JP4196900B2 - Combustion switching control system for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a combustion switching control system for a compression ignition internal combustion engine that controls combustion switching in a compression ignition internal combustion engine that performs so-called premixed combustion and normal combustion that is diffusion combustion.

  In a compression ignition internal combustion engine, when premixed combustion is performed for the purpose of suppressing NOx and smoke, as the operation state of the compression ignition internal combustion engine becomes a high load operation state and the engine load and the engine speed increase, The possibility of premature ignition increases. Therefore, a technique for performing premixed combustion at low / medium loads and normal combustion at high loads based on the operating state of the compression ignition internal combustion engine is disclosed (for example, see Patent Document 1). . In this technique, switching from premixed combustion to normal combustion is performed via multistage injection in which both premixed combustion and normal combustion are performed during one cycle. As a result, it is intended to facilitate combustion switching.

In addition, the amount of recirculated exhaust (so-called EGR gas, including already burned gas) supplied to the cylinder differs greatly between when premixed combustion is performed in a compression ignition internal combustion engine and when normal combustion is performed. . That is, in premixed combustion, a larger amount of EGR gas is required than in normal combustion in order to suppress premature ignition. Therefore, when switching between premixed combustion and normal combustion in a compression ignition internal combustion engine, a technique for switching between premixed combustion and normal combustion when the EGR gas amount becomes an amount suitable for switching between combustions has been disclosed. (For example, refer to Patent Document 2).
JP-A-11-324964 JP 2003-286876 A JP 2002-327638 A JP 2003-286880 A

  In a compression ignition internal combustion engine that switches between premixed combustion and normal combustion according to the operating condition, combustion switching is smoothly performed while avoiding unstable combustion and worsening of emissions when switching combustion. Therefore, fuel injection control different from the fuel injection control performed in the premixed combustion and the normal combustion is performed. As the fuel injection control at the time of this combustion switching, there is a case where multi-stage injection constituted by a plurality of fuel injections is performed for the above purpose.

  Here, when the fuel injection valve of the compression ignition internal combustion engine is connected to a pressure accumulating chamber such as a so-called common rail, more precise control of the fuel injection amount is possible by injecting fuel pressurized to a constant pressure. It becomes. However, if multiple fuel injections are performed at the time of combustion switching as described above, the injection pressure in the subsequent fuel injection fluctuates due to the pressure fluctuation in the pressure accumulating chamber caused by the previous fuel injection, and the accurate fuel injection amount Control becomes difficult. As a result, it may be difficult to achieve the purpose of fuel injection control during combustion switching.

  In the present invention, in view of the problems described above, in a compression ignition internal combustion engine that switches between premixed combustion and normal combustion in accordance with the operating state of the compression ignition internal combustion engine, variations in fuel injection amount at the time of combustion switching are made as much as possible. The purpose is to suppress combustion to smoother combustion switching.

In order to solve the above-described problems, the present invention provides a first fuel injection and a subsequent fuel injection when performing fuel injection a plurality of times in fuel injection control when switching from premixed combustion to normal combustion is performed. We focused on the fuel injection interval. Although the subsequent fuel injection amount varies due to the pressure fluctuation in the pressure accumulating chamber caused by the previous fuel injection, there is a fuel injection interval in which the variation is substantially constant regardless of the previous fuel injection amount. Therefore, by controlling fuel injection at the time of combustion switching according to this fuel injection interval, it becomes possible to more accurately control the fuel injection amount at the time of combustion switching, and smoother combustion switching can be achieved.

  Specifically, the present invention includes a pressure accumulating chamber for storing pressurized compression ignition internal combustion engine fuel, a fuel injection valve for injecting fuel stored in the pressure accumulating chamber into a cylinder of the compression ignition internal combustion engine, Combustion region determination means for determining which of the combustion regions corresponding to the combustion performed in the compression ignition internal combustion engine belongs to the operation state of the compression ignition internal combustion engine, and is determined by the combustion region determination unit By controlling the fuel injection condition of the fuel injection valve in accordance with the combustion region to be generated, so that premixed combustion is performed by forming a premixed gas by fuel injection earlier than the timing near the top dead center of the compression stroke; A combustion switching control system for a compression ignition internal combustion engine that switches between normal combustion performed by fuel injection at a timing near the top dead center of the compression stroke, wherein the compression ignition internal combustion engine is operated by the combustion region determination means When it is determined that the combustion region to which the operating state belongs has shifted from the premixed combustion region in which the premixed combustion is performed to the normal combustion region in which the normal combustion is performed, the premixed fuel injection during the premixed combustion is performed. The pre-injection near the fuel injection timing of the fuel injection is changed to the main injection performed at a predetermined interval from the pre-injection, and the interval between the pre-injection and the main injection is changed over time after the change of the fuel injection. Is maintained at the predetermined interval, the injection timing of the main injection is shifted toward the fuel injection timing near the top dead center of the compression stroke in normal combustion, and the fuel injection amount of the pre-injection is reduced and the main injection The combustion switching control means for switching the combustion performed in the compression ignition internal combustion engine from the premixed combustion to the normal combustion by increasing the amount of fuel injection.

  In the compression ignition internal combustion engine described above, the combustion region to which the operating state determined by the engine rotational speed, the engine load, etc. of the compression ignition internal combustion engine belongs, that is, the combustion region determined by the combustion region determination means is premixed. The combustion performed in the internal combustion engine is determined depending on whether the premixed combustion region where combustion is performed or the normal combustion region where normal combustion is performed. The premixed combustion region and the normal combustion region are determined by experiments or the like based on the likelihood of premature ignition during premixed combustion.

  Here, when premixed combustion is performed in a compression ignition internal combustion engine, the fuel injection is performed at a timing near the top dead center of the compression stroke, that is, at a timing earlier than the fuel injection timing at the time of normal combustion, thereby further mixing the intake air and the fuel. A premixed gas mixture is formed. As a result, NOx and smoke are suppressed. During normal combustion, so-called diffusion combustion is performed by injecting fuel at a time near the top dead center of the compression stroke.

  When the pre-combustion combustion is performed in the compression ignition internal combustion engine, the operating state of the compression ignition internal combustion engine fluctuates and the combustion region determined by the combustion region determination means shifts from the premix combustion region to the normal combustion region, Switching from premixed combustion to normal combustion is performed. At this time, the fuel injection control by the combustion switching control means is performed so that the combustion state does not become unstable and the emission does not deteriorate. Note that the premixed combustion in the present invention is not limited to the case where the premixed fuel is injected by a single fuel injection, but a plurality of times of fuel injection for reasons such as avoiding the fuel from adhering to the inner wall surface of the cylinder. This includes the case where the premixed fuel is injected.

The feature of fuel injection control by this combustion switching control means is that fuel injection at the time of combustion switching is two-stage injection of pre-injection and main injection, and the fuel injection interval between pre-injection and main injection is predetermined. It is a point to keep at intervals. Here, in this two-stage injection, immediately after the start of the two-stage injection, the pre-injection fuel injection timing is set close to the fuel injection timing at the time of premix combustion, so that the combustion state in the compression ignition internal combustion engine is premix combustion. Avoid sudden changes from. Then, by performing main injection at a predetermined interval after pre-injection, the basis of fuel injection in normal combustion after combustion switching is formed.

  The predetermined interval that is the fuel injection interval between the pre-injection and the main injection is a substantially constant variation in the fuel injection amount of the main injection after the pre-injection due to the pressure fluctuation in the pressure accumulating chamber that occurs when the pre-injection is performed. Is the fuel injection interval. The fuel injection valve is connected to a pressure accumulating chamber, which stabilizes the relationship between the opening time of the fuel injection valve and the fuel injection amount by always ensuring a constant injection pressure, thereby enabling more accurate fuel injection. Mainly for quantity control. Here, when the pre-injection is performed, the pressure in the pressure accumulating chamber fluctuates and pressure pulsation occurs. Therefore, as a result of the change in the injection pressure when the main injection is performed, the fuel injection amount of the main injection varies and it is difficult to accurately control it.

  However, due to the physical relationship such as the structure and volume of the pressure accumulator chamber and the distance of the oil passage between the fuel injection valve and the pressure accumulator chamber, the fuel injection amount of the main injection can be reduced even after the pre-injection. There is a fuel injection interval between the pre-injection and the main injection where the variation is stable, and this is the predetermined interval. In other words, the predetermined interval is a time during which the variation in the fuel injection amount of the main injection becomes substantially constant regardless of the ratio between the fuel injection amount of the pre-injection and the fuel injection amount of the main injection. it can. Therefore, by performing the pre-injection and the main injection at this predetermined interval, the valve opening time of the fuel injection valve is controlled in consideration of the stable variation in the fuel injection amount of the main injection, and the fuel injection amount of the main injection is reduced. It becomes possible to control accurately.

