Abstract:
A system for coupling a shaft and a hollow member with a blind seat coaxial therewith for housing an end portion of the shaft includes torsional coupling elements and axial coupling elements between the shaft and the member. The axial coupling elements include an annular element coaxial with the shaft and slidable relative thereto, a first shoulder which is formed on the shaft and can interfere with the annular element, and a connection device for connecting the annular element to the member in order to restrain the annular element against the first shoulder and to fix the shaft axially relative to the hollow member.

Description:
DESCRIPTION 
     The present invention relates to a system for coupling a shaft and a blind, hollow member according to the preamble to the main claim. 
     A coupling of the above-mentioned type is required, for example, in the assembly of a machine comprising a rotary shaft an end portion of which is intended to engage a blind seat of a hollow member coaxial with the shaft and fixed for rotation with a spider or with a sun gear of an epicyclic reduction gear. 
     A coupling of this type between the parts mentioned has to ensure the transmission of a twisting moment between the shaft and the blind, hollow member whilst locking them together axially. 
     Naturally, this latter characteristic is required to prevent disassembly of the parts or annoying vibrations in the unit. In particular, the operative situation in which a transmission shaft is housed in a blind, hollow member does not permit easy axial fixing of the shaft at both of its axial ends as in couplings with hollow members having through holes. 
     A first known coupling system provides for the use of friction clamping or shrunk-on joints fitted on the blind, hollow member externally in the region of the seat housing the rotary shaft. 
     Tightening of the friction joint brings about both torsional and axial locking between the shaft and the hollow member. However, this system requires a fairly precise coupling between the parts and has the disadvantage of leading to damage of the shafts coupled when there are large overloads. Moreover, the large clamping force, together with impurities which are deposited in the coupling region during the operative life of the machine, tend to weld the coupling surfaces together, in many cases making their disconnection substantially impossible without irreparable damage to the parts concerned. 
     Finally, the use of friction joints involves costs which render the coupling system as a whole economically unfavourable. 
     A second known system for coupling a shaft and a blind, hollow member provides for the use of locking grub screws for fixing them axially. These screws are normally screwed into radial holes in the hollow member in the region of the seats for housing the shaft and clamped against the surface of the shaft. 
     This system is quite easy to produce but has not been found very effective in clamping shafts axially where large forces are involved. 
     The problem upon which the present invention is based is to provide a system for coupling a shaft and a blind, hollow member, which is designed structurally and functionally to overcome all of the problems complained of with reference to the prior art mentioned. 
     This problem is solved by the invention by means of a coupling system formed in accordance with the following claims. 
    
    
     The characteristics and advantages of the invention will become clearer from the detailed description of an embodiment thereof given by way of non-limiting example, with reference to the appended drawings, in which: 
     FIG. 1 is a partial longitudinal section of a coupling system according to the invention, in an assembly stage, 
     FIG. 2 is a partial longitudinal section of the assembled coupling system, 
     FIG. 3 is a front view of the assembled coupling system, and 
     FIG. 4 is a partial longitudinal section of the coupling system, in a disassembly stage. 
    
