JP2006166649A - Piezoelectric-actuator driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric-actuator driver capable of properly suppressing vibration at the time of a displacement of a piezoelectric element. <P>SOLUTION: The series circuit of a piezoelectric element Pa, a charge/discharge coil 46, a capacitor 42, and a charge switch 44; and the series circuit of a piezoelectric element Pa, a charge/discharge coil 46, and a discharge switch 50, are driven by a plurality times of on/off operation of the charge switch 44 and the discharge switch 50, to carry out the charge control and discharge control of the piezoelectric element Pa. When increasing/decreasing the electric current amount exchanged between the piezoelectric elements Pa by the on/off operation, the switching from the off-operation to the on-operation is arranged to be executed when the electric current amount becomes zero, after executing the switching before the current amount becomes zero. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drive device for a piezoelectric actuator that performs charge control and discharge control of a piezoelectric element.

  A piezo actuator is an actuator in which a piezoelectric element such as a laminated body (piezo stack) in which a large number of piezoelectric elements are stacked is expanded and contracted by a piezoelectric effect. For example, in a common rail fuel injection device of a diesel engine, the piezoelectric actuator is disposed in a fuel injection valve. The The piezo actuator is a capacitive load, and can be switched between an expanded state and a contracted state by charging and discharging.

  As shown in FIG. 14, the drive device 80 that performs charge control and discharge control of the piezo actuator includes a charge switch 84 connected between the piezo element Pa and the coil 82 and the battery B, and the piezo element Pa and the coil 82. A discharge switch 86 connected to the series circuit is operated. Specifically, as a driving method of the driving device 80, a step-down chopper method in which the charging switch 84 and the discharging switch 86 are turned on and off at a plurality of times at high speed is employed (Patent Document 1). Hereinafter, this will be described in detail with reference to FIG.

  15A shows the transition of the operation mode of the charge switch 84, FIG. 15B shows the transition of the operation mode of the discharge switch 86, and FIG. 15C shows the current flowing through the piezo element Pa (FIG. FIG. 15 (d) shows the change in the voltage at the high potential side of the piezo element Pa, and FIG. 15 (e) shows the change in the charge flowing into the piezo element Pa and the charge flowing out from the piezo element Pa. The transition of the displacement of the element Pa is shown respectively.

  As shown in the figure, at the time of charge control, the charge switch 84 changes from an on operation to an off operation when the amount of current flowing through the piezo element Pa reaches a preset current value (the upper limit value of the current during charging). Can be switched. Further, during the discharge control, the discharge switch 86 is switched from the on operation to the off operation when the amount of current flowing through the piezo element Pa reaches a predetermined current value (the upper limit value of the current during discharge). On the other hand, the timing at which the charge switch 84 and the discharge switch 86 are switched from the off operation to the on operation is when the amount of current exchanged with the piezo element Pa becomes “0” (in the figure, zero crossing). ).

  However, when switching from the off operation to the on operation in the above mode, during charge control, the expansion of the piezo element Pa stops when the current amount (the amount of charge flowing into the piezo element Pa) becomes “0”. In the discharge control, the contraction of the piezo element Pa stops when the current amount (the amount of electric charge flowing out from the piezo element) becomes “0”. Then, as shown in FIG. 15E, the actual measurement result of the displacement of the piezo element Pa is a wavy shape having an inflection point at the timing of zero current due to the inertia of the piezo element Pa. When the piezo element Pa is displaced in such a manner, the drive target component driven by the expansion and contraction of the piezo element Pa vibrates in conjunction with the undulating displacement, so that the behavior of the drive target component becomes unstable. There is a fear. For example, in the case where the piezo element Pa is provided in the fuel injection valve, the behavior of a valve that is a drive target component becomes unstable, which may cause malfunction or fail to provide sufficient injection performance.

In order to avoid such a problem, it is conceivable to employ one that switches from an off operation to an on operation before the current becomes zero, as in Patent Document 2. However, in this case, the following inconvenience cannot be ignored. Firstly, during the on / off operation of the charge switch 84 and the discharge switch 86, since the switching from the off operation to the on operation is continued at a large current amount, noise due to a change in magnetic flux caused by the operation switching (Electromagnetic noise) increases. Second, since the switching from the off operation to the on operation is continued at a large current amount, the element life of the charge switch 84 and the discharge switch 86 is shortened. Thirdly, if the switching from the off operation to the on operation is continued at a large current amount, the controllability of the voltage of the piezo element Pa is degraded. This is because when charge control and discharge control are performed by the on / off operation, the total current amount from when the operation is switched to the off operation until the current amount becomes zero cannot be controlled. As described above, if switching from the off operation to the on operation is continued at a large current amount, the peak value of the current amount at the end of the on / off operation also becomes large, and the current amount from the end of the on / off operation. The total amount of current until becomes zero becomes large. This reduces the controllability of the voltage applied to the piezo element Pa.
JP-A-11-317551 European Patent Application No. 1139447

  The problem to be solved by the present invention is that it is difficult to appropriately suppress vibration when the piezoelectric element is displaced.

  In the following, means for achieving these objects and their effects are described.

