JP2007239488A - Fuel injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device capable of determining abnormality of feed back control of fuel pressure and appropriately coping with the same. <P>SOLUTION: A fuel pump is operated by feed back control to rise fuel pressure if fuel pressure NPC in a common rail drops due to mixing of air into fuel. Here, it is determined that air mixes in fuel (step S16: Yes) if accumulation value S of pressure difference of target fuel pressure PFIN from detected fuel pressure NPC gets a threshold C or greater. Then an integration term in feedback control of fuel pressure NPC to target fuel pressure PFIN is limited (step S18) according to the accumulation value S. Consequently, overshoot of fuel pressure due to elimination of air mixing at once can be avoided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pressure accumulating chamber that stores fuel in a high pressure state, a fuel pump that pumps fuel into the pressure accumulating chamber, detection means that detects fuel pressure in the pressure accumulating chamber, and fuel that injects fuel stored in the pressure accumulating chamber BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control apparatus including a control unit that feedback-controls the detected fuel pressure to a target fuel pressure by operating the fuel pump.

  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 the 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 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 from which fuel is pumped by the fuel pump decreases, there is a possibility that air may be mixed into the fuel pressurized and supplied (pressure-fed) to the common rail by the fuel pump. When air is mixed into the fuel, the amount of fuel pumped 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 pumped 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 pressure-fed fuel. In this case, the fuel is excessively pumped 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. Here, there is a technique described in Patent Document 1 below as a technique that considers air mixing into the fuel pump, but this is not due to the fact that a large amount of air is mixed into the fuel before gas shortage. As a countermeasure against air contamination, it was not always satisfactory.

In addition to the above air mixing, for example, even if there is a decrease in the pumping amount due to a temporary malfunction of the fuel metering valve of the fuel pump, etc., the fuel pressure may be greatly deviated from the target fuel pressure. It has become a thing.
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 provide a fuel injection control apparatus that can determine abnormality in fuel pressure feedback control and appropriately cope with this. .

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

  The invention according to claim 1 is based on the detected fuel pressure deviation with respect to the target fuel pressure, and diagnostic means for diagnosing the presence or absence of abnormality of the feedback control, and when it is determined that there is the abnormality, And limiting means for limiting the operation amount in such a manner that the degree of limitation of the operation amount of the fuel pump is increased as the degree of deviation of the detected fuel pressure is larger.

  In the above configuration, when it is determined that there is an abnormality, the fuel pressure detected with respect to the target fuel pressure may overshoot or undershoot when the feedback control is abnormal by limiting the operation amount of the fuel pump. Can be suitably suppressed. Moreover, since the degree of restriction of the operation amount of the fuel pump is increased as the degree of deviation is larger, it is possible to avoid a decrease in controllability caused by restricting feedback control more than necessary.

  Here, restricting the operation amount of the fuel pump means restricting the operation amount of the fuel pump by restricting the operation amount of the fuel pump itself, a calculation parameter used for calculation of the operation amount, or the like.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the diagnostic means judges abnormality of the feedback control based on the fact that the detected fuel pressure is lower than the target fuel pressure. .

  In the above configuration, the abnormality of the feedback control is determined based on the detected fuel pressure being lower than the target fuel pressure. Here, as a factor that the detected fuel pressure is lower than the target fuel pressure, for example, air is mixed in the fuel, or in a configuration in which the fuel pump includes a plurality of plungers, some of the plungers are temporarily fixed and cannot be pumped. It may become. In such a case, for example, if air is not mixed or the plunger is not fixed, an overshoot may occur in which the fuel pressure exceeds the target fuel pressure and is controlled to an excessively large value due to the reaction. In this regard, in the above configuration, such a situation can be appropriately dealt with by providing the limiting means.

