JP4525373B2 - 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 amount of EGR gas 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 11-324762 A JP 2002-327638 A JP 2003-286880 A JP 2000-64911 A

  In a compression ignition internal combustion engine that switches between premixed combustion and normal combustion according to the operating state, there is a large difference in the amount of EGR gas to be supplied into the cylinder between premixed combustion and normal combustion. That is, during premix combustion, pre-ignition tends to occur due to its characteristics, so that a larger amount of EGR gas is required than during normal combustion in order to avoid it. Therefore, in a compression ignition internal combustion engine, when switching combustion from premixed combustion to normal combustion, it is necessary to switch the amount of EGR gas supplied into the cylinder to an amount corresponding to each combustion.

  Here, the amount of EGR gas into the cylinder is normally adjusted by controlling a parameter related to the amount of EGR gas such as supercharging pressure to a value corresponding to combustion by feedback control. However, it is desirable to change the EGR gas amount as quickly as possible when switching combustion. However, depending on the response characteristics of the feedback control, the EGR gas amount may be accurately and quickly changed to the target amount. May be difficult.

  In the present invention, in view of the above-described problems, in a compression ignition internal combustion engine that performs switching between premixed combustion and normal combustion in accordance with the operation state of the compression ignition internal combustion engine, feedback control of a control parameter related to the amount of EGR gas is performed. An object of the present invention is to control the control parameter so that an amount of EGR gas corresponding to combustion is supplied into the cylinder.

  In the present invention, in order to solve the above-described problem, in a combustion switching control system that switches from premixed combustion to normal combustion, part or all of feedback control related to supercharging pressure that is a control parameter performed at the time of combustion switching. And paying attention to a predetermined period of changing the feedback control. By changing the feedback control related to the supercharging pressure, it is possible to adjust the response characteristic and quickly supply the EGR gas into the cylinder. On the other hand, the time for changing the feedback control is unnecessarily long. Therefore, it is difficult to perform normal feedback control satisfactorily. Therefore, the change of the feedback control is limited to a predetermined period.

  Specifically, the present invention relates to a fuel injection valve that injects fuel of a compression ignition internal combustion engine into a cylinder, and an operation state of the compression ignition internal combustion engine in a combustion region corresponding to combustion performed in the compression ignition internal combustion engine. Combustion region determination means for determining which one belongs to, and EGR control means for controlling the opening degree of the EGR valve to recirculate an amount of EGR gas in the cylinder according to the combustion performed in the compression ignition internal combustion engine And controlling the fuel injection condition of the fuel injection valve in accordance with the combustion region determined by the combustion region determining means, so that the fuel injection at a time earlier than the time near the top dead center of the compression stroke is predicted. A combustion switching control system for a compression ignition internal combustion engine that switches between premixed combustion performed by forming an air-fuel mixture and normal combustion performed by fuel injection at a timing near the compression stroke top dead center. A turbocharger provided in a supply / exhaust system of the compression ignition internal combustion engine, the turbocharger having a variable nozzle in which the opening degree of the nozzle receiving the energy of the exhaust is variable, and the actual in the compression ignition internal combustion engine Variable nozzle opening feedback that performs feedback control of the variable nozzle opening of the supercharger so that the actual supercharging pressure that is the supercharging pressure of the turbocharger becomes the target supercharging pressure corresponding to the combustion performed in the compression ignition internal combustion engine When the pressure difference between the target boost pressure and the actual boost pressure in the feedback control is greater than or equal to a predetermined boost pressure at the time of switching from the control means and premixed combustion to normal combustion, the variable nozzle Variable nozzle opening feedback control changing means for temporarily changing the feedback control of the variable nozzle opening by the opening feedback control means to increase the supercharging pressure, and Periodically between, in accordance with the pressure difference increases, a combustion switching control system for a compression ignition internal combustion engine becomes long.

  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 compression ignition 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. Note that the premixed combustion in the present invention is not limited to the case where the premixed fuel is injected by one 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. 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 the time of switching the combustion, it is preferable to perform the combustion switching smoothly by performing fuel injection in a mode different from the fuel injection at the time of premixed combustion and the fuel injection at the time of normal combustion.

  Here, when premixed combustion and normal combustion are performed, an appropriate amount of EGR gas corresponding to each combustion is recirculated into the cylinder by the EGR control means. The amount of EGR gas is determined in consideration of the combustion characteristics of premixed combustion and normal combustion in order to avoid an increase in combustion noise and deterioration of emissions in each combustion state.

  The adjustment of the EGR gas amount is performed through the supercharging pressure associated therewith being controlled by the feedback control means. Specifically, when the boost pressure is increased by adjusting the opening of the variable nozzle of the supercharger, the amount of EGR gas supplied into the cylinder is reduced accordingly, and conversely, when the boost pressure is reduced, Along with this, the amount of EGR gas supplied into the cylinder is increased. In the feedback control related to the supercharging pressure, the EGR gas amount is adjusted to an amount suitable for combustion by controlling the actual supercharging pressure to the target supercharging pressure corresponding to the combustion.

  In the compression ignition internal combustion engine, for example, the supercharger is a centrifugal supercharger provided in a supply / exhaust system of the compression ignition internal combustion engine, and the high pressure side supercharger having the variable nozzle, You may make it comprise from the low voltage | pressure side supercharger which is a centrifugal supercharger provided in the exhaust system of the further downstream of the exhaust system in which the high voltage | pressure side supercharger was provided. That is, two units of the high-pressure side supercharger and the low-pressure side supercharger may be provided in series along the exhaust flow. In this case, the high pressure side supercharger performs supercharging by the energy of the exhaust gas having a relatively high pressure discharged from the compression ignition internal combustion engine. Here, the high-pressure side supercharger is provided with a variable nozzle whose opening degree is variable, whereby the degree of supercharging by the high-pressure side supercharger can be adjusted. Further, a low-pressure supercharger is provided downstream of the high-pressure supercharger in the exhaust flow. The supercharging nozzle provided in the low-pressure supercharger may or may not have a variable opening. By using these two turbochargers and feedback-controlling the opening of the variable nozzle of the high-pressure supercharger, the actual supercharging pressure is adjusted to the supercharging pressure suitable for combustion, that is, the target supercharging pressure. The

  Here, when switching from premixed combustion to normal combustion, it is necessary to quickly reduce the amount of EGR gas supplied into the cylinder from an amount suitable for premixed combustion to an amount suitable for normal combustion. That is, it is necessary to reduce the amount of EGR gas by quickly increasing the supercharging pressure. However, if pre-mixed combustion or normal combustion is being performed and the feedback control related to normal supercharging pressure is not being performed, the supercharging pressure is set with a sufficiently fast response speed when switching combustion. It is difficult to change. On the other hand, it is possible to reduce the amount of EGR gas by shutting off the EGR valve, but if the EGR valve shut off continues for a long period of time, it will be supplied to the cylinder when combustion switches to normal combustion. There is a risk that the amount of EGR gas produced becomes too small and the combustion state is deteriorated.

