JP4544153B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a pressure accumulating chamber that stores fuel in a high pressure state, a pressure reducing valve that causes the fuel in the pressure accumulating chamber to flow out, a fuel pump that pressurizes and supplies fuel to the pressure accumulating chamber, and a detection means that detects the fuel pressure in the pressure accumulating chamber. And a fuel injection valve for injecting the fuel stored in the pressure accumulating chamber, the fuel injection device of the on-vehicle internal combustion engine, the pressure reducing valve is set in response to a pressure reducing request based on the difference between the fuel pressure in the pressure accumulating chamber and the target fuel pressure The present invention relates to a fuel injection control device that performs an opening operation.

  2. Description of the Related Art A fuel injection device including a common pressure accumulation chamber (common rail) that supplies high-pressure fuel to a fuel injection valve of each cylinder of a diesel engine is well known. According to this common rail type diesel engine, the fuel pressure in the common rail can be freely controlled according to the engine operating state, and as a result, the pressure of the fuel supplied to the fuel injection valve can be freely controlled.

  Specifically, usually, an appropriate value as the fuel pressure in the common rail is set as the target value (target fuel pressure) based on the operation amount of the accelerator pedal and the command injection amount for the fuel injection valve. Then, feedback control is performed so that the detected fuel pressure follows the target fuel pressure.

  In addition, the above fuel injection device is also well known that includes a pressure reducing valve that allows the fuel in the common rail to flow out to the fuel tank. As a result, when the fuel pressure in the common rail excessively exceeds the target fuel pressure, a request for reducing the fuel pressure in the common rail can be quickly responded.

  By the way, if the pressure reducing valve is opened during the period in which the fuel is injected through the fuel injection valve, the control accuracy of the fuel injection amount may be lowered. For example, even if the fuel injection valve is opened according to the command injection period corresponding to the detected fuel pressure, the actual injection amount is desired because the fuel pressure in the common rail decreases due to the opening of the pressure reducing valve. There is a risk that it will deviate from the injection amount.

  In view of this, a fuel injection control device that prevents the fuel injection period and the valve opening period of the pressure reducing valve from overlapping each other has been proposed, for example, as shown in Patent Document 1 below. As a result, when the fuel pressure in the common rail becomes excessively higher than the target fuel pressure, the fuel pressure can be quickly reduced while avoiding a decrease in fuel injection control accuracy.

  However, when the vehicle decelerates suddenly from the state where the accelerator pedal is depressed, the target fuel pressure decreases sharply, so the amount of fuel that flows out of the common rail to make the actual fuel pressure the target fuel pressure is also A large amount. However, when the valve opening period of the pressure reducing valve is limited as in the above control device, the actual fuel pressure cannot be sufficiently reduced by opening the valve once. For this reason, it is necessary to open and close the pressure reducing valve many times, and the fuel pressure in the common rail may not be able to follow the target fuel pressure appropriately.

It is not limited to avoiding the overlap between the fuel injection period and the opening period of the pressure reducing valve, but a permitting period for opening the pressure reducing valve is provided in order to suppress fluctuations in the fuel pressure in the pressure accumulating chamber due to the opening of the pressure reducing valve. However, the actual situation where the ability to follow the target fuel pressure is reduced is also common.
JP 2000-240494 A

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to suppress the fluctuation of the fuel pressure in the pressure accumulating chamber due to the opening of the pressure reducing valve and to follow the target fuel pressure of the fuel pressure in the pressure accumulating chamber. It is an object of the present invention to provide a fuel injection control device capable of achieving a favorable balance between maintaining high.

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

The invention according to claim 1 includes a pressure reducing means for opening the pressure reducing valve when a differential pressure obtained by subtracting the target fuel pressure from the fuel pressure in the pressure accumulating chamber is equal to or greater than a first predetermined value, When the differential pressure is equal to or greater than a first predetermined value and less than a second predetermined value, the valve opening of the pressure reducing valve is permitted only during a predetermined permission period, while being equal to or greater than the second predetermined value. Is not limited by the permission period regarding the opening of the pressure reducing valve, the first predetermined value is set to a pressure value at which a pressure reduction request is generated, and the second predetermined value is the permission According to the pressure reduction control limited to the period, it is set based on a pressure value that is assumed to be less able to follow the target fuel pressure .

  In the above configuration, when the differential pressure is not less than the first predetermined value and less than the second predetermined value, the opening of the pressure reducing valve is permitted within the permission period. For this reason, the fluctuation | variation of the fuel pressure by valve opening of a pressure reducing valve can be suppressed outside a permission period. On the other hand, when the differential pressure is greater than or equal to the second predetermined value, the opening of the pressure reducing valve is permitted even outside the permitted period. For this reason, for example, when the target fuel pressure suddenly decreases due to sudden release from the state where the accelerator pedal is depressed, and when the detected fuel pressure exceeds the target fuel pressure, the pressure reducing valve is opened even during the injection period. Therefore, it is possible to suitably suppress a decrease in followability with respect to the target fuel pressure. For this reason, according to the above configuration, it is preferable to achieve both the suppression of fluctuations in the fuel pressure in the pressure accumulating chamber due to the opening of the pressure reducing valve and the high followability of the fuel pressure in the pressure accumulating chamber to the target fuel pressure. be able to.

