JP2006217693A - Adjustment method for control mode of piezo actuator, and drive device of piezo actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve control performance in controlling the displacement of a piezo element while increasing or decreasing the amount of a current running through the piezo element functioning as an actuator, by repeating on/off-operations of a switching device for chopper control. <P>SOLUTION: A voltage of the piezo element is measured synchronously with the completion of on/off-operations of a charging switch. Based on this, a control mode of the displacement of the piezo element is adjusted so that the voltage of the piezo element may be a targeted voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention controls the electrical state quantity of the piezo element while increasing and decreasing the amount of current flowing through the piezo element functioning as an actuator by repeatedly turning on and off the switching element for chopper control. The present invention relates to a method for adjusting the control mode of a piezo actuator that adjusts the control mode. In addition, the present invention controls the electrical state quantity of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element for chopper control. The present invention relates to a driving device for a piezoelectric actuator.

  The piezoelectric 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 reverse piezoelectric effect. For example, the piezoelectric actuator is provided in a fuel injection valve in a common rail fuel injection device of a diesel engine. . The piezo actuator is a capacitive load, and can be switched between an expanded state and a contracted state by charging and discharging.

  The drive device for a piezo actuator extends and contracts the piezo actuator by charging and discharging a piezo element. As this drive device, one that controls the amount of displacement of the piezo element by charging and discharging the piezo element by chopper control is known (Patent Documents 1 to 4). This drive device repeats the increase and decrease of the amount of current flowing in the series circuit of the piezo element and the coil by repeating the ON / OFF operation of the switching element for charging according to the chopper control during the increase control of the displacement amount. Charge the piezo element. In addition, during the reduction control of the displacement amount, by repeating the ON / OFF operation of the discharge switching element for chopper control, the increase and decrease in the amount of current flowing in the series circuit of the piezo element and the coil are repeated, so that the piezo element Discharge.

  Further, in the above-described drive device, the piezoelectric element is controlled to a desired displacement amount by controlling the electrical state amount having a correlation with the displacement amount of the piezoelectric element such as a voltage as desired.

However, when the electrical state quantity is controlled by the chopper control, the electrical state quantity varies due to the current flowing through the series circuit even after the switching element is turned off. For this reason, if the electrical state quantity is controlled by chopper control, this may not be accurately controlled.
JP-A-11-317551 JP 2002-136156 A JP 2002-159190 A JP 2001-53348 A

  The present invention has been made to solve the above-described problems, and its purpose is to increase the amount of current flowing through a piezo element that functions as an actuator by repeatedly turning on and off a switching element for chopper control. Another object of the present invention is to provide a method for adjusting a control mode of a piezo actuator and a drive device for the piezo actuator, which can improve the control performance when controlling the displacement amount of the piezo element while reducing the piezo element.

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

  Means 1 controls the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeating the on and off operations of the switching element for chopper control. An adjustment method for adjusting a mode of control, wherein an electrical state quantity of the piezo element having a correlation with the displacement amount is measured before the end of the repetition of the on operation and the off operation, and based on the measurement result, Adjust the control mode.

  Since there are individual differences in the characteristics of the piezo element, the electrical state quantity of the piezo element is not uniquely determined by the on / off operation. Furthermore, because the characteristics of the piezo element change with temperature, the electrical state quantity of the piezo element is not uniquely determined by the above operation.

  On the other hand, the measured electrical state quantity of the piezo element becomes steady after the amount of current flowing through the piezo element becomes zero after the last switching from the on operation to the off operation. . Here, if the mode of controlling the amount of displacement is adjusted based on the electrical state quantity measured after becoming steady, the following inconvenience occurs due to the above-described variation in the characteristics of the piezoelectric element.

  That is, in this case, both the individual A that flows current through the piezo element due to the off operation after the end of the operation and the individual B for which the amount of current due to the off operation becomes zero at the end of the operation are charged. Adjustments are made to approximate the quantities. However, in this case, when the current amount of the individual A becomes zero at the end of the control due to a change in characteristics due to temperature or the like, and the individual B is switched to the off operation at the end of the control, the charging of the individual A is performed. There is a large difference between the amount and the charge amount of the individual B.

  In this regard, in the above method, by adjusting the control mode based on the state quantity measured before the end of the repetition of the above operation, it is possible to suppress the fluctuation of the state quantity, thereby improving the displacement amount control performance. Can be made.

  It should be noted that “before the end of repetition of the ON operation and OFF operation” includes the end of the repetition. Furthermore, the “adjustment of the control mode” includes not only the on / off operation mode but also the adjustment of the circuit characteristics of the drive circuit of the piezo element that controls the displacement amount.

  Note that, as with the means 2, the means 1 may adjust the control mode so that the measurement result matches the reference value.

  In the means 3, in the means 1 or 2, the control is performed by charging the piezoelectric element.

