JP6332070B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device that controls the state of fuel injection into an internal combustion engine.

  In the initial stage of the combustion process in a diesel engine, the fuel injected into the combustion chamber of each cylinder starts to burn rapidly due to self-ignition, so the in-cylinder pressure change rate tends to increase. Since there is a correlation between the in-cylinder pressure change rate and the combustion noise, the combustion noise deteriorates when the in-cylinder pressure change rate increases. Therefore, in order to reduce combustion noise, it is effective to suppress an abrupt in-cylinder pressure change. A technique described in Patent Document 1 is known as a technique for suppressing an abrupt in-cylinder pressure change. This is an injection system in which a required amount of fuel is divided into “pilot injection” and “main injection”, and pilot combustion by pilot injection is performed prior to main combustion by main injection. In this injection system, the injection conditions (injection amount, injection timing, etc.) of the pilot injection are corrected so that the maximum value of the in-cylinder pressure change rate in the main combustion becomes the target value. For example, when the maximum value of the change rate of the in-cylinder pressure is smaller than the target value, the pilot injection amount is increased. By doing so, since the in-cylinder temperature at the time of main injection can be increased, a sudden change in the in-cylinder pressure during main combustion can be suppressed, and combustion noise can be reduced.

JP 2005-282441 A

  Here, if mixing of the injected fuel and air is insufficient, an incomplete combustion state in which the injected fuel cannot be combusted will result, resulting in smoke deterioration. Generally, since mixing of air and fuel is promoted during the ignition delay period of the main combustion, smoke can be reduced by ensuring a sufficient ignition delay period of the main combustion. However, since the technique described in Patent Document 1 increases the injection amount of pilot injection, the ignition delay period of main combustion becomes shorter as the in-cylinder temperature rises. Therefore, the fuel injected at the time of the main injection cannot be sufficiently mixed with the air, resulting in a problem of smoke deterioration.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection control device capable of suppressing both the deterioration of smoke and the deterioration of combustion noise.

  A fuel injection control device according to one aspect of the present invention is a fuel injection control device configured to control the state of fuel injection into an internal combustion engine (10), and the in-cylinder pressure of the internal combustion engine increases with combustion. A target in-cylinder pressure change rate determining means (70) for determining a target in-cylinder pressure change rate, which is a target value of the in-cylinder pressure change rate in a predetermined period, to a value such that the combustion noise of the internal combustion engine does not exceed the target noise level; The in-cylinder pressure change rate includes a reference change rate component that is a component of in-cylinder pressure change caused by the piston operation of the internal combustion engine and a combustion change rate component that is a component of in-cylinder pressure change caused by combustion. Based on the rate component, an allowable gradient determining means (80) for determining an allowable value of the inclination of the heat generation rate in a predetermined period, and the inclination of the heat generation rate of the internal combustion engine becomes a target heat generation rate inclination equal to or less than the allowable value. Control injection state And a controlling means for (110).

  According to the fuel injection control device of the present invention, the target in-cylinder pressure change rate at each injection timing not exceeding the target noise level is calculated, and based on the reference change rate component that is a part of the target in-cylinder pressure change rate, The allowable value of the slope of the heat release rate at the injection timing is determined. Then, the injection state is controlled so that the inclination of the heat generation rate of the internal combustion engine becomes a target heat generation rate inclination equal to or less than the allowable value. Therefore, the main injection can be controlled so as not to exceed the target noise level. Therefore, deterioration of combustion noise can be suppressed. Further, since the control object is not the pilot injection but the main injection, it is not necessary to increase the injection amount of the pilot injection. Therefore, even in an injection system that performs split injection of pilot injection and main injection, it is possible to suppress a decrease in the ignition delay of main combustion as the pilot injection amount increases, and it is possible to suppress deterioration of smoke. Therefore, both the deterioration of smoke and the deterioration of combustion noise can be suppressed.

  Note that the reference numerals in parentheses in the scope of claims are intended only to exemplify corresponding configurations in the embodiments described later in order to facilitate understanding of the description, and are not intended to limit the content of the invention. Absent.

