JP4760733B2 - Internal combustion engine control system - Google Patents

Description

  The present invention relates to a technique for controlling a spark ignition internal combustion engine.

Conventionally, in spark ignition type internal combustion engines, the ignition timing is advanced ahead of MBT (Minimum spark advance for Best Torque), thereby promoting the temperature rise of the cooling water and improving the warm-up performance of the internal combustion engine. The technique to make is known (for example, refer patent document 1).
JP 2000-240547 A

  By the way, although the above-described conventional technology considers the warm-up property of the internal combustion engine, it does not consider exhaust emission, and thus may not be able to fully adapt to exhaust emission regulations.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique suitable for reducing exhaust emissions in a control system for a spark ignition type internal combustion engine in which the ignition timing can be advanced from MBT. is there.

  In order to solve the above-described problems, the present invention provides an internal combustion engine control system capable of advancing the ignition timing ahead of MBT, and using a technique for advancing the ignition timing ahead of MBT, The reduction was made.

  When the temperature in the cylinder (hereinafter referred to as “in-cylinder temperature”) is low, such as when the internal combustion engine is in a cold state, the fuel tends to adhere to the inner wall surface of the cylinder and the piston. Most of the fuel adhering to the inner wall surface of the cylinder and the piston (hereinafter referred to as “in-cylinder attached fuel”) is discharged from the cylinder without being burned without being used for combustion. At this time, if the catalyst disposed in the exhaust system of the internal combustion engine is in an inactive state, the above-described unburned fuel component is released into the atmosphere without being purified by the catalyst.

  In particular, when the internal combustion engine is started at a low temperature, the period from the start of the internal combustion engine to the activation of the catalyst becomes longer and the amount of in-cylinder attached fuel increases, so unburned fuel released into the atmosphere. There is a concern that the amount of components becomes excessive.

  In contrast, as a result of the inventor's earnest experiment and verification, when the ignition timing is advanced to the front of MBT (hereinafter referred to as “over-advanced angle”) in a spark ignition type internal combustion engine, the cylinder It has been found that unburned fuel components (eg HC) discharged from within are significantly reduced.

  This is because, when the ignition timing is over-advanced, the amount of the air-fuel mixture that burns before compression top dead center increases. In addition to the temperature effect, the pressure in the cylinder (hereinafter referred to as “in-cylinder pressure”) and the peak of the in-cylinder temperature are increased, and the fuel adhering in the cylinder and / or the fuel before adhering in the cylinder is vaporized and This is thought to be due to the promotion of oxidation.

According to the knowledge described above, it is considered that as the in-cylinder pressure and the in-cylinder temperature peaks, the unburned fuel component discharged from the cylinder decreases. It is considered that the peak of the in-cylinder pressure and the in-cylinder temperature becomes higher as the amount of air-fuel mixture that burns before compression top dead center increases. The amount of air-fuel mixture burned before compression top dead center increases as the combustion end time of the air-fuel mixture gets earlier. As a method of advancing the combustion end timing of the air-fuel mixture, a method of further advancing the ignition timing at the time of excessive advance is conceivable.

  By the way, if the ignition timing at the time of excessive advance is greatly advanced, there is a possibility that ignition will be performed before the fuel and air in the cylinder are uniformly mixed. If ignition is performed before the fuel and air in the cylinder are uniformly mixed, there is a possibility that poor ignition of the fuel or misfiring may occur.

  Further, when the advance amount of the ignition timing increases, the fuel entering the gap (clevis volume) between the piston, the piston ring, and the cylinder bore wall surface tends to increase. The fuel that has entered the clevis volume is likely to be discharged from the cylinder without being used for combustion.

  Therefore, if the advance amount of the ignition timing becomes excessive at the excessive advance angle, the amount of the unburned fuel component discharged from the cylinder may increase instead.

  Therefore, the control system for an internal combustion engine according to the present invention performs the process for increasing the combustion speed of the air-fuel mixture when the ignition timing is over-advanced, thereby minimizing the amount of advance of the ignition timing. The combustion end time of the air-fuel mixture was advanced.

