JP2005171931A - Fuel injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device preventing overlap of injection due to close injection of pre-injection and post-injection in a device performing multi-injection. <P>SOLUTION: This device is provided with an injector 2 injecting fuel to each cylinder and a control means 10 controlling the injector 2 according to operation state of an internal combustion engine 1, performs multiple times of injection to a cylinder during a combustion stroke of the internal combustion engine 1. The control means 10 is provided with specific operation state detection means S201, S202 detecting operation in an operation range performing close injection of pre-injection Q<SB>P</SB>performing injection before and post-injection Q<SB>M</SB>performing injection after pre-injection Q<SB>P</SB>in a plurality of injection, a state estimation means estimating combustion state or injection state of the internal combustion engine 1, and a determination means S205 monitoring combustion state and injection state by a condition estimation means determining a limit injection interval INTmin based on a predetermined change value under a combustion state or injection state changing according to injection interval INT between the pre-injection and post-injection . <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel injection control device.

  2. Description of the Related Art Conventionally, a pressure accumulation type fuel injection device that supplies high pressure fuel accumulated in a common rail as a pressure accumulation chamber from a injector to a diesel engine is known. In recent years, in this type of accumulator fuel injection system, so-called multi-injection, in which fuel is injected in multiple times during one combustion stroke, has been put into practical use due to the social demands for exhaust gas regulations and combustion noise reduction. Yes.

  The injection interval (interval) INT (see FIG. 8) between the injection and the post-injection is set without taking close proximity in consideration of variations in injector opening and closing responsiveness, changes over time, and the like. There was enough room. In addition, the injection interval INT is set to a predetermined constant value as an optimum value obtained in advance through experiments or the like.

  In recent years, since there is a further effect on exhaust gas and the like in a specific operation region, it is required to make the injection interval (interval) INT between the pre-injection and the post-injection closer.

  However, the prior art is easily affected by variations in injector opening and closing responsiveness due to machine differences and deterioration over time by making the injection interval INT close (see FIG. 8). If the injection interval INT is too close, an injection abnormality due to the overlap of the pre-injection and the post-injection is caused. In some cases, abnormal combustion may cause abnormal combustion, such as deterioration of exhaust gas, due to abnormal injection.

  The present invention has been made in view of such circumstances, and in the case of injection divided into a plurality of times during one combustion stroke, the overlap of injection due to proximity injection between the front injection and the rear injection is prevented. For the purpose.

  Another object is to provide a fuel injection control device capable of preventing abnormal combustion due to injection overlap or the like regardless of the difference in injectors provided for each cylinder of the internal combustion engine or deterioration with time.

  According to the first aspect of the present invention, the fuel cell includes an injector that injects fuel into the combustion chamber of each cylinder of the internal combustion engine, and a control unit that controls the injector in accordance with the operating state of the internal combustion engine. In a fuel injection control apparatus that performs a plurality of injections during a combustion stroke, the control means closely approaches a pre-injection that performs the injection first and a post-injection that performs the injection after the pre-injection. The specific operating state detecting means for detecting that the internal combustion engine is operated in the operating region to be injected, the state estimating means for estimating the combustion state or the injection state of the internal combustion engine, and the state estimating means determine the combustion state or the injection state. Determining means for monitoring and determining a limit injection interval based on a predetermined change amount in the combustion state or the injection state that changes in accordance with the size of the injection interval between the pre-injection and the post-injection. It is characterized in.

  According to this, when it is detected by the specific operating state detection means that the internal combustion engine is operated in the operation region where the pre-injection and the post-injection are in close proximity, the state estimation means for detecting the combustion state or the injection state of the internal combustion engine While monitoring the combustion state or the injection state, when the change in the combustion state or the injection state that changes according to the size of the injection interval reaches a predetermined change amount, it is possible to determine the limit injection interval by the determining means. Therefore, the control means for controlling the injector can prevent overlapping of injections when the fuel is injected in a plurality of times during one combustion stroke. For example, it is possible to learn the limit injection interval for preventing injection overlap each time an operation condition (operation region) for close injection is detected by the specific operation state detection means.

  It should be noted that the above-described limit injection interval refers to the valve closing command value and the post-injection of the pre-injection in which the two injections can be closest to each other without overlapping the pre-injection and the post-injection into one injection (overlapping injection). This is the interval at which the period from the valve opening command value is minimum.

  According to the second aspect of the present invention, the estimation of the combustion state or the injection state by the state estimating means includes the pre-injection including the rotational speed fluctuation of the internal combustion engine, the exhaust temperature, the in-cylinder pressure in the combustion chamber of the cylinder, and the excess air ratio. It is estimated based on the behavior influence value of the internal combustion engine by the post-injection.

  According to this, as a method for estimating the combustion state or the injection state, the behavior of the internal combustion engine by the pre-injection and the post-injection including the rotational speed fluctuation of the internal combustion engine, the exhaust temperature, the in-cylinder pressure in the combustion chamber of the cylinder, and the excess air ratio Influence values can be used.

  According to claim 3 of the present invention, the determination means monitors at least one of the four pieces of information and determines a change boundary point of the behavior influence value when the injection interval is reduced or expanded by the control of the injector. It is characterized by.

