JP2006214783A - Method for measuring displacement of piezoelectric actuator and drive device of piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly measure the displacement of a piezoelectric actuator for controlling the displacement of the piezoelectric actuator by repeating increasing operation and decreasing operation of current flowing through the piezoelectric element functioning as an actuator. <P>SOLUTION: For decompression controlling a piezoelectric element, when the displacement of the piezoelectric element is measured by the voltage while applying charging process to it, the displacement can not be measured as a unique value because of voltage vibration of the piezoelectric element. By using the integrated value of the voltage, those problems caused by the voltage vibration of the piezoelectric element is avoided and the displacement of the piezoelectric element is measured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for controlling the displacement amount of the piezo element by repeating an increase operation and a decrease operation of the amount of current flowing through the piezo element functioning as an actuator. The present invention relates to a measurement method for indirectly measuring. The present invention also relates to a drive device for a piezo actuator that controls an amount of displacement of the piezo element by repeating an increase operation and a decrease operation of an amount of current flowing through the piezo element that functions as an 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.

When performing such control, it is conceivable to use the voltage of the piezo element in order to measure the amount of displacement of the piezo element. However, during the above control, voltage oscillation is caused by the resistance component of the piezo element, the piezoelectric phenomenon, and the like. Therefore, the measured value of the displacement measured using the voltage is stepped and waved. The same measurement value may be taken at different timings, and it is difficult to accurately grasp the displacement amount of the piezo element.
JP-A-11-317551 JP 2002-136156 A JP 2002-159190 A JP 2001-53348 A

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to reduce the displacement amount of the piezo element by repeating an increase operation and a decrease operation of the amount of current flowing through the piezo element functioning as an actuator. The present invention relates to a method for measuring a displacement amount of a piezo actuator capable of appropriately measuring a displacement amount when controlling. Another object of the present invention is to appropriately measure and control the amount of displacement when controlling the amount of displacement of the piezo element by repeatedly increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator. It is an object of the present invention to provide a drive device for a piezo actuator capable of appropriately adjusting the aspect.

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

  In the first aspect, the displacement amount of the piezo element is controlled by repeatedly increasing and decreasing the amount of current flowing through the piezo element that functions as an actuator. A method for indirectly measuring the amount, based on an integral value with respect to time of a function including at least one of an amount of current flowing through the piezo element and a voltage of the piezo element as an independent variable. Measure the displacement.

  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.

  In the means 2, in the means 1, the integral value is an integral over time of any one of the voltage, the current, and a 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. Furthermore, since the product of current and voltage is the amount of change in energy supplied to the piezo element, the integral value of the product of current and voltage has a correlation with the amount of displacement of the piezo element.

  In the means 3, the displacement amount of the piezo element is controlled by repeatedly increasing and decreasing the amount of current flowing through the piezo element functioning as an actuator. The displacement is determined by the electrical state quantity of the piezo element. In this method, the amount of displacement is measured after performing a process of removing fluctuations in the measured value of the amount of displacement caused by vibration of the voltage of the piezoelectric element during the control.

  In the above method, the amount of displacement can be appropriately measured because the electrical state quantity after the process for removing the variation is performed.

  In the means 4, in the means 3, the measurement is performed as measurement of an integral value by a function time including the voltage of the piezo element as an independent variable.

  Since the function includes the voltage of the piezo element having a correlation with the displacement amount of the piezo element as an independent variable, the function 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 the vibration of the voltage or the like is suitably suppressed. For this reason, the displacement amount can be appropriately measured using the integral value of this function.

  In the means 5, the measurement is performed in the means 3 as a result of smoothing a function value including the voltage of the piezoelectric element as an independent variable.

  Since the function includes a voltage, which is a parameter having a correlation with the displacement amount of the piezo element, as an independent variable, the function has a correlation with the displacement amount. Then, by performing the smoothing process on the function value, the fluctuation of the function value caused by the vibration of the voltage can be suitably suppressed. For this reason, it is possible to appropriately measure the amount of displacement using the value of the function subjected to the smoothing process.

  Note that the means 5 may be the one that has been subjected to the smoothing process, as in the case of the means 6, and the voltage of the piezoelectric element has been subjected to the smoothing process by at least one of a smoothing circuit and software.

  In the means 7, in any one of the means 1 to 6, the control of the displacement amount is control for reducing the piezoelectric element by discharging the electric charge charged in the piezoelectric element, and the measurement of the displacement amount is as follows: This is performed in order to grasp the reduction speed of the piezo element.