  In the means 1, in the driving device of the piezo actuator for charging the piezo element by repeating the increase control and decrease control of the amount of current flowing through the series circuit of the piezo element and the coil functioning as the actuator, the increase from the decrease control to the increase is performed. Switching to control is performed before the amount of current becomes zero in the initial stage of the charging, and thereafter, control means is provided that becomes zero.

  In the means 2, in the means 1, the control means is configured to turn on a charge switch connected in the middle of a series circuit of the piezo element, the coil and the power feeding means, and thereby the piezo element, the coil, the charge switch, and the The increase control is performed using a closed loop circuit in which power supply units are connected in series, and the decrease control is performed using a closed loop circuit in which the piezo element, the coil, and the rectifier unit are connected in series by turning off the charging switch. I did it.

  The current amount of the means 1 and means 2 corresponds to the amount of charge flowing into the piezo element.

  The means 3 repeats the increase control and the decrease control of the amount of current flowing through the series circuit of the piezo element functioning as an actuator and the coil, so that the piezo actuator drive device that discharges the piezo element increases the increase from the decrease control. Switching to control is performed before the amount of current becomes zero at the initial stage of the discharge, and thereafter, control means is provided that becomes zero.

  In the means 4, in the means 3, the control means is a closed loop circuit in which the piezo element, the coil and the discharge switch are connected in series by turning on a discharge switch connected to the series circuit of the piezo element and the coil. The decrease control is performed using a closed loop circuit in which the piezoelectric element, the coil, the rectifying means, and the power supply means for charging the piezoelectric element are connected in series by turning off the discharge switch. To do.

  The current amount of the means 3 and means 4 corresponds to the amount of electric charge flowing out from the piezo element.

  When increasing or decreasing the current amount, the amount of current flowing through the piezo element quickly becomes a large value by switching to the increase control of the current amount at the initial stage. In other words, the rate of increase in current is large. For this reason, the amount of displacement of the piezoelectric element is also large. Therefore, if switching from the decrease control to the increase control is performed at the timing when the current amount becomes zero at this time, the vibration of the piezo element becomes remarkable.

  On the other hand, as described above, if switching from decrease control to increase control is performed before the amount of current becomes zero during charging control and discharging control in order to suppress the vibration, as described above. is there.

  In this respect, in the above means 1 to 4, in the initial stage of the current amount increase / decrease control, the switching from the decrease control to the increase control is performed before the current amount becomes zero, thereby suitably suppressing the vibration of the piezo element. can do. After that, switching from decrease control to increase control is performed when the current amount becomes zero, so that this switching is continued during charge control and discharge control before the current amount becomes zero. It is also possible to suitably suppress various problems that occur when performing. Therefore, the means 1 can appropriately suppress vibration when the piezo element is displaced.

  In means 5, in any one of means 1 to 4, the control means performs switching from the increase control to the decrease control when a predetermined period elapses after the increase control.

  When the increase / decrease control is repeated, the rate of increase in the current amount decreases in the latter period compared to immediately after the start of the increase / decrease control. Further, in some cases, when the increase control is continued, the current amount may once increase and then start to decrease.

  In this regard, according to the above configuration, the charge control and the discharge control can be suitably performed by switching from the increase control to the decrease control when the predetermined period has elapsed since the increase control. Further, in the above configuration, the peak value of the current amount tends to be smaller as the increase / decrease control is continued. For this reason, at the end of the increase / decrease control, the amount of current when the increase control is finally switched to the decrease control is reduced, so that it is possible to improve the control accuracy when the voltage value of the piezo element is controlled to a predetermined value. .

  Incidentally, it is desirable that the predetermined period is shorter than the amount of current increased by the increase control in the later stage of the increase control.

  In means 6, in any one of means 1 to 5, the control means switches from the increase control to the decrease control when the amount of current reaches a predetermined upper limit value.

  According to the said structure, it can avoid suitably that the said electric current amount becomes excess.

  In particular, when the means 6 has the structure of the means 5, the following excellent effects can be obtained.

  Immediately after the start of the increase / decrease control, the increase rate of the current amount becomes large. For this reason, when performing increase control for a predetermined period as by means 4, there is a concern that the amount of current becomes excessive depending on the setting mode of the predetermined period. If such a concern is avoided by setting the predetermined period short, the increase control becomes excessively short in the latter stage of the increase / decrease control, and the control can be switched to the decrease control with almost no increase in the current amount. is there. For this reason, charge control and discharge control may not be performed appropriately.

  In this regard, in the above configuration, the above-described concern can be avoided by switching from increasing control to decreasing control when the amount of current reaches the upper limit.

  In any one of the means 1 to 6, as in the case of the means 7, the control means increases the current from the decrease control by decreasing the current amount to a predetermined lower limit value at the initial stage of the increase / decrease control. Switching to control may be performed.

  In the means 8, in any one of the means 1 to 7, the control means starts from the decrease control based on at least one of the number of times of the increase / decrease control, the time when the increase / decrease control is performed, and the voltage of the piezo element. The timing for switching to increase control is determined when the amount of current becomes zero.

  In the above configuration, when switching from decrease control to increase control is performed at the timing when the amount of current becomes zero, the period during which the vibration of the piezo element becomes noticeable, in other words, the initial period of increase / decrease control is properly grasped. can do.

