JP2017057758A - Fuel injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device capable of realizing equal-pressure combustion with a simple constitution.SOLUTION: A control device is applied to a diesel engine including a fuel injection valve directly injecting a fuel into a combustion chamber. The control device controls equal-pressure combustion to keep a peak of a cylinder pressure in the combustion chamber after starting combustion, substantially constant according to an equal pressure target value Ptptg. In detail, the control device determines a target pressure waveform Tcurve on the basis of an operating state of the engine in a control period including a pressure rise period before the cylinder pressure reaches the equal-pressure target value Ptptg and an equal-pressure period after it reaches the equal-pressure target value Ptptg, in controlling the equal-pressure combustion. The control device divides a fuel injection amount requested per one combustion cycle of the engine and injects the same in multistage from the fuel injection valve to control the cylinder pressure Preal detected by a cylinder pressure sensor to the target pressure waveform Tcurve.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel injection control device applied to a diesel engine.

  Since the diesel engine causes the fuel injected from the fuel injection valve to self-ignite by compression of the combustion chamber, the compression ratio is higher than that of the gasoline engine, and the peak of the in-cylinder pressure in the combustion chamber generated by the combustion of the fuel increases. When the peak of the in-cylinder pressure exceeds the allowable upper limit value, there is a concern that the reliability of the engine is lowered. For this reason, it is also conceivable to increase the allowable upper limit value by improving the strength of the engine. However, increasing the strength of the engine may increase the weight and cost of the engine.

  Therefore, as can be seen in Patent Document 1 below, fuel that achieves isobaric combustion by performing fuel injection control at an injection rate that gradually increases the fuel injection amount immediately after the start of fuel injection of the fuel injection valve Injectors are known. Thereby, the peak of in-cylinder pressure is reduced. This fuel injection device includes a high pressure accumulator chamber that stores fuel in a high pressure state and a low pressure accumulator chamber that stores fuel in a low pressure state. The fuel injection device further includes a switching valve for switching the fuel supplied to the fuel injection valve to either the high pressure fuel from the high pressure accumulator chamber or the low pressure fuel from the low pressure accumulator chamber, and the injection start timing and injection end timing of the fuel injection valve And an on-off valve for controlling the motor. When the switching valve and the on-off valve are energized, fuel injection control is performed at an injection rate that gradually increases the fuel injection amount immediately after the start of fuel injection.

JP 2001-159379 A

  Here, in the fuel injection device described in Patent Document 1, in order to achieve isobaric combustion, a configuration such as a low pressure accumulator chamber and a switching valve is required in addition to a high pressure accumulator chamber and an on-off valve. Becomes complicated. As a result, there is a concern that the cost of the fuel injection system increases or the mountability of the fuel injection system on the mounting target is deteriorated.

  The main object of the present invention is to provide a fuel injection control device capable of realizing isobaric combustion with a simple configuration.

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

  The present invention is applied to a diesel engine (10) including a fuel injection valve (18) for directly injecting fuel into a combustion chamber (10a), and the peak of the in-cylinder pressure in the combustion chamber after the start of combustion is set to an equal pressure target value. When the isobaric combustion control is performed to keep the pressure approximately constant according to the pressure increase period before the in-cylinder pressure reaches the isobaric target value and the isobaric period after the isobaric target value is reached. A target setting unit that sets a target pressure, which is a time-series target value of the in-cylinder pressure, based on an operating state of the engine, and the engine to control the in-cylinder pressure in the combustion chamber to the target pressure. And an injection control unit that divides a fuel injection amount required per one combustion cycle and performs multi-stage injection from the fuel injection valve.

  In a diesel engine, in order to reduce noise and emissions, multistage injection is performed in which a fuel injection valve injects a plurality of times into a combustion chamber in one combustion cycle. The inventor of the present application is suitable to keep the peak of the in-cylinder pressure in the combustion chamber after the start of combustion substantially constant according to the isobaric target value by using multistage injection, and can properly carry out isobaric combustion control. And gained knowledge.

  Therefore, in the above invention, when performing the isobaric combustion control, in the control period including the pressure increasing period before the in-cylinder pressure reaches the isobaric target value and the isobaric period after reaching the isobaric target value, A target pressure that is a time-series target value of the in-cylinder pressure is set based on the operating state of the engine. The in-cylinder pressure is controlled to the target pressure by dividing the fuel injection amount required per one combustion cycle of the engine and performing multi-stage injection from the fuel injection valve. Thereby, it is possible to realize isobaric combustion with a simple configuration using multistage injection.

The whole block diagram of a vehicle-mounted engine system. The figure which shows an in-cylinder pressure waveform in case ideal pressure combustion is implement | achieved. The figure which shows the in-cylinder pressure waveform in case the equal pressure combustion using multistage injection is implement | achieved. The flowchart which shows the procedure of a fuel-injection control process. The figure which shows a target pressure waveform. The figure which shows an in-cylinder pressure waveform when an in-cylinder pressure exceeds the pressure limit value Plim. The figure which shows the specific example of a weight reduction correction process. The figure which shows the specific example of the calculation method of the actual inclination Pslpr1 of a cylinder pressure. The figure which shows the specific example of an inclination correction process. The figure which shows the specific example of an inclination correction process. The figure which shows the calculation method of the equal pressure target value Ptptg of in-cylinder pressure. The figure which shows the specific example of a maximum value correction process. The figure which shows the calculation method of the real inclination Pslprl which concerns on other embodiment.

  Hereinafter, an embodiment in which a fuel injection control device according to the present invention is applied to a multi-cylinder diesel engine equipped with a common rail fuel injection device will be described with reference to the drawings.

