JP2010053808A - Method for controlling exhaust-gas recirculation in internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when so-called external EGR control is effected, specific fuel consumption is sometimes decreased by retarding the ignition-timing. <P>SOLUTION: An internal combustion engine is equipped with an exhaust-gas recirculation system for recirculating exhaust-gas downstream of a throttle valve in the intake system, and a variable valve-timing mechanism for controlling opening/closing timing for at least either one of the intake valve and the exhaust valve. By the exhaust-gas recirculation control, according to the state of operation of the internal combustion engine, a changeover is executed between an exhaust-gas recirculation by the exhaust-gas recirculation system and a valve-timing control by the variable valve-timing mechanism. A retard quantity of ignition timing in execution of the exhaust-gas recirculation by the exhaust-gas recirculation system is learned. If the learned retard quantity is higher than the amount of determination of recirculation implementation to be set on the basis of the specific fuel consumption, exhaust-gas recirculation by the exhaust-gas recirculation system is suspended, and the valve timing control is performed by the variable-valve timing mechanism wherein at the ignition timing with the learned retard quantity, the specific fuel consumption is at most the amount of determination of recirculation implementation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device that recirculates exhaust gas to an intake system and a gas recirculation control method in an internal combustion engine that includes a variable valve timing mechanism that controls at least the opening / closing timing of one of an intake valve and an exhaust valve.

  Conventionally, in an internal combustion engine that performs recirculation of exhaust gas that mixes exhaust gas with intake air, deposits containing soot and the like may adhere to the combustion chamber due to long-term use. Due to the deposit, changes such as an increase in the temperature in the combustion chamber or an increase in the compression ratio occur, and knocking is likely to occur when exhaust gas recirculation control is performed. Therefore, in this type of internal combustion engine, ignition timing control is performed so as to prevent the occurrence of knocking by retarding the ignition timing.

For example, in the device described in Patent Document 1, it is determined whether or not the ignition timing or the retard amount of the ignition timing is in the surge generation region as a result of the ignition timing control, and the ignition timing is in the surge generation region. If it is determined that the exhaust gas recirculation is stopped, control is performed so that the exhaust gas recirculation is stopped or the exhaust gas recirculation amount is decreased from the normal case.
Japanese Patent Laid-Open No. 4-325752

  However, with such a configuration, the ignition timing is controlled to be retarded due to secular change in the combustion chamber, and when the ignition timing enters the surge generation region, the exhaust gas recirculation is stopped. Therefore, although surging due to knocking can be prevented, improvement in fuel efficiency due to exhaust gas recirculation cannot be expected. That is, in order to prevent surging, there is a problem that it becomes difficult to maintain fuel efficiency.

  Therefore, the present invention aims to eliminate such problems.

  That is, the exhaust gas recirculation control method for an internal combustion engine according to the present invention includes an exhaust gas recirculation pipe that recirculates the exhaust gas downstream from the throttle valve of the intake system, and a flow rate of the exhaust gas that passes through the exhaust gas recirculation pipe. An exhaust gas recirculation device comprising an exhaust gas recirculation control valve for adjusting the exhaust gas and an internal combustion engine comprising a variable valve timing mechanism for controlling the opening / closing timing of at least one of the intake valve and the exhaust valve. An exhaust gas recirculation control method for an internal combustion engine that switches between exhaust gas recirculation by an exhaust gas recirculation device and control of valve timing by a variable valve timing mechanism when exhaust gas recirculation is performed by the exhaust gas recirculation device When the retard amount of the ignition timing is learned and the learned retard amount exceeds the recirculation execution judgment amount set based on the fuel consumption rate, Which comprises carrying out the control of the valve timing by the variable valve timing mechanism fuel consumption rate is below reflux execution determination amount in the ignition timing by the retard amount learned to stop refluxing the exhaust gas by gas feedback device.

