JP2018123700A - Control device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to increase the chances of premixed compression auto-ignition combustion. When the engine operating state belongs to a first region R1, in order to perform premixed compression self-ignition combustion, first prefuel injection is performed at a first base prefuel injection timing, and then second The second pre-fuel injection is performed by the second base pre-fuel injection amount at the base pre-fuel injection timing, and then the main fuel injection is performed. When the engine operating state belongs to the second region R2 or the third region R3, the second base prefuel injection is performed without performing the first prefuel injection in order to perform the premixed compression self-ignition combustion. At a time earlier than the time, the second pre-fuel injection is performed by an amount larger than the second base pre-fuel injection amount, and then the main fuel injection is performed. When the engine operating state belongs to the fourth region R4, fuel injection for performing diffusion combustion is performed. [Selection] Figure 4

Description

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

  An internal combustion engine capable of switching between premixed compression self-ignition combustion and diffusion combustion is known (see, for example, Patent Document 1). In Patent Document 1, a region A and a region B are defined in an engine operating state region determined by the engine load and the engine speed. The region A is divided into a region a2, a region a1 on the low load side of the region a2, and a region a3 on the high load side of the region a2. When the engine operating state belongs to the region a2, premixed compression auto-ignition combustion is performed, and when the engine operating state belongs to the regions a1, a3, B, diffusion combustion is performed.

  Premixed compression self-ignition combustion has the advantage that the NOx emission amount and soot emission amount are small and the fuel consumption is small because the combustion temperature is lower than that of diffusion combustion. However, when the engine load becomes low or the engine load becomes high, it becomes difficult to perform premixed compression auto-ignition combustion. Therefore, in Patent Document 1, diffusion combustion is performed not only in the region B but also in the region a1 on the low load side of the region a2 where premixed compression autoignition combustion is performed and the region a3 on the high load side of the region a2. .

JP 2012-041892 A

  However, in Patent Document 1, premixed compression autoignition combustion is performed only in a limited engine operating state region called region a2, and the advantage of premixed compression autoignition combustion cannot be obtained sufficiently. There is a point.

  According to the present invention, the fuel injection valve configured to inject fuel into the cylinder, the in-cylinder oxygen density is higher than the predetermined first lower limit value, and the predetermined first upper limit is set. Lower than the first value, lower than the first lower limit value and higher than the predetermined second lower limit value, higher than the first upper limit value and higher than the predetermined second upper limit value. A determination unit configured to determine whether the value is lower, lower than the second lower limit value, or higher than the second upper limit value, and a fuel injection control unit, wherein the in-cylinder When it is determined that the oxygen density is higher than the first lower limit value and lower than the first upper limit value, the first base prefuel injection timing is changed to perform premixed compression auto-ignition combustion. 1 pre-fuel injection, then at the second base pre-fuel injection timing The second pre-fuel injection is performed by the base pre-fuel injection amount, and then the main fuel injection is performed, and it is determined that the in-cylinder oxygen density is lower than the first lower limit value and higher than the second lower limit value. Or when it is determined that the value is higher than the first upper limit value and lower than the second upper limit value, in order to perform premixed compression auto-ignition combustion, the first pre-fuel injection is not performed. , At a time earlier than the second base pre-fuel injection timing, the second pre-fuel injection is performed by an amount larger than the second base pre-fuel injection amount, then the main fuel injection is performed, and the in-cylinder oxygen When it is determined that the density is lower than the second lower limit value or higher than the second upper limit value, fuel injection for performing diffusion combustion is performed. And a control device for an internal combustion engine, comprising: a fuel injection control unit;

  Opportunities for premixed compression auto-ignition combustion can be increased.

1 is an overall view of an internal combustion engine. It is a partial longitudinal cross-sectional view of an internal combustion engine. It is a block diagram which shows the function of an electronic control unit. It is a diagram which shows each area | region R1, R2, R3, R4. It is a diagram explaining 3 times injection. It is a diagram explaining 2 times injection. It is a diagram explaining diffusion combustion injection. It is a diagram which shows an example of heat release rate dQ / dCA when injection is performed 3 times. It is a diagram which shows an example of the heat release rate dQ / dCA when injection is performed 3 times when the in-cylinder oxygen density is low. It is a diagram which shows an example of the heat release rate dQ / dCA when injection is performed three times when the in-cylinder oxygen density is high. It is a diagram which shows an example of the frequency distribution of an equivalence ratio when injection is performed 3 times when in-cylinder oxygen density is low. It is a diagram which shows an example of the frequency distribution of an equivalence ratio when injection is performed 3 times when the in-cylinder oxygen density is high. It is a diagram which shows an example of the frequency distribution of an equivalence ratio when two injections are performed. It is a flowchart which shows the fuel-injection control routine of 1st Example by this invention. It is a time chart explaining the transient process when an engine operation state transfers to a 2nd area | region from a 1st area | region. It is a time chart explaining the transient process when an engine operation state transfers to a 3rd area | region from a 1st area | region. It is a flowchart which shows the fuel-injection control routine of 2nd Example by this invention. It is a diagram explaining the 1st interval and the 2nd interval in 3 times injection.