  In the above method, in order to perform the control adjustment related to the charging process of the piezo element in the aspect of the means 1 and the means 2, the aspect of the piezo element expansion control such as the control of the charge amount of the piezo element is made appropriate. be able to.

  In the means 4, in any one of the means 1 to 3, the measurement is performed in synchronization with the end of the repetition of the on operation and the off operation.

  In the above method, by performing the above measurement in synchronization with the end of the repetition of the above operation, the amount of current after the switching from the on operation to the off operation can be reduced by changing the state quantity after adjustment based on the measurement. It can be reduced to about the amount of current up to zero.

  In the means 5, in the means 4, the state quantity is controlled by repeating the ON operation and the OFF operation for a predetermined period set in advance, and the measurement is synchronized with the elapse of the predetermined period. Do.

  In the above method, the state quantity can be controlled by a simple process by repeating the above operation for a predetermined period. In addition, since the control mode is adjusted based on the measurement performed in synchronization with the elapse of the predetermined period, the control performance can be improved.

  Note that, as in the means 6, the means 5 may include adjustment of the predetermined period in the adjustment of the control mode.

  Thereby, the mode of controlling the state quantity can be suitably adjusted.

  In the means 7, in any one of the means 1 to 6, the adjustment of the control mode includes adjustment of at least one of the on operation and the off operation.

  In the above method, the mode of controlling the state quantity can be suitably adjusted by adjusting the mode of the on / off operation.

  In the means 8, in any one of the means 1 to 7, the measurement is performed after performing a process of removing the fluctuation of the measured value of the state quantity caused by the vibration of the voltage of the piezoelectric element during the control.

  In the above method, since the state quantity is measured after the process for removing the fluctuation is performed, it is possible to avoid or suppress the occurrence of a situation where the same measurement value can be taken at different timings. For this reason, according to the said method, a state quantity can be measured appropriately.

  In the means 9, in any one of the means 1 to 7, the measurement is performed as measurement of an integral value by time of a function including at least one of a current flowing through the piezoelectric element and a voltage of the piezoelectric element as an independent variable.

  When the independent variable of the function includes the voltage of the piezo element, since the voltage has a correlation with the displacement amount, the function also has a correlation with the displacement amount. In addition, when the independent variable includes a current flowing through the piezo element, the integral value of the current has a correlation with the displacement amount, and thus the integral value of the function also has a correlation with the displacement amount. The integral value according to the time of the function is one in which the influence of the fluctuation of the function value due to voltage oscillation or the like is suitably suppressed. For this reason, the displacement amount of the piezo element can be appropriately measured using the integral value of this function.

  The integrated value is preferably an integrated value of any one of the voltage, the current, and the product of the voltage and the current.

  Here, the voltage is an amount having a correlation with the displacement amount of the piezoelectric element. Further, the integrated value of the current over time is also an amount having a correlation with the displacement amount of the piezoelectric element. Further, since the product of current and voltage has a correlation with the amount of change in energy of the piezo element, the integrated value of the product of current and voltage has a correlation with the amount of displacement of the piezo element.

  The means 10 drives a piezo actuator that controls the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element for chopper control. In the apparatus, the electrical state quantity of the piezo element having a correlation with the displacement amount is measured before the repetition of the on operation and the off operation, and the control mode is adjusted based on the measurement result. And

  The means 11 drives a piezo actuator that controls the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element for chopper control. In the apparatus, the control mode is adjusted based on an electrical state quantity of the piezo element having a correlation with the displacement amount measured before the end of the repetition of the on operation and the off operation. To do.

  Since there are individual differences in the characteristics of the piezo element, the electrical state quantity of the piezo element is not uniquely determined by the on / off operation. Furthermore, because the characteristics of the piezo element change with temperature, the electrical state quantity of the piezo element is not uniquely determined by the above operation.

  On the other hand, the measured electrical state quantity of the piezo element becomes steady after the amount of current flowing through the piezo element becomes zero after the last switching from the on operation to the off operation. . Here, when the displacement amount control mode is adjusted based on the electrical state quantity measured after becoming steady, the following inconvenience occurs due to the above-described variation in the characteristics of the piezoelectric element.

  That is, in this case, both the individual A that flows current through the piezo element due to the off operation after the end of the operation and the individual B for which the amount of current due to the off operation becomes zero at the end of the operation are charged. Adjustments are made to approximate the quantities. However, in this case, when the current amount of the individual A becomes zero at the end of the control due to a change in characteristics due to temperature or the like, and the individual B is switched to the off operation at the end of the control, the charging of the individual A is performed. There is a large difference between the amount and the charge amount of the individual B.

  In this regard, according to the means 10, the variation of the state quantity can be suppressed by adjusting the control mode based on the state quantity measured before the end of the repetition of the operation, and thus the displacement amount is controlled. Performance can be improved.

  Further, the means 11 realizes a driving device in which fluctuations in the state quantity are suppressed by adjusting the control mode based on the state quantity measured before the end of the repetition of the operation when the driving apparatus is manufactured. be able to.