(First embodiment)
Hereinafter, a first embodiment in which a drive device for a piezo actuator according to the present invention is applied to an actuator drive device provided in a fuel injection valve of a diesel engine will be described with reference to the drawings.

  FIG. 1 shows a configuration of a driving device for a piezo actuator and peripheral members thereof according to the present embodiment. As shown in FIG. 1, the drive device for the piezo actuator according to the present embodiment performs charge control and discharge control for the piezo element Pa to drive the fuel injection valve PI. It has an electronic control device 1 that controls the diesel engine and a control circuit 2 that is dedicated hardware for driving the piezo element Pa. Incidentally, electric power is supplied from the battery B to the electronic control device 1 and the control circuit 2.

  Here, the structure of the fuel injection valve PI will be described with reference to FIG.

  The fuel injection valve PI is provided with a cylindrical needle storage portion 12 at the tip of the body 10 thereof. The needle storage section 12 stores a nozzle needle 14 that can be displaced in the axial direction. The nozzle needle 14 is seated on an annular needle seat portion 16 formed at the distal end portion of the body 10, thereby blocking the needle storage portion 12 from the outside (combustion chamber of a diesel engine), while from the needle seat portion 16. By separating, the needle storage portion 12 is communicated with the outside. Further, high pressure fuel supplied from a common rail (not shown) to the high pressure fuel passage 18 is supplied to the needle storage portion 12.

  The back side of the nozzle needle 14 (the side opposite to the side facing the needle seat portion 16) faces the back pressure chamber 20. Fuel from the high-pressure fuel passage 18 is supplied to the back pressure chamber 20 through the orifice 22. Further, the back pressure chamber 20 is provided with a needle spring 24 that pushes the nozzle needle 14 toward the needle seat portion 16 side.

  The back pressure chamber 20 can communicate with the low pressure fuel passage 28 via the ball 26. The ball 26 is seated on the annular valve seat portion 30 on the back side, so that the low pressure fuel passage 28 and the back pressure chamber 20 are blocked and displaced toward the front end side of the body 10. The back pressure chamber 20 is communicated.

  The valve seat 30 side of the ball 26 is connected to a small diameter piston 34 via a pressure pin 32. The rear side of the small diameter piston 34 faces the tip of the large diameter piston 36 having a larger diameter than the small diameter piston 34. A displacement transmission chamber 38 is defined by the small diameter piston 34, the large diameter piston 36, and the inner peripheral surface of the body 10. The displacement transmission chamber 38 is filled with an appropriate fluid such as fuel.

  On the other hand, the large-diameter piston 36 is connected to the piezo element Pa on the rear side of the body 10. Incidentally, the back surface of the piezo element Pa facing the large-diameter piston 36 is fixed to the body 10.

  The piezo element Pa includes a laminated body (piezo stack) formed by laminating a plurality of piezoelectric elements, and functions as an actuator by expanding and contracting due to the piezoelectric effect. Specifically, the piezo element Pa is a capacitive load, and expands when charged and shrinks when discharged.

  When no current is supplied to the piezo element Pa and the piezo element Pa is in a contracted state, the force is exerted by the high-pressure fuel in the high-pressure fuel passage 18, so that the ball 26 and the small-diameter piston 34 are positioned behind the body 10. Become. At this time, the back pressure chamber 20 and the low pressure fuel passage 28 are blocked by the ball 26. For this reason, the nozzle needle 14 is pushed toward the distal end side of the body 10 by the fuel pressure (common rail pressure) in the back pressure chamber 20 and the needle spring 24, and is in a state of being seated on the needle seat portion 16 (valve closed state). .

  On the other hand, when current is supplied to the piezo element Pa and the piezo element Pa is in an extended state, the ball 26 moves to the tip side of the body 10. As a result, the back pressure chamber 20 communicates with the low pressure fuel passage 28. As a result, the pressure of the fuel in the back pressure chamber 20 decreases, and the force that the high pressure fuel in the needle housing portion 12 pushes the nozzle needle 14 toward the rear of the body 10 causes the fuel in the back pressure chamber 20 and the needle spring 24 to move. If it becomes larger than the force which pushes the nozzle needle 14 to the front of the body 10 more than predetermined, the nozzle needle 14 will be in the state (valve open state) separated from the needle seat part 16. FIG.

  Next, a circuit and a driving device for performing charge control and discharge control of the piezo element Pa will be described with reference to FIG.

  The power supplied from the battery B is first supplied to the DC / DC converter 40 which is a booster circuit. The DC / DC converter 40 boosts the voltage of the battery B (for example, “12 V”) to a high voltage (for example, “200 to 300 V”) for charging control of the piezo element Pa.

  The boosted voltage of the DC / DC converter 40 is applied to the capacitor 42. One terminal of the capacitor 42 is connected to the DC / DC converter 40 side, and the other terminal is grounded. When the boosted voltage of the DC / DC converter 40 is applied to the capacitor 42, the capacitor 42 stores electric charge to be supplied to the piezo element Pa. Incidentally, it is desirable that the capacitor 42 has a capacity (for example, about “several hundred μF”) such that the voltage hardly changes depending on the supply of electric charge for one charge control to the piezo element Pa.