  Referring to FIG. 1, an internal combustion engine 1 includes an engine body 2 including a plurality of, for example, four cylinders 2a. The cylinder 2 a is connected to a surge tank 4 through an intake branch pipe 3, and the surge tank 4 is connected to an outlet of a compressor 6 c of an exhaust supercharger 6 through an intake duct 5. The inlet of the compressor 6 c is connected to the air cleaner 8 through the intake air introduction pipe 7. An air flow meter 9 for detecting the amount of intake air is disposed in the intake air introduction pipe 7. A cooler 10 for cooling the intake air and a throttle valve 11 are sequentially arranged in the intake duct 5.

  The cylinder 2 a is connected to the inlet of the turbine 6 t of the exhaust supercharger 6 through the exhaust manifold 12 and the exhaust pipe 13 in order. The outlet of the turbine 6 t is connected to the catalyst 15 through the exhaust pipe 14. The exhaust pipe 13 upstream of the turbine 6 t and the exhaust pipe 14 downstream of the turbine 6 t are connected to each other by a waste gate valve 16. The surge tank 4 and the exhaust manifold 12 are connected to each other by an exhaust gas recirculation (hereinafter referred to as EGR) passage 17. An EGR control valve 18 for controlling the amount of EGR gas and a cooler 19 for cooling the EGR gas are disposed in the EGR passage 17.

  FIG. 2 shows in detail the engine body 2 of the first embodiment according to the present invention. Referring to FIG. 2, 30 is a cylinder block, 31 is a cylindrical cylinder bore formed in the cylinder block 30, 32 is a piston, 33 is a cylinder head, 34 is an intake port, 35 is an intake valve, 36 is an exhaust port, Reference numeral 37 denotes an exhaust valve, and 38 denotes a combustion chamber. An electronically controlled fuel injection valve 39 disposed so as to be located in the combustion chamber 38 is attached to the cylinder head 33. In the first embodiment according to the present invention, the fuel injection valve 39 includes a needle. When the needle is lifted away from the seat, fuel injection is started. When the needle is returned to the seat, that is, when the needle lift amount becomes zero, the fuel is injected. Injection is stopped. In this case, the fuel injection amount is changed by changing the needle lift amount and the valve opening time. In the first embodiment of the present invention, light oil as fuel is supplied to the fuel injection valve 39.

  Referring again to FIG. 1, the electronic control unit 50 comprises a digital computer and is connected to each other by a bidirectional bus 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a CPU (Microprocessor) 54, An input port 55 and an output port 56 are provided. For example, the surge tank 4 is provided with an intake pressure sensor 20 for detecting the pressure in the surge tank 4, that is, the intake pressure Pb. The output voltages of the air flow meter 9 and the intake pressure sensor 20 are input to the input port 55 via the corresponding A / D converters 57, respectively. Further, a load sensor 60 that generates an output voltage proportional to the amount of depression of the accelerator pedal 59 is connected to the accelerator pedal 59, and the output voltage of the load sensor 60 is input to the input port 55 via the corresponding AD converter 57. The Further, a crank angle sensor 61 for detecting the crank angle CA is connected to the input port 55. The CPU 54 calculates the engine speed based on the output pulse from the crank angle sensor 61. On the other hand, the output port 56 is connected to the fuel injection valve 39 of the cylinder 2 a, the actuator of the throttle valve 11, the wastegate valve 16, and the EGR control valve 18 via the corresponding drive circuits 58.

  FIG. 3 is a block diagram showing functions of the electronic control unit 50 in the first embodiment according to the present invention. Referring to FIG. 3, the electronic control unit 50 according to the first embodiment of the present invention includes a determination unit 50a and a fuel injection control unit 50b.