  In the vicinity of “0V” of the voltage of the piezo element, it is difficult for current to flow, and it is difficult to make it completely “0V”. For this reason, for example, if the reduction speed is measured by measuring the time required for the voltage of the piezo element to be “0 V”, the measurement error increases.

  On the other hand, when the displacement of the piezo element is measured during the control to set the voltage of the piezo element to “0 V”, and the reduction speed (discharge speed) is measured according to the time required until the displacement reaches a predetermined value, Due to the voltage oscillation of the piezo element, the reduction speed may not be uniquely determined.

  In this regard, in the above method, since the displacement amount is measured in the form of the means 1 to 6, the reduction speed can be suitably grasped.

  In the means 8, in the means 7, the reduction speed is grasped as a time required for the piezoelectric element to reduce to a point where the voltage of the piezoelectric element corresponds to an arbitrary value within “10 to 60V”. is there.

  When measuring the reduction speed, if the case where the voltage of the piezo element is in the vicinity of “0 V” is used, the error increases as described above. On the other hand, even if a location where the voltage of the piezo element is excessively high is used, the error increases.

  In this regard, in the above method, the reduction speed can be accurately measured by using the case where the voltage of the piezo element is “10 to 60 V”.

  The “time required for the piezo element to be reduced to a value corresponding to an arbitrary value” is a predetermined value corresponding to an arbitrary value within “10 to 60 V” when the configuration of the means 1 is provided. It means the time required for the integrated value to reach the value. In the case where the configuration of the means 3 is provided, it means the time required for the value of the function subjected to the processing for removing the fluctuations to reach a predetermined value corresponding to an arbitrary value within “10 to 60 V”. To do.

  In the means 9, in any one of the means 1 to 7, the increase operation is performed as an ON operation of the switching element for chopper control, and the decrease operation is performed as an OFF operation of the switching element.

  According to the above method, by using the chopper control, the piezo element can be easily charged or discharged, and the displacement amount can be easily controlled.

  The means 10 repeats an increase operation and a decrease operation of the amount of current flowing through the piezo element functioning as an actuator, so that the piezo actuator drive device that controls the displacement amount of the piezo element flows through the piezo element. Means for measuring the amount of displacement at the time of the control based on an integral value with respect to time of a function including at least one of a current amount 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. Then, the integral value according to the time of the function is one in which the influence of the fluctuation of the value of the function due to the voltage oscillation is suitably suppressed. For this reason, the amount of displacement can be suitably grasped using the integral value of this function. Then, by using the displacement amount thus measured, it is possible to suitably adjust the displacement amount control mode.

  The displacement amount may be measured by the method described in any one of the means 2, 7, and 8. Further, as the above control, chopper control may be applied as shown in the means 9.

  In the means 11, in the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the current amount flowing through the piezo element functioning as an actuator, the piezo element at the time of the control Means for measuring the amount of displacement after performing a process of removing the variation of the measured value of the amount of displacement caused by the vibration of the voltage of

  In the above configuration, the displacement amount is measured after the processing for removing the fluctuation is performed, and thus the displacement amount can be appropriately measured.

  In addition, you may perform the measurement of the said displacement amount by the method in any one of the said means 4-8. Further, as the above control, chopper control may be applied as shown in the means 9.

  In the means 12, in the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the current amount flowing through the piezo element functioning as an actuator, the current flows through the piezo element. The mode of the control is adjusted based on the displacement amount at the time of the control measured based on the integral value with respect to the time of the function including at least one of the current amount and the 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. Then, the integral value according to the time of the function is one in which the influence of the fluctuation of the value of the function due to the voltage oscillation is suitably suppressed. For this reason, the amount of displacement can be suitably grasped using the integral value of this function. Then, by using the displacement amount thus measured, it is possible to suitably adjust the displacement control mode when the drive device is manufactured.

  The displacement amount may be measured by the method described in any one of the means 2, 7, and 8. Further, as the above control, chopper control may be applied as shown in the means 9.

  The means 13 repeats an increase operation and a decrease operation of the amount of current flowing through the piezo element functioning as an actuator, so that in the piezo actuator drive device that controls the displacement amount of the piezo element, the piezo element at the time of the control The mode of the control is adjusted based on the displacement amount measured after the process of removing the variation in the measured value of the displacement amount due to the vibration of the voltage.

