Patent Publication Number: US-2005140240-A1

Title: Rotor, especially a short-circuit rotor for an electric machine, amd electric machine with a rotor

Description:
BACKGROUND INFORMATION  
      An asynchronous machine and/or a short-circuited rotor for an electrical machine with which the groove spacing is constant is made known in the book “Elektrontechnik—Fachkunde für Elektroberufe”, published by W. Girardet, Essen, 1980, page 234 ff. The disadvantage of short-circuited rotor designs of this type is that, despite the use of diverse, known design specifications that relate to the number of rotor grooves to use, the short-circuited rotor machines originally assessed as being quiet prove to be surprisingly extraordinarily noisy on the test stand. Even a diagonal orientation, i.e., a non-axial orientation of the rotor grooves, has proven unsuitable in many cases.  
     ADVANTAGES OF THE INVENTION  
      The rotor according to the present invention having the features of the main claim has the advantage that certain harmonic waves of the air gap field, which cause the electromagnetic noise by way of their pulsating forces and pulsating torques on the stator core, are weakened or eliminated entirely. A torque irregularity and/or torque ripple is also reduced.  
      Advantageous further developments of the rotor according to the main claim are possible due to the measures listed in the subclaims. A particularly favorable weakening of the pulsating forces and pulsating torques on the stator core is achieved when the groove spacing on the periphery is alternatingly larger and smaller; this has a particularly advantageous effect when the groove spacing on the periphery approximates a sine-dependent function.  
      A further enhanced result in terms of pulsating forces and pulsating torques was achieved by increasing and decreasing the groove spacing around the periphery twice.  
      According to a further configuration of the present invention, to prevent loss of power of the short-circuited rotor machine, the ratio of groove width to groove spacing is constant for each tooth.  
      An imbalanced state is largely prevented by using a symmetrical rotor configuration.  
      According to an independent claim, an electrical machine is also provided that includes a stator and a rotor according to the present invention. 
    
    
     DRAWING  
      An exemplary embodiment of a rotor according to the present invention and an electrical machine according to the present invention are shown in the embodiments.  
       FIG. 1  shows a side view of a rotor according to the present invention, and  
       FIG. 2  shows an electrical machine in a schematic depiction. 
    
    
     DESCRIPTION  
      A side view of a rotor  10  according to the present invention is shown in  FIG. 1 . Rotor  10  has grooves  13  and teeth  16 , which alternate on the periphery of rotor  10 . A bar  19  is inserted in each groove  13 , the bars being connected with each other by known short-circuiting rings at the two axial ends of rotor  10 .  
      Each tooth  16  has a tooth width B, referred to here as the width of root  22 . In the example shown in  FIG. 1 , a rotor  10  having a total of sixteen teeth  16  is shown, whereby rotor  10  has an axially symmetrical configuration and a point-symmetrical configuration relative to the center of rotor  10 . A tooth  16  with a smaller width B 1  abuts a broadest tooth  16  having a width B 0  in the clockwise direction. Abutting this, in turn, in the same direction, is an even narrow tooth  16  with a width B 2  and, abutting this is a tooth  16  with a width B 3 . A narrowest tooth  16  is located in the approximately “3 o&#39;clock” position and has width B 4 . Each tooth  16  has a groove spacing τ a . Abutting tooth  16  with the largest groove spacing τ n0  on each side is a tooth  16 , each having a smaller groove spacing τ n , resulting, in entirety, in a rotor  10  for an electrical machine and, in this case in particular, a short-circuited rotor for an asynchronous machine with which the groove spacings τ are not constant.  
      Abutting the narrowest tooth  16  in the “3 o&#39;clock” position, continuing in the clockwise direction, is a subsequently broader tooth  16  in each case, until a broadest tooth  16  is reached again in the “6 o&#39;clock” position. Due to the point-symmetry or the axial symmetry, an alternatingly increasing and decreasing groove spacing τ results on the periphery. As the computing rule for determining the groove spacing on the periphery, in particular with regard for their alternatingly increasing and decreasing extents, it is provided that groove spacing τ is a sine-dependent or nearly sine-dependent function.  
      As shown in  FIG. 1 , it is provided that groove spacing τ increases and decreases twice around the periphery of rotor  10 , which results in a two-fold periodicity. It is further provided that the ratio of tooth width B to groove spacing τ, considered for each tooth  16 , is constant. As a result, all teeth  16  have the same ratio.  
      In  FIG. 2 , an electrical machine  30  is shown in a schematic depiction, the electrical machine including a stator  33  and rotor  10  according to the present invention. It is provided that stator  33  has a four-pole configuration.  
      If rotor  10  does not have a rotationally symmetric or point-symmetric configuration, rotor  10  can become imbalanced. To eliminate the imbalance of rotor  10 , it is provided that grooves  39  are machined on the radially outwardly directed side, in tooth tips  36 , for example, to eliminate imbalances. For the same purpose, it can also be provided that a tooth  16  have an opening  42  which is situated such that it only minimally influences the electromagnetic properties.