JP2005330864A - Control method for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve improvement in exhaust emissions and early activation of an exhaust emission control catalyst when the exhaust emission control catalyst is in an inactive state. <P>SOLUTION: This is the control method for controlling an internal combustion engine 1 provided with a variable valve mechanisms 10 and 11 capable of varying opening valve characteristics of intake and exhaust valves 8 and 9, the exhaust emission control catalyst 21 provided in an exhaust system, and an exhaust throttle valve 2 provided in the exhaust system on the downstream side of the exhaust emission control catalyst 21. The variable valve mechanisms 10 and 11 and the exhaust throttle valve 22 are controlled so that the internal combustion engine 1 is operated with the usage of oxygen existing in the exhaust system located upstream of the exhaust throttle valve 22, and thereby a temperature of the exhaust emission control catalyst 21 can be rapidly raised while restricting exhaust emission into the atmosphere. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine having a variable valve mechanism, and more particularly to a control method for an internal combustion engine effective for early activation of an exhaust purification catalyst provided in an exhaust system.

As an internal combustion engine mounted on a vehicle or the like, one having a variable valve mechanism is widely known. In an internal combustion engine equipped with a variable valve mechanism, various techniques have been proposed to improve the catalyst activity and startability during cold using the variable valve mechanism (see, for example, Patent Document 1). ).
JP 2000-130194 A Japanese Patent No. 2775195 JP 2001-182570 A

  By the way, in recent years, regulations on exhaust emissions have been strengthened, and it has become difficult to cope with future regulations with the conventional techniques as described above.

  The present invention has been made in view of the above circumstances, and its purpose is to achieve early activation when the catalyst is inactive and further improvement of exhaust emission in an internal combustion engine equipped with a variable valve mechanism. is there.

  The present invention employs the following means in order to solve the above problems. That is, the present invention includes a variable valve mechanism capable of changing the valve opening characteristics of the intake and exhaust valves, an exhaust purification catalyst provided in the exhaust system, and an exhaust throttle valve provided in the exhaust system downstream of the exhaust purification catalyst. A method for controlling an internal combustion engine provided with a variable valve mechanism and a catalyst for operating an exhaust throttle valve so that the internal combustion engine is operated using oxygen present in an exhaust system upstream of the exhaust throttle valve The gist is to increase the exhaust temperature while regulating the exhaust emission into the atmosphere by performing the activity control.

  As a method of operating the internal combustion engine using oxygen present in the exhaust system upstream from the exhaust throttle valve, the variable valve operation is performed so that the intake valve is held closed and the exhaust valve opens in the intake stroke and the exhaust stroke. A method for controlling the valve mechanism and closing the exhaust throttle valve can be exemplified.

  When the intake valve is held closed and the exhaust valve is opened in the cylinder in the intake stroke, a part of the gas existing in the exhaust system upstream of the exhaust throttle valve flows into the cylinder. The gas flowing into the cylinder is used for fuel combustion, and is discharged again into the exhaust system during the subsequent exhaust stroke. The burned gas discharged from the cylinder remains in the exhaust system upstream of the exhaust throttle valve without being released into the atmosphere. The gas existing in the exhaust system upstream of the exhaust throttle valve and the exhaust purification catalyst are heated by receiving the heat of the burned gas remaining in the exhaust system.

If the intake / exhaust valves of the other cylinders operate in the same manner after the cylinder, the gas having a high temperature in the exhaust system upstream of the exhaust throttle valve is sucked into the other cylinders and used for combustion. For this reason, the burned gas discharged from the other cylinder during the exhaust stroke of the other cylinder becomes burned gas having a temperature higher than that of the previous cylinder. Since the burned gas discharged from the other cylinders also remains in the exhaust system upstream of the exhaust throttle valve, the temperature of the gas and the exhaust purification catalyst existing in the exhaust system further increases.

  When such an operation is performed in a plurality of cylinders or repeated in a plurality of cycles, the temperature of the gas and the exhaust purification catalyst rapidly rises in the exhaust system upstream of the exhaust throttle valve. Further, since the burned gas discharged from the internal combustion engine during the temperature raising process of the exhaust purification catalyst is not released into the atmosphere, deterioration of exhaust emission is also prevented.

  Accordingly, it is possible to achieve early activation of the exhaust purification catalyst while suppressing deterioration of exhaust emission when the exhaust purification catalyst is in an inactive state.

