JP4483824B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a pressure accumulating chamber for storing fuel in a high pressure state, a fuel pump for pumping fuel into the pressure accumulating chamber, a fuel injection valve for injecting fuel in the pressure accumulating chamber, and a detecting means for detecting the fuel pressure in the pressure accumulating chamber. And a fuel injection control device that feedback-controls the detected fuel pressure to the target value based on a cumulative value of the difference between the detected fuel pressure and the target value.

  As this type of control device, for example, as can be seen in Patent Document 1 below, PID control is used to control the fuel pressure of the accumulator chamber (common rail) common to each cylinder of a multi-cylinder diesel engine to its target value. Some determine the operating signal of the fuel pump. According to this control device, the actual fuel pressure in the common rail can be made to follow the target value.

  The target value is usually set based on the rotational speed of the output shaft of the diesel engine and the command value of the injection amount for the fuel injection valve. Specifically, the higher the rotational speed and the greater the injection amount, the higher the target value is set. For this reason, at the time of shifting from the acceleration request when the accelerator pedal is depressed to the deceleration request when the accelerator pedal is released, the target injection value decreases because the command injection amount decreases. Here, when the command injection amount becomes substantially zero, the main factor for reducing the actual fuel pressure in the common rail is leaked fuel that flows out from the common rail to the fuel tank through the clearance of the fuel injection valve. For this reason, there is a delay before the actual fuel pressure follows the target value.

  Furthermore, when the deceleration request is made, there is a possibility that fuel is pumped from the fuel pump to the common rail even though the actual fuel pressure exceeds the target value. This is a phenomenon that occurs when the integral term has a positive value before the deceleration request, and even after sudden deceleration, fuel is pumped from the fuel pump for a while due to the influence of this integral term. For this reason, further delay occurs in following the target value of the actual fuel pressure.

  Under the above circumstances, when an acceleration request occurs again before the actual fuel pressure follows the target value, the fuel injection is resumed with the actual fuel pressure in the common rail higher than the target value, and the exhaust characteristics deteriorate. There is also a fear.

In addition to the above, as a control device that performs feedback control of the fuel pressure, for example, there is also one described in Patent Document 2 below.
JP 2004-5446 A JP 2004-36498 A

  The present invention has been made to solve the above-described problems, and its purpose is to feedback-control the detected fuel pressure to the target value based on the accumulated value of the difference between the detected fuel pressure and the target value. Thus, an object of the present invention is to provide a fuel injection control device that can improve the followability of the fuel pressure when a pressure reduction is required.

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

According to the first aspect of the present invention, when the pressure reduction in the pressure accumulating chamber is requested , an amount of discharge is excessive because a value obtained by subtracting a command injection amount for the fuel injection valve from a discharge amount of the fuel pump determined by the feedback control is positive. a determination unit whether the determining whether it is, when it is determined that the excess by said determining means, advance the discharge amount of the fuel pump by decreasing correction of the ejection amount of the fuel pump that is determined by the feedback control And limiting means for limiting the amount to a predetermined amount or less.

  Regardless of when the pressure reduction is requested, when the discharge amount is excessive with respect to the injection amount, it is difficult to reduce the fuel pressure in the pressure accumulating chamber. In this regard, in the above configuration, it is determined whether or not the amount is excessive, and when it is determined that the amount is excessive, the discharge amount of the fuel pump is limited to a predetermined amount or less. For this reason, the delay in the followability of the fuel pressure due to the discharge amount being excessive with respect to the injection amount can be suitably suppressed.

  According to a second aspect of the present invention, in the first aspect of the invention, when the limiting means determines that the amount is excessive, the cumulative value is set to be equal to or less than a value corresponding to the predetermined amount. It is characterized by.

  In the above configuration, since the fuel pressure detected at the time of the pressure reduction request is higher than the target value, the factor that makes the discharge amount of the fuel pump excessive with respect to the injection amount is usually a cumulative value. For this reason, the discharge amount of the fuel pump can be limited to a predetermined amount or less by setting the accumulated value to a value corresponding to a predetermined amount or less.

  The value corresponding to the predetermined amount is the predetermined amount itself when the cumulative value dimension is the same as the discharge amount.

