JP5997061B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device including a fuel injection valve that injects fuel into an internal combustion engine.

  2. Description of the Related Art In recent years, in a diesel engine of an automobile, a multi-stage injection method that performs sub-injection with an injection amount smaller than that of main injection before and after main injection that generates output torque in one combustion cycle is widely adopted. For example, pilot injection in which injection is performed with a small injection amount before main injection has an effect of suppressing noise and NOx emission during fuel combustion. Further, the after injection performed immediately after the main injection is performed for the purpose of activating diffusion combustion and, in turn, reducing PM emission (see, for example, Patent Document 1).

JP 2008-196449 A

  By the way, in main injection in which a large amount of fuel is injected to obtain torque, the amount of combustion in the cylinder is large, and the temperature in the cylinder (in-cylinder temperature) becomes extremely high. Therefore, in the after injection that is performed immediately after the main injection, the fuel is injected in a high temperature environment, so that the fuel is ignited in a very short time after the injection (the ignition delay is very short). For this reason, since the fuel burns soon before it is sufficiently mixed with air, there is a problem that smoke is easily generated in the cylinder. In addition, the combustion temperature becomes insufficient due to insufficient mixing with air, and the smoke reoxidation effect, which is the purpose of after-injection, may be reduced.

  On the other hand, if the fuel is atomized by increasing the injection pressure during the combustion cycle as a whole and injecting under high pressure, it is possible to promote mixing with air. However, if pilot injection is performed at such a high injection pressure, the atomization of the fuel proceeds excessively and causes overdiffusion. As a result, the amount of combustion during pilot injection decreases, and there is a problem that ignition stability during the combustion cycle is impaired. In addition, when the main injection is performed at a high pressure, the amount of premixed combustion becomes excessive, resulting in a problem of worsening combustion noise.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to promote smoke reburning effects and reduce smoke generation while suppressing deterioration of combustion noise. .

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

In the first invention,
A fuel injection valve that injects fuel into the internal combustion engine, and at least a first injection and a second injection that is executed after the first injection and injects a smaller amount of fuel than the first injection per combustion cycle. A fuel injection control device for causing the fuel injection valve to perform,
Transformer means for controlling the fuel injection pressure of the fuel injection valve;
Smoke detecting means for detecting the amount of smoke generated in the internal combustion engine;
The transformation means is configured to start the combustion stroke at the injection pressure of the reference pressure value, increase the injection pressure to the increased pressure value by the second injection at the latest, and perform the second injection at the injection pressure of the increased pressure value. Control means for controlling,
The control means controls at least one of a pressure increase start timing for increasing the injection pressure or the increase pressure value based on the amount of smoke generated detected by the smoke detection means.

According to the first invention, since the second injection is executed at an injection pressure having an increased pressure value larger than the reference pressure value, the fuel can be atomized and injected as compared with the case of injecting at the reference pressure value. . As a result, even in a high temperature environment, the fuel can be sufficiently mixed with air, and the generation of smoke can be suppressed. Moreover, by sufficiently mixing with air, a sufficient combustion temperature is ensured by combustion, and the smoke reoxidation effect can be promoted.

  The control means controls at least one of the pressure increase start timing and the increase pressure value based on the smoke generation amount detected by the smoke detection means. That is, since the pressure increase start timing or the increased pressure value is controlled according to the amount of smoke generated actually, the amount of smoke generated can be reliably suppressed.

In a second aspect of the invention, the control means determines a reference pressure increase start time based on operating conditions, and advances the reference pressure increase start time based on the amount of smoke generated detected by the smoke detection means. To control the pressure increase start time.

According to the second invention, the control means controls the pressure increase start time by advancing the reference pressure increase start time determined based on the operating condition based on the smoke generation amount. Therefore, it is possible to determine the optimal pressure increase start time based on not only the operating conditions but also the amount of smoke generated, and the smoke can be reliably reduced.

In a third aspect of the invention, the control means determines the reference increase pressure value based on operating conditions, and increases the reference increase pressure value based on the amount of smoke generated detected by the smoke detection means. The increased pressure value is controlled.

According to the third aspect, the control means controls the increased pressure value by increasing the reference increased pressure value determined based on the operating condition based on the smoke generation amount. Therefore, it is possible to determine the optimal pressure increase start time based on the amount of smoke generated rather than the operating conditions, and the smoke can be reliably reduced.

In a fourth aspect of the invention, the control means controls the pressure increase start time with priority over the pressure increase value.

According to the fourth aspect of the invention, since the control means controls the pressure increase start time with priority over the pressure increase value, it is possible to increase the frequency of controlling the pressure increase start time that does not cause deterioration in fuel consumption. That is, it is possible to suppress the occurrence frequency of the control for increasing the increased pressure value from being relatively reduced, and to suppress the deterioration of fuel consumption.

1 is a system configuration diagram of an engine to which a fuel injection control device according to Embodiment 1 is applied. (A) is the schematic which shows the voltage transformer which concerns on Embodiment 1, (b) is the schematic which shows the small rail which concerns on the example of a change integrated with the fuel injection valve. It is a figure which shows the control aspect which concerns on Embodiment 1, Comprising: (a) is a timing chart of an injection pulse, (b) is a graph which shows a heat release rate, (c) is a graph which shows injection pressure. 3 is a flowchart for determining a pressure increase start time and an increase pressure value according to the first embodiment. 3 is a flowchart showing injection pressure control according to the first embodiment. 9 is a flowchart for determining a pressure increase start time and an increase pressure value according to the second embodiment. It is a figure which shows the control aspect which concerns on Embodiment 2, Comprising: (a) is a timing chart of an injection pulse, (b) is a graph which shows a heat release rate, (c) is a graph which shows injection pressure. The system block diagram of the engine to which the fuel-injection control apparatus which concerns on Embodiment 3 was applied. It is a graph which shows the relationship between an air fuel consumption and the amount of smoke generation. 10 is a flowchart for determining a pressure increase start time and an increase pressure value according to the third embodiment. 10 is a flowchart for determining a pressure increase start time and an increase pressure value according to the fourth embodiment. Schematic which shows the transformation apparatus which concerns on the example of a change. Schematic which shows the transformer which concerns on another example of a change.

  Next, the fuel injection control device 11 and its control method according to the embodiment will be described below. In the following embodiment, as shown in FIG. 1, a multi-cylinder diesel engine 10 (hereinafter referred to as the engine 10) is employed as the internal combustion engine, and the fuel injection control device 11 is applied to the engine 10 as an example. .

[Embodiment 1]
As shown in FIG. 1, the engine 10 is configured such that a piston 15 is accommodated in a cylinder 14 formed in a cylinder block 12 so as to be capable of reciprocating. A cylinder head 18 in which a combustion chamber 16 is defined is provided on the upper end surface of the cylinder block 12. An intake port 20 and an exhaust port 22 that open to the combustion chamber 16 are formed in the cylinder head 18. The intake port 20 and the exhaust port 22 are opened and closed by an intake valve 24 and an exhaust valve 26, respectively.

  The intake port 20 is connected to an intake pipe 28 for sucking outside air. During the intake stroke in which the intake valve 24 opens the intake port 20, the piston 15 descends in the cylinder 14 to generate a negative pressure. As a result, outside air sucked from the intake pipe 28 flows into the cylinder 14 through the intake port 20. An exhaust pipe 30 for discharging combustion gas is connected to the exhaust port 22. During the exhaust stroke in which the exhaust valve 26 opens the exhaust port 22, the exhaust gas pushed out of the combustion chamber 16 by the rise of the piston 15 is discharged to the exhaust pipe 30 through the exhaust port 22. .

