Patent Publication Number: US-2023164492-A1

Title: Dual axial magnetic flux induction speaker

Description:
CORRESPONDING APPLICATION 
     The present application claims the priority of the prior Swiss national application No CH 00425/20 filed on the 8th April 2020 in the name of Michel OLTRAMARE, the content of this prior application being incorporated by reference in its entirety into the present application. 
     TECHNICAL FIELD 
     The present invention relates to induction motor devices comprising at least one fixed coil, one mobile armature and magnets. Such a device may for example form an induction loudspeaker. 
     More precisely, the present invention relates to the means for driving the movement of the diaphragm of an induction loudspeaker. 
     PRIOR ART 
     The diaphragms of loudspeakers working in the low and medium frequencies are generally caused to move by an actuator or motor. There are mainly two types of actuators for loudspeakers: the actuators the most often used, with a mobile coil connected to the diaphragm, referred to as “voicecoil”, and induction actuators, with fixed coil and magnets, and a mobile armature fixed to the diaphragm. 
     Numerous patents relate to the composition of induction motors with a fixed coil: U.S. Pat. No. 2,621,261A, 4,965,839A, 5,062,140A, 5,742,696A, 6,359,996B1, 6,542,617B1 and also 8,009,857B2. These patents all mention radial magnetic flux actuators, with magnets placed all around a central core. 
     Other patents mention audio systems comprising two magnets and creating an axial magnetic flux: CN105491491A, CN109195077A, KR20140091365A, KR20180085393A, US2010054501A1, US2015271605A1, US2018206040A1, WO2013013502A1, WO2017028034A1. However, none of these inventions has adapted this system of axial magnetic flux to an induction system. 
     On conventional induction loudspeakers, as described in the patent U.S. Pat. No. 8,009,857B2, the magnets are placed radially inside or outside of a magnetic air space where the armature is moving. Thus configured, the magnets create a single magnetic field present over the whole circumference of the actuator. Since the magnetic field is generated by the magnets, a good quality of magnet is preferable. However, the higher the strength of the magnet, the lower is its Curie temperature, in other words the temperature at which it is demagnetized. However, the temperature in the core of a loudspeaker tends to rise rapidly. Although some patents provide solutions for cooling loudspeakers: GB1348535A, JPH03239099A, JPS5586288A, JPS56161798A, JPS59216394A or else the application PCT/IB2020/050963 filed on the 6 Feb. 2020 in the name of M. Michel OLTRAMARE, it is necessary to reach a compromise on the power of the magnet depending on the maximum temperature of its environment. 
     The magnetic field coupled to a variable electric field (supplied by the coil) creates a force in the armature, thus causing it to move, just like the diaphragm. The greater this force, the faster the armature moves, thus increasing the sensitivity of the loudspeaker. 
     Since the force for movement of the armature, and hence the sensitivity of the loudspeaker, is linked to the magnetic field, itself linked to the composition of the magnet, the physical limit is quickly reached. 
     DESCRIPTION OF THE INVENTION 
     The aim of the present invention is to improve the known systems, notably but not exclusively, loudspeakers. 
     The present invention allows the aforementioned drawbacks linked to the magnetic field to be overcome and provides a dual axial magnetic flux induction system. 
     For this purpose, the device such as a loudspeaker, such as defined in the introduction, is notably characterized in that it comprises a motor comprising two sources of magnetic fields, placed axially on either side of a central core. These magnetic field sources may be permanent ring magnets, or other shapes of bipolar permanent magnets such as disks or ring sections. Their poles are axially aligned with the core, but their polarities are opposing. The magnetic fields generated by these magnets are guided by the central core on the one hand and, on the other hand, by one or more members having a good magnetic conductivity and which close the magnetic circuit. Between the assembly comprising the core and the two magnets, and all of the members closing the magnetic field, is located an armature, attached to the diaphragm of the loudspeaker, and a fixed coil, supplied with AC current at a variable frequency creating a variable magnetic field. This magnetic field creates Foucault currents in the armature. These Foucault currents associated with the magnetic field generated by the magnets apply a force on the armature which is then moved with the diaphragm, which produces a sound wave. 