  According to this, at least one of the above four pieces of information (rotational speed fluctuation of the internal combustion engine, exhaust temperature, in-cylinder pressure in the combustion chamber of the cylinder, and excess air ratio) is monitored, and the injection interval is reduced or expanded. Since the change boundary point of the behavior influence value at the time is discriminated, the limit injection interval can be reliably determined from the behavior influence value that changes when the injection abnormality or the combustion abnormality occurs due to the proximity of the injection interval.

  According to claim 4 of the present invention, when the limit injection interval is compared with the optimum target injection interval corresponding to the operating state of the internal combustion engine calculated by the control means, and the target injection interval is smaller than the limit injection interval, It has a correction means for replacing the injection interval with a limit injection interval.

  According to this, the limit injection interval actually detected by the determination means is compared with the optimum target injection interval according to the operation state calculated by the control means, and when the target injection interval is smaller than the limit injection interval, Since the target injection interval is replaced with the limit injection interval, it can be replaced and updated with the learning-corrected limit injection interval, so that it is possible to prevent abnormal combustion due to overlap of injections, etc., regardless of the machine difference of the injector and deterioration over time.

  According to claim 5 of the present invention, it is preferable that the limit injection interval is a value obtained by multiplying the limit injection interval determined by the determining means by a margin coefficient or adding a margin amount.

  According to this, it is possible to further prevent injection overlap by using a value obtained by performing multiplication correction or addition correction in consideration of margin (safety) in the limit injection interval detected by the determination means.

  According to claim 6 of the present invention, it is preferable that the operation region detected by the specific operation state detection means is in an idle stable state.

  According to this, as an operation region where the limit injection interval is actually detected, it is in an idle stable state, so that there is no load demand without the driver's output request, or the vehicle is stopped without the driver's vehicle travel request, etc. It is possible to ensure a stable operation state.

  According to claim 7 of the present invention, the specific operation state detection means has operation condition setting means capable of setting the operation state in which the pre-injection and the post-injection are in close proximity by controlling the injector. And

  According to this, in the so-called search mode for actually detecting the limit injection interval, for example, the injection interval is reduced or expanded in distinction from the so-called normal mode in which the control means controls the injector according to the internal combustion engine. Becomes easy.

  Hereinafter, embodiments in which the fuel injection control device of the present invention is applied to an accumulator fuel injection control device will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram showing the overall configuration of the fuel injection system of the present embodiment. FIG. 2 is a flowchart showing a control process for learning a limit injection interval for performing close injection of the front injection and the rear injection in the ECU shown in FIG. FIG. 3 is a flowchart showing a part of the normal mode when the proximity injection is actually performed in the ECU shown in FIG. FIG. 4 is a graph for explaining the operation of the fuel injection control device of this embodiment.

  As shown in FIG. 1, an accumulator fuel injection control device includes an operation state or an operation condition of a multi-cylinder (for example, four-cylinder) diesel engine (hereinafter referred to as an engine) 1 mounted on a vehicle such as an automobile. The driving state of the vehicle and the operation amount (will) of the driver are detected by various sensors, and are transmitted to an engine control unit (engine control unit) (hereinafter referred to as ECU) 10 to be optimal by sensor signals from the various sensors. Multiple target injection amounts (command injection amounts), target injection timings (command injection timings), target injection periods (command injection periods) and target injection pressures (command injection pressures), which are controlled respectively. 4) injectors (electromagnetic fuel injection valves) 2, high pressure supply pump (fuel supply pump) (hereinafter referred to as supply pump) 3, etc. It has been made.

  The engine 1 is a four-cycle four-cylinder engine that includes a cylinder, a cylinder head, an oil pan, and the like. The intake port of each cylinder of the engine 1 is opened and closed by an intake valve (intake valve) 11, and the exhaust port is opened and closed by an exhaust valve (exhaust valve) 12. In each cylinder, a piston 14 connected to the crankshaft 13 via a connecting rod is slidably disposed.

  The injector 2 is attached to the cylinder head of the engine 1 corresponding to each cylinder. These injectors 2 include a fuel injection nozzle in which a nozzle needle for opening and closing the injection hole is slidably accommodated in a nozzle body in which the injection hole is formed, and an electromagnetic valve (needle drive means, Solenoid actuator) and needle biasing means such as a spring for biasing the nozzle needle in the valve closing direction.

  The fuel injection from the injector 2 to the engine 1 energizes and energizes a solenoid valve (not shown) that controls the fuel pressure in the back pressure control chamber (pressure control chamber) of the command piston connected to the nozzle needle. Electronically controlled by stopping (ON / OFF). While the solenoid valve of the injector 2 of each cylinder is open, the high-pressure fuel accumulated in the common rail 17 as the pressure accumulation chamber is injected into the combustion chamber of each cylinder of the engine 1. In addition, the fuel leaked from the internal leak of the injector 2 or the fuel discharged from the pressure control chamber (the fuel used to open the injector 2) is returned to the fuel tank 15 via the return pipe 33.

