JP5590467B2 - Variable valve timing control device - Google Patents

Description

  The present invention relates to a technical field of a variable valve timing control device that variably controls the opening and closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage.

  With the recent increase in environmental awareness, reduction of harmful components such as HC, CO, and NOx contained in exhaust gas discharged from an internal combustion engine of a vehicle has become a problem. As one of countermeasures for this, there is a technique in which an exhaust gas purifying catalyst is arranged in an exhaust passage of an internal combustion engine to purify these harmful components. Such a purification effect of the catalyst cannot be sufficiently obtained when the catalyst temperature is low as in the cold start, and therefore a technique for quickly and efficiently raising the catalyst temperature is desired. Yes.

  As an example of such a catalyst temperature raising technique, there is Patent Document 1, for example. In Patent Document 1, by adjusting the opening and closing timing of the intake and exhaust valves of the internal combustion engine, the valve overlap amount during the valve opening period is increased from that during normal operation, and the ignition timing for the air-fuel mixture in the combustion chamber is set to normal operation. Retarded from the time. Such control is referred to as so-called compression-slight lean control (hereinafter referred to as “compression S / L control” as appropriate), and can promote the temperature rise of the exhaust gas and improve the purification function.

JP 2002-235647 A

  In compression S / L control, the amount of valve overlap during the valve opening period is increased compared to during normal operation, so that the exhaust gas flows into the combustion chamber from the exhaust passage to make the air-fuel ratio lean, and the ignition timing is normal operation. Since retarding is sometimes performed, the combustion state in the combustion chamber becomes unstable and an abnormality such as misfire tends to occur. From the viewpoint of raising the temperature of the catalyst more quickly, it is preferable to raise the exhaust gas temperature by setting a large valve overlap amount and ignition timing retard amount. There is a dilemma that will become more prominent. Therefore, in order to prevent the occurrence of misfire in the internal combustion engine, the valve overlap amount and the ignition timing retard amount must be set conservatively compared to the target values, and the catalyst temperature rise is still insufficient. I can not say.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a variable valve timing control apparatus and method capable of efficiently raising the temperature of an exhaust gas purifying catalyst installed in an exhaust passage.

In order to solve the above problems, a variable valve timing control apparatus according to the present invention variably controls opening / closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purifying catalyst is disposed in an exhaust passage. In the apparatus, fuel injection means for directly injecting fuel into the combustion chamber, ignition means for igniting the air-fuel mixture in the combustion chamber, and the fuel injection means so that the air-fuel ratio becomes lean when the internal combustion engine is cold started The fuel is injected in the compression process, the ignition timing of the ignition means is retarded from that during normal operation, the overlap amount of the exhaust valve and the intake valve is set to the initial value, and the overlap amount the overlap amount but after being set to an initial value after a predetermined period of time to increase from the initial value, the exhaust valve and the intake Bal Characterized in that a control means for controlling.

  According to the present invention, it may be a predetermined period after the overlap amount is set to the initial value during the compression S / L control (a period until a predetermined time elapses as will be described later). (It may be a period until a predetermined judgment value is reached.) After that, the overlap amount is increased. Thereby, although it is in a cold state and the amount of overlap is suppressed at an initial stage where misfire is more likely to occur, the temperature rise effect of the catalyst is small, but the occurrence of misfire can be reliably prevented. On the other hand, after the initial stage when the warm-up progresses a little and the risk of misfire decreases, the amount of overlap is increased to actively increase the temperature of the catalyst, and rapid catalyst activation provides an excellent purification effect. can get.

Preferably, the apparatus includes temperature detection means for detecting the temperature of the catalyst, and the control means has a temperature equal to or lower than a predetermined value when a predetermined time has elapsed since the overlap amount was set to an initial value. When the predetermined period is reached, the overlap amount may be increased. According to this, activation of the catalyst is promoted by increasing the overlap amount when the catalyst temperature after a predetermined period of time is below a predetermined value (that is, when it is determined that the catalyst is not active). In addition, the exhaust purification action can be improved.

  Further preferably, the control means retards the closing timing of the exhaust valve and advances the opening timing of the intake valve to increase the overlap amount. The phase amount of the angle may be set larger than the phase amount of the advance angle of the intake valve. According to this, the amount of exhaust gas flowing into the exhaust passage where the catalyst is arranged can be increased by setting the phase amount of the retard angle of the exhaust valve to be larger than the phase amount of the advance angle of the intake valve. It is possible to further increase the temperature of the catalyst.