  According to a second aspect of the present invention, in the first aspect of the invention, the pressure reducing unit includes a first determining unit that determines whether the differential pressure is equal to or greater than the first predetermined value, and the differential pressure. And a second determination means for determining whether or not the pressure is greater than or equal to the second predetermined value; and when the differential pressure is greater than or equal to the second predetermined value, a period during which the pressure reducing valve is opened A period during which the pressure reducing valve is opened within the permission period when the differential pressure is greater than or equal to the first predetermined value and less than the second predetermined value. And setting means for setting.

  In the said structure, the said pressure reduction means can be comprised appropriately by providing a 1st judgment means, a 2nd judgment means, and a setting means.

According to a third aspect of the invention, in the invention described in claim 2, wherein the setting means, the end timing of the period for opening the pressure reducing valve when the differential pressure is the second predetermined value or more, before It is characterized in that the differential pressure is positive and falls below a third predetermined value set to a value below the first predetermined value.

In the above configuration, even when the pressure reduction control is not performed by opening the pressure reducing valve within the permission period because the fuel pressure in the pressure accumulating chamber exceeds the target fuel pressure, sufficient pressure reduction control cannot be performed. The decompression control can be appropriately performed by opening the decompression valve until the detected differential pressure is equal to or less than the third predetermined value.

  According to a fourth aspect of the present invention, in the second or third aspect of the invention, the setting means includes a calculating means for calculating a required valve opening time of the pressure reducing valve based on the differential pressure, and a valve opening time of the pressure reducing valve. And an upper limit guard means for setting an upper limit value of the required valve opening time and the upper limit value when the differential pressure is not less than the first predetermined value and less than the second predetermined value. The end timing of the period for opening the pressure reducing valve is set based on the smaller of the two.

  In the above configuration, by setting the upper limit value, a means for permitting the opening of the pressure reducing valve within the permitted period can be appropriately configured.

  The invention according to claim 5 is the invention according to any one of claims 2 to 4, wherein the pressure reducing valve is a normally closed type valve, and the permission period is a rotation angle of an output shaft of the in-vehicle internal combustion engine. The fuel injection control device opens the pressure reducing valve by directly energizing the pressure reducing valve with the voltage of the battery of the in-vehicle internal combustion engine.

  In the above configuration, since the pressure reducing valve is directly energized by the voltage of the battery, it is not necessary to include a boosting means for boosting the voltage of the battery. For this reason, the driver for energizing the pressure reducing valve can be simply configured. However, on the other hand, according to such a configuration, the responsiveness of the pressure reducing valve is lowered as compared with the case where the pressure reducing valve is opened through a driver having a pressure increasing means. For this reason, in such a configuration, the actual valve opening period of the pressure reducing valve becomes extremely short only by opening (opening operation) of the pressure reducing valve within the permission period, and the actual fuel pressure exceeds the target fuel pressure excessively. In such a case, it may not be possible to sufficiently meet the pressure reduction request. In particular, such a situation is likely to occur when a deceleration request is generated from the high rotation region. This is because the time interval of the permission period is shortened because the rotation speed in this case is large. For this reason, the said structure becomes a structure which can show | play suitably the effect of the invention of Claims 2-4.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the permission period is determined by a rotation angle of an output shaft of the in-vehicle internal combustion engine, and the second predetermined value is It is variably set based on the rotational speed of the output shaft of the in-vehicle internal combustion engine.

  In the above configuration, the second predetermined value is variably set according to the rotation speed. Here, the rotation speed is a parameter having a correlation with the time interval of the permission period. For this reason, in the above configuration, the second predetermined value is appropriately set in view of whether or not the decompression request can be satisfied by opening the decompression valve only during the permission period, depending on the rotational speed. Can be set. For this reason, the pressure reducing valve is improved while achieving a more suitable coexistence of suppressing the fluctuation of the fuel pressure in the pressure accumulating chamber due to the opening of the pressure reducing valve and maintaining high followability of the fuel pressure in the pressure accumulating chamber to the target fuel pressure. Can be operated.

(First embodiment)
Hereinafter, a first embodiment in which a fuel injection control device according to the present invention is applied to a fuel injection control device of a common rail diesel engine will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of the engine system according to the present embodiment.

  As shown in the figure, the fuel in the fuel tank 2 is pumped up by the fuel pump 6 through the fuel filter 4. The fuel pump 6 is supplied with power from a crankshaft, which is an output shaft of a diesel engine, and discharges fuel. Specifically, the fuel pump 6 includes an intake metering valve 8, and the amount of fuel discharged to the outside is determined by operating the intake metering valve 8. The fuel pump 6 includes several plungers, and these plungers reciprocate between a top dead center and a bottom dead center, whereby fuel is sucked and discharged.

