JP2018193919A - Fuel injection control method and fuel injection control device for diesel engine - Google Patents

Abstract

To reduce knocking noise appropriately even when ignition environment is deteriorated due to reduction in atmospheric pressure.SOLUTION: A fuel injection control device for a diesel engine performs a plurality of fuel injections during a single combustion stroke to provide a plurality of combustions in a cylinder. The fuel injection control device has a PCM 70 that controls fuel injections in the diesel engine. The PCM 70 performs a plurality of fuel injections during a compression stroke in such a way that each injection interval is almost equal and that the number of fuel injections is increased with reduction in atmospheric pressure. After the plurality of fuel injections, the PCM 70 performs a maximum quantity of fuel injection near the compression top-dead center, which is larger than any quantity of the plurality of fuel injections.SELECTED DRAWING: Figure 22

Description

  The present invention relates to a fuel injection control method and a fuel injection control device for a diesel engine that perform a plurality of times of fuel injection during a single combustion stroke to cause a plurality of times of combustion in a cylinder.

  Conventionally, various attempts have been made to reduce diesel engine noise (particularly noise caused by engine knocking, hereinafter simply referred to as “knock noise”). For example, Patent Document 1 calculates a time difference that can reduce a pressure level in a high-frequency region by the interference of combustion pressure waves as a target value of a generation time difference between combustion pressure waves generated by each of a plurality of fuel injections. A technique for controlling an interval between fuel injections performed a plurality of times based on a target value is disclosed. In this technique, the knocking noise is reduced by controlling the fuel injection interval to reduce the frequency component of the in-cylinder pressure in a specific frequency range (2.8 to 3.5 kHz). The “combustion pressure wave” is a pressure wave generated when the in-cylinder pressure rapidly increases due to combustion in the engine, and corresponds to a time-differentiated waveform of the in-cylinder pressure.

  By the way, the knocking sound generated from the engine has a transfer characteristic of the engine structural system, particularly a characteristic corresponding to the resonance frequency of the engine structural system. Specifically, a frequency band including the resonance frequency of the engine structural system (a frequency band having a certain width is obtained by combining resonance of components on the main transmission path of the engine. In such a band related to the resonance frequency is referred to as “resonance frequency band”), the knocking noise tends to increase. In general, there are a plurality of resonance frequency bands of the engine structural system. However, with the technique described in Patent Document 1 described above, only the knocking sound for a specific frequency band of 2.8 to 3.5 kHz is reduced. Therefore, each of the knocking sounds corresponding to a plurality of resonance frequency bands possessed by such an engine structural system cannot be appropriately reduced.

  Here, the knocking noise is in-cylinder pressure level (generally called “CPL (Cylinder Pressure Level)”) corresponding to the combustion excitation force in addition to the resonance of the engine structural system described above. The force index indicates high-frequency energy obtained by Fourier-transforming the in-cylinder pressure waveform. Hereinafter, the characteristic corresponds to “CPL”. This CPL corresponds to the heat generation rate indicating the mode of combustion in the cylinder, but the waveform of this heat generation rate changes under the influence of environmental conditions such as temperature and pressure, and the knocking sound is , Affected by the shape of the waveform of such heat release rate. Therefore, in order to appropriately reduce knocking noise, the interval between multiple fuel injections is set based on the timing at which the heat generation rate becomes maximum (peak), reflecting the influence of environmental conditions such as temperature and pressure. It is desirable to do.

  Focusing on this point, for example, Patent Document 2 discloses a technique for reducing knock noise corresponding to the resonance frequency of the engine structural system. In the technology disclosed in Patent Document 2, the engine system has a waveform trough portion that shows the frequency characteristics of the combustion pressure wave generated by the multiple times of combustion by controlling the intervals between the multiple times of fuel injection. By being included in the respective ranges of the plurality of resonance frequency bands, knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system is reduced.

  In the following, fuel injection control that is performed so as to reduce knock noise corresponding to a specific frequency of the engine (typically, the resonance frequency of the structural system) as disclosed in Patent Document 2 above, This is called “frequency control” as appropriate.

JP 2012-36798 A JP, 2006-217215, A

  In the low load range of a diesel engine, the level of combustion noise is higher than mechanical noise, running noise, intake / exhaust noise, etc., so that knock noise becomes conspicuous. Although the details will be described later, according to a study by the present inventor, it is found that the combustion noise level is reduced if the fuel is continuously injected in the cylinder by performing the fuel injection a plurality of times before the main injection. It was. However, if the ignition environment deteriorates due to a decrease in atmospheric pressure or the like, such continuous combustion becomes difficult to occur, and as a result, knock noise cannot be reduced appropriately.

  The present invention has been made to solve the above-described problems of the prior art, and is capable of appropriately reducing the knocking noise even when the ignition environment is deteriorated. An object is to provide an apparatus.

  In order to solve the above-described problems, the present invention is a fuel injection control method for a diesel engine in which fuel injection is performed a plurality of times during one combustion stroke to generate a plurality of combustions in a cylinder, and the injection interval Are substantially equal and the number of injections is increased in the compression stroke so that the lower the atmospheric pressure, the more fuel injection is performed in the compression stroke, and the plurality of times in the vicinity of the compression top dead center after the plurality of fuel injections. And performing a maximum amount of fuel injection that is greater than the amount of fuel injection.

  In the present invention configured as described above, when fuel injection including a plurality of pre-injections and main injections is performed, the plurality of pre-injections are injected as the injection intervals are substantially equal and the atmospheric pressure is lower. Execute to increase the number of times. Thereby, even if the ignition environment is deteriorated due to a decrease in the atmospheric pressure, the oxidation reaction of the fuel in the cylinder can be promoted by the pre-stage injection in which the number of injections is increased. Therefore, continuous heat generation can be reliably generated in the cylinder before the main injection. As a result, the amount of in-cylinder heat at the start of main combustion and thus the in-cylinder pressure can be increased, and the inclination of the in-cylinder pressure until the maximum in-cylinder pressure due to main combustion can be made gentle, and the high-frequency component of the knocking sound can be appropriately adjusted Can be reduced. Therefore, according to the present invention, even if the ignition environment is deteriorated due to a decrease in atmospheric pressure, it is possible to appropriately reduce the knocking sound.

In the present invention, it is preferable that the crank angle corresponding to the injection interval in a plurality of fuel injections decreases stepwise.
According to the present invention configured as described above, it is possible to more effectively generate heat continuously toward the main injection by the pre-stage injection by executing the plurality of pre-stage injections at an appropriate injection interval. it can.

Moreover, in this invention, Preferably, it has further the step which enlarges the crank angle corresponding to the injection interval in multiple times of fuel injection, so that the rotation speed of a diesel engine is high.
According to the present invention configured as described above, even if the time corresponding to the combustion stroke (combustion cycle) is changed according to the engine speed, the pre-stage injection can be executed at an appropriate injection interval.

In the present invention, it is preferable that the crank angle corresponding to the injection interval in the plurality of fuel injections is substantially constant regardless of the change in the load of the diesel engine.
According to the present invention configured as described above, when the engine load changes, the time corresponding to the combustion stroke does not change as in the case where the engine speed changes, so the injection interval defined by the crank angle. Can be made substantially constant.

