Ton generator

Abstract

Tone generator producing a tone by vibrating a membrane (72), comprising: a housing (1) with a first space (5) open to outside air through a sound emission hole (84), and a second space (6) separated from the first space (5) by the membrane (72);and a shielding plate (28) which is arranged in the first chamber (5) such that it faces the membrane (72) while being separated from the membrane (72), wherein when the membrane (72) is displaced to the first chamber (5) by a pressure difference between the first chamber (5) and the second chamber (6), the membrane (72) comes into contact with the shielding plate (28) to limit deformation of the membrane (72), the shielding plate (28) has a shape corresponding to the membrane (72), the membrane (72) has an inner circumferential section (721) which is convex towards the second chamber (6), and an outer circumferential section (722) which is inclined from an outer edge of the inner circumferential section towards the first chamber (5), and the shielding plate (28) has an inner circumferential section (281) which is convex away from the membrane (72), and an outer circumferential section (282) which is inclined away from the membrane (72) from an outer edge of the inner circumferential section.;

Description

Cross-reference to related registration The present application is based on the Japanese patent application JP 2017-12356 filed on January 26, 2017. Technical field The present invention relates to a tone generator. Background of the state of the art Patent document 1 describes a tone generator used for a vehicle warning signal or a vehicle approach warning device. In the tone generator disclosed in patent document 1, a shielding plate is installed in front of a diaphragm inside a base housing for the purpose of achieving both acoustic performance and a function to prevent the ingress of water or snow. State of the art documents Patent documents Patent document 1: JP 2016-25558 APatent document 2: US 4 399 334 APatent document 3: US 5 416 751 APatent document 4: EP 1 560 459 A2Patent document 5: US 2016 / 0 205 478 A1Patent document 6: DE 694 23 128 T2Patent document 7: DE 38 43 292 A1Patent document 8: JP 2004 179 698 APatent document 9: US 5 181 252 B Summary A tone generator is a sealed product, and an airtightness test is performed to ensure its watertightness and sealing properties. During the airtightness test, it is necessary to press the membrane with a clamping device or similar to prevent inversion of the membrane due to air pressure or the like, and to stabilize the test result. However, in the case where the shielding plate is installed in front of the diaphragm inside the base housing, there is a need to remove the shielding plate in order to hold the diaphragm using the clamping device, which leads to an increase in the number of parts and an increase in the cost of the mold. One object of the present invention is to create a tone generator that can perform an airtightness test without the use of a clamping device to hold a membrane. This problem is solved by a tone generator having the features of claim 1. An alternative tone generator is shown in claim 2. According to the setup described above, the deformation of the membrane is limited by contact between the membrane and the shielding plate, and the shielding plate becomes a substitute for a clamping device that presses the membrane. Therefore, the airtightness test can be performed without using a clamping device that presses (compresses) the membrane. Beneficial further training is subject to dependent claims. The tone generator can also have a drive unit that sets the diaphragm into vibration. The distance between the diaphragm and a contact surface of the shielding plate, which is in contact with the diaphragm, is greater than the displacement of the diaphragm when the diaphragm is set into vibration by the drive unit. According to the setup described above, contact between the membrane and the shielding plate can be prevented due to the sound generation process. The drive unit may comprise the following: a cylindrical core section of the diaphragm, which stands upright towards the second chamber; a voice coil wound around the core section; and a magnetic switching unit, which includes a cylindrical chamber coaxial with the core section. The magnetic switching unit displaces the core section within the cylindrical chamber by applying a magnetic field to the voice coil. The displacement of the diaphragm—when the diaphragm is set into vibration by the drive unit—is defined within a range in which the core section is held so that it is located within the cylindrical chamber. The offset amount of the membrane is defined, for example, by the area in which the core section is held so that it fits into the space in this way, and the distance between the membrane and the shielding plate is set so that it is greater than the offset amount, resulting in the ability to prevent contact between the membrane and the shielding plate due to the sound generation process. The distance between the membrane and the contact surface