JP6770642B2 - Internal combustion engine control method and control device - Google Patents

Description

The present invention relates to a control method and a control device for an internal combustion engine including a fuel injection valve that directly injects fuel into a cylinder and an ignition plug that directly sparks and ignites the fuel injected from the fuel injection valve.

In a so-called in-cylinder direct-injection internal combustion engine that injects fuel directly into the cylinder, the tip of the fuel injection valve is exposed in the combustion chamber and is easily affected by combustion in the cylinder. Deposits are likely to accumulate on the part. Then, if the accumulated deposit blocks a part of the fuel spray path, the actual spray pattern deviates from the design-time pattern (hereinafter, also referred to as a reference pattern).

By the way, fast idle control is known in which a stratified air-fuel mixture is formed around a spark plug after a cold start of an internal combustion engine and the ignition timing is retarded to after the compression top dead center. Conventionally, the wall guide type that reflects fuel spray to the cavity provided in the piston to form a stratified air-fuel mixture around the spark plug has been the mainstream, but in the wall guide type, a part of the collided fuel is the crown surface of the piston. It is easy to remain in the fuel, and the remaining fuel may burn to generate soot. For this reason, in recent years, when the demand for exhaust performance is increasing, a spray guide type that injects fuel toward the spark plug to form a stratified air-fuel mixture has attracted attention.

However, in the wall guide type, even if there is a slight deviation in the spray pattern, if it collides with the cavity, the fuel spray will proceed around the spark plug, whereas in the spray guide type, the spray pattern of the wall guide type will be used. There is no function to correct the deviation. Therefore, in the spray guide type, if the spray pattern deviates from the reference pattern, it becomes difficult to ensure combustion stability.

As a control for solving this problem, the JP 2012-87668 A1 determines that a deposit has adhered to the fuel injection valve when the number of fuel injections exceeds a predetermined value, and executes a control for removing the deposit. What to do is disclosed.

However, it is not possible to accurately determine whether or not a deposit is attached by the determination method using the number of fuel injections as in the above document.

Therefore, an object of the present invention is to provide a control method and a control device capable of accurately determining whether or not a deposit is attached to the tip of a fuel injection valve.

According to an aspect of the present invention, there is provided a control method for an internal combustion engine including a fuel injection valve that directly injects fuel into a cylinder and an ignition plug that directly sparks and ignites the fuel injected from the fuel injection valve. .. In the control method, after the engine is started, stratified combustion is executed in which the air-fuel mixture formed by injecting fuel from the fuel injection valve toward the discharge region of the ignition plug is executed, and during the period in which the stratified combustion is executed, The actual behavior, which is the behavior of the actual change in the engine rotation speed from the start of combustion of the internal combustion engine at the time of starting the engine, is compared with the preset reference behavior of the engine rotation speed from the start of combustion of the internal combustion engine, and the actual behavior is the reference. When the behavior is different, it is determined that the spray pattern has changed due to the presence of deposits at the tip of the fuel injection valve, and the deposit removal control for removing the deposits is executed .

FIG. 1 is an explanatory diagram of an overall configuration of an internal combustion engine system. FIG. 2 is an explanatory diagram of flow addition in the vicinity of the plug. FIG. 3 is a diagram showing an injection form of the fuel injection valve. FIG. 4 is a diagram for explaining a spray beam. FIG. 5 is a diagram showing the arrangement of the spark plug and the fuel injection valve. FIG. 6 is a diagram showing the relationship between the discharge region and the spray beam. FIG. 7 is a diagram for explaining contraction. FIG. 8 is an explanatory diagram of the tumble flow generated in the cylinder. FIG. 9 is an explanatory diagram of the tumble flow during the compression stroke. FIG. 10 is a diagram showing changes in turbulent flow intensity around the spark plug. FIG. 11 is an explanatory diagram of a plug discharge channel in the vicinity of the spark plug. FIG. 12A is a diagram showing the relationship between the fuel injection timing and the ignition timing. FIG. 12B is a diagram showing the relationship between the fuel injection timing and the ignition timing. FIG. 13 is a diagram for explaining the position of the spark plug and the combustion stability. FIG. 14 is a diagram showing the relationship between the position of the spark plug and the combustion stability. FIG. 15 is a flowchart showing a control routine executed by the controller. FIG. 16 is a timing chart when the deposit removal control is not executed. FIG. 17 is a timing chart when the deposit removal control is executed.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram of an overall configuration of an internal combustion engine system. In the internal combustion engine system 1, the internal combustion engine 10 is connected to the intake passage 51. Further, the internal combustion engine 10 is connected to the exhaust passage 52.