  The fuel from the fuel pump 6 is pressurized and supplied (pressure fed) to the common rail 10. The common rail 10 stores the fuel pumped from the fuel pump 6 in a high pressure state, and supplies the fuel to the fuel injection valve 14 of each cylinder (here, four cylinders are illustrated) via the high pressure fuel passage 12. The fuel injection valve 14 is connected to the fuel tank 2 through a low pressure fuel passage 16. The common rail 10 is provided with a pressure reducing valve 18 through which fuel in the common rail 10 can flow out to the fuel tank 2 via the low pressure fuel passage 16.

  The engine system includes various sensors that detect the operating state of the diesel engine, such as a fuel pressure sensor 20 that detects the fuel pressure in the common rail 10 and a crank angle sensor 22 that detects the rotation angle of the output shaft of the diesel engine. The engine system also includes an interface between the user and the fuel injection control device, such as an accelerator sensor 24 that detects an operation amount of an accelerator pedal.

  On the other hand, the electronic control unit (ECU 30) is mainly composed of a microcomputer, takes in the detection results of the various sensors, and operates various actuators such as the fuel injection valve 14, the pressure reducing valve 18, and the fuel pump 6 based on the detection results. Thus, the output of the diesel engine is controlled. Here, the fuel injection valve 14 includes an electromagnetic solenoid, and the nozzle needle is opened and closed as the nozzle needle is displaced in the axial direction of the fuel injection valve 14 depending on whether or not the electromagnetic solenoid is energized. . The pressure reducing valve 18 is also provided with an electromagnetic solenoid, and opens and closes depending on whether the electromagnetic solenoid is energized. Specifically, the pressure reducing valve 18 has a configuration in which a part of the movable iron core in the circumferential direction that causes opening and closing of the valve body is covered with an electromagnetic solenoid, as described in, for example, Japanese Patent Application Laid-Open No. 2002-61548. In this type, the movable iron core is further drawn into the electromagnetic solenoid by energizing the electromagnetic solenoid.

  The fuel injection valve 14 is operated by the ECU 30 via the driver 32, and the pressure reducing valve 18 is operated by the ECU 30 via the driver 34. The ECU 30 and the driver 32 are supplied with power by a battery 36. The driver 32 includes a booster circuit that boosts the voltage of the battery 36 and energizes the fuel injection valve 14 using the boosted voltage. On the other hand, the driver 34 directly energizes the pressure reducing valve 18 by the voltage of the battery 36 without increasing the voltage of the battery 36.

  FIG. 2 shows how the fuel injection valve 14 and the pressure reducing valve 18 are operated via the driver 32 and the driver 34. Specifically, FIG. 2A shows an energization mode of the fuel injection valve 14, FIG. 2B shows an open / closed state of the fuel injection valve 14, and FIG. 2C shows an energization mode of the pressure reducing valve 18. FIG. 2D shows the open / close state of the pressure reducing valve 18.

  As shown in FIG. 2A, when opening the fuel injection valve 14, the energization amount to the fuel injection valve 14 is once increased to a large value by the voltage boosted by the booster circuit, and then the battery 36 is used. The constant current is controlled by a circuit that generates a constant current with the voltage of. Thereby, as FIG.2 (b) shows, the fuel injection valve 14 opens quickly.

  On the other hand, when the pressure reducing valve 18 is opened as shown in FIG. 2C, a current generated using the voltage of the battery 36 is supplied to the pressure reducing valve 18 so that a desired constant current is reduced. When the valve 18 flows, the pressure reducing valve 18 is opened as shown in FIG.

  The driver 32 may be described in, for example, Japanese Patent Application Laid-Open No. 2001-14046. The driver 34 may be provided with only a circuit that generates a constant current among the drivers described in the publication.

  The ECU 30 performs fuel injection control so as to appropriately control the output of the diesel engine. In this fuel injection control, the fuel pump 6 (specifically, the intake metering valve 8) is operated so as to feedback-control the fuel pressure in the common rail 10 to a target fuel pressure set according to the operating state of the diesel engine. To do. Here, the target fuel pressure is calculated based on the command injection amount for the fuel injection valve 14 and the rotational speed of the diesel engine. The command injection amount is calculated based on the accelerator pedal operation amount and the rotational speed of the diesel engine. The target fuel pressure is set to a higher value as the diesel engine performs higher load and higher rotation.

