JP2007100626A - Control device for fuel injection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve exhaust emission and drivability by suitably detecting irregularity in following-up properties of fuel pressure in a common rail. <P>SOLUTION: High pressure fuel injected and supplied to an engine 0 is accumulated in the common rail 13. ECU 30 detects irregularity in following-up properties of fuel pressure in the common rail 13 in each divided operation range. Fuel pressure in the common rail 13 is controlled by performing fuel pressure feed back control based on difference between actual fuel pressure and target fuel pressure corrected to decompression side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a fuel injection system.

  As a fuel injection system for diesel engines, common rail fuel that accumulates high-pressure fuel equivalent to the fuel injection pressure in the common rail and injects the high-pressure fuel accumulated in the common rail to the engine via the fuel injection valve An injection system has been put into practical use. In this common rail fuel injection system, the fuel pressure in the common rail decreases when fuel injection is performed by the fuel injection valve. At this time, the high pressure fuel is discharged and supplied from the fuel supply pump to the common rail. It is held at a predetermined high pressure state.

  Here, the target fuel pressure is set in order to maintain the fuel pressure in the common rail in a predetermined high pressure state. Then, the amount of fuel discharged from the fuel supply pump is feedback controlled so that the actual fuel pressure matches the target fuel pressure. The target fuel pressure is calculated by the electronic control unit based on data detected from the engine speed, the accelerator opening sensor, and other various sensors (see, for example, Patent Document 1).

  However, in the common rail fuel injection system, there may be a followability abnormality in which the actual fuel pressure in the common rail cannot follow the target fuel pressure. The followability abnormality occurs due to an increase in leaked fuel from the fuel injection valve and a decrease in the amount of fuel discharged from the fuel supply pump due to changes over time. For example, in a fuel injection valve in which a nozzle needle slides in the nozzle body and fuel is injected along with the sliding, the clearance of the sliding portion may increase due to wear of the nozzle needle and the like. The leak fuel increases. Further, in the fuel supply pump, when the fuel leakage that occurs in the mechanism portion that delivers the high-pressure fuel increases due to aging, the fuel discharge amount decreases. Therefore, the followability of the actual fuel pressure with respect to the target fuel pressure is reduced, and a followability abnormality occurs. When the followability abnormality occurs as described above, the controllability of the fuel pressure in the common rail deteriorates. This causes a problem that drivability and exhaust emission deteriorate.

Further, it is considered that the followability abnormality does not appear evenly in all engine operation regions, and may appear only in a specific operation region, for example, at the initial stage of occurrence of the abnormality. Therefore, it is necessary to control the fuel pressure in accordance with the situation in which the followability abnormality has occurred.
JP-A-63-1610658

  The main object of the present invention is to provide a control device for a fuel injection system that can suitably detect an abnormality in the followability of the fuel pressure in the common rail and can improve exhaust emission and drivability.

  In the first aspect of the invention, the fuel injection system is connected to a common rail that accumulates high-pressure fuel, a fuel supply pump that pumps fuel to the common rail, a fuel pressure sensor that detects fuel pressure in the common rail, and a common rail. And a fuel injection valve for injecting high-pressure fuel. Then, the amount of fuel discharged from the fuel supply pump is feedback controlled so that the actual fuel pressure detected by the fuel pressure sensor matches the target fuel pressure.

  The fuel pressure in the common rail is controlled so as to follow the target value by fuel pressure feedback control. Here, if the amount of fuel leak from the fuel injection valve increases or the amount of fuel discharged from the fuel supply pump decreases with time, the actual fuel pressure will follow the target fuel pressure. Follow-up abnormality that cannot be performed occurs. Further, it can be assumed that this follow-up abnormality does not appear evenly in all engine operation areas, and may appear only in a specific operation area, for example, at an initial stage of occurrence of the abnormality.

  Therefore, the engine operating area is divided into a plurality of operating areas, and the occurrence of followability abnormality is determined for each of the divided operating areas. When it is determined that a follow-up abnormality has occurred, fail-safe processing is performed in the abnormality-occurring operation region. In this case, if the state in which the followability abnormality occurs is left as it is, the drivability and exhaust emission deteriorate due to the deterioration of the controllability of the fuel pressure. And deterioration of exhaust emissions can be suppressed. In this case, in particular, since the fail-safe process is performed only in the operation region where the abnormality has occurred, the fuel pressure can be controlled in accordance with the situation where the follow-up abnormality has occurred. In addition, deterioration of drivability due to excessive output restriction can be suppressed.