of the shielding plate that comes into contact with the membrane can be set within a range between 1 mm and 6 mm. If the distance between the shielding plate and the diaphragm is set to between 1 mm and 6 mm in this way, contact between the diaphragm and the shielding plate can be prevented due to the sound generation process. An outer edge of the inner circumferential section of the membrane comes into contact with an outer edge of the inner circumferential section of the shielding plate to limit the deformation of the membrane, and if the deformation of the membrane is limited by the shielding plate, a space (gap) is provided between the inner circumferential section of the membrane and the inner circumferential section of the shielding plate. Although the inner circumferential section of the membrane has low strength, the inner circumferential section of the membrane and the inner circumferential section of the shielding plate are brought into contact with each other at the outer edge, and the space is provided between the membrane and the shielding plate, resulting in the ability to reduce deformation or breakage of the membrane. Furthermore, the membrane can have an upright core section that projects from the outer edge of the inner circumferential section into the second space. If the deformation of the membrane is limited by the shielding plate, the membrane comes into contact with the shielding plate at the section where the upright section is formed. In this way, the membrane comes into contact with the shielding plate at the section where the upright section is formed, thus increasing the strength and thereby reducing the ability to deform or break (damage) the membrane. Brief description of the drawings Fig. 1 shows a representation of the complete assembly of a tone generator according to a first embodiment, wherein Fig. 1(a) shows a front view, Fig. 1(b) shows a view of a left side, and Fig. 1(c) shows a bottom view. Fig. 2 shows a cross-sectional view along line II-II from Fig. 1(a). Fig. 3 shows an enlarged view of a tone body from Fig. 2. Fig. 4 shows a front view of the tone generator from Fig. 1 with a cover removed. Fig. 5 shows a cross-sectional view along line VV from Fig. 4. Fig. 6 shows a cross-sectional view along line VV from Fig. 4. Fig. 7 shows an enlarged view of a section VII from Fig. 6. Fig. 8 shows an enlarged view of the tone body from Fig. 2. Fig. 9 shows an enlarged view of a tone body in a modification of the first embodiment. Description of the exemplary implementations Exemplary embodiments are described below according to the drawings. Identical or equivalent sections among the respective exemplary embodiments discussed below are designated by the same reference numerals in the drawings. First embodiment A first embodiment is described below with reference to Figures 1, 2, 3, 4, 5, 6, 7 to 8. A tone generator according to the present embodiment is, for example, installed on the outside of a vehicle compartment and is used to generate a warning tone. As shown in Figure 2, the tone generator has a housing 1 in which two compartments are provided. More precisely, as shown in Figures 1 and 2, the housing 1 has a base 2, a cover 3, and a container 4, all made of plastic. The base 2 has a base cylindrical section 21 with a substantially cylindrical shape. The disc-shaped cover 3 sits on an opening at one end of the base cylindrical section 21 such that the opening is covered. The disc-shaped container 4 is hermetically connected to the opening at the other end of the base cylindrical section 21 by adhesion. As shown in Fig. 2, a space in the base cylinder section 21 is divided into two spaces in an axial direction by a partition 22 provided in the base cylinder section 21. A first space 5 is provided by the base cylinder section 21, the partition 22 and the cover 3, and a second space 6 is provided by the base cylinder section 21, the partition 22 and the container 4. As shown in Figs. 2 and 4, the partition 22 has a circular through-hole 23 for communication between the first chamber 5 and the second chamber 6. As shown in Fig. 2, a tone generator 7 for generating a tone based on an electrical signal is arranged in the second chamber 6 such that the through-hole 23 is closed. As described below, the through-hole 23 is closed by the membrane 72 of the tone generator 7, and the second chamber 6 is separated from the first chamber 5 by the membrane 72. As shown in Figures 4 and 5, a ventilation hole 24 is provided in the partition 22 at a position spaced apart from the through-hole 23. The ventilation hole 24 is provided to reduce the occurrence of a pressure difference between the first chamber 5 and the second chamber 6 due to a temperature change. A ventilation film 25 extends over the ventilation hole 24. The ventilation film 25 blocks water while allowing air to pass through it and is made, for example, of Gore-Tex®. As shown in Figures 2 and 4, a shielding cylinder section 26 is connected to an open end of the partition 22. The shielding cylinder section 26 has a cylindrical shape that surrounds the through-hole 