Abstract:
Mechanical transmission for aeronautical applications, in which a kinematic chain housed inside a leakproof casing has a main power input shaft actuated by a thermal propulsion unit and a secondary power input shaft which can be actuated externally by means of a rotating head which can be coupled to the secondary shaft in a releasable manner by means of a magnetic assembly so as to allow rotation of the secondary shaft at low speed and when the main propulsion unit is inactive.

Description:
[0001]     The present invention relates to a mechanical transmission for aeronautical applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the aeronautical sector, the propulsive action generated by the main propulsion unit, normally a thermal engine, is transmitted to the various user appliances by means of a kinematic chain, normally of the type comprising gears.  
         [0003]     So as to allow operation of the user appliances or some of them when the main propulsion unit is switched off, an auxiliary actuating device, known as a “low-speed” actuating device, arranged in parallel with the main propulsion unit, is generally envisaged.  
         [0004]     The known auxiliary actuating devices comprise an axial seat formed on an end section of one of the shafts of the kinematic chain, and an external actuating head which, when low-speed operation is required, is inserted inside the seat and rotated manually by means of a crank or by means of a dedicated electrical or pneumatic actuator.  
         [0005]     The known solutions of the type described above, although used, are not very satisfactory both in terms of practicality of use and in terms of safety, and require continuous maintenance.  
         [0006]     The above essentially arises from the fact that, in order to insert the actuating head inside the associated seat, it is necessary to remove a cover which closes the casing in a fluid-tight manner, which cover, once operation has ended, must be reassembled so as to prevent the oil lubricating the kinematic chain from escaping. In order to prevent the lubricating oil from escaping during rotation of the pivot pin, it is envisaged mounting a sealing gasket on the shaft which has the seat. This gasket, in addition to increasing the manufacturing costs, requires special lubrication, continuous checking and must be replaced periodically.  
       SUMMARY OF THE INVENTION  
       [0007]     The object of the present invention is to provide a mechanical transmission for aeronautical applications which is able to solve in a simple manner the abovementioned problems and in particular allows low-speed operation without the need for removal of parts of the external casing and which, at the same time, is simple and inexpensive to produce and extremely efficient and reliable from a functional point of view.  
         [0008]     According to the present invention a mechanical transmission for aeronautical applications is provided, said transmission comprising: an external casing; a main power input shaft able to be actuated by a main propulsion unit and a secondary power input shaft which are housed inside the said casing; and auxiliary actuating means which can be coupled to the said secondary shaft in a releasable manner so as to rotate the said secondary shaft when the main propulsion unit is inactive, the said auxiliary actuating means comprising an external actuating head and means for angularly coupling the said actuating head to the said secondary shaft, characterized in that the said angular coupling means comprise first magnetic means coupled to the said secondary shaft in an angularly fixed position and second magnetic means mounted on the said actuating head.  
         [0009]     Preferably, the mechanical transmission described above also comprises a cover arranged so as to close a side opening of the said casing, the cover being positioned between the said secondary shaft and the said actuating head so as to close the casing in a fluid-tight manner also during actuation of the said secondary shaft by means of the said external actuating head.  
         [0010]     Preferably, moreover, the said first and second magnetic means comprise at least one first and at least one second magnet at least partially facing each other.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention will now be described with reference to the accompanying figures which illustrate a non-limiting example of embodiment thereof and where:  
         [0012]      FIGS. 1 and 2  show a partially sectioned view of a mechanical transmission for aeronautical applications constructed in accordance with the principles of the present invention, shown in two different operating conditions; and  
         [0013]      FIG. 3  shows a cross-section, on a much larger scale, along the line II-II of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In  FIG. 1, 1  denotes overall a mechanical transmission for aeronautical applications. The transmission  1  comprises an external casing  2  with the function of a support frame, which casing is permanently closed in a fluid-tight manner and houses a kinematic chain  3  which is partially shown. The kinematic chain  3 , which is of the type known per se, comprises a main driving shaft  4  for inputting the power, connected, again in manner known per se, to a main actuating motor  5 , and a secondary actuating shaft  6 , which is rotatable about a fixed axis  7  of symmetry, supported by a pair of bearings  8 , and is connected angularly to the main shaft  4  by means of a pair of gear wheels indicated by  10  and  11 . The secondary shaft  6  extends through a side opening  13  in the casing  2  and is provided with an external fixed lateral flange  14  against which, by means of a ring  15  screwed onto a terminal section  6   a  of the secondary shaft  6 , the internal race of the associated bearing  8  and a terminal collar  18  of an annular cup-shaped body  19  forming the axial extension of the secondary shaft  6  are clamped in pack form.  