  Specifically, the control system for an internal combustion engine according to the present invention includes an over-advance means for over-advancing the ignition timing of the spark ignition type internal combustion engine before MBT, and a combustion speed of the air-fuel mixture in the cylinder of the internal combustion engine. Combustion promoting means for increasing, and control means for increasing the combustion speed of the air-fuel mixture by the combustion promoting means when the over-advance angle means causes the ignition timing to advance excessively.

  According to this configuration, when the over-advance means causes the ignition timing to advance, the combustion acceleration means increases the combustion speed of the air-fuel mixture. In this case, even if the ignition timing is not significantly advanced, the amount of air-fuel mixture that burns before compression top dead center increases.

  Accordingly, it is possible to increase the peak of the in-cylinder pressure and the in-cylinder temperature without significantly advancing the ignition timing at the time of excessive advance. As a result, the unburned fuel component discharged from the cylinder can be suitably reduced.

  The control system for an internal combustion engine according to the present invention further includes acquisition means for acquiring the in-cylinder attached fuel amount, and the control means increases the combustion rate of the air-fuel mixture as the in-cylinder attached fuel amount acquired by the acquisition means increases. In this way, the combustion promoting means may be controlled.

  According to this configuration, the peak of the in-cylinder pressure and the in-cylinder temperature is increased as the amount of in-cylinder attached fuel increases. As a result, the unburned fuel component discharged from the cylinder can be reduced without significantly increasing the advance amount of the ignition timing even under the condition where the amount of in-cylinder attached fuel increases.

  As a method of increasing the combustion speed of the air-fuel mixture in the cylinder, a method of reducing the opening degree of the airflow control valve provided in the intake port of the internal combustion engine, a method of retarding the opening start timing of the intake valve, or each cylinder The method etc. which make the lift amount of the some intake valve provided in can differ can be illustrated.

  Note that the combustion speed of the air-fuel mixture increases as the opening degree of the airflow control valve decreases, the opening timing of the intake valves delays, or the relative difference between the lift amounts of the plurality of intake valves increases. Therefore, as the fuel adhering to the cylinder increases, the control means decreases the opening of the airflow control valve, increases the retard amount of the opening timing of the intake valves, or increases the relative difference between the lift amounts of the plurality of intake valves. You may do it.

  According to the present invention, it is possible to suitably reduce exhaust emission in a control system for a spark ignition internal combustion engine that can advance the ignition timing before MBT.

  Hereinafter, specific embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine control system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a four-stroke cycle spark ignition type internal combustion engine (gasoline engine) having a plurality of cylinders 2. The cylinder 2 of the internal combustion engine 1 is connected to the intake passage 30 through the intake port 3 and is connected to the exhaust passage 40 through the exhaust port 4.

  The intake port 3 is provided with a fuel injection valve 5 that injects fuel into the cylinder 2. The intake passage 30 is provided with a throttle valve 6 that controls the amount of air flowing through the intake passage 30. An intake pressure sensor 7 that measures the pressure (intake pressure) in the intake passage 30 is provided in the intake passage 30 downstream of the throttle valve 6. An air flow meter 8 that measures the amount of air flowing through the intake passage 30 is provided in the intake passage 30 upstream of the throttle valve 6.

  On the other hand, an exhaust purification device 9 is disposed in the exhaust passage 40. The exhaust purification device 9 includes a three-way catalyst, an NOx storage reduction catalyst, and the like, and purifies exhaust when it is in a predetermined activation temperature range.

  Further, the internal combustion engine 1 is provided with an intake valve 10 that opens and closes an open end of the intake port 3 facing the cylinder 2 and an exhaust valve 11 that opens and closes an open end of the exhaust port 4 facing the cylinder 2. The intake valve 10 and the exhaust valve 11 are driven to open and close by an intake camshaft 12 and an exhaust camshaft 13, respectively.

