Patent Publication Number: US-2023147217-A1

Title: Electric machine

Description:
RELATED APPLICATIONS 
     This application is a filing under 35 U.S.C. § 371 of International Patent Application PCT/EP2021/058463, filed Mar. 31, 2021, and claiming priority to German Patent Application DE 10 2020 204 725.1, filed Apr. 15, 2020. All applications listed in this paragraph are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an electric machine with a round housing, a stator, and a rotor on a rotor shaft. Such an electric machine functions in particular as an electric motor, but can also be used as a generator. 
     BACKGROUND 
     Temporally variable mechanical forces that act on the stator are formed by the magnetic forces in the gap between the stator and the rotor. These forces can be mathematically described as waves that spread out radially as well as tangentially. The waves overlap radially and tangentially with different spatial and temporal arrangements. The radial waves cause the housing to vibrate. The housing vibrations result in acoustic vibrations in the adjacent structures, or form sound waves in the surrounding air. 
     The stator is normally installed in the housing as rigidly as possible. The radial deformations of the stator cause by magnetic forces are transferred directly to the housing and result is disruptive noises when in operation. 
     The stator is frequently pressed into the housing or a stator mount. This results in a rigid connection over the entire contact surface area. Alternatively, the stator can be screwed to the end surfaces of the housing at axial holes therein. This results in contact surfaces at the ends, and a rigid connection between the stator and the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention shall be explained in greater detail below in reference to the attached drawings. Therein: 
         FIG.  1    shows a perspective view of an electric motor from the front; 
         FIG.  2    shows a perspective view of the stator for the electric motor in  FIG.  1   ; 
         FIG.  3    shows the electric motor in  FIG.  1   , with the bearing pins partially removed; 
         FIG.  4    shows the stator for the electric motor in  FIG.  2   , in an exploded view; 
         FIG.  5    shows a second electric motor from the front; 
         FIG.  6    shows a perspective view of the stator for the electric motor from  FIG.  5   . 
     
    
    
