JP4475212B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel for an in-vehicle internal combustion engine comprising: a pressure accumulating chamber that stores fuel in a high pressure state; a fuel pump that pressurizes and supplies the fuel to the pressure accumulating chamber; and a fuel injection valve that injects fuel stored in the pressure accumulating chamber. The present invention relates to a fuel injection control device that performs fuel injection control by operating the fuel injection device.

  As this type of fuel injection device, one having a common pressure accumulation chamber (common rail) for supplying 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 condition, and as a result, the fuel pressure supplied to the fuel injection valve can be freely controlled.

  The control of the fuel pressure in the common rail is normally performed by setting the target fuel pressure according to the operating state of the diesel engine, detecting the fuel pressure in the common rail, and performing feedback control of the detected fuel pressure to the target fuel pressure. Yes.

  By the way, when the remaining amount of fuel in the fuel tank pumped up by the fuel pump decreases, air may be mixed into the fuel pressurized and supplied to the common rail by the fuel pump. When air is mixed into the fuel, the amount of fuel pressurized and supplied into the common rail decreases, and the actual fuel pressure in the common rail falls below the target fuel pressure. For this reason, the fuel pump is operated by the feedback control so that the amount of fuel pressurized and supplied into the common rail is increased. However, since air mixing usually occurs intermittently, when the operation for increasing the amount of fuel is performed by the fuel pump, air may not be mixed into the pressurized fuel. In this case, the fuel is excessively pressurized and supplied to the common rail, and the fuel pressure in the common rail may increase excessively.

For this reason, there is a demand for a technique that determines whether air is mixed into the fuel and appropriately copes with this. In addition, there is a technique described in Patent Document 1 below as a technique that considers air mixing into the fuel pump, but this does not take into account that a large amount of air is mixed into the fuel before gas shortage, It was not always satisfactory as a countermeasure against air contamination.
JP 2000-282938 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to appropriately determine the entry of air into the fuel pressurized and supplied to the pressure accumulating chamber by the fuel pump and deal with this. An object of the present invention is to provide a fuel injection control device that can perform the above-described operation.

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

The first aspect of the present invention is an on-vehicle vehicle that includes a pressure accumulating chamber that stores fuel in a high pressure state, a fuel pump that pressurizes and supplies the fuel to the pressure accumulating chamber, and a fuel injection valve that injects fuel stored in the pressure accumulating chamber. In a fuel injection control device that performs fuel injection control by operating the fuel injection device for a fuel injection device of an internal combustion engine, means for taking in a detection result of a detection means for detecting fuel pressure in the pressure accumulating chamber, and the detection Control means for operating the fuel pump to feedback control the fuel pressure to the target fuel pressure, a fluctuation judging means for judging whether or not the fluctuation amount of the target fuel pressure is a predetermined value or less, and the detected fuel pressure is the target fuel pressure. based on lower than the fuel pressure, and a determining means and the air is mixed in the fuel, the determination means that the amount of the variation is below a predetermined and permit conditions for the determination Which comprises using.

In the above configuration, the detected fuel pressure is feedback-controlled to the target fuel pressure. However, when air is mixed into the fuel pumped up by the fuel pump and supplied under pressure, the amount of fuel supplied under pressure decreases, so the detected fuel pressure falls below the target fuel pressure. In the above configuration, it is possible to determine air contamination based on the fact that the detected fuel pressure is lower than the target fuel pressure using this property.
Moreover, in the said structure, it is set as permission conditions of air mixing determination that the fluctuation amount of target fuel pressure is below predetermined. For this reason, when the fuel pressure detected due to the fluctuation of the target fuel pressure is lower than the target fuel pressure, it is possible to suitably avoid erroneous determination as air mixing. In particular, if this permission condition is provided in the invention described in claim 2 or claim 3 to be described later, it is possible to set a reference value for the air mixing determination with respect to the timed time and the accumulated value to be a small value. It can be done quickly.

  According to a second aspect of the present invention, in the first aspect of the invention, the determination unit includes a detection unit that detects a state in which the detected fuel pressure is lower than the target fuel pressure by a predetermined threshold or more, and the state is And a time measuring means for measuring time to be continued, wherein the determination is performed when the time to be timed is equal to or longer than a predetermined time.

  In the above configuration, when the duration of the state in which the detected fuel pressure is lower than the target fuel pressure by a threshold or more is equal to or longer than a predetermined time, it is determined that air is mixed, so that noise in the detection result of the detection means is reduced. Misjudgments due to contamination and other factors can be avoided appropriately.

