JP2001157472A - Piezo actuator drive circuit - Google Patents

Abstract

[PROBLEMS] To enable charging and discharging of a piezo actuator without relying on switching operation of a switch provided on a circuit line. SOLUTION: A capacitor 3 which can be connected to and disconnected from a DC power supply 21 by switches 22 and 4 is provided to store a predetermined amount of electric charge for charging a piezo actuator in the capacitor 3, and charging switches 52c and 531 are charged when the piezo actuator is charged.
is turned on, the charging circuit 5c, which is a resonance circuit in which the capacitor 3, the inductor 51 and the piezo actuator 11 are connected in series, is closed to charge the piezo actuator 11 by resonance. At the time of discharging the piezo actuator, the discharge switch 4 is turned on, and the discharging circuit 5d, which is a resonance circuit in which the piezo actuator 11, the inductor 51 and the capacitor 3 are connected in series, is closed to collect the electric charge in the capacitor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezo actuator drive circuit.

[0002]

2. Description of the Related Art A piezo actuator is an actuator in which a laminate of piezoelectric materials expands and contracts due to a piezoelectric effect.
The fuel injection injector of the common rail fuel injection device for a diesel engine is provided in the injector for switching between opening and closing of the injector. The piezo actuator is a capacitive load, and can switch between an extended state and a contracted state by charging and discharging.

FIG. 7 shows an example of a driving circuit for a piezo actuator. When a charging switch 904 is turned on, the piezo actuator 901 is charged by a DC power supply 902 via a current limiting element 903 and extended. When the charge switch 904 is turned off, the extended state is maintained. On the other hand, from that state, the discharge switch 9
When 05 is turned on, the piezo actuator 901 discharges and contracts.

Japanese Patent Application Laid-Open No. Hei 10-308542 discloses a technique in which electric charges of a piezo actuator 901 are collected and used for the next charging. FIG. 8 shows the configuration of this circuit. In this circuit, a buffer capacitor 906 is provided downstream of the DC power supply 902, and diodes 907 and 908 are connected in parallel to the charge switch 904 and the discharge switch 905, respectively. Diode 9
07 and 908 are connected in the reverse bias direction with respect to the voltage of the capacitor 902. Further, the current limiting element 909 is configured by a coil that is an inductor.

[0005] The charging of the piezo actuator 901 is repeated by repeatedly turning on and off the charge switch 904 in a pulsed manner. The piezo actuator 901 is charged by the circuit formed by the coil 909, the piezo actuator 901 and the diode 907 by the electromagnetic energy accumulated in the coil 909 when the piezo actuator 9 is turned off.
01 voltage rises.

On the other hand, when the piezo actuator 901 is discharged, the discharge switch 905 is repeatedly turned on and off in a pulsed manner, contrary to the charging operation. Piezo actuator 90 when on
1, a circuit closed by the coil 909 and the discharge switch 905 converts the energy held in the piezo actuator 901 into electromagnetic energy of the coil 909, and turns off the piezo actuator 901 and the coil 9 when off.
09 and a diode 908 collect the data in the buffer capacitor 906.

[0007]

However, in the circuit described in Japanese Patent Application Laid-Open No. Hei 10-308542, it is necessary to configure a charge switch and a discharge switch so that switching can be performed when charging and discharging a piezo actuator. The circuit becomes complicated. Also, the recovery efficiency is not always good because of the switching loss.

[0008] The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a piezo actuator driving circuit which does not require a switching operation of a switch at the time of charging / discharging of a piezo actuator and has high recovery efficiency.

[0009]

According to the first aspect of the present invention, a capacitor for storing electric power by a DC power supply and a DC power supply and a capacitor are connected between the DC power supply and the capacitor prior to charging the piezoelectric actuator. And a power storage control switch that cuts off between the DC power supply and the capacitor after the power storage is completed, and an inductor interposed between the capacitor and the piezo actuator. A charging circuit forming an LC resonance circuit connected in series, and a discharge having an inductor interposed between a capacitor and a piezo actuator, forming a LC resonance circuit in which the capacitor, inductor and piezo actuator are connected in series Circuit and the charging circuit described above Allowed to comprise a charging switch for switching between opening and closing of the charging circuit provided on the line, and a discharge switch for switching between opening and closing of the discharge circuit provided in the line of the discharge circuit.

