JP4609200B2 - In-cylinder direct injection spark ignition internal combustion engine controller - Google Patents

Description

  The present invention relates to an in-cylinder direct injection type spark ignition internal combustion engine that directly injects fuel into a cylinder, and in particular, at a cold start in which early temperature rise (early activation) of an exhaust system catalytic converter is required. It relates to control of injection timing and ignition timing.

In Patent Document 1, as a catalyst warm-up method for a direct injection spark-ignition internal combustion engine, a period from the intake stroke to the ignition timing when the exhaust gas catalytic converter is in an unwarmed state lower than the activation temperature. In this case, it is possible to spread the fuel by the late injection in which the air-fuel mixture having a partial air-fuel ratio concentration is formed in the combustion chamber, the fuel is injected before this late injection, and the fuel of the late injection and the combustion of the late injection And at least two split injections of early injection for generating an air-fuel mixture leaner than the stoichiometric air-fuel ratio in the combustion chamber, and retarding the ignition timing by a predetermined amount from the MBT point, and no engine load A technique is described in which the ignition timing is set before the compression top dead center in the region, and the ignition timing is retarded until the compression top dead center in the low speed and low load region excluding the no-load region. The latter-stage injection is performed after the middle of the compression stroke, for example, at 120 ° BTDC to 45 ° BTDC.
Japanese Patent No. 3325230

  For early activation of the catalyst when the internal combustion engine is cold and HC reduction due to afterburning, retarding the ignition timing is effective. To obtain a greater effect, ignition after compression top dead center (ATDC) Ignition) is desirable. In order to perform stable combustion by ATDC ignition, it is necessary to shorten the combustion period. For this reason, it is necessary to increase the combustion speed (flame propagation speed) by strengthening the turbulence in the cylinder.

  In order to strengthen such disturbance, it is conceivable that the disturbance is generated in the cylinder by the energy of the fuel spray injected at a high pressure in the cylinder.

  However, in Patent Document 1, the first fuel injection (early injection) is performed during the intake stroke, and the second fuel injection (late injection) is performed from 120 ° BTDC to 45 ° BTDC during the compression stroke. Yes. As described above, before the last fuel injection is before the compression top dead center, even if the spray generates turbulence in the cylinder, the turbulence is attenuated after the compression top dead center, and the flame propagation in ATDC ignition Does not contribute to speed increase.

  For example, FIG. 7 shows the magnitude of turbulence in a cylinder when a gas flow control valve (for example, a tumble control valve) provided in an intake port is operated and when such a gas flow control valve is not provided. As shown, the turbulence (part A) generated during the intake stroke by operating the gas flow control valve attenuates with the progress of the compression stroke, and is temporarily accompanied by the collapse of the tumble flow in the latter half of the compression stroke. Although the turbulence increases (the portion indicated by reference symbol B), after the compression top dead center, as shown by the reference symbol C, it rapidly attenuates, and combustion improvement (improving flame propagation) using the turbulence cannot be expected so much. The same applies to turbulence caused by fuel spray, and even if turbulence is generated by fuel injection before compression top dead center, it does not contribute to ignition combustion after compression top dead center.

  For this reason, ATDC ignition is more advantageous for increasing exhaust temperature and reducing HC, but combustion stability is not established. Therefore, in Patent Document 1, the ignition timing is set to before compression top dead center (BTDC ignition) in the no-load region. Yes.

  The present invention aims to improve the combustion stability in ATDC ignition for early activation of the catalyst, reduction of HC, and the like based on such a situation.

The present invention provides a control device for an in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug. When the exhaust gas temperature needs to be raised, such as when the engine is cold, the ignition timing is set after the compression top dead center, and super retard combustion is performed to inject fuel before the ignition timing and after the compression top dead center. It is characterized by that. Note that in a NOx trap catalyst that adsorbs NOx, the sulfur component (SOx) adheres to the catalyst, so that the NOx adsorption performance deteriorates. However, it is also possible to raise the temperature of the exhaust gas during the SOx release process using the above-mentioned super retard combustion. In the present invention, a part of the fuel is injected in the latter half of the compression stroke so that the fuel injection amount after the compression top dead center does not become zero particularly during the period immediately after the start when the fuel pressure is low.