  In the above configuration, the displacement amount is measured after the processing for removing the fluctuation is performed, and thus the displacement amount can be appropriately measured. For this reason, it is possible to suitably adjust the control mode of the displacement amount using the measured displacement amount. Then, by using the displacement amount thus measured, it is possible to suitably adjust the displacement control mode when the drive device is manufactured.

  In addition, you may perform the measurement of the said displacement amount by the method in any one of the said means 4-8. Further, as the above control, chopper control may be applied as shown in the means 9.

(First embodiment)
Hereinafter, a first embodiment in which a method for measuring a displacement amount 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 (current amount increasing operation). 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 (current amount reduction operation). 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 (current amount increasing operation). 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 (current amount reduction operation). 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.

  However, when the voltage is measured at the end of the on / off operation, the measured voltage may fluctuate and thus 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 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 in detail above, the following effects can be obtained.

  (1) The displacement amount of the piezo element PE was measured based on the integral value of any of the current flowing through the piezo element PE, the voltage of the piezo element PE, and the product of the current and the voltage. For this reason, it is possible to appropriately measure the displacement amount of the piezo element PE as a unique value using an electrical state quantity in which voltage oscillation or the like is suitably suppressed.

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

  (3) 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.

  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 in the vicinity of “0V” of the voltage of the piezo element PE, it becomes difficult for the current to flow, and it is difficult to make it completely “0V”. In order to completely set the voltage of the piezo element PE to “0 V”, the short switch 48 is turned on.

  On the other hand, if the electrical state quantity of the piezo element PE is measured during the reduction control of the piezo element, and the discharge speed is measured by the time required for the state quantity to reach a predetermined value, the voltage of the piezo element PE There is a risk that the discharge rate may not be uniquely determined due to the vibration of. 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 effects according to the above (1) and (3) of the first embodiment, the following effects can be further 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.

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

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

  In each of the above embodiments, the electrical state quantity of the piezo element PE, which is measured as an equivalent value of the displacement amount of the piezo element PE, represents the voltage of the piezo element PE, the current flowing through the piezo element PE, the voltage and the current. Although any integral value of the product 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, even if a function that includes the voltage as an independent variable is subjected to a smoothing process or the like, a process that removes a variation in the measured value of the displacement due to the vibration of the voltage of the piezo element PE is performed. Good.

  In the first embodiment, the displacement amount of the piezo element PE is indirectly measured from the electrical state amount in synchronization with the end of the on / off operation. However, the present invention is not limited to this. When the control is performed to control the displacement amount of the piezo element PE to a desired value, the displacement amount of the piezo element PE cannot be appropriately measured as a unique value due to vibration of the voltage of the piezo element PE or the like. The application of the present invention is effective because of fear.

  -In the said 2nd and 3rd embodiment, even if it does not measure the discharge rate in the place where a voltage will be "10-60V", the effect according to said (1) can be acquired.

  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, when the drive device is manufactured, the displacement amount of the piezo element PE is indirectly measured from the electrical state amount, and the displacement amount control is adjusted based on the measured displacement amount. It is not restricted at the time of manufacture of the said drive device. That is, even when the displacement amount (electrical state amount) 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 displacement amount is reduced. When measuring at the time of control, there is a possibility that the displacement amount cannot be measured as a unique value due to voltage oscillation of the piezo element PE, etc., so that the application of the present invention is effective. At this time, in the third embodiment, when the discharge rate is measured using the processing by the digital circuit, the digital circuit is configured by the microcomputer 22 or the like. In the third embodiment, when the discharge rate is measured using processing by an analog circuit, for example, as shown in FIG. 18, a CR circuit 60 for measuring the voltage of the piezo element PE is provided. Is desirable. The CR circuit 60 is connected in parallel with both terminals of the piezo element PE. In the CR circuit 60, the voltage of the connection node N8 of the resistors 61 and 62 connected in series is taken in by the control device 20. A capacitor 63 is connected in parallel with the resistor 62 in order to smooth the voltage at the node N8.

  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. Furthermore, the control mode of the displacement amount of the piezo element PE is not limited to that illustrated in FIG. 3 above, and the above control is performed by repeating the increase and decrease operations of the amount of current flowing through the piezo element PE. If it is.