System configuration diagram of fuel injection system Schematic diagram of transformer Illustration of injection command signal and heat generation rate Processing flow of ECU in the first embodiment Illustration of in-cylinder pressure change rate Explanatory drawing of the allowable heat generation rate inclination and the target heat generation rate inclination in the first embodiment Explanatory diagram of the definition of heat release rate slope Explanatory drawing of the allowable heat generation rate inclination and the target heat generation rate inclination in the second embodiment Explanatory drawing of allowable heat generation rate inclination and target heat generation rate inclination in other embodiments

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, as shown in FIG. 1, a fuel injection system 11 in which a multi-cylinder diesel engine 10 (hereinafter referred to as the engine 10) is adopted as an internal combustion engine and an ECU 36 is applied to the engine 10 is illustrated. The engine 10 corresponds to the “internal combustion engine” in the claims.

  As shown in FIG. 1, the engine 10 is configured such that a piston (not shown) is accommodated in a cylinder block 12 so as to be able to reciprocate. A cylinder head (not shown) is provided on the upper end surface (front side of the paper 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. The intake port 20 and the exhaust port 22 are respectively provided with an intake valve and an exhaust valve (not shown). The exhaust valve and the intake valve play a role of adjusting the intake air amount and the exhaust air amount.

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

  The ECU 36 controls the injection pressure, injection amount, and injection timing of the fuel (light oil) supplied to the engine 10.

  The fuel injection system 11 includes a transformer 32 capable of transforming fuel pressure (injection pressure), and a plurality of fuel injection valves 34 for injecting fuel pumped from the transformer 32 into the combustion chambers 16 of the cylinders of the engine 10. And an ECU 36 for controlling the transformer 32 and the fuel injection valve 34.

  The fuel injection valve 34 is provided corresponding to each cylinder and is electronically controlled by the ECU 36. By the opening operation of the fuel injection valve 34, the fuel is injected into each cylinder.

  As shown in FIG. 2, the transformer 32 includes a small rail 38 provided corresponding to each fuel injection valve 34, a high pressure pump 40 that pumps fuel to the small rail 38, and each small rail 38 and the high pressure pump 40. An open / close valve 44 for selectively opening and closing the high-pressure pipe 42 to be connected is provided. The small rail 38 accumulates the high-pressure fuel supplied from the high-pressure pump 40 up to a predetermined rail pressure, and supplies the accumulated fuel to the fuel injection valve 34. When the fuel injection valve 34 is released, the fuel injection valve 34 supplies fuel to the combustion chamber 16 at an injection pressure equivalent to the pressure in the small rail 38. The on-off valve 44 is opened and closed by being controlled by the ECU 36 to control the amount of fuel supplied from the high-pressure pump 40 to the small rail 38. The fuel pressure sensor 56 is attached to each small rail 38 and measures the fuel pressure accumulated in the small rail 38, that is, the injection pressure.

  The ECU 36 includes a microcomputer 361 having a CPU, RAM, ROM and the like. The ECU 36 receives detection signals output from various sensors, and detects the operating state of the engine 10 based on these detection signals. The microcomputer 361 executes a control program stored in a storage medium such as a ROM, whereby a transient state determination unit 59, a target noise level determination unit 60, a target in-cylinder pressure change rate determination unit 70, an allowable heat generation rate gradient, which will be described later. It functions as determining means 80, target heat generation rate inclination determining means 90, injection command signal setting means 100, and injection condition correction determining means 120.

  The crank angle sensor 46 outputs a rotation angle signal that is a plurality of pulse signals to the ECU 36. The ECU 36 detects the rotation speed NE and the crank angle of the engine 10 based on the rotation angle signal. The accelerator opening sensor 47 outputs an accelerator opening signal to the ECU 36. The in-cylinder pressure sensor 55 is attached to one cylinder of the engine 10 and outputs an output signal corresponding to the in-cylinder pressure Pin in the combustion chamber 16 to the ECU 36.

