JPH0246784A - Driving apparatus for piezoelectric actuator - Google Patents

Abstract

PURPOSE:To make the high voltage generating part of a piezoelectric actuator small- sized and light-weighted, improve operating efficiency, and enable high speed and highly accurate driving, by a method wherein, when a charging voltage is lower than a prescribed applying voltage, it is applied after transformed into the applying voltage, and when it is higher than the applying voltage, the actuator is connected with a discharging circuit having a time constant corresponding with a specified capacitance. CONSTITUTION:The displacement value of an actuator 9a and a target displacement value are compared with each other, and a follow-up control signal for the target displacement value is calculated as a command value Vi. A polarity changeover.charge.discharge circuit 66 receives the detection result of a monitor circuit 68 to detect a driving voltage Vp applied to the piezoelectric actuator 9a, and outputs a driving signal Vd according to these two data. A power circuit 70 is constituted of a variable voltage step-up part 80 and a polarity changeover.charge. discharge part 90. The part 80 transforms the power supply voltage of a battery 41, according to the command value ¦Vi¦ inputted from a control circuit 60. The part 90 changes an output voltage f Vo from the part 80 into positive.inverse polarity, and applies it to the actuator 9a in order to discharge stored charge of the actuator 9a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric actuator drive device that adjusts a voltage applied to a piezoelectric actuator made of a piezoelectric element.

[Prior Art] Piezoelectric actuators that obtain a predetermined displacement using piezoelectric elements such as PZT have been widely adopted because they have high precision and high-speed response.

In order to drive the piezoelectric actuator, it is necessary to apply a voltage to the piezoelectric actuator according to the target displacement, and a drive device shown in FIG. 5 is used as a drive device for this purpose. This uses a voltage applied to the piezoelectric element of approximately ±500V, a driving frequency of DC-several 100H2, and has the following device configuration. That is, this piezoelectric element driving device includes a displacement sensor H that detects the displacement value of the piezoelectric actuator ACT.
C5 A control circuit CON that calculates a target voltage value to be applied to the piezoelectric actuator ACT based on the output of the displacement sensor HC and the target displacement value, a constant voltage power supply circuit C■ that outputs a constant voltage, and a constant voltage power supply circuit CV. It is comprised of a power amplifier AMP section, etc., which receives voltage power supply and supplies a target voltage to the voltage actuator based on the target voltage value.

By using such a piezoelectric actuator drive device, the voltage applied to the piezoelectric actuator is controlled to an optimal value to obtain a target displacement.

[Problems to be Solved by the Invention] However, the conventional piezoelectric actuator drive devices are not completely satisfactory, and the following problems remain.

First, due to the configuration of the drive device, the constant voltage power supply circuit CV is required to have the ability to generate a high voltage exceeding the maximum voltage applied to the piezoelectric actuator ACT. For this reason, a high voltage source is employed as the constant voltage power supply circuit CV, which increases the size of the device and makes it difficult to reduce power loss and emission. Furthermore,
When supplying positive and negative (±) voltages to the piezoelectric actuator ACT, it is also necessary to generate positive and negative voltages in the constant voltage power supply circuit CV, which leads to an increase in the size of the -layer device. .

Furthermore, the target voltage applied to the voltage actuator is controlled by the power amplifier section AMP.
The power loss in the MP is large compared to the power consumption of the piezoelectric actuator, the power efficiency is low, and the heat dissipation capacity is increased.

The present invention has been made in order to solve the above-mentioned problems, and it improves versatility by making the high voltage generating part that generates a desired displacement in a piezoelectric actuator small and lightweight.
It is an object of the present invention to provide a piezoelectric actuator drive device that can improve the efficiency and drive the piezoelectric actuator at high speed and with high precision.