  The supply pump 3 is a high-pressure supply pump that pressurizes sucked fuel and pumps high-pressure fuel from the discharge port to the common rail 17, and includes a feed pump (low-pressure supply pump) 6 that pumps fuel from the fuel tank 15. The fuel path from the feed pump 6 to the pressurization chamber of the supply pump 3 is adjusted by adjusting the degree of opening of the fuel path (valve opening or opening area) so that the amount of fuel discharged from the supply pump 3 to the common rail 17 ( A suction metering valve (linear solenoid actuator) 7 is attached as an electromagnetic actuator for changing the pump discharge amount and the pump pumping amount.

  The intake metering valve 7 is electronically controlled by a pump drive signal from the ECU 10 via a pump drive circuit (not shown), thereby adjusting the amount of fuel sucked from the feed pump 6 into the pressurized chamber of the supply pump 3. A fuel injection pressure (hereinafter referred to as a common rail pressure) supplied from each injector 2 into each cylinder of the engine 1 is changed. The supply pump 3 sucks fuel from the fuel tank 15 and pressurizes it, and pumps the fuel discharge amount commanded by the ECU 10 to the common rail 17. The common rail pressure in the common rail 17 is measured by a fuel pressure sensor 18 as a fuel pressure detecting means, and a pump drive command value (pump drive current value) and an injection amount command value (pulsed injector drive current, injector injection command pulse). ) Is calculated by the ECU 10.

  The common rail 17 continuously supplies high-pressure fuel corresponding to the fuel injection pressure, and high-pressure fuel stored in the common rail 17 is supplied from the support pump 3 via a supply pipe (hereinafter referred to as high-pressure pipe) 20. The A return pipe 21 for returning fuel from the common rail 17 to the fuel tank 15 is provided. The common rail 17 is provided with a normally closed pressure reducing valve 22 that can adjust the degree of opening of the return pipe 21. The pressure reducing valve 22 is electronically controlled by a pressure reducing valve driving current value applied from the ECU 10 via a pressure reducing valve driving circuit, so that the common rail pressure in the common rail 17 is quickly reduced from a high pressure to a low pressure, for example, when decelerating or when the engine is stopped. It has a function to reduce pressure. Instead of the pressure reducing valve 22, a pressure limiter for releasing the fuel pressure in the common rail 17 between the common rail 17 and the return pipe 21 so that the common rail pressure in the common rail 17 does not exceed the limit set pressure. May be attached.

  Here, the injector 2, the supply pump 3 and the common rail 17 constitute fuel injection means for supplying fuel to the engine 1.

  The ECU 10 includes a CPU for performing control processing and arithmetic processing, a storage device (memory such as ROM and RAM) for storing various programs and data, an input circuit, an output circuit, a power supply circuit, an injector drive circuit, a pump drive circuit, and the like. A microcomputer having a known structure configured to include functions is provided. The detection signal (voltage signal) output from the fuel pressure sensor 18, the detection signal output from the fuel temperature sensor 34, and the sensor signals from other various sensors are A / D converted by the A / D converter. Later, it is configured to be input to a microcomputer built in the ECU 10. Further, when the engine key is set to the IG position and an ignition switch (not shown) is turned on (ON), the ECU 10 controls, for example, the solenoid valve of the injector 2 and the suction metering of the supply pump 3 based on the control program stored in the memory. The actuator of each control component such as the valve 7, the actuator 40 that drives the throttle valve 39, and the EGR valve 42 that adjusts the exhaust gas recirculation amount (EGR amount) is electronically controlled.

  The ECU 10 receives the crankshaft rotation pulse and the camshaft rotation pulse from the crank angle sensor 4 attached to the crankshaft (crankshaft) 13 and the cam angle sensor 5 attached to the camshaft (camshaft) 23. The actual fuel pressure in the common rail 17 (actual common rail pressure) is held at the command injection pressure by determining the injection timing of the injector 2 and the pumping period of the supply pump 3 for each cylinder based on the signal. The crank angle sensor 4 includes a magnetic timing rotor (signal rotor) 24 fixed to the crankshaft 13 of the engine 1, an electromagnetic pickup coil disposed so as to face the peripheral surface of the timing rotor 24, and a magnetic flux. It is an electromagnetic rotation sensor composed of a permanent magnet (magnet) to be generated, and detects the rotation angle of the crankshaft 13. The ECU 10 detects the engine rotation speed (NE) by measuring the interval time of the crank angle signal (NE pulse signal). A plurality of convex teeth are formed on the timing rotor 24 at predetermined angles (for example, 10 °). When the timing rotor 24 rotates, the convex teeth approach and move away from the electromagnetic pickup coil, so that a crank angle signal (NE pulse signal) is output from the electromagnetic pickup coil by electromagnetic induction. The cam angle sensor 5 includes a magnetic timing rotor (signal rotor) 27 fixed to the cam shaft 23 of the engine 1, an electromagnetic pickup coil disposed so as to face the peripheral surface of the timing rotor 27, and An electromagnetic rotation sensor composed of a permanent magnet (magnet) or the like that generates magnetic flux, and detects the rotation angle of the cam shaft 23. In the timing rotor 27, a plurality of convex teeth are arranged for each predetermined angle.

