JP2007231770A - Fuel injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a fuel injection rate with higher accuracy by using a piezo-injector capable of successively adjusting a lift amount of a nozzle needle according to the displacement of an actuator. <P>SOLUTION: After a piezoelectric element is charged to open the piezo-injector, charging is temporarily stopped, to retain the nozzle needle at a low lift. At this time, a process (Fig. 9(a))for discharging part of charge of the piezoelectric element is performed. Thereby, the overshoot of the lift amount of the nozzle needle is suppressed. Then, the piezoelectric element is charged again, to retain the nozzle needle at a high lift. Following the end of an injection period to the piezo-injector, the piezoelectric element is discharged, to close the piezo-injector. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel injection control device that performs fuel injection by expanding and contracting a piezo element for a piezo injector capable of continuously adjusting a lift amount of a nozzle needle according to expansion and contraction of a piezo element that functions as an actuator.

  A common rail type diesel engine having a common pressure accumulating chamber (common rail) for supplying high pressure fuel to the fuel injection valve of each cylinder is well known. According to the common rail type diesel engine, the fuel pressure in the common rail can be freely controlled according to the engine operating state, and as a result, the fuel pressure supplied to the fuel injection valve can be freely controlled.

  In a diesel engine, a required fuel amount (required injection amount) is usually calculated based on the operation amount of the accelerator pedal and the rotational speed in order to generate a required torque corresponding to the operation amount of the accelerator pedal by the user. The Then, a command injection period of the fuel injection valve is set to inject the required injection amount of fuel.

  By the way, when the required amount of fuel is injected by a single fuel injection, the amount of nitrogen oxide (NOx) discharged from the diesel engine tends to increase as the fuel burns at once. For this reason, in order to reduce fuel consumption while reducing NOx emissions, it has also been proposed to perform so-called boot-type injection in which the fuel injection rate is increased stepwise by one injection.

  In order to perform boot-type injection, it is conceivable to use a piezo injector capable of continuously adjusting the lift amount of the nozzle needle according to the displacement of the actuator (Patent Document 1). According to this piezo injector, since the lift amount of the nozzle needle during the fuel injection can be controlled, not only the fuel injection amount but also the fuel injection rate can be controlled, thereby enabling the boot type injection. .

  However, even if charging to the piezo element is temporarily stopped to perform boot type injection by the piezo injector, the nozzle needle behavior is likely to become unstable, for example, when the fuel pressure in the common rail is high, and the desired injection rate. It becomes difficult to perform boot type injection.

It should be noted that not only the above-described boot-type injection, but also the fact that it is difficult to maintain high controllability when the injection rate is controlled as desired in fuel injection control using a piezo injector is generally common. ing.
US Pat. No. 6,520,423

  The present invention has been made to solve the above-described problems, and its object is to use a piezo injector capable of continuously adjusting the lift amount of the nozzle needle in accordance with the displacement of the actuator to further increase the fuel injection rate. An object of the present invention is to provide a fuel injection control device that can be controlled with high accuracy.

  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, after charging the piezo element to open the piezo injector, a part of the electric charge charged to the piezo element is held in order to maintain the lift amount at a predetermined lift amount. Discharging means for discharging is provided.

In the above configuration, when the piezo injector is opened by once charging the piezo element, the fuel pressure is applied to the tip of the nozzle needle, or the nozzle needle may overshoot in the valve opening direction due to inertia or the like. . In this case, it is difficult to hold the nozzle needle with a low lift. In this regard, in the above configuration, by partially discharging the electric charge charged in the piezo element after charging, it is possible to suppress the lift amount of the nozzle needle from being excessive, and it is possible to maintain a highly accurate low lift. It becomes. Therefore, according to the above configuration, the fuel injection rate can be controlled with higher accuracy.

  According to a second aspect of the present invention, in the first aspect of the invention, the fuel injection control device performs a boot type injection that gradually increases a fuel injection rate by the piezo injector, and the boot type injection is performed. After the discharging by the discharging means, the piezo element is charged again.

  In the above configuration, by using the discharge means, the injection rate at the low injection rate in the boot type injection can be controlled with high accuracy.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the discharging means includes a pressure of fuel supplied to the piezo injector, a holding period at the predetermined lift amount, and a target for the holding. A mode of the discharge process is set based on at least one of the lift amounts.

  In the above configuration, since the force required for the piezo element to displace the nozzle needle changes depending on the pressure of the fuel supplied to the piezo injector, in order to hold and control the nozzle needle with high accuracy with low lift It is desirable to variably set the mode of the discharge process according to the fuel pressure. In addition, since the lift amount of the nozzle needle tends to fluctuate as the holding period of the lift amount of the nozzle needle is longer, in order to hold and control the nozzle needle with high accuracy with a low lift, the discharge processing mode is set to the hold period. It is desirable to variably set it accordingly. Furthermore, if the target lift amount of the nozzle needle is different, the amount of displacement required for the piezoelectric element to be held at the same lift amount changes. It is desirable to variably set the discharge processing mode according to the target lift amount.

  In this regard, in the above configuration, by performing feedforward control that sets the discharge processing mode based on at least one of the above, the lift amount of the nozzle needle can be maintained with high accuracy with a low lift from the first fuel injection. It becomes possible to do.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the piezo injector includes a needle stopper to which a fluid pressure is applied to a side that increases a lift amount of the nozzle needle, and The pressure of the piezoelectric element in a period other than the discharge period by the discharge means in the holding period of the lift amount of the nozzle needle after the piezoelectric element is once charged after the piezoelectric element is pressurized by the extension of the piezoelectric element. Means for detecting a descent amount, and correction for correcting at least one of a charging process for opening the piezo injector and a discharging process by the discharging means so that the detected descent amount is a desired descent amount And a means.

  In the above configuration, the voltage of the piezo element is determined according to the charge amount of the piezo element and the amount of change in voltage due to the piezoelectric effect corresponding to the force applied to the piezo element. For this reason, if the voltage of the piezo element changes during the lift amount holding period, it is due to the discharge by the discharge means and the change in the voltage of the piezo element due to the change in the fluid pressure accompanying the change in the lift amount of the nozzle needle. It becomes. For this reason, the amount of voltage drop in the holding period other than the discharge period has a strong correlation with the amount of change in the fluid pressure, and thus has a strong correlation with the amount of change in the lift amount of the nozzle needle. In this regard, in the above configuration, the amount of change in the lift of the nozzle needle can be grasped with high accuracy in accordance with the amount of voltage drop. The lift amount of the nozzle needle can be held and controlled with high accuracy by feedback correction for correcting the discharge process and the charge process according to the lift change amount of the nozzle needle thus grasped.

