JP5003624B2 - Fuel pressure control device - Google Patents

Description

  The present invention detects a pressure accumulation chamber that stores fuel in a high pressure state, a fuel injection valve that injects the fuel supplied from the pressure accumulation chamber, a fuel pump that pumps fuel into the pressure accumulation chamber, and a fuel pressure in the pressure accumulation chamber Based on an integrated value of a difference between a target value of the fuel pressure in the pressure accumulating chamber set based on an operating state of the internal combustion engine and the detected fuel pressure. The present invention relates to a fuel pressure control device that operates the fuel pump so as to feedback-control the detected fuel pressure to the target value.

  As this type of fuel pressure control device, one that is applied to a pressure accumulation type fuel injection device having a common pressure accumulation chamber that supplies high pressure fuel to the fuel injection valve of each cylinder of a diesel engine is known. The fuel pressure control device operates a fuel pump that pumps fuel pumped up from the fuel tank to the pressure accumulating chamber in order to feedback control the fuel pressure (actual fuel pressure) in the pressure accumulating chamber detected by the fuel pressure sensor to a target value (target fuel pressure). Yes. Here, normally, the required discharge amount for the fuel pump is calculated by calculating a proportional term, an integral term, etc. based on the deviation between the actual fuel pressure and the target fuel pressure, and the fuel pump is operated based on this. Thereby, the actual fuel pressure can be controlled to an optimum value according to the engine operation state by setting the target fuel pressure for each engine operation state.

  By the way, the target fuel pressure may suddenly increase during sudden acceleration when the driver depresses the accelerator pedal suddenly. Under such circumstances, the deviation between the actual fuel pressure and the target fuel pressure becomes large, the integral term based on this increases excessively, and so-called overintegration may occur. In this case, even if the actual fuel pressure reaches the target fuel pressure, the actual fuel pressure cannot be maintained at the target fuel pressure, and so-called overshoot occurs in which the actual fuel pressure continues to increase. Thereby, an actual fuel pressure increases excessively and there exists a possibility that the reliability of a pressure accumulation chamber may fall. In addition, when the driver suddenly decelerates the accelerator pedal being depressed, the target fuel pressure may suddenly drop. Even in such a situation, the deviation between the actual fuel pressure and the target fuel pressure becomes large, and the integral term based on this is excessively reduced, and so-called overintegration may occur. In this case, even if the actual fuel pressure reaches the target fuel pressure, the actual fuel pressure cannot be maintained at the target fuel pressure, and so-called undershoot occurs in which the actual fuel pressure continues to further decrease. As a result, the actual fuel pressure is excessively reduced, and the operation reliability of the fuel injection valve may be reduced.

Therefore, in the prior art, in order to avoid an increase in the amount of overshoot or the amount of undershoot, it has been put into practical use to change the proportional gain, the integral gain, or the like used when calculating the proportional term, the integral term, or the like. Conventionally, it has also been proposed to reduce the target fuel pressure in anticipation of the amount of overshoot, or to provide a pressure reducing valve having a fuel pressure adjusting function in the pressure accumulation chamber. In addition to the above, as a conventional technique, for example, there is one found in Patent Document 1 below.
JP 2003-307149 A

  However, changes in the proportional gain, integral gain, etc. may deteriorate the responsiveness of the actual fuel pressure. Moreover, if the target fuel pressure is lowered, the proper injection pressure of the fuel injection valve cannot be maintained, and the engine output may be reduced. Furthermore, when the pressure reducing valve is provided in the pressure accumulating chamber, there is a disadvantage that the cost increases due to an increase in the number of parts.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel pressure control device that can suitably control the fuel pressure in the pressure accumulating chamber while suppressing an increase in the number of components. is there.

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

The invention according to claim 1 is a pressure accumulation chamber that stores fuel in a high pressure state, a fuel injection valve that injects the fuel supplied from the pressure accumulation chamber, a fuel pump that pumps fuel into the pressure accumulation chamber, and the pressure accumulation chamber applies a detection means for detecting a fuel pressure in a fuel injection system for an internal combustion engine having a, the differential pressure between the target value and the detected is the fuel pressure of the fuel pressure in the accumulation chamber which is set based on an operating state of the internal combustion engine Whether or not the target value suddenly changes in a fuel pressure control device that operates the fuel pump to feedback-control the detected fuel pressure to the target value based on an integral term calculated as a cumulative value obtained by multiplying an integral gain. A sudden change judging means for judging whether or not the sudden change judgment means judges that the fuel pressure is suddenly changed, and the detected fuel pressure is shifted by a predetermined amount in the direction of sudden change from the target value. Characterized in that the and a increasing means for increasing the case of changes to the target value, before the miracle component gain forcibly.

