.

In order to solve the above problems, the present invention provides an exhaust gas recirculation control device for an internal combustion engine comprising a plurality of cylinders and a plurality of intake branch pipes for introducing intake air into each of the cylinders. An exhaust gas recirculation pipe that recirculates a part of each as EGR gas to each of the air intake branch pipes, and an EGR provided in each of the air intake branch pipes to adjust the recirculation amount of the EGR gas based on the operating state of the internal combustion engine A valve, a knock sensor for detecting knocking vibration of the internal combustion engine, a knock intensity for each cylinder of the internal combustion engine based on a detection result of the knock sensor, and a maximum value of a difference value of the knock intensity for each cylinder And a controller that adjusts the recirculation amount of the EGR gas for each cylinder when the value exceeds a predetermined value .

  As described above, according to the present invention, it is possible to provide an exhaust gas recirculation control device for an internal combustion engine that can suppress the variation between cylinders in EGR gas distribution and improve fuel efficiency.

FIG. 1 is a schematic configuration diagram of an exhaust gas recirculation control device for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a diagram showing a method for storing the knock intensity of each cylinder of the exhaust gas recirculation control apparatus for an internal combustion engine according to the embodiment of the present invention. FIG. 3 is a flowchart showing an exhaust gas recirculation control processing procedure of the exhaust gas recirculation control device for the internal combustion engine according to the embodiment of the present invention. FIG. 4 is a flowchart showing an exhaust gas recirculation control and a cylinder specific knock control processing procedure of the exhaust gas recirculation control device for an internal combustion engine according to the embodiment of the present invention. FIG. 5 is a diagram showing a process based on the knock intensity by the cylinder specific knock control process of the exhaust gas recirculation control apparatus for the internal combustion engine according to the embodiment of the present invention.

  Hereinafter, an exhaust gas recirculation control apparatus for an internal combustion engine according to an embodiment of the present invention will be described in detail with reference to the drawings.

  In FIG. 1, a vehicle 1 equipped with an exhaust gas recirculation control apparatus for an internal combustion engine according to an embodiment of the present invention includes an internal combustion engine type engine 2 and an ECU (Engine Control Unit) 3 as a control unit. Has been.

  The engine 2 is constituted by an in-line four cylinder having at least one, for example, four cylinders. The engine 2 is not limited to the in-line four cylinders, and may be, for example, a V-type engine, and the number of cylinders is not particularly limited to four.

  The engine 2 includes a piston, a cylinder, a connecting rod, and the like (not shown), and is a four-cycle engine that performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston reciprocates the cylinder twice. It is configured.

  The piston housed in the cylinder is connected to the crankshaft via a connecting rod. The connecting rod converts the reciprocating motion of the piston into the rotational motion of the crankshaft.

  The cylinder head is provided with an ignition plug 4, an intake port 11, and an exhaust port 21. The spark plug 4 is disposed on the cylinder head with an electrode protruding into the combustion chamber, and its ignition timing is adjusted by the ECU 3.

  The intake port 11 is provided with an intake manifold 13 as an intake branch pipe. The intake manifold 13 introduces air into the combustion chamber. The intake manifold 13 is connected to an intake pipe 14 for sucking outside air. An intake passage 14 a communicating with the intake port 11 is formed in the intake pipe 14.

  The intake port 11 is provided with an intake valve 12. The intake valve 12 is opened and closed so as to communicate or block the intake passage 14a and the combustion chamber.

  The exhaust port 21 is provided with an exhaust manifold 23 for discharging the exhaust generated by the combustion of the air-fuel mixture in the combustion chamber to the outside of the vehicle. The exhaust manifold 23 is connected to the exhaust pipe 24. An exhaust passage 24 a communicating with the exhaust port 21 is formed in the exhaust pipe 24.

  The exhaust port 21 is provided with an exhaust valve 22. The exhaust valve 22 is opened and closed so as to communicate or block the exhaust passage 24a and the combustion chamber.

  A three-way catalyst 25 is provided in the exhaust pipe 24. The three-way catalyst 25 purifies exhaust gas discharged from the combustion chamber of the engine 2, that is, burnt gas.

