JP2008255995A - Fuel injection device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection device of an internal combustion engine capable of suppressing occurrence of torque shock upon selection of combustion and deterioration of exhaust gas properties. <P>SOLUTION: This fuel injection device is used for the internal combustion engine allowing selection between premixing compression ignition combustion and normal compression ignition combustion with pilot injection according to operating conditions, and the number of fuel injection is not changed upon the selection of combustion in this fuel injection device. In the internal combustion engine allowing selection between the premixing compression ignition combustion and the normal compression ignition combustion with the pilot injection, there is a fear of occurrence of the torque shock and the deterioration of the exhaust gas properties upon the selection of the combustion due to a difference in the number of fuel injection in each combustion. On the contrary, the number of the fuel injection is not changed upon the selection of the combustion according to this invention, therefore, the occurrence of the torque shock and the deterioration of the exhaust gas properties can be suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, fuel is injected once earlier than the injection timing (generally BTDC 10 ° to ATDC 10 °) when performing normal compression ignition combustion, ensuring time until ignition / combustion, and fuel is injected into the combustion chamber An internal combustion engine that has been premixed and then ignited and burned has been proposed. Such combustion is called premixed compression ignition combustion, and fuel and air are thoroughly mixed before combustion, so that low NOx and low smoke can be realized.

  On the other hand, in premixed compression ignition combustion, if the fuel injection amount increases, pre-ignition may occur prematurely. Therefore, operation by premixed compression ignition combustion is actually limited to an operation region where the fuel injection amount is relatively small. For this reason, in an internal combustion engine configured to perform premixed compression ignition combustion as described above, the fuel injection pattern is generally switched in accordance with the operating state of the engine so as to switch between premixed compression ignition combustion and normal compression ignition combustion. I have to. And there is a problem that torque shock occurs at the time of this switching.

  That is, as a fuel injection pattern in the case of performing the above normal compression ignition combustion, a pilot injection mode in which pilot injection is generally performed prior to main injection is generally adopted for the purpose of suppressing deterioration of combustion noise and exhaust properties. The Therefore, when switching between the premixed compression ignition combustion and the normal compression ignition combustion, the fuel injection pattern is switched between the premixed compression ignition combustion mode in which the fuel is injected once and the pilot injection mode. As a result, a torque shock occurs.

  As a technique for mitigating such a torque shock associated with the switching of the fuel injection pattern, for example, Patent Document 1 discloses a fuel injection pattern prior to the main injection and the normal injection mode in which only the main injection is performed according to the operating state of the engine. In an internal combustion engine that is switched between a pilot injection mode in which pilot injection is performed, a technique is disclosed in which a torque shock at the time of switching is reduced by gradually decreasing or increasing an injection interval when switching an injection pattern.

JP-A-5-1609 JP 2000-18077 A

  However, in practice, it is difficult to sufficiently reduce the torque shock even by such a method. This is because, for example, when the number of injections is changed from once to twice, when the injection is performed twice, the injection performed later is affected by the pressure pulsation caused by the injection performed first, etc. This is because the overall fuel injection amount changes from the expected value. Such a change in the fuel injection amount may cause deterioration of exhaust properties in addition to torque shock.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress occurrence of torque shock and deterioration of exhaust properties at the time of combustion switching in an internal combustion engine that switches combustion according to the operating state of the engine. It is to provide a fuel injection device for an internal combustion engine.

The present invention provides a fuel injection device for an internal combustion engine described in each claim as a means for solving the above-mentioned problems.
The invention according to claim 1 is a fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to an operating state, A fuel injection device for an internal combustion engine, characterized in that the number of fuel injections is not changed during switching.

In the internal combustion engine as described above, which switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection, a torque shock occurs at the time of combustion switching and exhaust due to the difference in the number of fuel injections in each combustion. Properties may deteriorate. On the other hand, according to the first aspect of the present invention, since the number of fuel injections is not changed at the time of switching the combustion, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of switching the combustion. .
In the claims and specification of the present application, the number of fuel injections means the number of fuel injections per explosion of the engine.

The invention according to claim 2 is the invention according to claim 1, wherein the number of fuel injections during the premixed compression ignition combustion is the same as the number of fuel injections during the normal compression ignition combustion.
According to the second aspect of the present invention, since the number of fuel injections is not changed in all operation states, occurrence of torque shock and deterioration of exhaust properties are suppressed even at the time of switching to combustion.