  Thereafter, the fuel injection timing of the main injection is shifted toward the fuel injection timing in the normal combustion, so that the switching from the premixed combustion to the normal combustion is advanced. At this time, the fuel injection interval between the pre-injection and the main injection is kept at a predetermined interval. Therefore, depending on the fuel injection timing of the pre-injection and the predetermined interval, when shifting the fuel injection timing of the main injection toward the fuel injection timing in normal combustion, the main injection may be advanced or delayed. is there.

  Further, when shifting the fuel injection timing of the main injection toward the fuel injection timing in the normal combustion, the fuel injection amount of the pre-injection is decreased and the fuel injection amount of the main injection is increased. That is, immediately after switching from premixed fuel injection during premixed combustion to preinjection and main injection, the fuel injection amount of preinjection is increased in order to avoid a sudden change in combustion state from premixed combustion. The fuel injection amount of the main injection is decreased, and finally the fuel injection amount of the pre-injection is decreased and the fuel injection amount of the main injection is increased so as to approach the normal combustion after switching.

  It should be noted that the control for changing the fuel injection timing and the fuel injection amount is preferably performed gradually in order to avoid a sudden change in the combustion state, but the combustion state does not become unstable or the emission does not deteriorate. It may be performed step by step in the range, or may be changed suddenly.

  As described above, the fuel injection control by the combustion switching control means is performed, so that the variation in the fuel injection amount when switching from the premixed combustion to the normal combustion according to the operation state of the compression ignition internal combustion engine, particularly the main injection. It is possible to suppress the variation in the fuel injection amount as much as possible. As a result, it is possible to more accurately control the fuel injection amounts of the pre-injection and the main injection at the time of combustion switching, so that smoother combustion switching can be performed.

  The fuel injection control by the combustion switching control means is executed when switching from premixed combustion to normal combustion. Conversely, when the combustion switching from the normal combustion to the premixed combustion is performed, if the fuel injection control by the combustion switching control means is reversibly executed, the smoother combustion switching can be similarly performed. .

Here, in the combustion switching control system of the compression ignition internal combustion engine, the fuel injection from the fuel injection valve when switching from premixed combustion to normal combustion by the combustion switching control means is performed during premixed combustion. The pre-injection close to the fuel injection timing and the main injection after the pre-injection at a predetermined interval from the pre-injection, and the fuel injection amount of the pre-injection A first fuel injection mode in which the fuel injection amount is greater than the fuel injection amount, the main injection close to the fuel injection timing during normal combustion, and the pre-injection before the main injection at a predetermined interval from the main injection. And a second fuel injection mode in which the fuel injection amount of the pre-injection is equal to or less than the fuel injection amount of the main injection.

  That is, as described above, the fuel injection control by the combustion switching control means is performed at the time of switching from the premixed combustion to the normal combustion, so that the combustion state in the compression ignition internal combustion engine is prevented from becoming unstable. In order to achieve smoother combustion switching, a first fuel injection mode that is close to fuel injection in premixed combustion and a second fuel injection mode that is close to normal combustion are provided. Since the first fuel injection mode is a fuel injection mode close to premixed combustion, the pre-injection fuel injection amount is larger than the main injection fuel injection amount. Further, since the second fuel injection mode is a fuel injection mode close to normal combustion, the pre-injection fuel injection amount is equal to or less than the main injection fuel injection amount.

  Naturally, in the first fuel injection mode and the second fuel injection mode, the fuel injection interval between the pre-injection and the main injection is maintained at the predetermined interval. When the fuel injection control by the fuel switching control means is performed, the premixed combustion is switched to the normal combustion in the order of the first fuel injection mode and the second fuel injection mode. As described above, the switching to the injection mode is considered to be performed gradually in order to avoid a sudden change in the combustion state, but stepwise within a range in which the combustion state does not become unstable or the emission does not deteriorate. Or you may go suddenly.

  In the combustion switching control system for the compression ignition internal combustion engine, the fuel injection start timing of the pre-injection in the first fuel injection mode may coincide with the fuel injection start timing of the premixed fuel injection. . This is because the first fuel injection mode is a fuel injection mode close to premixed combustion, so that the fuel injection start timing of pre-injection in the first fuel injection mode matches the fuel injection start timing of premixed combustion, It is possible to suppress the change in the combustion state as much as possible when shifting from the premixed combustion to the combustion in the first fuel injection mode.

  Furthermore, in order to suppress as much as possible the change in the combustion state when shifting from the premixed combustion to the combustion in the first fuel injection mode, paying attention to the fuel injection amount, the first fuel injection mode The sum of the fuel injection amount of the pre-injection and the fuel injection amount of the main injection may be the same as the fuel injection amount during premix combustion.

  In the combustion switching control system for the compression ignition internal combustion engine, the fuel injection start timing of the main injection in the second fuel injection mode is the same as that when the switching to normal combustion is performed by the combustion switching control means. You may make it correspond with the fuel injection start time of the fuel injection in the vicinity of the compression top dead center in normal combustion. This is because the second fuel injection mode is a fuel injection mode close to normal combustion, so that the second fuel injection mode matches the fuel injection start timing of main injection with the fuel injection start timing of normal combustion. It is possible to suppress the change in the combustion state as much as possible when shifting from the combustion in the fuel injection mode to the normal combustion.

In the combustion switching control system for a compression ignition internal combustion engine having the first fuel injection mode and the second fuel injection mode, the combustion in the compression ignition internal combustion engine is premixed according to the combustion region determined by the combustion region determination means. Alternatively, when switching to normal combustion, the switching combustion region boundary when switching from premixed combustion to normal combustion by the combustion switching control means is set higher than the switching combustion region boundary when switching from normal combustion to premixed combustion You may make it do.

  That is, when switching between premixed combustion and normal combustion, the standard for combustion switching depends on whether switching from premixed combustion to normal combustion or vice versa, that is, based on the direction of combustion switching. This changes the boundary of the combustion region. This is considered to be a case where the operation state stays for a relatively long time near the switching combustion region boundary where the premixed combustion and the normal combustion are switched depending on the operation state of the compression ignition internal combustion engine. In such a case, if the switching combustion region boundary is constant regardless of the direction of combustion switching, a so-called hunting state in which premixed combustion and normal combustion are frequently switched occurs.

  If a hunting state occurs during combustion switching, the combustion state becomes unstable and smooth combustion switching cannot be expected. Therefore, as described above, by changing the switching combustion region boundary based on the direction of combustion switching, hysteresis is given to the combustion switching control of the compression ignition internal combustion engine to suppress hunting. Here, it is a compression ignition internal combustion engine that sets the switching combustion region boundary when switching from premixed combustion to normal combustion to a higher load side than the switching combustion region boundary when switching from normal combustion to premixed combustion. This is because the premixed combustion or the normal combustion that is performed is continued as long as possible to avoid frequent combustion switching and instability of the combustion state.

  Further, in the combustion switching control system for a compression ignition internal combustion engine having the first fuel injection mode and the second fuel injection mode, when the combustion switching is performed by the combustion switching control means, the fuel injection in the second fuel injection mode is performed. A retention prohibiting means for immediately returning the combustion in the compression ignition internal combustion engine to the premixed combustion may be further provided when the performed time exceeds a predetermined residence time.

  When fuel injection is being performed in the second fuel injection mode, fuel injection control close to the mode of fuel injection during normal combustion is performed in the process of switching from premixed combustion to normal combustion. That is, the fuel injection amount at the time near the top dead center of the compression stroke is relatively large. On the other hand, since the combustion of the compression ignition internal combustion engine is not completely switched to normal combustion, the atmosphere at the time of premix combustion is not completely eliminated, for example, recirculation exhaust for avoiding premature ignition Still remains in the cylinder. Therefore, when fuel injection is performed in the second fuel injection mode, the combustion state tends to become unstable because the oxygen concentration in the cylinder is low and the fuel injection amount in the vicinity of the top dead center of the compression stroke is relatively large. .

  Therefore, if the fuel injection time in the second fuel injection mode exceeds the predetermined residence time, the combustion state becomes unstable, and there is a risk of misfire or deterioration of emission. In such a case, the combustion switching is forcibly interrupted in the compression ignition internal combustion engine that has been switched by the stay prohibiting means, and the combustion state is deteriorated by returning to premixed combustion again. Suppress. Therefore, the predetermined residence time is a threshold value that determines that the combustion state of the compression ignition internal combustion engine is deteriorated by continuing the fuel injection in the second fuel injection mode, and can be obtained in advance by an experiment or the like. is there.

