JP2008202524A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique removing particulate matter adhered to an exhaust system, in an internal combustion engine. <P>SOLUTION: The internal combustion engine comprises a variable valve mechanism changing a lift amount of at least an exhaust valve. The internal combustion engine comprises: an exhaust valve lift amount determination means determining a reference lift amount of the exhaust valve depending on operational statuses of the internal combustion engine; and an exhaust valve lift amount change means reducing the exhaust valve lift amount for each of predetermined periods so that the exhaust valve lift amount gets smaller than the lift amount determined by the exhaust valve lift amount determination means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine.

If deposits adhere to the intake system, the air-fuel ratio may become lean due to fuel adhering to the deposits. On the other hand, by delaying the advance speed of the variable valve timing mechanism, it is possible to follow the air-fuel ratio even when the volumetric efficiency increases rapidly during acceleration or the like (see, for example, Patent Document 1). .
JP 09-303165 A JP 2002-242713 A JP 2002-349302 A JP 2006-291747 A Japanese Patent No. 2722161

  By the way, if particulate matter (PM) such as soot adheres to the exhaust system and adheres to it, it becomes difficult to remove the PM. And if PM accumulates thickly in an exhaust system, this PM becomes a heat insulating material and it becomes difficult to cool exhaust. For this reason, the exhaust gas circulates at a high temperature, and the back pressure increases. Further, since the passage area such as the exhaust port is reduced, the back pressure is also increased. When the back pressure is increased in this way, the charging efficiency of the internal combustion engine is reduced when the amount of exhaust gas is large as in the case of high-speed high-load operation of the internal combustion engine, so that the engine output is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of removing particulate matter adhering to an exhaust system in an internal combustion engine.

In order to achieve the above object, an internal combustion engine according to the present invention provides:
An internal combustion engine having a variable valve mechanism that changes at least the lift amount of the exhaust valve,
An exhaust valve lift amount determining means for determining a reference lift amount of the exhaust valve according to an operating state of the internal combustion engine;
Exhaust valve lift amount changing means for making the lift amount of the exhaust valve smaller every predetermined period than the lift amount determined by the exhaust valve lift amount determining means;
It is characterized by providing.

  By reducing the lift amount of the exhaust valve, the flow rate of exhaust flowing from the cylinder to the exhaust port can be increased. And the particulate matter adhering to the exhaust system can be blown off by increasing the flow rate of the exhaust. The predetermined period may be before the particulate matter adhered to the exhaust system is fixed. That is, if the particulate matter is fixed, it is difficult to blow off even if the exhaust gas flow rate is increased. Therefore, the exhaust gas flow rate is increased before that occurs.

  The exhaust valve lift amount determination means determines a reference lift amount according to torque, exhaust performance, and the like required for the internal combustion engine. This reference lift amount is used except when the particulate matter adhering to the exhaust system is removed. When removing particulate matter adhering to the exhaust system, the flow rate of the exhaust gas flowing out to the exhaust port can be made faster than usual by making the lift amount of the exhaust valve smaller than the reference lift amount. .

  In the present invention, when reducing the lift amount of the exhaust valve by the exhaust valve lift amount changing means, the intake air amount of the internal combustion engine can be made larger than before reducing the lift amount of the exhaust valve. .

  Here, if the lift amount of the exhaust valve is reduced, the exhaust efficiency is reduced, and therefore the engine generated torque may be reduced. On the other hand, by increasing the intake air amount of the internal combustion engine, it is possible to improve intake efficiency and suppress a decrease in engine generated torque.

That is, in the present invention, the variable valve mechanism changes the operating angle of the intake valve,
When reducing the lift amount of the exhaust valve by the exhaust valve lift amount changing means, the operating angle of the intake valve can be made larger than before reducing the lift amount of the exhaust valve.

  Further, when the intake passage is provided with a throttle, the throttle opening may be increased.

  As a result, the intake air amount of the internal combustion engine can be increased, so that a decrease in engine generated torque due to a reduction in the lift amount of the exhaust valve can be suppressed.

The present invention further comprises particulate matter adhesion amount estimation means for estimating the amount of particulate matter adhering to the exhaust system,
The lift amount of the exhaust valve can be reduced when the particulate matter estimated by the particulate matter adhesion amount estimation means becomes equal to or greater than a threshold value.

