JP6023002B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device that executes fuel injection from a fuel injection valve in one combustion cycle by multistage injection performed in a plurality of times.

  The internal combustion engine is attached with a fuel supply system constituted by a pressure accumulating container to which fuel in a pressurized state is supplied, a fuel injection valve, a connection passage connecting the pressure accumulating container and the fuel injection valve, and the like. In recent years, a pressure sensor for detecting the fuel pressure inside such a fuel supply system has been provided, and the fuel injection valve is controlled based on the variation of the fuel pressure detected by the pressure sensor when the fuel injection from the fuel injection valve is executed. There has been proposed an apparatus that detects a characteristic parameter of an operation characteristic and performs operation control of the fuel injection valve based on the detected characteristic parameter (see Patent Document 1). In operation control of an internal combustion engine, it is often used to perform so-called multi-stage injection in which fuel injection from a fuel injection valve in one combustion cycle is performed in a plurality of times.

JP 2009-57925 A

  Here, in an internal combustion engine in which multi-stage injection is performed, pressure fluctuations in the fuel supply system at the time of execution of fuel injection in the second and subsequent stages are pressures generated by injection before that (pre-stage injection) The pulsating part of is included. In order to suppress the injection amount error due to the influence of the pressure pulsation, the characteristic parameter of the operating characteristic of the fuel injector is detected for each stage of the multi-stage injection and the fuel injection valve based on the detected value is detected. It is conceivable to correct the operation mode.

  In this case, if the operation mode of the injection stage to be detected is corrected simply based on the detected value of the characteristic parameter, the number of injection stages is divided into the combustion cycle including the fuel injection to be detected and the combustion cycle including the fuel injection to be corrected. Is changed based on the detection value detected at the second and subsequent injections where the influence of the pressure pulsation is large, even though the influence of the pressure pulsation is very small. There is a risk. Further, there is a possibility that the correction based on the detection value may not be executed in spite of the second and subsequent injections having a large influence of the pressure pulsation due to the upstream injection. In such a case, there is a high possibility that the injection amount error due to the pressure pulsation cannot be appropriately suppressed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel injection control device that can suitably suppress an injection amount error in each stage of fuel injection when performing multi-stage injection. .

A fuel injection control device for solving the above-described problem includes an internal combustion engine including a fuel supply system that supplies fuel in a pressurized state to a fuel injection valve, and a pressure sensor that detects fuel pressure inside the fuel supply system. The fuel injection from the fuel injection valve in a single combustion cycle is performed by multi-stage injection in which fuel injection is performed in a plurality of times. For each of the second and subsequent injections of the multi-stage injection, a characteristic parameter of the operating characteristic of the fuel injection valve is detected based on a fuel pressure fluctuation mode detected by the pressure sensor when the fuel injection is performed, and a natural number is set to “ N ”, a correction term for correcting the influence of the fuel pressure pulsation accompanying the preceding stage injection on the second and subsequent stages of the multistage injection is based on the (N + 1) th stage injection in the multistage injection (N + 1). ) A value corresponding to the injection at the stage is calculated separately based on the detected characteristic parameter. In the operation control of the fuel injection valve, the (N + 1) th stage injection in the multistage injection is executed based on a correction term calculated as a value corresponding to the (N + 1) th stage injection .

  In the above apparatus, for each of the injections after the second stage of the multi-stage injection, for correcting the influence of the fuel pressure pulsation accompanying the fuel injection (pre-stage injection) executed immediately before the injection stage to be reflected in the correction term A correction term is calculated. This correction term is not calculated in association with the injection position, such as a correction term corresponding to the main injection or a correction term corresponding to the pilot injection executed immediately before the main injection, but the multi-stage injection. The correction term corresponding to the second stage injection and the correction term corresponding to the third stage injection are calculated in association with the injection order. Therefore, when the number of stages of multistage injection changes between the combustion cycle including the fuel injection subject to calculation of the correction term and the combustion cycle including the fuel injection subject to reflection of the correction term, the correction term is reflected in the injection order in the combustion cycle. Is done according to.

  As a result, the correction term is not reflected in the second and subsequent injections, which are greatly affected by the pulsation of the fuel pressure due to the previous injection, or the correction term calculated based on such second and subsequent injections is It is avoided that it is applied to the first stage injection that is hardly affected by pulsation. Therefore, according to the above apparatus, when performing multi-stage injection, the correction term can be appropriately reflected in the fuel injection of each stage in accordance with the presence or absence of the previous stage injection, and the injection amount error in the fuel injection of each stage is preferable. Can be suppressed.

In the above apparatus, the at multiple injection (N) and stage injection in a reflection combustion cycle including a pre-Symbol reflecting target fuel injection calculation combustion cycle and the correction terms including the fuel injection calculation target correction term (N + 1 ) when the interval between the stage of injection are different, after resetting at the calculated combustion cycle (N + 1) correction term is calculated as a value corresponding to the stage of the injection to the initial value, the reflected combustion cycle It is preferable that the operation control of the fuel injection valve is performed.

  When the interval between the injections of the multi-stage injection changes, the timing at which the fuel pressure pulsation generated due to the fuel injection on the front stage reaches the execution period of the fuel injection on the rear stage also changes. Have different effects on the fuel injection on the rear stage side.

  According to the above apparatus, when the interval changes, the correction term whose reliability has decreased along with the change can be reset to the initial value. Can be avoided from being reflected in the fuel injection on the rear stage side. Therefore, even when the reliability of the correction term is lowered with the change of the interval, an increase in the injection amount error due to this can be suppressed.

In the apparatus, learning for learning a characteristic parameter of an operating characteristic of the fuel injection valve based on a fuel pressure fluctuation mode detected by the pressure sensor for each of a plurality of learning regions divided according to an operating state of the internal combustion engine. While executing the processing, the learning term learned in the learning processing can be reflected in each injection of the multistage injection. In such an apparatus, when the natural number is “N”, (N) in the multistage injection in the calculated combustion cycle including the fuel injection to be calculated by the correction term and the reflected combustion cycle including the fuel injection to be reflected by the correction term. when the learning region for morphism injection of stage are different, after resetting at the calculated combustion cycle (N + 1) correction term is calculated as a value corresponding to the stage of the injection to the initial value, the reflected combustion It is preferable to perform operation control of the fuel injection valve in a cycle.

  In the above apparatus, when the learning region is switched in accordance with the change of the engine operating state, the learning term applied to the fuel injection changes, so that the pulsation mode of the fuel pressure caused by the injection also changes. Therefore, in such a case, if the correction term calculated in the calculated combustion cycle is reflected in the reflected combustion cycle, the correction term becomes an inappropriate value, which may increase the injection amount error.

  According to the above apparatus, when the learning region is switched, the correction term is reset to the initial value, so that it is avoided that the correction term that is likely to be a value that does not match the actual condition is reflected in the fuel injection. can do.

The operating state of the internal combustion engine in the above apparatus can be the fuel injection amount or the fuel injection pressure.
When the fuel injection amount and the fuel injection pressure change greatly, the pulsation mode of the fuel pressure caused by the pre-stage injection also changes. Therefore, when such a change occurs, if the correction term calculated in the calculation combustion cycle is reflected in the reflection combustion cycle, the correction term may become an inappropriate value, leading to an increase in injection amount error.

  According to the above apparatus, the correction term is reset to the initial value when the fuel injection amount or the fuel injection pressure changes greatly. Therefore, the correction term that is likely to be no longer the actual value is reflected in the fuel injection. Can be avoided.

