WO2024252790A1 - Fluid control valve, fluid control device, and protection method for fluid control valve - Google Patents

Abstract

According to the present invention, a fluid control valve uses a piezo actuator that is formed by layering a plurality of piezo stacks. The fluid control valve applies drive voltage to the actuator to make the piezo stacks extend and contract and thereby makes a valve body contact and separate from a valve seat. To disperse the stress that acts on the piezo stacks during extension and contraction and suppress deterioration of a piezo stack that is close to the valve body, a first drive voltage that is applied to the piezo stack that is closest to the valve body is, over at least a prescribed period, lower than a second drive voltage that is applied to any one of the other piezo stacks.

Description

FLUID CONTROL VALVE, FLUID CONTROL DEVICE, AND METHOD FOR PROTECTING FLUID CONTROL VALVE

The present invention relates to a fluid control valve, a fluid control device, and a method for protecting a fluid control valve.

Patent Document 1 describes a fluid control valve that adjusts the valve opening by applying a drive voltage to a piezoelectric actuator made up of multiple piezoelectric stacks stacked together, causing the piezoelectric stacks to expand and contract.

By configuring multiple piezo stacks in this way to adjust the valve opening by expanding and contracting, it is possible to disperse the stress acting on the piezo stacks during expansion and contraction, compared to a configuration in which a single piezo stack is expanded and contracted to adjust the valve opening.

However, since piezo stacks are susceptible to degradation under high temperatures and high voltages, when the above-mentioned piezo actuator is used to control a high-temperature fluid, the piezo stack closest to the flow path of that fluid, in other words, the piezo stack closest to the valve body that constitutes the fluid control valve, becomes hotter than the other piezo stacks, and there is a risk that, for example, the piezo stack may deteriorate and short-circuit, impairing the function of the entire fluid control valve.

JP 2020-089037 A

The present invention was made to solve the above-mentioned problems, and its main objective is to suppress deterioration of the piezo stack close to the valve body while dispersing the stress acting on the piezo stack during expansion and contraction.

In other words, the fluid control valve according to the present invention comprises a valve seat, a valve body that moves toward and away from the valve seat, and an actuator that is made up of a plurality of stacked piezo stacks and to which a drive voltage is applied to drive the valve body, and is characterized in that a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks, at least for a predetermined period of time.

In such a fluid control valve, by stacking multiple piezo stacks, the stress acting on the piezo stack during expansion and contraction can be dispersed. In addition, since the first drive voltage applied to the piezo stack closest to the valve body is lower than the second drive voltage applied to any one of the other piezo stacks, deterioration of the piezo stack closest to the valve body can be suppressed even when controlling a high-temperature fluid.

The first drive voltage may be lower than the drive voltage applied to any other piezo stack, at least for a predetermined period of time.
In this case, the first drive voltage applied to the piezo stack closest to the valve body will be the lowest of the drive voltages applied to each piezo stack, so that deterioration of the piezo stack closest to the valve body can be more reliably suppressed.

The thermal effect of the high-temperature fluid may extend not only to the piezo stack closest to the valve body, but also to other piezo stacks close to the valve body. Specifically, the closer the piezo stack is to the valve body, the greater the thermal effect may be.
Therefore, it is preferable that the actuator has three or more piezo stacks, and that the drive voltage applied to the other piezo stacks closer to the valve body is lower than the drive voltage applied to the piezo stack farther from the valve body, at least for a predetermined period of time.
In this case, for example, by changing the drive voltage depending on the distance from the valve body, it is possible to suppress deterioration of each piezo stack other than the piezo stack closest to the valve body while taking into account thermal effects.

In order to reduce the number of parts and costs, it is preferable that the multiple piezo stacks are connected in parallel to a common power source.

It is preferable to include a voltage divider circuit interposed between the power supply and the piezo stack closest to the valve body.
In this case, the first driving voltage can be made lower than the second driving voltage with a simple circuit configuration.

However, even if a voltage divider circuit is used, if the original voltage of the first drive voltage and the second drive voltage becomes high, the first drive voltage also becomes high, and there is a risk that deterioration of the piezo stack close to the valve body cannot be suppressed as much as desired.
Therefore, it is preferable to provide a constant voltage circuit that is interposed between the power supply and the piezo stack closest to the valve body and that keeps the first drive voltage lower than the second drive voltage.
In this way, even if the base voltage becomes high, the first drive voltage is kept below a predetermined voltage, so that deterioration of the piezo stack close to the valve body can be more reliably suppressed.