In another aspect, the present invention provides a fuel injection control device for a diesel engine that performs fuel injection a plurality of times during a single combustion stroke to generate a plurality of times of combustion in the cylinder, and injects fuel into the cylinder. And a controller for controlling the fuel supply device. The controller has a plurality of compression strokes such that each of the injection intervals is substantially equal and the number of injections increases as the atmospheric pressure decreases. The fuel supply device is controlled so that the maximum amount of fuel injection is performed in the vicinity of the compression top dead center, which is greater than the injection amount of the plurality of fuel injections. It is characterized by that.
Even with the present invention configured as described above, even if the ignition environment is deteriorated due to a decrease in atmospheric pressure, continuous combustion is reliably generated in the cylinder before the main injection by the pre-stage injection with the increased number of injections. be able to. Therefore, the amount of in-cylinder heat at the start of main combustion, and hence the in-cylinder pressure, can be increased, and the inclination of the in-cylinder pressure until reaching the maximum in-cylinder pressure due to main combustion can be made gentle. Even so, the knocking noise can be reduced appropriately.

In the present invention, it is preferable that the controller controls the fuel supply device so that a crank angle corresponding to an injection interval in a plurality of fuel injections is decreased stepwise.
According to the present invention configured as described above, it is possible to more effectively generate heat continuously toward the main injection by the pre-stage injection by executing the plurality of pre-stage injections at an appropriate injection interval. it can.

In the present invention, it is preferable that the controller controls the fuel supply device such that the higher the rotational speed of the diesel engine, the larger the crank angle corresponding to the injection interval in the multiple fuel injections.
According to the present invention configured as above, even if the time corresponding to the combustion stroke is changed according to the engine speed, the pre-stage injection can be executed at an appropriate injection interval.

In the present invention, it is preferable that the controller controls the fuel supply device so that a crank angle corresponding to an injection interval in a plurality of fuel injections is substantially constant regardless of a change in a load of the diesel engine. To do.
According to the present invention configured as described above, when the engine load changes, the time corresponding to the combustion stroke does not change as in the case where the engine speed changes, so the injection interval defined by the crank angle. Can be made substantially constant.

  According to the fuel injection control method and the fuel injection control device for a diesel engine according to the present invention, it is possible to appropriately reduce the knock noise even when the ignition environment is deteriorated.

1 is a schematic diagram illustrating an overall configuration of a diesel engine system to which a fuel injection control device for a diesel engine according to an embodiment of the present invention is applied. It is a block diagram which shows the control system of the diesel engine by embodiment of this invention. It is a time chart which shows the typical fuel-injection pattern applied in embodiment of this invention. It is a graph which shows the heat release rate and CPL in two running scenes with a large difference in knock sound obtained from the actual running scene. It is a simulation result when combustion in a full load region is reproduced in a partial load region. It is the simulation result which compared the combustion waveform which reproduced the combustion in a full load area | region in the partial load area | region, and the combustion waveform with the minimum inclination of heat generation. It is the simulation result of the derived ideal combustion waveform. It is a graph which shows the relationship between an engine load and an ignition delay period. It is a schematic diagram which shows the example of a fuel-injection pattern in a partial load area | region and a full load area | region. It is a schematic diagram which shows the example of a fuel injection pattern which increased the frequency | count of injection in the partial load area | region. It is a conceptual diagram for demonstrating combustion when the frequency | count of injection is increased in a partial load area | region. It is a graph which shows the ignition delay period when the frequency | count of injection increases in a partial load area | region. It is a schematic diagram which shows the example of a fuel-injection pattern applied in a partial load area | region. It is a graph which shows a combustion waveform at the time of applying a 7 step | paragraph reference | standard injection pattern. It is a graph which shows CPL and the amount of smoke at the time of applying a 7th standard injection pattern. It is a graph which shows a combustion waveform at the time of applying the 1st and 2nd 7 step | paragraph improved injection pattern. It is a graph which shows CPL and the amount of smoke at the time of applying the 1st and 2nd 7 step improvement injection pattern. It is explanatory drawing about the sensitivity adjustment method of multistage injection performed in order to clarify the mechanism of CPL and a smoke amount. It is a graph which shows the sensitivity investigation result of each fuel injection of multistage injection in a partial load area | region. It is a graph which shows the combustion waveform by the fuel injection pattern obtained by the calibration based on the mechanism of CPL and a smoke amount. It is a graph which shows the various results at the time of applying a 6 step | paragraph improvement injection pattern in a partial load area | region. It is explanatory drawing about the control content which PCM performs in embodiment of this invention. It is a graph which shows the relationship between an engine speed and each injection space prescribed | regulated with the crank angle. It is a graph which shows the relationship between an engine load and each injection space prescribed | regulated with the crank angle. It is a graph which shows the relationship between atmospheric pressure and the frequency | count of injection. It is a flowchart which shows the fuel-injection control process by embodiment of this invention.

  Hereinafter, a fuel injection control method and a fuel injection control device for a diesel engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Device configuration>
FIG. 1 is a schematic diagram showing an overall configuration of a diesel engine system to which a fuel injection control device for a diesel engine according to an embodiment of the present invention is applied.

  The diesel engine shown in FIG. 1 is a four-cycle diesel engine mounted on a vehicle as a driving power source. Specifically, this diesel engine has a plurality of cylinders 2 and is driven by the supply of fuel mainly composed of light oil, and for introducing combustion air into the engine body 1. An intake passage 30, an exhaust passage 40 for discharging exhaust gas generated in the engine body 1, an EGR device 50 for returning a part of the exhaust gas passing through the exhaust passage 40 to the intake passage 30, And a turbocharger 60 driven by exhaust gas passing through the exhaust passage 40.

  In the intake passage 30, an air cleaner 31, compressors 61 a and 62 a of the turbocharger 60, a throttle valve 36, an intercooler 35, and a surge tank 37 are provided in this order from the upstream side. On the downstream side of the surge tank 37, there are provided independent passages communicating with the cylinders 2 individually, and the gas in the surge tank 37 is distributed to the cylinders 2 through the independent passages.

  In the exhaust passage 40, turbines 62b and 61b of the turbocharger 60 and an exhaust purification device 41 are provided in order from the upstream side.

  The turbocharger 60 is configured as a two-stage supercharging system that can efficiently obtain high supercharging throughout the entire region from a low rotation range to a high rotation range where the exhaust energy is low. That is, the turbocharger 60 includes a large turbocharger 61 for supercharging a large amount of air in a high rotation range, and a small turbocharger 62 that can perform supercharging efficiently even with low exhaust energy. The supercharging by the large turbocharger 61 and the small turbocharger 62 is switched according to the operating state (engine speed and load). The turbines 61b and 62b of the turbocharger 60 are rotated by receiving the energy of the exhaust gas flowing through the exhaust passage 40, and the compressors 61a and 62a rotate in conjunction with the rotation, whereby the air flowing through the intake passage 30 Is compressed (supercharged).

  The intercooler 35 is for cooling the air compressed by the compressors 61a and 62a.

  The throttle valve 36 opens and closes the intake passage 30. However, in the present embodiment, the engine is basically fully opened or maintained at a high opening degree close to that during operation of the engine, and is closed only when necessary, such as when the engine is stopped, to block the intake passage 30.

  The exhaust purification device 41 is for purifying harmful components in the exhaust gas. In the present embodiment, the exhaust purification device 41 includes an oxidation catalyst 41a that oxidizes CO and HC in the exhaust gas and a DPF 41b that collects soot in the exhaust gas.