  In the present embodiment, the engine 10 shown in FIG. 1 is mounted on a vehicle as an in-vehicle main machine. In the intake passage 11 of the engine 10, in order from the upstream side, an air flow meter 12 that detects the amount of intake air, an intercooler 13 that cools intake air supercharged by a turbocharger 16 that will be described later, and a throttle valve device 14. Is provided. The throttle valve device 14 adjusts the opening degree of the throttle valve 14a by an actuator such as a DC motor.

  A combustion chamber 10 a of each cylinder of the engine 10 is connected to the downstream side of the throttle valve device 14 in the intake passage 11 via a surge tank 15. The combustion chamber 10 a is partitioned by the cylinder block 10 b and the piston 17 of the engine 10. The engine 10 is provided with a fuel injection valve 18 having a tip projecting into the combustion chamber 10a. High pressure fuel (specifically, light oil) is supplied to the fuel injection valve 18 from a common rail 19 as a pressure accumulating container. Fuel is pumped from the fuel pump 20 to the common rail 19. In FIG. 1, only one cylinder is shown.

  The fuel injection valve 18 includes a needle and a body in which a plurality of injection holes for injecting fuel are formed at the tip, and the needle is accommodated therein. Between the inner surface of the body and the outer surface of the needle, an annular fuel passage that extends in the axial direction of the body and through which the fuel supplied from the common rail 19 passes is formed. A seating surface on which the tip of the needle is seated is formed on the inner surface of the body tip. A sac chamber is formed on the front end side of the body from the seating surface to collect fuel distributed in an annular shape in the fuel passage and to communicate with the injection holes. In this configuration, when the needle is seated on the seating surface, the gap between the fuel passage and the injection hole is cut off, and fuel injection is stopped. On the other hand, the fuel passage and the injection hole are communicated with each other by separating the needle from the seating surface by the energization operation. As a result, the fuel in the fuel passage is directly injected and supplied from the nozzle hole to the combustion chamber 10a through the sac chamber.

  Returning to the description of FIG. 1, the intake port and the exhaust port of each cylinder of the engine 10 are opened and closed by the intake valve 21 and the exhaust valve 22, respectively. Here, intake air cooled by the intercooler 13 by opening the intake valve 21 and external EGR described later are introduced into the combustion chamber 10a. When fuel is injected from the fuel injection valve 18 into the combustion chamber 10a with intake air or the like introduced, the fuel self-ignites due to compression of the combustion chamber 10a, and energy is generated by combustion. This energy is taken out as rotational energy of the crankshaft 23 of the diesel engine 10 via the piston 17. The gas used for combustion is discharged as exhaust into the exhaust passage 24 by opening the exhaust valve 22. A crank angle sensor 25 that detects the rotation angle of the crankshaft 23 is provided in the vicinity of the crankshaft 23.

  The vehicle is provided with a turbocharger 16. The turbocharger 16 includes an intake air compressor 16a provided in the intake passage 11, an exhaust turbine 16b provided in the exhaust passage 24, and a rotating shaft 16c that connects these. Specifically, the exhaust turbine 16b is rotated by the energy of the exhaust gas flowing through the exhaust passage 24, and the rotational energy is transmitted to the intake compressor 16a via the rotary shaft 16c, and the intake air is compressed by the intake compressor 16a. That is, the intake air is supercharged by the turbocharger 16. In the present embodiment, it is assumed that the turbocharger 16 can adjust the supercharging pressure of intake air by an energization operation.

  A purification device 26 that purifies the exhaust gas is provided on the downstream side of the turbocharger 16 in the exhaust passage 24.

  A part of the exhaust discharged to the exhaust passage 24 is recirculated to the intake passage 11 via the EGR passage 27. Specifically, the upstream side of the exhaust turbine 16 b in the exhaust passage 24 is connected to the surge tank 15 via the EGR passage 27. An EGR valve device 28 is provided in the EGR passage 27. The EGR valve device 28 adjusts the opening degree of the EGR valve 28a by an actuator such as a DC motor. Depending on the opening degree of the EGR valve 28a, a part of the exhaust discharged to the exhaust passage 24 is cooled by the EGR cooler 29 and then supplied to the surge tank 15 as an external EGR.

  The ECU 30, which is an electronic control device that controls the engine system, is mainly configured by a microcomputer including a known CPU, ROM, RAM, and the like. The ECU 30 includes an intake pressure sensor 31, an intake air temperature sensor 32, an exhaust gas temperature sensor 33, an in-cylinder pressure sensor 34 as a pressure detection unit, a fuel pressure sensor 35, a water temperature sensor 36, an accelerator sensor 37, an air flow meter 12, and a crank angle sensor 25. The detected value is input. The intake pressure sensor 31 detects the pressure in the surge tank 15, and the intake temperature sensor 32 detects the intake temperature in the surge tank 15. The exhaust temperature sensor 33 detects the temperature of the exhaust discharged from the combustion chamber 10a, and the in-cylinder pressure sensor 34 detects the pressure in the combustion chamber 10a (hereinafter referred to as “in-cylinder pressure”). The fuel pressure sensor 35 detects the fuel pressure in the common rail 19, and the water temperature sensor 36 detects the cooling water temperature of the engine 10. The accelerator sensor 37 detects the accelerator operation amount of the accelerator operation member of the driver, and specifically detects the depression amount of the accelerator pedal.

  The ECU 30 includes an engine including fuel injection control of the fuel injection valve 18, drive control of the fuel pump 20, drive control of the EGR valve device 28, and supercharging pressure control by the turbocharger 16 based on the detection values of the various sensors described above. 10 combustion control is performed.