  A spark plug 14 for igniting the air-fuel mixture in the cylinder 2 is disposed at the upper part of the cylinder 2. A piston 15 is slidably inserted into the cylinder 2. The piston 15 is connected to the crankshaft 17 via a connecting rod 16.

  A crank position sensor 18 that detects a rotation angle of the crankshaft 17 is disposed in the vicinity of the crankshaft 17. Furthermore, a water temperature sensor 19 for measuring the temperature of the cooling water circulating through the internal combustion engine 1 is attached to the internal combustion engine 1.

  A variable valve mechanism 120 that changes the rotational phase of the intake camshaft 12 relative to the crankshaft 17 is attached to the intake camshaft 12.

  The internal combustion engine 1 configured as described above is provided with an ECU 20. The ECU 20 is an electronic control unit that includes a CPU, a ROM, a RAM, and the like. The ECU 20 is electrically connected to various sensors such as the intake pressure sensor 7, the air flow meter 8, the crank position sensor 18, and the water temperature sensor 19 described above, and can input measurement values of the various sensors.

  The ECU 20 electrically controls the fuel injection valve 5, the throttle valve 6, the spark plug 14, and the variable valve mechanism 120 based on the measurement values of the various sensors described above. For example, the ECU 20 performs attached fuel reduction control for reducing the fuel attached to the wall surface in the cylinder 2.

  Hereinafter, the adhered fuel reduction control in this embodiment will be described.

  When the in-cylinder temperature is low, such as when the internal combustion engine 1 is in a cold state, the fuel tends to adhere to the inner wall surface of the cylinder 2 and the piston 15. Most of the fuel (in-cylinder attached fuel) adhering to the inner wall surface of the cylinder 2 and the piston 15 is discharged from the cylinder without being burned without being used for combustion. At that time, if the exhaust purification device 9 has not been heated to the activation temperature range, the above-mentioned unburned fuel component is released into the atmosphere without being purified.

  In particular, when the internal combustion engine 1 is started at a low temperature, etc., the period from the start of the internal combustion engine 1 to the activation of the exhaust gas purification device 9 becomes longer and the amount of fuel adhering to the cylinder increases. There is a risk that the amount of the unburned fuel component will be excessive.

  On the other hand, in the attached fuel reduction control, the ECU 20 decreases the in-cylinder attached fuel amount by advancing the operation timing (ignition timing) of the spark plug 14 from the MBT when the in-cylinder attached fuel amount increases. Thus, the amount of unburned fuel component discharged from the cylinder 2 is also reduced.

  According to the inventor's earnest experiment and verification, when the ignition timing is advanced from the MBT, as shown in FIG. 2, the unburned gas discharged from the cylinder 2 increases as the advance amount increases. It has been found that the amount of fuel component (HC) is reduced.

  Although this mechanism has not been clearly clarified, it is thought to be due to the following mechanism.

  FIG. 3 shows a case where the ignition timing is advanced (hereinafter referred to as “over-advance angle”) before MBT (ST1 in FIG. 3) and a case where the ignition timing is set to MBT (in FIG. 3). It is a figure which shows the result of having measured the state in the cylinder 2 in each of the case where the ignition timing is set to the compression top dead center (TDC) (ST3 in FIG. 3). The solid line in FIG. 3 shows the case where the ignition timing is over-advanced, the broken line shows the case where the ignition timing is set to MBT, and the dashed line shows the case where the ignition timing is set to compression top dead center (TDC). Yes.

  In FIG. 3, when the ignition timing is over-advanced, combustion occurs before the compression top dead center, compared to when the ignition timing is set to MBT and when the ignition timing is set to compression top dead center (TDC). The amount of air-fuel mixture produced increases. For this reason, the peak of the heat energy generated by the combustion of the air-fuel mixture (see the heat generation rate, generated heat amount, and combustion mass ratio in FIG. 3) shifts to before the compression top dead center.

