JP4239797B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  In an internal combustion engine, a variable valve timing device is known that changes the opening / closing timing of an intake valve or an exhaust valve to an optimal timing according to the engine operating state.

In addition, when starting an internal combustion engine or warming it up, a technology for increasing the exhaust gas temperature and quickly activating the catalyst by opening the valve timing of the exhaust valve with such a variable valve timing device is known. (For example, refer to Patent Document 1).
Japanese Utility Model Publication No. 5-96444 JP 2003-83032 A JP-A-5-59936 Japanese Utility Model Publication No. 5-96445

  By the way, immediately after starting the internal combustion engine, the combustion is in an unstable state, and in such a state, if the valve timing of the exhaust valve is opened quickly, a part of the fuel is discharged without being burned. Is concerned. If unburned fuel is discharged from the internal combustion engine when the catalyst has not reached the activation temperature immediately after the internal combustion engine is started, exhaust emission will be deteriorated.

  The present invention has been made in view of the circumstances as described above, and reduces unburned fuel discharged from an internal combustion engine at the time of cold start of the internal combustion engine, thereby preventing deterioration of exhaust emission. With the goal.

  In order to achieve the above object, the present invention employs the following configuration.

That is, in the control device for an internal combustion engine according to the present invention,
Cold start detection means for detecting a cold start of the internal combustion engine;
When the internal combustion engine is detected as being cold started by the cold start detection means, the operation at the opening timing of the exhaust valve of the internal combustion engine is longer in the cylinder than in the normal operation. Control means for controlling to exist,
It is characterized by providing.

  Immediately after starting the internal combustion engine, when the cylinder and the intake port are not warmed, the temperature of the intake air and fuel is low, so the injected fuel is difficult to atomize and the combustion state in the internal combustion engine is unstable. There is a concern that the injected fuel does not completely burn in the cylinder and is discharged as unburned fuel (mainly hydrocarbon (HC)). And in the state where the catalyst (exhaust gas purification means) provided in the exhaust system of the internal combustion engine is not activated, there is a concern that the exhaust gas discharged from the internal combustion engine may be discharged into the atmosphere as it is. Here, in order to burn (oxidize) HC, a high temperature field (atmosphere), oxygen (oxidizing atmosphere), and reaction time are required.

Therefore, in the present invention, the combustion gas in the cylinder is longer in the cylinder than in the normal operation (when the internal combustion engine is in normal operation) during the cold start of the internal combustion engine. It is controlled to exist. As a result, it is possible to lengthen the time from when the fuel starts to burn in the cylinder until the combustion gas is discharged, so that a high temperature field and oxygen can be secured in the cylinder ( Is the highest temperature field), and it is possible to increase the time for HC to react in the cylinder, so it is possible to promote the combustion of HC and reduce the HC discharged from the cylinder. It becomes possible.

  Here, the control means may control the combustion gas in the cylinder to be longer in the cylinder than in normal operation, for example, by delaying the opening timing of the exhaust valve or suppressing the lift amount of the exhaust valve. .

  That is, in the above configuration, when the cold start detection means detects that the internal combustion engine is in cold start, the control means includes at least an exhaust valve of the intake valve and the exhaust valve of the internal combustion engine. It is also preferable to retard the opening timing of the exhaust valve by controlling a valve timing varying mechanism that varies the opening / closing timing.

  Thus, by retarding the opening timing of the exhaust valve at the time of cold start of the internal combustion engine, it is possible to lengthen the time from when the fuel starts to burn in the cylinder until the exhaust valve is opened. A high temperature field and oxygen can be secured, and the time for reaction (oxidation) of HC in the cylinder can be increased, so that combustion (oxidation) of HC can be promoted. It becomes possible to reduce discharged HC.

  Further, in the above configuration, the control means is a variable valve that makes the lift amount of the exhaust valve of the internal combustion engine variable when the cold start detection means detects that the internal combustion engine is cold start time. It is also preferable to suppress the lift amount at the opening timing of the exhaust valve by controlling the mechanism.

  Further, in the above configuration, the control means changes the opening timing of the exhaust valve that is retarded to an advance side after a predetermined period of time has elapsed since the start of the internal combustion engine was detected by the cold start detection means. It is also preferable to do.