  The engine 2 is provided with an exhaust recirculation pipe 41 that communicates the intake passage 14a and the exhaust passage 24a. The exhaust gas recirculation pipe 41 is configured to perform EGR to recirculate part of the exhaust gas to the intake side. The exhaust gas recirculation pipe 41 is branched and connected to the intake manifold 13 of each cylinder. An EGR valve 42 as an exhaust gas recirculation control valve for adjusting the recirculation amount of exhaust gas corresponding to each cylinder is provided on the upstream side in the direction in which the exhaust gas at the connection portion of the exhaust gas recirculation pipe 41 with the intake manifold 13 is recirculated. ing.

  The EGR valve 42 is electrically connected to the ECU 3. The EGR valve 42 is configured to adjust the amount of exhaust gas recirculated to each cylinder by controlling the valve opening degree according to a command signal from the ECU 3.

  The ECU 3 includes a computer unit that includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a flash memory, an input port, and an output port.

  The ROM of the computer unit stores a program for causing the computer unit to function as the ECU 3 along with various control constants and various maps. That is, the computer unit functions as the ECU 3 when the CPU executes a program stored in the ROM.

  Various sensors such as a crank angle sensor 45, an accelerator opening sensor 46, and a knock sensor 47 are connected to the input port of the ECU 3.

  The crank angle sensor 45 outputs a rectangular crank angle signal for each predetermined crank angle as the engine 2 rotates. The ECU 3 calculates an engine speed that is the engine speed of the engine 2 based on the crank angle signal.

  The accelerator opening sensor 46 detects the amount of depression of an accelerator pedal (not shown) by the driver as the accelerator opening. Knock sensor 47 detects knocking vibration of engine 2 and outputs a knock signal corresponding to the magnitude of knocking vibration.

  On the other hand, various control objects such as the ignition plug 4 and the EGR valve 42 described above are connected to the output port of the ECU 3.

  The ECU 3 calculates the required load of the engine 2 based on the accelerator opening by the driver's operation, and calculates the intake air amount, fuel injection amount, and ignition timing of the engine 2 according to the required load. The ECU 3 controls the operating state of the engine 2 by controlling a throttle valve, an injector, and a spark plug 4 (not shown) so that the calculated intake air amount, fuel injection amount, and ignition timing are reached.

  The ECU 3 is configured to switch whether the EGR is executed (ON) or not (OFF) according to the operating state of the engine 2. For example, the ECU 3 switches EGR on and off based on an EGR map that is turned on or off depending on the engine speed and the engine load. This EGR map is divided into an EGR on region where EGR is turned on and an EGR off region where EGR is turned off, and which region is entered depends on the engine speed and engine load. Yes. This EGR map is experimentally obtained in advance and stored in the ROM of the ECU 3.

  For example, the ECU 3 obtains the engine load from a map in which the engine load is determined from the engine speed and the accelerator opening. The engine load map is experimentally obtained in advance and stored in the ROM of the ECU 3.

  The ECU 3 adjusts the EGR gas amount of each cylinder when it is determined that the variation between the cylinders of the EGR gas distribution is large based on the knock intensity for each cylinder in the state where the EGR is on.

  The ECU 3 calculates the knock intensity of each cylinder by the knock sensor 47 based on the combustion timing of each cylinder. For example, the ECU 3 calculates the knock intensity KSi (i is the cylinder number) of each cylinder from the vibration frequency of the cylinder block of the engine 2 detected by the knock sensor 47.

  The ECU 3 determines that the variation between the cylinders in the EGR gas distribution is large when the state where the maximum difference value of the knock strength KSi of each cylinder exceeds the predetermined value continues for the predetermined time Y [s] or longer. The predetermined value and the predetermined time are experimentally obtained in advance and stored in the ROM of the ECU 3.