  A supercharger 50 is provided in the intake pipe 28 and the exhaust pipe 30. The supercharger 50 recovers energy from the exhaust gas of the engine 10 and converts it into power, and pressurizes the intake air flowing through the intake pipe 28 of the engine 10 with the recovered power. The amount of air supplied to the engine 10 by the supercharger 50 can be increased, and the amount of combustible fuel is increased accordingly, so that the output of the engine 10 can be increased. In this embodiment, the supercharger 50 is provided in the exhaust pipe 30 and is driven by the energy of the exhaust gas, and is provided in the intake pipe 28 of the engine 10 and is driven by the rotational torque of the turbine wheel 51. A turbocharger having a compressor wheel 52 is employed. The turbine wheel 51 and the compressor wheel 52 are connected via a turbine shaft 53.

  The supercharging pressure sensor 54 is disposed on the downstream side of the intake pipe 28, detects the actual supercharging pressure Pb, and outputs an output signal corresponding to the actual supercharging pressure Pb.

  Next, fuel injection control from the fuel injection valve 34 by the ECU 36 will be described. The ECU 36 corresponds to the “fuel injection control device” in the claims.

  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 fuel injection valve 34 by a pulse signal (injection pulse) that defines the fuel injection amount and the injection timing. The injection pressure control by the ECU 36 will be described. The ECU 36 controls the pressure in the small rail 38 to be a predetermined value by opening and closing the on-off valve 44 of the transformer device 32. Thereby, the injection pressure of the fuel injected from the fuel injection valve 34 into the combustion chamber 16 is controlled.

  The injection control implemented in this embodiment is shown in FIG. The upper part of FIG. 3 shows the timing chart of the injection pulse, and the lower part of FIG. 3 shows the heat generation rate in the combustion chamber 16. The horizontal axis indicates the crank angle. As shown in FIG. 3, the ECU 36 causes the fuel injection valve 34 to execute pilot injection with an injection amount smaller than the main injection prior to main injection for generating torque. That is, the ECU 36 causes the fuel injection valve 34 to execute multi-stage injection of pilot injection and main injection in the combustion stroke of one combustion cycle. In addition, as shown in FIG. 3, since the pilot injection has a smaller amount of fuel to be injected than the main injection, the peak value of the heat generation rate is also small. In the present embodiment, the injection amount required in the main injection (the injection amount based on the required torque) is divided into a plurality of times and injected at short intervals. For example, what is shown in FIG. 3 divides the injection amount required in the main injection into three times, and divides the first, second, and third injection amount ratios to be 2: 3: 5, The injection is performed with an extremely short interval between the three injections. The division ratio of the injection amount is determined by a desired injection condition. In addition, the waveform of the main combustion in the lower stage of FIG. 3 corresponds to the “heat generation rate waveform” in the claims, and the value of the heat generation rate at the end of the n-th combustion in the division is about zero. In addition, the heat generation rate waveform is formed by increasing the heat generation rate by the (n + 1) th combustion and repeating this thereafter.

  The ECU 36 performs injection control on the fuel injection valve 34 so that the combustion noise generated in the combustion chamber 16 becomes the target noise level. Hereinafter, specific processing contents will be described with reference to FIG.

  First, in S101, it is determined whether or not the operating state of the engine 10 is in a transitional state. Specifically, when the difference between the actual boost pressure Pb detected by the boost pressure sensor 54 and the target boost pressure Pbr is not within a predetermined range, the transition state determination means 59 determines that the state is in a transient state. (Determined as Yes). On the other hand, when the difference between the actual supercharging pressure Pb and the target supercharging pressure Pbr is within a predetermined range, it is determined that there is no transient state (determined No). Here, for example, when the vehicle is accelerated, that is, when the accelerator pedal is depressed, the fuel injection amount from the fuel injection valve 34 is increased as the required torque of the engine 10 increases. However, the difference between the actual supercharging pressure Pb and the target supercharging pressure Pbr increases due to a delay (supercharging delay) until the intake air supercharged by the supercharger 50 is supplied to the combustion chamber 16. . Therefore, it can be determined whether or not the engine is in a transient state based on the difference between the actual boost pressure Pb and the target boost pressure Pbr. The target boost pressure Pbr is set based on the rotational speed NE, the accelerator opening, and the like. The predetermined range is a value that is appropriately set based on vehicle performance and the like.