  If the lift amount of the exhaust valve is reduced, the exhaust efficiency decreases, so it is not preferable to perform it frequently. Therefore, the lift amount of the exhaust valve is reduced after the particulate matter adheres to the exhaust system to some extent. The threshold is less than the particulate matter that adheres during the predetermined period.

  For example, it may be determined whether or not the particulate matter is adhered to a threshold value or more based on at least one of the travel distance of the vehicle, the time when the internal combustion engine is idling, and the time when the air-fuel ratio is rich.

  In the present invention, the lift amount of the exhaust valve can be reduced when the internal combustion engine has a low rotation and a low load.

  Here, when the internal combustion engine is operated at a high speed, the exhaust stroke time is short, and therefore, if the lift amount of the exhaust valve is reduced, it becomes impossible to exhaust all exhaust gas. Further, when the internal combustion engine is operated at a high load, the amount of exhaust gas increases, and therefore, if the lift amount of the exhaust valve is reduced, it becomes impossible to exhaust all exhaust gas. On the other hand, by reducing the lift amount of the exhaust valve at the time of low rotation and low load of the internal combustion engine, it is possible to suppress the exhaust from remaining in the cylinder. Thereby, the performance fall of an internal combustion engine can be controlled. However, if the lift amount of the exhaust valve is reduced during idle operation, the torque fluctuation may increase, and at this time, it may be prohibited to reduce the lift amount of the exhaust valve.

  The low rotation speed may be a rotation speed lower than the middle between the maximum rotation speed and the minimum rotation speed of the internal combustion engine. Further, the low load may be a load lower than the middle between the maximum load and the minimum load of the internal combustion engine.

According to the internal combustion engine of the present invention, particulate matter adhering to the exhaust system can be removed.

  Hereinafter, specific embodiments of the internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine 1 according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An intake passage 2 is connected to the internal combustion engine 1. A throttle 3 is provided in the middle of the intake passage 2. The throttle 3 is opened and closed by an electric actuator.

  Further, the internal combustion engine 1 is provided with an intake valve 5 and an exhaust valve 6. The opening / closing operation of the intake valve 5 is performed by the intake side actuator 50, and the opening / closing operation of the exhaust valve 6 is performed by the exhaust side actuator 60. If the lift amount of the exhaust valve 6 can be changed, the exhaust valve 6 may be opened / closed and the opening / closing timing or the lift amount may be changed by other means. Further, it is not always necessary to change the opening / closing timing of the intake valve 5 or the lift amount.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  Further, the ECU 10 includes an accelerator opening sensor 12 that outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver, and a crank position sensor 13 that detects the number of rotations of the crankshaft 9 via electric wiring. The output signals of these various sensors are connected to the ECU 10. The engine load is detected by the accelerator opening sensor 12, and the engine speed is detected by the crank position sensor 13.

  On the other hand, the throttle 3, the intake side actuator 50, and the exhaust side actuator 60 are connected to the ECU 10 via electric wiring, and these devices are controlled by the ECU 10.

  In this embodiment, the lift amount of the exhaust valve 6 is made smaller than usual for each predetermined period to increase the flow rate when the gas is discharged from the cylinder to the exhaust port (this process is hereinafter referred to as “PM removal”). Process "). Thereby, PM such as soot adhering to the exhaust valve 6 and the exhaust port 16 is blown off. Normally, the lift amount of the exhaust valve 6 is determined based on the engine speed and the engine load. This normal lift amount is obtained in advance by experiments or the like according to the output required for the internal combustion engine, and is stored in the ECU 10. In this embodiment, the ECU 10 that determines the normal lift amount of the exhaust valve 6 corresponds to the exhaust valve lift amount determining means in the present invention. Further, the ECU 10 that makes the lift amount of the exhaust valve 6 smaller than usual corresponds to the exhaust valve lift amount changing means in the present invention.

  However, if the lift amount of the exhaust valve 6 is made smaller than usual, the exhaust efficiency is lowered, and therefore the engine generated torque may be lowered. For this reason, in this embodiment, when the lift amount of the exhaust valve 6 is made smaller than usual, the opening time of the intake valve 5 is made longer than usual to improve the intake efficiency, thereby suppressing the decrease in engine generated torque. You may do it. Further, the lift amount of the intake valve 5 may be made larger than usual to improve intake efficiency. Further, the opening degree of the throttle 3 may be increased to improve intake efficiency. That is, the intake air amount of the internal combustion engine 1 may be increased.