  In particular, the ECU 30 performs fuel injection control for realizing isobaric combustion in the high load region of the engine 10. In the isobaric combustion, the peak of the in-cylinder pressure in the combustion chamber 10a after the start of combustion is kept substantially constant according to the isobaric target value. In FIG. 2, the waveform of the in-cylinder pressure with respect to the rotation angle position of the crankshaft 23 (hereinafter referred to as “crank angle position”) in the case of ideal isobaric combustion in the present embodiment is shown by a solid line. Further, in FIG. 2, for comparison, the waveform of the in-cylinder pressure in the case of performing single-stage injection after TDC without performing isobaric combustion is indicated by a one-dot chain line. Pmax is an allowable upper limit value of the in-cylinder pressure that can maintain the reliability of the engine 10, and Plim is a pressure limit value set to a value lower than the allowable upper limit value Pmax. Ptptg is an equal pressure target value that is a target value of the peak of the in-cylinder pressure after the start of combustion, and is a value set to be equal to or less than the pressure limit value Plim.

  In this embodiment, as shown by the solid lines in FIGS. 3B and 3C, isobaric combustion is realized by using multistage injection. The multi-stage injection is an injection in which the fuel injection amount required for generating the output torque of the engine 10 is divided and injected from the fuel injection valve 18 a plurality of times in one combustion cycle. In this embodiment, three-stage injection is used as multistage injection. In FIG. 3C, the waveform of the in-cylinder pressure in the case of performing single-stage injection in which the fuel injection amount required for the engine 10 in one combustion cycle is supplied from the fuel injection valve 18 by one injection is shown by a broken line. Indicated.

  When single-stage injection is performed after TDC as shown in FIG. 3A, the in-cylinder pressure is increased by combustion of fuel for single-stage injection after the in-cylinder pressure reaches a peak value at TDC in accordance with the volume change in the cylinder. Rise and fall. On the other hand, when multi-stage injection is performed, the in-cylinder pressure rises and falls every time the fuel for each injection stage burns, and three pressure peaks occur.

  FIG. 4 shows the procedure of the fuel injection control process according to this embodiment. This process is repeatedly executed by the ECU 30 at a predetermined cycle, for example.

  In this series of processes, first, in step S10, the operating state of the engine 10 is acquired. In the present embodiment, the operating state includes the engine rotation speed NE, the accelerator operation amount Acc detected by the accelerator sensor 37, and the supercharging pressure Pin detected by the intake pressure sensor 31. The engine speed NE may be calculated based on the detected value of the crank angle sensor 25.

  In subsequent step S11, it is determined whether or not the fuel injection control is performed in the isobaric combustion mode based on the operation state of the engine 10 acquired in step S10. Specifically, for example, it is determined whether or not the required output of the engine 10 ascertained from the operating state is equal to or higher than a predetermined output, or whether or not the required output of the engine 10 is a maximum output determined from the engine rotational speed NE. .

  In subsequent step S12, a target pressure waveform Tcurve of in-cylinder pressure for realizing isobaric combustion is set based on the operating state of the engine 10 acquired in step S10. The target pressure waveform Tcurve is a value of the in-cylinder pressure in a control period including a pressure increase period before the in-cylinder pressure reaches the equal pressure target value Ptptg and an equal pressure period after the in-cylinder pressure reaches the equal pressure target value Ptptg. The target pressure, which is a time-series target value, is defined. As shown in FIG. 5, the target pressure waveform Tcurve is defined by setting at least the start pressure Pst, the target slope Pslptg, and the equal pressure target value Ptptg based on the operating state of the engine 10. The start pressure Pst is the in-cylinder pressure at a predetermined crank angle position before the start of combustion in the compression stroke in which the volume of the combustion chamber 10a is reduced. Moreover, the broken line of FIG. 5 shows the in-cylinder pressure waveform when the fuel is not burned in the combustion chamber 10a.

  Incidentally, the target pressure waveform Tcurve is configured to set a pressure waveform including a plurality of pressure peaks corresponding to each injection stage, assuming that combustion is performed for each injection stage when multistage injection described later is performed. (See the broken line in FIG. 6).

  The setting method of the target pressure waveform Tcurve will be described in detail. In the present embodiment, the start pressure Pst and the first timing θ1 that is the crank angle position that becomes the start pressure Pst are set based on the operating state. Here, the start pressure Pst may be set based on, for example, the supercharging pressure Pin at the valve closing timing θip of the intake valve 21.

  The target inclination Pslptg is a target value for the in-cylinder pressure increase amount per unit rotation angle of the crankshaft 23. The timing at which the in-cylinder pressure reaches the equal pressure target value Ptptg is set to the second timing θ2 by increasing the in-cylinder pressure with the target inclination Pslpptg starting from the start pressure Pst. Further, the third timing θ3 that is the end timing of the period during which the constant pressure target value Ptptg is continued is set based on the operating state. In the present embodiment, among the target pressure waveform Tcurve, the waveform during the pressure rise period in which the in-cylinder pressure rises linearly from the first timing θ1 to the second timing θ2 is defined as the first pressure waveform, and the third from the second timing θ2 to the third. Let the waveform in the isobaric period until timing θ3 be the second pressure waveform. In the present embodiment, the process of step S12 corresponds to a target setting unit.

  Returning to the description of FIG. 4, in the subsequent step S13, first and second threshold values α and β used in steps S23 and S26 described later are set. Here, the first and second threshold values α and β may be set to fixed values, or may be variably set according to the operating state of the engine 10.

  In subsequent step S14, a pressure limit value Plim and a temperature limit value Tlim are set as upper limit threshold values.

  In the subsequent step S15, the multistage injection mode from the fuel injection valve 18 that realizes the target pressure waveform Tcurve is set based on the operating state of the engine 10. The multistage injection mode includes the start timing of each injection stage of multistage injection, the injection time of each injection stage, and the interval between injection stages that are temporally adjacent. The multi-stage injection mode may be set using, for example, a map that defines the multi-stage injection mode related to the operating state of the engine 10.

