JP2019183736A - Fuel injection system - Google Patents

Abstract

To provide a fuel injection system which can accurately detect that pre-injection and post-injection are overlapped on each other.SOLUTION: A fuel injection system (10) comprises: a pump (13); a pressure accumulation vessel (14) for accumulating fuel in a pressurized state; an injection valve (16) for injecting fuel; a pressure sensor (21) for detecting pressure in the pressure accumulator; and an ECU (17). The ECU performs injection control for making the injection valve perform pre-injection and post-injection within an injection period at a command interval, performs discharge control for making the pump discharge the fuel so as to set the pressure in the pressure accumulation vessel to target pressure on the basis of a command injection amount of the fuel injected by the injection valve, and a difference between the pressure detected by the pressure sensor and the target pressure, and when the pressure detected by the pressure sensor is lowered exceeding prescribed pressure with respect to the target pressure in a state that the injection control and the discharge control are performed, and also when a discharge amount of the pump is determined to be normal, the ECU determines that the pre-injection and the post-injection are overlapped on each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel injection system.

  2. Description of the Related Art Conventionally, there is a system that obtains an injection interval when the injection amount of fuel injected from a fuel injection valve increases rapidly by gradually shortening the interval between pre-injection and post-injection during an injection period (see Patent Document 1). .

JP 2007-23796 A

  By the way, in the system described in Patent Document 1, a rapid increase in the fuel injection amount is detected by a sensor (for example, a rotational speed sensor) that detects the operating state of the internal combustion engine. The operating state of the internal combustion engine is also affected by factors other than the fuel injection amount (for example, fuel injection timing). For this reason, the system described in Patent Document 1 cannot accurately determine the injection interval when the fuel injection amount suddenly increases, that is, the injection interval when the pre-injection and the post-injection overlap.

  The present invention has been made to solve these problems, and a main object of the present invention is to provide a fuel injection system capable of accurately determining that pre-injection and post-injection overlap.

A first means for solving the above problem is a fuel injection system (10),
A pump (13) for discharging fuel;
A pressure accumulator (14) for storing fuel discharged by the pump in a pressurized state;
An injection valve (16) for injecting the fuel stored in the pressure accumulating vessel;
A pressure sensor (21) for detecting the pressure in the pressure accumulating vessel;
An injection control unit that performs injection control to perform pre-injection and post-injection at a command interval by the injection valve during an injection period;
Based on the command injection amount of the fuel to be injected by the injection valve and the difference between the pressure detected by the pressure sensor and the target pressure, the pump causes the pressure in the pressure accumulating vessel to become the target pressure. A discharge control unit that executes discharge control for discharging the fuel;
In a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the pressure detected by the pressure sensor is lower than a predetermined pressure with respect to the target pressure, And when it determines with the discharge amount of the said pump being normal, the determination part which determines with the said front injection and the said back injection having overlapped,
Is provided.

  According to the above configuration, the fuel is discharged by the pump, and the fuel discharged by the pump is stored in the pressure accumulation container in a pressurized state. The fuel stored in the pressure accumulation container is injected by the injection valve, and the pressure in the pressure accumulation container is reduced. And the pressure in a pressure accumulation container is detected by a pressure sensor.

  An injection control part performs the injection control which makes a pre-injection and a post-injection by a command interval by an injection valve in an injection period. Further, the discharge control unit uses a pump so that the pressure in the pressure accumulating container is set to the target pressure based on the command injection amount of the fuel to be injected by the injection valve and the difference between the pressure detected by the pressure sensor and the target pressure. Discharge control for discharging fuel is executed. For this reason, in the state in which the injection control and the discharge control are executed, the pressure in the pressure accumulating container basically matches the target pressure.

  Here, when the post-injection is started before the pre-injection ends, that is, when the pre-injection and the post-injection overlap, the fuel injection amount increases rapidly. In this case, even if the discharge control is executed by the discharge control unit, the pressure in the pressure accumulating container is lower than the target pressure. Further, in the discharge control by the discharge control unit, the pressure in the pressure accumulating container is lower than the target pressure even when the pump discharge amount is smaller than the normal discharge amount.

  In this regard, in the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the determination unit is such that the pressure detected by the pressure sensor is lower than a predetermined pressure with respect to the target pressure, And when it determines with the discharge amount of a pump being normal, it determines with the front injection and the rear injection having overlapped. For this reason, when the discharge amount of the pump is not smaller than the discharge amount at the normal time, it can be determined that the pre-injection and the post-injection overlap. Furthermore, since the amount of fuel injected by the injection valve is accurately reflected in the pressure in the pressure accumulating vessel, the pressure detected by the pressure sensor is used to detect with good judgment that the pre-injection and the post-injection overlap. be able to. In addition, there is no need to execute special injection control (for example, control for gradually shortening the command interval) for determining that the pre-injection and the post-injection have overlapped. It can be determined that they overlap.

  In the discharge control, the discharge control unit causes the pump to discharge fuel based on the difference between the pressure detected by the pressure sensor and the target pressure so that the pressure in the pressure accumulating container becomes the target pressure. For this reason, if the pressure detected by the pressure sensor is lower than a predetermined pressure with respect to the target pressure, the discharge control unit increases the amount of fuel discharged by the pump. However, the pressure drop in the pressure accumulating vessel is not caused by a shortage of the pump discharge amount, but is caused by the overlap between the pre-injection and the post-injection. For this reason, if the pre-injection and the post-injection do not overlap in the next injection period, the pump discharge amount becomes excessive with respect to the appropriate discharge amount. As a result, the pressure detected by the pressure sensor exceeds the target pressure in the state where the injection control and the discharge control are executed next.

  Therefore, in the second means, the determination unit is configured such that the pressure detected by the pressure sensor is the target pressure in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed. And the pressure detected by the pressure sensor in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed next. When the target pressure is exceeded, it is determined that the pre-injection and the post-injection overlap. That is, in the state where the injection control and the discharge control are executed next, it can be determined that the discharge amount of the pump is normal because the pressure detected by the pressure sensor exceeds the target pressure.

