JP2006348758A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of appropriate deceleration while suppressing surging with a simple device structure by controlling timing of open and close of an exhaust valve. <P>SOLUTION: Although there is a case that surging occurs in an internal combustion engine including a turbocharger at a time of deceleration, supercharged air does not flow reversely and occurrence of surging is suppressed when a throttle opening control means opens a throttle valve. Although there is a case that pumping loss is not generated and engine brake is not generated by opening the throttle valve, negative work separately from pumping loss is generated when a variable valve control means controls the exhaust valve to open earlier and engine brake can be generated by using the work. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that controls the opening / closing timing of an exhaust valve.

  In an internal combustion engine having a turbocharger, when the throttle valve is suddenly closed (for example, when suddenly decelerating), a surge (pulsation) occurs in the turbocharger due to a sudden rise in pressure on the upstream side of the throttle valve. Sound) is known to occur. Usually, in order to prevent such a surge, control for suppressing an increase in supercharging pressure is performed. For example, Patent Document 1 describes a technique for suppressing an increase in supercharging pressure by operating an air bypass valve (ABV) when a throttle valve is suddenly closed.

  The above-described surge can be basically suppressed by opening the throttle valve after executing the fuel cut. However, if the throttle valve is opened at the time of deceleration, there is almost no pumping loss, so engine braking may be difficult to occur. Therefore, there are cases where the vehicle cannot be decelerated appropriately.

  Here, the following techniques are disclosed as techniques for generating engine braking satisfactorily. Patent Document 2 describes a technique for controlling an intake valve or an exhaust valve to a small operating angle when a closing speed of a throttle valve is equal to or higher than a predetermined value during deceleration of an internal combustion engine. Patent Document 3 describes a technique for delaying the timing for opening the exhaust valve during deceleration to a predetermined timing after the piston reaches exhaust bottom dead center.

Japanese Patent No. 3466909 JP-A-9-25836 JP-A-11-210507

  However, in the technique described in Patent Document 1 described above, since the air bypass valve is used, the configuration of the apparatus is increased in size and costs are increased. In addition, the techniques described in Patent Documents 2 and 3 may not be able to appropriately suppress the occurrence of a surge.

  The present invention has been made to solve such problems, and the object of the present invention is to control the timing of opening and closing the exhaust valve while suppressing the occurrence of surge with a simple device configuration. Another object of the present invention is to provide a control device for an internal combustion engine capable of performing appropriate deceleration.

  In one aspect of the present invention, an internal combustion engine control device includes throttle opening control means for controlling the opening of a throttle valve, and variable valve control means for variably controlling the opening / closing timing of an exhaust valve, The throttle opening control means opens the throttle valve when the internal combustion engine decelerates, and the variable valve control means controls the exhaust valve to open quickly when the internal combustion engine decelerates.

  The control apparatus for an internal combustion engine includes a throttle opening degree control unit that controls the opening degree of the throttle valve and a variable valve control unit that variably controls the opening / closing timing of the exhaust valve. Specifically, when the internal combustion engine is decelerated, the throttle opening control means opens the throttle valve, and the variable valve control means controls the exhaust valve to open quickly. Specifically, the variable valve control means opens the exhaust valve at a time earlier than the time when the exhaust stroke is performed.

  Normally, in an internal combustion engine having a turbocharger, a surge (pulsation noise) may occur during deceleration, but the supercharged air does not flow backward when the throttle opening control means opens the throttle valve. Surge generation is suppressed. Here, when the throttle valve is opened, there is a case where pumping loss does not occur and engine braking does not occur, but the variable valve control means controls opening of the exhaust valve quickly, so that it is separated from pumping loss. Since negative work occurs, the engine brake can be generated using this work. As described above, according to the control device for an internal combustion engine, at the time of deceleration, generation of engine brake can be ensured and appropriate deceleration can be performed while suppressing generation of surge. In this case, since the control device for the internal combustion engine does not suppress the occurrence of surge by performing control to reduce the supercharging pressure, it is not necessary to separately provide an air bypass valve or the like. It can be simplified.