During charging and discharging of the piezo actuator, the connection between the DC power supply and the capacitor is cut off, the charging circuit is closed during charging, and the discharging circuit is closed during discharging. Here, since the charging circuit and the discharging circuit form an LC resonance circuit including a capacitor and a piezo actuator,
The piezo actuator can be charged and discharged efficiently at a stretch without switching the charge switch and the discharge switch.

According to the second aspect of the present invention, the capacitance of the capacitor is set smaller than the capacitance of the piezo actuator.

[0012] With this setting, if resonance oscillation in the charging circuit can be performed freely, the capacitor can take a negative voltage. Therefore, it is possible to move the entire charge amount of the capacitor to the piezo actuator.

According to a third aspect of the present invention, in the configuration of the second aspect of the present invention, there is provided a charge stopping means for stopping the charging of the piezo actuator when the charge amount of the capacitor becomes zero.

Since the charging of the piezo actuator is stopped when the charge amount of the capacitor becomes 0, the control of the charging amount of the piezo actuator can be easily performed by setting the amount of charge of the capacitor by the DC power supply. For example, it can be accurately controlled by a capacitor voltage.

According to a fourth aspect of the present invention, in the configuration of the third aspect of the present invention, the charge stopping means includes a first diode connected in anti-parallel to the capacitor to inhibit a negative voltage of the capacitor, A second diode is provided on the circuit line so that the charging current of the piezo actuator is in the forward direction.

When charging the piezo actuator,
The first diode prevents the negative voltage of the capacitor voltage, and the second diode inhibits the current flowing backward from the piezo actuator to the capacitor. Therefore, when the capacitor voltage becomes zero, that is, when the capacitor becomes empty, an automatic operation is performed. The charging of the piezo actuator is stopped temporarily, and that state is maintained.

According to a fifth aspect of the present invention, in the configuration of the first to fourth aspects of the present invention, a diode is provided on the line of the discharge circuit so that the discharge current of the piezo actuator is in the forward direction.

When discharging the piezo actuator,
Since the diode prevents the current flowing backward from the capacitor to the piezo actuator, it is possible to prevent the piezo actuator from being charged and expanded again without relying on the opening operation of the discharge switch.

According to a sixth aspect of the present invention, in the configuration of the first to fifth aspects, the inductor forming the charging circuit and the inductor forming the discharging circuit have a common configuration.

By using a common inductor, the number of components can be reduced.

According to a seventh aspect of the present invention, in the configuration of the first to fifth aspects of the present invention, the inductor forming the charging circuit and the inductor forming the discharging circuit are configured separately.

The inductance of the inductor is a charging circuit,
Since the magnitudes of the charging current and the discharging current in the discharging circuit are specified, the charging speed and the discharging speed can be set independently.

According to an eighth aspect of the present invention, in the configuration of the sixth or seventh aspect, the capacitance of the capacitor is set smaller than the capacitance of the piezo actuator. In addition, a residual charge discharging switch for switching between closing and opening of a circuit that bypasses the capacitor through the piezo actuator and the inductor is provided.

By setting the capacitances of the capacitor and the piezo actuator as described above, the entire charge of the capacitor can be moved to the piezo actuator. Then, the electric charge remaining in the piezo actuator at the time of discharging the piezo actuator moves to the inductor of the discharge circuit by closing the circuit bypassing the capacitor, and is then immediately collected by the capacitor when opened, thereby further improving the collection efficiency. Can be.

According to a ninth aspect of the present invention, in the configuration of the first to fifth aspects of the present invention, the inductor forming the discharge circuit is configured by a transformer having an inductor forming the charging circuit as a secondary coil. .

At the time of discharging, the capacitor and the piezo actuator are connected via a transformer, so that the piezo actuator can be recovered to the capacitor without any remaining charge.

According to a tenth aspect of the present invention, in the configuration of the first to ninth aspects, a current limiting element is provided between the DC power supply and the capacitor in series with the capacitor.

Since the current from the DC power supply to the capacitor is limited when the capacitor is charged for driving the piezo actuator, it is possible to prevent deterioration of the storage control switch and the like.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows the configuration of a piezo actuator drive circuit according to the present invention. This piezo actuator drive circuit drives four piezo actuators 11, 12, 13, and 14, and is used for the common rail type fuel injection device of a four-cylinder diesel engine, for example.