  Note that “before the end of the repetition of the on operation and the off operation” includes the time when the operation ends. Furthermore, the “adjustment of the control mode” includes not only the on / off operation mode but also the adjustment of the circuit characteristics of the drive circuit of the piezo element that controls the displacement amount.

  In addition, as a specific configuration of the measurement, control, and adjustment of the control mode in the means 10 and 11, the means described in any one of the means 2 to 9 may be implemented.

(First embodiment)
Hereinafter, a first embodiment in which a method for adjusting a control mode of a piezoelectric actuator and a driving device for a piezoelectric actuator according to the present invention are applied to a piezoelectric actuator provided in a fuel injection valve of a diesel engine will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of the diesel engine fuel injection system. As shown in the figure, the fuel in the fuel tank 2 is pumped up by the feed pump built in the high-pressure fuel supply pump 6 through the fuel filter 4 and pressurized and supplied to the common rail 8. The fuel stored in the common rail 8 in a high pressure state is supplied to a fuel injection valve 12 provided in each cylinder of a four-cylinder diesel engine via a high-pressure fuel supply pipe 10. Each of the fuel injection valves 12 is connected to a low-pressure fuel supply pipe 14 for returning the leaked fuel that has come out from the fuel injection valve 12 to the fuel tank 2.

  Detection values of various sensors such as the fuel pressure sensor 16 that detects the fuel pressure in the common rail 8 are taken into the control device 20. And in the control apparatus 20, various actuators of diesel engines, such as the fuel injection valve 12, are operated based on such a detected value. Next, the piezo element provided in the fuel injection valve 12 and the control device 20 that performs charging and discharging will be described in detail.

  FIG. 2 shows the configuration of the piezo element included in the fuel injection valve 12 and the control device 20.

  As shown in the figure, the piezo element PE (piezo elements pa to pd corresponding to each cylinder) includes a laminated body (piezo stack) in which a plurality of piezoelectric elements are laminated, and this is expanded and contracted by a reverse piezoelectric effect. This functions as an actuator. Specifically, the piezo element PE is a capacitive load, and expands when charged and shrinks when discharged. Incidentally, the piezoelectric element PE according to the present embodiment uses a piezoelectric element of a piezoelectric material such as PZT.

  Here, a drive circuit for driving the piezo element PE will be described.

  The power supplied from the battery Ba is first supplied to the DC / DC converter 30 which is a booster circuit. The DC / DC converter 30 boosts the voltage (for example, “12 V”) of the battery Ba to a high voltage (for example, “200 to 300 V”) for charging the piezo element PE.

  The boosted voltage of the DC / DC converter 30 is applied to the capacitor 32. One terminal of the capacitor 32 is connected to the DC / DC converter 30 side, and the other terminal is grounded. When the boosted voltage of the DC / DC converter 30 is applied to the capacitor 32, the capacitor 32 stores electric charge to be supplied to the piezo element PE. Incidentally, it is desirable that the capacitor 32 has a capacity (for example, about “several hundred μF”) such that the voltage hardly changes by a single charging process to the piezo element PE.

  The high potential terminal side of the capacitor 32, that is, the DC / DC converter 30 side is connected to the high potential terminal side of the piezo element PE via the series connection body of the charge switch 34 and the charge / discharge coil 36. It is connected. And the terminal side which becomes the low electric potential of the piezo element PE is grounded.

  Specifically, a cylinder selection switch 38 is connected between each of the piezo elements pa to pd and the ground, thereby selecting which of the piezo elements pa to pd is to be charged or discharged. It is supposed to be. A bank selection switch 40 that connects the charge / discharge coil 36 to each of the parallel circuit of the piezoelectric element pa and the piezoelectric element pd and the parallel circuit of the piezoelectric element pb and the piezoelectric element pc are connected to the parallel circuit. . The bank selection switch 40 is a switch that allows only two cylinders to be used during simultaneous injection of a plurality of cylinders or during retreat travel. Incidentally, in the piezoelectric elements pa to pd, the piezoelectric element pa corresponds to the first cylinder, the piezoelectric element pb corresponds to the second cylinder, the piezoelectric element pc corresponds to the third cylinder, and the piezoelectric element pd corresponds to the fourth cylinder.

  One terminal of a discharge switch 42 is connected between the charge switch 34 and the charge / discharge coil 36, and the other terminal of the discharge switch 42 is grounded.

  A diode 44 is connected in parallel to the discharge switch 42. The diode 44 has a cathode connected between the capacitor 32 and the charge / discharge coil 36 and an anode connected to the ground. The diode 44, together with the capacitor 32, the charge switch 34, and the charge / discharge coil 36, constitutes a chopper circuit that charges the piezo element PE, and functions as a freewheeling diode.