  According to a third aspect of the present invention, in the second aspect of the present invention, when the limiting means determines that the amount is excessive, the fuel pump discharge rate is set to a predetermined amount. The operation signal is fixed, and the cumulative value is fixed to zero.

  In the above configuration, the discharge amount can be suitably limited by fixing the operation signal. In addition, by fixing the cumulative value to zero, it is possible to prevent the cumulative value from being continuously updated to a value that is not appropriate for fuel pressure control.

The invention of claim 4, wherein, in the invention described in any one of claims 1 to 3, the injection amount by the fuel injection valve and that the the detected pressure is approximate to the target value becomes a predetermined or higher and And a release means for releasing the restriction by the restriction means based on the establishment of the logical OR condition.

  In the above configuration, when the pressure approximates the target value, the pressure reduction request is eliminated. For this reason, it is considered that the follow-up performance is not lowered even if the restriction on the discharge amount is released. Further, when the injection amount by the fuel injection valve is equal to or greater than a predetermined value, it is considered that it is desired to supply the fuel to the pressure accumulating chamber in order to compensate for the fuel consumption in the pressure accumulating chamber due to fuel injection. In the above configuration, by using the logical sum condition for such a reason, it is possible to appropriately determine the release timing of the restriction on the discharge amount of the fuel pump.

  According to a fifth aspect of the invention, in the invention according to any one of the first to fourth aspects, the control device causes a fuel outflow from the pressure accumulating chamber due to fuel injection to a target value of the detected fuel pressure. Compensating by feedback control, and at the time of release by the release means, the initial value of the accumulated value by the feedback control is set to an amount that can compensate for the outflow of fuel from the pressure accumulation chamber by the fuel injection. It is characterized by that.

  In the above configuration, the outflow of fuel from the pressure accumulation chamber due to fuel injection is compensated by feedback control. For this reason, in the steady state, the accumulated value plays a role of a feed-forward term for compensating for the decrease in the fuel pressure due to the fuel injection. However, if the accumulated value remains at the time of release by the release means, the fuel pressure falls below the target value due to fuel injection, which is compensated by feedback control, and the control of the fuel pressure in the pressure accumulating chamber has been performed for a while. Not stable. Further, if the accumulated value is continuously calculated while the discharge amount is limited, the accumulated value does not become an appropriate value at the time of the release, so the control of the fuel pressure in the pressure accumulating chamber is not stabilized for a while. On the other hand, in the above configuration, the initial value of the accumulated value is set to an amount that can compensate for the outflow of fuel from the pressure accumulating chamber due to fuel injection, so that the control of the fuel pressure in the pressure accumulating chamber can be stabilized after the release. it can.

  According to a sixth aspect of the present invention, in the first aspect of the invention, when the limiting means determines that the excess is present, the fuel pump discharge amount is determined by the feedback control. The operation signal of the fuel pump is set so as to be smaller one of the predetermined amount and the predetermined amount.

  In the above configuration, by setting the operation signal so that the smaller one of the discharge amount of the fuel pump determined by the feedback control and the predetermined amount is set, the discharge amount can be made equal to or less than the predetermined amount. . In this case, since the feedback control based on the cumulative value is resumed when the discharge amount determined by the feedback control is equal to or less than a predetermined amount, the cumulative value can be set to an appropriate value at the time of restart.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the predetermined amount is zero.

  In the said structure, the fuel pressure in a pressure accumulation chamber can be rapidly reduced toward a target value by making discharge amount of a fuel pump into zero.

(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 adjusting 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 engine system includes various sensors that detect the operating state of the diesel engine, such as a fuel pressure sensor 20 that detects the fuel pressure in the common rail 12 and a crank angle sensor 22 that detects the rotation angle of the crankshaft 8. Further, the engine system includes an accelerator sensor 24 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 for the injection amount for the fuel injection valve 16 based on the rotational speed of the crankshaft 8 based on the detection value of the crank angle sensor 22 and the operation amount of the accelerator pedal detected by the accelerator sensor 24. (Command injection amount) is map-calculated.

  The target fuel pressure calculation unit B4 calculates a target fuel pressure based on the command injection amount and the rotation speed. Specifically, the target fuel pressure is calculated to be higher as the command injection amount is larger and the rotational speed is larger.