The piezo actuator drive circuit includes a capacitor 3 for holding electric energy for driving the piezo actuators 11 to 14, a DC power supply 21 for supplying power to the capacitor 3, and the like. DC power supply 21 is a battery or DC
A DC converter or the like, which applies a voltage of several tens to several hundreds of volts to the capacitor 3; The voltage applied to the capacitor 3 is a positive pressure. It is desirable that the capacitor 3 has almost no temperature dependence of the capacitance, for example, a film capacitor. In the operating temperature range, the capacitance of the capacitor is C1, and the capacitance of each of the piezo actuators 11 to 14 as the capacitive load is C2. Use the one set to be C2.

The capacitor 3 is connected in parallel with a diode 6 for preventing negative pressure, which will be described later, and connected in series with a charge path diode 54c connected in parallel and an energization path switch 4 which is a discharge start switch. is there.
The negative pressure preventing diode 6 is connected to the capacitor 3 in a reverse bias direction, and the charging path diode 54c is connected to the capacitor 3 in a forward bias direction.

A power storage control switch 22 and a power storage coil 23 as a current limiting element are provided in series between the DC power supply 21 and the capacitor 3, and a diode 24 is provided in the DC power supply 21 in a reverse bias direction. When the storage control switch 22 and the energization path changeover switch 4 are on, power is supplied to the capacitor 3 from the DC power supply 21 via the storage coil 23 during that time. The provision of the storage coil 23 prevents overcurrent at the time of feeding the capacitor 3 and prevents the storage control switch 2
2 is prevented from deteriorating.

Between the positive terminal of the capacitor 3 and the positive terminal of each of the piezo actuators 11 to 14, a charge switch 52c and a discharge path diode 54d connected in series and in parallel, and a coil 51 serving as a current limiting element are connected. And are connected. The negative terminals of the piezo actuators 11 to 14 are connected to the selection switches 53 connected in parallel, respectively.
1c, 532c, 533c, 534c and discharge path diodes 551d, 552d, 553d, 554d are connected. Selection switches 531c to 534c and discharge path diodes 551d to 554d are provided for each of the piezo actuators 11 to 14.

Selection switch 531 connected to piezo actuators 11 to 14 which are to be extended during charging
When turning on c-534c, the charge path diode 54
c, capacitor 3, charging switch 52c, coil 51,
A charging circuit 5c is formed by the selected piezo actuators 11 to 14 and the on selection switches 531c to 534c, and the selected piezo actuators 11 to 14 are charged from the capacitor 3 and the piezo actuators 11 to 14 are extended.

On the other hand, when the energizing path switch 4 is turned on, the piezo actuators 11 to 1 in the extended state are turned on.
4, discharge path diodes 551d to 554d corresponding to
A discharge circuit 5d is formed by the piezo actuators 11 to 14, the coil 51, the discharge path diode 54d, the capacitor 3, and the energization path switching switch 4. The discharge circuit 5d discharges electric charges from the piezo actuators 11 to 14 in the extended state, so that to shrink.

The coil 51 and the discharge path diode 5
4d is grounded via the residual charge discharging switch 7, and when the residual charge discharging switch 7 is turned on, the piezo actuators 11 to 14 in which the charge described later remains.
551d to 554d, the piezo actuators 11 to 14, the coil 51, and the remaining charge discharging switch 7 form a closed circuit.

The switches 22 to 7 are controlled to be turned on and off by a control unit such as a microcomputer (not shown).

The operation of the piezo actuator drive circuit will be described. FIG. 2 is a time chart showing an operation state of each part of the drive circuit. The capacitor 3 is charged in advance before the piezo actuators 11 to 14 are extended. First, the energization path switch 4 is turned on. This allows
DC power supply 21, power storage control switch 22, power storage control coil 23, capacitor 3, and energizing path switch 4
Then, the voltage of the capacitor 3 is increased by repeatedly switching the storage control switch 22. When the voltage of the capacitor 3 reaches the predetermined value V1, the switching operation is stopped (return to the switch-off state). As a result, a predetermined amount of electric charge is stored in the capacitor 3.