  If the target value changes suddenly, overintegration of the integral term may occur. For this reason, after the detected fuel pressure reaches the target value, the detected fuel pressure may further change in the direction of sudden change, and overshoot or undershoot may occur. In this regard, in the above invention, by providing the sudden change determination means and the increase means, it is determined that the target value changes suddenly, and the detected fuel pressure has changed to the value shifted by the predetermined amount or the target value. In this case, the integral gain used for the feedback control calculation is forcibly increased in order to eliminate the overintegration. As a result, the overintegration elimination speed can be increased, and thus the detected overshoot amount or undershoot amount of the fuel pressure can be suitably suppressed. For this reason, the detected fuel pressure can be suitably controlled, and as a result, a decrease in the reliability of the fuel injection device can be avoided.

  According to a second aspect of the invention, there is provided the invention according to the first aspect, further comprising release means for releasing the increase by the increase means based on the detected fuel pressure.

  If the detected fuel pressure is in the vicinity of the target value after the over-integration of the integral term is eliminated, the detected fuel pressure will fluctuate in the vicinity of the target value if the integral gain remains increased by the increasing means. There is a risk that controllability will be reduced. In this regard, in the above invention, by providing the canceling means, the integral gain can be increased only by a specific period by the increasing means, and as a result, the fluctuation of the integral term after the overintegration is eliminated can be suitably suppressed. Thereby, the controllability of the detected fuel pressure can be improved.

According to a third aspect of the invention, in the invention of claim 1 or 2, wherein said increasing means, when the fuel pressure to be the detected changes to shifted value the predetermined amount, before miracle component gain to force the The release means changes the detected fuel pressure to a value shifted by a second predetermined amount set to a value smaller than the predetermined amount in the direction of sudden change from the target value. In this case, the increase is canceled.

  In order to quickly eliminate the overintegration, it is desired that the period during which the integral gain is increased by the increasing means is made as long as possible after the detected fuel pressure reaches a value shifted by the predetermined amount. However, if this period is too long, the detected fuel pressure fluctuates near the target value, and the followability of the detected fuel pressure may be reduced. In this respect, the above-described invention can suitably suppress such a situation.

  The second predetermined amount is desirably set under the condition that the overintegration is quickly eliminated and the followability of the detected fuel pressure is not reduced.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the integral gain is set to a smaller value as a deviation between the detected fuel pressure and the target value is larger. The increasing means forcibly increases the integral gain by multiplying the integral gain set by the setting means by a predetermined coefficient larger than 1.

  In order to avoid a situation in which the detected fuel pressure varies greatly with respect to the target value, it is desirable that the integral gain be smaller as the deviation between the detected fuel pressure and the target value is larger. In the above invention, in view of this point, by providing the setting means, it is possible to suitably suppress the fluctuation of the detected fuel pressure. In addition, when the target value changes suddenly and the detected fuel pressure changes to a value deviated by a predetermined amount in the direction of sudden change from the target value or changes to the target value, the integral gain set by the setting means By multiplying by a predetermined coefficient larger than 1, the setting for increasing the integral gain can be easily performed.

Invention of claim 5, the invention according to any one of claims 1 to 4, wherein the increasing means, when the fuel pressure to be the detected changes to a value shifted by the predetermined amount, before miracle A means for forcibly increasing the minute gain, and waiting for the value to be shifted by the predetermined amount when it is determined that the sudden change is determined by the sudden change determination means. Then, when it is determined that the detected fuel pressure follows the target value without being shifted by the predetermined amount, the standby is canceled.

  Even if the target value is determined to change suddenly by the sudden change determination means, depending on the behavior of the detected fuel pressure, the detected fuel pressure may follow the target value without changing to a value deviated by the predetermined amount. Under such circumstances, when waiting for the detected fuel pressure to deviate by the predetermined amount, the detected fuel pressure has deviated by the predetermined amount for some reason after following the target value. When the value is reached, the integral gain may be forcibly increased. In this regard, in the above invention, when it is determined that the detected fuel pressure follows the target value without being shifted by the predetermined amount, such a situation can be avoided by canceling the standby. .

  The invention described in claim 6 is characterized in that in the invention described in any one of claims 1 to 5, there is provided mitigation means for mitigating a sudden change in the target value.

  A sudden change in the target value may lead to a decrease in the followability of the fuel pressure due to overintegration, as well as a deterioration in exhaust characteristics and an increase in combustion noise. In this regard, in the above invention, by providing the mitigation means, it is possible to improve the followability of the detected fuel pressure by suppressing overintegration, or to suitably avoid the deterioration of exhaust characteristics and the increase of combustion noise. it can.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the fuel pressure control device has a fuel amount assumed to flow out of the pressure accumulation chamber by fuel injection by the fuel injection valve. The operation amount of the fuel pump for replenishing at least a part is set by the feedback control.

