JP6218123B2 - Fuel injection control method and fuel injection control device for compression self-ignition engine - Google Patents

Description

  The present invention relates to a fuel injection control apparatus for a fuel injection control method of a compression self-ignition engine, and in particular, a compression self that causes a plurality of fuel injections in a cylinder by performing a plurality of fuel injections during a single combustion stroke. The present invention relates to a fuel injection control method and a fuel injection control method for an ignition engine.

  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 the interval between fuel injections performed a plurality of times based on a target value has been proposed. 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 suddenly increases due to combustion in the engine, and corresponds to a time-differentiated waveform of the in-cylinder pressure (hereinafter the same).

JP 2002-47975 A

  The knock 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, the frequency band including the resonance frequency of the engine structural system (the frequency band having a certain width is obtained by combining the resonances of components on the main transmission path of the engine). Then, such a band related to the resonance frequency is referred to as a “resonance frequency band”), and 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.

  By the way, 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 index indicates the high-frequency energy obtained by Fourier-transforming the in-cylinder pressure waveform. Hereinafter, the characteristic corresponds to “CPL”. This CPL is in accordance with the heat generation rate indicating the mode of combustion in the cylinder, but according to experiments conducted by the inventor, the waveform of the heat generation rate is determined based on environmental conditions such as temperature and pressure. It was found that the knocking sound was affected by the shape of the waveform of such heat release rate. For this reason, in order to appropriately reduce the knocking noise, the present inventor has determined that the fuel to be performed a plurality of times based on the timing at which the heat generation rate becomes maximum (peak) reflecting the influence of environmental conditions such as temperature and pressure. We thought it desirable to set the interval between injections. In the technique described in Patent Document 1 described above, the interval between fuel injections performed a plurality of times is controlled based on the timing at which the combustion pressure wave rises (corresponding to the timing at which the heat generation rate begins to rise), so that the knock noise Was not sufficient to reduce properly.

  In addition, when the engine load is relatively low or when the fuel is not ignitable in the engine combustion chamber, such as when the engine is cold, an ignition delay after fuel injection occurs and the timing at which the heat generation rate is maximized is delayed. . In this case, even if the interval between fuel injections to be performed a plurality of times is set based on the timing at which the heat generation rate is maximized as described above, the heat generation rate cannot be maximized at the intended timing, and a knock noise May not be sufficiently reduced.

  The present invention has been made to solve the above-described problems of the prior art, and is a compression self-ignition type capable of appropriately reducing knock noise corresponding to the resonance frequency of the engine structural system in a wide ignition environment. It is an object of the present invention to provide an engine fuel injection control method and a fuel injection control device.

In order to achieve the above object, a fuel injection control method for a compression self-ignition engine according to the present invention is a compression in which a plurality of fuel injections are performed during a single combustion stroke to generate a plurality of combustions in a cylinder. A fuel injection control method for a self-ignition engine, the step of determining the ignitability of the fuel based on the state of the engine, and the valley portion of the curve showing the frequency characteristics of the combustion pressure wave generated by multiple combustions, Setting the interval between the pre-injection and the main injection in the fuel injection performed a plurality of times so as to be included in the respective ranges of the plurality of resonance frequency bands of the engine structural system. The step of setting the interval between injections includes a step of increasing the interval between the pre-injection and the main injection as the ignitability of the fuel is worse.
In the present invention configured as described above, the valley portion of the curve indicating the frequency characteristic of the combustion pressure wave generated by the multiple times of combustion by controlling the interval between the pre-injection and the main injection in the multiple times of fuel injection However, the knock noise corresponding to each of the plurality of resonance frequency bands of the engine structural system can be appropriately reduced. it can. And the worse the ignitability of the fuel, the larger the interval between the pre-injection and the main injection, so that the heat generation interval between the pre-injection and the main injection due to the poor ignitability can be prevented. Thus, in a wide ignition environment, knocking noise corresponding to each of a plurality of resonance frequency bands of the engine structural system can be appropriately reduced. In this case, the overall level of the combustion pressure wave is not changed, so the fuel consumption and emissions are not deteriorated, and no additional sound insulation is added, so increasing the cost and weight of the device Absent.
The “frequency characteristic of the combustion pressure wave” described above corresponds to the frequency characteristic of the in-cylinder pressure level (CPL) corresponding to combustion in the engine.

In the present invention, it is preferable that the fuel injection control method for the compression self-ignition engine further sets the injection timing of the main injection to a timing corresponding to a predetermined crank angle, and based on the set fuel injection interval. It has the step which sets the injection timing of pre-injection and / or after-injection, and controls a fuel-injection apparatus so that pre-injection, main injection, and after-injection may be performed in those injection timings.
In the present invention configured as described above, since the injection timing of the pre-injection and / or the after-injection is set based on the set fuel injection interval on the basis of the injection timing of the main injection, the pre-injection and the main injection, and / Or frequency corresponding to the position of the valley of the curve indicating the frequency characteristic of the combustion pressure wave generated by the main injection and after injection is included in each of the plurality of resonance frequency bands of the engine structural system. In addition, it is possible to control the heat generation interval, thereby appropriately reducing the knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system.

Further, the fuel injection control device for a compression self-ignition engine of the present invention performs fuel injection for a compression self-ignition engine that performs a plurality of times of fuel injection during a single combustion stroke to cause a plurality of times of combustion in a cylinder. An ignition environment determination means for determining the ignitability of fuel based on the state of the engine, and a trough portion of a curve indicating frequency characteristics of combustion pressure waves generated by a plurality of combustions are the control system. The control means for setting the interval between the pre-injection and the main injection in the fuel injection performed a plurality of times so as to be included in the respective ranges of the plurality of resonance frequency bands of the The worse, the larger is the interval between the pre-injection and the main injection.
In the present invention configured as described above, the interval between the pre-injection and the main injection is controlled, and the valley portion of the curve indicating the frequency characteristic of the combustion pressure wave generated by the plurality of combustions is the engine structural system. Is included in the respective ranges of the plurality of resonance frequency bands of the engine, so that the knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system can be appropriately reduced. And the worse the ignitability of the fuel, the larger the interval between the pre-injection and the main injection, so that the heat generation interval between the pre-injection and the main injection due to the poor ignitability can be prevented. Thus, in a wide ignition environment, knocking noise corresponding to each of a plurality of resonance frequency bands of the engine structural system can be appropriately reduced.

In the present invention, it is preferable that the ignition environment determination unit determines that the lower the cylinder wall temperature of the engine, the worse the fuel ignitability.
In the present invention configured as described above, the lower the cylinder wall temperature, the larger the interval between the pre-injection and the main injection. Therefore, even when the cylinder wall temperature is low and the ignitability is poor, It is possible to prevent the heat generation interval from being shortened, thereby appropriately reducing the knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system in a wide ignition environment.

In the present invention, preferably, the fuel injection control device for a compression self-ignition engine is a fuel injection control device for a compression self-ignition engine equipped with a supercharger, and the ignition environment determination means is a supercharger for the engine. It is determined that the lower the pressure, the worse the fuel ignitability.
In the present invention configured as described above, the lower the supercharging pressure of the engine, the larger the interval between the pre-injection and the main injection. Therefore, even when the supercharging pressure of the engine is low and the ignitability is poor, It is possible to prevent the heat generation interval from the main injection from being shortened, and accordingly, in a wide ignition environment, it is possible to appropriately reduce the knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system.

