JP2005039990A - Piezo actuator drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize a charging and discharging process of a piezo actuator and reduce variation in behavior of expansion and contraction of a piezo actuator due to charging.
SOLUTION: Current adjusting means 4a and 4b for adjusting currents flowing through energization paths 31 and 32 between a piezoelectric actuator 2 and a capacitor 12 using a piezoelectric actuator 2 as a supply source or a supply destination, and driving power of the piezoelectric actuator 2 are detected. The power detection means 5, the target value output means 6 for outputting the target value of the driving power set in advance corresponding to each time point, and the detection value of the driving power as the target value for each time point of the driving period of the piezoelectric actuator 2. The charging / discharging control means 7 for controlling the current adjusting means 4a, 4b so as to obtain a value is provided to make the charging process and discharging process of the piezo actuator 2 uniform.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric actuator drive circuit.

  The piezo actuator uses a piezoelectric action of a piezoelectric material such as PZT, and is applied to, for example, a fuel injection device of an internal combustion engine and used as a means for switching between fuel injection and its stop in a fuel injection injector. Things are known. The piezo actuator has a capacitor structure in which piezoelectric layers and electrode layers made of a piezoelectric material are alternately stacked, and expands by charging and discharges when contracting. This is an actuator that is energized only when the piezo stack is extended and contracted.

  The piezo actuator drive circuit switches the operation state of the piezo actuator between expansion and contraction by driving by charging or discharging, and includes a power supply, current adjusting means for adjusting a current flowing using the piezo actuator as a supply destination or a supply source, Charge / discharge control means for controlling the current adjusting means when the piezoelectric actuator is driven.

  The drive voltage of the piezo actuator is required to have a voltage value that generates an electric field necessary to expand and contract the piezo stack. For this reason, the driving of the piezo actuator has conventionally been provided with a DC-DC converter for boosting a battery voltage, for example, 12 V to a high voltage of 150 V or more in a driving circuit (piezo actuator driving circuit). A capacitor is charged in advance from the DC converter to a capacitor at a high voltage, and the piezoelectric actuator is charged from a capacitor as a power source of the piezoelectric actuator. For example, a first energization path connecting a capacitor and a piezo actuator via an inductor, and a second energization path connecting the inductor and the piezo actuator bypassing the capacitor are provided. A charge switch for connecting / disconnecting one energization path and a discharge switch for connecting / disconnecting the second energization path are provided. When the piezo actuator is driven to charge, by repeatedly turning on and off the charging switch, a charging current that gradually increases during the on period of the charging switch is caused to flow through the first energization path, and gradually decreases by turning back at the peak current during the off period of the charging switch. A charging current is passed through the second energization path. During discharge driving of the piezo actuator, a discharge current that gradually increases during the ON period of the discharge switch is caused to flow through the second energization path by repeating ON / OFF of the discharge switch, and a discharge current that gradually decreases by returning to the peak current during the OFF period of the discharge switch. It flows in the first energization path.

  By the way, today, ceramic capacitors having a structure similar to that of a piezo stack have been put into practical use with a thickness of several μm, and the piezo stack has been made thinner and can be driven at a low voltage. It is thought to come. On the other hand, since the battery for automobiles tends to increase power consumption due to an increase in in-vehicle devices, it is considered to increase the battery voltage in order to reduce loss. The hybrid vehicle is equipped with a high-voltage battery system. For this reason, a circuit configuration in which the DC-DC converter is omitted is also being studied.

Further, as a device that does not use a DC-DC converter in the piezo actuator drive circuit, Patent Document 1 below discloses a circuit configuration in which a transformer is interposed between the battery and the piezo actuator, and the transformer boosting action is disclosed. By utilizing this, a high drive voltage can be applied to the piezo actuator. In this device, a charge switch is provided in the energization path connecting the battery and the primary coil, and a discharge switch is provided in the energization path connecting the piezo actuator and the secondary coil. In the charge drive, the charge switch is turned on and the current from the battery is supplied to the primary coil of the transformer, and then the charge switch is turned off to supply the flyback current to the secondary coil to charge the piezo actuator. . In the discharge drive, the discharge switch is turned on to pass a current from the piezo actuator to the secondary coil of the transformer, and then the discharge switch is turned off to flow the flyback current to the secondary coil. In this case, charging and discharging proceed by repeatedly turning on and off the switch.
JP 2002-101673 A

  However, in the conventional technique, the charging process and the discharging process are not uniform due to fluctuations in the output voltage of the capacitor and battery, that is, the output voltage of the power supply, and the fluctuation in the capacity of the piezo actuator, and the required charge amount is required. Time varies. For this reason, when the piezoelectric actuator is extended, the behavior is not uniform when the piezoelectric actuator is reduced, and for example, the extension speed and the reduction speed vary. Speaking of an example applied to the fuel injection device, there is a risk that the metering accuracy of the injection amount and the controllability of the injection timing will be reduced. In particular, it becomes a problem in the case of multi-injection including injection with a small injection amount command value.

  The present invention has been made in view of the above circumstances, and provides a piezo actuator driving circuit in which a charging process or a discharging process is uniform, charging and discharging are completed over a predetermined time, and the behavior of the piezo actuator is uniform. With the goal.

According to the first aspect of the present invention, there is provided a drive circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, and a power source and a current flowing with the piezo actuator as a supply destination or a supply source are adjusted. In a piezo actuator drive circuit comprising current adjustment means and charge / discharge control means for controlling the current adjustment means when the piezo actuator is driven,
Power detection means for detecting drive power of the piezoelectric actuator;
A target value output means for outputting a target value of the driving power set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means ends the driving period when the detected value of the driving power becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. Then, control for the current adjusting means is set.

  Since the driving power of the piezo actuator changes at a target value to be reached at each time point, the charging process and the discharging process are made uniform regardless of the output voltage of the power source, the variation in the capacity of the piezo actuator, and the like. For this reason, when a predetermined time has elapsed, it is known that a target amount of energy has been supplied or recovered by the piezoelectric actuator. Thereby, the dispersion | variation in the behavior of a piezo actuator can be reduced.