     By being so positioned, each magnet will create its own magnetic field. In this way, the total magnetic field generated in the loudspeaker is doubled in the armature compared with a conventional induction loudspeaker. This double magnetic field increases the force generated on the armature, and thus improves the sensitivity of the loudspeaker. 
     By doubling the magnets, the intensity of the magnetic field is increased without modifying the composition of the magnet, and without having to increase the current in the coil. If the current in the coil remains the same, the temperature within the motor does not change. If the composition of the magnet remains the same, the Curie temperature does not change, and the maximum temperature allowed inside of the loudspeaker also remains identical. 
     A compromise between the operating temperature of the loudspeaker and the quality of the magnets is thus avoided. 
     In embodiments, the present invention relates to an induction motor device comprising a fixed coil, a mobile armature within a magnetic air space, a central core, and it comprises at least two magnetic sources disposed axially on either side of the core central. 
     In embodiments, the magnetic sources are opposing, thus creating two distinct magnetic fields. 
     In embodiments, at least one of the magnetic sources comprises one or more bipolar permanent ring magnets. 
     In embodiments, at least one of the magnetic sources comprises one or more disk-shaped bipolar permanent magnets. 
     In embodiments, at least one of the magnetic sources comprises one or more bipolar permanent magnets in the form of ring sections. 
     In embodiments, the loudspeaker comprises at least one device such as described in the present application. 
     In embodiments, the loudspeaker comprises at least one diaphragm linked to the armature and caused to move by the armature. 
     In embodiments, the loudspeaker comprises a salad bowl to which the diaphragm is fixed and a housing fixing the induction motor device to the salad bowl. 
     In embodiments, the invention relates to a method for moving an object by means of an induction motor device such as described in the present application. 
     In embodiments, the object moved by the induction motor device is a diaphragm, for example the diaphragm of a loudspeaker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages will become apparent in the description hereinbelow, with reference to the appended drawings, in which: 
         FIG.  1    shows a cross-sectional perspective view of the motor of the loudspeaker comprising the dual axial magnetic flux induction system according to one embodiment of the invention, 
         FIG.  2    shows a cross-sectional view of the loudspeaker comprising the motor with the dual axial magnetic induction system according to one embodiment of the invention, 
         FIG.  3    shows a cross-sectional perspective view of the loudspeaker comprising the motor with the dual axial magnetic induction system according to one embodiment of the invention, 
         FIG.  4    shows an exploded view of the loudspeaker, showing all of the components of the motor and of the loudspeaker according to one embodiment of the invention, 
         FIG.  5    shows a cross-sectional view of the motor with a dual axial magnetic induction system, and a representation of the magnetic fields modeled by arrows according to one embodiment of the invention, 
         FIG.  6   a    shows a ring-shaped magnet according to one embodiment of the invention, 
         FIG.  6   b    shows a magnet in the form of ring sections according to one embodiment of the invention, 
         FIG.  6   c    shows a disk-shaped magnet according to one embodiment of the invention, 
         FIG.  7   a    shows a cross-sectional perspective view of the loudspeaker comprising the induction motor composed of ring magnets according to one embodiment of the invention, 
         FIG.  7   b    shows a cross-sectional perspective view of the loudspeaker comprising the induction motor composed of magnets in the form of ring sections according to one embodiment of the invention, 
         FIG.  7   c    shows a cross-sectional and perspective view of the loudspeaker comprising the induction motor composed of disk-shaped magnets according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS OF THE INVENTION 
     With reference to the figures, the induction motor  10  of the loudspeaker  20  comprises a core  2 , a bowl  3   b  and a base plate  3   a , all three formed from a magnetically conducting material, preferably steel or another equivalent material; a fixed coil  5  installed inside of said bowl  3   b  and supplied with an AC current; two permanent magnets  1   a ,  1   b , made of a highly magnetic material, preferably neodymium, an upper magnet  1   a  having a north face  11   a  and a south face  11   b , and a lower magnet  1   b  having a north face  12   a  and a south face  12   b.    