  Under the situation where the target value changes suddenly, generally, the target value of the amount of fuel injected from the fuel injection valve changes suddenly, and the amount of fuel flowing out of the pressure accumulating chamber tends to change suddenly due to fuel injection by the fuel injection valve. . Here, in the above invention, the operation amount of the fuel pump for replenishing at least a part of the fuel pump is set by feedback control. For this reason, when the detected fuel pressure changes in the direction opposite to the direction of sudden change, there is a possibility that the deviation between the detected fuel pressure and the target value increases. Since the feedback manipulated variable is changed only when the deviation increases, overintegration may occur, and the detected overshoot or undershoot of the fuel pressure may occur. Here, when the integral gain is set to be small in advance so as to suppress overintegration, the fuel amount to be pumped into the pressure accumulating chamber is set as an integral term while the fuel amount actually injected from the fuel injection valve is set as the target value. The time required for learning is prolonged. In this regard, in the above invention, by providing the increasing means, it is preferable to suppress the time required for the integral term to learn the feedback operation amount required for supplementing at least a part of the time. However, the occurrence of overshoot or undershoot of the detected fuel pressure can be suitably suppressed.

  Hereinafter, an embodiment in which a fuel pressure control device according to the present invention is applied to a multi-cylinder diesel engine equipped with a common rail fuel injection device will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of the engine system according to the present embodiment. As illustrated, the intake passage 12 of the diesel engine 10 communicates with a combustion chamber 20 defined by a cylinder block 16 and a piston 18 by opening the intake valve 14. In the combustion chamber 20, the tip of the fuel injection valve 22 is disposed so as to protrude. As a result, fuel can be supplied to the combustion chamber 20 by injection.

  When fuel is injected into the combustion chamber 20 by the fuel injection valve 22, the fuel is self-ignited by compression of the combustion chamber 20, and energy is generated by combustion. This energy is taken out as rotational energy of the output shaft (crankshaft 28) of the diesel engine 10 via the piston 18. The gas used for combustion is discharged as exhaust into the exhaust passage 32 by opening the exhaust valve 30.

  Fuel is supplied to the fuel injection valve 22 from the common rail 26 via the high-pressure fuel passage 24. The common rail 26 serves as a common pressure accumulation chamber that accumulates fuel pumped by the fuel pump 28 in a high pressure state and supplies the fuel to the fuel injection valves 22 of the respective cylinders. The fuel pump 28 is powered by the crankshaft 28 of the diesel engine 10, thereby pumping fuel from the fuel tank 38 via the fuel filter 36 and pumping the pumped fuel to the common rail 26. Specifically, the fuel pump 28 is provided with an intake metering valve (hereinafter referred to as SCV 40). The SCV 40 adjusts the amount of fuel discharged by the fuel pump 28 by adjusting the amount of fuel drawn into the fuel pump 28. That is, the amount of fuel pumped to the common rail 26 is adjusted by operating the SCV 40. For this reason, the fuel pressure in the common rail 26 can be controlled by the discharge amount of the fuel pump 28.

  The common rail 26 is provided with a pressure limiter 42 that discharges fuel to the outside of the common rail 26 in order to prevent the internal fuel pressure from becoming an abnormally high pressure. The fuel released by the pressure limiter 42, the leaked fuel flowing out from the fuel injection valve 22, and the surplus fuel in the fuel pump 28 are returned to the fuel tank 38 via the fuel return passage 44.

  The diesel engine 10 includes a crank angle sensor 46 that detects the rotation angle of the crankshaft 28 in the vicinity of the crankshaft 28, a fuel pressure sensor 48 that detects the fuel pressure (actual fuel pressure) in the common rail 26, and the temperature of the fuel in the fuel pump 28. A fuel temperature sensor 49 is provided to detect the above. These various sensors that detect the operating state of the diesel engine 10 and the output signal from the accelerator sensor 50 that detects the operation amount of the accelerator pedal are input to an electronic control unit (hereinafter, ECU 52).

  The ECU 52 is mainly composed of a microcomputer including a known CPU, ROM, RAM, and the like. The ECU 52 executes various control programs corresponding to the engine operating state each time by executing various control programs stored in the ROM. The ECU 52 performs fuel injection control and ignition control based on these input signals and operates the SCV 40 to control the actual fuel pressure to a target value (target fuel pressure).

  In FIG. 2, the functional block diagram of the process regarding the said fuel pressure control in this embodiment among the processes which ECU52 performs is shown.

  The injection amount calculation unit B2 determines the command value (command injection) of the injection amount for the fuel injection valve 22 based on the engine rotation speed based on the detection value of the crank angle sensor 46 and the accelerator operation amount based on the detection value of the accelerator sensor 50. Amount). Here, the command injection amount is set to a larger value as the accelerator operation amount is larger.

  The target fuel pressure calculation unit B4 calculates the target fuel pressure in the common rail 26 based on the command injection amount calculated by the injection amount calculation unit B2 and the engine speed. Here, the target fuel pressure is generally set to a higher value as the command injection amount is larger.

  The filter processing unit B6 calculates a value in which the degree of change in the target fuel pressure is relaxed. The calculation method of the filter process may be performed by, for example, a weighted average process of the previous sampling value of the target fuel pressure and the current sampling value or a moving average process.