  On the other hand, a diode 46 is connected to the charge switch 34 in parallel. The diode 46 has a cathode side connected to the capacitor 32 side and an anode side connected to the discharge switch 42 side. The diode 46, together with the capacitor 32, the charge / discharge coil 36, and the discharge switch 42, constitutes a chopper circuit that discharges the electric charge of the piezo element PE, and functions as a freewheeling diode.

  A short switch 48 and a diode 50 are connected in parallel with the piezo element PE between the charge / discharge coil 36 and the bank selection switch 40. The short switch 48 is for completely discharging the electric charge of the piezo element PE that could not be discharged by the chopper control. The diode 50 prevents the voltage of the piezo element PE from becoming negative.

  The control device 20 shown in FIG. 1 includes a microcomputer 22 and a control IC 24 in addition to the drive circuit. Here, the microcomputer 22 calculates the control condition of the displacement amount of the piezo element PE based on the detection values of various sensors that detect the operating state of the diesel engine and the like, and outputs it to the control IC 24. The control IC 24 drives the drive circuit based on the control conditions output from the microcomputer 22. Note that the control IC 24 and the microcomputer 22 capture information such as the current and voltage of the drive circuit and the piezo element PE based on the potentials of the nodes N1 to N7 of the drive circuit.

  Here, the control (charging process and discharging process) of the displacement amount of the piezo element PE according to the present embodiment will be described in detail.

  FIG. 3 shows aspects of the charging process and the discharging process. Here, FIG. 3A shows the transition of the injection signal output from the microcomputer 22 to the control IC 24 and instructing the injection period. FIG. 3B shows the transition of the charging period signal output from the microcomputer 22 to the control IC 24 and instructing the charging period. FIG. 3C shows the transition of the operation signal of the charging switch 34. FIG. 3D shows the transition of the operation signal of the cylinder selection switch 38 (here, one corresponding to the piezo element pa is illustrated). FIG. 3E shows the transition of the operation signal of the discharge switch 42. FIG. 3F shows transition of the operation signal of the bank selection switch 40 (here, the operation signal of the switch corresponding to FIG. 3D is illustrated). FIG. 3G shows the transition of the operation mode of the short switch 48. FIG. 3 (h) shows the transition of the voltage on the side where the piezoelectric element PE becomes a high potential. FIG. 3I shows the transition of current flowing through the piezo element PE (charge flowing into the piezo element PE, charge flowing out from the piezo element PE).

  As shown in the figure, the injection signal and the charging period signal are output from the microcomputer 22 to the control IC 24 at time t1, so that the control IC 24 starts chopper control by turning on / off the charging switch 34. Specifically, when the charge switch 34 is turned on, a closed loop circuit including a capacitor 32, a charge switch 34, a charge / discharge coil 36, and a piezo element pa is formed as shown in FIG. Thereby, the electric charge of the capacitor 32 is charged to the piezo element pa. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element pa increases. On the other hand, after the charging switch 34 is turned on, the charging switch 34 is turned off, thereby forming a closed loop circuit including the charging / discharging coil 36, the piezo element pa, and the diode 44 as shown in FIG. The Thereby, the flywheel energy of the charge / discharge coil 36 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. And in this embodiment, as shown in FIG. 3, when the amount of current becomes zero, the charging switch 34 is turned on again.

  The step-down chopper control in which the charge switch 34 is operated in the above manner is performed from time t1 to time t2, so that the piezo element pa is charged and the potential on the terminal side that becomes the high potential of the piezo element pa rises.

  On the other hand, when the injection signal is inverted at time t3 shown in FIG. 3, the control IC 24 starts the on / off operation of the discharge switch 42. Specifically, when the discharge switch 42 is turned on, a closed loop circuit is formed by the discharge switch 42, the charge / discharge coil 36, and the piezo element pa as shown in FIG. As a result, 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. Further, after the discharge switch 42 is turned on, the discharge switch 42 is turned off, so that a closed loop circuit is formed by the capacitor 32, the diode 46, the charge / discharge coil 36, and the piezoelectric element pa as shown in FIG. It is formed. Thereby, the flywheel energy of the charge / discharge coil 36 is recovered by the capacitor 32. At this time, as shown in FIG. 3, the amount of current flowing through the piezo element pa decreases. In the present embodiment, as shown in FIG. 3, when the amount of current becomes zero, the discharge switch 42 is turned on again.

  By performing the step-up chopper control in which the discharge switch 42 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. 4 and 5 represent the relationship between the amount of current Ip flowing through the piezo element pa, the inductance L of the charge / discharge coil 36, the voltage Vp of the piezo element pa, and the voltage Vc of the capacitor 32. It is.

  As shown in FIG. 3, the short switch 48 is turned on from time t4 to time t5 after the discharge of the piezo element pa by the boost chopper control is completed, so that the charge of the piezo element pa is completely discharged. To discharge.

