JP2009216035A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure idle stability while improving the exhaust emission during idle operation by prematurely closing an exhaust valve. <P>SOLUTION: The premature closing of the exhaust valve produces the blow back of exhaust gas by spark-advancing the closing timing of the exhaust valve 36. However, when the premature closing of the exhaust valve is performed during the idle operation, the amount of the blow back gas becomes excessive depending on the operating condition, and combustion state is deteriorated. To improve this problem, an ECU 50 corrects the closing timing of the exhaust valve 36 set by the premature closing of the exhaust valve according to the engine rotational speed during the idle operation. Therefore, the blow back flow of the exhaust gas can be properly controlled according to the combustion state while performing the premature closing of the exhaust valve during the idle operation. Consequently, a fuel economy performance and the exhaust emission during the idle operation can be improved, and also the idle stability can be secured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine equipped with a variable valve mechanism that variably sets a valve timing.

  Conventionally, as disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2001-355462), a control device for an internal combustion engine including a variable valve mechanism is known. In this type of prior art control device for an internal combustion engine, the exhaust valve early closing control is executed when the internal combustion engine is operating at a low speed and a low load.

  In the exhaust valve early closing control, the closing timing of the exhaust valve is advanced more than usual. Thereby, in the vicinity of the intake top dead center, a minus overlap period in which the intake valve and the exhaust valve are closed occurs. Since the exhaust gas remaining in the cylinder is compressed during the minus overlap period, exhaust gas blows back toward the intake system when the intake valve is opened. This blowback makes it possible to improve exhaust emission.

  Further, in the prior art, when performing idle operation, the exhaust valve is not closed early, but the exhaust valve is closed at the intake top dead center. As a result, the combustibility is stabilized by the amount of exhaust gas that is blown back little (or does not occur). Therefore, in the prior art, the idle stability is improved.

JP 2001-355462 A

  By the way, in the above-described prior art, the exhaust valve early closing control is not executed during the idling operation, and the combustibility is stabilized. In this case, since the exhaust valve early closing control has an advantage of improving exhaust emission and fuel efficiency, there is a demand for executing the exhaust valve early closing control even during idle operation.

  However, the exhaust gas blow-back flow varies depending on the operating state of the internal combustion engine. For this reason, if exhaust valve early closing control is performed during idle operation, the amount of blown back gas may become excessive depending on the operating state. In this case, the combustibility deteriorates and the idle stability is impaired. For this reason, the prior art has a problem that it is difficult to achieve both the early closing control and the idle stability even when the exhaust valve early closing control can be performed during the idling operation.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine capable of ensuring idle stability while improving fuel efficiency performance and exhaust emission during idle operation by exhaust valve early closing control. The object is to provide an engine control device.

According to a first aspect of the present invention, there is provided a variable valve mechanism for variably setting at least an exhaust valve timing among an intake valve and an exhaust valve of an internal combustion engine,
An exhaust valve early closing control means for advancing the closing timing of the exhaust valve by operating the variable valve mechanism and causing the exhaust gas to blow back into the intake system;
Rotation correspondence correcting means for correcting the closing timing of the exhaust valve set by the exhaust valve early closing control means during idle operation of the internal combustion engine according to the engine speed;
It is characterized by providing.

According to the second invention, in the first invention,
The rotation correspondence correcting unit is configured to retard the closing timing of the exhaust valve as the engine speed during the idle operation is higher.

According to a third invention, in the first or second invention,
Temperature detecting means for detecting the temperature state of the internal combustion engine;
The temperature corresponding correction means for retarding the closing timing of the exhaust valve, as the temperature state during the idle operation is higher,
It is set as the structure provided with.

  According to the first invention, the exhaust valve early closing control means can cause exhaust gas to blow back by advancing the closing timing of the exhaust valve during idle operation. At this time, the rotation correspondence correcting means can correct the closing timing of the exhaust valve set by the exhaust valve early closing control means in accordance with the engine speed. For this reason, even if the exhaust gas blowback flow rate increases or decreases according to the change in the engine speed, the blowback flow rate can be appropriately controlled by correcting the valve closing timing.

  Thereby, during idle operation, the effect of the exhaust valve early closing control can be maximized while avoiding deterioration of the combustion state due to the change in the rotational speed. Therefore, fuel efficiency performance and exhaust emission during idling can be improved, and at the same time, idling stability can be ensured.