  The high potential terminal side of the capacitor 42, that is, the DC / DC converter 40 side is connected to the high potential terminal side of the piezo element Pa via the series connection body of the charge switch 44 and the charge / discharge coil 46. It is connected. The terminal side at a low potential of the piezo element Pa is grounded via a resistor 48. Here, the charge switch 44 is composed of an N-channel MOS (Metal Oxide Semiconductor) transistor. In the figure, a diode 44a is a parasitic diode formed by forming a transistor, and has an anode connected to the charge / discharge coil 46 side and a cathode connected to the capacitor 42 side.

  One terminal of the discharge switch 50 is connected between the charge switch 44 and the charge / discharge coil 46, and the other terminal of the discharge switch 50 is grounded. Here, the discharge switch 50 is formed of an N-channel MOS transistor. Incidentally, in the figure, the diode 50a is formed by forming this transistor, and its anode is connected to the ground side, and its cathode is connected to the charge switch 44 and the charge / discharge coil 46 side.

  The drive device according to the present embodiment controls the charge of the piezo element Pa by operating the charge switch 44 connected in series to the piezo element Pa and the charge / discharge coil 46 and the capacitor 42. Further, by operating the discharge switch 50 connected to the series circuit of the piezo element Pa and the charge / discharge coil 46, the piezo element Pa is controlled to be discharged.

  Specifically, the control circuit 2 turns on / off the charge switch 44 and the discharge switch 50 via the drive circuit 60. The drive circuit 60 is configured to include a driver that is supplied with power from the terminal side of the capacitor 42 at a high potential and applies a high voltage to the charge switch 44 and the discharge switch 50.

  The on / off operation is performed on the terminal-side potential, which is a high potential of the piezo element Pa, or the amount of current flowing through the piezo element Pa (the amount of charge flowing into the piezo element Pa and the amount of charge flowing out of the piezo element Pa). Based on. Specifically, the terminal-side potential (potential of the node a), which is a high potential of the piezo element Pa, is taken into the control circuit 2 via the voltage monitor circuit 62 and the waveform processing circuit 64. Here, the voltage monitor circuit 62 is a circuit for dividing the voltage of the piezo element Pa into a voltage that can be handled by the control circuit 2. The waveform processing circuit 64 is a circuit that shapes the output of the voltage monitor circuit 62. On the other hand, the amount of current flowing through the piezo element Pa is measured by the potential between the piezo element Pa and the resistor 48 (potential of the node b).

  Here, the charge control and discharge control of the piezo element Pa according to the present embodiment will be described in detail.

  FIG. 3 shows aspects of charge control and discharge control. Here, FIG. 3A shows the transition of the drive signal output from the electronic control unit 1 to the control circuit 2 and instructing the control circuit 2 to perform charge control. FIG. 3B shows the transition of the drive signal output from the electronic control unit 1 to the control circuit 2 and instructing the control circuit 2 to perform discharge control. 3C shows the transition of the operation mode of the charge switch 44, and FIG. 3D shows the transition of the operation mode of the discharge switch 50. FIG. FIG. 3E shows the transition of the current flowing through the piezo element Pa (the charge flowing into the piezo element Pa and the charge flowing out of the piezo element Pa). FIG. 3F shows the high potential of the piezo element Pa. FIG. 3G shows the transition of the displacement of the piezo element Pa, respectively.

  As shown in the figure, at time t1, the electronic control device 1 outputs a drive signal for instructing charge control to the control circuit 2, so that the control circuit 2 starts an on / off operation of the charge switch 44. . Specifically, when the charging switch 44 is turned on, a closed loop circuit including a capacitor 42, a charging switch 44, a charging / discharging coil 46, a piezo element Pa, and a resistor 48 is formed as shown in FIG. Is done. Thereby, the electric charge of the capacitor 42 is charged into the piezo element Pa. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element Pa increases (current amount increase control). On the other hand, when the charging switch 44 is turned on after the charging switch 44 is turned on, as shown in FIG. 4B, a closed loop circuit including a charging / discharging coil 46, a piezo element Pa, a resistor 48, and a diode 50a. Is formed. Thereby, the flywheel energy of the charge / discharge coil 46 is charged in the piezo element Pa. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element Pa decreases (current amount reduction control).

  When the charge switch 44 is operated in the above-described manner, the piezo element Pa is charged, and the potential on the terminal side that becomes the high potential of the piezo element Pa increases.

  On the other hand, when a drive signal instructing discharge control is output from the electronic control unit 1 to the control circuit 2 at time t2 shown in FIG. 3, the control circuit 2 starts an on / off operation of the discharge switch 50. Specifically, when the discharge switch 50 is turned on, a closed loop circuit is formed by the discharge switch 50, the charge / discharge coil 46, the piezo element Pa, and the resistor 48, as shown in FIG. Thereby, the piezo element Pa is discharged. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element Pa increases (current amount increase control). Furthermore, after the discharge switch 50 is turned on, the discharge switch 50 is turned off, so that the capacitor 42, the diode 44a, the charge / discharge coil 46, the piezo element Pa, and the resistor 48 are used as shown in FIG. A closed loop circuit is formed. Thereby, the flywheel energy of the charge / discharge coil 46 is recovered by the capacitor 42. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element Pa decreases (current amount reduction control).

  When the discharge switch 50 is operated in the above-described manner, the piezo element Pa is discharged, and the potential on the terminal side that becomes the high potential of the piezo element Pa is lowered.