  The differential pressure calculation unit B6 calculates a differential pressure between the target fuel pressure and the detected fuel pressure based on the target fuel pressure and the fuel pressure detected by the fuel pressure sensor 20. This differential pressure is taken into the proportional term calculation unit B8, the integral term calculation unit B10, and the differential term calculation unit B12. Here, the proportional term calculation unit B8 calculates the proportional term by multiplying the differential pressure by the proportional gain. Further, the integral term calculation unit B10 calculates the integral term by multiplying the time integral value (cumulative value) of the differential pressure by the reciprocal of the integral gain. Further, the differential term calculation unit B12 calculates the differential term by multiplying the time differential value of the differential pressure by the differential gain. These proportional term, integral term and differential term all have the same dimensions as the discharge amount of the fuel pump 6.

  The proportional term, the differential term, the integral term, and the command injection amount are added by the adding unit B14. The output of the adding unit B14 becomes a command value (command discharge amount) of the discharge amount for the fuel pump 6.

  The output of the addition unit B14 is output to the drive current conversion unit B20 via the guard unit B16. The drive current conversion unit B20 is a drive current value (more precisely, a drive current value of the intake metering valve 10) that is an operation signal of the fuel pump 6 required for discharging the command discharge amount from the fuel pump 6. ). 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 PID control, the fuel pressure in the common rail 12 can be feedback controlled to the target fuel pressure.

  Incidentally, when the command discharge amount is calculated by the PID control, the problem shown in FIG. 3 occurs. 3 (a) shows the change of the accelerator pedal operation amount, FIG. 3 (b) shows the change of the injection amount, FIG. 3 (c) shows the change of the fuel pressure in the common rail 12, and FIG. (D) shows the transition of the feedforward term for compensating the fuel injection in the discharge amount of the fuel pump 6, FIG. 3 (e) shows the transition of the proportional term, and FIG. 3 (f) shows the integral term. FIG. 3G shows a change in the discharge amount of the fuel pump 6.

  As shown in the figure, when the accelerator pedal is depressed at time t1, the injection amount increases, so that the target fuel pressure indicated by the one-dot chain line in FIG. 3C also increases. For this reason, since the fuel pressure in the common rail 12 cannot be made the target fuel pressure by the feedforward control based on the command injection amount, the discharge amount that is insufficient to obtain the target fuel pressure is compensated by the feedback control. . That is, the proportional term corresponding to the difference between the target fuel pressure and the detected fuel pressure first increases, and the proportional term decreases with time, while the integral term increases. This increase in the integral term continues until the detected fuel pressure matches the target fuel pressure.

  When the accelerator pedal is released at time t2 just before the detected fuel pressure matches the target fuel pressure, the injection amount becomes zero and the target fuel pressure also decreases. For this reason, the detected fuel pressure becomes higher than the target fuel pressure. However, at this time, since the injection amount is set to zero, the main factors for reducing the fuel pressure in the common rail 12 are the leaked fuel leaking from the high pressure fuel passage 14 to the low pressure fuel passage 18 via the fuel injection valve 16. Become. For this reason, the time until the detected fuel pressure follows the target fuel pressure is determined by the amount of the leaked fuel.

  However, in practice, immediately after the accelerator pedal is released, the integral term has a large positive value. For this reason, fuel is discharged from the fuel pump 6 even though the detected fuel pressure is higher than the target fuel pressure. The fuel discharge from the fuel pump 6 is continued until time t3 when the proportional term and the integral term cancel each other. For this reason, the time t5 at which the detected fuel pressure follows the target fuel pressure is delayed from the time t4 that is assumed to follow the target fuel pressure on the assumption that no fuel is discharged immediately after the accelerator pedal is released. If the follow-up to the target fuel pressure is delayed, there is a high possibility that the accelerator pedal is depressed again before the target fuel pressure is followed. When the fuel injection is started by depressing the accelerator pedal again, the actual fuel pressure is higher than the target fuel pressure, so that the fuel spray shape is not appropriate, and the exhaust characteristics may be deteriorated. .