A tumble control valve 16 is provided in the intake passage 51. The tumble control valve 16 generates a tumble flow in the cylinder by closing a part of the cross section of the flow path of the intake passage 51.

A collector tank 46 is provided in the intake passage 51. The EGR passage 53b is also connected to the collector tank 46.

An air flow meter 33 is provided in the intake passage 51. The controller 50 connected to the air flow meter 33 acquires the intake amount in the intake passage 51 from the air flow meter 33. Further, an intake air temperature sensor 34 is provided in the intake passage 51. The controller 50 connected to the intake air temperature sensor 34 acquires the temperature of the air passing through the intake passage 51 from the intake air temperature sensor 34.

Further, an electronically controlled throttle 41 is provided in the intake passage 51, and the throttle opening degree is controlled by the controller 50.

Exhaust catalysts 44 and 45 for purifying exhaust gas are provided in the exhaust passage 52. A three-way catalyst or the like is used for the exhaust catalysts 44 and 45. Further, the exhaust passage 52 branches into an EGR passage 53 connected to the collector tank 46 on the way.

An EGR cooler 43 is provided in the EGR passage 53. Further, an EGR valve 42 is provided in the EGR passage 53. The EGR valve 42 is connected to the controller 50. Then, the opening degree of the EGR valve 42 is controlled by the controller 50 according to the operating conditions of the internal combustion engine 10.

The internal combustion engine 10 includes a spark plug 11, a fuel injection valve 12, an intake side variable valve mechanism 13, an exhaust side variable valve mechanism 14, and a fuel injection pump 15. The fuel injection valve 12 is a direct injection valve and is provided in the vicinity of the spark plug 11.

The spark plug 11 ignites sparks in the combustion chamber of the internal combustion engine 10. The spark plug 11 is connected to the controller 50, and the controller 50 as a control unit controls the spark ignition timing. The spark plug 11 also operates as a flow velocity sensor 23 as described later. The method of detecting the flow velocity will be described later.

The fuel injection valve 12 injects fuel directly into the combustion chamber of the internal combustion engine 10. The fuel injection valve 12 is connected to the controller 50, and the controller 50 as a control unit controls the fuel injection timing. In the present embodiment, so-called multi-stage injection, in which fuel injection is performed a plurality of times including an intake stroke, is performed. The fuel injection pump 15 supplies pressurized fuel to the fuel supply pipe connected to the fuel injection valve 12.

The intake side variable valve mechanism 13 changes the opening / closing timing of the intake valve. The exhaust side variable valve mechanism 14 changes the opening / closing timing of the exhaust valve. The intake side variable valve mechanism 13 and the exhaust side variable valve mechanism 14 are connected to the controller 50. Then, the controller 50 controls these opening / closing timings. Although the intake side variable valve mechanism 13 and the exhaust side variable valve mechanism 14 are shown here, one of them may be provided.

The internal combustion engine 10 is provided with a crank angle sensor 27 and an in-cylinder pressure sensor 35. The crank angle sensor 27 detects the crank angle in the internal combustion engine 10. The crank angle sensor 26 is connected to the controller 50 and sends the crank angle of the internal combustion engine 10 to the controller 50.

The in-cylinder pressure sensor 35 detects the pressure in the combustion chamber of the internal combustion engine 10. The in-cylinder pressure sensor 35 is connected to the controller 50. Then, the pressure of the combustion chamber in the internal combustion engine 10 is sent to the controller 50.

Further, the internal combustion engine 10 may include a knock sensor 21 and a fuel pressure sensor 24. The controller 50 reads the outputs from the above-mentioned various sensors and other sensors (not shown), and controls the ignition timing, valve timing, air-fuel ratio, etc. based on these.