  The relaxed target fuel pressure calculated by the filter processing unit B6 and the actual fuel pressure detected by the fuel pressure sensor 48 are the differential pressure calculation unit B8, the proportional term calculation unit B10, the differential term calculation unit B12, and the integral term calculation. This is taken in by a feedback control unit configured to include the unit B14 and the coefficient calculation unit B16. The differential pressure calculation unit B8 calculates a differential pressure between the relaxed target fuel pressure and the actual fuel pressure. This differential pressure is taken into the proportional term calculation unit B10, the differential term calculation unit B12, and the integral term calculation unit B14. Here, the proportional term calculation unit B10 calculates a proportional term by multiplying the differential pressure by a proportional gain. The differential term calculation unit B12 calculates the differential term by multiplying the time differential value of the differential pressure by a differential gain. Further, the integral term calculation unit B14 calculates an integral term by calculating a cumulative value obtained by multiplying the differential pressure by the integral gain (integration calculation of the differential pressure). The integral gain is set to a smaller value as the differential pressure is larger. This is to avoid a situation where the actual fuel pressure fluctuates greatly with respect to the target fuel pressure.

  The adding unit B17 adds the proportional term, the differential term, and the integral term. The output of the addition unit B17 is a discharge amount required for feedback control, and is a feedback operation amount for the SCV 40.

  The fuel injection valve leak fuel calculation unit B18 flows out from the common rail 26 to the fuel recirculation passage 44 via the fuel injection valve 22 based on the engine speed, the actual fuel pressure, and the fuel temperature detected by the fuel temperature sensor 49. The amount of leak to be calculated is calculated.

  The target fuel pressure change calculation unit B20 calculates the change amount of the target fuel pressure. Then, the fuel conversion unit B22 converts the actual fuel pressure into a fuel amount corresponding to the change amount of the target fuel pressure so as to calculate the fuel amount required to change the actual fuel pressure by the change amount of the target fuel pressure. In this conversion, the value “E / V” obtained by dividing the volume expansion coefficient E of the fuel by the sum V of the volume of the fuel passage between the fuel pump 28 and the common rail 26 and the volume of the common rail 26 is the target fuel pressure. This is done by multiplying the amount of change.

  The feedforward control unit B24 includes a leak amount calculated by the fuel injection valve leak fuel calculation unit B18, a fuel amount converted by the fuel conversion unit B22, and a command injection amount calculated by the injection amount calculation unit B2. The feedforward manipulated variable of SCV40 is calculated as the sum of.

  The feedforward operation amount calculated by the feedforward control unit B24 is taken into the feedforward contribution rate multiplication unit B26. Here, a substantial feedforward operation amount for operating the SCV 40 is calculated by multiplying the feedforward operation amount by a predetermined coefficient A (0 <A <1). The predetermined coefficient A determines the contribution ratio of the feedforward control in the control of the actual fuel pressure, and this processing is performed in order to improve both the responsiveness and followability of the actual fuel pressure. . That is, only with feedback control, the feedback manipulated variable is changed only after a deviation between the actual fuel pressure and the target fuel pressure occurs, so that the followability of the actual fuel pressure may be reduced. On the other hand, in the feedforward control, the required discharge amount that is assumed when the actual fuel pressure is controlled to the target fuel pressure can be made the actual discharge amount of the fuel pump 28 before the deviation between the actual fuel pressure and the target fuel pressure occurs. Therefore, the response of the actual fuel pressure can be improved. However, if the estimated required discharge amount deviates from the actual required discharge amount due to individual differences among the fuel injection valve 22, the common rail 26, and the fuel pump 28, the followability of the actual fuel pressure may be reduced. There is. For this reason, when the contribution ratio of feedforward control is large, even if feedback correction is added, it may be difficult to improve the followability of the actual fuel pressure. In the present embodiment, in view of this point, the predetermined coefficient A is set to an optimum value that can improve both the response and followability of the actual fuel pressure.

  The addition unit B28 adds the final feedback operation amount output from the addition unit B17 and the final feedforward operation amount output from the feedforward contribution rate multiplication unit B26. The output of the adding portion B28 becomes a command value (command discharge amount) of the discharge amount for the fuel pump 28. The drive current conversion unit B30 converts the command discharge amount into a drive current value of the SCV 40 required for discharging from the fuel pump 28. The SCV 40 is operated based on the drive current value converted by the drive current conversion unit B30. Incidentally, the fuel pump 28 is of a normally closed type in which the SCV 40 is in a closed state and does not discharge fuel when not energized.

  By the way, under the situation where the target fuel pressure changes suddenly, overintegration of the integral term occurs, and there is a possibility that overshoot or undershoot occurs. Therefore, in the present embodiment, the determination processing unit B32 is provided, and the coefficient calculation unit B16 is operated to forcibly increase the integral gain used for the calculation of feedback control according to the operating state of the diesel engine 10.

  FIG. 3 and FIG. 4 show the procedure for forcibly increasing the integral gain. This process is repeatedly executed by the ECU 52 at a predetermined cycle, for example.