  In one aspect of the control apparatus for an internal combustion engine, the variable valve control means shifts the timing for setting the exhaust valve to open from the exhaust stroke to the expansion stroke.

  In this aspect, the variable valve control means shifts the timing for setting the exhaust valve to open from the exhaust stroke to the expansion stroke. That is, the variable valve control means opens the exhaust valve in the expansion stroke and closes the exhaust valve in the exhaust stroke. Thereby, since negative work occurs in the compression stroke and the expansion stroke, it is possible to appropriately generate the engine brake using this work.

  In another aspect of the control apparatus for an internal combustion engine, the variable valve control means sets the exhaust valve to open when the internal combustion engine is in an expansion stroke and an exhaust stroke.

  In this aspect, the variable valve control means sets the exhaust valve to be open when the internal combustion engine is in the expansion stroke and the exhaust stroke. In the control apparatus for an internal combustion engine, since the exhaust valve is opened in the expansion stroke, the exhaust side gas is introduced into the cylinder. However, since the exhaust valve is also opened in the exhaust stroke, the introduced exhaust gas is introduced. The side gas can be properly discharged in the exhaust stroke. Thereby, since the recirculation of the gas on the exhaust side is suppressed, it becomes possible to obtain a good combustion state at the time of reacceleration after deceleration.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Vehicle configuration]
FIG. 1 is a schematic diagram showing the overall configuration of a vehicle to which the control device for an internal combustion engine according to the present embodiment is applied. In FIG. 1, a solid line arrow indicates the flow of gas or the like, and a broken line arrow indicates signal input / output.

  The vehicle mainly includes an air cleaner (AC) 2, an intake passage 3, a turbocharger 4, an intercooler 5, a throttle valve 6, a surge tank 7, an internal combustion engine 8, and a variable valve controller. 11 a, an exhaust passage 15, an accelerator opening sensor 18, and an ECU (Engine Control Unit) 20.

  The air cleaner 2 purifies air (intake air) acquired from the outside and supplies it to the intake passage 3. A compressor 4a of the turbocharger 4 is disposed in the intake passage 3, and the intake air is compressed (supercharged) by the rotation of the compressor 4a.

  In the intake passage 3, an intercooler 5 that cools intake air and a throttle valve 6 that adjusts the amount of intake air supplied to the internal combustion engine 8 are provided. The opening degree of the throttle valve 6 is controlled by a control signal S2 supplied from the ECU 20.

  The intake air that has passed through the throttle valve 6 is temporarily stored in the surge tank 7 and then flows into the cylinder (cylinder) 8 a of the internal combustion engine 8. The internal combustion engine 8 has at least one cylinder 8a. The internal combustion engine 8 can be an engine such as a gasoline engine or a diesel engine.

  The cylinder 8a is provided with an intake valve (not shown) for introducing intake air into the cylinder 8a and an exhaust valve (not shown) for discharging gas (exhaust gas) in the cylinder 8a. The exhaust valve is connected to the camshaft 11b, and the camshaft 11b is connected to the variable valve controller 11a. The variable valve controller 11a opens and closes the exhaust valve via the camshaft 11b. The variable valve controller 11a is a device capable of variably controlling the opening / closing timing (valve timing) of the exhaust valve. The variable valve control unit 11a is controlled by a control signal S3 supplied from the ECU 20.

  Exhaust gas generated by combustion in the internal combustion engine 8 is discharged to the exhaust passage 15. The exhaust gas rotates the turbine 4b of the turbocharger 4 provided in the exhaust passage 15. The rotational torque of the turbine 4b is transmitted to the compressor wheel in the supercharger 4 and the compressor 4a rotates, whereby the intake air passing through the turbocharger 4 is compressed (hereinafter, turbocharger). The intake air supercharged by 4 is also referred to as “supercharged air”).