  The determination unit 50a has a cylinder oxygen density that is higher than a predetermined first lower limit and lower than a predetermined first upper limit, or lower than the first lower limit and predetermined. Higher than the set second lower limit value, higher than the first upper limit value and lower than a predetermined second upper limit value, lower than the second lower limit value, or the second It is configured to determine whether the value is higher than the upper limit value.

  Here, the in-cylinder oxygen density is represented by, for example, engine torque. That is, when the engine torque TQ is low, the in-cylinder oxygen density is low, and when the engine torque TQ is high, the in-cylinder oxygen density is low. Therefore, in the first embodiment according to the present invention, the determination unit 50a determines that the in-cylinder oxygen density has the first lower limit value when the engine torque TQ is higher than the first lower limit torque TQL1 and lower than the first upper limit torque TQU1. In-cylinder oxygen density when the engine torque TQ is lower than the first lower limit torque TQL1 and higher than the second lower limit torque TQL2 (<TQL1). When it is determined that the engine torque TQ is lower than the first lower limit value and higher than the second lower limit value, and the engine torque TQ is higher than the first upper limit torque TQU1 and lower than the second upper limit torque TQU2 (> TQU1). When it is determined that the in-cylinder oxygen density is higher than the first upper limit value and lower than the second upper limit value, and the engine torque TQ is lower than the second lower limit torque TQL2, the in-cylinder oxygen density is lower than the second upper limit value. Lower than value And then Han斷, engine torque TQ cylinder oxygen density is higher than the second upper limit torque TQU2 is determined to be higher than the second upper limit.

  FIG. 4 shows the first lower limit torque TQL1, the second lower limit torque TQL2, the first upper limit torque TQU1, and the second upper limit torque TQU2 in the first embodiment according to the present invention. In the first embodiment according to the present invention, the first region R1 is defined by the first lower limit torque TQL1 and the first upper limit torque TQU1 in the engine operating state region determined by the engine torque TQ and the engine speed NE. The second region R2 is defined by the lower limit torque TQL1 and the second lower limit torque TQL2, and the third region R3 is defined by the first upper limit torque TQU1 and the second upper limit torque TQU2, and the first region R1, A fourth region R4 is defined in a region other than the second region R2 and the third region R3. In FIG. 4, W represents the full load. Further, the first lower limit torque TQL1, the second lower limit torque TQL2, the first upper limit torque TQU1, and the second upper limit torque TQU2 are preliminarily stored in the form of a map shown in FIG. 4 as a function of the engine speed NE, for example. It is stored in the ROM 52.

  Therefore, the determination unit 50a determines that the in-cylinder oxygen density is higher than the first lower limit value and lower than the first upper limit value when the engine operation state belongs to the first region R1, and the engine operation state Is in the second region R2, it is determined that the in-cylinder oxygen density is lower than the first lower limit value and higher than the second lower limit value, and the engine operating state belongs to the third region R3. When it is determined that the in-cylinder oxygen density is higher than the first upper limit value and lower than the second upper limit value, and the engine operating state belongs to the fourth region R4, the in-cylinder oxygen density is lower than the second lower limit value. It is determined that the value is lower than the value or higher than the second upper limit value. When the engine torque TQ is the first lower limit torque TQL1, it is determined that the engine operation state belongs to the first region R1 in one example, and the engine operation state belongs to the second region R2 in another example. To be judged. When the engine torque TQ is the second lower limit torque TQL2, in one example, it is determined that the engine operating state belongs to the second region R2, and in another example, the engine operating state is determined to belong to the fourth region R4. The When the engine torque TQ is the first upper limit torque TQU1, it is determined in one example that the engine operating state belongs to the first region R1, and in another example, the engine operating state is determined to belong to the third region R3. The When the engine torque TQ is the second upper limit torque TQU2, it is determined in one example that the engine operating state belongs to the third region R3, and in another example, it is determined that the engine operating state belongs to the fourth region R4. The

  In this case, the second region R2 is located on the low torque side of the first region R1 while being adjacent to the first region R1. The third region R3 is located on the high torque side of the first region R1 while being adjacent to the first region R1.