  In addition, a temperature detection unit that detects the temperature of the catalyst may be provided, and the control unit may increase the overlap amount when the temperature of the catalyst becomes a determination value lower than the activation temperature of the catalyst. . According to this, by starting to increase the overlap amount based on whether or not the catalyst temperature has reached the determination value, it is possible to promote the temperature rise of the catalyst and improve the exhaust gas purification action. As described above, in the present invention, the increase in the overlap amount may be started only by determining whether or not the catalyst temperature is equal to or higher than the determination value regardless of whether or not the predetermined time has elapsed.

In addition, when provided with a water temperature detecting means for detecting the water temperature of the internal combustion engine, and the water temperature is equal to or lower than a predetermined threshold, the control means sets the opening degree of the throttle valve provided in the intake passage larger than that during normal operation. Good. This predetermined threshold value is a threshold value for determining whether or not the engine is in a cold state. In the compressed S / L mode, as described above, misfire is more likely to occur than during normal operation. Therefore, in this aspect, by setting the throttle valve opening large, the amount of air sucked into the combustion chamber can be increased and combustion can be promoted to suppress the occurrence of misfire.
A variable valve timing control device according to the present invention is a variable valve timing control device that variably controls the opening and closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage. Fuel injection means for directly injecting fuel, ignition means for igniting the air-fuel mixture in the combustion chamber, water temperature detection means for detecting the water temperature of the internal combustion engine, temperature detection means for detecting the temperature of the catalyst, When the water temperature detected by the water temperature detecting means at the start of the internal combustion engine is equal to or lower than a predetermined threshold, fuel is injected from the fuel injection means in a compression stroke so that the air-fuel ratio becomes lean, and the ignition timing of the ignition means is normally set. Compressed light lean control that retards from the start of operation is started, and the overlap amount of the exhaust valve and intake valve opening period is set to the initial value. Control means for increasing the overlap amount from the initial value when a predetermined time has elapsed since the start of the compression light lean control and the temperature of the catalyst detected by the temperature detection means is not more than a predetermined value And.

  According to the present invention, it may be a predetermined period after the overlap amount is set to the initial value during the compression S / L control (a period until a predetermined time elapses as will be described later). (It may be a period until a predetermined judgment value is reached.) After that, the overlap amount is increased. Thereby, although it is in a cold state and the amount of overlap is suppressed at an initial stage where misfire is more likely to occur, the temperature rise effect of the catalyst is small, but the occurrence of misfire can be reliably prevented. On the other hand, after the initial stage when the warm-up progresses a little and the risk of misfire decreases, the amount of overlap is increased to actively increase the temperature of the catalyst, and rapid catalyst activation provides an excellent purification effect. can get.

1 is a schematic diagram showing a schematic configuration of a vehicle equipped with a variable valve timing control device according to the present invention. (A) NOx content in exhaust gas, (b) THC content in exhaust gas, (c) Intake pressure in intake passage 2 with respect to ignition timing of spark plug in compression S / L mode, (d It is a graph which shows the relationship of a fuel consumption rate. It is a graph which shows the relationship between valve overlap amount, exhaust gas temperature, and HC content contained in exhaust gas. It is a flowchart figure which shows operation | movement of the variable valve timing control apparatus which concerns on 1st Embodiment for every step. It is a graph which shows a time-dependent transition of the various parameters relevant to an engine. It is a flowchart figure which shows operation | movement of the valve timing control apparatus which concerns on 2nd Embodiment for every step.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle equipped with a valve timing control device according to the present invention. An intake passage 2 and an exhaust passage 3 are connected to the cylinder head of the engine 1 so as to communicate with the combustion chamber 4. The communication state can be controlled by providing an intake valve 5 between the intake passage 2 and the combustion chamber 4, and an exhaust valve 6 is provided between the exhaust passage 3 and the combustion chamber 4. The communication state can be controlled by. The intake valve 5 and the exhaust valve 6 are each provided with a variable valve timing adjusting device 7 (hereinafter referred to as “intake variable valve 7a” and “exhaust variable valve 7b”, respectively), and the opening / closing timing is adjusted. It is configured to be possible. Since the detailed structure of the valve timing adjusting device 7 is known, detailed description thereof will be omitted.

