JP7405016B2 - sound insulation device - Google Patents

Description

The technology disclosed herein relates to a sound insulation device.

2. Description of the Related Art Conventionally, a sound insulation device using a piezoelectric material is known as a sound insulation material for insulating external noise. For example, Patent Document 1 discloses a sound insulation device including two piezoelectric films and an analog control circuit. The control circuit of Patent Document 1 includes a negative capacitance circuit and an amplifier circuit using an operational amplifier.

JP2020-008663A

By the way, when the sound insulation device of Patent Document 1 is installed on the floor of a vehicle or the like, the second signal containing a large amount of noise is output to the second piezoelectric film, making it difficult to use the second piezoelectric film as a sound insulation material. The reality is that this is difficult. Although the control circuit disclosed in Patent Document 1 has noise countermeasures using a capacitor, the weak noise that gets into the control circuit is amplified by the negative capacitance circuit and the amplifier circuit, and the second piezoelectric film It is thought that it is output to . In order to remove this noise, it is conceivable to provide an additional filter circuit in the control circuit, but in this case, the phase of the second signal is likely to shift, and the circuit becomes larger, resulting in an increase in the number of parts and cost. undesirable.

The present invention was completed based on the above-mentioned circumstances, and is a sound insulation device using a piezoelectric film as a sound insulation material, in which noise in a signal amplified by a negative capacitance circuit and an amplifier circuit can be reduced by a simple configuration. The aim is to reduce

As a means for solving the above problems, the technology disclosed herein includes: a first piezoelectric film that has piezoelectricity and receives sound to be sound-insulated; and a control circuit electrically connected to the first piezoelectric film and the second piezoelectric film. The control circuit includes a negative capacitance circuit that is electrically connected to the first piezoelectric film and causes distortion in the first piezoelectric film that is opposite in phase to distortion in the first piezoelectric film caused by the sound; A second signal is electrically connected to the negative capacitance circuit and the second piezoelectric film, and is an amplified first signal output from the negative capacitance circuit to the first piezoelectric film, and outputs a second signal to the second piezoelectric film. and an amplifier circuit, wherein the amplifier circuit is configured by a step-up transformer circuit.

According to the above configuration, the first piezoelectric film and the negative capacitance circuit, and the second piezoelectric film are separated and insulated by the primary coil and the secondary coil of the step-up transformer circuit. This prevents noise that has entered the first piezoelectric film and the negative capacitance circuit from being amplified by the step-up transformer circuit, or noise that has entered the first piezoelectric film and the negative capacitance circuit from the second piezoelectric film. is prevented. As a result, the first signal can be amplified with less noise and output to the second piezoelectric film. Furthermore, even when this sound insulation device is installed in an environment where various noises may occur, it is possible to suitably exhibit sound insulation performance.

In a preferred embodiment of the sound insulation device, the negative capacitance circuit has the highest sound insulation effect due to the voltage changing unit capable of changing the voltage value of the first signal, the first piezoelectric film, and the second piezoelectric film. and a frequency setting section capable of setting a frequency of a sound, and the amplifier circuit has a configuration capable of changing an amplification factor of the second signal with respect to the first signal. By providing the frequency setting section in this way, it is possible to more reliably block out the sound of the set frequency. Here, if the voltage value of the first signal is increased, the first piezoelectric film can be given characteristics (peaky frequency characteristics) that have a particularly high sound insulation effect against sounds of the set frequency, and this The second piezoelectric film into which the second signal obtained by amplifying the signal is inputted can also exhibit a higher sound insulation effect than the first piezoelectric film while having frequency characteristics with the same tendency.

According to the present invention, in a sound insulation device using a piezoelectric film as a sound insulation material, noise in a signal amplified by a negative capacitance circuit and an amplifier circuit can be reduced with a simple configuration.