  The in-cylinder oxygen density is also expressed by, for example, an EGR rate (= EGR gas amount / in-cylinder gas amount). That is, when the EGR rate is high, the in-cylinder oxygen density is low, and when the EGR rate is low, the in-cylinder oxygen density is high. Therefore, in another embodiment (not shown), the determination unit 50a determines that the in-cylinder oxygen density has the first lower limit value when the EGR rate is higher than the first lower limit EGR rate and lower than the first upper limit EGR rate. And the in-cylinder oxygen density is the first lower limit value when the EGR rate is higher than the first upper limit EGR rate and lower than the second upper limit EGR rate. And the in-cylinder oxygen density is the first upper limit value when the EGR rate is lower than the first lower limit EGR rate and higher than the second lower limit EGR rate. Higher and lower than the second upper limit value. When the EGR rate is higher than the second upper limit EGR rate, it is determined that the in-cylinder oxygen density is lower than the second lower limit value, and the EGR rate is The in-cylinder oxygen density is higher than the second upper limit value when lower than the second lower limit EGR rate. To determine.

  On the other hand, the fuel injection control unit 50b is configured to perform fuel injection for performing premixed compression self-ignition combustion when the engine operating state belongs to the first region R1. That is, in the region R1, as shown in FIG. 5, the first pre-fuel injection FP1 is first performed, then the second pre-fuel injection FP2 is performed, and then the main fuel injection FM is performed. In this case, the first pre-fuel injection FP1 is performed by the first base pre-fuel injection amount qBFP1 at the first base pre-fuel injection timing tBFP1. The second pre-fuel injection FP2 is performed at the second base pre-fuel injection timing tBFP2 by the second base pre-fuel injection amount qBFP2. The main fuel injection FM is performed by the main fuel injection amount qFM at the main fuel injection timing tM. In one example, the first prefuel injection FP1, the second prefuel injection tFP2, and the main fuel injection FM are all performed during the compression stroke. Further, in the first embodiment according to the present invention, the first base pre-fuel injection timing tBFP1 is set before the timing tX2 that goes back by the predetermined interval dtX from the predetermined reference timing tX1, and from the timing tX2. After this, the second base pre-fuel injection timing tBFP2 is set. The reference time tX1 is, for example, the self-ignition timing of fuel by the second pre-fuel injection FP2. In the following, the fuel injection mode shown in FIG. 5 is referred to as three-time injection.

  When such three injections are performed, the fuel from the first prefuel injection FP1 first self-ignites, then the fuel from the second prefuel injection FP2 self-ignites, and then the fuel from the main fuel injection FM Self-ignite. In this case, the self-ignition of the fuel by the second prefuel injection FP2 is promoted by the combustion of the fuel by the first prefuel injection FP1. Further, the combustion of the fuel by the second pre-fuel injection FP2 promotes the self-ignition of the fuel by the main fuel injection FM.

  Further, the fuel injection control unit 50b is configured to perform another fuel injection for performing premixed compression auto-ignition combustion when the engine operating state belongs to the second region R2 or the third region R3. ing. That is, in the regions R2 and R3, as shown in FIG. 6, the first prefuel injection FP1 is not performed, the second prefuel injection FP2 is performed, and then the main fuel injection FM is performed. In this case, the second pre-fuel injection timing tFP2 is advanced from the second base pre-fuel injection timing tBFP2. Further, the second pre-fuel injection amount qFP2 is set larger than the second base pre-fuel injection amount qBFP2. In one example, the second pre-fuel injection amount qFP2 corresponds to the sum of the first base pre-fuel injection amount qFP1 and the second base pre-fuel injection amount qFP2. In the following, the fuel injection mode shown in FIG. 6 is referred to as double injection.

  When such double injection is performed, the fuel by the second pre-fuel injection FP2 self-ignites, and then the fuel by the main fuel injection FM self-ignites. In this case, the self-ignition of the fuel by the main fuel injection FM is promoted by the combustion of the fuel by the second pre-fuel injection FP2.

  Further, the fuel injection control unit 50b is configured to perform fuel injection for performing diffusion combustion when the engine operating state belongs to the fourth region R4. That is, in the region R4, as shown in FIG. 7, for example, the main fuel injection FM is performed once around the compression top dead center TDC. In this case, the main fuel injection FM is performed by the main fuel injection amount qFM at the main fuel injection timing tm. The fuel injected at this time is diffusely burned. In the following, the fuel injection mode shown in FIG. 7 is referred to as diffusion combustion injection. In another embodiment (not shown), pilot injection may be performed before main fuel injection.