1 is a schematic diagram showing a schematic configuration of an embodiment of a fuel injection control device. Sectional drawing which shows the cross-section of a fuel injection valve. (A) And (b) The timing chart which shows the relationship between a drive pulse and a fuel injection rate with each characteristic parameter of a fuel injection valve. (A)-(c) The timing chart which shows the relationship between the time waveform of fuel pressure, and the detection time waveform of a fuel injection rate. (A) And (b) The timing chart which shows the relationship between the detection time waveform of a fuel injection rate, and a basic time waveform. The conceptual diagram which shows the map structure of the map which memorize | stored the relationship between the target injection quantity in the learning area | region with little target injection quantity, target injection pressure, and each learning term. The conceptual diagram which shows the map structure of the map which memorize | stored the relationship between the target injection amount in the learning area | region with many target injection amounts, target injection pressure, and each learning term. The flowchart which shows the execution procedure of a correction | amendment term calculation process. The conceptual diagram which shows the relationship between the injection stage of multistage injection, and each difference correction term. The conceptual diagram which shows the reflection pattern of the difference correction term to each stage of multistage injection. The conceptual diagram which shows an example of the reflection aspect of the difference correction | amendment term when the number of injection stages reduces. The conceptual diagram which shows an example of the reflection aspect of the difference correction | amendment term when the injection stage number increases. The flowchart which shows the execution procedure of correction | amendment term reflection process. The conceptual diagram which shows an example of the reset aspect of a difference correction term. The timing chart which shows an example of transition of the learning term reflected in main injection, and a difference correction term.

Hereinafter, an embodiment of the fuel injection control device will be described.
As shown in FIG. 1, an intake passage 12 is connected to the cylinder 11 of the internal combustion engine 10. Air is sucked into the cylinder 11 of the internal combustion engine 10 through the intake passage 12. As the internal combustion engine 10, a diesel engine having a plurality of (four [# 1, # 2, # 3, # 4] in this embodiment) cylinders 11 is employed. The internal combustion engine 10 is provided with a direct injection type fuel injection valve 20 that directly injects fuel into the cylinder 11 for each cylinder 11 (# 1 to # 4). The fuel injected by opening the fuel injection valve 20 is ignited and burned in contact with the intake air compressed and heated in the cylinder 11 of the internal combustion engine 10. In the internal combustion engine 10, the piston 13 is pushed down by the energy generated by the combustion of fuel in the cylinder 11, and the crankshaft 14 is forcibly rotated. The combustion gas combusted in the cylinder 11 of the internal combustion engine 10 is discharged as exhaust gas into the exhaust passage 15 of the internal combustion engine 10.

  Each fuel injection valve 20 is individually connected to a common rail 34 via a branch passage 31a. The common rail 34 is connected to the fuel tank 32 through a supply passage 31b. A fuel pump 33 that pumps fuel is provided in the supply passage 31b. In the present embodiment, the fuel whose pressure has been increased by pumping by the fuel pump 33 is stored in the common rail 34 as a pressure accumulating container and is supplied to the inside of each fuel injection valve 20. In this embodiment, each fuel injection valve 20, the branch passage 31a, the supply passage 31b, the fuel pump 33, and the common rail 34 function as a fuel supply system.

  A return passage 35 is connected to each fuel injection valve 20. The return passages 35 are each connected to the fuel tank 32. A part of the fuel inside the fuel injection valve 20 is returned to the fuel tank 32 through the return passage 35.

Hereinafter, the internal structure of the fuel injection valve 20 will be described.
As shown in FIG. 2, a needle valve 22 is provided inside the housing 21 of the fuel injection valve 20. The needle valve 22 is provided in a state capable of reciprocating in the housing 21 (moving up and down in the figure). Inside the housing 21 is provided a spring 24 that constantly urges the needle valve 22 toward the injection hole 23 (the lower side in the figure). In addition, a nozzle chamber 25 is formed in the housing 21 at a position on one side (lower side in the figure) with the needle valve 22 interposed therebetween, and at a position on the other side (upper side in the figure). A pressure chamber 26 is formed.

  The nozzle chamber 25 is formed with an injection hole 23 that communicates the inside with the outside of the housing 21, and fuel is supplied from the branch passage 31 a (common rail 34) through the introduction passage 27. The pressure chamber 26 is connected to the nozzle chamber 25 and the branch passage 31a (common rail 34) via a communication passage 28. The pressure chamber 26 is connected to a return passage 35 (fuel tank 32) via a discharge passage 30.

  As the fuel injection valve 20, an electrically driven type is adopted. Specifically, a piezoelectric actuator 29 in which a piezoelectric element (for example, a piezoelectric element) that expands and contracts by input of a drive pulse (a valve opening signal or a valve closing signal) is provided inside the housing 21 of the fuel injection valve 20. A valve body 29 a is attached to the piezoelectric actuator 29. The valve body 29 a is provided inside the pressure chamber 26. Then, through the movement of the valve element 29 a by the operation of the piezoelectric actuator 29, one of the communication path 28 (nozzle chamber 25) and the discharge path 30 (return path 35) is selectively communicated with the pressure chamber 26. It has become.

  In the fuel injection valve 20, when a valve closing signal is input to the piezoelectric actuator 29, the piezoelectric actuator 29 contracts and the valve body 29 a moves, so that the communication path 28 and the pressure chamber 26 communicate with each other. At the same time, the communication between the return passage 35 and the pressure chamber 26 is blocked. Thereby, the nozzle chamber 25 and the pressure chamber 26 are communicated with each other in a state where the discharge of the fuel in the pressure chamber 26 to the return passage 35 (fuel tank 32) is prohibited. As a result, the pressure difference between the nozzle chamber 25 and the pressure chamber 26 becomes very small, and the needle valve 22 moves to a position where it closes the injection hole 23 by the urging force of the spring 24. Is not injected (valve closed state).

  On the other hand, when a valve opening signal is input to the piezoelectric actuator 29, the piezoelectric actuator 29 extends and the valve body 29a moves, whereby the communication between the communication passage 28 and the pressure chamber 26 is blocked. The return passage 35 and the pressure chamber 26 are in communication with each other. As a result, part of the fuel in the pressure chamber 26 is returned to the fuel tank 32 via the return passage 35 in a state in which the outflow of fuel from the nozzle chamber 25 to the pressure chamber 26 is prohibited. As a result, the pressure of the fuel in the pressure chamber 26 decreases and the pressure difference between the pressure chamber 26 and the nozzle chamber 25 increases, and the needle valve 22 moves against the biasing force of the spring 24 due to the pressure difference. In order to leave the injection hole 23, the fuel injection valve 20 is in a state where the fuel is injected (opened state) at this time.

  A pressure sensor 51 for detecting the fuel pressure PQ inside the introduction passage 27 is integrally attached to the fuel injection valve 20. For this reason, for example, the fuel in a portion near the injection hole 23 of the fuel injection valve 20 as compared with a device that detects the fuel pressure at a position away from the fuel injection valve 20 such as the fuel pressure in the common rail 34 (see FIG. 1). The pressure can be detected, and the change in the fuel pressure inside the fuel injection valve 20 accompanying the opening of the fuel injection valve 20 can be detected with high accuracy. One pressure sensor 51 is provided for each fuel injection valve 20, that is, for each cylinder 11 (# 1 to # 4) of the internal combustion engine 10.

  As shown in FIG. 1, the internal combustion engine 10 is provided with various sensors as peripheral devices for detecting an operation state. As these sensors, in addition to the pressure sensor 51, for example, an intake air amount sensor 52 for detecting the amount of air passing through the intake passage 12 (passage air amount GA), the rotational speed of the crankshaft 14 (engine rotational speed NE). ) Is provided. In addition, an accelerator sensor 54 for detecting an operation amount (accelerator operation amount ACC) of an accelerator operation member (for example, an accelerator pedal) is also provided.

  Moreover, as a peripheral device of the internal combustion engine 10, an electronic control unit 40 configured with an arithmetic processing unit is also provided. The electronic control unit 40 takes in the output signals of various sensors and performs various calculations based on the output signals, and controls the operation of the fuel injection valve 20 (injection amount control) and the operation of the fuel pump 33 based on the calculation results. Various controls related to the operation of the internal combustion engine 10 such as control (injection pressure control) are executed.