  According to such a configuration, for example, the exhaust gas recirculation is performed by the exhaust gas recirculation device, and deposits adhere to the combustion chamber of the internal combustion engine, so that the ignition timing is retarded to suppress knocking and the like. In this case, it is determined that there is a possibility that the fuel consumption rate in which the learned retardation amount exceeds the recirculation execution determination amount may be reduced, and the recirculation of exhaust gas by the exhaust gas recirculation device is stopped. Then, instead of the exhaust gas recirculation by the exhaust gas recirculation device, the valve timing is controlled by the variable valve timing mechanism, so that the exhaust gas recirculation is performed in the cylinder, the fuel consumption rate is reduced, the occurrence of knocking, etc. Can be suppressed.

  In order to improve the fuel efficiency when restarting the operation of the internal combustion engine, the learned retard amount is stored even after the engine is stopped, and the retard amount learned at the time of engine stop is the return execution determination amount. If the internal combustion engine is restarted in that state, the exhaust gas recirculation device is forced to recirculate the exhaust gas for a predetermined time, and the retard amount of the ignition timing within the predetermined time is learned. If the learned retardation amount is equal to or less than the exhaust gas recirculation execution determination amount, it is preferable to restart the exhaust gas recirculation by the exhaust gas recirculation device.

  The present invention is configured as described above, and when the retard amount of the ignition timing exceeds the recirculation execution determination amount for determining the recirculation of exhaust gas by the exhaust gas recirculation apparatus, the exhaust gas recirculation apparatus By performing valve timing control by a variable valve timing mechanism instead of exhaust gas recirculation, exhaust gas recirculation can be performed in the cylinder to suppress a reduction in fuel consumption rate and knocking.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

An engine 100 schematically showing the configuration of one cylinder in FIG. 1 is mounted on, for example, an automobile. The engine 100 includes an intake system 1, a cylinder 2, and an exhaust system 5. The intake system 1 is provided with a throttle valve 11 that opens and closes in response to an accelerator pedal (not shown), and an intake manifold 12 that integrally has a surge tank 13 is attached downstream of the throttle valve 11. A spark plug 8 is attached to the ceiling of the combustion chamber 23 formed in the upper part of the cylinder 2. A fuel injection valve 3 is attached to an intake port side end of the intake manifold 12. The fuel injection valve 3 is controlled by an electronic control device 4 described later. Further, an exhaust gas recirculation device 6 is connected between the surge tank 13 and the exhaust system 5 including the O ₂ sensor 51, the three-way catalyst 52, and the exhaust manifold 53.

  The exhaust gas recirculation device 6 has an exhaust gas recirculation pipe 61 connected at one end so as to communicate with the surge tank 13, and is provided in the exhaust gas recirculation pipe 61 and passes through the exhaust gas recirculation pipe 61. And an exhaust gas recirculation control valve 62 for controlling the flow rate of the exhaust gas. The other end of the exhaust gas recirculation pipe 61 is connected to the exhaust manifold 53 so as to communicate with the exhaust system 5 upstream of the three-way catalyst 52 provided in the exhaust 5 system. When the exhaust gas recirculation control valve 62 is controlled, that is, opened, the exhaust gas recirculation device 6 passes through the exhaust gas recirculation pipe 61 at a flow rate corresponding to the opening degree of the exhaust gas recirculation control valve 62, The refrigerant is returned to the downstream side of the throttle valve 11, that is, into the surge tank 13. The flow rate of the exhaust gas to be recirculated depends on the opening degree of the exhaust gas recirculation control valve 62, and the opening degree of the exhaust gas recirculation control valve 62 is controlled by the electronic control unit 4.

  The engine 100 includes a variable valve timing mechanism 9 for changing the opening / closing timing of the exhaust valve 24. The variable valve timing mechanism 9 uses a so-called oscillating cylinder mechanism, and includes a rotor fixed to the intake camshaft 91, a housing fitted outside the rotor, and an electromagnetic for rotating the housing relative to the rotor. An oil control valve 92 which is a four-way switching control valve, a pair of gears 94 and 95 which are attached to the housing and fixed to the exhaust camshaft 93 so as to mesh with each other, and attached to the end of the intake camshaft 91 A crank sensor 96 that outputs a crank angle signal and a cylinder discrimination signal, and a timing sensor 97 that is attached to the end of the exhaust cam shaft 93 and outputs an exhaust cam signal each time it rotates 240 ° CA (crank angle); It is the structure provided with.