  The cylinder head is provided with an in-cylinder injector 8 which is a fuel injection means disposed with the opening directed toward the combustion chamber in order to inject fuel directly into the combustion chamber 4. Further, the downstream side of the intake passage 4 shown in FIG. 1 is a manifold portion connected to the combustion chamber 4 for each cylinder, and an MPI injector 9 is provided for each cylinder. In-cylinder injector 8 and MPI injector 9 are supplied with fuel pressurized by a low-pressure fuel pump and a high-pressure fuel pump (not shown), and fuel is injected into combustion chamber 4 and intake passage 2. As a result, an intake air and an air-fuel mixture are formed. A spark plug 10 for igniting the air-fuel mixture is provided near the top of the cylinder head of each cylinder.

  The combustion chamber 4 includes a cylinder head (not shown), a piston 11 and a cylinder 12. The vertical movement of the piston 11 is transmitted to a crankshaft (not shown) via a connecting rod.

  The intake passage 2 is provided with an electronic throttle valve 13 (hereinafter referred to as “throttle 13” as appropriate) for adjusting the amount of air flowing into the combustion chamber 4. The opening of the throttle 13 is configured to be electronically controllable based on a control signal from the ECU 15 described later.

  The exhaust passage 3 exhausts exhaust gas downstream from the combustion chamber 4 of each cylinder, and a catalyst for purifying harmful components (for example, HC (unburned), CO, NOx, etc.) in the exhaust gas downstream. 14 is provided. Particularly in the present embodiment, the catalyst 14 is a three-way catalyst, and is provided in two stages at the front stage and the rear stage.

  The ECU 15 is an electronic control unit for controlling the engine 1. The ECU 15 includes an input device that receives detection information from various sensors, an output device that outputs control signals to various parts of the vehicle, a CPU that performs various arithmetic processes, and a ROM that stores various data processed by the CPU. And a storage device such as a RAM. Since the specific configuration of the ECU 15 is known, a detailed description thereof will be omitted in this specification. Here, the sensors that can input the detection information to the input device include a throttle position sensor 16 for detecting the opening degree of the throttle 13 and an upstream side of the catalyst for detecting the temperature of the exhaust gas flowing into the catalyst 14. A catalyst temperature sensor 17 installed, a water temperature sensor 18 for detecting the coolant temperature of the engine 1, and a crank angle sensor 19 for detecting the rotation angle of the crankshaft by outputting a signal in synchronization with the rotation of the crankshaft. An accelerator opening sensor 20 for detecting the degree of depression of the accelerator pedal is provided.

  Further, an ignition plug 10, an in-cylinder injector 8, an MPI injector 9, an intake variable valve 7a, an exhaust variable valve 7b, and the like are connected to the output side of the ECU 15. Thereby, the ignition timing of the spark plug 10, the fuel injection timing and fuel injection amount of the in-cylinder injector 8 and the MPI injector 9, the opening / closing timing of the intake valve 5 and the exhaust valve 6 by the intake variable valve 7a and the exhaust variable valve 7b. (Including an overlap described later) is controlled based on a control signal output from the ECU 15.

  Here, with reference to FIG. 2 and FIG. 3, the exhaust gas purification action in the compressed S / L mode will be specifically described. 2 shows (a) the content of NOx in the exhaust gas, (b) the content of THC in the exhaust gas, and (c) the intake passage 2 with respect to the ignition timing of the spark plug 10 in the compression S / L mode. It is a graph which shows the relationship between intake pressure and (d) fuel consumption rate. In FIG. 2, the delay amount of the fuel injection timing from the in-cylinder injector 8 is indicated by symbols “Δ”, “□”, and “◯” for the cases of 5 ° A, 10 ° A, and 20 ° A, respectively. is there.

  In the compression S / L mode, the valve overlap amount is set large, and the fuel injection timing from the in-cylinder injector 8 is retarded (retarded) from the intake process to the compression process. When this retard amount is increased (that is, when the advance amount is decreased), NOx and HC contained in the exhaust gas decrease as shown in FIGS. 2 (a) and 2 (b). This is because by increasing the retard amount of the fuel injection timing, the temperature rise of the exhaust gas becomes rapid and the catalyst 14 is easily activated. Such a tendency becomes more prominent as the retard amount of the injection timing of the in-cylinder injector 8 increases, as can be seen by comparing the symbols in the figure.