  The invention according to claim 5 is the invention according to any one of claims 1 to 3, wherein the piezo injector includes a needle stopper to which a fluid pressure is applied to a side to increase a lift amount of the nozzle needle, and Charging process for pressurizing the fluid by extension of the piezo element, taking in a detection result of a means for detecting stress of the piezo element, and opening the piezo injector according to the detected stress; It is characterized in that at least one of the discharge processes by the discharge means is corrected.

  In the above configuration, when the lift amount of the nozzle needle increases, the pressure of the fluid decreases, so that the force applied by the fluid to the piezo element decreases. For this reason, there is a correlation between the lift amount of the nozzle needle and the force applied to the piezo element. In this regard, in the above configuration, the lift amount of the nozzle needle can be grasped based on the stress of the piezo element. The lift amount of the nozzle needle can be held and controlled with high accuracy by feedback correction that corrects the discharge process and the charge process according to the lift amount thus grasped.

  According to a sixth aspect of the present invention, there is provided calculation means for calculating an electrical state quantity of the piezo element when the piezo injector is closed due to discharge of the piezo element based on an operating state of the internal combustion engine; Discharge means for discharging the piezo element until the state quantity calculated by the calculation means is obtained after the piezo element is charged to open the injector.

  Since the piezo injector is opened by charging the piezo element, and then the piezo injector is closed by discharging the piezo element, the electric charge still remains in the piezo element. This means that when the piezo injector is closed, it is not always necessary to discharge all charges of the piezo element. In this regard, in the above configuration, the electric state quantity of the piezo element when the piezo injector is closed is calculated, and the piezo element is discharged until the electric state quantity is reached, thereby reducing the next charge amount. Can be reduced. For this reason, according to the said structure, the power consumption at the time of fuel-injection control can be reduced.

  The invention according to claim 7 is the invention according to claim 6, wherein the fuel injection control device performs multi-stage injection control in which fuel injection is performed a plurality of times within one combustion cycle of an arbitrary cylinder. The discharge to the state quantity calculated by the means is performed for the fuel injection before the final stage in the multistage injection.

  In the above configuration, power consumption due to multistage injection can be suppressed, and the piezo element is completely discharged at the end of multistage injection in one combustion cycle of an arbitrary cylinder, thereby changing the valve opening condition of the piezo injector. Therefore, problems such as unintentional opening of the piezo injector can be avoided.

(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 using a piezo injector mounted on a diesel engine will be described with reference to the drawings.

  FIG. 1 shows an overall configuration of an engine system including the diesel engine. As shown in the drawing, the fuel pumped up from the fuel tank 2 is pressurized by the high-pressure fuel pump 4 and supplied to the common rail 6 in a high-pressure state. The common rail 6 stores the fuel supplied from the high pressure fuel pump 4 in a high pressure state, and supplies the fuel to the piezo injector 10 through the high pressure fuel passage 8. The piezo injector 10 is also connected to a low-pressure fuel passage 12 so that fuel can be returned to the fuel tank 2 via the low-pressure fuel passage 12.

  The electronic control unit (ECU 20) includes a microcomputer, a memory, and the like, and controls the output of the diesel engine. In this control, the ECU 20 detects the detection result of the fuel pressure sensor 14 that detects the fuel pressure in the common rail 6, the detection result of the crank angle sensor 16 that detects the rotation angle of the crankshaft of the diesel engine, and the operation amount of the accelerator pedal by the user. The detection results of various sensors such as the accelerator sensor 18 for detecting the detection are taken in and the detection results are referred to.

  FIG. 2 shows the configuration of the piezo injector 10.

  An injection port 32 that communicates the inside of the body 30 and the outside of the piezo injector 10 is formed at the tip of the body 30 of the piezo injector 10. In the body 30, a nozzle needle 34, a needle stopper 36, and a balance piston 38 are sequentially connected from the distal end side, and are housed so as to be displaceable in the axial direction along the inner wall of the body 30. High pressure fuel is supplied from the high pressure fuel passage 8 to the needle chamber 35 defined by the nozzle needle 34 and the inner wall of the body 30 and the balance chamber 39 on the back side of the balance piston 38.

  A back pressure chamber 41 formed by the rear surface of the body 30 of the needle stopper 36 and the inner wall of the body 30 communicates with the low pressure fuel passage 12 and is supplied with fuel from the low pressure fuel passage 12. . The back pressure chamber 41 is provided with a spring 40, whereby the needle stopper 36 is pushed toward the distal end side of the body 30.

  On the other hand, in the needle stopper 36, the surface side on the distal end side of the body 30 forms a first oil tight chamber 42 together with the inner wall of the body 30. The first oil-tight chamber 42 is connected to a second oil-tight chamber 46 located behind the body 30 with respect to the balance piston 38 via the transmission passage 44. The first oil-tight chamber 42, the transmission passage 44, and the second oil-tight chamber 46 are filled with fuel as a medium for transmitting power.

  The second oil-tight chamber 46 is a space defined by the surface of the piezo piston 48 on the tip side of the body 30 and the inner wall of the body 30. The piezo piston 48 includes a check valve 50 inside thereof, so that fuel can be supplied from the low pressure fuel passage 12 to the second oil tight chamber 46. The piezo piston 48 is connected to the piezo element 52 behind the piezo piston 48. The rear part of the piezo element 52 is connected and fixed to the body 30.

  The piezo element 52 includes a laminate (piezo stack) formed by laminating a plurality of piezoelectric elements, and functions as an actuator by expanding and contracting due to a reverse piezoelectric effect. Specifically, the piezo element 52 is a capacitive load, and expands when charged and contracts when discharged. Incidentally, the piezoelectric element 52 according to the present embodiment uses a piezoelectric element of a piezoelectric material such as PZT.

  In such a configuration, when energization of the piezo element 52 is started, the piezo piston 48 is displaced in the distal direction of the body 30 as the piezo element 52 extends. As a result, the fuel pressure in the second oil-tight chamber 46, the transmission passage 44, and the first oil-tight chamber 42 increases. The force that the high-pressure fuel in the needle chamber 35 pushes the nozzle needle 34 and the force that the fuel in the first oil-tight chamber 42 pushes the needle stopper 36 are the force that the spring 40 and the low-pressure fuel push the needle stopper 36 and the balance chamber. When the high-pressure fuel in 39 overcomes the force pushing the back surface of the balance piston 38, the nozzle needle 34 is displaced rearward of the body 30 and the piezo injector 10 is opened. Thereby, the fuel inside the body 30 is injected outside through the injection port 32.