  The EGR device 50 is for recirculating exhaust gas to the intake side. The EGR device 50 includes an EGR passage 50a that connects a portion of the exhaust passage 40 upstream of the turbine 62 and a portion of the intake passage 30 downstream of the intercooler 35, and an EGR that opens and closes the EGR passage 50a. And a relatively high pressure exhaust gas (high pressure EGR gas) discharged to the exhaust passage 40 is recirculated to the intake side.

  The engine body 1 is opposed to a cylinder block 3 in which a cylinder (cylinder) 2 extending in the vertical direction is formed, a piston 4 accommodated in the cylinder so as to be able to reciprocate (vertically move), and a crown surface of the piston 4. The cylinder head 5 is provided so as to cover the end surface (upper surface) of the cylinder from the side, and the oil pan 6 is provided on the lower side of the cylinder block 3 for storing lubricating oil.

  The piston 4 is connected to a crankshaft 7, which is an output shaft of the engine body 1, via a connecting rod (connecting rod) 8. A combustion chamber 9 is formed above the piston 4, and the fuel injected from an injector 20 as a fuel supply device is diffusely burned while being mixed with air. The piston 4 reciprocates due to the expansion energy associated with the combustion, and the crankshaft 7 rotates about the central axis. The piston 4 is provided with a dynamic vibration absorber that suppresses expansion and contraction resonance of the connecting rod 8. This dynamic vibration absorber will be described later.

  Here, the geometric compression ratio of the engine body 1, that is, the ratio of the combustion chamber volume when the piston 4 is at the bottom dead center to the combustion chamber volume when the piston 4 is at the top dead center is 12 or more and 15 The following is set (for example, 14). This geometric compression ratio of 12 or more and 15 or less is a considerably low value for a diesel engine. This is aimed at improving emission performance and thermal efficiency by suppressing the combustion temperature.

  The cylinder head 5 has an intake port 16 for introducing the air supplied from the intake passage 30 into the combustion chamber 9, and an exhaust port 17 for introducing the exhaust gas generated in the combustion chamber 9 into the exhaust passage 40. An intake valve 18 for opening and closing the opening on the combustion chamber 9 side of the intake port 16 and an exhaust valve 19 for opening and closing the opening on the combustion chamber 9 side of the exhaust port 17 are provided.

  An injector 20 that injects fuel into the combustion chamber 9 is attached to the cylinder head 5. The injector 20 is attached in such a posture that the tip portion on the piston 4 side faces the center of a cavity (not shown) as a recess provided on the crown surface of the piston 4. The injector 20 is connected to a pressure accumulation chamber (not shown) on the common rail side via a fuel flow path. High pressure fuel pressurized by a fuel pump (not shown) is stored in the pressure accumulating chamber, and the injector 20 receives fuel supplied from the pressure accumulating chamber and injects combustion into the combustion chamber 9. A fuel pressure regulator (not shown) is provided between the fuel pump and the pressure accumulating chamber to adjust the pressure in the pressure accumulating chamber, that is, the injection pressure that is the pressure of the fuel injected from the injector 20.

  Next, the control system of the diesel engine according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram showing a control system of the diesel engine according to the present embodiment. As shown in FIG. 2, the diesel engine according to the present embodiment is comprehensively controlled by a PCM (powertrain control module) 70. The PCM 70 is a microprocessor composed of a CPU, ROM, RAM, and the like.

  The PCM 70 is electrically connected to various sensors for detecting the operating state of the engine.

  For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects a rotation angle (crank angle) and a rotation speed of the crankshaft 7. The crank angle sensor SN1 outputs a pulse signal in accordance with the rotation of a crank plate (not shown) that rotates integrally with the crankshaft 7. Based on the pulse signal, the rotation angle and rotation of the crankshaft 7 are output. The speed (that is, the engine speed) is specified.

  In the vicinity of the air cleaner 31 (the portion between the air cleaner 31 and the compressor 61a) in the intake passage 30, an airflow sensor SN2 that detects the amount of air (fresh air amount) that passes through the air cleaner 31 and is sucked into each cylinder 2 is provided. Is provided.

  The surge tank 37 is provided with an intake manifold temperature sensor SN3 that detects the temperature of the gas in the surge tank 37, that is, the gas sucked into each cylinder 2.

  An intake manifold pressure sensor SN4 that detects the pressure of the air passing through this portion and the intake air taken into the cylinder 2 is provided in the portion of the intake passage 30 downstream of the intercooler 35.

  The engine body 1 is provided with a water temperature sensor SN5 that detects the temperature of cooling water that cools the engine body 1. An atmospheric pressure sensor SN6 that detects atmospheric pressure is provided.

  The PCM 70 controls each part of the engine while executing various determinations and calculations based on input signals from the various sensors described above. For example, the PCM 70 controls the injector 20, the throttle valve 36, the EGR valve 50b, the fuel pressure regulator, and the like. In the present embodiment, as shown in FIG. 2, the PCM 70 mainly controls the injector 20 to perform control related to fuel supplied to the cylinder 2 (fuel injection control). The PCM 70 corresponds to the “fuel injection control device for a diesel engine” in the present invention, and functions as a “controller” in the present invention.

  Here, the basic concept of the fuel injection control performed by the PCM 70 in the present embodiment will be described with reference to FIG. FIG. 3 is a time chart showing a typical fuel injection pattern applied in the present embodiment.

  In the present embodiment, as shown in FIG. 3, the PCM 70 performs a plurality of fuel injections (multi-stage injection) during one combustion stroke to cause a plurality of combustions in the cylinder. Specifically, the PCM 70 performs pilot injection relatively early, and then performs pre-injection at a timing relatively close to the main injection timing. In this injection pattern, it is possible to increase the air utilization rate by improving the premixability of fuel and air by performing the pilot injection that is the first injection. The pilot injection and the pre-injection, which is the next injection, cause pre-combustion, which is combustion with a small amount of heat generation, immediately before the main injected fuel burns, that is, immediately before main combustion occurs. The main injected fuel can be easily burned. In addition, the PCM 70 performs after-injection in which a smaller amount of fuel is injected into the combustion chamber 9 at a timing after the main injection so that soot generated in the combustion chamber 9 is combusted. To do.

  In FIG. 3, one pilot injection, pre-injection, main injection, and after-injection are shown, but at least one or more of these fuel injections (typically pre-injection) may be performed twice or more, It is not necessary to perform at least one or more of these fuel injections (typically after injection).

  Further, the PCM 70 applies a fuel injection pattern according to the operating state of the engine. That is, the PCM 70 determines the timing and period for executing pilot injection, pre-injection, main injection and after-injection, the number of execution times of pilot injection, pre-injection, main injection and after-injection, according to the engine load and engine speed, Change execution / non-execution of pilot injection, pre-injection, main injection, and after injection.

  Typically, the PCM 70 determines the basic injection timing of the main injection (hereinafter referred to as “reference main injection timing”) based on the required output corresponding to the accelerator opening of the driver, the operating state of the engine, and the like. Set). Further, the PCM 70 is pre-injected, for example, in order to cause combustion with a small amount of heat generation by pre-injection immediately before the main injected fuel is combusted, and to form a state in which the main injected fuel is easily combusted. The injection timing of the pre-injection is set as a timing at which the fuel spray is contained in a cavity provided on the crown surface of the piston 4 and a relatively rich air-fuel mixture is formed in the cavity. Further, the PCM 70 sets the injection timing of the after injection as a timing at which soot generated in the combustion chamber 9 by the fuel injection before the after injection is appropriately burned by the after injection.