  FIG. 3 shows a procedure of processing when the target fuel pressure rises rapidly. In this series of processes, first, in step S10, it is determined whether or not there is an acceleration determination. This process determines whether or not the amount of change (change rate) per time of the target fuel pressure is equal to or greater than a predetermined threshold value. In this embodiment, the accelerator operation amount having a correlation with the target fuel pressure is used, and the above determination is made indirectly based on whether or not the change rate of the accelerator operation amount is equal to or greater than a predetermined threshold value. If it is determined in step S10 that acceleration is determined, the process proceeds to step S12.

  In step S12, it is determined whether or not the actual fuel pressure is equal to or greater than “target fuel pressure + predetermined value α (α> 0)”. Here, even if the target fuel pressure suddenly rises to its maximum value, the predetermined value α is a decrease in reliability of the actual fuel pressure (for example, the common rail 26, the common rail 26, the fuel injection valve 22, and the high-pressure fuel). It is set to a value that does not overshoot to a value that causes fuel leakage from the connecting portion with the passage 24). If a positive determination is made in step S12, the process proceeds to step S14.

  In step S14, the integral gain increase coefficient a output from the coefficient calculation unit B16 shown in FIG. 2 is changed from 1 to a value greater than 1. Then, the integral gain is forcibly increased by multiplying the integral gain increase coefficient a by the integral gain variably set according to the differential pressure between the actual fuel pressure and the target fuel pressure. The integral gain increase coefficient a is preferably determined in advance through experiments or the like. After the process of this step is completed, the process proceeds to step S16.

  In step S16, it is determined whether or not the actual fuel pressure is equal to or less than “target fuel pressure + predetermined value β (α> β> 0)”. This process is for determining whether or not to cancel the forced increase of the integral gain. Therefore, it is desirable that the predetermined value β is an optimum value set under the condition that the overintegration is quickly eliminated and the followability of the actual fuel pressure is not reduced. This is because in order to lengthen the period for increasing the integral gain to quickly eliminate overintegration, if the predetermined value β is set to an excessively small value, the actual fuel pressure fluctuates in the vicinity of the target fuel pressure, and the followability of the actual fuel pressure It is because there exists a possibility that it may fall.

  When an affirmative determination is made in step S16, the process proceeds to step S18, and the integral gain increase coefficient a output from the coefficient calculation unit B16 is changed from a value greater than 1 to 1, thereby forcibly increasing the integral gain. Is released. On the other hand, when a negative determination is made in step S16, the process returns to step S14.

  On the other hand, when a negative determination is made in step S12, the process proceeds to step S20, and it is determined whether or not the actual fuel pressure is continuously decreasing for a predetermined period (N1 seconds). This process is for determining whether or not the possibility of occurrence of an overshoot of the actual fuel pressure has been eliminated. Here, it is desirable that the predetermined period is a period determined in advance by experiments or the like based on the integral gain. If a negative determination is made in step S20, the process returns to step S12.

  When a negative determination is made at step S10, when the process at step S18 is completed, or when an affirmative determination is made at step S20, the series of processes is temporarily terminated.

  FIG. 4 shows a processing procedure when the target fuel pressure is rapidly lowered. In this series of processes, first, in step S30, it is determined whether or not there is a deceleration determination. This process determines whether or not the amount of change (change rate) per time of the target fuel pressure is equal to or less than a predetermined threshold value. In the present embodiment, as in the case of step S10 shown in FIG. 3, the above determination is indirectly made based on whether or not the change rate of the accelerator operation amount is equal to or less than a predetermined threshold value. If it is determined in step S30 that there is a deceleration determination, the process proceeds to step S32.

  In step S32, it is determined whether or not the actual fuel pressure is equal to or less than “target fuel pressure−predetermined value γ (γ> 0)”. Here, the predetermined value γ is set to a value that does not undershoot until the actual fuel pressure falls below the lower limit value of the appropriate injection pressure of the fuel injection valve 22 even when the target fuel pressure suddenly drops to its minimum value. ing. If a positive determination is made in step S32, the process proceeds to step S34.

  In step S34, the integral gain increasing coefficient a output from the coefficient calculation unit B16 is changed from 1 to a value larger than 1, similarly to the process of step S14 shown in FIG. Then, the process proceeds to step S36. In step S36, it is determined whether or not the actual fuel pressure is equal to or greater than “target fuel pressure−predetermined value δ (γ> δ> 0)”. Here, the predetermined value δ is based on the condition that, as in step S16 shown in FIG. 3, the overintegration of the integral term is quickly eliminated and the followability of the actual fuel pressure is not reduced. It is desirable that the optimum value is set to.

  If an affirmative determination is made in step S36, the process proceeds to step S38, and the integral gain increase coefficient a output from the coefficient calculation unit B16 is changed from a value greater than 1 to 1, thereby forcibly increasing the integral gain. Is released. On the other hand, when a negative determination is made in step S36, the process returns to step S34.

  On the other hand, if a negative determination is made in step S32, the process proceeds to step S40, and it is determined whether or not the actual fuel pressure continues to increase for a predetermined period (N2 seconds). This process corresponds to the process of step S20 shown in FIG. Here, it is desirable that the predetermined period is a period determined in advance by an experiment or the like based on the integral gain, similarly to step S20 shown in FIG. If a negative determination is made in step S40, the process returns to step S32.