  On the other hand, when the piezo element 52 is discharged after being energized, the piezo piston 48 is displaced to the rear of the body 30 as the piezo element 52 contracts, so that the second oil-tight chamber 46, the transmission passage 44, and the first oil-tight chamber 42 are discharged. The fuel pressure inside decreases. Thereby, the force that the spring 40 and the low-pressure fuel push the needle stopper 36, the force that the high-pressure fuel in the balance chamber 39 pushes the back surface of the balance piston 38, and the force that the high-pressure fuel in the needle chamber 35 pushes the nozzle needle 34. When the fuel in the first oil-tight chamber 42 overcomes the force pushing the needle stopper 36, the acceleration of the nozzle needle 34 is directed toward the distal end side of the body 30, and the piezo injector 10 is closed. Thereby, fuel injection is complete | finished.

  In the piezo injector 10, the lift amount, which is the amount of displacement of the nozzle needle 34 toward the rear of the body 30, changes according to the displacement amount of the piezo element 52. For this reason, the lift amount can be arbitrarily controlled between the lift amount zero corresponding to the valve closing of the piezo injector 10 and the full lift amount which is the maximum lift amount. That is, for example, when the electrical state quantity is manipulated by energization of the piezo element 52, if a period in which the state quantity is constant is provided, the nozzle needle 34 stagnate with an intermediate lift amount. For this reason, after that energization control is resumed, lift control having a two-stage lift amount becomes possible. Thus, since the lift amount can be freely controlled by using the piezo injector 10, not only the fuel injection amount but also the fuel injection rate waveform in one fuel injection can be freely controlled. It becomes. Incidentally, the fuel injection rate here means the amount of fuel injected from the piezo injector 10 per unit time.

  FIG. 3 shows a configuration of a drive circuit for the piezo element 52 in the present embodiment.

  As shown in the drawing, the electric power supplied from the battery B to the ECU 20 is first supplied to a DC / DC converter 21 which is a booster circuit. The DC / DC converter 21 boosts the voltage of the battery B (for example, “12 V”) to a high voltage (for example, “200 to 300 V”) for charging the piezo element 52.

  The boosted voltage of the DC / DC converter 21 is applied to the capacitor 22. One terminal of the capacitor 22 is connected to the DC / DC converter 21 side, and the other terminal is grounded. When the boosted voltage of the DC / DC converter 21 is applied to the capacitor 22, the capacitor 22 stores electric charge to be supplied to the piezo element 52.

  The high potential terminal side of the capacitor 22, that is, the DC / DC converter 21 side is connected to the high potential terminal side of the piezo element 52 through a series connection body of the charge switch 23 and the charge / discharge coil 24. It is connected. The terminal side of the piezoelectric element 52 that is at a low potential is grounded. One terminal of a discharge switch 25 is connected between the charge switch 23 and the charge / discharge coil 24, and the other terminal of the discharge switch 25 is grounded.

  A diode 26 is connected in parallel to the discharge switch 25 in such a manner that the direction from the ground side to the side between the capacitor 22 and the charge / discharge coil 24 is the forward direction. The diode 26, together with the capacitor 22, the charge switch 23, and the charge / discharge coil 24, constitutes a chopper circuit that charges the piezo element 52, and functions as a freewheeling diode.

  On the other hand, a diode 27 is connected in parallel to the charge switch 23 in such a manner that the direction from the discharge switch 25 side to the capacitor 22 side is the forward direction. The diode 27, together with the capacitor 22, the charge / discharge coil 24, and the discharge switch 25, constitutes a chopper circuit that discharges the electric charge of the piezo element 52, and functions as a freewheeling diode.

  The drive circuit having the above configuration is driven by the microcomputer 28. Specifically, in the microcomputer 28, detection values of various sensors that detect the operation state of the diesel engine, the voltage of the piezo element 52 detected via the node N1, and the piezo element 52 detected via the node N2. Based on the current, the charge switch 23 and the discharge switch 25 are operated. Each of these operations is performed in the manner shown in FIG.

  FIG. 4A shows the transition of the operation mode of the charge switch 23, FIG. 4B shows the transition of the operation mode of the discharge switch 25, and FIG. 4C shows the current (operation) that flows through the piezo element 52. FIG. 4D shows the transition of the operating voltage of the piezo element 52. FIG.

  As shown in the figure, the piezo element 52 is charged while increasing / decreasing the operation current by chopper control by turning on / off the charging switch 23. Specifically, when the charging switch 23 is turned on, a closed loop circuit including the capacitor 22, the charging switch 23, the charging / discharging coil 24, and the piezo element 52 is formed. Thereby, the electric charge of the capacitor 22 is charged in the piezo element 52. At this time, the amount of current flowing through the piezo element 52 increases. On the other hand, after the charging switch 23 is turned on, the charging switch 23 is turned off, whereby a closed loop circuit including the charging / discharging coil 24, the piezo element 52, and the diode 26 is formed. Thereby, the flywheel energy of the charge / discharge coil 24 is charged in the piezo element 52. At this time, the amount of current flowing through the piezo element 52 decreases.

  By performing the step-down chopper control in which the charging switch 23 is operated in the above-described manner, the piezo element 52 is charged, and the potential on the terminal side that becomes the high potential of the piezo element 52 rises.

  On the other hand, the piezo element 52 is discharged while increasing / decreasing the operation current by the chopper control by turning on / off the discharge switch 25. Specifically, when the discharge switch 25 is turned on, a closed loop circuit is formed by the discharge switch 25, the charge / discharge coil 24, and the piezo element 52. Thereby, the piezo element 52 is discharged. At this time, the amount of current flowing through the piezo element 52 increases. Further, after the discharge switch 25 is turned on, the discharge switch 25 is turned off, whereby a closed loop circuit is formed by the capacitor 22, the diode 27, the charge / discharge coil 24, and the piezo element 52. Thereby, the flywheel energy of the charge / discharge coil 24 is recovered by the capacitor 22.

  By performing the step-up chopper control in which the discharge switch 25 is operated in the above-described manner, the piezo element 52 is discharged, and the potential on the terminal side that becomes the high potential of the piezo element 52 is lowered.

  In the present embodiment, the operation of the charge switch 23 and the discharge switch 25 is turned on for a predetermined time, and the current flowing through the piezo element 52 becomes zero, so that the state is changed from the off state to the on state. Switching is performed as a so-called constant on-time operation. Thereby, the rate of change of energy of the piezo element 52 can be made constant. For this reason, the energy supplied to the piezo element 52 can be controlled by the charging time by charging the piezo element 52 by the constant operation of the on time. If the energy of the piezo element 52 is constant, the extension amount of the piezo element 52 becomes substantially constant regardless of the temperature. Therefore, by performing the above-described constant on-time operation, the lift of the nozzle needle 34 can be performed with simple processing. The amount can be controlled. On the other hand, when the charging process is managed using the voltage of the piezo element 52, the amount of expansion of the piezo element 52 changes depending on the temperature of the piezo element 52, and therefore the lift amount of the nozzle needle 34 is controlled with high accuracy. Therefore, it is necessary to perform temperature correction of the target voltage of the piezo element 52. Note that details of the amount of displacement of the piezo element 52 being substantially constant when the energy is constant are described in, for example, Japanese Patent Application Laid-Open No. 2005-130561. Further, for example, Japanese Patent Application Laid-Open No. 2002-13156 discloses that the amount of energy supplied to the piezo element 52 per unit time can be made constant by the chopper control of the above aspect.