<Basic concept of control>
Next, the basic concept of control according to the embodiment of the present invention will be described with reference to FIG. 4 and subsequent drawings.

  As described above, the frequency control as disclosed in Patent Document 2 can reduce the knocking sound corresponding to a plurality of frequency bands such as the resonance frequency component, but reduces the overall level of the knocking sound. Is insufficient. In particular, in a low load range of a diesel engine, the level of combustion noise is greater than mechanical noise, running noise, intake / exhaust noise, and the like, and knock noise becomes noticeable. In order to reduce the level of the combustion noise, a method of reducing the maximum combustion pressure is conceivable. However, with this method, the smoke amount (soot generation amount) increases and the fuel consumption deteriorates. That is, basically, the knocking sound and the smoke amount are in a contradictory relationship, and the knocking sound and the fuel consumption are in a conflicting relationship.

  Therefore, the present inventor has made an effort to find an ideal combustion from the viewpoint of CPL in order to search for an ideal combustion that can appropriately reduce the knock noise without deteriorating smoke and fuel consumption. First, the inventor tried to find a clue that leads to CPL reduction from an actual running scene, focusing on a scene with a small knocking sound and a scene with a large knocking sound. As a result, the knock noise is small in the full load region where the combustion energy (torque) is the largest, whereas the knock noise is large in the light and medium load region on the low rotation side (that is, a level at which the knock noise can be heard). all right. In the following, the term “partial load region” for the entire load region will be used as appropriate to indicate such a light and medium load region on the low rotation side. Typically, an operation state in which the engine speed is about 1500 rpm and the engine load is about 500 kPa belongs to this partial load region.

  FIG. 4 shows the heat generation rate and CPL in two traveling scenes (specifically, a partial load region and a full load region) where the difference in knocking noise obtained from the actual traveling scene is large. FIG. 4A shows the crank angle on the horizontal axis, the heat generation rate on the vertical axis, and FIG. 4B shows the frequency on the horizontal axis and CPL on the vertical axis. . Specifically, graphs G11 and G13 show the heat generation rate and CPL obtained in the running scene in the partial load region, respectively, and graphs G12 and G14 show the running scene in the full load region, respectively. Shows the heat generation rate and CPL obtained. 4 (a) and 4 (b), focusing on the difference in combustion between the partial load region and the full load region, it can be seen that the high frequency energy is small in the full load region despite the large amount of generated heat (torque). . Therefore, the present inventor tried to find an ideal combustion waveform from the combustion waveform in the full load region where the knocking noise is small by utilizing simulation.

  FIG. 5 shows a simulation result when combustion in the full load region is reproduced in the partial load region. FIG. 5A shows the crank angle on the horizontal axis, the heat generation rate on the vertical axis, and FIG. 5B shows the frequency on the horizontal axis and CPL on the vertical axis. . Specifically, the graphs G11 to G14 are the same graphs as in FIGS. 4A and 4B, and the graph G15 shows the heat generation rate (graph G12) in the entire load region by the similar heat generation. The combustion waveform deformed so as to match the partial load region is shown, and the graph G16 shows the CPL when the combustion waveform of the deformed graph G15 is applied. From graph G16, it was found that CPL is greatly reduced by transferring the similar combustion waveform in the full load region to the partial load region. Therefore, the present inventor decided to examine how much CPL can be reduced by further simulation.

  FIG. 6 shows a simulation result comparing a combustion waveform in which combustion in the full load region is reproduced in a partial load region and a combustion waveform in which the inclination of heat generation is minimum. FIG. 6A shows the crank angle on the horizontal axis, the heat generation rate on the vertical axis, and FIG. 6B shows the frequency on the horizontal axis and CPL on the vertical axis. . Specifically, the graphs G13, G15, and G16 are the same graphs as FIGS. 5A and 5B, and the graph G17 is a combustion waveform that reproduces combustion in the full load region in the partial load region ( The combustion waveform which made the inclination the minimum under the same torque conditions as graph G15) is shown. This graph G17 has a combustion waveform in which the amount of heat generation is increased and the combustion slope is made gentler than that in the graph G15 at the rise of the heat generation rate, and the heat generation amount is reduced more than that in the graph G15 at the peak of the heat generation rate. is there. Further, the graph G18 shows the CPL when the combustion waveform of the graph G17 is applied. Comparing this graph G18 with graph G16 showing CPL in a combustion waveform in which combustion in the full load region is reproduced in the partial load region, it can be said that there is room for CPL reduction at a frequency of 1500 Hz or less. Therefore, the present inventor decided to study further reduction of CPL at a frequency of 1500 Hz or less by simulation.

  FIG. 7 shows a simulation result of the derived ideal combustion waveform. FIG. 7A shows the crank angle on the horizontal axis, the heat generation rate on the vertical axis, and FIG. 7B shows the frequency on the horizontal axis and CPL on the vertical axis. . Specifically, the graphs G13, G17, and G18 are the same graphs as FIGS. 6A and 6B, and the graph G19 is based on the combustion waveform (graph G17) having the smallest inclination of heat generation. The combustion waveform that can be realized with an actual machine (hereinafter referred to as “target combustion waveform”) is shown. It can be seen that the target combustion waveform shown in the graph G19 almost traces the combustion waveform with the minimum inclination of heat generation shown in the graph G17, except for the amount of combustion due to after-injection. Further, the graph G20 shows the CPL when the target combustion waveform of the graph G19 is applied. Thereby, according to a target combustion waveform, it turns out that CPL is reduced appropriately in the frequency of 1500 Hz or less.

  Through the simulation described above, a target combustion waveform (ideal combustion waveform) can be derived from a combustion waveform in which combustion in the full load region is reproduced in the partial load region. Therefore, the present inventor decided to investigate the combustion function to be controlled to realize this ideal combustion waveform. Specifically, the combustion function to be enhanced is extracted from the combustion in the full load region where the knocking noise is small. First, the present inventor compared the combustion in the partial load region and the combustion in the full load region in order to clarify the reason why the knocking noise is small in the combustion in the full load region. In particular, the present inventor examined an ignition delay period (a period from the start of fuel injection to the start of combustion) between combustion in the partial load region and combustion in the full load region.

  FIG. 8 shows the relationship between the engine load and the ignition delay period. FIG. 8A shows the engine load on the horizontal axis, the ignition delay period of pre-combustion (particularly, the period from pilot injection to the peak of pre-combustion) on the vertical axis, and FIG. The horizontal axis represents the engine load, and the vertical axis represents the main combustion ignition delay period (particularly, the period from main injection to main combustion start). 8 (a) and 8 (b), it can be seen that the ignition delay period becomes shorter in both pre-combustion and main combustion as the engine load increases. Particularly in the full load region, the ignition delay period is minimized. Therefore, the present inventor has considered a mechanism in which the knocking noise is reduced in the entire load region due to the short ignition delay period.

  Here, the mechanism of CPL deterioration and improvement due to ignition delay is considered. First, when the ignition delay period is long, the amount of unburned fuel (premixed gas amount) in the combustion chamber increases because the time from the start of fuel injection to the ignition of fuel is long. Therefore, when the ignition delay period is long, a large amount of fuel is burned in the combustion chamber, so that combustion becomes large and CPL deteriorates. On the other hand, when the ignition delay period is short, since the time from the start of fuel injection to the ignition of the fuel is short, the amount of unburned fuel (premixed gas amount) in the combustion chamber decreases. Therefore, when the ignition delay period is short, it is conceivable that a small amount of fuel burns in the combustion chamber, thereby reducing the combustion and improving the CPL.