23 and projects from the partition 22 to the cover 3. A beam-shaped coupling section 27 is connected to a portion of the shielding cylinder section 26 that is closer to the partition 22 than the opening end face is to the cover 3. The coupling section 27 extends from the shielding cylinder section 26 to a radially viewed inner side of the through-hole 23, and the shielding cylinder section 26 is connected to a shielding plate 28 through the coupling section 27.The shielding plate 28 is designed to prevent water flow during high-pressure washing and snow adhering to a surface of the cover 3 from reaching the clay body 7, and to prevent the clay body 7 from being damaged by water adhesion. The shielding plate 28 is arranged inside the housing 1 between a sound emission hole 84 and the membrane 72, which is described below. When the membrane 72 is displaced during the airtightness test, the shielding plate 28 is in contact with the membrane 72 and limits the deformation of the membrane 72. As shown in Fig. 2 and Fig. 5, the shielding plate 28 is arranged in the first chamber 5 in a state in which it is spaced away from the membrane 72 so that it faces the membrane 72, and it has a shape that corresponds to the membrane 72. More precisely, an inner circumferential section 281 of the shielding plate 28 has a dome shape that is convex on one side opposite the membrane 72. An outer circumferential section 282 is inclined (oblique) on the opposite side of the membrane 72. More precisely, the outer circumferential section 282 has a hollow, frustoconical shape that extends from an outer edge of the inner circumferential section 281 to the first space 5, and it is curved such that a cross-section of the outer circumferential section 282 is convex along the radial direction to the inner side. The inner circumferential section 281 and the outer circumferential section 282 each face an inner circumferential section 721 and an outer circumferential section 722 of the membrane 72, which is described below. According to the present embodiment, the shielding plate 28 is in contact with the membrane 72 at an outer edge of the inner circumferential section 281 and the outer circumferential section 282. The outer circumferential section 282 has a shape that corresponds to the outer circumferential section 722 when the membrane 72 is deformed, thereby preventing the membrane 72 from breaking. The inner circumferential section 281 is arranged closer to the container 4 than the separating section 22 in the axial direction of the base cylinder section 21, and the outer circumferential section 282 is arranged such that it passes through the through-hole 23. The end section of the outer circumferential section 282 on the opposite side to the inner circumferential section 281 has a cylindrical shape that projects towards the cover 3. As shown in Fig. 2, the outer circumferential section 282 is connected to the coupling section 27 at the end section of the cylindrical shape. As shown in Fig. 4, a plurality of coupling sections 27 are formed according to the present embodiment. A plurality of sound channels 81 are defined by the shielding cylinder section 26, the many coupling sections 27 and the shielding plate 28, and the sound generated by the sound-generating body 7 passes through the sound channels (sound channels) 81. The shielding plate 28 has a cylindrical section 283 that projects from the outer edge of the inner circumferential section 281 towards the cover 3. As shown in Fig. 2, a resonance chamber 82 is defined by the outer circumferential section 282, the cylindrical section 283, and the cover 3, and a resonance chamber 83 is defined by the inner circumferential section 281, the cylindrical section 283, and the cover 3. The sound pressure of the tone produced by the sound-generating body 7 is amplified by the resonance chamber 82 and the resonance chamber 83. As shown in Figs. 1, 2, and 4, a connecting element 29, having a substantially right-angled cylindrical shape, is formed on the outside of the base cylinder section 21 for electrically connecting the tone-generating body 7 to external wiring (not shown). As shown in Fig. 2, a section of the base cylinder section 21, on which the connecting element 29 is formed, has a through-hole that passes through the base cylinder section 21 to connect the interior of the connecting element 29 and the second chamber 6. A terminal 9 is arranged to pass through the through-hole. The connector 9 is fixed to the base cylinder section 21 by an adhesive inside the base cylinder section 21, and the through-hole provided for arranging the connector 9 is closed by the adhesive and the connector 9. The connector 9 is connected to a conductor pin 78, described below, in the second chamber 6. As shown in Figures 1 and 2, the cover 3 has a disc shape corresponding to the base cylinder section 21. A projecting section 31, extending towards the inside of the housing 1, is formed on a section of the cover 3 facing the coupling section 27 and the sound channel (tone channel) 81. A circular through-hole 32, for imitating the tone produced