  In the present embodiment, as shown in FIG. 5, so-called boot-type injection that increases the injection rate in two stages is performed. Here, since the lift amount at the time of low lift holding (boot portion) for holding at a low injection rate has a correlation with the extension amount of the piezo element 52, it is low by fixing the energy amount of the piezo element 52 constant. The lift holding can be controlled. However, when the fuel pressure in the common rail 6 is high, the behavior of the nozzle needle 34 at a low lift is likely to be unstable, and it becomes difficult to control the injection rate with high accuracy.

  FIG. 6 shows an aspect of boot-type injection when the fuel pressure in the common rail 6 is high. Specifically, FIG. 6 (a) shows the charging speed or discharging speed of the piezo element 52, FIG. 6 (b) shows the voltage of the piezo element 52, and FIG. 6 (c) shows the displacement of the piezo piston 48. 6 (d) shows the fuel pressure in the first oil tight chamber 42, FIG. 6 (e) shows the lift amount of the nozzle needle 34, and FIG. 6 (f) shows the injection rate of the piezo injector 10. .

  As shown in the figure, when the fuel pressure in the common rail 6 is high, the lift amount of the nozzle needle 34 becomes excessively large during the low lift holding period from charging to recharging of the piezo element 52, and the boot type injection is appropriately performed. You may not be able to do it. This is considered to be due to the following reason.

  In FIG. 7, the enlarged view of the front-end | tip part of the piezo injector 10 is shown. As shown in the drawing, when the nozzle needle 34 is closed at the tip of the body 30, the force F <b> 1 that the high-pressure fuel in the needle chamber 35 pushes the nozzle needle 34 upward is applied to the rear part of the nozzle needle 34. The following expression (c1) is expressed by the cross-sectional area Sa, the cross-sectional area Ss of the portion where the fuel pressure at the tip of the nozzle needle 34 is not applied, and the fuel pressure NPC of the high-pressure fuel.

F1 = (Sa−Ss) × NPC (c1)
On the other hand, in the present embodiment, the cross sectional area of the balance piston 38 is also made equal to the cross sectional area Sa of the rear part of the nozzle needle 34. For this reason, the force F2 by which the high-pressure fuel in the balance chamber 39 pushes the nozzle needle 34 toward the tip side is expressed by the following equation (c2).

F2 = Sa × NPC
However, since the fuel pressure Ps is also applied to the tip of the nozzle needle 34 when the piezo injector 10 is opened, the force F3 in which the high-pressure fuel in the needle chamber 35 pushes the nozzle needle 34 upward is expressed by the following equation (c3) It becomes.

F3 = (Sa−Ss) × NPC + Ss × Ps (c1)
Here, in order to open the nozzle needle when the piezo injector 10 is closed, the force in the second oil-tight chamber 42 can be ignored even if the force of the spring 40 or the force of the low-pressure fuel in the back pressure chamber 41 is ignored. At least "Ss x NPC" force must be generated by the fuel. On the other hand, when the piezo injector 10 is opened, the difference between the force caused by the high pressure fuel in the needle chamber 35 and the force caused by the high pressure fuel in the balance chamber 39 is changed from “Ss × NPC” to “Ss × (NPC−Ps). To change. Here, “Ps <NPC” is established when the nozzle needle 34 is in a low lift due to the effect of throttling the tip of the body 30 of the piezo injector 10. For this reason, the force required for the second oil-tight chamber 42 to open the piezo injector 10 tends to become an excessive force after the piezo injector 10 is opened. In particular, when the fuel pressure in the common rail 6 is high, the difference between the force caused by the high-pressure fuel in the needle chamber 35 and the force caused by the high-pressure fuel in the balance chamber 39 is likely to change greatly before and after opening the valve. For this reason, when the nozzle needle 34 is separated from the tip of the body 30, the acceleration tends to increase. Thereby, it is considered that the lift of the nozzle needle 34 becomes larger than the desired lift, making it difficult to control the low injection rate.

  Therefore, in the present embodiment, the piezo element 52 is temporarily charged to open the piezo injector 10, and then a part of the electric charge charged in the piezo element 52 is discharged to perform low lift holding.

  FIG. 8 shows a processing procedure of fuel injection control according to the present embodiment. The process shown in FIG. 8 is repeatedly executed by the microcomputer 28 at a predetermined cycle, for example.

  In this series of processes, first, in step S10, the rotation speed of the crankshaft detected by the crank angle sensor 16, the fuel pressure in the common rail 6 detected by the fuel pressure sensor 14, and the accelerator pedal detected by the accelerator sensor 18 are detected. The boot mode injection mode is set according to the operation amount. That is, the injection rate at the time of low lift of boot type injection (target lift amount of the nozzle needle 34), the low lift holding period, and the total injection period are set.

  In the subsequent step S12, the charging energy amount is set based on the low lift injection rate and the fuel pressure calculated in step S10. Here, by setting the charging energy amount at the time of low lift according to the injection rate of the low lift, the extension amount of the piezo element 52 can be commensurate with the low lift. The amount of charge energy is set according to the fuel pressure because the amount of expansion of the piezo element 52 and the amount of energy have a one-to-one relationship based on the premise that the force applied to the piezo element 52 is constant. This is because. That is, the force applied to the piezo element 52 is a force corresponding to the difference between the force caused by the high pressure fuel in the needle chamber 35 and the force caused by the high pressure fuel in the balance chamber 39, and this difference changes according to the fuel pressure. For this reason, by using the fuel pressure as a parameter having a correlation with the force applied to the piezo element 52, each energy amount required to achieve the low lift and the final high lift is set.