  In the present embodiment, as shown in FIG. 3, the charging process of the piezo element pa is performed by turning on / off the charging switch 34 for a predetermined period determined by the charging period signal. That is, control for extending the piezo element PE is performed by open loop control. In the present embodiment, when the displacement amount of the piezo element PE is controlled as desired, the electrical state amount of the piezo element PE having a correlation with the displacement amount of the piezo element PE is used as the control amount.

  Incidentally, the characteristics of the piezo element PE have variations due to individual differences. In addition, the characteristics of the piezo element PE may vary depending on the temperature. For this reason, when the open loop control is performed in the above-described manner, the piezo element PE may not necessarily be controlled to a desired displacement amount (electrical state amount). That is, for example, as illustrated in FIG. 6, when the period during which the on / off operation of the charging switch 34 is performed from time t <b> 1 to t <b> 2, the time point when the current amount becomes zero by the off operation is time t <b> 2. And the case 2 where the last switching time from the on operation to the off operation is time t2, the charge amount varies.

  The maximum value of the variation in the amount of charge caused by the variation in the characteristics of the piezoelectric element PE is from the time when the charging switch 34 is switched from the on operation to the off operation until the amount of current flowing through the piezoelectric element PE becomes zero. In the meantime, it may be larger than the total amount of current flowing into the piezo element PE. Here, this will be described with reference to FIG.

  FIG. 7A shows the transition of the charging period signal, FIG. 7B shows the transition of the current flowing through the piezo element individual A, and FIG. 7C shows the transition through the individual B different from the individual A. FIG. 7 (d) shows the transition of the current, and the transition of the voltage of the individual A and the individual B is shown in FIG. Incidentally, also in FIG. 7, the on operation of the charging switch 34 is performed for a predetermined time, and the off operation is performed until the amount of current becomes zero. In such a case, generally, the maximum value of the current amount can be reduced as time elapses, but in FIG. 7, the maximum value of the current amount is shown as the same for convenience.

  In FIG. 7, after the time t2 when the charging period ends, the voltage of the piezo element PE is measured when the amount of current flowing through the piezo element PE becomes zero and the voltage of the piezo element PE reaches a steady state. The case where the mode of the open loop control is adjusted so that the measured value becomes a desired value (reference value) is shown. Here, the current flowing through the piezo element PE and the voltage of the piezo element PE at the time of adjustment (immediately after adjustment is performed using the measurement value as a reference value) are indicated by solid lines. Thus, although the voltage values at the time of measurement match, there is a variation in the amount of change in voltage (the amount of change in the electrical state amount).

  Further, after adjusting the control mode in the above mode, two points are obtained: the amount of current flowing through the piezo element PE and the voltage of the piezo element PE when the characteristics of the individual A and the individual B change due to a temperature change or the like. Shown with a chain line. Here, for the individual A, at the time of adjustment, the time when the charge switch 34 was switched from the on operation to the off operation was the time t2, but after the adjustment, the current amount decreased to zero due to the off operation of the charge switch 34. The case where the point of time has changed to that at time t2 is shown. On the other hand, for the individual B, at the time of adjustment, the time when the current amount became zero by the turning-off operation of the charging switch 34 was the time t2, but after the adjustment, when the charging switch 34 was switched from the turning-on operation to the turning-off operation. Shows a case where changes to that at time t2. Under these circumstances, the voltage between the individual A and the individual B after the completion of the open loop control corresponds to a large error Δ (approximately twice the total current amount until the current amount becomes zero after switching to the off operation). Voltage error).

  As described above, after the on / off operation is completed, the control state is controlled by adjusting the control mode based on the electrical state quantity (voltage, etc.) measured when the charge amount of the piezo element PE becomes steady. There is a large variation in the electrical state quantity and the amount of change in the state quantity.

  Therefore, in the present embodiment, as shown in FIG. 8, the mode of the open loop control is measured in synchronization with time t <b> 2 that is the end of the repetition of the ON operation and the OFF operation (at the end of the ON / OFF operation). This is done based on the electrical state quantity. Incidentally, FIG. 8A shows the transition of the charging period signal, FIG. 8B shows the transition of the current flowing through the individual A of the piezo element, and FIG. 8C shows the current flowing through the individual B. FIG. 8D shows the transition of the voltage of the individual A and the individual B, respectively.

  In FIG. 8 as well, the current flowing through the piezo element PE and the voltage of the piezo element PE are indicated by a solid line when adjusted and by a two-dot chain line after adjustment.

  In FIG. 8, the voltage of the piezo element PE indicated by a two-dot chain line is not described, but this is because it overlaps the solid line. That is, the adjusted voltage transition (to be indicated by a two-dot chain line) for the individual A coincides with the voltage transition indicated by the solid line of the individual B, and the adjusted voltage (to be indicated by the two-dot chain line) for the individual B Is consistent with the voltage transition indicated by the solid line of the individual A. For this reason, the voltage error due to the open loop control is suppressed to about the total amount of current from the last switching to the off operation until the current becomes zero. In addition, variations in voltage variation (electrical state variation) are also suppressed.