  Next, FIG. 3 is a graph showing the relationship between the valve overlap amount, the exhaust gas temperature, and the HC content contained in the exhaust gas. In FIG. 3, the horizontal axis indicates the closing timing of the exhaust valve 6, and the vertical axis indicates the opening timing of the intake valve 5. Then, the valve overlap amount is small on the region side indicated by [1] in FIG. 3, and the valve overlap amount increases toward the region side indicated by [2]. In FIG. 3, the region indicated by [1] indicates the valve overlap amount in the normal operation mode, and the region indicated by [2] indicates the valve overlap amount in the compression S / L mode.

  In FIG. 3, the solid line indicates a contour line in which the amount of HC contained in the exhaust gas is equal, and the HC indicates that the closing timing of the exhaust valve 6 is retarded and the ordinate indicates that the opening timing of the intake valve 5 is advanced. It has been shown that the content of is reduced. On the other hand, the alternate long and short dash line indicates the temperature of the exhaust gas. The closing timing of the exhaust valve 6 is retarded, and the vertical axis indicates that it rises as the opening timing of the intake valve 5 advances. . That is, in the compression S / L mode, as the valve overlap amount increases, the temperature rise of the exhaust gas is promoted and the activation of the catalyst 14 is promoted.

  However, if the overlap amount is excessive, as in the region a indicated by hatching in FIG. 3, the combustion in the combustion chamber 4 is deteriorated, and conversely, HC increases and there is a risk of misfire. Therefore, in the compressed S / L mode, it is preferable to set the overlap amount so large that such a problem does not occur.

(First embodiment)
Subsequently, the first embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing the operation of the valve timing control apparatus according to the first embodiment for each stage, and FIG. 5 is a graph showing the change over time of various parameters related to the engine 1. In the following, the control contents will be described in order according to the flowchart shown in FIG. 4, and the change in the parameters associated therewith will be described with reference to FIG. 5 as appropriate.

  First, in the initial state (time t0 to t1), the vehicle is set in the normal operation mode, and as shown in FIG. 5 (a), HC contained in the exhaust gas starts to increase as the engine starts. At this time, as shown in FIG. 5 (b), the temperature of the catalyst 14 is low and is not yet in a state where a sufficient purification action can be exhibited. At the time of starting, the throttle opening, intake / exhaust variable valve, injection timing, ignition timing, and engine speed are controlled according to a target map prepared in advance.

  First, the ECU 15 determines whether or not the vehicle is in a stopped state by acquiring a detection value such as a vehicle speed sensor (not shown) (step S101). If the vehicle is in a stopped state (step S101: YES), the ECU 15 further acquires the output value of the accelerator opening sensor 20 to determine whether or not the vehicle driver is willing to start. (Step S102). In this embodiment, the presence or absence of the vehicle driver's intention to start is determined based on the detected value of the accelerator opening sensor 20, but the present invention is not limited to this. For example, the vehicle is in an idling state. You may perform by determining ON / OFF of the idling switch shown.

  When it is determined in step S102 that the driver does not intend to start (step S102: YES), the ECU 15 further determines whether or not the detected value T of the water temperature sensor 18 is lower than the first threshold T1. It is determined whether the engine 1 is in a cold state (step S103). The first threshold value T1 is stored in advance in the storage device of the ECU 15 by a theoretical method or an experimental method, based on how much the detected value T of the water temperature sensor 18 is lower than what degree C, the engine 1 is considered to be in a cold state. Use what you remember.

When the engine 1 is in a cold state (step S103: YES), the ECU 15 checks the detection values of various sensors installed in each part of the vehicle to determine whether or not the vehicle is normal, and then the vehicle The operation mode is switched from the “normal operation mode” to the “compression S / L mode”. In the example of FIG. 5, switching from the “normal operation mode” to the “compression S / L mode” is performed at time t1 . Following this, as will be described below for the variable valve 7, the ECU 15 variably controls the valve overlap amount according to the conditions, thereby making it more effective than the conventional simple compression S / L mode. The catalyst can be activated efficiently by raising the temperature of the exhaust gas discharged from the exhaust passage of the engine 1 efficiently.