  Further, the ECU 10 receives sensor signals from an accelerator opening sensor 30 that measures the amount of depression of the accelerator pedal (accelerator operation amount, accelerator opening), a cooling water temperature sensor 31 that detects the cooling water temperature of the engine 1, and the like. It is configured. Then, the ECU 10 calculates an optimal command injection pressure (= target fuel pressure: PFIN) according to the operating conditions of the engine 1, and discharges the intake metering valve 7 of the supply pump 3 via the pump drive circuit. It has a control means. Specifically, the ECU 10 calculates the target fuel pressure (PFIN) according to the engine speed (NE) and the command injection amount (QFIN), and in order to achieve the target fuel pressure (PFIN), The pump drive signal (pump drive current value) to the suction metering valve 7 of the supply pump 3 is adjusted to control the pumping amount (pump discharge amount) of fuel discharged from the supply pump 3.

  Further, the ECU 10 has a function of individually controlling the fuel injection amount injected from the injector 2 of each cylinder. Specifically, the ECU 10 includes basic injection amount determining means, command injection amount determining means, injection timing determining means, injection period determining means, and injector driving means. The basic injection amount determination means has a function of calculating an optimum basic injection amount (Q) based on the engine speed (NE), the accelerator opening (ACCP), and a characteristic map created by measurement in advance through experiments or the like. The command injection amount determination means takes into account the cooling water temperature (THW) detected by the cooling water temperature sensor 31 or the fuel leak temperature (fuel temperature: THF) detected by the fuel temperature sensor 34 in the basic injection amount (Q). It has a function of calculating the command injection amount (QFIN) in consideration of the injection amount correction amount. The injection timing determining means has a function of calculating a command injection timing (TFIN) from a command injection amount (QFIN), an engine rotation speed (NE), and a characteristic map created by measurement in advance through experiments or the like. The injection period determining means calculates the common pulse pressure (NPC), the command injection amount (QFIN), and the energization pulse time (injection command pulse time: TQ) to the injector 2 from the characteristic map created by measurement in advance through experiments or the like. Have The injector drive means applies a pulsed injector drive current (injector injection command pulse) to the solenoid valve of the injector 2 of each cylinder until the injection command pulse time (TQ) elapses from the command injection timing (TFIN). It has the function to do.

Here, the accumulator type fuel injection control device is in one cycle of the combustion cycle of the engine 1 (intake stroke-compression stroke-expansion stroke (explosion stroke) -exhaust stroke) for each injector 2 of each cylinder of the engine 1 (hereinafter referred to as the following). Multi-stage injection (multi-injection), in which fuel is injected in a plurality of times within one injection stroke while the crankshaft 13 of the engine 1 rotates twice (720 ° CA). It is configured to be possible. Incidentally, details, in addition to the normal injection mode of only the main injection Q _{M (see} FIG. 8) in the one-time injection stroke, one minute injection (pilot injection) prior to main injection Q _M performs Q _P pilot injection mode, is a multi-injection mode to be implemented (after injection form) is configured to perform a plurality of times a minute injection after multiple multi-injection mode or the main injection Q _M for performing a minute injection before and after the main injection Q _M Yes.

  Therefore, ECU10 is comprised so that the injection form may be determined according to the driving | running state of the engine 1. FIG. More specifically, an injection mode determining means for determining an optimal injection mode based on an engine speed (NE), an accelerator opening (ACCP), and a characteristic map (not shown) created by measurement in advance through experiments or the like is provided.

  In the following description of multi-stage injection, the injection mode will be described as a pilot injection mode (see FIG. 4).

  The ECU 10 includes multi-stage injection calculating means for calculating the pilot injection amount and the main injection amount in accordance with the operating state of the engine 1 when performing multi-stage injection. More specifically, the ECU 10 performs pilot injection from the engine rotation speed (NE) and the target injection amount QFIN) and a characteristic map (not shown) created by measurement in advance when performing the pilot injection mode. Means is provided for obtaining the main injection amount QM by obtaining the amount QP and subtracting the pilot injection amount QP from the target injection amount QFIN).

Further, ECU 10 is carrying out the multi-stage injection, the fuel between the main injection Q _M as later injection according to the operating condition of the engine 1, for injecting thereafter a pilot injection Q _P as before injection for injecting previously Interval calculation means for calculating an injection interval (interval) INT is provided. More specifically, the ECU 10 performs pilot injection from the engine rotation speed (NE) and the target injection amount QFIN) and a characteristic map (not shown) created by measurement in advance when performing the pilot injection mode. means for determining Q _P and injection interval INT between the main injection Q _M, in the practice of multi-injection mode, characteristics created by measuring by experiment such as the engine rotational speed (NE) and the target injection amount QFIN) and map means for determining the injection interval of the pilot injection Q _P is injected a plurality of times from a (not shown), in carrying out after-injection mode, the engine rotational speed (NE) and the target injection amount QFIN) in advance experimentally or the like Means for determining an injection interval of after-injection multiple times from a characteristic map (not shown) created by measurement.

  For the purpose of improving the control accuracy of the fuel injection amount, the common rail pressure (NPC) in the common rail 17 detected by the fuel pressure sensor 18 is a target fuel pressure (PFIN) set according to the operating state of the engine 1. It is preferable to perform feedback control of the pump drive current value to the supply pump 3 so as to substantially match. The pump drive current value to the intake metering valve 7 is preferably controlled by duty (DUTY) control. For example, by adjusting the pump drive signal ON / OFF ratio (energization time ratio, duty ratio) per unit time according to the deviation (ΔP) between the common rail pressure (NPC) and the target fuel pressure (PFIN) High-precision digital control is possible by using duty control that changes the valve opening of the quantity 7.