According to a second aspect of the present invention, there is provided a drive circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, and adjusting a power source and a current flowing using the piezo actuator as a supply destination or a supply source. In a piezo actuator drive circuit comprising current adjustment means and charge / discharge control means for controlling the current adjustment means when the piezo actuator is driven,
Current detecting means for detecting a driving current of the piezoelectric actuator;
A target value output means for outputting a target value of the driving current set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means ends the driving period when the detected value of the driving current becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. Then, control for the current adjusting means is set.

  Since the driving current of the piezo actuator changes at a target value that should be reached at each time point, the charging process and the discharging process are made uniform regardless of variations in the output voltage of the power supply and the capacity of the piezo actuator. For this reason, when a predetermined time has elapsed, it is known that a target amount of charge has been supplied or recovered by the piezo actuator. Thereby, the dispersion | variation in the behavior of a piezo actuator can be reduced.

  According to a third aspect of the present invention, in the configuration of the first or second aspect, the target value is a constant value.

  By setting the target values of the drive power and drive current to constant values, the output of the target value and the control of the current adjusting means can be easily performed. In addition, since the energy and charge, which are integrated values of drive power and drive current, change linearly with respect to time, the state of the piezo actuator can be easily grasped.

According to a fourth aspect of the present invention, there is provided a drive circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, and adjusting a power source and a current flowing using the piezo actuator as a supply destination or a supply source. In a piezo actuator drive circuit comprising current adjustment means and charge / discharge control means for controlling the current adjustment means when the piezo actuator is driven,
Voltage detecting means for detecting a voltage between terminals of the piezoelectric actuator;
A target value output means for outputting a target value of the voltage between the terminals set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means sets the drive period when the detected value of the inter-terminal voltage becomes the target value at each time point of the drive period and when the elapsed time from the start of the drive reaches a predetermined time. The control for the current adjusting means is set so as to end.

  Since the voltage between the terminals of the piezo actuator changes at a target value to be reached at each time point, the charging process and the discharging process are made uniform regardless of variations in the output voltage of the power source and the capacity of the piezo actuator. Thereby, the dispersion | variation in the behavior of a piezo actuator can be reduced.

  According to a fifth aspect of the present invention, in the configuration of the fourth aspect of the invention, the target value changes linearly with respect to the elapsed time from the start of driving.

  Since the voltage between the terminals of the piezoelectric actuator changes linearly with time, the state of the piezoelectric actuator can be easily grasped.

According to a sixth aspect of the present invention, there is provided a drive circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, and adjusting a power source and a current flowing using the piezo actuator as a supply destination or a supply source. In a piezo actuator drive circuit comprising current adjustment means and charge / discharge control means for controlling the current adjustment means when the piezo actuator is driven,
Drive energy detection means for detecting drive energy by detecting drive power of the piezoelectric actuator and integrating the detected drive power from the start of the drive period of the piezoelectric actuator;
A target value output means for outputting a target value of the driving energy set in advance corresponding to each time point for each time point of the driving period of the piezo actuator;
The charge / discharge control means ends the driving period when the detected value of the driving energy becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. Thus, the control for the current adjusting means is set.

  During the drive period of the piezo actuator, the drive energy from the start of the drive period changes at the target value that should be reached at each point of time, so the charging and discharging processes depend on the output voltage of the power supply and the variation in the capacity of the piezo actuator. It is made uniform. For this reason, when a predetermined time has elapsed, it is known that a target amount of energy has been supplied or recovered by the piezoelectric actuator. Thereby, the dispersion | variation in the behavior of a piezo actuator can be reduced.

A seventh aspect of the present invention proposes a preferred basic configuration by applying the first to sixth aspects of the present invention, wherein a piezoelectric actuator driving circuit is connected to the power source and the piezoelectric actuator via an inductor. 1 energization path and a second energization path that bypasses the power source and connects the inductor and the piezoelectric actuator,
As the current adjusting means, a charging switch for connecting and disconnecting the first energization path is provided,
The charge / discharge control means causes a charging current that gradually increases during an ON period of the charge switch to flow through the first energization path by repeatedly turning on and off the charge switch when the piezo actuator is charged, and turns off the charge switch. The charging current that gradually turns back by the peak current during the period is set to flow through the second energization path.

The invention according to claim 8 proposes another preferred basic configuration to which the invention of claims 1 to 6 is applied, and a first energization path connecting the power source and the piezoelectric actuator via an inductor. And a second energization path that bypasses the power source and connects the inductor and the piezoelectric actuator,
As the current adjusting means, a discharge switch for connecting and disconnecting the second energization path is provided,
When the piezoelectric actuator is driven to discharge, the charge / discharge control means causes a discharge current that gradually increases during an ON period of the discharge switch to flow through the second energization path by repeating ON / OFF of the discharge switch, thereby turning OFF the discharge switch. The discharge current that is gradually reduced by turning back at the peak current during the period is set to flow through the first energization path.

  According to a ninth aspect of the present invention, in the configuration of the seventh or eighth aspect of the invention, the charge / discharge control means uses the two values sandwiching the target value as threshold values and the detected value and the threshold value. Comparing means for binary comparison of the magnitude of the comparison, the judgment output when the detected value exceeds the threshold value on the large side and when the detected value falls below the threshold value on the small side And a comparison means having hysteresis that switches between, and based on the determination output, the switch is turned off when the detected value exceeds the large threshold value, and the detected value falls below the small threshold value. Set the switch to turn on when

  If the two threshold values sandwiching the target value are set to the desired sandwiching width, a filter effect that excludes disturbance noise and the like can be exhibited, and the target charge / discharge amount can be controlled with high accuracy.

  According to a tenth aspect of the present invention, in the configuration of the first to ninth aspects, the power source outputs a voltage between terminals of the battery.

  In such a configuration in which power is supplied without going through the DC-DC converter, variations in battery voltage directly affect the charging process of the piezo stack. According to the inventions of claims 1 to 8, the charging process and discharging process of the piezo stack are made uniform. This is particularly suitable.

(First embodiment)
FIG. 1 shows a piezo actuator drive circuit of the present invention. The piezo actuator 2 to be driven by the piezo actuator drive circuit is mounted on, for example, an injector that injects fuel in an internal combustion engine. In the case of a configuration having an injector for each cylinder, the piezo actuators 2 are connected in parallel by the number of cylinders, and a switch for selecting a cylinder is provided in series corresponding to each piezo actuator 2 on a one-to-one basis. The cylinder selection switch is turned on for the piezo actuator 2 corresponding to the cylinder to be injected, and only the piezo actuator 2 is selectively driven. The piezo actuator drive circuit receives a drive signal that defines the start timing of charge drive and the start time of discharge drive of the piezo actuator 2 from the ECU 9. If the drive signal conforms to the internal combustion engine, the valve opening timing and the valve closing timing of the injector are defined, and the length thereof defines the injection time. The ECU 9 is an electronic control unit constituted by a microcomputer or the like, and outputs a drive signal or the like based on a detection signal of a sensor that detects an operation state of each part of the internal combustion engine, for example.