  The fuel (light oil) supplied to the engine 10 is controlled by the accumulator fuel injection control device 11 for the fuel injection pressure, the injection timing, and the injection amount. The fuel injection control device 11 injects the fuel pressure (injection pressure) 32 that can transform the fuel pressure (injection pressure) and the fuel pressure-fed from the transformer 32 into the combustion chamber 16 of each cylinder of the engine 10. A plurality of fuel injection valves 34 (only one is shown in FIG. 1) and an ECU 36 (electronic control unit, control means) for controlling these transformer device 32 and fuel injection valve 34 are provided.

  The fuel injection valve 34 has a solenoid valve (not shown) electronically controlled by the ECU 36 and a nozzle 34a that injects fuel by opening the solenoid valve. The fuel injection valve 34 is attached to the cylinder head 18 with the tip of the nozzle 34a facing the combustion chamber 16 of each cylinder.

  As shown in FIG. 2A, the transformer 32 includes a small rail 38 (pressure accumulation rail) provided corresponding to each fuel injection valve 34, a high-pressure pump 40 that pumps fuel to the small rail 38, It basically comprises an open / close valve 44 for selectively opening / closing a high-pressure pipe 42 connecting each small rail 38 and the high-pressure pump 40. The small rail 38 accumulates high-pressure fuel supplied from the high-pressure pump 40 to a predetermined rail pressure, and supplies the accumulated fuel to the fuel injection valve 34. When the electromagnetic valve is opened, the fuel injection valve 34 supplies fuel to the combustion chamber 16 at an injection pressure substantially the same as the pressure in the small rail 38. The on-off valve 44 is opened and closed by the ECU 36 to control the amount of fuel supplied from the high-pressure pump 40 to the small rail 38 (that is, pressure).

  The ECU 36 is mainly composed of a microcomputer having a CPU, RAM, ROM and the like. The ECU 36 receives output signals output from the crank angle sensor 46, the fuel pressure sensor 50, the intake pressure sensor 54, the intake air temperature sensor 56, the intake air amount sensor 58, the smoke sensor (smoke detecting means) 81, the exhaust A / F sensor 82, and the like. The operation state of the engine 10 is detected based on these output signals. The ECU 36 functions as pressure determination means and start determination means described later by executing a control program stored in a storage medium such as a ROM.

  As shown in FIG. 1, the crank angle sensor 46 is disposed in the vicinity of the pulsar 60 that rotates in synchronization with the crankshaft of the engine 10, and is provided on the outer periphery of the pulsar 60 while the pulsar 60 rotates once. A plurality of pulse signals (rotation angle signals) corresponding to the number of teeth are output. The ECU 36 detects the rotational speed (NE) and the crank angle of the engine 10 based on the rotation angle signal output from the crank angle sensor 46.

  As shown in FIG. 2A, the fuel pressure sensor 50 is attached to each small rail 38 and measures the fuel pressure (that is, the injection pressure) accumulated in the small rail 38.

  The intake pressure sensor 54 is attached to the intake pipe 28 and measures the intake pressure (Pm) in the intake pipe 28. The intake air temperature sensor 56 is attached to the intake pipe 28 and measures the intake air temperature (Tm) passing through the intake pipe 28. The intake air amount sensor 58 is attached to the intake pipe 28 and measures the intake air amount (Ga) in the intake pipe 28.

  The smoke sensor 81 is attached to the exhaust pipe 30 and detects the amount of smoke (smoke generation amount) in the exhaust gas discharged from the exhaust pipe 30. The exhaust A / F sensor 82 is also attached to the exhaust pipe 30 and detects the air-fuel ratio (A / F value) of the exhaust gas discharged from the exhaust pipe 30.

  Between the intake pipe 28 and the exhaust pipe 30, an EGR device for returning a part of the exhaust gas to the intake system as EGR gas is disposed. This EGR device is basically configured by an EGR pipe 90 provided so as to communicate the intake pipe 28 and the exhaust pipe 30, and an EGR valve 91 including an electromagnetic valve or the like provided in the EGR pipe 90. Yes. The valve opening / closing of the EGR valve 91 is controlled by the ECU 36. By the valve opening of the EGR valve 91, the passage area of the EGR pipe 90, and thus the EGR rate (the ratio of the EGR gas returned to the cylinder 14 with respect to the entire exhaust gas) can be adjusted. That is, as the opening degree of the EGR valve 91 decreases, the EGR rate also decreases. When the EGR valve 91 is fully closed, the EGR pipe 90 is shut off and the EGR rate becomes “zero”.

  Next, the control configuration of the ECU 36 will be described in detail below. The ECU 36 performs injection control for the fuel injection valve 34 and injection pressure control for the transformer device 32.

[Injection control]
The injection control by the ECU 36 is performed by controlling the fuel injection amount and injection timing from the fuel injection valve 34. The ECU 36 calculates the optimal injection amount and injection timing based on the operating state of the engine 10, and controls the fuel injection of the fuel injection valve 34 based on the calculation result. Specifically, this injection control is performed by controlling the electric power supplied to the electromagnetic valve of the fuel injection valve 34 by a pulse signal (injection pulse) that defines the fuel injection amount and injection timing.

  The specific injection control implemented in Embodiment 1 is shown in FIG. 3A is a timing chart of the injection pulse, FIG. 3B is a heat generation rate in the combustion chamber 16, and FIG. 3C is a fuel injection pressure. The horizontal axis in FIG. 3 indicates the crank angle. As shown in FIG. 3A, the ECU 36 performs the after injection (second injection) immediately after the main injection (first injection) for generating torque with an injection amount smaller than the fuel injection amount of the main injection. Injection). Further, prior to the main injection, the ECU 36 executes pilot injection (third injection) with an injection amount smaller than that of the main injection. That is, the ECU 36 causes the fuel injection valve 34 to execute multistage injection including pilot injection, main injection, and after injection in one combustion cycle (combustion stroke).

[Injection pressure control]
Next, the injection pressure control by the ECU 36 will be described. In the injection pressure control, the ECU 36 opens and closes the opening / closing valve 44 of the transformer device 32 to control the pressure in the small rail 38 to be a predetermined rail pressure. Thereby, the injection pressure of the fuel injected from the fuel injection valve 34 into the combustion chamber 16 is controlled. The ECU 36 sets two target rail pressures, that is, a reference pressure value and an increased pressure value in one combustion cycle, specifically, a combustion stroke.

  As shown in FIG. 3C, the ECU 36 starts the combustion stroke at the injection pressure of the reference pressure value. Then, the injection pressure is increased from the middle of the combustion stroke, and the latter half (at least after injection) of the combustion stroke is executed with an injection pressure having an increased pressure value higher than the reference pressure value. In the first embodiment, pilot injection and main injection are performed at the injection pressure of the reference pressure value, and after injection is performed at the injection pressure of the increased pressure value.

  The ECU 36 functions as a start determination unit that determines the timing (pressure increase start timing) at which the injection pressure is increased from the reference pressure value to the increased pressure value. Specifically, the ECU 36 determines a reference pressure increase start time based on the operating conditions, and corrects (advances) the reference pressure increase start time based on the amount of smoke generated detected by the smoke sensor 81. Determine the pressure increase start time.