  According to a third aspect of the present invention, in the first aspect of the invention, the determination unit detects the state where the detected fuel pressure is lower than the target fuel pressure by a predetermined threshold or more, and the low state A difference between the target fuel pressure and the detected fuel pressure when the detected fuel pressure is detected by calculating means for calculating a cumulative value over a predetermined period, wherein the calculated cumulative value is not less than a predetermined value. The determination is sometimes performed.

  In the above configuration, the cumulative value of the difference between the target fuel pressure and the detected fuel pressure when it is detected that the threshold value is lower than the threshold value is calculated over a predetermined period. Then, when the cumulative value is greater than or equal to a predetermined value, air contamination determination can be performed to appropriately avoid erroneous determination due to noise contamination or other factors in the detection result of the detection means. it can. In particular, by using the accumulated value, it is possible to quantify the degree to which the fuel pressure detected in a predetermined period is lower than the target fuel pressure, so that it is possible to more appropriately determine air contamination.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, a means for taking in a detection result of a detecting means for detecting a remaining amount of fuel for a fuel tank pumped up by the fuel pump. In addition, the determination unit may use, as the determination permission condition, that the detected remaining fuel amount is equal to or less than a predetermined threshold value.

  In the above configuration, when the remaining amount of fuel in the fuel tank is small, air is likely to be mixed into the fuel pumped up by the fuel pump. For this reason, it is possible to appropriately determine the air contamination by setting the remaining fuel amount to be equal to or less than the threshold value as the permission condition for the air contamination determination. In particular, if the permission condition is provided in the case of having the configuration according to claim 2 or claim 3, the reference for the determination of the air mixing with respect to the time and the accumulated value can be set to a small value. Can be performed quickly.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, when the determination means determines that air is mixed in the fuel, the operation amount of the fuel pump by the control means is determined. An operation amount limiting means for limiting is further provided.

  In the above configuration, when air is mixed into the fuel, the fuel pressure in the pressure accumulating chamber is lower than the target fuel pressure. Therefore, the fuel pump is operated so as to increase the pressurized supply amount of the fuel by the feedback control. On the other hand, mixing of air into the fuel tends to occur intermittently. For this reason, when the fuel pump is operated to increase the pressurized supply amount due to the air mixing into the fuel, once the air mixing is eliminated, excess fuel is supplied into the pressure accumulating chamber. The fuel pressure may rise excessively. In this regard, in the above configuration, the amount of operation of the fuel pump is limited when it is determined that air has been mixed in, so that an excessive increase in the fuel pressure in the pressure accumulating chamber can be avoided.

The invention according to claim 6 is the invention according to claim 5 , wherein the control means determines the operation amount of the fuel pump according to an integrated value of a difference between the detected fuel pressure and the target fuel pressure. An integration term calculation means for calculating the integration term is provided.

  In the above configuration, since the integral term calculation means is provided, a steady divergence between the target fuel pressure in the pressure accumulation chamber and the actual fuel pressure can be compensated, and the followability of the actual fuel pressure to the target fuel pressure can be improved. it can. However, in this case, if the situation in which the actual fuel pressure decreases with respect to the target fuel pressure due to mixing of air into the pressurized fuel is supplied, the integration term becomes a very large value. And under such circumstances, once the mixing of air into the pressurized fuel is eliminated, the fuel pump is operated by the operation amount based on the integration term, so that the fuel is excessively supplied into the pressure accumulation chamber, The fuel pressure may rise excessively. In this regard, in the above configuration, when it is determined that air has been mixed in, the amount of operation of the fuel pump is limited, so that it is possible to appropriately increase the fuel pressure in the pressure accumulating chamber while improving the followability of the fuel pressure. It can be avoided.

According to a seventh aspect of the invention, in the sixth aspect of the invention, the operation amount limiting means limits the upper limit value of the integration term when the determination means determines that air has entered the fuel. It is characterized by.

  According to the above configuration, in order to limit the upper limit value of the integration term when it is determined that air is mixed, it is preferable to excessively increase the fuel pressure in the pressure accumulating chamber due to the integration term becoming excessive due to air mixing. Can be avoided.

The invention according to claim 8 limits the fuel injection amount from the fuel injection valve when the determination means determines that air has entered the fuel in the invention according to any one of claims 1 to 7. An injection amount limiting means is provided.

  In the above configuration, when it is determined that air is mixed, by limiting the fuel injection amount, the output of the internal combustion engine is limited, and as a result, the user can be informed of a decrease in the remaining amount of fuel and can be urged to refuel. .