  Therefore, in the combustion switching control system described above, when the pressure difference between the actual supercharging pressure and the target supercharging pressure is increased to a predetermined supercharging pressure or higher, that is, when switching from premixed combustion to normal combustion is performed. When the feedback control of the variable nozzle opening by the variable nozzle opening feedback control means regarding the supercharging pressure becomes difficult to respond sufficiently quickly, and the error amount in the feedback control increases, the variable nozzle opening feedback control is changed. The feedback control of the variable nozzle opening is changed by means. Accordingly, the predetermined supercharging pressure is an error amount in feedback control for determining that the feedback control of the variable nozzle opening is to be changed. Note that the change of feedback control here refers to changing part or all of the control parameters to values different from those in the previous feedback control or interrupting the feedback control itself. In other words, it means the control related to the supercharging pressure different from the normal and the control of the EGR gas amount associated therewith.

Then, by changing the feedback control of the variable nozzle opening related to the supercharging pressure during the predetermined period, the time during which feedback control different from normal is performed is limited, and the response speed of the feedback control is temporarily increased to increase the feedback control. While increasing the supply pressure from the beginning, it is possible to suppress as much as possible the influence of a rapid fluctuation in the actual supercharging pressure that occurs as a side effect. Therefore, the predetermined period is a period for maintaining a balance between improving the response speed of feedback control and suppressing side effects thereof.

  Further, the predetermined period is not constant, and is variably controlled based on the pressure difference. That is, as the pressure difference, which is an error amount in feedback control, increases, it is determined that the actual boost pressure needs to reach the target boost pressure more reliably, and the length of the predetermined period is increased. As a result, when feedback control is performed regarding the supercharging pressure, which is a control parameter related to the EGR gas amount, an amount of EGR gas corresponding to the combustion is supplied into the cylinder through the control of the opening of the variable nozzle.

  In the combustion switching control system for a compression ignition internal combustion engine, the variable nozzle opening feedback control changing unit is configured to change the variable nozzle opening feedback control unit during the predetermined period when the pressure difference is equal to or greater than the predetermined boost pressure. The variable nozzle opening feedback control according to the above may be interrupted, and the opening of the variable nozzle may be set to the maximum supercharging pressure opening at which the supercharging pressure becomes maximum. That is, by interrupting the feedback control of the variable nozzle opening and setting the opening of the variable nozzle to the maximum boost pressure opening, intake air is suddenly introduced into the cylinder and exhaust gas remaining in the cylinder (EGR gas is reduced). Here, the maximum supercharging pressure opening is the opening of the variable nozzle when the supercharging pressure becomes maximum within a range in which the opening of the variable nozzle can be changed. Naturally, the feedback control change of the variable nozzle opening is performed only during a predetermined period, so that, as described above, a rapid increase in the supercharging pressure according to the switching of the combustion is performed. In other words, it is possible to maintain a balance between the reduction in the amount of EGR gas and the influence of its side effects.

  Further, an intake air amount feedback control means for performing feedback control of the intake air amount so that an actual intake air amount that is an actual intake air amount in the compression ignition internal combustion engine becomes a target intake air amount corresponding to combustion performed in the compression ignition internal combustion engine. In the case of providing, after the opening degree of the variable nozzle is set to the maximum boost pressure opening degree, when the difference in the intake air amount between the target intake air amount and the actual intake air amount in the feedback control becomes a predetermined intake air amount or more, the variable nozzle May be temporarily changed from the maximum boost pressure opening to a provisional opening at which the boost pressure decreases.

  By this intake amount feedback control means, the intake amount is feedback-controlled so that an amount of intake air suitable for combustion performed in the compression ignition internal combustion engine is supplied to the cylinder. Here, when the opening degree of the variable nozzle of the high pressure side supercharger is set to the maximum boosting pressure degree, the back pressure in the exhaust passage of the compression ignition internal combustion engine rises, and the engine load rises. Further, as the back pressure increases, there is a risk that it is difficult to accurately control the EGR amount by the EGR control means. Therefore, paying attention to the intake air amount, which is a parameter related to the increase in back pressure, when the difference in intake air amount is greater than or equal to the predetermined intake air amount, it is determined that there is a risk of adverse effects due to the increase in back pressure. The opening of the nozzle is adjusted to the temporary opening, and the supercharging pressure is temporarily reduced. As a result, the back pressure is reduced, and these adverse effects can be avoided. Further, the intake air amount difference is calculated again, and when the intake air amount difference is lower than the predetermined intake air amount, the opening degree of the variable nozzle may be changed from the temporary excess to the boost pressure maximum opening degree.

Further, in the combustion switching control system for the compression ignition internal combustion engine, the variable nozzle opening feedback control changing means may be configured such that the variable nozzle opening feedback during the predetermined period when the pressure difference is not less than the predetermined supercharging pressure. In the feedback control of the variable nozzle opening by the control means, the value of the target supercharging pressure may be increased as the pressure difference increases. That is, by increasing the value of the target boost pressure in feedback control, the amount of error in feedback control temporarily increases. As a result, it is possible to raise the supercharging pressure and rapidly introduce the intake air into the cylinder and discharge the EGR gas. Naturally, the feedback control change related to the supercharging pressure is performed only for a predetermined period. By doing so, as described above, it is possible to maintain a balance between the increase in the supercharging pressure in accordance with the switching of the combustion, in other words, the decrease in the EGR gas amount and the influence of the side effects.