  The accelerator opening sensor 18 detects the amount of accelerator operation (accelerator opening) by the driver. Then, the accelerator opening sensor 18 supplies the detected accelerator opening to the ECU 20 as a signal S1.

  The ECU 20 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). The ECU 20 performs in-vehicle control based on outputs supplied from various sensors in the vehicle. In the present embodiment, the ECU 20 controls the throttle valve 6 and the variable valve controller 11a based on the accelerator opening supplied from the accelerator opening sensor 18. That is, the ECU 20 functions as throttle opening control means and variable valve control means.

  Here, a phenomenon that generally occurs when the throttle valve 6 is suddenly closed (that is, during sudden deceleration) will be described.

  At the time of sudden deceleration, the throttle valve 6 is suddenly closed, so that the pressure on the upstream side of the throttle valve 6 (hereinafter simply referred to as “upstream pressure”) rises rapidly. Therefore, high pressure air may flow back to the turbocharger 4 and a surge may occur in the turbocharger 4. Basically, a reverse flow to the turbocharger 4 does not occur by opening the throttle valve 6 after performing a fuel cut, so no surge occurs. However, when the throttle valve 6 is opened, the pumping loss hardly occurs, so that engine braking may be difficult to occur. Therefore, there are cases where the vehicle cannot be decelerated appropriately.

  Here, the deceleration control method according to the comparative example will be described with reference to FIG.

  The deceleration control according to the comparative example refers to control that opens the throttle valve 6 and opens the exhaust valve during the exhaust stroke when the internal combustion engine 8 is decelerated immediately after the high output state. Such control of the exhaust valve is normally performed when the vehicle is traveling. In the deceleration control according to the comparative example, fuel cut is executed.

  FIG. 2A shows a PV diagram when the deceleration control according to the comparative example is performed. That is, changes in the volume and pressure of the gas in the cylinder 8a in a series of combustion stroke cycles (intake → compression → expansion → exhaust) are shown. In FIG. 2A, the horizontal axis indicates the volume of gas in the cylinder 8a, and the vertical axis indicates the gas pressure in the cylinder 8a.

  2B and 2C show the opening / closing timing of the intake valve and the opening / closing timing of the exhaust valve in the deceleration control according to the comparative example. Specifically, FIGS. 2 (b) and 2 (c) show opening and closing timings in one cycle of the combustion stroke, with the horizontal axis showing time and the vertical axis showing opening and closing of the valve.

  First, in the intake stroke, the intake valve is opened as shown in FIG. As the piston moves toward the bottom dead center with the intake valve open, intake air is introduced into the cylinder 8a as indicated by an arrow 41 in FIG. Then, after the intake stroke ends, the intake valve is closed. Next, in the compression stroke, as the piston moves toward the top dead center, the intake air in the cylinder 8a is compressed as shown by the arrow 42 in FIG. To rise.

  In the expansion stroke, as the piston moves toward the bottom dead center, the intake air in the cylinder 8a is expanded and the pressure in the cylinder 8a decreases as indicated by the arrow 43 in FIG. To do. In this case, the intake air in the cylinder 8a passes through the same path as that during compression and is expanded. This is because combustion is not performed in the cylinder 8a because the fuel is cut. Next, in the exhaust stroke, the exhaust valve is opened as shown in FIG. When the exhaust valve is open, the piston moves toward the top dead center, whereby the gas in the cylinder 8a is discharged as shown by the arrow 44 in FIG. Then, after the exhaust stroke ends, the exhaust valve is closed.

  The work when the deceleration control according to the comparative example as described above is performed corresponds to the area of the shaded area M1 in FIG. The work corresponding to the area of the region M1 generally corresponds to a pumping loss. From this, it can be seen that the area of the region M1 is relatively small, and almost no pumping loss occurs. The pumping loss hardly occurs in this way because the upstream pressure is high. Therefore, when the control according to the comparative example described above is performed, even if the surge can be suppressed, the engine brake may not be appropriately generated using the pumping loss. Therefore, there is a case where sufficient deceleration cannot be obtained.