In the invention according to claim 3, in the invention according to claim 1 or 2, at least one of the fuel injection interval and the quantity distribution for each injection is not changed when the combustion is switched.
Changing the injection interval and the injection amount distribution of each injection at the time of switching the combustion may cause the generation of torque shock and the deterioration of exhaust properties. Therefore, according to the third aspect of the invention, it is possible to more reliably suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching.

  The invention according to claim 4 is a fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to the operating state, and is a fuel distillation property. In view of the above, there is provided a fuel injection device for an internal combustion engine, wherein whether or not to change the number of times of fuel injection is determined at the time of switching the combustion.

  In premixed compression ignition combustion, it is necessary to perform fuel injection at an early stage. Therefore, when switching from normal compression ignition combustion using pilot injection to premixed compression ignition combustion without changing the number of fuel injections, fuel injection is performed a plurality of times at an early stage. For this reason, it will be in the situation where bore flushing is easy.

  According to the fourth aspect of the present invention, whether or not to change the number of times of fuel injection at the time of switching the combustion in consideration of the distillation property of the fuel, which is one of the indexes indicating the ease of bore flushing. Therefore, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching while suppressing the occurrence of bore flushing.

According to a fifth aspect of the invention, in the fourth aspect of the invention, the distillation property estimating means for estimating the distillation property of the fuel, and the premixing from the normal compression ignition combustion based on the estimated distillation property. An injection number change necessity determining unit that determines whether or not the fuel can be injected without changing the number of fuel injections when changing to the compression ignition combustion. If it is determined that injection can be performed without bore flushing, the number of fuel injections is not changed when switching from the normal compression ignition combustion to the premixed compression ignition combustion, and injection cannot be performed without bore flushing. If it is determined, the number of fuel injections is decreased.
According to the invention described in claim 5, as in the invention described in claim 4, it is possible to suppress generation of torque shock and deterioration of exhaust properties at the time of switching combustion while suppressing occurrence of bore flushing.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the means for determining whether or not to change the number of injections further includes the number of fuel injections when switching from the normal compression ignition combustion to the premixed compression ignition combustion. It is determined whether or not injection can be performed so that sufficient mixing of fuel and air can be performed without changing the fuel, and when it is determined by the determination means that injection can be performed so that sufficient mixing can be performed, When switching from compression ignition combustion to the above premixed compression ignition combustion, the number of fuel injections is not changed, and if it is determined that injection cannot be performed so that sufficient mixing can be performed, the number of fuel injections is decreased.
According to the sixth aspect of the present invention, the generation of torque shock and the deterioration of exhaust properties at the time of combustion switching are suppressed while the occurrence of bore flushing is suppressed and premixed compression ignition combustion is performed satisfactorily. be able to.

According to a seventh aspect of the present invention, in the invention according to the fifth or sixth aspect, the determination means is configured to change a fuel injection interval and each injection at the time of switching from the normal compression ignition combustion to the premixed compression ignition combustion. The injection propriety is determined in consideration of the case where at least one of the quantity distribution to the change is changed.
Bore flushing that occurs when switching from normal compression ignition combustion to premixed compression ignition combustion without changing the number of fuel injections can be achieved, for example, by shortening the fuel injection interval or reducing the amount of initial injection. Can be suppressed. Further, if the amount distribution of the last injection is reduced, the mixing time required after the last injection is shortened.

  Therefore, by making it like the invention of Claim 7, the number of times of fuel injection does not change at the time of combustion switching increases, and it suppresses generation | occurrence | production of bore flashing in more cases, or generation | occurrence | production of bore flushing is suppressed. In addition, it is possible to suppress occurrence of torque shock and deterioration of exhaust properties at the time of combustion switching while performing premixed compression ignition combustion satisfactorily.

The invention according to claim 8 is a fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to an operating state, wherein the premixed compression ignition is used. When performing ignition combustion, it is determined whether or not the number of fuel injections is the same as the number of fuel injections during the normal compression ignition combustion in consideration of the distillation characteristics of the fuel. Providing equipment.
According to the eighth aspect of the invention, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties while suppressing the occurrence of bore flushing even at the time other than the combustion switching.