  Further, in the combustion switching control system for the compression ignition internal combustion engine, the variable nozzle opening feedback control changing means may be configured such that the variable nozzle opening feedback during the predetermined period when the pressure difference is not less than the predetermined supercharging pressure. The gain value in the feedback control of the variable nozzle opening by the control means may be increased as the pressure difference increases. That is, by increasing the gain value in the feedback control, the feedback control command amount temporarily increases. As a result, it is possible to raise the supercharging pressure and rapidly introduce the intake air into the cylinder and discharge the EGR gas. Naturally, the feedback control change related to the supercharging pressure is performed only for a predetermined period. By doing so, as described above, it is possible to maintain a balance between the increase in the supercharging pressure in accordance with the switching of the combustion, in other words, the decrease in the EGR gas amount and the influence of the side effects.

  Here, in the combustion switching control system of the compression ignition internal combustion engine up to the above, the low pressure side supercharger has a low pressure side variable nozzle in which the opening degree of the nozzle that receives the energy of the exhaust is variable, and the pressure difference is When the pressure is higher than a predetermined high supercharging pressure higher than the predetermined supercharging pressure, the opening of the low-pressure variable nozzle is further set to an opening at which the supercharging pressure is maximized, and the predetermined period is determined by the pressure difference You may set still longer than the period set when it is more than predetermined supercharging pressure.

  That is, when the pressure difference between the target supercharging pressure and the actual supercharging pressure further spreads beyond the predetermined supercharging pressure and exceeds the predetermined high supercharging pressure, the low-pressure side supercharger is equipped with a low-pressure side variable nozzle. In the case where the engine load is increased, priority is given to the increase of the supercharging pressure over the suppression of the increase in engine load, thereby reducing the pressure difference as much as possible and making the amount of EGR gas supplied into the cylinder an appropriate amount. The reason why the predetermined period is set to a longer period is to continue the feedback control change and to more reliably reduce the pressure difference.

  Here, in the combustion switching control system for the compression ignition internal combustion engine described above, the target boost pressure is determined based on the accelerator opening of the compression ignition internal combustion engine when switching from premixed combustion to normal combustion. In addition, during premixed combustion or normal combustion excluding the switching time, it may be determined based on the fuel injection amount from the fuel injection valve. That is, at the time of switching from premixed combustion to normal combustion, based on the accelerator opening, a change in the operating state of the compression ignition internal combustion engine is immediately detected to determine the target boost pressure while suppressing deterioration of the combustion state It becomes possible to switch the combustion more smoothly.

  Further, in the combustion switching control system for a compression ignition internal combustion engine up to the above, an exhaust bypass passage for bypassing the turbine of the supercharger for exhaust, an exhaust flow rate adjusting valve for adjusting a flow rate of exhaust in the exhaust bypass passage, And an intake air amount feedback control means for performing feedback control of the intake air amount so that an actual intake air amount that is an actual intake air amount in the compression ignition internal combustion engine becomes a target intake air amount corresponding to combustion performed in the compression ignition internal combustion engine. If the difference between the target intake air amount and the actual intake air amount is greater than or equal to a predetermined intake air amount when switching from premixed combustion to normal combustion, the opening of the EGR valve is fully closed and the exhaust gas is exhausted. The opening of the flow rate adjustment valve may be fully closed.

By this intake amount feedback control means, the intake amount is feedback-controlled so that an amount of intake air suitable for combustion performed in the compression ignition internal combustion engine is supplied to the cylinder. Then, the degree of supercharging by the supercharger can be adjusted by adjusting the exhaust amount flowing through the exhaust bypass passage by the exhaust flow rate adjusting valve. Here, when the intake air amount difference is equal to or larger than the predetermined intake air amount, that is, when the error amount is relatively large in the feedback control of the intake air amount, and the intake air amount corresponding to the combustion is not supplied to the cylinder, EGR When the opening of the valve is fully closed and the opening of the exhaust flow rate adjustment valve is fully closed, the turbocharger is composed of a high-pressure supercharger and a low-pressure supercharger The amount of exhaust flowing into both of them will be increased as much as possible. As a result, the degree of supercharging by these superchargers increases, it becomes possible to send more intake air into the cylinders and expel the remaining exhaust earlier, and the switching from premixed combustion to normal combustion is more possible It can be done promptly.

  In the combustion switching control system for a compression ignition internal combustion engine, when the intake air amount difference is equal to or greater than the predetermined intake air amount, the intake air amount feedback control by the intake air amount feedback control means during the predetermined period, The amount value may be increased as the intake air amount difference increases. That is, by increasing the value of the target intake air amount in the feedback control, the error amount of the feedback control temporarily increases. As a result, intake air can be rapidly introduced into the cylinder and EGR gas can be discharged. Naturally, the feedback control change of the intake air amount is performed only for a predetermined period. By doing so, as described above, it is possible to maintain a balance between the rapid increase in the intake air amount according to the switching of combustion, in other words, the decrease in the EGR gas amount, and the influence of the side effects.

  Further, in the combustion switching control system for the compression ignition internal combustion engine, when the difference in intake air amount is equal to or greater than the predetermined intake air amount, a gain value in feedback control of the intake air amount by the intake air amount feedback control means is set for the predetermined period. The difference may be increased as the intake air amount difference increases. That is, by increasing the gain value in the feedback control, the feedback control command amount temporarily increases. As a result, intake air can be rapidly introduced into the cylinder and EGR gas can be discharged. Naturally, the feedback control change of the intake air amount is performed only for a predetermined period. By doing so, as described above, it is possible to maintain a balance between the rapid increase in the intake air amount according to the switching of combustion, in other words, the decrease in the EGR gas amount, and the influence of the side effects.

  In a compression ignition internal combustion engine that switches between premixed combustion and normal combustion according to the operation state of the compression ignition internal combustion engine, when performing feedback control of a control parameter related to the EGR gas amount, an amount of EGR gas corresponding to the combustion is The control parameter can be controlled so as to be supplied into the cylinder.

