EP3343946B1

EP3343946B1 - Acoustic device, in particular for applications in the automotive industry

Info

Publication number: EP3343946B1
Application number: EP17210765.8A
Authority: EP
Inventors: Matteo De Cesare; Antonio BARBUTO; Nicola TORCOLINI; Federico Monti
Original assignee: Magneti Marelli SpA
Current assignee: Marelli Europe SpA
Priority date: 2016-12-27
Filing date: 2017-12-27
Publication date: 2021-03-24
Anticipated expiration: 2037-12-27
Also published as: CN108243373A; CN108243373B; EP3343946A1; IT201600131334A1

Description

FIELD OF THE INVENTION

The present invention relates to an acoustic device, in particular for applications in the automotive industry.

PRIOR ART

In the automotive industry use is already made of acoustic devices comprising a support; a microphone device connected to the support and having a sensitive area; an acoustic conduit obtained in a housing connected to the support and designed to convey the sound pressure waves generated by an external acoustic source towards the sensitive area of the microphone device. The acoustic device further comprises a membrane interposed between the microphone device and the acoustic conduit to protect the sensitive area from external agents.
The electric and acoustic devices used in the automotive industry must meet the standards required by vehicle manufacturers according to their position (for example, inside the passenger compartment or the engine compartment). For example, devices housed in the engine compartment must meet so-called ingress protection (IP rating) standards. In
particular, the ingress protection rating for these applications must be equal to at least 6K7; in other words the device must be protected against the ingress of external objects and dust (the meaning of the first term "6K") and, at the same time, the device must be protected against the ingress of liquid when immersed at a depth of 1 metre for 30 minutes (meaning of the second term "7"). Devices housed in the engine compartment must also meet the standards required by vehicle manufacturers in terms of the so-called specific ingress protection rating for high-pressure jets. In particular, the specific ingress protection rating for high-pressure jets must be equal to at least IP6K9K; high-pressure water/air jets are typically directed on the device during cleaning operations using tools capable of generating jets of water/air at a pressure of more than 5 bar.
Acoustic devices to be used in the automotive industry are disclosed, for example, in documents US2016234594 , US2014198932 and WO2013099068.
However, it has been found that the devices of the type known in the prior art are able to withstand jets of water/air directed on said device at a pressure of between 0.1 and 1 bar.