  In particular, in the present embodiment, in charge control and discharge control, switching from an off operation to an on operation is performed before the amount of current flowing through the piezo element Pa becomes zero at the beginning of charging or discharging, and thereafter This is done when the amount of current becomes zero. This is due to the following reason.

  At the initial stage of the on / off operation, the amount of current flowing through the piezo element Pa quickly becomes a large value by switching to the on operation. In other words, at the initial stage of the on / off operation, the current increase rate due to switching to the on operation is large. For this reason, the displacement amount of the piezo element Pa is also large. Therefore, when switching from the off operation to the on operation is performed at the timing when the amount of current becomes zero at this time, the piezoelectric element is enlarged as shown by a broken line in FIG. The displacement of Pa undulates and causes significant vibration. This vibration destabilizes the behavior of the large-diameter piston 36, the small-diameter piston 34, the ball 26, and further the nozzle needle 14, which are components to be driven by the piezo element Pa.

  In this regard, in this embodiment, in both the charge control and the discharge control, the vibration of the piezo element Pa is performed by switching from the off operation to the on operation before the current amount becomes zero in the initial stage of the on / off operation. It can suppress suitably. In addition, after that, the switching from the off operation to the on operation is performed when the current amount becomes zero, and this switching is continued during the charge control and the discharge control before the current amount becomes zero. It is also possible to suitably suppress various problems that occur when performing.

  That is, when switching from an off operation to an on operation is performed at a large current amount, noise (electromagnetic noise) due to a change in magnetic flux caused by the operation switching increases. On the other hand, in the present embodiment, such a problem is suppressed by performing switching from the off operation to the on operation for as short a time as possible at the beginning of the charge control or discharge control.

  Further, if the switching from the off operation to the on operation is performed at a large current amount, the lifetime of the charge switch 44, the discharge switch 50, etc. is shortened. This is due to the following two reasons. First, there is a reason that the temperature of the charge switch 44, the discharge switch 50, etc. rises due to the continued large current amount. Secondly, if the flow direction is reversed while a current is flowing, there is a reason that the life of the charge switch 44, the discharge switch 50, etc. is shortened due to a larger current flow than usual. . That is, the diode 50a is placed in such a state during charge control, and the diode 44a is placed in such a state during discharge control. On the other hand, in the present embodiment, such a problem is suppressed by performing switching from the off operation to the on operation for as short a time as possible at the beginning of the charge control or discharge control.

  Further, if the switching from the off operation to the on operation is continued at a large current amount, the controllability of the voltage of the piezo element Pa is lowered. That is, in this case, the amount of current when switching to the off operation at the end of the on / off operation also becomes large, and the total amount of current from when the off operation is performed until the amount of current becomes zero becomes large. On the other hand, after the off operation, the total amount of current flowing until the amount of current becomes zero cannot be controlled. Then, the total current amount from when the off operation is performed until the current amount becomes zero varies depending on changes in the individual or the environment. For this reason, as shown by the oblique lines in FIG. 6A, if the amount of current at the time of switching to the off operation at the end of the on / off operation is large, the piezo element Pa is finally applied to the piezo element Pa due to an individual or environmental change. Since the applied voltage value varies, the controllability such as the injection amount decreases. On the other hand, in the present embodiment, it is possible to reduce the amount of current when switching to the off operation at the end of the on / off operation.

  That is, in the present embodiment, as shown in FIG. 6B, the peak value of the current amount is obtained while the on / off operation is repeated in order to switch from the on operation to the off operation when a predetermined period Tmax elapses. Decrease gradually. By repeating the on / off operation, the potential difference between the piezoelectric element Pa and the capacitor 42 decreases during charge control, and the potential difference between the piezoelectric element Pa and ground decreases during discharge control. This is because the rate of increase in current during operation decreases. As a result, as indicated by hatching in FIG. 6B, the amount of current when switching to the off operation at the end of the on / off operation can be reduced.

  Here, the processing procedure of the charge control and the discharge control will be further described with reference to FIGS.

  FIG. 7 shows a charging control processing procedure.

  In this series of processing, first, in step S10, a counter N that counts the number of on / off operations is set to an initial value (“1”). In the subsequent step S12, the charging switch 44 is turned on. This ON operation is performed until the charging time, which is the time elapsed since the ON operation of the charging switch 44, reaches a predetermined period Tmax1 (step S14) or the amount of current flowing through the piezo element Pa reaches the upper limit value Imax1 ( Step S16) Continue. When the charging switch 44 is turned off (step S18), the turning-off operation is continued at least until the current amount becomes equal to or lower than the lower limit value (a value larger than “0”) (step S20). When the amount of current becomes lower than the lower limit value, the counter is incremented (step S22). Then, the processes from step S12 to step S22 are repeated until the counter value reaches a predetermined number (step S24). Here, the predetermined number of times is for determining a period in which a significant vibration occurs in the displacement of the piezo element Pa. In the present embodiment, as shown in FIG. 3, the predetermined number of times is three.

  On the other hand, when the counter value is equal to or greater than the predetermined number, the off operation is continued until the amount of current becomes zero (step S26). The processing from step S12 to step S26 is performed until the voltage of the piezo element Pa becomes equal to or higher than the target voltage Vmax (step S28).