  Further, when the exhaust purification catalyst is in an inactive state, the internal combustion engine may be in a cold state before the completion of warming up. When the internal combustion engine is in a cold state, the intake air temperature tends to be low, so that the fuel is difficult to vaporize (atomize). On the other hand, in the internal combustion engine according to the present invention, since the gas that has become high in the exhaust system upstream of the exhaust throttle valve is used instead of the intake air, there is an advantage that the fuel is easily vaporized (atomized).

  The catalyst activity control may be terminated when at least a part of the exhaust purification catalyst is activated.

  As a method for determining whether or not at least a part of the exhaust purification catalyst is activated, a method for determining that at least a part of the exhaust purification catalyst is activated when the floor temperature of the exhaust purification catalyst becomes equal to or higher than a predetermined temperature, When the exhaust temperature downstream of the exhaust purification catalyst becomes equal to or higher than the exhaust temperature upstream of the exhaust purification catalyst, a method for determining that at least a part of the exhaust purification catalyst is activated, or when the execution time of the catalyst activation control exceeds a predetermined time Examples thereof include a method for determining that at least a part of the exhaust purification catalyst is activated.

  By the way, if the amount of oxygen remaining in the exhaust system upstream of the exhaust throttle valve is lower than the amount of oxygen necessary for the operation of the internal combustion engine before at least a part of the exhaust purification catalyst is activated, the operation of the internal combustion engine may be continued. become unable. On the other hand, if the amount of oxygen remaining in the exhaust system upstream of the exhaust throttle valve falls below a predetermined amount, the exhaust throttle valve is temporarily opened or the exhaust throttle valve is kept slightly open. By doing so, oxygen may be replenished to the exhaust system upstream of the exhaust throttle valve.

  As a method of detecting the amount of oxygen remaining in the exhaust system upstream of the exhaust throttle valve, a method of estimating from the detection value of the oxygen sensor or air-fuel ratio sensor can be exemplified.

  Moreover, when the internal combustion engine which concerns on this invention is equipped with the centrifugal supercharger, it is preferable to fully open the wastegate valve of a centrifugal supercharger during execution of catalyst activity control.

  This is because the turbine housing of the centrifugal supercharger has a large heat capacity, and when all the exhaust gas passes through the turbine housing, the heat of the exhaust gas is lost to the turbine housing, and the gas temperature rises in the exhaust system upstream of the exhaust throttle valve. Because it becomes difficult.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to aim at early activation of an exhaust purification catalyst, improving the exhaust emission when an exhaust purification catalyst is in an inactive state.

Specific embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. In FIG. 1, the internal combustion engine 1 is a four-stroke cycle reciprocating engine.

  The cylinder head 2 of the internal combustion engine 1 is provided with a fuel injection valve 4 that directly injects fuel into the combustion chamber 3 and an ignition plug 5 that generates a spark in the combustion chamber 3.

  The cylinder head 2 is formed with an intake port 6 and an exhaust port 7 that communicate with the combustion chamber 3. The intake port 6 is opened and closed by an intake valve 8, and the exhaust port 7 is opened and closed by an exhaust valve 9. The intake valve 8 and the exhaust valve 9 are driven to open and close by an intake side variable valve mechanism 10 and an exhaust side variable valve mechanism 11.

  The intake side variable valve mechanism 10 and the exhaust side variable valve mechanism 11 are valve mechanisms that can arbitrarily change the valve opening characteristics of the intake valve 8 and the exhaust valve 9, particularly the opening / closing timing. Examples of such a valve operating mechanism include a mechanism for opening and closing the valve by an electric motor, a mechanism for opening and closing the valve by electromagnetic force, and a mechanism for opening and closing the valve by hydraulic pressure.

  An intake manifold 12 communicating with the intake port 6 is attached to the cylinder head 2. The intake manifold 12 communicates with the intake pipe 14 via the surge tank 13.

  The intake pipe 14 is connected to a compressor housing 151 of a centrifugal supercharger (turbocharger) 15. An intake duct 16 is connected to the compressor housing 151. An intercooler 17 is provided in the middle of the intake pipe 14, and a throttle valve 18 is provided in the intake pipe 14 downstream from the intercooler 17.