  Here, the predetermined period means a period from when the internal combustion engine is warmed up to a state where the discharged HC can be reduced without delaying the opening timing of the exhaust valve. Alternatively, it may be one that can represent the condition that the cylinder is warmed (one that can represent the amount of heat transmitted to the cylinder). As a representative example of the condition that the cylinder is warmed up, for example, the integrated value of the intake air amount (integrated intake air amount) after the start of the internal combustion engine and the number of explosions (ignition) (this can be obtained from the engine speed, for example). If the integrated value of the fuel injection amount becomes a predetermined value, this may be set as the predetermined period. Also, when the temperature of the intake port is in a state where fuel atomization is preferable, or the temperature of the exhaust port becomes a temperature at which HC discharged from the cylinder can be combusted (oxidized) at the exhaust port. In the case where the temperature field is necessary for burning unburned fuel in the exhaust port, this may be a predetermined period.

  Also, to change the retarded opening timing of the exhaust valve to the advance side, return the opening timing of the exhaust valve to the normal state (during normal engine operation), or advance it further than the normal state Means.

  After the predetermined period, the temperature of the exhaust discharged from the cylinder can be increased by advancing the opening timing of the exhaust valve, in particular, more advanced than the normal state, so that the catalyst can be warmed up. it can.

This is because by changing the exhaust valve to the advance side, part of the heat generated by the combustion in the cylinder is pushed down, that is, discharged before becoming torque. In addition, the torque decreases and the engine speed decreases. However, control for increasing the intake air amount (and increasing the fuel injection amount) is performed to suppress the decrease in torque and engine speed. As a result, a larger amount of high-temperature exhaust gas flows into the catalyst, so that further early activation of the catalyst can be achieved.

  Further, when the temperature of the exhaust port reaches a temperature at which HC discharged from the cylinder can be combusted (oxidized), the temperature of the exhaust discharged from the cylinder is set with the opening timing of the exhaust valve being further advanced. Can be made higher. If the opening timing of the exhaust valve is further advanced, there is a concern that the amount of HC discharged from the cylinder will increase, but even if HC is discharged from the cylinder, the HC is burned at the exhaust port ( Oxidation), the opening timing of the exhaust valve can be further advanced.

  In the above configuration, when the opening timing of the exhaust valve is retarded, the control means preferably delays the opening timing of the intake valve.

  When the opening timing of the exhaust valve is retarded, the valve overlap period in which both the exhaust valve and the intake valve are open (so-called valve overlap) may be long. When the valve overlap period becomes longer, the higher combustion gas temperature flows back toward the intake port, the wall temperature rises, fuel atomization improves, and HC decreases as a result. There is. However, if the amount of combustion gas that flows backward increases too much, the ratio of the combustion gas becomes considerably larger than that of fresh air, and the ratio of fresh air is small, so that the combustion itself becomes worse. . In order to avoid such a phenomenon, in the present invention, the opening timing of the intake valve is also retarded to set the valve overlap period to a desired period. A desired valve overlap period (valve overlap period that does not cause a problem) may be obtained in advance by experiment or the like, and the valve timing of the intake valve may be changed when this period is exceeded.

  In addition, by retarding the opening timing of the intake valve, the intake valve opens while the piston is approaching bottom dead center, so that negative pressure is generated when the intake valve opens, which causes fuel fog. Can be promoted. Accordingly, it is possible to improve the combustion stability of the internal combustion engine.

  In addition, said each structure can be employ | adopted combining as much as possible.

  According to the present invention, when the internal combustion engine is cold started, unburned fuel discharged from the internal combustion engine can be reduced to prevent the exhaust emission from deteriorating.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view for explaining a gasoline engine as an internal combustion engine according to Embodiment 1 of the present invention. First, the basic structure and function of the internal combustion engine 1 according to this embodiment will be described.

An internal combustion engine 1 shown in FIG. 1 is a gasoline engine that obtains output by repeating four cycles of an intake stroke, a compression stroke, an expansion stroke (explosion stroke), and an exhaust stroke. The internal combustion engine 1 forms a cylinder (combustion chamber) 2 therein. The fuel explosive force (combustion force) generated in the cylinder 2 is converted into the rotational force of the crankshaft 7 via the piston 3 and the connecting rod 4. Further, the cylinder 2 is provided with an intake port 5 A that forms the most downstream portion of the intake passage 5 and an exhaust port 6 A that forms the most upstream portion of the exhaust passage 6. The boundary between the intake port 5A and the cylinder 2 is opened and closed by an intake valve 8. The boundary between the exhaust port 6A and the cylinder 2 is opened and closed by an exhaust valve 9.