  In other words, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but the in-cylinder turbulence is generated and strengthened by the fuel injection performed during the expansion stroke after the compression top dead center. Flame propagation with ATDC ignition is facilitated. Therefore, super retard combustion with the ignition timing after the compression top dead center is established stably.

  Here, in the super retard combustion in which fuel is injected after compression top dead center as described above, if the fuel pressure is not sufficiently high, the particle size of the spray becomes large, and smoke and HC deteriorate. In the vicinity of the top dead center, for example, the in-cylinder pressure becomes 1.5 MPa or more. Therefore, the fuel cannot be sufficiently atomized without a fuel pressure of 2.0 MPa or more. On the other hand, when the engine is started, the fuel pressure starts to increase with the start of cranking and increases with the engine speed. Therefore, immediately after starting, there is a concern that smoke and HC are generated due to super retard combustion with insufficient fuel pressure. is there.

  Therefore, in the present invention, during the period immediately after the start when the fuel pressure is low, the fuel injection amount after the compression top dead center is decreased, and at least a part of the fuel is injected before the compression top dead center, that is, during the intake stroke or the compression stroke. . By reducing the injection amount after compression top dead center in this way, smoke and HC deterioration due to low fuel pressure are suppressed.

  In this case, it is desirable to control so that the ratio of injection after compression top dead center decreases as the fuel pressure decreases. Under the condition that the injection after compression top dead center is less than the predetermined minimum injection time, the total amount of fuel is reduced. It is desirable to inject during the intake stroke or the compression stroke.

  It is also desirable to advance the ignition timing as the injection amount decreases after compression top dead center when the fuel pressure is low.

  Further, since the particle size of the fuel spray is greatly influenced by the fuel temperature, it is desirable to correct the injection amount ratio between the injection after the compression top dead center and the injection before the compression top dead center according to the fuel temperature. . Specifically, since the particle size of the fuel spray increases as the fuel temperature decreases, the injection amount after compression top dead center is decreased.

  In addition, as a mode of super retard combustion in a state where the fuel pressure is sufficiently high, in addition to a mode in which the entire amount of fuel is injected after the compression top dead center, the fuel injection is divided into two times, and the first injection is compression top dead There is a mode in which the second injection is performed after the compression top dead center while being performed before the point. In the former case, when the fuel pressure is low, the injection is divided into two times and a part of the fuel is injected before the compression top dead center. In the latter case, when the fuel pressure is low, the ratio of the second injection amount is decreased. become.

The control method of the present invention is a control method for a direct injection type spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug, and in a cold engine state. In the first stage of the start-up when the fuel pressure is lower than the predetermined pressure P2, the entire amount of fuel is injected during the intake stroke before the compression top dead center or during the compression stroke and ignited before the compression top dead center. In a second stage between the fuel pressure of a predetermined pressure P1 (where P1> P2) and P2, a part of the fuel is injected in the latter half of the compression stroke , and the remaining fuel is injected after the compression top dead center. In the third stage where the fuel is injected and ignited after the compression top dead center delayed from the injection timing, and the fuel pressure reaches P1, the ratio of the fuel injection amount after the compression top dead center than in the second stage It is characterized by performing super retarded combustion that became large

  According to the present invention, it is possible to sufficiently ensure the combustion stability of the super retard combustion in which the ignition timing is set after the compression top dead center. For example, at the time of cold start, the catalyst is activated early and the HC due to the afterburning. Reduction can be achieved. Immediately after startup when the fuel pressure becomes insufficient, a part of the fuel is injected before the compression top dead center, so that smoke and HC deterioration due to insufficient fuel pressure can be avoided.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration explanatory view showing a system configuration of a direct injection type spark ignition internal combustion engine to which the present invention is applied.