  According to the second aspect of the invention, the rotation correspondence correcting unit can correct the valve closing timing of the exhaust valve to the retard side as the engine speed during idling is higher. Thereby, at the time of low rotation, since the blow-back flow rate is relatively small, it is possible to keep the valve closing timing of the exhaust valve advanced. As a result, exhaust valve early closing control can be positively performed while suppressing the influence of blowback on the combustion state.

  Further, when the engine speed is high, the valve closing timing of the exhaust valve can be retarded accordingly. As a result, the increase in the exhaust gas blow-back flow rate due to the increase in rotation can be canceled out by retarding the valve closing timing, and the exhaust gas blow-back flow rate can be appropriately controlled according to the stability of combustion. it can.

  According to the third invention, the temperature correspondence correcting means can correct the valve closing timing of the exhaust valve to the retard side as the temperature state during the idling operation is higher. In this case, for example, when the water temperature is low, such as during cold first idle operation, the internal combustion engine has a large friction and high load operation is performed.Therefore, there is a surplus in the combustion state, and the exhaust gas blow-back flow rate can be increased. Become.

  Therefore, at the time of a low water temperature with a large discharge amount of HC or the like, the valve closing timing of the exhaust valve can be maintained in the advanced state, and the effect of the exhaust valve early closing control can be sufficiently exhibited. Further, for example, when the water temperature is high such as during hot idle operation, there is no allowance in the combustion state, so that the closing timing of the exhaust valve can be retarded. Thereby, the influence of blowback can be suppressed and stabilization of the combustion state can be prioritized.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. First, FIG. 1 shows an overall configuration diagram for explaining the system configuration of the first embodiment. The system of this embodiment includes a multi-cylinder internal combustion engine 10 mounted on a vehicle, for example, and a combustion chamber 14 is provided between each piston and a piston 12. Further, the piston 12 of each cylinder is connected to the crankshaft 16. The internal combustion engine 10 includes a crank angle sensor 18 for detecting the rotation angle (crank angle) of the crankshaft 16.

  Each cylinder of the internal combustion engine includes an intake passage 20 through which intake air flows toward the combustion chamber 14 and an exhaust passage 22 through which exhaust gas flows out of the combustion chamber 14. The intake passage 20 is provided with an air flow meter 24 for detecting the intake air amount and an electronically controlled throttle valve 26 for adjusting the intake air amount. The throttle valve 26 is driven by a throttle motor 28 based on the accelerator opening and the like.

  Each cylinder of the internal combustion engine has a fuel injection valve 30 that injects fuel into the intake air, an ignition plug 32 that ignites the air-fuel mixture, and an intake valve 34 that opens and closes the combustion chamber 14 with respect to the intake passage 20. And an exhaust valve 36 for opening and closing the combustion chamber 14 with respect to the exhaust passage 22. The opening and closing timing (valve timing) of the intake valve 34 is variably set by the intake VVT 38. The opening / closing timing of the exhaust valve 36 is variably set by the exhaust VVT 40. These VVTs (Variable Valve Timing system = variable valve timing mechanism) 38 and 40 constitute the variable valve mechanism of the present embodiment.

  The VVTs 38 and 40 are configured by using a known technique as described in, for example, Japanese Patent Application Laid-Open No. 2003-293711. The intake VVT 38 advances or retards the phase (opening timing and closing timing) of the intake valve 34 in accordance with a command signal input from the ECU 50 described later.

  Similarly, the exhaust-side VVT 40 advances or retards the phase of the exhaust valve 36 in accordance with a command signal from the ECU 50. On the other hand, the internal combustion engine 10 includes a water temperature sensor 42 as temperature detecting means for detecting the temperature of the cooling water.

  Furthermore, the system of the present embodiment includes an ECU (Electronic Control Unit) 50 for controlling the operating state of the internal combustion engine 10. The ECU 50 is constituted by a microcomputer having a storage circuit such as a ROM or a RAM.

  A sensor system including the crank angle sensor 18, the air flow meter 24, the water temperature sensor 42 and the like is connected to the input side of the ECU 50. Various actuators including a throttle motor 28, a fuel injection valve 30, a spark plug 32, VVTs 38 and 40 are connected to the output side of the ECU 50.