  In the subsequent step S14, based on the lift amount at the time of low lift of the boot type injection, the holding period of the low lift and the fuel pressure, the timing of the discharge process for discharging a part of the charge of the piezo element 52, the discharge energy amount, and the energy release speed Set. Here, as the lift amount at the time of low lift is smaller, the pressure Ps applied by the high-pressure fuel in the needle chamber 35 to the tip of the nozzle needle 34 becomes smaller, so the nozzle needle 34 is displaced excessively to the higher lift side. Appropriate conditions for suppressing this change according to the lift amount. For this reason, in the present embodiment, the start timing of the discharge process, the amount of energy to be discharged, and the energy release speed of the piezo element 52 during the discharge are variably set according to the lift amount. In addition, if the holding period of the low lift is long, the lift amount of the nozzle needle 34 is likely to fluctuate. Therefore, an appropriate condition for keeping the nozzle needle 34 at a low lift varies depending on the holding time. For this reason, in the present embodiment, the start timing of the discharge process, the amount of energy to be discharged, and the energy release speed of the piezo element 52 during the discharge are variably set according to the holding time. Furthermore, since the force required for the piezo element 52 to hold the nozzle needle 34 varies depending on the fuel pressure in the common rail 6, an appropriate condition for keeping the nozzle needle 34 at a low lift depends on the fuel pressure. Also changes. For this reason, in this embodiment, the start time of the discharge process, the amount of energy to be discharged, and the energy release speed of the piezo element 52 at the time of discharge are variably set according to the fuel pressure.

  When the process of step S14 is completed, the process proceeds to step S16. In step S16, a process of charging the piezo element 52 is performed in order to open the piezo injector 10. Here, the charge energy amount determined in step S12 is charged. This can be easily performed by lengthening the time of the charging process shown in FIG. 4 in proportion to the amount of charging energy. However, the time for which the charging switch 23 is turned on may be variably set according to the amount of charging energy so that the supply speed of the energy supplied to the piezo element 52 can be made variable.

  When the process in step S16 is completed, the process waits until the discharge time determined in step S14 is reached. When the discharge time comes (step S18: YES), in step S20, a process for partially discharging the charge of the piezo element 52 is performed. Here, in order to obtain the energy release speed determined in step S14, the time for turning on the discharge switch 25 is variably set, and the discharge switch 25 is used over the discharge processing time corresponding to the amount of discharge energy. Perform chopper control.

  When the partial discharge process is thus completed, the process proceeds to step S22. In step S22, first, the charging process is performed again when the holding period determined in step S10 elapses, and further, the electric charge of the piezo element 52 is discharged as the injection period elapses, whereby the piezo injector 10 is discharged. Is closed.

  FIG. 9 shows an aspect of boot type injection by the above processing. 9 (a) to 9 (f) correspond to the previous FIGS. 6 (a) to 6 (f).

  As shown in the drawing, after the piezo element 52 is charged, charging of the piezo element 52 is stopped until the discharge time is reached, and when the discharge time is reached, a part of the electric charge of the piezo element 52 is discharged. Thereby, the nozzle needle 34 can be held at a low lift, and then the piezo element 52 is charged again, so that the boot-type injection can be appropriately performed.

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

  (1) After charging the piezo element 52 to open the piezo injector 10, a part of the charge charged in the piezo element 52 was discharged in order to keep the lift amount at a predetermined lift amount. Thereby, it can suppress that the lift amount of the nozzle needle 34 becomes excessive, and a highly accurate low lift holding | maintenance is attained. Therefore, the fuel injection rate can be controlled with higher accuracy.

  (2) Boot-type injection that gradually increases the fuel injection rate by the piezo injector 10 was performed by charging, partially discharging, and recharging the piezo element 52. Thereby, the injection rate at the time of the low injection rate in boot type injection can be controlled with high accuracy.

  (3) Based on the fuel pressure in the common rail 6, the target lift amount of the nozzle needle 34, and the holding period due to the low lift, feedforward control is performed to set the mode of the discharge process. It is possible to hold the lift amount of 34 with high accuracy with a low lift.

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

  In the present embodiment, feedback control of the lift amount is performed in addition to the feed forward control of the lift amount of the nozzle needle 34 by the partial discharge process based on the process of step S14 of FIG. At this time, as shown in FIG. 10, the amount of change in the lift amount at the time of holding the low lift is the voltage drop of the piezo element 52 during the low lift holding period when the discharge process of step S20 of FIG. 8 is not performed. Grasp by. That is, the voltage drop amount Δ1 of the voltage Vb at the start of the partial discharge process of the piezo element 52 with respect to the peak voltage Va of the piezo element 52 by the first charge of the piezo element 52 and the voltage Vc at the end of the partial discharge process. The amount of change in the lift amount of the nozzle needle 34 is grasped by the sum of the voltage drop amount Δ2 of the voltage Vd at the start of the recharging process.

  Here, the voltage of the piezo element 52 is determined by the amount of charge charged in the piezo element 52 and the piezoelectric effect generated by the force applied to the piezo element 52 from the outside. For this reason, it is considered that a change in the voltage of the piezo element 52 is caused by a change in the force applied to the piezo element 52 in a period in which the partial discharge process is not performed in the low lift holding period. In other words, it may be caused by a change in the fuel pressure in the first oil-tight chamber 42. Since the change in the fuel pressure has a correlation with the change in the volume of the first oil tight chamber 42, the change in the fuel pressure has a correlation with the lift change amount of the nozzle needle 34. For this reason, as shown in FIG. 11, the amount of change in lift can be grasped from the amount of voltage drop of the piezo element 52.

  FIG. 11 shows the relationship between the voltage drop amount, the lift change amount, and the fuel pressure when the force applied to the nozzle needle 34 is balanced. As shown in the drawing, the lift change amount increases as the voltage drop amount “Δ1 + Δ2” increases. This is considered that the larger the voltage drop amount of the piezo element 52 is, the larger the amount of decrease in the fuel pressure in the first oil-tight chamber 42 is, which means that the amount of increase in the volume of the first oil-tight chamber 42 is large. This is because it means that the amount of increase in the lift amount of the nozzle needle 34 is large. Further, if the amount of change in the lift amount is constant, the voltage drop amount “Δ1 + Δ2” increases as the fuel pressure increases. This is because, as described above, the higher the fuel pressure, the greater the force generated by the high pressure fuel in the balance chamber 39 than the force generated by the high pressure fuel in the needle chamber 35. For this reason, even if the volume change amount of the 1st oil tight chamber 42 is the same, the fall amount of the fuel pressure in the 1st oil tight chamber 42 by this volume change becomes so large that a fuel pressure is high.

  FIG. 12 shows a processing procedure of fuel injection control according to the present embodiment. The process shown in FIG. 12 is repeatedly executed by the microcomputer 28 at a predetermined cycle, for example. In FIG. 12, the same steps as those shown in FIG. 8 are given the same step numbers for the sake of convenience.

  In this series of processing, the amount of voltage drop before and after the discharge processing in step S18 shown in FIG. 8 is calculated in step S21. Specifically, before and after the discharge process, the voltage of the piezo element 52 is detected based on the voltage of the node N1 shown in FIG. 3, and the amount of voltage drop is calculated accordingly.