by the tone-generating element 7, is provided in a section of the cover 3 inside the projecting section 31. A beam-shaped coupling section 33 is connected to an open end section of the through-hole 32. The coupling section 33 extends to the radial inner side of the through-hole 32 and is connected to the shielding plate 34. The shielding plate 34 is disc-shaped and is arranged to cover the cylindrical section 283 of the shielding plate 28. As shown in Fig. 1, according to the present embodiment, many coupling sections 33 are formed, and many sound emission holes 84 (tone emission holes) are provided by dividing the through-hole 32 through the many coupling sections 33. The tone emission holes 84 open the first chamber 5 to the environment and emit the sound produced by the tone-generating body 7 to the outside. As shown in Fig. 2, a section of the cover 3, located on the radially outer side of the projecting section 31, has a cylindrical section 35 projecting towards the partition 22. The cylindrical section 35 is arranged on a section of the first chamber 5 corresponding to the partition 22, and an end piece of the cylindrical section 35 is arranged in a section surrounded by the base cylindrical section 21, the partition 22, and the shielding cylindrical section 26. As a result, a resonance chamber is provided to amplify the sound pressure of the tone produced by the tone-generating body 7. More precisely, a resonance chamber 85 is formed by the base cylindrical section 21, the partition 22, the outer circumferential section of the cover 3, and the cylindrical section 35. A resonance chamber 86 is formed by the partition 22, the shielding cylindrical section 26, the outer circumferential section of the cover 3, the projecting section 31, and the cylindrical section 35. A portion of the projecting section 31 extends to the radially outer side and is connected to the cylindrical section 35. As described above, the first chamber 5 is equipped with resonance chambers 82, 83, 85, and 86 for amplifying the sound pressure of the tone produced by the sound-generating body 7. By forming the many resonance chambers as described above, a high sound pressure can be achieved across a wide frequency band. As shown in Figs. 2 and 3, the sound-generating body 7 has a substantially stepped cylindrical frame 71, a diaphragm 72, and a drive unit 73 that sets the diaphragm 72 into vibration. The frame 71 is open at both ends in the axial direction, and one of the two openings of the frame 71, the one with the larger opening width, is closed by the diaphragm 72. The frame 71 is hermetically connected to the partition 22 by adhering to the end section on the side where the opening is closed by the membrane 72. The frame 71 has a through-hole 74 for communication between the inside and outside of the frame 71, and a section (partially) of the second chamber 6 is defined by the space inside the frame 71. In other words, the second chamber 6 is separated from the first chamber 5 by the partition 22 and the membrane 72. As shown in Figures 3 and 5, the inner circumferential section 721 of the membrane 72 has a dome shape that is convex towards the first chamber 5. The outer circumferential section 722 of the membrane 72 is inclined (oblique) towards the first chamber 5. More precisely, the outer circumferential section 722 has a hollow, frustoconical shape that extends from the outer edge of the inner circumferential section 721 to the first chamber 5 and is curved such that a cross-section along the radial direction is convex towards the inner side. The inner circumferential section 721 and the outer circumferential section 722 each face the inner circumferential section 281 and the outer circumferential section 282 of the shielding plate 28. The outer edges of the inner circumferential section 721 and the inner circumferential section 282 have the same shape. More precisely, the outer edge of the inner circumferential section 721 is circular, and the outer edge of the inner circumferential section 282 is circular with the same diameter as the outer edge of the inner circumferential section 721. As described below, at the time of the airtightness test of the tone generator, the inner circumferential section 721 is displaced towards the first chamber 5. The membrane 72 is deformed in such a way that it expands (stretches) towards the first chamber 5 and is in contact with the shielding plate 28. More precisely, as shown in Figures 6 and 7, the outer circumferential section 722 is in contact with the outer circumferential section 282. As described above, according to the present embodiment, the outer edges of the circumferential section 721 and the inner circumferential section 281 have the same shape. When the membrane 72 is deformed as described above, the membrane 72 and the shielding plate 28 are arranged such that the outer edge of the inner circumferential section 721 is in contact with the outer edge of the inner circumferential section 281. In the present embodiment, if the membrane 72 is deformed as described above, the inner circumferential section 281 has a greater (stronger) curvature than that of the inner circumferential section 721, so that a gap is defined between the inner circumferential section 721 and the inner circumferential section 281. As described below, a tone is generated in the sound-generating body 7 by the vibration of the diaphragm 72. To generate a tone with a sufficiently high sound pressure, the distance between the diaphragm 72 and the shielding plate 28 must be increased to a certain extent. Furthermore, the distance between an area of ​​the diaphragm 72 in contact with the shielding plate 28 and an area of ​​the shielding plate 28 in contact with the diaphragm 72 is set such that it is greater than the displacement of the diaphragm 72 caused by the sound generation process, thus preventing the diaphragm 72 from coming into contact with the shielding plate 28 during sound generation. For example, it is preferred that the distance between the surface of the membrane 72 that is in contact with the shielding plate 28 and the surface of the shielding plate 28 that is in contact with the membrane 72 is defined within a range between 1 mm and 6 mm. In the present embodiment, the distance between the outer circumferential section 282 and the outer circumferential section 722 is defined as 2 mm. The distance between the surface of the membrane 72, which is in contact with the shielding plate 28, and the surface of the shielding plate 28, which is in contact with the membrane 72, is preferably set such that a coil former 75, described below, is held in a space 776 when the membrane 72 is displaced during the airtightness test. This is because the coil former 75 must return to an initial position in the space 776 after the membrane 72 has been displaced following the airtightness test. For example, the axial dimension of the coil former 75 and the thickness of the upper plate 772, described below, are set such that the condition in which the coil former 75 is arranged in the space 776 is maintained. However, if the coil former 75 can return to the initial position by a restoring force of the membrane 72, as shown in Fig.As shown in Figure 8, the coil body 75 is moved out of space 776 by relocating the membrane 72 during the airtightness test. In the present embodiment, the inner circumferential section 281 is arranged closer to the container 4 than the partition 22 in the axial direction of the base cylinder section 21, and the outer circumferential section 282 is arranged such that it passes through the through-hole 23. As a result, if the deformation of the membrane 72 is limited by the contact between the shielding plate 28 and the membrane 72, the membrane 72 is displaced without inversion, as shown by a dashed line in Fig. 3. In other words, when the diaphragm 72 comes into contact with the shielding plate 28, the inner circumferential section 721 is closer to its initial position than the end section of the diaphragm 72 that is fixed to the frame 71 in the axial direction of the frame 71. More precisely, if the end section of the coil former 75, described below and connected to the diaphragm 72, is defined as an end section 751, then the end section 751 is closer to its initial position in the axial direction of the coil former 75 than the section of the diaphragm 72 that is fixed to the frame 71. A dotted line in Fig. 3 indicates a position of the diaphragm 72 that is fixed to the frame 71. The inversion state (reversal state) of the membrane 72 is shown by a dashed line with two dots in Fig. 3, that is, the end section 751 of the coil body 75 moves beyond the dotted line.If the membrane 72 is reversed in this way, the membrane 72 cannot return to its initial position due to its own restoring force. A spring section 723 is connected to the end of the outer circumferential section 722 at a distance from the inner circumferential section 721. The spring section 723 has an annular shape when viewed in the axial direction of the outer circumferential section 722. The spring section 723 has an S-shaped cross-section along the radial direction. The diaphragm 72 is connected to the frame 71 at the end section of the spring section 723. In the present embodiment, the inner circumferential section 721, the outer circumferential section 722, and the spring section 723 are formed from a single thin film. The drive unit 73 is arranged such that it closes one of the narrower openings of the two openings of the frame 71. As shown in Fig. 3, the drive unit 73 has a coil former 75, a voice coil 76 and a magnetic switching unit 77. The coil former 75 has a cylindrical shape, is connected to the outer edge of the inner circumferential section 721 of the diaphragm 72, and projects from the diaphragm 72 towards the second chamber 6. The voice coil 76 is wound around the outside of the coil former 75. The coil former 75 comprises an upright section and a core section. The magnetic switching unit 77 is designed to apply a magnetic field to the voice coil 76. The magnetic switching unit 77 has a disc-shaped magnet 771 with one surface and another surface, an upper plate 772 connected to one surface of the magnet 