  A fuel injection valve 10 is provided in the intake port 5A corresponding to each cylinder 2. The fuel injection valve 10 is an electromagnetically driven on / off valve that injects fuel into the intake port 5A (in the direction toward the cylinder 2) at an appropriate amount and at an appropriate timing. The air-fuel mixture introduced into the cylinder 2 is ignited by an electric spark generated by the spark plug 15 at an appropriate timing.

  Further, the internal combustion engine 1 is equipped with a variable valve timing mechanism (hereinafter referred to as a VVT mechanism) 90 that variably controls the opening / closing operation timing of the exhaust valves 9 provided corresponding to the cylinders 2.

  The VVT mechanism 90 is attached to the distal end portion of the exhaust camshaft 91 of the internal combustion engine 1 so as to be rotatable relative to the exhaust camshaft 91. An exhaust cam sprocket (not shown) provided to rotate integrally with the VVT mechanism 90, and an intake cam sprocket (not shown) provided to rotate integrally with the intake camshaft 81 at the tip of the intake camshaft 81. (Omitted) is connected to the crankshaft 7 of the internal combustion engine 1 through a timing chain (not shown) and a crankshaft / sprocket (not shown) provided to rotate integrally with the crankshaft 7. Yes.

  The relationship between the crankshaft / sprocket and the exhaust cam sprocket (or intake cam sprocket) is that the exhaust cam sprocket (or intake cam sprocket) rotates once while the crankshaft / sprocket rotates twice. A plurality of exhaust cams 92 and intake cams 82 are provided on the exhaust camshaft 91 and the intake camshaft 81, respectively, so as to be integrally rotatable. The exhaust cam 92 and the intake cam 82 open and close the exhaust valve 9 and the intake valve 8 based on the pressure.

The VVT mechanism 90 is an electronic control unit (ECU: Electronic Control).
Unit) is hydraulically driven based on a command signal of 20, and has a function of adjusting a relative rotation phase with the exhaust camshaft 91 to a desired state. That is, the intake camshaft 81 rotates in synchronization with the crankshaft 7, whereas the relative rotation phase between the exhaust camshaft 91 and the crankshaft 7 is made variable by the VVT mechanism 90.

  In the internal combustion engine 1, the opening / closing valve operation timing of the exhaust valve 9 (relative operation timing with respect to the crankshaft 7) is appropriately changed through such a function of the VVT mechanism 90.

  The exhaust passage 6 is connected to a muffler (not shown) downstream. An exhaust purification device (exhaust gas) for purifying exhaust components such as nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), and PM contained in the exhaust gas is disposed in the middle of the exhaust passage 6. (Purification means) 11 is provided.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 for controlling the internal combustion engine 1. The ECU 20 includes a logical operation circuit including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a backup RAM, and the like. Based on signals from various sensors, for example, the ECU 20 The operating state is detected, and the various components of the internal combustion engine 1 are comprehensively controlled.

  The ECU 20 is introduced into the cylinder 2 through a crank position sensor 12 attached to the internal combustion engine 1, a water temperature sensor 13 that outputs a signal corresponding to the temperature (cooling water temperature) of the cooling water circulating in the internal combustion engine 1, and the intake passage 5. An air flow meter 14 that outputs a signal corresponding to the flow rate of air (intake air amount), and a cam angle sensor (shown in the figure) that is provided in the vicinity of the exhaust camshaft 91 and outputs a signal every time the exhaust camshaft 91 rotates by a certain angle. Various sensors such as an accelerator position sensor (not shown) that outputs a signal corresponding to the amount of depression of an accelerator pedal (not shown) by the driver are connected via electrical wiring, and the output signals of the various sensors described above are It is input to the ECU 20.

  Further, the ECU 20 executes input of output signals of various sensors, calculation of engine speed, calculation of torque, calculation of fuel injection amount, calculation of fuel injection timing, and the like in a basic routine to be executed at regular intervals. Various signals input by the ECU 20 and various control values obtained by the ECU 20 in the basic routine are temporarily stored in the RAM of the ECU 20.

  Further, the ECU 20 reads various control values from the RAM in interrupt processing triggered by input of signals from various sensors and switches, elapse of a predetermined time, or input of a pulse signal from the crank position sensor 12, and the like. The fuel injection valve 10 and the like are controlled according to the control value, and the drive control (hereinafter referred to as valve timing control) of the VVT mechanism 90 as described below is periodically executed. Here, the ECU 20 constitutes a control means and a cold start detection means.