  When the actual fuel pressure in the common rail 10 greatly exceeds the target fuel pressure, it is assumed that a pressure reduction request has occurred, and the fuel pressure in the common rail 10 is controlled to be reduced by opening the pressure reducing valve 18. The opening operation of the pressure reducing valve 18 is basically performed in a period other than the fuel injection period, as shown in FIG. 3, in order to suppress a decrease in accuracy of the injection amount via the fuel injection valve 14. Incidentally, FIG. 3A shows the fuel injection mode of the first cylinder, FIG. 3B shows the fuel injection mode of the second cylinder, and FIG. 3C shows the fuel injection mode of the third cylinder. FIG. 3D shows the fuel injection mode of the fourth cylinder. Further, in FIG. 3, four-stage injection in which two-stage pilot injection p, one-stage pre-injection pr, and one-stage main injection m are illustrated.

  As described above, by prohibiting the opening operation of the pressure reducing valve 18 during the fuel injection period, it is possible to suppress a decrease in control accuracy of the actually injected fuel. However, for example, when the accelerator pedal is released when the rotational speed of the output shaft of the diesel engine is high, the target fuel pressure decreases rapidly, so that the fuel pressure in the common rail 10 is more than the target fuel pressure. Become bigger. For this reason, the surplus fuel amount in the common rail 10 for making it follow target fuel pressure becomes large.

  However, when the rotational speed of the diesel engine is high, the time interval between an arbitrary fuel injection period and the next fuel injection period is shortened, and a sufficient amount of fuel is supplied by opening the pressure reducing valve 18. There is a possibility that it cannot flow out of the common rail 10.

  In particular, in the present embodiment, this problem is serious because the pressure reducing valve 18 is operated with a constant current generated from the voltage of the battery 36. That is, as shown in FIG. 2A, when the booster circuit is used, the time required until a desired constant current flows through the electromagnetic solenoid is shortened. As shown in d), when the constant current is directly generated by the voltage of the battery 36, the time required for the constant current to flow increases, and consequently the time required from the start of energization to the valve opening. T is prolonged. For this reason, the responsiveness with respect to the opening operation of the pressure reducing valve 18 is low, and it becomes more difficult to ensure sufficient actual valve opening time.

  Further, in the present embodiment, the pressure reducing valve 18 is configured such that a part of the outer periphery of the movable iron core is covered with an electromagnetic solenoid. In such a configuration, it is required that the axis of the movable iron core be accurately aligned with the axis of the electromagnetic solenoid in order to apply a magnetic force evenly to any angle in the radial direction of the movable iron core. For this reason, the clearance between the outer periphery of the movable part in the pressure reducing valve 18 connected to the movable iron core and the inner periphery of the fixed part of the pressure reducing valve 18 is reduced to restrict the displacement of the movable iron core in the radial direction. The Rukoto. However, when the clearance is reduced in this way, the force required to open the pressure reducing valve 18 is increased, and as a result, the responsiveness of the pressure reducing valve 18 is lowered.

  As described above, the present embodiment has a merit that the configuration of the driver 34 and the like can be simplified, but has a demerit that it is difficult to improve the responsiveness of the pressure reducing valve 18. By providing a period during which the opening operation of 18 is prohibited, it is more difficult to perform sufficient pressure reduction control.

  Therefore, in this embodiment, when the differential pressure of the detected fuel pressure with respect to the target fuel pressure is not less than the first predetermined value and less than the second predetermined value, the pressure reducing valve is used in a period other than the fuel injection period (permission period). When the differential pressure is equal to or higher than the second predetermined value, the differential pressure is equal to or higher than the first predetermined value in a mode in which the opening operation of the pressure reducing valve 18 is permitted even during the fuel injection period. At some time, the pressure reducing valve 18 is opened. Hereinafter, this will be described in detail with reference to FIG.

  FIG. 4 shows a processing procedure of pressure reduction control according to the present embodiment. This process is repeatedly executed by the ECU 30, for example, at a predetermined cycle.

  In this series of processes, first, in step S10, the first threshold A is calculated by adding a predetermined value Δ1 to the target fuel pressure, and the second threshold is calculated by adding the predetermined value Δ2 to the target fuel pressure. . Here, the predetermined value Δ1 is set to an amount in which the fuel pressure in the common rail 10 exceeds the target fuel pressure and a request for reducing the fuel pressure in the common rail 10 is generated. Specifically, for example, when the actual fuel pressure in the common rail 10 exceeds the target fuel pressure, there is a concern that the exhaust characteristics may deteriorate due to the fuel spray shape deviating from the desired one upon fuel injection. Is set. On the other hand, the predetermined value Δ2 is set based on an amount assumed that sufficient pressure reduction control cannot be performed by pressure reduction control limited to a period other than the fuel injection period.

  When the process of step S10 is completed in this way, in steps S12 and S14, the fuel pressure detected by the fuel pressure sensor 20 is less than the first threshold A (step S12: NO), or more than the first threshold A. It is determined whether it is less than the second threshold B (step S14: NO) or more than the second threshold B (step S14: YES). And when it is more than 1st threshold value A and less than 2nd threshold value B, the process of step S16-S26 is performed in order to open the pressure-reduction valve 18 in periods other than a fuel injection period.