  Then, the ECU 50 performs operation control by driving each actuator while detecting the operation state of the internal combustion engine by the sensor system. This operation control includes idle operation control for maintaining the engine speed at the target idling speed when the internal combustion engine is in an idle state.

  In this case, the target idle speed is variably set according to the temperature of the cooling water detected by the water temperature sensor 42, for example. That is, for example, during the first idle operation in the cold state (during cold F / I), as shown in FIG. 5 described later, the idle target rotational speed is set to a rotational speed higher than normal. Further, at the time of hot idle operation after warm-up, a lower idle target rotational speed is used than at the time of cold F / I.

  Further, the operation control by the ECU 50 includes normal valve timing control, exhaust valve early closing control, rotation correspondence correction control, and temperature correspondence correction control performed using the VVTs 38 and 40. Hereinafter, these controls will be described.

(Normal valve timing control)
The ECU 50 executes normal valve timing control (hereinafter referred to as normal control) using the VVTs 38 and 40 when the exhaust valve early closing control is not executed, for example, during acceleration operation of the internal combustion engine. FIG. 2 shows the relationship between the valve lift amount and the crank angle in the normal control. FIG. 2 shows an example of normal control.

  As shown in this figure, in the normal control, the closing timing of the exhaust valve 36 is set in the vicinity of the intake top dead center. Thereby, the overlap period of the valves 34 and 36 is provided in the vicinity of the intake top dead center. As a result, when the normal control is executed, the exhaust gas blow-back flow rate is reduced or almost no blow-back occurs compared with the exhaust valve early closing control.

(Exhaust valve early closing control)
In the present embodiment, the exhaust valve early closing control is executed when the idling operation is performed. FIG. 3 shows the relationship between the valve lift amount and the crank angle in the exhaust valve early closing control. As shown in this figure, in the exhaust valve early closing control, the phase (opening timing and closing timing) of the exhaust valve 36 is advanced by, for example, the VVT 40. As a result, the exhaust valve 36 is closed at a timing earlier than the normal control.

  As a result, in the vicinity of the intake top dead center, a minus overlap period occurs in which both the intake valve 34 and the exhaust valve 36 are closed. During the minus overlap period, the exhaust gas left in the combustion chamber 14 is compressed to a high temperature / high pressure state. Since the residual exhaust gas is blown back from the combustion chamber 14 toward the intake port when the intake valve 34 is opened, the effect shown in FIG. 4 below can be obtained in the exhaust valve early closing control.

  FIGS. 4A to 4C show the relationship between the parameters related to the combustion state of the internal combustion engine and the temperature of the blowback gas. As for the normal control in the figure, in order to make a comparison under the same conditions as the exhaust valve early closing control, a case where blowback gas equivalent to the exhaust valve early closing control is generated by valve overlap is illustrated.

  In the early closing control of the exhaust valve, high-temperature and high-pressure blown-back gas is generated as compared with the normal control, so that the intake negative pressure is smaller than that in the normal control as shown in FIG. As a result, the pumping loss is reduced, so that the fuel efficiency can be improved. Moreover, the blow-back gas that has flowed back to the intake port collides with the injected fuel. For this reason, in the exhaust valve early closing control, as shown in FIG. 4B, the atomization degree of the injected fuel is increased and the combustion state is improved. As a result, fuel consumption performance and exhaust emission can be improved.

  Further, in the exhaust valve early closing control, the high-temperature blown-back gas is recompressed. Therefore, as shown in FIG. 4C, the gas temperature at the compression end is higher than that in the normal control, and combustion is improved. Can be promoted. In addition, since the exhaust gas blown back contributes to combustion again, a so-called EGR (internal EGR) effect is produced, and exhaust emission can be further improved.

  However, the exhaust gas blow-back flow varies depending on the operating state of the internal combustion engine. For this reason, if exhaust valve early closing control is performed during idle operation, the amount of blown back gas may become excessive depending on the operating state. Therefore, in the present embodiment, the rotation correspondence correction control and the temperature correspondence correction control are performed during the idling operation, and the valve closing timing of the exhaust valve is corrected according to the operation state. Thus, the effect of the above-described exhaust valve early closing control and idle stability are made compatible.