In the present invention, preferably, the ignition environment determining means determines that the lower the oxygen concentration in the intake air of the engine, the worse the fuel ignitability.
In the present invention configured as described above, the interval between the pre-injection and the main injection increases as the oxygen concentration in the intake air of the engine is lower. Therefore, even when the oxygen concentration in the intake air of the engine is low and the ignitability is poor. It is possible to prevent the heat generation interval between the injection and the main injection from being shortened, thereby appropriately reducing the knocking noise corresponding to each of a plurality of resonance frequency bands of the engine structural system in a wide ignition environment. it can.

In the present invention, it is preferable that the control unit fixes the injection timing of the main injection, advances the injection timing of the pre-injection and / or pre-injects the fuel injection as the ignitability of the fuel is poor. Increase the amount.
In the present invention configured as described above, as the ignitability of the fuel is worse, the injection timing of the pre-injection is advanced to increase the interval between the pre-injection and the main injection, or the fuel injection amount of the pre-injection is increased. Increase the amount to improve the ignitability of the fuel. Thus, knock noise corresponding to each of a plurality of resonance frequency bands of the engine structural system can be appropriately reduced in a wide ignition environment.

In the present invention, preferably, the control means sets the injection timing of the main injection to a timing corresponding to a predetermined crank angle, and the injection timing of the pre-injection and / or the after-injection based on the set fuel injection interval. And the fuel injection device is controlled to perform pre-injection, main injection, and after-injection at those injection timings.
In the present invention configured as described above, since the injection timing of the pre-injection and / or the after-injection is set based on the set fuel injection interval on the basis of the injection timing of the main injection, the pre-injection and the main injection, and / Or frequency corresponding to the position of the valley of the curve indicating the frequency characteristic of the combustion pressure wave generated by the main injection and after injection is included in each of the plurality of resonance frequency bands of the engine structural system. In addition, it is possible to control the heat generation interval, thereby appropriately reducing the knocking noise corresponding to each of the plurality of resonance frequency bands of the engine structural system.

  According to the fuel injection control method and the fuel injection control device for a compression self-ignition engine according to the present invention, it is possible to appropriately reduce the knocking noise corresponding to the resonance frequency of the engine structural system in a wide ignition environment.

1 is a schematic diagram showing an overall configuration of a diesel engine system to which a fuel injection control device for a compression self-ignition engine according to an embodiment of the present invention is applied. It is a figure which shows the piston and connecting rod of the engine by embodiment of this invention. It is the III-III arrow line view of FIG. It is the IV-IV arrow line view of FIG. 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 explanatory drawing of the mechanism which a knock sound generate | occur | produces. It is explanatory drawing of the mechanism which a knock sound generate | occur | produces. It is explanatory drawing about the basic concept of the method of reducing a knock sound by controlling the frequency characteristic of CPL in embodiment of this invention. It is explanatory drawing about the influence which the frequency | count of fuel injection (the frequency | count which generates heat in an engine) has on the frequency characteristic of CPL. It is explanatory drawing about the influence which the timing (timing which generates heat) which performs fuel injection when performing fuel injection twice or more has the frequency characteristic of CPL. It is explanatory drawing about the mechanism in which the peak and trough of the curve which shows the frequency characteristic of CPL generate | occur | produce. It is explanatory drawing about the basic concept of the control method of the heat generation interval by embodiment of this invention. It is a flowchart of the fuel-injection control process which PCM of the diesel engine by embodiment of this invention performs. It is a flowchart of the fuel-injection form determination process in which the fuel-injection control apparatus of the compression self-ignition engine by embodiment of this invention determines the form of fuel-injection. It is a map referred when the fuel-injection control apparatus by embodiment of this invention determines ignition environment based on a driving | running state. It is explanatory drawing which shows the fuel injection pattern correct | amended according to an ignition environment, and the heat release rate waveform implement | achieved by each fuel injection pattern. It is a diagram which shows the relationship between each parameter of a fuel injection form, and an ignition environment. It is a diagram which shows the frequency characteristic of the vibration level of a knock sound. It is a diagram which shows the relationship between a heat generation space | interval and the frequency of the valley in the curve of the frequency characteristic of CPL. It is a diagram which shows the relationship between the shift | offset | difference of the frequency of two vibrations which interfere, and the sound pressure level amplification amount by resonance of those vibrations.

  Hereinafter, a fuel injection control measure for a compression self-ignition engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Device configuration>
First, a diesel engine system to which a fuel injection control measure for a compression self-ignition engine according to the present embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram showing an overall configuration of a diesel engine system to which a fuel injection control measure of a compression self-ignition engine according to this embodiment 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 the injector 20 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 dynamic vibration absorber will be described in detail with reference to FIGS. 2 is a view showing the piston 4 and the connecting rod 8 of the engine according to the embodiment of the present invention, FIG. 3 is a view taken along arrows III-III in FIG. 2, and FIG. 4 is a view taken along arrows IV-IV in FIG. FIG.

  As shown in FIGS. 3 and 4, the piston pin 80 is hollow in cross section, and a through hole 80 a extending in the central axis direction of the piston pin 80 is formed at the center of the piston pin 80. A press-fit portion 80b into which the fixed portion 90a of the dynamic vibration absorber 90 is press-fitted is provided at the center portion of the inner peripheral surface of the through hole 80a in the central axis direction of the piston pin 80. The inner diameter of the through hole 80a in the press-fit portion 80b is smaller than the inner diameter of the through hole 80a in the other part.

  In the inside of the piston pin 80 (in the through hole 80a), the piston 4, the piston pin 80, and the small end portion 8a of the connecting rod 8 are integrally prevented from resonating with the large end portion 8b of the connecting rod 8 in the combustion stroke. Two dynamic vibration absorbers 90 are provided. These two dynamic vibration absorbers 90 are respectively located on both sides of a plane passing through the center in the central axis direction of the piston pin 80 (that is, a plane passing through the center and perpendicular to the central axis of the piston pin 80). ing.

  In the combustion stroke, a lubricating oil film (a spring connecting the piston pin 80 and the small end portion 8a of the connecting rod 8) between the piston pin 80 and the pin insertion hole of the connecting rod 8, and the boss portion of the piston pin 80 and the piston 4 are used. The lubricating oil film (spring connecting the piston pin 80 and the piston 4) between the pin support hole 4d of 4c is lost, and as a result, the piston 4, the piston pin 80 and the small end portion 8a of the connecting rod 8 are integrated. To resonate with the large end 8b. However, in the present embodiment, the resonance is suppressed by the dynamic vibration absorber 90 provided on the piston pin 80, and noise due to the resonance can be reduced.

  On the other hand, in the intake stroke, the compression stroke, and the exhaust stroke, respectively, between the piston pin 80 and the pin insertion hole 8d of the connecting rod 8, and between the piston pin 80 and the pin support hole 4d of the boss portion 4c of the piston 4, respectively. Lubricating oil film exists. As a result, resonance that occurs in the combustion stroke does not occur. That is, since the dynamic vibration absorber 90 is provided on the piston pin 80, in the intake stroke, the compression stroke, and the exhaust stroke, a lubricating oil film (piston pin 80 and connecting rod between the piston pin 80 and the pin insertion hole of the connecting rod 8 is used. 8), the transmission of vibration from the dynamic vibration absorber 90 to the connecting rod 8 can be suppressed, and an increase in noise can be prevented. Furthermore, since the dynamic vibration absorber 90 is provided in the piston pin 80, space can be used effectively and enlargement of the piston 4 can be avoided.

  Next, the control system of the diesel engine according to the present embodiment will be described with reference to FIG. FIG. 5 is a block diagram showing a control system of the diesel engine according to the present embodiment. As shown in FIG. 5, 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.