  As a means for determining whether or not the engine is in the transient state in S101, various means are adopted such as determination based on the actual supercharging pressure Pb and a transitional state when the accelerator opening is equal to or greater than a predetermined value. sell.

  When it is determined in S101 that the operating state is in a transient state (when determined as Yes), the transient state determination unit 59 transmits a signal to the target noise level determination unit 60, and the process proceeds to S102. In S102, the current operating conditions (rotational speed NE, accelerator opening, etc.) are acquired. If an operating condition is acquired in S102, it will progress to S103.

  In S103, based on a map stored in advance in the ECU 36, a target noise level that is a target value of the combustion noise corresponding to the acquired operating condition is determined. Specifically, in the target noise level determining means 60 in the microcomputer 361, a map of the target noise level using the rotational speed, the accelerator opening, etc. as parameters is stored in advance. When the target noise level is determined in S103, the target noise level determination unit 60 transmits a signal related to the determined target noise level to the target in-cylinder pressure change rate determination unit 70. After transmitting the signal regarding the target noise level, the process proceeds to S104.

  In S104, a target in-cylinder pressure change rate that is a target value of a change rate of in-cylinder pressure (in-cylinder pressure change per unit crank angle) based on the target noise level determined in S103 based on a map stored in advance in the ECU 36. Pc is determined. The rate of change of in-cylinder pressure is defined as the rate of change during a period in which the in-cylinder pressure in main combustion increases, and the period in which the in-cylinder pressure in main combustion increases corresponds to a “predetermined period” in the claims. In the target in-cylinder pressure change rate determining means 70 in the microcomputer 361, a map of the in-cylinder pressure change rate using the noise level as a parameter is stored in the ECU 36 in advance. Here, the target in-cylinder pressure changes with respect to the upper-limit in-cylinder pressure change rate corresponding to the target noise level, that is, the upper limit value that exceeds the target noise level when the in-cylinder pressure change rate exceeds it. The change rate Pc is set as a value equal to or less than the upper limit in-cylinder pressure change rate.

  Here, the pressure change in the cylinder includes at least a pressure change caused by the piston operation of the internal combustion engine (hereinafter referred to as motoring pressure) and a pressure change caused when the fuel burns. Therefore, the target in-cylinder pressure change rate Pc is the target value of the in-cylinder pressure change rate including the combustion change rate component that is a component of the in-cylinder pressure change caused by combustion in addition to the reference change rate component Pd that is a component related to the motoring pressure. It is. The motoring pressure is, so to speak, a pressure change caused only by the piston operation during one combustion cycle. In this embodiment, the pressure change rate of the motoring pressure is stored in the ECU 36 in advance.

  As shown in FIG. 5, the crank angle before TDC (compression top dead center), that is, the reference change rate component Pd during the compression step is the crank angle after TDC, that is, the reference change rate component during the expansion stroke. Greater than Pd.

  In the present embodiment, the target in-cylinder pressure change rate Pc is uniquely determined with respect to the target noise level. That is, the target in-cylinder pressure change rate Pc becomes a constant value at any combustion timing. When the target in-cylinder pressure change rate Pc is determined in S104, the target in-cylinder pressure change rate determining unit 70 transmits a signal related to the target in-cylinder pressure change rate Pc to the allowable heat generation rate inclination determining unit 80. After transmitting a signal regarding the target in-cylinder pressure change rate Pc, the process proceeds to S105. The target in-cylinder pressure change rate determining means 70 corresponds to “target in-cylinder pressure change rate determining means” in the claims.

  In S105, the allowable heat generation rate inclination determining means 80 calculates the allowable value Pf of the combustion change rate component, which is the difference between the reference change rate component Pd stored in the ECU 36 in advance and the target in-cylinder pressure change rate Pc, for each crank angle. Is calculated. The allowable value Pf of the combustion change rate component before the TDC, that is, the combustion change rate component during the compression process is smaller than the allowable value Pf of the combustion change rate component after the TDC, that is, during the expansion stroke. When the allowable value Pf of the combustion change rate component is calculated in S105, the process proceeds to S106.