  According to a third aspect of the present invention, in the second aspect of the present invention, the limiting means determines an operation amount of the fuel pump according to an integrated value of a differential pressure 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, for example, if the situation in which the actual fuel pressure decreases with respect to the target fuel pressure due to, for example, mixing of air into the pumped fuel continues, the integration term becomes a very large value. Under such circumstances, once the mixing of air into the pumped fuel is eliminated, the fuel is excessively supplied into the pressure accumulating chamber by the feedback control based on the integration term, and the fuel pressure may increase 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 fourth aspect of the present invention, in the invention according to the third aspect, the diagnosing means includes a calculating means for calculating a cumulative value over time of a differential pressure between the detected fuel pressure and the target fuel pressure, When the absolute value of the cumulative value as the deviation is equal to or greater than a predetermined value, it is determined that an abnormality has occurred.

  In the above-described configuration, it is possible to appropriately determine whether the detection result of the detection unit is mixed with noise or other factors due to an abnormality in the feedback control when the absolute value of the accumulated value is equal to or greater than a predetermined value. Can be avoided. In particular, by using the absolute value of the cumulative value, the degree of deviation between the detected fuel pressure and the target fuel pressure can be quantified, so that the abnormality can be determined more appropriately.

  According to a fifth aspect of the invention, in the fourth aspect of the invention, the limiting means limits the integration term according to a magnitude of an absolute value of the cumulative value as the degree of deviation. .

  In the above configuration, the absolute value of the accumulated value is a parameter having a correlation with the magnitude of the absolute value of the integration term. For this reason, by restricting the integral term according to the magnitude of the absolute value of the accumulated value, it is possible to restrict this according to the degree to which the absolute value of the integral term becomes excessively large. A decline in sex can be avoided.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the control means includes basic value calculation means for calculating a basic value of the target fuel pressure in accordance with an operating state of the internal combustion engine. A guard calculating means for calculating at least one of an upper limit value and a lower limit value of the target fuel pressure according to the operating state of the internal combustion engine, and based on the magnitude relationship between the value calculated by the guard calculating means and the basic value, Setting means for setting the target fuel pressure, and the limiting means limits the value calculated by the guard calculating means according to the degree of deviation.

  In the above configuration, if the lower limit value is limited according to the degree of deviation, it is possible to suitably suppress the possibility that the fuel pressure is excessively lowered and fuel injection cannot be performed. Moreover, if the upper limit value is limited, it is possible to suitably suppress the fuel pressure from becoming excessively large.

  According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the limiting means is configured to change the absolute value of the differential value between the detected fuel pressure and the target fuel pressure as the degree of deviation. The value calculated by the guard calculating means is limited.

  In the above configuration, in order to limit the value calculated by the guard calculating means according to the magnitude of the absolute value of the differential pressure, according to the degree of deviation, in other words, according to the extent to which the absolute value of the differential pressure increases. Thus, it is possible to limit the above value, and to avoid a decrease in controllability due to an unnecessary limit.

  The invention according to claim 8 is the invention according to claim 5 or 7, wherein the limiting means increases the limit value used for the limit in proportion to the absolute value of the cumulative value or the absolute value of the differential pressure. It is characterized by.

  According to the above configuration, in order to increase the limit value in proportion to the absolute value, the limit degree can be increased as the degree of deviation increases.

  The invention according to claim 9 is the invention according to claim 5 or 7, wherein the limiting means gradually reduces the rate of change of the limit value used for the limit with respect to the absolute value of the cumulative value or the absolute value of the differential pressure. It is characterized by making it.

  According to the above configuration, since the limit value increases as the absolute value increases, the limit degree can be increased as the degree of deviation increases. Further, in the above configuration, since the change rate of the limit value with respect to the absolute value is gradually decreased, the limit value at the beginning of the deviation can be set to a relatively large value, and as a result, an early countermeasure can be taken when the deviation occurs. It can be performed.

  According to a tenth aspect of the present invention, in the invention according to the fifth or seventh aspect, the limiting means gradually increases the rate of change of the limiting value used for the limiting with respect to the absolute value of the cumulative value or the absolute value of the differential pressure. It is characterized by making it.

  According to the above configuration, since the limit value increases as the absolute value increases, the limit degree can be increased as the degree of deviation increases. Further, in the above configuration, since the change rate of the limit value with respect to the absolute value is gradually increased, when the deviation is small, the limit value becomes a small value, and the normal feedback control can be respected as much as possible.