  The timing for performing the PM removal processing is before PM adheres to the exhaust valve 6 or the like to some extent and the PM is fixed. This timing may be determined as follows.

(1) When the cumulative travel distance of the vehicle is equal to or greater than a predetermined distance There is a correlation between the cumulative distance of the vehicle and the amount of PM adhering to the exhaust system. The longer the cumulative distance of the vehicle, the greater the amount of PM adhesion. . Therefore, an integrated distance that is “before PM adheres to the exhaust valve 6 and the like to some extent and before PM adheres” is obtained in advance through experiments and set as a threshold value. Then, the actual travel distance of the vehicle is accumulated, and the PM removal process is performed when the accumulated distance becomes equal to or greater than a threshold value. Note that the PM amount adhering to the exhaust system may be estimated based on the accumulated travel distance of the vehicle, and the PM removal process may be performed based on the estimated value.

(2) When the accumulated time of the idling operation of the internal combustion engine 1 is equal to or longer than a predetermined time Since the variation of the air-fuel ratio is large and the combustion state is easily deteriorated during the idling operation of the internal combustion engine 1, the amount of PM generated is large. Furthermore, since the amount of exhaust is small during idle operation, PM tends to adhere to the exhaust valve 6 and the like. For this reason, there is a correlation between the accumulated time of idle operation of the internal combustion engine 1 and the amount of PM adhering to the exhaust system, and the accumulated amount of PM increases as the accumulated time of idle operation becomes longer. Therefore, the idle operation integration time that is “before PM adheres to the exhaust valve 6 and the like to some extent and before PM adheres” is obtained in advance through experiments and set as a threshold value. Then, the actual idle operation time of the internal combustion engine 1 is accumulated, and the PM removal process is performed when the accumulated time becomes equal to or greater than a threshold value. Note that the PM amount adhering to the exhaust system may be estimated based on the accumulated idle operation time of the internal combustion engine 1, and the PM removal process may be performed based on the estimated value.

(3) When the accumulated time during which the internal combustion engine 1 is operated with the air-fuel ratio rich is over a predetermined time When the internal combustion engine 1 is operated with the air-fuel ratio rich, the concentration of unburned fuel in the exhaust due to incomplete combustion Becomes higher. In addition, the air-fuel ratio is made rich during high-load operation, and at this time the amount of exhaust is large. Furthermore, when climbing a hill or traveling on a highway, a rich air-fuel ratio continues for a long time, and a large amount of PM is generated. In this way, when operating at a rich air-fuel ratio, PM tends to adhere to the exhaust valve 6 and the like. Therefore, there is a correlation between the accumulated time during which the internal combustion engine 1 is operated with the air-fuel ratio being rich and the amount of PM adhering to the exhaust system. The amount increases. Therefore, an integrated time that is “before PM adheres to the exhaust valve 6 and the like to some extent and before PM is fixed” is obtained in advance through experiments and set as a threshold value. Then, the operating time of the internal combustion engine 1 with the air-fuel ratio being rich is integrated, and the PM removal process is performed when the integrated time becomes equal to or greater than the threshold value. The PM amount adhering to the exhaust system may be estimated based on the accumulated time during which the internal combustion engine 1 has been operated with the air-fuel ratio being rich, and the PM removal process may be performed based on this estimated value.

  Note that the PM removal processing may be performed when any of the conditions is satisfied by combining the cases (1) to (3).

  Here, in the above (1) to (3), the amount of PM adhering to the exhaust system is indirectly estimated, and the PM removal processing is performed when this PM amount becomes equal to or greater than a threshold value. In other words, in this embodiment, the ECU 10 that accumulates the travel distance of the vehicle, the idle operation time of the internal combustion engine 1, or the operation time of the internal combustion engine 1 with the air-fuel ratio rich is estimated. Corresponds to means.

  In this embodiment, the PM removal process is performed when the internal combustion engine 1 is operated at a low rotation and a low load.

  Here, FIG. 2 is a diagram showing the relationship between the engine speed, the engine load, and the operation region in which PM removal processing is performed. The operation is performed in the hatched operating region shown in the figure.