However, even if the first drive voltage is made lower than the second drive voltage for a specified period of time, if the first drive voltage higher than the second drive voltage is applied for a long period of time during other periods, the deterioration of the piezo stack close to the valve body cannot be suppressed as much as desired.
Therefore, it is preferable that the average value of the first drive voltage applied during the drive period from the start to the end of drive of the actuator is lower than the average value of the second drive voltage applied during the drive period.
In this case, since the first drive voltage is lower on average than the second drive voltage during the drive period in which the drive voltage is applied to the piezo stack, deterioration of the piezo stack close to the valve body can be suppressed.

In addition, the fluid control valve according to the present invention comprises a valve seat, a valve body which moves toward and away from the valve seat, and an actuator which is formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve body, and is characterized in that, of two piezo stacks included in the plurality of piezo stacks, the drive voltage applied to the piezo stack closer to the valve body is lower than the drive voltage applied to the piezo stack farther from the valve body.
In such a fluid control valve, by stacking multiple piezo stacks, the stress acting on the piezo stacks during expansion and contraction can be dispersed, and the piezo stacks closer to the valve body can be prevented from deteriorating more rapidly than the piezo stacks farther from the valve body.

Furthermore, the fluid control valve according to the present invention is characterized in comprising: a valve seat, a valve body which moves toward and away from the valve seat, an actuator formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve body, a diagnostic piezo stack which is stacked closer to the valve body than the actuator, and a degradation diagnosis circuit which applies a diagnostic voltage different from the drive voltage to the diagnostic piezo stack.
In such a fluid control valve, by stacking multiple piezo stacks, the stress acting on the piezo stack during expansion and contraction can be distributed, and by using a diagnostic piezo stack and a deterioration diagnosis circuit to diagnose deterioration of the piezo stack closer to the valve body than the actuator, when controlling a high-temperature fluid, it is possible to predict the degree of deterioration of the piezo stack that is closer to the valve body among the piezo stacks that make up the actuator, and suppress deterioration of that piezo stack.

It is preferable to provide a sensor for detecting leakage current from the piezo stack closest to the valve body when the diagnostic voltage is applied.
In this case, the decrease in the internal resistance of the piezo stack closest to the valve body can be used as an indication of the degree of deterioration of that piezo stack.

Furthermore, a fluid control device according to the present invention is characterized by comprising the above-mentioned fluid control valve.
Such a fluid control device can achieve the same effects as the above-mentioned fluid control valve.

In addition, the method for protecting a fluid control valve according to the present invention is a method for protecting a fluid control valve comprising a valve seat, a valve body that moves toward and away from the valve seat, and an actuator formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve body, characterized in that a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks, for at least a predetermined period of time.
According to this method, by stacking multiple piezo stacks, the stress acting on the piezo stack during expansion and contraction can be dispersed, and since the first drive voltage is lower than the second drive voltage, deterioration of the piezo stack close to the valve body can be suppressed even when controlling a high-temperature fluid.

Furthermore, the method for protecting a fluid control valve according to the present invention is a method for protecting a fluid control valve comprising a valve seat, a valve body that moves toward and away from the valve seat, and an actuator formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve body, characterized in that a diagnostic voltage different from the drive voltage is applied to a diagnostic piezo stack that is stacked closer to the valve body than the actuator.
According to this method, by stacking multiple piezo stacks, it is possible to distribute the stress acting on the piezo stack during expansion and contraction, and by diagnosing the deterioration of the piezo stack closer to the valve body than the actuator using a diagnostic piezo stack and a deterioration diagnosis circuit, when controlling a high-temperature fluid, it is possible to predict the degree of deterioration of the piezo stack closest to the valve body among the piezo stacks that make up the actuator, and suppress the deterioration of that piezo stack.

The present invention, configured in this way, can distribute the stress acting on the piezo stack during expansion and contraction while suppressing deterioration of the piezo stack close to the valve body.

1 is an overall schematic diagram of a fluid control device according to a first embodiment of the present invention; FIG. 2 is an overall schematic view of the fluid control valve according to the embodiment; FIG. 2 is a circuit diagram of a drive circuit according to the embodiment. FIG. 11 is a circuit diagram of a drive circuit according to a modified example of the embodiment. FIG. 11 is a circuit diagram of a drive circuit according to a modified example of the embodiment. FIG. 11 is a circuit diagram of a drive circuit according to a modified example of the embodiment. FIG. 13 is an overall schematic view of a fluid control valve according to a second embodiment. 2 is a schematic diagram of a drive circuit and a degradation diagnosis circuit according to the embodiment;

<Device configuration of the first embodiment>
A first embodiment of a fluid control valve 3 according to the present invention will be described with reference to the drawings.