  When a negative determination is made at step S30, when the process at step S38 is completed, or when an affirmative determination is made at step S40, the series of processes is temporarily terminated.

  FIG. 5 shows an example of fuel pressure control when there is a forced increase process of integral gain by the above process. Specifically, FIG. 5A shows the transition of the acceleration determination flag state, FIG. 5B shows the transition of the deceleration determination flag state, and FIG. 5C shows the transition of the actual fuel pressure NPC. FIG. 5D shows the transition of the state of the integral gain change flag at the time of acceleration determination, FIG. 5E shows the transition of the state of the integral gain change flag at the time of deceleration determination, and FIG. ) Shows the transition of the integral gain increase coefficient a, and FIG. 5 (g) shows the transition of the integral term.

  As shown in FIG. 5, after the acceleration determination flag is turned on at time t1, as shown in FIG. 5A, the actual fuel pressure NPC is set to the target at time t2 as shown by the solid line in FIG. 5C. By reaching a value larger than the fuel pressure PFIN by the predetermined value α, the integral gain change flag is turned on as shown in FIG. 5D, and the integral gain increases as shown by the solid line in FIG. The coefficient a is changed from 1 to a value greater than 1. Then, at time t3, as indicated by the solid line in FIG. 5C, the actual fuel pressure NPC has reached a value that is larger than the target fuel pressure PFIN by a predetermined value β, and as shown in FIG. The change flag is turned off, and the integral gain increase coefficient a is changed from a value larger than 1 to 1 as shown by a solid line in FIG. Therefore, at time t5, as shown by the solid line in FIG. 5C, the actual fuel pressure NPC quickly converges to the target fuel pressure PFIN.

  On the other hand, after the deceleration determination flag is turned on at time t6 as shown in FIG. 5 (b), the actual fuel pressure NPC is predetermined from the target fuel pressure PFIN at time t7 as shown by the solid line in FIG. 5 (c). When the value γ has reached a small value, the integral gain change flag is turned on as shown in FIG. 5 (e), and the integral gain increase coefficient a is 1 as shown by the solid line in FIG. 5 (f). To a value greater than 1. Then, as shown by the solid line in FIG. 5C at time t8, the actual fuel pressure NPC has reached a value that is smaller than the target fuel pressure PFIN by a predetermined value δ, and as shown in FIG. The change flag is turned off, and the integral gain increase coefficient a is changed from a value larger than 1 to 1 as shown by a solid line in FIG. For this reason, at time t9, as shown by the solid line in FIG. 5C, the actual fuel pressure NPC quickly converges to the target fuel pressure PFIN.

  On the other hand, when the integral gain is not forcibly increased, the actual fuel pressure NPC is increased at time t5 later than time t4 or t10 later than time t9 as shown by the dotted line in FIG. It converges to the target fuel pressure PFIN. Thus, in this embodiment, overintegration of the integral term can be suitably suppressed.

  FIG. 6 shows a relationship between an integral term of the drive current of the SCV 40 and the discharge amount of the fuel pump 28. Specifically, FIG. 6A shows the above relationship during acceleration, and FIG. 6B shows the above relationship during deceleration. The points (A) to (H), the points (C ′), (D ′), (G ′), and the point (H ′) in FIG. 6 are the points (A) to (A) to FIG. It corresponds to the point (H), the points (C ′), (D ′), (G ′) and the point (H ′). By eliminating the over-integration, it can be confirmed that the drive current of the SCV 40 during acceleration is reduced by the integral term, and the drive current of the SCV 40 during deceleration is increased by the integral term.

  FIG. 7 shows an example of fuel pressure control in the case where there is no forced increase processing of the integral gain by the above processing. Specifically, FIGS. 7A to 7F correspond to FIGS. 5A to 5F.

  As shown in the figure, after the acceleration determination flag is turned on at time t1 as shown in FIG. 7A, the actual fuel pressure NPC is shown as shown by the solid line in FIG. 7C from time t2 to t3. Is continuously decreased for N1 seconds without reaching a value larger than the target fuel pressure PFIN by the predetermined value α, and therefore, the integral gain increase process is not performed. Further, as shown in FIG. 7 (b) at time t4, after the deceleration determination flag is turned on, from time t5 to t6, as shown by the solid line in FIG. 7 (c), the actual fuel pressure NPC becomes the target fuel pressure PFIN. Since the value continuously decreases for N2 seconds without reaching a value smaller than the predetermined value γ, the integral gain is not increased.

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

  (1) When it is determined that there is acceleration determination and the actual fuel pressure is equal to or greater than the “target fuel pressure + predetermined value α”, the integral gain increase coefficient a is increased from 1 to a value greater than 1, thereby integrating gain Forcibly increased. As a result, it is possible to increase the rate of elimination of overintegration of the integral term, and thus it is possible to suitably suppress the overshoot amount of the actual fuel pressure.