  An exhaust manifold 19 communicating with the exhaust port 7 is attached to the cylinder head. The exhaust manifold 19 is connected to the turbine housing 152 of the centrifugal supercharger 15. The exhaust pipe 20 is connected to the turbine housing 152.

  An exhaust purification catalyst 21 is disposed in the middle of the exhaust pipe 20. An exhaust throttle valve 22 is provided in the exhaust pipe 20 downstream of the exhaust purification catalyst 21.

  An oxygen concentration sensor 23 is attached between the exhaust purification catalyst 21 and the exhaust throttle valve 22 in the exhaust pipe 20.

  The exhaust pipe 20 upstream of the exhaust purification catalyst 21 is provided with an upstream exhaust temperature sensor 24, and the exhaust pipe 20 downstream of the exhaust purification catalyst 21 and upstream of the oxygen concentration sensor 23 is provided with a downstream exhaust temperature sensor 25. Is provided.

  The exhaust manifold 19 and the exhaust pipe 20 communicate with each other by a bypass passage 26 that bypasses the turbine housing 152, and a wastegate valve 27 is provided in the bypass passage 26.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 28. The ECU 28 is an arithmetic and logic circuit composed of a CPU, ROM, RAM, backup RAM, and the like.

The ECU 28 is electrically connected to the oxygen concentration sensor 23, the upstream side exhaust temperature sensor 24, and the downstream side exhaust temperature sensor 25, and can input output signals of these various sensors.

  The ECU 28 is electrically connected to the fuel injection valve 4, spark plug 5, intake side variable valve mechanism 10, exhaust side variable valve mechanism 11, throttle valve 18, exhaust throttle valve 22, and wastegate valve 27. Can be controlled.

  In the present embodiment, the ECU 28 performs the catalyst activation control when the exhaust purification catalyst 21 is in an inactive state as in the period from the cold start to the completion of the warm-up operation.

  In the catalyst activity control, the ECU 28 is located upstream of the exhaust throttle valve 22 in the exhaust system upstream of the exhaust throttle valve 22 (in this case, that is, the exhaust port 7, the exhaust manifold 19, the turbine housing 152, the bypass passage 26, and the exhaust pipe 20). And the intake side variable valve mechanism 11, the exhaust side variable valve mechanism 11, and the exhaust throttle valve 22 are controlled so that the internal combustion engine 1 is operated using oxygen existing in the exhaust gas purification catalyst 21. To do.

  Hereinafter, the catalyst activity control will be specifically described with reference to FIG. FIG. 2 is a flowchart showing a catalyst activity control routine. The catalyst activation control routine is a routine that is stored in advance in the ROM of the ECU 28, and is a routine that is repeatedly executed by the ECU 28 at predetermined time intervals.

  In the catalyst activation control routine, the ECU 28 first determines in S101 whether the catalyst activation flag is a value other than “1”. The catalyst activation flag is a storage area provided in advance in the RAM of the ECU 28. “1” is stored when the exhaust purification catalyst 21 is in an active state, and “0” when the exhaust purification catalyst 21 is in an inactive state. Is memorized.

  When it is determined in S101 that the catalyst activation flag is “1”, the ECU 28 ends the execution of this routine.

  If it is determined in S101 that the catalyst activation flag is not “1” (that is, the catalyst activation flag is “0”), the ECU 28 proceeds to S102. In S102, the ECU 28 outputs an output signal from the oxygen concentration sensor 22 (hereinafter referred to as oxygen concentration: Oc), an output signal from the upstream exhaust temperature sensor 24 (hereinafter referred to as upstream exhaust temperature: Tu), and a downstream exhaust temperature. An output signal of the sensor 25 (hereinafter referred to as downstream exhaust temperature: Td) is input.

  In S103, the ECU 28 compares the upstream exhaust temperature: Tu inputted in S102 with the downstream exhaust temperature: Td to determine whether or not the exhaust purification catalyst 21 is in an inactive state.

  When at least a part of the exhaust purification catalyst 21 is in an activated state, hydrocarbons, carbon monoxide, nitrogen oxides and the like in the exhaust are oxidized and reduced in the exhaust purification catalyst 21 to generate reaction heat. Since this reaction heat is transmitted to the exhaust gas flowing through the exhaust purification catalyst 21, the temperature of the exhaust gas flowing out from the exhaust purification catalyst 21 is equal to or higher than the temperature of the exhaust gas flowing into the exhaust purification catalyst 21.