  Next, the injection control method of the present embodiment having the above-described configuration will be described with reference to FIGS. 2, 3, and 4.

  As shown in FIG. 2, in S201 (S is a step) and S203, it is determined whether or not it is in an operation state in which a pilot injection mode which is a learning precondition is performed. If the learning precondition is satisfied, the limit injection interval INTmin at which close injection is possible without overlap of injection is obtained for each cylinder according to the learning condition in accordance with the control processing from S204 to S207.

  Specifically, in S201, (1) First, whether or not the combustion state of the engine 1 is in an idle stable state based on signals from various sensors and switches that detect the operating state of the engine 1 or the engine 1 attached to the vehicle. Confirm. If it is not in the idling stable state, as shown in FIG. 2, the process proceeds to S202 to determine the normal mode, and the control process is terminated. Conversely, if it is in the idle stable state, the process proceeds to S203. The various sensors and switches that can detect the operating state of the engine 1 include a gear position, a clutch, a starter, a fuel pressure sensor 18, a crank angle sensor 4, an accelerator opening sensor, an idle accelerator position sensor 40, an exhaust temperature sensor, and the like. is there.

(2) Next, a range determined in advance so that signals from various sensors capable of detecting environmental conditions attached to the engine 1 or the vehicle can be in a specific operation state in the operation region assumed as the operation state of the engine 1. Check if it is inside. Various sensors that can detect environmental conditions include a fuel temperature sensor 34, an idle accelerator position sensor 40, an intake air amount sensor 44, an intake air temperature sensor 45, an O ₂ sensor 37, an exhaust gas temperature sensor, and the like.

  (3) Next, it is confirmed that the engine load is within a predetermined range by signals from various sensors, switches, and control command values that can detect the load state of the engine 1 or the engine 1 attached to the vehicle. Examples of these include electric fans for radiators, electric heaters, hydrides, electromagnetic brakes and other switches that can detect electric loads, sensors, air conditioners, compressors such as power steering, switches that can detect pump loads, sensors and idle speed There is a change amount or a change amount of the ISC injection amount necessary for maintaining the idle rotation speed at a predetermined value.

  (4) Finally, it is confirmed that the injection amount command value, the ISC correction amount, the fuel injection pressure, the injection timing command value, etc., which indicate that the engine speed is stable, are within a predetermined range.

  If all of the above (1) to (4) are satisfied and it is not an implementation prohibition condition specified separately, it is determined that the learning precondition is satisfied, and the process proceeds to S203.

In S203, as a learning execution condition, a condition for experimentally operating a specific operation region within a predetermined range for obtaining the limit injection interval INTmin is set. Specifically, pilot injection Q _P , main injection Q _M , injection interval INT, and the like for controlling the injector 2 to perform learning control are set, and injector drive pulses TQP, TQM, and interval TINT for controlling the injector 2 therefrom. Set various control command values.

  In S204, an experimental operation is performed in a direction to artificially reduce the injection interval INT for each cylinder. For example, first, an experimental operation is performed in a direction in which the injection interval INT is artificially reduced from the first cylinder (hereinafter referred to as # 1 cylinder).

  In S205, a change in the combustion state of the engine that is influenced by the degree of reduction (proximity) of the injection interval INT is monitored using the engine speed fluctuation ΔNE as an engine operating characteristic representing the combustion state of the engine 1, and a predetermined threshold value is obtained. It is determined whether or not S1 (see FIG. 4) or less.

Here, the engine rotational speed fluctuation ΔNE represents the influence of the behavior of the engine 1 due to the pre-injection (pilot injection Q _P ) and the post-injection (main injection Q _M ). Here, as shown in FIG. 4, the main main injection Q clogging injection interval INT of the pilot injection Q _P is away enough to _M is relatively large injection mode for forming a torque of the engine 1, the injection interval Regardless of the expansion / contraction of INT, the engine speed fluctuation ΔNE is substantially constant. In contrast, in the injection mode to the pilot injection Q _P overlaps the main injection Q _M, for small injection quantity QP of the pilot injection Q _P contributes injection amount to the torque applied to the main injection amount QM is increased rapidly, the In such an abnormal injection mode, the combustion state of the engine 1 becomes unstable (abnormal), and the engine speed fluctuation ΔNE increases. Even injection mode process to close the injection interval INT which lies between these two injection mode, the more you shrink, approaching the same combustion condition as the injection mode to the pilot injection Q _P overlaps the main injection Q _M Therefore, as shown in FIG. 4, there is a change boundary point at which the change in the engine rotation speed fluctuation ΔNE characteristic changes suddenly. For this reason, the limit injection interval INTmin is determined by using a predetermined threshold value S1 set to exceed the predetermined change amount ΔS with respect to the change boundary point. Accordingly, the limit injection interval INTmin can be set as a limit injection interval INTmin immediately before the engine speed fluctuation ΔNE characteristic shown in FIG. 4 changes suddenly, and the limit injection interval INTmin can be set as a guard value for preventing overlapping of injections. Here, the engine rotation speed fluctuation ΔNE represents the influence of the behavior of the engine 1 by the pre-injection (pilot injection Q _P ) and the post-injection (main injection Q _M ). In addition, the limit injection interval INTmin means that the front injection and the rear injection overlap each other, and the two injections can be closest to each other without overlapping one injection (overlapping injection). This is the interval at which the period from the valve opening command value is minimized.