The invention according to claim 9 is the invention according to claim 8, wherein the distillation property estimation means for estimating the distillation property of the fuel and the estimated distillation property when the premixed compression ignition combustion is performed. Thus, it is necessary to determine whether or not the number of injections needs to be changed even if the number of fuel injections during premixed compression ignition combustion is the same as the number of fuel injections during normal compression ignition combustion. And the determination means determines that injection can be performed without bore flushing, the number of fuel injections during the premixed compression ignition combustion is the number of fuel injections during the normal compression ignition combustion. If it is determined that injection cannot be performed without bore flushing, the number of fuel injections during premixed compression ignition combustion is the number of fuel injections during normal compression ignition combustion. Ri is reduced.
According to the ninth aspect of the invention, the same operation and effect as the eighth aspect of the invention can be obtained.

According to a tenth aspect of the invention, in the ninth aspect of the invention, the means for determining whether or not to change the number of injections further determines the number of fuel injections during the premixed compression ignition combustion and the fuel injection during the normal compression ignition combustion Even if the number of times is the same as the number of times, it is determined whether or not the fuel and air can be injected so that sufficient mixing can be performed. When the number of fuel injections during compression ignition combustion is the same as the number of fuel injections during normal compression ignition combustion, and when it is determined that injection cannot be performed so that sufficient mixing can be performed, fuel injection during premixed compression ignition combustion The number of times is reduced from the number of fuel injections during the normal compression ignition combustion.
According to the tenth aspect of the present invention, generation of torque shock and suppression of deterioration of exhaust properties are suppressed while suppressing occurrence of bore flushing and performing premixed compression ignition combustion well even at times other than combustion switching. Can be achieved.

In the invention described in claim 11, in the invention described in claim 9 or 10, the determination means considers whether or not the injection is possible in consideration of changing at least one of a fuel injection interval and an amount distribution for each injection. Determine.
According to the invention described in claim 11, the number of times of fuel injection is not changed, and in many cases, the occurrence of bore flushing is suppressed, or the occurrence of bore flushing is suppressed and premixed compression ignition is performed. It is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties while ensuring good combustion.

In the invention of claim 12, in the invention of any one of claims 4 to 11, the number of times of fuel injection is not changed at the time of switching from the normal compression ignition combustion to the premixed compression ignition combustion However, at the time of switching, at least one of the fuel injection interval and the quantity distribution for each injection is not changed.
According to the twelfth aspect of the invention, as in the third aspect of the invention, it is possible to more reliably suppress the generation of torque shock and the deterioration of the exhaust properties at the time of switching the combustion.

  According to the first aspect of the present invention, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching. In addition, according to the second aspect of the present invention, occurrence of torque shock and deterioration of exhaust properties are suppressed even at times other than during combustion switching. Furthermore, according to the third aspect of the present invention, it is possible to more reliably suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of switching combustion.

  According to the fourth and fifth aspects of the invention, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching while suppressing the occurrence of bore flushing. According to the sixth aspect of the present invention, the generation of torque shock and the deterioration of exhaust properties during combustion switching are suppressed while the occurrence of bore flushing is suppressed and the premixed compression ignition combustion is performed satisfactorily. Can be achieved. Further, according to the invention described in claim 7, in many cases, the combustion switching is performed while suppressing the occurrence of bore flushing or suppressing the occurrence of bore flushing and performing premixed compression ignition combustion satisfactorily. It is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time.

  According to the eighth and ninth aspects of the invention, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties while suppressing the occurrence of bore flushing even at times other than the time of combustion switching. According to the invention described in claim 10, the generation of torque shock and the deterioration of exhaust properties are suppressed while suppressing the occurrence of bore flushing and performing the premixed compression ignition combustion well even at the time other than the combustion switching. Can be suppressed. According to the eleventh aspect of the present invention, it is possible to reduce the torque shock while suppressing the occurrence of bore flushing in many cases or suppressing the occurrence of bore flushing and performing premixed compression ignition combustion satisfactorily. Generation and deterioration of exhaust properties can be suppressed.

  According to the twelfth aspect of the invention, as in the third aspect of the invention, it is possible to more reliably suppress the generation of torque shock and the deterioration of the exhaust properties at the time of combustion switching.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or similar components are denoted by common reference numerals.

