JP4238752B2 - Control device for internal combustion engine - Google Patents

Description

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

  A first fuel injection valve that directly injects fuel into the cylinder, and a second fuel injection valve that injects fuel into the intake passage, and stratified combustion using the first fuel injection valve, and second fuel injection An internal combustion engine that performs switching between homogeneous combustion using a valve and performing the same is known (for example, see Patent Document 1).

  In such an internal combustion engine, when fuel injection at the first fuel injection valve is stopped during homogeneous combustion, deposits accumulate in the injection hole of the first fuel injection valve, and in the worst case, the injection hole is closed by the deposit. May be. In order to prevent this, it is preferable to perform fuel injection by the first fuel injection valve even during homogeneous combustion. The fuel injection by the first fuel injection valve during the homogeneous combustion is preferably performed not in the compression stroke but in the intake stroke as in stratified combustion in order to increase the mixing time with intake air.

  The fuel injected from the second fuel injection valve and supplied into the cylinder together with the intake air from the intake passage is easily vaporized in the cylinder due to the progress of atomization in the intake passage, and into the cylinder together with the intake air. Since it is widely dispersed, it is easy to form a good homogeneous mixture. On the other hand, the fuel injected into the cylinder in the intake stroke by the first fuel injection valve reduces the intake temperature in the cylinder due to the latent heat of vaporization, thereby improving the intake charging efficiency.

  Thus, in the case of supplying the required amount of fuel into the cylinder by both the first fuel injection valve and the second fuel injection valve during homogeneous combustion, the fuel injection of the first fuel injection valve is performed in order to improve the intake charge efficiency. It is preferable to set the respective fuel injection ratios of the first fuel injection valve and the second fuel injection valve with respect to the required amount of fuel so that the amount is larger than the minimum amount only for preventing deposit accumulation.

  By the way, when the homogeneous combustion is performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, if the injected fuel is not almost completely vaporized, the combustion air-fuel ratio becomes leaner and the combustion deteriorates. In particular, the fuel directly injected into the cylinder by the first fuel injection valve is less likely to be vaporized than the injected fuel of the second fuel injection valve supplied into the cylinder while being atomized together with the intake air. In order to vaporize this almost completely, an air flow control valve is provided in the engine intake system and closed to generate a strong swirl flow such as swirl flow or tumble flow in the cylinder during the intake stroke. It has been proposed to use for fuel vaporization. Since the strong swirl flow generated in the intake stroke may continuously disperse the stratified mixture in the compression stroke, it is preferable not to generate a swirl flow in the cylinder during stratified combustion.

JP 7-103049 A JP 2002-364409 A

  Thus, when the air flow control valve is provided in the above-described internal combustion engine, the air flow control valve is closed when the combustion method is switched from stratified combustion to homogeneous combustion with a lean air-fuel ratio. However, even if the airflow control valve is closed, a strong swirling flow is not generated immediately in the cylinder due to a response delay of the intake air. Thereby, until the strong swirl flow is generated, the vaporization of the injected fuel from the first fuel injection valve is insufficient and the homogeneous combustion may be deteriorated.

  Accordingly, an object of the present invention is to provide an air flow control valve that is closed during homogeneous combustion to generate a swirling flow in the cylinder, a first fuel injection valve that directly injects fuel into the cylinder, and fuel to the intake passage. Switching between stratified combustion using the first fuel injection valve and homogeneous combustion at a lean air-fuel ratio using both the first fuel injection valve and the second fuel injection valve In the control apparatus for an internal combustion engine, the deterioration of the homogeneous combustion immediately after closing the air flow control valve when switching from stratified combustion to homogeneous combustion is improved.

  An internal combustion engine control apparatus according to a first aspect of the present invention includes an air flow control valve that is closed during homogeneous combustion and generates a swirling flow in a cylinder, and a first that directly injects fuel into the cylinder. A fuel injection valve and a second fuel injection valve for injecting fuel into the intake passage are provided, and stratified combustion using the first fuel injection valve and both the first fuel injection valve and the second fuel injection valve are used. In the control apparatus for an internal combustion engine that performs switching between homogeneous combustion at a lean air-fuel ratio, the first air flow control valve is closed when the switching from the stratified combustion to the homogeneous combustion is performed for a set period from the first time. The homogeneous combustion is performed by decreasing the set fuel injection ratio of the fuel injection valve and increasing the set fuel injection ratio of the second fuel injection valve.