  When injection control and discharge control are executed, even if the pressure detected by the pressure sensor is lower than the target pressure by more than a predetermined pressure, it is not caused by the overlap between the pre-injection and the post-injection There is also. For example, there may be a tendency that the injection amount by the fuel injection valve slightly increases from the appropriate injection amount, or the discharge amount by the pump slightly decreases from the appropriate discharge amount.

  Therefore, in the third means, the determination unit detects the pressure detected by the pressure sensor from the target pressure in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed. A first calculation unit that calculates a pressure deviation obtained by subtracting the pressure deviation, and when the command interval is shorter than the predetermined interval, the pressure deviation calculated by the first calculation unit is longer than the predetermined interval. Sometimes the pre-injection and the post-injection overlap when it is determined that the pressure deviation calculated by the first calculation unit is larger than a predetermined pressure deviation and the pump discharge amount is normal. It is determined that

  According to the above configuration, the pressure deviation obtained by subtracting the pressure detected by the pressure sensor from the target pressure is calculated by the first calculation unit in a state where the injection control and the discharge control are executed. The pressure deviation calculated by the first calculation unit when the command interval is shorter than the predetermined interval exceeds the predetermined pressure deviation with respect to the pressure deviation calculated by the first calculation unit when the command interval is longer than the predetermined interval. If it is large, it is determined that the pre-injection and the post-injection overlap. For this reason, it is possible to determine whether or not the pressure deviation when the command interval is shorter than the predetermined interval is large with reference to the pressure deviation when the command interval is longer than the predetermined interval. Therefore, it is possible to accurately detect that the pre-injection and the post-injection overlap each other by suppressing the influence of factors other than the command interval on the pressure drop in the pressure accumulating vessel.

  According to a fourth aspect, the discharge control unit is configured to control the inside of the pressure accumulating container based on a command injection amount of the fuel to be injected by the injection valve and a difference between the pressure detected by the pressure sensor and a target pressure. A command calculation unit that calculates a command discharge amount of the fuel to be discharged by the pump so that the pressure becomes the target pressure, and the injection control by the injection control unit and the discharge control by the discharge control unit are executed; And an estimation calculation unit that calculates an estimated discharge amount of the fuel discharged by the pump based on the pressure detected by the pressure sensor before and after the determination, and the determination unit includes the injection control unit The command discharge amount calculated by the command calculation unit is calculated by the estimation calculation unit in a state where the injection control by the discharge control and the discharge control by the discharge control unit are executed. Most exceeds a predetermined amount with respect to the estimated discharge amount issued, and when the discharge amount of the pump is determined to be normal, it is determined that the said post injection and preinjection overlap.

  According to the above configuration, the command calculation unit calculates the command discharge amount of the fuel to be discharged by the pump so that the pressure in the pressure accumulating container becomes the target pressure. The estimation calculation unit calculates an estimated discharge amount of the fuel discharged by the pump based on the pressure detected by the pressure sensor before and after the injection control and the discharge control are executed. Here, when the pre-injection and the post-injection overlap each other and the injection amount by the fuel injection valve increases rapidly, the pressure in the pressure accumulating container rapidly decreases from before to after the injection control and the discharge control are executed. For this reason, the estimated discharge amount is calculated to be small, and the estimated discharge amount is smaller than the command discharge amount.

  In this regard, according to the above configuration, the determination unit is configured such that the command discharge amount is larger than the predetermined amount with respect to the estimated discharge amount and the pump discharge amount is normal in a state where the injection control and the discharge control are executed. When it is determined that there is, it is determined that the pre-injection and the post-injection overlap. That is, when the pressure detected by the pressure sensor falls below a predetermined pressure with respect to the target pressure, the command discharge amount is larger than the predetermined amount with respect to the estimated discharge amount, so that the pre-injection and the post-injection Can be determined to overlap. Furthermore, it is possible to determine that the pre-injection and the post-injection overlap using the command discharge amount used in the discharge control.

  In a state where the injection control and the discharge control are executed, even if the commanded discharge amount exceeds the predetermined amount with respect to the estimated discharge amount, it may not be caused by the overlap between the pre-injection and the post-injection. For example, there may be a tendency that the injection amount by the fuel injection valve slightly increases from the appropriate injection amount, or the discharge amount by the pump slightly decreases from the appropriate discharge amount.

  Therefore, in the fifth means, in the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the estimation calculation unit calculates the command discharge amount calculated by the command calculation unit. A second calculation unit configured to calculate a discharge amount deviation obtained by subtracting the calculated estimated discharge amount, and the determination unit calculates the discharge calculated by the second calculation unit when the command interval is shorter than a predetermined interval. When the command interval is longer than the predetermined interval, the amount deviation is larger than the predetermined discharge amount deviation with respect to the discharge amount deviation calculated by the second calculation unit, and the discharge amount of the pump is normal It is determined that the pre-injection and the post-injection overlap.

  According to the above configuration, the discharge amount deviation obtained by subtracting the estimated discharge amount from the command discharge amount is calculated by the second calculation unit in a state where the injection control and the discharge control are executed. The discharge amount deviation calculated by the second calculation unit when the command interval is shorter than the predetermined interval is a predetermined discharge amount with respect to the discharge amount deviation calculated by the second calculation unit when the command interval is longer than the predetermined interval. When the deviation is larger than the deviation, it is determined that the pre-injection and the post-injection overlap. For this reason, it is possible to determine whether or not the discharge amount deviation when the command interval is shorter than the predetermined interval is large based on the discharge amount deviation when the command interval is longer than the predetermined interval. Therefore, it is possible to accurately detect that the pre-injection and the post-injection overlap each other by suppressing the influence of factors other than the command interval on the pressure drop in the pressure accumulating vessel.

  In a sixth means, the determination unit is configured such that the pressure detected by the pressure sensor with respect to the target pressure in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed. And the pressure detected by the pressure sensor is the target when the injection control by the injection control unit and the discharge control by the discharge control unit are executed next. When the pressure is exceeded, it is determined that the discharge amount of the pump is normal.