  The power supply 1 has a vehicle-mounted battery 11 and a capacitor 12 connected in parallel to the output terminal thereof, and outputs a voltage for charging the piezo actuator 2. For example, a battery system of 42V can be adopted as the battery 11. The capacitor 12 preferably has a sufficiently large capacitance.

  A first energization path 31 connecting the power source 1 and the piezo actuator 2 via the inductor 301 is provided, and the first energization path 31 further includes a first current in series between the power source 1 and the inductor 301. A switching element 4a is interposed. The first switching element 4a is composed of a MOSFET, and a parasitic diode (hereinafter referred to as a first parasitic diode) 41a is connected so that a voltage between terminals of the capacitor 12 (hereinafter referred to as a capacitor voltage as appropriate) is reverse biased. Is done.

  Further, the inductor 301 and the piezoelectric actuator 2 are connected by the second energization path 32. The energization path 32 has a second switching element 4b connected to the midpoint of connection between the inductor 301 and the first switching element 4a. The second energization path 32 bypasses the power source 1 and forms a closed circuit that passes through the inductor 301, the piezoelectric actuator 2, and the second switching element 4b. The second switching element 4b is also composed of a MOSFET, and its parasitic diode (hereinafter referred to as second parasitic diode) 41b is connected so that the capacitor voltage is reverse-biased.

  Control signals are respectively input to the gates of the switching elements 4a and 4b from driver circuits 8a and 8b, which will be described later. When the switching elements 4a and 4b are turned on and off, currents that cause the piezoelectric actuator 2 to be a supply destination or a supply source (Hereinafter, referred to as piezo actuator current as appropriate) is adjusted. The switching element 4a is for driving the piezoelectric actuator 2 to be charged, and is hereinafter referred to as a charging switch 4a as appropriate. The switching element 4b is for discharge driving of the piezo actuator 2, and is hereinafter referred to as a discharge switch 4b as appropriate.

  A resistor 51 having a low resistance value (for example, 0.01Ω) is provided between the piezoelectric actuator 2 and the ground. The piezoelectric actuator current is detected by the voltage between the terminals.

  A voltage between terminals of the piezoelectric actuator 2 (hereinafter referred to as a piezoelectric actuator voltage as appropriate) is input to the multiplication circuit 53 through the buffer 52 together with a voltage between terminals of the resistor 51 as a current detection signal. The multiplication circuit 53 constitutes the power detection means 5 together with the buffer 52 and the resistor 51, and outputs a product proportional to the product of the piezo actuator voltage and the piezo actuator current, that is, the drive power of the piezo actuator 2 (hereinafter referred to as an output signal). Called power detection signal). For example, 1V is output for 100W. The buffer 52 is provided in order to receive the piezoelectric actuator voltage with high impedance.

  The power detection signal is used to control the charge switch 4a and the discharge switch 4b in the switch control circuit 7 which is a charge / discharge control means. In the switch control circuit 7, the comparator 71a, resistors 72a and 73a, the AND gate 74a, and the one-shot circuit 75a constitute a circuit part for controlling the charge switch 4a. Further, the inverting amplifier 70b, the comparator 71b, the resistors 72b and 73b, the AND gate 74b, the one-shot circuit 75b, and the inverter 76b that invert positive and negative constitute a circuit part for controlling the charge switch 4b.

  First, the circuit portion for controlling the charge switch 4b will be described. The power detection signal is input to the negative input terminal of the comparator 71a. The output signal of the reference voltage generation circuit 6a is input to the + input terminal of the comparator 71a via the resistor 72a. The reference voltage generation circuit 6a is variable in output voltage, and generates and outputs a reference voltage set by the ECU 9. The input voltage at the (+) input terminal of the comparator 71a is subjected to hysteresis by the resistor 72a and the resistor 73a connected between the (+) input terminal and the output terminal of the comparator 71a. If the power detection signal is sufficiently low, the output voltage of the comparator 71a is at “1” level. If the magnitude of the power detection signal exceeds the reference voltage + hysteresis, the output voltage of the comparator 71a becomes “0” level. At the same time, the input voltage at the (+) input terminal decreases to the reference voltage minus the hysteresis. On the contrary, when the magnitude of the power detection signal is lower than the reference voltage minus the hysteresis from this state, the output voltage of the comparator 71a becomes “1” level and the input voltage at the (+) input terminal becomes the reference voltage + Increases to hysteresis.

  The output voltage of the comparator 71a is input to an AND gate 74a that generates an input signal to the driver circuit 8a of the charging switch 4a. The driver circuit 8a turns on the charging switch 4a when the output of the AND gate 74a is at "1" level. . In addition to the output signal of the comparator 71a, the output signal of the one-shot circuit 75a is input to the AND gate 74a. The one-shot circuit 75a outputs a pulse signal having a fixed length (150 μsec) when an external drive signal is triggered by a rising edge. Therefore, when the drive signal rises to the “1” level, the charging switch 4a is switched on and off based on the magnitude of the power detection signal for a certain period of time immediately after that. When the pulse signal is not output, the charging switch 4a is fixed off. That is, the pulse signal defines the length of the charging period of the piezo actuator 2.

  On the other hand, the circuit portion for controlling the discharge switch 4b is a circuit having a similar basic configuration to the circuit for controlling the charge switch 4a, and the difference will be mainly described. At the time of discharge driving, the piezo actuator current flows with the piezo actuator 2 as the supply source, so the direction is reversed and the power detection signal takes a negative value. For this reason, the power detection signal is inverted by the inverting amplifier 70b and input to the (−) input terminal of the comparator 71b. The output signal of the reference voltage generation circuit 6b is input to the + input terminal of the comparator 71b via the resistor 72b. The reference voltage generation circuit 6b generates and outputs a reference voltage set by the ECU 9. Until the magnitude of the power detection signal exceeds the reference voltage + hysteresis, the output voltage of the comparator 71b is “1” level. When the magnitude of the power detection signal exceeds the reference voltage + hysteresis, The output voltage of the comparator 71b becomes “0” level, and the input voltage at the (+) input terminal decreases to the reference voltage−hysteresis. On the contrary, when the magnitude of the power detection signal is lower than the reference voltage-hysteresis from this state, the output voltage of the comparator 71b becomes “1” level and the input voltage at the (+) input terminal becomes the reference voltage + It rises to the amount of hysteresis.