  Therefore, the present inventor considered improving the CPL by adjusting the fuel injection pattern to shorten the ignition delay period. However, although the CPL is improved by shortening the ignition delay period, since the knocking sound and the amount of smoke are in a trade-off relationship as described above, the amount of smoke increases. Although it is necessary to consider such a smoke amount, the present inventor first considered an achievement means necessary for controlling the ignition delay period.

  FIG. 9 schematically shows examples of fuel injection patterns in the partial load region and the full load region. In the example shown in FIG. 9, pilot injection, pre-injection, main injection, and after injection are performed in the partial load region, and two pre-injections and main injection are performed in the full load region. More specifically, in the partial load region, fuel injection is performed a plurality of times at relatively long intervals. This is to secure the time for using the swirl flow in the combustion chamber and the penetration of fuel injection to improve the mixing of the fuel and air in the combustion chamber. On the other hand, in the full load region, fuel injection is performed a plurality of times at relatively short intervals. This is because, in the full load region, the environment in which the fuel and air in the combustion chamber can be sufficiently mixed is secured, so that it is not necessary to use a swirl flow or penetration as in the partial load region. In particular, in the full load region, the amount of fuel injection to be performed a plurality of times is increased stepwise while bringing the fuel injections to be close to each other (hereinafter referred to as “slope injection” as appropriate).

  Thus, in the partial load region, since the injection interval of the plurality of fuel injections is long, the ignition delay period becomes long, whereas in the full load region, the injection interval of the plurality of fuel injections is short, so that the ignition is delayed. It is considered that the delay period is shortened. Therefore, first, the present inventor considered increasing the number of fuel injections in the partial load region in order to shorten the injection interval and shorten the ignition delay period.

  FIG. 10 schematically shows an example of a fuel injection pattern in which the number of injections is increased in the partial load region. As shown in the lower part of FIG. 10, in the partial load region, the pre-injection is increased once, that is, the pre-injection is performed twice.

  FIG. 11 shows a conceptual diagram for explaining combustion when the number of injections is increased in the partial load region. FIG. 11A shows a combustion image in the combustion chamber when the number of injections is increased in the partial load region, and FIG. 11B shows a combustion image in the combustion chamber in the full load region. As shown in FIG. 11 (b), in the full load region, the injection amount increases stepwise, and therefore combustion (energy) continuously increases in the combustion chamber. Further, as shown in FIG. 11A, when the number of injections is increased in the partial load region, small combustion (energy) is dispersed in the combustion chamber, and ignition is performed sequentially. That is, even in the partial load region, by increasing the number of injections, combustion similar to the full load region can be formed in the combustion chamber. Therefore, the ignition delay period can be shortened in the partial load region.

  FIG. 12 shows the ignition delay period when the number of injections is increased in the partial load region. Specifically, FIG. 12A shows the ignition delay period before and after the increase in the number of injections in the pre-combustion, and FIG. 12B shows the increase in the number of injections in the main combustion before and after the increase. Indicates the ignition delay period. 12 (a) and 12 (b), it can be seen that when the number of injections is increased in the partial load region, the ignition delay period is shortened for both pre-combustion and main combustion (particularly main combustion).

  Therefore, the present inventor decided to examine the calibration of the fuel injection pattern combining the increase in the number of injections and the slope injection in order to shorten the ignition delay period in the partial load region. In this case, the maximum number of injections applied to the fuel injection pattern was seven. For example, a fuel injection pattern including three pilot injections, two pre-injections, one main injection, and one after injection was used. In addition, the injection amount of each of these fuel injections is also changed as appropriate.

  FIG. 13 schematically shows an example of a fuel injection pattern applied in the partial load region. In FIG. 13, in order to shorten the ignition delay period in the partial load region, fuel injection is performed seven times and the injection amount is increased stepwise (that is, slope injection is performed). An example of a pattern is shown. Hereinafter, the fuel injection pattern as shown in FIG. 13 is appropriately referred to as a “seven-stage reference injection pattern”.

  FIG. 14 shows a combustion waveform when the seven-stage reference injection pattern is applied. FIG. 14 shows the crank angle on the horizontal axis and the heat generation rate on the vertical axis. Specifically, the graphs G11 and G19 are the same graphs as those in FIGS. 4A and 7A, respectively. That is, the graph G11 shows a combustion waveform according to the original fuel injection pattern in the partial load region (hereinafter referred to as “reference injection pattern” as appropriate) in which the increase in the number of injections and the slope injection are not applied. Graph G19 shows a target combustion waveform based on a combustion waveform (see graph G17 in FIG. 6A) in which the inclination of heat generation is minimum. On the other hand, graph G21 shows the combustion waveform when the seven-stage reference injection pattern is applied. From this graph G21, it can be seen that the target combustion waveform can be substantially reproduced when the seven-stage reference injection pattern is applied.

  FIG. 15 shows the CPL and the smoke amount when the seven-stage reference injection pattern is applied. Specifically, FIG. 15A shows the CPL when the reference injection pattern and the seven-stage reference injection pattern are applied. FIG. 15A shows that the CPL is greatly improved when the seven-stage reference injection pattern is applied, compared to when the reference injection pattern is applied. On the other hand, FIG. 15B shows the smoke amount when the reference injection pattern and the seven-stage reference injection pattern are applied. FIG. 15B shows that when the seven-stage reference injection pattern is applied, the smoke amount is worse than when the reference injection pattern is applied. Therefore, the present inventor decided to study the improvement of the smoke amount by such a seven-stage reference injection pattern.

  FIG. 16 shows combustion waveforms when the first and second seven-stage improved injection patterns obtained by improving the seven-stage reference injection pattern are applied. In FIGS. 16A and 16B, the horizontal axis indicates the crank angle, and the vertical axis indicates the heat generation rate.

Specifically, in FIG. 16A, a graph G21 is the same graph as FIG. 14, that is, shows a combustion waveform when the seven-stage reference injection pattern is applied, and the graph G22 is the first graph. The combustion waveform at the time of applying a 7-stage improved injection pattern is shown. This first seven-stage improved injection pattern eliminates a dent (valley) at the rising portion of the combustion waveform and smoothes the rising of the combustion waveform (stabilizes the slope), compared to the seven-stage reference injection pattern, Further, this is an injection pattern in which the peak of the combustion waveform is advanced and the calorific value at the rising portion of the combustion waveform corresponding to the main combustion is reduced. Such a first seven-stage improved injection pattern attempts to reduce the amount of smoke. Note that the dent (valley) at the rising portion of the combustion waveform has a sharp rise when returning from the dent, and thus becomes a large factor of knocking noise, particularly impact noise containing a lot of high-frequency components.
Further, in the first seven-stage improved injection pattern, in order to further reduce the amount of smoke, the after-injection is retarded from the seven-stage reference injection pattern, so that the mixing period of fuel and air is extended. . The reason why the combustion waveform is advanced in the first seven-stage improved injection pattern as described above is to suppress a torque drop (deterioration of fuel consumption) due to the retard of the after injection.

  On the other hand, in FIG. 16B, a graph G22 is the same graph as FIG. 16A, that is, shows a combustion waveform when the first seven-stage improved injection pattern is applied. The combustion waveform at the time of applying the 2nd 7 step | paragraph improved injection pattern is shown. This second seven-stage improved injection pattern is basically the same pattern as the first seven-stage improved injection pattern, but differs from the first seven-stage improved injection pattern in that the fuel injection pressure is increased. . By increasing the fuel injection pressure in this way, it is intended to improve the homogenization of the fuel and reduce the amount of smoke.