  The reference pressure increase start time is a provisional pressure increase start time considered to be able to optimally suppress the amount of smoke generated from the current operating conditions. In the first embodiment, the ECU 36 stores a map of the reference pressure increase start time in which the engine speed (NE) and the fuel injection amount (Q) in the main injection are parameters. Then, the ECU 36 determines the reference pressure increase start time using the map from the current rotation speed and the injection amount.

  The ECU 36 determines whether or not to advance the reference pressure increase start timing based on the difference between the smoke generation amount detected by the smoke sensor 81 in the previous combustion cycle and the target smoke level determined from the current operating conditions. To do. The target smoke level is an ideal (optimally reduced) amount of smoke generated under the current operating conditions. Similar to the reference pressure increase start time, the ECU 36 stores in advance a map of the target smoke level using the rotation speed and the injection amount as parameters. Then, the ECU 36 determines a target smoke level using the map from the current rotation speed and injection amount.

  The ECU 36 calculates the difference between the smoke generation amount detected by the smoke sensor 81 and the target smoke level under the current operating conditions (hereinafter referred to as a smoke difference value). When the smoke difference value is equal to or greater than the predetermined value α, the ECU 36 determines to advance the reference pressure increase start timing. The predetermined value α may be 0, or a dead zone in a predetermined range may be set.

  When the reference pressure increase start timing is advanced (when the smoke difference value is equal to or larger than the predetermined value α), the ECU 36 calculates the smoke difference value calculated in the current combustion cycle and the smoke difference calculated in the previous combustion cycle. Based on the value, the reference pressure increase start time is corrected by feedback control. More specifically, the ECU 36 determines a correction amount for advancing the reference pressure increase start timing by PID control based on the current smoke difference value and the previous smoke difference value. Then, the ECU 36 tentatively determines the timing advanced by the correction amount from the reference pressure increase start timing as the pressure increase start timing.

  On the other hand, when the reference pressure increase start time is not advanced (when the smoke difference value is smaller than the predetermined value α), the ECU 36 has advanced the correction amount calculated in the previous combustion cycle from the reference pressure increase start time. The timing is determined as the pressure increase start time.

  Here, if the pressure increase start timing is advanced too much (accelerated), excessive combustion noise may occur. Therefore, the ECU 36 determines a limit pressure increase start time that is a limit value for advancing the reference pressure increase start time. That is, the limit pressure increase start time is an advance angle guard value that is introduced to prevent excessive combustion noise from being generated. In the first embodiment, the timing at which the main injection ends is set as the limit pressure increase start timing.

  Then, the ECU 36 determines whether or not the tentatively determined pressure increase start timing is advanced from the limit pressure increase start timing. If the pressure increase start time is retarded from the limit pressure increase start time, the pressure increase start time is determined. On the other hand, if the tentatively determined pressure increase start timing is on the more advanced side than the limit pressure increase start timing, the ECU 36 determines the limit pressure increase start timing (that is, at the end of main injection) as the pressure increase start timing. To do.

  When the ECU 36 determines that the pressure increase start time is on the more advanced side than the limit pressure increase start time, the ECU 36 responds to the abnormality. In the first embodiment, an abnormality detection signal is stored in the RAM of the ECU 36 as an abnormality response. Thus, the operator can recognize that some abnormality may have occurred by confirming that the abnormality detection signal is stored in the RAM during maintenance or the like.

  As the cause of the abnormality, for example, the malfunction of the fuel injection valve 34, the abnormality of the DPF differential pressure due to the failure of the DPF (Diesel Particulate Filter (not shown)), the smoke sensor 81, the exhaust A / F sensor 82, etc. A sensor failure may be considered.

  The ECU 36 functions as a pressure determining unit that determines the reference pressure value and the increased pressure value. The ECU 36 determines a reference pressure value according to operating conditions such as the rotational speed and the injection amount. Then, the transformer 32 (open / close valve 44) is controlled so that the measured value of the fuel pressure sensor 50 is maintained at the reference pressure value from the start of the combustion stroke to the pressure increase start timing.

  On the other hand, for the increased pressure value, the ECU 36 determines an optimum value that can suppress the amount of smoke generated based on the operating conditions. The parameters indicating the operating conditions include the injection amount in main injection, the rotation speed of the engine 10, the intake temperature of the engine 10, the in-cylinder pressure of the engine 10, and the like. Based on at least one of these parameters, the ECU 36 calculates an increased pressure value.

  In the first embodiment, a map of increased pressure values using the injection amount and the rotation speed as parameters is stored in the ECU 36 in advance. Then, the ECU 36 determines an increased pressure value using a map from the current injection amount and the rotational speed.

  When the combustion stroke reaches the pressure increase start time, the ECU 36 controls the transformer 32 (open / close valve 44) to increase the injection pressure. When the measured value of the fuel pressure sensor 50 reaches the increased pressure value, the transformer device 32 is controlled to maintain the fuel pressure sensor 50 at the increased pressure value. Here, the ECU 36 controls the transformer 32 so that the measured value of the fuel pressure sensor 50 becomes the increased pressure value before the start of the after injection at the latest.

[Fuel injection control method]
Next, a fuel injection control method by the fuel injection control device 11 will be described. First, the case where the increase pressure value and the pressure increase start time are determined will be described with reference to the flowchart of FIG.

  The ECU 36 acquires the current operating conditions (rotation speed, injection amount, injection timing, etc.) (step S10). Next, the ECU 36 determines a limit pressure increase start time at the end of the main injection (step S11). Further, the ECU 36 determines a reference pressure value from the current rotation speed and injection amount (step S12), and also determines an increased pressure value from the rotation speed and injection amount using a map (step S13).

  Next, the ECU 36 determines the reference pressure increase start time from the rotation speed and the injection amount using a map (step S14), and determines the target smoke level using the map from the rotation amount and the injection amount (step S15). The ECU 36 acquires the amount of smoke generated in the previous combustion cycle detected by the smoke sensor 81 (step S16). Then, the ECU 36 calculates a smoke difference value that is the difference between the previous smoke generation amount and the target smoke level (step S17).

  When the smoke difference value is smaller than the predetermined value (YES in step S18), the ECU 36 adds the correction amount calculated in the previous combustion cycle to the reference pressure increase start time determined in step S14. That is, the timing at which the previous correction amount is advanced from the reference pressure increase start timing is determined as the pressure increase start timing (step S19).

  In step S18, when the smoke difference value is equal to or larger than the predetermined value (NO in step S18), the ECU 36 determines a correction amount by PID control from the current smoke difference value and the previous smoke difference value (step S20). Then, the timing advanced from the reference pressure increase start time by the correction amount is provisionally determined as the pressure increase start time (step S21).

  Next, the ECU 36 determines whether or not the pressure increase start timing tentatively determined in step S21 is smaller than the limit pressure increase start timing (on the retard side). When the pressure increase start time is smaller than the limit pressure increase start time (delay side) (YES in step S22), the pressure increase start time is determined (step S23). On the other hand, when step S22 is NO, the ECU 36 determines the limit pressure increase start time determined in step S11 (that is, at the end of the main injection) as the pressure increase start time (step S24). Further, the ECU 36 stores the abnormality detection signal in the RAM (step S25).

  Next, the case where the ECU 36 performs fuel injection control based on the increased pressure value and the increased pressure start time determined in the above flow will be described with reference to the flowchart of FIG. First, the ECU 36 controls the on-off valve 44 so that the measured value by the fuel pressure sensor 50 becomes the reference pressure value, and starts the combustion stroke (step S30).