  In the combustion switching control system for a compression ignition internal combustion engine having the first fuel injection mode and the second fuel injection mode, a part of the exhaust discharged from the compression ignition internal combustion engine is recirculated to an intake system. The first fuel injection mode, further comprising: a circulation device; and an EGR gas amount detection means for detecting or estimating an exhaust amount recirculated to the intake system of the compression ignition internal combustion engine by the exhaust gas recirculation device It is determined that the main injection becomes misfired based on the exhaust amount detected or estimated by the EGR gas amount detection means and the fuel injection conditions of the pre-injection and the main injection when fuel injection is performed by Then, the fuel injection timing of the main injection in the first fuel injection mode is advanced so that the interval between the pre-injection and the main injection is shorter than the predetermined interval. It may be.

  When fuel injection is being performed in the first fuel injection mode, fuel injection control close to the mode of fuel injection during premixed combustion is performed in the process of switching from premixed combustion to normal combustion. . Furthermore, the amount of exhaust gas recirculated by the exhaust gas recirculation device to avoid premature ignition is relatively large due to the influence of the combustion state during premixed combustion. For this reason, depending on the recirculation exhaust amount and the fuel injection amount, the injected fuel of the main injection may not burn well and may misfire. For example, when the recirculation exhaust amount is relatively large or when the pre-injection fuel injection amount is relatively small, there is a high possibility that the injected fuel of the main injection will misfire.

  Therefore, in such a case, it is possible to avoid as much as possible that the combustion state becomes a misfire state by shortening the fuel injection interval between the pre-injection and the main injection without maintaining the predetermined interval. In other words, maintaining the fuel injection interval at a predetermined interval more accurately controls the fuel injection amount of the main injection, so that the combustion switching is prioritized to more reliably avoid the combustion state from becoming a misfire state. Do. If it is determined that the main injection becomes misfired, and if it is determined that the misfire state does not occur, the fuel injection interval between the pre-injection and the main injection may be returned to the predetermined interval again.

  In the combustion switching control system for a compression ignition internal combustion engine having the first fuel injection mode and the second fuel injection mode, a part of the exhaust discharged from the compression ignition internal combustion engine is recirculated to an intake system. The second fuel injection mode, further comprising: a circulation device; and an EGR gas amount detection means for detecting or estimating an exhaust amount recirculated to the intake system of the compression ignition internal combustion engine by the exhaust gas recirculation device When the EGR gas amount is detected and estimated by the EGR gas amount detection means is larger than a predetermined gas amount, the fuel injection in the second fuel injection mode may not be performed. .

  As described above, when fuel injection is performed in the second fuel injection mode, fuel injection control close to the mode of fuel injection during normal combustion is performed in the process of switching from premixed combustion to normal combustion. Has been done. That is, the fuel injection amount at the time near the top dead center of the compression stroke is relatively large. On the other hand, since the combustion of the compression ignition internal combustion engine is not completely switched to normal combustion, the atmosphere at the time of premix combustion is not completely eliminated, and recirculation exhaust for avoiding premature ignition is not performed. It still remains in the cylinder. If the amount of fuel injection near the top dead center of the compression stroke is large with a relatively large amount of recirculated exhaust gas, there is a risk that the amount of soot generated will increase due to insufficient oxygen in the cylinder.

  Therefore, in such a case, the fuel injection in the second fuel injection mode is not performed, that is, the fuel injection in the first fuel injection mode is performed even in the state where the fuel injection is originally performed in the second fuel injection mode. By continuing the process, it becomes possible to avoid a large amount of soot.

  Here, in the combustion switching control system of the compression ignition internal combustion engine up to the above, when switching to the normal combustion is performed by the combustion switching control means, the timing earlier than the fuel injection in the vicinity of the compression stroke top dead center in the normal combustion In addition, pilot injection may be performed with a fuel injection interval for pilot with respect to the fuel injection. By performing the pilot injection, it is possible to suppress combustion noise during normal combustion.

  Here, the pilot fuel injection interval is a fuel injection interval that is different from the predetermined interval. That is, during normal combustion, unlike the combustion switching, the interval between two fuel injections (pilot injection and fuel injection near the top dead center of the compression stroke) is determined with emphasis on suppression of combustion noise.

  In the combustion switching control system for the compression ignition internal combustion engine, the pilot fuel injection interval and the predetermined interval may be determined based on control maps independent of each other.

  As described above, the pilot fuel injection interval is set to suppress combustion noise during normal combustion, and the predetermined interval is used to suppress variations in the fuel injection amount of the main injection caused by pressure fluctuations in the pressure accumulating chamber. Is set. When the transition to normal combustion is finally completed in the combustion switching, the combustion noise during normal combustion may become significant unless the front and rear fuel injection intervals are switched from the predetermined interval to the pilot fuel injection interval as soon as possible. There is. Therefore, by preparing a control map for determining each fuel injection interval independently and switching the control map when determining the fuel injection interval, the fuel injection interval is immediately changed from the predetermined interval to the pilot fuel injection interval. It is possible to switch.

  In a compression ignition internal combustion engine that switches between premixed combustion and normal combustion according to the operating state of the compression ignition internal combustion engine, variation in fuel injection amount at the time of combustion switching is suppressed as much as possible, and smoother combustion switching is achieved. Can be done.

  Here, an embodiment of a combustion switching control system for a compression ignition internal combustion engine according to the present invention will be described based on the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a compression ignition internal combustion engine (hereinafter simply referred to as “internal combustion engine”) 1 to which the present invention is applied and a control system thereof. The internal combustion engine 1 is a compression ignition type internal combustion engine having four cylinders 2. Further, a fuel injection valve 3 for directly injecting fuel into the combustion chamber of the cylinder 2 is provided. The fuel injection valve 3 is connected to a pressure accumulating chamber 4 that stores fuel pressurized to a predetermined pressure. An intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 is connected to a combustion chamber via an intake port. Similarly, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 is connected to a combustion chamber via an exhaust port. Here, the intake port and the exhaust port are provided with an intake valve and an exhaust valve, respectively.

  The intake branch pipe 7 is connected to the intake pipe 8. Further, an intake throttle valve 10 that adjusts the flow rate of the intake air flowing through the intake pipe 8 is located at a portion of the intake pipe 8 that is located immediately upstream of the intake branch pipe 7. An air flow meter 9 for detecting the amount of intake air flowing through the pipe 8 is provided. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10. On the other hand, the internal combustion engine 1 is provided with an EGR device 21. The EGR device 21 recirculates a part of the exhaust gas flowing through the exhaust branch pipe 12 to the intake branch pipe 7. The EGR device 21 includes an EGR passage 22 extending from the exhaust branch pipe 12 (upstream side) to the intake branch pipe 7 (downstream side), and an EGR for cooling EGR gas provided in order from the upstream side on the EGR passage 22. A cooler 23 and an EGR valve 24 for adjusting the flow rate of EGR gas are included.

  An intake pipe 8 positioned between the air flow meter 9 and the intake throttle valve 10 is provided with a compressor side of a supercharger 16 that operates using exhaust energy as a drive source. A turbine side is provided. Here, as shown in FIG. 2, the supercharger 16 is a two-stage supercharger in which a low-pressure supercharger 16b and a high-pressure supercharger 16a are configured in series. First, after being pressurized to the first stage supercharging pressure by the low pressure side supercharger 16b by exhaust, it is cooled by the intake air cooling intercooler 16c provided in the downstream intake pipe, and further, the high pressure side supercharger 16a. To increase the desired supercharging pressure. Here, the high-pressure side supercharger 16a in the supercharger 16 is a so-called variable displacement centrifugal supercharger, and is finally adjusted by adjusting the opening of the variable nozzle of the high-pressure side supercharger 16a. It is possible to finely adjust the supercharging pressure to be reached.

  Further, a bypass passage 17 for avoiding exhaust gas flowing into the turbine side of the high pressure side supercharger 16a of the supercharger 16 is provided from the site of the exhaust branch pipe 12 upstream of the high pressure side supercharger 16a. It connects with the site | part of the exhaust passage between the turbine side of the high voltage | pressure side supercharger 16a, and the turbine side of the low voltage | pressure side supercharger 16b. A flow path switching valve 18 for controlling the flow of exhaust gas in the bypass passage 17 is provided in the latter part. Therefore, when the flow path switching valve 18 is closed, the exhaust gas sequentially flows into the turbine side of the high pressure side supercharger 16a and the low pressure side supercharger 16b, so that the internal combustion engine 1 has a relatively high supercharge. Generate pressure. On the other hand, when the flow path switching valve 18 is open, the exhaust gas does not flow into the turbine side of the high-pressure supercharger 16a but flows into only the turbine side of the low-pressure supercharger 16b. Therefore, the supercharging performed by the supercharger 16 becomes a one-stage supercharging, and the final supercharging pressure is reduced as compared with the case where the flow path switching valve 18 is closed and the two-stage supercharging is performed. The switching of the exhaust flow by the flow path switching valve 18 is performed according to the combustion in the internal combustion engine 1, and the control thereof will be described later.