  Therefore, in this embodiment, when the pressure reduction in the common rail 12 is requested, when the discharge amount of the fuel pump 6 determined based on the integral term is excessive with respect to the injection amount by the fuel injection valve 16, the command discharge amount of the fuel pump 6 is set. Limit to “0”. Hereinafter, this will be described in detail with reference to FIG.

  FIG. 4 shows a processing procedure relating to the restriction of the discharge amount of the fuel pump 6 according to the present embodiment. This process is repeatedly executed by the ECU 30, for example, at a predetermined cycle.

  In this series of processing, first, in step S10, the command discharge amount of the fuel pump 6 is calculated. Details of this processing are as shown in FIG. In the subsequent step S12, is the logical product condition established that the detected fuel pressure is greater than the target fuel pressure by a specified value α (> 0) or more and that the command injection amount is substantially zero (preferably zero)? Judge whether or not. Here, the detected fuel pressure being greater than the target fuel pressure by the specified value α or more is a condition for determining that a pressure reduction request in the common rail 12 has occurred. Further, the command injection amount being substantially zero is a condition for determining that the discharge amount of the fuel pump 6 is excessive with respect to the injection amount of the fuel injection valve 16.

  If it is determined in step S12 that the logical product condition is satisfied, the command discharge amount is set to zero and the integral term is set to zero in step S14. Here, the command discharge amount is made zero by the guard part B16 shown in FIG. In the subsequent step S16, whether or not the logical sum condition that the detected fuel pressure is smaller than the target fuel pressure plus the specified value β and that the command injection amount is larger than the threshold γ (> 0) is satisfied. Determine whether. Here, the fact that the detected fuel pressure is smaller than the target fuel pressure plus the specified value β is a condition for determining that the detected fuel pressure follows the target fuel pressure. If the target fuel pressure is followed, it is considered desirable to cancel the restriction on the discharge amount of the fuel pump 6 and start normal control, and therefore it is determined whether or not this condition is satisfied. Further, when the command injection amount is larger than the threshold value γ, the fuel in the common rail 12 is consumed by the fuel injection. Therefore, it is considered that the fuel discharge from the fuel pump 6 is necessary to compensate for this. It is determined whether or not this condition is met.

  In step S16, while a negative determination is made, both the command discharge amount and the integral term are fixed to zero, and when a positive determination is made, this series of processing is once ended. Thus, when the logical sum condition is satisfied, the fuel is discharged from the fuel pump 6 by normal control.

  FIG. 5 shows a control mode of the fuel pressure by the above processing. 5A to 5G correspond to the previous FIG. 3A to FIG. 3G.

  As shown in the figure, after the accelerator pedal is depressed at time t11, when the accelerator pedal is released at time t12 before the detected fuel pressure follows the target fuel pressure, the integral term is a large positive value immediately before that. Has the value of Here, since the integral term is larger than the absolute value of the proportional term, the command discharge amount determined by the feedback control is excessive with respect to the injection amount. Therefore, at time t12, the integral term and the command discharge amount are set to zero. For this reason, after time t12, fuel is not discharged from the fuel pump 6, and the fuel pressure in the common rail 12 decreases to the target fuel pressure at a decrease rate determined by the amount of leaked fuel described above. When the difference between the detected fuel pressure and the target fuel pressure becomes smaller than the specified value β, the feedback control is resumed.

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

  (1) When it is determined that the discharge amount of the fuel pump 6 determined according to the integral term is excessive with respect to the injection amount by the fuel injection valve 16 when the pressure reduction in the common rail 12 is requested, the discharge amount of the fuel pump 6 The integral term was fixed to zero. Thereby, discharge of the fuel pump 6 can be limited, and it can be avoided that the integral term is continuously updated to a value that is not appropriate for fuel pressure control.

(2) the pressure is detected on the basis of the establishment of the logical sum condition of the injection amount by the fuel injection valve 16 to approximate a target value is predetermined or higher, releasing the restriction of the discharge amount of the fuel pump 6. Thereby, the cancellation | release timing of the restriction | limiting of the discharge amount of the fuel pump 6 can be determined appropriately.

  (3) Based on the fact that the injection amount of the fuel injection valve 16 becomes zero at the time of a pressure reduction request, it can be easily and appropriately determined that the discharge amount is excessive.

(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 functional block of fuel pressure control in the ECU 30 according to the present embodiment.