When the timing to extend the piezo actuators 11 to 14 comes, the selection switch 531 corresponding to the piezo actuators 11 to 14 to be extended (hereinafter referred to as the piezo actuator 11).
c is turned on, and then the charging switch 52c is turned on. Thereby, the charging path capacitor 54c, the capacitor 3,
The charging circuit 5c including the coil 51, the piezo actuator 11, and the selection switch 531c is closed. The charging circuit 5c is an LC resonance circuit. At this time, since C1 ≦ C2, the maximum value of the charge amount of the piezo actuator 11 can reach the initial charge amount of the capacitor (the above-mentioned charge amount) by the resonance action. Then, due to the negative pressure preventing action of the negative pressure preventing diode 6 and the reverse current preventing action of the charging path diode 54c, the outflow of charges from the capacitor 3 causes
It stops when the charge amount of the capacitor 3 is 0. Thus, electrical energy C1 V1 ² accumulated in the capacitor 3
/ 2 move to the piezo actuator 11 and stop in that state.

The piezo actuator 11 extends with the movement of the electric charge to the piezo actuator 11, and the electric energy C1 V stored in the capacitor 3 as described above.
When 1 ^2/2 all move to the piezoelectric actuator 11, the piezoelectric actuator 11 holds the extended state the movement of the above as the charge is stopped. Next, the switches 52c and 531c are turned off.

When the timing to reduce the size of the piezo actuator 11 comes, as shown in the latter half of the time chart, the energization path switch 4 is turned on again. Thereby, the diode 551d, the piezo actuator 11,
A discharge circuit 5d including a coil 51, a discharge path diode 54d, a capacitor 3, and a conduction path switch 4
Is closed. Since the discharge circuit 5d is also an LC resonance circuit, the piezo actuator 11 is discharged by the resonance action of the discharge circuit 5d, and the electric charge of the piezo actuator 11 is collected in the capacitor 3. Also in this case, the discharging circuit 5
As the current d, only a current in the charge recovery direction defined by the discharge path diodes 551d and 541d is allowed, and after a certain time, the movement of the charge is stopped. As a result, the piezo actuator 11 is prevented from being recharged and expanded, so that it is not necessary to open the charging circuit 5d by opening the selection switch 531c or the like to prohibit recharging of the piezo actuator 11, thereby reducing the control burden. I'm done.

Since C1.ltoreq.C2, the charge remains in the piezo actuator 11 according to C1 and C2, unlike during charging. However, when the remaining charge discharging switch 7 is turned on, the discharge path diode 551d and the piezo actuator 1
1, the closed circuit composed of the coil 51 and the remaining charge discharging switch 7 is formed, and the electric energy of the remaining charge is converted into the electromagnetic energy of the coil 51. Next, when the remaining charge discharging switch 7 is turned off, the coil 5
The electromagnetic energy stored in 1 is instantaneously transferred to the capacitor 3
The electrical energy supplied to the piezo actuator 11 can be efficiently recovered to the capacitor 3 except for a very small loss in the coil 51 and the like.

As described above, in the present piezo actuator driving circuit, after the capacitor 3 is completely charged, the DC power supply 21 is cut off, and the charging circuit 5c, which is an LC resonance circuit including the capacitor 3, the coil 51, and the piezo actuator 11, and the discharging circuit By 5d, charging and discharging can be performed at once without depending on the switching operation of the switch. Then, the electric charge collected in the capacitor 3 is transferred to the piezo actuator 1 next time.
2, 13, and 14 can be reused as energy at the time of extension, and power consumption can be saved.

In the subsequent extension of the piezo actuators 12 to 14, the recovered electric energy has already been stored in the capacitor 3. Insufficient (the capacitor voltage does not reach the specified value V1)
Only charging is sufficient, and charging of the capacitor 3 is completed immediately. After completion, expansion and contraction of the piezo actuators 12 to 14 are performed as in the first half of the time chart.

(Second Embodiment) FIG. 3 shows the configuration of a piezo actuator driving circuit according to a second embodiment of the present invention. In the configuration of the first embodiment shown in FIG. 1, the coils are separately provided for the charging circuit and the discharging circuit. In the drawing, the portions denoted by the same reference numerals as those in FIG. 1 are substantially the same as those in the first embodiment. Since the operation is performed, the description will focus on the differences.

The selection switches 531c to 531c corresponding to the selected piezoelectric actuators 11 to 14 to be extended.
When 534c is turned on, the capacitor 3, the charging path diode 54c, the charging switch 52c, the charging coil 56c,
A charging circuit 5Ac is formed by the selected piezo actuator 11 and the selection switches 531c to 534c. The charging circuit 5Ac is an LC resonance circuit substantially equivalent to the charging circuit 5c of the first embodiment.