  Here, an embodiment of a combustion switching control system for a compression ignition internal combustion engine according to the 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.

  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 and the low-pressure side supercharger 16b in the supercharger 16 are so-called variable displacement centrifugal superchargers, and the opening degree of the variable nozzle of each supercharger is adjusted. This makes it possible to finely adjust the supercharging pressure finally reached.

  An EGR device 21 is provided inside the supercharger 16. The EGR device 21 recirculates a part of the exhaust discharged from the turbine side of the high pressure side supercharger 16a to the compressor side. The EGR device 21 includes an EGR passage 22 extending from the turbine side (upstream side) to the compressor side (downstream side), and EGR gas cooling provided in order from the upstream side along the exhaust flow on the EGR passage 22. And an EGR valve 24 for adjusting the flow rate of the EGR gas.

  Further, an exhaust bypass passage 17 for avoiding exhaust from flowing into the turbine of the high-pressure supercharger 16a of the supercharger 16 is provided from the portion of the exhaust branch pipe 12 upstream of the high-pressure supercharger 16a. It is a portion of an exhaust passage between the turbine side of the high pressure side supercharger 16a and the turbine side of the low pressure side supercharger 16b, and is connected to a portion downstream of the exhaust introduction portion of the EGR device 21. An exhaust flow rate adjusting valve 18 for adjusting the flow rate of exhaust gas in the exhaust bypass passage 17 is provided in the latter part. Therefore, when the exhaust flow rate adjustment 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. At this time, a part of the exhaust gas is recirculated by the EGR device 21 to the compressor side of the high-pressure supercharger 16a. On the other hand, as the opening of the exhaust flow rate adjustment valve 18 increases, the amount of exhaust flowing into the turbine of the high pressure side supercharger 16a decreases, and the exhaust energy acting on the turbine side of the low pressure side supercharger 16b increases. Go. As a result, the final supercharging pressure is lower than when the exhaust flow rate adjusting valve 18 is closed and the two-stage supercharging is performed. The adjustment of the exhaust flow rate by the exhaust flow rate adjustment 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 variable nozzle of the EGR valve 24, the actuator 11, the high pressure side supercharger 16a and the low pressure side supercharger 16b, the opening degree of the exhaust flow rate adjusting valve 18 and the like are also determined by the ECU 2.
It is controlled according to the command from 0.

  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.

  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. 3, the horizontal axis 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.

  Further, when premixed combustion is performed in the internal combustion engine 1, a relatively high supercharging pressure is required to introduce intake air into the cylinder 2. Therefore, during premix combustion, the exhaust flow rate adjustment valve 18 is closed to increase the boost pressure in the internal combustion engine 1. On the other hand, during normal combustion, the degree of opening of the exhaust flow rate adjustment valve 18 is avoided in order to avoid deterioration of the combustion state due to an excessive increase in the back pressure in the exhaust branch pipe 12 due to a relatively large engine load. Is increased as the engine load increases.

  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 emissions may deteriorate when switching combustion.

Therefore, at the time of switching from premixed combustion to normal combustion, the fuel injection valve is operated so that combustion according to the transition 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. 4A. As the engine load of the internal combustion engine 1 increases, fuel injection in the transition state of combustion is executed in the order of FIGS. 4B and 4C. Finally, fuel injection during normal combustion is performed as shown in FIG.

  First, at the time of premix combustion, as shown in FIG. 4A, fuel injection is performed from the fuel injection valve 3 at the 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 performed at an early stage and main-stage two-stage injection performed after the pre-injection are performed. This is a transition of combustion that combines 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 premixed combustion to normal combustion. It is the aspect of the fuel injection in a state.

  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 from the premixed combustion is started, 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. Become. Therefore, by adjusting the valve opening time of the fuel injection valve 3 in the main injection so as to eliminate the variation, the fuel injection amount of the main injection can be controlled more accurately.

  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. Therefore, more accurate fuel injection can be performed, so that smoother combustion switching can be performed. 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, feedback control of the variable nozzle opening degree of the high pressure side supercharger 16a is executed. The feedback control of the variable nozzle opening is executed not only when the main combustion switching control is performed, but also when premixed combustion or normal combustion is performed in the internal combustion engine 1. The control content is that the actual supercharging pressure (hereinafter referred to as “actual supercharging pressure”) is a supercharging pressure suitable for combustion performed in the internal combustion engine 1 (hereinafter referred to as “target supercharging pressure”). As much as possible, the feedback control is performed with respect to the opening of the variable nozzle of the high-pressure supercharger 16a. When the process of S101 ends, the process proceeds to S102.

  In S102, 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 S103, and when it is determined that the operating state does not belong to the premixed combustion region R1, this control is terminated.

In S103, 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 S102 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 S104. If it is determined that the operating state has not shifted to the normal combustion region R2, this control is terminated.

  In S104, an error amount ΔPim related to the supercharging pressure in the feedback control of the variable nozzle opening is calculated. This error amount ΔPim is expressed by the difference between the target boost pressure and the actual boost pressure. The larger the error amount ΔPim, the larger the command amount for adjusting the supercharging pressure in the feedback control of the variable nozzle opening. When the process of S104 ends, the process proceeds to S105.

  In S105, it is determined whether or not the boost pressure error amount ΔPim calculated in S104 is equal to or greater than a predetermined boost pressure K1. That is, in the feedback control of the variable nozzle opening, it is determined whether or not the difference between the actual supercharging pressure and the target supercharging pressure increases and the actual supercharging pressure is not greatly deviated from the target supercharging pressure. The If the actual supercharging pressure greatly deviates from the target supercharging pressure, the balance between fresh air and EGR gas in the cylinder 2 may be lost, and the combustion state may deteriorate. In other words, since the feedback control of the variable nozzle opening is not working efficiently, the amount of EGR gas corresponding to the combustion is not supplied into the cylinder 2 when switching from the premixed combustion to the normal combustion. It is determined whether or not there is. Therefore, the predetermined supercharging pressure K1 is a threshold value for determining the effectiveness of feedback control of the variable nozzle opening.