(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 continuously operating the valve opening amount of the intake metering valve 10. 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 12. In the common rail 12, the fuel pumped from the fuel pump 6 is stored in a high pressure state, and the stored fuel is stored in the fuel injection valve 16 of each cylinder (here, four cylinders are illustrated) via the high pressure fuel passage 14. Supplied. 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 that communicates with the common rail 12 side, and a low pressure chamber 22 that communicates 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 various sensors that detect the operating state of the diesel engine, such as a fuel pressure sensor 32 that detects the fuel pressure in the common rail 12 and a crank angle sensor 34 that detects the rotation angle of the crankshaft 8. Further, the engine system includes an accelerator sensor 36 that detects an operation amount of an accelerator pedal 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 value of fuel pressure (target fuel pressure) set according to the operating state of the diesel engine. Hereinafter, feedback control will be described in detail with reference to FIG.

  FIG. 2 is a functional block diagram of processing related to feedback control of the target fuel pressure in the common rail 12 among the processing performed by the ECU 30.

  The injection amount calculation unit B2 is a command value (injection amount command value for the fuel injection valve) based on the rotational speed of the crankshaft 8 based on the detection value of the crank angle sensor 34 and the operation amount of the accelerator pedal detected by the accelerator sensor 36. (Command injection amount) is calculated as a map.

  The target fuel pressure calculation unit B4 calculates a basic value of the target fuel pressure based on the command injection amount and the rotation speed. The fuel pressure guard B6 sets the target fuel pressure based on the basic fuel pressure calculated by the target fuel pressure calculator B4 and the upper and lower limits. That is, when the basic value is larger than the upper limit value, the upper limit value is set as the target fuel pressure, when the basic value is smaller than the lower limit value, the lower limit value is set as the target fuel pressure, and when the basic value is greater than or equal to the lower limit value and less than or equal to the upper limit value. The basic value is the target fuel pressure.

  Based on the target fuel pressure and the fuel pressure detected by the fuel pressure sensor 32, the differential pressure calculation unit B8 calculates a differential pressure between the target fuel pressure and the detected fuel pressure. This differential pressure is taken into the proportional term calculation unit B10, the integral term calculation unit B12, and the differential term calculation unit B14. Here, the proportional term calculation unit B10 calculates the proportional term by multiplying the differential pressure by the proportional gain. Further, the integral term calculation unit B12 calculates the integral term by multiplying the time integral value of the differential pressure by the reciprocal of the integral gain. Further, the differential term calculation unit B14 calculates the differential term by multiplying the time differential value of the differential pressure by the differential gain. The integral term calculated by the integral term calculating unit B12 is subjected to upper / lower limit guard processing by the integral term guard unit B16. That is, in the integral term guard unit B16, when the calculated integral term is larger than the upper limit guard value, the upper limit guard value is set as an integral term, and when the integral term is smaller than the lower limit guard value, the lower limit guard value is set. Is set as an integral term, and when the integral term is not less than the lower limit guard value and not more than the upper limit guard value, the calculated integral term is adopted as it is.

  The proportional term, derivative term, and integral term are added by the adding unit B18. The output of the addition unit B18 becomes a command value (command discharge amount) of the discharge amount for the fuel pump 6.

  The drive current conversion unit B20 converts the command discharge amount into the drive current value of the fuel pump 6 required for discharging from the fuel pump 6 (more precisely, the drive current value of the intake metering valve 10). . Here, the command discharge amount is converted into a drive current value using, for example, an “n” -order (n ≧ 1) polynomial for the command discharge amount. The fuel pump 6 is operated based on the drive current value calculated by the drive current conversion unit B20.

  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. For this reason, the command discharge amount for the fuel pump 6 is increased by the feedback control. 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.

  As shown in the figure, when air starts to be mixed into the fuel at time t1, the behavior of the fuel pressure indicated by the solid line in the figure becomes unstable, and the followability to the target fuel pressure indicated by the one-dot chain line in the figure decreases. When air is mixed, the detected fuel pressure is basically lower than the target fuel pressure. However, due to the fact that the feedback control shown in FIG. 2 increases the discharge amount of the fuel pump 6 so as to compensate for the decrease in the fuel pressure, and there is a tendency for air mixing to occur intermittently. After the detected fuel pressure falls below the target fuel pressure, a phenomenon that exceeds the target fuel pressure occurs, whereby the detected fuel pressure fluctuates up and down with respect to the target fuel pressure.

