Abstract:
The invention relates to a machine, in particular a generator, which has a bearing ( 19 ) supported on a hub ( 22 ), whereby a bearing part of the bearing ( 19 ) is loaded by a spring element ( 25 ) producing an axial force (FA). The spring element ( 25 ) is plastically deformed.

Description:
BACKGROUND INFORMATION  
       [0001]     The present invention relates to a generator according to the general class of the independent claim.  
         [0002]     A generator is known from DE 19804328 A1, in the case of which the generator shaft is supported by a movable bearing in the vicinity of a housing part. A spring element inserted in the hub loads the outer ring of the movable bearing with an axial force to achieve a defined rolling movement of the rolling body in the movable bearing and thereby achieve a longer service life of the movable bearing. Due to the selected axial fixation of the spring element using a special spring disk, the movable bearing design disclosed in the publication named hereinabove results in a hub that is axially relatively large in size. In addition, the fixation of the spring elements disclosed therein allows only a limited amount of pretensioning force to be achieved. Moreover, a relatively complicated configuration of the parts is necessary to achieve an axial pretensioning force. Due to production tolerances in the assembly process, the adjustment of the axial pretensioning force is not guaranteed with sufficient accuracy, and it is an additional assembly process.  
       ADVANTAGES OF THE INVENTION  
       [0003]     The generator according to the invention having the features of the main claim has the advantage that, due to the plastically deformed spring element and the spring characteristic curve of the spring element that is therefore utilized in the plastic range, a well-defined axial force is achieved with relatively great spring travel during assembly in a relatively narrow force range.  
         [0004]     Advantageous further developments of the generator according to the main claim are possible as a result of the measures listed in the subclaims. If the spring element has a spring constant c between 18 and 70 N/mm in the plastic range, a sufficiently accurate axial force is attained by the spring element across the compression travel of the spring element given standard tolerances for the generator components.  
         [0005]     A particularly favorable compact design of the spring element results when the plastic range begins after an elastic compression travel between 3 and 3.5 mm. If the plastic range begins below 1.5 mm, the tolerances to be selected for the pretensioned components must be so low that fabrication is too expensive. If a greater elastic compression travel is selected, an undesired axial extension of the hub is attained. To prevent the pretension and/or axial force on the bearing from becoming too great when the plastic range of the spring element is fully utilized, it should be possible to adjust a change in axial force ΔFA of 100 N across a plastic compression travel between 1.5 and 3.5 mm. In favorable cases, axial force FA is between 350 N and 650 N. If the axial force is lower, the service life of the movable bearing is greatly limited, since the rolling movements of the rolling bodies are not ideal. If the axial force is greater than 650 N, the service life of the bearing is reduced due to the increased pressing of rolling bodies between the bearing rings.  
         [0006]     The spring element is centered by the hub. This provides an advantage, namely that the spring element does not bear against the bore of the hub, which would result in a loss of axial force, which could reduce the axial force on the movable bearing.  
         [0007]     According to a further embodiment, it is provided that the spring element has a carrier region from which at least one spring arm extends. The carrier region has the task of acting as a centering element and therefore offers a good hold for the at least one spring arm. A particularly space-saving design results due to the fact that the at least one spring arm extends in the peripheral direction.  
         [0008]     To achieve a favorable material utilization with the spring element, it is provided that cross sections of the spring element loaded with the axial force are exposed to essentially identical mechanical loads. 
     
    
     DRAWING  
       [0009]      FIG. 1  shows a machine with a cross-sectional view through the movable bearing.  
         [0010]      FIG. 2  shows a spacial view of the spring element.  
         [0011]      FIG. 3  shows a top view of the spring element.  
         [0012]      FIG. 4  shows a force-travel diagram for the course of axial force across the compression travel of the spring element. 
     