A sectional view showing a vehicle equipped with a sound insulation device according to an embodiment Diagram showing the configuration of the sound insulation device in Figure 1 Circuit diagram showing the circuit provided in the control unit

An embodiment of the present invention will be described using a sound insulation device 10 mounted on a vehicle 1 as an example, with reference to FIGS. 1 to 3. Note that the symbols F, Rr, U, D, IN, and OUT shown in each figure indicate the front and rear in the vehicle traveling direction, the upper and lower sides in the vertical direction (vertical direction), the indoor side, and the outdoor side, respectively. However, the above-mentioned direction is only determined for convenience and should not be interpreted in a limited manner.

As shown in FIG. 1, the vehicle 1 includes wheels 2, 2 that are rotationally driven to make the vehicle 1 run, and a floor panel that forms part of the framework of the vehicle 1 and constitutes the floor surface of the passenger compartment. 3, and seats 4, 4 supported by the floor panel 3 and on which an occupant can sit. In this vehicle 1, as the vehicle 1 drives or travels, contact noise (road noise) generated when the tires mounted on the wheels 2, 2 come into contact with the road surface, engine noise, etc. are transmitted as noise through the floor panel 3. Propagates to the interior space of the vehicle. Therefore, the vehicle 1 is equipped with a sound insulation device 10 for reducing such noise.

Note that in the technology disclosed herein, "sound insulation" means an effect of suppressing the transmission of sound (sound waves) and improving transmission loss. In other words, the term "sound insulation" does not only mean completely blocking the transmission of sound (sound waves).

For example, as shown in FIG. 1, the sound insulation device 10 is installed on the floor surface (indoor side surface) of the floor panel 3 below the seat 4 at the front of the vehicle. The sound insulation device 10 includes a sound insulation section 20 attached to the floor panel 3 and a control circuit 30 that controls driving of the sound insulation section 20. Therefore, in this embodiment, the upper side of the sound insulation device 10 corresponds to the indoor side, and the lower side of the sound insulation device 10 corresponds to the outdoor side.

The sound insulation section 20 includes a first piezoelectric film 21, a second piezoelectric film 22, and a cylindrical frame 23 that supports the first piezoelectric film 21 and the second piezoelectric film 22 in a stretched state. The first piezoelectric film 21 is disposed relatively to the outside of the vehicle, and the second piezoelectric film 22 is disposed relatively to the interior of the vehicle. Since the noise generated when the vehicle 1 is running is mainly generated from the foot side of the vehicle 1, in this sound insulation part 20, the noise to be insulated is mainly generated from the side of the floor panel 3, that is, the side of the first piezoelectric film 21. It will be incident from Here, the first piezoelectric film 21 is fixed to the frame 23 at a position slightly apart from the floor panel 3 so as not to contact the floor panel 3, and the floor panel 3 inhibits vibrations due to noise transmitted through the floor panel 3. It is now possible to receive (sensing) without being affected. Further, the first piezoelectric film 21 and the second piezoelectric film 22 are fixed to the frame 23 so as to be separated from each other without contacting each other. The first piezoelectric film 21 and the second piezoelectric film 22 are disposed close to each other while facing each other. It is preferable that the first piezoelectric film 21 and the second piezoelectric film 22 be arranged as close to each other as possible in order to further reduce the phase difference between the sounds caused by the two piezoelectric films.

The first piezoelectric film 21 and the second piezoelectric film 22 are mainly composed of piezoelectric materials 21A and 22A that exhibit a piezoelectric effect and an inverse piezoelectric effect. That is, the piezoelectric materials 21A and 22A have a film shape, and when vibrating in the thickness direction (thickness direction of the floor panel 3), stress and strain (elastic strain) are generated along the surface direction. It has the property of causing polarization in the thickness direction and generating voltage. In other words, the piezoelectric materials 21A and 22A generate voltage in the thickness direction by vibrating in the thickness direction upon receiving sound (sound wave). Furthermore, the piezoelectric materials 21A and 22A have a property that, when a voltage is applied in the thickness direction, expansion/contraction strain is induced in the elastic region along the surface direction according to the polarity of the voltage.