  FIG. 1 is a view showing a direct injection diesel engine equipped with a fuel injection device according to an embodiment of the present invention. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and an intake air cooling device (intercooler) 18 for cooling intake air flowing in the intake duct 13 is arranged around the intake duct 13. Is done. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intake air cooling device 18, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20. An exhaust gas purifier 44 is connected to the outlet of the exhaust turbine 21.
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. Further, an EGR cooling device (EGR cooler) 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooling device 26, and the EGR gas is cooled by the engine cooling water.

  On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. The fuel sucked from the fuel tank 46 by a low-pressure pump (not shown) is further pressurized and supplied into the common rail 27 by an electrically controlled fuel pump 28 having a variable discharge amount. The fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 through each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump 28 is set so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. The discharge amount is controlled.

  The electronic control unit (ECU) 30 is a digital computer and includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, and the like connected to each other by a bidirectional bus 31. An output port 36 is provided. A signal from the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. The accelerator pedal 40 is connected to a load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 (hereinafter referred to as accelerator depression amount) L. The output voltage of the load sensor 41 corresponds to the corresponding AD converter. 37 to the input port 35. Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, and the like via corresponding drive circuits 38.

  Signals input to the input port 35 are sent to the CPU 34. The CPU 34 uses these signals and data stored in the ROM 32, RAM 33, etc. to determine the injection pattern such as the amount and timing of fuel injection related to the present invention. Calculate or determine control values for controlling other engines. Then, the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, and the like are operated in accordance with this injection pattern and control value.

  Next, combustion control of the diesel engine having the above configuration will be described. That is, in the present embodiment, in the diesel engine, premixed compression ignition combustion and normal compression ignition combustion using one pilot injection are switched according to the operating state. The combustion is switched by switching the fuel injection pattern with the fuel injection device.

  FIG. 2 is a flowchart showing a control routine of combustion control (that is, fuel injection control) performed in the diesel engine. This control routine is executed by the ECU 30 by interruption every predetermined time. When this control routine starts, first, in step 101, the operation state parameter is read. Here, the operating state parameter is a parameter that serves as an index of the operating state of the engine. In the present embodiment, the operating state parameter is the engine speed N and the accelerator depression amount L.

  When the engine speed N and the accelerator depression amount L are read in step 101, in the following step 103, it is determined whether or not an execution condition for premixed compression ignition combustion is satisfied. That is, it is determined here whether premixed compression ignition combustion or normal compression ignition combustion is performed according to the operating state.

  This determination is performed based on, for example, a map as shown in FIG. In FIG. 3, the horizontal axis is the engine speed N, and the vertical axis is the accelerator depression amount L. Here, it is determined that the premixed compression ignition combustion execution condition is satisfied when the operation state at that time is in the region S where the engine speed N shown in FIG. 3 is relatively small and the accelerator depression amount L is relatively small. To do. In other words, premixed compression ignition combustion is not performed in the case of high speed / high load operation (that is, in the region H). This is because, in the case of high speed / high load operation (that is, in the region H), the amount of fuel injection increases. Therefore, if fuel injection is performed early in order to perform premixed compression ignition combustion, premature ignition occurs. This is because there is a risk of it. The map shown in FIG. 3 is created in advance for this purpose and stored in the ROM 32.

If it is determined in step 103 that the execution condition is not satisfied, the routine proceeds to step 105, where pilot injection and subsequent main injection are performed (two injections in total). At this time, main injection is performed in the vicinity of compression top dead center, and normal compression ignition combustion is performed in which fuel is ignited and burned while being mixed with air.
On the other hand, if it is determined in step 103 that the above execution condition is satisfied, the routine proceeds to step 107, where two fuel injections are performed early. In this case, pre-mixed compression ignition combustion is performed because the fuel is sufficiently mixed with the air by the early injection and before the ignition / combustion.

  As described above, in the present embodiment, the fuel injection pattern is switched in accordance with the operating state, thereby switching between premixed compression ignition combustion and normal compression ignition combustion using pilot injection. In particular, in the present embodiment, fuel injection is performed the same number of times (that is, twice) in the fuel injection pattern in the case of performing the premixed compression ignition combustion and the fuel injection pattern in the case of performing the normal compression ignition combustion. It has become. The purpose of this is to suppress torque shock and deterioration of exhaust properties that occur at the time of switching between two combustion modes (that is, switching between fuel injection patterns).