  In this way, it is possible to improve the control performance by measuring the electrical state quantity of the piezoelectric element PE such as voltage in synchronization with the end of the on / off operation and adjusting the control mode based on this measurement. It becomes.

  Incidentally, such adjustment of the control mode includes not only the change of the charging period and the ON operation time, but also the change of the circuit characteristics of the drive circuit shown in FIG.

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

  (1) The electrical state quantity of the piezo element PE was measured in synchronization with the end of the on / off operation of the charge switch 34, and the displacement control mode was adjusted based on the measured state quantity. Thereby, variation in the amount of charge (electrical state amount) of the piezo element PE after the end of the on / off operation can be suitably suppressed, and accordingly, variation in the displacement amount of the piezo element PE is suitably suppressed. be able to.

(2) The displacement amount of the piezo element PE is controlled by charging and discharging the piezo element PE while increasing and decreasing the current amount of the piezo element PE by chopper control. Thereby, the displacement amount of the piezo element PE can be easily controlled.
(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  When the voltage is measured at the end of the on / off operation as in the first embodiment, since the measured voltage fluctuates, this may not be accurately grasped. In particular, the voltage of the piezo element PE is accompanied by voltage oscillation due to the resistance component of the piezo element PE, the piezoelectric phenomenon, and the like. As shown in FIG. 9, the equivalent circuit of the piezo element PE is connected in series to a mechanical component expressed as an LCR series circuit, a capacitor connected in parallel to the LCR series circuit, and the parallel circuit. And the electrical component expressed by the series equivalent resistance. For this reason, each time a current flows, the voltage across the piezo element PE varies depending on the voltage generated by the series equivalent resistance. Thus, it is difficult to uniquely determine the amount of displacement of the piezo element PE based on the measurement of the voltage of the piezo element PE.

  Therefore, in the present embodiment, the piezo element at the end of the on / off operation is based on the integrated value of the current flowing through the piezo element PE, the voltage of the piezo element PE, or the product of the voltage and the current. The displacement amount (electrical state amount) of PE is measured.

  FIG. 10 shows the transition of the voltage of the piezo element PE and the transition of the integrated value of the voltage. FIG. 11 shows the transition of the current of the piezo element PE and the transition of the integrated value of the current. Further, FIG. 12 shows the transition of the current of the piezo element PE, the transition of the voltage, and the transition of the total energy (the integrated value of the product of the voltage and the current). As shown in FIGS. 10 to 12, the integrated value of the current, the voltage, and the product of the voltage and the current with respect to the time is one in which the influence of the vibration component is suppressed. For this reason, the electrical state quantity of the piezo element PE can be appropriately measured as a unique value, and as a result, the displacement amount of the piezo element PE can be uniquely determined.

  In particular, in the examples shown in FIGS. 10 to 12, the integrated value of the voltage is easy to handle as a measured value of the electrical state quantity of the piezo element PE since the vibration component of the voltage is removed.

  According to the embodiment described above in detail, the following effects can be obtained in addition to the effects (1) and (2) of the first embodiment.

  (3) The integral value of any of the current flowing through the piezoelectric element PE, the voltage of the piezoelectric element PE, and the product of the current and voltage was measured. Since this is an electrical state quantity in which voltage oscillation or the like is suitably suppressed, the electrical state quantity of the piezo element PE can be appropriately measured as a unique value.

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

  In this embodiment, the mode of reduction control of the piezo element PE is adjusted. In other words, the mode of control (discharge process) for adjusting the charge amount of the piezo element PE to zero is adjusted. Specifically, the reduction speed (discharge speed) is adjusted. However, for example, if the discharge speed is measured by measuring the time required for the voltage of the piezo element PE to be “0 V”, the measurement error increases. This is because the current hardly flows near “0V” of the voltage of the piezo element PE, and it is difficult to obtain a complete “0V”. The short switch 48 is turned on in order to completely set the voltage of the piezo element PE to “0V”.

  On the other hand, if the electrical state quantity of the piezo element PE is measured during the reduction control of the piezo element PE and the discharge speed is measured by the time required until the state quantity reaches a predetermined value, There is a possibility that the discharge rate may not be uniquely determined due to the vibration of the voltage. FIG. 13 shows the transition of the voltage of the piezo element PE and the transition of the current flowing through the piezo element PE. As shown in FIG. 13, when the discharge rate (discharge time) is measured by the time required for the voltage of the piezo element PE to drop to a predetermined voltage Vt greater than zero, the measured discharge rate is not uniquely determined. (In the figure, it can take three values indicated by arrows).

  Therefore, in the present embodiment, the discharge rate is measured based on the integration value of the current flowing through the piezoelectric element PE, the voltage of the piezoelectric element PE, and the product of the voltage and current.