  When the combustion stroke is started, first, pilot injection is executed (step S31). In this pilot injection, as shown in FIG. 3A, fuel is supplied from the fuel injection valve 34 to the combustion chamber 16 at a reference pressure value for a short time. At this time, as shown in FIG. 3B, in the pilot injection, the heat generation rate changes to a mountain shape having a predetermined height.

  When a predetermined time elapses after the pilot injection, the ECU 36 starts the main injection while maintaining the reference pressure value (step S32). In this main injection, as shown in FIG. 3A, more fuel is supplied to the combustion chamber 16 than in the pilot injection, and a large torque is obtained. Further, as shown in FIG. 3B, the heat generation rate in the main injection changes in a mountain shape higher than that in the pilot injection, and the heat generation amount increases.

  When the main injection ends and the pressure increase start time comes (Yes in Step S33), the ECU 36 controls the on-off valve 44 to start pressure increase in the small rail 38 (Step S34). That is, as shown in FIG. 3C, the ECU 36 sets the injection pressure to the reference pressure value after a predetermined time has elapsed after the injection pulse of the main injection ends (in the case of step S24, at the end of the main injection). To increase pressure value to increase pressure value. At this time, the ECU 36 controls the transformer 32 so that the injection pressure increases linearly. Further, the ECU 36 controls the transformer 32 so that the injection pressure reaches the increased pressure value before the after injection is started.

  Here, as described above, the pressure increase start time is determined by correcting the reference pressure increase start time. Therefore, as shown in FIG. 3C, the injection pressure starts to be increased at a timing earlier than the reference pressure increase start timing by the correction amount.

  When the measured value of the fuel pressure sensor 50 reaches the increased pressure value (Yes in step S35), the ECU 36 controls the on-off valve 44 to finish increasing the injection pressure (step S36). Then, the ECU 36 starts after-injection while maintaining the injection pressure at the increased pressure value (step S37).

  Here, as shown in FIG. 3 (b), after injection is executed after the end of the main injection, the temperature in the combustion chamber 16 when starting the after injection is in a very high temperature state. Yes. When fuel is injected under such a high temperature condition, the fuel is ignited in a very short time.

  However, in the first embodiment, the injection pressure is increased to a high increase pressure value before the after injection is started. By injecting the fuel with such a large injection pressure, atomization of the fuel is promoted, and the fuel can be burned in a sufficiently mixed state with air. As a result, it is possible to suppress the occurrence of smoke in the after injection. Further, when the fuel is sufficiently mixed with the air, a high combustion temperature can be secured, and the smoke reoxidation effect by the after combustion can be improved.

  Moreover, the pressure increase start time is determined by correcting (advancing) the reference pressure increase start time determined from the operating conditions based on the amount of smoke generated. That is, not only the operating conditions but also the optimum reference pressure start time in consideration of the actual smoke generation amount is determined. As a result, even if there are variations in environmental factors such as atmospheric pressure, intake air temperature, EGR rate, and fuel properties such as cetane number, the amount of smoke generated is reliably suppressed in accordance with these changes. can do.

  The fuel injection control device 11 according to the first embodiment described above has the following operational effects.

  1. Since the after injection is executed at an injection pressure having an increased pressure value larger than the reference pressure value, the fuel can be sufficiently mixed with the air even in a high temperature environment. Thereby, in after injection, the amount of smoke generated can be suppressed. Moreover, the pressure increase start time is determined in consideration of the actual amount of smoke generated in addition to the operating conditions. Therefore, the amount of smoke generated can be reliably suppressed even when there are variations in environmental changes and fuel properties.

  2. The ECU 36 sets a limit pressure increase start time as an advance angle guard value and defines a limit of the advance amount of the pressure increase start time. Therefore, excessive combustion noise is prevented from occurring by greatly advancing the pressure increase start timing. Here, in Embodiment 1, since the end time of the main injection is determined as the limit pressure increase start time, the limit pressure increase start time can be easily determined. For this reason, it becomes possible to reduce the control burden of ECU36.

  3. The ECU 36 sets the limit pressure increase start timing at the end of the main injection, so that the pressure increase of the injection pressure is started after the end of the main injection. For this reason, the main injection is executed with an injection pressure having a reference pressure value lower than the increased pressure value. Accordingly, there is no case where the fuel pressure is excessively atomized due to the increase of the injection pressure in the main injection, and the premixed combustion becomes excessive and the combustion noise is not deteriorated.

  4). When the ECU 36 determines that the pressure increase start time is ahead of the limit pressure increase start time by correction, the ECU 36 stores the abnormality detection signal in the RAM. Therefore, the operator who has confirmed the signal at the time of maintenance can recognize that there is a possibility that an abnormality has occurred in the fuel injection control device 11. As a result, early detection of an abnormality is promoted, and it is possible to prevent failure and damage from getting worse. Further, since the abnormality is related to the injection control, the cause can be easily specified, and the maintenance work can be performed efficiently. Even when the abnormality detection signal is stored in the RAM, the fuel injection control device 11 is not necessarily in failure, and there is a possibility of a temporary failure. Accordingly, in the first embodiment, the abnormality detection signal is merely stored in the RAM, and the driver is not actively notified of the abnormality.

  5. Since the pilot injection is executed at an injection pressure having a reference pressure value smaller than the increased pressure value, excessive diffusion does not occur due to excessive atomization of the fuel. Therefore, ignition stability during the combustion cycle can be maintained.

[Embodiment 2]
Next, a fuel injection control apparatus according to Embodiment 2 will be described. In the second embodiment, only the parts different from the first embodiment will be described, and the description of the same components and the same effects as those in the first embodiment will be omitted.

  In the first embodiment, the pressure increase start timing is controlled based on the operating conditions and the amount of smoke generated, and the increased pressure value is determined based only on the operating conditions. On the other hand, in the second embodiment, the increased pressure value is controlled based on the amount of smoke generated in addition to the pressure increase start timing. That is, in the second embodiment, when the predetermined condition is satisfied, control is performed to correct (increase) the increased pressure value according to the amount of smoke generated.

  Here, the ECU 36 is set to preferentially control the pressure increase start time. In other words, when the pressure increase start timing is advanced and the effect of suppressing the amount of smoke generated is still insufficient (not reaching the target smoke level), control is performed to increase the increased pressure value.

  Specifically, the control of the increased pressure value is performed by increasing the reference increased pressure value determined based on the operating condition based on the smoke generation amount. The reference increased pressure value is determined based on operating conditions such as the rotational speed and the injection amount. In the second embodiment, a map using the rotation speed and the injection amount as parameters is stored in the ECU 36 in advance, and the reference increase pressure value is determined using the map.

  The correction amount when correcting the reference increase pressure value is the correction amount of the increase pressure value by performing PID control based on the current smoke difference value and the previous smoke difference value, similarly to the correction amount at the pressure increase start time. Is determined. The ECU 36 provisionally determines a value obtained by adding the calculated correction amount to the reference increase pressure value as the increase pressure value.

  The ECU 36 of the second embodiment determines a limit increase pressure value in addition to the limit pressure increase start time. In the first embodiment, the end of main injection is set as the limit pressure start time, but in the second embodiment, the limit pressure start time is determined based on the limit noise level.