  That is, first, in step S16, based on the target fuel pressure and the detected fuel pressure, a required energization time that is a time required for reducing the fuel pressure in the common rail 10 to the target fuel pressure is calculated. Here, the required energization time is calculated in view of the fact that the decrease rate of the fuel pressure due to the outflow of fuel from the common rail 10 by opening the pressure reducing valve 18 decreases as the fuel pressure decreases. This can be performed, for example, by storing in advance in the ECU 30 data defining the relationship between the fuel pressure drop rate of the common rail 10 and the fuel pressure when the pressure reducing valve 18 is in the open state.

  In the subsequent step S18, the upper limit value of the energization time is calculated based on the rotational speed of the diesel engine. Here, the rotation speed is a parameter having a correlation with a time interval between an arbitrary fuel injection period and the next fuel injection period. For this reason, the time from the start of energization to the start timing of the next fuel injection period can be determined by the upper limit value. When the upper limit value is calculated in this way, in step S20, the pressure reducing valve 18 is energized (opening operation) starting from the end timing of an arbitrary fuel injection period. If the energization time reaches the upper limit (step S22: YES) or the energization time reaches the required energization time (step S24: YES), the energization is stopped in step S26.

  On the other hand, if it is determined in steps S12 and S14 that the detected fuel pressure is greater than or equal to the second threshold value B, the processes of steps S28 to S34 are performed.

  Here, first, in step S28, energization of the pressure reducing valve 18 is immediately started regardless of which region the crank angle region of the diesel engine is. In subsequent step S30, a third threshold C is calculated by adding a predetermined value Δ3 to the target fuel pressure. The threshold value C is set to a value that is equal to or higher than the target fuel pressure and smaller than the second threshold value B, and more preferably a value that is equal to or lower than the first threshold value A. Further, the predetermined value Δ3 is set to a value for determining whether or not the amount of decrease in the fuel pressure has reached an amount that can stop the opening operation of the pressure reducing valve 18. When it is determined that the fuel pressure detected by opening the pressure reducing valve 18 is equal to or lower than the third threshold C (step S32: YES), the power supply to the pressure reducing valve 18 is stopped.

  Note that when it is determined in step S12 that the value is less than the threshold value A, or when the processes in steps S26 and S34 are completed, this series of processes is temporarily ended.

  FIG. 5 illustrates an example of the pressure reduction control. Specifically, FIG. 5 (a1) and FIG. 5 (b1) show the behavior of the fuel pressure and the state of the pressure reducing valve 18 when the fuel pressure exceeds the first threshold A but does not reach the second threshold B, respectively. 5 (a2) and FIG. 5 (b2) show the behavior of the fuel pressure and the operation state of the pressure reducing valve 18 when the fuel pressure exceeds the second threshold value B, respectively. Incidentally, in FIGS. 5 (a1) and 5 (a2), the fuel pressure detected by the fuel pressure sensor 20 is indicated by a solid line, and the target fuel pressure is indicated by a one-dot chain line.

  As shown in FIG. 5 (a1) and FIG. 5 (b1), when the fuel pressure exceeds the first threshold A but does not reach the second threshold B, the time after the time t1 when the fuel pressure becomes equal to or higher than the first threshold A The opening operation (energization) of the pressure reducing valve 18 is performed. Then, the pressure reducing valve 18 is closed (energization is stopped) at time t2 when the required energization time calculated in step S16 of FIG. 4 elapses. Then, after that, fuel injection is performed after time t3, so that the fuel pressure in the common rail 10 further decreases.

  On the other hand, as shown in FIGS. 5 (a2) and 5 (b2), when the target fuel pressure rapidly decreases and the fuel pressure exceeds the second threshold B, the pressure reducing valve 18 is immediately opened, so the common rail 10 The fuel pressure inside falls quickly. On the other hand, when the opening operation of the pressure reducing valve 18 is prohibited during the fuel injection period even though the fuel pressure exceeds the second threshold B, as shown by a two-dot chain line in FIG. Since the fuel pressure in the common rail 10 decreases stepwise by many opening / closing operations of the pressure reducing valve 18, the time required for the fuel pressure to decrease near the target fuel pressure is prolonged.

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

  (1) When the fuel pressure is greater than or equal to the first threshold A and less than the second threshold B, the period for opening the pressure reducing valve 18 is set to a period other than the fuel injection period, while the fuel pressure is greater than or equal to the second threshold B In this case, the period for opening the pressure reducing valve 18 was set according to the detected amount of decrease in fuel pressure. Accordingly, when the pressure is not less than the first threshold A and less than the second threshold B, the opening of the pressure reducing valve 18 during the fuel injection period is prohibited. For this reason, it is possible to avoid the actual injection amount from deviating from the desired injection amount due to the opening of the pressure reducing valve 18 during the fuel injection period. On the other hand, when the fuel pressure is equal to or higher than the second threshold B, the opening operation of the pressure reducing valve 18 during the fuel injection period is permitted. For this reason, for example, when the target fuel pressure is suddenly reduced by releasing it suddenly from the state where the accelerator pedal is depressed, when the detected fuel pressure exceeds the target fuel pressure, the pressure reducing valve 18 is opened even during the injection period. It can be operated, and a decrease in follow-up performance with respect to the target fuel pressure can be suitably suppressed. For this reason, it is possible to perform the opening / closing operation of the pressure reducing valve 18 in such a manner that the followability of the fuel pressure in the common rail 10 to the target fuel pressure is maintained high while suitably suppressing the decrease in the control accuracy of the fuel injection amount.