  FIG. 14 shows the transition of the voltage of the piezo element PE and the transition of the integrated value of the voltage. FIG. 15 shows the transition of the current of the piezo element PE and the transition of the integrated value of the current. Further, FIG. 16 shows the transition of the current of the piezo element PE, the transition of the voltage, and the transition of the total energy (integral value of the product of the voltage and the current). As shown in FIG. 14 to FIG. 16, the influence of the vibration component is suppressed in the integral value of the current, the voltage, and the product of the voltage and the current over time. For this reason, the electrical state quantity of the piezo element PE can be appropriately measured as a unique value, and the discharge rate can be appropriately measured based on this.

  Incidentally, in the present embodiment, the discharge rate is measured as the time required for the integrated value to reach a predetermined value corresponding to an arbitrary value within the range of “10 to 60 V” of the voltage of the piezo element PE. This is because the measurement error of the discharge rate becomes large even when a place where the voltage of the piezo element PE is excessively high is used.

  According to the present embodiment described above, in addition to the effect according to the effect (3) of the previous first embodiment and the effect (3) of the previous second embodiment, the following effect is further obtained. It will be obtained.

  (4) By measuring the discharge speed as the time required for the integrated value to reach a predetermined value corresponding to an arbitrary value within “10 to 60 V”, the discharge speed can be accurately measured.

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

  In the present embodiment, the voltage of the piezo element PE is used when measuring the discharge rate. Then, a smoothing process is applied as a process for removing the variation in the measured value of the displacement amount (electrical state quantity) of the piezo element PE caused by the voltage signal at the time of control. FIG. 17 shows the transition between the voltage of the piezo element PE and the same voltage subjected to smoothing processing. As shown in FIG. 17, by performing the smoothing process, the voltage oscillation is removed, and the discharge rate can be uniquely defined.

  Incidentally, this smoothing process may be either a process using an analog circuit such as a CR circuit or a process using a digital circuit using a microcomputer or the like. However, in the case of processing by a digital circuit, the change in voltage cannot be measured properly unless the operating speed of the microcomputer, the analog / digital converter, the digital signal processing circuit, or the like is high to some extent. On the other hand, if processing by an analog circuit is employed, appropriate processing can be performed with a simple configuration.

  Also according to the present embodiment described above, it is possible to obtain an effect according to the third embodiment.

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

  In each of the above embodiments, the on-operation time of the switching elements (charge switches 34 and 42) for chopper control is constant, and the switching from the off operation to the on operation is performed at the timing when the amount of current flowing through the piezo element PE becomes zero. I went there, but it is not limited to this. For example, the on / off operation may be performed in the manner illustrated in FIGS. 17 and 18. FIG. 18 shows an example in which switching from the on operation to the off operation is performed at a timing when the amount of current reaches a predetermined upper limit, and switching from the off operation to the on operation is performed at a timing when the amount of current becomes zero. Further, in FIG. 19, the switching from the on operation to the off operation is performed at a timing when the current amount becomes a predetermined upper limit value, and the switching from the off operation to the on operation is performed with a predetermined lower limit value where the current amount is larger than zero. An example performed at the following timing is shown. In any of these cases, it can be seen that the amount of current flowing after time t2, which is the timing for ending the on / off operation, varies. For this reason, even in such a case, the problem described with reference to FIG. Therefore, the electrical state quantity correlated with the displacement amount of the piezo element PE is measured in synchronization with the timing of ending the on / off operation, and the control method of the displacement amount is adjusted based on the state quantity thus measured. It is effective to do.

  In each of the above embodiments, the electrical state quantity correlated with the displacement amount of the piezo element PE is measured in synchronization with the end of the on / off operation, but this is not restrictive. In short, it is only necessary to improve the control performance by measuring the electrical state quantity of the piezo element PE before the end of the on / off operation and adjusting the mode of controlling the displacement based on this. At this time, the number of measurement points is not limited to one. For example, by measuring electrical state quantities at multiple locations and adjusting these measurement results to match the desired values (respective reference values), variations in the amount of change in electrical state quantities can be achieved. It may be reduced.

  In each of the above embodiments, the drive device that controls the displacement amount of the piezo actuator by open loop control is exemplified, but the present invention is not limited thereto. For example, after the control mode such as setting of the on-time is adjusted in the mode illustrated in the above embodiment at the time of manufacturing the drive device, the control mode may be finely adjusted by feedback control by the drive device. Good.

  In the above embodiment, the electrical state quantity correlated with the displacement amount of the piezo element PE is measured at the time of manufacturing the drive device, and the displacement amount control is adjusted based on the measured electrical state quantity. It is not restricted at the time of manufacture of the said drive device. That is, even when the electrical state quantity of the piezo element PE is measured by the control device 20 and the mode of controlling the displacement amount of the piezo element PE is adjusted by the control device 20, the on / off operation ends. The application of the present invention for measuring the electrical state quantity of the piezo element PE before is effective.