  In the second aspect of the present invention, the engine operation area is divided into a plurality of operation areas using the engine speed as a parameter. In general, the target fuel pressure is set with the engine speed as a parameter, and accordingly, the state of occurrence of a follow-up abnormality varies depending on the engine speed. By dividing the operation region using the engine speed as a parameter, fail-safe processing can be performed for follow-up abnormality that occurs only in a specific engine rotation region.

  When the fuel pressure tracking abnormality occurs, the state in which the deviation of the fuel pressure is not eliminated continues for a relatively long time. Therefore, as described in claim 3, during the feedback control, the deviation of the fuel pressure, which is the difference between the actual fuel pressure and the target fuel pressure, is not less than a predetermined determination value, and the state is not less than the predetermined determination time. If the state continues, it may be determined that a follow-up abnormality has occurred.

  In the invention described in claim 4, the target fuel pressure is corrected to the reduced pressure side as fail-safe processing. In this case, since the output of the engine is limited, the situation where the engine is controlled at a high output in a state where the controllability is reduced is solved. In addition, when fuel pressure feedback control is performed using a method that includes integral operation, if the deviation is not eliminated due to follow-up abnormality and the integral term becomes excessively large accordingly, the operation region moves from the abnormal operation region to the normal region. In this case, the controllability of the fuel pressure in the normal region is deteriorated due to the influence of the integral term calculated in the abnormal operation region. On the other hand, by correcting the target fuel pressure to the reduced pressure side in the abnormal operation region, the integral term in the abnormal operation region becomes smaller, thereby reducing the controllability of the fuel pressure when shifting to the normal region. Can be suppressed.

  When a follow-up abnormality occurs, for example, if the target fuel pressure is corrected to the reduced pressure side uniformly in all engine operation regions, the target fuel pressure is lowered even in the normal region. As a result, an unnecessarily low engine output is generated in the normal region, leading to deterioration of drivability. By performing the pressure reduction correction of the target fuel pressure only in the operation region where the abnormality has occurred, excessive engine output is not restricted, and deterioration of drivability can be suppressed.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. The present embodiment embodies the present invention as a common rail fuel injection system for a vehicle diesel engine, and a detailed configuration thereof will be described below.

  FIG. 1 is a configuration diagram showing an outline of a common rail fuel injection system. In FIG. 1, a multi-cylinder diesel engine (hereinafter referred to as an engine) 10 is provided with an electromagnetic injector 11 for each cylinder. These injectors 11 are connected to a common rail (pressure accumulation pipe) 13 common to multiple cylinders via a fuel transmission pipe 12. It is connected to the. The injector 11 has a configuration using, for example, a three-way solenoid valve, and fuel is injected as the nozzle needle slides in the nozzle body. Leakage fuel generated with the operation of the injector 11 is discharged to the fuel tank 15 through the leak pipe 14. A high-pressure pump 20 as a fuel supply pump is connected to the common rail 13 via a high-pressure fuel pipe 16, and high-pressure fuel corresponding to the injection pressure is continuously accumulated in the common rail 13 as the high-pressure pump 20 is driven. The high-pressure pump 20 is driven as the engine 10 rotates, and fuel is repeatedly sucked and discharged in synchronization with the engine rotation. The high pressure pump 20 is provided with an electromagnetically driven suction metering valve (SCV) 21 at its fuel suction portion, and the feed pump 23 is connected to the fuel tank 15 via a low pressure fuel pipe 22. The low-pressure fuel pumped up from the fuel tank 15 by the feed pump 23 is sucked into the fuel chamber of the pump 20 through the suction metering valve 21.

  In practice, the high-pressure pump 20, the suction metering valve 21, and the feed pump 23 are integrated into a pump unit. Since the configuration is well known, a detailed description thereof will be omitted, and the configuration will be briefly described here. That is, in the pump unit, a low pressure fuel path and a high pressure fuel path are formed in the housing member, and the feed pump 23 and the intake metering valve 21 are provided in the low pressure fuel path. Then, the low-pressure fuel supplied through the low-pressure fuel path is increased by the high-pressure pump 20 as the intake metering valve 21 is opened, and the high-pressure fuel is discharged through the high-pressure fuel path.

  The common rail 13 is provided with a fuel pressure sensor 24, and the fuel pressure in the common rail 13 is detected by the fuel pressure sensor 24. The common rail 13 is provided with an electromagnetically driven (or mechanical) pressure reducing valve 25. When the fuel pressure rises excessively, the pressure reducing valve 25 is opened, and the fuel is supplied to the fuel tank via the leak pipe 14. The pressure is reduced by being discharged to 15.