  If the monitored engine speed fluctuation ΔNE is greater than or equal to the predetermined threshold value S1 with respect to the reduced injection interval INT, the process proceeds to S206, and the limit injection interval INTmim # 1 of the # 1 cylinder is set to INTmin (INTmim). # 1 = INTmin). Conversely, when the engine speed fluctuation ΔNE to be monitored is equal to or smaller than the predetermined threshold value S1, the process returns to S204 to further reduce the injection interval INT.

  In S207, it is determined whether or not the limit injection interval INTmin of all the cylinders of the engine 1 (four cylinders # 1 to # 4 in this embodiment) has been obtained. If the limit injection interval INTmin for all cylinders can be acquired, the control process is terminated. Conversely, if the limit injection interval INTmin as the learning value for all the cylinders has not been acquired, the control processing from S204 to S206 is repeated for each of the other cylinders.

  Even if all of the control processes from S201 to S207 are not completed while the learning precondition is satisfied, for example, even if there is only a formation time for learning the limit injection interval INTmi # 1 in the # 1 cylinder, # 1 By updating the learning value of the limit injection interval INTmim # 1 of the cylinder, the combustion state of the entire # 1 cylinder to # 4 cylinder of the engine 1 is improved as compared with that not updated. In this case, when a function for storing that the learning value of the limit injection interval INTmim # 1 has been updated only for the # 1 cylinder is added to the control process of S204, for example, It is preferable to start learning from any of # 2 cylinder to # 4 cylinder except for one cylinder.

Note that, S201 and S202 are specific operating condition for detecting that the engine 1 and the main injection Q _M at operating region to close injection as a post-injection and the pilot injection Q _P as before injection is operated It is a detection means. S201 constitutes means for detecting a stable operation such as an idle stable state as a learning precondition. S202 constitutes an operating condition setting means that can set the operating state in which the pre-injection and the post-injection are in close proximity by controlling the injector 2 in a pseudo manner. S205 includes state estimation means for estimating the combustion state or injection state of the engine 1 based on the engine rotational speed fluctuation ΔNE. S205 includes a determination unit that monitors the engine speed fluctuation ΔNE by the state estimation unit and determines the limit injection interval INTmin based on the combustion state or the injection state that changes according to the magnitude of the injection interval INT.

  Next, as shown in FIG. 3, by performing the control processing from S301 to S304, the limit injection interval INTmim # 1 learned in the learning mode is used as a guard value, for example, in the normal mode of the actual control of the injector 2 Control of the injector 2 at the injection interval INT smaller than the injection interval INTmim # 1 is prevented.

  Specifically, in S301, an optimal injection mode is obtained according to the operating state of the engine 1. At this time, when the pilot injection mode is set, the ECU 10 reads an optimal injection interval (hereinafter referred to as a target injection interval) INT corresponding to the operating state.

  In S302, it is determined whether or not the target injection interval INT calculated (read) in S301 is equal to or smaller than the previously detected limit injection interval INTmim (for example, the limit injection interval INTmim # 1 of the # 1 cylinder). judge. If the target injection interval INT is greater than the limit injection interval INTmim, the process proceeds to S303, and the injector 2 is controlled with the target injection interval INT being maintained. Conversely, if the target injection interval INT is less than or equal to the limit injection interval INTmim, the process proceeds to S304, where the target injection interval INT is replaced with the limit injection interval INTmim, and a guard value that prevents overlapping of injections is set to the target injection interval INT. Set. As a result, abnormal combustion due to proximity injection is prevented.

  Here, S302, S303, and S304 constitute correction means for replacing the target injection interval INT with the limit injection interval INTmim when the target injection interval INT is equal to or less than the limit injection interval INTmim.

Next, the operation and effect of the present embodiment will be described. (1) The engine 10 is operated in an operation region in which the ECU 10 causes the pre-injection (pilot injection Q _P ) and the post-injection (main injection Q _M ) to be in close proximity. Specific operating state detecting means S201, S202 for detecting that the engine is running, and monitoring the engine speed fluctuation ΔNE indicating changes such as deterioration in the combustion state or the injection state, and the combustion state that changes according to the magnitude of the injection interval INT or Determination means S205 for determining the limit injection interval INTmin based on the injection state is provided. Therefore, while monitoring the engine speed fluctuation ΔNE, it is possible to determine the limit injection interval by the determination means when the combustion state or the change in injection state ΔNE that changes according to the magnitude of the injection interval INT reaches the predetermined change amount S1. is there. Therefore, the ECU 10 can prevent overlapping of injections when the fuel is injected in a plurality of times during one combustion stroke. For example, it is possible to learn the limit injection interval for preventing injection overlap each time an operation condition (operation region) for close injection is detected by the specific operation state detection means.