The fluid control valve 3 of this embodiment is used in a fluid control device 100 that controls the flow rate of a fluid, such as a process gas, supplied to a chamber, for example, in a semiconductor manufacturing process.

As shown in FIG. 1, the fluid control device 100 includes a block 1 in which an internal flow path FC is formed, a flow rate detection mechanism 2 that detects the flow rate of the fluid flowing through the internal flow path FC, a fluid control valve 3 that controls the fluid, a drive circuit 331 electrically connected to the fluid control valve 3, a housing 4 that houses the flow rate detection mechanism 2, the fluid control valve 3, and the drive circuit 331, and a control unit 5 that controls the operation of the fluid control valve 3.

A flow rate detection mechanism 2, a fluid control valve 3, and a housing 4 are attached to the block 1.
In this embodiment, a high-temperature (e.g., 100 degrees or higher) process gas flows through the internal flow path FC of block 1, and to prevent the gas from being cooled, block 1 is heated to a high temperature by a heater (not shown).

The flow rate detection mechanism 2 has a thermal flow rate detection sensor and measures the flow rate of the process gas flowing through the internal flow path FC. The flow rate detection sensor may be of a differential pressure type, Coriolis type, ultrasonic type, or the like.

The fluid control valve 3 is a piezoelectric valve that controls the process gas in the internal flow path FC, and is provided downstream of the flow rate detection mechanism 2 in this example. The fluid control valve 3 may also be provided upstream of the flow rate detection mechanism 2.

As shown in FIG. 2, the fluid control valve 3 is a normally closed type fluid control valve that includes a valve seat 31, a valve body 32, a piezoelectric actuator 33, a plunger 34, and a casing 35, and is configured so that the valve body 32 moves toward and away from the valve seat 31 as the piezoelectric actuator 33 expands and contracts.

More specifically, the piezo actuator 33 is held at one end of the casing 35 and extends to the other end of the casing 35, thereby pushing the valve body 32 via the plunger 34 and creating a distance between the valve seat 31 and the valve body 32. Here, the other end of the casing 35 is the side where the block 1 in which the internal flow path FC is formed is provided (in other words, the side where the valve seat 31 and the valve body 32 are provided).

The piezo actuator 33 has a plurality of piezo stacks X that expand and contract when a driving voltage greater than 0 V is applied thereto, and these piezo stacks X are stacked in the direction in which the piezo actuator 33 expands and contracts.
When a drive voltage is applied from the drive circuit 331, the piezo stacks X expand and contract, causing the piezo actuator 33 to expand and contract.

2, the piezo actuator 33 of this embodiment includes three piezo stacks X1, X2, and X3 arranged in order from bottom to top along the vertical direction. Here, the upward and downward directions respectively indicate the directions toward one end and the other end of the casing 35. The valve seat 31 and the valve body 32 are arranged below the piezo stack X1, and the piezo stack X1 is the piezo stack X closest to the valve body 32 in this embodiment.
Although the piezo stack X in FIG. 2 is arranged along the vertical direction, it may be arranged along a direction intersecting the vertical direction, for example, along the horizontal direction.

The piezo stack X is formed, for example, by stacking multiple piezo elements, and each piezo stack X is arranged in a row so that it expands and contracts in the same direction.

In addition, the piezo actuator 33 of this embodiment is equipped with three piezo stacks X with uniform dimensions and performance, but the dimensions and performance of each piezo stack X may be different, and it is sufficient for the piezo actuator 33 to be equipped with two or more piezo stacks X.

2, the drive circuit 331 applies a drive voltage to each piezo stack X. This drive voltage is controlled in response to a drive signal from the control unit 5, which will be described later.
In this embodiment, the drive voltages applied to the three piezo stacks X1, X2, and X3 are distinguished by being called drive voltages V1, V2, and V3, respectively.

The drive circuit 331 also has a common power supply PS to which each piezo stack X is connected in parallel, as shown in FIG. 3.