  The ECU 30 is an electronic control unit including a known microcomputer composed of a CPU, ROM, RAM, EEPROM, and the like. The ECU 30 includes various signals such as a rotation speed sensor and an accelerator opening sensor in addition to a detection signal of the fuel pressure sensor 24. Detection signals are sequentially input from the sensor. Then, the ECU 30 determines an optimal fuel injection amount and injection timing based on engine operation information such as engine rotation speed and accelerator opening, and outputs an injection control signal corresponding to the fuel injection amount to the injector 11. Thus, fuel injection from the injector 11 to the combustion chamber is controlled in each cylinder.

  Further, the ECU 30 calculates the target value of the fuel pressure (injection pressure) in the common rail 13 based on the operating state of the engine 10 and discharges the fuel from the high-pressure pump 20 so that the actual fuel pressure matches the target fuel pressure. Control the amount. This control is fuel pressure feedback control using a PID control method, and the actual fuel pressure follows the target fuel pressure. PID control is a control method based on proportional operation, integral operation and differential operation, and the proportional term, integral term and differential term are calculated based on the deviation of the fuel pressure. The fuel pressure deviation is the difference between the actual fuel pressure and the target fuel pressure.

  Actually, the fuel discharge amount command value to the high pressure pump 20 is determined based on the deviation of the fuel pressure, and the fuel discharge amount command value is converted into the command current value of the intake metering valve 21. Then, the opening degree of the intake metering valve 21 is controlled based on the command current value. Thereby, the opening degree of the intake metering valve 21 is adjusted, and the fuel discharge amount by the high-pressure pump 20 is adjusted accordingly.

  FIG. 2 is a diagram showing the relationship among the target fuel pressure in the common rail 13, the engine speed, and the accelerator opening. According to FIG. 2, the target fuel pressure is set to a low value in a low speed range where the engine speed is slow, and is set to a high value as the speed increases. In the middle rotation range, the target fuel pressure shows the highest numerical value, and when the engine speed enters the high rotation range, the target fuel pressure is lowered. The target fuel pressure is set to a low value when the accelerator opening is small, and is set to a large value as the accelerator opening is increased.

  By the way, if the injector 11 is used for a long period of time, the clearance of the sliding portion between the nozzle body and the nozzle needle is widened due to a change with time, and the amount of fuel leakage may increase. Further, in the high-pressure pump 20, there is a possibility that the fuel discharge amount may decrease due to a change with time of a mechanism portion that discharges high-pressure fuel. Therefore, a followability abnormality may occur in which the actual fuel pressure cannot follow the target fuel pressure.

  During the fuel pressure feedback control, the ECU 30 determines that the follow-up abnormality is present when the fuel pressure deviation is equal to or greater than a predetermined determination value and the state continues for a predetermined determination time.

  Further, it is considered that the followability abnormality does not appear evenly in all engine operation regions, and may appear only in a specific engine operation region, for example, at the initial stage of occurrence of abnormality.

  Therefore, in this system, the engine operation region is divided into a plurality of regions using the rotation speed of the engine 10 as a parameter, and occurrence of a follow-up abnormality is determined for each of these operation regions. When a follow-up abnormality occurs, a decompression correction is performed as a fail-safe process to correct the target fuel pressure to the pressure-reducing side within the abnormality-occurring operation area where the follow-up abnormality has occurred. By performing the pressure reduction correction, the deviation of the fuel pressure is reduced, and the followability of the actual fuel pressure by the fuel pressure feedback control is improved. On the other hand, pressure reduction correction of the target fuel pressure is not performed in a normal region that is an operation region in which no followability abnormality has occurred.

  Incidentally, if a follow-up abnormality occurs in the low rotation range, the target fuel pressure is also low, so the influence of the follow-up abnormality is small. Further, in the high speed range, the high pressure pump 20 driven by the engine 10 also becomes high speed, the number of times of fuel discharge is increased, and a sufficient fuel discharge amount can be obtained. Further, since the target fuel pressure is medium, when a followability abnormality occurs in a high rotation range, the influence of the followability abnormality is small. On the other hand, the number of fuel discharges of the high-pressure pump 20 is not sufficient in the middle rotation region, and the target fuel pressure is higher than that in other regions. For this reason, when the followability abnormality occurs in the middle rotation range, the problem of the followability abnormality becomes remarkable.

  Next, a control method for causing the actual fuel pressure to follow the target fuel pressure will be described. FIG. 3 is a flowchart showing the follow-up abnormality determination process. The follow-up abnormality determination process is repeatedly executed by the ECU 30 at a predetermined time period.