  In such a configuration, the opening / closing timing of the exhaust valve 24, that is, the valve timing, is changed by the variable valve timing mechanism 9 operated by the opening / closing timing signal p output from the electronic control device 4. That is, when the variable valve timing mechanism 9 receives the opening / closing timing signal p, the oil control valve 92 controls the direction and amount of hydraulic fluid flowing into and out of the housing. As a result, the relative angle of the housing with respect to the rotor changes, and a desired rotational phase difference is generated between the intake camshaft 91 and the exhaust camshaft 93 to variably control the valve timing. That is, the opening / closing timing of the intake valve 21 and the opening / closing timing of the exhaust valve 24 are changed by changing the opening / closing timing of the exhaust valve 24 while constantly opening / closing the intake valve 21 with respect to the rotation of the crankshaft. The relative phase difference can be freely changed within a predetermined angle range. Further, the exhaust gas can be left in the cylinder 2 by making the closing timing of the exhaust valve 24 earlier, so that the exhaust gas is recirculated in the cylinder 2 or mixed with the intake air, so-called internal EGR is performed. It becomes.

  The electronic control unit 4 is mainly configured by a microcomputer system including a central processing unit 41, a storage unit 42, an input interface 43, and an output interface 44. The central processing unit 41 controls the operation of the engine 100 by executing various programs described below stored in the storage device 42. Information necessary for operation control of the engine 100 is input to the central processing unit 41 via the input interface 43, and the central processing unit 41 includes the fuel control valve 3, the exhaust gas recirculation control valve 62, and the oil control valve 92. A control signal is output via the output interface 44.

Specifically, the input interface 43 outputs an air flow rate signal a output from the air flow meter 71 for detecting the air flow rate flowing into the intake manifold 12, and an output from the rotation speed sensor 72 for detecting the engine speed. The rotation speed signal b, the vehicle speed signal c output from the vehicle speed sensor 73 for detecting the vehicle speed, the IDL signal d output from the idle switch 74 for detecting the open / closed state of the throttle valve 11, and the cooling of the engine 100 A water temperature signal f output from the water temperature sensor 76 for detecting the water temperature, a voltage signal h output from the O ₂ sensor 51, and a knocking sensor 75 for detecting a knocking state based on a change in combustion pressure. A knocking signal e or the like is input. On the other hand, from the output interface 44, the ignition signal m for the spark plug 8, the fuel injection signal n for the fuel control valve 3, the valve opening / closing signal o for the exhaust gas recirculation control valve 62, the variable valve timing mechanism 9 An opening / closing timing signal p or the like is output to the oil control valve 92.

  In such a configuration, the electronic control unit 4 is set according to the operating state using the air flow rate signal a output from the air flow meter 71 and the rotation speed signal b output from the rotation speed sensor 72 as main information. The fuel injection amount is calculated using the coefficient to determine the fuel injection time corresponding to the fuel injection amount, that is, the energization time for the fuel injection valve 3, and the fuel injection valve 3 is controlled by the determined energization time. Is injected into the intake system 1. Such fuel injection control itself may apply what is known in this field.

  The electronic control unit 4 determines the ignition timing of the spark plug 8 according to the driving situation and outputs an ignition signal m to the ignition plug 8. The electronic control device 4 determines the ignition timing based on the knocking signal e from the knocking sensor 75. Control to retard. In this retard timing control, the electronic control unit 4 learns the retard amount at the retarded ignition timing and stores it in the storage device 42. The learned retard amount, that is, the retard learning amount akgrg is updated every predetermined time, and the latest one is stored in the storage device 42 even after the ignition switch is turned off.