  In the present embodiment, the injection pressure control is executed as follows. That is, first, a control target value (target injection pressure) for the fuel pressure in the common rail 34 is calculated based on the passage air amount GA and the engine rotational speed NE, and the fuel is set so that the actual fuel pressure becomes the target injection pressure. The operation amount (fuel pressure feed amount or fuel return amount) of the pump 33 is adjusted. Through the adjustment of the operation amount of the fuel pump 33, the fuel pressure in the common rail 34, in other words, the fuel injection pressure of the fuel injection valve 20 is adjusted to a pressure corresponding to the engine operating state.

  In the present embodiment, the injection amount control is basically executed as follows. That is, first, based on the operation state of the internal combustion engine 10 (specifically, the accelerator operation amount ACC and the engine speed NE), a control target value (target fuel injection amount TQ) for the fuel injection amount is calculated and injected. A pattern is selected. Thereafter, based on the target fuel injection amount TQ and the engine speed NE, various control target values for each injection of the injection pattern selected at this time are calculated. Then, each fuel injection valve 20 is driven to open individually according to these control target values. Thus, an amount of fuel corresponding to the operation state is injected from each fuel injection valve 20 in an injection pattern suitable for the operation state of the internal combustion engine 10 at that time so as to be supplied into each cylinder 11 of the internal combustion engine 10. Become.

  In the present embodiment, a plurality of injection patterns obtained by combining pilot injection and after injection with main injection are set in advance, and these injection patterns are stored in the electronic control unit 40. When executing the injection amount control, one of these injection patterns is selected. Various control target values include control target values (target injection amounts) for the fuel injection amount of each injection such as main injection, pilot injection, and after injection, main injection start timing, interval between pilot injections, pilot injection A control target value for each injection execution time such as an interval between the main injection and the main injection is calculated.

  Then, for each stage of fuel injection in the multi-stage injection, a control target value (target injection period TAU) for the valve opening period of the fuel injection valve 20 is set from a model formula based on the target injection amount and the fuel pressure PQ. . In this embodiment, a physical model that models a fuel supply system including the common rail 34, each branch passage 31a, each fuel injection valve 20, and the like is constructed, and the target injection period TAU is calculated through the physical model. Specifically, a model expression having variables such as a target injection amount and a fuel pressure PQ, which will be described later, a learning term, an initial adjustment term, a difference correction term, and the like are determined and stored in advance in the electronic control unit 40. Through this, the target injection period TAU is calculated.

  A drive pulse is output from the electronic control unit 40 in accordance with the control target value of the execution timing and the target injection period TAU for each stage of fuel injection in the multi-stage injection, and each fuel injection is based on the input of this drive pulse. The valves 20 are driven to open individually. As a result, an amount of fuel commensurate with the engine operating state at that time is injected from each fuel injection valve 20 in an injection pattern suitable for the engine operating state and supplied into each cylinder 11 of the internal combustion engine 10. The rotational torque commensurate with the engine operating state is applied to the crankshaft 14. As described above, in the present embodiment, when fuel is injected from the fuel injection valve 20 in one combustion cycle, multistage injection is performed in which fuel injection is performed in a plurality of times.

  In the present embodiment, a learning process for learning a plurality of characteristic parameters regarding the operating characteristics of the fuel injection valve 20 based on the fuel pressure PQ detected by the pressure sensor 51 is executed. The learning process is executed on condition that an execution condition for determining that the operating state of the internal combustion engine 10 is a stable state with little change is satisfied. Whether or not the execution condition is satisfied is determined by a small change amount of the engine rotational speed NE per unit period or a small change amount of the accelerator operation amount ACC per unit period.

FIG. 3 shows an example of characteristic parameters learned by the learning process.
As shown in FIG. 3, in the present embodiment, the valve opening delay time τd, the injection rate increasing speed Qup, the maximum injection rate Qmax, the valve closing delay time τe, and the injection rate decreasing rate Qdn are adopted as the characteristic parameters. Specifically, the valve opening delay time τd is from the time when the electronic control unit 40 outputs the valve opening signal (FIG. 3A) to the fuel injector 20 until the fuel injection from the fuel injector 20 is actually started. The injection rate increasing speed Qup is the increasing speed of the fuel injection rate (FIG. 3B) after the opening operation of the fuel injection valve 20 is started. Further, the maximum injection rate Qmax is the maximum value of the fuel injection rate, and the valve closing delay time τe is the closing operation of the fuel injection valve 20 after the valve closing signal is output from the electronic control unit 40 to the fuel injection valve 20 ( Specifically, this is the time until the needle valve 22 starts to move toward the valve closing side. Further, the injection rate decrease rate Qdn is a rate at which the fuel injection rate decreases after the valve closing operation of the fuel injection valve 20 is started.

In the learning process, first, a time waveform (detection time waveform) of the actual fuel injection rate is formed based on the fuel pressure PQ detected by the pressure sensor 51.
The fuel pressure inside the fuel injection valve 20 (specifically, the nozzle chamber 25) decreases as the lift amount increases when the fuel injection valve 20 is driven to open, and then lifts when the valve is driven to close. As the amount decreases, it increases. In the present embodiment, the valve opening delay time τd, the injection rate increasing speed Qup, the maximum injection rate Qmax, and the valve closing delay are based on the transition of the fuel pressure inside the fuel injection valve 20 (specifically, the fuel pressure PQ). The time τe and the injection rate decrease speed Qdn are specified. And the time waveform (detection time waveform) of an actual fuel injection rate is formed by those specified values. The time waveform of the fuel pressure PQ is a waveform formed on the basis of values smoothed by using a low-pass filter or corrected by the fuel pressure PQ detected by the pressure sensor 51 corresponding to the non-injection cylinder. Is used.

FIG. 4 shows the relationship between the time waveform of the fuel pressure PQ and the detection time waveform of the fuel injection rate.
As shown in FIG. 4, in detail, first, an average value of the fuel pressure PQ (FIG. 4 (c)) in a predetermined period T1 immediately before the opening operation of the fuel injection valve 20 is started is calculated, and the same average is calculated. The value is stored as the reference pressure Pbs. The reference pressure Pbs is used as a pressure corresponding to the fuel pressure inside the fuel injection valve 20 when the valve is closed.

  Next, a value obtained by subtracting the predetermined pressure P1 from the reference pressure Pbs is calculated as the operating pressure Pac (= Pbse−P1). The predetermined pressure P1 corresponds to the change in the fuel pressure PQ, that is, the movement of the needle valve 22 even when the needle valve 22 is in the closed position when the fuel injection valve 20 is driven to open or close. This is a pressure corresponding to a change in the fuel pressure PQ that does not contribute.

  Thereafter, in a period in which the fuel pressure PQ drops immediately after the start of fuel injection execution, a straight line L1 in which the difference from the fuel pressure PQ becomes the smallest (in FIG. 4, the vertical axis of orthogonal coordinates is the fuel injection rate and the horizontal axis is time Is obtained using the least square method, and an intersection A between the straight line L1 and the operating pressure Pac is calculated. The timing corresponding to the point AA where the intersection A is returned to the past timing by the detection delay of the fuel pressure PQ is the timing when the fuel injection by the fuel injection valve 20 is started (injection start timing Tos, FIG. )). The detection delay is a period corresponding to the delay of the change timing of the fuel pressure PQ with respect to the pressure change timing of the nozzle chamber 25 (see FIG. 2) of the fuel injection valve 20, and the distance between the nozzle chamber 25 and the pressure sensor 51. This is a delay caused by the above. In the present embodiment, the time from the timing when the valve opening signal (FIG. 4A) is output from the electronic control unit 40 to the fuel injection valve 20 to the injection start timing Tos is specified as the valve opening delay time τd.

  Further, in the rising period in which the fuel pressure PQ once rises after the fuel injection is started, the straight line L2 in which the difference from the fuel pressure PQ becomes the smallest (in FIG. 4, the vertical axis of the orthogonal coordinates is the fuel injection rate. (A linear function with time on the horizontal axis) (FIG. 4B) is obtained using the least square method, and an intersection B between the straight line L2 and the operating pressure Pac is calculated. Then, the timing corresponding to the point BB where the intersection B is returned to the past timing by the detection delay is specified as the timing when the fuel injection by the fuel injection valve 20 is stopped (injection stop timing Tce).