  (2) When it is determined that there is deceleration determination and the actual fuel pressure is equal to or less than the “target fuel pressure−predetermined value γ”, the integral gain increase coefficient a is increased from 1 to a value greater than 1, thereby integrating gain Forcibly increased. As a result, the speed of eliminating the overintegration of the integral term can be increased, and as a result, the undershoot amount of the actual fuel pressure can be suitably suppressed.

  (3) After forcibly increasing the integral gain, if the actual fuel pressure is equal to or less than the “target fuel pressure + predetermined value β” or equal to or greater than the “target fuel pressure−predetermined value δ”, the integral gain increase coefficient a is By changing the value greater than 1 to 1, the forced increase in integral gain was canceled. Thereby, after cancellation of overintegration, it is possible to suitably suppress the actual fuel pressure from fluctuating near the target fuel pressure and the followability of the actual fuel pressure from being lowered.

  (4) Acceleration or deceleration determination is made, and the actual fuel pressure continuously decreases or increases for the predetermined period without reaching the “target fuel pressure + predetermined value α” or the “target fuel pressure−predetermined value γ”. When it is determined that the integral gain is not forcibly increased. As a result, when there is no risk of overshoot or undershoot of the actual fuel pressure, it is possible to avoid a situation where the integral gain is forcibly increased.

  (5) A filter processing unit B6 is provided to alleviate a sudden change in the target fuel pressure. As a result, the followability of the actual fuel pressure can be improved, and deterioration of exhaust characteristics and increase in combustion noise can be suitably avoided.

(6) The predetermined coefficient A of the feedforward contribution rate multiplication unit B26 is set to 0 <A <1. For this reason, since overintegration always occurs when the target fuel pressure changes suddenly, the utility value of the process for forcibly increasing the integral gain is high.
(Other embodiments)
The above embodiment may be modified as follows.

  In the above embodiment, the feedforward control is contributed together with the feedback control. However, the present invention is not limited to this, and it may be configured only by the feedback control. In this case, since the target fuel pressure changes abruptly, the overintegration of the integral term occurs particularly remarkably, so that the utility value of the present invention is the highest. However, in the feedforward contribution rate multiplication unit B26 shown in FIG. 2, the actual fuel pressure is basically controlled by feedforward control by setting the predetermined coefficient to A = 1, and errors in the feedforward control are reduced. Even in the case of feedback correction, the application of the present invention is effective because overintegration may occur in the integral term of the feedback control when the target fuel pressure suddenly increases. That is, for example, when the fuel is pumped up from the fuel tank 38 by the fuel pump 28, a pressure loss occurs when the fuel passes through the fuel filter 36, and the pressure on the downstream side of the fuel filter 36 decreases. In particular, when the target fuel pressure rises rapidly, the amount of fuel sucked from the fuel tank 38 by the fuel pump 28 increases, and the pressure loss increases. Thereby, air in the fuel may be separated on the downstream side of the fuel filter 36 to generate bubbles. In this case, the amount of fuel pumped up by the fuel pump 28 decreases by the volume of the bubbles, and the amount of fuel pumped from the fuel pump 28 into the common rail 26 decreases by the volume of the bubbles. For this reason, the actual discharge amount of the fuel pump 28 becomes smaller than the required discharge amount, and the deviation between the actual fuel pressure and the target fuel pressure increases, so that overintegration may occur. Even in such a case, the application of the present invention is effective.

  In the above embodiment, it is indirectly determined whether or not the target fuel pressure changes suddenly based on the detected value of the accelerator operation amount, but whether or not the target fuel pressure changes suddenly based on the parameter indicating the operating state of the diesel engine 10 is determined. The determination process is not limited to this. For example, it may be determined from the rate of change of the command injection amount for the fuel injection valve 22 calculated by the injection amount calculation unit B2 shown in FIG. Further, the determination is not limited to indirectly, but may be directly determined from the target fuel pressure calculated by the target fuel pressure calculation unit B4 shown in FIG.

  In the above embodiment, when the target fuel pressure changes suddenly, the threshold value that triggers forcibly increasing the integral gain is shifted from the target fuel pressure by a predetermined amount (α> 0 or γ> 0) in the direction of sudden change. The value is not limited to this. This threshold value may be set to the target fuel pressure (α = 0 or γ = 0). Even in this case, an effect according to the effect of the above embodiment can be obtained.

  In the above embodiment, the integral gain is forcibly increased by multiplying the basic integral gain by the integral gain increase coefficient a, but the present invention is not limited to this. For example, when the deviation between the actual fuel pressure and the target fuel pressure is large, the normal integral gain may be forcibly switched to an integral gain larger than this.

  In the above embodiment, if a negative determination is made in step S20 shown in FIG. 3 or step S40 shown in FIG. 4, the process returns to step S12 shown in FIG. 3 or step S32 shown in FIG. For example, even if a predetermined time elapses, the actual fuel pressure deviates by a predetermined amount (α> 0 or γ> 0) in the direction of sudden change from the target fuel pressure, which is a threshold value that triggers forcibly increasing the integral gain. If the value does not reach the specified value, the series of processes may be temporarily terminated.

