Patent Publication Number: US-2020284320-A1

Title: Wear compensation for shafts supported on friction bearings

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application under 35 U.S.C. § 371 of International Application No. PCT/EP2017/078274 filed on Nov. 6, 2017, and claims benefit to German Patent Application No. DE 10 2016 223 833.7 filed on Nov. 30, 2016. The International Application was published in German on Jun. 7, 2018 as WO 2018/099687 A2 under PCT Article 21(2). 
    
    
     FIELD 
     The invention relates to an arrangement comprising a friction-bearing supported first gear ( 101 ) with a pitch diameter d 1  and a friction-bearing supported second gear ( 103 ) with a pitch diameter d 2  and to a method for improving the wear resistance of such an arrangement. 
     BACKGROUND 
     If a first gear with a pitch diameter d 1  and a second gear with a pitch diameter d 2  intermesh with each other, a nominal dimension for the distance of an axis of rotation of the first gear from an axis of rotation of the second gear will, according to solutions as known from the prior art, amount to 
         N   a =( d   1   +d   2 )/2. 
     Friction bearings are being increasingly used in wind turbine gearboxes. They have positive effects in terms of noise and vibration characteristics. Wind turbines, however, are subject to operating conditions that involve an increased wear of the friction bearings. Among these conditions are frequent starts and stops as well as idle operation. 
     An axial offset in the gearings of gears intermeshing with each other is a result of the wear. Such offset is only tolerable within certain limits. Any additional wear will lead to damages. 
     SUMMARY 
     In an embodiment, the present invention provides an arrangement. The arrangement includes a friction-bearing supported first gear with a pitch diameter d 1  and a friction-bearing supported second gear with a pitch diameter d 2 . The first gear and the second gear intermesh with each other and a distance a between an axis of rotation of the first gear and an axis of rotation of the second gear increase during operation by up to Δ a   wear . A nominal dimension N a  is provided for the distance a, wherein N a =(d 1 +d 2 −Δ a   wear )/2. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  shows two gears intermeshing with each other; and 
         FIG. 2  shows a bearing of the gears. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention avoid certain drawbacks inherent in solutions known from the prior art. Embodiments of the invention increase the lifetime of an arrangement with friction-bearing supported gears under adverse operating conditions. 
     An arrangement according to embodiments of the invention comprises a friction-bearing supported, preferably exclusively friction-bearing supported, first gear and a friction-bearing supported, preferably exclusively friction-bearing supported, second gear. The first gear and the second gear intermesh with each other. An axis of rotation of the first gear and an axis of rotation of the second gear run preferably parallel to each other. The two axes of rotation are—apart from changes as a result of wear and/or bearing clearance 
     The first gear is preferably fixed on a first shaft, the second gear on a second shaft. In this case, the gears are friction-bearing supported via the shafts. In particular, the first shaft and the second shaft are friction-bearing supported, preferably exclusively. 
     The fixation of the two gears on the shafts is carried out at least in a non-rotatable manner such that an at least non-rotatable connection exists in each case between the first shaft and the first gear as well as between the second shaft and the second gear. Preferably, the first shaft and the first gear as well as the second shaft and the second gear are in each case fixed immovably in relation to each other, that is to say, without a relative degree of freedom of movement. 
     During operation, that is to say, from starting up to closing down the arrangement, wear occurs in friction bearings, by which the first gear or, as the case may be, the first shaft, and the second gear or, as the case may be, the second shaft, are supported. In the process, a distance a between an axis of rotation of the first gear or, as the case may be, of the first shaft, and an axis of rotation of the second gear or, as the case may be, of the second shaft, increases by up to Δ a   wear . Preferably, Δ a   wear  not only comprises a wear-related increase of the distance a, but also an increase of the distance a as a result of bearing clearance of the two shafts. 
     The distance a is defined as length of the shortest distance of all distances connecting the two axes of rotation. 
     If the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, at the time of starting up is a Beginn  and at the time of closing down is a Ende , the following applies: 
         a   Beginn   ≤a   Ende   ≤a   Beginn +Δ a   wear .
 
     According to embodiments of the invention, the following applies: 
         N   a =( d   1   +d   2 −Δ a   wear )/2.
 