  On the other hand, when the exhaust purification catalyst 21 is in an inactive state, hydrocarbons, carbon monoxide, nitrogen oxides and the like in the exhaust are not oxidized / reduced in the exhaust purification catalyst 21, so that no reaction heat is generated. In addition, the heat of the exhaust is transmitted to the exhaust purification catalyst 21. Therefore, when the exhaust purification catalyst 21 is in an inactive state, the temperature of the exhaust gas flowing out from the exhaust purification catalyst 21 becomes lower than the temperature of the exhaust gas flowing into the exhaust purification catalyst 21.

According to the above consideration, the ECU 28 can determine that the exhaust purification catalyst 21 is in an inactive state when the downstream exhaust temperature: Td is lower than the upstream exhaust temperature: Tu in S103, and the downstream exhaust temperature. When the exhaust gas temperature Td is equal to or higher than the upstream exhaust temperature Tu, it can be determined that the exhaust purification catalyst 21 is in an active state.

  If it is determined in S103 that the exhaust purification catalyst 21 is in an inactive state, the ECU 28 proceeds to S104. In S104, the ECU 28 determines whether or not the oxygen concentration: Oc input in S102 is equal to or higher than a predetermined concentration: C.

  If it is determined in S104 that the oxygen concentration: Oc is equal to or higher than the predetermined concentration: C, the ECU 28 proceeds to S105. In S105, the ECU 28 controls the exhaust throttle valve 22 to be fully closed.

  In S106, the ECU 28 controls the wastegate valve 27 to be fully opened.

  In S107, the ECU 28 holds the intake valve 8 closed as shown in FIG. 3 and the intake side variable valve mechanism 10 and the exhaust side variable valve so that the exhaust valve 9 is opened in the intake stroke in addition to the exhaust stroke. The mechanism 11 is controlled. In addition, the dotted line in FIG. 3 has shown the lift curve at the time of normal.

  When the processes of S105, S106, and S107 described above are executed, the intake valve 8 is kept closed and the exhaust valve 9 is opened in the cylinder in the intake stroke. When only the exhaust valve 9 is opened in the cylinder in the intake stroke, part of the gas existing in the exhaust system upstream of the exhaust throttle valve 22 flows into the cylinder and is used for combustion together with the fuel injected from the fuel injection valve 4. Is done.

  Since the exhaust valve 9 is opened during the exhaust stroke of the cylinder, the burned gas in the cylinder is again discharged to the exhaust system. At this time, since the exhaust throttle valve 22 is closed, the burned gas discharged from the cylinder remains in the exhaust system upstream of the exhaust throttle valve 22 without being released into the atmosphere. The gas present in the exhaust system upstream of the exhaust throttle valve 22 and the exhaust purification catalyst 21 are heated by receiving the heat of the burned gas.

  When the intake valve 8 and the exhaust valve 9 of the other cylinders operate in the same manner after the cylinder, the gas that has become hot in the exhaust system upstream of the exhaust throttle valve 22 is sucked into the other cylinders and used for combustion. become. For this reason, the burned gas discharged from the other cylinder during the exhaust stroke of the other cylinder becomes burned gas having a temperature higher than that of the previous cylinder. Since the burned gas discharged from the other cylinders also remains in the exhaust system upstream of the exhaust throttle valve 22, the gas existing in the exhaust system and the exhaust purification catalyst 21 are further heated.

  When such an operation is performed in a plurality of cylinders, the temperature of the gas and the exhaust purification catalyst 21 is quickly raised in the exhaust system upstream of the exhaust throttle valve 22. Further, in the process of raising the temperature of the exhaust purification catalyst 21 as described above, the burned gas discharged from the internal combustion engine 1 remains upstream of the exhaust throttle valve 22, so the burned gas is not purified by the exhaust purification catalyst 21. Will not be released into the atmosphere.

  Incidentally, in the present embodiment, a turbine housing 152 having a large heat capacity is disposed in the exhaust system upstream of the exhaust throttle valve 22. For this reason, when the burned gas discharged from the internal combustion engine 1 flows through the turbine housing 152, the heat of the burned gas is taken away by the turbine housing 152, and it becomes difficult for the exhaust purification catalyst 21 to rise in temperature.