  In S106, based on the allowable value Pf of the combustion change rate component calculated in S105, an allowable heat generation rate gradient HRR1 that is an allowable value of the heat generation rate gradient for each combustion timing (for each crank angle) is calculated. Specifically, the allowable heat generation rate gradient determining unit 80 calculates the allowable heat generation rate gradient HRRl as the combustion change rate component allowable value Pf multiplied by the predetermined correction coefficient A. As shown in FIG. 6, the allowable heat generation rate gradient HRR1 tends to be smaller in the crank angle before TDC, that is, the value in the compression process period than in the crank angle after TDC, that is, in the expansion stroke period. is there. When the allowable heat generation rate gradient HRRl is calculated in S106, the allowable heat generation rate gradient determining unit 80 transmits a signal related to the allowable heat generation rate gradient HRRl to the target heat generation rate gradient determining unit 90. After transmitting a signal related to the allowable heat generation rate gradient HRR1, the process proceeds to S107. The predetermined correction coefficient A is a value that is appropriately determined within an allowable range based on vehicle performance and the like. The allowable heat generation rate inclination HRRl corresponds to “allowable value” in the claims, and the allowable heat generation rate inclination determination means 80 corresponds to “allowable inclination determination means”.

  In S107, as shown in FIG. 6, a target heat generation rate gradient HRRt, which is a heat generation rate gradient that is a parameter for determining the injection conditions of injection, is set to an arbitrary value smaller than the allowable heat generation rate gradient HRRl at a desired combustion timing. Determine the value. The process of S107 is executed by the target heat generation rate inclination determining means 90. When the target heat generation rate inclination HRRt is determined in S107, the target heat generation rate inclination determination means 90 transmits a signal related to the target heat generation rate inclination HRRt to the injection command signal setting means 100. After transmitting a signal related to the target heat generation rate gradient HRRt, the process proceeds to S108.

  In S108, the target injection conditions are determined by the injection command signal setting means 100 so that the inclination of the heat generation rate in the main combustion accompanying the main injection becomes the target heat generation rate inclination HRRt determined in S107. Specifically, as shown in FIG. 7, in the point of the heat generation rate HRRO at the start of combustion accompanying the first injection (hereinafter referred to as zero point) and the combustion accompanying the third injection that is the last injection. The target injection condition is determined so that the slope of the line segment L1 connecting the points of the maximum heat release rate HRRmax becomes the target heat release rate slope HRRt. Hereinafter, the point at which the heat generation rate is maximized in the combustion accompanying the n-th injection is referred to as the “n-th maximum point”. Here, the target injection condition may be any of a target injection pressure in each injection divided in the main combustion, a target division ratio that is a division ratio of the injection amount of each injection, and an injection interval of each injection. It should be noted that the target heat generation rate slope HRRt is “target heat generation rate slope” in the claims, the target heat generation rate slope determination means 90 is “target slope setting means”, and the target injection condition is “injection state”. Equivalent to.

  The determination of various injection conditions may use a map stored in advance in the ECU 36 or may be calculated each time using a mathematical formula. For example, when the injection control is performed so that the injection amount of the first injection is increased by a predetermined amount without changing the injection amount of the main injection, the third injection amount is controlled to be decreased accordingly, so the third injection The maximum value of the heat generation rate in the combustion associated with is small. That is, the inclination of heat generation rate during main combustion can be reduced. On the other hand, when the injection control is performed so as to increase the injection amount of the third injection, the maximum value of the heat generation rate in the combustion accompanying the third injection becomes large. That is, the slope of the heat release rate during main combustion can be increased. When the injection condition is determined in S108, the injection command signal setting unit 100 transmits an injection command signal based on the determined injection condition to the drive circuit 110 to drive the drive circuit 110. After the injection command signal is transmitted to the drive circuit 110, the process proceeds to S109. The drive circuit 110 corresponds to “control means” in the claims.

  In S <b> 109, the injection control is executed by the drive circuit 110 based on the injection command signal received from the injection command signal setting unit 100. Specifically, a control signal is transmitted from the drive circuit to each fuel injection valve 34 or the transformer device 32, whereby fuel is injected from the fuel injection valve 34 and the combustion stroke of the main combustion is started. If a control signal is transmitted in S109, it will progress to S110.