  According to a second aspect of the present invention, there is provided the control apparatus for an internal combustion engine according to the first aspect, wherein the homogeneous combustion is performed by retarding an ignition timing during the set period. It is characterized by that.

  According to a third aspect of the present invention, there is provided the control device for an internal combustion engine according to the first or second aspect, wherein the set period is at the time of switching from the stratified combustion to the homogeneous combustion. It is determined based on at least one of the engine speed and the intake pipe negative pressure.

  According to the control apparatus for an internal combustion engine of the first aspect of the present invention, during the set period from when the air flow control valve is closed when switching from stratified combustion to homogeneous combustion, the intake response delays in the cylinder. In order not to generate a strong swirling flow, the set fuel injection ratio of the first fuel injection valve is decreased and the set fuel injection ratio of the second fuel injection valve is increased, so that the required fuel amount is injected by both fuel injection valves. It has become. Thereby, the amount of fuel injected by the first fuel injection valve which is not sufficiently atomized and hardly vaporized when supplied into the cylinder is reduced, and is sufficiently atomized and easily vaporized when supplied into the cylinder. Since the amount of fuel injected by the second fuel injection valve is increased, the injected fuel can be sufficiently vaporized even if a strong swirling flow does not occur in the cylinder, and the deterioration of homogeneous combustion at this time can be improved. Can do.

  During the set period, the intake air amount cannot be sufficiently reduced by the airflow control valve, so that a strong swirling flow cannot be generated in the cylinder. Thereby, during this set period, the fuel injection amount is increased to prevent the combustion air-fuel ratio from further leaning. Accordingly, since the engine output increases as it is, in the control apparatus for an internal combustion engine according to claim 2 according to the present invention, the ignition timing is retarded during the set period to perform the homogeneous combustion, and the homogeneous combustion engine The output is stabilized.

  The set period is preferably coincident with the period from when the airflow control valve is closed to when a strong swirl flow is generated in the cylinder. During the period until a strong swirl flow is generated in the cylinder, the engine speed is The higher the intake pipe negative pressure is, the closer the intake pipe negative pressure is to the atmospheric pressure, and the faster the intake flow velocity supplied into the cylinder becomes shorter. Accordingly, in the control apparatus for an internal combustion engine according to claim 3 according to the present invention, in the control apparatus for the internal combustion engine according to claim 1 or 2, the engine rotation at the time of switching from stratified combustion to homogeneous combustion is performed. It is determined based on at least one of the number and the intake pipe negative pressure.

  FIG. 1 is a schematic longitudinal sectional view of an internal combustion engine to which a control device according to the present invention is attached, and FIG. 2 is a schematic plan view of the internal combustion engine of FIG. In these drawings, 1 is an engine body, and 2 is a surge tank common to each cylinder. An intake passage 3 communicates the surge tank 2 with each cylinder, and 4 is an intake pipe on the upstream side of the surge tank 2. A throttle valve 5 is disposed in the intake pipe 4 immediately upstream of the surge tank 2. The throttle valve 5 is not mechanically connected to the accelerator pedal, but can be freely set by a driving device such as a step motor. An exhaust passage 6 communicates with each cylinder.

  In the engine body 1, 7 is a pair of intake valves, 8 is a pair of exhaust valves, 9 is a piston, and 10 is a spark plug. Reference numeral 11 denotes a first fuel injection valve for directly injecting fuel into the cylinder. The intake passage 3 and the exhaust passage 6 are bifurcated in order to communicate into the cylinder via the pair of intake valves 7 and the pair of exhaust valves 8. A second fuel injection valve 12 is disposed in one path 3a of the bifurcated intake passage 3. In addition, an air flow control valve 13 capable of closing the path is disposed in the other path 3 b of the intake passage 3. One path 3a of the intake passage 3 in which the second fuel injection valve 12 is arranged is configured as a swirl flow generation path that generates a swirl flow such as a swirl flow or a tumble flow in the cylinder by the intake air passing therethrough.