The control unit 5 is a computer equipped with a CPU, memory, an input/output interface, etc., and by making the CPU and peripheral devices cooperate in accordance with a predetermined program stored in a predetermined area of the memory, it has at least the functions of a flow rate calculation unit 51 and a valve control unit 52, as shown in FIG. 2.
The control unit 5 in this embodiment is housed in a housing 4 .

As shown in FIG. 1, the flow rate calculation unit 51 calculates the flow rate of the process gas flowing through the internal flow path FC based on the output value of the flow rate detection mechanism 2.

As shown in FIG. 1, the valve control unit 52 outputs a drive signal to the drive circuit 331 based on the set flow rate input from the outside and the calculated flow rate calculated by the flow rate calculation unit 51, and applies a drive voltage to each piezo stack X to adjust the valve opening of the fluid control valve 3.

In this embodiment, below the piezo actuator 33 there is an internal flow path FC through which high-temperature process gas flows, and a block 1 that is heated by a heater to prevent the gas from liquefying. The piezo stack X1, which is located closest to these and closest to the valve body 32, is more likely to reach a high temperature state than the other piezo stacks X2 and X3.

Thus, the fluid control valve 3 is configured such that, when the drive voltage V1 applied to the piezo stack X1 closest to the valve body 32 among the multiple piezo stacks X possessed by the piezo actuator 33 is defined as a first drive voltage, and the drive voltage V2 or V3 applied to either one of the other piezo stacks X2 or X3 is defined as a second drive voltage, the first drive voltage is lower than the second drive voltage for at least a predetermined period of time.
In particular, in this embodiment, both drive voltages V2 and V3 are second drive voltages, that is, the drive voltage V1 is configured to be lower than the drive voltages V1, V2, and V3 applied to each of the piezo stacks X1, X2, and X3 (the first drive voltage is configured to be the lowest of the drive voltages applied to each piezo stack).
However, the first driving voltage does not need to be the lowest among the driving voltages applied to each piezo stack X, but it suffices if it is lower than the second driving voltage applied to at least one of the other piezo stacks X.

The specified period may be any length such that deterioration of the piezo stack X1 closest to the valve body 32 is suppressed more than deterioration of the other piezo stacks X2 or X3, and may be, for example, more than half the driving period from the start to the end of driving of the actuator.
Here, the drive period may be the period from when the application of the drive voltage begins to when the application of the drive voltage ends, or it may be the period from when multiple pulsed applications of the drive voltage begin to when the application of the drive voltage ends, or it may be, for example, the period required for one step in a semiconductor manufacturing process.

The predetermined period may also be the period during which a high drive voltage V2 or V3 (second drive voltage) is applied to the piezo stack X2 or X3, for example, the period during which the difference between the rated voltage of the piezo stack X and the second drive voltage is equal to or less than a certain value, or the period during which the ratio of the rated voltage to the second drive voltage is equal to or less than a certain value.

However, even if the first drive voltage is made lower than the second drive voltage for a specified period of time, if a first drive voltage higher than the second drive voltage is applied for a long period of time during other periods, the deterioration of the piezo stack X1 close to the valve body 32 cannot be suppressed as much as desired.

Therefore, it is preferable that the average value of the first drive voltage applied during the drive period of the actuator is lower than the average value of the second drive voltage applied during the drive period.

As shown in FIG. 3, this embodiment includes a voltage divider circuit C1 between the power source PS that applies a drive voltage to each piezo stack X and the piezo stack X1 that is closest to the valve body 32, making the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages).

The drive voltage V1 applied from the power supply PS via the voltage divider circuit C1 to the piezo stack X1 closest to the valve body 32 is the first drive voltage, and the drive voltage V2 or V3 applied from the power supply PS to the other piezo stack X2 or X3 without passing through the voltage divider circuit C1 is the second drive voltage.
When the first drive voltage is applied in this manner, the predetermined period corresponds to the entire period during which the drive voltage is applied to each piezo stack X from the power source PS.

Here, this voltage dividing circuit C1 has two resistors RA having the same resistance value, and the drive voltage V1 (first drive voltage) is half the drive voltages V2 and V3 (second drive voltages). Note that the type and number of resistors RA constituting the voltage dividing circuit C1 may be appropriately changed in order to obtain a desired first drive voltage.
The resistor RA may be a variable resistor.