  That is, normally, the premixed compression ignition combustion is performed by one fuel injection at an early stage. Therefore, in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection, the fuel injection is performed at the time of combustion switching. The number of times will be changed. When such a change in the number of fuel injections is performed, that is, for example, when the number of injections is changed from once to twice, the injection that is performed later when the number of injections becomes two is performed first. The fuel injection amount may change from the expected value due to the effect of pressure pulsation due to injection (such pressure pulsation may occur when using fuel that is more compressible than diesel oil, such as dimethyl ether) Easy to occur). That is, there may be a step in the change in the total fuel injection amount with the change in the number of fuel injections. As a result, torque shock occurs and exhaust properties deteriorate.

  On the other hand, in the present embodiment, the number of fuel injections during the premixed compression ignition combustion is the same as the number of fuel injections during the normal compression ignition combustion, and therefore the number of fuel injections during the switching of the combustion. Is not changed. For this reason, the problem of the change of the fuel injection amount as described above does not occur, and the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching can be suppressed. In the case of the present embodiment, since the number of fuel injections is not changed in all operation states, occurrence of torque shock and deterioration of exhaust properties are suppressed even when the combustion is switched.

  In the present embodiment, as described above, it is determined whether to perform premixed compression ignition combustion (early twice injection) or normal compression ignition combustion (pilot injection + main injection). At the same time, other fuel injection conditions, for example, total fuel injection amount, pre-injection (for example, first injection of pilot injection or early two-time injection) and post-injection (for example, second injection of main injection or early two-time injection) The injection interval, the injection amount distribution, the detailed injection timing, and the like are also determined in accordance with each operating state (that is, each combination of the engine speed N and the accelerator depression amount L). That is, for example, a map for determining each of the above injection conditions is created in advance from the engine speed N and the accelerator depression amount L, stored in the ROM 32, and determined based on them. Then, actual fuel injection is performed according to each injection condition determined according to these operating states.

  By the way, changing the injection interval and the injection amount distribution between the pre-injection and the post-injection at the time of switching the combustion may cause the generation of torque shock and the deterioration of exhaust properties. Therefore, in order to more reliably suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching, it is preferable not to change the injection interval and the injection amount distribution at the time of switching the combustion.

  For this reason, for example, in the operation state adjacent to the boundary line C of FIG. 3 (that is, the operation state in the vicinity of the boundary line C), these injection conditions are set so that the injection interval and the injection amount distribution are the same. You may set the value of the map which determines. If it does in this way, it can control that the above-mentioned injection interval and injection quantity distribution are changed when a driving state changes slightly and combustion changes. Alternatively, at the time of switching of combustion, the injection interval and the injection amount distribution are not changed, and thereafter, control is performed so as to gradually become an appropriate value (a value determined by a map or the like corresponding to the operation state). Good.

  FIG. 4 is a timing chart showing an example of a fuel injection pattern (that is, a control pattern of the fuel injection valve 6) corresponding to each combustion. The horizontal axis indicates the crank angle, and the vertical axis indicates the needle of the fuel injection valve 6. The lift amount is shown. This figure shows a fuel injection pattern corresponding to each combustion in the vicinity of the boundary line C where the combustion is switched. That is, for example, when the operating state moves from the H region to the S region in FIG. 3, the fuel injection pattern is changed from the upper pattern in FIG. 4 to the lower pattern. In this example, when the combustion is switched, the above-described injection interval between the pre-injection and the post-injection and the injection amount distribution are not changed.

  In the above description, the fuel injection pattern for premixed compression ignition combustion and the fuel injection pattern for normal compression ignition combustion are described as an example in which two fuel injections are performed. The invention is not limited to this, and the number of fuel injections may be greater than three, for example.

  Next, another embodiment of the present invention will be described with reference to FIGS. The configuration shown in FIG. 5 is basically the same as the configuration shown in FIG. 1 except that a density sensor 48 for measuring the fuel density is attached to the common rail 27. The density sensor 48 constitutes a distillation property estimation means for estimating the fuel distillation property. That is, in this embodiment, the density of the fuel is used as a value indicating the distillation property of the fuel (that is, a distillation property parameter described later). A signal from the density sensor 48 is input to the input port 35 via the corresponding AD converter 37.