  When it is determined that the error amount ΔPim of the supercharging pressure is equal to or greater than the predetermined supercharging pressure K1, that is, when it is determined that the feedback control of the variable nozzle opening is not working efficiently, the process proceeds to S106. On the other hand, if it is determined that the error amount ΔPim of the supercharging pressure is not equal to or greater than the predetermined supercharging pressure K1, that is, if it is determined that the feedback control of the variable nozzle opening is working efficiently, the process proceeds to S110.

  In S106, a predetermined period TD1 is calculated. This predetermined period TD1 is a period in which the feedback control of the variable nozzle opening is changed in S107 described later. For the calculation of the predetermined period TD1, the model diagram of FIG. 7 is shown. In FIG. 7, the horizontal axis represents the supercharging pressure error amount ΔPim, and the vertical axis represents the predetermined time TD1. As for the relationship between the error amount ΔPim and the predetermined time TD1, the predetermined time TD1 becomes longer as the error amount ΔPim becomes equal to or higher than the predetermined boost pressure K1 and the value thereof increases. When the process of S106 ends, the process proceeds to S107.

  In S107, part or all of the feedback control of the variable nozzle opening performed in S101 is changed. At this time, the change in feedback control of the variable nozzle opening is performed only during the predetermined period TD1 calculated in S106. An example of changing the feedback control of the variable nozzle opening will be shown below.

<Example 1 of feedback control change of variable nozzle opening>
First, the feedback control of the variable nozzle opening performed in S101 is interrupted. At the same time, the variable nozzle opening is fully closed, that is, the supercharging pressure maximum opening at which the supercharging pressure becomes maximum in the range of change in the opening of the variable nozzle. By doing in this way, a supercharging pressure rises and the amount of EGR gas supplied into the cylinder 2 decreases. As described above, this series of processes is performed only during the predetermined period TD1, and after this period has elapsed, the variable nozzle opening is returned to the initial opening, and the feedback of the initial variable nozzle opening is again performed. Control is executed. By such feedback control change, the EGR gas remaining in the cylinder 2 is expelled, and the environment is quickly shifted from an environment suitable for premixed combustion to an environment suitable for normal combustion. By performing the control change only during the predetermined period TD1, it is possible to avoid that the amount of fresh air supplied into the cylinder 2 becomes excessive and the air-fuel ratio becomes excessively lean during normal combustion after the transition. It becomes.

<Example 2 of feedback control change of variable nozzle opening>
Second, the value of the target boost pressure, which is a control parameter in the feedback control of the variable nozzle opening performed in S101, is changed. Specifically, the target boost pressure is changed to a desired value and a larger value is set as the target boost pressure. The new target boost pressure value is set larger as the boost pressure error amount ΔPim increases. And the change of the value of this target supercharging pressure is also performed limited to the predetermined period TD1 similarly to the above-described first modification. Therefore, after this period has elapsed, the feedback control of the initial variable nozzle opening is executed again.

  As the target boost pressure is temporarily increased, the amount of error in feedback control of the variable nozzle opening increases, and finally the command amount for boost pressure adjustment increases. Therefore, by changing the feedback control in this manner, the EGR gas remaining in the cylinder 2 is expelled, and the environment is quickly shifted from an environment suitable for premixed combustion to an environment suitable for normal combustion, By changing the feedback control only during the predetermined period TD1, it is possible to avoid the amount of fresh air supplied into the cylinder 2 from becoming excessive and the air-fuel ratio from becoming excessively lean during normal combustion after the transition. Is possible.

<Example 3 of feedback control change of variable nozzle opening>
Third, the value of the gain that is a control parameter in the feedback control of the variable nozzle opening performed in S101 is changed. Specifically, the gain value is changed to a value that should be originally set, and is changed to a larger value. The new gain value is set larger as the boost pressure error amount ΔPim increases. The change of the gain value is also limited to the predetermined period TD1 as in the first modification described above. Therefore, after this period has elapsed, the feedback control of the initial variable nozzle opening is executed again.

  When the gain is temporarily increased, the command amount for final supercharging pressure adjustment increases. Therefore, by changing the feedback control in this manner, the EGR gas remaining in the cylinder 2 is expelled, and the environment is quickly shifted from an environment suitable for premixed combustion to an environment suitable for normal combustion, By changing the feedback control only during the predetermined period TD1, it is possible to avoid the amount of fresh air supplied into the cylinder 2 from becoming excessive and the air-fuel ratio from becoming excessively lean during normal combustion after the transition. Is possible.

  One of these examples of feedback control change of the variable nozzle opening is performed in S107. When the process of S107 ends, the process proceeds to S108.

  In S108, it is determined whether or not the boost pressure error amount ΔPim calculated in S104 is equal to or higher than a predetermined high boost pressure K2. The predetermined high supercharging pressure K2 is a value considerably larger than the predetermined supercharging pressure K1. Accordingly, in S108, it is determined whether or not the pressure difference between the actual boost pressure and the target boost pressure is greatly increased in the internal combustion engine 1. That is, it is determined whether or not the pressure difference is not reduced despite the change in feedback control of the variable nozzle opening in S107 described above. Such a state is, for example, when the internal combustion engine 1 shifts from a state in which premixed combustion is performed under a very light load state to a state in which rapid combustion is accelerated and normal combustion is performed in a short time. Can occur. If it is determined that the error amount ΔPim is equal to or greater than the predetermined high boost pressure K2, that is, if the increase in the pressure difference is significant, the process proceeds to S109. On the other hand, when it is determined that the error amount ΔPim is not greater than or equal to the predetermined high boost pressure K2, that is, when the increase in the pressure difference is not significant, the present control is terminated.

  In S109, the opening of the variable nozzle of the low pressure side supercharger 16b (hereinafter referred to as “low pressure side variable nozzle”) is fully closed, that is, the boost pressure is maximized in the range of change in the opening of the low pressure side variable nozzle. The opening is By doing in this way, the degree of supercharging by the supercharger 16 is improved as much as possible, and the enlarged pressure difference is eliminated. After the process of S109, this control is terminated.

  In S110, since it is determined that the feedback control of the variable nozzle opening is working efficiently, the feedback control of the variable nozzle opening executed in S101 is continuously performed. After the processing of S110, this control is terminated.

