Patent Publication Number: US-2017373546-A1

Title: Electric machine designed to limit sound nuisance

Description:
This invention relates to the field of electric machines and relates more particularly to electric machines comprising at least one stator. 
     An electric machine is a machine, also called a motor, which comprises at least one stator. The stator comprises teeth forming coils. Powering each of the coils creates a magnetic field within the stator, with a rotor orienting itself along the field lines. 
     In the field of motor vehicles, these electric machines are used, for example, in electrical systems such as supercharged electric compressors. 
     For example, these machines are used in the induction system in order to improve the vehicle&#39;s performance, to compensate for the lag time of a conventional turbocharger on start-up, or during the vehicle&#39;s transient phases. 
     However, this type of machine is a source of noise. In fact, the electromagnetic forces created on the stator and rotor cause high-frequency micro-displacements within the audible range of the human ear, between 1,000 and 20,000 Hz. The vibrations are transmitted along the entire structure of the machine and spread through the air and into the machine&#39;s supports. Although the noises driven by the machine towards the support can be reduced by dampers, the intrinsic noises of the machine are more difficult to deal with. 
     One solution to this noise involves reducing the effects of the radial forces. The effects of the radial forces are reduced, for example, by creating recesses in the material on the external face of the stator, in the extension of the stator teeth. This solution enables a gain in deformation, allowing the radial forces on the part in contact with the stator to be reduced by 10%. This gain helps partially to reduce the noise but it still remains audible to the human ear. 
     The aim of this invention is therefore to overcome one or more of the drawbacks of machines of the prior art by proposing an electric machine configured so as to limit sound nuisance. 
     For this reason, the present invention proposes an electric machine comprising at least one stator, the stator being formed by a body and teeth arranged on the inner face of the body of the stator, characterized in that the stator comprises at least one internal recess formed in the body of the stator. 
     In fact, it is the mechanical stress that contributes to sound nuisance by promoting radial forces. Reducing the effects of radial forces via recesses thus limits sound nuisance. 
     According to an embodiment of the invention, the recess extends longitudinally in the stator body parallel to a longitudinal axis of the stator. 
     According to an embodiment of the invention, the internal recess has any geometric form capable of limiting the mechanical stress on the stator. 
     According to an embodiment of the invention, the width of the internal recess is less than the width of a stator tooth. 
     According to an embodiment of the invention, the internal recess is a cylinder or an ellipse. 
     According to an embodiment of the invention, the width of the internal recess is arranged in the axis of a stator tooth. 
     According to an embodiment of the invention, the internal recess is formed in the stator body at a sufficient distance from an internal face  221  of the stator body so as not to disturb the magnetic field. 
     According to an embodiment of the invention, the stator comprises at least two external recesses formed on the external face of the stator. 
     According to an embodiment of the invention, the external recess forms a groove oriented longitudinally along the longitudinal axis of the stator. 
     According to an embodiment of the invention, the external recess  25  is centered between two internal recesses  24  and overlaps, at each of its sides, an internal recess  24 . 
     The invention also relates to the use of the electric machine according to the invention in an electric supercharger for a motor vehicle. 
     The invention also concerns an electric supercharger equipped with an electric machine according to the invention. 
    
    
     
       Further aims, features and advantages of the invention will emerge more clearly from the following description with reference to the accompanying figures, given by way of example, in which: 
         FIG. 1  is a schematic representation of a cross-sectional view of a device according to the invention, 
         FIG. 2  is a schematic representation of a detail of a device according to the invention. 
     
    
    