  Incidentally, the total value of the fuel injection amount by the multi-stage injection required in one combustion cycle is a region sandwiched between the target pressure waveform Tcurve and the in-cylinder pressure waveform shown by the broken line as shown by the solid line in FIG. Is set according to the area St from the first timing θ1 to the third timing θ3. The larger the area St is, the larger the total fuel injection amount is set. The total value of the fuel injection amounts is a fuel injection amount that contributes to the output torque generation of the engine 10 required per combustion cycle, and this fuel injection amount is divided and assigned to each injection stage.

  In subsequent step S16, in order to control the in-cylinder pressure waveform to the target pressure waveform Tcurve, the fuel injection valve 18 performs multistage injection in the multistage injection mode set in step S15. In the present embodiment, the processes in steps S15 and S16 constitute an injection control unit.

  In the subsequent step S17, a waveform of the in-cylinder pressure (hereinafter referred to as “actual in-cylinder pressure Preal”) detected by the in-cylinder pressure sensor 34 during multi-stage injection is acquired. The acquired waveform of the actual in-cylinder pressure Preal is stored in a storage unit (specifically, a memory) provided in the ECU 30.

  In the subsequent step S18, it is determined whether or not the exhaust temperature Tex detected by the exhaust temperature sensor 33 exceeds the temperature limit value Tlim. When an affirmative determination is made in step S18, the process proceeds to step S19, and among the multistage injections set in the next combustion cycle, the final stage fuel injection amount is corrected to decrease. Specifically, the injection time for the final stage is shortened. The process of step S19 is a process for avoiding a decrease in reliability of the exhaust system due to an excessive increase in the exhaust temperature. It should be noted that as the value obtained by subtracting the temperature limit value Tlim from the exhaust temperature Tex is larger, the degree of reduction in the fuel injection amount may be set larger.

  If a negative determination is made in step S18, the process proceeds to step S20. In the processing after step S20, processing for eliminating the excess pressure, the inclination deviation, and the maximum pressure deviation is performed. The excessive pressure is a phenomenon in which the actual in-cylinder pressure Preal exceeds the pressure limit value Plim. The inclination shift is a phenomenon in which the waveform of the actual in-cylinder pressure Preal deviates from the first pressure waveform during the pressure increase period. The maximum pressure deviation is a phenomenon in which the waveform of the actual in-cylinder pressure Preal deviates from the second pressure waveform during the equal pressure period.

  In the present embodiment, in the waveform of the actual in-cylinder pressure Preal under the condition where multi-stage injection is being performed, (1) determination as to whether or not an overpressure has occurred, and (2) whether or not an inclination deviation has occurred. Judgment and (3) Judgment of whether or not the maximum pressure deviation has occurred is carried out in the order of (1), (2), and (3) in order of decreasing priority. In other words, if an excess pressure, an inclination error, and a maximum pressure error occur simultaneously in one combustion cycle, it is first determined that an excess pressure has occurred, and the excess pressure is eliminated based on the determination result. The process for doing is implemented. Then, after it is determined that an inclination deviation has occurred after the process for eliminating the excess pressure, the process for eliminating the inclination deviation is performed based on the determination result. Furthermore, if it is determined that the maximum pressure deviation has occurred after the process for eliminating the tilt deviation is performed, the process for eliminating the maximum pressure deviation is performed based on the determination result.

  Specifically, in step S20, it is determined whether or not an excessive pressure has occurred. Specifically, it is determined whether or not the actual in-cylinder pressure Preal acquired in the current combustion cycle exceeds the pressure limit value Plim. In the present embodiment, the process of step S20 corresponds to an upper limit determination unit.

  If an affirmative determination is made in step S20, the process proceeds to step S21, and the fuel injection amount of the injection stage corresponding to the combustion in which the actual in-cylinder pressure Preal exceeds the pressure limit value Plim among the multistage injections in order to eliminate the excess pressure, A reduction correction process for correcting the reduction in the next combustion cycle is performed. Specifically, the fuel injection amount at the injection stage set in step S15 of the next combustion cycle is corrected to decrease. In the present embodiment, the process of step S21 corresponds to a weight reduction correction unit. Hereinafter, the reduction correction process will be described with reference to FIGS. 6 and 7.

  First, FIG. 6 shows a case where the actual in-cylinder pressure Preal exceeds the pressure limit value Plim in the current combustion cycle. FIG. 6A shows an injection pulse (injection command signal) of multistage injection of the fuel injection valve 18, and FIG. 6B shows a transition of in-cylinder pressure. Here, in FIG. 6B, the in-cylinder pressure waveform when ideal isobaric combustion control is performed when multistage injection is used is indicated by a broken line, and the waveform of the actual in-cylinder pressure Preal is indicated by a solid line. As indicated by a broken line in FIG. 6B, the peak value of the actual in-cylinder pressure Preal corresponding to the second and third stage injections of the three stage injections exceeds the pressure limit value Plim. The reason why the actual in-cylinder pressure Preal exceeds the pressure limit value Plim is due to fuel-related factors.

  Specifically, the fuel property used in the vehicle may differ from the fuel property assumed when the target pressure waveform Tcurve is adapted in relation to the operating state of the engine 10. Specifically, the actual cetane number of light oil may be lower than the cetane number assumed when it is adapted. When the cetane number is low, the ignitability of the fuel is deteriorated, and the combustion of the fuel injected at the first stage of the multistage injection may be delayed. In this case, the first stage fuel burns together with the fuel injected in the second stage. As a result, the in-cylinder pressure increases significantly, and the actual in-cylinder pressure Preal may exceed the pressure limit value Plim.

  In FIG. 6, it is assumed that the target pressure waveform Tcurve has three pressure peaks corresponding to the three-stage multi-stage injection in the range of the pressure limit value Plim or less. The pressure rise due to the combustion of the fuel for the second stage and the fuel for the second and third stages is excessive. In this case, the in-cylinder pressure is excessively increased when the fuel for the second stage is combusted, and the in-cylinder pressure is excessively increased when the fuel for the third stage is combusted. It is considered that the in-cylinder pressure rises excessively as a result of the pressure rise under the condition where the pressure is applied.