[Deceleration control method]
Hereinafter, the deceleration control according to the present embodiment will be described. The deceleration control according to the present embodiment is performed so as to ensure the occurrence of engine braking while suppressing the occurrence of a surge during deceleration, that is, appropriate deceleration.

(First embodiment)
The deceleration control according to the first embodiment will be described. This deceleration control is executed by the ECU 20.

  First, the ECU 20 determines whether or not the vehicle is decelerating based on the accelerator opening (corresponding to the signal S1) supplied from the accelerator opening sensor. When it is determined that the vehicle is decelerating, the ECU 20 performs fuel cut and sets the throttle valve 6 to open. The reason why the throttle valve 6 is opened is to suppress a surge generated by the backflow of the supercharged air to the turbocharger 4. Further, when it is determined that the vehicle is decelerating, the ECU 20 controls the variable valve controller 11a so that the exhaust valve is opened during the expansion stroke. In other words, the ECU 20 performs control (rapid opening control) that accelerates the timing of opening the exhaust valve from the exhaust stroke to the expansion stroke.

  Here, the deceleration control according to the first embodiment will be specifically described with reference to FIG.

  FIG. 3A shows a PV diagram when the deceleration control according to the first embodiment is performed. In FIG. 3A, the horizontal axis indicates the gas volume in the cylinder 8a, and the vertical axis indicates the gas pressure in the cylinder 8a.

  3B and 3C show the opening / closing timing of the intake valve and the opening / closing timing of the exhaust valve in the deceleration control in the first embodiment. Specifically, FIGS. 3B and 3C show opening and closing timings in one cycle of the combustion stroke, with the horizontal axis indicating time and the vertical axis indicating opening and closing of the valve.

  First, in the intake stroke, the ECU 20 opens the intake valve as shown in FIG. When the intake valve is open, the piston moves toward the bottom dead center, whereby intake air is introduced into the cylinder 8a as indicated by an arrow 51 in FIG. Then, after the intake stroke is completed, the intake valve is closed. Next, in the compression stroke, as the piston moves toward the top dead center, the intake air in the cylinder 8a is compressed as indicated by the arrow 52 in FIG.

  After such a compression stroke, the ECU 20 controls the variable valve controller 11a so that the exhaust valve is opened as shown in FIG. As a result, immediately after the exhaust valve is opened, the pressure in the cylinder 8a suddenly drops as indicated by the arrow 53 in FIG. Then, as the piston moves toward the bottom dead center, as indicated by an arrow 54 in FIG. 3A, the volume in the cylinder 8a increases with a constant pressure. Specifically, since the exhaust valve is open, the gas flows in from the exhaust port provided in the cylinder 8a when the piston moves toward the bottom dead center. After completion of the expansion stroke as described above, the ECU 20 controls the variable valve controller 11a so that the exhaust valve is closed.

  Next, in the exhaust stroke, as the piston moves toward the top dead center, the pressure in the cylinder 8a increases as indicated by the arrow 55 in FIG. In this case, since the exhaust valve is closed and the gas in the cylinder 8a is not discharged, the pressure in the cylinder 8a increases as the piston moves toward top dead center.

  The work when the deceleration control according to the first embodiment described above is performed substantially corresponds to the area of the shaded area M2 in FIG. Specifically, the work corresponding to the area of the region M2 is a negative work that occurs during compression and expansion (hereinafter, this work is also referred to as “compression loss”). It can be seen that the magnitude of this compression loss is considerably larger than the work corresponding to the above-described region M1 (see FIG. 2A). That is, sufficiently large work can be generated by performing the deceleration control according to the first embodiment. Thereby, the control device of the internal combustion engine 8 can generate an engine brake using this compression loss. That is, normally, the engine brake is generated using the pumping loss, but if the throttle valve 6 is opened during deceleration, a sufficient pumping loss does not occur. Therefore, in the control device for the internal combustion engine 8 according to the present embodiment, A compression loss is generated by performing the deceleration control described above, and an engine brake is generated using the compression loss.