(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 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 powered by a crankshaft 8 that is an output shaft of a diesel engine and discharges fuel. Specifically, the fuel pump 6 includes an intake metering valve 10, and the amount of fuel discharged to the outside is determined by operating the intake metering valve 10. Further, the fuel pump 6 includes two 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 12. The common rail 12 stores the fuel pumped from the fuel pump 6 in a high pressure state and supplies the fuel to the fuel injection valve 16 of each cylinder (here, four cylinders are illustrated) via the high pressure fuel passage 14. The fuel injection valve 16 is connected to the fuel tank 2 via a low pressure fuel passage 18.

  The common rail 12 is provided with a pressure regulator 20 for allowing the fuel to escape to the low-pressure fuel passage 18 when the fuel pressure exceeds a predetermined value. The pressure regulator 20 prevents the fuel pressure in the common rail 12 from rising beyond the upper limit value of the pressure resistance.

  The pressure regulator 20 includes a high pressure chamber 21 communicating with the common rail 12 side and a low pressure chamber 22 communicating with the low pressure fuel passage 18 side. The high-pressure chamber 21 and the low-pressure chamber 22 can communicate with each other through a hole 24 provided in the shielding member 23. However, this hole 24 is normally shielded by a valve 26 pressed against the shielding member 23 by a spring 25. When the fuel pressure in the high pressure chamber 21 becomes equal to or higher than the predetermined value, the force by which the fuel pressure in the high pressure chamber 21 pushes the valve 26 through the hole 24 overcomes the force by which the spring 25 presses the valve 26 against the shielding member 23. The valve 26 opens. The diameter of the hole 24 provided in the shielding member 23 is enlarged on the low pressure chamber 22 side, and once the valve 26 is opened, the open state is easily maintained.

  The engine system includes a fuel pressure sensor 32 that detects the fuel pressure in the common rail 12, a crank angle sensor 34 that detects the rotation angle of the crankshaft 8, a remaining amount sensor 36 that detects the remaining amount of fuel in the fuel tank 2, and the like. Various sensors are provided for detecting the operating state of the engine and the operating environment. Further, the engine system includes an accelerator sensor 38 that detects an operation amount of an accelerator pedal that is operated in response to a user's acceleration request.

  On the other hand, the electronic control unit (ECU 40) is composed mainly of a microcomputer, takes in the detection results of the various sensors, and controls the output of the diesel engine based on this.

  The ECU 40 performs fuel injection control so as to appropriately control the output of the diesel engine. In this fuel injection control, the fuel pressure in the common rail 12 is feedback-controlled to a target fuel pressure that is set according to the operating state and operating environment of the diesel engine.

  FIG. 2 shows a processing procedure of the feedback control. This process is repeatedly executed by the ECU 40, for example, at a predetermined cycle.

  In this series of processes, first, in step S10, a command injection amount when operating the fuel injection valve 16 is captured. This command injection amount is calculated by another process (not shown) based on the detected value of the accelerator sensor 38 and the detected value of the crank angle sensor 34. In the subsequent step S12, the detected value of the rotational speed by the crank angle sensor 34 is fetched. In step S14, the target fuel pressure in the common rail 12 is set based on the command injection amount and the rotational speed.

  In the subsequent step S16, the detected value of the fuel pressure by the fuel pressure sensor 32 is captured. In the subsequent step S18, an operation amount for feedback control of the detected value of the fuel pressure to the target fuel pressure is calculated. Here, the operation amount of the fuel pump 6 is an energization amount to the intake metering valve 10. Specifically, it is the duty for the intake metering valve 10. In the fuel pump 6, the opening degree of the intake metering valve 10 is continuously adjusted according to the energization amount to the intake metering valve 10.

  The feedback control is PID control. For this reason, a proportional term, a differential term, and an integral term are calculated based on the difference between the detected value of the fuel pressure and the target fuel pressure, and an operation amount corresponding to each term is calculated.

  When the operation amount is calculated in step S18, the fuel pump 6 is operated in step S20 according to the calculated operation amount.

  By performing feedback control in such a manner, the actual fuel pressure in the common rail 12 can be controlled to the target fuel pressure that is variably set according to the operating state of the diesel engine.

  By the way, when the remaining amount of fuel in the fuel tank 2 decreases, there is a possibility that air is mixed into the fuel pumped up by the fuel pump 6 and pumped to the common rail 12. In this case, since sufficient fuel is not pumped to the common rail 12, the fuel pressure in the common rail 12 decreases. However, this mixing of air can occur intermittently. In this case, once the air mixing is eliminated, there is a possibility that excessive fuel is supplied into the common rail 12. FIG. 3 illustrates such a situation.

  FIG. 3 (a) shows the actual fuel pressure with a solid line and the target fuel pressure with a one-dot chain line, respectively, regarding the transition of the fuel pressure in the common rail 12, and FIG. 3 (b) shows the operation amount of the fuel pump 6 (in detail, The transition of the operation amount of the intake metering valve 10) is shown.