On the other hand, when the discharge switch 52d is turned on,
Discharge path diodes 551d to 554d corresponding to the extended piezo actuators 11 to 14, the piezo actuators 11 to 14, discharge coil 56d, discharge switch 52d, discharge path diode 54d, capacitor 3
Thus, a discharge circuit 5Ad for discharging the electric charges of the piezo actuators 11 to 14 in the extended state is formed. The discharge circuit 5Ad is an LC resonance circuit substantially equivalent to the discharge circuit 5d of the first embodiment.

FIG. 4 is a time chart showing the operation of the present piezo actuator driving circuit. As shown in the first half of the time chart, a predetermined amount of electric charge is accumulated in the capacitor 3 by the switching of the electric storage control switch 22, and the piezo to be extended is extended. When the selection switch 531c and the charge switch 52c corresponding to the actuators 11 to 14 (hereinafter, described as the piezo actuator 11) are turned on,
The charging circuit 5Ac is closed and the piezo actuator 11 is charged.

On the other hand, as shown in the second half of the time chart,
When the discharge switch 52d is turned on, the discharge circuit 5Ad is closed, the piezo actuator 11 discharges, and the capacitor 3
Will be collected.

Here, the charging coil 56c and the discharging coil 5
Since 6d is a current limiting element, the charging rate and the discharging rate are specified respectively according to the inductance. Therefore, in the present embodiment, the charging speed and the discharging speed can be set independently.

The collection of the remaining charge of the piezo actuator 11 is performed by turning on and off the remaining charge discharging switch 7 as in the first embodiment.

(Third Embodiment) FIG. 5 shows the configuration of a piezo actuator driving circuit according to a third embodiment of the present invention. In the configuration of the first embodiment shown in FIG. 1, the charging circuit and the discharging circuit are different from each other. In the figure, the portions denoted by the same reference numerals as those in FIG. 1 have substantially the same operation as the first embodiment. Therefore, the difference will be mainly described.

The charging circuit 5Bc for charging the piezo actuators 11 to 14 includes a capacitor 3 and a transformer 5 described later.
7, the secondary coil 572, the charging path diode 54c,
The charging switch 52c, the selected piezo actuators 11 to 14 and the selection switches 531c to 534c form an LC resonance circuit substantially equivalent to the charging circuits 5c and 5Ac of the first and second embodiments.

The discharge circuit 5Bd includes a discharge path diode 55 corresponding to the extended piezoelectric actuators 11 to 14.
1d to 554d, and their piezo actuators 11 to 1
4. A primary circuit closed by the primary coil 571 of the transformer 57 and the discharge switch 58d, a discharge path diode 59d for defining a current direction when discharging the piezo actuators 11 to 14, the transformer primary coil 571 and the electromagnetic Transformer secondary side coil 5 which is electrically coupled
72 and a secondary side circuit closed by the capacitor 3 to form an LC resonance circuit.

FIG. 6 is a time chart showing the operation of the present piezo actuator drive circuit. A predetermined amount of electric charge is accumulated in the capacitor 3 by switching of the storage control switch 22, and the piezo actuators 11 to 1 which are about to expand.
4 (hereinafter, described as a piezo actuator 11)
Switch 531c and charge switch 5 corresponding to
When the switch 2c is turned on, the charging circuit 5Bc is closed and the piezo actuator 11 is charged.

On the other hand, when the discharge switch 58d is turned on, the primary circuit of the discharge circuit 5Bd is closed and a current flows through the primary coil 571 of the transformer. Current flows through the secondary circuit. Thus, the piezo actuator 11 discharges and is collected by the capacitor 3.

In each of the above embodiments, the negative voltage prevention diode connected in parallel to the capacitor and the charging path diode connected in series in the charging circuit cause the charging circuit to be turned off when the capacitor voltage becomes zero. It is stopped, and all the energy held in the capacitor is moved to the piezo actuator as described above.Equal energy control is used, but if the capacitor voltage becomes 0 V using the capacitor voltage detection system The configuration may be such that the charge switch is turned off, and in this case, equal charge control is performed.

Further, each of the switches may be a bipolar transistor or an FET, and may be configured to control the base current and the gate voltage to limit the current.

Although the present embodiment has been described as applied to a common rail type fuel injection device, the present invention can be applied to other uses using a piezo actuator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a piezo actuator driving circuit according to a first embodiment of the present invention.

FIG. 2 is a time chart showing the operation of the piezo actuator drive circuit.