  The means for calculating the feedback manipulated variable is not limited to the one based on the proportional integral differential calculation of the deviation between the actual fuel pressure and the target fuel pressure. For example, the feedback manipulated variable may be calculated only by proportional integral calculation. The application of the present invention is particularly effective because there is a possibility that the degree of overintegration will be increased if there is no differential operation that can improve the response of the fuel pressure.

  In the above embodiment, the integral gain is forcibly increased both when the target fuel pressure rapidly increases and when the target fuel pressure decreases. For example, processing for increasing the integral gain may be performed at least one of them, for example, processing for forcibly increasing the integral gain only under a situation where the actual fuel pressure rises excessively.

  In the above embodiment, the fuel pump 28 is a normally closed type, but is not limited thereto. The fuel pump 28 may be of a normally open type in which the SCV 40 is opened to discharge fuel when not energized.

  In the embodiment described above, the intake metering valve is provided in the fuel pump 28 to control the fuel pressure in the common rail 26, but this is not restrictive. A discharge metering valve that controls the fuel pressure in the common rail 26 by adjusting the amount of fuel discharged from the fuel pump 28 may be provided.

The figure which shows the whole structure of the engine system concerning one Embodiment. The block diagram which shows the process regarding the fuel pressure control in the common rail concerning the embodiment. The flowchart which shows the procedure of the forced increase process of the integral gain at the time of the rapid increase of the target fuel pressure concerning the embodiment. The flowchart which shows the procedure of the forced increase process of the integral gain at the time of the rapid fall of the target fuel pressure concerning the embodiment. The time chart which shows the aspect of the fuel pressure control process (when there exists a forced increase process of an integral gain) concerning the embodiment. The figure which shows transition of the integral term accompanying the said fuel pressure control process. The time chart which shows the aspect of the fuel pressure control process (when there is no forced increase process of an integral gain) concerning the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 22 ... Fuel injection valve, 24 ... High pressure fuel passage, 26 ... Common rail, 28 ... Fuel pump, 28 ... Crankshaft, 36 ... Fuel filter, 38 ... Fuel tank, 40 ... Suction metering valve (SCV) 52 ... ECU (one embodiment of fuel pressure control device)

Claims (7)

A pressure accumulating chamber for storing fuel in a high pressure state; a fuel injection valve for injecting the fuel supplied from the pressure accumulating chamber; a fuel pump for pumping fuel into the pressure accumulating chamber; and a detecting means for detecting the fuel pressure in the pressure accumulating chamber; Applied to a fuel injection device of an internal combustion engine comprising:
Based on the integral term is calculated as the cumulative value although the integral gain by multiplying the pressure difference between the fuel pressure which the is the detection target value of the accumulation chamber of the fuel pressure that is set based on the operating state of the internal combustion engine, is the detection In the fuel pressure control device for operating the fuel pump to feedback control the fuel pressure to the target value,
Sudden change judging means for judging whether or not the target value suddenly changes;
When the fuel pressure that is has been and said detection determines that a sudden change by the sudden change determining means is changed to a shifted value or the target value a predetermined amount in a direction the sudden change than the target value, forcing the front miracle component gain A fuel pressure control device comprising an increasing means for increasing the fuel pressure.   2. The fuel pressure control apparatus according to claim 1, further comprising a release unit that cancels the increase by the increase unit based on the detected fuel pressure. It said increasing means, when the fuel pressure to be the detected changes to a value shifted by the predetermined amount, which forcibly increasing the pre miracle component gain,
The release means increases the increase when the detected fuel pressure changes to a value shifted by a second predetermined amount set to a value smaller than the predetermined amount in the direction of sudden change from the target value. 3. The fuel pressure control device according to claim 1, wherein the fuel pressure control device is released. Setting means for setting the integral gain to a smaller value as the deviation between the detected fuel pressure and the target value increases;
The increase means forcibly increases the integral gain by multiplying the integral gain set by the setting means by a predetermined coefficient larger than one. The fuel pressure control device according to the item. Said increasing means, when the fuel pressure to be the detected changes to shifted value the predetermined amount, and be one which forcibly increasing the pre miracle component gain, is the determined to a sudden change by the sudden change determination means And a means for waiting for the value to deviate by the predetermined amount, and the target is determined to be suddenly changed by the sudden change determining means and the detected fuel pressure is not deviated by the predetermined amount. The fuel pressure control device according to any one of claims 1 to 4, wherein the standby is canceled when it is determined to follow the value.   The fuel pressure control apparatus according to any one of claims 1 to 5, further comprising a mitigating means for mitigating a sudden change in the target value.   The fuel pressure control device sets an operation amount of the fuel pump for replenishing at least a part of a fuel amount assumed to flow out of the pressure accumulating chamber by fuel injection by the fuel injection valve by the feedback control. The fuel pressure control device according to claim 1, wherein the fuel pressure control device is a fuel pressure control device.

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