  FIG. 8 shows an example of the heat generation rate dQ / dCA (for example, J / degCA) when the pre-mixed compression auto-ignition combustion is performed by performing the three injections described with reference to FIG. Shown with solid lines. In FIG. 8, the dotted line indicates the fuel combustion contribution CFP1 by the first prefuel injection FP1, the one-dot chain line indicates the fuel combustion contribution CFP2 by the second prefuel injection FP2, and the two-dot chain line indicates the main fuel injection FM. Fuel combustion contributions CM are shown respectively. Further, tIG1 represents the self-ignition timing of the fuel by the first prefuel injection FP1, tIG2 represents the self-ignition timing of the fuel by the second prefuel injection FP2, and tIGM represents the self-ignition timing of the fuel by the main fuel injection, respectively. Show.

  As shown in FIG. 8, the heat generation rate dQ / dCA increases smoothly. Therefore, combustion is stable and no excessive noise is generated.

  However, if, for example, the engine torque TQ decreases beyond the first lower limit torque TQL1, and if the injection is continued three times, the in-cylinder oxygen density is low at this time, the combustion of the fuel by the first prefuel injection FP1 does not occur. May become unstable. Therefore, the fuel combustion by the second pre-fuel injection may be unstable, and the fuel combustion by the main fuel injection may be unstable. An example of the heat generation rate dQ / dCA and the combustion contributions CFP1, CFP2, CM of each fuel injection in this case is shown in FIG.

  On the other hand, even if the engine torque TQ increases beyond the first upper limit torque TQU1, if the injection is continued three times, the in-cylinder oxygen density is high at this time, so the fuel by the first prefuel injection FP1 burns rapidly. There is a risk. As a result, the heat generation rate dQ / dCA may increase while greatly fluctuating. Therefore, excessive torque fluctuation may occur, and excessive noise may occur. An example of the heat generation rate dQ / dCA and the combustion contributions CFP1, CFP2, CM of each fuel injection in this case is shown in FIG.

  For this reason, conventionally, when the engine operating state belongs to the first region R1, injection is performed three times to perform premixed compression auto-ignition combustion, and when the engine operating state is outside the first region R1, diffusion combustion is performed. I was trying to do it. However, if it does in this way, the opportunity to perform premix compression auto ignition combustion will decrease, and the advantage of premix compression auto ignition combustion cannot fully be acquired.

  Therefore, in the first embodiment according to the present invention, when the engine torque TQ falls below the first lower limit torque TQL1, that is, when the engine operating state belongs to the second region R2, or the engine torque TQ is the first. When the engine torque exceeds the upper limit torque TQU1, that is, when the engine operating state belongs to the third region R3, the premixed compression self-ignition combustion is performed by performing the two-time injection described with reference to FIG. I have to.

  In the second injection, since the first pre-fuel injection FP1 is not performed, rapid combustion or unstable combustion of the fuel by the first pre-fuel injection FP1 does not occur. However, if the second pre-fuel injection timing tFP2 remains the second base pre-fuel injection timing tBFP2, and the second pre-fuel injection amount qFP2 remains the second base pre-fuel injection amount qBFP2, There is a possibility that the fuel by the pre-fuel injection of 2 does not self-ignite well. In this regard, in the first embodiment according to the present invention, the second pre-fuel injection timing tFP2 is advanced with respect to the second base pre-fuel injection timing tBFP2, and the second pre-fuel injection amount qFP2 is set to the second base. The pre-fuel injection amount qBFP2 is increased. As a result, good self-ignition of fuel by the second pre-fuel injection is ensured. That is, even if premixed compression auto-ignition combustion is performed outside the first region R1, stable combustion is obtained and noise is limited.

  Therefore, in the first embodiment according to the present invention, the region where the premixed compression auto-ignition combustion is performed is expanded from only the first region R1 to the second region R2 and the third region R3. become.

  11, 12, and 13 show various examples of the frequency distribution D of the equivalence ratio Φ in the vicinity of the self-ignition timing of the fuel. The solid line in FIG. 11 shows the frequency distribution D when the injection is performed three times when the engine operating state belongs to the second region R2. The solid line in FIG. 12 indicates the frequency distribution D when the injection is performed three times when the engine operating state belongs to the third region R3. The solid line in FIG. 13 indicates the frequency distribution D when the injection is performed twice when the engine operating state belongs to the second region R2 or the third region R3. In addition, in FIGS. 11 to 13, the dotted line shows the frequency distribution D when the injection is performed three times when the engine operating state belongs to the first region R1. Further, in FIG. 11 to FIG. 13, DFP1 indicates the frequency distribution D for the fuel by the first prefuel injection FP1, DFP2 indicates the frequency distribution D for the fuel by the second prefuel injection FP2, and DM indicates the main fuel injection. The frequency distribution D about the fuel by FM is shown, respectively. When the air-fuel ratio is the stoichiometric air-fuel ratio, the equivalent ratio Φ is 1, and when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the equivalent ratio Φ is smaller than 1, and the air-fuel ratio is richer than the stoichiometric air-fuel ratio. If there is, the equivalent ratio Φ becomes larger than 1.