  Note that while the operation mode is set to the compression S / L mode, the compression S / L mode flag is set to ON in the ECU 15, and the detection values of the various sensors performed in step S104 are checked every predetermined period. By executing this, when an abnormality is detected, this flag may be turned OFF to return from the compression S / L mode to the normal operation mode. In the compressed S / L mode, the engine 1 is more likely to misfire (that is, a load is imposed on the engine 1) than in the normal operation mode. Thus, in the abnormal state (for example, fuel is supplied to each injector). When the fuel pressure cannot be sufficiently obtained due to an abnormality in the pump, etc., it is preferable to return to the normal operation mode with less burden to prevent the vehicle from falling into a serious failure state. In the present embodiment, in step S104, it is confirmed whether the compression S / L mode flag is ON.

  As described above, various conditions for executing the compression S / L mode are determined in steps S101 to S103. However, if any of the conditions is not satisfied, the operation mode is changed to the compression S / L mode. The normal operation mode is continued without switching (step S101: NO, step S102: NO, step S103: NO).

  When the compression S / L mode is executed, as shown after time t1 in FIG. 5 (f), the ignition timing of the spark plug 10 is retarded (retarded) from that during normal operation, and the overlap amount is variably controlled. By doing so, the fuel is injected from the injector in the compression process so that the air-fuel ratio becomes lean. As described above, in the compressed S / L mode, the air-fuel ratio is lean and the ignition timing is also shifted, so that the combustion of the air-fuel mixture in the combustion chamber 4 becomes unstable and may easily misfire. This is because the exhaust gas enters the combustion chamber 4 from the exhaust valve 6 due to the internal EGR, and the CO 2 gas tends to remain in the combustion chamber 4, and the engine 1 is in a cold state. This is thought to be due to the slow combustion and the tendency to misfire. As described with reference to FIGS. 2 and 3, in order to quickly raise the temperature of the catalyst 14, by setting such a large amount of overlap and retard, high temperature gas to the exhaust passage 3 can be set. It is preferable to increase the flow rate. However, if the overlap amount is set abruptly immediately after the execution of the compressed S / L mode, the risk of misfire will increase. Therefore, in the prior art, in order to prevent the misfire of the engine 1 in practice, the overlap and the retard amount must be set conservatively, and it is difficult to sufficiently improve the heating rate of the catalyst 14. There is a problem that.

  The overlap amount is adjusted by retarding the closing timing of the exhaust valve or advancing the opening timing of the intake valve according to a command from the ECU 15. Particularly in this embodiment, the overlap amount is adjusted by retarding the closing timing of the exhaust valve and advancing the opening timing of the intake valve.

  Such a problem is solved by the control described below. First, the ECU 15 sets the overlap amount to an initial value by setting the phase angles of the intake variable valve 7a and the exhaust variable valve 7b to initial phase angles θin_initial and θout_initial, respectively (step S105). The initial value of the overlap amount set in this way is set so small that a situation in which misfire occurs due to a sudden increase in the overlap amount immediately after execution of the compression S / L mode is not caused.

  At this time, the ECU 15 changes the opening degree of the throttle valve 13 provided in the intake passage so as to be larger than that during normal operation, as shown in FIG. In the compressed S / L mode, as described above, misfire is more likely to occur than during normal operation. Therefore, by setting the opening degree of the throttle valve 13 large, the amount of air sucked into the combustion chamber 4 is increased and the combustion is promoted to suppress the occurrence of misfire.

  Further, in the compression S / L mode, as shown in FIG. 5E, the ECU 15 controls the fuel injection timing of the in-cylinder injector 8 so that it is during the compression process of the engine 1. As a result, in the compression S / L mode, the combustion speed of the air-fuel mixture can be increased compared to the case of the normal operation mode in which the direct injection timing is the intake process, so that the ignition timing of the spark plug 10 can be retarded as will be described later. The width can be increased. Note that the injection timing of the MPI injector 9 may be reduced during the compression process as necessary, similarly to the in-cylinder injector 8, to reduce HC.

  Subsequently, after a predetermined time has elapsed since the overlap amount is set to the initial value (step S106: YES), the ECU 15 acquires the detection value T of the catalyst temperature sensor 17 and determines whether or not it is lower than the determination value T2. Determination is made (step S107). Here, the determination value T2 is the activation temperature of the catalyst 14. Since the warm-up proceeds as the operation period becomes longer after the engine 1 is started, the combustion in the combustion chamber 4 is gradually stabilized and becomes difficult to misfire. Therefore, in step S107, the temperature of the catalyst 14 is sensed, and when it is determined that the catalyst 14 is not activated because the temperature of the catalyst 14 is still lower than the determination value T2 (step S107: YES), an increase in overlap is started. (Step S108). Note that while the predetermined period has not elapsed in step S106, the ECU 15 returns the process to step 105 and waits.