  According to the above configuration, in the state where the injection control and the discharge control are executed next, similarly to the second means, the pump discharge amount is normal because the pressure detected by the pressure sensor exceeds the target pressure. It can be determined that

  In a seventh means, the injection control unit sets the command interval at the time when it is determined that the pre-injection and the post-injection are overlapped by the determination unit as the shortest interval. When the learning is performed and the injection control is subsequently executed, the command interval is set so as not to be shorter than the shortest interval.

  According to the above configuration, it is possible to learn, as the shortest interval, the command interval when it is determined that the front and rear injections are overlapped in the injection valve determined that the front injection and the rear injection overlap. Further, in the injection valve in which the pre-injection and the post-injection overlap, when the injection control is subsequently executed, the command interval is set not to be shorter than the shortest interval. For this reason, unless the pre-injection and the post-injection overlap, the pre-injection and the post-injection can be performed at the command interval.

The schematic diagram which shows the structure of a fuel-injection system. The graph which shows the relationship between an injection interval and the injection quantity. The time chart which shows the injection rate and rail pressure of case 1. FIG. The time chart which shows the injection rate and rail pressure of case 2. FIG. The time chart which shows the injection rate and rail pressure of case 3. FIG. The time chart which shows the injection rate, discharge command signal, and rail pressure of each cylinder. The flowchart which shows the procedure which determines the overlap with front injection and back injection in 1st Embodiment. The flowchart which shows the procedure which determines the overlap with front injection and back injection in 2nd Embodiment. The flowchart which shows the procedure which determines the overlap with front injection and back injection in 3rd Embodiment.

(First embodiment)
Hereinafter, a first embodiment embodied in a common rail fuel injection system for a four-cylinder on-board diesel engine will be described with reference to the drawings.

  As shown in FIG. 1, the fuel injection system 10 is a pressure accumulation type (common rail type) fuel injection system. The fuel injection system 10 includes a feed pump 12, a high-pressure pump 13, a common rail 14, a pressure reducing valve 15, an injector 16, an ECU 17, and the like. The fuel injection system 10 injects fuel into each cylinder of the diesel engine 18 at an appropriate timing.

  The feed pump 12 draws fuel from the fuel tank 19 and discharges it to the high-pressure pump 13 side. The high-pressure pump 13 (pump) sucks and pressurizes fuel by a plunger (not shown) driven reciprocally so as to synchronize with the engine 18 based on the driving force of the engine 18 and discharges the fuel to the common rail 14 side. The amount of fuel discharged by the high-pressure pump 13 is controlled by the ECU 17.

  The common rail 14 (pressure accumulation container) stores the fuel discharged by the high pressure pump 13 in a pressurized state. The pressure reducing valve 15 is opened to discharge the fuel in the common rail 14 to the low pressure side passage 19 </ b> A communicating with the fuel tank 19, thereby reducing the fuel pressure in the common rail 14. The open / close state of the pressure reducing valve 15 is controlled by the ECU 17.

  The plurality of injectors 16 (injection valves) are connected to the common rail 14 in parallel. The injector 16 injects fuel stored in the common rail 14 into each cylinder. The injector 16 is a known electromagnetic drive type or piezoelectric drive type injector that controls the fuel injection amount by controlling the pressure in the control chamber that applies fuel pressure to the nozzle needle in the valve closing direction.

  The pressure sensor 21 detects the fuel pressure in the common rail 14. The rotational speed sensor 22 detects the rotational speed of the crankshaft of the engine 18. The accelerator sensor 23 detects the amount of depression of the accelerator pedal of the vehicle. Detection signals of these sensors 21 to 23 are input to the ECU 17.

  The ECU 17 (Electronic Control Unit) is a known microcomputer including a CPU, ROM, RAM, storage device, input / output interface, and the like. The ECU 17 determines the opening / closing timing of the injector 16 based on the rotational speed of the engine 18 detected by the rotational speed sensor 22, the depression amount of the accelerator pedal detected by the accelerator sensor 23, a control map stored in advance in the ROM, and the like. Control. The opening / closing timing of the injector 16 includes the timing and period of pre-injection and the timing and period of post-injection. The ECU 17 causes the CPU to execute various programs stored in the ROM so that an injection control unit, a discharge control unit, a determination unit, a first calculation unit, a command calculation unit, an estimation calculation unit, a second calculation unit, and the like, which will be described later. Realize the function.

  First, an outline of fuel pressure control in the common rail 14 by the ECU 17 will be described. The ECU 17 determines a target pressure in the common rail 14 (hereinafter referred to as “target pressure Pt”), and controls the high pressure pump 13 and the pressure reducing valve 15 so that the pressure in the common rail 14 becomes the target pressure Pt.

  That is, the ECU 17 calculates a fuel discharge amount (hereinafter referred to as “command discharge amount Qt”) to be discharged by commanding the high-pressure pump 13 in order to set the fuel pressure in the common rail 14 to the target pressure Pt. Further, the ECU 17 calculates a fuel discharge amount (hereinafter referred to as “estimated discharge amount Qa”) that is estimated to be actually discharged from the high-pressure pump 13 to the common rail 14.

  Thereafter, the ECU 17 calculates a corrected discharge amount for setting the fuel pressure in the common rail 14 to the target pressure Pt based on the difference between the command discharge amount Qt and the estimated discharge amount Qa. The corrected discharge amount is a corrected discharge amount (hereinafter referred to as “F / B corrected discharge amount Qf”) for setting (matching) the estimated discharge amount Qa to the command discharge amount Qt. The ECU 17 controls the high-pressure pump 13 so that a fuel having a discharge amount obtained by adding the F / B corrected discharge amount Qf to the command discharge amount Qt is discharged from the high-pressure pump 13.

  At this time, when the command discharge amount Qt becomes a value equal to or greater than 0, the ECU 17 causes the high pressure pump 13 to discharge fuel with a discharge amount obtained by adding the F / B corrected discharge amount Qf to the command discharge amount Qt. The high pressure pump 13 is controlled. On the other hand, when the command discharge amount Qt becomes a negative value, the ECU 17 opens the pressure reducing valve 15 with the discharge amount from the high-pressure pump 13 set to zero.