  When the airflow control valve 13 is closed, intake air is supplied into the cylinder only from one path 3a of the intake passage 3, and a strong swirling flow is generated in the cylinder. On the other hand, if the airflow control valve 13 is opened, the intake air is supplied into the cylinder from both paths 3a and 3b of the intake passage, and the intake air supplied from the other path 3b into the cylinder is A swirl flow is not generated in the cylinder because the swirl is impeded by colliding with the airflow supplied from the path 3a into the cylinder and trying to swivel in the cylinder.

  Reference numeral 20 denotes a control device, which is driven by a driving device such as an opening of a throttle valve 5 driven by a driving device such as a step motor, a step motor or a negative pressure actuator, based on the engine speed and the engine load. It controls the opening and closing of the airflow control valve 13, the fuel injection timing and fuel injection amount of the first fuel injection valve 11 and the second fuel injection valve 12, the ignition timing of the spark plug 10, and the like.

  The internal combustion engine injects fuel in the latter half of the compression stroke by the first fuel injection valve 11, guides the injected fuel to the vicinity of the spark plug 10 using the cavity 9a on the top surface of the piston 9, and at the time of ignition, the vicinity of the spark plug 10 It is possible to perform stratified combustion that forms a combustible air-fuel mixture. In such stratified combustion, since the opening degree of the throttle valve 5 can be maintained relatively large, the pumping loss is reduced, thereby reducing the fuel consumption.

  However, it is difficult to inject a large amount of fuel in the latter half of the compression stroke and vaporize it sufficiently until ignition to obtain a combustible mixture. In this internal combustion engine, the required amount of fuel becomes relatively large or the latter half of the compression stroke. When the time becomes shorter, stratified combustion is abandoned, fuel is injected during the intake stroke, and homogeneous combustion is performed to form a homogeneous mixture in the cylinder at the time of ignition. The entire operation region of the internal combustion engine is divided as shown in FIG. 3, and stratified combustion is performed in the operation region A on the low-rotation / low-load side, and leaner than the stoichiometric air-fuel ratio in the operation region B of medium rotation or medium load. The homogeneous combustion is performed at the air-fuel ratio, and the homogeneous combustion is performed at the air-fuel ratio richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the operation region C of high rotation or high load. Homogeneous combustion at a lean air-fuel ratio can also maintain the opening of the throttle valve 5 relatively large, reducing pumping loss and fuel consumption.

  In order to improve the homogeneous combustion, it is necessary to sufficiently vaporize the injected fuel before ignition and to thoroughly mix it with the intake air and distribute it throughout the cylinder. The fuel injected from the second fuel injection valve 12 is easily vaporized in the cylinder because it is supplied into the cylinder while being atomized together with the intake air that passes through one passage 3a of the intake passage 3, and also in the entire cylinder. Dispersed is advantageous for the formation of a good homogeneous mixture. Thereby, at the time of homogeneous combustion, if a required amount of fuel can be injected only by the second fuel injection valve 12, a good homogeneous air-fuel mixture can be easily formed.

  However, when the fuel injection of the first fuel injection valve 11 is stopped during the homogeneous combustion in this way, since the first fuel injection valve 11 has an injection hole that opens in the cylinder, deposits are accumulated in the injection hole. In the worst case, the nozzle hole may be clogged. Accordingly, it is preferable to perform fuel injection by the first fuel injection valve even during homogeneous combustion. In the internal combustion engine, both the first fuel injection valve 11 and the second fuel injection valve 12 are used during homogeneous combustion. The fuel is injected during the intake stroke. In the homogeneous combustion, the second fuel injection valve 12 can perform not only the intake synchronous injection but also non-simultaneous intake injection in which fuel is injected before the intake valve is opened.

  The fuel injected into the cylinder from the first fuel injection valve 11 at the time of homogeneous combustion is advantageous for improving the intake charging efficiency and increasing the engine output because the in-cylinder temperature is lowered by the latent heat of vaporization. Thereby, at the time of homogeneous combustion, the fuel injection ratio of the first fuel injection valve 11 with respect to the required fuel amount is set so that the injected fuel is larger than the minimum amount intended only to prevent deposit accumulation.