  For example, as shown in FIG. 2, the ECU 3 stores a knock strength KSi of each cylinder. When the ECU 3 calculates a new knock strength KSi for a certain cylinder, the ECU 3 deletes the knock strength KSi stored in the cylinder and updates it with the new knock strength KSi. Each time the ECU 3 calculates a new knock strength KSi, the ECU 3 calculates the difference value of the knock strength of each cylinder, and determines the inter-cylinder variation in the EGR distribution.

  The ECU 3 makes an ignition retard request if the knock magnitude KSi of each cylinder is equal to or greater than a preset knock threshold. The ECU 3 calculates the ignition retard request amount according to the difference between the knock magnitude KSi and the knock threshold. The ignition retard requirement amount increases as the difference between the knock magnitude KSi and the knock threshold value increases.

  The ECU 3 makes an ignition advance request if the knock magnitude KSi of each cylinder is less than a preset knock threshold. The ECU 3 calculates the ignition advance request amount according to the difference between the knock magnitude KSi and the knock threshold. The ignition advance request amount increases as the difference between the knock magnitude KSi and the knock threshold value increases.

  The ECU 3 determines that the EGR gas amount is small for the cylinder for which the ignition retard request has been made, calculates an EGR valve opening increase correction value from the ignition retard request amount, and increases the opening of the EGR valve 42.

  In the ROM of the ECU 3, a limit value for increasing the EGR valve opening degree is stored in advance in order to prevent misfire due to an increase in the EGR rate. If the EGR valve opening increase correction value is equal to or less than the opening increase limit value, the ECU 3 increases the opening of the EGR valve 42 by the EGR valve opening increase correction value.

  If the EGR valve opening increase correction value exceeds the opening increase limit value, the ECU 3 increases the opening of the EGR valve 42 by the opening increase limit value, and the deficiency from the EGR valve opening increase correction value. Just perform an ignition retard.

  The ECU 3 determines that the amount of EGR gas is large for the cylinder for which the ignition advance request has been made. When the ignition advance request amount exceeds a preset advance angle limit value, the ECU 3 determines that the ignition advance is excessive due to excessive EGR, and calculates an EGR valve opening decrease correction value from the ignition advance request amount. The opening degree of the EGR valve 42 is reduced. When the ignition advance request amount is equal to or less than a preset advance angle limit value, the ECU 3 advances the ignition timing by the ignition advance request amount.

  In the ROM of the ECU 3, a limit value for reducing the EGR valve opening is set in advance in order to prevent the occurrence of knocking due to the decrease in the EGR rate. The ECU 3 reduces the opening degree of the EGR valve 42 by the EGR valve opening degree decrease correction value if the EGR valve opening degree reduction correction value is equal to or less than the opening reduction limit value.

  If the EGR valve opening decrease correction value exceeds the opening decrease limit value, the ECU 3 reduces the opening of the EGR valve 42 by the opening decrease limit value, and the deficiency from the EGR valve opening decrease correction value. Only perform the ignition advance.

  The determination of the knock intensity is executed in accordance with the combustion timing of each cylinder, and the control of the EGR valve 42 and the ignition timing based on the determination result are executed in accordance with the next combustion timing of the corresponding cylinder.

  Exhaust gas recirculation control processing by the exhaust gas recirculation control apparatus for an internal combustion engine according to the present embodiment configured as described above will be described with reference to FIGS. 3 and 4. Note that the exhaust gas recirculation control process described below is started when the ECU 3 starts operation, and is executed in synchronization with the combustion timing of each cylinder.

  In step S1, the ECU 3 determines whether or not the operation state of the engine 2 is in the EGR on region from the engine speed, the engine load, and the coolant temperature of the engine 2. If it is determined that it is not in the EGR-on region, the ECU 3 ends the process.

  When it is determined that it is in the EGR on region, in step S2, the ECU 3 calculates the knock strength of the cylinder at the current combustion timing by the knock sensor 47, and updates the knock strength of the corresponding cylinder.

  In step S3, the ECU 3 determines whether or not the state in which the maximum value of the difference value of the knock magnitude for each cylinder exceeds a predetermined value continues for a predetermined time Y [s] or longer.