FIG. 2 is a diagram for explaining the positional relationship between the spark plug 11 and the fuel injection valve 12. As described above, the fuel injection valve 12 is a direct injection valve and is provided in the vicinity of the spark plug 11. Therefore, a part of the injected fuel passes near the discharge gap, which makes it possible to impart flow to the vicinity of the spark plug. The provision of flow will be described later.

FIG. 3 shows a form of fuel spray injected from the fuel injection valve 12. FIG. 4 is a view of the plane including the circle A in FIG. 3 as viewed from the direction of arrow IV in FIG.

The fuel injection valve 12 of the present embodiment injects fuel from six injection holes. When the fuel sprays (hereinafter, also referred to as spray beams) injected from the six injection holes are B1-B6, each spray beam has a conical shape in which the spray cross section becomes wider as the distance from the injection holes increases. Further, the cross sections of the spray beams B1-B6 cut in a plane including the circle A are arranged in an annular shape at equal intervals as shown in FIG.

FIG. 5 is a diagram showing the positional relationship between the spray beams B1-B6 and the spark plug 11. The fuel injection valve 12 is arranged on the one-point chain line C, which is a bisector of the angle formed by the central axis B2c of the spray beam B2 and the central axis B3c of the spray beam B3.

FIG. 6 is a diagram showing the positional relationship between the spark plug 11 and the spray beam B3 when FIG. 5 is viewed from the direction of the arrow VI. In FIG. 6, the discharge region sandwiched between the center electrode 11a and the outer electrode 11b is arranged within the range sandwiched between the upper outer edge of the spray beam B3 in the figure and the lower outer edge in the figure. Although not shown, when FIG. 5 is viewed from the direction opposite to the arrow VI, the positional relationship between the spark plug 11 and the spray beam B2 is the same as that of FIG. 6, and the discharge region is the upper outer edge and the lower side of the spray beam B2. It is arranged within the range sandwiched by the outer edge on the side. That is, the discharge region is within a range sandwiched between the plane including the upper outer edge of the spray beam B2 and the upper outer edge of the spray beam B3, and the plane including the lower outer edge of the spray beam B2 and the lower outer edge of the spray beam B3. The spark plug 11 is arranged so as to be arranged.

FIG. 7 is a diagram for explaining the effect when the spray beam B1-B6 and the spark plug 11 are in the positional relationship shown in FIGS. 5 and 6.

The fuel injected from the fuel injection valve 12 splits into droplets and becomes a spray, and moves forward while taking in the surrounding air as shown by the thick arrow in the figure. This creates turbulence in the airflow around the spray.

Further, when there is an object (including a fluid) in the surroundings, the fluid is attracted to the object by the so-called Coanda effect and flows along the object. That is, so-called contraction occurs in which the spray beam B2 and the spray beam B3 are attracted to each other as shown by the thin arrow in FIG. As a result, a very strong turbulence is generated between the spray beam B2 and the spray beam B3, so that the turbulence intensity around the spark plug 11 increases.

Here, the change in the strength of the tumble flow will be described.

FIG. 8 is an explanatory diagram of the tumble flow generated in the cylinder. FIG. 9 is an explanatory diagram of the tumble flow collapse. In these figures, an intake passage 51, an exhaust passage 52, a spark plug 11, a fuel injection valve 12, and a tumble control valve 16 are shown. Further, the center electrode 11a and the outer electrode 11b of the spark plug 11 are shown. Further, in FIG. 8, the tumble flow in the cylinder in the suction stroke is indicated by an arrow. In FIG. 9, the tumble flow in the cylinder during the compression stroke is indicated by an arrow.

When the tumble control valve 16 is closed in the suction stroke, the intake air flows unevenly toward the upper side of the intake passage 51 in the figure and flows into the cylinder. As a result, as shown in the figure, a tumble flow that swirls in the vertical direction is formed in the cylinder. After that, the combustion chamber in the cylinder is narrowed as the piston rises in the compression stroke. When the combustion chamber becomes narrower, the tumble flow is crushed, gradually becoming unable to maintain that flow (Fig. 9), and eventually collapsing.