  Furthermore, an intersection C between the straight line L1 and the straight line L2 is calculated, and a difference between the fuel pressure PQ and the operating pressure Pac at the intersection C (virtual pressure drop ΔP [= Pac−PQ]) is obtained. Further, a value obtained by multiplying the virtual pressure drop ΔP by a gain G1 set based on the target injection amount and the target injection pressure is calculated as a virtual maximum fuel injection rate VRt (= ΔP × G1). Further, a value obtained by multiplying the virtual maximum fuel injection rate VRt by a gain G2 set based on the target injection amount and the target injection pressure is calculated as a maximum injection rate Qmax (= VRt × G2). In the present embodiment, values set at the time of detection by the pressure sensor 51 of the fuel pressure PQ used for forming the detection time waveform are adopted as the target injection amount and the target injection pressure used for setting the gains G1 and G2. The

Thereafter, a time CC at which the intersection C is returned to the past time by the detection delay is calculated, and a point D that becomes the virtual maximum fuel injection rate VRt in the simultaneous CC is specified.
And the time corresponding to this point D is specified as the time (valve closing start time Tcs) when the valve closing operation of the fuel injection valve 20 is started. In the present embodiment, the time from the timing when the valve closing signal is output from the electronic control unit 40 to the fuel injection valve 20 to the valve closing start timing Tcs is specified as the valve closing delay time τe.

  Further, a straight line L3 connecting the point D and the injection start timing Tos (specifically, the point at which the fuel injection rate becomes “0” at the same time Tos) is obtained, and the slope (specifically, the unit L3) The amount of increase in fuel injection rate per hour) is specified as the injection rate increase speed Qup.

  Further, a straight line L4 connecting the point D and the injection stop timing Tce (specifically, the point at which the fuel injection rate becomes “0” at the same time Tce) is obtained, and the slope of the straight line L4 (specifically, unit time) The amount of decrease in the fuel injection rate per hit) is specified as the injection rate decrease rate Qdn.

  In the present embodiment, a trapezoidal time waveform formed by the valve opening delay time τd, the injection rate increasing speed Qup, the maximum injection rate Qmax, the injection rate decreasing speed Qdn, and the valve closing delay time τe thus specified. Is used as a detection time waveform for the fuel injection rate. In the present embodiment, the valve opening delay time τd, the injection rate increasing speed Qup, the maximum injection rate Qmax, the injection rate decreasing speed Qdn, and the valve closing delay time τe correspond to the characteristic parameters of the operating characteristics of the fuel injection valve 20. To do.

  On the other hand, in the learning process of the present embodiment, a basic time waveform for the fuel injection rate is calculated based on various calculation parameters such as a target injection amount, a control target value for execution timing, a target injection pressure, and the like. In the present embodiment, the relationship between the engine operation region determined by these calculation parameters and the basic time waveform suitable for the operation region is obtained in advance based on the results of various experiments and simulations and stored in the electronic control unit 40. Then, the electronic control unit 40 calculates a basic time waveform from the above relationship based on various calculation parameters.

  FIG. 5 shows an example of the basic time waveform. As shown in FIGS. 5A and 5B, the basic time waveforms include valve opening delay time τdb, injection rate increasing speed Qupb, maximum injection rate Qmaxb, valve closing delay time τeb, and injection rate decreasing speed Qdnb. A trapezoidal waveform defined by is set.

  In the learning process of the present embodiment, learning terms for a plurality of characteristic parameters of the fuel injection valve 20 are learned based on the relationship between the detected time waveform and the basic time waveform. That is, first, during the operation of the internal combustion engine 10, the detected time waveform and the basic time waveform are compared, and the difference between the characteristic parameters of those waveforms is sequentially calculated. Specifically, the difference between the characteristic parameters includes a difference Δτd (= τdb−τd) in the valve opening delay time, a difference ΔQup (= Qupb−Qup) in the injection rate increase speed, and a difference ΔQmax (= Qmaxb in the maximum injection rate). -Qmax), a difference ΔQdn (= Qdnb−Qdn) in the injection rate reduction speed, and a difference Δτe (= τeb−τe) in the valve closing delay time. Then, the weighted average values of these differences Δτd, ΔQup, ΔQmax, ΔQdn, Δτe are calculated, and the weighted average values compensate the learning terms Gτd, GQup, GQmax, It is stored in the electronic control unit 40 as GQdn and Gτe.

  The variation of the detected value of the pressure sensor 51 that accompanies the opening and closing of the fuel injection valve 20 is caused by a change over time in the components of the fuel supply system (such as deposit adhesion to the injection hole 23 of the fuel injection valve 20). In addition to the gradual change over time, it also changes in the short term due to the influence of various factors such as noise superimposed on the detection signal and fuel properties (temperature, properties).

  In the present embodiment, in order to suppress unnecessary changes in the learning terms Gτd, GQup, GQmax, GQdn, and Gτe due to such short-term changes in the detected value fluctuation mode, the differences Δτd, ΔQup, Weighted average values of ΔQmax, ΔQdn, and Δτe are calculated and stored as learning terms.

  In the apparatus according to the present embodiment, a plurality of learning areas defined by the fuel injection pressure (specifically, target injection pressure) and the fuel injection amount (specifically, target injection quantity) are defined. Learning terms are learned and stored.

  As shown in FIG. 6, the electronic control unit 40 stores a map that stores the relationship between the target injection amount, the target injection pressure, and each learning term in the learning region where the target injection amount is small. This map is learned and updated based on the fluctuation mode of the fuel pressure PQ at the time of execution of pilot injection (specifically, its leading stage injection). In this embodiment, when calculating the target injection period TAU for pilot injection, main injection (when the target injection amount is small), and after injection, the target injection amount and target injection pressure of the fuel injection to be calculated Each learning term is calculated from the map shown in FIG.

  As shown in FIG. 7, the electronic control unit 40 stores a map that stores the relationship between the target injection amount, the target injection pressure, and each learning term in a learning region where the target injection amount is relatively large. This map is learned and updated based on the fluctuation mode of the fuel pressure PQ when the main injection is executed in a situation where the target injection amount is relatively large. When calculating the target injection period TAU of the main injection (when the target injection amount is relatively large), each learning term is calculated from the map shown in FIG. 7 based on the target injection amount and the target injection pressure of the main injection. Is calculated.

  Further, in the present embodiment, before the change in operating characteristics over time is detected, the difference between the above characteristic parameters between the so-called new fuel injection valve 20 and the standard operating characteristic fuel injection valve is detected. These differences are stored in advance in the electronic control unit 40 as initial adjustment terms for compensating for variations in operating characteristics caused by individual differences in the fuel injection valves 20. Specifically, the initial adjustment terms Sτd, SQup, SQmax, SQdn, and Sτe include a difference Δτd in the valve opening delay time, a difference in injection rate increase ΔQup, a difference in maximum injection rate ΔQmax, and a rate of decrease in injection rate when new. Difference ΔQdn and valve closing delay time difference Δτe are stored. In the apparatus of this embodiment, the differences Δτd, ΔQup, ΔQmax, ΔQdn, and Δτe are detected with the fuel injection valve 20 attached to a dedicated device, and the calculation result is the internal combustion engine of the fuel injection valve 20. 10 is stored in the electronic control unit 40 at the time of assembly.

  The pressure fluctuation in the fuel supply system at the time of executing the second and subsequent fuel injections in the multi-stage injection includes a pulsation of the fuel pressure generated by the preceding fuel injection (pre-stage injection). The pulsation of the fuel pressure is not constant, and varies depending on the interval between injections, the fuel injection pressure, the fuel injection amount of the preceding injection, and the like. Therefore, if learning of the learning term is executed without considering the fuel pressure pulsation associated with the preceding injection, an unnecessary change in the time waveform of the fuel pressure PQ or the detection time waveform is caused in the detection process. This contributes to a decrease in term learning accuracy.