  By the way, the plunger of the high-pressure pump 13 is driven to reciprocate in synchronization with the engine 18. For this reason, the ECU 17 executes arithmetic processing for calculating the command discharge amount Qt, the estimated discharge amount Qa, and the like at every timing when the pressurization by the plunger of the high pressure pump 13 reaches the top dead center. The operation of the valve 15 is controlled. The arithmetic processing timing is a predetermined timing from when the discharge by the high-pressure pump 13 is completed to when the injection by the injector 16 is started.

  Therefore, the ECU 17 outputs a drive signal for controlling the high-pressure pump 13 and the pressure reducing valve 15 by the next calculation start timing after the calculation process is completed. Then, at the next calculation start timing, calculation processing for calculating the command discharge amount Qt, the estimated discharge amount Qa, and the like is executed again. That is, control commands to the high pressure pump 13 and the pressure reducing valve 15 are made every period (period) in which the plunger reciprocates once.

  Since the command discharge amount Qt and the estimated discharge amount Qa are not mass flow but volume flow, the flow rate (volume flow) regardless of whether the mass flow is constant or the fuel temperature and pressure change. Changes. Therefore, hereinafter, the flow rates such as the command discharge amount Qt and the estimated discharge amount Qa are flow rates converted into a reference state (for example, a state where the fuel temperature is 40 ° C. and the fuel pressure is 1 atm).

  Next, a procedure for the ECU 17 to calculate the command discharge amount Qt will be described. The ECU 17 determines the amount of fuel to be injected from the injector 16 during the current injection, the amount of fuel leakage generated in the injector 16 during the current injection, and the differential pressure ΔP between the target pressure Pt and the pressure detected by the pressure sensor 21. Based on the above, the command discharge amount Qt is calculated.

  Specifically, the command injection amount based on the open command signal output from the ECU 17 to the injector 16 at the time of the current injection is determined as a fuel amount to be injected by the injector 16 at the time of the current injection. . However, when the command injection amount is less than the preset minimum injection amount, the minimum injection amount is determined as the amount of fuel to be injected by the injector 16 during the current injection.

  Further, the amount of fuel leakage generated in the injector 16 at the time of the current injection is shown in a map or the like stored in the ROM using the fuel injection period (the valve opening period of the injector 16), fuel temperature, fuel pressure, and the like as parameters. Calculated based on

  Here, “current injection time” refers to a period from the calculation start timing to the next calculation start timing. The “amount of fuel to be injected from the injector 16”, that is, the “command injection amount based on the open command signal” is determined by the ECU 17 based on a parameter indicating the operating state of the engine 18.

  Further, the target pressure Pt refers to the target pressure Pt determined at the calculation start timing, and the differential pressure ΔP refers to the differential pressure between the pressure detected at the calculation start timing and the target pressure Pt.

  In the present embodiment, when the calculated command discharge amount Qt exceeds the capability (maximum discharge amount) of the high pressure pump 13, the maximum discharge amount of the high pressure pump 13 is determined as the command discharge amount Qt. When the calculated command discharge amount Qt is smaller than the minimum discharge amount of the high pressure pump 13, the minimum discharge amount of the high pressure pump 13 is determined as the command discharge amount Qt.

  Next, the procedure by which the ECU 17 calculates the estimated discharge amount Qa will be described. When fuel is supplied to the common rail 14, the fuel pressure in the common rail 14 increases. When fuel is discharged from the common rail 14, the fuel pressure in the common rail 14 decreases. Therefore, the ECU 17 calculates the estimated discharge amount Qa based on the pressure change amount in the common rail 14 (discharge side of the high-pressure pump 13) generated during a preset period and the amount of fuel injected from the injector 16 during that period. calculate.

  Here, the “preset period” refers to a period from the previous calculation start timing to the calculation start timing (hereinafter referred to as “previous period”). In this embodiment, the amount of pressure change in the common rail 14 detected by the pressure sensor 21 is used as the amount of pressure change in the common rail 14 that occurred in the previous period.

  In principle, the ECU 17 injects from the injector 16 a value obtained by adding the amount of fuel leakage generated in the injector 16 during the previous period to the command injection amount based on the open command signal output to the injector 16 during the previous period. It is calculated as the amount of fuel that has been released.

  However, when the command injection amount is less than the preset minimum injection amount, a value obtained by adding the amount of fuel leakage generated in the injector 16 during the previous period to the minimum injection amount was injected from the injector 16 during the previous period. Calculated as the amount of fuel.

  FIG. 2 is a graph showing the relationship between the injection interval and the injection amount (the sum of the pre-injection and the post-injection). The injection interval is a period from the end of the drive command signal for the injector 16 in the pre-injection to the start of the drive command signal in the post-injection.

  As indicated by the solid line and the broken line, the relationship between the injection interval and the injection amount differs depending on the individual injectors 16. When the interval between the pre-injection and the post-injection is shortened in the injector 16, the nozzle needle in the post-injection is moved before the nozzle needle (valve element) lifted by the pre-injection is seated on the seat (valve seat). Lifting may begin. In this case, the amount of fuel injected by the injector 16 increases rapidly as compared to the case where the post-injection is started after the pre-injection is completed, that is, the case where the pre-injection and the post-injection do not overlap.

  In case 1, the interval between the pre-injection and the post-injection is long as shown in FIG. 3 in both the solid line and the broken line. In the injection rate graph, the area of the lower part of the graph represents the injection amount. The pressure in the common rail 14 before the pre-injection is performed (hereinafter referred to as “rail pressure”) is defined as a pressure P1, and the rail pressure after the post-injection and the discharge by the high-pressure pump 13 is defined as a pressure P2.

  In case 1, when the pre-injection is performed, the rail pressure is reduced in accordance with the injection amount of the pre-injection. Then, after the pre-injection is completed, the post-injection is performed, and the rail pressure is reduced according to the injection amount of the post-injection. Thereafter, the fuel is discharged by the high-pressure pump 13, and the rail pressure is increased to the pressure P2. Here, the ECU 17 calculates the command discharge amount Qt so that the fuel pressure in the common rail 14 becomes the target pressure Pt. For this reason, the pressure difference dp1 obtained by subtracting the pressure P2 from the target pressure Pt is a pressure difference close to zero.