  However, the first fuel injection valve 11 is suitable for forming a combustible air-fuel mixture near the spark plug during stratified combustion, and the fuel spray shape (for example, a relatively thin fan shape) and the fuel injection direction are selected. In addition, since the injected fuel enters the cavity 9a of the piston 9 in the first half of the intake stroke, it is not suitable for dispersing the fuel throughout the cylinder during homogeneous combustion.

  In particular, when performing homogeneous combustion at a lean air-fuel ratio, if the injected fuel is not vaporized almost completely, the air-fuel ratio becomes leaner and combustion worsens. Thus, in the internal combustion engine, the air flow control valve 13 is closed and generated in the cylinder during homogeneous combustion, particularly in order to vaporize and disperse the fuel injected from the first fuel injection valve 11 well. It is intended to take advantage of the strong swirl that is generated. However, even when the airflow control valve 13 is closed when the combustion system changes from stratified combustion to lean air-fuel ratio homogeneous combustion, a strong swirling flow cannot be generated immediately in the cylinder due to the response delay of the intake air. If the vaporization of the fuel injected from the first fuel injection valve 11 becomes insufficient before the strong swirl flow is generated, the homogeneous combustion at this time will deteriorate.

  FIG. 4 is a time chart showing each control performed by the control device 20 for improving the deterioration of the homogeneous combustion. This time chart shows a case in which the combustion system changes from stratified combustion to lean combustion at a lean air-fuel ratio at time t1 due to changes in engine speed and engine load. As a result, at time t1, the combustion mode flag is switched from 0 (stratified combustion) to 1 (homogenous combustion with a lean air-fuel ratio). At the same time, the air flow control valve 13 being opened in the stratified combustion is closed. Even when the air flow control valve 13 is closed in this way, the period until time t2 until only the intake air that has passed through only one passage 3a of the intake passage 3 is actually supplied into the cylinder due to the response delay of the intake air. Is required.

  The set fuel injection ratio of the first fuel injection valve 11 is 100% at the time of stratified combustion, but when this is switched to the homogeneous combustion, this is the set fuel injection ratio a% (for example, 50%) at the time of homogeneous combustion. The fuel injection ratio is changed to a smaller value. The set fuel injection ratio of the second fuel injection valve 12 is 0% at the time of stratified combustion, but this is changed to the set fuel injection ratio b% (100% − at the time of homogeneous combustion) when switching to the homogeneous combustion. a%) to a larger fuel injection ratio.

  Thereby, immediately after time t1, a strong swirl flow is not generated in the cylinder, but the fuel injection amount from the first fuel injection valve 11 which is disadvantageous for the formation of a good homogeneous mixture is reduced, and good homogeneous Since the fuel injection amount from the second fuel injection valve 12 that is advantageous for the formation of the air-fuel mixture is increased, a relatively good homogeneous air-fuel mixture can be formed even at this time.

  As time elapses from time t1 and approaches time t2, a swirl flow is generated in the cylinder, and this gradually increases. Therefore, the first fuel injection that can be vaporized and dispersed well by the swirl flow The amount of fuel from the valve 11 increases. Thereby, the fuel injection ratio of the first fuel injection valve 12 is gradually increased so that the fuel injection amount from the first fuel injection valve 11 is gradually increased, and the fuel injection amount from the second fuel injection valve 12 is increased. The fuel injection ratio of the second fuel injection valve 12 is gradually reduced so as to gradually decrease the fuel consumption. Thus, if the fuel injection amount from the first fuel injection valve 11 is increased, the charging efficiency is increased by the latent heat of vaporization, which is advantageous for increasing the engine output.