     Said induction motor  10  may be equipped with various shapes of magnets, such as ring magnets  1   a  and  1   b  shown in  FIGS.  6   a  and  7   a   , magnets taking the form of ring sections such as the upper magnets in the form of ring sections  1   c  and the lower magnets in the form of ring sections  1   d  shown in  FIGS.  6   b  and  7   b   , or else magnets in the form of disks such as the upper magnet in the form of a disk  1   e  and the lower magnet in the form of a disk  1   f  shown in  FIGS.  6   c  and  7   c   . These examples are non-limiting but illustrative and other equivalent shapes are possible. 
     Said magnets are installed so as to have their said north faces, respectively  11   a  and  12   a , in contact with said core  2 , said south face of the upper magnet  11   b  in contact with said bowl  3   b  and said south face of the lower magnet  12   b  in contact with said base plate  3   a , in such a manner as to form between said core  2 , said upper magnet  1   a , said lower magnet  1   b , said bowl  3   b , said base plate  3   a  and said fixed coil  5 , a magnetic air space  6 . Within said magnetic air space  6  an armature  4  is installed composed of a conductive material, preferably aluminum, and connected to a loudspeaker diaphragm  7 . The attachment system for connecting the diaphragm  7  to the armature  4  may for example comprise tabs  21  of the armature  4  which are fixed to studs  22  of the diaphragm. Other equivalent means of attachment are possible, for example the bonding of the armature  4  to the diaphragm  7 , an additional coupling element, clip-mounting, etc. 
     The assembly of said loudspeaker  20  illustrated in  FIG.  2    comprises said induction motor  10 , said diaphragm  7  fixed to the salad bowl  8   a , and a loudspeaker housing  8   b  used to fix said motor  10  with said salad bowl  8   a.    
     Said magnets  1   a  and  1   b  may also be installed in an opposing manner, with respectively said south faces  11   b  and  12   b  in contact with said core  2 , without the principle of operation of said induction motor  10  being altered, in an equivalent construction. 
     Said ring magnets  1   a  and  1   b  may be replaced by magnets taking the form of ring sections  1   c  and  1   d  or in the form of a disk  1   e  and  1   f  such as illustrated in the present application. 
     With reference to  FIG.  5   , said upper magnets  1   a  and lower magnets  1   b  are positioned such that their poles in contact with said core  2  are the same. Said upper and lower magnets  1   a  and  1   b  create two distinct magnetic fields: an upper magnetic field  9   a  and a lower magnetic field  9   b . Said upper magnetic field  9   a , generated by said upper magnet  1   a , firstly passes through said core  2 , then said magnetic air space  6  from the inside to the outside and then interacts with said armature  4 . It subsequently returns to said south face  11   b  of said upper magnet  1   a  through said fixed coil  5  and said bowl  3   b . Said lower magnetic field  9   b , generated by said lower magnet  1   b , firstly passes through said core  2 , then said magnetic air space  6 , from the inside to the outside. It also interacts with said armature  4  then returns to said south face  12   b  of said lower magnet  1   b  via said fixed coil  5 , said bowl  3   b  and said base plate  3   a . Thus, within said magnetic air space  6 , and notably in said armature  4 , said magnetic fields  9   a  and  9   b  have the same direction and the same sense, which represents double the magnetic intensity with respect to a conventional induction system with a single radial magnetic flux. 
     Said magnetic fields  9   a  and  9   b , coupled to the electric field generated by said fixed coil  5 , create a force in said armature  4 . This force drives the movement of said armature  4 , linked to said diaphragm  7  for example by the means  21 ,  22  described hereinabove. 
     Thus, by increasing the intensity of the magnetic field experienced by said armature  4 , the force applied to said armature  4  is increased and hence the performance characteristics of said loudspeaker  20  are enhanced. 
     The embodiments are described by way of illustrative examples and must not be considered as limiting. Other embodiments may call upon means equivalent to those described for example. The embodiments may also be combined together depending on the circumstances, or means used in one embodiment may be used in another embodiment.