771, and a yoke 773 connected to the other surface of the magnet 771. The yoke 773 has a base section 774, a magnet 771, an upper plate 772, and a cylindrical section 775. The base section 774 is disc-shaped and connected to the magnet 771. The magnet 771 is located between the base section 774 and the upper plate 772. The cylindrical section 775 projects from the outer circumferential section of the base section 774 toward the membrane 72 in the axial direction of the base section 774. The upper plate 772 and the yoke 773 are made of a magnetic material such as iron and each corresponds to a first magnetic section and a second magnetic section, respectively. The magnet 771 and the upper plate 772 are arranged inside the cylindrical section 775. A cylindrical space 776 is provided between the magnet 771 and the upper plate 772 on the one hand and the cylindrical section 775 on the other. The coil former 75 is arranged so that it coincides with the space 776 in the axial direction and is inserted into the space 776. The magnetic circuit unit 77 is arranged such that the magnet 771, the upper plate 772, and the cylindrical section 775 are located inside the frame 71, and the bottom section 774 closes the opening of the frame 71. The coil former 75 sits in the space 776. A magnetic field, generated between the side face of the upper plate 772 and the side face of the cylindrical section 775, is applied to the voice coil 76, which is wound around the coil former 75. When an electric current is applied to the voice coil 76 while the magnetic field is applied, the coil former 75 is axially displaced into a position where it is positioned within the space 776. Consequently, the diaphragm 72 vibrates and a sound is produced. The displacement (offset) of the diaphragm 72 when set into vibration by the drive unit is defined within a range in which the coil former 75 remains held in position within the space 776. More precisely, the diaphragm 72 vibrates such that a surface of the upper plate 772, adjacent to the diaphragm 72, is held between the diaphragm 72 and the end of the coil former 75 that is located away from the diaphragm 72 in the axial direction of the coil former 75. The tone generating body 7 has a lead pin 78 which is electrically connected to the voice coil 76, and the voice coil 76 is electrically connected to an external wiring by the lead pin 78 being press-fitted into the terminal 9. Such a tone generator is arranged on the exterior of a vehicle, and more precisely, it is positioned on the front bumper of the vehicle such that the cover 3 is located at the front of the vehicle relative to the base 2. When the voice coil 76 is excited, the diaphragm 72 vibrates without contact with the shielding plate 28, and a tone is generated. The tone produced by the tone-generating element 7 passes through a gap defined between the shielding plate 28 and the diaphragm 72, and through the tone channel (sound channel) 81. The sound pressure is amplified by the resonance chambers 82, 83, 85, and 86, and the tone is emitted to the outside through a tone emission hole 84 or the like. During the airtightness test of the tone generator, a pressure difference is created between the first chamber 5 and the second chamber 6. More precisely, the pressure in the first chamber 5 is reduced by closing the ventilation hole 24, or the second chamber 6 is pressurized by introducing air from the ventilation hole 24 into the second chamber 6, so that the pressure in the second chamber 6 becomes higher than the pressure in the first chamber 5. As a result, the inner circumferential section 721 of the membrane 72 is displaced towards the first chamber 5, and the membrane 72 is deformed so that it expands towards the first chamber 5. At this point, the deformed membrane 72 comes into contact with the shielding plate 28, thereby limiting the deformation of the membrane 72. In other words, the shielding plate 28, which is located inside the housing 1, prevents inversion or deformation of the membrane 72, instead of a clamping device pressing on the membrane 72. Therefore, the airtightness test can be performed without using a clamping device that presses on the membrane 72. In the present embodiment, when the diaphragm 72 is deformed as described above, the outer edge of the inner circumferential section 721 comes into contact with the outer edge of the inner circumferential section 281. Since the coil former 75 is connected to the outer edge of the inner circumferential section 721 to improve strength, breakage of the diaphragm 72 can be limited when the diaphragm 72 comes into contact with the shielding plate 28 at the outer edge of the inner circumferential section 721. In the present embodiment, when the membrane 72 is deformed as described above, the membrane 72 comes into contact with the shielding plate 28 at the outer circumferential section 722 and the outer edge of the inner circumferential section 721, and a gap is defined between the inner circumferential section 721 and the inner circumferential section 281. Therefore, breakage of the membrane 72 at the inner