  Furthermore, by continuously opening the pressure reducing valve 18 when the fuel pressure is equal to or higher than the second threshold B, the number of opening operations is reduced as compared with the case where the opening operation of the pressure reducing valve 18 is prohibited during the fuel injection period. As a result, the exhaustion of the pressure reducing valve 18 can be suppressed.

  (2) The end timing of the period during which the pressure reducing valve 18 is opened when the fuel pressure is equal to or higher than the second threshold B is set to be when the detected fuel pressure is equal to or lower than the third threshold C. As a result, even if the decompression valve 18 is opened only during a period other than the fuel injection period, it is possible to appropriately respond to the decompression request even under a situation in which it is difficult to perform sufficient decompression control.

  (3) The end timing of the period for opening the pressure reducing valve 18 is set based on the smaller of the required energization time and the upper limit value when the fuel pressure is equal to or higher than the first threshold A and lower than the second threshold B. did. Thereby, the means for prohibiting the opening operation of the pressure reducing valve 18 during the fuel injection period can be appropriately configured.

  (4) The pressure reducing valve 18 is a normally closed type valve, and the pressure reducing valve 18 is opened by directly energizing the pressure reducing valve 18 using the voltage of the battery 36. Thereby, it is not necessary to provide the driver 34 with a booster circuit, and the driver 34 can be simply configured, but the responsiveness of the pressure reducing valve 18 is lowered. For this reason, it is the structure which can show | play suitably the effect of the process shown in previous FIG.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 6 shows a processing procedure of pressure reduction control according to the present embodiment. This process is repeatedly executed by the ECU 30, for example, at a predetermined cycle. In FIG. 6, the same steps as those in FIG. 4 are given the same step numbers for the sake of convenience.

  In this series of processing, first, the first threshold value A and the second threshold value B are calculated in step S10a. However, in this step S10a, the predetermined value Δ2 is variably set according to the rotational speed of the diesel engine. Here, the rotation speed is a parameter having a correlation with a time interval between the fuel injection period and the next fuel injection period. The shorter this time interval, the more difficult it is to perform sufficient pressure reduction control by prohibiting the opening operation of the pressure reducing valve 18 during the fuel injection period. For this reason, when the rotational speed is high, the predetermined value Δ2 is variably set so that pressure reduction control in a mode that permits the opening operation of the pressure reducing valve 18 during the fuel injection period can be preferentially performed compared to when the rotational speed is low. To do.

  Further, in the process shown in FIG. 6, when the fuel pressure is equal to or higher than the first threshold A and lower than the second threshold B, the opening operation of the pressure reducing valve 18 during the fuel injection period is prohibited in step S22a. That is, when fuel injection is started via the fuel injection valve 14 (step S22a: YES), the energization is stopped even if the required energization time has not elapsed.

  According to the present embodiment described above, in addition to the effects (1), (2), and (4) of the first embodiment, the following effects can be obtained.

  (5) The predetermined value Δ2 is variably set based on the rotational speed of the output shaft of the diesel engine. Accordingly, in view of the fact that whether or not the decompression request can be satisfied even if the opening operation of the decompression valve 18 during the fuel injection period is prohibited changes according to the rotational speed, the predetermined value Δ2 is appropriately set. can do.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the present embodiment, the pressure reducing valve 18 is of a normally open type that is opened when power is not applied. Then, as shown in FIG. 7A, the fuel pressure (opening pressure) in the common rail 10 that opens the pressure reducing valve 18 is adjusted in accordance with the energization amount to the pressure reducing valve 18. When the detected fuel pressure indicated by the solid line is increased by a predetermined value Δ with respect to the target fuel pressure indicated by the alternate long and short dash line in FIG. 7B, the pressure reducing valve 18 is opened as shown in FIG. As described above, the energization amount for the pressure reducing valve 18 is adjusted.

  FIG. 8 shows a processing procedure of pressure reduction control according to the present embodiment. This process is repeatedly executed by the ECU 30, for example, at a predetermined cycle.

  In this series of processes, first, in step S40, a target fuel pressure calculated by another logic (not shown) is captured. In a succeeding step S42, it is determined whether or not it is a fuel injection period. If it is determined that it is not the fuel injection period, in step S44, the fuel pressure threshold value β for opening the pressure reducing valve 18 is calculated by adding the predetermined value Δ1 in step S10 of FIG. 4 to the target fuel pressure. To do. On the other hand, if it is determined that the fuel injection period is in step S42, the threshold β is calculated in step S46 by adding the predetermined value Δ2 in step S10 of FIG. 4 to the target fuel pressure.