  FIG. 8 shows a procedure for discharging control.

  In this series of processing, first, in step S30, a counter N that counts the number of on / off operations is set to an initial value (“1”). In the subsequent step S32, the discharge switch 50 is turned on. This ON operation is performed until the discharge time, which is the time elapsed after the discharge switch 50 is turned ON, reaches a predetermined period Tmax2 (step S34) or the amount of current flowing through the piezo element Pa reaches the upper limit value Imax2 ( Step S36) Continue. When the discharge switch 50 is turned off (step S38), the off operation is continued at least until the current amount becomes equal to or lower than the lower limit value (a value larger than “0”) (step S40). When the amount of current becomes lower than the lower limit value, the counter is incremented (step S42). The processes from step S32 to step S42 are repeated until the counter value reaches a predetermined number (step S44). Here, the predetermined number of times is for determining a period in which a significant vibration occurs in the displacement of the piezo element Pa. In the present embodiment, as shown in FIG. 3, the predetermined number of times is three.

  On the other hand, when the counter value is equal to or greater than the predetermined number, the off operation is continued until the amount of current becomes zero (step S46). The processing from step S32 to step S46 is performed until the voltage of the piezo element Pa becomes equal to or lower than the target voltage Vmin (step S48). Incidentally, when the discharge control of the piezo element Pa is completed, it is desirable that the voltage be “0 V”. However, when the target voltage Vmin is set to “0V”, the processing from step S32 to step S46 is repeated again even though the voltage of the piezo element Pa is substantially “0V”. In order to avoid this, in this embodiment, a margin is provided for the target voltage Vmin, which is set to a value slightly larger than “0V”.

  In the charge control and discharge control, a current flows through a series LC resonance circuit basically composed of the piezo element Pa and the charge / discharge coil 46. Therefore, the current has a sine wave shape. Therefore, in this embodiment, the predetermined periods Tmax1 and Tmax2 are set sufficiently shorter than the time constant of the LC resonance circuit, so that the increasing rate of the current amount during the ON operation is made substantially constant.

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

  (1) In both the charge control and the discharge control, the vibration of the piezo element Pa is suitably suppressed by switching from the off operation to the on operation before the current amount becomes zero in the initial stage of the on / off operation. Can do. In addition, after that, the switching from the off operation to the on operation is performed when the current amount becomes zero, and this switching is continued during the charge control and the discharge control before the current amount becomes zero. It is also possible to suitably suppress various problems that occur when performing.

  (2) The switching from the on operation to the off operation is performed when a predetermined period Tmax1, Tmax2 elapses after the on operation. As a result, as the on / off operation is repeated, the charge control and the discharge control can be suitably performed even when the upper limit value cannot be reached due to a decrease in the increasing rate of the current amount. That is, when switching is not performed during the predetermined periods Tmax1 and Tmax2, if the current amount cannot reach the upper limit value, the off operation cannot be performed, so that a large amount of charge is thrown into the piezo element. The accuracy of the voltage value applied to the piezo element Pa is lowered. On the other hand, in the present embodiment, it is possible to avoid a decrease in accuracy by setting to switch to the off operation before the amount of current decreases. Further, when the increase rate is reduced, the current amount becomes a substantially sine wave shape, and thus the piezo element Pa vibrates. On the other hand, in the present embodiment, in the later stage of the on / off operation, the change in the voltage on the terminal side, which becomes the high potential of the piezo element Pa, can be made a gentle slope, and thus the charge control and discharge of the piezo element Pa Control can be stably terminated.

  Furthermore, by switching from the on operation to the off operation after the elapse of the predetermined periods Tmax1, Tmax, the amount of current when the last on operation at the end of the on / off operation is switched to the off operation is reduced. For this reason, the control accuracy at the time of controlling the final applied voltage (charge energy or energy of the piezo element Pa during discharge) of the piezo element Pa to the target value can also be improved.

  (3) Switching from the on operation to the off operation is performed when the amount of current flowing through the piezo element Pa reaches a predetermined upper limit value. As a result, the predetermined periods Tmax1 and Tmax are set to values at which the charge control and discharge control of the piezo element Pa can be appropriately performed even in the later stage of the on / off operation, and the initial current of the on / off operation is set. An excessive amount can be avoided.

  That is, immediately after the start of the on / off operation, the increasing rate of the current amount becomes large. For this reason, when it is attempted to perform the ON operation over the predetermined periods Tmax1, Tmax2, there is a concern that the amount of current becomes excessive depending on the setting mode of the predetermined periods Tmax1, Tmax2. In order to avoid such a concern by setting the predetermined periods Tmax1 and Tmax2 to be short, the ON time becomes excessively short in the later stage of the ON / OFF operation, and the OFF operation is performed with almost no increase in the current amount. May be switched to. In this case, charge time and discharge time become long, and charge control and discharge control cannot be performed appropriately. In this regard, as a condition for performing the switching, in addition to the condition that the predetermined periods Tmax1 and Tmax2 have elapsed, the condition that the amount of current flowing through the piezo element Pa reaches a predetermined upper limit value is applied. These problems can be avoided.

  (4) Based on the number of on / off operations, the timing for switching from the off operation to the on operation when the amount of current becomes zero is determined. As a result, the above operations are performed while properly grasping the period during which the vibration of the piezo element Pa is noticeable when switching from the off operation to the on operation is performed at a timing when the amount of current becomes zero. Can do.