  When the above-described three injections are performed in the second region R2, that is, when the in-cylinder oxygen density is low, as shown in FIG. Moves to the lean side. Therefore, combustion becomes unstable. On the other hand, when the third injection is performed in the third region R3, that is, when the in-cylinder oxygen density is high, as shown in FIG. 12, the distribution D is larger than that in the first region R1 (dotted line). Moves to the rich side. Therefore, combustion is activated.

  On the other hand, when the above-described two injections are performed in the second region R2 or the third region R3, as shown in FIG. 13, the distribution DFP2 about the fuel by the second pre-fuel injection FP2 is equivalent. The width becomes wider around the ratio Φ = 1. This is because the second pre-fuel injection timing tFP2 is advanced. Further, the distribution DFP2 having an equivalent ratio Φ of 1 is high. This is because the second pre-fuel injection amount qFP2 is increased.

  Accordingly, conceptually expressed, the fuel injection control unit 50b determines that the in-cylinder oxygen density is higher than the first lower limit value and lower than the first upper limit value. In order to carry out the operation, the first pre-fuel injection is performed at the first base pre-fuel injection timing, and then the second pre-fuel injection is performed at the second base pre-fuel injection timing by the second base pre-fuel injection amount. Then, the main fuel injection is performed, and it is determined that the in-cylinder oxygen density is lower than the first lower limit value and higher than the second lower limit value or higher than the first upper limit value and the second upper limit value. In order to perform premixed compression auto-ignition combustion, the first base fuel injection is not performed, and the second base is started earlier than the second base prefuel injection timing. Perform a second pre-fuel injection by an amount greater than the pre-fuel injection amount, then the main fuel Injection is performed, and when it is determined that the in-cylinder oxygen density is lower than the second lower limit value or higher than the second upper limit value, fuel injection for performing diffusion combustion is performed. It is configured.

  FIG. 14 shows a routine for executing the fuel injection control of the first embodiment according to the present invention. This routine is executed by interruption every predetermined time. Referring to FIG. 14, in step 100, it is determined whether or not the engine operating state belongs to the first region R1. When the engine operating state belongs to the first region R1, the routine then proceeds to step 101 where the above-described three-time injection is performed. On the other hand, when the engine operating state does not belong to the first region R1, the process proceeds from step 100 to step 102 to determine whether the engine operating state belongs to the second region R2 or the third region R3. Is done. When the engine operating state belongs to the second region R2 or the third region R3, the process proceeds to step 103, where the above-described double injection is performed. When the engine operating state does not belong to the second region R2 or the third region R3, the process proceeds from step 102 to step 104, and the above-described diffusion combustion injection is performed.

  Next, a second embodiment according to the present invention will be described. Hereinafter, differences from the first embodiment according to the present invention will be described.

  In the first embodiment according to the present invention, when the region to which the engine operating state belongs shifts from the first region R1 to the second region R2 due to the decrease in the engine torque TQ, the fuel injection mode is switched from the three-time injection to the two-time injection. It is done. Further, when the region to which the engine operating state belongs shifts from the first region R1 to the third region R3 due to the increase of the engine torque TQ, the fuel injection mode is switched from the three-time injection to the two-time injection. In this case, in the first embodiment according to the present invention, the first prefuel injection amount qFP1 is decreased to zero in a stepped manner, the second prefuel injection amount qFP2 is increased in a stepped manner, and the second prefuel injection is performed. Timing tFP2 is advanced stepwise.

  However, at the time of transition in which the engine torque TQ decreases, the intake air amount temporarily becomes larger than the target value. On the other hand, in the second injection, as described above, the second prefuel injection timing tFP2 is advanced, and the second prefuel injection amount qFP2 is increased. As a result, in the first embodiment according to the present invention, there is a risk that the fuel from the second pre-fuel injection FP2 may burn suddenly at the time of transition from the first region R1 to the second region R2. If such rapid combustion is performed in a region where the engine torque TQ is relatively low, such as the second region R2, excessive torque fluctuations may occur, and excessive noise may occur.