  FIG. 3 shows an example in which the target fuel pressure once increases and then increases again. As shown in the drawing, at time t1, the fuel pressure in the common rail 12 temporarily decreases from the target fuel pressure due to the mixing of air into the fuel. As a result, the amount of operation of the fuel pump 6 is increased in order to increase the amount of fuel pumped to the common rail 12. However, the amount of operation of the fuel pump 6 decreases as the amount of decrease in fuel pressure with respect to the target fuel pressure decreases. In particular, during the period from time t2 to time t3 when the fuel pressure becomes higher than the target fuel pressure due to the elimination of air mixing, the amount of operation of the fuel pump 6 also decreases. However, after time t3, when the fuel pressure in the common rail 12 falls below the target fuel pressure again, for example, when air is mixed into the fuel again, the operation amount of the fuel pump 6 is increased. After that, when the mixing of air is eliminated again, the amount of fuel pumped to the common rail 12 by the fuel pump 6 becomes excessive, and an overshoot in which the fuel pressure greatly exceeds the target fuel pressure occurs (time t4).

  Such a phenomenon is likely to occur because the integration control is adopted in the feedback control shown in FIG. That is, in the integral control, the operation amount is set in accordance with an integral term obtained by multiplying the integrated value of the difference between the detected values of the fuel pressure with respect to the target fuel pressure by the gain. For this reason, if the state in which the detected value of the fuel pressure is lower than the target fuel pressure is continued due to air being mixed into the fuel, the operation amount of the fuel pump 6 tends to become a large amount. On the other hand, in order to improve the followability of the detected value of the fuel pressure with respect to the target fuel pressure that is variably set according to the operating state of the diesel engine, it is desired to increase the gain of the integral term as much as possible. For this reason, when it is designed to improve the fuel followability as much as possible, the above-described overshoot is particularly likely to occur due to the mixing of air into the fuel.

  Here, when an overshoot occurs and the fuel pressure tends to increase beyond the upper limit value of the pressure resistance of the common rail 12, the pressure regulator 20 is opened. As a result, the fuel in the common rail 12 is released to the fuel tank 2 via the low-pressure fuel passage 18, so that the fuel pressure in the common rail 12 is prevented from rising above the pressure resistance, but the pressure regulator 20 is opened. It is desirable to avoid overshooting of the fuel pressure by control without causing it.

  In order to avoid the overshoot, a guard may be provided for the operation amount of the fuel pump 6. However, this is very difficult for the following reasons. That is, the amount of leaked fuel flowing out from the high pressure fuel passage 14 to the low pressure fuel passage 18 via the fuel injection valve 16 varies due to individual differences of the fuel injection valves 16. The leak amount may vary depending on the command injection amount, fuel properties, fuel temperature, and the like. Therefore, in order to be able to pump the fuel amount necessary to compensate for such a leak amount, the maximum value of the operation amount determined by these must be set as the upper limit guard. However, in this case, when the leak amount is not maximized, the fuel pressure in the common rail 12 may overshoot even as the pumping amount below the upper limit guard. For this reason, it is very difficult to avoid overshoot caused by air mixing by providing an upper limit guard for the operation amount in the feedback control.

  Therefore, in the present embodiment, it is determined that air is mixed into the fuel based on a state in which the detected fuel pressure is lower than the target fuel pressure. Specifically, air contamination is determined based on the fact that the detected fuel pressure is lower than the target fuel pressure. This will be described below.

  FIG. 4 shows a processing procedure for the air mixing determination. This process is repeatedly executed by the ECU 40, for example, at a predetermined cycle.

  In this series of processing, first, in step S10, it is determined whether or not an air mixing determination precondition is satisfied. Here, when the absolute value of the difference between the target fuel pressure PFIN (i) of the current sampling cycle and the target fuel pressure PFIN (i−1) of the previous sampling cycle is equal to or less than the threshold value A, it is determined that the precondition is satisfied. To do. This is because there is a response delay in following the detected fuel pressure when the target fuel pressure fluctuates, so that the detected fuel pressure can be lower than the target fuel pressure even when air is not mixed in the fuel. This is a condition provided in consideration of

  In subsequent step S12, it is determined whether or not the detected fuel pressure is lower than the target fuel pressure by a predetermined threshold B or more. This threshold value B is set to a value larger than the fluctuation amount at which the detected fuel pressure fluctuates in the vicinity of the target fuel pressure when the feedback control shown in FIG. 2 is normal. If it is lower than the threshold value B, the counter value t (i) is incremented by “Δt” in step S14. In a succeeding step S16, it is determined whether or not the counter value t (i) is equal to or larger than the threshold value C. Here, the threshold C is set to a time that cannot be assumed when fuel injection control is normal, as the duration of the state in which the fuel pressure detected is lower than the target fuel pressure by a predetermined threshold B or more.