  In FIG. 3, in step S <b> 101, it is determined whether or not the occurrence of an abnormality other than the follow-up abnormality that is the current determination target has already been determined. Specifically, in another abnormality determination process, it is determined whether or not a fuel leakage abnormality has occurred due to a crack in the fuel pipe, etc., and by referring to the determination result, an abnormality other than the followability abnormality is determined. Determine occurrence. Next, in step S102, it is determined whether the fuel pressure deviation ΔPc is equal to or greater than a predetermined determination value Th. Here, the difference between the actual fuel pressure and the target fuel pressure is the fuel pressure deviation ΔPc, and the deviation ΔPc varies with changes in the fuel pressure. In subsequent step S103, it is determined whether or not the fuel discharge amount command value is greater than or equal to a predetermined determination value. In step S104, it is determined whether or not the current operation region is the same operation region as the previous process. If it is the same operating region from the previous time, NO is determined in step S104, and if the engine rotational speed is changed to another operating region, YES is determined in step S104.

  If all of steps S101 to S104 are YES, the process proceeds to step S105, and the followability abnormality counter is incremented by one. On the other hand, if any of steps S101 to S104 is NO, the process proceeds to step S110, and the followability abnormality counter is cleared to zero.

  In step S106, it is determined whether or not the value of the follow-up abnormality counter is equal to or greater than a predetermined determination value K. If YES, the process proceeds to step S107, and it is determined that a follow-up abnormality has occurred. Then, the process proceeds to step S108, the followability abnormality data is stored in a backup memory such as a standby RAM or EEPROM in correspondence with the current operation region, and then this process is terminated. If step S106 is NO, it is assumed that no follow-up abnormality has occurred, and then this process ends.

  The following tracking abnormality determination process will be described more specifically based on the timing chart of FIG. At timing t1, the target fuel pressure indicated by a broken line increases due to, for example, an accelerator operation by the driver, and the actual fuel pressure increases according to the target pressure. At this time, since the fuel pressure deviation ΔPc is equal to or greater than the predetermined determination value Th, the follow-up abnormality counter increases. Then, it is determined that a follow-up abnormality has occurred at a timing t2 when the follow-up abnormality counter becomes a value equal to or greater than a predetermined determination value K. Thereafter, when the fuel pressure deviation ΔPc becomes less than the predetermined determination value Th, the followability abnormality counter is cleared to zero.

  FIG. 5 shows a flowchart of the fuel pressure feedback control process.

  First, in step S201, the engine rotation speed, accelerator opening, fuel pressure, and the like are read from various sensors. In subsequent step S202, the target fuel pressure is calculated from the engine speed and the accelerator opening with reference to the target fuel pressure map created based on the relationship of FIG. In step S203, it is determined whether or not the current operation region is an abnormality occurrence operation region based on the followability abnormality data that is the abnormality determination result of the followability abnormality determination process of FIG. If the current operation region is an abnormal operation region, the target fuel pressure is corrected to the reduced pressure side in step S204, and then the process proceeds to step S205. Proceed to step S205 (ie, without correcting the target fuel pressure to the reduced pressure side).

  Finally, in step S205, the fuel discharge amount command value of the high-pressure pump 20 is calculated based on the deviation between the target fuel pressure and the actual fuel pressure, and the instruction of the intake metering valve 21 is based on the discharge amount command value. Calculate the current value.

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

  Since the occurrence of follow-up abnormality is determined for each of the operation areas divided into a plurality, and the fail-safe process is performed in the abnormality determination area, it is possible to suppress deterioration of drivability and exhaust emission. Moreover, since the fail-safe process can be performed by limiting the operation region to the abnormal operation region by dividing the operation region, it is possible to suppress deterioration of drivability due to excessive output restriction.

  Since the engine operation region is divided using the engine rotation speed as a parameter, the followability abnormality determination can be suitably performed for each operation region having a different tendency. Thereby, for example, the occurrence of the followability abnormality can be determined in the middle rotation range where the problem of the followability abnormality is remarkable, and fail safe can be suitably implemented.

  Since the target fuel pressure is corrected to the pressure-reducing side as a fail-safe process at the time of occurrence of the follow-up abnormality, it is possible to eliminate a situation where the engine is controlled at a high output level while the controllability is lowered.