  In addition, as air is mixed, the integral term indicated by the two-dot chain line in the figure also starts to fluctuate greatly. Here, since the mixture of air basically lowers the detected fuel pressure below the target fuel pressure, the integral term tends to increase while fluctuating after time t1.

  Then, when the detected value greatly falls below the target fuel pressure after time t2, the command discharge amount is increased by the feedback control shown in FIG. In particular, at this time, the integral term increases. 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 t3).

  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 command discharge amount is set according to the integral term obtained by multiplying the integrated value of the difference between the detected fuel pressure and the target fuel pressure by the gain. For this reason, if the state in which the fuel pressure detected when air is mixed into the fuel is kept below the target fuel pressure, the amount of operation of the fuel pump 6 tends to be large. On the other hand, in order to improve the followability of the detected 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 overshoot occurs and the fuel pressure exceeds 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 beyond 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.

  It is also conceivable to provide a guard in advance for the operation amount of the fuel pump 6 in order to avoid overshoot. 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 an overshoot caused by air mixing by setting an upper limit guard in advance 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, and at this time, feedback control is performed according to the degree of deviation of the detected fuel pressure with respect to the target fuel pressure. Limit the integral term. This will be described below.

  FIG. 4 shows a processing procedure of the feedback control when the air is mixed. 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 (n) of the current sampling cycle and the target fuel pressure PFIN (n−1) of the previous sampling cycle is 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 even if no air is mixed in the fuel, the detected fuel pressure may deviate from the target fuel pressure. This is a condition that is taken into consideration.

  In subsequent step S12, it is determined whether or not the differential pressure of the target fuel pressure with respect to the detected fuel pressure is equal to or greater than a predetermined differential pressure B. Here, the differential pressure B is set to a value larger than the amount of fluctuation in 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 determined that the pressure difference is equal to or higher than the differential pressure B, a process of adding the current differential pressure Δ (n) of the target fuel pressure with respect to the detected fuel pressure to the accumulated value S is performed in step S14.

  In the subsequent step S16, it is determined whether or not the accumulated value S is equal to or greater than a predetermined threshold value C. Here, the threshold value C is set to a value that cannot be assumed as the cumulative value S when the target fuel pressure is in a steady state and when the feedback control is normal.

  If it is determined that the value is equal to or greater than the threshold C (determination of air mixing into the fuel), a limit value of the upper limit guard value of the integral term is calculated in step S18. As shown in FIG. 5, this calculation is set so that the limit value increases in proportion to the cumulative value S as the cumulative value S increases. Incidentally, the limit value is to reduce the upper limit guard value set by the integral term guard unit B16 shown in FIG. 2, and the integral term is obtained by subtracting the limit value from the upper limit guard value used in normal times. The upper limit guard value that is actually used by the guard unit B16. For this reason, the larger the limit value, the lower the upper limit guard value used for the guard process of the integral term guard unit B16.

  In subsequent step S20, the integral term is limited by setting an upper limit guard value based on the limit value calculated in step S18.

  On the other hand, when a negative determination is made in steps S10 and S12, the accumulated value S is initialized in step S22.

  When a negative determination is made in step S16 or when the processing in steps S20 and S22 is completed, the series of processing shown in FIG.

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

  (1) Based on the differential pressure between the target fuel pressure and the detected fuel pressure, the presence or absence of air in the fuel is diagnosed, and when it is determined that there is an abnormality, the degree of deviation between the target fuel pressure and the detected fuel pressure The upper limit guard value was limited in such a manner that the limit value of the upper limit guard value of the integral term was increased as the value of. Thereby, it can suppress suitably that the fuel pressure detected with respect to the target fuel pressure at the time of air mixing overshoots. Moreover, since the upper limit guard value of the integral term is limited according to the degree of deviation, it is possible to avoid a decrease in controllability due to limiting the integral term more than necessary.