  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. 5, the PCM 70 mainly controls the injector 20 to perform control (fuel injection control) related to the fuel supplied to the cylinder 2. The PCM 70 corresponds to “a fuel injection control measure for a compression self-ignition engine” in the present invention, and functions as a “control unit” and an “ignition environment determination unit” 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. 6 is a time chart showing a typical fuel injection pattern applied in the present embodiment. In this embodiment, as shown in FIG. 6, the PCM 70 increases the air utilization rate together with the main injection (main injection) for injecting fuel for generating engine torque into the combustion chamber 9 in the vicinity of the compression top dead center. In order to improve the ignitability of the main injection, pre-injection is performed in which a smaller amount of fuel than the main injection is injected into the combustion chamber 9 at a timing before the main injection. 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. For example, the PCM 70 performs each of such pre-injection and after-injection in a predetermined operating region of the engine defined in advance.

  The PCM 70 sets a 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 for the main injection. To do. In addition, the PCM 70 causes the pre-injected fuel spray to form a state in which the main injected fuel is easy to burn by causing combustion with a small amount of heat generation by pre-injection immediately before the main injected fuel is combusted. Is set in the cavity provided on the crown surface of the piston 4 and the injection timing of the pre-injection is set as a timing at which 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.

<Control contents according to this embodiment>
Next, in this embodiment, the fuel injection control performed by the PCM 70 in order to suppress the knocking noise of the diesel engine will be specifically described.

  First, with reference to FIG.7 and FIG.8, the mechanism which a knock noise generate | occur | produces is demonstrated. As shown in FIG. 7, the knocking sound is generated by combustion excitation force generated by combustion in the engine, such as main routes (engine transmission pistons, connecting rods, crankshafts, engine blocks, etc.). The structure transfer characteristic is radiated through the resonance frequency of the engine structural system).

In FIG. 8, a graph G11 shows the relationship between the crank angle and the in-cylinder pressure (combustion pressure), and a graph G12 shows the combustion acceleration obtained by subjecting the in-cylinder pressure in the graph G11 to FFT processing (fast Fourier transform processing). The frequency characteristic of CPL (high-frequency energy of about 1 to 4 kHz obtained by FFT processing of the in-cylinder pressure waveform with the combustion excitation force index) corresponding to the vibration force is shown. Further, the graph G13 shows the structure transfer characteristic of the engine (specifically, the frequency characteristic of engine structural attenuation), and the graph G14 shows the time-varying waveform of the engine proximity sound. The characteristic obtained by applying the engine structure transfer characteristic shown in the graph G13 to the frequency characteristic of the CPL shown in the graph G12 is a characteristic obtained by performing FFT processing on the time-varying waveform of the close sound shown in the graph G14. Substantially coincides with the above, and this indicates the characteristic of the knocking sound (see graph G15).
Note that, in the graph G14, a portion that greatly fluctuates in time as indicated by the broken line region R11 is heard as a knocking sound. In the graph G15, the energy sum of 1 to 4 kHz shown in the broken line region R12 is used as a representative value of the knocking sound.

  As described above, since the knock sound is affected by the frequency characteristic of the CPL, in this embodiment, the knock sound is reduced by controlling the frequency characteristic of the CPL. Here, with reference to FIG. 9, a basic concept of a technique for reducing knock noise by controlling the frequency characteristics of CPL in the present embodiment will be described. The “frequency characteristic of CPL” corresponds to the frequency characteristic of the combustion pressure wave generated by the combustion of fuel in the engine.

  In FIG. 9, a graph G21 is a basic CPL frequency characteristic (for example, a basic output set based on a required output corresponding to the accelerator opening of the driver, an engine operating state (engine speed or engine load), and the like. The graphs G23, G24, and G25 show the frequency characteristics of structural resonances of various components of the engine. For example, the graph G23 shows the frequency characteristic related to the structural resonance of the connecting rod of the engine, the graph G24 shows the frequency characteristic related to the crankshaft of the engine, and the graph G25 shows the frequency characteristic related to the structural resonance of the engine block. Here, it is assumed that the structural resonance shown in the graph G23 has a greater influence on the knock sound than the structural resonances shown in the graphs G24 and G25. In this case, a knock sound having a frequency characteristic as shown in the graph G26 is generated from the frequency characteristic of the CPL shown in the graph G21 and the structural resonance of the engine components shown in the graphs G23 to G25. From the graph G26, it can be seen that the knocking sound is increased in the frequency band FB1, and specifically, it is understood that a large peak is generated in the curve indicating the knocking sound in the frequency band FB1. This is because, in the frequency band FB1, there is a peak in the curve indicating the CPL in the graph G21, and there is a peak in the curve indicating the structural resonance of the engine components (those having a large effect on the knocking noise) in the graph G23. This is probably because it has occurred.

  In the present embodiment, the valley portion of the curve indicating the CPL is located in the frequency band FB1 where the peak is generated in the curve indicating the structural resonance of the engine component of the graph G23 (which has a large effect on the knocking sound). In other words, the frequency characteristic of the CPL is controlled so that the valley portion of the curve indicating the CPL is included in the frequency band FB1. Specifically, as shown in the graph G22, the CPL frequency characteristic in which the valley portion of the CPL curve is included in the frequency band FB1 is realized. When such a frequency characteristic of CPL shown in the graph G22 is applied, as shown in the graph G27, the knocking sound is greatly reduced in the frequency band FB1. In this case, since the overall level of the CPL is not changed, the knocking noise can be appropriately reduced without deteriorating fuel consumption and emission while ensuring the required engine output.

  Next, a method for controlling the frequency characteristics of the CPL to a desired characteristic (for example, the frequency characteristic as shown in the graph G22) in this embodiment will be described with reference to FIGS.

  FIG. 10 is a diagram for explaining the influence of the number of times of fuel injection (the number of times heat is generated in the engine) on the frequency characteristics of the CPL. In FIG. 10, a graph G31 shows a waveform of a heat generation rate with respect to a crank angle when only one fuel injection is performed (for example, when only main injection is performed), and a graph G32 shows two fuel injections. The graph of the heat release rate with respect to the crank angle in the case of performing the pre-injection and the main injection (for example, the case of performing the pre-injection and the main injection) is shown. Shows the waveform of the heat generation rate with respect to the crank angle.

  When only one fuel injection is performed, as shown in the graph G34, the frequency characteristics are such that the CPL gradually decreases as the frequency increases. In this case, it can be seen that peaks and valleys are not generated in the curve indicating the frequency characteristics of the CPL. On the other hand, when fuel injection is performed twice and three times, as shown in graphs G35 and G36, it can be seen that peaks and valleys occur in the curves indicating the frequency characteristics of the CPL. From this, it is considered that when fuel injection is performed two or more times, that is, when two or more combustions (heat generation) are generated in the engine, peaks and valleys are generated in the curve indicating the frequency characteristics of CPL. Also, from the graphs G35 and G36, it is understood that the number of peaks and valleys of the curve indicating the frequency characteristics of the CPL is larger when the fuel injection is performed three times than when the fuel injection is performed twice. .

  FIG. 11 is a diagram for explaining the influence of the fuel injection timing (heat generation timing) when performing combustion twice or more on the frequency characteristics of the CPL. Here, when two fuel injections (pre-injection and main injection) are performed, the simulation results (actual experimental results) when the timing for performing the pre-injection in the previous stage is fixed and the timing for performing the main injection in the subsequent stage is changed. Not).