  An intake passage 4 is connected to the combustion chamber 3 formed by the piston 2 of the internal combustion engine 1 via an intake valve (not shown), and an exhaust passage 5 is connected via an exhaust valve (not shown). Has been. The intake passage 4 is provided with an air flow meter 6 for detecting the amount of intake air, and an electronically controlled throttle valve 7 whose opening degree is controlled via an actuator 8 by a control signal. The exhaust passage 5 is provided with a catalytic converter 10 for purifying exhaust gas, and air-fuel ratio sensors 11 and 12 are provided on the upstream side and the downstream side, respectively. Further, the upstream air-fuel ratio sensor 11 is provided. Is provided with an exhaust gas temperature sensor 13 for detecting the exhaust gas temperature at the inlet side of the catalytic converter 10.

  A spark plug 14 is disposed at the central top of the combustion chamber 3. A fuel injection valve 15 that directly injects fuel into the combustion chamber 3 is disposed on the side of the combustion chamber 3 on the intake passage 4 side. The fuel that has been regulated to a predetermined pressure by the high-pressure fuel pump 16 and the pressure regulator 17 is supplied to the fuel injection valve 15 via the high-pressure fuel passage 18. Therefore, when the fuel injection valve 15 of each cylinder is opened by the control pulse, an amount of fuel corresponding to the valve opening period is injected. Reference numeral 19 denotes a fuel pressure sensor for detecting the fuel pressure, and reference numeral 20 denotes a low-pressure fuel pump that sends fuel to the high-pressure fuel pump 16.

  In addition, the internal combustion engine 1 is provided with a water temperature sensor 21 for detecting the engine cooling water temperature and a crank angle sensor 22 for detecting a crank angle. Further, an accelerator opening sensor 23 is provided for detecting the amount of depression of the accelerator pedal by the driver.

  The fuel injection amount, injection timing, ignition timing, etc. of the internal combustion engine 1 are controlled by the control unit 25. The control unit 25 receives detection signals from the various sensors described above. The control unit 25 determines whether to use a combustion method, that is, homogeneous combustion or stratified combustion, according to the engine operating conditions detected by these input signals, and in response to this, opens the electronic control throttle valve 7. The fuel injection timing and fuel injection amount of the fuel injection valve 15, the ignition timing of the spark plug 14, and the like are controlled. After the warm-up is completed, in a predetermined region on the low-speed and low-load side, as normal stratified combustion operation, fuel injection is performed at an appropriate timing in the compression stroke, and ignition is performed at a timing before the compression top dead center. Done. The fuel spray is collected in the vicinity of the spark plug 14 in a layered manner, thereby realizing extremely lean stratified combustion with an air-fuel ratio of about 30 to 40. Further, in a predetermined region on the high speed and high load side, as normal homogeneous combustion operation, fuel injection is performed during the intake stroke, and ignition is performed in the vicinity of the MBT point before the compression top dead center. In this case, the fuel becomes a homogeneous mixture in the cylinder. As the homogeneous combustion operation, there are homogeneous stoichiometric combustion in which the air-fuel ratio is the stoichiometric air-fuel ratio and homogeneous lean combustion in which the air-fuel ratio is lean about 20 to 30 depending on the operating conditions.

  The present invention performs super retard combustion so that the exhaust gas temperature becomes high at the time of cold start of the internal combustion engine 1 where early temperature rise of the catalytic converter 10 is required. The fuel injection timing and ignition timing will be described with reference to FIG.

  FIG. 2 shows three examples of super retard combustion. In Example 1, the ignition timing is set to 15 ° to 30 ° ATDC (for example, 20 ° ATDC), and the fuel injection timing (specifically, the fuel injection start timing) is shown. Is set after the compression top dead center and before the ignition timing. At this time, the air-fuel ratio is set to the stoichiometric air-fuel ratio or slightly lean (about 16 to 17).

  That is, in order to promote catalyst warm-up and reduce HC, ignition timing retardation is effective, and ignition after top dead center (ATDC ignition) is desirable, but in order to perform stable combustion with ATDC ignition, It is necessary to shorten the combustion period, and for this purpose, flame propagation due to turbulence must be promoted. As described above, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but in the present invention, by the high pressure fuel injection performed during the expansion stroke after the compression top dead center. The gas flow is generated, and thereby the turbulence in the cylinder can be generated and strengthened. Therefore, flame propagation by ATDC ignition is promoted and stable combustion is possible.