  Furthermore, when the engine 100 is stopped and the piston 25 is at the bottom dead center, the amount of air or the mass of air entering the cylinder 2 and the amount of air or the mass of air entering the cylinder 2 during the operation of the engine 100 are the same. An EGR control program for performing exhaust gas recirculation control by the exhaust gas recirculation device 6, that is, external EGR control when the load factor as a ratio is in a predetermined range is stored in the electronic control device 4. In the EGR control program, when the ignition timing control for retarding the ignition timing is performed while the external EGR control is being performed, the retard amount of the ignition timing is learned, and the retard learning is performed. When the amount akgrg exceeds the recirculation execution determination amount set based on the fuel consumption rate, the recirculation of the exhaust gas in the external EGR control is stopped, and the fuel consumption rate is less than the recirculation execution determination amount at the ignition timing with the retarded learning amount akgrg. The valve timing control by the variable valve timing mechanism 9 is programmed. A schematic procedure of the EGR control program is shown in FIG.

  In the following description, the engine 100 is assumed to be deposited in the combustion chamber 23 due to long-term use, and is operated in a region where the load factor performs EGR control. And Further, in the ignition timing retarding control, the ignition timing is set by retarding the amount of retardation calculated in accordance with the load factor from the knocking limit setting value when the ignition timing is advanced. . Alternatively, the knocking sensor is used for the retard amount obtained by advancing the retard amount by the retard amount from the most retarded amount that is uniformly retarded in the entire load factor range with respect to the knock limit setting value. The ignition timing may be retarded by correcting with a correction amount based on 75 knocking signals.

  In such an operating state, first, in step S1, the retard amount of the ignition timing is learned. That is, deposits adhere to the combustion chamber 23 due to secular change, for example, the temperature in the combustion chamber 23 is high, and knocking is likely to occur, and ignition is performed based on the knocking signal from the knock sensor 75. The timing is retarded. The learning conditions for the retard amount of the ignition timing may be those for learning the retard amount in the ignition timing control known in this field.

  Next, in step S2, the retard learning amount akgrg that is executing the external EGR control is compared with the reflux execution determination amount, and it is determined whether or not the retard learning amount akgrg exceeds the reflux execution determination amount. This recirculation execution determination amount is set based on a retard amount that reduces the fuel consumption rate (fuel consumption with respect to torque) by continuing external EGR control when external EGR control is performed at various load factors. is there. The fuel efficiency rate in the external EGR control decreases as the load factor increases, shows a high value in the driving state at a low load factor, and decreases as the load factor increases. On the other hand, when the opening / closing timing of the exhaust valve 24 is controlled by the variable valve timing mechanism 9, the fuel consumption rate can be maintained at a substantially constant value.

  If the result of determination in step S2 is that the retard learning amount akgrg is less than or equal to the reflux execution determination amount, that is, the retard learning amount akgrg is advanced from the reflux execution determination amount, the external EGR control is continued. Returning to step S1, if the retard learning amount akgrg exceeds the reflux execution determination amount, that is, if the retard learning amount akgrg is delayed from the reflux execution determination amount, the process proceeds to step S3.

  In step S3, the control of the exhaust gas recirculation device 6 is stopped. That is, the exhaust gas recirculation control valve 62 is fully closed to stop the exhaust gas recirculation via the exhaust gas recirculation pipe 61. In step S4, control of the variable valve timing mechanism 9 is started instead of control of the exhaust gas recirculation device 6. Once external EGR control is stopped, the variable valve timing mechanism 9 controls the opening / closing timing of the exhaust valve 24 until the ignition switch is turned off, that is, until the current operation is completed, and is mixed with the intake air. The amount of exhaust gas to be adjusted is adjusted. In other words, the external EGR control is not executed after the execution of step S3 even if the updated retarded learning amount akgrg may be less than or equal to the reflux execution determination amount. Specifically, the variable valve timing mechanism 9 closes the exhaust valve 24 before the piston 25 reaches the top dead center, thereby leaving a part of the exhaust gas to be exhausted in the cylinder 2. Then, the intake valve 21 is opened to mix the exhaust gas with the intake air.