  When the voltage drop amount is calculated in this way, in the next processing cycle of the process shown in FIG. 12, after the process of step S14, as a process of step S15, feedback based on the detected value of the voltage drop amount and the previous fuel pressure is performed. Take control. Specifically, the amount of discharge energy determined by the process of step S14 is feedback corrected in the manner shown in FIG. That is, a required amount of the lift change amount is determined in advance, and a required value of the voltage drop amount is obtained from this required amount and the previous detected value of the fuel pressure. When the detected value is larger than the required value of the voltage drop amount, the discharge energy amount is increased. As a result, the lift amount of the nozzle needle 34 is reduced, so that the increase amount of the volume of the first oil-tight chamber 42 is reduced and the hydraulic pressure is increased, so that the voltage drop amount is reduced. Incidentally, the required amount of lift change amount is set to a value that avoids the overshoot of the lift amount as shown in FIG.

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

  (4) Feedback correction of the discharge energy amount due to the partial discharge process so that the voltage drop amount of the piezo element 52 during the holding period of the lift amount of the nozzle needle 34 other than the partial discharge process period is a desired drop amount. did. Thereby, the lift amount of the nozzle needle 34 can be held and controlled with higher accuracy.

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

  In this embodiment, a sensor that detects the stress of the piezo element 52 is provided, and feedback control is performed by grasping the lift amount of the nozzle needle 34 according to the stress of the piezo element 52. Here, when the force applied to the nozzle needle 34 is balanced, the stress of the piezo element 52, the fuel pressure in the common rail 6, and the lift amount of the nozzle needle 34 have the relationship shown in FIG.

  As shown in the drawing, the lift amount decreases as the stress of the piezo element 52 increases. This is because the greater the stress, the greater the force applied to the piezo element 52, so the fuel pressure in the first oil-tight chamber 42 is higher and the volume of the first oil-tight chamber 42 is smaller. That is, when the volume of the first oil tight chamber 42 is small, the lift amount of the nozzle needle 34 is small, so the lift amount decreases as the stress increases. If the lift amount is the same, the higher the fuel pressure in the common rail 6, the greater the stress on the piezo element 52. As described above, the higher the fuel pressure, the greater the force generated by the high pressure fuel in the balance chamber 39 than the force generated by the high pressure fuel in the needle chamber 35. Therefore, the first requirement is required to compensate for this. This is because the fuel pressure in the oil-tight chamber 42 increases.

  Accordingly, the needle lift amount at the time of low lift is estimated from the stress of the piezo element 52 after the partial discharge process, and in accordance with this, the charge energy amount determined by the process of step S12 of FIG. At least one of the speed, the discharge timing determined by the processing in step S14, the discharge energy amount, and the energy release speed is feedback-corrected.

  Incidentally, as shown in FIG. 15, the stress of the piezo element 52 is detected by using a single piezoelectric element of the piezo elements 52 as a stacked body of a plurality of piezoelectric elements as the stress sensor 52s. That is, when a force is applied to the piezo element 52 from the outside, a voltage is generated by the piezoelectric effect according to the stress of the piezo element 52, and this is used as stress information.

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

  (5) The lift amount of the nozzle needle 34 is highly accurate by correcting at least one of the charging process and the partial discharging process for opening the piezo injector 10 according to the lift amount grasped from the detected stress. Can be held and controlled.

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

  In the present embodiment, the chopper control for the charging process and the discharging process of the piezo element 52 is performed in the mode shown in FIG. That is, the charge switch 23 and the discharge switch 25 are turned off when the current flowing through the piezo element 52 reaches a predetermined peak value Ip, and the charge switch 23 and the discharge switch 25 are turned off when the current flowing through the piezo element 52 becomes zero. The discharge switch 25 is turned on. In other words, when the current flowing through the piezo element 52 reaches the peak value Ip, switching from the increase operation to the decrease operation is performed, and when the current flowing through the piezo element 52 becomes zero, the decrease operation is changed to the increase operation. Switch. However, an upper limit value is set in advance for the increase operation time, and when the upper limit value is reached, the operation is switched to the decrease operation even if the current flowing through the piezo element 52 does not reach the peak value Ip. This is a measure taken because the rate of increase of current in the ON state of the charge switch 23 and the discharge switch 25 decreases with the passage of time from the start of the charge process and the discharge process.

  By performing the charging process and discharging process of the piezo element 52 in the above-described manner, the charge charge amount and the discharge charge amount can be increased in proportion to the charge time and the discharge time. That is, when performing the above operation for switching to the off operation when the peak value Ip is reached, the amount of charge charged (discharged) during the charge time (discharge time) t is such that the area of each triangle shown in FIG. In view of (base) × (height) / 2 ”, it can be approximated by“ t × Ip / 2 ”. For this reason, the charge of the piezo element 52 can be managed easily and directly.

  For this reason, in this embodiment, the charge amount of the piezo element 52 is managed in the charging process and the discharging process, not the energy. Hereinafter, the application example is shown about the case where the chopper control of FIG. 16 is applied to the 1st-3rd embodiment.

<When applied to the first embodiment>
In step S12 shown in FIG. 8, the target voltage of the piezo element 52 is further set according to the temperature of the piezo element 52 in addition to the boot injection mode and the fuel pressure. Here, the temperature of the piezo element 52 is used because a piezoelectric coefficient, which is a change in the amount of displacement of the piezo element 52 with respect to a change in the voltage of the piezo element 52, changes depending on the temperature of the piezo element 52. Here, the temperature of the cooling water of the diesel engine may be simply used as the temperature of the piezo element 52 here. For example, the capacity of the piezo element 52 is calculated by detecting the charge amount and voltage of the piezo element 52. Thus, the temperature of the piezo element 52 may be estimated. Incidentally, details of this method focusing on the fact that the apparent capacitance defined by the change in voltage with respect to the change in charge changes according to the temperature are described in, for example, Japanese Patent Application Laid-Open No. 2002-21620.

  Further, in step S14 of FIG. 8, in addition to the discharge timing, the discharge charge amount and the discharge speed are set. Here, instead of the discharge charge amount, a target voltage after discharge of the piezo element 52 may be set. Further, the discharge rate can be adjusted by the peak value Ip shown in FIG.

<When applied to the second embodiment>
In addition to the changes when applied to the first embodiment, in step S15 shown in FIG. 12, the discharge charge amount may be feedback-corrected in accordance with the voltage drop amount. At this time, in FIG. 13, the amount of discharge energy is replaced with the amount of discharge charge.

<When applied to the third embodiment>
In addition to the changes when applied to the first and second embodiments, in step S15 shown in FIG. 12, the target of the piezo element 52 during charging is based on the stress and fuel pressure of the piezo element 52. At least one of the voltage, the charging speed, the discharge timing determined by the processing in step S14, the discharge charge amount, and the discharge speed is feedback-corrected.