  Returning to FIG. 1, an intercooler 15 for cooling the intake air that has been pressurized by the high-pressure supercharger 16 a in the supercharger 16 and is heated to the intake pipe 8 downstream from the supercharger 16. Is provided. Further, the turbine side of the supercharger 16 is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected to a muffler downstream. An exhaust purification catalyst 14 that purifies exhaust from the internal combustion engine 1 is provided in the middle of the exhaust pipe 13.

  The internal combustion engine 1 is also provided with an electronic control unit (hereinafter referred to as “ECU”) 20 for controlling the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, and the like for storing various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  Here, the fuel injection valve 3 performs an opening / closing operation by a control signal from the ECU 20. That is, according to a command from the ECU 20, the fuel injection timing and the fuel injection amount from the fuel injection valve 3 are controlled for each injection valve in accordance with the operation state such as the engine load and engine speed of the internal combustion engine 1. In the internal combustion engine 1, premixed combustion or normal combustion is performed. The combustion control performed in the internal combustion engine 1 will be described later. Further, the opening degree of the EGR valve 24, the actuator 11, the variable nozzle of the high-pressure supercharger 16a, the opening / closing of the flow path switching valve 18 and the like are also controlled according to commands from the ECU 20.

  Further, an accelerator opening sensor 26 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the accelerator opening and calculates an engine load required for the internal combustion engine 1 based on the signal. The crank position sensor 25 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1, and the engine rotational speed of the internal combustion engine 1, the engine rotational speed and the gear. The vehicle speed or the like of the vehicle on which the internal combustion engine 1 is mounted is calculated from the ratio or the like.

  Further, the air flow meter 9 is electrically connected to the ECU 20, and the ECU 20 acquires the amount of intake air flowing through the intake pipe 8. Further, an in-cylinder pressure sensor 27 that detects the pressure in the cylinder 2 is provided, and the ECU 20 acquires the in-cylinder pressure by being electrically connected to the ECU 20. Further, an oxygen concentration sensor 28 for detecting the oxygen concentration of the intake air in the intake branch pipe 7 is provided, and the ECU 20 acquires the oxygen concentration of the intake air by being electrically connected to the ECU 20. Further, an intake pressure sensor 29 for detecting the intake pressure in the intake branch pipe 7 is provided, and the ECU 20 acquires the intake pressure by being electrically connected to the ECU 20.

Here, in the internal combustion engine 1 described above, switching between premixed combustion and normal combustion is performed based on the operating state of the internal combustion engine 1 represented by the engine speed and the engine load. FIG. 3 shows the relationship between the combustion region to which the operating state of the internal combustion engine 1 belongs and the combustion performed in the internal combustion engine 1. FIG. 3
The horizontal axis of the graph shown in FIG. 4 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1. Here, the operating state of the internal combustion engine 1 is represented by the engine rotational speed and the engine load, and belongs to one of the combustion regions of the premix combustion region R1 on the low load side and the normal combustion region R2 on the high load side.

  When the engine load of the internal combustion engine 1 increases and the amount of fuel supplied to the combustion chamber increases, or when the engine rotation speed increases and the substantial time for forming the premixed gas in the combustion chamber decreases, it is formed in the combustion chamber. The premixed gas mixture is not uniform and pre-ignition tends to occur. Therefore, when the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1 in which premature ignition can be avoided, premixed combustion is performed to improve emissions and reduce combustion noise. Further, when the internal combustion engine 1 belongs to the normal combustion region R2 where it is difficult to avoid premature ignition, high engine output is achieved by performing normal combustion which is so-called diffusion combustion instead of premixed combustion.

  As described above, premixed combustion or normal combustion is performed according to the combustion region to which the operating state of the internal combustion engine 1 belongs, but at the time of premixed combustion, the fuel injection timing is earlier than the timing near the top dead center of the compression stroke. As a result, fuel is injected from the fuel injection valve 3 to form a premixed gas in the cylinder 2. In order to suppress premature ignition at the time of premixed combustion, when the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1, the opening degree of the EGR valve 24 is set by the ECU 20 and the operating state of the internal combustion engine 1 is normally set. The EGR gas is controlled to be opened more than when belonging to the combustion region R2, and more EGR gas is supplied into the cylinder 2 through the intake branch pipe 7. That is, when premixed combustion and normal combustion are performed, the opening degree of the EGR valve 24 is controlled to an opening degree suitable for each combustion.

  Here, when premixed combustion is performed in the internal combustion engine 1, a relatively high boost pressure is required to introduce intake air into the cylinder 2. Therefore, during premix combustion, the flow path switching valve 18 is closed to increase the boost pressure in the internal combustion engine 1. On the other hand, at the time of normal combustion, the flow path switching valve 18 is opened to avoid the deterioration of the combustion state accompanying the increase in the exhaust pressure in the exhaust branch pipe 12.

  In the internal combustion engine 1 configured as described above, when the engine load of the internal combustion engine 1 increases and the combustion region to which the operating state of the internal combustion engine 1 belongs changes from the premixed combustion region R1 to the normal combustion region R2, premixing is performed. It is necessary to switch from combustion to normal combustion. However, even in such a case, even if the opening degree of the EGR valve 24 is controlled from the premixed combustion to the closing side suitable for normal combustion by a command from the ECU 20, the intake branch pipe 7 and the EGR passage The amount of EGR gas supplied into the cylinder 2 due to the volume of 22 or the like does not immediately change to the amount of EGR gas suitable for normal combustion. As a result, the combustion state may become unstable or the emission may be deteriorated.

  Therefore, at the time of switching from premixed combustion to normal combustion, the fuel injection valve is operated so that combustion according to the transient state is performed in the internal combustion engine 1 so that the combustion state does not become unstable or the emission deteriorates. The fuel injection from 3 is controlled. The fuel injection control at the time of the combustion switching will be described based on FIGS. 4 and 5.

  FIG. 4 shows the state of fuel injection when switching from premixed combustion to normal combustion is performed. The state of fuel injection during premixed combustion is shown in FIG. 4 (a). As the engine load of the internal combustion engine 1 increases, fuel injection is controlled in the order of FIGS. 4 (b) and 4 (c). Fuel injection during normal combustion is performed as shown in FIG.

First, during premix combustion, as shown in FIG. 4A, fuel injection is performed from the fuel injection valve 3 at a premix combustion injection start timing HCCI_ainj earlier than the compression stroke top dead center TDC. Incidentally, Q in the figure means the fuel injection amount. Therefore, in the present embodiment, switching from premixed combustion in which fuel injection of fuel injection amount 25 is performed at premixed combustion injection start timing HCCI_ainj to normal combustion is performed. The fuel injection amount in FIG. 4 is merely an example, and the embodiment of the present invention is not limited to this fuel injection amount.

  Here, fuel injection shown in FIG. 4B is performed as the first stage for normal combustion. The mode of fuel injection shown in FIG. 4B is referred to as a first fuel injection mode. In the first fuel injection mode, pre-injection that is performed at an early stage and two-stage injection that is performed after the pre-injection are performed. This is a transient combination of fuel injection in premix combustion before switching and fuel injection in normal combustion after switching so that the combustion state does not change suddenly when switching from premix combustion to normal combustion. This is a mode of fuel injection.

  At this time, the pre-injection fuel injection start timing Pre_ainj is coincident with the premixed combustion injection start timing HCCI_ainj, and the pre-injection fuel injection amount (Q = 23) and the main injection fuel injection amount (Q = 2). The sum is the same as the fuel injection amount (Q = 25) at the time of premix combustion just before switching. That is, in the first fuel injection mode at the stage where the combustion switching is started from the premixed combustion, it is possible to suppress a sudden change in the combustion state by approaching the fuel injection mode during the premixed combustion.

  Here, pressurized fuel stored in the pressure accumulating chamber 4 is injected from the fuel injection valve 3, but once the fuel injection valve 3 is opened, the pressure in the pressure accumulating chamber 4 is locally reduced. Are reflected on the inner wall of the pressure accumulating chamber 4 to cause pressure pulsation. This pressure pulsation attenuates with the passage of time, but even when the pressure pulsation is still remarkable, even if the fuel injection valve 3 is opened again to perform fuel injection, the injection pressure of the fuel injection valve 3 varies, so the valve opening time And the fuel injection amount vary, and it becomes difficult to accurately control the fuel injection amount. This causes a variation in the fuel injection amount of the main injection when performing the two-stage injection of the pre-injection and the main injection as shown in FIG.

  Furthermore, since the pressure fluctuation in the pressure accumulating chamber 4 increases as the fuel injection amount for pre-injection increases, the variation in the fuel injection amount for main injection also tends to increase. When the variation in the main injection amount becomes large, it becomes difficult to inject fuel corresponding to the combustion switching, and there is a possibility that the combustion state becomes unstable or the emission deteriorates.