Examples of such piezoelectric materials 21A and 22A include polymeric piezoelectric materials (for example, polyvinidene fluoride (PVdF), etc.) and piezoelectric ceramics (barium titanate, lead zirconate titanate (PZT), etc.). be able to. Note that the piezoelectric materials 21A and 22A are not limited to those described above and can be changed as appropriate. Further, each of the piezoelectric materials 21A and 22A is provided with a pair of electrodes 21E and 21E and a pair of electrodes 22E and 22E on both surfaces thereof, respectively, for applying and extracting voltage. Such electrodes 21E, 21E, 22E, 22E can be constructed by, for example, depositing metal on piezoelectric materials 21A, 22A or bonding metal plates together, but are not limited thereto. In this embodiment, the first piezoelectric film 21 and the second piezoelectric film 22 have the same configuration such as dimensions and materials, and have the same mechanical properties, electrical properties, and piezoelectric properties.

The control circuit 30 includes a negative capacitance circuit 40 and an amplifier circuit 60. The negative capacitance circuit 40 is configured to operate in the same manner as a capacitor having a negative capacitance in the control circuit 30. For example, as shown in FIG. 3, the negative capacitance circuit 40 of this embodiment includes an operational amplifier 41, a variable resistor 42, a capacitor 43, and a semi-fixed resistor 44. The first piezoelectric film 21 is connected to a non-inverting input terminal of the operational amplifier 41, and a capacitor 43 and a semi-fixed resistor 44 are connected to form a positive feedback loop. In other words, the first piezoelectric film 21 is connected in parallel to the non-inverting input terminal of the operational amplifier 41 and the ground, which is equivalent to the first piezoelectric film 21 being connected in parallel to the negative capacitor in the control circuit 30. . Further, negative feedback is applied to the inverting input terminal of the operational amplifier 41 via a variable resistor 42 (a portion of the resistor 42B). Such a negative capacitance circuit 40 is configured to emit positive charge when a positive voltage is applied, for example.

In the negative capacitance circuit 40, when the negative capacitance circuit 40 is coupled to the first piezoelectric film 21, a positive or negative voltage generated when a sound wave is incident on the first piezoelectric film 21 is connected to the negative capacitance circuit 40. 40, positive or negative charges are released from the negative capacitance circuit 40 toward the first piezoelectric film 21, respectively. This reduces polarization within the first piezoelectric film 21 and reduces distortion of the first piezoelectric film 21. In other words, the charges released by the negative capacitance circuit 40 cause distortion that is in the opposite phase to the elastic distortion, and the apparent distortion is reduced. Therefore, it can be said that the apparent elastic modulus of the first piezoelectric film 21, defined as the ratio of external force to apparent strain, has increased, and the first piezoelectric film 21 behaves as if it had become harder. . As a result, the displacement (vibration) of the first piezoelectric film 21 that occurs in the direction of propagation of sound waves is also reduced, the transmission of sound waves is suppressed, and the first piezoelectric film 21 can function as a sound insulating material.

Here, in the negative capacitance circuit 40, by adjusting the impedance of the resistor 42A and the resistor 42B in the variable resistor 42, the capacitance of the capacitor 43, the resistance value of the semi-fixed resistor 44, etc., the complex It is known that the real and imaginary parts of the capacitance can be varied. Furthermore, it is known that by adjusting the semi-fixed resistor 44, the frequency characteristics of the loss coefficient (the ratio of the imaginary part to the real part of the complex capacitance) of the negative capacitance circuit 40 can be changed. That is, by appropriately setting the configurations of the variable resistor 42, the capacitor 43, and the semi-fixed resistor 44, for example, the loss coefficient of the negative capacitance circuit 40 can be adjusted to the dielectric loss of the first piezoelectric film 21 in any frequency band. It is possible to almost match the coefficient. As a result, the sound frequency (peak frequency) at which the first piezoelectric film 21 (and by extension, the second piezoelectric film) has the highest sound insulation effect can be set in the frequency range of the noise to be sound-insulated. Specifically, by increasing the resistance value of the semi-fixed resistor 44 in the negative capacitance circuit 40, the sound frequency at which the sound insulation effect is highest can be lowered, and by decreasing the resistance value of the semi-fixed resistor 44, the sound insulation effect can be lowered. You can raise the frequency of the sound for the best effect. As a preferred example, if the capacitor 43 is made of the same material as the piezoelectric material 21A in the first piezoelectric film 21, the loss coefficient can be easily adjusted to the first piezoelectric film 21 (more specifically, regardless of temperature or frequency). , the loss coefficient of the piezoelectric material 21A).