  (2) Based on the fact that the detected fuel pressure is lower than the target fuel pressure, it is possible to appropriately determine the presence or absence of air mixing.

  (3) The command discharge amount of the fuel pump 6 was calculated according to the integral term based on the difference between the detected fuel pressure and the target fuel pressure. As a result, a steady deviation between the target fuel pressure in the common rail 12 and the actual fuel pressure can be compensated, and the followability of the actual fuel pressure to the target fuel pressure can be improved. 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 pumped fuel or the like continues, the integral term becomes a very large value. Under such circumstances, once the mixing of air into the pumped fuel is eliminated, the fuel pump 6 is operated according to the command discharge amount based on the integral term, so that the fuel in the common rail 12 becomes excessive. There is a risk that the fuel pressure will rise excessively. In this respect, in the present embodiment, when it is determined that air is mixed, by limiting the upper limit guard value of the integral term, the followability of the fuel pressure is improved, and the fuel pressure in the common rail 12 is excessively increased. Can be suitably avoided.

  (4) The detection result of the fuel pressure sensor 0 is determined by determining that there is an abnormality when the accumulated value S with the passage of time of the differential pressure of the target fuel pressure with respect to the detected fuel pressure is equal to or greater than a predetermined threshold C. It is possible to appropriately avoid misjudgment due to noise contamination and other factors. In particular, by using the cumulative value S, it is possible to quantify the degree to which the detected fuel pressure is lower than the target fuel pressure, and therefore it is possible to more appropriately determine abnormality.

  (5) By increasing the degree of restriction of the integral term as the cumulative value S increases, this can be restricted according to the extent to which the integral term becomes excessively large. A decrease can be avoided.

(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 feedback control at the time 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 processes, first, the processes of steps S10 and S12 shown in FIG. 4 are performed. If an affirmative determination is made in step S12, the absolute value Sa of the cumulative value of the differential pressure between the target fuel pressure and the detected fuel pressure is calculated in step S14a. Here, the absolute value Sa of the cumulative value is calculated, although the command discharge amount basically increases when air is mixed, as shown in FIG. 3, the detected fuel pressure is increased or decreased with reference to the target fuel pressure. This is because there is a possibility that the command discharge amount becomes an excessively small value due to a large fluctuation. If the command discharge amount becomes excessively small, the fuel pressure undershoots and fuel may not be able to be injected via the fuel injection valve 16, so in this embodiment to cope with such a situation, The absolute value Sa of the cumulative value is used.

  In the subsequent step S30, (a) the condition that the absolute value of the differential pressure of the target fuel pressure with respect to the detected fuel pressure is greater than or equal to a predetermined threshold D, and (b) the absolute value Sa of the cumulative value is greater than or equal to the threshold C. It is determined whether or not at least one of the conditions is true. Here, the threshold value D is used to determine whether or not the detected fuel pressure can be controlled to be largely separated from the target fuel pressure due to the detected fuel pressure being largely separated from the target fuel pressure. Is set to a value. For example, as shown in FIG. 3 above, when the behavior of the fuel pressure becomes unstable due to air mixing, and the detected fuel pressure greatly exceeds the target fuel pressure, the fuel pressure detected by the reaction greatly falls below the target fuel pressure. There is a risk that feedback control will be performed. In this case, the fuel pressure in the common rail 12 may be too low, and fuel injection may not be performed. The threshold value D is for judging such a situation.

  When an affirmative determination is made in step S30, a restriction target and a restriction value are selected in step S32. In the present embodiment, the restriction targets are the upper limit value and lower limit value of the fuel pressure guard part B6 shown in FIG. 2, the upper limit guard value and lower limit guard value of the integral term guard part B16, and the command output from the addition part B18. Discharge amount.