  Therefore, in the first fuel injection mode, the fuel injection interval between the pre-injection and the main injection is maintained at the predetermined interval Pint2. The predetermined interval Pint2 is a time determined by the correlation between the fuel injection valve 3 and the pressure accumulating chamber 4. FIG. 5 shows the result of experimentally measuring the variation in the fuel injection amount of the main injection when pre-injection is performed from the fuel injection valve 3 and then main injection is performed. The horizontal axis of the graph of FIG. 5 is the fuel injection interval between the pre-injection and the main injection, and the vertical axis is the fuel injection variation ΔQ of the main injection. This variation is a difference between the fuel injection amount actually injected from the fuel injection valve 3 and the target fuel injection amount during the valve opening time for achieving the target fuel injection amount.

  In FIG. 5, the total fuel injection amount of the pre-injection and the main injection is the same amount, and the fuel injection mode is different in the ratio between the fuel injection amount of the pre-injection and the fuel injection amount of the main injection. A variation in the fuel injection amount of the main injection with respect to the injection interval is shown. As described above, the variation in the fuel injection amount of the main injection varies depending on the relationship between the pre-injection and the main injection, and among them, regardless of the ratio between the fuel injection amount of the pre-injection and the fuel injection of the main injection, There is a fuel injection interval in which the variation in the fuel injection amount of the main injection becomes substantially constant. In the present embodiment, it is recognized that the variation in the fuel injection amount of the main injection becomes substantially constant when the fuel injection interval is in the vicinity of 2.5 msec.

This is because the pressure pulsation generated in the pressure accumulating chamber 4 by opening the fuel injection valve 3 in the pre-injection becomes substantially constant depending on the shape of the pressure accumulating chamber 4 and the connection state between the fuel injection valve 3 and the pressure accumulating chamber 4. This can be considered as one of the causes. Therefore, the fuel injection interval at which the variation in the fuel injection amount of the main injection becomes substantially constant is determined according to the actual conditions of the fuel injection valve 3 and the pressure accumulating chamber 4.

  Here, if the predetermined interval Pint2 in the first fuel injection mode is set to a time in the vicinity of 2.5 msec, the variation in the fuel injection amount of the main injection can be made substantially constant regardless of the correlation between the pre-injection and the main injection. Therefore, it is possible to more accurately control the fuel injection amount of the main injection by adjusting the valve opening time of the fuel injection valve 3 in the main injection to eliminate the variation.

  In the first fuel injection mode, the pre-injection fuel injection start timing Pre_ainj is the same period as the premixed combustion injection start timing HCCI_ainj, and the valve opening time τ1 of the pre-injection is the target fuel injection amount. This is the time during which (Q = 23) can be injected. And after completion | finish of pre-injection, main injection is started with the predetermined space | interval Pint2. Accordingly, the fuel injection start timing Main_ainj of the main injection is a timing when the pre-injection valve opening time τ1 and the predetermined interval Pint2 have elapsed from the fuel injection start timing Pre_ainj of the pre-injection. Therefore, depending on the valve opening time τ1 of the pre-injection and the predetermined interval Pint2, it is determined whether the fuel injection start timing Main_ainj of the main injection is before or after the compression stroke top dead center TDC.

  Next, the fuel injection timings of the pre-injection and the main injection are shifted to the advance side as time elapses after the fuel injection in the first fuel injection mode is started. At this time, the fuel injection interval between the pre-injection and the main injection is maintained at a predetermined interval Pint2. As the fuel injection timing shifts to the advance side, the pre-injection fuel injection amount is decreased and the main injection fuel injection amount is increased.

  The shift of the fuel injection timing to the advance side is performed until the fuel injection start timing Main_ainj of the main injection coincides with the fuel injection timing in the vicinity of the compression stroke TDC in the normal combustion performed after the combustion switching. Thereby, the fuel injection mode at the time of combustion switching shifts from the first fuel injection mode to the second fuel injection mode. The state of fuel injection in the second fuel injection mode is shown in FIG.

  In the second fuel injection mode, as described above, the fuel injection amount (Q = 2) of the pre-injection is reduced from the fuel injection amount of the pre-injection in the first fuel injection mode, and the fuel injection amount of the main injection ( Q = 23) is increased from the fuel injection amount of the main injection in the first fuel injection mode. The fuel injection start timing Main_ainj of the main injection is the same period as the fuel injection timing in the vicinity of the compression stroke TDC in the normal combustion after the combustion switching, and the fuel injection interval between the pre-injection and the main injection is a predetermined interval Pint2. It is. Therefore, the pre-injection fuel injection start timing Pre_ainj is a time before the pre-injection valve opening time τ2 and the predetermined interval Pint2 from the main injection fuel injection start timing Main_ainj.

  From the above, the second fuel injection mode can be said to be a fuel injection mode that is closer to the fuel injection mode during normal combustion than the first fuel injection mode that is close to the fuel injection mode during premixed combustion. By passing through the second fuel injection mode, it becomes possible to smoothly switch the combustion from the premixed combustion to the normal combustion.

  Next, after the second fuel injection mode shown in FIG. 4 (c) is performed, the mode is switched to the fuel injection mode during normal combustion shown in FIG. 4 (d), and the combustion is switched from premixed combustion to normal combustion. Ends. In this embodiment, in addition to the main injection, pilot injection at a timing earlier than the main injection is performed. Unlike the pre-injection at the time of combustion switching, this pilot injection is not a fuel injection having a fuel injection interval that can suppress the variation in the fuel injection amount of the main injection shown in FIG. This fuel injection has a pilot fuel injection interval Pint0 that can suppress combustion noise caused by the main injection as much as possible with respect to the main injection.

  Therefore, during normal combustion, the fuel injection interval between the pilot injection and the main injection is set by giving priority to the suppression of the combustion noise of the main injection over the suppression of the variation in the fuel injection amount of the main injection caused by the pilot injection. Therefore, the pilot injection fuel injection start timing Pilot_ainj is a time before the pilot injection valve opening time τ3 and the pilot fuel injection interval Pint0 from the main injection fuel injection start timing Main_ainj.

  In this embodiment, the fuel injection amount immediately after the normal combustion switching is Q = 2 for pilot injection, Q = 25 for main injection, and Q = 27 in total. This is because the total fuel injection amount has increased in response to an increase in the engine load of the internal combustion engine 1 during the transition from premixed combustion to normal combustion.

  As shown in FIG. 4, when the premixed combustion is switched to the normal combustion, the fuel injection amount of the main injection can be varied as much as possible through the fuel injection modes of the first fuel injection mode and the second fuel injection mode. By performing the fuel injection more accurately while suppressing the above, smoother combustion switching is possible. Here, when switching the combustion from the premixed combustion to the normal combustion in the internal combustion engine 1, the combustion switching control shown in FIG. 6 is performed in order to perform smoother combustion switching. Hereinafter, the combustion switching control will be described. Note that the combustion switching control in the present embodiment is a routine that is repeatedly executed by the ECU 20 at a constant cycle.

  In S101, it is determined whether or not the operating state represented by the engine speed and the engine load of the internal combustion engine 1 belongs to the premixed combustion region R1. When it is determined that the operating state belongs to the premixed combustion region R1, the process proceeds to S102, and when it is determined that the operating state does not belong to the premixed combustion region R1, this control is terminated.

  In S102, it is determined whether or not the operating state of the internal combustion engine 1 determined to belong to the premixed combustion region R1 in S101 has shifted to the normal combustion region R2. That is, it is determined whether a change in the combustion region, which is a condition for switching the combustion in the internal combustion engine 1 from the premixed combustion to the normal combustion, has occurred. If it is determined that the operating state has shifted to the normal combustion region R2, the process proceeds to S103. If it is determined that the operating state has not shifted to the normal combustion region R2, this control is terminated.

  In S103, fuel injection in the first fuel injection mode shown in FIG. 4B is started. That is, the fuel injection is composed of two stages of pre-injection and main injection, and the fuel injection interval is maintained at the predetermined interval Pint2. Here, the predetermined interval Pint2 is calculated from the control map for calculating Pint2 shown in FIG. The control map is a control map in which a predetermined interval Pint2 corresponding to each engine rotation speed is stored using the engine rotation speed of the internal combustion engine 1 as a parameter.

  Then, as time passes after the fuel injection in the first fuel injection mode is started, as described above, the pre-injection and the main injection are shifted to the advance side while maintaining the fuel injection interval at the predetermined interval Pint2. At this time, the fuel injection amount of the main injection is increased while the fuel injection amount of the pre-injection is decreased. When the process of S103 ends, the process proceeds to S104.