  According to this control, when switching from premixed combustion to normal combustion is performed, if it is determined that the feedback control of the variable nozzle opening is not working efficiently, all or the feedback control of the variable nozzle opening is By changing a part, the amount of EGR gas or fresh air corresponding to the normal combustion after the transition can be quickly supplied into the cylinder.

  Further, in the feedback control of the variable nozzle opening described above, the target supercharging pressure may be adjusted based on the control map shown in FIG. FIG. 8A is a control map related to the target supercharging pressure when the first fuel injection mode and the second fuel injection mode are performed, that is, when the combustion is in a transition state, and the combustion is performed using the accelerator opening as a parameter. It is a control map for calculating a suitable target boost pressure. FIG. 8B is a control map related to the target boost pressure when premixed combustion or normal combustion is performed, that is, when combustion is not in a transition state, and combustion is performed using the fuel injection amount from the fuel injection valve 3 as a parameter. 3 is a control map for calculating a target supercharging pressure suitable for the engine.

  As described above, when the combustion is in the transition state, by calculating the target boost pressure based on the accelerator opening, it becomes possible to immediately reflect the fluctuation of the operating state of the internal combustion engine in the boost pressure. Smoother combustion switching can be performed while suppressing deterioration of the combustion state. Further, when the combustion is not in the transition state, the target boost pressure is calculated based on the fuel injection amount, so that it is possible to reflect the combustion state of the internal combustion engine and generate the boost pressure corresponding to the combustion state. Become.

  A second embodiment of the combustion switching control performed at the time of switching from premixed combustion to normal combustion will be described with reference to FIG. FIG. 9 shows a flowchart regarding combustion switching control. In the combustion switching control shown in FIG. 9, the same processes as those of the combustion switching control shown in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted. Further, this combustion switching control is control performed by the ECU 20.

  In this control, after the processing of S101, the process proceeds to S201. In S201, intake air amount feedback control is executed. The intake air amount feedback control is executed not only when the main combustion switching control is performed, but also when premixed combustion or normal combustion is performed in the internal combustion engine 1. The content of the control is that the actual intake air amount supplied to the cylinder 2 (hereinafter referred to as “actual intake air amount”) is an intake air amount suitable for combustion performed in the internal combustion engine 1 (hereinafter referred to as “target intake air amount”). As much as possible, the engine element related to the intake air amount (for example, the opening degree of the intake throttle valve 10) is feedback-controlled based on the detection value by the air flow meter 9. When the process of S201 ends, the process proceeds to S102.

  In this control, when the process of S106 is completed, the process proceeds to S202. In S202, the variable nozzle opening feedback control executed in S101 is interrupted. Thereafter, the process proceeds to S203, in which the variable nozzle opening is fully closed, that is, the supercharging pressure maximum opening at which the supercharging pressure becomes maximum within the range of change in the opening of the variable nozzle. That is, the process shown in the first example of the feedback control change of the variable nozzle opening described above is performed in S202 and S203. When the process of S203 ends, the process proceeds to S204.

In S204, an error amount ΔGn related to the intake air amount in the intake air amount feedback control is calculated. This error amount ΔGn is represented by the difference between the target intake air amount and the actual intake air amount. The larger the error amount ΔGn, the larger the command amount for adjusting the intake air amount in the intake air amount feedback control. When the process of S204 ends, the process proceeds to S205.

  In S205, it is determined whether or not the error amount ΔGn calculated in S204 is equal to or greater than a predetermined intake amount K3. That is, in the feedback control of the intake air amount, the difference between the actual intake air amount and the target intake air amount is increased, and it is determined whether or not the actual intake air amount is greatly deviated from the target intake air amount that should originally be. When the actual intake air amount deviates significantly from the target intake air amount, the back pressure in the exhaust branch pipe 12 increases excessively, which may result in an increase in engine load and difficulty in controlling the EGR amount. Therefore, in S205, it is determined whether or not an excessive increase in back pressure has occurred based on the error amount ΔGn. Therefore, the predetermined intake air amount K3 is a threshold value for that purpose.

  If it is determined that the error amount ΔGn of the intake air amount is greater than or equal to the predetermined intake air amount K3, that is, if it is determined that an excessive increase in back pressure has occurred, the process proceeds to S206. On the other hand, if it is determined that the error amount ΔGn of the intake air amount is not equal to or greater than the predetermined intake air amount K3, that is, if it is determined that an excessive increase in back pressure has not occurred, the process proceeds to S207.

  In S206, the variable nozzle opening of the high-pressure supercharger 16a is temporarily changed to a temporary opening. This temporary opening is an opening on the side where the supercharging pressure is lower than the maximum supercharging pressure opening set in S203. Accordingly, the back pressure of the exhaust branch pipe 12 is thereby reduced, and the intake air amount error ΔGn is accordingly reduced. When the process of S206 ends, the process of S205 is performed again.

  In S207, when the variable nozzle opening of the high-pressure supercharger 16a is set to the temporary opening, it is reset to the maximum boosting pressure, and the variable nozzle opening is set to the maximum boosting pressure. If so, keep it. After the processing of S207, this control is terminated.

  According to this control, when switching from premixed combustion to normal combustion is performed, if it is determined that the feedback control of the variable nozzle opening is not working efficiently, all or the feedback control of the variable nozzle opening is By changing a part, the amount of EGR gas or fresh air corresponding to the normal combustion after the transition can be quickly supplied into the cylinder. Furthermore, the excessive increase in the back pressure can be suppressed by the processing after S204.

  Further, the adjustment of the target intake air amount in the intake air amount feedback control described above may be performed in the same manner as in the case of the target boost pressure based on the control map shown in FIG. 8 described above. In other words, when combustion is in a transition state, the target intake air amount is calculated based on the accelerator opening, so that fluctuations in the operating state of the internal combustion engine can be immediately reflected in the intake air amount, thereby deteriorating the combustion state. The combustion can be switched more smoothly while suppressing the above. Further, when the combustion is not in the transition state, by calculating the target intake air amount based on the fuel injection amount, it becomes possible to reflect the combustion state of the internal combustion engine and supply the intake air in an amount corresponding to the combustion state. .