  When it is determined that the state in which the maximum difference value of the knock intensity for each cylinder exceeds the predetermined value continues for the predetermined time Y [s] or longer, in step S4, the ECU 3 performs FIG. The cylinder-specific knock control as shown in FIG.

  On the other hand, when it is determined that the state in which the maximum difference value of the knock intensity for each cylinder exceeds the predetermined value has not continued for the predetermined time Y [s] or longer, in step S5, the ECU 3 controls the ignition timing of all the cylinders. The normal knock control is performed.

Next, the exhaust gas recirculation control and the cylinder specific knock control will be described with reference to FIG.
In step S11, the ECU 3 determines whether or not the knock intensity of the corresponding cylinder, which is the current combustion timing, is greater than or equal to a preset knock threshold.

  When it is determined that the knock magnitude of the corresponding cylinder is equal to or greater than a preset knock threshold, in step S12, the ECU 3 calculates an ignition retard request value from the difference between the knock magnitude and the knock threshold.

  In step S13, the ECU 3 calculates an EGR valve opening increase correction value from the ignition retard request value.

  In step S14, the ECU 3 determines whether or not the EGR valve opening increase correction value is larger than the opening increase limit value.

  When it is determined that the EGR valve opening increase correction value is larger than the opening increase limit value, in step S15, the ECU 3 increases the opening degree of the EGR valve 42 corresponding to the corresponding cylinder by the opening increase limit value. The ignition timing corresponding to the cylinder is ignited by a shortage from the EGR valve opening increase correction value, and the process is terminated.

  On the other hand, when it is determined that the EGR valve opening increase correction value is not larger than the opening increase limit value, in step S16, the ECU 3 corrects the EGR valve opening increase correction corresponding to the corresponding cylinder. Increase the value and finish the process.

  When it is determined in step S11 that the knock magnitude of the corresponding cylinder is not equal to or greater than a preset knock threshold, in step S17, the ECU 3 calculates an ignition advance request value from the difference between the knock magnitude and the knock threshold.

  In step S18, the ECU 3 determines whether or not the ignition advance request value is larger than the advance limit value.

  If it is determined that the ignition advance request value is greater than the advance limit value, in step S19, the ECU 3 calculates an EGR valve opening decrease correction value from the ignition advance request value.

  In step S20, the ECU 3 determines whether or not the EGR valve opening decrease correction value is larger than the opening decrease limit value.

  If it is determined that the EGR valve opening decrease correction value is larger than the opening decrease limit value, the ECU 3 decreases the opening of the EGR valve 42 corresponding to the corresponding cylinder by the opening decrease limit value in step S21. The ignition timing corresponding to the cylinder is advanced by the shortage from the EGR valve opening decrease correction value, and the process is terminated.

  On the other hand, if it is determined that the EGR valve opening decrease correction value is not greater than the opening decrease limit value, the ECU 3 corrects the opening of the EGR valve 42 corresponding to the corresponding cylinder in step S22. Decrease the value and finish the process.

  If it is determined in step S18 that the ignition advance request value is not greater than the advance limit value, in step S23, the ECU 3 advances the ignition timing corresponding to the corresponding cylinder by the ignition advance request value, and ends the process. .

The operation by such an exhaust gas recirculation control process will be described with reference to FIG.
As shown in FIG. 5, when the knock strength is 1st cylinder> 2nd cylinder> 3rd cylinder> 4th cylinder, the EGR rate is 4th cylinder> 3rd cylinder> 2nd cylinder> 1st cylinder. Become.

  The first cylinder and the second cylinder whose knock intensity is equal to or greater than the knock threshold are ignition retard requests. In the first cylinder and the second cylinder, the opening degree of the EGR valve 42 is increased in accordance with the difference between the knock magnitude and the knock threshold value, the EGR rate is increased, and the variation in the EGR distribution among the cylinders is suppressed.

  The No. 3 and No. 4 cylinders whose knock intensity is less than the knock threshold are ignition advance requests. In the third cylinder, since the ignition advance request value is equal to or less than the advance limit value, the ignition advance is advanced by the ignition advance request value, and knocking is suppressed.