Effects of the First Embodiment
In the fluid control valve 3 of the present embodiment configured as described above, by stacking a plurality of piezo stacks X, it is possible to disperse the stress acting on the piezo stacks X during expansion and contraction. In addition, since the first drive voltage is lower than the second drive voltage, it is possible to suppress deterioration of the piezo stack X1 close to the valve body 32 even when controlling a high-temperature fluid.

Here, as another configuration for preventing deterioration of the piezo stack X1 closest to the valve body 32, it is also possible to consider disposing a spacer or the like between the piezo stack X1 closest to the valve body 32 and the internal flow path FC and the block 1.
In comparison, in the fluid control valve 3 of the present embodiment, the first drive voltage, which is lower than the second drive voltage but greater than 0 V, can be applied to the piezo stack X1 closest to the valve body 32. This makes it possible to prevent deterioration of the nearest piezo stack X1, while also achieving both space saving and ensuring the amount of expansion and contraction of the piezo actuator 33.

In addition, in this embodiment, the average value of the first drive voltage applied during the drive period is lower than the average value of the second drive voltage applied during the drive period, so deterioration of the piezo stack X1 close to the valve body 32 can be suppressed.

In addition, since multiple piezo stacks X are connected in parallel to a common power supply PS, the number of parts and costs can be reduced.

Furthermore, a voltage divider circuit C1 is provided between the power supply PS and the piezo stack X1 closest to the valve body 32, so that the first drive voltage can be made lower than the second drive voltage with a simple circuit configuration.

Incidentally, in a piezoelectric actuator 33 in which multiple piezo stacks X are connected in parallel to a common power source PS, if even one piezo stack X suffers a malfunction such as a short circuit, the function of the entire piezo actuator 33 will be impaired, even if the other piezo stacks X are normal.
As described above, the piezo stack X deteriorates quickly when a high voltage is applied in a high-temperature environment, and the piezo stack X1 close to the valve body 32 is easily exposed to high temperatures.
However, in the fluid control valve 3 of the present embodiment, the drive voltage V1 (first drive voltage) is set lower than the drive voltages V2 and V3 (second drive voltages), so that it is possible to prevent the piezo stack X1 closest to the valve body 32 from failing earlier than the other piezo stacks X2 or X3, which would result in impairment of the function of the piezo actuator 33 as a whole.

<Modification of the First Embodiment>
In the above embodiment, the voltage divider circuit C1 is used to make the first drive voltage lower than the second drive voltage, but another method may be used.

For example, a plurality of power sources PS may be provided in the piezoelectric actuator 33, and the first drive voltage and the second drive voltage may be generated from different power sources PS.
In this way, a first drive voltage that is lower than the second drive voltage and higher than 0 V can be freely created over a predetermined period of time, and the expansion and contraction of the piezo stack X1 closest to the valve body 32 can be freely adjusted to be used for adjusting the valve opening degree, while deterioration of this piezo stack X1 can be suppressed.
Furthermore, even if the piezo stack X1 closest to the valve body 32 is short-circuited due to deterioration, since it is not connected to a power source in parallel with the other piezo stacks X2 or X3, the piezo actuator 33 as a whole can be driven by the other piezo stacks X2 or X3.
In this case, the predetermined period can be freely set.

Also, as shown in FIG. 4, instead of the voltage divider circuit C1, a constant voltage circuit C2 that keeps the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages) may be interposed between the power source PS and the piezo stack X1 closest to the valve body 32.
If the first drive voltage is generated using the voltage divider circuit C1, the first drive voltage will also become high when the voltage of the source of the drive voltage becomes high. On the other hand, if the first drive voltage is generated using the constant voltage circuit C2, the first drive voltage will not exceed a predetermined voltage, so that deterioration of the piezo stack X1 close to the valve body 32 can be more reliably suppressed even if the source voltage becomes high.

The predetermined voltage may be set to, for example, a value smaller than the rated voltage of the piezo stack X. Alternatively, the predetermined voltage may be set based on the drive voltage required to maximize or minimize the valve opening.
In this case, the predetermined period is a period during which the source voltage of the drive voltage is higher than the predetermined voltage set in the constant voltage circuit C2.

The specific circuit configuration of the constant voltage circuit C2 may be one that uses a Zener diode ZD. Note that the constant voltage circuit C2 may also be one that uses, for example, a three-terminal regulator.

Also, to make the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages), as shown in FIG. 5, a Zener diode ZD, for example, may be connected in series to the piezo stack X1 closest to the valve body 32, or as shown in FIG. 6, a resistor RA may be connected in series to the piezo stack X1 closest to the valve body 32 and the Zener diode ZD.