  In this embodiment, in order to suppress a decrease in the learning accuracy of such learning terms, when forming the detection time waveform for the second and subsequent stages of injection, the time waveform of the fuel pressure PQ that is the basis thereof is changed to the previous stage injection. A process of superimposing a pressure time waveform (correction waveform) that can cancel the accompanying pressure pulsation is executed. Through this process, the influence of the fuel pressure pulsation associated with the pre-injection is removed from the detection time waveform, an appropriate value is detected as the difference between the parameters, and an appropriate value is learned as the learning value. .

  The correction waveform is based on the injection pattern of the combustion cycle including the fuel injection to be corrected, the target injection amount of each injection, the interval between the injections, and the target injection pressure. Each is calculated. Based on the results of various experiments and simulations, the relationship between the injection pattern, the target injection amount for each injection, the interval between each injection, the target injection pressure, and the correction waveform suitable for each injection after the second stage of multistage injection It is obtained in advance and stored in the electronic control unit 40. In the present embodiment, a correction waveform for the second and subsequent injections of the multi-stage injection is calculated and used based on this relationship.

  Even if the correction waveform is superimposed on the time waveform of the fuel pressure PQ, it is difficult to remove all of the fuel pressure pulsation associated with the pre-injection, so an injection amount error due to the fuel pressure pulsation remains. In the present embodiment, difference correction terms Kτd, KQup, KQmax, KQdn, and Kτe for correcting such an error are calculated. That is, first, the differences Δτd, ΔQup, ΔQmax, ΔQdn, Δτe of the above-described parameters for the fuel injection subject to calculation of the difference correction term are detected, and the learning term reflected in calculating the target injection period TAU of the fuel injection. Gτd, GQup, GQmax, GQdn, and Gτe are read. Then, the difference between the above parameters and the difference between the learning terms (= Δτd−Gτd, ΔQup−GQup, ΔQmax−GQmax, ΔQdn−GQdn, Δτe−Gτe) are calculated, and these differences are calculated as the difference correction terms Kτd, KQup. , KQmax, KQdn, Kτe are temporarily stored. Note that the process of calculating the difference correction term in this way is executed separately for the second and subsequent fuel injections in the multi-stage injection.

  In this embodiment, the learning terms Gτd, GQup, GQmax, GQdn, Gτe, the initial adjustment terms Sτd, SQup, SQmax, SQdn, Sτe, and the difference correction terms Kτd, KQup, KQmax, KQdn, Kτe are described above. It is used as a calculation parameter for calculating the target injection period TAU based on the model formula. By calculating the target injection period TAU for each stage of fuel injection in the multi-stage injection in this manner, the influence of the variation in operating characteristics due to the change of the fuel injection valve 20 over time, and the influence of the fluctuation in operating characteristics due to individual differences. And the influence due to the fuel pressure pulsation accompanying the pre-injection are respectively compensated. The difference correction terms Kτd, KQup, KQmax, KQdn, Kτe are reflected in the model equation when calculating the target injection period TAU of the fuel injection in the combustion cycle subsequent to the combustion cycle including the fuel injection to be calculated. . In the present embodiment, the process for calculating the learning term and the process for calculating the difference correction term based on the fuel pressure PQ are performed by the pressure sensor 51 corresponding to each cylinder 11 (# 1 to # 4) of the internal combustion engine 10. It is executed based on the output signal.

  Here, in the first stage injection in the multistage injection, since the execution timing of the immediately preceding fuel injection is far, the influence of the fuel pressure pulsation accompanying the fuel injection is very small. On the other hand, in the second and subsequent injections in the multi-stage injection, the execution timing of the immediately preceding fuel injection (previous injection) is very close, so the influence of fuel pressure pulsation accompanying the fuel injection is large.

  For this reason, for example, the difference correction term is simply calculated based on calculating the difference correction term based on the fuel pressure PQ at the time of executing the main injection and reflecting the difference correction term when calculating the target injection period TAU of the main injection immediately after. When applied to the target injection stage, it may not be possible to appropriately remove the influence of fuel pressure pulsation associated with the previous stage injection. Specifically, when the number of injection stages of multi-stage injection is reduced due to changes in engine operating conditions, etc., the influence of the fuel pressure pulsation is large despite the fact that the influence of the fuel pressure pulsation is very small. The target injection period TAU may be calculated based on a difference correction term calculated based on the second and subsequent fuel injections. In addition, when the number of injection stages of multi-stage injection increases, the difference correction term is not calculated even though the injection is in the second and subsequent stages where the influence of fuel pressure pulsation due to the previous stage injection is large. The term may not be reflected when calculating the target injection period TAU. In such a case, there is a high possibility that the injection amount error due to the influence of the pressure pulsation cannot be appropriately suppressed.

  In this embodiment, the difference correction term is not calculated in association with the injection position, such as a correction term corresponding to the main injection, a correction term corresponding to the pilot injection executed immediately before the main injection, or the like. It is calculated as a value related to the injection order such as a correction term corresponding to the first-stage injection of the multi-stage injection and a correction term corresponding to the second-stage injection.

  FIG. 8 shows an execution procedure of a process for calculating a difference correction term (correction term calculation process). This correction term calculation process is executed by the electronic control unit 40 every time fuel injection after the second stage in the multistage injection is executed.

  As shown in FIG. 8, in this process, first, when calculating the differences Δτd, ΔQup, ΔQmax, ΔQdn, Δτe, it is specified which stage of the multistage injection the fuel injection to be calculated is. (Step S11). Then, the differences Δτd, ΔQup, ΔQmax, ΔQdn, Δτe calculated at this time and the differences between the learning terms Gτd, GQup, GQmax, GQdn, Gτe applied to the fuel injection to be calculated are the same. The calculated value is stored as a difference correction term corresponding to the injection stage specified in the process of step S11 (step S12). By executing such processing separately for the second and subsequent fuel injections in the multi-stage injection, the difference correction terms Kτd, KQup, KQmax, KQdn, and Kτe for the second and subsequent fuel injections are calculated for each. .

FIG. 9 shows the relationship between the injection stage of multi-stage injection and the difference correction term.
As shown in FIG. 9, through the execution of the correction term calculation process, a value calculated based on the second stage injection is stored as a difference correction term K2 corresponding to the second stage injection, and the third stage injection is performed. The originally calculated value is stored as a difference correction term K3 corresponding to the third stage injection. Also, the value calculated based on the fourth stage injection is stored as a difference correction term K4 corresponding to the fourth stage injection, and the value calculated based on the fifth stage injection is stored in the fifth stage injection. It is stored as the corresponding difference correction term K5. Thus, when “N” is a natural number, a value calculated based on the (N + 1) th stage fuel injection is stored as a difference correction term K (N + 1) corresponding to the (N + 1) th stage fuel injection. The Note that an initial value (“0” in the present embodiment) is set as a difference correction term corresponding to an injection stage that has not been executed in multistage injection.

Hereinafter, the operation of calculating the difference correction term in this way will be described.
In the present embodiment, the difference correction term is calculated in association with the injection position such as a correction term corresponding to the main injection or a correction term corresponding to the pilot injection executed immediately before the main injection. Rather, the difference correction term K2 corresponding to the second-stage injection and the difference correction term K3 corresponding to the third-stage injection are calculated in association with the injection order.