  As shown in the drawing, in this embodiment, feed-forward control based on the command injection amount is not performed, and the outflow of fuel from the common rail 12 due to fuel injection is compensated by feedback control of the detected fuel pressure to the target fuel pressure.

  A case corresponding to FIG. 3 in this case is shown in FIG. 7A to 7C and 7E to 7G correspond to FIGS. 3A to 3C and 3E to 3G, respectively.

  As shown in the figure, in this case, the fuel injection by the fuel injection is performed before the time t21 when a steady state in which the fuel outflow from the common rail 12 by the fuel injection and the fuel pumping by the fuel pump 6 are balanced is realized. Is compensated by the integral term. At time t21, when the accelerator pedal is depressed, the injection amount increases. Furthermore, the target fuel pressure increases as the injection amount increases. Therefore, an increase in the amount of fuel flowing out of the common rail 12 due to an increase in the injection amount and an increase in the amount of fuel required for the fuel pump 6 due to an increase in the target fuel pressure are compensated by feedback control.

  When the accelerator pedal is released at time t22, the injection amount becomes zero, and the target fuel pressure decreases accordingly. For this reason, the detected fuel pressure becomes higher than the target fuel pressure. Thereby, although the proportional term becomes negative, the integral term has a large positive value, so the discharge amount of the fuel pump 6 becomes positive. The fuel discharge by the fuel pump 6 continues until time t23 when the proportional term and the integral term cancel each other. The duration is longer than that shown in FIG. Therefore, the time t25 at which the detected fuel pressure follows the target fuel pressure is greatly delayed compared to the time t24 that is assumed to follow when the fuel pump 6 stops discharging immediately after the accelerator pedal is released. To do.

  Hereinafter, the discharge amount limiting method of the fuel pump 6 according to this embodiment for eliminating the delay with respect to the target fuel pressure will be described.

  FIG. 8 shows a processing procedure relating to the discharge amount restriction of the fuel pump 6 according to the present embodiment. This process is repeatedly executed by the ECU 30, for example, at a predetermined cycle.

  Even in this series of processing, first, in step S20, the command discharge amount is calculated. Also in the subsequent step S22, whether or not the logical product condition that the detected fuel pressure follows the target fuel pressure and the command injection amount is substantially zero is satisfied, as in step S12 of FIG. Determine whether. When it is determined in step S22 that the logical product condition is satisfied, it is determined in step S24 whether or not the command discharge amount is greater than zero. This determination is for determining whether or not the command discharge amount calculated by the processing shown in FIG. 6 is an appropriate discharge amount when the logical product condition is satisfied in step S22.

  When it is determined in step S24 that the command discharge amount is greater than zero, the command discharge amount for the fuel pump 6 is forcibly set to zero. This process is a process performed by the guard unit B16 of FIG. When the process of step S26 is completed or when a negative determination is made in step S22 or step S24, the series of processes shown in FIG.

  FIG. 9 shows a restriction mode of the discharge amount of the fuel pump 6 by the above control. 9A to 9C and 9E to 9G correspond to the previous FIGS. 7A to 7C and 7E to 7G.

  As shown in the figure, when the accelerator pedal is depressed at time t31, the discharge amount of the fuel pump 6 increases. When the accelerator pedal is released at time t32, since the integral term has a large positive value, the discharge amount of the fuel pump 6 becomes excessive with respect to the injection amount even though the proportional term is negative. . For this reason, the command discharge amount is set to zero in step S26 of FIG.

  After time t32, since the detected fuel pressure is higher than the target fuel pressure, the integral term gradually decreases. Then, after time t33 when the integral term and the proportional term cancel each other, the fuel pump 6 is operated based on the command discharge amount determined by the processing shown in FIG.

  According to this embodiment described above in detail, the following effect can be obtained in addition to the effect (3) of the first embodiment.

  (4) When it is determined that the discharge amount of the fuel pump 6 determined in accordance with the integral term is excessive with respect to the injection amount by the fuel injection valve 16 when a pressure reduction request in the common rail 12 is requested, the command discharge amount determined by feedback control And “zero”, whichever is smaller, is the final command discharge amount for the fuel pump 6. Thereby, the discharge amount can be reduced to zero or less. In this case, since the integral term decreases and the feedback control is resumed when the command discharge amount calculated based on the integral term becomes zero, the integral term can be set to an appropriate value upon resumption.