For example, in FIG. 6, the Zener diode ZD is disposed on the power supply side, but the positional relationship of each element may be changed as appropriate.
In these cases, the predetermined period is the entire period during which the drive voltage is applied to each piezo stack X from the power source PS.

In the above embodiment, the first drive voltage is maintained higher than 0 V by the voltage divider circuit C1 for a predetermined period of time, but the first drive voltage may be 0 V. In other words, applying the first drive voltage also includes not applying the drive voltage for a predetermined period of time.
In this case, the deterioration of the piezo stack X1 close to the valve body 32 can be more reliably suppressed.

Further, a configuration may be adopted in which the drive voltage is not always applied to the piezo stack X1 closest to the valve body 32, and for example, the piezo stack X1 does not have to be connected to the power source PS.
In this case, the piezo stack X1 closest to the valve body 32 is not connected to a power source in parallel with the other piezo stacks X2 and X3, so even if the piezo stack X1 closest to the valve body 32 is affected by heat and short-circuits or the like, the valve opening adjustment function of the entire piezo actuator 33 is not impaired.
Furthermore, by simply changing the circuit configuration, the piezo stack X1 closest to the valve body 32 can be used like a spacer without significantly changing the structure of a conventional fluid control valve, and deterioration of the other piezo stacks X close to the valve body 32 can be suppressed.

In the above embodiment, attention was focused only on the first drive voltage applied to the piezo stack X1 closest to the valve body 32. However, the thermal effect of the high-temperature fluid may extend not only to the piezo stack X1 closest to the valve body 32, but also to the other piezo stacks X2 or X3 close to the valve body 32.
Specifically, the piezo stack X2, which is the second closest to the valve body 32, may be subject to the second greatest thermal effect.

Therefore, when the piezo actuator 33 has three piezo stacks X as in the above embodiment, it is preferable that, among the other piezo stacks X2 or X3, the drive voltage V2 applied to the piezo stack X2 closer to the valve body 32 is lower than the drive voltage V3 applied to the piezo stack X3 farther from the valve body 32 for at least a predetermined period of time.
In this way, it is possible to suppress deterioration not only of the piezo stack X1 closest to the valve body 32, but also of the piezo stack X2 second closest to the valve body 32.

In addition, the first drive voltage may be applied collectively to a plurality of continuously stacked piezo stacks X, including the piezo stack X1 closest to the valve body 32. For example, the drive voltages V1 and V2 applied to the piezo stacks X1 and X2 in the above embodiment may be the first drive voltage.
In this way, deterioration of the multiple piezo stacks X arranged closer to the valve body 32 can be suppressed collectively.

In the above embodiment, the piezo actuator 33 is composed of three piezo stacks X1, X2, and X3, but the number of piezo stacks X that make up the actuator may be two, four or more, as long as there is more than one.

In the above embodiment, a configuration was described in which the average value of the first drive voltage applied during the drive period is made lower than the average value of the second drive voltage applied during the drive period, but even if such a configuration is not adopted, it is sufficient as long as the first drive voltage is lower than the second drive voltage during a predetermined period, thereby suppressing deterioration of the piezo stack X1 close to the valve body 32.

The fluid control valve 3 in the above embodiment is a normally closed type, but it may be a normally open type.

In the above embodiment, a first drive voltage lower than the second drive voltage applied to at least one of the other piezo stacks X is applied to the piezo stack X1 closest to the valve body 32. Alternatively, the piezo stacks X may be configured such that, of two piezo stacks X included in the plurality of piezo stacks X, the drive voltage applied to one of the piezo stacks X closer to the valve body 32 is lower than the drive voltage applied to the other piezo stack X farther from the valve body 32.
Even with this configuration, by stacking multiple piezo stacks X, the stress acting on the piezo stacks X during expansion and contraction can be dispersed, and one piezo stack X closer to the valve body 32 can be prevented from deteriorating more rapidly than the other piezo stack X farther from the valve body 32.

<Device configuration of the second embodiment>
Next, a second embodiment of the fluid control valve 3 according to the present invention will be described with reference to the drawings.

The fluid control valve 3 of the second embodiment differs from that of the first embodiment in that it further includes a diagnostic piezo stack Y and a deterioration diagnosis circuit C3, and in that the control unit 5 has a deterioration diagnosis function.
Below, these differences will be explained, and explanations of commonalities will be omitted where appropriate.