  In case 2 in the broken line in FIG. 2, the interval between the pre-injection and the post-injection is shorter than in case 1 described above. In case 2, as shown in FIG. 4, since the pre-injection and the post-injection do not overlap, the rail pressure changes as in FIG. 3, although the interval is shortened.

  In case 3 in the solid line of FIG. 2, the interval between the pre-injection and the post-injection is the same length as in case 2 above. However, in case 3, the pre-injection and the post-injection overlap, and the injection amount is increased compared to case 2. In case 3, as shown in FIG. 5, the pre-injection and the post-injection overlap, and the injection rate is increased by the post-injection before the injection rate of the pre-injection becomes zero. For this reason, when the pre-injection and the post-injection are completed, the rail pressure is greatly reduced as compared with the case 2. Thereafter, the fuel is discharged by the high-pressure pump 13, and the rail pressure is increased to the pressure P2.

  Here, the ECU 17 calculates the command discharge amount Qt so that the fuel pressure in the common rail 14 becomes the target pressure Pt. However, in case 3, the actual injection amount is larger than the assumed injection amount. For this reason, the pressure difference dp2 obtained by subtracting the pressure P2 from the target pressure Pt is larger than the pressure difference dp1. That is, when the pre-injection and the post-injection overlap, the pressure P2 falls below the predetermined pressure with respect to the target pressure Pt.

  FIG. 6 is a time chart showing the injection rate, discharge command signal, and rail pressure of each cylinder. # 1 to # 4 represent the first to fourth cylinders. The discharge command signal represents a period during which fuel is discharged by the high-pressure pump 13.

  At timing t1, the ECU 17 determines the amount of fuel to be injected from the injector 16 at the time of the current injection, the amount of fuel leakage generated at the injector 16 at the time of the current injection, and the pressure detected by the target pressure Pt and the pressure sensor 21. The command discharge amount Qt is calculated based on the differential pressure ΔP. Here, since the differential pressure ΔP is 0, the command discharge amount Qt is the sum of the amount of fuel to be injected from the injector 16 and the amount of fuel leakage generated in the injector 16.

  Subsequently, the pre-injection and post-injection are performed by the injector 16 of the first cylinder # 1, and the fuel obtained by adding the F / B corrected discharge amount Qf to the command discharge amount Qt is discharged by the high-pressure pump 13. The amount of decrease in rail pressure due to pre-injection and post-injection is the decrease amount Δp1. In the previous injection control and discharge control, if the commanded discharge amount Qt and the estimated discharge amount Qa match, the F / B corrected discharge amount Qf becomes zero. At this time, the pre-injection and the post-injection do not overlap, and the rail pressure after discharge by the high-pressure pump 13 matches the target pressure Pt.

  At the timing t2, the ECU 17 is based on the change in rail pressure generated from the timing t1 (previous calculation timing) to the timing t2 (current calculation timing), and the amount of fuel injected from the injector 16 during that period. The estimated discharge amount Qa is calculated. Here, the change amount of the rail pressure is zero. Further, the ECU 17 calculates the command discharge amount Qt in the same manner as the timing t1.

  Subsequently, pre-injection and post-injection are performed by the injector 16 of the third cylinder # 3, and fuel obtained by adding the F / B corrected discharge amount Qf to the command discharge amount Qt is discharged by the high-pressure pump 13. At this time, the pre-injection and the post-injection overlap, and the rail pressure decrease amount Δp2 due to the pre-injection and post-injection is larger than the decrease amount Δp1. On the other hand, the command discharge amount Qt calculated at the timing t2 is equal to the command discharge amount Qt calculated at the timing t1. For this reason, the rail pressure after discharge by the high-pressure pump 13 is lower than the target pressure Pt by the pressure difference dp2. Note that the change amount of the rail pressure generated from the timing t2 to the timing t3 is also the pressure difference dp2.

  At timing t3, the ECU 17 calculates the estimated discharge amount Qa based on the amount of change in rail pressure (pressure difference dp2) generated from timing t2 to timing t3 and the amount of fuel injected from the injector 16 during that period. To do. Here, since the change amount of the rail pressure is the pressure difference dp2, the estimated discharge amount Qa is calculated to be smaller than the command discharge amount Qt calculated at the timing t2. For this reason, the F / B corrected discharge amount Qf for making the estimated discharge amount Qa the command discharge amount Qt (matching) is calculated as a positive discharge amount. Further, the ECU 17 performs command discharge based on the amount of fuel to be injected from the injector 16, the amount of fuel leakage generated in the injector 16, and the differential pressure ΔP between the target pressure Pt and the pressure detected by the pressure sensor 21. The quantity Qt is calculated. Here, since the differential pressure ΔP is the pressure difference dp2, the command discharge amount Qt is calculated to be larger than the command discharge amount Qt calculated at the timings t1 and t2.

  Subsequently, pre-injection and post-injection are performed by the injector 16 of the fourth cylinder # 4, and fuel obtained by adding the F / B corrected discharge amount Qf to the command discharge amount Qt is discharged by the high-pressure pump 13. At this time, the pre-injection and the post-injection do not overlap, and the rail pressure decrease amount Δp1 due to the pre-injection and post-injection is smaller than the decrease amount Δp2. On the other hand, the command discharge amount Qt calculated at the timing t3 is larger than the command discharge amount Qt calculated at the timings t1 and t2. For this reason, the rail pressure after discharge by the high-pressure pump 13 is higher than the target pressure Pt by the pressure difference dp3.

  That is, when the pre-injection and the post-injection overlap as in the third cylinder # 3, the fuel injection amount increases rapidly. In this case, even if fuel is discharged by the high-pressure pump 13, the rail pressure is lower than the target pressure Pt. However, even if the pre-injection and the post-injection do not overlap, the rail pressure is lower than the target pressure Pt even when the discharge amount of the high-pressure pump 13 is smaller than the discharge amount at the normal time.