  As described above, according to the deceleration control according to the first embodiment, at the time of deceleration, it is possible to ensure the generation of the engine brake and suppress the appropriate deceleration while suppressing the generation of the surge. In this case, since the control device for the internal combustion engine 8 does not suppress the occurrence of surge by performing control to reduce the supercharging pressure, it is not necessary to separately provide an air bypass valve or the like. The configuration of the control device can be simplified.

  Note that the control device for the internal combustion engine 8 closes the throttle valve 6 and opens the exhaust valve when the upstream pressure is sufficiently reduced (specifically, when the pressure is almost atmospheric). The control which returns the timing to perform from an expansion stroke to an exhaust stroke is performed. Here, the control for setting the throttle valve 6 closed during deceleration and opening the exhaust valve during the exhaust stroke is referred to as “normal deceleration control”. That is, the control device for the internal combustion engine 8 switches from the deceleration control according to the first embodiment to the normal deceleration control when the upstream pressure sufficiently decreases. This is because the surge is not generated when the upstream pressure is sufficiently reduced. In this way, by switching the deceleration control, it is possible to perform a good acceleration during re-acceleration while maintaining the deceleration state.

(Second Embodiment)
Next, deceleration control according to the second embodiment will be described.

  The deceleration control according to the second embodiment is different from the deceleration control according to the first embodiment described above in that the exhaust valve is opened in both the expansion stroke and the exhaust stroke. In the deceleration control according to the first embodiment, since the exhaust valve is opened during the expansion stroke, the exhaust side gas is introduced into the cylinder 8a during the expansion stroke, but during the exhaust stroke after the expansion stroke. Since the exhaust valve is closed, the exhaust gas introduced into the cylinder 8a is not discharged. As a result, the action of returning the exhaust side gas to the cylinder 8a works. Therefore, a good combustion state may not be obtained at the time of reacceleration after deceleration, that is, good acceleration may not be obtained. Therefore, in the deceleration control according to the second embodiment, the exhaust valve is opened not only during the expansion stroke but also during the exhaust stroke. Since the control according to the second embodiment is not a control that simply shifts the opening timing of the exhaust valve, the exhaust valve is preferably constituted by an electromagnetic valve or the like.

  Here, the deceleration control according to the second embodiment will be specifically described with reference to FIG. In the deceleration control according to the second embodiment, when it is determined that the vehicle is decelerating based on the accelerator opening, the fuel cut is executed and the throttle valve 6 is set to open. Moreover, the deceleration control according to the second embodiment is also executed by the ECU 20.

  FIG. 4A shows a PV diagram when the deceleration control according to the second embodiment is performed. In FIG. 4A, the horizontal axis indicates the gas volume in the cylinder 8a, and the vertical axis indicates the gas pressure in the cylinder 8a.

  4B and 4C show the opening / closing timing of the intake valve and the opening / closing timing of the exhaust valve in the deceleration control in the second embodiment. Specifically, FIG. 4B and FIG. 4C show the opening and closing timings in one cycle of the combustion stroke, and the horizontal axis shows time and the vertical axis shows opening and closing of the valve.

  First, in the intake stroke, the ECU 20 opens the intake valve as shown in FIG. When the intake valve is open, the piston moves toward the bottom dead center, whereby intake air is introduced into the cylinder 8a as indicated by an arrow 61 in FIG. Then, after the intake stroke is completed, the intake valve is closed. Next, in the compression stroke, as the piston moves toward the top dead center, the intake air in the cylinder 8a is compressed as indicated by the arrow 62 in FIG.