  In FIG. 11, a graph G41 shows a heat generation rate when the fuel injection timing (reference main injection timing) before the change is applied to the main injection, and a graph G43 shows a case where the heat generation rate shown in the graph G41 is applied. The frequency characteristic of CPL is shown. On the other hand, the graph G42 shows the heat generation rate when the fuel injection timing for the main injection is changed (specifically, delayed) from the reference main injection timing. Specifically, in the graph G42, the timing at which the peak value (maximum value) of the heat generation rate is generated by the main injection is delayed by time T1 (for example, 0.5 msec) from the graph G41. When such a heat release rate shown in the graph G42 is applied, a frequency characteristic of CPL as shown in the graph G44 is obtained.

  From graphs G43 and G44, when the fuel injection is performed twice, that is, when the combustion (heat generation) is generated twice, the frequency characteristics of the CPL may change if the timing for generating the heat is changed. Recognize. Specifically, it can be seen that the number of peaks and valleys of the curve showing CPL changes, and the frequency corresponding to the positions of the peaks and valleys of the curve showing CPL changes. Therefore, the timing at which heat generation occurs, particularly the interval at which the peak value of the heat generation rate due to each of the two combustions (hereinafter referred to as “heat generation interval” as appropriate) is the peak and valley of the curve indicating CPL. It is considered that the frequency corresponding to the position of is affected.

FIG. 12 is a diagram for explaining a mechanism in which peaks and valleys of a curve indicating CPL are generated. FIG. 12A shows a time change of the combustion pressure wave by the pre-injection, a time change of the combustion pressure wave by the main injection, and a frequency F41 corresponding to the peak portion in the curve indicating the CPL of the graph G44 of FIG. The time change of the synthetic | combination pressure wave which synthesize | combined these combustion pressure waves is shown. In this case, the interval (heat generation interval) at which the peak value occurs in the heat generation rate waveform by each of the pre-injection and the main injection is assumed to be T21 (hereinafter the same). Further, it is assumed that the period T22 (= 1 / F41 × 1000) of the combustion pressure wave due to the pre-injection and the main injection at the frequency F41 substantially coincides with the heat generation interval T21.
At the frequency F41, the generation timing of the combustion pressure wave due to the main injection substantially coincides with the timing corresponding to the period T21 of the combustion pressure wave due to the pre-injection, so the combustion pressure wave due to the pre-injection and the combustion pressure wave due to the main injection are in phase. Will interfere. Therefore, the peak portion of the combustion pressure wave caused by the pre-injection overlaps the peak portion of the combustion pressure wave caused by the main injection (see the broken line region R21), and the valley portion of the combustion pressure wave caused by the pre-injection and the combustion pressure caused by the main injection. The valley of the wave overlaps (see broken line region R22). As a result, a combined pressure wave obtained by synthesizing the combustion pressure wave due to the pre-injection and the combustion pressure wave due to the main injection is amplified (see arrow A21). As a result, as shown in the graph G44 of FIG. 11, a peak occurred in the curve indicating the CPL at the frequency F41.

On the other hand, FIG. 12 (B) shows the time change of the combustion pressure wave by the pre-injection and the time of the combustion pressure wave by the main injection at the frequency F42 corresponding to the valley portion in the curve indicating the CPL of the graph G44 of FIG. The change and the time change of the synthetic pressure wave which synthesize | combined these combustion pressure waves are shown. The period T23 (= 1 / F42 × 1000) of the combustion pressure wave by the pre-injection and the main injection at the frequency F42 corresponds to almost twice the heat generation interval T21.
At the frequency F42, the combustion pressure wave due to the main injection is generated at a timing corresponding to almost half of the cycle T23 of the combustion pressure wave due to the pre-injection, so the combustion pressure wave due to the pre-injection and the combustion pressure wave due to the main injection are in opposite phases. Will interfere. Therefore, the valley portion of the combustion pressure wave caused by the pre-injection overlaps the peak portion of the combustion pressure wave caused by the main injection (see the broken line region R23), and the peak portion of the combustion pressure wave caused by the pre-injection and the combustion pressure caused by the main injection. The valley of the wave overlaps (see broken line region R24). As a result, the combined pressure wave obtained by synthesizing the combustion pressure wave by the pre-injection and the combustion pressure wave by the main injection is attenuated (see arrow A22). As a result, as shown in the graph G44 of FIG. 11, valleys occurred in the curve indicating the CPL at the frequency F42.

Here, the relationship between the position where the peaks and valleys are generated in the frequency characteristics of the CPL and the heat generation interval can be expressed by the following equations (1) and (2). In the expressions (1) and (2), “Δt” is the heat generation interval, and “n” is “1, 2, 3,...”.
Frequency at which peaks occur fn = n / Δt × 1000 (1)
Frequency at which valleys occur fn = (n−0.5) / Δt × 1000 (2)

  In addition, in FIG. 11, although the result at the time of performing 2 times of fuel injection (pre-injection and main injection) was shown, also when performing 3 times of fuel injection (pre-injection, main injection, and after-injection) It was confirmed that similar results were obtained. Specifically, even when three fuel injections are performed, the peaks and valleys of the curve indicating the CPL according to the intervals (heat generation intervals) at which the respective peak values of the heat generation rates due to the three combustions occur. It was found that the frequency corresponding to the position of changed. FIG. 11 shows a simulation result using a predetermined model (combustion model or the like), but it has been confirmed that such a result can also be obtained by an experiment using an actual machine. Furthermore, in the above, the influence of the heat generation interval on the frequency characteristics of the CPL was examined by changing the heat generation interval when performing multiple fuel injections. However, the influence of these on the frequency characteristics of CPL was investigated by changing the height and slope of the heat release rate waveform. As a result, it was found that even if the height and slope of the heat release rate waveform were changed, only the magnitude of the CPL was changed, and the number of peaks and valleys of the CPL curve and their frequencies were hardly changed.

  From the foregoing, it has been found that the heat generation interval when performing multiple fuel injections affects the frequency characteristics of the CPL. In response to such a result, in the present embodiment, by controlling the heat generation interval when performing multiple fuel injections, the frequency characteristics of the CPL can be set to desired characteristics (for example, the frequency characteristics as shown in the graph G22). ). Specifically, in the present embodiment, the PCM 70 sets the interval of fuel injection to be performed a plurality of times in order to realize a heat generation interval such that the CPL frequency characteristic becomes a desired characteristic. More specifically, the PCM 70 has a frequency characteristic of the CPL so as to realize a frequency characteristic of the CPL such that a valley portion of the curve is included in a range of a resonance frequency band (for example, see FIG. 9) of the engine structural system. Based on the heat generation interval for obtaining the above, the interval of fuel injection to be performed a plurality of times is set.

  FIG. 13 is a diagram for explaining the basic concept of the method for controlling the heat generation interval according to the present embodiment. FIG. 13 schematically shows the heat generation rate by pre-injection, the heat generation rate by main injection, and the heat generation rate by after injection in order from the left. In the present embodiment, the PCM 70 is configured to realize the heat generation interval T31 between the pre-injection and the main injection and the heat generation interval T32 between the main injection and the after injection so that the frequency characteristic of the CPL becomes a desired characteristic. In addition, intervals for performing each of pre-injection, main injection, and after-injection are set. Then, the PCM 70 controls the injector 20 so as to perform each of the pre-injection, the main injection, and the after-injection at the fuel injection timing corresponding to the interval thus set.

  Next, specific processing of fuel injection control executed by the PCM 70 will be described with reference to FIGS. 14 to 18.

FIG. 14 is a flowchart of the fuel injection control process executed by the PCM 70. 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, as shown in FIG. 14, in step S <b> 1, the PCM 70 acquires various 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 SN5 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. A required injection amount of fuel to be made (specifically, a fuel injection amount of main injection) is set.