  The second embodiment in FIG. 2 is an example in which the fuel injection is divided into two, and the first fuel injection is performed during the intake stroke, and the second fuel injection is performed after the compression top dead center. The ignition timing and the air-fuel ratio (the air-fuel ratio obtained by combining the two injections) are the same as those in the first embodiment.

  Thus, if fuel injection (intake stroke injection) is performed during the intake stroke prior to fuel injection after compression top dead center (expansion stroke injection), the disturbance due to fuel spray in the intake stroke injection is attenuated in the latter half of the compression stroke. However, since the injected fuel is diffused throughout the combustion chamber and contributes to the promotion of HC afterburning by ATDC ignition, the HC reduction and It is effective for raising the exhaust temperature.

  In the third embodiment of FIG. 2, the fuel injection is divided into two, the first fuel injection is performed in the compression stroke, and the second fuel injection is performed after the compression top dead center. As described above, when the fuel injection (compression stroke injection) is performed during the compression stroke prior to the fuel injection after the compression top dead center (expansion stroke injection), the compression stroke injection is compared with the intake stroke injection of the second embodiment. However, since the disturbance of the turbulence due to the fuel spray is delayed, the turbulence due to the first fuel injection remains, and the second fuel injection is performed after the compression top dead center, which is generated by the first fuel injection. The turbulence can be strengthened to promote the turbulence, and the gas flow can be further strengthened near the compression top dead center.

  In the case of Example 3, the first compression stroke injection may be in the first half of the compression stroke, but if it is set in the second half of the compression stroke (after 90 ° BTDC), the disturbance near the top dead center can be further increased. In particular, if the first compression stroke injection is 45 ° BTDC or later, more desirably 20 ° BTDC or later, the gas flow after compression top dead center can be further enhanced.

  As described above, according to the super retarded combustion of the first to third embodiments, the turbulence in the cylinder can be generated and strengthened by the fuel spray immediately before the ignition, and the flame propagation is promoted to perform stable combustion. be able to. In particular, by retarding the ignition timing from 15 ° to 30 ° ATDC, a sufficient afterburning effect for early activation of the catalyst and reduction of HC can be obtained. In other words, even if the ignition timing is greatly delayed in this way, the fuel injection is delayed until just before that, and the generation time of the turbulence is also delayed, so that the combustion improvement by improving the flame propagation can be achieved.

  Next, the control at the time of cold start related to the fuel pressure will be described. Here, as the super retard combustion, the third embodiment of FIG. 2 described above (the fuel injection is divided into two, the first fuel injection is performed during the compression stroke, and the second fuel injection is performed at the compression top dead center. 2) will be described as an example, but the embodiment 1 or the embodiment 2 in FIG. 2 may be used. When starting from a cold state, it is desirable to perform super retarded combustion immediately after starting to increase the exhaust gas temperature as described above, but immediately after starting (for example, about 1 to 2 seconds from the start of cranking). In the meantime, the fuel pressure is insufficient, and smoke and HC deteriorate. FIG. 4 shows the change in fuel pressure after cranking is started, which is similar to the rise in engine speed, but after cranking starts, for example, an initial explosion occurs near point a, and further engine rotation occurs. As the number increases, the fuel pressure reaches the target fuel pressure. FIG. 5 shows the relationship between the fuel pressure and the fuel particle size when fuel is injected near the compression top dead center. As shown, the lower the fuel pressure, the larger the particle size. Smoke and HC deteriorate.

  Therefore, in this embodiment, as shown in FIG. 3B, the fuel pressure reaches the predetermined pressure P1 in FIG. 4 (for example, set to about 2 MPa which is equal to or higher than the in-cylinder pressure at the compression top dead center). Compared with the super retard combustion when the fuel pressure is sufficient ((a) of FIG. 3), the injection amount of the expansion stroke injection I2 after the compression top dead center is reduced, and the compression stroke injection I1 before the compression top dead center The injection is increased. At this time, as the injection amount of the expansion stroke injection I2 decreases, the ignition timing ADV is advanced. The fuel injected as the compression stroke injection I1 during the compression stroke diffuses into the cylinder before the injection timing of the expansion stroke injection I2 and forms a lean air-fuel mixture, so that smoke and HC deteriorate even if the fuel pressure is somewhat low Is suppressed.