  If it is determined that the counter value t (i) is equal to or greater than the threshold value C, it is determined in step S18 that air is mixed into the fuel. In step S20, the pressure control guard flag is turned on. Thereby, as shown in FIG. 5, the upper limit guard value of the integral term is reduced. Incidentally, FIG. 5 shows a map in which the horizontal axis is the rotation speed and the vertical axis is the upper limit guard value. Further, in step S20, the injection amount is limited. Thereby, since the output of the diesel engine is limited, it is possible to make the user aware of a decrease in the remaining amount of fuel and to prompt fueling. Further, the travel distance can be extended by restricting the injection amount in a situation where the remaining amount of fuel is low. Furthermore, when the injection amount (command injection amount) is limited, the target fuel pressure calculated by the processing shown in FIG. 2 is reduced, so that the integral term can be suppressed from becoming excessively large.

  On the other hand, if it is determined in step S10 that the precondition is not satisfied, or if it is determined in step S12 that it is less than the threshold value B, the counter value t (i) is initialized in step S22.

  When it is determined in step S16 that the counter value t (i) is less than the threshold value C, or when the processes in steps S20 and S22 are completed, this series of processes is temporarily terminated.

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

  (1) When the state in which the detected fuel pressure is lower than the target fuel pressure by the threshold value B or more is continued for a time period equal to or more than the threshold value C, it is determined that air is mixed into the fuel. Thereby, it is possible to appropriately avoid erroneous determination due to noise mixed in the detection result of the fuel pressure sensor 32 or the fuel pressure detected by other factors being lower than the target fuel pressure.

  (2) When the fluctuation amount of the target fuel pressure is equal to or less than the threshold value A, the air mixing determination is permitted. As a result, it is possible to preferably avoid erroneously determining that the air is mixed by the fuel pressure detected due to the fluctuation of the target fuel pressure being lower than the target fuel pressure. Further, the threshold value C can be set to a small value, and the determination can be made quickly when air is mixed.

  (3) Perform integral control to determine the operation amount of the fuel pump 6 according to the integrated value of the difference between the detected value of the fuel pressure and the target fuel pressure, and reduce the upper limit guard value of the integral term when it is determined that air is mixed did. This integral control can improve the followability of following the fuel pressure to the target fuel pressure, but tends to cause overshooting of the fuel pressure due to intermittent mixing of air into the fuel. In this regard, in the present embodiment, by reducing the upper limit guard value of the integral term at the time of air mixing determination, it is possible to suitably avoid an excessive increase in the fuel pressure in the common rail 12 while improving the followability of the fuel pressure. it can.

  (4) The fuel injection amount from the fuel injection valve 16 was limited when it was determined that air was mixed into the fuel. As a result, the output of the diesel engine is limited, and as a result, the user can be informed of a decrease in the remaining amount of fuel and prompted to refuel.

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

  In the present embodiment, when the detected fuel pressure is lower than the target fuel pressure by a threshold B or more, an accumulated value of these differences is calculated, and air mixing is determined based on the accumulated value. This cumulative value includes not only the duration of the state in which the detected fuel pressure is lower than the target fuel pressure, but also the degree of decrease in the detected fuel pressure with respect to the target fuel pressure. For this reason, the said fall degree can be reflected in determination of air mixing.

  FIG. 6 shows a procedure of processing according to the air mixing determination according to the present embodiment. This process is repeatedly executed by the ECU 40, for example, at a predetermined cycle.

  In this series of processes, first, in steps S30 and S32, the same processes as in steps S10 and S12 of FIG. 4 are performed. Then, when it is determined that the fuel pressure detected in step S32 is lower than the target fuel pressure by the threshold B or more, the process proceeds to step S34. In step S34, a difference Δ (i) obtained by subtracting the detected fuel pressure NPC (i) from the target fuel pressure PFIN (i) is calculated. In the subsequent step S36, the cumulative value S of the difference Δ (i) between the target fuel pressure PFIN (i) and the detected fuel pressure NPC (i) is calculated.

  In a succeeding step S38, it is determined whether or not the cumulative value S is equal to or greater than the threshold value D. Here, the threshold value D is set as a value of the cumulative value S that cannot be assumed when fuel injection control is normal. If it is determined that the accumulated value S is equal to or greater than the threshold value D, the same processing as in step S20 of FIG. 4 is performed, such as turning on the pressure control guard flag in step S40.