In S110, the injection condition correction determining unit 120 calculates an actual heat generation rate gradient HRRr that is a gradient of the heat generation rate of main combustion accompanying the injection executed by the injection command signal in S109. Specifically, first, an in-cylinder pressure Pin at the time of main combustion is calculated based on a signal input from the in-cylinder pressure sensor 55. Next, based on the in-cylinder pressure Pin, the heat generation rate dQ is obtained by the following formula 1.
(Equation 1)
dQ = (Vdp + KpdV) / (K-1)
Here, K is the specific heat ratio, and V is the volume of the combustion chamber 16. Next, the actual heat generation rate gradient HRRr can be obtained by differentiating the obtained heat generation rate dQ once. When the actual heat generation rate gradient HRRr is obtained in S110, the process proceeds to S111.

  In S111, the injection condition correction determination unit 120 determines whether or not the absolute value of the difference between the target heat generation rate gradient HRRt and the actual heat generation rate gradient HRRr is equal to or less than a predetermined value α. When it is determined that the absolute value of the difference is equal to or less than the predetermined value α (when determined to be Yes), the processing flow of FIG. 4 is terminated. On the other hand, when it is determined that the absolute value of the difference is not less than or equal to the predetermined value α (when determined No), the process proceeds to S112, and the map of the injection condition and the target heat generation rate gradient HRRt is updated. The processing of S110 to S112 is performed by the injection condition correction determining means 120. The difference between the target heat generation rate inclination HRRt and the actual heat generation rate inclination HRRr corresponds to the “inclination difference amount” in the claims, and the range of −α to α corresponds to the “predetermined range”. .

  Next, the effect in this embodiment is demonstrated.

  (1) A target in-cylinder pressure change rate Pc at each injection timing that does not exceed the target noise level is calculated, and based on the allowable value Pf of the combustion change rate component that is the difference between the reference change rate component Pd and the target in-cylinder pressure change rate Pc. Thus, the target heat generation rate gradient HRRt at each injection timing is determined. Then, the main injection is controlled so that the inclination of the heat generation rate of the main combustion accompanying the main injection becomes the target heat generation rate inclination HRRt. That is, the main injection is controlled so as not to exceed the target noise level. Therefore, deterioration of combustion noise can be suppressed. Further, since the target of injection control is not the pilot injection but the main injection, there is no need to increase the injection amount of the pilot injection. Therefore, even in an injection system that performs multistage injection of pilot injection and main injection, it is possible to suppress a decrease in the ignition delay of main combustion as the pilot injection amount increases, and sufficiently promote mixing of injected fuel and air As a result, smoke deterioration can be suppressed. Therefore, both the deterioration of smoke and the deterioration of combustion noise can be suppressed.

  (2) When the absolute value of the difference between the actual heat generation rate gradient HRRr and the target heat generation rate gradient HRRt is not less than or equal to the predetermined value α after the main combustion associated with the main injection controlled to achieve the target heat generation rate gradient HRRt In this case, the injection conditions for the main injection are determined again. Therefore, the injection conditions based on the target heat generation rate gradient HRRt once determined can be corrected. Therefore, it is possible to execute the injection control for reliably realizing the target heat generation rate gradient HRRt as compared with the case where no correction is made.

  (3) Generally, when the operation state is in a transient state, a situation may occur in which a desired amount of air is not supplied into the cylinder due to a delay in supercharging. Therefore, in the conventional fuel injection control device, the injection timing is controlled to be retarded, and the ignition delay period of the main injection is sufficiently ensured so that the injected fuel and air are sufficiently mixed to suppress unburned fuel and smoke. To do. However, by delaying the injection timing, the ignition delay period becomes longer, the premix amount increases, the pressure change rate increases, and the slope of the heat generation rate increases, so that the noise may deteriorate. That is, when the operating state is in a transient state, deterioration of combustion noise can be a problem. In the present embodiment, when the operating condition is not in a transient state, the process shown in FIG. 4 is not executed. For this reason, the ECU 36 executes the series of processes shown in FIG. 4 on the condition that the combustion noise is particularly required to be reduced, so that the combustion noise is reliably ensured when the operation state is in the transient state. Can be suppressed.