[Means for Solving the Problems] The means configured in the present invention to solve the above problems are as follows: Adjust the voltage applied to a piezoelectric actuator made of a piezoelectric element with a predetermined capacity, and set the displacement value of the piezoelectric actuator to a target displacement. A driving device for a piezoelectric actuator that directly controls the piezoelectric actuator, comprising: voltage determining means that determines an applied voltage to be applied to the piezoelectric actuator based on the target displacement one time; and charging voltage detecting means that detects a charging voltage of the piezoelectric actuator. , when the charging voltage detected by the charging voltage detection means is lower than the applied voltage determined by the voltage determining means, voltage applying means transforms the power supply voltage into an applied voltage and applies it to the piezoelectric actuator; The gist of the piezoelectric actuator drive device is characterized in that it includes a discharge means for connecting the piezoelectric actuator to a discharge circuit having a time constant corresponding to the predetermined capacity when the voltage is higher than the predetermined capacity.

[Function j] The piezoelectric actuator driven by the piezoelectric actuator drive device of the present invention is a fixed piezoelectric actuator, and is electrically equivalent to a capacitance. Therefore, the piezoelectric actuator has the property of storing the supplied electric charge.

Therefore, the charging voltage detection means in the drive device of the present invention has the function of detecting the charging voltage of the piezoelectric actuator, and detects the electrical initial value of the piezoelectric actuator during control.

Further, the voltage determining means of the drive device of the present invention determines the applied voltage to be applied to the piezoelectric actuator from the target displacement value to be generated in the piezoelectric actuator.

When the charging voltage detecting means and the voltage determining means obtain information necessary for controlling the piezoelectric actuator, the voltage applying means or the discharging means having the following effects are selectively operated.

The voltage applying means operates when the charging voltage detected by the charging voltage detecting means is lower than the applied voltage determined by the voltage determining means, that is, when it is necessary to control the voltage applied to the piezoelectric actuator to be higher than the current charging voltage. . Then, a voltage obtained by transforming the power supply voltage to an applied voltage is applied to the piezoelectric actuator.

The discharging means operates when the charging voltage is higher than the applied voltage, that is, when the voltage to be applied to the piezoelectric actuator needs to be controlled to be lower than the charging voltage, and operates to control the piezoelectric actuator according to a predetermined capacity of the piezoelectric actuator. Connect to a time constant discharge circuit. Here, the discharge circuit with a time constant according to the predetermined capacity of the piezoelectric actuator is
It interacts with a predetermined capacity of the piezoelectric actuator to discharge the charge accumulated in the piezoelectric actuator with desired characteristics. Therefore, the terminal voltage of the piezoelectric actuator, that is, the displacement of the piezoelectric actuator, decreases while showing a time change based on the time constant of the discharge circuit.

Hereinafter, in order to more specifically explain the piezoelectric actuator drive device of the present invention, a detailed description will be given using examples.

[Example] Figure 1 is a schematic diagram of a system that uses a capacitive piezoelectric actuator in the drive section of a fuel injection valve that injects pressurized fuel into a diesel engine over a commanded period (fuel injection time). It is a diagram.

As shown in the figure, each cylinder of the diesel engine 1 includes
A fuel injection valve 3 (3a) that injects fuel into the combustion chamber
, 3b, 3c, 3d) are provided. Air is taken into the diesel engine 1 from a supercharger 5 via an intake manifold 7.

The fuel injection valve 3 has a known configuration using a piezoelectric actuator, and includes a needle valve that opens and closes an injection hole through which fuel is injected, and a built-in piezoelectric actuator 9 (9a, 9b, 9).
c, 9d・), and its piezoelectric actuator 9
The needle valve is driven by the expansion and contraction of the needle. Such a fuel injection valve 3 is connected via a fuel supply pipe 11 to a fuel pressure accumulation pipe 13 common to each cylinder. The fuel accumulator pipe 13 has a pressure accumulator chamber 15 having a constant volume therein, and the fuel in the pressure accumulator chamber 15 is supplied to the fuel injection valve 3 via the fuel supply pipe 11 .

On the other hand, the pressure accumulation chamber 15 is connected to a discharge port of a fuel supply pump 19 whose discharge pressure can be controlled via a fuel supply pipe 17, and receives fuel pressurized to a predetermined pressure from the fuel supply pump 19. . Fuel in a fuel reservoir tank 23 is fed under pressure to this fuel supply pump 19 from a fuel pump 21 .