  On the other hand, when it is determined at step S30 that the precondition is not satisfied, or when it is determined at step S32 that the precondition is less than the threshold value B, the accumulated value S is initialized at step S42. When it is determined in step S38 that the accumulated value S is less than the threshold value D, or when the processes in steps S40 and S42 are completed, this series of processes is temporarily terminated.

  By determining air mixing in the above-described manner, air mixing can also be determined in the case shown in FIG.

  Fig.7 (a) and FIG.7 (b) show the example of the behavior of the fuel pressure at the time of air mixing. Here, FIG. 7A shows an example in which a state where the target fuel pressure is lower than the fuel pressure at which the target fuel pressure is detected by the threshold B or more continues for the threshold C or more. On the other hand, in FIG. 7B, a state occurs in which the target fuel pressure is considerably lower than the detected fuel pressure, but the duration of the state in which the target fuel pressure is lower than the detected fuel pressure by the threshold B or more does not reach the threshold C. An example is shown. In the case of the example shown in FIG. 7B, it cannot be determined that air is mixed in the process shown in FIG. On the other hand, according to the above-described determination method, the degree of decrease in the detected fuel pressure with respect to the target fuel pressure is quantified by the accumulated value, so that it can be determined that air is mixed also in the case of FIG.

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

  (5) When the detected fuel pressure is lower than the target fuel pressure by the threshold value B or more, the cumulative value S of the difference between the target fuel pressure and the detected fuel pressure is calculated, and the cumulative value S is the threshold value D or more Then, the air mixing judgment was made. This makes it possible to appropriately avoid misjudgment caused by the mixing of noise in the detection result of the fuel pressure sensor 32 or the fuel pressure detected by other factors being lower than the target fuel pressure.

(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 previous second embodiment, the predetermined period for calculating the cumulative value of the difference between the target fuel pressure and the detected fuel pressure is the period during which the detected fuel pressure continues to be lower than the target fuel pressure by a threshold B or more. On the other hand, in the present embodiment, the predetermined period is set to a predetermined time interval T. Incidentally, the time interval T is set to an interval that does not cause the accumulated value to become large due to noise or the like mixed into the output of the fuel pressure sensor 32.

  FIG. 8 shows a processing procedure for determining air contamination according to the present embodiment. This process is repeatedly executed by the ECU 40, for example, at a predetermined cycle.

  In this series of processing, first, in step S50, it is determined whether or not the precondition is satisfied as in step 10 of FIG. If it is determined that the precondition is satisfied, the counter value t is incremented in step S52. In a succeeding step S54, it is determined whether or not the counter value t is equal to or less than the predetermined time interval T. If it is determined that the time interval is equal to or less than the time interval T, it is determined in step S56 whether or not the fuel pressure detected with respect to the target fuel pressure is lower than a threshold value B. When it is determined that the threshold value B is lower than the threshold value B, a detected fuel pressure difference Δ (i) with respect to the target fuel pressure is calculated in step S58. In the subsequent step S60, a cumulative value S of the difference Δ (i) is calculated.

  When the accumulated value S is calculated in this way, it is determined whether or not the accumulated value S is greater than or equal to the threshold value D in step S62. This threshold value D is set to a value that cannot be assumed when fuel injection control is normal. Then, if it is determined that the threshold value D is greater than or equal to the threshold value D, processing similar to that in step S20 of FIG. 4 is performed, such as turning on the pressure control guard flag in step S64.

  On the other hand, when it is determined in step S50 that the precondition is not satisfied, or when it is determined in step S54 that the counter value t is larger than the time interval T, in step S66, the counter value t and the accumulated value S are set. initialize.

  When it is determined in step S56 that the threshold value is less than B, when it is determined in step S62 that it is less than the threshold value D, or when the processes in steps S64 and S66 are completed, this series of processes is temporarily terminated. To do.

  By performing the air mixing determination in the above mode, air mixing can be determined even in the case shown in FIG.

  FIG. 9A and FIG. 9B show an example of the behavior of the fuel pressure when air is mixed. Here, FIG. 9A shows an example in which a state where the target fuel pressure is lower than the fuel pressure at which the target fuel pressure is detected by the threshold B or more continues for the threshold C or more. On the other hand, FIG. 9B shows a case where the state where the target fuel pressure is lower than the detected fuel pressure by the threshold B or more does not continue beyond the threshold C shown in FIG. 4, but occurs intermittently. In the case shown in FIG. 9B, air mixing cannot be determined by the process shown in FIG. On the other hand, according to the process shown in FIG. 8, the air mixing can be determined also in the case shown in FIG. 9B.