  In S104, when performing fuel injection in the first fuel injection mode, the valve opening times of the fuel injection valves 3 in pre-injection and main injection are adjusted so that a target amount of fuel is injected. Specifically, the actual fuel injection amount from the fuel injection valve 3 can be influenced by a pressure difference between a predetermined pressure in the pressure accumulation chamber 4 (that is, fuel injection pressure) and the pressure in the cylinder 2. That is, at the opening timing of the fuel injection valve 3, the fuel injection amount per unit time decreases as the pressure in the cylinder 2 increases.

  Therefore, the valve opening time of the fuel injection valve 3 is determined based on the cylinder pressure detected by the cylinder pressure sensor 27, the intake pressure detected by the intake pressure sensor 29, and the fuel injection conditions for pre-injection and main injection. The target fuel is injected by pre-injection or main injection. For example, as the intake pressure detected by the intake pressure sensor 29 becomes higher, the opening time of the fuel injection valve 3 is corrected to be longer in order to inject a target amount of fuel, and at the time of main injection than during pre-injection. Since the pressure in the cylinder 2 is higher, the opening time of the fuel injection valve 3 is corrected to be longer than that during pre-injection in order to inject a target amount of fuel during main injection.

  Further, when determining the valve opening time of the fuel injection valve 3 at the time of main injection, the variation in the main injection amount that is stably generated by setting the fuel injection interval between the pre-injection and the main injection to the predetermined interval Pint2 is also taken into consideration. . When the process of S104 ends, the process proceeds to S105.

  In S105, it is determined whether or not a first predetermined time t1 has elapsed since the start of fuel injection in the first fuel injection mode. The first predetermined time t1 is a predetermined time during which fuel injection in the first fuel injection mode is continued when switching from premixed combustion to normal combustion is performed. When it is determined that the first predetermined time t1 has elapsed, the process proceeds to S106, and when it is determined that the first predetermined time t1 has not elapsed, the processes after S104 are performed again.

  In S106, fuel injection in the second fuel injection mode shown in FIG. 4C is started. That is, the fuel injection timing of the pre-injection and the main injection in the first fuel injection mode is advanced to make the fuel injection timing of the main injection near the top dead center in the compression stroke, and the fuel injection interval is set to the predetermined interval Pint2. Maintained. At this time, as described above, the fuel injection amount of the main injection is larger than the fuel injection amount of the pre-injection, which is close to the fuel injection mode during normal combustion. When the process of S106 ends, the process proceeds to S107.

  In S107, as in S104, when performing fuel injection in the second fuel injection mode, the valve opening times of the fuel injection valves 3 in pre-injection and main injection are adjusted so that a target amount of fuel is injected. The When the process of S107 ends, the process proceeds to S108.

  In S108, it is determined whether or not a second predetermined time t2 has elapsed since the start of fuel injection in the second fuel injection mode. The second predetermined time t2 is a predetermined time during which fuel injection in the second fuel injection mode is continued when switching from premixed combustion to normal combustion is performed. If it is determined that the second predetermined time t2 has elapsed, the process proceeds to S109, and if it is determined that the second predetermined time t2 has not elapsed, the processes after S107 are performed again.

  In S109, fuel injection at the time of normal combustion shown in FIG. 4 (d) is performed. During normal combustion, the above-described pilot injection is performed in addition to the main injection at the timing near the top dead center of the compression stroke. Here, the pilot fuel injection interval Pint0, which is the fuel injection interval between the pilot injection and the main injection, is a control map that is independent of the control map for calculating Pint2 shown in FIG. 7 (a). It is calculated from the control map for calculating Pint0 shown in FIG. The control map is a control map in which the pilot fuel injection interval Pint0 corresponding to each engine speed is stored using the engine speed of the internal combustion engine 1 as a parameter.

  As described above, the control map for calculating the predetermined interval Pint2 and the pilot fuel injection interval Pint0 is independent of the former in the fuel injection interval for suppressing variations in main injection due to pre-injection, and the latter is This is because it is a fuel injection interval for suppressing combustion noise due to main injection, and the setting purpose of each is different. As a result, it is possible to immediately switch from the fuel injection mode in the second fuel injection mode to the fuel injection mode during normal combustion, thereby more reliably suppressing combustion noise during normal combustion.

  According to this control, by performing fuel injection in the first fuel injection mode and the second fuel injection mode, it is possible to suppress variation in the fuel injection amount as much as possible and perform smoother combustion switching. In this control, the processing of S101 and S102 mainly corresponds to the combustion region determination means in the present invention, and the processing from S103 to S109 mainly corresponds to the combustion switching control means in the present invention.

  In this control, pre-injection and advancement of the fuel injection timing of the main injection are performed with the passage of time after the fuel injection in the first fuel injection mode is started, and the first predetermined time t1 has elapsed. Later, the fuel injection is switched to the second fuel injection mode. Here, without determining whether the first predetermined time t1 has elapsed, the fuel injection timing and the fuel injection amount of the pre-injection and the main injection are changed from the fuel injection in the first fuel injection mode, and the second fuel injection mode is used. You may make it transfer to fuel injection.

  The fuel injection at the time of combustion switching shown in FIG. 4 or FIG. 6 is performed at the time of switching from premixed combustion to normal combustion. Here, when switching from the normal combustion to the premixed combustion, the fuel injection control at the time of switching the combustion may be performed reversibly. That is, fuel injection in the second fuel injection mode is started from the state where normal combustion is performed. Then, with the passage of time, the pre-injection and the main injection are shifted to the retard side while maintaining the predetermined interval Pint2, the pre-injection fuel injection amount is increased, and the main injection fuel injection amount is decreased. Then, the shift to the premixed combustion is achieved through the fuel injection in the first fuel injection mode.

  Here, FIG. 8 shows the boundaries of the combustion region at the time of switching from premixed combustion to normal combustion and at the time of switching from normal combustion to premixed combustion. FIG. 8A is a boundary of the combustion region at the time of switching from premixed combustion to normal combustion, and is the same as the boundary of the combustion region shown in FIG. FIG. 8B is a boundary of the combustion region at the time of switching from normal combustion to premixed combustion, and this boundary is indicated by a solid line. In addition, the boundary of the dotted line in FIG.8 (b) is a boundary shown to Fig.8 (a). That is, when switching between normal combustion and premixed combustion in the internal combustion engine 1, the boundary of the combustion region for determining switching from premixed combustion to normal combustion is determined as switching from normal combustion to premixed combustion. Set to a higher load side than the boundary of the combustion region for

  As described above, hysteresis is applied to the boundary of the fuel region for determining the combustion switching depending on the direction of the combustion switching (switching from premixed combustion to normal combustion or switching from normal combustion to premixed combustion). By giving, it becomes possible to avoid a so-called hunting state at the time of combustion switching. Here, the boundary of the combustion region at the time of switching from the premixed combustion to the normal combustion is set on the higher load side than the boundary of the combustion region at the time of switching from the normal combustion to the premixed combustion. In order to prevent the combustion state from becoming unstable by reducing the frequency of combustion switching by continuing the combustion performed in 1 (either premixed combustion or normal combustion) as long as possible. is there.

  Next, another embodiment of the combustion switching control for switching the combustion from the premixed combustion to the normal combustion in the internal combustion engine 1 shown in FIG. 1 will be described based on FIG. 9 and FIG. Note that the combustion switching control in the present embodiment is a routine that is repeatedly executed by the ECU 20 at a constant cycle. Moreover, about the process same as combustion switching control shown in FIG. 6, detailed description is abbreviate | omitted by attaching | subjecting the same reference number.

In this embodiment, as shown in FIG. 10, the combustion region S1 (fuel injection in the first fuel injection mode is performed) to which the operating state of the internal combustion engine 1 for switching from premixed combustion to normal combustion belongs. Combustion region) and S2 (combustion region in which fuel injection is performed in the second fuel injection mode) are set. That is, when the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1, premixed combustion is performed in the internal combustion engine 1, and the combustion region to which the operating state belongs is S1, S2, R2 as the engine load increases. By changing, fuel injection corresponding to each combustion region described below is performed.

  In this control, if it is determined in S101 that the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1, the process proceeds to S201. In S201, when the operating state of the internal combustion engine 1 belongs to the combustion region S1 as the engine load increases, the fuel injection in the first fuel injection mode described above is executed. That is, the fuel injection is composed of two stages of pre-injection and main injection, and the fuel injection interval is maintained at the predetermined interval Pint2. And as time passes since the fuel injection in the first fuel injection mode is started, that is, as the engine load increases, the pre-injection and the main injection maintain the fuel injection interval at the predetermined interval Pint2, as described above. It is shifted to the advance side. At this time, the fuel injection amount of the main injection is increased while the fuel injection amount of the pre-injection is decreased. When the process of S201 ends, the process proceeds to S202.