Next, in step S5, the PCM 70 executes a fuel injection mode determination process for determining the fuel injection mode (specifically, the fuel injection amount and the injection timing). Details of the fuel injection mode determination process will be described later.
After the process of step S5, 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.

Here, the fuel injection mode determination process executed in step S5 of the fuel injection control process will be described with reference to FIG.
When the fuel injection configuration determination process is started, as shown in FIG. 15, in step S21, the PCM 70 acquires various types of information related to the engine operating state. Specifically, the PCM 70, in addition to the detection signals output from the various sensors SN1 to SN5 described above, the boost pressure, the estimated cylinder wall temperature, the intake manifold oxygen concentration, and the target determined in step S3 of the fuel injection control process described above. Get information including torque.

  Next, in step S22, the PCM 70 reads the reference main injection timing based on the information acquired in step S21. Specifically, the PCM 70 refers to a map in which the reference main injection timing corresponding to a predetermined crank angle is set in advance using the target torque and the engine speed as parameters, and corresponds to the target torque and the engine speed acquired in step S21. Read the reference main injection timing.

Next, in step S23, the PCM 70 performs a basic time interval between the injection end timing of the pre-injection and the injection start timing of the main injection (hereinafter referred to as “pre-main reference time interval”), and the main injection. Basic time interval between the end timing and the injection start timing of after injection (hereinafter referred to as “main-after reference time interval”), basic fuel injection amount of pre-injection (hereinafter referred to as “reference pre-injection amount”) And a basic fuel injection amount of after-injection (hereinafter referred to as “reference after-injection amount”).
The pre-main reference time interval and the main-after reference time interval are curves indicating the frequency characteristics of the CPL within the range of the resonance frequency band of the engine structural system in the operating state of the engine with good fuel ignitability. It is set in advance as a time interval that includes a valley portion.
In addition, as for the reference pre-injection amount and the reference after-injection amount, basic values corresponding to the operating state of the engine are preset as maps and are read from the maps.

  Next, in step S24, the PCM 70 determines whether or not the engine operating state is a transient state. For example, the PCM 70 determines whether or not the engine operating state is in a transient state based on the accelerator opening detected by the accelerator opening sensor and the rate of change of the accelerator opening.

  As a result, when the operating state of the engine is a transient state, the process proceeds to step S25, and the PCM 70 determines the ignitability of fuel in the current combustion chamber 9 (hereinafter referred to as “ignition environment”) as an estimated cylinder wall temperature. , Based on the supercharging pressure and intake manifold oxygen concentration. Specifically, regarding the estimated cylinder wall temperature, a first threshold T1, a second threshold T2, a third threshold T3, and a fourth threshold T4 are set in advance from the highest. When the estimated cylinder wall temperature obtained in step S21 is equal to or higher than T1, the ignition environment based on the estimated cylinder wall temperature is the best ignition environment (hereinafter referred to as “ignition environment I”), and the cylinder. When the estimated wall temperature is T2 or more and less than T1, the ignition environment based on the estimated cylinder wall temperature is the second best ignition environment (hereinafter referred to as “ignition environment II”), and the estimated cylinder wall temperature. Is T3 or more and less than T2, the ignition environment based on the estimated cylinder wall temperature is the third best ignition environment (hereinafter referred to as “ignition environment III”), and the estimated cylinder wall temperature is T4 or more and T3. If the temperature is less than T4, the ignition environment based on the estimated cylinder wall temperature is the fourth best ignition environment (hereinafter referred to as “ignition environment IV”), and if the estimated cylinder wall temperature is less than T4, the cylinder wall The ignition environment based on the estimated temperature value is determined to be the ignition environment with the lowest ignitability (hereinafter referred to as “ignition environment V”).

  As for the boost pressure, similarly to the estimated cylinder wall temperature, the first threshold P1, the second threshold P2, the third threshold P3, and the fourth threshold P4 are set in order from the highest. ing. And when the supercharging pressure acquired in step S21 is P1 or more, the ignition environment based on the supercharging pressure is the ignition environment I, and when the supercharging pressure is P2 or more and less than P1, the ignition environment based on the supercharging pressure. Is the ignition environment II, when the supercharging pressure is P3 or more and less than P2, the ignition environment based on the supercharging pressure is the ignition environment III, and when the supercharging pressure is P4 or more and less than P3, it is based on the supercharging pressure When the ignition environment is the ignition environment IV and the supercharging pressure is less than P4, it is determined that the ignition environment based on the supercharging pressure is the ignition environment V.

  Further, regarding the intake manifold oxygen concentration, similarly to the estimated cylinder wall temperature and the supercharging pressure, the first threshold C1, the second threshold C2, the third threshold C3, and the fourth threshold C4 in descending order. Is preset. When the intake manifold oxygen concentration acquired in step S21 is P1 or more, the ignition environment based on the intake manifold oxygen concentration is the ignition environment I, and when the intake manifold oxygen concentration is P2 or more and less than P1, the ignition environment based on the intake manifold oxygen concentration. Is the ignition environment II, when the intake manifold oxygen concentration is P3 or more and less than P2, the ignition environment based on the intake manifold oxygen concentration is the ignition environment III, and when the intake manifold oxygen concentration is P4 or more and less than P3, it is based on the intake manifold oxygen concentration When the ignition environment is the ignition environment IV and the intake manifold oxygen concentration is less than P4, it is determined that the ignition environment based on the intake manifold oxygen concentration is the ignition environment V.

  Then, the PCM 70 determines the ignition environment having the lowest ignitability among the ignition environments based on the estimated cylinder wall temperature, the boost pressure, and the intake manifold oxygen concentration as the current engine ignition environment.

  On the other hand, if it is determined in step S24 that the engine operating state is not a transient state, the process proceeds to step S26, where the PCM 70 determines the ignition environment based on the engine load (specifically, the required injection amount) and the rotational speed. judge. In this case, the PCM 70 refers to a map as shown in FIG. 16, and determines an ignition environment corresponding to the engine load and the rotational speed acquired in step S21. In the map of FIG. 16, the high load region where the engine load is highest at the same engine speed is the ignition environment I, and the medium and high load region where the engine load is the second highest after the ignition environment I is the ignition environment II. The medium load region where the engine load is high next to the environment II is the ignition environment III, and the low load region where the engine load is the lowest is the ignition environment IV.

  After step S25 or S26, the process proceeds to step S27, in which the PCM 70 performs a pre-injection time interval (hereinafter referred to as “pre-main time interval”) between the pre-injection injection end timing and the main injection start timing. The fuel injection amount (hereinafter referred to as “pre-injection amount”) and the injection timing of main injection (hereinafter referred to as “main injection timing”) are determined according to the ignition environment determined in step S25 or S26. Correction is made from the pre-main reference time interval read in step S23, the reference pre-injection amount, and the reference main injection timing read in step S22.

FIG. 17 is an explanatory diagram showing a fuel injection pattern corrected according to the ignition environment and a heat release rate waveform realized by each fuel injection pattern.
As described above, the pre-main reference time interval and the pre-after reference time interval are within the range of the resonance frequency band of the engine structural system in the engine operating state where the fuel ignitability is good, that is, in the ignition environment I. Is set as a time interval in which a valley portion of a curve indicating the frequency characteristic of CPL is included. Therefore, when the ignition environment determined in step S25 or S26 is the ignition environment I with the best ignitability, the PCM 70 does not correct the pre-main reference time interval. Further, the reference pre-injection amount and the reference main injection timing are not corrected.