  Therefore, in the state in which the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed, the rail pressure is lower than a predetermined pressure with respect to the target pressure Pt, and the high-pressure pump 13 If the discharge amount is normal, it can be determined that the pre-injection and the post-injection overlap. When the rail pressure falls below the predetermined pressure with respect to the target pressure Pt, the estimated discharge amount Qa calculated at the timing t3 is calculated to be smaller than the command discharge amount Qt calculated at the timing t2. Further, if the discharge amount of the high-pressure pump 13 is normal, the rail pressure is increased in the state where the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed in the next second cylinder # 2. The target pressure Pt is exceeded. Based on such an idea, the ECU 17 determines an overlap between the pre-injection and the post-injection.

  FIG. 7 is a flowchart showing a procedure for determining an overlap between the pre-injection and the post-injection. This series of processing is repeatedly executed by the ECU 17.

  First, at the calculation processing timing, the command discharge amount Qt of the high-pressure pump 13 is calculated by the above-described procedure (S10). The injector 16 injects a command injection amount of fuel by pre-injection and post-injection (S11). The command discharge amount Qt of fuel is discharged by the high-pressure pump 13 (S12). The rail pressure is detected by the pressure sensor 21 (S13). The rail pressure before the fuel is injected by the injector 16 is detected at the previous calculation processing timing.

  Subsequently, the estimated discharge amount Qa of the high-pressure pump 13 is calculated by the above-described procedure (S14). The discharge amount deviation dQ_L at the long interval is calculated (S15). Specifically, when the command interval (command interval) between the pre-injection and the post-injection is longer than a predetermined interval (predetermined interval), the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed. In this state, a discharge amount deviation dQ_L is calculated by subtracting the estimated discharge amount Qa from the command discharge amount Qt.

  Subsequently, it is determined whether or not the command interval in the current injection is shorter than the predetermined interval (S16). The predetermined interval is set to an interval at which the overlap between the pre-injection and the post-injection starts to occur, for example, 0.3 ms. In this determination, when it is determined that the command interval in the current injection is shorter than the predetermined interval (S16: YES), the discharge amount deviation dQ_S at the short interval is calculated (S17). Specifically, in a state where the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed, a discharge amount deviation dQ_S obtained by subtracting the estimated discharge amount Qa from the command discharge amount Qt is calculated.

  Subsequently, it is determined whether or not the discharge amount deviation dQ_S at the short interval exceeds the predetermined discharge amount deviation dq with respect to the discharge amount deviation dQ_L at the long interval (S18). That is, it is determined whether dQ_S> dQ_L + dq. In this determination, if it is determined that dQ_S> dQ_L + dq (S18: YES), whether or not the rail pressure detected by the pressure sensor 21 when the fuel discharge by the next high pressure pump 13 is finished is higher than the target pressure Pt. (S19).

  In the determination of S19, when it is determined that the rail pressure detected at the end of the next discharge is higher than the target pressure Pt (S19: YES), in the injection in the cylinder when it is determined that dQ_S> dQ_L + dq, It is determined that the post injection overlaps. In the cylinder (injector 16) determined that the pre-injection and the post-injection are overlapped, the command interval when it is determined that the overlap has occurred is learned as the shortest interval (shortest interval). Then, when fuel is subsequently injected into the cylinder, the command interval is set so as not to be shorter than the shortest interval (predetermined interval) (S20). Thereafter, this series of processing is temporarily terminated (END).

  On the other hand, if a negative determination is made in any one of S16, S18, and S19, this series of processes is temporarily terminated (END).

  In addition, the process of S10 corresponds to the process as a command calculation part, the process of S11 corresponds to the process as an injection control part, the process of S10 and S12 corresponds to the process as a discharge control part, and the process of S14. The process of S15 and S17 is equivalent to the process as a 2nd calculation part, and the process of S16, S18-S20 is equivalent to the process as a determination part.

  The embodiment described in detail above has the following advantages.

  In the state where the injection control of the injector 16 and the discharge control of the high-pressure pump 13 are executed, the ECU 17 has a pressure detected by the pressure sensor 21 that is lower than a predetermined pressure with respect to the target pressure Pt. When it is determined that the discharge amount of the pump 13 is normal, it is determined that the pre-injection and the post-injection overlap. For this reason, when the discharge amount of the high-pressure pump 13 is not smaller than the discharge amount at the normal time, it can be determined that the pre-injection and the post-injection overlap. Further, since the fuel injection amount by the injector 16 is accurately reflected in the pressure in the common rail 14, it is accurately determined that the pre-injection and the post-injection have overlapped by using the pressure detected by the pressure sensor 21. can do.

  -There is no need to execute special injection control (for example, control for gradually shortening the command interval) for determining that the front injection and the rear injection overlap, and the front injection and the rear injection overlap during normal injection control. Can be determined.

  In the state where the injection control and the discharge control are executed next, it can be determined that the discharge amount of the high-pressure pump 13 is normal when the pressure detected by the pressure sensor 21 exceeds the target pressure Pt.

  When the pressure detected by the pressure sensor 21 falls below a predetermined pressure with respect to the target pressure Pt, the command discharge amount Qt is larger than the predetermined amount with respect to the estimated discharge amount Qa. It can be determined that the post injection overlaps.

  It can be determined that the pre-injection and the post-injection have overlapped using the command discharge amount Qt and the estimated discharge amount Qa used in the discharge control.

  In the state where the injection control and the discharge control are executed, even if the command discharge amount Qt exceeds the estimated discharge amount Qa by a predetermined amount, it may not be caused by the overlap of the pre-injection and the post-injection. . For example, there may be a tendency that the injection amount by the injector 16 slightly increases from an appropriate injection amount, or the discharge amount by the high-pressure pump 13 slightly decreases from an appropriate discharge amount. In this state, in a state where the injection control and the discharge control are executed, a discharge amount deviation dQ obtained by subtracting the estimated discharge amount Qa from the command discharge amount Qt is calculated. When the discharge amount deviation dQ_S calculated when the command interval is shorter than the predetermined interval is larger than the predetermined discharge amount deviation dq with respect to the discharge amount deviation dQ_L calculated when the command interval is longer than the predetermined interval. It is determined that the pre-injection and the post-injection overlap. Therefore, it is possible to determine whether or not the discharge amount deviation dQ_S when the command interval is shorter than the predetermined interval is large with reference to the discharge amount deviation dQ_L when the command interval is longer than the predetermined interval. Therefore, it is possible to accurately detect that the pre-injection and the post-injection overlap by suppressing the influence of factors other than the command interval on the pressure drop in the common rail 14.