  (4) When all of the injection amounts required for main injection are injected at once, the control targets for obtaining a desired heat generation rate gradient are the injection amount of pilot injection, the injection interval between pilot injection and main injection, etc. However, there is a concern about the deterioration of smoke due to the shortened ignition delay period of the main combustion. On the other hand, in the case where the injection amount required in the main injection is divided into a plurality of times and injected as in the present embodiment, the control target for obtaining a desired heat generation rate gradient is the injection amount of each divided injection. The injection pressure and the injection interval can be considered. According to these controls, the ignition delay period of the main combustion is not shortened, the deterioration of smoke is suppressed, and the control target is increased compared to the case where all the required injection amounts are injected at once. This increases the degree of freedom of control.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. In addition, description is simplified or abbreviate | omitted about the part which overlaps with 1st Embodiment.

  In the first embodiment, an arbitrary value smaller than the allowable heat generation rate gradient HRRl is determined as the target heat generation rate gradient HRRt. Determine the value of. That is, as shown in FIG. 8, the allowable heat generation rate gradient HRRl at a predetermined crank angle is determined to be the target heat generation rate gradient HRRt.

  Next, effects obtained by the present embodiment will be described.

  Since the allowable heat generation rate gradient HRRl is calculated for a predetermined target noise level, if injection is performed so that the allowable heat generation rate gradient HRRl becomes the value at any injection time, even if the injection timing is changed The magnitude of the combustion noise generated by the main combustion can be made equal. Therefore, by adopting the configuration of the present embodiment, it is possible to prevent the vehicle occupant from feeling uncomfortable with the change in the combustion noise.

(Other embodiments)
In addition, this invention is not limited to the said Example, As long as it belongs to the technical scope of this invention, you may deform | transform as follows.

  In the above embodiment, a map of the target in-cylinder pressure change rate Pc with the target noise level as a parameter is stored in the ECU 36 in advance, so that the target in-cylinder pressure change rate Pc at any combustion timing (crank angle). Was set to a constant value. However, the map stored in advance in the ECU 36 may determine the target in-cylinder pressure change rate Pc using both the target noise level and the crank angle as parameters. In this case, the target in-cylinder pressure change rate Pc is a variable that depends on the combustion timing.

  In the second embodiment, the value of the allowable heat generation rate gradient HRRl is determined as the target heat generation rate gradient HRRt. However, as shown in FIG. 9, the target heat generation rate gradient HRRt is set to be equal to or less than the allowable heat generation rate gradient HRR1 when the combustion start time is earlier than TDC (hereinafter referred to as before TDC), and the time after TDC (hereinafter referred to as “below”) , After TDC), the allowable heat generation rate gradient HRRl or less and greater than the time value before TDC may be used. In general, the allowable heat generation rate gradient HRR1 is greater after TDC than before TDC because the reference change rate component Pd is smaller after TDC than before TDC. For this reason, by adopting the above-described configuration, it is possible to suppress the occupant from feeling uncomfortable with the change in combustion noise as compared with the case where the target heat generation rate gradient HRRt after TDC is smaller than that before TDC.

  The target heat generation rate gradient HRRt at a predetermined time may be made smaller as the reference change rate component Pd at that time is larger. In other words, the target heat generation rate gradient HRRt may be increased as the reference change rate component Pd is smaller.

  In the above embodiment, the heat release rate slope HRR is defined as the slope of the line segment L1 connecting the zero point of the main injection and the third maximum point. However, the definition is not limited to this, and for example, it may be defined as the slope of a linear approximation line obtained by the least square method based on the zero point and the maximum point of each time.

  In the above embodiment, the fuel injection valve 34 is caused to execute the multi-stage injection of the pilot injection and the main injection in one combustion cycle. However, the single injection of only the main injection may be performed in one combustion cycle. Further, after-injection may be performed after main injection.