  When the processes of step S44 and step S46 are completed, the energization amount is calculated based on the threshold value β in step S48. That is, the energization amount is calculated based on the relationship shown in FIG. 7A so that the valve opening pressure becomes the threshold value β. In step S50, the pressure reducing valve 18 is energized with the energization amount calculated in step S48.

  According to the process shown in FIG. 8, when the differential pressure of the actual fuel pressure with respect to the target fuel pressure is not less than the predetermined value Δ1 and less than the predetermined value Δ2, the opening of the pressure reducing valve 18 is prohibited during the fuel injection period. . Further, when the differential pressure between the actual fuel pressure and the target fuel pressure is equal to or greater than the predetermined value Δ2, the opening of the pressure reducing valve 18 is permitted during the fuel injection period.

  Also according to the present embodiment described above, it is possible to obtain an effect according to the effect (1) of the first embodiment.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  In the first and second embodiments, when the fuel pressure is equal to or higher than the second threshold B, the pressure reducing valve 18 is immediately opened. In this case, when the opening operation of the pressure reducing valve 18 and the fuel injection period overlap, the injection amount may deviate from a desired value. That is, the fuel injection control is normally performed by determining a command injection period (energization time) for the fuel injection valve 14 from the fuel pressure in the common rail 10 and the required injection amount. For this reason, the command injection period determined by using the detected value of the fuel pressure immediately before the fuel injection may be deviated from an appropriate value when the required injection amount is injected due to a decrease in the fuel pressure due to the opening of the pressure reducing valve 18. is there. On the other hand, the processes in steps S28 to S34 in FIGS. 4 and 6 are performed during deceleration. During this deceleration, the previous injection amount and the injection amount corresponding to the operation amount of the accelerator pedal are usually used to suppress a sudden decrease in the injection amount and a torque shock due to a sudden decrease in the output torque of the diesel engine. A so-called annealing process is performed in which the weighted average value is calculated as the current injection amount. For this reason, even if the actual injection amount is reduced from the assumed injection amount due to the overlap between the valve opening of the pressure reducing valve 18 and the fuel injection period, this is the required injection according to the operation amount of the accelerator pedal. There is no significant drop in volume. In addition, the actual fuel pressure can quickly follow the target fuel pressure.

  However, from the viewpoint of suppressing a decrease in the control accuracy of the injection amount, when the fuel pressure is equal to or higher than the second threshold value B and the fuel cut is performed, the processes in steps S28 to S34 in FIGS. 4 and 6 are performed. You may do it. Conversely, when the processes of steps S28 to S34 in FIGS. 4 and 6 are performed, the fuel cut may be forcibly performed.

  In the first and second embodiments, the period during which the pressure reducing valve 18 is opened when the fuel pressure is equal to or greater than the second threshold value B is set in the same manner as the processing in step S16 in FIGS. The required energization time may be obtained. In this case, the required energization time is a parameter for determining whether the amount of decrease in the fuel pressure has reached a value at which the opening operation of the pressure reducing valve 18 may be stopped.

  In the first and second embodiments, the predetermined values Δ1 and Δ2 may be variably set according to the fuel pressure detected by the fuel pressure sensor 20. That is, in the above two embodiments, the opening operation of the pressure reducing valve 18 is performed when the error between the detected fuel pressure and the target fuel pressure PFIN is equal to or larger than “Δ1 / PFIN”. The value changed according to the target fuel pressure. On the other hand, the predetermined values Δ1 and Δ2 may be variably set according to the target fuel pressure so as not to increase the error.

  In the first and second embodiments, when the fuel pressure is not less than the first threshold A and less than the second threshold B, the opening operation (energization) of the pressure reducing valve 18 during the fuel injection period is prohibited. However, instead of this, the actual valve opening state of the pressure reducing valve 18 may be prohibited. That is, as shown in FIG. 2, since a response delay occurs between the start of energization of the pressure reducing valve 18 and the start of actual energization, the actual valve opening state and fuel injection are anticipated in anticipation of this response delay. Duplication with a period may be prohibited. Even in this case, the time between the opening operation of the pressure reducing valve 18 and the actual opening time varies depending on the voltage of the battery 36 and the like. Overlap with the fuel injection period cannot be allowed. Therefore, the pressure-reducing valve 18 with low responsiveness can exhibit the effects of the first and second embodiments particularly suitably as compared with those with high responsiveness. no change.

  In each of the above embodiments, when the fuel pressure is greater than or equal to the first threshold A and less than the second threshold B, the valve opening of the pressure reducing valve 18 is limited under the restriction that the period other than the fuel injection period is a permitted period. Although (opening operation) was performed, the permission period is not limited to a period other than the fuel injection period. For example, as can be seen in Patent Document 1, a period other than the sampling timing of the detected value of the fuel pressure by the fuel pressure sensor 20 may be set as the permission period.