(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 first embodiment, the timing for switching from the off operation to the on operation when the current amount becomes zero is determined based on the number of on / off operations. On the other hand, in this embodiment, the said timing is determined based on the time which passed after starting ON / OFF operation.

  That is, as illustrated in FIG. 9 when charging control is performed, switching from the off operation to the on operation is performed when the current amount becomes zero after a predetermined time T has elapsed since the start of the on / off operation. Like that. For charging control, for example, in the process of FIG. 7 above, steps S10 and S22 are omitted, and instead of step S24, the elapsed time since the start of the on / off operation is compared with a predetermined time T. You may implement | achieve by providing. As for the discharge control, for example, in the process of FIG. 8, steps S30 and S42 are omitted, and instead of step S44, a process of comparing the elapsed time after starting the on / off operation with a predetermined time T is performed. You may implement | achieve by providing.

  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.

  (5) Based on the time elapsed since the start of the on / off operation, the timing for switching from the off operation to the on operation when the amount of current becomes zero is determined. Thereby, when switching from the off operation to the on operation is performed at a timing when the amount of current becomes zero, each of the above operations can be performed while appropriately grasping a period in which the vibration of the piezo element becomes significant. .

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

  In the first embodiment, the timing for switching from the off operation to the on operation when the current amount becomes zero is determined based on the number of on / off operations. On the other hand, in the present embodiment, the timing is determined based on the terminal-side voltage that is a high potential of the piezo element Pa.

  That is, as illustrated in FIG. 10 when charging control is performed, when the voltage on the terminal side that becomes the high potential of the piezo element Pa becomes greater than or equal to the threshold A with the start of the on / off operation, switching from the off operation to the on operation is performed. This is done when the amount of current becomes zero. For charging control, for example, steps S10 and S22 are omitted in the process of FIG. 7 described above, and instead of step S24, the voltage on the terminal side that is the high potential of the piezo element Pa is compared with the threshold A. You may implement | achieve by providing. As for the discharge control, for example, in the process of FIG. 8, steps S30 and S42 are omitted, and instead of step S44, a process of comparing the voltage on the terminal side at which the piezoelectric element Pa becomes a high potential with the threshold A is performed. You may implement | achieve by providing.

  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.

  (6) The timing of switching from the off operation to the on operation when the amount of current becomes zero is determined based on the voltage on the terminal side that becomes a high potential of the piezo element Pa. Thereby, when switching from the off operation to the on operation is performed at a timing when the amount of current becomes zero, each of the above operations can be performed while appropriately grasping a period in which the vibration of the piezo element becomes significant. .

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

  In the first embodiment, switching from the on operation to the off operation is performed when the amount of current flowing through the piezo element Pa reaches a predetermined upper limit, and when a predetermined period Tmax1, Tmax2 has elapsed since the on operation. I tried to do it. On the other hand, in this embodiment, switching from the on operation to the off operation is performed when a predetermined period Tmax1, Tmax2 has elapsed since the on operation.

  In this case, as illustrated in FIG. 11 for charging control, the on operation time is constant, so that the peak value of the current amount decreases as the number of on / off operations is increased. As for the charging control, for example, step S16 may be omitted in the process of FIG. 7 described above, and the charging may be waited until the charging time reaches a predetermined period Tmax1 in step S14. As for the discharge control, for example, in the process of FIG. 8, step S36 may be omitted, and in step S34, the process may wait until the discharge time reaches a predetermined period Tmax2.

  Also according to the present embodiment described above, the effects (1), (2), and (4) of the first embodiment can be obtained.

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

  In the first embodiment, the number of on / off operations for determining the timing for switching from the off operation to the on operation when the amount of current becomes zero is “3”. For example, “2” may be used as shown in FIG.

  In the second and third embodiments as well, as in the fourth embodiment, the amount of current flowing through the piezo element Pa is a predetermined upper limit value from the condition for switching from the on operation to the off operation. You may omit the condition when you reach

  In the first to third embodiments, even if the conditions for switching from the on operation to the off operation and the conditions when the predetermined period Tmax1, Tmax2 elapses after the on operation is omitted, It is possible to obtain the effects (1) and (4) of the first embodiment, the effect (5) of the previous second embodiment, and the effect (6) of the previous third embodiment. it can.

  The amount of current to be switched when the amount of current is not switched to zero when switching from the off operation to the on operation may not be constant every time.

  The method for determining the timing for switching from the off operation to the on operation when the amount of current becomes zero is not limited to the method exemplified in the first to third embodiments. For example, you may determine based on the increase rate of the electric current at the time of ON operation.

  The method for determining the timing for ending the on / off operation in the charge control or the discharge control is not limited to those exemplified in step S28 of FIG. 7 or step S48 of FIG. For example, the processing illustrated in step S28 of FIG. 7 or step S48 of FIG. 8 may be performed at the end of the on operation.