  At this time, the ratio between the expansion stroke injection I2 and the compression stroke injection I1 is different depending on the fuel pressure, and the ratio is controlled so that the ratio of the expansion stroke injection I2 decreases as the fuel pressure decreases. Therefore, smoke and HC deterioration at the stage where the fuel pressure is low are surely avoided.

  Under the condition that the fuel pressure is very low and the expansion stroke injection I2 is equal to or shorter than the predetermined minimum injection time, the entire amount of fuel is injected during the compression stroke, as shown in FIG. That is, the ratio of the expansion stroke injection I2 is 0, and the compression stroke injection I1 is 100%. Specifically, when the fuel pressure is lower than the pressure P2 in FIG. 4, the entire amount of fuel is injected during the compression stroke.

  Therefore, the change in the mode of injection over time from the start of cranking changes in three stages. First, during the first stage where the fuel pressure is very low, specifically, the fuel pressure from the start of cranking Until the pressure P2 is reached, the entire amount of fuel is injected during the compression stroke as shown in FIG. At this injection timing, the in-cylinder pressure is lower than the compression top dead center, and mixing is also accelerated before ignition. Therefore, even if the fuel pressure is low, the initial explosion can be started reliably, and smoke and HC Deterioration is avoided. Next, in the second stage in which the fuel pressure is between P2 and P1 in FIG. 4, the injection is performed in the form divided into the expansion stroke injection I2 and the compression stroke injection I1 as shown in FIG. 3B. . In this state, since the ignition timing is retarded from the compression top dead center, the action of increasing the exhaust gas temperature is started early while suppressing the deterioration of smoke and HC. Then, in the third stage after the fuel pressure reaches the pressure P1 in FIG. 4, the original super retarded combustion shown in FIG. 3A is performed, and the effect of raising the exhaust gas temperature is obtained to the maximum.

  The particle size of the fuel spray is also influenced by the fuel temperature, and the particle size increases as the fuel temperature decreases. Therefore, the injection amount ratio between the expansion stroke injection I2 and the compression stroke injection I1 may be corrected so that the injection amount of the expansion stroke injection I2 decreases as the fuel temperature decreases.

  FIG. 6 is a flowchart showing an example of the super retard combustion switching process based on the above-described fuel pressure. First, in step 1, it is determined whether or not there is an exhaust temperature increase request based on the intake air temperature, the oil water temperature, etc. If requested, the process proceeds to the super retard control in step 2. If there is no exhaust temperature increase request, the routine proceeds to step 7 for normal injection control. Here, the entire amount of fuel is injected before the compression top dead center, that is, during the compression stroke or the intake stroke.

  In step 3, it is determined whether the fuel pressure is less than or equal to a predetermined value. If the fuel pressure is less than or equal to the predetermined value, in step 5, as described above, the injection amount of the expansion stroke injection is reduced and the injection during the compression stroke or the intake stroke The fuel injection divided into two times is executed with the amount increased. If the fuel pressure is sufficient, the process proceeds to step 4, and it is determined whether the fuel temperature is equal to or lower than a predetermined value. If the fuel temperature is sufficiently high, the process returns to step 2 to perform predetermined super retard combustion. In step 5, more specifically, the injection amount of the expansion stroke injection and the injection amount of the injection during the compression stroke or the intake stroke are set according to the fuel pressure and the fuel temperature. In step 6, it is determined whether the injection amount of the expansion stroke injection is not less than a predetermined lower limit value. If it is less than the lower limit value, the routine proceeds to normal injection control in step 7.