  This limit noise level is determined from operating conditions (rotation speed, injection amount, etc.), and defines the limit level of combustion noise. Specifically, a map of the limit noise level using the rotation speed and the injection amount as parameters is stored in the ECU 36 in advance. Then, the ECU 36 determines a limit noise level using a map from the current rotation speed and the injection amount.

  The ECU 36 is configured to determine a limit pressure increase start time from the determined limit noise level. That is, in the second embodiment, the pressure increase start time at which the combustion noise at the limit level is generated is set as the limit pressure increase start time. Accordingly, if the limit noise level is not exceeded, the limit pressure increase start time may be set during the main injection, and the pressure increase start time may be set during the main injection.

  On the other hand, the limit increase pressure value is determined by the ECU 36 based on operating conditions such as the rotational speed and the injection amount. Specifically, a map of the limit increasing pressure value using the rotation speed and the injection amount as parameters is stored in the ECU 36 in advance. Then, the ECU 36 determines a limit increasing pressure value using a map from the current rotational speed and the injection amount.

  The ECU 36 determines whether or not the increased pressure value determined by increasing the reference increased pressure value is smaller than the limit increased pressure value. When the increased pressure value is smaller than the limit increased pressure value, the ECU 36 determines the increased pressure value. On the other hand, when the increased pressure value is greater than or equal to the limit increased pressure value, the ECU 36 determines the limit increased pressure value as the increased pressure value and performs an abnormality response.

  In the second embodiment, as an abnormality response, an abnormality detection signal is stored in the RAM, and a warning lamp (MIL, not shown) provided on the driver's seat side is displayed. Further, the ECU 36 gives a command to reduce the EGR rate to the EGR device. That is, the ECU 36 forcibly reduces the amount of smoke generated by decreasing the opening degree of the EGR valve 91 and decreasing the EGR rate. Specifically, the ECU 36 is set to fully close the EGR valve 91 so that the EGR rate becomes zero. However, if the EGR rate is reduced, it is not always necessary to set the EGR rate to zero.

  Next, the case where the increased pressure value and the pressure increase start timing are determined in the second embodiment will be described with reference to the flowchart of FIG.

  The ECU 36 acquires the current operating condition (step S40), and determines the limit noise level using the map from the current rotation speed and the injection amount (step S41). Next, the ECU 36 determines the limit pressure increase start time from the determined limit noise level (step S42). Moreover, ECU36 determines a limit increase pressure value using a map from the present rotation speed and injection amount (step S43). Further, the ECU 36 determines a reference pressure value from the current injection amount and rotation speed using a map (step S44).

  Next, the ECU 36 determines a reference pressure increase start time and a reference pressure increase value using a map from the rotation speed and the injection amount (steps S45 and S46). Further, the ECU 36 determines a target smoke level from the rotation amount and the injection amount with a map (step S47), and acquires the smoke generation amount in the previous combustion cycle detected by the smoke sensor 81 (step S48). Then, the ECU 36 calculates a smoke difference value that is the difference between the previous smoke generation amount and the target smoke level (step S49).

  When the smoke difference value is smaller than the predetermined value (YES in step S50), the ECU 36 adds the correction amount of the pressure increase start time calculated in the previous combustion cycle to the reference pressure increase start time determined in step S45. That is, the timing at which the advance of the previous correction amount is advanced from the reference pressure increase start time is determined as the pressure increase start time (step S51).

  Next, the ECU 36 adds the correction amount for the increased pressure value calculated in the previous combustion cycle to the reference increased pressure value determined in step S46. That is, a value obtained by increasing the reference correction pressure value by the previous correction amount is determined as the increase pressure value (step S52).

  In step S50, when the smoke difference value is equal to or larger than the predetermined value (NO in step S50), the ECU 36 corrects the pressure increase start time by PID control from the current smoke difference value and the smoke difference value calculated in the previous combustion cycle. Is determined (step S53). Then, the timing advanced from the reference pressure increase start time by the correction amount is provisionally determined as the pressure increase start time (step S54).

  Next, the ECU 36 determines whether or not the determined pressure increase start time is smaller than the limit pressure increase start time (retarded side). When the pressure increase start time is smaller than the limit pressure increase start time (YES in step S55), the pressure increase start time is determined (step S56). Further, the ECU 36 adds the correction amount of the increased pressure value calculated in the previous combustion cycle to the reference increased pressure value, and determines the increased pressure value (step S57).

  On the other hand, if step S55 is NO, the ECU 36 determines the limit pressure increase start time determined in step S42 as the pressure increase start time (step S58). Then, the ECU 36 determines the correction amount of the increased pressure value based on the current smoke difference value calculated in step S49 and the smoke difference value calculated in the previous combustion cycle (step S59). Specifically, the correction amount of the increased pressure value is determined by PID control using the previous and current smoke difference values.

  Next, the ECU 36 provisionally determines a value obtained by adding the correction amount obtained in step S59 to the reference increased pressure value as an increased pressure value (step S60). Then, it is determined whether or not the determined increase pressure value is smaller than the limit increase pressure value (step S61).

  When the increased pressure value is smaller than the limit increased pressure value (YES in step S61), the ECU 36 determines the increased pressure value (step S62). On the other hand, when the increase pressure value is equal to or greater than the limit increase pressure value (NO in step S61), the ECU 36 determines the limit increase pressure value as the increase pressure value (step S63). Then, the ECU 36 stores the abnormality detection signal in the RAM and turns on the warning lamp on the driver's seat side (step S64). Further, the ECU 36 fully closes the EGR valve 91 of the EGR device, and temporarily sets the EGR rate to zero (step S65).

  Then, the ECU 36 controls the fuel injection valve 34 and the transformer device 32 based on the increased pressure value and the pressure increase start timing determined in the flowchart of FIG. The injection control by the ECU 36 is performed in the same procedure as in the first embodiment (the flowchart in FIG. 5).

  FIG. 7 shows an example when the ECU 36 performs injection control based on the increased pressure value and the pressure increase start time determined in the flowchart of FIG. 7A shows a timing chart of injection pulses, FIG. 7B shows a heat generation rate in the combustion chamber 16, and FIG. 7C shows fuel injection pressure. The horizontal axis in FIG. 7 indicates the crank angle.

  In this example, as shown in FIG. 7C, the limit pressure increase start time is set after the start of the main injection. Further, the pressure increase start timing is set to a timing when a predetermined time has elapsed from the start of the main injection as a result of advancement of the correction amount from the reference pressure increase start timing. That is, in this example, the increase in the injection pressure is started during the main injection, and the pressure is increased to the increased pressure value during the main injection.

  Thus, by increasing the injection pressure from the reference pressure value to the increased pressure value during the main injection, the average injection pressure of the main injection increases, and the amount of smoke generated during the main injection can be suppressed. Further, as in the first embodiment, after injection is performed at an increased pressure value, the amount of smoke generated during after injection is suppressed.

  Here, as shown in FIG. 7B, immediately after the start of the main injection, the heat generation rate is rapidly increased (the inclination is large). At this time, if the injection pressure is large, the combustion noise becomes very large. However, in the second embodiment, by determining the limit pressure increase start time based on the limit noise level, as shown in FIG. 7C, the limit pressure increase start time is delayed from the timing at which the main injection starts ( Set with a delay). As a result, the pressure increase start timing is retarded from the start of main injection, and the injection pressure is increased with a shift from the timing at which the heat generation rate suddenly increases to the retard side.