  As described above, in this embodiment, the overlap amount is first set to an initial value, and after a predetermined time has elapsed, an increase in the overlap amount is started in consideration of the progress of warm-up, while preventing the occurrence of misfire. The catalyst temperature can be increased efficiently.

The temperature detection of the catalyst 14 in step S 107, when it is difficult to detect the catalyst temperature directly, may be estimated from the elapsed time from the cooling water temperature and time of starting the engine, the step S103 The cold state determination of the engine 1 may be used as it is.

  The increase in overlap in step S108 is preferably increased at a predetermined speed as time passes, as shown at times t2 to t3 in FIG. Alternatively, an overlap value at which the combustion of the engine 1 does not become unstable at each catalyst temperature may be defined in advance, and may be increased to an appropriate overlap value according to the detection result of the catalyst temperature.

  Particularly in the present embodiment, when adjusting the overlap amount, the ECU 15 sets the retardation amount of the exhaust valve 6 to be larger than the advance amount of the intake valve 5. According to this, since the amount of exhaust gas flowing into the exhaust passage in which the catalyst 14 is disposed can be increased, the temperature rise of the catalyst 14 can be further accelerated.

  Then, the ECU 15 determines whether or not the overlap value has reached the clip value (step S109), and changes the overlap value until it becomes sufficiently large. When the clip value is reached as shown at times t3 to t4 in FIG. 5D (step S109: YES), the compression S / L mode is terminated (step S110), and the operation mode is shifted to the normal operation mode (step S111). ). The end timing of the compressed S / L mode may be set based on the elapsed time after the overlap value reaches the clip value, for example.

  In the normal operation mode in step S111, the ignition timing is set based on the target map value, the air-fuel ratio is set to the target map value, and then feedback control is performed as appropriate. The idle speed of the engine 1 is appropriately feedback controlled. Since these controls are publicly known, detailed description will be omitted here. Such a series of controls may be programmed in advance so as to be automatically executed when the vehicle is started.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing the operation of the valve timing control device according to the second embodiment for each stage. Note that changes over time of various parameters related to the engine 1 are the same as those in FIG. 5 shown in the first embodiment. Hereinafter, the control contents will be described in order according to the flowchart shown in FIG. However, step S201 to step S206 are the same as step S101 to step S106 of the first embodiment, and thus description thereof is omitted.

  The ECU 15 acquires the detection value T of the catalyst temperature sensor 17 after a predetermined time has elapsed since the overlap amount is set to the initial value in step S206, and determines whether or not it is higher than the determination value T3 (step S107). ). Here, the determination value T3 is defined as a temperature value lower than the activation temperature of the catalyst 14 (corresponding to T2 in the first embodiment). Since the warm-up proceeds as the operation period becomes longer after the engine 1 is started, the combustion in the combustion chamber 4 is gradually stabilized and becomes difficult to misfire. Therefore, in step S207, the temperature of the catalyst 14 is sensed, and when it is determined that the warm-up has progressed to some extent because the detected value becomes higher than the determination value T3 (step S207: YES), an increase in overlap is started. (Step S208). Note that while the predetermined period has not elapsed in step S206, the ECU 15 returns the process to step 205 and waits. The increase in overlap in step S208 may be increased at a predetermined speed as time passes, as shown at times t2 to t3 in FIG. Alternatively, an overlap value at which the combustion of the engine 1 does not become unstable at each catalyst temperature may be defined in advance, and may be increased to an appropriate overlap value according to the detection result of the catalyst temperature.

  Then, the ECU 15 determines whether or not the overlap value has reached the clip value (step S209), and changes the overlap value until it becomes sufficiently large. When the clip value is reached as shown at times t3 to t4 in FIG. 5D (step S209: YES), the compression S / L mode is terminated (step S210), and the normal operation mode is entered (step S211). ). The end timing of the compressed S / L mode may be set based on the elapsed time after the overlap value reaches the clip value, for example.

  In the normal operation mode in step S211, the ignition timing is set based on the target map value, the air-fuel ratio is set to the target map value, and then feedback control is performed as appropriate, and the idle speed of the engine 1 is appropriately feedback controlled.

  As described above, in this embodiment, the overlap amount is first set to an initial value, and after a predetermined time has elapsed, an increase in the overlap amount is started in consideration of the progress of warm-up, while preventing the occurrence of misfire. The catalyst temperature can be increased efficiently.