  Next, the valve timing control of the present embodiment will be described.

  The present embodiment is characterized in that valve timing control for retarding the opening timing of the exhaust valve 9 is performed when the internal combustion engine 1 is cold started.

  By delaying the opening timing of the exhaust valve 9 by the valve timing control of the present embodiment, it is possible to lengthen the time from when the fuel starts to burn in the cylinder 2 until the exhaust valve 9 is opened. It is possible to secure a high temperature field and oxygen, and to allow time for HC to react in the cylinder 2, thereby making it possible to promote the combustion of HC and to reduce the discharged HC. It becomes possible.

  FIG. 2 is a flowchart showing a valve timing control routine executed every predetermined time through the ECU 20.

  When the process shifts to this routine, the ECU 20 first determines in step S101 whether the internal combustion engine 1 has been started. Whether or not the internal combustion engine 1 has started may be determined, for example, based on whether or not the internal combustion engine 1 has rotated more than a predetermined set rotational speed. If the determination is affirmative, the process proceeds to step S102. If the determination is negative, the routine is temporarily exited.

  In step S102, it is determined whether or not the internal combustion engine 1 is cold. Whether or not the internal combustion engine 1 is cold is determined by, for example, calculating the temperature of the cooling water circulating in the internal combustion engine 1 based on the output signal of the water temperature sensor 13, and the calculated temperature is higher than a predetermined temperature. It is good to judge whether it is low. When the determination is affirmative, the process proceeds to step S103, and when the determination is negative, the routine is temporarily exited.

  In step S103, the valve opening timing of the exhaust valve 9 is retarded by controlling the VVT mechanism 90.

  By delaying the valve opening timing of the exhaust valve 9 and controlling the combustion gas in the cylinder 2 to be long in the cylinder, the fuel gas is started to burn until the combustion gas is discharged in the cylinder. Since the time can be lengthened, it becomes possible to promote the combustion of HC and to reduce the discharged HC.

  In a succeeding step S104, it is determined whether or not a predetermined period has elapsed after the internal combustion engine 1 is started. Thereby, it is determined whether the combustion state of the internal combustion engine 1 is stable.

  Here, the predetermined period may be, for example, time or may represent a condition that the cylinder 2 is warm. As a representative example of the condition that the cylinder 2 is warmed, an integrated value of the intake air amount detected by an air flow meter may be used, or an integrated value of the injected fuel injection amount may be used. Or the number of explosions. Further, it may be a period until the temperature of the exhaust purification device 11 reaches the activation temperature, and the temperature of the exhaust port 6A is the temperature at which HC in the exhaust discharged from the cylinder 2 can be combusted in the exhaust port 6A. It may be a period until.

  If the determination in step S104 is affirmative, the process proceeds to step S105. If the determination is negative, the routine is temporarily exited.

  In step S105, the VVT mechanism 90 is controlled to change the valve opening timing of the exhaust valve 9 to the advance side.

  After a predetermined period after the cold start of the internal combustion engine 1, the combustion state of the internal combustion engine 1 is stable and the HC emission is suppressed, so the opening timing of the exhaust valve 9 is changed to the advance side. By doing so, the temperature of the exhaust gas discharged from the cylinder 2 is raised, the exhaust gas purification device 11 is warmed up, and the exhaust gas purification device 11 is activated early. If the exhaust port 6A reaches a temperature at which HC can be combusted after the predetermined period, even if HC is discharged from the cylinder 2, the HC can be combusted in the exhaust port 6A. The opening timing of the exhaust valve 9 can be further advanced.

  As described above, according to the present embodiment, when the internal combustion engine 1 is cold-started, the valve timing control for retarding the valve opening timing of the exhaust valve 9 is performed, so that the fuel starts to burn in the cylinder 2. Since the time until the exhaust valve 9 is opened can be lengthened, the combustion of HC can be promoted, and the HC discharged from the cylinder 2 can be reduced. Therefore, it becomes possible to prevent the exhaust emission from deteriorating.

  In this embodiment, the VVT mechanism 90 has been described as a mechanism for variably controlling the opening / closing operation timing of the exhaust valve 9. However, the present invention is not limited to this, and an electromagnetic force generated when an excitation current is applied is used. Thus, an electromagnetic drive mechanism that drives the exhaust valve back and forth may be applied.