Therefore, when a stratified air-fuel mixture is formed around the spark plug 11 and fast idle control (hereinafter, also referred to as FIR control) for retarding the ignition timing to after the compression top dead center is executed, ignition occurs at the time of spark plug ignition. The flow around the plug 11 is weakening. Therefore, the arc generated between the electrodes 11a and 11b of the spark plug 11 (hereinafter, also referred to as the plug discharge channel CN) is not sufficiently extended, and misfire or partial burn is likely to occur.

Therefore, in the present embodiment, the characteristic that the turbulent flow strength around the spark plug 11 is increased by injecting fuel is utilized to create a situation in which the plug discharge channel CN is extended after the tumble flow collapses.

FIG. 10 is a timing chart showing a change in turbulent flow intensity around the spark plug 11 when fuel injection is performed after the compression top dead center. The horizontal axis of FIG. 10 shows the crank angle, and the vertical axis shows the turbulent flow strength around the spark plug 11. As described above, the strength of the tumble flow gradually decreases, so that the turbulent flow strength around the spark plug 11 also decreases accordingly. However, if fuel injection is performed after the compression top dead center, the turbulent flow intensity increases for a predetermined period after the fuel injection. During this period when the turbulent flow intensity is increasing due to fuel injection, the plug discharge channel CN is likely to extend. In particular, the timing at which the turbulent flow intensity peaks is suitable as the ignition timing.

FIG. 11 is an explanatory diagram of the plug discharge channel CN. FIG. 11 shows the center electrode 11a and the outer electrode 11b of the spark plug 11, and the extended plug discharge channel CN. Further, here, the fuel injection valve 12 is omitted in order to pay attention to the state of the plug discharge channel CN. If a flow is given in the vicinity of the spark plug so that the plug discharge channel CN is sufficiently extended, the tip of the fuel injection valve 12 does not necessarily have to face the spark plug 11, and even if it faces in a different direction, the combustion chamber It may be an embodiment in which the flow is applied in the vicinity of the spark plug by reflecting the fuel.

The flow near the spark plug 11 after the tumble flow collapse is small. Therefore, when spark ignition is performed, the plug discharge channel CN is normally generated so as to straddle the center electrode 11a and the outer electrode 11b substantially linearly. However, in the present embodiment, the flow is imparted to the vicinity of the spark plug 11 by fuel injection by the fuel injection valve 12 between the time when the tumble flow collapses and the time when the plug discharge channel CN is generated. Then, due to the applied flow, the plug discharge channel CN between the center electrode 11a and the outer electrode 11b is extended as shown in FIG.

By doing so, it is possible to impart flow to the combustion chamber after the tumble flow collapse and extend the plug discharge channel CN, so that partial burn and misfire can be suppressed and combustion stability can be improved. In particular, as will be described later, it is possible to stably ignite sparks even in a situation where flame propagation is more difficult than usual, such as when EGR is used or when lean burn is adopted.

12A and 12B are diagrams showing an example of a fuel injection pattern for extending the plug discharge channel CN. In addition to the intake stroke and expansion stroke of the multi-stage injection described above, further fuel injection may be performed between the time when the tumble flow collapses and the generation of the plug discharge channel (FIG. 12A), or the expansion stroke injection of the multi-stage injection is tumbled. This may be performed after the flow collapse and before the generation of the plug discharge channel (Fig. 12B).

By the way, since the fuel injection valve 12 that injects fuel directly into the cylinder is exposed to combustion flame and combustion gas, so-called deposits are likely to be accumulated around the injection hole. Then, when the deposit blocks the course of fuel spraying, for example, as shown in FIG. 13, the spraying pattern such as the shape and traveling direction of the spray beam is a reference set to increase the flow intensity around the spark plug 11 by fuel injection. It deviates from the pattern. As a result, even if fuel is injected, the flow strength around the spark plug 11 does not increase, and the combustion stability of the internal combustion engine 10 may decrease.

In addition, the exhaust temperature during FIR control may not reach the target exhaust temperature due to the decrease in combustion stability. Here, the relationship between the combustion stability and the exhaust temperature will be described.