  The fuel injection valve PI is not limited to that illustrated in FIG. For example, what is illustrated in FIG. 13 may be used. In FIG. 13, the same members as those in FIG. In the fuel injection valve shown in FIG. 13, the fuel from the high-pressure fuel passage 18 (back pressure chamber 20) has a force that pushes the valve 70 toward the distal end side of the body 10 and a force that pushes the valve 70 toward the valve seat portion 30. The directions are opposite to each other. In particular, by making the areas to which the fuel pressures in the opposite directions are applied equal to each other, the energy required to displace the ball 26 by the piezo element Pa can be greatly reduced.

  The drive circuit that drives the piezo element Pa is not limited to that illustrated in FIG. For example, the charge switch 44 and the discharge switch 50 are not limited to those provided with N-channel MOS transistors, and may be appropriate switching elements. However, in this case, (a) a rectifying means that allows the current from the charge / discharge coil 46 to flow to the piezo element Pa when the charge switch is turned off during charge control, and prevents the reverse current flow; (B) A separate rectifying means for allowing the current from the piezo element Pa to flow to the ground side through the charge / discharge coil 46 and preventing the reverse current flow when the discharge switch is turned off during discharge control is provided. It is desirable. Further, the power supply means for supplying power to the piezo element Pa through the charge / discharge coil 46 is not limited to the one that includes the capacitor 42, the DC / DC converter 40, and the battery B. For example, even if the capacitor 42 is not provided, it is possible to supply electric power with an appropriate voltage to the piezo element Pa using the boosted voltage of the DC / DC converter 40. For example, if the voltage of the battery B is sufficiently high, the DC / DC converter 40 may not be provided.

  The fuel injection valve is not limited to a fuel injection valve used for a diesel engine, and may be a fuel injection valve used for a cylinder injection gasoline engine, for example.

The figure which shows the whole structure of 1st Embodiment of the drive device of the piezoelectric actuator concerning this invention. Sectional drawing which shows the cross-sectional structure of the fuel injection valve of the embodiment. The time chart which shows charge control and discharge control of the piezo element in the same embodiment. The figure which shows the charge control aspect of the embodiment. The figure which shows the discharge control aspect of the embodiment. The time chart for demonstrating the charge control of the embodiment. The flowchart which shows the procedure of the charge control of the embodiment. The flowchart which shows the procedure of the discharge control of the embodiment. The time chart which shows the charge control aspect of 2nd Embodiment. The time chart which shows the charge control aspect of 3rd Embodiment. The time chart which shows the charge control aspect of 4th Embodiment. The time chart which shows the charge control aspect in the modification of the said 1st Embodiment. Sectional drawing which shows the cross-sectional structure of the fuel injection valve in the modification of the said 1st Embodiment. The figure which shows the structure of the drive device of the conventional piezoelectric actuator. The time chart which shows the charge control and discharge control of a piezoelectric element by the said conventional drive device.

Explanation of symbols

  Pa ... piezo element, PI ... fuel injection valve, B ... battery, 1 ... electronic control device, 2 ... control circuit, 42 ... capacitor, 44 ... charge switch, 46 ... charge / discharge coil, 50 ... discharge switch.

Claims (8)

In a drive device for a piezo actuator that charges the piezo element by repeating increase control and decrease control of the amount of current flowing through the series circuit of the piezo element and the coil functioning as an actuator,
A drive device for a piezo actuator, comprising control means for performing switching from the decrease control to the increase control before the amount of current becomes zero in the initial stage of the charge, and then when the current amount becomes zero. .   The control means is a closed loop in which the piezo element, the coil, the charge switch, and the power supply means are connected in series by turning on a charge switch connected in the middle of the series circuit of the piezo element, the coil, and the power supply means. 2. The piezoelectric actuator according to claim 1, wherein the increase control is performed using a circuit, and the decrease control is performed using a closed loop circuit in which the piezo element, the coil, and the rectifier are connected in series by turning off the charging switch. Drive device. In a drive device for a piezo actuator that discharges the piezo element by repeating increase control and decrease control of the amount of current flowing through the series circuit of the piezo element and the coil functioning as an actuator,
A drive device for a piezo actuator, comprising control means for performing switching from the decrease control to the increase control before the amount of current becomes zero at the initial stage of the discharge, and thereafter, when the current amount becomes zero. .   The control means performs the increase control using a closed loop circuit in which the piezo element, the coil, and the discharge switch are connected in series by turning on a discharge switch connected to the series circuit of the piezo element and the coil. 4. The piezo according to claim 3, wherein the reduction control is performed using a closed loop circuit in which the piezo element, the coil, the rectifying means, and a power supply means for charging the piezo element are connected in series by turning off the discharge switch. Actuator drive.   5. The drive device for a piezo actuator according to claim 1, wherein the control unit performs switching from the increase control to the decrease control when a predetermined period elapses after the increase control. 6.   The piezo actuator driving apparatus according to claim 1, wherein the control unit performs switching from the increase control to the decrease control when the amount of current reaches a predetermined upper limit value.   The piezo actuator according to any one of claims 1 to 6, wherein the control means switches from the decrease control to the increase control by decreasing the current amount to a predetermined lower limit value at an initial stage of the increase / decrease control. Drive device.   The control means switches the decrease control to the increase control based on at least one of the number of times of the increase / decrease control, the time when the increase / decrease control is performed, and the voltage of the piezo element, and the current amount becomes zero. 8. The drive device for a piezo actuator according to claim 1, wherein the timing to be performed is determined.

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