    
     DESCRIPTION  
       [0013]     In  FIG. 1 , a machine  10  and, here in particular, one of its bearing arrangements  13 , is depicted in a sectional view. The parts of bearing arrangement  13  are a shaft  16 , a bearing  19 , a hub  22 , and a spring element  25 . Hub  22  is part of a bearing plate and accommodates bearing  19 , designed as rolling bearing, with its outer ring  31  in its cylindrical bore  28 . Bearing  19  carries shaft  16  using rolling bodies  34  and an inner ring  37 . In this example, machine  10  is designed as a generator, whereby shaft  16  is usually composed of steel, and hub  22 , which is configured integral with the bearing plate, is composed of an aluminum alloy.  
         [0014]     For the fabrication of machine  10 , different linear tolerances—axial linear tolerances, in this case—apply for the individual components of machine  10  to be manufactured. When individual parts that are manufactured individually are combined, extreme combinations result. With machines  10  configured as generators, an attempt is usually made to compensate for the different tolerances in a bearing arrangement  13  facing away from the machine drive. Due to the different linear tolerances, the axial position of a shaft shoulder  40  can be different than that of an end surface  43  of hub  22 , for example. An extreme position is depicted in  FIG. 1 . Another extreme position  401  is also sketched, in which shaft shoulder  40  is shifted further to the right due to production tolerances. The position of bearing  19  on shaft shoulder  40  also shifts, so that a side of bearing  19 —shown on the right in the illustration—moves to position  191 .  
         [0015]     If, given a variability in tolerance position of this nature, machine  10  is no longer driven by a belt, as is standard, but rather via gears internal to an internal combustion engine, for example, a bearing force acting in the radial direction is lacking in the bearing arrangement  13 , which would otherwise result in a defined rolling of rolling body  34  in bearing  19 .  
         [0016]     In installation and drive cases of this nature, a spring element  25  is provided inside bearing arrangement  13  that, due to its axially-acting force, causes outer ring  31  to shift in the direction toward shaft shoulder  40 , thereby bringing about a radial force on rolling body  34 . If this radial force reaches a certain minimum amount, a defined rolling of rolling body  34  is induced, and the service life of bearing  19  can therefore be extended. Spring element  25  must produce an axial force FA on bearing  19  within the extreme positions that occur, the axial force being located within a certain range. With the variant of a bearing arrangement  13  depicted in  FIG. 1 , spring element  25  loads bearing part outer ring  31  with axial force FA. With variabilities that are this great, to ensure that the axial force acting on the bearing part is neither to small nor too great, it is provided that the spring element is plastically deformed while it exerts axial force on the bearing part in the installed state.  FIG. 2  shows a power-force diagram of the spring element. Travel s is shown on the x-axis and axial force FA is shown on the y-axis. Starting at the beginning, variable s 0  represents the axial length of spring element  25  in the unloaded state. If spring element  25  is now compressed axially, the axial extension of spring element  25  is reduced. After the elastic compression travel Δse has been completed, the spring element has axial extension s 1 . After this value, i.e., if spring element  25  is compressed even further, the deformation of spring element  25  is plastic. When axial expansion s 1  of spring element  25  is reached, the minimally required axial force FA min  is simultaneously reached. The force-travel curve is now clearly flatter than the force-travel curve in the elastic range of spring element s 25 . With regard for bearing arrangement  13 , variable s 1  means that s 1  is the maximum permissible axial extension of spring element  25  in bearing arrangement  13 . s 1  therefore corresponds to the maximum installation length between an end face  46  in hub  22  and a right end face  49  of bearing  19 . Axial extension s 2  is permissible as the minimal distance between end faces  46  and  49 , refer also to  FIG. 2 . The definition of s 2  is that, given this axial extension of spring element  25 , a maximum permissible axial force FA is barely not exceeded.  
         [0017]     The structural design of spring element  25  is explained in greater detail with reference to  FIGS. 3 and 4 . In the top view of spring element  25 , a carrier region  52  that is preferably configured annular in shape is clearly shown. A plurality of spring arms  55  extend away from this carrier region  52  on its radial outer side. As a minimal requirement with regard for spring element  25 , it is provided that at least one spring arm  55  extends away from carrier region  52 . This at least one spring arm  55  extends in the peripheral direction in relation to the axis of shaft  16  of machine  10 . To achieve the most favorable utilization of installation space possible for spring element  25 , two spring arms  55  each extend from the periphery of carrier region  52 , starting at a point on the circumference, the spring arms pointing away from each other. Spring arms  55  have cross sections configured such that the axial force load causes essentially identical mechanical loads in spring arms  55 .  
         [0018]     Carrier region  52  enables spring element  25  to be centered by hub  22 , refer also to  FIG. 1 . For this purpose, it is provided that hub  22  has a radially inwardly directed projection  58  that ends in an axially oriented projection  61  shortly before it reaches shaft  16 . This shaft  61  has a radially outwardly machined surface, and via this, centers carrier region  52 —and, therefore, spring element  25 —on its inwardly oriented contour.  
         [0019]     Various physical properties for spring element  25  have proven particularly favorable. To ensure that only permissible axial force increases occur across the plastic compression travel between s 1  and s 2 , it is provided that the spring constant is between 18 and 70 N/mm, in accordance with the standard definition. Moreover, it has been shown that the plastic range of deformation of spring element  25  favorably begins after an elastic compression travel between 2 and 3.5 mm. It has also been shown that the change in axial force ΔFA in a plastic compression travel between 1.5 and 3.5 mm is favorably located in a range of 100 N. For a favorable service life forecast of bearing  19 , it is necessary that spring element  25  produce an axial force FA of 350 to 650 N.