  Since a strong swirl flow is generated in the cylinder at time t2, at time t2, the fuel injection ratios of the first fuel injection valve 11 and the second fuel injection valve 12 are the respective values at the time of homogeneous combustion. The set fuel injection ratios are a% and b%. The set fuel injection ratios of the first fuel injection valve 11 and the second fuel injection valve 12 at the time of the homogeneous combustion may be constant in all the homogeneous combustion regions, but may be set to be different for each engine operating state. . For example, in the high load or high rotation operation region C, it is preferable to further increase the charging efficiency. Therefore, the set fuel injection ratio of the first fuel injection valve 11 is set to be higher than that in the medium load or medium rotation operation region B. It may be set larger and the set fuel injection ratio of the second fuel injection valve 12 may be set smaller than that in the operation region B of medium load or medium rotation.

  Thus, even if the set fuel injection ratio of the first fuel injection valve 11 is set to be large and the fuel injection amount from the first fuel injection valve 11 is increased, the in-cylinder temperature is maintained in this homogeneous combustion operation region C. Since the fuel is high, the vaporization of the injected fuel from the first fuel injection valve 11 becomes relatively good, and in this operation region C, the homogeneous combustion is performed at the stoichiometric air-fuel ratio or the rich air-fuel ratio. Even if part of the fuel injected from the fuel injection valve 11 does not vaporize, the combustion air-fuel ratio does not become abnormally lean, and the combustion hardly deteriorates.

  In the homogeneous combustion in the operation region C, it is preferable to open the airflow control valve and supply a large amount of intake air into the cylinder. Further, a relatively strong turbulence can be generated in the cylinder by this large amount of intake air, whereby the fuel injected by the first fuel injection valve is sufficiently vaporized and dispersed.

  By the way, at the time of stratified combustion, the opening degree of the throttle valve 5 is very large. On the other hand, at the time of homogeneous combustion of the lean air-fuel ratio, the required amount of fuel is not so much, and in order to maintain the desired lean air-fuel ratio range, The intake volume must be reduced. Therefore, the opening degree of the throttle valve 5 is decreased when switching from stratified combustion to lean air-fuel ratio homogeneous combustion. Furthermore, since the airflow control valve 13 is also closed, the intake air amount is also reduced thereby.

  However, it is at time t2 after the air flow control valve 13 is closed that the desired intake air amount is realized due to the intake response delay, and before that time, more intake air than necessary is supplied into the cylinder. At this time, the fuel injection amounts of the first fuel injection valve 11 and the second fuel injection valve 12 are increased to prevent the air / fuel ratio from exceeding the desired lean air / fuel ratio range and becoming lean. Thereby, since the engine output increases more than necessary as it is, in this embodiment, the ignition timing is retarded at time t1 to decrease the engine output. Thereafter, the ignition timing is gradually advanced as the intake air amount is decreased to stabilize the engine output, and the set ignition timing for the homogeneous combustion at the lean air-fuel ratio is set at time t2.

  In order to realize the above-described control, a period T from time t1 to t2, that is, a period T from when the airflow control valve 13 is closed to when a strong swirling flow is generated in the cylinder is set in advance. It is necessary to keep. This period T varies depending on the engine speed or intake pipe negative pressure when the airflow control valve 13 is closed, that is, when switching from stratified combustion to homogeneous combustion. The higher the engine speed, or the closer the intake pipe negative pressure is to the atmospheric pressure, the faster the intake air flow velocity that passes through one passage 3a of the intake passage 3, and therefore, it becomes easier to generate a strong swirl flow in the cylinder. . Thereby, the setting period T from time t1 to t2 can be set as shown in the tendency shown in FIG. 6 depending on the engine speed or intake pipe negative pressure when switching from stratified combustion to homogeneous combustion.

  In the time chart shown in FIG. 4, the case where the stratified combustion is switched to the homogeneous combustion of the lean air-fuel ratio when the operation region is changed from A to B has been described. Before carrying out the homogeneous combustion in step 1, the homogeneous combustion at the stoichiometric air-fuel ratio or rich air-fuel ratio may be carried out. FIG. 5 is a time chart showing each control in this case. Differences from the time chart of FIG. 4 will be described below.