As shown in FIG. 7 , the fluid control valve 3 of the second embodiment includes a diagnostic piezo stack Y that is stacked closer to the valve body 32 than the piezo actuator 33 is.
The diagnostic piezo stack Y in this embodiment is located below the piezo actuator 33 and is sandwiched between the piezo actuator 33 and the valve body 32.
In this embodiment, the diagnostic piezo stack Y is provided integrally with the multiple piezo stacks X that constitute the piezo actuator 33, but may be provided separately.

To this piezo stack Y for diagnosis, a degradation diagnosis circuit C3 applies a diagnosis voltage D which is separate from the drive voltage.
As shown in FIG. 8, the degradation diagnostic circuit C3 has a power supply PS2 to which the diagnostic piezo stack Y is connected, and a current sensor A for detecting leakage current from this diagnostic piezo stack Y.

Here, the leakage current is the current flowing through the diagnostic piezo stack Y, which increases as the diagnostic piezo stack Y deteriorates and its resistance decreases.

7, the degradation diagnosis circuit C3 applies a diagnostic voltage D to the diagnostic piezo stack Y in response to a diagnostic signal from the control unit 5, which will be described later. When the diagnostic voltage D is applied, the current sensor A detects a current leaking from the diagnostic piezo stack Y, and outputs a signal indicating the detected value to the control unit 5.
The diagnostic voltage D may be applied to the diagnostic piezo stack Y continuously or intermittently at a predetermined voltage. Also, it may be applied only when diagnosis is desired.
The diagnostic voltage D is preferably lower than the drive voltage so that the diagnostic piezo stack Y does not deteriorate quickly.

In this embodiment, as shown in Figures 7 and 8, the driving circuit 331 is not connected to the diagnostic piezo stack Y, and no driving voltage is applied to it.

The control unit 5 of the second embodiment has at least the functions of a flow rate calculation unit 51, a valve control unit 52, a diagnostic voltage control unit 53, a memory unit 54, and a degradation diagnosis unit 55.

The diagnostic voltage control unit 53 outputs a diagnostic signal to the degradation diagnostic circuit C3 based on a diagnostic command input from the outside, and controls the diagnostic voltage D.

The memory unit 54 stores reference values for diagnosing the degree of deterioration of the piezo stack X.

Degradation diagnostic unit 55 compares the detection value indicated by the signal from degradation diagnostic circuit C3 with a reference value stored in memory unit 54 to diagnose the degree of degradation of diagnostic piezo stack Y.
The deterioration diagnosis unit 55 outputs the degree of deterioration of the diagnostic piezo stack Y as a diagnosis result. In addition, the deterioration degree of the piezo stack X constituting the piezo actuator 33 may be predicted from the deterioration degree of the diagnostic piezo stack Y and output as a diagnosis result.

Effects of the Second Embodiment
In the fluid control valve 3 of this embodiment configured in this manner, by stacking a plurality of piezo stacks X, it is possible to disperse the stress acting on the piezo stack X during expansion and contraction. In addition, by using the deterioration diagnosis circuit C3 to diagnose the deterioration of the diagnostic piezo stack Y that is stacked closer to the valve body 32 than the piezo actuator 33, it is possible, when controlling a high-temperature fluid, to predict the degree of deterioration of the piezo stack X that is closer to the valve body, among the piezo stacks X that constitute the piezo actuator 33, and to suppress the deterioration of that piezo stack X.

In addition, a sensor is provided to detect leakage current from the diagnostic piezo stack Y, so that a decrease in the internal resistance of the diagnostic piezo stack Y can be used for diagnosis as an indication of the degree of deterioration of the piezo stack X that constitutes the piezo actuator 33.

<Modification of the second embodiment>
In the above embodiment, no drive voltage is applied to the diagnostic piezo stack Y, but a drive voltage may be applied to the diagnostic piezo stack Y.

In the above embodiment, only one diagnostic piezo stack Y is disposed below the piezo actuator 33, but an additional diagnostic piezo stack Y may be provided in the same position or in another position.
For example, if an additional diagnostic piezo stack Y is provided above the piezo actuator 33, it is possible to predict the degree of deterioration of the piezo stack X that is far from the valve body among the multiple piezo stacks X that make up the piezo actuator 33, and to know the difference in the degree of deterioration between this and the piezo stacks closer to the valve body.
Furthermore, if the additional diagnostic piezo stack Y is sandwiched between a plurality of piezo stacks X that constitute the piezo actuator 33, the degree of deterioration of the two piezo stacks X adjacent to the additional diagnostic piezo stack Y can be predicted.