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

  (6) Calculate a cumulative value S of the difference between the target fuel pressure and the detected fuel pressure when the detected fuel pressure is lower than the target fuel pressure B by a predetermined time interval T or less. When it is equal to or greater than the threshold value D, the air mixing determination is performed. This makes it possible to appropriately avoid misjudgment caused by the mixing of noise in the detection result of the fuel pressure sensor 32 or the fuel pressure detected by other factors being lower than the target fuel pressure.

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

  In the present embodiment, the condition for permitting the determination of air mixing includes that the remaining amount of fuel in the fuel tank 2 is less than a predetermined threshold.

  FIG. 10 shows a procedure of processing according to the determination of air mixing according to the present embodiment. This process is repeatedly executed by the ECU 40, for example, at a predetermined cycle.

  In this series of processing, first, in step S70, it is determined whether or not the precondition is satisfied as in step S10 of FIG. If it is determined that the precondition is satisfied, it is determined in step S72 whether or not the remaining amount of fuel detected by the remaining amount sensor 36 is equal to or less than a predetermined threshold G. This threshold value G is used to determine whether or not the remaining amount is likely to cause air to be mixed into the fuel pumped up by the fuel pump 6 and pumped to the common rail 12.

  If it is determined that the fuel pressure is less than or equal to the threshold value G, it is determined in step S74 whether or not the fuel pressure detected from the target fuel pressure is lower than the threshold value B, as in step 12 of FIG. If it is determined that the state is lower than the threshold value B, the counter value t (i) is incremented in step S76 as in step S14 of FIG. In the subsequent step S78, the counter value t (i) is compared with the threshold value E. This threshold value E is set based on a time that cannot be assumed when fuel injection control is normal. However, since this threshold value E is used to determine air contamination under the condition that the remaining amount of fuel is equal to or less than the threshold value G, it can be set to a value smaller than the threshold value C shown in FIG. It is. That is, in the process shown in FIG. 4, the threshold value C is used to determine the air contamination from the continuation of the state where the target fuel pressure is lower than the detected fuel pressure by the threshold value B or more without taking the remaining fuel amount into consideration. Set to a sufficiently large value. On the other hand, in the present embodiment, in order to take into account the remaining amount of fuel, it is possible to more quickly determine whether air is mixed based on the behavior of the fuel pressure.

  If it is determined in step S78 that the counter value t (i) is greater than or equal to the threshold value E, it is determined in step S80 that air is mixed, and in step S82, the same processing as in step S40 in FIG. 4 is performed.

  On the other hand, when it is determined that the precondition is not satisfied in step S70, when it is determined that the threshold value G is exceeded in step S72, or when it is determined that the threshold value is less than threshold value B in step S74, the counter value is determined in step S84. t (i) is initialized.

  Note that when it is determined in step S78 that it is less than the threshold value E, or when the processing of steps S80 and S84 is completed, this series of processing is temporarily ended.

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

  (7) The fact that the remaining amount of fuel to be detected is equal to or less than a predetermined threshold G is used as a permitting condition for air mixing determination. As a result, the threshold value E for the duration of the state in which the fuel pressure detected below the target fuel pressure is lower than the threshold value B can be set to a value as small as possible, so that the determination of air contamination can be made quickly.

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

  -For example, in the previous first embodiment, even if the condition that the fluctuation amount of the target fuel pressure is equal to or less than the predetermined condition is not provided as the permission condition for the air mixing determination, by setting the threshold value C to a large value, air mixing is prevented. Can be determined.

  In the second and third embodiments, as exemplified in the previous fourth embodiment, the condition for permitting the air mixing determination includes that the remaining amount of fuel is equal to or less than a predetermined threshold. May be.

  The restriction on the operation amount of the fuel pump 6 is not limited to the purpose of avoiding the opening of the pressure regulator 20. For example, the pressure resistance of the fuel pump 6 usually changes according to the rotation speed. Specifically, the breakdown voltage decreases in the low rotation region. For this reason, even if the fuel pressure in the common rail 12 is not near the upper limit value of the pressure resistance, there is a concern that the deterioration of the fuel pump 6 is promoted when the fuel pressure becomes higher than normal in a region where the rotational speed is low. For this reason, overshooting of the fuel pressure with respect to the target fuel pressure due to air mixing is desirably avoided in order to suppress deterioration of the fuel pump 6 even when it is not near the upper limit value of the pressure resistance of the common rail 12. .

  Furthermore, even if the pressure regulator 20 is not provided, avoiding overshoot of the fuel pressure in the common rail 12 is effective because it can suppress an increase in combustion noise and deterioration of drivability due to overshoot. is there.