(2) As a method for estimating the combustion state or the injection state affected by the proximity injection, the engine speed fluctuation representing the influence of the engine 1 behavior by the pre-injection (pilot injection Q _P ) and the post-injection (main injection Q _M ) It is preferable to estimate from the detected value of ΔNE. That is, the pilot injection Q _P is overlaps the main injection Q _M, contributes injection amount to the torque applied minute injection amount QP is the main injection amount QM of the pilot injection Q _P increases rapidly due to the proximity injection. In such an abnormal injection mode, the combustion state of the engine 1 becomes unstable (abnormal) and the engine speed fluctuation ΔNE increases, so that it is easy to determine the limit injection interval INT.

  (3) Since the determination unit S205 monitors the engine speed fluctuation ΔNE and controls the injector 2 in a direction to reduce the magnitude of the injection interval INT, it determines the change boundary point of the engine speed fluctuation ΔNE. The limit injection interval INTmin can be reliably determined from the engine speed fluctuation ΔNE that changes due to the injection abnormality or the combustion abnormality due to the proximity of the injection interval INT.

  (4) The limit injection interval INTmin actually detected by the determination means S205 in the learning mode is compared with the optimum target injection interval INT corresponding to the operating state calculated in the normal mode of the ECU 10, and compared with the limit injection interval INTmin. When the target injection interval INT is small, the target injection interval INT is replaced with the limit injection interval INTmin, so that the replacement can be updated with the learning-corrected limit injection interval INTmin. It is possible to prevent abnormal combustion due to overlapping of the two.

  (5) It is preferable that the driving | running | working area | region detected by specific driving | running state detection means S201, S202 exists in an idle stable state. According to this, as an operation region in which the limit injection interval INTmin is actually detected, in an idle stable state, a no-load state without a driver's output request or a vehicle-stop operation without a driver's vehicle travel request It is possible to ensure a stable operation state.

(6) specified operating condition detecting means S201, S202 is an operation state to close the injection and preinjection _{Q P} and after-injection _{Q M,} with an operating condition setting means S202 that can be set by controlling the injector 2 . According to this, in the so-called search mode (learning mode) for actually detecting the limit injection interval INTmin, the injection interval INT is reduced, for example, in distinction from the so-called normal mode in which the ECU 10 controls the injector 2 according to the engine 1. Or it becomes easy to carry out pseudo control so as to enlarge.

(Second, third and fourth embodiments)
Hereinafter, other embodiments to which the present invention is applied will be described. In the following embodiments, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and description thereof will not be repeated.

  In the first embodiment, the engine speed fluctuation ΔNE is used as a method for estimating the combustion state or injection state affected by the proximity injection, but the engine 1 shown in each of the second, third, and fourth embodiments. May be used.

  In the second embodiment, as shown in FIG. 5, the exhaust gas temperature is used as a method for estimating the combustion state or injection state affected by the proximity injection. FIG. 5 is a graph for explaining the operation of the fuel injection control apparatus of the second embodiment.

The ECU 10 receives a signal from an exhaust temperature sensor attached to the engine 1 and monitors information on the exhaust temperature of the engine 1. Incidentally, when performing pilot injection Q _P of the minute injection amount QP before the main injection Q _M, prior the injection interval INT continue to shrink, the injected fuel of the injected fuel and the main injection Q _M of the pilot injection Q _P there is no little difference in the ignition timing, the exhaust temperature caused a similar abrupt heat generation shall be performed only main injection Q _M is increased.

  In the third embodiment, as shown in FIG. 6, engine in-cylinder pressure is used as a method for estimating the combustion state or injection state affected by the proximity injection. FIG. 6 is a graph for explaining the operation of the fuel injection control apparatus of the third embodiment.

  The ECU 10 receives a signal from an in-cylinder pressure sensor attached to the engine 1 and monitors information on the in-cylinder pressure in the combustion chamber of the engine 1. Note that, by reducing (adjacent) the injection interval INT, rapid heat generation occurs and the engine cylinder pressure increases.

In the fourth embodiment, as shown in FIG. 7, an excess air ratio λ is used as a method for estimating the combustion state or injection state affected by the proximity injection. FIG. 7 is a graph for explaining the operation of the fuel injection control apparatus of the fourth embodiment. The ECU 10 receives a signal from an O ₂ sensor 37 attached to the engine 1 and monitors information on the excess air ratio λ after combustion. In addition, since the injected fuel is rapidly ignited by reducing (adjacent) the injection interval INT, the smoke does not react with the air in the combustion chamber surrounding the injected fuel and the excess air ratio λ decreases. .

As described above, as a method for estimating the combustion state or the injection state affected by the proximity injection, the exhaust temperature in the second embodiment and the third implementation are used instead of the engine speed fluctuation ΔNE in the first embodiment. Even if any one of the in-cylinder pressure in the combustion chamber of the engine 1 in the form and the excess air ratio λ in the fourth embodiment is used, the same effect as in the first embodiment can be obtained. These engine speed fluctuation ΔNE, exhaust temperature, in-cylinder pressure, and excess air ratio λ all represent the effects of engine 1 behavior due to pre-injection (pilot injection Q _P ) and post-injection (main injection Q _M ). is there.