The fuel injection valves 3 are each connected to a fuel reservoir tank 23 via a fuel return conduit 25 to form a fuel circulation path, and the fuel that has not been co-supplied to the diesel engine 1 during injection is stored in the reservoir. Return to tank 23. Note that the fuel pump 21 is provided to feed the fuel in the fuel reservoir tank 23 into the fuel supply pump 19, and even if the fuel pump 21 is not provided, the fuel supply pump 19
If it is possible to suck fuel into the fuel pump 21
There is no need to specifically provide this.

Diesel engine 1 includes:
A rotation speed sensor 27 that detects the rotation speed of the crankshaft, and a cylinder discrimination sensor 2 that outputs a signal at a predetermined crank angle.
9. Cooling water temperature sensor 31 that detects engine cooling water temperature
, a supercharging pressure sensor 33 for detecting supercharging pressure, a fuel pressure sensor 35 for detecting fuel pressure in the pressure accumulating chamber 15, and the like are provided. Furthermore, in order to detect the required load on the diesel engine 1, an accelerator sensor 39 is provided that detects the amount of depression of the accelerator pedal 37.

The battery 41 is a normal vehicle-mounted +12V voltage source, and supplies power to an engine controller 43 and a piezoelectric actuator drive device 45 that drives a piezoelectric actuator built into each fuel injection valve 3, as shown in the figure. Here, the engine controller 43 calculates the fuel injection amount and fuel injection time of the diesel engine 1 based on the outputs of the above-mentioned sensors, and sends a signal SVx indicating the target displacement value VX to the piezoelectric actuator drive device 45. At the same time, it outputs a control signal to the pump drive device 47 that drives the fuel supply pump 19. Therefore, the engine controller 43 is required to have high-speed and high-precision information processing ability, and to satisfy this requirement, it is constructed of logic circuits centered on a CPU, ROM, and RAM.

Next, the configuration of the piezoelectric actuator drive device 45 will be explained based on FIG. 2. Piezoelectric actuator drive device 4
5 is each piezoelectric actuator 9 built in the fuel injection valve 3
In order to drive blocks a to 9d independently, four systems of drive blocks 45a to 45d are provided. These four drive systems 45a to 45d have the same configuration, and only differ in the value of the target displacement value signal SVx manually inputted from the engine controller 43 and the timing of the manual input. Therefore, FIG. 2 shows only a block diagram of the drive block 45a that drives the piezoelectric actuator 9a, and explanations of other drive blocks are omitted to avoid duplication.

The drive block 45a shown in FIG. 2 can be roughly divided into:
Displacement sensor 5 detecting displacement of piezoelectric actuator 9a
0, a control circuit 60 that outputs a command value IVil and a drive signal Vd based on a displacement feedback signal Vf, which is a detection signal of the displacement sensor 50, and a target displacement value signal 5Vxa from the engine controller 43; the command value 1Vil and the drive signal; It is constituted by three parts of a power circuit 70 which receives Vd and outputs a drive voltage vp to the piezoelectric actuator 9a. In this embodiment, the displacement X appearing on the piezoelectric actuator 9a and the drive voltage vp applied will be described as being in a proportional relationship.

First, the control circuit 60 will be explained.

Displacement feed puncture signal Vf from displacement sensor 50 and target displacement 1 direct signal 5V from engine controller 43
xa is a command (1i
Vi is calculated. That is, the current displacement value of the piezoelectric actuator 9a and the target displacement value are compared, and the signal necessary for additionally controlling the actual displacement value of the piezoelectric actuator 9a to the target displacement value is calculated as the command value Vi. . Therefore, the calculation control circuit 62 is configured to perform calculations based on the drive characteristics of the piezoelectric actuator 9a to be controlled.

The command value Vi outputted from the arithmetic control circuit 62 is manually input to the absolute value circuit 64, where it is converted into an absolute value and the command value IV11 actually given to the power circuit 70 is created. This is the command value ■[, which is the calculation result of the target displacement value 5Vxa and the displacement feed puncture signal Vf, is "positive" or "negative".
Although the power circuit 70 of this embodiment varies, the power circuit 70 of this embodiment is
This is to control the drive voltage Vp applied to the piezoelectric actuator 9a only as a "positive" voltage.