  Moreover, as shown in FIG. 7C, the injection pressure gradually increases (linearly) from the reference pressure value to the increased pressure value. For this reason, the combustion pressure is suppressed from increasing due to a sudden increase in the injection pressure at the initial stage of the main injection (that is, the time when the heat generation rate suddenly increases).

  Here, since the increase pressure value is increased by a correction amount from the reference increase pressure value, the average injection pressure during the main injection can be sufficiently increased. Then, after injection is performed while maintaining the increased pressure value, it is possible to reliably reduce the amount of smoke generated in the after injection. That is, in the second embodiment, the effect of suppressing the smoke generation amount is enhanced by correcting both the pressure increase start timing and the increase pressure value based on the smoke generation amount.

  The fuel injection control device according to Embodiment 2 described above has the following operational effects.

  1. Since the reference pressure increase start time and the reference pressure increase value determined based on the operating conditions are corrected based on the smoke generation amount, the amount of smoke generation is reduced as compared with the case where only the pressure increase start time is corrected as in the first embodiment. The suppression effect can be further enhanced.

  2. The ECU 36 increases the increased pressure value only when the smoke suppression effect is insufficient by simply advancing the pressure increase start timing. That is, the correction of the pressure increase start time is performed with priority over the pressure increase value, and therefore the frequency of increasing the pressure increase value is relatively low. Therefore, it can suppress that the fuel consumption of the engine 10 deteriorates.

  3. Since the limit pressure increase start time is determined based on the limit noise level, the injection pressure is prevented from increasing when the heat generation rate at the start of the main injection suddenly increases. Therefore, even when the pressure increase is started during the main injection, excessive combustion noise does not occur. Moreover, since the injection pressure is gradually increased, the increase in combustion noise during main injection is further suppressed.

  4). Since the limit increasing pressure value is set based on the operating conditions, it is possible to set an appropriate limit increasing pressure value according to the operating conditions. For example, when the rotation amount and the injection amount are small, the ratio of the driving torque of the high-pressure pump 40 to the output torque of the engine 10 increases. In this case, if a small limit increasing pressure value is set, deterioration of fuel consumption can be effectively suppressed.

  5. When the ECU 36 determines that the increased pressure value obtained by correcting the reference increased pressure value is equal to or greater than the limit increased pressure value, the ECU 36 performs an abnormality response. That is, if a sufficient smoke suppression effect cannot be obtained even by correcting both the pressure increase start timing and the increased pressure value, there is a high possibility that some abnormality has occurred in the fuel injection control device. In this case, the ECU 36 turns on the warning lamp on the driver's seat side so that the driver can quickly know the abnormality. In addition, the ECU 36 controls the EGR device when an abnormality occurs and temporarily sets the ERG rate to zero, so that the smoke generation amount can be forcibly reduced.

  In the second embodiment, the control of the pressure increase start time is executed with priority over the pressure increase value, but the control of the pressure increase value may be prioritized with the pressure increase start time. However, in this case, since the frequency at which the increased pressure value is increased increases, the fuel consumption of the engine 10 may be reduced. Further, the control based on the smoke generation amount may be performed only for the increased pressure value, and the pressure increase start timing may be determined only from the operating conditions (not corrected based on the smoke generation amount).

  In the injection control shown in FIG. 7, the case where the timing at which a predetermined time has elapsed from the start of the main injection is determined as the limit pressure increase start timing is shown. However, if it is in a range that does not exceed the limit noise level, the limit pressure increase start timing may be set at the same timing as the start of the main injection or may be set earlier than the start of the main injection.

  In the second embodiment, the injection pressure is linearly increased from the reference pressure value to the increased pressure value. However, as indicated by a broken line in FIG. 7C, the injection pressure may be increased in a quadratic function form (curved) from the reference pressure value to the increased pressure value. In this case, the injection pressure can be gradually increased as compared with the case where the injection pressure is increased linearly. Therefore, even when the pressure increase starts at the initial stage of the main injection in which the heat generation rate rises rapidly, it is possible to effectively suppress the generation of a large combustion noise.

  Immediately after the start of the pressure increase, the injection pressure is increased gradually (inclination is gentle), and after a predetermined time, the injection pressure is increased stepwise so as to increase the inclination of the increase in injection pressure. Also good. Also in this case, since the injection pressure at the initial stage of the main injection can be reduced, combustion noise can be suppressed.

[Embodiment 3]
Next, the fuel injection control device 13 according to the third embodiment will be described. In the third embodiment, only the parts different from the first and second embodiments will be described, and the description of the same parts and the same effects as the first and second embodiments will be omitted.

  FIG. 8 shows the engine 10 provided with the fuel injection control device 13 according to the third embodiment. The fuel injection control device 13 of the third embodiment includes an in-cylinder pressure sensor 52 (CPS) that measures the pressure in the cylinder 14 (in-cylinder pressure). As will be described later, the in-cylinder pressure sensor 52 also functions as noise detection means for detecting combustion noise.

  The in-cylinder pressure sensor 52 is attached to the cylinder head 18 of at least one cylinder of the engine 10. The output signal of the in-cylinder pressure sensor 52 is input to the ECU 36 after noise is removed by the low-pass filter 80 (LPF).

  In the third embodiment, the control based on the smoke generation amount is performed only for the pressure increase start timing, and the increase pressure value is determined based only on the operating conditions.

  Further, the ECU 36 according to the third embodiment determines whether or not the pressure increase start timing can be corrected (advanced) from the limit noise level without determining the limit pressure increase start timing as in the first and second embodiments. ing.

  Specifically, the ECU 36 determines whether or not to correct the pressure increase start time by comparing the actually generated combustion noise and the limit noise level. The limit noise level is determined based on operating conditions (a map based on the rotation speed and the injection amount), as in the second embodiment. The combustion noise is estimated by the ECU 36 from the measured value of the in-cylinder pressure sensor 52. Specifically, the combustion noise is estimated using the differential value of the in-cylinder pressure measured by the in-cylinder pressure sensor 52.

  Here, the fuel injection control device 13 of the third embodiment does not include the smoke sensor 81 (see FIG. 1) described in the first embodiment, and cannot directly detect the amount of smoke generated. Therefore, the ECU 36 indirectly detects (estimates) the amount of smoke generated using the detection value of the exhaust A / F sensor 82. As shown in FIG. 9, the relationship between the air-fuel ratio of the exhaust A / F sensor 82 and the amount of smoke generated is large when the air-fuel ratio is rich, and the amount of smoke generated becomes linear as the air-fuel ratio goes toward lean. It has the characteristic which becomes small automatically. Using this relationship, the ECU 36 estimates the smoke generation amount from the detection value of the exhaust A / F sensor 82. Therefore, the exhaust A / F sensor 82 of the third embodiment also functions as smoke detection means.

  FIG. 10 is a flowchart when the ECU 36 determines the pressure increase start timing and the pressure increase value in the third embodiment.

  The ECU 36 acquires the current operating condition (step S70), and determines the target noise level using the map from the acquired operating condition (rotation speed and injection amount) (step S71). Further, the ECU 36 determines a reference pressure value, an increased pressure value, and a reference pressure increase start time from the operating conditions using a map (steps S72, S73, S74).

  Next, the ECU 36 estimates (calculates) combustion noise from the in-cylinder pressure measured by the in-cylinder pressure sensor 52 in the previous combustion cycle (S75). Further, the ECU 36 determines a target smoke level from the operating conditions (step S76).