According to the present invention, by stacking multiple piezo stacks, it is possible to disperse the stress acting on the piezo stack during expansion and contraction. In addition, since the first drive voltage applied to the piezo stack closest to the valve body is lower than the second drive voltage applied to any one of the other piezo stacks, it is possible to suppress deterioration of the piezo stack closest to the valve body even when controlling a high-temperature fluid.

100... Fluid control device FC... Internal flow path 1... Block 2... Flow rate sensor 3... Fluid control valve 31... Valve seat 32... Valve body 33... Piezo actuator 331... Drive circuit 4... Housing 5... Control unit C1... Voltage dividing circuit C2... Constant voltage circuit C3... Deterioration diagnosis circuit PS... Power supply PS2... Power supply A... Leak current sensor X... Piezo stack X1... Piezo stack X2 closest to the valve body... Other piezo stack X3... Other piezo stack Y... Diagnostic piezo stack

Claims (13)

A valve seat;
a valve body that moves toward and away from the valve seat;
an actuator including a plurality of piezo stacks stacked together, the actuator driving the valve body when a drive voltage is applied thereto;
A fluid control valve, characterized in that a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks over at least a predetermined period of time. The fluid control valve of claim 1, characterized in that the first drive voltage is lower than the drive voltages applied to any of the other piezo stacks for at least a predetermined period of time. the actuator includes three or more piezo stacks;
2. The fluid control valve according to claim 1, wherein a drive voltage applied to a piezo stack closer to the valve body among the other piezo stacks is lower than a drive voltage applied to a piezo stack farther from the valve body, at least for a predetermined period of time. The fluid control valve according to claim 1 or 2, characterized in that the multiple piezo stacks are connected in parallel to a common power source. The fluid control valve according to claim 3, further comprising a voltage divider circuit disposed between a power source that applies a drive voltage to each of the piezo stacks and the piezo stack closest to the valve body. The fluid control valve according to claim 3, further comprising a constant voltage circuit disposed between a power source that applies a drive voltage to each piezo stack and the piezo stack closest to the valve body, and that keeps the first drive voltage lower than the second drive voltage. The fluid control valve according to any one of claims 1 to 5, characterized in that the average value of the first drive voltage applied during the drive period from the start to the end of drive of the actuator is lower than the average value of the second drive voltage applied during the drive period. A valve seat;
a valve body that moves toward and away from the valve seat;
an actuator including a plurality of piezo stacks stacked together, the actuator driving the valve body when a drive voltage is applied thereto;
Among two piezo stacks included in the plurality of piezo stacks,
A fluid control valve, wherein a drive voltage applied to a piezo stack closer to the valve body is lower than a drive voltage applied to a piezo stack farther from the valve body. A valve seat;
a valve body that moves toward and away from the valve seat;
an actuator including a plurality of piezo stacks stacked together, the actuator being adapted to drive the valve body when a drive voltage is applied thereto;
a diagnostic piezo stack disposed closer to the valve body than the actuator;
a deterioration diagnostic circuit for applying a diagnostic voltage different from the drive voltage to the diagnostic piezo stack. The fluid control valve according to claim 7, further comprising a sensor that detects leakage current from the piezo stack closest to the valve body when the diagnostic voltage is applied. A fluid control device comprising a fluid control valve according to any one of claims 1 to 8. A method for protecting a fluid control valve comprising: a valve seat; a valve body that moves toward and away from the valve seat; and an actuator that is formed by stacking a plurality of piezo stacks and that drives the valve body when a drive voltage is applied thereto, the method comprising the steps of:
A method for protecting a fluid control valve, comprising the steps of: applying a first drive voltage to the piezo stack closest to the valve body, the first drive voltage being lower than a second drive voltage applied to any one of the other piezo stacks, for at least a predetermined period of time. A method for protecting a fluid control valve comprising: a valve seat; a valve body that moves toward and away from the valve seat; and an actuator that is formed by stacking a plurality of piezo stacks and that drives the valve body when a drive voltage is applied thereto, the method comprising the steps of:
A method for protecting a fluid control valve, comprising applying a diagnostic voltage different from the drive voltage to a diagnostic piezo stack that is stacked closer to the valve body than the actuator.

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