In FIG. 10, the reflection pattern of the difference correction term to each stage of multistage injection is shown.
As shown in FIG. 10, when two-stage injection consisting of one-stage pilot injection and main injection is executed in a combustion cycle (reflection combustion cycle) including fuel injection to be reflected in the difference correction term, The difference correction term K2 corresponding to the eye injection is reflected in the main injection. In addition, when the three-stage injection including the first-stage pilot injection, the main injection, and the after injection is executed, the difference correction term K2 is reflected in the main injection, and the after-injection corresponds to the third-stage fuel injection. The difference correction term K3 to be reflected is reflected. Further, when the three-stage injection including the second-stage pilot injection and the main injection is executed, the difference correction term K2 is reflected in the second-stage pilot injection, and the difference correction term K3 is reflected in the main injection. Is done. When four-stage injection including two-stage pilot injection, main injection, and after injection is executed, the difference correction term K2 is reflected in the second stage pilot injection, and the difference correction term K3 is reflected in the main injection. The difference correction term K4 corresponding to the fourth-stage fuel injection is reflected in the after injection. When five-stage injection including three-stage pilot injection, main injection, and after injection is executed, the difference correction term K2 is reflected in the second-stage pilot injection, and the difference correction term is added to the third-stage pilot injection. K3 is reflected, the difference correction term K4 is reflected in the main injection, and the difference correction term K5 corresponding to the fifth fuel injection is reflected in the after injection. Thus, in the apparatus of the present embodiment, the difference correction term is reflected according to the injection order of the multistage injection.

  Therefore, even if the number of injection stages of the multistage injection changes between the combustion cycle including the fuel injection subject to calculation of the difference correction term (calculated combustion cycle) and the reflected combustion cycle, the difference correction term calculated in association with the injection order is used. Based on this, fuel injection in the second and subsequent stages of the reflected combustion cycle is executed.

  FIG. 11 shows an example of how the difference correction term is reflected when the number of injection stages in the reflected combustion cycle decreases with respect to the number of injection stages in the calculated combustion cycle. In the example shown in FIG. 11, in the calculated combustion cycle, three-stage fuel injection consisting of two-stage pilot injection and main injection is executed. Therefore, the difference correction term K2 corresponding to the second-stage injection is calculated based on the second-stage pilot injection in the calculated combustion cycle, and the difference correction term K3 corresponding to the third-stage injection is calculated based on the main injection. . In this example, two-stage fuel injection consisting of one-stage pilot injection and main injection is executed in the reflected combustion cycle. Therefore, the difference correction term K2 is reflected when calculating the target injection period TAU for the main injection in the reflection combustion cycle. As described above, in this example, the difference correction term K2 calculated based on the pilot injection (second stage injection) immediately before the main injection in the calculated combustion cycle is used as the pilot injection (first stage injection) immediately before the main injection in the reflected combustion cycle. Is not reflected, but is reflected in the main injection (second-stage injection). That is, the number of injection stages of the multistage injection changes from three to two, but the second stage injection of the reflected combustion cycle (in this example, the third stage in the calculated combustion cycle) based on the difference correction term K2 corresponding to the second stage injection. Main injection corresponding to eye injection) is performed.

  As is clear from the example shown in FIG. 11, according to the present embodiment, when the number of injection stages of multi-stage injection is reduced, based on the injections after the second stage that are greatly affected by the pulsation of the fuel pressure caused by the previous stage injection. It is avoided that the calculated difference correction terms (K2, K3...) Are applied to the leading stage injection having almost no such influence.

  FIG. 12 shows an example of how the difference correction term is reflected when the number of injection stages in the reflected combustion cycle increases with respect to the number of injection stages in the calculated combustion cycle. In the example shown in FIG. 12, two-stage fuel injection consisting of one-stage pilot injection and main injection is executed in the calculated combustion cycle. Therefore, the difference correction term K2 corresponding to the second stage injection is calculated based on the main injection in the calculated combustion cycle. In this example, in the reflected combustion cycle, three-stage fuel injection including two-stage pilot injection and main injection is executed. Therefore, the difference correction term K2 is reflected when calculating the target injection period TAU for the second stage pilot injection of the reflected combustion cycle, and the difference correction term K3 is reflected when calculating the target injection period TAU of the main injection. . In this example, since the third stage injection is not executed in the calculated combustion cycle, an initial value is set as the difference correction term K3. Therefore, in this example, although the difference correction term corresponding to the pilot injection immediately before the main injection in the calculated combustion cycle (first stage injection) is not calculated, the pilot injection immediately before the main injection in the reflected combustion cycle (second stage injection) The difference correction term K2 calculated based on the main injection (second stage injection) in the calculated combustion cycle is reflected.

  As is clear from the example shown in FIG. 12, according to the present embodiment, when the number of injection stages of multi-stage injection is increased, the second stage injection (in some cases, which is greatly influenced by the pulsation of the fuel pressure caused by the previous stage injection) It is avoided that the difference correction term is not reflected in (including the third stage injection).

  As described above, according to the present embodiment, even when the number of injection stages changes between the calculated combustion cycle and the reflected combustion cycle, the fuel injection of each stage is performed in accordance with the presence or absence of the preceding stage injection when executing the multistage injection. The difference correction term can be appropriately reflected, and an injection amount error in fuel injection at each stage can be suitably suppressed.

  Here, when the interval between the injections of the multi-stage injection changes, the fuel pressure pulsation resulting from the fuel injection on the front stage side (N stage) reaches the execution period of the fuel injection on the rear stage side ([N + 1] stage). Since the timing of the change also changes, the influence of the fuel pressure pulsation on the fuel injection on the rear stage is also different. Such an interval change occurs when the engine operating range is determined by the accelerator operation amount ACC, the engine rotational speed NE, the intake air amount, etc., and the exhaust gas temperature needs to be raised in order to maintain the function of the exhaust purification device. It also occurs due to changes in the engine operating environment, such as changes in various demands as the cooling water temperature rises.

  Moreover, when the target injection pressure or the target injection amount changes with the change of the engine operating state and the learning region is switched, the learning term reflected in the calculation of the target injection period TAU changes, so that it is caused by the pre-stage injection. The pulsation mode of the generated fuel pressure also changes. In a situation where the target injection pressure and the target injection amount change greatly, the pulsation mode of the fuel pressure caused by the pre-stage injection also changes greatly.

  Therefore, when the interval or learning region changes between the calculated combustion cycle and the reflected combustion cycle, the difference correction term calculated in the calculated combustion cycle is reflected in the calculation of the target injection period TAU in the reflected combustion cycle. The difference correction term becomes an inappropriate value that does not match the actual condition, which may increase the injection amount error. Therefore, in this embodiment, when the interval between injections and the learning region are different between the calculated combustion cycle and the reflected combustion cycle, the difference correction term is reset to the initial value, and then the target injection period TAU of the reflected combustion cycle is set. The calculation is executed.

  Hereinafter, a calculation process including a process for resetting such a difference correction term to an initial value, and a process for reflecting the difference correction term when calculating the target injection period TAU in each stage of the multi-stage injection (correction term reflection process) will be described in detail. To do.

  FIG. 13 shows an execution procedure of the correction term reflection process. The series of processes shown in the flowchart of FIG. 6 is executed by the electronic control unit 40 as an interrupt process at predetermined intervals. This correction term reflection process is a process that forms part of the process of calculating the target injection period TAU, and is executed each time the calculation of the target injection period TAU of each stage in the multi-stage injection is executed.

  As shown in FIG. 13, in this process, first, the interval (specifically, the control target value) between the injection stage (N + 1 stage) to which the difference correction term is reflected and the immediately preceding injection stage (N stage) is determined. It is determined whether the calculated combustion cycle is different from the reflected combustion cycle (step S21).

  If the intervals are the same (step S21: NO), whether or not the learning region for the injection stage (N + 1 stage) for calculation of the target injection period TAU is different between the calculated combustion cycle and the reflected combustion cycle. Determination is made (step S22).

  If the learning regions are the same (step S22: NO), the difference correction term K (N + 1) corresponding to the (N + 1) -th stage fuel injection stored at this time, that is, the calculated combustion cycle is calculated. The difference correction term K (N + 1) thus made is reflected in the calculation of the target injection period TAU for the fuel injection at the (N + 1) -th stage (step S23).

  On the other hand, if the interval is different between the calculated combustion cycle and the reflected combustion cycle (step S21: YES), or if the learning region is different (step S22: YES), it is stored at this time (N + 1). ) The difference correction term K (N + 1) corresponding to the stage fuel injection is reset to the initial value (step S24). The reset difference correction term K (N + 1) is reflected in the calculation of the target injection period TAU of the (N + 1) -th stage fuel injection (step S23).