(Other embodiments)
In the present embodiment described above, the pilot injection mode has been described among the multistage injections that are performed in a plurality of times during one combustion stroke. However, the after injection mode, or the pilot injection, the main injection, and the after injection are performed three times. The injection form to inject may be sufficient.

  In the present embodiment described above, the optimum target injection interval INT corresponding to the operating state calculated in the normal mode of the ECU 10 is compared. When the target injection interval INT is smaller than the limit injection interval INTmin, the target injection interval The limit injection interval INTmin actually detected by the determination unit S205 is used as the limit injection interval INTmin that replaces INT with the limit injection interval INTmin. However, allowance (safety) is expected for the limit injection interval INTmin detected by the determination unit S205. A value obtained by multiplication correction or addition correction can be used. Thereby, the overlap prevention of injection can be further achieved.

  In the present embodiment described above, the limit injection interval INTmin is obtained by controlling the injector 2 in the direction in which the injection interval INT is reduced. Conversely, even if the injector 2 is controlled in the direction in which it is increased, the limit injection interval INTmin is determined. Can be requested.

In the present embodiment described above, the engine speed fluctuation ΔNE, the exhaust temperature, the cylinder as the engine 1 behavior influence value representing the influence of the engine 1 behavior due to the pre-injection (pilot injection Q _P ) and the post-injection (main injection Q _M ). Although it has been described that one of the internal pressure and the excess air ratio λ is monitored to determine the change boundary point of the engine 1 behavior influence value, the engine rotational speed fluctuation ΔNE, the exhaust temperature, the in-cylinder pressure, and the air A plurality of engine 1 behavior influence values including the excess rate λ may be monitored, and when any one of them shows a behavior influence value indicating an overlap between the pre-injection and the post-injection, the time may be recognized as the limit injection interval. .

1 is a configuration diagram illustrating an overall configuration of a fuel injection system according to a first embodiment of the present invention. 2 is a flowchart illustrating a control process for learning a limit injection interval for performing close injection of pre-injection and post-injection in the ECU in FIG. 1. FIG. 2 is a flowchart showing a part of a normal mode when the proximity injection is actually performed in the ECU in FIG. 1. FIG. It is a graph explaining the action | operation of the fuel-injection control apparatus of 1st Embodiment. It is a graph explaining the action | operation of the fuel-injection control apparatus of 2nd Embodiment. It is a graph explaining the action | operation of the fuel-injection control apparatus of 3rd Embodiment. It is a graph explaining the action | operation of the fuel-injection control apparatus of 4th Embodiment. FIG. 5 is a schematic diagram for explaining an injection interval between a pre-injection and a post-injection, which is injected a plurality of times during one combustion stroke.

Explanation of symbols

1 engine (internal combustion engine)
2 Injector (fuel injection valve, electromagnetic fuel injection valve)
3 Supply pump (high pressure supply pump, fuel supply pump)
7 Suction metering valve 10 ECU (Engine control unit, control means, correction means)
17 Common rail (accumulation chamber)

Claims (7)

An injector for injecting fuel into a combustion chamber of each cylinder of the internal combustion engine; and a control means for controlling the injector in accordance with an operating state of the internal combustion engine, and during one combustion stroke of the internal combustion engine with respect to the cylinder In a fuel injection control device that performs a plurality of injections,
The internal combustion engine is operated in an operation region in which the control means makes a close injection of a pre-injection in which the injection is performed first and a post-injection in which the injection is performed after the pre-injection among the plurality of injections. Specific operating state detecting means for detecting the combustion state, state estimating means for estimating the combustion state or injection state of the internal combustion engine, and monitoring the combustion state or the injection state by the state estimating means, and the pre-injection and the post-injection A fuel injection control device comprising: a determination unit that determines a limit injection interval based on the combustion state that changes in accordance with the magnitude of the injection interval during the period or a predetermined amount of change in the injection state. The estimation of the combustion state or the injection state by the state estimation means is performed for the pre-injection and the post-rejection including the rotational speed fluctuation of the internal combustion engine, the exhaust temperature, the in-cylinder pressure in the combustion chamber of the cylinder, and the excess air ratio. The fuel injection control device according to claim 1, wherein the estimation is based on a behavior influence value of the internal combustion engine due to injection. The determination unit monitors at least one of the four pieces of information, and determines a change boundary point of the behavior influence value when the injection interval is reduced or expanded by the control of the injector. The fuel injection control device according to claim 2. Comparing the limit injection interval with an optimum target injection interval according to the operating state of the internal combustion engine calculated by the control means;
4. The apparatus according to claim 1, further comprising a correcting unit that replaces the target injection interval with the limit injection interval when the target injection interval is smaller than the limit injection interval. 5. Fuel injection control device. 5. The fuel injection control device according to claim 4, wherein the limit injection interval is obtained by multiplying the limit injection interval determined by the determination unit by a margin coefficient or adding an allowance amount. The fuel injection control device according to any one of claims 1 to 5, wherein the operation region is in an idle stable state. 2. The operating condition setting unit capable of controlling the injector to set an operation state in which the pre-injection and the post-injection are in close proximity injection. The fuel injection control device according to any one of claims 6 to 6.

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