  In the injector 16 in which it is determined that the pre-injection and the post-injection have overlapped, the command interval when it is determined that the front and rear injections have overlapped can be learned as the shortest interval. Further, in the injector 16 in which the pre-injection and the post-injection overlap, when the injection control is subsequently executed, the command interval is set so as not to be shorter than the shortest interval. For this reason, unless the pre-injection and the post-injection overlap, the pre-injection and the post-injection can be performed at the command interval.

  When an affirmative determination is made in S16 of FIG. 7 (S16: YES), an overlap determination process after S17 is executed, and when a negative determination is made in the determination of S16 (S16: NO), an overlap determination process after S17 Do not execute. Therefore, the overlap determination process can be executed only when necessary, and the processing load on the ECU 17 can be reduced.

(Second Embodiment)
Hereinafter, the second embodiment will be described focusing on differences from the first embodiment. In the second embodiment, the discharge amount deviation dQ_L and the discharge amount deviation dQ_S are not distinguished, and the overlap between the pre-injection and the post-injection is determined based on the command discharge amount Qt and the estimated discharge amount Qa. In addition, about the part same as 1st Embodiment, description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  FIG. 8 is a flowchart showing a procedure for determining an overlap between the pre-injection and the post-injection. This series of processing is repeatedly executed by the ECU 17. The process of S10 to S14 in FIG. 8 is the same as the process of S10 to S14 in FIG.

  Subsequently, the discharge amount deviation dQ is calculated (S21). Specifically, in a state where the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed, a discharge amount deviation dQ obtained by subtracting the estimated discharge amount Qa from the command discharge amount Qt is calculated.

  Subsequently, it is determined whether or not the discharge amount deviation dQ is larger than a predetermined amount (S22). The predetermined amount is set to a value by which it can be determined that the estimated discharge amount Qa is smaller than the command discharge amount Qt due to the overlap between the pre-injection and the post-injection. In this determination, when it is determined that the discharge amount deviation dQ is larger than the predetermined amount (S22: YES), it is determined whether or not the discharge amount of the high-pressure pump 13 is normal (S23). Specifically, when the command interval is longer than the predetermined interval, it is determined whether or not the rail pressure detected by the pressure sensor 21 is substantially equal to the target pressure Pt in a state where the injection control and the discharge control are executed.

  Subsequently, it is determined whether or not the command interval has changed (S24). Specifically, it is determined whether or not the command interval is shorter than the predetermined interval. The predetermined interval may be the same as the predetermined interval of the first embodiment. In this determination, when it is determined that the command interval has changed (S24: YES), it is determined that the pre-injection and the post-injection overlap (S25). Thereafter, this series of processing is temporarily terminated (END).

  On the other hand, if a negative determination is made in any of the processes of S22 to S24, this series of processes is temporarily terminated (END).

  In addition, the process of S10 corresponds to the process as a command calculation part, the process of S11 corresponds to the process as an injection control part, the process of S10 and S12 corresponds to the process as a discharge control part, and the process of S14. This corresponds to the process as the estimation calculation unit, and the processes in S22 to S24 correspond to the process as the determination unit.

  The embodiment described in detail above has the following advantages. Here, only advantages different from the first embodiment will be described.

  When the pressure detected by the pressure sensor 21 falls below a predetermined pressure with respect to the target pressure Pt, the command discharge amount Qt is larger than the predetermined amount with respect to the estimated discharge amount Qa. It can be determined that the post injection overlaps. That is, it is not necessary to calculate the discharge amount deviation dQ_L and the discharge amount deviation dQ_S separately.

  Note that the second embodiment can be implemented with the following modifications.

  -In the process of S23, you may determine whether the discharge amount of the high pressure pump 13 is normal by another method.

  -In the process of S24, you may determine whether the injection control from which a command interval changes is performed. Further, the process of S24 can be omitted.

(Third embodiment)
Hereinafter, the third embodiment will be described focusing on differences from the first embodiment. In the third embodiment, the overlap between the pre-injection and the post-injection is determined based on the pressure deviation dP_L at the long interval and the pressure deviation dP_S at the short interval. In addition, about the part same as 1st Embodiment, description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  FIG. 9 is a flowchart showing a procedure for determining an overlap between the pre-injection and the post-injection. This series of processing is repeatedly executed by the ECU 17. The processes in S31 to S33 in FIG. 9 are the same as the processes in S11 to S13 in FIG.

  Subsequently, the pressure deviation dP_L at the long interval is calculated (S34). Specifically, when the command interval between the pre-injection and the post-injection is longer than the predetermined interval, the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed. Then, a pressure deviation dP_L obtained by subtracting the rail pressure detected by the pressure sensor 21 is calculated.

  Subsequently, it is determined whether or not the command interval in the current injection is shorter than the predetermined interval (S35). In this determination, when it is determined that the command interval in the current injection is shorter than the predetermined interval (S35: YES), the pressure deviation dP_S at the short interval is calculated (S36). Specifically, the pressure deviation dP_S obtained by subtracting the rail pressure detected by the pressure sensor 21 from the target pressure Pt in a state where the pre-injection and post-injection by the injector 16 and the fuel discharge by the high-pressure pump 13 are executed. calculate.

  Subsequently, it is determined whether or not the pressure deviation dP_S at the short interval is larger than the pressure deviation dP_L at the long interval beyond the predetermined pressure deviation dp (S37). That is, it is determined whether dP_S> dP_L + dp. In this determination, if it is determined that dP_S> dP_L + dp (S37: YES), whether or not the rail pressure detected by the pressure sensor 21 when the fuel discharge by the next high-pressure pump 13 is finished is higher than the target pressure Pt. (S38).

  In the determination of S38, when it is determined that the rail pressure detected at the end of the next discharge is higher than the target pressure Pt (S38: YES), in the injection in the cylinder when it is determined that dP_S> dP_L + dp, It is determined that the post injection overlaps (S39). Thereafter, this series of processing is temporarily terminated (END).