Hereinafter, the operation of reflecting the difference correction term in this way will be described.
In the present embodiment, when the interval between the (N) th stage injection and the (N + 1) th stage injection in the multistage injection is different between the calculated combustion cycle and the reflected combustion cycle, the (N + 1) th stage in the calculated combustion cycle. The difference correction term K (N + 1) calculated as a value corresponding to the eye injection is reset to the initial value. Then, calculation of the target injection period TAU in the reflected combustion cycle is executed. For this reason, when the reliability of the difference correction term K (N + 1) decreases with the change in the interval, the difference correction term K (N + 1) can be reset to the initial value. It is possible to avoid that the difference correction term K (N + 1) that is highly likely to disappear is reflected in the fuel injection on the rear stage side ([N + 1] stage).

  Also, when the learning region for the (N) -th stage fuel injection in the multi-stage injection differs between the calculated combustion cycle and the reflected combustion cycle, it is calculated as a value corresponding to the (N + 1) -th stage injection in the calculated combustion cycle. The calculated difference correction term K (N + 1) is reset to the initial value, and then the target injection period TAU in the reflected combustion cycle is calculated. Therefore, when the operation state of the internal combustion engine 10 (specifically, the target injection pressure or the target injection amount) changes to the extent that the learning region is switched, the difference is reduced when the reliability of the difference correction term K (N + 1) is reduced. The correction term K (N + 1) can be reset to the initial value. As a result, it is possible to avoid that the difference correction term K (N + 1), which is likely to be no longer a value in accordance with the actual condition, is reflected in the fuel injection on the rear stage side ([N + 1] stage).

  FIG. 14 shows an example of a reset mode for such a difference correction term. In the example shown in FIG. 14, three-stage fuel injection including two-stage pilot injection and main injection is executed in both the calculated combustion cycle and the reflected combustion cycle. Therefore, the difference correction term K2 corresponding to the second-stage injection is calculated based on the second-stage pilot injection in the calculated combustion cycle, and the difference correction term K3 corresponding to the third-stage injection is calculated based on the main injection. . In this example, the interval between the first stage of pilot injection (first stage injection) and the second stage of pilot injection (second stage injection) or the second stage of the pilot injection between the calculated combustion cycle and the reflected combustion cycle. The interval between (second stage injection) and main injection (third stage injection) changes. Therefore, in the reflected combustion cycle, the difference correction terms K2 and K3 corresponding to the fuel injection (second-stage injection and third-stage injection) on the rear stage of these intervals are reset to the initial values, and then the target of each injection stage This is reflected in the calculation of the injection period TAU.

  By resetting the initial value of the difference correction term in this way, for example, a negative value is reflected where a positive value should be reflected as the difference correction value. It is avoided that it is reflected when calculating the period TAU. Therefore, according to the present embodiment, the reliability of the difference correction term calculated in the calculated combustion cycle is reduced in accordance with the change in the interval between the injections, the change in the learning region, the change in the target injection pressure and the target injection amount. Even in this case, an increase in the injection amount error due to this can be suppressed.

  Hereinafter, specific examples of the learning term update mode and the difference correction term calculation mode will be described with reference to FIG. FIG. 15 shows an example of the transition of the learning term and the difference correction term reflected in the main injection in the reflected combustion cycle.

  Prior to time t11 in the example shown in FIG. 15, the difference correction terms for the second and subsequent injections of the multi-stage injection are calculated in the calculated combustion cycle. At this time, since the execution condition is not satisfied, learning of the learning value is not executed, and the learning value reflected in the main injection is a constant value. The difference correction term and the learned value are reflected in the calculation of the target injection period TAU of the main injection in the reflection combustion cycle.

  When the interval between the main injection and its pre-stage injection changes with the change in the engine operating environment at time t11, the target of the main injection in the reflected combustion cycle until the interval becomes constant thereafter (time t11 to t12). Each time the calculation of the injection period TAU is executed, the difference correction term reflected in the main injection is reset to the initial value prior to the calculation.

  When the interval between the main injection and its pre-stage injection becomes constant at time t12, the difference correction term calculated in the calculated combustion cycle is not reset and is reflected in the calculation of the target injection period TAU of the main injection in the reflected combustion cycle. Become so. Thereafter, the calculation of the difference correction term based on the time waveform of the fuel pressure PQ at the time of main injection execution and the reflection of the difference correction term to the main injection are repeatedly executed (time t12 to t13). At this time, the difference correction term reflected in the main injection gradually changes according to slight changes in the engine operating region and the engine operating environment.

  When the execution condition is satisfied at time t13, learning of the learning term is started. As a result, the learning term gradually changes so that the difference between the parameters becomes “0” thereafter, and the difference correction term gradually changes to the initial value in accordance with this change. At this time, the learning term is learned in such a manner that the correction amount corrected by the difference correction term so far is transferred to the learning term.

  By repeating such learning of the learning term, at time t14, the learning term converges to a constant value, and the difference correction term converges to the initial value (0). Then, when learning of the learning value is continued thereafter, the learning value remains unchanged for a while and the difference correction term remains unchanged as the initial value.

When the execution condition is not satisfied at time t15, learning of the learning value is stopped. Thereafter, the difference correction term reflected in the main injection gradually changes.
As described above, according to the present embodiment, the following effects can be obtained.

  (1) The difference correction term is not calculated in association with the injection position, but is calculated as a value associated with the injection order. Therefore, when performing the multi-stage injection, the difference correction term can be appropriately reflected in the fuel injection of each stage in accordance with the presence or absence of the previous stage injection, and the injection amount error in the fuel injection of each stage can be suitably suppressed. it can.

  (2) When the interval between the (N) th stage injection and the (N + 1) th stage injection in the multistage injection differs between the calculated combustion cycle and the reflected combustion cycle, the (N + 1) th stage in the calculated combustion cycle The difference correction term K (N + 1) calculated as a value corresponding to injection is reset to the initial value. In addition, calculation of the target injection period TAU in the reflection combustion cycle is executed. Therefore, it is possible to avoid that the difference correction term K (N + 1) which is highly likely to be no longer a value in accordance with the actual situation is reflected in the fuel injection on the rear stage ([N + 1] stage). Therefore, even when the reliability of the difference correction term calculated in the calculated combustion cycle is reduced with a change in the interval between injections, an increase in the injection amount error due to this can be suppressed.

  (3) When the learning region for the (N) -th stage fuel injection in the multi-stage injection differs between the calculated combustion cycle and the reflected combustion cycle, as a value corresponding to the (N + 1) -th stage injection in the calculated combustion cycle The calculated difference correction term K (N + 1) is reset to the initial value, and the target injection period TAU in the reflected combustion cycle is calculated. Therefore, it is possible to avoid that the difference correction term K (N + 1) which is highly likely to be no longer a value in accordance with the actual situation is reflected in the fuel injection on the rear stage ([N + 1] stage). Therefore, even if the reliability of the difference correction term calculated in the calculated combustion cycle is reduced due to changes in the learning region, target injection pressure, and target injection amount, an increase in injection amount error due to this is suppressed. Can do.

The above embodiment may be modified as follows.
The initial value of the difference correction term is not limited to “0”, and an arbitrary value can be set.
In the learning process, the difference itself is stored as learning terms Gτd, GQup, GQmax, GQdn, and Gτe without calculating the weighted average values of the differences Δτd, ΔQup, ΔQmax, ΔQdn, and Δτe of the plurality of characteristic parameters. It may be.

  -As a parameter which divides a learning field, not only using target injection pressure and target injection quantity, but arbitrary values can be used. As the parameter, for example, only one of the target injection pressure and the target injection amount can be used, or the engine rotational speed NE, the passage air amount GA, the accelerator operation amount ACC, the intake air amount, or the like can be used.

  ・ Learning and reflecting learning terms, storing and reflecting initial adjustment terms, calculating and reflecting correction waveforms, omitting any two, or omitting all Also good.