FIG. 14 is a diagram for explaining the relationship between combustion stability and exhaust temperature. The horizontal axis of FIG. 14 is the position of the center of gravity of combustion [deg. CA]. The "combustion stability limit" in the figure is the combustion stability when noise or vibration becomes an upper limit value that can be tolerated by the occupant. The target exhaust temperature in the figure is a target value of the exhaust temperature during FIR control, and is a value set from the viewpoint of early activation of the exhaust catalysts 44 and 45. The solid line A in the figure shows the case of the above-mentioned reference pattern, and the solid line B shows the case of deviating from the reference pattern.

As shown in FIG. 14, it is known that the exhaust temperature becomes higher as the center of gravity of combustion becomes closer to the retard side. On the other hand, the combustion stability decreases as the center of gravity of combustion becomes closer to the retard side. In the reference pattern (solid line A), the combustion stability can be ensured to the retard side by extending the plug discharge channel CN described above. Then, when the combustion stability limit is reached, the exhaust temperature is equal to or higher than the target exhaust temperature.

On the other hand, if it deviates from the reference pattern, the combustion stability limit becomes the advance angle side with respect to the reference pattern. Therefore, when the combustion stability has characteristics such as the solid line B, the exhaust temperature at the combustion stability limit becomes lower than the target exhaust temperature.

Therefore, in order to ensure the combustion stability of the internal combustion engine 10, if a deposit is accumulated on the fuel injection valve 12, it is necessary to remove it. Then, in order to remove the deposit at an accurate timing, it is important to accurately determine whether or not the deposit is accumulated, that is, whether or not there is deposit at the tip of the fuel injection valve 12. ..

Therefore, the controller 50 determines whether or not a deposit is accumulated and removes the deposit by the control described below.

FIG. 15 is a flowchart showing a control routine executed by the controller 50. The controller 50 is programmed to execute this control routine. This routine is executed at the time of starting the cold engine of the internal combustion engine 10 from the determination of switching to FIR control to the end of FIR control. Hereinafter, the steps will be described.

In step S100, the controller 50 uses the detection value of the crank angle sensor 27 to calculate dR / dt, which is the slope of the increase in the engine rotation speed after the internal combustion engine 10 starts combustion.

In step S110, the controller 50 determines whether or not the dR / dt acquired in step S100 is larger than the threshold value X as the reference behavior. When the spray pattern changes due to the accumulation of deposits, the combustion stability decreases compared to the case where no deposits are accumulated, resulting in a delay in the initial explosion and a decrease in output, resulting in a slow increase in the engine speed. .. Therefore, in step S110, it is determined whether or not a deposit is accumulated at the tip of the fuel injection valve 12 using dR / dt. The threshold value X is a value smaller than the slope of the increase in the engine rotation speed after the start of combustion in a state where no deposit is accumulated on the fuel injection valve 12. The reason why the value smaller by a predetermined amount is used is that if the exhaust temperature when the combustion stability reaches the combustion stability limit is equal to or higher than the target exhaust temperature, the decrease in the combustion stability can be tolerated. Therefore, the predetermined amount is determined based on the characteristics of the change in combustion stability due to the accumulation of deposits. The parameter used for determining whether or not the deposit is accumulated is not limited to dR / dt. Parameters other than dR / dt will be described later.

If the controller 50 determines in step S110 that dR / dt is greater than the threshold value X, the controller 50 executes the process of step S120, and if it determines that dR / dt is equal to or less than the threshold value X, executes the process of step S130.

In step S120, the controller 50 performs normal FIR control. The normal FIR control referred to here is an FIR control that does not execute the deposit removal control described later.

The controller 50 determines the start of the deposit removal control in step S130, and increases the target value of the fuel injection pressure (hereinafter, also referred to as the target fuel pressure) in step S140 as compared with the case where the deposit removal control is not executed. .. The reason for increasing the target fuel pressure is to increase the fuel flow velocity in the vicinity of the injection hole of the fuel injection valve 12, thereby blowing off the deposit. The target fuel pressure after the increase may be, for example, the maximum fuel pressure that can be realized by the fuel injection pump 15, or the fuel pressure that can blow off the deposit obtained by experiments or the like.