  In addition, during a transition in which the engine torque TQ increases, the intake air amount temporarily becomes smaller than the target value. On the other hand, in the second injection, as described above, the first pre-fuel injection FP1 is not performed. As a result, in the first embodiment according to the present invention, the fuel produced by the second pre-fuel injection FP2 may not easily burn. If the combustion is unstable in such a region where the engine torque TQ is relatively high as in the third region R2, excessive torque fluctuation may occur and excessive noise may occur.

  Therefore, in the second embodiment according to the present invention, when switching from three injections to two injections, transient processing is first performed, and then switching to two injections is performed. Next, this transient process will be described.

  Next, with reference to FIG. 15, a transient process when the region to which the engine operating state belongs shifts from the first region R1 to the second region R2 will be described. In FIG. 15, time t1a is the timing when the region to which the engine operating state belongs shifts from the first region R1 to the second region R2, that is, the timing when the required engine torque TQr decreases beyond the first lower limit torque TQL1. Show. In the example shown in FIG. 15, when the intake pressure Pb detected by the intake pressure sensor 20 starts to decrease at time t1b, the first pre-fuel injection amount qFP1 starts to decrease gradually. Further, the second pre-fuel injection amount qFP2 starts to increase gradually. Further, the second pre-fuel injection timing tFP2 starts to be gradually advanced. The first pre-fuel injection amount qFP1, the second pre-fuel injection amount qFP2, and the second pre-fuel injection timing tFP2 at this time are calculated based on, for example, the intake pressure Pb. Therefore, as shown in FIG. 15, each time the intake pressure Pb decreases, the first prefuel injection amount qFP1 is decreased, the second prefuel injection amount qFP2 is increased, and the second prefuel injection timing is increased. tFP2 is advanced. Here, in the second embodiment according to the present invention, the decrease dq1 of the first prefuel injection amount qFP1 and the increase dq2 of the second prefuel injection amount qFP2 are equal to each other. Next, when the first pre-fuel injection amount qFP1 becomes zero at time t1c, the transient process is terminated. On the other hand, in the second embodiment according to the present invention, the main fuel injection amount qFM is kept constant. In FIG. 15, the dotted line indicates the actual intake pressure. In FIG. 15, two-dot chain lines indicate the first prefuel injection amount qFP1, the second prefuel injection amount qFP2, and the second prefuel injection timing tFP2 in the first embodiment according to the present invention. Yes.

  Next, with reference to FIG. 16, a transient process when the region to which the engine operating state belongs shifts from the first region R1 to the third region R3 will be described. In FIG. 16, time t2a is the timing at which the region to which the engine operating state belongs shifts from the first region R1 to the third region R3, that is, the timing at which the required engine torque TQr rises beyond the first upper limit torque TQU1. Show. In the example shown in FIG. 16, when the intake pressure Pb detected by the intake pressure sensor 20 starts to increase at time t2b, the first pre-fuel injection amount qFP1 starts to gradually decrease. Further, the second pre-fuel injection amount qFP2 starts to increase gradually. Further, the second pre-fuel injection timing tFP2 starts to be gradually advanced. The first pre-fuel injection amount qFP1, the second pre-fuel injection amount qFP2, and the second pre-fuel injection timing tFP2 at this time are calculated based on, for example, the intake pressure Pb. Therefore, as shown in FIG. 16, every time the intake pressure Pb decreases, the first prefuel injection amount qFP1 is decreased, the second prefuel injection amount qFP2 is increased, and the second prefuel injection timing is increased. tFP2 is advanced. Here, in the second embodiment according to the present invention, the decrease dq1 of the first prefuel injection amount qFP1 and the increase dq2 of the second prefuel injection amount qFP2 are equal to each other. Next, when the first pre-fuel injection amount qFP1 becomes zero at time t2c, the transient process is terminated. On the other hand, in the second embodiment according to the present invention, the main fuel injection amount qFM is kept constant. In FIG. 15, the dotted line indicates the actual intake pressure. In FIG. 15, two-dot chain lines indicate the first prefuel injection amount qFP1, the second prefuel injection amount qFP2, and the second prefuel injection timing tFP2 in the first embodiment according to the present invention. Yes.

  In the second embodiment according to the present invention, since such transient processing is performed, torque fluctuation is limited and noise is limited at the time of transition from the first region R1 to the second region R2 or the third region R3. Is done.