         [0015]     The cup-shaped body  19  has an annular end wall  20 , against which the ring  15  presses, and a side wall  21  which extends through the opening  13 . The side wall  21  is hollow and houses a ring  22  of permanent magnets  23  which are equally spaced and locked inside the said side wall  21  in fixed positions, as shown in  FIG. 3 . According to a variant, not shown, the ring  22  of magnets  23  is replaced by a single magnet or by a pair of diametrically opposite magnets.  
         [0016]     Still with reference to  FIGS. 1 and 2 , the cup-shaped body  19  extends inside a hollow cover  25  which forms part of the casing  2  and which closes the opening  13  in a fluid-tight manner. The hollow cover  25  has, in particular, an end wall  26  perpendicular to the axis  7  and a cylindrical side wall  27  which extends coaxially with respect to the axis  7 , surrounds the side wall  21  with radial play and terminates in an external radial flange  28  connected to the casing  2  by means of a plurality of screws  29 .  
         [0017]     The side wall  27  defines a reference pivot for a removable, hollow, actuating head  31  which extends outside the casing  2  and is coupled to the walls  26  and  27  in a manner rotatable about the axis  7 .  
         [0018]     The hollow head  31  forms, together with the cup-shaped body  19  and the ring  22  of magnets  23 , part of a magnetic device  32  ( FIGS. 2 and 3 ) for actuating the kinematic chain  3  at low speed. The magnetic device  32  is arranged parallel to the main motor  5  so as to allow an operator to rotate, in the case in question manually, the secondary shaft  6  when not actuated by the said main motor  5 .  
         [0019]     In the particular example described, the head  31  has the form of an overturned cup, surrounds the cover  25  and comprises an end wall  33  facing and situated at a distance from the wall  26  of the cover  25  and a side wall  34  surrounding the wall  27  with radial play. The side wall  34  has an internal seat inside which a ring  35  of permanent magnets  36  coaxial with and outside the ring  22  of magnets  23  is arranged and locked in a fixed position, as shown in  FIG. 3 . According to a variant not shown, the ring  35  of magnets is replaced by a single magnet or by a pair of magnets arranged diametrically opposite each other.  
         [0020]     Still with reference to  FIG. 3 , the head  31  is provided with an external fastening pin  37  which extends from the wall  33  coaxially with respect to the axis  7  and to which, in the particular example described, a crank  38  is coupled in an angularly fixed manner, said crank allowing the operator to rotate manually the said head  31 . Alternatively, the crank  38  is replaced by an electric, hydraulic or pneumatic actuator, a spindle of which is able to be coupled to the pin  37 .  
         [0021]     During use, when the kinematic chain  3  must be driven at low speed, namely when the main motor  5  is inactive, the operator simply couples the head  31  to the cover  25  and rotates it manually by means of the crank  38  or by means of any other actuator. Following coupling of the head  31  to the cover  25 , since the cover  25  is pervious to the magnetic fields produced by the magnets  23  and  36 , a magnetic angular coupling is established between the two rings  22  and  35  of magnets and therefore between the head  31  and the secondary shaft  6  so that the secondary shaft  6 , following rotation of the head  31 , is driven rotationally about the axis  7 .  
         [0022]     From the above it is obvious how the use of a magnetic device  32  for actuation of the kinematic chain  3  in low speed mode.allows, above all, the provision of an external casing  2  which is permanently leakproof. This is due essentially to the fact that, also during low-speed operation, no part of the external casing  2  must be removed with respect to the condition where operation occurs by means of the main motor. Consequently, compared to the known solutions, the problems associated with loss of lubrication fluid are totally eliminated and it is no longer necessary to provide special sealing gaskets requiring continuous maintenance and periodic replacement, with an obvious reduction in costs.  
         [0023]     The magnetic device  32  described is, moreover, relatively simple from a constructional point of view, unaffected by external agents and therefore does not require maintenance operations.  
         [0024]     From the above it is obvious that the transmission  1  described may be subject to modifications and variations which do not depart from the protective scope of the present invention. In particular, it is obvious that the magnetic device  32  may be used, independently of the type of main motor and could comprise magnets different from those indicated by way of example and chosen depending on the actuating torque to be transmitted from the outside.  
         [0025]     Finally, the head  31  could have constructional features different from those described by way of example and/or be coupled to the casing in a manner different from that indicated.