In step S150, the controller 50 determines whether or not the center of gravity of combustion has reached the target position. The controller 50 repeats the determination in step S150 until the center of gravity of combustion reaches the target position, and then determines in step S160 whether or not the combustion stability is stable. Specifically, the combustion stability that can be tolerated from the viewpoint of vibration and noise is set as the target combustion stability, and it is determined whether or not the current combustion stability is higher than the target combustion stability.

Then, when the determination in step S160 is repeated until the combustion becomes stable, the target fuel pressure is reduced to the target fuel pressure in the normal FIR control in step S170. In step S160, the combustion that was not initially stable is considered to be stable because the deposit has been removed.

As described above, after increasing the target fuel pressure, the controller 50 determines whether or not the combustion stability is higher than the target stability when the combustion center of gravity reaches the target position, and if it is higher, the target fuel pressure is used for normal FIR control. Return to the target fuel pressure of. When the fuel pressure is increased, the friction of the fuel injection pump 15 increases, so that the fuel efficiency performance deteriorates by continuing to maintain the high fuel pressure. Therefore, if the controller 50 determines that the deposits have been removed in step S160, the controller 50 reduces the fuel pressure in step S170.

In addition, step S140-S170 is "adhesion removal control" in this embodiment. However, S150-S170 is not essential. This is because the treatment in steps S150-S170 is for suppressing deterioration of fuel efficiency performance due to execution of the deposit removal control, and does not perform an action of removing the deposits.

Next, the effect of this embodiment will be described.

FIG. 16 is a timing chart when the above-mentioned deposit removal control is not executed. This timing chart is a comparative example and is not included in the present embodiment.

In the chart of engine speed R, combustion stability and combustion center of gravity, the solid line indicates the state without deposit (hereinafter, also referred to as normal state), and the broken line indicates the state with deposit (hereinafter, also referred to as deteriorated state). Is shown.

When the engine start is determined at the timing T0 and cranking is started, the engine rotation speed R rises to a predetermined rotation speed and maintains the rotation speed. Then, combustion starts at timing T1, and the engine speed R starts to rise again. Further, as the engine rotation speed increases, the rotation speed of the fuel injection pump 15 driven by the internal combustion engine 10 also increases, so that the fuel pressure increases.

The engine speed R increases with the start of combustion in both the normal state and the deteriorated state, and once overshoots, it converges to the idle speed. The above-mentioned dR / dt is the slope of the increase in the rotation speed from the timing T1 to the overshoot. As described above, the slope of increase is smaller in the deteriorated state than in the normal state.

When the engine rotation speed R becomes the idle rotation speed at the timing T2 and the fuel pressure rises to the target fuel pressure, the controller 50 determines whether or not FIR control is permitted and sets the FIR permission flag. The determination is made based on the engine speed, the oil / water temperature, the intake air temperature, the intake pressure, the inclination of the vehicle, and the like, as in the known determination. In the present embodiment, the case where FIR control is permitted will be described, but FIR control is not permitted when the friction of the internal combustion engine 10 is large, for example, when the engine is started at an extremely low temperature.

When the FIR control is started at the timing T2, the combustion center of gravity is retarded due to the retardation of the ignition timing in both the normal state and the deteriorated state, and the combustion stability is lowered accordingly. Under normal conditions, combustion stability higher than the target combustion stability can be maintained. On the other hand, in the deteriorated state, the plug discharge channel CN does not extend sufficiently, so that the combustion stability becomes lower than the target combustion stability. However, since early activation of the exhaust catalysts 44 and 45 is indispensable in order to clear the regulation value of the exhaust performance, the ignition timing cannot be returned to the advance side. Therefore, the idle operation must be continued with the combustion stability being low, the vehicle vibration and noise during FIR control become large, and the commercial value is lowered.

FIG. 17 is a timing chart when the above-mentioned deposit removal control is executed. In the chart of the engine speed R and the center of gravity of combustion, the solid line indicates the normal state, and the broken line indicates the deteriorated state. In the fuel pressure chart, the solid line shows the case where the deposit removal control is executed, and the broken line shows the case where the deposit removal control is not executed. In the combustion stability chart, the solid line shows the case where the deposit removal control is executed, the broken line A shows the normal state, and the broken line B shows the deteriorated state and the case where the deposit removal control is not executed.