  The logic output of the comparator 71b is input to an AND gate 74b that generates an input signal to the driver circuit 8b of the discharge switch 4b. The driver circuit 8b turns on the discharge switch 4b when the logic output of the AND gate 74b is at "1" level. The one-shot circuit 75b is controlled by a drive signal input via the inverter 76b, and outputs a pulse signal having a fixed length (for example, 150 μsec) at the rising edge of the output signal of the inverter 76b, that is, the falling edge of the drive signal. To do. Therefore, when the drive signal falls to the “0” level, the discharge switch 4b is switched on and off based on the magnitude of the power detection signal for the certain length of time immediately thereafter. That is, the pulse signal defines the length of the discharge period of the piezoelectric actuator 2.

  FIG. 2 is a timing chart showing the operation of each part of the piezo actuator drive circuit. The first half is when the piezo actuator 2 is extended, that is, when it is charged, and the second half is when it is reduced, that is, when it is discharged. The reference voltage of the reference voltage generation circuits 6a and 6b set by the ECU 9 will be described as a constant value during the charge drive period and the discharge drive period. In the initial state, the capacitor 12 is charged to the battery voltage. The charge switch 4a and the discharge switch 4b are off. The piezoelectric actuator voltage is 0V. Here, when the drive signal rises to the “1” level, the one-shot circuit 75a is triggered to output a pulse signal that defines the charging period. The power detection signal from the multiplier circuit 53 is 0V, and the logical output of the comparator 71a is at “1” level. Accordingly, the charging switch 4 a is turned on, and charging of the piezo actuator 2 is started using the first energization path 31. The piezoactuator current increases, and as the charging proceeds, the piezoactuator voltage increases. As a result, the drive power also increases. When the power detection signal exceeds the reference voltage + hysteresis, the logic output of the comparator 71a changes to “0” level and the charge switch 4a is turned off. However, the energy stored in the inductor 301 causes the second parasitic diode The gradually decreasing flywheel current continues to flow to the piezo actuator 2 using the second energization path 32 passing through 41b. At this time, the driving power gradually decreases.

  When the magnitude of the power detection signal falls below the reference voltage-hysteresis, the logic output of the comparator 71a becomes “1” level again, and the charge switch 4a is turned on. This is repeated. Since the reference voltage is a constant value, the driving power is maintained substantially constant at each point in the charging period. The driving power at this time is defined by the reference voltage output from the reference voltage generating circuit 6a, and the reference voltage generating circuit 6a outputs the target value of the driving power at each point in the charging period. As a result, the driving power is maintained substantially constant at the target value defined by the reference voltage at each time point during the charging period, and the accumulated energy of the piezo actuator 2 given as an integrated value of the driving power is the elapsed time from the start of charging. It rises in direct proportion to the time, that is, the elapsed time since the drive signal was output.

  When the output period of the pulse signal from the one-shot circuit 75a ends and the input signal of the AND gate 74a reaches the “0” level, the charging switch 4a is fixed to OFF and the charging is completed.

  As described above, since the accumulated energy of the piezo actuator 2 rises in direct proportion to the elapsed time from the start of charging, the process in which the accumulated energy of the piezo actuator 2 follows regardless of the change in the battery voltage or the change in the capacity of the piezo actuator 2. That is, the charging process is uniform. Further, the accumulated energy when the charging switch 4a is fixed off, that is, when the charging is completed can be made constant without integrating the integrated value of the driving power.

  Next, the operation when the piezoelectric actuator 2 is reduced, that is, when discharging is described. As described above, when the piezo actuator 2 has been extended, the target amount of energy stored in the piezo actuator 2 is accumulated. The charge switch 4a and the discharge switch 4b are off. The piezo actuator voltage is a voltage corresponding to the stored energy, but is different when the capacity of the piezo actuator 1 changes with temperature or the like. Here, when the drive signal falls to the “0” level, the one-shot circuit 75b is triggered to output a pulse signal that defines the discharge period. The power detection signal from the multiplier circuit 53 is 0V, and the logical output of the comparator 71b is at “1” level. Accordingly, the discharge switch 4b is turned on, and discharge is started using the second energization path 32. The piezo actuator current increases, and as the discharge proceeds, the piezo actuator voltage decreases. As a result, the drive power also increases. When the magnitude of the power detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71b changes to the “0” level and the discharge switch 4b is turned off, but the first energy is stored in the inductor 301. The gradually decreasing flywheel current continues to flow from the piezo actuator 2 to the capacitor 12 using the first energization path 31 passing through the parasitic diode 41a. At this time, the driving power gradually decreases.

  When the magnitude of the power detection signal falls below the reference voltage-hysteresis, the output of the comparator 71b becomes “1” level again, and the discharge switch 4b is turned on. This is repeated. Therefore, the driving power is maintained substantially constant at each point in the discharge period. The driving power at this time is defined by the reference voltage output from the reference voltage generating circuit 6b, and the reference voltage generating circuit 6b outputs the target value of the driving power at each point in the discharge period. Accordingly, the driving power is maintained substantially constant at the target value defined by the reference voltage at each time point during the discharging period, and the accumulated energy of the piezo actuator 2 that is an integrated value of the driving power is the elapsed time from the start of discharging. That is, it linearly decreases with respect to the elapsed time after the drive signal is output.

  When the pulse signal from the one-shot circuit 75b is not output, the output of the AND gate 74b becomes “0” level, the discharge switch 4b is fixed to OFF, and the discharge is completed.

  As described above, since the accumulated energy of the piezo actuator 2 linearly decreases with respect to the elapsed time from the start of discharge, the remaining energy of the piezo actuator 2 follows regardless of the change in the battery voltage or the change in the capacity of the piezo actuator 2. The process, that is, the discharge process is uniform. Further, the discharge switch 4b is fixed to OFF with the completion of the recovery of the stored energy without integrating the integrated value of power.