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

  Also in the present embodiment, fuel pressure control is performed by the processing shown in FIG. 6 as in the second embodiment.

  FIG. 10 shows a processing procedure relating to the discharge amount restriction of the fuel pump 6 according to the present embodiment. In FIG. 10, the same steps as those in FIG. 4 are given the same step numbers for convenience.

  Also in this series of processes, the processes of steps S10 to S16 are performed. When an affirmative determination is made in step S16, in step S18, the initial value of the integral term is made to correspond to the amount of fuel outflow from the common rail 12 when the feedback control is resumed. This is because the fuel outflow from the common rail 12 is compensated by the integral term in the steady state of the fuel pressure control shown in FIG. When the initial value of the integral term is zero when the feedback control is resumed, the fuel outflow from the common rail 12 is initially compensated by the proportional term, and the integral term gradually increases, so that the final steady state is obtained. Will be realized. However, in this case, it takes time until the steady state is realized. For this reason, in this embodiment, the initial value of the integral term is set to be equivalent to the amount of fuel flowing out from the common rail 12, thereby stabilizing the fuel pressure control by feedback control at an early stage.

  Here, the command injection amount may be simply used as an integral term. However, in order to stabilize the fuel pressure control at an early stage, it is more desirable to set the sum of the leak amount flowing out from the high pressure fuel passage 14 to the low pressure fuel passage 18 via the fuel injection valve 16 and the fuel injection amount. Here, the leak amount may be calculated by map calculation using parameters having a correlation with the leak amount, such as the rotational speed of the crankshaft 8, the fuel pressure, and the command value of the injection period for the fuel injection valve 16 (command injection period). Here, the static leak, which is a leak when the fuel is not injected, increases as the fuel pressure in the common rail 12 increases. The dynamic leak returned from the high pressure fuel passage 14 to the low pressure fuel passage 18 during fuel injection increases as the number of injections per unit time increases, the injection time increases, and the fuel pressure increases. The number of injections per unit time is determined by the rotation speed, and the injection time is determined by the command injection period.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects according to the above (1) to (3) of the first embodiment.

  (5) When the feedback control is restarted, the initial value of the integral term is set to an amount that can compensate for the fuel outflow from the common rail 12 due to fuel injection, so that the control of the fuel pressure in the common rail 12 is stabilized immediately after the restart. be able to.

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

  In the case where the fuel pressure control shown in FIG. 2 is performed, the process shown in FIG. 8 may be performed.

  -Control which compensates the outflow of the fuel from the common rail 12 by fuel injection by feedback control to the target fuel pressure of the detected fuel pressure is not restricted to what was illustrated in previous FIG. For example, in the control shown in FIG. 6, the discharge amount for compensating the change in the target fuel pressure may be given as a feedforward term.

  In the first embodiment, when the feedback control is resumed, the initial value of the integral term may be set to an amount that can compensate for the static leak. That is, in the case of the first embodiment, the fuel flowing out from the common rail 12 by fuel injection is compensated by the feedforward term. Therefore, in the steady state of the fuel pressure control, the integral term is a value that compensates for the static leak. For this reason, when the feedback control is restarted, the initial value of the integral term is set to an amount that compensates for the static leak, so that the control can be stabilized immediately after the restart.

  In the first and third embodiments, the actual discharge amount of the fuel pump 6 can be made zero by fixing the integral term to zero without setting the command discharge amount to zero.

  The fuel pressure control is not limited to calculating the command discharge amount according to the integral term and the like, and converting the command discharge amount into the drive current of the fuel pump 6. For example, the drive current value is directly set according to the integral term or the like. It may be determined. For example, when this is applied to the first embodiment, when it is determined that the discharge amount of the fuel pump 6 determined by the feedback control is excessive with respect to the injection amount at the time of a pressure reduction request, the drive is performed with the discharge amount being zero. What is necessary is just to fix to an electric current value.