  When the internal combustion engine 1 is operated at a high load, the amount of exhaust increases. Therefore, if the lift amount of the exhaust valve 6 is made smaller than usual, the amount of burned gas remaining in the cylinder increases. Further, when the internal combustion engine 1 is operated at a high speed, the exhaust stroke time is shortened. Therefore, if the lift amount of the exhaust valve 6 is made smaller than usual, the amount of burned gas remaining in the cylinder increases. Thereby, there exists a possibility that engine generated torque may fall. Therefore, the PM removal process is not performed in such an operating state.

  On the other hand, the PM removal process may not be performed even when the internal combustion engine 1 is in an operating state in which torque fluctuation is likely to occur, such as during idling.

  By the way, immediately after the fuel cut is completed and the fuel injection is started, the internal combustion engine 1 is often operated at a low rotation and a low load, and the ignition timing is delayed in order to suppress the torque shock at the start of the fuel injection. The generated torque is suppressed by making it square. In such a case, even if the lift amount of the exhaust valve is reduced, the influence on the internal combustion engine 1 is small. Therefore, the lift amount of the exhaust valve may be reduced at such a time.

  Next, FIG. 3 is a flowchart showing a flow of PM removal processing according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, at least one of the travel distance, the idle operation time, and the rich air-fuel ratio is accumulated.

  In step S102, it is determined whether at least one of the values accumulated in step S101 is equal to or greater than a threshold value. That is, it is determined whether PM has adhered to the exhaust valve 6 or the like to some extent and is before PM is fixed.

  If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, this routine is temporarily terminated.

  In step S103, it is determined whether an execution condition for PM removal control is satisfied. That is, it is determined whether or not the driving state is indicated by hatching in FIG. The determination is made based on output signals from the accelerator opening sensor 12 and the crank position sensor 13.

  If an affirmative determination is made in step S103, the process proceeds to step S104. If a negative determination is made, this routine is temporarily terminated.

  In step S104, the lift amount of the exhaust valve 6 is made smaller than usual, and the lift amount of the intake valve 5 is made larger than usual. That is, PM adhering to the exhaust valve 6 and the like is blown away while suppressing a decrease in engine-generated torque.

  In step S105, the value accumulated in step S101 is returned to zero.

  In this way, the PM adhering to the exhaust valve 6 and the exhaust port 16 can be blown off by the exhaust force by making the lift amount of the exhaust valve 6 smaller than usual. Thereby, since adhesion of PM can be suppressed, an increase in back pressure can be suppressed and a decrease in engine generated torque can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example. It is the figure which showed the relationship between an engine speed, an engine load, and the operation area | region which performs PM removal processing. It is the flowchart which showed the flow of PM removal processing by an Example.

Explanation of symbols

1 Internal combustion engine 2 Intake passage 3 Throttle 5 Intake valve 6 Exhaust valve 9 Crankshaft 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor 16 Exhaust port 50 Intake side actuator 60 Exhaust side actuator

Claims (5)

An internal combustion engine having a variable valve mechanism that changes at least the lift amount of the exhaust valve,
An exhaust valve lift amount determining means for determining a reference lift amount of the exhaust valve according to an operating state of the internal combustion engine;
Exhaust valve lift amount changing means for making the lift amount of the exhaust valve smaller every predetermined period than the lift amount determined by the exhaust valve lift amount determining means;
An internal combustion engine comprising:   2. The intake air amount of the internal combustion engine is increased when the lift amount of the exhaust valve is reduced by the exhaust valve lift amount changing means than before the lift amount of the exhaust valve is reduced. The internal combustion engine described in 1. The variable valve mechanism changes the operating angle of the intake valve,
3. The operating angle of the intake valve is increased when the lift amount of the exhaust valve is reduced by the exhaust valve lift amount changing means than before the lift amount of the exhaust valve is reduced. The internal combustion engine described. It further comprises particulate matter adhesion amount estimation means for estimating the amount of particulate matter adhering to the exhaust system,
The internal combustion engine according to any one of claims 1 to 3, wherein the lift amount of the exhaust valve is reduced when the particulate matter estimated by the particulate matter adhesion amount estimation means exceeds a threshold value.   The internal combustion engine according to any one of claims 1 to 4, wherein the lift amount of the exhaust valve is reduced when the internal combustion engine is under low rotation and low load.

Images