  In the above configuration, in an environment where deposits adhere to the combustion chamber 23 due to secular change and knocking is likely to occur, the exhaust gas recirculation device 6 is controlled, and external EGR control for recirculating the exhaust gas to the surge tank 13 is performed. The ignition timing is retarded in response to changes in the operating state. When the ignition timing is retarded, the retard amount at that time is learned (step S1), and when the operating state of the engine 100 in which the retard learning amount akgrg exceeds the reflux execution determination amount is determined (step S2, "Yes") The external EGR control is stopped (step S3), and the control of the variable valve timing mechanism 9 with a good fuel consumption rate is performed (step S4), so that a reduction in the fuel consumption rate can be suppressed. In this case, by setting the recirculation execution determination amount based on the fuel consumption rate with respect to the retard learning amount akgrg, it is possible to suppress the occurrence of torque fluctuation due to the retard of the ignition timing, that is, the driving state in which surging of the vehicle occurs. Is possible.

  Next, as described above, when the retard learning amount akgrg exceeds the recirculation execution determination amount and the external EGR control is stopped, the operation of the engine 100 is stopped, and then the operation of the engine 100 is restarted. To explain. In the following description, it is assumed that after the engine 100 is restarted, the operating state, that is, the load factor has reached the region where the external EGR control is performed. When the load factor does not reach the area where the external EGR control is performed, the retard learning amount akgrg in the previous operation is maintained, and the control of the variable valve timing mechanism 9 is performed instead of the external EGR control.

  In such a situation, in step S11, the external EGR control is forcibly executed for a predetermined time from the time when the load factor reaches the operation region of the external EGR control. That is, in the previous operation of the engine 100, the external EGR control is stopped and switched to the operation state in which the control of the variable valve timing mechanism 9 is performed instead. For this reason, the retard learning amount akgrg that exceeds the reflux execution determination amount is stored even after the ignition switch is turned off, so that the external EGR control is not performed in the current operation. In such a state, the exhaust gas recirculation control valve 62 of the exhaust gas recirculation device 6 is opened only for a predetermined time, and the exhaust gas is recirculated to the surge tank 13 via the exhaust gas recirculation pipe 61. The predetermined time may be an actual elapsed time from the time when the load factor reaches the operating range of the external EGR control, or the time may be converted by counting the number of ignitions of an arbitrary cylinder. Good. In this embodiment, the predetermined time is set to a length during which the learning of the retard amount, that is, the update of the retard learning amount akgrg can be performed a plurality of times, for example, three times.

  In step S12, learning of the retard amount of the ignition timing during the execution of the external EGR control as described above, that is, updating of the retard learning amount akgrg is performed. In step S12, as described above, the prescribed number of updates is performed three times. Thereafter, in step S13, the retard learning amount akgrg is compared with the reflux execution determination amount. If the updated retard learning amount akgrg exceeds the reflux execution determination amount, the program is terminated. Then, the valve timing control (internal EGR control) by the variable valve timing mechanism 9 is executed. On the other hand, if a result is obtained that the retard learning amount akgrg updated this time is less than or equal to the reflux execution determination amount, the process proceeds to step S14. That is, during this operation, the deposit state in the combustion chamber 23 has further changed, and the ignition timing is advanced by forcibly performing external EGR control. As a result, the retard learning amount akgrg is recirculated. The amount is less than the execution determination amount. In step S14, external EGR control is performed in response to the result of step S13.

  The control in steps S11 to S14 described above is effective to cope with a change in the engine 100 over time, that is, a change in the state of deposit adhesion in the combustion chamber 23. That is, in the previous operation of the engine 100, deposits in the combustion chamber 23 are attached, so that it is necessary to retard the ignition timing based on the knocking signal e of the knocking sensor 75. Then, as a result of the retard control, the external EGR control is stopped, and the variable valve timing mechanism 9 is controlled instead. When the external EGR control is stopped, the control of the variable valve timing mechanism 9 in which the fuel consumption rate at the retard amount is better than that of the external EGR control is continued. That is, the control of the variable valve timing mechanism 9 is continued at the fuel consumption rate corresponding to the retard amount corresponding to the retard amount equal to or less than the reflux execution determination amount. While the operation in that state is continued, the deposit in the combustion chamber 23 may disappear.