FIG. 3 is a circuit diagram of a piezo actuator drive circuit according to a second embodiment of the present invention.

FIG. 4 is a time chart showing the operation of the piezo actuator drive circuit.

FIG. 5 is a circuit diagram of a piezo actuator drive circuit according to a third embodiment of the present invention.

FIG. 6 is a time chart showing the operation of the piezo actuator drive circuit.

FIG. 7 is a circuit diagram showing a typical example of a conventional piezo actuator drive circuit.

FIG. 8 is a circuit diagram showing another typical example of a conventional piezo actuator drive circuit.

[Explanation of symbols]

11, 12, 13, 14 Piezo actuator 21 DC power supply 22 Storage control switch 23 Storage control coil 24 Diode 3 Capacitor 4 Energization path switch 5c, 5Ac, 5Bc Charge circuit 51 Coil 52c Charge switch 531c, 532c, 533c, 534c Selection switch 54c Charge path diode 56c Charging coil 571 Primary coil 5d, 5Ad, 5Bd Discharge circuit 52d, 58d Discharge switch 54d Discharge path diode 551d, 552d, 553d, 554d, 59d Discharge path diode 56d Discharge coil 57 Trans 6 Negative voltage prevention Diode 7 Residual charge discharge switch

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // F04B 9/00 H01L 41/08 K (72) Inventor Yasuhiro Fukagawa 14 Iwatani, Shimowasukamachi, Nishio-shi, Aichi Co., Ltd. Japan Auto Parts Research Institute (72) Inventor Toshihiko Inoka 1-1-1, Showa-cho, Kariya-shi, Aichi F-term in Denso Corporation (reference) 3G066 AA07 AB02 AC09 AD12 BA00 CC05U CD26 CE27 CE29 3H075 AA03 CC25 DB02 EE12

Claims (10)

[Claims] In a piezo actuator driving circuit for controlling switching between charging and discharging of a piezo actuator, a capacitor for storing electric power by a DC power supply and a capacitor connected between the DC power supply and the capacitor prior to charging the piezo actuator are connected. A storage control switch that stores electricity for charging the piezo actuator and shuts off between the DC power supply and the capacitor after the completion of the storage, and an inductor interposed between the capacitor and the piezo actuator, and the capacitor, the inductor, and the piezo actuator are connected in series. And a discharge circuit having an inductor interposed between the capacitor and the piezo actuator, the discharge circuit forming an LC resonance circuit in which the capacitor, the inductor, and the piezo actuator are connected in series. Road, a charging switch provided on the line of the charging circuit for switching between closing and opening of the charging circuit, and a discharging switch provided on the line of the discharging circuit for switching between closing and opening of the discharging circuit. A piezo actuator drive circuit characterized by the following. 2. The piezo actuator drive circuit according to claim 1, wherein the capacitance of the capacitor is set smaller than the capacitance of the piezo actuator. 3. The piezo actuator drive circuit according to claim 2, further comprising a charge stopping means for stopping the charging of said piezo actuator when the charge amount of said capacitor becomes zero. 4. The piezo actuator drive circuit according to claim 3, wherein said charge stopping means is connected to a first diode connected in anti-parallel to said capacitor to inhibit a negative voltage of said capacitor, and a line of said charging circuit. A piezo actuator drive circuit comprising a second diode provided so that the charging current of the piezo actuator is in a forward direction. 5. The piezo actuator drive circuit according to claim 1, wherein a diode is provided on a line of the discharge circuit such that a discharge current of the piezo actuator is in a forward direction. 6. A piezo actuator driving circuit according to claim 1, wherein said inductor forming said charging circuit and said inductor forming a discharging circuit have a common configuration. 7. The piezo actuator drive circuit according to claim 1, wherein the inductor forming the charging circuit and the inductor forming the discharge circuit are separate from each other. 8. The piezo actuator drive circuit according to claim 6, wherein the capacitance of the capacitor is set smaller than the capacitance of the piezo actuator, and the piezo actuator and the inductor are connected to each other. A piezo actuator drive circuit including a residual charge discharging switch for switching between closing and opening of a circuit bypassing the capacitor. 9. The piezo actuator driving circuit according to claim 1, wherein the inductor forming the discharging circuit is a transformer having a secondary coil as an inductor forming the charging circuit. Drive circuit. 10. The piezo actuator drive circuit according to claim 1, wherein a current limiting element is provided between said DC power supply and said capacitor in series with a capacitor.