Since the timing T0 to the timing T2 are the same as those in FIG. 16, the description thereof will be omitted. Even after the FIR control is started at the timing T2, the combustion center of gravity is retarded and the combustion stability is lowered, which is the same as in FIG.

However, since the controller 50 executes the deposit removal control, the fuel pressure becomes higher than the target fuel pressure in the normal FIR control. Combustion stability approaches the combustion stability in the normal state (broken line A) because the deposits are blown off by the fuel injected at a high fuel pressure. Then, at the timing T3 when the center of gravity of combustion reaches the target position, the combustion stability becomes equivalent to the normal state. Therefore, at the timing T3, the controller 50 switches the target fuel pressure to the target fuel pressure in the normal FIR control, and the actual fuel pressure drops to the target fuel pressure in the normal FIR control.

Note that FIG. 17 shows a case where the deposits are blown off before the center of gravity of combustion reaches the target position, but the timing at which the deposits are blown off may be later than this. In this case, the combustion stability becomes lower than the target combustion stability once, and becomes equivalent to the normal state after the deposits are blown off.

Next, a modified example of this embodiment will be described.

(Modification example 1)
Whether or not a deposit has accumulated on the fuel injection valve 12 is determined by the behavior of the change in engine speed from the start of cranking to the first explosion, instead of dR / dt, which is the behavior of the change in engine speed after the first explosion. It may be judged based on. For example, the time from the start of cranking to the first explosion in a state where no deposit is accumulated is used as a reference value, and if there is a delay of a predetermined time from the reference value, it is determined that the deposit is accumulated. .. Whether or not the first explosion has occurred can be judged from the fluctuation of the in-cylinder pressure.

(Modification 2)
The deposit removal control may be a control for advancing the ignition timing in order to intentionally generate light knocking instead of the control for increasing the fuel pressure. It has been experimentally confirmed that the deposit is blown off by pressure vibration when knocking occurs. Therefore, the ignition timing at which light knocking that does not cause deterioration of the internal combustion engine 10 is obtained in advance by an experiment or the like, and when the execution of the deposit removal control is decided, the ignition timing is advanced to the ignition timing.

(Modification 3)
The deposit removal control may be a control that outputs a signal indicating that the fuel injection valve 12 needs to be maintained, instead of the control that raises the fuel pressure. Specifically, it is a control that notifies the driver by turning on a warning light or the like, or a control that outputs the signal when a diagnostic device for maintenance is connected. According to these controls, the maintenance person can carry out various maintenances for removing the deposit adhering to the tip of the fuel injection valve 12.

The control may be performed when the combustion stability is not improved even if the above-mentioned control for increasing the fuel pressure or the control for generating light knocking is executed.

Next, the effect of this embodiment will be described.

In the present embodiment, the actual behavior, which is the behavior of the actual change in the engine rotation speed at the time of starting the engine, is compared with the preset reference behavior, and when the actual behavior is different from the reference behavior, the tip of the fuel injection valve 12 is set. Judge that there is deposit. As a result, it is possible to accurately determine in a short time that deposits are attached to the tip of the fuel injection valve 12. Further, it can be determined that deposits are attached to the tip of the fuel injection valve 12 during FIR control immediately after the engine is started, that is, before the internal combustion engine 10 is in a normal operating state.

In the present embodiment, when it is determined that there is a deposit at the tip of the fuel injection valve 12, the deposit removal control is executed. Thereby, the combustion stability can be improved.

In the present embodiment, the deposit removal control is executed during the period during which the stratified combustion is executed immediately after the engine is started, that is, during the FIR control. Since it is particularly susceptible to changes in fuel spray during stratified combustion, it can be easily determined whether or not the deposits have been removed by the deposit removal control.

In the present embodiment, as the deposit removal control, a control is executed in which the fuel injection pressure (fuel pressure) is increased as compared with the case where it is determined that there is no deposit at the tip of the fuel injection valve 12. By injecting fuel at a high fuel pressure, deposits can be blown off and combustion stability can be improved.