  A third embodiment of the combustion switching control that is performed at the time of switching from premixed combustion to normal combustion will be described with reference to FIG. FIG. 10 shows a flowchart regarding combustion switching control. In the combustion switching control shown in FIG. 10, the same processing as the processing of the combustion switching control shown in FIG. 6 is denoted by the same reference numeral, and detailed description thereof is omitted. Further, this combustion switching control is control performed by the ECU 20.

  In this control, when the process of S101 ends, the process proceeds to S301. In S301, the intake air amount feedback control is executed as in S201. After the process of S301, the process proceeds to S102.

  In this control, when the process of S107 is completed, the process proceeds to S302. In S302, an error amount ΔGn related to the intake air amount in the intake air amount feedback control is calculated. This error amount ΔGn is represented by the difference between the target intake air amount and the actual intake air amount. The larger the error amount ΔGn, the larger the command amount for adjusting the intake air amount in the intake air amount feedback control. When the process of S302 ends, the process proceeds to S303.

  In S303, it is determined whether or not the error amount ΔGn calculated in S302 is equal to or greater than a predetermined intake air amount K4. That is, in the feedback control of the intake air amount, when the difference between the actual intake air amount and the target intake air amount is increasing, it means that the amount of intake air corresponding to the combustion is not supplied into the cylinder 2. Therefore, the predetermined intake air amount K4 is a threshold value for determining whether or not an appropriate amount of intake air is supplied into the cylinder 2. If it is determined that the error amount ΔGn of the intake air amount is greater than or equal to the predetermined intake air amount K4, that is, if it is determined that an appropriate amount of intake air is not being supplied into the cylinder 2, the process proceeds to S304. On the other hand, if it is determined that the error amount ΔGn of the intake air amount is not equal to or greater than the predetermined intake air amount K4, that is, if it is determined that an appropriate amount of intake air is being supplied into the cylinder 2, the process proceeds to S306.

  In S304, the exhaust amount flowing into the turbines of the high-pressure supercharger 16a and the low-pressure supercharger 16b is set by fully closing the opening of the EGR valve 24 and fully closing the opening of the exhaust flow rate adjusting valve 18. Increase as much as possible. As a result, the degree of supercharging by these superchargers increases, it becomes possible to send more intake air into the cylinder 2 and drive out the remaining exhaust earlier, and switching from premixed combustion to normal combustion is possible. It can be done more quickly. When the process of S304 ends, the process proceeds to S305.

  In S305, part or all of the intake air amount feedback control executed in S301 is changed. At this time, the change in the intake air amount feedback control is performed only during the predetermined period TD1 calculated in S106. An example of changing the intake air amount feedback control is shown below.

<Example 1 of change in intake air amount feedback control>
First, the value of the target intake air amount, which is a control parameter in the intake air amount feedback control executed in S301, is changed. Specifically, the target intake air amount is changed to a value that should be originally set, and a larger value is set as the target intake air amount. The value of the new target intake air amount is set larger as the intake air amount error amount ΔGn increases. Then, the change in the value of the target intake air amount is performed only during the predetermined period TD1. Therefore, after this period has elapsed, the initial intake air amount feedback control is executed again.

  As the target intake air amount is temporarily increased, the error amount in the intake air amount feedback control increases, and finally the command amount for adjusting the intake air amount increases. Therefore, by changing the feedback control in this manner, the EGR gas remaining in the cylinder 2 is expelled, and the environment is quickly shifted from an environment suitable for premixed combustion to an environment suitable for normal combustion, By changing the feedback control only during the predetermined period TD1, it is possible to avoid the amount of fresh air supplied into the cylinder 2 from becoming excessive and the air-fuel ratio from becoming excessively lean during normal combustion after the transition. Is possible.

<Example 2 of change in intake air amount feedback control>
Second, the gain value that is a control parameter in the intake air amount feedback control executed in S301 is changed. Specifically, the gain value is changed to a value that should be originally set, and is changed to a larger value. The new gain value is set to increase as the intake air amount error amount ΔGn increases. The change of the gain value is also limited to the predetermined period TD1 as in the first modification described above. Therefore, after this period has elapsed, the initial intake air amount feedback control is executed again.

  As the gain is temporarily increased, the command amount for final intake air amount adjustment increases. Therefore, by changing the feedback control in this manner, the EGR gas remaining in the cylinder 2 is expelled, and the environment is quickly shifted from an environment suitable for premixed combustion to an environment suitable for normal combustion, By changing the feedback control only during the predetermined period TD1, it is possible to avoid the amount of fresh air supplied into the cylinder 2 from becoming excessive and the air-fuel ratio from becoming excessively lean during normal combustion after the transition. Is possible.

  One of the examples of the intake air amount feedback control change is performed in S305. After the processing of S305, this control is terminated.

  Next, in S306, since it is determined that an appropriate amount of intake air is being supplied into the cylinder 2, the intake air amount feedback control executed in S301 is continuously performed. After the process of S306, this control is terminated.

  According to this control, when switching from premixed combustion to normal combustion is performed, if it is determined that the feedback control of the variable nozzle opening is not working efficiently, all or the feedback control of the variable nozzle opening is By changing a part, the amount of EGR gas or fresh air corresponding to the normal combustion after the transition can be quickly supplied into the cylinder. Further, when it is determined that an appropriate amount of intake air is not being supplied into the cylinder 2, all or part of the intake amount feedback control is changed, so that an amount of EGR gas corresponding to the normal combustion after the transition or Fresh air can be quickly supplied into the cylinder.