  Next, the ECU 36 estimates (detects) the amount of smoke generated from the measured value of the exhaust A / F sensor 82 measured in the previous combustion cycle (step S77). Then, the ECU 36 calculates a smoke difference value (step S78), and determines whether or not the smoke difference value is smaller than a predetermined value α (step S79).

  When the smoke difference value is smaller than the predetermined value α (YES in step S79), the ECU 36 increases the pressure obtained by adding (advancing) the correction amount calculated in the previous combustion cycle to the reference pressure increase start timing. The starting time is determined (step S80).

  On the other hand, if the smoke difference value is greater than or equal to the predetermined value α (NO in step S79), the ECU 36 determines whether or not the combustion noise calculated in step S75 is smaller than the target noise level (step S81).

  If the combustion noise is smaller than the target noise level (YES in step S81), a correction amount is determined from the smoke difference value calculated in the current combustion cycle and the smoke difference value calculated in the previous combustion cycle (step S82). . Then, the determined correction amount added to the reference pressure increase start time (advanced) is determined as the pressure increase start time (step S83).

  On the other hand, when the combustion noise is equal to or higher than the target noise level (NO in step S81), the ECU 36 adds (advances) the correction amount determined in the previous combustion cycle to the reference pressure increase start time, and sets the pressure increase start time. Determine (step S84). Then, the ECU 36 stores the abnormality detection signal in the RAM (step S85).

  As described above, according to the fuel injection control device 13 according to the third embodiment, the ECU 36 determines whether or not to advance the pressure increase start time from the actually generated combustion noise, and therefore excessive combustion noise is generated. Can be surely prevented.

  In the third embodiment, since the smoke generation amount is indirectly detected from the exhaust A / F sensor 82, it is not necessary to provide the smoke sensor 81 as in the first and second embodiments.

  In the third embodiment, as in the first embodiment, the pressure increase start timing is corrected in consideration of the smoke generation amount, so that the smoke generation amount can be suppressed. In the third embodiment, whether or not the pressure increase start time can be corrected is determined based on a comparison between the limit noise level and the combustion noise. Therefore, the pressure increase start time may be set during the main injection as long as it does not exceed the limit noise level. In this case, the amount of smoke generated during main injection can also be suppressed.

[Embodiment 4]
Next, a fuel injection control apparatus according to Embodiment 4 will be described below. In the fourth embodiment, only parts different from the first to third embodiments will be described.

  The fuel injection control device of Embodiment 4 has basically the same configuration as the fuel injection control device 13 of Embodiment 3. However, the fourth embodiment is different from the third embodiment in that, in addition to the pressure increase start timing, the increased pressure value is controlled based on the amount of smoke generated. That is, in the fourth embodiment, when the smoke suppression effect cannot be sufficiently obtained by the correction (advance angle) based on the pressure increase start timing, the increase pressure value is corrected (pressure increase) to complement the smoke suppression effect.

  In the fourth embodiment, the case where the increase pressure value and the pressure increase start time are determined will be described with reference to the flowchart of FIG.

  The ECU 36 acquires the current operating condition (step S90), and determines the limit noise level using the map from the operating condition (rotation speed and injection amount) (step S91). Further, the ECU 36 determines a limit increase pressure value, a reference pressure value, a reference pressure start time, and a reference increase pressure value from the operating conditions using a map (steps S92, S93, S94, S95).

  Next, the ECU 36 estimates (calculates) combustion noise from the in-cylinder pressure of the in-cylinder pressure sensor 52 measured in the previous combustion cycle (step S96). Then, the ECU 36 determines a target smoke level from the operating conditions using a map (step S97).

  Next, the ECU 36 estimates (detects) the amount of smoke generated from the measured value of the exhaust A / F sensor 82 detected in the previous combustion cycle (step S98). Then, the ECU 36 calculates a smoke difference value (step S99), and determines whether or not the smoke difference value is smaller than a predetermined value α (step S100).

  When the smoke difference value is smaller than the predetermined value α (YES in step S100), the ECU 36 adds (advances) the correction amount calculated in the previous combustion cycle to the reference pressure increase start time, and sets the pressure increase start time. Determine (step S101). Next, the correction amount calculated in the previous combustion cycle is added (increased pressure) to the reference increased pressure value to determine the increased pressure value (step S102).

  On the other hand, if the smoke difference value is greater than or equal to the predetermined value α (NO in step S100), the ECU 36 determines whether or not the combustion noise calculated in step S96 is smaller than the target noise level (step S103).

  When the combustion noise is smaller than the target noise level (YES in step S103), a correction amount is determined from the smoke difference value (step S104), and the correction amount is added (advanced) to the reference pressure increase start timing. The pressure increase start time is determined (step S105). Further, a value obtained by adding the previous correction amount to the reference increased pressure value is determined as the increased pressure value (step S106).

  On the other hand, if the combustion noise is equal to or higher than the target noise level (NO in step S103), the ECU 36 adds (advances) the correction amount determined in the previous combustion cycle to the reference pressure increase start time, and sets the pressure increase start time. Determine (step S107).

  Then, the ECU 36 determines a correction amount for the increased pressure value from the smoke difference value determined in the current combustion cycle and the smoke difference value determined in the previous combustion cycle (step S108).

  Next, the ECU 36 tentatively determines a value obtained by adding a correction amount (increased pressure) to the reference increased pressure value as the increased pressure value (step S109). Then, the ECU 36 determines whether or not the increased pressure value is smaller than the limit increased pressure value (step S110).

  If step S110 is YES, the increased pressure value is determined (step S111). On the other hand, if step S110 is NO, the increase pressure value is determined as the limit increase pressure value (step S112). Then, the ECU 36 lights the warning lamp on the driver's seat side (step S113) and forcibly sets the EGR rate to zero (step S114).

  Thus, according to the fuel injection control apparatus according to the fourth embodiment, as in the third embodiment, it is determined whether or not the pressure increase start timing is corrected (advanced) based on the actually generated combustion noise. Therefore, excessive combustion noise can be surely prevented.

  In addition, as in the second embodiment, since both the pressure increase start timing and the increased pressure value are controlled based on the smoke generation amount, the effect of suppressing the smoke generation amount can be enhanced. In addition, since the pressure increase start time is corrected with priority over the pressure increase value, deterioration of fuel consumption can be suppressed.

[Example of change]
(1) The transformer device 32 according to the first to fourth embodiments has a configuration in which a small rail 38 is separately provided on each fuel injection valve 34 as shown in FIG. However, as shown in FIG. 2B, a small rail 38 may be provided integrally with each fuel injection valve 34.

  (2) Further, as shown in the transformer 69 of FIG. 12, a high-pressure rail 62 connected to the high-pressure pump 40 and a normal-pressure common rail 64 also connected to the high-pressure pump 40 are connected via an on-off valve 44. A configuration can also be adopted. The high pressure rail 62 accumulates fuel in a high pressure state. On the other hand, fuel is stored in the normal pressure common rail 64 at a pressure lower than that of the high pressure rail 62. A plurality of fuel injection valves 34 are connected to the normal pressure common rail 64, and fuel is supplied from the normal pressure common rail 64 to each fuel injection valve 34.