The block diagram which shows the structure of 1st Embodiment of the measuring method of the displacement amount 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 measuring method of the displacement amount at the time of control of the displacement amount of the piezo element concerning the embodiment. The time chart explaining the measuring method of the displacement amount at the time of control of the displacement amount of the piezo element concerning the embodiment. The time chart explaining the measuring method of the displacement amount at the time of control of the displacement amount of the piezo element concerning the embodiment. The time chart explaining the subject which 2nd Embodiment tends to solve. The time chart explaining the measuring method of the displacement amount concerning the embodiment. The time chart explaining the measuring method of the displacement amount concerning the embodiment. The time chart explaining the measuring method of the displacement amount concerning the embodiment. The time chart explaining the measuring method of the amount of displacement concerning a 3rd embodiment. The circuit diagram which shows the structure of the drive device of the piezoelectric actuator concerning the modification of 3rd 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 (13)

For controlling the displacement amount of the piezo element by repeating the increase and decrease operations of the amount of current flowing through the piezo element functioning as an actuator, the displacement amount is indirectly determined by the electrical state quantity of the piezo element. It is a method to measure,
A piezo actuator that measures the amount of displacement during the control based on an integral value of a function time including at least one of an amount of current flowing through the piezo element and a voltage of the piezo element as an independent variable. Of measuring the amount of displacement.   The method for measuring a displacement amount of a piezo actuator according to claim 1, wherein the integral value is an integral value with respect to a time of any one of the voltage, the current, and a product of the voltage and the current. For controlling the displacement amount of the piezo element by repeating the increase and decrease operations of the amount of current flowing through the piezo element functioning as an actuator, the displacement amount is indirectly determined by the electrical state quantity of the piezo element. It is a method to measure,
The displacement amount is measured based on the electrical state amount after the process of removing the variation in the measured value of the displacement amount due to the vibration of the voltage of the piezoelectric element during the control is performed. Of measuring the displacement of a piezo actuator.   4. The method for measuring a displacement amount of a piezo actuator according to claim 3, wherein the measurement is performed as measurement of an integral value according to a function time including a voltage of the piezo element as an independent variable.   The method for measuring a displacement amount of a piezo actuator according to claim 3, wherein the measurement is performed by measuring a value of a function including a voltage of the piezo element as an independent variable and performing a smoothing process.   6. The method for measuring a displacement amount of a piezo actuator according to claim 5, wherein the smoothing process is performed by smoothing the voltage of the piezoelectric element by at least one of a smoothing circuit and software.   The control of the displacement amount is control for reducing the piezoelectric element by discharging the electric charge charged in the piezoelectric element, and the measurement of the displacement amount is performed in order to grasp the reduction speed of the piezoelectric element. Item 7. A method for measuring a displacement amount of a piezo actuator according to any one of Items 1 to 6.   8. The piezo actuator according to claim 7, wherein the reduction speed is grasped as a time required for the piezo element to reduce to a point where the voltage of the piezo element corresponds to an arbitrary value within “10 to 60 V”. Of measuring the amount of displacement.   The measurement of the displacement amount of the piezo actuator according to claim 1, wherein the increase operation is performed as an ON operation of a switching element for chopper control, and the decrease operation is performed as an OFF operation of the switching element. Method. In the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the amount of current flowing through the piezo element functioning as an actuator,
And a means for measuring the amount of displacement at the time of control based on an integral value of a function time including at least one of an amount of current flowing through the piezoelectric element and a voltage of the piezoelectric element as an independent variable. Drive device for piezo actuator. In the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the amount of current flowing through the piezo element functioning as an actuator,
Means for measuring the amount of displacement based on the electrical state amount after the process of removing the variation of the measured value of the amount of displacement caused by the vibration of the voltage of the piezo element during the control; A drive device for a piezoelectric actuator characterized by the above. In the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the amount of current flowing through the piezo element functioning as an actuator,
Based on the displacement amount at the time of the control measured based on the integral value of the time including a function including at least one of the amount of current flowing through the piezoelectric element and the voltage of the piezoelectric element as an independent variable, the mode of the control is A drive device for a piezo actuator characterized by being adjusted. In the driving device of the piezo actuator for controlling the displacement amount of the piezo element by repeating the increase operation and the decrease operation of the amount of current flowing through the piezo element functioning as an actuator,
The mode of the control is adjusted based on the displacement amount measured after performing the process of removing the variation in the measured value of the displacement amount caused by the vibration of the voltage of the piezoelectric element during the control. A drive device for a piezoelectric actuator.

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