Further, the command value Vi of the arithmetic control circuit 62 is also input manually to the polarity switching/charging/discharging controller 66 .

In addition to the command value Vi, the polarity switching/charging/discharging circuit 66 receives the driving voltage v actually applied to the piezoelectric actuator 9a.
The monitor circuit that detects p The monitor (
Ii V m is input, and a drive signal Vd as shown in Table 1 is output based on these two data. In addition, in FIG. 2, a single signal line is depicted as the drive signal Vd for simplicity, but in reality, as shown in Table 1, A to
It has six signal lines up to F, and the output voltage of each signal line A to F is set to High based on the command value Vi and monitor value Vm.
h (hereinafter referred to as “H”) or Low (hereinafter referred to as “L”)
).

Table 1 Next, as described above, the command values 1 and 11 outputted from the control circuit 60 and the drive signals Vd of the 6 systems are manually inputted, and the voltage of the battery 41 is appropriately transformed to drive the piezoelectric actuator 9a.
The power circuit 70 that applies the drive voltage Vp to the power source will be explained.

The power circuit 70 includes a variable voltage booster 80 that transforms the power supply voltage of the battery 41 according to a command flIVil manually inputted from the control circuit 60, and a variable voltage booster 80 that converts the output voltage VO output from the variable voltage booster 80 into positive and negative directions. It consists of two parts: a polarity switching/charging/discharging section 90 that switches the polarity and applies an electric charge to the piezoelectric actuator 9a or discharges the charged charge of the piezoelectric actuator 9a.

First, the variable voltage booster 80 will be explained.

The power line of battery battery 41 is connected to step-up transformer 82 via chopper circuit 81 which is a part of variable voltage step-up section 80.
connected to the primary side of the Therefore, step-up transformer 82
The primary side of the transformer is intermittently excited by the switching operation of the chopper circuit 81, and a voltage based on the switching frequency of the chopper circuit 81 and the turns ratio of the step-up transformer 82 is induced on the secondary side of the step-up lance 82. Ru. The AC voltage thus induced on the secondary side of the step-up transformer 82 becomes a stable DC voltage (output voltage Vo) through a rectifier and smoothing circuit.
is converted and output.

The PWM controller 84 controls the switching timing of the chopper circuit 81 and changes the value of the output voltage 0 according to the command value IVi.

That is, the PWM controller 84 includes a voltage detection circuit 85 that detects the output voltage VO of the variable voltage booster 80, an error amplifier 86 that amplifies the difference between the command value IVi, and a current detector that detects the output current of the variable voltage booster 80. The output of the circuit 87 is manually generated, and the output voltage Vo is fed back to ensure correspondence with the command value IVil.

Furthermore, the output of the variable voltage step-up section 80 is manually supplied to a polarity switching/charging/discharging section 90 that operates based on six systems of drive signals output from the polarity switching/charging/discharging controller 66 .

The detailed configuration of this polarity switching/charging/discharging gB90 is shown in FIG. As shown in the figure, the polarity switching/charging/discharging section 90 includes a transistor Tra used as a switching element.
, Trb, Trc, and Trd are bridge-connected, and a resistor R and a transistor Tr are connected in parallel with the transistor Trb.
A resistor R and a transistor T'f are connected in parallel with the transistor Trc.Then, its output terminal is connected to both ends of the piezoelectric actuator 9a to be controlled. The value r is a value that is appropriately determined by comprehensively determining the switching performance of each transistor T'' of the electrical capacitance C1 of the piezoelectric actuator 9a, the driving frequency of the piezoelectric actuator 9a, and the like.

Six systems of drive signals Vd output from the charge/discharge controller 66 during polarity switching are used as base signals of these six transistors Tr, that is, 0N10FF signals,
The transistor Tr whose output of the drive signal Vd is "H" is ON.
state, and the transistor Tr of rLJ becomes OFF state. In addition, the connection method is as shown in the figure, with the subscripts raJ to rfJ of each transistor Tr and the drive signal Vd.
This is done in correspondence with the output systems rAJ to rFJ.