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 of the compression ignition internal combustion engine according to the first embodiment of the present invention, it is a diagram showing the relationship between the intake air amount error amount and a predetermined time TD1 in the combustion switching control. 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 calculating a target supercharging pressure when combustion is in a transition state, and when combustion is not in a transition state It is a figure which shows the control map for calculating a target supercharging pressure. 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. 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)
3 ... Fuel injection valve 7 ... Intake branch pipe 8 ... Intake pipe 12 ... Exhaust branch pipe 16 ... Supercharger 16a ... High pressure side supercharger 16b・ ・ ・ ・ Low pressure side turbocharger 17 ・ ・ ・ ・ Exhaust bypass passage 18 ・ ・ ・ ・ Exhaust flow adjustment valve 20 ・ ・ ・ ・ ECU
21 ... EGR device 22 ... EGR passage 24 ... EGR valve 25 ... Crank position sensor 26 ... Accelerator opening sensor R1 ... Premix combustion region R2 ... ··· Normal combustion region Pint2 ··· Predetermined interval Pint0 ··· Pilot fuel injection interval

Claims (11)

A fuel injection valve that injects the fuel of the compression ignition internal combustion engine into the cylinder;
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;
EGR control means for controlling the opening of an EGR valve so as to recirculate an amount of EGR gas in the cylinder according to 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,
A turbocharger provided in a supply / exhaust system of the compression ignition internal combustion engine, the turbocharger having a variable nozzle in which an opening degree of a nozzle receiving the energy of exhaust is variable;
Feedback control of the variable nozzle opening of the supercharger so that the actual supercharging pressure, which is the actual supercharging pressure in the compression ignition internal combustion engine, becomes the target supercharging pressure corresponding to the combustion performed in the compression ignition internal combustion engine Variable nozzle opening feedback control means for performing,
When switching from premixed combustion to normal combustion, if the pressure difference between the target boost pressure and the actual boost pressure in the feedback control is greater than or equal to a predetermined boost pressure, the variable nozzle opening feedback control is performed for a predetermined period. Variable nozzle opening feedback control changing means for temporarily changing the feedback control of the variable nozzle opening by the means to increase the supercharging pressure, and
The combustion switching control system for a compression ignition internal combustion engine, wherein the predetermined period becomes longer as the pressure difference becomes larger. The supercharger is
A centrifugal supercharger provided in a supply / exhaust system of the compression ignition internal combustion engine, the high pressure side supercharger having the variable nozzle;
The low-pressure supercharger, which is a centrifugal supercharger provided in an exhaust system further downstream of the exhaust system provided with the high-pressure supercharger. The combustion switching control system for a compression ignition internal combustion engine.   The variable nozzle opening feedback control changing means interrupts the feedback control of the variable nozzle opening by the variable nozzle opening feedback control means for the predetermined period when the pressure difference is not less than the predetermined supercharging pressure, and The combustion switching control system for a compression ignition internal combustion engine according to claim 1 or 2, wherein the opening degree of the variable nozzle is set to a supercharging pressure maximum opening degree at which a supercharging pressure is maximized. An intake air amount feedback control means for performing feedback control of the intake air amount so that an actual intake air amount that is an actual intake air amount in the compression ignition internal combustion engine becomes a target intake air amount corresponding to combustion performed in the compression ignition internal combustion engine;
After the variable nozzle opening is set to the maximum boost pressure opening, when the difference in intake air amount between the target intake air amount and the actual intake air amount in the feedback control is equal to or greater than a predetermined intake air amount, the opening of the variable nozzle 4. The combustion switching control system for a compression ignition internal combustion engine according to claim 3, wherein the pressure is temporarily changed from the maximum boost pressure opening to a provisional opening at which the boost pressure decreases.   The variable nozzle opening feedback control changing means is configured to perform the target overshoot in the variable nozzle opening feedback control by the variable nozzle opening feedback control means for the predetermined period when the pressure difference is not less than the predetermined boost pressure. The combustion switching control system for a compression ignition internal combustion engine according to claim 1 or 2, wherein a value of a supply pressure is increased as the pressure difference increases.   The variable nozzle opening feedback control changing means sets a gain value in feedback control of the variable nozzle opening by the variable nozzle opening feedback control means for the predetermined period when the pressure difference is equal to or greater than the predetermined supercharging pressure. 3. The combustion switching control system for a compression ignition internal combustion engine according to claim 1, wherein the pressure difference is increased as the pressure difference increases. The low pressure side supercharger has a low pressure side variable nozzle in which the opening degree of the nozzle that receives the energy of the exhaust gas is variable,
When the pressure difference is equal to or higher than a predetermined high supercharging pressure higher than the predetermined supercharging pressure, the opening of the low pressure side variable nozzle is further set to an opening at which the supercharging pressure becomes maximum, and the predetermined period is 3. The combustion switching control system for a compression ignition internal combustion engine according to claim 2, wherein the pressure difference is set to be longer than a period set when the pressure difference is equal to or greater than the predetermined boost pressure.   The target boost pressure is determined based on the accelerator opening of the compression ignition internal combustion engine at the time of switching from premixed combustion to normal combustion, and at the time of premixed combustion or normal combustion excluding the switching time, The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 1 to 7, wherein the combustion switching control system is determined based on a fuel injection amount from a fuel injection valve. An exhaust bypass passage for bypassing the turbocharger turbine for exhaust;
An exhaust flow rate adjusting valve for adjusting the flow rate of the exhaust gas in the exhaust bypass passage;
An intake air amount feedback control means for performing feedback control of the intake air amount so that an actual intake air amount that is an actual intake air amount in the compression ignition internal combustion engine becomes a target intake air amount corresponding to combustion performed in the compression ignition internal combustion engine; Prepared,
If the difference in intake air amount between the target intake air amount and the actual intake air amount exceeds a predetermined intake air amount when switching from premixed combustion to normal combustion, the opening of the EGR valve is fully closed and the exhaust gas flow rate adjustment is performed. The combustion switching control system for a compression ignition internal combustion engine according to any one of claims 1, 2, 3, 5, and 6, wherein the valve opening is fully closed.   When the intake air amount difference is equal to or larger than the predetermined intake air amount, the target intake air amount is increased as the intake air amount difference increases in the intake air amount feedback control by the intake air amount feedback control means for the predetermined period. The combustion switching control system for a compression ignition internal combustion engine according to claim 9.   When the intake air amount difference is equal to or greater than the predetermined intake air amount, the gain value in the intake air amount feedback control by the intake air amount feedback control means is increased as the intake air amount difference increases during the predetermined period. A combustion switching control system for a compression ignition internal combustion engine according to claim 9.

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