     DETAILED DESCRIPTION 
     In view of the background above, a fundamental problem addressed by the present disclosure is how to attach the stator in an electric machine to the housing such that the impact on the housing by the radial deformations of the stator resulting from radial forces is kept to a minimum. 
     In some aspects, this problem is solved according to the first claim through fastening elements which rigidly connect the stator to the housing in the circumferential direction, but exhibit a radial flexibility. The torques in the stator are rigidly transferred to the housing by the fastening means according to the invention, while these fastening means remain flexible when reacting to radial deformations of the stator, such that the deformations are not transferred to the housing, or are extremely dampened. The fastening elements result in a rigid connection in the circumferential, or tangential, direction, but are flexible in the radial direction. 
     In particular, the fastening elements transfer compressive and tensile forces from the stator to the housing in the circumferential direction, but only allow a limited radial movement of the stator in relation to the housing. As a result of this anisotropic property of the fastening elements, there is the same non-rotating connection between the stator and the rotor as with conventional electric machines, but the radial forces coming from the stator have only a minimal impact on the housing. This results in less vibration and a significant noise reduction. 
     In a preferred embodiment of the electric machine according to the invention, the fastening elements are formed by hinged levers placed between the housing and the stator, which can pivot radially on the housing. By way of example, the shaft of the hinged lever extends circumferentially, or in the tangential direction, and has pivot heads at each end. The hinged levers allow for small radial movements of the stator, but rigidly connect the stator to the housing in the circumferential direction, transmitting compressive and tensile forces from the stator to the housing in a tangential direction. 
     The hinged levers can be advantageously supported on the housing at one pivot head and on the stator at the other pivot head. These pivot heads can pivot about an axis that is parallel to the axis of the rotor. Alternatively, the desired anisotropic properties of the hinged levers can be obtained through the material selection, or a combination of materials with different mechanical properties. By way of example, the fastening elements can be made of an elastic material, preferably an elastomer. The desired differences in stiffness in the radial direction and in the circumferential direction can be obtained through the geometric design. The fastening elements can also be composite components made of metal and rubber. The fastening elements can also be formed by hinged levers in which the pivot heads are coated with an elastomer. The elastomer part would then exhibit the desired deformability or flexibility in the radial direction. 
     The stator in the electric machine preferably comprises a packet of stator plates, in the manner known per se. The stator plates have radially protruding eyelets. Bearing pins are placed in the eyelets, extending parallel to the rotor shaft. The hinged levers serving as fastening elements are attached to the bearing pins at one end and to the housing at the other end. These bearing pins extend axially all the way through the packet of stator plates, but are not rigidly connected to the housing in the radial direction. The pivotal connection of the other pivot head to the housing is preferably obtained through a socket formed on the end surface of the housing. 
     To obtain a rotationally symmetrical support for the stator in the housing, numerous hinged levers can be distributed evenly about the circumference of the stator. There are preferably four to eight, particularly preferably six, hinged levers evenly distributed about the circumference of each end of the housing. 
     Instead of hinged levers between the housing and the stator, the fastening elements can also be formed as an integral part of the stator. With a stator comprised of a packet of stator plates, the fastening elements can be formed by radial slits on the circumference of the stator plates, and these radial slits can partially overlap and border on narrow plate webs that can bend radially. The plate webs do not bend in the circumferential direction, or tangential direction, but they do bend in response to radial waves, and the radial deformations of the stator caused by them. The radial slits therefore prevent a spreading of the radial waves to the adjacent plate webs in the radial direction on the stator plates, and thus effectively decouple the housing from the vibrations in the stator. 
     The stator ideally has numerous radial slits distributed evenly over its circumference. Four to eight radial slits, which overlap by approximately one third, forms an optimal compromise between rigidity of the outer edge of the stator along the circumference, and flexibility in the radial direction. 
     The simplified illustration of the electric motor in  FIG.  1    has a cylindrical housing  10  in which a stator  20  is placed such that it cannot rotate. A concentric rotor  30  rotates inside the stator  20 . There are hinged levers  40  between the stator  20  and the rotor  30 . 
     The front end surface  11  and rear end surface  12  of the housing  10  form flanges. Round sockets  13  are formed at the transition between the end surfaces  11 ,  12  and the cylindrical housing wall. Beads  14  protrude radially outward between the front end surface  11  and the rear end surface  12 . 
     The stator  20  comprises a packet of stator plates  21  with eyelets  22  that protrude radially outward thereon (see  FIG.  4   ). 
     The rotor  30  rotates on a rotor shaft  31  that can rotate in the housing  10 . The rotor shaft  31  forms the motor shaft for the electric motor. Because the rotor  30  is on the inside, and the stator  20  is on the outside, this design is referred to as an internal rotor. The opposing magnetic attractive forces and repelling forces between the stator  20  and the rotor  30  cause the rotor shaft  31  to rotate. 
     As can be readily seen in  FIG.  4    in particular, the hinged levers  40  each have a shaft  41  that extends tangentially, and pivot heads  42  and  43  on the ends of the shaft  41 . There are six hinged levers  40  on each of the end surfaces  11 ,  12 , evenly distributed over the circumference of the stator  20 . 
     There are bearing pins  50  in the eyelets  22  on the stator plates  21 , which extend parallel to the rotor shaft  31  in the axial direction. The bearing pins  50  sit in the corresponding beads  14  on the housing  10 . The hinged levers  40  are pivotally connected at their first pivot heads  42  on the axial ends of the bearing pins  50  (see  FIG.  3   ,  FIG.  4   ). The pivot heads  43  on the other ends of the hinged levers  40  are pivotally supported in the sockets  13  on the housing  10 . 
     The rigid but pivotally supported hinged levers  40  rigidly connect the stator  20  to the housing  10  in the circumferential direction, but form a flexible connection in the radial direction. Tangential compressive and tensile forces in the stator  20  are thus transferred rigidly to the housing  10  in the circumferential direction, while the eyelets  200  on the stator plates  21  can move slightly in the radial direction in the sockets  14  formed on the housing  10 . The hinged levers  40  therefore react in a flexible manner to radial deformations of the stator  20 . Radial waves are therefore not transferred from the stator  20  to the housing  10 . 
     In the second embodiment of an electric motor, shown in  FIGS.  5  and  6   , the stator also comprises a packet of parallel stator plates  61 . The stator plates  61  have radial slits  62  on their outer edges that are evenly distributed over the entire circumference of the stator  60 . The radial slits  62  are partially overlapping, and border on narrow plate webs  63 . There are fastening holes  64  for bearing pins (not shown), which extend axially through the stator. Radial deformations of the stator  60  are compensated for by the radial slits  62 . The relatively narrow plate webs  63  on the stator plates  61  can give slightly in the radial direction by bending in an elastic manner. 
     The words “comprising” and “having” in the claims do not exclude the presence of other elements. The indefinite articles “a” or “one” do not exclude the existence of a plurality. A single element can carry out the functions of numerous elements specified in the claims. 
     REFERENCE SYMBOLS 
     
         
           10  housing 
           11  end surface 
           12  end surface 
           13  socket 
           14  bead 
           20  stator 
           21  stator plate 
           22  eyelet 
           30  rotor 
           31  rotor shaft 
           40  hinged lever 
           41  shaft 
           42  pivot head 
           43  pivot head 
           44  hole (in ( 42 ) 
           50  bearing pin 
           60  stator 
           61  stator plate 
           62  radial slit 
           63  plate web 
           64  fastening hole