Since the 6-system connected drive signal Vd is output with the specifications shown in Table 1 above, the polarity switching/charging/discharging unit 9 operates in response to this.
0 controls the drive voltage Vp of the piezoelectric actuator 9a as follows.

First, the command value ■l≧0, and the piezoelectric actuator 9a
A case in which a voltage in the "positive" direction should be applied will be explained.

At this time, if the command value V1≧monitor value V m, then
It is necessary to further increase the voltage currently applied to the piezoelectric actuator 9a. Therefore, the transistor Tra
, Trc, and the output voltage VO output from the variable voltage booster 80 is applied to the piezoelectric actuator 9a with the same polarity. In this way, the voltage applied to the piezoelectric actuator 9a is increased to bring the generated displacement closer to the target displacement, but since this generated displacement is detected by the displacement sensor 50 and fed back to the control circuit 60, the generated displacement of the piezoelectric actuator 9a is accurately determined. The drive voltage Vp applied is further finely adjusted so as to achieve the target displacement.

Conversely, when command fiVi<monitor value Vm, it is necessary to lower the terminal voltage of piezoelectric actuator 9a. In this case, only the transistors Trc and Tre are
A "H" signal is output. As a result, a discharge circuit is formed in the piezoelectric actuator 9a through the transistor Trc, the resistor R, and the transistor Tre, and is determined by the electrical capacitance C of the piezoelectric actuator 9a and the resistance value r of the resistor R in the discharge circuit. The discharge of the charged charge is started according to the time constant set. The drop in the piezoelectric actuator 9a pane voltage due to the discharge of the charged charge is constantly detected by the monitor value Vm, and the displacement sensor 50 also detects a decrease in the generated displacement of the piezoelectric actuator 9a due to the drop in the terminal voltage. The circuit is formed only during the period when the command value Vi=mini monitor m, and eventually the piezoelectric actuator 9a
The degree of occurrence of is subjected to follow-up feedback control to the target displacement.

FIG. 4 shows changes in the terminal voltage of the piezoelectric actuator 9a due to the operation of the polarity switching/charging/discharging section 90. As shown in the figure, when the transistors Tra and Trc turn on, the command value Vi and the piezoelectric actuator 9
It changes while completely matching the drive voltage Vp applied to a. Also, from the command value Vi, the piezoelectric actuator 9a
When the terminal voltage of becomes large, the transistor Tre turns on instead of the transistor Tra, and when the drive voltage Vp becomes less than the specified value due to the characteristics according to the time constant of the discharge circuit, and the drive voltage Vp falls below the command value Vi, the transistor Tr is turned on again.
a is turned on, and as a result, feedback control is performed so that the command value Vi and the drive voltage Vp always match.

The circuit operation of the polarity switching/charging/discharging unit 90 as described above is such that during the period when the command value Vi is negative, the rF(J signal is applied only to the transistor T located at the target position of the bridge circuit). (See Section 1), a voltage of opposite polarity to the above is applied, or a discharge circuit in the opposite direction is formed.Therefore,
Similarly to the above, the generated displacement of the piezoelectric actuator 9a is always
Additional value feedback control will be applied to the target displacement.

The piezoelectric actuator drive device of this embodiment configured and operated as described above has the following effects.

The piezoelectric actuator drive device of the embodiment has a command value Vi
The configuration is such that the power supply voltage of the dispersion 41 is boosted to an optimum value by chopper control based on the absolute value of , and a high voltage required for driving the piezoelectric actuator 9a is obtained. Therefore, a large and heavy high-voltage power supply is not required, and the device can be configured to be wider and smaller.

Furthermore, since the polarity switching/charging/discharging section 90 is provided, it is possible to control the piezoelectric actuator 9a with a simple configuration that generates a "positive" voltage as a voltage source. This results in
Further miniaturization and weight reduction of the power supply section can be achieved.