  Thus, according to this piezo actuator drive circuit, the charging process and discharging process of the piezo actuator 2 are uniform, and variations in behavior such as expansion and contraction of the piezo actuator 2 can be reduced. Thereby, for example, the injection timing and the injection amount can be made constant. The ECU 9 is configured so that the reference voltage generation circuits 6a and 6b output a constant voltage as a reference voltage, but according to the required operating characteristics of the piezo actuator 2, the driving period (charging period, discharging period) is increased. For each time point, a reference voltage that defines a target value of driving power corresponding to each time point may be output. For example, the reference voltage is high in the first half of the driving period and low in the second half. When the reference voltage is a constant voltage, the reference voltage generation circuits 6a and 6b need not be configured so that the output voltage value is set by the ECU 9.

  FIG. 3 shows the change over time of the displacement of the piezo actuator during the charging process. The displacement of the piezo actuator increases as the accumulated energy increases with time. In the drawing, in addition to the present piezoelectric actuator drive circuit (present invention), another piezoelectric actuator drive circuit (comparative example) to be compared with the present piezoelectric actuator drive circuit is shown. In the control method of the comparative example, the charging switch 4a is driven at a constant ON period, and charging ends when a predetermined time elapses from the start of charging as the charging period. Then, during the charging period, an integrated value (driving energy) of the driving power of the piezo actuator is detected, and the length of the on period in the next charging period is determined based on the difference between the driving energy at the end of the charging period and its target value. It is reset. Even in this case, the desired displacement can be obtained by making the drive energy of the piezo actuator constant at the target value, but when the ambient temperature is low and the capacity of the piezo actuator is reduced, the piezo actuator voltage rises at once due to charging. However, because the difference between the power supply voltage and the piezo actuator voltage becomes small and the current does not flow easily, the energy input speed to the piezo actuator tends to decrease toward the end of the charging period. On the other hand, when the ambient temperature is high and the capacity of the piezo actuator is increased, the time constant of the resonance circuit composed of the piezo actuator and the inductor is increased, so that the off period of the charge switch at the beginning of the charging period is increased. For this reason, there is a tendency that the energy input speed to the piezo actuator becomes slower toward the initial side of the charging period. As described above, when the capacitance of the piezo actuator varies due to a change in ambient temperature, the displacement profile of the piezo actuator is not constant.

  On the other hand, in this piezo actuator driving circuit, the charging switch 4a is controlled so that the driving power becomes a target value defined by the reference voltage output from the reference voltage generating circuit 6a at each point in the charging period. The displacement of the piezo actuator 2 defined by the reference voltage output by the reference voltage generation circuits 6a and 6b regardless of variations in the capacity of the piezo actuator 2 at each time point in the middle of the charging period of a predetermined length. Is obtained over time. In the present embodiment, the target temporal profile of the displacement of the piezo actuator 2 is a straight line. For this reason, the reference voltage output from the reference voltage generation circuit 6a is set to a constant value at each time point in the charging period so that the temporal profile of the accumulated energy of the piezo actuator 2 is linear. Similarly, during the discharge period, it is a matter of course that a temporal profile of the displacement of the piezo actuator 2 defined by the reference voltage output from the reference voltage generating circuit 6b can be obtained regardless of variations in the capacitance of the piezo actuator 2. .

(Second Embodiment)
FIG. 4 shows a piezo actuator drive circuit according to the second embodiment of the present invention. The basic structure of this piezo actuator drive circuit is the same as that of the first embodiment. In the figure, the same reference numerals are given to the parts that operate in the same way as in the first embodiment, and the differences from the first embodiment. The explanation will be focused on.

  In this piezo actuator drive circuit, the input signal input to the (−) input terminal of the comparator 71a and the input signal input to the (−) input terminal of the comparator 71b via the inverting amplifier 70b are supplied to the piezo actuator 2 as the supply destination. This is a voltage between terminals of the resistor 51 which is current detection means for detecting a current (piezo actuator current) flowing as a supply source (hereinafter, the voltage between the terminals is appropriately referred to as a current detection signal). Further, the switch control circuit 7A inputs the reference voltages output from the reference voltage generation circuits 6aA and 6bA and the resistance values of the resistors 72aA, 73aA, 72bA, and 73bA that define the hysteresis amount to the (−) input terminal of the comparator 71a. As the input signal to be replaced with the current detection signal is set as appropriate. The reference voltage generation circuits 6aA and 6bA output a constant voltage set by the ECU 9A as in the first embodiment. The ECU 9A substantially does not change the set voltage values of the reference voltage generation circuits 6aA and 6bA as necessary when the input signal input to the (−) input terminal of the comparator 71a is replaced with the current detection signal. The same as that of the first embodiment.

  FIG. 5 is a timing chart showing the operating state of each part of the piezo actuator drive circuit. When the drive signal becomes “1” level, the one-shot circuit 75a is triggered and a pulse signal defining the charging period is output. The current detection signal is 0V, and the output of the comparator 71a is at the “1” level. Accordingly, the charging switch 4a is turned on and charging is started. The piezo stack current increases and charging proceeds. When the current detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71a changes to “0” level and the charging switch 4a is turned off. However, the flywheel current that gradually decreases due to the energy accumulated in the inductor 301 is reduced. The piezo actuator 2 continues to flow as a supply destination.

  When the current detection signal falls below the reference voltage-hysteresis, the logic output of the comparator 71a becomes “1” level again, and the charge switch 4a is turned on. This is repeated. Therefore, the piezo actuator current is maintained substantially constant in the range of the reference voltage ± hysteresis. As a result, the accumulated charge amount of the piezo actuator 2, which is an integrated value of the piezo actuator current, increases in direct proportion to the elapsed time from the start of charging, that is, the elapsed time after the drive signal is output.

  When the pulse signal from the one-shot circuit 75a is not output, the logic output of the AND gate 74b becomes “0” level, the charge switch 4b is fixed to OFF, and charging is completed.

  As described above, since the charge amount of the piezo actuator 2 increases in direct proportion to the elapsed time from the start of charging, the process in which the accumulated charge of the piezo actuator 2 follows regardless of the change in the battery voltage or the change in the capacity of the piezo actuator 2. That is, the charging process is uniform. Further, without accumulating the integrated value of the piezo actuator current, the accumulated charge amount when the charging switch 4a is fixed off, that is, when the charging is completed can be set as a target charge amount.