  In S202, when the operating state of the internal combustion engine 1 belongs to the combustion region S2 as the engine load increases, the fuel injection in the second fuel injection mode described above is executed. That is, the fuel injection timing of the pre-injection and the main injection in the first fuel injection mode is advanced to make the fuel injection timing of the main injection near the top dead center in the compression stroke, and the fuel injection interval is set to the predetermined interval Pint2. Maintained. At this time, as described above, the fuel injection amount of the main injection is larger than the fuel injection amount of the pre-injection, and the fuel injection mode is close to the fuel injection mode during normal combustion. When the process of S202 ends, the process proceeds to S203.

  Here, the fuel injection in the second fuel injection mode has a fuel injection mode close to the fuel injection mode at the time of normal combustion in which the fuel injection amount of the main injection is larger than the fuel injection amount of the pre-injection as described above. . On the other hand, when switching from premixed combustion to normal combustion is performed, as described above, the opening degree of the EGR valve 24 is set to an opening degree suitable for normal combustion, that is, an opening degree that reduces the amount of EGR gas. . However, even if the opening degree of the EGR valve 24 is changed to the target opening degree, the amount of EGR gas in the cylinder 2 is not immediately changed to the target amount. Therefore, in the atmosphere in the cylinder 2 where the EGR gas is higher than that in the normal combustion, the fuel injection in the second fuel injection mode close to the fuel injection mode in the normal combustion is performed, so that the emission is deteriorated, and soot is generated. May become noticeable.

  Therefore, in S203, the operating state of the internal combustion engine 1 continuously stays in the combustion region S2 in order to avoid that the fuel injection time in the second fuel injection mode is prolonged and the generation of soot becomes significant. It is determined whether or not the existing S2 residence time ts2 exceeds the predetermined residence time t3. That is, it is determined whether or not the fuel injection in the second fuel injection mode executed in S202 is executed beyond the predetermined residence time t3. Therefore, the predetermined residence time t3 is a threshold value for determining that the generation of soot becomes significant as the fuel injection time in the second fuel injection mode becomes longer. If it is determined that the S2 residence time ts2 exceeds the predetermined residence time t3, the process proceeds to S204. If it is determined that the S2 residence time ts2 does not exceed the predetermined residence time t3, the process proceeds to S205.

  In S204, since the S2 residence time ts2 exceeds the predetermined residence time t3, there is a concern about the occurrence of soot, and even if the operation state of the internal combustion engine 1 belongs to the combustion region S2, the internal combustion engine 1 The combustion state is returned to premixed combustion. Accordingly, fuel injection as shown in FIG. 4A is performed. Further, not only the fuel injection mode but also the states of the EGR valve 24 and the supercharger 16 are set to a state corresponding to the premixed combustion. After the process of S204, this control is terminated.

In S205, when the operating state of the internal combustion engine 1 belongs to the normal combustion region R2, fuel injection during normal combustion shown in FIG. 4D is performed. Furthermore, during normal combustion, in addition to the main injection at the timing near the top dead center of the compression stroke, the above-described pilot injection is performed. After the process of S205, this control is terminated.

  According to this control, by performing fuel injection in the first fuel injection mode and the second fuel injection mode, it is possible to suppress variation in the fuel injection amount as much as possible and perform smoother combustion switching. Furthermore, by limiting the time during which fuel injection is performed in the second fuel injection mode, it becomes possible to avoid the occurrence of soot at the time of combustion switching. In this control, the process of S101 mainly corresponds to the combustion region determination means in the present invention, the process of S201 and S202 mainly corresponds to the combustion switching control means in the present invention, and the processes of S203 and S204 are mainly performed. This corresponds to the retention prohibiting means in the present invention.

  Next, another embodiment of the combustion switching control for switching the combustion from the premixed combustion to the normal combustion in the internal combustion engine 1 shown in FIG. 1 will be described based on FIG. Note that the combustion switching control in the present embodiment is a routine that is repeatedly executed by the ECU 20 at a constant cycle. Moreover, about the process same as the combustion switching control shown in FIG. 6, detailed description is abbreviate | omitted by attaching | subjecting the same reference number. In the present embodiment, as in the second embodiment, as shown in FIG. 10, combustion regions S1 and S2 to which the operating state of the internal combustion engine 1 for switching from premixed combustion to normal combustion belongs are set. Is done.

  In this control, if it is determined in S101 that the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1, the process proceeds to S301. In S301, as in S201 during the combustion switching control in the second embodiment, when the operating state of the internal combustion engine 1 belongs to the combustion region S1 as the engine load increases, the fuel injection in the first fuel injection mode described above is performed. Is executed. When the process of S301 ends, the process proceeds to S302.

  In S302, the ignition timing of the injected fuel of the main injection in the first fuel injection mode is estimated. Specifically, as the amount of EGR gas estimated based on signals from the oxygen concentration sensor 28 and the intake pressure sensor 29 increases, it is estimated that the ignition timing of the injected fuel by the main injection is delayed, and the injection by the pre-injection As the amount of fuel decreases, it is estimated that the ignition timing of the injected fuel by the main injection is delayed. When the process of S302 ends, the process proceeds to S303.

  In S303, based on the ignition timing of the injected fuel by the main injection estimated in S302, it is determined whether or not the injected fuel is in a misfire state without igniting. For example, if the estimated ignition timing is later than the reference timing, it is determined that the vehicle is misfiring. If it is determined in S303 that the fuel injected by the main injection is misfired, the process proceeds to S305, and if it is determined that the injected fuel is not misfired, the process proceeds to S304.

  In S304, the fuel injection interval between the pre-injection and the main injection in the first fuel injection mode is set to a predetermined interval Pint2. That is, if the fuel injection interval between the pre-injection and the main injection is the predetermined interval Pint2, that state is maintained, and when the fuel injection interval between the pre-injection and the main injection is shortened by S305 described later, the fuel injection interval To the predetermined interval Pint2. When the process of S304 ends, the process proceeds to S306.

In S305, the fuel injection interval between the pre-injection and the main injection in the first fuel injection mode is shortened. The fuel injection start timing of the main injection in the first fuel injection mode is after the elapse of the predetermined interval Pint2 from the end of the pre-injection as described above. This is to stabilize the variation in the fuel injection amount of the main injection due to the pre-injection. However, it is not preferable that the fuel injection start timing of the main injection is delayed by maintaining the predetermined interval Pint2 and the injected fuel enters a misfire state. Therefore, when it is determined in S303 that the injected fuel is in a misfire state, the fuel injection interval between the pre-injection and the main injection is shortened to prevent the injected fuel from the main injection from becoming in a misfire state. Prioritize. When the process of S305 ends, the process proceeds to S306.

  In S306, it is determined whether or not the amount of EGR gas supplied to the cylinder 2 estimated based on signals from the oxygen concentration sensor 28 and the intake pressure sensor 29 is larger than a predetermined gas amount E0. This predetermined gas amount E0 is a threshold value for determining whether or not to start fuel injection in the second fuel injection mode. In this control, when the operating state of the internal combustion engine 1 belongs to the combustion region R2, fuel injection in the second fuel injection mode is performed in principle. However, since the fuel injection in the second fuel injection mode is a fuel injection mode close to the fuel injection at the time of normal combustion as described above, the fuel injection mode in the second fuel injection mode with a relatively large amount of EGR gas in the cylinder 2 is used. When fuel injection is executed, soot formation becomes significant.

  Therefore, in this control, when the EGR gas amount supplied into the cylinder 2 is larger than the predetermined gas amount E0, even if the operating state of the internal combustion engine 1 belongs to the combustion region R2, the second fuel injection mode is used. Fuel injection is not performed, and fuel injection in the first fuel injection mode is continued. Therefore, if it is determined in S306 that the amount of EGR gas supplied to the cylinder 2 is greater than the predetermined gas amount E0, the processing from S302 is performed again. On the other hand, when the amount of EGR gas supplied to the cylinder 2 is equal to or less than the predetermined gas amount E0, the process proceeds to S307.

  In S307, fuel injection in the second fuel injection mode is executed while the EGR gas amount supplied to the cylinder 2 is equal to or less than the predetermined gas amount E0 and the operation state of the internal combustion engine 1 belongs to the combustion region S2. Is done. When the process of S307 ends, the process proceeds to S308.

  In S308, fuel injection during normal combustion shown in FIG. 4 (d) is performed when the operating state of the internal combustion engine 1 belongs to the normal combustion region R2. During normal combustion, the above-described pilot injection is performed in addition to the main injection at the timing near the top dead center of the compression stroke. After the processing of S308, this control is terminated.

  According to this control, by performing fuel injection in the first fuel injection mode and the second fuel injection mode, it is possible to suppress variation in the fuel injection amount as much as possible and perform smoother combustion switching. Furthermore, it is possible to avoid misfire when fuel injection is executed in the first fuel injection mode, and to avoid generation of soot when fuel injection is executed in the second fuel injection mode. In this control, the process of S101 mainly corresponds to the combustion region determination means in the present invention, and the processes from S301 to S308 mainly correspond to the combustion switching control means in the present invention.