  FIG. 17 shows the CPL and the smoke amount when the first and second seven-stage improved injection patterns are applied. Specifically, FIG. 17A shows the CPL when the reference injection pattern, the seven-stage reference injection pattern, and the first and second seven-stage improved injection patterns are applied. FIG. 17A shows that the CPL is further improved when the first and second seven-stage improved injection patterns are applied than when the seven-stage reference injection pattern is applied. On the other hand, FIG. 17B shows the smoke amount when the reference injection pattern, the seven-stage reference injection pattern, and the first and second seven-stage improved injection patterns are applied. From FIG. 17B, when the first and second seven-stage improved injection patterns are applied, the smoke amount is improved as compared with the case where the seven-stage reference injection pattern is applied, but the reference injection pattern is applied. It can be seen that the smoke amount is still worse than the case. Therefore, the present inventor considered that it is difficult to further reduce the smoke amount only by improving the after injection and the injection pressure in the first and second seven-stage improved injection patterns. Therefore, the present inventor decided to unravel the factors that determine the CPL and the amount of smoke in multistage injection.

  FIG. 18 is an explanatory diagram of a sensitivity adjustment method for multi-stage injection that is performed in order to clarify the mechanism of CPL and the amount of smoke. FIG. 18A shows an example of a fuel injection pattern applied to the mechanism elucidation. This fuel injection pattern includes seven-stage injection including pilot injection 1, pilot injection 2, pre-injection 1, pre-injection 2, main injection, after-injection 1, and after-injection 2. FIG. 18B shows an example of a combustion waveform when the fuel injection pattern of FIG. 18A is applied. In this combustion waveform, region R11 corresponds to combustion by pilot injection 1 and pilot injection 2, region R12 corresponds to combustion by pre-injection 1, region R13 corresponds to combustion by pre-injection 2, and region R14 corresponds to main injection. And it corresponds to the combustion by the after injection 1.

  Here, the present inventor has sought to elucidate the function provided in each fuel injection in the multistage injection by investigating the heat generation and smoke sensitivity with respect to the injection amount for each fuel injection in the multistage injection. In this investigation, the knock noise was substituted with the calorific value by replacing the slope of the heat generation rate having a high correlation with CPL with the change in the calorific value per unit injection amount.

  FIG. 19 shows the result of the sensitivity investigation of each fuel injection of the multi-stage injection in the partial load region. Specifically, FIG. 19A shows a change in the amount of heat generated per unit injection amount for pilot injection 1, pilot injection 2, pre-injection 1, pre-injection 2, and after-injection 1. FIG. This change in the amount of generated heat uniquely indicates a knock sound (CPL). From FIG. 19A, it can be seen that the change in height of the heat generation amount is large for the pilot injection 2 and the pre-injection 1. That is, it can be seen that pilot injection 2 and pre-injection 1 have a greater influence on knock noise (CPL) than other fuel injections. On the other hand, FIG. 19B shows changes in the smoke amount per unit injection amount for pilot injection 1, pilot injection 2, pre-injection 1, pre-injection 2 and after-injection 1. FIG. From FIG. 19B, it can be seen that the smoke amount changes greatly with respect to the pre-injection 1, the pre-injection 2, and the after-injection 1. That is, it can be seen that the pre-injection 1, the pre-injection 2, and the after-injection 1 have a greater influence on the smoke amount than other fuel injections.

  From the investigation results shown in FIGS. 19A and 19B, the CPL and the smoke amount that the magnitude of the CPL depends on the fuel injection in the previous stage and the magnitude of the smoke quantity depends on the fuel injection in the subsequent stage. The mechanism of was found. Therefore, based on this mechanism, the present inventor calibrates the fuel injection pattern in order to reduce the CPL by adjusting the fuel injection at the front stage and to reduce the smoke amount by adjusting the fuel injection at the rear stage. I decided to do it.

  FIG. 20 shows a combustion waveform based on the fuel injection pattern obtained by the calibration based on the mechanism of the CPL and the smoke amount as described above. FIG. 20 shows the crank angle on the horizontal axis and the heat generation rate on the vertical axis. Specifically, the graph G11 is the same graph as FIG. 4A, that is, shows a combustion waveform based on the reference injection pattern, and the graph G24 is obtained by calibration based on the mechanism of the CPL and the smoke amount. Moreover, the combustion waveform by the fuel-injection pattern in the partial load area | region is shown. The latter fuel injection pattern is composed of six stages of fuel injection, and is hereinafter referred to as “six-stage improved injection pattern” as appropriate. This six-stage improved injection pattern is basically an injection pattern in which the front-stage fuel injection in the above-described seven-stage injection pattern (seven-stage reference injection pattern, first and second seven-stage improved injection patterns) is eliminated. It is.

  Specifically, in the six-stage improved injection pattern, the pre-combustion is included in the main combustion, thereby eliminating the depression (valley) at the rising portion of the combustion waveform and making the rising of the combustion waveform gentle (region R21). reference). Thereby, CPL is reduced. In particular, the high frequency component of the knocking sound is reduced. In the six-stage improved injection pattern, the shape of the combustion waveform corresponding to the main combustion is trapezoidal by multistage injection (see region R22) to reduce the amount of smoke. Further, in the six-stage improved injection pattern, after injection is retarded to further reduce the amount of smoke. In this case, the main combustion is advanced in the six-stage improved injection pattern in order to suppress the torque drop (deterioration of fuel consumption) due to the retard of the after injection.

  FIG. 21 shows various results when the six-stage improved injection pattern is applied in the partial load region. First, FIGS. 21A and 21B show the ignition delay periods in the pre-combustion and main combustion when the reference injection pattern and the six-stage improved injection pattern are applied, respectively. 21A and 21B, when the six-stage improved injection pattern is applied, the ignition delay period may be shorter in both the pre-combustion and the main combustion than when the reference injection pattern is applied. Recognize.

  Next, FIG. 21C shows CPL when the reference injection pattern and the six-stage improved injection pattern are applied. From FIG. 21 (c), it can be seen that when the six-stage improved injection pattern is applied, the CPL becomes smaller than when the reference injection pattern is applied (for example, about 6 dB lower).

  Next, FIG. 21D shows the smoke amount when the reference injection pattern and the six-stage improved injection pattern are applied. From FIG. 21 (d), it can be seen that the smoke amount is the same when the six-stage improved injection pattern is applied and when the reference injection pattern is applied. This means that when the six-stage improved injection pattern is applied, the smoke amount is improved as compared with the case where the above-described seven-stage standard injection pattern and the first and second seven-stage improved injection patterns are applied. To do.

  Next, FIG. 21 (e) shows the CO amount and the HC amount when the reference injection pattern and the six-stage improved injection pattern are applied. From FIG. 21 (e), when the six-stage improved injection pattern is applied, the CO amount becomes smaller (for example, about 20% reduction) than when the reference injection pattern is applied, and the six-stage improved injection pattern It can be seen that the amount of HC is the same when applied and when the reference injection pattern is applied. This is considered to be because when the six-stage improved injection pattern is applied, the fuel (unburned fuel) adhering to the cylinder is reduced.