circumferential section 721, which has low strength, can be prevented. Furthermore, in a case where the membrane 72 is reversed by the displacement (offset) of the inner circumferential section 721 during the airtightness test, as shown by a dashed line with two dots in Fig. 3, it will be difficult for the membrane 72 to return to its original shape or position by its own recovery force when the pressure difference between the first chamber 5 and the second chamber 6 decreases. As described above, according to the present embodiment, a state in which the coil former 75 is arranged in the space 776 during the airtightness test can be maintained by adjusting the dimensions of the coil former 75 or the like. However, such a state can also be maintained by other methods. For example, as shown in Fig. 9, a plate 777 made of a non-magnetic material such as aluminum can be stacked on the upper plate 772 in such a way as to maintain the state in which the coil former 75 is positioned in the space 776. Further examples of implementation The present invention is not limited to the embodiments described above and can be suitably modified within the scope described in the claims. For example, the inner circumferential section 721 and the outer circumferential section 722 can be formed from different elements. Additionally, a gap can be defined between the outer circumferential section 722 and the outer circumferential section 282 when the membrane 72 comes into contact with the shielding plate 28, for example by providing a recessed section on the surface of the outer circumferential section 282 that comes into contact with the outer circumferential section 722. The inner circumferential section 281, the outer circumferential section 282, the inner circumferential section 721, and the outer circumferential section 722 can have shapes that differ from those of the first embodiment. For example, the inner circumferential sections 281 and 721 can have a cylindrical shape. Furthermore, the inner circumferential section 281 can have a shape that is convex towards the second space 6. The cross-sections of the outer circumferential section 282 and the outer circumferential section 722 along the radial direction can be linear.

Claims

Tone generator producing a tone by vibrating a membrane (72), comprising: a housing (1) with a first space (5) open to outside air through a sound emission hole (84), and a second space (6) separated from the first space (5) by the membrane (72);and a shielding plate (28) which is arranged in the first chamber (5) such that it faces the membrane (72) while being separated from the membrane (72), wherein when the membrane (72) is displaced to the first chamber (5) by a pressure difference between the first chamber (5) and the second chamber (6), the membrane (72) comes into contact with the shielding plate (28) to limit deformation of the membrane (72), the shielding plate (28) has a shape corresponding to the membrane (72), the membrane (72) has an inner circumferential section (721) which is convex towards the second chamber (6), and an outer circumferential section (722) which is inclined from an outer edge of the inner circumferential section towards the first chamber (5), and the shielding plate (28) has an inner circumferential section (281) which is convex away from the membrane (72), and an outer circumferential section (282) which is inclined away from the membrane (72) from an outer edge of the inner circumferential section.; Tone generator producing a tone by vibrating a membrane (72), comprising: a housing (1) with a first space (5) open to outside air through a sound emission hole (84), and a second space (6) separated from the first space (5) by the membrane (72); and a shielding plate (28) which is arranged in the first chamber (5) such that it faces the membrane (72) while being separated from the membrane (72), wherein when the membrane (72) is displaced to the first chamber (5) by a pressure difference between the first chamber (5) and the second chamber (6), the membrane (72) comes into contact with the shielding plate (28) to limit deformation of the membrane (72), the shielding plate (28) has a shape corresponding to the membrane (72), the membrane (72) has an inner circumferential section (721) which is convex towards the first chamber (5), and an outer circumferential section (722),which is inclined from an outer edge of the inner circumferential section towards the first space (5), and the shielding plate (28) has an inner circumferential section (281) that is convex away from the membrane (72), and an outer circumferential section (282) that is inclined from an outer edge of the inner circumferential section away from the membrane (72), the outer edge of the inner circumferential section of the membrane (72) comes into contact with the outer edge of the inner circumferential section of the shielding plate (28) to limit the deformation of the membrane (72), and when the deformation of the membrane (72) is limited by the shielding plate (28), a space is provided between the inner circumferential section of the membrane (72) and the inner circumferential section of the shielding plate (28). Tone generator according to claim 1 or 2, wherein the outer circumferential section of the membrane (72) comes into contact with the outer circumferential section of the shielding plate (28) in order to limit the deformation of the membrane (72). Tone generator according to one of claims 1 to 3, wherein the membrane (72) has an upright core section (75) with a cylindrical shape, which extends upright from the outer edge of the inner circumferential section to the second space (6), and when the deformation of the membrane (72) is limited by the shielding plate (28), the membrane (72) comes into contact with the shielding plate (28) at a section where the upright section is formed. Tone generator according to one of claims 1 to 4, wherein the outer edge of the inner circumferential section of the shielding plate (28) has the same shape as the outer edge of the inner circumferential section of the membrane (72). Tone generator according to claim 5, wherein the outer edge of the inner circumferential section of the membrane (72) has a circular shape, and the outer edge of the inner circumferential section of the shielding plate (28) has a circular shape which has the same diameter as the outer edge of the inner circumferential section of the membrane (72). Tone generator according to one of claims 1 to 6, wherein a distance between the membrane (72) and a contact surface of the shielding plate (28) which comes into contact with the membrane (72) is defined within a range between 1 mm and 6 mm. Tone generator according to one of claims 1 to 7, which further comprises a drive unit (73) that sets the diaphragm (72) into vibration, wherein a distance between the diaphragm (72) and a contact surface of the shielding plate that is in contact with the diaphragm (72) is greater than an offset amount of the diaphragm (72) when the diaphragm (72) is set into vibration by the drive unit (28). Tone generator according to claim 8, wherein the drive unit comprises: the upright core section (75) of the diaphragm (72) having a cylindrical shape, extending upright from the outer edge of the inner circumferential section to the second space (6); a voice coil (76) wound around the core section (75); and a magnetic switching unit (77) in which a cylindrical space (776) is defined coaxially to the core section (75) for displacing the core section (75) inside the cylindrical space (776) by applying a magnetic field to the voice coil (76), wherein the displacement amount of the diaphragm (72), when the diaphragm (72) is set into vibration by the drive unit, is defined within a range in which the core section (75) remains arranged in the cylindrical space (776). Tone generator according to claim 9, wherein the magnetic circuit unit comprises: a magnet (771) with one surface and another surface; a first magnetic section (772) connected to one surface of the magnet (771); and a second magnetic section (773) with a base section (774) connected to the other surface of the magnet (771), and a cylindrical section (775) projecting axially from an outer circumferential section of the base section, wherein the cylindrical space (776) is provided between the magnet (771) and the first magnetic section (772), and the cylindrical section (775). A tone generator according to claim 9 or 10, further comprising: a frame (71) that secures the diaphragm (72), wherein, when the deformation of the diaphragm (72) is limited by contact between the shielding plate (28) and the diaphragm (72), the stroke of an end section (751) of the core section (75) connected to the diaphragm (72) up to the shielding plate (28) is less than the stroke up to the height of an end section of the diaphragm (72) that is secured to the frame (71) in the axial direction of the core section (75), starting from the initial position with no pressure difference. Tone generator according to one of claims 1 to 11, wherein when the pressure difference between the first space (5) and the second space (6) is reduced compared to a state in which the deformation of the membrane (72) is limited by the contact between the membrane (72) and the shielding plate (28), the membrane (72) returns to an original shape or position by means of an inherent restoring force of the membrane (72). Tone generator according to claim 9 or 10, wherein when the deformation of the diaphragm (72) is limited by the contact between the diaphragm (72) and the shielding plate (28), the core section (75) is arranged outside the cylindrical space (776), and when the pressure difference between the first space (5) and the second space (6) is reduced compared to a state in which the deformation of the diaphragm (72) is limited by the contact between the diaphragm (72) and the shielding plate (28), the diaphragm (72) returns to an original shape or position by its own restoring force, and the core section (75) returns to being arranged in the cylindrical space (776) by the return of the diaphragm (72) to its original shape or position.

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