  Therefore, the cylinder in the period from the compression stroke to the expansion stroke is obtained by a synergistic effect of the temperature increase / pressure increase effect due to the combustion of the air-fuel mixture and the compression effect due to the upward movement of the piston 15 (operation from the bottom dead center to the top dead center). The peak values of internal pressure and in-cylinder temperature are significantly increased. As a result, it is considered that vaporization and oxidation of the fuel adhering to the cylinder 2 and / or the fuel before adhering to the cylinder 2 are promoted.

  Therefore, the ECU 20 causes the ignition timing to be over-advanced when the amount of fuel adhering in the cylinder is expected to increase. As a case where the amount of in-cylinder attached fuel is expected to increase, when the internal combustion engine 1 is cold-started, or when the internal combustion engine 1 is in a warm-up operation state, the actually measured value of the in-cylinder attached fuel amount exceeds the allowable amount. A case where the estimated value of the in-cylinder attached fuel amount exceeds the allowable amount or the like can be exemplified.

As a method for actually measuring the amount of fuel adhering to the cylinder, a method for optically measuring the liquid film thickness in the cylinder 2 and a method for actually measuring it, or a sensor for measuring the conductivity in the cylinder 2 can be used. A method for converting the measured value of the sensor into the in-cylinder attached fuel amount can be exemplified. The method for estimating the amount of fuel adhering to the cylinder includes at least the cooling water temperature, the cumulative fuel injection amount from the time of engine startup, the cumulative intake air amount from the time of engine startup, the current fuel injection amount, the intake pressure, and the air-fuel ratio. A method of estimating from the correlation between one and the amount of in-cylinder attached fuel can be exemplified.

  When the amount of fuel adhering to the cylinder is expected to increase, if the ignition timing of the spark plug 14 is over-advanced, the fuel adhering to the cylinder can be reduced and the unburned fuel component discharged from the cylinder 2 Can also be reduced.

  Incidentally, since the unburned fuel component discharged from the cylinder 2 decreases as the ignition timing advance amount increases, it is preferable to increase the ignition timing advance amount as the in-cylinder attached fuel amount increases.

  However, if the advance amount of the ignition timing becomes excessive, there is a possibility that the spark plug 14 operates before the fuel and air (intake air) in the cylinder 2 are uniformly mixed. If the spark plug 14 is operated before the fuel and air are uniformly mixed, poor ignition and misfire are likely to occur.

  In addition, when the ignition timing is greatly advanced, the fuel entering the clevis volume may increase. The fuel that has entered the clevis volume is easily discharged from the cylinder 2 without being burned.

  Therefore, there is a concern that the unburned fuel component discharged from the cylinder 2 may increase when the ignition timing at the time of excessive advance is greatly advanced.

  Therefore, in the attached fuel reduction control of this embodiment, when it is predicted that the in-cylinder attached fuel will increase, the ECU 20 performs processing for increasing the combustion rate of the air-fuel mixture in addition to the ignition timing over-advance processing (hereinafter, referred to as “fuel ratio”). (Referred to as “combustion promotion treatment”).

  In the combustion acceleration process, the ECU 20 uses the variable valve mechanism 120 to retard the valve opening start timing (IVO) of the intake valve 10 from the intake top dead center. In this case, the intake valve 10 does not open until halfway through the intake stroke. Therefore, when the intake valve 10 is opened, the pressure in the cylinder 2 becomes negative. As a result, the kinetic energy of the intake air that flows into the cylinder 2 after the intake valve 10 is opened increases. When the kinetic energy of the intake air increases, the kinetic energy of the tumble flow or swirl flow generated in the cylinder 2 increases (in other words, the strength of the tumble flow or swirl flow is enhanced).

  Thus, when the airflow in the cylinder 2 is strengthened, the flame propagation speed and the combustion speed after the operation of the spark plug 14 are increased. When the flame propagation speed and the combustion speed are increased, the amount of air-fuel mixture burned before compression top dead center increases. As a result, the peak of in-cylinder pressure and in-cylinder temperature is increased.