  In the present embodiment, the VVT mechanism 90 that varies the opening / closing timing of the exhaust valve 9 is provided and the VVT mechanism 90 is controlled to retard the opening timing of the exhaust valve. For example, a variable valve mechanism that makes the lift amount of the exhaust valve 9 of the internal combustion engine 1 variable is provided, and the variable valve mechanism is controlled so as to suppress the lift amount at the opening timing of the exhaust valve 9. It may be controlled so that the combustion gas is long in the cylinder. Moreover, a VVT mechanism and a variable valve mechanism may be provided.

FIG. 3 is a flowchart showing a valve timing control routine executed every predetermined time through the ECU 20 in the second embodiment of the present invention.

  In the present embodiment, the VVT mechanism 90 provided in the exhaust valve 9 described in the first embodiment is also provided in the intake valve 8. Further, when the opening timing of the exhaust valve is retarded at the time of cold start of the internal combustion engine, valve timing control is performed to retard the opening timing of the intake valve. In addition, the same code | symbol is attached | subjected about the component similar to Example 1, and the description is abbreviate | omitted. Also, steps S101, 102, and 104 shown in FIG. 3 are the same as steps S101, 102, and 104 in the flowchart described with reference to FIG.

  In step S201 following step S102, the opening timing of the exhaust valve 9 is retarded by controlling the VVT mechanism, and further, the opening timing of the intake valve 8 is retarded.

  By controlling in this way, in addition to the effects described in the first embodiment, it is possible to suppress the valve overlap period from becoming longer by retarding the valve opening timing of the exhaust valve 9, so that It is possible to suppress the deterioration of the combustion state of the internal combustion engine 1 due to the longer valve overlap period. Further, by delaying the valve opening timing of the intake valve 8, a negative pressure can be generated when the intake valve 8 is opened. This can promote fuel atomization and stabilize the combustion of the internal combustion engine 1. It is possible to improve the performance.

  Although the timing for opening the intake valve 8 by retarding is not particularly limited, it is substantially the same as the opening timing of the exhaust valve 9 so that the valve overlap period is always a desired period. Preferably there is.

  In step S202 following step S104, the valve opening timing of the exhaust valve 9 is changed to the advance side by controlling the VVT mechanism, and the valve opening timing of the intake valve 8 is also changed to the advance side.

  As described above, the valve opening timing of the exhaust valve 9 is changed to the advance side after a predetermined period after the cold start of the internal combustion engine 1. However, even in this case, the valve overlap period is always constant. The combustion stability of the internal combustion engine 1 can be improved by changing the valve opening timing of the intake valve 8 to the advance side so that the desired period is reached.

  As described above, according to this embodiment, the valve timing control for retarding the valve opening timing of the exhaust valve 9 and retarding the valve opening timing of the intake valve 8 during the cold start of the internal combustion engine 1 is performed. By doing so, it is possible to reduce the HC discharged from the cylinder 2 and improve the combustion stability of the internal combustion engine 1. Therefore, it becomes possible to prevent the exhaust emission from deteriorating.

1 is a schematic view showing an internal combustion engine according to an embodiment of the present invention. The flowchart figure which shows the valve timing control routine of the internal combustion engine which concerns on Example 1 of this invention. The flowchart figure which shows the valve timing control routine of the internal combustion engine which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Piston 4 Connecting rod 5 Intake passage 5A Intake port 6 Exhaust passage 6A Exhaust port 7 Crankshaft 8 Intake valve 81 Intake camshaft 82 Intake cam 9 Exhaust valve 90 Valve timing variable mechanism (VVT mechanism)
91 Exhaust cam shaft 92 Exhaust cam 10 Fuel injection valve 11 Exhaust purification device 12 Crank position sensor 13 Water temperature sensor 14 Air flow meter 15 Spark plug 20 ECU

Claims (2)

Cold start detection means for detecting a cold start of the internal combustion engine;
When the internal combustion engine is detected as being cold started by the cold start detection means, the operation at the opening timing of the exhaust valve of the internal combustion engine is longer in the cylinder than in the normal operation. Control means for controlling to exist,
With
The control means controls a valve timing variable mechanism that varies the opening / closing timing of the intake valve and the exhaust valve of the internal combustion engine when the cold start detection means detects that the internal combustion engine is cold start time. control device for the internal combustion engine you characterized by retarding the opening timing of the opening timing and the intake valve of the exhaust valve Te.   The control means changes the opening timing of the exhaust valve that is retarded to an advance side after a predetermined period of time has elapsed since the start of the internal combustion engine was detected by the cold start detection means. Item 2. A control device for an internal combustion engine according to Item 1.

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