(Fifth embodiment)
Hereinafter, a fifth embodiment will be described with reference to the drawings, focusing on differences from the first embodiment.

  In the present embodiment, a piezo injector 10a that performs a binary operation of opening and closing according to charging and discharging of the piezo element is used. Hereinafter, the structure of the piezo injector 10a will be described with reference to FIG.

  A columnar needle storage portion 72 is provided at the tip of the body 70 of the piezo injector 10a. The needle storage portion 72 stores a nozzle needle 74 that is displaceable in the axial direction. The nozzle needle 74 is seated on an annular needle seat portion 76 formed at the distal end portion of the body 70, thereby blocking the needle storage portion 72 from the outside (combustion chamber of a diesel engine), while from the needle seat portion 76. By separating, the needle storage part 72 is communicated with the outside. Further, high pressure fuel is supplied to the needle storage portion 72 via the high pressure fuel passage 8.

  The back side of the nozzle needle 74 (the side opposite to the side facing the needle seat portion 76) faces the back pressure chamber 80. Fuel from the high-pressure fuel passage 8 is supplied to the back pressure chamber 80 via the orifice 82. Further, the back pressure chamber 80 is provided with a needle spring 84 that pushes the nozzle needle 74 toward the needle seat portion 76.

  The back pressure chamber 80 can communicate with the low pressure fuel passage 12 via a ball 86. The ball 86 is seated on the annular valve seat 90 on the back side thereof, so that the low pressure fuel passage 12 and the back pressure chamber 80 are blocked and displaced toward the front end side of the body 70. The back pressure chamber 80 is communicated.

  The valve seat 90 side of the ball 86 is connected to a small diameter piston 94 via a pressure pin 92. The rear side of the small diameter piston 94 faces the tip of the large diameter piston 96 having a larger diameter than the small diameter piston 94. A displacement transmission chamber 98 is defined by the small diameter piston 94, the large diameter piston 96, and the inner peripheral surface of the body 70. The displacement transmission chamber 98 is filled with an appropriate fluid such as fuel.

  On the other hand, the large-diameter piston 96 has a rear side of the body 70 connected to a piezo element 52a similar to the piezo element 52 shown in FIG. Incidentally, the piezo element 52 a is fixed to the body 70 on the back side facing the large-diameter piston 96.

  When no current is supplied to the piezo element 52a and the piezo element 52a is in the contracted state, the force is exerted by the high pressure fuel in the high pressure fuel passage 8, so that the ball 86 and the small diameter piston 94 are positioned behind the body 70. Become. At this time, the back pressure chamber 80 and the low pressure fuel passage 12 are blocked by the ball 86. For this reason, the nozzle needle 74 is pushed toward the distal end side of the body 70 by the pressure of the fuel in the back pressure chamber 80 (the pressure of the fuel in the common rail 6) and the elastic force of the needle spring 84, and is seated on the needle seat portion 76. (A closed state).

  On the other hand, when current is supplied to the piezo element 52 a and the piezo element 52 a is in the extended state, the ball 86 moves to the tip side of the body 70. As a result, the back pressure chamber 80 communicates with the low pressure fuel passage 12. As a result, the pressure of the fuel in the back pressure chamber 80 is reduced, and the force that the high pressure fuel in the needle housing portion 72 pushes the nozzle needle 74 to the rear of the body 70 causes the fuel in the back pressure chamber 80 and the needle spring 84 to move. If it becomes larger than the force which pushes the nozzle needle 74 to the front of the body 70 more than predetermined, the nozzle needle 74 will be in the state (valve open state) separated from the needle seat part 76. FIG.

  In the case of such a configuration, the lift amount of the nozzle needle 74 cannot be controlled with high accuracy, so that boot-type injection cannot be performed. Therefore, in the present embodiment, multistage injection control is performed in which some of the pilot injection, pre-injection, main injection, after-injection, and post-injection are selected within one cycle of the combustion cycle, and these selected injections are performed. . Here, the pilot injection promotes the mixing of fuel and air just before ignition by injection of extremely minute fuel. The pre-injection shortens the ignition timing delay after the main injection, suppresses the generation of nitrogen oxides (NOx), and reduces combustion noise and vibration. The main injection contributes to the generation of output torque of the diesel engine and has the maximum injection amount during multi-stage injection. After-injection recombusts particulate matter (PM). Post-injection controls the temperature of the exhaust and regenerates the aftertreatment device of a diesel engine such as a diesel particulate filter (DPF).

  By the way, if charging and complete discharging of the piezo element 52a are repeated each time these multistage injections are performed, the power consumption during discharge increases. This is because, when the discharge switch 25 is in the ON state, the capacitor 22 can recover a part of the charge charged in the piezo element 52a when the discharge switch 25 is in the OFF state. This is because the charge is not recovered because the discharge is performed by the closed loop circuit formed by the discharge switch 25, the charge / discharge coil 24, and the piezo element 52a.

  Therefore, in the present embodiment, the remaining energy amount of the piezo element 52a when the piezo injector 10a is closed is calculated, and the piezo element 52a is discharged until the remaining energy amount is reached. Thereby, in the multistage injection, since all the charge amount is not discharged, power consumption can be suppressed.

  FIG. 18 shows a processing procedure of fuel injection control according to the present embodiment. The process shown in FIG. 18 is repeatedly executed by the microcomputer 28 at a predetermined cycle, for example.

  In this series of processes, first, in step S30, the number of injection stages for dividing and injecting the fuel of the required injection amount is calculated based on the required injection amount corresponding to the operation amount of the accelerator pedal and the rotation speed of the crankshaft. Here, when the number of injection stages is “1”, only main injection is performed. When the number of injection stages is “2” or more, pilot injection, pre-injection, and after-injection are performed in addition to main injection. It will be. At this time, the final number of injection stages is set in consideration of whether there is a request for post injection performed by another logic.

  In the subsequent step S32, the command injection period and the command injection start timing of each injection stage of the number of injection stages calculated in step S30 are calculated.

  In the subsequent step S34, the remaining energy amount when the piezo injector 10 is closed is map-calculated based on the fuel pressure in the common rail 6. This map is preliminarily adapted by experiments or the like. The remaining energy amount is set according to the fuel pressure even in the piezo injector 10a shown in FIG. 17, in order to open the valve, the high-pressure fuel causes the ball 86 to move to the valve seat 90 side. This is because, for example, the piezo element 52a has to give a force to overcome the pushing force. For this reason, the force of the piezo element 52a when the nozzle needle 74 is seated on the needle seat portion 76 changes depending on the fuel pressure.