  In addition, as a factor that the actual in-cylinder pressure Preal exceeds the pressure limit value Plim, there is also a factor related to the environment around the vehicle. Specifically, the factors relating to the actual environment may differ from the factors relating to the environment assumed when the target pressure waveform Tcurve is adapted in relation to the operating state of the engine 10. Specifically, for example, the actual intake air temperature may be lower than the intake air temperature assumed when it is adapted. When the intake air temperature is low, the in-cylinder pressure at the time of ignition is higher than when the intake air temperature is high. As a result, combustion occurs when the in-cylinder pressure level is increased, and the actual in-cylinder pressure Preal may exceed the pressure limit value Plim.

  Next, FIG. 7 shows a case where the weight reduction correction process is performed in the combustion cycle next to the combustion cycle shown in FIG. FIG. 7A shows an injection pulse of multistage injection, and FIG. 7B shows a transition of the actual in-cylinder pressure Preal. 6 and 7, the target pressure waveform Tcurve is the same, and the actual in-cylinder pressure Preal before correction indicated by the broken line in FIG. 7B is the actual in-cylinder pressure indicated by the solid line in FIG. 6B. Corresponds to Preal.

  As shown in FIG. 7B, the fuel injection amount is corrected to decrease by shortening the fuel injection time of the second and third stages of the three-stage injection. A peak can appear in the actual in-cylinder pressure Preal corresponding to each injection stage of the multi-stage injection. For this reason, the peak value of the actual in-cylinder pressure Preal corresponding to the injection stage in which the fuel injection amount is corrected to be reduced can be reduced. In the present embodiment, for the injection stage that exceeds the pressure limit value Plim, the degree of reduction in the fuel injection amount is increased as the value obtained by subtracting the pressure limit value Plim from the peak value of the actual in-cylinder pressure Preal is larger. In this embodiment, the second and third stage fuel injection start timings are not corrected.

  In FIG. 7, if the increase in the in-cylinder pressure at the time of combustion for the second stage fuel is reduced, the level of the entire in-cylinder pressure waveform is lowered, and therefore, at least the second stage fuel injection amount may be corrected for reduction. That is, when the pressure limit value Plim is exceeded at the peak of the plurality of actual in-cylinder pressures Preal, the fuel injection amount of the injection stage corresponding to the peak of the actual in-cylinder pressure Preal exceeding the pressure limit value Plim may be corrected first.

  The injection stage for which the amount of reduction is corrected can be specified from the waveform of the actual in-cylinder pressure Preal. Specifically, the portion of the acquired actual in-cylinder pressure Preal waveform in one combustion cycle that exceeds the pressure limit value Plim is sequentially identified from the rear in the time axis. As a result, the injection stage corresponding to the waveform portion of the actual in-cylinder pressure Preal that exceeds the pressure limit value Plim is specified as the reduction correction target.

  Returning to the description of FIG. 4 above, if it is determined in step S20 that no excess pressure has occurred, the process proceeds to step S22, and the actual slope Pslprl is calculated. The actual inclination Pslprl is an actual in-cylinder pressure increase amount per unit rotation angle Δθ of the crankshaft 23 during the pressure increase period. In the present embodiment, as shown in FIG. 8, the actual inclination Pslprl is calculated by approximating the increase in the actual in-cylinder pressure Preal with a linear line during the pressure increase period. Specifically, the primary straight line Pbase set in accordance with the first pressure waveform is set such that the sum of the differences between the primary straight line Pbase and the actual in-cylinder pressure Preal (the area of the hatched portion in FIG. 8) is less than a predetermined value. The slope (ΔP / Δθ) of the primary straight line Pbase is defined as the actual slope Pslprl. Here, the primary straight line Pbase may be defined so as to pass, for example, the start pressure Pst. In addition, what is necessary is just to calculate the area Sp of the shaded part of FIG. 8 by the following formula (eq1).

続くステップＳ２３では、傾斜ずれが発生しているか否かを判定する。具体的には、実傾斜Ｐｓｌｐｒｌと目標傾斜Ｐｓｌｐｔｇとの差の絶対値が第１閾値α未満であるか否かを判定する。なお本実施形態において、ステップＳ２３の処理が第１判定部に相当する。

In a succeeding step S23, it is determined whether or not a tilt deviation has occurred. Specifically, it is determined whether or not the absolute value of the difference between the actual slope Pslprl and the target slope Pslpgt is less than the first threshold value α. In the present embodiment, the process of step S23 corresponds to a first determination unit.

  If a negative determination is made in step S23, the process proceeds to step S24, and the waveform of the actual in-cylinder pressure Preal during the pressure increase period is the first in the fuel injection mode set in step S15 of the next combustion cycle in order to eliminate the tilt shift. An inclination correction process is performed to correct the pressure waveform so as to approach the pressure waveform. In the present embodiment, the process of step S24 corresponds to a first correction unit.

  In particular, in the present embodiment, when it is determined that the actual gradient Pslprl during the pressure increase period is smaller than the target gradient Pslpgt by the first threshold value α, the first-stage injection pulse of the multistage injection set in step S15 of the next combustion cycle is advanced. Inclination correction processing for making a corner is performed. As a result, the actual inclination Pslprl during the pressure increase period is increased. In the present embodiment, the process of advancing the first-stage injection pulse corresponds to the process of the first control unit.