  On the other hand, if a negative determination is made in any one of S35, S37, and S38, this series of processes is temporarily terminated (END).

  In addition, the process of S31 corresponds to the process as an injection control part, the process of S32 corresponds to the process as a discharge control part, the process of S34 and S36 corresponds to the process as a 1st calculation part, S35, S37 The process of S39 corresponds to the process as the determination unit.

  The embodiment described in detail above has the following advantages. Here, only advantages different from the first embodiment will be described.

  In the state where the injection control and the discharge control are executed, the pre-injection and the post-injection are overlapped even if the pressure detected by the pressure sensor 21 is lower than the target pressure Pt by a predetermined pressure. It may not be the cause. In this state, in a state where the injection control and the discharge control are executed, a pressure deviation dP obtained by subtracting the pressure detected by the pressure sensor 21 from the target pressure Pt is calculated. When the pressure deviation dP_S calculated when the command interval is shorter than the predetermined interval is larger than the pressure deviation dP_L calculated when the command interval is longer than the predetermined interval, the pre-injection is performed. And post-injection are determined to overlap. For this reason, it is possible to determine whether or not the pressure deviation dP_S when the command interval is shorter than the predetermined interval is large based on the pressure deviation dP_L when the command interval is longer than the predetermined interval. Therefore, it is possible to accurately detect that the pre-injection and the post-injection overlap by suppressing the influence of factors other than the command interval on the pressure drop in the common rail 14.

  It should be noted that each of the above embodiments can be implemented with the following modifications. About the same part as the said embodiment, description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  The calculation of the F / B corrected discharge amount Qf can be omitted. In that case, instead of the process of S19 in FIG. 7 and the process of S38 in FIG. 9, the rail pressure detected by the pressure sensor 21 when the fuel discharge by the high pressure pump 13 is completed next time is substantially equal to the target pressure Pt. It may be determined whether or not.

  The order of the injection control of the injector 16 and the discharge control of the high-pressure pump 13 can be reversed.

  The engine 18 is not limited to a diesel engine, but may be a direct injection gasoline engine including a delivery pipe (pressure accumulating vessel). Further, in the pressure accumulation type fuel injection system 10, the fuel is not limited to light oil and gasoline, and a mixed fuel with alcohol can also be used.

  DESCRIPTION OF SYMBOLS 10 ... Fuel injection system, 13 ... High pressure pump, 14 ... Common rail, 16 ... Injector, 17 ... ECU, 21 ... Pressure sensor.

Claims (7)

A pump (13) for discharging fuel;
A pressure accumulator (14) for storing fuel discharged by the pump in a pressurized state;
An injection valve (16) for injecting the fuel stored in the pressure accumulating vessel;
A pressure sensor (21) for detecting the pressure in the pressure accumulating vessel;
An injection control unit that performs injection control to perform pre-injection and post-injection at command intervals by the injection valve during an injection period;
Based on the command injection amount of the fuel to be injected by the injection valve and the difference between the pressure detected by the pressure sensor and the target pressure, the pump causes the pressure in the pressure accumulating vessel to become the target pressure. A discharge control unit that executes discharge control for discharging the fuel;
In a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the pressure detected by the pressure sensor is lower than a predetermined pressure with respect to the target pressure, And when it determines with the discharge amount of the said pump being normal, the determination part which determines with the said front injection and the said back injection having overlapped,
A fuel injection system (10) comprising:   In the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the determination unit is configured such that the pressure detected by the pressure sensor exceeds a predetermined pressure with respect to the target pressure. And when the pressure detected by the pressure sensor exceeds the target pressure in the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed next. The fuel injection system according to claim 1, wherein it is determined that the pre-injection and the post-injection overlap. The determination unit
A first calculation unit that calculates a pressure deviation obtained by subtracting the pressure detected by the pressure sensor from the target pressure in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed; Have
The pressure deviation calculated by the first calculation unit when the command interval is shorter than the predetermined interval is equal to the pressure deviation calculated by the first calculation unit when the command interval is longer than the predetermined interval. 2. The fuel injection system according to claim 1, wherein, when it is determined to be larger than a predetermined pressure deviation and the discharge amount of the pump is normal, it is determined that the pre-injection and the post-injection overlap each other. The discharge control unit sets the pressure in the pressure accumulating container to the target pressure based on a command injection amount of the fuel to be injected by the injection valve and a difference between the pressure detected by the pressure sensor and the target pressure. A command calculation unit for calculating a command discharge amount of the fuel to be discharged by the pump,
Estimated discharge of the fuel discharged by the pump based on the pressure detected by the pressure sensor before and after the injection control by the injection control unit and the discharge control by the discharge control unit are executed. An estimation calculation unit for calculating an amount;
The determination unit calculates the command discharge amount calculated by the command calculation unit by the estimation calculation unit in a state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed. The pre-injection and the post-injection are determined to be overlapped when it is determined that the estimated discharge amount is larger than a predetermined amount and the discharge amount of the pump is normal. Fuel injection system. In the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the estimated discharge amount calculated by the estimation calculation unit is calculated from the command discharge amount calculated by the command calculation unit. A second calculation unit for calculating the subtracted discharge amount deviation;
The determination unit calculates the discharge amount deviation calculated by the second calculation unit when the command interval is shorter than the predetermined interval, by the second calculation unit when the command interval is longer than the predetermined interval. The determination is made that the pre-injection and the post-injection overlap each other when it is determined that the discharge amount deviation is larger than a predetermined discharge amount deviation and the discharge amount of the pump is normal. The fuel injection system described.   In the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed, the determination unit is configured such that the pressure detected by the pressure sensor exceeds a predetermined pressure with respect to the target pressure. And when the pressure detected by the pressure sensor exceeds the target pressure in the state where the injection control by the injection control unit and the discharge control by the discharge control unit are executed next. The fuel injection system according to claim 3, wherein the pump discharge amount is determined to be normal.   The injection control unit learns, as the shortest interval, the command interval when it is determined that the pre-injection and the post-injection are determined to be overlapped by the determination unit. The fuel injection system according to any one of claims 1 to 6, wherein when performing injection control, the command interval is set so as not to be shorter than the shortest interval.

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