  When the remaining energy amount is calculated in this way, the process proceeds to step S36. In step S36, in each injection, a discharge process is performed until the energy amount of the piezo element 52a becomes the above-mentioned remaining energy amount so that the piezo injector 10a is opened by charging processing and the piezo injector 10a is closed at a predetermined timing. . Note that the final stage injection is a process of completely discharging the electric charge of the piezo element 52a from the viewpoint of safety and the like.

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

  (6) After calculating the remaining energy amount of the piezo element 52a when the piezo injector 10a is closed due to the discharge of the piezo element 52a, charging the piezo element 52a to open the piezo injector 10a, The piezo element 52a was discharged until Thereby, the power consumption at the time of fuel injection control can be reduced.

  (7) Discharge up to the amount of remaining energy was performed for fuel injection before the final stage in multi-stage injection. Accordingly, it is possible to avoid problems such as unintentional valve opening of the piezo injector 10a due to changes in the valve opening conditions of the piezo injector 10a while suppressing power consumption due to multistage injection.

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

  In the second embodiment, the target of feedback correction is not limited to the amount of discharge energy. For example, the start time of partial discharge processing, the speed at which energy is released from the piezo element 52, and further, the partial discharge before discharge The amount of charging energy may be used.

  In the second and third embodiments, only feedback control may be performed without performing feedforward control. At this time, for example, in the third embodiment, the detection of the stress of the piezo element 52 waits until the force applied to the nozzle needle 34 is assumed to be stable after the charging process for opening the piezo injector 10. It is desirable to do this later.

  In the fourth embodiment, the charge management method of the piezo element 52 is not limited to the simple management method based on the period of chopper control and the peak value Ip shown in FIG. For example, regardless of the mode of chopper control, the charge of the piezo element 52 may be managed by the time integral value of the current flowing through the piezo element 52 detected by the voltage of the node N2 shown in FIG.

  In the first to fourth embodiments, the boot type injection is performed. However, the present invention is not limited to this, and the application of the present invention is effective when performing the fuel injection control for holding the nozzle needle 34 with a low lift. is there.

  In the fifth embodiment, even if the piezo injector 10a is closed by calculating the remaining charge amount when the piezo injector 10a is closed and discharging the piezo element 52a until the remaining charge amount is reached. Good. Here, when calculating the remaining charge amount, it is desirable to use the temperature of the piezo element 52 a in addition to the fuel pressure in the common rail 6.

  The drive circuit for performing chopper control is not limited to the one illustrated in FIG. 3 above, but performs chopper control using the flyback current of the transformer as exemplified in Japanese Patent Laid-Open No. 8-177678, for example. It may be a thing. Further, for example, the charging process and the discharging process of the piezo element 52 may be performed by a method other than the chopper control.

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

The figure which shows the whole structure of the engine system in 1st Embodiment. Sectional drawing which shows the cross-sectional structure of the piezoelectric injector of the embodiment. The figure which shows the structure of ECU concerning the embodiment. The time chart which shows the operation mode of the piezoelectric element concerning the embodiment. The time chart which shows the injection rate waveform at the time of the fuel injection in the same embodiment. The time chart explaining the problem at the time of performing boot type injection. The figure for examining the cause of the above-mentioned problem. The flowchart which shows the process sequence of the fuel-injection control concerning the said embodiment. The time chart which shows the process aspect for boot type injection in the embodiment. The time chart which shows the feedback correction aspect of operation of the piezo element concerning 2nd Embodiment. The figure which shows the relationship between the voltage drop amount and the lift variation | change_quantity of a nozzle needle. The flowchart which shows the process sequence of the fuel-injection control concerning the said embodiment. The figure which shows the feedback correction method based on the amount of voltage drops in the embodiment. The figure which shows the estimation method of the lift amount of the nozzle needle in 3rd Embodiment. The figure which shows the stress sensor which detects the stress of the piezo element in the embodiment. The time chart which shows the aspect of the chopper control concerning 4th Embodiment. Sectional drawing which shows the cross-sectional structure of the piezo injector concerning 5th Embodiment. The flowchart which shows the process sequence of the fuel-injection control concerning the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 6 ... Common rail, 10 ... Piezo injector, 23 ... Charge switch, 25 ... Discharge switch, 52 ... Piezo element, 20 ... ECU (one Embodiment of a fuel-injection control apparatus).

Claims (7)

With respect to a piezo injector capable of continuously adjusting the lift amount of a nozzle needle according to expansion and contraction of a piezo element that functions as an actuator, in a fuel injection control device that performs fuel injection by extending and contracting the piezo element,
Discharge means for discharging a part of the electric charge charged in the piezo element so as to hold the lift amount at a predetermined lift amount after charging the piezo element to open the piezo injector. A fuel injection control device. The fuel injection control device performs boot-type injection that gradually increases the fuel injection rate by the piezo injector,
2. The fuel injection control device according to claim 1, wherein the boot-type injection is performed by charging the piezo element again after discharging by the discharging means.   The discharge means sets the mode of the discharge process based on at least one of the pressure of the fuel supplied to the piezo injector, the holding period at the predetermined lift amount, and the target lift amount at the holding time. The fuel injection control device according to claim 1 or 2. The piezo injector includes a needle stopper that applies a fluid pressure to the side that increases the lift amount of the nozzle needle, and pressurizes the fluid by extension of the piezo element.
Means for once detecting the voltage drop amount of the piezo element in a period other than the discharge period by the discharge means in the holding period of the lift amount of the nozzle needle after charging the piezo element;
And a correction means for correcting at least one of a charging process for opening the piezo injector and a discharging process by the discharging means so as to make the detected lowering amount a desired lowering amount. The fuel injection control device according to claim 1. The piezo injector includes a needle stopper that applies a fluid pressure to the side that increases the lift amount of the nozzle needle, and pressurizes the fluid by extension of the piezo element.
The detection result of the means for detecting the stress of the piezo element is captured, and at least one of a charging process for opening the piezo injector and a discharging process by the discharging means is corrected according to the detected stress. The fuel injection control device according to claim 1. For a piezo injector that opens and closes by charging and discharging a piezo element that functions as an actuator and is mounted in an internal combustion engine, the piezo element is extended by charging the piezo element and discharged by discharging the piezo element. In a fuel injection control device that performs fuel injection control by reducing the element,
Calculating means for calculating an electrical state quantity of the piezo element when the piezo injector is closed by discharging of the piezo element based on an operating state of the internal combustion engine;
A fuel injection control device comprising: discharge means for discharging the piezo element until the state quantity calculated by the calculation means is reached after the piezo element is charged to open the piezo injector. The fuel injection control device performs multi-stage injection control for performing fuel injection a plurality of times within one combustion cycle of an arbitrary cylinder.
7. The fuel injection control device according to claim 6, wherein the discharge up to the state quantity calculated by the calculating means is performed for the fuel injection before the final stage in the multi-stage injection.

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