  On the other hand, if the ignition environment determined in step S25 or S26 is the ignition environment II, the ignitability of the fuel is worse than the ignition environment I. Therefore, the pre-main reference time interval set based on the ignition environment I is used. When the injection timing is determined, the timing at which the peak value of the heat generation rate due to the pre-injection occurs is later than in the ignition environment I. That is, an ignition delay in pre-injection occurs. As a result, as indicated by a broken line in the heat generation rate waveform of the ignition environment II in FIG. 17, the heat generation interval between the pre-injection and the main injection is such that the desired frequency characteristic of CPL can be obtained (FIG. 17). It becomes shorter than the “target interval” in the heat release rate waveform. Therefore, in the ignition environment II, as shown in the injection pattern of FIG. 17, the pre-main time interval is corrected to be expanded from the pre-main reference time interval, and the pre-injection injection timing is advanced with respect to the main injection timing. By making the angle, as shown by the solid line in the heat generation rate waveform of FIG. 17, the heat generation interval between the pre-injection and the main injection due to poor ignitability is prevented.

  Further, when the ignition environment determined in step S25 or S26 is the ignition environment III, the ignition quality of the fuel is even worse than the ignition environment II, and therefore the timing at which the peak value of the heat generation rate due to the pre-injection occurs is the ignition environment II. It will be slower than the case. Therefore, it is necessary to correct the pre-main time interval so as to be further expanded as compared with the case of the ignition environment II. However, if the play main time interval is increased too much, the original function of pre-injection, which is to improve the ignitability of main injection, cannot be performed. Further, if the injection timing of the pre-injection is advanced to some extent by expanding the play main time interval, it is impossible to advance the timing at which the peak value of the heat generation rate of the pre-injection occurs even if the injection timing is further advanced. Therefore, shortening the heat generation interval between the pre-injection and the main injection due to poor ignitability cannot be prevented only by increasing the pre-main time interval. Therefore, in the ignition environment III, as shown in the injection pattern of FIG. 17, the pre-main time interval is corrected to be expanded from the pre-main reference time interval, and the pre-injection injection timing is advanced with respect to the main injection timing. In addition, the pre-injection amount is corrected so as to increase from the reference pre-injection amount, and the heat generation rate due to pre-injection steeply rises and the timing at which the peak value occurs is advanced, thereby causing the heat generation rate of FIG. As indicated by the solid line in the waveform, the heat generation interval between the pre-injection and the main injection due to poor ignitability is prevented.

  In addition, when the ignition environment determined in step S25 or S26 is the ignition environment IV, the ignitability of the fuel is even worse than the ignition environment III. Therefore, the timing at which the peak value of the heat generation rate due to the pre-injection occurs is the ignition environment III. It will be slower than the case. Therefore, it is necessary to correct the pre-injection amount so as to increase further than in the case of the ignition environment III. However, if the pre-injection amount is increased too much, emissions and fuel consumption deteriorate. Further, in the ignition environment IV having relatively poor ignitability, the ignition delay in the pre-injection cannot be sufficiently suppressed only by increasing the pre-injection amount. Therefore, in the ignition environment IV, as shown in the injection pattern of FIG. 17, by retarding the main injection timing from the reference main injection timing, as shown by the solid line in the heat generation rate waveform of FIG. Shortening the heat generation interval between the pre-injection and the main injection due to badness is prevented. Further, the PCM 70 sets the injection timing of the after injection to the main injection timing so that the main-after time interval remains the main-after reference time interval even when the main injection timing is retarded from the reference main injection timing. Is retarded by the amount retarded from the reference main injection timing.

  Further, when the ignition environment determined in step S25 or S26 is the ignition environment V, this ignition environment V specifically corresponds to the cold start, and the ignitability of the fuel is even worse than the ignition environment IV. The timing at which the peak value of the heat generation rate due to the pre-injection occurs is later than in the case of the ignition environment IV. Therefore, the ignition delay in the pre-injection cannot be sufficiently suppressed only by correcting the main injection timing to be retarded from the reference main injection timing and expanding the pre-main time interval as in the case of the ignition environment IV. The heat generation interval between the injection and the main injection cannot be expanded to the target interval. Therefore, in the ignition environment V, as shown in the injection pattern of FIG. 17, the main injection timing is retarded from the reference main injection timing, and the number of pre-injections (number of stages) is increased by one as in the ignition environment IV. As shown in the solid line in the heat generation rate waveform of FIG. 17, the pre-injection due to poor ignitability and the main injection are caused by causing the timing at which the peak value of the heat generation rate by pre-injection to occur earlier. Prevent shortening of heat generation interval.

How to correct the above-described pre-main time interval, pre-injection amount, and main injection timing in accordance with the ignition environment will be described with reference to FIG. FIG. 18 is a diagram showing the relationship between each parameter of the fuel injection mode and the ignition environment.
FIG. 18A is a diagram showing the relationship between the pre-main time interval and the ignition environment, where the horizontal axis shows the ignition environment and the vertical axis shows the pre-main time interval. As shown in FIG. 18A, in order to prevent the heat generation interval between the pre-injection and the main injection from being shortened as the ignitability deteriorates in the order of the ignition environments I, II, and III, the pre-main time interval is It is corrected to enlarge. Also, as described above, in the ignition environment III, the pre-injection timing is advanced to the limit due to the expansion of the pre-main time interval, and correction can be made so that the pre-main time interval is further increased. Since this is not possible, in the ignition environment IV, the pre-main time interval is maintained at the same value as in the ignition environment III.

  FIG. 18B is a diagram illustrating the relationship between the pre-injection amount and the ignition environment, where the horizontal axis indicates the ignition environment and the vertical axis indicates the pre-injection amount. As shown in FIG. 18 (b), in the ignition environment II in which the ignitability is good next to the ignition environment I, the heat generation interval between the pre-injection and the main injection is corrected by increasing the pre-main time interval. Therefore, the pre-injection amount is not corrected. On the other hand, in the ignition environments III and IV, which have poorer ignitability than the ignition environment II, the shortening of the heat generation interval between the pre-injection and the main injection cannot be sufficiently prevented only by correcting the pre-main time interval. In order to suppress the ignition delay, the pre-injection amount is corrected so as to increase as the ignitability deteriorates.

  FIG. 18C is a diagram showing the relationship between the main injection timing and the ignition environment, where the horizontal axis shows the ignition environment and the vertical axis shows the main injection timing. As shown in FIG. 18 (c), in the ignition environments II and III, the pre-injection is performed by correcting the pre-main time interval to be increased and by correcting the pre-injection amount to be increased. Since the heat generation interval with the main injection can be prevented from being shortened, the main injection timing is not corrected. On the other hand, in the ignition environment IV, which has a lower ignitability than the ignition environment III, the pre-main time interval and the pre-injection amount alone cannot be sufficiently prevented from shortening the heat generation interval between the pre-injection and the main injection. In order to prevent the heat generation interval between the injection and the main injection from being shortened, the main injection timing is corrected to be retarded.

  As described above, in order to prevent the heat generation interval between the pre-injection and the main injection from being shortened, in the ignition environment II having the best ignitability after the ignition environment I, the pre-injection having a small influence on the engine emission performance and the fuel consumption. Only the correction that expands the main time interval is performed, and in the ignition environment III that is less ignitable than the ignition environment II, the correction that increases the pre-injection amount within the range that does not affect the emission performance and fuel consumption is also performed. Furthermore, in the ignition environment IV with poor ignitability, correction is also made to retard the main injection timing within a range that does not significantly affect the engine output torque, etc., so it affects the engine's emission performance, fuel consumption, output torque, etc. Pre-injection and main-injection that can realize a heat generation interval that achieves the desired frequency characteristics of CPL in a wide range of ignition environments while suppressing the influence. And it is possible to set the injection timing of the after-injection.