  In the second to fourth embodiments, the electrical state quantity of the piezo element PE measured as an equivalent value of the displacement amount of the piezo element PE is expressed by the voltage of the piezo element PE, the current flowing through the piezo element PE, Although the integration value of either the product of the voltage and the current or the voltage is smoothed, the present invention is not limited to this. For example, it may be an integral value of a function including at least one of the current and the voltage as an independent variable. In addition, the function including the above voltage as an independent variable is subjected to a process for removing fluctuations in the measured value of the electrical state quantity caused by the vibration of the voltage of the piezo element PE, such as a function subjected to a smoothing process. There may be.

  In addition, the configuration of the drive device for the piezoelectric actuator, such as the configuration of the drive circuit for the piezoelectric actuator, may be changed as appropriate. Further, the piezo actuator is not limited to that provided in the fuel injection valve of the diesel engine.

The block diagram which shows the structure of 1st Embodiment of the adjustment method of the control aspect of the piezoelectric actuator concerning this invention, and the drive device of the actuator. The circuit diagram which shows the structure of the drive device of the embodiment. The time chart which shows the control aspect of the displacement amount of the piezoelectric element in the embodiment. The time chart which shows the aspect of expansion | extension control of the piezo element in the embodiment. The time chart which shows the aspect of the reduction | restoration control of the piezo element in the embodiment. The time chart for demonstrating the problem at the time of expansion | extension control. The time chart explaining the problem in adjustment of expansion | extension control. The time chart explaining the adjustment method of the aspect of the expansion | extension control concerning the said embodiment. The equivalent circuit diagram of a piezo element. The time chart explaining the measurement method of the electrical state quantity at the time of control of the displacement amount of the piezo element concerning 2nd Embodiment. The time chart explaining the measurement method of the electrical state quantity at the time of control of the displacement amount of the piezoelectric element concerning the embodiment. The time chart explaining the measurement method of the electrical state quantity at the time of control of the displacement amount of the piezoelectric element concerning the embodiment. The time chart explaining the subject which 3rd Embodiment tends to solve. The time chart explaining the measurement method of the electrical state quantity concerning the embodiment. The time chart explaining the measurement method of the electrical state quantity concerning the embodiment. The time chart explaining the measurement method of the electrical state quantity concerning the embodiment. The time chart for demonstrating the problem which it is going to solve in the modification of each said embodiment. The time chart for demonstrating the problem which it is going to solve in the modification of each said embodiment.

Explanation of symbols

  PE ... piezo element 32 ... capacitor 34 ... charge switch 36 ... charge / discharge coil 42 ... discharge switch 24 ... control IC 22 ... microcomputer.

Claims (11)

Controlling the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element according to chopper control. An adjustment method for adjusting,
The electrical state quantity of the piezoelectric element having a correlation with the displacement amount is measured before the end of the repetition of the on operation and the off operation, and the control mode is adjusted based on the measurement result. Adjustment method of actuator control mode.   The method for adjusting a control mode of a piezo actuator according to claim 1, wherein the control mode is adjusted in order to make the measurement result coincide with a reference value.   The method for adjusting a control mode of a piezo actuator according to claim 1 or 2, wherein the control is performed by a charging process of the piezo element.   The method for adjusting a control mode of a piezo actuator according to any one of claims 1 to 3, wherein the measurement is performed in synchronization with the end of repetition of the on operation and the off operation.   The piezo actuator according to claim 4, wherein the control of the state quantity is performed by repeating the ON operation and the OFF operation for a predetermined period set in advance, and the measurement is performed in synchronization with the elapse of the predetermined period. Of adjusting the control mode.   The method for adjusting a control mode of a piezo actuator according to claim 5, wherein the adjustment of the control mode includes adjustment of the predetermined period.   The method for adjusting a control mode of a piezo actuator according to claim 1, wherein the adjustment of the control mode includes adjustment of at least one mode of the on operation and the off operation.   The control of a piezo actuator according to any one of claims 1 to 7, wherein the measurement is performed after a process for removing a variation in a measurement value of the state quantity caused by vibration of a voltage of the piezo element during the control is performed. A method of adjusting the aspect.   The piezoelectric actuator according to any one of claims 1 to 7, wherein the measurement is performed as measurement of an integral value by a function time including at least one of a current flowing through the piezoelectric element and a voltage of the piezoelectric element as an independent variable. Control method adjustment method. In a drive device for a piezo actuator that controls the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element according to chopper control,
The electrical state quantity of the piezoelectric element having a correlation with the displacement amount is measured before the end of the repetition of the on operation and the off operation, and the control mode is adjusted based on the measurement result. Actuator drive. In a drive device for a piezo actuator that controls the amount of displacement of the piezo element while increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator by repeatedly turning on and off the switching element according to chopper control,
A piezoelectric actuator characterized in that the control mode is adjusted based on an electrical state quantity of the piezoelectric element having a correlation with the displacement amount measured before the end of repetition of the ON operation and the OFF operation. Drive device.

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