     This invention relates to an electric machine  1 . The electric machine  1  comprises at least one stator  2 , shown in  FIGS. 1 and 2 . The electric machine also comprises a rotor  3  arranged inside the stator  2 . More precisely, the rotor  3  is arranged in a space  4  formed at the center of the stator  2 . 
     According to an embodiment of the invention, the electric machine is a direct- or alternating-current, synchronous or asynchronous machine or any type of electric machine of the same type. 
     According to an embodiment of the invention, the electric motor is a Switched Reluctance Motor (SRM). 
     According to an embodiment of the invention, the stator comprises a body formed by a stack of thin sheets forming a ring, also called a laminated core, the internal face of which is provided with recesses open to the interior to receive the phase windings that form a coil. 
     According to an embodiment of the invention, the rotor has permanent magnets. 
     The stator  2  is formed of at least one body  21 . According to an embodiment of the invention, the stator is formed of several bodies. The stator is also formed of several teeth  22 . The teeth  22  are arranged on the inner face  221  of the stator body delimiting the space  4  in which the rotor is located. The stator  2  comprises n teeth  22 , n being between 4 and 12, and very preferably 6. Around each tooth  22  a winding is arranged that thus forms the coils  23  of the stator. The supply of each of these coils  23  allows a magnetic field to be created in the stator  2 . 
     According to an embodiment of the invention, the rotor  3  comprises rotor teeth  32  oriented along the field lines of the stator  2 . The number of teeth of the rotor  3  ranges between 2 and 8, and preferably 4. 
     Within the scope of the invention, the stator  2  comprises at least one internal recess  24 . This internal recess  24  is formed in the actual body  21  of the stator. The internal recess  24  is formed in the body  21  of the stator  2  and extends longitudinally, along the longitudinal axis  31  of the stator, over at least part of the stator, into the body  21  of the stator  2 . More precisely, the internal recess  24  extends parallel to the axis  31  of the stator. 
     Within the scope of the invention, the longitudinal axis  31  of the stator is defined as being the axis  31  along which the stator extends, passing through the center of the stator, namely the axis  31  around which the stator is arranged. 
     According to an embodiment of the invention, the internal recess  24  extends longitudinally along the entire length of the stator  2 . 
     According to an embodiment of the invention, the width L ei  of the internal recess  24  is greater than the width L s  of a tooth  22  of the stator  2 . 
     Within the scope of the invention, the width, of the recess and stator teeth, is defined by the magnitude oriented along a plane P perpendicular to a plane passing through the radius R of the stator, in contrast to the height, which is defined by the magnitude passing through the radius R of the stator. Within the scope of the invention, the internal recess  24  has any possible geometric form. More precisely, the internal recess  24  has any geometric form limiting the mechanical stress on the stator  2 . In fact, it is the mechanical stress that contributes to sound nuisance by promoting radial forces. Reducing the effects of these forces thus limits sound nuisance. 
     According to an embodiment of the invention, the internal recess  24  is a cylinder whose generatrix has any form enabling the mechanical stress on the stator to be limited. 
     According to an embodiment of the invention, the internal recess  24  is round. 
     According to an embodiment of the invention, the internal recess  24  is oval, its width L ei  being greater than its height h ei . 
     According to an embodiment of the invention, the internal recess is square or rectangular. For example, the internal recess  24  is rectangular or square, with rounded corners. 
     According to an embodiment of the invention, the internal recess  24  is elliptical, more precisely the internal recess  24  is an elliptical cylinder whose width is greater than its height. 
     The internal recess  24  is arranged in the axis of a stator tooth  22 . More precisely, the internal recess  24  is arranged in a part of the body  21  of the stator  2  extending a tooth  22  of the stator. 
     According to an embodiment, the internal recess  24  is formed in the stator body at a sufficient distance from the internal face  221  of the stator body so as not to disturb the magnetic field. More precisely, the shorter distance D ei  between an edge of the internal recess  24  and the internal face  221  of the stator body is greater or the same as the width of a stator tooth divided by two (L s /2). Such an arrangement avoids changing the magnetic field of the electric machine. 
     According to an embodiment of the invention, the internal recess  24  is arranged in the body  21  of the stator  2  and on the periphery of the body  21 . This means that the internal recess  24  is closer to the external face  222  of the stator  2  than the internal face  221  of the stator  2 . 
     Within the scope of the invention, the external face  222  of the stator  2  is that which does not comprise a tooth  22  and that is arranged on the outside of the stator  2  if we consider that the internal face  221  of the stator delimits an area  4  of the stator  2  in which the rotor  3  is arranged. 
     According to an embodiment of the invention, the stator  2  comprises a number of recesses  24  identical to the number of teeth  22  of the stator. For example, if the stator comprises six teeth, the stator comprises six internal recesses  24 . 
     According to a variation of the invention, the stator  2  comprises at least one external recess  25  formed on the external face of the stator, shown in  FIG. 2 . 
     This external recess  25  forms a groove oriented along the axis  31  of the rotor  3 . The external recess  25  is offset in relation to the teeth  22  of the stator. The external recess  25  is centered between two internal recesses  24 . 
     According to an embodiment of the invention, the width of the external recess  25  is such that it overlaps, at each of its sides, an internal recess  24 . 
     According to an embodiment of the invention, the machine comprises two external recesses  25 , the distance D ex  between two external recesses  25  being less than the width L ei  of an internal recess  24 . The stator  2  thus comprises an alternation of internal recesses  24  and external recesses  25 . The depth of the external recess  25  is within 0 and a remaining thickness of the stator body greater than or equal to the width of a stator tooth divided by two (L s /2). Within the scope of the invention, remaining thickness means the remaining thickness between the bottom of the recess and the internal face  221  of the stator or the start of a stator tooth  22 . 
     According to an embodiment of the invention, the stator  2  comprises a number of external recesses  25  identical to the number of stator teeth  22 . For example, if the stator comprises six teeth, the stator comprises six external recesses  25 . 
     Such a stator  2  according to the invention enables a gain of 50% in terms of mechanical stress. 
     The invention also concerns the use of such a machine according to the invention in an electric supercharger for a motor vehicle. 
     The invention also concerns an electric supercharger equipped with such a machine  1  according to the invention. More precisely, the invention also relates to an electric compressor equipped with a switched reluctance motor according to the invention. This electric supercharger for a motor vehicle comprises a compressor wheel and an electric machine according to the invention, to drive the compressor wheel. 
     The scope of the present invention is not limited to the details given above and permits embodiments in numerous other specific forms without departing from the field of application of the invention. Consequently, the present embodiments must be considered as being by way of illustration and can be changed without, however, departing from the scope defined by the claims.