  In the present embodiment, the increase of the overlap amount is started after the elapse of a predetermined time and when the catalyst temperature is higher than the determination value T3. On the other hand, the condition for starting the increase in the overlap amount may be only whether the catalyst temperature is higher than the determination value T3.

  As described above, according to the present invention, a predetermined period (a period until a predetermined time elapses after the overlap amount is set to the initial value at the time of compression S / L control or a specific parameter such as a catalyst temperature may be used. (It may be a period until the predetermined determination value is reached.) After that, the overlap amount is increased. Thereby, although it is in a cold state and misfire is more likely to occur, by suppressing the amount of overlap, the temperature rise effect of the catalyst 14 is small, but the occurrence of misfire can be reliably prevented. On the other hand, after the initial stage when the warm-up progresses a little and the risk of misfire decreases, the amount of overlap is increased to actively increase the temperature of the catalyst, and rapid catalyst activation provides an excellent purification effect. can get.

  The present invention is applicable to a variable valve timing control device that variably controls the opening and closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage.

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Exhaust passage 4 Combustion chamber 5 Intake valve 6 Exhaust valve 7 Variable valve 7a Intake variable valve 7b Exhaust variable valve 8 In-cylinder injector 9 MPI injector 10 Spark plug 11 Piston 12 Cylinder 13 Electronic throttle Valve (throttle)
14 Catalyst 15 ECU
16 Throttle position sensor 17 Catalyst temperature sensor 18 Water temperature sensor 19 Crank angle sensor 20 Accelerator opening sensor

Claims (6)

In a variable valve timing control device that variably controls the opening and closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage,
Fuel injection means for directly injecting fuel into the combustion chamber;
Ignition means for igniting the air-fuel mixture in the combustion chamber;
At the time of cold start of the internal combustion engine, fuel is injected from the fuel injection means in a compression stroke so that the air-fuel ratio becomes lean, the ignition timing of the ignition means is retarded from that during normal operation, and the exhaust valve and The exhaust valve and the exhaust valve are set so that the overlap amount during the valve opening period of the intake valve is set to an initial value, and the overlap amount is increased from the initial value after a predetermined period after the overlap amount is set to the initial value. And a control means for controlling the intake valve. Comprising temperature detecting means for detecting the temperature of the catalyst;
The control means increases the overlap amount when the predetermined period is reached when the temperature of the catalyst when the predetermined time has elapsed after setting the overlap amount to an initial value is equal to or less than a predetermined value. The variable valve timing control device according to claim 1. The control means retards the valve closing timing of the exhaust valve and advances the valve opening timing of the intake valve to increase the overlap amount,
3. The variable valve timing control device according to claim 1, wherein a phase amount of the retard angle of the exhaust valve is set larger than a phase amount of the advance angle of the intake valve. Comprising temperature detecting means for detecting the temperature of the catalyst;
2. The variable valve timing control device according to claim 1, wherein the control unit increases the overlap amount when the temperature of the catalyst becomes a determination value lower than an activation temperature of the catalyst. 3. Water temperature detection means for detecting the water temperature of the internal combustion engine, and when the water temperature is equal to or lower than a predetermined threshold, the control means sets the opening of the throttle valve provided in the intake passage larger than that during normal operation. The variable valve timing control device according to any one of claims 1 to 4, wherein the variable valve timing control device is characterized in that: In a variable valve timing control device that variably controls the opening and closing timings of an exhaust valve and an intake valve of an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage,
Fuel injection means for directly injecting fuel into the combustion chamber;
Ignition means for igniting the air-fuel mixture in the combustion chamber;
Water temperature detecting means for detecting the water temperature of the internal combustion engine;
Temperature detecting means for detecting the temperature of the catalyst;
When the water temperature detected by the water temperature detecting means at the start of the internal combustion engine is equal to or lower than a predetermined threshold, fuel is injected from the fuel injection means in a compression stroke so that the air-fuel ratio becomes lean, and the ignition timing of the ignition means is set. Compressed light lean control that retards from normal operation is started, the overlap amount of the exhaust valve and intake valve opening period is set to the initial value, and a predetermined time has elapsed after starting the compressed light lean control And a control means for increasing the overlap amount from the initial value when the temperature of the catalyst detected by the temperature detection means is equal to or lower than a predetermined value.

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