  The process for advancing the injection pulse will be described with reference to FIG. In FIG. 9B, the waveform of the actual in-cylinder pressure Preal before being advanced is indicated by a broken line, and the waveform of the actual in-cylinder pressure Preal after being advanced is indicated by a solid line. 7 and 9, the target pressure waveform Tcurve is the same, and the actual in-cylinder pressure Preal before correction indicated by the broken line in FIG. 9B is the actual in-cylinder pressure indicated by the solid line in FIG. 7B. Corresponds to Preal.

  As shown in the figure, before the first-stage injection pulse is advanced, during the pressure increase period, the first-stage fuel in the multi-stage injection is not burned at each injection. For this reason, the actual inclination Pslprl is smaller than the target inclination Pslpptg, and the deviation between the target inclination Pslptg and the actual inclination Pslprl is large. For this reason, the first-stage injection pulse is advanced to increase the actual inclination Pslprl. In this embodiment, the first stage fuel injection time is lengthened while the first stage injection start timing and injection end timing are advanced, and the fuel injection amount increase correction is performed. This avoids delaying the combustion of the first-stage fuel and increases the actual slope Pslprl during the pressure increase period.

  Here, if the first-stage injection pulse is advanced to increase the actual inclination Pslprl, the peak of the in-cylinder pressure during the isobaric period decreases due to the advance angle of the injection pulse. For this reason, in the present embodiment, in the combustion cycle next to the combustion cycle in which the injection pulse is advanced, the second step is performed to correct the decrease in the actual in-cylinder pressure Preal during the equal pressure period due to the advance angle of the injection pulse. An inclination correction process for correcting the embodiment of the subsequent injection stages is performed. Specifically, in order to correct the decrease in the actual in-cylinder pressure Preal, at least one of the interval times of the first and second stages and the fuel injection time of the second stage in the multistage injection is corrected. In the present embodiment, the process of correcting at least one of the first and second stage interval times and the second stage fuel injection time corresponds to the process of the second control unit. Hereinafter, the inclination correction process for correcting the first and second stage interval times and the second stage fuel injection time will be described with reference to FIG. 10 and 9, the target pressure waveform Tcurve is the same, and the actual in-cylinder pressure Preal before correction indicated by the broken line in FIG. 10B is the actual in-cylinder pressure indicated by the solid line in FIG. 9B. Corresponds to Preal.

  As illustrated, in the present embodiment, the second stage injection start timing is advanced without correcting the second stage injection end timing. For this reason, the first and second stage intervals are shortened, and the second stage fuel injection amount is corrected to be increased. As a result, the decrease in the actual in-cylinder pressure Preal during the equal pressure period due to the advance angle of the first-stage injection pulse is corrected.

  Returning to the description of FIG. 4 above, when an affirmative determination is made in step S23, the process proceeds to step S25 to calculate the actual maximum pressure Ptprl. The actual maximum pressure Ptprl is a parameter obtained by quantifying the deviation between the average value of the actual in-cylinder pressure Preal and the second pressure waveform during the equal pressure period. In the present embodiment, as shown in FIG. 11, the peak value of the actual in-cylinder pressure Preal corresponding to the second and third stage injections and the average value of the minimum values of the actual in-cylinder pressure Preal sandwiched between these peak values are obtained. Calculated as the maximum pressure Ptprl.

  Note that the present invention is not limited to the above-described calculation method. For example, the actual in-cylinder pressure Preal corresponding to the third-stage injection from the peak value of the actual in-cylinder pressure Preal corresponding to the second-stage injection in the waveform of the actual in-cylinder pressure Preal. The average value up to the peak value may be calculated as the actual maximum pressure Ptprl.

  In a succeeding step S26, it is determined whether or not the maximum pressure deviation has occurred. Specifically, it is determined whether or not the absolute value of the difference between the actual maximum pressure Ptprl and the equal pressure target value Ptptg is less than the second threshold value β. In the present embodiment, the process of step S26 corresponds to a second determination unit.

  When an affirmative determination is made in step S26, the process proceeds to step S27, and maximum value correction processing is performed to eliminate the maximum pressure deviation. This process is performed as either a process for reducing the fluctuation range of the actual in-cylinder pressure Preal during the equal pressure period, or a process for bringing the average value of the actual in-cylinder pressure Preal during the equal pressure period closer to the equal pressure target value Ptptg. Specifically, the maximum value correction process corrects at least one of the interval times of the second and third stages and the fuel injection time of the third stage in the multistage injection. In the present embodiment, the process of step S27 corresponds to a second correction unit. Hereinafter, the maximum value correction process will be described with reference to FIG.

  In FIG. 12B, the waveform of the actual in-cylinder pressure Preal before the maximum value correction processing is indicated by a broken line, and the waveform of the actual in-cylinder pressure Preal after the maximum value correction processing is indicated by a solid line. 12 and 10, the target pressure waveform Tcurve is the same, and the actual in-cylinder pressure Preal before correction indicated by a broken line in FIG. 12B is the actual in-cylinder pressure indicated by the solid line in FIG. 10B. Corresponds to Preal.

  FIG. 12 shows a process for shortening the second and third stage intervals and a process for increasing the third stage fuel injection time as the maximum value correction process. Specifically, the third stage injection end timing is not corrected, and the third stage injection start timing is advanced. Thereby, in the next combustion cycle, the intervals of the second stage and the third stage are shortened, and the fuel injection amount of the third stage is corrected to be increased.

  In addition, in the state where the pressure excess, the inclination deviation, and the maximum pressure deviation are occurring at the same time, when the weight loss correction process for eliminating the pressure excess is performed, if the inclination deviation and the maximum pressure deviation are eliminated, The inclination correction process and the maximum value correction process are not performed. In addition, when the inclination correction process for eliminating the inclination deviation is performed in the state where the inclination deviation and the maximum pressure deviation are generated, if the maximum pressure deviation is eliminated, the maximum value correction process is not performed.

  According to the embodiment described in detail above, the following effects can be obtained.