It is a figure showing the schematic structure of the compression ignition internal combustion engine to which the combustion switching control system of the compression ignition internal combustion engine which concerns on the Example of this invention is applied. It is a figure showing schematic structure of the two-stage supercharger used for the combustion switching control system of the compression ignition internal combustion engine which concerns on the Example of this invention. In the combustion switching control system of the compression ignition internal combustion engine according to the embodiment of the present invention, it is a diagram showing a combustion region to which the operation state of the compression ignition internal combustion engine belongs. It is a figure which shows the transition of the fuel-injection aspect performed at the time of the switching from premix combustion to normal combustion in the combustion switching control system of the compression ignition internal combustion engine which concerns on the Example of this invention. In the combustion switching control system for a compression ignition internal combustion engine according to the embodiment of the present invention, the variation in the fuel injection amount in the rear fuel injection and the fuel injection interval of the two-stage injection when performing the two-stage injection from the fuel injection valve FIG. 4 is a flowchart relating to combustion switching control performed when switching from premixed combustion to normal combustion in the combustion switching control system for a compression ignition internal combustion engine according to the first embodiment of the present invention. In the combustion switching control system for a compression ignition internal combustion engine according to the first embodiment of the present invention, a control map for determining a fuel injection interval at the time of combustion switching and a control map for determining a fuel injection interval at the time of normal combustion are shown. FIG. In the combustion switching control system for a compression ignition internal combustion engine according to the first embodiment of the present invention, the boundary of the combustion region that determines the combustion switching from premixed combustion to normal combustion, and the combustion switching from normal combustion to premixed combustion It is a figure which shows the boundary of the combustion area | region which determines these. 7 is a flowchart relating to combustion switching control performed when switching from premixed combustion to normal combustion in a combustion switching control system for a compression ignition internal combustion engine according to a second embodiment of the present invention. In the combustion switching control system of the compression ignition internal combustion engine according to the second embodiment of the present invention, it is a diagram showing a combustion region to which the operation state of the compression ignition internal combustion engine belongs. It is a flowchart regarding the combustion switching control performed at the time of switching from the premixed combustion to the normal combustion in the combustion switching control system of the compression ignition internal combustion engine according to the third embodiment of the present invention.

Explanation of symbols

1. Compression compression internal combustion engine (internal combustion engine)
7 .... Intake branch pipe 8 .... Intake pipe 12 .... Exhaust branch pipe 16 .... Supercharger 20 .... ECU
21 ... EGR device 25 ... Crank position sensor 26 ... Accelerator opening sensor 27 ... In-cylinder pressure sensor 28 ... Oxygen concentration sensor 29 ... Intake pressure sensor R1・ ・ ・ ・ Premixed combustion area R2 ・ ・ ・ Normal combustion area Pint2 ・ ・ ・ Predetermined interval Pint0 ・ ・ ・ ・ ・ ・ Fuel injection interval for pilot

Claims (12)

A pressure accumulating chamber for storing fuel of a pressurized compression ignition internal combustion engine;
A fuel injection valve for injecting fuel stored in the pressure accumulating chamber into a cylinder of the compression ignition internal combustion engine;
Combustion region determination means for determining which operation state of the compression ignition internal combustion engine belongs to which of the combustion regions corresponding to the combustion performed in the compression ignition internal combustion engine,
By controlling the fuel injection condition of the fuel injection valve in accordance with the combustion region determined by the combustion region determining means, the premixed gas is formed by fuel injection earlier than the timing near the top dead center of the compression stroke. A combustion switching control system for a compression ignition internal combustion engine that performs switching between premixed combustion performed in this way and normal combustion performed by fuel injection at a timing near the compression stroke top dead center,
When it is determined by the combustion region determination means that the combustion region to which the operation state of the compression ignition internal combustion engine belongs has shifted from the premixed combustion region where premixed combustion is performed to the normal combustion region where normal combustion is performed, The premixed fuel injection at the time of combustion is changed to a pre-injection near the fuel injection timing of the premixed fuel injection and a main injection performed at a predetermined interval from the pre-injection, and the time elapsed after the change of the fuel injection Accordingly, the injection timing of the main injection is shifted toward the fuel injection timing in the vicinity of the compression stroke top dead center in the normal combustion in a state where the interval between the pre-injection and the main injection is maintained at the predetermined interval. Combustion switching control for switching combustion performed in the compression ignition internal combustion engine from premixed combustion to normal combustion by reducing the fuel injection amount of the injection and increasing the fuel injection amount of the main injection Combustion switching control system for a compression ignition internal combustion engine, characterized in that it comprises a stage.   The predetermined interval is a time during which a variation in the fuel injection amount of the main injection becomes substantially constant regardless of a ratio between the fuel injection amount of the pre-injection and the fuel injection amount of the main injection. Item 4. A combustion switching control system for a compression ignition internal combustion engine according to Item 1. Fuel injection from the fuel injection valve when switching from premixed combustion to normal combustion is performed by the combustion switching control means,
The pre-injection close to the fuel injection timing at the time of premixed combustion, the main injection after the pre-injection is performed at a predetermined interval with respect to the pre-injection, and the fuel injection amount of the pre-injection is set. A first fuel injection mode in which the fuel injection amount is greater than the main fuel injection amount;
The main injection close to the fuel injection timing at the time of normal combustion and the pre-injection before the main injection at a predetermined interval from the main injection are performed, and the fuel injection amount of the pre-injection is A second fuel injection mode in which the fuel injection amount is less than or equal to the main injection;
The combustion switching control system for a compression ignition internal combustion engine according to claim 1 or 2, characterized by comprising:   The combustion switching control system for a compression ignition internal combustion engine according to claim 3, wherein the fuel injection start timing of the pre-injection in the first fuel injection mode coincides with the fuel injection start timing of the premixed fuel injection. .   The fuel injection start timing of the main injection in the second fuel injection mode is the fuel injection start of the fuel injection in the vicinity of the compression top dead center in the normal combustion when switching to normal combustion is performed by the combustion switching control means 4. The combustion switching control system for a compression ignition internal combustion engine according to claim 3, wherein the timing coincides with the timing.   The sum of the fuel injection amount of the pre-injection and the fuel injection amount of the main injection in the first fuel injection mode is the same as the fuel injection amount during premixed combustion. The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 5 to 6.   Switching combustion when switching from premixed combustion to normal combustion by the combustion switching control means when switching combustion in the compression ignition internal combustion engine to premixed combustion or normal combustion according to the combustion region determined by the combustion region determining means The combustion switching of the compression ignition internal combustion engine according to any one of claims 3 to 6, wherein the region boundary is set to a higher load side than the switching combustion region boundary when switching from normal combustion to premixed combustion. Control system.   When combustion switching is performed by the combustion switching control means, if the time during which fuel injection is performed in the second fuel injection mode exceeds a predetermined residence time, the residence in which the combustion in the compression ignition internal combustion engine immediately returns to premixed combustion The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 3 to 6, further comprising prohibition means. An exhaust gas recirculation device for recirculating a part of the exhaust gas discharged from the compression ignition internal combustion engine to an intake system;
EGR gas amount detection means for detecting or estimating the amount of exhaust gas recirculated to the intake system of the compression ignition internal combustion engine by the exhaust gas recirculation device,
When fuel injection is performed in the first fuel injection mode, the main injection is performed based on the exhaust amount detected or estimated by the EGR gas amount detection means and the fuel injection conditions of the pre-injection and the main injection. Is determined to be in a misfire state, the fuel injection timing of the main injection in the first fuel injection mode is advanced so that the interval between the pre-injection and the main injection is shorter than the predetermined interval. A combustion switching control system for a compression ignition internal combustion engine according to any one of claims 3 to 6. An exhaust gas recirculation device for recirculating a part of the exhaust gas discharged from the compression ignition internal combustion engine to an intake system;
EGR gas amount detection means for detecting or estimating the amount of exhaust gas recirculated to the intake system of the compression ignition internal combustion engine by the exhaust gas recirculation device,
If the EGR gas amount detected or estimated by the EGR gas amount detection means is larger than a predetermined gas amount when fuel injection is performed in the second fuel injection mode, fuel injection in the second fuel injection mode is performed. The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 3 to 6, wherein the combustion switching control system is not performed.   When switching from premixed combustion to normal combustion is performed by the combustion switching control means, a pilot fuel injection interval is provided for the fuel injection at a time earlier than fuel injection near the compression top dead center in the normal combustion. The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 1 to 6, wherein pilot injection is performed.   The combustion switching control system for a compression ignition internal combustion engine according to claim 11, wherein the pilot fuel injection interval and the predetermined interval are determined based on mutually independent control maps.

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