  As described above, in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to the operating state, by switching the number of fuel injections in each combustion, it is possible to switch combustion, etc. It is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties associated with. However, in premixed compression ignition combustion, it is necessary to perform fuel injection at an early stage. Therefore, when switching from normal compression ignition combustion using pilot injection to premixed compression ignition combustion without changing the number of fuel injections, fuel injection is performed a plurality of times at an early stage. For this reason, it will be in the situation where bore flushing is easy. Therefore, in this embodiment, the density of the fuel is measured by the density sensor 48, the fuel distillation property is estimated from the measured value, and the number of fuel injections is controlled based on the measured fuel density to prevent the occurrence of bore flushing. Yes.

  Next, combustion control (that is, fuel injection control) performed in the present embodiment will be described. Note that the combustion control (that is, fuel injection control) performed in the present embodiment has a common part with the combustion control (that is, fuel injection control) described above with reference to the control routine of FIG. In principle, explanations of these parts are omitted.

  FIG. 6 is a flowchart showing a control routine of combustion control (that is, fuel injection control) executed in the present embodiment. This control routine is executed by the ECU 30 by interruption every predetermined time. When this control routine starts, first, in step 201, the distillation property parameter is read. Here, the distillation property parameter is a parameter serving as an index of the distillation property of the fuel used, and in the case of the present embodiment, is the fuel density.

In the subsequent step 203, the operation state parameter is read in the same manner as in step 101 of FIG. Also in this embodiment, the operating state parameters are the engine speed N and the accelerator depression amount L.
When the engine speed N and the accelerator depression amount L are read in step 203, it is determined in the next step 205 whether or not the premixed compression ignition combustion execution condition is satisfied. The control at this step is the same as the control at step 103 in FIG. If it is determined in step 205 that the execution condition is not satisfied, the routine proceeds to step 207, where pilot injection and subsequent main injection are performed (total of two injections). The control at this step is the same as the control at step 105 in FIG.

  On the other hand, if it is determined in step 205 that the above-described execution condition is satisfied, the process proceeds to step 209, and it is determined whether or not early injection is possible. That is, here, it is determined whether or not early two-time injection can be performed without causing bore flushing from the distillation characteristics of the fuel, the operation state (that is, each injection condition determined by the operation state), and the like.

  That is, for example, the limit value on the advance side of the injection timing without bore flushing is calculated based on the distillation characteristics of the fuel, and the injection timing of the first fuel injection determined from the operating state is on the advance side of this limit value. If there is, it is determined that early two-time injection is impossible, and if it is on the retarded side, it is determined that it is possible.

  Alternatively, a map is prepared in advance to determine whether or not bore flushing occurs from the fuel distillation characteristics and the injection timing and injection amount of the first fuel injection (pre-injection) determined from the operating state. Based on this, it may be determined whether or not the early two-time injection can be performed. That is, the lower the fuel evaporability, the earlier the injection timing of the first fuel injection determined from the operating state, and the greater the injection amount, the easier the bore flushing occurs. For this reason, it is possible to determine whether or not bore flushing occurs from the fuel distillation properties and the injection timing and injection amount of the first fuel injection (pre-injection) determined from the operating state.

  Further, in step 209, in addition to the above-described condition that the bore flushing is not performed, it is determined that the early twice injection can be performed only when it is determined that the fuel and air can be sufficiently mixed after the fuel injection. You may make it do. The determination about the mixing is performed based on, for example, the distillation characteristics of the fuel and the injection timing and injection amount of the second fuel injection (post injection) determined from the operating state. That is, the lower the fuel evaporative property, the later the injection timing of the second fuel injection determined from the operating state, and the larger the injection amount, the more difficult it becomes to mix the fuel and air sufficiently. Therefore, whether or not sufficient mixing of fuel and air is possible after fuel injection from the distillation characteristics of the fuel and the injection timing and injection amount of the second fuel injection (post injection) determined from the operating state. Can be judged.