  In the above embodiment, the injection amount required in the main injection is divided into a plurality of times and injected, but all may be injected at once. In this case, as an injection condition for realizing the target heat generation rate gradient HRRt, it is conceivable to control the injection pressure during one cycle.

  -Although fuel injection system 11 in the above-mentioned embodiment shall be provided with transformer device 32, it may not be provided with transformer device 32 but may be provided with a common rail used for a general diesel engine system.

  In the above embodiment, when it is determined in S111 that the absolute value of the difference between the target heat generation rate gradient HRRt and the actual heat generation rate gradient HRRr is not less than or equal to the predetermined value α (when determined No). The map of the injection condition and the target heat generation rate gradient HRRt is updated (S112). However, when the injection condition is not determined based on the map in S108, for example, when calculating each time using a mathematical formula, if it is determined No in S111, the process may be repeated from S101. In that case, the main injection condition is again calculated by a mathematical formula in S108.

DESCRIPTION OF SYMBOLS 10 Engine, 11 Fuel injection system, 16 Combustion chamber, 32 Transformer, 34 Fuel injection valve, 36 ECU, 50 Supercharger, 52 In-cylinder pressure sensor, 54 Supercharging pressure sensor, 60 Target noise level determination means, 70 Target cylinder Internal pressure change rate determination means, 80 allowable heat generation rate inclination determination means, 90 target heat generation rate inclination determination means, 100 injection command signal setting means, 110 drive circuit, 120 injection condition correction determination means

Claims (7)

A fuel injection control device configured to control an injection state of fuel to an internal combustion engine (10),
A target in-cylinder pressure change rate that is a target value of the in-cylinder pressure change rate during a predetermined period in which the in-cylinder pressure of the internal combustion engine rises with combustion is determined to a value that does not cause the combustion noise of the internal combustion engine to exceed the target noise level. A target in-cylinder pressure change rate determining means (70);
The target in-cylinder pressure change rate includes a reference change rate component that is a component of in-cylinder pressure change caused by the piston operation of the internal combustion engine, and a combustion change rate component that is a component of in-cylinder pressure change caused by combustion. An allowable inclination determining means (80) for determining an allowable value of the inclination of the heat generation rate in the predetermined period based on the reference change rate component;
A fuel injection control device comprising: control means (110) for controlling the injection state so that the inclination of the heat generation rate of the internal combustion engine becomes a target heat generation rate inclination equal to or less than the allowable value.   The target at a time after the piston of the internal combustion engine reaches the top dead center, rather than the target heat generation rate gradient when combustion starts before the piston of the internal combustion engine reaches the top dead center in one combustion cycle. The fuel injection control device according to claim 1, further comprising target inclination setting means (90) for setting the target heat generation rate inclination so that the heat generation rate inclination becomes larger.   The said control means divides | segments the request | requirement injection amount in one injection into multiple times, and controls the injection state so that one heat release rate waveform may be formed by multiple injections. The fuel injection control device according to 1 or 2.   The control means includes an injection pressure of each injection divided into a plurality of times, a division ratio of the injection amount, and an injection interval of each injection so that the inclination of the heat generation rate in the internal combustion engine becomes the target heat generation rate inclination. 4. The fuel injection control device according to claim 3, wherein at least one is controlled.   The control means determines the slope difference when the slope difference amount, which is the difference between the slope of the actual heat release rate and the target heat release rate slope, is not within a predetermined range allowable for the target noise level. The injection state is controlled based on at least one of the target injection pressure of each injection divided into a plurality of times so that the amount falls within the predetermined range, the target division ratio of the injection amount, and the target injection interval of each injection. The fuel injection control device according to claim 3 or 4, wherein   3. The fuel injection control device according to claim 1, wherein the control unit controls an injection pressure of the injection so that an inclination of a heat generation rate in the internal combustion engine becomes the target heat generation rate inclination. 4. .   The control means determines the slope difference when the slope difference amount, which is the difference between the slope of the actual heat release rate and the target heat release rate slope, is not within a predetermined range allowable for the target noise level. The fuel injection control device according to claim 1 or 2, wherein an injection state is controlled based on a target injection pressure such that an amount falls within the predetermined range.

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