  The ECU 36 controls the pressure in the normal pressure common rail 64 by opening and closing the on-off valve 44 and adjusting the amount of high pressure fuel flowing from the high pressure rail 62 to the normal pressure common rail 64. That is, in the initial stage of the combustion stroke, the ECU 36 controls the on-off valve 44 so that the normal pressure common rail 64 becomes the reference pressure value. When increasing the injection pressure, the ECU 36 opens the on-off valve 44 and supplies high pressure fuel from the high pressure rail 62 to the normal pressure common rail 64. As a result, the pressure in the normal pressure common rail 64 is increased to the increased pressure value, and the fuel is injected from the fuel injection valve 34 at the increased pressure value.

  (3) Further, as shown in the transformer 70 in FIG. 13, the high-pressure rail 62 and the normal-pressure common rail 64 may be independent from each other (not connected to each other). A plurality of high-pressure pipes 66 and a plurality of low-pressure pipes 68 are led out from the high-pressure rail 62 and the normal-pressure common rail 64 corresponding to the fuel injection valves 34, respectively. The high-pressure pipes 66 and the low-pressure pipes 68 are joined by the opening / closing valve 44. The ECU 36 can control the opening / closing valve 44 to adjust the mixing ratio of the high-pressure fuel supplied from the high-pressure rail 62 and the low-pressure fuel supplied from the normal-pressure common rail 64. . Thereby, the pressure of the fuel supplied to the fuel injection valve 34 can be changed as appropriate.

  That is, in the first half of the combustion stroke, the ECU 36 controls the opening / closing valve 44 so that the low pressure fuel becomes larger than the high pressure fuel so that the pressure of the fuel supplied to the fuel injection valve 34 becomes the reference pressure value. When the injection pressure is increased, the ECU 36 controls the opening / closing valve 44 so that the high-pressure fuel becomes larger than the low-pressure fuel, thereby increasing the pressure of the fuel supplied to the fuel injection valve 34. Value. Note that a switching valve may be employed instead of the on-off valve 44.

  (4) In the first embodiment, the limit pressure increase start time is set at the end of the main injection, and in the second embodiment, the limit pressure increase start time is determined based on the limit noise level. However, it is also possible to determine the limit pressure start time by other methods.

  For example, the timing after the elapse of a predetermined time from the start of the main injection may be determined as the limit pressure increase start timing. When the limit pressure increase start time is set in this way, the pressure increase start time can be set at a timing when the initial stage of the main injection is removed, so that increase in combustion noise can be effectively suppressed. In addition, the limit pressure start time can be easily determined, and the control burden on the ECU 36 can be reduced.

  It is also possible to determine the limit pressure increase start timing from at least one of the rotational speed, the injection amount, and the intake air temperature.

  For example, a limit pressure increase start time map using the rotation speed and the injection amount as parameters may be stored in the ECU 36 in advance, and the limit pressure increase start time may be determined using the map. Thereby, it is possible to determine an appropriate limit pressure increase start time according to the operating conditions.

  Further, when the limit pressure increase start timing is determined using the intake air temperature as a parameter, it is possible to cope with a change in the ignition delay of the main injection caused by the intake air temperature. For example, when the intake air temperature is low, the ignition delay in the main injection becomes large, so that the timing at which the heat generation rate rapidly increases is also delayed. In this case, if the limit pressure increase start timing is retarded, it is possible to suppress an increase in combustion noise.

  (5) In Embodiments 1 to 4, the limit increase pressure value is determined based on the rotation speed and the injection amount. However, the limit increase pressure value may be determined by another method.

  For example, the limit increasing pressure value may be determined based on the injection timing of the main injection. As a result, for example, when the injection timing of the main injection is close to the top dead center of the piston 15 (high isovolume) and the fuel efficiency is improved, it is possible to control so as to largely determine the limit increasing pressure value. It becomes.

  Further, when the in-cylinder pressure sensor 52 is provided, the combustion noise during the after injection may be estimated, and the limit increase pressure value may be controlled so that the combustion noise during the after injection does not become excessive.

  Furthermore, as a parameter of the limit increasing pressure value, a structural limit value (pressure increase limit) of the transformer 32 may be added in addition to the operating conditions such as the rotation speed.

  (6) In the first to fourth embodiments, the pilot injection is executed before the main injection, but the pilot injection is not necessarily executed.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 32 ... Transformer apparatus (transformer means), 34 ... Fuel injection valve, 36 ... ECU (control means), 52 ... In-cylinder pressure sensor (noise detection means), 69 ... Transformer apparatus (transformer means), 70 ... Transformer Device (transformation means), 81... Smoke sensor (smoke detection means), 82... Exhaust A / F sensor (smoke detection means).

Claims (9)

A fuel injection valve (34) for injecting fuel into the internal combustion engine (10) is provided, and is executed at least after the first injection and after the first injection, and injects a smaller amount of fuel than the first injection per combustion cycle. A fuel injection control device for causing the fuel injection valve to perform the second injection.
Transformer means (32, 69, 70) for controlling the fuel injection pressure of the fuel injection valve;
Smoke detecting means (81, 82) for detecting the amount of smoke generated in the internal combustion engine;
The combustion stroke is started at the injection pressure of the reference pressure value, the increase of the injection pressure is started during the first injection, and the pressure is increased to the increased pressure value during the first injection, and the injection of the increased pressure value is performed. Control means (36) for controlling the transformer means to perform the second injection with pressure,
The control means determines a reference pressure increase start timing based on operating conditions, and advances the reference pressure increase start time based on the amount of smoke generated detected by the smoke detection means, thereby increasing the injection pressure. the fuel injection control apparatus characterized by controlling the pressure increase start period which boosted the. The control means determines the reference increase pressure value based on operating conditions, and controls the increase pressure value by increasing the reference increase pressure value based on the amount of smoke generated detected by the smoke detection means. The fuel injection control device according to claim 1 . The fuel injection control device according to claim 2 , wherein the control means controls the pressure increase start timing with priority over the pressure increase value. The control means determines a limit pressure increase start time that is a limit value for advancing the reference pressure increase start time, and advances the reference pressure increase start time based on the amount of smoke generated detected by the smoke detection means. 4. The fuel injection control device according to claim 3 , wherein when the angle is determined to be advanced, the increase pressure value is controlled when it is determined that the advance is ahead of the limit pressure increase start timing. 5. The fuel injection control device according to claim 4 , wherein the control means determines a limit noise level of the internal combustion engine based on operating conditions, and determines the limit pressure increase start time based on the determined limit noise level. . 5. The fuel injection control device according to claim 4 , wherein the control means determines the limit pressure increase start timing based on at least one of a rotational speed of the internal combustion engine, an injection amount of the fuel injection valve, and an intake air temperature of the internal combustion engine. . Comprising noise detection means (52) for detecting combustion noise of the internal combustion engine,
The control means determines the limit noise level of the internal combustion engine based on operating conditions, and controls the increased pressure value when the combustion noise detected by the noise detection means is larger than the limit noise level. Item 4. The fuel injection control device according to Item 3 . Wherein, the reference increase pressure value to determine the limit increase pressure value is a limit value for boosted the claim 2 wherein the increased pressure value for controlling the transformer means so as not to exceed the limit increase pressure values - The fuel injection control device according to any one of claims 7 to 9. The control means is based on at least one of the rotational speed of the internal combustion engine, the injection amount of the fuel injection valve, the injection timing of the first injection, the in-cylinder pressure of the internal combustion engine, and the pressure increase limit of the transformer means. The fuel injection control device according to claim 8, wherein a limit increasing pressure value is determined.

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