  In the first and second embodiments, the driver 34 is configured with a booster circuit, or the movable iron core of the pressure reducing valve 18 is not covered by the electromagnetic solenoid, and the movable iron core is outside the electromagnetic solenoid. The electromagnetic solenoid may be pulled in the axial direction. Even if it is such a structure, the effect of said (1)-(3) of previous 1st Embodiment can be acquired.

  In the third embodiment, the predetermined values Δ1 and Δ2 may be variably set according to the rotation speed and the fuel pressure.

  -In addition, the number of cylinders of the diesel engine may be changed as appropriate. Moreover, not only a diesel engine but a cylinder injection type gasoline engine may be used, for example.

The figure which shows the whole structure of the engine system in 1st Embodiment. The time chart which shows the control aspect of the fuel injection valve and pressure-reduction valve concerning the embodiment. The time chart which shows the area | region where opening operation of the pressure-reduction valve in the embodiment is permitted. The flowchart which shows the process sequence of pressure reduction control concerning the embodiment. The time chart which illustrates the aspect of pressure reduction control concerning the embodiment. The flowchart which shows the process sequence of pressure reduction control concerning 2nd Embodiment. The time chart which shows the characteristic of the pressure-reduction valve concerning 3rd Embodiment. The flowchart which shows the process sequence of pressure reduction control concerning the embodiment.

Explanation of symbols

  6 ... fuel pump, 10 ... common rail, 14 ... fuel injection valve, 18 ... pressure reducing valve, 30 ... ECU (electronic control unit).

Claims (6)

A pressure accumulating chamber for storing fuel in a high pressure state; a pressure reducing valve for discharging the fuel in the pressure accumulating chamber; a fuel pump for pressurizing and supplying fuel to the pressure accumulating chamber; a detecting means for detecting a fuel pressure in the pressure accumulating chamber; A fuel injection device for an in-vehicle internal combustion engine comprising a fuel injection valve for injecting fuel stored in a chamber, and a fuel for opening the pressure reduction valve in response to a pressure reduction request based on a difference between a fuel pressure in the pressure storage chamber and a target fuel pressure In the injection control device,
A pressure reducing means for opening the pressure reducing valve when a differential pressure obtained by subtracting the target fuel pressure from the fuel pressure in the pressure accumulating chamber is equal to or greater than a first predetermined value;
The pressure reducing means permits opening of the pressure reducing valve only during a predetermined permission period when the differential pressure is not less than a first predetermined value and less than a second predetermined value. When it is greater than or equal to a predetermined value of 2, there is no restriction by the permission period regarding the opening of the pressure reducing valve,
The first predetermined value is set to a pressure value at which a pressure reduction request occurs,
The fuel injection control apparatus according to claim 1, wherein the second predetermined value is set based on a pressure value that is assumed to be less likely to follow the target fuel pressure by pressure reduction control limited to the permission period .   The pressure reducing means determines whether or not the differential pressure is greater than or equal to the first predetermined value, and determines whether or not the differential pressure is greater than or equal to the second predetermined value. When the differential pressure is greater than or equal to the second predetermined value, a period for opening the pressure reducing valve is set according to a decrease amount of the fuel pressure in the pressure accumulating chamber, and the differential pressure is 2. A setting unit configured to set a period for opening the pressure reducing valve within the permission period when the first predetermined value or more is less than the second predetermined value. The fuel injection control device described. The setting means, the end timing of the period for opening the pressure reducing valve when the differential pressure is the second predetermined value or more, the previous SL differential pressure is positive first below a predetermined value 3. The fuel injection control device according to claim 2, wherein the fuel injection control device is set to be equal to or less than a third predetermined value set to a certain value.   The setting means further comprises calculation means for calculating a required valve opening time of the pressure reducing valve based on the differential pressure, and upper limit guard means for setting an upper limit value of the valve opening time of the pressure reducing valve, wherein the pressure difference An end timing of a period for opening the pressure reducing valve is set based on a smaller one of the required valve opening time and the upper limit value when the value is equal to or greater than the first predetermined value and less than the second predetermined value. The fuel injection control device according to claim 2, wherein the fuel injection control device is a fuel injection control device. The pressure reducing valve is a normally closed type valve,
The permission period is determined by the rotation angle of the output shaft of the in-vehicle internal combustion engine;
5. The fuel injection according to claim 2, wherein the fuel injection control device opens the pressure reducing valve by directly energizing the pressure reducing valve with a voltage of a battery of the in-vehicle internal combustion engine. Control device. The permission period is determined by the rotation angle of the output shaft of the in-vehicle internal combustion engine;
The fuel injection control device according to any one of claims 1 to 5, wherein the second predetermined value is variably set based on a rotation speed of an output shaft of the on-vehicle internal combustion engine.

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