  Based on the operating state of the engine 10, a target pressure waveform Tcurve for carrying out the isobaric combustion control was set. The waveform of the actual in-cylinder pressure Preal was controlled to the target pressure waveform Tcurve by dividing the fuel injection amount required per combustion cycle and performing multistage injection from the fuel injection valve 18. Thereby, it is possible to achieve isobaric combustion with a simple configuration using multistage injection without significantly changing the fuel injection system. Therefore, it is possible to avoid an increase in the cost of the fuel injection system and a deterioration in the mounting capability of the fuel injection system on the vehicle.

  Multistage injection was performed in such a manner that the first stage fuel injection was performed during the pressure increase period. For this reason, the waveform of the actual in-cylinder pressure Preal during the pressure increase period can be controlled as desired, and as a result, the actual in-cylinder pressure Preal can be made closer to the first pressure waveform.

  When it is determined that the pressure exceeding the actual cylinder pressure Preal exceeds the pressure limit value Plim, the fuel injection amount of the injection stage corresponding to the combustion in which the actual cylinder pressure Preal exceeds the pressure limit value Plim among the multistage injections is determined. A reduction correction process was performed to correct the reduction in the next combustion cycle. For this reason, in the next combustion cycle, the peak value of the actual in-cylinder pressure Preal corresponding to the injection stage in which the fuel injection amount is corrected to be reduced can be reduced. As a result, the actual in-cylinder pressure Preal can be made equal to or less than the pressure limit value Plim.

  When it is determined that the absolute value of the difference between the actual inclination Pslprl and the target inclination Pslpgt is equal to or greater than the first threshold value α, the waveform of the actual in-cylinder pressure Preal during the pressure increase period approaches the first pressure waveform in the next combustion cycle. An inclination correction process for correcting the multi-stage injection mode was performed. In particular, when it is determined that the value obtained by subtracting the actual inclination Pslprl from the target inclination Pslptg is equal to or greater than the first threshold value α, the first-stage injection pulse of the multistage injection is advanced in the next combustion cycle. Then, in order to correct the decrease in the actual in-cylinder pressure during the equal pressure period due to the advance angle of the injection pulse, the second and subsequent injection stages are performed in the combustion cycle following the combustion cycle in which the injection pulse is advanced. The aspect was corrected. Thereby, the waveform of the actual in-cylinder pressure Preal during the pressure increase period can be brought close to the first pressure waveform.

  When it is determined that the absolute value of the difference between the actual maximum pressure Ptprl and the equal pressure target value Ptptg is equal to or greater than the second threshold value β, a maximum value correction process for correcting the third stage injection mode is performed in the next combustion cycle. It was. For this reason, the waveform of the actual in-cylinder pressure Preal in the equal pressure period can be brought close to the second pressure waveform.

  (1) Determining whether or not an overpressure has occurred, (2) Determining whether or not an inclination deviation has occurred, (3) Determining whether or not a maximum pressure deviation has occurred, (1), (2 ) And (3) in order of decreasing priority. As a result, various correction processes were performed such that the priority decreased in the order of the weight loss correction process, the inclination correction process, and the maximum value correction process. Therefore, the fuel injection mode can be corrected so that the waveform of the actual in-cylinder pressure Preal approaches the target pressure waveform Tcurve after the actual in-cylinder pressure Preal is set to be equal to or less than the pressure limit value Plim. Therefore, it is possible to achieve isobaric combustion while accurately avoiding a decrease in the reliability of the engine 10.

  Of the determination as to whether or not the inclination deviation occurred and the determination as to whether or not the maximum pressure deviation occurred, the determination as to whether or not the inclination deviation occurred was prioritized. As a result, the inclination correction process is given priority among the inclination correction process and the maximum value correction process. According to the inclination correction process, the peak of the in-cylinder pressure corresponding to the first stage can be generated, but the peak value of the in-cylinder pressure corresponding to the second and third stages is lowered. For this reason, the waveform of the actual in-cylinder pressure Preal can be efficiently controlled to the target pressure waveform Tcurve by performing the maximum value correction process in the combustion cycle after performing the inclination correction process.

  -Multi-stage injection in which the amount of fuel that contributes to generation of output torque of the engine 10 is divided and injected is performed. For this reason, compared with the case where the fuel amount which contributes to the production | generation of output torque is injected at once, the fall degree of the fuel pressure of a sac chamber in a fuel injection period can be made small. Thereby, the average injection pressure of the fuel injection valve 18 during the fuel injection period can be increased, and the generation of smoke accompanying the combustion of fuel can be suppressed.

(Other embodiments)
The above embodiment may be modified as follows.

  The method for calculating the actual inclination Pslprl is not limited to the one exemplified in the above embodiment. For example, as shown in FIG. 13, the actual inclination Pslprl may be calculated based on the maximum value and the minimum value of the actual in-cylinder pressure Preal during the pressure increase period. Specifically, the actual slope Pslprl may be calculated by a least square method based on these local maximum values and local minimum values.

  In the above embodiment, when it is determined that an excess of pressure has occurred, the reduction correction process is performed in the next combustion cycle. However, the present invention is not limited to this, and the reduction correction process may be performed in the subsequent combustion cycles. Note that the inclination correction process and the maximum value correction process may also be performed in subsequent combustion cycles, as in the reduction correction process.

  Of the processes shown in FIG. 4, the processes in steps S25 to S27 may be omitted. Thereby, the determination of excess pressure is performed preferentially among the determination of excess pressure in step S20 and the determination of inclination deviation in step S23.

  Further, among the processes shown in FIG. 4, the processes in steps S22 to S24 may be omitted. In this case, when a negative determination is made in step S20, the process may proceed to step S25. Thereby, the determination of excess pressure is performed preferentially among the determination of excess pressure in step S20 and the determination of maximum pressure deviation in step S26.