  Next, the operation when the piezoelectric actuator 2 is reduced, that is, when discharging is described. As described above, when the piezo actuator 2 has been extended, a predetermined amount of electric charge is accumulated in the piezo actuator 2. The charge switch 4a and the discharge switch 4b are off. The piezo actuator voltage is a voltage corresponding to the amount of charge, but is different when the capacity of the piezo actuator 2 changes with temperature or the like. Here, when the drive signal becomes “0” level, the one-shot circuit 75b is triggered to output a pulse signal that defines the discharge period. The current detection signal is 0 V, and the output of the comparator 71b is “1” level. Accordingly, the discharge switch 4b is turned on and discharge is started. The piezo actuator current increases, and as the discharge proceeds, the piezo actuator voltage decreases. The direction of the current is opposite to that during charging. When the current detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71b changes to “0” level and the discharge switch 4b is turned off. However, the flywheel current that gradually decreases due to the energy accumulated in the inductor 301 is reduced. The flow continues using the piezo actuator 2 as the supply source.

  When the current detection signal falls below the reference voltage-hysteresis, the logic output of the comparator 71b becomes “1” level again, and the discharge switch 4b is turned on. This is repeated. Therefore, the discharge current is maintained substantially constant. As a result, the charge amount of the piezoelectric actuator 2 decreases linearly with respect to the elapsed time from the start of discharge, that is, the elapsed time after the drive signal is output.

  When the pulse signal from the one-shot circuit 75b is not output, the logic output of the AND gate 74b becomes “0” level, the discharge switch 4b is fixed to OFF, and the discharge is completed.

  As described above, since the charge amount of the piezo actuator 2 linearly decreases with respect to the elapsed time from the start of discharge, the remaining charge of the piezo actuator 2 follows regardless of the fluctuation of the battery voltage or the capacity of the piezo actuator 2. The process and discharge process are uniform. Further, the discharge switch is fixed to OFF with the completion of the collection of the accumulated charges without calculating the integrated value of the current.

  Thus, according to this piezo actuator drive circuit, the charging process and discharging process of the piezo actuator 2 are uniform, and variations in the behavior of the piezo actuator 2 can be reduced. Thereby, for example, the injection timing and the injection amount can be made constant.

(Third embodiment)
FIG. 6 shows a piezo actuator drive circuit according to a third embodiment of the present invention. The basic structure of this piezo actuator drive circuit is the same as that of the first embodiment. In the figure, the same reference numerals are given to the parts that operate in the same way as in the first embodiment, and the differences from the first embodiment. The explanation will be focused on.

  In this piezo actuator drive circuit, two resistors 54 and 55 connected in series are provided between both terminals of the piezo actuator 2 in place of the resistor 51 for current detection, and the piezo actuator voltage is divided. Press. Resistors 54 and 55 have high resistance. For example, the resistor 54 is 900 kΩ and the resistor 55 is 100 kΩ. The resistors 54 and 55 together with the buffer 56 that receives the divided voltage constitute voltage detecting means 5B that detects the piezoelectric actuator voltage. The output of the buffer 56 is output to the (−) input terminals of the comparators 71a and 71b (hereinafter, the output signal of the buffer circuit 56 is appropriately referred to as a voltage detection signal).

  In the switch control circuit 7B, the comparators 71a and 71b are connected to resistors 72aB and 73aB and resistors 72bB and 73bB for applying hysteresis, respectively, as in the above embodiments.

  The reference voltage generation circuit 6B is target value output means for generating a reference voltage input to the (+) input terminals of the comparators 71a and 71b via the resistors 72aB and 72bB, and changes the output according to the elapsed time. It has become. A capacitor 61 is connected to the resistors 72aB and 72bB, and charging and discharging are performed by constant current circuits 62a and 62b. The first constant current circuit 62 a is connected to the positive voltage source 63 and charges the capacitor 61. The second constant current circuit 62b is connected to the ground 64 and discharges the capacitor 61. The first constant current circuit 62a operates while a pulse signal is output from the one-shot circuit 75a, and the second constant current circuit 62b operates while a pulse signal is output from the one-shot circuit 75b. The current value supplied by the constant current circuits 62a and 62b is set by the ECU 9B, for example, by the duty of the pulse signal that opens and closes the charge / discharge circuit of the capacitor 61 as the current value setting signal.

  Only the output signal of the comparator 71b out of the comparators 71a and 71b is logically inverted by the inverter 77b and input to the AND gate 74b.

  FIG. 7 is a timing chart showing the operating state of each part of the piezo actuator driving circuit. When the driving signal becomes “1” level, the one-shot circuit 75a is triggered and a pulse signal defining the charging period is output. The voltage detection signal is 0V, and the logic output of the comparator 71a is at the “1” level. On the other hand, charging of the capacitor 61 is started by the output of the pulse signal, and the reference voltage starts to rise, so that the logical output of the comparator 71a changes to “0” level. Accordingly, the charging switch 4a is turned on and charging is started. The piezo actuator voltage rises and charging proceeds. When the voltage detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71a changes to the “0” level and the charge switch 4a is turned off. However, the flywheel current that gradually decreases due to the energy accumulated in the inductor 301 is reduced. The actuator 2 continues to flow with the supply source, and the piezoelectric actuator voltage continues to rise.

  When the increase rate of the piezo actuator voltage becomes dull and the voltage detection signal falls below the reference voltage-hysteresis, the logic output of the comparator 71a becomes “1” level again, and the charge switch 4a is turned on. This is repeated.

  On the other hand, since the capacitor 61 is charged with a constant current, electric charge is stored in the capacitor 61 in direct proportion to the elapsed time after the drive signal rises to the “1” level, and the reference voltage generated by the capacitor 61 is It rises in direct proportion to the elapsed time. Therefore, the piezo actuator voltage rises in direct proportion to the elapsed time.

  When the output of the one-shot circuit 75a becomes “0” level, the logic output of the AND gate 74a becomes “0” level, the charging switch 4a is fixed to OFF, and charging is completed. At the same time, the operation of the constant current circuit 62a is turned off and the reference voltage is fixed.