  When the interval between the (N) th stage injection and the (N + 1) th stage injection in the multistage injection differs between the calculated combustion cycle and the reflected combustion cycle, the fuel injections after the (N + 1) th stage in the multistage injection The difference correction terms [K (N + 1), K (N + 2)...] Corresponding to can be reset. In addition, it is also possible to reset all the difference correction terms when the intervals are different. According to the apparatus, when the influence of the fuel pressure pulsation accompanying the N-th stage fuel injection reaches the difference correction term [K (N + 2)...] Corresponding to the fuel injection after the (N + 2) -th stage, It is avoided that the difference correction term [K (N + 2)...], Which is likely to be no longer a value in accordance with the change of the interval, is reflected in the fuel injection after the (N + 2) stage. it can.

  In the above embodiment, when the interval between the (N) th stage injection and the (N + 1) th stage injection in the multistage injection is different between the calculated combustion cycle and the reflected combustion cycle, the difference correction term K (N + 1) Was reset. Instead, the difference correction term K (N + 1) may be reset when the difference between the intervals between the calculated combustion cycle and the reflected combustion cycle is equal to or greater than a predetermined value. If the influence on the difference correction term due to the change in the interval is very small, the difference correction term K (N + 1) should be reset even if the interval is slightly different between the calculated combustion cycle and the reflected combustion cycle. Instead, it may be reflected in the calculation of the target injection period TAU.

  The difference correction term corresponding to the fuel injection after the (N + 1) -th stage in the multi-stage injection when the learning region for the (N) -th stage fuel injection in the multi-stage injection differs between the calculated combustion cycle and the reflected combustion cycle. [K (N + 1), K (N + 2)...] May be reset. In addition, it is possible to reset all the difference correction terms when the learning regions are different. According to such an apparatus, when the influence of the fuel pressure pulsation associated with the N-th stage fuel injection reaches the difference correction term [K (N + 2)...] Corresponding to the (N + 2) -th stage and subsequent fuel injections, The difference correction term [K (N + 2)...] That is likely not to be a value in accordance with the actual state due to the change in the learning region is reflected in the fuel injection after the (N + 2) stage. Can be avoided.

  In the above embodiment, the difference correction term K (N + 1) is reset to the initial value when the learning region for the (N) -th stage fuel injection in the multi-stage injection differs between the calculated combustion cycle and the reflected combustion cycle. I did it. As a condition for resetting the difference correction term K (N + 1) to the initial value, a condition that the operation region of the internal combustion engine 10 has changed can be set. As such conditions, for example, a condition such as “the difference in target injection amount between the calculated combustion cycle and the reflected combustion cycle is not less than a predetermined value” or a “target between the calculated combustion cycle and the reflected combustion cycle is set. For example, the condition that the difference in the injection pressures is equal to or greater than a predetermined value can be set.

One of the processing in step S21 and the processing in step S22 of the correction term reflection processing (FIG. 13) may be omitted.
The characteristic parameter of the operating characteristic of the fuel injection valve 20 can be arbitrarily changed. For example, only one of the valve opening delay time τd, the injection rate increasing speed Qup, the maximum injection rate Qmax, the injection rate decreasing speed Qdn, and the valve closing delay time τe is used as a characteristic parameter, or only two are used as characteristic parameters. Or only three of them can be used as characteristic parameters, or only four of them can be used as characteristic parameters. In addition, the time when the fuel injection rate reaches the maximum injection rate, the time when the fuel injection rate starts to decrease from the maximum injection rate, the time when the fuel injection rate becomes “0”, and the like can be newly adopted as characteristic parameters. .

  If the pressure that is an index of the fuel pressure inside the fuel injection valve 20 (specifically, in the nozzle chamber 25), in other words, the fuel pressure that changes with the change in the fuel pressure can be properly detected. The pressure sensor 51 is not limited to being directly attached to the fuel injection valve 20, and the manner of attaching the pressure sensor 51 can be arbitrarily changed. Specifically, the pressure sensor 51 may be attached to a portion (branch passage 31 a) between the common rail 34 and the fuel injection valve 20 in the fuel supply passage, or may be attached to the common rail 34.

  Instead of the type of fuel injection valve 20 driven by the piezoelectric actuator 29, a type of fuel injection valve driven by an electromagnetic actuator having a solenoid coil or the like may be employed.

  The fuel injection control device can be applied not only to an internal combustion engine having four cylinders but also to an internal combustion engine having one to three cylinders, or an internal combustion engine having five or more cylinders.

  The fuel injection control device can be applied not only to a diesel engine but also to a gasoline engine using gasoline fuel and a natural gas engine using natural gas fuel.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder, 12 ... Intake passage, 13 ... Piston, 14 ... Crankshaft, 15 ... Exhaust passage, 20 ... Fuel injection valve, 21 ... Housing, 22 ... Needle valve, 23 ... Injection hole, 24 ... Spring, 25 ... Nozzle chamber, 26 ... Pressure chamber, 27 ... Introduction passage, 28 ... Communication passage, 29 ... Piezoelectric actuator, 29a ... Valve element, 30 ... Discharge passage, 31a ... Branch passage, 31b ... Supply passage, 32 ... Fuel Tank, 33 ... fuel pump, 34 ... common rail, 35 ... return passage, 40 ... electronic control unit, 51 ... pressure sensor, 52 ... intake air amount sensor, 53 ... crank sensor, 54 ... accelerator sensor.

Claims (5)

The fuel injection system is applied to an internal combustion engine having a fuel supply system that supplies fuel in a pressurized state to a fuel injection valve and a pressure sensor that detects fuel pressure inside the fuel supply system. In a fuel injection control device that performs fuel injection from the fuel injection valve in a single combustion cycle by performing multi-stage injection,
The device is
For each of the second and subsequent injections of the multi-stage injection, separately detecting a characteristic parameter of an operating characteristic of the fuel injection valve based on a variation of fuel pressure detected by the pressure sensor at the time of execution of fuel injection ,
When the natural number is “N”, a correction term for correcting the influence of the fuel pressure pulsation associated with the previous stage injection on the second and subsequent stages of the multistage injection is based on the (N + 1) th stage injection in the multistage injection. in the (N + 1) value corresponding to the stage of injection, calculated separately on the basis of the detected characteristic parameter,
In the fuel injection valve operation control, the (N + 1) -th stage injection in the multi-stage injection is executed based on a correction term calculated as a value corresponding to the (N + 1) -th stage injection. apparatus. The fuel injection control device according to claim 1,
The apparatus wherein the multiple injection (N) and stage injection in a reflection combustion cycle including a pre-Symbol reflecting target fuel injection calculation combustion cycle and the correction terms including the fuel injection calculation target correction term (N + 1 ) when the interval between the stage of injection are different, after resetting at the calculated combustion cycle (N + 1) correction term is calculated as a value corresponding to the stage of the injection to the initial value, the reflected combustion cycle A fuel injection control device for controlling the operation of the fuel injection valve in the above. The fuel injection control device according to claim 1 or 2,
The device is
For each of a plurality of learning regions partitioned by the operating state of the internal combustion engine, a learning process for learning a characteristic parameter of an operating characteristic of the fuel injection valve based on a fuel pressure fluctuation mode detected by the pressure sensor is executed. , The learning term learned in the learning process is reflected in each injection of the multi-stage injection,
Learning region for morphism injection of (N) th stage in the multistage injection are different between the reflection combustion cycle including a pre-Symbol reflecting target fuel injection calculation combustion cycle and the correction terms including the fuel injection calculation target correction term Occasionally, after having reset in the calculated combustion cycle (N + 1) correction term is calculated as a value corresponding to the stage of the injection to the initial value, executes the operation control of the fuel injection valve in the reflected combustion cycle A fuel injection control device. The fuel injection control device according to claim 3, wherein
The fuel injection control device characterized in that the operation state is a fuel injection amount. The fuel injection control device according to claim 3 or 4,
The fuel injection control device characterized in that the operating state is a fuel injection pressure.