(Correction control for rotation)
In this correction control, the valve closing timing of the exhaust valve set by the exhaust valve early closing control is corrected in accordance with the engine speed during the idling operation. If the engine speed increases during execution of the exhaust valve early closing control, the compression time when the exhaust gas blow-back is recompressed in the combustion chamber is shortened. In general, the amount of blow-by gas that leaks from the fitting clearance of the piston ring to the crank chamber side increases or decreases according to the compression time. Therefore, when the compression time becomes shorter, the blow-by gas decreases.

  Further, when the compression time is shortened, the amount of heat conducted from the gas in the combustion chamber to the cylinder wall surface is also reduced. As a result, in the compression stroke, exhaust gas with little leakage is compressed at a high temperature, so that in the next intake stroke, a large amount of blown back gas is generated at a relatively high temperature, and this blown back gas again enters the combustion chamber. It is sucked into internal EGR gas.

  Therefore, in the early closing control of the exhaust valve, if the advance amount of the exhaust valve 36 is constant, the exhaust gas blow-back flow rate, that is, the amount of internal EGR gas increases as the engine speed increases, and the combustion state is increased. It will get worse. FIG. 5 shows the relationship between the engine speed Ne during idle operation and the blowback flow rate. In the steady state of idle operation, the engine speed is controlled to be substantially equal to the target idle speed.

  As shown in this figure, it is understood that when the engine speed (idle target speed) is high, the blowback flow rate increases. Therefore, in the rotation correction control, the valve closing timing of the exhaust valve 36 is corrected to the retard side as the engine speed during idling increases. According to this configuration, the blow-back flow rate is relatively small during low rotation, so that the valve closing timing of the exhaust valve can be maintained in an advanced state. Thereby, the exhaust valve early closing control can be positively performed while suppressing the influence of the blowback on the combustion state.

  Further, when the engine speed is high, the valve closing timing of the exhaust valve 36 can be retarded accordingly. As a result, the increase in the exhaust gas blow-back flow rate due to the increase in rotation can be canceled out by retarding the valve closing timing, and the exhaust gas blow-back flow rate can be appropriately controlled according to the stability of combustion. it can. Therefore, during idle operation, the effect of the exhaust valve early closing control means can be maximized while avoiding deterioration of the combustion state due to a change in the rotational speed.

(Temperature correction control)
FIG. 6 shows a load state and a combustion state during the idle operation for each of the cold F / I operation and the hot idle operation. During the cold F / I operation, the internal combustion engine has a large friction, and therefore a high load operation is performed. In high-load operation, the amount of intake air (intake negative pressure) increases, so there is a margin in the combustion state even if a certain amount of blowback occurs. On the other hand, during the hot idle operation, a relatively low load state is obtained, and thus the stability of the combustion state against exhaust gas blow-back is lower than that during the cold F / I operation.

  Therefore, in the temperature-adaptive correction control, the valve closing timing of the exhaust valve 36 is retarded as the coolant temperature increases. That is, when the water temperature is low, the exhaust gas blow-back flow rate can be increased, so that the valve closing timing can be maintained in the advanced state, and the effect of the exhaust valve early closing control can be sufficiently exhibited. In particular, during the cold F / I operation, the fuel is rich, and the amount of HC and the like is large. Therefore, the exhaust emission can be improved by the exhaust valve early closing control.

  Further, when the water temperature is high, the closing timing of the exhaust valve 36 can be retarded. Thus, for example, during hot idle operation, the influence of blowback can be suppressed, and stabilization of the combustion state can be prioritized.

  FIG. 7 is a characteristic diagram showing the relationship between the closing timing of the exhaust valve, the engine speed and the water temperature. This characteristic diagram is obtained by converting the contents of the above-described rotation correspondence correction control and temperature correspondence correction control into data, and is stored in advance in the ECU 50 as, for example, two-dimensional map data. As shown in FIG. 7, the closing timing of the exhaust valve 36 is corrected to the retard side as the engine speed Ne during idle operation is higher and the coolant temperature is higher.

[Specific Processing for Realizing Embodiment 1]
FIG. 8 shows a flowchart of a routine executed by the ECU 50 in order to realize the system operation of the present embodiment. Note that the routine shown in FIG. 8 is repeatedly executed during operation of the internal combustion engine.