    
     The embodiment described below relates to the coupling of a rotary transmission shaft to an epicyclic reduction gear and, in particular, to a blind, hollow member fixed for rotation with the spider of the reduction gear. 
     With reference to FIG. 1, a rotary transmission shaft, indicated  10 , is intended to be inserted in a blind seat  12  in a hollow member  12   a  of an epicyclic reduction gear  14 . 
     The seat  12  is coaxial with the shaft  10  and is generally cup-shaped so as to house an end portion of the shaft  10 . The blind, hollow member  12   a  is fixed for rotation with a spider element  18  of the epicyclic reduction gear  14 . 
     Torsional coupling between the shaft  10  and the hollow member  12   a  is achieved by means of a tongue  11  which enables a twisting moment to be transmitted between the shaft  10  and the epicyclic reduction unit  14 . 
     In FIG. 1, the set of parts is shown during an assembly stage when the shaft  10  is only partially inserted in the blind seat  12  of the hollow member. 
     An annular element  20  is mounted for sliding coaxially on the shaft  10 . A spring ring  22 , generally a Seeger ring, is disposed in an annular groove  23  formed on the shaft, thus defining on the shaft a first shoulder which can interfere with the annular element  20  during its movement along the shaft. 
     An annular surface  21  which can interfere with the portion of the ring  22  which projects from the shaft  10  is advantageously defined in the element  20 . 
     The element  20  also has a plurality of first and second through-holes indicated  24  and  26 , respectively. Only two of these are shown in the section plane of FIG.  1 . These through-holes are disposed in a generally annular arrangement and are spaced apart angularly at regular intervals and intercalated with one another. 
     The holes  24 ,  26  house respective pluralities of first connection screws  28  and second screws  30 . The screws  30  serve as elements for closing the holes  26 , the function of which will be described in detail below. 
     Respective blind threaded holes  32 , of which only one is shown in FIG. 1, are formed in the blind, hollow member  12   a  in positions corresponding to and facing the holes  24 , for engagement by the screws  28 . 
     Two annular grooves  34   a ,  36   a  are also formed in the annular element  20  for housing two respective sealing rings  34   b ,  36   b . These sealing rings are in contact with the shaft  10  and with the hollow member  12   a , respectively, so as to ensure that the coupling region is leaktight when coupling has taken place. 
     A second shoulder, generally indicated  37  is advantageously provided on the shaft  10  for interfering with the annular element  20  during the disconnection of the shaft  10  from the hollow member  12   a . This shoulder  37  is defined by an extension of the shaft  10  with a larger diameter than the end portion (the upper half of the drawing of FIG.  1 ). Alternatively, the shoulder  37  is formed by a second Seeger ring  40  disposed in an annular groove  41  formed on the shaft  10  (the lower half of the drawing of FIG.  1 ). 
     The shoulder  37  can interfere with the annular element  20  during its sliding relative to the shaft  10  and, in particular, with an annular surface  42  formed thereon. 
     The operation of the system during coupling, when assembled, and during disconnection is described in detail below with reference to FIGS. 1,  2  and  4 , respectively. 
     FIG. 1 shows the shaft  10  partially inserted in the blind seat  12 . The annular element  20  is positioned in a manner such that the connection screws  28  are disposed opposite the holes  32  in the hollow member. 
     The position of the first shoulder  22  is selected at a distance such that, when the shaft is fully inserted, the connection screws  28  can be tightened in the holes  32  so as to fix the shaft  10  axially in the blind seat  12 . 
     Axial movement of the shaft  10  relative to the member  12   a  is therefore prevented in one direction by the end of the blind seat  12  and in the other direction by the abutment between the Seeger ring  22  and the annular element  20  clamped to the hollow member  12   a . In this coupling position, the rings  34   b ,  36   b  ensure that the seat  12  of the shaft  10  is leaktight, protecting the coupling surfaces from contact with oxidizing agents or external impurities such as to jeopardize their subsequent disconnection. 
     The system according to the invention enables the shaft  10  and the member  12   a  to be disconnected easily as described below with reference to FIG.  4 . 
     The screws  28  are first of all disengaged from the holes  24  so as to release the annular element  20  from the member  12   a . The screws  30  are disengaged from the holes  26  and, in their place, respective operating screws  42 , longer than the screws  20 , are screwed into these holes. 
     The operating screws  42  are then screwed into the second holes  26  until their free ends are brought into abutment with the outer radial surface of the hollow member  12   a.    
     Further tightening of the operating screws  42  brings about axial sliding of the annular element  20  relative to the shaft  10  away from the hollow member  12   a , to a position (FIG. 4) in which the annular element is brought to interfere with the second shoulder. From this position, further tightening of the screws  42  causes the shaft  10  to slide out of the blind seat  12 , together with the annular element  20 . 
     It should be noted that the alternating arrangement of the connection screws and the operating screws  42  at regular intervals, as shown in FIG. 3, together with the tightening operations performed on the screws uniformly, enable coupling and disconnection to be carried out without any misalignment between the shaft and the annular element. 
     Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.