Furthermore, although the piezoelectric actuator driving device of the embodiment obtains a high voltage by skillfully applying digital technology as described above, it is not possible to draw the charge of the piezoelectric actuator 9a into its power source portion. However, in the polarity switching/charging/discharging section 90 of the embodiment, a discharging circuit that draws in the charged charges of the piezoelectric actuator 9a can be easily formed by the command of the drive signal Vd, and there is no problem in discharging the charged charges. Moreover, a resistor R with a resistance f[r selected appropriately according to the electrical capacity C of the piezoelectric actuator 9a, etc. is inserted into the discharge circuit. "For this reason,
This prevents the driving voltage Vp of the piezoelectric actuator 9a from becoming too low compared to the command value v1 due to overdischarge (see Fig. 4), further improving the control ability of the piezoelectric actuator 9a, and making effective use of the power source. It will be planned.

Although the above embodiment has been described assuming that the displacement generated by the piezoelectric actuator 9a is proportional to the drive voltage Vp, even if these relationships exhibit hysteresis characteristics, it is possible to change the logic of the control circuit 60. Similarly, a highly versatile system having the control accuracy and responsiveness of the above embodiment can be easily constructed.

Further, in the above embodiment, the discharge circuit constituted by the polarity switching/charging/discharging section 90 is constructed using the resistor R and the transistor Tre or Trf, and when the piezoelectric actuator 9a is discharged, the charge is always charged only through the resistor R. discharge is being performed. However, as described above, the resistor R is appropriately determined depending on the driving frequency and electrical capacitance C of the piezoelectric actuator 9a, the switching performance of the transistor Tr, and the like. Therefore, when constructing a system for changing the drive frequency of the piezoelectric actuator 9a, various resistance values r1, r2. It is possible to embody the present invention in various ways without departing from the gist of the present invention, such as making it possible to select a plurality of discharge circuits using resistors r3...

[Effects of the Invention] As described above in detail with reference to embodiments, the piezoelectric actuator drive device of the present invention generates the drive voltage to be applied to the piezoelectric actuator only when necessary, and tracks the generated displacement of the piezoelectric actuator to the target displacement. This is a value feedback control.

Therefore, wasteful power consumption and heat generation are prevented, and the power saving and downsizing of the system are both improved, which is an excellent effect.

Further, the discharging means for discharging the piezoelectric actuator includes a discharging circuit with a time constant corresponding to the capacitance of the piezoelectric element. Therefore, even when lowering the terminal voltage of the piezoelectric actuator, it is avoided to discharge the charged charge more than necessary, making effective use of the power supply, as well as providing excellent controllability and responsiveness, and reducing the voltage applied to the piezoelectric actuator. This provides a piezoelectric actuator drive device that allows easy analog control of voltage and displacement of the piezoelectric actuator.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a fuel injection system using a piezoelectric actuator drive device according to an embodiment of the present invention, and FIG.
The figure is a block diagram of the piezoelectric actuator drive device, Figure 3 is an electric circuit diagram of its polarity switching/charging/discharging gf5, and Figure 4 is a block diagram of the piezoelectric actuator drive device.
The figure shows a same polarity switching/charging/discharging section, and FIG. 5 shows a configuration explanatory diagram of a conventional piezoelectric actuator drive device.
・9a...Piezoelectric actuator 41...
Battery 45a... Drive block diagram 53... Displacement sensor 60... Control circuit 80... Variable voltage step-up section 90... Polarity switching/charging/discharging section agent Patent attorney Tsutomu Sadate (and 2 others) No. Figure 4 vp ------Vi

Claims (1)

[Scope of Claims] 1. A piezoelectric actuator drive device that adjusts a voltage applied to a piezoelectric actuator made of a piezoelectric element with a predetermined capacity and controls the displacement value of the piezoelectric actuator to a target displacement value, comprising: , a voltage determining means for determining an applied voltage to be applied to the piezoelectric actuator; a charging voltage detecting means for detecting a charging voltage of the piezoelectric actuator; and a charging voltage detected by the charging voltage detecting means is determined by the voltage determining means. voltage applying means for converting the power supply voltage into an applied voltage and applying it to the piezoelectric actuator when the charging voltage is lower than the applied voltage; and when the charging voltage is higher than the applied voltage, discharging the piezoelectric actuator with a time constant according to the predetermined capacity. A driving device for a piezoelectric actuator, comprising: a discharge means connected to a circuit;