  Here, when only the above condition (a) is established, the upper limit value and the lower limit value of the fuel pressure guard part B6 are selected as the restriction targets. This is because, for example, when the detected fuel pressure temporarily exceeds the target fuel pressure after air mixing, the detected fuel pressure may be significantly lower than the target fuel pressure, so the lower limit value of the target fuel pressure is limited. It aims at suppressing that the detected fuel pressure falls too much. Further, when only the above condition (A) is satisfied, only the upper limit guard value and the lower limit guard value of the integral term guard unit B16 are subject to restriction. This purpose is the same as that of the first embodiment, but in this embodiment, since the absolute value Sa of the cumulative value is used, not only the upper limit guard value but also the lower limit guard value is subject to restriction. In other words, if the fuel pressure detected by destabilizing the fuel pressure due to air mixing greatly exceeds the target fuel pressure, the integral term may become excessively small, which may lead to an undershoot of the fuel pressure. Also restrict. Further, when both of the above conditions (a) and (b) are satisfied, in addition to the upper limit value and lower limit value of the fuel pressure guard part B6 and the upper limit guard value and lower limit guard value of the integral term guard part B16 Thus, the command discharge amount output from the adding unit B18 may be limited. Here, the command discharge amount is limited when the upper limit value and the lower limit value of the fuel pressure guard part B6 and the upper limit guard value and the lower limit guard value of the integral term guard part B16 are considered to be insufficient. This is done to make up.

  The selection of the limit value is, for example, as illustrated in FIGS. 7A to 7C, the absolute value of the differential pressure of the fuel pressure with respect to the detected fuel pressure, the absolute value Sa of the cumulative value, and the limit value. Is a process of selecting one of a plurality of maps showing the relationship. In FIG. 7, in addition to the map (FIG. 7 (a)) in which the limit value increases in proportion to each absolute value, a map (FIG. 7 (b) in which the increase rate of the limit value increases as each absolute value increases. )) And a map (FIG. 7C) in which the increase rate of the limit value decreases as the absolute values increase. Here, if a map is used in which the increase rate of the limit value increases as the absolute value increases, when a deviation occurs between the detected fuel pressure and the target fuel pressure, the normality is as much as possible when the degree of deviation is small. You can respect the control. In addition, if a map is used in which the increase rate of the limit value decreases as the absolute value increases, when a deviation occurs between the detected fuel pressure and the target fuel pressure, measures against overshoot and undershoot are taken early. be able to.

  When the process of step S32 of FIG. 6 is completed, the processes of steps S34 to S38 are performed as appropriate. Here, in step S34, the upper limit value and the lower limit value of the fuel pressure guard part B6 are calculated using the selected map. Based on this limit value, in step S40, an upper limit value and a lower limit value that are actually used for the guard process are calculated by the fuel pressure guard unit B6. That is, a value obtained by subtracting the limit value from the upper limit value used in the normal state or a value obtained by adding the limit value to the lower limit value used in the normal state is set as the upper limit value and the lower limit value that are actually used for the guard process.

  In step S36, the upper limit guard value and the lower limit guard value of the integral term guard unit B16 are calculated using the selected map. Based on the limit value, in step S40, the integral term guard unit B16 calculates an upper limit guard value and a lower limit guard value that are actually used for guard processing. That is, a value obtained by subtracting the limit value from the upper limit guard value used in the normal state or a value obtained by adding the limit value to the lower limit guard value used in the normal state is set as the upper limit guard value and the lower limit guard value that are actually used for the guard process. .

  Further, in step S38, the limit value of the command discharge amount output from the adding unit B18 is calculated using the selected map. Based on the limit value, the command discharge amount is guarded in step S40. That is, the maximum value of the discharge amount determined by the discharge capacity of the fuel pump 6 is subtracted by the limit value as the upper limit value of the command discharge amount, and based on the magnitude of this upper limit value and the command discharge amount output from the adding unit B18, The final command discharge amount is calculated.

  On the other hand, when a negative determination is made in steps S10 and S12, the process proceeds to step S42 to initialize the absolute value Sa of the accumulated value.

  When a negative determination is made in step S30 or when the processes in steps S40 and S42 are completed, this series of processes is temporarily terminated.

  According to this embodiment described above, in addition to the effects (1) to (5) of the first embodiment, the following effects can be obtained.

  (6) As the degree of deviation between the target fuel pressure and the detected fuel pressure is larger, the fuel pressure is excessively limited by limiting the upper limit value and the lower limit value of the fuel pressure guard B6. It is possible to suitably suppress the occurrence of a situation where fuel injection cannot be performed due to a drop or a situation where the fuel pressure becomes excessively large.