  Next, FIG. 21 (f) shows the fuel efficiency when the reference injection pattern and the six-stage improved injection pattern are applied. From FIG. 21 (f), it can be seen that the fuel efficiency is the same when the six-stage improved injection pattern is applied and when the reference injection pattern is applied.

  From the above, according to the six-stage improved injection pattern, knock noise can be significantly reduced in the partial load region without causing deterioration of emissions such as smoke or fuel consumption.

<Control according to this embodiment>
Next, the control according to the embodiment of the present invention based on the basic concept described in the above section will be specifically described.

  FIG. 22 is an explanatory diagram for the control performed by the PCM 70 in the embodiment of the present invention. FIG. 22 schematically shows fuel injection performed a plurality of times, with time shown in the horizontal direction (uniquely corresponding to the crank angle), fuel injection amount in the vertical direction. In the present embodiment, the PCM 70 performs one main injection, three previous injections before the main injection, and one subsequent injection after the main injection in the partial load region as described above. . The front-stage injection includes at least the pre-injection (the pilot injection may or may not be included), and the rear-stage injection is the after injection. In the following, each of the three previous-stage injections will be referred to as “first-stage injection”, “second-stage injection” and “third-stage injection”, the main injection will be referred to as “fourth-stage injection”, and the subsequent-stage injection will be referred to as “ This is called “fifth stage injection”.

  In particular, in the present embodiment, as shown by the solid line L11 in FIG. 22, the PCM 70 steps the fuel injection amount applied to each of the first-stage injection, the second-stage injection, and the third-stage injection toward the main injection. Increase, that is, perform slope injection. As a result, the heat generation rate is continuously increased by the first-stage injection, the second-stage injection, and the third-stage injection, so that the in-cylinder heat amount at the start of main combustion and thus the in-cylinder pressure are increased. By so doing, the inclination of the in-cylinder pressure up to the maximum in-cylinder pressure due to main combustion can be made gentle, and the high-frequency component of the knocking sound can be reduced appropriately.

In the present embodiment, the PCM 70 substantially sets the injection intervals T11, T12, T13, and T14 between the first stage injection, the second stage injection, the third stage injection, the fourth stage injection, and the fifth stage injection. Keep it constant. In particular, by making the injection intervals T11, T12, and T13 substantially constant, heat can be continuously generated toward the main injection by the first-stage injection, the second-stage injection, and the third-stage injection.
As shown in FIG. 22, the injection intervals T11, T12, and T13 when viewed in time are substantially constant, but when viewed in terms of the crank angle, these intervals are not constant. Specifically, the width of the crank angle corresponding to the injection interval becomes smaller as it proceeds to the rear side (retard side). That is, “the crank angle width corresponding to the injection interval T11> the crank angle width corresponding to the injection interval T12> the crank angle width corresponding to the injection interval T13”. This is because the closer to TDC, the lower the rotational speed of the crankshaft 7 defined by the crank angle.

  In the present embodiment, the PCM 70 changes the injection interval according to the engine speed. The setting of the injection interval according to the engine speed will be described with reference to FIG. FIG. 23 shows the relationship between the engine speed and the injection interval defined by the crank angle. Graph G31 shows the injection interval between the first-stage injection and the second-stage injection, graph G32 shows the injection interval between the second-stage injection and the third-stage injection, and graph G33 shows the third-stage injection and 4th-stage injection. The injection interval with the stage injection is shown, and the graph G34 shows the injection interval between the fourth stage injection and the fifth stage injection. In FIG. 23, for convenience of explanation, the graphs G31 to G34 are shifted from each other, but actually, these graphs G31 to G34 are substantially overlapped.

  As shown in FIG. 23, the PCM 70 increases the injection interval defined by the crank angle as the engine speed increases. This is because the higher the engine speed, the faster the rotation angle of the crankshaft 7 and the shorter the time corresponding to one combustion stroke (combustion cycle). Therefore, if the injection interval defined by the crank angle is increased as the engine speed increases, the injection interval as viewed in time can be hardly changed depending on the engine speed. Further, the PCM 70 changes all of the injection intervals of each fuel injection at an approximately equal ratio in accordance with the engine speed. In this way, even when the engine speed changes, the relationship between the injection intervals is maintained substantially constant.

  Further, in this embodiment, the PCM 70 does not change the injection interval according to the engine load. This will be described with reference to FIG. FIG. 24 shows the relationship between the engine load and the injection interval defined by the crank angle. The graph G41 shows the injection interval between the first-stage injection and the second-stage injection, the graph G42 shows the injection interval between the second-stage injection and the third-stage injection, and the graph G43 shows the third-stage injection and 4 The injection interval with the stage injection is shown, and the graph G44 shows the injection interval between the fourth stage injection and the fifth stage injection. In FIG. 24, for convenience of explanation, the graphs G41 to G44 are shown shifted from each other, but actually, these graphs G41 to G44 almost overlap each other.

  As shown in FIG. 24, the PCM 70 makes the injection interval defined by the crank angle substantially constant regardless of the engine load. That is, the PCM 70 does not change the injection interval even when the engine load changes. This is because when the engine load changes, only the required fuel injection amount changes, and the time corresponding to one combustion stroke does not change as in the case where the engine speed changes. However, since the pulse width of the control signal supplied to the injector 20 changes when the fuel injection amount changes according to the engine load, it is preferable to change the timing of performing each fuel injection according to the change in the pulse width.

Further, in the present embodiment, the PCM 70 changes the number of injections according to the atmospheric pressure. The setting of the number of injections corresponding to the atmospheric pressure will be described with reference to FIG. FIG. 25 shows the relationship between the atmospheric pressure (horizontal axis) and the number of injections (vertical axis) applied to multistage injection. As shown in FIG. 25, the PCM 70 increases the number of injections from 5 to 6 when the atmospheric pressure becomes lower than a predetermined temperature. In other words, the PCM 70 sets the number of injections to 5 when the atmospheric pressure is equal to or higher than the predetermined temperature, and sets the number of injections to 6 when the atmospheric pressure is lower than the predetermined temperature. When the number of injections is increased from 5 to 6 times, the PCM 70 adds a new fuel injection before the first injection (the above-described first stage injection) in the five fuel injections. . That is, the PCM 70 increases the number of times of the pre-stage injection by one.
In this way, even if the ignition environment deteriorates due to a decrease in atmospheric pressure, the fuel injection reaction in the cylinder is promoted by the pre-stage injection with the increased number of injections, and continuously in the cylinder before the main injection. To ensure proper combustion. Thereby, even if the ignition environment deteriorates due to a decrease in atmospheric pressure, it is possible to appropriately reduce the knocking sound.

In addition, when increasing the number of injections of the front stage injection as described above, the total injection quantity of the front stage injection may be increased as the number of injections increases, while maintaining the total injection quantity of the front stage injection constant. Further, the number of injections of the pre-stage injection may be increased. In the latter case, as the number of injections increases, the injection amount in the previous stage injection applied before the increase is reduced.
In the example shown in FIG. 25, the number of injections is switched between 5 times and 6 times depending on whether the atmospheric pressure is lower than the predetermined temperature or whether the atmospheric pressure is higher than the predetermined temperature. This is not a limitation. In another example, the number of injections may be changed more finely according to the atmospheric pressure. For example, as the atmospheric pressure decreases, the number of injections may be increased from 5 times → 6 times → 7 times, and so on.

  Next, with reference to FIG. 26, the flowchart of the fuel-injection control process which PCM70 performs is demonstrated. This fuel injection control process is started and executed repeatedly when the ignition of the vehicle is turned on and the PCM 70 is powered on.