  FIG. 7 is a diagram showing a relationship among the limit value LT on the advance side of the injection timing without bore flushing, the fuel injection period IT, the fuel / air mixing period MT, and the combustion period BT. The horizontal axis indicates the crank angle, and the vertical axis indicates the needle lift amount of the fuel injection valve 6. In this example, ignition is performed at the compression top dead center.

  If it is determined in step 209 that the early two injections are possible, the process proceeds to step 211, where two fuel injections are performed early, and premixed compression ignition combustion is performed. The control at this step is the same as the control at step 107 in FIG. On the other hand, if it is determined in step 209 that the early twice injection is impossible, the routine proceeds to step 213, where one fuel injection is performed early. Thus, premixed compression ignition combustion is performed while avoiding bore flushing.

  As described above, in the present embodiment, in step 209, in consideration of the fuel distilling property, which is one of the indexes indicating the ease of bore flushing, the early twice injection is performed without causing bore flushing. It is determined whether or not it can be performed. Thereby, generation | occurrence | production of the torque shock at the time of combustion switching and deterioration of exhaust property can be suppressed, avoiding bore flushing.

  Further, in addition to the above-described condition that the bore flushing is not performed in step 209, it is determined that the early twice injection can be performed only when it is determined that the fuel and air can be sufficiently mixed after the fuel injection. In this case, it is possible to suppress the occurrence of torque shock and the deterioration of exhaust properties at the time of combustion switching while suppressing the occurrence of bore flushing and performing premixed compression ignition combustion satisfactorily.

  In another embodiment, in step 209, by changing the injection interval determined from the operating state, the injection amount distribution, or the like, it is possible to inject twice early without bore flushing or without bore flushing and fuel. When the early injection can be performed twice so that the air can be sufficiently mixed, it may be determined that the early injection can be performed twice.

  That is, the above-described bore flushing can be suppressed, for example, by shortening the fuel injection interval or reducing the amount distribution of the first injection. Further, if the amount distribution of the last injection is reduced, the mixing time required after the last injection is shortened. If it is determined that early twice injection is possible in this way, the number of times of fuel injection is not changed at the time of combustion switching, and in many cases the occurrence of bore flushing is suppressed or It is possible to suppress generation of torque shock and deterioration of exhaust properties at the time of combustion switching while suppressing occurrence of flushing and performing premixed compression ignition combustion satisfactorily.

  Also, in the above, one or two fuel injections are performed in the fuel injection pattern when premixed compression ignition combustion is performed, and two fuel injections are performed in the fuel injection pattern when normal compression ignition combustion is performed. However, the present invention is not limited to this, and a larger number of fuel injections may be used.

  Furthermore, in the above description, the density (specific gravity) is used as the distillation property parameter, but the present invention is not limited to this, and other factors such as T50 (50% distillation temperature) and total aroma content can be used. It can implement also using the value showing a distillation property.

FIG. 1 is a diagram showing a direct injection diesel engine equipped with a fuel injection device according to an embodiment of the present invention. FIG. 2 is a flowchart showing a control routine of combustion control (that is, fuel injection control) performed in the diesel engine shown in FIG. FIG. 3 is a map that may be used in step 103 of the control routine of FIG. FIG. 4 is a timing diagram showing an example of a fuel injection pattern (that is, a control pattern of a fuel injection valve) corresponding to each of normal compression ignition combustion and premixed compression ignition combustion. FIG. 5 is a view showing a direct injection diesel engine equipped with a fuel injection device according to another embodiment of the present invention. FIG. 6 is a flowchart showing a control routine of combustion control (that is, fuel injection control) executed in the diesel engine shown in FIG. FIG. 7 is a diagram showing a relationship among the limit value LT on the advance side of the injection timing without bore flushing, the fuel injection period IT, the fuel / air mixing period MT, and the combustion period BT.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 5 Combustion chamber 6 Electrically controlled fuel injection valve 6a Fuel supply pipe 27 Common rail 28 Fuel pump 30 Electronic control unit 46 Fuel tank 48 Density sensor (distillation property estimation means)

Claims (12)

A fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to an operating state,
A fuel injection device for an internal combustion engine, wherein the number of times of fuel injection is not changed when the combustion is switched.   2. The fuel injection device for an internal combustion engine according to claim 1, wherein the number of fuel injections during the premixed compression ignition combustion is the same as the number of fuel injections during the normal compression ignition combustion.   The fuel injection device for an internal combustion engine according to claim 1 or 2, wherein at least one of a fuel injection interval and an amount distribution for each injection is not changed during the switching of the combustion. A fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to an operating state,
A fuel injection device for an internal combustion engine, in which whether or not to change the number of fuel injections is determined when the combustion is switched in consideration of the distillation characteristics of the fuel. Distillation property estimation means for estimating the distillation property of the fuel;
Based on the estimated distillation properties, it is determined whether or not injection can be performed without changing the number of times of fuel injection when changing from the normal compression ignition combustion to the premixed compression ignition combustion. An injection number change necessity determination means to perform,
When it is determined by the determination means that injection can be performed without bore flushing, the number of times of fuel injection is not changed at the time of switching from the normal compression ignition combustion to the premixed compression ignition combustion, and bore flushing is not performed. The fuel injection device for an internal combustion engine according to claim 4, wherein the number of times of fuel injection is decreased when it is determined that the fuel cannot be injected.   The injection number change necessity determining means further allows sufficient mixing of fuel and air without changing the number of fuel injections when switching from the normal compression ignition combustion to the premixed compression ignition combustion. It is determined whether or not the fuel can be injected, and if it is determined by the determination means that the fuel can be injected so that sufficient mixing can be performed, the fuel is changed when the normal compression ignition combustion is switched to the premixed compression ignition combustion. 6. The fuel injection device for an internal combustion engine according to claim 5, wherein the number of fuel injections is decreased when it is determined that injection cannot be performed so that sufficient mixing can be performed without changing the number of injections.   The determination means takes into account the case where at least one of the fuel injection interval and the amount distribution for each injection is changed when switching from the normal compression ignition combustion to the premixed compression ignition combustion. The fuel injection device for an internal combustion engine according to claim 5 or 6, wherein the propriety is determined. A fuel injection device used in an internal combustion engine that switches between premixed compression ignition combustion and normal compression ignition combustion using pilot injection according to an operating state,
When performing the premixed compression ignition combustion, it is determined whether to make the number of fuel injections the same as the number of fuel injections during the normal compression ignition combustion in consideration of the distillation characteristics of the fuel. Engine fuel injection device. Distillation property estimation means for estimating the distillation property of the fuel;
When the premixed compression ignition combustion is performed, the number of fuel injections during the premixed compression ignition combustion is made the same as the number of fuel injections during the normal compression ignition combustion based on the estimated distillation properties. An injection number change necessity determination means for determining whether or not injection can be performed without bore flushing,
When it is determined by the determination means that injection can be performed without bore flushing, the number of fuel injections during the premixed compression ignition combustion is made the same as the number of fuel injections during the normal compression ignition combustion, and no bore flushing is performed. 9. The fuel injection device for an internal combustion engine according to claim 8, wherein when it is determined that the fuel cannot be injected, the number of fuel injections during the premixed compression ignition combustion is reduced from the number of fuel injections during the normal compression ignition combustion. .   The means for determining whether or not the number of injections needs to be changed further allows the fuel and air to be sufficiently mixed even if the number of fuel injections during the premixed compression ignition combustion is the same as the number of fuel injections during the normal compression ignition combustion. It is determined whether or not the fuel can be injected, and if it is determined by the determining means that the fuel can be injected so that sufficient mixing can be performed, the number of fuel injections during the premixed compression ignition combustion is set to the normal compression ignition combustion time. When the number of fuel injections is the same as the number of fuel injections and when it is determined that the fuel cannot be injected so that sufficient mixing can be performed, the number of fuel injections during the premixed compression ignition combustion is reduced from the number of fuel injections during the normal compression ignition combustion. The fuel injection device for an internal combustion engine according to claim 9.   The fuel injection device for an internal combustion engine according to claim 9 or 10, wherein the determination means determines whether or not the injection is possible in consideration of a case where at least one of a fuel injection interval and an amount distribution for each injection is changed.   When the number of times of fuel injection is not changed at the time of switching from the normal compression ignition combustion to the premixed compression ignition combustion, at least one of the fuel injection interval and the amount distribution for each injection is changed at the time of the switching. The fuel injection device for an internal combustion engine according to any one of claims 4 to 11, which is not changed.

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