  On the other hand, in the catalyst activity control according to the present embodiment, the waste gate valve 27 is fully opened, so that the amount of burned gas flowing through the turbine housing 152 can be minimized, and the exhaust purification catalyst 21 can be quickly moved. Temperature rise can be realized.

If the amount of oxygen remaining in the exhaust system upstream of the exhaust throttle valve 22 falls below the amount of oxygen required for combustion per cylinder before the exhaust purification catalyst 21 is activated, that is, in step S104 of the catalyst activation control routine. If it is determined that the concentration: Oc is lower than the predetermined concentration: C, the ECU 28 temporarily opens the exhaust throttle valve 22 in S108 to supply oxygen to the exhaust system upstream of the exhaust throttle valve 22.

  In this case, part of the high-temperature gas staying upstream of the exhaust throttle valve 22 is replaced with the air downstream of the exhaust throttle valve 22, so that the oxygen concentration: Oc in the exhaust system upstream of the exhaust throttle valve 22 increases. In addition, most of the high-temperature gas remaining upstream of the exhaust throttle valve 22 remains upstream of the exhaust throttle valve 22, so that the effect of promoting the temperature increase of the exhaust purification catalyst 21 can be maintained.

  The catalyst activity control as described above ends when the exhaust purification catalyst 21 is activated. Specifically, when the ECU 28 determines the activity of the exhaust purification catalyst 21 in the process of repeatedly executing the catalyst activity control routine (determined in S103 that the downstream exhaust temperature: Td is equal to or higher than the upstream exhaust temperature: Tu), The processes of S109 and S110 are executed.

  In S109, the ECU 28 controls the intake side variable valve mechanism 10 so that the intake valve 8 opens in the intake stroke, and the exhaust side variable valve mechanism 11 so that the exhaust valve 9 opens in the exhaust stroke. And the exhaust throttle valve 22 is controlled to open. Next, the ECU 28 changes the value of the catalyst activation flag to “1” in S110, and ends the execution of this routine.

  Therefore, according to the present embodiment, when the exhaust purification catalyst 21 is in an inactive state, it is possible to achieve early activation of the exhaust purification catalyst 21 while suppressing deterioration of exhaust emission.

The figure which shows schematic structure of the internal combustion engine to which this invention is applied. Flowchart showing a catalyst activity control routine Timing chart showing opening / closing operation of intake / exhaust valve in catalyst activity control

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 7 ... Exhaust port 8 ... Intake valve 9 ... Exhaust valve 10 ... Intake side variable valve mechanism 11 ... Exhaust side variable valve mechanism 15 ..Centrifuge supercharger 19 ... exhaust manifold 20 ... exhaust pipe 21 ... exhaust purification catalyst 22 ... exhaust throttle valve 23 ... oxygen concentration sensor 24 ... upstream exhaust temperature sensor 25 ..Downstream exhaust temperature sensor 26 ... Bypass passage 27 ... Wastegate valve 28 ... ECU

Claims (5)

Determining whether or not the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine is in an inactive state;
When the exhaust purification catalyst is in an inactive state, the variable valve mechanism is controlled so that the intake valve remains closed and the exhaust valve opens in the intake stroke and the exhaust stroke. A control method for an internal combustion engine, comprising: performing catalyst activity control for controlling an exhaust throttle valve provided in a downstream exhaust passage to a closed state. 2. The control of the internal combustion engine according to claim 1, wherein when the exhaust temperature downstream of the exhaust purification catalyst becomes equal to or higher than the exhaust temperature upstream of the exhaust purification catalyst, the execution of the catalyst activity control is terminated. Method. The amount of oxygen remaining in the exhaust passage upstream of the exhaust throttle valve is obtained based on the detection value of the oxygen concentration sensor provided in the exhaust passage. When the residual oxygen amount is less than a predetermined amount, the exhaust throttle valve is temporarily stopped. 2. The method of controlling an internal combustion engine according to claim 1, wherein the valve is opened automatically. The amount of oxygen remaining in the exhaust passage upstream of the exhaust throttle valve is determined based on the detection value of the oxygen concentration sensor provided in the exhaust passage. When the residual oxygen amount is less than the predetermined amount, the exhaust throttle valve is 2. The method for controlling an internal combustion engine according to claim 1, wherein the valve opening is opened. The method for controlling an internal combustion engine according to claim 1, wherein when the catalyst activity control is executed, the wastegate valve of the centrifugal supercharger is fully opened.

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