  After such a compression stroke, the ECU 20 controls the variable valve controller 11a so that the exhaust valve is opened as shown in FIG. As a result, immediately after the exhaust valve is opened, the pressure in the cylinder 8a suddenly drops as indicated by the arrow 63 in FIG. Then, as the piston moves toward the bottom dead center, as indicated by an arrow 64 in FIG. 4A, the volume in the cylinder 8a increases with a constant pressure. Specifically, since the exhaust valve is open, the gas flows in from the exhaust port provided in the cylinder 8a when the piston moves toward the bottom dead center.

  The ECU 20 controls the variable valve controller 11a so that the exhaust valve continues to be opened after the end of the expansion stroke. That is, the ECU 20 controls the variable valve controller 11a so that the exhaust valve is opened even in the exhaust stroke (see FIG. 4C).

  In the exhaust stroke, as the piston moves toward the top dead center, the gas in the cylinder 8a is discharged as indicated by the arrow 65 in FIG. In this case, since the exhaust valve is open, the gas in the cylinder 8a is discharged in a state where the pressure is constant as the piston moves toward the top dead center. And ECU20 controls the variable valve control part 11a so that an exhaust valve may be closed after completion | finish of the above exhaust stroke.

  The work when the deceleration control according to the second embodiment described above is performed corresponds to the area of the shaded area M3 in FIG. The work corresponding to the area of the region M3 is a compression loss that occurs during compression and expansion. It can be seen that the magnitude of this compression loss is considerably larger than the work corresponding to the above-described region M1 (see FIG. 2A). Therefore, the control device for the internal combustion engine 8 can generate sufficient engine braking using this compression loss.

  As described above, according to the deceleration control according to the second embodiment, at the time of deceleration, it is possible to perform appropriate deceleration by ensuring the generation of engine brake while suppressing the generation of surge. In the deceleration control according to the second embodiment, the exhaust valve is opened in the expansion stroke and the exhaust stroke to suppress the recirculation of the gas on the exhaust side, so that a good combustion state is obtained at the time of reacceleration after the deceleration. Is possible. Furthermore, according to the deceleration control according to the second embodiment, the surge can be suppressed without separately providing an air bypass valve or the like, so that the configuration of the control device for the internal combustion engine 8 can be simplified.

  Note that the control device for the internal combustion engine 8 changes the deceleration control according to the second embodiment to the normal deceleration control when the upstream pressure is sufficiently reduced (specifically, when the pressure becomes substantially atmospheric pressure). Switch. Specifically, the throttle valve 6 is closed and the timing for opening the exhaust valve is switched from the expansion stroke and the exhaust stroke to the exhaust stroke only. As a result, it is possible to perform good acceleration during re-acceleration while maintaining the deceleration state.

1 is a schematic diagram showing a schematic configuration of a vehicle to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. It is a figure for demonstrating the deceleration control method which concerns on a comparative example. It is a figure for demonstrating the deceleration control which concerns on 1st Embodiment. It is a figure for demonstrating the deceleration control which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Intake passage 4 Turbocharger 6 Throttle valve 7 Surge tank 8 Internal combustion engine 8a Cylinder 11a Variable valve control part 11b Camshaft 15 Exhaust passage 18 Accelerator opening sensor 20 ECU

Claims (3)

Throttle opening control means for controlling the opening of the throttle valve;
Variable valve control means for variably controlling the opening and closing timing of the exhaust valve,
The throttle opening control means opens the throttle valve when the internal combustion engine decelerates,
The control apparatus for an internal combustion engine, wherein the variable valve control means controls the exhaust valve to open quickly when the internal combustion engine is decelerated.   2. The control apparatus for an internal combustion engine according to claim 1, wherein the variable valve control means shifts a timing for setting the exhaust valve to open from an exhaust stroke to an expansion stroke. 2. The control device for an internal combustion engine according to claim 1, wherein the variable valve control means sets the exhaust valve to be open when the internal combustion engine is in an expansion stroke and an exhaust stroke.

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