  Returning to FIG. 15, in step S27, the pre-main time interval, the pre-injection amount, and the main injection timing are determined according to the ignition environment determined in step S25 or S26. After the correction from the reference main injection timing, the process proceeds to step S28, and the PCM 70 performs pre-injection, main injection, and after-injection based on the corrected pre-main time interval, pre-injection amount, and main injection timing. Determine the injection timing. Thereafter, the PCM 70 ends the fuel injection mode determination process and returns to the main routine.

Next, specific numerical values of the pre-main time interval and the main-after time interval will be described with reference to FIGS.
FIG. 19 is a diagram showing frequency characteristics of the vibration level of knock sound transmitted from the main route to each of the five main bearing caps (MBC # 1 to # 5) in the in-line four-cylinder engine. As shown in FIG. 19, the vibration level of the knock sound has peaks at approximately 1300 Hz, 1700 Hz, 2500 Hz, and 3500 Hz. It can be said that the frequency of these peaks indicates the resonance frequency in the main route. The resonance frequency in these main routes is determined mainly by the balance between the mass of the piston 4 and the rigidity of the connecting rod 8, and is the same regardless of the type of engine such as a gasoline engine or diesel engine, or the size of the engine. It is considered to be a value of about. In other words, in any engine, it is considered that the knock noise of the entire engine can be effectively reduced by reducing the knock noise in the frequency bands peaking at 1300 Hz, 1700 Hz, 2500 Hz, and 3500 Hz.

  Of these resonance frequency bands, the frequency band having the highest peak in the vicinity of 3500 Hz has a mechanical configuration that cancels structural resonance (specifically, a dynamic vibration absorber that suppresses expansion and contraction resonance of the connecting rod 8 in the combustion stroke). 90) is provided in the engine body 1, the weight increase of the engine body 1 is small. Therefore, the knocking noise having a peak at 3500 Hz is realized by the dynamic vibration absorber 90, and the PCM 70 exhibits the frequency characteristics of CPL in order to reduce the knocking sound having a peak at 1300 Hz, 1700 Hz, and 2500 Hz. The pre-main time interval and the main-after time interval are controlled so that valley portions in the curve occur in predetermined frequency bands including peaks of 1300 Hz, 1700 Hz, and 2500 Hz, respectively.

  FIG. 20 is a diagram showing the relationship between the heat generation interval and the valley frequency in the curve of the frequency characteristics of CPL. In FIG. 20, the horizontal axis indicates the heat generation interval, and the vertical axis indicates the frequency of the combustion pressure wave. Further, the curve shown by the solid line in FIG. 20 interferes so that the combustion pressure waves caused by two fuel injections that are temporally adjacent (that is, pre-injection and main injection, or main injection and after-injection) cancel each other. Thus, the frequency at which valleys appear in the curve indicating the frequency characteristics of CPL is shown.

As shown in FIG. 20, when the heat generation interval is set to about 0.9 msec, valleys appear in the curves indicating the frequency characteristics of CPL in the frequency bands including 1700 Hz and 2500 Hz, respectively. Further, when the heat generation interval is set to about 2.0 msec, a valley is generated in a curve indicating the frequency characteristics of CPL in frequency bands including 1300 Hz and 1700 Hz, respectively. As shown in FIG. 19, the peak at 1700 Hz is the largest among the peaks at 1300 Hz, 1700 Hz, and 2500 Hz. Therefore, the pre-main injection interval is set so that the heat generation interval between the pre-injection and the main injection is about 0.9 msec, and the main-after time interval is set so that the heat generation interval between the main injection and the after injection is about It is good to set it to be 2.0 msec. Specifically, the pre-main injection interval is about 1.7 msec which is longer than the desired heat generation interval of 0.9 msec in order to advance the injection timing of the pre-injection in consideration of the poor ignitability of the fuel. It is good to do. On the other hand, the main-after time interval is preferably about 2.0 msec, which is equal to the desired heat generation interval of 2.0 msec, because the ignitability during after-injection is good.
As a result, in the frequency band including the maximum peak of 1700 Hz, the combustion pressure wave due to the pre-injection and the main injection and the combustion pressure wave due to the main injection and the after-injection can be made to interfere with each other so as to cancel each other. It is possible to increase the size of valleys generated in the curve indicating the frequency characteristics of CPL. That is, it is possible to effectively reduce knock noise in a frequency band having a peak at 1700 Hz.

FIG. 21 is a diagram showing the relationship between the frequency shift of two vibrations that interfere with each other and the sound pressure level amplification amount due to resonance of those vibrations. As shown in FIG. 21, when two vibrations interfere with each other so that the peaks of the waveforms overlap, if the frequency shift between the two vibrations is smaller than 150 Hz, the resonance of those vibrations The sound pressure level amplification amount increases rapidly. This means that the structural resonance in the resonance frequency band is greatly reduced by making the difference between the peak of the resonance frequency in the main route and the frequency corresponding to the valley position in the curve indicating the frequency characteristics of the CPL be 150 Hz or less. And knocking noise can be reduced appropriately.
Specifically, for the pre-main injection interval, the frequencies corresponding to the valley positions in the curve indicating the frequency characteristics of the CPL are set to 1700 Hz ± 150 Hz and 2500 Hz ± 150 Hz. According to the above equation (2) and FIG. 20, by setting the pre-main injection interval to 1.7 ± 0.1 msec, the frequency corresponding to the position of the valley in the curve indicating the frequency characteristic of CPL is 1700 Hz ± 150 Hz, The heat generation interval between the pre-injection and the main injection can be controlled to be 2500 Hz ± 150 Hz. Further, by setting the main-after time interval to 2.0 ± 0.1 msec, the main injection and the main injection are performed so that the frequencies corresponding to the valley positions in the curve indicating the frequency characteristics of the CPL are 1300 Hz ± 150 Hz and 1700 Hz ± 150 Hz. The heat generation interval with after injection can be controlled.

  Next, effects of the fuel injection control method and the fuel injection control device for the compression self-ignition engine according to the above-described embodiment of the present invention will be described.

  First, by setting the interval between the pre-injection and the main injection to 1.7 ± 0.1 msec, the heat generation interval between the pre-injection and the main injection is set to the frequency of the combustion pressure wave generated by the pre-injection and the main injection. The frequency corresponding to the position of the valley of the curve indicating the characteristics can be controlled to be 1700 Hz ± 150 Hz and 2500 Hz ± 150 Hz, which corresponds to 1700 Hz and 2500 Hz among the main resonance frequencies of the engine structural system It is possible to effectively reduce the knocking sound. In this case, the overall level of the combustion pressure wave is not changed, so the fuel consumption and emissions are not deteriorated, and no additional sound insulation is added, so increasing the cost and weight of the device Absent.

  In addition, by setting the interval between the main injection and the after injection to 2.0 ± 0.1 msec, the heat generation interval between the main injection and the after injection is set to the frequency of the combustion pressure wave generated by the main injection and the after injection. The frequency corresponding to the position of the valley of the curve indicating the characteristics can be controlled to be 1300 Hz ± 150 Hz and 1700 Hz ± 150 Hz, which corresponds to 1300 Hz and 1700 Hz among the main resonance frequencies of the engine structural system It is possible to effectively reduce the knocking sound. In particular, both the heat generation interval between the pre-injection and the main injection and the heat generation interval between the main injection and the after injection are at the positions of the valleys of the curves indicating the frequency characteristics of the combustion pressure waves generated by these fuel injections. Since the corresponding frequency is controlled to be 1700 Hz ± 150 Hz, it is possible to increase the size of the valley generated at the position of 1700 Hz ± 150 Hz in the curve indicating the frequency characteristics of the combustion pressure wave. Among the main resonance frequencies, knock noise corresponding to 1700 Hz having a particularly large peak can be reduced more effectively.