A signal V1 (first signal) is output from the output terminal of the operational amplifier 41. In the negative capacitance circuit 40, the voltage value of the signal V1 can be changed by changing the ratio between the resistor 42A and the resistor 42B that constitute the variable resistor 42 (voltage changing section). Specifically, when the resistance value of the resistor 42A is RA, the resistance value of the resistor 42B is RB, the voltage value of the signal V0 input to the non-inverting input terminal of the operational amplifier 41 is VA, and the voltage value of the signal V1 is VB. In this case, the relationship VB=VA*(1+RB/RA) is obtained. Here, the resistor 42A and the resistor 42B are preferably set so that the maximum voltage is output within a range where the circuit does not oscillate and the first piezoelectric film 21 itself does not start emitting sound.

Note that in the negative capacitance circuit 40, the operational amplifier 41 is connected to DC power supplies 31 and 32 for driving the arithmetic circuit. Further, the negative capacitance circuit 40 includes a plurality of capacitors 33 for reducing noise. Note that two resistors may be used instead of the variable resistor 42 and the semi-fixed resistor 44.

As shown in FIG. 3, the amplifier circuit 60 includes a primary coil 61, a secondary coil 62, and a semi-fixed resistor 63. Two coils, the primary coil 61 and the secondary coil 62, are magnetically coupled to constitute a step-up transformer circuit 60A. In the step-up transformer circuit 60A, the primary coil 61 and the secondary coil 62 are configured such that the number of turns Ns of the secondary coil 62 is greater than the number Np of turns of the primary coil 61. The voltage Vs of the secondary coil 62 is set higher (boosted) than the voltage Vp of the primary coil 61. The output terminal of the negative capacitance circuit 40 is connected to the step-up transformer circuit 60A via a semi-fixed resistor 63, and the output voltage of the operational amplifier 41 is applied to the primary coil 61. This allows the output voltage from the negative capacitance circuit 40 to be amplified on the secondary coil 62 side. In the amplifier circuit 60, by changing the turns ratio of the primary coil 61 and the secondary coil 62, the transformation ratio of the signal V2 to the signal V1 can be changed. Specifically, in general, the turns ratio and transformation ratio of the primary coil 61 and the secondary coil 62 are equal, and a relationship of Vp/Vs=Np/Ns is observed. Note that in this amplifier circuit 60, the primary coil 61 and the secondary coil 62 do not increase the power, but are called an amplifier circuit in a broad sense in that they amplify the voltage.

Note that the semi-fixed resistor 63 functions as a voltage dividing resistor and can be additionally provided in front of the step-up transformer circuit 60A. In the amplifier circuit 60, by increasing or decreasing the resistance of the semi-fixed resistor 63, the ratio of the input voltage of the step-up transformer circuit 60A to the input voltage of the amplifier circuit 60 can be decreased or increased. Therefore, in the amplifier circuit 60, by interposing the semi-fixed resistor 63 and setting the amplification factor of the step-up transformer circuit 60A to a large value, adjustment of the semi-fixed resistor 63 allows the step-up transformer circuit 60A (and thus the amplification The output voltage from circuit 60) can be adjusted to any desired magnitude. Further, since the input voltage of the step-up transformer circuit 60A is adjusted in the amplifier circuit 60, it is preferable that it does not affect the output from the capacitor circuit 40 to the first piezoelectric film 21, for example.