  The super retarded combustion of the present invention can also be used for releasing sulfur poisoning when a NOx trap catalyst is used as the exhaust system catalytic converter 10. The NOx trap catalyst adsorbs NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releases the adsorbed NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is rich, and purifies by catalytic action. However, when the sulfur component (SOx) in the fuel is bound to the catalyst, the NOx adsorption performance is lowered. For this reason, it is necessary to perform a treatment (so-called sulfur poisoning release) for forcibly raising the temperature of the catalyst and releasing SOx at an appropriate time. The super retarded combustion according to the present invention can obtain a very high exhaust temperature, and therefore is suitable for the sulfur poisoning release processing of the NOx trap catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the system structure of the whole internal combustion engine which concerns on this invention. The characteristic view which shows the fuel injection timing and ignition timing of the super retard combustion of this invention. The characteristic view which shows an example of the fuel injection timing according to fuel pressure, and an ignition timing. The characteristic view which shows the fuel pressure change at the time of engine starting. The characteristic view which shows the relationship between a fuel pressure and a fuel particle size. The flowchart which shows the process of switching control of super retarded combustion. Explanatory drawing which shows the change of the disturbance in a cylinder in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Combustion chamber 10 ... Catalytic converter 14 ... Spark plug 15 ... Fuel injection valve 19 ... Fuel pressure sensor 25 ... Control unit

Claims (8)

In a direct injection type spark ignition internal combustion engine control device having a fuel injection valve for directly injecting fuel into a cylinder and having an ignition plug, the ignition timing is compression top dead center in a predetermined operating state. While being set later, super retard combustion is performed in which fuel is injected before this ignition timing and after compression top dead center, while the fuel injection amount after compression top dead center does not become zero during the period immediately after the start when the fuel pressure is low A control device for an in-cylinder direct injection spark ignition internal combustion engine, characterized in that a part of the fuel is injected in the latter half of the compression stroke so as to decrease at the same time. 2. In-cylinder direct injection spark ignition according to claim 1, wherein in super retard combustion, the entire amount of fuel is injected after compression top dead center, and when the fuel pressure is low, a part of the fuel is injected in the latter half of the compression stroke. Control device for internal combustion engine. In super retard combustion, the fuel injection is divided into two times, the first injection is performed in the latter half of the compression stroke, the second injection is performed after the compression top dead center, and when the fuel pressure is low, the ratio of the second injection amount is decreased. 2. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 1, wherein: 2. The direct injection spark ignition internal combustion engine according to claim 1 , wherein the entire amount of fuel is injected before the compression top dead center under the condition that the injection after the compression top dead center is equal to or shorter than a predetermined minimum injection time. Engine control device. The in-cylinder direct injection type according to any one of claims 1 to 4 , wherein the injection amount ratio between the injection after the compression top dead center and the injection before the compression top dead center is corrected according to the fuel temperature. Control device for spark ignition internal combustion engine. The in-cylinder direct injection spark-ignition internal combustion engine according to any one of claims 1 to 5 , wherein the super retard combustion is executed when a temperature increase of the exhaust gas is required as a predetermined operation state. Engine control device. The in-cylinder direct injection spark ignition internal combustion engine control device according to any one of claims 1 to 6 , wherein the ignition timing in the super retard combustion is 15 ° to 30 ° CA after compression top dead center. A control method for an in-cylinder direct injection spark ignition internal combustion engine having a fuel injection valve for directly injecting fuel into a cylinder and having an ignition plug, wherein the fuel pressure is a predetermined pressure when starting in an engine cold state In the first stage at the beginning of the start, which is lower than P2, the entire amount of fuel is injected during the intake stroke before the compression top dead center or during the compression stroke and ignited before the compression top dead center, and the fuel pressure is a predetermined pressure P1. (However, in the second stage between P1> P2) and P2, a part of the fuel is injected in the latter half of the compression stroke , and the remaining fuel is injected after the compression top dead center. In the third stage in which ignition is performed after the compression top dead center and the fuel pressure reaches P1, the super retarded combustion in which the ratio of the fuel injection amount after the compression top dead center is larger than that in the second stage. In-cylinder direct injection spark ignition internal combustion engine Control method.

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