  FIG. 4 is a diagram showing the relationship between the amount of unburned fuel component (HC) discharged from the cylinder 2 and the ignition timing. The dashed line in FIG. 4 shows the result of measuring the amount of unburned fuel component (HC emission amount) discharged from the cylinder 2 when the combustion promotion process is not executed (when the combustion promotion process is not executed). The solid line in FIG. 4 shows the result of measuring the HC emission amount when the combustion promotion process is executed (when the combustion promotion process is executed). Note that the two measurement results shown in FIG. 4 are the results measured when the operating conditions other than the valve opening start timing of the intake valve 10 are the same.

  According to the measurement result of FIG. 4, in the region where the ignition timing is advanced before MBT, the HC emission amount at the time of executing the combustion promotion process is smaller than the HC emission amount at the time of not executing the combustion acceleration process. This is thought to be due to the increase in the amount of air-fuel mixture burned before compression top dead center due to the execution of the combustion acceleration process.

  Therefore, when the HC emission amount is suppressed to a certain amount (for example, Ahc in FIG. 4) or less, the ignition timing (t1 in FIG. 4) at the time of executing the combustion promotion process is the ignition timing (t1 in FIG. 4). It can be made later than t2) in FIG. As a result, it is possible to suppress the occurrence of problems due to a large advance of the ignition timing.

  Hereinafter, the execution procedure of the adhered fuel reduction control in the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing an attached fuel reduction control routine. This routine is a routine previously stored in the ROM of the ECU 20 and is periodically executed by the ECU 20. In addition, when the ECU 20 executes the attached fuel reduction control routine, the over-advance angle means, the combustion acceleration means, the acquisition means, and the control means according to the present invention are realized.

  In the routine of FIG. 5, the ECU 20 first calculates the in-cylinder attached fuel amount Dpfuel in S101.

  In S102, the ECU 20 determines whether or not the in-cylinder attached fuel amount Dpfuel calculated in S101 is equal to or greater than a predetermined amount. The predetermined amount is a value determined so that the total amount of unburned fuel components discharged from all the cylinders 2 of the internal combustion engine 1 is less than a regulated amount (for example, Ahc shown in FIG. 4).

  If a negative determination is made in S102 (Dpfuel <predetermined amount), the ECU 20 ends the execution of this routine without executing the ignition timing over-advance angle and combustion promotion processing. On the other hand, when an affirmative determination is made in S102 (Dpfuel ≧ predetermined amount), the ECU 20 proceeds to S103.

  In S103, the ECU 20 reads the target valve opening start timing IVOtrg of the intake valve 10 calculated by a separate valve timing control routine.

  In S104, the ECU 20 calculates a retardation correction amount Δvt of the valve opening start timing of the intake valve 10. The retardation correction amount Δvt is a variable value that is increased or decreased according to the in-cylinder attached fuel amount Dpfuel. At this time, the retardation correction amount Δvt may be increased as the in-cylinder attached fuel amount Dpfuel increases, and may be decreased as the in-cylinder attached fuel amount Dpfuel decreases.

  In S105, the ECU 20 adds the retardation correction amount Δvt calculated in S104 to the target valve opening start timing IVOtrg read in S103, and the addition result (= IVOtrg + Δvt) is the target of the intake valve 10. The valve opening start time IVOtrg is set. Then, the ECU 20 operates the variable valve mechanism 120 in accordance with the target valve opening start timing IVOtrg set in S104.

  Subsequently, in S106, the ECU 20 executes an excessive advance angle of the ignition timing. The advance amount of the ignition timing at that time may be a predetermined fixed value. The fixed value described above is, for example, a range in which poor fuel ignition or misfire cannot occur, and is preferably a value within which the amount of fuel entering the clevis volume is within an allowable range.

  When the ECU 20 executes the routine of FIG. 5 in this manner, the combustion speed of the air-fuel mixture increases as the in-cylinder attached fuel amount Dpfuel increases, so that the HC emission amount becomes less than the regulated amount without greatly advancing the ignition timing. Can be suppressed.