  As a method for determining whether or not the discharge amount of the fuel pump 6 determined according to feedback control is excessive with respect to the injection amount by the fuel injection valve 16, the condition that the command injection amount is substantially zero is established It is not limited to the presence or absence of. For example, when the value obtained by subtracting the command injection amount from the discharge amount determined by feedback control is positive, it may be determined that the amount is excessive. In addition, a pressure reducing valve that performs a binary operation to communicate and block the common rail 12 and the fuel tank 2, and to which an opening operation signal is output by the ECU 30 when the fuel pressure in the common rail 12 is equal to or higher than a predetermined value. In the configuration provided, the time when the pressure reducing valve is opened may be determined as the excess.

  -The limit of the discharge amount of the fuel pump 6 is not limited to zero. For example, a slight amount of fuel may be allowed to be discharged according to the injection amount at the time of request for pressure reduction.

  The metering valve provided in the fuel pump 6 is not limited to a valve whose opening degree can be continuously adjusted, and may be a binary operation of an opening operation and a closing operation. Further, the metering valve is not limited to the suction metering valve, and may be a discharge metering valve that directly adjusts the discharge amount, for example.

The figure which shows the whole structure of the engine system concerning 1st Embodiment. The functional block diagram regarding the fuel pressure control concerning the embodiment. The time chart explaining the problem by the fuel pressure control. 9 is a flowchart showing a processing procedure for limiting the discharge amount according to the embodiment. The time chart which shows transition of the fuel pressure by the said restriction | limiting. The functional block diagram regarding the fuel pressure control concerning 2nd Embodiment. The time chart explaining the problem by the fuel pressure control. 9 is a flowchart showing a processing procedure for limiting the discharge amount according to the embodiment. The time chart which shows transition of the fuel pressure by the said restriction | limiting. 9 is a flowchart showing a processing procedure for limiting the discharge amount according to the third embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Fuel tank, 6 ... Fuel pump, 12 ... Common rail, 20 ... Fuel pressure sensor, 30 ... ECU (one Embodiment of a fuel-injection control apparatus).

Claims (7)

An internal combustion engine comprising: a pressure accumulating chamber for storing fuel in a high pressure state; a fuel pump for pumping fuel into the pressure accumulating chamber; a fuel injection valve for injecting fuel in the pressure accumulating chamber; and a detecting means for detecting the fuel pressure in the pressure accumulating chamber. In a fuel injection control device that is applied to the feedback control of the detected fuel pressure to the target value based on the accumulated value of the difference between the detected fuel pressure and the target value,
When a pressure reduction request is made in the pressure accumulating chamber, it is determined whether or not the discharge amount is excessive by subtracting the command injection amount for the fuel injection valve from the discharge amount of the fuel pump determined by the feedback control. Judgment means,
Limiting means for limiting the discharge amount of the fuel pump to a predetermined amount or less by correcting the decrease of the discharge amount of the fuel pump determined by the feedback control when the determination means determines that the amount is excessive. A fuel injection control device comprising:   2. The fuel injection control device according to claim 1, wherein, when it is determined that the limiting means is excessive, the cumulative value is set to be equal to or less than a value corresponding to the predetermined amount.   When it is determined that the amount is excessive, the limiting unit fixes the operation signal of the fuel pump and fixes the accumulated value to zero so that the discharge amount of the fuel pump is set to a predetermined amount. The fuel injection control device according to claim 2. Further comprising releasing means injection amount by the fuel injection valve and that the the detected pressure is approximate to the target value based on the establishment of the logical sum condition and that a predetermined or more, releases the restriction by the restricting means The fuel injection control device according to any one of claims 1 to 3. The control device compensates the outflow of fuel from the pressure accumulation chamber due to fuel injection by feedback control to the target value of the detected fuel pressure, and
The release value by the release means is such that an initial value of the cumulative value by the feedback control is an amount capable of compensating for the outflow of fuel from the pressure accumulating chamber by the fuel injection. The fuel injection control device according to any one of the above.   When it is determined that the limiting means is excessive, the discharge amount of the fuel pump is the smaller one of the discharge amount of the fuel pump determined by the feedback control and the predetermined amount. 2. The fuel injection control apparatus according to claim 1, wherein an operation signal of the fuel pump is set as described above.   The fuel injection control device according to claim 1, wherein the predetermined amount is zero.

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