  In addition, the lower the engine load at the same engine speed and the worse the ignitability of the fuel, the more the pre-injection timing is advanced and the interval between the pre-injection and the main injection is expanded, resulting in poor ignitability. Therefore, it is possible to prevent the heat generation interval between the pre-injection and the main injection from being shortened, and in a wide ignition environment, it corresponds to the resonance frequency bands of the engine structural system of 1700 Hz ± 150 Hz and 2500 Hz ± 150 Hz, respectively. Knock noise can be appropriately reduced.

  Also, the lower the engine load at the same engine speed and the worse the ignitability of the fuel, the more the fuel injection amount of the pre-injection is increased to improve the ignitability of the fuel. It is possible to prevent the heat generation interval between the injection and the main injection from being shortened, so that, in a wide ignition environment, knocking sounds corresponding to the resonance frequency bands of the engine structural system of 1700 Hz ± 150 Hz and 2500 Hz ± 150 Hz, respectively. Can be appropriately reduced.

  Also, the lower the engine load at the same engine speed and the worse the ignitability of the fuel, the retarded the injection timing of the main injection and the after injection timing so as to maintain the interval between the main injection and the after injection. Therefore, even when the injection timing of the pre-injection cannot be advanced, it is possible to prevent the heat generation interval between the pre-injection and the main injection from being shortened due to poor fuel ignitability. Also, when the injection timing of the main injection is retarded in response to a decrease in engine load, the injection timing of the after injection is also retarded to maintain the interval between the main injection and the after injection. Curve showing the frequency characteristics of combustion pressure waves generated by main injection and after injection even when the injection timing of main injection is retarded to prevent shortening of the heat generation interval between pre-injection and main injection The heat generation interval can be controlled so that the frequency corresponding to the position of the valley of the engine is included in the respective ranges of 1300 Hz ± 150 Hz and 1700 Hz ± 150 Hz, which are a plurality of resonance frequency bands of the engine structural system. In a wide range of ignition environments, the knock sound corresponding to each of the multiple resonance frequency bands of the engine structural system It can be reduced appropriately.

  In Ignition Environment II, which has the best ignitability after Ignition Environment I, the heat generation interval between the pre-injection and main injection can be shortened only by controlling the injection timing of the pre-injection, which has little impact on engine emission performance and fuel efficiency. In the ignition environment III, which has a lower ignitability than the ignition environment II, the pre-injection fuel injection amount is increased to improve the ignitability of the pre-injection. Reducing the heat generation interval between pre-injection and main-injection is surely prevented, so pre-injection due to poor ignitability while suppressing effects on engine emission performance, fuel consumption, output torque, etc. The heat generation interval between the main injection and the main injection can be reliably prevented, so that, in a wider ignition environment, each of the multiple resonance frequency bands of the engine structural system. It is possible to appropriately reduce the knocking sound corresponding to.

  Further, the lower the cylinder wall temperature, the engine supercharging pressure, and / or the oxygen concentration of the intake air, the larger the interval between the pre-injection and the main injection, so the cylinder wall temperature, the engine supercharging pressure, and / or Even when the oxygen concentration in the intake air is low and the ignitability is poor, it is possible to prevent the heat generation interval between the pre-injection and the main injection from being shortened. It is possible to appropriately reduce the knock sound corresponding to each of the bands of 1300 Hz ± 150 Hz and 1700 Hz ± 150.

  The dynamic vibration absorber 90 suppresses resonance in a frequency band having a peak in the vicinity of 3500 Hz having the highest frequency among a plurality of resonance frequency bands of the engine structural system, and the PCM 70 is low in the resonance frequency band. In order to reduce knock noise having peaks at 1300 Hz, 1700 Hz, and 2500 Hz on the frequency side, predetermined frequency bands in which the valley portions in the curve indicating the frequency characteristics of the CPL include peaks at 1300 Hz, 1700 Hz, and 2500 Hz, respectively. As described above, since the pre-main time interval and the main-after time interval are controlled, the knock noise corresponding to the resonance frequency band on the high frequency side where the weight increase of the engine is small even if a mechanical structure is provided is the dynamic vibration absorption. If a mechanical structure is provided while reducing the weight of the engine, the weight of the engine will increase. The knocking sound corresponding to the resonance frequency band on the low frequency side that becomes sharper can be reduced by controlling the fuel injection interval, thereby minimizing the increase in the weight of the engine and reducing the engine structural system. Knock sound corresponding to each of the plurality of resonance frequency bands can be appropriately reduced.

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

Claims (8)

A fuel injection control method for a compression self-ignition engine that performs a plurality of times of fuel injection during a single combustion stroke to cause a plurality of times of combustion in a cylinder,
Determining fuel ignitability based on engine conditions;
In the fuel injection performed multiple times so that the valley portion of the curve indicating the frequency characteristics of the combustion pressure wave generated by the multiple times of combustion is included in the respective ranges of the multiple resonance frequency bands of the engine structural system Setting an interval between the pre-injection and the main injection,
The step of setting the interval between the pre-injection and the main injection includes the step of increasing the interval between the pre-injection and the main injection as the ignitability of the fuel is worse. Fuel injection control method.   Further, the injection timing of the main injection is set to a timing corresponding to a predetermined crank angle, the injection timing of the pre-injection and / or the after-injection is set based on the set fuel injection interval, and the pre-injection timing is set at those injection timings. The fuel injection control method for a compression self-ignition engine according to claim 1, further comprising a step of controlling the fuel injection device to perform injection, main injection, and after injection. A fuel injection control device for a compression self-ignition engine that performs a plurality of times of fuel injection during a single combustion stroke to cause a plurality of times of combustion in a cylinder,
Ignition environment determination means for determining the ignitability of the fuel based on the state of the engine;
In the fuel injection performed multiple times so that the valley portion of the curve indicating the frequency characteristics of the combustion pressure wave generated by the multiple times of combustion is included in the respective ranges of the multiple resonance frequency bands of the engine structural system Control means for setting the interval between the pre-injection and the main injection,
The fuel injection control device for a compression self-ignition engine, wherein the control means increases the interval between the pre-injection and the main injection as the ignitability of the fuel is worse.   The fuel injection control device for a compression self-ignition engine according to claim 3, wherein the ignition environment determination means determines that the ignitability of the fuel is worse as the cylinder wall temperature of the engine is lower. The fuel injection control device of the compression self-ignition engine is a fuel injection control device of a compression self-ignition engine equipped with a supercharger,
The fuel injection control device for a compression self-ignition engine according to claim 3 or 4, wherein the ignition environment determination means determines that the lower the supercharging pressure of the engine, the worse the fuel ignitability.   The fuel injection control device for a compression self-ignition engine according to any one of claims 3 to 5, wherein the ignition environment determination means determines that the lower the oxygen concentration in the intake air of the engine, the worse the fuel ignitability. .   The control means fixes the injection timing of the main injection, advances the injection timing of the pre-injection and / or increases the fuel injection amount of the pre-injection as the ignitability of the fuel is worse. A fuel injection control device for a compression self-ignition engine according to any one of claims 1 to 6.   The control means sets the injection timing of the main injection to a timing corresponding to a predetermined crank angle, sets the injection timing of pre-injection and / or after-injection based on the set fuel injection interval, The fuel injection control device for a compression self-ignition engine according to any one of claims 3 to 7, wherein the fuel injection device is controlled to perform pre-injection, main injection, and after-injection at a timing.

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