  When the fuel injection control process is started, in step S1, the PCM 70 acquires various types of information related to the driving state of the vehicle. Specifically, the PCM 70 is currently set to the accelerator opening detected by the accelerator opening sensor, the vehicle speed detected by the vehicle speed sensor, and the vehicle transmission in addition to the detection signals output from the various sensors SN1 to SN6 described above. The information including the gear stage etc. which are present is acquired.

  Next, in step S2, the PCM 70 sets a target acceleration based on the information acquired in step S1. Specifically, the PCM 70 determines the acceleration corresponding to the current vehicle speed and gear stage from acceleration characteristic maps (created in advance and stored in a memory or the like) defined for various vehicle speeds and various gear stages. A characteristic map is selected, and a target acceleration corresponding to the current accelerator opening is determined with reference to the selected acceleration characteristic map.

  Next, in step S3, the PCM 70 determines a target torque of the engine for realizing the target acceleration determined in step S2. Specifically, the PCM 70 determines a target torque within a range of torque that can be output by the engine based on the current vehicle speed, gear stage, road surface gradient, road surface μ, and the like.

  Next, in step S4, the PCM 70 injects from the injector 20 to obtain the target torque based on the target torque determined in step S3 and the engine speed determined based on the output signal from the crank angle sensor SN1. The required injection amount of fuel to be made (mainly the fuel injection amount of the main injection) is set.

Next, in step S5, the PCM 70 determines the fuel injection mode (including the fuel injection amount and the injection timing, in other words, the fuel injection pattern). Basically, in the present embodiment, when the engine operating state is included in the partial load region, the PCM 70 is a fuel injection mode including first to fifth injections, and the first to third injections. A fuel injection mode is adopted in which the fuel injection amount applied to the main injection is increased stepwise toward the main injection, and the injection intervals of the first to fifth injections are made substantially constant (FIG. 22). reference). Further, the PCM 70 sets an injection interval of each fuel injection according to the engine speed. In particular, the PCM 70 applies the injection interval according to the current engine speed with reference to a map that defines the relationship between the engine speed and the injection interval defined by the crank angle as shown in FIG. In this case, the PCM 70 changes all the injection intervals of each fuel injection at an equal ratio according to the engine speed. However, the PCM 70 makes the injection interval defined by the crank angle substantially constant regardless of the engine load (see FIG. 24).
Further, the PCM 70 refers to the map that defines the relationship between the atmospheric pressure and the number of injections as shown in FIG. 25, and applies the number of injections corresponding to the current atmospheric pressure detected by the intake manifold temperature sensor SN3. To. In the example shown in FIG. 25, the PCM 70 sets the number of injections to 5 when the atmospheric pressure is equal to or higher than the predetermined temperature, and sets the number of injections to 6 when the atmospheric pressure is lower than the predetermined temperature. To do.

  Next, in step S6, the PCM 70 controls the injector 20 based on the required injection amount determined in step S4 and the fuel injection mode determined in step S5. After step S6, the PCM 70 ends the fuel injection control process.

<Effect>
Next, the function and effect of the embodiment of the present invention will be described.

  According to this embodiment, when performing fuel injection including a plurality of preceding injections and a main injection, the PCM 70 injects the plurality of preceding injections as the injection intervals are substantially equal and the atmospheric pressure is lower. Execute to increase the number of times. Thereby, even if the ignition environment is deteriorated due to a decrease in the atmospheric pressure, the oxidation reaction of the fuel in the cylinder can be promoted by the pre-stage injection in which the number of injections is increased. Therefore, continuous heat generation can be reliably generated in the cylinder before the main injection. As a result, the amount of in-cylinder heat at the start of main combustion and thus the in-cylinder pressure can be increased, and the inclination of the in-cylinder pressure until the maximum in-cylinder pressure due to main combustion can be made gentle, and the high-frequency component of the knocking sound can be reduced appropriately. Can be reduced. Therefore, according to the present embodiment, even if the ignition environment is deteriorated due to a decrease in atmospheric pressure, it is possible to appropriately reduce the knocking sound.

  Further, according to the present embodiment, the PCM 70 gradually decreases the crank angle corresponding to the injection interval of the previous stage injection that is performed a plurality of times as the PCM 70 proceeds to the rear stage side (retarding side). By executing at intervals, it is possible to generate heat more effectively toward the main injection by the pre-stage injection.

  Further, according to the present embodiment, the PCM 70 increases the injection interval defined by the crank angle as the engine speed increases, so even if the time of the combustion stroke (combustion cycle) changes according to the engine speed. The pre-stage injection can be executed at an appropriate injection interval.

  Further, according to the present embodiment, when the engine load changes, the PCM 70 does not change the time corresponding to the combustion stroke (combustion cycle) unlike the case where the engine speed changes. The prescribed injection interval can be made substantially constant.

1 Engine Body 2 Cylinder 4 Piston 7 Crankshaft 8 Connecting Rod 20 Injector 30 Intake Passage 40 Exhaust Passage 60 Turbocharger 70 PCM

Claims (8)

A fuel injection control method for a diesel engine in which fuel injection is performed a plurality of times during one combustion stroke to cause a plurality of combustions in a cylinder,
Performing a plurality of fuel injections in the compression stroke such that each of the injection intervals is substantially equal and the number of injections increases as the atmospheric pressure is lower;
After the plurality of fuel injections, in the vicinity of the compression top dead center, performing a maximum amount of fuel injection larger than the injection amount of the plurality of fuel injections;
A fuel injection control method for a diesel engine, comprising:   The fuel injection control method for a diesel engine according to claim 1, wherein a crank angle corresponding to an injection interval in the plurality of fuel injections decreases stepwise.   The fuel injection control method for a diesel engine according to claim 1 or 2, further comprising a step of increasing a crank angle corresponding to an injection interval in the plurality of fuel injections as the rotational speed of the diesel engine is higher.   The fuel injection of the diesel engine according to any one of claims 1 to 3, wherein a crank angle corresponding to an injection interval in the plurality of fuel injections is substantially constant regardless of a change in a load of the diesel engine. Control method. A fuel injection control device for a diesel engine that performs fuel injection a plurality of times during a single combustion stroke to generate a plurality of times of combustion in a cylinder,
A fuel supply device for injecting fuel into the cylinder;
A controller for controlling the fuel supply device,
The controller is
Each of the injection intervals is approximately equal, and the number of injections is increased as the atmospheric pressure is lower.
After the plurality of fuel injections, in the vicinity of the compression top dead center, a maximum amount of fuel injection larger than the injection amount of the plurality of fuel injections is performed.
A fuel injection control device for a diesel engine, wherein the fuel supply device is controlled as described above.   6. The fuel injection control device for a diesel engine according to claim 5, wherein the controller controls the fuel supply device so that a crank angle corresponding to an injection interval in the plurality of fuel injections is decreased stepwise.   The said controller controls the said fuel supply apparatus so that the crank angle corresponding to the injection interval in the said multiple times of fuel injection may be enlarged, so that the rotation speed of the said diesel engine is high. Fuel injection control device for diesel engines.   The said controller controls the said fuel supply apparatus so that the crank angle corresponding to the injection interval in the said multiple times of fuel injection may become substantially constant irrespective of the change of the load of the said diesel engine. The fuel-injection control apparatus of the diesel engine as described in any one of thru | or 7.

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