  (7) Establishment of the condition that the absolute value of the differential pressure of the target fuel pressure with respect to the detected fuel pressure is equal to or greater than a predetermined threshold D and the condition that the absolute value Sa of the cumulative value is equal to or greater than the threshold C By selecting the restriction target according to the presence or absence, the operation amount of the fuel pump 6 can be more appropriately restricted.

  (8) By preparing a plurality of maps that define the relationship between the absolute value of the difference between the target fuel pressure and the detected fuel pressure, the absolute value of the cumulative value, and the limit value, the operation amount of the fuel pump 6 is more appropriately limited. Can be done.

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

  FIG. 8 shows a processing procedure of feedback control at the time 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 processes, first, the processes of steps S10 and S12 of FIG. 4 are performed. If an affirmative determination is made in step S12, a counter that counts the time during which the absolute value of the differential pressure between the detected fuel pressure and the target fuel pressure is equal to or greater than the differential pressure B is incremented in step S50. In step S52, it is determined whether or not the value of the counter is equal to or greater than a threshold value E. This threshold value E is set to a time that cannot be assumed as the time when the absolute value of the differential pressure between the detected fuel pressure and the target fuel pressure is equal to or higher than the differential pressure B when the feedback control is normally performed. For this reason, when it becomes more than threshold E, it can be judged that air mixed into fuel.

  When it is determined in step S52 that it is equal to or greater than the threshold value E, the process proceeds to step S54. In step S54, a restriction target is selected. Here, when the counter value is small, the upper limit value and the lower limit value of the fuel pressure guard part B6 are limited, and the upper limit guard value and the lower limit guard value of the integral term guard part B16 are limited by the counter value becoming a predetermined value or more. Then, select the restriction target as appropriate. At this time, in addition to the counter value, the restriction target may be selected according to the differential pressure between the detected fuel pressure and the target fuel pressure.

  When the restriction target is selected in this way, the processes of steps S56 to S60 are appropriately performed. These processes correspond to the processes of steps S34 to S38 shown in FIG. 6, but the limit value is calculated according to the counter value. However, in this case, in addition to the counter value, the limit value may be calculated according to the differential pressure between the detected fuel pressure and the target fuel pressure. This may be performed using a map that defines the relationship between the counter value and the differential pressure and the limit value, and the limit value calculated by the map that defines the relationship between the counter value and the limit value is determined according to the differential pressure. You may carry out by correcting.

  When the processing of steps S56 to S60 is completed in this way, the processing of step S40 shown in FIG. 6 is performed.

  When a negative determination is made in the processing of steps S10 and S12, the counter value is initialized in step S62. Further, when the processes in steps S40 and S62 are completed, the series of processes is temporarily ended.

  Also according to the present embodiment described above, the effects in accordance with the effects (1) to (5) of the previous first embodiment, and the above (6) and (7) of the previous second embodiment. The effect according to the effect can be obtained.

(Other embodiments)
The above embodiments may be implemented with the following modifications.

  The limitation of the operation amount of the fuel pump 6 for the purpose of avoiding overshoot of the fuel pressure 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. .

  Further, even if the pressure regulator 20 is not provided, avoiding overshoot of the fuel pressure in the common rail 12 is effective in suppressing an increase in combustion noise and deterioration of drivability due to overshoot.

  In each of the above embodiments, the amount of operation of the fuel pump 6 is limited to cope with the mixing of air into the fuel, but this is not a limitation. For example, when the plunger of the fuel pump 6 is temporarily fixed and cannot be pumped, the fuel pressure decreases, so the command discharge amount is increased to increase the fuel pressure. However, if the operation of the plunger returns to normal at this time, the fuel pressure may overshoot due to an excessive integral term. Further, for example, when the nozzle needle of the fuel injection valve 16 is temporarily fixed and cannot be opened, the pressure is excessively increased and the fuel pressure temporarily rises. Therefore, the discharge amount is decreased so as to reduce the fuel pressure. However, if the fuel injection valve 16 returns to the normal state at this time, the fuel pressure may undershoot due to the integral term being too small. According to the processing exemplified in the first to third embodiments, there is an effect of avoiding such a situation.