  -The number of injection stages of multi-stage injection may be other than three. However, the multistage injection may be performed in such a manner that the first stage fuel injection is performed during the pressure increase period. Further, in order to improve the accuracy of the isobaric combustion in the isobaric period, it is desirable that three or more stages of multistage injection be performed.

  -As a process for determining whether or not the actual in-cylinder pressure Preal is deviated from the first pressure waveform during the pressure increase period, an integrated value of the difference between the actual in-cylinder pressure Preal and the first pressure waveform is calculated during the pressure increase period. The presence or absence of deviation may be determined based on the magnitude of the integrated value.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 10a ... Combustion chamber, 18 ... Fuel injection valve, 30 ... ECU.

Claims (7)

Applied to a diesel engine (10) comprising a fuel injection valve (18) for directly injecting fuel into the combustion chamber (10a);
The pressure rise before the in-cylinder pressure reaches the equal pressure target value when the equal pressure combustion control is performed to keep the peak of the in-cylinder pressure in the combustion chamber substantially constant according to the equal pressure target value after the start of combustion. A target setting unit that sets a target pressure that is a time-series target value of in-cylinder pressure based on an operating state of the engine in a control period that includes a period and an equal pressure period after reaching the equal pressure target value;
An injection control unit that divides a fuel injection amount required per combustion cycle of the engine and performs multi-stage injection from the fuel injection valve in order to control the in-cylinder pressure in the combustion chamber to the target pressure. A fuel injection control device.   2. The fuel injection control device according to claim 1, wherein the injection control unit performs the multi-stage injection in such a manner that the first-stage fuel injection is performed in the pressure increase period. An acquisition unit that acquires an actual in-cylinder pressure that is an actual in-cylinder pressure in the combustion chamber;
An upper limit determination unit that determines whether or not the actual in-cylinder pressure exceeds an upper limit threshold on the high pressure side than the equal pressure target value at the time of performing the multi-stage injection,
When it is determined that the actual in-cylinder pressure exceeds the upper limit threshold, the injection control unit determines the fuel injection amount of the injection stage corresponding to the combustion in which the actual in-cylinder pressure exceeds the upper limit threshold in the multistage injection. The fuel injection control device according to claim 1, further comprising a reduction correction unit that corrects reduction in a combustion cycle after the next time of the engine. An acquisition unit that acquires an actual in-cylinder pressure that is an actual in-cylinder pressure in the combustion chamber;
A deviation determination unit that determines whether or not a deviation from the target pressure has occurred with respect to the actual in-cylinder pressure in at least one of the pressure increase period and the equal pressure period when the multistage injection is performed;
When it is determined that a deviation in the actual in-cylinder pressure has occurred, the injection control unit determines that the actual in-cylinder pressure approaches the target pressure in the next and subsequent combustion cycles of the engine. The fuel injection control device according to any one of claims 1 to 3, further comprising a deviation correction unit that corrects the difference. The deviation determination unit determines, as the deviation determination, whether an inclination of an increase change in the actual in-cylinder pressure during the pressure increase period is smaller than a predetermined value with respect to an inclination of the target pressure,
The injection control unit
A first control unit that advances the injection command signal of the first stage of the multi-stage injection when it is determined that the inclination of the increase change in the actual in-cylinder pressure during the pressure increase period is smaller than a predetermined value with respect to the inclination of the target pressure. When,
Second control for correcting the embodiments of the second and subsequent injection stages so as to correct the decrease in the actual in-cylinder pressure during the equal pressure period caused by advancing the injection command signal of the first stage of the multi-stage injection. And a fuel injection control device according to claim 4. An acquisition unit that acquires an actual in-cylinder pressure that is an actual in-cylinder pressure in the combustion chamber;
An upper limit determination unit that determines whether or not the actual in-cylinder pressure has exceeded an upper limit threshold on the high pressure side than the equal pressure target value when the multistage injection is performed;
A deviation determination unit that determines whether or not a deviation from the target pressure has occurred with respect to the actual in-cylinder pressure in at least one of the pressure increase period and the equal pressure period when the multistage injection is performed;
The injection control unit
When it is determined that the actual in-cylinder pressure exceeds the upper limit threshold, the fuel injection amount of the injection stage corresponding to the combustion in which the actual in-cylinder pressure exceeds the upper limit threshold among the multistage injections A weight reduction correction unit that performs weight reduction correction in the combustion cycle of
Deviation correction that corrects the embodiment of the multi-stage injection so that the actual in-cylinder pressure approaches the target pressure in the next and subsequent combustion cycles of the engine when it is determined that a deviation in the actual in-cylinder pressure has occurred. And
The correction by the reduction correction unit is preferentially performed among the correction by the reduction correction unit based on the determination result of the upper limit determination unit and the correction by the deviation correction unit based on the determination result of the deviation determination unit. The fuel injection control apparatus according to 1. The deviation determination unit
A first determination unit configured to determine whether or not a deviation from the target pressure occurs with respect to the actual in-cylinder pressure during the pressure increase period when the multi-stage injection is performed;
A second determination unit that determines whether or not a deviation from the target pressure has occurred with respect to the actual in-cylinder pressure during the equal pressure period when the multi-stage injection is performed,
The deviation correction unit is
A first correction unit that corrects an injection stage corresponding to the pressure increase period when the first determination unit determines that a deviation of the actual in-cylinder pressure occurs in the pressure increase period;
A second correction unit configured to correct the injection stage corresponding to the equal pressure period when the second determination unit determines that the actual in-cylinder pressure shift occurs in the equal pressure period. And
Of the correction by the first correction unit based on the determination result of the first determination unit and the correction by the second correction unit based on the determination result of the second determination unit, the correction by the first correction unit is prioritized. The fuel injection control device according to claim 6 implemented.

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