  As described above, since the piezo actuator voltage rises in direct proportion to the elapsed time from the start of charging, the process that the piezo actuator voltage follows and the charging process are uniform regardless of the fluctuation of the battery voltage or the capacity of the piezo actuator 2. is there.

  Next, the operation when the piezoelectric actuator 2 is reduced, that is, when discharging is described. As described above, in a state where the piezo actuator 2 has been extended, the piezo actuator voltage is a specified voltage. The charge switch 4a and the discharge switch 4b are off. Here, when the drive signal becomes “0” level, the one-shot circuit 75b is triggered to output a pulse signal that defines the discharge period. The second constant current circuit 62b is turned on, and the capacitor 61 is discharged at a constant discharge rate. The discharge rate at this time is the current value of the constant current circuit 62b. As a result, the reference voltage decreases linearly with respect to the elapsed time from when the drive signal becomes “0” level. When the voltage detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71b becomes “0” level. Accordingly, the discharge switch 4 is turned on and discharge is started. A current flows through the capacitor 12 with the piezo actuator 2 as a supply source, the discharge proceeds, and the piezo actuator voltage decreases. When the voltage detection signal falls below the reference voltage-hysteresis, the output of the comparator 71b changes to “1” level and the discharge switch 4b is turned off. Continue to flow to the capacitor 12.

  At this time, since the discharge current is a gradually decreasing current, when the rate of decrease of the piezoelectric actuator voltage becomes slow and the voltage detection signal exceeds the reference voltage + hysteresis, the output of the comparator 71b becomes “0” level again, and the discharge The switch 4b is turned on. This is repeated. Therefore, the piezo actuator voltage decreases approximately linearly with respect to the elapsed time from the start of discharge.

  When the pulse signal from the one-shot circuit 75b is not output, the output of the AND gate 74b becomes “0” level, the discharge switch 4b is fixed to OFF, and the discharge driving of the piezoelectric actuator 2 is finished.

  As described above, since the piezo actuator voltage decreases linearly with respect to the elapsed time from the start of discharge, the process that the piezo actuator voltage follows, that is, the discharge process, regardless of the change in the battery voltage or the capacity of the piezo actuator 2. It is uniform.

  Thus, according to this piezo actuator drive circuit, the charging process and discharging process of the piezo actuator 2 are uniform, and variations in the behavior of the piezo actuator 2 can be reduced. Thereby, for example, the injection timing and the injection amount can be made constant. The ECU 9B is configured so that the constant current circuits 62a and 62b output a constant current as a reference voltage source, but according to the required operating characteristics of the piezo actuator 2, the driving period (charging period, discharging period) For each time point, the constant current value may be variably output so as to be a reference voltage that defines a target value of the drive voltage corresponding to each time point. For example, the constant current value is high in the first half of the driving period and low in the second half.

(Fourth embodiment)
FIG. 8 shows a piezo actuator drive circuit according to a fourth embodiment of the present invention. The basic structure of this piezo actuator drive circuit is the same as that of the first embodiment. In the figure, the same reference numerals are given to the parts that operate in the same way as in the first embodiment, and the differences from the first embodiment. The explanation will be focused on.

  In this piezo actuator driving circuit, an energy measuring circuit 53C is provided instead of the multiplication circuit, which receives as input the piezo actuator voltage and a detection signal of the current flowing into and out of the piezo actuator 2. The energy measuring circuit 53C constitutes the drive energy detecting means 5C together with the buffer 52 and the resistor 51. The energy measurement circuit 53C includes a multiplication circuit equivalent to the multiplication circuit of the first embodiment and an integration circuit that integrates a power detection signal output therefrom. From the integration circuit, an integrated value of the driving power of the piezoelectric actuator 2, that is, a signal proportional to the driving energy (driving energy detection signal) is output. The drive energy detection signal is a voltage signal that increases when the piezo actuator 2 is charged and decreases when the current takes a negative value during the discharge period, and serves as an index of the accumulated energy of the piezo actuator 2. In order to avoid accumulation of errors, the integration circuit may be reset, for example, prior to the start of the charging period, under the control of the ECU 9C.

  And this drive energy detection signal is input into the switch control circuit 7C which is a charging / discharging control means. Specifically, the input signal is input to the (−) input terminal of the comparator 71a and the input signal is input to the (−) input terminal of the comparator 71b via the inverting amplifier 70b.

  The reference voltage generation circuits 6aC and 6bC are target value output means for generating a reference voltage to be input to the (+) input terminals of the comparators 71a and 71b via the resistors 72aC and 72bC. The output is changed accordingly. The reference voltages output from the reference voltage generation circuits 6aC and 6bC and the resistance values of the resistors 72aC, 73aC, 72bC, and 73bC that define the hysteresis are input signals input to the (−) input terminal of the comparator 71a. As a matter of course, it can be adapted as appropriate.

  The reference voltage generation circuit 6aC has a value (energy target value) corresponding to a target energy value to be charged in the piezo actuator 2 at the end of the charging period when the driving energy of the piezo actuator 2 is 0 at the start of the charging period. ) So that the reference voltage is output linearly with respect to time. The reference voltage generation circuit 6bC outputs the reference voltage linearly with respect to time so that the driving energy of the piezo actuator 2 becomes the energy target value at the start of the discharge period and finally becomes 0 at the end of the discharge period. . The time profile of the reference voltage is set according to the time profile required for displacement of the piezoelectric actuator 2 during the charging period or discharging period based on the correlation between the accumulated energy of the piezoelectric actuator 2 and the displacement of the piezoelectric actuator 2. do it. Of course, different aging profiles may be used for the charging period and the discharging period.

  In the present embodiment, in the control of the charge switch 4a and the discharge switch 4b, the length of the on period of the charge switch 4a and the discharge switch 4b is determined based on the drive energy detection signal at each time point during the charge period or the discharge period. , 6bC is set to be a reference voltage to be output, and a drive energy aging profile corresponding to the reference voltage aging profile is obtained. Therefore, as shown in FIG. 3, not only the final displacement of the piezo actuator 2 but also the halfway displacement, that is, the temporal profile of the displacement of the piezo actuator 2 is always constant regardless of the fluctuation of the capacity of the piezo actuator 2. can do.