  However, when the external EGR control is stopped in the control in the above-described steps S1 to S4, the external EGR control is stopped because the retard learning amount akgrg is not reset or initialized even when the engine 100 is operated next time. The engine 100 is operated as it is. However, on the other hand, as described above, the factor relating to knocking in the combustion chamber 23 may change, that is, disappear while the control of the variable valve timing mechanism 9 is being executed. In such an operating state, if the external EGR control is stopped, the external EGR control in which the fuel consumption rate with respect to a certain retard amount that is equal to or less than the reflux execution determination amount is better than that in the control of the variable valve timing mechanism 9. Can not be carried out. That is, there arises a problem that the driving cannot be maintained by increasing the fuel consumption rate.

  Therefore, in the previous operation, while the operation in which the external EGR control is stopped is continued, the control of the variable valve timing mechanism 9 is continued regardless of the change in the combustion chamber 23. When the engine is stopped, when the engine 100 is operated again, the control in the above-described steps S11 to S14 is executed in order to consider the change in the combustion chamber 23.

  Therefore, by forcibly executing the external EGR control, it is determined whether or not the state in the combustion chamber 23 has changed by changing the retard amount of the ignition timing during the forced execution of the external EGR control. Can do. In addition, since the external EGR control is resumed when the retard amount of the ignition timing, that is, the updated retard learning amount akgrg becomes equal to or less than the recirculation execution determination amount, the variable valve timing mechanism 9 also operates at the same retard learning amount akgrg. It is possible to achieve a driving state with a higher fuel efficiency than in the case of control.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above embodiment, the description has been given of the case where the opening / closing timing of the intake valve 21 can be changed with respect to the opening / closing timing of the exhaust valve 24. However, the opening / closing timing of the exhaust valve 24 can be changed with respect to the opening / closing timing of the intake valve 21. Furthermore, the opening / closing timing of both the intake valve 21 and the exhaust valve 24 may be mutually changeable. The variable valve timing mechanism itself for the intake valve 21 and the exhaust valve 24 may be one that is known in this field.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  As an application example of the present invention, external EGR control by an exhaust gas recirculation device and exhaust gas control by a variable valve timing mechanism can be used for an internal combustion engine that is switched according to a load factor.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of embodiment of this invention. The flowchart which shows the outline of the control procedure of the embodiment. The flowchart which shows the outline of the control procedure of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Intake system 4 ... Electronic control unit 6 ... Exhaust gas recirculation device 9 ... Variable valve timing mechanism 11 ... Throttle valve 21 ... Intake valve 24 ... Exhaust valve 61 ... Exhaust gas recirculation line 62 ... Exhaust gas recirculation control valve

Claims (2)

Exhaust gas comprising an exhaust gas recirculation pipe that recirculates the exhaust gas downstream from the throttle valve of the intake system, and an exhaust gas recirculation control valve that adjusts the flow rate of the exhaust gas that passes through the exhaust gas recirculation pipe In an internal combustion engine including a recirculation device and a variable valve timing mechanism that controls opening / closing timing of at least one of an intake valve and an exhaust valve, exhaust gas recirculation by an exhaust gas recirculation device and a variable valve timing mechanism according to an operating state An exhaust gas recirculation control method for an internal combustion engine that switches between valve timing control and
Learn the retard amount of the ignition timing when the exhaust gas recirculation by the exhaust gas recirculation device
If the learned retard amount exceeds the recirculation execution judgment amount set based on the fuel consumption rate, the fuel consumption rate is recirculated at the ignition timing with the learned retard amount by stopping the exhaust gas recirculation by the exhaust gas recirculation device. An exhaust gas recirculation control method for an internal combustion engine, in which valve timing is controlled by a variable valve timing mechanism that is equal to or less than an execution determination amount. The learned retard amount is memorized even after the engine stops,
The retard amount learned at the time of engine stop is stored in excess of the recirculation execution judgment amount, and when the operation of the internal combustion engine is resumed in that state, the exhaust gas recirculation device is forcibly recirculated for a predetermined time. And
Learn retard amount of ignition timing within a predetermined time,
The exhaust gas recirculation control method for an internal combustion engine according to claim 1, wherein when the learned retard amount is equal to or less than the exhaust gas recirculation execution determination amount, recirculation of the exhaust gas by the exhaust gas recirculation device is resumed.

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