  FIG. 17 shows a routine for executing the fuel injection control of the second embodiment according to the present invention. This routine is executed by interruption every predetermined time. Referring to FIG. 17, in step 100, it is determined whether or not the engine operation state belongs to the first region R1. When the engine operating state belongs to the first region R1, the routine then proceeds to step 101 where the above-described three-time injection is performed. On the other hand, when the engine operating state does not belong to the first region R1, the process proceeds from step 100 to step 102 to determine whether the engine operating state belongs to the second region R2 or the third region R3. Is done. When the engine operating state belongs to the second region R2 or the third region R3, the routine proceeds to step 102a, where it is determined whether or not the engine operating state belonged to the first region R1 in the previous processing cycle. The When the engine operating state belongs to the first region R1 in the previous processing cycle, that is, when the region to which the engine operating state belongs shifts from the first region R1 to the second region R2 or the third region R3. Next, the routine proceeds to step 102b where the above-described transient processing is performed. Next, the routine proceeds to step 103. When the engine operating state does not belong to the first region R1 in the previous processing cycle, that is, when the region to which the engine operating state belongs remains the second region R2 or the third region R3, the steps 102a to 103 are performed. Proceed to In step 103, the above-described double injection is performed. When the engine operating state does not belong to the second region R2 or the third region R3, the process proceeds from step 102 to step 104, and the above-described diffusion combustion injection is performed.

  By the way, in the third injection, as described above, the first pre-fuel injection FP1, the second pre-fuel injection FP2, and the main fuel injection FM are sequentially performed. In this case, as shown in FIG. 18, the first prefuel injection timing tFP1 and the second prefuel injection timing tFP2 are separated by the first interval dtY1, and the second prefuel injection timing tFP2 is separated from the second prefuel injection timing tFP2. It is separated from the main fuel injection timing tFM by the second interval dtY2. However, as the engine speed NE increases, the first interval dtY1 and the second interval dtY2 become shorter. As a result, when the engine speed NE increases, it becomes difficult to reliably perform the first prefuel injection FP1, the second prefuel injection FP2, and the main fuel injection FM.

  Therefore, in another embodiment (not shown), the above-described three injections are performed when the engine speed NE is lower than a predetermined upper limit speed, and when the engine speed NE is higher than the upper limit speed, the above-described three injections are performed. Two injections are performed. In this way, even when the engine speed NE is high, the second pre-fuel injection FP2 and the main fuel injection FM are reliably performed, and thus premixed compression self-ignition combustion is performed well. In other words, the opportunity for premixed compression auto-ignition combustion is increased.

  On the other hand, the first interval dtY1 and the second interval dtY2 become longer as the engine speed NE becomes lower. Therefore, the injection is continued twice even when the engine speed NE is low.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Engine main body 39 Fuel injection valve 50 Electronic control unit 50a Judgment part 50b Fuel injection control part R1 1st area | region R2 2nd area | region R3 3rd area | region R4 4th area | region FP1 1st pre fuel injection FP2 Second pre-fuel injection FM main fuel injection

Claims (1)

A fuel injection valve configured to inject fuel into the cylinder;
The in-cylinder oxygen density is higher than a predetermined first lower limit and lower than a predetermined first upper limit, or lower than the first lower limit and predetermined second. It is higher than a lower limit value, higher than the first upper limit value and lower than a predetermined second upper limit value, lower than the second lower limit value, or higher than the second upper limit value. A determination unit configured to determine whether it is high;
A fuel injection control unit,
When it is determined that the in-cylinder oxygen density is higher than the first lower limit value and lower than the first upper limit value, the first base prefuel injection is performed in order to perform premixed compression auto-ignition combustion. A first pre-fuel injection at a time, then a second pre-fuel injection amount by a second base pre-fuel injection amount at a second base pre-fuel injection time, then a main fuel injection,
It is determined that the in-cylinder oxygen density is lower than the first lower limit value and higher than the second lower limit value, or higher than the first upper limit value and lower than the second upper limit value. In order to perform premixed compression auto-ignition combustion, the second base pre-fuel is injected at a time earlier than the second base pre-fuel injection timing without performing the first pre-fuel injection. Perform a second pre-fuel injection by an amount greater than the injection amount, then perform a main fuel injection,
When it is determined that the in-cylinder oxygen density is lower than the second lower limit value or higher than the second upper limit value, fuel injection for performing diffusion combustion is performed.
A fuel injection control unit configured as described above,
A control device for an internal combustion engine, comprising:

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