  As shown in FIG. 8, the ECU 50 first determines whether or not the internal combustion engine is idling (step 100). When this determination is not established, normal valve timing control is performed by delaying the valve closing timing of the exhaust valve 36 to the vicinity of the intake top dead center, for example (step 102). When the determination is established, the engine speed Ne is acquired using the detection signal of the crank angle sensor 18, and the cooling water temperature is acquired by the water temperature sensor 42 (step 104).

  Next, in step 106, the valve closing timing of the exhaust valve 36 in the exhaust valve early closing control is set by referring to the map data of FIG. 7 according to the acquired engine speed and water temperature. Thereby, the valve closing timing corrected according to the engine speed and the water temperature can be obtained. The exhaust valve early closing control can be performed by driving the exhaust VVT 40 in accordance with the set value of the valve closing timing.

  As described above, according to the present embodiment, the exhaust gas blowback flow rate can be appropriately controlled according to the combustion state while executing the exhaust valve early closing control during the idling operation. Therefore, fuel efficiency performance and exhaust emission during idling can be improved, and at the same time, idling stability can be ensured.

  In the above embodiment, step 106 in FIG. 8 shows a specific example of the exhaust valve early closing control means, the rotation correspondence correction means, and the temperature correspondence correction means. For the rotation correspondence correction means and the temperature correspondence correction means, the map data in FIG. 7 also shows a specific example.

  In the embodiment, the higher the engine speed, the more retarded the closing timing of the exhaust valve 36 is. However, the present invention is characterized in that the valve closing timing is corrected according to the engine speed during idle operation. If necessary, the lower the engine speed during idle operation, the closer the exhaust valve is closed. The valve timing may be delayed.

  In the embodiment, the exhaust valve closing timing is corrected according to the cooling water temperature detected by the water temperature sensor 42. However, the present invention is not limited to the cooling water temperature, and may be configured to correct the valve closing timing in accordance with parameters other than the cooling water temperature as long as the parameters reflect the temperature state of the internal combustion engine. Examples of parameters include exhaust gas temperature and lubricating oil temperature.

  In the embodiment, the exhaust valve early closing control means is configured to generate exhaust gas blow-back by generating a minus overlap period. However, the exhaust valve early closing control means of the present invention is not necessarily required to cause the minus overlap period as long as exhaust gas blows back.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view for explaining a system configuration according to a first embodiment of the present invention. It is explanatory drawing which shows the relationship between the valve lift amount and crank angle in normal valve timing control. It is explanatory drawing which shows the relationship between the valve lift amount and crank angle in exhaust valve early closing control. It is explanatory drawing which shows the relationship between the intake negative pressure of an internal combustion engine, the atomization degree of the injection fuel, the temperature of a compression end, and the temperature of blow-back gas. It is explanatory drawing which shows the relationship between the blow-back flow rate of exhaust gas, and idle rotation speed. It is explanatory drawing which shows the load state and combustion state in idle operation about each of cold first idle operation and hot idle operation. It is a characteristic diagram which shows the relationship between the valve closing timing of an exhaust valve, idle rotation speed, and cooling water temperature. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Combustion chamber 16 Crankshaft 18 Crank angle sensor 20 Intake passage 22 Exhaust passage 24 Air flow meter 26 Throttle valve 28 Throttle motor 30 Fuel injection valve 32 Spark plug 34 Intake valve 36 Exhaust valve 38, 40 VVT (variable motion) Valve mechanism)
42 Water temperature sensor (temperature detection means)
50 ECU

Claims (3)

A variable valve mechanism for variably setting the valve timing of at least the exhaust valve of the intake valve and the exhaust valve of the internal combustion engine;
An exhaust valve early closing control means for advancing the closing timing of the exhaust valve by operating the variable valve mechanism and causing the exhaust gas to blow back into the intake system;
Rotation correspondence correcting means for correcting the closing timing of the exhaust valve set by the exhaust valve early closing control means during idle operation of the internal combustion engine according to the engine speed;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the rotation correspondence correcting unit is configured to retard the closing timing of the exhaust valve as the engine speed during the idle operation is higher. Temperature detecting means for detecting the temperature state of the internal combustion engine;
The temperature corresponding correction means for retarding the closing timing of the exhaust valve, as the temperature state during the idle operation is higher,
The control device for an internal combustion engine according to claim 1, comprising:

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