DESCRIPTION OF THE INVENTION

The purpose of the present invention is therefore to provide an acoustic device, in particular for applications in the automotive industry, that overcomes the drawbacks of the prior art.
According to the present invention there is provided an acoustic device, in particular for applications in the automotive industry, as claimed in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described with reference to the accompanying drawing, which illustrates a non-limiting embodiment thereof, in which the accompanying Figure is a cross-sectional view of an acoustic device produced according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In Figure 1 denoted as a whole by reference numeral 1 is an integrated device 1 comprising a support 2 bearing a microphone device 3 formed by a body 4 typically having a parallelepiped shape provided with a first and a second main face 6, 7 and with a side surface 8. The body 4 is typically formed by a structural layer of semi-conducting material, such as silicon, which may be covered in conducting/insulating layers that are not illustrated. The microphone device 3 is fixed to the support 2 in correspondence of the main face 6 defining an upper surface and is provided with a sensitive area 5. The sensitive area 5 may be formed on the inside or on top of the main face 6 of the body 4. For example, the sensitive area 5 may be a membrane delimited at the bottom by a cavity buried in the body, or by a suspended membrane or comprise one or more layers arranged on top of the main face 6.
The support 2 has a parallelepiped shape with an area or base that is greater than the plate 3.
The device further comprises a housing 9 fixed on top of the support 2. In other words, the support 2 is interposed between the housing 9 and the microphone device 3. According to a preferred embodiment, the housing 9 is made of a metal material. According to an alternative embodiment, the housing 9 is partially defined by a moulded body made of a standard moulding material, typically a plastic material, such as resin.
The housing 9 internally delimits an acoustic conduit 10 provided with a symmetry axis X. In particular, the acoustic conduit 10 is defined by a funnel-shaped upper portion 11 which faces the acoustic source and a lower portion 12. The upper portion 11 is coaxial to the symmetry axis X, and is defined by a truncated cone-shaped surface 13 tapered towards the lower portion 12, which is also coaxial to the symmetry axis X and defined by a cylindrical surface 14.
According to a preferred embodiment, the acoustic conduit 10 is made of a metal material. According to a further embodiment, the acoustic conduit 10 is made of a plastic material.
The device 1 further comprises a membrane 15 which is interposed between the support 2 and the lower portion 12 of the acoustic conduit 10. The membrane 15 is rather thin and is designed to protect the sensitive area 5 and is oilproof, waterproof and dustproof. The membrane 15 is made of a plastic material.
The lower portion 12 is L-shaped. In other words, the lower portion 12 is divided into a section 12A in communication with the upper portion 11 and coaxial to the symmetry axis X and a section 12B provided with an axis Y that is substantially orthogonal to the symmetry axis X and in communication with the sensitive area 5. In this way, the membrane 15 is not directly exposed to the impact of any objects that enter the inside of the acoustic conduit 10 or of a high-pressure jet of water/air directed on the device 1. The elbow bend in the lower portion 12 thus makes it possible to protect the membrane 15 against impacts with any objects that enter the inside of the acoustic conduit 10 and enables the energy of a high-pressure jet of water/air directed on the device 1 to be dissipated.
As regards the transmission of the sound waves, the following condition must be met: $\frac{λ_{MIN}}{3} \geq ϕ_{GUIDE}$
with $with λ_{MIN} = \frac{c_{sound}}{f}$

λ_MIN wavelength of the sound pressure waves coming from the external acoustic sources;
c_sound speed of propagation in the air of the sound pressure waves coming from the external acoustic sources;
f frequency of the sound pressure waves coming from the external acoustic sources; and
Φ_guide diameter of the inner surface (14) of the lower portion 12.

In other words, the diameter Φ_guide of the inner surface 14 of the lower portion 12 is at maximum one third of the minimum wavelength λ_MIN οf the sound pressure waves coming from the external acoustic sources. And the minimum wavelength λ_MIN of the sound pressure waves coming from the external acoustic sources is at least three times larger than the diameter Φ_guide of the inner surface 14 of the lower portion 12.
The minimum wavelength λ_MIN of the sound pressure waves for dimensioning the diameter Φ_guide (and, thus, the diameter Φ_guide) is determined at the end of a test phase as a function of the external acoustic sources that generate the pressure waves that hit the microphone device 3.
It has in fact been experimentally verified that with a value equal to one third of the minimum wavelength λ_MIN of the sound pressure waves coming from the external acoustic sources, the acoustic conduit 10 does not introduce significant distortions up to the characteristic frequency.
According to a preferred embodiment, the diameter Φ_guide of the inner surface 14 of the portion 12 is constant. In other words, the section 12A and the section 12B have the same inside diameter Φ_guide.
According to a possible embodiment, the diameter Φ_guide of the inner surface 14 of the portion 12 is variable. In other words, the section 12A and the section 12B have different diameters; in particular, the section 12B has a smaller diameter than the section 12A.
The upper funnel-shaped portion 11 is made to convey and amplify the sound pressure waves coming from the external acoustic sources towards the lower portion 12. The diameter of the cylindrical surface 14 and the angle that is formed between the truncated cone-shaped surface 13 and the cylindrical surface 14 are determined so as to progressively amplify the sound waves, as the frequency increases, without introducing distortions in the range of frequencies typical of the sound field (e.g., between 50Hz and 10kHz).
The microphone device 3 is connected to the outside via a through hole 16 made through the support 2 and is in communication with the acoustic conduit 10. In the embodiment that is shown, the through hole 16 is vertically superimposed on the sensitive area 5 and thus on the acoustic conduit 10, but it could be laterally offset or arranged in any suitable position and configuration.
The support 2 may be of any known type. According to a preferred embodiment, the support 2 may consist of a printed circuit board (PCB) made of an organic material or other organic multilayer substrate (such as, for instance, a Bismaleimide Triazine (BT) layer) for example of the land grid array (LGA) or ball grid array (BGA) type. Alternatively, the support 2 may, in turn, consist of a supporting plate made of a semi-conducting material, typically silicone.
According to a preferred embodiment, the device 1 further comprises a heating element 17 that is arranged close to the acoustic conduit 10. According to a preferred embodiment, the heating element 17 is arranged close to the L-shaped bend in the lower portion 12. According to further embodiments which are not illustrated, the heating element 17 is arranged in correspondence of the connection between the upper portion 11 and the lower portion 12 of the acoustic conduit 10. The heating element 17 is controlled so as to heat the surface 13 and the surface 14, so that any deposits of particles or oil on such surfaces 13, 14 evaporate without undermining the transfer of the sound waves towards the sensitive area 5.
According to an alternative embodiment that is not illustrated, the microphone device 3 is fixed to the support 2 in correspondence of the main face 7 defining a lower surface and is interposed between the housing 9 and the support 2. In this case, the microphone device 3 is directly facing the acoustic conduit 10 and there is no need to provide the through hole 16 through the support 2.
The device described above achieves several advantages. Firstly, it is simple and economical to produce and the L-shaped bend in the lower portion 12 of the acoustic conduit 10 and the presence of the membrane 15 result in an effective solution that is able to meet the stringent standards required in terms of the ingress protection rating and of the specific ingress rating for high-pressure jets.