The second piezoelectric film 22 is connected to the output terminal of the amplifier circuit 60. Specifically, both terminals of the secondary coil 62 are connected to the electrodes 22E on both sides of the second piezoelectric film 22, and the electrode 22E on the negative potential side is grounded. Here, in the step-up transformer circuit 60A, the signal V1 from the operational amplifier 41 of the negative capacitance circuit 40 input to the primary coil 61 side is input to the primary coil 61 and the secondary coil 62 as described above. The voltage is amplified based on the turns ratio and output to the second piezoelectric film 22 as a signal V2 (second signal) having the same phase. Therefore, it is possible to cause distortion in the same phase as that caused in the first piezoelectric film 21 in the second piezoelectric film 22, and to reduce the distortion caused by the propagation of sound in the second piezoelectric film 22. , can be canceled by piezoelectrically induced distortion caused by the voltage applied to the second piezoelectric film 22. This increases the apparent elastic modulus of the second piezoelectric film 22, which can be effective in insulating sound. In addition, since the voltage applied to the second piezoelectric film 22 is amplified, it can be driven with a force greater than that of the first piezoelectric film 21. Thereby, the second piezoelectric film 22 can function as a sound insulation material with a higher sound insulation effect (transmission loss) than the first piezoelectric film 21.

Here, in the control circuit 30, an amplifier circuit 60 is interposed between the second piezoelectric film 22 and the negative capacitance circuit 40. In the amplifier circuit 60, since the primary coil 61 and the secondary coil 62 are electrically insulated by the step-up transformer circuit 60A, the electrical characteristics of the negative capacitance circuit 40 by the second piezoelectric film 22 are In addition, it is possible to prevent noise that has entered the first piezoelectric film 21 and the negative capacitance circuit 40 from being amplified by the amplifier circuit 60. Further, according to the step-up transformer circuit 60A, no phase shift occurs between the primary coil 61 and the secondary coil 62. With such a configuration, even if the sound insulation device 10 is installed in an environment where noise easily enters the control circuit 30 such as the floor panel 3, the influence of noise is suppressed and the second piezoelectric film 22 is Functions can be performed more reliably. Further, while suppressing noise, it is possible to suppress the occurrence of a phase shift in the signals applied to the first piezoelectric film 21 and the second piezoelectric film 22 by the control circuit 30.

Next, the effects of this embodiment will be explained. According to the present embodiment, by connecting the negative capacitance circuit 40 to the first piezoelectric film 21, it is possible to reduce vibrations of the first piezoelectric film 21 caused by sound incident on the first piezoelectric film 21, and 1 piezoelectric film 21 can be used as a sound insulation material. In addition, when amplifying the signal V1 output from the negative capacitance circuit 40 to the first piezoelectric film 21 and outputting it to the second piezoelectric film 22, the control circuit 30 is connected to the primary coil 61 by the step-up transformer circuit 60A. It is electrically insulated from the secondary coil 62. As a result, noise that has entered the first piezoelectric film 21 and the negative capacitance circuit 40 may be amplified by the operational amplifier 41 or the amplifier circuit 60, or the noise that has entered the first piezoelectric film 21 and the negative capacitance circuit 40 may be amplified by the operational amplifier 41 or the amplifier circuit 60. This prevents noise from entering. As a result, even when the sound insulation device 10 is installed in an environment where noise easily enters, the signal V1 output from the negative capacitance circuit 40 to the first piezoelectric film 21 is amplified while suppressing noise amplification and phase shift. and can be appropriately output to the second piezoelectric film 22. In addition, the second piezoelectric film 22 can be appropriately driven with a force larger than that of the first piezoelectric film 21 and can be distorted in the same phase as the first piezoelectric film 21. It can be used as a sound insulation material having a higher sound insulation effect than the film 21. In other words, the second piezoelectric film 22 can effectively insulate noise that could not be completely insulated by the first piezoelectric film 21 .

Note that from the viewpoint of suppressing the vibration characteristics of the first piezoelectric film 21 and the transmission of the negative capacitance circuit 40, the voltage value of the signal V1 and the amplification factor of the negative capacitance circuit 40 are limited to a relatively small range, and the first It is difficult to significantly increase the sound insulation effect of the piezoelectric film 21. However, according to the technology disclosed herein, even if the voltage value of the signal V1 or the amplification factor of the negative capacitance circuit 40 is small, the step-up transformer circuit 60A suppresses noise amplification and increases the output of the signal V2. can be increased. As a result, effective sound insulation can be realized mainly by the second piezoelectric film 22.