In the present embodiment, when the combustion stability becomes higher than the combustion stability limit after the start of the deposit removal control, the deposit removal control is terminated. As a result, the time for maintaining the high fuel pressure does not become unnecessarily long, and the deterioration of the fuel efficiency performance due to the execution of the deposit removal control can be suppressed.

In the present embodiment, as the behavior of the actual change in the engine rotation speed at the time of starting the engine, the slope dR / dt of the increase in the engine rotation speed after the internal combustion engine 10 starts combustion is used, so that the presence or absence of deposits is determined. There is no need to install a new sensor or the like to do this.

In the present embodiment, fuel is injected from the fuel injection valve 12 toward the discharge region of the spark plug 11, and the spark plug 11 is generated while the air flow is turbulent around the discharge region due to the fuel injected from the fuel injection valve 12. Spark ignition is performed by. According to the present embodiment, since the plug discharge channel is extended due to the turbulence of the air flow generated by the fuel injection, stable stratified combustion is possible even after the tumble flow collapses.

In the present embodiment, as the deposit removal control, a control for outputting a signal indicating that the fuel injection valve 12 needs to be maintained may be executed. By executing the control, when vibration or noise increases due to a decrease in combustion stability, it becomes easy to identify the cause.

Although the embodiments of the present invention have been described above, the above embodiments are only a part of the application examples of the present invention, and the technical scope of the present invention is limited to the specific configurations of the above embodiments. Absent.

Claims (7)

A fuel injection valve that injects fuel directly into the cylinder,
An ignition plug that directly sparks and ignites the fuel injected from the fuel injection valve,
In the control method of the internal combustion engine provided with
After starting the engine, stratified combustion is performed to burn the air-fuel mixture formed by injecting fuel from the fuel injection valve toward the discharge region of the spark plug.
During the period of performing the stratified combustion,
The actual behavior is the behavior of the actual change in engine speed from a combustion start of the internal combustion engine, compared with a reference behavior of the engine rotational speed from the start of combustion preset the internal combustion engine at the time of engine start, before Symbol When the actual behavior is different from the reference behavior, it is determined that the spray pattern has changed due to the presence of deposits at the tip of the fuel injection valve, and the deposit removal control for removing the deposits is executed.
Internal combustion engine control method. In the method for controlling an internal combustion engine according to claim 1,
The deposit removal control is a control for increasing the fuel injection pressure as compared with the case where it is determined that there is no deposit at the tip of the fuel injection valve.
Internal combustion engine control method. In the method for controlling an internal combustion engine according to claim 1 or 2.
When the combustion stability becomes higher than the combustion stability limit after the start of the deposit removal control, the deposit removal control is terminated.
Internal combustion engine control method. In the method for controlling an internal combustion engine according to any one of claims 1 to 3.
The behavior is the slope of the increase in the engine speed after the internal combustion engine starts combustion.
Internal combustion engine control method. In the method for controlling an internal combustion engine according to any one of claims 1 to 4.
During the execution of the stratified combustion, spark ignition is performed by the spark plug while the airflow is turbulent around the discharge region due to the fuel injected from the fuel injection valve.
Internal combustion engine control method. In the method for controlling an internal combustion engine according to claim 1,
The deposit removal control is a control that outputs a signal to the outside indicating that the fuel injection valve needs to be maintained.
Internal combustion engine control method. A fuel injection valve that injects fuel directly into the cylinder,
An ignition plug that directly sparks and ignites the fuel injected from the fuel injection valve,
A sensor that acquires the engine speed and
A control unit that controls the fuel injection valve and the spark plug,
In the control device of an internal combustion engine equipped with
The control unit
After starting the engine, stratified combustion is performed to burn the air-fuel mixture formed by injecting fuel from the fuel injection valve toward the discharge region of the spark plug.
During the period of performing the stratified combustion,
The actual behavior, which is the behavior of the actual change in the engine rotation speed from the start of combustion of the internal combustion engine at the time of starting the engine, is compared with the preset reference behavior of the engine rotation speed from the start of combustion of the internal combustion engine. When the behavior is different from the reference behavior, it is determined that the spray pattern has changed due to the presence of deposits at the tip of the fuel injection valve, and the deposit removal control for removing the deposits is executed. Engine control device.

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