  In the fourth cylinder, the ignition advance request value becomes larger than the advance limit value, and it is determined that the excessive advance angle is EGR, and the opening degree of the EGR valve 42 is reduced according to the difference between the knock magnitude and the knock threshold. As a result, the EGR rate decreases, and the variation in the EGR distribution among cylinders is suppressed.

  As described above, the above-described embodiment includes the ECU 3 that calculates the knock intensity for each cylinder based on the knock signal output from the knock sensor 47 and adjusts the recirculation amount of the EGR gas for each cylinder based on the knock intensity. .

  Thereby, the presence or absence of variation between cylinders in EGR gas distribution is determined based on the knock strength for each cylinder, and the recirculation amount of EGR gas for each cylinder is adjusted based on the knock strength for each cylinder. For this reason, the fuel consumption can be improved by suppressing variations between cylinders in EGR gas distribution.

  Further, the ECU 3 adjusts the recirculation amount of the EGR gas for each cylinder when the state where the maximum value of the difference value of the knock magnitude for each cylinder exceeds the predetermined value continues for the predetermined time Y [s] or longer.

  Thereby, when the state where the maximum value of the difference value of the knock intensity for each cylinder exceeds the predetermined value continues for the predetermined time Y [s] or more, it is determined that there is variation between the cylinders in the EGR gas distribution. For this reason, it is possible to reliably determine the case where there is a variation among the cylinders in the EGR gas distribution, and it is possible to suppress the variation between the cylinders in the EGR gas distribution and improve the fuel efficiency.

  Further, the ECU 3 determines whether the ignition retard request or the ignition advance request is made based on the difference between the knock magnitude and the knock threshold, and the cylinder of the ignition retard request increases the opening of the EGR valve 42, and the cylinder of the ignition advance request Decreases the opening of the EGR valve 42.

  Thereby, the recirculation amount of the EGR gas for each cylinder is adjusted based on the difference between the knock magnitude and the knock threshold. For this reason, the knock intensity of each cylinder approaches the knock threshold, and variations in the EGR gas distribution among cylinders can be suppressed to improve fuel efficiency.

  Further, when the ECU 3 calculates the opening correction value of the EGR valve 42 based on the difference between the knock magnitude and the knock threshold and corrects the opening of the EGR valve 42, if the opening correction value is larger than the limit value, The opening is corrected by the limit value, and the ignition timing is corrected for the shortage.

  Thereby, when the recirculation amount of the EGR gas for each cylinder is adjusted, the opening degree of the EGR valve 42 is limited by the limit value. For this reason, misfiring due to an increase in the EGR rate and knocking due to a decrease in the EGR rate can be suppressed.

  While embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that changes may be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

1 vehicle 2 engine (internal combustion engine)
3 ECU (control unit)
13 Intake manifold (intake branch pipe)
24 exhaust pipe 24a exhaust passage 41 exhaust recirculation pipe 42 EGR valve 45 crank angle sensor 46 accelerator opening sensor 47 knock sensor

Claims (3)

An exhaust gas recirculation control device for an internal combustion engine comprising a plurality of cylinders and a plurality of intake branch pipes for introducing intake air into each of the cylinders,
An exhaust gas recirculation pipe that recirculates a part of the exhaust gas of the internal combustion engine to each of the intake branch pipes as EGR gas;
An EGR valve provided in each of the intake branch pipes to adjust the recirculation amount of the EGR gas based on the operating state of the internal combustion engine;
A knock sensor for detecting knocking vibration of the internal combustion engine;
A knock intensity for each cylinder of the internal combustion engine is detected based on a detection result of the knock sensor, and when the maximum difference value of the knock intensity for each cylinder exceeds a predetermined value, the EGR gas is returned for each cylinder. An exhaust gas recirculation control device for an internal combustion engine, comprising: a control unit that adjusts a flow rate. 2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the control unit adjusts the recirculation amount of the EGR gas for each cylinder based on a difference between a knock intensity for each cylinder and a preset knock threshold. . 3. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein when the recirculation amount of the EGR gas for each cylinder is adjusted, the control unit restricts an opening degree of the EGR valve with a limit value.

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