  Since the driving power is a time differential value of the driving energy, the present embodiment sets the target value of the driving energy from the start of the charging period and discharging period in advance for each time point, so that In this way, it is intended to set the time profile of the displacement of the piezo actuator 2 during the charging period and the discharging period as a target profile. However, the driving power to be output at that time for some reason during the charging period and the discharging period is Even if there is a deviation from the expected value, the actual drive energy follows so that it converges to the target value of the drive energy. Can be reduced

  In each of the above embodiments, the piezoelectric actuator 2 is directly driven from the capacitor 12 charged with the battery voltage. However, the battery is charged with a voltage obtained by boosting the battery voltage with a DC-DC converter. The present invention can also be applied.

It is a circuit diagram of the 1st piezo actuator drive circuit of the present invention. It is a timing chart which shows the operating state of the said piezoelectric actuator drive circuit. It is a graph explaining the action | operation of the said piezoelectric actuator drive circuit. It is a circuit diagram of the 2nd piezo actuator drive circuit of the present invention. It is a timing chart which shows the operating state of the said piezoelectric actuator drive circuit. It is a circuit diagram of the 3rd piezoelectric actuator drive circuit of the present invention. It is a timing chart which shows the operating state of the said piezoelectric actuator drive circuit. It is a circuit diagram of the 4th piezoelectric actuator drive circuit of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 11 Battery 12 Capacitor 2 Piezo actuator 31 1st electricity supply path 32 2nd electricity supply path 301 Inductor 4a Charge switch (current adjustment means)
4b Discharge switch (current adjusting means)
5 Power detection means 5A Current detection means 5B Voltage detection means 5C Drive energy detection means 6a, 6b, 6aA, 6bA, 6B, 6aC, 6bC Reference voltage generation circuit (target value output means)
7, 7A, 7B, 7C Switch control circuit (charge / discharge control means)
71a, 71b Comparator (comparison means)

Claims (10)

A driving circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, a power source, current adjusting means for adjusting a current flowing using the piezo actuator as a supply destination or a supply source, and the piezo actuator In a piezo actuator drive circuit having charge / discharge control means for controlling the current adjusting means at the time of driving,
Power detection means for detecting drive power of the piezoelectric actuator;
A target value output means for outputting a target value of the driving power set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means ends the driving period when the detected value of the driving power becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. A piezo actuator drive circuit characterized in that control for the current adjusting means is set. A driving circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, a power source, current adjusting means for adjusting a current flowing using the piezo actuator as a supply destination or a supply source, and the piezo actuator In a piezo actuator drive circuit having charge / discharge control means for controlling the current adjusting means at the time of driving,
Current detecting means for detecting a driving current of the piezoelectric actuator;
A target value output means for outputting a target value of the driving current set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means ends the driving period when the detected value of the driving current becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. A piezo actuator drive circuit characterized in that control for the current adjusting means is set.   3. The piezo actuator drive circuit according to claim 1, wherein the target value is a constant value. A driving circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, a power source, current adjusting means for adjusting a current flowing using the piezo actuator as a supply destination or a supply source, and the piezo actuator In a piezo actuator drive circuit having charge / discharge control means for controlling the current adjusting means at the time of driving,
Voltage detecting means for detecting a voltage between terminals of the piezoelectric actuator;
A target value output means for outputting a target value of the voltage between the terminals set in advance corresponding to each time point for each time point of the driving period of the piezoelectric actuator;
The charge / discharge control means sets the drive period when the detected value of the inter-terminal voltage becomes the target value at each time point of the drive period and when the elapsed time from the start of the drive reaches a predetermined time. A piezo actuator driving circuit, wherein control for the current adjusting means is set so as to be terminated.   5. The piezo actuator drive circuit according to claim 4, wherein the target value changes linearly with respect to an elapsed time from the start of driving. A driving circuit for driving a piezo actuator whose operation state is switched by driving by charging or discharging, a power source, current adjusting means for adjusting a current flowing using the piezo actuator as a supply destination or a supply source, and the piezo actuator In a piezo actuator drive circuit having charge / discharge control means for controlling the current adjusting means at the time of driving,
Drive energy detection means for detecting drive energy by detecting drive power of the piezoelectric actuator and integrating the detected drive power from the start of the drive period of the piezoelectric actuator;
A target value output means for outputting a target value of the driving energy set in advance corresponding to each time point for each time point of the driving period of the piezo actuator;
The charge / discharge control means ends the driving period when the detected value of the driving energy becomes the target value at each time point of the driving period and when the elapsed time from the start of driving reaches a predetermined time set in advance. A piezo actuator drive circuit characterized in that control for the current adjusting means is set. 7. The piezo actuator driving circuit according to claim 1, wherein a first energization path that connects the power source and the piezo actuator via an inductor, and a second that bypasses the power source and connects the inductor and the piezo actuator. With a current-carrying path of
As the current adjusting means, a charging switch for connecting and disconnecting the first energization path is provided,
The charge / discharge control means causes a charging current that gradually increases during an ON period of the charge switch to flow through the first energization path by repeatedly turning on and off the charge switch when the piezo actuator is charged, and turns off the charge switch. A piezo actuator drive circuit that is set so that a charging current that is gradually reduced by turning back at a peak current in a period flows through the second energization path. 7. The piezo actuator drive circuit according to claim 1, wherein a first energization path that connects the power source and the piezo actuator via an inductor, and a second that bypasses the power source and connects the inductor and the piezo actuator. With a current-carrying path of
As the current adjusting means, a discharge switch for connecting and disconnecting the second energization path is provided,
When the piezoelectric actuator is driven to discharge, the charge / discharge control means causes a discharge current that gradually increases during an ON period of the discharge switch to flow through the second energization path by repeating ON / OFF of the discharge switch, thereby turning OFF the discharge switch. A piezo actuator drive circuit which is set so that a discharge current which is gradually reduced by turning back at a peak current in a period flows through the first energization path. 9. The piezoelectric actuator drive circuit according to claim 7, wherein the charge / discharge control means compares the detected value with the threshold value using two values sandwiching the target value as threshold values. Comparing means for binary judgment of magnitude,
Comparing means having hysteresis that switches the judgment output when the detected value exceeds the large threshold value and when the detected value falls below the small threshold value is provided for the judgment output. And a piezo actuator driving circuit configured to turn off the switch when the detected value exceeds a large threshold value and to turn on the switch when the detected value falls below a small threshold value.   10. A piezo actuator drive circuit according to claim 1, wherein the power source outputs a voltage between terminals of the battery.

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