  The limitation of the operation amount of the fuel pump 6 at the time of air mixing determination is not limited to limiting the upper limit guard value of the integral term, but directly limiting the operation amount, for example, limiting the duty for the fuel pump 6. There may be.

  -The feedback control of the fuel pressure in the common rail 12 is not limited to PID control. However, if the integration term for determining the operation amount of the fuel pump 6 is used according to the integrated value of the difference between the detected value of the fuel pressure and the target fuel pressure, the operation amount is excessive when air is intermittently mixed. Therefore, the application of the present invention is particularly effective.

  -The injection amount limitation is not limited to limiting the command injection amount. For example, the operation amount of an accelerator pedal used for calculating the command injection amount may be limited.

  The fuel pump 6 is not limited to the fuel pump 6 whose discharge amount is adjusted by continuously adjusting the valve opening amount by the duty. For example, the discharge amount may be adjusted by a binary operation of opening and closing the valve.

  The internal combustion engine is not limited to a diesel engine, and may be, for example, a cylinder injection gasoline engine.

The figure which shows the structure of the engine system concerning 1st Embodiment. The flowchart which shows the procedure of the feedback control of the fuel pressure concerning the embodiment. The time chart which shows the behavior of the fuel pressure when air mixes in fuel. The flowchart which shows the process sequence of the air mixing determination concerning the said embodiment. The figure which shows the change method of the upper limit guard value of the integral term concerning the embodiment. The flowchart which shows the process sequence of the air mixing determination concerning 2nd Embodiment. The figure explaining the merit of the air mixing determination concerning the embodiment. The flowchart which shows the process sequence of the air mixing determination concerning 3rd Embodiment. The figure explaining the merit of the air mixing determination concerning the embodiment. The flowchart which shows the process sequence of the air mixing determination concerning 4th Embodiment.

Explanation of symbols

  2 ... Fuel tank, 6 ... Fuel pump, 12 ... Common rail, 16 ... Fuel injection valve, 40 ... Electronic control unit (ECU).

Claims (8)

A fuel injection device for an in-vehicle internal combustion engine comprising: a pressure accumulating chamber that stores fuel in a high pressure state; a fuel pump that pressurizes fuel into the pressure accumulating chamber; and a fuel injection valve that injects fuel stored in the pressure accumulating chamber. In a fuel injection control device that performs fuel injection control by operating the fuel injection device,
Means for capturing the detection result of the detection means for detecting the fuel pressure in the pressure accumulation chamber;
Control means for operating the fuel pump to feedback control the detected fuel pressure to a target fuel pressure;
Fluctuation judging means for judging whether or not the fluctuation amount of the target fuel pressure is a predetermined value or less
Determination means for determining that air is mixed in the fuel based on a state in which the detected fuel pressure is lower than the target fuel pressure ;
The fuel injection control apparatus according to claim 1, wherein the determination means uses that the variation amount is equal to or less than a predetermined value as a condition for permitting the determination .   The determination unit includes a detection unit that detects a state in which the detected fuel pressure is lower than a target threshold by a predetermined threshold, and a timing unit that counts a time during which the state is continued. 2. The fuel injection control device according to claim 1, wherein the determination is performed when a predetermined time is equal to or longer than a predetermined time.   The determination means includes a detection means for detecting a state in which the detected fuel pressure is lower than a target threshold by a predetermined threshold, and a target fuel pressure with respect to the detected fuel pressure when the low state is detected. The difference according to claim 1, further comprising a calculating means for calculating a cumulative value over a predetermined period for the difference, wherein the determination is performed when the calculated cumulative value is equal to or greater than a predetermined value. Fuel injection control device. The fuel tank in which the fuel is pumped up by the fuel pump further comprises means for capturing the detection result of the detection means for detecting the remaining amount of fuel,
The fuel injection control device according to claim 1, wherein the determination unit uses, as the determination permission condition, that the detected remaining fuel amount is equal to or less than a predetermined threshold value. . 5. The operation amount limiting means for limiting an operation amount of the fuel pump by the control means when the determination means determines that air is mixed in the fuel. A fuel injection control device according to claim 1. The control means includes an integration term calculation means for calculating an integration term for determining an operation amount of the fuel pump in accordance with an integrated value of a difference between the detected fuel pressure and the target fuel pressure. The fuel injection control device according to claim 5 . The fuel injection control device according to claim 6, wherein the operation amount restriction unit restricts an upper limit value of the integration term when the determination unit determines that air is mixed into the fuel. The injection amount limiting means for limiting a fuel injection amount from the fuel injection valve when the determination means determines that air is mixed into the fuel. fuel injection control device.

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