     In this context, N a  refers to a nominal dimension for the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, at the time of starting up. d 1  refers to a pitch diameter of the first gear, d 2  correspondingly to a pitch diameter of the second gear. 
     A nominal dimension is defined in Hoischen, Hesser: “Technisches Zeichnen”, 33rd edition, Comelson Verlag, 2013, page 163. Nominal dimension accordingly is a reference value used to determine an upper and a lower limit. 
     A pitch diameter is defined in Steinhilper, Sauer “Konstruktionselemente des Maschinenbaus 2—Grundlagen von Maschinenelementen für Antriebsaufgaben”, 5th edition, Springer-Verlag, 2012, page 398. 
     The invention takes into account the capability of the gearing of the first gear and of the second gear to tolerate an axial offset of the first shaft and of the second shaft without damages. The nominal dimension N a  is selected such that a negative axial offset is present at the time of starting up. The axial offset increases with wear. The absolute value of the axial offset, however, initially decreases. In this manner, the capability of the gearings of the first gear and of the second gear to tolerate an axial offset is optimally utilized. 
     Caused by production, deviations of the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, from the nominal dimension N a  can occur. T a   −  refers to a production-related maximum downward deviation of the distance a between the first shaft and the second shaft from the nominal dimension N a . Thus, the following applies 
     
       
      
       N 
       a 
       −T 
       a 
       − 
       ≤a.  
      
     
     a min  refers to a minimum value for the distance a between the first shaft and the second shaft that is tolerated by the gearings of the first gear and of the second gear. In order for the gearings of the first gear and of the second gear to intermesh without damages, a min ≤a must therefore apply. 
     Against this background, the arrangement is configured according to further developments such that the following applies: 
     
       
      
       a 
       min 
       ≤N 
       a 
       −T 
       a 
       − 
      
     
     In order to determine T a   −  or Δ a   wear , this equation can optionally be equivalently transformed as follows: 
         T   a   − ≤( d   1   +d   2 −Δ a   wear )/2− a   min  
 
       or, as the case may be, 
       Δ a   wear   ≤d   1   +d   2 −2*( a   min   +T   a   − ).
 
     Let T a   +  refer to a maximum upward deviation of the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, from the nominal dimension N a . Thus, the following applies 
         a≤N   a   +T   a   + . 
     Let a maximum value of the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, that is tolerated by the gearings of the first gear and of the second gear be referred to as a max . In order for the gearings of the first gear and of the second gear to intermesh without damages, a≤a max  must therefore apply. 
     The arrangement is preferentially developed further in such a manner that the following applies: 
         N   a   −T   a   + +Δ a   wear /2≤ a   max  
 
     In order to determine T a   +  or Δ a   wear , this equation can be optionally equivalently transformed as follows: 
         N   a   ≤a   max   −T   a   + −Δ a   wear /2
 
       or, as the case may be, 
       Δ a   wear ≤2*( a   max   −T   a   +   −N   a ).
 
     In the context of the present invention, involute-toothed gears are particularly advantageous because they tolerate a high axial offset. High deviations of the distance a between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, from the nominal dimension N a  can thus be realized by means of an involute-toothed first and second gear. 
     A method according to the invention provides to select the nominal dimension N a  for the distance between the axis of rotation of the first gear or, as the case may be, of the first shaft, and the axis of rotation of the second gear or, as the case may be, of the second shaft, such that the following applies: 
         N   a =( d   1   +d   2 )/2. 
     A first gear  101  and a second gear  103  intermesh with each other as illustrated in  FIG. 1 . The first gear  101  is supported rotatably about a first axis of rotation  105 . The second gear  103  is supported rotatably about a second axis of rotation  107 . 
     The first axis of rotation  105  and the second axis of rotation  107  run at a distance  109  from one another. In particular, both axes of rotation  105 ,  107  are aligned parallel to each other. 
     Caused by the deadweight of the first gear  101 , a first normal force  111  acts in the first axis of rotation  105 . Correspondingly, a second normal force  113  acts in the second axis of rotation  107  caused by the deadweight of the second gear  103 . 
     In addition, gearing forces  113  resulting from the meshing of a gearing of the first gear  101  and of a gearing of the second gear  103  act along a connecting line between the first axis of rotation  105  and the second axis of rotation  109 . 
     The first normal force  111  and the second normal force  113  and the gearing forces  115  load the bearing of the first gear  101  and of the second gear  103  and there lead to wear. This is illustrated in  FIG. 2 . 
       FIG. 2  shows a first friction bearing  201 , by which the first gear  101  is rotatably supported, and a second friction bearing  203 , by which the second gear  103  is rotatably supported. The first normal force  111 , the second normal force  113 , and the gearing forces lead to material abrasion  205  in the first bearing  201  and in the second bearing  203  due to wear. 
     The material abrasion  205  involves an increased distance  109  between the first axis of rotation  105  and the second axis of rotation  107 . In order to compensate for this, the illustrated exemplary embodiment is put into operation with a reduced distance  207  between the first axis of rotation  105  and the second axis of rotation  107 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 
     REFERENCE CHARACTERS 
     
         
         
           
               101  First gear 
               103  Second gear 
               105  First axis of rotation 
               107  Second axis of rotation 
               109  Distance 
               111  First normal force 
               113  Second normal force 
               115  Gearing forces 
               201  First bearing 
               203  Second bearing 
               205  Material abrasion 
               207  Reduced distance