Further, in this embodiment, by providing the semi-fixed resistor 44 which is a frequency setting section, it is possible to more reliably insulate sounds with frequencies close to the frequency of the noise to be insulated. Since the second piezoelectric film 22 is controlled by the signal V2 (a signal obtained by amplifying the signal V1 for controlling the first piezoelectric film 21), the frequency characteristic of the second piezoelectric film 22 has the same tendency as the frequency characteristic of the first piezoelectric film 21. While having this, it exhibits a higher sound insulation effect than the first piezoelectric film 21. In other words, it is possible to more effectively block out noise at a targeted frequency. This also makes it possible to suppress the amplification of noise in a frequency band different from that of the noise to be insulated, thereby greatly increasing the output of the signal V2.

<Other embodiments>
The present invention is not limited to the embodiments described above and illustrated in the drawings; for example, the following embodiments are also included within the technical scope of the present invention.
(1) In the above embodiment, the configuration in which the sound insulation section 20 is attached to the floor panel 3 is limited, but the present invention is not limited to this. For example, the sound insulation section 20 may be provided on a door trim, a dash panel, etc. of the vehicle 1.
(2) In the above embodiment, the first piezoelectric film 21, the second piezoelectric film 22, and the floor panel 3 were spaced apart from each other. However, between the first piezoelectric film 21, the second piezoelectric film 22, and the floor panel 3, the vibrations of the first piezoelectric film 21 and the second piezoelectric film 22 are not inhibited, and the vibrations are not propagated to each other. A moderately soft material may be used. As a result, it is possible to suppress the first piezoelectric film 21 and the second piezoelectric film 22 from slightly bending due to their own weight, and it is possible to more accurately receive (sensing) vibrations caused by noise, and the entire film vibrates uniformly. This makes it possible to improve sound insulation accuracy. A suitable example of such a material is ultra-soft polyurethane foam.
(3) Further, other elements may be connected to the control circuit 30 as long as the essence of the technology disclosed herein is not impaired.

DESCRIPTION OF SYMBOLS 1... Vehicle, 3... Floor panel, 10... Sound insulation device, 21... First piezoelectric film, 22... Second piezoelectric film, 40... Negative capacitance circuit, 60... Amplifying circuit, 60A... Step-up transformer circuit, V1... Signal ( 1st signal), V2...signal (2nd signal)

Claims (2)

a first piezoelectric film that has piezoelectricity and receives sound to be sound-insulated;
a second piezoelectric film having piezoelectricity and disposed opposite to the first piezoelectric film;
a control circuit electrically connected to the first piezoelectric film and the second piezoelectric film;
a frame installed on a surface of a panel member constituting a vehicle interior on the interior side of the vehicle interior, and supporting the first piezoelectric film and the second piezoelectric film in a state where they are arranged facing each other with a distance between them;
Equipped with
The control circuit includes:
a negative capacitance circuit that is electrically connected to the first piezoelectric film and causes distortion in the first piezoelectric film that is opposite in phase to the distortion of the first piezoelectric film caused by the sound;
A second signal that is electrically connected to the negative capacitance circuit and the second piezoelectric film and is an amplified first signal output from the negative capacitance circuit to the first piezoelectric film is sent to the second piezoelectric film. an output amplifier circuit;
Equipped with
The amplifier circuit is configured by a step-up transformer circuit,
The first piezoelectric film, which is disposed on the side closer to the panel member with respect to the second piezoelectric film, includes a first layer made of a piezoelectric material exhibiting a piezoelectric effect and an inverse piezoelectric effect; a pair of first electrodes each attached to cover each side of the first layer;
The second piezoelectric film includes a second layer made of a piezoelectric material exhibiting a piezoelectric effect and an inverse piezoelectric effect, and a pair of films each attached to the second layer so as to cover each of both sides of the second layer. a second electrode;
In the sound insulation device, a surface of the first piezoelectric film opposite to the second piezoelectric film is disposed to face a surface of the panel member on the passenger compartment side with a distance therebetween . A first soft material is interposed between the first piezoelectric film and the second piezoelectric film,
The sound insulation device according to claim 1, wherein a second soft material is interposed between the first piezoelectric film and the panel member .

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