In this embodiment, an example in which the ignition timing at the time of over-advancement is fixed at a fixed time has been described, but the ignition timing at the time of over-advancement may be changed according to the in-cylinder attached fuel amount Dpfuel. In this case, as long as the ignition timing determined according to the in-cylinder attached fuel amount Dpfuel is after the predetermined upper limit value, only the ignition timing over-advancement angle is performed without performing the combustion promotion processing. When the ignition timing determined in accordance with the in-cylinder attached fuel amount Dpfuel is earlier than the upper limit value, the ignition timing is limited to the upper limit value to perform the advance angle, and the combustion acceleration process is performed. May be.

  Further, in this embodiment, the example in which the variable valve mechanism 120 is used to increase the combustion speed of the air-fuel mixture has been described, but the air-fuel mixture combustion is reduced by reducing the opening of the air flow control valve 31 as shown in FIG. The speed may be increased.

  The airflow control valve 31 is a valve that is disposed in the intake port 3 downstream of the fuel injection valve 5 and is rotatable about a fulcrum provided on the bottom surface of the intake port 3. FIG. 6 shows a state in which the airflow control valve 31 is closed.

  As shown in FIG. 6, when the airflow control valve 31 is closed, the airflow is biased upward in the intake port 3, so that a tumble flow is generated in the cylinder 2. The strength of the tumble flow (in other words, the tumble ratio) at that time increases as the opening degree of the airflow control valve 31 decreases.

  Therefore, if the opening degree of the airflow control valve 31 is reduced as the in-cylinder attached fuel amount Dpfuel increases, the same effect as in the above-described embodiment can be obtained.

  The air flow generated in the cylinder is not limited to the tumble flow, and may be a swirl flow.

It is a figure which shows schematic structure of the control system of an internal combustion engine. It is a figure which shows the relationship between the unburned fuel component (HC) discharged | emitted from the inside of a cylinder, and ignition timing. It is a figure which shows the relationship between an ignition timing and the state in a cylinder. It is a figure which shows the relationship between ignition timing and the amount of unburned fuel components (HC discharge | emission amount) discharged | emitted from the inside of a cylinder. It is a flowchart which shows an adhesion fuel reduction control routine. It is a figure which shows the other Example of the control system of an internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Intake port 4 ... Exhaust port 5 ... Fuel injection valve 6 ... Throttle valve 7. ....... Intake pressure sensor 8 ... Air flow meter 9 ... Exhaust gas purification device 14 ... Spark plug 15 ... Piston 16 ... Connecting rod 17 ... Crank Shaft 18 ... Crank position sensor 19 ... Water temperature sensor 20 ... ECU
30 ... Air intake passage 31 ... Air flow control valve 40 ... Exhaust passage 120 ... Variable valve mechanism

Claims (4)

Over-advance means for over-advancing the ignition timing of the spark ignition internal combustion engine before MBT;
Combustion promoting means for increasing the combustion speed of the air-fuel mixture in the cylinder of the internal combustion engine;
Control means for increasing the combustion rate of the air-fuel mixture by the combustion promoting means when the over-advance means over-ignites the ignition timing;
An internal combustion engine control system comprising: The acquisition unit according to claim 1, further comprising an acquisition unit configured to acquire an amount of fuel attached to a cylinder of the internal combustion engine.
The control system for an internal combustion engine, wherein the control means controls the combustion accelerating means so that the combustion rate of the air-fuel mixture increases as the amount of attached fuel obtained by the obtaining means increases.   3. The internal combustion engine according to claim 1, wherein the combustion promoting means increases the combustion speed of the air-fuel mixture by narrowing the opening of an airflow control valve disposed in the intake port of the internal combustion engine. Control system.   3. The control system for an internal combustion engine according to claim 1, wherein the combustion promoting means increases the combustion speed of the air-fuel mixture by retarding the opening start timing of the intake valve of the internal combustion engine.

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