  Further, when the followability abnormality occurs, the integral term in the fuel pressure feedback control does not become excessively large if the deviation of the fuel pressure is reduced with the correction of the target fuel pressure. Therefore, when the operation region moves from the abnormal operation region to the normal region, deterioration of controllability can be suppressed. That is, in the operation region where the follow-up abnormality has occurred, the state in which the fuel pressure deviation is large continues and the integral term increases accordingly, so when the operation region shifts from the abnormality occurrence operation region to the normal region, Under the influence of the calculated integral term, the controllability of the fuel pressure in the normal region decreases. On the other hand, by correcting the target fuel pressure to the reduced pressure side in the abnormal operation region, the integral term in the abnormal operation region becomes smaller, thereby reducing the controllability of the fuel pressure when shifting to the normal region. Can be suppressed.

  When a follow-up abnormality occurs, if the target fuel pressure is corrected uniformly to the reduced pressure side in all operating regions, the target fuel pressure is reduced even in the normal region, and an unnecessary reduction in engine output occurs. Here, by performing the correction on the fuel pressure reduction side only in the abnormal operation region, excessive engine output is not limited, and deterioration of drivability can be suppressed.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

  In the above embodiment, the operation region is divided into three regions of a low rotation region, a medium rotation region, and a high rotation region due to the difference in engine rotation speed. Good. Furthermore, in addition to or instead of the rotation speed, the accelerator opening may be used as a parameter, and the operation region may be divided based on the parameter. As a result, it is possible to reduce the divided operation region in which occurrence of the follow-up abnormality is determined, and finer fuel pressure feedback control can be performed.

  In the above embodiment, the target fuel pressure map is defined by the relationship among the target fuel pressure, the engine speed, and the accelerator opening, but this may be changed and the target fuel pressure map may be defined by other parameters. . For example, the fuel injection amount by the injector may be used instead of the accelerator opening.

  In the above embodiment, when the state in which the deviation of the fuel pressure is not eliminated continues, it is determined that the followability abnormality has occurred, but this is changed, and the integrated value of the deviation of the fuel pressure is equal to or greater than a predetermined determination value. When it becomes, it may be determined that a tracking abnormality has occurred.

  In the above-described embodiment, the target fuel pressure is corrected to the pressure reduction side as the fail-safe process, but this may be changed to reduce the fuel injection amount by the injector 11. In other words, the fuel pressure follow-up abnormality is improved by suppressing the total fuel consumption of the common rail system (injector 11, common rail 13, high pressure pump 20, etc.). Therefore, suppressing the fuel injection amount by the injector 11 is also effective. it is conceivable that. In this case, the followability to the target fuel pressure is improved when the target fuel pressure is increased by reducing the fuel injection amount as fail-safe processing. Further, an upper limit value may be provided for the fuel discharge amount as the fail-safe process.

It is a lineblock diagram showing an outline of a common rail type fuel injection system in an embodiment of the invention. 3 is a target fuel pressure map showing an operation region. It is a flowchart which shows a followability abnormality determination process. It is a time chart which shows followability abnormality judging processing. It is a flowchart which shows a fuel pressure feedback control process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Injector as fuel injection valve, 13 ... Common rail, 20 ... High pressure pump as fuel supply pump, 24 ... Fuel pressure sensor, 30 ... ECU as abnormality determination means and fail safe means

Claims (4)

A common rail for accumulating high-pressure fuel for injection and supply to the engine, a fuel supply pump for pumping fuel to the common rail, a fuel pressure sensor for detecting fuel pressure in the common rail, and a high-pressure fuel connected to the common rail for injecting high-pressure fuel The fuel injection is applied to a fuel injection system comprising: a fuel injection valve that performs feedback control of a fuel discharge amount by the fuel supply pump so that an actual fuel pressure detected by the fuel pressure sensor matches a target fuel pressure In the system control unit,
An abnormality determination means that divides the engine operating region into a plurality of operating regions, and determines for each of the divided operating regions the occurrence of followability abnormality in which the actual fuel pressure cannot follow the target fuel pressure;
Fail-safe means for performing fail-safe processing within the abnormality-occurring operation region when it is determined by the abnormality determining means that a follow-up abnormality has occurred;
A control device for a fuel injection system.   2. The fuel injection system control device according to claim 1, wherein the operating region is divided into a plurality of regions using the rotational speed of the engine as a parameter.   The abnormality determination unit is configured to perform follow-up when a deviation between an actual fuel pressure and a target fuel pressure is a predetermined value or more and the state continues for a predetermined time or more during feedback control of the fuel discharge amount. The control device for a fuel injection system according to claim 1, wherein the control device is determined to be abnormal.   The fuel injection system control device according to any one of claims 1 to 3, wherein the fail-safe means corrects the target fuel pressure to a reduced pressure side.

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