  -The feedback control of the fuel pressure in the common rail 12 is not limited to PID control. However, if the operation amount of the fuel pump 6 is determined in accordance with the integrated value of the difference between the detected value of the fuel pressure and the target fuel pressure, the operation amount tends to be excessive when air is intermittently mixed. Is particularly effective.

  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 whole structure of the engine system concerning 1st Embodiment. The functional block diagram of the feedback control process of the fuel pressure concerning the embodiment. The time chart which shows the behavior of the fuel pressure at the time of air mixing. The flowchart which shows the process sequence of the feedback control in the embodiment. The figure which shows the calculation aspect of the limit value of the embodiment. The flowchart which shows the process sequence of the feedback control in 2nd Embodiment. The figure which shows the calculation aspect of the limit value of the embodiment. The flowchart which shows the process sequence of the feedback control in 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Fuel tank, 6 ... Fuel pump, 12 ... Common rail, 16 ... Fuel injection valve, 40 ... ECU (one Embodiment of a fuel-injection control apparatus).

Claims (10)

A pressure accumulating chamber for storing fuel in a high pressure state; a fuel pump for pumping fuel to the pressure accumulating chamber; a detecting means for detecting fuel pressure in the pressure accumulating chamber; and a fuel injection valve for injecting fuel stored in the pressure accumulating chamber. A fuel injection control device comprising a control means for feedback-controlling the detected fuel pressure to a target fuel pressure by operating the fuel pump for a fuel injection device for an on-vehicle internal combustion engine comprising:
Diagnosing means for diagnosing the presence or absence of abnormality of the feedback control based on the detected deviation of the fuel pressure with respect to the target fuel pressure;
Limiting means for limiting the operation amount in such a manner that the degree of limitation of the operation amount of the fuel pump is increased as the degree of deviation of the detected fuel pressure with respect to the target fuel pressure is increased when it is determined that there is an abnormality. A fuel injection control device comprising:   2. The fuel injection control apparatus according to claim 1, wherein the diagnosis unit determines that the feedback control is abnormal based on the detected fuel pressure being lower than the target fuel pressure.   The limiting unit includes an integration term calculation unit that calculates an integration term for determining an operation amount of the fuel pump according to an integrated value of a differential pressure between the detected fuel pressure and the target fuel pressure. The fuel injection control device according to claim 2.   The diagnostic means includes a calculation means for calculating a cumulative value over time of a differential pressure between the detected fuel pressure and the target fuel pressure, and an absolute value of the cumulative value as the deviation is a predetermined value. 4. The fuel injection control device according to claim 3, wherein it is determined that there is an abnormality when it is above.   5. The fuel injection control device according to claim 4, wherein the limiting means limits the integration term according to a magnitude of an absolute value of the cumulative value as the degree of deviation. The control means includes a basic value calculation means for calculating a basic value of the target fuel pressure according to an operating state of the internal combustion engine, and at least one of an upper limit value and a lower limit value of the target fuel pressure according to an operating state of the internal combustion engine. And a setting unit for setting the target fuel pressure based on the magnitude relationship between the value calculated by the guard calculating unit and the basic value,
The fuel injection control device according to claim 1, wherein the limiting unit limits a value calculated by the guard calculating unit in accordance with the degree of deviation.   The limiting means limits the value calculated by the guard calculating means according to the magnitude of the absolute value of the differential pressure between the detected fuel pressure and the target fuel pressure as the degree of deviation. The fuel injection control device according to claim 6.   The fuel injection control device according to claim 5 or 7, wherein the limiting means increases a limiting value used for the limiting in proportion to an absolute value of the cumulative value or an absolute value of the differential pressure.   The fuel injection control device according to claim 5 or 7, wherein the limiting means gradually decreases a changing speed of a limiting value used for the limiting with respect to the absolute value of the cumulative value or the absolute value of the differential pressure.   The fuel injection control device according to claim 5 or 7, wherein the limiting means gradually increases a change rate of the limiting value used for the limiting with respect to the absolute value of the cumulative value or the absolute value of the differential pressure.

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