Claims

An acoustic device (1), in particular for applications in the automotive industry, comprising:
a support (2);

a microphone device (3), which is connected to the support (2) and has a sensitive area (5);

an acoustic conduit (10), which is designed to convey the sound pressure waves generated by an external acoustic source towards the sensitive area (5); wherein the acoustic conduit (10) has a funnel-shaped portion (11) which is provided with a first symmetry axis (X) and is designed to convey and amplify the sound pressure waves coming from the external acoustic source towards a cylindrical portion (12) in communication with the sensitive area (5); and

a membrane (15), which is interposed between the microphone device (3) and the cylindrical portion (12) of the acoustic conduit (10) so as to protect the sensitive area (5) from external agents;

wherein the cylindrical portion (12) of the acoustic conduit (10) is L-shaped and is divided into a first section (12A), which is in communication with the funnel-shaped portion (11) and is coaxial to the first symmetry axis (X), and a second section (12B), which is provided with a second axis (Y), which is substantially orthogonal to the first symmetry axis (X).
A device according to claim 1 and comprising a heating device (17), which is arranged in correspondence of the acoustic conduit (10) so as to heat a surface (13, 14) of the acoustic conduit (10).
A device according to claim 2, wherein the heating device (17) is arranged in correspondence of the L-shaped curve of the cylindrical portion (12).
A device according to anyone of the previous claims, wherein the support (2) is interposed between the membrane (15) and the microphone device (3); and wherein the microphone device (3) is connected to the outside through a through hole (17) made through the support (2) and is in communication with the acoustic conduit (10).
A device according to anyone of the claims from 1 to 3, wherein the microphone device (3) is interposed between the membrane (15) and the support (2).
A device according to anyone of the previous claims, wherein the acoustic conduit (10) is made of a metal material.
A device according to anyone of the claims from 1 to 5, wherein the acoustic conduit (10) is made of a plastic material.
A device according to anyone of the previous claims, wherein the acoustic conduit (10) is obtained in a housing (9) made of a metal material.
A device according to anyone of the claims from 1 to 7, wherein the acoustic conduit (10) is obtained in a housing (9) made of a plastic material.