  When the operating region changes from A to B (time t0), the combustion method flag changes from 0 (stratified combustion) to 1 (homogenous combustion of the lean air-fuel ratio). At this time, the air flow control valve 13 is closed. First, the opening of the throttle valve 5 is made relatively small, and the intake air amount is reduced for homogeneous combustion at the stoichiometric air-fuel ratio. However, the intake air amount is decreased only gradually, and a relatively large amount of fuel is supplied into the cylinder by the first fuel injection valve 11 and the second fuel injection valve 12 in order to realize the stoichiometric air-fuel ratio. As a result, the engine output increases as it is, so that the ignition timing is significantly retarded.

  Until the change in the intake air amount associated with the change in the opening of the throttle valve 5 is stabilized (until time t1), the homogeneous combustion at the stoichiometric air-fuel ratio is performed, and the fuel injection ratio of the first fuel injection valve 11 in this homogeneous combustion is lean. It is smaller than the set fuel injection ratio a% in the air-fuel ratio homogeneous combustion, and the fuel injection amount of the second fuel injection valve 12 is increased, which is advantageous for the formation of a good homogeneous mixture. The fuel injection amounts of the first fuel injection valve 11 and the second fuel injection valve 12 are decreased along with a decrease in the intake air amount so as to maintain the stoichiometric air-fuel ratio, and the ignition timing gradually advances as the engine output decreases accordingly. Horned.

  When the intake air amount becomes stable at time t1, the air flow control valve 13 is closed, and the opening of the throttle valve 5 is slightly increased so that the desired intake air amount for the homogeneous combustion of the lean air-fuel ratio is realized. . Thus, homogeneous combustion at a lean air-fuel ratio is started during a set period T (time t1 to time t2) similar to the time chart of FIG. In the present embodiment, at time t1 when the airflow control valve 13 is closed, the change in the intake air amount due to the decrease in the opening of the throttle valve 5 is stable. It can be eliminated and homogeneous combustion at a lean air-fuel ratio can be further stabilized.

  In the present embodiment, in the homogeneous combustion at the stoichiometric air-fuel ratio, the airflow control valve 12 is kept open, and at this time, no swirl flow is generated in the cylinder. Since this is homogeneous combustion targeting the stoichiometric air-fuel ratio, the air-fuel ratio does not become very lean even if part of the fuel injected from the first fuel injection valve 11 does not vaporize, and This is to prevent the homogeneous combustion at the stoichiometric air-fuel ratio from becoming unstable due to a change in the intake air amount accompanying the closing of the airflow control valve 13.

It is a schematic longitudinal cross-sectional view which shows the internal combustion engine to which the control apparatus by this invention is attached. FIG. 2 is a schematic plan view of the internal combustion engine of FIG. 1. It is a figure which shows the driving | operation area | region of the internal combustion engine of FIG. It is a time chart which shows each control at the time of switching from stratified combustion to homogeneous combustion by the control device of the present invention. It is another time chart which shows each control at the time of switching from stratified combustion to homogeneous combustion by the control device of the present invention. It is a graph which shows the tendency of a setting period.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine main body 3 ... Intake passage 11 ... 1st fuel injection valve 12 ... 2nd fuel injection valve 13 ... Airflow control valve 20 ... Control apparatus

Claims (3)

  An airflow control valve that is closed during homogeneous combustion to generate a swirling flow in the cylinder, a first fuel injection valve that injects fuel directly into the cylinder, and a second fuel injection that injects fuel into the intake passage An internal combustion engine that switches between stratified combustion using the first fuel injection valve and homogeneous combustion at a lean air-fuel ratio using both the first fuel injection valve and the second fuel injection valve. In the control device, the set fuel injection ratio of the first fuel injection valve is decreased and the second fuel is reduced during a set period from when the airflow control valve is closed when switching from the stratified combustion to the homogeneous combustion. A control apparatus for an internal combustion engine, wherein the homogeneous combustion is performed by increasing a set fuel injection ratio of an injection valve.   2. The control apparatus for an internal combustion engine according to claim 1, wherein the homogeneous combustion is performed by retarding an ignition timing during the set period.   3. The control of the internal combustion engine according to claim 1, wherein the set period is determined based on at least one of an engine speed and an intake pipe negative pressure at the time of switching from the stratified combustion to the homogeneous combustion. apparatus.

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